JPS61218625A - Resin composition for forming water vapor proof and protecting film for solar cell - Google Patents

Abstract

PURPOSE:The titled composition having improved screen printing characteristics and curing characteristics, comprising a bisphenol epoxy resin having a relationship between molecular weight and molecular cohesive force satisfying a specific condition, a specified curing agent and a curing promoter of an organometallic compound. CONSTITUTION:(A) 100pts.wt bisphenol epoxy resin having the formula SIGMAxiXi=400-1,000 (xi is weight fraction of epoxy resin i to the whole epoxy resin used; Xi is average molecular weight of epoxy resin i) is blended with (B) 20-50pts.wt. modified acid anhydride curing agent obtained by esterifying 10-65mol% acid anhydride (preferably hexahydrophthalic anhydride, etc.) with a polyhydric alcohol, and (C) 1-5pts.wt. based on 100pts.wt. total amounts of the components A and B of an organometallic compound (preferably tin octylate, etc.) as a curing promoter, to give the aimed composition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a solar cell, and particularly to a resin composition capable of forming a moisture-proof protective film on the light-receiving surface of the solar cell.

[Conventional technology]

In recent years, research and development of solar power generation systems has been active as part of the development of new energy resources to replace petroleum, and the surface protection materials that make up the light-receiving surface of solar cells can be broadly classified into glass and hardening resin. This latter curable resin has excellent curing properties in the air, and has excellent film transparency, surface hardness,
It provides a protective film with excellent scratch resistance, abrasion resistance, bending resistance, heat resistance, water resistance, weather resistance, and adhesion to the substrate surface. The resin composition used for this purpose is
Conventionally, silicone resins, urethane resins, epoxy acrylate resins, urethane acrylate resins, epoxy resins, etc. have been known, but silicone resins are expensive and are suitable for use in photoelectric semiconductors due to moisture permeation, such as amorphous silicon, semicrystalline silicon, polycrystalline silicon, etc. In urethane resin systems, heat resistance and storage stability after mixing two components are
In addition, epoxy acrylate or urethane acrylate, which have excellent curability, are required as solar cell protective films due to problems such as water resistance and coloration due to the action of photosensitizers, that is, a decrease in light transmittance. There was nothing that could satisfy all the characteristics. On the other hand, epoxy resin has good hardness, heat resistance,
Although it exhibits excellent properties as a protective film such as water resistance and adhesion, when used as a protective film for solar cells, it has the disadvantage that coloring curing agents cannot be used due to light transmittance. For example, it is difficult to use primary to tertiary amine-based or phenol-based curing agents because they become colored or become colored during long-term use, inhibiting light transmission. The most convenient curing agent system from the viewpoint of optical transparency is an acid anhydride system.
This acid anhydride has the disadvantage that it easily evaporates during the curing process of the resin due to its low viscosity and low vapor pressure.As a result, the coating film may not cure, the surface layer of the coating film may become sticky, or it may not cure properly. Due to a difference in the equivalence ratio of epoxy groups and acid anhydride groups during the process, the cured product has the disadvantage of not being able to fully exhibit its properties, such as poor moisture resistance. A method of over-blending acid anhydride is known as a method to avoid such drawbacks, but in this case, the remaining acid anhydride significantly reduces water resistance, leading to deterioration of the amorphous and reducing the photoelectric conversion effect. There was a problem with the decline.

On the other hand, such a protective film for a solar cell is required to have good printing properties by screen printing in addition to the coating film properties and curing properties described above. In other words, this type of protective film for solar cells needs to be printed by screen printing because it needs to have a complex shape such as the electrode lead-out part and a certain film thickness suitable for moisture proofing. The resin does not flow, sag, or bleed, in other words, it has good dimensional accuracy and is capable of defoaming the bubbles that are trapped when the resin passes through the screen mesh. This is necessary from the viewpoint of light transmission. In other words, by lowering the viscosity of the resin, the antifoaming properties can be improved, but bleeding, sagging, etc. will occur, and conversely, if the viscosity is increased, even if bleeding and sagging can be prevented, the antifoaming properties will not be satisfactory. It was there. In fact, epoxy acrylate, urethane acrylate, urethane resin, etc. have excellent dimensional accuracy, but many bubbles remain in the cured coating, and silicone resins, epoxy resins, etc., which have a slow curing speed, have good antifoaming properties but have poor dimensional accuracy. It had the disadvantage of lacking in

[Purpose and outline of the invention]

The purpose of the present invention is to solve the above-mentioned drawbacks of conventional resin compositions, especially epoxy resin compositions, which have been used as protective films for solar cells, and to prevent the drawbacks due to curing agents and to provide excellent curing properties. Another object of the present invention is to provide an epoxy resin protective film for a solar cell, which eliminates the problems that occur during screen printing.

The present inventor has been conducting research to achieve the above objective, and in this research, it was found that the printability during screen printing is largely dependent on the correlation between the molecular weight of the epoxy resin used and the molecular cohesive force. It was discovered by chance that when certain characteristics are within a limited range, excellent printing characteristics can be exhibited.

Among the epoxy resins in this specific range, we discovered that bisphenol-type epoxy resins, which have excellent toughness and transparency, are the most effective in terms of the properties of their cured products, and based on these new facts, we Furthermore, as a result of continuing research on curing agents and curing accelerators to be used in combination, the present invention was finally completed.
00 (however, Xi is the weight fraction based on the total epoxy resin used in the epoxy resin, XL is the average molecular weight of the epoxy resin), (b) 20 parts by weight based on 100 parts by weight of the epoxy resin. ~50 parts by weight of a modified acid anhydride curing agent, 10 to 65 mol% of which is esterified with a polyhydric alcohol, and (c) 1 to 100 parts by weight of the total of the epoxy resin and the curing agent. The present invention relates to a moisture-proof protective film-forming resin composition for solar cells, which contains 5M parts of an organometallic compound.

〔Effect of the invention〕

In the present invention, a bisphenol type epoxy resin is particularly used among the epoxy resins that satisfy the above-mentioned specific formula, in other words, the relationship between molecular weight and molecular cohesive force is within a specific range. In particular, the following three methods are used: selecting an acid anhydride curing agent esterified with a polyhydric alcohol in the above-mentioned specific ratio as a curing agent, and using an organometallic compound as a curing accelerator in this case. By using these three methods in combination, it is possible to solve the conventional difficulties that occur during screen printing, namely, the inability to satisfy defoaming properties and dimensional stability at the same time. It satisfies the characteristics required for a protective film for solar cells, and in particular, it has the effect of providing a protective film with excellent transparency and high water or moisture resistance, which could not be achieved with conventional epoxy resin protective films. do.

For example, with cycloaliphatic epoxy resin, there are no problems with transparency and translucency, but because the resin viscosity is low and the molecular cohesion is weak, pattern edges sag during the curing process, significantly reducing dimensional accuracy and the cured film. It is hard and brittle, resulting in poor flexibility.Also, with phenol novolak plastic or Talesol novolak type epoxy resin, the cured coating becomes colored and cannot withstand use due to its translucency, which is the lifeblood of solar cells. .

[Structure of the invention]

The epoxy resin used in the present invention is ΣXL
It is a bisphenol type epoxy resin in the range of XL=400 to 1000 (where xL is the weight fraction of the epoxy resin to the total epoxy resin used, and xi is the average molecular weight of the epoxy resin).

Here, the meaning of the above-mentioned ΣX y X knee 400 to 1000 will be explained using an example below. For example, epoxy resin A
For example, if the weight fraction of epoxy resin B is 30% and the average molecular weight is 2000, and the latter one whose weight fraction is 20% and the average molecular weight of epoxy resin B is 500 is used, Σx 1 X L -0.3X200 + 0.7X5
00=950. In this way, ΣXLXL is 400
The epoxy resin is selected and used so that it falls within the range of 1,000 to 1,000. At this time, for example, if an epoxy resin with an average molecular weight of 1000 is used, the weight fraction will be 1, so ΣX engineering x engineering = 1 x 1000-1000.

That is, in the present invention, the epoxy resin may be used alone, but preferably two or more types are used in combination.

In the present invention, bisphenol type epoxy resins are particularly selected from among the epoxy resins within the range represented by the above specific formula. In this case, the bisphenol type epoxy resin has an epoxy equivalent of 150 to 220.
0, preferably 180 to 1200, such as Epicoat 815.827.82 manufactured by Yuka Shell Co., Ltd.
8.834.1001.1002.1004.1007
etc. However, in the present invention, a phenol novolac type or talesol novolac epoxy resin may be used in combination in an amount of 20 parts by weight or less per 100 parts by weight of the bisphenol type epoxy resin.

In the present invention, as the curing agent, an acid anhydride curing agent in which 10 to 65 mol % of the curing agent is esterified with a polyhydric alcohol is used. As the acid anhydride, acid anhydrides such as hexahydrophthalic anhydride, methylhexahydrophthalic acid, and methyltetrahydrophthalic acid are suitable, but 21'X
Acid anhydrides conventionally used in this type of field can also be used. Typical examples of the polyhydric alcohol for esterification include dihydric or trihydric alcohols, and specific examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, and glycerin. can be used, and other tetrahydric to hexavalent polyhydric alcohols can also be used. The degree of esterification in this case is 10 to 65 mol% of the acid anhydride, and if the esterification does not reach 10%, the cured product will become unstable, the moisture resistance of the protective film will be poor, and the surface strength will deteriorate. descend. On the other hand, 65 mol%
If the amount is more than
Use 0 to 40 parts by weight.

The curing accelerator used in the present invention is an organometallic compound, and usually a metal salt of an organic acid is used.

The organic acid in this case is a carboxylic acid having 8 to 28 carbon atoms, particularly preferably an aromatic or aliphatic carboxylic acid, and the metal is cobalt, zinc, tin, etc., and among them, tin is preferred. Specific examples include tin, cobalt, and zinc salts of octylic acid, naphthenic acid, and dibutyllauric acid. These curing accelerators can be used in a wide range of epoxy resin/acid equivalent ratio of 0.2 to 1.0, and in terms of weight, preferably 1 to 5 parts by weight per 100 parts by weight of bisphenol type epoxy resin. It is 2 to 4 parts by weight.

The composition of the present invention may further contain other conventional additives as required, such as antifoaming agents, colloidal silica,
Specific examples include organic resin-based thixotropic agents and compling agents.

[Example] Hereinafter, the method for producing the curing agent used in the present invention will be listed as a reference example, and the present invention will be specifically explained with reference to Examples.

Reference Example 1 Hexahydrophthalic anhydride 154g (1 mol) and propylene glycol 15. 2 g (0.2 mol) was charged into a reaction vessel and reacted at 100-120°C for 6 hours to obtain a viscous modified curing agent.

Reference Example 2 154 g (1 mol) of hexahydrophthalic anhydride and 31.8 g (0.3 mol) of diethylene glycol were charged into a reaction vessel and reacted at 100 to 120° C. for 6 hours to obtain a viscous modified curing agent.

Reference Example 3 168 g (1 mol) of methylhexahydrophthalic anhydride and 13.8 g (0.15 mol) of glycerin were placed in a reaction vessel and reacted at 100 to 120°C for 6 hours to obtain a viscous modified curing agent. .

Example 1 Epicoat 834 (manufactured by Shell Chemical Co., Ltd., average molecular weight, 4
70) IQOg, 20g of the modified curing agent obtained in Reference Example 1, and 3.6g of tin octylate,) 5g of luol, 5g of butanol
Table 1 shows the properties when the mixture was well mixed with g and screen printed on a stainless steel plate using a 150 mesh polyester screen, and then cured in an oven at 150°C for 1 hour.

Example 2 Ebiko) 815 (manufactured by Shell Chemical Co., Ltd., average molecular weight, 33
0) 50 g, Epicor) 1002 (same as above, 1
1100) 50, 20 g of the modified curing agent obtained in Reference Example 2, 2.4 g of zinc octylate, and 20 g of cellosolve acetate were mixed well, printed on a stainless steel plate using a 150 mesh polyester screen, and then cured in an oven at 150°C for 1 hour. Table 1 shows the characteristics when

Example 3 Epicote 834.50g, Epicote 1002.40
g, Epikote 1004 (manufactured by Shell Chemical Co., Ltd., average molecular weight, 1400) 10 g, modified curing agent 30 obtained in Reference Example 3
g, tin octylate 5.2 g, cellosolve acetate 2
Table 1 shows the properties when 0g of the mixture was well mixed, printed on a stainless steel plate using a 150 mesh polyester screen, and then cured in an oven at 150°C for 1 hour.

Comparative Example 1 Table 1 shows the properties of a product printed and cured in the same manner as in Example 1 except for tin octylate.

Comparative Example 2 Table 1 shows the properties of a product printed and cured in the same manner using 34 g of hexahydrophthalic anhydride instead of the modified curing agent of Example 2.

Comparative Example 3 Epicote 815g, 70g, Epicote 834.30
Table 1 shows the properties of a product obtained by mixing well, 25 g of the modified curing agent obtained in Reference Example 1, and 3.6 g of tin octylate, printing and curing in the same manner.

Example 4 In Example 1, cobalt naphthenate was used instead of tin octylate, and the other conditions were the same as in Example 1.

The results were almost the same as in Example 1.

Example 5 In Example 2, dibutyltin laurate was used in place of zinc octylate, and the other conditions were the same as in Example 2. The results were almost the same as in Example 2.

As described above, it was possible to obtain a resin composition that has excellent curing properties after screen printing and excellent properties as a moisture-proof protective film for solar cells.The resin composition of the present invention is useful as a solar cell protective film. However, it is also useful for other applications that require light transmittance and moisture resistance, such as optical sensor protective films and optical disk moisture-proof protective films.

(that's all)

Claims (1)

[Claims] (1) (A) Bisphenol type epoxy resin in the range of Σx_i 20 to 5 parts by weight per 100 parts by weight of the epoxy resin
0 parts by weight of a modified acid anhydride curing agent, of which 10 to 65 mol% is esterified with a polyhydric alcohol, and (c) 1 to 5 parts by weight based on a total of 100 parts by weight of the epoxy resin and the curing agent. 1. A resin composition capable of forming a moisture-proof protective film for a solar cell, comprising: an organometallic compound.