Patent Grant
9507283
Field of the Invention
The present invention relates to an electrophotographic photosensitive member and a method of producing an electrophotographic photosensitive member, and to a process cartridge and an electrophotographic apparatus each including the electrophotographic photosensitive member.
Description of the Related Art
An electrophotographic photosensitive member containing an organic photoconductive substance (sometimes referred to as “charge-generating substance”) has been vigorously developed as an electrophotographic photosensitive member to be mounted on an electrophotographic apparatus. The electrophotographic photosensitive member generally includes a support and a photosensitive layer containing a charge-generating substance on the support. In addition, the photosensitive layer is generally of a laminate type (forward layer type) obtained by laminating a charge-generating layer and a charge-transporting layer in the stated order from the support side.
In an electrophotographic process, a variety of members such as a developer, a charging member, a cleaning blade, paper, and a transferring member (hereinafter sometimes referred to as “contact member”) have contact with the surface of the electrophotographic photosensitive member. Therefore, characteristics required of the electrophotographic photosensitive member include a reduction in image deterioration due to a contact stress with such contact member or the like. In particular, in recent years, the electrophotographic photosensitive member has been desired to be further improved in sustainability of an effect of reducing the image deterioration due to the contact stress and in suppression of a potential variation at the time of repeated use along with improvement of durability of the electrophotographic photosensitive member.
To relax the contact stress sustainably and suppress the potential variation at the time of the repeated use of the electrophotographic photosensitive member, International Patent WO 2010/008095, Japanese Patent No. 4975181, and Japanese Patent No. 5089815 each propose a method of forming a matrix-domain structure in a surface layer using a siloxane resin having a siloxane structure incorporated into its molecular chain. In International Patent WO 2010/008095, it is disclosed that the use of a polyester resin having incorporated therein a specific siloxane structure can achieve both the sustainable relaxation of the contact stress and the suppression of the potential variation at the time of the repeated use of the electrophotographic photosensitive member.
Each of the electrophotographic photosensitive members disclosed in the documents can achieve both the sustainable relaxation of the contact stress and the suppression of the potential variation at the time of the repeated use. However, additional improvements in the sustainable relaxation of the contact stress and the suppression of the potential variation have been desired in order to achieve an increase in speed of an electrophotographic apparatus and an increase in number of printed sheets. Meanwhile, the inventors of the present invention have advanced studies, and as a result, have found that the additional improvements in the sustainable relaxation of the contact stress and the suppression of the potential variation can be achieved by incorporating a specific polycarbonate resin upon formation of the matrix-domain structure.
An object of the present invention is to provide an electrophotographic photosensitive member that achieves both sustainable relaxation of a contact stress and the suppression of a potential variation at the time of its repeated use, and a method of producing the electrophotographic photosensitive member. Another object of the present invention is to provide a process cartridge and an electrophotographic apparatus each including the electrophotographic photosensitive member.
The present invention relates to an electrophotographic photosensitive member including: a support; a charge-generating layer on the support; and a charge-transporting layer on the charge-generating layer, which contains a charge-transporting substance and a resin, in which: the charge-transporting layer is a surface layer of the electrophotographic photosensitive member; the charge-transporting layer includes a matrix-domain structure having: a domain which includes a polycarbonate resin A including: a structural unit represented by one of the following formulae (A-1) and (A-2); a structural unit represented by the following formula (B); and a structural unit represented by the following formula (C); and a matrix which includes a charge-transporting substance and a resin D including a structural unit represented by the following formula (D); a content of the structural unit represented by one of the formulae (A-1) and (A-2) in the polycarbonate resin A is from 5% by mass to 25% by mass based on a total mass of the polycarbonate resin A; a content of the structural unit represented by the formula (B) in the polycarbonate resin A is from 35% by mass to 65% by mass based on the total mass of the polycarbonate resin A; and a content of the structural unit represented by the formula (C) in the polycarbonate resin A is from 10% by mass to 60% by mass based on the total mass of the polycarbonate resin A,
in the formula (A-1): Z11 and Z12 each independently represent an alkylene group having 1 to 4 carbon atoms; R11 to R14 each independently represent an alkyl group having 1 to 4 carbon atoms, or a phenyl group; and n11 represents a number of repetitions of a structure within parentheses, and an average of n11 in the formula (A-1) ranges from 10 to 150;
in the formula (A-2): Z21 to Z23 each independently represent an alkylene group having 1 to 4 carbon atoms; R16 to R27 each independently represent an alkyl group having 1 to 4 carbon atoms, or a phenyl group; and n21, n22, and n23 each independently represent a number of repetitions of a structure within parentheses, an average of n21 and an average of n22 in the formula (A-2) each range from 1 to 10, and an average of n23 in the formula (A-2) ranges from 10 to 200;
in the formula (C): Y31 represents an oxygen atom or a sulfur atom; and R31 to R34 each independently represent a hydrogen atom or a methyl group;
in the formula (D): m41 represents 0 or 1; X41 represents an o-phenylene group, a m-phenylene group, a p-phenylene group, a bivalent group having two p-phenylene groups bonded with a methylene group, or a bivalent group having two p-phenylene groups bonded with an oxygen atom; Y41 represents a single bond, an oxygen atom, a methylene group, an ethylidene group, a propylidene group, a cyclohexylidene group, a phenylmethylene group, or a phenylethylidene group; and R41 to R48 each independently represent a hydrogen atom or a methyl group.
The present invention also relates to a process cartridge, including: the electrophotographic photosensitive member; and at least one unit selected from the group consisting of a charging unit, a developing unit, a transfer unit, and a cleaning unit, the member and the unit being supported integrally, in which the process cartridge is removably mounted onto an electrophotographic apparatus body.
The present invention also relates to an electrophotographic apparatus, including: the electrophotographic photosensitive member; a charging unit; an exposing unit; a developing unit; and a transfer unit.
The present invention also relates to a method of producing an electrophotographic photosensitive member including: a support; a charge-generating layer on the support; and a charge-transporting layer on the charge-generating layer, the charge-transporting layer being a surface layer of the electrophotographic photosensitive member, the method including: preparing an application liquid for a charge-transporting layer, the application liquid containing: a polycarbonate resin A including: a structural unit represented by one of the formulae (A-1) and (A-2); a structural unit represented by the formula (B); and a structural unit represented by the formula (C); a resin D including a structural unit represented by the formula (D); and a charge-transporting substance; and forming a coating film of the application liquid for a charge-transporting layer, followed by drying the coating film, to thereby form the charge-transporting layer, a content of the structural unit represented by one of the formulae (A-1) and (A-2) in the polycarbonate resin A being from 5% by mass to 25% by mass based on a total mass of the polycarbonate resin A, a content of the structural unit represented by the formula (B) in the polycarbonate resin A being from 35% by mass to 65% by mass based on the total mass of the polycarbonate resin A, a content of the structural unit represented by the formula (C) in the polycarbonate resin A being from 10% by mass to 60% by mass based on the total mass of the polycarbonate resin A.
According to the embodiments of the present invention, it is possible to provide the excellent electrophotographic photosensitive member that achieves both sustainable relaxation of a contact stress and the suppression of a potential variation at the time of its repeated use, and the method of producing the excellent electrophotographic photosensitive member. In addition, according to the embodiments of the present invention, it is possible to provide the process cartridge and the electrophotographic apparatus each including the electrophotographic photosensitive member.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
In the present invention, the charge-transporting layer of an electrophotographic photosensitive member has a matrix-domain structure including a matrix and a domain.
The domain contains a polycarbonate resin A. The polycarbonate resin A has a structural unit represented by the following formula (A-1) or the following formula (A-2), a structural unit represented by the following formula (B), and a structural unit represented by the following formula (C).
The matrix contains a resin D having a structural unit represented by the following formula (D), and a charge-transporting substance.
Z11 and Z12 in the formula (A-1) each independently represent an alkylene group having 1 to 4 carbon atoms, that is, a methylene group, an ethylene group, a propylene group, or a butylene group. Z11 and Z12 each preferably represent a propylene group in terms of the relaxation of the contact stress.
R11 to R14 in the formula (A-1) each independently represent an alkyl group having 1 to 4 carbon atoms (i.e. a methyl group, an ethyl group, a propyl group, or a butyl group) or a phenyl group. R each preferably R11 to R14 represent a methyl group in terms of the relaxation of the contact stress.
n11 in the formula (A-1) represents the number of repetitions of a structure within parentheses and the average of n11 in the formula (A-1) ranges from 10 to 150. When the average of n11 ranges from 10 to 150, the domain each the polycarbonate resin A is uniformly formed in the matrix containing the charge-transporting substance and the resin D having a structural unit represented by the following formula (D). The average of n11 particularly preferably ranges from 40 to 80.
Table 1 below shows examples of the structural unit represented by the formula (A-1).
Z21 to Z23 in the formula (A-2) each independently represent an alkylene group having 1 to 4 carbon atoms, that is, a methylene group, an ethylene group, a propylene group, or a butylene group. Z22 and Z22 each preferably represent a propylene group and Z23 preferably represents an ethylene group in terms of the relaxation of the contact stress.
R16 to R27 in the formula (A-2) each independently represent an alkyl group having 1 to 4 carbon atoms (i.e. a methyl group, an ethyl group, a propyl group, or a butyl group) or a phenyl group. R each preferably R16 to R27 represent a methyl group in terms of the relaxation of the contact stress.
n21, n22, and n23 in the formula (A-2) each independently represent the number of repetitions of a structure within parentheses, and the average of n21 and the average of n22 in the formula (A-2) each range from 1 to 10, and the average of n23 ranges from 10 to 200. When the average of n21 and the average of n22 each range from 1 to 10, and the average of n23 ranges from 10 to 200, the domain is containing the polycarbonate resin A is uniformly formed in the matrix containing the charge-transporting substance and the resin D. The average of n21 and the average of n22 each preferably range from 1 to 5, and the average of n23 preferably ranges from 40 to 120.
Table 2 below shows examples of the structural unit represented by the formula (A-2).
With regard to the structural units represented by the formula (A-1) and the formula (A-2), out of the structural units, a structural unit represented by the formula (A-1-1), (A-1-2), (A-1-3), (A-1-4), (A-1-5), (A-2-1), (A-2-2), (A-2-3), (A-2-4), (A-2-5), or (A-2-6) is preferred. In addition, the polycarbonate resin A may have a siloxane structure represented by the following formula (A-E) at an end thereof.
In the formula (A-E), n51 represents the number of repetitions of a structure in parentheses and the average of n51 in the formula (A-E) ranges from 10 to 60.
In the formula (C), Y31 represents an oxygen atom or a sulfur atom. In the formula (C), R31 to R34 each independently represent a hydrogen atom or a methyl group.
Examples of the structural unit represented by the formula (C) are shown below.
Of those, a structural unit represented by the formula (C-1), (C-2), or (C-3) is preferred.
Further, the content of the structural unit represented by the formula (A-1) or the formula (A-2) with respect to the total mass of the polycarbonate resin A is from 5% by mass to 25% by mass. The content of the structural unit represented by the formula (B) with respect to the total mass of the polycarbonate resin A is from 35% by mass to 65% by mass. In addition, the content of the structural unit represented by the formula (C) with respect to the total mass of the polycarbonate resin A is from 10% by mass to 60% by mass.
In addition, the polycarbonate resin A may further have a structural unit represented by the following formula (E).
Y51 in the formula (E) represents a single bond, a methylene group, an ethylidene group, a propylidene group, a phenylmethylene group, or a phenylethylidene group. R51 to R58 in the formula (E) each independently represent a hydrogen atom or a methyl group.
Examples of the structural unit represented by the formula (E) are shown below.
Of those, a structural unit represented by the formula (E-4), (E-5), (E-6), (E-7), (E-8), or (E-9) is preferred.
In addition, the polycarbonate resin A may have a structural unit represented by the following formula (F).
In the formula (F), R61 to R68 each independently represent a hydrogen atom or a methyl group.
Examples of the structural unit represented by the formula (F) are shown below.
Of those, a structural unit represented by the formula (F-1) or (F-2) is preferred.
Next, the resin D having the structural unit represented by the formula (D) is described.
In the formula (D): m41 represents 0 or 1; when m41 represents 1, X41 represents an o-phenylene group, a m-phenylene group, a p-phenylene group, a bivalent group having two p-phenylene groups bonded with a methylene group, or a bivalent group having two p-phenylene groups bonded with an oxygen atom. One kind of group represented by X41 may be used alone, or may be used in combination with any one of an o-phenylene group, a m-phenylene group, a p-phenylene group, a bivalent group having two p-phenylene groups bonded with a methylene group, or a bivalent group having two p-phenylene groups bonded with an oxygen atom.
In the formula (D), Y41 represents a single bond, an oxygen atom, a methylene group, an ethylidene group, a propylidene group, a cyclohexylidene group, a phenylmethylene group, or a phenylethylidene group. Of those, a propylidene group is preferred. In the formula (D), R41 to R48 each independently represent a hydrogen atom or a methyl group.
Table 3 below shows examples of the structural unit represented by the formula (D).
Of those, a structural unit represented by the formula (D-2), (D-3), (D-4), (D-5), (D-6), (D-7), (D-8), (D-9), (D-20), (D-24), (D-25), (D-26), (D-27), (D-28), (D-29), or (D-30) is preferred.
The charge-transporting layer has the matrix-domain structure that has the matrix containing the charge-transporting substance and the resin D, and has, in the matrix, the domain containing the polycarbonate resin A. The matrix-domain structure in the present invention can be confirmed by observing the surface of the charge-transporting layer or observing a section of the charge-transporting layer.
The observation of the state of the matrix-domain structure or the measurement of the domain can be performed with, for example, a commercially available laser microscope, optical microscope, electron microscope, or atomic force microscope. The observation of the state of the matrix-domain structure or the measurement of the domain can be performed with the microscope at a predetermined magnification.
The number average particle diameter of the domain each containing the polycarbonate resin A is preferably from 10 nm to 1,000 nm. In addition, the particle size distribution of the particle diameters of the respective domains is preferably narrower from the viewpoints of the uniformity of a coating film of an application liquid for a charge-transporting layer and the uniformity of a contact stress-relaxing effect. The number average particle diameter of the domain is calculated as described below. 100 Domains are arbitrarily selected from the domain observed through the observation of a section obtained by vertically cutting the charge-transporting layer with a microscope. The maximum diameters of the respective selected domains are measured and the maximum diameters of the respective domains are averaged. Thus, the number average particle diameter of the domain is calculated. It should be noted that when the section of the charge-transporting layer is observed with the microscope, image information on its depth direction is obtained, and hence a three-dimensional image of the charge-transporting layer can also be obtained.
The matrix-domain structure of the charge-transporting layer can be formed by forming the charge-transporting layer using a coating film of an application liquid for a charge-transporting layer containing the charge-transporting substance, the polycarbonate resin A, and the resin D.
When the matrix-domain structure is uniformly formed in the charge-transporting layer, the sustainable relaxation of the contact stress is exhibited in an additionally effective manner. In addition, the incorporation of the polycarbonate resin A may facilitate the formation of the domain. This is probably because the polycarbonate resin A has the structural unit represented by the formula (B) and the structural unit represented by the formula (C), and hence compatibility between the polycarbonate resin A and the resin D is improved, liquid stability is thus maintained in the application liquid for a charge-transporting layer, and the formation of the matrix-domain structure is facilitated at the time of the formation of the coating film of the application liquid for a charge-transporting layer.
It is assumed that when the compatibility between the polycarbonate resin A and the resin D is improved, the localization of the polycarbonate resin A having the siloxane structure toward an interface between the charge-transporting layer and a charge-generating layer is suppressed, and hence a potential variation at the time of the repeated use of the electrophotographic photosensitive member can be suppressed. In addition, it is assumed that when the matrix-domain structure is formed, the polycarbonate resin A is uniformly present in the charge-transporting layer, and hence the sustainable relaxing effect of the electrophotographic photosensitive member on the contact stress is exhibited.
In addition, in the polycarbonate resin A in the present invention, the content of the structural unit represented by the formula (A-1) or the formula (A-2) is from 5% by mass to 25% by mass based on the total mass of the polycarbonate resin A, the content of the structural unit represented by the formula (B) is from 35% by mass to 65% by mass based on the total mass of the polycarbonate resin A, and the content of the structural unit represented by the formula (C) is from 10% by mass to 60% by mass based on the total mass of the polycarbonate resin A.
When the contents of those structural units fall within the ranges, the domain is uniformly formed in the matrix containing the charge-transporting substance and the resin D. Thus, the sustainable relaxation of the contact stress is effectively exhibited. In addition, the localization of the polycarbonate resin A toward the interface between the charge-generating layer and the charge-transporting layer is suppressed, and hence the potential variation at the time of the repeated use of the electrophotographic photosensitive member is suppressed.
Further, from the viewpoint of uniformly forming the domain in the matrix, the content of the polycarbonate resin A in the charge-transporting layer is preferably from 5% by mass to 50% by mass, more preferably from 10% by mass to 40% by mass based on whole resins in the charge-transporting layer.
In addition, when the polycarbonate resin A contains the structural unit represented by the formula (E), the content of the structural unit represented by the formula (E) with respect to the total mass of the polycarbonate resin A is preferably from 1% by mass to 30% by mass. When the content falls within the range, the domain is uniformly formed in the matrix containing the charge-transporting substance and the resin D.
In addition, when the polycarbonate resin A contains the structural unit represented by the formula (F), the content of the structural unit represented by the formula (F) with respect to the total mass of the polycarbonate resin A is preferably from 1% by mass to 25% by mass. When the content falls within the range, the domain is uniformly formed in the matrix containing the charge-transporting substance and the resin D.
The polycarbonate resin A is a copolymer including the structural unit represented by the formula (A-1) or the formula (A-2), the structural unit represented by the formula (B), and the structural unit represented by the formula (C). The form of the copolymer may be any form such as block copolymerization, random copolymerization, or alternating copolymerization.
From the viewpoint of forming the domain in the matrix containing the charge-transporting substance and the resin D, the weight-average molecular weight of the polycarbonate resin A to be used in the present invention is preferably from 30,000 to 200,000, more preferably from 40,000 to 150,000.
In the present invention, the weight-average molecular weight of the resin is a weight-average molecular weight in terms of polystyrene measured according to a conventional method, specifically a method described in Japanese Patent Application Laid-Open No. 2007-79555.
The copolymerization ratio of the polycarbonate resin A to be used in the present invention can be confirmed by a conversion method based on a peak area ratio between the hydrogen atoms of the resins (constituent hydrogen atoms of the resins) obtained by 1H-NMR measurement as a general approach.
The polycarbonate resin A to be used in the present invention can be synthesized by a conventional phosgene method, for example. In addition, the polycarbonate resin A can also be synthesized by a transesterification method.
Synthesis examples of the polycarbonate resin A to be used in the present invention are described below.
The polycarbonate resin A can be synthesized by employing a synthesis method described in Japanese Patent Application Laid-Open No. 2007-199688. In the present invention as well, the polycarbonate resin A shown in the column “Synthesis Example” of Table 4 was synthesized by employing the same synthesis method from raw materials corresponding to the structural unit represented by the formula (A-1) or (A-2), the structural unit represented by the formula (B), and the structural unit represented by the formula (C). Table 4 shows the construction and weight-average molecular weight (Mw) of the synthesized polycarbonate resin A. Table 5 shows comparative synthesis examples of a polycarbonate resin H synthesized by the same method as that for the polycarbonate resin A.
The column “Formula (A-1) or (A-2)” in Table 4 or 5 means the structural unit represented by the formula (A-1) or (A-2) to be incorporated into the polycarbonate resin A or the polycarbonate resin H. When the structural units each represented by the formula (A-1) or (A-2) are used as a mixture, the column shows the kinds of, and a mass mixing ratio between, the structural units. The column “Formula (C)” means the structural unit represented by the formula (C) to be incorporated into the polycarbonate resin A or the polycarbonate resin H. The column “Formula (E) or (F)” means the structural unit represented by the formula (E) or the formula (F) to be incorporated into the polycarbonate resin A or the polycarbonate resin H. The column “Average of n51 in formula (A-E)” means the average number of repetitions n51 of a structure within parentheses in the formula (A-E) to be incorporated into the polycarbonate resin A or the polycarbonate resin H. The column “Content (% by mass) of formula (A-1) or (A-2)” means the content (% by mass) of the structural unit represented by the formula (A-1) or the formula (A-2) in the polycarbonate resin A or the polycarbonate resin H. The column “Content (% by mass) of formula (B)” means the content (% by mass) of the structural unit represented by the formula (B) in the polycarbonate resin A or the polycarbonate resin H. The column “Content (% by mass) of formula (C)” means the content (% by mass) of the structural unit represented by the formula (C) in the polycarbonate resin A or the polycarbonate resin H. The column “Content (% by mass) of formula (E) or (F)” means the content (% by mass) of the structural unit represented by the formula (E) or the formula (F) in the polycarbonate resin A or the polycarbonate resin H. The column “Content (% by mass) of formula (A-E)” means the content (% by mass) of the structural unit represented by the formula (A-E) in the polycarbonate resin A or the polycarbonate resin H. The column “Mw” means the weight-average molecular weight of the polycarbonate resin A or the polycarbonate resin H.
Although the charge-transporting layer as the surface layer of the electrophotographic photosensitive member of the present invention contains the polycarbonate resin A and the resin D, any other resin may be further mixed and used together with the resins. Examples of the other resin that may be mixed and used together with the resins include an acrylic resin, a polyester resin, and a polycarbonate resin.
In addition, the resin D is preferably free of any structural unit represented by the formula (A-1) or the formula (A-2) from the viewpoint of the uniform formation of the matrix-domain structure.
The charge-transporting layer as the surface layer of the electrophotographic photosensitive member of the present invention contains the charge-transporting substance. Examples of the charge-transporting substance include a triarylamine compound, a hydrazone compound, a butadiene compound, and an enamine compound. One kind of those charge-transporting substances may be used alone, or two or more kinds thereof may be used. Of those, a triarylamine compound is preferably used as the charge-transporting substance from the viewpoint of improving electrophotographic characteristics.
Next, the construction of the electrophotographic photosensitive member of the present invention is described.
As described above, the electrophotographic photosensitive member of the present invention includes a support, a charge-generating layer on the support, and a charge-transporting layer on the charge-generating layer. In addition, in the electrophotographic photosensitive member of the present invention, the charge-transporting layer is a surface layer (outermost layer) of the electrophotographic photosensitive member.
Further, the charge-transporting layer of the electrophotographic photosensitive member of the present invention contains the charge-transporting substance. In addition, the charge-transporting layer contains the polycarbonate resin A and the resin D. Further, the charge-transporting layer may have a laminated structure, and in such case, the layer is formed so that at least the charge-transporting layer on the outermost surface side has the above-mentioned matrix-domain structure.
In general, as the electrophotographic photosensitive member, a cylindrical electrophotographic photosensitive member produced by forming a photosensitive layer on a cylindrical support is widely used, but the member may be formed into, for example, a belt or sheet shape.
The support is preferably conductive (conductive support) and a support made of a metal such as aluminum, an aluminum alloy, or stainless steel may be used.
In the case of a support made of aluminum or an aluminum alloy, the support to be used may be an ED tube or an EI tube or one obtained by subjecting the tube to cutting, electro-chemical buffing, or a wet- or dry-honing process. Further, a support made of a metal or a support made of a resin having a layer obtained by forming aluminum, an aluminum alloy, or an indium oxide-tin oxide alloy into a film by means of vacuum deposition may be used.
In addition, a support obtained by impregnating conductive particles such as carbon black, tin oxide particles, titanium oxide particles, or silver particles in a resin or the like, or a plastic having a conductive resin may be used.
The surface of the support may be subjected to, for example, cutting treatment, roughening treatment, or alumite treatment.
A conductive layer may be formed between the support and the undercoat layer to be described later or the charge-generating layer for the purpose of suppressing the occurrence of interference fringes or covering a flaw of the support surface. The conductive layer can be formed by applying an application liquid for a conductive layer, which is prepared by dispersing conductive particles in a resin, onto the support to form a coating film, and drying or curing the resultant coating film.
Examples of the conductive particles include carbon black, acetylene black, metal powders made of, for example, aluminum, nickel, iron, nichrome, copper, zinc, and silver, and metal oxide powders made of, for example, conductive tin oxide and ITO.
In addition, examples of the resin include a polyester resin, a polycarbonate resin, a polyvinyl butyral, an acrylic resin, a silicone resin, an epoxy resin, a melamine resin, a urethane resin, a phenol resin, and an alkyd resin.
As a solvent to be used for the application liquid for a conductive layer, there are given, for example, an ether-based solvent, an alcohol-based solvent, a ketone-based solvent, and an aromatic hydrocarbon solvent.
The thickness of the conductive layer is preferably from 0.2 μm to 40 μm, more preferably from 1 μm to 35 μm, still more preferably from 5 μm to 30 μm.
The undercoat layer may be formed between the support or the conductive layer and the charge-generating layer. The undercoat layer can be formed by applying an application liquid for an undercoat layer containing a resin onto the support or the conductive layer to form a coating film, and drying or curing the resultant coating film.
Examples of the resin in the undercoat layer include polyacrylic acids, methylcellulose, ethylcellulose, a polyamide resin, a polyimide resin, a polyamideimide resin, a polyamide acid resin, a melamine resin, an epoxy resin, a polyurethane resin, and a polyolefin resin.
The thickness of the undercoat layer is preferably from 0.05 μm to 7 μm, more preferably from 0.1 μm to 2 μm. The undercoat layer may further contain semiconductive particles, an electron-transporting substance, or an electron-accepting substance.
The charge-generating layer is formed on the support, conductive layer, or undercoat layer.
Examples of the charge-generating substance to be used in the electrophotographic photosensitive member of the present invention include azo pigments, phthalocyanine pigments, indigo pigments, and perylene pigments. Only one kind of those charge-generating substances may be used, or two or more kinds thereof may be used. Of those, metallophthalocyanines such as oxytitanium phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine are particularly preferred because of their high sensitivity.
Examples of the resin to be used in the charge-generating layer include a polycarbonate resin, a polyester resin, a butyral resin, a polyvinyl acetal resin, an acrylic resin, a vinyl acetate resin, and a urea resin. Of those, a butyral resin is particularly preferred. One kind of those resins may be used alone, or two or more kinds thereof may be used as a mixture or as a copolymer.
The charge-generating layer can be formed by applying an application liquid for a charge-generating layer, which is prepared by dispersing a charge-generating substance together with a resin and a solvent, to form a coating film, and drying the resultant coating film. Further, the charge-generating layer may also be a deposited film of a charge-generating substance.
Examples of the dispersion method include methods each using a homogenizer, an ultrasonic wave, a ball mill, a sand mill, an attritor, or a roll mill.
A ratio between the charge-generating substance and the resin falls within the range of preferably from 1:10 to 10:1 (mass ratio), particularly preferably from 1:1 to 3:1 (mass ratio).
The solvent to be used for the application liquid for a charge-generating layer is selected depending on the solubility and dispersion stability of each of the resin and charge-generating substance to be used. As an organic solvent to be used, there are given, for example, an alcohol solvent, a sulfoxide solvent, a ketone solvent, an ether solvent, an ester solvent, and an aromatic hydrocarbon solvent.
The thickness of the charge-generating layer is preferably 5 μm or less, more preferably from 0.1 μm to 2 μm.
Further, any of various sensitizers, antioxidants, UV absorbers, plasticizers, and the like may be added to the charge-generating layer, if required. An electron-transporting substance or an electron-accepting substance may also be incorporated into the charge-generating layer to prevent the flow of charge from being disrupted in the charge-generating layer.
The charge-transporting layer is formed on the charge-generating layer.
The charge-transporting layer as the surface layer of the electrophotographic photosensitive member of the present invention contains the charge-transporting substance. Examples of the charge-transporting substance include a triarylamine compound, a hydrazone compound, a butadiene compound, and an enamine compound. Of those, a triarylamine compound is preferably used as the charge-transporting substance in terms of improvements in electrophotographic characteristics.
Examples of the charge-transporting substance are shown below.
The charge-transporting layer contains the polycarbonate resin A and also contains the resin D, but as described above, any other resin may further be mixed and used together with the resins. The other resin that may be mixed and used together with the resins is as described above. The charge-transporting layer can be formed by applying an application liquid for a charge-transporting layer, which is obtained by dissolving a charge-transporting substance and the above-mentioned resins into a solvent, to form a coating film, and drying the resultant coating film.
A ratio between the charge-transporting substance and the resins falls within the range of preferably from 4:10 to 20:10 (mass ratio), more preferably from 5:10 to 12:10 (mass ratio).
Examples of the solvent to be used for the application liquid for a charge-transporting layer include ketone solvents, ester solvents, ether solvents, and aromatic hydrocarbon solvents. Those solvents may be used each alone or as a mixture of two or more kinds thereof. Of those solvents, it is preferred to use any of the ether solvents and the aromatic hydrocarbon solvents from the viewpoint of resin solubility.
The charge-transporting layer has a thickness of preferably from 5 μm to 50 μm, more preferably from 10 μm to 35 μm.
In addition, an antioxidant, a UV absorber, a plasticizer, or the like may be added to the charge-transporting layer, if required.
A variety of additives may be added to each layer of the electrophotographic photosensitive member of the present invention. Examples of the additives include: an antidegradant such as an antioxidant, a UV absorber, or a light resistant stabilizer; and fine particles such as organic fine particles or inorganic fine particles. Examples of the antidegradant include a hindered phenol-based antioxidant, a hindered amine-based light resistant stabilizer, a sulfur atom-containing antioxidant, and a phosphorus atom-containing antioxidant. Examples of the organic fine particles include polymer resin particles such as fluorine atom-containing resin particles, polystyrene fine particles, and polyethylene resin particles. Examples of the inorganic fine particles include metal oxides such as silica and alumina.
For the application of each of the application liquids corresponding to the above-mentioned respective layers, any of the application methods may be employed, such as a dip coating method, a spray coating method, a spinner coating method, a roller coating method, a Meyer bar coating method, and a blade coating method.
In addition, an uneven shape (a concave and a convex) may be formed in the surface of the charge-transporting layer as the surface layer of the electrophotographic photosensitive member of the present invention. A known method can be adopted as a method of forming the uneven shape. Examples of the forming method include: a method involving spraying the surface of the charge-transporting layer with abrasive particles to form concaves; a method involving bringing a mold having the uneven shape into press contact with the surface to form the uneven shape; a method involving causing condensation on the surface of the coating film of the applied application liquid for a surface layer, and then drying the coating film to form concaves; and a method involving irradiating the surface with laser light to form concaves. Of those, a method involving bringing a mold having the uneven shape into press contact with the surface of the surface layer of the electrophotographic photosensitive member to form the uneven shape is preferred. A method involving causing condensation on the surface of the coating film of the applied application liquid for a surface layer, and then drying the coating film to form concaves is also preferred.
In
The surface of the electrophotographic photosensitive member 1 to be rotationally driven is uniformly charged to a positive or negative predetermined potential by a charging unit 3 (primary charging unit: a charging roller or the like). Next, the uniformly charged surface of the electrophotographic photosensitive member 1 receives exposure light 4 (image exposure light) output from an exposing unit (not shown) such as slit exposure or laser beam scanning exposure. Thus, electrostatic latent images corresponding to a target image are sequentially formed on the surface of the electrophotographic photosensitive member 1.
The electrostatic latent images formed on the surface of the electrophotographic photosensitive member 1 are developed with toners in the developers of a developing unit 5 to provide toner images. Next, the toner images formed and borne on the surface of the electrophotographic photosensitive member 1 are sequentially transferred onto a transfer material P (such as paper) by a transfer bias from a transfer unit 6 (such as a transfer roller). It should be noted that the transfer material P is taken out of a transfer material-supplying unit (not shown) and fed into a gap between the electrophotographic photosensitive member 1 and the transfer unit 6 (abutting portion) in synchronization with the rotation of the electrophotographic photosensitive member 1.
The transfer material P onto which the toner images have been transferred is separated from the surface of the electrophotographic photosensitive member 1 and then introduced to a fixing unit 8. The transfer material P is subjected to image fixation to be printed out as an image-formed product (print or copy) to the outside of the apparatus.
The surface of the electrophotographic photosensitive member 1 after the transfer of the toner images is cleaned by removal of the remaining developer (toner) after the transfer by a cleaning unit 7 (such as a cleaning blade). Subsequently, the cleaned surface of the electrophotographic photosensitive member 1 is subjected to neutralization treatment with pre-exposure light (not shown) from a pre-exposing unit (not shown) and then repeatedly used in image formation. It should be noted that, as illustrated in
Of the constituents including the electrophotographic photosensitive member 1, the charging unit 3, the developing unit 5, the transfer unit 6, and the cleaning unit 7, a plurality of them may be selected and integrally supported as a process cartridge. In addition, the process cartridge may be designed so as to be removably mounted onto an electrophotographic apparatus body. In
Hereinafter, the present invention is described in more detail with reference to specific examples. However, the present invention is not limited thereto. It should be noted that “part(s)” means “part(s) by mass” in the examples.
An aluminum cylinder having a diameter of 24 mm and a length of 257 mm was used as a support.
Next, 10 parts of SnO2-coated barium sulfate (conductive particle), 2 parts of titanium oxide (pigment for controlling resistance), 6 parts of a phenol resin, and 0.001 part of silicone oil (leveling agent) were used together with a mixed solvent of 4 parts of methanol and 16 parts of methoxypropanol, to thereby prepare an application liquid for a conductive layer.
The application liquid for a conductive layer was applied onto the support by dip coating to form a coating film, and the resultant coating film was cured (thermally cured) at 140° C. for 30 minutes, to thereby form a conductive layer having a thickness of 15 μm.
Next, 3 parts of N-methoxymethylated nylon and 3 parts of copolymer nylon were dissolved in a mixed solvent of 65 parts of methanol and 30 parts of n-butanol, to thereby prepare an application liquid for an undercoat layer.
The application liquid for an undercoat layer was applied onto the conductive layer by dip coating to form a coating film, and the resultant coating film was dried at 100° C. for 10 minutes, to thereby form an undercoat layer having a thickness of 0.7 μm.
Next, hydroxygallium phthalocyanine (charge-generating substance) having a crystal structure showing peaks at Bragg angles 2θ±0.2° of 7.5°, 9.9°, 16.3°, 18.6°, 25.1°, and 28.3° in CuKα characteristic X-ray diffraction was prepared. 10 Parts of the hydroxygallium phthalocyanine were added to a solution prepared by dissolving 5 parts of a polyvinyl butyral resin (trade name: S-LEC BX-1, manufactured by Sekisui Chemical Co., Ltd.) in 250 parts of cyclohexanone. The resultant mixture was dispersed by a sand mill apparatus using glass beads each having a diameter of 1 mm under a 23±3° C. atmosphere for 1 hour. After the dispersion, 250 parts of ethyl acetate were added to prepare an application liquid for a charge-generating layer.
The application liquid for a charge-generating layer was applied onto the undercoat layer by dip coating to form a coating film, and the resultant coating film was dried at 100° C. for 10 minutes, to thereby form a charge-generating layer having a thickness of 0.26 μm.
Next, 9 parts of a charge-transporting substance represented by the formula (G-1), 1 part of a charge-transporting substance represented by the formula (G-3), 3 parts of the polycarbonate resin A (1) synthesized in Synthesis Example 1, and 7 parts of the resin D (weight-average molecular weight: 120,000) containing a structural unit represented by the formula (D-2) and a structural unit represented by the formula (D-3) at a ratio of 5:5 were dissolved in a mixed solvent containing 30 parts of dimethoxymethane and 50 parts of orthoxylene to prepare an application liquid for a charge-transporting layer.
The application liquid for a charge-transporting layer was applied onto the charge-generating layer by dip coating to form a coating film, and the resultant coating film was dried for 1 hour at 120° C. to form a charge-transporting layer having a thickness of 16 μm. It was confirmed that in the formed charge-transporting layer, domains each containing the polycarbonate resin A (1) were formed in a matrix containing the charge-transporting substances and the resin D.
Thus, an electrophotographic photosensitive member whose surface layer was the charge-transporting layer was produced. Table 6 shows the constructions of the resins in the charge-transporting layer.
Next, evaluation is described.
Evaluation was performed for a variation (potential variation) of bright section potentials in 6,000-sheet repeated use, relative values for torque at an initial stage and after 6,000-sheet repeated use, and observation of the surface of the electrophotographic photosensitive member in measurement of the torque. In addition, after the preparation of the application liquid for a charge-transporting layer, part of the application liquid was sampled and the application liquid was evaluated for its liquid stability. In addition, a coating film was formed by using the sampled application liquid and was evaluated for its surface roughness. Further, image evaluation was performed by using the electrophotographic photosensitive member subjected to the evaluation for the surface roughness.
(Evaluation for Potential Variation)
A laser beam printer Color Laser JET CP4525dn manufactured by Hewlett-Packard was used as an evaluation apparatus. Evaluation was performed under an environment of a temperature of 23° C. and a relative humidity of 50%. The exposure amount (image exposure amount) of a 780-nm laser light source of the evaluation apparatus was set so that the light intensity on the surface of the electrophotographic photosensitive member was 0.40 μJ/cm2. Measurement of the potentials (dark section potential and bright section potential) of the surface of the electrophotographic photosensitive member was performed at a position of a developing device after replacing the developing device by a fixture fixed so that a probe for potential measurement was located at a position of 130 mm from the end of the electrophotographic photosensitive member toward the center thereof. The dark section potential at an unexposed part of the electrophotographic photosensitive member was set to −500 V, laser light was radiated, and the bright section potential obtained by light attenuation from the dark section potential was measured. Further, A4-size plain paper was used to continuously output an image on 6,000 sheets, and variations of the bright section potentials before and after the output were evaluated. A test chart having a printing ratio of 5% was used. The results are shown in the column “Potential variation” in Table 11.
(Evaluation for Relative Value for Torque)
A driving current (current A) of a rotary motor of the electrophotographic photosensitive member was measured under the same conditions as those in the evaluation for the potential variation described above. This evaluation was performed for evaluating an amount of contact stress between the electrophotographic photosensitive member and the cleaning blade. The resultant current shows how large the amount of contact stress between the electrophotographic photosensitive member and the cleaning blade is.
Moreover, an electrophotographic photosensitive member for comparison of a relative value for torque was produced by the following method. That is, an electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the polycarbonate resin A (1) used in the resins in the charge-transporting layer of the electrophotographic photosensitive member in Example 1 was not used and only the resin D containing a structural unit represented by the formula (D-2) and a structural unit represented by the formula (D-3) at a ratio of 5:5 was used. The resultant electrophotographic photosensitive member was used as the electrophotographic photosensitive member for comparison. The produced electrophotographic photosensitive member for comparison was used to measure a driving current (current B) of a rotary motor of the electrophotographic photosensitive member in the same manner as in Example 1.
A ratio of the driving current (current A) of the rotary motor of the electrophotographic photosensitive member using the polycarbonate resin A thus obtained to the driving current (current B) of the rotary motor of the electrophotographic photosensitive member not using the polycarbonate resin A was calculated. The resultant value of (current A)/(current B) was defined as a relative value for torque. The relative value for torque represents a degree of reduction in contact stress between the electrophotographic photosensitive member and the cleaning blade. As the relative value for torque becomes smaller, the degree of reduction in contact stress between the electrophotographic photosensitive member and the cleaning blade becomes larger. The results are shown in the column “Relative value for torque at initial stage” in Table 11.
Subsequently, A4-size plain paper was used to continuously output an image on 6,000 sheets of the paper. A test chart having a printing ratio of 5% was used. After that, measurement of a relative value for torque after the 6,000-sheet repeated use was performed. The relative value for torque after the 6,000-sheet repeated use was measured in the same manner as in the evaluation for the relative value for torque at the initial stage. In this case, the electrophotographic photosensitive member for comparison was also subjected to the 6,000-sheet repeated use, and the resultant driving current of the rotary motor was used to calculate the relative value for torque after the 6,000-sheet repeated use. The results are shown in the column “Relative value for torque after 6,000-sheet repeated use” in Table 11.
(Evaluation for Matrix-Domain Structure)
A section of the charge-transporting layer, obtained by cutting the charge-transporting layer in a vertical direction with respect to the electrophotographic photosensitive member produced by the above-mentioned method, was observed using an ultra-deep profile measurement microscope VK-9500 (manufactured by KEYENCE CORPORATION). In this process, an area of 100 μm×100 μm (10,000 μm2) in the surface of the electrophotographic photosensitive member was defined as a visual field and observed at an object lens magnification of 50× to measure the maximum diameters of 100 formed domains selected at random in the visual field. An average was calculated from the measured maximum diameters and provided as a number average particle diameter. The results are shown in the column “Number average particle diameter” in Table 11.
(Evaluation for Liquid Stability)
Part of the application liquid for a charge-transporting layer prepared by the above-mentioned method was sampled immediately after the preparation, and was stored at rest in a refrigerator (temperature: 0° C.) for 2 weeks. The application liquid immediately after the preparation and the application liquid after 2 weeks of the refrigerated storage were visually evaluated. The results are shown in the columns “Liquid stability immediately after preparation” and “Liquid stability after 2 weeks of refrigerated storage” in Table 11.
(Evaluation for Surface Roughness)
In the evaluation for the liquid stability, the liquid stability of the application liquid for a charge-transporting layer stored at rest in the refrigerator for 2 weeks was visually observed. After that, the liquid was stirred with a homogenizer (Physcotron manufactured by MICROTEC CO., LTD.) at 1,000 rpm for 3 minutes. The application liquid for a charge-transporting layer after the stirring was applied by dip coating onto the aluminum cylinder having formed thereon the conductive layer, the undercoat layer, and the charge-generating layer to form a coating film, and the coating film was dried at 120° C. for 1 hour. Thus, a charge-transporting layer having a thickness of 15 μm was formed. The surface of the charge-transporting layer was subjected to measurement with a surface roughness-measuring device (SURFCORDER SE-3400 manufactured by Kosaka Laboratory Ltd.), and was subjected to evaluation (evaluation length: 10 mm) based on a ten-point average roughness (Rzjis) evaluation in JIS B 0601:2001. The results are shown in the column “Surface roughness” in Table 11.
(Image Evaluation)
Image evaluation was performed by using the electrophotographic photosensitive member subjected to the evaluation for the surface roughness. A laser beam printer Color Laser JET CP4525dn manufactured by Hewlett-Packard Company was used as an evaluation apparatus. The evaluation was performed under an environment having a temperature of 23° C. and a relative humidity of 50%. The exposure amount (image exposure amount) of a laser light source having a wavelength of 780 nm for the evaluation apparatus was set so that a light quantity on the surface of the electrophotographic photosensitive member was 0.40 μJ/cm2.
In the image evaluation, A4 size plain paper was used and a monochromatic halftone image was output on the paper. Then, an output image was visually evaluated by the following criteria. The results are shown in the column “Image evaluation” in Table 11.
Rank A: An entirely uniform image is observed.
Rank B: Extremely slight image unevenness is observed.
Rank C: Image unevenness is observed.
Rank D: Conspicuous image unevenness is observed.
Electrophotographic photosensitive members were each produced in the same manner as in Example 1 except that in Example 1, the polycarbonate resin A of the charge-transporting layer was changed as shown in Table 6. Then, the electrophotographic photosensitive members were evaluated in the same manner as in Example 1. It was confirmed that in the formed charge-transporting layer, domains each containing the polycarbonate resin A were formed in a matrix containing the charge-transporting substance and the resin D. Table 11 shows the results.
Electrophotographic photosensitive members were each produced in the same manner as in Example 1 except that in Example 1, the resin D of the charge-transporting layer was changed as shown in Table 6. Then, the electrophotographic photosensitive members were evaluated in the same manner as in Example 1. It was confirmed that in the formed charge-transporting layer, domains each containing the polycarbonate resin A were formed in a matrix containing the charge-transporting substance and the resin D. Table 11 shows the results.
It should be noted that the structural unit(s) and composition thereof in the resin D and the weight-average molecular weight of the resin D were as follows.
(D-4)/(D-5)=5/5; 120,000
(D-6)/(D-2)=7/3; 120,000
(D-7); 100,000
(D-8)/(D-9)=3/7; 110,000
(D-20); 80,000
(D-20)/(D-28)=7/3; 70,000
(D-29)/(D-30)=3/7; 90,000
(D-30); 80,000
(D-25)/(D-29)=3/7; 80,000
(D-26)/(D-20)=5/5; 90,000
(D-20)/(D-29)/(D-24)=3/5/2; 80,000
Electrophotographic photosensitive members were each produced in the same manner as in Example 1 except that in Example 1, resin D, mixing ratio between the polycarbonate resin A and the resin D, and the charge-transporting substance of the charge-transporting layer were changed as shown in Table 6. Then, the electrophotographic photosensitive members were evaluated in the same manner as in Example 1. It was confirmed that in the formed charge-transporting layer, domain structures each containing the polycarbonate resin A were formed in a matrix containing the charge-transporting substance and the resin D. Table 11 shows the results.
Electrophotographic photosensitive members were each produced in the same manner as in Example 1 except that in Example 1, the polycarbonate resin A, the resin D, mixing ratio between the polycarbonate resin A and the resin D, and the charge-transporting substance of the charge-transporting layer were each changed as shown in Tables 7, 8, and 9. Then, the electrophotographic photosensitive members were evaluated in the same manner as in Example 1. It was confirmed that in the formed charge-transporting layer, domains each containing the polycarbonate resin A were formed in a matrix containing the charge-transporting substance and the resin D. Tables 12, 13, and 14 show the results.
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that in Example 1, the used solvent was changed to a mixed solvent containing 30 parts of dimethoxymethane, 50 parts of orthoxylene, and 6.4 parts of methyl benzoate. Then, the electrophotographic photosensitive member was evaluated in the same manner as in Example 1. It was confirmed that in the formed charge-transporting layer, domain structures each containing the polycarbonate resin A were formed in a matrix containing the charge-transporting substances and the resin D. Table 14 shows the results.
Electrophotographic photosensitive members were each produced in the same manner as in Example 1 except that in Example 1, the polycarbonate resin A was changed to the polycarbonate resin H shown in Table 10. Then, the electrophotographic photosensitive members were evaluated in the same manner as in Example 1. In each of Comparative Examples 1 to 5 and 12 to 15, the application liquid for a charge-transporting layer separated after 2 weeks of refrigerated storage. In addition, it was confirmed that in the charge-transporting layer formed in each of Comparative Examples 6 to 11 and 16 to 18, domains each containing the polycarbonate resin H were formed in a matrix containing the charge-transporting substances and the resin D. Table 15 shows the results.
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that in Example 1, the resin D was not used and such a change as shown in Table 10 was performed. No matrix-domain structure was confirmed because the formed charge-transporting layer did not contain the resin D. The electrophotographic photosensitive member was evaluated in the same manner as in Example 1. Table 15 shows the results.
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that in Example 1, the polycarbonate resin A was not used and such a change as shown in Table 10 was performed. No matrix-domain structure was confirmed because the formed charge-transporting layer did not contain the polycarbonate resin A. The electrophotographic photosensitive member was evaluated in the same manner as in Example 1. Table 15 shows the results.
The column “Resin A/resin D mixing ratio” in Tables 6 to 9 means the mass mixing ratio (mass ratio) of the polycarbonate resin A to the resin D. The column “CTS” in Tables 6 to 9 represents a charge-transporting substance and means a compound represented by any one of the formulae (G-1) to (G-5).
The column “Polycarbonate resin H” in Table 10 means the polycarbonate resin H in each comparative synthesis example in Table 5. The column “Resin H/resin D mixing ratio” in Table 10 means the mass mixing ratio (mass ratio) of the polycarbonate resin H to the resin D. The column “CTS” in Table 10 represents a charge-transporting substance and means a compound represented by any one of the formulae (G-1) to (G-5).
Comparison between Examples and Comparative Examples shows that in each of Examples, the charge-transporting layer contains the polycarbonate resin A, and hence both the suppressing effect on the potential variation at the time of the repeated use of the electrophotographic photosensitive member and the sustainable relaxing effect on the contact stress are achieved. The foregoing is demonstrated by the potential variation of the evaluation method, and the presence of torque-reducing effects in the evaluation for the relative values for torque at the initial stage and after the 6,000-sheet repeated use.
Comparison between Examples and Comparative Examples 1 to 5 and 12 to 15 shows that when the structural unit represented by the formula (C) is incorporated into the polycarbonate resin A, compatibility between the polycarbonate resin A and the resin D improves, and the domains are uniformly formed in the matrix. Accordingly, an excellent suppressing effect on the potential variation is obtained. In addition, the comparison shows that the liquid stability of the application liquid for a charge-transporting layer after 2 weeks of the storage at rest in the refrigerator is held. In addition, the comparison shows that when the liquid stability is good, the result of the image evaluation is also good.
In addition, comparison between Examples and Comparative Examples 10, 11, and 18 shows that in each of Examples, the polycarbonate resin A is incorporated, and hence the liquid stability of the application liquid for a charge-transporting layer after 2 weeks of the storage at rest in the refrigerator is held. In addition, the comparison shows that when the liquid stability is good, the result of the image evaluation is also good.
In view of the foregoing, the incorporation of proper amounts of the structural unit represented by the formula (B) and the structural unit represented by the formula (C) may provide an excellent suppressing effect on the potential variation and an excellent torque-reducing effect.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-064093, filed Mar. 26, 2014, and Japanese Patent Application No. 2015-025384, filed Feb. 12, 2015 which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
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| 2015-025384 | Feb 2015 | JP | national |
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