Abstract:
A latent image carrier includes a thin-walled cylinder with a chargeable photosensitive layer. The latent image carrier is configured to form an electrostatic latent image corresponding to an optically written image. A cylindrical damper including an elastic body disposed inside the latent image carrier. A first end of the cylindrical damper includes a wall extending inward toward an axis of the damper. A second end of the damper, opposite the first end along the axis of the damper, includes an opening, which is open in an axial direction. The wall includes a through-hole connecting an internal cavity and an outside of the damper. An outer diameter of an outermost part of the first end of the damper along the axis of the damper is smaller than an outer diameter of an outermost part of the second end of the damper along the axis of the damper.

Description:
This application is a divisional of application Ser. No. 11/328,295, filed Jan. 10, 2006, which is a divisional of application Ser. No. 10/456,583, filed Jun. 9, 2003 and claims priority to JP 2002-169218, filed on Jun. 10, 2002, and JP 2002-170655, filed on Jun. 11, 2002, and JP 2002-181552, filed on Jun. 21, 2002, and JP 2002-195224, filed on Jul. 3, 2002, and JP 2003-113709, filed on Apr. 18, 2003, the entire contents of each of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to a technology for preventing noise caused by vibrational resonance produced in a latent image carrier due to a thin-walled structure of an image forming apparatus. 
   2) Description of the Related Art 
   In image forming apparatuses like a copying machine, a facsimile, a printer, and a printing machine, steps of charging, writing, developing, and transferring are carried out for a photoreceptor as a latent image carrier. In the step of transferring, a toner image that is transferred on a recording medium like a recording paper is fixed to give a copy or a printout. 
   A structure that employs a non-contact charging method with aerial discharge using a corona charger is used for charging of the photoreceptor. However, in the structure, discharge products like ozone and nitrogen oxide are generated during discharging which may result in deterioration of environment or deterioration of charging characteristics on the photoreceptor. Therefore, a contact charging method, which does not generate the problems and enables to apply low voltage, is proposed as a substitute for an aerial discharge. A structure that injects charge by applying voltage between the photoreceptor and any one of a brush, a roller, and a blade of a conductive material that is kept in contact with the photoreceptor is known as one of the contact charging methods. 
   In the contact charging method, it is possible to apply low voltage and there is no generation of discharge products. However, since any one of a brush, a roller, and a blade made of a conductive material is in direct contact with the photoreceptor, it is easy to carry out reverse transition of deposits of toner etc. that remain on the photoreceptor. The deposits that have undergone reverse transition hinder the injection of charge and may deteriorate the charging characteristics. Furthermore, when a charging member is left without being used in a charging process for hours, a portion of the charging member that is in contact with the photoreceptor, changes shape due to permanent deformation. As a result, when the charging process is carried out again, there is no uniform contact of the charging member with the surface of the photoreceptor, which may result in charging unevenness. 
   To solve this problem, a unit that forms a charging range between the photoreceptor and the charging member is proposed. The charging member is disposed so that a prescribed minute interval is maintained between the photoreceptor and the charging member. The unit is an intermediate structure of non-contact and contact charging methods. A charging method (proximity charging method) has been employed in recent years. In this method, a prescribed minute interval is provided between the photoreceptor and the charging member such as a brush, a roller, and a blade of a conductive material, and charging is carried out by applying either of only dc voltage and dc voltage superimposed by an ac voltage. 
   In a structure which employs the proximity charging method, in a case where the charging member is a roller, a film of prescribed thickness is wound on both ends of the charging roller in its axial direction for setting of a gap and size of the minute gap is prescribed by thickness of the film. 
   Maintaining the prescribed size of the minute gap is an important condition to have no variation in the charging characteristics. When it is assumed that the size of the minute gap is maintained, the uniform charging becomes possible by applying of dc voltage for which setting is comparatively easy. However, when the size of the gap varies considerably, there is a considerable variation in a charging electrical potential in proportion to the variation in the size of the gap. Therefore, conventionally, various ideas have been thought up to achieve uniform charging characteristics even in a case where the size of the gap is varied by superimposing ac voltage on dc voltage. 
   On the other hand, apart from the charging unit, a developing unit is there to set the charging characteristics, i.e. bias characteristics. In a case of the developing unit, a developing method that uses either of a one-component developer and a two-component developer, is known. In the developing unit which uses the two-component developer, a developer that includes a carrier made of a magnetic material (substance) for an insulating toner, is agitated by an agitator. The toner is then deposited by charging on the carrier and the developer is made to be in contact with the photoreceptor. 
   In a developer carrier used in the developing unit, a developing sleeve, which can carry the developer on its surface, is used and a magnetic roll with a plurality of south poles and north poles lined up alternately on it is provided inside the developing sleeve. In the developer carrier, the developer is drawn up by magnetic force of the magnetic roll and a magnetic brush is formed by making the developer erected in the form of a brush on the surface of the developer carrier. 
   When the magnetic brush carried on the surface of the magnetic sleeve comes in contact with the electrostatic latent image that is formed on the photoreceptor based on either of image information and a paper document image, a developing bias is applied between the photoreceptor and the magnetic sleeve as the developer carrier. Due to the developing bias, the toner in the magnetic brush undergoes electrostatic absorption by the electrostatic latent image thereby forming a toner image. 
   As a developing bias, a bias as follows is used. The bias superimposes the ac voltage on the dc voltage to improve the developing capability, carry out the developing to the electrostatic latent image identically with utmost clarity, and improve uniformity of dots. Moreover, the bias has a first peak value V 1  for transferring the toner from the developer carrier to the photoreceptor and a second peak value V 2  for transferring the toner from the photoreceptor to the developer carrier. A method using the bias as a developer bias, in which a vibrating electric field is created in a developing area between the developer carrier and the photoreceptor and charged toner is applied on the photoreceptor, is known. 
   For the ac voltage which is superimposed on dc voltage, a rectangular waveform as in  FIG. 44 , a sine waveform as in  FIG. 45 , a triangular waveform as in  FIG. 46 , or a duty bias as shown in  FIG. 47  is used. 
   In a case of using the duty bias shown in  FIG. 47 , a ½ value of the waveform differs from an average value of time integral. In  FIG. 47 , such a bias as follows is used. That is, the bias includes a time required for application of the first peak value V 1  and a time required for application of the second peak value V 2 . At the first peak value V 1 , an electric field is created such that the electric field is biased in a direction in which the toner is transferred from the developing sleeve to the photoreceptor. At the second peak value V 2 , an electric field is created such that the electric field is biased in a direction in which the toner is transferred from the photoreceptor to the developing sleeve. 
   In a case of using the duty bias, by optimizing a frequency of ac voltage, a duty ratio (=t 1 /(t 1 +t 2 )×100% in  FIG. 47 ), and a peak-to-peak value i.e. a difference between a maximum value of ac voltage (V 1 ) and a minimum value of ac voltage (V 2 ), it is possible to deposit the toner efficiently on an image area of the photoreceptor or not to deposit the toner on non-image area of the photoreceptor. Moreover, the optimization also enables the adjustment for increasing the density of an image while improving the uniformity of toner dots identical to the latent image. 
   Among methods which use the other developer i.e. the one-component developer, a jumping developing is a known method. In the jumping developing, an electrostatic latent image on the photoreceptor is developed while the developing sleeve as the developer carrier of the developing unit and the photoreceptor are maintained in the non-contact state. In the jumping developing, a layer of the one-component developer is formed on the developing sleeve. More specifically, a magnetic roll having a plurality of south poles and north poles lined up alternately on it and facing the electrostatic latent image carrier, is fixed on the developing sleeve. Furthermore, a toner brush is formed in a developing area and the developer (toner) is splashed and applied on the photoreceptor by applying a developing bias obtained by superimposing an ac component on a dc component, to the developing sleeve. Fogged toner is then returned in the direction of the developing sleeve and the latent image is visualized as a toner image. 
   When the developer is a one-component developer, in the same manner as the two-component developer, the developing bias method is used. In the developing bias method, by varying the peak-to-peak value, frequency, and duty ratio, it is possible to deposit the toner efficiently on the image area of the photoreceptor or not to deposit the toner on the non-image area of the photoreceptor. Moreover, the image density is increased while improving the uniformity of toner dots. 
   Depending on a setting of the bias characteristics that is carried out in the charging unit and the developing unit, noise is caused by applying ac voltage during shifting of the photoreceptor. Following is a reason for the generation of noise. A lighter weight conductive material in cylindrical form is used for the photoreceptor. Concretely, an aluminum cylinder having thin walls is used for the photoreceptor with a structure that resonates easily. Besides, not only units used in charging and developing processes are disposed facing the photoreceptor, but units for carrying out writing, transferring, and cleaning processes are also disposed facing the photoreceptor. In particular, the unit that carries out the cleaning process is disposed close to the photoreceptor, other than the units for charging process and developing process. Therefore, the photoreceptor can resonate easily due to vibrating electric field created when ac voltage is applied. Furthermore, due to a cleaning blade of the cleaning unit that is in contact with the photoreceptor, the vibrations are generated in the thin-walled cylinder due to repetition of deformation and restoration of shape of the cleaning blade when the cleaning blade scrapes the photoreceptor, and resonance in the photoreceptor produces noise. 
   That is, the image forming apparatuses like a copying machine, a printer, a facsimile, or a multifunction machine including any functions of these have been known widely. The image carrier drum includes either of a photoreceptor drum on surface of which a toner image is formed by charging, exposing, and developing and an intermediate transfer drum on surface of which a toner image is transferred from the photoreceptor and formed. The image carrier drum vibrates due to an external force that imparts vibrations, thereby resulting in generation of noise from the image carrier drum. For example, image forming units like a charging unit and a cleaning unit are provided around the photoreceptor drum. The charging member vibrates due to effect of ac voltage applied to the charging unit. The charging member vibrates due to stick-slip which is caused by the cleaning blade that is in pressed contact with the surface of the image carrier drum. The stick-slip starts as the image carrier drum rotates. The vibrations are transmitted to the image carrier drum to make the image carrier drum vibrate, and to thereby generate noise. A user may feel unpleasant because of noise. Therefore, measures have been taken in conventional techniques by providing the damper inside the image carrier drum to minimize vibrations of the image carrier drum to reduce the noise. 
   On the other hand, an image forming apparatus explained below has been in practical use to enable conservation of energy. The image forming apparatus uses a toner having a low melting point, and is structured such that a transferred toner image can be fixed on the recording medium at comparatively low temperature. However, a case of using the toner having a low melting point tend to generate noise easily as compared to a case of using a toner having a high melting point. Therefore, it is found that the conventional damper is unable to reduce the noise sufficiently. It is not sure that the use of the toner having a low melting point increases the noise. However, additives like wax or the like contained in the toner tend to stick to the surface of the image carrier drum. Since the amount of the additive that is deposited becomes non-uniform depending on an image pattern, a component like the cleaning blade in contact with the surface of the image carrier drum does not move uniformly. It is considered that loud noise that is generated in the image carrier drum is due to vibrations caused by non-uniform movement of the cleaning blade. 
   A structure in which the photoreceptor is made solid i.e. a solid cylinder has been disclosed, for example, in Japanese Patent Application Laid Open Publication (“JPA”) No. HEI 07-72641, as the conventional structures to reduce the noise. Furthermore, a structure in which at least two of an elastic body and a cylinder member are fitted inside the photoreceptor and resonance in peripheral wall of the thin-walled cylinder is reduced has been disclosed in JPA No. HEI 11-184308, for the same purpose. 
   Moreover, there is another structure made by using a cylinder unit in which the damper is inserted inside the cylinder to reduce vibrations of the cylinder and therefore the noise is minimized. This type of structure has been disclosed in JPA No. HEI 11-35167 and JPA No. HEI 10-97158. 
   In recent years, products which can be recycled are promoted with an object of protection of environment and saving of resources. Same thing is expected about the cylinder unit. To have better recycling of a product formed by a plurality of components, it is necessary that the product be structured in such a way that each component of the product can be dismantled easily after the product is used and the dismantled component can be reused or can be reprocessed. However, in the conventional cylinder unit, the damper inserted inside the cylinder is fixed to the cylinder and therefore it is difficult to remove the damper from the cylinder. Thus, the conventional cylinder unit is found difficult to be recycled. 
   However, in the structure for prevention of noise, increase in cost of the photoreceptor and complications in structures are matters of concern. When the photoreceptor is structured using a solid body, it not only raises the cost but also increases weight. Due to increase in the weight, there is an increase in driving force required for rotation, which results in increase in inertial force. The increase in weight of the photoreceptor affects its portability, which may result in damaging the surface of the photoreceptor or causing an injury to a person due to heavy weight on dropping of the photoreceptor during replacement job. If a plurality of damping structures are provided inside the photoreceptor, there is a rise in cost due to the increased number of components and assembling processes. 
   Moreover, the image forming apparatus that uses the toner having a low melting point tends to generate noise easily as compared to the case of using the toner having a high melting point. Therefore, the conventional damper is unable to reduce the noise sufficiently. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to solve at least the problems in the conventional technology. 
   According to one aspect of this invention, an image forming apparatus includes a latent image carrier that includes an arrangement of any of a belt and a thin walled hollow cylinder, the latent image carrier having a first surface and a second surface. The apparatus also includes a bias applying unit that has an arrangement for approaching towards the first surface of the latent image carrier, in which the bias applying unit sets bias characteristics of the latent image carrier. The apparatus further includes a vibration absorber that absorbs vibrations in the latent image carrier, in which the vibration absorber is made to touch the second surface of the latent image carrier. 
   According to another aspect of this invention, an image forming apparatus includes a toner image forming unit that forms a toner image on an image carrier drum using a toner having an outflow start temperature less than or equal to 102° C. measured by flow tester method. The apparatus also includes a damper provided inside the image carrier drum, in which the damper is made of a material with a tangent of loss tan δ of the damper is greater than or equal to 0.5. The tangent of loss is a value of damping effect. 
   According to still another aspect of this invention, a drum unit includes a cylinder, a shaft that extends inside and supports the cylinder, and a damper disposed inside the cylinder. The cylinder, the shaft, and the damper are assembled such that when the shaft is pulled out from the cylinder, the damper moves in the axial direction of the cylinder together with the shaft and is removed from the cylinder. 
   According to still another aspect of this invention, an image forming module includes an image carrier drum, and a shaft that extends inside and supports the drum. The module also includes a damper disposed inside the drum, in which the drum, the shaft, and the damper are assembled such that when the shaft is pulled out from the drum, the damper moves in the axial direction of the drum together with the shaft and is removed from the drum. The module further includes an image forming element that forms an image on the drum. The image carrier drum and the image forming element are assembled together as an integrated assembly. 
   According to still another aspect of this invention, the image forming apparatus includes an image carrier drum, a shaft that extends inside and supports the drum, and a damper disposed inside the drum. The drum, the shaft, and the damper are assembled such that when the shaft is pulled out from the drum, the damper moves in the axial direction of the drum together with the shaft and is removed from the drum. 
   According to still another aspect of this invention, a method of insertion and removal of a damper into and from an image carrier drum includes inserting the damper into the image carrier drum from an opening on one end in an axial direction of the image carrier drum and thereby mounting the damper inside the drum. The method also includes removing the damper from an opening on other end in the axial direction of the image carrier drum. 
   According to still another aspect of this invention, a drum unit includes an image carrier drum, and a damper. The damper is inserted into the image carrier drum from an opening on one end in an axial direction of the image carrier drum to thereby mount the damper inside the drum, and the damper mounted inside the drum is removed from an opening on other end in the axial direction of the image carrier drum. 
   According to still another aspect of this invention, an image forming module includes a drum unit having an image carrier drum and a damper, in which the damper is inserted into the image carrier drum from an opening on one end in an axial direction of the image carrier drum to thereby mount the damper inside the drum, and the damper mounted inside the drum is removed from an opening on other end in the axial direction of the image carrier drum. The module also includes an image forming unit that forms a toner image on the image carrier drum. The drum unit and the image forming unit are detachable from a main body of the image forming apparatus. 
   According to still another aspect of this invention, an image forming apparatus includes an image forming module. The image forming module includes a drum unit having an image carrier drum, and a damper, in which the damper is inserted into the image carrier drum from an opening on one end in an axial direction of the image carrier drum to thereby mount the damper inside the drum, and the damper mounted inside the drum is removed from an opening on other end in the axial direction of the image carrier drum. The apparatus also includes an image forming unit that forms a toner image on the image carrier drum. The drum unit and the image forming unit are detachable from a main body of the image forming apparatus. 
   According to still another aspect of this invention, an image forming apparatus includes a drum unit having an image carrier drum to form a toner image and a damper. The damper is inserted into the image carrier drum from an opening on one end in an axial direction of the image carrier drum to thereby mount the damper inside the drum, and the damper mounted inside the drum is removed from an opening on other end in the axial direction of the image carrier drum. 
   The other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of an image forming unit in an image forming apparatus according to a first embodiment of the present invention; 
       FIG. 2  illustrates a roller around which a photoreceptor belt used in the image forming unit shown in  FIG. 1  is wound; 
       FIG. 3  illustrates another structure of the roller shown in  FIG. 2 ; 
       FIG. 4  illustrates still another structure of the roller shown in  FIG. 2 ; 
       FIG. 5  illustrates still another structure of the roller shown in  FIG. 2 ; 
       FIG. 6  illustrates a structure for prevention of noise in the image forming apparatus shown in  FIG. 1 ; 
       FIG. 7  illustrates another example of the structure for prevention of noise shown in  FIG. 6 ; 
       FIG. 8  illustrates a photoreceptor belt used in the image forming apparatus shown in  FIG. 1 ; 
       FIG. 9  illustrates another example of the image forming apparatus; 
       FIG. 10  illustrates a developing unit used in the image forming apparatus shown in  FIG. 9 ; 
       FIG. 11  illustrates a latent image carrier used in the image forming apparatus in  FIG. 9 ; 
       FIG. 12  illustrates another structure of the latent image carrier used in the image forming apparatus in  FIG. 11 ; 
       FIG. 13  is a graphical of noise characteristics in the structure of the latent image carriers shown in  FIG. 11  and  FIG. 12 ; 
       FIG. 14  illustrates an application related to the image forming apparatus; 
       FIG. 15  is a schematic diagram of an image forming unit in an image forming apparatus according to a second embodiment of the present invention; 
       FIG. 16  is a longitudinal cross section of an image carrier drum with a damper disposed inside the drum; 
       FIG. 17  is a longitudinal cross section of a damper which is different in shape than the damper in  FIG. 16 ; 
       FIG. 18  illustrates a charging roller that is in contact with a surface of the image carrier drum; 
       FIG. 19  illustrates a charging unit formed by a brush roller; 
       FIG. 20  illustrates a charging unit formed by a magnetic brush unit; 
       FIG. 21  is a schematic diagram of an image forming unit in an image forming apparatus according to a third embodiment of the present invention; 
       FIG. 22  is a longitudinal cross section of a cylinder unit in  FIG. 21 ; 
       FIG. 23  is an exploded perspective view of an image carrier drum and a flange in  FIG. 22 ; 
       FIG. 24  is a cross section of a state when a shaft and a damper are moved from the state shown in  FIG. 22 ; 
       FIG. 25  is a cross section of another example of the damper; 
       FIG. 26  is a cross section of still another example of the damper; 
       FIG. 27  is a cross section of still another example of the damper; 
       FIG. 28  is a cross section of still another example of the damper; 
       FIG. 29  is a cross section of a cylinder unit in which a flange having a first cylinder member and a second cylinder member is used; 
       FIG. 30  is a perspective view of the first and the second cylinder members; 
       FIG. 31  is a cross section of a state while the first and the second cylinder members are assembled with the image carrier drum; 
       FIG. 32  is a schematic diagram of an image forming unit in an image forming apparatus according to a fourth embodiment of the present invention; 
       FIG. 33  is a longitudinal cross section of a drum unit in  FIG. 32 ; 
       FIG. 34  is a cross section of a state before the damper is inserted into the image carrier drum; 
       FIG. 35  is a cross section of a state after the damper is inserted into the image carrier drum; 
       FIG. 36  is a cross section of a state when the damper has come in contact with the flange; 
       FIG. 37  is a cross section of a state when the damper is pushed out further after the flange is removed from the image carrier drum; 
       FIG. 38  is a cross section of an example of inserting and removing the damper into and from the image carrier drum by pulling the damper by a force imparting member; 
       FIG. 39  is a longitudinal cross section of another example of the drum unit; 
       FIG. 40  is a cross section of a state after the shaft and the damper are moved from positions shown in  FIG. 39 ; 
       FIG. 41  is a cross section of a drum unit in which the damper is formed by a compression coil spring; 
       FIG. 42  is a cross section of an example of using the flange having a first and a second flange members; 
       FIG. 43  is schematic cross section of another example of the image forming apparatus; 
       FIG. 44  is a graph of an example of a developing bias; 
       FIG. 45  is a graph of another example of the developing bias; 
       FIG. 46  is a graph of still another example of the developing bias; and 
       FIG. 47  is a graph of still another example of the developing bias. 
   

   DETAILED DESCRIPTION 
   Exemplary embodiments of an image forming apparatus, a drum unit, an image forming module, and a method for insertion and removal of a damper into and from an image carrier drum are explained in detail below with reference to the accompanying drawings. The present invention is not limited only to the following embodiments. 
     FIG. 1  is a schematic diagram of an image forming unit of an image forming apparatus  100  according to a first embodiment. In the image forming apparatus  100 , a photoreceptor that functions as a latent image carrier, is formed by a belt (hereinafter, “photoreceptor belt  101 ”). The photoreceptor belt  101  is wound around among a plurality of rollers  102  to  104  and can move in a direction indicated by an arrow A. A charging unit  105 , a writing unit  106  (in  FIG. 1 , only optical path is shown), a developing unit  107 , a transferring unit  108 , and a cleaning unit  109  are disposed around the photoreceptor belt  101  along the direction of movement of the belt to carry out image forming processing. 
   The rollers  102  to  104  are arranged such that the photoreceptor belt  101  forms a triangle turned upside down as shown in  FIG. 1  and a vertex of the triangle is a transferring position. 
   The charging unit  105  is one of the units which sets bias characteristics in the photoreceptor belt  101 . As shown in  FIG. 1  and  FIG. 2 , the charging unit  105  is a unit adopting a non-contact method and has a charging roller  105 A provided close to the photoreceptor belt  101  maintaining a prescribed gap (G) that is set. Both ends of a shaft  105 B of the charging roller  105 A in its axial direction are biased by an elastic body  105 C like a spring etc. towards the photoreceptor belt  101 . A displacement caused by the biasing is regulated by an abutting member  105 D that includes a film wound around both ends in the axial direction of the charging roller. The abutting member  105 D protrudes from the peripheral surface of the charging roller  105 A towards the photoreceptor belt  101 . 
   In the embodiment, the prescribed gap (G) maintained by the abutting member  105 D is set according to the type of a developer that is used in the developing unit  107 . In the case of the one-component developer that uses only magnetic toner as developer, the gap is less than or equal to 300 μm and in the case of the two-component developer with toner and magnetic carrier that are mixed, the gap is less than or equal to 500 μm. The pushing by the elastic body  105 C maintains the gap. The difference in the gap is irrespective of the developer that is used, and prevents deterioration of the developing capability when dc and ac voltages are applied. 
   Direct voltage is applied to the charging roller  105 A via the prescribed gap G defined by the abutting member  105 D due to constant voltage control of dc −700V through a control circuit (not shown). At the same time, alternate voltage is applied due to low current control and an aerial discharge is carried out to the photoreceptor belt  101 . Thus, the photoreceptor belt  101  is charged uniformly. 
   When the photoreceptor belt  101  charged uniformly by the charging unit  105  moves, the writing unit  106  carries out optical writing. An electrostatic latent image according to either of image information and a paper document image, is formed due to the optical writing. The electrostatic latent image is processed to form a visualized image by a developer (toner), which is supplied by the developing unit  107 . The visualized toner image is transferred on a recording paper S that is fed by a paper-feeding unit not shown. The image is transferred on the paper by the transferring unit  108  that includes a transfer roller provided against the roller  103  that is at the vertex of the lower part of the triangle formed by the photoreceptor belt  101 . The transferred toner image is fixed on the recording paper S by a fixing unit (not shown), and discharged. The cleaning unit  109  removes residual toner and residual charge on the photoreceptor belt  101 , after transferring of the image. The photoreceptor belt  101  moves again toward the charging unit  105 , thereby preparing for the next image forming. 
   The structure of the charging unit  105  is not restricted only to a non-contact roller with respect to the photoreceptor belt  101 . A structure that has a roller in contact with the photoreceptor belt  101 , a structure that uses a conductive brush as a charging member, and even a magnetic brush that uses magnetic particles, can be used. 
     FIG. 3  illustrates a supporting structure of the photoreceptor belt  101 . The photoreceptor belt  101  is wound around among the rollers  102  to  104 . The roller  102  facing the charging unit is provided with a vibration absorber  110  on the surface of the roller  102 . The vibration absorber  110  uses a strong vibration absorbing material  110 A that contains an elastic material like butyl rubber or nitrile rubber. 
   The structure of the vibration absorber  110  can be varied by substituting the vibration absorber provided on the roller  102  by either of structures as follows. One of the structures has a strong vibration absorbing material  110 B in form of a solid block which is press fitted in the hollow cylindrical roller  102  as shown in  FIG. 4 . The other structure has a strong vibration absorbing material  110 C in form of a block with a hollow inside of the block as shown in  FIG. 5 . In any structure of the vibration absorber  110 , the elastic body made by either of butyl rubber and nitrile rubber is used. The vibration absorber  110  is provided in either of an axial direction of the roller  102  where the absorber tends easily to deform by bending and an area around this axial direction. 
   Tangent of loss tan δ for any of the strong vibration absorbing material  110 A or the strong vibration absorbing blocks  110 B and  110 C, is set to be greater than or equal to 0.5. The tangent of loss tan δ means a tangent of a phase angle δ (loss angle) of stress and strain in the material used as the strong vibration absorbing material  110 A or the strong vibration absorbing material blocks  110 B and  110 C. Value tan δ denotes intrinsic damping effect value of the material, and the greater the value of tan δ, the greater the damping effect is. Therefore, in the embodiment, generation of harsh noise is minimized by at least making the value of tangent of loss tan δ greater than or equal to 0.5 irrespective of use of the strong vibration absorbing material  110 A and the strong vibration absorbing blocks  110 B and  110 C. The results of experiment regarding the settings of loss value tan δ are mentioned in the latter part. 
   When dc voltage and in addition ac voltage are applied to the charging unit  105  as one of the units for setting the bias characteristics, the photoreceptor belt  101  that corresponds the thin-walled member, resonates due to the vibrating electric field in the charging unit  105 . 
   Since the resonance produced in the photoreceptor belt  101  is reduced due to absorption of vibrations by the roller  102  that is in contact with the photoreceptor belt  101 , the resonance in the photoreceptor belt  101  is suppressed, thereby preventing noise caused by the resonance. The photoreceptor belt  101  in particular, which is a thin-walled structure, tends to resonate easily. However, when the photoreceptor belt  101  resonates, the resonance is controlled by a vibration absorbing function of the vibration absorbing material  110 A or the vibration absorbing materials  110 B and  110 C which function as vibration absorber  110  when resonance is produced, there is almost no generation of noise. 
   As a modification of the structure in the embodiment, a drive roller of the photoreceptor belt  101  may be used as a roller provided with the vibration absorber  110 . In this case, to transmit the driving force from the drive roller to the photoreceptor belt  101 , the vibration absorber  110  is provided on the drive roller that is in stronger contact with the photoreceptor belt as compared to the contact of the other roller with the photoreceptor. By providing the vibration absorber  110  in the drive roller, the resonance produced in the photoreceptor belt  101  can be dealt with in the most effective manner and can be reduced efficiently. 
   Following is an explanation of another example in which a vibration absorption function is provided for the photoreceptor belt  101 .  FIG. 6  illustrates a structure in which the vibration absorber  110  is provided on a supporting plate  111  that is provided on an inner side of the photoreceptor belt  101 . The supporting plate  111  functions as a guide for the photoreceptor belt  101 . The supporting plate  111  is a flat plate made of hard material and the vibration absorber  110  is provided on the side of the supporting plate  111  opposite to the side thereof that faces the photoreceptor belt  101 . 
     FIG. 7  illustrates a structure in which the charging unit  105  as one of the units for setting the bias characteristics in  FIG. 6  is disposed in a position opposite to the supporting plate  111  sandwiching the photoreceptor belt  101 . In this case also, the vibration absorber  110  is provided on the side of the supporting plate  111  opposite to the side thereof that faces the photoreceptor belt  101 . 
   According to the first embodiment, vibrations generated in the charging unit  105  when the bias is superimposed with the ac and dc voltages respectively by the charging unit  105  are propagated to the photoreceptor belt  101 . When the vibrations are propagated, the photoreceptor belt  101  starts resonating. By propagating the resonance to the supporting plate  111  that is in contact with the photoreceptor belt  101 , the vibration absorber  110  absorbs the resonance. Thus, the resonance in the photoreceptor belt  101  is minimized thereby preventing the generation of noise. 
   Following is an explanation of a structure in which the photoreceptor belt  101  itself prevents.  FIG. 8  is a cross section of the photoreceptor belt  101 . The photoreceptor belt  101  is structured by superimposing a photosensitive layer  101 B on a surface of a substrate  101 A made of a thin metal foil or the like. On the opposite side of the photosensitive layer  101 B beyond the substrate  101 A is the vibration absorber  110  that is formed by an elastic body using either of a butyl rubber and nitrile rubber. 
   The vibration absorber  110  is provided on the side opposite to the photosensitive layer  110 B via the substrate  101 A, and therefore vibrations in the photoreceptor belt  101  are minimized due to absorption by the vibration absorber  110  thereby minimizing resonance in the photoreceptor belt and preventing the noise. 
   Why the vibrations are produced in the charging unit  105  has been explained above. The cleaning unit  109  provided with the cleaning blade is a unit that generates vibrations while being in contact with the photoreceptor belt  101 . Vibrations caused by deformation due to scraping of the cleaning blade and by scraping during restoration of the shape after deformation, are also absorbed in the same manner as absorption of the resonance produced by the charging unit  105 . The image forming apparatus in the invention includes a copying machine, a printer, a facsimile, and a printing machine. 
   Following is an explanation of still another embodiment of the present invention.  FIG. 9  is a schematic diagram of an image forming apparatus according to another embodiment. An image forming apparatus  20  in  FIG. 9  is a copying machine in which a thin-walled cylinder is used as a latent image carrier and plurality of the latent image carriers are provided to allow image formation of plural colors. The image forming apparatus  20  in  FIG. 9  employs a method of transferring an image of each color separation to the same intermediate transfer body one after another and performing collective transfer of the images superimposed on the intermediate transfer body to a sheet like recording medium such as paper. 
   The image forming apparatus  20  includes units as follows. The units include image forming units  21 C,  21 Y,  21 M, and  21 BK that form images of each color according to an image on a document. The units also include a transferring unit  22  that is disposed opposite to the image forming units  21 C,  21 Y,  21 M, and  21 BK. The units further include a manual feed tray  23  and a paper feeding cassette  24  as sheet-like medium feeding units for feeding a sheet-like recording medium to each transfer area where the image forming units  21 C,  21 Y,  21 M, and  21 BK and the transferring unit are disposed opposite to each other. The units further include register rollers  30  that feed a recording medium according to timing of image forming by the image forming units  21 C,  21 Y,  21 M, and  21 BK after transferring from the manual feed tray  23  and the paper feeding cassette  24 . The units further include a fixing unit  1  that carries out fixing on the recording medium after the image is transferred in the transfer area. 
   In the image forming apparatus  20 , any of sheet-like recording media can be used as a sheet-like medium. The sheet-like recording medium includes an ordinary paper used for copy in general (hereinafter “ordinary paper”), an OHP sheet, a 90K paper like a postcard and a card, a cardboard of basis weight greater than or equal to 100 g/m 2  and an envelope that are so-called special purpose sheets having a heat capacity more than that of the above types of sheets (hereinafter, simply referred to as “special purpose sheet”). 
   The image forming units  21 C,  21 Y,  21 M, and  21 BK carry out developing of cyan, yellow, magenta, and black colors respectively. Although the toner color handled by each image forming unit is different, the structures of the units are the same. Therefore, the structure of the image forming unit  21 C, as a representative of the image forming units  21 Y,  21 M, and  21 BK, is explained below with reference to  FIG. 10 . 
   The image forming unit  21 C has a known structure, which is illustrated in  FIG. 10 . The unit  21 C includes a photoreceptor drum  25 C as an electrostatic latent image carrier, and also a charging unit  27 C, a developing unit  26 C, and a cleaning unit  28 C that are disposed around the drum  25 C in this order along the rotational direction F of the drum  25 C. Further, writing light is received between the charging unit  27 C and the developing unit  26 C. The image forming apparatus  20  in  FIG. 9  has the transferring unit  22  that is extended in a slanting direction, and therefore the transferring unit  22  occupies less space as compared to the space occupied by the transferring unit  22  provided in a horizontal direction. 
   The charging unit  27 C includes, as shown in  FIG. 10 , of a roller having the structure similar to that in  FIG. 2 . Abutting members that protrude towards the photoreceptor drum  25 C are provided on both ends of the roller in the axial direction to set a prescribed gap between the photoreceptor drum  25 C and the roller of the charging unit  27 C. The prescribed gap is explained later. 
   The developing unit  26 C uses a biaxial agitation method carried out by agitating screws  26 C 1  and  26 C 2  which are two agitators that carry out mixing and agitating of toner supplied from a toner cartridge with magnetic carrier. Developer is frictionally charged due to agitation and magnetic carrier toner is adhered to the developer. The developer is carried on a surface of a developing sleeve  26 C 3  as a developer carrier, and is provided with a magnetic roller that has north and south poles lined up inside. The developer is supplied toward the photoreceptor  25 C after a layer thickness is regulated by a doctor blade  26 C 4 . 
   The developing sleeve  26 C 3  in the developing unit  26 C is disposed to set a prescribed gap from the photoreceptor drum  25 C. In the structure shown in  FIG. 10 , the prescribed gap is set to be less than or equal to 500 μm, preferably to 470 μm. This prescribed gap is set to allow the capability of toner adhesion to an electrostatic latent image on the photoreceptor drum to be enhanced, the developing capability of continuous black image to be improved, and uniform and identical development with utmost clarity of fine lines such as characters and dots etc to be realized. It is possible to maintain uniform and high developing capability of toner dots by giving identical reproducibility to the electrostatic latent image by setting the gap less than or equal to 500 μm. Making the prescribed gap greater than 500 μm does not guarantee good capability. 
   The abutting members (not shown) provided on both ends of the developing sleeve  26 C 3  in the axial direction are used for setting the gap between the developing sleeve  26 C 3  and the photoreceptor drum  25 C. The abutting member is a member protruding toward the photoreceptor drum  25 C that is similar to the abutting member  105 D in the charging unit  105  shown in  FIG. 2 . In the embodiment, an abutting roller is used. The protruding roller is larger than the photoreceptor drum  25 C and has an outer diameter equivalent to an amount of protruding more than the prescribed gap. 
   The structure in which the prescribed gap is set, enables to carry out splashing of toner to an image area on the latent image carrier and returning of toner from non-image area to the developer carrier due to the bias characteristics according to the type of developer used in efficient manner. This can optimize the electrical field effect by the bias and reliably prevent deterioration of developing capability and production of resonance in the latent image carrier. 
   The developing sleeve  26 C 3  maintains the gap of 470 μm from the photoreceptor drum  25 C and carries a developer that includes toner and carrier made of the magnetic material. A negatively charged developing bias supplied from a power supply (not shown) is applied to the developing sleeve  26 C 3 . Negatively charged toner is splashed and applied on an area of exposure of the photoreceptor drum  25 C based on an electric field created between the sleeve  16 C 3  and the drum  25 C, thereby carrying out developing. Thus, a toner image is formed. 
   The developing bias to be used includes a first electric potential area V 1  and a second electric potential area V 2  generated by superposing ac voltage on dc voltage as shown in  FIG. 47 . The first electric potential area V 1  in which toner is moved from the developing sleeve  26 C 3  to the photoreceptor drum  25 C, and the second electric potential area V 2  in which toner is moved from the photoreceptor drum  25 C to the developing sleeve  26 C 3 . The negatively charged toner in the brush-like developer on the surface of the developing sleeve  26 C 3  is adhered, due to an electrostatic force, to an area of electrostatic latent image on the photoreceptor  25  by the developing bias. 
   At this time, an electrostatic force is produced so that a positively charged carrier is moved to an area of non-electrostatic latent image on the photoreceptor  25 . However, due to restraining of carrier by a magnetic force of a magnetic roll in a developing roller  26 C 1 , the positively charged carrier is not moved on to the photoreceptor drum  25 C. Using of such a type of developing bias improves capability of toner deposition on the electrostatic latent image on the photoreceptor drum  25 C, improves developing capability of continuous black image, and enables uniform developing with utmost clarity of fine lines such as characters and dots etc. identical to the electrostatic latent image. 
   In  FIG. 10 , a process cartridge is structured by supporting at least one from among the charging unit  27 C which sets the bias characteristics to the photoreceptor drum  25 C, the developing unit  26 C, and the cleaning unit  28 C having a cleaning blade  28 C 1  that is in contact with the photoreceptor drum  25 C, by the same support as that of the photoreceptor drum  25 C. The process cartridge is detachable from the main body of the image forming apparatus. Moreover, image forming units for four colors can be collectively drawn out to an outer side. 
   The cleaning unit is provided not only for the photoreceptor drum  25 C. In addition, a cleaning unit  27 C 1  is provided for cleaning a roller used in the charging unit  27 C. The cleaning unit  27 C 1  eliminates foreign matters like dust and toner reversely transferred from the photoreceptor drum  25 C to the charging unit  27 C, thereby preventing variation in the electric field due to charging unevenness and carrying out stable and uniform charging. 
   On the other hand, the photoreceptor drum  25 C is a cylinder of 0.75 millimeter thick metal with a photosensitive layer provided on the surface of the cylinder and a vibration absorber provided inside the cylinder. 
     FIG. 11  and  FIG. 12  illustrate the internal structure of the photoreceptor drum  25 C. The vibration absorber (shown by reference numeral  110 ′ and  110 ″ for convenience) that is formed by an elastic material containing either of butyl rubber and nitrile rubber is fitted inside the photoreceptor drum  25 C. The vibration absorber shown  110 ′ in  FIG. 11  is in the form of a solid cylinder and the vibration absorber  110 ″ shown in  FIG. 12  is in the form of a hollow cylinder. It is noted that the vibration absorber  110 ′ explained hereinafter includes the vibration absorber  110 ″ when the two absorbers do not need to be individually explained. The vibration absorber  110 ′ is provided in either of an area of the roller  102  in its axial direction where the roller tends to easily deform by bending and a region around this area. 
   The tangent of loss tan δ of the vibration absorber  110 ′ is set to be greater than or equal to 0.5 for the following reason. The tangent of loss tan δ means a tangent of phase angle δ (loss angle) of stress and strain in the material to be used in the vibration absorber, and the greater the value of tan δ, the greater the damping effect is. 
   Following is a result of experiment carried out for measurement of the tangent of loss tan δ, and the measurement was carried out according to a non-resonant vibration method that is prescribed in the Japanese Industrial Standards (JIS) K7244-4. A sample having a thickness of 2 millimeters, a width of 5 millimeters, and a length of 30 millimeters was used as a specimen and a result was achieved by carrying out measurement at applying frequency of 30 Hertz. The solid cylinder as shown in  FIG. 11  and the hollow cylinder as shown in  FIG. 12  which have different values of tangent of loss tan δ were prepared for samples for the experiment. 
     FIG. 13  is graphical representation of results of the experiment. Acoustic power is on a vertical axis and the tangent of loss tan δ is on a horizontal axis in this figure. It is evident from the result of the experiment that vibrations were reduced to a satisfactory level of hearing (high frequency sound is not harsh to ears) when the value of tan δ is 0.5 or more in the solid cylindrical vibration absorber  110 ′ of  FIG. 11 . Similarly, vibrations were reduced to a satisfactory level of hearing when the value of tan δ is 0.6 or more in the hollow cylindrical vibration absorber  110 ″ of  FIG. 12 . Moreover, even stronger vibration reduction effect can be achieved when the value of tan δ is 0.8 or more. Apart from noise due to the developing unit, noise due to the charging unit and cleaning blades was also measured together during the experiment. 
   From these results, practically satisfactory damping effect can be achieved by setting the tangent of loss tan δ to 0.5 or more and even better damping effect can be achieved when the value of tangent of loss tan δ is set to 0.8 or more. Thus, resonance (noise) produced in the developing unit  26 , the charging unit  27 , and the cleaning blade can be reduced. The structure of the vibration absorber  110 ′ in the photoreceptor drum  25 C is not limited to the photoreceptor drum  25 C that forms an image of cyan color only, but the same structure can be used in the other photoreceptor drums as well. 
   The tangent of loss tan δ of the solid cylindrical vibration absorber  110 ′ of  FIG. 11  is smaller than the tangent of loss tan δ of the hollow cylindrical vibration absorber  110 ″ of  FIG. 12  because of the difference in masses of the two vibration absorbers  110 ′ and  110 ″. The harsh noise can be reduced effectively by changing the resonating frequency of the photoreceptor drum to the low frequency. The hollow cylinder is a favorable from the material cost point of view since this cylinder uses less amount of material than the solid cylinder. 
   The vibration absorber  110 ′ is integrated into the photoreceptor drum  25 C by either of press fitting and bonding. Assume that an inner diameter of the photoreceptor drum is D and an outer diameter of the vibration absorber  110 ′ is d. If the vibration absorber  110 ′ is press fitted and d is less than D, then damping effect and noise reduction effect cannot be achieved because the vibration absorber is not fitted tightly to the inner surface of the photoreceptor. Conversely, if d is excessively greater than D, excessive force is required for fixing the damper inside the photoreceptor. This creates difficulties in assembling and may result in deformation of the photoreceptor while assembling. Therefore, it is preferable that a relation between D and d is in a range of D≦d≦(D+1) mm. 
   Following is an explanation of the photoreceptor drum in which the vibration absorber  110 ′ is inserted. As a photoreceptor used in image processing based on the electrophotographic method, one that uses an inorganic semiconductor material like selenium or amorphous silicon, etc., one that uses an organic semiconductor material, and one as a combination of the two are known. In recent years, the organic photoconductors (photoreceptors) (OPC) have been used widely due to their low cost, a high degree of flexibility in designing, and non-polluting nature. 
   As the organic photoreceptor used in electrophotography, those as follows are known photoreceptors. That is, the organic photoreceptor includes a photoreceptor of photoconductive resins represented by polyvinyl carbazole (PVK), a charge transfer complex type photoreceptor represented by PVK-TNF (2,4,7-trinitrofluorenone), a pigment dispersing type photoreceptor represented by phthalocyanine binder, and a function separated type photoreceptor used as a combination of charge generating material and charge carrying material. Especially, the function separated type photoreceptors have been focused on. The mechanism in the electrostatic latent image forming in the function separated type photoreceptors is as follows. When light is irradiated after the photoreceptor is charged, the light passes through a transparent charge carrying layer, and is absorbed by the charge generating material in the charge generating layer. The charge generating material that has absorbed the light generates charge carriers and these charge carriers are injected into the charge carrying layer. The charge carriers move inside the charge carrying layer according to an electric field generated by charging and an electrostatic latent image is formed due to neutralization of charge on the surface of the photoreceptor. 
   In the function separated type photoreceptors, it is known and useful to use a combination of the charge carrying material that absorbs light mainly in an ultraviolet region with the charge generating material that absorbs light mainly in a visible region. 
   However, the organic-based electrophotographic photoreceptors have poor mechanical and chemical durability, which is a known shortcoming. Most of the charge carrying materials is developed as low molecular compounds. However, the low molecular compounds do not have a capacity to form a membrane independently. Therefore, the compounds are dispersed into or mixed with inactive high molecules to be used. Generally, the charge carrying layer, including the low molecular charge carrying material and inactive high molecules, is soft and has poor mechanical durability. In the electrophotography process, mechanical load exerted by various parts coming in contact (developing unit, charging unit, transfer paper, cleaning brush, cleaning blade etc.) tends to break the membrane easily. 
   Therefore, a protective layer that contains filler to protect a photosensitive layer and to improve the durability of the photosensitive layer is also provided on the photosensitive layer as a top layer. A material used for the protective layer includes resins such as ABS resin, ACS resin, olefin vinyl monomer copolymer, chlorinated polyether resin, allyl resin, phenolic resin, polyacetal resin, polyamide resin, polyamide imide resin, polyacrylate resin, polyallyl sulfone resin, polybutylene resin, polybutylene terephthalate resin, polycarbonate resin, polyether sulfone resin, polyethine resin, polyethelene terephthalate resin, polyimide resin, acrylic resin, polymethale pentane resin, polypropylene resin, polyphenylene oxide resin, polysulfone resin, AS resin, AB resin, BS resin, polyurethane resin, polyvinyl chloride resin, polyvinyledene chloride resin, and epoxy resin. A filler to be added to further improve the wear resistance of the protective layer includes fluororesin like polytetra fluoroethylene, and silicon resin, and these resins dispersed with inorganic materials like titanium oxide, tin oxide, potassium titanate, silica, alumina, etc. 
   Quantity of the filler to be added to the protective layer by weight is normally in a range of 10% to 40%, preferably in a range of 20% to 30%. When the quantity of the filler is less than 10%, the wear is increased, which deteriorates the durability. When the quantity of the filler is more than 40%, rise in electric potential in a bright area during exposure is increased and photographic sensitivity drops to the extent that cannot be neglected, hence more than 40% is not desirable. Moreover, dispersion-assisting agent can be added to the protective layer to improve dispersion of the filler. A dispersion-assisting agent used in paints can be used for adding. Normally, the quantity of the dispersion-assisting agent with respect to the quantity of the filler contained is in a range of 0.5% to 4%, preferably in a range of 1% to 2%. Furthermore, adding of charge carrying material to the protective layer is also effective and an antioxidant can also be added if necessary. A method of forming the protective layer includes a normal coating method like a spraying method. 
   The thickness of the protective layer is in a range of 0.5 μm to 10 μm, preferably in a range of about 4 μm to 6 μm. An intermediate layer can be provided between the photosensitive layer and the protective layer of the photoreceptor used in the embodiment. Normally, a binder resin is used as a main component in the intermediate layer. The resins for the binder or the like include polyamide, alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinyl buteral, or polyvinyl alcohol. A method of forming the intermediate layer includes the normal coating method. The appropriate thickness of the intermediate layer is in a range of about 0.05 μm to 2 μm. 
   The inventors of the present invention carried out an experiment on the noise reduction effect when the vibration absorber was fitted inside the photoreceptor having the above structure, and the following result was obtained. Following is an explanation about the photoreceptor that is used in this experiment. 
   A photoreceptor for evaluation is similar to the one explained in the previous embodiment that employs a hollow cylinder having an outer diameter of 30 millimeters, an inner diameter of 28.5 millimeters, and a wall thickness of 0.75 millimeter. 
   (1) Making of Photoreceptor (No. 1) for Evaluation 
   Solutions of compositions given below were sequentially coated on an aluminum drum having an outer diameter φ30 millimeters and dried. The solutions include a coating solution for undercoat layer, a coating solution for charge generating layer, and a coating solution for charge carrying layer. When the coated layers were dried, the undercoat layer of thickness 3.5 μm, the charge generating layer of thickness 0.2 μm, and the charge carrying layer of thickness 25 μm were formed. Thus, electrophotographic photoreceptor (photoreceptor No. 1) for evaluation was obtained. 
   Coating Solution for Undercoat Layer: 
   Alkyd resin: 6 weight parts (Bekkozol 1307-60-EL made by DAINIPPON INK &amp; CHEMICALS INDUSTRIES) 
   Melamine resin: 4 weight parts (Super Bekkamine G-821-60 made by DAINIPPON INK &amp; CHEMICALS INDUSTRIES) 
   Titanium oxide: 40 weight parts 
   Methyl ethyl ketone: 200 weight parts 
   Coating Solution for Charge Generating Layer: 
   Trisazo pigments with the formulation as shown in chemical formula 1: 2.5 weight parts 
   
     
               
       
           
           
       
    
   
   Polyvinyl butyral (UCC:XYHL): 0.25 weight parts 
   cyclohexanone: 200 weight parts 
   methyl ethyl ketone: 80 weight parts 
   Coating Solution for Charge Carrying Layer: 
   Bisphenol A-type polycarbonate: 10 weight parts (Panlite K1300 made by TEIJIN) 
   Low molecular charge carrying material with the formulation as shown in chemical formula 2: 10 weight parts 
   
     
               
       
           
           
       
    
   
   Methylene chloride: 100 weight parts 
   (2) Making of Photoreceptor (No. 2) for Evaluation 
   The photoreceptor (No. 2) for evaluation was made by forming a protective layer with a thickness of 2 μm on the charge carrying layer of the photoreceptor (No. 1) using a coating solution for protective layer with the formulation given below. The remaining layers of the photoreceptor (No. 2) were the same as in the photoreceptor (No. 1). 
   Coating Solution for Protective Layer: 
   Charge carrying material with the formulation as shown in chemical formula 3: 2 weight parts 
   
     
               
       
           
           
       
    
   
   A-type polycarbonate: 4 weight parts 
   Methylene chloride: 100 weight parts 
   (3) Making of Photoreceptor (No. 3) for Evaluation 
   The photoreceptor (No. 3) for evaluation was made by forming a protective layer with a thickness of 2 μm on the charge carrying layer of the photoreceptor (No. 1) using a coating solution for protective layer with the formulation shown in chemical formula 3. The remaining layers of the photoreceptor (No. 3) were the same as in the photoreceptor (No. 1). 
   Coating Solution for Protective Layer: 
   Charge carrying material with the formulation as shown in chemical formula 3: 4 weight parts 
   A-type polycarbonate: 4 weight parts 
   Titanium oxide: 1 weight part 
   Methylene chloride: 100 weight parts 
   (4) Making of Photoreceptor (No. 4) for Evaluation 
   The photoreceptor (No. 4) for evaluation was made by substituting titanium oxide for a filler which was dispersed in the protective layer of the photoreceptor (No. 3), by aluminum oxide. The remaining layers of the photoreceptor (No. 4) were the same as in the photoreceptor (No. 3). 
   The inventors of the present invention achieved following results by carrying out experiments using the photoreceptors for evaluation No. 1 to No. 4. The experiments were carried out on quality of images on each of the photoreceptors and on noise caused by the case where the vibration absorber was fitted in the photoreceptor. 
   In the experiments, a continuous paper-feeding test was carried out with a digital copying machine IMAGIO MF 200 (trade name) made by RICOH COMPANY, LTD. The image quality (overall evaluation of image density, resolution etc.) was found to be very good. A F-to-C ratio between molecules of fluorine and carbon on the surface of the photoreceptor as an index for deposition of fluorine-based material existing on the surface of the photoreceptor was found to be zero. Moreover, during running of the copying machine, the amount of decrease Δd from an initial value in the thickness of the photosensitive layer was found to be appropriate and hard copies having high definition could be obtained with stability during long period of time. 
   In the photoreceptors No. 1 to No. 4, the vibration absorber  110 ′ was fitted as shown in  FIG. 11  and  FIG. 12  and developing bias in which ac voltage was superimposed on dc voltage was applied to the photoreceptors. As a result, resonance in the photoreceptors was reduced, transmission of vibrations of a cleaning blade was prevented, and prevention of noise generation was confirmed. 
   Following is an explanation of practical application of the present invention. 
     FIG. 14  illustrates a laser printer as an example of the image forming apparatus that uses a one-component developer using magnetic toner as a developer. In a case of using the one component developer, structure of a basic image forming section resembles to that of an image forming apparatus that uses a two-component developer. 
   In  FIG. 14 , reference numeral  50  is an image carrier in the form of a drum (hereinafter “photoreceptor drum”) provided inside the main body of the printer. Right side of the figure is a front side of the printer. When the printer is in use, the photoreceptor drum  50  rotates in a direction of an arrow shown in the figure (in counterclockwise direction). To start with, a charging roller  51  charges the surface of the photoreceptor drum  50  uniformly and then writing is carried out by irradiating laser light L from an optical writing unit thereby forming an electrostatic latent image on the surface of the photoreceptor drum  50 . 
   A developing unit  52  provided adjacent to the photoreceptor drum  50  includes a developing roller  53 . A prescribed gap between the photoreceptor drum  50  and the developing roller  53  is set to 300 μm or less, preferably 280 μm. The one-component developer stored in a developer storage  68  is carried on the surface of the developing roller  53  and is supplied to the photoreceptor drum. The prescribed gap is set to prevent deterioration of developing capability when dc voltage is applied and further ac voltage is applied in addition, similar to the case of using the two-component developer. When this gap is excessively large and the developing roller  53  is farther away from the photoreceptor drum  50 , the improvement in the developing capacity when the ac voltage image is superimposed on the dc voltage, is affected. When the gap is set to be less than 300 μm i.e. to be made narrow, it is possible to further improve the high developing capacity such that a developed image is identical to a latent image having utmost clarity and toner dots are uniform. To maintain this prescribed gap, an abutting roller is used like in the case of the developing sleeve  26 C 3  as shown in  FIG. 10 . 
   To adhere magnetic toner as the one-component developer to the photoreceptor drum  50 , a developing bias having dc voltage superimposed by ac voltage on it by a power source not shown is applied to the developing roller  53  in addition to an electrostatic absorption force of an electrostatic latent image formed on the surface of the photoreceptor drum  50  are applied combined on the developing roller  53 . The magnetic toner is supplied to the photoreceptor drum  50  by the developing roller  53  in the developing unit  52  through rotation of the photoreceptor drum  50  to develop an electrostatic latent image on the photoreceptor drum  50 . 
   The developing unit  52  includes known components such as a developing blade  54  that scrapes the developing roller  53  thereby carrying out frictional charging to toner, an agitating shaft  55  and an agitator  56  that agitate and carry the toner, and a toner ending sensor  57  that detects the quantity of the toner remaining in the developing unit. 
   In the structure shown in  FIG. 14 , a vibration absorber is included in the photoreceptor drum  50  similarly as shown in  FIG. 10 . For the structure, the structures shown in  FIG. 11  and  FIG. 12  are used. 
   In  FIG. 14 , a sheet-like recording material which is stored in a paper-feeding cassette (not shown) is fed along the rotation of the photoreceptor drum  50 , and the recording material stops for a time when it is held between a pair of register rollers  59 . When the pair of register rollers  59  rotates with the timing matched with that of an image on the photoreceptor drum  50 , the recording material is guided by a part  70 A on an outer surface of a cartridge case  70  and forwarded to a transfer nip between the photoreceptor drum  50  and the transfer roller  60 . A toner image on the photoreceptor drum  50  is transferred to the recording material through a transfer bias from the transfer roller  60 . 
   After transferring of the image to the recording material, the recording material is decharged by a decharging pin  61  and carried upward through a carrier path in a state of the material as indicated by a reference numeral S. The recording material is then guided to a fixing nip formed at a position where a pressure roller and a fixing roller of the fixing unit not shown are in contact with each other. Here, the transferred image is fixed by heat and pressure, and the recording material is discharged to a paper discharging section with an image surface facing downward. 
   Residual toner on the photoreceptor drum  50  after having transferred the image is eliminated by a cleaning blade  58  of the cleaning unit  57  through the rotation of the photoreceptor drum  50 . The photoreceptor drum  50  is kept ready for recharging by the charging roller  51 . 
   In the laser printer structured as shown in  FIG. 14 , the photoreceptor drum  50 , the charging roller  51 , the developing unit  52 , and the cleaning unit  57  etc., are accommodated in the cartridge case  70  as a casing of the printer, thereby forming a process cartridge  71 . The main body of the image forming apparatus is made compact in size by improving an accuracy of relative position of each component with respect to the other component. The handling is made easier by enabling the replacement of parts at a time instead of replacing them at different times. The maintenance of the image forming apparatus is made simple to make its life longer. 
   Thus, according to the first embodiment, the vibration absorber is disposed on the side opposite to the surface facing the unit in which the bias characteristics are set in the latent image carrier. Therefore, due to the bias characteristics, the vibration absorber that is in contact with the latent image carrier absorbs a part of the vibrations in the latent image carrier, which is caused by the vibrating electric field generated when ac voltage is applied. This enables to reduce the resonance of the latent image carrier, thereby preventing noise. Even if the latent image carrier is either of a belt and a thin-walled cylinder, noise can be prevented without increasing the mass and complicating the structure of the latent image carrier. 
   Further, since the vibration absorber is in the form of a roller and the strong vibration absorbing material is provided either on the surface of the absorber or inside the absorber, the propagation of vibrations is prevented when the roller is in contact with the latent image carrier. Thus, the noise due to resonance in the latent image carrier is prevented. 
   Moreover, since the drive roller is used as the vibration absorber when the latent image carrier is in the form of a belt, a material that comes in firm contact with the latent image carrier, can be used as a damper. This facilitates the absorption of vibrations generated in the latent image carrier and enables to reduce the resonance in the latent image carrier by using the existing structure. 
   When the latent image carrier is a belt, the vibration absorber is provided on the opposite side of the surface of the supporting plate where the supporting plate is in contact with the latent image carrier. The supporting plate is made of a rigid body in the form of a flat plate that is in contact with the belt. Therefore, the vibration absorber absorbs the vibrations generated in the belt without obstructing the movement, and resonance produced in the latent image carrier can be reduced. 
   Since the vibration absorber is disposed in a position opposite to the unit in which the bias characteristics with respect to the latent image carrier are set, the resonance can be reduced in the most effective manner at the origin of resonance produced in the latent image carrier due to the bias characteristics. 
   Since the latent image carrier is a substrate in the form of a thin belt made of a material that absorbs strong vibrations, the material can reduce the vibrations of the latent image carrier as compared to the case where a photosensitive layer is provided on the surface of the thin belt-like substrate. Therefore, there is no need to have a special arrangement for damping and hence no extra cost is needed. 
   By setting the value of tangent of loss tan δ which affects the damping effect to a value greater than or equal to 0.5, the frequency of resonance can be varied to the frequency range in which high frequency sound that is harsh to ears is not generated. Therefore, even when the noise is generated from the latent image carrier, the same effect as that of reducing the noise can be achieved. 
   Since the vibration absorber is in the solid cylindrical form, it is possible to vary the resonance frequency of the latent image carrier to the low frequency range efficiently by using the difference of mass compared to that of the hollow cylindrical form. Thus, the resonance caused by the vibrations of the latent image carrier can be prevented and noise can be reduced in an efficient manner. 
   It is possible to reduce the material cost by using the vibration absorber in the hollow cylindrical form. In a case of the structure that leads to the reduction in the material cost, in other words, even in a case where it is difficult to decrease the resonance frequency due to the mass different from that in a case of the solid cylindrical form, deterioration of the damping effect can be prevented reliably by setting the value of tangent of loss tan δ which affects the damping effect to a value greater than or equal to 0.6. 
   Moreover, since the vibration absorber is fitted inside the latent image carrier by either of press fitting and bonding, it is thoroughly integrated with the latent image carrier thereby reducing the resonance in the latent image carrier in an efficient manner. 
   A second embodiment of this invention will be explained below. 
     FIG. 15  is a cross section of a schematic structure of an image forming apparatus that uses an image carrier drum in the form of a hollow cylinder according to the second embodiment. An image carrier drum  202  in the figure is a photoreceptor drum with a photosensitive layer provided on an outer peripheral surface of a circular cylindrical tube made of a conductive metal like aluminum. In an example shown in  FIG. 15 , an image forming module  218  is structured by assembling the image carrier drum  202  integrally with an image forming unit that forms a toner image as explained later. The image carrier drum  202  is rotatably supported by a case  219  of the image forming module  218 , and is driven by a drive motor (not shown) in the clockwise direction in  FIG. 15 . At this time, a charging roller  220  as an example of a charging unit rotatably supported by the case  219  is rotated, and a charging voltage is applied to the charging roller  220 . Thereby, the surface of the image carrier drum  202  is charged to a prescribed polarity. In this image forming apparatus, a spacer including a tape  201  is wound around each end of the charging roller  220  in its longitudinal direction. The tape  201  is in contact with the outer peripheral surface of the image carrier drum  202  and the charging roller  220  is in a position such that there is a minute gap with respect to the surface of the image carrier drum  202 . 
   A modulated laser beam L emitted from an exposing unit (not shown) is irradiated on the surface of the image carrier drum after charging, and an electrostatic latent image is formed on the image carrier drum. It is noted that the exposing unit is provided separately apart from the image forming module  218 . This electrostatic latent image is visualized as a toner image by a developing unit  222 . The toner image is carried on a transfer belt  208  and is transferred to a recording medium P like a transfer paper etc. that travels in a direction of an arrow A by an action of a transfer brush  209 . The transfer brush  209  is an example of a transferring unit. When the toner image having been transferred to the recording medium P passes through a fixing unit (not shown), the toner image is fixed on the recording medium P due to effect of heat and pressure. A residual toner on the image carrier drum that is left after the transferring of the toner image is eliminated by combined action of a cleaning brush  229  and a cleaning blade  230  of a cleaning unit  227 . 
   The developing unit  222  includes a developing case  223  formed with a part of the case  219  of the image forming module  218 , and a developing roller  224  rotatably supported by the developing case  223 . The developing case  223  contains developer D. The rotating developing roller  224  carries the developer D and transfers it. The transferred developer visualizes the electrostatic latent image. In this case, the two-component developer including toner and carrier, is used. When a decrease in toner density of the developer is detected, the developing case  223  is replenished with the toner from a toner container  233 . The cleaning unit  227  includes a cleaning case  228  also formed with a part of the case  219  of the image forming module  218 . The cleaning brush  229  and the cleaning blade  230  are supported by the cleaning case  228 . Thus, in the image forming apparatus shown in  FIG. 15 , the image carrier drum  202  and the image forming units, arranged around the drum, such as the charging roller  220 , the developing roller  224 , the cleaning brush  229 , and the cleaning blade  230  are integrally assembled to the case  219  to form the image forming module  218 . The image forming module  218  is detachable from the casing (not shown) of the image forming apparatus and can be replaced by a new image forming module when the module reaches end of its life. 
   Thus, in the image forming apparatus, the toner image is formed on the surface of the rotating image carrier drum  202 , and the formed toner image is then transferred to the recording medium P to achieve a recorded image. The fixing unit fixes the toner image that has been transferred on the recording medium P. The toner having a low melting point is used in the developing unit to enable the fixing of the toner image in the fixing unit at a comparatively low surface temperature of a fixing roller, for example, 145° C. The image forming apparatus forms a toner image on the image carrier drum using toner having an outflow start temperature, measured by flow tester method, of less than or equal to 102° C., preferably in a range of 99° C. to 102° C. A Shimadzu Flow Tester CFT500 made by SHIMADZU SEISAKUSHO is used for measurement of the outflow start temperature by the flow tester method. 
   This flow tester is provided to melt a test sample in a cylinder by heating the cylinder from outside, apply pressure with a constant load by a piston from the topside of the cylinder, and extrude the test sample through pores in a die disposed at a bottom of the cylinder. A temperature at which the melted test sample starts extruding from the pores of the die is an outflow start temperature. By using toner having an outflow start temperature less than or equal to 102° C., the toner image is formed on the image carrier drum. Specifically, the toner is used under setting conditions as follows, load exerted on the piston: 10 kg/cm 2 , temperature rising rate: 3.0° C./min, diameter of pore in the die: 0.5 millimeter, and die length: 10 millimeters. The flow tester method is described in Japanese Patent Application Laid Open Publications No. 2001-147551 and No. 2001-75106. 
   The charging roller  220  is disposed on the outer peripheral surface of the image carrier drum  202  in  FIG. 15  and the cleaning blade  230  is in contact with the surface of the drum. When charging voltage having ac voltage superimposed on dc voltage is applied to the charging roller  220 , the charging roller  220  vibrates due to the application of the ac voltage. Further, the cleaning blade  230  vibrates due to stick-slip during rotation of the image carrier drum  202 . These vibrations transmitted to the image carrier drum  202  may cause the drum  202  to vibrate and lead to generation of noise. Especially, when the toner having a low melting point is used, a large amount of noise may be generated in the conventional image forming apparatus thereby causing the user to feel uncomfortable. As a tube of the image carrier drum  202 , a thin-walled hollow cylinder made of aluminum is used. This tube has an outer diameter of about 30 millimeters, an inner diameter of about 28.5 millimeters, and a wall thickness of about 0.75 millimeter. The conventional image forming apparatus tends to generate noise easily when the image carrier drum  202  formed of such a thin tube is used. 
   Therefore, a damper  204  is provided inside the image carrier drum  202  in the image forming apparatus as shown in  FIG. 15  and FIG.  16 . The damper  204  shown in  FIG. 17  can also be used. The damper  204  is formed of a material having a tangent of loss tan δ greater than or equal to 0.5. The tangent of loss tan δ is a tangent of a phase angle δ (loss angle) of stress and strain in the material. The greater the value of tangent of loss tan δ, the greater the damping effect is. 
   In the image forming apparatus, considering the characteristics of this type of damping material, the damper  204  made of the material having a tangent of loss tan δ greater than or equal to 0.5 is provided to effectively suppress vibrations of the rotating image carrier drum  202 . Even by using the toner having a low melting point, it is possible to reduce the noise generated in the image carrier drum  202  during image formation to an extremely low level. A rubber material like butyl rubber, nitrile rubber etc. can be used as a material having the tangent of loss tan δ greater than or equal to 0.5. 
   The inventors of the present invention provided the damper  204  made of rubber as shown in  FIG. 17  having a value of the tangent of loss tan δ 0.5 and the damper  204  made of ABS resin having a value of the tangent of loss tan δ less than 0.5 inside the image carrier drum  202  respectively as shown in  FIG. 15 , and carried out image forming to find out if the noise was audible to a person who was present in the vicinity of the image forming apparatus. The charging voltage in which an ac voltage was superimposed on dc voltage was applied on the charging roller  220 . The inventors used two types of toner. One of the toners had an outflow start temperature of 102° C. or less and had a low melting point such that the toner image could be fixed at a surface temperature of the fixing roller of about 145° C. in the experimental apparatus. The other toner had the outflow start temperature of higher than 102° C. and a high melting point such that the toner image could be fixed at a surface temperature of the fixing roller of about 175° C. The tangent of loss tan δ of the damper  204  was measured according to a non-resonant vibration method prescribed in JIS K7244-4. A specimen having a thickness of 2 millimeters, a width of 5 millimeters, and a length of 30 millimeters was used, and measurement was carried out at applied frequency of 30 Hertz. The results of the experiment are shown in table 1. 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Toner having a high 
               Toner having a low 
             
             
                 
               melting point 
               melting point 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               Damper made of ABS 
               No generation of 
               Generation of noise 
             
             
               resin 
               noise 
             
             
               Damper made of rubber 
               No generation of 
               No generation of noise 
             
             
               having tan δ 0.5 
               noise 
             
             
                 
             
           
        
       
     
   
   In table 1, “generation of noise” means that the person observing the experiment being in the vicinity of the image forming apparatus could clearly hear the noise, and “no generation of noise” means that the noise was not heard. As can be seen in table 1, even with the toner having the low melting point, when the damper  204  made of a material that had the tangent of loss tan δ 0.5 was inserted inside the image carrier drum  202 , generation of noise was not noticed. With the same toner, when the damper  204  made of a material that had the tangent of loss tan δ less than 0.5, generation of noise was confirmed. When the same experiment was carried out without inserting the damper inside the image carrier drum, significant noise generation was recognized by using either of the toners. 
   When the damper  204  is formed of a material that has the tangent of loss tan δ greater than 0.5, particularly 0.6 or more, or even 0.8 or more, the damping effect to the image carrier drum  202  can be improved considerably. 
   When a toner including a metallic salt of high fatty acid like a zinc stearate is used as a toner for the image forming apparatus, a part of the toner gets deposited on the surface of the image carrier drum  202 . Due to the toner deposited on the surface, the coefficient of friction of the toner with the cleaning blade decreases thereby improving slip of an edge of the cleaning blade  230 . This reduces vibrations in the cleaning blade and further improves the effect of preventing noise generation. 
   The damper  204  in  FIG. 16  is in a solid circular cylindrical form whereas the damper  204  in  FIG. 17  is in a hollow circular cylindrical form. When the solid damper  204  as shown in  FIG. 16  is used, the weight of the damper  204  is increased, and thereby the overall weight of the assembly of the damper  204  and the image carrier drum  202  increases. Thus, high frequency noise that is harsh to ears can be reduced effectively. On the other hand, when the hollow damper  204  as shown in  FIG. 17  is used, the material used for the damper can be reduced and the cost can be also reduced. In such a case, the tangent of loss tan δ, the weight, the form, especially the thickness of the damper  204  has to be set appropriately to obtain required damping effect. It is possible to use the damper  204  molded in a hollow circular cylindrical form, and it is also possible to structure the damper  204  in the hollow circular cylindrical form by rolling up the sheet-like material. According to the latter method, the damper  204  in the hollow circular cylindrical form can be fabricated at a low cost using the sheet-like material thereby reducing the cost considerably. 
   As a method of fixing the damper  204  into the image carrier drum  202 , methods as follows can be employed. One of the methods is realized by inserting, by press fitting, a damper into the image carrier drum  202 . More specifically, the damper has a setting such that d is slightly larger than D where d is an outer diameter of the damper  204  before being inserted into the image carrier drum  202  and D is an inner diameter of the image carrier drum  202 . Another method is realized by setting d to be slightly smaller than D, inserting such a damper  204  into the image carrier drum  202 , and fixing the damper  204  to the inner wall surface of the image carrier drum  202  with an adhesive. Sufficient damping effect can be achieved by using either of the methods. However, in the case of press fitting the damper inside the image carrier drum, if d is smaller than D, then the damper  204  is not fitted tightly against the inner wall surface of the image carrier drum  202  thereby deteriorating the damping effect. Conversely, if d is excessively larger than D, excessive force is required for inserting the damper  204  into the image carrier drum  202 . This not only creates difficulties in assembling but also results in deformation of the image carrier drum during assembling. Therefore, it is preferable to have a relation between values of D and d such that D≦d≦(D+1) millimeter. 
   When the damper is fixed inside the image carrier drum by press fitting, there is no need to use an adhesive and the cost for this fixing can be reduced. Besides, the damper  204  can be removed from the image carrier drum  202  easily and can be recycled. Whereas, when the damper  204  is fixed inside the image carrier drum  202  by using the adhesive, it can be fixed very firmly. 
   The image forming apparatus in  FIG. 15  has the cleaning blade  230  that is in press contact with the surface of the image carrier drum  202  to clean the surface thereof after transferring of the toner image. It is possible to eliminate foreign matters like paper dust etc. that are caught between the cleaning blade  230  and the surface of the image carrier drum  202  by rotating the image carrier drum in the reverse direction by only a small angle when the image carrier drum is stopped. A mode for a reverse direction of rotation is set. In this mode, the image carrier drum  202  is rotated in a reverse direction to a rotating direction i.e. a forward direction of the image carrier drum  202  during formation of the toner image on the drum. However, when the mode is set, the noise that originates from the vibrations of the cleaning blade  230  may be generated not only during the rotation of the drum in the forward direction but also during the rotation of the drum in the reverse direction. In the conventional image forming apparatus, noise tends to be generated particularly just before the image carrier drum  202  stops its rotation, and when the image carrier drum  202  performs operations of forward rotation, stop, reverse rotation, and stop, a loud noise is generated twice consecutively. However, by providing the damper  204  having the structure, inside the image carrier drum  202 , it is possible to prevent generation of loud noise even during reverse rotation of the image carrier drum  202 . 
   Following is the explanation of the image carrier drum  202  in which the damper  204  is fitted. As a photosensitive layer of the image carrier drum used in electrophotography, those as follows are known. That is, the photosensitive layer includes a photosensitive layer using an inorganic semiconductor material such as selenium and amorphous silicon, a photosensitive layer using an organic semiconductor material, and a photosensitive layer using a combination of the two. In recent years, the organic photosensitive layer has been used widely due to its low cost, a high degree of flexibility in photoreceptor designing, and non-polluting nature. The damper mentioned above can be fitted in the image carrier drum having either of the photosensitive layers. 
   As the organic photosensitive layer used in electrophotography, those as follows are known. That is, the organic photosensitive layer includes a photosensitive layer of photoconductive resins represented by polyvinyl carbazole (PVK), a charge transfer complex type photosensitive layer represented by PVK-TNF (2,4,7-trinitrofluorenone), a pigment dispersing type photosensitive layer represented by phthalocyanine binder, and a function separated type photosensitive layer used as a combination of charge generating material with charge carrying material. Especially, the function separated type photosensitive layer has been focused on. The mechanism of forming the electrostatic latent image in the function separated type photosensitive layer is as follows. That is, when light is irradiated after charging of the photosensitive layer, the light passes through a transparent charge carrying layer and is then absorbed by the charge generating material in the charge generating layer. The charge generating material that has absorbed the light generates charge carrier, and the charge carrier is injected in the charge carrying layer to move in the charge carrying layer according to an electric field created by charging. Then, an electrostatic latent image is formed due to neutralization of charges on the surface of the photosensitive layer. In the function separated type photosensitive layer, it is known and useful to use a combination of the charge carrying material that absorbs light mainly in the ultraviolet region with the charge generating material that absorbs light mainly in the visible region. 
   However, the organic photosensitive layer has poor mechanical and chemical durability, which is a known shortcoming. Most of the charge carrying materials is developed as low molecular compounds. However, since the low molecular compounds do not have a capacity to form a membrane independently, the compounds are used after being dispersed in and mixed with inactive high molecules. Generally, the charge carrying layer, formed of the low molecular charge carrying material and inactive high molecules, is soft and has poor mechanical durability. In the electrophotography process, mechanical load exerted by various parts coming in contact (developing, transfer paper, cleaning brush, and cleaning blade etc.) tends to break the layer easily due to repetitive use of the layer. 
   Therefore, the protective layer can be provided on the photoreceiving layer as a top layer made of these materials to protect the photosensitive layer and to improve the durability thereof. As explained above, adding of charge carrying materials to the protective layer is also effective, and an antioxidant can also be added if necessary. 
   Moreover, an intermediate layer can be provided between the photosensitive layer and the protective layer. Normally, a binder resin is used as a main component in the intermediate layer. Polyamide, alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinyl buteral, polyvinyl alcohol etc. are examples of the binder resin. The intermediate layer is formed by the normal coating method. The appropriate thickness of the intermediate layer is in a range of approximately 0.05 μm to 2 μm. 
   When the image carrier drum has the protective layer on its surface, the breaking of the photosensitive layer is suppressed. Due to this, the cleaning blade can be pressed against the image carrier drum with even stronger force. Therefore, it is possible to clean wax etc. in the toner that gets deposited on the image carrier drum when the toner having a low melting point is used. Moreover, the variation in the friction coefficient of the surface of the image carrier drum is reduced. That is, it is possible to have better cleaning and better noise prevention. 
   When filler is included in the protective layer, the breaking of the photosensitive layer can be suppressed reliably thereby further improving the effect of the protective layer. 
   When the charge carrying material is included in the photoelectric layer, the breaking of the photosensitive layer can be suppressed reliably thereby further improving the effect of the protective layer. 
   In the image forming apparatus in  FIG. 15 , the image forming module  218  is structured by integrally assembling the image carrier drum  202  and a plurality of image forming units used for forming the toner image on the drum  202 . However, the image forming module  218  can be structured by integrally assembling at least the drum  202  and the cleaning blade  230  that cleans the surface of the drum  202  after transferring of the toner image. In such a case, values of resilience and Young&#39;s modulus etc. vary due to temperature and humidity of an area around the cleaning blade  230 . When the temperature and humidity increase, the cleaning blade tends to vibrate easily and the image carrier drum tends to generate noise easily. 
   Therefore, it is useful to provide an environmental control unit to maintain at least either one of the temperature and the pressure of the image forming module at a predetermined value or below. Concretely, a sensor  203  that detects either of temperature and humidity or both is provided in the image forming module  218  as shown in  FIG. 15 . When the sensor  203  detects that either of temperature and pressure or both inside the image forming module  218  is a predetermined value or more, a fan (not shown) provided in the casing of the image forming apparatus starts. The fan blows air inside the image forming module  218  in the direction indicated by arrows E and cools down the cleaning blade  203 . This reduces the generation of noise more effectively. 
   In the image forming apparatus shown in  FIG. 15 , the charging unit is formed with the charging roller  220  that is disposed close to the image carrier drum  202 . The image carrier drum  202  with the damper inserted into it, can also be used in an image forming apparatus that uses any other type of charging units as shown in  FIG. 18  to  FIG. 20 . Each of the charging units shown in  FIG. 18  to  FIG. 20  is a contact type charging unit that is in contact with the surface of the image carrier drum  202  formed with a photoreceptor drum that rotates in a direction of an arrow to charge the image carrier drum  202 . Each of the charging units is formed with a charging roller  220 A, a brush roller  220 B, or a magnetic brush unit  220 C. 
   The charging roller  220 A shown in  FIG. 18  is formed with a core metal  237   a  and a conductive rubber layer  237   b  fixed on its outer peripheral surface. Two ends of the core metal  237   a  are supported by bearings (not shown) such that the core metal can rotate freely. The charging roller  220 A is pressed against the image carrier drum  202  by a pressurizing unit (not shown) with prescribed pressure and rotates following the rotation of the image carrier drum  202 . Concretely, the rubber layer  237   b  having medium resistance of about 1×10 5  ohm-cm covers the core metal  237   a  having a diameter of 9 millimeters. A diameter of the charging roller  220 A is 16 millimeters. The core metal  237   a  is connected to a power source  250 , which applies a prescribed bias to the charging roller  220 A. Due to application of the bias, the outer surface of the image carrier drum  202  is charged uniformly to a prescribed polarity and electric potential. The damper is fitted inside the image carrier drum  202 . Due to the effect of the damper, the generation of noise in the image carrier drum is reduced even when the charging voltage in which ac voltage is superimposed on dc voltage is applied to the charging roller  220 A. 
   In an example shown in  FIG. 19 , a brush  247   b  of the brush roller  220 B is in contact with the surface of the image carrier drum  202  with a prescribed pressure so as to have a prescribed nip. The brush is made of any of carbon, copper sulfide, metal, and metallic oxides, and is subjected to conductivity processing. The brush is wound or stuck around a metal or any other core metal subjected to conductivity processing to form the charging roller (brush roller)  220 B. 
   More specifically, a tape in which a conductive rayon fiber REC-B made by UNITICA CO., LTD. is used as a pile fabric, is wound spirally as the brush  247   b  around the core metal  247   a  with a diameter of 6 millimeters to form the brush roller  220 B having an outer diameter of 14 millimeters and a length of 250 millimeters along the axial direction. Note that the core metal  247   a  also acts as an electrode. The brush has a density of 300 deniers/50 filaments and 155 threads per one square millimeter. The brush  202 B is inserted into a pipe having a diameter of 12 millimeters by rotating in one direction and fitted in such a way that the brush and the pipe are concentric. Hair of the brush can be bent on one side by leaving the brush in a high temperature and high humidity atmosphere. The resistance value of the brush roller  220 B is 1×10 5  ohms for an applied voltage of 100 volts. 
   This resistance value is calculated from the current that passes when the brush roller  220 B is brought into contact with the metal drum having a diameter of 30 millimeters with a nip width of 3 millimeters and a voltage of 100 volts is applied to the core metal  247   a . The resistance value of the brush roller has to be 10 4  ohms or more so that even if a defective part of the low withstand voltage such as a pinhole is produced on the image carrier drum as a charged body, there is no poor charging of the charging nip due to an excessive leakage current in this part and defective image forming is prohibited. The resistance value of the brush roller has to be 10 7  ohms or less to inject sufficient charge on the surface of the image carrier drum. 
   The material for the brush includes REC-C, REC-M1, REC-M10 in addition to REC-B made by UNITICA CO., LTD, SA-7 made by TORAY CO., LTD, Thunderon made by NIHON SANMO CO., LTD, Belltron made by KANEBO CO., LTD, Clacarbo made by KURARAY CO., LTD, a material obtained by dispersing carbon into rayon, and Lobal made by MITSUBISHI RAYON CO., LTD. It is preferable that a line of brush is in a range of 3 deniers to 10 deniers, and the brush is in a range of 10 filaments to 100 filaments per bunch, and has 80 threads to 600 threads per millimeter. The preferable length of brush hair is in a range of 1 millimeter to 10 millimeters. 
   The brush roller  220 B in the example is driven to rotate at a prescribed circumferential velocity (speed of the surface) in a reverse direction (counter direction) to the rotating direction of the image carrier drum  202 . The brush roller  220 B is in contact with the surface of the image carrier drum  202  with a different speed as that of the drum. A power supply  250  applies a prescribed charging voltage to the brush roller  220 B, and the rotating image carrier drum is charged uniformly to a prescribed polarity and electric potential by the brush roller in contact with the drum. In the example, the brush roller  220 B carries out the contact charging to the image carrier drum dominantly by direct injection charging, and the surface of the image carrier drum is charged to almost the same electric potential as the applied charging voltage to the brush roller. The damper is fitted inside the image carrier drum  202  in  FIG. 19  as well. Due to the effect of the damper, the generation of noise in the image carrier drum  202  is reduced even if the charging voltage in which ac voltage is superimposed on dc voltage is applied to the brush roller  220 B. 
   In an example in  FIG. 20 , a charging unit that uses a magnetic brush is provided adjacent to the image carrier drum  202 . A magnetic brush MB is arranged such that it is in contact with the peripheral surface of the image carrier drum  202  with a prescribed nip. 
   A magnetic brush unit  220 C in the example includes a non-magnetic sleeve  257   a  that supports the magnetic brush MB and a magnetic roller (not shown) incorporated in the non-magnetic sleeve  257   a . Various types of ferrite particles like Zn—Cu ferrite can be used as particles for the magnetic brush. More specifically, the magnetic brush is formed as follows. The Zn—Cu ferrite particles of an average particle size: 25 μm are mixed with Zn—Cu ferrite particles of an average particle size: 10 μm in the ratio of weights 1:0.05 respectively. The ferrite particles of an average particle size 25 μm which have peaks in respective positions of the average particle size, are coated with a resin layer of medium resistance to give magnetic particles. The sleeve  257   a  is coated with the coated magnetic particles by a thickness of 1 millimeter to form the magnetic brush. 
   The magnetic particles are carried on the sleeve  257   a  by magnetic force of the magnetic roller that is incorporated in the sleeve  257   a . Such a magnetic brush MB forms a charging nip having a width of about 5 millimeters (width of the direction of rotation) between the magnetic brush MB and the image carrier drum  202 , and enables to adjust the gap between the sleeve  257   a  that holds the magnetic particles and the image carrier drum  202  to about 500 μm. 
   Moreover, it is preferable that the non-magnetic sleeve  257   a  is rotated so that the surface of the sleeve  257   a  moves in the direction opposite to the direction of moving of the surface of the image carrier drum at a speed double with respect to the peripheral velocity of the image carrier drum. It is also preferable that the magnetic brush is made to scrape the surface of the image carrier drum, and that the image carrier drum and the magnetic brush are in uniform contact with each other. A prescribed charging voltage is applied to the sleeve  257   a  by the power source  250  and the image carrier drum is charged uniformly to a prescribed polarity and electric potential through the magnetic brush MB. The damper is fitted inside the image carrier drum  202  in  FIG. 20  as well. Due to the effect of the damper, the generation of noise in the image carrier drum  202  is reduced even if the charging voltage in which ac voltage is superimposed on dc voltage is applied to the drum  202  by using a contact type charging unit like the magnetic brush unit  220 C in the example. 
   The present invention can be applied to a color image forming apparatus in which plurality of image carrier drums, i.e. photoreceptor drums are lined up. Moreover, the present invention is also applicable to any types of image forming apparatuses like a printer, a facsimile, a copying machine, and a multifunction machine of these apparatuses. 
   Thus, the example of the image carrier drum that is formed with a photoreceptor drum and is provided with the damper inside the image carrier drum is explained here. However, even in a case of the image carrier drum formed with an intermediate transfer drum to which the toner image is transferred from the photoreceptor, the generation of noise from the intermediate transfer drum can be reduced effectively by providing the damper inside the intermediate transfer drum. Moreover, the generation of noise can be reduced by providing the damper inside the roller that supports the photoreceptor in the form of an endless belt and the intermediate transfer belt. 
   Thus, according to the second embodiment, the generation of noise can be effectively reduced even if the toner having a low melting point is used. 
   A third embodiment of this invention will be explained below. 
     FIG. 21  is a cross section of an image forming unit of an image forming apparatus provided with an image carrier drum according to the third embodiment. An image carrier drum  202  in the figure is a photoreceptor drum which includes a photosensitive layer provided on an outer peripheral surface of a circular cylindrical tube made of a conductive metal like aluminum. The image carrier drum  202  is supported by a shaft  301  that extends through inside the image carrier drum  202  as explained later. Both ends of the shaft  301  along its length are supported by a case  219  of an image forming module  218 . The image carrier drum  202  supported by the shaft  301  is rotated by a drive motor (not shown) in a clockwise direction as shown in  FIG. 21 . During rotation of the image carrier drum  202 , a charging unit formed with a charging roller  220  rotatably supported by the case  219  rotates while being in contact with the outer peripheral surface of the image carrier drum  202 . The surface of the image carrier drum  202  is charged to a prescribed polarity by applying a charging voltage to the charging roller  220 . 
   A modulated laser beam L emitted from an exposing unit (not shown) is irradiated on the surface of the image carrier drum  202  after being charged to form an electrostatic latent image on the image carrier drum. The exposing unit is provided separately apart from the image forming module  218 . This electrostatic latent image is visualized as a toner image by a developing unit  222 . The toner image is carried on a transfer belt  208  and is transferred to a transfer paper P that travels in a direction of an arrow A by an action of a transfer brush  209 . The toner image having been transferred to the transfer paper P is fixed on the transfer paper by a fixing unit (not shown). A residual toner on the image carrier drum after the transferring of the toner image is eliminated by combined action of a charging brush  229  and a cleaning blade  230  of a cleaning unit  227 . 
   The developing unit  222  includes a developing case  223  that is formed with a part of the case  219  of the image forming module  218  and a developing roller  224  that is rotatably supported by the developing case  223 . The developing case  223  contains developer D. The developer D is carried on the rotating developing roller  224  and transferred, and the electrostatic latent image is visualized by the transferred developer. In this case, a two-component developer, which includes toner and carrier, is used as the developer. When a decrease in toner density of the developer is detected, the toner is replenished from a toner container  233 . The cleaning unit  227  includes a cleaning case  228  that is also formed with a part of the case  219  of the image forming module  218 . The cleaning brush  229  and the cleaning blade  230  are supported by the cleaning case  228 . The toner recovered from the image carrier drum  202  is returned to the toner container  233  through a toner carrier tube  231  connected to the case  219 . 
   Thus, in the image forming apparatus shown in  FIG. 21 , the image carrier drum  202  and the image forming units provided around the drum  202  such as the charging roller  220 , the developing roller  224 , the cleaning brush  229 , the cleaning blade  230  are integrally assembled to the case  219  and the image forming module  218  is formed thereby. The image forming module  218  is detachable from a casing (not shown) of the image forming apparatus and can be replaced by a new image forming module when the module reaches end of its life. 
     FIG. 22  is a longitudinal cross section of the image carrier drum  202 . Ordinary flanges  303  and  303 A are fitted to ends of the image carrier drum  202  in its axial direction of this figure. The shaft  301  passes through the flanges  303  and  303 A and extends through inside the image carrier drum  202 . The image carrier drum  202  is supported by the shaft  301  through the flanges  303  and  303 A. The shaft  301  is disposed concentrically with the image carrier drum  202  and extends through the center of the image carrier drum  202 . 
   A gear  305  is integrated on the outer periphery of the flange  303 . A counter gear (not shown) engages with the gear  305 . A drive motor (not shown) rotates the flange  303  by transmitting the rotations through the gear  305  and the counter gear. The rotations of the flange  303  are transmitted to the image carrier drum  202 , and the image carrier drum  202  rotates around the axis of its center. As shown in  FIG. 23 , a notch  306  is formed at an edge of the image carrier drum  202 . A protrusion  307  provided on the flange  303  is engaged in the notch  306  thereby transmitting the rotation of the flange  303  to the image carrier drum  202 . The flanges  303  and  303 A may be press fitted into the ends of the image carrier drum  202 , or may be fixed to the image carrier drum  202  with an adhesive. The flanges  303  and  303 A may also be engaged with the image carrier drum  202  by clearance fit. When the flanges  303  and  303 A are engaged by the clearance fit, it is necessary to hold the flanges by using thrust stoppers (not shown), which are provided to stop the flanges  303  and  303 A from moving in the axial direction of the image carrier drum  202  and coming off. A sidewall of the case  219  shown in  FIG. 21  can be used as the thrust stopper. 
   The shaft  301  passing through the flanges  303  and  303 A may be fixed to the flanges by press fit. The shaft  301  may also be engaged with the flanges  303  and  303 A such that the flanges can rotate freely around the shaft  301 . In the former case, the shaft  301  rotates together with the flange  303 , flange  303 A, and the image carrier drum  202  whereas in the latter case the shaft  301  does not rotate. In either of the cases, the shaft  301  is supported by the case  219  as shown in  FIG. 21 . 
   The charging roller  220  and the cleaning blade  230  are in contact with the outer peripheral surface of the image carrier drum  202  as shown in  FIG. 21 . When a charging voltage having ac voltage superimposed on dc voltage is applied to the charging roller  220 , the charging roller  220  vibrates due to the application of the ac voltage. Further, the cleaning blade  230  vibrates due to stick-slip during rotation of the image carrier drum  202 . These vibrations are transmitted to the drum  202 , and the drum  202  vibrates. If these vibrations become strong, then noise is produced. 
   Therefore, a damper  204  ( 204 G) is disposed inside the image carrier drum  202  of this embodiment as shown in  FIG. 21  and  FIG. 22 . The damper  204 G shown in the figures is in the form of a cup having almost U-shaped longitudinal cross sectional form. The shaft  301  passes through a hole  310  that is made in the bottom wall of the damper  204 G. The damper  204 G can be made of an appropriate material like an elastic material, a rigid material such as rubber, resin, and metal, or a combination of these materials. The damper  204  having an outer diameter slightly smaller than an inner diameter of the image carrier drum  202  is used, and such a damper  204  may be fixed to the inner wall surface of the image carrier drum  202  with an adhesive. Alternatively, the damper  204  having an outer diameter before being inserted into the drum  202  that is slightly bigger than an inner diameter of the drum  202  is used. When such a damper  204  is inserted inside the drum  202 , the damper  204  may be elastically deformed in the direction in which the diameter is contracted. Thus, the damper  204  may be pressed against the inner wall surface of the drum  202  and fixed to the drum  202 . 
   Thus, a cylinder unit  312  is integrally formed with the cylinder (the image carrier drum  202  in the example), a shaft that supports the cylinder, and a damper that is disposed inside the cylinder. The shaft  301  passes through the cylinder and further extends. In the example shown in  FIG. 22 , the pair of flanges  303  and  303 A is also included in the cylinder unit  312 . The damper  204  is provided inside the image carrier drum  202 , which makes it possible to reduce the vibrations in the image carrier drum  202  and effectively suppress the generation of noise. 
   The image carrier drum  202  goes on deteriorating with time and when it reaches end of its life, the image forming module  218  shown in  FIG. 21  is removed from the body of the apparatus and replaced by a new image forming module. The image forming module  218  removed from the body of the apparatus is recycled. That is, the cylinder unit  212  is removed from the case  219  of the image forming module  218  and disassembled into components. The components that can be reused in the existing condition are reused as they are, and the other components are subjected to prescribed recycling processing and are provided for reuse. 
   To facilitate the recycling of the cylinder unit  212 , i.e. to be able to remove the damper  204  from the image carrier drum  202 , the cylinder unit  212  is structured as follows. As shown in  FIG. 22 , a protrusion  313  having a diameter bigger than that of the shaft  301  is integrated with the shaft  301 . A portion  311  of the damper  204  facing the protrusion  313 , is positioned such that the portion  311  is in contact with the protrusion  313 . The flange  303 A on the other side is pulled out from the shaft  301  and removed. In the case where the flange  303 A is fixed to the image carrier drum  303  with an adhesive, the flange  303 A is applied with force to break the adhesive and is separated from the shaft  301  and the image carrier drum  202 . 
   Then, the shaft  301  is moved in the direction shown by an arrow B in  FIG. 22 , i.e. in the axial direction of the image carrier drum  202 . When the shaft  301  is moved, the protrusion  313  that is fixed to the shaft  301  comes in contact with a portion  311  of the damper  204  (hereinafter “contacting portion”) and pushes the area in the direction of the arrow B. Due to this, the damper  204  moves in the axial direction of the image carrier drum, i.e. the direction of the arrow B together with the shaft  301 . In the case where the damper  204  is fixed to the inner wall surface of the image carrier drum  202  with an adhesive, the damper  204  is pushed in the direction of the arrow B to break the adhesive, and is moved in the direction of the arrow B. 
   While moving the damper  204 , the shaft  301  slides with respect to the flange  303 . As shown in  FIG. 24 , when the shaft  301  is moved further in the direction of the arrow B, the damper  204  moving together with the shaft  301  pushes the flange  303 , and therefore the flange  303  is removed from the image carrier drum  202 . In this case also, when the flange  303  is fixed to the image carrier drum  202  with an adhesive, by applying an external force to the flange, the adhesive is broken. Moreover, when the shaft  301  is moved further in the direction of the arrow B, the damper  204  is eventually removed from the image carrier drum  202 . In the case where the flange  303  is fixed to the image carrier drum  202  by clearance fit, the flange  303  can be removed from the image carrier drum  202  before the damper  204  comes in contact with the flange  303 . Thus, just by pulling out the shaft  301 , the damper  204  and the flange  303  can be removed from the image carrier drum  202  thereby enabling disassemble of the cylinder unit with ease and at a low cost without using any special tools. 
   As explained above, the cylinder, the shaft  301 , and the damper  204  are assembled such that when the shaft  301  is pulled out from the cylinder as the image carrier drum  202 , the damper  204  moves in the axial direction of the cylinder together with the shaft  301  and is removed from the cylinder. Moreover, in the cylinder unit  312 , the protrusion  313  protruding in the radial direction of the shaft  301  is provided on the shaft  301 . The damper  204  has the contacting portion  311  that comes in contact with the protrusion  313  when the shaft  301  is pulled out from the cylinder. The protrusion  313  is brought into contact with the contacting portion  311  and the damper  204  is moved together with the shaft  301  thereby simplifying the structure of the cylinder unit  312 . 
   Furthermore, the contacting portion  311  of the damper  204  is positioned at the front end in the movement direction of the damper  204 . Therefore, if the damper  204  is made of an elastic material, the damper  204  is deformed by reducing its diameter when the shaft  301  and the damper  204  move in the direction of the arrow B, which allows the damper  204  to be easily moved inside the image carrier drum. Assume that the protrusion  313  fixed to the shaft  301  is structured such that the protrusion  313  pushes the rear end of the damper  204  made of an elastic material in the movement direction of the damper  204 . The frictional force that acts between the damper  204  and the inner wall surface of the image carrier drum is exerted on the damper  204 . Due to this frictional force, the damper  204  expands in the radial direction and cannot be moved smoothly. However, since the contacting portion  311  is at the front end of the damper  204  in the direction of its movement, there is no hindrance to the movement of the damper. 
   The shaft  301 , the damper  204 , the flange  303 , and the flange  303 A which are disassembled in the above manner, can be reused as they are only by cleaning these components. Moreover, since the damper  204  in the cylinder unit  312  is disposed in the space surrounded by the image carrier drum  202 , the flange  303 , and the flange  303 A, the damper  204  is not contaminated by either of dust and toner during the use of the cylinder unit  312 . Therefore, the damper  204  can also be reused without cleaning after it is separated from the image carrier drum. 
   The assembling of the cylinder unit  312  is also facilitated. For example, the damper  204  is disposed on the left side of the image carrier drum  202  in  FIG. 22  and the shaft  301  on which the flanges  303  and  303 A are not fixed is inserted inside the image carrier drum  202  from the left end of the drum  202 . While inserting the shaft  301 , the shaft  301  is passed through the hole  310  of the damper  204 , and the contacting portion  311  of the damper  204  is pushed by the protrusion  313  provided on the shaft  301 . While pressurizing the damper  204  in the direction of the arrow B in  FIG. 22 , the shaft  301  together with the damper  204  is inserted into the image carrier drum  202 . Then, the flanges  303  and  303 A are fitted to the ends of the shaft  301  and also fitted on the ends of the image carrier drum  202  thereby fitting the damper  204  inside the image carrier drum  202 . 
   Further, as shown in  FIG. 25  and  FIG. 27 , the damper  204  can also be integrally coupled to the shaft  301 .  FIG. 25  illustrates an example of fixing a hollow circular cylindrical shaped damper  204  to the shaft  301 , and  FIG. 26  illustrates an example of using a damper  204  in which a plurality of circular discs  204 A are integrated with a base  204 B and fixing the base  204 B to the shaft  301 .  FIG. 27  illustrates an example of fixing a plurality of circular shaped discs  204 C to the shaft  301  to form a damper  204 . 
   For disassembling the components of cylinder units  312  shown in  FIG. 25  to  FIG. 27 , when the shaft  301  is moved in the direction of the arrow B after the flange  303 A is separated from the shaft  301  in the same manner as explained above, the damper  204  that is integrally coupled to the shaft  301  also moves with the shaft  301 , which allows the flange  303  and the damper  204  to be separated from the image carrier drum  202 . The rest of the structures shown in  FIG. 25  to  FIG. 27  are practically similar to those shown in  FIG. 21  to  FIG. 24 . 
   The effect similar to that of the cylinder units  312  shown in  FIG. 25  to  FIG. 27  can be achieved also by fixing a solid cylindrical damper to the shaft  301 . However, when the solid damper is moved inside the image carrier drum  202 , the solid damper undergoes a considerable amount of frictional force from the inner wall surface of the image carrier drum  202 , and therefore smooth movement of the damper becomes difficult. When the dampers  204 , shown in  FIG. 25  to  FIG. 27 , are made of an elastic material in particular, the dampers  204  undergo elastic deformation easily when they are moved inside the image carrier drum  202 . Therefore, the frictional force exerted by the inner wall surface of the image carrier drum  202  decreases and the dampers  204  can be moved easily. 
   Moreover, in the example shown in  FIG. 22 , when the diameter of the image carrier drum  202  is small, the diameters of the damper  204  and the protrusion  313  also become smaller, and a contact area between the protrusion  313  and contacting portion  311  of the damper  204  becomes smaller. Therefore, when the shaft  301  is moved in the direction of the arrow B, the pressure per unit area of the contact surface between the protrusion  313  and the contacting portion  311  increases. Therefore, especially in the case of the damper  204  made of an elastic material, the portion of the damper  204  pushed by the protrusion  313  undergoes considerable elastic deformation. Due to the elastic deformation, the force is not conveyed properly from the protrusion  313  to the damper  204 , and therefore the damper  204  may not be moved smoothly. To avoid this, the damper  204  is integrally coupled to the shaft  301  to make it move easily together with the shaft  301  when the shaft  301  is pulled out from the cylinder as shown in the examples in  FIG. 25  to  FIG. 27 . Thus, the damper  204  can reliably be moved and can be removed from the image carrier drum  202  easily. 
   The cylinder unit  312  has a pair of flanges  303  and  303 A fitted to the ends of the cylinder formed with the image carrier drum  202  in the axial direction. The cylinder is supported by the shaft  301  through these flanges  303  and  303 A. The shape of the damper is set so that the damper  204  moves in the axial direction of the cylinder to come in contact with the flange  303  and pushes the flange  303 , and then the flange  303  is removed from the cylinder. Therefore, as explained above, the flange  303  can be separated from the cylinder just by pulling out the shaft  301 . Thus, the workability can be enhanced. 
   The damper  204  can be formed by an appropriate material as explained above. As shown in  FIG. 28 , in a case of pulling out the shaft  301  from the image carrier drum  202 , if a portion  314  of the damper coming in contact with the flange  303  is made of a rigid material, by bringing the portion  314  of the damper into contact with the flange  303  and pressurizing the flange  303 , the force can be appropriately conveyed to the flange  303 . Thus, the flange can be separated easily from the image carrier drum  202 . The portion  314  of the damper can be made of ABS resin or metal having a Young&#39;s modulus of about 2 to 3 GPa. 
   When the portion  314  of the damper is made of the rigid material, if the speed at which the shaft  301  is pulled out is high, the portion  314  of the damper impacts against the flange  303  and may damage the flange  303 . In a case of such concern, the portion  314  of the damper coming in contact with the flanges  303  may be made of an elastic material. For example, the portion  314  of the damper is made of rubber having a Young&#39;s modulus of about 0.5 to 1.5 MPa. Thus, even when the portion  314  impacts against the flange  303 , the damage of the flange  303  can be prevented and reused without any trouble. 
   As shown in  FIG. 29 , the flange  303  can be structured to have a first cylinder member  315  that fits to the ends of the cylinder formed with the image carrier drum  202  in the axial direction and a second cylinder member  316  that fits into the first cylinder member  315 . In this example, a gear  305  is formed on the first cylinder member  315 .  FIG. 30  is an exploded perspective view of the first cylinder member  315  and the second cylinder member  316 . To fit the flange  303  to the image carrier drum  202 , as shown in  FIG. 31 , the first cylinder member  315  is fitted into the end of the image carrier drum  202  and then the second cylinder member  316  is fitted into the first cylinder member  315 . In this case, assume that an outer diameter of the second cylinder member  316  before it is fitted into the first cylinder member  315  is D 1 , a thickness of a part of the first cylinder member  315  that is inserted in the image carrier drum  202  is T, and an inner diameter of the image carrier drum  202  is D 2 . Each diameter and thickness are set so as to be D 1 +2T&gt;D 2 . Thus, when the second cylinder member  316  is fitted in the first cylinder member  315  as shown in  FIG. 29 , the part of the first cylinder member  315  that is inserted into the image carrier drum  202  is in press contact with the inner wall surface of the image carrier drum  202  and the whole of the flange  303  is fixed to the image carrier drum  202 . 
   Thus, the second cylinder member  316  is fitted in the first cylinder member  315 , the first cylinder member  315  is made to be in pressed contact with the inner wall surface of the cylinder of the drum  202  and the flange is fixed on the cylinder. A plurality of slits  340  is formed in the first cylinder member  315  as shown in  FIG. 30 , and therefore the first cylinder member  315  can be pressed easily against the inner wall surface of the image carrier drum  202  by the second cylinder member  316 . The shaft  301  is passed through a hole  342  in the second cylinder member  316  as shown in  FIG. 29 . The shaft  301  can be assembled with the image carrier drum  202  after fixing the flange  303  to the image carrier drum  202 . The shaft  301  can also be inserted into the image carrier drum  202  before fixing the flange  303  to the image carrier drum  202 . For the flange  303 A ( FIG. 22 ,  FIG. 25 ), any of the flanges shown in  FIG. 29  to  FIG. 31  can be used. 
   When the flange  303  is structured in this manner, if the diameter of the front end of the damper  204  that faces the flange  303  is made smaller as shown in  FIG. 29  and the damper  204  is moved together with the flange  303  in the direction of the arrow B, then it is preferable to structure such that a front end surface  341  of the front end comes in contact only with the second cylinder member  316 . That is, the arrangement is made such that the damper  204  moves in an axial direction of the cylinder, the front end surface  341  of the damper  204  comes in contact only with the second cylinder member  316 , and pushes the second cylinder member  316 . With this arrangement, the second cylinder member  316  and the first cylinder member  315  are separated apart from each other due to the second cylinder member  316  pushed by the damper  204 . Thus, the first cylinder member  315  and the second cylinder member  316  can be removed from the image carrier drum  202  without applying heavy load on them. This prevents causing of any damage to the first cylinder member  315  and the second cylinder member  316  thereby enabling their reuse without any processing after disassembling. 
   According to the embodiment, the damper  204  can be integrated with the cylinder including the image carrier drum  202  as an integral assembly by press fitting the damper on the inner wall surface of the cylinder due to elastic property of the damper  204 . When the damper  204  is fixed to the image carrier drum  202  without using any adhesive material, the shaft  301  can be pulled out from the image carrier drum  202  easily thereby facilitating disassembling of the image carrier drum  202 . 
   As explained above, the cylinder of the image carrier drum  202 , the pair of the flanges  303  and  303 A, and the shaft  301  are assembled together to rotate as an integrated assembly by press fitting the flanges  303  and  303 A to the shaft  301  so as to be fixed to each other. Therefore, the flanges  303  and  303 A cannot rotate around the shaft  301  since they are fixed. This prevents the sliding contact between the shaft  301  and the flanges  303  and  303 A thereby preventing wearing away of the three. Thus, the shaft  301  and the flanges  303  and  303 A can be reused after disassembling without carrying out any special machining process on them. 
   In the embodiment, the cylinder is the image carrier drum  202  on which a toner image is formed. In other words, although the cylinder in this example is a photoreceptor drum, when the cylinder is any device other than the image carrier drum, these structures can be employed. Concretely, the cylinder includes an image carrier drum that includes intermediate transfer body on which a toner image formed on the photoreceptor drum is transferred, a charging roller, a developing roller, transfer paper carrier roller, and any other cylinder formed as a support for a structure. 
   Moreover, the image forming apparatus in  FIG. 21  includes the image carrier drum  202 , and the image forming module that is assembled by integrating the image forming elements like the charging roller  220 , the developing roller  224 , the cleaning brush  229 , and the cleaning blade  230  to form the image on the image carrier drum  202 . It is a normal practice to reduce the size and weight of this image forming module to make it easy to handle. 
   Therefore, since small sized elements are used in the image forming module, the life of the image forming module is short. In the image forming apparatus in  FIG. 21 , an arrangement is made to replenish the toner container  233  with toner. However, when there is no arrangement for replenishment of the toner and when the structure is made such that the image forming module is to be replaced after the toner in the developing unit gets exhausted, the life of the image forming module becomes further short. The short life of the image forming module implies increased number of the image forming modules that are manufactured and are in the market. Therefore, it is important to facilitate the disassembling of the cylinder unit  312  and improve recycling. By structuring the cylinder unit  312  as mentioned in the embodiment, the cylinder unit  312  can be easily recycled, and the demand can be surely satisfied. 
   The cylinder unit can also be made discretely detachable from the main body of the image forming apparatus. In this case, it is a normal practice to set the life of the image carrier drum longer than that of the image forming unit that forms an image on the image carrier drum and to go on replacing the image carrier drum while the image forming apparatus is being used. In such a case also, by structuring the cylinder unit  312  as mentioned in this embodiment to improve recycling, it is possible to reuse the components of the cylinder unit  312  easily. 
   Thus, according to the third embodiment, the recycling is facilitated by structuring the cylinder unit such that it can be easily disassembled. 
   A fourth embodiment of this invention will be explained below. 
     FIG. 32  is a schematic diagram of an image forming section of the image forming apparatus that uses an image carrier drum according to the fourth embodiment. An image carrier drum  202  in the figure is a photoreceptor drum which includes a circular tube made of a conductive metal like aluminum with a photosensitive layer provided on an outer peripheral surface. The image carrier drum  202  is rotatably supported by a case  219  of a process cartridge  218  and is rotated by a drive motor (not shown) in the clockwise direction in  FIG. 32 . A charging unit including a charging roller  220  rotatably supported by the case  219  is in contact with the image carrier drum  202  and rotates. By applying a charging voltage to the charging roller  220 , a surface of the image carrier drum  202  is charged to a prescribed polarity. 
   A modulated laser beam L is irradiated on the surface of the image carrier drum  202  after being charged, the beam being emitted from an exposing unit (not shown) provided separately apart from the process cartridge. Thereby an electrostatic latent image is formed on the image carrier drum  202 . This electrostatic latent image is visualized as a toner image by a developing unit  222 . The toner image is carried on a transfer belt  208  and is transferred to a recording medium P such as a transfer paper that travels in a direction of an arrow A, by an action of a transfer brush  209  as an example of the transfer unit. The toner image having been transferred to the recording medium P is fixed on the recording medium by the fixing unit (not shown). A residual toner on the image carrier drum that remains after the transferring of the toner image is eliminated by combined action of a cleaning brush  229  and a cleaning blade  230  of a cleaning unit  227 . 
   The developing unit  222  includes a developing case  223  formed with a part of the case  219  of the process cartridge  218  and a developing roller  224  rotatably supported by the developing case  223 . The developing case  223  contains developer D. The rotating developing roller  224  carries and conveys the developer D. The conveyed developer visualizes the electrostatic latent image. In this case, a dry two-component developer including toner and carrier, is used as developer, and when a decrease in toner density of the developer is detected, the toner is replenished from a toner container. 
   The cleaning unit  227  includes the cleaning case  228  also formed with a part of the case  219  of the process cartridge  218 . The cleaning brush  229  and the cleaning blade  230  are supported by the cleaning case  228 . The toner recovered from the image carrier drum  202  is returned to the toner container  233  through a toner carrier tube  231  connected to the case  219 . 
     FIG. 33  is a longitudinal cross section of the image carrier drum  202 . Flanges  303  and  303 A are fitted at each end of the image carrier drum  202  in the axial direction. The flanges  303  and  303 A are rotatably supported by the case  219  ( FIG. 32 ), and the image carrier drum  202  is thereby rotatably supported by the case  219 . It is possible to omit one of the flanges  303  and  303 A. It is also possible to omit both the flanges, and both ends of the image carrier drum  202  can be rotatably supported directly by the case  219 . When it is necessary to distinguish these flanges  303  and  303 A from each other, the flange  303  is referred to as a first flange and the flange  303 A is referred to as a second flange. 
   A gear  305  is integrated on the outer peripheral surface of the second flange  303 A. A counter gear, which is not shown in the figure, is engaged with the gear  305 . A drive motor, which is also not shown in the figure, rotates the second flange  303 A by transmitting the rotations through these gears. The rotations of the flange  303 A are transmitted to the image carrier drum  202 , and the drum  202  rotates around the central axis of the flange  303 A. A notch  306  is made at an end of the image carrier drum  202  as shown in  FIG. 23 . A protrusion  307  provided on the second flange  303 A is engaged in the notch  306  thereby preventing relative rotation of the second flange  303 A and the image carrier drum  202  and transmitting the rotation of the flange  303 A to the image carrier drum  202 . 
   The flanges  303  and  303 A may be press fitted into openings at the ends of the image carrier drum  202  or may be fixed to the image carrier drum  202  with an adhesive. The flanges  303  and  303 A can also be engaged with the image carrier drum by clearance fit. When the flanges  303  and  303 A are engaged by clearance fit, it is necessary to hold the flanges by using thrust stoppers not shown in the figure, which are provided to stop the flanges  303  and  303 A from moving in the axial direction of the image carrier drum  202  and from being removed from the drum  202 . A sidewall of the case  219  shown in  FIG. 32  can be used as a thrust stopper. 
   The charging roller  202  and the cleaning blade  230  are in contact with the outer peripheral surface of the image carrier drum  202  as shown in  FIG. 32 . When a charging voltage having ac voltage superimposed on dc voltage, is applied to the charging roller  220 , the charging roller  220  vibrates due to the application of the ac voltage. Further, the cleaning blade  230  vibrates due to stick-slip during rotation of the image carrier drum  202 . These vibrations are transmitted to the image carrier drum  202 , due to which the drum  202  vibrates. When these vibrations become strong, noise is produced. 
   Therefore, a damper  404  is disposed inside the image carrier drum  202  of this example as shown in  FIG. 32  and  FIG. 33 . The damper  404  includes a cylinder  417  having an outer peripheral surface  414  that is fixed to the inner peripheral surface of the image carrier drum  202 , and a sidewall  410 . The damper  404  is in the form of a cup having almost U-shaped longitudinal cross sectional form. An end of the damper  404  opposite to the sidewall  410  is kept open as an open end. 
   The damper  404  can be made of an appropriate material such as an elastic material, a rigid material such as rubber, resin, and metal, or a combination of these materials. 
   The damper  404  having an outer diameter slightly smaller than an inner diameter of the image carrier drum  202  may be used and fixed to the inner surface of the image carrier drum  202  with an adhesive. The damper  404  having an outer diameter before being inserted into the drum  202  that is slightly bigger than an inner diameter of the drum  202  may be used and inserted into the image carrier drum  202 . When the damper  404  is inserted into the drum  202 , the damper  404  undergoes elastic deformation in the direction of contraction of the diameter. Thus, the damper  404  can be fixed inside the image carrier drum  202  by making a pressed contact with an inner surface of the drum  202 . 
   Thus, the damper  404  mounted inside the image carrier drum  202  is held inside the image carrier drum  202  due to the pressed contact with the inner surface of the image carrier drum  202 . The pressed contact is attributed to the elasticity of the material of the damper. Alternatively, the damper  404  is fixed on the inner wall surface of the image carrier drum  202  with an adhesive. The damper  404  may also be fixed on the inner wall surface of the image carrier drum  202  using both elasticity and the adhesive. 
   The damper  404 , which is provided inside the image carrier drum  202 , reduces vibrations of the image carrier drum  202  and effectively suppresses the generation of noise. 
   Moreover, in the image forming apparatus of this example, an integrated drum unit  434  is structured by assembling the image carrier drum  202  with the damper  404  that is mounted inside the drum and the pair of flanges  303  and  303 A. It is also possible to structure the integrated drum unit  434  without the flanges  303  and  303 A. The drum unit  434  includes at least the image carrier drum  202  and the damper  404 . 
   Further, in the image forming apparatus of this example, the process cartridge  218  is structured by assembling the drum unit  434  integrated with the image forming units such as the charging roller  220 , the developing unit  222 , the cleaning unit  227 , which are disposed around the drum unit  434 . Suitable image forming units can be selected for forming the process cartridge  218 . In short, the process cartridge includes a drum unit and at least an image forming unit that forms a toner image on an image carrier drum of the drum unit. The process cartridge is detachable from the main body of the image forming apparatus. The image forming apparatus of this example includes either of the process cartridge  218  and the drum unit  434 . 
   The image carrier drum  202  goes on deteriorating with time and when it reaches end of its life, the process cartridge  218  shown in  FIG. 32  is removed from the main body of the image forming apparatus and replaced by a new process cartridge. The process cartridge  218  removed from the main body of the image forming apparatus is recycled. In recycling process, the image carrier drum  202  is removed from the case  219  of the process cartridge  219 . The image carrier drum  202  and the components that are assembled together with the drum are disassembled. The components that can be reused in the existing condition are reused as they are, and the rest of the components are subjected to predetermined machining or treatment process, and are provided for reuse. 
   To facilitate the recycling of the image carrier drum  202 , the damper  404 , and the flanges  303  and  303 A that are assembled with the drum, the following method is employed to easily assemble and disassemble these components. 
     FIG. 34  and  FIG. 35  are cross sections of how a damper  404  is fixed to an image carrier drum  202 . In the example shown here, an image carrier drum  202  without flanges  303  and  303 A fixed on it is prepared. A sidewall  410  of the damper  404  is made to face an opening  411  on one end in the axial direction of the image carrier drum  202  as shown in  FIG. 34 . In the examples shown in  FIG. 34  and  FIG. 35 , the damper  404  is made of an elastic material like rubber. An outer diameter of the damper  404  before being inserted into the image carrier drum  202  is set to be slightly bigger than an inner diameter of the image carrier drum  202 . 
   In the state as shown in  FIG. 34 , a force imparting member  413  in the form of a rod is inserted into a cylinder  417  of the damper  404  in the direction of an arrow B from the opening end of the damper  404 . A front-end  413 A of the force imparting member  413  is brought into contact with the sidewall  410  of the damper  404  and the force imparting member  413  is pushed further in the direction of the arrow B along the axial direction of the image carrier drum  202 . Thus, the damper  404  is thrust inside the image carrier drum  202  as shown in  FIG. 35  and moved up to the position shown in  FIG. 33 . Then, the force imparting member  413  is pulled in a direction opposite to that of the arrow B and pulled out from the image carrier drum. Thus, the damper  404  having the outer diameter before being inserted into the drum  202  that is slightly bigger than an inner diameter of the image carrier drum  202 , can be inserted and mounted inside the image carrier drum  202  with ease. 
   The damper  404  mounted inside the image carrier drum  202  is fixed to the image carrier drum  202  by pressing an outer peripheral surface  414  of the cylinder  417  against the inner peripheral surface of the drum  202  by the elasticity. The first flange  303  and the second flange  303 A are fixed on the opening  411  and an opening  412  on both ends in the axial direction of the drum  202  respectively as shown in  FIG. 33 . The image carrier drum  202  thus formed is assembled with the case  219  shown in  FIG. 32  and used. 
   The outer peripheral surface  414  of the damper  404  can also be fixed to the inner peripheral surface of the image carrier drum  202  with an adhesive. When the damper  404  is made of a rigid material, the damper  404  can be inserted into the image carrier drum  202  and fixed to the inner peripheral surface of the image carrier drum  202  in the same manner as explained above. 
   When the image carrier drum  202  and the damper  404  are to be disassembled, first of all the first flange  303  is removed from the image carrier drum  202  as shown in  FIG. 33 . When the flange  303  is fixed to the image carrier drum  202  with an adhesive, a force is applied to the flange  303  to break the adhesive, and the flange  303  is separated apart from the image carrier drum  202 . Then, as shown in  FIG. 36 , the force imparting member  413  is inserted into the image carrier drum  202  from the opening  411 , and further inserted into the cylinder  417  from the open end of the damper  404 , and the front end  413 A of the force imparting member  413  is brought into contact with the sidewall  410 . The force imparting member  413  is further pushed in the direction of an arrow B. Due to this, the damper  404  moves in the axial direction of the image carrier drum  202  that is the direction of the arrow B. Even if the damper  404  is fixed to the inner peripheral surface of the image carrier drum  202  with an adhesive, the damper  404  can be moved in the direction of the arrow B by thrusting the damper  404  in the direction of the arrow B and breaking the adhesive. 
   Thus, by thrusting the force imparting member  413  in the direction of the arrow B, the sidewall  410  of the damper  404  that moves due to pressure applied by the force imparting member  413  comes in contact with the second flange  303 A and pushes this flange as shown in  FIG. 36 . Therefore, the flange  303 A is separated apart from the image carrier drum  202 . In this case also, when the flange  303 A is fixed to the image carrier drum  202  with an adhesive, pushing the flange  303 A results in breaking the adhesive. When the force imparting member  413  is moved further in the direction of the arrow B, the damper  404  is also separated apart from the image carrier drum  202 . Then, the force imparting member  413  is pulled out from the image carrier drum  202 . Thus, the damper  404  and the flange  303 A can be separated apart from the image carrier drum  202  just by pushing the damper  404  by the force imparting member  413  thereby enabling the disassembling of components at a low cost. 
   The damper  404  and the flanges  303  and  303 A, having been disassembled in the above manner, require only cleaning for reuse. Moreover, since the damper  404  before being disassembled is disposed in the space surrounded by the image carrier drum  202 , the flange  303  and the flange  303 A, it is not contaminated by either of dust and toner during the use of the image carrier drum  202 . Therefore, the damper  404  can also be reused without cleaning after it is separated from the image carrier drum. 
   As explained above, in the method for inserting and removing the damper into and from the image carrier drum of this example, the damper  404  is inserted into the image carrier drum  202  from the opening  411  on one end in the axial direction of the image carrier drum  202 . The damper  404  is mounted inside the image carrier drum  202  and is removed from the opening  412  on the other end in the axial direction of the image carrier drum  202 . The drum unit  434  includes the image carrier drum  202  and the damper  404 . More specifically, the damper  404  is inserted into the image carrier drum  202  from the opening  411  on one end in the axial direction of the drum  202 , mounted inside the image carrier drum  202 , and then removed from the image carrier drum  202  through the opening  412  on the other end in the axial direction of the drum  202 . 
   Based on the method as explained above, the damper  404  can be mounted inside the image carrier drum  202  or can be removed from the drum  202  by carrying out simple operation thereby facilitating the recycling process. Only the same operation is required for mounting and removing the damper  404 . 
   Besides, according to the method for inserting and removing the damper into and from the image carrier drum of this example, the damper  404  is moved in the axial direction of the image carrier drum  202  by exerting an external force on the damper  404  by the force imparting member  413  and mounted inside the image carrier drum  202 . Similarly, the damper  404  is moved inside the image carrier drum  202  in its axial direction by exerting an external force by the force imparting member  413  and is removed from the image carrier drum. The damper  404  is applied with an external force exerted by the force imparting member  413 , is moved inside the image carrier drum  202  in its axial direction, and is mounted inside the image carrier drum  202 . The damper  404  is applied with an external force exerted by the force imparting member  413 , is moved inside the image carrier drum  202  in its axial direction, and is removed from the image carrier drum. Thus, operating the force imparting member  413  enables the damper  404  to be inserted into and removed from the image carrier drum  202  in a simple manner. 
   Moreover, when being inserted into and removed from the image carrier drum  202 , the damper  404  moves inside the image carrier drum  202  in the axial direction of the drum. This direction is simply called a movement direction. The sidewall  410  of the damper  404  is integrated in the front end of the movement direction of the cylinder  417  of the damper  404 . The force imparting member  413  is in contact and engaged with the sidewall  410  and pushes the damper. Thus, the sidewall  410  of the damper  404  forms an engaging portion with which the force imparting member  413  is engaged. Hereinafter, reference numeral  401  is assigned to this engaging portion formed with the sidewall  410 . 
   As explained above, the damper  404  of this example includes the engaging portion  401  with which the force imparting member  413  is engaged on the front end of the movement direction when the damper  404  moves inside the image carrier drum  202  in the axial direction of the drum  202 . The force imparting member  413  exerts an external force on the engaging portion  401  in the direction of movement of the damper  404  and moves the damper  404  in the axial direction of the image carrier drum  202 . 
   Thus, at least a part of the outer diameter of the damper  404  can be made to contract by the external force applied by the force imparting member  413  to the engaging portion  401  in the axial direction of the image carrier drum  202 . Therefore, the damper  404  can be moved smoothly inside the image carrier drum  202 . In other words, the damper  404  shown in the figure is made of an elastic material and the outer diameter of the damper  404  before insertion is set to be slightly bigger that the inner diameter of the image carrier drum  202 . Therefore, when the damper  404  is pushed slightly in the direction of the arrow B by the force imparting member  413  as shown in  FIG. 35 , the damper  404  tends to stop for a while due to the frictional force acting between the inner peripheral surface of the image carrier drum  202  and the outer peripheral surface  414  of the damper  404 . However, by further pushing the engaging portion  401  by the force imparting member  413 , the damper  404  made of an elastic material tends to be extended in the axial direction, and the damper  404  undergoes elastic deformation in the direction of contraction of the diameter as shown by an arrow C in  FIG. 35 . Therefore, the damper  404  can be moved smoothly. Similar deformation occurs when the damper  404  is pushed out from the image carrier drum. 
   When the force imparting member  413  pushes the rear end of the damper  404  in its axial direction and the damper  404  is made of an elastic material, the frictional force acting between the damper  404  and the inner peripheral surface of the image carrier drum  202  is exerted on the damper  404 . Therefore, the damper  404  expands in the radial thereby hindering the smooth movement of the damper  404 . However, disposing the engaging portion  401  on the front end in the direction of movement of the damper  404  prevents such an inconvenience. 
   In the example explained above, the damper  404  is pushed by the force imparting member  413  in the axial direction of the image carrier drum  202  and is mounted inside the image carrier drum  202 . Similarly, the damper  404  is pushed by the force imparting member  413  in the axial direction and is removed from the image carrier drum  202 . The engaging portion  401  of the damper  404  is pushed by the force imparting member  413  from one end to the other end of the image carrier drum  202  to move the damper  404  inside the drum  202 . 
   On the other hand, an engaging portion of a damper can be pulled by a force imparting member from one end to the other end of the image carrier drum  202  to move the damper inside the drum  202 .  FIG. 38  is a cross section of an example of how a damper  404  is pulled out from an image carrier drum  202 . A sidewall  410  of this damper  404  i.e. an engaging portion  401  has an engagement hole  435 . A hook  450 A is provided at a front end of a force imparting member  450  which is inserted inside the image carrier drum  202  through a hole  436  at the center of the flange  303 A. The hook  450 K is engaged in the engagement hole  435 . By pulling the force imparting member  450  in the direction of an arrow B, the damper  404  can be removed from inside of the image carrier drum  202 . In this case as well, the damper  404  pushes the flange  303 A, and therefore the flange  303 A can be removed from the image carrier drum  202 . When the damper  404  is inserted into the image carrier drum  202 , with a flange  303  separated apart from the image carrier drum  202 , the hook  450 A of the force imparting member  450  is engaged in the engagement hole  435  of the damper  404  and the damper  404  is pulled in the direction of the arrow B. 
   The rest of the structure other than the drum unit  434  shown in  FIG. 38  can also be structured similar to the drum unit explained earlier. In the case of the drum unit shown in  FIG. 38 , an external force is exerted by the force imparting member  450  on the engaging portion  401  in the axial direction of the image carrier drum  202  to contract at least a part of the outer diameter of the damper  404 . Therefore, the damper  404  can be made to move smoothly inside the image carrier drum  202 . 
   In the example explained above, as a force imparting member that moves the damper  404  inside the image carrier drum  202 , an exclusively made force imparting member  450  ( 450 A) is used. However, as this force imparting member, a shaft disposed inside the image carrier drum and supporting the drum can also be used.  FIG. 39  is a cross section of an example of such type of force imparting member. In a drum unit  434  in the figure, a shaft  437  passes through an image carrier drum  202  and is press fitted into flanges  330  and  330 A. A damper  404  shown in  FIG. 39  is similar to the damper  404  explained in the earlier example. The damper  404  in  FIG. 39  includes a cylinder  417  that has an outer peripheral surface fixed to an inner peripheral surface of the image carrier drum  202  and a sidewall  410  that is integrated on the front end in the movement direction of the cylinder  417 . The sidewall  410  has an engaging portion  401 . Moreover, the engaging portion  401  is formed by the sidewall  410  of the damper  404  that is disposed inside the image carrier drum  202 . The engaging portion  401  has a hole  438  having a diameter bigger than that of the shaft  437  that supports the image carrier drum  202 . The shaft  437  passes through the hole  438 . 
   The shaft  437  is rotatably supported by the case  219  of the process cartridge  218  shown in  FIG. 32 . The shaft  437  is a component of the process cartridge  437 . Moreover, the shaft  437  has a bigger diameter portion  439 , which can be engaged with the engaging portion  401  of the damper  404 . 
   Following is a procedure for assembling the damper  404  inside the image carrier drum  202 . The damper  404  is disposed on the left side of the image carrier drum  202  in  FIG. 39 . The shaft  437  that is without the flanges  303  and  303 A fixed is inserted into the drum  202  from the opening on the left end of the drum  202 . The shaft  437  is further passed through the hole  438  in the damper  404 . The engaging portion  401  of the damper  404  is pushed by the bigger diameter portion  439  of the shaft  437 , and the damper  404  is pushed in the direction of the arrow B in  FIG. 39 . While the damper  404  is pushed, the shaft  437  together with the damper  404  is inserted inside the image carrier drum  202 . Then, the flanges  303  and  303 A are fitted on the ends of the shaft  437  and also on the openings at the ends of the image carrier drum  202 . Thus, the damper  404  is mounted inside the image carrier drum  202 . 
   When the damper  404  is to be removed from the image carrier drum  202 , the first flange  303  is pulled out from the shaft  437  first, and the shaft  437  is made to move in the direction shown by the arrow B in  FIG. 39 , i.e. in the axial direction of the image carrier drum  202 . The bigger diameter portion  439  of the shaft  437  comes in contact with the engaging portion  401  of the damper  404  and pushes the portion  401  in the direction of the arrow B. Due to this, the damper  404  moves in the axial direction of the image carrier drum i.e. in the direction of the arrow B together with the shaft  437 . When the damper  404  is fixed to the inner peripheral surface of the image carrier drum with an adhesive, the damper  404  is pushed in the direction of the arrow B thereby breaking the adhesive to allow the damper  404  to be moved further in the direction of the arrow B. While doing this, the shaft  437  slides with respect to the second flange  303 A. When the shaft  437  is continued to be moved in the direction of the arrow B, the damper  404  moving together with the shaft  437  pushes the second flange  303 A thereby separating the flange  303 A apart from the image carrier drum  202  as shown in  FIG. 40 . When the shaft  437  is moved further in the direction of the arrow B, the damper  404  is also separated apart from the image carrier drum  202 . When the flange  303 A is fitted to the image carrier drum  202  by clearance fit, the flange  303 A can also be separated from the image carrier drum  202  before the damper  404  comes in contact with the flange  303 A. 
   The structure can also be made such that the shaft  437  is supported by the main body of the image forming apparatus, the shaft  437  is left on the main body of the image forming apparatus, and the drum unit  434  is pulled out from the shaft  437  and can be fitted to the shaft  437  again. In such a case, the drum unit  434  is removed from the main body of the image forming apparatus. Then, as shown in  FIG. 34  to  FIG. 37 , the damper  404  is removed from inside of the image carrier drum  202  using an exclusive force imparting member  413 , or the damper  404  is mounted inside the drum  202  using the exclusive force imparting member  413 . Thus, the damper  404  can be easily inserted into and removed from the image carrier drum  202 . 
   The rest of the structure of the drum unit  434  apart from those shown in  FIG. 39  and  FIG. 40  is similar to the structure shown in  FIG. 32  to  FIG. 37 . 
   The damper  404  can also be formed by a compression coil spring  440  as shown in  FIG. 41 . Due to its elastic nature, the compression coil spring  440  is in pressed contact with the inner peripheral surface of the image carrier drum  202 . Alternatively, the compression coil spring  440  can also be fixed to the inner peripheral surface of the image carrier drum  202  with an adhesive. 
   The damper  404  formed by the compression coil spring  440  is to be inserted into the image carrier drum  202  by following method. The first flange  303  is separated from the image carrier drum  202 , and a hook  450 A of a force imparting member  450  is engaged with an engaging portion  401 A at one end of the compression coil spring  440 . The force imparting member  450  is pulled in the direction of an arrow B thereby inserting the damper  404  into the image carrier drum  202  from an opening  411  on one end in the axial direction of the drum  202 . 
   When the damper  404  formed by the compression coil spring  440  is to be removed, the compression coil spring  440  is pulled by the force imparting member  450  in the direction of the arrow B in the same manner as explained above. Thus, the damper  404  formed by the compression coil spring  440  can be removed from the image carrier drum  202  through an opening  412  on the other end in the axial direction of the image carrier drum  202 . In this case, the compression coil spring  440  pushes the second flange  303 A thereby removing the flange  303 A from the image carrier drum  202 . The rest of the structure can be formed similarly to the example mentioned above. An external force is exerted on the engaging portion  401 A in the axial direction of the image carrier drum  202  by the force imparting member  450  to reduce at least a part of an outer diameter of the compression coil spring  440 , and the compression coil spring  440  can be easily moved inside the image carrier drum  202 . This action is similar to that in other structures. 
   Thus, as mentioned in the examples above, at least a portion of the damper that is in contact with the inner wall surface of the image carrier drum  202  is formed by an elastic material. The damper  404  makes a pressed contact with the inner wall surface of the image carrier drum  202  by the elastic nature i.e. restoring force, and is held inside the drum  202 . When the damper  404  is fixed to the image carrier drum  202  without using an adhesive, it can be moved easily in the axial direction inside the image carrier drum  202 . 
   In the example shown in  FIG. 41 , when the damper  404  that is to be removed from the image carrier drum  202  is moved inside the drum  202 , the damper  404  pushes the flange  303 A fitted on the opening  412  on one end in the axial direction of the image carrier drum  202  and separates the flange  303 A apart from the image carrier drum  202 . Thus, the flange  303  can be separated apart from the image carrier drum  202  just by pushing action by the damper  404 , which makes it possible to enhance the workability. 
   When the flange  303 A is fitted to the image carrier drum  202  by either of press fit and clearance fit without using an adhesive, the flange  303 A can be removed from the drum  202  when the damper  404  is removed from the drum  202 . The flange  303 A can be removed by using a small amount of force and without any damage caused to it. 
   Moreover, as shown in  FIG. 42 , the second flange  303 A can be structured such that it has a cylindrical first flange member  415  that fits in the opening  412  at the end in the axial direction of the image carrier drum  202  and a second flange member  416  that fits in the first flange member  415 . In this example, a gear  305  is formed on the first flange member  415 . This is similar to the case in the exploded perspective view in  FIG. 30 . Dimensions of flanges are basically the same as the dimensions in  FIG. 31 . 
   This structure enables to disengage the second flange member  416  from the first flange member  415  using a small amount of force by pushing the second flange member  416  by the damper  404 . Thus, the flange members  415  and  416  can be separated apart easily from the image carrier drum  202  without exerting considerable force. This prevents damage to the first flange member  415  and the second flange member  416  and these flanges can be reused in the existing condition. This structure can be also used when the force imparting member is formed by the shaft  437  or when the force imparting member is structured as shown in  FIG. 38  and  FIG. 41 . 
   As shown in  FIG. 42 , it is also possible to form at least a part  410 A of a sidewall  410  of the damper  404  that pushes the second flange member  416 , with a rigid material like metal. Due to such a structure, the force exerted by the force imparting member  413  can be transmitted directly to the second flange member  416 , and the second flange member  416  can be removed easily from the first flange member  415 . 
   The other structures in the examples shown in  FIG. 42  to  FIG. 44  are similar to the examples explained above. 
   In the image forming apparatus shown in  FIG. 32 , the drum unit  434  and the image forming units such as the charging roller  220 , the developing unit  222 , the cleaning unit  227  which form an image on the image carrier drum  202  are integrally assembled to the process cartridge  218 . Therefore, when the process cartridge  218  reaches end of its life, the cartridge may be replaced thereby facilitating maintenance of the image forming apparatus. 
   It is a normal practice to reduce the size and weight of the process cartridge to make it easy to handle. Due to use of small sized components in the process cartridge, the life of the process cartridge is short. In the image forming apparatus in  FIG. 32 , an arrangement is made to replenish the toner container  233  with toner. However, if there is no such an arrangement for replenishment of the toner and the structure is made such that the process cartridge is replaced after the developing unit is run out of the toner, the life of the process cartridge becomes further shorter. The short life of the process cartridge implies an increased number of process cartridges that are made and are in the market. Therefore, it is important to facilitate the disassembling of the image carrier drum  202 , the damper  404 , and the flanges  303  and  303 A to improve recycling. This can be done in a reliable manner by assembling or disassembling the image carrier drum  202 , the damper  404 , and the flanges  303  and  303 A as mentioned in the embodiment to enable easy recycling. 
   The image forming apparatus shown in  FIG. 32  is structured such that a transferred toner image can be fixed on the recording medium P at comparatively low temperature and a toner having a low melting point is used to enable conservation of energy. Concretely, the toner having a low melting point is used in the developing unit to enable the fixing of the toner image in the fixing unit at comparatively low surface temperature of the fixing roller, for example 145° C. The image forming apparatus forms a toner image on the image carrier drum using a toner having an outflow start temperature less than or equal to 120° C. preferably in a range of 99° C. to 102° C. measured by flow tester method. The measurement of outflow start temperature by the flow tester method is already explained above and hence omitted here. 
   A case of using the toner having a low melting point tends to generate noise easily as compared to a case of using a toner having a high melting point. It is not quite sure why the use of the toner having a low melting point increases the noise. However, It is considered that additive like wax contained in the toner tends to stick to the surface of the image carrier drum. Since the amount of the additive deposited becomes non-uniform according to an image pattern, a component like the cleaning blade, which is in contact with the surface of the image carrier drum, does not move uniformly. Therefore, it is thought that loud noise is produced in the image carrier drum due to vibrations caused by non-uniform movement of the cleaning blade. 
   Therefore, it is desirable to use the damper  404  as explained earlier, which is made of a material having a tangent of loss tan δ greater than or equal to 0.5. The tangent of loss tan δ is a tangent of a phase angle δ (loss angle) of stress and strain in a material. The greater the value of the tangent of loss tan δ, the greater the damping effect is. Considering the characteristics of this type of damping material, the damper  404  made of the material having a tangent of loss tan δ greater than or equal to 0.5 is provided inside the image carrier drum  202  to effectively damp the rotating drum  202 . By using the toner having a low melting point, it is possible to reduce the noise generated in the rotating image carrier drum  202  during image formation to an extremely low level. A rubber material such as butyl rubber and nitrile rubber can be used as a material that has the tangent of loss tan δ greater than or equal to 0.5. 
   When a toner including a metallic salt of high fatty acid like zinc stearate is used for the image forming apparatus, a part of the toner gets deposited on the surface of the image carrier drum  202 . Due to the toner deposited on the surface, the coefficient of friction of the cleaning blade  230  decreases thereby smoothening sliding of an edge of the cleaning blade  230 . This reduces vibrations in the cleaning blade  230  and improves the prevention of noise considerably. 
   The present invention can be applied to an image forming apparatus of any form apart from that mentioned in  FIG. 32 . It can also be applied to an image forming apparatus shown in  FIG. 43 . In the image forming apparatus shown in  FIG. 43 , a charging roller  520  charges an image carrier drum  202  rotating in the direction of an arrow. The charged surface of the drum  202  is irradiated with a laser beam L emitted from an exposing unit (not shown) to form a first electrostatic latent image on the image carrier drum  202 . The electrostatic latent image is visualized as a yellow toner image by a yellow developing device  522 Y in the developing unit  522 . The yellow toner image is then transferred to an intermediate transfer belt  550  that is rotating in the direction of an arrow E. A cleaning unit  527  cleans the surface of the image carrier drum after transferring of the yellow image. 
   Similarly, a second electrostatic latent image is formed on the image carrier drum  202 . The latent image is visualized as a magenta toner image by a magenta developing device  522 M in the developing unit  522 . This toner image is then transferred to the intermediate transfer belt  550  and is superimposed on the yellow toner image, which has already been transferred. In a similar way, a cyan toner image and a black toner image are sequentially formed on the image carrier drum  202  by a cyan developing device  522 C and a black developing device  522 BK in the developing unit  522  respectively, and these toner images are superposedly transferred to the intermediate transfer belt  550 . 
   The superimposed toner images transferred to the intermediate transfer belt  550  are then transferred to a recording medium P that is fed from a paper feeding unit  551 . When the recording medium passes through a fixing unit  552 , the toner images are fixed on the recording medium. 
   A damper  404  is mounted in the image carrier drum  202  of this image forming apparatus. The damper  404  is inserted into the image carrier drum  202  and then removed in the same manner as explained above. In a case of the image forming unit in  FIG. 43 , a process cartridge  518  can be formed by assembling the image carrier drum  202 , at least one image forming unit for forming a toner image on the image forming drum, and the intermediate transfer belt  550 . 
   Thus, the embodiments in which the image carrier drum is formed by a photoreceptor drum are explained above. These structures can also be used when the image carrier drum is formed by an intermediate transfer drum on which a toner image is transferred from the photoreceptor. 
   As explained above, according to the present invention, the vibration absorber is disposed on the side opposite to the surface facing the unit in which the bias characteristics for the latent image carrier are set. Therefore, due to the bias characteristics, the vibration absorber that is in contact with the latent image carrier absorbs a part of the vibrations in the latent image carrier, which is caused by the vibrating electric field generated when ac voltage is applied. This enables to reduce the resonance in the latent image carrier, thereby preventing noise. Even if the latent image carrier is either of a belt and a thin-walled cylinder in particular, noise can be prevented without increasing the mass and without complicating the structure of the latent image carrier. 
   Further, the vibration absorber is in the form of a roller and the strong vibration absorbing material is provided either on the surface of or inside the roller, and therefore even if the roller comes in contact with the latent image carrier, the propagation of vibrations to the latent image carrier is prevented. Thus, the noise due to resonance in the latent image carrier is prevented. 
   Moreover, since the drive roller is used as the vibration absorber when the latent image carrier is in the form of a belt, a damper can be used for a material in firm contact with the latent image carrier. This facilitates the absorption of vibrations generated in the latent image carrier and enables to reduce the resonance in the latent image carrier by using the existing structure. 
   When the latent image carrier is a belt, the vibration absorber is provided on the opposite side to the surface of the supporting plate which is in contact with the latent image carrier. The supporting plate is made of a rigid body in the form of a flat plate and is in contact with the belt. Therefore, the vibration absorber absorbs the vibrations generated in the belt without obstructing the movement, and resonance in the latent image carrier can be reduced. 
   Since the vibration absorber is disposed in a position opposite to the unit in which the bias characteristics for the latent image carrier are set, the resonance can be reduced in the most efficient manner at the origin of resonance in the latent image carrier due to the bias characteristics. 
   When the latent image carrier is a substrate in the form of a thin belt and has a photosensitive layer on the surface of the substrate, the substrate is made of a material that absorbs strong vibrations. Therefore, the substrate can reduce it&#39;s own vibrations and there is no need to have a special arrangement for damping and hence no extra cost. 
   By setting the value of the tangent of loss tan δ which affects the damping effect to be greater than or equal to 0.5, the frequency of resonance can be changed to the frequency band in which high frequency sound harsh to ears is not produced. Therefore, even when the noise is generated from the latent image carrier, the same effect as that of reducing the noise can be achieved. 
   Since the vibration absorber is in the solid cylindrical form, it is possible to change the resonance frequency of the latent image carrier to the low frequency band efficiently by using the difference in mass, unlike the hollow cylindrical form. Thus, the resonance caused by the vibrations of the latent image carrier can be prevented and noise can be reduced in efficient manner. 
   It is possible to reduce the material cost by using the vibration absorber in the hollow cylindrical form. In a case of the structure that leads to the reduction in the material cost, in other words, even in a case where it is difficult to decrease the resonance frequency due to the mass unlike a case of the solid cylindrical form, deterioration of the damping effect can be prevented reliably by setting the value of the tangent of loss tan δ, which affects the damping effect, to be greater than or equal to 0.6. 
   Moreover, since the vibration absorber is fitted inside the latent image carrier by either of press fitting and fixing by an adhesive, it is thoroughly integrated with the latent image carrier thereby reducing the resonance in the latent image carrier in efficient manner. 
   The generation of noise can be reduced effectively by using a toner having a low melting point. 
   The cylinder unit can be disassembled easily thereby facilitating recycling. 
   The image carrier drum and the damper can be disassembled easily thereby facilitating recycling. 
   The present document incorporates by reference the entire contents of Japanese priority documents, 2002-169218 filed in Japan on Jun. 10, 2002, 2002-170655 filed in Japan on Jun. 11, 2002, 2002-181552 filed in Japan on Jun. 21, 2002, 2002-195224 filed in Japan on Jul. 3, 2002 and 2003-113709 filed in Japan on Apr. 18, 2003. 
   Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.