JP2009188105A - Film for protecting rear surface of solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration caused by UV rays, especially, coloring by the UV rays. <P>SOLUTION: A film for protecting rear surface of a solar cell is the film formed of a biaxially-oriented polyester film which is composed of a polyester composition containing a benzotriazol system UV absorber by 0.1 to 5 wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a film for solar cell back surface protective film and a solar cell back surface protective film using the same.

  In recent years, the photovoltaic power generation system has been spreading as one of power generation means using clean energy. As described in Japanese Utility Model Publication No. Hei 6-38264, for example, a solar cell panel used in a photovoltaic power generation system has a plurality of plate-like solar cell elements between a light receiving side glass substrate and a back side protective film. It is common to have a structure in which a sealing resin is filled in the gaps inside.

  The protective film on the back side, that is, the back side protective film, requires excellent mechanical properties, heat resistance and moisture resistance, and polyester films are widely used. For example, Japanese Patent Application Laid-Open Nos. 2007-70430 and 2006-270025 propose a solar cell back surface protective film using a polyethylene terephthalate film.

  The conventional solar cell market is centered on consumer demand mounted on residential roofs of ordinary households in Japan. In this case, the amount of ultraviolet light incident from the back of the solar panel is small, and the back is not visible to the human eye. The demand for suppressing UV degradation was not high for the back surface protective film located on the back surface.

  However, the solar cell market has expanded rapidly in recent years, and the demand for industrial use, in which a large number of solar cell panels are installed side by side on a vast area, is spreading worldwide. Because the light reflected from the solar cell panel is incident on the back surface of the solar cell panel and the back surface of the solar cell is often exposed to the human eye, the solar cell back surface protection film is also required to suppress UV degradation. In particular, there is an increasing demand for suppressing discoloration due to ultraviolet rays.

  However, the conventional solar cell panel has poor weather resistance when used as a back surface protective film for solar cells for industrial use, and is particularly colored due to UV deterioration, so it cannot be used as the outermost layer of the solar cell back surface protective film. Met.

  Thus, the solar cell back surface protective film cannot be prevented from being deteriorated by ultraviolet rays if it is composed only of a conventional polyester fill. For this reason, it has to be used by being bonded to another base material, for example, an expensive fluorine-based sheet, so that the production process becomes very complicated and the cost is very expensive.

JP 2007-70430 A JP 2006-270025 A

  An object of the present invention is to solve the problems of the prior art and to provide a film for protecting a back surface of a solar cell in which deterioration due to ultraviolet rays is suppressed, and in particular, coloring due to ultraviolet rays is suppressed.

  That is, this invention is a film for solar cell back surface protective films which consists of a biaxially oriented polyester film, Comprising: This biaxially oriented polyester film contains 0.1 to 5 weight% of benzotriazole type ultraviolet absorbers. It is a film for solar cell back surface protective films characterized by consisting of.

  ADVANTAGE OF THE INVENTION According to this invention, the film for solar cell back surface protective films which the deterioration by ultraviolet rays was suppressed and the coloring by ultraviolet rays was especially suppressed can be provided.

Hereinafter, the present invention will be described in detail.
[polyester]
As the polyester of the polyester composition constituting the film for protecting a back surface of a solar cell of the present invention, a polyester comprising an aromatic dicarboxylic acid component and a diol component is used.
Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyldicarboxylic acid. Examples of the diol component include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol.

  Polyester is preferably polyethylene terephthalate or polyethylene-2,6-naphthalenedicarboxylate. The polyester may be a homopolymer, a copolymer, or a blend thereof.

[Ultraviolet absorber]
The polyester composition constituting the film for protecting a back surface of a solar cell of the present invention contains 0.1 to 5% by weight, preferably 0.5 to 4% by weight of a benzotriazole-based ultraviolet absorber. If it is less than 0.1% by weight, the effect of preventing deterioration due to ultraviolet rays is inferior, and the discoloration of the polyester tends to increase. On the other hand, if it exceeds 5% by weight, the mechanical properties of the film deteriorate.

  Examples of benzotriazole ultraviolet absorbers include 2,2′-methylenebis (4-tert-octyl-6-benzotriazolyl) phenol and 2,2′-methylenebis (4-cumylphenyl-6-benzotriazolyl) phenol. 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-ditert-butylphenyl) -5-chlorobenzotriazole, 2- (2 ′ -Hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2- (2'-hydroxy- 3 ', 5'-Dicumylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-carboxyphenyl) It can be exemplified 2- (2'-hydroxyphenyl) benzotriazoles such as benzotriazole. Of these, 2,2'-methylenebis (4-tert-octyl-6-benzotriazolyl) phenol and 2,2'-methylenebis (4-cumylphenyl-6-benzotriazolyl) phenol are preferable.

  The molecular weight of the benzotriazole-based ultraviolet absorber in the present invention is preferably 500 to 1000. By using a benzotriazole UV absorber with a molecular weight within this range, the amount of UV absorber thermally decomposed or volatilized during film production can be kept low, and the amount that bleeds out on the film surface. The effect of preventing deterioration due to ultraviolet rays can be sufficiently obtained, and at the same time, a transparent film having a low haze can be obtained by uniformly dispersing the ultraviolet absorber.

  The melting point of the benzotriazole ultraviolet absorber in the present invention is preferably 150 to 300 ° C. When the melting point is less than 150 ° C., the heat resistance is inferior, and the polyester composition is easily decomposed during melt kneading, which is not preferable. On the other hand, if it exceeds 300 ° C., the solubility in polyester is likely to be insufficient, and dispersion failure is liable to occur.

[the film]
The film for solar cell back surface protective film of this invention consists of a biaxially-oriented polyester film comprised from the polyester composition containing a benzotriazole type ultraviolet absorber. By being a biaxially oriented polyester film, sufficient mechanical strength required as a film for a solar cell back surface protective film can be obtained. If it is an unstretched film or a uniaxially oriented film, the mechanical strength may be insufficient, and it is not suitable as a film for a solar cell back surface protective film.

[Weatherability]
The film for a solar cell back surface protective film of the present invention has a ΔYI value of preferably 0 to 30, more preferably 0 to 10, after 15 days of ultraviolet irradiation with an eye super tester having an ultraviolet illuminance of 100 mW / cm ² . If the ΔI value exceeds 30, the film turns yellow and the appearance of the solar cell is remarkably impaired, which is not preferable. On the other hand, when a film for a solar cell back surface protective film is formed as a film without blending a benzotriazole-based UV absorber with polyester, the film is greatly yellowed and the ΔYI value exceeds 50.

In addition, 15 days of ultraviolet irradiation with an eye super tester for 15 days with an ultraviolet illuminance of 100 mW / cm ² corresponds to about 15 years of ultraviolet deterioration due to direct sunlight in outdoor use. Since it is not exposed to direct sunlight but only reflected light from the surroundings, it corresponds to about 30 years assuming that the amount of ultraviolet light is ½ of direct light.

[Additive]
In the present invention, it is preferable to add a lubricant to the polyester composition in order to make the film slippery and improve handling.

  In the present invention, other additives such as pigments, dyes, reinforcing agents, fillers, heat resistance improvers, antioxidants, plasticizers, weather resistance improvers, lubricants, as long as the physical properties of the resulting film are not impaired. A mold release agent, a crystal nucleating agent, a fluidity improver, an antistatic agent, a stabilizer, a crosslinking agent, a terminal blocking agent, or a molecular chain extender may be added. As antioxidant, a phenolic antioxidant and phosphorus antioxidant are preferable, and it is preferable to use these together. As the stabilizer, a hindered amine stabilizer is preferable.

[Production method]
The polyester composition constituting the film is preferably obtained by melting and kneading polyester and a benzotriazole ultraviolet absorber at a temperature at which the polyester melts. The temperature of this melt kneading is, for example, 200 to 300 ° C. At the time of melt kneading, for example, after mixing each component with a turnbull mixer or a Henschel mixer, a method of kneading each component with an extruder or a roll can be used. In the final stage of polymerization of the polyester, a polyester composition may be obtained by adding a benzotriazole ultraviolet absorber to the melted polyester.

  The film for protecting a back surface of a solar cell of the present invention is obtained by melt-extruding a polyester composition containing a benzotriazole-based ultraviolet absorber into a film shape and cooling and solidifying it with a casting drum to form an unstretched film. Stretched at (Tg + 60) ° C. once or twice or more in the longitudinal direction so that the total draw ratio is 3 to 6 times, and then stretched in the width direction at Tg to (Tg + 60) ° C. It can be obtained by stretching so as to be doubled and further performing heat treatment at 180 ° C. to 255 ° C. for 1 to 60 seconds as necessary.

  Stretching in the longitudinal direction and the transverse direction may be performed by sequential biaxial stretching or simultaneous biaxial stretching. In order to increase the dimensional stability during heating, for example, a method of shrinking in the longitudinal direction in a heat treatment step disclosed in JP-A-57-57628, or a film disclosed in JP-A-1-275031 is relaxed in a suspended state. A heat treatment method can be used. The thickness of the obtained biaxially stretched film is preferably 25 to 300 μm, more preferably 50 to 250 μm.

  You may provide an easily-adhesive coating film in the film for solar cell back surface protective films of this invention. An easy-adhesive coating film is provided by applying an aqueous liquid containing an acrylic resin containing a crosslinking component or a component forming a polyester resin film to a stretchable polyester film, followed by drying, stretching, and heat treatment. Can do. When providing a coating film, the thickness of a coating film becomes like this. Preferably it is 0.01-1 micrometer.

Hereinafter, the present invention will be further described by examples.
Each characteristic value was measured by the following method.

(1) Intrinsic Viscosity The viscosity of a solution using an orthochlorophenol solvent was measured at 35 ° C.

(2) Ultraviolet resistance It carried out on condition of the following using the ultraviolet-ray deterioration acceleration tester (eye super UV tester SUV-W131 Iwasaki Electric Co., Ltd. product). The ultraviolet illuminance was 100 mW / cm ² .
UV irradiation was performed at 60 ° C. × 50% RH for 15 days, and YI (yellow index) values before and after irradiation were measured using a color difference meter (Σ-90 type manufactured by Nippon Denshoku Industries Co., Ltd.). The difference (ΔYI) in YI before and after irradiation was determined and judged according to the following criteria. Here, X, Y, and Z are tristimulus values of light defined in the international CIE standard.
YI = 100 / Y × (1.28 × X−1.06 × Z)
A: 0 ≦ ΔY ≦ 10
○: 10 <ΔY ≦ 30
×: 30 <ΔY

[Example 1]
4% by weight of 2,2′-methylenebis (4-tert-octyl-6-benzotriazolyl) phenol (Adekastab LA-31, molecular weight 659, melting point 195 ° C., manufactured by Asahi Denka Kogyo Co., Ltd.) as a UV absorber, and as a lubricant A polyethylene terephthalate (intrinsic viscosity: 0.65) composition containing 800 ppm of bulk silicon oxide particles having an average particle size of 2.5 μm was melt extruded onto a rotating cooling drum maintained at 20 ° C. to obtain an unstretched film. Next, the film was stretched 3.5 times at 100 ° C. in the longitudinal direction, then stretched 3.8 times at 110 ° C. in the transverse direction, heat-set while shrinking 2.5% in the width direction at 225 ° C., and a thickness of 50 μm. The film for solar cell back surface protective films was obtained. The evaluation results are shown in Table 1.

[Example 2]
Except having changed the quantity of the ultraviolet absorber as shown in Table 1, it carried out similarly to Example 1, and obtained the film for solar cell back surface protective films of thickness 50 micrometers. The evaluation results are shown in Table 1.

[Example 3]
The ultraviolet absorber was changed to benzotriazole-based 2,2′-methylenebis (4-cumylphenyl-6-benzotriazolyl) phenol (Adekastab LA-46, molecular weight 659, melting point 210 ° C., manufactured by Asahi Denka Kogyo). In the same manner as in Example 1, a film for solar cell back surface protective film having a thickness of 50 μm was obtained. The evaluation results are shown in Table 1.

[Example 4]
The ultraviolet absorber is a benzotriazole-based 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole (Adeka Stub LA-36, manufactured by Asahi Denka Kogyo Co., Ltd., molecular weight 315, melting point) Except for changing to 139 ° C., a film for protecting the back surface of a solar cell having a thickness of 50 μm was obtained in the same manner as in Example 1. Since the molecular weight and melting point were low, the effect was weak because the thermal stability was somewhat poor. The evaluation results are shown in Table 1.

[Comparative Example 1]
A film for protecting a back surface of a solar cell having a thickness of 50 μm was obtained in the same manner as in Example 1 except that no ultraviolet absorber was contained. The evaluation results are shown in Table 1.

[Comparative Example 2]
A film for solar cell back surface protective film having a thickness of 50 μm was obtained in the same manner as in Example 1 except that the amount of the ultraviolet absorber to be contained was changed as shown in Table 1. The obtained film was remarkably deteriorated in mechanical properties, was frequently cut during production, and was inferior in stable film-forming property. The evaluation results are shown in Table 1.

[Comparative Example 3]
Except for changing the ultraviolet absorber to bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane (Adekastab LA-51, molecular weight 469, melting point 225 ° C., manufactured by Asahi Denka Kogyo), which is a benzophenone ultraviolet absorber. In the same manner as in Example 1, a film for solar cell back surface protective film having a thickness of 50 μm was obtained. The evaluation results are shown in Table 1.

  The film for protecting a back surface of a solar cell of the present invention is suppressed from deterioration due to ultraviolet rays and can be suitably used as a protective film for a back surface of a solar cell.

Claims (4)

  A film for protecting a back surface of a solar cell comprising a biaxially oriented polyester film, wherein the biaxially oriented polyester film comprises a polyester composition containing 0.1 to 5% by weight of a benzotriazole-based ultraviolet absorber. A film for solar cell back surface protective film.   The film for solar cell back surface protective films of Claim 1 whose molecular weight of a benzotriazole type ultraviolet absorber is 500-1000.   The benzotriazole UV absorber is 2,2′-methylenebis (4-tert-octyl-6-benzotriazolyl) phenol and / or 2,2′-methylenebis (4-cumylphenyl-6-benzotriazolyl) The film for solar cell back surface protective films of Claim 1 which is phenol. The film for solar cell back surface protective film of Claim 1 whose (DELTA) YI value after ultraviolet irradiation for 15 days is 0-30 with an eye super tester with ultraviolet illuminance of 100 mW / cm < ² >.