JP4815237B2 - Intermediate transfer belt and image forming apparatus using the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate transfer belt and an image forming apparatus using the same, and more particularly, a carbon black film forming solution excellent in carbon black dispersibility, and an intermediate transfer belt and an image forming apparatus molded using the carbon black film forming solution. About.

  Conventionally, in order to produce an endless belt having uniform and stable electrical characteristics, a carbon black dispersion liquid in which carbon black is dispersed in a dispersion medium is prepared, and a resin varnish is further added to form a film forming liquid. . In particular, an endless belt is obtained by centrifugal molding using polyimide as a resin varnish. The most important characteristics of this belt are electrical characteristics and mechanical characteristics, and it is required to control the film to be semiconductive or to improve the belt strength and flexibility. Therefore, a method for optimizing important characteristics such as specific surface area, oil supply amount, and volatile content of carbon black has been proposed (see, for example, Patent Document 1).

  Further, a method for defining an index defined by the oil absorption amount and the volatile content has been proposed (see, for example, Patent Document 2).

Furthermore, a technique for making carbon black very fine and improving dispersibility is also known (see, for example, Patent Document 3).
JP 2001-131410 A JP 2001-152013 A JP 2004-279531 A

  However, even when these known techniques are used, the characteristics of the intermediate transfer belt are not sufficiently improved.

  The present invention has been made in view of the above-described circumstances, and pays attention to the difference between the volume average particle size of carbon black in the carbon black dispersion and the volume average particle size of the carbon black-dispersed polyimide film-forming solution. Is controlled within ± 0.1μm, the affinity between carbon black and polyimide is excellent, and the electrical and mechanical properties of the intermediate transfer belt can be improved, which makes it possible to improve the uniformity of the electrical properties, as well as the belt strength and flexibility. It is an object of the present invention to provide a transfer belt and a high-quality image forming apparatus equipped with the intermediate transfer belt.

  In order to solve the above-mentioned problems, the invention according to claim 1 is directed to an image forming apparatus manufactured by a centrifugal molding method by diluting a carbon black dispersion comprising surface-treated carbon black, a dispersant and a solvent with a solvent. The intermediate transfer belt is characterized by a polyimide intermediate transfer belt in which the volume average particle size difference between carbon black before and after the dilution is within 0.1 μm.

  The invention according to claim 2 is characterized in that the polyimide intermediate transfer belt is characterized in that the number of bendings measured with an MIT testing machine exceeds 1000 and the elastic modulus is 4 GPa or more. And

  The invention described in claim 3 includes at least a charging device that forms an electrostatic latent image on the image carrier, a developing device that forms a toner image on the image carrier using a developer corresponding to each color, and An intermediate transfer device that sequentially superimposes and temporarily transfers the toner image on an endless intermediate transfer belt, and temporarily transfers the temporary transfer image on the intermediate transfer belt to a transfer material; and the transfer material An image forming apparatus having a fixing device for fixing the toner image on the transfer material by heating or pressurizing the upper toner image, wherein the intermediate transfer belt is an intermediate transfer belt according to claim 1. To do.

  According to the present invention, in an intermediate transfer belt of an image forming apparatus for producing a carbon black dispersion comprising surface-treated carbon black, a dispersant, and a solvent by diluting the solvent with a solvent, and before and after the dilution. The difference in the volume average particle size of carbon black is 0.1 μm or less. Due to the polyimide intermediate transfer belt, the difference in volume average particle size of carbon black before and after dilution with a solvent is very small within ± 0.1 μm. Therefore, the affinity between carbon black and polyimide is excellent, and as a result, the uniformity of electrical characteristics and mechanical characteristics of the intermediate transfer belt can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The carbon black film forming liquid for molding the intermediate transfer belt of the present invention is composed of carbon black, polyimide, and a dispersion medium. Each constituent material will be described.

1. Carbon black The carbon black used for the intermediate transfer belt of the present invention is an aggregate of fine particles obtained by incomplete combustion of various hydrocarbons or compounds containing carbon, and has a chemical composition of 98% or more of carbon. It is a general term for carbon materials close to pure carbon.

  The types of carbon black are generally classified according to the production method as shown in Table 1, and are roughly divided into the pyrolysis method of raw material hydrocarbons and the incomplete combustion method (see Table 1). Is subdivided. The contact method classified as an incomplete combustion method is a manufacturing method in which a flame is brought into contact with iron or stone, and the contact method includes a channel method or a gas black method (roller method) which is an improved method thereof. The channel black is a representative product of the contact method, and is collected by bringing a flame into contact with the bottom surface of the channel steel.

  The furnace method is a method in which a raw material hydrocarbon is continuously pyrolyzed by combustion heat of fuel and air to generate carbon black, and the furnace method is classified into a gas furnace method and an oil furnace method.

  The thermal method is a special production method in which natural gas is used as a raw material carbon source and combustion and thermal decomposition are repeated periodically. The feature is that carbon black having a large particle size can be obtained.

  Acetylene black is a kind of thermal process that uses acetylene as a raw material. However, the thermal decomposition of acetylene is an exothermic reaction while other raw materials are endothermic, so it is possible to omit the combustion cycle in the thermal process. This is because continuous operation is possible. The characteristics of acetylene black are that it develops crystallinity compared to ordinary carbon black and has a high structure, so it has excellent conductivity, and is used as a conductivity-imparting agent for dry batteries and various rubbers and plastics. Yes.

Table 1 is a classification according to the manufacturing method of carbon black.
(1) Basic characteristics of carbon Important factors when carbon black is blended and dispersed in rubber, resin, paint and ink vehicles to impart functions such as reinforcement, blackness, and conductivity are the particle size and particle size. These are the physicochemical properties of the structure and the particle surface, and these are usually called the three major characteristics of carbon black, and various carbon blacks are produced with combinations of various ranges of these characteristic values.

The above three basic characteristics of carbon black are represented by the following numerical values in the following (i), (ii), and (iii).
(I) Particle size: Particle size and surface area (ii) Structure: DBP oil supply (ml / 100 g) and structure index (iii) Surface chemical properties: Volatile content (%) and pH

(2) Physical characteristics of carbon black (i) Structure of carbon black particles Carbon black particles have a network plane structure in which the minimum unit of the particles is 30 to 40 bonded with a carbon six-membered ring as a network. Crystal particles stacked at almost equal intervals (3.5 to 3.9 mm) by the Van der Waals force, concentrically and densely arranged near the particle surface, but the arrangement is internal (bulk) It becomes irregular as it goes. Such a feature is more conspicuous as fine particles, and thermal black having large particles maintains a regular orientation state almost to the center. A structure in which 1,000 to 2,000 crystal particles are aggregated to form one primary particle, and these particles are chemically and physically bonded is called a structure.

(Ii) Particle size and distribution of carbon black The carbon black particles exist in a state where the particles are fused together like a skewered dumpling, and each spherical particle characterizes a mountain and valley of dumplings and dumplings. However, the particle diameter in which this is regarded as a single particle is closely related to performance in various applications, such as reinforcement and blackness.

(Iii) Agglomerates of carbon black and their distribution As described above, the carbon black particles form an agglomerate structure that can be described in a dumpling or a bunch of grapes, which is called a structure. Depending on the degree of agglomeration, it is classified into a high (high), normal (medium), and low (low) structure. When blended with rubber, tensile stress and extrusion characteristics, when blended with ink and paint vehicles and resins. It is an important factor having a great influence on dispersibility, blackness, viscosity, conductivity, and the like.

  In the structure, condensed polycyclic aromatic hydrocarbons produced through complex chemical reactions in a production furnace at 1,400 ° C. or higher are condensed into fine droplets, forming a precursor as a nucleus and colliding with each other. It is thought that it was formed by fusion and solidification. The structure can be controlled by selecting the shape of the furnace and the dynamic thermodynamic conditions in the furnace. For example, a technique of adding a trace amount of an alkali metal salt is effective.

  The structure is measured by the amount of oil supply, compression void ratio, bulk density, morphological analysis of electron microscope images, etc., but the most commonly used oil supply amount is more entangled with each other, that is, the higher the high structure carbon black. This is an application of the phenomenon of absorbing oil of oil, which was once determined by the hand-kneading method using linseed oil, but is now obtained by measurement with a DBP (Dibutyl Phtalate) absorber meter that mechanizes the same principle. It is the mainstream to evaluate with numerical values.

(Iv) Specific surface area and non-porous specific surface area of carbon black The specific surface area of carbon black is almost determined by the size of a single particle, but as with other solids, it has an interaction with other substances on the surface, so it is extremely One of the important characteristics. It is considered that pores are generally present on the surface of carbon black, and fine voids are present in the fused part between the particles, and when the specific surface area is measured, the value obtained depends on the measurement principle. It is necessary to clearly distinguish whether or not it includes the surface area in the pores. Those including the surface area in the pores are referred to as the total specific surface area, and those excluding the surface area in the pores are referred to as the non-porous specific surface area. In general, the specific surface area is measured by a low-temperature nitrogen adsorption method or iodine adsorption method using the BET equation, and the non-porous specific surface area is a CTAB adsorption method, an electron microscope, a “t” method, or the like.

(3) Chemical characteristics of carbon black (i) Element composition and impurities Carbon black contains a small amount of oxygen, hydrogen, sulfur, ash and the like. Hydrogen is contained as a residue in the dehydrogenation reaction during the carbonization process of the hydrocarbon, which is the raw material, sulfur is caused by the raw material oil and fuel oil, and ash is also contained in the raw material oil and water for cooling. It is caused. On the other hand, oxygen includes basic oxides that are bonded by contact with air after the formation of carbon black particles, and acidic oxides that are secondarily generated by reaction with nitrogen dioxide, ozone, nitric acid, etc. Is considered to exist on the particle surface.

  Sulfur exists in both chemically bound and free forms, free sulfur can be extracted with solvents and aqueous alkali sulfides, while bound sulfur is completely intact even at high temperatures of 1,000 ° C. It is said that it will not leave. The composition of the ash is sodium, magnesium chloride and sulfate, calcium carbonate, iron oxide, silica, etc., and the compound is furnace black (carbon black by furnace method) rather than channel black (carbon black by channel method). ) Tend to be more.

(Ii) Surface Functional Groups Most of the chemical reactivity of carbon black is derived from chemical functional groups known as surface oxides and active hydrogen. It is generally said that the functional group of the acidic oxide is a carboxyl group, a hydroxyl group, a quinone group, or a lactone group, and these are often represented by volatile composition, volatile content, pH, and the like.

  Any of the above-mentioned types of carbon black can be used as the carbon black used in the carbon black film forming solution used in the present invention. Moreover, the carbon black used for the carbon black film-forming solution used in the present invention can be surface-treated as necessary.

(4) Carbon black treatment method The carbon black treatment method will be described below. The surface of carbon black particles has a condensed aromatic ring and can be subjected to various surface treatments described below.

(I) Surface oxidation treatment When carbon black is surface treated with an oxidizing agent, a carboxyl group or a phenolic hydroxyl group is introduced into the condensed aromatic ring on the surface of the carbon black particles. Furthermore, the condensed aromatic ring on the surface of carbon black reacts with the following various reagents as shown in Reaction Formula 1, and various functional groups can be introduced onto the particle surface.

(Ii) Surfactant dispersion Carbon black can be dispersed with a normal anionic surfactant, nonionic surfactant, cationic surfactant, amphoteric surfactant, and the like. Preferred surfactants include interfacial polyoxyethylene alkyl ether acetates, dialkyl sulfosuccinates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polyoxypropylene block copolymers, and acetylene glycol surfactants. Agents.

(Iii) Polymer (resin) dispersion Carbon black can be dispersed by steric hindrance repulsion of the polymer dispersant. Examples of the polymer dispersant usable for such polymer dispersion include poly (N-vinyl-2-pyrrolidone), poly (N, N′-diethylacrylazide), poly (N-vinylformamide), and poly (N-vinylformamide). (N-vinylacetamide), poly (N-vinylphthalamide), poly (N-vinylsuccinamide), poly (N-vinylurea), poly (N-vinylpiperidone), poly (N-vinylcaprolactam), Examples thereof include poly (N-vinyloxazoline), and a single or a plurality of polymer dispersants can be added. In addition to this, within the scope of the object of the present invention, a polymer material, a surfactant, and a dispersion stabilizer for inorganic salt damage can be used.

(Iv) Encapsulation treatment Carbon black is coated with a resin and dispersed in a solvent. Alternatively, a resin in which carbon black is impregnated, that is, a resin in which carbon black is present on the surface layer, inside, or the entire surface. Its characteristics can improve properties such as dispersion stability, surface wettability, rheological properties and electrical properties. In particular, with regard to dispersion stability, the dispersibility of the graft chain in a good solvent (easily dispersible in the dispersion medium and stability after dispersion) is remarkably improved, and in terms of electrical properties, the carbon black particles are polymer matrix. Since it is easily and uniformly dispersed in the inside, there is a feature that a constant resistance value can be obtained over a wide area.

(V) Grafting treatment The grafting treatment of carbon black can be classified as follows based on the grafting mechanism.

(A) Graft polymerization on the surface of carbon black In this method, a vinyl monomer is polymerized using a polymerization initiator in the presence of carbon black, and the growing polymer chain generated in the system is captured on the surface of the carbon black particles. .

(B) Graft polymerization from the carbon black surface This is a method of growing a graft chain from a polymerization initiating group introduced into the carbon black surface.

(C) Graft reaction between carbon black surface and polymer This is a method based on a reaction between a functional group on the carbon black surface and a reactive polymer.

  Among these, the method (a) can be most easily performed, but since a non-graft polymer is predominantly produced, a product having a large graft ratio cannot be obtained. On the other hand, in the method (b), the polymer (graft chain) grows outward from the surface of the carbon black, so that a polymer having a high graft rate can be obtained. Furthermore, according to the method (c), the molecular weight and number of graft chains can be controlled, and a graft having a relatively high graft ratio can be obtained.

(Vi) Gas Phase Oxidation Method This is a method for oxidizing the surface of carbon black by gas phase such as ozone treatment or plasma treatment. By irradiating the carbon black with plasma and bringing it into contact with high energy of plasma or ozone, hydroxyl or This is a method of introducing a carboxyl group.

  Next, a typical carbon black film forming process will be described.

  As step A, initial step A is performed in which a pigment, vehicle, and solvent are premixed (premixed) and then main dispersed (kneaded dispersed) to obtain a carbon black dispersion.

  Next, as Step B, Step B is performed in which the carbon black dispersion obtained in Step A is diluted and adjusted to obtain a film forming solution.

  Below, these processes A and B are further demonstrated.

a. Pre-mixing process (premixing)
It is the optimum mixing composition for applying to the main disperser in the next step, and is the step of producing paste in the optimum flow state. The vehicle is infiltrated into the carbon black particle aggregate to completely wet the surface, and the coarse particle aggregate is This is a process performed for crushing.

b. Main dispersion process (grinding dispersion)
This is a process in which particle aggregates wetted with a vehicle are dispersed by impact energy or shear energy to a particle size required for a film-forming solution. Carbon black is dispersed until it is close to an aggregate (aggregate). In this step, the resin component in the vehicle is adsorbed on the surface.

c. Dilution adjustment process (let down)
It is a process of adding a necessary amount of resin (polyimide), solvent and additives to a high pigment concentration paste and adjusting the dilution until the desired viscosity and composition are obtained. Various resin solutions and solvents are added to the paste with a high pigment concentration. Since it is added, it is a step in which the pigment is diluted so as not to cause re-aggregation by adjusting the addition speed, order, temperature, stirring conditions and the like.

  As the dispersing device, various dispersers are used for reasons such as the viscosity of the dispersion, the evaporation of the solvent, the production method, or the final dispersed particle size. The main dispersers are listed below.

  a. Kneading type: kneader, planetary mixer, etc .; the greater the viscosity of the raw material, the greater the shear stress that is generated, so it is widely used for kneading hard pastes.

  b. Compression shear type: 3-roll mill, 2-roll mill; Dispersing machine that applies a large shear stress while applying pressure to the gap between rollers. It is applied to high viscosity (up to about 1,000 Pa · s) and high adhesive strength. ing.

  c. Stir mixing type: colloid mill, Kady Mill, etc .; an impeller rotating at a high peripheral speed (300 to 1,200 m / min) gives a high shear rate.

d. Grinding shear type: bead mill, ball mill, etc .; disperser that disperses by impact and shear stress of balls and beads. Shear stress of about 10 ² to 10 ³ Pa is applied to the ball mill and 10 ⁴ to 10 ⁵ Pa is applied to the bead mill. . Both bead mills and ball mills are used to disperse volatile low-viscosity materials (possible up to several Pa · s).

2. Polyimide Next, polyimide will be described. The polyimide is generally obtained by a condensation reaction between an aromatic polyvalent carboxylic acid anhydride or a derivative thereof and an aromatic diamine. Because it has insoluble and infusible properties due to its rigid main chain structure, a polyamic acid (or polyamic acid or polyimide precursor) soluble in an organic solvent is first synthesized from an acid anhydride and an aromatic diamine. Molding is performed by various methods, and then polyimide is obtained by dehydration cyclization (imidization) by heating or a chemical method (see Chemical Reaction Formula 2).

(In the formula, Ar ¹ represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, and Ar ² represents a divalent aromatic residue containing at least one carbon 6-membered ring.) Examples of the aliphatic polycarboxylic acid anhydride include ethylene tetracarboxylic dianhydride, cyclopentane tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetra Carboxylic dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) Sulfonic dianhydride 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, 2 , 2-bis (3,4-dicarboxylphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, , 4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4 , 9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, and the like. These may be used alone or in admixture of two or more.

  Examples of the aromatic diamine (diamine component) that can be used include m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 4,4′-diaminodiphenyl ether, 3 , 3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, bis (3-aminophenyl) sulfide, (3-aminophenyl) (4-aminophenyl) sulfide, bis (4-aminophenyl) sulfide, bis (3 -Aminophenyl) sulfide, (3-aminophenyl) (4-aminophenyl) sulfoxide, bis (3-aminophenyl) sulfone, (3-aminophenyl) (4-aminophenyl) sulfone, bis (4-aminophenyl) Sulfone, 3,3′-dia Nobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis [4- (3- Aminophenoxy) phenyl] methane, bis [4- (4-aminophenoxy) phenyl] methane, 1,1-bis [4- (3-aminophenoxy) phenyl] ethane, 1,1-bis [4- (4- Aminophenoxy) phenyl] -ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane, 2,2-bis [ 4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, , 2-bis [4- (3-aminophenoxy) phenyl] butane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3-bis (3-aminophenoxy) benzene, 1,3- Bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (3-aminophenoxy) biphenyl, 4 , 4′-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3- Aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfoxide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) ) Phenyl] ether, 1,4-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 4,4′-bis [3- (4-Aminophenoxy) benzoyl] diphenyl ether, 4,4′-bis [3- (3-aminophenyl) Noxy) benzoyl] diphenyl ether, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethyl) Benzyl) phenoxy] diphenylsulfone, bis [4- {4- (4-aminophenoxy) phenoxy} phenyl] sulfone, 1,4-bis [4- (4-aminophenoxy) phenoxy] -α, α-dimethylbenzyl] Examples include benzene, 1,3-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene. These are used alone or in admixture of two or more.

  A polyimide precursor (polyamic acid) can be obtained by polymerizing the aromatic polyvalent carboxylic acid anhydride component and the diamine component in a substantially equimolar organic polar solvent. The manufacturing method of a polyamic acid is demonstrated concretely.

  Examples of the organic polar solvent used in the polymerization reaction of polyamic acid include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide, formamide solvents such as N, N-dimethylformamide and N, N-diethylformamide, and N, N. -Acetamide solvents such as dimethylacetamide, N, N-diethylacetamide, pyrrolidone solvents such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, phenol, o-, m-, or p-cresol, Phenolic solvents such as xylenol, halogenated phenol and catechol; ether solvents such as tetrahydrofuran, dioxane and dioxolane; alcohol solvents such as methanol, ethanol and butanol; cellosolve such as butyl cellosolve or hexamethyl Phosphoramides, .gamma.-butyrolactone, etc. can be mentioned, it is desirable to use these as the sole or mixed solvent. The solvent is not particularly limited as long as it dissolves polyamic acid, but N, N-dimethylacetamide and N-methyl-2-pyrrolidone are particularly preferable.

  First, 1 type or multiple types of diamine is melt | dissolved in said organic solvent, or is diffused in slurry form in inert gas atmosphere, such as argon and nitrogen. When at least one aromatic polycarboxylic acid anhydride or derivative thereof is added to this solution in a solid state, an organic solvent solution state or a slurry state, a ring-opening polyaddition reaction occurs with heat generation. The viscosity of the polymerization solution is rapidly increased to obtain a high molecular weight polyamic acid solution. The reaction temperature at this time is −20 ° C. to 100 ° C., preferably 60 ° C. or less. The reaction time ranges from 30 minutes to 12 hours.

  In this reaction, contrary to the addition procedure, first, the aromatic polycarboxylic anhydride or derivative thereof is first dissolved or diffused in an organic solvent, and the solution or slurry of the diamine solid or organic solvent in this solution. May be added. Moreover, you may make it react simultaneously, and the mixing order of an acid dianhydride component and a diamine component is not limited.

  The above aromatic polycarboxylic acid anhydride or derivative thereof and the aromatic diamine component are weighed approximately equimolarly and dissolved in the organic polar solvent. In the present invention, the order of adding the aromatic tetracarboxylic dianhydride and the aromatic diamine is not limited. They may be added simultaneously, or an organic polar solvent in which each is dissolved may be mixed in an equimolar amount.

  As described above, the polyamic acid composition according to the present invention is obtained by subjecting an aromatic polyvalent carboxylic acid anhydride or a derivative thereof and an aromatic diamine component to an equimolar amount by a polymerization reaction in an organic polar solvent. A polyamic acid solution in which the product is uniformly dissolved in the organic polar solvent is obtained.

  Although these polyamic acid compositions can be easily synthesized as described above, it is easy to obtain a commercially available polyimide varnish in which the polyamic acid composition is dissolved in an organic solvent. Is possible. For example, Trenys (manufactured by Toray Industries, Inc.), U-Varnish (manufactured by Ube Industries, Ltd.), Rika Coat (manufactured by Shin Nippon Chemical Co., Ltd.), Optmer (manufactured by JSR), SE812 (manufactured by Nissan Chemical Industries), CRC8000 (manufactured by Sumitomo Bakelite) Etc. can be mentioned representatively.

3. Next, the dispersion medium used in the present invention will be described. As the dispersion medium used in the present invention, those used as a solvent for polyamic acid can be preferably used. Examples include amide solvents such as NMP (N-methylpyrrolidone), DMF (N, N-dimethylformamide), DMAc (N, N-dimethylacetamide), polyamic acids such as γ-butyrolactone, and polyimide resins. Dipolar solvents, ethyl lactate, methoxymethyl propionate, propylene glycol monomethyl ether acetate, etc. used are used, and the amount used is controlled so as to have a necessary solid content and viscosity. Of these, NMP (N-methyl-2-pyrrolidone) is most preferred.

  Here, a method for manufacturing the intermediate transfer endless belt will be described. A typical method for producing a belt substrate using the polyimide resin film of the present invention is a centrifugal molding method. This is because a raw material solution (hereinafter sometimes referred to as coating solution) as a belt material is poured from a spray or nozzle into a cylindrical mold that rotates a resin solution dissolved in a solvent, and this mold is rotated at high speed. However, the method of producing an endless belt by a method of forming an endless shaped body by expanding the coating liquid by the centrifugal force and solidifying the film as a uniform film (so-called centrifugal molding method), according to this method, Since the applied coating solution is expanded by centrifugal force, a coating layer having a relatively uniform thickness is easily obtained.

  In this belt formation by centrifugal molding, after applying a fluid coating solution to the inner surface of a cylindrical mold, it is rotated by a high-speed centrifugal force to make the film thickness uniform, and the surface energy of aggregation of the coating solution is obtained. The coating film is spread and spread with a force to overcome, and the film is made uniform. The coating solution is prepared by diluting the raw material varnish with a solvent to the mold. Therefore, the coating solution is uniformly applied to the inner surface of the mold when rotating at high speed, but gradually accumulates at the bottom of the mold when the rotation is stopped or the rotational speed is reduced. Therefore, according to this centrifugal molding method, the solvent must be removed and solidified while maintaining the state of a uniform solution film.

  The intermediate transfer belt molded using the carbon black film-forming solution used in the present invention has a carbon black volume average particle size in the carbon black dispersion obtained from the above-described step A and the carbon black dispersion obtained from the step B. The difference in volume average particle size of the polyimide film forming solution is within ± 0.1 μm. If it does in this way, the shock aggregation at the time of adding polyimide is suppressed. Because of the good affinity between polyimide and carbon black, the intermediate transfer belt has excellent electrical characteristics and mechanical characteristics. Image forming devices such as electrophotographic copiers and laser printers equipped with such belts have high image quality. A stable image can be obtained stably. If the difference in volume average particle diameter exceeds ± 0.1 μm, the uniformity of electrical characteristics (surface resistance and volume resistance are within one digit) will be reduced, belt strength (elasticity of 4 GPa or more) and flexibility (MIT test). The folding resistance (number of MIT) by the machine is 1000 times or less), which is not preferable.

  In order to improve the affinity between polyimide and carbon black, it is preferable to perform the surface treatment of carbon black as described above.

The particle size is measured using a Microtrac Ultra Fine Particle Size Analyzer (UPA-EX150) manufactured by Nikkiso Co. , Ltd. Today, in electrophotographic apparatuses, color apparatuses such as color copiers and color printers are increasing in response to demands from the market.

  A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photoconductor, and a toner is attached by these developing devices to form a composite toner image on the photoconductor, and the toner image is transferred. A so-called one-drum type that records a color image on a sheet, and a plurality of photoconductors provided side by side are each provided with a developing device, and a single-color toner image is formed on each photoconductor. There is a so-called tandem type that sequentially transfers and records a composite color image on a sheet.

  Comparing a one-drum type and a tandem type image forming apparatus (electrophotographic apparatus), the former has only one photosensitive member, so that there is an advantage that the size can be relatively reduced and the cost can be reduced. Since a full-color image is formed by repeating image formation a plurality of times (usually 4 times) using a photoconductor, it is difficult to increase the image formation speed. The latter has the disadvantage of increasing the size and cost. However, there is an advantage that the speed of image formation is easy.

  As shown in FIG. 1, the latter tandem type electrophotographic apparatus includes a direct transfer system in which an image on each photoconductor 1 is sequentially transferred onto a sheet s conveyed by a sheet conveying belt 3 by a transfer apparatus 2. As shown in FIG. 2, the images on the respective photoconductors 1 are once sequentially transferred to the intermediate transfer member 4 by the primary transfer device 2, and then the images on the intermediate transfer member 4 are sheeted by the secondary transfer device 5. There is an indirect transfer system that performs batch transfer to s. Although the transfer device 5 is an example employing a transfer conveyance belt, a roller-shaped method may be adopted.

  Comparing the direct transfer method and the indirect transfer method, the former requires that the paper feeding device 6 is disposed upstream of the tandem image forming apparatus T in which the photoreceptors 1 are arranged, and the fixing device 7 is disposed downstream. However, there is a drawback of increasing the size in the sheet conveying direction. On the other hand, the latter indirect transfer type transfer device can set the secondary transfer position relatively freely. In addition, the sheet feeding device 6 and the fixing device 7 can be arranged so as to overlap the tandem type image forming apparatus T, which is advantageous in that the size can be reduced.

  In the former, the fixing device 7 is arranged close to the tandem type image forming apparatus T so as not to increase the size in the sheet conveying direction. For this reason, the fixing device 7 cannot be disposed with a sufficient margin that the sheet s can bend, and an impact when the leading edge of the sheet s enters the fixing device 7 (particularly with a thick sheet) or the fixing device. Due to the difference in speed between the sheet conveyance speed when passing through the sheet 7 and the sheet conveyance speed by the transfer conveyance belt, there is a drawback that the fixing device 7 tends to affect image formation on the upstream side.

  On the other hand, in the latter case, the fixing device 7 can be disposed with a sufficient margin that the sheet s can be bent, so that the fixing device 7 can hardly affect the image formation. In view of the above, in the present invention, the indirect transfer system of the tandem type electrophotographic apparatus is preferable.

  In this type of color electrophotographic apparatus, as shown in FIG. 2, the transfer residual toner remaining on the photoreceptor 1 after the primary transfer is removed by a photoreceptor cleaning device to clean the surface of the photoreceptor 1; It is preferable to prepare for another image formation. Further, it is preferable to prepare for re-image formation by removing the transfer residual toner remaining on the intermediate transfer body 3 after the secondary transfer by the intermediate transfer body cleaning device 5 to clean the surface of the intermediate transfer body 3.

  FIG. 3 shows such a tandem indirect transfer type electrophotographic apparatus. In the figure, reference numeral 100 is a copying apparatus main body, 200 is a paper feed table on which the copying apparatus is placed, 300 is a scanner mounted on the copying apparatus main body 100, and 400 is an automatic document feeder (ADF) mounted thereon.

  The copying machine main body 100 is provided with an endless belt-shaped intermediate transfer member 10 at the center. As shown in FIG. 3, in the illustrated example, it is wound around three support rollers 14, 15, and 16 so as to be able to rotate and convey clockwise in the figure. In this illustrated example, an intermediate transfer body cleaning device 17 for removing residual toner remaining on the intermediate transfer body 10 after image transfer is provided on the left of the second support roller 15 among the three.

  Further, among the three images, four images of yellow, cyan, magenta, and black are arranged on the intermediate transfer member 10 stretched between the first support roller 14 and the second support roller 15 along the conveyance direction. The tandem image forming apparatus 20 is configured by arranging the forming units 18 side by side.

  An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG. On the other hand, a secondary transfer device 22 is provided on the side opposite to the tandem image forming apparatus 20 with the intermediate transfer body 10 interposed therebetween. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer body 10 is transferred to a sheet.

  A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.

  The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the image-transferred sheet to the fixing device 25. Of course, a transfer roller or a non-contact charger may be arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this sheet conveying function together. In the illustrated example, under such a secondary transfer device 22 and a fixing device 25, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet in parallel with the tandem image forming device 20 described above. Is provided.

  When making a copy using such a color electrophotographic apparatus, an original is set on the document table 30 of the automatic document feeder 400 or the automatic document feeder 400 is opened and placed on the contact glass 32 of the scanner 300. A document is set and the automatic document feeder 400 is closed and pressed. When a start switch (not shown) is pressed, the set document is transported by the automatic document feeder 400 and moved onto the contact glass 32. Then, the document set on the other contact glass 32 is The scanner 300 is immediately driven to travel on the first traveling body 33 and the second traveling body 34. Then, light is emitted from the light source by the first traveling body 33 and reflected light from the document surface is further reflected and reflected toward the second traveling body 34 by the mirror of the second traveling body 34 to form the imaging lens 35. Then, the light enters the reading sensor 36 and the content of the original is read.

  When a start switch (not shown) is pressed, one of the support rollers 14, 15, and 16 is rotationally driven by a drive motor (not shown), and the other two support rollers are driven to rotate, thereby rotating the intermediate transfer member 10. Transport. At the same time, the photoconductors 40 are rotated by the individual image forming means 18 to form black, yellow, magenta, and cyan monochrome images on the photoconductors 40, respectively. Then, as the intermediate transfer member 10 is conveyed, the single color images are sequentially transferred to form a composite color image on the intermediate transfer member 10.

  On the other hand, when a start switch (not shown) is pressed, one of the sheet feeding rollers 42 of the sheet feeding table 200 is selectively rotated, and the sheet is fed out from one of the sheet cassettes 44 provided in multiple stages in the paper bank 43 to be separated. The sheets are separated one by one by a roller 45 and placed in a paper feed path 46, transported by a transport roller 47, guided to a paper feed path 48 in the copying machine main body 100, and abutted against a registration roller 49 and stopped.

  Alternatively, the sheet feeding roller 50 rotates to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual sheet feeding path 53, and abutted against the registration roller 49 and stopped.

  Then, the timing is adjusted to the composite color image on the intermediate transfer body 10, the registration roller 49 rotates, the sheet is fed between the intermediate transfer body 10 and the secondary transfer device 22, and is transferred by the secondary transfer device 22. A color image is recorded on the sheet. The sheet after the image transfer is conveyed by the secondary transfer device 22 and sent to the fixing device 25. After the transfer image is fixed by applying heat and pressure by the fixing device 25, the sheet is switched by the switching claw 55. The paper is discharged by a discharge roller 56 and stacked on a paper discharge tray 57. Alternatively, it is switched by the switching claw 55 and is put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is also recorded on the back surface, which is then discharged onto the discharge tray 57 by the discharge roller 56. The

  On the other hand, the intermediate transfer member 10 after the image transfer is prepared by the intermediate transfer member cleaning device 17 to remove residual toner remaining on the intermediate transfer member 10 after the image transfer, so that the tandem image forming device 20 can prepare for another image formation. Here, the registration roller 49 is generally used while being grounded, but a bias may be applied to remove paper dust from the sheet.

  In the tandem-type image forming apparatus 20 described above, the individual image forming means 18 is more specifically described as follows. For example, as shown in FIG. 3, a charging device 60, a developing device 61, 1, A next transfer device 62, a photoconductor cleaning device 63, a charge removal device 64, and the like are provided.

Next, an example of forming an intermediate transfer belt using the above-described carbon black film forming solution will be described.
The carbon black dispersion was prepared using the following materials.
Carbon black (Degussa Special Black4) 12 parts by weight Polyimide varnish (Ube Industries U varnish S) 7 parts by weight Polyimide varnish (Ube Industries U varnish A) 7 parts by weight Solvent NMP (N-methylpyrrolidone) 74 parts by weight Part Dispersant (Sorbit activator: Nippon Oil & Fats UNIOX ST30E) X parts by weight Dispersion was carried out for 72 hours with a ball mill (media made by zirconia: 0.03 mm diameter).

(1) Preparation of carbon black-containing polyimide film-forming solution (i) A predetermined amount of U-varnish A and U-varnish S are put into a weighed container,
(Ii) Add a predetermined amount of NMP,
(Iii) stirring and defoaming,
(Iv) A predetermined amount of the carbon black (CB) dispersion is added,
(V) stirring and degassing,
(Vi) Rotate for about 2 hours with a lab rotor (or ball mill) to allow the solution to blend.
A carbon black-containing polyimide film-forming solution was prepared by the above steps i to vi.

(2) Evaluation of dispersion and film-forming solution Volume average particle diameter: Volume average particle diameter was determined using a Nikkiso Microtrack Ultrafine Particle Size Analyzer (UPA-EX150).

(3) Molding of endless belt An endless belt (film thickness of 80 μm, average surface resistance value: 10 ¹¹ Ω / □) was prepared by the centrifugal molding method described above using a carbon black-containing polyimide film forming solution.

(4) Evaluation of endless belt Surface resistance: Surface resistance of endless belt using Hi-Lester manufactured by Mitsubishi Chemical Corporation (DC500V, 10 seconds value, 10 points are measured and the difference between the maximum log value and the minimum log value is calculated) Asked.

The elastic modulus was obtained under the following conditions using the following apparatus.
Autograph AG-IS (Shimadzu Corporation)
Sample shape: 20mm x 120mm
Distance between chucks: 50mm
Tensile speed: 10 mm / min

MIT was determined under the following conditions using the following apparatus.
MIT tester (Toyo Seiki)
Sample shape: 15mm x 120mm
Bending angle: 135 °
Bending speed: 175 times / min
Load: 1kgf

The endless belt produced in Example 2 was attached to the image forming apparatus shown in FIG. 3, and the halftone image density to be formed was adjusted to approximately 0.8. About the obtained halftone image, the degree of occurrence of a blurred image, which is a spot-like density unevenness, was evaluated. With respect to the obtained halftone image, the degree of occurrence of a blurred image that is spotted density unevenness was evaluated.
◎: Very good ○: Good △: No problem in actual use ×: Very bad Evaluation of the endless belt produced in Example 2 gave ◎, and a very good result was obtained.

1 is a schematic cross-sectional view of a direct transfer type tandem type electrophotographic apparatus according to the present invention. 1 is a schematic sectional view of an indirect transfer type tandem type electrophotographic apparatus using an intermediate transfer member of the present invention. 1 is a cross-sectional view of the entire structure of an indirect transfer tandem electrophotographic apparatus using an intermediate transfer member of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Transfer apparatus 3 Sheet belt 4 Intermediate transfer body 5 Transfer apparatus 6 Paper feeder 7 Fixing apparatus 10 Intermediate transfer body 14, 15, 16 Support roller 17 Intermediate transfer body cleaning apparatus 18 Image forming means 20 Tandem image forming apparatus 21 Exposure device 22 Secondary transfer device 23 Between rollers 24 Secondary transfer belt 25 Fixing device 26 Fixing belt 27 Pressure roller 28 Sheet reversing device 32 Contact glass 33 First traveling body 34 Second traveling body 35 Imaging lens 40 Photosensitive body 42 Paper feed roller 43 Paper bank 44 Paper feed cassette 45 Separation roller 46, 48 Paper feed path 47 Transport roller 49 Registration roller 50 Paper feed roller 51 Manual feed tray 52 Separation roller 53 Paper feed path 55 Switching claw 56 Paper discharge roller 57 Paper output tray 60 Charging device 61 Developing device 62 Primary transfer Location 63 photoconductor cleaning device 64 discharging device 100 a copying apparatus main body 200 feeder table 300 Scanner 400 automatic document feeder (ADF)
s sheet

Claims (3)

A polyimide intermediate transfer belt of an image forming apparatus,
A carbon black dispersion liquid comprising a surface-treated carbon black, a polyimide varnish, a dispersant, and a solvent, and having a volume average particle diameter A of 0.24 μm to 0.27 μm of the carbon black is prepared. A black dispersion is diluted with the solvent and the polyimide varnish to prepare a carbon black film forming liquid in which the volume average particle diameter of the carbon black is within the volume average particle diameter A + 0.1 μm, and the carbon black film forming A polyimide intermediate transfer belt produced by centrifugal molding using a liquid.   2. The polyimide intermediate transfer belt according to claim 1, wherein the polyimide intermediate transfer belt has a number of bendings of 1,000 and a modulus of elasticity of 4 GPa or more as measured by an MIT test machine. At least a charging device that forms an electrostatic latent image on the image carrier, a developing device that forms a toner image using a developer corresponding to each color on the image carrier, and an intermediate that travels the toner image endlessly An intermediate transfer device that sequentially superimposes and temporarily transfers the image on the transfer belt, and temporarily transfers the temporary transfer image on the intermediate transfer belt to the transfer material, and the toner image on the transfer material is heated or pressurized. An image forming apparatus having a fixing device for fixing a toner image on the transfer material,
The image forming apparatus, wherein the intermediate transfer belt is the intermediate transfer belt according to claim 1.

Images