JP4619208B2 - Polyimide resin belt with isotropic dielectric constant in the surface direction - Google Patents

Description

  The present invention relates to a polyimide resin belt used in an electrophotographic copying machine, a printer, a facsimile, a composite machine of these, a digital printing machine, and the like provided with a color image forming apparatus, and a method for manufacturing the same. More specifically, the present invention relates to a polyimide resin belt having a seamless shape and a method for manufacturing the same, which can further improve the image quality / speed and reliability of a color image forming apparatus, and can further freely select a transfer medium such as paper.

  In a color image forming apparatus using an electrophotographic method, a toner image formed of an inorganic or organic photoreceptor is electrostatically carried on a transfer member one color at a time and superimposed to form a four-color composite image. Then, the transfer process is performed twice, that is, batch transfer onto a transfer material such as paper. Therefore, it is known that the surface resistivity and volume resistivity of the transfer belt are important control factors for achieving various process requirements.

In the color image forming apparatus described above, various studies have been made on the electrical characteristics of the transfer belt, particularly the volume resistivity, for the purpose of accurately transferring the toner image in order to improve the quality of the formed image. For example, in Patent Documents 1 to 3, the volume resistivity in the thickness direction is controlled in the range of 10 ⁸ to 10 ¹⁷ Ω · cm, and the maximum value of the volume electrical resistance value is in the range of 1 to 100 times the minimum value. An intermediate transfer member is disclosed.

  Moreover, since it is excellent in heat resistance, mechanical strength, and environmental resistance characteristics, a polyimide resin intermediate transfer member using a polyimide resin has been studied. Patent Document 4 discloses a conductive polyimide seamless belt in which conductive carbon black such as acetylene black and ketjen black is dispersed in a polyimide resin. Patent Document 5 discloses a conductive material whose surface is treated with a silane coupling agent. An intermediate transfer member is disclosed in which a stock solution of polyamic acid in which a metal oxide is dispersed is cast-molded on a metal sheet and then both ends of the obtained film are joined.

  However, with such a conventional intermediate transfer member, even when the volume resistivity value is set within a predetermined range, the problem of unevenness in the formed image cannot be eliminated. This is because it is not simply the distribution state of the primary particles of the conductive fine particles, but is caused by the anisotropy of the dielectric constant in the plane direction caused by the macroscopic dispersion state and the structure directionality. Therefore, even if there is little variation in the volume resistivity of the intermediate transfer member, the unevenness of the formed image cannot be completely removed.

  In addition, an intermediate transfer member used in the image forming apparatus is desired not only to be stretched during use but also to have no waviness in the surface direction in an initial state incorporated in the image forming apparatus. In other words, the transfer surface of the intermediate transfer member needs to be flat, and if the intermediate transfer member has waviness, the transfer image is distorted, color misregistration occurs due to a difference in peripheral speed, or the adhesion to the paper is weakened. Cause unevenness in image quality.

  2. Description of the Related Art In recent years, with the speeding up of image forming apparatuses, many tandem color image forming apparatuses having a plurality of photoconductors each having a developing device for each color have been developed. In a tandem color image forming apparatus, regardless of whether the intermediate transfer method or the transfer conveyance method is used, the peripheral length of the intermediate transfer member needs to be large (large diameter), and the peripheral length must be large (large diameter). However, it is desired to reduce the surface undulation as much as possible.

  Generally, the molecular structure of polyimide-based resin is often relatively flat, and when the solvent of the liquid raw material is volatilized, the molecules are layered to form a film. However, it is easy to develop anisotropy in the plane direction. As a result, the electrical characteristics appear as undulation in the plane direction due to the occurrence of anisotropy of dielectric constant and the orientation of the conductive fine particles. The anisotropy in the surface direction tends to occur more easily as the peripheral length of the intermediate transfer member becomes larger (larger diameter).

  Patent Document 6 discloses a polyimide film having a maximum value of MOR-c of 1.35 or less with little variation in physical properties at any point in the film plane, using MOR-c as an index of the molecular orientation state. Has been. However, since this polyimide film does not contain conductive fillers such as carbon black, it is an insulating film and has the problem that it does not have the electrical characteristics that are indispensable as an intermediate transfer member, that is, it does not have the characteristic of flowing electricity in the thickness direction of the film. Have.

  On the other hand, a rotational molding method has been studied as a method for producing an intermediate transfer member made of polyimide resin. In Patent Document 7, the liquid material is put into a cylindrical mold and the liquid material is placed in the cylindrical mold by centrifugal acceleration that is approximately 112 times the gravitational acceleration. A manufacturing method for uniformly casting on a peripheral surface is disclosed.

  However, in the manufacturing method disclosed in the above publication, the structure of the carbon black is also oriented in the direction due to the flow caused by the input of the liquid raw material or centrifugal force, so that the MOR-c tends to increase. The problem of unevenness in the formed image due to the anisotropy of the dielectric constant cannot be eliminated.

  Patent Document 9 discloses a heat-resistant deformable tubular film obtained by jetting a mist-like heat-resistant resin liquid onto a molding drum at a substantially non-centrifugal rotational speed. However, this tubular film is heated at a temperature of 120 ° C. by a rotational molding method to form a film on the inner peripheral surface of the cylindrical mold, and then peeled off from the cylindrical mold and a new metal is formed on the inner peripheral surface of the belt. It is manufactured by a manufacturing method in which a mold is inserted and heated at 250 ° C. or higher. Thus, when a new mold is inserted into the inner peripheral surface of the belt and the polyimide precursor is subjected to an imide conversion reaction, the polyimide molecular chains are oriented in the circumferential direction, and conductive fine particles such as carbon black are also aligned in the orientation direction. It becomes a distributed state. As a result, there is room for improvement because the dielectric constant in the plane direction has anisotropy.

Further, in an intermediate transfer member having an anisotropy of dielectric constant in the surface direction, the dielectric constant is changed by repeatedly passing an excessive current, and there is a problem that the range of the dielectric constant 7 to 12 required as the intermediate transfer member is not satisfied. is there. As a result, defects on the image such as toner scattering are generated, the life of the intermediate transfer member is shortened, maintenance work such as replacement is increased, and the running cost is increased, leading to inferior reliability as an image forming apparatus. .
Japanese Patent Laid-Open No. 3-100579 Japanese Patent Laid-Open No. 5-200904 JP-A-5-345368 JP-A-5-77252 Japanese Patent Laid-Open No. 10-63115 JP 2002-154168 A JP 2001-38750 A JP 2004-287005 A JP 2000-263568 A

  In view of various problems in the prior art, an object of the present invention is to provide a polyimide resin belt that can achieve accurate transfer in a color image forming apparatus and can stably obtain a high-quality transfer image for a long period of time. It is in providing the manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventor has a dielectric constant in the range of 7 to 12, and an index representing the anisotropy of the dielectric constant in the plane direction: the maximum value of MOR-c It has been found that a polyimide resin belt having an isotropic dielectric constant in the plane direction with a surface roughness of 1.2 or less can achieve the above object. Based on this knowledge, further studies have been made and the present invention has been completed.

  That is, the present invention provides the following polyimide resin belt.

  Item 1. A polyimide resin belt having a dielectric constant in the range of 7 to 12, and an index indicating the anisotropy of dielectric constant in the plane direction at any location of the polyimide resin belt: the maximum value of MOR-c is 1 .Polyimide resin belt having isotropic dielectric constant in the plane direction of 2 or less.

  Item 2. Item 5. The polyimide resin belt according to Item 1, wherein the polyimide resin belt contains 75 to 87% by weight of polyimide resin and 13 to 25% by weight of conductive filler.

  Item 3. Item 3. The polyimide resin belt according to Item 1 or 2, wherein the polyimide resin belt is a seamless belt having a thickness of about 80 to 120 μm and a circumferential length of about 350 to 3000 mm.

  Item 4. Item 4. The polyimide resin belt according to any one of Items 1 to 3, wherein the polyimide resin is a polyimide resin or a polyamideimide resin.

  Item 5. Item 5. An intermediate transfer member comprising the polyimide resin belt according to any one of Items 1 to 4.

Item 6. A method for producing a polyimide resin belt having an isotropic dielectric constant in a plane direction according to Item 1,
(1) A liquid material in which conductive filler is uniformly dispersed on the inner peripheral surface of a cylindrical mold rotating at a centrifugal acceleration of about 0.5 to 5.0 times the gravitational acceleration is applied with a uniform thickness by a spray method. The process of
(2) The cylindrical mold is heated at a temperature of about 100 to 140 ° C. while being rotated at a centrifugal acceleration of about 0.5 to 5.0 times the gravitational acceleration, and a coating having a nonvolatile content concentration of 35% by weight or more. And (3) a method of heating the coating film at a temperature of about 250 ° C. or higher while attached to the inner peripheral surface of the cylindrical mold.

  Hereinafter, the present invention will be described in detail.

  The polyimide resin belt of the present invention has a dielectric constant of 7 to 12, preferably 7 to 11, at any location of the polyimide resin belt, and represents an anisotropy of dielectric constant in the plane direction. : A polyimide resin belt having an isotropic dielectric constant in the plane direction, wherein the maximum value of MOR-c is 1.2 or less, preferably 1.1 or less, more preferably 1.05 or less. And

  Here, the measurement of the dielectric constant in the plane direction uses a molecular orientation meter (MOA-6020 manufactured by Oji Scientific Instruments Co., Ltd.) that obtains the degree of molecular orientation from the intensity of the microwave transmitted through the test piece. The measurement principle is a method of irradiating a microwave every time the sample is rotated by a certain angle, measuring the transmission intensity of the microwave, and measuring the anisotropy of the dielectric constant in the plane direction of the sample.

  For example, as shown in FIG. 1, in a sample having an anisotropic dielectric constant, the angle dependency (orientation pattern) of the transmission intensity in polar coordinates is an ellipse, and the minor axis direction of the orientation pattern is the direction with the maximum dielectric constant. The long axis direction of the pattern indicates the direction with the minimum dielectric constant. The dielectric constant (ε) is expressed as an average value of all measured dielectric constants, and specifically means, for example, the value of “ε′ave” in FIG. In addition, the degree of ellipse of the alignment pattern (ratio of major axis to minor axis) means the orientation degree, that is, MOR (Microwave Orientation Ratio) indicating the anisotropy of dielectric constant.

  Here, since MOR is influenced by the thickness of the sample, in practice, thickness correction is performed, and MOR-c converted to a desired thickness (90 μm in the present invention) is used. If MOR-c is used, it is possible to compare the isotropy of dielectric constant even in samples having different thicknesses. Specifically, MOR-c is derived from the following formula (I).

MOR-c = {t _c (MOR-1) / t _s } +1 (I)
Here, _{t s} is the thickness of the sample, _{t c} is to be corrected thickness (90 [mu] m), MOR values obtained by the measurement, MOR-c show the MOR value after correction. By using this MOR-c value, the isotropy of the dielectric constant in the sample surface direction can be evaluated more easily and in a short time. Note that the closer the value of MOR-c is to 1.000, the more isotropic the belt is.

  The polyimide resin used in the present invention may be non-thermoplastic or thermoplastic. Thermoplastic polyimide resins have the advantage that endless tubular belts can be molded using melt extrusion, but are inferior to non-thermoplastic polyimide resins in terms of heat resistance. For this reason, it is preferable to select a non-thermoplastic polyimide resin particularly when applied to a functional belt for a copying machine.

  Polyimide resins include polyimide resins (especially aromatic polyimide resins) and polyamideimide resins (particularly aromatic polyamideimide resins), which can be appropriately selected and used in the present invention. There are no particular restrictions on the types and combinations of starting materials for the polyimide resin and polyamideimide resin.

  Examples of the starting material for the polyimide resin include an acid component containing an aromatic tetracarboxylic dianhydride and an amine component containing an aromatic diamine.

  Examples of the aromatic tetracarboxylic dianhydride include biphenyltetracarboxylic dianhydride and the like. Specifically, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride (a-BPDA ) 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA), 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, and two of the above Examples thereof include blended biphenyltetracarboxylic dianhydride.

  Examples of the aromatic diamine include diaminodiphenyl ether, specifically, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and the like.

  Examples of the starting material for the polyamide-imide resin include an acid component containing trimellitic acid or a derivative thereof, and an amine component containing aromatic diisocyanate.

  The acid component of the polyamide-imide resin contains trimellitic acid or its anhydride, acid chloride, etc., but trimellitic anhydride is preferred from the viewpoint of reactivity, heat resistance, solubility, and the like. In addition to trimellitic acid or a derivative thereof, other acid components may be contained. For example, tetracarboxylic acids such as pyromellitic acid, biphenyltetracarboxylic acid, biphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, biphenylethertetracarboxylic acid, ethylene glycol bistrimellitate, propylene glycol bistrimellitate, or anhydrides thereof; Aliphatic acids such as acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid Dicarboxylic acid; terephthalic acid, isophthalic acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, aromatic dicarboxylic acid such as naphthalenedicarboxylic acid, etc. It is. At least one of these acidic components can be used in addition to trimellitic acid or a derivative thereof. In particular, benzophenone tetracarboxylic acid anhydride, biphenyl tetracarboxylic acid anhydride, and the like are preferable.

  When the total acid component is 100 mol%, trimellitic acid or a derivative thereof is preferably 50 mol% or more, particularly 50 to 90 mol% of trimellitic anhydride and benzophenonetetracarboxylic anhydride. The thing which 10-50 mol% of a product and / or biphenyltetracarboxylic anhydride contains is preferable at the point of dimensional stability.

  Examples of the aromatic isocyanate include 4,4′-diphenylmethane diisocyanate bitolylene diisocyanate, 3,3′-diphenylsulfone diisocyanate, isophorone disissocyanate, 4,4′-dicyclohexylmethane diisocyanate, m-xylene disissocyanate, Examples thereof include p-xylene disissocyanate and 1,4-cyclohexylene diisocyanate.

  In order to obtain a polyimide resin belt having a dielectric constant of 7 to 12 in the present invention, a conductive filler is blended with the polyimide resin. Examples of the conductive filler include carbon black; metal oxides such as tin oxide and titanium oxide (including those whose surface is coated with tin oxide); metals such as copper, iron, nickel, and aluminum; barium titanate; Examples thereof include lead zirconate titanate; conductive silica; and conductive polymers such as polyaniline and polyacetylene. A dielectric constant in the above range can be achieved by dispersing one or more of these suitable ones in a polyimide resin. Among these, carbon black having low conductivity is preferably selected. The conductive properties may be controlled by grafting a polymer on the surface of the carbon black particles or coating an insulating material, and the surface of the carbon black particles may be oxidized. In particular, oxidized furnace black and channel black are preferable. The conductive filler is preferably spherical (granular), acicular, or flat, and the average particle diameter may be about 15 to 200 nm.

  Specifically, Degussa's “Special Black 4”, “Special Black 5”, “Special Black 250”, “Printex V”, Mitsubishi Chemical “MA100”, “MA100R”, “MA7”, etc. A single type or a plurality of types of carbon blacks may be used in combination.

  The compounding amount of the conductive filler is about 13 to 25% by weight, preferably about 13 to 20% by weight, based on the total weight of the polyimide resin belt. When the amount is less than 13% by weight, a structure is easily formed, and the formed image may be uneven due to the anisotropy of the dielectric constant in the surface direction. Further, the dielectric constant is easily changed by repeatedly passing an excessive current. On the other hand, when the blending amount exceeds 25% by weight, the polyimide resin belt loses its strength as an intermediate transfer member, and the intermediate transfer member is damaged due to long-term use. turn into.

  The polyimide resin is in the range of about 75 to 87% by weight, preferably about 80 to 85% by weight, based on the total weight of the polyimide resin belt.

  The polyimide resin belt of the present invention can be used as an intermediate transfer member. The thickness and circumference can be appropriately determined according to the purpose of use. For example, the thickness is about 80 to 120 μm, preferably about 90 to 100 μm, and the circumference is about 350 to 3000 mm. In recent years, it has been desired to use a belt having a long circumference in order to improve the printing speed, but in general, when the circumference becomes large, the anisotropy of the dielectric constant in the surface direction becomes remarkable and a desired transfer belt can be obtained. There is no problem. However, the polyimide resin belt of the present invention is a belt having a large circumferential length, has an isotropic dielectric constant in the surface direction, and maintains high quality. For example, even if the belt has a large circumference of about 1500 to 3000 mm, it retains an excellent isotropic dielectric constant. In addition, this polyimide resin belt has a seamless seamless belt shape, and enables high-quality image formation as compared with an intermediate transfer member obtained by processing a flat film into a seamless shape by seaming.

  The method for producing the polyimide resin belt of the present invention is preferably based on a rotational molding method using a spray method. This is because it is easier to obtain a film with better dimensional accuracy than the melt extrusion method, and when a non-thermoplastic polyimide resin with excellent heat resistance is selected, molding by the melt extrusion method is impossible. Because. In any part of the polyimide resin belt, an index representing the anisotropy of the dielectric constant in the plane direction: means for making the maximum value of MOR-c 1.2 or less is the polyimide resin intermediate transfer of the present invention. In the manufacturing process of the member, this is achieved by making the flow of the liquid raw material as small as possible and making the molecular chain of the polyimide resin non-oriented in the plane direction.

  As a method for producing a polyimide resin belt, (1) a liquid in which a conductive filler is uniformly dispersed on the inner peripheral surface of a cylindrical mold rotating at a low speed with a centrifugal acceleration of 0.5 to 5.0 times the gravitational acceleration. A step of applying the raw material in a uniform thickness by a spray method, (2) at a temperature of 100 to 140 ° C. while the cylindrical mold is rotated at a low speed with a centrifugal acceleration of 0.5 to 5.0 times the gravitational acceleration. A step of volatilizing the solvent by heating to form a film having a non-volatile content of 35% by weight or more; (3) converting the polyimide and / or volatilizing the solvent while the film is attached to the inner peripheral surface of the cylindrical mold. And a step of heating at a temperature and a time sufficient to cause the heat treatment to occur.

  The centrifugal acceleration (G) used in the present invention is derived from the formula (II).

G (m / s ² ) ＝ r ・ ω ² ＝ r ・ (2 ・ π ・ n) ² (II)
Here, r is the radius (m) of the cylindrical mold, ω is the angular velocity (rad / s), and n is the number of rotations per second (the number of rotations during 60 s is rpm). The gravitational acceleration (g) to be compared is 9.8 (m / s ² ).

  First, the liquid raw material is prepared. As a liquid raw material, when the material of the polyimide resin belt is a polyimide resin, a polyamic acid solution in which a previous polyamic acid that is not substantially imidized is dissolved in a solvent may be mentioned. Further, when the material of the polyimide resin belt is a polyamide-imide resin, a polyamide-imide resin solution in which a polyamide-imide resin that has been imide-closed by a polymerization method in a solution using an acid chloride method or an isocyanate method is dissolved in a solvent is used. Can be mentioned.

  The solvent to be used is preferably an aprotic organic polar solvent. For example, N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”), N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, hexamethylphosphoamide, 1,3-dimethyl-2-imidazolidinone and the like are used. One or two or more of these solvents may be used. In particular, NMP is preferable. What is necessary is just to determine the usage-amount of a solvent so that it may become about 200-700 weight part (preferably about 250-500 weight part) with respect to 100 weight part of total amounts of the acid component and amine component of a raw material.

  When a conductive filler such as carbon black is added to the above liquid raw material, the viscosity increases, so it may be difficult to pulverize the conductive filler due to the impact force between balls performed in a dispersing machine such as a ball mill. is there. In order to add the conductive filler and uniformly disperse it in the liquid raw material, it must be accompanied by an interfacial phenomenon of pulverization of the conductive filler performed by a disperser and “wetting” by the solvent liquid of the conductive filler being loosened. Don't be. According to the experiments by the present inventors, when the viscosity of the solution is in the range of 0.5 to 10.0 Pa · s, preferably 1.0 to 5.0 Pa · s, the dispersion deterioration of the conductive filler is minimized. Can be suppressed. The dispersion method is not particularly limited, and examples thereof include a dispersion method using a ball mill method, an ultrasonic mill method, or the like. In addition, an imidazole compound (2-methylimidazole, 1,2-dimethylimidazole, 2-methyl-4-methylimidazole, 2-ethyl-4-ethylimidazole, 2- You may add additives, such as a phenyl imidazole) and surfactant (fluorine-type surfactant etc.).

  The liquid raw material is made by spraying a liquid raw material in which a conductive filler is uniformly dispersed on the inner peripheral surface of a cylindrical mold rotating at a low speed with a centrifugal acceleration of 0.5 to 5.0 times the acceleration of gravity. It is applied in a thickness (see, for example, FIG. 2A). That is, the liquid raw material is supplied by the spray method at a low speed rotation of 0.5 to 5.0 times the acceleration of gravity, so that the shearing force applied in the rotation direction is small, and the orientation of molecular chains, carbon black, etc. The structure orientation of the conductive filler can be suppressed. However, if the centrifugal acceleration is less than 0.5 times the gravitational acceleration, there is a risk that the supplied liquid raw material may flow down (drink) without being in close contact with the inner peripheral surface of the cylindrical mold. On the other hand, if the acceleration is greater than 5.0 times the gravitational acceleration, orientation of molecular chains and structure orientation of conductive fillers such as carbon black will occur due to shear force in the rotational direction applied during supply. Moreover, the liquid raw material flows due to centrifugal force, and conductive fillers such as carbon black are also oriented in the flow direction to form a structure, which is not preferable. In particular, it is more preferable to rotate at a centrifugal acceleration of 0.8 to 4.0 of gravitational acceleration.

  Further, the effect of applying by the spray method can be instantaneously brought into close contact with the inner peripheral surface of the rotating cylindrical mold by atomizing the liquid raw material to minimize the flow during supply. The material can be supplied at the same rotational speed without being greatly affected by the viscosity of the liquid material. A thin coating film can be easily obtained, and the non-volatile concentration of the liquid raw material can be set high.

  The liquid source supply means applies the liquid source to the inner peripheral surface of the cylindrical mold by moving the liquid source in the direction of the axis of rotation of the cylindrical mold rotating while being discharged by the spray method. The shape of the spray is not particularly limited and can be used as appropriate, such as a circle or rectangle. Also, the size is not particularly limited, and it can be designed to have an appropriate discharge pressure depending on the combination with the viscosity of the liquid material to be discharged. The distance between the spray head and the cylindrical mold may be arbitrary, and is preferably about 5 mm to 200 mm. There is no particular limitation on the discharge pressure method, but a compressed air or a high viscosity liquid-compatible MONO pump, a carrier pump, or the like is used.

  As described above, when the liquid material is applied to the inner peripheral surface of the cylindrical mold by the spray method, it is not necessary to make the film thickness uniform by flowing the liquid material by high-speed rotation of the cylindrical mold. Moreover, the influence on the electrical characteristics of the polyimide resin belt caused by the flow of the raw material can be avoided. It is preferable to apply a mold release agent to the inner peripheral surface of the cylindrical mold so that the polyimide resin does not adhere. Although there is no restriction | limiting in the kind of mold release material, What is necessary is just what is not attacked by the vapor | steam of the water of the solvent of a liquid raw material, or the water generated from resin at the time of a heating reaction.

  In the liquid resin film forming step, the solvent is used at a temperature of 100 to 140 ° C. while rotating at a low speed with a centrifugal acceleration of 0.5 to 5.0 times (preferably 0.8 to 4.5 times) the weight acceleration. Is volatilized to make the nonvolatile content concentration 35% by weight or more, thereby forming a film on the inner peripheral surface of the cylindrical mold (see, for example, FIG. 2B). In general, it is known that polyamic acid, which is a precursor of polyimide resin, hardly undergoes thermal imidization reaction when heated at 70 to 80 ° C., and eventually becomes saturated at a nonvolatile concentration of about 26% by weight. Therefore, after making it progress in the range of 10-30% of imidation by heating at the temperature of 100-140 degreeC, a solvent can be removed and a non volatile matter density | concentration can be 35 weight% or more. When heated at a temperature higher than 140 ° C., rapid solvent volatilization occurs, which may cause not only deterioration of the surface state of the formed film, but also a problem that the dielectric constant is outside the range of 7 to 12 required as an intermediate transfer member. .

  In the polyimide resin film forming step, the temperature is increased over 80 to 200 minutes (preferably over 100 to 160 minutes) while adhering to the inner peripheral surface of the cylindrical mold, depending on the type of polyimide resin. . The heating rate is preferably about 1.5 to 0.8 ° C./min. Next, a polyimide resin film can be formed by heating at a temperature at which the polyimide is completely converted and / or at a temperature and time sufficient to completely volatilize the solvent (for example, FIG. 2C). See). Usually, the temperature may be increased to about 250 ° C. or higher. In the case of a polyimide resin, for example, heat treatment can be performed at 280 to 350 ° C. for 30 to 90 minutes, and in the case of a polyamideimide resin, for example, heat treatment can be performed at 250 to 300 ° C. for 30 to 90 minutes to form a polyimide resin film. By performing film formation while adhering to the inner peripheral surface of the cylindrical mold, shrinkage caused by imidization reaction or solvent volatilization can be suppressed, and the polymer chains can be uniformly oriented in the plane direction by the stress.

  In particular, polyimide resins using biphenyltetracarboxylic dianhydride and diaminodiphenyl ether as raw materials monomers, acid anhydrides and aromatics composed of trimellitic anhydride and benzophenonetetracarboxylic anhydride and / or biphenyltetracarboxylic anhydride Polyamideimide resin using isocyanate as a raw material monomer has a characteristic that in-plane orientation is relaxed when heated at a high temperature of about 250 ° C. or higher, and it tends to be non-oriented.

  The polyimide resin belt produced in this way has a maximum value of an index indicating the anisotropy of the dielectric constant in the plane direction: MOR-c of 1.2 or less, preferably 1.1 at any part of the belt. Hereinafter, an intermediate transfer member having an isotropic dielectric constant in the plane direction, more preferably 1.05 or less, and excellent dimensional stability such as flatness is obtained.

  The polyimide resin belt of the present invention has an isotropic dielectric constant in the surface direction, and the dielectric constant hardly changes even when an excessive current is repeatedly applied. Therefore, the polyimide resin belt is accurate when used as an intermediate transfer member of a color image forming apparatus. Transfer can be realized, and a high-quality transfer image can be obtained stably for a long period of time. Further, since the life of the intermediate transfer member is extended and maintenance-free is realized, there is an advantage that the reliability as a color image forming apparatus is improved. Furthermore, since the transfer surface of the intermediate transfer member is flat without undulation, a good image can be obtained.

  The color image forming apparatus is an electrophotographic image forming apparatus including at least one polyimide resin belt according to the present invention. By providing the polyimide resin belt of the present invention as an intermediate transfer belt, a direct transfer belt or a transfer / fixing belt, a high-quality transfer image can be obtained.

  When used as a transfer and fixing belt, it is effective to form a non-adhesive resin film on the surface in order to improve the releasability of the toner adhering to the surface. Examples of the non-adhesive resin film material include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). A fluorine-based resin or the like is preferable. Further, an elastic silicone resin, a fluororubber resin, an elastic fluorosilicone resin, an elastic polysiloxane, or the like may be used.

  According to the polyimide resin belt of the present invention, the formed image is not uneven, accurate transfer can be realized, and good image quality can be obtained. That is, the polyimide resin belt of the present invention has an excellent characteristic that it has an isotropic dielectric constant in the surface direction. Therefore, for example, when used as an intermediate transfer belt of a color image forming apparatus, it is possible to appropriately perform charge charging stability and slow charging, and obtain a high-quality transfer image stably for a long period of time. Become.

  The contents of the present invention will be specifically described below based on examples, but the present invention is not limited thereto.

Example 1
20 kg of a polyamic acid solution of a polyimide precursor prepared by synthesizing 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether in N-methyl-2-pyrrolidone was prepared. . This solution had a viscosity of 3.0 Pa · s and a nonvolatile content concentration of 18.0% by weight. To this solution, 0.55 kg of carbon black (“MA100” manufactured by Mitsubishi Chemical Corporation) and 2.0 kg of N-methyl-2-pyrrolidone were added, and the carbon black was uniformly dispersed by a ball mill.

  This carbon black-dispersed polyimide precursor solution had a nonvolatile content concentration of 18.40% by weight. Of the nonvolatile matter weight, the carbon black content was 13.25% by weight. The average particle size of carbon black in the solution was 0.32 μm, and the maximum particle size was 0.76 μm.

  The “nonvolatile content concentration” in this specification is a value calculated as follows. The sample is precisely weighed in a heat-resistant container such as a metal cup, and the weight of the sample at this time is Ag. The heat-resistant container containing the sample is placed in an electric oven, heated and dried while sequentially heating at 120 ° C. × 15 minutes, 180 ° C. × 15 minutes, 280 ° C. × 30 minutes. (Weight) is Bg. The values of A and B of five samples of the same sample were measured (n = 5), and applied to the following formula (III) to determine the nonvolatile content concentration. The average value of the five samples was adopted as the nonvolatile content concentration in the present invention.

Nonvolatile content concentration = B / A x 100 (%) (III)
While rotating a cylindrical mold having an outer diameter of 324 mm, an inner diameter of 300 mm, and a length of 500 mm at a centrifugal acceleration (approximately 154 rpm) that is 4.0 times the gravitational acceleration, carbon black-dispersed polyimide is applied to the inner peripheral surface of the cylindrical mold. The precursor solution was uniformly applied at 480 mm by a spray method. The coating thickness was calculated from the nonvolatile content concentration, and was determined so that the thickness of the polyimide resin belt was 90 μm. Thereafter, while rotating at a centrifugal acceleration (about 154 rpm) of 4.0 times the gravitational acceleration, the temperature was raised to 130 ° C. over 30 minutes, and then kept at 130 ° C. for 90 minutes to evaporate the solvent. The nonvolatile content concentration was about 55% by weight.

  Next, this tubular product is put into a high-temperature heating furnace while adhering to the inner peripheral surface of the cylindrical mold, and the temperature is raised to 320 ° C. over 150 minutes (heating rate: about 1.27 ° C./min). Polyimide conversion was completed by heating at 60 ° C. for 60 minutes. Thereafter, the polyimide resin belt was taken out from the mold after being cooled to room temperature, cut into a width of 350 mm, and used as an intermediate transfer belt of a color image forming apparatus. The results are shown in Table 1.

  Next, the dielectric constant in the plane direction was measured to obtain MOR-c. When a polyimide resin belt sample is irradiated with microwaves, the transmission intensity of the absorbed microwave differs from the anisotropy of the sample, so the major and minor axes of polar coordinates (orientation pattern) representing the difference in transmission intensity The ratio was determined as an index MOR value indicating the molecular orientation state. The orientation angle and the degree of anisotropy can be known from the orientation pattern. A total of 4 pieces of 4 cm × 4 cm sample pieces were cut out from a total of 4 places, 2 places in the width direction of the polyimide resin belt and 2 places in the circumferential direction, and each sample had a diameter of 15 mm at a measurement frequency of 19 to 20 GHz. The site was measured. This was corrected with the reference thickness (90 μm), and MOR-c was measured (see the above formula (I)). The measurement results are shown in Table 2.

Example 2
Using the same carbon black-dispersed polyimide precursor solution as in Example 1, a cylindrical mold having an outer diameter of 740 mm, an inner diameter of 700 mm, and a length of 700 mm was obtained at a centrifugal acceleration (about 45 rpm) of 0.8 times the gravitational acceleration. While rotating, a carbon black-dispersed polyimide precursor solution was uniformly applied at 650 mm by spraying on the inner peripheral surface of the cylindrical mold. The coating thickness was calculated from the nonvolatile content concentration, and was determined so that the thickness of the intermediate transfer member was 90 μm.

  After that, while rotating at a centrifugal acceleration (about 45 r.p.m.) which is 0.8 times the gravitational acceleration, the temperature was raised to 110 ° C. over 60 minutes, and then kept at 110 ° C. for 90 minutes to evaporate the solvent. The nonvolatile content concentration was about 42% by weight. Next, this tubular product is put into a high-temperature heating furnace while adhering to the inner peripheral surface of the cylindrical mold, and the temperature is raised to 320 ° C. over 150 minutes (temperature increase rate: about 1.40 ° C./min). Polyimide conversion was completed by heating at 90 ° C. for 90 minutes.

  Then, it cooled to normal temperature and took out the polyimide resin belt from the metal mold | die. Four points were sampled in the same manner as in Example 1, and the MOR-c value of this sample was measured. The results are shown in Table 3.

Example 3
20 kg of polyamideimide solution consisting of 90 mol% trimellitic anhydride, 5 mol% benzophenone tetracarboxylic anhydride, 5 mol% biphenyltetracarboxylic anhydride and 100 mol% aromatic diisocyanate was prepared. . This solution had a viscosity of 50.0 Pa · s and a nonvolatile content concentration of 14.0% by weight. To this solution, 0.50 kg of carbon black (“Special Black 4” manufactured by Degussa) and 6.0 kg of N-methyl-2-pyrrolidone were added, and the carbon black was uniformly dispersed by a ball mill. This carbon black-dispersed polyamideimide solution had a nonvolatile content concentration of 12.45% by weight. Of the nonvolatile matter weight, the carbon black content was 15.15% by weight. The average particle size of carbon black in the solution was 0.28 μm, and the maximum particle size was 0.58 μm.

  While rotating a cylindrical mold with an outer diameter of 324 mm, an inner diameter of 300 mm, and a length of 500 mm at a centrifugal acceleration (approximately 163 rpm) 4.5 times the gravitational acceleration, a carbon black-dispersed polyamide is applied to the inner peripheral surface of the cylindrical mold. The imide solution was uniformly applied at 450 mm by a spray method. The coating thickness was calculated from the nonvolatile content concentration, and was determined such that the thickness of the polyamideimide resin belt was 90 μm. Then, while rotating at a centrifugal acceleration (about 109 r.p.m.) 2.0 times the gravitational acceleration, the temperature was raised to 140 ° C. over 30 minutes, and then kept at 140 ° C. for 90 minutes to evaporate the solvent. The nonvolatile content concentration was about 60% by weight. Next, this tubular product is put into a high-temperature heating furnace while adhering to the inner peripheral surface of the cylindrical mold, and heated to 260 ° C. (temperature increase rate: about 1.00 ° C./min) over 120 minutes. The solvent was volatilized by heating at 90 ° C. for 90 minutes.

  Thereafter, the polyamide-imide resin belt was taken out from the mold after cooling to room temperature, cut into a width of 350 mm, and used as an intermediate transfer belt of a color image forming apparatus. The results are shown in Table 1. Further, as in Example 1, four points were sampled and MOR-c values were measured. The results are shown in Table 4.

Comparative Example 1
A specified amount of the carbon black-dispersed polyimide precursor solution obtained in Example 1 was introduced into the inner peripheral surface of a cylindrical mold having an outer diameter of 324 mm, an inner diameter of 300 mm, and a length of 500 mm using a nozzle-type discharge device. Here, the nozzle type means that the solution is discharged from a minute opening and the raw material is supplied into the mold in a streak form without being atomized as in the spray method (the same applies hereinafter). Next, the carbon black-dispersed polyimide precursor solution was cast to a uniform coating thickness on the inner peripheral surface at a centrifugal acceleration (about 772 rpm) 100 times the gravitational acceleration. When the centrifugal acceleration is small, the precursor solution is not sufficiently flowed, and the film is formed while the coating film thickness at the portion charged into the cylindrical mold is large. For this reason, in the rotational molding method using centrifugal force, it is necessary to uniformly cast the precursor solution on the inner peripheral surface of the cylindrical mold with a large centrifugal acceleration.

  Thereafter, the rotation was changed to a centrifugal acceleration (about 172 r.p.m.) which was 5.0 times the gravitational acceleration, the temperature was raised to 130 ° C. over 30 minutes, and then kept at 130 ° C. for 90 minutes to volatilize the solvent. The nonvolatile content concentration was about 52% by weight. Next, this tubular product is put into a high-temperature heating furnace while adhering to the inner peripheral surface of the cylindrical mold, and the temperature is raised to 320 ° C. over 150 minutes (heating rate: about 1.27 ° C./min). Polyimide conversion was completed by heating at 60 ° C. for 60 minutes.

  Thereafter, the polyimide resin belt was taken out from the mold after being cooled to room temperature, cut into a width of 350 mm, and used as an intermediate transfer belt of a color image forming apparatus. The results are shown in Table 1. Thereafter, in the same manner as in Example 1, four points were sampled and MOR-c values were measured. The results are shown in Table 5.

Comparative Example 2
In Example 3, while rotating a cylindrical mold having an outer diameter of 324 mm, an inner diameter of 300 mm, and a length of 500 mm at a centrifugal acceleration (about 163 rpm) of 4.5 times the gravitational acceleration, The obtained carbon black-dispersed polyamideimide solution was discharged with a nozzle-type discharge device. Spiral discharge was performed by moving the nozzle in the direction of the axis of rotation of the rotating cylindrical mold.

  Thereafter, the centrifugal acceleration (about 772 r.p.m.) which is 100 times the gravitational acceleration was changed, and by continuing to rotate the cylindrical mold, the spiral streaks disappeared in about 10 minutes due to the fluidity of the solution. Then, while rotating at a centrifugal acceleration (about 772 r.p.m.) 100 times the gravitational acceleration, the temperature was raised to 130 ° C. over 90 minutes, and then kept at 130 ° C. for 60 minutes for solvent volatilization. Next, this tubular product is put into a high-temperature heating furnace while adhering to the inner peripheral surface of the cylindrical mold, and the temperature is raised to 260 ° C. over 120 minutes (heating rate: about 1.08 ° C./min). The solvent was volatilized by heating at 90 ° C. for 90 minutes.

  Thereafter, the polyamide-imide resin belt was taken out from the mold after cooling to room temperature, cut into a width of 350 mm, and used as an intermediate transfer belt of a color image forming apparatus. The results are shown in Table 1. Thereafter, in the same manner as in Example 1, four points were sampled and MOR-c values were measured. The results are shown in Table 6.

Comparative Example 3
20 kg of a polyamic acid solution of a polyimide precursor prepared by synthesizing 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine in N-methyl-2-pyrrolidone was prepared. This solution had a viscosity of 5.0 Pa · s and a nonvolatile content concentration of 18.0% by weight. Carbon black (“DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.): 0.28 kg and N-methyl-2-pyrrolidone: 3.0 kg were added to this solution, and the carbon black was uniformly dispersed with a ball mill. This carbon black-dispersed polyimide precursor solution had a nonvolatile content concentration of 16.67% by weight. Of the nonvolatile matter weight, the carbon black content was 7.22% by weight. The average particle size of carbon black in the solution was 0.87 μm, and the maximum particle size was 5.86 μm.

  While rotating a cylindrical mold having an outer diameter of 326 mm, an inner diameter of 312 mm, and a length of 500 mm at a centrifugal acceleration (about 151 rpm) that is 4.0 times the gravitational acceleration, carbon black-dispersed polyimide is applied to the inner peripheral surface of the cylindrical mold. The precursor solution was uniformly applied at 480 mm by a spray method. The coating thickness was calculated from the nonvolatile content concentration, and was determined so that the thickness of the polyimide resin belt was 90 μm. Thereafter, while rotating at a centrifugal acceleration (about 151 r.p.m.) which is 4.0 times the gravitational acceleration, the temperature was raised to 120 ° C. for 30 minutes, and then kept at 120 ° C. for 90 minutes to volatilize the solvent. And the tubular thing was taken out from the internal peripheral surface of this cylindrical metal mold | die. The non-volatile content concentration of this tubular product was about 40% by weight.

Next, in order to remove the remaining solvent along with imidation of the tubular product, this was inserted into an aluminum cylindrical mold having a surface roughness R _Z = 2.0 μm, an outer diameter of 300 mm, and a length of 380 mm, and dried with hot air I put it in the plane. It was made to reach 450 degreeC in 180 minutes, and it heated at the 450 degreeC for 30 minutes. Finally, it was cooled to room temperature, taken out from the mold, cut into a width of 350 mm, and used as an intermediate transfer belt of a color image forming apparatus. The results are shown in Table 1. Thereafter, in the same manner as in Example 1, four points were sampled and MOR-c values were measured. The results are shown in Table 7.

  As can be seen from the image evaluation results in Table 1 and the MOR-c values in Tables 2 to 7, the polyimide resin belts (polyimide resin belts or polyamideimide resin belts) of Examples 1 and 3 have a dielectric constant of 7. The maximum value of MOR-c was set within the range of the present invention (1.2 or less), and it was suggested that a good image can be obtained in any case.

  On the other hand, the polyimide resin belts of Comparative Examples 1 to 3 (polyimide resin belt or polyamideimide resin belt) have a maximum value of MOR-c that is out of the scope of the present invention even if the dielectric constant is in the range of 7 to 12. As a result, accurate transfer could not be realized and image defects occurred. Note that a film having a dielectric constant outside the range of 7 to 12 as in Patent Document 6 cannot achieve both the charging and discharging performance essential for the intermediate transfer member regardless of the maximum value of MOR-c. It is difficult to form an image.

  From the results of Examples 1 to 3 (Tables 2 to 4), the conductive filler is uniformly dispersed on the inner peripheral surface of the cylindrical mold rotating at a low speed with a centrifugal acceleration of 0.5 to 5.0 times the gravitational acceleration. The liquid material is applied at a uniform thickness by a spray method, and the solvent is volatilized at a temperature of 100 to 140 ° C. while rotating at a low speed with a centrifugal acceleration of 0.5 to 5.0 times the gravitational acceleration. A step of forming a film with a concentration of 35% by weight or more, and a temperature and time sufficient to completely convert the polyimide while the film is attached to the inner peripheral surface of the cylindrical mold or to completely evaporate the solvent. It can be seen that a polyimide resin belt having an isotropic dielectric constant in the plane direction where the maximum value of MOR-c is 1.2 or less can be obtained by a manufacturing method comprising a heating step.

It is a schematic diagram of MOR evaluation using the molecular orientation meter (Oji Scientific Instruments Co., Ltd. MOA-6020). It is a schematic diagram of the manufacturing process of the polyimide resin belt of this invention.

Claims (6)

A polyimide resin belt having a dielectric constant in the range of 7 to 12, and an index indicating the anisotropy of dielectric constant in the plane direction at any location of the polyimide resin belt: the maximum value of MOR-c is 1 A polyimide resin belt having an isotropic dielectric constant in the plane direction of 2 or less ,
(1) A liquid material in which conductive filler is uniformly dispersed on the inner peripheral surface of a cylindrical mold rotating at a centrifugal acceleration of about 0.5 to 5.0 times the gravitational acceleration is applied with a uniform thickness by a spray method. The process of
(2) The cylindrical mold is heated at a temperature of about 100 to 140 ° C. while being rotated at a centrifugal acceleration of about 0.5 to 5.0 times the gravitational acceleration, and a coating having a nonvolatile content concentration of 35% by weight or more. Forming, and
(3) A step of heating the coating film at a temperature of about 250 ° C. or higher with the film attached to the inner peripheral surface of the cylindrical mold.
A polyimide resin belt manufactured by a manufacturing method including: The polyimide resin belt according to claim 1, wherein the polyimide resin belt contains 75 to 87% by weight of a polyimide resin and 13 to 25% by weight of a conductive filler. The polyimide resin belt according to claim 1, wherein the polyimide resin belt is a seamless belt having a thickness of about 80 to 120 μm and a circumferential length of about 350 to 3000 mm. The polyimide resin belt according to claim 1, wherein the polyimide resin is a polyimide resin or a polyamideimide resin. An intermediate transfer member comprising the polyimide resin belt according to claim 1. Index indicating dielectric anisotropy in the plane direction at any part of the belt having a dielectric constant of 7 to 12: isotropic in the plane direction where the maximum value of MOR-c is 1.2 or less A method for producing a polyimide resin belt having a dielectric constant,
(1) A liquid material in which conductive filler is uniformly dispersed on the inner peripheral surface of a cylindrical mold rotating at a centrifugal acceleration of about 0.5 to 5.0 times the gravitational acceleration is applied with a uniform thickness by a spray method. The process of
(2) The cylindrical mold is heated at a temperature of about 100 to 140 ° C. while being rotated at a centrifugal acceleration of about 0.5 to 5.0 times the gravitational acceleration, and a coating having a nonvolatile content concentration of 35% by weight or more. And (3) a method of heating the coating film at a temperature of about 250 ° C. or higher while attached to the inner peripheral surface of the cylindrical mold.

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