WO2013008455A1

WO2013008455A1 - Solar cell backside protective sheet and solar cell

Info

Publication number: WO2013008455A1
Application number: PCT/JP2012/004458
Authority: WO
Inventors: 猿渡　昌隆; 安川　秀範; 裕紀杉; 島田　健志郎
Original assignee: 東洋アルミニウム株式会社; 東洋インキＳｃホールディングス株式会社; トーヨーケム株式会社; 東洋モートン株式会社
Priority date: 2011-07-11
Filing date: 2012-07-10
Publication date: 2013-01-17
Also published as: TWI559562B; CN103650156B; KR101871293B1; KR20140040765A; CN103650156A; JP6046620B2; JPWO2013008455A1; TW201304168A

Abstract

Provided is a solar cell backside protective sheet which has excellent long-term reliability and moist heat resistance, and has excellent adhesiveness in low-temperature environments, and also has low cost and excellent coating properties; also provided is a solar cell module. In this solar cell backside protective sheet, an adhesive layer which bonds to at least one surface of the thickest of an outer layer substrate, a middle layer substrate and an inner layer substrate is adhered by means of an adhesive containing: a main component containing linear polyester polyols of a specific configuration, polyester polyurethane polyols and a bisphenol type epoxy resin; and a curing agent containing isocyanurate. The aforementioned adhesive contains 4-12 parts by weight of the solids content of the curing agent per 100 parts by weight of the solids content of the main component.

Description

Solar cell back surface protection sheet and solar cell module

The present invention relates to a solar cell back surface protection sheet used on the back surface of a solar cell module, and a solar cell module including the solar cell back surface protection sheet.

In recent years, photovoltaic power generation that converts light energy into electrical energy by utilizing a quantum effect peculiar to semiconductors has been attracting attention as the head of clean energy. A solar cell module is used for photovoltaic power generation, and a solar cell back surface protection sheet (so-called back sheet) is provided for the purpose of protection and insulation from the back surface.

The solar cell module is required to have a service life of a long period of more than ten years, and the long-term reliability is also required for the backsheet that protects it. In addition, the backsheet is required to have insulation against electricity generated from a power generation element called a cell and good adhesion to a sealing material for sealing the cell. In order to meet these demands, conventionally, back sheets obtained by laminating various resin films and metal foils via an adhesive have been proposed (for example, Patent Documents 1 and 2).
Further, an outdoor polyurethane adhesive containing a polyester polyol or a polyester polyurethane polyol has been proposed (Patent Document 3).

JP 2010-278375 A JP 2009-290201 A JP 2010-043238 A

バック Backsheets are strongly required to have long-term reliability. In order to realize this, the adhesive used for the backsheet is required to have good adhesion and weather resistance that can withstand long-term use. Further, it is required that the adhesive is inexpensive and can be easily applied by a general coating method such as gravure coating or comma coating. Furthermore, it is required to be excellent in wet heat resistance and exhibit an excellent adhesive force even in an environment lower than normal temperature. The conventional backsheet has room for further improvement in these respects.

The present invention has been made in view of the above background, and is excellent in long-term reliability, wet heat resistance, excellent adhesiveness in a low-temperature environment, and further excellent in cost and coating properties. The main object is to provide a sheet and a solar cell module.

As a result of intensive studies to achieve the above object, the present inventor used an adhesive containing a main agent and a curing agent having a specific composition, and a specific amount of the specific curing agent with respect to the main agent. The inventors have found that the above object can be achieved and have completed the present invention.

That is, the solar cell back surface protective sheet according to the present invention includes at least 1) an outer layer base material having weather resistance, 2) an intermediate layer base material, and 3) a seal for sealing a power generation element used in the solar cell module. An adhesive layer composed of a stopper and an inner layer base material having good adhesiveness and joining at least one side of the thickest base material among the outer layer base material, the intermediate layer base material, and the inner layer base material is the following (1) Formed of a main agent containing (3) and an adhesive containing a curing agent of (4) below,
The adhesive has a solid content of 4 to 12 parts by weight based on 100 parts by weight of the main component solids.
(1) a dibasic acid component containing 40 to 70 mol% of an aromatic dibasic acid and 30 to 60 mol% of an aliphatic dibasic acid having 9 to 10 carbon atoms, and an aliphatic dihydric alcohol 30 having 5 or more carbon atoms A linear polyester polyol having a weight average molecular weight of 70,000 to 80,000 obtained by reacting with a dihydric alcohol component containing ˜40 mol%.
(2) a dibasic acid component containing 60 to 80 mol% of an aromatic dibasic acid and 20 to 40 mol% of an aliphatic dibasic acid having 9 to 10 carbon atoms, and an aliphatic dihydric alcohol 70 having 5 or more carbon atoms A polyester polyurethane polyol having a weight average molecular weight of 30,000 to 40,000, which is obtained by reacting a polyester polyol obtained by reacting with a dihydric alcohol component containing ˜80 mol% with an organic diisocyanate.
(3) A bisphenol type epoxy resin having a number average molecular weight of 1,000 to 2,000.
(4) A polyisocyanate having an isocyanurate of isophorone diisocyanate.
The thickness of the thickest substrate is preferably 125 to 350 μm, and the adhesive amount of the adhesive layer in contact with the thickest substrate is in the range of more than 5 g / m ² and 30 g / m ² or less. Is preferred.
Moreover, it is preferable that there are a plurality of the intermediate layer base materials, and at least a part thereof is bonded to each other via the adhesive layer.
The linear polyester polyol is preferably 60 to 80% by weight in a total of 100% by weight of the linear polyester polyol and the polyester polyurethane polyol.

The solar cell module according to the present invention includes the solar cell back surface protective sheet of the above aspect.

According to the solar cell back surface protective sheet of the present invention, the solar cell back surface protective sheet is excellent in long-term reliability and wet heat resistance, and is excellent in adhesiveness in a low-temperature environment, and is excellent in cost and coating properties. And the outstanding effect that a solar cell module can be provided is produced.

It is a figure which shows the layer structure of the solar cell back surface protection sheet produced in the Example. It is a figure which shows the layer structure of the solar cell back surface protection sheet produced by the comparative example.

Hereinafter, the present invention will be described in detail. It goes without saying that other embodiments may also belong to the category of the present invention as long as they match the gist of the present invention. In the present specification, the description “any number A to any number B” means a range larger than the numbers A and A but smaller than the numbers B and B.

The solar cell back surface protective sheet of the present invention includes at least 1) an outer layer base material having weather resistance, 2) an intermediate layer base material, and 3) a sealing material for sealing a power generation element used in a solar cell module; It is comprised from the inner-layer base material which has favorable adhesiveness. In the solar cell back surface protective sheet of the present invention, the adhesive layer for bonding at least one surface of the thickest base material among the outer layer base material, the intermediate layer base material, and the inner layer base material has the following (1) to (3). It is formed with the main ingredient containing this and the adhesive agent containing the hardening | curing agent of following (4). Therefore, within the range that satisfies the above conditions, the solar cell back surface protective sheet of the present invention can also bond the substrates to each other with another adhesive. An inner layer base material is arrange | positioned in the surface layer by the side of a light emitting element among solar cell back surface protection sheets, and an outer layer base material is arrange | positioned in the position most spaced apart from the light emitting element. The intermediate layer base material may be singular or plural. The solar cell back surface protection sheet is required to have voltage resistance. It is preferable to provide the voltage resistance mainly to the intermediate layer base material. However, when a plurality of intermediate layer base materials are provided, all of the intermediate layer base materials may not have voltage resistance. In the following description, the term “adhesive” refers to the adhesive of the present invention containing the main agent containing the following (1) to (3) and the curing agent (4) below.

In the solar cell back surface protective sheet of the present invention, the thickness of the thickest substrate among the outer layer substrate, the intermediate layer substrate, and the inner layer substrate is preferably 125 to 350 μm. Moreover, it is preferable that the adhesive amount after drying of the adhesive layer in contact with the thickest substrate is in the range of more than 5 g / m ² and 30 g / m ² or less. The reason will be described later. The thickest substrate may be any of an outer layer substrate, an intermediate layer substrate, and an inner layer substrate, but the intermediate layer substrate is preferably the thickest substrate. In addition, when the outer layer base material or the inner layer base material is the thickest base material, the application surface of the above-mentioned adhesive amount is one surface, but when the intermediate layer base material is the thickest base material, the intermediate layer base material It is preferable that at least one of the two joint surfaces of the material satisfies the above coating conditions. In the case where the intermediate layer base material is the thickest base material, it is more preferable that the adhesive layer of the present invention has a range of more than 5 g / m ² and 30 g / m ² or less at the two joining surfaces. . Moreover, the said adhesive agent can be applied suitably also to joining of base materials other than the thickest base material. That is, the adhesive of the present invention can be suitably used for all the joining of each base material (for example, plastic film, metal foil, etc.) constituting the solar cell back surface protective sheet.

The adhesive of the present invention is a polyurethane adhesive containing a main agent and a curing agent. The adhesive may be a two-component mixed adhesive that mixes the main agent and the curing agent at the time of use, or may be a one-component adhesive in which the main agent and the curing agent are mixed in advance. . Moreover, the type which mixes a several main ingredient and / or several hardening | curing agent at the time of use may be sufficient.

The main component of the adhesive is (1) a dibasic acid component containing 40 to 70 mol% of an aromatic dibasic acid and 30 to 60 mol% of an aliphatic dibasic acid having 9 to 10 carbon atoms, and 5 or more carbon atoms. A linear polyester polyol having a weight average molecular weight of 70,000 to 80,000 obtained by reacting with a dihydric alcohol component containing 30 to 40 mol% of an aliphatic dihydric alcohol, and (2) an aromatic dibasic acid A dibasic acid component containing 60 to 80 mol% and an aliphatic dibasic acid having 9 to 10 carbon atoms and 20 to 40 mol%, and a divalent compound containing 70 to 80 mol% of an aliphatic dihydric alcohol having 5 or more carbon atoms A polyester polyurethane polyol having a weight average molecular weight of 30,000 to 40,000 obtained by reacting an organic diisocyanate with a polyester polyol obtained by reacting with an alcohol component, and (3) a number average Molecular weight contains bisphenol type epoxy resin of 1,000-2,000.
The curing agent for the adhesive contains (4) a polyisocyanate having an isocyanurate of isophorone diisocyanate. The adhesive of the present invention contains 4 to 12 parts by weight of the solid content of the curing agent with respect to 100 parts by weight of the solid content of the main agent. More preferably, it is 6 to 12 parts by weight, and still more preferably 8 to 10 parts by weight.

[(1) Linear polyester polyol]
The linear polyester polyol (hereinafter also simply referred to as “polyester polyol”) used in the present invention comprises 40 to 70 mol% of an aromatic dibasic acid and 30 to 60 mol% of an aliphatic dibasic acid having 9 to 10 carbon atoms. The dibasic acid component contained is reacted with a dihydric alcohol component containing 30 to 40 mol% of an aliphatic dihydric alcohol having 5 or more carbon atoms. As long as the above conditions are satisfied, a dibasic acid or a polyhydric alcohol component having another structure may be included.

Examples of the dibasic acid and its ester compound include isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, phthalic anhydride, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride Examples thereof include acid, maleic anhydride, itaconic anhydride and ester compounds thereof.

In the present invention, these can be used in appropriate combinations, but the aromatic dibasic acid is 40 to 70 mol% (preferably 50 to 60 mol%) and the aliphatic dibasic having 9 to 10 carbon atoms based on the total amount of the dibasic acid. The acids are combined so as to be 30 to 60 mol% (preferably 40 to 50 mol%).

If the amount of aromatic dibasic acid used is less than 40 mol%, sufficient heat resistance and viscoelasticity may not be obtained. Moreover, by setting it as 70 mol% or less, adhesive force can be exhibited more effectively. Further, by setting the aliphatic dibasic acid having 9 to 10 carbon atoms to 30 mol% or more, the ester bond degree of the polyester polyol is made appropriate, the hydrolysis base point is suppressed, and long-term wet heat resistance is more effectively brought out. be able to. Further, by setting the aliphatic dibasic acid having 9 to 10 carbon atoms to 60 mol% or less, it is possible to appropriately adjust the heat resistance and viscoelasticity and to more effectively express the adhesive force.

Among the above exemplified compounds, the aromatic dibasic acid is preferably terephthalic acid, dimethyl terephthalate, isophthalic acid, or phthalic anhydride from the viewpoint of reactivity in the transesterification reaction. As the aliphatic dibasic acid having 9 to 10 carbon atoms, azelaic acid having 9 carbon atoms and sebacic acid having 10 carbon atoms are preferable from the viewpoint of high lipophilicity, hydrophobicity, and suppression of water absorption into the polymer. .

Specific examples of the polyhydric alcohol include, for example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-butylene glycol, 1,4-cyclohexane. Examples include dimethanol, 1,9-nanonediol, and 3-methyl-1,5-pentanediol. These may be used singly or in combination of two or more, but an aliphatic dihydric alcohol having 5 or more carbon atoms is used in a proportion of 30 to 40 mol% (preferably 32 to 38 mol%) based on the total amount of polyhydric alcohol.

In the dihydric alcohol component, by controlling the proportion of aliphatic dihydric alcohol having 5 or more carbon atoms to 30 mol% or more, it is possible to suppress the increase in hydrolysis base point by making the ester bond degree of the polyester polyol appropriate, and long-term moisture resistance Thermal properties can be extracted more effectively. Moreover, the solubility to the organic solvent of a product becomes favorable by making the ratio of an aliphatic dihydric alcohol 40 mol% or less, and the applicability | paintability of an adhesive agent becomes favorable.

Among the above exemplified compounds, as aliphatic dihydric alcohols having 5 or more carbon atoms, neopentyl glycol having 5 carbon atoms and having improved side chain stability and 3-methyl-1,5-pentane having 6 carbon atoms Diol, 1,6-hexanediol and the like that are highly lipophilic and hydrophobic and suppress water absorption into the polymer are preferred.

The weight average molecular weight of the polyester polyol is 70,000 to 80,000 from the viewpoint of ensuring cohesive strength, stretchability and adhesive strength. Among these, from the viewpoint of the solubility of the resin, the viscosity, and the coating property (handleability) of the adhesive, it is more preferably 72,000-78,000.
In the present invention, the number average molecular weight was measured using GPC (gel permeation chromatography) “HPC-8020” manufactured by Tosoh Corporation. GPC is liquid chromatography that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on the difference in molecular size. In the measurement of the present invention, “LF-604” (manufactured by Showa Denko KK: GPC column for rapid analysis: 6MMID × 150MM size) is connected in series to the column, the flow rate is 0.6 ML / MIN, and the column temperature is 40. It carried out on the conditions of (degreeC) and the determination of the weight average molecular weight (Mw) was performed in polystyrene conversion.

[(2) Polyester polyurethane polyol]
The polyester polyurethane polyol used in the present invention comprises 60 to 80 mol% (preferably 65 to 75 mol%) of an aromatic dibasic acid and 20 to 40 mol% (preferably 25 to 40 mol%) of an aliphatic dibasic acid having 9 to 10 carbon atoms. 35 mol%) and a dihydric alcohol component containing 70 to 80 mol% (preferably 72 to 78 mol%) of an aliphatic dihydric alcohol having 5 or more carbon atoms. The polyester polyol obtained is reacted with an organic diisocyanate.

By making the amount of aromatic dibasic acid used 60 mol% or more, heat resistance and viscoelasticity can be obtained effectively. On the other hand, the adhesive force can be more effectively exhibited by setting it to 80 mol% or less. Further, by setting the aliphatic dibasic acid having 9 to 10 carbon atoms to 20 mol% or more, the ester bond degree of the polyester polyol is made appropriate, the hydrolysis base point is suppressed, and long-term wet heat resistance is more effectively brought out. be able to. Further, by making the aliphatic dibasic acid having 9 to 10 carbon atoms 40 mol% or less, it is possible to appropriately adjust the heat resistance and viscoelasticity and to exhibit the adhesive force more effectively. It is done. Furthermore, by controlling the proportion of aliphatic dihydric alcohols having 5 or more carbon atoms to 70 mol% or more, the ester bond degree of the polyester polyol is appropriately controlled to prevent the hydrolysis base point from increasing, and the long-term moist heat resistance is more effective. Can be withdrawn. Moreover, the solubility to the organic solvent of a product becomes favorable by making the ratio of aliphatic dihydric alcohol 80 mol% or less, and the applicability | paintability of an adhesive agent becomes favorable.

Here, the explanation of the aromatic dibasic acid, the aliphatic dibasic acid and the aliphatic dihydric alcohol having 5 or more carbon atoms is the same as described above.

Organic diisocyanate is not particularly limited. Specific examples include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and the like. It is done. These can be used alone or in combination of two or more. From the viewpoint of reducing yellowing of the adhesive over time, it is preferable to use an aliphatic or alicyclic isocyanate compound for the urethane cross-linking part.

By using the polyester polyurethane polyol and the polyester polyol in combination, the degree of ester bond (described later) as the whole polyol component can be lowered, and as a result, the hydrolysis starting point can be reduced and the heat and moisture resistance can be increased.

The weight average molecular weight of the polyester polyurethane polyol is 30,000 to 40,000 in view of adjusting the viscosity as an adhesive in consideration of the large weight average molecular weight of the polyester polyol and the high viscosity. Among these, 32,000 to 38,000 is more preferable.

[(3) Bisphenol type epoxy resin]
The bisphenol type epoxy resin used in the present invention preferably has a number average molecular weight of 1,000 to 2,000 and an epoxy equivalent of 500 to 1,000 g / eq. By including the bisphenol type epoxy resin, it is expected that the epoxy group reacts with the carboxyl group generated by hydrolysis of the ester bond to suppress the decrease in molecular weight due to the hydrophobicity of the bisphenol skeleton.

Among the bisphenol-type epoxy resins, bisphenol A-type epoxy resins and bisphenol F-type epoxy resins are preferable from the viewpoint of maintaining shear strength, and these can be used alone or in combination of two or more.

The number average molecular weight of the bisphenol type epoxy resin may be 1,000 to 2,000 from the viewpoints of adjusting the heat resistance and viscoelasticity of the cured adhesive film and adjusting the solution viscosity. If the number average molecular weight of the bisphenol-type epoxy resin is less than 1,000, sufficient heat resistance may not be obtained. Moreover, adhesive force can be more effectively exhibited by a number average molecular weight being 2,000 or less. In the present invention, the use of a high molecular weight polyol is expected to reduce the viscosity of the adhesive solution by using a low molecular weight epoxy resin, thereby improving the coating property. However, the number average molecular weight is 2,000. By making it below, the solution viscosity can be effectively reduced. The number average molecular weight of the bisphenol type epoxy resin is preferably 1,200 to 1,800 from the balance between wet heat resistance and low temperature adhesive strength.

The content of the bisphenol-type epoxy resin is preferably 50% by weight or less in 100% by weight of the main agent solid content from the viewpoint of adjusting the viscoelasticity of the cured adhesive film, and more preferably 20 to 40% by weight in consideration of adhesive strength. .

[Main agent containing the above components]
The composition ratio of the polyester polyol and the polyester polyurethane polyol (hereinafter collectively referred to as “polyol component”) is not particularly limited, but the polyester polyol is used in an amount of 60 to 80% by weight in a total of 100% by weight of the polyol component. It is preferable to use 65 to 75% by weight. By setting the ratio of the polyester polyol in the polyol component to 80% by weight or less, the heat and humidity resistance can be more effectively brought out. On the other hand, when the proportion of the polyester polyol is 60% by weight or more, the adhesive strength at low temperatures can be improved. Accordingly, the ratio of the polyester polyol in the polyol component is preferably in the range of 60 to 80% by weight from the balance between wet heat resistance and low temperature adhesive force.

In the present invention, when the ratio of ester bond by reaction of carboxyl group and hydroxyl group in the polyol component (reaction ratio of carboxyl group and hydroxyl group is 1: 1) is expressed as the degree of ester bond (mol / 100 g) in the molecule. It is desirable to design to be less than 1. That is, by setting the degree of ester bond to less than 1, the ratio of ester bonds can be reduced to increase hydrolysis resistance, and deterioration of adhesive strength over time can be further suppressed to improve long-term wet heat resistance. In this respect, the present invention uses a dibasic acid having a large molecular weight of 9 to 10 and a polyhydric alcohol having a large molecular weight of 5 or more as a dibasic acid, so in unit weight (in 100 g). The ester bond degree of becomes small.

In particular, considering the compatibility of the adhesive strength at room temperature and the adhesive strength at high temperatures (80 to 150 ° C., etc.), the ester bond degree of the polyol component is preferably in the range of 0.75 to 0.99. Such an ester bond degree can be achieved within the range of the ratio of the aromatic dibasic acid in the dibasic acid component and the carbon number of the polyhydric alcohol in the adhesive used in the present invention. Further, the acid value (mgKOH / g) of the polyol component is preferably 5 or less, and more preferably 2 or less.

In addition to the polyol component and the bisphenol-type epoxy resin, the main component of the adhesive can contain any additive as long as the effects of the present invention are not impaired. Examples of the additive include a silane coupling agent, a reaction accelerator, a leveling agent, and an antifoaming agent.

Examples of the silane coupling agent include trialkoxysilanes having a vinyl group such as vinyltrimethoxysilane and vinyltriethoxysilane, 3-aminopropyltriethoxysilane, and N- (2-aminoethyl) 3-aminopropyltrimethoxy. Trialkoxysilanes having amino groups such as silane; glycidyl groups such as 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and 3-glycidoxypropyltriethoxysilane; The trialkoxysilane which has is mentioned. These silane coupling agents can be used alone or in combination of two or more.

The amount of the silane coupling agent added is preferably 0.5 to 5% by weight, more preferably 1 to 3% by weight, based on the total amount of the main agent. If it is less than 0.5% by weight, the effect of improving the adhesive strength by adding the silane coupling agent is poor, and even if it exceeds 5% by weight, no further improvement in performance is observed.

Examples of the reaction accelerator include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimaleate; 1,8-diaza-bicyclo (5,4,0) undecene-7,1,5 -Tertiary amines such as diazabicyclo (4,3,0) nonene-5,6-dibutylamino-1,8-diazabicyclo (5,4,0) undecene-7; reactive tertiary amines such as triethanolamine 1 type, or 2 or more types of reaction accelerators selected from these groups can be used.

Examples of leveling agents include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl group-containing polydimethylsiloxane, polyetherester-modified hydroxyl group-containing polydimethylsiloxane, and acrylic copolymers. Methacrylic copolymer, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic acid alkyl ester copolymer, lecithin and the like.

Examples of the antifoaming agent include silicone resins, silicone solutions, copolymers of alkyl vinyl ethers, acrylic acid alkyl esters, and methacrylic acid alkyl esters.

[Curing agent]
The curing agent used in the present invention includes a polyisocyanate having an isocyanurate of isophorone diisocyanate. This isocyanurate has a long pot life after mixing with the main agent, good solution stability, and long-term wet heat resistance of the adhesive. The isocyanurate content is 50 to 100% by weight in the polyisocyanate. In addition, isocyanurate means the trimer of diisocyanate.

In the present invention, the curing agent can contain any polyisocyanate in an amount of less than 50% by weight in addition to the above polyisocyanate. However, in terms of suppressing yellowing of the adhesive, it is preferably a low yellowing type aliphatic or alicyclic polyisocyanate.

Specifically, one or more selected from low molecular weight polyisocyanate, polyurethane isocyanate obtained by reacting low molecular weight polyisocyanate with water or polyhydric alcohol, dimer of low molecular weight isocyanate, etc. may be used in combination. it can.

Examples of the low molecular weight polyisocyanate include hexamethylene diisocyanate, phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, diphenylmethane-4,4-diisocyanate, 3,3-dimethyl-4,4-biphenylene diisocyanate, Examples include dicyclohexylmethane-4,4-diisocyanate, isophorone diisocyanate, and mixtures thereof. Examples of the polyhydric alcohol to be reacted with these low molecular weight polyisocyanates include those described above as raw materials for the polyester polyol in the previous stage for producing the polyester polyurethane polyol.

The curing agent may optionally be a known oxazoline compound, for example, 2,5-dimethyl-2-oxazoline, 2,2- (1,4-butylene) -bis (2), as long as the effects of the present invention are not impaired. -Oxazoline) or hydrazide compounds such as isophthalic acid dihydrazide, sebacic acid dihydrazide, adipic acid dihydrazide and the like.

As described above, the main agent and the curing agent have a hardener solid content of 4 to 12 parts by weight with respect to 100 parts by weight of the main agent solid content. By setting the amount of the curing agent to 4 parts by weight or more, the wet heat resistance can be improved more effectively. Moreover, the adhesive force in low temperature can be more effectively exhibited by making a hardening | curing agent into 12 weight part or less. Therefore, the amount of the curing agent is 4 to 12 parts by weight from the balance between wet heat resistance and adhesive strength at low temperature.
Further, it is preferable that the isocyanate group in the curing agent is blended so that the equivalent ratio is 1.0 to 10.0 with respect to the total of the hydroxyl groups of the polyester polyol and the polyester polyurethane polyol in the main agent. Considering the disappearance of isocyanate groups due to the reaction with water and the aging time after lamination, it is preferably 3.0 to 7.0.

[Solar cell back surface protection sheet]
Examples of the weather resistant outer layer base material 1) include polyolefin resins such as polyethylene (PE) (high density polyethylene, low density polyethylene, linear low density polyethylene), polypropylene (PP), polybutene, and (meth) acrylic. Resin, polyvinyl chloride resin, polystyrene resin, polyvinylidene chloride resin, saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, polycarbonate resin, fluororesin, polyvinylidene fluoride resin, polyvinyl fluoride resin Polyvinyl acetate resins, acetal resins, polyester resins (polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate), polyamide resins, and other various resin films or sheets can be used. These resin films or sheets may be stretched in a uniaxial or biaxial direction.

In the outer layer base material 1), a white pigment such as titanium oxide or barium sulfate or a black pigment such as carbon may be mixed for the purpose of absorbing or reflecting ultraviolet rays. Moreover, you may mix well-known additives, such as well-known ultraviolet absorbers other than a coloring pigment, a moisture absorber (drying agent), an oxygen absorber, and antioxidant.

The thickness of the outer layer base material 1) is not limited, but can be, for example, about 10 to 350 μm, preferably about 10 to 100 μm.

As the intermediate layer base material 2), for example, polyethylene terephthalate resin, ethylene trifluoroethylene film, and other various resin films or sheets can be used. These resin films or sheets may be stretched in a uniaxial or biaxial direction.

The thickness of the intermediate layer substrate 2) is not limited, but is preferably 30 to 350 μm, more preferably 100 to 350 μm, still more preferably 125 to 350 μm, and particularly preferably 150 to 300 μm. preferable.
In order to protect the solar cell module from damage due to voltage application, the solar cell back surface protection sheet may be required to have a partial discharge voltage of 600 V or 1,000 V depending on the power generation capacity of the solar cell. . Since the partial discharge voltage depends on the thickness of the solar cell back surface protection sheet, the base material constituting the solar cell back surface protection sheet is required to be thicker than the base material constituting the food packaging laminate. Among the base materials constituting the solar cell back surface protection sheet, the intermediate layer base material 2) responsible for voltage resistance mainly bears “thickness”. Therefore, the thickness of the intermediate layer base material 2) is preferably 100 to 350 μm as described above. On the other hand, when the base material which comprises a solar cell back surface protection sheet becomes thick, a price will become high. Therefore, the thickness of the intermediate layer base material 2) is preferably 125 to 350 μm.

For example, polyethylene (PE) (high-density polyethylene, low-density polyethylene, linear low-density polyethylene) is used as a sealing material for sealing a power generating element used in a solar cell module and an inner layer base material having good adhesiveness. ), Polyolefin resin such as polypropylene (PP), polybutene, (meth) acrylic resin, polyvinyl chloride resin, polystyrene resin, polyvinylidene chloride resin, saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, Polycarbonate resin, fluororesin, polyvinyl fluoride resin, polyvinyl acetate resin, acetal resin, polyester resin (polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate), polyamide resin, and other various types Resin film It is possible to use a solid or sheet. These resin films or sheets may be stretched in a uniaxial or biaxial direction.

The thickness of the inner layer base material is not limited, but is, for example, 10 to 350 μm, preferably about 30 to 250 μm, more preferably 30 to 100 μm.

Further, in the present invention, at least the above three layers may be used, and other arbitrary layers known as the constitution of the solar cell back surface protective sheet may be further laminated. For example, a solar cell back surface protective sheet comprising an olefin layer of 125 to 350 μm as an inner layer substrate, a polyethylene terephthalate film layer of 125 to 350 μm as an intermediate layer substrate, and a fluorine layer of 10 to 100 μm as an outer layer substrate can be exemplified.

As described above, at least one side of the thickest substrate among the outer layer base material 1), the intermediate layer base material 2), and the inner layer base material 3) is joined by the adhesive. The bonding method is not particularly limited, but an adhesive is applied to one side of one laminated base material by gravure printing, comma coating, dry laminating, etc., and the solvent is stripped, and then bonded to the other laminated base material, Alternatively, it may be cured under heating. The thickness of the thickest base material among the outer layer base material, the intermediate layer base material, and the inner layer base material and the amount of the adhesive layer after drying can be appropriately designed. The thickness of the thickest base material is 125 to 350 μm. The amount of the adhesive layer after drying applied to at least one surface of the laminate substrate is preferably more than 5 g / m ² and not more than 30 g / m ² as described above. More preferably, by more than 5 g / ^{m 2,} and at 25 g / ^{m 2} or less, more preferably, 6 g / ^{m 2} or more and 20 g / ^{m 2} or less. Since the specific gravity of the adhesive excluding the organic solvent is about 1.1 g / cm ³ , 1.1 g / m ² can be converted to about 1 μm / m ² . Therefore, the amount of the adhesive layer is about 4.5 to 27.3 μm in terms of thickness. By making the amount of the adhesive layer after drying exceed 5 g / m ² , it is possible to more effectively reduce the influence of hydrolysis on the adhesive layer. In addition, by setting the amount of the adhesive layer to 30 g / m ² or less, the organic solvent in the adhesive can be easily volatilized at the time of drying before being bonded to the base material.

When the solar cell back surface protective sheet of the present invention is manufactured by industrially laminating a plurality of base materials and then completing the curing of the adhesive layer in a state of being wound in a roll shape, the present inventors have conducted intensive studies. As a result, it was found that industrial productivity can be further improved in the following embodiments. That is, the thickness of the thickest substrate among the outer layer substrate, the intermediate layer substrate, and the inner layer substrate is 125 to 350 μm, and the amount of the adhesive layer is more than 5 g / m ² and not more than 30 g / m ² Thus, the laminate is wound into a roll in the adhesive development process after applying the adhesive while effectively satisfying the electrical insulation with respect to the light emitting elements disposed in the solar cell module. However, it has been found that floating (hereinafter referred to as tunneling) in the roll-shaped laminate can be more effectively suppressed. As a result, it is possible to provide a solar cell back surface protective sheet with high industrial productivity in the adhesiveness development process after the application of the adhesive.

The solar cell back surface protective sheet of the present invention is installed in a solar cell module by adhering the inner layer base material side with a sealing material for sealing the power generation element of the solar cell module. The configuration of the solar cell module of the present invention is not particularly limited, and a known solar cell module can be used.

According to the solar cell back surface protective sheet of the present invention, at least one surface of the thickest base material among the outer layer base material, the intermediate layer base material, and the interior base material is bonded by the specific adhesive described above. Adhesives with good agent performance and weather resistance that can withstand long-term use are obtained. As a result, a solar cell back surface protective sheet with high long-term reliability can be provided. In addition, the adhesive used in the present invention is inexpensive and has a characteristic that it can be easily applied by a general coating method such as gravure coating or comma coating. Furthermore, the solar cell back surface protective sheet of the present invention is resistant to moist heat by using an adhesive in which the ratio of the main agent and the curing agent is 4 to 12 parts by weight of the curing agent solid content with respect to 100 parts by weight of the main agent solid content. Excellent adhesion at low temperatures. That is, it is possible to provide a solar cell back surface protective sheet that is excellent in long-term reliability and wet heat resistance, is excellent in adhesiveness in a low temperature environment, and is excellent in cost and coating properties.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples. In the examples, parts refer to parts by weight.

Example 1
25 kg of titanium oxide particles were added to 100 kg of low density polyethylene resin (LDPE) having a density of 0.91 g / cm ³ and kneaded sufficiently to prepare an LDPE resin composition. Subsequently, it was extruded with an extruder to produce a first film having a thickness of 50 μm.

Next, a 250 μm thick polyethylene terephthalate film (manufactured by Toyobo Co., Ltd .: Toyobo Ester Film E5102) was prepared as a second film having excellent electrical insulation. Further, a PVF film (manufactured by DuPont, 38 μm) was prepared as the third film. These films were bonded by a dry laminating method using an adhesive for dry laminating.
The adhesive for dry lamination is as follows.

Charge 119.5 parts of dimethyl terephthalate, 92.2 parts of ethylene glycol, 72.2 parts of neopentyl glycol and 0.02 part of zinc acetate to a reactor, and heat to 160-210 ° C. with stirring under a nitrogen stream. A transesterification reaction was performed. After distillation of 97% of the theoretical amount of methanol, 93.0 parts of isophthalic acid and 130.0 parts of azelaic acid were charged and heated to 160 to 270 ° C. for esterification reaction. The reaction vessel was gradually depressurized to 1 to 2 Torr, and when the acid value became 0.8 mgKOH / g or less, the reaction under reduced pressure was stopped to obtain a polyester polyol having a weight average molecular weight of 75,000. A resin solution in which the concentration of the polyester polyol obtained by dilution with ethyl acetate was 50% was designated as polyol A.

A reactor was charged with 94.2 parts of neopentyl glycol, 91.7 parts of 1,6-hexanediol, 37.6 parts of ethylene glycol, 211.5 parts of isophthalic acid, and 122.9 parts of sebacic acid. The esterification reaction was carried out by heating to 160 to 250 ° C. with stirring. The reaction vessel was gradually depressurized to 1 to 2 Torr, and when the acid value became 1 mgKOH / g or less, the reaction under reduced pressure was stopped to obtain a polyester polyol in the previous stage having a weight average molecular weight of 6,000. To the obtained polyester polyol, 22.9 parts of isophorone diisocyanate was gradually added and reacted by heating at 100 to 150 ° C. After reacting for 6 hours, a polyester polyurethane polyol having a weight average molecular weight of 35,000 was obtained. Polyol B was a resin solution in which the concentration of the polyester polyurethane polyol obtained by dilution with ethyl acetate was 50%.

Polyol A 100 parts (solid content 50 parts), polyol B 40 parts (solid content 20 parts), number average molecular weight 1,200 and epoxy equivalent 600 g / eq of bisphenol A type epoxy resin 30 parts and epoxy group-containing organosilane coupling agent 3 A resin solution with a solid content of 50% obtained by heating, dissolving and mixing the parts at 70 ° C. and diluting with ethyl acetate was used as the main agent 1.
The total ester bond degree of polyol A and polyol B in the main agent 1 is 0.89 when determined as follows.
That is, assuming that the reaction is performed with dibasic acid: dihydric alcohol = 1: 1 (molar ratio) which is a raw material of each polyol, the number of ester bonds is set to 1. The average molecular weight (equivalent) of the dibasic acid and dihydric alcohol in the polyol is calculated. The ester bond degree is defined as the number of ester bonds (subtracting dehydration during the reaction) divided by the molecular weight.
Formula) Degree of ester bond = 1 / molecular weight value (unit / g) = 100 / molecular weight value (unit / 100g)
Since the ester bond degree of polyol A is 0.93 and the ester bond of polyol B is 0.79, the ester bond degree of main agent 1 is
(0.93 × 100 + 0.79 × 40) / (100 + 40) = 0.89
It becomes.

Curing agent 1 was obtained by diluting a trimer of isophorone diisocyanate with ethyl acetate to give a resin solution having a solid content of 50%.

A solution in which the main agent 1 and the curing agent 1 were blended at a solid content of 100: 12 (weight ratio) and diluted with ethyl acetate to a solid content of 30% was used as an adhesive solution.

The adhesive solution was adjusted so that the amount of the adhesive layer after drying was 10 g / m ^2, and the first to third films were laminated to obtain a laminate of 210 mm × 295 mm (A4 size). . After the lamination, with the 210 mm × 295 mm (A4 size) laminate being placed almost horizontally, aging was performed at 60 ° C. for 7 days to cure the adhesive, thereby producing a back protective sheet for solar cells.
The adhesive strength (25 ° C., 15 ° C.), the adhesive strength after the weather resistance test (25 ° C.), and tunneling were evaluated by the methods described later.

Examples 2-4
The solar system is the same as in Example 1 except that 100 parts of the main agent 1 is 10 parts (Example 2), 6 parts (Example 3), and 4 parts (Example 4) of the curing agent 1, respectively. A battery back protection sheet was prepared and evaluated.

Comparative Example 1
A solar cell back surface protective sheet was prepared and evaluated in the same manner as in Example 1 except that the solid content of the curing agent 1 was changed to 14 parts with respect to the main component 1 having a solid content of 100 parts.

Examples 5 to 11
Using the adhesive solution of Example 2, the amount of the adhesive layer after drying was 3 g / m ² (Example 5), 5 g / m ² (Example 6), 15 g / m ² (Example 7), and 20 g. / M ² (Example 8), 25 g / m ² (Example 9), 30 g / m ² (Example 10), 35 g / m ² (Comparative Example 11) The back surface protection sheet for solar cells was produced and evaluated in the same manner as described above.

Example 12
A 100 μm thick polyethylene terephthalate film (manufactured by Toyobo Co., Ltd .: Toyobo Ester Film E5100) was used in place of the 250 μm thick polyethylene terephthalate film as the second film, and the same adhesive solution as in Example 2 was used. And the solar cell back surface protection sheet was produced and evaluated like Example 1 except having adjusted so that the hardening | curing agent 1 might be 10 weight part.

Comparative Example 2, Examples 13-16
The type of resin film used was the same as in Example 1, and the adhesive used was changed.
Polyol A 40 parts (solid content 20 parts), polyol B 100 parts (solid content 50 parts), number average molecular weight 1,200 and epoxy equivalent 600 g / eq of bisphenol A type epoxy resin 30 parts and epoxy group-containing organosilane coupling agent 3 A resin solution having a solid content of 50% obtained by heating, dissolving and mixing the parts at 70 ° C. and diluting with ethyl acetate was used as the main agent 2.

For 100 parts of main agent 2, curing agent 1 is 14 parts (Comparative Example 2), 12 parts (Example 13), 10 parts (Example 14), 6 parts (Example 15), 4 parts (implemented). Except for Example 16), a back protective sheet for solar cell was prepared and evaluated in the same manner as in Example 1.

Examples 17 and 18
Instead of an epoxy resin having a number average molecular weight of 1,200, a bisphenol A type epoxy resin having a number average molecular weight of 1,400 and an epoxy equivalent of 700 g / eq (Example 17), a number average molecular weight of 1,000 and an epoxy equivalent of 500 g / eq A back protective sheet for solar cell was prepared and evaluated in the same manner as in Example 2 except that 30 parts of each of bisphenol A type epoxy resins (Example 18) were used.

Comparative Example 3
A resin solution having a solid content of 50% was used as the main agent 3 in the same manner as in Comparative Example 1, except that the polyol A was 120 parts (solid content 60 parts) and the polyol B was 20 parts (solid content 10 parts).
Except that the base material 3 and the curing agent 1 were blended at a ratio of 100: 14 (weight ratio), diluted with ethyl acetate and adjusted to a solid content of 30%, and used as an adhesive solution, the sun was applied as in Example 1. A battery back protection sheet was prepared and evaluated.

Comparative Example 4 (Polyol B not used)
A solar cell back surface protective sheet was prepared and evaluated in the same manner as in Comparative Example 1 except that polyol B was not used and polyol A was changed to 140 parts (solid content: 70 parts).

Comparative Example 5 (no use of polyol A)
A solar cell back surface protective sheet was prepared and evaluated in the same manner as in Comparative Example 1 except that polyol A was not used and polyol B was changed to 140 parts (solid content: 70 parts).

Comparative Example 6 (Different curing agents)
Dilute isophorone diisocyanate trimer with ethyl acetate to cure 50% solids resin solution instead of tolylene diisocyanate TMP adduct with ethyl acetate to cure 50% solids resin solution Agent 2 was obtained. Moreover, 14 parts of solid content of the hardening | curing agent 2 was used with respect to the main ingredient 1 of solid content 100 parts. Except this, it carried out similarly to Example 1, and produced and evaluated the back surface protection sheet for solar cells.

Comparative Examples 7 and 8 (polyol A is not used)
Charge 99.6 parts of dimethyl terephthalate, 92.2 parts of ethylene glycol, 72.2 parts of neopentyl glycol, 0.02 part of zinc acetate and heat to 160-210 ° C with stirring under a nitrogen stream. After transesterification, 97% of the theoretical amount of methanol was distilled off, and then 77.5 parts of isophthalic acid and 129.6 parts of adipic acid were charged and heated to 160 to 240 ° C. to carry out the esterification reaction. The reaction can was gradually depressurized to 1-2 torr. The reaction under reduced pressure was stopped when the acid value was 0.8 mgKOH / g or less to obtain a polyester polyol (degree of ester bond 0.90 mol / 100 g) having a weight average molecular weight of 60,000. A resin solution having a solid content of 50% obtained by dilution with ethyl acetate was designated as polyol C.
Instead of 100 parts polyol A, 100 parts polyol C was used. Moreover, 14 parts (comparative example 7) or 10 parts (comparative example 8) of solid content of the hardening | curing agent 1 were used with respect to the main ingredient 1 of solid content 100 parts. Except this, it carried out similarly to Example 1, and produced and evaluated the back surface protection sheet for solar cells.
The polyol C has a weight average molecular weight of 60,000 and does not contain an aliphatic dibasic acid having 9 to 10 carbon atoms, and therefore does not correspond to the polyester polyol A in the present invention.

Comparative Example 9 (does not contain bisphenol type epoxy resin)
40 parts of polyol A (20 parts of solid content), 100 parts of polyol B (50 parts of solid content) and 3 parts of an epoxy group-containing organosilane coupling agent were heated, dissolved and mixed at 70 ° C., and diluted with ethyl acetate. A resin solution having a solid content of 50% was used as the main agent 4. Further, 14 parts of the curing agent 1 was used with respect to 100 parts of the main agent 4. Except this, it carried out similarly to Example 1, and produced and evaluated the back surface protection sheet for solar cells.

Comparative Example 10
A back protective sheet for solar cells in the same manner as in Example 2 except that 30 parts of bisphenol A type epoxy resin having a number average molecular weight of 800 and an epoxy equivalent of 400 g / eq was used instead of the epoxy resin having a number average molecular weight of 1,200. Were made and evaluated.

Hereinafter, the evaluation method will be described.
<25 ° C initial adhesive strength, 15 ° C adhesive strength>
The solar cell back surface protective sheet (sample) produced in Examples and Comparative Examples was cut into a width of 15 mm and a length of about 150 mm, and the adhesive strength (= peel strength) was measured according to a JIS K6854T type peel test. The peeling strength was measured by peeling each resin film layer 180 ° at a tensile rate of 100 mm / min in an atmosphere of 25 ° C. and 15 ° C. using a testing machine, and evaluated according to the following criteria.
◎: 12N / 15mm or more ○: 9N / 15mm or more and less than 12N △: 6N / 15mm or more and less than 9N ×: Less than 6N / 15mm

<Adhesive strength after weather resistance test>
Dump heat (test conditions 85 ° C., 85%), 1,000 hours later, 2,000 hours later (corresponding to an actual outdoor exposure state of 10 years or more) in an atmosphere of 25 ° C. in the same manner as before the test. The peel strength retention rate (%) was calculated with the initial value being 100%, and evaluated according to the following criteria.
◎: Strength retention of 95% or more after 2,000 hours ○: Strength retention of 85% or more and less than 95% after 2,000 hours Δ: Strength retention of 60% or more and less than 85% after 2,000 hours ×: 60 after 2,000 hours Less than% strength retention

<Tunneling (floating of roll-shaped solar cell back surface protection sheet)>
In Examples and Comparative Examples, the first film to the third film are laminated, and a 1 m wide long laminate is wound around the outer periphery of a paper tube having an outer diameter (diameter) of 170 mm for a length of 10 m, and rolled. A layered laminate was obtained. The roll-shaped laminate was erected with the winding core in the vertical direction, and aged at 60 ° C. for 7 days to obtain a solar cell back surface protective sheet. The presence or absence of lifting of the roll-shaped solar cell back surface protective sheet was observed. Evaluation was made based on the following criteria by the number of places where the float occurred. “Floating” means that a gap is formed between the adhesive layer and the substrate.
○: No floating △: Within 5 floating points ×: 5 or more floating points

<Partial discharge>
The measurement was performed in air and in oil by a method based on the IEC partial discharge test (IEC61730-2, IEC606664-1).
○: 1,000 V or more measured in air and in oil △: 1,000 V or more measured only in oil ×: Less than 1,000 V in any measuring method Partial discharge evaluation is Although it is not necessarily an essential property for the solar cell back surface protective sheet, it is good in any sample except Example 12 using a 100 μm thick polyethylene terephthalate film instead of a 250 μm polyethylene terephthalate film as the second film. Results were obtained.

This application claims priority based on Japanese Patent Application No. 2011-153066 filed on July 11, 2011, the entire disclosure of which is incorporated herein.

Claims

At least 1) an outer layer base material having weather resistance, 2) an intermediate layer base material, and 3) an encapsulant for sealing a power generation element used in a solar cell module and an inner layer base material having good adhesiveness Configured,
An adhesive layer that joins at least one surface of the thickest base material among the outer layer base material, the intermediate layer base material, and the inner layer base material contains a main agent containing the following (1) to (3); ) Of an adhesive containing a curing agent,
The solar cell back surface protective sheet, wherein the adhesive contains 4 to 12 parts by weight of the solid content of the curing agent with respect to 100 parts by weight of the solid content of the main agent.
(1) a dibasic acid component containing 40 to 70 mol% of an aromatic dibasic acid and 30 to 60 mol% of an aliphatic dibasic acid having 9 to 10 carbon atoms, and an aliphatic dihydric alcohol 30 having 5 or more carbon atoms A linear polyester polyol having a weight average molecular weight of 70,000 to 80,000 obtained by reacting with a dihydric alcohol component containing ˜40 mol%.
(2) a dibasic acid component containing 60 to 80 mol% of an aromatic dibasic acid and 20 to 40 mol% of an aliphatic dibasic acid having 9 to 10 carbon atoms, and an aliphatic dihydric alcohol 70 having 5 or more carbon atoms A polyester polyurethane polyol having a weight average molecular weight of 30,000 to 40,000, which is obtained by reacting a polyester polyol obtained by reacting with a dihydric alcohol component containing ˜80 mol% with an organic diisocyanate.
(3) A bisphenol type epoxy resin having a number average molecular weight of 1,000 to 2,000.
(4) A polyisocyanate having an isocyanurate of isophorone diisocyanate.
2. The thickness of the thickest substrate is 125 to 350 μm, and the adhesive amount of the adhesive layer in contact with the thickest substrate is in the range of more than 5 g / m 2 and 30 g / m 2 or less. Solar cell back surface protection sheet.
The solar cell back surface protective sheet according to claim 1 or 2, wherein there are a plurality of the intermediate layer base materials, and at least some of them are adhered to each other via the adhesive layer.
The solar cell back surface protection according to any one of claims 1 to 3, wherein the linear polyester polyol is 60 to 80 wt% in a total of 100 wt% of the linear polyester polyol and the polyester polyurethane polyol. Sheet.
A solar cell module comprising the solar cell back surface protective sheet according to any one of claims 1 to 4.