JP3919723B2 - TRANSFER METHOD, TRANSFER DEVICE, IMAGE FORMING METHOD, AND IMAGE FORMING DEVICE - Google Patents

Description

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

  Conventionally, a so-called switchback method and a one-pass method are known as methods for transferring an image onto both surfaces of a recording medium such as transfer paper. In the switchback method, first, a visible image is transferred to one surface of the transfer member that transfers a visible image on an image carrier such as a photosensitive member to the recording member through the recording member. Then, after the recording medium is inverted and switched back to the transfer means, the visible image is transferred to the other surface. On the other hand, the one-pass method forms images on both sides of the recording medium without switching back the recording medium by applying a visible image transfer process to both sides of the recording medium as a transfer means. The one-pass method is superior to the switchback method in the following points. That is, it is possible to avoid an increase in cost by providing a complicated mechanism for switchback and an increase in image formation time due to switchback. As an image forming apparatus that realizes such a one-pass method, for example, the one described in Patent Document 1 is known.

  In addition, an image forming apparatus that realizes a one-pass method is known that includes a first intermediate transfer member and a second intermediate transfer member (for example, those described in Patent Document 2). This type of image forming apparatus moves the surfaces of both intermediate transfer members endlessly while forming a nip by bringing the first intermediate transfer member and the second intermediate transfer member into contact with each other. Then, in the process of transporting the recording medium sandwiched in the nip to the downstream side in the endless movement direction of the second intermediate transfer body from the nip, the recording medium is previously transferred from the image carrier to the second intermediate transfer body via the first intermediate transfer body. 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 a photoconductor. Therefore, when a paper material such as transfer paper is used as the recording body, the paper dust applied to the image carrier. Can be suppressed. Therefore, it is possible to suppress problems such as image deterioration due to adhesion of paper dust.

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

  The present inventors are also developing the following apparatus as another improved apparatus including the first intermediate transfer member and the second intermediate transfer member. That is, in order to omit the transfer process from the first intermediate transfer member to the second intermediate transfer member, the second intermediate transfer member is separated from the image carrier that carries a visible image for transfer to the first intermediate transfer member. An image carrier that carries a visible image to be transferred to the camera is provided. Even in such a configuration, the recording medium is not brought into direct contact with the image carrier, so that problems such as image deterioration due to adhesion of paper dust to the image carrier can be suppressed.

  However, in the case of including the first intermediate transfer belt and the second intermediate transfer belt, it is easy to generate wrinkles on the recording medium during double-sided transfer. This problem occurs particularly when an intermediate transfer belt that is endlessly moved while being stretched on a plurality of stretching members is used as the first intermediate transfer body and the second intermediate transfer body (hereinafter referred to as both intermediate transfer bodies). It occurred remarkably. Therefore, the present inventors conducted extensive research on the cause of wrinkles on the recording medium, and have found the following. That is, as the first intermediate transfer member and the second intermediate transfer member, those that exhibit elasticity as a whole are generally used from the viewpoint of ensuring good transferability by being in close contact with the recording member. However, when the intermediate transfer members exhibiting good elasticity are brought into pressure contact with each other to form a nip, each of them is elastically deformed into a complicated shape at the nip and bites into a wedge shape (wave shape). In this way, when the recording medium is sandwiched between the nips in which the both intermediate transfer bodies bite into each other in a wedge shape (wavy shape), wrinkles are generated in the recording body in accordance with the wedge shape.

  The present invention has been made in view of the above background, and an object thereof 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 paper is used as the recording body while also realizing one-pass double-sided transfer, and also suppresses wrinkles generated on the recording body. It is.

In order to achieve the above object, according to the first aspect of the present invention, a first intermediate transfer member to which a visible image on an image carrier is transferred, and a visible image on the first intermediate transfer member are transferred. A step of moving the surfaces of both intermediate transfer members endlessly while contacting the second intermediate transfer member to form a nip, and the second intermediate transfer from the image carrier through the first intermediate transfer member After the first visible image is transferred to the body and the second visible image is transferred from the image carrier to the first intermediate transfer body, the recording medium sandwiched in the nip is moved to the surface of both intermediate transfer bodies. And transferring the first visible image on the second intermediate transfer member to one surface of the recording member, while the second visible image on the first intermediate transfer member is transferred to the one side of the recording member. In a transfer method for transferring a visible image to both sides of a recording medium by a double-sided transfer process that performs the process of transferring to the other side of the recording body. Te, and with the first intermediate transfer member and the second intermediate transfer member, with using a material having an elastic layer made of an elastic material, respectively, as second intermediate transfer member, than the first intermediate transfer member, the and it is characterized in the use of those hardly deformed in the thickness direction of the sandwiched the recording material to the nip.
According to a second aspect of the present invention, there is provided a first intermediate transfer member to which a visible image on an image carrier is transferred, and a second intermediate transfer member to which a visible image on the first intermediate transfer member is transferred. It is endlessly moved the respective surface while forming a nip by contacting with each other on the surface, transferring the first visual image to the second intermediate transfer member through the first intermediate transfer member from the image bearing member In addition, after transferring the second visible image from the image carrier to the first intermediate transfer member, the recording medium sandwiched in the nip is conveyed along with the surface movement of both intermediate transfer members, The first visible image on the second intermediate transfer member is transferred to one surface of the recording member, while the second visible image on the first intermediate transfer member is transferred to the other surface of the recording member. and, in the transfer apparatus for transferring a visible image on both surfaces of the recording medium, and with the first intermediate transfer member and the second intermediate transfer body, respectively With use those having an elastic layer made of sexual material, as second intermediate transfer member, than the first intermediate transfer member, the use of which is difficult to deform in the thickness direction of the recording material sandwiched the nip It is a feature .
Also, the invention of claim 3 is the transfer device 請 Motomeko 2, of the said first intermediate transfer member and the second intermediate transfer member, characterized in that at least one of a multi-layer structure Is.
According to a fourth aspect of the present invention, there is provided the transfer device according to the third aspect , wherein the surface layer in the multilayer structure is made of a material having better toner releasability than the other layers. .
The invention according to claim 5 is the transfer device according to any one of claims 2 to 4 , wherein the first intermediate transfer member and the second intermediate transfer member are stretched endlessly while being stretched by a plurality of stretch members. It is an intermediate transfer belt that can be moved.
The invention of claim 6 is the transfer apparatus according to claim 5 , wherein at least one of a plurality of stretching members that stretch the first intermediate transfer belt as the first intermediate transfer member is on the image carrier. The transfer bias member applies a transfer bias to the back surface of the first intermediate transfer belt so as to electrostatically transfer the visible image to the first intermediate transfer belt .
Also, the invention of claim 7 is the transfer apparatus according to claim 5 or 6, said at least one of the plurality of stretching members for stretching the first intermediate transfer belt, but either one of the intermediate transfer belt And a transfer bias member for a recording medium that applies a transfer bias to the back surface of the first intermediate transfer belt in order to electrostatically transfer the visible image to the recording medium.
The invention according to claim 8 is the transfer apparatus according to claim 7 , wherein at least one of the plurality of stretching members that stretch 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 that applies a transfer bias to the back surface of the second intermediate transfer belt in order to electrostatically transfer an image to the recording medium.
The invention according to claim 9 is the transfer apparatus according to claim 8 , wherein the two transfer bias members for the recording medium are respectively connected to the first intermediate transfer belt and the second intermediate transfer belt at the nip. It is arrange | positioned so that it may contact | abut on a back surface.
The invention according to claim 10 is the transfer device according to any one of claims 5 to 9 , wherein the surface resistance of the first intermediate transfer belt is 10 ⁵ to 10 ¹² [Ω / □]. To do.
The invention according to claim 11 is the transfer device according to claim 7, 8 or 9 , wherein the surface resistance of the second intermediate transfer belt is 10 ⁵ to 10 ¹² [Ω / □]. Is.
A twelfth aspect of the present invention is the transfer device according to any one of the fifth to eleventh aspects , characterized in that the base material of the second intermediate transfer belt is made of polyimide.
The invention of claim 13, which a one of the transfer device according to claim 5 or 1 2, the thickness of the upper Symbol second intermediate transfer belts is characterized in that it is a 50 to 600 [[mu] m] It is .
Also, the invention of claim 14 includes the steps of forming a visible image on the image carrier, and the double-sided transfer step for transferring the visible image on the image carrier on both sides of the recording material, after the double-sided transfer step And 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 method according to claim 1 is used as the double-sided transfer step. A transfer process is performed.
According to a fifteenth aspect of the present invention, there is provided 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 material that passes through the transfer device. An image forming apparatus that includes a fixing unit that fixes a visible image on both sides and forms an image on both sides of a recording medium, wherein the transfer device is any one of claims 2 to 13. To do.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to the fifteenth aspect , the transfer device according to the ninth aspect is used, and the surface of both intermediate transfer belts of the two transfer bias members for the recording medium. 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 arrangement on the downstream side in the moving direction. It is characterized by that .
Also, the invention of claim 17 is the image forming apparatus according to claim 15 or 16, as the image carrier, with using those plurality of bearing a visible image to be transferred to the first intermediate transfer member, As the above-mentioned transfer device, a device configured to transfer a visible image carried on each image carrier on the first intermediate transfer member in a superimposed manner is used .

In these inventions, in the process of transporting the recording body sandwiched between the nips along with the surface movement of the two intermediate transfer bodies, the visible image on the second intermediate transfer body is transferred to one surface of the recording body. Then, the visible image on the first intermediate transfer member is transferred to the other surface of the recording member. In such a configuration, a visible image can be transferred onto both sides of the recording medium by a one-pass method in which the recording medium is not passed twice through the nip by switchback, but only once through the nip.
In these inventions, the visible image is always transferred from the image carrier to the intermediate transfer member and then transferred to the recording member, so that the recording member is visible on both sides without directly contacting the image carrier. Transfer the image. Therefore, when a paper material such as transfer paper is used as the recording body, it is possible to suppress the adhesion of paper powder to the image carrier.
Further, in these inventions , the second intermediate transfer member is less likely to be deformed in the thickness direction of the recording member than the first intermediate transfer member. Try to transform. As a result, the wedge-shaped (wavy) biting of both intermediate transfer members in the nip is suppressed and the intermediate transfer members come into contact with each other more smoothly. Can be suppressed.
Therefore, while realizing one-sided double-sided transfer, it is possible to suppress the adhesion of paper dust to the image carrier when paper is used as the recording material, and to suppress wrinkles generated on the recording material. effective.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the printer, showing the printer from the front direction. 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). Yes. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. 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 as an image carrier, a drum cleaning device 2Y, a charge eliminating device 3Y, a charging device 4Y, and a developing device 5Y. Etc. In the photoreceptor 1Y, an aluminum cylinder having a diameter of 30 to 100 [mm] is covered with a surface layer of an organic semiconductor that is a photoconductive substance. An amorphous silicon surface layer may be coated. Further, it may be a belt shape instead of a drum shape. The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1 </ b> Y is exposed and scanned by the laser beam L to carry a Y electrostatic latent image. The Y electrostatic latent image is developed into a Y toner image by the 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 the toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. Further, the charge removal device 3Y removes the residual charge of the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other process cartridges 6M, C, and K, M, C, and K toner images are similarly formed on the photoreceptors 1M, C, and K, and are primarily transferred onto the first intermediate transfer belt 8. The developing device may use a two-component developer containing toner and a magnetic carrier, or may use only 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 disposed below the process cartridges 6Y, 6M, 6C, and 6K, and an image data processing device E1 is disposed on the left side in the drawing. 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 each photoconductor in the process cartridges 6Y, 6M, 6C, and 6K with a laser beam L emitted based on the exposure scanning control signal. Electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K exposed by this irradiation. The exposure device 7 irradiates the photoconductor with a laser beam (L) emitted from a light source through a plurality of optical lenses and mirrors while scanning with a polygon mirror rotated by a motor. Instead of the exposure apparatus 7 having such a configuration, an exposure unit that irradiates LED light from the LED array may be employed. In addition, a sealing member (not shown) is provided on the casing of the exposure device 7 in order to prevent contamination of internal parts due to the toner falling from the photosensitive members 1Y, 1M, 1C, and 1K disposed above the exposure device 7. Provided.

  On the lower side of the exposure apparatus 7 in the figure, 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 so as to overlap in the vertical direction. It is installed. Each of these cassettes is housed in a state of a bundle of transfer sheets in which a plurality of transfer sheets P as recording bodies are stacked. On the right side of the second paper cassette 26 in the drawing, a manual tray 25 having a manual paper feed roller 30 is provided so as to extend from the side surface of the housing, not within the housing of the printer body. Also, a transfer bundle is placed.

  Between the two paper feeding cassettes (25, 26) and the manual feed tray 25, a paper feeding path 32 having a pair of registration rollers 31 and a paper feeding guide path 33 that joins the paper feeding path are arranged. The paper feed guide path 33 has a pair of transport rollers 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 accommodated in the first paper cassette 25 and the second paper cassette 26, respectively. Then, the uppermost transfer paper P is sent out toward the paper feed path 32 by being driven to rotate by a driving means (not shown). The transferred transfer paper P is sandwiched between a first registration roller 31 a and a second registration roller 31 b of a 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, but once the recording medium is sandwiched between the rollers, the rotation of both rollers is temporarily stopped. Then, rotation is resumed at an appropriate timing, and the transfer paper P is sent out to a secondary transfer nip described later. It functions as a pair of timing rollers. 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 feed tray 27. Then, the uppermost transfer paper P is sent out toward the paper feed guide path 33 by being driven to rotate by a driving means (not shown). The transferred transfer paper P reaches the vicinity of the end of the paper feed path 32 through a pair of conveying rollers 34 that are rotated in the forward direction while being in contact with each other by a driving unit (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 photoreceptors 1Y, 1M, 1C, and 1K undergo a transfer process by a transfer device. This transfer apparatus 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, and includes a first intermediate transfer belt 8, four primary transfer rollers 9Y, M, C, K, A first cleaning device 10 is provided. A secondary transfer backup roller 12, a first cleaning backup roller 13, a tension roller 14 and the like are also 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 three rollers while being stretched around these three rollers. The four primary transfer rollers 9Y, 9M, 9C, and 9K, which are transfer bias rollers, sandwich the first intermediate transfer belt 8 that is moved endlessly in this way between the photoreceptors 1Y, 1M, 1C, and 1K, respectively. The next transfer nip is formed. Then, upon receiving a power supply (not shown), a primary transfer bias having a polarity (for example, plus) opposite to that of the toner is applied to the back surface (loop inner peripheral surface) of the first intermediate transfer belt 8. In addition to the four primary transfer rollers 9Y, 9M, 9C, and 9K, all the above-described three rollers are electrically grounded. The first intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof. At each primary transfer nip, Y, M, C, and K toner images on the photoreceptors 1Y, 1M, 1C, and 1K are primarily transferred in an overlapping manner by the action of nip pressure and 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 over which the first intermediate transfer belt 8 is stretched is disposed so as to bite into a second intermediate transfer belt 16 described later. By such a biting arrangement, a secondary transfer nip is formed in which the first intermediate transfer belt 8 and the second intermediate transfer belt 16 are in wide contact with each other 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 visible four-color toner 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. The transfer residual toner that has not been secondarily transferred to the second intermediate transfer belt 16 or the transfer paper P is attached to the first intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the first cleaning device 10. Specifically, the first intermediate transfer belt 8 includes a first cleaning device 10 disposed so as to abut on the outer surface (front surface) side of the loop, and a first cleaning device disposed on the inner surface side 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, 9M, 9C, and 9K of the bias application system, a charger system 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. . A secondary transfer roller 17, a nip expansion roller 19, a tension roller 20, a backup roller 21 and the like are also provided. While being stretched around these four rollers, the second intermediate transfer belt 16 is endlessly moved clockwise in the drawing by the rotational drive of at least one of the rollers. The secondary transfer backup roller 12 of the first transfer unit 15 described above bites into the bridge portion of the second intermediate transfer belt 16 between the secondary transfer roller 17 and the nip expansion roller 19 to form a secondary transfer nip. . The secondary transfer roller 17 serving as a transfer bias roller for the recording medium is a metal roller or a roller in which a conductive rubber layer is coated on a core metal and has a polarity (for example, plus polarity) opposite to that of toner by a power source (not shown). A secondary transfer bias is supplied. All the other rollers in the second transfer unit 24 are grounded.

  The 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 it out. However, if this four-color toner image is the first toner image to be transferred to the first surface (the surface facing upward on the stack unit 40 described later) which is one surface of the transfer paper P, the transfer is performed. 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 secondary transfer nip as a nip. The 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 portion 40), The registration roller pair 31 feeds 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 combined 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, it is in close contact with the first surface of the transfer paper P, but is not secondarily transferred there.

  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 its moving direction. The second intermediate transfer belt 16 is brought into contact with the first intermediate transfer belt portion whose direction of movement is being reversed to form a secondary transfer nip. Therefore, at the outlet of the secondary transfer nip, the first intermediate transfer belt 8 is separated from the transfer sheet P, and the transfer sheet P is held and conveyed 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 the tertiary transfer unit along with the endless movement. In the tertiary transfer portion of the second transfer unit 24, a transfer charger 23 is disposed on a stretched portion of the second intermediate transfer belt 16 by the backup roller 21 via a predetermined gap. The transfer sheet P on the second intermediate transfer belt 16 is given a charge of the opposite polarity (for example, plus polarity) to the toner by the transfer charger 23 on the second surface side. By applying this charge, the first toner image sandwiched between the first surface of the transfer paper P and the second intermediate transfer belt 16 is thirdarily transferred to the first surface of the transfer paper P to form a full color image. . The transfer device including two transfer units (15, 24) transfers the second toner image onto the second surface of the transfer paper P at the second transfer nip in the preceding stage and then transfers the second toner image at the third transfer unit. That is, the first toner image is transferred onto the first surface. As a member to which the primary transfer bias and the secondary transfer bias are applied, members having other shapes such as a brush may be used instead of the rollers (9, 17). Further, instead of the electrostatic transfer method in which a transfer bias is applied to the member, a non-contact discharge method may be employed.

  In the second transfer unit 24, the transfer paper P on which double-sided 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. The second intermediate transfer belt 16 after passing through the tertiary transfer portion 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. The If the second cleaning device 18 is always in contact with the second intermediate transfer belt 16, the first toner image secondarily transferred onto the second intermediate transfer belt 16 is also cleaned. Therefore, the second cleaning device 18 is brought into contact with and separated from the second intermediate transfer belt 16 by being swung in the direction of the arrow in the figure by a swing mechanism (not shown). 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 the first toner image.

  Above the second transfer unit 24 in the figure, a fixing device 35 as a fixing means is disposed. The fixing device 35 has two fixing rollers 35a and 35b that contact each other while rotating in the forward direction to form a fixing nip. Each of the fixing rollers 35a and 35b has heating means such as a halogen lamp (not shown), and heats the transfer paper P sandwiched between the fixing nips from both sides. By this heating, the full color images respectively formed on both surfaces of the transfer paper P are fixed on the transfer paper P by the softening of the toner constituting the image. After the fixing, the transfer paper P is reversed along the reversing guide member 36 and then discharged to the outside through the paper discharge roller pair 37. And it is stacked on the stack part 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 respectively detected by temperature detection means (not shown). This temperature detection means transmits to the control part E2 arrange | positioned in the uppermost part in the housing of a printer main body. Based on the detection result of the surface temperature sent from the temperature detection means, the control unit E2 performs ON / OFF control of the power supply to the heat generating means of the fixing rollers 35a, b, and the surface temperature of the fixing rollers 35a, b. Is maintained within a certain range (target range). However, when the single-sided print mode in which an image is formed only on one side of the transfer paper P is executed, the image can be fixed with a smaller amount of heat than in the double-sided print mode. This is because an image is formed only on one side, and therefore the amount of toner on the transfer paper P is smaller than that on both sides. Therefore, in the single-sided printing mode, energy saving can be achieved by lowering the target range of the surface temperature than in the double-sided printing mode. In addition, since a single color image has a smaller amount of toner than a full color image, it is possible to save energy 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 movement direction, the printer 100 performs toner images from both sides of the transfer paper P by the transfer device. The transfer process is performed. Therefore, image formation by the one-pass method can be performed on both surfaces of the transfer paper P. Further, since the transfer paper P is not directly brought into contact with the photoconductor (1Y, M, C, K) as the image carrier, it is possible to suppress the adhesion of paper powder to the photoconductor. As in the printer 100, a plurality of image carriers such as photoconductors are arranged side by side, 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 tandem method. In contrast, after forming a visible image on one image carrier and transferring it to the intermediate transfer member, the visible image is formed again on the image carrier and transferred onto 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 visible image formation and transfer must be repeated. On the other hand, in the tandem method, 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 shortened.

  As described above, the first toner image is formed prior to the second toner image. Then, after secondary transfer from the first intermediate transfer belt 8 to the second intermediate transfer belt 16 at the secondary transfer nip, it is tertiary transferred onto the first surface of the transfer paper at the tertiary transfer portion. The first surface is a surface facing upward in the stack portion 40. Therefore, the transfer sheets P stacked on the stack unit 40 are sequentially stacked with the first toner image formed in the front direction facing up and the second toner image formed thereafter facing up. Go. In this printer 100, in order to align the page numbers of the transfer sheets P stacked in this way in order from the smallest, the images having two page numbers that are odd and even are consecutive. One toner image is formed. For example, the second page image is formed as the first toner image prior to the first page image. As a result, even if documents of several pages are output continuously, the page numbers can be aligned in order from the bottom in the stack unit 40. However, when executing the single-sided print mode in which an image is formed only on the second surface of the transfer paper P, the images are formed in order from the image with the smallest page number, and each image is secondarily transferred onto the second surface of the transfer paper P. . Thus, even in the single-sided printing mode, the page numbers can be aligned in order from the bottom in the stack unit 40.

  In the four photoreceptors 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 each formed color toner image changes into a mirror image and a normal image in the process of reaching the transfer paper P through two transfer processes of primary transfer and secondary transfer. By forming a normal image on each photoconductor, a normal image is formed on the second surface of the transfer paper P as well. On the other hand, since each color toner image formed for the first toner image is subjected to the third transfer, the transfer process is increased once more than the second toner image. Therefore, it is formed as a mirror image on each photoconductor. As a result, a normal image, a mirror image, and a normal image change 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, BK containing toner to be supplied to the developing devices in the process cartridges (6Y, M, C, 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. Although 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, a wireless connection may be adopted. An operation indicator 51 such as a touch panel is fixed to the left front corner of the printer main 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 printing mode and the double-sided printing mode described above is performed by operating a mode switching button prepared on the operation display 51. Further, the selection of the paper type (selection of the paper storage cassette) is also performed by operating the operation indicator 51. However, the switching of these 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, the 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 printer main body toward the front side to expose the first transfer unit (15). . The exposure facilitates 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, 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 surface, can be attached to and detached from 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 main body in the front-rear direction. It is not a configuration in which the upper surface of the printer main body on which the stack unit 40 is formed is an upper door that can be freely opened and closed, and the toner bottles BY, BM, BC, and BK are attached and detached vertically. 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 arranged below the front door 52, and are configured to be attached to and detached from the printer main body by sliding movement in the front-rear direction. Even if the front door 52 is opened, the detachability of the first paper cassette 25 and the second paper cassette 26 and the operability of input to the operation display 51 are not impaired.

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 have the same ease of deformation in the thickness direction. Then, in the secondary transfer nip, particularly 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 in a complicated manner under the influence of the pressure 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, and are wedged (wavy). If the transfer paper P is passed through the secondary transfer nip in which the surfaces of both belts are wedged (wavy) in this way, wrinkles are generated on the transfer paper P following the wedge shape.

  Therefore, in the printer 100, the second intermediate transfer belt 16 that is more difficult to deform 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 deform in the thickness direction than the first intermediate transfer belt 8, so that the second intermediate transfer is mainly difficult to deform at the secondary transfer nip. It tries to deform following the belt 16. Then, as shown in FIG. 5, the wedge-shaped (wavy) biting of both belts in the secondary transfer nip is suppressed, and both belts come into contact more smoothly. Therefore, 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 securely brought into contact with each other with a lower nip pressure by coming into contact smoothly, the transfer is caused by agglomerating the toner by applying excessive pressure during transfer. Defects can also be suppressed.

  In this embodiment, as the second intermediate transfer belt 16, a resin material is used as a base material, and the surface hardness is 95 degrees in JIS-A. On the other hand, the first intermediate transfer belt 8 is made of rubber and has a surface hardness of 50 [degrees] in JIS-A. When a multilayer belt is used, the surface hardness is always measured using the entire multilayer belt. The surface hardness thus measured indicates the difficulty of deformation in the thickness direction of the belt. Therefore, a belt having a higher surface hardness is less likely to be deformed in the thickness direction. Of the two belts, the belt that is more easily deformed in the thickness direction (the first intermediate transfer belt 8 in this example), from the viewpoint of securing a certain degree of adhesion between the belts at the secondary transfer nip. It is desirable to use 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 hardly deforms in the thickness direction, has a multilayer structure. ing. This is for the reason explained below. That is, the other intermediate belt, that is, the first intermediate transfer belt 8 that is more easily deformed, must exhibit sufficient elasticity while exhibiting electrical resistance that can realize electrostatic transfer. Don't be. Therefore, it is common to use an elastic material as the base material of the belt, and to disperse a conductive material such as carbon black as a resistance adjusting agent to exert a desired electric resistance. However, in general, the elastic material becomes harder as the content of the resistance adjusting agent 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 used. Then, while suppressing the dispersion amount of the resistance adjusting agent to some extent for the base material layer made of an elastic material, it becomes possible to disperse the resistance adjusting agent in a large amount for the other layers (for example, the surface layer and the lower layer). As a result, the desired electric resistance can be exhibited while exhibiting good elasticity as a whole belt. In addition, if a material having a surface energy lower than that of the base material layer is used as a material for this other layer, and this other layer is provided as a surface layer serving as an image holding surface, it functions as a release promoting layer for the toner image. You can also As a result, toner separation from the first intermediate transfer belt 8 in the secondary transfer nip is promoted, and it is possible to suppress transfer defects caused by leaving untransferred toner on the belt. Needless to say, the second intermediate transfer belt 16 can also have a multilayer structure. Moreover, the base material of a belt is a belt material which comprises it in the belt of a single layer structure. Moreover, in the belt of a multilayer structure, it is the material which comprises the thickest layer (base layer). In addition, the multilayered belt includes a belt in which a base material is simply coated with a release promoting layer, and a belt in which a rubber layer or the like is provided for exhibiting good elasticity.

  There is no particular limitation on the resin material used for the base material of the second intermediate transfer belt 16. However, in this embodiment, polyimide is used. This is because polyimide having excellent heat resistance is used for the base material of the second intermediate transfer belt 16 so that the entire belt exhibits heat resistance. Examples of the resin material that can exhibit heat resistance include polyamide in addition to polyimide. Further, various resin materials can be used when the entire belt does not need to exhibit heat resistance. For example, polycarbonate, fluorine-based resin (ETFE, PVDF), methyl methacrylate resin, butyl methacrylate resin, ethyl acrylate resin, butyl acrylate resin, or the like may be used. Further, for example, a modified acrylic resin (silicone-modified acrylic resin, vinyl chloride resin-modified acrylic resin, acrylic / urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer, and the like may be used. Further, for example, rosin-modified maleic acid 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, it may be a styrene resin (a homopolymer or copolymer containing styrene or a styrene-substituted product). Examples of the styrene resin include 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 copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene- A phenyl acrylate copolymer). Examples thereof include styrene-methacrylic acid ester copolymers (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, and the like). Furthermore, a styrene-α-chloroacrylic acid methyl copolymer, a styrene-acrylonitrile-acrylic acid ester copolymer, and the like. A mixture of two or more of the resin materials listed above can also be used.

  There are no particular restrictions on the rubber material or elastomer used for the first intermediate transfer belt 8. Examples include butyl rubber, fluorine-based rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, and the like. 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, ricone 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 second intermediate transfer belt 16 is configured in a multilayer structure by covering the front side (transfer surface side) or the back side of the layer having the resin material exemplified above as a base with the layer made of the rubber material or elastomer exemplified above. It is also possible. Further, the first intermediate transfer belt 8 may be configured in a multilayer structure by covering the front side (transfer surface side) or the back side of the layer made of the rubber material or elastomer as the base material with a layer made of the exemplified resin material. 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, the adhesion between the toner and the belt can be reduced to improve the toner image cleaning property, and transfer defects during secondary transfer and tertiary transfer can be suppressed. The material for the release promoting layer is not particularly limited as long as it has a surface energy lower than that of the substrate. For example, a fluororesin is mentioned. Further, for example, one or two or more kinds of powders and particles such as fluorine compounds, carbon fluoride, titanium dioxide, and silicon carbide may be dispersed in a material such as resin or rubber. In the case of using a fluorine-based rubber material, it is possible to reduce the energy by making the surface unevenly rich in fluorine by performing heat treatment.

  There is no particular limitation on the resistance adjuster dispersed in the belt material. Examples thereof include carbon black, graphite, metal powders such as aluminum and nickel, tin oxide, titanium oxide, antimony oxide, and indium oxide. Further, for example, conductive metal oxides such as potassium titanate, antimony oxide-tin oxide composite oxide (ATO), indium oxide-tin oxide composite oxide (ITO), and conductive metal oxides may be used. Further, for example, in contrast to the conductive ones listed so far, 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 electrical resistance value of the material.

  There are no particular restrictions on the manufacturing method of the first intermediate transfer belt 8 and the second intermediate transfer belt 16. 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, a dipping method in which a cylindrical mold is dipped in a solution of a material and pulled up may be used. Further, for example, a casting method in which a material is injected into an inner mold or an outer mold, a method in which a compound is wound around a cylindrical mold, and vulcanization polishing is performed. Furthermore, a belt may be manufactured by combining two or more of these exemplified methods.

  FIG. 8 is a cross-sectional view showing an intermediate transfer belt (8, 16) comprising a base layer and a release promoting layer. FIG. 11 shows a three-layer intermediate transfer 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 releasability are sequentially laminated on the base layer. It is sectional drawing which shows a belt (8, 16). The base layer is made of, for example, a material in which a stretchable material such as a fluororesin having a small elongation or a rubber having a large elongation is stretched. 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. The thickness depends on the hardness of the material, but if it is too thick, the surface expansion and contraction becomes excessively large and cracks are likely to occur in the release promoting layer. Further, since the amount of expansion / contraction increases, it becomes easy to generate expansion / contraction in the image. The hardness HS of the elastic layer is desirably set to 10 ≦ HS ≦ 65 [°: JIS-A]. This is because if the hardness HS is lower than 10 [°: JIS-A], it is difficult to form the belt with high dimensional accuracy.

  Various methods are conceivable 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 having little elongation such as a fluororesin, and an elastic layer is formed thereon. In addition, a material that prevents elongation such as canvas may be put into a rubber material having a large elongation in the base layer to function 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 body include natural fibers such as cotton and silk. In addition, inorganic fibers such as polyester fiber, nylon fiber, acrylic fiber, carbon fiber, glass fiber, and boron fiber, and metal fiber such as iron fiber and copper fiber may be used. Further, one or two or more selected from these may be processed into a thread form or a woven cloth form. The yarn-like material may be any twisting method such as a twist of one or a plurality of filaments, a single twisted yarn, various twisted yarns, or a double yarn. It is also possible to subject these materials to a conductive treatment.

  In the present embodiment, an example in which an intermediate transfer belt that is endlessly moved while being stretched around a plurality of rollers is used as the first intermediate transfer body and the second intermediate transfer body has been described. You may use the thing of a shape. However, the following advantages are obtained when the intermediate transfer belt is used. That is, as in the secondary transfer nip shown in FIG. 1, one belt is deformed and stretched so as to be wound around the stretched portion of the other belt by the stretch member, so that a considerably long secondary transfer nip is formed. 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 secured, so that the process line speed can be increased and the image formation time can be shortened. Further, since both belts can be arranged in various tension shapes, the degree of freedom in layout in the main body can be increased as compared with the case of using a roller or drum shape.

The first intermediate transfer belt 8 and the second intermediate transfer belt 16 are each adjusted to have a surface resistance in the range of 10 ⁵ to 10 ¹² [Ω / □]. This is for the reason explained below. That is, when the surface resistance is less than 10 ⁵ [Ω / □], it is difficult to realize electrostatic transfer because the transfer bias applied to the back surface of the belt leaks from the belt surface to the photoreceptor or the grounding member that contacts the transfer bias. Because it becomes. Further, if the surface resistance exceeds 10 ¹² [Ω / □], the current flowing through the belt is insufficient, and it becomes difficult to realize electrostatic transfer.

  As described above, in the present embodiment, polyimide is used as the resin material constituting the base material of the second intermediate transfer belt 16. This is for the reason explained below. That is, the transfer paper P conveyed while being held on the second intermediate transfer belt 16 is sent to the fixing device 35 for the fixing process of the toner image. Since the fixing device 35 generates a high temperature of about 140 [° C.], 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, it deteriorates due to heating and causes various problems. In order to suppress such a problem, it is conceivable to dispose the second intermediate transfer belt 16 and the fixing device 35 sufficiently apart. However, when the second intermediate transfer belt 16 and the fixing device 35 are arranged apart from each other, the transfer paper P that is freely bent 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 the two. The transfer paper P held by the second intermediate transfer belt 16 carries a 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 heat-resistant 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 arranged 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 the range of 50 to 600 [μm]. This is for the reason explained below. That is, if the thickness is less than 50 [μm], the intermediate transfer belt 16 becomes brittle and easily broken. Further, if the thickness is larger than 600 [μm], the thickness of the base material made of a resin material exhibiting elasticity is excessively increased, 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 do. By setting the thickness to 600 [μm] or less, such properties can be easily exhibited.

  FIG. 6 is a schematic configuration diagram showing a first modified apparatus of the printer according to the present embodiment. In the first modification apparatus 100A, the positional relationship of each process cartridge 6Y, M, C, K and exposure apparatus 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 above the process cartridges 6Y, 6M, 6C, and 6K.

  In the first transfer unit 15, the surface hardness according to JIS-A of the first intermediate transfer belt 8 is adjusted to 50 degrees in the same manner as the printer shown in FIG. 1. In order to achieve such a relatively soft surface hardness, not a single layer structure as shown in FIG. 7, but a multilayer structure as shown in FIG. 8 or FIG. 11, and an elastic material is used for any of the layers. It has been. Further, in the first transfer unit 15 in the first modification apparatus 100A, a second tension roller 60 and a tertiary transfer backup roller 61 are added as a plurality of rollers for stretching the first intermediate transfer belt 8. Yes.

  As shown in FIG. 6, the second intermediate transfer belt 16 has its surface hardness adjusted to 95 [degrees] according to JIS-A, similarly to the printer shown in FIG. Of the plurality of rollers that stretch the second intermediate transfer belt 16, the nip expansion roller (19 in FIG. 1) and the backup roller (21 in FIG. 1) are eliminated. Further, the transfer charger (23 in FIG. 1) disposed to face 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 added. 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 the 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. is doing. The separation roller 63 is an alternative to the backup roller of the printer 100 shown in FIG. 1. The separation roller 63 separates the transfer paper P from the second intermediate transfer belt 16 that changes the moving direction by about 90 ° in accordance with the curvature thereof. 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 periphery in the first modification apparatus 100A. The secondary transfer backup roller 12 pressing the two intermediate transfer belts from the back surface of the first intermediate transfer belt 8 toward the secondary transfer roller 17 serving as 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 source. 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. The secondary transfer employs a transfer system in which the toner is electrostatically attracted toward the secondary transfer roller 17 which is a transfer bias member for the recording medium.

  FIG. 10 is an enlarged configuration diagram showing the tertiary transfer nip and its periphery in the first modification apparatus 100A. The tertiary transfer backup roller 61 pressing the two intermediate transfer belts from the back surface of the first intermediate transfer belt 8 toward the tertiary transfer roller 62 as a transfer bias member for the recording medium is the same as the secondary transfer backup roller. Is grounded. On the other hand, a tertiary transfer bias having the same polarity as the toner (negative polarity in the illustrated example) is applied to the tertiary transfer roller 62 by a power source. The first toner image secondarily transferred onto the second intermediate transfer belt 16 at the second transfer nip is electrostatically pushed toward the third transfer backup roller 61 side due to the influence of the third 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. This employs an electrostatic extrusion transfer system in which toner is electrostatically pushed toward the transfer paper P from the side of the tertiary transfer roller 62 which is a transfer bias member for the recording medium. Conventionally, in such a transfer method, during the third transfer, the second toner image that has been secondarily transferred to the second surface of the transfer paper P at the second transfer nip is electrostatically similar to the first toner image. The present inventors thought that the ink was extruded and returned to the first intermediate transfer belt 8. However, when actually tested, it was surprising that the second toner image could be held on the second surface of the transfer paper P without electrostatic extrusion. In the tertiary transfer method, unlike the transfer charger of the printer 100 shown in FIG. 1, the first toner image and the second toner image can be thirdarily transferred while being in close contact with the transfer paper P. it can. Therefore, it is possible to avoid toner dust caused by charging the exposed second surface of the transfer paper P and to form a higher quality image. Moreover, generation | occurrence | production of ozone accompanying a corona charge can also be avoided.

  It should be noted 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 figure and connecting the tertiary transfer roller 62 to the ground and pulling it to the tertiary transfer backup roller 61 does not work. It 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 from the second surface of the transfer paper P onto the first intermediate transfer belt 8. It was pulled back and brought back. Therefore, the tertiary transfer at the tertiary transfer nip needs to be performed by the electrostatic transfer of the extrusion method. That is, of the two transfer bias members for the recording medium, the toner image is transferred from the transfer bias member for the recording medium to the one disposed on the downstream side of the surface movement direction of the intermediate transfer belts. A transfer bias having a polarity for electrostatically moving the paper P away from the paper P is applied.

  Also in the printer 100A of the first modified apparatus configured as described above, the toner image is formed from both sides of the transfer paper P in the process of transporting the transfer paper P from the secondary transfer nip to the downstream side. The transfer process is performed. Therefore, image formation by the one-pass method can be performed on both surfaces of the transfer paper P. Further, since the transfer paper P is not brought into direct contact with each photoconductor (1Y, M, C, K), it is possible to suppress paper dust from adhering to the photoconductor. Further, one of the two intermediate transfer belts (second intermediate transfer belt 16) is less likely to be deformed in the thickness direction than the other, so that it is likely to be deformed mainly at the secondary transfer nip or the tertiary transfer nip. The surface of the material tries to deform according to the surface that is hard to deform. As a result, the wedge-shaped (waving) biting of both belts in the secondary transfer nip and the tertiary transfer nip can be 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 also formed in addition to the secondary transfer nip as a nip due to the contact of the two belts. The present invention that suppresses wrinkles is particularly effective.

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

  The second modification apparatus 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, 6M, 6C, and 6K for the first system have the photoreceptors 1Y, 1M, 1C, and 1K respectively attached to the first intermediate transfer belt 8 above the first transfer unit 15 in the drawing. It arrange | positions so that it may contact | abut. Then, Y, M, C, and K toner images are formed on the first intermediate transfer belt 8 for primary transfer. The four-color toner image obtained by the superimposing primary transfer corresponds to the second toner image in the printer according to the embodiment. Then, 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 come into contact with each other in the clockwise endless movement in the drawing.

On the other hand, the process cartridges 76Y, 76M, 76C, 76K for the second system abut the photoreceptors 71Y, 71M, 71C, 71K on the second intermediate transfer belt 16 respectively below the second transfer unit 24 in the figure. It is arranged to make it. Then, Y, M, C, and K toner images are formed on the second intermediate transfer belt 16 for primary transfer. The four-color toner image obtained by the superimposing primary transfer corresponds to the first toner image in the printer according to the embodiment. The second intermediate transfer belt 16 is fed to the above-described secondary transfer nip as the counterclockwise endless movement of the second intermediate transfer belt 16 in the drawing. The optical writing of the process cartridges 76Y, 76M, 76C for the second system to the photoreceptors 71Y, 71M, 71C, 71K 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 device 7 for the first system is disposed above the process cartridges 6Y, 6M, 6C, and 6K for the first system in the drawing .

  The second modification apparatus 100B includes a printer unit 90 for printing an image on the transfer paper P, and a paper feed unit 91 as a recording material storage unit for storing the transfer paper P to be supplied to the printer unit. It is composed of separate bodies. The paper feed unit 91 rotates the paper feed roller 92 pressed against the uppermost transfer paper P in the bundle of transfer paper accommodated therein at a predetermined timing, thereby transferring the transfer paper P to the printer unit. It feeds out toward 90 paper feed paths 88. The fed transfer paper P passes through a plurality of conveying roller pairs and is then sandwiched between rollers of a registration roller pair 31 disposed near the end of the paper feed path 88. Then, 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. It is sent out toward.

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

  In the second modification apparatus 100B, two-stage secondary transfer, upstream secondary transfer and downstream secondary transfer, is performed in the secondary transfer nip. Specifically, the transfer paper P fed into the secondary transfer nip first passes through the upstream secondary transfer portion in the nip. In the upstream secondary transfer portion, both intermediate transfer belts (8, 16) are sandwiched between the upstream secondary transfer opposing roller 82 and the upstream secondary transfer roller 84. Then, the toner image on any one of the intermediate transfer belts is secondarily transferred to any one surface of the transfer paper P under the influence of the upstream secondary transfer electric field formed between both rollers. In the illustrated example, in the upstream secondary transfer portion, the upstream secondary transfer roller 81 that is in contact with the back surface of the second intermediate transfer belt 16 has a positive upstream secondary having a polarity opposite to the charging polarity of the toner. A transfer bias is applied. Therefore, 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 (in the drawing), which is the other surface of the transfer paper P. Secondary transfer is performed on the surface facing upward. In the illustrated example, the electrostatic attraction transfer method is adopted as the upstream secondary transfer method.

  The transfer sheet P that has been subjected to the upstream secondary transfer in this manner then enters the downstream secondary transfer portion. In the downstream secondary transfer portion, both intermediate transfer belts (8, 16) are sandwiched between the downstream secondary transfer opposing roller 84 and the downstream secondary transfer roller 83. Then, the toner image on any one of the intermediate transfer belts is secondarily transferred to any one surface of the transfer paper P under the influence of the downstream secondary transfer electric field formed between both rollers. In the illustrated example, in the downstream secondary transfer portion, the downstream secondary transfer roller 83 that is in contact with the back surface of the second intermediate transfer belt 16 has a negative downstream secondary transfer bias that is the same as the charging polarity of the toner. Applied. Therefore, the first toner image on the second intermediate transfer belt 16 is electrostatically pushed from the downstream secondary transfer roller 83 side toward the downstream secondary transfer counter roller 84 side, and one side of the transfer paper P is transferred. Is secondarily transferred to the first surface (the surface facing downward in the figure). In the illustrated example, an electrostatic extrusion transfer system is adopted as a downstream secondary transfer system. The present inventors have confirmed by experiments that the following reverse transfer is not caused when the two-step next transfer as shown in the figure is adopted. That is, the second toner image previously transferred onto the second surface of the transfer paper P is reversely transferred from the second surface toward the first intermediate transfer belt 8 during the downstream secondary transfer. It is a phenomenon.

  The transfer paper P on which the toner images are secondarily transferred on both sides at the secondary transfer nip moves from the right side to the left side in the drawing along with the endless movement of both intermediate transfer belts (8, 16), and reaches the fixing device 35. Delivered. In addition to the two fixing rollers 35a and 35b, the fixing device 35 includes two stretching rollers, a first fixing belt 35c, a second fixing belt 35d, and the like. The first fixing belt 35c is endlessly moved clockwise in the drawing while being stretched between the fixing roller 35a and one of the stretching rollers. The second fixing belt 35d is endlessly moved counterclockwise in the drawing while being stretched between the fixing roller 35b and the other stretching roller. The first fixing belt 35c and the second fixing belt 35d moved endlessly in this way are in contact with each other to form a fixing nip 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 pressed from both sides in the process of being sandwiched by the fixing nip and conveyed from the left side to the right side in the figure. The toner images on both sides are fixed.

  The transfer paper P that has been subjected to fixing processing 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 on the left side surface of the printer in the drawing. It is discharged on the part 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 in a non-contact manner, and the belts gradually move toward the secondary transfer nip. Move to get closer. Thus, the sheet feeding path 88 is disposed in a region where the intermediate transfer belts face each other in a non-contact manner. The transfer paper P discharged from the registration roller pair 31 disposed near the end of the paper feed path 88 passes through a region in which both intermediate transfer belts move toward each other toward the secondary transfer nip, It is surely and smoothly guided toward the secondary transfer nip. Therefore, even if the transfer paper P is thin and extremely weak, it is difficult for jamming to occur.

  On the other hand, both intermediate transfer belts are opposed to each other in a non-contact manner downstream of the secondary transfer nip in the belt moving direction, and move so as to gradually move away from each other. The fixing device 35 is arranged so that the end portion on the transfer paper receiving side enters the region where the both 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 to occur.

  In the case where two-stage secondary transfer of upstream secondary transfer and downstream secondary transfer is performed in the nip as in the second modification apparatus 100B, the secondary transfer nip and its surrounding configuration are shown in FIG. The configuration shown in FIG. Compared with the configuration shown in FIG. 13, the two secondary transfer counter rollers (82, 84) in the first transfer unit 15 and the two secondary transfer rollers (81, 83) in the second transfer unit 24 However, it can be seen that the units are replaced. In the upstream secondary transfer portion, an upstream secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the upstream secondary transfer roller 81 that is in contact with the back surface of the first intermediate transfer belt 8. . The first toner image on the second intermediate transfer belt 16 is electrostatically attracted toward the upstream side secondary transfer roller 81 and secondarily transferred onto the first surface of the transfer paper P (electrostatic attraction). Transfer method). On the other hand, in the downstream secondary transfer portion, the downstream 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. Then, the second toner image on the first intermediate transfer belt 8 is electrostatically pushed from the downstream side secondary transfer roller 83 side toward the downstream side secondary transfer counter roller 84 side, and the second toner image on the transfer paper P is transferred. Secondary transfer is performed on two surfaces (electrostatic extrusion transfer method). The present inventors have confirmed by experiments that the following reverse transfer is not caused when the two-step secondary transfer shown in the figure 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 toward 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 drawing, 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 secondary transfer portion, a negative upstream secondary transfer bias that is the same as the charging polarity of the toner is applied to the upstream secondary transfer roller 81 that is 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 pushed from the upstream side secondary roller 81 side toward the upstream side secondary transfer counter roller 82 side, and the first toner image on the transfer paper P is transferred. Secondary transfer onto the surface (electrostatic extrusion transfer method). On the other hand, in the downstream secondary transfer portion, the downstream 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. Then, the second toner image on the first intermediate transfer belt 8 is electrostatically pushed from the downstream side secondary transfer roller 83 side toward the downstream side secondary transfer counter roller 84 side, and the second toner image on the transfer paper P is transferred. Secondary transfer is performed on two surfaces (electrostatic extrusion transfer method). The present inventors have confirmed by experiments that the following reverse transfer is not caused when the two-step secondary transfer shown in the figure 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 toward the second intermediate transfer belt 16 during the downstream secondary transfer. It is a phenomenon.

  Further, the configuration shown in FIG. 16 may be adopted as the secondary transfer nip and its surrounding configuration. In the drawing, 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 secondary transfer portion, a negative upstream secondary transfer bias that is the same as the toner charging polarity is applied to the upstream secondary transfer roller 81 that is 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 pushed from the upstream side secondary transfer roller 81 side toward the upstream side secondary transfer counter roller 82 side, so that the second toner image on the transfer paper P is transferred. Secondary transfer is performed on two surfaces (electrostatic extrusion method). On the other hand, in the downstream secondary transfer portion, the downstream 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. Applied. Then, the first toner image on the second intermediate transfer belt 16 is electrostatically pushed from the downstream secondary transfer roller 83 side toward the downstream secondary transfer counter roller 84 side, and the first toner image on the transfer paper P is transferred. Secondary transfer is performed on one surface (electrostatic extrusion transfer method). The present inventors have confirmed by experiments that the following reverse transfer is not caused when the two-step secondary transfer shown in the figure is employed. That is, the second toner image previously transferred onto the second surface of the transfer paper P is reversely transferred from the second surface toward the first intermediate transfer belt 8 during the downstream secondary transfer. It is a phenomenon.

  Although the example in which the rollers (81, 83) are employed 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 employed. Further, the example in which the rollers (82, 84) are employed as the counter electrode member facing the transfer bias member for the recording medium has been described, but a non-roller counter electrode member may be employed. FIG. 17 is a schematic diagram showing the secondary transfer nip and the surrounding configuration when a non-roller transfer bias member for a recording medium and a non-roller counter electrode member are employed. In the drawing, the stretched portion between the stretching roller 85 and the downstream secondary transfer roller 83 in the first intermediate transfer belt 8 is the stretched portion between the two stretching rollers 86 and 87 in the second intermediate transfer belt 16. A secondary transfer nip is formed in contact with the portion. The upstream secondary transfer blade 88, which is a non-roller transfer bias member for the recording medium, is in contact with the back surface of the former stretched portion upstream 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, a counter electrode plate 89, which is a non-roller counter electrode member, is provided on both the upstream side secondary transfer blade 88 and the downstream side secondary transfer roller 83 of the first transfer unit 15 on the back surface of the latter extended portion. It contacts so as to face. This is a metal plate, conductive resin plate, plate with a conductive resin sheet coated on the surface of a non-conductive substrate, etc., and is supported by a support member (not shown) so as to maintain a contact state with the back surface of the belt. ing. The counter electrode plate 89 is grounded.

  In the drawing, in the upstream secondary transfer portion, the upstream secondary transfer blade 88 that is in contact with the back surface of the first intermediate transfer belt 8 has a positive upstream secondary having a polarity opposite to the charging polarity of the toner. 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 2 on the first surface of the transfer paper P. Next transferred (electrostatic pulling method). On the other hand, in the downstream secondary transfer portion, the downstream 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. Applied. Then, the second toner image on the first intermediate transfer belt 8 is electrostatically pushed out from the downstream side secondary transfer roller 83 side toward the counter electrode plate 89 side, and 2 on the second surface of the transfer paper P. Next transfer (electrostatic extrusion transfer method). The present inventors have confirmed through experiments that even in such a case, reverse transcription during downstream secondary transfer is not caused.

  By the way, it is assumed that the configuration shown in FIG. 18 is adopted as the secondary transfer nip and its surrounding configuration. In the drawing, the positions of the rollers in the secondary transfer nip are the same as those 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. 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 onto the first surface of the transfer paper P. (Electrostatic attracting 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 confirmed by experiment.

In the two-stage secondary transfer, after the transfer from the first intermediate transfer belt 8 to the second surface of the transfer paper P is performed on the upstream side, the second transfer of the transfer paper P is performed from the second intermediate transfer belt 16 on the downstream side. There are two cases: a case where the transfer is performed on two surfaces and a case where the transfer is performed in the reverse order. In addition, two types of transfer methods, namely an electrostatic attraction method and an electrostatic extrusion method, are established on the upstream side and the downstream side, respectively. Therefore, by combining these, eight kinds of 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 transfer 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 during downstream secondary transfer.

  As shown in Table 1, in the eight two-stage secondary transfer methods, the secondary transfer during the secondary transfer on the downstream side did not occur only in the four ways of experiment numbers 3, 4, 7, and 8. Met. These are the two-stage secondary transfer methods shown in FIGS. 13, 16, 14 (or 17) and FIG. When attention is paid to these, it can be seen that all downstream secondary transfer is performed by the electrostatic extrusion method. On the other hand, paying attention to Experiment Nos. 1, 2, 5, and 6 in which reverse transfer occurred, it can be seen that 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, reverse transfer is caused unless the electrostatic extrusion transfer method is adopted for the downstream secondary transfer. In the first embodiment apparatus 100A described above, the same eight methods can be established for continuous transfer (“secondary, third order” or “third order, second order”) in the nip. As a result of testing all of these eight patterns, the present inventors have obtained the same result that reverse transfer is caused unless the extrusion electrostatic transfer method is adopted at the subsequent transfer in the continuous transfer.

  In FIG. 12 described above, a paper conveyance path as a recording medium discharge path is formed in the housing of the printer unit 90. This paper conveyance path is composed of the conveyance paths listed next. That is, the 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 conveyance path composed of these is a straight line without bending, and the inclination from the horizontal direction is 0 [°], that is, the conveyance in the horizontal direction is performed. Yes. 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 from the horizontal direction on the leading end side of the transfer paper P in the middle of discharge to 0 [°]. It has become. That is, the transfer paper P is sent out toward the paper feed path 88 in a posture in which the front end side is horizontal. In such a configuration, the transfer paper P is not bent in the paper conveyance path until the transfer paper P is discharged from the paper supply unit 91 to the outside through the printer unit 90. Therefore, even when thick paper or the like that is difficult to bend is used as the transfer paper P, it can be conveyed without bending creases in the paper conveyance path, and jamming can be suppressed.

  So far, examples of using a drum-shaped photoconductor as a latent image carrier have been described. However, other types such as a belt-shaped photoconductor may be used. Further, although the example in which the second intermediate transfer belt 16 is less deformable than the first intermediate transfer belt 8 has been described, the first intermediate transfer member may be more difficult to deform than the second intermediate transfer member. The present invention can also be applied to an image forming apparatus that uses a liquid developer containing toner and a liquid carrier instead of a powder toner. Although the electrophotographic printer has been described, the present invention can also be applied to a direct recording type image forming apparatus. In this direct recording method, regardless of the latent image carrier, an image is directly formed by forming a pixel image by directly adhering a toner group that has been ejected in a dot shape from a toner flying device to an intermediate transfer member or a recording member. It is a method to form. Further, the printer that performs the primary transfer, the secondary transfer, and the tertiary transfer by electrostatic transfer has been described. However, the present invention can also be applied to an image forming apparatus that performs at least one transfer by heat transfer. It is. The heat transfer means that the transfer source such as the first intermediate transfer member and the transfer destination such as the second intermediate transfer member are brought into close contact while heating to soften the toner image and then separated from each other. 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 apparatus 100A according to the embodiment, the image is transferred from the photoconductors 1Y, 1M, 1C, and 1K, which are image carriers, to the second intermediate transfer belt 16 via the first intermediate transfer belt 8. The first toner image which is the first visible image is transferred to the 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 second surface, which is the other surface of the transfer paper P. ing. In this 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 (photoconductors 1Y, 1M, 1C, 1C, K). Therefore, it is possible to avoid an increase in cost due to the provision of the photoconductor for forming each toner image individually.

  In the second modification apparatus, the second toner image transferred from the first system photoreceptors 1Y, 1M, 1C, and 1K to the first intermediate transfer belt 8 is transferred to the second surface of the transfer paper P. Thus, the first toner image transferred to the second intermediate transfer belt 16 from the second system photoreceptors 71Y, 71M, 71C, 71C, which is another image carrier, is transferred to the first surface of the transfer paper P. . In such a configuration, unlike the printer 100 and the second modification apparatus 100A that form both toner images with the same photoreceptor group, both toner images can be formed substantially in parallel. As a result, the double-sided transfer speed can be increased as compared with the printer 100 and the first modification apparatus 100B.

Further, in the printer 100 and each modified apparatus, the first intermediate transfer belt 8 and the second intermediate transfer belt 16 that are at least one of the intermediate transfer members are multi-layered, so that the belt as a whole has good elasticity. The desired electrical resistance can be exhibited while exhibiting the above.
Further, since the surface layer in the multilayer structure is a release promoting layer made of a material having a toner release property superior to that of the other layers, the toner image is transferred to the belt surface during transfer from the belt to the transfer paper P. Therefore, it is possible to suppress a defective image such as a transfer omission.
In addition, as the first intermediate transfer body and the second intermediate transfer body, an intermediate transfer belt that is endlessly moved while being stretched around rollers as a plurality of stretching members is used, so that a roller or drum-shaped one is used. As a result, the secondary transfer nip can be lengthened. As a result, the process line speed can be increased to shorten the image forming time. Furthermore, since both belts can be arranged in various stretch shapes, the degree of freedom of layout in the main body can be increased as compared with the case of using a roller or drum shape.
In addition, four of the plurality of stretching members that stretch the first intermediate transfer belt 8 are arranged so that the toner images on the photoreceptors 1Y, 1M, 1C, and 1K are electrostatically transferred 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. In such a configuration, the toner image can be electrostatically primary transferred from the photoreceptor (1Y, M, C, K) to the first intermediate transfer belt 8.

  In the second modification apparatus 100B, the second intermediate device is separated from the first system photoreceptors 1Y, 1M, 1C, and 1K for forming the second toner image to be transferred to the first intermediate transfer belt 16. Photoreceptors 71Y, M, C, and K for the 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 statically transfer the toner images on the second system photoreceptors 71Y, 71M, 71C, and 71K to the second intermediate transfer belt 16. A primary transfer roller (79Y, M, C, K), which is a transfer member member that applies a transfer bias member to the back surface of the belt for electrotransfer. With such a configuration, the toner image can be electrostatically transferred to the second intermediate transfer belt 16 from the photoreceptors (71Y, M, C, K) for the second system.

  Moreover, in each aspect shown in FIGS. 13 to 16 in the second modification apparatus 100B, at least one of the plurality of stretching members that stretch the first intermediate transfer belt 8 is any one of the intermediate transfer belts. In order to electrostatically transfer the upper toner image onto the transfer paper P, a transfer bias member for a recording medium that applies a transfer bias to the back surface of the first intermediate transfer belt 8 is provided (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 the recording medium.

  Further, in the printer 100 and each modified apparatus, at least one of the plurality of stretching members that stretch the second intermediate transfer belt 16 electrostatically transfers the toner image on any one of the intermediate transfer belts to the transfer paper P. 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 transfer (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 a transfer bias member for the recording medium.

  Further, in each modified apparatus, the secondary transfer roller 17 and the tertiary transfer roller 62 which are two transfer member members for the recording medium (or the upstream side secondary transfer roller 81 and the downstream side secondary transfer roller 83) However, they are disposed so as to contact 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 nip. Therefore, when transferring a toner image to one of the surfaces by applying a charge to the transfer paper P not sandwiched in the nip by a transfer charger, foreign matters such as toner contaminate the electrode of the transfer charger, and the image A situation in which the quality is deteriorated can be avoided.

Further, in the printer 100 and each modified apparatus, since the first intermediate transfer belt 8 having a surface resistance of 10 ⁵ to 10 ¹² [Ω / □] is used, the first intermediate transfer belt from the photosensitive member is used. The electrostatic primary transfer to 8 can be realized with certainty.
Further, since the second intermediate transfer belt 16 having a surface resistance of 10 ⁵ to 10 ¹² [Ω / □] is used, from the first intermediate transfer belt 8 to the second intermediate transfer belt 16 or the transfer paper P. The electrostatic secondary transfer can be reliably realized.
Further, as the second intermediate transfer belt 16, the base material is made of polyimide, so that the second intermediate transfer belt 16 exhibits heat resistance. As a result, 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 toner image is prevented from being disturbed due to frictional contact with the paper guide member. Various problems caused by heating the second intermediate transfer belt 16 by the fixing device 35 can be suppressed.
In addition, since the second intermediate transfer belt 16 which is the intermediate transfer belt which is not easily deformed is one having a thickness adjusted to 50 to 600 [μm], the first intermediate transfer belt 8 is suppressed while suppressing its tearing. In addition, it is possible to easily exhibit the property of being difficult to deform in the thickness direction.
Further, as a transfer bias member for stretching the first intermediate transfer belt 8 and a transfer bias member for stretching the second intermediate transfer belt 16, primary transfer rollers (9Y, M, C) that are rotatable transfer bias rollers, respectively. , K) The secondary transfer roller 17 is used. With such a configuration, it is possible to avoid wear and deterioration of the belt due to frictional contact with the transfer bias member, which occurs when a non-rotating body that does not rotate with the endless movement of the belt is used as the transfer bias member.

  Further, in the second modified apparatus, the downstream side 2 which is the downstream side of the upstream side secondary transfer roller 81 and the downstream side secondary transfer roller, which is disposed on the downstream side in the surface movement direction of both intermediate transfer belts. The secondary transfer roller 81 is electrostatically moved so that the toner image is moved away from the downstream secondary transfer roller 81 side toward the transfer paper P, that is, a polarity bias capable of realizing an electrostatic extrusion transfer system. It is made to apply. In such a configuration, it is possible to avoid reverse transfer of the toner image by secondary transfer of the downstream secondary transfer onto the transfer paper P by the electrostatic attraction transfer method.

  Further, in the second modified apparatus, after the transfer paper P is received from the paper feed unit 91, the paper transport path as the recording material transport path from the time when the transfer paper P is sent to the secondary transfer nip to the time when it is discharged out of the printer unit 90, It has a straight shape without bending. The inclination angle of the paper transport 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 accommodating means. In such a configuration, even when a thick paper or the like that is difficult to bend is used as the transfer paper P for the reason described above, it can be conveyed without bending creases in the paper conveyance path, and jamming can be suppressed.

  Further, in the printer 100 and each modification device according to the embodiment, a plurality of ones (1Y, M, C, K) that carry a toner image to be transferred to the first intermediate transfer belt 8 as the photoconductor as an image carrier. ) Is used. The transfer device having the first transfer unit 15 and the second transfer unit 24 is configured to transfer the toner images carried on the respective photoconductors on the first intermediate transfer belt 8 in a superimposed manner. Used. In this configuration, toner images of different colors can be superimposed and transferred onto the first intermediate transfer belt 8 to form other color toner images. Moreover, by superposing toner images by a so-called tandem method, a toner image of a different color is sequentially formed on one photoconductor, and is superposed and transferred onto the first intermediate transfer belt 8. The formation speed of the other color toner image can be increased.

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

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for Y of the printer. FIG. 2 is a perspective view illustrating an image forming system including the printer and a personal computer. FIG. 4 is an enlarged cross-sectional view showing a secondary transfer nip when a first intermediate transfer belt and a second intermediate transfer belt are used that are equally good in deformation in the thickness direction. FIG. 3 is an enlarged cross-sectional view showing a secondary transfer nip of the printer. The schematic block diagram which shows a 1st modification apparatus. FIG. 3 is an enlarged side view showing an intermediate transfer belt having a single layer structure. FIG. 3 is an enlarged side view showing an 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 surroundings. FIG. 3 is an enlarged side view showing an intermediate transfer belt having a three-layer structure. The schematic block diagram which shows the 2nd modification apparatus. The schematic diagram which shows the 1st example of the secondary transfer nip and its surrounding structure in the 2nd modification apparatus. The schematic diagram which shows the 2nd example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 3rd example of the secondary transfer nip and surrounding structure. The schematic diagram which shows the 4th example of the secondary transfer nip and surrounding structure. FIG. 10 is a schematic diagram illustrating a fifth example of the secondary transfer nip and the surrounding configuration. The schematic diagram which shows a comparative example with a secondary transfer nip and surrounding structure.

Explanation of symbols

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

Claims (17)

A first intermediate transfer member to which a visible image on the image carrier is transferred and a second intermediate transfer member to which the visible image on the first intermediate transfer member is transferred are brought into contact with each other to form a nip. The surface of both intermediate transfer members is moved endlessly, the first visible image is transferred from the image carrier to the second intermediate transfer member via the first intermediate transfer member, and the image After the second visible image is transferred from the carrier to the first intermediate transfer member, the recording member sandwiched in the nip is conveyed along with the surface movement of both intermediate transfer members. And transferring the second visible image on the first intermediate transfer body to the other surface of the recording body while transferring the first visible image of the recording medium to the one surface of the recording body. In a transfer method in which a visible image is transferred to both sides of a recording medium by a double-sided transfer process,
And with the first intermediate transfer member and the second intermediate transfer member, with using a material having an elastic layer made of an elastic material, respectively, as second intermediate transfer member, than the first intermediate transfer member, in the nip What is claimed is: 1. A transfer method comprising using a recording material that is not easily deformed in the thickness direction of the recording material sandwiched. A first intermediate transfer member visible image on the image carrier is brought into transfer a visible image on the first intermediate transfer member is brought into contact with each other of the surface at the second intermediate transfer member is caused to transfer nip each surface is endlessly moved while forming a via first intermediate transfer member from the image bearing member and transferring the first visual image to the second intermediate transfer member, and, from the image bearing member After the second visible image is transferred to the first intermediate transfer body, the recording medium sandwiched in the nip is conveyed along with the surface movement of both intermediate transfer bodies, and the first intermediate image on the second intermediate transfer body is transferred. A visible image is transferred to one side of the recording body, while a second visible image on the first intermediate transfer body is transferred to the other side of the recording body and is transferred to both sides of the recording body. In a transfer device that transfers a visible image,
And with the first intermediate transfer member and the second intermediate transfer member, with using a material having an elastic layer made of an elastic material, respectively, as second intermediate transfer member, than the first intermediate transfer member, in the nip What is claimed is: 1. A transfer apparatus comprising: a recording material that is not easily deformed in a thickness direction of the recording material sandwiched . A transfer device 請 Motomeko 2,
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 3 ,
The transfer device according to claim 1, wherein the surface layer in the multilayer structure is made of a material having better toner releasability than the other layers. The transfer device according to any one of claims 2 to 4 ,
The 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 stretch members. The transfer device according to claim 5 ,
At least one of a plurality of stretching members that stretch the first intermediate transfer belt serving as the first intermediate transfer member is configured to transfer the visible image on the image carrier onto the first intermediate transfer belt. 1. A transfer device, which is a transfer bias member for applying a transfer bias to the back surface of an intermediate transfer belt . A transfer device 請 Motomeko 5 or 6,
At least one of a plurality of stretching members that stretch the first intermediate transfer belt has a back surface of the first intermediate transfer belt to electrostatically transfer a visible image on any one of the intermediate transfer belts to the recording medium. And a transfer bias member for a recording medium for applying a transfer bias to the recording medium. The transfer device according to claim 7 ,
At least one of the plurality of stretching members that stretch the second intermediate transfer belt has a back surface of the second intermediate transfer belt to electrostatically transfer the visible image on any one of the intermediate transfer belts to the recording medium. And a transfer bias member for a recording medium for applying a transfer bias to the recording medium. The transfer device according to claim 8 ,
2. The transfer apparatus according to claim 2, wherein the two transfer bias members for the recording medium are disposed so as to contact 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 5 to 9 ,
The 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 7, 8 or 9 ,
The transfer device, wherein the second intermediate transfer belt has a surface resistance of 10 ⁵ to 10 ¹² [Ω / □]. The transfer device according to any one of claims 5 to 11 ,
A transfer apparatus, wherein the base material of the second intermediate transfer belt is made of polyimide. Be any of the transfer device of claims 5 to 1 2,
Transfer device the thickness of the upper Symbol second intermediate transfer belts is characterized in that it is a 50 to 600 [[mu] m]. Forming a visible image on the image bearing member, a double-sided transfer step of transferring the visible image on the image bearing member on both sides of the recording medium, a visible image on both sides of the recording member after the double-sided transfer step And an image forming method for forming images on both sides of the recording medium by performing a fixing step,
2. The image forming method according to claim 1, wherein the double-sided transfer step in the transfer method of claim 1 is performed as the double-sided transfer step. 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 body, and a fixing that fixes the visible image on both sides of the recording body via the transfer device And an image forming apparatus that forms images on both sides of the recording medium.
As the transfer device, the image forming apparatus characterized by using one of any one of claims 2 to 13. The image forming apparatus according to claim 15 .
As the transfer device, the one of claim 9 is used,
Of the two transfer bias members for the recording medium, the visible image is recorded from the side of the transfer bias member for the recording medium for the one disposed on the downstream side of the surface movement direction of the intermediate transfer belts. An image forming apparatus, wherein a bias having a polarity for electrostatic movement is applied so as to move away from the body . The image forming apparatus 請 Motomeko 15 or 16,
As the image carrier, a plurality of members that carry a visible image transferred to the first intermediate transfer member are used. As the transfer device, the visible image carried on each image carrier is used as the first intermediate member. An image forming apparatus using an apparatus configured to superimpose and transfer onto a transfer body.

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