JP2007305634A - Adhesive sheet for solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive sheet for solar cells that can be formed to a uniform thickness stably without allowing an ethylene-based copolymer to stay in a T die or to be solidified in film formation. <P>SOLUTION: In the adhesive sheet A for solar cells, not less than three sheet layers 1, 1, and the like made of an ethylene-based copolymer and an organic peroxide are laminated integrally. A cross-linking aid is contained in both outermost sheet layers 1a, 1b in the sheet layers 1, 1, and the like by 0-0.1 pts.wt. to 100 pts.wt. of the ethylene-based copolymer. A cross-linking aid is contained in intermediate sheet layers 1c, 1c, and the like in the sheet layers 1a, 1b, and the like by 0.1-3 pts.wt. to 100 pts.wt. of the ethylene-based copolymer. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 a solar cell module is produced.

  A solar cell module consisting of a silicon or selenium semiconductor wafer is under reduced pressure on a laminate obtained by overlaying an upper transparent protective material on the upper surface of a solar cell element with adhesive sheets laminated on both sides and a lower substrate protective material on the lower surface. It is manufactured by heating while deaeration 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 for a solar cell used in such a solar cell module, for example, a sealing composition in which a silane coupling agent and an organic peroxide are mixed with an ethylene-vinyl acetate copolymer in Patent Document 1 is used. A sheet formed from a product is proposed, and it is described that 0.1 to 10 parts of a polyfunctional crosslinking aid is used in the sealing composition. In addition, as a method for forming a sheet from the sealing composition, a method for forming an extrusion film from a T-die disposed at the tip of an extruder is disclosed.

  Patent Document 2 discloses a protective sheet for a solar cell module made of an ethylene copolymer containing an organic peroxide. As the organic peroxide, dialkyl peroxide (A), alkyl peroxyester, and peroxy A solar comprising a mixture of at least one peroxide (B) selected from the group consisting of ketals at a weight ratio of (A) / (B) of 10/90 to 90/10 A protection sheet for battery modules has been proposed, and it is further described that a crosslinking aid may be added in order to increase the crosslinking rate and crosslinking efficiency. And as a method of forming this solar cell module protective sheet, a resin composition comprising an ethylene copolymer, an organic peroxide and a crosslinking aid is melt-kneaded at 80 to 130 ° C. with an extruder, and the extruder A method for forming an extrusion film from a T-die disposed at the tip of the film is disclosed.

  Here, when a solar cell adhesive sheet such as a sheet obtained from the resin composition and a solar cell module protective sheet is formed using a T die, the temperature in the T die is 80 to 110 ° C. Then, the melt viscosity of the resin composition becomes high, and the resin composition tends to stay in the T-die. Then, since the contact time between the resin composition developed in a sheet form in the T die and the inner surface of the T die having a high temperature becomes longer, the organic peroxide in the resin composition in contact with the inner surface of the T die is reduced. It decomposes and the crosslinking of the resin proceeds. Therefore, the melt viscosity of the resin composition is further increased, and the resin composition stays in the T-die, so that a sheet having a uniform thickness cannot be formed. In addition, since the resin is cross-linked in this way and the melt viscosity of the resin composition is increased, the residence time of the resin composition in the T-die is further increased, so that the cross-linking of the resin further proceeds, There was also a situation in which the resin solidified in the T-die and the sheet could not be extruded.

  On the other hand, when forming the adhesive sheet for solar cells as described above, if the temperature in the T die is 110 to 130 ° C., the temperature on the inner surface of the T die is high. The developed resin composition is heated by the inner surface of the T die, the organic peroxide in the resin composition in contact with the inner surface of the T die is decomposed, and the crosslinking of the resin proceeds. Therefore, the melt viscosity of the resin composition is further increased, and the resin composition stays in the T-die, resulting in a problem that a sheet having a uniform thickness cannot be obtained. In addition, if the resin composition stays in the T die, the contact time between the resin composition developed in the form of a sheet and the inner surface of the T die becomes longer, and the crosslinking of the resin further proceeds. There was also a situation in which the sheet could not be extruded due to solidification.

Japanese Patent Publication No. 6-35575 JP 11-26791 A

  The present invention provides an adhesive sheet for a solar cell that can stably form a uniform thickness without causing an ethylene copolymer to stay or solidify in a T-die during film formation.

  As shown in FIG. 1, the solar cell adhesive sheet A of the present invention is formed by laminating and integrating three or more sheet layers 1, 1... Made of an ethylene-based copolymer and an organic peroxide. It is an adhesive sheet for solar cells, and the cross-linking aid is 0 to 0.1 with respect to 100 parts by weight of the ethylene-based copolymer on the outermost sheet layers 1a and 1b on both sides of the sheet layers 1 and. Are contained in parts by weight and the remaining sheet layers 1c, 1c, other than the outermost sheet layers 1a, 1b on both sides of the sheet layers 1, 1. In contrast, 0.1 to 3 parts by weight of a crosslinking aid is contained.

  The ethylene-based copolymer used for the sheet layer 1 is a copolymer of ethylene and a copolymerizable monomer that can be copolymerized with ethylene, and such a 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.

  On the other hand, if the amount of the copolymerizable monomer contained in the ethylene-based copolymer is small, the resulting solar cell adhesive sheet may have insufficient transparency, and the power generation efficiency of the solar cell element may be reduced. 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.

  When the melt flow rate of the ethylene copolymer is small, the film-forming stability of the solar cell adhesive sheet may be reduced, whereas when the melt flow rate is large, the mechanical strength of the solar cell adhesive sheet is insufficient. 1 to 100 g / 10 min is preferable. The melt flow rate of the ethylene copolymer in the present invention refers to a value measured under conditions of a temperature of 190 ° C. and a load of 2.16 kgf (21.18 N) in accordance with JIS K7210.

  Here, the solar cell adhesive sheet A is used by being interposed 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 by thermocompression bonding under reduced pressure. The solar cell element and the upper and lower protective material are bonded. The ethylene-based copolymer is excellent in transparency and adhesiveness among transparency, adhesiveness and heat resistance particularly required for an adhesive sheet for solar cells, but has low heat resistance, and is a solar cell module. There is a problem that it deforms under high temperature conditions during the manufacturing process. Therefore, a crosslinking assistant and an organic peroxide are included in the ethylene copolymer constituting the solar cell adhesive sheet A, and the ethylene copolymer is crosslinked by heat applied during the production of the solar cell module. The heat resistance of the solar cell adhesive sheet A is improved.

  However, in the film forming process of the solar cell adhesive sheet A as will be described later, when the ethylene copolymer is crosslinked, the ethylene copolymer stays in the T-die and the thickness is uniform. The adhesive sheet cannot be obtained, or the ethylene-based copolymer is solidified in the T-die and the solar battery adhesive sheet cannot be formed.

  Therefore, at the time of film formation, the two-side outermost sheet layers 1a and 1b of the adhesive sheet A for solar cells, which are easily brought into direct contact with the inner surface of the T die at the time of film formation, should not contain a crosslinking assistant, Alternatively, by reducing the amount of the crosslinking aid contained in the outermost sheet layers 1a and 1b on both sides, the crosslinking of the ethylene copolymer during the formation of the solar cell adhesive sheet A can be prevented, and the solar cell While maintaining the film-forming stability of the adhesive sheet A for the use, while increasing the amount of the crosslinking aid in the remaining sheet layers 1c, 1c... Except for the outermost sheet layers 1a, 1b on both sides. The ethylene copolymer is sufficiently cross-linked at the time of manufacturing the battery module to impart heat resistance to the entire solar cell adhesive sheet A.

  And as a crosslinking adjuvant contained in the said sheet layer 1, the polyfunctional monomer which has 2 or more of an allyl group, a vinyl group, an acryloyl group, or a methacryloyl group is mentioned, These stabilize a polymer radical and crosslink efficiency And the concentration of cross-linking points promotes gel formation. Examples of the polyfunctional monomer include diallyl phthalate, diallyl itaconate, diallyl maleate, triallyl isocyanurate, triallyl cyanurate, triallyl phosphate, divinylbenzene; 1,6-hexanediol di (meth) acrylate. (Meth) such as ethylene oxide modified bisphenol A di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ε-caprolactone modified dipentaerythritol Examples include acrylates and alkyl-modified dipentaerythritol (meth) acrylates, which may be used alone or in combination of two or more.

  Further, when the amount of the crosslinking aid contained in the outermost sheet layers 1a and 1b on both sides of the solar cell adhesive sheet A is large, the ethylene copolymer is crosslinked in the T-die and the melt viscosity becomes high, The ethylene-based copolymer stays in the T-die and it becomes impossible to obtain an adhesive sheet for a solar cell with a uniform thickness, or the ethylene-based copolymer is cross-linked and solidified in the T-die, and the solar cell. Since it becomes impossible to extrude the adhesive sheet for use from the T-die, it is limited to 0 to 0.1 parts by weight with respect to 100 parts by weight of the ethylene copolymer, and preferably 0 to 0.08 parts by weight.

  The amount of the crosslinking aid contained in the remaining sheet layers (hereinafter referred to as “intermediate sheet layers”) 1c, 1c... Excluding the outermost sheet layers 1a, 1b on both sides of the adhesive sheet A for solar cells. Is less, the crosslinking of the ethylene-based copolymer becomes insufficient, the heat resistance of the adhesive sheet for solar cells is insufficient, and the durability of the resulting solar cell module is lowered, while on the other hand, Since the film-forming stability and mechanical strength of the battery adhesive sheet are lowered, the amount is limited to 0.1 to 3 parts by weight with respect to 100 parts by weight of the ethylene copolymer, and 0.2 to 2.5 weights. Part is preferred.

  Further, as the organic peroxide used for the sheet layer 1, when an organic peroxide having a one-hour half-life temperature of less than 100 ° C. is used, when the ethylene copolymer is melt-kneaded with an extruder, an organic peroxide is used. The peroxide decomposes and the crosslinking of the ethylene copolymer proceeds in the extruder or in the T die, and the ethylene copolymer tends to stay in the extruder or in the T die. It may not be possible to obtain an adhesive sheet for solar cells, or the ethylene copolymer retained in the T die may be cross-linked and solidified, and the solar cell adhesive sheet may not be extruded from the T die. The one-hour half-life temperature is preferably 100 ° C. or higher, more preferably 105 to 140 ° C.

  Examples of the organic peroxide having a 1-hour half-life temperature of 100 ° C. or higher include dicumyl peroxide (136 ° C.), t-butylperoxy-2-ethylhexyl monocarbonate (119 ° C.), and t-butylperoxy. Benzoate (125 ° C.), 1,1-di (t-butylperoxy) -2-methylcyclohexane (102 ° C.), 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane ( 106 ° C.), 1,1-di (t-hexylperoxy) cyclohexane (107 ° C.), 1,1-di (t-butylperoxy) cyclohexane (111 ° C.), 2,2-di (4,4- Di (t-butylperoxy) cyclohexyl) propane (114 ° C.), t-hexylperoxyisopropyl monocarbonate (115 ° C.), t-butyl peroxy Oxyisopropyl monocarbonate (118 ° C.), t-butyl peroxylaurate (118 ° C.), 2,5-dimethyl-2,5-di (benzoylperoxy) hexane (119 ° C.), t-hexyl peroxybenzoate ( 119 ° C), t-butylperoxymaleic acid (119 ° C), t-butylperoxy-3,5,5-trimethylhexanoate (119 ° C), t-butylperoxyacetate (121 ° C), 2, 2-di (t-butylperoxy) butane (122 ° C.), n-butyl-4,4-di (t-butylperoxy) valerate (127 ° C.), di-t-hexyl peroxide (136 ° C.), t-Butylcumyl peroxide (137 ° C.), di (2-t-butylperoxyisopropyl) benzene (138 ° C.), 2,5-dimethyl -2,5-di (t-butylperoxy) hexane (138 ° C), di-t-butylperoxide (144 ° C), 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne -3 (150 ° C.), p-menthane hydroperoxide (151 ° C.), etc., may be used alone or in combination of two or more. The temperature in the parenthesis represents a 1 hour half-life temperature.

  And when there is little quantity of the organic peroxide contained in the said sheet layer 1, the bridge | crosslinking of an ethylene-type copolymer will become inadequate, the heat resistance of the adhesive sheet for solar cells is insufficient, and the solar cell obtained On the other hand, the durability of the module may be reduced. On the other hand, if the organic peroxide is decomposed during the thermocompression bonding process when manufacturing the solar cell module, low molecular weight compounds such as acetone and carbon dioxide are present. Occurring in large quantities, bubble expansion occurs between the facing surfaces of the solar cell element and the protective material, the adhesion between the solar cell element and the protective material is lowered, and the protective function of the solar cell element may be reduced. Therefore, 0.3-3 weight part is preferable with respect to 100 weight part of ethylene-based copolymer, and 0.4-2.5 weight part is more preferable. In addition, although content of the organic peroxide of any one layer among the said sheet layers 1 should just be in the said range, the organic peroxide in all the layers 1, 1, ... of the said sheet layer 1 is sufficient. The content of is preferably in the above range.

  Furthermore, a coupling agent can be added to the sheet layer 1 for the purpose of enhancing the adhesiveness of the solar cell adhesive sheet A, as long as the physical properties of the solar cell adhesive sheet A are not impaired. As such a coupling agent, a silane coupling agent having one or more functional groups selected from the group consisting of an amino group, a glycidyl group, a methacryloxy group, and a mercapto group is preferably used. Examples include 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-mercaptopropyltrimethoxysilane. May be.

  In addition, each sheet layer 1 of the solar cell adhesive sheet A of the present invention has a light stabilizer, 2,6-di-t-butyl-4, if necessary, as long as the physical properties are not impaired. Additives such as antioxidants such as methylphenol and ultraviolet absorbers such as 2-hydroxy-4-methoxybenzophenone may be added.

  If the thickness of each of the outermost sheet layers 1a, 1b on both sides of the solar cell adhesive sheet A is thin, the film formation stability of the solar cell adhesive sheet may be insufficient. Since the heat resistance of the adhesive sheet for use may be insufficient and the durability of the resulting solar cell module may be lowered, it is preferably 5 to 30% of the total thickness of the adhesive sheet A for solar cells. In addition, although the thickness of the outermost sheet layer 1a and the outermost sheet layer 1b in the said adhesive sheet A for solar cells may not be the same thickness, it is preferable that it is the same thickness.

  Next, the film forming method of the adhesive sheet A for solar cells of the present invention will be described. For film formation of the adhesive sheet for solar cells of the present invention, two or more extruders can be formed by a multilayer extrusion apparatus or the like in which one extruder is connected to one T die via one feed block, for example, A multi-layer extrusion apparatus having extruders corresponding to the number of layers of the solar cell adhesive sheet to be formed is prepared. The two extruders of this multi-layer extrusion apparatus are equipped with ethylene-based co-polymers for both outermost sheet layers 1a and 1b. While supplying a polymer, a crosslinking aid, an organic peroxide, and a resin composition comprising a coupling agent and other additives added as necessary, the intermediate sheet layers 1c, 1c,. Supply a resin composition comprising an ethylene-based copolymer, a crosslinking aid and an organic peroxide, and a coupling agent and other additives added as necessary, and the resin composition in each extruder Melt kneaded and fed to the feed block The outermost sheet layer 1a, the intermediate sheet layers 1c, 1c,... And the outermost sheet layer 1b are extruded into a sheet shape from the T die disposed at the tip of the feed block so as to be laminated in this order. Film formation can be performed by cooling, solidifying and winding the extruded molten sheet with a cooling roll. When there are multiple sheet layers made of the same resin composition, melt kneading is performed with one extruder, and the molten resin composition extruded from the extruder is branched into a predetermined number of layers before feeding. The film may be supplied to the block.

  Moreover, in the film forming process of the adhesive sheet A for solar cells, if the temperature at which the resin composition of the sheet layer 1 is melt-kneaded in the extruder is high, the organic peroxide in the resin composition is decomposed. Since the crosslinking of the ethylene copolymer proceeds, the temperature is preferably 10 ° C. or more lower than the one-hour half-life temperature of the organic peroxide used, and two or more organic peroxides are used. In some cases, the organic peroxide used is preferably at a temperature that is at least 10 ° C. lower than the one-hour half-life temperature of the lowest organic peroxide.

  Further, the solar cell adhesive sheet A is preferably embossed on the surface in order to improve the deaeration in the thermocompression bonding step when the solar cell module is manufactured. In addition, as a method of embossing the surface of the adhesive sheet A for solar cells, a known method is used. For example, a molten sheet immediately after being extruded from a T die is used as an embossing roll having an embossed pattern on the surface. And a rubber roll disposed opposite to the embossing roll, pressing the embossing roll against the molten sheet, and embossing the surface of the solar cell adhesive sheet A. The once produced solar cell adhesive sheet A may be heated again to a molten state and embossed as described above.

  And as a method of manufacturing a solar cell module using the adhesive sheet A for solar cells of this invention, while laminating | stacking an upper transparent protective agent via the adhesive sheet A for solar cells on the upper surface of a solar cell element, a solar cell. A laminated body in which the lower substrate protective material is laminated on the lower surface of the element via the solar cell adhesive sheet A, and this laminated body is heated and pressure-bonded under reduced pressure, so that the upper and lower surfaces of the solar cell element are applied to the solar cell. A solar cell module in which protective materials are laminated and integrated via the adhesive sheet A can be obtained.

  In addition, as a heating condition at the time of thermocompression bonding the above laminated body under reduced pressure, in order to reliably decompose the organic peroxide in the adhesive sheet for solar cells and to sufficiently crosslink the ethylene-based copolymer The organic peroxide used is preferably heated at a temperature 20 ° C. or more higher than the one-hour half-life temperature of the organic peroxide used for 5 to 10 minutes, and when using two or more organic peroxides, the organic peroxide used is It is preferable to heat 5 to 10 minutes at a temperature that is 20 ° C. or more higher than the one-hour half-life temperature of the highest organic peroxide.

  And when the gel fraction of the solar cell adhesive sheet A after the thermocompression bonding is low, the heat resistance of the solar cell adhesive sheet is insufficient, and the durability of the resulting solar cell module may be reduced. Therefore, it is preferably 70% by weight or more.

  The adhesive sheet for solar cells of the present invention is an adhesive sheet for solar cells in which three or more sheet layers composed of an ethylene-based copolymer and an organic peroxide are laminated and integrated. The outermost sheet layers on both sides contain 0 to 0.1 parts by weight of a crosslinking aid with respect to 100 parts by weight of the ethylene copolymer, and the remaining sheets other than the outermost sheet layers on both sides of the sheet layer Since the layer contains 0.1 to 3 parts by weight of a crosslinking aid with respect to 100 parts by weight of the ethylene-based copolymer, when forming the solar cell adhesive sheet, The ethylene copolymer does not crosslink and stay in the T-die or solidify. Therefore, the solar cell adhesive sheet has a uniform thickness, and the solar cell element and the protective material are connected to the solar cell. Through the battery adhesive sheet It is possible to crimp integrated into.

  Further, the remaining sheet layer excluding the outermost sheets on both sides of the solar cell adhesive sheet contains a sufficient amount of cross-linking aid, and the solar cell adhesive sheet is sufficiently heated by the heat applied during the production of the solar cell module. Is imparted with a cross-linked structure to improve heat resistance. Therefore, the adhesive sheet for solar cells of the present invention reliably maintains excellent adhesion over a long period of time even when used outdoors where the temperature is high, and the resulting 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 to 3, Comparative Example 1)
A three-layer coextrusion device is prepared in which three extruders are connected to one T-die via one feed block, and two of these extruders are used for the outermost sheet layers 1a and 1b on both sides. The remaining one machine is for the intermediate sheet layer 1c, and two extruders for the outermost sheet layers 1a and 1b on both sides are fed into an ethylene-vinyl acetate copolymer (vinyl acetate content: 25% by weight, melt flow rate: 20 g). / 10 minutes) 100 parts by weight of a predetermined amount of organic peroxide (dicumyl peroxide, t-butylperoxy-2-ethylhexyl monocarbonate, 2,5-dimethyl-2,5-di ( t-butylperoxy) hexane), crosslinking aid (triallyl isocyanurate, diallyl phthalate) and coupling agent (3-glycidoxypropyltrimethoxysilane), and 2,6-di-t-butyl- 4-me While supplying a resin composition comprising 0.1 part by weight of tilphenol and 0.3 part by weight of 2-hydroxy-4-methoxybenzophenone, an ethylene-vinyl acetate copolymer is fed into one extruder for the intermediate sheet layer 1c. 100 parts by weight of a combination (vinyl acetate content: 25% by weight, melt flow rate: 20 g / 10 min), a predetermined amount of organic peroxide (dicumyl peroxide, t-butylperoxy-2-l) shown in Table 1 Ethyl hexyl monocarbonate, t-butyl peroxybenzoate), crosslinking aid (triallyl isocyanurate, trimethylolpropane triacrylate, diallyl phthalate) and coupling agent (3-glycidoxypropyltrimethoxysilane), and 2 , 6-di-tert-butyl-4-methylphenol and 2-hydroxy-4-methyl A resin composition consisting of 0.3 parts by weight of xylbenzophenone was supplied and melt-kneaded at a temperature 15 ° C. lower than the one-hour half-life temperature of the organic peroxide used in each of three extruders. The molten resin composition is supplied to one feed block from the extruder of the machine, and the outermost sheet layer 1a, the intermediate sheet layer 1c, and the outermost sheet layer 1b are provided from the T die disposed at the tip of the feed block. A three-layer adhesive sheet A for a solar cell having a thickness of 0.6 mm and a width of 1250 mm was formed by coextrusion so that the layers were sequentially laminated and integrated so that the thickness ratio was 25:50:25.

  And when it continued forming the extrusion sheet | seat A for solar cells over 24 hours as mentioned above, in Examples 1-3, even if 24 hours pass after starting film formation, it is extrusion. Although the ethylene-vinyl acetate copolymer did not stay in the machine or in the T-die, it was possible to stably form the solar cell adhesive sheet A having a uniform thickness. The thickness of both end portions in the width direction of the adhesive sheet A becomes thinner as time passes, and after 5 hours from the start of film formation, the ethylene-vinyl acetate copolymer solidified at both end portions of the sheet extrusion port of the T-die The gel is formed on both outermost sheet layers 1a and 1b of the obtained solar cell adhesive sheet A, and the solar cell adhesive sheet has a uniform thickness. A cannot be obtained.

(Comparative Examples 2 and 3)
Table 1 shows an ethylene-vinyl acetate copolymer (vinyl acetate content: 25% by weight, melt flow rate: 20 g / 10 min), 100 parts by weight in a single-layer extrusion apparatus having a T-die disposed at the tip of the extruder. A predetermined amount of organic peroxide (dicumyl peroxide, t-butylperoxybenzoate), a crosslinking aid (triallyl isocyanurate, diallyl phthalate) and a coupling agent (3-glycidoxypropyltrimethoxy) Silane) and 0.1 part by weight of 2,6-di-t-butyl-4-methylphenol and 0.3 part by weight of 2-hydroxy-4-methoxybenzophenone. After melt-kneading at a temperature 15 ° C. lower than the half-life time, it is extruded into a sheet from a T-die disposed at the tip of the extruder, and has a thickness of 0.6 mm and a width of 1250 mm. An adhesive sheet for a solar cell of the first layer was formed.

  Then, when the solar cell adhesive sheet was continuously formed by extrusion for 24 hours or more as described above, in Comparative Example 3, even after 24 hours had elapsed from the start of film formation, the inside of the extruder or T Although the ethylene-vinyl acetate copolymer did not stay in the die, a solar cell adhesive sheet having a uniform thickness could be formed stably. In Comparative Example 2, the width of the solar cell adhesive sheet was The thickness of both ends in the direction decreases with time, and after 4 hours from the start of film formation, the solidified ethylene-vinyl acetate copolymer is clogged at both ends of the sheet extrusion port of the T die. Can be visually confirmed, and a gel is generated in the obtained adhesive sheet for solar cells, so that an adhesive sheet for solar cells with a uniform thickness cannot be obtained.

  For the solar cell adhesive sheets obtained in Examples and Comparative Examples, the gel fraction before and after crosslinking and the temperature and humidity cycle test were measured in the following manner, and the results are shown in Table 1.

  In Table 1, the types and contents of the organic peroxide, the crosslinking aid and the coupling agent in the solar cell adhesive sheets of Comparative Example 2 and Comparative Example 3 consisting of one layer are the same as those in “Intermediate Sheet Layer 1c”. It described in the column. The temperature in parentheses described after the organic peroxide compound name in Table 1 indicates the 1-hour half-life temperature of the organic peroxide.

(Gel fraction before crosslinking of adhesive sheet for solar cell)
A solar cell adhesive sheet obtained 1 hour and 24 hours after the start of film formation was prepared. In the solar cell adhesive sheet, a portion (indicated as “sheet end” in Table 1) spaced from the edge in the width direction by 5 cm toward the center along the width direction and a center portion in the width direction (in Table 1, “ About 0.2 g of a test piece was cut out from each other. The exact balance value of this test piece was S (g).

Next, 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 W (g of dry residue) ) And the gel fraction was calculated using the following formula (1). In Comparative Example 1 and Comparative Example 2, since the solar cell adhesive sheet 24 hours after the start of film formation was not obtained, the solar cell adhesive obtained 1 hour after the start of film formation. The gel fraction was measured using only the sheet.
Gel fraction (% by weight) = 100 × W / S (1)

(Gel fraction after crosslinking of solar cell adhesive sheet)
1 hour after the start of film formation, the solar cell adhesive sheet was crosslinked at the heating temperature and heating time shown in the column of “Heating conditions when the sheet was crosslinked” in Table 1, and the sun after crosslinking A test piece was cut out from the center in the width direction of the battery adhesive sheet, and the gel fraction was measured in the same manner as described above.

(Temperature and humidity cycle test)
A solar cell adhesive sheet obtained 24 hours after the start of film formation was prepared. A plurality of silicon semiconductor wafers for solar cells connected via an interconnector are arranged in a row, and a transparent flat glass is laminated on the upper surface of these silicon semiconductor wafers for solar cells via an adhesive sheet for solar cells. Then, a polyvinyl fluoride sheet was laminated on the lower surface of the solar cell silicon semiconductor wafer via a solar cell adhesive sheet to produce a laminate.

  This laminated body is crosslinked at a heating temperature and a heating time shown in Table 1 under a reduced pressure of 1.3 kPa, and a transparent flat glass is laminated and integrated on the upper surface of the silicon semiconductor wafer for solar cells via an adhesive sheet for solar cells. And the solar cell module by which the polyvinyl fluoride sheet was laminated | stacked and integrated on the lower surface of the silicon semiconductor wafer for solar cells through the adhesive sheet for solar cells was manufactured.

  The solar cell module thus obtained is left for 6 hours under the condition of −20 ° C., and then the temperature is raised from −20 ° C. to 85 ° C. over 1 hour and the humidity is 85% RH. Then, the process was allowed to stand again for 6 hours, and the process of cooling the temperature from 85 ° C. to −20 ° C. over 1 hour was taken as one cycle, and the appearance of the solar cell module after repeating this cycle 10 times was visually observed. The presence or absence of discoloration of the adhesive sheet for solar cells and the presence or absence of peeling between the transparent flat glass and the polyvinyl fluoride sheet and the silicon semiconductor wafer for solar cells were evaluated. In Comparative Example 1 and Comparative Example 2, the solar cell adhesive sheet 24 hours after the start of film formation could not be obtained, and therefore the temperature and humidity resistance cycle test could not be performed.

It is the longitudinal cross-sectional view which showed the adhesive sheet for solar cells of this invention.

Explanation of symbols

1 Sheet layer
1a, 1b Outermost sheet layer
1c Intermediate sheet layer A Solar cell adhesive sheet

Claims (4)

An adhesive sheet for a solar cell in which three or more sheet layers comprising an ethylene copolymer and an organic peroxide are laminated and integrated, and the ethylene copolymer layer is formed on both outermost sheet layers of the sheet layer. The crosslinking aid is contained in an amount of 0 to 0.1 parts by weight with respect to 100 parts by weight of the coalescence, and 100 parts by weight of the ethylene copolymer is added to the remaining sheet layer other than the outermost sheet layers on both sides of the sheet layer. The adhesive sheet for solar cells, wherein 0.1 to 3 parts by weight of a crosslinking aid is contained relative to the solar cell. The adhesive sheet for solar cells according to claim 1, wherein the sheet layer contains 0.3 to 3 parts by weight of an organic peroxide with respect to 100 parts by weight of the ethylene copolymer. The adhesive sheet for solar cells according to claim 1 or 2, wherein the organic peroxide has a one-hour half-life temperature of 100 ° C or higher. 2. The solar cell adhesive sheet according to claim 1, wherein the thickness of each of the outermost sheet layers on both sides is 5 to 30% of the thickness of the entire solar cell adhesive sheet.

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