JP2012058605A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt unit that includes an endless belt, a crown-shaped roller over which the belt is passed, and a predetermined member that is in press-contact with the roller through the belt, thereby suppressing the time-related deterioration of the roller, as well as image forming apparatuses having the belt unit such as a copier, a facsimile, and a printer.SOLUTION: A belt unit of the present invention includes: an endless belt 11; a crown-shaped opposed roller 72 over which the belt 11 is passed at a position opposite to a contact member 64 that is contact with the belt 11 and is in press-contact with the contact member 64 through the belt 64; and resistant members 31 that are in contact with the peripheral surface of each end of the opposed roller 72 and impart resistance to the rotation of the opposed roller 72.

Description

  The present invention relates to a belt unit having an endless belt and a crown-shaped roller around which the belt is wound, and an image forming apparatus such as a copying machine, a facsimile, and a printer having the belt unit.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine, a facsimile machine, or a printer, an image forming apparatus having a belt unit having an endless belt and a roller around which the belt is wound is known. (For example, see [Patent Document 1] to [Patent Document 3]).

  In such a belt unit or image forming apparatus, such a roller may have a so-called crown shape. This is because, for example, in such an image forming apparatus, when the belt is an intermediate transfer belt and the roller is a transfer counter roller, the print quality, that is, the image formation is performed even when thick paper with an uneven surface is used. This is because the quality is required to be high.

  In other words, such uneven paper is difficult to fully adhere to the intermediate transfer belt, and the effective transfer electric field is difficult to increase, and even when a transfer bias is applied, discharge occurs in the gap between the uneven paper and the intermediate transfer belt. There is a problem that a characteristic abnormal image such as “uneven paper blank” or “uneven paper blur” tends to occur.

  As a means for solving such a problem, a method is known in which the intermediate transfer belt is made to have a low hardness, and pressure is further applied to physically reduce the gap between the intermediate transfer belt and the paper. The intermediate transfer belt has elasticity, and a transfer nip is formed by contacting the transfer roller from the outer peripheral surface of the intermediate transfer belt at a position facing the transfer counter roller via the intermediate transfer belt and pressurizing with high pressure. However, at this time, with the aim of equalizing the contact pressure at the transfer nip and stabilizing the contact for preventing discharge when the transfer counter roller is a bias application roller, the transfer counter roller is crown-shaped, that is, a The shape of the middle bulge is as follows. The crown shape of the transfer counter roller is also effective for preventing meandering during the running of the intermediate transfer belt. Various techniques have been proposed as belt meandering prevention techniques (see, for example, [Patent Document 1] to [Patent Document 3]).

  By the way, when the intermediate transfer belt is an elastic belt, the transfer pressure is increased, and the transfer counter roller is crown-shaped, the circumferential surface of the end of the transfer counter roller deteriorates over time. May crack and wear. In the transfer facing roller in which cracks and wear occur, the intermediate transfer belt runs poorly, and it is difficult to apply a bias at the end portion, and the image density is likely to be lowered only at the end portion of the image. In addition, if the transfer counter roller cracks or wears, the wear powder generated by the transfer roller wraps around the inner circumference of the intermediate transfer belt stretching system, and stains the intermediate transfer belt, the intermediate belt drive roller and the tension roller. Problems can also arise.

  However, there has not been proposed a technique for paying attention to such a problem and solving it. Such a problem is not limited to the configuration exemplified above, and has an endless belt and a crown-shaped roller around which the belt is wound, and a predetermined member is provided on the roller via the belt. Can be generated in a belt unit that is in pressure contact and an image forming apparatus such as a copier, a facsimile, or a printer that includes the belt unit.

  The present invention is a belt unit that includes an endless belt and a crown-shaped roller around which the belt is wound, and a predetermined member is pressed against the roller via the belt. It is an object of the present invention to provide a belt unit that suppresses deterioration over time, and an image forming apparatus such as a copying machine, a facsimile machine, and a printer having the belt unit.

  In order to achieve the above object, the invention according to claim 1 is characterized in that the endless belt and the contact member that is in contact with the endless belt are wound around the belt, and the contact member is interposed through the belt. The belt unit has a crown-shaped counter roller pressed against each other, and a resistance member that abuts against the peripheral surface of each end of the counter roller and provides resistance to rotation of the counter roller.

  According to a second aspect of the present invention, in the belt unit according to the first aspect, the belt unit includes an urging unit for pressing the resistance member against the peripheral surface.

  According to a third aspect of the present invention, in the belt unit according to the first or second aspect, the position where the resistance member abuts on the opposing roller is a position where the abutting member abuts on the belt in the moving direction of the belt. It is a downstream position in the rotation direction of the opposite roller from the position where the straight line connecting the center and the rotation center of the opposite roller intersects the peripheral surface of the opposite roller.

  According to a fourth aspect of the present invention, in the belt unit according to any one of the first to third aspects, the belt unit includes contact / separation means for contacting / separating the resistance member with the opposing roller.

  According to a fifth aspect of the present invention, in the belt unit according to any one of the first to fourth aspects, the resistance member is a roller, and driving means for rotationally driving the resistance member is provided.

  According to a sixth aspect of the present invention, in the belt unit according to any one of the first to fifth aspects, a portion of the resistance member that comes into contact with the opposing roller has a slidability.

  According to a seventh aspect of the present invention, in the belt unit according to any one of the first to sixth aspects, the belt has an elastic layer.

  According to an eighth aspect of the present invention, in the belt unit according to any one of the first to ninth aspects, the belt is an image carrier, and the belt and the abutting member are opposed to each other in the belt. The image carried on the recording medium is transferred to another medium.

  According to a ninth aspect of the present invention, there is provided an image forming apparatus having the belt unit according to any one of the first to seventh aspects.

  The present invention includes an endless belt, a crown-shaped counter roller in which the belt is wound at a position facing the contact member in contact with the belt, and the contact member is pressed against the belt through the belt, Since the belt unit has a resistance member that abuts the peripheral surface of each end of the counter roller and provides resistance to rotation of the counter roller, the stress of the counter roller is reduced or eliminated with a relatively simple configuration using the resistance member. Thus, it is possible to provide a belt unit that can suppress deterioration over time, improve durability, improve stability over time of belt rotation, and contribute to improvement in image quality.

  If the biasing means for pressing the resistance member against the peripheral surface is provided, the stress of the counter roller can be reduced or eliminated with a relatively simple configuration by the resistance member pressed against the counter roller by the biasing means. Thus, it is possible to provide a belt unit that can suppress deterioration over time, improve durability, improve stability over time of belt rotation, and contribute to improvement in image quality.

  The position where the resistance member abuts against the counter roller is a circumferential surface of the counter roller and a straight line connecting the center of the position where the contact member abuts the belt and the rotation center of the counter roller in the moving direction of the belt. If the position is located downstream of the position where the counter roller rotates in the rotational direction of the counter roller, the stress of the counter roller is quickly reduced as a component toward the center of rotation with a relatively simple configuration using a resistance member. In addition, it is possible to provide a belt unit which can be eliminated and deterioration over time can be suppressed, durability can be improved, stability of belt rotation with time can be improved, and image quality can be improved.

  By providing contact / separation means for bringing the resistance member into and out of contact with the opposing roller, the resistance of the opposing roller can be reduced or eliminated with a relatively simple configuration using the resistance member, and the resistance member is brought into and out of contact with the opposing roller. Together with the reduction of the deterioration over time, the deterioration over time can be suppressed, the durability is improved and the stability of the rotation of the belt over time is improved, and the image quality is improved. A belt unit that can contribute can be provided.

  If the resistance member is a roller and has a driving means for rotationally driving the resistance member, the resistance of the counter roller can be increased by rotating the resistance member as a roller together with a relatively simple configuration using the resistance member. It is possible to provide a belt unit that can contribute to the improvement of image quality by reducing or eliminating the above, suppressing deterioration over time, improving durability and improving stability over time of belt rotation. .

  If the portion of the resistance member that contacts the counter roller has slidability, the resistance member and the counter roller can be prevented from deteriorating with a relatively simple configuration using the resistance member having slidability. A belt unit that can relieve or eliminate stress on the opposing roller, suppress deterioration over time, improve durability, improve stability over time of belt rotation, and contribute to improving image quality Can be provided.

  If the belt has an elastic layer, while improving the adhesion of the belt, the resistance of the counter roller can be reduced or eliminated with a relatively simple structure using a resistance member, and deterioration over time can be suppressed. The belt unit that can improve the image quality and improve the stability of the rotation of the belt over time can be provided.

  If the belt is an image carrier, and the image carried on the belt is transferred to another medium in a region where the belt and the contact member face each other, it is relatively easy to use the resistance member. The configuration can relieve or eliminate the stress on the opposing roller, suppress deterioration over time, improve durability, improve stability over time of belt rotation, and improve transferability to improve image quality. A belt unit that can contribute to improvement can be provided.

  Since the present invention is in an image forming apparatus having such a belt unit, it is possible to relieve or eliminate the stress of the opposing roller with a relatively simple configuration using a resistance member, to suppress deterioration with time, and to improve durability. It is possible to provide an image forming apparatus in which the stability over time of the rotation of the belt is improved and the image quality can be improved.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic perspective view of a part of a belt unit provided in the image forming apparatus shown in FIG. 1. FIG. 5 is a schematic front view of another part of the belt unit provided in the image forming apparatus shown in FIG. 1. It is the schematic explaining the function of the resistance member with which the belt unit shown in FIG. 2, FIG. 3 was equipped. It is the schematic explaining the phenomenon which arises in the conventional belt unit.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a full-color laser printer, but may be other image forming apparatuses such as other types of printers, facsimile machines, copying machines, printing machines, and multifunction machines of copying machines and printers. The image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside. The image forming apparatus 100 can form an image using plain paper generally used for copying, OHP sheets, thick paper such as cards and postcards, and envelopes as sheet-like recording media. .

  The image forming apparatus 100 is a first image carrier capable of forming an image as an image corresponding to each color separated into yellow, magenta, cyan, and black by carrying toner as an image forming substance. A tandem structure in which photosensitive drums 20Y, 20M, 20C, and 20BK, which are photosensitive bodies as latent image carriers, are arranged in parallel, in other words, a tandem system is adopted.

  The photoconductor drums 20Y, 20M, 20C, and 20BK are endless shapes that are intermediate transfer members serving as flexible second image carriers that are rotatably supported by a frame (not shown) of the main body 99 of the image forming apparatus 100. The transfer belt 11 as an intermediate transfer belt, which is a belt, is arranged in parallel at equal intervals in this order from the upstream side in the A1 direction, which is the counterclockwise direction in FIG. Y, M, C, and BK added after the numerals of the respective symbols indicate members for yellow, magenta, cyan, and black.

  Each of the photosensitive drums 20Y, 20M, 20C, and 20BK is an image forming unit 60Y that is an image forming unit for forming yellow (Y), magenta (M), cyan (C), and black (BK) images. It is provided in 60M, 60C and 60BK.

  The photoconductive drums 20Y, 20M, 20C, and 20BK are positioned on the outer peripheral surface side of the transfer belt 11 that is configured as an endless belt disposed substantially at the center inside the main body 99, that is, on the image forming surface side.

  The transfer belt 11 is movable in the direction of the arrow A1 while facing the photosensitive drums 20Y, 20M, 20C, and 20BK. Visible images, that is, toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are respectively superimposed and transferred onto the transfer belt 11 that moves in the direction of the arrow A1, and then a sheet as a recording material that is a recording medium. The image is transferred onto the transfer paper S as a batch. Therefore, the image forming apparatus 100 is an intermediate transfer type, in other words, an indirect transfer type image forming apparatus. Therefore, the image forming apparatus 100 is a tandem indirect transfer type image forming apparatus.

  The lower portion of the transfer belt 11 faces the photosensitive drums 20Y, 20M, 20C, and 20BK, and the opposed portions transfer the toner images on the photosensitive drums 20Y, 20M, 20C, and 20BK. A primary transfer portion 58 for transferring to the transfer belt 11 is formed.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. As described above, by voltage application by primary transfer rollers 12Y, 12M, 12C, and 12BK as primary transfer means disposed at positions facing the respective photosensitive drums 20Y, 20M, 20C, and 20BK with the transfer belt 11 interposed therebetween, The timing is shifted from the upstream side in the A1 direction toward the downstream side.

  Although not shown, the transfer belt 11 has a substrate having a thickness of 50 to 150 μm, an elastic layer having a thickness of 150 to 1000 μm formed on the substrate, and a thickness of 0.1 to 10 μm formed on the elastic layer. And a surface layer as a protective surface layer.

  The substrate is made of polyimide, which is a single layer resin material, but may be formed of PA, PC, ETFE, or the like. The substrate is in the same order as the resistance of a normal single-layer type intermediate transfer belt, and in order to realize this, a carbon-containing conductive material or an ionic conductive material is mixed and molded, and the inner peripheral surface is 10 ^ 9 to 10 ^ 11Ω / □. There are a variety of manufacturing methods.

  The elastic layer is made of a flame retardant rubber, and is formed on the same resistance order as the base. Examples of the flame retardant rubber include chloroprene rubbers. The manufacturing method of the elastic layer is as follows. Drop the undiluted solution into a mold that surrounds the outside, and heat and create it while changing the heating conditions. Then, after cooling, it moves to the inside, and after processing the primer on the surface, an elastic layer is manufactured by roller coating or dipping. There are various other molding methods. The electrical characteristics of the elastic layer are also important, and the stock solution is appropriately molded at a constant volume resistivity: ρv = 1E8-12Ω · cm.

  Finally, a surface layer is formed, and this layer is made of a material having a weak adhesion to the toner. For example, urethane, PC, fluorine resin, silicon resin and the like. In this case as well, the stock solution is always molded appropriately so that the volume resistivity: front side is 10 ^ 10 to 10 ^ 12Ω / □.

  The transfer belt 11 is configured as described above, and as a whole, the resistance and hardness are as follows. The thickness is 400 to 1000 μm, which is thicker than the thickness 40 to 150 μm of the inelastic belt not having the elastic layer.

Resistance characteristics Volume resistivity: ρv = 10 ^ 8-10 ^ 12Ω · cm
Surface resistance on inner and outer surfaces: ρs = 10 ^ 10-10 ^ 12Ω / □
Hardness Micro hardness meter Md-1 value: 50-80
In JIS A, a value of 70 to 90 and other mechanical characteristics include curl stiffness, which are described in, for example, Japanese Patent Application Laid-Open No. 2007-108794.

  The transfer belt 11 has a width corresponding to the A4-sized transfer sheet S in the width direction. Therefore, the image forming apparatus 100 can form an image on the transfer sheet S of A3 vertical size at the maximum.

  The image forming apparatus 100 is disposed in the main body 99 so as to oppose the four image forming units 60Y, 60M, 60C, and 60BK and the respective photosensitive drums 20Y, 20M, 20C, and 20BK. A transfer belt unit 10 as an intermediate transfer unit, which is a belt unit provided, and a secondary transfer device 5 as a secondary transfer means disposed on the right side of the transfer belt 11 in FIG. And an optical scanning device 8 serving as an exposure unit as a writing unit, which is an optical writing unit serving as a latent image forming unit disposed oppositely below the image forming units 60Y, 60M, 60C, and 60BK.

  The image forming apparatus 100 is also conveyed into the main body 99 toward a secondary transfer unit 57 that is a secondary transfer nip as a transfer nip between the transfer belt 11 and the secondary transfer device 5. A sheet feeding device 61 as a paper feeding cassette capable of stacking a large number of transfer sheets S, and a recording sheet S conveyed from the sheet feeding device 61 are used to form a toner image by the image forming units 60Y, 60M, 60C, and 60BK. It has a registration roller pair 4 that feeds toward the secondary transfer portion 57 at a predetermined timing that matches the formation timing, and a sensor (not shown) that detects that the leading edge of the transfer paper S has reached the registration roller pair 4. Yes.

  The image forming apparatus 100 also includes a fixing device 6 as a belt-fixing type fixing unit for fixing the toner image, that is, an unfixed toner image, onto the transfer sheet S on which the toner image is transferred, and a sheet feeding device. A feeding roller (not shown) that feeds the transfer sheet S fed from the feeding device 61 is provided, a paper feed path 32 in which a registration roller pair 4 and a fixing device 6 are arranged in the middle, and a position at the end of the paper feeding path 32 Disposed on the transfer belt unit 10 is a discharge roller 7 serving as a discharge roller pair that is a discharge roller for discharging the image output product, which is the fixed transfer paper S, to the outside of the main body 99, and yellow, cyan. , Toner bottles 9Y, 9M, 9C, 9BK filled with toners of magenta and black, and a transfer disposed on the upper side of the main body 99 and discharged to the outside of the main body 99 by the discharge roller 7. And a paper discharge tray 17 as a sheet discharge unit for stacking S.

The image forming apparatus 100 also includes a driving device including a driving motor (not shown) as a driving unit (not shown) that rotates and drives the photosensitive drums 20Y, 20M, 20C, and 20BK in the main body 99, and is unnecessary due to image formation. A waste toner bottle (not shown) for storing the toner, and a control means 91 including a CPU (not shown), a memory, etc. for controlling the overall operation of the image forming apparatus 100.
The image forming units 60 </ b> Y, 60 </ b> M, 60 </ b> C, 60 </ b> BK, the transfer belt unit 10, the optical scanning device 8, and the fixing device 6 constitute an image forming unit located above the sheet feeding device 61.

  In addition to the transfer belt 11, the transfer belt unit 10 includes primary transfer rollers 12Y, 12M, 12C, and 12BK as primary transfer bias rollers, and a drive roller 72 that is a drive member around which the transfer belt 11 is wound. A counter roller 74 as a stretching roller, tension rollers 75 and 33 as support rollers for stretching the transfer belt 11 together with the driving roller 72 and the cleaning roller 74, and the transfer belt 11. And a cleaning device 13 as a belt cleaning device which is an intermediate transfer member cleaning device for cleaning the surface of the transfer belt 11.

  The transfer belt unit 10 also applies a primary transfer bias independently to a drive system (not shown) including a drive motor (not shown) that drives the drive roller 72 to rotate, and to the primary transfer rollers 12Y, 12M, 12C, and 12BK. A power supply as a first transfer bias applying unit (not shown) and a first transfer bias control unit realized as a function of the control unit 91 are included.

  2 or 3, the transfer belt unit 10 is connected to a driving roller 72 and is subjected to secondary transfer with a secondary transfer roller 64 provided in the secondary transfer device 5 as described later. A power source 30 as a second transfer bias applying means for applying a bias; an auxiliary pressing roller 31 as a resistance member that abuts against the peripheral surface of each end of the driving roller 72 and provides resistance to rotation of the driving roller 72; Functions as a pressing spring 36 as a biasing member for pressing each auxiliary pressing roller 31 against the peripheral surface of the driving roller 72 and a contacting / separating unit for contacting each auxiliary pressing roller 31 with the driving roller 72. In addition, a drive unit 37 that functions as a drive unit that rotationally drives each auxiliary pressing roller 31 is provided.

  Although not shown, the transfer belt unit 10 has a spring as a biasing member that biases the drive roller 72 toward the secondary transfer roller 64. In FIG. 2, the size, shape and the like of each member shown in the figure are exaggerated. For example, the thickness of the transfer belt 11 is shown to be thicker than actual, and the shape of the drive roller 72 is also exaggerated from the crown shape described later. The same applies to other drawings.

  As shown in FIG. 1, the driving roller 72, the cleaning counter roller 74, and the stretching rollers 75 and 33 are support rollers that are wound around the transfer belt 11 so as to be able to rotate and convey. The cleaning facing roller 74 and the stretching rollers 75 and 33 are driven rollers that rotate with the transfer belt 11 that is rotationally driven by the driving roller 72. Of the support rollers 72, 74, 75, 33, only the tension roller 33 abuts on the outer peripheral surface of the transfer belt 11, and the other support rollers 72, 74, 75 are on the inner peripheral surface of the transfer belt 11. It is in contact with a certain back surface.

  The primary transfer rollers 12Y, 12M, 12C, and 12BK press the transfer belt 11 from the back surface thereof toward the photosensitive drums 20Y, 20M, 20C, and 20BK to form primary transfer nips as transfer nips. The primary transfer nip is formed in a portion of the transfer belt 11 that extends between the cleaning facing roller 74 and the stretching roller 75. The cleaning counter roller 74 and the stretching roller 75 have a function of stabilizing the primary transfer nip.

  In each primary transfer nip, a primary transfer electric field is formed between the photosensitive drums 20Y, 20M, 20C, and 20BK and the primary transfer rollers 12Y, 12M, 12C, and 12BK due to the influence of the primary transfer bias. . The toner images of the respective colors formed on the photosensitive drums 20Y, 20M, 20C, and 20BK have the primary transfer electric field and the pressure that sandwiches the transfer belt 11 between the driving roller 72 and the secondary transfer roller 64. Primary transfer is performed on the transfer belt 11 due to the influence of the nip pressure.

  The driving roller 72 is in contact with the secondary transfer roller 64 via the transfer belt 11, and the secondary transfer portion 57 is formed by winding the transfer belt 11 at a position facing the secondary transfer roller 64. . Therefore, the driving roller 72 also serves as a secondary transfer counter roller as a counter roller.

  The driving roller 72 is a firing roller having a low-hardness foamed layer in consideration of preventing scratches on the transfer belt 11 and increasing the width of the secondary transfer portion 57 in the A1 direction, that is, the nip width. . The driving roller 72 is a bias application roller by applying a repulsive bias of −2 to −10 kV to the shaft core by the power supply 30. The resistance of the material of the driving roller 72 is adjusted to a volume resistivity: ρv = 10 ^ 8 to 10 ^ 12 Ω · cm by mixing ion conductive materials. In terms of shape, the central part is a cylindrical part, but the diameter is reduced by about 0.5 mm at the end part.

This crown shape prevents or suppresses meandering of the transfer belt 11. That is, since the transfer belt 11 has an elastic layer and is relatively thick, when it is wound around a roller having a small radius of curvature, it is difficult to follow the peripheral surface of the roller, causing blurring and meandering. Although the drive roller 72 has a crown shape, the secondary transfer unit 57 that is wound around the drive roller 72 is prevented or suppressed from being shaken or meandered, and the secondary transfer is performed well.
As already mentioned, the crown shape is exaggerated in the figure, but in reality the diameter of both ends is about 0.5 mm smaller than the central φ20 mm, resulting in a crown of about 2.5%. Yes.

  The tension roller 75 is a metal roller having a width corresponding to the width of the transfer belt 11 in the width direction. The tension roller 75 applies a slight pressing force to the transfer belt 11, and transfers the wedge-shaped space on the upstream side in the A1 direction formed by the transfer belt 11 and the secondary transfer roller 64 in the secondary transfer portion 57. It has a function as an entrance guide member that is formed so that the paper S smoothly enters the secondary transfer portion 57. The entrance guide member may be a fixing member that is not in the form of a roller such as the stretching roller 75 but has a R-shaped surface that contacts the transfer belt 11.

The cleaning counter roller 74 has a function as a tension roller as a pressure member that gives the transfer belt 11 a predetermined tension suitable for transfer.
Each auxiliary pressing roller 31 is a frustoconical cylindrical roller having the same shape. Each auxiliary pressing roller 31 is rotationally driven by the drive unit 37 at a speed that deviates from the rotational speed of the drive roller 72 at the contact position with the drive roller 72. This speed will be described later.

  The auxiliary pressing rollers 31 have their rotational center axes kept in a twisted relationship with the rotational central axis of the driving roller 72 by the drive unit 37, and the auxiliary pressing rollers 31 are symmetrical with respect to the center in the width direction. It is supported to occupy. This is because each auxiliary pressing roller 31 is brought into contact with the peripheral surface of the conical portion at each end of the driving roller 72 so that the peripheral surface of each auxiliary pressing roller 31 is along.

Each auxiliary pressing roller 31 abuts on the peripheral surface of each end of the driving roller 72 to give resistance against rotation of the driving roller 72, so that the surface layer of the driving roller 72 is in a position of contact with the driving roller 72. It is necessary to apply a frictional force acting in the direction opposite to the rotational direction. However, in consideration of the length of time of contact with the driving roller 72, the friction coefficient of the surface of each auxiliary pressing roller 31 is made smaller than the friction coefficient of the inner peripheral surface of the transfer belt 11, specifically, The surface layer of the auxiliary pressing roller 31 is made of Teflon (registered trademark).
The other points regarding each auxiliary pressing roller 31 will be described later.

  The power source 30 serves to cause the driving roller 72 to function as a bias roller as described above, and the toner carried on the transfer belt 11 is applied to the driving roller 72 by applying a direct current or a voltage in which an alternating current is superimposed on the driving roller 72. A secondary transfer bias, which is a bias having the same polarity as the charging polarity of the toner constituting the image, is applied. The driving roller 72 functions as a repulsive roller that generates a repulsive force on the toner image carried on the transfer belt 11 by applying a bias from the power supply 30, and thereby the toner image applied to the secondary transfer unit 57 is statically transferred onto the transfer paper S. A transition electric field is formed for electrotransfer. The power supply 30 is connected to second transfer bias control means realized as one function of the control means 91, and the timing of bias application by the drive roller 72 is controlled.

  Although not shown, the drive unit 37 that functions as contact / separation means is configured by a mechanism including a solenoid or a pinion rack. The drive unit 37 that functions as drive means includes a motor as a drive source.

  The cleaning device 13 is disposed to the left of the cleaning counter roller 74 in FIG. The cleaning device 13 is disposed so as to contact the transfer belt 11 at a position facing the cleaning counter roller 74, that is, at a position downstream of the secondary transfer portion 57 and upstream of the primary transfer portion 58 in the A1 direction. A cleaning blade 13a and a case 13b in which the cleaning blade 13a is housed.

The cleaning device 13 cleans the transfer belt 11 by scraping and removing foreign matters such as residual toner on the transfer belt 11 with a cleaning blade 13a.
The transfer belt unit 10 can be integrally attached to and detached from the main body 99.

The sheet feeding device 61 accommodates a plurality of transfer sheets S in a state of a stack of transfer sheets, and is disposed in the lower part of the main body 99.
The sheet feeding device 61 has a feeding roller 3 as a sheet feeding roller pressed against the upper surface of the uppermost transfer sheet S, and the feeding roller 3 is driven to rotate counterclockwise at a predetermined timing. Thus, the uppermost transfer sheet S is separated one by one and fed toward the registration roller pair 4. In this respect, the paper feed roller 3 also functions as a separation roller.
The transfer sheet S delivered from the sheet feeding device 61 reaches the registration roller pair 4 through the sheet feeding path 32 and is sandwiched between the rollers of the registration roller pair 4.

  The secondary transfer device 5 is disposed to face the drive roller 72. The secondary transfer device 5 is disposed so as to sandwich the transfer belt 11 with the drive roller 72, so that the toner image on the transfer belt 11 can be transferred to the transfer paper S passing between the transfer belt 11. A secondary transfer roller 64 which is a rotating body which is a transfer roller as a transfer member which is a secondary transfer member.

  The secondary transfer device 5 is also arranged on the upstream side of the secondary transfer unit 57 in the A1 direction, and the transfer sheet S fed toward the secondary transfer unit 57 by the registration roller pair 4 is transferred to the secondary transfer unit 57. A guide plate 38 serving as a paper guide for guiding the transfer paper S in a guided manner and a downstream side of the secondary transfer portion 57 in the A1 direction. And a separation plate 39 that separates the transfer sheet S on which the toner image has been transferred from the secondary transfer roller 64 and conveys the transfer sheet S toward the fixing device 6.

  The secondary transfer device 5 also includes a cleaning device (not shown) that cleans the secondary transfer roller 64 and a spring (not shown) as a biasing member that biases the secondary transfer roller 64 toward the drive roller 72. Yes.

  The secondary transfer roller 64 and a part of the transfer belt 11 near the secondary transfer portion 57 are disposed so as to face the paper feed path 32, thereby forming the secondary transfer portion 57. The secondary transfer roller 64 functions as a contact member that contacts the transfer belt 11 and forms the secondary transfer portion 57. In this way, the secondary transfer roller 64 and the transfer belt 11 face each other, and the close contact area is the secondary transfer portion 57.

  Although not shown in the drawings, the secondary transfer roller 64 is a grounded metal core and a foamed material obtained by blending an ionic conductive agent or carbon black with urethane or EPDM provided around the metal core. And a surface layer formed on the surface of the member. Examples of the ionic conductive agent include lithium ions and sodium ions. Such a member may be formed of an elastic rubber material and a low friction layer formed on the surface of the elastic rubber material. The resistance of such a member is preferably on the order of approximately the same as that of the transfer belt 11, and is set to 10 ^ 9 to 10 ^ 12 Ω · cm. The surface hardness is adjusted to a JIS-A hardness of 30 degrees or more. The surface layer is formed by coating a resin material, thereby eliminating the influence of long-term toner filming and the like. As the resin material, Teflon (registered trademark) is used. This increases the durability over time.

  Although not shown in the drawings, the guide plate 38 is a highly slidable sliding member affixed to the base for lowering the coefficient of friction in a portion where the sliding between the metallic base and the transfer paper S is large. have. The sliding member is Teflon (registered trademark), but may be a PET film.

  The fixing device 6 includes a heating roller 62 that is a hollow metal roller having a heater (not shown) therein, a fixing belt 63 wound around the heating roller 62, and a rubber member around which the fixing belt 63 is wound together with the heating roller 62. A pressure roller 69, which is a hollow roller that presses against the fixing belt 63 between the fixing roller 68 and the fixing roller 68 and forms a fixing nip 70 as a nip portion that is a pressure contact portion, and a pressure roller 69. And a heater (not shown) provided.

  The fixing device 6 also includes a tension roller 73 around which the fixing belt 63 is wound together with the heating roller 62 and the fixing roller 68, and a tension roller 73 so as to apply an urging force to the tension roller 73 in the direction of increasing the tension of the fixing belt 63. The fixing device 6 includes a spring (not shown) as a biasing member that biases the fixing belt 63 from the inside to the outside, a thermistor (not shown) as a temperature detecting means for detecting the temperature of the fixing belt 63, and the fixing device 6. And a fixing case 85 as a casing that surrounds and encloses the structure so that the structure related to the worker cannot be directly touched.

  The fixing device 6 passes the transfer paper S carrying a toner image between the fixing nips 70 so that the toner image carried on the transfer paper S is applied to the surface of the transfer paper S by the action of heat and pressure. It has become established.

  The yellow, cyan, magenta, and black toners in the toner bottles 9Y, 9M, 9C, and 9BK are polymerized toners in which the wax component is uniformly dispersed therein. Less precipitation to the outside. The toner of each color is supplied to the developing devices 80Y, 80M, 80C, and 80BK provided in the image forming units 60Y, 60M, 60C, and 60BK by a predetermined supply amount through a conveyance path (not shown).

  The image forming units 60Y, 60M, 60C, and 60BK have the same configuration. The image forming units 60Y, 60M, 60C, and 60BK are primarily transferred as image forming means around the photosensitive drums 20Y, 20M, 20C, and 20BK along the rotation direction B1 that is clockwise in FIG. Rollers 12Y, 12M, 12C, and 12BK, cleaning devices 71Y, 71M, 71C, and 71BK that are cleaning devices as cleaning means, a static elimination device that is not shown as static elimination means, and charging that performs AC charging to form a charging bias There are charging devices 79Y, 79M, 79C, 79BK as charging means provided with rollers 51Y, 51M, 51C, 51BK, and developing devices 80Y, 80M, 80C, 80BK as developing means for developing with two-component developer. is doing.

  The image forming units 60Y, 60M, 60C, and 60BK can be pulled out from the main body 99 along guide rails (not shown) fixed to the main body 99, and can be pushed into the main body 99. In contrast, the process cartridge is detachably installed. When the image forming units 60Y, 60M, 60C, and 60BK as process cartridges are pushed into the main body 99, they are loaded and positioned at predetermined positions suitable for image formation. Making a process cartridge in this way is very preferable because it can be handled as a replacement part, so that the maintainability is remarkably improved. In addition, since the life of each part, which is an element of the process cartridge, is equal, unnecessary replacement is prevented and suppressed, and the structure is further preferable.

  In the image forming apparatus 100 having such a configuration, when a signal indicating that a color image should be formed is input by the user, printing including image information corresponding to a full-color image that is a desired image to be formed by the control unit 91 is performed. The image forming job, which is a job, is stored and held in the memory, the driving roller 72 is driven, the transfer belt 11, the cleaning facing roller 74, and the stretching rollers 75 and 33 are driven to rotate, and the photosensitive drums 20Y and 20M are driven. , 20C, 20BK are rotationally driven in the B1 direction.

  As the photosensitive drums 20Y, 20M, 20C, and 20BK are rotated in the B1 direction, the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20BK are uniformly charged to a predetermined polarity by the charging bias by the charging devices 79Y, 79M, 79C, and 79BK. The exposure scans or irradiations of light-modulated laser light directed upward in the main scanning direction, which approximately coincides with the vertical direction of the drawing in FIG. 1, correspond to the respective colors of yellow, magenta, cyan, and black. A latent image corresponding to the image information is formed by the electrostatic latent image, and the electrostatic latent image is subjected to toners of yellow, magenta, cyan, and black by developing biases of developing devices 80Y, 80M, 80C, and 80BK and toner charging. Is developed and visualized to form a single-color image composed of toner images of magenta, cyan, and black.

  Note that the control unit 91 decomposes the image information stored in the memory into color information of each color of yellow, magenta, cyan, and black when driving the optical scanning device 8 to form an electrostatic latent image corresponding to each color. The optical scanning device 8 is driven based on each color image information which is monochromatic image information separated into each color.

  The yellow, magenta, cyan, and black toner images obtained by development are sequentially from the yellow toner image located on the most upstream side in the A1 direction, in the order of a magenta toner image, a cyan toner image, and a black toner image. The primary transfer bias formed by the primary transfer rollers 12Y, 12M, 12C, and 12BK is primarily transferred to the same position on the transfer belt 11 rotating in the A1 direction to perform color superposition. A composite color image, which is a full-color toner image, is formed and carried thereon.

  On the other hand, when a signal indicating that a color image should be formed is input, the feeding roller 3 provided in the sheet feeding device 61 rotates to feed out the transfer sheet S and separate the sheets one by one into the sheet feeding path 32. The transfer sheet S fed in and fed into the paper feed path 32 is further transported by a transport roller (not shown) and stops in a state where it abuts against the registration roller pair 4.

  In accordance with the timing at which the composite color image superimposed on the transfer belt 11 moves to the secondary transfer portion 57 as the transfer belt 11 rotates in the A1 direction, in other words, the sheet feeding timing is measured, and the registration roller pair 4 Rotates, and in the secondary transfer portion 57, the composite color image carried on the transfer belt 11 is brought into close contact with the transfer sheet S fed into the secondary transfer portion 57, and is acted by the action of the secondary transfer bias and the nip pressure. Secondary transfer is performed collectively on the transfer sheet S, which is another medium, and recording is performed.

  At this time, since the transfer belt 11 has an elastic layer and the driving roller 72 has a crown shape, the transfer paper S is transferred by the secondary transfer unit 57 even when the transfer paper S is, for example, uneven paper. S is in close contact with the transfer belt 11 and the toner image on the transfer belt 11, and even when a secondary transfer bias is applied, discharge between the transfer sheet S and the transfer belt 11 is prevented or suppressed, and the effective transfer electric field is good. In addition, the pressure is equalized while the nip pressure is stable, and the secondary transfer is favorably performed.

  The transfer sheet S is transported by the secondary transfer device 5 and fed into the fixing device 6, and when passing through the fixing nip 70, that is, the fixing portion between the fixing belt 63 and the pressure roller 69 in the fixing device 6, heat and pressure are transferred. As a result, the carried toner image, that is, the synthesized color image is fixed.

  The transfer sheet S on which the composite color image has been fixed, which has passed through the fixing device 6, is discharged out of the main body 99 through the discharge roller 7 and stacked on the discharge tray 17 at the top of the main body 99.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are cleaned by removing residual transfer toner, which is residual toner that remains after transfer, and becomes unnecessary toner, by wiping it from the surface with the cleaning devices 71Y, 71M, 71C, and 71BK. The charge is removed by the device, the surface potential is initialized, and the next charging is performed by the charging devices 79Y, 79M, 79C, and 79BK. Transfer residual toner removed from the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20BK by the cleaning devices 71Y, 71M, 71C, and 71BK is stored in a waste toner bottle.

  The transfer belt 11 that has passed through the secondary transfer portion 57 after the secondary transfer is wiped off untransferred residual toner that is unnecessary toner remaining on the surface after the transfer by the cleaning blade 13a provided in the cleaning device 13, Removed and cleaned to prepare for the next transfer. The transfer residual toner removed from the surface of the transfer belt 11 by the cleaning device 13 is stored in a waste toner bottle.

  Here, the significance of providing the auxiliary pressing roller 31 will be described by comparing FIGS. 4 and 5 as appropriate. FIG. 4 shows the operation of the auxiliary pressing roller 31, and FIG. 5 shows the phenomenon that occurs when the auxiliary pressing roller 31 is not provided. In addition, illustration of the transfer belt 11 is abbreviate | omitted in Fig.4 (a) and FIG.5 (b).

  As described above, since the driving roller 72 has a crown shape and a nip pressure is applied to the secondary transfer portion 57, the driving roller 72 has the same speed as the moving speed of the transfer belt 11 in the central portion thereof. Although it rotates, a moving speed and a speed difference of the transfer belt 11 occur at the end. Even in the portion where the speed difference occurs, the driving roller 72 is gripped with the transfer belt 11, so that the driving roller 72 is forced to rotate at the end of the transfer belt 11 that moves faster than this. You will receive power.

  Therefore, as shown in FIGS. 4A and 5A, in the secondary transfer portion 57 that is a nip, a shearing force Fnip is generated in the width direction of the secondary transfer portion 57 along the A1 direction. In these drawings, the angle θ is a phase based on a certain point on the peripheral surface of the drive roller 72 with the rotation center of the drive roller 72 as the center, and the angle θ = α is in the width direction. The phase of the center position is shown. Also, the angle θ = β shown in FIG. 4A is the phase at the position where the auxiliary driving roller 31 is in contact with the driving roller 72, and a nip is formed between the auxiliary driving roller 31 and the driving roller 72. In this case, the phase of the center position of the nip in the width direction in the A1 direction is shown.

  The shearing force Fnip is formed when the driving roller 72 receives a force in a direction in which the driving roller 72 is forcedly rotated by the transfer belt 11 moving faster than the driving roller 72 at the end thereof. At the center and the end, the end tends to rotate at a higher angular velocity. Therefore, as shown in FIGS. 4B and 5B, a strain ε is generated between the central portion and the end portion, and the driving roller 72 is deformed.

  If the influence of the shearing force Fnip is small to some extent, even if the strain ε is generated, the deformation of the driving roller 72 is only elastic deformation, and the strain ε is not accumulated. However, since the shear stress due to the shear force Fnip works only in one direction as indicated by arrows in FIGS. 4A and 5A, the strain ε accumulates as plastic deformation strain over time. It will be done. FIG. 5B shows the state of the accumulation, and it is shown that the strain ε increases at the timing of passing through the position of θ = α, in other words, at the timing of θ = 2πn + α.

  In this way, when the strain ε is accumulated and exceeds the allowable strain range of the driving roller 72, the driving roller 72 is deteriorated due to a crack or the like, and in the worst case, is destroyed. As a mechanism of such deterioration, for example, when the strain ε generates a force such as pulling the fiber constituting the foaming roller, and the strain amount is relatively large and a certain degree of elongation occurs, the fracture starts. Can be considered. Accumulation of strain ε is slightly mitigated when slippage occurs between the end portion of the drive roller 71 and the transfer belt 11, but in this case, wear of the drive roller 72 and the transfer belt 11 occurs.

  As described above, the driving roller 72 is a low-hardness foaming roller in consideration of preventing scratches on the transfer belt 11 and increasing the nip width, and stress due to accumulation of strain ε. On the other hand, if the strain ε is about 10%, it is an allowable range, but the accumulated strain ε can exceed this range. The foam roller may have a relatively low durability, and in this case, the deterioration tends to progress with time. Curing may occur when a flame retardant is mixed in the foamed layer. In addition, since the driving roller 72 is a bias roller, when discharge occurs, deterioration can proceed in combination with accumulation of strain ε. Furthermore, the transfer belt 11 may be shaken at the entrance of the secondary transfer portion 57. However, when the shake occurs, the frictional force fluctuates between the driving roller 72 and the transfer belt 11 at the entrance, resulting in shear stress. This also increases the accumulation of strain ε, which can be a factor that causes the drive roller 72 to deteriorate.

  As described above, the driving roller 72 may be worn, cracked or even broken due to the accumulation of the strain ε. Further, the transfer belt 11 may be worn. If at least one of these occurs, the transfer belt 11 may run poorly, and it is difficult to apply a bias at the end portion, and the image density can be reduced only at the end portion of the image. Further, when the driving roller 72 is cracked or worn, and the transfer belt 11 is worn, the wear powder generated thereby wraps around the inner periphery of the transfer belt 11, and the transfer belt 11, the driving roller 72, the cleaning counter roller 74, and the tensioning belt. The rollers 75 and 33 are soiled, and the running failure of the transfer belt 11 can be accelerated. Further, if the cleaning counter roller 74 becomes dirty, the function of the cleaning device 13 is deteriorated, which may cause image formation failure. This can also occur when the driving roller 72 is a high hardness roller such as a solid roller. The stress applied to the end surface of the secondary transfer counter roller becomes a force such as pulling on the fibers constituting the foam roller. If it is extended to some extent, destruction begins. It occurs due to the amount of distortion.

  However, when the auxiliary pressing roller 31 is provided so as to contact the peripheral surface of each end of the driving roller 72 and resistance against rotation of each end is given, as shown in FIG. 4A, the auxiliary driving roller 31 is provided. At the position of θ = β where the roller contacts the driving roller 72, a shear force Fopt opposite to the shear force Fnip acts, and the overall shear force F becomes Fnip + Fopt, which is sufficiently smaller than the shear force Fnip. Thus, as shown in FIG. 5B, the accumulation of strain ε is improved. Specifically, the accumulation of strain ε is suppressed or eliminated. Thus, by applying a load in the opposite direction to the rotation of the driving roller 72 with a relatively simple configuration in which the auxiliary pressing roller 31 is provided, the absolute value of the strain ε can be kept low, and the durability of the driving roller 72 can be reduced. Will improve.

  As a result, deterioration, destruction, wear, and wear of the transfer belt 11 due to cracks and the like of the drive roller 72 are eliminated or alleviated, and the running failure of the transfer belt 11 due to these is eliminated or suppressed, and the bias is also applied to the end portion. Is applied satisfactorily and the image density is stabilized. In addition, wear powder generated by cracking / wearing of the drive roller 72 and wear of the transfer belt 11 wraps around the inner periphery of the transfer belt 11, and the transfer belt 11, the drive roller 72, the cleaning counter roller 74, and the stretching roller 75. 33 is eliminated or suppressed from causing poor running of the transfer belt 11. Further, the cleaning counter roller 74 is contaminated, so that the function of the cleaning device 13 is deteriorated to cause image formation defects.

  The driving unit 37 functioning as a driving unit performs rotational driving of the auxiliary pressing roller 31, so that the driving speed of the auxiliary pressing roller 31 and the rotation direction of the auxiliary pressing roller 31 can be obtained at a higher level or more reliably. Is set so as to be behind the rotational speed of the drive roller 72 at the contact position. In this setting, the ratio of the diameter at the center and the end of the drive roller 72 is also taken into consideration. The rotation direction of the auxiliary pressing roller 31 is the same as the rotation direction of the driving roller 72 at the contact position with the driving roller 72, and the rotation speed of the auxiliary pressing roller 31 is slower than the rotation speed of the end portion of the driving roller 72. May be. The drive unit 37 that functions as a drive unit is configured to set the rotation speed and the rotation direction of the auxiliary pressing roller 31 under the control of the control unit 41. In this respect, the control means 41 functions as a resistance member drive control means.

  The drive unit 37 functioning as the contact / separation means sets the timing so that such advantages can be obtained at a higher level or more reliably when the auxiliary pressing roller 31 is brought into contact with or separated from the drive roller 72. For example, at least the auxiliary pressing roller 31 is brought into contact with the driving roller 72 when the transfer belt 11 is driven by the rotational driving of the driving roller 72. This contact mode may be intermittent. Even after the end of the travel, the auxiliary pressing roller 31 may be brought into contact with the driving roller 72 so as to eliminate or suppress the accumulation of the strain ε. In this case, the rotation direction of the auxiliary pressing roller 31 is the driving roller. The rotation direction of the driving roller 72 is opposite to the rotation direction at the position of contact with 72. The drive unit 37 functioning as the contact / separation means is configured to set the contact / separation timing of the auxiliary pressing roller 31 with respect to the drive roller 72 under the control of the control means 41. In this respect, the control means 41 functions as a resistance member contact / separation control means.

  Such an advantage can be obtained by appropriately setting the shearing force Fopt by adjusting the pressing force and frictional force of the auxiliary pressing roller 31 against the driving roller 72. For example, the pressing force is adjusted by adjusting the urging force on the pressing spring 36, and the friction force is adjusted by adjusting the urging force and adjusting the slidability of the surface of the auxiliary pressing roller 31. In this respect, the surface of the auxiliary pressing roller 31 is covered with Teflon (registered trademark) to obtain slidability. This slidability is higher than the frictional force between the driving roller 72 and the transfer belt 11. Such an advantage can be satisfactorily obtained by the range in which the frictional force between the auxiliary pressing roller 31 and the auxiliary pressing roller 31 is small. Moreover, it is excellent also in that durability over time is increased by being coated with Teflon (registered trademark).

  The position where the auxiliary pressing roller 31 is brought into contact with the driving roller 72 is essentially an extended line in the direction in which the secondary transfer roller 64 is pressed against the driving roller 72. Although the pressing direction and the direction to be pressed are opposite to each other on a straight line, it is statically good. However, in this embodiment, the position closer to the entrance than the exit of the secondary transfer unit 57, more specifically, FIG. 4 (a), it is located downstream of the secondary transfer section 57 in the rotational direction of the drive roller 72 relative to the position indicated by the symbol X. The X position is a line connecting the center of the secondary transfer portion 57 where the auxiliary pressing roller 31 is in contact with the driving roller 72 in the A1 direction, that is, the position where θ = α and the rotation center of the driving roller 72, and the driving roller. It is a position where the peripheral surface of 72 intersects.

  The reason for this is as follows. The drive roller 72 is distorted in the circumferential direction and the radial direction by the torque of itself at the secondary transfer portion 57 which is a transfer nip portion. This strain state is a shearing force Fnip in the circumferential direction and a strong compressive force in the radial direction, which is a complicated state. When the auxiliary pressing roller 31 is brought into contact with the driving roller 72 at such a position, the deformation state of the driving roller 72 changes the circumferential strain state to the radial strain state, that is, the compressive force received by the foam layer, etc. The tensile force inside 72 is relaxed, and the strain state is relaxed. This relaxation phenomenon acts at an early timing so that the stress applied to the driving roller 72 by the foamed layer or the like in the secondary transfer portion 57 is quickly performed, and the shearing force Fopt is also reduced.

  From the above-mentioned static balance, it is better that the position is closer to the position X, but it is better that the pressing force of the auxiliary pressing roller 31 against the driving roller 72 is smaller than that of the secondary transfer portion 57. The position where 31 abuts on the driving roller 72 is determined after comparing these.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, the contact / separation means may be omitted, but considering the deterioration due to the constant contact between the resistance member and the opposing roller, the contact / separation means is provided so that the resistance member contacts the opposing roller at an appropriate time. Is preferred. However, this may be omitted in consideration of the cost merit of omitting the contacting / separating means, and the resistance member may be disposed at a fixed position. In this case, the urging means is omitted, and the resistance member is disposed at a position where the pressing force of the resistance member against the opposing roller can be appropriately obtained so that the frictional force of the resistance member against the opposing roller can be obtained satisfactorily.

  The driving means may be omitted, but it is preferable to provide the driving means from the viewpoint of obtaining the above-mentioned advantages. However, when the driving means is omitted, the resistance member may not be a roller such as the auxiliary pressing roller 31, but may be a non-rotating member in which a portion contacting the opposing roller forms a curved surface or the like and smoothly contacts. .

  The contact member may not be a rotating member such as the secondary transfer roller 64 but may be a fixedly arranged member. Also, in the case of a rotating member, the contact member is not a roller such as the secondary transfer roller 64. An endless belt may be used.

  The belt unit is not provided with an intermediate transfer member as an endless belt like the transfer belt unit 10, but may be provided with a latent image carrier such as a photosensitive member as an endless belt, Instead of an image carrier such as an intermediate transfer member or a latent image carrier, a belt such as a recording medium conveyance belt may be provided as an endless belt.

  If these conditions are satisfied, an image forming apparatus to which the present invention is applied can adopt a direct transfer method instead of the indirect transfer method described above, even if it is a tandem type. The image forming apparatus is not a so-called tandem type image forming apparatus, but a so-called one-drum type image forming apparatus that sequentially forms toner images of respective colors on a single photosensitive drum and sequentially superimposes the color toner images to obtain a color image. The intermediate transfer member can be applied to the image forming apparatus in the same manner, and in addition, the toner image of each color is developed on an image carrier such as a sheet-like organic photoreceptor, but the color superposition itself is separate. The present invention can also be applied to image forming apparatuses such as a method using a toner, a method using a plurality of intermediate transfer members, and a method using intermediate color toner.

  In addition, in recent years, in accordance with demands from the market, color image forming apparatuses, such as color copiers and color printers, have increased in number, but image forming apparatuses can only form monocolor images. It may be.

  When a developer is used as an image forming material used in such an image forming apparatus, the developer is not limited to a two-component developer but may be a one-component developer. Furthermore, the image forming substance may be ink or the like.

  The image forming apparatus may not be a copier, a printer, and a facsimile machine, but may be a single unit thereof, or may be a multi-function machine of another combination such as a copier and printer. .

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 10 Belt unit 11 Endless belt, image carrier 31 Resistance member 36 Energizing means 37 Contacting / separating means, drive means 57 Area | region where a belt and an abutting member oppose 64 Abutting member 72 Opposing roller 100 Image forming apparatus A1 Belt Movement direction S Other media

JP 2006-71818 A JP 2002-130252 A JP 2009-265421 A

Claims (9)

An endless belt,
A crown-shaped counter roller in which the belt is wound at a position facing the contact member in contact with the belt, and the contact member is pressed against the belt via the belt;
A belt unit having a resistance member that abuts against the peripheral surface of each end of the counter roller and provides resistance to rotation of the counter roller. The belt unit according to claim 1, wherein
A belt unit comprising biasing means for pressing the resistance member against the peripheral surface. The belt unit according to claim 1 or 2,
The position where the resistance member abuts against the counter roller is a circumferential surface of the counter roller and a straight line connecting the center of the position where the contact member abuts the belt and the rotation center of the counter roller in the moving direction of the belt. A belt unit characterized in that the belt unit is located at a downstream side in the rotation direction of the opposite roller with respect to the position where the crossing and the crossing. The belt unit according to any one of claims 1 to 3,
A belt unit comprising contact / separation means for contacting / separating the resistance member to / from the opposing roller. The belt unit according to any one of claims 1 to 4,
A belt unit characterized in that the resistance member is a roller and has a driving means for rotationally driving the resistance member. The belt unit according to any one of claims 1 to 5,
The belt unit according to claim 1, wherein a portion of the resistance member that comes into contact with the counter roller has slidability. The belt unit according to any one of claims 1 to 6,
The belt unit, wherein the belt has an elastic layer. The belt unit according to any one of claims 1 to 9,
A belt unit, wherein the belt is an image carrier, and an image carried on the belt is transferred to another medium in a region where the belt and the contact member face each other.   An image forming apparatus comprising the belt unit according to claim 1.

Images