Electrophotographic belt, electrophotographic image forming apparatus, and conductive resin mixture

Abstract

To provide an electrophotographic belt that has sufficiently small unevenness of surface resistivity and is excellent in durability.SOLUTION: An electrophotographic belt has a conductive base layer. The base layer includes crystalline polyester, an acrylonitrile-butadiene-styrene copolymer, and carbon black. The base layer has a matrix-domain structure having a matrix including the crystalline polyester, and domains including the acrylonitrile-butadiene-styrene copolymer. The carbon black is unevenly distributed in the domains. The crystalline polyester has a structure part of a styrene-ethylene-butadiene-styrene copolymer in a molecule.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an electrophotographic belt, an electrophotographic image forming apparatus including the electrophotographic belt, and a conductive resin mixture. [Background technology]

[0002] In electrophotographic image forming apparatuses, endless electrophotographic belts made of thermoplastic resin are used as a transport transfer belt for transporting a transfer material or an intermediate transfer belt. Such electrophotographic belts are required to be inexpensive, have high strength, and print high-resolution images. Patent Document 1 discloses an electrophotographic belt formed from a semiconductive resin mixture having a sea-island structure in which nylon regions, in which nylon and carbon black are dispersed, are dispersed in a sea region of polyphenylene sulfide (hereinafter also referred to as "PPS") and discloses that an electrophotographic belt having such a configuration can suppress uneven resistance (variation in surface resistivity).

[0003] Furthermore, Patent Document 2 discloses the following method. A method for producing a conductive electrophotographic belt by biaxially stretching a preform molded from a resin mixture containing a crystalline polyester and at least one selected from polyetheresteramide and polyetheramide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-195957 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-054942 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the method described in Patent Document 2, an electrophotographic belt can be produced at low cost. The semiconductive resin mixture described in Patent Document 1 uses carbon black as a conductive agent. Therefore, compared to the electrophotographic belt described in Patent Document 2, which uses an ionic conductive agent such as polyether ester amide as a conductive agent, the semiconductive resin mixture is superior in that it has low environmental dependency of conductivity. Therefore, the present inventors attempted to produce an electrophotographic belt by a biaxial stretching method using the semiconductive resin mixture having a sea-island structure described in Patent Document 1.

[0006] However, the preform formed from the semiconductive resin mixture according to Patent Document 1 could not be biaxially stretched.

[0007] One aspect of the present disclosure is to provide an electrophotographic belt that can be produced at low cost, has sufficiently small variations in surface resistivity, and has low environmental dependency of conductivity. Another aspect of the present disclosure is to provide an electrophotographic image forming apparatus that can form high-quality electrophotographic images. Still another aspect of the present disclosure is to provide a conductive resin mixture that can be used in a biaxial stretching method. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, An electrophotographic belt, It has a conductive base layer, the base layer comprises a crystalline polyester, an acrylonitrile-butadiene-styrene copolymer, and carbon black; the base layer has a matrix-domain structure having a matrix containing the crystalline polyester and domains containing the acrylonitrile-butadiene-styrene copolymer; the carbon black is unevenly distributed in the domains, The crystalline polyester has a structural portion of a styrene-ethylene-butadiene-styrene copolymer in the molecule, and an electrophotographic belt is provided. According to another aspect of the present disclosure, there is provided an electrophotographic image forming apparatus including the electrophotographic belt as an intermediate transfer belt, and a conductive resin mixture usable in a biaxial stretching molding method. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, an electrophotographic belt can be obtained that can be produced at low cost, has sufficiently small unevenness in surface resistivity, and has low environmental dependency of conductivity. According to another aspect of the present disclosure, an electrophotographic image forming apparatus that can form high-quality electrophotographic images can be obtained. According to yet another aspect of the present disclosure, a conductive resin mixture that can be used in a biaxial stretching method can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing an example of a full-color electrophotographic image forming apparatus that utilizes an electrophotographic process. [Figure 2] FIG. 2 is a schematic cross-sectional view of an injection molding device used in the examples. [Figure 3] FIG. 2 is a schematic cross-sectional view of a primary blow molding device used in the examples. [Figure 4] FIG. 2 is a schematic cross-sectional view of a secondary blow molding device used in the examples. [Figure 5] 1 is an explanatory diagram illustrating an example of the configuration of an electrophotographic belt according to the present disclosure. [Figure 6] FIG. 1 is a diagram showing a reaction scheme between a maleic acid-modified portion in an m-SEBS molecule and a terminal hydroxy group of a raw material polyester (when cPES is PET). DETAILED DESCRIPTION OF THE INVENTION

[0011] In this disclosure, unless otherwise specified, the expressions "XX to YY" and "XX to YY" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints. Furthermore, when a numerical range is described in stages, any combination of the upper and lower limits of each numerical range is disclosed.

[0012] The present inventors speculate that the reason why the preform using the semiconductive resin mixture disclosed in Patent Document 1 could not be biaxially stretched is as follows: The domains disclosed in Patent Document 1 contain nylon and carbon black. Because nylon is a crystalline resin, when a heated preform is stretched for biaxial stretching, nylon spherulites rapidly grow with the carbon black as crystal nuclei, resulting in high hardness. As a result, it is believed that the domains cannot be stretched in accordance with the stretching of the matrix. Based on these considerations, the inventors conducted extensive research and selected, as the constituent material of the matrix, a crystalline polyester that can exhibit excellent strength, and, as the constituent material of the domain, an acrylonitrile-butadiene-styrene copolymer (hereinafter also referred to as "ABS") that has low compatibility with crystalline polyester and low crystallinity.

[0013] As a result, the conductive resin mixture obtained by dispersing ABS containing carbon black in crystalline polyester was as follows: That is, it had a matrix-domain structure with a matrix containing crystalline polyester and domains containing ABS, and the carbon black was unevenly distributed in the domains. However, minute cracks were observed at the interface between the matrix and the domains. There was concern that if a preform formed using such a resin mixture were biaxially stretched, the interface between the matrix and the domains would break during stretching. Therefore, the present inventors recognized that, in order to obtain an electrophotographic belt by biaxial stretching using such a resin mixture, it would be necessary to develop technology to prevent cracks from occurring at the interface between the matrix and the domains of the resin mixture.

[0014] Based on this understanding, further investigations led to the following discovery. Specifically, by further adding a maleic acid-modified styrene-ethylene-butadiene-styrene copolymer when melt-kneading a crystalline polyester as a raw material with ABS having dispersed carbon black, a resin mixture can be obtained in which the occurrence of cracks between the matrix and the interface is effectively prevented. Hereinafter, the crystalline polyester as a raw material may be referred to as the "raw material polyester." Furthermore, the maleic acid-modified styrene-ethylene-butadiene-styrene copolymer may be referred to as "m-SEBS."

[0015] The inventors consider the reason why the use of m-SEBS in preparing a resin mixture prevents cracks from occurring at the interface between the matrix and domains as follows: Since m-SEBS contains styrene blocks in its molecule, it has a high affinity with the styrene blocks in the ABS molecule. Meanwhile, the maleic acid-modified portion in the m-SEBS molecule reacts with the terminal hydroxyl group of the raw polyester during melt-kneading with the raw polyester (see Figure 6). As a result, an SEBS-modified crystalline polyester containing SEBS as a structural moiety is obtained. As a result, in the resin mixture according to the present disclosure, the SEBS structural moiety in the crystalline polyester in the matrix interacts with the styrene blocks of ABS in the domains, improving the affinity at the interface between the matrix and domains. It is believed that this results in the suppression of cracks from occurring between the matrix and domains. In this disclosure, the crystalline polyester as a component of the resin mixture refers to the SEBS-modified crystalline polyester described above.

[0016] Hereinafter, a resin mixture according to one embodiment of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiment.

[0017] 1. Conductive resin mixture A resin mixture according to one embodiment of the present disclosure includes a crystalline polyester, an acrylonitrile-butadiene-styrene copolymer, and carbon black. It has a matrix-domain structure with a matrix containing the crystalline polyester and domains containing the acrylonitrile-butadiene-styrene copolymer. The carbon black is unevenly distributed in the domains. Furthermore, the crystalline polyester molecule contains a styrene-ethylene-butadiene-styrene copolymer (SEBS) structural moiety. In other words, it is an SEBS-modified crystalline polyester. Such a resin mixture can be produced, for example, by mixing a mixture of crystalline polyester and m-SEBS as raw materials with ABS in which carbon black has been dispersed, followed by melt-kneading. Hereinafter, the mixture of crystalline polyester and m-SEBS may be referred to as "masterbatch A," and the ABS in which carbon black has been dispersed may be referred to as "masterbatch B."

[0018] 1-1. Crystalline polyester (raw polyester) The crystalline polyester raw material can be obtained by polycondensation of a dicarboxylic acid and a diol, polycondensation of an oxycarboxylic acid or a lactone, or polycondensation using a plurality of these components. A polyfunctional monomer may also be used in combination. The crystalline polyester may be a homopolyester containing one type of ester bond, or a copolyester (copolymer) containing multiple ester bonds.

[0019] Suitable examples of the crystalline polyester include at least one selected from the group consisting of polyalkylene terephthalates and polyalkylene naphthalates, which have high crystallinity and excellent heat resistance. Copolymers of polyalkylene naphthalates and polyalkylene isophthalates are also suitable. The number of carbon atoms of the alkylene in polyalkylene terephthalate, polyalkylene naphthalate, and polyalkylene isophthalate is preferably 2 or more and 16 or less, from the viewpoint of obtaining high crystallinity and heat resistance. More specifically, the crystalline polyester is preferably polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or a copolymer containing these. These can be used alone or in combination of two or more.

[0020] 1-2. Acrylonitrile-butadiene-styrene copolymer (ABS) ABS can be obtained by chain polymerization of acrylonitrile, butadiene, and styrene. Alternatively, it can be obtained by compounding an acrylonitrile-styrene copolymer with butadiene rubber. Furthermore, the properties it exhibits vary depending on the ratio of each component. A high acrylonitrile content results in excellent heat resistance and mechanical strength, a high butadiene content results in excellent impact resistance, and a high styrene content results in excellent gloss and processability. In the present invention, considering use as an electrophotographic belt, an ABS containing a high amount of acrylonitrile, which has excellent mechanical strength, is preferred, but is not particularly limited.

[0021] 1-3. Carbon black The carbon black that can be used includes, for example, acetylene black, furnace black, channel black, and thermal black. Carbon black has a wide variety of crystallinity and bonding states, and its shape and size are also characterized by various manufacturing and pulverization methods. These carbon blacks can be used alone or in combination of two or more types. The carbon black content in the base layer is preferably 1% by mass or more relative to the base layer, from the viewpoint of imparting electrical conductivity to the electrophotographic belt. Furthermore, from the viewpoint of suppressing physical deterioration such as cracking and wear due to friction with other sliding members (e.g., transfer rollers, tension rollers, etc.), the carbon black content in the base layer is preferably 30% by mass or less relative to the base layer. The carbon black content can be determined from the amount of residue when the electrophotographic belt is dissolved in a solvent or the like. Furthermore, "carbon black is unevenly distributed in the domains" means that the domain uneven distribution index of carbon black, which will be described later, is 80% or more. The domain uneven distribution index is preferably 85% or more.

[0022] 1-4. Maleic acid modified styrene-ethylene-butadiene-styrene copolymer (m-SEBS) m-SEBS can be obtained by modifying a styrene-ethylene-butadiene-styrene copolymer with maleic acid. SEBS copolymers can be obtained by chain polymerization of styrene, ethylene, and butadiene. Alternatively, they can be obtained by hydrogenating a portion of the butadiene portion (—CH2-CH═CH-CH2-) of a styrene-butadiene-styrene copolymer. When the hard segment, styrene, is contained in large amounts, the copolymer exhibits excellent thermal stability, while when the soft segments, ethylene and butadiene, are contained in large amounts, the copolymer exhibits excellent flexibility and impact resistance. Since the copolymer is used as an interfacial reinforcing agent in the present invention, the ratio of each component is not particularly limited. However, a large amount of styrene is preferred from the viewpoint of obtaining excellent mechanical strength. Furthermore, a large amount of styrene is also preferred from the viewpoint of good compatibility with the styrene portion of the ABS copolymer. Specifically, the styrene content of the m-SEBS copolymer is preferably 20% by mass or more.

[0023] 1-4.Additives Other components may be added to at least one of Masterbatch A and Masterbatch B to the extent that the effects of the present disclosure are not impaired. Examples of other components include antioxidants, UV absorbers, organic pigments, inorganic pigments, pH adjusters, crosslinking agents, compatibilizers, release agents, coupling agents, lubricants, etc. These additives may be used alone or in combination of two or more. The amount of additive used can be set appropriately and is not particularly limited.

[0024] The conductive resin mixture produced by the method according to the present disclosure can be applied to known molding methods such as injection molding, extrusion molding, blow molding, compression molding, and injection-compression molding, and can be produced in any shape. For example, when producing a seamless belt, blow molding, extrusion molding, and the like are suitable. Since the conductive resin mixture produced by the method disclosed in the present invention has a matrix-domain structure, a molded article made from the conductive resin mixture also has the same matrix-domain structure.

[0025] In addition to the seamless belt, the conductive resin mixture according to the present disclosure can also be used for solar cell substrates, etc. It can also be used for electronic equipment parts such as generators, electric motors, voltage regulators, rectifiers, sensors, LED lamps, semiconductors, computers, and printed circuit boards, lighting parts, household and office equipment parts such as refrigerator parts, air conditioner parts, and copier parts, automobile-related parts, various molded articles such as films, containers, pipes, tubes, and hoses, and fibers.

[0026] 2. Electrophotographic belts An electrophotographic belt according to one embodiment of the present disclosure has at least a conductive base layer. Fig. 5(a) shows a perspective view of an electrophotographic belt 500 having an endless belt shape according to one embodiment of the present disclosure. An example of the layer structure is a monolayer structure in which the cross section taken along line AA' in Fig. 5(a) is composed of only a base layer 501 containing the conductive resin mixture, as shown in Fig. 5(b-1). In this case, an outer surface 500-1 of the base layer 501 becomes the toner carrying surface (outer surface) of the electrophotographic belt.

[0027] Another example of the layer structure is one in which the cross section taken along line AA' has a laminated structure having a base layer 501 and a second layer 502 covering the outer peripheral surface of the base layer 501, as shown in Fig. 5(b-2). When the second layer 502 is provided, an outer surface 500-1 of the second layer 502 becomes the toner carrying surface of the electrophotographic belt. One of the functions of the second layer is to improve the releasability of the toner.

[0028] An example of the second layer is a layer having excellent abrasion resistance and containing a cured product of an active energy ray-curable resin. Such a second layer can be provided, for example, by applying a composition containing an active energy ray-curable resin, such as a photocurable resin, to the outer peripheral surface of the base layer and curing it. Suitable examples of active energy ray-curable resins include acrylic resins. Conductive particles may also be added to adjust the surface resistivity of the second layer. Examples of conductive particles include carbon black, graphite, carbon nanotubes, carbon microcoils, zinc oxide, and zinc antimonate. Also, a third layer (not shown) may be provided to cover the inner peripheral surface of the base layer 501. Examples of the third layer include a resin layer for reinforcing the first layer and a conductive layer for making the inner peripheral surface of the electrophotographic belt conductive.

[0029] 2-1. Base layer According to one embodiment of the present disclosure, a substrate layer having an endless shape includes a crystalline polyester, an acrylonitrile-butadiene-styrene copolymer, and carbon black. The substrate layer has a matrix-domain structure having a matrix containing the crystalline polyester and domains containing the acrylonitrile-butadiene-styrene copolymer. The carbon black is unevenly distributed in the domains, and the crystalline polyester molecule contains a styrene-ethylene-butadiene-styrene copolymer structural moiety.

[0030] The transferability of the toner basically depends on the electrical properties of the base layer. To obtain a high-quality electrophotographic image, the surface resistivity of the base layer should be, for example, 1.0×10 3 Ω / □~1.0×10 13 It is preferable that the surface resistivity is 1.0×10 3 If the surface resistivity is 1.0×10 Ω / □ or more, the resistance is prevented from decreasing significantly, the transfer electric field can be easily obtained, and the occurrence of missing images and roughness can be effectively suppressed. 13 If it is Ω / □ or less, it is possible to more effectively prevent the transfer voltage from becoming excessive, and it is possible to effectively prevent the power supply from becoming large and the cost from increasing.

[0031] The thickness of the base layer is not particularly limited, but is preferably 40 μm to 500 μm, particularly 50 μm to 100 μm, from the viewpoint of ensuring flexibility since the base layer is disposed in a bent state inside an electrophotographic image forming apparatus. The base layer can be produced using the conductive resin mixture described above, for example, through the following steps (i) to (iii).

[0032] Step (i): A test-tube shaped preform made of the conductive resin mixture is obtained. Step (ii): The preform is stretched in its longitudinal direction while a gas is introduced into the preform, thereby stretching it in two axes, the longitudinal direction and the circumferential direction, to obtain a biaxially stretched molded product (hereinafter also referred to as a "bottle") (biaxial stretch blow molding). Step (iii): Both ends of the bottle are cut to obtain an endless biaxially stretched cylindrical film.

[0033] In step (i), first, a masterbatch A containing crystalline polyester and m-SEBS as raw materials and a masterbatch B containing ABS in which carbon black is dispersed are prepared. Next, to prepare masterbatch A, the raw materials, crystalline polyester and m-SEBS, are mixed and further subjected to hot melt kneading. The temperature at this time is preferably, for example, 220°C or higher and 330°C or lower, and the time is, for example, 3 to 5 minutes. This is because the reaction between the raw material polyester and m-SEBS can be sufficiently promoted and thermal degradation of the resin can be prevented. The obtained masterbatch A is preferably pelletized.

[0034] Masterbatch B is prepared by mixing ABS with a predetermined amount of carbon black and then kneading the mixture under heat at a temperature of 190°C or higher and 270°C or lower for a period of time of, for example, 3 to 5 minutes. The resulting masterbatch B is preferably pelletized. It is preferable to prepare masterbatches A and B in advance in this manner, and then mix them to prepare the resin mixture according to the present disclosure. This allows the carbon black to be more reliably distributed unevenly in the domains containing ABS in the resin mixture. That is, in the resin mixture according to the present disclosure, it is preferable to distribute the carbon black unevenly in the domains containing ABS and prevent the carbon black from coming into direct contact with the crystalline polyester. This prevents the formation of spherulites of the crystalline polyester with the carbon black as a nucleus when a preform formed from the resin mixture is biaxially stretched, and can prevent poor stretching due to increased hardness in the matrix portion.

[0035] The thus obtained masterbatch A and masterbatch B are melted to prepare a resin mixture according to the present disclosure. The resulting resin mixture is then molded into a test-tube-shaped preform. The preform molding method is not particularly limited, and examples include the following methods. As shown in FIG. 2 , the melt of the resin mixture is injected into a preform mold consisting of a cavity mold 203 and a core mold 207 using an injection molding apparatus 201, and solidified within the preform mold to form a preform 205 having a predetermined shape. At this time, the temperature of the preform mold into which the melt is injected is preferably kept, for example, at 40°C or below. The melt injected into the mold cools and solidifies within the mold, but rapid cooling at this time can prevent the crystallization of the crystalline polyester from progressing. By suppressing the crystallization of the crystalline polyester within the preform, the biaxial crystal orientation of the crystalline polyester can be more accurately controlled during the stretch-blow molding in step (ii). When molding a preform by injection molding, the resin mixture according to the present disclosure and the molding of the preform proceed simultaneously. That is, the resin mixture according to the present disclosure is prepared during the process of heating and melt-kneading master batch A and master batch B in the extruder of the injection molding machine, and the molten resin mixture is then injected into the cavity of the molding die. As a result, a preform made of the resin mixture is molded.

[0036] Next, in step (ii), the preform is biaxially stretched and blow-molded. First, as shown in FIG. 3(a), the preform 205 is placed in a heating furnace 301 and heated to a temperature at which it can be stretched. The heating time is preferably within one minute. Limiting the heating time to five minutes or less prevents the crystallization of the crystalline polyester within the preform during heating. The heated preform is transported in the direction of arrow 305. Next, a blow mold 303, which is formed by combining a left mold 303-1 and a right mold 303-2 to form a cylindrical cavity 303-3 therein, is lowered in the direction of arrow 307 from directly above the heated preform 205. Then, as shown in FIG. 3(b), it is placed at the mouth of the blow mold 303.

[0037] It is preferable to place the heated preform in the mouth of the blow mold in a short time (for example, within 20 seconds) so that the temperature of the heated preform does not drop before the start of the next biaxial stretching step. This prevents the preform from gradually cooling, which would otherwise cause the crystalline polyester to crystallize. The heating temperature of the preform may be calculated in advance by observing the endothermic peak or baseline shift during heating using a differential scanning calorimeter (DSC) for the resin mixture that constitutes the preform, or it may be determined from the glass transition temperature (Tg).

[0038] As shown in FIG. 3(c), the heated preform 205 placed in the blow mold 303 is stretched in the longitudinal direction of the preform 205 by driving the stretch rod 309 in the direction of arrow 311. This stretching is called the primary stretching. Synchronously with the drive of the stretch rod 309, gas is introduced into the preform 205 from its opening (arrow 313) to expand the preform in its circumferential direction. This is called the secondary stretching. Examples of the gas blown into the preform 205 include air, nitrogen, carbon dioxide, and argon. As a result, the preform 205 expands in each direction indicated by arrows 315 in FIG. 3(c), adhering to the inner wall of the cavity 303-3 and then cooling and solidifying in that state. Next, the right mold 303-1 and left mold 303-2 of the blow mold 303 are separated, and a bottle-shaped molded product (hereinafter also referred to as a "blow bottle") is removed from the blow mold 303.

[0039] Next, as shown in FIG. 3(d), the mouth side portion of the obtained blown bottle 317 and the upper end portion opposite the mouth side are cut to obtain a biaxially stretched cylindrical film 319 that will serve as the base layer. Before cutting the blown bottle 317, a heat treatment may be performed as necessary to adjust the surface roughness of the outer periphery of the blown bottle or to fine-tune the crystallinity of the crystalline polyester. Specifically, for example, as shown in FIG. 4, the blown bottle 317 is placed in a cylindrical mold 401, and then the blown bottle is filled with gas. Then, to prevent the gas from leaking from inside the blown bottle, outer molds are attached to the top and bottom of the mold 401, and the mold 401 is heated while rotating using a roller-shaped heater 403 abutting against the outer periphery of the mold 401. The heating temperature is, for example, about 130 to 190°C, and the heating time is, for example, about 60 seconds, so that the entire circumference of the blown bottle is heated uniformly.

[0040] The application of the electrophotographic belt according to the present disclosure is not limited to an intermediate transfer belt, but can also be suitably used as, for example, a transport transfer belt.

[0041] <Electrophotographic image forming apparatus> An example of an electrophotographic image forming apparatus using an electrophotographic belt according to one embodiment of the present disclosure as an intermediate transfer belt will be described below. As shown in Fig. 1, this electrophotographic image forming apparatus has a so-called tandem configuration in which electrophotographic stations of multiple colors are arranged side by side in the rotation direction of the intermediate transfer belt. In the following description, the reference numerals of components relating to the colors yellow, magenta, cyan, and black are respectively given suffixes Y, M, C, and k, but the suffixes may be omitted for similar components.

[0042] In FIG. 1, photosensitive drums (photoconductors, image carriers) 1Y, 1M, 1C, and 1k are surrounded by charging devices 2Y, 2M, 2C, and 2k, exposure devices 3Y, 3M, 3C, and 3k, developing devices 4Y, 4M, 4C, and 4k, and an intermediate transfer belt (intermediate transfer member) 6. The photosensitive drum 1 is rotated in the direction of arrow F (counterclockwise) at a predetermined peripheral speed (process speed). The charging device 2 charges the peripheral surface of the photosensitive drum 1 to a predetermined polarity and potential (primary charging). The exposure device 3, a laser beam scanner, outputs a laser beam that is on / off modulated in response to image information input from an external device such as an image scanner or computer (not shown), scanning and exposing the charged surface of the photosensitive drum 1. This scanning and exposure forms an electrostatic latent image on the surface of the photosensitive drum 1 according to the desired image information.

[0043] The developing devices 4Y, 4M, 4C, and 4k contain toner of each color component: yellow (Y), magenta (M), cyan (C), and black (k), respectively. The developing device 4 to be used is selected based on image information, and developer (toner) is developed on the surface of the photosensitive drum 1, visualizing the electrostatic latent image as a toner image. In this embodiment, a reversal development method is used, in which toner is deposited on the exposed portion of the electrostatic latent image for development. The charging device, exposure device, and developing device constitute an electrophotographic image forming means.

[0044] The intermediate transfer belt 6 is an electrophotographic belt having an endless shape. The intermediate transfer belt 6 is stretched by a plurality of rollers 20, 21, and 22 so that the outer circumferential surface of the intermediate transfer belt 6 abuts against the surface of the photosensitive drum 1. In this embodiment, the roller 20 is a tension roller that controls the tension of the intermediate transfer belt 6 to a constant level, the roller 22 is a drive roller for the intermediate transfer belt 6, and the roller 21 is an opposing roller for secondary transfer. The intermediate transfer belt 6 is rotated in the direction of arrow G by the drive of the roller 22. Primary transfer rollers 5Y, 5M, 5C, and 5k are disposed at primary transfer positions facing the photosensitive drum 1 across the intermediate transfer belt 6.

[0045] The unfixed toner images of each color formed on the photosensitive drum 1 are electrostatically transferred sequentially onto the intermediate transfer belt 6 by applying a primary transfer bias of opposite polarity to the charge polarity of the toner to the primary transfer roller 5 from a constant voltage source or constant current source (not shown). A full-color image is then obtained on the intermediate transfer belt 6, with the unfixed toner images of four colors superimposed on top of each other. The intermediate transfer belt 6 rotates while carrying the toner images thus transferred from the photosensitive drum 1. After each rotation of the photosensitive drum 1 after the primary transfer, the surface of the photosensitive drum 1 is cleaned of any residual toner by a cleaning device 11, and the image formation process is repeated.

[0046] At the secondary transfer position of the intermediate transfer belt 6 facing the transport path of the recording material 7 serving as a transfer medium, a secondary transfer roller (transfer unit) 9 is disposed in pressure contact with the toner image bearing surface of the intermediate transfer belt 6. At the back side of the intermediate transfer belt 6 at the secondary transfer position, a counter roller 21 is disposed, which serves as an opposing electrode to the secondary transfer roller 9 and to which a bias is applied. When the toner image on the intermediate transfer belt 6 is transferred to the recording material 7, a bias of the same polarity as the toner is applied to the counter roller 21 by a transfer bias application means 28, for example, −1000 to −3000 V, causing a current of −10 to −50 μA to flow. The transfer voltage at this time is detected by a transfer voltage detection means 29. Furthermore, downstream of the secondary transfer position, a cleaning device (belt cleaner) 12 is provided to remove toner remaining on the intermediate transfer belt 6 after the secondary transfer.

[0047] The recording material 7 passes through a conveying guide 8 and is conveyed in the direction of arrow H, and is introduced into the secondary transfer position. The recording material 7 introduced into the secondary transfer position is then sandwiched and conveyed at the secondary transfer position, at which time a constant voltage bias (transfer bias) controlled to a predetermined value is applied from a secondary transfer bias application means 28 to an opposing roller 21 of the secondary transfer roller 9. By applying a transfer bias of the same polarity as the toner to the opposing roller 21, the four-color full-color image (toner image) superimposed on the intermediate transfer belt 6 at the transfer position is transferred all at once to the recording material 7, and an unfixed full-color toner image is formed on the recording material. The recording material 7 to which the toner image has been transferred is introduced into a fixing unit (not shown) and heated and fixed. [Example]

[0048] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. Materials used in manufacturing electrophotographic belts according to the examples and comparative examples are shown below.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

[0052] [Table 4]

[0053] (Methods for measuring and evaluating physical properties) The methods for measuring and evaluating the characteristic values ​​of the electrophotographic belts according to the examples and comparative examples are as follows (1) to (5). (Evaluation 1) Evaluation of surface resistivity The surface resistivity of the base layer of the electrophotographic belt was measured by a method conforming to JIS-K6911. The measuring device used was a high resistance meter (trade name: Hiresta UP MCP-HT450, manufactured by Mitsubishi Chemical Analytic Co., Ltd.) with a main electrode having an inner diameter of 50 mm, a guard ring electrode having an inner diameter of 53.2 mm, and a probe (trade name: UR-100, manufactured by Mitsubishi Chemical Analytic Co., Ltd.) with an outer diameter of 57.2 mm. The surface resistivity was measured per unit area (1 cm) of the electrophotographic belt. 2 ) and is expressed in units of [Ω / □].

[0054] The prepared electrophotographic belt base layer was left standing for 24 hours in an environmental test chamber controlled at a temperature of 23°C and a relative humidity of 50%. Thereafter, a voltage of 250V was applied to the electrophotographic belt for 10 seconds under an environment of a temperature of 23°C and a relative humidity of 50%, and the surface resistivity of the electrophotographic belt base layer was measured at four points in the circumferential direction. The average value of the obtained surface resistivities was used as an index of the surface resistivity at normal temperature and normal humidity. The surface resistivity unevenness was determined as the logarithm of the ratio of the maximum value to the minimum value in the measured surface resistivity. 10 It is expressed as (maximum value / minimum value).

[0055] (Evaluation 2) Carbon black domain distribution index The ratio of carbon black present in the domains to the carbon black present in the entire electrophotographic belt is defined as the carbon black domain distribution index, which was calculated using a thermogravimetric analyzer (trade name: TGA / DSC3+, manufactured by Mettler Toledo). First, the mass W of the sample cut out from the electrophotographic belt D&M was measured. Next, the sample was heated from 25°C to 380°C at a heating rate of 10°C / min and held at 380°C for 4 hours, after which the mass of carbon black in the domain and matrix (mass W CBD&CBM ) was measured. (W D&M -W CBD&CBM) is the mass reduced by decomposition of the resin in the matrix portion and the resin in the domain portion. (W CBD&CBM / W D&M )×100 was taken as the mass proportion A of carbon black contained in the entire electrophotographic belt.

[0056] The proportion of carbon black present in the domains was calculated using the following method. First, a sample cut out from an electrophotographic belt is immersed in an alkaline solution overnight to dissolve the crystalline polyester in the matrix, then washed with pure water and dried, after which the mass W of the domain is measured. D was measured. Next, the sample was heated from 25°C to 380°C at a heating rate of 10°C / min and held at 380°C for 4 hours, after which the mass of carbon black in the domain (W CBD ) was measured. (W CBD / W D )×100 was defined as the mass proportion B of carbon black contained in the domain portion. (W CBD / W CBD&CBM The value (%) calculated by multiplying the domain distribution index by 100 is the domain distribution index of carbon black (CB). The closer this domain distribution index is to 100%, the more the carbon black is distributed unevenly in the domains.

[0057] (Evaluation 3) Crack evaluation Cracks were evaluated using a scanning electron microscope (trade name: Ultra55, manufactured by Carl Zeiss) to observe the cross section of the resin molded product (a test-tube-shaped preform before biaxial stretching) and the cross section of the electrophotographic belt, and images of the cross sections were obtained. The presence or absence of cracks in the resin molded product and the electrophotographic belt (i.e., the presence or absence of cracks after blow molding) was determined from the obtained images. A cryomicrotome (trade name: UC6, manufactured by Leica) was used to expose the observation surface. To distinguish between the matrix and domains, the observation surface was exposed using the cryomicrotome, and then subjected to vapor staining with a 4% OsO4 aqueous solution to stain the butadiene component. This staining determined that the portion containing the butadiene component was an ABS copolymer.

[0058] (Rating 4) Durability rating In accordance with JIS P8115, test pieces were cut to a size of 10 mm wide and 100 mm long, and the number of times until breakage was measured using an MIT type folding endurance tester (No. 307 MIT type folding endurance tester manufactured by Yasuda Seiki Seisakusho Co., Ltd.) under the following conditions. Measurement conditions: bending speed 180 times / min, bending angle 135° left and right, tensile load 9.8N.

[0059] (Evaluation 5) Digital reproducibility of electrophotographic image forming devices An electrophotographic image forming apparatus having the configuration shown in Figure 1 was equipped with an intermediate transfer belt as an electrophotographic belt, and the apparatus was left standing for 24 hours in an environmental test chamber controlled at a temperature of 30°C and a relative humidity of 80%. An unfixed image at the time when a fine line image (30 lines / 5 mm) was transferred onto paper was then output, and this was fixed without pressure in an oven at 100°C to obtain an image. The image was observed using a magnifying glass to check for toner scattering in each fine line image, and evaluated according to the following criteria. <Evaluation criteria> Rank A: There are no fine line images where toner scattering occurred. Rank B: 1 to 5 fine line images with toner scattering. Rank C: There are 6 to 10 fine line images where toner scattering occurred. Rank D: 11 or more fine line images where toner scattering occurred.

[0060] [Example 1] (Creating the base layer) <Pre-blend sample 1, Pre-blend sample 2> The various materials were pre-blended in advance to obtain the material composition ratios shown in Table 5A. Specifically, ABS1 and CB1 were pre-blended to form pre-blend sample 1 (master batch B). Furthermore, a pre-blend of cPES1 and m-SEBS1 was used as pre-blend sample 2 (master batch A).

[0061] <Amorphous thermoplastic resin mixture 1> Next, the preblend sample 1 was melt-kneaded using a twin-screw extruder (product name: TEX30α, manufactured by The Japan Steel Works, Ltd.) to prepare an amorphous thermoplastic resin mixture. The melt-kneading temperature was adjusted to be in the range of 190°C or higher and 270°C or lower, and the melt-kneading time was approximately 3 to 5 minutes. The obtained amorphous thermoplastic resin mixture was pelletized to prepare amorphous thermoplastic resin mixture 1. <Crystalline thermoplastic resin mixture 1> Similarly, preblend sample 2 was melt-kneaded using a twin-screw extruder (product name: TEX30α, manufactured by The Japan Steel Works, Ltd.) to prepare a crystalline thermoplastic resin mixture. The melt-kneading temperature was adjusted to be within the range of 220°C or higher and 330°C or lower, and the melt-kneading time was approximately 3 to 5 minutes. The obtained crystalline thermoplastic resin mixture was pelletized to prepare crystalline thermoplastic resin mixture 1.

[0062] Next, the obtained amorphous thermoplastic resin mixture 1 was dried at a temperature of 90°C for 10 hours, and the crystalline thermoplastic resin mixture 1 was dried at a temperature of 140°C for 10 hours. The pelletized amorphous thermoplastic resin mixture 1 and crystalline thermoplastic resin mixture 1 were loaded into an injection molding machine (product name: SE180D, manufactured by Sumitomo Heavy Industries, Ltd.) so as to obtain the material blending ratios shown in Table 5A. Then, the cylinder temperature was set to 250 to 300°C, and the mixture was injection molded into a test-tube-shaped mold whose temperature was controlled at 30°C to produce a preform. The obtained preform had a test-tube shape with an outer diameter of 50 mm, an inner diameter of 46 mm, and a length of 150 mm.

[0063] Next, the preform was stretched in two directions, the longitudinal direction and the circumferential direction, using a biaxial stretching molding device. First, as shown in FIG. 3(a), the preform 205 was placed in a heating device 301 equipped with a non-contact heater (not shown) for heating the preform 205, and heated with the heater so that the outer surface temperature of the preform reached 120 to 160°C. Next, a blow mold 303, whose mold temperature was maintained at 30°C, was lowered in the direction of arrow 307 onto the heated preform 205, and the heated preform 205 was placed in the mouth of the blow mold 303 (FIG. 3(b)). Next, as shown in FIG. 3(c), a stretching rod 309 was driven in the direction of arrow 311, and air adjusted to a temperature of 23°C was introduced into the interior of the preform 205 from its mouth, as shown by arrow 313 in FIG. 3(c). In this way, the preform 205 was stretched in two directions and adhered to the inner wall of the blow mold. Next, the right mold 303-1 and the left mold 303-2 of the blow mold 303 were separated, and a bottle-shaped molded product (blow bottle) 317 was taken out from the blow mold 303.

[0064] Next, the resulting blown bottle 317 was set in a nickel cylindrical mold 401 produced by electroforming as shown in Figure 4, and an outer mold 405 was attached. An air pressure of 0.1 MPa was applied to the inside of the blown bottle, and the pressure was adjusted so that no air leaked to the outside, thereby causing the outer surface of the blown bottle 317 to adhere tightly to the inner surface of the cylindrical mold. Furthermore, while rotating the nickel cylindrical mold 401, it was heated to 130 to 190°C using a heater 403, and heated uniformly for a total of 60 seconds.

[0065] Thereafter, air at a temperature of 25°C was blown onto this nickel cylindrical mold to cool it to room temperature (25°C) over 1 minute, and the air pressure applied to the inside of blown bottle 317 was released to obtain blown bottle 317 whose dimensions had been improved by annealing. From the dimensions of preform 205 and blown bottle 317, the biaxial stretching ratios were found to be 4.0 times for the transverse stretching ratio (circumferential direction) Lp and 4.3 times for the longitudinal stretching ratio (direction perpendicular to the circumferential direction) La. Next, as shown in FIG. 3(d), the mouth side portion of the blown bottle 317 and the portion opposite to the mouth side were cut to prepare a base layer for an electrophotographic belt having a circumference of 630 mm, a width of 250 mm, and a thickness of 70 μm.

[0066] (Preparation of surface layer coating liquid) The acrylic resin mixture shown in Table 4 was weighed in a ratio of AN / PTFE / GF / SL / IRG = 66 / 20 / 1.0 / 12 / 1.0 (mass ratio converted to solid content), and the solution was subjected to a coarse dispersion treatment, which was then dispersed using the high-pressure emulsifying disperser described below. High-pressure emulsifier / disperser, product name: Nanovaita, manufactured by Yoshida Kikai Kogyo Co., Ltd. This dispersion treatment was continued until the 50% average particle size of the contained PTFE reached 200 nm. The resulting dispersion was used as a surface layer coating liquid.

[0067] (Formation of surface layer) The base layer was fitted onto the outer periphery of a cylindrical mold (circumferential length 630 mm), the edges were sealed, and the mold was then immersed in a container filled with the surface layer coating liquid and pulled up so that the relative speed between the liquid level of the curable composition and the electrophotographic belt base layer was constant. In this way, a coating film made of the coating liquid was formed on the surface of the electrophotographic belt base layer. Depending on the desired film thickness of the surface layer, the pulling speed (the relative speed between the liquid level of the curable composition and the electrophotographic belt base layer) and the solvent ratio of the curable composition can be adjusted.

[0068] In this example, the lifting speed was set to 10 to 50 mm / sec, and the film thickness of the surface layer was adjusted to about 3 μm. In this example, the coating direction refers to the direction opposite to the direction in which the electrophotographic belt base layer is lifted. In other words, the location where it is first lifted from the coating liquid is the most upstream. The electrophotographic belt base layer coated with the coating liquid was removed from the cylindrical mold and dried for 1 minute in an environment of 23°C under exhaust air. The drying temperature and drying time were adjusted appropriately depending on the type of solvent, solvent ratio, and film thickness. Thereafter, a UV irradiator (product name: UE06 / 81-3, manufactured by Eye Graphics Co., Ltd.) was used on the coating film, and an integrated light dose of 600 mJ / cm was applied. 2 The coating was cured by irradiating it with ultraviolet light until it reached a temperature of 100°C.

[0069] The thickness of the surface layer was determined by destructive testing in which an electrophotographic belt base layer separately prepared under the same conditions was cut and the cross section was observed with an electron microscope (product name: XL30-SFEG, manufactured by FEI). As a result of the destructive testing, the thickness of the surface layer was found to be 2.8 μm. In this way, an electrophotographic belt having a surface layer formed on the outer peripheral surface of the base layer was obtained. This electrophotographic belt was subjected to the above-mentioned (Evaluation 1) to (Evaluation 5). The evaluation results are shown in Table 6A.

[0070] [Examples 2 to 16] Except for the material types and blending amounts shown in Tables 5A and 5B below, electrophotographic belts were produced and evaluated in the same manner as in Example 1. The evaluation results are shown in Tables 6A and 6B.

[0071] [Comparative Examples 1 to 6] Except for using the materials and their blending amounts as shown in Table 5B below, an electrophotographic belt was produced and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6B. Comparative Example 1 did not contain the m-SEBS copolymer as an interface reinforcing agent, and it was confirmed that cracks were present at the interface between the crystalline polyester and the ABS copolymer. In Comparative Example 2, the carbon black content was too low, so the surface resistivity was 1×10 14 [Ω / □], which was outside the range suitable for an electrophotographic belt.

[0072] No ABS copolymer was included in Comparative Example 3. The reason why blow molding was not possible is thought to be that when the preform was heated during the first blow, spherulitization with the carbon black as the crystal nucleus was promoted, causing the preform to harden. No crystalline polyester was included in Comparative Example 4. The reason why blow molding was not possible is thought to be that when the preform was biaxially stretched, the strength was not increased by oriented crystallization, and the preform broke at the locally thinned portion. Comparative Example 5 was the same as Example 2, except that a styrene-ethylene-butadiene-styrene copolymer not modified with maleic acid was used as the interfacial reinforcing agent. Because a styrene-ethylene-butadiene-styrene copolymer not modified with maleic acid was used as the interfacial reinforcing agent, the interfacial reinforcing effect was not sufficient, and cracks were present in the resin molded product. Therefore, as shown in Table 6, the number of cycles until failure in the MIT test was lower than that of Example 2.

[0073] [Table 5A]

[0074] [Table 5B]

[0075] [Table 6A]

[0076] [Table 6B] [Explanation of symbols]

[0077] 1 Photosensitive drum 2. Charging device 3 Exposure equipment 4. Developing device 5 Primary transfer roller 6 Intermediate transfer belt 7 Recording material 9 Secondary transfer roller 11 Cleaning device (drum cleaner) 12 Cleaning device (belt cleaner) 20 Tension roller 21 Opposing roller 22 Drive roller 28 Transfer bias applying means 29 Transfer high voltage detection means 205 Preform 303 Blow mold 309 Stretching rod 317 Blow Bottle

Claims

1. An electrophotographic belt, It has a conductive base layer, the base layer comprises a crystalline polyester, an acrylonitrile-butadiene-styrene copolymer, and carbon black; the base layer has a matrix-domain structure having a matrix containing the crystalline polyester and domains containing the acrylonitrile-butadiene-styrene copolymer; the carbon black is unevenly distributed in the domains, The crystalline polyester has a structural portion of a styrene-ethylene-butadiene-styrene copolymer in the molecule.

2. The surface resistivity of the base layer is 1.0×10 ３ Ω / □ to 1.0 x 10 １３ 2. The electrophotographic belt according to claim 1, wherein the surface roughness is Ω / □.

3. 3. The electrophotographic belt according to claim 1, wherein the content of said carbon black in said base layer is 1% by mass or more and 30% by mass or less with respect to said base layer.

4. 4. The electrophotographic belt according to claim 1, wherein the domain uneven distribution index of the carbon black contained in the base layer is 80% or more.

5. 5. The electrophotographic belt according to claim 1, wherein the crystalline polyester is at least one selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, and copolymers containing these.

6. 6. An electrophotographic image forming apparatus comprising the electrophotographic belt according to claim 1 as an intermediate transfer belt.

7. A conductive resin mixture, comprising a crystalline polyester, an acrylonitrile-butadiene-styrene copolymer, and carbon black; a matrix-domain structure having a matrix containing the crystalline polyester and domains containing the acrylonitrile-butadiene-styrene copolymer; the carbon black is unevenly distributed in the domains, The conductive resin mixture is characterized in that the crystalline polyester has a structural portion of a styrene-ethylene-butadiene-styrene copolymer in the molecule.

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