Electrophotographic belt and electrophotographic image forming apparatus

Abstract

To provide a belt for electrophotography that continuously has excellent toner cleaning characteristics even in image formation in a high-speed area.SOLUTION: A belt for electrophotography with an endless belt shape has a base layer and a surface layer provided on the base layer. The surface layer includes a (meth)acrylic resin and has holes having openings in an outer surface of the surface layer. When an area having a length of 10 μm in a circumferential direction of the belt for electrophotography and a width equal to the full width of the belt for electrophotography is set in an arbitrary position on the outer surface of the surface layer, at least one opening is present in the area which communicates, inside the surface layer, with an opening present outside the area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to electrophotographic belts, such as transport transfer belts and intermediate transfer belts, used in electrophotographic image forming apparatuses such as photocopiers and printers, and to electrophotographic image forming apparatuses. [Background technology]

[0002] Some electrophotographic image forming apparatuses use an intermediate transfer belt to transfer an unfixed toner image from an electrophotographic photoreceptor to a recording medium such as paper. Furthermore, electrophotographic image forming apparatuses equipped with an intermediate transfer belt may also include a cleaning blade to clean any remaining toner on the toner-carrying surface (hereinafter also referred to as the "outer surface") of the intermediate transfer belt after the secondary transfer process. The cleaning blade is made of an elastic material such as urethane rubber. In recent years, with the increasing demand for greater durability in electrophotographic image forming apparatuses, there is a need for longer-term stability in the cleaning properties of the outer surface of the intermediate transfer belt. Patent Document 1 discloses an image forming apparatus equipped with an intermediate transfer body having grooves on its surface layer with an average spacing between adjacent grooves of 2 μm to 10 μm. It is disclosed that such an intermediate transfer body reduces the contact area between the surface layer of the intermediate transfer body and the cleaning blade, thereby improving the durability of the cleaning blade. However, in an intermediate transfer belt having grooves on its outer surface, the grooves gradually disappear as the outer surface is repeatedly rubbed by the cleaning blade. As a result, friction between the outer surface and the cleaning blade increases, which can lead to wear of the cleaning blade and a decrease in cleaning performance. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-191511 [Overview of the project] [Problems that the invention aims to solve]

[0004] At least one aspect of this disclosure is toward providing an electrophotographic belt capable of maintaining excellent toner cleaning characteristics over a long period of time. Another aspect of this disclosure is toward providing an electrophotographic image forming apparatus capable of stably forming high-quality electrophotographic images over a long period of time. [Means for solving the problem]

[0005] According to one aspect of the present disclosure, an electrophotographic belt having an endless belt shape, It has a base layer and a surface layer provided on the base layer, The surface layer contains (meth)acrylic resin and has pores with openings on the outer surface of the surface layer. An electrophotographic belt is provided, wherein when a region is set at any position on the outer surface of the surface layer, the circumferential length of the electrophotographic belt is 10 μm and the width is equal to the total width of the electrophotographic belt, there is at least one opening within the region that communicates with an opening outside the region and within the interior of the surface layer. Furthermore, according to another aspect of the present disclosure, an electrophotographic image forming apparatus is provided, comprising an electrophotographic belt and a cleaning blade having at least a portion in contact with the outer circumferential surface of the electrophotographic belt. [Effects of the Invention]

[0006] According to one aspect of this disclosure, an electrophotographic belt capable of maintaining excellent toner cleaning characteristics over a long period of time can be obtained. Furthermore, according to another aspect of this disclosure, an electrophotographic image forming apparatus capable of stably forming high-quality electrophotographic images over a long period of time can be obtained. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the surface configuration of an electrophotographic belt according to one aspect of this disclosure. [Figure 2]Diagram illustrating the effects achieved by the electrophotographic belt relating to this disclosure. [Figure 3] Diagram illustrating the effect of ionic liquids on PFPE dispersibility [Figure 4] Schematic diagram of an electrophotographic image forming apparatus relating to one aspect of this disclosure [Figure 5] A schematic diagram showing an example of the configuration of a belt cleaning device. [Figure 6] Diagram illustrating the evaluation method for electrophotographic belts. [Modes for carrying out the invention]

[0008] In this specification, the expressions "XX or greater and YY or less" and "XX to YY" that represent numerical ranges mean numerical ranges that include the lower and upper limits, unless otherwise specified. Furthermore, when numerical ranges are described in steps, any combination of the upper and lower limits of each numerical range is disclosed. The embodiments for carrying out the present invention will be described below with reference to the drawings, but the scope of this disclosure is not limited to these embodiments, and modifications that do not impair the spirit of this disclosure are also included in the present invention. The inventors investigated how to obtain an electrophotographic belt with excellent toner cleaning characteristics over a long period of time. They confirmed that by providing numerous voids with openings on the surface of the intermediate transfer body, the total area of ​​the voids increases relative to the surface area of ​​the electrophotographic belt, thereby reducing the coefficient of friction between the electrophotographic belt and the cleaning blade. This is thought to be because the increased total area of ​​the voids reduces the contact area between the surface layer of the electrophotographic belt and the cleaning blade.

[0009] Furthermore, it has been found that when voids are connected inside the surface layer of the intermediate transfer body and any opening on the surface of the electrophotographic belt communicates with other openings, the friction coefficient between the electrophotographic belt and the cleaning blade can be further reduced. Regarding the reduction of the friction coefficient due to the communication, the following mechanism is presumed. When the openings on the surface of the electrophotographic belt are not connected and are covered by the cleaning blade, the pressure inside the openings decreases. Therefore, the cleaning blade is adsorbed on the surface of the electrophotographic belt, increasing the frictional force (Fig. 2(a)). On the other hand, when they are connected, even if the openings on the belt surface are covered by the cleaning blade, air enters from other non-covered communication holes, so the adsorbing force due to the pressure drop does not act on the cleaning blade, and no increase in the frictional force occurs (Fig. 2(b)).

[0010] Based on the result that the nip width between the cleaning blade and the electrophotographic belt obtained from the structural analysis is 10 μm and the above presumed mechanism, the following idea was reached. That is, when a predetermined region as described below is set at an arbitrary position on the outer surface of the surface layer of the electrophotographic belt, the increase in the friction coefficient due to the adsorption of the cleaning blade to the electrophotographic belt can be suppressed when the following conditions are satisfied. Predetermined region: A region where the circumferential length of the electrophotographic belt is 10 μm and the width is equal to the total width of the electrophotographic belt. Condition: Inside the region, there is at least one opening that communicates with an opening existing outside the region inside the surface layer. Hereinafter, the electrophotographic belt according to one aspect of the present disclosure will be described in detail. Note that the electrophotographic belt according to the present disclosure is not limited to the following specific configurations.

[0011] <Electrophotographic belt> Fig. 1 is a schematic view of the outer peripheral surface of an electrophotographic belt 5 according to one aspect of the present disclosure. The electrophotographic belt 5 has a base layer 51 and a surface layer 52. A plurality of voids 60 having openings are provided on the outer surface of the surface layer 52. The voids 60 communicate with voids having other openings through the inside of the surface layer 52. The opening width and the number of openings of the opening part are not particularly limited as long as toner cleaning can be stably performed, but it is preferable that there are 5 or more openings with a width of 0.10 μm or more and 0.30 μm or less in a region of 1 μm square. Note that the width of the opening means the "maximum width of the opening part". If the number of openings in a region of 1 μm square is less than 5, the area of the cleaning blade part that abuts on the part where no opening is provided increases, so that the frictional force generated between the cleaning blade and the electrophotographic belt becomes large, which is not preferable.

[0012] The ratio of the pores in the surface layer 52 including the pores 60 having the opening part, that is, the porosity, preferably is 25% or more and 50% or less. If the porosity is less than 25%, the number of communicating openings is small and the effect of sufficiently reducing the friction coefficient cannot be obtained. On the other hand, if the porosity exceeds 50%, the hardness of the surface layer decreases and it becomes easy to wear. Note that the calculation method of the "porosity" will be described later. The electrophotographic belt 5 may have an elastic layer between the base layer and the surface layer.

[0013] <Base layer> Examples of the material used for the base layer include the following. Thermoplastic resins such as polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polysulfone, polyarylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyphenylene sulfide, polyethersulfone, polyether nitrile, thermoplastic polyimide, polyether ether ketone, thermotropic liquid crystal polymer, and polyamic acid. These can be used alone or in combination of two or more.

[0014] The base layer can typically be enriched with conductive materials to impart conductivity. Examples of conductive materials include carbon-based conductive particles such as carbon black, carbon fiber, and carbon nanotubes, as well as inorganic conductive particles such as metal oxides like zinc antimonate, zinc oxide, tin oxide, and titanium oxide. When used as an intermediate transfer belt, the base layer has a volume resistivity of 1 × 10⁻⁶. 8 Ω cm or more 1×10 12 It is preferable that the resistivity is adjusted to a range of Ω·cm or less. Furthermore, the surface resistivity of the base layer is 1 × 10⁻⁶. 8 Ω / □ or more 1×10 14 It is preferable that the ratio is adjusted to a range of Ω / □ or less.

[0015] As a method for processing the base layer, known methods for processing thermoplastic resins or thermosetting resins can be used. As a method for processing thermoplastic resins, for example, the resin composition can be pelletized and an endless belt-shaped electrophotographic belt can be obtained using known molding methods such as continuous melt extrusion molding, injection molding, stretch blow molding, or inflation molding.

[0016] <Surface layer> The surface layer consists of a binder resin and additives such as a photopolymerization initiator, a conductivity imparting agent, and a dispersant. As the binder resin, styrene resin, acrylic resin, methacrylic resin, epoxy resin, polyester resin, polyether resin, silicone resin, and polyvinyl butyral resin, as well as mixtures thereof, can be used. Binder resins are used to improve toner transferability and ensure mechanical strength. Among the binder resins mentioned above, acrylic resins or methacrylic resins are preferred because they can form numerous pores with open ends. Hereinafter, acrylic resins and methacrylic resins will be collectively referred to as (meth)acrylic resins. Examples of polymerizable monomers for forming (meth)acrylic resin include (i) or (ii) below. It is also possible to use polymerizable monomers that are commercially available as paints.

[0017] (i) At least one acrylate selected from the group consisting of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, alkyl acrylate, benzyl acrylate, phenyl acrylate, ethylene glycol diacrylate, and bisphenol A diacrylate.

[0018] (ii) At least one methacrylate selected from the group consisting of pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, ditrimethylolpropane tetramethacrylate, dipentaerythritol hexamethacrylate, alkyl methacrylate, benzyl methacrylate, phenyl methacrylate, ethylene glycol dimethacrylate, and bisphenol A dimethacrylate.

[0019] Among these, high hardness is preferable when considering friction with other components such as the photoreceptor and cleaning blade. For this reason, it is preferable to use a large amount of bifunctional or crosslinkable monomers in the (meth)acrylic resin to achieve even higher hardness. Furthermore, to form (meth)acrylic resins from such polymerizable monomers, methods include adding a photopolymerization initiator and polymerizing them using electron beams or ultraviolet light.

[0020] Examples of photopolymerization initiators include: radical-generating photopolymerization initiators such as benzophenone, thioxanthone derivatives, benzyldimethyl ketal, α-hydroxyketone, α-hydroxyalkylphenone, α-aminoketone, α-aminoalkylphenone, monoacylphosphine oxide, bisacylphosphine oxide, hydroxybenzophenone, aminobenzophenone, titanocene derivatives, oxime esters, and oxyphenyl acetate.

[0021] The thickness of the surface layer is preferably between 1 μm and 20 μm. By making the surface layer thickness 1 μm or more, desirable durability can be ensured by maintaining toner transferability and suppressing peeling from the base layer. Furthermore, by making the surface layer thickness 20 μm or less, desirable flexibility can be obtained. Examples of surface layer processing methods include dip coating, spray coating, flow coating, shower coating, roll coating, spin coating, and ring coating. By applying and molding the coating liquid using these known molding methods, an endless belt-shaped electrophotographic belt can be obtained.

[0022] One method for imparting voids with openings to the surface of an electrophotographic belt involves dispersing perfluoropolyether (PFPE), which is incompatible with the (meth)acrylic resin that forms the main component of the surface layer, in a coating solution, and then removing the PFPE after the surface layer has been formed. To use this method, it is desirable that the PFPE remains finely dispersed from the coating solution to the formation of the surface layer and does not aggregate even when in close proximity.

[0023] PFPE is an oligomer or polymer having perfluoroalkylene oxy as a repeating unit. Examples of perfluoroalkylene oxy repeating units include: difluoromethylene oxy (-CF2O-), tetrafluoroethylene oxy (-CF2CF2O-), and hexafluoropropylene oxy (-CF2CF2CF2-O- or -C(CF3)FCF2O-).

[0024] As the PFPE, either a PFPE having reactive functional groups that can bond with or nearly bond with the binder resin, or a PFPE having non-reactive functional groups that do not bond with or nearly bond with the binder resin, may be used. PFPE having the above-mentioned reactive functional groups exhibits good compatibility with the binder resin through interaction, allowing for stable dispersion of PFPE within the binder resin. When the binder resin is formed by an addition reaction, examples of the above-mentioned reactive functional groups that undergo an addition reaction with the monomer for forming the binder resin include acrylic groups, methacrylic groups, and oxysilanyl groups.

[0025] Examples of PFPEs having acrylic or methacrylic groups include: "Fluorolink MD500", "Fluorolink MD700", "Fluorolink 5101X", "Fluorolink 5113X", "Fluorolink AD1700" (all trade names, manufactured by Solvay Specialty Polymers), and "Optoul DAC" (trade name, manufactured by Daikin Industries, Ltd.).

[0026] Furthermore, when the binder resin is formed by an addition reaction, examples of non-reactive functional groups that do not undergo an addition reaction with the monomers for forming the binder resin include hydroxyl groups, trifluoromethyl groups, and methyl groups. Examples of such PFPEs include: "Fonblin D2", "Fonblin M60", "Fluorolink S10" (all product names, manufactured by Solvay Specialty Polymers), "Demnam S-20", "Demnam S-65", and "Demnam S200" (all product names, manufactured by Daikin Industries, Ltd.).

[0027] One method for dispersing PFPE in the binder resin is to mix a dispersant with a coating solution containing the polymerizable monomer and PFPE. The dispersant is a compound having a moiety that is compatible with both the perfluoroalkyl chain and the hydrocarbon chain, i.e., a compound with amphiphilic and fluorine-averse properties. Surfactants, amphiphilic block copolymers, and amphiphilic graft copolymers are preferred.

[0028] Among these, the dispersant is preferably (i) or (ii) below: (i) a block copolymer obtained by copolymerizing a vinyl monomer having a fluoroalkyl group with an acrylate or methacrylate; (ii) a comb-shaped graft copolymer obtained by copolymerizing an acrylate or methacrylate having a fluoroalkyl group with a methacrylate macromonomer having polymethyl methacrylate as a side chain.

[0029] In this embodiment, an ionic liquid was used to further improve the dispersibility of PFPE. An ionic liquid is a liquid composed of cations (positive ions) and anions (negative ions), and is a salt that exists as a liquid over a wide temperature range. In particular, by using relatively large organic ions as the constituent ions of such a salt, it refers to a salt having a melting point of 100°C or lower. In this embodiment, an ionic liquid having the anion shown in the following structural formula (1) was used.

[0030] [ka] (In structural formula (1), m and n each independently represent integers between 1 and 4, respectively.)

[0031] Specific examples of anions that satisfy structural formula (1) include the following: bis(trifluoromethanesulfonyl)imide ion, bis(perfluoroethanesulfonyl)imide ion, bis(perfluoropropanesulfonyl)imide ion, bis(nonafluorobutanesulfonyl)imide ion (also called bis(perfluorobutanesulfonyl)imide ion), trifluoromethanesulfonylperfluoropropanesulfonylimide ion, trifluoromethanesulfonylperfluorobutanesulfonylimide ion, etc. The reason why PFPE is finely dispersed in the binder resin by an ionic liquid containing anion having the structure shown in structural formula (1) is speculated as follows:

[0032] The ether structure of PFPE contains a lone pair of electrons. Therefore, as shown in Figure 3, the ether structure of PFPE interacts with the cations of the ionic liquid, resulting in a greater number of cations being present near the ether structure. A counterion, an anion, is present near the cation. In this case, if the anion has the structure shown in structural formula (1) above, which contains multiple perfluoroalkyl groups within the molecule, then a greater number of perfluoroalkyl groups are present near the PFPE. This inhibits the aggregation of PFPE molecules, allowing them to be finely dispersed as small droplets within the surface layer. Note that the PFPE shown in Figure 3 is just an example; p and q are integers of 0 or greater, and p and q cannot be 0 simultaneously. R represents a terminal group of PFPE, selected from reactive or non-reactive functional groups described later.

[0033] The cation species constituting the above ionic liquid is not particularly limited, and any cation that forms an ionic liquid in combination with the sulfonylimide ion shown in structural formula (1) above can be used. Preferred examples of this cation include cations selected from the group of structures shown in structural formulas (2) to (7) below, or cations having a reactive functional group shown in structural formula (8) below.

[0034] [ka]

[0035] In structural formulas (2) to (7), R1 to R 15 Each of these independently represents a hydrocarbon group having 1 to 8 carbon atoms. Examples of the hydrocarbon group include, for example, the following hydrocarbon groups. i) A linear or branched saturated hydrocarbon group having 1 to 8 carbon atoms. ii) A linear or branched unsaturated hydrocarbon group having 2 to 8 carbon atoms. iii) A substituted or unsubstituted saturated alicyclic hydrocarbon group having 3 to 8 carbon atoms. iv) A substituted or unsubstituted unsaturated alicyclic hydrocarbon group having 4 to 8 carbon atoms. v) A substituted or unsubstituted aromatic hydrocarbon group having 6 carbon atoms (phenyl group). Here, examples of the substituents of the saturated alicyclic hydrocarbon group, the unsaturated alicyclic hydrocarbon group, and the aromatic hydrocarbon group include an alkyl group having 1 to 3 carbon atoms. Note that the number of carbon atoms in the "hydrocarbon group having 1 to 8 carbon atoms" is the number of carbon atoms including the carbon atoms of the substituent.

[0036]

Chemical formula

[0037] In Structural Formula (8), R 16 ~R 18 each independently represents a hydrocarbon group having 1 to 8 carbon atoms. Examples of the hydrocarbon group include the same groups as R1 to R 15 in Structural Formulas (2) to (7). Further, R 19 represents hydrogen or a methyl group, and l represents an integer of 1 or more and 8 or less. Hereinafter, details of each of the cations a) to g) will be described. a) Imidazolium-based ion (Structural Formula (2)), b) Ammonium-based ion (Structural Formula (3)), c) Pyridinium-based ion (Structural Formula (4)), d) Piperidinium-based ion (Structural Formula (5)), e) Pyrrolidinium-based ion (Structural Formula (6)), f) Phosphonium-based ion (Structural Formula (7)), g) Acryloyl or methacryloyl-based ion (Structural Formula (8)).

[0038] ) a) Imidazolium-based ion Specific examples of the imidazolium-based ion shown in the above Structural Formula (2) are given below. 1-ethyl-3-methylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-hexyl-3-methylimidazolium ion, 1-methyl-3-octylimidazolium ion, 1-(tert-butyl)-3-methylimidazolium ion, 1-phenyl-3-methylimidazolium ion, 1-(2,4-dimethylphenyl)-3-methylimidazolium ion.

[0039] b) Ammonium ions Specific examples of ammonium ions shown in the above structural formula (3) are listed below. N,N,N-trimethyl-N-propylammonium ion (TMPA), N,N,N-tributyl-N-methylammonium ion, N,N,N-trioctyl-N-methylammonium ion, N-butyl-N,N,N-trimethylammonium ion, N-(tert-butyl)-N,N,N-trimethylammonium ion, N-phenyl-N,N,N-trimethylammonium ion, N-(2,4-dimethylphenyl)-N,N,N-trimethylammonium ion.

[0040] c) Pyridinium ions Specific examples of pyridinium ions shown in the above structural formula (4) are listed below. 1-ethylpyridinium ion, 1-butylpyridinium ion, 1-hexylpyridinium ion, 1-(tert-butyl)pyridinium ion, 1-phenylpyridinium ion, 1-(2,4-dimethylphenyl)pyridinium ion.

[0041] d) Piperidinium ions Specific examples of piperidinium-based ions shown in the above structural formula (5) are listed below. N-methyl-N-ethylpiperidinium ion, N-methyl-N-propylpiperidinium ion, N-(tert-butyl)-N-methylpiperidinium ion, N-phenyl-N-methylpiperidinium ion, N-(2,4-dimethylphenyl)-N-methylpiperidinium ion.

[0042] e) Pyrrolidinium ions Specific examples of pyrrolidinium-based ions shown in the above structural formula (6) are listed below. N-methyl-N-propylpyrrolidinium ion, N-methyl-N-butylpyrrolidinium ion, N-(tert-butyl)-N-methylpyrrolidinium ion, N-phenyl-N-methylpyrrolidinium ion, N-(2,4-dimethylphenyl)-N-methylpyrrolidinium ion.

[0043] f) Phosphonium ions Specific examples of phosphonium ions shown in the above structural formula (7) are listed below. Trimethylpropylphosphonium ion, tributylmethylphosphonium ion, triethylpentylphosphonium ion, (tert-butyl)-trimethylphosphonium ion, phenyl-trimethylphosphonium ion, (2,4-dimethylphenyl)-trimethylphosphonium ion.

[0044] g) Methacryloyl or acryloyl ions Specific examples of methacryloyl or acryloyl ions shown in the above structural formula (8) are listed below. (2-Acryloyloxyethyl)trimethylammonium ion, (2-methacryloyloxyethyl)trimethylammonium ion, (2-acryloyloxyethyl)tributylammonium ion, (2-methacryloyloxyethyl)tributylammonium ion. By immersing the electrophotographic belt, after coating and curing the coating solution, in a fluorine solvent, PFPE can be removed, and voids are formed in the areas where PFPE was present.

[0045] The surface layer of the electrophotographic belt 5 may contain a conductivity imparting agent to provide conductivity. Examples of conductivity imparting agents include carbon-based conductive particles such as carbon black, carbon fiber, and carbon nanotubes, and metal oxide particles such as zinc antimonate, zinc oxide, tin oxide, and titanium oxide. Other examples of additives include filler particles, lubricants, conductivity enhancers, curing agents, antioxidants, UV absorbers, pH adjusters, crosslinking agents, pigments, and thickeners, all of which are known in this field.

[0046] The thickness of the electrophotographic belt is preferably 10 μm to 500 μm, and particularly preferably 30 μm to 150 μm. In addition to being used as a belt, the electrophotographic belt according to this disclosure may also be used by winding it around or covering drums or rolls used as electrophotographic components.

[0047] <Electrophotographic image forming apparatus> Figure 4 shows an example of an image forming apparatus configured as an electrophotographic apparatus, which incorporates the electrophotographic belt according to this disclosure as an intermediate transfer body. This image forming apparatus performs color image formation on a recording medium S such as paper supplied from a paper feed cassette 20 using four toners represented by C, M, Y, and K, respectively, with image forming stations for each color arranged in a substantially horizontal direction. Each of these image forming stations is equipped with a photosensitive drum 1c, 1m, 1y, and 1k. Here, by adding the subscripts "c," "m," "y," or "k" to the reference symbols, it is indicated which color image forming station the component with the reference symbol belongs to: cyan (c), magenta (m), yellow (y), or black (k). The image forming apparatus is equipped with a laser scanner 3, which is a laser optical unit, and from this, laser beams 3c, 3m, 3y, and 3k corresponding to the image signals of each color are emitted toward the respective photosensitive drums 1c, 1m, 1y, and 1k. Since all image forming stations have the same structure, the image forming station for K color (black) will be described here. The photosensitive drum 1k is surrounded by a conductive roller 2k, which is a contact charging device, a developer 4k, a conductive roller 8k, which is a primary transfer roller, and a toner recovery blade 14k, which is used to clean the photosensitive drum 1k. The developer 4k is equipped with a developing roller 41k, which is a developer material carrier that develops the latent image on the photosensitive drum 1k, a developing container 42k that holds the toner supplied to the developing roller 41k, and a developing blade 43k that regulates the amount of toner on the developing roller 41k and applies an electric charge.

[0048] The electrophotographic belt 5 is configured as an endless belt and is provided in common to each color image forming station. It is stretched over the secondary transfer opposing roller 92, tension roller 6, and drive roller 7, and rotated in the direction of the arrow shown by the drive roller 7. In the section between the tension roller 6 and the drive roller 7, the electrophotographic belt 5 sequentially contacts the surfaces of the photosensitive drums 1c, 1m, 1y, and 1k, and is pressed towards the photosensitive drums 1c, 1m, 1y, and 1k by the primary transfer rollers 8c, 8m, 8y, and 8k, respectively. As a result, the toner images formed on the surfaces of the photosensitive drums 1c, 1m, 1y, and 1k are transferred to the surface of the electrophotographic belt 5, which is an intermediate transfer body. A secondary transfer roller 9 is provided opposite the opposing roller 92, and the electrophotographic belt 5 is pressed towards the opposing roller 92 by the secondary transfer roller 9. A secondary transfer voltage is applied to the secondary transfer roller 9 from the power supply via the current detection circuit 10. The secondary transfer roller 9 and the opposing roller 92 constitute the secondary transfer section. The recording medium S passes through the feed roller 12 and the transport roller 13, and at the position of the opposing roller 92, it passes through the nip between the electrophotographic belt 5 and the secondary transfer roller 9, thereby transferring the toner image held on the outer surface of the electrophotographic belt 5. As a result, an image is formed on the surface of the recording medium S. The recording medium S, on which the toner image has been transferred, passes through the fuser 15, which consists of a pair of rollers, a heating roller 151 and a pressure roller 152, thereby fixing the image, and is discharged into the output tray 21. A cleaning blade 33 that contacts the outer surface of the electrophotographic belt 5 is provided at the position of the tension roller 6. Toner that remains on the outer surface of the electrophotographic belt 5 without being transferred to the recording medium S is removed from the electrophotographic belt 5 and recovered by the belt cleaning device 30.

[0049] Figure 5(a) is a hypothetical cross-sectional view illustrating the mounting position of the cleaning blade 33 if the electrophotographic belt 5 and tension roller 6 were not present and the cleaning blade 33, described later, was not elastically deformed. Figure 5(b) is a schematic cross-sectional view illustrating the configuration of the belt cleaning device 30. The belt cleaning device 30 comprises a cleaning container 31 and a cleaning action unit 32 provided inside the cleaning container 31. The cleaning container 31 is configured as part of the frame of an intermediate transfer belt unit (not shown). The cleaning action unit 32 comprises a cleaning blade 33 as a cleaning member and a support member 34 that supports the cleaning blade 33. The cleaning blade 33 is an elastic blade (rubber part) made of urethane rubber (polyurethane), which is an elastic material. The support member 34 is formed of sheet metal made of plated steel plate (sheet metal part). The cleaning blade 33 is bonded to the support member 34 to constitute the cleaning action unit 32.

[0050] The cleaning blade 33 is a plate-shaped member that is elongated in one direction and has a predetermined thickness. Of the two substantially orthogonal sides of the cleaning blade 33, one side in the longitudinal direction extends along a direction substantially perpendicular to the belt conveying direction (hereinafter also referred to as the "thrust direction"), and one end of the side in the short direction contacts the electrophotographic belt 5. The cleaning unit 32 is configured to be pivotable. Specifically, the support member 34 is pivotably supported via a pivot shaft 36 fixed to the cleaning container 31. The support member 34 is pressurized by a pressure spring 35, which is a biasing means provided inside the cleaning container 31. The pressure from the pressure spring 35 causes the cleaning unit 32 to move around the pivot shaft 36, biasing (pressing) the cleaning blade 33 against the electrophotographic belt 5. The pressure springs 35 are positioned at both ends of the support member 34 in the longitudinal direction (axial direction of the pivot shaft 36), and the cleaning blade 33 is pressed against the electrophotographic belt 5. A tension roller 6 is positioned on the inside of the electrophotographic belt 5, facing the cleaning blade 33. The cleaning blade 33 is in contact with the electrophotographic belt 5 in a counter-direction with respect to the belt conveying direction. Specifically, the cleaning blade 33 is in contact with the surface of the electrophotographic belt 5 such that the tip of the free end in its short direction faces upstream in the belt conveying direction. As a result, a blade nip portion 37 is formed between the cleaning blade 33 and the electrophotographic belt 5. At the blade nip portion 37, the cleaning blade 33 scrapes toner from the surface of the moving electrophotographic belt 5.

[0051] In this embodiment, the mounting position of the cleaning blade 33 is set as follows: the setting angle θ is 24°, the penetration amount δ is 1.5 mm, and the contact pressure is 0.6 N / cm. Here, the set angle θ is the angle between the tangent line of the tension roller 6 at the intersection of the electrophotographic belt 5 and the cleaning blade 33, and a line parallel to the plane of the cleaning blade 33 that is opposite to the electrophotographic belt 5. Furthermore, the penetration depth δ is the length in the direction normal to the free end of the cleaning blade 33 (the thickness direction of the cleaning blade 33) where it overlaps with the electrophotographic belt 5. The thickness of the cleaning blade 33 is 2 mm, its thrust length is 245 mm, and its hardness is 77 degrees according to the JIS K 6253 standard. Since the thrust length of the electrophotographic belt 5 is 250 mm, the cleaning blade 33 is in contact with the electrophotographic belt 5 over almost its entire width. In addition, the pressing force from the cleaning blade 33 at the blade nip portion 37 is defined as the linear pressure in the longitudinal direction and is measured using a film-type roller pressure distribution measurement system (product name: PINCH, manufactured by Nitta Corporation). By setting the system as described above, curling and slipping noises of the cleaning blade 33 in high-temperature, high-humidity environments (temperature 30°C / relative humidity 80%) can be suppressed, resulting in good cleaning performance. Furthermore, by setting the system in this way, poor cleaning in low-temperature, low-humidity environments (temperature 15°C / relative humidity 10%) can be suppressed, resulting in good cleaning performance.

[0052] Furthermore, urethane rubber and synthetic resin generally have high frictional resistance due to sliding, and the cleaning blade 33 is prone to curling in the initial stages. Therefore, it is preferable to apply an initial lubricant such as graphite fluoride to the surface of the free end of the cleaning blade 33 that comes into contact with the electrophotographic belt 5 in advance. The color of printed materials changes depending on the operating environment and other conditions of the image forming apparatus. Therefore, it is necessary to measure the density as needed and provide feedback to the control mechanism inside the unit. The toner image for density correction is transferred to the surface of the electrophotographic belt 5 and then transported to the position of the drive roller 7 as the electrophotographic belt 5 rotates. The toner density is detected by a density detection sensor 160 located on the opposite side of the electrophotographic belt 5 from the drive roller 7. During periods other than the period when the toner image to be secondary transferred to the recording medium S is primary transferred onto the electrophotographic belt 5, an adjustment toner image (patch image) is formed on the electrophotographic belt 5. The image forming conditions are adjusted according to the results. [Examples]

[0053] Examples and comparative examples are shown below to illustrate the present disclosure in detail, but the disclosure is not limited to these. The characteristics and performance evaluation methods for the electrophotographic belts fabricated in the examples and comparative examples are as follows: [Evaluation 1] to [Evaluation 4].

[0054] [Evaluation 1] Evaluation of the communication distance of the surface layer of the electrophotographic belt. In this embodiment, the distance over which pores communicate within the surface layer (communication distance) was evaluated using the following method.

[0055] (Sample preprocessing) A sample piece was obtained by cutting an electrophotographic belt 5 into a 30 mm square. Then, the sample piece was masked with polyimide tape (product name: heat-resistant polyimide tape 7414, manufactured by 3M) to the shape shown in Figure 6. The polyimide tape was cut larger than the sample piece, covering approximately 3 / 4 of the top surface 61 of the sample piece, and the excess polyimide tape that remained after covering the entire top surface was folded towards the cut end (outer surface) to cover the surface layer portion within the cut end (outer surface). Next, the masked sample piece was immersed in liquid fluoroelastomer (product name: X-71-359, manufactured by Shin-Etsu Chemical Co., Ltd.). After 60 minutes, the masked sample piece was removed, and the excess liquid fluoroelastomer was removed. Then, the masked sample piece was fired at 200°C for 60 minutes. With the mask still attached to the surface of the fired sample piece, platinum sputtering was performed, after which the polyimide tape mask was removed.

[0056] By immersing a sample piece in fluorine elastomer with its surface layer masked, the fluorine elastomer penetrates from the openings in the unmasked portion of the sample piece through interconnected pores within the surface layer to the masked portion. Within the openings of the masked portion, there are openings that communicate with the openings in the unmasked portion and openings that do not. The fluorine elastomer penetrates into the openings in the masked portion that communicate with the openings in the unmasked portion. The mask covers the end face (outer surface) of the cut sample piece, preventing the fluorine elastomer from penetrating from the end face.

[0057] (Sample evaluation) Sample pieces of electrophotographic belts that had undergone the above sample pretreatment were observed from the surface layer side using SEM and elemental analysis (elemental mapping) using energy-dispersive X-ray spectroscopy (EDX). In this evaluation, three elements, Pt (platinum), F (fluorine), and Si (silicon), were mapped. Since Pt is present in the non-masked areas but not in the masked areas, the presence or absence of Pt was used to determine the masked and non-masked areas and their boundary lines. The presence or absence of F and Si was used to determine the presence or absence of fluorine elastomer. In Figure 6, the openings of pores where fluorine elastomer was detected are indicated by black circles 62, and the openings of pores where fluorine elastomer was not detected are indicated by white circles 63. For openings within the mask portion where fluorine elastomer was detected, the distance from the boundary line between the mask portion and the non-mask portion, which is substantially perpendicular to the circumferential direction of the electrophotographic belt, to the opening furthest from the boundary line, was measured and defined as the communication distance. Based on the above communication distance, the electrophotographic belts were ranked according to the following criteria. Rank A: Communication distance of 15 μm or more Rank B: Communication distance of 10 μm or more, and less than 15 μm. Rank C: Communication distance less than 10 μm

[0058] [Evaluation 2] Evaluation of porosity of the surface layer of electrophotographic belts The porosity of the surface layer was determined by measuring the pore volume V of an electrophotographic belt using nitrogen adsorption and desorption.v The results were derived using the following method. An automatic gas / vapor adsorption amount analyzer (product name: BELSORP18PLUS-HT, manufactured by Nippon Bell Co., Ltd.) was used as the measuring device. After pretreatment in which an electrophotographic belt was left to stand at 100°C for 5 hours under reduced pressure and degassing, measurements were taken at a temperature of 77K using nitrogen gas as the adsorbate. Vacancy volume V v The calculation was derived from the adsorption volume of nitrogen gas at a relative pressure of 1.0 on the nitrogen adsorption isotherm. In this case, it was assumed that the nitrogen in the pores had condensed into liquid nitrogen through capillary condensation, and the volume of liquid nitrogen was derived as 1 / 643 times the volume of nitrogen gas. The porosity was calculated using the following formula (1), where V0 is the volume of the surface layer assuming the surface layer is solid, and Vv is the sum of the volumes of the pores. V0 was derived from the product of the area of ​​the measured sample and the thickness of the surface layer. Porosity (volume %) = (V v / V0)×100 ····(1)

[0059] [Evaluation 3] Evaluation of the coefficient of dynamic friction of electrophotographic belts The friction coefficient measurement tool used was a specially made tool for evaluation purposes. An electrophotographic belt was tensioned by two rollers, with one tensioning roller acting as an opposing roller and a cleaning blade in contact with it. The cleaning blade was not configured to oscillate as shown in Figure 5, but rather to have a fixed cleaning action part 20. In the definition shown in Figure 5(a), the set angle θ was set to 24° and the penetration amount δ to 1.5 mm. The friction coefficient was measured under standard conditions of room temperature 25°C and relative humidity 50%.

[0060] Using the above measuring tool, 0.80 g / mm² per unit area was measured on the electrophotographic belt. 2Toner was applied, and the intermediate transfer belt was moved at a speed of 210 mm / sec to perform a recovery operation in which the cleaning blade collected the toner on the intermediate transfer belt. During this time, the normal force N acting on the cleaning blade and the frictional force F acting on the roller opposite the cleaning blade were monitored for 30 seconds at a sampling rate of 10 ms (milliseconds). Then, the friction coefficient μ of the electrophotographic belt was calculated from the arithmetic mean values ​​(Favg, Navg) of all the obtained data (3001 points) using the following formula (2). μ = Favorg / Navg ····(2)

[0061] [Evaluation 4] Evaluation of toner cleaning performance An electrophotographic image forming apparatus with the configuration shown in Figure 4 was used, and an electrophotographic belt was mounted as an intermediate transfer body. Then, a cleaning blade was positioned on the outer surface of the electrophotographic belt with a set angle θ of 24° and an intrusion depth δ of 1.5 mm, similar to Evaluation 3. The durability of the toner cleaning performance of the electrophotographic belt was evaluated using this electrophotographic image forming apparatus. Specifically, under conditions of 15°C and 10% relative humidity, yellow (Y) toner and magenta (M) toner were used on A4 size paper (product name: Extra; manufactured by OCE, basis weight 80g / m²). 2An image forming operation was performed to form a solid red image. Then, after forming 100,000 of these solid images, the following toner cleaning performance evaluation test was performed. Specifically, the image forming operation for the solid red image was performed with the secondary transfer voltage turned off (0V). With the secondary transfer voltage turned off (0V), the solid red image consisting of Y toner and M toner that was primarily transferred onto the outer surface of the electrophotographic belt is not secondarily transferred onto the paper. Therefore, all the toner on the outer surface of the electrophotographic belt enters the contact area with the cleaning blade, and cleaning is performed by the cleaning blade. After that, the secondary transfer voltage was turned on, and the process of forming a solid white image on A4 size paper was performed. Here, if the Y toner and M toner on the outer surface of the electrophotographic belt are completely removed by the cleaning blade, no toner will be transferred onto the paper passed through in the above solid white image formation process. On the other hand, if the toner constituting the red image on the outer surface of the electrophotographic belt remains after the cleaning process, toner will adhere to the paper. In this evaluation, 400,000 solid red images were created. The cleaning performance evaluation test described above was then performed every 100,000 images. In other words, a total of four cleaning performance evaluation tests were conducted. The solid white images obtained from each cleaning performance evaluation test were visually observed. If streaks were observed in the solid white images, caused by toner that had slipped through the cleaning blade due to chipping of the cleaning blade and remained as streaks on the outer surface of the electrophotographic belt, it was determined that a cleaning failure had occurred. The images were then ranked according to the criteria in Table 1 below. In Table 1, "OK" means no cleaning failure occurred, and "NG" means cleaning failure occurred.

[0062] [Table 1]

[0063] [Materials used in the preparation of the surface layer forming coating solution in the examples and comparative examples] The materials used in preparing the surface layer forming coating solutions for the examples and comparative examples are shown in Table 2 below. <Coating liquid materials>

[0064] [Table 2]

[0065] [Preparation of coating solutions 1-8 for surface layer formation] The materials were mixed in the proportions listed in Table 3 below using a stirring homogenizer (manufactured by AS ONE Corporation) to prepare a coating solution for forming a surface layer.

[0066] [Table 3]

[0067] [Preparation of coating solutions C-1 to C-2 for surface layer formation] A coating solution for surface layer formation was prepared by mixing each material in the proportions listed in Table 4 below using a stirring homogenizer (manufactured by AS ONE Corporation).

[0068] [Table 4]

[0069] (Example 1) In this embodiment, an electrophotographic belt according to this embodiment was fabricated using a polyimide base layer (circumference 712 mm) manufactured by cylindrical extrusion molding. The base layer was fitted onto the outer circumference of a cylindrical mold, the ends were sealed, and the mold was immersed in a container filled with surface layer forming coating liquid 1. The mold was then pulled up while maintaining a constant relative speed between the liquid surface of the curable composition and the base layer, thereby forming a coating film on the surface of the base layer. The pulling speed (relative speed between the liquid surface of the curable composition and the base layer) and the solvent ratio of the curable composition can be adjusted according to the desired film thickness. In this example, the pulling speed was set to 10-50 mm / second, and the film thickness of the surface layer was adjusted to 4 μm. In this example, the coating direction refers to the direction opposite to the direction in which the base layer is pulled up. That is, the point where the base layer is first pulled out of the coating liquid is the upstream point. The coating film was dried for 3 minutes in a 70°C environment under exhaust. The drying temperature and drying time can be appropriately adjusted based on the solvent type, solvent ratio, and film thickness. After that, the coating film was irradiated using a UV irradiator (product name: UE06 / 81-3, manufactured by iGraphic Co., Ltd.) with an integrated light intensity of 500 mJ / cm². 2 The coating was cured by irradiating it with ultraviolet light until it reached the desired state.

[0070] The cured base layer of the coating was immersed in a fluorine-based solvent (product name: Novec7300, manufactured by 3M) for 10 minutes, and then removed and the fluorine-based solvent was dried. This removed the PFPE from the cured coating and formed a surface layer with interconnected pores. The base layer, on which the surface layer had formed, was removed from the cylindrical mold. The thickness of the surface layer was measured by destructive testing, which involved cutting an electrophotographic belt prepared separately under the same conditions and observing its cross-section with an electron microscope (product name: XL30-SFEG, manufactured by FEI). The destructive testing revealed that the thickness of the surface layer was 4.0 μm. It was also confirmed that the voids were interconnected.

[0071] (Examples 2-8) Except for using surface layer forming coating solutions 2 to 8 to form the surface layer, electrophotographic belts according to Examples 2 to 8 were fabricated and evaluated in the same manner as in Example 1. The evaluation results of the electrophotographic belts described in Examples 1 to 8 are shown in Table 5. In all of the examples, in evaluation 4, no toner cleaning failures occurred during the 400,000-sheet paper feeding process, and the belt was determined to be a rank A electrophotographic belt. After the test, the area near the contact point between the cleaning blade and the electrophotographic belt was observed, and no noticeable wear marks were found on the cleaning blade.

[0072] [Table 5]

[0073] (Comparative Example 1) An electrophotographic belt according to Comparative Example 1 was fabricated and evaluated in the same manner as in Example 1, except that surface layer forming solution C-1 was used to form the surface layer. (Comparative Example 2) Using the surface layer forming solution C-2, a surface layer was formed in the same manner as in Example 1, and fine grooves were formed in the surface layer by imprint processing, and then evaluated. The fine grooves formed on the surface layer consist of multiple grooves extending approximately circumferentially around the electrophotographic belt. The spacing between adjacent grooves was 20.0 μm, the (opening) width was 1.0 μm, and the depth was 0.5 μm.

[0074] Table 6 shows the evaluation results for the electrophotographic belts related to Comparative Examples 1 and 2. In all comparative examples, evaluation 4 showed toner cleaning failures during the 400,000-sheet paper feeding process, and the belt was determined to be an electrophotographic belt of rank B to D. Observation of the area near the contact point between the cleaning blade and the electrophotographic belt after the test confirmed the presence of wear marks on the cleaning blade.

[0075] [Table 6] [Explanation of Symbols]

[0076] 51 Base layer 52 Surface layer 60 aperture

Claims

1. An electrophotographic belt having an endless belt shape, It has a base layer and a surface layer provided on the base layer, The surface layer contains (meth)acrylic resin and has pores with openings on the outer surface of the surface layer. When a region is set at any position on the outer surface of the surface layer, the region has a circumferential length of 10 μm and a width equal to the total width of the electrophotographic belt, there is at least one opening within the region that communicates with an opening outside the region and within the interior of the surface layer. Within a 1 μm square area on the outer surface of the surface layer, there are five or more openings with a width of 0.10 μm or more and 0.30 μm or less. An electrophotographic belt characterized in that, assuming the surface layer is solid, the volume of the surface layer is V0, and the sum of the volumes of the voids is VV, and the porosity calculated using the following formula (1) is 25% or more and 50% or less. Porosity (volume %) = (V V / V 0) × 100 .... (1)

2. An electrophotographic image forming apparatus comprising an electrophotographic belt as described in Claim 1 and a cleaning blade having at least a portion of its contact with the outer circumferential surface of the electrophotographic belt.

Images