JP2006113284A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of obtaining a satisfactory transfer image by making it possible to set the speed of transfer by a simple configuration. <P>SOLUTION: The color image forming apparatus 1 includes: an image forming section 108 having photoreceptor drums 21 for holding developer images formed with developers, which match corresponding hues, in accordance with information about an image separated into colors; a transfer belt unit 30 having a transfer belt 31 disposed in pressure contact with the rotating photoreceptor drums 21 and moved in the direction of the rotation of the photoreceptor drums 21, thereby transferring the developer images formed on the corresponding photoreceptor drums; and a transfer roller 36 by which the developer images transferred to the transfer belt 31 are further transferred onto recording paper. The speed at which the transfer belt 31 is moved is higher than the peripheral speed of each photoreceptor drum 31. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly, to an image forming apparatus such as a copying machine, a printer, and a facsimile employing an electrophotographic method as an image forming method, and transferring a developer image formed on an image carrier The present invention relates to a color image forming apparatus to be transferred onto.

  In recent years, colorization is becoming common in image forming apparatuses, and color image forming apparatuses are increasingly employed as color image forming apparatuses develop.

  The color image forming apparatus transfers (primary transfer) a developer image (color image information by a developer having a plurality of hues) formed on a photosensitive drum in an image forming unit to the intermediate transfer member. There is known a method in which a developer image laminated on a sheet is transferred onto a sheet (secondary transfer).

  In the transfer process of a color image forming apparatus, the speed difference between the peripheral speed of the photosensitive drum and the sheet transport speed by the direct transfer method, the peripheral speed of the photosensitive drum by the offset method, and the moving speed of the intermediate transfer body are usually Is theoretically (1: 1), but is actually different.

The reason for this is that the above-mentioned speed difference is different depending on the transfer method, such as improvement in reproducibility of fine lines in print quality, prevention of missing print characters, prevention of fog, and the like (see Patent Document 1). reference).
JP 2001-97610 A

  However, this speed difference is not always constant by the color image forming apparatus. The contact pressure between the photosensitive drum and the transfer member (recording paper or intermediate transfer member), the peripheral speed (process speed) of the photosensitive drum, Since it varies depending on the smoothness of the recording paper and the intermediate transfer member used, the resistance value, the installation environment of the color image forming apparatus, and the like, it is not easy to set an optimum transfer speed.

  In particular, according to the conventional photosensitive drum 121 and intermediate transfer roller 135 as shown in FIG. 4, the recording paper 131 or the intermediate transfer body 132 is sandwiched and transferred, as shown in FIG. There are a plurality of optimum speed ratios (peak values P1, P2 in the figure) between the peripheral speed and the conveyance speed of the recording paper 131 or the moving speed of the intermediate transfer body 132, and the optimum speed ratios are the process speed and the color image. Since it is determined by a plurality of factors such as the installation environment of the forming apparatus, the electric field of the transfer roller, and the contact pressure, it is more complicated to set the transfer speed.

  The present invention has been made in view of the above-described conventional problems, and in a color image forming apparatus, a color image forming apparatus capable of setting a transfer speed with a simple configuration and obtaining a good transfer image. Is intended to provide.

  Each configuration of the color image forming apparatus according to the present invention for solving the above-described problems is as follows.

  The color image forming apparatus according to claim 1 includes: an image forming unit including an image carrier that carries a developer image formed by a developer that matches each hue according to color-separated image information; A primary transfer means provided with an intermediate transfer body that is in pressure contact with the image carrier and moves along the rotational direction of the image carrier to transfer the developer image formed on the image carrier; In the color image forming apparatus provided with a secondary transfer unit that transfers the developer image transferred onto the transfer medium, the moving speed of the intermediate transfer member is faster than the peripheral speed of the image carrier. It is characterized by this.

In addition to the configuration described in claim 1, the color image forming apparatus described in claim 2 has a moving speed of the intermediate transfer member,
(Peripheral speed of image carrier) <(Movement speed of intermediate transfer member) ≦ (Peripheral speed of image carrier) × 104%
It is characterized in that it is defined to satisfy the relationship.

  According to a third aspect of the present invention, in addition to the structure described in the first or second aspect, the developer image formed on the image carrier is transferred to the peripheral speed of the image carrier and the movement of the intermediate transfer member. It is characterized in that it is formed in a contracted state in the sub-scanning direction corresponding to the speed difference from the speed.

  According to a fourth aspect of the present invention, in addition to the configuration described in the third aspect, the image information of the developer image is transmitted to the periphery of the image carrier by an image control unit provided in the color image forming apparatus. The writing is performed on the image carrier in a contracted state in the sub-scanning direction corresponding to the speed difference between the speed and the moving speed of the intermediate transfer member.

  In addition to the configuration described in claim 3, the color image forming apparatus described in claim 5 is configured to store image information of the developer image by image processing by an image control unit provided in the color image forming apparatus. In accordance with the speed difference between the peripheral speed of the body and the moving speed of the intermediate transfer body, writing is performed on the image carrier based on image information that has been subjected to image processing in a contracted state in the sub-scanning direction. It is.

  According to the first to fifth aspects of the present invention, the color image forming apparatus includes the image carrier that carries the developer image formed by the developer that matches each hue in accordance with the color-separated image information. Image forming means and a primary transfer provided with an intermediate transfer body that is pressed against the rotating image carrier and moves along the rotation direction of the image carrier to transfer the developer image formed on the image carrier. And a secondary transfer means for transferring the developer image transferred to the intermediate transfer member onto a transfer medium. By setting the speed faster than the speed, the transfer speed can be set with a simple configuration, and a good transfer image can be obtained.

  In addition to the common effects obtained by the inventions according to claims 1 to 5, the following effects can be obtained according to the inventions described in each claim.

Specifically, according to the invention described in claim 2, the moving speed of the intermediate transfer member is
(Peripheral speed of image carrier) <(Movement speed of intermediate transfer member) ≦ (Peripheral speed of image carrier) × 104%
By defining so as to satisfy this relationship, the developer image formed on the image carrier can be stably transferred to the intermediate transfer member.

  According to the invention described in claim 3, originally, when the intermediate transfer member is moved at a speed higher than the peripheral speed of the image carrier, the image transferred to the intermediate transfer member is stretched by the speed difference. By forming the developer image formed on the image carrier in a contracted state in the sub-scanning direction corresponding to the speed difference between the peripheral speed of the image carrier and the moving speed of the intermediate transfer member, the intermediate transfer member The image that is stretched when transferred to can be made the same size as the actual image.

  According to the fourth aspect of the present invention, the image information of the developer image is converted into a speed difference between the peripheral speed of the image carrier and the moving speed of the intermediate transfer member by the image control unit provided in the color image forming apparatus. Accordingly, the image stretched when transferred to the intermediate transfer member can be made to have the same size as the actual image.

  According to the invention described in claim 5, the image information of the developer image is obtained by image processing by an image control unit provided in the color image forming apparatus, and the peripheral speed of the image carrier and the moving speed of the intermediate transfer member. The image that is stretched when transferred to the intermediate transfer member is actually written on the image carrier based on the image information that has been processed in the sub-scanning direction corresponding to the speed difference of Can be the same size as the image.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is an example of an embodiment for carrying out the invention, and is an explanatory diagram (a cross-sectional view from the rear) showing the overall configuration of a color image forming apparatus according to an embodiment of the present invention. FIG. FIG. 6 is an explanatory diagram showing a positional relationship between a transfer belt and a photosensitive drum constituting the toner.

  As shown in FIG. 1, the color image forming apparatus 1 of the present embodiment has a developer image (hereinafter, referred to as toner) formed by a developer (hereinafter referred to as toner) that matches each hue in accordance with color-separated image information. Hereinafter, a process printing unit 20 (20a, 20b, 20c, 20d) constituting a plurality of image forming means provided with a photosensitive drum 21 (21a, 21b, 21c, 21d) carrying a toner image), An endless transfer belt 31 serving as an intermediate transfer belt constituting a primary transfer unit for transferring a plurality of toner images in a stacked manner, and a toner image laminated and transferred on the transfer belt 31 are collectively transferred onto a recording sheet as a transfer medium. A color image forming apparatus including a transfer roller 36 constituting a secondary transfer unit, wherein the plurality of process printing units 20a, 20b, 20c, and 20d are transferred to the transfer belt 3. In which arranged side by side along the.

Here, the positional relationship between the color image forming apparatus 1 and the operator in the present embodiment is such that the operator is located on the other side of the color image forming apparatus 1 shown in FIG. That is, the side surface (not shown) of the color image forming apparatus 1 is the operation side, and the left-right direction in front view in FIG. 1 is opposite to the left-right direction when the operator faces the operation side.
In the following description, the front side (F side) indicates the operator side, and the rear side (R side) indicates the rear side of the color image forming apparatus 1, that is, the surface side shown in FIG.

First, the overall configuration of the color image forming apparatus 1 will be described.
A color image forming apparatus 1 according to the present embodiment is a so-called digital color printer, which color-separates image information, forms an image for each hue, and outputs a color image, as shown in FIG. In general, the image forming unit 108 and the sheet feeding unit 109 are configured to record a multicolor image or a single color image on the basis of a print job from an information processing apparatus (not shown) such as a personal computer connected to the outside. It is formed on top.

  The image forming unit 108 uses an electrophotographic method to form a multicolor image using each color of yellow (Y), magenta (M), cyan (C), and black (K). The unit 10, the process printing unit 20, the fixing unit 27, and a transfer belt unit 30 as a primary transfer unit including the transfer belt 31, a transfer roller 36, and a transfer belt cleaning unit 37 are configured.

The schematic configuration of the image forming unit 108 is that a fixing unit 27 is arranged on the upper part of one end side of the casing 1 a of the color image forming apparatus 1 and extends from one end side to the other end side of the casing 1 a below the fixing unit 27. A transfer belt unit 30 is disposed, a process printing unit 20 is disposed below the transfer belt unit 30, and an exposure unit 10 is disposed below the process printing unit 20. A transfer belt cleaning unit 37 is provided on the other end side of the transfer belt unit 30. Further, a paper discharge tray 43 is provided adjacent to the fixing unit 27 above the image forming unit 108.
A paper feeding unit 109 is configured below the image forming unit 108.

  In the present embodiment, four process printing units 20a, 20b, 20c, and 20d corresponding to the respective colors of black (K), yellow (Y), magenta (M), and cyan (C) are transferred as the process printing unit 20. The belts 31 are sequentially provided along the belt 31.

  The process print unit 20a of the hue transferred first among the toner images transferred onto the transfer belt 31, that is, the process print unit 20a of the hue arranged farthest from the transfer roller 36 has a black hue. A toner is provided and a black toner image is first formed on the transfer belt 31.

  These process printing units 20a, 20b, 20c, and 20d are arranged in parallel in a substantially horizontal direction (left and right direction in the drawing) in the casing 1a, and photosensitive drums 21a, 21b, which are image carriers for each color. 21c, 21d, chargers 22a, 22b, 22c, 22d for charging the photosensitive drums 21a, 21b, 21c, 21d, developing units 23a, 23b, 23c, 23d, cleaner units 24a, 24b, 24c, 24d, etc., respectively. I have.

  Here, the symbols a, b, c, and d attached to the components corresponding to the respective colors correspond to the respective colors of black (K), yellow (Y), magenta (M), and cyan (C). However, in the following description, the constituent elements provided for the respective colors are collectively shown in the photosensitive drum 21, except for the case where the constituent elements corresponding to a specific color are specified. The charging unit 22, the developing unit 23, and the cleaner unit 24 are described.

  The photosensitive drum 21 is disposed so that a part of the outer peripheral surface thereof is in contact with the surface of the transfer belt 31, and the charger 22, the developing device 23, and the cleaner unit as an electric field generating unit along the outer peripheral surface of the drum. 24 are arranged close to each other.

  The charger 22 is a roller-type charger, and is disposed so as to contact the outer peripheral surface of the photosensitive drum 21 on the substantially opposite side to the position where the transfer belt unit 30 is disposed across the photosensitive drum 21. In this embodiment, a roller-type charger is used as the charger 22. However, a brush-type charger, a charger-type charger, or the like may be used instead of the roller-type charger.

  The developing unit 23 stores toner of each color of black (K), yellow (Y), magenta (M), and cyan (C) for each developing unit 23, and rotates the photosensitive drum (in the drawing). (In the direction of arrow A) of FIG. Then, each color toner is supplied to the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 21 so as to be visualized.

  The cleaner unit 24 is disposed on the upstream side of the charger 22 in the rotation direction of the photosensitive drum. In addition, the cleaner unit 24 includes a cleaning blade 241, and the cleaning blade 241 is disposed in contact with the outer peripheral surface of the photoconductive drum 21 to scrape and collect residual toner on the photoconductive drum 21. Has been.

  The exposure unit 10 generates an electrostatic latent image by irradiating each photosensitive drum 21 with a laser beam for each color based on image data for printing, and mainly includes a laser irradiation unit 11a. It comprises a laser scanning unit (LSU) 11 provided, a polygon mirror 12, and reflection mirrors 13a, 13b, 13c, 13d, 14a, 14b, and 14c that reflect laser light for each color.

  Further, the exposure unit 10 has an image control unit (not shown) provided in the color image forming apparatus 1 in the sub-scanning direction corresponding to the speed difference between the peripheral speed of the photosensitive drum 21 and the moving speed of the transfer belt 31. The electrostatic latent image in a contracted state is controlled so as to be generated on the photosensitive drum 21.

  The laser light emitted from the laser irradiation unit 11a is color-separated by the polygon mirror 12 and then reflected by the reflection mirrors 13a to 13d and 14a to 14c so as to be irradiated on the respective photosensitive drums 21 for each color. It has become.

  The laser scanning unit 11 may be configured to use a writing head in which light emitting elements such as EL (Electro Luminescence) and LED (Light Emitting Diode) are arranged in an array instead of the laser irradiation unit 11a.

The transfer belt unit 30 mainly includes a transfer belt 31, a transfer belt drive roller 32, a transfer belt driven roller 33, a transfer belt tension mechanism 34, and intermediate transfer rollers 35a, 35b, 35c, and 35d.
In the following description, the intermediate transfer rollers 35a, 35b, 35c, and 35d are collectively referred to as the intermediate transfer roller 35 when used.

  The transfer belt 31 is endlessly formed using a film having a thickness of about 75 μm to 120 μm. As the material of the transfer belt 31, polyimide, polycarbonate, a thermoplastic elastomer alloy, or the like is mainly used.

  The transfer belt 31 is stretched by a transfer belt driving roller 32, a transfer belt driven roller 33, a transfer belt tension mechanism 34, and an intermediate transfer roller 35 so that the surface thereof is in contact with the outer peripheral surface of the photosensitive drum 21. The transfer belt drive roller 32 is configured to move in the sub-scanning direction (arrow B direction in the figure) by the driving force of the transfer belt drive roller 32.

  The transfer belt driving roller 32 is disposed on one end side of the housing 1a, drives the transfer belt 31 to convey the transfer belt 31, and transfers the transfer belt 31 in a state where the transfer belt 31 and the recording paper are overlapped. The recording paper is conveyed while being pressed between and pressed.

  The peripheral speed of the transfer belt drive roller 32, that is, the moving speed of the transfer belt 31 conveyed by the transfer belt drive roller 32 is set with a speed difference of + 4% with respect to the peripheral speed of the photosensitive drum 21. Yes.

  The transfer belt driven roller 33 is disposed on the other end side of the housing 1a, and the transfer belt 31 together with the transfer belt driving roller 32 is extended substantially horizontally from one end side to the other end side of the housing 1a.

  The intermediate transfer roller 35 is disposed in an inner space of the transfer belt 31 that is wound from the transfer belt driving roller 32 to the transfer belt driven roller 33, and has an axis centered on the photosensitive drum 21 as shown in FIG. On the other hand, it is arranged at a position shifted in the left-right direction in the drawing to the downstream side in the moving direction of the transfer belt 31, presses the inner surface of the transfer belt 31, and A part of the nip is wound so as to obtain a predetermined nip amount.

  The intermediate transfer roller 35 includes a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm, and an outer peripheral surface of the metal shaft is coated with an elastic material having conductivity such as EPDM and urethane foam.

  The intermediate transfer roller 35 transfers a toner image formed on the photosensitive drum 21 to the transfer belt 31, that is, a high voltage transfer bias, that is, a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner. Is applied, and a high voltage is uniformly applied to the transfer belt 31 by an elastic material.

  The transfer roller 36 constitutes a secondary transfer means for transferring the developer image transferred to the transfer belt 31 onto a recording sheet, and is opposed to the transfer belt drive roller 32 in a substantially horizontal and parallel manner. A transfer belt 31 wound around the transfer belt drive roller 32 is disposed so as to be pressed against the transfer belt 31 at a predetermined nip, and is used to transfer a multicolor toner image formed on the transfer belt 31 onto a recording sheet. A voltage, that is, a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner is applied.

  Further, in order to obtain a nip between the transfer belt 31 and the transfer roller 36 steadily, either the transfer belt drive roller 32 or the transfer roller 36 is made of a hard material such as metal, and the other roller Is made of a soft material such as elastic rubber or foamable resin.

  A registration roller 26 is provided below the transfer belt driving roller 32 and the transfer roller 36. The registration roller 26 is configured to align the leading edge of the recording paper supplied from the paper feeding unit 109 and the leading edge of the toner image on the transfer belt 31 and convey the toner to the transfer roller 36 side.

  The transfer belt cleaning unit 37 is provided in the vicinity of the transfer belt driven roller 33, and includes a cleaning blade 37a disposed so as to contact the transfer belt 31, and scrapes and collects residual toner on the transfer belt 31 by the cleaning blade 37a. Have been to.

  Further, the transfer belt cleaning unit 37 is disposed in the vicinity of the process printing unit 20a on the upstream side in the moving direction of the transfer belt 31 from the process printing unit 20a.

  As shown in FIG. 1, the fixing unit 27 includes a pair of fixing rollers 271 configured by a heating roller 27a and a pressure roller 27b, and a conveying roller 27c above the fixing roller 271. It is carried in from below 271 and carried out above carrying roller 27c.

  A paper discharge roller 28 is provided above the fixing unit 27, and the recording paper conveyed from the conveyance roller 27 c is discharged onto the paper discharge tray 43 by the paper discharge roller 28.

  The fixing of the toner image by the fixing unit 27 is controlled by controlling heating means (not shown) such as a heater lamp provided inside or close to the heating roller 27a based on a detection value of a temperature detector (not shown). The heating roller 27a is maintained at a predetermined temperature (fixing temperature), and the recording paper on which the toner image has been transferred is heated and pressed while being rotated and conveyed by being sandwiched between the heating roller 27a and the pressure roller 27b. The toner image is thermally fixed.

  Adjacent to the fixing unit 27, a double-sided document conveying path S3 for double-sided printing is formed from the rear to the bottom of the fixing unit 27 to the vicinity of the paper feed unit 109, and is arranged in the vertical direction on the double-sided document conveying path S3. The recording paper is reversed toward the transfer roller 36 in a state where the recording paper is reversed by the provided conveying rollers 29a and 29b.

  Specifically, the transport roller 29a is disposed behind the fixing unit 27, and the transport roller 29b is disposed below the transport roller 29a in the vertical direction and is disposed at substantially the same position as the registration roller 26 in the lateral direction. Yes.

Next, the configuration of the paper feeding unit 109 will be described.
The paper feed unit 109 includes a manual feed tray 41 and a paper feed cassette 42 for storing recording paper used for image formation, and the image forming unit 108 records the recording paper one by one from the manual feed tray 41 or the paper feed cassette 42. To be supplied to.

  As shown in FIG. 1, the manual feed tray 41 is expanded to one side end (right side in the figure) of the casing 1a of the color image forming apparatus 1, and outward when used, and to one side end when not used. It is provided so that it can be stored, and a small number (necessary number) of recording sheets of the type desired by the user are placed and taken into the housing 1a of the color image forming apparatus 1 one by one.

  A pickup roller 41a is provided below the exposure unit 10 in the casing 1a of the color image forming apparatus 1 on the downstream side of the recording paper feeding direction (in the direction of arrow C in the figure) by the manual feed tray 41. Conveying rollers 41b, 41c, and 41d are provided substantially horizontally on the downstream side in the paper direction.

  The pickup roller 41a comes into contact with the surface of one end portion of the recording paper fed from the manual feed tray 41 and reliably conveys the paper one by one by the frictional resistance of the roller.

  The most downstream conveying roller 41d is provided above the conveying rollers 41b and 41c, and thereby conveys the recording sheet upward.

  The above-described pickup roller 41a and transport rollers 41b, 41c, and 41d constitute a recording paper transport path S1.

  On the other hand, the paper feed cassette 42 is provided below the image forming unit 108 and the exposure unit 10 in the housing 1a, and records a large amount of recording paper having a size defined by the specifications of the apparatus or a size predetermined by the user. Can be accommodated.

  A pickup roller 42a is provided on one end portion (left end portion in the figure) of the paper feed cassette 42. The pickup roller 42a is disposed obliquely upward on the downstream side in the recording paper conveyance direction (arrow D direction in the figure). A conveyance roller 42b is provided.

  The pickup roller 42a comes into contact with the surface of one end of the recording paper at the top of the recording paper set in the paper feeding cassette 42, and reliably picks up and conveys the paper one by one by the frictional resistance of the roller. Yes.

  The conveyance roller 42b is configured to convey the recording sheet fed from the pickup roller 42a upward to the image forming unit 108 along the recording sheet conveyance path S2 formed on one end side in the housing 1a. .

Next, image output by the color image forming apparatus 1 of the present embodiment will be described.
The color image forming apparatus 1 transfers the toner image on the photosensitive drum 21 onto the recording paper supplied from the paper supply unit 109 via the transfer belt 31 by a so-called intermediate transfer method (offset method). Has been.

First, the charger 22 uniformly charges the outer peripheral surface of the photosensitive drum 21 to a predetermined potential.
By irradiating the charged photosensitive drum 21 with laser light from the exposure unit 10, an electrostatic latent image for each color is generated on the photosensitive drum 21 for each color.

  In the present embodiment, the exposure unit 10 generates an electrostatic latent image generated on the photosensitive drum 21 with the peripheral speed of the photosensitive drum 21 by an image control unit (not shown) provided in the color image forming apparatus 1. The transfer belt 31 is controlled so as to be generated in a contracted state in the sub-scanning direction corresponding to the speed difference with the moving speed of the transfer belt 31.

  Next, toner is supplied from the developing unit 23 to the outer peripheral surface of the photosensitive drum 21, and the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 21 is visualized as a toner image by the toner.

Then, the toner image generated on the photosensitive drum 21 is transferred to the transfer belt 31.
The transfer of the toner image from the photosensitive drum 21 to the transfer belt 31 is performed by applying a high voltage to the intermediate transfer roller 35 disposed in contact with the back side of the transfer belt 31.

  By applying a high voltage with a polarity (+) opposite to the toner charging polarity (-) to the intermediate transfer roller 35, the transfer belt 31 is uniformly applied with a high voltage by the intermediate transfer roller 35 and has a reverse polarity. (+). As a result, the toner image of the charged polarity (−) on the photosensitive drum 21 is transferred onto the transfer belt 31 when the photosensitive drum 21 is in rotational contact with the transfer belt 31.

  Each color toner image formed on each photoconductive drum 21 is sequentially superimposed and transferred as the transfer belt 31 moves and rotationally contacts each photoconductive drum 21, and the color toner is transferred onto the transfer belt 31. An image is formed.

  In this manner, the electrostatic latent images visualized with toner on the photosensitive drum 21 for each color are stacked on the transfer belt 31, and the print image is reproduced on the transfer belt 31 as a multicolor toner image. The

  In this embodiment, since the moving speed of the transfer belt 31 conveyed by the transfer belt driving roller 32 is set with a speed difference of + 4% with respect to the peripheral speed of the photosensitive drum 21, the photosensitive drum The toner image formed on 21 is stretched in the sub-scanning direction corresponding to this speed difference and transferred to the transfer belt 31.

  However, since a toner image that is preliminarily contracted under the control of the image control unit is formed on the photosensitive drum 21, the toner image that is stretched and transferred onto the transfer belt 31 is an actual size toner image. It becomes.

  The multicolor toner image transferred onto the transfer belt 31 is transferred from the transfer belt 31 onto the recording paper by the transfer roller 36 at a position where the transfer belt 31 moves and the recording paper and the transfer belt 31 overlap. The

  The toner adhering to the transfer belt 31 due to contact with the photosensitive drum 21 or the toner remaining on the transfer belt 31 without being transferred onto the recording paper by the transfer roller 36 causes toner color mixing in the next step. Therefore, it is removed and collected by the transfer belt cleaning unit 37.

Next, the recording paper supply operation by the paper supply unit 109 will be described.
When recording paper placed on the manual feed tray 41 is used, the recording paper is fed into the apparatus one by one from the manual feed tray 41 by the pickup roller 41a at a timing controlled by an instruction on an operation panel (not shown). It is captured.

  The recording sheet taken into the apparatus is conveyed to the image forming unit 108 along the recording sheet conveying path S1 by the conveying rollers 41b, 41c, and 41d.

  On the other hand, when recording paper stored in the paper feed cassette 42 is used, the recording paper is separated and fed one by one from the paper feed cassette 42 by the pickup roller 42a, and along the recording paper transport path S2 by the transport roller 42b. It is conveyed to the image forming unit 108.

  The recording paper conveyed from the manual feed tray 41 or the paper feed cassette 42 is conveyed to the transfer roller 36 side at a timing when the leading edge of the recording paper and the leading edge of the toner image on the transfer belt 31 are aligned by the registration roller 26. The toner image on the transfer belt 31 is transferred onto the recording paper.

  The recording sheet on which the toner image has been transferred is conveyed substantially vertically and reaches the fixing unit 27, where the toner image is thermally fixed on the recording sheet by the heating roller 27a and the pressure roller 27b.

  The recording paper that has passed through the fixing unit 27 is discharged face down onto the paper discharge tray 43 by the paper discharge roller 28 in the case of a single-sided print request.

  On the other hand, in the case of a double-sided printing request, after the recording paper is chucked by the paper discharge roller 28, the paper discharge roller 28 is rotated in the reverse direction to guide the recording paper to the double-sided document transport path S3. Transport to roller 26.

At this time, the front side of the recording sheet is reversed while the surface to be transferred is reversed.
That is, the end that becomes the start side during the first transfer is the end side during the back transfer, and the end that becomes the end side during the first transfer is the start side during the back transfer.

Then, after the toner image is transferred and thermally fixed on the back surface of the recording paper, it is discharged onto the paper discharge tray 43 by the paper discharge roller 28.
As described above, the transfer operation to the recording paper is performed.

  Here, the transfer state at the time of primary transfer by the configuration of the color image forming apparatus 1 of the present embodiment will be described in detail based on the apparatus configuration.

  In the present embodiment, as shown in FIG. 2, the intermediate transfer roller 35 is transferred to the photosensitive drum 21 in the left-right direction in FIG. The belt 31 is arranged at a position shifted downstream in the moving direction of the belt 31 and presses the inner surface of the transfer belt 31, whereby the outer surface of the transfer belt 31 winds a part of the outer peripheral surface of the photosensitive drum 21 and is predetermined. The nip amount is provided.

  By disposing the intermediate transfer roller 35 as described above, the transfer belt 31 can form a nip portion in a wide range with respect to the photosensitive drum 31, and further contact with the photosensitive drum 31 by the tension of the transfer belt 31. Therefore, the pressure applied to the nip portion of the transfer belt 31 is reduced and the pressure is concentrated as compared with the conventional configuration in which the nip is obtained by being sandwiched between the intermediate transfer roller 35 and the photosensitive drum 21. Can be avoided.

  Accordingly, it is possible to reduce the influence of the pressure fluctuation at the portion of the transfer belt 31 that is in contact with the photosensitive drum 31 during the primary transfer. Thereby, stable toner image transfer can be realized.

  Further, since the transfer belt 31 moves at a speed faster than the peripheral speed of the photosensitive drum 21, the tension on the downstream side of the photosensitive drum 21 in the moving direction of the transfer belt 31 is lower than the upstream side. In addition, the electric field applied to the transfer belt 31 is lower on the downstream side than the upstream side in the moving direction of the transfer belt 31 from the upstream side. As a result, it is possible to suppress unnecessary transfer of toner to the transfer belt 31 except when the photosensitive drum 21 and the transfer belt 31 are in contact with each other and transfer is normally performed. Transcription can be realized.

Next, the transfer state of the toner image in the primary transfer by the color image forming apparatus 1 of the present embodiment will be described based on examples.
FIG. 3 is an explanatory diagram showing a transfer state of a toner image according to a speed difference between the photosensitive drum and the transfer belt at the time of primary transfer in the color image forming apparatus of one example of the present embodiment.

  In this example, when primary transfer is performed in the color image forming apparatus 1 according to the above-described embodiment, the toner image is changed by changing the speed difference between the moving speed of the transfer belt 31 and the peripheral speed of the photosensitive drum 21. These transfer states are compared.

  The evaluation criteria for the transfer state are: (1) presence / absence of missing characters, (2) reproducibility of fine lines, (3) printing density (measured with a Macbeth densitometer), (4) life deterioration of the photosensitive drum (scratches, It is based on each item of cracks).

  In the evaluation of the transfer state, the transfer images transferred by the speed difference between the moving speed of each transfer belt 31 and the peripheral speed of the photosensitive drum 21 are relatively compared and evaluated based on the above evaluation criteria. .

  FIG. 3 shows the speed difference between the peripheral speed of the photosensitive drum 21 and the moving speed of the transfer belt 31 as a speed ratio of the moving speed of the transfer belt 31 to the peripheral speed of the photosensitive drum 21.

  As shown in FIG. 3, it is apparent that the transfer state of the toner image during the primary transfer in the color image forming apparatus 1 affects the speed difference between the peripheral speed of the photosensitive drum 21 and the moving speed of the transfer belt 31. The transfer state is worse as the moving speed of the transfer belt 31 is slower than the peripheral speed of the photosensitive drum 21, and the transfer state is improved as the moving speed of the transfer belt 31 is increased.

  In the present embodiment, the transfer state of the toner image due to the difference between the circumferential speed of the photosensitive drum 21 and the moving speed of the transfer belt 31 indicates that the moving speed of the transfer belt 31 is 4% to the circumferential speed of the photosensitive drum 21. A good transfer state peak is reached at a speed as fast as 5%.

  That is, according to this embodiment, in the color image forming apparatus using the offset method, it is good when the moving speed of the transfer belt 31 in the primary transfer is about 4% to 5% faster than the peripheral speed of the photosensitive drum 21. Transfer of a toner image can be performed.

  As described above, according to the color image forming apparatus 1 of the present embodiment, in the primary transfer, the moving speed of the transfer belt 31 is set to be higher than the peripheral speed of the photosensitive drum 21. Good transfer of the toner image can be realized.

  Furthermore, by setting the moving speed of the transfer belt 31 to a speed that is 4% faster than the peripheral speed of the photosensitive drum 21, a particularly good toner image transfer can be realized.

  Further, according to the present embodiment, the intermediate transfer roller 35 is disposed at a position where the axis of the intermediate transfer roller 35 is shifted in the left-right direction in FIG. Therefore, when the transfer belt 31 comes into contact with the photosensitive drum 31 due to the tension of the transfer belt 31, the pressure applied to the nip portion of the transfer belt 31 can be reduced and pressure concentration can be avoided. As a result, it is possible to reduce the influence of the pressure fluctuation at the portion of the transfer belt 31 that is in contact with the photosensitive drum 31, thereby realizing more stable transfer of the toner image.

  Further, according to the present embodiment, the toner image formed on the photosensitive drum 21 is controlled by the image control unit, and corresponds to the speed difference between the peripheral speed of the photosensitive drum 21 and the moving speed of the transfer belt 31. Since the electrostatic latent image generated on the photosensitive drum 21 is contracted in the sub-scanning direction, the toner image formed on the photosensitive drum 21 is transferred to the peripheral speed of the photosensitive drum 21 and the transfer. Even if the belt 31 is stretched in the sub-scanning direction and transferred to the transfer belt 31 due to the speed difference with the moving speed of the belt 31, the toner image transferred to the transfer belt 31 has an actual size, and a toner image similar to the actual image information is obtained. Can be formed.

  In this embodiment, the image information of the toner image formed on the photosensitive drum 21 is subtracted by the image control unit in accordance with the speed difference between the peripheral speed of the photosensitive drum 21 and the moving speed of the transfer belt 31. Although writing is performed on the photosensitive drum 21 in a contracted state in the scanning direction, the present invention is not limited to this, and for example, image information of a toner image formed on the photosensitive drum 21 is obtained. Based on the image information processed in the sub-scanning direction corresponding to the speed difference between the peripheral speed of the photosensitive drum 21 and the moving speed of the transfer belt 31 by image processing in the image control unit, the photosensitive drum 21 may be written.

  Further, the color image forming apparatus of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the plurality of process printing units 20 as image forming means are arranged in parallel in the horizontal direction, but may be arranged in parallel in the vertical direction.

  Further, the present invention is not limited to the configuration of the image forming unit, the primary transfer unit, the secondary transfer unit, and the like constituting the color image forming apparatus, but is applied to those using an intermediate transfer member. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram (a cross-sectional view from the rear) illustrating an overall configuration of a color image forming apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing a positional relationship between a transfer belt and a photosensitive drum constituting the color image forming apparatus. FIG. 6 is an explanatory diagram illustrating a transfer state of a toner image according to a speed difference between a photosensitive drum and a transfer belt at the time of primary transfer in a color image forming apparatus according to an example of the present embodiment. FIG. 10 is an explanatory diagram illustrating a positional relationship between a photosensitive drum of a conventional image forming apparatus, a recording sheet conveyed, and an intermediate transfer roller. FIG. 10 is an explanatory diagram illustrating a transfer state of a toner image corresponding to a speed difference between a photosensitive drum and a recording sheet conveyed in a conventional image forming apparatus.

Explanation of symbols

1 Color image forming apparatus 20, 20a, 20b, 20c, 20d Process printing unit (image forming means)
21, 21a, 21b, 21c, 21d Photosensitive drum (image carrier)
30 Transfer belt unit (primary transfer means)
31 Transfer belt (intermediate transfer member)
35, 35a, 35b, 35c, 35d Intermediate transfer roller 36 Transfer roller (secondary transfer means)

Claims (5)

An image forming unit having an image carrier that carries a developer image formed by a developer that matches each hue according to color-separated image information, and an image carrier that is in pressure contact with the rotating image carrier and the image carrier Primary transfer means having an intermediate transfer body for transferring the developer image formed on the image carrier by moving along the rotation direction of the image, and the developer image transferred to the intermediate transfer body on the transfer medium In a color image forming apparatus comprising a secondary transfer means for transferring,
The color image forming apparatus, wherein the intermediate transfer member has a moving speed higher than a peripheral speed of the image carrier. The moving speed of the intermediate transfer member is
(Peripheral speed of image carrier) <(Movement speed of intermediate transfer member) ≦ (Peripheral speed of image carrier) × 104%
The color image forming apparatus according to claim 1, wherein the color image forming apparatus is defined so as to satisfy the above relationship.   The developer image formed on the image carrier is formed in a contracted state in the sub-scanning direction corresponding to the speed difference between the peripheral speed of the image carrier and the moving speed of the intermediate transfer member. The color image forming apparatus according to claim 1.   The image information of the developer image is contracted in the sub-scanning direction corresponding to the speed difference between the peripheral speed of the image carrier and the moving speed of the intermediate transfer member by the image control unit provided in the color image forming apparatus. 4. The color image forming apparatus according to claim 3, wherein the color image forming apparatus is written on the image carrier.   The image information of the developer image is obtained in the sub-scanning direction corresponding to the speed difference between the peripheral speed of the image carrier and the moving speed of the intermediate transfer member by image processing by an image control unit provided in the color image forming apparatus. 4. The color image forming apparatus according to claim 3, wherein the color image forming apparatus is written on the image carrier based on the image information subjected to image processing in a contracted state.

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