JP4684840B2 - Resin composition for seamless belt and seamless belt - Google Patents

Description

  The present invention relates to a resin composition for a seamless belt and a seamless belt obtained by molding the composition. More specifically, in an image forming apparatus such as an electrophotographic copying machine or a laser printer, it is excellent in durability, heat resistance and surface smoothness, which is used for a photoreceptor, a charging belt, a transfer belt, a fixing belt, and the like, and is stable. The present invention relates to a resin composition for a seamless belt having electrical resistance characteristics and a seamless belt using the composition.

  In an electrophotographic apparatus, a rotating body made of metal, plastic, rubber, or the like is used for a photoreceptor, a charged body, a transfer body, a fixing body, and the like. As a rotating body, a drum-like or a belt-like one made of a resin is known. However, if the belt has a seam, a defect due to the seam occurs in the output image. It is necessary to use a belt (seamless belt).

When a seamless belt is used as a rotating body, in addition to mechanical properties such as tensile strength, heat resistance and durability against heat cycle are required.
Also, in color laser printers or color copiers using electrophotographic technology, cyan, yellow, magenta and black basic color toners are used for repeated transfer, so the seamless belt used for them has a coefficient of thermal expansion. It must be small and have excellent dimensional stability.
Therefore, thermosetting polyimide or heat-resistant fluororesin is used as the resin for the seamless belt.

On the other hand, it is important that electrophotographic transfer belts, intermediate transfer belts, fixing belts and the like for copying machines and printers have stable electric resistance characteristics. In order to transfer and fix the toner, it is necessary to control the electric resistance to 10 ⁶ to 10 ¹³ Ω · cm. Furthermore, the difference between the surface resistance value and the volume resistance value is small, the surface resistance value and the volume resistance value with respect to the change with time are small, the dependence of the surface resistance value and the volume resistance value on the environmental change is low, etc. Required.

  Since thermosetting polyimides and heat-resistant fluororesins used for seamless belts are insulative, attempts have been made to reduce resistance by adding various conductive fillers. Commonly used conductive fillers include carbon materials having a graphite structure such as carbon black, graphite, vapor grown carbon fiber, carbon fiber, metal materials such as metal fiber, metal powder, metal foil, and metal oxides, Examples thereof include inorganic fillers coated with metal (Patent Document 1, Patent Document 2, Patent Document 3). In particular, in order to obtain high conductivity by mixing a small amount of conductive filler, it has become clear that refinement of conductive filler, increase in aspect ratio, increase in specific surface area, etc. are effective. Carbon black having a very large surface area and hollow carbon fibrils (carbon nanotubes) having a small fiber diameter are used.

  However, since carbon black and carbon nanotubes have a large specific surface area and high surface energy, they tend to form aggregates and are poorly dispersible in the resin. As a result, when added to the resin, the mechanical strength decreases. Therefore, there is a problem that electric resistance characteristics vary.

Japanese Patent Laid-Open No. 2000-248086 JP 2003-255640 A JP 2003-246927 A

  An object of the present invention is to provide a resin composition for a seamless belt that exhibits stable electrical resistance characteristics and is excellent in surface smoothness, durability and heat resistance, and a seamless belt using the composition.

As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be solved by using a resin composition containing a specific vapor grown carbon fiber as a conductive filler, and the present invention has been completed. It came to do.
That is, this invention relates to the resin composition for seamless belts which consists of the following structures, its manufacturing method, and the seamless belt using the composition.

[1] A heat-resistant resin having a glass transition temperature of 100 ° C. or higher and / or a melting point of 200 ° C. or higher, and vapor grown carbon fiber having an average fiber diameter of 50 to 130 nm are added in an amount of 1 to 30 with respect to 100 parts by mass of the heat-resistant resin. A resin composition for a seamless belt, containing part by mass and having a volume resistance value in a range of 1 × 10 ⁶ to 1 × 10 ¹³ Ωcm.
[2] The resin composition for a seamless belt as described in 1 above, further containing 1 to 10 parts by mass of conductive carbon black with respect to 100 parts by mass of the heat resistant resin.
[3] The resin composition for seamless belts according to 1 or 2, wherein the heat resistant resin is at least one of a thermoplastic resin and a thermosetting resin.
[4] The heat-resistant resin is a fluorine-based resin, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polysulfone, polyethersulfone, polybenzimidazole, polyphenylene sulfide, polyethylene naphthalate, polyarylate, or aromatic. 3. The resin composition for a seamless belt as described in 1 or 2 above, which is at least one selected from polyamide resins.
[5] The resin composition for a seamless belt as described in 4 above, wherein the heat resistant resin is a fluororesin, polyimide, polyamideimide or polyetheretherketone.
[6] The resin composition for a seamless belt as described in 1 above, wherein the vapor-grown carbon fiber has a specific surface area of 10 to 50 m ² / g and an average aspect ratio of 65 to 500.
[7] The resin composition for a seamless belt as described in 6 above, wherein the vapor-grown carbon fiber has a specific surface area of 15 to 40 m ² / g and an average aspect ratio of 100 to 200.
[8] The resin composition for a seamless belt as described in 1, 6 or 7, wherein the number of branches per length of the vapor grown carbon fiber is 0.3 / μm or less.
[9] The method for producing a resin composition for a seamless belt according to any one of 1 to 8 above, wherein the vapor-grown carbon fiber is melt-mixed with the heat-resistant resin. A method for producing a resin composition for a seamless belt, characterized by suppressing breakage to 20% or less.
[10] A seamless belt comprising the resin composition as described in any one of 1 to 8 above, which is substantially unstretched.
[11] The seamless belt as described in 10 above, wherein the thermal conductivity is 0.8 W / mK or more.
[12] The seamless belt as described in 10 above, wherein the 10-point average roughness (Rz) in measurement at a cutoff wavelength of 2.5 mm is 10 μm or less.
[13] The seamless belt as described in 10 above, wherein the difference between the surface resistance value and the volume resistance value is within 2 digits.
[14] The seamless belt as described in 10 above, wherein the fluctuation of the surface resistance value with respect to the charging applied voltage is within 2 digits.
[15] The seamless belt as described in 10 above, wherein the ratio (Ra / Rh) of the volume resistance value Ra at normal temperature and humidity and the volume resistance value Rh at high temperature and high humidity is in the range of 0.03 to 30.
[16] The seamless belt as described in 10 above, wherein the ratio (R _100V / R _1000V ) of the volume resistance value R _100V when _100V is applied to the volume resistance value R _1000V when 1000V is applied is in the range of 0.03 to 30.
[17] The seamless belt according to any one of 10 to 16 above, which is used for a transfer belt, an intermediate transfer belt, a transfer fixing belt, an intermediate transfer fixing belt, or a fixing belt used in an image forming apparatus using electrophotographic technology. .

  The seamless belt of the present invention uses a specific vapor grown carbon fiber as a conductive filler, so that more stable electric resistance characteristics (small difference between surface resistance value and volume resistance value, surface resistance value against change with time) And the volume resistance value is less time-dependent and the environmental resistance of the surface resistance value and volume resistance value is low.) Also, surface smoothness, flexibility, durability / heat resistance (ie, high temperature resistance) (Wrinkle generation and dimensional changes are small when used repeatedly under pressure for a long time), and photosensitive belts, charging belts, and transfer for image forming devices such as (color) laser printers and (color) electrophotographic copying machines It can be preferably used for a belt and a fixing belt.

Hereinafter, the present invention will be described in detail.
The heat resistant resin used in the present invention is a heat resistant resin having a glass transition temperature of 100 ° C. or higher and / or a melting point of 200 ° C. or higher, and any thermoplastic resin and thermosetting resin satisfying this condition. Can be used. Specifically, fluorine-based resin, polyimide resin, polyamideimide resin, polyetherimide resin, polyetheretherketone resin, polysulfone resin, polyethersulfone resin, polybenzimidazole resin, polyphenylene sulfide resin, polyethylene naphthalate resin, At least one selected from polyarylate resins and aromatic polyamide resins is preferred.
Among these, fluorine resin, polyimide resin (PI), polyamideimide resin (PAI) or polyether ether ketone resin (PEEK) is suitable.

  The fluororesin is a generally known thermoplastic homopolymer or copolymer type fluororesin, from which a glass transition temperature of 100 ° C. or higher and / or a melting point of 200 ° C. or higher is selected. Preferred is a perfluoro copolymer (copolymer). Specifically, copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and ethylene (ETFE), tetrafluoroethylene, hexafluoropropylene and perfluoroalkyl Examples thereof include ternary copolymers with vinyl ether. These polymers have a heat distortion temperature of about 70 to 110 ° C. and heat resistance of about 150 to 260 ° C.

The polyimide resin refers to all resins having an imide bond in the structure, and includes thermoplastic or thermosetting polyimide.
The thermoplastic polyimide has thermoplasticity while having an imide group. Therefore, since it melts or softens itself at a predetermined temperature or higher, it can be directly extruded. This property is found in polyimides having functional groups that provide flexibility between molecules such as ether bonds (two or more), alkylene bonds (C3 or more), and carbonyl groups in the main chain. Specifically, for example, pyromellitic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, bis Organic acid dianhydrides such as (2,3-dicarboxyphenyl) methane dianhydride and bis {4- [3- (4-aminophenoxy) benzoyl] phenyl} ether, 4,4′-bis (3-amino Phenoxy) biphenyl, bis {4- (3-aminophenoxy) phenyl} sulfone, 2,2′-bis {4- (3-aminophenoxy) phenyl} propane and the like in an organic polar solvent (N -Methylpyrrolidone, N, N-dimethylacetamide, etc.) and the reaction is gradually carried out with stirring. In this reaction, polycondensation to a polymer having a required molecular weight and imide cyclization after polycondensation are performed, and reaction is performed all at once to polyimide. In addition, the extrusion temperature to a film is about 300-400 degreeC.

  Thermosetting polyimide does not melt in the state of polyimide. Therefore, the seamless belt is molded in two stages, in which the thermoplastic precursor, that is, the polyamic acid, is primarily molded and then imidized separately. This polyimide includes, for example, pyromellitic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, bis ( 2,3-dicarboxyphenyl) methane dianhydride and other organic acid dianhydrides and p-phenylenediamine, 4,4′-diaminodiphenyl, 4,4′-diaminodiphenylmethane, 4,4′-diaminophenyl ether, etc. The organic diamine equivalent can be gradually reacted with stirring in an organic solvent (N-methylpyrrolidone, N, N-dimethylacetamide, etc.). This reaction is a polycondensation reaction for obtaining a polyamic acid having a desired molecular weight, and must not be accompanied by a ring-closing reaction to imidization. For this purpose, it is necessary to maintain the low temperature and to react gradually. The above examples are polyimides having no amino group, but so-called polyamide imides containing amino groups can be used as well. Polyamideimide uses tricarboxylic acid monoanhydride as an organic acid, and organic diamine can be obtained by polycondensation reaction in an organic solvent in an equivalent amount by combining those exemplified above. In addition, the heat distortion temperature of the said polyimide resin is 200-400 degreeC, and heat resistance is about 250-350 degreeC.

  The average fiber diameter of the vapor grown carbon fiber used in the present invention is preferably 50 to 130 nm. When the average fiber diameter is smaller than 50 nm, the surface energy increases exponentially, and the cohesive force between the fibers rapidly increases. When such a vapor grown carbon fiber is simply kneaded with a resin, it is not sufficiently dispersed, and aggregates are scattered in the resin matrix, so that a conductive network cannot be formed. When a large shearing force is applied at the time of kneading, the aggregate can be broken and dispersed in the matrix, but when the aggregate breaks, the fiber breaks up and the desired conductivity cannot be obtained. On the other hand, if the average fiber diameter exceeds 130 nm, it is necessary to mix more carbon fibers in order to obtain desired conductivity, which adversely affects other physical properties such as mechanical strength and bending characteristics.

The aspect ratio of the vapor grown carbon fiber used in the present invention is preferably 65 to 500, more preferably 100 to 200.
If the aspect ratio is large (that is, the fiber length is long), the fibers are entangled and cannot be easily loosened, and sufficient dispersion cannot be obtained. On the other hand, if the aspect ratio is less than 65, 10% by mass or more of fillers must be added to form a conductive linking skeleton structure, and the fluidity and tensile strength of the resin are significantly reduced, which is preferable. Absent.

  The degree of branching of the vapor grown carbon fiber used in the present invention is preferably 0.3 piece / μm or less. More preferably, it is 0.2 piece / micrometer or less, More preferably, it is 0.1 piece / micrometer or less. If the degree of branching exceeds 0.3 / μm, the carbon fibers form a strong aggregate, and it is difficult to efficiently impart conductivity with a small amount.

The average interplanar spacing d ₀₀₂ of the vapor grown carbon fiber used in the present invention by X-ray diffraction is preferably 0.345 nm or less, more preferably 0.343 nm or less, and further preferably 0.340 nm or less. When the average interplanar spacing d ₀₀₂ exceeds 0.345 nm, the graphite crystal is not sufficiently developed, and therefore the resistivity of the carbon fiber alone increases 10 times or more as compared with the crystallized one. Furthermore, when mixed with resin or the like, it becomes difficult to transfer electrons between carbon fiber / resin / carbon fiber. Specifically, the same level of conductivity cannot be obtained unless a filler amount twice or more is added compared to carbon fibers in which graphite crystals are developed.

The BET specific surface area of the vapor grown carbon fiber used in the present invention is preferably 10 to 50 m ² / g, more preferably 15 to 40 m ² / g. When the BET specific surface area is increased, the surface energy of the carbon fiber is increased and the adhesion / cohesion force is increased, which makes dispersion difficult. Furthermore, the interfacial area between the matrix and the carbon fibers becomes large, so that the matrix cannot sufficiently cover the fibers, or the probability of peeling the carbon fibers from the matrix increases. As a result, when a composite with a resin is produced, not only electrical conductivity but also mechanical strength is deteriorated, which is not preferable.

The ratio (Id / Ig) of the peak height (Id) of the band from 1341 to 1349 cm ⁻¹ and the peak height (Ig) of the band from 1570 to 1578 cm ^{−1 in} the Raman scattering spectrum of the vapor grown carbon fiber used in the present invention. ) Is preferably 0.1 to 1.4. More preferably, it is 0.15-1.3, More preferably, it is 0.2-1.2.

The vapor grown carbon fiber having the above-described properties used in the present invention can be produced by thermally decomposing a carbon source (organic compound) in the presence of an organic transition metal compound.
The carbon source (organic compound) used as the raw material for the carbon fiber may be a gas such as toluene, benzene, naphthalene, ethylene, acetylene, ethane, natural gas, carbon monoxide, or a mixture thereof. Of these, aromatic hydrocarbons such as toluene and benzene are preferred.
An organic transition metal compound contains the transition metal used as a catalyst. The transition metal is an element in Periodic Tables 4-10. Preferred organic transition metal compounds include ferrocene and nickelocene.

  Sulfur compounds such as sulfur and thiophene can be used as a co-catalyst for efficiently removing gas such as hydrogen adsorbed on the surface of the transition metal catalyst particles and enhancing the catalytic activity in a pyrolysis reaction atmosphere.

  A reducing gas such as hydrogen is used as a carrier gas, and the organic compound, the organic transition metal compound, and the sulfur compound are supplied to a reaction furnace heated to 800 to 1300 ° C. and subjected to a thermal decomposition reaction to obtain carbon fibers.

  As a form of the raw material, a material obtained by dissolving an organic transition metal compound and a sulfur compound in an aromatic hydrocarbon, or a material vaporized at 500 ° C. or lower can be used. However, in the case of a liquid raw material, vaporization / decomposition of the raw material occurs on the reaction tube wall, and a raw material concentration distribution is locally generated in the reaction tube, so that the produced carbon fibers tend to aggregate. Therefore, as a form of the raw material, a vaporized raw material having a constant raw material concentration in the reaction tube is preferable.

  The transition metal catalyst and sulfur compound promoter ratio (transition metal / (transition metal + sulfur)) is preferably 15 to 35% by mass. In the case of 15% by mass or less, the catalytic activity is increased, the number of fiber branches is increased, or the fibers are radially formed, which increases the interaction between the fibers and forms a strong aggregate, which is not preferable. . On the other hand, when the amount is 35% by mass or more, hydrogen adsorbed on the catalyst cannot be sufficiently removed, and therefore, supply of a carbon source to the catalyst is hindered, and carbon particles other than carbon fibers are generated.

  The number of branches of carbon fibers and the degree of loosening of the aggregates are determined by the raw material concentration at the time of synthesis. That is, when the raw material concentration in the gas phase is high, non-uniform nuclei of catalyst particles are generated on the surface of the generated carbon fiber, and further carbon fiber is generated from the surface of the carbon fiber to form a frosted carbon fiber. Moreover, carbon fibers produced at a high concentration are entangled and cannot be easily loosened. Therefore, the ratio of the raw material supply amount in the reaction tube to the carrier gas flow rate is preferably 1 g / liter or less, more preferably 0.5 g / liter, and even more preferably 0.2 g / liter.

  In order to remove organic substances such as tar adhering to the carbon fiber surface, heat treatment is preferably performed at 900 to 1300 ° C. in an inert atmosphere. In order to improve the electrical conductivity of the carbon fiber, it is preferable to further develop a crystal by performing a heat treatment at 2000 to 3500 ° C. in an inert atmosphere.

  The heat treatment furnace used to develop the crystal may be any furnace that can be maintained at a desired temperature of 2000 ° C. or higher, preferably 2300 ° C. or higher, and any ordinary apparatus such as an Atchison furnace, a resistance furnace, a high-frequency furnace, etc. But you can. Moreover, depending on the case, the method of heating by energizing powder or a molded object directly can also be used.

  The atmosphere for the heat treatment is a non-oxidizing atmosphere, preferably an atmosphere of one or more rare gases such as argon, helium and neon. The heat treatment time is preferably as short as possible from the viewpoint of productivity. If heating is continued for a long time, the product yield deteriorates because it sinters and hardens. Therefore, after the temperature of the center part of the molded body or the like reaches the target temperature, it is sufficient to hold the temperature for 10 minutes to 1 hour.

Boron carbide (B ₄ C), boron oxide (B ₂ ) are used in the graphitization treatment of heating at 2000 to 3500 ° C. in an inert atmosphere in order to further develop the carbon fiber crystals and improve the conductivity. Boron compounds such as O ₃ ), elemental boron, boric acid (H ₃ BO ₃ ), and borate may be mixed.

The amount of boron compound added depends on the chemical and physical properties of the boron compound to be used and cannot be specified unconditionally. For example, when boron carbide (B ₄ C) is used, the amount of boron compound is about 0.1% relative to the carbon fiber. The range is from 05 to 10% by mass, preferably from 0.1 to 5% by mass.

  By the heat treatment with the boron compound, the carbon crystallinity of the carbon fiber is improved and the conductivity is improved. The amount of boron contained in the carbon fiber crystal or on the crystal surface is preferably 0.01 to 5% by mass. In order to improve the conductivity of the carbon fiber and the affinity with the resin, more preferably 0.1 mass% or more of boron is required. Further, the amount of boron that can be substituted into the graphene sheet is about 3% by mass, and more than that, especially 5% by mass or more of boron exists as boron carbide or boron oxide, which is not preferable because it may cause a decrease in conductivity.

  In order to improve the affinity between the carbon fiber and the resin, the carbon fiber can be oxidized to introduce a phenolic hydroxyl group, a carboxyl group, a quinone group, or a lactone group on the fiber surface. Furthermore, surface treatment may be performed with a silane-based, titanate-based, aluminum-based, or phosphate ester-based coupling agent.

In the present invention, carbon black can be further added as a conductive filler. When vapor-grown carbon fiber and carbon black are used in combination, and carbon black is uniformly dispersed, there is a phenomenon that the variation in conductivity is reduced.
Carbon black that can be used generally has an average particle diameter of 1 to 500 μm and a volume resistance of about 10 ¹ to 10 ⁴ Ω · cm. Examples thereof include acetylene black, kettin black, oil furnace black, and thermal black.

The resin composition for a seamless belt of the present invention contains the above heat-resistant resin, vapor grown carbon fiber, and optionally carbon black.
The compounding amount of the vapor grown carbon fiber is 1 to 30 parts by mass, preferably 3 to 15 parts by mass with respect to 100 parts by mass of the heat resistant resin. When the compounding amount of the vapor grown carbon fiber is less than 1 part by mass, it is difficult to form a conductive network, and desired conductivity cannot be obtained. On the other hand, if it exceeds 30% by mass, the flexibility required for the seamless belt cannot be obtained.
When carbon black is blended, the blending amount is preferably 1 to 10 parts by mass, more preferably 2 to 5 parts by mass with respect to 100 parts by mass of the heat resistant resin. When the blending amount of carbon black exceeds 10 parts by mass, the flexibility required for the seamless belt cannot be obtained, and many problems such as a decrease in surface smoothness occur.

When mixing and kneading the above components, it is preferable to suppress breakage of the vapor grown carbon fiber as much as possible. Specifically, the fracture rate of vapor grown carbon fiber is preferably suppressed to 20% or less, more preferably 15% or less, and particularly preferably 10% or less. The breaking rate can be evaluated by comparing the aspect ratios of carbon fibers before and after mixing and kneading (for example, measured by an electron microscope (SEM) photographic image).
In order to perform mixing and kneading while suppressing breakage of the vapor grown carbon fiber as much as possible, for example, the following method can be used.

  Generally, when an inorganic filler is melt-kneaded into a thermoplastic resin or a thermosetting resin, a high shear force is applied to the aggregated inorganic filler, the inorganic filler is broken and refined, and the inorganic filler is uniformly dispersed in the molten resin. Let As a kneading machine that generates a high shearing force, a machine that uses a stone mortar mechanism or a machine that introduces a kneading disk that applies a high shearing force into a screw element using a twin screw extruder is used. However, when such a kneader is used, the vapor grown carbon fiber breaks during the kneading step. Further, in the case of a single screw extruder having a weak shearing force, fiber breakage can be suppressed, but fiber dispersion is not uniform. Therefore, in order to achieve uniform dispersion while suppressing fiber breakage, it is possible to reduce the shear force with a co-directional twin-screw extruder that does not use a kneading disk, or to apply a high shear force such as a pressure kneader. However, it is desirable to use a special mixing element that can achieve dispersion over time or in a single screw extruder.

  Moreover, in order to fill the inorganic filler in the resin, the wettability of the inorganic filler with respect to the molten resin is important. When the inorganic filler is introduced into the molten resin, the area corresponding to the interface between the molten resin and the inorganic filler is reduced. It is essential to increase. As a method for improving wettability, for example, there is a method of oxidizing the surface of vapor grown carbon fiber.

In the case where the vapor grown carbon fiber used in the present invention is in a fluffy state having a bulk specific gravity of about 0.01 to 0.1 g / cm ³ , it is easy to entrain air. Deaeration is difficult with a directional twin-screw extruder, and filling is difficult. In such a case, a batch-type pressure kneader is preferable as a kneader having good filling properties and minimizing fiber breakage. What knead | mixed with the batch type pressure kneader can be thrown into a single screw extruder before solidification, and can be pelletized.

The resin composition for a seamless belt of the present invention has a volume resistivity value of 1 × 10 ⁶ to 1 × 10 ¹³ Ωcm, preferably 1 × 10 ⁶ by adjusting the physical properties of the vapor grown carbon fiber and the blending amount thereof. ⁷ to 1 × 10 ¹⁰ Ωcm, more preferably 1 × 10 ⁸ to 1 × 10 ⁹ Ωcm.

After preparing a composition in which the above components are mixed and dispersed, this is formed into a seamless belt. As the molding method, a dry molding method or a wet molding method can be preferably used.
The dry molding method is a method in which a matrix resin is directly melt-extruded from an annular die in the absence of an organic solvent. The wet molding method is a method in which a primary molding is performed in a plasticized state or a solution state in the presence of an organic solvent, and then the solvent is removed to form a desired seamless belt shape. In the primary molding, the plasticized composition can be formed into a tubular shape while casting toward the outer periphery of the metal drum, or directly extruded from an annular die. A centrifugal casting method is preferred in which it is poured into a metal drum in a solution state and molded while rotating.

  The organic solvent used in the wet molding method is selected from those that swell or dissolve the heat-resistant resin (polyamic acid in the case of thermosetting polyimide), but in the centrifugal casting method, an organic solvent that is completely dissolved is used. It is necessary to adjust the amount used.

An example of a method for forming a seamless belt by a centrifugal casting method using thermosetting polyimide as the heat resistant resin will be described.
First, the starting material is subjected to a polycondensation reaction in the organic solvent to obtain a polyamic acid solution. The conductive filler is mixed and dispersed therein as described above. Next, a predetermined amount of polyamic acid solution is poured into a metal drum corresponding to a seamless belt having a desired size (diameter and width), the drum is heated from the outside, and rotation is started. At a predetermined temperature (generally higher than the boiling point of the organic solvent and lower than the imidization temperature), the solvent is gradually removed by evaporation and the polyamic acid is solidified while being uniformly cast over the entire inner surface when centrifuged for a predetermined time. Is formed as an endless belt. The obtained endless belt is peeled off from the drum, fitted into a cylindrical mold, and the whole is put into a heating oven. The temperature is gradually raised to 250 ° C. and then gradually raised to 400 ° C. (Secondary molding). During this time, an imidization reaction is gradually performed to obtain a seamless belt having a thermosetting polyimide as a matrix. In addition, the cylindrical metal mold | die used in the said secondary shaping | molding is for mainly performing a secondary process, maintaining a shape, and is not essential. Moreover, also when shape | molding with a centrifugal casting method with respect to heat resistant resins other than a thermosetting polyimide, it can carry out according to the procedure in the case of a polyimide.

  In any of the dry molding method and the wet molding method, other molding conditions are not particularly limited, and appropriate conditions may be selected according to the selected composition. However, in the dry molding method, it is preferable that melt molding from an annular die is extruded to room temperature and taken up substantially without stretching.

  The seamless belt of the present invention obtained as described above is excellent in surface smoothness, and has a 10-point average roughness (Rz) of 10 μm or less, preferably 8 μm or less, when measured at a cutoff wavelength of 2.5 mm.

  The seamless belt of the present invention can have a thermal conductivity of 0.8 W / mK or more. If the thermal conductivity is 0.8 W / mK or more, the temperature of the seamless belt is made uniform, and the generation of wrinkles is suppressed. In addition, the heat dissipation is good, the maximum temperature reached during continuous use can be lowered, and the durability can be increased.

The seamless belt of the present invention has stable electric resistance characteristics. In particular,
(1) The difference between the surface resistance value and the volume resistance value is within two digits;
(2) The variation of the surface resistance value with respect to the applied charging voltage is within 2 digits
(3) The ratio of the volume resistance value R _100V when _100V is applied to the volume resistance value R _1000V when 1000V is applied (R _100V / R _1000V ) is in the range of 0.03 to 30; and / or (4) normal temperature and humidity The ratio (Ra / Rh) of the volume resistance value Ra at the time and the volume resistance value Rh at the time of high temperature and high humidity can be in the range of 0.03 to 30.

Regarding (1): In a resin composite material molded body containing a conventional conductive filler, there is a large difference between the surface resistance value and the volume resistance value, and the case is expressed by (surface resistance value / volume resistance value). The difference is often 10 ² or more. However, in the seamless belt using the vapor grown carbon fiber of the present invention, the dispersion of the carbon fiber is performed well, so the value is 10 ² or less (the difference is within 2 digits). And the material exhibits stable electrical resistance characteristics as a whole.

Regarding the above (2) and (3): When the seamless belt is used for a transfer belt, an intermediate transfer belt, etc., it is necessary to control the voltage according to the type and environment of the image. Since the above control becomes difficult if there is a fluctuation, it is preferable that the voltage dependence of the resistance value is small. In the seamless belt of the present invention, the fluctuation range of the surface resistance value with respect to the applied charging voltage can be within 2 digits (within 10 ² ), preferably within 1 digit (within 10 ¹ ), and the volume resistance when 100 V is applied. The ratio (R _100V / R _1000V ) between the value R _100V and the volume resistance value R _1000V when 1000V is applied can be adjusted within the range of 0.03 to 30, preferably 0.1 to 10.

  Regarding the above (4): In a seamless belt with a controlled resistance value used for a transfer belt, an intermediate transfer belt, etc., it is preferable that the fluctuation of the resistance value due to the environment is small. In the seamless belt of the present invention, The ratio (Ra / Rh) of the volume resistance value Ra to the volume resistance value Rh at high temperature and high humidity can be adjusted within the range of 0.03 to 30, preferably 0.1 to 10. Here, the normal temperature and normal humidity refers to an environment having a temperature of 23 ° C. and a humidity of 55% Rh, and the high temperature and high humidity refers to an environment of a temperature of 30 ° C. and a humidity of 80% Rh.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these ranges.

Examples 1-6, Comparative Examples 1-9
Table 1 shows the blending conditions of Examples and Comparative Examples. According to the composition shown in Table 1, the resin and the conductive filler were melt-kneaded and the kneaded product was formed into a film to prepare a film for measuring volume resistivity.
Details of the resin used, the conductive filler, the method for measuring the aggregate of the conductive filler, the kneading conditions, the molding conditions, and the evaluation method of the molded film are shown below. Further, Table 1 also shows the volume resistivity, the evaluation of the presence / absence of agglomerates, and the fiber breaking rate of each Example and Comparative Example.

[Kneading method]
B) Thermoplastic resin A ikekai bi-directional extruder (PCM30) was used. The kneading temperature was 280 ° C.
B) Thermosetting resin A pressure kneader (kneading capacity: 10 liters) manufactured by Toshin Co., Ltd. was used, and the temperature was set to 60 ° C.

[Molding method]
B) Thermoplastic resin Laboplast mill (manufactured by Toyo Seiki Co., Ltd.) using a copolymer of tetrafluoroethylene and ethylene (ETFE; manufactured by Asahi Glass Co., Ltd., Aflon type COP-55AXT, melting point: 260 ° C.) as a fluororesin. ) A single screw extruder and a cylindrical film forming die (diameter 10 cm, thickness 200 μm) were used. Molding was performed at 290 ° C.
B) Thermosetting resin DMF solution of polyamic acid obtained using 4,4′-diaminodiphenyl ether as the aromatic diamine and pyromellitic dianhydride as the aromatic tetracarboxylic dianhydride (solid content concentration: 18) 0.5%, solution viscosity 3000 poise) was used. A specific amount of vapor grown carbon fiber was added to them, and the dispersion was kneaded. Next, cast into a cylindrical SUS, heat treated at 140 ° C./15 minutes, 200 ° C./20 minutes, 250 ° C./30 minutes, 300 ° C./30 minutes, 350 ° C./30 minutes to give a black polyimide tube having a thickness of about 50 μm. Obtained.

[Vapor grown carbon fiber]
A) VGCF (registered trademark): Vapor grown carbon fiber (average fiber diameter: 150 nm, average fiber length: 10 μm, specific surface area: 13 m ² / g, aspect ratio: 67, I ₀ = 0.2) manufactured by Showa Denko used. The average fiber length of 5 μm (aspect ratio: 33) was adjusted by jet mill grinding.
B) VGCF-S: Showa Denko vapor phase carbon fiber (average fiber diameter: 100 nm, average fiber length: 11 μm, specific surface area: 20 m ² / g, aspect ratio: 110, I ₀ = 0.2) . The average fiber length of 5 μm (aspect ratio: 50) was adjusted by jet mill grinding.
C) VGNF (registered trademark): Vapor grown carbon fiber (average fiber diameter: 80 nm, average fiber length: 10 μm, specific surface area: 25 m ² / g, aspect ratio: 125, I ₀ = 0.2) manufactured by Showa Denko used. The average fiber length of 5 μm (aspect ratio: 63) was adjusted by jet mill grinding.
D) Carbon nanotube (CNT: hollow carbon fibril): PEI masterbatch (RMB8515-00: containing 15% by mass of CNT) manufactured by Hyperion Catalysis Co., Ltd. was used. CNT has an average fiber diameter of 10 nm, an average fiber length of 5 μm, a specific surface area of 250 m ² / g (catalog value), and an aspect ratio of 500.

[Conductive carbon black]
KB (Ketjen Black) EC600JD: manufactured by Lion Corporation was used. Specific surface area 800 m ² / g.

[Measurement and evaluation method of physical properties]
The physical properties of a film sample cut out from a tubular product obtained by molding the resin composition obtained above were measured and evaluated by the following methods.

B) Volume resistance value in the thickness direction and surface resistance value:
Cut out 10 cm x 10 cm from the sample and leave it in an environment of normal temperature and humidity (temperature 23 ° C, humidity 55% Rh) and high temperature and humidity (temperature 30 ° C, humidity 80% Rh) for 24 hours. The volume resistance value and the surface resistance value at 100V were measured using a digital ultrahigh resistance / microammeter R8340 manufactured by Advantest Corporation and an HR probe manufactured by Mitsubishi Chemical Corporation.

B) Agglomerates of carbon fibers: The fracture surface of the film sample was observed with an electron microscope (SEM) (2000 times), and the presence or absence of agglomerates of fibers was evaluated according to the following criteria.
Agglomerate size (major axis)
○: Less than 0.5 μm,
(Triangle | delta): Less than 0.5-5 micrometers,
X: Over 5 μm.
C) Carbon fiber breaking rate (%): determined by the following formula.
Carbon fiber breaking rate (%) = {1− (aspect ratio of carbon fiber of composition molded product / aspect ratio of carbon fiber before mixing and kneading)} × 100
Here, the aspect ratio was measured and calculated by electron microscope SEM observation.

D) Raman scattering spectrum: measured by a peak intensity ratio (I ₀ = I ₁₃₆₀ / I ₁₅₈₀ ) of ₁₅₈₀ cm ⁻¹ and 1360 cm ⁻¹ .

E) Ten-point average roughness (Rz):
Measured in the direction of the vertical magnification from the average line of the roughness curve, the average of the absolute values of the altitude of the highest peak from the highest peak to the fifth, and the average of the absolute values of the elevation of the lowest peak to the fifth Calculated from the sum of the values.
F) Thermal conductivity: Measured by a hot wire method using a rapid thermal conductivity meter manufactured by Kyoto Electronics Industry Co., Ltd. The test sample was used as a 100 × 100 × 2 mm-thick shape by stacking films.

Claims (17)

1-30 parts by mass of a heat-resistant resin having a glass transition temperature of 100 ° C or higher and / or a melting point of 200 ° C or higher, and a vapor grown carbon fiber having an average fiber diameter of 50-130 nm with respect to 100 parts by mass of the heat-resistant resin And a volume resistance value in the range of 1 × 10 ⁶ to 1 × 10 ¹³ Ωcm.   The resin composition for a seamless belt according to claim 1, further comprising 1 to 10 parts by mass of conductive carbon black with respect to 100 parts by mass of the heat resistant resin.   The resin composition for a seamless belt according to claim 1 or 2, wherein the heat resistant resin is at least one of a thermoplastic resin and a thermosetting resin.   The heat-resistant resin is made of fluorine resin, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polysulfone, polyethersulfone, polybenzimidazole, polyphenylene sulfide, polyethylene naphthalate, polyarylate, and aromatic polyamide resin. The resin composition for a seamless belt according to claim 1 or 2, which is at least one selected.   The resin composition for a seamless belt according to claim 4, wherein the heat-resistant resin is a fluororesin, polyimide, polyamideimide, or polyetheretherketone. The resin composition for a seamless belt according to claim 1, wherein the vapor-grown carbon fiber has a specific surface area of 10 to 50 m ² / g and an average aspect ratio of 65 to 500. The resin composition for a seamless belt according to claim 6, wherein the vapor-grown carbon fiber has a specific surface area of 15 to 40 m ² / g and an average aspect ratio of 100 to 200.   The resin composition for a seamless belt according to claim 1, 6 or 7, wherein the number of branches per length of the vapor grown carbon fiber is 0.3 / μm or less.   It is a manufacturing method of the resin composition for seamless belts in any one of Claims 1-8 which melt-mixes vapor-grown carbon fiber with heat resistant resin, Comprising: The fracture | rupture of the said vapor-grown carbon fiber at the time of melt-mixing A method for producing a resin composition for a seamless belt, characterized by being suppressed to 20% or less.   A seamless belt comprising the resin composition according to claim 1 and being substantially unstretched.   The seamless belt according to claim 10, wherein the thermal conductivity is 0.8 W / mK or more.   The seamless belt according to claim 10, wherein a 10-point average roughness (Rz) in measurement at a cutoff wavelength of 2.5 mm is 10 µm or less.   The seamless belt according to claim 10, wherein a difference between the surface resistance value and the volume resistance value is within two digits.   The seamless belt according to claim 10, wherein the variation of the surface resistance value with respect to the charging applied voltage is within 2 digits.   The seamless belt according to claim 10, wherein the ratio (Ra / Rh) of the volume resistance value Ra at normal temperature and humidity and the volume resistance value Rh at high temperature and high humidity is in the range of 0.03 to 30. Seamless belt according to claim 10 100 V applied at a volume resistance value R _{100 V} and 1000V applied when volume resistivity ratio R _1000V of (R _100V / R _1000V) is in the range of 0.03 to 30. The seamless belt according to any one of claims 10 to 16, which is used for a transfer belt, an intermediate transfer belt, a transfer fixing belt, an intermediate transfer fixing belt, or a fixing belt used in an image forming apparatus using an electrophotographic technique.