JPH10272725A - Heat-resistant base - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat resistant base of not high cost for forming extremely small recesses and projections on the surface of an insulated base and provided with the high conversion efficiency for converting beams into electricity. SOLUTION: The surface roughness Rmax of a heat-resistant base measured based oh JIS B0651 is in the range of 1-50 μm and the pitch of projections is formed in the range of 1-50 μm, and a polyimide resin film is formed on the rough surface, and the surface roughness Rmax of the film is in the range of 1-10 μm, and the pitch of projections is formed in the range of 0.1-20 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat-resistant substrate. More 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 has use 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 Conventionally, 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. When the insulating substrate is used for an integrated solar cell, surface smoothness is required. Therefore, a method of polishing a stainless steel plate into a very smooth mirror surface with a surface roughness Rmax of less than 40 nm and a pitch of protrusions of less than 4 nm. It has been known. However, polishing the surface of the stainless steel plate into an extremely smooth mirror surface as described above is costly and extremely disadvantageous economically. As a method of solving this, a method of forming a coating of an electrically insulating resin such as a polyimide resin on the surface of a stainless steel plate has been proposed,
It has been put into practical use (Japanese Patent Publication No. 6-59715).

In order to improve the efficiency of converting light into electricity when used in solar cell applications, contrary to the method of making the surface of an insulating substrate a super smooth mirror surface as described above, recently, A method for forming fine irregularities on the surface of an insulating substrate has been proposed (Japanese Patent Application Laid-Open No. 7-254721). According to this method, the incident light beam is irregularly reflected by the minute unevenness of the insulating substrate, and the light is converted into electricity efficiently by being enclosed in the minute unevenness of the insulating substrate. However, in the method described in Japanese Patent Application Laid-Open No. 7-254721, 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. There was a disadvantage.

[0004]

SUMMARY OF THE INVENTION Under such circumstances, the present inventors have made intensive studies to provide a heat-resistant substrate in which all the above-mentioned disadvantages of the prior art have been solved at once. is there. The objects of the present invention are as follows. 1. To provide a heat-resistant substrate which does not increase the cost for forming fine irregularities on the surface of an insulating substrate. 2. To provide a heat-resistant substrate having high light-to-electricity conversion efficiency.

[0005]

In order to solve the above-mentioned problems, according to the present invention, in a heat-resistant substrate having a surface of a stainless steel plate coated with a polyimide resin, the stainless steel plate is measured in accordance with JIS B0651. Surface roughness Rmax is in the range of 0.1 to 50 μm, and the pitch of projections is 1
５０50 μm, the thickness of the polyimide resin coating is in the range of 1-50 μm, and the surface roughness Rmax of this coating is in the range of 0.1-10 μm, and the pitch of the projections is Provided is a heat-resistant substrate characterized by being in a range of 0.1 to 20 μm.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The heat-resistant substrate according to the present invention has a base made of a stainless steel plate. In the present invention, a stainless steel plate refers to a special steel having excellent corrosion resistance as compared with ordinary carbon steel. In most cases, the main component is a chromium steel having a Cr content of about 12% or more, which contains Ni, 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 called 13 chromium stainless steel because the Cr content is 13%, and SUS301,
304, 305, and 310 (all are JIS symbols; the same applies hereinafter). The standard composition of ferritic carbon steel is that it is referred to as 18 chromium stainless steel since its Cr content is 18%, and examples thereof include SUS430 and 434. The standard composition of the austenitic carbon steel is 18% stainless steel since the Cr content is 18% and the Ni content is 8%, and examples thereof include SUS410 and THR100.

[0007] The surface roughness of the stainless steel plate is determined by JIS.
B0601, a value defined in JIS B
Surface roughness Rmax measured in accordance with No. 0651 is 0.1 to
It is necessary that the range of 50 μm and the pitch of the projections be in the range of 1 to 50 μm. Surface roughness Rmax of stainless steel plate
Is less than 0.1 and the pitch of the projections is less than 1 μm, it is difficult to form fine irregularities on the surface of the stainless steel plate, which increases the cost, which is not preferable. Surface roughness Rma
When x exceeds 50 μm, and when the pitch of the protrusions is 5
If the thickness exceeds 0 μm, the irregularities become too large, and the object of the present invention of irregularly reflecting incident solar light and sealing it on the surface of the insulating substrate is not achieved.

The thickness of the stainless steel plate is generally 0.0
It is preferred to select from a range of 5 to 5 mm, and particularly preferable is a range of 0.1 to 1 mm. In order to form such fine irregularities on the surface of the stainless steel plate, there are mechanical polishing method, hairline processing method, dull finishing method of rolling with roughened rolls, annealing acid cleaning method after rolling, dendrite shape Any method such as a plating method such as a crystal precipitation method may be used.

In the present invention, the term "polyimide resin" means polyimide, polyamideimide, polyetherimide, or a mixture thereof, which is soluble in a solvent. The polyimide resin also includes a mixture of a solvent-soluble resin such as polysulfone and polyether polysulfone as the second component.

As specific examples of the polyimide resin, benzophenonetetracarboxylic dianhydride (BTDA);
Two kinds of aromatic diisocyanates, that is, 4,4'-
Those obtained by copolymerizing diphenylmethane diisocyanate and 2,4-tolylene diisocyanate, for example, those having a structure represented by the following structural formula [I] can be mentioned.

[0011]

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[0012]

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[0013]

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As another specific example, a compound synthesized from biphenyltetracarboxylic dianhydride (BPDA) and an aromatic diamine via a polyamic acid has the following structural formula [II]:
And those having a structure represented by Structural Formula [III].

[0015]

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[0016]

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Still another specific example is a copolymerization of a structure having about 80 mol% of a repeating unit of the following structural formula [IV] and about 20 mol% of a repeating unit of the following structural formula [V]: Co) Polyimide.

[0018]

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[0019]

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Commercially available polyimide resins which correspond to the above-mentioned polyimide resins include Torlon (Amoco, USA) (the structural formula is as exemplified in the following [VI]), and Ultem (General Electric, USA). (Polyetherimide) (the structural formula of which is as exemplified in the following [VII]).

[0021]

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[0022]

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The above-mentioned copolymer (co) polyimide and copolymer (co) polyamideimide have a relative viscosity (ηinh) of 0.1 to 10 dl / g (in N-methylpyrrolidone, a concentration of 0.5% by weight, 30% by weight). (Measured at ° C).

In order to form a film of the above-mentioned polyimide resin on the stainless steel plate, it is applied as a solution dissolved in a solvent. Usable solvents include N-methylpyrrolidone, N, N′-dimethylformamide, o-methylphenol, m-methylphenol, p-methylphenol, o-chlorophenol, p-chlorophenol,
Examples thereof include 2,4-dichlorophenol and diethylene glycol dimethyl ether. Among them, N-methylpyrrolidone and N, N'-dimethylformamide are preferred. The concentration of the resin in the coating solution is preferably selected in the range of 1 to 25% by weight so as to obtain a viscosity such that the coating operation can be performed smoothly.

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 coating amount on the surface of the stainless steel plate is adjusted by adjusting the concentration of the resin in the coating solution, the viscosity of the coating solution, and the like, so that the thickness of the wet coating film is 3 to 300.
The coating operation is repeated and adjusted so that the coating after application and drying has a predetermined 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.
Heating is performed in a temperature range of 0 ° C. for a period of 5 to 60 minutes to make the residual solvent concentration of the film on the substrate surface sufficiently low. For example, when the solvent is N, N'-dimethylformamide,
When the substrate is used for an amorphous solar cell substrate, the residual solvent concentration that does not adversely affect the CVD operation under vacuum is 5%.
It needs to be less than about 0 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 heating temperature is low, the heating time is lengthened, and when the heating temperature is high, the heating time is generally shortened.

The thickness of the film formed on the surface of the substrate ranges from 1 to
The range is 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 the risk of causing dielectric breakdown when used as an electronic component increases, which is not preferable. On the other hand, if the thickness of the coating exceeds 50 μm, the residual solvent tends to remain in the coating, and the unevenness of the surface of the stainless steel plate of the base is buried, which is not preferable.

In the heat-resistant substrate according to the present invention, the surface of the polyimide resin film has a surface roughness Rmax measured in accordance with JIS B0651 in the range of 0.1 to 10 μm and a pitch of the projections in the range of 0.1 to 20 μm. Range. Surface roughness Rma
If x 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 film, which increases the cost, which is not preferable. Surface roughness Rmax is 1
If it exceeds 0 μm, and the pitch of the projections exceeds 20 μm, the irregularities become too large, and the object of the present invention of irregularly reflecting incident sunlight and sealing it on the surface of the insulating substrate is not achieved.

As a method of forming the above-mentioned fine irregularities on the surface of the polyimide resin film, a physical method such as a texture, a method of matting the surface of the film with a calender roll, a microgravure roll, or the like, And a method of etching with hydrazine.

In the heat-resistant substrate according to the present invention, fine irregularities are formed on the surface of the stainless steel plate of the base, and very fine irregularities are also formed on the polyimide resin film on the surface of the stainless steel plate. Since the incident sunlight can be preferably diffusely reflected and sealed on the surface of the insulating substrate, the photoelectric conversion efficiency can be improved. Heat-resistant substrates are used for substrates for photoelectric conversion devices, such as substrates for solar cells, substrates for optical sensors, and substrates for optical switches, as well as substrates for electronic devices, such as substrates for printed wiring and substrates for thermal heads. Widely used.

[0031]

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 departs from the gist.

[Production Example of Copolymerized Polyimide] Based on the description in Example 4 of US Pat. No. 3,708,458, 3,3 ', 4,4'-benzophenonetetracarboxylic anhydride and 80 mol% of tolylene diisocyanate (about 80 mol% of 2,4-isomer and about 20 2,5-isomer)
Mol% of a mixture) and a mixture containing 20 mol% of 4,4'-diphenylmethanediisocyanate,
Using N′-dimethylformamide (DMF) as a solvent,
A copolymerized polyimide was synthesized. The relative viscosity (ηinh) of the obtained copolymerized polyimide was 0.6 dl / g (in N-methylpyrrolidone, concentration 0.5% by weight, temperature 30 ° C.).

Example 1 The copolymerized polyimide produced in the above production example was dissolved in DMF to obtain a solution having a solid content of 15% by weight, and the solution was filtered through a filter having a pore size of 1 μm to obtain a solution for forming a film. On the other hand, the size is 300mm x 300
A SUS304 stainless steel plate having a thickness of 0.3 mm and a thickness of 0.3 mm was used as a substrate, and the surface of the substrate was roughened by a hairline processing method. The surface roughness Rmax was 2 μm, and the pitch of the projections was 20 μm.
m fine irregularities were formed. On one surface of this stainless steel plate, the above-mentioned solution for forming a film is applied by a die coater at room temperature, immediately put in an oven at 80 ° C., maintained at this temperature for 5 minutes, and then gradually heated to 350 ° C. At this temperature for 5 minutes. In the obtained heat-resistant substrate, the thickness of the copolymer polyimide film was 10 μm, the surface roughness Rmax was 0.2 μm, and the pitch of the projections was 2 μm.

Example 2 In the example described in Example 1, the substrate was made of SUS30 having a size of 300 mm × 300 mm.
4 A stainless steel plate, which was dulled using a die roll to roughen the surface, and the surface roughness Rmax was changed to 3 μm, and the pitch of projections was changed to 24 μm to form fine irregularities, A heat-resistant substrate on which a coating was formed was obtained in the same procedure. The resulting heat-resistant substrate had a thickness of 12 μm of the copolymer polyimide film and a surface roughness Rmax of 0.3 μm.
m, the pitch of the projections was 2.4 μm.

Example 3 In the example described in Example 1, the substrate was made of SUS30 having a size of 300 mm × 300 mm.
4 stainless steel plate, except that the surface was roughened (2D finish) by rolling with an annealing acid after rolling to form fine irregularities with a surface roughness Rmax of 1 μm and a pitch of projections of 10 μm. A heat-resistant substrate having a coating formed thereon was obtained in the same procedure as in the example. The resulting heat-resistant substrate had a copolymer polyimide film thickness of 15 μm and a surface roughness Rmax of 0.1 μm.
m, the pitch of the projections was 1 μm.

[Comparative Example] In the example described in Example 1,
Surface roughness Rmax is 100 nm, pitch of projections is 100 n
A heat-resistant substrate having a coating formed thereon was obtained in the same procedure as in the same example, except that the substrate was changed to one having an extremely fine unevenness of m. In the obtained heat-resistant substrate, the thickness of the copolymer polyimide film was 15 μm.

[Application Example] The surface of the coating of the heat-resistant substrate obtained by the methods described in Examples 1 to 3 and Comparative Example
First, a 200-nm-thick Ag electrode layer was formed as a lower electrode by a sputtering method. 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, Examples 1 to 3 were obtained.
The one using the heat-resistant substrate of No. 3 showed a value that was 35 to 70% higher than that using the substrate of the comparative example.

[0038]

The present invention has the following particularly advantageous effects, and its industrial value is extremely large. 1. 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 stainless steel plate. It is suitable for applications. 2. The heat-resistant substrate according to the present invention can be manufactured at low cost because the fine irregularities formed on the surface of the stainless steel plate are not ultra-fine, which would increase the cost for forming the same. 3. The heat-resistant substrate according to the present invention has fine irregularities formed on the surface of a stainless steel plate, and a thin film of a polyimide resin is formed on the surface so as not to fill the minute irregularities. In this case, the incident sunlight can be preferably diffusely reflected and confined to the surface of the insulating substrate, so that the photoelectric conversion efficiency can be improved.

Claims (2)

[Claims] 1. A heat-resistant substrate having a surface of a stainless steel plate on which a polyimide resin film is formed, wherein the stainless steel plate has a surface roughness Rmax measured in accordance with JIS B0651 in the range of 0.1 to 50 μm. Pitch is 1
The thickness of the polyimide resin film is in the range of 1 to 50 μm, the surface roughness Rmax of this film is in the range of 0.1 to 10 μm, and the pitch of the projections is 0 μm. A heat-resistant substrate having a thickness in the range of 1 to 20 μm. 2. The surface of a stainless steel plate is mechanically polished,
The heat-resistant substrate according to claim 1, wherein the substrate is roughened by any one of a hairline processing method, a dull finishing method, an annealing acid cleaning method after rolling, and a plating method.