JP4559342B2 - Adhesive sheet for solar cell - Google Patents

Description

  The present invention relates to a solar cell adhesive sheet that is suitably used to join a solar cell element and a protective material when manufacturing a solar cell module.

  A solar cell module made of a silicon or selenium semiconductor wafer has a laminated body obtained by superposing an upper transparent protective material on the upper surface of a solar cell element laminated with an adhesive sheet and a lower substrate protective material on the lower surface under reduced pressure. It is manufactured by heating with air, and laminating and integrating a protective material on the upper and lower surfaces of the solar cell element via an adhesive sheet.

  As an adhesive sheet used for such a solar cell module, Patent Document 1 discloses a sealing composition, an ethylene-vinyl acetate copolymer, an organic peroxide, a photosensitizer, and a silane coupling agent. A sealing composition for sealing a mixed electronic material has been proposed, and it is further disclosed that a (meth) acrylic acid ester and / or an allyl group-containing compound may be added.

  However, the sealing sheet made of the above-described sealing composition is produced in a large amount of low molecular weight compounds such as acetone and carbon dioxide with the decomposition of the organic peroxide during the production of the solar cell module, There has been a problem that bubble expansion occurs between the opposed surfaces of the solar cell element and the upper and lower protective material, and the solar cell element and the upper and lower protective material are partially separated.

  Moreover, in order to increase the productivity of the solar cell module, the heating time can be shortened by adding an organic peroxide that decomposes at a low temperature to the sealing sheet or heating the solar cell element at a high temperature. When trying to complete the cross-linking reaction, the peeling between the solar cell element and the protective material due to the above-mentioned bubble expansion further worsened, and on the contrary, the productivity of the solar cell module was lowered.

  Therefore, it is conceivable to reduce the amount of the organic peroxide to be contained in the sealing sheet, but when the content of the organic peroxide is thus reduced, the ethylene-vinyl acetate copolymer is crosslinked. As a result, the heat resistance of the sealing sheet is insufficient, and another problem that the durability of the obtained solar cell module becomes insufficient occurs.

Japanese Patent Publication No. 6-35575

  The present invention provides an adhesive sheet for a solar cell that is excellent in heat resistance and adhesiveness, and that does not cause bubble expansion between opposed surfaces of a solar cell element and a protective material when used for manufacturing a solar cell module. To do.

  The solar cell adhesive sheet of the present invention is a solar cell adhesive sheet comprising 100 parts by weight of an ethylene-based copolymer and 0.05 to 0.5 parts by weight of an organic peroxide, which is either an acryloyl group or a methacryloyl group. A polyfunctional monomer having a total of 4 or more of either or both is contained.

  The ethylene copolymer used in the adhesive sheet for solar cells of the present invention is a copolymer of ethylene and a copolymerizable monomer that can be copolymerized with ethylene, and the copolymerizable monomer is not particularly limited. Examples thereof include vinyl acetate, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, maleic acid, maleic anhydride, maleic acid ester and the like, and vinyl acetate is preferable. In addition, the said copolymerizable monomer may be copolymerized with ethylene independently, or 2 or more types may be copolymerized with ethylene.

  And when there is little content of the copolymerizable monomer contained in the said ethylene-type copolymer, the transparency of the adhesive sheet for solar cells obtained may be insufficient, and the power generation efficiency of a solar cell element may fall. On the other hand, if the amount is too large, the film-forming stability and mechanical strength of the adhesive sheet for solar cells may be insufficient, so 5 to 50% by weight is preferable.

  On the other hand, if the melt flow rate of the ethylene copolymer is small, the film-forming stability of the solar cell adhesive sheet is lowered, whereas if it is large, the mechanical strength of the solar cell adhesive sheet is insufficient. 1-100 g / 10 min is preferred. In addition, the melt flow rate of the ethylene-based copolymer in the present invention refers to that measured according to JIS K 7210.

  Although the ethylene-based copolymer has excellent physical properties such as transparency and adhesiveness, it has a problem that it is deformed under high temperature conditions during the manufacturing process of the solar cell module because of low heat resistance. . Then, the heat resistance of the adhesive sheet for solar cells is improved by including an organic peroxide in the adhesive sheet for solar cells and crosslinking the ethylene copolymer.

  That is, the solar cell adhesive sheet is used by interposing between the upper transparent protective material and the lower substrate protective material and the solar cell element during the production of the solar cell module, and the solar cell is subjected to thermocompression bonding under reduced pressure. The element and the upper and lower protective material are bonded. The organic peroxide contained in the solar cell adhesive sheet is decomposed by the heat applied during the thermocompression bonding step to crosslink the ethylene copolymer.

  The organic peroxide used in the present invention is not particularly limited, but when an organic peroxide having a 1 minute half-life temperature of 140 ° C. or lower is used, ethylene is formed in the extruder during the film forming process of the solar cell adhesive sheet. When the resin composition containing a copolymer and an organic peroxide is melt-kneaded, the organic peroxide is decomposed, and the ethylene copolymer is cross-linked in the extruder to produce a gel. Since film formation may be difficult, it is preferable to use an organic peroxide having a 1 minute half-life temperature of 140 ° C. or higher.

  Examples of organic peroxides having a 1 minute half-life temperature of 140 ° C. or higher include dicumyl peroxide (175 ° C.), t-butylperoxy-2-ethylhexyl monocarbonate (161 ° C.), and t-butyl peroxybenzoate. (167 ° C.), 1,1-di (t-butylperoxy) -2-methylcyclohexane (142 ° C.), 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane (147 ° C), 1,1-di (t-hexylperoxy) cyclohexane (149 ° C), 1,1-di (t-butylperoxy) cyclohexane (154 ° C), 2,2-di (4,4-di) (T-butylperoxy) cyclohexyl) propane (154 ° C.), t-hexylperoxyisopropyl monocarbonate (155 ° C.), 2,5-dimethyl 2,5-di (3-methylbenzoylperoxy) hexane (156 ° C.), 2,5-dimethyl-2,5-di (benzoylperoxy) hexane (158 ° C.), t-butylperoxyisopropyl monocarbonate ( 159 ° C.), t-butyl peroxylaurate (159 ° C.), t-butyl peroxyacetate (160 ° C.), t-hexyl peroxybenzoate (160 ° C.), 2,2-di (t-butyl peroxy) Butane (160 ° C.), t-butyl peroxy-3,5,5-trimethylhexanoate (166 ° C.), t-butyl peroxymaleic acid (168 ° C.), n-butyl-4,4-di (t -Butylperoxy) valerate (173 ° C), t-butylcumyl peroxide (173 ° C), di (2-t-butylperoxyisopropyl) (175 ° C), di-t-hexyl peroxide (177 ° C), 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (180 ° C), di-t-butyl peroxide ( 186 ° C.), 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 (194 ° C.), p-menthane hydroperoxide (200 ° C.) and the like. Also, two or more of them may be used in combination. The temperature in the parenthesis represents a 1 minute half-life temperature.

  And when there is little content of the organic peroxide contained in the adhesive sheet for solar cells, the crosslinking of the ethylene-based copolymer does not proceed, and the heat resistance of the adhesive sheet for solar cells becomes insufficient. While the durability of the solar cell module will be insufficient, a large amount of low molecular weight compounds such as acetone and carbon dioxide will accompany the decomposition of the organic peroxide during the thermocompression bonding process when manufacturing the solar cell module. Is generated between the opposing surfaces of the solar cell element and the protective material, the adhesiveness between the solar cell element and the protective material is reduced, and the protective function of the solar cell element is reduced. It is limited to 0.05 to 0.5 part by weight with respect to 100 parts by weight of the copolymer, and is preferably 0.2 to 0.4 part by weight.

  The adhesive sheet for solar cells of the present invention contains a polyfunctional monomer for the purpose of easily forming a crosslinked structure in the ethylene copolymer. This polyfunctional monomer has a total of 4 or more of either one or both of acryloyl groups and methacryloyl groups, that is, 4 or more acryloyl groups, 4 or more methacryloyl groups, or a total of 4 acryloyl groups and methacryloyl groups. Have more than one.

  The polyfunctional monomer has a total of 4 or more of either one or both of acryloyl group and methacryloyl group, and facilitates the crosslinking reaction of the ethylene copolymer, so it is contained in the adhesive sheet for solar cells. Even if the amount of the organic peroxide to be reduced is reduced, a sufficient cross-linked structure can be formed in the ethylene copolymer, and an adhesive sheet for solar cells having sufficient heat resistance can be obtained.

  As described above, the above adhesive sheet for solar cells contains a polyfunctional monomer having a total of 4 or more of either one or both of acryloyl group and methacryloyl group (hereinafter sometimes simply referred to as “polyfunctional monomer”). Thus, the amount of organic peroxide contained in the sheet can be reduced while providing sufficient heat resistance to the solar cell adhesive sheet, and the solar cell adhesive sheet of the present invention produces a solar cell module. In doing so, bubble expansion due to the low molecular weight compound generated with the decomposition of the organic peroxide does not occur.

  Moreover, since the amount of organic peroxide contained in the sheet is reduced as described above, the solar cell adhesive sheet performs the thermocompression bonding process at a high temperature and completes the crosslinking reaction in a short time. Therefore, the productivity of the solar cell module can be improved.

  Examples of the polyfunctional monomer include ditrimethylolpropane tetraacrylate, ditrimethylolpropane tetramethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol monohydroxypentaacrylate, dipentaerythritol monohydroxypentamethacrylate, dipentaerythritol. Hexaacrylate, dipentaerythritol hexamethacrylate, ε-caprolactone modified dipentaerythritol acrylate, ε-caprolactone modified dipentaerythritol methacrylate, alkyl modified dipentaerythritol acrylate, alkyl modified dipentaerythritol methacrylate, etc. May be used in Two or more kinds may be used in combination.

  And when there is little content of the polyfunctional monomer contained in the said adhesive sheet for solar cells, bridge | crosslinking of an ethylene-type copolymer may become inadequate and the heat resistance of the adhesive sheet for solar cells may become inadequate. On the other hand, when the amount is large, the polyfunctional monomers react with each other, and on the contrary, the crosslinking of the ethylene copolymer may be insufficient, so 0.05 to 100 parts by weight of 100 parts by weight of the ethylene copolymer. 2 parts by weight is preferred.

  Moreover, a coupling agent can be added to the said adhesive sheet for solar cells in order to improve the adhesiveness. As such a coupling agent, a silane coupling agent having one or two or more functional groups selected from the group consisting of an amino group, a glycidyl group, a methacryloxy group and a mercapto group is suitably used. Examples include aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane. May be.

  The solar cell adhesive sheet of the present invention may contain additives such as antioxidants, ultraviolet absorbers, light stabilizers and the like within a range not impairing the physical properties thereof. Furthermore, a crosslinking aid other than the above polyfunctional monomer, for example, a polyfunctional monomer in which one or both of acryloyl group and methacryloyl group are 3 or less may be added.

  Next, the manufacturing method of the adhesive sheet for solar cells is demonstrated. For the production of the solar cell adhesive sheet of the present invention, the T-die method is preferably used. For example, an ethylene copolymer, an organic peroxide, and either or both of an acryloyl group and a methacryloyl group are used. A resin composition composed of polyfunctional monomers having a total of four or more is supplied to an extruder, melt-kneaded at a temperature at which the organic peroxide is not substantially decomposed, and then a sheet from a T die attached to the tip of the extruder And a method of extruding the molten sheet with a cooling roll.

  And if the temperature at the time of melt-kneading the resin composition in the extruder is high, the organic peroxide is decomposed in the extruder, the crosslinking of the ethylene copolymer proceeds, and a gel is generated. Since it may be difficult to form a solar cell adhesive sheet, the temperature is preferably 40 ° C. or more lower than the one-minute half-life temperature of the organic peroxide used. Moreover, when using together 2 or more types of organic peroxide, it is preferable that it is 40 degreeC or more lower than the lowest 1 minute half life temperature.

  Moreover, it is preferable that the surface of the adhesive sheet for solar cell is embossed in order to improve the deaeration property in the thermocompression bonding process at the time of manufacturing the solar cell module. In addition, as a method of embossing the surface of the adhesive sheet for solar cells, a known method is used, for example, a molten sheet immediately after being extruded from a T die, an embossing roll having an embossed pattern on the surface, There is a method in which the embossing roll is supplied between a rubber roll disposed opposite to the embossing roll, the embossing roll is pressed against the molten sheet, and the surface of the solar cell adhesive sheet is embossed. Alternatively, the solar cell adhesive sheet once manufactured may be heated again to a molten state, and then embossed as described above.

  As a method for producing a solar cell module using the solar cell adhesive sheet of the present invention, the upper transparent protective material is provided on the upper surface of the solar cell element via the solar cell adhesive sheet, and the lower surface via the solar cell adhesive sheet. Laminating a lower substrate protective material to produce a laminated body, and heating the laminated body under a reduced pressure to stack and integrate the protective material on the upper and lower surfaces of the solar cell element via a solar cell adhesive sheet. Manufactured by.

  As a heating condition of the laminate, it is preferable to heat it for 5 to 10 minutes at a temperature equal to or higher than the 1-minute half-life temperature of the organic peroxide to be used. In addition, it is preferable that the gel fraction of the adhesive sheet for solar cells after thermocompression bonding is 70 weight% or more from a heat resistant viewpoint.

The gel fraction in the present invention refers to a solar cell adhesive sheet that is hot-pressed in the thickness direction of the sheet under the thermocompression bonding conditions at the time of manufacturing a solar cell module, and then 0.2 g of a test piece is cut out from the solar cell adhesive sheet. The test piece was immersed in 50 ml of xylene at 110 ° C. for 12 hours, the insoluble matter was filtered through a 200 mesh wire mesh, the residue on the wire mesh was vacuum dried, and the weight A (g) of the dry residue was determined. It is measured and the gel fraction is calculated using the following formula.
Gel fraction (% by weight) = 100 × A / 0.2

  During the production of this solar cell module, as described above, the solar cell adhesive sheet constituting the solar cell module is excellent in heat resistance, and the amount of organic peroxide contained in the sheet is reduced. Therefore, bubble expansion caused by a low molecular weight compound generated with decomposition of the organic peroxide occurs between the facing surfaces of the solar cell element and the protective material constituting the solar cell module, and the solar cell element And the protective material are not peeled off, and the obtained solar cell module has excellent durability.

  The solar cell adhesive sheet of the present invention is a solar cell adhesive sheet comprising an ethylene copolymer and a predetermined amount of organic peroxide, and has a total of four or more of either one or both of acryloyl groups and methacryloyl groups. Since it has a configuration containing a functional monomer, a solar cell module is manufactured by laminating and integrating a solar cell element and a protective material laminated and integrated on the upper and lower surfaces of the solar cell element via an adhesive sheet for solar cell. In the thermocompression bonding step, the polyfunctional monomer can easily form a crosslink of the ethylene-based copolymer, and can provide a crosslink structure necessary for expressing sufficient heat resistance with a small amount of organic peroxide. it can.

  Therefore, according to the solar cell adhesive sheet of the present invention, when manufacturing a solar cell module, the amount of low molecular weight compounds generated along with the decomposition of the organic peroxide is suppressed, and the bubble bulging caused by the low molecular weight compounds is suppressed. Therefore, the solar cell element and the protective material can be firmly bonded and integrated.

  In addition, as described above, the adhesive sheet for solar cells of the present invention has a small amount of organic peroxide contained in the sheet, and does not cause bubble expansion when manufacturing a solar cell module. The crimping step can be performed at a high temperature and can be completed in a short time, and thus the productivity of the solar cell module can be improved.

  Furthermore, since the solar cell adhesive sheet of the present invention has a sufficient cross-linked structure and has excellent heat resistance, it can reliably obtain excellent adhesiveness over a long period of time. The solar cell module has excellent durability.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Examples 1-3, Comparative Examples 1-4)
100 parts by weight of an ethylene-vinyl acetate copolymer (vinyl acetate content: 25% by weight, melt flow rate: 20 g / 10 min), a predetermined amount of dicumyl peroxide (1 minute) shown in Table 1 as an organic peroxide Half-life temperature: 175 ° C., t-butyl peroxy-2-ethylhexyl monocarbonate (1 minute half-life temperature: 161 ° C.) or t-butyl peroxybenzoate (1 minute half-life temperature: 167 ° C.), polyfunctional monomer As shown in Table 1, a predetermined amount of dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol tetraacrylate or triallyl isocyanurate, 2,6-di-t-butyl-4-methylphenol as an antioxidant 1 part by weight, 2-hydroxy-4-methyl as UV absorber After 0.3 parts by weight of xylbenzophenone and 0.2 parts by weight of 3-glycidoxypropyltrimethoxysilane as a silane coupling agent are supplied to the extruder and melt-kneaded at 120 ° C., they are attached to the tip of the extruder. The adhesive sheet for solar cells having a thickness of 0.6 mm and a width of 1250 mm was obtained by extrusion from a T-die.

  Gel fraction after heating the obtained adhesive sheet for solar cell under the heating conditions described later, and the appearance and temperature and humidity resistance cycle test of the solar cell module produced using the obtained adhesive sheet for solar cell The results were evaluated as shown below, and the results are shown in Table 1.

(Gel fraction)
The obtained solar cell adhesive sheet was hot-pressed in the thickness direction of the sheet under the heating conditions shown in Table 1, and then 0.2 g of a test piece was cut out from the solar cell adhesive sheet.

The test piece is immersed in 50 ml of xylene at 110 ° C. for 12 hours, the insoluble matter is filtered through a 200-mesh wire mesh, the residue on the wire mesh is vacuum dried, and the weight A (g) of the dry residue is measured. The gel fraction was calculated using the following formula.
Gel fraction (% by weight) = 100 × A / 0.2

(Appearance of solar cell module)
A transparent flat glass is laminated on the upper surface of a silicon semiconductor wafer for solar cells via an adhesive sheet for solar cells, and a polyvinyl fluoride sheet is laminated on the lower surface of the silicon semiconductor wafer for solar cells via an adhesive sheet for solar cells. A laminate was prepared.

  This laminated body was thermocompression bonded under the heating conditions shown in Table 1 under a reduced pressure of 1.3 kPa, and the transparent flat glass was laminated and integrated on the upper surface of the silicon semiconductor wafer for solar cells via an adhesive sheet for solar cells, and A solar cell module in which a polyvinyl fluoride sheet was laminated and integrated on the lower surface via a solar cell adhesive sheet was produced. The appearance of the obtained solar cell module was visually observed to determine the presence or absence of bubbles and peeling.

(Temperature and humidity cycle test)
A solar cell module was produced in the same manner as the method for measuring the appearance of the solar cell module.
According to JIS C 8917 temperature and humidity cycle test A-2, the obtained solar cell module was heated from room temperature to + 85 ° C. at a heating rate of 105 ° C./1.2 hours. Then, after being left in an atmosphere of + 85 ° C. and 85% RH for 2.5 hours, the temperature was lowered to −20 ° C. at a temperature lowering rate of 105 ° C./1.2 hours, held at −20 ° C. for 1 hour, The process of heating up to + 85 ° C. at a rate of temperature increase of 105 ° C./1.2 hours was taken as one cycle, and the appearance of the solar cell module after 10 cycles was visually observed to determine the presence or absence of abnormalities such as discoloration and peeling. .

Claims (2)

A solar cell adhesive sheet comprising 100 parts by weight of an ethylene copolymer and 0.05 to 0.5 parts by weight of an organic peroxide, and has a total of 4 or more of either one or both of acryloyl groups and methacryloyl groups. The adhesive sheet for solar cells characterized by containing the polyfunctional monomer. The polyfunctional monomer having a total of 4 or more of either one or both of acryloyl group and methacryloyl group is contained in an amount of 0.05 to 2 parts by weight based on 100 parts by weight of the ethylene copolymer. The adhesive sheet for solar cells according to claim 1.