Patent Publication Number: US-7917079-B2

Title: Recording material charging apparatus and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-020805 filed Jan. 31, 2007. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a recording material charging apparatus and an image forming apparatus such as a copier and a printer. 
     (ii) Related Art 
     An image forming apparatus such as a copier and a printer can use not only a general copier paper but also a special paper such as a paper imaging a leathery pattern having premium accents and a Japanese-paper flavor as a recording material. However, such a special paper has an inconvenience that it is difficult for a transcription of a toner image to carry out evenly because concavo-convex patterns are formed on its surface in order to have premium accents. 
     Therefore, as an art for forming an excellent image for the recording material having the concavo-convex pattern formed, for example, one for decreasing roughness of a surface of a sheet by using a white toner or a transparent toner in advance before forming an image by a color toner (for example, refer to JP-A-2006-78883 (PP. 5 to 6)) and one for giving oscillation when transcribing a toner image on a sheet (for example, refer to JP-A-2005-134745 (PP. 7 to 8)) or the like have been known. 
     SUMMARY 
     According to an aspect of the invention, there is provided a recording material charging apparatus comprising: a pre-transcription charging section arranged between a transcribing section that transcribes a toner image retained by a toner image retaining body on a recording material having concavity and convexity and a conveying section that conveys the recording material to the transcribing section and is arranged closest to the transcribing section, the pre-transcription charging section charging the recording material that is to be conveyed to the transcribing section; and a voltage supplying section that supplies voltage of a polarity opposite to a charging polarity of the toner image retained in the toner image retaining body to the pre-transcription charging section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figure, wherein: 
         FIG. 1  is a view showing an example of the constitution of an image forming apparatus according to the present invention; 
         FIG. 2  is a view explaining the constitution of an area between a resist roll and a secondary transcribing portion T 2 ; 
         FIG. 3  is a view explaining a configuration of a cross section of the pre-transcription charging roll; 
         FIGS. 4A and 4B  are views showing a general modification formation of the pre-transcription charging roll when the pre-transcription charging roll having a different hardness is used; 
         FIG. 5  is a view showing a time shift of a surface potential of the paper P (a potential of the surface of the paper) that is charged by the pre-transcription charging roll; 
         FIG. 6  is a view a view showing a relation between an applied voltage to the pre-transcription charging roll and a transcription rate in the concave portion of the paper P; 
         FIG. 7  is a view showing a result of checking if a defect of an image is generated or not from a viewpoint of a transfer defect in the concave portion of the paper P by using a paper of LETHAC 66 of 151 g/m 2 , a paper of LETHAC 66 of 203 g/m 2 , and a paper of LETHAC 66 of 250 g/m 2  that are adjusted into a water content of 6% and those paper that are adjusted into a water content of 4%; 
         FIG. 8  is a view explaining a configuration of an area between a resist roll and a secondary transcribing portion T 2 ; 
         FIG. 9  is a view comparing a quality of an image depending on dispersal to the pre-transcription charging roll of the toner in the case of changing a distance between the middle transcription belt and the pre-transcription charging roll; 
         FIG. 10  is a view explaining a configuration of an area between the resist roll and the secondary transcribing portion T 2 ; and 
         FIG. 11  is a view comparing a quality of an image due to an unevenness of transfer when an amount of heat radiated from the pre-transcription heating roll is changed by changing the surface temperature on the pre-transcription heating roll. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to the attached drawings, the exemplary embodiments of the present invention will be described in detail. 
     First Exemplary Embodiment 
       FIG. 1  is a view showing an example of the constitution of an image forming apparatus  1  to which the exemplary embodiment of the present invention is applied. The image forming apparatus  1  shown in  FIG. 1  is a digital color printer of a so-called tandem type and the image forming apparatus  1  is provided with an image forming process unit  20  for forming an image corresponding to the image data of each color; a control unit  60  for controlling the operation of the image forming apparatus  1 ; an image processing unit  22  for providing predetermined image processing to the image data that is received from an outside apparatus, for example, a PC (a personal computer)  3  and an image reading apparatus  4  or the like; a main storing unit  90  that is realized by, for example, a Hard Disk Drive in which a processing protocol or the like is recorded; and a power source unit  95  for supplying a power to each unit. 
     The image forming process unit  20  is provided with four image forming units  30 Y,  30 M,  30 C, and  30 K forming toner images of yellow (Y), magenta (M), cyan (C), and black (K) that are arranged in parallel at regular intervals, respectively (these units are named generally as “an image forming unit  30 ”). 
     The image forming unit  30  is provided with a photosensitive drum  31  as an example of a toner image retaining body on which an electrostatic latent image is formed while rotating in an arrow A direction; a charging roll  32  for charging a surface of the photosensitive drum  31  at a predetermined potential; a developing unit  33  for developing an electrostatic latent image that is formed on the photosensitive drum  31 ; and a drum cleaner  34  for cleaning the surface of the photosensitive drum  31  after a primary transcription. 
     The charging roll  32  is composed of a roll member that a conductive elastic body layer and a conductive surface layer are laminated in series on a core metal made of aluminum and stainless steel or the like. Then, supplied with a charging bias from a charging power source (not illustrated) that is provided within the power source unit  95 , the charging roll  32  evenly charges the surface of the photosensitive drum  31  at a predetermined voltage while dependently rotating for the photosensitive drum  31 . 
     The developing unit  33  is formed as developing units  33 Y,  33 M,  33 C, and  33 K for developing respective color toners such as yellow (Y), magenta (M), cyan (C), and black (K), respectively, on each image forming unit  30 . Each developing unit  33  may develop an electrostatic latent image on the photosensitive drum  31  by holding a binary developing agent made of each color toner and a magnetic carrier and applying a direct voltage or a developing bias that a direct voltage is superimposed on an alternative voltage to the developing roll. In addition, respective developing units  33  are connected by toner containers  35 Y,  35 M,  35 C, and  35 K for storing respective color toners and a toner conveying path (not illustrated), and respective developing units  33 , are configured so that a toner is supplied by a screw for supplying (not illustrated) that is disposed in the toner carriage path. 
     The drum cleaner  34  is configured so that a cleaning blade made of a polyurethane rubber or the like contacts the photosensitive drum  31  across an axial direction in a direction opposed to a rotational direction of the photosensitive drum  31  (namely, “a counter direction”). Then, the drum cleaner  34  may remove the toner remaining on the surface of the photosensitive drum  31 . 
     Further, the image forming process unit  20  is provided with a laser exposure apparatus  26  for exposing each photosensitive drum  31  that is disposed to each image forming unit  30 ; a middle transcription belt  41  as an example of the toner image retaining body on which each color toner image formed on each photosensitive drum  31  of each image forming unit  30  is multiply-transcribed; a primary transcription roll  42  for transcribing (primarily transcribing) each toner image of each image forming unit  30  on the middle transcription belt  41  by a primary transcribing portion T 1  in series; a secondary transcription roll  40  as an example of a transcribing section for collectively transcribing (secondarily transcribing) a superimposed toner image transcribed on the middle transcription belt  41  on a paper P that is a recording material (a recording paper) by a secondary transcribing portion T 2 ; a pre-transcription charging roll  100  as an example of a pre-transcription charging section for charging the paper P before proceeding into the secondary transcribing portion T 2 ; a pre-transcription heating roll  150  as an example of a pre-transcription heating section for heating the paper P before proceeding into the secondary transcribing portion T 2 , which is arranged contacting the pre-transcription charging roll  100  by pressurizing; and a fixing apparatus  80  for fixing the secondarily-transcribed image on the paper P. 
     The laser exposure apparatus  26  is provided with a semiconductor laser  27  as a light source; a scan optical system (not illustrated) for scanning and exposing a laser beam on the photosensitive drum  31 ; a rotational polygon mirror  28  that is formed, for example, by a regular hexahedron; and a laser driver  29  for controlling driving of the semiconductor laser  27 . In the laser driver  29 , the image data from the image processing unit  22  and a light amount control signal from the control unit  60  or the like are inputted so as to control lighting and output light amount of the semiconductor laser  27 . 
     The middle transcription belt  41  is formed by a no-end belt shaped in a film that an appropriate dose of a conductive agent such as carbon black is contained in a resin, for example, polyimide or polyamide. Then, its volume resistivity is determined in the range from 10 6  or about 10 6  to 10 14  or about 10 14  Ωcm, for example, and its thickness is about 0.1 mm, for example. The middle transcription belt  41  is driven in circle by various rolls at a predetermined rate in a B direction shown in  FIG. 1 . As these various rolls, a driving roll  47  that is driven by a motor (not illustrated) that is excellent in a constant rate property; support rolls  48   a  and  48   b  for supporting the middle transcription belt  41 ; a tension roll  46  for preventing meandering of the middle transcription belt  41  while giving a certain tensile force to the middle transcription belt  41 ; and a backup roll  49  for supporting the middle transcription belt  41  at the secondary transcribing portion T 2  are disposed. 
     Each of the primary transcription roll  42  and the secondary transcription roll  40  is composed of a roll member that a conductive elastic body layer and a conductive surface layer are laminated in series on a core metal made of aluminum and stainless steel or the like. Then, supplied with a primary transcription bias from a primary transcription power source (not illustrated) that is provided within the power source unit  95 , the primary transcription roll  42  may transcribe a toner image that is formed on the middle transcription belt  41  by each image forming unit  30 . In addition, supplied with a secondary transcription bias from a secondary transcription power source (not illustrated) that is provided within the power source unit  95 , the secondary transcription roll  40  may transcribe the toner image that is retained on the middle transcription belt  41  on the paper P. 
     A fixing apparatus  80  is provided with a fixing roll  82  having a heat source therein and a pressurization roll  83  that is arranged by pressurizing with respect to this fixing roll  82 . Then, allowing the paper P retaining an unfixed toner image to pass through the nip area between the fixing roll  82  and the pressurization roll  83 , the toner image is fixed on the paper P. 
     In the image forming apparatus  1  according to the present exemplary embodiment having the above-described configuration, an image forming process unit  20  may carry out the image forming operation under control of the control unit  60 . In other words, the image data inputted from the PC 3  and the image reading apparatus  4  or the like is provided with a predetermined image process by the image processing unit  22  to be stored in the laser exposure apparatus  26 . Then, for example, in the image forming unit  30 Y of yellow (Y), the surface of the photosensitive drum  31  that is evenly charged by the charging roll  32  at a predetermined potential is scanned and exposed by a laser beam of which lighting is controlled on the basis of the image data from the image processing unit  22  by the laser exposure apparatus  26  and an electrostatic latent image is formed on the photosensitive drum  31 . The formed electrostatic latent image is developed by the developing units  33 Y, and on the photosensitive drum  31 , a toner image of yellow (Y) is formed on the photosensitive drum  31 . Also in image forming units  30 M,  30 C, and  30 K, respective color toner images of magenta (M), cyan (C), and black (K) are formed in the same way. 
     Respective toner images formed by respective image forming units  30  are electrostatically transcribed in series by the primary transcription roll  42  to which a predetermined primary transcription bias is applied from a transcription power source (not illustrated) on the middle transcription belt  41  moving in a circle in an arrow B direction of  FIG. 1 , and then, a toner image superimposed on the middle transcription belt  41  is formed. This superimposed toner image is conveyed toward the secondary transcribing portion T 2  on which the secondary transcription roll  40  and the backup roll  49  are arranged in accordance with movement of the middle transcription belt  41 . 
     On the other hand, the paper P is removed from a paper retaining unit  71  by a pickup roll  72  for discharge of the paper P to be conveyed up to the position of a resist roll  74  for regulating the position of the paper along a conveying path R 1 . Then, the paper P is conveyed from the resist roll  74  toward the secondary transcribing portion T 2  in synchronization with a timing that the superimposed toner image is conveyed toward the secondary transcribing portion T 2 . In this case, the paper P may pass through a nip area between the pre-transcription charging roll  100  and the pre-transcription heating roll  150  on a conveying path between the resist roll  74  and the secondary transcribing portion T 2 . Then, as described later, the surface of the side of the secondary transcription of the paper P is charged at a predetermined potential by the pre-transcription charging roll  100 . Therewith, being heated by the pre-transcription heating roll  150 , water content in the paper P is evaporated and the paper P is controlled to have a resistance value in a predetermined range. 
     Further, the paper P is conveyed to the resist roll  74  also from a double-faced conveying path R 2  and a conveying path R 3  from a paper retaining portion for manual paper feed  75 . 
     After passing through the nip area between the pre-transcription charging roll  100  and the pre-transcription heating roll  150 , in the secondary transcribing portion T 2 , the superimposed toner image is electrostatically transcribed (secondarily transcribed) on the paper P in block due to an effect of a transcription electric field that is formed between the secondary transcription roll  40  to which the secondary transcription bias is applied and the backup roll  49 . 
     When the superimposed toner image is electrostatically transcribed on the paper P, the paper P is separated from the middle transcription belt  41  to be conveyed to a fixing apparatus  80 . An unfixed toner image on the paper P that is conveyed to the fixing apparatus  80  is fixed on the paper P being provided with fixing processing due to heat and a pressure by means of the fixing apparatus  80 . Then, the paper P on which a fixed image is formed is conveyed to a paper loading unit  91  that is disposed on a discharge unit of the image forming apparatus  1 . On the other hand, the toner attached to the middle transcription belt  41  after the secondary transcription is removed by a belt cleaner  45  contacting the middle transcription belt  41  to be prepared for a next image formation cycle. 
     In this way, image formation by the image forming apparatus  1  is carried out repeated in the number of times equivalent to the designated number of copies. 
     Consequently, the pre-transcription charging roll  100  and the pre-transcription heating roll  150 , which are arranged contacting by pressurizing each other in the conveying path between the resist roll  74  and the secondary transcribing portion T 2  will be described in detail. 
       FIG. 2  is a view explaining the constitution of an area between the resist roll  74  and the secondary transcribing portion T 2 . As shown in  FIG. 2 , the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are arranged at the downstream side in a conveying direction of the paper P of the resist roll  74  and on the position on the conveying path of the paper P upward from the secondary transcribing portion T 2 . In addition, the pre-transcription charging roll  100  is arranged at the side (the face contacting the middle transcription belt  41  at the secondary transcribing portion T 2 ) of the secondary transcription face of the paper P, and the pre-transcription heating roll  150  is arranged at the side (the face-contacting the secondary transcription roll  40  at the secondary transcribing portion T 2 ) of its rear face. Then, the paper P conveyed from the resist roll  74  is configured so that the transcription processing is carried out at the secondary transcribing portion T 2  after passing through the nip area between the pre-transcription charging roll  100  and the pre-transcription heating roll  150 . 
     As shown in  FIG. 3  (a view explaining a configuration of a cross section of the pre-transcription charging roll  100 ), the pre-transcription charging roll  100  is configured in such a manner that on a conductive shaft  101 , namely, a roll member having an outer diameter of 14 mm, for example, made of aluminum and a stainless steel or the like, a first layer  102 , for example, made of a polyurethane rubber foam that an appropriate dose of a conductive agent such as carbon black is contained; a second layer  103  having a thickness of 500 μm that is made of a chloroprene rubber that an appropriate dose of a conductive agent such as carbon black coating the surface of the first layer  102  is contained; and a third layer  104  having a film thickness of 10 μm made of a polytetrafluoroethylene (PTFE) distributed polyurethane emulsion spray-coating the surface of the second layer  103  are laminated. Then, the pre-transcription charging roll  100  is configured so as to have a volume resistivity about 10 7  Ωcm (when 100V is applied) and an elastic hardness about 30° (ASKER C: SRIS 0101). 
     In addition, the pre-transcription charging roll  100  is provided with a bias of a polarity opposed to a toner polarity from a pre-transcription charging power source  951  as an example of a voltage supplying section that is disposed in the power source unit  95 . Thereby, the pre-transcription charging roll  100  may charge the secondary transcription face of the paper P at a predetermined potential of a polarity opposed to a toner polarity. 
     The pre-transcription heating roll  150  is a roll member having an outer diameter of 20 mm that a pipe roll  151  made of, for example, aluminum and a stainless steel is coated with a silicone rubber layer having a thickness of 0.5 μm on which surface fluorine contained resin is evenly applied. Then, the volume resistivity of the pre-transcription heating roll  150  is determined to be about 10 6.5 Ω (when 100V is applied). In addition, a halogen heater of a rated power 600 W is deployed within the pipe roll  151  and a predetermined power is supplied to the halogen heater  152  from a pre-transcription heater power source  952  disposed within the power source unit  95 . Thereby, the pre-transcription heating roll  150  may heat the paper P from its rear face side. 
     Further, the pipe roll  151  is earthed and the pre-transcription heating roll  150  may also function as an opposed electrode of the pre-transcription charging roll  100 . 
     In addition, the pre-transcription charging roll  100  is rotatably driven at an equal rate as the resist roll  74  by a driving motor (not illustrated) and the pre-transcription heating roll  150  is configured so as to dependently rotate for the pre-transcription charging roll  100 . 
     Further, a bias supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100  and a power supplied from the pre-transcription heater power source  952  to the halogen heater  152  can be adjusted, respectively, under the control of the control unit  60  (refer to  FIG. 1 ). Thereby, determination of the charging amount to be supplied from the pre-transcription charging roll  100  and the surface temperature of the pre-transcription heating roll  150  can be changed, respectively (further, refer to the third exemplary embodiment). 
     In the image forming apparatus  1  according to the present exemplary embodiment, disposing the above-described pre-transcription charging roll  100  and pre-transcription heating roll  150  on the conveying path between the resist roll  74  and the secondary transcribing portion T 2 , charging and heating are carried out at the same time for the paper P just before proceeding into the secondary transcribing portion T 2 . Thereby, even in the case that, for example, the paper P having concavity and convexity on its surface is used, a transcription rate of the superimposed image at the secondary transcribing portion T 2  is determined so as to be even on the entire face of the paper P. 
     In recent years, as a recording medium used for the image forming apparatus, various kinds of papers are used. Among them, a paper imaging a leathery pattern having premium accents and a Japanese-paper flavor or the like are also sold as a recording material. For example, LETHAC 66 (a trade name) manufactured by Tokush Paper Kabushiki Kaisha is a representative thereof. 
     However, a special paper such as LETHAC 66 has concavo-convex patterns on its surface by an embossing finish or the like in order to have premium accents. Therefore, according to the related-art image forming apparatus, it is difficult to transcribe a toner image sufficiently till such a concave portion and this involves an inconvenience such that unevenness of density is easily formed on the image. In other words, in the concave portion of the paper P having concavo-convex patterns thereon, a transcription electric field becomes very weak at the secondary transcribing portion T 2  in the concave portion of the paper P having concavo-convex patterns thereon, so that a transcription rate of a toner from the middle transcription belt  41  is decreased. Such a degree of lowering of the transcription rate of the toner may be different depending on a particle diameter and a charging amount of the toner and a material of the middle transcription belt  41  as an image retaining body or the like, however, mainly, it is different depending on a size and a depth of the concave portion. If the depth of the concave portion is about 5 to 10 μm, for example, an influence on a quality of an image due to lowering of the transcription-rate is not so large, however, if the depth of the concave portion is about 80 μm, for example, like LETHAC 66, deterioration of a quality of an image due to defect of transcription cannot be ignored. In addition, according to the image forming apparatus  1  of a so-called tandem type using the middle transcription belt  41 , the toner image has a large charging amount due to the primary transcription on each image forming unit  30 , so that an adherence with the middle transcription belt  41  is strong and therefore, this image forming apparatus  1  has a tendency to make lowering of the transcription rate in the concave portion larger. 
     Thus, in the case of using the paper P having concavo-convex patterns thereon, a low density portion (unevenness of density) along the concave portion due to lowering of the transcription rate in the concave portion is generated, and as a result, a quality of an image may be decreased. 
     Therefore, the image forming apparatus  1  according to the present invention is configured in such a manner that the paper P just before proceeding into the secondary transcribing portion T 2  is charged by the pre-transcription charging roll  100  so that a toner image can be sufficiently transcribed up to the concave portion of the paper P, on which surface concavo-convex patterns are formed. 
     As described above, the pre-transcription charging roll  100  according to the present invention is soft and its elastic hardness is about 30° (ASKER C: SRIS 0101). Therefore, the surface of the pre-transcription charging roll  100  is easily deformed in accordance with the concavo-convex patterns of the paper P, so that a charging amount can be put in the interior part of the concave portion. Thereby, the pre-transcription charging roll  100  may supply a sufficient charging amount up to the interior part of the concave portion by putting a discharge distance from the surface of the pre-transcription charging roll  100  closer. 
     Normally, the embossing finishing for the paper is completed by allowing the paper to pass, for example, between a rubber roll and a metal roll having the concavo-convex patterns thereon and embossing the paper. The depth of concavity and convexity is decided by a type of a metal roll. There are various depths and, for example, the above-described LETHAC 66 has the depth in the range of several μm to 80 μm. Here, in  FIGS. 4A and 4B , a general modification shape of the pre-transcription charging roll  100  in the case of using the pre-transcription charging rolls  100  having different harnesses is shown. 
     As shown in  FIG. 4A , in the case that the hardness of the pre-transcription charging roll  100  is high (for example, the hardness is about not less than 35°), a discharge distance becomes longer because the change amount of the pre-transcription charging roll  100  on the concave portion of the paper is small. As a result, it is not possible to efficiently give an electric charge in the concave portion. On the other hand, as shown in  FIG. 4B , in the case that the hardness of the pre-transcription charging roll  100  is lower (for example, the hardness is not more than 30°), the discharge distance becomes shorter because the modification amount of the pre-transcription charging roll  100  in the concave portion of the paper is larger. As a result, the electric charge is given up to the interior part of the concave portion. 
     Thus, since the pre-transcription charging roll  100  according to the present exemplary embodiment has a soft elastic hardness about 30° (ASKER C: SRIS 0101), the modification amount is increased in accordance with the depth of the concave portion, so that the discharge distance is made closer depending on the depth of the concave portion. Therefore, the pre-transcription charging roll  100  may supply a sufficient charging amount up to the interior part of the concave portion in spite of the depth of the concave portion. Thereby, a toner sucking force due to the charged electric charge supplied from the pre-transcription charging roll  100  and an effect of the transcription electric field in the secondary transcribing portion T 2  are multiplied so as to improve the transcription rate of the toner to the concave portion. 
     Further, in the case of using the roll member having an elastic hardness more than 30° or about 30° (ASKER C: SRIS 0101), for example, not less than 35° or about 35° (ASKER C: SRIS 0101), the above-described effect so as to shorten the discharge distance is hardly realized, so that the charged electric charge to realize a transcription rate 85% or about 85% in the concave portion shown in a rear stage of  FIG. 6  cannot be given. 
     From the above-described view point, as the pre-transcription charging section, it is preferable that a contact charging section as a pre-transcription charging roll  100  is used. For example, according to a charging section for carrying out charging due to discharge like a corotoron-type and a scorotron-type, for example, an electric charge charging a peripheral part of the concave portion and an entrance portion of the concave portion prevents the sufficient charging amount from being supplied up to the interior part of the concave portion and it is difficult to supply the sufficient charging amount. 
     In addition, the pre-transcription charging roll  100  may supply the sufficient charging amount up to the interior part of the concave portion due to the above-described mechanism if its elastic hardness is not more than 30° (ASKER C: SRIS 0101), however, it is preferable that the elastic hardness is not less than 15° (ASKER C: SRIS 0101) from a view point of manufacture. 
     In addition, the image forming apparatus  1  according to the present invention is configured so that the resistance value of the paper P is determined to be within a predetermine range by heating the paper P by means of the pre-transcription heating roll  150  to evaporate water content of the paper P while being charged by the pre-transcription charging roll  100  at the same time. 
     For example, in a moist season like a Japanese rainy season or the like, a rate of water content of the paper P may be increased up to about 6% being retained in the paper retaining unit  71 . If a user uses such a moist paper P as it is, the pre-transcription charging roll  100  cannot sufficiently charge the paper P in many cases. In such a case, even if the pre-transcription charging roll  100  charges the paper P, in the secondary transcribing portion T 2 , the charging amount whereby the toner image is sufficiently charged up to the concave portion of the paper P cannot be retained in the concave portion. 
     Therefore, the image forming apparatus  1  according to the present invention may carry out charging of the paper P by means of the pre-transcription charging roll  100  and heating by means of the pre-transcription heating roll  150  at the same time. Further, the image forming apparatus  1  according to the present invention may be configured so as to heat the paper P by means of the pre-transcription heating roll  150  before charging by means of the pre-transcription charging roll  100  arranging the pre-transcription heating roll  150  at the upstream side from the pre-transcription charging roll  100  and at the downstream side from the resist roll  74 . 
     Successively, the arrangement position between the pre-transcription charging roll  100  and the pre-transcription heating roll  150  relating to the secondary transcribing portion T 2  will be described. 
     In consideration of the fact that attenuation of an electric charge retained on the paper is fast, according to the information forming apparatus  1  of the present invention, the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are arranged on the conveying path between the resist roll  74  and the secondary transcribing portion T 2 . Thereby, the configuration such that the paper P can attain to the secondary transcribing portion T 2  before attenuation of the electric charge on the paper P that is charged by the pre-transcription charging roll  100  is realized. 
     At first,  FIG. 5  is a view showing a time shift of a surface potential of the paper P (a potential of the surface of the paper) that is charged by the pre-transcription charging roll  100 . In  FIG. 5 , in the case of charging the paper P by means of the pre-transcription charging roll  100  to 3,500 V, the time shifts of the surface potential of the paper P when the paper P is heated by means of the pre-transcription heating roll  150  of which surface temperature is determined to be 145° C. and when the paper P is not heated are shown. In addition, the used paper P is a paper of LETHAC 66 and its weight is 151 g/m 2  and its original water content is 6%. Further, the surface potential of the paper P is obtained by a method for measuring the surface potential of the paper P closing the paper P to the earthed metal plate. 
     As shown in  FIG. 5 , the voltage of the paper P that is not heated is attenuated from 3,500 V to about 0 V for several msec. In addition, the attenuation rate of the paper P that is heated at 145° C. is dramatically lower than that of the paper P that is not heated, however, the attenuation of the voltage is generated in increments of a second. Since the secondary transcribing portion T 2  of the image forming apparatus  1  is closed to the fixing apparatus  80 , in consideration of the fact that a degree of humidity is relatively high due to a moisture vapor when the fixing apparatus  80  heats the paper P and further, the concavo-convex patterns are formed on the surface like LETHAC 66 has a large surface area and this makes it easy to such a humidity for a short time, as a result of  FIG. 5 , in order to control the paper P to retain a sufficient charging amount in the secondary transcribing portion T 2 , it is a condition to charge the paper P by means of the pre-transcription charging roll  100  before 1 to 2 seconds of approach of the paper P into the secondary transcribing portion T 2  in order to control the paper P to retain the sufficient charging amount in the secondary transcribing portion T 2 . 
     Next,  FIG. 6  is a view showing a relation between an applied voltage to the pre-transcription charging roll  100  when using a paper of LETHAC 66 and its weight is 151 g/m 2  and its original water content is 6% as the paper P and a transcription rate in the concave portion of the paper P. In  FIG. 6 , the case that the paper P is heated by the pre-transcription heating roll  150  of which surface temperature is determined to be 145° C. and the case that the paper P is not heated are shown. In addition, the transcription rate is a value representing a density of the image in the concave portion when the toner image is transcribed and fixed with respect to the image density on the paper P when the toner images retained on the middle transcription belt  41  are entirely transcribed on the paper P to be fixed thereon by a percentage. 
     It is known that a difference between the image density in the concave portion of the paper P and the image density in a peripheral part thereof is not so visible by eyes and the transcription rate of the concave portion that is at a level of no problem is in the range of not less than 85% according to an empirical rule. In order to realize the transcription rate of 85% in the concave portion in the image forming apparatus  1  according to the present exemplary embodiment, as being known from  FIG. 6 , it is a condition to determine an applied voltage to the pre-transcription charging roll  100  to be 2,800 V to 4,700 V. In this case, it is necessary to determine the resistance value of the paper P to be within a predetermined range by carrying out heating operation of the paper by means of the pre-transcription heating roll  150 . Further, as being known from  FIG. 6 , when the heating operation by means of the pre-transcription heating roll  150  is not applied to the paper P, the transcription rate 85% in the concave portion cannot be realized. 
     Therefore, according to the image forming apparatus  1  of the present exemplary embodiment, on the basis of a potential attenuation property of the page P heated to 145° C. that is obtained in  FIG. 5  and a condition such that a lower limit potential for realizing the transcription rate 85% in the concave portion obtained in  FIG. 6  is not less than 2,800V, the arrangement relation between the pre-transcription charging roll  100  and the pre-transcription heating roll  150  relating to the position of the secondary transcribing portion T 2  is determined. 
     Thus, according to the image forming apparatus  1  of the present exemplary embodiment, even if the attenuation of the potential is generated on the paper P, the pre-transcription charging roll  100  is arranged closed to the secondary transcribing portion T 2  so that a lower limit value forming a sufficient transfer electric field for transferring a toner image in the concave portion of the paper P is maintained in the secondary transcribing portion T 2 . Then, in this case, a practical arrangement position such that the pre-transcription charging roll  100  can be arranged closed to the secondary transcribing portion T 2  is realized by heating the paper P by means of the pre-transcription heating roll  150  and adjusting the resistance value of the paper P. 
     In addition, in such a configuration of the image forming apparatus  1  of the present exemplary embodiment, after charging the paper P by means of the pre-transcription charging roll  100  and heating the paper P by means of the pre-transcription heating roll  150  are carried out, if other member contacts the paper P, an electric charge given to the paper P is discharged from that member and heat is absorbed. Therefore, the configuration that no member is arranged among the secondary transcribing portion T 2 , the pre-transcription charging roll  100 , and the pre-transcription heating roll  150  is preferable. 
     Therefore, in such a configuration of the image forming apparatus  1  of the present exemplary embodiment, being arranged closed to the secondary transcribing portion T 2 , the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are arranged at the downstream side of the resist roll  74  for conveying the paper P toward the secondary transcribing portion T 2  in synchronization with timing that the superimposed toner image on the middle transcription belt  41  is conveyed to the secondary transcribing portion T 2 . 
     In this case, in order to prevent a transcription misalignment from being generated when unevenness is generated in the conveying rate of the paper P on the secondary transcribing portion T 2  due to the influences of the pre-transcription charging roll  100  and the pre-transcription heating roll  150  that are arranged between the secondary transcribing portion T 2  and the resist roll  74 , a frictional force among the pre-transcription charging roll  100 , the pre-transcription heating roll  150 , and the paper P becomes smaller than a frictional force between the middle transcription belt  41  and the paper P. Specifically, a surface material and a surface roughness or the like of the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are determined so that a relation that μ 1 &lt;μ 2 &lt;μ 3  is established between a static friction coefficient μ 1  between the pre-transcription charging roll  100  and the secondary transcription face of the paper P, a static friction coefficient μ 2  between the pre-transcription heating roll  150  and the rear face of the paper P (the secondary transcription face and the opposite side face), and a static friction coefficient μ 3  between the middle transcription belt  41  and the secondary transcription face of the paper P, respectively. For example, these static friction coefficients are adjusted as follows; namely, μ 1 =0.35, μ 2 =0.48, and μ 3 =0.62, respectively. 
     Thereby, even if the conveying force of the paper P in the secondary transcribing portion T 2  is made larger than the conveying forces in the pre-transcription charging roll  100  and the pre-transcription heating roll  150  and a force so as to generate an unevenness in the conveying rate of the paper P by means of the pre-transcription charging roll  100  and the pre-transcription heating roll  150  is effected, the image forming apparatus  1  of the present exemplary embodiment is determined so that its effect is realized in the transcription image due to the conveying force of the paper P in the secondary transcribing portion T 2 . 
     Here, a measurement method of a static friction coefficient will be described. As a measurer, HEIDON Tribogear μs Type 94i is used. Then, in the case of measuring two members, fixing one of them to a probe of the measurer and fixing other one on a plate that is disposed on the position opposed to other one, these two members are measured under a predetermined pressurization. For example, in the case of measuring the static friction coefficient μ 1  between the pre-transcription charging roll  100  and the secondary transcription face of the paper P, at first, the paper P is cut so as to be the same size as a probe made of a metal plate with a diameter about 30 mm to be pasted to the probe. In addition, fixing the pre-transcription charging roll  100  on the position opposed to the probe by a jig so as to allow the pre-transcription charging roll  100  to contact the probe. In this case, the probe and the pre-transcription charging roll  100  are vertically superimposed and fixed so that the probe is located upward and the pre-transcription charging roll  100  is located downward. Then, moving the probe in a horizontal direction, the static friction coefficient μ 1  is measured. Further, a vertical drag (an empty weight) and a force to be added for moving the probe in parallel are determined at a predetermined value by the measurer. 
     Next, according to the image forming apparatus  1  of the present exemplary embodiment, by using a paper of LETHAC 66 of 151 g/m 2 , a paper of LETHAC 66 of 203 g/m 2 , and a paper of LETHAC 66 of 250 g/m 2  that are adjusted into a water content of 6% under environment that a temperature is 28° C. and a relative humidity is 86% and those paper that are adjusted into a water content of 4% under environment that a temperature is 28° C. and a relative humidity is 75%, it is checked if a defect of an image is generated or not from a viewpoint of a transference defect in the concave portion. This result is shown in  FIG. 7 . In  FIG. 7 , a process speed of the image forming apparatus  1  is defined as 52 mm/sec, and the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are arranged at the upstream side position from the secondary transcribing portion T 2  by 55 mm. In addition, 3,500V is applied to the pre-transcription charging roll  100  and the pre-transcription heating roll  150  is determined to be not heated, be heated at 125° C., and be heated at 145° C. In addition, as the elastic hardness of the pre-transcription charging roll  100 , 30° (ASKER C: SRIS 0101) is used. 
     As shown in  FIG. 7 , in the case of not heating, except the case that the paper of LETHAC 66 of 151 g/m 2  is determined to have a water content of 4%, a defect of an image of a level such that the all transcription defects in the concave portion cannot be ignored is generated. In addition, in the state of heating the pre-transcription heating roll  150  at 125° C., when a paper of LETHAC 66 of 203 g/m 2  is determined to have water content 6% and in the paper of the paper of LETHAC 66 of 250 g/m 2 , the same defect of the image is generated. This may be attributed to the fact that water content in these papers P cannot be sufficiently evaporated according to a heating process at 125° C. by means of the pre-transcription heating roll  150  and in the secondary transcribing portion T 2 , the resistance value of the paper P so as to maintain the sufficient electric charge for transcribing the toner image on the concave portion of the paper P cannot be realized. 
     On the contrary, in the state of heating the pre-transcription heating roll  150  at 145° C., with respect to the all papers P used for a test, an excellent quality of an image that the transcription defect in the concave portion is not visible is obtained. 
     Accordingly, it is preferable to adopt setting for heating the pre-transcription heating roll  150  not less than 145° C. 
     However, as shown in  FIG. 3 , the pre-transcription charging roll  100  according to the present exemplary embodiment is configured so that the third layer  104  made of a polytetrafluoroethylene (PTFE) distributed polyurethane emulsion is arranged as a surface layer. For example, the pre-transcription charging roll  100  according to the present exemplary embodiment may be configured by a roll member of an electric charge injection type as a contact charging section having a fur and a brush of which liner diameter is determined so as to be able to progress into the concave portion of the paper P formed on its surface. 
     In addition, the pre-transcription charging roll  100  also may be configured so as to be able to take shelter to the position separated from the conveying path by means of a moving mechanism (not illustrated) in the case that a paper having no concavo-convex patterns, for example, a regular paper is used as the paper P. 
     Further, providing a resistance measuring section for measuring a resistance value of the paper P at the upstream side in the conveying direction of the paper P of the pre-transcription charging roll  100  and the pre-transcription heating roll  150 , when the resistance value of the paper P is measured to be not more than a predetermined value, it is possible to control the image forming apparatus  1  so as to carry out the charging processing by means of the pre-transcription charging roll  100  and carry out heating processing by means of the pre-transcription heating roll  150 . In this case, as the resistance measuring section, for example, a system for applying a predetermined voltage to a pair of conductive roll members and measuring the resistance value of the paper P due to a current value passing through this roll member can be used. 
     In addition, providing a surface roughness measuring section for measuring a surface roughness of the paper P at the upstream side in the conveying direction of the paper P of the pre-transcription charging roll  100  and the pre-transcription heating roll  150 , when the surface roughness of the paper P is measured to be not less than a predetermined value, it is possible to control the image forming apparatus  1  so as to carry out the charging processing by means of the pre-transcription charging roll  100  and carry out heating processing by means of the pre-transcription heating roll  150 . In this case, as the surface roughness measuring section, a system including, for example, a light emission portion for irradiating a light to the paper P and a light receiving portion for measuring its reflection light for measuring the surface roughness of the paper P due to a light amount to be measured by a light receiving portion can be used. 
     As described above, according to the image forming apparatus  1  of the present exemplary embodiment, it is possible to realize the configuration maintaining a charging amount that can transcribe a toner image sufficiently up to the concave portion of the paper P in the secondary transcribing portion T 2  by carrying out the charging processing by means of the pre-transcription charging roll  100  and the heating processing by means of the pre-transcription heating roll  150  for the paper P at the same time in the conveying path between the resist roll  74  and the secondary transcribing portion T 2 . 
     Thereby, the toner image can be sufficiently transcribed up to the concave portion of the paper P having concavity and convexity and it is possible to provide an excellent image with little unevenness. 
     Second Exemplary Embodiment 
     According to the first exemplary embodiment, the configuration for fixing and arranging the pre-transcription charging roll  100  and the pre-transcription heating roll  150  in the conveying path between the resist roll  74  and the secondary transcribing portion T 2  is described. According to the second exemplary embodiment, the configuration that the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are moving along the conveying path will be described. Further, the same configurations as the first exemplary embodiment are given the same reference numerals and marks and their detailed explanations are herein omitted. 
       FIG. 8  is a view explaining a configuration of an area between the resist roll  74  and the secondary transcribing portion T 2  in the image forming apparatus  1  according to the present exemplary embodiment. As shown in  FIG. 8 , the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are configured so as to be able to move in a direction of the side of the resist roll  74  or in a direction of the side of the secondary transcribing portion T 2  along the conveying path of the paper P between the resist roll  74  and the secondary transcribing portion T 2  by the moving mechanism (not illustrated). 
     Then, according to the image forming apparatus  1  according to the present exemplary embodiment, for example, under an environment that a relative humidity is high or in the case of using a thick paper P that is difficult to evaporate water content sufficiently, the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are moved along the conveying path of the paper P in a direction of the side of the secondary transcribing portion T 2 . Thereby, by moving the pre-transcription charging roll  100  and the pre-transcription heating roll  150  at the position where the attenuation of the potential of the paper P is decreased as shown in  FIG. 5 , it is unnecessary to increase a bias to be supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100  or it is possible to use an economical and portable pre-transcription charging power source  951 . 
     In addition, according to the image forming apparatus  1  according to the present exemplary embodiment, in the vicinity of the side facing to the side of the pre-transcription charging roll  100  of the middle transcription belt  41 , a shielding member  180  for electrically shielding the middle transcription belt  41  and the pre-transcription charging roll  100  is arranged. The shielding member  180  is made of a conductive metal plate or the like, for example, and a bias having the same polarity as the polarity of the toner retained in the middle transcription belt  41  is supplied from the power source unit  95  or is earthed. 
     Thereby, in the case that the pre-transcription charging roll  100  moves in a direction of the side of the secondary transcribing portion T 2  along the conveying path of the paper P, the shielding member  180  prevents the toner retained in the middle transcription belt  41  from being transferred to the pre-transcription charging roll  100  provided with a bias of an opposite polarity of the toner polarity. 
     Therefore, in the case that the pre-transcription charging roll  100  is moved in a direction of the side of the secondary transcribing portion T 2  along the conveying path of the paper P, it is prevented that the toner transferred to the pre-transcription charging roll  100  spoils the secondary transfer face of the paper P and the defect of the image is generated. 
     Here,  FIG. 9  is a view comparing a quality of an image depending on dispersal to the pre-transcription charging roll  100  of the toner in the case of changing a distance between the middle transcription belt  41  and the pre-transcription charging roll  100  when the pre-transcription charging roll  100  is moved in a direction of the side of the secondary transcribing portion T 2  along the conveying path of the paper P. In  FIG. 9 , a process speed of the image forming apparatus  1  is defined as 52 mm/sec, 3,500 V is applied to the pre-transcription charging roll  100 , and the pre-transcription heating roll  150  is determined to be at 145° C. In addition, as the elastic hardness of the pre-transcription charging roll  100 , 30° (ASKER C: SRIS 0101) is used. In addition, as the paper P, a paper of LETHAC 66 of 151 g/m 2  is used. 
     As shown in  FIG. 9 , according to the configuration without arranging the shielding member  180 , when a distance between the middle transcription belt  41  and the pre-transcription charging roll  100  is not more than 6 mm, the defect of the image due to dispersal of the toner to the pre-transcription charging roll  100  is generated. In this case, an unintended electric field formed between the surface of the pre-transcription charging roll  100  and the middle transcription belt  41  depends on a distance and if such a distance is not more than 6 mm, the toner is dispersed because a coulomb force acting on the toner on the middle transcription belt  41  is large or electric discharge is caused or the like. On the contrary to this, it is considered that disperse of the toner is not generated because a coulomb force is small or electric discharge is not caused or the like when such a distance is not less than 8 mm. On the other hand, in the configuration arranging the shielding member  180 , even when a distance between the middle transcription belt  41  and the pre-transcription charging roll  100  is 2 mm, the defect of the image due to toner dispersal to the pre-transcription charging roll  100  is not generated. 
     In addition, in a test shown in  FIG. 9 , under any condition, an excellent quality of an image that the transfer defect in the concave portion of the paper P is not visible is obtained. 
     As described above, according to the image forming apparatus  1  according to the present exemplary embodiment, for example, under an environment that a relative humidity is high or in the case of using a thick paper P that is difficult to evaporate water content sufficiently, the pre-transcription charging roll  100  and the pre-transcription heating roll  150  are moved along the conveying path of the paper P in a direction of the side of the secondary transcribing portion T 2 . Therewith, in the vicinity of the side facing to the side of the pre-transcription charging roll  100  of the middle transcription belt  41 , the shielding member  180  for electrically shielding the middle transcription belt  41  and the pre-transcription charging roll  100  is arranged. 
     Thereby, it is unnecessary to increase a bias to be supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100  or it is possible to use an economical and portable pre-transcription charging power source  951 . In addition, the toner is prevented from transferred from the middle transcription belt  41  to the pre-transcription charging roll  100  and generation of the defect of the image due to toner dispersal is prevented. 
     Third Exemplary Embodiment 
     According to the first exemplary embodiment, in the conveying path between the resist roll  74  and the secondary transcribing portion T 2 , the configuration of arranging the pre-transcription charging roll  100  and the pre-transcription heating roll  150  is described. According to the third exemplary embodiment, the configuration of adjusting a bias to be supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100  and a power to be supplied from the pre-transcription heater power source  952  to the halogen heater  152  of the pre-transcription heating roll  150  will be described. Further, the same configurations as the first exemplary embodiment are given the same reference numerals and marks and their detailed explanations are herein omitted. 
       FIG. 10  is a view explaining a configuration of an area between the rest roll  74  and the secondary transcribing portion T 2  in the image forming apparatus  1  according to the present exemplary embodiment. The image forming apparatus  1  according to the present exemplary embodiment, as described with reference to the first exemplary embodiment, is configured so as to be able to adjust a bias to be supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100  and a power to be supplied from the pre-transcription heater power source  952  to the halogen heater  152  of the pre-transcription heating roll  150 . Then, as shown in  FIG. 10 , the image forming apparatus  1  according to the present exemplary embodiment has a configuration such that a heat shielding member  190  for shielding a heat radiated from the pre-transcription heating roll  150  from being transmitted to the secondary transcription roll  40  is arranged between the pre-transcription heating roll  150  and the secondary transcription roll  40 . The heat shielding member  190  in this case is configured by a material having a high heat shield property, for example, fluorine contained resin. 
     Then, according to the image forming apparatus  1  according to the present exemplary embodiment, by increasing a bias to be supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100 , for example, under an environment that a relative humidity is high or in the case of using a thick paper P that is difficult to evaporate water content sufficiently, a lower limit value forming a sufficient transfer electric field for transferring a toner image in the concave portion of the paper P is determined to be maintained in the secondary transcribing portion T 2 . In addition, by increasing a power to be supplied from the pre-transcription heater power source  952  to the halogen heater  152  of the pre-transcription heating roll  150 , for example, under an environment that a relative humidity is high or in the case of using a thick paper P that is difficult to evaporate water content sufficiently, the resistance value of the paper P is adjusted so that a lower limit value forming a sufficient transfer electric field for transferring a toner image in the concave portion of the paper P is maintained in the secondary transcribing portion T 2 . 
     In this case, when a power to be supplied to the halogen heater  152  is increased, a heat radiated from the pre-transcription heating roll  150  may raise a temperature of the secondary transcription roll  40  that is arranged on the above of the pre-transcription heating roll  150 . If a temperature of the secondary transcription roll  40  is raised, the resistance value of the secondary transcription roll  40  is varied, and in the secondary transcribing portion T 2 , a size of a transfer electric field formed between the secondary transcription roll  40  and the backup roll  49  to which the secondary transfer bias is applied is changed and the transfer unevenness may be generated. 
     Therefore, the image forming apparatus  1  according to the present exemplary embodiment is configured so that it is difficult for a heat radiated from the pre-transcription heating roll  150  to transmit to the secondary transcription roll  40  by arranging the heat shielding member  190  between the pre-transcription heating roll  150  and the secondary transcription roll  40 . Thereby, even if a power to be supplied to the halogen heater  152  is raised, rise in a temperature of the secondary transcription roll  40  is prevented and generation of the transfer unevenness caused by variation of the resistance value of the secondary transcription roll  40  is prevented. 
     Here,  FIG. 11  is a view comparing a quality of an image due to an unevenness of transfer when an amount of heat radiated from the pre-transcription heating roll  150  is changed by changing the surface temperature on the pre-transcription heating roll  150 . In  FIG. 11 , as the paper P, a paper of LETHAC 66 of 203 g/m 2  having water content adjusted into 4% and 6% is used. A process speed of the image forming apparatus  1  is defined as 52 mm/sec, as a bias applied to the pre-transcription charging roll  100 , in the case of LETHAC 66 adjusting water content into 4%, 3,500 V is applied to the pre-transcription charging roll  100 , and in the case of LETHAC 66 adjusting water content into 6%, 4000 V is applied to the pre-transcription charging roll  100 . In addition, as the elastic hardness of the pre-transcription charging roll  100 , 30° (ASKER C: SRIS 0101) is used. In addition, the surface temperature of the pre-transcription heating roll  150  is determined to be at 125° C. in the case of LETHAC 66 adjusting water content into 4%, and the surface temperature of the pre-transcription heating roll  150  is determined to be at 145° C. in the case of LETHAC 66 adjusting water content into 6%. Then, in the configuration that the heat shielding member  190  is arranged and the configuration that the heat shielding member  190  is not arranged, respective LETHACS 66 are continuously scanned up to 50,000 sheets. Evaluation of a quality of an image due to unevenness of transfer is carried out by using a bond paper for each 500 sheets. 
     As shown in  FIG. 11 , according to the configuration that the heat shielding member  190  is not arranged, in a paper of LETHAC 66 that the surface temperature on the pre-transcription heating roll  150  is determined to be at 145° C. and a water content is 6%, when 10,000th sheet is scanned, a defect of an image due to unevenness of transfer is generated. On the other hand, in the configuration that the heat shielding member  190  is arranged, in a paper of LETHAC 66 that the surface temperature on the pre-transcription heating roll  150  is determined to be at 145° C. and a water content is 6%, even when 50,000th sheet is scanned, a defect of an image due to unevenness of transfer is not generated. 
     In addition, in the test that the surface temperature is determined to be at 125° C. shown in  FIG. 11 , in any of the configuration that the heat shielding member  190  is arranged and the configuration that the heat shielding member  190  is not arranged, an excellent quality of an image that the transfer defect in the concave portion of the paper P is not visible is obtained. 
     Further, depending on the paper P, it may be assumed that the paper P that is heated by the pre-transcription heating roll  150  indirectly raises a temperature of the secondary transcription roll  40 . In order to treat such a case, the configuration that a non-contact cooling section for cooling the paper P is provided in the area among the pre-transcription charging roll  100 , the pre-transcription heating roll  150 , and the secondary transcribing portion T 2  may be available. 
     As described above, the image forming apparatus  1  according to the present exemplary embodiment is configured such that a bias to be supplied from the pre-transcription charging power source  951  to the pre-transcription charging roll  100  and a power to be supplied from the pre-transcription heater power source  952  to the halogen heater  152  of the pre-transcription heating roll  150  can be adjusted for example, in the case that a relative humidity is high or in the case of using a thick paper P that is difficult to evaporate water content. Therewith, the heat shielding member  190  is arranged between the pre-transcription heating roll  150  and the secondary transcription roll  40 . 
     Thereby, even in the case that a relative humidity is high or in the case of using a thick paper P that is difficult to evaporate water content sufficiently, it is possible to determine the lower limit value forming a sufficient transfer electric field for transferring a toner image in the concave portion of the paper P to be maintained in the secondary transcribing portion T 2 . In addition, rise in a temperature of the secondary transcription roll  40  is prevented and generation of the transfer unevenness caused by variation of the resistance value of the secondary transcription roll  40  is prevented. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.