JP2006272839A - Seamless belt and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a seamless belt which can be produced by a method wherein a hot film making step using a polyamide acid is efficiently performed in a short period of time, and which has proper flexibility even if a large amount of a conductive filler such as carbon black is incorporated. <P>SOLUTION: In this seamless belt which is manufactured by using polyamide-acid varnish consisting of a 5-30 wt.% polymer and a 95-70 wt.% solvent, the solvent is a mixed one which contains at least one kind of 10-70 wt.% compound, selected from among aprotic solvents with a boiling point of less than 200°C, as a first component, and which contains at least one kind of 90-30 wt.% compound, selected among aprotic solvents with a boiling point of 200°C or more, as a second component. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a seamless belt used in an electrophotographic image forming apparatus such as a copying machine, a laser beam printer, a facsimile, and a composite device thereof, and more particularly, for fixing, for a photoreceptor substrate, for intermediate transfer, The present invention relates to a seamless belt used for paper conveyance and transfer fixing.

    In an electrophotographic image forming apparatus, generally, an electrostatic latent image corresponding to an image obtained by an image reading device is formed on the surface of a charged photoreceptor, and a toner image is formed by a developing device. It is electrostatically transferred (primary transfer) to an intermediate transfer member composed of a seamless belt, transferred again from the intermediate transfer member to paper or the like (secondary transfer), and heated and fixed by a fixing roll or a fixing belt. At this time, the use of a seamless belt is being considered not only for the intermediate transfer member but also for fixing that also serves as a photosensitive member and transfer.

Conventionally, a plastic material has been used as a material for such a seamless belt for reasons such as good moldability and light weight, and this plastic material has excellent heat resistance, mechanical strength, and environmental resistance. Therefore, a polyimide belt using a polyimide resin has been studied. Moreover, as a characteristic requested | required of the belt material used for an electrostatic transfer system, it has what is called a medium resistance whose surface resistance value is about 10 < ⁸ > -10 < ¹³ > (omega | ohm) * cm. In general, in order to ensure such characteristics, a method of incorporating a conductive filler such as carbon black in a polyimide resin is used (see, for example, Patent Document 1 or 2).
JP-A-5-77252 JP-A-10-63115

  However, conductive fillers such as carbon black present in the resin significantly reduce the flexibility of the resin, and if such a belt is incorporated in an apparatus, the life of the semiconductive belt may be shortened. There is. In other words, the period until parts breakage such as the occurrence of cracks in the belt is shortened, leading to a result of increasing the labor and running costs such as belt replacement in the electrophotographic image forming apparatus.

  In addition, in order to prevent such flexibility from being lost as much as possible, a method of heat-treating the polyamic acid heating film forming process at a sufficient temperature and time has been devised. There is a problem that it is difficult to ensure, which is not desirable from the aspect of production efficiency of the seamless belt.

  Accordingly, an object of the present invention is to provide a seamless belt having good flexibility even when a polyamic acid heating film-forming process is efficiently performed in a short time and a large amount of conductive filler such as carbon black is contained. There is to do.

  As a result of intensive studies, the present inventors have found that the above object can be achieved by the seamless belt and the manufacturing method thereof shown below, and have completed the present invention.

  The present invention provides a method for producing a seamless belt using a polyamic acid varnish comprising 5 to 30% by weight of a polymer and 95 to 70% by weight of a solvent, wherein the solvent has a boiling point of less than 200 ° C. as a first component. 10 to 70% by weight of at least one compound selected from aprotic solvents, and 90 to 30% by weight of at least one compound selected from aprotic solvents having a boiling point of 200 ° C. or higher as the second component. It is a mixed solvent containing.

  In the present invention, the cause of the decrease in flexibility in the polyimide belt is due to the solvent evaporation contained in the polyamic acid varnish at the time of heat imidization, and by controlling the solvent evaporation rate in the solvent removal step during film formation, It has been found that the flexibility of the seamless belt can be improved. As for the solvent components, a mixed solvent made of a plurality of components having different boiling points compared to the case of using only one solvent and having a mixing ratio within a predetermined range is useful for improving the flexibility of the seamless belt. It has been found that. Specifically, by dividing a plurality of components of the solvent constituting the polyamic acid varnish into two parts based on a boiling point of 200 ° C. and mixing at a ratio in the above range, the polyamic acid heating film forming step can be performed in a short time. It is possible to provide a seamless belt that is efficient and has good flexibility even when a large amount of conductive filler such as carbon black is contained.

  The present invention provides a method for producing a seamless belt using a polyamic acid varnish comprising 5 to 30% by weight of a polymer and 95 to 70% by weight of a solvent, wherein the solvent has a boiling point of less than 200 ° C. as a first component. 10 to 70% by weight of at least one compound selected from aprotic solvents, and at least one compound selected from aprotic solvents having a boiling point of 200 ° C. or higher as a second component and a complex having a boiling point of 200 ° C. or higher. It is a mixed solvent containing 90 to 30% by weight of a total amount of cyclic tertiary amines or basic organic compound catalysts having a boiling point of 200 ° C. or higher.

  As described above, by adjusting the solvent components and controlling the solvent evaporation rate in the solvent removal step during film formation, it is possible to produce a seamless belt having good flexibility. The present invention further promotes imidization more effectively by mixing a predetermined amount of an imidization accelerator having a high boiling point with respect to the imidization accelerator to be added to the solvent, and at the same time, effectively improves the flexibility. Improvements can be made. Therefore, it has become possible to efficiently perform the polyamic acid heating film forming process in a short time and to provide a method for producing a seamless belt having excellent characteristics.

  The present invention is a process for producing the above-described seamless belt comprising a polyimide resin as a main component, wherein the polyamic acid varnish whose polyimide resin is a polyimide precursor is heated at 150 ° C. or higher to evaporate the solvent by 90% or more. Thereafter, it is obtained by further imide conversion by heating above 200 ° C.

  The present invention has found that the flexibility is improved by controlling the heating temperature that is largely involved in the solvent evaporation rate in the solvent removal step during film formation. In other words, by using a solvent composed of a plurality of components having different boiling points and changing the heating temperature stepwise to evaporate the solvent and imidize, the polyamic acid heating film forming process can be efficiently performed in a short time. And it became possible to produce a seamless belt having excellent flexibility. In particular, when an imidization accelerator is added, the function of the high boiling point imidization accelerator can be effectively utilized in the high temperature treatment stage, and imidization can be promoted more effectively.

  The present invention is the above-described seamless belt manufacturing method, characterized in that the folding strength of the belt is 200 times or more.

  The present invention also provides a seat belt manufactured by the above manufacturing method. Furthermore, the folding strength of the belt is 200 times or more.

  The belt produced in the present invention has excellent flexibility, and in particular, a belt having a predetermined value or more of folding resistance, which is an index of the belt, has a mechanical strength required for a belt material used in a transfer method or the like. A seamless belt satisfying elasticity and excellent in flexibility and a method for producing the same can be provided. The value of “belt bending resistance” is based on a measurement value based on the measurement method described in [Example] <Evaluation method> described later.

  As described above, according to the seamless belt of the present invention, the polyamic acid heating film-forming step can be efficiently performed in a short time, and even when a large amount of carbon black is contained, the seamless has good flexibility. Can provide a belt. For this reason, it is possible to extend the service life with a low-cost belt, and it is possible to reduce maintenance work such as belt replacement and running cost.

  Hereinafter, embodiments of the present invention will be described.

  The seamless belt of the present invention is a seamless belt mainly composed of a polyimide resin, and the polyimide resin is converted to an imide by using a polyamic acid varnish composed of 5 to 30% by weight of a polymer and 95 to 70% by weight of a solvent. It was obtained.

  Here, the solvent for forming the polyamic acid varnish is 10 to 70% by weight of at least one compound selected from aprotic solvents having a boiling point of less than 200 ° C. as the first component, and a boiling point of 200 ° C. as the second component. A mixed solvent containing 90 to 30% by weight of at least one compound selected from the above aprotic solvents is preferable.

  By adjusting the component composition of the solvent on the basis of the heating imidization temperature of 200 ° C., it is possible to efficiently control the solvent evaporation rate in the solvent removal step during film formation. Moreover, in the mixed solvent of a solvent having a boiling point of less than 200 ° C. and a solvent having a boiling point of 200 ° C. or more, the ratio of the former to the mixed solvent is less than 10% by weight, the polyamic acid varnish in the imidization stage The solvent component becomes excessive and the flexibility is improved, but the strength of the belt may be lowered. On the other hand, if it exceeds 70% by weight, the solvent component in the polyamic acid varnish in the imidization stage is insufficient, which may cause a decrease in flexibility and an increase in brittleness. In particular, when a large amount of conductive filler is contained, it is possible to produce a seamless belt having good flexibility by adjusting the component composition of such a solvent.

  As the solvent for the polymerization reaction, the above-described tetracarboxylic dianhydride and diamine can be used as appropriate. However, as an aprotic solvent having a boiling point of 200 ° C. or higher, γ-butyllactone, N-methyl-2-pyrrolidone, hexa Examples include methyl phosphortriamide and tetramethylene sulfone.

  Examples of aprotic solvents having a boiling point of less than 200 ° C. include N-methylpropionamide, N-methylcaprolactam, N, N-diethylformamide, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethyl. Examples include acetamide and dimethyl sulfoxide.

  Moreover, it is preferable to contain a heterocyclic tertiary amine having a boiling point of 200 ° C. or higher or a basic organic compound catalyst having a boiling point of 200 ° C. or higher as the imidization accelerator.

  Examples of the heterocyclic tertiary amines having a boiling point of 200 ° C. or higher include imidazole, phenylimidazole and benzimidazole. Examples of the basic organic compound catalyst having a boiling point of 200 ° C. or higher include quinoline and isoquinoline.

  At this time, the solvent is 10 to 70% by weight of at least one compound selected from aprotic solvents having a boiling point of less than 200 ° C. as the first component, and aprotic having a boiling point of 200 ° C. or more as the second component. The total amount of at least one compound selected from solvents and a heterocyclic tertiary amine having a boiling point of 200 ° C. or higher or a basic organic compound catalyst having a boiling point of 200 ° C. or higher is 90 to 30% by weight. A mixed solvent is preferred.

  Even when an imidization accelerator is added to a solvent, as described above, a seamless belt having good flexibility can be obtained by adjusting the components of the solvent and controlling the solvent evaporation rate in the solvent removal step during film formation. The same numerical range and effectiveness can be ensured for the boiling point and the mixing ratio of the two components, which are the criteria for solvent adjustment.

  The polyamic acid solution for producing the polyimide resin can be prepared, for example, by reacting an aromatic tetracarboxylic dianhydride with an aromatic diamine or an aliphatic diamine in an organic polar solvent.

  here. As the polyamic acid solution used as the raw material liquid for the polyimide resin, for example, a polyamic acid solution obtained by polymerizing tetracarboxylic dianhydride or its derivative and diamine in a solvent can be used.

（式中、Ｒは４価の有機基であり、芳香族、脂肪族、環状脂肪族、芳香族と脂肪族を組み合せたもの、またはそれらの置換された基である。） The polyamic acid is obtained by reacting tetracarboxylic dianhydride or a derivative thereof with an approximately equimolar amount of diamine in an organic solvent, and is usually used in the form of a solution. Such a tetracarboxylic dianhydride is represented by the following general formula (1), for example.
[Formula 1]

(In the formula, R is a tetravalent organic group, and is an aromatic, aliphatic, cycloaliphatic, a combination of aromatic and aliphatic, or a substituted group thereof.)

  Specific examples of the tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3′4,4′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetra. Carboxylic dianhydride, 2,3,3 ′, 4-biphenyltetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic Acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ) Sulfone dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, ethylenetetracarboxylic dianhydride and the like. That.

On the other hand, examples of diamines include 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane, 3,3′-dichlorobenzidine, 4,4′-diaminodiphenyl sulfide, 3 , 3′-diaminodiphenylsulfone, 1,5-diaminonaphthalene, m-phenylenediamine, p-phenylenediamine, 3,3′-dimethyl-4,4′-biphenyldiamine, benzidine, 3,3′-dimethylbenzidine, 3,3′-dimethoxybenzidine, 4,4′-diaminophenylsulfone, 4,4′-diaminophenyl sulfide, 4,4′-diaminodiphenylpropane, 2,4-bis (β-amino-tert-butyl) toluene Bis (p-β-amino-tert-butylphenyl) ether, bis (p-β-methyl-δ) Aminophenyl) benzene, bis-p- (1,1-dimethyl-5-amino-pentyl) benzene, 1-isopropyl-2,4-m-phenylenediamine, m-xylylenediamine, p-xylylenediamine, di (P-aminocyclohexyl) methane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, diaminopropyltetramethylene, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2-bis-3-aminopropoxyethane, 2,2-dimethylpropyleneamine, 3-methoxyhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylene Diamine 3-methylheptamethylenediamine, 5-methylnonamethylenediamine, 2,11-diaminododecane, 2,17-diaminoeicosadecane, 1,4-diaminocyclohexane, 1,10-diamino-1,10- Dimethyldecane, 1,12-diaminooctadecane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, piperazine H ₂ N (CH ₂ ) ₃ O (CH ₂ ) ₂ O (CH ₂ ) NH ₂ ,
H ₂ N (CH ₂ ) ₃ S (CH ₂ ) ₃ NH ₂ ,
_{H 2 N (CH 2) 3} N (CH 2) 2 (CH 2) 3 NH 2,
Etc.

  Examples of the aromatic diamine include 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylethane, 4,4′-diaminodiphenylpropane, and 4,4′-diaminodiphenyl. Examples include sulfone, 4,4′-diaminodiphenyl sulfide, m-phenylenediamine, p-phenylenediamine, m-toluylenediamine, p-toluylenediamine, benzidine, and 1,5-diaminonaphthalene.

  Furthermore, examples of the aliphatic diamine include hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, diaminopropyl, tetramethylene diamine, 3-methylheptamethylene diamine, 4,4-dimethyl- Heptabis- (3-aminopropoxymethane), 2,2-dimethylpropylenediamine, 3-methoxyhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 3-methylheptamethylenediamine , 5-methylnonamethylenediamine, 2,11-diaminododecane, 1,4-diaminocyclohexane, 1,10-diamino-1,10-dimethyldecane, 1,12-diaminooctadecane, 4,4′-diamino 3,3'-dimethyl dicyclohexylmethane Singh, 4,4'-diaminodicyclohexylmethane, 4,4'-diaminodiphenyl cyclohexane, 1,4-cyclohexane bis (methylamine) and the like.

  A polyamic acid is obtained by reacting the tetracarboxylic dianhydride (a) and the diamine (b) in an organic polar solvent. The monomer concentration (concentration of (a) + (b) in the solvent) at that time is set according to various conditions, but is preferably 5 to 30% by weight. Moreover, it is preferable to set reaction temperature to 80 degrees C or less, Most preferably, it is 5-50 degreeC, and reaction time is 0.5 to 10 hours. Thus, polyamic acid is produced | generated by making an acid dianhydride component and a diamine component react in an organic polar solvent, and solution viscosity rises with the progress of the reaction. In the present invention, by utilizing this phenomenon, the viscosity at 25 ° C. in a B-type viscometer of a polyamic acid solution containing a conductive filler can be adjusted to 1 to 1000 Pa · s. Moreover, the adjustment by the monomer concentration is also possible.

  Moreover, in order to improve the lubricity of the film surface, fillers such as silica, alumina and calcium phosphate can be mixed.

  In addition, carbon black such as ketjen black or acetylene black, metal such as aluminum or nickel, metal oxide compound such as titanium oxide or tin oxide, conductive powder such as potassium titanate, or polyaniline One or two or more suitable materials such as conductive polymers such as polyacetylene can be used.

  The carbon black used in the present invention has an average particle size of 5 to 100 nm, preferably 10 to 70 nm, and more preferably 15 to 60 nm. Those having an average particle diameter of less than 5 nm are substantially difficult to obtain. When the average particle diameter exceeds 100 nm, the surface roughness, mechanical strength and electrical properties of the polyimide resin composition containing the carbon black This is because it is difficult to obtain a practically satisfactory one from the viewpoint of resistance controllability.

  The said average particle diameter shows the average particle diameter based on the primary particle diameter measured with the electron microscope etc. In addition, the carbon black may have its electric resistance controlled by grafting a polymer on the particle surface or coating an insulating material, or may oxidize the carbon black particle surface.

  Examples of the carbon black used in the present invention include furnace black and channel black. Specifically, as the furnace black, “Special Black 550”, “Special Black 350”, “Special Black 250”, “Special Black 100”, “Printex 35”, “Print Mitsubishi” manufactured by Degussa Huls, Inc. “MA 7”, “MA 77”, “MA 8”, “MA 11”, “MA 100”, “MA 100R”, “MA 220”, “MA 230”, manufactured by Cabot Corporation, “MONARCH” 1300 "," MONARCH 1100 "," MONARCH 1000 "," MONARCH 900 "," MONARCH 880 "," MONARCH 800 "," MONARCH 700 "," MOGUL L "," REGAL 400R ", VULCAN XC-72R ”and the like, and“ Color Black FW200 ”,“ Color Black FW2 ”,“ Color Black FW2V ”,“ Color Black FW1 ”,“ Color Black ”,“ Black Black ”manufactured by Degussa Huls, Inc. “Special Black 6”, “Color Black S170”, “Color Black S160”, “Special Black 5”, “Special Black 4”, “Special Black 4A”, “Printex 150T”, “Printex P” "Printex 140U", "Printex 140V", etc. are listed, and single and multiple types of carbon black You may use together.

  Within the scope of the object of the present invention, a polymer material, a surfactant, and a dispersion stabilizer for inorganic salt damage can be used in order to enhance the dispersibility of carbon black.

  Next, in order to prepare a semiconductive polyamic acid solution, diamine and acid dianhydride are dissolved in an organic polar solvent, and the carbon black dispersion is added to the polyamic acid solution obtained after the polymerization reaction. A method of mixing and stirring, a method of dissolving a diamine and an acid dianhydride in the carbon black dispersion, and a polymerization reaction, etc. are mentioned. In order to make the dispersibility of carbon black uniform, the latter method is used. preferable.

  The semiconductive polyamic acid solution is applied to the inner peripheral surface of a cylindrical mold that is mirror-finished by a dispenser. The solution applied to the inner surface is defoamed and leveled by high-speed rotation of centrifugal molding to obtain a resin layer having a uniform thickness and high accuracy. The number of rotations is usually 500 to 2000 rpm, preferably 800 to 1500, although it depends on the mold diameter.

  The semiconductive polyamide varnish formed into a uniform coating film by rotational molding in a metal mold is dried while being slowly rotated in the mold.

  At this time, heating temperature is 150 degreeC or more, 160-200 degreeC is preferable and 170-190 degreeC is more preferable. When the temperature is lower than 150 ° C., the solvent in the polyamic acid solution slowly evaporates, so that a sufficient heating time is required, and the heating time cannot be shortened, so that productivity cannot be improved. On the other hand, when the temperature exceeds 200 ° C., the viscosity of the polyamic acid varnish is remarkably reduced, and thickness unevenness and repelling in the film surface occur due to solvent evaporation, so that sufficient dimensional stability cannot be obtained.

  By heating at this stage, the solvent is evaporated by 80% or more, more preferably 90% or more, and then the imide conversion is carried out by further heating above 200 ° C. Usually, the heating temperature at this time is not lower than the solvent evaporation temperature and not higher than 450 ° C., preferably 250 to 400 ° C., and the heating time is 10 to 60 minutes. After cooling, it is released from the mold to obtain the intended semiconductive seamless belt.

  About the obtained semiconductive seamless belt, in order to confirm the function, predetermined characteristics, such as surface resistivity, are measured. In particular, in the present invention, the evaluation of flexibility is important, and the folding strength of the belt is preferably 200 times or more. If it is less than 200 times, the semiconductive belt becomes short-lived when incorporated in the apparatus, and there is a risk of inconvenience in maintenance. A belt having a bending strength of 200 times or more can be said to be a seamless belt that satisfies the mechanical strength and elasticity required for a belt material used in a transfer system or the like and has excellent flexibility. The “belt bending resistance” referred to here is based on the following <Evaluation Method> measurement method.

  Hereinafter, the present invention will be further described with reference to specific examples. In addition, the evaluation items in Examples and the like were measured as follows. In addition, it cannot be overemphasized that this invention is not limited to this Example and evaluation method.

<Evaluation method>
(1) Folding strength According to JIS P8110, the number of reciprocal bending until the test piece (total length 110 mm / width 15 mm) broke was measured.

<Example 1>
After dispersing 200 g of carbon black (MA100, manufactured by Mitsubishi Chemical Corporation, furnace black, average particle diameter of 22 nm based on primary particles) in 1800 g of N-methyl-2-pyrrolidone (NMP) by stirring with a ball mill at room temperature for 12 hours. Then, it was filtered through a # 400 stainless steel mesh to obtain a carbon dispersion having a carbon concentration of 10%. This carbon liquid 192.39 g was transferred to a 5000 mL four-necked flask, and a mixed solvent of N-methyl-2-pyrrolidone 1000 g and N, N-dimethylacetamide 1040.13 g and p-phenylenediamine 227.09 g (2.1 mol). ) And dissolved while stirring at room temperature. Subsequently, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride 617.86 (2.1 mol) was added and reacted at a temperature of 20 ° C. for 1 hour, and then heated at 75 ° C. for 20 hours. By stirring the solution, a carbon black-containing polyimide precursor solution having a solution viscosity of 160 Pa · s as measured by a B-type viscometer (solid content concentration: 20 wt%, carbon black addition amount: 25 parts with respect to the resin) was obtained. This carbon black-containing polyimide precursor solution was used as a varnish for forming a semiconductive seamless belt. Next, after rotating for 10 minutes at 1500 rpm in a rotary molding machine to form a uniform thickness layer, while rotating at 50 rpm, the hot air blowing solvent evaporation rate of 90% from the outside of the metal cylindrical mold is 90%. I went until. Next, the temperature was increased to 380 ° C. to complete the removal of the solvent and imidization. Then, it cooled and peeled from the metal mold | die, and obtained the 75 micrometer semiconductive seamless belt.

<Example 2>
A 75 μm semiconductive material was prepared in the same manner as in Example 1 except that the mixed solvent in Example 1 was 1000 g of N-methyl-2-pyrrolidone, 949.41 g of N, N-dimethylacetamide, and 90.72 g of 2-phenylimidazole. I got a seamless belt.

<Comparative Example 1>
A 75 μm semiconductive seamless belt was obtained in the same manner as in Example 1 except that the mixed solvent in Example 1 was N-methyl-2-pyrrolidone alone.

<Comparative example 2>
A 75 μm semiconductive seamless belt was obtained in the same manner as in Example 1 except that the mixed solvent in Example 1 was N, N-dimethylacetamide alone.

<Comparative Example 3>
A 75 μm semiconductive seamless belt was obtained in the same manner as in Example 1 except that the rotary drying process at 130 ° C. was performed for the time required for the rotary drying process performed in Example 1.

<Evaluation results>
As a result of evaluating the sample, it was as shown in Table 1.

表１に示すように、実施例１および２は耐屈曲性に優れることが分かった。

As shown in Table 1, Examples 1 and 2 were found to have excellent bending resistance.

Claims (6)

  In the method for producing a seamless belt produced using a polyamic acid varnish comprising 5 to 30% by weight of a polymer and 95 to 70% by weight of a solvent, the solvent is an aprotic solvent having a boiling point of less than 200 ° C. as a first component A mixed solvent containing 10 to 70% by weight of at least one compound selected from: and 90 to 30% by weight of at least one compound selected from aprotic solvents having a boiling point of 200 ° C. or higher as the second component A process for producing a seamless belt, characterized in that   In the method for producing a seamless belt produced using a polyamic acid varnish comprising 5 to 30% by weight of a polymer and 95 to 70% by weight of a solvent, the solvent is an aprotic solvent having a boiling point of less than 200 ° C. as a first component And at least one compound selected from an aprotic solvent having a boiling point of 200 ° C. or higher as a second component and a heterocyclic third compound having a boiling point of 200 ° C. or higher. A method for producing a seamless belt, which is a mixed solvent containing a total amount of secondary amines or basic organic compound catalysts having a boiling point of 200 ° C. or higher and 90 to 30% by weight.   A process for producing a seamless belt mainly composed of a polyimide resin, wherein the polyamide acid varnish whose polyimide resin is a polyimide precursor is heated at 150 ° C. or more to evaporate the solvent by 90% or more, and further 200 ° C. The method for producing a seamless belt according to claim 1 or 2, wherein the seamless belt is obtained by imide conversion by heating beyond.   The method for producing a seamless belt according to any one of claims 1 to 3, wherein the folding strength of the belt is 200 times or more.   A seamless belt produced by the production method according to claim 1.   6. The seamless belt according to claim 5, wherein the folding strength of the belt is 200 times or more.