JPH11227099A - Heat resistant substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the strength and form microrecessed and projecting parts on the surface at a low cost and further, enhance the light-electricity conversion efficiency by forming a coat of a polyimide resin composed of blended insulating microparticles containing an aromatic diamine and an aromatic tetracarboxylic acid and/or a derivative thereof as a dissolved substance, on the surface of a metal plate. SOLUTION: A coat composed of a polyimide resin obtained from a polyimide precursor solution prepared by dissolving (A) an aromatic diamine, an aromatic tetracarboxylic acid and/or a derivative thereof as dissolved substances in a solvent and blending (B) insulating microparticles, is formed on the surface of a metal plate. The metal plate is preferably of stainless steel, aluminum, copper, an aluminum alloy or the like with a thickness of 0.05-5 mm, and the solvent is preferably a chemical compound with an ether group and an alcoholic hydroxyl group in the same molecule as a non-proton polar solvent to be used alone or in a mixed form. Further, the insulating microparticles are preferably silica, alumina, zirconia titania with an average grain dia. of 0.05-5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat-resistant substrate. Specifically, the present invention relates to a heat-resistant substrate suitable for the field of electronic materials, and the heat-resistant substrate according to the present invention is suitably used as a substrate for a photoelectric conversion device such as a solar cell, an optical sensor, and an optical switch.

[0002]

2. Description of the Related Art Insulating substrates for electronic materials have been widely used as substrates for solar cells, substrates for printed wiring, substrates for thermal heads and the like. In the case where the insulating substrate is used for an integrated solar cell, surface smoothness is required. Therefore, the metal plate is polished into an extremely smooth ultra-mirror surface having a surface roughness Rmax of less than 40 nm and a pitch of projections of less than 4 nm. Methods are known. However, polishing the surface of the metal plate to a super-mirror shape as described above is costly and extremely disadvantageous economically. As a method for solving this, a technique of forming a film of an electrically insulating resin such as a polyimide resin on the surface of a metal plate has been proposed and put to practical use (Japanese Patent Publication No. 6-59715).

However, when the above-mentioned coating film is coated with a polyimide resin solution having a high degree of polymerization on the surface of a metal plate, the polymer concentration must be reduced in order to obtain a solution viscosity that can be applied. There is. Also,
Because many polyimides are hardly soluble or insoluble in organic solvents, solutions of polyimide precursors that are soluble in organic solvents have been used in various applications. As such a polyimide precursor solution, a solution comprising a polyamic acid (polyamic acid) represented by the following general formula is known.

[0004]

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These polyamic acid solutions are produced by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride in a solvent.
JP-A-6-10999, JP-A-62-275165, JP-A-64-5057, Japanese Patent Publication No. 2-3814
No. 9, Japanese Patent Publication No. 2-38150, Japanese Patent Laid-Open No. 1-2
No. 9987, JP-A-58-122920, JP-B-1-34454, and JP-A-58-185624.
Publication, Journal of Polymer Sc
ence, Macromolecular Revi
ews Vol. 11P. 199 (1976), U.S. Pat. No. 4,238,528, JP-B-3-4588,
JP-B-7-3024, JP-A-7-41556, JP-A-7-62095, JP-A-7-1333
49, JP-A-7-149896, JP-A-6-149
JP-207014, JP-B-7-17870,
Japanese Patent Publication No. 7-17871, IBM Technology
al Disclosure Bulletin Vo
l. 20 No. 6P. 2041 (1977) or the like, a solvent using an aprotic polar solvent as a solvent, or a water-soluble ether-based compound as a solvent, as disclosed in JP-A-6-1915.
Various solutions have been proposed, such as those using a mixed solvent selected from a water-soluble alcohol compound, a water-soluble ketone compound and water.

As the polyimide precursor as a solute in the polyimide precursor solution, various polymers other than polyamic acid are known. For example, Macuromo
recules Vol. 22 p. 4777 (198
9) and Polyimidesand Other Hi
gh Temperature Polymers.
P. 45 (1991), a polyamic acid ester represented by the following general formula:

[0007]

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[0008] Macromolecules Vo
l. 24 p. 3475 (1991) discloses a polyamic acid trimethylsilyl ester represented by the following general formula:

[0009]

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[0010] Journal of Polymer
Science Part B Vol. 8P. 29
(1970), Journal of Polymer
Science Part B Vol. 8P. 5
59 (1970), The Chemical Society of Japan, Vol. 1972
P. 1992, Journal of Polymer
Science Polymer Chemistry
Edition Vol. 13P. 365 (197
No. 5) discloses a polyamic acid bis (diethylamide) represented by the following formula.

[0011]

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The above-mentioned precursors are all polymers having a high degree of polymerization. When a polyimide coating film is obtained from a solution containing these polymers as a solute, the polymer solution is generally used as a base material such as copper or glass. Coated on top,
The solvent is removed and imidization is performed to obtain a polyimide coating film.
However, when coating a polymer solution having such a high degree of polymerization, there is a problem that the solid content concentration must be reduced in order to obtain a viscosity of a solution that can be applied because the polymer has a high degree of polymerization. there were. Also, in order to increase the productivity, if the solid content concentration is increased, the viscosity of the solution becomes high, and there is also a problem that the coating cannot be performed, and even if the coating can be performed, good mechanical,
There was a problem that a coating film or a film having thermal characteristics could not be obtained. Further, the polymer solution is hard to withstand long-term storage, and it is extremely difficult to store the polymer solution for a long time while maintaining the degree of polymerization of the polymer.

Further, in recent years, in order to improve the moldability of polyimide, a larger number of thermoplastic polyimides have been developed. However, the same problem as when a polyimide coating film is obtained as described above, that is, when the concentration of the polyimide precursor solution is increased, the viscosity increases, and when used for impregnation or the like, the handling is reduced, such as a decrease in productivity. Becomes difficult. Further, the problem that it is extremely difficult to store the polymer solution for a long period of time while maintaining the degree of polymerization has not been solved.

On the other hand, in order to improve the conversion efficiency of light into electricity when used in solar cell applications, recently,
As opposed to the method of making the surface of an insulating substrate a very smooth mirror surface as described above, a technique of forming fine irregularities on the surface of the insulating substrate has been proposed (Japanese Patent Application Laid-Open No. 7-254721). According to this method, incident solar light is irregularly reflected by fine irregularities on the insulating substrate, and the efficiency of converting light into electricity is improved by being confined in the fine irregularities on the insulating substrate. However, JP-A-7-
The method described in Japanese Patent No. 254721 has a drawback that the irregularities formed on the surface of the insulating substrate are too fine, and the process of forming the extremely fine irregularities inevitably increases the cost.

[0015]

Under such circumstances, the present inventors have made intensive studies and completed the present invention as a result of providing a heat-resistant substrate which can solve the above-mentioned drawbacks of the prior art at once. is there. The objects of the present invention are as follows. 1. To provide high-strength heat-resistant substrates with high productivity. 2. To provide a heat-resistant substrate having fine irregularities formed on its surface at low cost. 3. To provide a heat-resistant substrate having high light conversion efficiency.

[0016]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies and as a result, have found that the surface of a heat-resistant substrate in which a polyimide resin film is formed on the surface of a stainless steel plate is finely divided. The possibility of improving the light-to-electricity conversion efficiency was obtained by forming the irregularities. Also, as a polyimide resin film, if a polyimide precursor solution was used as a solute in combination with a specific monomer, knowing that a polyimide resin film having good strength and good physical properties can be obtained, and, The present inventors have achieved that the present invention can be applied to the production of the heat-resistant substrate, and have completed the present invention. That is, the present invention
Obtained from a polyimide precursor solution in which (A) an aromatic diamine and an aromatic tetracarboxylic acid and / or a derivative thereof are dissolved in a solvent as a solute and (B) insulating fine particles are blended on the surface of the metal plate. A heat-resistant substrate characterized in that a coating film of a polyimide resin is formed.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. (1) Metal Plate The metal plate which is the base of the heat-resistant substrate of the present invention is selected from stainless steel, aluminum, copper, aluminum alloy and the like. As stainless steel, special steel having better corrosion resistance than ordinary carbon steel is desirable. Most of stainless steel is Cr
Mainly chromium steel with a content of about 12% or more.
i, Mo, Ti, Nb, and the like. From the viewpoint of the structure, it can be classified into a martensite type, a ferrite type, an austenite type and the like. The standard composition of martensitic carbon steel is that the Cr content is usually about 13%,
13 Chromium stainless steel, SUS301, 30
4, 305, and 310 (all are JIS symbols; the same applies hereinafter). The standard composition of ferritic carbon steel is usually 18 chromium stainless steel since the Cr content is usually about 18%, and examples thereof include SUS430 and 434. The standard composition of the austenitic carbon steel is usually called 18-8 stainless steel because the Cr content is about 18% and the Ni content is about 8%.
THR100 and the like. The surface of the metal plate does not need to be polished so as to have a super mirror-like smooth surface, and it is not necessary to adjust the surface roughness to a specific range.
The thickness of the metal plate is generally preferably selected in the range of 0.05 to 5 mm, and particularly preferably 0.1 to 1 mm.
Range.

(2) Polyimide Resin In the present invention, the term "polyimide resin" refers to an organic polymer having an imide structure represented by the following general formula (I) in which at least 80 mol% of the repeating units of the polymer chain is usually used. To tell. The polyimide resin is thermoplastic, has a high thermal decomposition temperature, and exhibits heat resistance. Specifically, the glass transition temperature measured with a DSC measuring device (DSC-7, manufactured by Perchielmer) is usually 320 ° C. or lower.

[0019]

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The term "polyimide precursor" refers to an organic compound that becomes a polyimide by ring closure by heating or chemical action.
Here, “ring closed” means that an imide ring structure is obtained. The polyimide precursor dissolved as a solute in a solvent is a polyimide precursor solution.
Here, in the present application, the solvent is a liquid compound at a body pressure of 25 ° C.

The polyimide precursor solution is a polyimide precursor solution in which an aromatic diamine and an aromatic tetracarboxylic acid and / or a derivative thereof are dissolved in a solvent as a solute. The carboxylic acid and / or the derivative thereof forms a thermoplastic polyimide represented by the general formula (A). As the solute,
4,4′-oxydianiline represented by the structural formula (1) and / or
Alternatively, a combination of 3,4'-oxydianiline represented by the structural formula (2) and 4,4'-oxydiphthalic acid and / or a derivative thereof represented by the general formula (3), or represented by the structural formula (1) 4,4'-oxydianiline or 3,4'-oxydianiline represented by the structural formula (2), and paraphenylenediamine represented by the structural formula (4);
And the combination with 4,4'-oxydiphthalic acid or a derivative thereof shown in the following are preferred.

Further, a part of 4,4'-oxydiphthalic acid or a derivative thereof represented by the general formula (3) is
Or a dicarboxylic acid anhydride represented by the general formula (6). In this case, the polyimide obtained by controlling the component ratio of 4,4′-oxydiphthalic acid or a derivative thereof to the carboxylic acid represented by the general formula (5) or the dicarboxylic anhydride represented by the general formula (6) It becomes possible to control the hot melt fluidity. At this time, the component molar ratio of 4,4'-oxydiphthalic acid or a derivative thereof to the carboxylic acid represented by the general formula (5) or the dicarboxylic anhydride represented by the general formula (6) is 100: 0 to 10
0:20 is preferable, and 100: 0 to 100: 11 is more preferable. When the component molar ratio of the carboxylic acid represented by the general formula (5) or the dicarboxylic anhydride represented by the general formula (6) to 4,4'-oxydiphthalic acid or the derivative 100 thereof represented by the general formula (3) exceeds 20, There is a tendency that only a polyimide film having low strength can be obtained.

[0023]

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Further, 4,4'-oxydiphthalic acid or a part of the derivative thereof represented by the general formula (3) may be replaced with 4,4'-oxydiphthalic dianhydride represented by the structural formula (7). At this time, the structural formula (7) for 4,4′-oxydiphthalic acid or its derivative 100 shown in the general formula (3)
The molar ratio of 4,4'-oxydiphthalic dianhydride shown in the above is preferably from 0 to 100. By adjusting this ratio, the viscosity of the polyimide precursor solution can be finely adjusted. When this ratio exceeds 1, a polyimide precursor solution having a high concentration and a low viscosity, which is a feature of the present invention, cannot be obtained.

[0025]

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Further, in the structural formula (1),
4'-oxydianiline or 3,3 represented by the structural formula (2)
Even when a part of 4'-oxydianiline is replaced with an amine represented by the general formula (8), the thermal melt fluidity of polyimide can be controlled. In this case, the ratio of 4,4'-oxydianiline represented by the structural formula (1) or 3,4'-oxydianiline represented by the structural formula (2) to the amine represented by the general formula (8) is 100: 0. ~ 100: 20 is preferred, and 1
00: 0 to 100: 11 is more preferred. When the molar ratio of the amine represented by the general formula (8) to 4,4'-oxydianiline represented by the structural formula (1) or 3,4'-oxydianiline 100 represented by the structural formula (2) exceeds 20, the strength is increased. Tend to obtain only a polyimide film having a low.

[0027]

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In the present invention, when preparing a polyimide precursor solution in which a polyimide precursor containing paraphenylenediamine represented by the structural formula (4) as a solute is dissolved in a solvent, the structural formula (4) The molar ratio of paraphenylenediamine represented by the formula (4) to 4,4'-oxydianiline represented by the structural formula (1) or 3,4'-oxydianiline represented by the structural formula (2) may be set to any value. With respect to paraphenylenediamine represented by the structural formula (4) and 4,4'-oxydianiline represented by the structural formula (1) or 3,4'-oxydianiline 100 represented by the structural formula (2), the structural formula (4 )) Is preferably 50 or less, more preferably 20 or less. If this molar ratio is greater than 50, the high temperature properties of the resulting polyimide will change significantly.

In the present invention, as the solvent, any solvent can be used as long as it dissolves the above-mentioned polyimide precursor and gives a uniform solution. Examples thereof include a compound having an alcoholic hydroxyl group, a water-soluble ether compound, a water-soluble alcoholic compound, and an amine compound. These solvents may be used alone or as a mixture of two or more.
Among them, a compound having an ether group and an alcoholic hydroxyl group in the same molecule as the aprotic polar solvent is preferably used alone or in combination, and particularly preferably, diethylene glycol monomethyl ether and / or N, N-dimethylformamide is used. . Also, a mixture of an aprotic polar solvent and a water-soluble alcohol is preferable,
Preferred is a mixture of -methyl-2-pyrrolidone and a water-soluble alcohol. Furthermore, it is preferable to use an amine compound alone or a mixed solvent containing an amine compound.

Examples of aprotic polar solvents include N-methyl-2-pyrrolidone, N, N-dimethylformamide,
N, N-dimethylacetamide, dimethylsulfoxide and the like can be mentioned, among which N, N-dimethylformamide is particularly preferred. Examples of the compound having an ether group and an alcoholic hydroxyl group in the same molecule include, for example, 2-
Methoxyethanol, 2-ethoxyethanol, 2-
(Methoxymethoxy) ethoxyethanol, 2-isopropoxyethanol, 2-butoxyethanol, tetrahydrofurfuryl alcohol, diethylene glycol,
Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monoethyl ether, tetraethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol,
Examples thereof include dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, polyethylene glycol, and polypropylene glycol. Of these, diethylene glycol monomethyl ether is particularly preferable.

Further, as the water-soluble ether compound, for example, tetrahydrofuran, dioxane, 1,2
-Dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and the like. Further, as the water-soluble alcohol-based compound,
For example, methanol, ethanol, 1-propanol,
2-propanol, tert-butyl alcohol, 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, 1,2,6-hexanetriol and the like can be mentioned.

Further, any amine compound may be used, but a tertiary amine is preferably used. Among these, it is particularly preferable to use triethylamine and dimethylaminoethanol. When using a mixed solvent of N-methyl-2-pyrrolidone and the water-soluble alcohol as the aprotic polar solvent, it is preferable to use methanol and ethanol as the water-soluble alcohol, and to use other water-soluble alcohols. When used, the storage stability of the polyimide precursor may deteriorate. The mixing ratio (weight ratio) of N-methyl-2-pyrrolidone and the water-soluble alcohol is preferably from 80:20 to 60:40, and more preferably from 75:25 to 65:35. If the mixing ratio of N-methyl-2-pyrrolidone and the water-soluble alcohol is not in this range, a uniform and transparent polyimide precursor solution may not be obtained, or storage stability may be deteriorated.

The concentration of the polyimide precursor in the polyimide precursor solution of the present invention is preferably 30% by weight or more.
It is more preferably at least 35% by weight, even more preferably at least 40% by weight. If it is less than 30% by weight, the viscosity is too low, and it is difficult to obtain a uniform coating film. The viscosity of the polyimide precursor solution is preferably 100 poise or less, more preferably 85 poise or less, and even more preferably 60 poise or less. If the viscosity of the polyimide precursor solution exceeds 100 poise, the productivity may decrease when used for impregnation. In addition, the viscosity here refers to DVL manufactured by Tokimec Co., Ltd.
20 ° C using a BII type digital viscometer (B type viscometer)
Was measured for rotational viscosity. The above polyimide precursor solution can be produced by sequentially adding an aromatic diamine and an aromatic tetracarboxylic acid and / or a derivative thereof to a solvent. The order of addition may be any order.

(3) Insulating Fine Particles In the present invention, insulating fine particles are added to the polyimide precursor solution. Insulating fine particles that can be used preferably have an average particle diameter in the range of 0.05 to 5 μm. As insulating fine particles, silica, alumina, zirconia,
Titania, magnesium oxide, magnesium carbonate, calcium carbonate, calcium sulfate, barium sulfate, aluminum oxide and the like can be mentioned, and preferred are silica, alumina, zirconia and titania, and particularly preferred is silica. The amount of the fine powder mixed with the polyimide-based precursor solution varies depending on its type, average particle size, thickness of the coating, use of the heat-resistant substrate, and the like. % By weight, especially 2
It is preferred to be in the range of 0 to 400% by weight. If the compounding amount of the fine powder is less than 5% by weight, it is difficult to form fine irregularities on the surface of the film, and if the compounding amount exceeds 500% by weight, pinholes are liable to occur in the film, which is not preferable. In addition, in addition to the insulating fine particles described above, the polyimide precursor solution may optionally include, for example, a filler such as an organic silane, a pigment, conductive carbon black and metal particles, an abrasive, a dielectric, and a lubricant. Other known additives such as agents can be added and blended within a range that does not impair the effects of the present invention.

(4) Polyimide coating To form a polyimide resin coating on the surface of the metal plate, a polyimide precursor solution described above is applied on the surface of the metal plate and dried to remove the solvent. Then, a polyimide precursor coating film is obtained, which is obtained by imidization. Examples of the coating method include a spin coating method, a doctor blade coating method, a bar coating method, a roll coating method, and a flow coating method. The amount of coating on the surface of the stainless steel plate is adjusted by adjusting the concentration of the solid content of the coating solution, the viscosity of the coating solution, and the like, so that the thickness of the coating film in a wet state is about 3 to 300 μm, and the coating after coating and drying is predetermined The coating operation is repeated and adjusted to obtain a film having a thickness.

When the coating operation is completed, the coating film is dried by heating. The heating condition depends on the type of the polyimide resin, the type of the solvent, the use of the obtained substrate, and the like.
Above, preferably in a temperature range of 250 to 400 ° C.,
Heating is performed in a range of 60 minutes to reduce the residual solvent concentration of the film on the substrate surface to a sufficiently low value. For example, when the solvent is N, N'-dimethylformamide and the substrate is used for an amorphous solar cell substrate, the residual solvent concentration that does not adversely affect the CVD operation under vacuum needs to be less than about 50 ppm. . In the heating of the substrate during drying, if the solvent is rapidly heated, the solvent may rapidly evaporate and the surface properties of the coating may be deteriorated. Therefore, it is preferable to gradually heat the substrate. In general, when the dry heating degree is low, the time is lengthened, and when the dry heating degree is high, the time is shortened.

The thickness of the film formed on the surface of the substrate is generally in the range of 1 to 70 μm, preferably 5 to 50 μm.
If the thickness of the coating is less than 1 μm, defects such as pinholes are likely to occur in the coating, and there is a high risk of dielectric breakdown when used as an electronic component.
If the thickness exceeds 0 μm, the residual solvent tends to remain on the coating film, and neither is preferable.

In the heat-resistant substrate according to the present invention, the surface of the polyimide resin film has a value defined by JIS B0601, and the surface roughness Rmax measured in accordance with JIS B0651 is preferably 0. .1 to 2.0 μm
And the pitch of the projections is in the range of 0.1 to 5 μm.
When the surface roughness Rmax of the coating is less than 0.1 μm and the pitch of the projections is less than 0.1 μm, it is difficult to form fine irregularities on the surface of the coating, which is not preferable because the cost increases.
When the surface roughness Rmax of the coating exceeds 2.0 μm and the pitch of the projections exceeds 5 μm, the irregularities become too large, and the object of the present invention is to diffuse incident sunlight rays and confine it to the surface of the insulating substrate. It is not preferred because it is not achieved.

[0039]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the following description unless it exceeds the gist. Example 1 5.50 g of 3,4'-oxydianiline was dissolved in 15.00 g of N, N-dimethylformamide. To this was added 9.50 g (1 equivalent) of 4,4'-oxydiphthalic acid. When stirring was continued for 1 hour, a uniform pale brown transparent solution was obtained (solid content concentration: 50% by weight). When the viscosity of this solution was measured, it was 2.6 poise. Further, a fine silica powder having an average particle diameter of 0.1 μm was added to this solution so as to be 300% by weight with respect to the solid content and uniformly mixed. The solution was filtered through a filter having a pore diameter of 1 μm to form a film. Solution. 300mm x 300m in size
m, one side of a SUS304 stainless steel plate having a thickness of 0.3 mm, the above-mentioned solution for forming a film is applied at room temperature by a die coater, and immediately placed in an oven at 80 ° C.
This temperature was maintained for 5 minutes, then gradually increased to 350 ° C., and maintained at this temperature for 5 minutes. The resulting heat-resistant substrate had a polyimide coating thickness of 10 μm and a surface roughness Rmax.
Was 0.3 μm and the pitch of the projections was 0.6 μm.

Example 2 The same procedure as in Example 1 was repeated except that the fine silica powder
m, and a heat-resistant substrate having a coating film formed thereon was obtained in the same procedure as in the same example except that the amount was changed to 200% by weight. The resulting heat-resistant substrate had a thickness of 12 μm of the copolymerized polyimide film and a surface roughness Rmax of 0.6 μm.
m, the pitch of the protrusions was 1.2 μm.

Example 3 5.50 g of 3,4'-oxydianiline was dissolved in 15.00 g of diethylene glycol monomethyl ether. To this, 9.50 g of 4,4'-oxydiphthalic acid (1
Equivalent). When stirring was continued for 1 hour, a uniform pale brown transparent solution was obtained (solid content concentration: 50% by weight).
When the viscosity of this solution was measured, it was 51.5 poise. Further, silica fine powder was mixed with this solution in the same manner as in Example 1 above, and thereafter, a heat-resistant substrate was manufactured in the same manner as in Example 1.
m, the surface roughness Rmax is 0.3 μm, and the pitch of the projections is 0.
It was 6 μm.

Comparative Example 1 4.70 g of 3,4'-oxydianiline was dissolved in 34.00 g of diethylene glycol monomethyl ether. This is followed by 7.3 of 4,4'-oxydiphthalic dianhydride.
0 g (1 equivalent) was added. After stirring for 5 hours,
The viscosity of the solution exceeded 2,000 poise, and the viscosity could not be measured (solid content: 30% by weight).

Comparative Example 2 A heat-resistant substrate having a film formed thereon was obtained in the same procedure as in Example 1 except that silica fine powder was not added to the film forming solution. . In the obtained heat-resistant substrate, the thickness of the copolymer polyimide film was 13 μm, the surface roughness Rmax of the film was 0.01 μm, and the pitch of the projections was 0.05 μm.

Application Example First, a 200 nm-thick Ag electrode layer was formed as a lower electrode on the surface of the coating of the heat-resistant substrate obtained by the methods described in Examples 1 to 3 and Comparative Example 2. did. Further, a 500 nm thick amorphous silicon film (photoelectric conversion layer) having a pin junction was formed on the Ag electrode layer by a CVD method. Finally, a 100 nm ITO film was formed as a transparent electrode by a sputtering method to obtain a solar cell. As a result of measuring the photoelectric conversion efficiency of the obtained solar cell, those using the heat-resistant substrates of Examples 1 and 2 were 3
The value was 5 to 50% higher.

[0045]

The present invention has the following particularly advantageous effects, and its industrial value is extremely large. Such a heat-resistant substrate is suitably used as a substrate of a photoelectric conversion device such as a substrate for a solar cell, a substrate for an optical sensor, a substrate for an optical switch, and an electronic device such as a substrate for a printed wiring and a substrate for a thermal head. It is also used for applications such as substrates.

1) Since the polyimide precursor solution used in the heat-resistant substrate according to the present invention has a relatively low viscosity despite its high concentration, the polyimide-based resin coating has high productivity and good physical properties. A membrane can be manufactured. 2) The heat-resistant substrate according to the present invention is excellent in heat resistance, chemical resistance, electric insulation, etc. since a thin film of a polyimide resin but without pinholes is formed on the surface of the metal plate. Suitable for material applications.

3) The heat-resistant substrate according to the present invention does not require the formation of ultra-fine irregularities on the surface of the metal plate, and the fine irregularities are formed on the surface of the polyimide resin film formed on the surface of the stainless steel plate. Since it is formed, it can be manufactured at low cost without increasing the cost for forming it. 4) Since the heat-resistant substrate according to the present invention has a polyimide-based resin film having fine irregularities formed on the surface of the metal plate, when used as a solar cell substrate, it preferably diffuses incident light rays irregularly. Since it can be contained on the surface of the insulating substrate, the photoelectric conversion efficiency can be improved.

Claims (10)

[Claims] A polyimide comprising (A) an aromatic diamine and an aromatic tetracarboxylic acid and / or a derivative thereof dissolved in a solvent as a solute, and (B) an insulating fine particle blended on the surface of a metal plate. A heat-resistant substrate comprising a polyimide resin coating film obtained from a precursor solution. 2. The heat-resistant coating film according to claim 1, wherein said coating film is obtained by blending 5 to 500% by weight of insulating fine particles having an average particle size of 0.05 to 5 μm with respect to the polyimide resin. Substrate. 3. The heat-resistant substrate according to claim 1, wherein the thickness of the coating is in the range of 5 to 50 μm. 4. The coating film has a surface roughness Rmax of 0.1 to 2.0.
The heat-resistant substrate according to any one of claims 1 to 3, wherein the pitch of the protrusions is 0.1 to 5 m. 5. The heat-resistant substrate according to claim 1, wherein the insulating fine particles are any of silica, alumina, zirconia, and titania. 6. The heat-resistant substrate according to claim 1, wherein the thermoplastic polyimide resin has the following general formula (I). Embedded image 7. The aromatic diamine is 4,4′-oxydianiline represented by the following structural formula (1) and / or 3,4′-oxydianiline represented by the following structural formula (2), and is an aromatic tetracarboxylic acid. The heat-resistant substrate according to any one of claims 1 to 6, wherein the acid and / or a derivative thereof is 4,4'-oxydiphthalic acid and / or a derivative thereof represented by the following general formula (3). Embedded image 8. The aromatic diamine is 4,4′-oxydianiline represented by the following structural formula (1), 3,4′-oxydianiline represented by the following structural formula (2), and paraphenylenediamine. The heat-resistant substrate according to any one of claims 1 to 6, wherein the aromatic tetracarboxylic acid and / or a derivative thereof is 4,4'-oxydiphthalic acid and / or a derivative thereof represented by the following general formula (3). Embedded image 9. The heat-resistant substrate according to claim 1, wherein the solute concentration is 30% by weight or more and the viscosity is 100 poises or less. 10. A polyimide resin coating film formed by applying a polyimide precursor solution on the surface of a metal plate and performing heat imidization.
9. The heat-resistant substrate according to any one of to 9.