JP2001164183A - Insulating coating, method for preparign the same, and insulating film obtainable from the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulating coating that is low in viscosity enough to easily apply to even though it contains a polyimide precursor and an insulating filler in a high solids content in an organic solvent; a method preparing easily the same; and an insulating film that can be obtained from the coating and includes no void, no bubble and no crack. SOLUTION: A tetracarboxylic acid dianhydride such as pyromellitic acid dianhydride is reacted with a diamine such as diaminodiphenyl ether in a solvent to produce a carboxylic dianhydride, to which water or an optional alcohol is added to open the terminal anhydride ring to produce the carboxylic acid. Then, a diamine such as diaminodiphenyl ether is added to the carboxylic acid to form a polyimide precursor solution. An insulating filler is added to the solution to prepare an insulating coating. The coating is applied to a substrate and is heated to obtain an insulating film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an insulating paint containing an insulating filler in a polyimide precursor solution, a method for producing the same, and an insulating film obtained therefrom.

[0002]

2. Description of the Related Art Conventionally, epoxy resin, polyimide resin and silicone resin have been widely used as insulating sealing materials for semiconductor chips and flexible printed circuit boards as electronic circuit parts, insulating films for interlayer insulating films and protective films. . In recent years, as the processing temperature and the operating temperature environment of these electronic circuit components have become higher, the requirements for the durability of the coating have become more and more severe. As a result, polyimide resins, which have better high-temperature durability and insulating properties than epoxy resins, have received particular attention.

The above-mentioned insulating film made of a polyimide resin has been formed into a polyimide film through a process in which a polyimide precursor solution is applied to a substrate, heat-treated, a solvent is evaporated, and then thermal imidization is performed. In the process of obtaining a polyimide film through a heat treatment from this polyimide precursor solution, because the solvent evaporates, voids and bubbles in the film,
There is a problem that cracks are generated, and as a result, insulation properties are reduced. By the way, the polyimide precursor solution is a solution in which a polyamic acid generated by polycondensation of a tetracarboxylic dianhydride and an aromatic diamine is dissolved in a solvent such as dimethylformamide or N-methylpyrrolidone as a solute. . Since the solute polyamic acid is a polymer having a high degree of polymerization, the polyamic acid solution had essentially high viscosity even at a low concentration. In addition, since polyamic acid having a high degree of polymerization has low solubility in a solvent, it has been difficult to increase the solid concentration in order to reduce the amount of solvent evaporation as a measure against the above-mentioned problem.

[0004] On the other hand, as another attempt to increase the solid content in the polyimide precursor solution, an insulating filler such as alumina, boron nitride or silica is added to the polyimide precursor solution to form voids or bubbles in the obtained coating. There is known a method for reducing cracks. However, when an insulating filler is added to a conventional polyamic acid solution that is inherently low in concentration and high in viscosity, the viscosity further increases, making it difficult to disperse the filler or make coating difficult. Had.

[0005]

In view of the above, it is an object of the present invention to provide an insulating coating which has a low viscosity and is easy to apply even when a polyimide precursor and an insulating filler are contained in an organic solvent at a high solid content ratio. To provide a method for producing an insulating paint capable of uniformly dispersing a polyimide precursor and an insulating filler in an organic solvent and obtaining an insulating paint with good productivity, and from this insulating paint. It is an object of the present invention to provide an insulating film which does not contain voids, bubbles or cracks in the film.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, a specific carboxylic acid and a specific diamine forming a polyimide precursor have been dissolved in an organic solvent. The dissolved polyimide precursor solution is
Even if it has a high solid content ratio, it has a low viscosity, the insulating filler can be easily and uniformly dispersed, and has a low viscosity.Moreover, when this insulating paint is applied on a substrate and heated, The present inventors have found that an insulating coating free of voids and cracks can be obtained, and have reached the present invention.

That is, the gist of the present invention is that first, a carboxylic acid represented by the general formula (1) for forming a polyimide precursor and a diamine represented by the general formula (2) are mixed in an organic solvent in an amount of 5 to 8%.
An insulating paint characterized by containing an insulating filler in a polyimide precursor solution in which 0% by weight is dissolved.

[0008]

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[Wherein, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, and four carbonyl groups are directly linked to different carbon atoms in the residue; Each two of them are paired and are bonded to adjacent carbon atoms in the six-membered carbon ring, and R ′ represents a divalent aromatic residue containing at least one six-membered carbon ring; 'Represents hydrogen or a monovalent organic group having 7 or less carbon atoms, R''' represents a divalent aromatic residue containing at least one carbon 6-membered ring, and n
Represents an integer of 1 to 20. ]

Second, in a solvent, one mole of the tetracarboxylic dianhydride represented by the general formula (3) is added to one mole of the general formula (4)
Are reacted at a ratio of 0.1 to 0.95 mol to form a carboxylic dianhydride represented by the general formula (5), and water or any alcohol is added to form a terminal acid anhydride group. After ring opening to obtain a carboxylic acid represented by the general formula (1),
With respect to 1 mol of the carboxylic acid represented by the general formula (1), 0.95 to 1.05 mol of the diamine represented by the general formula (2) is added to form a polyimide precursor solution, and further an insulating filler is added. A method for producing an insulating paint.

[0011]

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[Wherein, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, and four carbonyl groups are directly linked to different carbon atoms in the residue; Each two of them are paired and are bonded to adjacent carbon atoms in the six-membered carbon ring, and R ′ represents a divalent aromatic residue containing at least one six-membered carbon ring; 'Represents hydrogen or a monovalent organic group having 7 or less carbon atoms, R''' represents a divalent aromatic residue containing at least one carbon 6-membered ring, and n
Represents an integer of 1 to 20. ]

Third, there is provided an insulating film comprising a polyimide represented by the following structural formula (6) and an insulating filler obtained by applying the insulating coating material to a substrate and heating the coating.

[0014]

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[Wherein, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, and four carbonyl groups are directly linked to different carbon atoms in the residue; Two of them are paired and are bonded to adjacent carbon atoms in the six-membered carbon ring, and R ′ and R ′ ″ are divalent aromatic residues containing at least one six-membered carbon ring. Is shown. m +
l is an integer of 10 to 5000. ]

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, terms used in the present invention will be described. (1) Polyimide An organic polymer in which 80 mol% or more of the repeating unit of the polymer chain has an imide structure. And this organic polymer shows heat resistance. (2) Polyimide precursor An organic compound which becomes a polyimide by ring closure by heating or chemical action. In the present invention, the polyimide precursor is a carboxylic acid represented by the general formula (1) and a diamine represented by the general formula (2) Consisting of Here, ring closure means that an imide ring structure is formed.

(3) Polyimide precursor solution The polyimide precursor is dissolved in a solvent. Here, the solvent refers to a compound which is liquid at 25 ° C. (4) Viscosity The rotational viscosity at 20 ° C. was measured using a DVL-BII type digital viscometer (B type viscometer) manufactured by Tokimec Co., Ltd. (5) Solute concentration It is a numerical value expressing the weight ratio of the polyimide precursor in the solution in percentage. (6) Insulating coating An insulating coating obtained by applying an insulating coating on a base material such as copper, aluminum, glass, etc., and heating it. Insulating coatings and those used after being peeled off from the substrate are called insulating films, and these insulating coatings and insulating films fall into the category of insulating coatings.

The insulating coating material of the present invention comprises a polyimide precursor solution in which a carboxylic acid represented by the general formula (1) and a diamine represented by the general formula (2) forming a polyimide precursor are dissolved in an organic solvent. It contains an insulating filler. Wherein R is a tetravalent aromatic residue containing at least one carbon 6-membered ring, the four carbonyl groups are directly linked to different carbon atoms in the residue, and two of the four
Each of them is paired and is bonded to an adjacent carbon atom in the six-membered carbon ring, and R ′ represents a divalent aromatic residue containing at least one six-membered carbon ring. R ″ represents hydrogen or a monovalent organic group having 7 or less carbon atoms, and R ′ ″ represents at least 1
Represents a divalent aromatic residue containing six carbon 6-membered rings, wherein n is 1
Represents an integer of up to 20. Specific examples of R are arbitrarily selected from the following structural formula groups.

[0019]

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R is preferably selected from the following structural formula groups.

[0021]

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R is particularly preferably selected from the following structural formula group.

[0023]

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The above R may be selected from two or more types as well as a single type. Further, specific examples of R ′ are arbitrarily selected from the following structural formula groups.

[0025]

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R ′ is preferably selected from the following structural formula group.

[0027]

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R ′ is particularly preferably selected from the following structural formula groups.

[0029]

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The above R 'may be selected not only alone but also two or more kinds.

Further, as specific examples of R ′ ″, those described above as R ′ can be similarly used. The same or different R 'and R''' may be used. Preferred and particularly preferred R '''are the same as those of R'.

The concentration of the polyimide precursor in the polyimide precursor solution is 5 to 80% by weight, and if the concentration is lower than 5% by weight, it is difficult to obtain a predetermined insulating film thickness only by adjusting the coating apparatus. , So that repeated application is required, and the productivity is reduced. On the other hand, if the concentration is higher than 80% by weight, it may be difficult to stably dissolve the polyimide precursor. In consideration of productivity, a more preferable concentration range is a range of 10 to 55% by weight. Within this range, conventionally known coating methods such as screen printing and other spin coating methods, bar coating methods, spray coating methods, dip coating methods, casting methods, and potting methods, and insulating coatings suitable for sealing coating methods are obtained. be able to.

The organic solvent used in the present invention is not particularly limited as long as a stable solution can be obtained. Examples thereof include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, and hexamethylphosphoryltriol. Amide, sulfolane, N,
Polar solvents containing N, S, P atoms in molecules such as N'-dimethylimidazolidinone, N-methylcaprolactam, and cellsolves such as cellsolve and phenylcellsolve;
Ethyl acetate cellosolve, butyl acetate cellosolve such as cellosolves, methyl carbitol, carbitols such as ethyl carbitol, ethyl carbitol,
Carbitol acetates such as butyl carbitol acetate, carbitol diethers such as dimethyl carbitol (diglyme) and diethyl carbitol, alcohols such as cyclohexanol and benzyl alcohol, ketones such as cyclohexanone and isophorone, γ-butyrolactone And the like, and these may be used alone or as a mixture of two or more.

The type of the solvent can be appropriately selected depending on the desired evaporation rate and the viscosity of the paste. However, it is better to use a highly polar organic solvent containing N, S or P in the molecule. Is more soluble,
When it is desired to increase the film thickness, it is preferable to use a strongly polar organic solvent in order to obtain a polyimide precursor solution having a higher concentration.

The viscosity of the polyimide precursor solution is 2
00 poise or less is preferable, 100 poise or less is more preferable, and 80 poise or less is further preferable.

Next, a preferred production method for obtaining a polyimide precursor solution will be described. First, a tetracarboxylic dianhydride represented by the general formula (3) is reacted with a diamine represented by the general formula (4) in a solvent to produce a carboxylic dianhydride represented by the general formula (5). The reaction temperature at this time is preferably from -30C to 70C, more preferably from -20C to 40C. Next, water or an alcohol is added to the reaction solution to cause a reaction, thereby generating a carboxylic acid represented by the general formula (1), thereby obtaining a carboxylic acid solution represented by the general formula (1).
The reaction temperature at this time is preferably from 0 to 80 ° C, and from 20 to 80 ° C.
70 ° C. is more preferred. In this case, if necessary, dimethylaminoethanol or the like may be used as a catalyst. Further, by adding a diamine represented by the general formula (2) to the solution of the carboxylic acid represented by the general formula (1),
A polyimide precursor solution can be obtained.

The ratio of the tetracarboxylic dianhydride represented by the general formula (3) to the diamine represented by the general formula (4) for producing the carboxylic dianhydride represented by the general formula (5) is determined by the ratio of tetracarboxylic acid 0.1 mole of diamine per mole of dianhydride
０．９0.95 mol, more preferably 0.45-
0.9 mole. If the diamine is less than 0.1 mol or more than 0.95 mol per 1 mol of the tetracarboxylic dianhydride, the carboxylic dianhydride represented by the general formula (5) becomes difficult to obtain. Further, the amount of water or alcohol to be reacted with the anhydride group of the carboxylic dianhydride is preferably the same molar amount as the acid anhydride group at the terminal or a slightly excessive amount. The alcohol used here is not particularly limited, but examples thereof include methyl alcohol and ethyl alcohol. When these alcohols are used, R ″ in the general formula (1) is a methyl group and an ethyl group, respectively.

Further, the addition amount of the diamine represented by the general formula (2) is based on 1 mol of the carboxylic acid represented by the general formula (1) obtained as described above and the amount of the diamine represented by the general formula (2) 0.95 to 1.05 mol, more preferably 0.97
１．０1.03 mol. If the addition ratio of the diamine represented by the general formula (2) is out of the range of 0.95 to 1.05 mol, the desired polyimide precursor tends to be hardly obtained. The temperature at this time is preferably −30 ° C. to 120 ° C., and more preferably −20 ° C. to 80 ° C. As described above, a polyimide precursor solution can be obtained. In synthesizing a solution of the carboxylic acid represented by the general formula (1),
The order of mixing the monomer and the solvent may be any order, and the method of adding the diamine represented by the general formula (2) is to add the diamine represented by the general formula (2) to the carboxylic acid solution while stirring as a solid or as a solution.

An insulating coating is obtained by adding an insulating filler to the polyimide precursor solution. The method for producing the insulating paint is not limited, for example, a method of mixing the polyimide precursor solution obtained as described above and a solvent in which the insulating filler is dispersed, the insulating filler directly in the polyimide precursor solution. A method of adding and dispersing can be exemplified. The method of dispersing the insulating filler in the solvent or the polyimide precursor solution can be performed by a known method, for example, a homomixer, a ball mill disperser, a bead mill disperser, a two-roll, a three-roll, a Laboplast mill disperser And the like.

Examples of the insulating filler used in the present invention include silica, ceramics, such as alumina, boron nitride, aluminum nitride, and zinc borate. Examples of mica include mica, muscovite, phlogopite, and synthetic mica. And silica, alumina and boron nitride are preferred. These may be used alone or in combination of two or more. The particle size of the insulating filler is not particularly limited, but is preferably 0.01 to 20 μm in consideration of the uniformity of filler dispersion. If the particle size exceeds 20 μm, the dispersibility of the filler may decrease.

In the insulating paint of the present invention, the content of the insulating filler is determined by the sum of the carboxylic acid represented by the general formula (1) and the diamine represented by the general formula (2) in the polyimide precursor solution.
It is preferably contained in the range of 5 to 1000 parts by weight, more preferably in the range of 30 to 700 parts by weight, and even more preferably in the range of 30 to 500 parts by weight with respect to 00 parts by weight. When the amount of the insulating filler is less than 5 parts by weight based on 100 parts by weight of the total of the carboxylic acid represented by the general formula (1) and the diamine represented by the general formula (2) in the polyimide precursor solution, voids are formed in the obtained insulating coating. Or an air bubble may be contained, and if it exceeds 1000 parts by weight, the insulating coating may be cracked. The viscosity of the insulating paint of the present invention is preferably 3000 poise or less, and more preferably 5 to 200 poise, from the viewpoint of handling during application.

In order to obtain an insulating film, an insulating paint is applied on a substrate, heated to evaporate the solvent, and then imidized the polyimide precursor. The imidization temperature is 200 ° C or higher,
Preferably, heating is performed at 250 ° C. or more, more preferably 300 ° C. or more, for 5 minutes or more, particularly 300 ° C. or more, for 30 minutes or more. The resulting insulating film has the structural formula (6)
And an insulating filler, which is used as an insulating coating while being in close contact with the substrate, and used as an insulating film peeled from the substrate.

As described above, the insulating coating of the present invention is used, for example, for the production of insulating sealing materials for semiconductor chips and flexible printed boards as electronic circuit components, interlayer insulating films, and protective films. . It can also be used for heat-resistant insulation.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments. The present invention is not limited to these examples.

Example 1 8.22 g (41.1 mm) of diaminodiphenyl ether
ol) was dissolved in 55.0 g of N, N-dimethylacetamide and stirred at room temperature. To this, 11.9 (54.8 mmol) of pyromellitic dianhydride was added over 1 minute, and the mixture was stirred at room temperature for 2 hours. 1.32 g of methanol (41.1
mmol) and 0.066 g of dimethylaminoethanol
Was added and stirred on a 70 ° C. water bath for 2 hours to obtain a carboxylic acid represented by the following formula.

[0046]

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After cooling to room temperature, 2.74 g (13.7 mmol) of diaminodiphenyl ether was added, and stirring was further continued for 1 hour to obtain a homogeneous yellow-orange transparent solution (solute concentration: 30% by weight). When the viscosity of this solution was measured, it was 21.4 poise. Next, silica particles as an insulating filler [SO-C3, manufactured by Admatechs Co., Ltd., based on 100 parts by weight of the solute in this solution.
(Average particle size: 1 μm) was added in a proportion of 100 parts by weight and dispersed by a bead mill to obtain an insulating paint having a viscosity of 120 poise. 200 mg of this insulating paint was applied dropwise onto a glass plate and then dried at 80 ° C. for 5 hours under a nitrogen atmosphere.
Heat imidation was performed at 300 ° C. for 5 hours in a nitrogen atmosphere to obtain an insulating film having a maximum thickness of 25 μm. Microscopic observation of the internal cross section of this coating showed no voids or cracks of 0.1 μm or more.

Example 2 The polyimide precursor solution obtained in Example 1 was diluted with dimethylacetamide so that the solute concentration became 20% by weight, and the solute 10 in the diluted polyimide precursor solution was further diluted.
20 parts by weight of silica particles (average particle size: 1 μm)
It was contained in a proportion of 0 parts by weight and dispersed by a bead mill to obtain an insulating paint having a viscosity of 45 poise. Next, an insulating film was obtained from the obtained insulating paint in the same manner as in Example 1. The maximum thickness of the coating was 17 μm, and no voids or cracks of 0.1 μm or more were observed inside the coating.

Comparative Example 1 16.00 g (80.0 m) of diaminodiphenyl ether
mol) is converted to N, N-dimethylacetamide 78.05.
g and kept at room temperature. To this, 17.45 g (80.0 mmol) of pyromellitic dianhydride was gradually added over 2 hours, and further stirred for 6 hours, whereby the solution gelled. (Solute concentration 30% by weight).

Comparative Example 2 16.00 g of diaminodiphenyl ether (80.0 m
mol) was dissolved in 190 g of N, N-dimethylacetamide and kept at room temperature. To this, 17.45 g (80.0 mmol) of pyromellitic dianhydride was gradually added over 2 hours, and the mixture was further stirred for 6 hours to obtain a polyamic acid solution having a viscosity of 250 poise. (Solute concentration 15% by weight). Using this solution, an insulating paint was prepared under the same conditions as in Example 2, but the viscosity increased significantly during mixing, and the insulating filler could not be dispersed.

Comparative Example 3 The polyimide precursor solution obtained in Example 1 without adding silica particles was treated in the same manner as in Example to form a polyimide film (maximum thickness 12 μm). A void of 0.1 μm or more was observed inside the polyimide coating.

Example 3 25.18 g (232.9 mm) of paraphenylenediamine
ol) and 8.23 g of diaminodiphenyl ether (4
1.1 mmol) with N, N-dimethylacetamide 3
The solution was stirred at room temperature. This is 3,3 ',
89.56 g (304.4 mmol) of 4,4'-biphenyltetracarboxylic dianhydride (hereinafter abbreviated as BPDA)
Was added for 1 minute, and the mixture was stirred at room temperature for 2 hours. 2.92 g (91.3 mmol) of methanol and 0.146 g of dimethylaminoethanol were added, and the mixture was stirred on a 70 ° C. water bath for 2 hours to obtain a carboxylic acid shown below. (X: y = 85:
15 mol%)

[0053]

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After cooling to room temperature, 2.80 g (25.9 mmol) of paraphenylenediamine and 0.91 g (4.6 mmol) of diaminodiphenyl ether were added, and stirring was further continued for 1 hour to obtain a homogeneous red-brown transparent solution. (The solute concentration was 30% by weight, and the charged molar ratio of paraphenylenediamine and diaminodiphenyl ether was 85:15). When the viscosity of this solution was measured, it was 40 poise. Then, solute 1 in this solution
Silica particles (SO-C2, manufactured by Admatechs Co., Ltd., average particle size: 0.5 μm) as an insulating filler were added to 100 parts by weight in a proportion of 100 parts by weight, and dispersed by a bead mill. Obtained an insulating paint of 100 poise. An insulating coating was obtained from this insulating paint in the same manner as in Example 1. The maximum thickness of this coating was 28 μm, and no voids or cracks of 0.1 μm or more were observed in the internal cross section of the coating.

Example 4 The polyimide precursor solution obtained in Example 3 was diluted with dimethylacetamide so that the solute concentration became 15% by weight, and the solute 10 in the diluted polyimide precursor solution was further diluted.
The silica particles used in Example 3 were added to 200 parts by weight of 0 parts by weight.
Add in parts by weight, disperse with bead mill,
An insulating paint having a viscosity of 20 poise was obtained. Next, an insulating film was obtained from the obtained insulating paint in the same manner as in Example 1. The maximum thickness of the coating is 11 μm, and 0.1 μm
No voids or cracks of m or more were observed.

Example 5 36.0 g (179.8 m) of diaminodiphenyl ether
mol) is converted to N, N-dimethylacetamide 232.7.
g and stirred at room temperature. BPDA58.
8 g (199.8 mmol) in 1 minute,
Stirred for hours. 1.9 g of methanol (159.9 mmo
l) and 0.096 g of dimethylaminoethanol were added, and the mixture was stirred on a 70 ° C. water bath for 2 hours to obtain a carboxylic acid of the following formula.

[0057]

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After cooling to room temperature, 4.0 g (20.0 mmol) of diaminodiphenyl ether was added, and stirring was further continued for 1 hour to obtain a uniform yellow-orange transparent solution (solute concentration: 30% by weight). When the viscosity of this solution was measured, it was 31.0 poise. Next, silica particles (SO-C2, manufactured by Admatechs Co., Ltd., SO-C2, average particle size: 0.5 μm) as an insulating filler were added to 100 parts by weight of the solute in this solution at a ratio of 100 parts by weight. The mixture was dispersed in a bead mill to obtain an insulating paint having a viscosity of 100 poise. An insulating coating was obtained from this insulating paint in the same manner as in Example 1. The maximum thickness of this coating was 35 μm, and no voids or cracks of 0.1 μm or more were observed in the internal cross section of the coating.

Example 6 19.4 g (179.8 mmol) of paraphenylenediamine
l) was dissolved in 189.9 g of N, N-dimethylacetamide and stirred at room temperature. 58.8g of BPDA
(199.8 mmol) was added over 1 minute, and the mixture was stirred at room temperature for 2 hours. 1.9 g (59.9 mmol) of methanol and 0.095 g of dimethylaminoethanol were added, and 70
The mixture was stirred on a hot water bath for 2 hours to obtain a carboxylic acid shown below.

[0060]

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After cooling to room temperature, 2.2 g (20.0 mmol) of paraphenylenediamine was added, and stirring was further continued for 1 hour to obtain a uniform black-green transparent solution (solute concentration: 30% by weight). When the viscosity of this solution was measured, it was 15 poise. Next, silica particles (SO-C2, manufactured by Admatechs Co., Ltd., average particle size: 0.5 μm) as an insulating filler are contained in 100 parts by weight of the solute in the solution at a ratio of 300 parts by weight, The dispersion was dispersed by a bead mill to obtain an insulating paint having a viscosity of 170 poise. An insulating coating was obtained from this insulating paint in the same manner as in Example 1. The maximum thickness of this coating was 55 μm, and no voids or cracks of 0.1 μm or more were observed in the internal cross section of the coating.

Example 7 20.1 g of 3,4'-oxydianiline (100.0 m
mol) was dissolved in 250 g of N, N-dimethylacetamide and stirred at room temperature. 62.3 g (200.8 mmol) of 4,4'-oxydiphthalic dianhydride was added to 1
And stirred at room temperature for 2 hours. Methanol 9.6
g (300 mmol) and 0.48 g of dimethylaminoethanol were added, and the mixture was stirred on a 70 ° C. water bath for 2 hours to obtain a carboxylic acid represented by the following formula.

[0063]

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After cooling to room temperature, 20.1 g (100.0 mmol) of 3,4'-oxydianiline was added, and stirring was further continued for 1 hour to obtain a uniform black-brown transparent solution (solute concentration). 30% by weight). When the viscosity of this solution was measured, it was 1.2 poise. Next, alumina particles (AKP-20, manufactured by Sumitomo Chemical Co., Ltd., average particle size: 0.5 μm) as an insulating filler were contained in 100 parts by weight of the solute in this solution at a ratio of 300 parts by weight, and dispersed by a bead mill. Thus, an insulating paint having a viscosity of 130 poise was obtained. An insulating coating was obtained from this insulating paint in the same manner as in Example 1. The maximum thickness of this coating was 48 μm, and no voids or cracks of 0.1 μm or more were observed in the internal cross section of the coating.

[0065]

As described above, the insulating coating of the present invention has a low viscosity and is easy to apply even if the polyimide precursor and the insulating filler are contained in the organic solvent in a high solid content ratio.
Further, according to the method for producing an insulating coating of the present invention, even if the polyimide precursor and the insulating filler are contained in the organic solvent at a high solid content ratio and have a low viscosity, it is easy to uniformly disperse them. , And can be manufactured with high productivity. Furthermore, the insulating coating obtained from the insulating coating of the present invention does not contain voids, bubbles and cracks, and thus has high insulation durability.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiro Eguchi 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Central Research Laboratory (72) Inventor Fumiko Okui 23 Uji Kozakura, Uji City, Kyoto Unitika Central F-term in the laboratory (reference) 4J002 CM041 DE146 DF016 DJ016 DJ056 DK006 FD016 GQ01 GQ05 HA03 4J038 DJ031 HA166 HA316 HA476 HA546 KA06 KA08 NA21 PB09 PC03 PC08

Claims (4)

[Claims] 1. A polyimide precursor solution in which a carboxylic acid represented by the general formula (1) and a diamine represented by the general formula (2) for forming a polyimide precursor are dissolved in an organic solvent in an amount of 5 to 80% by weight. An insulating paint comprising an insulating filler. Embedded image [Wherein, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, four carbonyl groups are directly linked to different carbon atoms in the residue, and two of the four Each of which is paired and is attached to an adjacent carbon atom in the six-membered carbon ring, R ′ is a divalent aromatic residue containing at least one six-membered carbon ring, and R ″ is hydrogen Alternatively, it represents a monovalent organic group having 7 or less carbon atoms, R ′ ″ represents a divalent aromatic residue containing at least one carbon 6-membered ring, and n represents an integer of 1 to 20. ] 2. In the general formulas (1) and (2), R represents R ′ and R ′ ″ from the structural formula group A shown below.
2. The insulating paint according to claim 1, wherein each is at least one selected from Structural Formula Group B. 3. Embedded image 3. A solvent in which a diamine represented by the general formula (4) is reacted at a ratio of 0.1 to 0.95 mol with respect to 1 mol of a tetracarboxylic dianhydride represented by the general formula (3) in a solvent. hand,
A carboxylic acid dianhydride represented by the general formula (5) is generated, and water or an arbitrary alcohol is added to open a terminal acid anhydride group to obtain a carboxylic acid represented by the general formula (1). It is known that 0.95 to 1.05 mol of the diamine represented by the general formula (2) is added to 1 mol of the carboxylic acid represented by the general formula (1) to form a polyimide precursor solution, and that an insulating filler is further added. Characteristic method for producing insulating paint. Embedded image [Wherein, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, four carbonyl groups are directly linked to different carbon atoms in the residue, and two of the four Each of which is paired and is attached to an adjacent carbon atom in the six-membered carbon ring, R ′ is a divalent aromatic residue containing at least one six-membered carbon ring, and R ″ is hydrogen Alternatively, it represents a monovalent organic group having 7 or less carbon atoms, R ′ ″ represents a divalent aromatic residue containing at least one carbon 6-membered ring, and n represents an integer of 1 to 20. ] 4. An insulating coating comprising a polyimide represented by the following structural formula (6) and an insulating filler obtained by applying the insulating coating composition according to claim 1 to a substrate and heating the coating. Embedded image [Wherein, R represents a tetravalent aromatic residue containing at least one carbon 6-membered ring, four carbonyl groups are directly linked to different carbon atoms in the residue, and two of the four Each is paired and is attached to an adjacent carbon atom in the 6-membered carbon ring, wherein R ′ and R ′ ″ are at least one carbon 6
It represents a divalent aromatic residue containing a membered ring. m + 1 is 10-5
000 is an integer. ]