JP4993846B2 - Method for producing endless tubular polyimide film - Google Patents

Description

  The present invention relates to a method for producing an improved non-conductive or semi-conductive endless tubular polyimide film. The semiconductive endless tubular polyimide film is used, for example, as an electrophotographic intermediate transfer belt.

  It is well known that a non-conductive tubular polyimide film is generally processed into a belt shape and used, for example, as a belt for conveying a heated article or as an electrophotographic fixing belt.

  A semiconductive tubular polyimide film obtained by mixing and dispersing conductive carbon black in a nonconductive tubular polyimide film is used as an intermediate transfer belt for, for example, a copying machine, a printer, a facsimile machine, and a printing machine.

  And as a manufacturing method of these non-conductive and semi-conductive tubular polyimide films, a predetermined molding material is once formed into a flat film, and then processed into a tubular shape by connecting both ends of the film, by centrifugal casting. A method of forming an endless tubular film at once is known. Further, for example, Patent Document 1 filed by the applicant of the present application also describes that the centrifugal casting is performed under substantially no centrifugal force.

  As a forming raw material for these tubular polyimide films, a polyamic acid (or polyamic acid) solution having a high molecular weight (number average molecular weight is usually about 10,000 to 30,000), which is a polyimide polymer precursor, is generally used.

  Specific examples of the polyamic acid solution include 1,2,4,5-benzenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and 3,3. Aromatic tetracarboxylic dianhydrides that bind acid anhydride groups to point-symmetrical positions such as', 4,4'-benzophenone tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride Polycondensation reaction of an equimolar amount of the product with an aromatic diamine such as p-phenylenediamine, 4,4′-diaminodiphenyl ether, and 4,4′-diaminodiphenylmethane at a low temperature that does not imidize in an organic polar solvent Is manufactured.

  The process for producing a polyimide film usually employs a three-step process in which a polyamic acid solution as a forming raw material is once produced, formed into a polyamic acid film, and finally imidized to obtain a polyimide film. No method has been adopted for forming a polyimide film directly from the starting material monomer in substantially one step.

  However, since the polyamic acid solution obtained by the above molding method has a pot life, there is a drawback that partial gelation tends to occur gradually upon storage. This gelation is more likely to proceed at higher temperatures, but progresses with time even at low temperatures, and even if the amount of gelation is extremely small, the physical properties of the final polyimide film will be adversely affected, and flatness may be deteriorated. I will invite you. In the film mixed with conductive carbon black, this leads to an increase in variation in electric resistance.

  In addition, the polyamic acid resin has a limit in solubility in an organic polar solvent, and has a drawback that it cannot be increased in concentration (the concentration of nonvolatile components in the solution is at most 25% by weight). With a low-concentration polyamic acid solution, it is difficult to form a thicker film at one time, and a large amount of the solvent is required and a lot of time is required for the evaporation removal.

  In addition, since three steps are required as described above, the time and cost required for all the steps are required, and there is room for improvement from the viewpoint of efficiency and economic efficiency.

Incidentally, Patent Document 2 describes a molding method using a new raw material composition for the polyimide film molding from the polyamic acid solution. This is an aromatic tetracarboxylic acid whose main component is an asymmetric aromatic tetracarboxylic acid or ester thereof (specifically, 2,3,3 ′, 4′-biphenyltetracarboxylic acid or ester thereof is 60 mol% or more). This is a molding method using a monomer-based solution composition in which equimolar amounts of an acid component and an aromatic diamine component are mixed. Patent Document 2 discloses a method in which the solution composition is applied and cast on a glass plate and heated (stepwise temperature increase between 80 to 350 ° C.) to be used for flat film molding, silver powder, copper powder, A method of mixing carbon black or the like and providing it to a heat resistant conductive paste is disclosed.
JP 2000-263568 A Japanese Patent Laid-Open No. 10-182820

  In the present invention, instead of the conventional method of forming a tubular polyimide film through a polyamic acid solution, a substantially monomeric raw material solution comprising an aromatic tetracarboxylic acid component and an aromatic diamine component is rotated by a rotary molding machine. To provide a method for forming a high-quality endless (seamless) non-conductive or semi-conductive endless tubular polyimide film that is supplied directly into a drum and is substantially simple and economical in one step. With the goal.

  As a result of intensive studies to solve the above problems, the present inventor has found that a fragrance comprising a specific amount of asymmetric aromatic tetracarboxylic acid or ester thereof and a specific amount of symmetric aromatic tetracarboxylic acid or ester thereof. By forming a substantially monomeric mixed solution obtained by mixing an aromatic tetracarboxylic acid component and an aromatic diamine component in an approximately equimolar amount into a tubular product by a rotational molding method, and imidizing by heat treatment The present inventors have found that a high-quality endless tubular polyimide film can be produced.

  Further, the present inventor has an aromatic tetracarboxylic acid component and an aromatic diamine component comprising a specific amount of asymmetric aromatic tetracarboxylic acid or ester thereof and a specific amount of symmetric aromatic tetracarboxylic acid or ester thereof. A semiconductive polyimide precursor composition in which a specific amount of carbon black is dispersed in a substantially monomeric mixed solution mixed in an approximately equimolar amount is formed into a tubular product by a rotational molding method, and is subjected to heat treatment. Then, it was found that a high quality semiconductive endless tubular polyimide film can be produced by imidization.

  Based on these findings, the present invention was completed by further research.

  That is, this invention provides the manufacturing method of the following nonelectroconductive or semiconductive endless tubular polyimide films.

  Item 1. The aromatic tetracarboxylic acid component consisting of 15 to 55 mol% of the asymmetric aromatic tetracarboxylic acid or ester thereof and 85 to 45 mol% of the symmetric aromatic tetracarboxylic acid or ester thereof and the aromatic diamine component are approximately equimolar. A method for producing an endless tubular polyimide film, characterized in that a substantially monomeric mixed solution mixed in an amount is formed into a tubular product by a rotational molding method and imidized by heat treatment.

  Item 2. The aromatic tetracarboxylic acid component consisting of 15 to 55 mol% of the asymmetric aromatic tetracarboxylic acid or ester thereof and 85 to 45 mol% of the symmetric aromatic tetracarboxylic acid or ester thereof and the aromatic diamine component are approximately equimolar. The semi-conductive solution in which 1 to 35 parts by weight of carbon black is dispersed with respect to 100 parts by weight of the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component in the mixed solution in a substantially monomer state mixed in an amount. A method for producing a semiconductive endless tubular polyimide film, wherein a monomer mixed solution is formed into a tubular product by a rotational molding method, and heat-treated to imidize.

  Item 3. A semiconductive endless tubular polyimide film used for an electrophotographic intermediate transfer belt manufactured by the manufacturing method according to Item 2.

  The present invention is described in detail below.

  The endless tubular polyimide film of the present invention (hereinafter also referred to as “tubular PI film”) uses a specific aromatic tetracarboxylic acid component and an aromatic diamine component as molding raw materials. Specifically, the non-conductive tubular PI film of the present invention uses a specific aromatic tetracarboxylic acid component and an aromatic diamine component as molding raw materials. The semiconductive tubular PI film of the present invention uses a predetermined amount of carbon black (hereinafter also referred to as “CB”) as a raw material in order to impart conductivity in addition to the above-described forming raw material.

As the aromatic tetracarboxylic acid component forming raw material, the aromatic tetracarboxylic acid component includes an asymmetric aromatic tetracarboxylic acid component (asymmetric aromatic tetracarboxylic acid or at least one of its esters) and a symmetric aromatic tetracarboxylic acid. A mixture with an acid component (at least one of symmetrical aromatic tetracarboxylic acids or esters thereof) is used.

An asymmetric aromatic tetracarboxylic acid is a compound in which four carboxyl groups are bonded to positions that are not point targets on a monocyclic or polycyclic aromatic ring (benzene nucleus, naphthalene nucleus, biphenyl nucleus, anthracene nucleus, etc.), or 2 Four monocyclic aromatic rings (such as benzene nuclei) were bonded to a position in which four carboxyl groups were not point-targeted to a compound such as —CO—, —CH ₂ —, —SO ₂ — or the like, or a compound bridged by a single bond. Compounds.

  Specific examples of the asymmetric aromatic tetracarboxylic acid include 1,2,3,4-benzenetetracarboxylic acid, 1,2,6,7-naphthalenetetracarboxylic acid, 2,3,3 ′, 4′-biphenyl. Tetracarboxylic acid, 2,3,3 ′, 4′-benzophenonetetracarboxylic acid, 2,3,3 ′, 4′-diphenyl ether tetracarboxylic acid, 2,3,3 ′, 4′-diphenylmethanetetracarboxylic acid, 2 , 3,3 ′, 4′-diphenylsulfone tetracarboxylic acid and the like.

  Examples of the asymmetric aromatic tetracarboxylic acid ester used in the present invention include the above-mentioned asymmetric aromatic tetracarboxylic acid diesters (half-esters), and specifically, the asymmetric aromatic tetracarboxylic acid described above. Among the four carboxyl groups, a compound in which two carboxyl groups are esterified and one of two adjacent carboxyl groups on the aromatic ring is esterified can be mentioned.

Examples of the two esters in the asymmetric aromatic tetracarboxylic acid diester include di-lower alkyl esters, preferably di-C _1-3 alkyl esters (particularly dimethyl esters) such as dimethyl esters, diethyl esters, and dipropyl esters. It is done.

  Of the above asymmetric aromatic tetracarboxylic acid diesters, 2,3,3 ′, 4′-biphenyltetracarboxylic acid dimethyl ester and 2,3,3 ′, 4′-biphenyltetracarboxylic acid diethyl ester are preferred, 2,3,3 ′, 4′-biphenyltetracarboxylic acid dimethyl ester is preferably used.

The asymmetric aromatic tetracarboxylic acid diester can be produced commercially or by a known method. For example, the corresponding asymmetric aromatic tetracarboxylic dianhydride 1 is easily reacted with a corresponding alcohol (lower alcohol, preferably C _1-3 alcohol) 2 (molar ratio) by a known method. Can be manufactured. Thereby, the acid anhydride of a raw material reacts with alcohol, and a ring is opened, and the diester (half ester) which has an ester group and a carboxyl group, respectively on adjacent carbon on an aromatic ring is manufactured.

The symmetric aromatic tetracarboxylic acid is a compound in which four carboxyl groups are bonded to a point-symmetrical position on a monocyclic or polycyclic aromatic ring (benzene nucleus, naphthalene nucleus, biphenyl nucleus, anthracene nucleus, etc.), Alternatively, four carboxyl groups are dotted on a compound in which two monocyclic aromatic rings (benzene nucleus, etc.) are bridged by a group such as —CO—, —O—, —CH ₂ —, —SO ₂ — or the like, or a single bond. A compound bonded at a symmetrical position can be mentioned.

  Specific examples of the symmetric aromatic tetracarboxylic acid include 1,2,4,5-benzenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, and 3,3 ′, 4,4′-biphenyl. Tetracarboxylic acid, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid, 3,3 ′, 4,4′-diphenyl ether tetracarboxylic acid, 3,3 ′, 4,4′-diphenylmethane tetracarboxylic acid, 3 , 3 ′, 4,4′-diphenylsulfone tetracarboxylic acid and the like.

  Examples of the symmetric aromatic tetracarboxylic acid ester used in the present invention include the above-mentioned symmetrical aromatic tetracarboxylic acid diesters (half-esters), and specifically, the symmetric aromatic tetracarboxylic acid described above. Among the four carboxyl groups, a compound in which two carboxyl groups are esterified and one of two adjacent carboxyl groups on the aromatic ring is esterified can be mentioned.

Examples of the two esters in the symmetric aromatic tetracarboxylic acid diester include di-lower alkyl esters, preferably C _1-3 alkyl esters (particularly dimethyl esters) such as dimethyl esters, diethyl esters, and dipropyl esters. .

  Among the above symmetrical aromatic tetracarboxylic acid diesters, 3,3 ′, 4,4′-biphenyltetracarboxylic acid dimethyl ester, 3,3 ′, 4,4′-biphenyltetracarboxylic acid diethyl ester, 2,3, 5,6-Benzenetetracarboxylic acid dimethyl ester is preferable, and 3,3 ′, 4,4′-biphenyltetracarboxylic acid dimethyl ester is particularly preferably used.

In addition, the said symmetrical aromatic tetracarboxylic-acid diester can be manufactured commercially or by a well-known method. For example, it can be easily produced by reacting the corresponding symmetrical aromatic tetracarboxylic dianhydride 1 with the corresponding alcohol (lower alcohol, preferably C _1-3 alcohol etc.) 2 (molar ratio). . Thereby, the acid anhydride of a raw material reacts with alcohol, and a ring is opened, and the diester (half ester) which has an ester group and a carboxyl group, respectively on adjacent carbon on an aromatic ring is manufactured.

  The mixing ratio of the asymmetric and symmetric aromatic tetracarboxylic acid or ester thereof is about 15 to 55 mol% (preferably 20 to 50 mol%) of the asymmetric aromatic tetracarboxylic acid or ester thereof. Aromatic tetracarboxylic acid or its ester is specified at about 85 to 45 mol% (preferably 80 to 50 mol%). In particular, it is preferable to use about 20 to 50 mol% of asymmetric and tetracarboxylic acid diesters and about 80 to 50 mol% of symmetric aromatic tetracarboxylic acid diesters.

  In addition, it becomes essential to mix | blend the said symmetrical and asymmetrical aromatic tetracarboxylic acid component for the following reason. Only with the symmetric aromatic tetracarboxylic acid or its ester, the polyimide film exhibits crystallinity, so that the film is pulverized during the heat treatment and cannot be formed into a film. On the other hand, an asymmetric aromatic tetracarboxylic acid or its ester alone is molded as an endless tubular PI film, but the yield strength and elastic modulus of the obtained film are weak. In addition to the poor responsiveness of the belt, there are problems such as belt elongation occurring at an early stage.

  On the other hand, when an aromatic tetracarboxylic acid or an ester thereof having the above-mentioned mixing ratio is used, extremely high film-formability (moldability) is possible, and a semiconductive endless tube having high yield strength and elastic modulus. A PI film is obtained.

  In addition, it is considered that the addition of asymmetric aromatic tetracarboxylic acid or its ester bends the polyamic acid molecule, thereby creating flexibility.

  And the coexistence effect of the said symmetrical and asymmetrical aromatic tetracarboxylic acid or its ester is most effectively exhibited when both have the mixing ratio shown above.

Aromatic diamine component As the aromatic diamine component, a compound having two amino groups on one aromatic ring, or two or more aromatic rings (such as a benzene nucleus) are -O-, -S-, -CO-. , —CH ₂ —, —SO—, —SO ₂ — and the like, or compounds having two amino groups bridged by a single bond. Specifically, for example, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylthioether, 4,4′-diaminodiphenylcarbonyl, 4, Examples include 4′-diaminodiphenylmethane, 1,4-bis (4-aminophenoxy) benzene, and the like. Among these, 4,4′-diaminodiphenyl ether is particularly preferable. This is because by using these aromatic diamine components, the reaction proceeds more smoothly and a tougher and higher heat-resistant film can be produced.

Organic polar solvent The organic polar solvent used in the mixed solution in a substantially monomeric state is preferably an aprotic organic polar solvent, such as N-methyl-2-pyrrolidone (hereinafter referred to as “NMP”), N, N—. Dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, 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. The amount of the organic polar solvent used is about 65 to 300 parts by weight (preferably about 80 to 230 parts by weight, more preferably about 100 parts by weight of the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component. And about 100 to 200 parts by weight).

Carbon black (CB)
In producing the semiconductive tubular PI film of the present invention, CB powder is used for imparting electric resistance characteristics in addition to the above-described components. The reason why carbon black is used is that it is mixed and dispersible and stable with the prepared monomer mixed solution (compared to other generally known conductive materials of metals and metal oxides). And no adverse effects on the polycondensation reaction.

  This CB powder has various physical properties (electrical resistance, volatile content, specific surface area, particle size, pH value) depending on its production raw materials (natural gas, acetylene gas, coal tar, etc.) and production conditions (combustion conditions). , DBP oil absorption, etc.). Those with a high conductivity index with a developed structure (which is often found in CB powder produced from acetylene gas as a raw material) can provide a predetermined electric resistance with a relatively small filling amount, but the mixing and dispersibility is not so good. . Although the conductivity index is not high, the oxidized CB powder having a low PH value, and the CB powder containing a large amount of volatile matter, need a relatively large filling for a predetermined electric resistance. It is easy to obtain a belt with excellent storage stability and uniform electrical resistance.

  This conductive CB powder usually has an average particle diameter of about 15 to 65 nm, and particularly when used for an electrophotographic belt film for an intermediate transfer belt such as a toner copying machine or a color copying machine. A thing of about 40 nm is suitable.

  For example, channel black, oxidized furnace black, and the like can be given. Specific examples include Special Black 4 (PH3, volatile content 14%, particle size 25 nm) and Special Black 5 (PH3, volatile content 15%, particle size 20 nm) manufactured by Degussa.

  The amount of the CB powder added is about 1 to 35 parts by weight (preferably with respect to 100 parts by weight of the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component which are the raw materials for forming the mixed solution in a substantially monomeric state. Is preferably about 5 to 25 parts by weight.

  Here, the reason why the CB powder is used in the above range is to give the film volume resistivity (Ω · cm) (VR) and surface resistivity (Ω / □) (SR) in the semiconductive region. . Note that the lower limit is about 1 part by weight or more because this amount is necessary to obtain sufficient conductivity, and the upper limit is about 35 parts by weight or less because lower resistance is required. This is for the purpose of maintaining the moldability and preventing the physical properties of the film from being lowered.

Preparation of monomer mixed solution A predetermined amount of an aromatic tetracarboxylic acid component, an aromatic diamine component and an organic polar solvent are mixed to prepare a substantially monomer mixed solution for molding (hereinafter also referred to as “monomer mixed solution”). Prepared. The non-conductive tubular PI film and the semiconductive tubular PI film of the present invention are different only in the presence or absence of CB powder, and the monomer mixed solution as a forming raw material is prepared under the same conditions. The preparation procedure is not particularly limited. This is because the aromatic tetracarboxylic acid component used in the present invention is substantially different from the diamine component at a low temperature (for example, 30 to 40 ° C. or lower), unlike the case of using a highly reactive aromatic tetracarboxylic dianhydride. This is one of the advantages in preparing a monomer mixed solution.

  The monomer mixed solution is prepared by mixing and dissolving in an organic polar solvent at a reaction ratio of approximately equimolar amounts of the above-described aromatic tetracarboxylic acid component and aromatic diamine component. Since these components are monomers, they are easily dissolved in an organic polar solvent, can be uniformly dissolved at a high concentration, and the resulting solution can be maintained in a substantially monomer state. In the present invention, the monomer mixed solution is used as a forming raw material.

  Here, the substantially equimolar amount means a reaction ratio at which a polycondensation reaction between an aromatic tetracarboxylic acid component and an aromatic diamine component proceeds smoothly to obtain a polyimide having a predetermined high molecular weight. The substantial monomer state means that most of each component is in a monomer state in the mixed solution, but a low-molecular polycondensation reaction product such as an oligomer does not adversely affect the present invention. A small amount may be contained.

  The amount of the organic polar solvent used is about 65 to 300 parts by weight (preferably about 80 to 230 parts by weight, more preferably 100 parts by weight of the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component as raw materials. Preferably, it may be determined to be about 100 to 200 parts by weight. Since the mixed solution in a substantially monomer state is easily dissolved in the organic polar solvent, there is an advantage that the amount of the solvent to be used can be reduced as much as possible.

  Hereinafter, the preparation method of a monomer mixed solution is illustrated.

  As a first example, first, the above-mentioned predetermined mol% of symmetric and asymmetric aromatic tetracarboxylic acid components are mixed and dissolved in an organic polar solvent. To this solution, an aromatic tetracarboxylic acid component and an approximately equimolar amount of an aromatic diamine component are added with stirring and uniformly dissolved to obtain a monomer mixture solution for molding.

  As a second example, a solution comprising the predetermined amount of the symmetric aromatic tetracarboxylic acid component and the equimolar amount of the aromatic diamine component, a predetermined amount of the asymmetric aromatic tetracarboxylic acid component and the equimolar amount of the solution. Each solution comprising an aromatic diamine component is prepared separately. Each of these solutions is mixed so that the two kinds of aromatic tetracarboxylic acid components are in a predetermined mol% to obtain a monomer mixed solution for molding.

  As a third example, a uniform monomer mixture solution is prepared by simultaneously adding a predetermined amount of symmetric and asymmetric aromatic tetracarboxylic acid components and aromatic diamine components to an organic polar solvent.

  The concentration of nonvolatile components in the monomer mixed solution of the present invention is about 45% by weight (particularly about 30 to 45% by weight), whereas the conventional polyamic acid solution is at most 25% by weight. Can do. The “nonvolatile content concentration” used in the present specification means a concentration measured by the method described in Examples. By using a high-concentration monomer mixed solution, the polymerization reaction proceeds rapidly and the molding time can be shortened. In addition, a film having a film thickness can be easily produced, and since the amount of the solvent used is small, the cost can be suppressed and the solvent can be easily removed by evaporation.

  It should be noted that an imidazole compound (2-methylimidazole, 1,2-dimethylimidazole, 2-methyl-4-methylimidazole, 2-ethyl-4 is added to the monomer mixed solution as long as the effect of the present invention is not adversely affected. Additives such as -ethylimidazole, 2-phenylimidazole) and surfactants (fluorine surfactants, etc.) may be added.

  Further, in the production of a semiconductive tubular PI film, a semiconductive monomer mixed solution in which carbon black is dispersed in a monomer mixed solution is used. The method for mixing the CB powder into the monomer mixed solution is not particularly limited as long as a known method such as stirring is used. In the case of this stirring, it is preferable to use a ball mill, whereby a semiconductive monomer mixed solution for molding in which CB is uniformly dispersed is obtained.

  As described above, the carbon black is used in an amount of 1 to 35 parts by weight, preferably 5 to 25 parts by weight based on 100 parts by weight of the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component.

Manufacturing method of endless tubular polyimide film Next, a method for forming a tubular PI film using the prepared monomer mixed solution or semiconductive monomer mixed solution will be described. Hereinafter, although the shaping | molding means using a monomer mixed solution is demonstrated, the shaping | molding means using a semiconductive monomer mixed solution can be implemented similarly.

  As this molding means, a rotational molding method using a rotary drum is adopted. First, the monomer mixed solution is poured into the inner surface of the rotating drum and uniformly cast on the entire inner surface.

  In the injection / casting method, for example, an amount of the monomer mixed solution corresponding to obtaining the final film thickness is injected into a stopped rotating drum, and then the rotational speed is gradually increased to a speed at which centrifugal force works. Cast uniformly over the entire inner surface with centrifugal force. Alternatively, injection and casting can be performed without using centrifugal force. For example, a horizontally long slit-like nozzle is disposed on the inner surface of the rotating drum, and the nozzle is rotated (at a speed higher than the rotating speed) while the drum is slowly rotated. In this method, the monomer mixture solution for molding is uniformly sprayed from the nozzle toward the inner surface of the drum.

  In both methods, the inner surface of the rotating drum is mirror-finished, and barriers for preventing liquid leakage are provided around both ends. The drum is placed on a rotating roller and indirectly rotated by the rotation of the roller.

  For heating, a heat source such as a far infrared heater is disposed around the drum, and indirect heating from the outside is performed. The size of the drum is determined by the size of the desired semiconductive tubular PI film.

  In the heating, the inner surface of the drum is gradually heated to first reach about 100 to 190 ° C., preferably about 110 to 130 ° C. (first heating stage). The temperature raising rate may be about 1 to 2 ° C./min, for example. It is maintained at the above temperature for 30 to 120 minutes, and about half or more of the solvent is volatilized to form a self-supporting tubular film. In order to perform imidization, it is necessary to reach a temperature of 280 ° C. or higher. However, when heated at such a high temperature from the beginning, the polyimide exhibits high crystallization, which not only affects the dispersion state of CB but also is tough. There is a problem that a thick film is not formed. Therefore, as the first heating stage, the upper limit temperature is suppressed to about 190 ° C. at most, and the polycondensation reaction is terminated at this temperature to obtain a tough tubular PI film.

  When this step is completed, heating is performed to complete imidization as the second heating step, and the temperature is about 280 to 400 ° C. (preferably about 300 to 380 ° C.). In this case as well, it is preferable not to reach this temperature all at once from the temperature of the first heating stage, but to gradually increase the temperature to reach that temperature.

  The second heating step may be performed with the endless tubular film adhered to the inner surface of the rotating drum. When the first heating step is finished, the endless tubular film is peeled off from the rotating drum, taken out, and separately imidized. For heating to 280 to 400 ° C. The time required for this imidization is usually about 2 to 3 hours. Therefore, the time required for all the steps of the first and second heating stages is usually about 4 to 7 hours.

  Thus, the non-conductive (or semi-conductive) PI film of the present invention is produced. The thickness of the film is not particularly limited, but is usually about 30 to 200 μm, preferably about 60 to 120 μm. In particular, when used as an electrophotographic intermediate transfer belt, about 75 to 100 μm is preferable.

In the case of a semiconductive PI film, the semiconductivity of this film is an electric resistance characteristic determined by coexistence of volume resistivity (Ω · cm) (VR) and surface resistivity (Ω / □) (SR). This characteristic is imparted by mixing and dispersing the CB powder. The resistivity range can be freely changed basically depending on the mixing amount of the CB powder. The resistivity ranges of the film of the present invention are VR: 10 ² to 10 ¹⁴ and SR: 10 ³ to 10 ^15. Preferred ranges are VR: 10 ⁶ to 10 ¹³ , SR: 10 ⁷ to 10 ^14. Can be illustrated. These resistivity ranges can be easily achieved by adopting the blending amount of the above-mentioned CB powder. In addition, the content of CB in the film of the present invention is usually about 5 to 25% by weight, preferably about 8 to 20% by weight.

  The semiconductive PI film of the present invention has a very homogeneous electrical resistivity. That is, the semiconductive PI film of the present invention is characterized by small variations in logarithmically converted values of the surface resistivity SR and volume resistivity VR, and the standard deviation of logarithmically converted values of all measurement points in the film is 0.2. Or less, preferably 0.15 or less.

The semiconductive PI film of the present invention has a wide variety of uses depending on functions such as excellent electrical resistance characteristics. For example, an important application requiring charging characteristics is an electrophotographic intermediate transfer belt such as a color copying machine or a color printer. The semiconductivity (resistivity) necessary for the belt is, for example, VR10 ⁹ to 10 ¹² or SR10 ¹⁰ to 10 ¹³ , and the semiconductive endless tubular PI film of the present invention can be suitably used.

  Since this invention is comprised as mentioned above, there exist the following effects.

  An endless tubular polyimide film can be obtained directly by a combination of a polyimide monomer material having a specific composition and rotational molding means.

  Compared to the conventional production of endless tubular polyimide films via polyamic acid, the time can be greatly reduced. This not only shortened the time, but also led to the rationalization of the process control and the more stable quality of the film.

  The obtained endless tubular polyimide film has been widely used for various other applications. Among them, the semiconductive endless tubular film is more effective as an electrophotographic intermediate transfer belt for color copying machines, color printers, etc. It was also used for.

  Next, the present invention will be described in further detail with reference to comparative examples.

In addition, the yield strength (yield point stress), the breaking strength, the volume resistivity (VR), the surface resistivity (SR), and the non-volatile content in this example are measured as follows.
<Yield Strength (MPa) (abbreviated as σ _Y ) and Breaking Strength (MPa) (abbreviated as σ _cr )>
The film obtained in each example was cut into a width of 5 mm and a length of 100 mm, and this was used as a test piece and measured with a uniaxial tensile tester (manufactured by Shimadzu Corporation, Autograph) at a tension span of 40 mm and a strain rate of 200 mm / min. did. Σ _Y and σ _cr were read from the recorded _SS curve.

  The yield strength and breaking strength are important strength factors in designing a material as a belt, and at least the yield strength is required to be 120 MPa. This is because there should be no plastic deformation (dimensional change due to elongation) due to stress applied during mounting.

Further, the breaking strength needs to be greater than the yield strength, which contributes to the life (toughness) of the belt rotation. As a guideline, at least σ _cr / σ _Y = 1.10 or more is required.
<VR and SR>
The obtained tubular film was cut into a length of 400 mm as a sample, and a resistance measuring instrument “HIRESTA IP / HR Blob” manufactured by Mitsubishi Chemical Corporation was used to make five vertical and vertical positions at equal pitches in the width direction ( A total of 40 points of 8 places in the (circumferential) direction were measured, and indicated as an average value of the whole.

Note that VR was measured after 10 seconds had elapsed while applying a voltage of 100 V, and SR was measured after 10 seconds had elapsed while applying voltage of 500 V.
<Non-volatile content>
A sample (monomer mixed solution or the like) is precisely weighed in a heat-resistant container such as a metal cup, and the weight of the sample at this time is Ag. Put the heat-resistant container containing the sample in an electric oven, heat and dry while heating up in order of 120 ℃ × 12min, 180 ℃ × 12min, 260 ℃ × 30min, and 300 ℃ × 30min. The weight of the solid content (non-volatile content 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 (I) 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 (%) (I)
Example 1
2,3,3 ', 4'-biphenyltetracarboxylic acid dimethyl ester (a half-ester reaction product of 1 mole of 2,3,3', 4'-biphenyltetracarboxylic dianhydride and 2 moles of methyl alcohol) ) 716.0 g (2.0 mol) and 4,4′-diaminodiphenyl ether 400.0 g (2.0 mol) were mixed in 1540 g of NMP solvent at room temperature and uniformly dissolved. This solution had a non-volatile content concentration of 34.6% by weight, a solution viscosity of about 250 mPa · s, substantially no polycondensation reaction, and was a stable solution in a monomer state. Hereinafter, this is referred to as an asymmetric monomer solution A.

  On the other hand, 3,3 ′, 4,4′-biphenyltetracarboxylic acid dimethyl ester (a reaction product of 1 mole of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 2 moles of methyl alcohol in half) Ester) 716.0 g (2.0 mol) and 4,4'-diaminodiphenyl ether 400.0 g (2.0 mol) were mixed in 1540 g of NMP solvent at room temperature and uniformly dissolved. This solution had a non-volatile content concentration of 34.6% by weight, a solution viscosity of about 250 mPa · s, substantially no polycondensation reaction, and was a stable solution in a monomer state. Hereinafter, this is referred to as a symmetric monomer solution B.

  The asymmetric monomer solution A and the symmetric monomer solution B are fluorinated surfactants (Effects of Tochem Products Co., Ltd., EF) in the respective amount ratios described in EX · 1 and EX · 2 shown in Table 1. -351) Along with 0.037% by weight (vs. non-volatile content), both were thoroughly mixed and defoamed. This was each molded monomer solution, and a predetermined amount was collected from each of the solutions, poured into a rotating drum, and molded under the following conditions.

  Rotating drum: An internal mirror-finished metal drum having an inner diameter of 100 mm and a width of 530 mm was placed on two rotating rollers and arranged to rotate with the rotation of the rollers.

Injection amount of the monomer solution C for molding ... 45.9g
Heating temperature: A far-infrared heater was disposed on the outer surface of the drum so that the inner surface temperature of the drum was controlled at 170 ° C.

  First, with the rotating drum stopped, 45.9 g of the same monomer solution was uniformly injected into the bottom of the drum. Thereafter, rotation was started immediately, the speed was gradually increased, reached 24 rad / s, and evenly cast on the entire inner surface, and heating was started. The heating was gradually raised to 170 ° C., and the heating was continued at that temperature for 90 minutes while maintaining its rotation.

  When the 90 minutes of rotation and heating were completed, the mixture was cooled to room temperature, and the rotating drum was removed as it was and left in a hot air retention oven to start heating for imidization. This heating also reached 350 ° C. while gradually raising the temperature. Then, after heating at this temperature for 30 minutes, the tubular PI film formed on the inner surface of the drum was peeled off after being cooled to room temperature. The results in each example are listed in Table 2.

比較例１
実施例１の非対称性モノマ溶液Ａと対称性モノマ溶液Ｂとを使って、表１に示したＥＸ・３〜６に記載する各々の量比で混合する以外は、該例と同一条件で各々に成形、イミド化し、回転ドラムから剥離し、取出して測定した。各々の場合の結果は表２に記載した。

Comparative Example 1
Each of the asymmetric monomer solution A and the symmetric monomer solution B of Example 1 is mixed under the same conditions as those of the example except that they are mixed in the respective amount ratios described in EX · 3 to 6 shown in Table 1. And imidized, peeled off from the rotating drum, taken out and measured. The results in each case are listed in Table 2.

Example 2
Using the asymmetric monomer solution A and the symmetric monomer solution B in Example 1, at the quantitative ratios described in Table 1, EX. CB powder (pH 3, particle size 23 nm) 14.0 g (8.33 parts by weight with respect to 100 parts by weight of the total amount of all monomers) was added to the mixture, and thoroughly mixed and dispersed with a ball mill, and finally defoamed. This was used as a semiconductive monomer solution for molding. The non-volatile content in the semiconductive monomer solution was 36.8% by weight, and the CB concentration in the non-volatile content was 9.19% by weight.

  And 45.9g was extract | collected from this solution, this was inject | poured in the rotating drum like Example 1, and it shape | molded on the same conditions, Then, it imidized. The obtained imidized film was peeled off from the rotating drum, taken out and measured. The results are shown in Table 2.

Comparative Example 2
Using the asymmetric monomer solution A and the symmetric monomer solution B of Example 1 and mixing them uniformly in the same manner as in the examples, at the respective amount ratios described in EX · 8, 9 shown in Table 1. In the same manner as in Example 2, CB powder was added in an amount of 8.33 parts by weight with respect to 100 parts by weight of the total amount of monomers, and thoroughly mixed and dispersed with a ball mill, and finally defoamed. This was used as a semiconductive monomer solution for molding. The non-volatile content in the semiconductive monomer solution was 36.8% by weight, and the CB concentration in the non-volatile content was 9.19% by weight.

  And 45.9g each was extract | collected from this liquid A and the liquid B, this was inject | poured in the rotating drum like Example 1, and it shape | molded on the same conditions. After imidation, it was peeled off from the rotating drum, taken out and measured. The results in each case are listed in Table 2.

Claims (3)

Approximately equimolar and the asymmetric aromatic di- esters 15 to 55 mol% and symmetry aromatic aromatic tetracarboxylic acid component consisting of di esters 85-45 mol% of tetracarboxylic acid and an aromatic diamine component of the tetracarboxylic acid A method for producing an endless tubular polyimide film, characterized in that a substantially monomeric mixed solution mixed in an amount is formed into a tubular product by a rotational molding method and imidized by heat treatment. Approximately equimolar and the asymmetric aromatic di- esters 15 to 55 mol% and symmetry aromatic aromatic tetracarboxylic acid component consisting of di esters 85-45 mol% of tetracarboxylic acid and an aromatic diamine component of the tetracarboxylic acid The semi-conductive solution in which 1 to 35 parts by weight of carbon black is dispersed with respect to 100 parts by weight of the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component in the mixed solution in a substantially monomer state mixed in an amount. A method for producing a semiconductive endless tubular polyimide film, wherein a monomer mixed solution is formed into a tubular product by a rotational molding method, and heat-treated to imidize. A semiconductive endless tubular polyimide film used for an electrophotographic intermediate transfer belt manufactured by the manufacturing method according to claim 2.