JP6376432B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  2. Description of the Related Art Conventionally, in an image forming apparatus, when sudden speed fluctuations occur in an intermediate transfer belt as an endless belt-like image carrier that is endlessly moved while being stretched by a plurality of stretching rollers, a photosensitive member is formed at a primary transfer nip. From this, the image transferred onto the intermediate transfer belt expands and contracts. For this reason, light and shade occurs in a portion of the image that should have a constant image density, and an abnormal image called a shock jitter occurs.

  The sudden change in the speed of the intermediate transfer belt described above may occur when the transfer paper enters the secondary transfer nip where the image on the intermediate transfer belt is secondarily transferred to the transfer paper, or when the transfer paper exits the secondary transfer nip. Occurs when

  In the image forming apparatus described in Patent Document 1, the transfer paper is transported toward the secondary transfer nip, and before the transfer paper enters the secondary transfer nip, the rotation cam of the contact / separation mechanism is driven, The secondary transfer roller, which is a transfer member that contacts the intermediate transfer belt and forms a secondary transfer nip, is forcibly moved away from the intermediate transfer belt. Thereby, a minute gap is formed between the secondary transfer roller and the intermediate transfer belt, and the occurrence of shock jitter when the transfer paper enters the secondary transfer nip can be suppressed. Immediately after the leading edge of the transfer paper enters the minute gap, a spring is attached to release the forced movement of the secondary transfer roller by driving the rotating cam and bias the secondary transfer roller toward the intermediate transfer belt. The secondary transfer roller is pressed toward the intermediate transfer belt by the force. As a result, the secondary transfer roller comes into contact with the intermediate transfer belt, and a sufficient transfer pressure is exerted at the secondary transfer nip during the transfer process to suppress the occurrence of transfer failure.

  Also, the secondary transfer roller is forced to be separated from the intermediate transfer belt by driving the rotating cam after the transfer of the image on the intermediate transfer belt to the transfer paper and before the transfer paper passes through the secondary transfer nip. Move. Thereby, it is said that the occurrence of shock jitter when the trailing edge of the transfer paper passes through the secondary transfer nip can be suppressed.

  However, an image may be formed up to the vicinity of the rear end of the transfer paper. In this case, if the separation operation is started after the transfer of the image on the intermediate transfer belt to the transfer paper, the separation operation is not completed until the transfer paper passes through the secondary transfer nip, and a shock jitter may occur. Also, if the separation operation is attempted to complete before the trailing edge of the transfer paper comes out, the transfer pressure becomes insufficient, and whiteout occurs in the image at the trailing edge of the transfer paper.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing shock jitter and suppressing trailing edge blanking.

In order to achieve the above object, an invention according to claim 1 is directed to an endless belt-like image carrier that is rotatably supported by a plurality of tension rollers, and an urging means that urges the image carrier. A transfer member that forms a transfer nip by contacting a front surface that is an outer peripheral surface; and a separation unit that separates the transfer member from the image carrier against the urging force of the urging unit. A transfer device for transferring a toner image carried on the front surface of the carrier to a transfer material sandwiched in a transfer nip, and the transfer member from the image carrier prior to the transfer material entering the transfer nip. In the image forming apparatus including a control unit that controls the separation unit so as to release the separation after the transfer material enters the transfer nip after the separation, the transfer member transfers the transfer member that has passed through the transfer nip. To carry and carry materials An endless belt stretched rotatably by a plurality of stretching rollers, one of a plurality of stretching rollers that stretch the transfer member, and a tension roller that stretches the image carrier The transfer nip is formed between the image carrier and the transfer member, and when viewed from the rotation axis direction of a stretching roller that stretches the transfer member, the transfer material is transferred to the transfer nip. The rotation axis center of the tension roller of the transfer member that forms the transfer nip is perpendicular to the direction passing through and passes through the rotation axis center of the tension roller of the image carrier that forms the transfer nip. The controller is configured to be positioned upstream of the transfer material conveyance direction, and the control means maintains the release of the separation means until the transfer material passes through the transfer nip, and the transfer material passes through the transfer nip. Then Until timber enters into the transfer nip, so that the transfer member from the image bearing member are separated, is characterized in that for controlling said separating means.

  According to the present invention, it is possible to suppress the shock jitter when the transfer material passes through the transfer nip, and to suppress the trailing edge whiteout of the image.

FIG. 2 is a schematic configuration diagram illustrating a main part of a printer. FIG. 2 is a schematic diagram schematically illustrating a belt cleaning device and a surrounding configuration in the printer. The figure which represented the shape of the toner typically in order to demonstrate shape factor SF-1. The figure which represented the shape of the toner typically in order to demonstrate shape factor SF-2. FIG. 3 is a diagram schematically illustrating a toner shape. FIG. 3 is an enlarged schematic configuration diagram in the vicinity of a secondary transfer belt showing a gradation pattern and an optical sensor. The enlarged schematic diagram which shows the chevron patch formed in the secondary transfer belt. FIG. 4 is a schematic diagram illustrating a toner consumption pattern formed on an intermediate transfer belt or a secondary transfer belt. FIG. 3 is a schematic diagram illustrating an example of a turn-up prevention pattern formed on the secondary transfer belt. FIG. 3 is an enlarged sectional view of a secondary transfer nip. AA sectional drawing of FIG. FIG. 3 is a schematic diagram for explaining an arrangement relationship between a secondary transfer roller and a secondary transfer counter roller. FIG. 4 is a schematic diagram illustrating a state when transfer paper passes through a secondary transfer nip. The graph which investigated the vibration of the primary transfer part when the front-end | tip of a transfer paper approached the secondary transfer nip without performing contact / separation operation, and when the rear end of the transfer paper passed through the secondary transfer nip. The figure which shows an example of the timing chart of a secondary transfer. The figure which shows the other example of the timing chart of a secondary transfer. The figure which compared the paper interval time of the conventional printer and the printer of this embodiment.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. . The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

Hereinafter, as an embodiment of an image forming apparatus to which the present invention is applied, a so-called tandem type intermediate transfer type 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 showing a main part of the printer.
The printer includes four process units 6Y, 6M, 6C, and 6K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). The four process units 6Y, 6M, 6C, and 6K respectively have drum-shaped photoconductors 1Y, 1M, 1C, and 1K that are latent image carriers. Around the photoreceptors 1Y, 1M, 1C, and 1K, charging devices 2Y, 2M, 2C, and 3K, developing devices 5Y, 5C, 1M, and 1K, drum cleaning devices 4Y, 4M, 4C, and 1K, a neutralization device (not shown) ) Etc. The process units 6Y, 6M, 6C, and 6K use Y, M, C, and K toners of different colors, but have the same configuration. Above the process units 6Y, 6M, 6C, and 6K, an optical writing unit 20 for irradiating the surface of the photoreceptors 1Y, 1M, 1C, and 1K with the laser light L to write an electrostatic latent image is arranged. It is installed.

  Below the process units 6Y, 6M, 6C, and 6K, a transfer unit 7 is disposed as a belt device including an endless intermediate transfer belt 8 that is an image carrier. In addition to the intermediate transfer belt 8, a plurality of stretching rollers disposed inside the loop, a secondary transfer device 200 disposed outside the loop, a tension roller 16, a belt cleaning device 100, a lubricant applying device 300, and the like have.

  Inside the loop of the intermediate transfer belt 8, there are four primary transfer rollers 9Y, 9M, 9C, 9K, a driven roller 10, a drive roller 11, a secondary transfer counter roller 12, and three cleaning counter rollers 13, 14. 15 and an application brush opposing roller 17 are disposed. Each of these rollers functions as a stretching roller that stretches the intermediate transfer belt 8 around a part of its peripheral surface to stretch the belt. It should be noted that the cleaning counter rollers 13, 14, and 15 do not necessarily have to have a function of applying a certain tension. Therefore, it may be driven to rotate as the intermediate transfer belt 8 rotates. The intermediate transfer belt 8 is moved endlessly in the counterclockwise direction in the figure by the rotation of the driving roller 11 that is driven to rotate counterclockwise in the figure by a driving means (not shown).

  The four primary transfer rollers 9Y, 9M, 9C, and 9K disposed inside the belt loop sandwich the intermediate transfer belt 8 between the photoreceptors 1Y, 1M, 1C, and 1K. As a result, primary transfer nips for Y, M, C, and K in which the front surface of the intermediate transfer belt 8 and the photoreceptors 1Y, 1M, 1C, and 1K contact are formed. A primary transfer bias having a polarity opposite to that of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K by a power source (not shown).

  The secondary transfer device 200 disposed outside the loop of the intermediate transfer belt 8 includes a secondary transfer belt 204 stretched around the secondary transfer roller 18, the separation roller 205, the optical sensor unit facing roller 206, and the cleaning facing roller 207. have. Outside the loop of the secondary transfer belt 204, an optical sensor unit 150, a secondary transfer cleaning device 230, and a secondary transfer lubricant applying device 220 are disposed. The optical sensor unit 150 is opposed to the optical sensor unit facing roller 206 with the secondary transfer belt 204 interposed therebetween. The secondary transfer cleaning device 230 includes a secondary transfer belt cleaning brush 208 and a secondary transfer belt cleaning blade 209 that come into contact with a portion of the secondary transfer belt 204 that is wound around the cleaning facing roller 207. The secondary lubricant application device 220 includes a lubricant 210 and a secondary lubricant application brush 211. The secondary transfer lubricant application brush 211 is in contact with a region downstream of the secondary transfer cleaning blade 209 in the direction of movement of the secondary transfer belt at the portion wound around the cleaning facing roller 207 of the secondary transfer belt 204. Yes.

  A plurality of sheet guide members 213 are provided in the belt width direction between the optical sensor unit 150 and the secondary transfer belt 204. A shutter (not shown) is provided between the optical sensor unit 150 and the secondary transfer belt 204 in order to prevent toner and the like from adhering to the optical element when the sensor is not detected. The shutter is configured to be freely turned on and off by a motor (not shown). In the present embodiment, the shutter configuration is a mechanical shutter, but may be combined with an air shutter or the like.

  As the lubricant 210 applied to the front surface of the secondary transfer belt 204, a fatty acid metal salt having a linear hydrocarbon structure is used. The fatty acid metal salt contains at least one fatty acid selected from stearic acid, palmitic acid, myristic acid and oleic acid, and at least one metal selected from zinc, aluminum, calcium, magnesium and lithium The fatty acid metal salt containing is mentioned. In particular, zinc stearate is the most preferable material in terms of cost, quality stability, and reliability because it is produced on an industrial scale and has been used in many fields. However, the higher fatty acid metal salt generally used industrially is not a single compound composition of its name, but includes other fatty acid metal salts, metal oxides, and free fatty acids that are more or less similar. Fatty acid metal salts are no exception.

These lubricants are supplied in a powder form by the secondary transfer lubricant application brush 211 in small amounts. Specifically, the lubricant 210 solid-molded on the block is scraped and applied by the secondary lubricant application brush 211. As another method of supplying the lubricant to the secondary transfer belt 204, there is a method of supplying the lubricant by externally adding the lubricant to the toner and attaching the toner to the secondary transfer belt at a predetermined timing. is there. However, when the lubricant is supplied by externally adding the lubricant to the toner, the supply amount depends on the output image area and cannot always be supplied to the entire belt surface. Therefore, when the lubricant is to be stably supplied to the entire surface of the secondary transfer belt with a simple apparatus configuration, a method of scraping and applying the solid lubricant with a brush as in this embodiment is preferable.
In order to scrape off the lubricant 210 with the secondary transfer lubricant application brush 211, the lubricant 210 is pressed against the secondary transfer lubricant application brush 211 by a lubricant pressurizing means (not shown) which is an elastic body such as a spring.

  The secondary transfer roller 18 is driven by a driving source (not shown) to rotate the secondary transfer belt 204 and bring the secondary transfer belt 204 into contact with the intermediate transfer belt 8 to form a secondary transfer nip as a transfer nip. The secondary transfer belt 204 can be driven and rotated by the intermediate transfer belt 8, but the transfer from the intermediate transfer belt 8 is difficult to be transmitted when the transfer paper P passes during printing. Therefore, it is not preferable because speed fluctuation is likely to occur.

  The secondary transfer counter roller 12 disposed inside the belt loop of the intermediate transfer belt 8 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 204 with the secondary transfer roller 18. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 8 and the secondary transfer belt 204 abut is formed. A secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer counter roller 12 by a power source (not shown).

  Further, the three cleaning counter rollers 13, 14, 15 sandwich the intermediate transfer belt 8 between the cleaning brush rollers 101, 104, 107 of the belt cleaning device 100. As a result, a cleaning nip is formed in which the front surface of the intermediate transfer belt 8 and the cleaning brush rollers 101, 104, and 107 come into contact with each other. The belt cleaning device 100 can be replaced integrally with the intermediate transfer belt 8. However, when the belt cleaning device 100 and the intermediate transfer belt 8 have different life settings, the belt cleaning device 100 may be detachable from the printer main body independently of the intermediate transfer belt 8. Details of the belt cleaning apparatus 100 will be described later.

  The printer includes a paper feed unit 30 having a paper feed cassette 31 that accommodates the transfer paper P, a paper feed roller 32 that feeds the transfer paper P from the paper feed cassette 31 to a paper feed path, and the like. In addition, a registration roller pair 33 (not shown) that receives the transfer paper sent from the paper supply unit 30 and sends it to the secondary transfer nip at a predetermined timing is provided on the right side of the secondary transfer nip in the drawing. Yes.

  In addition, the fixing device 40 having the heating roller 41 and the pressure roller 42 that receives the transfer paper P sent out from the secondary transfer nip and performs fixing processing of the toner image on the transfer paper P is described above. The next transfer nip is provided on the left side of the drawing. Further, Y, M, C, and K toner supply devices (not shown) for supplying Y, M, C, and K toners to the developing devices 5Y, M, C, and K are provided as necessary.

  In recent years, in addition to plain paper that has been widely used as transfer paper, special transfer paper used for thermal transfer such as special paper having an uneven surface or iron print as a design has been increasingly used. When such special paper is used, transfer defects are more likely to occur when the toner image on the intermediate transfer belt 8 on which the color toners are superimposed is secondarily transferred onto the paper, as compared with the case of conventional plain paper.

  Therefore, in this printer, the intermediate transfer belt 8 is provided with an elastic layer having low hardness so that the transfer layer can be deformed with respect to the toner layer or transfer paper having poor smoothness. By providing the intermediate transfer belt 8 with an elastic layer having low hardness and making the intermediate transfer belt 8 elastic, the surface of the intermediate transfer belt 8 can be deformed following local irregularities. Thereby, without excessively increasing the transfer pressure with respect to the toner layer, good adhesion can be obtained, there is no loss of transfer of characters, and there is no transfer unevenness even on paper with poor smoothness, A transfer image having excellent uniformity can be obtained.

  In this printer, the intermediate transfer belt 8 is composed of at least a rigid base layer that is relatively flexible, a flexible elastic layer, and a surface coating layer formed of spherical particle particles.

  First, the base layer will be described. As a constituent material of the base layer, a resin containing a filler (or additive) for adjusting electric resistance, that is, a so-called electric resistance adjusting material can be given.

  As the resin constituting the base layer, from the viewpoint of flame retardancy, for example, a fluorine-based resin such as PVDF, ETFE, a polyimide resin or a polyamideimide resin is preferable, and from the viewpoint of mechanical strength (high elasticity) and heat resistance, In particular, a polyimide resin or a polyamideimide resin is suitable.

Examples of the electrical resistance adjusting material contained in the resin constituting the base layer include metal oxide, carbon black, an ionic conductive agent, and a conductive polymer material. Examples of the metal oxide include zinc oxide, tin oxide, titanium oxide, zirconium oxide, aluminum oxide, and silicon oxide. Moreover, in order to improve dispersibility, the thing which surface-treated in advance for the metal oxide is also mentioned. Examples of carbon black include ketjen black, furnace black, acetylene black, thermal black, and gas black. Examples of the ionic conductive agent include tetraalkylammonium salts, trialkylbenzylammonium salts, alkylsulfonates, alkylbenzenesulfonates, alkyl sulfates, glycerol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene fatty acids. Alcohol ester, alkyl betaine, lithium perchlorate, etc. are mentioned, and these may be used in combination.
In addition, an electrical resistance adjusting material is not limited to the said exemplary compound.

The resistance value of the base layer is preferably 1 × 10 ⁸ to 1 × 10 ¹⁴ [Ω / □] in terms of surface resistance and 1 × 10 ⁷ to 1 × 10 ¹³ [Ω · cm] in terms of volume resistance. The amount of carbon black is included so as to achieve the above resistance value, but from the viewpoint of mechanical strength, a material that can be achieved with an addition amount that does not easily break the film and is not easily cracked is selected.
That is, using a coating liquid in which the resin component (for example, polyimide resin precursor or polyamideimide resin precursor) and the electrical resistance adjusting material are appropriately adjusted, electrical characteristics (surface resistance and volume resistance) and mechanical strength A balanced base layer is preferred.

  In the case of carbon black, the content of the electric resistance adjusting material is 10 to 25 wt%, preferably 15 to 20 wt% of the total solid content in the coating liquid. Moreover, as content in the case of a metal oxide, it is 1-50 wt% of the total solid of a coating liquid, Preferably it is 10-30 wt%. When the content is less than the range of each of the electric resistance adjusting materials, it becomes difficult to obtain uniformity of the resistance value, and the fluctuation of the resistance value with respect to an arbitrary potential increases. On the other hand, when the content is larger than the above ranges, the mechanical strength of the intermediate transfer belt is lowered, which is not preferable in practical use.

Next, the elastic layer laminated | stacked on a base layer is demonstrated.
As the elastic layer, an acrylic rubber currently on the market can be used. However, among the various crosslinking systems (epoxy groups, active chlorine groups, carboxyl groups) of acrylic rubber, the carboxyl group crosslinking system is excellent in rubber properties (especially compression set) and processability, so select the carboxyl group crosslinking system. It is preferable to do.

The elastic layer preferably has a Martens hardness of 0.2 [N / mm ² ] to 0.8 [N / mm ² ] when pressed into 10 microns. It is difficult to produce an elastic layer of acrylic rubber having a Martens hardness of less than 0.2 [N / mm ² ], and when the Martens hardness exceeds 0.8 [N / mm ² ], the image quality for a paper type having surface irregularities decreases. Resulting in. The Martens hardness can be measured by setting the indentation depth to 10 [μm] with a commercially available micro hardness meter, for example, Fisher Scope HM2000LT manufactured by Fischer Instruments.

  The film thickness of the elastic layer is preferably 100 [μm] to 1000 [μm]. If the thickness is less than 100 [μm], the image quality for a paper type having surface irregularities is lowered. If the thickness exceeds 1000 [μm], the shrinkage of the rubber becomes strong, and the warping of the belt end portion becomes large.

Since acrylic rubber alone has a high resistivity, it is necessary to add a conductive agent. Carbon or an ionic conductive agent can be added to control the resistivity. However, since the rubber hardness is important, it is preferable to use an ionic conductive agent that is effective when added in a small amount and does not affect the rubber hardness. Specifically, it is preferable to add 0.01 to 3 parts of various perchlorates and ionic liquids with respect to 100 parts of rubber. If the addition amount of the ionic conductive agent is less than 0.01 part, the effect of reducing the resistivity cannot be obtained, and if the addition amount exceeds 3 parts, the possibility that the conductive agent blooms or bleeds to the belt surface becomes high. The resistance value of the elastic layer is adjusted so that the surface resistance is 1 × 10 ⁸ to 1 × 10 ¹³ [Ω / □] and the volume resistance is 1 × 10 ⁷ to 1 × 10 ¹² [Ω · cm]. It is preferable.

Next, the surface layer formed on the elastic layer will be described.
The surface layer is formed and formed of spherical resin fine particles. The material of the spherical resin fine particles is not particularly limited, but the spherical fine resin particles (hereinafter simply referred to as “spherical resin particles”) mainly composed of resins such as acrylic resin, melamine resin, polyamide resin, polyester resin, silicone resin, and fluorine resin. "). Further, the surface of particles made of these resin materials may be subjected to surface treatment with a different material. Further, the resin particles referred to here include a rubber material. A structure in which the surface of spherical particles made of a rubber material is coated with a hard resin is also applicable.
Moreover, it may be hollow or porous. Among these resins, silicone resin fine particles are most preferred as those having a slipperiness and a high function capable of imparting releasability to toner and abrasion resistance.

  The spherical resin fine particles are preferably particles produced in a spherical shape by a polymerization method or the like, and those closer to a true sphere are more preferable. Further, the particle diameter is preferably monodisperse having a volume average particle diameter of 0.5 μm to 5 μm and a sharp distribution. When the average particle size is less than 0.5 μm, the aggregation between the fine particles is remarkable, and it becomes difficult to uniformly apply the acrylic rubber to the elastic layer surface. On the other hand, if the average particle diameter exceeds 5 μm, the unevenness of the belt surface after application of the fine particles becomes large, resulting in toner cleaning failure.

  Furthermore, since the particles are often insulative, if the particle size is too large, a residual charging potential due to the particles causes a problem that image disturbance occurs due to accumulation of this potential during continuous image output. Such monodispersed spherical resin particles can be easily and uniformly aligned by directly applying the powder directly onto the resin layer and smoothing.

  The timing for applying the spherical resin particles to the surface of the elastic layer of acrylic rubber is not particularly limited, and can be any before or after vulcanization of the rubber.

  The surface of the intermediate transfer belt 8 is coated with a lubricant by a lubricant coating device 300 in order to protect the belt surface. The lubricant application device 300 is a coating that applies to the surface of the intermediate transfer belt 8 a solid lubricant 302 such as a zinc stearate lump, and a lubricant powder that is in contact with the solid lubricant and scraped off from the solid lubricant by rotation. And a coating brush roller 301 as a member. Although the lubricant application device 300 is provided in the present embodiment, it may not be necessary depending on the toner to be used, the material of the intermediate transfer belt, and the surface friction coefficient, and is not necessarily applied.

FIG. 2 is a schematic diagram schematically showing the belt cleaning device 100 and the surrounding configuration.
In the figure, the belt cleaning device 100 includes three cleaning units. Specifically, the pre-cleaning unit 100a for roughly removing the non-transfer toner on the intermediate transfer belt 8 is charged to a polarity (positive polarity) opposite to the normal charging polarity (negative polarity) on the intermediate transfer belt 8. And a reversely charged toner cleaning unit 100b for removing the toner that has been removed. Further, a regular charged toner cleaning unit 100c for removing the toner charged to the regular charge polarity on the intermediate transfer belt 8 is provided.

  Each of the cleaning units 100a, 100b, and 100c has cleaning brush rollers 101, 104, and 107, and recovery rollers 102, 105, and 108 that recover toner attached to the cleaning brush roller. Further, scraping blades 103, 106, and 109 are provided as scraping members that come into contact with the collecting roller and scrape toner from the roller surface. Each of the cleaning units 100a, 100b, and 100c includes flickers 116, 117, and 118 that scrape off the toner on the cleaning brush roller.

  Further, the belt cleaning apparatus 100 includes a conveying screw 110 as a conveying unit for conveying the toner removed by the cleaning units 100a, 100b, and 100c to a waste toner tank (not shown) provided in the image forming apparatus main body. Is provided.

  When image information is sent from a personal computer or the like, the printer rotates the drive roller 11 to move the intermediate transfer belt 8 endlessly. The stretching rollers other than the driving roller 11 are driven and rotated by the belt. At the same time, the photosensitive members 1Y, 1M, 1C, and 1K of the process units 6Y, 6M, 6C, and 6K are rotationally driven. Further, an electrostatic latent image is formed by irradiating the charged surface with laser light L while uniformly charging the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K with the charging devices 2Y, 2M, 2C, and 2K. To do.

  The electrostatic latent images formed on the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K are developed by the developing devices 5Y, 5M, 5C, and 5K, so that the Y, M on the photoreceptors 1Y, 1M, 1C, 1K are developed. , C, K toner images are obtained. The Y, M, C, and K toner images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 8 in the above-described primary transfer nips for Y, M, C, and K. As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 8.

  On the other hand, in the paper feed unit, the transfer paper P is sent out from the paper feed cassette one by one by the paper feed roller 32 and conveyed to the pair of registration rollers. Then, at a timing that can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 8, the registration roller pair is driven to transfer the transfer paper P to the secondary transfer nip so that the four-color superimposed toner image on the belt is transferred. Batch transfer onto the transfer paper P is performed. Thereby, a full-color image is formed on the surface of the transfer paper P. The transfer paper P after full-color image formation is conveyed from the secondary transfer nip to the fixing device and subjected to toner image fixing processing.

  For the photoreceptors 1Y, 1M, 1C, and 1K after the Y, M, C, and K toner images are primarily transferred to the intermediate transfer belt 8, the remaining toner is cleaned by the drum cleaning devices 4Y, 4M, 4C, and 4K. Apply. Then, after neutralizing with a neutralizing lamp (not shown), it is uniformly charged with the charging devices 2Y, 2M, 2C, and 3K, and is ready for the next image formation.

  Further, the intermediate transfer belt 8 after the primary transfer onto the transfer paper P is subjected to a transfer residual toner cleaning process by the belt cleaning device 100.

Next, toner suitable for the printer of this embodiment will be described.
The toner preferably used in this printer preferably has a volume average particle diameter of 3 to 6 [μm] in order to reproduce minute dots of 600 dpi or more. A toner having a ratio (Dv / Dn) of volume average particle diameter (Dv) to number average particle diameter (Dn) in the range of 1.00 to 1.40 is preferable. The closer (Dv / Dn) is to 1.00, the sharper the particle size distribution. With such a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution is uniform, a high-quality image with little background fogging can be obtained, and the electrostatic transfer method has a high transfer rate. can do.

The toner shape factor SF-1 is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 180. FIG. 3 is a diagram schematically showing the shape of the toner for explaining the shape factor SF-1. The shape factor SF-1 indicates the ratio of the roundness of the toner shape and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.
SF-1 = {(MXLNG) ² / AREA} × (100π) / 4 (1)
When the value of SF-1 is 100, the shape of the toner becomes a true sphere, and becomes larger as the value of SF-1 increases.

FIG. 4 is a diagram schematically showing the shape of the toner in order to explain the shape factor SF-2. The shape factor SF-2 indicates the ratio of unevenness in the shape of the toner, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100 / (4π).
SF-2 = {(PERI) ² / AREA} × 100 / (4π) (2)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated. When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factors SF-1 and SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

The toner has a substantially spherical shape and can be represented by the following shape rule.
FIGS. 5A, 5B, and 5C are diagrams schematically illustrating toner shapes.
5A, 5 </ b> B, and 5 </ _b > C, the substantially spherical toner has a major axis r ₁ , a minor axis r ₂ , and a thickness r ₃ (provided that r ₁ ≧ r ₂ ≧ r ₃ ). In the toner, the ratio of the major axis to the minor axis (r ₂ / r ₁ ) (see FIG. 5B) is 0.5 to 1.0, and the ratio of the thickness to the minor axis (r ₃ / r ₂ ) (see FIG. 5C) is preferably in the range of 0.7 to 1.0. If the ratio of the major axis to the minor axis (r ₂ / r ₁ ) is less than 0.5, the distance from the true spherical shape is inferior, so dot reproducibility and transfer efficiency are inferior, and high quality image quality cannot be obtained. On the other hand, when the ratio of the thickness to the short axis (r ₃ / r ₂ ) is less than 0.7, it becomes close to a flat shape and a high transfer rate like a spherical toner cannot be obtained. In particular, when the ratio of the thickness to the short axis (r ₃ / r ₂ ) is 1.0, the rotating body has the long axis as the rotation axis, and the toner fluidity can be improved.
Note that r ₁ , r ₂ , and r ₃ were measured with a scanning electron microscope (SEM) while taking and observing photographs while changing the viewing angle.

In this printer, image density control for optimizing the image density of each color is executed when the power is turned on or every time a predetermined number of prints are performed.
In the image density control, first, as shown in FIG. 6, the gradation patterns Sk, Sm, Sc, Sy of the respective colors as toner patterns are converted into optical sensors 151Y, 151M, 151M of the optical sensor unit 150 on the secondary transfer belt 204. It is automatically formed at a position facing 151C and 151K. The gradation pattern of each color is composed of 10 toner patches having an area of 2 [cm] × 2 [cm] having different image densities. The charging potentials of the photoreceptors 1Y, 1M, 1C, and 1K when creating the gradation patterns Sk, Sm, Sc, and Sy for each color are different from the uniform drum charging potential in the printing process, and gradually increase in value. To do. Then, while forming a plurality of patch electrostatic latent images for forming a gradation pattern image on the photoreceptors 1Y, 1M, 1C, and 1K by scanning with laser light, they are used for Y, M, C, and K, respectively. Development is performed by the developing devices 5Y, 5M, 5C, and 5K. During this development, the value of the developing bias applied to the Y, M, C, and K developing rollers is gradually increased. By such development, gradation pattern images of Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K. These are secondarily transferred so as to be arranged at predetermined intervals in the main scanning direction (belt width direction) of the secondary transfer belt 204. At this time, the toner adhesion amount of the toner patch in the gradation pattern of each color is about 0.1 [mg / cm ² ] at the minimum and 0.55 [mg / cm ² ] at the maximum, and the toner Q / d distribution When measured, it is almost aligned with the regular charging polarity.

  The toner patterns Sk, Sm, Sc, and Sy formed on the secondary transfer belt 204 pass through the positions facing the optical sensors 151Y, 151M, 151C, and 151K as the secondary transfer belt 204 moves endlessly. . At this time, the optical sensors 151Y, 151M, 151C, and 151K receive an amount of light corresponding to the toner adhesion amount per unit area with respect to the toner patch of each gradation pattern.

  Next, from the output voltages of the optical sensors 151Y, 151M, 151C, and 151K when each color toner patch is detected and the adhesion amount conversion algorithm, the adhesion amount of each color gradation pattern in each toner patch is calculated and calculated. Adjust the imaging conditions based on the amount of adhesion. Specifically, a function (y = ax + b) indicating a straight line graph is calculated by regression analysis based on the result of detecting the toner adhesion amount on the toner patch and the development potential when each toner patch is imaged. Then, an appropriate development bias value is calculated by substituting a target value of image density into this function, and development bias values for Y, M, C, and K are specified.

  The memory stores an image forming condition data table in which several tens of development bias values and appropriate drum charging potentials individually corresponding to the values are associated in advance. For each process unit 6Y, 6M, 6C, 6K, a developing bias value closest to the specified developing bias value is selected from the image forming condition table, and the drum charging potential associated therewith is specified.

The printer also performs color misregistration correction processing when the power is turned on or whenever a predetermined number of prints are performed. In this color misregistration correction process, Y, M, C, and K color toners called chevron patches PV as shown in FIG. 7 are respectively provided at one end and the other end in the width direction of the secondary transfer belt 204. An image for color misregistration detection is formed as a toner pattern composed of an image. As shown in FIG. 7, the chevron patch PV has a predetermined pitch in the belt moving direction, which is the sub-scanning direction, with the toner images of Y, M, C, and K being inclined by about 45 [°] from the main scanning direction. Is a line pattern group arranged in. The amount of the chevron patch PV attached is about 0.3 [mg / cm ² ].

  By detecting each color toner image in the chevron patch PV formed at both ends in the width direction of the secondary transfer belt 204, the following is detected. That is, the position of each color toner image in the main scanning direction (photosensitive member axial direction), the position in the sub-scanning direction (belt moving direction), the magnification error in the main scanning direction, and the skew from the main scanning direction are detected. The main scanning direction here refers to the direction in which the laser light is phased on the surface of the photosensitive member as it is reflected by the polygon mirror. For such Y, M, and C toner images in the chevron patch PV, the detection time difference from the K toner image is read by the optical sensors 151Y, 151M, 151C, and 151K. In the figure, the vertical direction of the paper surface corresponds to the main scanning direction, and after the Y, M, C, and K toner images are arranged in order from the left, the postures are different from those by 90 [°]. , Y toner images are further arranged. Based on the difference between the actual measurement value and the theoretical value of the detection time differences tyk, tmk, and tck with respect to K as the reference color, the shift amount in the sub-scanning direction of each color toner image, that is, the registration shift amount is obtained. Then, on the basis of the amount of registration deviation, the optical writing start timing for the photosensitive member 1 is corrected every other polygon mirror surface of the optical writing unit (not shown), that is, one scanning line pitch as one unit, and each color is corrected. To reduce the registration error of the toner image. Further, the inclination (skew) of each color toner image from the main scanning direction is obtained based on the difference in the amount of deviation in the sub-scanning direction between both ends of the belt. Based on the result, surface tilt correction of the optical system reflection mirror is performed to reduce skew of each color toner image. As described above, the color misregistration correction process is a process that corrects the optical writing start timing and surface tilt based on the detection timing of each toner image in the chevron patch PV to reduce registration deviation and skew deviation. By such color misregistration correction processing, it is possible to suppress the occurrence of color misregistration of an image due to a shift in the formation position of each color toner image on the transfer paper due to a temperature change or the like.

  In addition, if the image forming operation with a low image area continues, the amount of old toner that remains in the developing device for a long time increases, so the amount of deteriorated toner with deteriorated toner charging characteristics, etc. Deterioration of the image quality and the deterioration of image quality. In order to prevent such deteriorated toner from staying in the developing device, a refresh mode that is toner forced consumption control for forcibly discharging the toner from the developing device to the non-image area of the photoreceptor 1 is executed at a predetermined timing. New toner is replenished to the developing device whose toner density has been reduced by the forced discharge of the toner, whereby the deteriorated toner in the developing device is replaced with new toner.

  In the present embodiment, a toner consumption amount of each developing device 5Y, 5M, 5C, 5K and an operation time of each developing device 5Y, 5M, 5C, 5K are stored in a control unit (not shown). Then, at a predetermined timing, each developing device is checked whether or not the toner consumption amount is a small amount equal to or less than a threshold with respect to the operation time of the developing device within a predetermined period, and the refresh mode is executed for the developing device below the threshold.

When the refresh mode is executed, a toner consumption pattern is created as a toner pattern in a non-image area corresponding to the interval between images (paper interval) on the photosensitive member, and the developing device consumes toner when forming the toner consumption pattern. To do. The toner consumption pattern thus formed is transferred to the intermediate transfer belt 8 and formed on the intermediate transfer belt 8 as shown in FIG. The adhesion amount of the toner consumption pattern is determined based on the toner consumption amount with respect to the operation time of the developing device for a predetermined period, and the maximum adhesion amount per unit area on the intermediate transfer belt is about 1.2 [mg / cm ² ]. May be. Further, when the toner Q / d distribution of the toner consumption pattern (a) transferred to the intermediate transfer belt 8 is measured, it is substantially aligned with the normal charging polarity. In this embodiment, the size of the toner consumption pattern is 25 [mm] × 250 [mm].
The toner consumption pattern may be transferred to the secondary transfer belt 204 and removed by the secondary transfer cleaning device 230, or may be removed by the belt cleaning device 100 without being transferred to the secondary transfer belt 204. .

  Further, during the normal image formation, the toner hardly adheres to the secondary transfer belt 204. As a result, when continuous paper passing or the like is performed, there is no toner between the secondary transfer belt 204 and the secondary transfer cleaning blade 209, and the lubricating effect by the toner cannot be obtained. As a result, the frictional force is increased, the contact portion of the secondary transfer cleaning blade 209 with the secondary transfer belt 204 is turned over, and a cleaning failure may occur, causing the back side of the transfer paper to be stained. Therefore, in the printer of this embodiment, a turn-up prevention pattern as a toner pattern is formed on the secondary transfer belt 204 for each predetermined number of sheets and is input to the secondary transfer cleaning blade 209. As a result, the lubricating effect of the toner can be maintained, and the secondary cleaning blade 209 can be prevented from turning up.

  In this embodiment, as described above, a toner pattern such as a gradation pattern and a color misregistration detection image is formed on the secondary transfer belt 204 and is input to the secondary transfer cleaning blade 209. As a result, sufficient toner exists between the secondary transfer cleaning blade 209 and the secondary transfer belt 204 corresponding to the portions where the toner patterns are formed. Therefore, when the anti-flipping pattern is formed over the entire belt width direction, the toner is already supplied to the portion where the lubricating effect is obtained, and the toner is wasted. Therefore, as shown in FIG. 9, the toner density in the belt width direction of the anti-flipping pattern may be changed based on the toner pattern input to the secondary transfer cleaning blade 209 immediately before. As shown in FIG. 9, a density adjustment pattern, a color misregistration detection image, and a toner consumption pattern are formed at the center in the belt width direction. Therefore, the toner density in the center portion (d) of the anti-flipping pattern is minimized. Further, the toner density in the portion (c) in the figure corresponding to the portion where the color misregistration prevention pattern and the toner consumption pattern of the turn-up prevention pattern are formed is the second lowest. Further, the toner density at the portion (a) in the drawing corresponding to the vicinity of both ends in the belt width direction of the turn-up preventing pattern is maximized. It should be noted that only the toner consumption pattern is inputted to the part (b) of the turn prevention pattern in the same manner as the part (a) in the figure. However, the toner of the toner pattern formed in the central portion of the belt moves to this portion. Therefore, more toner is present between the secondary transfer cleaning blade 209 and the secondary transfer belt 204 than at both ends in the belt width direction. Accordingly, the toner density at the position (b) in the figure is the second highest. In this way, by changing the toner concentration of the anti-flipping pattern in the belt width direction based on the toner pattern input to the secondary transfer cleaning blade before the anti-flipping pattern, the toner consumption is suppressed and the curling is suppressed. Can be prevented.

Next, a contact / separation mechanism as a separation means for contacting / separating the secondary transfer belt 204 to / from the intermediate transfer belt 8 will be described.
FIG. 10 is an enlarged cross-sectional view of the secondary transfer nip.
In the figure, a secondary transfer counter roller 12 that partially wraps the intermediate transfer belt 8 around its inner peripheral surface on the inner peripheral surface side of the intermediate transfer belt 8 is configured to place the deformable intermediate transfer belt 8 around its own peripheral surface. It plays a role of backing up and maintaining the shape along a certain curvature. The secondary transfer belt 204 is in contact with the secondary transfer counter roller 12 on the intermediate transfer belt 8 from the front surface side of the intermediate transfer belt 8 to form a secondary transfer nip N.

  The secondary transfer roller 18 is rotatably held by the roller unit holder 70 via a bearing (not shown). The roller unit holder 70 is configured to be rotatable about a rotation shaft 70 a provided so as to take a posture parallel to the rotation axis of the secondary transfer roller 18. When the roller unit holder 70 rotates in the counterclockwise direction in the drawing around the rotation shaft 70a, the secondary transfer roller 18 held by the roller unit holder 70 comes close to the secondary transfer counter roller 12. As a result, the secondary transfer belt 204 is pressed against and brought into contact with the intermediate transfer belt 8, and a secondary transfer nip is formed. Further, when the roller unit holder 70 rotates in the clockwise direction in the drawing around the rotation shaft 70a, the secondary transfer roller 18 held by the roller unit holder 70 is separated from the secondary transfer counter roller 12. To go. As a result, the secondary transfer belt 204 is separated from the intermediate transfer belt 8.

  In the printer of this embodiment, the biasing coil spring 71 always biases the end of the roller unit holder 70 opposite to the rotation shaft 70 a toward the intermediate transfer belt 8. The urging coil spring 71 always applies a force to the roller unit holder 70 to rotate counterclockwise in the figure about the rotation shaft 70a, thereby causing the secondary transfer roller 18 to move to the intermediate transfer belt 8. It is energizing towards. That is, the urging means for urging the secondary transfer roller 18 toward the intermediate transfer belt 8 is configured by the urging coil spring 71, the roller unit holder 70, the rotation shaft 70 a of the roller unit holder 70, and the like. Yes.

  The secondary transfer roller 18 is rotationally driven in the counterclockwise direction in the figure by transmitting the rotational driving force of a roller drive motor (not shown) via a drive transmission means (not shown) such as a gear. These roller drive motors and drive transmission means are also held by the roller unit holder 70 and are configured to rotate together with the secondary transfer roller 18 and the roller unit holder 70.

11 is a cross-sectional view taken along line AA in FIG.
The secondary transfer roller 18 includes a roller portion 18A, a first shaft member 18B and a second shaft member 18C that protrude from both end surfaces in the axial direction of the roller portion 18A and extend in the rotational axis direction, and a first idle roller 34 described later. And a second idling roller 35. The roller portion 18A includes a cylindrical hollow cored bar 18a and an elastic layer 18b made of an elastic material fixed to the peripheral surface thereof. Examples of the metal constituting the hollow metal core 18a include stainless steel and aluminum, but are not limited to these materials.

  The elastic layer 18b is desirably 70 [°] or less in terms of JIS-A hardness. Further, the elastic layer 18b having a JIS-A hardness of about 50 [°] may be formed of epichlorohydrin rubber exhibiting a certain degree of conductivity. As a rubber material exhibiting conductivity, EPDM or Si rubber in which carbon is dispersed, NBR having an ionic conductivity function, urethane rubber, or the like may be used instead of the above-described conductive epichlorohydrin rubber.

  The secondary transfer belt 204 wound around the secondary transfer roller 18 is a seamless belt made of polyimide resin or polyamide resin. Specifically, it is the same as the base layer of JP2012-208485A.

  The secondary transfer counter roller 12 that is wound around the intermediate transfer belt 8 passes through the roller portion 12b, which is a cylindrical main body portion, and the rotational center of the roller portion 12b in the rotational axis direction, while passing through the roller portion 12b. And a through-shaft member 12a that idles on its surface. The penetrating shaft member 12a is made of a metal member, and the roller portion 12b is rotatably supported on its peripheral surface so as to be idled.

  The roller section 12b as the main body section is composed of a drum-shaped hollow core 12c, an elastic layer 12d made of an elastic body fixed on the peripheral surface thereof, and balls press-fitted to both ends in the axial direction of the hollow core 12c. Bearing 12e. For this reason, the ball bearing 12e rotates on the through shaft member 12a together with the hollow core metal 12c while supporting the hollow core metal 12c. The elastic layer 12d is press-fitted into the outer peripheral surface of the hollow cored bar 12c. The through shaft member 12 a is rotatably supported by a first bearing 52 fixed to the first side plate 28 of the transfer unit 7 that stretches the intermediate transfer belt 8 and a second ball bearing 53 fixed to the second side plate 29. Has been. However, most of the time during the print job, the through shaft member 12a is stopped without being driven to rotate. The penetrating shaft member 12a freely idles the roller portion 12b to be rotated along with the endless movement of the intermediate transfer belt 8 on its peripheral surface.

  The elastic layer 12d fixed on the peripheral surface of the hollow core metal 12c is composed of a conductive rubber material whose resistance value is adjusted by adding an ionic conductive agent so as to exhibit a resistance of 7.5 [LogΩ] or more. Has been. The reason why the electric resistance of the elastic layer 12d is adjusted within a predetermined range is as follows. That is, in the case of a transfer sheet having a relatively small size in the roller axis direction such as A5 size, the intermediate transfer belt 8 and the secondary transfer belt 204 are in direct contact within the secondary transfer nip without the transfer sheet. This is because the transfer current is not concentrated at the location. By making the electric resistance of the elastic layer 12d larger than the resistance of the transfer paper P, it is possible to suppress such transfer current concentration.

  As the conductive rubber material constituting the elastic layer 12d, foamed rubber is used so as to exhibit an elasticity of about 40 [°] in Asker-C hardness. By forming the elastic layer 12d with such a foamed rubber, the elastic layer 12d is flexibly deformed in the thickness direction in the secondary transfer nip N, and the secondary transfer nip having a certain size in the transfer paper conveyance direction. N can be formed. The elastic layer 12d has a Tyco shape in which the outer diameter of the central portion is larger than the outer diameter of the end portion. In other words, the secondary transfer counter roller 12 is formed in the shape of a Tyco having the outer diameters of the end portions 12B and 12C smaller than the central portion 12A. By using a roller having a Tyco shape, when the secondary transfer roller 18 is urged toward the intermediate transfer belt 8 by the urging coil spring 71 (see FIG. 10) to form the secondary transfer nip N, the deflection is generated. It is possible to prevent the pressure at the central portion 12A from being released.

  In the penetrating shaft member 12a of the secondary transfer opposing roller 12, a pair of cams 50 constituting a part of the separating means are provided in both end regions that are not located in the roller portion 12b in the entire region in the longitudinal direction. , 51 are fixed. That is, the first cam 50 is fixed to one end region in the longitudinal direction of the penetrating shaft member 12a. The cam 50 is integrally formed with the cam portion 50A and the true circular roller portion 50B side by side in the axial direction. Has been. The cam 50 is fixed to the penetrating shaft member 12a by screwing a screw 80 penetrating the roller portion 50B into the penetrating shaft member 12a. In the cam 51, a cam portion 51A and a true circular roller portion 51B are integrally formed side by side in the axial direction. The cam 51 has the same configuration as the cam 50 and is fixed to the other end region in the longitudinal direction of the penetrating shaft member 12a. doing. A drive receiving pulley 54 is fixed to a region outside the cam 51 in the axial direction of the through shaft member 12a. A detected disk 59 is fixed on the further outside of the drive receiving pulley 54.

  A cam driving motor 58 serving as cam driving means for rotating the cams 50 and 51 in the forward direction and the reverse direction is fixedly disposed on the second side plate 29 of the transfer unit 7. The cam drive motor 58 rotates a motor pulley 57 provided on its output shaft, and transmits a driving force to a drive receiving pulley 54 fixed to the through shaft member 12a via a timing belt 56. With such a configuration, the penetrating shaft member 12a can be rotated by operating the cam drive motor 58. At this time, even if the penetrating shaft member 12a is rotated, the roller portion 12b can be freely idled on the penetrating shaft member 12a, so that the intermediate transfer belt 8 prevents the roller portion 12b from being rotated. There is no. In addition, by using a stepping motor as the cam drive motor 58, the motor rotation angle can be freely set without providing a rotation angle detection means such as an encoder. Of course, a rotation angle detection means may be provided to detect the rotation angle of the cam drive motor 58.

  The outer peripheral surfaces 50C and 51C of the cam portions 50A and 51A of the cam 50 and the cam 51 are formed as follows. That is, when the through-shaft member 12a stops rotating at a predetermined rotation angle, the respective cam portions 50A and 51A abut against the secondary transfer roller 18, and the secondary transfer roller 18 is biased by the biasing coil spring 71 of the roller unit holder 70. It is formed to push back against the urging force. That is, by controlling the rotational positions of the cams 50 and 51, the secondary transfer roller 18 is moved in the direction approaching the secondary transfer counter roller 12 (and thus the intermediate transfer belt 8), so that the secondary transfer counter roller is moved. The distance L between the shafts 12 and the secondary transfer roller 18 is adjusted. By adjusting the distance L between the axes of the secondary transfer counter roller 12 and the secondary transfer roller 18, the gap between the secondary transfer belt 204 and the intermediate transfer belt 8 in the secondary transfer nip N can be adjusted.

  In this embodiment, the inter-axis distance L between the secondary transfer counter roller 12 and the secondary transfer roller 18 is adjusted by at least the cam 50, the cam 51, and the cam drive motor 58. In other words, at least the cam 50, the cam 51, and the cam drive motor 58 constitute a separating unit 500 that separates the secondary transfer belt 204 from the intermediate transfer belt 8. The secondary transfer counter roller 12 as a rotatable support member freely idles the roller portion 12b on the penetrating shaft member 12a penetrated with respect to the cylindrical roller portion 12b. When the penetrating shaft member 12a rotates, the cams 50 and 51 fixed to both ends in the axial direction of the penetrating shaft member 12a rotate as a unit. Thereby, the cams 50 and 51 on both end sides can be rotated only by providing a drive transmission mechanism for transmitting drive to the penetrating shaft member 12a on one end side in the axial direction.

  In this printer, while the hollow cored bar 18a of the secondary transfer roller 18 is grounded, a secondary transfer bias having the same polarity as the toner is applied to the hollow cored bar 12c of the secondary transfer counter roller 12. Thereby, in the secondary transfer nip N, a secondary transfer electric field for electrostatically moving the toner from the secondary transfer counter roller 12 side toward the secondary transfer roller 18 side is formed between both rollers. That is, the first bearing 52 that rotatably receives the metal through-shaft member 12a of the secondary transfer counter roller 12 is composed of a conductive slide bearing. The conductive first bearing 52 is connected to a high voltage power supply 61 serving as transfer means for outputting a secondary transfer bias. The secondary transfer bias output from the high voltage power supply 61 is supplied to the secondary transfer counter roller 12 via the conductive first bearing 52. In the secondary transfer counter roller 12, a metal penetrating shaft member 12a, a metal ball bearing 12e, a metal hollow core 12c, and a conductive elastic layer 12d are sequentially transmitted.

  The detected disk 59 fixed to one end of the through shaft member 12a has a test portion 59a that rises in the axial direction at a predetermined position in the rotation direction of the through shaft member 12a. On the other hand, an optical sensor 60 serving as a detection unit is fixed to the sensor bracket 501 fixed to the second side plate 29 of the transfer unit 7. When the penetrating shaft member 12a rotates and the penetrating shaft member 12a is positioned within a predetermined rotation angle range, the test portion 59a of the detected disk 59 enters between the light emitting element and the light receiving element of the optical sensor 60. The optical path between the two is blocked. When the light receiving element of the optical sensor 60 receives light from the light emitting element, it transmits a light reception signal to the control means 600.

  The control means 600 is constituted by a well-known computer, and here, in particular, the optical sensor 60 and the cam drive motor 58 are connected. The control means 600 operates the cam drive motor 58 by calculating the timing at which the light reception signal from the light receiving element of the optical sensor 60 stops and the drive amount of the cam drive motor 58 from that timing. Further, based on the calculated driving amount, the rotational angle positions of the cam portions 50a and 51a of the cams 50 and 51 fixed to the through shaft member 12a are detected, and the cams 50 and 51 are stopped at a predetermined position. It has a function.

The cams 50 and 51 abut against the secondary transfer roller 18 at a predetermined rotation angle, and push the secondary transfer roller 18 back in a direction away from the secondary transfer counter roller 12 against the urging force of the urging coil spring 71 (hereinafter referred to as “the secondary transfer roller 18”). , This pushback is referred to as "press down"). The amount of pushing back at this time (hereinafter referred to as “the amount of pushing down”) is determined by the rotational angle position of the cams 50 and 51. The greater the amount by which the secondary transfer roller 18 is pushed down by the cams 50 and 51, the greater the inter-axis distance L between the secondary transfer opposing roller 12 and the secondary transfer roller 18. In the secondary transfer roller 18, a first idling roller 34 is provided on the first shaft member 18 </ b> B that rotates integrally with the roller portion 18 </ b> A so as to idle. The first idling roller 34 has a donut disk shape whose outer diameter is slightly larger than that of the roller portion 18A.
And it has the function as a ball bearing itself, and can idle | slide on the surrounding surface of the 1st shaft member 18B. A second idling roller 35 having the same configuration as the first idling roller 34 is provided on the second shaft member 18C of the secondary transfer roller 18 so as to be idling. In the secondary transfer counter roller 12, the cams 50 and 51 fixed to the through shaft member 12a are arranged at the predetermined rotational angle positions so that the outer peripheral surfaces 50C and 51C of the cam portions 50A and 51A abut against the idle rollers 34 and 35, respectively. Is formed. Specifically, the cam portion 50 </ b> A of the first cam 50 fixed to one end side of the penetrating shaft member 12 a abuts on the first idling roller 34 of the secondary transfer roller 18. At the same time, the cam portion 51A of the second cam 51 fixed to the other end side of the penetrating shaft member 12a hits the second idling roller 35 of the secondary transfer roller 18. The idling rollers 34 and 35 abutted against the cams 50 and 51 are prevented from rotating along with the abutment, but the rotation of the secondary transfer roller 18 is not prevented thereby. Even if the idling rollers 34 and 35 stop rotating, the idling rollers are ball bearings, so that the shaft members 18B and 18C of the secondary transfer roller 18 freely rotate independently of the idling rollers 34 and 35. Because it can. By stopping the rotation of the idling rollers 34 and 35 in accordance with the abutment by the cam portions 50A and 51A of the cam, the occurrence of friction between the two is avoided, and the belt drive motor and the secondary transfer roller 18 caused by the friction are prevented. It is also possible to avoid an increase in torque of the drive motor.

  It is preferable to change the pressing amount according to the thickness of the transfer paper. In this printer, as shown in FIG. 11, a thickness information acquisition unit 700 for acquiring the thickness information of the transfer paper supplied to the secondary transfer nip N is provided. . As the thickness information acquisition unit 700, a thickness detection sensor that actually detects the thickness of the transfer paper conveyed in the paper feed path may be used, or a data input unit that receives thickness information data input from an operator. It may be used. Examples of the thickness detection sensor include an optical sensor that detects light transmittance in the thickness direction, and a sensor that detects the amount of roller movement when a sheet is sandwiched between a pair of conveyance rollers.

  The control unit 600 is configured to adjust the amount of depression of the secondary transfer roller 18 according to the acquisition result by the thickness information acquisition unit 700. More specifically, a data table indicating the relationship between the thickness information of the transfer paper and the corresponding rotation stop position (agreement with the amount of pressing down) of the penetrating shaft member 12a is stored in a data storage unit such as a ROM in the control unit 600. I am letting.

  The control means 600 specifies the rotation stop position corresponding to the transfer sheet thickness acquisition result from the data table. The cam drive motor 58 is operated to rotate the through shaft member 12a to the rotation stop position. As described above, in the present embodiment, the control unit 600 is configured to execute the process of causing the transfer sheet to enter the secondary transfer nip N after the stop positions of the multistage cams 50 and 51 are determined. . Thus, by setting a secondary transfer push-down amount suitable for the thickness of the transfer paper (setting the cam position), it is possible to suppress both a shock when entering the front end of the paper and a shock when releasing the push-down.

  As described above, the control means 600 can be configured so that the optical sensor 60 detects the rotation stop position of the penetrating shaft member 12a at the timing when the optical sensor 60 detects the detected portion 59a of the detected disk 59. Further, the control means 600 may be configured to perform based on the drive amount of the stepping motor that is the cam drive motor 58 from the timing at which the optical sensor 60 detects the detected portion 59a of the detected disk 59.

  In the present embodiment, the cams 50 and 51 that adjust the distance between the secondary transfer belt 204 wound around the secondary transfer roller 18 and the intermediate transfer belt 8 wound around the secondary transfer counter roller 12 are secondary transfer. The case where it arrange | positions to the opposing roller 12 side was shown. However, it is of course possible to adjust the surface distance between the secondary transfer belt 204 and the intermediate transfer belt 8 by other methods. For example, a pressing member may be provided on the roller unit holder 70 and the surface distance (interval X) between the secondary transfer belt 204 and the intermediate transfer belt 8 may be adjusted by the cams 50 and 51.

Next, features of the present embodiment will be described.
Conventionally, when the trailing edge of the transfer sheet P passes through the secondary transfer nip, the urging force of the urging coil spring 71 causes the secondary transfer roller 18 to move vigorously and hit the intermediate transfer belt 8. Shock jitter occurs on impact. Therefore, conventionally, when the trailing edge of the transfer paper P passes through the secondary transfer nip, the secondary transfer roller 18 is separated by a cam, and after the removal, the secondary transfer roller 18 is gradually brought closer by driving the cam. By doing so, the shock jitter when the transfer paper comes off was suppressed. However, in this case, if the separation operation is attempted to complete before the trailing edge of the transfer paper comes off, the transfer pressure when the image near the trailing edge of the image is secondarily transferred to the transfer paper becomes insufficient. White spots occur in the image at the trailing edge of the paper. Therefore, in this embodiment, the following configuration is adopted to suppress shock jitter when the transfer paper P passes through the secondary transfer nip, and when the rear end of the transfer paper passes through the secondary transfer nip. The secondary transfer roller 18 was not separated.

FIG. 12 is a schematic diagram for explaining the positional relationship between the secondary transfer roller 18 and the secondary transfer counter roller 12.
As shown in this figure, in this embodiment, the secondary transfer roller 18 as the first roller is offset from the secondary transfer counter roller 12 as the second roller on the upstream side in the transfer paper conveyance direction. doing. Specifically, the secondary transfer roller is more than a straight line that is orthogonal to the conveyance direction J after passing through the secondary transfer nip N of the transfer paper P and passes through the rotation center O1 of the secondary transfer counter roller 12. The 18 rotation centers O2 are located upstream in the transfer sheet conveyance direction. With such a configuration, after the trailing edge of the transfer paper P passes through the secondary transfer nip N, the secondary transfer roller 18 can be gradually brought closer to the secondary transfer counter roller 12. Thus, after the transfer paper P has passed through the secondary transfer nip N, the secondary transfer roller 18 can be prevented from striking the intermediate transfer belt 8 with the urging force of the urging coil spring 71, and the impact can be suppressed. Can be suppressed. As a result, shock jitter when the transfer paper P passes through the secondary transfer nip N can be suppressed.

This will be specifically described below with reference to FIG.
After the trailing edge of the transfer paper P passes through the secondary transfer nip, the transfer paper P is carried on the secondary transfer belt 204 and conveyed. As shown in FIG. 13A, when the trailing edge of the transfer paper P passes through the secondary transfer nip, the secondary transfer roller 18 tries to lift the secondary transfer belt 204 by the biasing force of the biasing coil spring. At this time, the trailing edge of the transfer paper that has passed through the secondary transfer nip hits a portion of the intermediate transfer belt 8 that is wound around the secondary transfer counter roller 12. Therefore, the movement of the secondary transfer roller 18 is restricted, and the secondary transfer roller 18 slightly moves toward the intermediate transfer belt. As shown in FIG. 13B, when the transfer paper P is further conveyed by the secondary transfer belt 204, the trailing edge of the transfer paper P is moved by the biasing force of the biasing coil spring 71 of the secondary transfer roller 18. Then, the intermediate transfer belt 8 moves along the winding portion of the secondary transfer counter roller 12. That is, the rear end of the transfer paper P is conveyed in a form that gradually rises along the curvature of the secondary transfer counter roller 12. As a result, the secondary transfer roller 18 gradually approaches the secondary transfer counter roller 12 as the transfer paper P is conveyed. Then, as shown in FIG. 13C, the transfer paper P is conveyed to a position H where the distance from the surface of the secondary transfer belt 204 to the intermediate transfer belt 8 is the same as the thickness of the transfer paper P. Then, the secondary transfer belt 204 contacts the intermediate transfer belt 8 with a predetermined pressure.

  In this way, the secondary transfer roller 18 is offset from the secondary transfer counter roller 12 on the upstream side in the transfer paper conveyance direction, so that the secondary transfer roller 18 is gradually moved as shown in FIG. It can be brought close to the secondary transfer counter roller 12. Thereby, after the transfer paper P passes through the secondary transfer nip N, the secondary transfer roller 18 can be prevented from strikingly striking the intermediate transfer belt 8 together with the secondary transfer belt 204. As a result, the shock jitter after the transfer paper P passes through the secondary transfer nip can be suppressed.

  Furthermore, in this embodiment, as described above, the intermediate transfer belt 8 has an elastic layer. As a result, when the secondary transfer roller 18 abuts against the intermediate transfer belt 8 together with the secondary transfer belt 204, the elastic layer of the intermediate transfer belt 8 acts as a cushion to reduce the impact. As a result, the shock jitter after the transfer paper P passes through the secondary transfer nip can be suppressed.

FIG. 14 shows the case where the leading edge of the transfer paper enters the secondary transfer nip N without performing the contact / separation operation by the cams 50 and 51 and the case where the trailing edge of the transfer paper passes through the secondary transfer nip N. It is the graph which investigated the vibration of the primary transfer part. 14A and 14B, the urging force of the urging coil spring 71 that urges the secondary transfer roller 18 is different from each other.
14A and 14B, the vibration of the primary transfer portion when the transfer paper P passes through the secondary transfer nip can be suppressed to an allowable value or less. The allowable value is the vibration of the primary transfer portion when the shock jitter is at the allowable level.

  In this embodiment, the intermediate transfer belt 8 is provided with an elastic layer, but the secondary transfer belt 204 may be provided with an elastic layer. Further, an elastic layer may be provided on both the intermediate transfer belt 8 and the secondary transfer belt 204. By providing an elastic layer on both the intermediate transfer belt 8 and the secondary transfer belt 204, it is possible to further reduce the impact when the secondary transfer roller 18 hits the intermediate transfer belt 8 together with the secondary transfer belt 204. . Thereby, it is possible to further suppress the shock jitter when the transfer paper P passes through the secondary transfer nip.

  Further, the natural frequency of the intermediate transfer belt 8 may be separated from the frequency of vibration caused by impact when the secondary transfer roller 18 hits the intermediate transfer belt 8 together with the secondary transfer belt 204. Specifically, by devising the circumference of the intermediate transfer belt 8 and the like, the natural frequency of the intermediate transfer belt 8 is set so that the secondary transfer roller 18 hits the intermediate transfer belt 8 together with the secondary transfer belt 204. Can be separated from shock frequency. This also can suppress shock jitter when the transfer paper P passes through the secondary transfer nip.

FIG. 15 is a diagram illustrating an example of a timing chart of secondary transfer.
As shown in FIG. 15, before the transfer paper enters the secondary transfer nip N, the control unit 600 drives the cams 50 and 51 to contact the secondary transfer roller 18, thereby causing the secondary transfer belt 204 to move. It is separated from the intermediate transfer belt 8. Then, immediately before the transfer paper P enters the secondary transfer nip N, the control unit 600 drives the cams 50 and 51, and when the image on the intermediate transfer belt 8 enters the secondary transfer nip N, the cam 50 and 51 are separated from the secondary transfer roller 18. Thereby, when the image is secondarily transferred to the transfer paper P, a predetermined transfer pressure can be obtained, and a good image can be obtained without white spotting or the like at the leading edge of the image. When the leading edge of the transfer paper P enters the secondary transfer nip, the cams 50 and 51 are in contact with the secondary transfer roller 18, and the secondary transfer belt 204 is separated from the intermediate transfer belt 8. . Therefore, load fluctuation when the leading edge of the transfer paper P enters the secondary transfer nip N is suppressed, and shock jitter when the transfer paper P enters can be suppressed.

  Further, in this embodiment, as described above, the shock jitter when the transfer paper P passes through the secondary transfer nip N is suppressed to an allowable level or less. Therefore, it is not necessary to drive the cams 50 and 51 to move the secondary transfer roller 18 away from the intermediate transfer belt 8 when the trailing edge of the transfer paper comes out. Thereby, the rear end of the image can be secondarily transferred onto the transfer paper P with a predetermined transfer pressure. Therefore, it is possible to prevent the occurrence of secondary transfer defects such as a drop in the transfer pressure and the occurrence of white spots in the image during secondary transfer at the rear end of the image.

  When the toner pattern formed between the sheets is secondarily transferred to the secondary transfer belt 204, the cams 50 and 51 are driven to bring the cams 50 and 51 into contact with the secondary transfer roller 18 and the secondary transfer belt 204 is driven. The transfer belt 204 is separated from the intermediate transfer belt 8.

  When the toner pattern transferred to the secondary transfer belt 204 is the gradation pattern shown in FIG. 6 or the color misregistration detection image shown in FIG. 7, the toner pattern is detected by the optical sensor 151. When the cam contact / separation operation is started, the following problems occur. That is, there is a problem in that the toner pattern may not be detected with high accuracy due to vibration caused by the cam contact / separation operation, the tilt angle of the sensor, and the focal length. Accordingly, as shown in FIG. 16, after the detection of the toner pattern on the secondary transfer belt 204 by the optical sensor is completed, the cams 50 and 51 are driven to move the secondary transfer belt 204 from the intermediate transfer belt 8. It may be separated. As a result, vibration due to the cam contact / separation operation and fluctuation of the tilt angle and focal length of the sensor can be eliminated, and the toner pattern can be detected with high accuracy. As a result, various feedbacks can be performed with high accuracy.

FIG. 17 is a diagram comparing the sheet interval time between the conventional printer and the printer of this embodiment.
Conventionally, shock jitter occurs when the transfer paper passes through the secondary transfer nip. Therefore, in order to suppress this shock jitter, when the transfer sheet passes through the secondary transfer nip, the cam is driven to separate the secondary transfer belt 204 from the intermediate transfer belt 8. Accordingly, in order to secondarily transfer the toner pattern formed between the sheets to the secondary transfer belt 204, the cams 50 and 51 are driven immediately after the separation operation, and the secondary transfer belt 204 is intermediately moved at a predetermined transfer pressure. It is brought into contact with the transfer belt 8. After the secondary transfer belt 204 comes into contact with the intermediate transfer belt 8 with a predetermined transfer pressure, the toner pattern needs to enter the secondary transfer nip. There is an interval.

  On the other hand, in the present embodiment, as described above, when the transfer paper passes through the secondary transfer nip, the shock jitter is suppressed to an allowable level or less even if the secondary transfer belt 204 is not separated from the intermediate transfer belt 8. be able to. Accordingly, as shown in FIG. 17B, the secondary transfer belt 204 can be kept in contact with the intermediate transfer belt 8 even when the transfer paper passes through the secondary transfer nip. Therefore, compared to the conventional configuration in which the secondary transfer belt 204 once separated from the intermediate transfer belt 8 is once again brought into contact with the intermediate transfer belt 8 with a predetermined transfer pressure, and then the toner pattern enters the secondary transfer nip. The interval from the trailing edge of the transfer paper to the leading edge of the toner pattern can be shortened. Thereby, productivity can be improved compared with the conventional printer.

What has been described above is an example, and the present invention has a specific effect for each of the following aspects.
(Aspect 1)
An image carrier such as an endless belt-like intermediate transfer belt 8 that is rotatably stretched by stretching members such as a plurality of stretching rollers, and biasing means (in this embodiment, a biasing coil spring 71, a roller unit holding member) And the secondary transfer belt 204 that forms a transfer nip by being abutted against the front surface which is the outer peripheral surface of the image carrier. And a separating means 500 for separating the transfer member from the image carrier against the urging force of the urging means, and the toner image carried on the front surface of the image carrier is sandwiched in the transfer nip. Prior to the transfer material entering the transfer nip, the transfer member is moved away from the image carrier, and the transfer material is transferred to the transfer nip. After entering, move away. In an image forming apparatus such as a printer that includes a control unit 600 that controls the separation unit so as to remove the elastic member, an elastic layer is provided on the image carrier and / or the transfer member, and the control unit 600 passes the transfer material through the transfer nip. After that, the separating unit 500 is controlled so that the transfer member is separated from the image carrier before the next transfer material enters the transfer nip.
As described above, the shock jitter when the trailing edge of the transfer material such as transfer paper passes through the transfer nip such as the secondary transfer nip is vigorous due to the biasing force of the biasing means when the transfer material passes through the transfer nip. The transfer member moves and hits an image carrier such as an intermediate transfer belt. The impact at that time becomes a shock jitter, which affects the image.
Therefore, in (Aspect 1), an elastic layer is provided on the image carrier and / or the transfer member. Thus, after the transfer material has passed through the transfer nip, the elastic force of the image carrier and / or the transfer member when the transfer member abuts against the image carrier such as the intermediate transfer belt 8 by the urging force of the urging means. The layer acts as a cushion and reduces the impact force. Thereby, shock jitter when the transfer material passes through the transfer nip can be suppressed. As a result, it is not necessary to separate the transfer member from the image carrier by the separating means until the transfer material passes through the transfer nip. Therefore, it is possible to employ a configuration in which the transfer member is separated from the image carrier after the transfer material has passed through the transfer nip. By adopting this configuration, it is possible to maintain a sufficient transfer pressure until the transfer material passes through the transfer nip, and it is possible to prevent white spots from occurring at the trailing edge of the image.

(Aspect 2)
An image carrier such as an endless belt-like intermediate transfer belt 8 that is rotatably supported by a plurality of stretching rollers, and an urging means (in this embodiment, an urging coil spring 71, a roller unit holding body 70, and a roller A secondary transfer belt which is urged by a rotation shaft 70a of the unit holder 70 and abuts against a front surface which is an outer peripheral surface of the image carrier to form a transfer nip such as a secondary transfer nip N A transfer member such as 204 and a separating unit 500 for separating the transfer member from the image carrier against the urging force of the urging unit, and a toner image carried on the front surface of the image carrier is placed in the transfer nip. The transfer member is separated from the image carrier before the transfer material enters the transfer nip and the transfer device such as the secondary transfer device 200 for transferring to the sandwiched transfer material, and the transfer material enters the transfer nip. Release the separation In the image forming apparatus such as a printer having the control unit 600 for controlling the separation unit 500, the transfer member is rotated by a plurality of stretching rollers so as to carry and transfer the transfer material that has passed through the transfer nip. An endless belt stretched in a possible manner, one of a plurality of stretching rollers (secondary transfer roller 18 in the present embodiment) that stretches a transfer member, and a tension belt that stretches an image carrier. A transfer nip is formed by sandwiching the image carrier and the transfer member with one of the rollers (secondary transfer counter roller 12 in the present embodiment), and the rotation axis direction of the tension roller that stretches the transfer member When viewed from above, the tension of the transfer member that forms the transfer nip is perpendicular to the direction in which the transfer material exits the transfer nip and passes through the center of the rotation axis of the tension roller of the image carrier that forms the transfer nip. Rotating roller The control unit 600 is configured so that the center is positioned on the upstream side in the transfer material conveyance direction, and the control unit 600 waits until the next transfer material enters the transfer nip after passing through the transfer nip. The separation unit 500 is controlled so that the transfer member is separated from the first member.
According to (Aspect 2), as described with reference to FIG. 13, the tension of the image carrier that forms a transfer nip is perpendicular to the direction in which the transfer material such as the transfer paper P passes through the transfer nip. The rotation axis center of the tension roller (secondary transfer roller 18 in this embodiment) of the transfer member that forms the transfer nip rather than the line passing through the rotation axis center of the roller (secondary transfer counter roller 12 in this embodiment). However, shock jitter can also be suppressed by configuring it so as to be located upstream of the transfer material conveyance direction. As described above with reference to FIG. 13, even after the transfer material passes through the transfer nip, the rear end of the transfer material comes into contact with the portion where the secondary transfer counter roller 12 of the image carrier is wound. The secondary transfer roller 18 is restricted from moving toward the secondary transfer counter roller. Thereafter, the transfer material carried on the transfer member and conveyed is moved while the rear end thereof is in contact with the portion of the image carrier wound around the secondary transfer counter roller 12 by the urging force of the urging means. That is, it moves along the curvature of the secondary transfer counter roller 12. As a result, the position of the trailing edge of the transfer sheet gradually rises, and the secondary transfer roller 18 gradually approaches together with the transfer member along with that, and finally the transfer member comes into contact with the intermediate transfer belt 8. Thus, the transfer member and the secondary transfer roller can be prevented from striking against the image bearing member, and shock jitter when the transfer material passes through the transfer nip can be suppressed. As a result, it is not necessary to separate the transfer member from the image carrier by the separating means until the transfer material passes through the transfer nip. Therefore, it is possible to employ a configuration in which the transfer member is separated from the image carrier after the transfer material has passed through the transfer nip. By adopting this configuration, it is possible to maintain a sufficient transfer pressure until the transfer material passes through the transfer nip, and it is possible to prevent white spots from occurring at the trailing edge of the image.

(Aspect 3)
In (Aspect 1), the transfer member is rotatably stretched by a plurality of tension rollers so as to carry and transfer a transfer material such as transfer paper P that has passed through the transfer nip such as the secondary transfer nip N. An endless belt, one of a plurality of stretching rollers (secondary transfer roller 18 in the present embodiment) that stretches a transfer member, and a stretching roller that stretches an image carrier such as the intermediate transfer belt 8 A transfer nip is formed by sandwiching the image carrier and the transfer member with one of them (secondary transfer counter roller 12 in this embodiment), and viewed from the direction of the rotation axis of the stretching roller that stretches the transfer member. The transfer member stretching roller that forms the transfer nip is perpendicular to the direction in which the transfer material passes through the transfer nip and passes through the rotation axis of the stretching roller of the image carrier that forms the transfer nip. The rotation axis center of the Configured so as to be positioned on improving flow side.
With this configuration, as described in (Aspect 2), it is possible to suppress shock jitter when the transfer material such as the transfer paper P passes through the transfer nip such as the secondary transfer nip N. Thereby, the shock jitter when the transfer material passes through the transfer nip can be further suppressed.

(Aspect 4)
In (Aspect 1) to (Aspect 3), the transfer member is an endless belt that is rotatably stretched by a plurality of tension rollers, and after the rear end of the transfer material has passed through the transfer nip, the separating means Thus, the toner pattern is transferred to the transfer member until the transfer member is separated from the image carrier.
As described above, when the transfer sheet passes through the secondary transfer nip, unlike the conventional configuration, the secondary transfer belt 204 is not separated from the intermediate transfer belt 8. Accordingly, as described with reference to FIG. 17, the distance from the trailing edge of the transfer paper to the leading edge of the toner pattern can be made shorter than in the conventional configuration. As a result, compared to the conventional configuration, it is possible to shorten the paper interval when transferring the toner pattern to the transfer member, and it is possible to suppress a decrease in productivity.

(Aspect 5)
In (Aspect 4), the control unit includes a detection unit such as an optical sensor 151 that is disposed to face the front surface of the transfer member such as the secondary transfer belt 204 and detects the toner pattern transferred to the transfer member. After the detection unit detects the toner pattern, 600 controls the separation unit 500 to separate the transfer member from the image carrier such as the intermediate transfer belt 8.
According to (Aspect 5), as described with reference to FIG. 16, the toner pattern can be detected with high accuracy by the detection unit.

(Aspect 6)
An intermediate transfer belt 8, a transfer member that is urged by a spring 71 and abuts against the intermediate transfer belt 8 to form a transfer nip for transferring a toner image on the intermediate transfer belt 8 to a paper such as a transfer paper, and a transfer member Between the intermediate transfer belt 8 and the cams 50 and 51 for separating the intermediate transfer belt 8 from the intermediate transfer belt 8 until the next paper enters the transfer nip. And a control means 600 for controlling the rotations of 50 and 51, and an elastic layer is provided on the intermediate transfer belt 8 and / or the transfer member.
According to (Aspect 6), after the paper has passed through the transfer nip, when the transfer member urges against the intermediate transfer belt 8 with the urging force of the spring, the intermediate transfer belt 8 and / or the elastic layer of the transfer member is Acts as a cushion and reduces impact force. Thereby, it is possible to suppress shock jitter when the paper passes through the transfer nip. As a result, the transfer member need not be separated from the intermediate transfer belt 8 by the cams 50 and 51 until the paper passes through the transfer nip. Therefore, it is possible to employ a configuration in which the transfer member is separated from the intermediate transfer belt 8 after the paper passes through the transfer nip. By adopting this configuration, it is possible to maintain a sufficient transfer pressure until the paper passes through the transfer nip, and it is possible to prevent white spots from occurring at the trailing edge of the image.

(Aspect 7)
In (Aspect 6), the transfer member is a secondary transfer roller.
Even if the transfer member is a secondary transfer roller, the elastic layer of the intermediate transfer belt 8 and / or the secondary transfer roller can act as a cushion to reduce the impact force, and the effect described in (Aspect 6) can be obtained. be able to.

(Aspect 8)
In (Aspect 6), the transfer member is the secondary transfer belt 204.
Even if the transfer member is used as the secondary transfer belt 204, the elastic layer of the intermediate transfer belt 8 and / or the secondary transfer belt 204 can act as a cushion, and the impact force can be reduced. Can be obtained.

(Aspect 9)
In (Aspect 8), the first roller such as the secondary transfer roller 18 among the plurality of rollers that stretch the secondary transfer belt 204 and the secondary of the plurality of rollers that stretch the intermediate transfer belt 8. A transfer nip is formed by sandwiching the intermediate transfer belt 8 and the secondary transfer belt 204 with a second roller such as the transfer counter roller 12, and the secondary transfer belt 204 forms an intermediate transfer belt downstream of the transfer nip. Via the second roller.
According to (Aspect 9), as described above with reference to FIG. 13, when the paper such as the transfer paper passes through the transfer nip, the first roller such as the secondary transfer roller 18 is gradually subjected to the secondary transfer. The second roller such as the facing roller 12 can be approached. Thereby, it is possible to suppress the secondary transfer belt 204 from striking against the intermediate transfer belt 8 together with the first roller, and it is possible to suppress shock jitter when the paper passes through the transfer nip.

(Aspect 10)
In any one of (Aspect 6) to (Aspect 9), a toner pattern is formed on the transfer member after the trailing edge of the paper passes through the transfer nip and until the transfer member is separated from the intermediate transfer belt 8 by the cams 50 and 51. Transcript.
According to (Aspect 10), unlike the conventional configuration, the transfer member is not separated from the intermediate transfer belt 8 when the rear end of the paper passes through the transfer nip. Therefore, the distance from the trailing edge of the transfer paper to the leading edge of the toner pattern can be made shorter than in the conventional configuration. As a result, compared to the conventional configuration, it is possible to shorten the paper interval when transferring the toner pattern to the transfer member, and it is possible to suppress a decrease in productivity.

(Aspect 11)
In (Aspect 10), the optical sensor 151 that detects the toner pattern transferred to the transfer member is provided, and the control unit 600 separates the transfer member from the intermediate transfer belt 8 after the optical sensor 151 detects the toner pattern.
According to (Aspect 11), as described with reference to FIG. 16, the toner pattern can be detected with high accuracy by the optical sensor 151.

(Aspect 12)
In any one of (Aspect 6) to (Aspect 11), the control unit 600 separates the transfer member from the intermediate transfer belt 8 before the paper enters the transfer nip, and after the paper enters the transfer nip, The rotation of the cams 50 and 51 is controlled so as to release the separation.
According to (Aspect 12), as described in the embodiment, it is possible to suppress shock jitter when the leading edge of the paper enters the transfer nip. Further, after the paper enters the transfer nip, the toner image on the intermediate transfer belt 8 can be transferred to the paper with a predetermined transfer pressure, and transfer defects can be suppressed.

(Aspect 13)
A secondary transfer belt 204 that is urged by a spring 71 and abuts against the intermediate transfer belt 8 to form a transfer nip for transferring a toner image on the intermediate transfer belt 8 to paper; a secondary transfer; The secondary transfer belt 204 is separated from the intermediate transfer belt 8 between the cams 50 and 51 for separating the belt 204 from the intermediate transfer belt 8 and the time from when the paper passes through the transfer nip until the next paper enters the transfer nip. A control means 600 for controlling the rotation of the cams 50 and 51, a first roller such as the secondary transfer roller 18 among a plurality of rollers for stretching the secondary transfer belt 204, and an intermediate transfer A transfer nip is formed by sandwiching the intermediate transfer belt 8 and the secondary transfer belt 204 with a second roller such as the secondary transfer counter roller 12 among a plurality of rollers that stretch the belt 8. Transfer belt 204 is provided so as winding around the second roller via the intermediate transfer belt 8 on the downstream side of the transfer nip.
According to (Aspect 13), as described with reference to FIG. 13, when the paper passes through the transfer nip, the first transfer roller 18 or the like is gradually moved to the secondary transfer counter roller 12 or the like. The second roller can be approached. Thereby, it is possible to suppress the secondary transfer belt 204 from striking against the intermediate transfer belt 8 together with the first roller, and it is possible to suppress shock jitter when the paper passes through the transfer nip.

(Aspect 14)
In (Aspect 13), the toner pattern is applied to the secondary transfer belt 204 after the trailing edge of the paper passes through the transfer nip and before the secondary transfer belt 204 is separated from the intermediate transfer belt 8 by the cams 50 and 51. Transcript.
According to (Aspect 13), unlike the conventional configuration, the transfer member is not separated from the intermediate transfer belt 8 when the trailing edge of the paper passes through the transfer nip. Therefore, the distance from the trailing edge of the transfer paper to the leading edge of the toner pattern can be made shorter than in the conventional configuration. As a result, compared to the conventional configuration, it is possible to shorten the paper interval when transferring the toner pattern to the transfer member, and it is possible to suppress a decrease in productivity.

(Aspect 15)
In (Aspect 14), the optical sensor 151 that detects the toner pattern transferred to the secondary transfer belt 204 is provided, and the control unit 600 performs intermediate transfer of the secondary transfer belt 204 after the optical sensor 151 detects the toner pattern. Separate from the belt 8.
According to (Aspect 15), as described with reference to FIG. 16, the toner pattern can be detected with high accuracy by the optical sensor 151.

(Aspect 16)
In any one of (Aspect 13) to (Aspect 15), the control unit 600 separates the transfer member from the intermediate transfer belt 8 before the paper enters the transfer nip, and after the paper enters the transfer nip, the controller 600 separates the transfer member. The rotation of the cams 50 and 51 is controlled so as to release the.
According to (Aspect 16), as described in the embodiment, shock jitter can be suppressed when the leading edge of the paper enters the transfer nip. Further, after the paper enters the transfer nip, the toner image on the intermediate transfer belt 8 can be transferred to the paper with a predetermined transfer pressure, and transfer defects can be suppressed.

7: transfer unit 8: intermediate transfer belt 9Y, M, C, K: primary transfer roller 10: driven roller 11: drive roller 12: secondary transfer counter rollers 13, 14, 15: cleaning counter roller 16: tension roller 17: Application brush opposing roller 18: secondary transfer rollers 50, 51: cam 70: roller unit holder 70a: rotating shaft 71: biasing coil spring 150: optical sensor units 151Y, 151M, 151C, 151K: optical sensor 200: secondary Transfer device 204: Secondary transfer belt 500: Separating means 600: Control means N: Secondary transfer nip O1: Rotation center of secondary transfer counter roller O2: Rotation center of secondary transfer roller P: Transfer paper

JP 2012-18369 A

Claims (13)

An endless belt-like image carrier that is rotatably supported by a plurality of stretching rollers;
A transfer member that is urged by the urging means and abuts against a front surface that is an outer peripheral surface of the image carrier to form a transfer nip, and the transfer member resists the urging force of the urging means. A transfer device having a separating means for separating from the carrier, and transferring the toner image carried on the front surface of the image carrier to a transfer material sandwiched in a transfer nip;
Prior to the transfer material entering the transfer nip, the transfer member is separated from the image carrier, and the separation means is controlled to release the separation after the transfer material enters the transfer nip. And an image forming apparatus including a control unit.
The transfer member is an endless belt that is rotatably stretched by a plurality of stretching rollers so as to carry and convey the transfer material that has passed through the transfer nip,
The transfer nip is sandwiched between the image carrier and the transfer member by one of a plurality of tension rollers that stretch the transfer member and one of the tension rollers that stretch the image carrier. Formed,
Rotation of the tension roller of the image carrier that forms a transfer nip perpendicular to the direction in which the transfer material exits the transfer nip when viewed from the rotation axis direction of the tension roller that stretches the transfer member The rotation shaft center of the stretching roller of the transfer member forming the transfer nip is located on the upstream side in the transfer material conveyance direction with respect to the line passing through the shaft center,
The control means maintains the release of the separation means until the transfer material passes through the transfer nip, and after the transfer material passes through the transfer nip, the next transfer material enters the transfer nip. The image forming apparatus is characterized in that the separation unit is controlled so that the transfer member is separated from the image carrier. The image forming apparatus according to claim 1 ,
From the rear end of the front Symbol transfer material exits the transfer nip, between from said image bearing member by said separating means to said transfer member is separated, characterized in that to transfer the toner pattern on the transfer member Image forming apparatus. The image forming apparatus according to claim 2 ,
A detecting unit disposed opposite to the front surface of the transfer member and detecting a toner pattern transferred to the transfer member;
The image forming apparatus according to claim 1, wherein the control unit controls the separation unit to separate the transfer member from the image carrier after the detection unit detects a toner pattern. An intermediate transfer belt;
A transfer member that is biased by a spring and contacts the intermediate transfer belt to form a transfer nip for transferring the toner image on the intermediate transfer belt to paper;
A cam for separating the transfer member from the intermediate transfer belt;
The separation of the transfer member from the intermediate transfer belt is released until the paper passes through the transfer nip, and the paper passes from the transfer nip until the next paper enters the transfer nip. Control means for controlling the rotation of the cam so as to separate the transfer member from the intermediate transfer belt,
An elastic layer is provided on the intermediate transfer belt and / or the transfer member,
The transfer member is an endless belt that is rotatably stretched by a plurality of stretching rollers so as to carry and convey the transfer material that has passed through the transfer nip,
When viewed from the direction of the rotation axis of the tension roller that stretches the transfer member, the rotation axis of the tension roller of the intermediate transfer belt is perpendicular to the direction in which the paper exits the transfer nip and forms the transfer nip. An image forming apparatus, characterized in that the center of the rotation axis of the tension roller of the transfer member forming the transfer nip is located on the upstream side in the paper conveyance direction with respect to the line passing through the center .   The image forming apparatus according to claim 4, wherein the transfer member is a secondary transfer belt. The intermediate transfer belt and the secondary transfer include a first roller of a plurality of rollers that stretch the secondary transfer belt and a second roller of the plurality of rollers that stretch the intermediate transfer belt. The transfer nip is formed across a belt,
6. The image forming apparatus according to claim 5, wherein the secondary transfer belt is provided so as to be wound around the second roller via the intermediate transfer belt on the downstream side of the transfer nip.   5. The toner pattern is transferred to the transfer member after the trailing edge of the paper passes through the transfer nip and before the transfer member is separated from the intermediate transfer belt by the cam. The image forming apparatus according to claim 6. An optical sensor for detecting the toner pattern transferred to the transfer member;
The image forming apparatus according to claim 7, wherein the control unit separates the transfer member from the intermediate transfer belt after the optical sensor detects a toner pattern.   The control means separates the transfer member from the intermediate transfer belt before the paper enters the transfer nip, and rotates the cam so as to release the separation after the paper enters the transfer nip. 9. The image forming apparatus according to claim 4, wherein the image forming apparatus is controlled. An intermediate transfer belt;
A secondary transfer belt that is biased by a spring and abuts against the intermediate transfer belt to form a transfer nip for transferring the toner image on the intermediate transfer belt to paper;
A cam for separating the secondary transfer belt from the intermediate transfer belt;
The separation of the secondary transfer belt from the intermediate transfer belt is released until the paper passes through the transfer nip, and after the paper passes through the transfer nip until the next paper enters the transfer nip. Control means for controlling the rotation of the cam so that the secondary transfer belt is separated from the intermediate transfer belt,
The intermediate transfer belt and the secondary transfer include a first roller of a plurality of rollers that stretch the secondary transfer belt and a second roller of the plurality of rollers that stretch the intermediate transfer belt. The transfer nip is formed across a belt,
The image forming apparatus, wherein the secondary transfer belt is provided to be wound around the second roller via the intermediate transfer belt on the downstream side of the transfer nip.   A toner pattern is transferred to the secondary transfer belt after the trailing edge of the paper passes through the transfer nip and before the secondary transfer belt is separated from the intermediate transfer belt by the cam. The image forming apparatus according to claim 10. An optical sensor for detecting a toner pattern transferred to the secondary transfer belt;
The image forming apparatus according to claim 11, wherein the control unit separates the secondary transfer belt from the intermediate transfer belt after the optical sensor detects a toner pattern.   The control means separates the secondary transfer belt from the intermediate transfer belt prior to the paper entering the transfer nip, and releases the separation after the paper enters the transfer nip. The image forming apparatus according to claim 10, wherein the rotation of the image forming apparatus is controlled.

Images