JP7604309B2 - Electrophotographic belt and electrophotographic image forming apparatus - Google Patents

Description

This disclosure relates to an electrophotographic belt that can be used, for example, as an intermediate transfer belt in an electrophotographic image forming apparatus such as a copying machine or a printer, and to an electrophotographic image forming apparatus.

In electrophotographic image forming apparatuses, a tandem system is widely adopted in which a toner image of each color, YMCK, formed on a photoconductor for each color is primarily transferred onto an intermediate transfer belt, and then a full-color image is obtained by secondary transfer onto a transfer material (recording medium) such as paper.
In such an electrophotographic image forming apparatus (hereinafter also referred to as "image forming apparatus"), an electrophotographic belt having an elastic layer may be used as an intermediate transfer belt in order to further improve the image quality of an electrophotographic image. Such an electrophotographic belt can reduce the pressure acting on the toner in the secondary transfer section, and can suppress the occurrence of an image defect called a hollow phenomenon. In addition, since the electrophotographic belt has excellent adhesion between the electrophotographic belt and paper in the secondary transfer section, it is also effective in improving the secondary transferability of the toner to thick paper or paper having unevenness.

In addition, in order to further increase the efficiency of toner transfer to paper in the secondary transfer section, the toner carrying surface (hereinafter also referred to as the outer surface) of the electrophotographic belt may be configured with a surface layer with excellent toner release properties. Patent Document 1 discloses an intermediate transfer belt in which (a) a resin base layer, (b) an elastic layer containing a resin with rubber elasticity, and (c) a surface layer containing urethane rubber and a hydrophobic filler and having a water contact angle of 90° or more are laminated in this order. Polytetrafluoroethylene (PTFE) is exemplified as the hydrophobic filler. It is further disclosed that the average particle size of the hydrophobic filler is preferably 0.1 to 2.0 μm, and that the content of the hydrophobic filler in the surface layer is preferably 40 to 100 parts by weight when the hydrophobic filler is a fluororesin filler.

JP 2015-203854 A

When the toner carrying surface (hereinafter also referred to as "outer surface") of the intermediate transfer belt is cleaned with a cleaning blade, the cleaning blade may turn over or produce a rattling sound. In order to prevent such turning over or rattling sound, it is effective to sufficiently reduce the coefficient of friction between the transfer belt and the cleaning blade. However, according to the study by the present inventors, in order to sufficiently reduce the coefficient of friction of the surface layer containing PTFE particles, it is necessary to contain a large amount of PTFE particles, and on the other hand, as the content of PTFE particles increases, the surface layer becomes harder, and the hardness difference between the elastic layer and the surface layer becomes larger, so that when the intermediate transfer belt is bent and installed in an electrophotographic image forming apparatus, cracks may occur in the surface layer or peeling may occur between the elastic layer and the surface layer.
I found out.
One aspect of the present disclosure is directed to providing an electrophotographic belt having an excellent outer surface cleanability and being resistant to cracking in the surface layer or peeling from the elastic layer even when the belt is mounted in an electrophotographic image forming apparatus and used to form an electrophotographic image. Another aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus capable of stably forming high-quality electrophotographic images.

According to one aspect of the present disclosure, there is provided an electrophotographic belt having a base layer, an elastic layer provided on the base layer, and a surface layer provided on the elastic layer, the surface layer containing a binder resin and polytetrafluoroethylene particles, the content of the polytetrafluoroethylene particles being 200 parts by mass or more per 100 parts by mass of the binder resin, and the number average particle diameter of the polytetrafluoroethylene particles being 200 nm or less. According to another aspect of the present disclosure, there is provided an electrophotographic image forming apparatus having the electrophotographic belt as an intermediate transfer belt.

According to one aspect of the present disclosure, it is possible to obtain an electrophotographic belt that has excellent cleaning properties on the outer surface and is resistant to cracking in the surface layer or peeling from the elastic layer even when bent. According to another aspect of the present disclosure, it is possible to obtain an electrophotographic image forming apparatus that can stably form high-quality electrophotographic images.

1 is a cross-sectional view of an electrophotographic image forming apparatus including an electrophotographic belt having an endless shape as an intermediate transfer belt according to one embodiment of the present disclosure. 1 is a cross-sectional view of an electrophotographic belt having an endless shape in a direction perpendicular to a circumferential direction according to one embodiment of the present disclosure. FIG. 4 is a diagram for explaining curling of a cleaning blade. 1 is a graph showing the relationship between the number average particle diameter of PTFE particles and the Martens hardness of a surface layer containing a predetermined amount of PTFE particles.

An electrophotographic belt having an endless belt shape according to at least one embodiment of the present disclosure will be described in detail below. Note that the technical scope of the present disclosure is not limited to the following description.
The electrophotographic belt is used as an intermediate transfer belt 7 in an electrophotographic image forming apparatus shown in FIG. 1, for example. A cross section of the electrophotographic belt in a direction perpendicular to the circumferential direction is shown in FIG. 2. The electrophotographic belt has a structure in which at least a base layer 21, an elastic layer 22, and a surface layer 23 are laminated. When the electrophotographic belt is used as an intermediate transfer belt, the surface layer 23 constitutes a toner image carrying surface. Note that the electrophotographic belt according to the present disclosure is not limited to the laminated structure of these three layers, and may have a primer layer between the layers for improving adhesion, a stress relaxation layer for suppressing cracking of the surface layer 23, or an intermediate layer for suppressing bleeding.

(Base layer)
The base layer 21 has the shape of an endless belt.
Examples of materials suitable for the base layer 21 include the following: polyether ether ketone, polyethylene terephthalate, polybutylene naphthalate, polyester, polyimide, polyamide, polyamideimide, polyacetal, polyphenylene sulfide, polyvinylidene fluoride, and the like.

The resin for the base layer 21 may be made conductive by adding conductive compounds such as metal powder, conductive oxide powder, conductive carbon, lithium salt, and ionic liquid. In the following examples, polyvinylidene fluoride to which polyalkylene glycol and lithium salt have been added is used from the viewpoint of obtaining excellent productivity and conductivity, but combinations of other resins and conductive agents as exemplified may also be used. The thickness of the base layer 21 is preferably 10 μm or more and 500 μm or less. If it is less than 10 μm, the mechanical strength is significantly reduced, and if it is more than 500 μm, the rigidity becomes too strong, making it difficult to use as an intermediate transfer body.

(Elastic layer)
The elastic layer 22 provided on the outer peripheral surface of the base layer 21 needs to have a suitable degree of flexibility in order to conform to the surface shape of the recording medium. Materials suitable for such an elastic layer include the following: rubber materials such as silicone rubber, urethane rubber, chloroprene rubber, and acrylic rubber; and elastomer materials such as olefin elastomer, styrene elastomer, polyamide elastomer, polyester elastomer, and polyurethane elastomer.

The elastic layer 22 may be made conductive by adding a conductive compound such as metal powder, conductive oxide powder, conductive carbon, lithium salt, or ionic liquid. In the following examples, a polyurethane elastomer to which polyalkylene glycol, which is a thermoplastic elastomer, and lithium salt have been added was used from the viewpoint of obtaining excellent productivity, but combinations of other resins and conductive agents exemplified may also be used.

The thickness of the elastic layer 22 is preferably 100 μm to 1000 μm, and more preferably 200 μm to 500 μm. The JIS-A hardness of the elastic layer 22 is preferably 80 degrees or less. The amount of conductive agent mixed into the elastic layer 22 is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of urethane rubber. This provides the elastic layer 22 with stable conductivity suitable for an intermediate transfer belt.

The elastic layer 22 may also contain additives such as fillers, crosslinking accelerators, crosslinking retarders, crosslinking assistants, scorch inhibitors, antiaging agents, softeners, heat stabilizers, flame retardants, flame retardant assistants, UV absorbers, and rust inhibitors. For example, flame retardancy may be required for the intermediate transfer belt because electricity is passed through the transfer section. Examples of flame retardants include metal hydroxides such as magnesium hydroxide and aluminum hydroxide that utilize heat absorption, platinum compounds and phenolic compounds that suppress thermal decomposition, intumescent compounds that have an oxygen blocking effect, and phosphate ester condensation compounds.

Examples of the filler include reinforcing fillers such as fumed silica, crystalline silica, wet silica, fumed titanium oxide, and cellulose nanofibers.
Furthermore, in order to improve adhesion, a primer layer (not shown) may be provided between the base layer 21 and the elastic layer 22, if necessary. The thickness of the primer layer is preferably 0.1 μm or more and 2 μm or less from the viewpoint of reducing cohesive failure in the primer layer.

(Surface layer)
The surface layer 23 provided on the outer peripheral surface of the elastic layer contains a binder resin 23-1 and polytetrafluoroethylene particles (PTFE particles) 23-2. The thickness of the surface layer 23 is preferably 0.5 μm to 20 μm. The PTFE particles 23-2 impart excellent toner releasability and excellent cleaning properties to a surface 23-5 of the surface layer 23 opposite to the surface facing the elastic layer 22 (hereinafter, also referred to as the "outer surface"). The outer surface 23-5 of the surface layer constitutes the toner carrying surface of the electrophotographic belt 7.
As the binder resin, urethane resin and urethane acrylate resin are preferred because of their excellent abrasion resistance and flex resistance.
Methods for forming a surface layer containing a urethane resin include a method in which a coating material for forming a surface layer is applied by spray coating or dip coating, and then cured by heating or by exposure to light such as electron beams or ultraviolet rays.

The content of the PTFE particles in the surface layer is 200 parts by mass or more relative to 100 parts by mass of the binder resin. More preferably, it is 250 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the binder resin. By adjusting the content of the PTFE particles in the surface layer within such a range, the friction between the outer surface of the electrophotographic belt and the cleaning blade can be reduced, and the cleaning blade can be prevented from turning over. As a result, the outer surface of the electrophotographic belt can be stably cleaned. The cleaning blade is arranged so that at least a part of it contacts the outer peripheral surface of the surface layer of the electrophotographic belt.
The number average particle size of the PTFE particles in the surface layer is 200 nm or less.
That is, as described above, when the content of PTFE particles relative to 100 parts by mass of the binder resin in the surface layer is increased from 200 parts by mass, in the case where the number average particle size of the PTFE particles exceeds 200 nm, the Martens hardness of the surface layer increases rapidly as shown in Fig. 4. An excessive increase in Martens hardness causes cracks to occur in the surface layer when the electrophotographic belt is bent, and also leads to peeling from the elastic layer.
On the other hand, when the number average particle size of the PTFE particles was 200 nm or less, no excessive increase in the Martens hardness of the surface layer was observed even when the content of the PTFE particles in the surface layer was increased from 200 parts by mass.
Thus, in order to obtain an electrophotographic belt having excellent cleaning properties on the outer surface and excellent flex resistance, it is effective to set the content of PTFE particles in the surface layer to 200 parts by mass or more per 100 parts by mass of the binder resin and to set the number average particle size of the PTFE particles to 200 nm or less.
For example, commercially available PTFE particles having a number average particle diameter of 200 nm or less can be used. Examples of commercially available products include "Algoflon L100" (product name, manufactured by Solvay, number average particle diameter of primary particles: 50 nm) and "Lublon L-5" (product name, manufactured by Daikin Industries, Ltd., number average particle diameter of primary particles: 200 nm). The number average particle diameter of the PTFE particles is preferably 50 nm or more.

(Image forming apparatus)
An example of an image forming apparatus using an electrophotographic belt according to this embodiment will be described with reference to Fig. 1. An electrophotographic image forming apparatus 100 shown in Fig. 1 is a color electrophotographic image forming apparatus (color laser printer).
In this image forming apparatus, image forming units Py, Pm, Pc, and Pk of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in the moving direction along the flat portion of the intermediate transfer belt 7, which is the electrophotographic belt according to this embodiment. Here, 1Y, 1M, 1C, and 1K respectively represent electrophotographic photosensitive members, 2Y, 2M, 2C, and 2K respectively represent charging rollers, 3Y, 3M, 3C, and 3K respectively represent laser exposure devices, 4Y, 4M, 4C, and 4K respectively represent developing devices, and 5Y, 5M, 5C, and 5K respectively represent primary transfer rollers. Since the basic configuration of each image forming unit is the same, only the yellow image forming unit Py will be described in detail as to the image forming units.

The yellow image forming unit Py has a drum-shaped electrophotographic photosensitive member (hereinafter also referred to as the "photosensitive drum" or "first image carrier") 1Y as an image carrier. The photosensitive drum 1Y is formed by laminating a charge generating layer, a charge transport layer, and a surface protection layer in that order on an aluminum cylinder as a base. The yellow image forming unit Py also has a charging roller 2Y as a charging means. By applying a charging bias to the charging roller 2Y, the surface of the photosensitive drum 1Y is uniformly charged.

Above the photosensitive drum 1Y, a laser exposure device 3Y is disposed as an image exposure means. The laser exposure device 3Y scans and exposes the uniformly charged surface of the photosensitive drum 1Y according to image information, forming an electrostatic latent image of a yellow color component on the surface of the photosensitive drum 1Y. The electrostatic latent image formed on the photosensitive drum 1Y is developed with toner, which is a developer, by a developing device 4Y as a developing means. The developing device 4Y is equipped with a developing roller 4Ya, which is a developer carrier, and a regulating blade 4Yb, which is a developer amount regulating member, and also contains yellow toner, which is a developer. The developing roller 4Ya, to which the yellow toner is supplied, is lightly pressed against the photosensitive drum 1Y in the developing section, and is rotated with a speed difference in the forward direction from the photosensitive drum 1Y. The yellow toner transported to the developing section by the developing roller 4Ya adheres to the electrostatic latent image formed on the photosensitive drum 1Y by applying a developing bias to the developing roller 4Ya. As a result, a visible image (yellow toner image) is formed on the photosensitive drum 1Y.

The intermediate transfer belt 7 is stretched around a drive roller 71, a tension roller 72, and a driven roller 73, and is moved (rotationally driven) in the direction of the arrow in the figure while in contact with the photosensitive drum 1Y.
The yellow toner image formed on the photosensitive drum (first image carrier) that has reached the primary transfer portion Ty is primarily transferred onto the intermediate transfer belt 7 by a primary transfer body (primary transfer roller 5Y) that is arranged opposite the photosensitive drum 1Y via the intermediate transfer belt 7.

Similarly, the above image forming operation is performed in each of the magenta (M), cyan (C) and black (K) units Pm, Pc and Pk as the intermediate transfer belt 7 moves, and toner images of the four colors, yellow, magenta, cyan and black, are layered on the intermediate transfer belt 7. The four color toner layers are transported as the intermediate transfer belt 7 moves, and at the secondary transfer section T', they are transferred together by the secondary transfer roller 8 as secondary transfer means onto the transfer material S (hereinafter also referred to as the "second image carrier") that is transported at a predetermined timing. In such secondary transfer, a transfer voltage of several kV is usually applied to ensure a sufficient transfer rate.

The transfer material S is supplied to the conveying path by a pickup roller 13 from a cassette 12 in which the transfer material S is stored. The transfer material S supplied to the conveying path is conveyed to the secondary transfer section T' in synchronization with the four-color toner image transferred to the intermediate transfer belt 7 by a conveying roller pair 14 and a registration roller pair 15. The toner image transferred to the transfer material S is fixed by a fixing device 9 to become, for example, a full-color image. The fixing device 9 has a fixing roller 91 equipped with a heating means and a pressure roller 92, and fixes the unfixed toner image on the transfer material S by heating and pressurizing it. The transfer material S is then discharged outside the machine by a conveying roller pair 16, a discharge roller pair 17, etc.

A cleaning unit 11 for the intermediate transfer belt 7 is disposed downstream of the secondary transfer section T' in the drive direction of the intermediate transfer belt 7, and removes residual toner that has not been transferred to the transfer material S at the secondary transfer section T' and remains on the intermediate transfer belt 7. As described above, the electrical transfer process of the toner image is repeated from the photoconductor to the intermediate transfer belt and from the intermediate transfer belt to the transfer material. In addition, the electrical transfer process is further repeated by repeating recording on multiple transfer materials.

Example 1
(Preparation of base layer pellets)
The following materials were kneaded using a twin-screw kneader (product name: PCM30, manufactured by Ikegai Corporation) to obtain pellets.
Polyvinylidene fluoride (product name: Solef 9007, manufactured by Solvay Specialty Polymers Japan, Ltd.) 95 parts by mass Lithium perchlorate (anhydrous 98%, manufactured by Kanto Chemical Co., Ltd.) 0.7 parts by mass Ethylene oxide-propylene oxide copolymer (Pluronic F-127, manufactured by BASF Corporation) 4.3 parts by mass

"Pluronic F-127" is a nonionic surfactant represented by the following structural formula: In the structural formula, a and c each independently represent an integer in the range of 60 to 70, and b represents an integer in the range of 90 to 100.
HO-(CH ₂ CH ₂ O) a-(CH ₂ (CH(CH ₃ )O) b-(CH ₂ CH ₂ O) c-H

(Preparation of Pellets for Elastic Layer)
The following materials were kneaded using a twin-screw kneader (product name: PCM30, manufactured by Ikegai Corporation) to obtain pellets.
Thermoplastic polyurethane (product name: Elastollan 1175A10W, manufactured by BASF Japan Ltd.) 98 parts by mass Lithium perchlorate (anhydrous 98%, manufactured by Kanto Chemical Co., Ltd.) 0.2 parts by mass Ethylene oxide-propylene oxide copolymer (Pluronic F-127, manufactured by BASF Corporation) 1.8 parts by mass

(Preparation of a two-layer belt consisting of a base layer and an elastic layer)
The pellets for the base layer and the pellets for the elastic layer prepared above were used to prepare a two-layer belt by co-extrusion.
Specifically, a single screw extruder (product name: GT40, manufactured by Plastics Engineering Research Institute Co., Ltd.) was prepared for each of the pellets for the base layer and the pellets for the elastic layer. Then, the two single screw extruders were connected to a cylindrical die for co-extrusion and cylindrical extrusion molding was performed to produce a two-layer belt having an endless belt shape.
Specifically, the molten resins discharged from the single screw extruder were extruded through a cylindrical co-extrusion die so that the inner layer was polyvinylidene fluoride and the outer layer was thermoplastic polyurethane. The thicknesses of the layers were set to 115 μm and 250 μm depending on the relative ratio of the take-up speed of the cylindrical take-up machine and the feeder speed of the base layer pellets and the elastic layer pellets. During the take-up process, the resin was cooled and solidified by contacting with a cooling mandrel provided between the cylindrical die and the cylindrical take-up machine, and the solidified resin was cut to a width of 460 mm by a cylindrical cutter installed under the cylindrical take-up machine to obtain a two-layer belt.
The hardness of the elastic layer was measured with a JIS A rubber hardness tester and found to be 75 degrees.

(Surface modification of elastic layer)
In order to improve the adhesion between the elastic layer and the surface layer, the surface of the elastic layer on which the surface layer was to be formed was irradiated with UV light using an excimer lamp (manufactured by M.D. COM, Inc.) that emits a single wavelength of 172 nm as an excimer UV irradiation unit. Specifically, a two-layer belt consisting of a base layer and an elastic layer was fitted into a cylindrical core, and irradiation was performed for 30 minutes in a space into which nitrogen gas was flowed while rotating the core located 1 mm away from the surface of the excimer lamp at a rotation speed of 5 rpm.

(Preparation of surface layer)
The following materials were mixed to prepare a coating material for forming a surface layer. The amount of PTFE particles in the coating material for forming a surface layer prepared here was adjusted so that the content of the PTFE particles was 300 parts by mass per 100 parts by mass of polyurethane in the dry coating film of the coating material for forming a surface layer.
Aqueous polyurethane resin solution (product name: Hydran WLS-201, manufactured by DIC Corporation, solid content ratio 35%)
100 parts by mass of PTFE particles (product name: Algoflon L100; manufactured by Solvay, number average particle size of primary particles: 50 nm)
105 parts by weight

The two-layer belt prepared above was fitted into a core and rotated at 90 rpm, while a spray gun (product name: W-101, manufactured by Anest Iwata Corporation) was used to apply a surface layer-forming paint to the outer surface of the elastic layer. The amount of the surface layer-forming paint discharged was set so that the dry thickness of the coating film of the surface layer-forming paint would be 1 μm. The two-layer belt on which the coating film of the surface layer-forming paint was formed was heated in a heating furnace at a temperature of 130° C. for 30 minutes, and then removed from the heating furnace to obtain an electrophotographic belt B1.

Example 2
An electrophotographic belt B2 was obtained in the same manner as in Example 1, except that the material of the surface layer-forming coating material was changed as follows. The amount of PTFE particles in the surface layer-forming coating material prepared here was adjusted so that the content of the PTFE particles was 300 parts by mass per 100 parts by mass of polyurethane in the dry coating film of the surface layer-forming coating material.
(Preparation of Surface Layer)
- 100 parts by mass of polyurethane resin aqueous solution (product name: Hydran 201, manufactured by DIC Corporation, solid content ratio 35%) - 105 parts by mass of PTFE particles (product name: Lubron L-5, manufactured by Daikin Industries, Ltd., number average particle size of primary particles 200 nm)

Example 3
An electrophotographic belt B3 was obtained in the same manner as in Example 1, except that the material of the surface layer-forming coating material was changed as follows: The amount of PTFE particles in the surface layer-forming coating material prepared here was adjusted so that the content of the PTFE particles was 200 parts by mass per 100 parts by mass of polyurethane in the dry coating film of the surface layer-forming coating material.
(Preparation of Surface Layer)
- Polyurethane resin aqueous solution (product name: Hydran 201, manufactured by DIC Corporation, solid content ratio 35%) 100 parts by mass - PTFE particles (product name: Algoflon L100, manufactured by Solvay, number average particle size of primary particles 50 nm)
70 parts by weight

Example 4
An electrophotographic belt B4 was obtained in the same manner as in Example 1, except that the material of the surface layer-forming coating material was changed as follows: The amount of PTFE particles in the surface layer-forming coating material prepared here was adjusted so that the content of the PTFE particles was 200 parts by mass per 100 parts by mass of polyurethane in the dry coating film of the surface layer-forming coating material.
(Preparation of Surface Layer)
- 100 parts by mass of polyurethane resin aqueous solution (product name: Hydran 201, manufactured by DIC Corporation, solid content ratio 35%) - 70 parts by mass of PTFE particles (product name: Lubron L-5; manufactured by Daikin Industries, Ltd., number average particle size of primary particles 200 nm)

<Comparative Example 1>
An electrophotographic belt B11 was obtained in the same manner as in Example 1, except that the material of the surface layer-forming coating material was changed as follows. The amount of PTFE particles in the surface layer-forming coating material prepared here was adjusted so that the content of the PTFE particles was 200 parts by mass per 100 parts by mass of polyurethane in the dry coating film of the surface layer-forming coating material.
(Preparation of Surface Layer)
- 100 parts by mass of aqueous polyurethane resin solution (product name: Hydran 201, manufactured by DIC Corporation, solid content ratio 35%) - 70 parts by mass of PTFE particles (product name: Lubron L-2; manufactured by Daikin Industries, Ltd., number average particle size of primary particles 250 nm)

<Comparative Example 2>
An electrophotographic belt B12 was obtained in the same manner as in Example 1, except that the material of the surface layer-forming coating material was changed as follows. The amount of PTFE particles in the surface layer-forming coating material prepared here was adjusted so that the content of the PTFE particles was 150 parts by mass per 100 parts by mass of polyurethane in the dry coating film of the surface layer-forming coating material.
(Preparation of Surface Layer)
- 100 parts by mass of polyurethane resin aqueous solution (product name: Hydran 201, manufactured by DIC Corporation, solid content ratio 35%) - 52.5 parts by mass of PTFE particles (product name: Lubron L-5; manufactured by Daikin Industries, Ltd., number average particle size of primary particles 200 nm)

[Evaluation method]
The electrophotographic belts according to the above-mentioned respective Examples and Comparative Examples were mounted on an electrophotographic image forming apparatus (product name: imageRUNNER ADVANCE C7580; manufactured by Canon Inc.) shown in FIG. 1, and allowed to stand for 100 hours in a high-temperature and high-humidity environment (temperature 30° C./relative humidity 80%).
Thereafter, in the high temperature and high humidity environment, 300,000 electrophotographic images were continuously printed under the following conditions.
Paper used: Japanese Industrial Standards (JIS) A3 size plain paper (product name: CS068; manufactured by Canon Inc.);
Printed image: Test chart with image duty of 5%.

[Evaluation 1: Evaluation of the Generation of Abnormal Noise from the Cleaning Unit and the Occurrence of Turning Over of the Cleaning Blade]
During the printing of the 300,000 sheets, the occurrence of abnormal noise from the cleaning unit (hereinafter, "chatter noise") and curling of the cleaning blade (hereinafter, "curling") was observed and evaluated according to the following criteria.
Rank A: Neither "turning over" nor "buzzing noise" occurred.
Rank B: A "rattling noise" occurred, but no "turning up" occurred.
Rank C: "Rattling noise" and "turning up" occurred.

Regarding "turning up," as shown in FIG. 3, the blade holding member 31 holds the upper surface 32a of the cleaning blade 32. Normally, the vicinity of the tip of the lower surface 32b of the cleaning blade 32 opposite the upper surface 32a comes into contact with the outer surface of the electrophotographic belt 33, and cleans the surface of the electrophotographic belt 33 while the electrophotographic belt 33 moves in the direction of the arrow 34. It was determined that "turning up" had occurred when the vicinity of the tip of the upper surface 32a of the cleaning blade 32 came into contact with the electrophotographic belt 33.

[Evaluation 2: Surface layer cracking/peeling, image defects]
After printing 300,000 sheets, the electrophotographic belt was removed from the electrophotographic image forming apparatus, and the outer surface of the electrophotographic belt was observed with an optical microscope with an objective lens of 20 times magnification to evaluate the presence or absence of cracks in the surface layer and peeling from the elastic layer. After the observation, the electrophotographic belt was again mounted on the electrophotographic image forming apparatus, and three sheets of A3-sized plain paper were printed in succession with an image duty of 100%, i.e., a Bk (black) intermediate gradation in the entire printing area, which corresponds to one or more revolutions of the electrophotographic belt. The above intermediate gradation means "16 gradations on the lighter side of the 256 gradations". The three images obtained were then visually observed to evaluate the presence or absence of cracks in the surface layer and chipping or unevenness in the image due to peeling from the elastic layer. The evaluation results were ranked according to the following criteria.

Rank A: No cracking or peeling of the surface layer was observed. In addition, no image defects due to transfer unevenness were observed.
Rank B: Slight cracks in the surface layer are visible, but no image defects due to transfer unevenness are observed.
Rank C: The surface layer was cracked and peeled off, and image defects due to transfer unevenness also occurred.

Table 1 shows the evaluation results of the elastic intermediate transfer belts produced in each Example and Comparative Example. The elastic intermediate transfer belts of Examples 1 to 4 have an average particle size of polytetrafluoroethylene of 50 nm to 200 nm, which is smaller than the average particle size of polytetrafluoroethylene used in Comparative Example 1. Therefore, the mechanical strength of the surface layer is high, and there was no peeling of the surface layer or image defects due to transfer unevenness caused by cracks in the surface layer throughout durability.
In addition, the elastic intermediate transfer belts of Examples 1 to 4 have a larger polytetrafluoroethylene content than Comparative Example 2, and therefore have the effect of further reducing the frictional force with the cleaning blade. As a result, blade curling and chattering did not occur throughout the durability test.

Claims (10)

An electrophotographic belt having a base layer, an elastic layer provided on the base layer, and a surface layer provided on the elastic layer,
The surface layer is
A binder resin;
and polytetrafluoroethylene particles,
The content of the polytetrafluoroethylene particles is 200 parts by mass or more relative to 100 parts by mass of the binder resin,
The polytetrafluoroethylene particles have a number average particle size of 200 nm or less. The electrophotographic belt according to claim 1, wherein the number-average particle diameter of the polytetrafluoroethylene particles is 50 nm or more. The electrophotographic belt according to claim 1 or 2, wherein the content of the polytetrafluoroethylene particles is 250 parts by mass or more per 100 parts by mass of the binder resin. The electrophotographic belt according to any one of claims 1 to 3, wherein the content of the polytetrafluoroethylene particles is 300 parts by mass or less per 100 parts by mass of the binder resin. The electrophotographic belt according to any one of claims 1 to 4, wherein the electrophotographic belt has an endless belt shape. The electrophotographic belt according to claim 5, wherein the base layer has an endless belt shape, the elastic layer is provided on the outer peripheral surface of the base layer, and the surface layer is provided on the outer peripheral surface of the elastic layer. The electrophotographic belt according to any one of claims 1 to 6, wherein the binder resin is a urethane resin or a urethane acrylate resin. The toner image transfer apparatus includes an image carrier that carries a toner image, and an intermediate transfer belt that carries and transports the toner image that has been primarily transferred from the image carrier to a transfer material for secondary transfer,
The intermediate transfer belt is
A base layer, an elastic layer provided on the base layer, and a surface layer provided on the elastic layer,
The surface layer is
A binder resin;
and polytetrafluoroethylene particles,
The content of the polytetrafluoroethylene particles is 200 parts by mass or more relative to 100 parts by mass of the binder resin,
The electrophotographic image forming apparatus is characterized in that it is constituted by an electrophotographic belt, in which the number average particle diameter of the polytetrafluoroethylene particles is 200 nm or less. The electrophotographic image forming apparatus according to claim 8, wherein the base layer has an endless belt shape, the elastic layer is provided on the outer peripheral surface of the base layer, and the surface layer is provided on the outer peripheral surface of the elastic layer. 10. The electrophotographic image forming apparatus according to claim 8, further comprising a cleaning blade disposed so as to be in contact with at least a portion of an outer circumferential surface of the surface layer of the electrophotographic belt.

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