JP2004206074A - Transfer method, transfer device, image forming method, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device that hinders paper dust from sticking to an image carrier while accomplishing one-pass system double-sided transfer and, further, that hinders occurrences of wrinkles in a recording medium. <P>SOLUTION: The transfer device includes a first intermediate transfer belt 8 and a second intermediate transfer belt 16 which are endlessly moved while forming a nip by the contact of their surfaces. During the process in which transfer paper P held in the nip is conveyed further downstream of the nip in the direction of the belt movement, a first toner image pre-transferred to the second intermediate transfer belt 16 from a photoreceptor via the first intermediate transfer belt 8 is transferred to a first face of the transfer paper P. At the same time as this, a second toner image pre-transferred to the first intermediate transfer belt 8 from the photoreceptor is transferred to a second face of the transfer paper. In addition, the second intermediate transfer belt 16 used here is less deformable than the first intermediate transfer belt 8 in the thickness direction. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a transfer method, a transfer device, an image forming method, and an image forming apparatus for transferring a visible image to both sides of a recording medium such as transfer paper by a so-called one-pass method.

  2. Description of the Related Art Conventionally, a so-called switchback method and a one-pass method have been known as methods for transferring an image to both sides of a recording medium such as transfer paper. In the switchback method, first, a visible image on an image carrier such as a photoreceptor is transferred to a recording medium through a recording medium to transfer the visible image to one surface thereof. Then, after the recording medium is turned over and switched back to the transfer unit, the visible image is transferred to the other surface. On the other hand, in the one-pass system, as a transfer unit, a visible image is transferred from both sides of a recording body to form images on both sides without switching back the recording body. The one-pass method is superior to the switchback method in the following points. That is, an increase in cost due to the provision of a complicated mechanism for switchback and an increase in image forming time due to switchback can be avoided. As an image forming apparatus that realizes such a one-pass method, for example, an image forming apparatus described in Patent Document 1 is known.

  Further, among image forming apparatuses that realize the one-pass method, there is known an image forming apparatus including a first intermediate transfer member and a second intermediate transfer member (for example, one described in Patent Document 2). This type of image forming apparatus moves the surfaces of both intermediate transfer bodies endlessly while abutting the first intermediate transfer body and the second intermediate transfer body to form a nip. Then, in the process of transporting the recording material sandwiched between the nip to the downstream side in the endless movement direction of the second intermediate transfer member from the nip, the recording material is previously transferred from the image carrier to the second intermediate transfer member via the first intermediate transfer member. The first visible image is transferred to the first surface of the recording medium. On the other hand, the second visible image previously transferred from the image carrier to the first intermediate transfer member is transferred to the second surface of the recording member. According to the improved apparatus having such a configuration, the recording medium is not brought into direct contact with the image carrier such as the photoconductor, and therefore, when a paper material such as transfer paper is used as the recording medium, paper dust on the image carrier is reduced. Adhesion can be suppressed. Therefore, problems such as image deterioration due to the adhesion of paper powder can be suppressed.

JP-A-1-209470 JP-A-8-160703

  The present inventors are also developing the following device as another improved device including the first intermediate transfer member and the second intermediate transfer member. That is, in order to omit the transfer step from the first intermediate transfer member to the second intermediate transfer member, the second intermediate transfer member is provided separately from the image bearing member that carries a visible image to be transferred to the first intermediate transfer member. Provided with an image carrier for carrying a visible image to be transferred to a recording medium. Even in such a configuration, since the recording medium does not come into direct contact with the image carrier, it is possible to suppress problems such as image deterioration due to adhesion of paper powder to the image carrier.

  However, in the apparatus provided with the first intermediate transfer belt and the second intermediate transfer belt, wrinkles were easily generated on the recording medium during the double-side transfer. This wrinkle is particularly caused when an intermediate transfer belt that is endlessly moved while being stretched by a plurality of stretching members is used as a first intermediate transfer body and a second intermediate transfer body (hereinafter, both intermediate transfer bodies). It was noticeable. The inventors of the present invention have conducted intensive studies on the causes of wrinkles on a recording medium, and have found the following. That is, as the first intermediate transfer member and the second intermediate transfer member, those which exhibit elasticity as a whole are generally used from the viewpoint of ensuring good transferability by making good contact with the recording medium. However, if a nip is formed by pressing the two intermediate transfer members exhibiting good elasticity, each of the intermediate transfer members is elastically deformed into a complicated shape by the nip and bites each other in a wedge shape (wavy shape). As described above, the recording medium is sandwiched between the nips in which the two intermediate transfer bodies bite into each other in a wedge shape (wavy shape), whereby wrinkles are generated in the recording material following the shape of the wedge.

  The present invention has been made in view of the above background, and an object of the present invention is to provide the following transfer method, transfer device, image forming method, and image forming apparatus. That is, a transfer method that can suppress the adhesion of paper dust to the image carrier when a paper material is used as a recording medium and also suppress wrinkles generated on the recording medium while realizing one-pass double-sided transfer. It is.

In order to achieve the above object, a first aspect of the present invention is a step of endlessly moving the surfaces of both intermediate transfer bodies while forming a nip by bringing the first intermediate transfer body and the second intermediate transfer body into contact with each other. And, in the process of transporting the recording medium sandwiched between the nips along with the surface movement of the two intermediate transfer bodies, while transferring the visible image on the second intermediate transfer body to one surface of the recording body, Transferring the visible image to both sides of the recording medium by performing a double-side transfer step of performing a step of transferring the visible image on the first intermediate transfer body to the other surface of the recording medium. As a combination of the first intermediate transfer member and the second intermediate transfer member, a combination in which one is less likely to be deformed in the thickness direction of the recording body sandwiched between the nips than the other is used.
Further, the invention according to claim 2 includes a first intermediate transfer member and a second intermediate transfer member that move the surface endlessly while forming a nip by bringing the surfaces into contact with each other. While the visible image on the second intermediate transfer body is being transferred to one surface of the recording medium in the process of being conveyed along with the surface movement of the intermediate transfer body, the visible image on the first intermediate transfer body is being transferred. Is transferred to the other side of the recording medium, and a visible image is transferred to both sides of the recording medium, wherein one of the first intermediate transfer body and the second intermediate transfer body is a combination of the first and second intermediate transfer bodies. Also, a combination that is hardly deformed in the thickness direction of the recording body sandwiched between the nips is used.
The invention according to claim 3 is the transfer device according to claim 2, wherein the first visible image transferred from the image carrier to the second intermediate transfer member via the first intermediate transfer member is transferred to the one of the first and second intermediate transfer members. While transferring to the surface, the second visible image transferred from the image carrier to the first intermediate transfer member is transferred to the other surface.
The invention according to claim 4 is the transfer device according to claim 2, wherein a visible image is transferred from the image carrier to the first intermediate transfer member, while another visible image is transferred to another image carrier. To the second intermediate transfer member.
The invention according to claim 5 is the transfer device according to claim 2, 3 or 4, wherein at least one of the first intermediate transfer member and the second intermediate transfer member has a multilayer structure. It is assumed that.
According to a sixth aspect of the present invention, in the transfer device of the fifth aspect, the surface layer in the multilayer structure is made of a material having better toner releasability than other layers. .
The invention according to claim 7 is the transfer device according to any one of claims 2 to 6, wherein the first intermediate transfer body and the second intermediate transfer body are endless while being stretched by a plurality of stretching members, respectively. It is an intermediate transfer belt that can be moved.
The invention according to claim 8 is the transfer device according to claim 7, wherein at least one of the plurality of stretching members for stretching the first intermediate transfer belt as the first intermediate transfer member is provided on the image carrier. And a transfer bias member for applying a transfer bias to the back surface of the first intermediate transfer belt to electrostatically transfer the visible image to the first intermediate transfer belt.
According to a ninth aspect of the present invention, there is provided the transfer device according to the eighth aspect, wherein the transfer device has the configuration of the transfer device according to the fourth aspect, and a plurality of stretches for stretching the second intermediate transfer belt as the second intermediate transfer body. At least one of the members is a transfer bias member that applies a transfer bias to the back surface of the second intermediate transfer belt so as to electrostatically transfer the visible image on the another image carrier to the second intermediate transfer belt. It is characterized by the following.
According to a tenth aspect of the present invention, in the transfer device of the eighth or ninth aspect, at least one of the plurality of stretching members for stretching the first intermediate transfer belt is provided on one of the intermediate transfer belts. It is a transfer bias member for a recording medium, which applies a transfer bias to the back surface of the first intermediate transfer belt to electrostatically transfer a visible image to the recording medium.
An eleventh aspect of the present invention is the transfer device according to the tenth aspect, wherein at least one of the plurality of stretching members that stretches the second intermediate transfer belt is visible on any one of the intermediate transfer belts. It is a transfer bias member for a recording medium, which applies a transfer bias to the back surface of the second intermediate transfer belt so that an image is electrostatically transferred to the recording medium.
According to a twelfth aspect of the present invention, in the transfer device of the eleventh aspect, the two transfer bias members for a recording medium are respectively provided at the nip at the first intermediate transfer belt and the second intermediate transfer belt. It is characterized by being provided so as to be in contact with the back surface.
According to a thirteenth aspect of the present invention, in the transfer device according to any one of the eighth to twelfth aspects, the first intermediate transfer belt has a surface resistance of 10 ⁵ to 10 ¹² [Ω / □]. Is what you do.
According to a fourteenth aspect of the present invention, in the transfer device of the ninth, tenth, eleventh, or twelfth aspect, the surface resistance of the second intermediate transfer belt is 10 ⁵ to 10 ¹² [Ω / □]. It is assumed that.
According to a fifteenth aspect of the present invention, in the transfer device of the seventh to fourteenth aspects, the base material of the second intermediate transfer belt is made of polyimide.
According to a sixteenth aspect of the present invention, in the transfer device of the seventh to fifteenth aspects, a thickness of the first intermediate transfer belt and the second intermediate transfer belt, which is not easily deformed, is 50 to 600 μm. ].
The invention according to claim 17 is the transfer device according to claim 9, wherein the transfer bias member that stretches the first intermediate transfer belt, and the transfer bias member that stretches the second intermediate transfer belt. Are rotatable transfer bias rollers.
Further, the invention according to claim 18 includes a step of forming a visible image on the image carrier, a double-side transfer step of transferring the visible image on the image carrier to both sides of the recording medium, and a step after the double-side transfer step. A step of fixing a visible image on both sides of the recording body to form an image on both sides of the recording body, wherein the double-sided transfer step is the double-sided transfer method according to claim 1. The method is characterized by performing a step.
The invention according to claim 19 is an image carrier that carries a visible image, a transfer device that transfers the visible image on the image carrier to both sides of the recording material, and a recording device that passes through the transfer device. 18. An image forming apparatus comprising: a fixing unit for fixing a visible image on both sides; and forming an image on both sides of a recording medium, wherein the transfer device according to claim 2 is used as the transfer device. Is what you do.
According to a twentieth aspect of the present invention, in the image forming apparatus of the nineteenth aspect, the transfer device of the twelfth aspect is used, and the surface of both intermediate transfer belts of the two transfer bias members for a recording medium is used. A bias having a polarity for electrostatically moving the visible image away from the transfer bias member for the recording medium toward the recording medium is applied to the one disposed on the further downstream side in the moving direction. It is characterized by having done.
According to a twenty-first aspect of the present invention, in the image forming apparatus according to the nineteenth or twentieth aspect, after receiving the recording medium discharged from the recording medium storage means for storing the recording medium, the recording medium is sent to the nip, and thereafter, the image forming apparatus main body is The recording medium transport path until the recording medium is discharged out of the recording medium is formed into a shape without bending, and the inclination angle from the horizontal direction is set from the horizontal direction on the leading end side of the recording medium being discharged from the recording medium storage unit. Is characterized by the same inclination angle.
According to a twenty-second aspect of the present invention, in the image forming apparatus of any one of the nineteenth to twenty-first aspects, a plurality of the image bearing members that carry a visible image transferred to the first intermediate transfer member are used. In addition, as the transfer device, a device configured to transfer a visible image carried on each image carrier on the first intermediate transfer member is used.
According to a twenty-third aspect of the present invention, in the image forming apparatus according to the twenty-second aspect, a plurality of the other image bearing members that carry a visible image transferred to the second intermediate transfer member are used as the other image bearing member. The transfer device according to claim 4, wherein the transfer device is configured to transfer the visible image carried on each of the different image carriers by superimposing the visible image on the second intermediate transfer member. It is characterized by the following.

According to these inventions, in the process of transporting the recording material sandwiched between the nips along with the surface movement of the two intermediate transfer members, the visible image on the second intermediate transfer member is transferred to one surface of the recording member. Then, the visible image on the first intermediate transfer member is transferred to the other surface of the recording member. In such a configuration, the visible image can be transferred to both sides of the recording medium by a one-pass method in which the recording medium does not pass through the nip twice by switchback, but only passes through the nip once.
In these inventions, the visible image is always transferred from the image bearing member to the intermediate transfer member and then to the recording member, so that the recording member does not come into direct contact with the image bearing member and can be visible on both surfaces thereof. Transfer the image. Therefore, when a paper material such as transfer paper is used as the recording medium, it is possible to suppress the adhesion of paper dust to the image carrier.
Furthermore, in these inventions, one of the first intermediate transfer member and the second intermediate transfer member is less likely to be deformed in the thickness direction of the recording body than the other. Trying to deform according to the difficult person. As a result, wedge-shaped (undulating) biting of the two intermediate transfer members in the nip is suppressed, and the two intermediate transfer members come into contact with each other more smoothly, so that wrinkles generated on the recording material sandwiched between the nips are reduced. Can be suppressed.
Therefore, while realizing one-pass double-sided transfer, it is possible to suppress the adhesion of paper powder to the image carrier when a paper material is used as a recording medium, and also to suppress wrinkles generated on the recording medium. effective.

Hereinafter, an embodiment of an electrophotographic printer (hereinafter, simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied.
First, a basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the present printer, and shows the printer from the front. In the figure, the printer 100 includes four process cartridges 6Y, M, C, and K for generating toner images of yellow, magenta, cyan, and black (hereinafter, referred to as Y, M, C, and K). I have. These use Y, M, C, and K toners of different colors as image forming substances, but otherwise have the same configuration, and are replaced when the end of their life. Taking a process cartridge 6Y for generating a Y toner image as an example, as shown in FIG. 2, a drum-shaped photosensitive member 1Y serving as an image carrier, a drum cleaning device 2Y, a static elimination device 3Y, a charging device 4Y, and a developing device 5Y Etc. are provided. In the photoreceptor 1Y, an aluminum cylinder having a diameter of 30 to 100 [mm] is coated with a surface layer of an organic semiconductor which is a photoconductive substance. An amorphous silicon surface layer may be coated. Further, instead of the drum shape, a belt shape may be used. The charging device 4Y uniformly charges the surface of the photoconductor 1Y rotated clockwise in the figure by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1Y is exposed and scanned by a laser beam L to carry a Y electrostatic latent image. This Y electrostatic latent image is developed into a Y toner image by a developing device 5Y using Y toner. Then, primary transfer is performed on a first intermediate transfer belt 8 described later. The drum cleaning device 2Y removes toner remaining on the surface of the photoconductor 1Y after the intermediate transfer process. Further, the charge removing device 3Y removes the charge remaining on the photoconductor 1Y after cleaning. By this charge elimination, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. Similarly, in the other process cartridges 6M, 6C, and 6K, M, C, and K toner images are formed on the photoconductors 1M, 1C, and 1K, and are primarily transferred onto the first intermediate transfer belt 8. The developing device may use a two-component developer containing a toner and a magnetic carrier, or may use only a toner powder. Further, the toner may be a pulverized toner manufactured by a pulverization method or a toner formed in a spherical shape, and a toner having a particle size of about 6 [μm] is preferable.

  An exposure device 7 is provided below the process cartridges 6Y, M, C, and K in the figure, and an image data processing device E1 is provided on the left side in the figure. The image data processing device E1 generates an exposure scanning control signal based on an image information signal sent from a personal computer or the like and sends it to the exposure device 7. The exposure device 7 serving as a latent image forming unit irradiates the respective photoconductors of the process cartridges 6Y, 6M, 6C, and 6 with laser light L emitted based on the exposure scanning control signal. Electrostatic latent images for Y, M, C, and K are formed on the photoconductors 1Y, 1M, 1C, and 1K exposed by the irradiation. The exposure device 7 irradiates a photoconductor with laser light (L) emitted from a light source via a plurality of optical lenses and mirrors while scanning with a polygon mirror rotated by a motor. Instead of the exposure device 7 having such a configuration, an exposure unit that irradiates the LED light from the LED array may be employed. In addition, a sealing member (not shown) is provided on the housing of the exposure device 7 in order to prevent contamination of internal components due to toner falling from the photoconductors 1Y, 1M, 1C, and 1K disposed above the housing. Provided.

  A first paper cassette 25 having a first paper feed roller 28 and a second paper cassette 26 having a second paper feed roller 29 are arranged vertically below the exposure device 7 so as to overlap in the vertical direction. Is established. Each of these cassettes contains therein a transfer paper bundle in which a plurality of transfer papers P as recording media are stacked. On the right side of the second paper cassette 26 in the figure, a manual feed tray 25 having a manual paper feed roller 30 is provided so as to extend not from inside the housing of the printer main body but from the side of the housing. Also, a transfer bundle is placed thereon.

  A paper feed path 32 having a pair of registration rollers 31 and a paper feed guide path 33 converging therewith are provided between the two paper feed cassettes (25, 26) and the manual feed tray 25. The paper feed guide path 33 has a transport roller pair 34. The first paper feed roller 28 and the second paper feed roller 29 are in contact with the first transfer paper P of the transfer paper bundle contained in the first paper cassette 25 and the second paper cassette 26, respectively. The uppermost transfer paper P is sent out toward the paper feed path 32 by being rotationally driven by a driving unit (not shown). The transferred transfer paper P is sandwiched between the first registration roller 31a and the second registration roller 31b of the registration roller pair disposed near the end of the paper feed path 32. The registration roller pair 31 rotates both rollers in the forward direction so as to sandwich the transfer paper P. However, as soon as the recording medium is sandwiched between the rollers, the rotation of both rollers is temporarily stopped. Then, the rotation is restarted at an appropriate timing, and the transfer paper P is sent out to a secondary transfer nip described later. It functions as a timing roller pair. On the other hand, the manual paper feed roller 30 is in contact with the uppermost transfer paper P of the transfer paper bundle placed on the manual paper feed tray 27. The uppermost transfer paper P is sent out toward the paper feed guide path 33 by being rotationally driven by a drive unit (not shown). The fed transfer paper P reaches the vicinity of the end of the paper feed path 32 via the rollers of the pair of transport rollers 34 which are rotated in the forward direction while being in contact with each other by driving means (not shown). Then, it is sandwiched between the first registration roller 31a and the second registration roller 31b.

  The electrostatic latent images for Y, M, C, and K formed on the respective photoconductors 1Y, 1M, 1C, and 1K undergo a transfer process by a transfer device. This transfer device has a first transfer unit 15 and a second transfer unit 24. The first transfer unit 15 is disposed above the process cartridges 6Y, 6M, 6C, and 6K in the figure, and includes a first intermediate transfer belt 8, four primary transfer rollers 9Y, 9M, C, and K, A first cleaning device 10 and the like are provided. Further, a secondary transfer backup roller 12, a first cleaning backup roller 13, a tension roller 14, and the like are provided. The first intermediate transfer belt 8 as the first intermediate transfer member is endlessly moved counterclockwise in the figure by the rotational driving of at least one of the rollers while being stretched by these three rollers. The four primary transfer rollers 9Y, 9M, C, and K, which are transfer bias rollers, sandwich the first intermediate transfer belt 8 thus moved endlessly between the photoconductors 1Y, 1M, 1C, and 1K, respectively. A next transfer nip is formed. Then, upon receiving a power supply (not shown), a primary transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (the inner circumferential surface of the loop) of the first intermediate transfer belt 8. The above-described three rollers provided in addition to the four primary transfer rollers 9Y, M, C, and K are all electrically grounded. The first intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K with the endless movement. In each primary transfer nip, the Y, M, C, and K toner images on the photoconductors 1Y, 1M, 1C, and 1K are superimposed and primarily transferred by the action of a nip pressure and a primary transfer bias. As a result, a four-color superimposed toner image (hereinafter, referred to as a four-color toner image) is formed on the first intermediate transfer belt 8. The secondary transfer backup roller 12 which stretches the first intermediate transfer belt 8 is located at a position where the secondary transfer backup roller 12 bites into a second intermediate transfer belt 16 described later. With such a biting arrangement, a secondary transfer nip is formed to make the first intermediate transfer belt 8 and the second intermediate transfer belt 16 abut widely in the circumferential direction. In the secondary transfer nip, the first transfer belt 8 and the second intermediate transfer belt 16 are brought into contact with each other while moving their surfaces in the same direction. The four-color toner image, which is a visible image, formed on the first intermediate transfer belt 8 is secondarily transferred to the second intermediate transfer belt 16 or the transfer paper P at the secondary transfer nip. After passing through the secondary transfer nip, untransferred toner that has not been secondary-transferred onto the second intermediate transfer belt 16 or the transfer paper P adheres to the first intermediate transfer belt 8. This is cleaned by the first cleaning device 10. More specifically, the first intermediate transfer belt 8 has a first cleaning device 10 disposed so as to contact the outer surface (front surface) of the loop, and a first cleaning device 10 disposed on the inner surface of the loop. It is sandwiched between the cleaning backup roller 13. Then, the transfer residual toner on the front surface is mechanically or electrostatically collected by the first cleaning device 10 and cleaned. Instead of the four primary transfer rollers 9Y, M, C, and K of the bias application type, a charger type that discharges from the electrodes may be used.

  The second transfer unit 24 of the transfer device is disposed on the right side of the first transfer unit 15 in the drawing, and includes a second intermediate transfer belt 16, a second cleaning device 18, a transfer charger 23, and the like. . Further, a secondary transfer roller 17, a nip extension roller 19, a tension roller 20, a backup roller 21, and the like are also provided. The second intermediate transfer belt 16 is endlessly moved clockwise in the drawing by the rotational driving of at least one of the rollers while being stretched over these four rollers. The secondary transfer backup roller 12 of the first transfer unit 15 described above cuts into a bridge portion of the second intermediate transfer belt 16 between the secondary transfer roller 17 and the nip extension roller 19 to form a secondary transfer nip. . The secondary transfer roller 17, which is a transfer bias roller for a recording medium, is a metal roller or a roller in which a conductive rubber layer is coated on a metal core, and has a polarity (for example, positive polarity) opposite to that of the toner by a power source (not shown). A secondary transfer bias is supplied. All other rollers in the second transfer unit 24 are grounded.

  The above-described registration roller pair 31 is directed toward the secondary transfer nip at a timing at which the transfer paper P sandwiched between the rollers can be brought into close contact with the four-color toner image primarily transferred onto the first intermediate transfer belt 8. Send out. However, if the four-color toner image is a first toner image to be transferred to a first surface (a surface facing upward on a stack unit 40 described later) which is one surface of the transfer paper P, the transfer is performed. The paper P is not sent out. Therefore, at this time, the first toner image on the first intermediate transfer belt 8 is secondarily transferred onto the second intermediate transfer belt 16 by the action of the nip pressure and the secondary transfer bias at the nip, which is the secondary transfer nip. You. On the other hand, when the four-color toner image on the first intermediate transfer belt 8 is the second toner image to be transferred to the second surface of the transfer paper P (the surface facing downward on the stack unit 40), The registration roller pair 31 sends out the transfer paper P in synchronization with the second toner image. Therefore, the second toner image is secondarily transferred to the second surface, which is the other surface of the transfer paper P, at the secondary transfer nip, and becomes a full-color image in combination with the white color of the transfer paper P. At this time, the first toner image previously transferred to the second intermediate transfer belt 16 is brought into close contact with the first surface of the transfer paper P sent to the secondary transfer nip. However, since the first toner image is attracted to the belt side by the action of the secondary transfer bias, the first toner image is in close contact with the first surface of the transfer sheet P, but is not necessarily secondarily transferred thereto.

  In the first transfer unit 15 described above, the secondary transfer backup roller 12 stretches the first intermediate transfer belt 8 in a shape that substantially reverses the moving direction thereof. Then, the first intermediate transfer belt portion whose moving direction is being reversed is brought into contact with the second intermediate transfer belt 16 to form a secondary transfer nip. Therefore, at the exit of the secondary transfer nip, the first intermediate transfer belt 8 is separated from the transfer paper P, and the transfer paper P is conveyed while being held only on the surface of the second intermediate transfer belt 16. Then, in the second transfer unit 24, the second intermediate transfer belt 16 is sent to a tertiary transfer unit with the endless movement of the belt. In the tertiary transfer portion of the second transfer unit 24, a transfer charger 23 is disposed with a predetermined gap between the second intermediate transfer belt 16 and the portion stretched by the backup roller 21. The transfer paper P on the second intermediate transfer belt 16 is provided with a charge of the opposite polarity (for example, positive polarity) to the toner by the transfer charger 23 on the second surface side. Due to the application of the electric charge, the first toner image sandwiched between the first surface of the transfer paper P and the second intermediate transfer belt 16 is tertiarily transferred to the first surface of the transfer paper P to be a full-color image. . The transfer device including the two transfer units (15, 24) transfers the second toner image to the transfer paper P at the second transfer nip at the second stage on the second surface thereof, and then transfers the second toner image to the third transfer portion at the third transfer portion. The first-stage toner image is transferred to one surface at a later stage. The member to which the primary transfer bias or the secondary transfer bias is applied may be a member having another shape such as a brush instead of the rollers (9, 17). Further, a non-contact discharge method may be adopted instead of an electrostatic transfer method in which a transfer bias is applied to a member.

  In the second transfer unit 24, the transfer paper P on which double-side transfer has been completed by the tertiary transfer is separated from the second intermediate transfer belt 16 and sent to a fixing device 35 described later. After passing through the tertiary transfer section, the second intermediate transfer belt 16 is sandwiched between the backup roller 21 and the second cleaning device 18 so that the transfer residual toner on the surface is mechanically or electrostatically cleaned. You. If the second cleaning device 18 is always in contact with the second intermediate transfer belt 16, the first toner image secondary-transferred onto the second intermediate transfer belt 16 will also be cleaned. Therefore, the second cleaning device 18 is brought into contact with and separated from the second intermediate transfer belt 16 by being swung about a swing shaft 18a in the direction of the arrow by a swing mechanism (not shown). Then, at least while the first toner image passes through the cleaning position, the first toner image is separated from the second intermediate transfer belt 16 to avoid cleaning of the first toner image.

  A fixing device 35 serving as a fixing unit is disposed above the second transfer unit 24 in the drawing. The fixing device 35 has two fixing rollers 35a and 35b which form a fixing nip by abutting on each other while rotating in the forward direction. Each of the fixing rollers 35a and 35b has a heating means such as a halogen lamp (not shown), and heats the transfer paper P sandwiched in the fixing nip from both sides. By this heating, the full-color images formed on both surfaces of the transfer paper P are fixed on the transfer paper P by softening the toner constituting the full-color images. After being fixed, the transfer paper P is reversed along the reversing guide member 36, and is then discharged out of the apparatus via the paper discharge roller pair 37. Then, the sheets are stacked on a stack section 40 formed on the upper surface of the housing of the printer body.

  The surface temperatures of the two fixing rollers 35a and 35b are detected by temperature detecting means (not shown). This temperature detecting means transmits the temperature to the control unit E2 disposed at the top of the housing of the printer body. The control unit E2 controls ON / OFF of the power supply to the heat generating means of the fixing rollers 35a and 35b based on the detection result of the surface temperature sent from the temperature detecting means to control the surface temperature of the fixing rollers 35a and 35b. Is maintained within a certain range (target range). However, when the single-sided print mode for forming an image only on one side of the transfer paper P is being executed, the image can be fixed with a smaller amount of heat than in the double-sided print mode. This is because the image is formed only on one side, and the amount of toner on the transfer paper P is smaller than that on both sides. Therefore, if the target range of the surface temperature is set lower in the single-sided print mode than in the double-sided print mode, energy can be saved. Further, since the toner amount of the single-color image is smaller than that of the full-color image, energy can be saved by switching the target range of the surface temperature according to the difference between the single-color print mode and the full-color print mode. .

  As described above, in the process of transporting the transfer paper P from the secondary transfer nip to the downstream side in the belt moving direction from the secondary transfer nip, the printer 100 transfers the toner image Is performed. Therefore, an image can be formed on both sides of the transfer paper P by the one-pass method. Further, since the transfer paper P is not brought into direct contact with the photoconductors (1Y, M, C, K) as image carriers, it is possible to suppress the adhesion of paper powder to the photoconductor. Note that, as in the present printer 100, a plurality of image carriers such as photoconductors are arranged and arranged, and a visible image formed by each is continuously superimposed and transferred to form a superimposed image such as a multicolor image. The method is called a tandem method. On the other hand, after a visible image is formed on one image carrier and transferred to the intermediate transfer member, a visible image is formed again on the image carrier and the image is superimposed and transferred on the visible image on the intermediate transfer member. There is also a method of forming a superimposed image by repeating the process. In this method, the steps of forming and transferring a visible image must be repeatedly performed. On the other hand, in the tandem system, a plurality of visible images to be superimposed and transferred can be formed almost simultaneously on the corresponding image carriers, so that the image forming time can be greatly reduced.

  As described above, the first toner image is formed prior to the second toner image. Then, after the secondary transfer from the first intermediate transfer belt 8 to the second intermediate transfer belt 16 at the secondary transfer nip, the toner image is tertiary-transferred to the first surface of the transfer paper at the tertiary transfer section. The first surface is a surface facing upward in the stack section 40. Accordingly, the transfer papers P stacked in the stack unit 40 are sequentially stacked with the first toner image formed earlier facing upward and the second toner image formed thereafter facing upward. Go. In order to arrange the page numbers of the transfer sheets P stacked in this manner in ascending order, the printer 100 performs the above-described operations for the image having two consecutive page numbers of odd and even numbers, with the page number having the larger page number first. Formed as one toner image. For example, the image of the second page is formed as the first toner image prior to the image of the first page. In this case, even if originals of several pages are continuously output, the stack unit 40 can arrange the page numbers in order from the bottom. However, when executing the single-sided print mode in which an image is formed only on the second side of the transfer sheet P, the images are formed in order from the page having the smallest page number, and the images are secondarily transferred to the second side of the transfer sheet P, respectively. . Thus, even in the single-sided print mode, the stack section 40 can arrange the page numbers in order from the bottom.

  In the four photoconductors 1Y, 1M, 1C, and 1K, each color toner image formed for the second toner image is formed as a non-mirror image (hereinafter, referred to as a normal image). This is because the formed toner image of each color changes to a mirror image and a normal image in the process of reaching the transfer paper P through two transfer steps of primary transfer and secondary transfer. By forming a normal image on each photoconductor, a normal image is also formed on the second surface of the transfer paper P. On the other hand, since each color toner image formed for the first toner image is performed until the third transfer, the number of transfer steps is one more than that of the second toner image. Therefore, a mirror image is formed on each photoconductor. As a result, a normal image, a mirror image, and a normal image are changed every transfer, and a normal image can be formed on the first surface of the transfer paper P.

  A bottle container 54 is disposed above the first transfer unit 15 in the drawing. In the bottle container 54, toner bottles BY, BM, BC, and BK containing toner to be supplied to the developing devices in the process cartridges (6Y, M, C, and K) are stored.

  As shown in FIG. 3, the printer 100 forms an image based on an image information signal sent from a personal computer (hereinafter, referred to as a personal computer) 200 or the like. FIG. 3 shows an example of the image forming system in which the personal computer 200 and the printer 100 are connected by a communication cable, but a wireless connection may be adopted. An operation display 51 composed of a touch panel or the like is fixed to the front left corner of the printer body. The user can input various parameters such as image forming process conditions and paper conditions according to the guide display appearing on the display of the operation display 51. Switching between the single-sided print mode and the double-sided print mode is performed by operating a mode switching button provided on the operation display 51. The selection of the paper type (the selection of the paper storage cassette) is also performed by operating the operation display 51. However, the switching of the modes and the selection of the paper type can also be performed by transmitting a setting signal from the personal computer 200.

  A front door 52 is provided on the front surface of the printer main body so as to be freely opened and closed. When the front door 52 is opened, a support 53 that supports the first transfer unit (15) (not shown) is largely exposed. The support 53 is configured to be slidable on a guide rail (not shown) in the front-rear direction of the printer main body, and is pulled out from the inside of the printer main body toward the front side to expose the first transfer unit (15). . The exposure facilitates the maintenance and inspection work of the first transfer unit. When the front door 52 is opened, the end faces of the toner bottles BY, BM, BC, and BK in the bottle container 54 disposed above the support 53 are exposed. The toner bottles BY, BM, BC, and BK each having an exposed end face are detachably attached to the bottle container 54 in the front-rear direction of the printer. When the front door 52 is opened, the toner bottles BY, BM, BC, and BK can be attached to and detached from the printer body in the front-rear direction. This is not a configuration in which the upper surface of the printer main body in which the stack portion 40 is formed is an openable and closable upper door, which is opened to attach and detach the toner bottles BY, BM, BC, and BK in the vertical direction. Therefore, even when an optional scanner device (not shown) is arranged above the printer 100 to constitute a copier, the toner bottles BY, BM, BC, and BK can be attached and detached. The first paper cassette 25 and the second paper cassette 26 described above are disposed below the front door 52, and are configured to be attached to and detached from the printer main body by sliding in the front-rear direction. Opening the front door 52 does not impair the attachment / detachment of the first paper cassette 25 and the second paper cassette 26 and the operability of input to the operation display 51.

Next, a characteristic configuration of the printer 100 according to the present embodiment will be described.
It is assumed that the first intermediate transfer belt 8 and the second intermediate transfer belt 16 each have the same degree of ease of deformation in the thickness direction. Then, in the secondary transfer nip, in particular, in a region sandwiched between the secondary transfer backup roller 12 and the secondary transfer roller 17, the surfaces of both belts are elastically deformed complicatedly under the influence of the pressing by the rollers. Then, as shown in FIG. 4, the surfaces of both belts are elastically deformed into a complicated shape at the secondary transfer nip, so that the two belts bite into each other in a wedge shape (undulating shape). When the transfer paper P is passed through the secondary transfer nip in which the surfaces of both belts bite into each other in a wedge-like manner (corrugation), the transfer paper P follows the shape of the wedge and causes wrinkles on the transfer paper P.

  Therefore, in the present printer 100, the second intermediate transfer belt 16 that is less likely to be deformed in the thickness direction than the first intermediate transfer belt 8 is used. In such a configuration, the second intermediate transfer belt 16 is less likely to be deformed in the thickness direction than the first intermediate transfer belt 8, so that the first intermediate transfer belt 8 is less likely to be deformed mainly at the secondary transfer nip. It tries to deform following the belt 16. Then, as shown in FIG. 5, wedge-shaped (undulating) biting of the two belts in the secondary transfer nip is suppressed, and the two belts come into contact more smoothly, so that the transfer sandwiched between the secondary transfer nips Wrinkles generated on the paper P can be suppressed. In addition, since the two belt surfaces can be surely brought into close contact with each other with a lower nip pressure due to the smooth contact, transfer by applying excessive pressure at the time of transfer to aggregate the toner. Defects can also be reduced.

  In the present embodiment, the second intermediate transfer belt 16 is made of a resin material and has a surface hardness of 95 [degrees] according to JIS-A. On the other hand, the first intermediate transfer belt 8 is made of rubber and has a surface hardness of 50 [degree] according to JIS-A. When a belt having a multilayer structure is used, the surface hardness is always measured using the entire belt having the multilayer structure. The surface hardness measured in this way indicates the difficulty of deformation of the belt in the thickness direction. Therefore, a belt having a higher surface hardness is less likely to be deformed in the thickness direction. Note that, of the two belts, the one that is easily deformed in the thickness direction (the first intermediate transfer belt 8 in this example) is selected from the viewpoint of securing a certain degree of adhesion between the two belts at the secondary transfer nip. It is desirable to use one having a surface hardness of 65 [degrees] or less according to JIS-A.

  Of the first intermediate transfer belt 8 and the second intermediate transfer belt 16, at least the first intermediate transfer belt 8, which is the other belt that is different from the one that is less likely to deform in the thickness direction, has a multilayer structure. ing. This is for the following reason. That is, the other belt, that is, the first intermediate transfer belt 8, which is the one that is easily deformed, must exhibit sufficient elasticity and not exhibit electrical resistance enough to realize electrostatic transfer. No. Therefore, an elastic material is generally used as a base material of the belt, and a conductive material such as carbon black is dispersed as a resistance adjusting agent in the elastic material to exert a desired electric resistance. However, in general, the elastic material becomes harder as the content of the resistance modifier increases. For this reason, if the dispersion amount of the resistance adjusting agent is increased to such an extent that the desired electrical resistance can be exhibited, the elastic material may not be able to exhibit the desired elasticity. Therefore, a multilayer structure is adopted. Then, while the dispersion amount of the resistance adjusting agent is suppressed to some extent in the base material layer made of the elastic material, the resistance adjusting agent can be dispersed in a large amount in the other layers (for example, the surface layer and the lower layer). As a result, the desired electrical resistance can be exhibited while exhibiting good elasticity of the entire belt. Further, as a material for the other layer, a material having a lower surface energy than that of the base material layer is used, and if the other layer is provided as a surface layer serving as an image holding surface, the layer functions as a toner image release promoting layer. You can also. Thus, it is possible to promote toner separation from the first intermediate transfer belt 8 in the secondary transfer nip, and to suppress transfer failure due to remaining transfer residual toner on the belt. It is needless to say that the second intermediate transfer belt 16 may have a multilayer structure. In the case of a belt having a single-layer structure, the base material of the belt is a belt material constituting the belt. In the case of a belt having a multilayer structure, it is a material constituting the thickest layer (base layer). In addition, the belt having a multilayer structure includes a belt in which a substrate is simply coated with a release promoting layer, and a belt in which a rubber layer or the like for exhibiting good elasticity is provided.

  The resin material used for the base material of the second intermediate transfer belt 16 is not particularly limited. However, in this embodiment, polyimide is used. This is because the use of polyimide having excellent heat resistance for the base material of the second intermediate transfer belt 16 allows the entire belt to exhibit heat resistance. Examples of the resin material capable of exhibiting heat resistance include polyamide in addition to polyimide. When it is not necessary to exhibit heat resistance to the entire belt, various resin materials can be used. For example, a polycarbonate, a fluorine-based resin (ETFE, PVDF), a methyl methacrylate resin, a butyl methacrylate resin, an ethyl acrylate resin, a butyl acrylate resin, or the like may be used. Further, for example, modified acrylic resin (silicone-modified acrylic resin, vinyl chloride resin-modified acrylic resin, acryl / urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, etc. may be used. Further, for example, rosin-modified maleic resin, phenol resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, ionomer resin, and the like may be used. Further, for example, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral resin, modified polyphenylene oxide resin, and the like may be used. Further, for example, a styrene-based resin (a homopolymer or a copolymer containing styrene or a styrene-substituted product) may be used. The styrene resin includes, for example, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, and styrene-maleic acid copolymer. Such as coalescence. Further, for example, styrene-acrylate copolymers (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene- Phenyl acrylate copolymer). Further, for example, styrene-methacrylate copolymers (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, and the like) and the like. Further, styrene-α-chloromethyl acrylate copolymer, styrene-acrylonitrile-acrylate copolymer and the like can be used. Two or more of the resin materials listed above may be used in combination.

  There is no particular limitation on the rubber material or elastomer used for the first intermediate transfer belt 8. For example, butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber and the like can be mentioned. Further, ethylene-propylene rubber, ethylene-propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, and the like may be used. Further, epichlorohydrin rubber, silicone rubber, fluorine rubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile rubber and the like may be used. Further, a thermoplastic elastomer (for example, polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, or fluororesin) may be used. It is also possible to use a mixture of two or more of the materials listed above.

  The front side (transfer surface side) or the back side of the layer having the resin material exemplified above as the base material is coated with the layer formed of the rubber material or the elastomer exemplified above to form the second intermediate transfer belt 16 in a multilayer structure. It is also possible. Alternatively, the first intermediate transfer belt 8 may be configured to have a multilayer structure by coating a layer made of the exemplified resin material on the front side (transfer surface side) or the back side of the layer based on the exemplified rubber material or elastomer. It is possible. Further, a release promoting layer may be provided on the surface of the first intermediate transfer belt 8 or the second intermediate transfer belt. By providing the release promoting layer, it is possible to reduce the adhesive force between the toner and the belt, improve the cleaning performance of the toner image, and suppress the transfer failure during the secondary transfer and the tertiary transfer. The material of the release promoting layer is not particularly limited as long as it has a lower surface energy than the base material. For example, a fluorine resin may be used. Further, for example, powders or particles of a fluorine compound, fluorocarbon, titanium dioxide, silicon carbide, or the like may be dispersed in a material such as a resin or rubber by one or more kinds. In the case where a fluorine-based rubber material is used, it is possible to reduce the energy by performing heat treatment so that fluorine is unevenly distributed on the surface.

  There is no particular limitation on the resistance adjuster to be dispersed in the belt material. For example, carbon black, graphite, metal powder such as aluminum and nickel, tin oxide, titanium oxide, antimony oxide, indium oxide and the like can be mentioned. Further, for example, a conductive metal oxide such as potassium titanate, antimony oxide-tin oxide composite oxide (ATO), indium oxide-tin oxide composite oxide (ITO), or a conductive metal oxide may be used. Further, for example, contrary to the conductive materials listed above, insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate may be used. In this case, it goes without saying that it is used to increase the electric resistance value of the material.

  The method for manufacturing the first intermediate transfer belt 8 and the second intermediate transfer belt 16 is not particularly limited. For example, there is a centrifugal molding method in which a material is poured into a rotating cylindrical mold to form a belt. Further, for example, a spray coating method in which a liquid paint is sprayed to form a film, or a dipping method in which a cylindrical mold is immersed in a material solution and pulled up, may be used. Further, for example, a casting method in which a material is poured into an inner mold and an outer mold, a method in which a compound is wound around a cylindrical mold, and vulcanization polishing may be performed. Further, a belt may be manufactured by combining two or more of these exemplified methods.

  FIG. 8 is a sectional view showing an intermediate transfer belt (8, 16) including a base layer and a release promoting layer. FIG. 11 shows an intermediate transfer of a three-layer structure in which an elastic layer made of a material having excellent elasticity such as rubber, and a release promoting layer made of a material having excellent toner release properties are sequentially laminated on a base layer. It is sectional drawing which shows a belt (8, 16). The base layer is made of, for example, a fluororesin having a low elongation or a material in which a non-elongation material such as a canvas is added to a rubber having a high elongation. Such a material is the substrate described above.

  As the material of the elastic layer, the rubber materials and thermoplastic elastomers listed above can be used. Although the thickness depends on the hardness of the material, if the thickness is too large, the expansion and contraction of the surface becomes excessively large and cracks are easily generated in the release promoting layer. Further, since the amount of expansion / contraction increases, the image tends to expand and contract. The hardness HS of the elastic layer is preferably set to 10 ≦ HS ≦ 65 [°: JIS-A]. If the hardness HS is lower than 10 [°: JIS-A], it becomes difficult to form the belt with high dimensional accuracy.

  Various methods can be considered as a method for suppressing the elongation of the elastic layer. For example, there is a method in which a base layer is coated with a resin layer made of a material with low elongation such as a fluororesin, and an elastic layer is formed thereon. Alternatively, an elastic material such as canvas may be added to a highly elongate rubber material to serve as a core, and an elastic layer may be formed on the base layer including the core.

  Examples of the material that functions as the core include natural fibers such as cotton and silk. Further, inorganic fibers such as polyester fiber, nylon fiber, acrylic fiber, carbon fiber, glass fiber, and boron fiber, and metal fibers such as iron fiber and copper fiber may be used. Further, one or more selected from these may be processed into a thread or woven fabric. The thread may be of any kind, such as twisted one or a plurality of filaments, single twisted yarn, multi-twisted yarn, twin yarn, and the like. These materials can be subjected to a conductive treatment.

  In the present embodiment, an example has been described in which an intermediate transfer belt that is endlessly moved while being stretched by a plurality of rollers is used as the first intermediate transfer member and the second intermediate transfer member. A shape may be used. However, in the case of using the respective intermediate transfer belts, there are the following advantages. That is, as shown in the secondary transfer nip shown in FIG. 1, one belt is deformed and stretched so as to be wound around a stretched portion of the other belt by a stretch member, thereby forming a considerably long secondary transfer nip. Can be formed. As a result, a long contact time between the four-color toner image and the transfer paper P or the second intermediate transfer belt 16 can be ensured, so that the process linear speed can be increased and the image forming time can be reduced. In addition, since both belts can be arranged in various stretched shapes, the degree of freedom in the layout inside the main body can be increased as compared with the case of using rollers or drums.

The surface resistance of each of the first intermediate transfer belt 8 and the second intermediate transfer belt 16 is adjusted to a range of 10 ⁵ to 10 ¹² [Ω / □]. This is for the following reason. That is, when the surface resistance is less than 10 ⁵ [Ω / □], the transfer bias applied to the back surface of the belt leaks from the belt surface to the photosensitive member or the ground member contacting the belt, and it is difficult to realize the electrostatic transfer. Because it becomes. On the other hand, if the surface resistance exceeds 10 ¹² [Ω / □], the current flowing through the belt becomes insufficient and it becomes difficult to realize electrostatic transfer.

  As described above, in the present embodiment, polyimide is used as the resin material forming the base material of the second intermediate transfer belt 16. This is for the following reason. That is, the transfer paper P conveyed while being held by the second intermediate transfer belt 16 is sent to the fixing device 35 for fixing the toner image. Since a high temperature of about 140 ° C. is generated from the fixing device 35, if the distance between the fixing device 35 and the second intermediate transfer belt 16 is short, the second transfer belt 16 is heated by the heat from the fixing device 35. It will be heated. Then, when the intermediate transfer belt 16 is inferior in heat resistance, the intermediate transfer belt 16 is deteriorated by heating and causes various problems. In order to suppress such a problem, it is conceivable to arrange the second intermediate transfer belt 16 and the fixing device 35 sufficiently apart from each other. However, when the second intermediate transfer belt 16 and the fixing device 35 are disposed apart from each other, the transfer paper P, which flexes freely due to the influence of gravity, cannot be directly transferred from the belt to the fixing device 35. It is necessary to provide a paper guide member between them. The transfer paper P held by the second intermediate transfer belt 16 carries the toner image not only on the front surface but also on the back surface, and the toner image on the back surface is rubbed by the paper guide member and is disturbed. Therefore, in the present embodiment, the second intermediate transfer belt 16 is made to have heat resistance as a whole by using polyimide as the material of the base material. In such a configuration, the second intermediate transfer belt 16 and the fixing device 35 are disposed close to each other so that the paper guide member can be omitted, and the second intermediate transfer is performed by the fixing device 35 while avoiding the disturbance of the toner image. Various problems caused by heating the belt 16 can be suppressed.

  The thickness of the second intermediate transfer belt 16 is adjusted within a range of 50 to 600 [μm]. This is for the following reason. That is, if the thickness is less than 50 [μm], the intermediate transfer belt 16 is fragile and easily broken. If the thickness is larger than 600 [μm], the thickness of the substrate made of a resin material exhibiting elasticity is too large, and the second intermediate transfer belt 16 is deformed in the thickness direction more than the first intermediate transfer belt 8. This is because it becomes difficult to exhibit the property of being difficult to perform. By setting the thickness to 600 [μm] or less, such properties can be easily exhibited.

  FIG. 6 is a schematic configuration diagram illustrating a first modification of the printer according to the present embodiment. In the first modification 100A, the positional relationship of each of the process cartridges 6Y, M, C, K and the exposure device 7 with respect to the first transfer unit 15 is opposite to that of the printer 100 shown in FIG. Specifically, the process cartridges 6Y, 6M, 6C, and 6K are disposed above the first transfer unit 15, and the exposure device 7 is disposed further above the process cartridges.

  In the first transfer unit 15, the surface hardness of the first intermediate transfer belt 8 according to JIS-A is adjusted to 50 [degrees] as in the printer shown in FIG. In order to realize such a relatively soft surface hardness, instead of a single layer structure as shown in FIG. 7, a multilayer structure as shown in FIGS. 8 and 11 is used. Has been. In the first transfer unit 15 of the first modified example apparatus 100A, a second tension roller 60 and a tertiary transfer backup roller 61 are additionally provided as a plurality of rollers for stretching the first intermediate transfer belt 8. I have.

  6, the surface hardness of the second intermediate transfer belt 16 is adjusted to 95 [degrees] according to JIS-A, similarly to the printer shown in FIG. The nip extension roller (19 in FIG. 1) and the backup roller (21 in FIG. 1) among the plurality of rollers that stretch the second intermediate transfer belt 16 are eliminated. Further, the transfer charger (23 in FIG. 1) disposed opposite to the backup roller via the second intermediate transfer belt 16 is also eliminated. Instead, a tertiary transfer roller 62, a separation roller 63, and a second tension roller 64 are additionally provided. The tertiary transfer roller 62 sandwiches two intermediate transfer belts with the tertiary transfer backup roller 61 in the first transfer unit 15 to form a tertiary transfer nip. This tertiary transfer nip is continuous with a secondary transfer nip formed by sandwiching two intermediate transfer belts between the secondary transfer backup roller 12 and the secondary transfer roller 17 on the upstream side. are doing. The separation roller 63 replaces the backup roller of the printer 100 shown in FIG. 1, and separates the transfer paper P from the second intermediate transfer belt 16 which changes the moving direction by about 90 [°] according to its curvature. It is sent to the fixing device 35. The second cleaning device 18 cleans the transfer residual toner on the second intermediate transfer belt 16 while being backed up by the tension roller 20.

  FIG. 9 is an enlarged configuration diagram showing the secondary transfer nip and its surroundings in the first modification 100A. The secondary transfer backup roller 12, which presses the two intermediate transfer belts from the back surface of the first intermediate transfer belt 8 toward the secondary transfer roller 17, which is a transfer bias member for a recording medium, is grounded. On the other hand, a secondary transfer bias having a polarity opposite to that of the toner (plus polarity in the illustrated example) is applied to the secondary transfer roller 17 by a power supply. The first toner image on the first intermediate transfer belt 8 is electrostatically attracted to the secondary transfer roller 17 side by the influence of the secondary transfer bias, and is electrostatically transferred onto the second intermediate transfer belt 16. Is done. In the secondary transfer, a transfer method is employed in which the toner is electrostatically attracted toward the secondary transfer roller 17 as a transfer bias member for a recording medium.

  FIG. 10 is an enlarged configuration diagram showing the tertiary transfer nip and its surroundings in the first modification 100A. A tertiary transfer backup roller 61 pressing the two intermediate transfer belts from the back surface of the first intermediate transfer belt 8 toward a tertiary transfer roller 62 serving as a transfer bias member for a recording medium is similar to the secondary transfer backup roller. Grounded. On the other hand, to the tertiary transfer roller 62, a tertiary transfer bias having the same polarity (minus polarity in the illustrated example) as the toner is applied by a power supply. The first toner image secondary-transferred onto the second intermediate transfer belt 16 at the secondary transfer nip is electrostatically extruded toward the tertiary transfer backup roller 61 under the influence of the tertiary transfer bias. It is. Then, tertiary transfer is performed on the first surface of the transfer paper P sandwiched between the two intermediate transfer belts. An electrostatic extrusion transfer method in which toner is electrostatically extruded toward the transfer paper P from the tertiary transfer roller 62 serving as a transfer bias member for a recording medium is employed. Conventionally, in the transfer method, at the time of the tertiary transfer, the second toner image secondarily transferred to the second surface of the transfer paper P at the secondary transfer nip first is also electrostatically similar to the first toner image. The present inventors thought that it would be pushed out and returned to the first intermediate transfer belt 8. However, upon actual testing, surprisingly, it was surprising that the second toner image could be retained on the second surface of the transfer paper P without being extruded electrostatically. In the tertiary transfer method, unlike the transfer charger of the printer 100 shown in FIG. 1, it is possible to tertiary transfer the first toner image while keeping both the first toner image and the second toner image in close contact with the transfer paper P. it can. Therefore, toner dust due to charging the exposed second surface of the transfer paper P can be avoided, and a higher quality image can be formed. Further, generation of ozone due to corona charging can be avoided.

  Note that the method of applying a tertiary transfer bias having a polarity opposite to that of the toner to the tertiary transfer backup roller 61 in the same figure, connecting the tertiary transfer roller 62 to ground, and drawing the tertiary transfer backup roller 61 to the tertiary transfer backup roller 61 does not work. Was. The first toner image on the second intermediate transfer belt 16 is electrostatically attracted to the first surface of the transfer paper P, and at the same time, the second toner image is transferred onto the first intermediate transfer belt 8 from the second surface of the transfer paper P. They pulled him back. Therefore, the tertiary transfer in the tertiary transfer nip needs to be performed by extrusion type electrostatic transfer. In other words, the toner image is transferred from the transfer bias member for the recording medium to the transfer bias member for the recording medium which is disposed further downstream in the surface moving direction of the two intermediate transfer belts. A transfer bias having a polarity for electrostatically moving the paper toward the paper P is applied.

  Also in the printer 100A of the first modified example configured as described above, in the process of transferring the transfer sheet P from the secondary transfer nip to the downstream side, the toner image is transferred from both sides of the transfer sheet P to the transfer sheet P. Is performed. Therefore, an image can be formed on both sides of the transfer paper P by the one-pass method. Further, since the transfer paper P does not directly contact each of the photoconductors (1Y, M, C, K), it is possible to suppress the adhesion of paper powder to the photoconductor. Further, one of the two intermediate transfer belts (the second intermediate transfer belt 16) is less likely to be deformed in the thickness direction than the other, so that the one that is easily deformed mainly in the secondary transfer nip or the tertiary transfer nip is used. Tries to deform following the surface that is less likely to deform. As a result, wedge-shaped (wavy) biting of the two belts in the secondary transfer nip and the tertiary transfer nip is suppressed, and wrinkles generated on the transfer paper P sandwiched between these nips can be suppressed. In the printer 100A of this modification, a tertiary transfer nip is formed in addition to the secondary transfer nip as a nip formed by the abutment of the two belts. The present invention for suppressing wrinkles is particularly effective.

  FIG. 12 is a schematic configuration diagram illustrating a second modification of the printer according to the embodiment. In the second modified example device 100B, the first transfer unit 15 and the second transfer unit 24 respectively stretch the first intermediate transfer belt 8 and the second intermediate transfer belt 16 in a horizontally long shape. Then, the first intermediate transfer belt 8 and the second intermediate transfer belt 16 disposed below the figure in the figure are brought into contact with each other at a horizontally elongated portion to form a secondary transfer nip.

  The second modification 100B includes two process cartridges for each color. One for the first system and one for the second system. Among these, the process cartridges 6Y, M, C, and K for the first system have the photoconductors 1Y, M, C, and K on the first intermediate transfer belt 8 above the first transfer unit 15 in the drawing. It is arranged to be in contact. Then, Y, M, C, and K toner images for superimposed primary transfer are formed on the first intermediate transfer belt 8. The four-color toner image obtained by the superimposed primary transfer corresponds to the second toner image in the printer according to the embodiment. Then, with the endless movement of the first intermediate transfer belt 8 in the clockwise direction in the drawing, the first intermediate transfer belt 8 is sent to the secondary transfer nip where the first intermediate transfer belt 8 and the second intermediate transfer belt 16 abut.

On the other hand, the process cartridges 76Y, M, C, and K for the second system abut the photosensitive members 71Y, M, C, and K on the second intermediate transfer belt 16 below the second transfer unit 24 in the drawing. It is arranged to make it. Then, Y, M, C, and K toner images for superimposed primary transfer are formed on the second intermediate transfer belt 16. The four-color toner image obtained by the superimposed primary transfer corresponds to the first toner image in the printer according to the embodiment. Then, the second intermediate transfer belt 16 is sent to the above-described secondary transfer nip with the endless movement in the counterclockwise direction in the drawing. The optical writing to the photoconductors 71Y, M, C, K of the process cartridges 76Y, M, C, K for the second system is performed by the exposure device 77 for the second system. The exposure device 77 is disposed below the process cartridges 76Y, M, C, and K for the second system in the drawing. On the other hand, the exposure system 7 for the first system is disposed above the process cartridges 6Y, 6M, 6C and 6K for the first system in the drawing.
This is the second

  In the second modified example apparatus 100B, a printer unit 90 for printing an image on transfer paper P, and a paper feed unit 91 as a recording medium housing unit for storing the transfer paper P to be supplied to the printer unit are provided. It is configured separately. The paper feeding unit 91 rotates the paper feeding roller 92 pressed against the uppermost transfer paper P of the bundle of transfer papers housed therein at a predetermined timing, thereby transferring the transfer paper P to the printer unit. The paper is fed out to the paper feed path 88 of the paper feeder 90. The transferred transfer paper P passes through a plurality of transport roller pairs, and is then sandwiched between rollers of a registration roller pair 31 disposed near the end of the paper feed path 88. The secondary transfer nip is synchronized with the second toner image on the first intermediate transfer belt 8 of the first transfer unit 15 and the first toner image on the second intermediate transfer belt 16 of the second transfer unit 25. Sent out to.

  FIG. 13 is a schematic diagram showing a secondary transfer nip and its surrounding configuration in the second modification 100B. The first transfer unit 8 has an upstream secondary transfer facing roller 82 and a downstream secondary transfer facing roller 84 as two of a plurality of stretching rollers for stretching the first intermediate transfer belt 8. are doing. The second transfer unit has an upstream secondary transfer roller 81 and a downstream secondary transfer roller 84 as two of a plurality of stretching rollers that stretch the second intermediate transfer belt 16. ing. In the secondary transfer nip, the portion between the two secondary transfer opposed rollers (82, 84) in the first intermediate transfer belt 8 is extended between the two secondary transfer rollers (81, 83) in the second intermediate transfer belt 16. Formed in the part. Both the secondary transfer opposing rollers (82, 84) are grounded.

  In the second modified example apparatus 100B, two-stage secondary transfer of upstream secondary transfer and downstream secondary transfer is performed in the secondary transfer nip. Specifically, the transfer paper P sent to the secondary transfer nip first passes through the upstream secondary transfer portion in the nip. In the upstream secondary transfer section, both intermediate transfer belts (8, 16) are sandwiched between an upstream secondary transfer facing roller 82 and an upstream secondary transfer roller 84. Then, under the influence of the upstream-side secondary transfer electric field formed between the two rollers, the toner image on one of the intermediate transfer belts is secondarily transferred to one of the surfaces of the transfer paper P. In the illustrated example, the upstream secondary transfer roller 81, which is in contact with the back surface of the second intermediate transfer belt 16, in the upstream secondary transfer unit is provided with a positive upstream secondary transfer roller having a polarity opposite to the charging polarity of the toner. A transfer bias is applied. Accordingly, the second toner image on the first intermediate transfer belt 8 is electrostatically attracted toward the upstream-side secondary transfer roller 81, and the second surface (the other surface in FIG. The image is secondary-transferred to the surface facing upward. In the illustrated example, the electrostatic attraction transfer method is employed as the upstream secondary transfer method.

  The transfer paper P on which the upstream secondary transfer has been performed in this way then enters the downstream secondary transfer section. In the downstream secondary transfer section, both intermediate transfer belts (8, 16) are sandwiched between the downstream secondary transfer facing roller 84 and the downstream secondary transfer roller 83. Then, under the influence of the downstream secondary transfer electric field formed between the two rollers, the toner image on one of the intermediate transfer belts is secondarily transferred to either one surface of the transfer paper P. In the illustrated example, in the downstream secondary transfer section, the downstream secondary transfer roller 83 which is in contact with the back surface of the second intermediate transfer belt 16 is supplied with a downstream secondary transfer bias having the same negative polarity as the charged polarity of the toner. Has been applied. Accordingly, the first toner image on the second intermediate transfer belt 16 is electrostatically extruded from the downstream side secondary transfer roller 83 toward the downstream side secondary transfer opposing roller 84, and one side of the transfer paper P Is secondary-transferred to the first surface (the surface facing downward in the figure). In the illustrated example, an electrostatic extrusion transfer method is adopted as the downstream secondary transfer method. The present inventors have experimentally confirmed that the following reverse transcription does not occur when the following two-step transfer is employed as shown in the figure. That is, the second toner image previously transferred to the second surface of the transfer paper P is reversely transferred from the second surface to the first intermediate transfer belt 8 during the secondary transfer on the downstream side. It is a phenomenon.

  The transfer paper P, on which the toner images are secondarily transferred to both sides in the secondary transfer nip, moves from the right side to the left side in the drawing with the endless movement of the two intermediate transfer belts (8, 16), and is transferred to the fixing device 35. Handed over. The fixing device 35 includes two stretching rollers, a first fixing belt 35c, a second fixing belt 35d, and the like, in addition to the two fixing rollers 35a and 35b. The first fixing belt 35c is endlessly moved clockwise in the figure while being stretched between the fixing roller 35a and one of the stretching rollers. Further, the second fixing belt 35d is endlessly moved counterclockwise in the figure while being stretched between the fixing roller 35b and the other stretching roller. The first fixing belt 35c and the second fixing belt 35d, which are moved endlessly in this manner, form a fixing nip by being brought into contact with each other while being heated from the back side by the fixing rollers 35a and 35b, respectively. The transfer paper P sent from the secondary transfer nip to the fixing device 35 is heated or pressurized from both sides while being sandwiched by the fixing nip and conveyed from left to right in the drawing. Thus, the toner images on both sides are fixed.

  The transfer paper P on which the fixing process has been performed by the fixing device 35 passes through a pair of paper discharge rollers 37 disposed on the left side of the fixing device 35 in the drawing, and is then fixed to the left side of the printer in the drawing. It is discharged onto the unit 40.

  On the upstream side of the secondary transfer nip in the belt moving direction, the first intermediate transfer belt 8 and the second intermediate transfer belt 16 face each other without contact, and the belts gradually move toward the secondary transfer nip. Move to get closer. The paper feed path 88 is disposed in a region where the two intermediate transfer belts face each other in a non-contact manner. The transfer paper P discharged from the pair of registration rollers 31 disposed near the end of the paper feed path 88 passes through a region where the two intermediate transfer belts move closer to each other toward the secondary transfer nip. It is reliably and smoothly guided toward the secondary transfer nip. Therefore, even if the transfer paper P is made of a thin and extremely weak waist, a jam or the like hardly occurs.

  On the other hand, also on the downstream side of the secondary transfer nip in the belt moving direction, the two intermediate transfer belts face each other without contact, and move so as to gradually move away from each other. The fixing device 35 is disposed so that the end on the transfer paper receiving side enters the area where the two intermediate transfer belts face each other in a non-contact manner. The transfer paper P sent out from the secondary transfer nip is reliably and smoothly guided to the fixing device 35 entering the area. Therefore, this also makes it difficult for jams and the like to occur.

  When the two-stage secondary transfer, that is, the upstream secondary transfer and the downstream secondary transfer, is performed in the nip as in the second modified example device 100B, the secondary transfer nip and its surrounding configuration are shown in FIG. May be adopted. Compared to the configuration shown in FIG. 13, two secondary transfer opposing rollers (82, 84) in the first transfer unit 15 and two secondary transfer rollers (81, 83) in the second transfer unit 24 Is replaced between the units. In the upstream side secondary transfer section, an upstream side secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the upstream side secondary transfer roller 81 abutting on the back surface of the first intermediate transfer belt 8. . Then, the first toner image on the second intermediate transfer belt 16 is electrostatically attracted toward the upstream secondary transfer roller 81 and is secondarily transferred to the first surface of the transfer paper P (electrostatic attraction) Transfer method). On the other hand, in the downstream secondary transfer section, a downstream secondary transfer bias having the same negative polarity as the charge polarity of the toner is applied to the downstream secondary transfer roller 83 in contact with the back surface of the first intermediate transfer belt 8. Have been. Then, the second toner image on the first intermediate transfer belt 8 is electrostatically extruded from the downstream secondary transfer roller 83 side toward the downstream secondary transfer opposing roller 84 side, and the second toner image on the transfer paper P Secondary transfer is performed on two surfaces (electrostatic extrusion transfer method). The present inventors have experimentally confirmed that the following reverse transcription does not occur when the two-stage secondary transfer as shown is employed. That is, the first toner image previously transferred to the first surface of the transfer paper P is reversely transferred from the first surface to the second intermediate transfer belt 16 during the downstream secondary transfer. It is a phenomenon.

  Further, the configuration shown in FIG. 15 may be adopted as the secondary transfer nip and its surrounding configuration. In the figure, the upstream secondary transfer roller 81 stretches the second intermediate transfer belt 16, while the downstream secondary transfer roller 83 stretches the first intermediate transfer belt 8. In the upstream side secondary transfer section, a negative upstream side secondary transfer bias having the same polarity as the charged polarity of the toner is applied to the upstream side secondary transfer roller 81 in contact with the back surface of the second intermediate transfer belt 16. Then, the first toner image on the second intermediate transfer belt 16 is electrostatically extruded from the upstream secondary roller 81 toward the upstream secondary transfer opposing roller 82, and the first toner image on the transfer paper P The image is secondarily transferred to the surface (electrostatic extrusion transfer method). On the other hand, in the downstream secondary transfer section, a downstream secondary transfer bias having the same negative polarity as the charge polarity of the toner is applied to the downstream secondary transfer roller 83 in contact with the back surface of the first intermediate transfer belt 8. Have been. Then, the second toner image on the first intermediate transfer belt 8 is electrostatically extruded from the downstream secondary transfer roller 83 side toward the downstream secondary transfer opposing roller 84 side, and the second toner image on the transfer paper P Secondary transfer is performed on two surfaces (electrostatic extrusion transfer method). The present inventors have experimentally confirmed that the following reverse transcription does not occur when the two-stage secondary transfer as shown is employed. That is, the first toner image previously transferred to the first surface of the transfer paper P is reversely transferred from the first surface to the second intermediate transfer belt 16 during the downstream secondary transfer. It is a phenomenon.

  Further, the configuration shown in FIG. 16 may be employed as the secondary transfer nip and its surrounding configuration. In the figure, the upstream secondary transfer roller 81 stretches the first intermediate transfer belt 8, while the downstream secondary transfer roller 83 stretches the second intermediate transfer belt 16. In the upstream side secondary transfer section, a negative upstream side secondary transfer bias having the same polarity as the charged polarity of the toner is applied to the upstream side secondary transfer roller 81 in contact with the back surface of the first intermediate transfer belt 8. . Then, the second toner image on the first intermediate transfer belt 8 is electrostatically extruded from the upstream side secondary transfer roller 81 side toward the upstream side secondary transfer opposing roller 82 side, and the second toner image on the transfer paper P Secondary transfer is performed on two surfaces (electrostatic extrusion method). On the other hand, in the downstream secondary transfer section, a negative secondary transfer bias having the same negative polarity as the toner charging polarity is applied to the downstream secondary transfer roller 83 in contact with the back surface of the second intermediate transfer belt 16. Has been applied. Then, the first toner image on the second intermediate transfer belt 16 is electrostatically extruded from the downstream secondary transfer roller 83 toward the downstream secondary transfer opposing roller 84, and the first toner image on the transfer paper P Secondary transfer is performed on one surface (electrostatic extrusion transfer method). The present inventors have experimentally confirmed that the following reverse transcription does not occur when the two-stage secondary transfer as shown is employed. That is, the second toner image previously transferred to the second surface of the transfer paper P is reversely transferred from the second surface to the first intermediate transfer belt 8 during the secondary transfer on the downstream side. It is a phenomenon.

  Although an example in which the rollers (81, 83) are used as the transfer bias member for the recording medium has been described with reference to FIGS. 13 to 16, a non-roller-shaped member may be used. Further, although an example has been described in which rollers (82, 84) are employed as the opposing electrode members opposing the transfer bias member for a recording medium, a non-roller-shaped opposing electrode member may be employed. FIG. 17 is a schematic diagram showing a secondary transfer nip and its surrounding configuration when a non-roller transfer bias member for a recording medium and a non-roller counter electrode member are employed. In the figure, the extending portion between the extension roller 85 and the downstream secondary transfer roller 83 in the first intermediate transfer belt 8 is the extension between the two extension rollers 86 and 87 in the second intermediate transfer belt 16. A secondary transfer nip is formed in contact with the portion. An upstream secondary transfer blade 88, which is a non-roller transfer bias member for a recording medium, is in contact with the back surface of the former expanded portion on the upstream side of the downstream secondary transfer roller 83 in the belt moving direction. . This is made of a conductive rubber material, and is supported by a support member (not shown) so as to maintain a contact state with the back surface of the belt. On the other hand, on the back surface of the latter extended portion, a counter electrode plate 89 which is a non-roller-shaped counter electrode member is provided on both the upstream secondary transfer blade 88 and the downstream secondary transfer roller 83 of the first transfer unit 15. Abuts against each other. This is a metal plate, a conductive resin plate, a plate in which a conductive resin sheet is coated on the surface of a non-conductive substrate, or the like, and is supported by a support member (not shown) so as to maintain a contact state with the back surface of the belt. ing. Further, the counter electrode plate 89 is grounded.

  In the figure, in the upstream secondary transfer portion, a positive upstream secondary transfer roller 88 having a polarity opposite to the charging polarity of the toner is applied to the upstream secondary transfer blade 88 contacting the back surface of the first intermediate transfer belt 8. A transfer bias is applied. Then, the first toner image on the second intermediate transfer belt 16 is electrostatically attracted from the counter electrode plate 89 side toward the upstream secondary transfer blade 88 side, and the second toner image is transferred onto the first surface of the transfer paper P. Next is transferred (electrostatic attraction method). On the other hand, in the downstream secondary transfer section, a negative secondary transfer bias having the same negative polarity as the toner charging polarity is applied to the downstream secondary transfer roller 83 in contact with the back surface of the first intermediate transfer belt 8. Has been applied. Then, the second toner image on the first intermediate transfer belt 8 is electrostatically extruded from the downstream secondary transfer roller 83 toward the counter electrode plate 89, and the second toner image is transferred onto the second surface of the transfer paper P. Next transfer is performed (electrostatic extrusion transfer method). The present inventors have experimentally confirmed that, even in such a case, reverse transcription during downstream secondary transfer is not caused.

  Incidentally, it is assumed that the configuration shown in FIG. 18 is employed as the secondary transfer nip and its surrounding configuration. In this figure, the arrangement position of each roller in the secondary transfer nip is the same as the configuration shown in FIG. However, the polarity of the downstream secondary transfer bias applied to the downstream secondary transfer roller 83 is different from that shown in FIG. 15, and is a positive polarity opposite to the charging polarity of the toner. In such a configuration, in the downstream secondary transfer, the first toner image on the second intermediate transfer belt 16 is electrostatically attracted toward the downstream secondary transfer bias to perform the secondary transfer on the first surface of the transfer paper P. (Electrostatic attraction transfer method). However, at the same time, the second toner image previously transferred to the first surface of the transfer paper P is also electrostatically attracted and reversely transferred from the first surface to the first intermediate transfer belt 8. The inventors have confirmed by experiments.

In the two-stage secondary transfer, after the transfer of the transfer paper P to the second surface from the first intermediate transfer belt 8 on the upstream side, the transfer of the transfer paper P from the second intermediate transfer belt 16 to the downstream side is performed. There are two cases: transfer to two surfaces and transfer in the reverse order. Further, two types of transfer systems, that is, an electrostatic attraction system and an electrostatic extrusion system, respectively, are established on the upstream side and the downstream side. Therefore, when these are combined, eight two-stage secondary transfer methods can be established. The present inventors tested all of these eight two-stage secondary transfer methods and examined the presence or absence of reverse transcription during downstream secondary transfer. Table 1 below shows the relationship between these eight two-stage secondary transfer methods and the presence or absence of reverse transfer at the time of secondary transfer on the downstream side.

  As shown in Table 1, in the eight two-stage secondary transfer methods, the secondary transfer did not occur at the time of the secondary transfer on the downstream side only in the four types of experiment numbers 3, 4, 7, and 8. Met. These are the two-stage secondary transfer methods previously shown in FIG. 13, FIG. 16, FIG. 14 (or FIG. 17), and FIG. Focusing on these, it can be seen that the downstream secondary transfer is all performed by the electrostatic extrusion method. On the other hand, paying attention to Experiment Nos. 1, 2, 5, and 6 in which the reverse transfer has occurred, it can be seen that in all of them, the downstream secondary transfer is performed by the electrostatic attraction method. Therefore, it has been found that when the two-stage secondary transfer method is performed, the reverse transfer is caused unless the electrostatic extrusion transfer method is adopted for the downstream secondary transfer. In the apparatus 100A of the first embodiment described above, the same eight methods are established for continuous transfer (“secondary, tertiary” or “tertiary, secondary”) in the nip. The present inventors have also conducted tests on these eight cases, and have obtained the same result that reverse transfer is caused unless the extrusion electrostatic transfer method is employed during the subsequent transfer in continuous transfer.

  In FIG. 12 described above, a paper transport path as a recording medium discharge path is formed in the housing of the printer unit 90. This paper transport path is composed of the transport paths listed below. That is, the above-described paper feed path 88, the secondary transfer nip, the fixing conveyance path by the second fixing belt 35d of the fixing device, the fixing nip, and the paper discharge path from this to the paper discharge roller pair 37. . As shown in the figure, the paper transport path composed of these has a straight shape without bending, and has a tilt from the horizontal direction of 0 [°], that is, performs horizontal transport. I have. On the other hand, the paper feed unit 91 that discharges the transfer paper P toward the paper feed path 88 of the printer unit 90 sets the inclination angle of the leading end side of the transfer paper P being discharged from the horizontal direction to 0 [°]. It has become. That is, the transfer paper P is sent out toward the paper feed path 88 with the leading end side horizontal. In this configuration, the transfer paper P is not bent in the paper transport path from the time when the transfer paper P is discharged from the paper feeding unit 91 to the time when the transfer paper P is discharged to the outside through the printer unit 90. Therefore, even when the transfer paper P is made of hard-to-bend thick paper or the like, the transfer paper P can be conveyed in the paper conveyance path without imparting a curl, and the occurrence of jam can be suppressed.

  So far, an example in which a drum-shaped photoconductor is used as the latent image carrier has been described, but other types such as a belt-shaped photoconductor may be used. Further, the example in which the second intermediate transfer belt 16 is harder to deform than the first intermediate transfer belt 8 has been described, but the first intermediate transfer body may be harder to deform than the second intermediate transfer body. Further, the present invention can be applied to an image forming apparatus using a liquid developer containing a toner and a liquid carrier instead of the powder toner. In addition, although an electrophotographic printer has been described, the present invention can be applied to an image forming apparatus of a direct recording system. In the direct recording method, an image is formed directly by forming a pixel image by directly adhering a toner group, which is ejected in the form of dots from a toner flying device, to an intermediate transfer member or a recording member without using a latent image carrier. It is a method of forming. In addition, although the description has been given of the printer in which the primary transfer, the secondary transfer, and the tertiary transfer are all performed by the electrostatic transfer, the invention can be applied to an image forming apparatus in which at least one of the transfer is performed by the heat transfer. It is. Note that the heat transfer is performed by bringing a transfer source such as a first intermediate transfer member and a transfer destination such as a second intermediate transfer member into contact with each other while heating to soften the toner image, and then separating the two. In this method, a toner image is transferred from a transfer source to a transfer destination.

  As described above, in the printer 100 and the first modification 100A according to the embodiment, the image is transferred from the photoconductors 1Y, 1M, 1C, and 1K to the second intermediate transfer belt 16 via the first intermediate transfer belt 8. A first toner image as a first visible image is transferred to a first surface, which is one surface of the transfer paper P. On the other hand, the second toner image, which is the second visible image, transferred from the photoreceptors 1Y, 1M, 1C, and 1K to the first intermediate transfer belt 8 is transferred to the other surface of the transfer paper P, that is, the second surface. ing. In such a configuration, the first toner image to be transferred to the first surface of the transfer paper P and the second toner image to be transferred to the second surface are the same photoconductor group (photoconductor 1Y, M, C, K). Therefore, it is possible to avoid an increase in cost due to providing a photoconductor for forming each toner image individually.

  In the second modified example, the second toner image transferred from the photoconductors 1Y, 1M, 1C, and 1K for the first system to the first intermediate transfer belt 8 is transferred onto the second surface of the transfer paper P. The first toner image transferred to the second intermediate transfer belt 16 from the photosensitive member 71Y, M, C, K for the second system, which is another image carrier, is transferred to the first surface of the transfer paper P. . In such a configuration, unlike the printer 100 or the second modified example apparatus 100A in which both toner images are formed by the same photoconductor group, the formation of both toner images can be performed substantially in parallel. Thus, the double-side transfer speed can be increased as compared with the printer 100 and the first modification 100B.

Further, in the printer 100 and each of the modified examples, since the first intermediate transfer belt 8 and the second intermediate transfer belt 16, which are at least one of the intermediate transfer members, have a multi-layer structure, the entire belt has good elasticity. While exhibiting a desired electrical resistance.
Further, since the surface layer in the multilayer structure is a release-promoting layer made of a material having a higher toner release property than other layers, the toner image is transferred from the belt to the transfer paper P on the belt surface. And a defective image such as omission during transfer can be suppressed.
Further, since the first and second intermediate transfer members each use an intermediate transfer belt that can be moved endlessly while being stretched by a plurality of rollers as tension members, a roller or drum-shaped member is used. Thus, the secondary transfer nip can be made longer. Thus, the process linear velocity can be increased to shorten the image forming time. Furthermore, since both belts can be arranged in various stretched shapes, the degree of freedom in layout in the main body can be increased as compared with the case where a roller or a drum-shaped belt is used.
Four of the plurality of stretching members that stretch the first intermediate transfer belt 8 are used to electrostatically transfer the toner images on the photoconductors 1Y, 1M, 1C, and 1K to the first intermediate transfer belt 8. A primary transfer roller (9Y, M, C, K) is a transfer bias member for applying a transfer bias to the back surface of the belt. With this configuration, the toner image can be electrostatically primary-transferred from the photoconductors (1Y, M, C, K) to the first intermediate transfer belt 8.

  Further, in the second modified example device 100B, the second intermediate photosensitive member 1Y, M, C, K for forming the second toner image to be transferred to the first intermediate transfer belt 16 is provided separately from the second intermediate photosensitive member 1Y. Photoconductors 71Y, M, C, and K for a second system for forming a first toner image to be transferred to the transfer belt 16 are provided. Four of the plurality of stretching members that stretch the second intermediate transfer belt 16 apply the toner images on the second-system photoconductors 71Y, M, C, and K to the second intermediate transfer belt 16. A primary transfer roller (79Y, M, C, K) is a transfer member for applying a transfer bias member to the back surface of the belt for performing electrotransfer. In such a configuration, the toner image can be electrostatically primary-transferred from the second-system photoconductors (71Y, M, C, K) to the second intermediate transfer belt 16.

  13 to 16 in the second modified example device 100B, at least one of the plurality of stretching members for stretching the first intermediate transfer belt 8 is connected to any one of the intermediate transfer belts. It is a transfer bias member for a recording medium for applying a transfer bias to the back surface of the first intermediate transfer belt 8 so as to electrostatically transfer the upper toner image onto the transfer paper P (81, 83). In such a configuration, the toner image can be electrostatically transferred from any one of the intermediate transfer belts to the transfer paper P by using the stretching member of the first intermediate transfer belt 8 as a transfer bias member for a recording medium.

  In the printer 100 and each of the modified examples, at least one of the plurality of stretching members that stretches the second intermediate transfer belt 16 applies the toner image on any one of the intermediate transfer belts to the transfer paper P by electrostatic. It is a transfer bias member for a recording medium that applies a transfer bias to the back surface of the second intermediate transfer belt 16 for transferring (17, 62, 81, 83). In such a configuration, the toner image can be electrostatically transferred from any one of the intermediate transfer belts to the transfer paper P by using the stretching member of the second intermediate transfer belt 16 as the transfer bias member for the recording medium.

  Further, in each of the modified examples, the secondary transfer roller 17 and the tertiary transfer roller 62, which are two transfer member members for the recording medium, (or the upstream secondary transfer roller 81 and the downstream secondary transfer roller 83) ) Are arranged so as to abut the back surface of the intermediate transfer belt at the secondary transfer nip. In such a configuration, unlike the printer 100, the toner images can be electrostatically transferred to both sides of the transfer paper P in the nips. Therefore, when a transfer charger applies a charge to the transfer paper P not sandwiched between the nips and transfers a toner image to one of the surfaces, foreign substances such as toner contaminate the electrodes of the transfer charger, and the It is possible to avoid a situation where the quality is deteriorated.

Further, in the printer 100 and each of the modified examples, the first intermediate transfer belt 8 has a surface resistance of 10 ⁵ to 10 ¹² [Ω / □]. 8 can be reliably realized.
Since the second intermediate transfer belt 16 has a surface resistance of 10 ⁵ to 10 ¹² [Ω / □], the first intermediate transfer belt 8 transfers the second intermediate transfer belt 16 and the transfer paper P to each other. Can be reliably achieved.
Further, the second intermediate transfer belt 16 is made of polyimide, so that the second intermediate transfer belt 16 exhibits heat resistance. Thus, the second intermediate transfer belt 16 and the fixing device 35 are arranged close to each other so that the paper guide member can be omitted, and the disturbance of the toner image due to the friction with the paper guide member is avoided. Further, various problems caused by heating the second intermediate transfer belt 16 by the fixing device 35 can be suppressed.
Further, since the second intermediate transfer belt 16 which is the one which is hardly deformed and whose thickness is adjusted to 50 to 600 [μm] is used, the first intermediate transfer belt 8 is prevented from being broken. It is possible to easily exhibit the property of being less likely to be deformed in the thickness direction.
Further, as a transfer bias member that stretches the first intermediate transfer belt 8 and a transfer bias member that stretches the second intermediate transfer belt 16, the primary transfer rollers (9Y, M, C), which are rotatable transfer bias rollers, respectively. , K) using the secondary transfer roller 17. With this configuration, it is possible to avoid abrasion and deterioration of the belt due to frictional contact with the transfer bias member that occurs when a non-rotating member that does not rotate with the endless movement of the belt is used as the transfer bias member.

  Further, in the second modified example, of the upstream secondary transfer roller 81 and the downstream secondary transfer roller, the downstream secondary transfer roller 81 that is disposed more downstream in the surface movement direction of both the intermediate transfer belts. With respect to the next transfer roller 81, the toner image is electrostatically moved away from the downstream side secondary transfer roller 81 toward the transfer paper P, that is, a bias having a polarity capable of realizing the electrostatic extrusion transfer method is applied. The voltage is applied. In such a configuration, it is possible to avoid reverse transfer of the toner image due to secondary transfer of the downstream secondary transfer to the transfer paper P by the electrostatic attraction transfer method.

  Further, in the second modified example, after the transfer paper P is received from the paper feeding unit 91, the paper conveyance path, which is the recording medium conveyance path from the time when the transfer paper P is sent to the secondary transfer nip to the time when the transfer paper P is discharged out of the printer unit 90, It has a straight shape without bending. The inclination angle of the paper conveyance path from the horizontal direction is set to be the same as the inclination angle from the horizontal direction on the leading end side of the transfer paper P being discharged from the paper supply unit 91 serving as the recording medium housing means. With this configuration, for the above-described reason, even when the transfer paper P is made of hard-to-bend thick paper or the like, the transfer paper P can be conveyed in the paper conveyance path without forming a curl, and the occurrence of jam can be suppressed.

  In the printer 100 and each of the modified examples according to the embodiment, a plurality of photoconductors (1Y, M, C, and K) that carry a toner image to be transferred to the first intermediate transfer belt 8 are used as photoconductors as image carriers. ) Is used. As a transfer device having the first transfer unit 15 and the second transfer unit 24, a transfer device configured to transfer the toner images carried on the respective photoconductors onto the first intermediate transfer belt 8 in a superimposed manner is used. Used. With such a configuration, toner images of different colors can be superposed and transferred on the first intermediate transfer belt 8 to form a toner image of another color. In addition, by performing the superposition of the toner images by the so-called tandem method, a toner image of a different color is sequentially formed on one photoconductor, and compared with a configuration in which the toner images are superimposed and transferred to the first intermediate transfer belt 8. Thus, the formation speed of the other color toner image can be increased.

  In the second modified example apparatus 100B, the second toner image transferred from the first-system photoconductor as the image carrier to the first intermediate transfer belt 8 is transferred to the second surface of the transfer paper P. The first toner image transferred to the second intermediate transfer belt 16 from the second-system photoconductor, which is another image carrier, is transferred to the first surface of the transfer paper P. A plurality of photoconductors (71Y, M, C, K) that carry the toner image transferred to the second intermediate transfer belt 16 are used as the photoconductors for the second system. In such a configuration, by providing a plurality of photoconductors for forming a multicolor toner image on both sides of the transfer paper P, each color toner image for the first toner image and each color toner for the second toner image are provided. The toner image can be formed in parallel. Therefore, compared with the printer 100 or the first modified example apparatus 100A which cannot form both toner images (first and second) in parallel, the multi-color toner image is formed on both sides of the transfer sheet P while increasing the printing speed. Can be formed.

FIG. 1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a process unit for Y of the printer. FIG. 2 is a perspective view showing an image forming system including the printer and a personal computer. FIG. 5 is an enlarged cross-sectional view illustrating a secondary transfer nip when a first intermediate transfer belt and a second intermediate transfer belt that are easily deformable in the thickness direction are equally good. FIG. 2 is an enlarged sectional view showing a secondary transfer nip of the printer. The schematic block diagram which shows a 1st modification example apparatus. FIG. 3 is an enlarged side view illustrating the intermediate transfer belt having a single-layer structure. FIG. 3 is an enlarged side view showing the intermediate transfer belt having a multilayer structure. FIG. 3 is an enlarged configuration diagram showing a secondary transfer nip and its surroundings. FIG. 3 is an enlarged configuration diagram showing a tertiary transfer nip and its periphery. FIG. 3 is an enlarged side view illustrating an intermediate transfer belt having a three-layer structure. The schematic block diagram which shows a 2nd modification example apparatus. FIG. 9 is a schematic diagram showing a first example of a secondary transfer nip and its surrounding configuration in the second modified example apparatus. FIG. 9 is a schematic diagram showing a second example of the secondary transfer nip and the surrounding configuration. FIG. 9 is a schematic diagram illustrating a third example of the secondary transfer nip and the surrounding configuration. FIG. 9 is a schematic diagram showing a fourth example of the secondary transfer nip and the surrounding configuration. FIG. 9 is a schematic view showing a fifth example of the secondary transfer nip and the surrounding configuration. FIG. 9 is a schematic diagram illustrating a comparative example of a secondary transfer nip and a surrounding configuration.

Explanation of reference numerals

1Y, M, C, K Photoconductor (image carrier)
8 1st intermediate transfer belt (1st intermediate transfer body)
15 First transfer unit (part of transfer device)
16 Second intermediate transfer belt (second intermediate transfer body)
24 Second transfer unit (other part of transfer device)
71 Photoconductor for second system (another image carrier)
P Transfer paper (recording material)

Claims (23)

A step of endlessly moving the surfaces of both the intermediate transfer members while forming the nip by bringing the first intermediate transfer member and the second intermediate transfer member into contact with each other; While the visible image on the second intermediate transfer member is transferred to one surface of the recording medium in the process of being conveyed along with the surface movement, the visible image on the first intermediate transfer member is transferred to the recording medium. In the transfer method of transferring a visible image to both sides of the recording medium by a double-sided transfer step of performing a step of transferring to the other side of the
A transfer method, wherein a combination of the first intermediate transfer member and the second intermediate transfer member is such that one of the first and second intermediate transfer members is harder to deform in the thickness direction of the recording member sandwiched between the nips than the other. A first intermediate transfer member and a second intermediate transfer member that move the surfaces endlessly while forming a nip by bringing the surfaces into contact with each other, and the recording material sandwiched between the nips is moved along with the surface movement of the two intermediate transfer members; In the process of transporting, the visible image on the second intermediate transfer member is transferred to one surface of the recording medium, while the visible image on the first intermediate transfer member is transferred to the other surface of the recording member. In a transfer device for transferring a visible image to both sides of the recording medium,
A transfer apparatus, wherein a combination of the first intermediate transfer member and the second intermediate transfer member is such that one of the first and second intermediate transfer members is harder to deform in the thickness direction of the recording member sandwiched between the nips than the other. The transfer device according to claim 2,
The first visible image transferred from the image bearing member to the second intermediate transfer member via the first intermediate transfer member is transferred to the one surface, while the first visible image is transferred from the image bearing member to the first intermediate transfer member. A transfer device for transferring the transferred second visible image to the other surface. The transfer device according to claim 2,
A transfer device for transferring a visible image from an image carrier to the first intermediate transfer member, while transferring another visible image from another image carrier to the second intermediate transfer member. The transfer device according to claim 2, 3, or 4,
A transfer device, wherein at least one of the first intermediate transfer member and the second intermediate transfer member has a multilayer structure. The transfer device according to claim 5, wherein
A transfer device, wherein the surface layer in the multilayer structure is made of a material having better toner releasability than other layers. The transfer device according to claim 2, wherein:
A transfer apparatus, wherein the first intermediate transfer member and the second intermediate transfer member are intermediate transfer belts that are endlessly moved while being stretched by a plurality of stretching members. The transfer device according to claim 7,
At least one of a plurality of stretching members that stretches the first intermediate transfer belt as the first intermediate transfer body is used to electrostatically transfer the visible image on the image carrier to the first intermediate transfer belt. (1) A transfer device, which is a transfer bias member that applies a transfer bias to the back surface of the intermediate transfer belt. 9. The transfer device according to claim 8, wherein
5. The transfer device according to claim 4, wherein at least one of the plurality of stretching members that stretches the second intermediate transfer belt serving as the second intermediate transfer member converts the visible image on the another image carrier to the second intermediate transfer belt. A transfer bias member for applying a transfer bias to the back surface of the second intermediate transfer belt so as to perform electrostatic transfer on the second intermediate transfer belt. The transfer device according to claim 8, wherein:
At least one of a plurality of stretching members for stretching the first intermediate transfer belt is a back surface of the first intermediate transfer belt for electrostatically transferring a visible image on any one of the intermediate transfer belts to the recording medium. A transfer bias member for applying a transfer bias to the recording medium. The transfer device according to claim 10,
At least one of a plurality of stretching members for stretching the second intermediate transfer belt is a back surface of the second intermediate transfer belt for electrostatically transferring a visible image on any one of the intermediate transfer belts to the recording medium. A transfer bias member for applying a transfer bias to the recording medium. The transfer device according to claim 11,
A transfer device, wherein the two transfer bias members for a recording medium are disposed so as to abut on the back surfaces of the first intermediate transfer belt and the second intermediate transfer belt at the nip. The transfer device according to any one of claims 8 to 12, wherein
A transfer device, wherein the first intermediate transfer belt has a surface resistance of 10 ⁵ to 10 ¹² [Ω / □]. The transfer device according to claim 9, 10, 11, or 12,
The transfer device, wherein the surface resistance of the second intermediate transfer belt is 10 ⁵ to 10 ¹² [Ω / □]. The transfer device according to claim 7, wherein:
A transfer device, wherein the base material of the second intermediate transfer belt is made of polyimide. The transfer device according to claim 7, wherein:
The transfer device, wherein the one of the first intermediate transfer belt and the second intermediate transfer belt, which is not easily deformed, has a thickness of 50 to 600 [μm]. The transfer device according to claim 9,
The transfer device according to claim 1, wherein the transfer bias member that stretches the first intermediate transfer belt and the transfer bias member that stretches the second intermediate transfer belt are rotatable transfer bias rollers. A step of forming a visible image on the image carrier, a two-side transfer step of transferring the visible image on the image carrier to both sides of the recording medium, and a step of forming the visible image on both sides of the recording medium after the two-side transfer step. Performing a fixing step to form an image on both sides of the recording medium,
2. An image forming method according to claim 1, wherein the double-sided transfer step is a double-sided transfer step in the transfer method according to claim 1. An image carrier for carrying a visible image, a transfer device for transferring the visible image on the image carrier to both sides of the recording body, and fixing for fixing the visible image to both sides of the recording body via the transfer device And an image forming apparatus for forming images on both sides of a recording medium.
An image forming apparatus comprising: the transfer device according to claim 2. The image forming apparatus according to claim 19,
As the transfer device, the transfer device according to claim 12 is used,
For one of the two transfer bias members for recording medium, which is disposed further downstream in the surface movement direction of both the intermediate transfer belts, the visible image is recorded from the transfer bias member for recording medium. An image forming apparatus, wherein a bias having a polarity for electrostatically moving the body toward the body is applied. The image forming apparatus according to claim 19, wherein
After receiving the recording medium ejected from the recording medium housing means for accommodating the recording medium, the recording medium transport path from being sent to the nip to being discharged out of the image forming apparatus main body has a shape without bending, and An image forming apparatus, wherein the inclination angle from the horizontal direction is the same as the inclination angle from the horizontal direction on the leading end side of the recording medium being discharged from the recording medium storage means. The image forming apparatus according to any one of claims 19 to 21,
As the image carrier, a plurality of image carriers that carry a visible image transferred to the first intermediate transfer member are used, and as the transfer device, the visible image carried by each image carrier is transferred to the first intermediate transfer member. An image forming apparatus comprising: a transfer member configured to transfer the image on a transfer member. The image forming apparatus according to claim 22,
5. The image transfer apparatus according to claim 4, wherein a plurality of the image bearing members carry a visible image to be transferred to the second intermediate transfer member, and the transfer device is a plurality of the image transfer members. An image forming apparatus comprising: a structure in which a visible image carried on an image carrier is superimposed and transferred on the second intermediate transfer body.

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