JP6433890B2 - Polyimide precursor solution - Google Patents

Description

  The present invention relates to a polyimide precursor solution. The polyimide molded body obtained from this polyimide precursor solution has excellent mechanical strength and high heat resistance.

  Molded products made of aromatic polyimide obtained from aromatic tetracarboxylic dianhydride and aromatic diamine are excellent in heat resistance, mechanical strength, electrical properties, solvent resistance, etc. Widely used in aircraft and aircraft fields. Since this aromatic polyimide has poor solubility, the polyamic acid that is the polyimide precursor is usually NMP (N-methyl-2-pyrrolidone), DMF (N, N-dimethylformamide), DMAc (N, N-dimethyl). A solution dissolved in an amide solvent such as acetamide) is applied onto the surface of the base material and then cured (imidized) at a high temperature to obtain a polyimide molded body such as a film or a belt. When the amide solvent is used as a solvent in the polyamic acid solution, the amide solvent is released into the atmosphere at the time of polyimide molding, so there is a point to be improved from the viewpoint of environmental compatibility.

  Therefore, a polyimide precursor solution that does not use the amide solvent has been proposed.

  For example, Patent Documents 1 to 6 propose a polyimide precursor solution obtained by dissolving a salt of a polyamic acid and a basic compound in water that does not substantially contain an organic solvent.

  However, the polyimide precursor solution containing a high concentration of water as disclosed in Patent Documents 1 to 6 has a leveling property when applied and molded on the surface of the substrate because of the high surface tension inherent to water. This is not sufficient, and there has been a problem that a film repelling phenomenon occurs and thickness unevenness is likely to occur. There was also a problem with storage stability.

  Patent Documents 7 and 8 are obtained by reacting a tetracarboxylic acid component and a diamine component in the presence of a strongly basic compound such as triethylamine or triethylenediamine using a solvent containing a specific alcohol as a reaction solvent. A polyimide precursor solution is proposed. However, when an alcohol mixed with a strongly basic compound such as triethylamine or triethylenediamine is used as a polymerization solvent, it is difficult to obtain a polyimide precursor having a high polymerization degree, and there is also a problem in storage stability.

JP-A-8-59832 JP 2002-226582 A International Publication No. 2012/8543 International Publication No. 2013/35806 International Publication No. 2013/105610 JP 2013-144750 A JP 2013-144751 A JP 2014-31445 A

  Therefore, the present invention solves the above-described problems, and can produce a polyimide molded body having excellent mechanical strength, is excellent in environmental compatibility, and has good storage stability and leveling properties. The purpose is to provide.

As a result of diligent research to solve the above problems, the inventors of the present invention dissolved a salt of polyamic acid and a specific basic compound in a specific solvent to obtain a uniform polyimide precursor solution. It has been found that a polyimide molded body having excellent mechanical strength can be produced, and the present invention has been completed.
That is, the present invention has the following purpose.
1) A polyimide precursor solution obtained by dissolving a salt of a polyamic acid and a weakly basic compound having an acid dissociation constant (pKa) of 8.5 or less and 4.5 or more in a solvent containing a polyhydric alcohol.
2) The said polyimide precursor solution whose solvent containing a polyhydric alcohol is a mixed solvent of a polyhydric alcohol and water.
3) The said polyimide precursor solution whose mixed solvent shows water content of less than 70 mass%.
4) The polyimide precursor solution using an isolated solid polyamic acid as the polyamic acid.

  Since the polyimide precursor solution of the present invention does not use an amide solvent, it is excellent in environmental compatibility, has excellent storage stability and coating leveling, and uses a relatively high boiling point solvent such as a polyhydric alcohol. Therefore, process control during molding becomes easy, and a coating film having a uniform thickness can be obtained. Therefore, the polyimide precursor solution of the present invention can be suitably used as a polyimide precursor solution, and a polyimide molded body having excellent characteristics can be obtained from this solution.

  The polyimide precursor in the present invention is an aromatic polyimide precursor, and is a homopolymer or copolymer of polyamic acid having a structural unit represented by the general formula (1). The polyimide obtained from this polyimide precursor is preferably a non-thermoplastic polyimide, and its glass transition temperature is preferably 250 ° C. or higher.

  Here, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, and each of the tetravalent divalent groups forms a pair, and each pair of divalent groups is adjacent to the carbon 6-membered ring. Provided by carbon atoms.

  R 'represents a divalent aromatic residue having 1 to 4 carbon 6-membered rings.

  The polyamic acid can be obtained by reacting a tetracarboxylic acid component with a diamine component.

  The tetracarboxylic acid component is a tetracarboxylic acid having an aromatic ring (tetracarboxylic acid, dianhydride or esterified product thereof), specifically, for example, pyromellitic acid, 3, 3 ′, 4 , 4′-biphenyltetracarboxylic acids, 2,3,3 ′, 4′-biphenyltetracarboxylic acids, 2,2 ′, 3,3′-biphenyltetracarboxylic acids, 4,4′-oxydiphthalic acids, 3,3 ', 4,4'-benzophenonetetracarboxylic acids, 3,3', 4,4'-diphenylsulfonetetracarboxylic acids, p-terphenyltetracarboxylic acids, m-terphenyltetracarboxylic acids, etc., and mixtures thereof Can be mentioned.

  Among these, pyromellitic acids, 3,3 ′, 4,4′-biphenyltetracarboxylic acids, 3,3 ′, 4,4′-benzophenone tetracarboxylic acids, 4,4′-oxydiphthalic acids, and their Mixtures are preferred.

  The diamine component is an aromatic diamine. Specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenyl ether (4,4′-oxydianiline), 3,4 '-Oxydianiline, 4,4'-diaminodiphenylmethane, 2,4-toluenediamine, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis (4-aminophenoxy) -Benzene, 1,3-bis (3-aminophenoxy) -benzene, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis (4-amino-3-carboxyphenyl) methane, 2,4-diamino Toluene and the like can be mentioned.

  Of these, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and mixtures thereof are preferred.

  As the polyamic acid, it is preferable to use an isolated solid polyamic acid. The use of the isolated solid polyamic acid means that a solid polyamic acid polymerized in advance in another system is used in the production of the polyimide precursor solution of the present invention. As the solid polyamic acid, for example, polyamic acid powder obtained by suspension polymerization of a tetracarboxylic acid component and a diamine component can be preferably used. The polyamic acid by the suspension polymerization method can be obtained, for example, by a method described in Japanese Patent Nos. 2951484 and 3386856. That is, approximately equimolar amounts of the tetracarboxylic acid component and the diamine component can be obtained by reacting in a poor solvent that does not dissolve the polyamic acid. The reaction temperature is preferably -20 to 60 ° C, particularly preferably 0 to 30 ° C. When the reaction is carried out in a poor solvent in this way, the reaction product polyamic acid is not dissolved in the poor solvent but is suspended in the solvent. The solvent can be removed to obtain a powdery polyamic acid. Here, the poor solvent means a solvent having a polyamic acid solubility of less than 1 g at 25 ° C. with respect to 100 g of the solvent. Specifically, solvents such as ethers and ketones can be used. Of these, THF (tetrahydrofuran), acetone and mixtures thereof are preferably used. A solid polyamic acid having a high degree of polymerization can be obtained by such a suspension polymerization method, and a polyimide precursor solution having a high degree of polymerization can be obtained using this. The content of the poor solvent in the obtained powdery polyamic acid is preferably less than 1% by mass with respect to the total mass of the powder.

  The polyimide precursor solution of the present invention has a polyamic acid and acid dissociation constant (pKa) of 8.5 or less, 4.5 or more, preferably 8.5 or less, 5.5 or more, more preferably 8.5 or less, A salt composed of 7.0 or more weakly basic compound is used as a polyimide precursor. Here, pKa of a basic compound is one of the indexes for quantitatively expressing the strength of a base, and is a value of an acid dissociation constant of a conjugate acid of the base. That is, it is represented by the negative common logarithm of the equilibrium constant (Ka) of the dissociation reaction in which protons are released from the acid, and is obtained by performing acid-base titration at a measurement temperature of 25 ° C. A larger pKa value indicates a stronger base. Typical examples of weakly basic compounds having a pKa of 8.5 or less and 4.5 or more include nitrogen-containing heterocyclic compounds. Specifically, pyridine derivatives such as pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole Imidazole derivatives such as 1-methyl-4-ethylimidazole, quinoline derivatives such as quinoline and isoquinoline, and the like. Of these, 1,2-dimethylimidazole and 2-ethyl-4-methylimidazole are preferably used. In addition, about the basic compound which has several pKa value, let the maximum value be the pKa value of the basic compound.

  As a compounding quantity of the weak basic compound with respect to the said polyamic acid, 1-4 mol is preferable with respect to 1 mol of structural units of a polyamic acid, and 1.5-3 mol is more preferable. Two or more weakly basic compounds may be blended, and in that case, the total blending amount thereof may be within the above range.

  The polyimide precursor solution of the present invention can be obtained by adding a solvent containing a weak basic compound and a polyhydric alcohol to the polyamic acid and dissolving it. Here, the polyhydric alcohol refers to an organic compound having two or more alcoholic hydroxyl groups in one molecule. Specific examples of the polyhydric alcohol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5 -Pentanediol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, 1,2,6-hexane Examples include triol, diethylene glycol, dipropylene glycol, triethylene glycol, and tetraethylene glycol. Of these, ethylene glycol and diethylene glycol are preferably used.

  As the solvent containing the polyhydric alcohol, a solvent composed only of the polyhydric alcohol can be used, or a mixed solvent of the polyhydric alcohol and water can be used. In any solvent, polyhydric alcohols may be used alone or in combination. From the viewpoint of reducing raw material costs, a mixed solvent of polyhydric alcohol and water is preferably used. The water content in the mixed solvent of polyhydric alcohol and water is preferably less than 70% by mass with respect to the total mass of the solvent, from the viewpoint of storage stability, coating leveling properties and film strength, and is 60% by mass. More preferably, it is less than.

  The solvent containing the polyhydric alcohol preferably does not contain a solvent other than the polyhydric alcohol and water. In particular, the content of the amide solvent is less than 2% by mass with respect to the total mass of the solvent from the viewpoint of environmental compatibility. It is preferable that it is less than 1% by mass. The amide solvent is an organic solvent having an amide bond in which a hydrogen atom may be substituted with an alkyl group. For example, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N— Examples include dimethylacetamide.

  When setting it as a solution, 0.1-60 mass% is preferable, as for the density | concentration of the said polyimide precursor, 1-40 mass% is more preferable, and 10-30 mass% is still more preferable. The concentration of the polyimide precursor is calculated as a ratio of the total mass of the polyamic acid and the weak basic compound to the total mass of the polyimide precursor solution.

  Further, the intrinsic viscosity [η] of the polyimide precursor is preferably 0.7 or more, more preferably 1.0 or more, and further preferably 1.2 or more. The larger the value of [η], the easier it is to obtain a product with good properties such as strength and elastic modulus when the ring is closed to form polyimide. [Η] is a value directly related to the molecular weight of the polymer, and is measured in a N, N-dimethylacetamide solvent at a polyimide precursor concentration of 0.5 mass% and 25 ° C.

  The polyimide precursor solution of the present invention can also be obtained by directly reacting a tetracarboxylic acid component and a diamine component in a solvent containing a polyhydric alcohol in which a weakly basic compound coexists. However, in this case, since the decomposition reaction of the tetracarboxylic acid component, which is a monomer, proceeds during the polymerization reaction, it may be difficult to obtain a polyamic acid having a high degree of polymerization. It is preferable to obtain by dissolving a polyamic acid and a weakly basic compound in a solvent containing a polyhydric alcohol. If the polyimide precursor solution contains a polyhydric alcohol or water, the molecular weight of the polyamic acid may decrease due to long-term storage. Therefore, it is preferable that the powdered polyamic acid is made into a solution immediately before molding of the polyimide. The obtained polyamic acid solution has a storage temperature of preferably 10 ° C or lower, more preferably 0 ° C or lower.

  The polyimide precursor solution of the present invention can be processed into a film or belt by a usual method, or a film can be formed. For processing into a film, a polyimide precursor solution is obtained by casting a solution of a polyimide precursor to a desired thickness on a substrate such as a glass plate by a film applicator, removing the solvent, and then imidizing by heating. . Similarly, if the solution is applied onto the target substrate, dried and heated, the substrate can be coated with polyimide.

  Furthermore, the polyimide precursor solution of the present invention is, for example, a known material such as a pigment, conductive carbon black and metal particles, a lithium secondary battery active material, an abrasive, a dielectric, a lubricant, and the like. The filler can be blended. In addition, other polymers and solvents such as ethers, monohydric alcohols, ketones, esters, halogenated hydrocarbons, hydrocarbons and the like can be added as long as the effects of the present invention are not impaired.

  Films and coatings produced from the polyimide precursor solution of the present invention include, for example, various electrical insulating films (heat-resistant insulating tape, heat-resistant adhesive tape, high-density magnetic recording base, capacitor, FPC, etc.), intermediate transfer belts for copying machines , Fixing belts for copying machines, electrodes for lithium secondary batteries, sliding members filled with fluororesin or graphite, structural members reinforced with glass fibers or carbon fibers, various spacers (insulating spacers for power transistors, magnetic head spacers, Power relay spacers, transformer spacers, etc.), wire / cable insulation coatings, enamel coating materials (solar cells, low-temperature storage tanks, space insulation, integrated circuits, slot liners, etc.), ultrafiltration membranes, gas separation membranes, etc. It is suitably used for production.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited only to these Examples.

<Preparation of polyamic acid powder>
The polyamic acid powder used in Examples and Comparative Examples was prepared as follows.

<Polyamic acid powder A>
According to the method described in Example 1 of Japanese Patent No. 2995184, polyamic acid powder was obtained from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA). That is, 21.9 g of PMDA was dissolved in 500 ml of THF and kept at 0 ° C. To this, 500 ml of THF solution of 20.0 g of ODA was gradually added and reacted at 0 ° C. for 2 hours to obtain a suspension containing polyamic acid. A polyamic acid was isolated from the suspension to obtain a polyamic acid powder. [Η] of the polyamic acid at this time was 1.50. This is designated as polyamic acid powder A.

<Polyamic acid powder B>
According to the method described in Example 3 of Japanese Patent No. 2951484, a polyamic acid powder is formed from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA). Obtained. That is, 2.96 g of BPDA was suspended in 50 ml of THF and kept at 0 ° C. A solution obtained by dissolving 2.00 g of ODA in 50 ml of THF was gradually added thereto and reacted at 0 ° C. for 2 hours to obtain a suspension of polyamic acid. A polyamic acid was isolated from the suspension to obtain a polyamic acid powder. [Η] of the polyamic acid at this time was 2.19. This is designated as polyamic acid powder B.

<Polyamic acid powder C>
A polyamic acid powder was obtained from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA). Specifically, 8.06 g of BPDA was suspended in 60 ml of acetone and kept at room temperature (20 ° C.). A solution obtained by dissolving 2.91 g of PDA in 129 ml of acetone was gradually added thereto and reacted at room temperature for 1 hour to obtain a polyamic acid suspension. A polyamic acid was isolated from the suspension to obtain a polyamic acid powder. [Η] of the polyamic acid at this time was 1.85. This is designated as polyamic acid powder C.

  The characteristics of the polyimide precursor solutions obtained in the following examples and comparative examples were evaluated by the following methods.

<Storage stability>
When the intrinsic viscosity of the polyamic acid after the polyimide precursor solution is allowed to stand at 25 ° C. for 100 hours is measured and the rate of change is less than 10%, the storage stability is “good” and the rate of change is 10% or more. In some cases, the storage stability was determined to be “bad”.

<Leveling properties>
The polyimide precursor solution was applied on a glass plate as a base material using a film applicator, and the coating film was applied at 50 ° C. for 10 minutes, 80 ° C. for 30 minutes, 120 ° C. for 30 minutes, 200 ° C. Heat treatment was performed at 20 ° C. for 20 minutes, 300 ° C. for 20 minutes, and then 350 ° C. for 10 minutes to form a polyimide film coating having a thickness of about 20 μm. Then, after peeling a polyimide film from a glass plate and cutting out to 10 square cm square, the thickness of arbitrary nine places was measured. When the fluctuation range of the thickness was less than ± 10% with respect to the average value, the leveling property was judged as “good”, and when the fluctuation range was ± 10% or more, the leveling property was judged as “bad”.

<Film strength characteristics>
When the tensile strength of the polyimide film is measured based on ASTM D882 and the tensile strength of the polyimide film is 12 kg / mm ² or more, the mechanical strength is “good” and the tensile strength of the polyimide film is less than 12 kg / mm ² . In some cases, the mechanical strength was determined to be “bad”.

[Example 1]
25 Mixtures of polyamic acid powder A and 1,2-dimethylimidazole (pKa 7.7) (1,2-dimethylimidazole is used in an amount of 2.5 moles per mole of polyamic acid constituent unit) It melt | dissolved in ethylene glycol at ° C and polyimide precursor solution A-1 which has a density | concentration of 15 mass% as a polyimide precursor was obtained. Table 1 shows the results of characterization of this precursor solution.

[Example 2]
25 mixture of polyamic acid powder B and 1,2-dimethylimidazole (pKa 7.7) (1,2-dimethylimidazole is used in an amount of 2.5 moles per mole of polyamic acid constituent unit) It melt | dissolved in ethylene glycol at 0 degreeC and obtained polyimide precursor solution B-1 which has a density | concentration of 15 mass% as a polyimide precursor. Table 1 shows the results of characterization of this precursor solution.

[Example 3]
A polyimide precursor solution B-2 was obtained in the same manner as in Example 2 except that 2-ethyl-4-methylimidazole (pKa 8.3) was used as the basic compound. Table 1 shows the results of characterization of this precursor solution.

[Example 4]
A polyimide precursor solution A-2 was obtained in the same manner as in Example 1 except that diethylene glycol was used as the solvent. Table 1 shows the results of characterization of this precursor solution.

[Example 5]
A polyimide precursor solution B-3 was obtained in the same manner as in Example 2 except that diethylene glycol was used as the solvent. Table 1 shows the results of characterization of this precursor solution.

[Example 6]
A polyimide precursor solution A-3 was obtained in the same manner as in Example 1 except that a mixed solvent of ethylene glycol and water (mixing mass ratio ethylene glycol: water = 80: 20) was used as the solvent. Table 1 shows the results of characterization of this precursor solution.

[Example 7]
A polyimide precursor solution B-4 was obtained in the same manner as in Example 2 except that a mixed solvent of ethylene glycol and water (mixing mass ratio ethylene glycol: water = 80: 20) was used as the solvent. Table 1 shows the results of characterization of this precursor solution.

[Example 8]
25 A mixture of polyamic acid powder C and 1,2-dimethylimidazole (pKa 7.7) (1,2-dimethylimidazole is used in an amount of 2.5 moles per mole of the polyamic acid constituent unit). It melt | dissolved in the mixed solvent (mixing mass ratio ethylene glycol: water = 80: 20) at ethylene glycol and water, and the polyimide precursor solution C-1 which has a density | concentration of 15 mass% as a polyimide precursor was obtained. Table 1 shows the results of characterization of this precursor solution.

[Example 9]
A polyimide precursor solution B-5 was obtained in the same manner as in Example 2 except that a mixed solvent of ethylene glycol and water (mixing mass ratio ethylene glycol: water = 50: 50) was used as the solvent. Table 1 shows the results of characterization of this precursor solution.

[Example 10]
A polyimide precursor solution C-2 was obtained in the same manner as in Example 8 except that a mixed solvent of diethylene glycol and water (mixing mass ratio diethylene glycol: water = 60: 40) was used as the solvent. Table 1 shows the results of characterization of this precursor solution.

[Comparative Example 1]
The polyimide precursor solution A-4 was tried to be obtained in the same manner as in Example 1 except that methanol was used as the solvent. However, the polyamic acid powder A was not completely dissolved and a uniform solution could be obtained. could not.

[Comparative Example 2]
The polyimide precursor solution B-6 was tried to be obtained in the same manner as in Example 2 except that ethanol was used as a solvent. However, the polyamic acid powder B was not completely dissolved and a uniform solution could be obtained. could not.

[Comparative Example 3]
The polyimide precursor solution B-7 was obtained in the same manner as in Example 2 except that the solvent was n-butanol, but the polyamic acid powder B could not be completely dissolved and a uniform solution could be obtained. could not.

[Comparative Example 4]
A polyimide precursor solution A-5 was obtained in the same manner as in Example 1 except that triethylamine (pKa 11.8), which is a strongly basic compound, was used as the basic compound. Table 1 shows the results of characterization of these precursor solutions.

[Comparative Example 5]
A polyimide precursor solution A-6 was obtained in the same manner as in Example 1 except that triethylenediamine (pKa 8.8), which is a strongly basic compound, was used as the basic compound. Table 1 shows the results of characterization of these precursor solutions.

[Comparative Example 6]
A polyimide precursor solution B-8 was obtained in the same manner as in Example 2 except that the solvent was water. Table 1 shows the results of characterization of these precursor solutions.

[Comparative Example 7]
A polyimide precursor solution B-9 was obtained in the same manner as in Example 2 except that the solvent was water and the basic compound was triethylamine (pKa 11.8), which is a strongly basic compound. Table 1 shows the results of characterization of these precursor solutions.

  From the results, it can be seen that the polyimide precursor solution of the present invention is excellent in storage stability and leveling properties. Furthermore, it turns out that the polyimide film obtained from this polyimide precursor solution has the outstanding mechanical strength. In addition, since no amide solvent is used, it is excellent in environmental compatibility.

  The polyimide precursor solution of the present invention can be suitably used for the production of an electric insulating film such as FPC, a belt for a copying machine, an electrode for a lithium secondary battery, an electric wire / cable insulating coating, and a film separation.

Claims (2)

A polyimide precursor solution in which a salt of a polyamic acid and a weakly basic compound having an acid dissociation constant (pKa) of 8.5 or less and 4.5 or more is dissolved in a mixed solvent of polyhydric alcohol and water, The polyimide precursor solution whose water content of a mixed solvent is 40 mass% or less . The polyimide precursor solution according to claim 1 , wherein an isolated solid polyamic acid is used as the polyamic acid.