JP2006133701A - Multilayer electrophotographic photoreceptor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer electrophotographic photoreceptor having high repetition stability and high sensitivity even when used at high temperature and high humidity. <P>SOLUTION: In the multilayer electrophotographic photoreceptor, the following resins (A) and (B) are contained as a binder resin in a charge generating layer in the following respective amounts based on the total amount of the binder resin in the charge generating layer. (A) A polyvinyl butyral resin having a degree of butyralization of 60 to <70 mol%: 40-80 wt.%, (B) a polyvinyl butyral resin having a degree of butyralization of ≥70 mol%; 20-60 wt.%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multi-layer electrophotographic photosensitive member used in an image forming apparatus such as a copying machine, a facsimile machine, and a printer.

  In an image forming apparatus, various photosensitive members having sensitivity in a wavelength region of a light source used in the apparatus are used. One is an inorganic photoreceptor using an inorganic material such as selenium for the photosensitive layer, and the other is an organic photoreceptor using an organic material for the photosensitive layer. Organic photoconductors are easy to manufacture and have a wide range of research in recent years because they have a wide variety of material choices such as charge generators, charge transport agents, binder resins, and the like, and have a high degree of freedom in functional design.

For example, Patent Document 1 below discloses an electrophotographic photoreceptor using a polyvinyl butyral resin having a specific structure as a binder resin for the purpose of improving the long-term storage stability of the charge generation layer dispersion. However, in the electrophotographic photoreceptor described in Patent Document 1, when a large number of sheets are printed under high temperature and high humidity, the residual potential is high, the sensitivity is lowered, and fog may occur. Therefore, it is desired to develop an electrophotographic photosensitive member having high repeatability even when used at high temperature and high humidity as well as normal temperature and pressure.
JP-A-9-179316

  SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer electrophotographic photosensitive member having high sensitivity and high sensitivity even when used under high temperature and high humidity.

The multilayer electrophotographic photoreceptor of the present invention for solving the above problems is a multilayer electrophotographic photoreceptor in which at least a charge generation layer and a charge transport layer are provided on a conductive substrate. As the binder resin, the following resins (A) and (B) are respectively contained in the following contents with respect to the total amount of the binder resin in the charge generation layer.
(A) Polyvinyl butyral resin having a butyralization degree of 60 mol% or more and less than 70 mol%: 40% by weight or more and 80% by weight or less (B) Polyvinyl butyral resin having a butyralization degree of 70 mol% or more: 20% by weight or more and 60% by weight or less

Another multilayer electrophotographic photosensitive member of the present invention for solving the above problems is a multilayer electrophotographic photosensitive member in which at least a charge generation layer and a charge transport layer are provided on a conductive substrate, As the binder resin of the charge generation layer, the following resins (C) and (D) are respectively contained in the following contents with respect to the total amount of the binder resin of the charge generation layer.
(C) Polyvinyl butyral resin having a hydroxyl group content of 30 mol% or more: 40 wt% or more and 80 wt% or less (D) Polyvinyl butyral resin having a hydroxyl group content of less than 30 mol%: 20 wt% or more and 60 wt% or less

  Furthermore, in addition to the above configuration, the multilayer electrophotographic photoreceptor of the present invention has a maximum peak at least at a Bragg angle 2θ ± 0.2 ° = 27.2 ° as a charge generator in a CuKα characteristic X-ray diffraction spectrum. The charge generation layer contains titanyl phthalocyanine having.

  According to the present invention, the resins (A) and (B) having different degrees of butyralization or the resins (C) and (D) having different hydroxyl contents are used in a specific ratio as the binder resin of the charge generation layer. The residual potential (surface potential) can be effectively reduced and high sensitivity can be obtained. Further, even when used under high temperature and high humidity, it is possible to obtain a highly sensitive laminated electrophotographic photoreceptor having high repeatability.

  The multilayer electrophotographic photosensitive member of the present invention is provided with at least a charge generation layer and a charge transport layer on a conductive substrate, and a specific polyvinyl butyral resin is used as a binder resin for the charge generation layer. Is.

<Preparation of charge generation layer>
The charge generation layer in the multilayer electrophotographic photosensitive member of the present invention contains a binder resin, a charge generation agent, and the like.

(1) Binder Resin In the present invention, the binder resin for the charge generation layer contains a polyvinyl butyral resin. The “polyvinyl butyral resin” here is represented by the following formula (I).

In the present invention, the binder resin of the charge generation layer contains the following two resins (A) and resin (B).
(A) Polyvinyl butyral resin having a butyralization degree of 60 mol% or more and less than 70 mol% (B) Polyvinyl butyral resin having a butyralization degree of 70 mol% or more

  Here, the “degree of butyralization” refers to a compositional ratio of monomers having a butyral group expressed as a molar ratio, and can be expressed by the following formula using p, q, and r in the above formula (I). .

The degree of butyralization can be obtained from the IR absorption spectrum with an infrared spectrophotometer. That is, the IR absorption spectrum of a polyvinyl butyral film is obtained with an infrared spectrophotometer, the amount of hydroxyl group and residual acetyl group is obtained using a calibration curve, and the degree of butyralization is calculated.
(Method of calculation)
Hydroxyl group (mol%) = Calculated from IR absorption intensity of hydroxyl group Residual acetyl group (mol%) = Calculated from IR absorption intensity of acetyl group Butyralization degree (mol%) = 100− (hydroxyl group (mol%) + residual acetyl group ( mol%))

  If the degree of butyralization is high, that is, 70 mol% or more, the number of hydroxyl groups in the molecule decreases. That is, the hydroxyl group content is less than 30 mol%. And when only such a polyvinyl butyral resin is used, the initial sensitivity under normal temperature normal pressure and high temperature high pressure will fall.

  On the other hand, if the degree of butyralization is low, that is, 60 mol% or more and less than 70 mol%, the number of hydroxyl groups in the molecule increases. That is, the hydroxyl group content is 30 mol% or more. When only such a polyvinyl butyral resin is used, the sensitivity after printing a large number of sheets under high temperature and high pressure is reduced.

Therefore, the contents of the resins (A) and (B) are preferably set as follows with respect to the total amount of the binder resin in the charge generation layer.
Resin (A): 40% by weight to 80% by weight Resin (B): 20% by weight to 60% by weight

  The reason why the amount is as described above is that when the amount of the resin (A) is less than 40% by weight or when the amount of the resin (B) is more than 60% by weight, it is under normal temperature and normal pressure and high temperature and high pressure. This is because the initial sensitivity may be lowered. If the amount of the resin (A) is greater than 80% by weight or the amount of the resin (B) is less than 20% by weight, the sensitivity after printing a large number of sheets under high temperature and high pressure may decrease. Because there is.

  The “hydroxyl group content” of the polyvinyl butyral resin refers to a molar ratio of the composition ratio of monomers having a hydroxyl group, and can be calculated from the IR absorption intensity of the hydroxyl group as described above.

  The content of the resin (A) is preferably 40% by weight or more and 70% by weight or less based on the total amount of the binder resin in the charge generation layer. The content of the polyvinyl butyral resin (B) is preferably 30% by weight to 60% by weight with respect to the total amount of the binder resin in the charge generation layer.

  In the present invention, the binder resin of the charge generation layer may be constituted only by the resins (A) and (B), but if necessary, a resin other than the polyvinyl butyral resin may be further added to form the charge generation layer. The binder resin may be configured.

  Examples of the resin other than the polyvinyl butyral resin herein include, for example, a styrene polymer, a styrene-butadiene copolymer, a styrene-acrylonitrile copolymer, a styrene-maleic acid copolymer, an acrylic polymer, and a styrene-acrylic resin. Copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester, polyamide, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone resin Thermoplastic resins such as polyether resins, silicone resins, epoxy resins, phenol resins, urea resins, melamine resins, unsaturated polyesters, alkyd resins, polyurethanes, other cross-linkable thermosetting resins, and epoxy resins. Relate, urethane - like photocurable resin such as acrylate. Resins other than these polyvinyl butyral resins can be used alone or in combination of two or more.

(2) Charge generator As the charge generator that can be used in the present invention, for example, metal-free phthalocyanine, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, titanyl phthalocyanine (for example, α-titanyl phthalocyanine, Y-titanyl phthalocyanine), V -Phthalocyanine pigments such as hydroxygallium phthalocyanine, perylene pigments, bisazo pigments, diketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, trisazo pigments, indigo pigments, azurenium pigments, cyanine pigments, Organic photoconductors such as pyrylium pigments, ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments, selenium, - tellurium, selenium - arsenic, cadmium sulfide, an inorganic photoconductive material and the like such as amorphous silicon. Of course, these charge generating agents may be used alone or in combination of two or more.

  In particular, phthalocyanine-based pigments, particularly metal-free phthalocyanine, titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine are used as a charge generator. It is preferable in terms of electrical characteristics of the photoreceptor when used as an exposure light source.

  In particular, in the present invention, it is preferable to contain titanyl phthalocyanine as a charge generator. In the present invention, specific examples of the charge generating agent include Y-type titanyl phthalocyanine, titanyl phthalocyanine having a maximum peak at a Bragg angle 2θ ± 0.2 ° = 27.2 ° in a CuKα characteristic X-ray diffraction spectrum; And titanyl phthalocyanine described in JP-A-175382. When titanyl phthalocyanine is used as a charge generating agent for the charge generating layer, a highly sensitive laminated electrophotographic photosensitive member can be obtained.

(3) Other components In the charge generation layer, other components such as antioxidants, radical scavengers, singlet quenchers, ultraviolet absorbers, softening agents, etc., as long as they do not adversely affect image formation. Agents, plasticizers, surface modifiers, extenders, thickeners, dispersion stabilizers, waxes, acceptors, donors, dispersion media, and the like. In order to improve sensitivity, for example, known sensitizers such as terphenyl, halonaphthoquinones, and acenaphthylene may be used in combination with the charge generator.

  When preparing the charge generation layer, a solvent may be used. Examples of the solvent herein include alcohols (methanol, ethanol, isopropyl alcohol, etc.), ethers (tetrahydrofuran, dioxane, etc.), ketones (acetone, methyl ethyl ketone, cyclohexanone, etc.), esters (ethyl acetate, butyl acetate, etc.) ), Aromatic hydrocarbons (benzene, toluene, xylene, etc.).

  The thickness of the charge generation layer after drying is 0.05 to 5 μm, preferably 0.1 to 3 μm. In the charge generation layer, the charge generation agent may be contained in an amount of 5 to 1000 parts by mass, preferably 30 to 500 parts by mass with respect to 100 parts by mass of the binder resin.

<Preparation of charge transport layer>
The charge transport layer contains components such as a charge transport agent and a binder resin.

(A) Charge transport agent Examples of the charge transport agent include diphenoquinone derivatives, benzoquinone derivatives, naphthoquinone derivatives, anthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, thioxanthone derivatives (2,4,8-trinitrothioxanthone, etc.), fluorenone derivatives (3 , 4,5,7-tetranitro-9-fluorenone derivative, etc.), anthracene derivative, acridine derivative, dinitrobenzene, dinitroanthracene, dinitroacridine, succinic anhydride derivative, maleic anhydride derivative, dibromomaleic anhydride derivative, etc. Examples thereof include compounds having acceptability.

  A hole transporting agent can also be used as the charge transporting agent. Examples of such hole transporting agents include stilbene compounds (HT-1 and the like), N, N, N ′, N′-tetraphenylbenzidine derivatives, N, N, N ′, N′-tetraphenylphenylenediamine. Derivatives, N, N, N ′, N′-tetraphenylnaphthylenediamine derivatives, N, N, N ′, N′-tetraphenylphenanthrylenediamine derivatives, 2,5-di (4-methylaminophenyl)- Oxadiazole compounds such as 1,3,4-oxadiazole, styryl compounds such as 9- (4-diethylaminostyryl) anthracene, carbazole compounds such as polyvinylcarbazole, organic polysilane compounds, 1-phenyl-3- Pyrazoline compounds such as (p-dimethylaminophenyl) pyrazoline, hydrazone compounds, indoles Compounds, oxazole compounds, isoxazole compounds, thiazole compounds, Chiajizoru compounds, imidazole compounds, pyrazole compounds, and nitrogen-containing cyclic compounds, such as triazole compounds, and condensed polycyclic Conductor compound.

(B) Binder resin As the binder resin of the charge transport layer, for example, polycarbonate resin, polyester, polyarylate, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, polyethylene, polypropylene, Alkyd resin, polyamide, polyurethane, polyvinyl butyral, phenol resin, melamine resin and the like can be mentioned. In particular, in the present invention, it is preferable to use a Z-type polycarbonate resin as the binder resin of the charge transport layer.

(C) Other components Tetrohydrofuran, polyester, or the like may be added to the charge transport layer as other components. In addition, for example, an antioxidant, a radical scavenger, a singlet quencher, an anti-degradation agent such as an ultraviolet absorber, a softener, a plasticizer, a surface modifier, an extender, an increase agent, as long as it does not adversely affect image formation. You may add a sticking agent, a dispersion stabilizer, a wax, an acceptor, a donor, etc.

  A solvent may be used when forming the charge transport layer. Examples of the solvent herein include aromatic hydrocarbons (such as ethers such as tetrahydrofuran and dioxane, benzene, toluene, and xylene), halogenated solvents (such as dichloromethane and 1,2-dichloroethane), and ketones ( Acetone, methyl ethyl ketone, cyclohexanone, etc.), esters (ethyl acetate, butyl acetate, etc.), aprotic polar solvents (N, N-dimethylformamide, dimethyl sulfoxide, etc.).

  The film thickness of the charge transport layer after drying is 2 to 100 μm, preferably 5 to 50 μm. In the charge transport layer, the electron transport agent may be contained in an amount of 10 to 500 parts by mass, preferably 30 to 200 parts by mass with respect to 100 parts by mass of the binder resin. Moreover, when using together an electron transport agent and a hole transport agent, the total amount is 10-500 mass parts with respect to 100 mass parts of binder resin, Preferably it is good to make it contain in the ratio of 30-200 mass parts.

<Conductive substrate>
The conductive substrate usable in the present invention is not particularly limited as long as it is a conductive material. For example, iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel Examples thereof include simple metals such as palladium, indium, stainless steel and brass, plastic materials on which the metal is vapor-deposited or laminated, and glass coated with aluminum iodide, tin oxide, indium oxide and the like. The conductive substrate is used in the form of a drum or a sheet according to the structure of the image forming apparatus to be used. In addition, it is preferable that this electroconductive base | substrate has sufficient mechanical strength.

<Preparation of multilayer photoconductor>
In the present invention, the multilayer photoconductor is formed by laminating a charge transport layer containing a charge transport agent and a charge generation layer containing a charge generator on a conductive substrate directly or via an intermediate layer. Composed. Further, a photoconductive layer containing a charge transporting agent together with a charge generating agent may be combined with a charge transporting layer and a charge generating layer.

  Examples of materials that can be used for the intermediate layer between the multilayer photoreceptor and the conductive substrate include, for example, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl butyral, an aluminum anodic oxide film, polyacrylic acid, celluloses, and N-methoxymethyl. Nylon gelatin, starch, polyurethane, polyamide, polyimide, casein and the like. Then, particles of titanium oxide, tin oxide, and aluminum oxide may be dispersed in these materials. Furthermore, alcohol (methanol, ethanol, isopropyl alcohol, etc.) may be used as the dispersion medium.

  In addition, an intermediate layer, a barrier layer, or the like may be formed between the charge generation layer and the charge transport layer constituting the multilayer photoconductor as long as the characteristics of the photoconductor are not impaired. A protective layer may be formed on the surface of the photosensitive layer.

  A laminated type photoconductor is prepared by mixing a charge generating agent and a charge transporting agent together with an appropriate binder resin and solvent using a roll mill, ball mill, attritor, paint shaker, ultrasonic disperser, etc. The dispersion may be applied on a conductive substrate by a known means and dried.

  EXAMPLES Hereinafter, the laminated electrophotographic photosensitive member of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited only to the following examples.

[Examples 1-9 and Comparative Examples 1-7]
An electrophotographic photoreceptor was prepared by the following method.

<Preparation of intermediate layer>
Using 100 parts by weight of alcohol-soluble polyamide resin (Toray CM-8000) as the binder resin of the intermediate layer, 100 parts by weight of titanium oxide (TA-300 manufactured by Fuji Titanium Industry) as the pigment, and 1000 parts by weight of methanol as the dispersion medium, The mixture was mixed and dispersed in a ball mill (zirconia beads having a diameter of 1 mm) for 24 hours to prepare a coating solution for the intermediate layer. Next, the coating solution was applied onto a conductive substrate (aluminum base tube having an outer diameter of 30 mm) using a fluororesin blade, and then dried at 130 ° C. for 30 minutes. Thereby, an intermediate layer having an average film thickness of 5 μm was formed.

<Preparation of charge generation layer>
First, 1 part by weight of Y-type titanyl phthalocyanine as a pigment was added to 39 parts by weight of isopropyl alcohol as a dispersion medium and dispersed by an ultrasonic disperser to obtain a primary dispersion for a charge generation layer. Next, the polyvinyl butyral resin shown in Table 1 (Esreck B / K (KS) manufactured by Sekisui Chemical Co., Ltd.) was dissolved in 6 parts by weight of isopropyl alcohol at the ratio shown in Tables 2 and 3 to generate charges. A layer resin solution was obtained. In addition, the polyvinyl butyral resin dissolved here is 1 weight part in total. And the compounding ratio of the resins 1-6 shown in Table 2 and Table 3 has shown the content (weight%) with respect to the binder resin whole quantity of a charge generation layer. The structural formula of Y-type titanyl phthalocyanine is shown in the following formula (II).

  Next, the charge generation layer coating solution was prepared by adding the charge generation layer resin solution to the charge generation layer primary dispersion and then performing secondary dispersion again using an ultrasonic disperser. Next, using a fluororesin blade, the charge generation layer coating solution was applied onto the intermediate layer and dried at 110 ° C. for 5 minutes. As a result, a charge generation layer having an average film thickness of 0.5 μm was obtained.

<Preparation of charge transport layer>
First, 80 parts by weight of a hole transporting agent (a stilbene compound represented by the following formula (III)) is added to 200 parts by weight of tetrohydrofuran and dispersed by an ultrasonic disperser. Obtained. Next, 90 parts by weight of Z-type polycarbonate (Panlite TS2050 manufactured by Teijin Kasei Co., Ltd.) and 10 parts by weight of polyester E1 (Toyobo Byron 200) are dissolved in 600 parts by weight of tetrahydrofuran as a binder resin for use in the charge transport layer. A resin liquid was obtained. Next, the charge transport layer resin solution was added to the primary charge transport layer dispersion and dispersed again using an ultrasonic disperser to obtain a charge transport layer coating solution. Then, using a fluororesin blade, this charge transport layer coating solution was applied to the charge generation layer and dried at 110 ° C. for 30 minutes. As a result, a charge transport layer having a thickness of 30 μm was formed on the charge generation layer to produce a multilayer electrophotographic photoreceptor.

<Evaluation test>
The laminated electrophotographic photoreceptors obtained in Examples 1 to 9 and Comparative Examples 1 to 7 were mounted on a commercially available laser printer (LBP-450: manufactured by Canon Inc.), and normal temperature and humidity (20 ° C., An evaluation test was performed at a relative humidity of 65% and high temperature and high humidity (32.5 ° C., relative humidity of 80%). Specifically, using A4 size paper, the charging potential (potential corresponding to the white portion of the document at the development position) and sensitivity after the initial (before printing) and 1000 sheets printing and sensitivity (black of the document at the development position). Solid portion potential) was measured.

  Table 4 shows the measurement results when the laminated electrophotographic photosensitive members of Examples 1 to 9 are used, and Table 5 shows the measurement results when the laminated electrophotographic photosensitive members of Comparative Examples 1 to 7 are used. In Tables 4 and 5, “N / N” indicates a test result under normal temperature and normal humidity (20 ° C., relative humidity 65%), and “H / H” indicates high temperature and high humidity (32. 5 shows that the test results were obtained under a relative humidity of 80%. In Tables 4 and 5, “sensitivity difference” shows the result of subtracting the initial sensitivity value from the post-printing sensitivity value, and “charging difference” subtracts the initial charging value from the post-printing charging value. The results are shown.

  As shown in Table 5, in Comparative Examples 1 to 3 and Comparative Example 5, only a polyvinyl butyral resin having a butyralization degree of 60 mol% or more and less than 70 mol% (polyvinyl butyral resin having a hydroxyl group content of 30 mol% or more) is used. Or 90% by weight or more of such a resin, it can be seen that the sensitivity is lowered under high temperature and high humidity.

  In Comparative Example 4 and Comparative Examples 6 to 7, only a polyvinyl butyral resin having a butyralization degree of 70 mol% or more (polyvinyl butyral resin having a hydroxyl group content of less than 30 mol%) is used, or such a resin. Since 70% by weight or more is used, it can be seen that the value of the surface potential in the initial stage (before printing) is large and the sensitivity is lowered.

On the other hand, according to Table 4, in Examples 1 to 9, the surface potential value (sensitivity value) is relatively small and high sensitivity under any conditions of normal temperature and normal humidity and high temperature and high humidity. I understand. It can also be seen that the value of the sensitivity difference is small, and the degree to which the sensitivity decreases after printing is small. Further, regarding the charging value, the difference in value before and after printing is small under both normal temperature and normal humidity and high temperature and high humidity conditions, and the multilayer electrophotographic photosensitive member of the present invention has repeated stability. I understand that it is expensive.

Claims (3)

A laminated electrophotographic photosensitive member in which at least a charge generation layer and a charge transport layer are provided on a conductive substrate,
A laminate type electrophotographic photosensitive material containing the following resins (A) and (B) as binder resins for the charge generation layer in the following amounts with respect to the total amount of the binder resin for the charge generation layer: body.
(A) Polyvinyl butyral resin having a butyralization degree of 60 mol% or more and less than 70 mol%: 40% by weight or more and 80% by weight or less (B) Polyvinyl butyral resin having a butyralization degree of 70 mol% or more: 20% by weight or more and 60% by weight or less A laminated electrophotographic photosensitive member in which at least a charge generation layer and a charge transport layer are provided on a conductive substrate,
A multilayer electrophotographic photosensitive film containing the following resins (C) and (D) as the binder resin of the charge generation layer in the following amounts relative to the total amount of the binder resin of the charge generation layer: body.
(C) Polyvinyl butyral resin having a hydroxyl group content of 30 mol% or more: 40 wt% or more and 80 wt% or less (D) Polyvinyl butyral resin having a hydroxyl group content of less than 30 mol%: 20 wt% or more and 60 wt% or less 2. The charge generation layer contains titanyl phthalocyanine having a maximum peak at a Bragg angle 2θ ± 0.2 ° = 27.2 ° in a CuKα characteristic X-ray diffraction spectrum as a charge generation agent. Or a multilayer electrophotographic photosensitive member according to 2;