JP2008281786A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus and an image forming method by which toner consumption is suppressed as far as possible, and color shift is made small by using toner as lubricant. <P>SOLUTION: In a four-cycle type color printer, a cleaner blade for removing toner remaining on an intermediate transfer belt is installed to contact with/separate from the intermediate transfer belt. The blade separates from the intermediate transfer belt in timing T1 when a Y image of a first color is primarily transferred to the intermediate transfer belt, and holds a separate state thereafter, then press-contacts with the intermediate transfer belt in timing T2 when a K image of a fourth color is primarily transferred. When an image is present at the trailing end K' of the K image and integrated toner amount of four colors in areas Y', M', C' and K' is smaller than a predetermined threshold, the toner is applied to the image non-forming areas Y", M", C" and K" of the intermediate transfer belt as the lubricant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an electrophotographic color image forming apparatus and an image forming method.

  In general, as a color image forming apparatus such as an electrophotographic copying machine or a printer, four color toner images sequentially formed on one photoconductor are sequentially primary-transferred onto an intermediate transfer belt and synthesized. A four-cycle method is known in which the image is secondarily transferred onto a recording medium.

  In this type of four-cycle image forming apparatus, the cleaner blade for removing residual toner from the intermediate transfer belt is separated from the intermediate transfer belt while the primary transferred toner image is passing, and the intermediate transfer is performed after the secondary transfer. Driven to press against the belt. The secondary transfer roller is also driven so as to come into pressure contact with the intermediate transfer belt after the fourth color toner image has been primarily transferred.

  When a material having rigidity such as polycarbonate is used for the intermediate transfer belt, the deflection of the intermediate transfer belt changes when the cleaner blade and the secondary transfer roller come in contact with each other, and the belt moving speed in the primary transfer portion changes. Had a bug. As a result, color misregistration between the four colors occurred. In particular, the color shift due to the contact and separation of the cleaner blade is remarkable, and when the frictional force between the cleaner blade and the intermediate transfer belt increases, the speed fluctuation at the time of contact and separation (especially, when pressing) tends to increase.

  In order to prevent color misregistration caused by the pressure contact operation of the cleaner blade, conventionally, as described in Patent Documents 1, 2, and 3, toner is periodically supplied onto the intermediate transfer belt to cause friction with the cleaner blade. It has been proposed to reduce force. Since the toner contains a lubricant and the like, this is a measure focusing on the effect of reducing the frictional force between the cleaner blade and the intermediate transfer belt.

However, the above-described countermeasure has a problem that toner consumption is enormous because toner that is not always secondarily transferred is supplied to the non-image forming area of the intermediate transfer belt. Although the color misregistration is certainly solved, it is not a preferable measure that the toner consumption increases more than necessary.
JP 2005-106919 A JP 2005-250215 A JP 2004-264700 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus and an image forming method capable of reducing color misregistration using toner as a lubricant while minimizing toner consumption.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
In a four-cycle type image forming apparatus in which four-color toner images sequentially formed on one photoconductor are sequentially transferred and synthesized on an intermediate transfer belt, and the synthesized image is secondarily transferred onto a recording medium.
A cleaner member for removing toner remaining on the intermediate transfer belt;
Driving means for pressing / separating the cleaner member against the intermediate transfer belt;
Control means for controlling the image forming process;
With
The control means has an image in the cleaner member press-contact area at the rear end portion of the fourth color image, and the four-color integrated toner amount from the press start portion to the rear end of the image in each of the four color image forming areas is predetermined. The toner is applied as a lubricant to the non-image forming area on the intermediate transfer belt from the cleaner member press-contact start portion to at least the rear end of the image,
It is characterized by.

An image forming method according to the present invention includes:
In a four-cycle image forming method in which four-color toner images sequentially formed on one photoconductor are primarily transferred and synthesized on an intermediate transfer belt in sequence, and the synthesized image is secondarily transferred onto a recording medium.
The cleaner member is separated from the intermediate transfer belt at the first timing when the first color image is primarily transferred onto the intermediate transfer belt, and the cleaner is moved at the second timing when the fourth color image is primarily transferred. The member is pressed against the intermediate transfer belt,
When an image exists in the cleaner member press-contact area at the rear end portion of the fourth color image, and the four-color integrated toner amount from the press-contact start portion to the rear end of the image is less than a predetermined threshold in each of the four color image forming areas And applying toner as a lubricant to a non-image forming region on the intermediate transfer belt from the cleaner member press-contact start portion to at least the rear end of the image,
It is characterized by.

  In the image forming apparatus and the image forming method according to the present invention, the toner member is applied to the non-image forming area of the intermediate transfer belt by applying the toner to the non-image forming area of the intermediate transfer belt, which is generated when the cleaner member presses against the intermediate transfer belt By reducing the frictional force, color misregistration is prevented. The timing at which the cleaner member presses against the intermediate transfer belt is normally the rear end portion of the fourth color image passing through the primary transfer portion, and the color shift of the rear end portion of the fourth color image is easily noticeable. Therefore, the toner as the lubricant is applied when the image exists in the cleaner member press-contact area in the rear end portion of the fourth color image, and in the four-color image forming area from the press start portion to the rear end of the image. The case where the four-color integrated toner amount is smaller than a predetermined threshold value is assumed. As a result, toner consumption can be minimized.

  The frictional force between the intermediate transfer belt and the cleaner member changes in accordance with the amount of residual toner in the cleaner member pressure contact area, environmental conditions (temperature, humidity, etc.), and durability conditions (cumulative operation time of the intermediate transfer belt, etc.). Therefore, it is preferable to make the determination based on at least one of the four-color integrated toner amount, environmental conditions, and durability conditions.

  Embodiments of an image forming apparatus and an image forming method according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of color printer)
FIG. 1 shows a schematic configuration of a color printer 1 which is an embodiment of an image forming apparatus according to the present invention. The color printer 1 generally includes a photoconductor unit 10, a developing unit 15, an intermediate transfer unit 20, a laser scanning unit 14, a fixing unit 45, and a paper feeding unit 40.

  The photoreceptor unit 10 includes a photoreceptor drum 11, a charger 12, a cleaner blade 13, and the like. The developing unit 15 is composed of Y (yellow), M (magenta), C (cyan), and K (black) developing devices 16 (16Y, 16M, 16C, and 16K) that are integrated with the support shaft 17 as arrows It is installed so as to be rotatable in the A direction. The intermediate transfer unit 20 is configured to hold an intermediate transfer belt 21 on a roller 24 provided with a driving roller 22, a driven roller 23, and a coil spring 28 for applying tension so as to be rotatable endlessly in the direction of arrow B. 25 and a primary transfer roller 26. Further, a cleaner blade 30 for residual toner is provided.

  In the image formation, first, image data is input from an external computer or the like, and four color images are exposed to the photosensitive drum 11 from the laser scanning unit 14 in the order of Y, M, C, K (electrostatic latent image). Image formation) and development (toner image formation) by the developing device 16 of each color. This toner image is primarily transferred onto the intermediate transfer belt 21 by an electric field applied from the primary transfer roller 26 for each color, and four color images are superimposed on the intermediate transfer belt 21.

  For color matching of the four color toner images in the primary transfer, a detection hole formed on one side of the intermediate transfer belt 21 is detected by a position detection sensor SE1 (see FIG. 4), and image writing to each photosensitive drum 11 is performed. This is done by matching the timing.

  On the other hand, the paper is fed one by one from the paper feed unit 40 by the paper feed roller 41, passes through the pair of transport rollers 42, and is supported by the intermediate transfer belt 21 and the secondary transfer roller 27 supported by the drive roller 22. Then, the composite image is secondarily transferred from the intermediate transfer belt 21 by the electric field applied from the secondary transfer roller 27. Thereafter, the sheet is heated and fixed by toner in the fixing unit 45, and is discharged from the discharge roller pair 5 onto the discharge tray 6.

  The configuration and operation of each image forming unit are well known in the art and will not be described in detail.

(Intermediate transfer unit)
As shown in FIG. 2, the cleaning blade 30 is pressed / separated by a cleaner blade contact / separation mechanism 31 at a predetermined timing described below with respect to the intermediate transfer belt 21. The cleaner blade contact / separation mechanism 31 includes a bracket 32 that holds the cleaner blade 30, a coil spring 34, a cam 35, and a motor (not shown).

  That is, the bracket 32 is rotatable about the support shaft 33 and is elastically biased in the direction of arrow C by the coil spring 34. The cam 35 is connected to a motor (not shown) via a support shaft 36, and the side surface 32 a of the bracket 32 is elastically pressed against the outer peripheral surface by the spring force of the coil spring 34. When the small diameter portion of the cam 35 is in contact with the side surface 32 a, the cleaner blade 30 is in pressure contact with the intermediate transfer belt 21, and this pressure contact force is applied by the coil spring 34. On the other hand, when the cam 35 is rotated 90 °, the large diameter portion of the cam 35 contacts the side surface 32a, the bracket 32 rotates in the direction opposite to the arrow C with the support shaft 33 as a fulcrum, and the cleaner blade 30 Separated from the intermediate transfer belt 21.

  The cleaner blade 30 is separated from the intermediate transfer belt 21 while the primary transferred toner image is passing, and is pressed against the intermediate transfer belt 21 after the secondary transfer. Specifically, the cleaner blade 30 is normally set in a state of being pressed against the intermediate transfer belt 21, and as shown in FIGS. 5A and 5B, the image forming process is started and the first color Y toner is started. The image is separated from the intermediate transfer belt 21 at the timing T1 during the primary transfer of the image, and thereafter the separation state is maintained, and the intermediate at the timing T2 during the primary transfer of the K toner image of the fourth color. Residual toner is removed by pressure contact with the transfer belt 21.

  The toner image primarily transferred onto the intermediate transfer belt 21 is secondarily transferred onto the paper as described above after the fourth color K toner image is primarily transferred. Accordingly, the secondary transfer roller 27 is also provided with a contact / separation mechanism (not shown) similar to the contact / separation mechanism 31 and is pressed against the intermediate transfer belt 21 only in a region where the secondary transfer is performed.

(Control part)
Here, the control unit of the printer will be described with reference to FIG. This control unit is configured with the CPU 50 as the center. The CPU 50 includes a pixel counter CL that counts the number of pixels of each color of the input image data, an environmental condition detection sensor SE2 such as temperature and humidity (see FIG. 1), and a print function. A signal from an endurance counter TC for counting the cumulative number of sheets is input. The CPU 50 controls the image forming drive mechanism including the cleaner blade contact / separation mechanism 31 and the contact / separation mechanism of the secondary transfer roller 27.

(Occurrence of color shift)
The cleaning blade 30 is made of, for example, urethane rubber. The intermediate transfer belt 21 is made of a resin material such as polyphenylene sulfide, polycarbonate, polyimide, and has rigidity. Here, the rigidity of the intermediate transfer belt 21 means a Young's modulus of about 1 to 5 GPa. Incidentally, the Young's modulus of rubber is about 1.5 to 5 MPa.

  When the intermediate transfer belt 21 is made of a material having rigidity, the deflection of the intermediate transfer belt 21 changes when the cleaner blade 30 contacts and separates, and the belt moving speed in the primary transfer portion changes. Normally, the intermediate transfer belt 21 moving in a stretched state as shown by a solid line in FIG. 3 bends as shown by a dotted line when the cleaner blade 30 is pressed. As described above, when the deflection of the intermediate transfer belt 21 changes and the moving speed fluctuates, a color shift occurs between the four color images.

  Such a color shift will be described with reference to FIG. FIG. 6 schematically shows a case where an A4 size sheet is continuously passed in the long side direction to form an image. A curve MC is a color shift between the M image and the C image, and a curve MK is a curve MK. A color shift between the M image and the K image, and a curve MY indicates a color shift between the M image and the Y image. Since the secondary transfer roller 27 and the cleaner blade 30 are separated during the primary transfer of the Y image, color misregistration occurs with respect to the M image and the C image in which no contact / separation operation occurs. Further, since the secondary transfer roller 27 and the cleaner blade 30 are in pressure contact with each other during the primary transfer of the K image, color misregistration occurs.

  As apparent from FIG. 6, in one color image, the color shift between the Y image and the K image due to the contact and separation of the cleaner blade 30 at the rear end of the image becomes considerably large. In the present embodiment, as will be described below, the color misregistration (the region indicated by the symbol G in FIG. 6) when the cleaner blade 30 is in pressure contact is made as small as possible to eliminate the increase in color misregistration.

  FIG. 7 shows the results of actual measurement of the relationship between the torque of the cleaner portion (the portion where the cleaner blade 30 presses against the intermediate transfer belt 21) and the color misregistration amount of the K image. Although there are some variations depending on the actual measurement timing, as the torque increases, the amount of deflection of the intermediate transfer belt 21 increases, and as a result, the amount of color misregistration tends to increase.

  FIG. 8 shows the result of actual measurement of the dependency of the friction coefficient μ between the intermediate transfer belt 21 and the cleaner blade 30 depending on the environmental conditions (low temperature / low humidity, normal temperature / normal humidity, high temperature / high humidity). Although there are some variations depending on the actual measurement timing, the friction coefficient μ tends to increase as the temperature and humidity increase.

  The other cause of the increased frictional force is the ratio of the image to the image forming area (hereinafter referred to as coverage). Coverage is the average amount of toner per unit area. Since the toner functions as a lubricant that reduces the frictional force, the frictional force between the cleaner blade 30 and the intermediate transfer belt 21 tends to increase as the coverage decreases. Further, the cumulative number of images formed by the intermediate transfer belt 21 increases, and the frictional force increases as the surface becomes rough.

(Resolve color drift)
Therefore, in this embodiment, an image is present in the cleaner blade pressure contact area (see reference numeral K ′ in FIG. 5A) at the rear end portion of the K image, and pressure welding starts in each of the four color image formation areas. When the four-color integrated toner amount from the first part to the rear end of the image (see symbols Y ′, M ′, C ′, and K ′ in FIG. 5A) is less than a predetermined threshold value, the image is transferred from the cleaner blade pressure contact starting part to the rear of the image. Toner is applied as a lubricant to a non-image forming area (see symbols Y ″, M ″, C ″, K ″ in FIG. 5B) on the intermediate transfer belt 21 to the end. Since extra toner is applied to the pressure contact areas Y ″, M ″, C ″, K ″ of the cleaner blade 30, a lubricating effect by the toner (reduction of frictional force between the blade 30 and the belt 21) occurs. The color shift of the K image in the rear end region of the image indicated by the symbol G in FIG. 6 is reduced, and the color shift of all four colors is reduced.

  The toner functions as a lubricant because a metal soap such as zinc stearate or calcium stearate is added to the toner.

  The toner as a lubricant may be applied to all of the non-image forming areas Y ", M", C ", K" for a four-color image or to any image non-image forming area. May be. Of the four color toners, a toner having a high content of the lubricant component may be selected and applied, or priority may be given to the application from the developing device 16 having a large amount of remaining toner. Further, the amount of toner applied as a lubricant may be adjusted according to the variation in the frictional force between the cleaner blade 30 and the intermediate transfer belt 21. That is, it may be determined according to the four-color integrated toner amount, environmental conditions such as temperature and humidity, and the degree of surface roughness of the intermediate transfer belt 21 (accumulated number of prints by the belt 21 = durable time).

  The threshold of the four-color integrated toner amount serving as a reference for whether or not to apply toner as a lubricant is, for example, a frictional force between the blade 30 and the belt 21 that causes a K image color misregistration of 0.08 mm or more. It is preferable to preliminarily determine a threshold value under severe conditions that occur in the process, and to switch the threshold value so as to decrease according to the environmental conditions and the accumulated number of prints as shown in Table 1 below.

  In the present embodiment, the necessary amount of toner is applied only when it is necessary to reduce the frictional force between the blade 30 and the belt 21 (when there is an image at the rear end of the K image). The color shift at the trailing edge of the image can be minimized as much as the toner consumption.

(Control procedure)
Here, the main part of the control procedure executed by the CPU 50 in this embodiment will be described with reference to FIG. First, after the control is started, the CPU 50 obtains information on the number of pixels of each color image from the pixel counter CL, temperature, humidity, and accumulated print count information from the environmental condition detection sensor SE2 (step S1). Subsequently, it is determined whether or not an image exists in the rear end portion K ′ of the K image. If no image exists (NO in step S2), normal image forming processing is executed (step S3).

  If an image exists at the rear end portion of the K image (YES in step S2), the four-color integrated toner amount in the regions Y ′, M ′, C ′, and K ′ is compared with the threshold value, and the four-color integration is performed. If the toner amount is larger than the threshold (NO in step S4), normal image forming processing is executed (step S3). If the four-color integrated toner amount is less than the threshold value (YES in step S4), the toner application region and the toner application amount are determined (step S5). The toner application region determined in step S5 is also the determination of the developing device 16 that applies toner as a lubricant. Further, the toner application amount is determined based on the number of pixels of the image, temperature / humidity, and the cumulative number of prints so that the frictional force between the blade 30 and the belt 21 can minimize the color misregistration amount of the K image.

1 is a schematic configuration diagram illustrating a color printer which is an example of an image forming apparatus according to the present invention. It is explanatory drawing which shows the contacting / separating mechanism of a cleaner blade. FIG. 6 is an explanatory diagram illustrating the bending of an intermediate transfer belt. It is a block diagram which shows the control part of a color printer. (A), (B) is a chart showing the movement of each color toner image primarily transferred onto the intermediate transfer belt and the contact / separation timing of the cleaner blade. It is a graph which shows the color shift amount of a color image. It is a graph which shows the relationship of the color shift amount of K image with respect to the torque of a cleaner part. 6 is a graph showing the relationship of the frictional force between the cleaner blade and the intermediate transfer belt with respect to environmental conditions. It is a flowchart figure which shows an example of a control procedure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Color printer 10 ... Photosensitive unit 11 ... Photosensitive drum 20 ... Intermediate transfer unit 21 ... Intermediate transfer belt 30 ... Cleaner blade 31 ... Contacting / separating mechanism 50 ... CPU

Claims (3)

In a four-cycle type image forming apparatus in which four-color toner images sequentially formed on one photoconductor are sequentially transferred and synthesized on an intermediate transfer belt, and the synthesized image is secondarily transferred onto a recording medium.
A cleaner member for removing toner remaining on the intermediate transfer belt;
Driving means for pressing / separating the cleaner member against the intermediate transfer belt;
Control means for controlling the image forming process;
With
The control means has an image in the cleaner member press-contact area at the rear end portion of the fourth color image, and the four-color integrated toner amount from the press start portion to the rear end of the image in each of the four color image forming areas is predetermined. The toner is applied as a lubricant to the non-image forming area on the intermediate transfer belt from the cleaner member press-contact start portion to at least the rear end of the image,
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit determines a toner amount to be applied as a lubricant based on at least one of the four-color integrated toner amount, environmental conditions, and durability conditions. apparatus. In a four-cycle image forming method in which four-color toner images sequentially formed on one photoconductor are primarily transferred and synthesized on an intermediate transfer belt in sequence, and the synthesized image is secondarily transferred onto a recording medium.
The cleaner member is separated from the intermediate transfer belt at the first timing when the first color image is primarily transferred onto the intermediate transfer belt, and the cleaner is moved at the second timing when the fourth color image is primarily transferred. The member is pressed against the intermediate transfer belt,
When an image exists in the cleaner member press-contact area at the rear end portion of the fourth color image, and the four-color integrated toner amount from the press-contact start portion to the rear end of the image is less than a predetermined threshold in each of the four color image forming areas And applying toner as a lubricant to a non-image forming region on the intermediate transfer belt from the cleaner member press-contact start portion to at least the rear end of the image,
An image forming method.

Images