JP2012098613A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of changing over between standard picture quality and high picture quality and of prolonging service life of a component of a fixing device.SOLUTION: An image forming device comprises: an image carrier for carrying a toner image; an intermediate transfer body for primarily transferring the toner image carried on the image carrier; a repulsion member for applying an electric field so as to move the toner image transferred to the intermediate transfer body to a transfer paper sheet; a secondary transfer member for pressing the repulsion member at a position opposite to the repulsion member through the intermediate transfer body; and secondary transfer member compression means for compressing a secondary transfer member. The secondary transfer member includes a plurality of shaft sections having different outer diameters from one another at both ends thereof in a longitudinal direction. The secondary transfer member compression means is capable of changing over compressing positions with respect to the plurality of shaft sections.

Description

  The present invention relates to an image forming apparatus capable of switching between standard image quality and high image quality and capable of extending the life of components of a fixing device.

  In an electrophotographic image forming apparatus, toner is transferred onto paper at an intermediate transfer unit, and then the toner is fixed at a fixing unit to output a printed copy. From the user, various paper types on the market are used. Therefore, it is desired to perform printing with stable image quality.

  In the on-demand printing field, a technology has been developed to print images in good condition on a paper surface with various irregularities by applying a high pressure in the paper transfer process. Yes.

  However, the conventional secondary transfer high pressure applying mechanism employs large parts and a complicated apparatus configuration in order to achieve both strength and accuracy. For this reason, the price is expensive, and it is difficult for general users to obtain an inexpensive image forming apparatus capable of high-quality printing.

  Inexpensive image forming apparatuses often have to adopt a simple configuration, but the high-pressure secondary transfer high-pressure application mechanism cannot be adopted because of its complicated configuration. For this reason, the image quality of an inexpensive image forming apparatus becomes general. For these reasons, it is difficult to obtain high-quality image quality for an image forming apparatus that employs a simple configuration.

  Further, an image forming apparatus capable of switching on-demand image quality in which a user designates high-quality image quality only for a specific paper type requires a complicated configuration as described above, and is expensive. It becomes. This is also difficult for users to get.

  The following is a conventional technique capable of switching the image quality on demand.

  Patent Document 1 describes a technique related to a nip pressure distribution varying unit in a fixing device. Specifically, the pressure distribution is made uniform by providing a plurality of support members inside the pressure roller and moving the positions of the support members.

  According to the technique of Patent Document 1, even if the fixing load is increased or decreased in accordance with the thickness of the recording material or the finished gloss state, there is no reduction in gloss, uneven gloss, uneven fixing, insufficient fixing strength, wrinkles, etc. Can be provided, and an image forming apparatus having the fixing device can be provided.

  However, the following problems exist in the above-described prior art.

  The technique described in Patent Document 1 has a nip pressure distribution varying unit of the fixing device and makes the nip pressure uniform, but there is a problem that the component configuration is complicated and a simple component configuration cannot be realized. To do.

  Further, in connection with the above problem, there is a problem that a simple component configuration cannot be realized in the mode selection of the nip pressure of the fixing device.

  The present invention has been made in view of the above problems, and can switch between the standard image quality mode and the high image quality mode with a simple device configuration of the secondary transfer unit, and the length of parts of the fixing device. An object of the present invention is to provide an image forming apparatus capable of extending the service life.

  The image forming apparatus according to the present invention includes an image carrier that carries a toner image, an intermediate transfer member that primarily transfers the toner image of the image carrier, and the toner image transferred to the intermediate transfer member. A repulsive member that applies an electric field for moving the repulsive member, a secondary transfer member that presses the repulsive member at a position facing the repulsive member via the intermediate transfer member, and the secondary transfer member. Secondary transfer member pressurizing means for pressing, and the secondary transfer member includes a plurality of shaft portions having different outer diameters at both ends in the longitudinal direction, and the secondary transfer member pressurizing means includes the plurality of shafts. It is possible to switch the pressure position with respect to the part.

  According to the present invention, there is provided an image forming apparatus capable of switching between a standard image quality mode and a high image quality mode with a simple apparatus configuration of a secondary transfer unit and extending the life of components of a fixing device. can do.

FIG. 2 is a configuration diagram of a secondary transfer unit of the image forming apparatus according to the embodiment of the present invention. FIG. 2 is a configuration diagram of a secondary transfer unit of the image forming apparatus according to the embodiment of the present invention. 1 is an overall schematic diagram of an image forming apparatus according to an embodiment of the present invention. It is a block diagram of the repulsion roller which concerns on embodiment of this invention. It is a figure which shows distribution of the nip pressure of the secondary transfer part which concerns on embodiment of this invention. 5 is a flowchart illustrating control of the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 3 is an overall schematic diagram of the entire image forming apparatus according to the present embodiment. First, the configuration and operation outline of the image forming apparatus (tandem type color copying machine) according to the present embodiment will be described.

  An image forming apparatus (color copying machine 1) according to the present embodiment includes an image forming unit 1A located at the center of the apparatus main body, a paper feeding unit 1B located below the image forming unit 1A, and an image forming unit 1A. It has a document conveying section 1C and a scanner section 1D located above.

  An intermediate transfer belt 21 as an intermediate transfer member having a transfer surface extending in the horizontal direction is disposed in the image forming unit 1A, and an image of a color having a complementary color relationship with the color separation color is disposed on the upper surface of the intermediate transfer belt 21. The structure for forming is provided. That is, the photoreceptors 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the intermediate transfer belt 21. Has been.

  Each of the photoreceptors 3Y, 3M, 3C, and 3B is configured by a drum that can rotate in the same direction (counterclockwise direction), and around the charging device 4Y that performs image forming processing in the rotation process, 4M, 4C, 4B, developing devices 8Y, 8M, 8C, 8B, primary transfer rollers 7Y, 7M, 7C, 7B, and photoreceptor cleaning devices 6Y, 6M, 6C, 6B are arranged. An exposure device 5 is disposed above the image forming unit 1A.

  Each developing device 8Y, 8M, 8C, and 8B contains respective color toners. The intermediate transfer belt 21 has a configuration that is wound around the driving roller 2B and the driven roller 2A and can move in the same direction at a position facing the photoconductors 3Y, 3M, 3C, and 3B.

  An intermediate transfer belt cleaning device 10 for cleaning the surface of the intermediate transfer belt 21 is provided at a position facing the driven roller 2A.

  The surface of the photoreceptor 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photoreceptor 3Y based on image information from the scanner unit 1D. The electrostatic latent image is visualized as a toner image by a developing device 8Y containing yellow toner, and the toner image is primary-transferred onto the intermediate transfer belt 21 by a primary transfer device 7Y to which a predetermined bias is applied. Transcribed.

  The other photoconductors 3M, 3C, and 3B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 21 and superimposed. After the transfer, the toner remaining on the photoreceptors 3Y, 3M, 3C, and 3B is removed by the photoreceptor cleaning devices 6Y, 6M, 6C, and 6B. The potentials of the photoreceptors 3Y, 3M, 3C, and 3B are initialized by a charge removal lamp (not shown) and are prepared for the next image forming process.

  The paper feed unit 1B separates and feeds a paper feed tray 1B1 for stacking and storing papers as recording media one by one from the top of the paper P in the paper feed tray 1B1 (not shown) ), A pair of conveyance rollers 1B2 for conveying the fed paper, and after the paper is temporarily stopped and the oblique deviation is corrected, the leading edge of the image on the intermediate transfer belt 21 coincides with a predetermined position in the conveyance direction. It has a registration roller pair 1B3 that is sent out toward the nip at timing.

  A sensor (not shown) for detecting the reflectance of the paper surface is provided upstream of the registration roller pair 1B3. When the value is different from the sensor output in the previous process, the intermediate transfer belt 21 or the repulsive roller 2C is switched.

  A toner image (hereinafter referred to as toner) primarily transferred from the photoreceptors 3Y, 3M, 3C, and 3B onto the intermediate transfer belt 21 includes a bias (AC, pulse, etc.) superimposed by a secondary transfer bias applying unit (not shown). ) Is applied to the repulsive roller 2C, and is secondarily transferred onto the sheet by the action of an electric field with the secondary transfer roller 9B via the intermediate transfer belt 21.

  Thereafter, the sheet on which the toner is secondarily transferred to the surface is firmly fixed on the surface by the action of heat and pressure in the fixing device 11, and is discharged from the discharge tray 13 through the discharge roller 12.

  Other configurations include a manual feed tray 1A1, a separation roller 1A2, a contact glass 1C1, a document table 1C3, a transport belt 9A, a transport drive roller 9C, and a double-sided image forming apparatus 20.

  In the present embodiment, the primary transfer unit is configured such that a (+) transfer bias roller (not shown) is inserted from the back surface of the intermediate transfer belt 21 through a bearing (not shown) and a compression spring (not shown) through the intermediate transfer belt 21. The photoconductors 3Y, 3M, 3C and 3B are pressed by a predetermined pressure.

  (+) The position of the transfer bias roller in contact with the intermediate transfer belt 21 needs to be set so as to contact a position offset by 1 to 2 mm downstream from the center position of the photoreceptors 3Y, 3M, 3C, and 3B. is there. The (+) transfer bias roller rotates with the intermediate transfer belt 21.

The primary transfer rollers 7Y, 7M, 7C, and 7B used in the present embodiment are configured in such a manner that a rubber material having a medium resistance electric characteristic is wound around a metal core. The volume resistivity is 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁷ to 10 ⁹ Ω · cm. The material is not limited to foam rubber, and medium resistance solid rubber can be used as well.

  In the primary transfer process of the present embodiment, the primary transfer bias is applied to the primary transfer roller using a constant current power source having a polarity of (+), and the current setting value is in the range of approximately 20 to 40 μA. is there.

The repulsive roller 2 </ b> C used in the present embodiment is configured in such a manner that a rubber material having a medium resistance electric characteristic is wound around a metal core. The repulsive roller 2C is made of medium resistance solid rubber, and its volume resistivity is in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁷ to 10 ⁹ Ω · cm.

The secondary transfer roller 9B is made of a medium resistance foamed rubber, and its volume resistivity is 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁷ to 10 ⁹ Ω · cm.

  In the secondary transfer process of this embodiment, the repulsive roller 2C is applied with a (−) polarity bias having the same polarity as that of the toner and a constant current power source is used, and the current setting value is in the range of approximately 30 to 50 μA. is there.

  A secondary transfer electric field is applied in the direction in which the toner of the (−) polarity on the intermediate transfer belt 21 is pushed out to the transfer paper side with the secondary transfer roller 9B connected to the ground as an opposite.

  The intermediate transfer belt 21 used in the present embodiment is, as a specific example, a single layer belt PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF. (Polyvinylidene fluoride), PPS (polyphenylene sulfide), and the like are made of a medium resistance resin whose resistance is adjusted by carbon dispersion or ionic conductive agent blending.

The volume resistivity is in the range of 10 ⁶ to 10 ¹⁰ Ω · cm, preferably 10 ⁸ to 10 ¹⁰ Ω · cm. The surface resistivity is in the range of 10 ⁶ to 10 ¹² Ω / □, preferably 10 ⁸ to 10 ¹² Ω / □.

  Further, the thickness is in the range of 50 to 100 μm, the Young's modulus (longitudinal elastic modulus) is preferably 3000 Mpa or more, and sufficient mechanical strength is required to withstand elongation, bending, wrinkling, and undulation by driving.

  Other examples of the intermediate transfer belt 21 include PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), PPS (polyphenylene). The resistance is slightly higher than the volume resistivity of the belt layer itself only on the surface side of the intermediate transfer belt 21 of a single-layer structure of a medium resistance resin whose resistance is adjusted by mixing carbon in a material such as sulfide) or by adding an ionic conductive agent. Even in the case of using a belt provided with the surface layer, the same effect is obtained. The thickness of the surface layer is preferably about 1 to 10 μm.

  The belt with a high resistance layer on the surface is used especially for belts that control resistance by dispersing carbon in the resin. There is a phenomenon that occurs in the secondary transfer process to the paper in the raised state (a phenomenon in which the transfer current concentrates due to the dispersion of the carbon dispersion state and the toner in that portion is repelled and whitened). This is because by providing a high resistance layer on the belt surface, local concentration of the transfer current can be alleviated and abnormal images (so-called “white spots”) can be improved.

  Further examples of the intermediate transfer belt 21 include PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), PPS (polyphenylene). Sulfide) and other materials such as carbon dispersion, or on a base layer of 50 to 100 μm composed of a medium resistance resin whose resistance is adjusted by blending an ionic conductive agent, carbon dispersion or ions as well as rubber materials such as urethane, NBR, and CR An elastic layer made of a material whose resistance is adjusted by blending a conductive agent is provided in an amount of 100 to 500 μm, and the surface layer is coated with a fluorine-based rubber or resin (or a hybrid material thereof) having a thickness of about 1 to 10 μm. Surface to reduce the stickiness of elastic material There is similarly effective even when using a multi-layer belt with attached particles.

  By using such an elastic intermediate transfer belt, the elastic layer can be used even on paper having a low density of paper fibers of the transfer material or on a type of transfer material called so-called embossed paper having 50-200 μm irregularities on the paper surface. A solid filling improvement effect is known in which the toner transferability to the concave portion is improved because it follows the concave portion.

  FIG. 1 is a configuration diagram of a secondary transfer unit according to the present embodiment, and a high-pressure mode (mode 1) corresponding to a paper type generally called an embossed paper having an uneven shape on the surface. It is embodiment regarding.

  As an embodiment relating to the pressure switching of the secondary transfer unit, first, the characteristics of the transfer paper conveyed from the paper feeding unit are detected by a paper thickness sensor (not shown) or a paper roughness sensor (not shown).

  As a result of the detection, when it is determined that the sheet is embossed paper, the secondary transfer roller 9B is repulsive as shown in FIG. 1 with the intermediate transfer belt 21 held between the pressure plate A18a and the load P1 at the position of the journal A16a. Pressed against the roller 2C. Further, the user himself / herself may appropriately select the paper type by using the operation panel or the printer driver.

  The repulsive roller 2C is provided by molding conductive rubber or conductive foamed rubber as an elastic body on the core metal 2D. Both ends are supported and rotated by the housing by bearings (not shown). The outer diameter shape of the elastic body on the repulsive roller 2C is formed so that the rubber thickness at the center is about 0.1 to 0.5 mm thicker than the rubber thickness at both ends, and has a so-called drum shape.

  On the other hand, the secondary transfer roller 9B is provided by molding conductive rubber or conductive foamed rubber as an elastic body on the cored bar 9D. The journals 16a and 16b at both ends of the cored bar 9D are supported and rotated by bearings 17a and 17b, and the intermediate transfer belt 21 is sandwiched by the action of the pressure plate 18a and the pressure spring 19a with respect to the repulsive roller 2C. It is pressed with a load P1 by the pressure plate A18a at the position of the journal A16a. A secondary transfer nip is formed by the elastic pressure contact action of the repulsive roller 2C, the intermediate transfer belt 21, and the secondary transfer roller 9B.

  In this embodiment, the nip pressure is set to a high pressure in order to cope with uneven paper such as embossed paper. The range is approximately 0.2 to 0.4 Mpa.

  The journal A16a provided at the end of the secondary transfer roller 9B has substantially the same core diameter as that of the transfer roller portion, and is in the vicinity of the area where pressure is applied to the repulsive roller 2C. On the other hand, the amount of deflection of the repulsive roller 2C can be kept small by pressing the pressure plate 18a through the bearing 17a. At the same time, a high pressure and uniform nip pressure distribution is obtained by the drum-shaped action of the repulsive roller 2C.

  FIG. 2 is a configuration diagram of the secondary transfer unit according to the present embodiment. The present embodiment is a mode in the case of a paper type having a smooth surface, generally called standard paper.

  As an embodiment relating to the pressure switching of the secondary transfer unit, the characteristic of the transfer paper P conveyed from the paper feeding unit 1B is detected by a paper thickness sensor (not shown) or a paper roughness sensor (not shown), and the detection is performed. As a result, when it is determined that the sheet is a standard sheet, the secondary transfer roller 9B is positioned at the position of the journal B16b with the pressure plate B18b at the load P2 (P1> P2) with the intermediate transfer belt 21 held between the repulsive roller 2C. Pressed. Further, the user himself / herself may appropriately select the paper type by using the operation panel or the printer driver.

  The repulsive roller 2C is provided by molding conductive rubber or conductive foamed rubber as an elastic body on the core metal 2D. Both ends are supported and rotated by the housing by bearings (not shown). The outer diameter shape of the elastic body on the repulsive roller 2C is formed so that the rubber thickness at the center is about 0.1 to 0.5 mm thicker than the rubber thickness at both ends, and has a so-called drum shape.

  On the other hand, the secondary transfer roller 9B is provided by molding conductive rubber or conductive foamed rubber as an elastic body on the cored bar 9D. The journals 16a and 16b at both ends of the cored bar 9D are supported and rotated by bearings 17a and 17b, and the intermediate transfer belt 21 is sandwiched by the action of the pressure plate 18b and the pressure spring 19b with respect to the repulsive roller 2C. It is pressed by the load P1 by the pressure plate B18b at the position of the journal B16b. A secondary transfer nip is formed by the elastic pressure contact action of the repulsive roller 2C, the intermediate transfer belt 21, and the secondary transfer roller 9B.

  In the present embodiment, the nip pressure is set to a low pressure in order to correspond to the standard paper, and is in the range of about 0.05 to 0.2 MPa.

  The journal B16b provided at the end of the secondary transfer roller 9B has a core diameter smaller than that of one journal B16b of the secondary transfer roller 9B, and is a distance from the area where pressure is applied to the repulsive roller 2C. Therefore, although the amount of bending of the secondary transfer roller 9B is increased by pressing the pressure plate 18b with the pressure spring 19b through the bearing 17b through the bearing 17b, the low pressure is exerted by the drum-shaped action of the repulsive roller 2C. And uniform nip pressure distribution.

  For switching between the pressure plate 18a and the pressure plate 18b, two pairs of cams (not shown) are provided, and the pressure plate to be pushed up is selected.

  In the above embodiment, a uniform secondary transfer pressure distribution can be obtained in the longitudinal direction of the roller in both the low pressure mode and the high pressure mode, and a mode with a low pressure setting is usually used. Therefore, an excessive load is not applied to the functional parts. Therefore, it is possible to extend the life of the parts.

  FIG. 4 is a configuration diagram of a repulsive roller according to the present embodiment. Examples of the repulsive rollers 2C and 2D include the following.

  The shape of the core metal 2D is inner diameter φ20 / outer diameter φ24. The repulsive roller 2C has an elastic layer thickness of 4 mm / outer diameter φ32.

  The repulsive roller 2 </ b> C has a drum shape, and an embodiment having an outer diameter shape as shown in FIGS. 4A to 4C is possible.

  d1 = φ32, d2 = φ32.5 to φ33.0, and the difference between the outer diameters of d1 and d2 is preferably in the range of 0.5 to 1.0 mm.

  In the case of the trapezoidal shape of FIG. 4A, the flat portion L1 is preferably provided in the center of the roller, and L1 = 50 to 100 mm is desirable.

  Also in FIGS. 4B and 4C, the portion with the largest outer diameter is set substantially at the center.

  FIG. 5 is a view showing the nip pressure distribution of the secondary transfer portion according to the present embodiment. The length of each roller when the nip pressure of the secondary transfer portion is high at the load position of the journal A16a (mode 1) and when the load pressure is low at the load position of the journal B16b (mode 2). It explains how the secondary transfer nip pressure distribution in the direction changes.

  Conventionally, process conditions and machine settings such as detecting the paper thickness with a sensor and switching transfer conditions such as transfer current and transfer pressure or switching fixing conditions such as fixing temperature and fixing nip width according to the paper thickness A method for switching the conditions has already been disclosed and is known as a known technique.

  FIG. 5a shows the nip pressure distribution (average pressure: small / pressure deviation) when the nip pressure of the secondary transfer portion is low (the load position is the position of journal B16b) (mode 2). :small).

  The initial mode setting of the secondary transfer portion nip pressure after the start-up of the apparatus is a low pressure (mode 2) (standard paper correspondence) setting as described with reference to FIG. In this mode 2, although the average pressure is low, the deflection of the secondary transfer roller 9B itself is large due to the pressurization to the journal B16b, but the pressure deviation in the longitudinal direction can be suppressed small by the action of the drum shape of the repulsive roller 2C. Is possible.

  FIG. 5b shows the pressure distribution when the weighted pressure alone is the high pressure P1 while maintaining the weighted position (journal B16b position) in mode 2 (average pressure: medium / pressure deviation: large). When only the secondary transfer pressure is switched to the high pressure setting and the pressure is increased, the cored bar of the repulsive roller 2C and the secondary transfer roller 9B is further greatly bent. In the part, the pressure hardly increases.

  Moreover, since the pressure deviation between both ends and the central part becomes very large, a deviation occurs in the uneven transferability in the longitudinal direction of the roller, and in particular, the uneven transferability is poor in the central part for embossed paper. End up.

  In addition, since the secondary transfer current is uneven in the longitudinal direction of the roller even in the flat portion on the transfer paper, a problem of transfer unevenness (image density unevenness) occurs.

  FIG. 5c shows the nip pressure distribution (average pressure: large / pressure deviation) when the nip pressure of the secondary transfer portion is high (the load position is the position of the journal A16a) (mode 1). :small).

  When embossed paper is supported in mode 1 (high pressure), the pressure position is switched to the journal A16a, and the load is also switched to the high pressure P1 setting. As a result, the average pressure can be increased, and the pressure deviation in the longitudinal direction of the roller can be suppressed by the drum-shaped action of the repulsive roller 2C.

  FIG. 6 is a flowchart showing the control of the image forming apparatus according to the present embodiment. The operation of switching between mode 1 and mode 2 according to the unevenness (roughness) of the surface of the transfer paper or the thickness of the transfer paper is described.

  First, when a print job is executed, a paper feeding operation is started (step S601). Next, the characteristics of the transfer paper conveyed from the paper supply unit are detected by the paper thickness sensor and the paper roughness sensor (step S602).

  If it is detected that the paper is other than standard paper (embossed paper, transfer paper whose thickness or roughness is both a predetermined value or more) (YES in step S602), the secondary transfer roller of the secondary transfer unit is Transfer is performed in mode 1 (the weighted position of the journal A16a is a high pressure) (pressure plate A • ON) (step S603).

  When it is detected that the sheet is a standard sheet (step S602 / NO), the secondary transfer roller of the secondary transfer unit performs transfer in mode 2 (the weighted position of the journal B16b is a low pressure) (pressure plate B • ON). (Step S604).

  When all the print jobs are completed (step S605 / YES), the pressure plates of the secondary transfer roller A and B are separated from the journals A16a and B16b, and are turned off (step S606).

  If all the print jobs are not completed (step S605 / NO), the paper feeding operation is resumed (step S601).

  The embodiment described above can also be configured as follows.

  The image forming apparatus according to the present embodiment is characterized in that the secondary transfer member pressurizing unit can switch the pressurizing force.

  The image forming apparatus according to the present embodiment includes an unevenness detecting unit that detects unevenness on the surface of the transfer paper, and a paper thickness detecting unit that detects the thickness of the transfer paper, and is detected by the unevenness detecting unit and the paper thickness detecting unit. Based on the result, it is possible to switch the pressure position and pressure of the secondary transfer member pressure unit.

  In the image forming apparatus according to the present embodiment, the repulsive member is composed of a core metal extending along the longitudinal direction and a coating member coated on the core metal, and the coating member is an elastic body or a foam, The outer diameter of the central portion in the direction is larger than the outer diameters at both ends.

  The image forming apparatus according to the present embodiment includes an image carrier that forms a toner image on the surface, an intermediate transfer member to which a toner image is transferred from the image carrier, and a toner on the intermediate transfer member that is inside the intermediate transfer member. A repulsive member for applying an electric field for moving the image onto the transfer paper, a secondary transfer member that sandwiches the intermediate transfer member and is pressed against the repulsive member, and a repulsive member that sandwiches the intermediate transfer member and holds the secondary transfer member Secondary transfer pressurizing means that presses against the shaft, and has a plurality of shaft portions with different outer diameters at both ends of the secondary transfer member, and the secondary transfer pressurizing means is attached to the plurality of shaft portions. It has the means to switch a press position, It is characterized by the above-mentioned.

  The image forming apparatus of this embodiment is characterized in that the pressing force is also switched in conjunction with a plurality of pressing position switching operations of the secondary transfer pressurizing unit.

  The image forming apparatus according to the present embodiment includes a roughness sensor that detects unevenness of the transfer paper surface provided in the transfer paper conveyance region between the paper feeding unit and the secondary transfer unit, and the transfer paper surface roughness is a predetermined value. It has a circuit for determining that it has become large, and a switch that is turned ON / OFF by the determination of this circuit, and the pressing position switching operation of the secondary transfer pressurizing means is performed based on these determination results. And

  In the image forming apparatus of the present embodiment, the repulsive member has a medium-resistance elastic body or foam on the base, and the repulsive member has a drum shape in which the outer diameter of the central portion is larger than the outer diameters of both ends. It is characterized by having.

  The image forming apparatus according to the present embodiment is characterized in that the amount of bending of the secondary transfer member at the time of maximum pressurization is substantially equal to ½ of the deviation of the diameter of the repulsive member in the longitudinal direction.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments, it will be understood that various modifications and changes may be made specifically without departing from the broader spirit and scope of the invention as defined in the claims. is there.

1 Color copier (image forming device)
DESCRIPTION OF SYMBOLS 1A Image formation part 1B Paper feed part 1B1 Paper feed tray 1B2 Conveyance roller pair 1B3 Registration roller pair 1C Document conveyance part 1D Scanner part 2A Driven roller 1
2B Drive roller 2C Repulsive roller 2D Repulsive roller core 3Y, M, C, B Photoconductor 4Y, M, C, B Charging device 5 Exposure device 6Y, M, C, B Photoconductor cleaning device 7Y, M, C, B Primary transfer roller 8Y, M, C, B Developing device 9A Conveying belt 9B Secondary transfer roller 9C Conveying drive roller 9D Secondary transfer roller cored bar 10 Intermediate transfer belt cleaning device 11 Fixing device 12 Discharge roller 13 Discharge tray 16a Journal A
16b Journal B
17a Bearing A
17b Bearing B
18a Pressure plate A
18b Pressure plate B
19a Pressure spring A
19b Pressure spring B
21 Intermediate transfer belt

JP 2009-128877 A

Claims (4)

An image carrier for carrying a toner image;
An intermediate transfer member that primarily transfers the toner image of the image carrier;
A repulsive member acting on an electric field for moving the toner image transferred to the intermediate transfer member to transfer paper;
A secondary transfer member that presses the repulsive member at a position facing the repulsive member via the intermediate transfer member;
A secondary transfer member pressurizing unit that pressurizes the secondary transfer member;
The secondary transfer member includes a plurality of shaft portions having different outer diameters at both ends in the longitudinal direction,
2. The image forming apparatus according to claim 1, wherein the secondary transfer member pressurizing unit is capable of switching a pressurizing position with respect to the plurality of shaft portions.   The image forming apparatus according to claim 1, wherein the secondary transfer member pressurizing unit can switch a pressurizing force. Unevenness detecting means for detecting unevenness on the surface of the transfer paper;
Paper thickness detecting means for detecting the thickness of the transfer paper,
3. The pressure position and pressure of the secondary transfer member pressing means can be switched based on detection results of the unevenness detecting means and the paper thickness detecting means. Image forming apparatus. The repulsive member is composed of a core bar extending along the longitudinal direction and a covering member coated on the core bar,
4. The image forming apparatus according to claim 1, wherein the covering member is an elastic body or a foam, and an outer diameter of a central portion in a longitudinal direction is larger than outer diameters of both ends.

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