Intermediate transfer body and electrophotographic image forming apparatus

Abstract

To provide a member for electrophotography that maintains uniform low adhesion to toner for a long period to prevent image unevenness.SOLUTION: A member for electrophotography has a base layer and a surface layer. The surface layer includes at least one of an acrylic resin and a (meth)acrylic resin, perfluoropolyether having a specific structure, and a fluorine-containing copolymer. The fluorine-containing copolymer has a first polymerization unit that is derived from at least one of methyl acrylate and methyl (meth)acrylate, and a second polymerization unit that is derived from at least one of methyl acrylate having a fluoroalkyl group and methyl (meth)acrylate having a fluoroalkyl group. The molar ratio of the first polymerization unit to the second polymerization unit is 7-12. The member for electrophotography has a Mw of 80000 or more and 150000 or less. The ratio of Mw to Mn (Mw / Mn) is 3.0 or more and 6.5 or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an electrophotographic member used in an electrophotographic image forming apparatus such as a copying machine or a printer, and an electrophotographic image forming apparatus.

Background Art

[0002] One of the electrophotographic members used in an electrophotographic image forming apparatus is an intermediate transfer belt. The intermediate transfer belt is used in an electrophotographic image forming method in which toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are superimposed on a toner image carrying surface (hereinafter also referred to as “outer surface”), and then transferred onto paper all at once to obtain a full-color image. In order to meet the demand for further improvement in the process speed of recent electrophotographic image forming apparatuses, further improvement in transfer characteristics is required for the intermediate transfer belt. And for that purpose, it is effective to reduce the toner adhesion force on the outer surface of the intermediate transfer belt. Patent Document 1 discloses an electrophotographic belt having a base layer and a surface layer, the surface layer including a binder resin, a perfluoropolyether (PFPE), and a comb-shaped graft copolymer, the comb-shaped graft copolymer being a copolymer of an acrylate or methacrylate having a fluoroalkyl group and a methacrylate macromonomer having polymethyl methacrylate in a side chain, having a number average molecular weight of 11,000 or more and 15,000 or less, and a peak top molecular weight of 24,000 or more and 40,000 or less. And Patent Document 1 discloses that the comb-shaped graft copolymer can improve the dispersibility of PFPE in the binder resin, and as a result, the average major axis of the domain made of PFPE in the surface layer can be made to be a small size such as 1 to 60 nm.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Further, Patent Document 1 discloses the following in paragraph 0037 from the viewpoints of easier migration of PFPE to the surface of the electrophotographic belt and further imparting toner releasability to the surface of the electrophotographic belt. That is, as the PFPE, it is preferable to use one having a non-reactive functional group such as a hydroxyl group so that the PFPE does not bind to the binder resin. According to the studies by the present inventors, PFPE having a hydroxyl group at the molecular terminal (hereinafter also referred to as "PFPE-OH") can be dispersed in a non-reactive state with an acrylic resin or a methacrylic resin, which is a binder resin, in the surface layer. PFPE-OH present in the binder resin in a non-reactive state with the binder resin is excellent in the migration property to the outer surface of the electrophotographic belt and can more rapidly recover the toner releasability of the outer surface. However, the electrophotographic belt provided with a surface layer in which PFPE-OH is dispersed in an acrylic resin or a methacrylic resin may have unevenness in the toner releasability of its outer surface.

[0005] One aspect of the present disclosure is directed to providing an electrophotographic member having excellent uniformity in low adhesion of toner on the toner image bearing surface. Another aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus capable of stably forming a high-quality electrophotographic image.

Means for Solving the Problems

[0006] According to one aspect of the present disclosure, it has a base layer and a surface layer Intermediate transfer body and the surface layer contains at least one of an acrylic resin and a methacrylic resin, perfluoropolyether (PFPE), and a fluorine-containing copolymer, the PFPE has a structure represented by the following structural formula (1), HO-H2C-(CF2O)p (CF2CF2O) q -CH2-OH (1) (In the structural formula (1), p and q each independently represent an integer of 1 or more.) The fluorine-containing copolymer is a first polymerized unit derived from at least one of methyl acrylate (MA) and methyl methacrylate (MMA), and a second polymerized unit derived from at least one of methyl acrylate having a fluoroalkyl group (F-MA) and methyl methacrylate having a fluoroalkyl group (F-MMA), and has a molar ratio (first polymerized unit / second polymerized unit) of the first polymerized unit to the second polymerized unit is 7 to 12, a weight average molecular weight (Mw) is 80,000 or more and 150,000 or less, and a ratio (Mw / Mn) of the number average molecular weight (Mn) to Mw is 3.0 or more and 6.5 or less, characterized in that Intermediate transfer body is provided. Also, according to another aspect of the present disclosure, an electrophotographic image forming apparatus including the above-described member for photography is provided.

Effects of the Invention

[0007] According to one aspect of the present disclosure, a lower toner adhesion property on the toner-carrying surface enables obtaining a more uniform electrophotographic member. Also, according to another aspect of the present disclosure, an electrophotographic image forming apparatus capable of stably forming a high-quality electrophotographic image can be obtained.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, with reference to the drawings, preferred embodiments of the present disclosure will be described in detail. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments should be appropriately changed according to the configuration of the device to which the present disclosure is applied and various conditions, and are not intended to limit the scope of the present disclosure only thereto. The inventors of the present invention have speculated as follows about the reason why an electrophotographic belt having a surface layer formed by dispersing PFPE-OH in an acrylic resin or a methacrylic resin has uneven toner releasability on its outer surface. That is, a surface layer formed by dispersing PFPE in an acrylic resin or a methacrylic resin, which is a binder resin, is usually formed by curing a coating film of a surface layer-forming paint containing a monomer that is a raw material of the binder resin, PFPE, and their solvents. However, PFPE-OH is almost insoluble in the solvents of the raw material monomers of acrylic resins and methacrylic resins. Therefore, immediately after the preparation of the surface layer-forming paint, even if PFPE-OH can be highly dispersed in the surface layer-forming paint, PFPE-OH aggregates as time passes from the preparation. Therefore, it is considered that the surface layer formed using the surface layer-forming paint in which the dispersion state of PFPE-OH is disrupted has a non-uniform dispersion state of PFPE-OH, and as a result, unevenness occurs in the toner releasability of the outer surface. Based on such considerations, the inventors of the present invention have repeatedly studied to obtain a dispersant capable of stably dispersing PFPE-OH in the surface layer-forming paint. As a result, it has a first polymerization unit derived from at least one of methyl acrylate (MA) and methyl methacrylate (MMA), and a second polymerization unit derived from at least one of methyl acrylate having a fluoroalkyl group (F-MA) and methyl methacrylate having a fluoroalkyl group (F-MMA). It has been found that a fluorine-containing copolymer in which the molar ratio of the first polymerization unit to the second polymerization unit (first polymerization unit / second polymerization unit) is 7 to 12, the weight average molecular weight (Mw) is 80,000 or more and 150,000 or less, and the ratio of the number average molecular weight (Mn) to Mw (Mw / Mn) is 3.0 or more and 6.5 or less can be stably dispersed in a coating material for forming a surface layer containing PFPE-OH as a raw material monomer of an acrylic resin and a methacrylic resin.

[0010] (Schematic and operation of the image forming apparatus) FIG. 1 is a schematic cross-sectional view of an electrophotographic image forming apparatus including an endless belt-shaped electrophotographic member (hereinafter also referred to as an "electrophotographic belt") as an intermediate transfer belt according to one aspect of the present embodiment. As shown in FIG. 1, this image forming apparatus is provided with four process units, which are image forming means including a charging means, an exposure means, a developing means, a cleaner, etc., around a photosensitive drum as an image carrier. The images on the photosensitive drum formed in each process unit are sequentially multiplexed and transferred to the outer surface of the electrophotographic belt that moves adjacent to the photosensitive drum at a plurality of primary transfer portions, and a full-color toner image is formed. Thereafter, the toner image formed on the outer surface of the electrophotographic belt at the secondary transfer portion is collectively transferred onto a recording material. The toner image on the recording material is then melted and fixed onto the recording material by heat and pressure at a fixing portion.

[0011] Hereinafter, details of the electrophotographic image forming apparatus will be described. This image forming apparatus has four image forming units Y, M, C, and K for forming images of each color of Y, M, C, and K arranged in parallel in order from left to right in the drawing. Each image forming unit Y, M, C, and K includes a drum-type electrophotographic photoreceptor (hereinafter referred to as a "drum") 1 as an image carrier, a charging roller 2 as a charging means, an exposure device 3 as an exposure means, a developing device 4 as a developing means, a primary transfer roller 5 as a primary transfer means, and a drum cleaner 6.

[0012] The electrophotographic belt 7 having an endless shape that constitutes an intermediate transfer body is stretched between three parallel rollers: a secondary transfer opposing roller 8 that also serves as a driving roller, a deviation correction roller 9 that also serves as a tension roller, and a driven roller 10. The deviation correction roller 9 is disposed on the side of the first image forming unit Y, the secondary transfer opposing roller 8 is disposed on the side of the fourth image forming unit K, and the driven roller 10 is disposed below the secondary transfer roller 8. The surface of the electrophotographic belt on the side opposite to the outer surface between the deviation correction roller 9 and the driven roller 10 is in contact with the upper surface of the drum 1 of each of the image forming units Y, M, C, and K. Also, by aligning and adjusting the deviation correction roller 9, it is possible to suppress the deviation of the electrophotographic belt.

[0013] The primary transfer rollers 5 of each of the image forming units Y, M, C, and K are disposed inside the electrophotographic belt between the deviation correction roller 9 and the driven roller 10, and are each pressed against the upper surface of the drum 1 with the electrophotographic belt 7 interposed therebetween. The contact portions between the drum 1 of each of the image forming units Y, M, C, and K and the electrophotographic belt 7 are each a primary transfer nip portion T1. The contact portion between the electrophotographic belt 7 and the secondary transfer roller 12 is a secondary transfer nip portion T2. A registration roller pair 13 is disposed upstream of the secondary transfer nip portion T2 in the recording material conveyance direction. Also, downstream of the secondary transfer nip portion T2 in the recording material conveyance direction, a recording material conveyance belt device (not shown) and a fixing device are sequentially disposed.

[0014] The operation for forming a full-color image is as follows. The first to fourth image forming units Y, M, C, and K are driven at a predetermined control timing of the image forming sequence. By this driving, each drum 1 is rotationally driven in the clockwise direction of the arrow at a predetermined same speed. Then, the electrophotographic belt 7 is also rotated by the secondary transfer opposing roller 8 in the counterclockwise direction of the arrow at the same speed as the rotational speed of the drum 1.

[0015] The surface of the rotating drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2. The charged surface of the drum 1 is image-exposed by the exposure device 3. In the present embodiment, the exposure device 3 is a laser scanner, which outputs laser light modulated corresponding to the image information signal to scan-expose the charged surface of the drum 1. Thereby, an electrostatic image (electrostatic latent image) corresponding to the scan-exposure pattern is formed on the drum surface. The formed electrostatic image is developed into a toner image by the developing device 4.

[0016] By the electrophotographic process as described above, in the first image forming unit Y, a yellow toner image corresponding to the yellow component image among the color separation component images of the full-color original image is formed on the surface of the drum 1. In the second image forming unit M, a magenta toner image corresponding to the magenta component image, and in the third image forming unit C, a cyan toner image corresponding to the cyan component image are formed at predetermined control timings, respectively. Also, in the fourth image forming unit K, a black toner image corresponding to the black component image is formed at a predetermined control timing.

[0017] Then, in the primary transfer nip portion T1 of the first image forming unit Y, the yellow toner image formed on the drum 1 is primarily transferred onto the outer surface of the electrophotographic belt 7 that is rotationally driven. Next, in the primary transfer nip portion T1 of the second image forming unit M, the magenta toner image formed on the drum 1 is superposed on the yellow toner image on the outer surface of the electrophotographic belt 7 and primarily transferred. Further, in the same manner, in the primary transfer nip portions T1 of the third image forming unit C and the fourth image forming unit K, the cyan toner image and the black toner image are sequentially primarily transferred onto the outer surface of the electrophotographic belt 7.

[0018] That is, on the outer surface of the electrophotographic belt 7, toner images of Y, M, C, and K are sequentially superposed on each other in a predetermined manner and superimposed (multi-transferred) to form a full-color unfixed toner image. In each primary transfer nip portion T1, the primary transfer of the toner image from the drum 1 to the electrophotographic belt 7 is as follows. That is, a predetermined primary transfer bias is applied from a primary transfer power supply unit (not shown) to the primary transfer roller 5, and the toner image is electrostatically transferred from the drum 1 to the electrophotographic belt 7.

[0019] The primary transfer bias has a polarity opposite to the charging polarity of the toner and is a DC voltage of a predetermined potential. Also, in each image forming unit Y·M·C·K, the surface of the drum 1 after passing through the primary transfer nip portion is cleaned by the drum cleaner 6 to remove the remaining primary transfer toner and is repeatedly used for image formation.

[0020] The unfixed toner image of the full-color image synthetically formed on the electrophotographic belt 7 as described above is conveyed by the subsequent rotation of the electrophotographic belt 7 and reaches the secondary transfer nip portion T2, which is the contact portion between the secondary transfer roller 12 and the electrophotographic belt 7. At the timing when the image leading edge of the full-color unfixed toner image formed on the outer surface of the electrophotographic belt 7 reaches the secondary transfer nip portion T2, the start of rotation of the registration roller pair 13 is controlled so that the print start position of the recording material P coincides with the secondary transfer nip portion T2. In the process of the recording material P being nipped and conveyed through the secondary transfer nip portion T2, a secondary transfer bias of a predetermined potential with a polarity opposite to the charging polarity of the toner is applied from the secondary transfer power supply unit to the secondary transfer roller 12. The secondary transfer bias has a polarity opposite to the charging polarity of the toner and is a DC voltage of a predetermined potential.

[0021] As a result, the full-color unfixed toner image on the outer surface of the electrophotographic belt 7 is collectively secondarily transferred to the recording material P. The recording material P that has exited the secondary transfer nip portion T2 is separated from the electrophotographic belt 7 and introduced into the fixing device by the recording material conveyance belt device. Therefore, the toner of each color toner image is melted and mixed to be fixed (fixed image formation) on the surface of the recording material as a full-color printed image, and the full-color print is discharged outside the machine.

[0022] After the recording material is separated, the outer surface of the electrophotographic belt 7 is cleaned of secondary transfer residual toner by the cleaner 11 during the subsequent rotation process of the electrophotographic belt 7, in preparation for the next electrophotographic image forming process. The cleaner 11 collects the secondary transfer residual toner adhering to the outer surface of the electrophotographic belt, which is scraped off by the cleaning blade, into a recovery toner box (not shown) inside the cleaner 11.

[0023] The patch sensor 20 (toner image detection means) having a function of detecting the image density is provided at a position facing the electrophotographic belt portion stretched by the stretching roller 10. It is a sensor that optically detects the reflected light and scattered light of the light irradiated on the adjustment toner image (patch image) formed on the electrophotographic belt 7. An adjustment toner image (patch image) is formed on the outer surface of the electrophotographic belt 7 during a period other than the period when the toner image to be secondarily transferred to the recording material is primarily transferred. The image forming conditions are adjusted according to the result.

[0024] Hereinafter, the electrophotographic belt 7 will be described in detail. The electrophotographic belt of the present disclosure has a base layer and a surface layer on the base layer. (Electrophotographic Belt) The electrophotographic belt 7 according to one aspect of the present disclosure has, for example, a base layer 31 and a surface layer 32 provided on the outer periphery of the base layer 31 as shown in FIG. 2. The surface 32-2 on the side opposite to the side facing the base layer 31 of the surface layer 32 constitutes the toner image carrying surface (outer surface) of the electrophotographic belt 7.

[0025] <Base Layer> As the material constituting the base layer 31, a resin having mechanical strength and flex resistance as an electrophotographic belt for an image forming apparatus is preferable. Examples of such resins include polyamide, polyacetal, polyarylate, polycarbonate, polyphenylene ether, polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polysulfone, polyethersulfone, and the like. Other examples include polyphenyl sulfide, polybutylene terephthalate, polyether ether ketone, polyvinylidene fluoride, polyvinyl fluoride, polyether amide copolymer, polyurethane copolymer, polyimide, polyamideimide, and the like. The base layer 31 is preferably formed from one of these resins or a mixture thereof.

[0026] To the base layer 31, a conductive substance can usually be added to impart conductivity. Examples of the conductive substance include carbon-based inorganic conductive particles such as carbon black, carbon fiber, and carbon nanotubes, and inorganic conductive particles such as metal oxides such as zinc antimonate, zinc oxide, tin oxide, and titanium oxide. The base layer 31 preferably has a volume resistivity adjusted to be in the range of 1E+8 [Ω·cm] or more and 1E+12 [Ω·cm] or less. Also, the base layer 31 preferably has a surface resistivity adjusted to be in the range of 1E+8 [Ω / □] or more and 1E+14 [Ω / □] or less.

[0027] By setting the volume resistivity of the base layer 31 to 1E+12 [Ω·cm] or less, a decrease in primary transferability and secondary transferability due to application of a predetermined transfer bias can be suppressed. Also, by setting the volume resistivity of the base layer 31 to 1E+8 [Ω·cm] or more, the occurrence of resistance unevenness can be suppressed, and the occurrence of transfer unevenness and the like, and the occurrence of image defects can be prevented. Also, by setting the surface resistivity of the base layer 31 within the above range, image defects due to peeling discharge when the transfer material separates from the electrophotographic belt and toner scattering can be reduced. And the thickness of the base layer 31 is preferably 40 μm or more and 200 μm or less in terms of mechanical strength and flex resistance.

[0028] Also, it is preferable that the electrophotographic belt after forming the surface layer 32 on the base layer 31 shows a similar value for the electrical resistance. For this reason, it is preferable that the surface layer 32 of the electrophotographic belt is also semiconductive. That is, it is preferable that the volume resistivity of the electrophotographic belt is adjusted in the range of 1E+8 [Ω·cm] or more and 1E+12 [Ω·cm] or less. Also, it is preferable that the surface resistivity of the electrophotographic belt is adjusted in the range of 1E+8 [Ω / □] or more and 1E+14 [Ω / □] or less. In order to adjust the volume resistivity and surface resistivity of the electrophotographic belt, it is preferable to include a conductive agent in the surface layer 32. As the conductive agent contained in the surface layer 32, the same conductive agent that can be used for the base layer 31 can be used.

[0029] <Surface layer> The surface layer 32 contains at least one of an acrylic resin and a methacrylic resin as a binder resin, and also contains PFPE-OH and a fluorine-containing copolymer.

[0030] <Binder resin> In the present disclosure, it is characterized in that an acrylic resin is used as the matrix resin. The acrylic resin is used to disperse PFPE, ensure adhesion to the base layer 31, and ensure the characteristics of mechanical strength, and a methacrylic resin or an acrylic resin is preferably used. Hereinafter, the methacrylic resin and the acrylic resin are collectively referred to as an acrylic resin.

[0031] Examples of the polymerizable monomer for forming the acrylic resin include the following (i) or (ii). As the polymerizable monomer, those commercially available as paints can also be used. (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. (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.

[0032] Among these, considering rubbing against other members such as photoreceptors and cleaning blades, it is preferably of high hardness. For this reason, it is also preferable to use a large amount of a bifunctional or higher crosslinkable monomer for the acrylic resin to make it harder.

[0033] Also, to form an acrylic resin from such a polymerizable monomer, there is a method of adding a photoinitiator and polymerizing it with an electron beam or ultraviolet rays. Examples of the photoinitiator include radical-generating photoinitiators such as benzophenone, thioxanthone-based, benzyldimethylketal, α-hydroxyketone, α-hydroxyalkylphenone, α-aminoketone, and α-aminoalkylphenone. Others include radical-generating photoinitiators such as monoacylphosphine oxide, bisacylphosphine oxide, hydroxybenzophenone, aminobenzophenone, titanocene-based, oxime ester, and oxyphenylacetic acid ester.

[0034] The content of the above acrylic resin is preferably 20% by mass or more and 70% by mass or less based on the mass of the total solid content of the surface layer 32 from the viewpoint of film strength on the low content side and from the viewpoints of PFPE and the dispersant component relatively on the high content side.

[0035] <pfpe-oh>

[0036] As described above, PFPE-OH is non-reactive with acrylic resins and methacrylic resins that constitute the matrix, and can form fine domains in the matrix containing these resins. Further, since it is not chemically bonded to the resin constituting the matrix, it has excellent migratability to the outermost surface of the surface layer and can impart good toner releasability to the outermost surface.

[0037] PFPE-OH has, for example, specifically, a structure represented by the following structural formula (1). HO-H2C-(CF2O) p (CF2CF2O) q -CH2-OH (1) In structural formula (1), p and q each independently represent an integer of 1 or more. Examples of PFPE-OH having the structure represented by structural formula (1) include "Fomblin® D2" (manufactured by Solvay Specialty Polymers) and "Fluorolink® D4000" (manufactured by Solvay Specialty Polymers). The weight average molecular weight Mw of the PFPE-OH is preferably 1000 or more and 9000 or less from the viewpoint of the migratability of the PFPE-OH to the surface of the electrophotographic belt. The weight average molecular weight referred to here is a value measured by a liquid chromatography analyzer (manufactured by Shimadzu Corporation) for a 1,1,2,2,3,3,4-heptafluorocyclopentane solution of PFPE-OH. Note that 1,1,2,2,3,3,4-heptafluorocyclopentane is commercially available, for example, as "Zeorora H" (trade name, manufactured by Nippon Zeon Co., Ltd.). Further, the content of PFPE-OH in the surface layer is preferably 10% by mass or more and 40% by mass or less with respect to the mass of the total solid content of the surface layer. By setting it within this range, it is possible to better balance the imparting of stable toner releasability to the outermost surface of the surface layer and the high strength of the surface layer.

[0038] That the PFPE-OH contained in the surface layer has a hydroxyl group can be confirmed, for example, by the following method. First, an electrophotographic belt including a surface layer is immersed in a fluorine solvent to extract the PFPE-OH. Examples of commercially available fluorine solvents include "Asahiklin AE-3000" (trade name, manufactured by AGC Inc.), "Zeorola H" (trade name, manufactured by Nippon Zeon Co., Ltd.), and "Novec 7300" (trade name, manufactured by 3M). Next, the fluorine solvent is evaporated from the extract to isolate the extracted PFPE-OH. The presence of a hydroxyl group in the obtained FT-IR spectrum chart of PFPE-OH can be confirmed by observing the presence or absence of a peak at 3400 cm -1 to confirm the presence of a hydroxyl group in the PFPE-OH molecule. Also, NMR 19 F measurement is performed, and the molecular structure of PFPE-OH can be confirmed by observing fluorine signals derived from -OCF2O- (-40 ppm to -60 ppm), -OCF2CH2- (around -80 ppm), and -OCF2CF2O- (around -90 ppm).

[0039] PFPE-OH is insoluble in non-aqueous compositions. This can be confirmed by the following method. First, an electrophotographic belt including a surface layer is immersed in a fluorine solvent to extract the PFPE-OH. Next, after the fluorine solvent is volatilized from the extract to isolate PFPE, it is mixed with a verification solvent at a certain ratio and phase separation is visually confirmed.

[0040] <Fluorine-containing copolymer> The fluorine-containing copolymer functions as a dispersant for stably existing PFPE-OH as domains in the matrix in the surface layer. The fluorine-containing copolymer has a first polymerization unit derived from at least one of methyl acrylate (MA) and methyl methacrylate (MMA), and a second polymerization unit derived from at least one of methyl acrylate having a fluoroalkyl group (F-MA) and methyl methacrylate having a fluoroalkyl group (F-MMA). And the molar ratio of the first polymerization unit to the second polymerization unit (first polymerization unit / second polymerization unit) is 7 to 12. Also, the weight average molecular weight (Mw) is 80,000 or more and 150,000 or less, and further, the ratio of the number average molecular weight (Mn) to Mw (Mw / Mn) is 3.0 or more and 6.5 or less. Such a fluorine-containing copolymer has a site highly affinity for both the perfluoroalkyl chain of PFPE-OH and acrylic resin or methacrylic resin. As the first polymerization unit, it is preferably a methyl methacrylate unit represented by the following structural formula (2).

[0041]

Chemical formula

[0042] As the second polymerization unit, it is preferably a perfluoroalkyl ethyl methacrylate unit represented by the following structural formula (3).

[0043]

Chemical formula

[0044] In such a fluorine-containing copolymer, the fluoroalkyl group of the second polymerization unit adsorbs to PFPE-OH, and the first polymerization unit has a high affinity for acrylic resins and methacrylic resins used as binder resins, and a steric hindrance effect that suppresses the aggregation of PFPE-OH works. The copolymerization ratio of the first polymerization unit and the second polymerization unit defined in the present disclosure exhibits good dispersion performance because the balance between the adsorption performance of the fluoroalkyl group and the acrylic affinity is in a desirable range with respect to PFPE insoluble in the non-aqueous composition. Also, the range of the weight average molecular weight Mw, and the ratio Mw / Mn of the number average molecular weight Mn to the weight average molecular weight Mw is suitable for the dispersant to sufficiently coat PFPE-OH and exhibit dispersion performance. Since PFPE-OH used in the present disclosure is insoluble in the non-aqueous composition and is liquid rather than solid particles, it is estimated that by widening the molecular weight distribution of the dispersant, PFPE-OH can be coated evenly without omission for PFPE-OH in a state where the dispersion particle size is unstable and amorphous. As a result, even when PFPE-OH insoluble in the non-aqueous composition is used, the sedimentation of PFPE-OH is suppressed, and the distribution of PFPE-OH after the formation of the surface layer becomes fine and uniform, so that the low adhesion on the surface of the electrophotographic belt can be maintained uniformly over a long period of time.

[0045] The copolymerization ratio of the first polymerization unit and the second polymerization unit can be measured with a nuclear magnetic resonance (NMR) apparatus. Specifically, the above-mentioned dispersant is used, and after removing the solvent under reduced pressure at 90 °C for about 3 hours using a centrifuge, the solid matter is recovered, dissolved in deuterated chloroform, and NMR is measured. 1 From the integral value of the signal intensity in the H-NMR chart, the polymerization ratio of the first polymerization unit and the second polymerization unit can be calculated. Shown in Figure 4 1 Using an example of an H-NMR signal intensity chart, a specific method for calculating the polymerization ratio of the first polymerization unit and the second polymerization unit will be described. Calculate the integration value of peak A at 3.6 ppm due to CH-3 (the methyl group enclosed by the dotted line in the above structural formula (2)) contained in the first polymerization unit and the integration value of peak B at 4.3 ppm due to CH2 (the methylene group enclosed by the dotted line in the above structural formula (3)) contained in the second polymerization unit, respectively. In the example shown in Figure 4, the integration value of peak A was 28.2 and the integration value of peak B was 2.0. These numerical values indicate the abundance ratio (molar ratio) of the measured nucleus (H). Since peak A is due to CH3, it reflects 3 Hs, and since peak B is due to CH2, it reflects 2 Hs. When these are converted by the number ratio of Hs, it becomes the molar ratio of the first polymerization unit and the second polymerization unit, and the first polymerization unit = 28.2 / 3 ≈ 9, the second polymerization unit = 2.0 / 2 = 1 is calculated. Therefore, the polymerization ratio (first polymerization unit / second polymerization unit) in this case is 9.

[0046] The number average molecular weight and the weight average molecular weight can be measured by a gel permeation chromatography (GPC) apparatus. Specifically, dissolve the above dispersant in tetrahydrofuran. Inject the dissolved solution into a column (trade name; TSK-GEL MULTIPORE HXL-M; manufactured by Tosoh Corporation), and pass the column at a certain flow rate. Measure the elution time distribution with a gel permeation chromatograph apparatus (HLC-8220 manufactured by Tosoh Corporation) that elutes the components adsorbed on the column, and calculate the molecular weight distribution from a calibration curve prepared in advance using a polystyrene standard sample with a known molecular weight (for example, trade name: TSKgel standard polystyrene, product numbers "0005202" to "0005221"). Based on the results, calculate the number average molecular weight and the weight average molecular weight.

[0047] Copolymers of methyl methacrylate (F-MMA) having a fluoroalkyl group and methyl methacrylate (MMA) are commercially available. For example, Aron (registered trademark) GF-150, GF-300, GF-400, GF-420 manufactured by Toagosei Co., Ltd., FD-420 of Kyoeisha Chemical Co., Ltd., etc. can be mentioned.

[0048] Using these commercially available materials, the dispersant of the present disclosure having a polymerization ratio of the first polymerization unit / the second polymerization unit, a number average molecular weight, and a weight average molecular weight within a predetermined numerical range can be prepared by the following method. That is, the above-mentioned commercially available copolymer can be prepared using a preparative HPLC apparatus (trade name: LC-908; manufactured by Nippon Analytical Industry Co., Ltd.). As the column, for example, "JAIGEL-1H", "JAIGEL-2H", "JAIGEL-3H", "JAIGEL-4H", and "JAIGEL-5H" (all trade names; manufactured by Nippon Analytical Industry Co., Ltd., diameter 20 × 600 mm: preparative column) can be used. Specifically, the above-mentioned commercially available material is injected into the column, the solution is collected every elution time, and dispersants with different molecular weight distributions are obtained. Each solution is measured for its molecular weight distribution by the above GPC apparatus and its copolymerization ratio by an NMR apparatus. A dispersant having a desired copolymerization ratio, number average molecular weight Mn, and weight average molecular weight Mw is selected from the separated solutions. A plurality of separated solutions may be mixed and adjusted. In this way, it is possible to obtain the dispersant according to the present disclosure.

[0049] That the dispersant of the present disclosure is used in the electrophotographic belt can be confirmed by the following method. First, after immersing in the above-mentioned fluorine solvent (for example, Asahiklin AE-3000, trade name, manufactured by AGC Inc.) to remove PFPE, the PFPE used in the present disclosure does not dissolve, and it is immersed again in a solvent excellent in the solubility of the dispersant to extract the dispersant. Examples of such solvents include butyl acetate, ethyl acetate, MEK, MIBK, and the like. The copolymerization ratio of the extract is measured by NMR, and Mn and Mw are measured by GPC. The content of the above dispersant is preferably 5% by mass or more and 30% by mass or less, more preferably 15% by mass or more and 25% by mass or less, based on the mass of the total solid content of the surface layer.

[0050] <Conductive agent> In order to impart conductivity to the surface layer 32, a conductive agent can be added. Examples of the conductive agent include carbon-based inorganic conductive particles such as carbon black, carbon fiber, and carbon nanotube, and metal oxides such as zinc antimonate, zinc oxide, tin oxide, and titanium oxide.

[0051] <Matrix-domain structure> As schematically shown in FIG. 3, in the cross section in the thickness direction of the surface layer 32, a matrix-domain structure in which domains 32-5 containing PFPE-OH are dispersed in a matrix 32-3 containing a binder resin is observed.

[0052] PFPE-OH has a very small surface free energy. Therefore, by incorporating PFPE-OH into the surface layer of the electrophotographic belt, due to its small surface free energy, it migrates to the interface between the surface layer and air, that is, the outermost surface side of the surface layer, and excellent toner releasability can be imparted to the surface of the surface layer 32.

[0053] Also, in the surface layer 32, the domains 32-5 of PFPE-OH exist in a more uniform size in the matrix 32-3 containing an acrylic resin or a methacrylic resin due to the action of the fluorine-containing copolymer having the above-described specific structure. Therefore, in the surface layer 32, it is difficult for unevenness to occur in the distribution of the domains containing PFPE-OH. As a result, it is possible to prevent the occurrence of portions where the amount of migration of PFPE-OH to the outermost surface of the surface layer is large and small, and unevenness in the amount of PFPE present on the outermost surface.

[0054] Preferably, the domain consists substantially of only PFPE-OH, but within the scope where the effects of the present invention are exhibited, in addition to PFPE-OH in the domain, a compound other than PFPE-OH may be contained. Also, an additive compatible with PFPE-OH may be added for the purpose of imparting other properties. Furthermore, even when the inside of the domain is not completely filled with PFPE-OH and voids exist, the effects of the present disclosure can be exhibited.

[0055] The matrix-domain structure can be confirmed by cutting out the electrophotographic belt and observing the cross-section in the thickness direction of the surface layer 32 of the electrophotographic belt with a scanning electron microscope (SEM). Here, as the major axis of the domain observed in the cross-section, it is preferable that the standard deviation is 1 nm or more and 50 nm or less, particularly 15 nm or more and 37 nm or less.

[0056] Regarding the domain containing PFPE-OH, it can be identified by detecting it with elemental analysis methods such as energy-dispersive X-ray analysis (EDX), TOF-SIMS, and Auger spectroscopy. For example, when the domain of the electrophotographic belt of the present disclosure was subjected to elemental analysis by EDX, a fluorine element was detected, and it was identified that the domain was a domain containing PFPE-OH. In addition, by TOF-SIMS, fragments of a fluorocarbon ether structure derived from PFPE-OH can also be observed from the domain.

[0057] <Method for manufacturing electrophotographic belt> The specific manufacturing method of the electrophotographic belt of the present disclosure will be described below. Note that the present disclosure is not limited to the following manufacturing method.

[0058] The base layer 31 of the electrophotographic belt can be produced by the following method. For example, when a thermosetting resin such as polyimide is used, carbon black, which is a conductive agent, is dispersed as a varnish together with a precursor of the thermosetting resin or a soluble thermosetting resin and a solvent, and this varnish is coated on the mold of a centrifugal molding device. Next, a semiconductive film is formed through a baking process of the coated film.

[0059] Also, when using a thermoplastic resin, carbon black as a conductive agent, the thermoplastic resin, and, if necessary, further additives are mixed, and melt-kneaded with a twin-screw kneading device or the like to produce a semiconductive resin composition. Next, a semiconductive film can be obtained by an extrusion method in which this resin composition is extruded into the shape of a sheet, film, or seamless belt by melt extrusion. The seamless belt may be formed by extruding it as an extrusion belt from a cylindrical die, or by joining sheets formed by extrusion to make it seamless. In addition to this molding method, molding can also be performed using hot pressing or injection molding. The film thickness of the semiconductive film that becomes the base layer 31 is preferably 30 μm or more and 150 μm or less.

[0060] Also, the semiconductive film that becomes the base layer 31 is preferably subjected to a crystallization treatment for the purpose of strengthening the mechanical strength and durability of the electrophotographic belt. Examples of the crystallization treatment include annealing at a temperature equal to or higher than the glass transition temperature of the resin used, thereby promoting the crystallization of the resin used. The electrophotographic belt thus obtained is not only excellent in mechanical strength and durability, but also excellent in terms of abrasion resistance, chemical resistance, slidability, toughness, and flame retardancy.

[0061] Next, as a method for forming the surface layer 32 of the electrophotographic belt, the following method can be mentioned. First, a polymerizable monomer, a polymerization initiator, PFPE-OH, a dispersant, a conductive agent, and other additives for forming the binder resin, which is the constituent member described above for the surface layer 32, are dissolved and dispersed in a suitable organic solvent to obtain a coating liquid for the surface layer. Next, it is applied onto the outer periphery of the base layer 31 by a method such as ring coating, dip coating, or spray coating, and drying is carried out at 60 to 90 °C for the purpose of removing the organic solvent. Thereafter, it is cured by ultraviolet irradiation using an ultraviolet irradiation machine to obtain the electrophotographic belt of the present disclosure.

[0062] Also, the thickness of the surface layer 32 is preferably 2 μm or more and 10 μm or less. By setting the thickness of the surface layer 32 to 2 μm or more, it is possible to ensure durability by achieving both maintenance of low adhesion and suppression of peeling. By setting the thickness of the surface layer 32 to 10 μm or less, the required flexural resistance performance can be obtained.

Example

[0063] <Preparation of Dispersants 1 to 11> Dispersants 1 to 11 having the physical properties shown in Table 1 below were prepared by fractionating a solvent-based fluorine powder dispersant (trade name: FD-420, manufactured by Kyoeisha Chemical Co., Ltd.) using the above-described preparative HPLC apparatus.

Table 1

[0064] <Example 1> A coating material 1 for forming a surface layer was prepared by mixing the materials shown in Table 2 below using a stir-type homogenizer (manufactured by AS ONE Corporation).

[0065]

Table 2

[0066] An electrophotographic belt made of polyimide equipped in a full-color copier (trade name: iRC2620, manufactured by Canon Inc.) was used as the base layer 31, and a coating film of the coating material for forming the surface layer was formed on the outer peripheral surface of the base layer 31, and the coating film was dried at a temperature of 70 °C for 3 minutes. Then, the coating film was irradiated with ultraviolet light so that the integrated light amount became 500 mJ / cm 2 to cure the coating film. Thus, an electrophotographic belt 1 having a surface layer with a film thickness of 4 μm was obtained.

[0067] The types and molecular weights (Mw) of the PFPE-OH used, and the MMA / F-MMA copolymerization ratio, molecular weights (Mn, Mw), and addition amounts of the dispersants are shown in Table 3. In Table 3, the addition amount of the dispersant was described as the content in the total solid content. The total solid content was calculated by excluding the methyl ethyl ketone as the solvent and the solvent content of the dispersant from the components of the composition. The coating material 1 for forming the surface layer and the electrophotographic belt 1 were subjected to the following evaluations 1 to 5.

[0068] <Evaluation 1: Evaluation of the liquid stability of the coating material for forming the surface layer> The coating material for forming the surface layer was placed in a glass bottle with a diameter of 10 mm and a height of 30 mm and allowed to stand still, and it was evaluated according to the following criteria based on the number of days until a separation layer was visually observed. A: 5 days or more B: 1 day to 4 days C: Less than 1 day

[0069] <Evaluation 2: Evaluation of the dispersion uniformity of the domain> The uniformity of the dispersion state of PFPE-OH in the surface layer was evaluated by the standard deviation of the major axis of the PFPE-OH domain. The major axis of the PFPE-OH domain was observed by using a scanning electron microscope (trade name: S-4800, manufactured by Hitachi High-Technologies Corporation) for the cross-section in the thickness direction of the surface layer of the electrophotographic belt. First, a sample in which a cross-section in the thickness direction appeared from the surface layer of the electrophotographic belt was cut out using a microtome (trade name: EM UC7, manufactured by Leica Microsystems). Then, an SEM image of a portion where at least 1 or more domains could be confirmed in a unit area of 15 μm 2 when the cross-section was magnified 20,000 times was used. When the number of domains was 10 or less, the major axis lengths of all the domains in the visual field were measured. When the number of domains exceeded 10, 10 domains were randomly selected, and the major axis lengths of the domains were measured. This operation was repeated 10 times for different positions of the cross-section, and the standard deviation of the major axis lengths of a total of 100 domains measured in 10 cross-section SEM images was calculated.

[0070] <Evaluation 3: Image evaluation - image quality rank> The electrophotographic belt was replaced with and mounted on the electrophotographic belt installed in a full-color electrophotographic image forming apparatus (product name: iRC2620; manufactured by Canon Inc.), and an electrophotographic image was formed. The formed image is a solid blue image with magenta and cyan overlaid. Then, for each of the first image 1, the 300,000th image 2, and the 600,000th image 3 immediately after the start of image formation, the presence or absence of image defects due to poor image transfer from the intermediate transfer belt was evaluated. The evaluation was performed by five evaluators visually observing and based on the following criteria. The rank with the largest number of evaluators was taken as the evaluation result. Rank A: There is no visible deterioration in image quality due to poor transfer. Rank B: There is almost no deterioration in image quality due to poor transfer. Rank C: Deterioration in image quality due to poor transfer is visible.

[0071] <Evaluation 4: Toner Adhesion Evaluation - Contact Angle> The toner adhesion of the outer surface of the electrophotographic belt was evaluated by the contact angle of normal hexadecane (n-HD). The n-HD contact angle was measured at a total of 12 points in the circumferential direction at 4 points and in the longitudinal direction at 3 points for the electrophotographic belts of the examples and comparative examples, and the average value and standard deviation were calculated. The measurement was performed using a contact angle meter (product name: PCA-11, manufactured by Kyowa Interface Science Co., Ltd.). The measurement of the contact angle was carried out immediately before the start of image formation (initial) in Evaluation 3 above, immediately after 300,000 image formations (after 300k), and immediately after 600,000 image formations (after 600k).

[0072] <Evaluation 5: Image Evaluation - Density Unevenness> The presence or absence of density differences between image 1 and image 2 and between image 1 and image 3 used for the evaluation of the image quality rank in Evaluation 3 above, and when a density difference was recognized, the degree thereof was visually observed by five evaluators and evaluated according to the following criteria. The rank with the largest number of evaluators was taken as the evaluation result. Rank A: No density difference is seen with respect to the first image. Rank B: A slight density difference is confirmed with respect to the first image. Rank C: An obvious density difference is confirmed with respect to the first image.

[0073] <Examples 2 to 3> Surface layer forming paints 2 to 3 were prepared in the same manner as in Example 1, except that dispersant 1 was changed to dispersant 2 or dispersant 3. Then, electrophotographic belts 2 to 3 were produced in the same manner as in Example 1, except that surface layer forming paint 2 or surface layer forming paint 3 was used. Surface layer forming paints 2 to 3 and electrophotographic belts 2 to 3 were evaluated in the same manner as in Example 1. <Example 4> Surface layer forming paint 4 was prepared in the same manner as in Example 1, except that PFPE-OH1 was changed to PFPE-OH2 (trade name: Fluorolink D4000, manufactured by Solvay Specialty Polymers). Then, electrophotographic belt 4 was produced in the same manner as in Example 1, except that surface layer forming paint 4 was used. Surface layer forming paint 4 and electrophotographic belt 4 were evaluated in the same manner as in Example 1. <Examples 5 to 6> Surface layer forming paints 5 to 6 were prepared in the same manner as in Example 1, except that dispersant 1 was changed to dispersant 4 or dispersant 5. Then, electrophotographic belts 5 to 6 were produced in the same manner as in Example 1, except that surface layer forming paint 5 or surface layer forming paint 6 was used. Surface layer forming paints 5 to 6 and electrophotographic belts 5 to 6 were evaluated in the same manner as in Example 1. <Example 7> Surface layer forming paint 7 was prepared in the same manner as in Example 1, except that the addition amount of dispersant 1 was changed to 25% by mass. Then, electrophotographic belt 7 was produced in the same manner as in Example 1, except that surface layer forming paint 7 was used. Surface layer forming paint 7 and electrophotographic belt 7 were evaluated in the same manner as in Example 1. <Example 8> Surface layer forming paint 8 was prepared in the same manner as in Example 1, except that the addition amount of dispersant 1 was changed to 5.1% by mass. Then, electrophotographic belt 8 was produced in the same manner as in Example 1, except that surface layer forming paint 8 was used. Surface layer forming paint 8 and electrophotographic belt 8 were evaluated in the same manner as in Example 1.

[0074] <Comparative Examples 1 to 6> Except that the dispersant 1 was changed to dispersants 6 to 11, surface layer forming paints 9 to 14 were prepared in the same manner as in Example 1. Then, electrophotographic belts 9 to 14 were produced in the same manner as in Example 1, except that each of these surface layer forming paints was used. The surface layer forming paints 9 to 14 and the electrophotographic belts 9 to 14 were evaluated in the same manner as in Example 1. Table 4 shows the evaluation results of the electrophotographic belts according to the above Examples and Comparative Examples.

[0075]

Table 3

[0076]

Table 4

Explanation of Signs

[0077] 7 Electro-photographic belt 31 Base layer 32 Surface layer

Claims

1. An intermediate transfer body having a base layer and a surface layer, wherein the surface layer contains at least one of an acrylic resin and a methacrylic resin, perfluoropolyether (PFPE), and a fluorine-containing copolymer, the PFPE has a structure represented by the following structural formula (1), HO—H ２ C—(CF ２ O) ｐ (CF ２ CF ２ O) ｑ —CH ２ —OH (1) (In structural formula (1), p and q each independently represent an integer of 1 or more) the fluorine-containing copolymer has a first polymerization unit derived from at least one of methyl acrylate (MA) and methyl methacrylate (MMA), and a second polymerization unit derived from at least one of methyl acrylate having a fluoroalkyl group (F-MA) and methyl methacrylate having a fluoroalkyl group (F-MMA), the molar ratio of the first polymerization unit to the second polymerization unit (first polymerization unit / second polymerization unit) is 7 to 12, the weight average molecular weight (Mw) is 80,000 or more and 150,000 or less, and the ratio of the number average molecular weight (Mn) to Mw (Mw / Mn) is 3.0 or more and 6.5 or less. The intermediate transfer body is characterized by this.

2. The intermediate transfer body according to claim 1, wherein the content of the copolymer in the surface layer is 5% by mass or more and 30% by mass or less based on the total solid content of the surface layer.

3. The intermediate transfer body according to claim 1, wherein the weight average molecular weight of the PFPE is 1,000 or more and 9,000 or less.

4. The intermediate transfer body according to any one of claims 1 to 3, wherein the surface layer has a matrix-domain structure having a domain containing the PFPE in its thickness direction, and the standard deviation of the major axis of the domain is 1 nm or more and 50 nm or less.

5. The intermediate transfer body according to claim 4, wherein the standard deviation of the major axis of the domain observed in the cross section in the thickness direction of the surface layer is 1 nm or more and 50 nm or less.

6. The intermediate transfer body according to any one of claims 1 to 5, wherein the intermediate transfer body is an endless belt for electrophotography.

7. An electrophotographic image forming apparatus including an intermediate transfer body, wherein the intermediate transfer body is composed of an electrophotographic member having a base layer and a surface layer, the surface layer contains at least one of an acrylic resin and a methacrylic resin, perfluoropolyether (PFPE), and a fluorine-containing copolymer, the PFPE has a structure represented by the following structural formula (1), HO-H ２ C-(CF ２ O) ｐ (CF ２ CF ２ O) ｑ -CH ２ -OH (1) (In structural formula (1), p and q each independently represent an integer of 1 or more) the fluorine-containing copolymer has a first polymerized unit derived from at least one of methyl acrylate (MA) and methyl methacrylate (MMA); a second polymerized unit derived from at least one of methyl acrylate having a fluoroalkyl group (F-MA) and methyl methacrylate having a fluoroalkyl group (F-MMA); and a molar ratio of the first polymerized unit to the second polymerized unit (first polymerized unit / second polymerized unit) is 7 to 12; an electrophotographic image forming apparatus, wherein a weight average molecular weight (Mw) is 80,000 or more and 150,000 or less, and a ratio of a number average molecular weight (Mn) to Mw (Mw / Mn) is 3.0 or more and 6.5 or less.

Images