JP2004323834A - Method for manufacturing seamless tubular polyimide film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a seamless tubular polyimide film having non-electroconductive property or semi-electroconductive property by directly feeding a raw material solution in a monomer state comprising of an aromatic tetracarboxylic acid component and an aromatic diamine component into a rotating drum of a rotational molding machine. <P>SOLUTION: The method for manufacturing a seamless tubular polyimide film is characterized by molding a mixed solution in a monomer state obtained by mixing an aromatic tetracarboxylic acid component composed of 15-55 mol% of an unsymmetrical aromatic tetracarboxylic acid or its ester and 85-45 mol% of a symmetrical aromatic tetracarboxylic acid or its ester and an aromatic diamine component in nearly equivalent molar quantities, and by heat treating to effect an imidation. This invention also relates to a method for manufacturing a semi-electroconductive seamless tubular polyimide film characterized by effecting an imidation by dispersing 1-35 pts.wt. of carbon black into 100 pts.wt. of the mixed solution in a monomer state, and use of the film as an intermediate transfer belt of an electrophotographic system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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 nonconductive tubular polyimide film is generally processed into a belt shape and used as, for example, a belt for conveying heated articles or as a fixing belt of an electrophotographic system.

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

  Then, as a method for producing these non-conductive and semi-conductive tubular polyimide films, a method of forming a predetermined molding material into a flat film once and then connecting both ends of the film to form a tube, and centrifugal casting. 2. Description of the Related Art A method of forming an endless tubular film at once is known. In addition, for example, Patent Document 1 by the present applicant describes that the centrifugal casting is performed under substantially no centrifugal force to perform molding.

  As a raw material for forming 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.

  The polyamic acid solution specifically includes, for example, 1,2,4,5-benzenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 Aromatic tetracarboxylic dianhydrides in which acid anhydride groups are bonded at point-symmetric positions such as', 4,4'-benzophenonetetracarboxylic dianhydride and 2,3,6,7-naphthalenetetracarboxylic dianhydride -Condensation reaction between an equimolar amount of a product and an aromatic diamine such as p-phenylenediamine, 4,4'-diaminodiphenylether, or 4,4'-diaminodiphenylmethane at a low temperature that does not cause imidation in an organic polar solvent. It has been manufactured.

  The method for producing a polyimide film usually employs three steps of once producing a polyamic acid solution as a raw material for forming these, forming this into a polyamic acid film, and finally imidizing to obtain a polyimide film. A method of directly forming a polyimide film from a monomer as a starting material in substantially one step has not been adopted.

  However, since the polyamic acid solution obtained by the above-mentioned molding method has a pot life, there is a disadvantage that partial gelation easily occurs gradually during storage. This gelation is easy to progress as the temperature is high, but it progresses with time even at a low temperature, and even if there is a very small amount of gelation, it will not only adversely affect the physical properties of the final polyimide film, but also deteriorate the flatness. I will invite you. This leads to an increase in variation in electric resistance in the film mixed with conductive carbon black.

  Further, the polyamic acid resin has a drawback that its solubility in an organic polar solvent is limited and its concentration cannot be increased (the concentration of nonvolatile components in the solution is up to 25% by weight at most). 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 much time is required for removing the solvent by evaporation.

  Further, 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 in terms of efficiency and economy.

Meanwhile, Patent Document 2 discloses 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 containing an asymmetric aromatic tetracarboxylic acid or an ester thereof as a main component (specifically, 60 mol% or more of 2,3,3 ′, 4′-biphenyltetracarboxylic acid or an ester thereof). 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 Literature 2 discloses a method in which the solution composition is applied to a glass plate, cast and heated (stepwise raised in temperature between 80 to 350 ° C.) to be subjected to flat film molding, silver powder, copper powder, There is disclosed a method of mixing carbon black or the like to provide a heat-resistant conductive paste.
JP 2000-263568 A JP-A-10-182820

  The present invention replaces the conventional method of forming a tubular polyimide film through a polyamic acid solution, and feeds a raw material solution in a substantially monomer state comprising an aromatic tetracarboxylic acid component and an aromatic diamine component to a rotary molding machine. Disclosed is a method of forming a high-quality endless (seamless) non-conductive or semi-conductive endless tubular polyimide film in a simple and economical manner by feeding directly into a drum in substantially one step. With the goal.

  The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, have found that an aromatic compound comprising a specific amount of an asymmetric aromatic tetracarboxylic acid or an ester thereof and a specific amount of a symmetric aromatic tetracarboxylic acid or an ester thereof A mixed solution in a substantially monomer state, in which an aromatic tetracarboxylic acid component and an aromatic diamine component are mixed in substantially equimolar amounts, is formed into a tubular material by a rotational molding method, and is heat-treated for imidization. It was found that a high quality endless tubular polyimide film could be produced.

  Further, the present inventors have found that an aromatic tetracarboxylic acid component and an aromatic diamine component consisting of a specific amount of an asymmetric aromatic tetracarboxylic acid or an ester thereof and a specific amount of a symmetric aromatic tetracarboxylic acid or an 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 substantially equimolar amounts is formed into a tubular article by a rotational molding method, and heat-treated. It has been found that a high-quality semiconductive endless tubular polyimide film can be produced by imidization.

  The present invention has been completed by further research based on these findings.

  That is, the present invention provides the following method for producing a nonconductive or semiconductive endless tubular polyimide film.

  Item 1. A substantially equimolar amount of an aromatic tetracarboxylic acid component and an aromatic diamine component comprising 15 to 55 mol% of an asymmetric aromatic tetracarboxylic acid or an ester thereof and 85 to 45 mol% of a symmetric aromatic tetracarboxylic acid or an ester thereof. A method for producing an endless tubular polyimide film, comprising: forming a mixed solution in a substantially monomer state, which is mixed in an amount, into a tubular material by a rotational molding method, and heat-treating the mixture to imidize it.

  Item 2. A substantially equimolar amount of an aromatic tetracarboxylic acid component and an aromatic diamine component comprising 15 to 55 mol% of an asymmetric aromatic tetracarboxylic acid or an ester thereof and 85 to 45 mol% of a symmetric aromatic tetracarboxylic acid or an ester thereof. In a substantially monomeric mixed solution mixed in an amount, 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. A method for producing a semiconductive endless tubular polyimide film, wherein a monomer mixture solution is formed into a tubular material by a rotational molding method, and is heat-treated to be imidized.

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

  Hereinafter, the present invention will be described in detail.

  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 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 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-mentioned forming raw material.

Aromatic tetracarboxylic acid component The aromatic tetracarboxylic acid component, which is a forming raw material, includes an asymmetric aromatic tetracarboxylic acid component (at least one of asymmetric aromatic tetracarboxylic acid or an ester thereof) and a symmetric aromatic tetracarboxylic acid. A mixture with an acid component (at least one of symmetric aromatic tetracarboxylic acids or esters thereof) is used.

The asymmetric aromatic tetracarboxylic acid is a compound in which four carboxyl groups are bonded to a monocyclic or polycyclic aromatic ring (benzene nucleus, naphthalene nucleus, biphenyl nucleus, anthracene nucleus, etc.) at a position which is not symmetrical, or number of monocyclic aromatic rings (benzene nucleus, etc.) _{-CO -, - CH 2 -,} - SO 2 - group or 4 carboxyl groups in compounds crosslinked with a single bond or the like attached to a position which is not the point symmetry 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'-diphenylethertetracarboxylic acid, 2,3,3 ', 4'-diphenylmethanetetracarboxylic acid, , 3,3 ', 4'-diphenylsulfonetetracarboxylic acid and the like.

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

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

  Among the asymmetric aromatic tetracarboxylic acid diesters, 2,3,3 ′, 4′-biphenyltetracarboxylic acid dimethyl ester and 2,3,3 ′, 4′-biphenyltetracarboxylic acid diethyl ester are preferable, and in particular, 2,3,3 ', 4'-Biphenyltetracarboxylic acid dimethyl ester is preferably used.

The asymmetric aromatic tetracarboxylic acid diester can be commercially available or can be produced by a known method. For example, it is easily prepared by a known method such as reacting the corresponding asymmetric aromatic tetracarboxylic dianhydride 1 with the corresponding alcohol (lower alcohol, preferably C _1-3 alcohol or the like) 2 (molar ratio). Can be manufactured. Thereby, the acid anhydride of the raw material reacts with the alcohol to open the ring, thereby producing a diester (half ester) having an ester group and a carboxyl group on adjacent carbons on the aromatic ring.

In addition, a symmetric aromatic tetracarboxylic acid is a compound in which four carboxyl groups are bonded to point-symmetric positions on a monocyclic or polycyclic aromatic ring (benzene nucleus, naphthalene nucleus, biphenyl nucleus, anthracene nucleus, etc.) or two monocyclic aromatic ring (benzene nucleus, etc.) -CO -, - O -, - CH 2 -, - SO 2 - groups or 4 carboxyl groups in compounds crosslinked with a single bond, such as a point Compounds bound at symmetrical positions are included.

  Specific examples of the symmetric aromatic tetracarboxylic acid include 1,2,4,5-benzenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 3,3 ′, 4,4′-biphenyl Tetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 3,3 ′, 4,4′-diphenylethertetracarboxylic acid, 3,3 ′, 4,4′-diphenylmethanetetracarboxylic acid, , 3 ', 4,4'-diphenylsulfonetetracarboxylic acid and the like.

  Examples of the symmetric aromatic tetracarboxylic acid ester used in the present invention include the diesters (half esters) of the above-mentioned symmetric aromatic tetracarboxylic acids, and specifically, the above-mentioned symmetric aromatic tetracarboxylic acids And two carboxyl groups of the four carboxyl groups are esterified, and one of two adjacent carboxyl groups on the aromatic ring is esterified.

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

  Among the above symmetric aromatic tetracarboxylic 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 symmetric aromatic tetracarboxylic acid diester can be manufactured commercially or by a well-known method. For example, it can be easily produced by reacting a corresponding symmetric aromatic tetracarboxylic dianhydride 1 with a corresponding alcohol (lower alcohol, preferably C _1-3 alcohol or the like) 2 (molar ratio). . Thereby, the acid anhydride of the raw material reacts with the alcohol to open the ring, thereby producing a diester (half ester) having an ester group and a carboxyl group on adjacent carbons on the aromatic ring.

  The mixing ratio of the asymmetric and symmetric aromatic tetracarboxylic acids or esters thereof is about 15 to 55 mol% (preferably 20 to 50 mol%) of the asymmetric aromatic tetracarboxylic acids or esters thereof. The 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 an asymmetric and tetracarboxylic diester and about 80 to 50 mol% of a symmetric aromatic tetracarboxylic diester.

  In addition, it is essential to mix | blend the said symmetric and asymmetric aromatic tetracarboxylic acid component for the following reasons. If only the symmetric aromatic tetracarboxylic acid or its ester is used, the polyimide film exhibits crystallinity, so that the film is powdered during the heat treatment and cannot be formed into a film. On the other hand, only an asymmetric aromatic tetracarboxylic acid or an ester thereof can be formed as an endless tubular PI film, but the yield strength and elastic modulus of the obtained film are weak, and when the film is used as a rotating belt, it can be driven. In addition to the poor response, there is a problem that belt elongation occurs at an early stage.

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

  In addition, it is considered that the addition of the asymmetric aromatic tetracarboxylic acid or its ester causes the polyamic acid molecule to bend, resulting in flexibility.

  The above-mentioned coexistence effect of the symmetric and asymmetric aromatic tetracarboxylic acids or esters thereof is most effectively exerted when the two are in the above-mentioned mixing ratio.

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) represented by -O-, -S-, -CO- _{, -CH 2 -, - SO -} , - SO 2 - compound having a group or two amino groups which are crosslinked with a single bond, and the like. Specifically, for example, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylether, 4,4′-diaminodiphenylthioether, 4,4′-diaminodiphenylcarbonyl, 4, 4'-diaminodiphenylmethane, 1,4-bis (4-aminophenoxy) benzene, and the like. Among them, 4,4′-diaminodiphenyl ether is particularly preferred. 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 As the organic polar solvent used in the mixed solution in a substantially monomer state, an aprotic organic polar solvent is preferable, for example, N-methyl-2-pyrrolidone (hereinafter, referred to as "NMP"), N, N-. Dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, hexamethylphosphamide, 1,3-dimethyl-2-imidazolidinone and the like are used. One or more of these may be a mixed solvent. In particular, NMP is preferred. 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 80 to 230 parts by weight, based on 100 parts by weight of the total amount of the raw material aromatic tetracarboxylic acid component and aromatic diamine component). , 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 components. The reason why carbon black is used is that its dispersibility and stability with the prepared monomer mixture solution (compared to other commonly known conductive materials of metals and metal oxides) (change over time after mixing and dispersing). And no adverse effect on the polycondensation reaction.

  The CB powder has various physical properties (electrical resistance, volatile matter, specific surface area, particle size, PH value) depending on the production raw materials (natural gas, acetylene gas, coal tar, etc.) and production conditions (combustion conditions). , DBP oil absorption, etc.). In the case of a structure having a high conductivity index (which is common in CB powders produced using acetylene gas as a raw material), a predetermined electric resistance can be obtained with a relatively small filling amount, but the mixing and dispersibility is not so good. . Oxidized CB powder having a low PH value but low PH value, and CB powder containing a large amount of volatile matter require a relatively large amount of filling for a given electric resistance. It is easy to obtain a belt with excellent storage stability and uniform electric resistance.

  This conductive CB powder usually has an average particle size of about 15 to 65 nm, and particularly when used for a film for an intermediate transfer belt of an electrophotographic system such as a toner copying machine and a color copying machine, the average particle size is 20 to 65 nm. Those having a thickness of about 40 nm are preferred.

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

  The amount of the CB powder to be added is about 1 to 35 parts by weight (preferably 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 monomer state). Is about 5 to 25 parts by weight).

  The reason why the CB powder is used in the above range is to give the film a volume resistivity (Ω · cm) (VR) and a 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, lower resistance is lower. The reason is that, in addition to the development, the formability is maintained and the physical properties of the film itself are prevented from being reduced.

Preparation of Monomer Mixed Solution A predetermined amount of an aromatic tetracarboxylic acid component, an aromatic diamine component and an organic polar solvent is mixed to form a mixed solution in a substantially monomer state for molding (hereinafter, also referred to as a “monomer mixed solution”). Be prepared. The difference between the non-conductive tubular PI film and the semiconductive tubular PI film of the present invention is only 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 where a highly reactive aromatic tetracarboxylic dianhydride is used. This is one of the advantages in preparing a monomer mixture solution.

  The monomer mixture solution is prepared by mixing and dissolving the aromatic tetracarboxylic acid component and the aromatic diamine component in an organic polar solvent at a reaction ratio of approximately equimolar amounts. 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 kept substantially in a monomer state. The present invention uses the mixed solution in the monomer state 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. Further, the substantially monomeric state means that most of each component is in a monomeric state in a mixed solution, but a low-molecular-weight polycondensation reaction product of an oligomer or the like within a range not adversely affecting the present invention. A small amount may be contained.

  Further, the amount of the organic polar solvent used is about 65 to 300 parts by weight (preferably about 80 to 230 parts by weight, based on 100 parts by weight of the total amount of the raw material aromatic tetracarboxylic acid component and aromatic diamine component). Preferably, it is determined to be about 100 to 200 parts by weight. Since the produced mixed solution in a substantially monomeric state is easily dissolved in the above-mentioned organic polar solvent, there is an advantage that the amount of the solvent used can be reduced as much as possible.

  Hereinafter, a method for preparing a monomer mixture solution will be exemplified.

  As a first example, first, a predetermined mol% of the symmetric and asymmetric aromatic tetracarboxylic acid components is mixed and dissolved in an organic polar solvent. To this solution, an aromatic diamine component having substantially the same mole as the aromatic tetracarboxylic acid component is added with stirring and uniformly dissolved to obtain a monomer mixture solution for molding.

  As a second example, a solution consisting of the predetermined amount of the symmetric aromatic tetracarboxylic acid component and an equimolar amount of the aromatic diamine component, and a predetermined amount of the asymmetric aromatic tetracarboxylic acid component and an equimolar amount of the same Solutions comprising the aromatic diamine component are each separately prepared. The respective solutions are mixed so that the two kinds of aromatic tetracarboxylic acid components have a predetermined mol% to obtain a monomer mixture solution for molding.

  As a third example, a predetermined amount of a symmetric and asymmetric aromatic tetracarboxylic acid component and an aromatic diamine component are simultaneously added to an organic polar solvent to prepare a uniform monomer mixed solution.

  The non-volatile component concentration in the monomer mixture solution of the present invention is a high concentration solution up to about 45% by weight (particularly about 30 to 45% by weight), while the conventional polyamic acid solution is at most 25% by weight. Can be. The “non-volatile 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. Further, a film having a large thickness can be easily produced, and the amount of the solvent to be used is small, so that the cost is suppressed and the evaporation and removal of the solvent are simplified.

  The imidazole-based compound (2-methylimidazole, 1,2-dimethylimidazole, 2-methyl-4-methylimidazole, 2-ethyl-4) is contained in the above-mentioned monomer mixed solution within a range that does not adversely affect the effects of the present invention. Additives such as -ethylimidazole, 2-phenylimidazole) and surfactants (fluorinated surfactants and the like) may be added.

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

  As described above, the amount of carbon black used is 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.

Next, a method for forming a tubular PI film using the prepared monomer mixed solution or semiconductive monomer mixed solution will be described. Hereinafter, the molding means using the monomer mixed solution will be described, but the molding means using the semiconductive monomer mixed solution can be similarly implemented.

  As the forming means, a rotary forming 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 over the entire inner surface.

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

  In either method, the inner surface of the rotating drum is mirror-finished, and barriers are provided around both edges to prevent liquid leakage. The drum is mounted on a rotating roller, and is rotated indirectly by the rotation of the roller.

  For heating, a heat source such as a far-infrared heater is arranged around the drum, and indirect heating is performed from the outside. 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 heating rate may be, for example, about 1 to 2 ° C./min. The above temperature is maintained 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, but heating at such a high temperature from the beginning causes the polyimide to exhibit high crystallization and not only affect the dispersion state of CB, but also toughness. However, there is a problem that a thin film is not formed. Therefore, in the first heating step, the upper limit temperature is kept at most to about 190 ° C., and the polycondensation reaction is terminated at this temperature to obtain a tough tubular PI film.

  After this step is completed, heating is performed as a second heating step to complete the imidization, and the temperature is about 280 to 400 ° C (preferably about 300 to 380 ° C). Also in this case, it is preferable that the temperature is not increased at once from the temperature of the first heating stage, but is gradually increased 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. After the first heating step, the endless tubular film is peeled from the rotating drum, taken out, and separately imidized. To 280 to 400 ° C. for heating. 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 steps is usually about 4 to 7 hours.

  Thus, the non-conductive (or semi-conductive) PI film of the present invention is manufactured. The thickness of this 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, the thickness is preferably about 75 to 100 μm.

In the case of a semiconductive PI film, the semiconductivity of this film is an electrical resistance characteristic determined by a balance between volume resistivity (Ω · cm) (VR) and surface resistivity (Ω / □) (SR). This property is imparted by mixing and dispersing the CB powder. Basically, the range of the resistivity can be freely changed by the mixing amount of the CB powder. The range of the resistivity of the film of the present invention is VR: 10 ² to 10 ¹⁴ , SR: 10 ³ to 10 ¹⁵ , and the preferable ranges are VR: 10 ⁶ to 10 ¹³ , SR: 10 ⁷ to 10 ^14. Can be exemplified. These ranges of resistivity can be easily attained by employing the compounding amount of the CB powder described above. 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 uniform electric resistivity. That is, the semiconductive PI film of the present invention has a feature that the logarithmic conversion values of the surface resistivity SR and the volume resistivity VR are small, and the standard deviation of the logarithmic conversion values of all the measurement points in the film is 0.2. Within, preferably 0.15 or less.

The semiconductive PI film of the present invention has a wide variety of uses due to its excellent electric resistance characteristics and other functions. For example, as an important use requiring charging characteristics, an electrophotographic intermediate transfer belt such as a color copying machine and a color printer can be used. The belt required semiconductive as (resistivity), for example VR10 ⁹ to 10 ^12, SR10 is ¹⁰ 10 ^13, it can be used semi-conductive endless tubular PI film of the present invention suitably.

  Since the present invention is configured as described above, it has the following effects.

  An endless tubular polyimide film can be directly obtained by combining a polyimide raw material having a specific composition with a rotational molding means.

  Compared with the conventional endless tubular polyimide film production via a polyamic acid, the time can be greatly reduced. This not only shortens the time, but also leads to a drastic rationalization of the process control and to obtain a more stable quality of the film.

  The obtained endless tubular polyimide film has come to be widely used for various applications.In particular, a semiconductive endless tubular film is more effective as an electrophotographic intermediate transfer belt such as a color copying machine and a color printer. Also used to.

  Next, the present invention will be described in more detail with reference to Examples along with Comparative Examples.

The yield strength (yield point stress), rupture strength, volume resistivity (VR), surface resistivity (SR) and non-volatile content referred to in this example are values 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 (Autograph manufactured by Shimadzu Corporation) at a tensile 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 curve.

  The yield strength and the breaking strength are important strength factors in designing the material of the 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 the stress applied during mounting.

Also, the breaking strength needs to be higher than the yield strength, which contributes to the service life (toughness) of the belt rotation. As a guide, at least σ _cr / σ _Y = 1.10 or more is required.
<VR and SR>
A sample obtained by cutting the obtained tubular film to a length of 400 mm was used as a sample, and a resistance measuring instrument “Hiresta IP / HR Brobe” manufactured by Mitsubishi Chemical Corporation was used to make five locations at equal pitches in the width direction. The measurement was carried out at a total of 40 locations, eight locations in the circumferential direction, and the average value was shown.

VR was measured after 10 seconds under a voltage of 100 V, and SR was measured after 10 seconds under a 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 defined as Ag. The heat-resistant container containing the sample was placed in an electric oven, and heated and dried at 120 ° C x 12 minutes, 180 ° C x 12 minutes, 260 ° C x 30 minutes, and 300 ° C x 30 minutes while heating sequentially. The weight of the solid content (the weight of the non-volatile content) is Bg. The values of A and B of five samples of the same sample were measured (n = 5), and the non-volatile content was determined by applying the following formula (I). The average value of the five samples was adopted as the nonvolatile content concentration in the present invention.

Non-volatile content concentration = B / A x 100 (%) (I)
Example 1
2,3,3 ', 4'-biphenyltetracarboxylic acid dimethyl ester (half ester of a reaction product of 1 mol of 2,3,3', 4'-biphenyltetracarboxylic dianhydride and 2 mol of methyl alcohol ) 716.0 g (2.0 mol) and 400.0 g (2.0 mol) of 4,4'-diaminodiphenyl ether were mixed at room temperature in 1540 g of NMP solvent and uniformly dissolved. This solution had a nonvolatile content of 34.6% by weight, a solution viscosity of about 250 mPa · s, had substantially no polycondensation reaction, and was a stable solution in a monomer state. Hereinafter, this is referred to as asymmetric monomer solution A.

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

  Then, the asymmetric monomer solution A and the symmetric monomer solution B were mixed at the respective quantitative ratios EX · 1 and EX · 2 shown in Table 1 with a fluorine-based surfactant (EF manufactured by Tochem Products Co., Ltd.). -351) With 0.037% by weight (vs. non-volatile content), both were thoroughly mixed and defoamed. This was used as each monomer solution for molding, and a predetermined amount was collected from each of the solutions, poured into a rotating drum, and molded under the following conditions.

  Rotating Drum: A metal drum with an inner mirror surface having an inner diameter of 100 mm and a width of 530 mm was placed on two rotating rollers, and was arranged so as to rotate with the rotation of the rollers.

Injection amount of molding monomer solution C: 45.9 g
Heating temperature: A far-infrared heater was arranged on the outer surface of the drum, and 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, the rotation was started immediately, and the speed was gradually increased to reach 24 rad / s. The heating gradually increased to 170 ° C., and heating was performed at that temperature for 90 minutes while maintaining the rotation.

  When the rotation and heating for 90 minutes were completed, the mixture was cooled to room temperature, the rotating drum was detached as it was, and left standing in a hot-air stagnation oven to start heating for imidization. This heating also reached 350 ° C. while gradually increasing the temperature. After heating at this temperature for 30 minutes, the tube was cooled to room temperature and the tubular PI film formed on the inner surface of the drum was peeled and taken out. The results in each case are described 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 was mixed under the same conditions as in Example 1 except that mixing was performed at the respective ratios shown in EX.3 to 6 shown in Table 1. And imidized, peeled from the rotating drum, taken out and measured. The results in each case are shown in Table 2.

Example 2
First, using the asymmetric monomer solution A and the symmetric monomer solution B in Example 1 and uniformly mixing them in a quantitative ratio described in EX.7 shown in Table 1, as in the example, 14.0 g (8.33 parts by weight based on 100 parts by weight of the total amount of all monomers) was added to the mixture, and the mixture was sufficiently mixed and dispersed by a ball mill, and finally defoamed. This was used as a semiconductive monomer solution for molding. The nonvolatile content in the semiconductive monomer solution was 36.8% by weight, and the CB concentration in the nonvolatile content was 9.19% by weight.

  Then, 45.9 g of the solution was collected, poured into a rotating drum in the same manner as in Example 1, molded under the same conditions, and then imidized. The obtained imidized film was peeled from the rotating drum, taken out and measured. The results are shown in Table 2.

Comparative Example 2
First, the asymmetric monomer solution A and the symmetric monomer solution B of Example 1 were uniformly mixed in the same ratios as those of EX.8 and 9 shown in Table 1 in the same manner as in this example. In the same manner as in Example 2, 8.33 parts by weight of CB powder was added to 100 parts by weight of the total amount of all monomers, mixed and dispersed sufficiently by a ball mill, and finally defoamed. This was used as a semiconductive monomer solution for molding. The nonvolatile content in the semiconductive monomer solution was 36.8% by weight, and the CB concentration in the nonvolatile content was 9.19% by weight.

  Then, 45.9 g of each of the liquid A and the liquid B was collected, poured into a rotary drum as in Example 1, and molded under the same conditions. After imidation, the film was peeled from the rotating drum, taken out, and measured. The results in each case are shown in Table 2.

Claims (3)

A substantially equimolar amount of an aromatic tetracarboxylic acid component and an aromatic diamine component comprising 15 to 55 mol% of an asymmetric aromatic tetracarboxylic acid or an ester thereof and 85 to 45 mol% of a symmetric aromatic tetracarboxylic acid or an ester thereof. A method for producing an endless tubular polyimide film, comprising: forming a mixed solution in a substantially monomer state, which is mixed in an amount, into a tubular material by a rotational molding method, and heat-treating the mixture to imidize it. A substantially equimolar amount of an aromatic tetracarboxylic acid component and an aromatic diamine component comprising 15 to 55 mol% of an asymmetric aromatic tetracarboxylic acid or an ester thereof and 85 to 45 mol% of a symmetric aromatic tetracarboxylic acid or an ester thereof. In a substantially monomeric mixed solution mixed in an amount, 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. A method for producing a semiconductive endless tubular polyimide film, wherein a monomer mixture solution is formed into a tubular material by a rotational molding method, and is heat-treated to be imidized. A semiconductive endless tubular polyimide film used for an electrophotographic intermediate transfer belt manufactured by the manufacturing method according to claim 2.