Patent Publication Number: US-6219081-B1

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus of the type in which thermal energy is imagewise patterned applied to a toner sheet with a thin film, and after several steps of peeling-off and development, an imagewise patterned thin film is finally transferred onto an image supporting member. 
     2. Description of the Background Art 
     An image forming apparatus is known in which thermal energy is imagewise applied to a toner sheet with a thin film thereon, an imagewise patterned thin film is transferred from the toner sheet onto an image receiving sheet by the step of peeling-off/development, and the imagewise patterned thin film is transferred again from the image receiving sheet onto a permanent image supporting member (JP-A-7-290731). 
     FIG. 5 is a schematic diagram showing this image forming apparatus. The image forming apparatus includes a photosensitive member supplying section  132 , an image forming drum  134 , a photosensitive member fixing/releasing mechanism  136  located on the image forming drum  134 , a laminate mechanism  138  disposed along the outer circumference of the image forming drum  134 , an exposure head  140 , a peeling-off mechanism  142 , a paper supplying section  144 , a laminate section  146 , a fixing section  148 , a peeling-off section  150 , a tray section  152 , and a control unit. 
     An image receiving member  12  and a toner sheet  10  of a first color (for example, C (cyan))are supplied from the photosensitive member supplying section  132  to the image forming drum  134 . 
     The image receiving member  12  is fixed onto the drum  134  by means of the photosensitive member fixing/releasing mechanism  136 . 
     Then, the toner sheet is pressed against the image forming drum by means of the laminate mechanism  138 , so that the toner sheet  10  is laminated on the image receiving member  12 . Then, a laser exposure of the laminated sheet is carried out in a heat mode by use of the exposure head  140 , which is controlled in accordance with an image signal by the control unit. As a result, an image is recorded on the toner sheet as a latent image. 
     Thereafter, the toner sheet  10  is peeled off from the image receiving member  12  fixed onto the image forming drum  134 , by means of the a peeling-off mechanism  142 , and only the coloring material of the image formed as the latent image is transferred to the image receiving member  12 , and developed. Subsequently, the coloring materials of images of second to fourth colors (for example, Y (yellow), M (magenta), C(cyan) and K (black)), which are to be formed as latent images, are transferred to the image receiving member  12  and developed in similar ways. 
     The image receiving member  12  having the images of all the colors formed thereon is peeled off from the drum  134 , and transported to the laminate section  146 . In the laminate section  146 , a paper sheet (final image supporting member)  14  that is supplied from the paper supplying section  144  is registered with and superposed on the image receiving member  12  by a register roller pair  75 . Then, the resultant is transported to the fixing section  148 . In the fixing section  148 , it is nipped and transmitted with a heating/fixing roller pair  76 , whereby the image is heated and fixed. Thereafter, in the peeling-off section  150 , the imagewise patterned coloring material is transferred from the image receiving member  12  onto the paper sheet  14 , and the paper sheet  14  bearing the image transferred thereon is discharged as a hard copy into the tray section  152 . 
     In the conventional apparatus described in the prior art discussion as above, the lamination of the image receiving member laminated on and the paper sheet is nipped with the heating/fixing roller pair  76  of the fixing section  148 , and simultaneously compressed and heated. However, it is necessary to position the image receiving member  12  relative to the paper sheet  14  or put those to be in register before the heating/fixing process. Such simultaneous positioning of two things, viz., the image receiving member  12  and the paper sheet  14 , requires fine adjustments for the transporting speeds of them, for example, and leads to increase of the possibility of causing the jam and displacements (or out-of-register of them). A possible reliable solution to the problem of the jam and the out-of-register is to take the following procedure. That is, following the transferring of the latent image to the image receiving member  12  and the developing of it, the image receiving member  12  is stripped off from the drum, and taken out of the apparatus by manual. Then it is manually superposed on the paper sheet  14  as the final image supporting member, and the image is transferred again to the paper sheet. In the process of the re-transferring process including the taking the image receiving member out of the apparatus by manual, dust inevitably sticks to those members. The sticking of dust forms a cause to deteriorate the quality of the resultant image. 
     Accordingly, an object of the present invention is to provide an image forming apparatus in which an overall image forming process is automated while securing a stable transporting capability, and carried out in a through-process manner, prevents the dust sticking, and well performs the re-transferring of the image onto the paper sheet. 
     SUMMARY OF THE INVENTION 
     To achieve the above object, there is provided an image forming apparatus comprising: a first drum having an image receiving portion on which a toner sheet with an image forming thin film is superimposed in a state that the image forming thin film of the toner sheet is layered on the image receiving portion of the first drum; an exposure section for applying imagewise thermal energy toward the first drum through the toner sheet side; and a second drum for holding a final image supporting sheet thereon for finally supporting an image thereon; wherein after an image is formed through the likewise application of the thermal energy by the exposure section, the toner sheet is separated from the image receiving portion of the first drum, an image is transferred onto the image receiving portion, and the final image supporting sheet is pressed against a predetermined location on the image receiving portion by a relative movement of the first drum to and from the second drum. 
     In the image forming apparatus thus constructed, the image receiving portion includes an image receiving sheet and an image receiving layer layered on the image receiving sheet. 
     Further, the image receiving sheet is supplied from a sheet supplying portion located within the fist drum, through an axially oriented opening formed in the surface of the first drum, to the surface of the first drum, and is taken up by a take-up portion located within the first drum. 
     In the invention, after the image is formed and the image is transferred to the image receiving portion, the image receiving portion is not peeled off the first drum. The final image supporting sheet is pressed against a predetermined location on the image receiving portion by use of the second drum. Therefore, the superposing of the two sheets is reliable and easy. Accordingly, an overall image forming process is automated wile securing a stable transporting capability, and hence carried out in a through-process manner. Therefore, the dust sticking is prevented, and the re-transferring of the image onto the paper sheet is well performed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, advantages and features of the invention will be apparent when carefully reading the detailed description in connection with the drawings: 
     FIG. 1 is a side view showing an image forming apparatus which an embodiment of the present invention; 
     FIG. 2 is a set of sectional views showing a sequence of an image forming process applied to the image forming apparatus of the invention; 
     FIG. 3 is a side view schematically showing a relationship between an image receiving drum and a sheet drum in a color image forming apparatus according to another embodiment of the present invention; 
     FIG. 4 is a partially cross sectional view showing a relationship between the image receiving drum and the sheet drum  34  in the image forming apparatus of FIG. 3; 
     FIG. 5 is a side view showing a conventional image forming apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Image forming apparatuses which are the preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1 is a cross sectional view showing a model of an image forming apparatus which an embodiment of the present invention. FIG. 1 is a set of cross sectional views showing a color image forming process which is applied to the image forming apparatus shown in FIG.  1 . It should be understood that the image forming process shown in FIG. 2 is given by way of example, and hence it may take any of other variety of processes. Before proceeding with description of the image forming apparatus shown in FIG. 1, the color image forming process shown in FIG. 2 will briefly be describe. A toner sheet and an image receiving layer (image receiving sheet), which are described in detail in the specification of Japanese Patent Application No. 5-275749, filed by the applicant of the present patent application, are available for those used in the color image forming apparatus of the present embodiment. 
     Structures of the respective sheets shown in FIG. 2 will be described. 
     A toner sheet  10  is formed with a support member  18 , an photo thermal conversion layer  19 , formed on the support member  18  and containing optical-to-thermal material, a support member  18 , a heat peeling-off layer  20  formed on the photo thermal conversion layer  19 , and a toner layer  22  formed on the heat peeling-off layer  20 . 
     The support member  18  of the toner sheet  10  has a function to mechanically supporting the photo thermal conversion layer  19 , the heat peeling-off layer  20  and the toner layer  22 . For this reason, a material of the support member  18  is preferably high in mechanical strength and heat resistance and exhibits high resistance for organic solvent. 
     In a case that the exposing light is radiated on the support member  18   9   f  the toner sheet structure, it is essential that a transmittance of the support member  18  to an radiation light wave length is high. Where a laser is used for a light source and it is reduced in diameter into a small spot of 10 μm (diameter), it is desirable that a refractive index of the support member  18  is small. 
     The photo thermal conversion layer  19  has a function to absorb a laser beam used as a heating/recording means or high density energy light emitted from a light source, such as a xenon flash lamp, and to transform it into thermal energy. When a laser device is used for the heating/recording means is preferably a semiconductor laser, for example, a laser diode (LD). Light absorbing material, such as organic coloring material, is contained in the photo thermal conversion layer  19 . Where a thermal head is used for the heating/recording means, the toner sheet not including the photo thermal conversion layer  19  may be used. 
     In the image recording process according to the invention, the photo thermal conversion layer  19  is heated to an extremely high temperature at time of high density energy irradiation. When the photo thermal conversion layer  19  changes its properties or is molten due to the extreme temperature rise, part of the photo thermal conversion layer  19  is transferred to an image receiving sheet  12  in a peeling-off process, thereby possibly causing a color mixing. For this reason, it is required that the photo thermal conversion layer  19  used in an image recording method of the invention less changes its properties by heat than the heat peeling-off layer  20 , which will be described later. 
     In a state of no high density energy light radiation or no heating, the heat stripping-off layer  20  intervenes between the photo thermal conversion layer  19  or the support member  18  an the toner layer  22  to join them together. The heat stripping-off layer  20  also prevents such an undesired situation that in the process of the stripping-off/development, part of the high density energy light irradiation region of the photo conductive conversion layer  19  is transferred to the image receiving sheet  12 , thereby causing a color mixing. It further improves a recording sensitivity. In other words, the heat stripping-off layer  20  receives heat that is absorbed by the photo conductive conversion layer  19  or heat from the support member  18  to reduce a bonding force between the photo conductive conversion layer  19  or the support member  18  and the heat stripping-off layer  20  or a cohesive force. 
     The toner layer  22  contains organic pigments of yellow (M), magenta (M), cyan (C) and black (K). A protecting film may be stuck over the surface of the toner layer  22 , if necessary. 
     The toner sheet  10  consists of the respective layers described above, which are layered on the support member  18 . In a normal state, the heat stripping-off layer  20  and the toner layer  22  are strongly bonded together. When it is heated directly by the heating/recording means, such as a thermal head or a laser, or indirectly through an photo conductive conversion operation by the photo conductive conversion layer  19 , a thermal reaction, e.g., thermal decomposition reaction, takes place in a heated portion of the heat stripping-off layer  20 . The result is to greatly reduce the bonding force between the photo conductive conversion layer  19  or the support member  18  and the toner layer  22 . Accordingly, only the heated portion of the heat stripping-off layer  20  is changed in its property to be easy to be stripped off. 
     The image receiving sheet  12  has a structure including a supporting member  26 , a cushion layer  28  formed on the supporting member  26 , and an image receiving layer  16  formed on the cushion layer  28 . Image receiving sheets having other structures than the structure mentioned above may be used for the image receiving sheet  12  of the invention. Some examples of those structures (not shown) are: a structure in which the image receiving layer  16  serves also as the cushion layer, another structure not including the cushion layer  28 , and an additional structure in which the supporting member  26  serves also as the image receiving layer  16 . 
     The cushion layer  28  is elastic, and absorbs a pressing force which acts between the toner sheet  10  and the image receiving sheet  12  in the transferring process. Further, it closely joins the toner layer  22  of the toner sheet  10  to the supporting member  26  of the image receiving sheet  12 . It also allows foreign particles, dust and the like which are present between them to be buried therein. 
     The image receiving layer  16  is provided for receiving an imagewise heated toner layer  22 . Generally, it contains a polymer material as a main component. It is required that the polymer used for the image receiving layer  16  has an appropriate affinity with the toner layer  22 , and an appropriate wetting. The image receiving layer  16  may also serve as the cushion layer  28 , although not illustrated. 
     In a state shown in FIG. 2A before the toner sheet  10  and the image receiving sheet  12  are laminated, a protecting sheet  17  is layered on the image receiving layer  16  of the image receiving sheet  12  in a case that it is required. In such a case, it is preferable that the protecting sheet  17  is removed and cast away. 
     The image receiving layer  16  of the image receiving sheet  12  is adhesive. Because of this nature of the image receiving layer  16 , the heated portion of the toner layer  22  of the toner sheet  10  is easily separated from the toner sheet  10  and transferred to the image receiving layer  16  when it comes in contact with the image receiving layer  16 . The image receiving layer  16  is separable. As will subsequently be described, a final image supporting sheet (referred to as a “paper sheet”)  14  and the image receiving sheet  12  are tightly laminated together, and heated and pressed together, and then those are separated one from the other, and as a result, the image receiving layer  16  is peeled off from the cushion layer  28  and transferred onto the paper sheet  14 . 
     A process for forming a color image by a heat mode recording method using a laser head, which is an embodiment of the present invention, will be described along with a sequence of image recording steps shown in FIGS. 2A through 2F. 
     One color is first selected from among the colors, Y (yellow), M (magenta), C(cyan) and K (black). The toner sheet  10  is transported to above the image receiving sheet  12  of the selected color so as to confront the toner layer  22  of the toner sheet  10  with the image receiving layer  16  of the image receiving sheet  12  (FIG.  2 A). The protecting sheet  17  of the image receiving sheet  12  is peeled off from image receiving sheet  12 , and the toner layer  22  and the image receiving sheet  12  are laminated together (FIG.  2 B). In this case, to secure a quality image, it is necessary to bond the toner layer  22  to the image receiving layer  16  by a uniform adhesive force by pressing those sheets together and heating them by laminating means, such as heating rollers. 
     As shown in FIG. 2C, the toner sheet  10  is imagewise exposed to a laser light, which is emitted from a laser source  24   a  of a laser head  24  and reduced in diameter by an image forming lens  24   b  is radiated on the transparent support member  18  of the toner sheet  10 . In this case, the laser beam is radiated on the transparent support member  18  of the toner sheet  10 . Then, the laser light is transformed into heat by the photo conductive conversion layer  19  of the toner sheet  10 . The transformed heat conducts to the heat stripping-off layer  20 , and an image is recorded in the form of a latent image. In an alternative, the image may be recorded by imagewise heating the toner sheet  10  by use of heating/recording means, such as a thermal head. Through the image recording operation, an adhesion force acting on between the toner layer  22  and the heated portion of the heat stripping-off layer  20  is reduced. As a result, the toner layer  22  is put in a state that it is easily peeled off from the heat stripping-off layer  20 . Reference numeral  23  in FIG. 2C indicates a portion where the adhesion force is reduced in the heat stripping-off layer  20 . 
     For the lamination of the  10  and the image receiving sheet  12  by use of the laminating means, viz., the adhesion joining of the toner layer  22  and the image receiving layer  16 , the lamination or the adhesion joining may be applied to only the irradiation portions by laser light or the heated portions of the laser head  24 , viz., the image recording portion, and if necessary, it may be applied to the overall surfaces of both the sheets. 
     Subsequently, as shown in FIG. 2D, the toner sheet  10  is separated from the image receiving sheet  12 , and the image is developed. As already stated, the heated portion of the toner layer  22  of the toner sheet  10  decreases in its bonding force to the photo conductive conversion layer  19 , while its adhesion force to the image receiving layer  16  increases. Because of this, it is now placed in a state that it is easily peeled off from the toner sheet  10 . 
     The image receiving layer  16  is adhesive. Therefore, when the toner sheet  10  is separated the image receiving sheet  12  while pressing them, by use of pressing means such as peeling-off rollers, the non heated portion of the toner layer  22  is peeled off from the image receiving layer  16  without creating any irregular peeling-off. At the same time, the heated portion of the toner layer  22  is peeled off and transferred to the image receiving layer  16 , and the transferred toner layer is developed to form an image in the image receiving layer  16 . 
     After the image formation of the selected one color is completed, the sequence of steps shown in FIGS. 2A to  2 D are repeated by use of a toner sheet of another color as in the above process, to form another color image in the image receiving sheet  12  by the step of peeling-off/development. 
     In this way, the images of all the four colors of Y, M, C and K (or three colors of H, M and C) are transferred to the image receiving sheet  12  (image receiving layer  16 ) by the step of peeling-off/development, whereby a color image is formed. After the image forming processes of all the colors are completed, the paper sheet  14  and the image receiving sheet  12  (image receiving layer  16 ) are laminated, and heated and pressed together as shown in FIG. 2E, and then the paper sheet  14  is peeled off from the image receiving sheet  12  as shown in FIG.  2 F. 
     As already stated, the image receiving layer  16  of the image receiving sheet  12  is separable, and its surface before it is hardened is adhesive before it is hardened. Therefore, in a case where the image receiving layer  16  has such a property as to be hardened when it receives ultraviolet rays, the following procedure may be taken for the image transferring. That is, after the paper sheet  14  and the image receiving layer  16  are joined together, ultraviolet rays are radiated on the image receiving layer  16  to harden the layer  16 , and then it is stripped off. By so doing, the image receiving layer  16  is peeled off from the cushion layer  28  and bonded to the paper sheet  14 , thereby effecting the transfer of the color image onto the paper sheet  14 . 
     An image forming apparatus  30  which is an embodiment of the present invention will be described with reference to FIG.  1 . 
     The image forming apparatus  30  is generally made of up a first drum (referred to as an “image receiving drum”)  32 , a second drum (referred to as a “sheet drum”)  34 , and an exposure head  36 . The image receiving drum  32  holds on the surface thereof an image receiving sheet  12  which contains an image receiving layer  16  capable of receiving a toner layer  22  of a toner sheet  10 . The sheet drum  34  holds at a location being confronted with the image receiving sheet  12  a paper sheet  14  to which an image formed on the image receiving sheet  12  is to be transferred. The exposure head  36  is used for carrying out an imagewise exposing process of the toner sheet  10  laminated on the image receiving sheet  12  held on the image receiving drum  32 . 
     To be more specific, the image forming apparatus  30  is provided with a photosensitive member supplying section  31  for supplying image the toner sheet  10  and the image receiving sheet  12  to the image receiving drum  32 . The photosensitive member supplying section  31  includes a photosensitive member station  53 , a pair of take-out rollers  54 , and a cutter  55 . The photosensitive member station  53  contains a rolled image receiving member  12  and rolled photosensitive members (referred to as “photosensitive members”), such as a plurality of coloring material sheets, e.g., normal toner sheets of four colors C, M, Y and K (or three colors C, M and Y) and special color sheets used in the printing field. The cutter  55  cuts a member taken out of the photosensitive member station  53  a predetermined length. 
     The image receiving sheet  12  is supplied to the image receiving drum  32 , and its leading end of the image receiving sheet  12  is clamped to a sheet clamping/clamping-removal mechanism  32   a  by a clamp or the like, and wound around the drum with a turn of the image receiving drum  32 . At this time, the trailing end of the image receiving sheet  12  is also clamped to the sheet clamping/clamping-removal mechanism  32   a . At least one of the leading end clamping portion and the trailing end clamping portion is movable in accordance with a sheet length. 
     Then, a toner sheet  10  is laminated on the image receiving sheet  12  held on the image receiving drum  32  in exactly the same process and wound on the drum. The toner sheet  10  is laminated on the image receiving sheet  12  by the utilization of a pressure applied by a roller  58  of a laminating mechanism  38 . An image receiving layer  16  as the uppermost layer of the image receiving sheet  12  is adhesive. The image receiving sheet  12  is wound while being pressed at a predetermined pressure by the roller  58 . Therefore, the image receiving layer  16  of the image receiving sheet  12  may be bonded to the toner layer  22  of the toner sheet  10  at a uniform adhesive force without wrinkles. 
     In order to secure a uniform and strong lamination of the toner sheet  10  to the image receiving sheet  12 , it is preferable that the heating of those sheets is performed during the pressurizing by the roller  58 . For the heating condition, 130° C., preferably 100° C. or lower, is preferable in the light of thermal mechanical properties, for example, thermal expansion coefficient of the members, and when taking into consideration restrictions of its influence on the exposure laser spot. Such a pressurizing may be achieved by any other suitable means than the roller  58 , for example, a bar-like pressing member with a sharpened tip. 
     The sheets mentioned above are preferable because wrinkles and the like may be taken out of the sheets by stretching the sheets when those are wound on the drums. The image receiving drum  32  may be provided with sheet absorbing means, if necessary. Additionally, a circumferential length of the image receiving drum  32  is selected to be longer than an image recording length. 
     With the process thus far described, the steps of FIGS. 2A and 2B are executed. 
     The exposure head  36 , which will next be described, includes a modulating means, and further a laser head  24  (see FIG. 2C) and a sub-scanning means  61 . The laser head  24  includes a laser source  24   a  for emitting high density energy light, such as a laser beam, an image forming lens  24   b  for adjusting a beam spot diameter of the laser light, and the like. The sub-scanning means  61  moves the laser head  24  in the axial direction (vertical to a paper surface of the drawing) of the image receiving drum  32 , thereby performing a sub-scanning operation. A main scan for the toner sheet  10  by laser light is carried out by the utilization of a rotation of the image receiving drum  32 . 
     In an alternative, a moving means is installed on the image receiving drum  32 , and the sub-scanning means is not installed on the exposure head  36 . The sub-scanning operation is performed in a manner that the image receiving drum  32  is moved in the axial direction while rotating the drum in the main-scan direction. 
     The modulation of the laser light by the image signal is carried out in a known manner. In the case of the semiconductor laser, for example, a current injected into the laser is controlled by a signal. The above-mentioned image signal is transferred from an image reader located outside the image forming apparatus  30  of the embodiment, an image processor and various storing media to the control unit  54 . After subjected to a necessary process, it is transferred to the exposure head  36 . In the exposure head  36 , a control of a heat mode exposure by use of the laser head  24  is performed. 
     The control unit  54  controls the respective portions of the image forming apparatus  30  of the embodiment, such as the sub-scan by the sub-scanning means  61  of the exposure head  36 , the main scan based on the rotation of the image receiving drum  32 , and a rotation of the sheet drum  34 , and an overall control sequence of the image forming apparatus. 
     A signal which is controlled in accordance with an image signal by the control unit  54  is sent to the exposure head  36 . A modulation of the laser light is modulated in accordance with this. At this time, the photo conductive conversion layer of an image portion of the toner sheet  10  is placed to an easy toner peeling-off state. This indicates that an image has been recorded, and also indicates that the image transfer onto the image receiving sheet  12  is completed (see FIG.  2 C). 
     Subsequently, the sheet clamping/clamping-removal mechanism  32   a  is removed. The toner sheet  10  is stripped off from the image receiving sheet  12  on the image receiving drum  32 . An image on the toner sheet  10 , which is recorded as a latent image thereon, is transferred onto the image receiving sheet  12  and developed, whereby an image is formed on the image receiving sheet  12  (see FIG.  2 D). 
     In a peeling-off mechanism  42 , a peeling-off roller  62  is turned about a fulcrum  67   a  supported, by shaft, on an arm  67  to be brought into contact with and separated from the roller  36 . Pressing means  68  is provided which presses the peeling-off roller  62  the lamination consisting of the image receiving sheet  12  and the toner sheet  10  on the image receiving drum  32  with the aid of the arm  67 . 
     An adhesive force of the toner layer  22  imagewise reduces by the heat mode exposure, and the arm  67  is turned about the fulcrum  67   a  toward the lamination the toner sheet  10  bearing an image as a latent image and the image receiving sheet  12 . A comb-gear guide plate  65 , which turns in unison with those members, is inserted to between the image receiving sheet  12  and the toner sheet  10 , and the lamination is pressed by pressing the toner sheet  10  of the lamination by the peeling-off roller  62  which rotates in unison with those members. It is possible to easily insert the comb-gear guide plate  65  to between the toner sheet  10  and the image receiving sheet  12  if one of those sheets is longer or shorter in bonding length than the other. Thereafter, the image receiving drum  32  is rotated, and the peeling-off roller  62  and division rollers  63  and  64 , which rotate together with the peeling-off roller  62 , are rotated. With the rotations, the toner sheet  10  is moved along the comb-gear guide plate  65  and caused to be nipped between the peeling-off roller  62  and the division roller  63 . In this way, the toner sheet  10 , while being pressed by the peeling-off roller  62 , is transported in a state that it is nipped between the peeling-off roller  62  and the division roller  63 , and peeled off from the image receiving sheet  12 . 
     The peeled off toner sheet  10  travels along a transport path, and reaches a selector section  50 . In the selector section, the sheet, if it is the toner sheet  10 , is selectively discharged to a casting tray  52   b , located outside the image forming apparatus  30 . The steps of FIGS. 1B to D are sequentially repeated for three to four colors, whereby a color image is formed on the image receiving sheet  12  (see FIG.  2 E). During this execution of the steps, the toner sheet  10  is sequentially changed to one other sheet. 
     The sheet drum  34  is disposed under the image receiving drum  32  in the embodiment, and has a function to hold paper sheets  14  to which toner images formed on the image receiving sheet  12  are to be transferred. The paper sheet  14  is supplied from a paper supplying device  44 , and the paper supplying device  44  is provided with a manual insertion portion  44   a  and a paper supplying tray  73 . The paper supplying device  44  is designed to have a generation construction. It supplies the paper sheets  14  at given timings to the sheet drum  34  with the aid of a paper supplying roller  72  and the like. The toner sheet  10  laminated on the image receiving sheet  12  is sequentially changed to another toner sheet of each color. Because of this, design is made so that the image receiving drum  32  is movable (brought into contact with and separated from) relative to the sheet drum  34  so as not interrupt the sheet changing operation. The sheet drum  34  may be disposed at a location vertical to the image receiving drum  32  other than the location under the same or on the side of the image receiving drum  32 . 
     After the image transferring from the toner sheet  10  to the image receiving sheet  12  on the image receiving drum  32  is completed, the sheet drum  34  moves relative to the image receiving drum  32  to come in contact with the latter while timing the positioning of the image receiving sheet  12  to the paper sheet  14 . For the drum moving mechanism, it is considered that a mechanism in which only the sheet drum  34  is moved is the simplest in construction. 
     The sheet drum  34  is a heating drum containing heating means therein. It brings an image formed on the image receiving sheet  12  on the image receiving drum  32  into contact with the image receiving sheet  12  on the sheet drum  34 , and fuses and fixes the image while carrying out the image transferring. 
     A new paper sheet  14  to which an image is to be transferred is set on the sheet drum  34  or a paper sheet  14  to which an image has been transferred is removed from the same. To make those operations easy, the sheet drum  34 , like the image receiving drum  32 , may be provided with a sheet clamping/clamping-removal mechanism  34   a . The sheet drum  34  may be designed such that air suction holes are formed in the outer peripheral of the sheet drum  34 , and the paper sheet  14  is attracted by an absorbing means. 
     If so designed, the paper sheet  14  may be wound on the outer periphery of the sheet drum  34  without wrinkling the paper sheet. Use of the combination of the absorbing means and the sheet clamping/clamping-removal mechanism  34   a  is preferable. Either of them may be used as a matter of course. 
     The paper sheet  14  may be attached to the sheet drum  34  before the image forming process commences or at the end of forming an image on the image receiving sheet  12 . When the paper sheet  14  is attached to the sheet drum  34  before the image forming process commences, a subsequent process will be carried out in a through-process manner. 
     The paper sheet  14 , which has undergone the image transferring thereto and the fixing of the transferred image on the sheet drum  34 , s peeled off from the sheet drum  34  by a peeling-off mechanism  42   a  constructed as of the image receiving drum  32 . And the paper sheet travels on the transport pat and reaches the selector section  50 . In the selector section  50 , the paper sheet  14  is selectively sent to a take-out tray  52   a  of a tray section  52 , which is located outside the image forming apparatus  30 . 
     The image receiving sheet  12  on the image receiving drum  32 , which has undergone the image transferring thereto, also travels on the transport path, and in the selector section  50 , it is selectively discharged toward the casting tray  52   b  of the tray section  52 , located outside the image forming apparatus  30 . 
     Through the process, a full color image is formed as a hard copy on the paper sheet  14 . 
     According to the above-mentioned embodiment, an image formed on the image receiving sheet  12  on the image receiving drum  32  may directly be transferred onto a paper sheet  14  on the sheet drum  34 . Therefore, the overall process may be automated and continuously be carried out. Further, the image forming apparatus may be realized which prevents the dust attachment during the image forming process. 
     A color image forming apparatus according to another embodiment of the present invention will be described. 
     FIG. 3 is a side view schematically showing a color image forming apparatus according to another embodiment of the present invention. In FIG. 3, like reference numerals are used to designate like or equivalent portions in the FIG. 1 embodiment, and hence description of those portions will be omitted. 
     A difference of the image forming apparatus of the present embodiment from that shown in FIG. 1 resides in that it includes an image receiving drum  90  with a function of supplying an image receiving sheet and taking up the same. The supplying of the toner sheet  10  in this embodiment is similar to that in the FIG. 1 embodiment. The exposure, the image transferring to the paper sheet  14 , the peeling off and the discharging to the devices located outside the image forming apparatus are also similar to those in the FIG. 1 embodiment. 
     The image receiving drum  90  is arranged such that it is capable of successively supplying and taking up an image receiving sheet  92 , and the supplying and removing functions of the image receiving sheet  92  are mechanized. An image forming method for forming an image on the toner sheet  10  onto the image receiving sheet  92  is similar to that shown in the FIG. 1 embodiment. 
     FIG. 4 is a partially cross sectional view showing a relationship between the image receiving drum and the sheet drum  34  in the image forming apparatus of FIG. 3. A construction of the image receiving drum  90  follows. An image-receiving-sheet supplying port  93  and an image-receiving-sheet take-up port  94  as axial slits of the image receiving drum  90 , are disposed while being confronted with each other. A sheet clamping/removal mechanism  91  used for the toner sheet  10  is disposed between the image-receiving-sheet supplying port  93  and the image-receiving-sheet take-up port  94 . An image-receiving-sheet supplying roll  95  and an image-receiving-sheet take-up roll  96  are disposed within the image receiving drum  90 . 
     In the image forming apparatus of this embodiment, the supplying roll  95  for supplying the image receiving sheet  92  and the take-up roll  96  for taking up the same, which are placed within the image receiving drum  90 , are first driven, and a new portion of the image receiving sheet  92  is fed out through the image-receiving-sheet supplying port  93  onto the surface of the image receiving drum  90 , and are set thereon. A toner sheet  10  of the first color (for example, black (K)) is clamped onto the image receiving sheet  92  on the image receiving drum  90  by the sheet clamping/removal mechanism  91 , and set (pressed and bonded) on the surface of the image receiving sheet  92  by the laminating mechanism  38 . 
     As described above, the image receiving sheet  92  is adhesive. Therefore, when the toner sheet  10  is wound and pressed while pressing it at a given pressing force by the laminating mechanism  38 , the toner sheet  10  is not wrinkled as matter of course. Additionally, the heel piece  11  of the toner sheet  10  is bonded to the image receiving layer of the image receiving sheet  92  on the image receiving drum  90  at a uniform adhesion force. 
     Subsequently, the paper sheet  14  is set onto the sheet drum  34  and image forming processes are carried out in similar manners to those in the first embodiment. 
     After the image forming processes have been completed, the image receiving drum  90  and the sheet drum  34  are positioned at their leading ends in a similar manner to that shown in FIG. 3 in the first embodiment, and are brought into contact with each other. An image formed on the a 12   a  on the image receiving drum  90  is brought into contact with the paper sheet  14  on the sheet drum  34 , and the transferring of the image is performed while synchronously rotating both the drums (see FIG.  2 F). 
     According to the present embodiment, an image formed on the image receiving sheet  92  on the image receiving drum  90  may directly be transferred onto a paper sheet  14  on the sheet drum  34 . Therefore, the overall process may be automated and continuously be carried out. Further, the image forming apparatus may be realized which prevents the dust attachment during the image forming process. Furthermore, an image forming apparatus which is considerably easy in its handling is realized since the setting of the image receiving sheet  92  is automated. 
     While some specific embodiments of the present invention have been described, it should be understood that the invention is not limited to those embodiments, but it may variously be changed, modified, and altered without the true spirits of the invention. In the above-mentioned embodiments, the laser exposure head is used for the thermal energy applying means. An apparatus for recording an image by heating by the use of a thermal head may also be realized within the scope of the invention. 
     As seen from the foregoing description, in the present invention, a drum for the paper sheet is provided, and it is brought into contact with the drum holding an image receiving sheet thereon, whereby the image transferring is carried out again. Therefore, the invention succeeds in providing an image forming apparatus having the following advantages. Occurrence of paper jam is suppressed. An overall image forming process is automated while securing a stable transporting capability, and carried out in a through-process manner. The dust sticking is prevented. Further, the re-transferring of the image onto the paper sheet is well performed.