JP2006145805A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an excellent image free of a white void at an image center part due to a failure in transfer by suppressing cohesion of toner and transferring a toner image to an intermediate transfer belt with shearing force. <P>SOLUTION: The image forming apparatus having at least the intermediate transfer belt 501 which moves on the surface of a photoreceptor 101 while being brought into contact with the photoreceptor 101, a primary transfer roller 507 which forms a transfer electric field between the photoreceptor and intermediate transfer belt 501 to transfer a toner image formed on the photoreceptor onto the intermediate transfer belt 501, and a secondary transfer roller 600 which transfers the toner image held on the intermediate transfer belt 501 onto recording materials of various sizes, is characterized in that the linear speed difference between the photoreceptor 101 and the intermediate transfer belt 501 is ≥0.7 mm/s, the difference in dynamic friction coefficient is ≥0.03, and the primary transfer pressure of the primary transfer roller 507 is ≤15 N/m. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus for an electrophotographic process such as a copying machine, a printer, and a facsimile. More specifically, the present invention relates to an intermediate transfer member such as an intermediate transfer belt, an image carrier such as a photosensitive drum, and an intermediate transfer from an image carrier. The present invention relates to a transfer device such as a transfer roller that moves toner to a body, and a transfer system that combines them.

Means for transferring a toner image from an image carrier to an intermediate transfer member or a recording material are roughly classified into a non-contact bias application method using a corotron and a contact bias application method using a transfer roller. In recent years, the contact method is often used because of the small amount of ozone generated when a bias is applied and because it also serves as a transfer (auxiliary) means for an intermediate transfer member and a recording material.
When the transfer roller is used, the roller is pressed against the photosensitive drum with the intermediate transfer belt interposed therebetween. However, when the transfer process is performed by bringing the photosensitive drum and the intermediate transfer belt into contact with each other as described above, an abnormal image called “worm biting” may occur. “Insect bite” is a phenomenon in which when transferring a toner image such as characters and fine lines, the edge portion of the toner image is transferred cleanly, but the central portion of the image is not transferred and falls out white.

There are two main mechanisms for the occurrence of this insect eater. One is an “edge effect” in which a transfer electric field concentrates on an edge portion of a toner image. As a result, a sufficient electric field is not applied to the toner at the center portion of the toner image as much as the edge portion, and the toner becomes difficult to be transferred. The other is that toner is agglomerated as “packing” by applying pressure to the toner layer on the photosensitive drum during transfer. The toner layer before transfer forms a layer with appropriate gaps between toner particles. However, when pressure is applied during transfer, a force that is tightly pressed is applied. At this time, the toner at the edge portion can be dispersed so as to collapse to the peripheral portion without the toner layer, but the toner at the central portion cannot release the applied pressure, and is solidified and aggregated. . The toner packed in this way has increased adhesion to the surface of the photosensitive drum, and even if a transfer electric field is applied, it cannot move to the intermediate transfer belt side, and becomes “worm bite”.
In order to prevent “worm biting”, it is necessary to have means for suppressing the above-mentioned cause of occurrence or means for transcribing and transferring the cause of occurrence. However, the edge effect is a physical phenomenon according to electromagnetism, and cannot be prevented as long as the transfer electric field is uniformly applied across the width of the transfer roller.

The following can be considered as measures to prevent “worm eaters”.
1. In order to suppress the packing as much as possible, the transfer pressure (contact pressure of the transfer roller against the photosensitive drum) is weakened.
2. In order to suppress packing, the toner itself has a characteristic that it is difficult to aggregate. (Since the resins are not in direct contact with each other, the additive is devised or the shape is made to have a high degree of circularity. Use of polymerized toner, etc.)
3. By controlling the surface state of the intermediate transfer belt, the adhesion force to the belt is increased rather than the drum, and the packed toner is also moved to the intermediate transfer belt side. (Controls friction coefficient, surface free energy, surface tension, etc.)
4). By changing the moving speed (linear speed) between the surface of the photosensitive drum and the surface of the intermediate transfer belt, the toner is moved by applying a shearing force to the toner layer.
Most of the insect biting prevention techniques that have been proposed heretofore employ one or more of these methods. In particular, a technique characterized by providing a difference in linear velocity is disclosed as follows.
Patent Document 1 discloses a technique in which a transfer material is set to a linear velocity of 1.002 times to 1.02 times with respect to an image carrier and a transfer pressure is set to 10 to 70 g / cm.
Patent Document 2 discloses a technique in which the relationship between the friction coefficients is such that image carrier ≦ intermediate transfer member ≦ recording material, and a linear velocity difference is provided between the image carrier and the intermediate transfer member.
In Patent Document 3, a toner having a linear speed ratio of 0.9% or more between the photosensitive member and the intermediate transfer member, a toner having a shape factor of 134 or less and an average particle diameter of 5 μm to 9 μm, and dynamic friction on the surface of the photosensitive member is used. A technique for setting the coefficient to 0.9 or less is disclosed.

JP 2000-162899 A Japanese Patent Laid-Open No. 06-332324 Japanese Patent Laid-Open No. 2004-029435

However, insect bite may not be improved even if the above-mentioned 1 to 4 are used. In the experiments by the present inventors, there were some cases in which insect bite deteriorated by giving a linear velocity difference.
As a result of detailed experiments on insect eaters, the following was qualitatively found.
1. The linear speed difference needs to be set so that the intermediate transfer belt is faster than the photosensitive drum, and the actual speed difference is more important than the speed ratio. The reason is that when the linear velocity of the belt is faster than that of the drum, the toner on the drum receives a shearing force in the belt traveling direction while passing through the nip portion, and toner particles per unit area when transferred from the drum to the belt Therefore, the toner layer is effectively thinned at the nip portion, and packing is difficult to occur. On the other hand, if the belt linear velocity is slowed down, the shearing force works in the direction opposite to the belt traveling direction, but the reverse phenomenon causes the effective toner layer at the nip to thicken, resulting in terrible packing. Insect eaters are not improved. Further, the difference is more important than the ratio, as a matter of course, considering that the insect eating is improved by the above principle. This is because the shearing force and the effect of thinning the toner layer are determined by how much the belt advances with respect to the drum per unit time. If the ratio is set, the degree of the effect depends on the process linear velocity of the image forming apparatus.

2. Simply adding a linear speed difference does not provide a bug-eating improvement effect. The dynamic friction coefficient of the intermediate transfer belt must be larger than that of the photosensitive drum, and if it is equal or conversely small, the insect bite is worsened by providing a linear speed difference. The reason is that if the photosensitive drum has a larger coefficient of dynamic friction, which is one of the parameters for ease of toner adhesion, even if the shear force is applied by making a difference in linear velocity or packing is minimized, the nip exit When the drum and the belt are separated, the toner tends to remain on the drum side. In order for toner to be transferred to the belt side when a shearing force is applied, the dynamic friction coefficient of the belt needs to be large.
3. If the pressure applied to the toner during transfer is excessive and excessive packing occurs, insect biting will not be improved completely even if other process conditions are changed.

  In view of the above problems, the present invention sets each transfer process condition obtained by further experiments based on a qualitative tendency to have a quantitative property, so that a good image without a worm-eating image can be obtained. It is to provide.

In order to solve the above problems, the present invention is characterized by the following.
1. The image forming apparatus of the present invention has a mechanism that can be repeatedly used by rotating, and an image carrier capable of carrying a latent image, and a charging member in contact with or close to the surface of the image carrier. A charging device for charging the toner, a latent image forming device for forming a latent image on the image carrier, a developing device for developing toner by attaching the toner to the latent image on the image carrier, and a surface movement while contacting the image carrier An intermediate transfer member, a primary transfer roller that forms a transfer electric field between the image carrier and the intermediate transfer member, and transfers a toner image formed on the image carrier onto the intermediate transfer member; In an image forming apparatus having a secondary transfer roller for transferring a toner image held on a recording material of various sizes, a linear velocity difference between the image carrier and the intermediate transfer member is 0.7 mm / s. And the difference in coefficient of dynamic friction is 0.03 or more, and the primary The primary transfer pressure of the transfer roller is 15 N / m or less.
2. The intermediate transfer member is a belt member, and a Young's modulus of the belt member is 5000 Mpa or less.
3. The primary transfer roller has a hardness of Asker C of 60 ° or less.
4). The dynamic friction coefficient is controlled by applying a lubricant to at least one of the image carrier and the intermediate transfer member.

According to the present invention, since toner packing can be suppressed and a toner image can be transferred to an intermediate transfer member with a shearing force, an image forming apparatus capable of obtaining a good image without insect bite can be provided.
Further, it is possible to provide an image forming apparatus capable of providing a margin for worm-eaten and discharge phenomena and capable of realizing an appropriate dynamic friction coefficient between the image carrier and the intermediate transfer member easily and inexpensively.

  The best mode for carrying out the present invention will be described below with reference to the drawings. The following description is an example of the best mode of the present invention, and it is easy for those skilled in the art to make other embodiments within the scope of the claims by making changes and modifications within the scope of the claims. However, this does not limit the scope of the claims.

FIG. 1 is an overall configuration diagram showing an example in which the image forming apparatus of the present invention is applied to a full-color laser printer. FIG. 2 is an enlarged view showing a main part of the image forming apparatus shown in FIG.
Here, a full color laser printer will be described as an example. The image forming apparatus includes an image forming unit 1, a writing unit 2, a paper feed tray 3, a paper transport unit 4, and a fixing device 5.
The image forming apparatus includes an intermediate transfer belt 501 at substantially the center of the inside thereof. The intermediate transfer belt 501 is an endless belt made of a heat-resistant material such as polyimide or polyamide and made of a base adjusted to a medium resistance, and is supported by being wound around four rollers 502, 503, 508, and 509. It is rotationally driven in the direction of arrow A.

Below the intermediate transfer belt 501, four image forming units corresponding to yellow (Y), magenta (M), cyan (C), and black (K) toners are arranged along the belt surface of the intermediate transfer belt 501. It is out. Each image forming unit has photoconductors 101, 102, 103, and 104. Around each photoconductor, charging devices 201, 202, 203, and 204 for applying a charge to the surface of the photoconductor are formed on the surface of the photoconductor. Developing devices 401, 402, 403, and 404 that develop the latent image with each color toner to form a toner image, and cleaning devices 301, 302, 303, and 304 that clean the surface of the photoreceptor after the toner image transfer are arranged. .
Below the four image forming units, there is provided a writing unit 2 that exposes the surface of each charged photoconductor based on image data of each color to form a latent image.
Primary transfer rollers 507, 506, 505, and 504 that primarily transfer the toner image formed on the photoconductor onto the intermediate transfer belt 501 are disposed at positions facing each photoconductor with the intermediate transfer belt 501 interposed therebetween. Has been. The primary transfer roller is connected to a power source (not shown), and a predetermined voltage is applied.

The secondary transfer roller 600 is pressed against the outside of the portion of the intermediate transfer belt 501 supported by the roller 502. The secondary transfer roller 600 is connected to a power source (not shown) and is applied with a predetermined voltage. A contact portion between the secondary transfer roller 600 and the intermediate transfer belt 501 is a secondary transfer portion, and a toner image on the intermediate transfer belt 501 is transferred onto a transfer sheet.
An intermediate transfer belt cleaning device 520 that cleans the surface of the intermediate transfer belt 501 after the secondary transfer is provided outside the portion of the intermediate transfer belt 501 supported by the roller 509.
Above the secondary transfer unit, a fixing device 5 is provided that semipermanently fixes the toner image on the transfer paper to the transfer paper.
Below the image forming apparatus, there is provided a paper feed tray 3 on which transfer paper is placed and the transfer paper is fed toward the secondary transfer unit.

The operation of the image forming apparatus having the above configuration will be described. When an image signal is input from an external device such as a personal computer to the image forming apparatus, a digital image signal obtained by converting the image signal into four colors of yellow, magenta, cyan, and black is created and written by an image signal processing unit (not shown). The image signal is sent to unit 2.
The surfaces of the photoconductors 101, 102, 103, and 104 are uniformly charged by the charging devices 201, 202, 203, and 204, respectively. Then, the writing unit 2 exposes the surface of the corresponding photoconductor based on the image signal of each color to form a latent image on each photoconductor.

  The latent images formed on the surfaces of the photoconductors are developed by the developing devices 401, 402, 403, and 404, respectively, and become toner images of the respective colors. The toner images carried on the respective photoconductors are respectively transferred to primary transfer rollers 507, 506, to which primary transfer voltages having a polarity opposite to the polarity of the toner are applied at the contact portion between the photoconductor and the intermediate transfer belt 501. By 505 and 504, primary transfer is performed by sequentially superimposing on the surface of the intermediate transfer belt 501 moving in the arrow A direction. The surface of each photoconductor after the toner image is primarily transferred is cleaned by cleaning devices 301, 302, 303, and 304, respectively, in preparation for the next image forming process.

In this manner, the four color toner images are superimposed on the intermediate transfer belt 501 to finally form a color toner image, which reaches the secondary transfer portion as the intermediate transfer belt 501 moves.
On the other hand, one of the transfer sheets placed on the sheet feeding tray 3 is fed by a sheet feeding roller, conveyed to a registration roller, and waits. The registration roller feeds the transfer paper in accordance with the timing at which the color toner image on the intermediate transfer belt 501 reaches the secondary transfer portion. Then, in the secondary transfer portion, the color toner image on the intermediate transfer belt 501 is secondarily transferred onto the transfer sheet collectively by the secondary transfer roller 600 to which a voltage having the same polarity as the primary transfer voltage is applied. The intermediate transfer belt 501 after the secondary transfer is cleaned of toner remaining on the surface thereof by an intermediate transfer belt cleaning device 520.
The transfer paper onto which the color toner image has been transferred is then conveyed to the fixing device 5, where the final color image is fixed by heat and pressure by passing through the nip between the fixing belt and the pressure roller. The transfer paper on which the color image is formed is discharged by a paper discharge roller.

  FIG. 3 is an enlarged view of a primary transfer portion of the black (K) station in FIG. The black station will be described. The following description is the same for other color stations. The photosensitive drum 104 and the intermediate transfer belt 501 are driven and rotated by a driving motor (not shown), the photosensitive drum 104 is rotated clockwise, and the intermediate transfer belt 501 is rotated rightward in the drawing. The linear velocity can be set independently, and the linear velocity of the intermediate transfer belt 501 is set to 0.7 mm / s or more, for example, 2 mm / s faster than the photosensitive drum 104. The primary transfer roller 504 rotates counterclockwise at the same linear velocity as the intermediate transfer belt 501 by being rotated with the intermediate transfer belt 501. Of course, independent drive, the same drive as the intermediate transfer belt 501, or a configuration that rotates with the intermediate transfer belt 501 may be employed. Further, a relationship of μ501−μ104 ≧ 0.03 is established between the dynamic friction coefficient μ104 on the surface of the photosensitive drum 104 and the dynamic friction coefficient μ501 on the surface of the intermediate transfer belt. For example, μ104 = 0.2 and μ105 = 0.3 may be set. Furthermore, a transfer pressure of 15 N / m or less is obtained by using a spring (not shown) that presses the primary transfer roller 504 toward the photosensitive drum 104. For example, when the primary transfer roller 504 having a length of 200 mm and a weight of 100 g is brought into contact with the photosensitive drum 104 by a 1N spring, a transfer pressure of about 9.7 N / m can be obtained.

  FIG. 4 is a diagram showing the contribution of the linear velocity difference and the dynamic friction coefficient difference to the insect eater. The horizontal axis is the linear velocity difference, the vertical axis is the insect bite rank, and the experimental results when the dynamic friction coefficient difference is 0.01 and 0.03 are shown. The transfer pressure is fixed at 8.5 N / m. According to this experiment, when the linear velocity difference is 0.7 mm / s or more and the dynamic friction coefficient difference is 0.03 or more, the insect bite rank 4 is acceptable.

FIG. 5 is a diagram illustrating the contribution of transfer pressure to insect eaters. FIG. 5 shows the experimental results when the transfer pressure is varied under the condition that the linear velocity difference is 1.5 mm / s and the dynamic friction coefficient difference is 0.11 and the worm-eating rank 5 in FIG. 4 is sufficiently stable. In the range where the transfer pressure is greater than 15 N / m, the insect bite rank is lowered.
As described above, by setting the primary transfer pressure to 15 N / m, the linear velocity difference between the intermediate transfer member and the photosensitive member is set to 0.7 mm / s or more, and the dynamic friction coefficient difference is set to 0.03 or more. Since the toner image can be transferred to the intermediate transfer member with a shearing force, a good image free from insect biting can be obtained.

FIG. 6 is a diagram illustrating the contribution of the Young's modulus of the intermediate transfer belt to the insect eater. FIG. 4 is a graph in which the Young's modulus of the intermediate transfer belt is changed and plotted under conditions of a linear speed difference of 1.5 mm / s, a dynamic friction coefficient difference of 0.1, and a transfer pressure of 8.5 N / m, which are the conditions indicating rank 5 in FIG. is there. When it exceeds 5000 Mpa, the rank falls below 5, and although it is an allowable level, it is understood that the margin is lost. Therefore, for example, a belt having a Young's modulus of 4000 Mpa is used as the intermediate transfer belt 501 in consideration of the margin.
By setting the Young's modulus (hardness) of the intermediate transfer belt to 5000 MPa or less, the belt surface shape can be made to follow the toner layer, the effective pressure applied to the toner layer is reduced, and the insect bite is more resistant to insect biting. Therefore, a configuration with a high margin can be obtained.

FIG. 7 is a diagram showing the contribution of the primary transfer roller hardness to the transferability. The transferability rank after the solid image is transferred is plotted on the vertical axis, and the roller hardness of the primary transfer roller is plotted on the horizontal axis. A drop in transferability rank is observed from around 60 °. This is because when the hardness of the roller is increased, the nip width with the photosensitive drum is reduced, the discharge phenomenon is likely to occur, and the transferability is insufficient. Accordingly, for example, a sponge roller having an Asker C of 40 ° is used as one transfer roller 504, 505, 506, 507.
By setting the hardness of the primary transfer roller to Asker C 60 ° or less, an effect of widening the nip width between the photoreceptor and the intermediate transfer belt is produced. Further, by setting the transfer pressure to 15 N / m or less in order to improve insect biting, it is possible to increase the margin for the occurrence of a discharge phenomenon that tends to occur when the nip width decreases.

FIG. 8 is an enlarged view of a cleaning device for a photosensitive drum having a zinc stearate coating mechanism. The cleaning devices 301 to 304 for the photoconductive drums 101 to 104 are provided with a zinc stearate application mechanism as a lubricant, and applied to the photoconductive drums 101 to 104. The solid lubricant 312 obtained by solidifying zinc stearate is pressed against a rotatable application brush 311 by a spring 313, so that the application brush 311 scrapes off the zinc stearate particles and continuously continues to the photosensitive drum 104. Can be applied. If it is desired to apply zinc stearate to the intermediate transfer belt 501, the intermediate transfer belt cleaning device 520 may have the same configuration.
In order to keep the dynamic friction coefficient between the photoconductor and the intermediate transfer belt in the above-mentioned predetermined relationship, when the selection is made by the selection of these materials or the surface shape, severe restrictions are imposed on the selection of the materials, or surface processing is performed. There is a tendency to increase costs. Therefore, by applying the lubricant, the dynamic friction coefficient can be controlled more easily and inexpensively, and the worm-eaten image can be improved.

1 is an overall configuration diagram illustrating an example in which an image forming apparatus of the present invention is applied to a full-color laser printer. It is a block diagram of the image formation part of the full-color laser printer of FIG. FIG. 3 is an enlarged view of a primary transfer portion of a black (K) station in FIG. 2. It is a figure which shows the contribution of the linear velocity difference and the friction coefficient difference with respect to an insect bite. It is a figure which shows the contribution of the transcription pressure with respect to an insect eater. It is a figure which shows the contribution of the Young's modulus of an intermediate transfer belt with respect to a bug eater. It is a figure which shows the contribution of the primary transfer roller hardness with respect to transferability. It is an enlarged view of a cleaning device for a photosensitive drum having a zinc stearate coating mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Writing unit 3 Paper feed tray 4 Paper conveyance part 5 Fixing device 101,102,103,104 Photosensitive drum (In order of Y, C, M, K)
301, 302, 303, 304 Cleaning device (Y, C, M, K in order)
311 Lubricant application brush 312 Solid lubricant 313 Spring 501 Intermediate transfer belts 504, 505, 506, 507 Primary transfer rollers (in order of K, M, C, Y)
520 Intermediate Transfer Belt Cleaning Device 600 Secondary Transfer Roller

Claims (4)

An image carrier that has a mechanism that can be repeatedly used by rotating and that can carry a latent image;
A charging device that charges the image carrier by bringing the charging member into contact with or close to the surface of the image carrier; and
A latent image forming apparatus for forming a latent image on an image carrier;
A developing device for developing the toner by attaching toner to the latent image on the image carrier;
An intermediate transfer member that moves on the surface while in contact with the image carrier;
A primary transfer roller that forms a transfer electric field between the image carrier and the intermediate transfer member, and transfers the toner image formed on the image carrier onto the intermediate transfer member;
In an image forming apparatus having a secondary transfer roller for transferring a toner image held on an intermediate transfer member onto a recording material of various sizes,
The linear velocity difference between the image carrier and the intermediate transfer member is 0.7 mm / s or more, the difference in coefficient of dynamic friction is 0.03 or more, and the primary transfer pressure of the primary transfer roller is 15 N / s. An image forming apparatus, wherein the image forming apparatus is m or less. The image forming apparatus according to claim 1.
The intermediate transfer member is a belt member, and the Young's modulus of the belt member is 5000 Mpa or less. The image forming apparatus according to claim 1, wherein
The image forming apparatus, wherein the primary transfer roller has an Asker C of 60 ° or less. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the dynamic friction coefficient is controlled by applying a lubricant to at least one of an image carrier and an intermediate transfer member.

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