JP2012056975A - Adhesive composition for laminated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive preventing the floating and separation of a composite sheet at processing and molding of the composite sheet as construction materials for exterior with heat or the like by suppressing the foamability at curing for exhibiting the adhesive force, hardly damaging the appearance when being used as the construction material for the exterior under outdoor exposure, and capable of maintaining the high adhesive strength.SOLUTION: The adhesive composition for the laminated sheet is the one using a main agent and a curing agent, wherein, the main agent contains a polycarbonate urethane polyol (A) having a number-average molecular weight of from 5,000 to 25,000, and the glass transition temperature of from -50 to 10°C, and the curing agent contains a polyisocyanate (B). The proportion of the whole isocyanate groups of the polyisocyanate (B) based on the hydroxy groups of the polyol (A) is 0.5-10 expressed in terms of equivalent ratio, and the number of the terminal functional groups of OH contained in one molecule of the polyol (A) is from 2.1 to 5 in the adhesive composition.

Description

  The present invention relates to an adhesive composition for laminated sheets suitable for outdoor industries used for plastic films, metal foils and the like. In detail, it is related with the adhesive composition used when bonding a plastic film, metal foil, etc., and forming a solar cell back surface protection sheet.

  In recent years, as a multilayer (composite) film used for outdoor industrial applications, for example, barrier materials, roofing materials, solar panel materials, window materials, outdoor flooring materials, lighting protection materials, automobile members, signboards, stickers, etc., aluminum or A laminated film made by bonding a metal foil or metal plate such as copper or steel plate or a metal vapor-deposited film and a plastic film such as polypropylene, polyvinyl chloride, polyester, fluororesin or acrylic resin has been used. It was. As an adhesive for bonding a metal foil, a metal plate or a metal vapor-deposited film and a plastic film in these multilayer films, a polyurethane-based adhesive exhibiting excellent adhesive performance is known.

  Japanese Patent Laid-Open No. 10-218978 (Patent Document 1) discloses a polyester resin in consideration of balance, which can give excellent initial cohesive force and adhesive force, and a polyurethane-based adhesive using the polyester resin. Yes.

  Japanese Laid-Open Patent Publication No. 06-116542 (Patent Document 2) discloses a polyurethane adhesive for forming a composite laminate film for food packaging.

  Furthermore, Japanese Unexamined Patent Application Publication No. 2007-136911 (Patent Document 3) discloses a solar cell back surface sealing sheet provided with an adhesion improving layer made of a polyester resin or a polyester polyurethane resin.

However, when a sheet for sealing the back surface of a solar cell is formed using an adhesive containing a polyester resin or a polyester polyurethane resin as disclosed in Patent Documents 1 to 3, the sheet is sealed for a long time under high temperature and high humidity. If this occurs, hydrolysis occurs in the polyester-based resin or polyester-polyurethane-based resin, resulting in a decrease in adhesive strength, which may cause output deterioration as a solar cell. Further, in the case of a polyester resin or a polyester polyurethane resin, yellowing occurs when exposed to the sun's ultraviolet rays over time.

Japanese Patent Application Laid-Open No. 2003-238930 (Patent Document 4) describes moderate tackiness for accurate positioning in the production process and strong adhesive force required even when the final product is placed under high temperature and high humidity for a long time. As an adhesive material for forming a membrane, such as a touch panel and a keyboard, which is difficult to decrease, an adhesive made of a resin obtained by copolymerizing polycarbonate diol and polyester diol is disclosed.
And it is suggested that a trifunctional or higher functional component is used as a raw material for the polyester diol (paragraph [0027]).

Further, JP 2008-004691 A (Patent Document 5) describes a polyester resin, a polyester polyurethane resin, or a polycarbonate urethane resin in order to improve hydrolysis resistance in a solar cell back surface sealing sheet. , An adhesive containing at least one of a carbodiimide compound, an oxazoline compound, and an epoxy compound is disclosed.
The use of trifunctional isocyanates such as adducts, burettes and isocyanurates formed from diisocyanates is disclosed as a raw material for polyester polyurethane resins or polycarbonate urethane resins (paragraph [0022]).

  Further, WO2009 / 072431 (Patent Document 6) discloses a polyurethane-polyol-based adhesive using polycarbonate diol as a raw material, suggesting application to a solar cell backsheet (paragraphs [0043] to [0053]. Examples, claims [7], [0003] paragraphs, etc.).

By the way, there are various configurations of solar cell back surface protection sheets. For example, there are a type in which various plastic films are laminated, and a type in which various plastic films and a water vapor barrier layer are laminated.
When laminating using a thermosetting adhesive, the adhesive is sandwiched between substrates to be bonded such as a plastic film or a water vapor barrier layer under a high temperature and a high pressure for a very short time. The adhesive layer is sufficiently cured at a temperature of about 0 C for about 3 days to 1 week. While it is preferred to age under a humidity controlled environment, this is not necessarily so. Moreover, the environmental conditions at the time of aging differ for every manufacturer of a solar cell backsheet.
Accordingly, the adhesive is required to be less susceptible to environmental conditions during aging.
However, when the conventional polyurethane-polyol-based adhesive using polycarbonate diol as a raw material is aged under high humidity, bubbles are generated in the adhesive layer. When the water vapor barrier layer is provided, the generation of bubbles in the adhesive layer adjacent to the water vapor barrier layer is significant.
Many solar cell modules are placed in an outdoor environment and assumed to be used for a long time. Accordingly, the solar cell back surface protection sheet constituting the solar cell module is also required to have reliability such as maintaining the initial adhesive force even when exposed to high temperature and high humidity. The solar cell back surface protective sheet in which bubbles are generated in the adhesive layer during aging cannot meet the long-term reliability requirement.

JP-A-10-218978 Japanese Patent Laid-Open No. 06-116542 JP 2007-136911 A JP 2003-238930 A JP 2008-004691 A International Publication WO2009 / 072431 Pamphlet

  An object of the present invention is to provide a solar cell back surface protection sheet that can maintain an initial high adhesive force between various sheet-like members even when exposed to a high temperature and high humidity environment. An object of the present invention is to provide an adhesive composition that can be produced without being generated.

The adhesive for laminated sheets of the present invention is an adhesive composition for laminated sheets using a main agent and a curing agent,
A polycarbonate urethane polyol (A) having a number average molecular weight of 5,000 to 25,000 and a glass transition temperature of −50 to 10 ° C.
The curing agent comprises polyisocyanate (B);
The total isocyanate group of the polyisocyanate (B) is 0.5 to 10 in equivalent ratio with respect to the hydroxyl group of the polyol (A),
The polyol (A) is an adhesive composition for laminated sheets, wherein the number of OH terminal functional groups contained in one molecule is 2.1 to 5.

Moreover, in the adhesive for laminated sheets of the present invention, the total isocyanate group of the polyisocyanate (B) is 1.0 to 2.5 in an equivalent ratio with respect to the hydroxyl group of the polyol (A).
The polyol (A) preferably has 2.0 to 2.5 OH terminal functional groups in one molecule.

  Moreover, in the adhesive for laminated sheets of the present invention, the polyol (A) is a polyfunctional polyol having a polycarbonate diol (A-1), a diisocyanate (A-2), and three or more hydroxyl groups, Or it is suitable that it is a polycarbonate urethane polyol obtained by reaction with the polyfunctional polyisocyanate (A-3) which has three or more isocyanate groups.

Furthermore, the present invention comprises an adhesive layer formed from the adhesive composition for laminated sheets according to any one of the above inventions, and two or more sheet-like members laminated via the adhesive layer. Regarding the back surface protection sheet for solar cells provided,
One of the sheet-like members is preferably a metal foil or a plastic film with a vapor deposition layer formed by vapor-depositing a metal oxide or a nonmetal inorganic oxide on at least one surface of the plastic film.

Furthermore, the present invention provides a solar cell surface protective material (I) located on the light receiving surface side of the solar cell, a solar cell (III), and an ethylene-vinyl acetate copolymer system filler layer located on the non-light receiving surface side of the solar cell. (IV) and a solar cell module comprising the solar cell back surface sealing sheet (V) formed in contact with the non-light-receiving surface side ethylene-vinyl acetate copolymer filler layer,
The solar cell back surface sealing sheet (V) is formed by using the solar cell back surface protection sheet (V ′) according to the invention,
The solar cell module of the present invention may further include a light-receiving surface side ethylene-vinyl acetate copolymer filler layer (II) between the solar cell surface protective material (I) and the solar cell (III). Is preferred.

  According to the present invention, there is provided a back surface protection sheet for solar cells that does not generate bubbles even when aged in a high humidity environment, and can maintain an initial high adhesive force between various sheet-like members even when exposed to a high temperature and high humidity environment. Now available.

The adhesive for laminated sheets of the present invention uses a main agent and a curing agent, and the main agent is polycarbonate urethane polyol (A).
The polycarbonate urethane polyol (A) used in the present invention has a number average molecular weight in the range of 5,000 to 25,000, preferably 8,000 to 15,000.
When the number average molecular weight of the polycarbonate urethane polyol (A) is less than 5,000, the cohesive force of the adhesive layer before reacting sufficiently with the polyisocyanate (B) described later, that is, before aging, is insufficient. By the way, when laminating a plurality of sheet-like members and industrially producing a back protection sheet for solar cells, an adhesive is used between the adherend substrates such as a plastic film and a water vapor barrier layer for a short time under high temperature and pressure. Is wound up in a roll shape, and the core of the roll is turned upside down in an environment of about 40 to 60 ° C. for about 3 days to 1 week. Is fully cured. If the cohesive force of the adhesive layer before aging is insufficient, the laminated sheet-like members are likely to be displaced when wound into a roll shape and during aging after winding, resulting in a high occurrence rate of defective products and poor yield. .

On the other hand, when the number average molecular weight of the polycarbonate urethane polyol (A) is larger than 25,000, the bulk of the adhesive layer itself is large, but the wettability between the adhesive layer and the sheet-like member is low. It is difficult to ensure winding slip and initial adhesive strength.
When the sheet-like members having significantly different thicknesses are bonded together, the initial adhesive strength cannot be ensured particularly when the number average molecular weight of the polycarbonate urethane polyol (A) is larger than 25,000.
A solar cell back surface protective sheet may be formed by pasting together sheet-like members having significantly different thicknesses for various reasons. When pasting sheet-like members having significantly different thicknesses, the curing stress generated in the adhesive layer becomes non-uniform. Furthermore, when the adhesive strength is measured, a large deflection occurs in a laminate in which sheet-like members having significantly different thicknesses are bonded as compared to a laminate in which sheet-like members having the same thickness are bonded.
That is, if the molecular weight of the polycarbonate urethane polyol (A) is too large, the wettability is poor, the cohesive force is large, and a large deflection is applied to the adhesive layer in which the uneven curing stress is generated. In the case of a laminated body in which members are bonded together, it is extremely difficult to ensure the initial adhesive force.

The glass transition temperature of the polycarbonate urethane polyol (A) used in the present invention is −50 to 10 ° C., preferably in the range of −30 to 0 ° C.
When the glass transition temperature of the polycarbonate urethane polyol (A) is lower than −50 ° C., the adhesive strength is remarkably lowered by the heat and humidity resistance test. In addition, sufficient adhesive strength before the aging process cannot be obtained, and there is a risk of winding misalignment during aging. In addition, the elasticity at the initial stage of curing is small, and the generated bubbles cannot escape from the vapor-deposited PET and the adhesive layer, and foaming tends to be observed. On the other hand, when the glass transition temperature of the polycarbonate urethane polyol (A) is higher than 10 ° C., the elasticity at the time of curing is large, and in the case of bonding sheet-like parts having significantly different thicknesses, the adhesive layer has a large and uneven curing. Since stress is generated and the deflection at the time of peeling is large, it is difficult to ensure the initial adhesive force.
What is the glass transition temperature?
1283504368031_0
This is the temperature at which glass transition occurs in the solid material, and the glass transition temperature of the polycarbonate urethane polyol (A) is determined by a DSC (Differential Scanning Calorimetry) apparatus at a heating rate of 10 ° C./min. It is a value measured by.

The polycarbonate urethane polyol (A) used in the present invention has an average of 2.1 to 5 hydroxyl groups, preferably 2.1 to 2.5, in one molecule.
The average number of hydroxyl groups per molecule is defined as “(hydroxyl value of polyol (A) × (number average molecular weight of polyol (A)) / 56,100)”.
When the amount of the hydroxyl group of the polycarbonate urethane polyol (A) is less than 2.1, the crosslinking is difficult to proceed, and not only the moist heat resistance after aging may be deteriorated, but also the aging curing reaction is slow. Under the influence of humidity, a lot of bubbles may be generated.
On the other hand, when the amount of the hydroxyl group of the polycarbonate urethane polyol (A) is more than five, there is a problem that gelation tends to occur when the polycarbonate urethane polyol (A) itself is produced, and it is difficult to synthesize. In addition, it is preferable that the hydroxyl group of a polyol (A) is primary.

  Such polycarbonate urethane polyol (A) is, for example, polycarbonate diol (A-1), diisocyanate (A-2), polyfunctional polyol having three or more hydroxyl groups, or three or more isocyanates. It can be obtained by a urethanization reaction with a polyfunctional polyisocyanate (A-3) having a group.

Examples of the polycarbonate diol (A-1) include hexanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol, 1,9-nonanediol, and 2-methyl-1,8. -Polycarbonate polyols based on one or more diols such as octanediol. Commercially available products include, for example, Ube Industries' Etanacol UH-100, UH-200, UH-300, UHC50-200, UHC50-100, or UC-100, Kuraray Kuraray Polyol C-2090, C-2090R, Alternatively, C-3090, Placel CD210, CD210PL, CD220, CD220PL manufactured by Daicel Corporation, or polycarbonate diol T6002, T6001, T5651, T5650J, T4671, T4672, T4692 or T4691 manufactured by Asahi Kasei Corporation may be used. These may be used alone or in any combination of two or more.
In the present invention, it is weight that the main agent has a polycarbonate structure in terms of improving long-term wet heat resistance of the adhesive layer after aging. The main agent is not polycarbonate urethane polyol, but polyester polyol, polyester urethane polyol, polybutadiene diol, polyether polyol, polyether urethane polyol, etc. There is a possibility that the adhesive strength is significantly deteriorated.

  Examples of the diisocyanate (A-2) include, but are not limited to, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5- And diisocyanates such as naphthalene diisocyanate, hexamethylene diisocyanate, bis (4-isocyanatocyclohexyl) methane, or hydrogenated diphenylmethane diisocyanate. As the diisocyanate (A-2), these may be used alone, or two or more kinds may be arbitrarily combined and used.

  Of the polyfunctional polyol having three or more hydroxyl groups, or the polyfunctional polyisocyanate (A-3) having three or more isocyanate groups, the polyfunctional polyol includes glycerin, trimethylolpropane, 1, Examples include polyols having three or more hydroxyl groups such as 2,4-butanetriol, 1,2,3-propanetriol, 1,2,5-pentanetriol, hexanetriol, pentaerythritol, sorbitol.

Of the polyfunctional polyol having three or more hydroxyl groups or the polyfunctional polyisocyanate (A-3) having three or more isocyanate groups, the polyfunctional polyisocyanate is a diisocyanate multimer (3 amounts). , Pentamers, and 7-mers), allophanate-modified products (such as allophanate-modified products produced by the reaction of diisocyanates with monools or polyhydric alcohols), biuret-modified products (generated by reaction of diisocyanates with water). Biuret modified products, etc.), polyol modified products (polyol modified products produced by reaction of diisocyanate and polyhydric alcohol, etc.), etc. may be used, and these may be used alone or in any combination of two or more. Or may be used.
As diisocyanate used for formation of polyfunctional polyisocyanate, the thing similar to what was illustrated as (A-2) can be illustrated.

  When obtaining the polycarbonate urethane polyol (A), in order to adjust the glass transition temperature of the polycarbonate urethane polyol (A), a dihydric alcohol other than the polycarbonate diol (A-1) may be used in combination. Two or more kinds of these dihydric alcohols can be used in any combination. For example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,9-nanonediol Or 3-methyl-1,5-pentanediol and the like.

The glass transition temperature of the polycarbonate urethane polyol (A) thus obtained is more preferably −50 to 10 ° C.
When the glass transition temperature is less than −50 ° C., the elasticity at the initial stage of curing is small, the generated bubbles cannot escape from the layer between the deposited PET and the adhesive layer, and foaming tends to be observed. However, when the temperature is higher than 10 ° C., when a sheet-like member having a significantly different thickness is bonded, the adhesive strength tends to be lowered in the T-type peel test.

The adhesive for laminated sheets of the present invention contains polyisocyanate (B) as a curing agent with respect to the polycarbonate urethane polyol (A).
The polyisocyanate (B) used in the present invention is blended so that the total isocyanate group of the polyisocyanate (B) is 0.5 to 10 in an equivalent ratio with respect to the total of the hydroxyl groups of the polyol (A). Preferably, it mix | blends in 1.0-2.5.
If the isocyanate group of the polyisocyanate (B) is less than 0.5 with respect to the total of hydroxyl groups of the polyol (A), the adhesive strength after aging may not be sufficiently maintained over a long period of time.

On the other hand, when the isocyanate group of the polyisocyanate (B) is larger than 10, the usable time (pot life) as an adhesive is very short, which may make it difficult to use.
Furthermore, when the isocyanate group of the polyisocyanate (B) is larger than 10, the stress at the time of curing generated in the adhesive layer increases, resulting in the following problems.
The solar cell back surface protective sheet tends to thicken a part of the sheet-like member used for improving the partial discharge voltage, and recently, a sheet having a thickness of about 100 μm to 300 μm is often used.
On the other hand, a thin plastic film of about 10 μm to 50 μm on which a metal oxide or non-metal inorganic oxide having a water vapor barrier property is vapor-deposited is used for the back surface protection sheet of the solar cell in order to prevent a decrease in output due to the influence of water. In order to adjust the film thickness as a back sheet, a thin sheet-like member of about 10 μm to 50 μm may be used. That is, the solar cell back surface protective sheet may be formed by bonding sheet-like members having significantly different thicknesses for various reasons.
When pasting sheet-like members having significantly different thicknesses, the curing stress generated in the adhesive layer becomes non-uniform. When the adhesive strength is measured, a large deflection occurs in a laminate in which sheet-like members having significantly different thicknesses are bonded, as compared to a laminate in which sheet-like members having the same thickness are bonded.
Therefore, since a large deflection is applied to the adhesive layer having a large and uneven curing stress, it is extremely difficult to secure an initial adhesive force in the case of a laminated body in which sheet-like members having significantly different thicknesses are bonded. Become.

The polyisocyanate (B) used in the present invention is not limited to the following, but a compound derived from a known diisocyanate can be preferably used. For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, bis (4-isocyanatocyclohexyl) methane, or water Compounds derived from diisocyanates such as added diphenylmethane diisocyanate, i.e., diisocyanurate, trimethylolpropane adduct, biuret type, prepolymer having isocyanate residue (low polymer obtained from diisocyanate and polyol), isocyanate residue Uretdione isomers having a group, allophanate isomers, or composites thereof, etc., which are used alone Good to be used even in an arbitrary combination of two or more thereof.
As the polyisocyanate (B) used in the present invention, an aliphatic or alicyclic isocyanate or a derivative thereof is used for the purpose of reducing yellowing over time because it is also used for outdoor use. Is preferred. Among them, it is particularly preferable to use a derivative of isophorone diisocyanate or a derivative of hexamethylene diisocyanate, and it is preferable to use a derivative of isophorone diisocyanate because of its high heat resistance.

  Various additives such as a silane coupling agent, a reaction accelerator, and a leveling agent can be blended in the adhesive for laminated sheets of the present invention.

As a known additive used in the present invention, a silane coupling agent is preferably included when it is desired to improve the adhesive strength to the metal foil.
Examples of the silane coupling agent used in the present invention include trialkoxysilane having a vinyl group such as vinyltrimethoxysilane and vinyltriethoxysilane, 3-aminopropyltriethoxysilane, and N- (2-aminoethyl). Trialkoxysilane having an amino group such as 3-aminopropyltrimethoxysilane; 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltriethoxy Examples include trialkoxysilane having a glycidyl group such as silane. These may be used alone or in any combination of two or more.

  It is preferable that the addition amount of the silane coupling agent used by this invention is 0.5-5 weight part with respect to 100 weight part of solid content of polycarbonate urethane polyol (A), and is 1-3 weight part. It is more preferable. If the addition amount of the silane coupling agent is less than 0.5 parts by weight, the effect of improving the adhesive strength to the metal foil by adding the silane coupling agent is poor, and even if it is added in an amount of more than 5 parts by weight, the performance will be higher. There is no improvement.

As a known additive used in the present invention, a known reaction accelerator can be used when it is desired to accelerate the curing reaction.
Examples of the reaction accelerator used in the present invention include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimaleate; 1,8-diaza-bicyclo (5,4,0) undecene Tertiary amines such as -7,1,5-diazabicyclo (4,3,0) nonene-5,6-dibutylamino-1,8-diazabicyclo (5,4,0) undecene-7; Reactive tertiary amines and the like. These may be used alone or in any combination of two or more.

  The reaction accelerator used in the present invention is preferably in the range of 0.005 to 0.2 parts by weight, more preferably 0.01 to 0.1 parts by weight based on 100 parts by weight of the solid content of the polycarbonate urethane polyol (A). Part. If the addition amount of the reaction accelerator is less than 0.005 parts by weight, there is a possibility that a sufficient acceleration effect of the curing reaction may not be obtained, and if it is more than 0.2 parts by weight, the curing reaction is too early and the solution is stable. There is a risk of damaging sex.

As a known additive used in the present invention, a known leveling agent or antifoaming agent can be added to the main agent for the purpose of improving the laminate appearance.
Examples of the leveling agent used in the present invention include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl group-containing polydimethylsiloxane, and polyetherester-modified hydroxyl group-containing polydimethylsiloxane. Acrylic copolymer, methacrylic copolymer, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic acid alkyl ester copolymer, lecithin and the like. These may be used alone or in any combination of two or more.

  The leveling agent used in the present invention is preferably in the range of 0.05 to 3 parts by weight, more preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the solid content of the polycarbonate urethane polyol (A). If the amount of the leveling agent added is less than 0.05 weight, sufficient leveling properties may not be improved. If the amount is more than 3 parts by weight, the adhesive strength of the adhesive may be greatly deteriorated. is there.

Examples of the antifoaming agent used in the present invention include known resins such as silicone resins, silicone solutions, and copolymers of alkyl vinyl ethers, alkyl acrylates and alkyl methacrylates. These may be used alone or in any combination of two or more.
The range of 0.05-3 weight part is preferable with respect to 100 weight part of solid content of polycarbonate urethane polyol (A), and, as for the antifoamer used by this invention, More preferably, it is 0.1-2 weight part. If the addition amount of the antifoaming agent is less than 0.05 weight, a sufficient antifoaming effect may not be obtained, and if it is more than 3 parts by weight, the adhesive strength of the adhesive may be greatly deteriorated. is there.

Next, the solar cell back surface protective sheet using the adhesive composition of the present invention will be described.
A simple one of the solar cell modules has a configuration in which a filler and a glass plate are sequentially laminated on both sides of the solar cell element. Since a glass plate is excellent in transparency, weather resistance, and scratch resistance, it is still generally used as a sealing sheet on the solar light receiving surface side. However, on the non-light-receiving surface side that does not require transparency, a solar cell back surface protection sheet (hereinafter referred to as a back surface protection sheet) other than the glass plate has been developed by each company in terms of cost, safety, and workability. It is being replaced.

As the back surface protection sheet, a monolayer film such as a polyester film, a polyester film provided with a metal oxide or non-metal oxide vapor deposition layer, a polyester film, a fluorine-based film, an olefin film, an aluminum foil, etc. The multilayer film which laminated | stacked the film is mentioned.
The back surface protective sheet having a multilayer structure can impart various performances depending on the multilayer structure. For example, insulating properties can be imparted by using a polyester film, weather resistance can be imparted by using a fluorine-based film, and water vapor barrier properties can be imparted by using an aluminum foil.
What kind of back surface protection sheet is used can be appropriately selected depending on the product and application in which the solar cell module is used.

In order to produce a multilayer film using the adhesive according to the present invention, a conventionally used method can be employed. For example, on one side of one laminate base material, an adhesive is applied by a comma coater or a dry laminator, and after the solvent is stripped off, the other laminate base material is bonded and cured at room temperature or under heating. It is preferable to bond together under heating. Specifically, it is preferable that after bonding under pressure at 50 to 80 ° C., the mixture is allowed to stand at 40 to 60 ° C. for about 3 to 7 days, and then aging (adhesion of the adhesive layer proceeds). Amount of adhesive applied to the laminate substrate surface is preferably about 1 to 50 g / m ^2. As the laminate base material, an arbitrary base material can be selected in any number depending on the application, and when the multilayer structure has three or more layers, the present invention can be applied to all or a part of the lamination of each layer. Can be used.

Hereinafter, various sheet-like members used for forming the back surface protection sheet will be exemplified.
The sheet-like member constituting the solar cell back surface protection sheet is not particularly limited, and examples thereof include a plastic film, a metal foil, and a material obtained by depositing a metal oxide or a nonmetal oxide on the plastic film.

As the plastic film, for example, a polyester resin film such as polyethylene terephthalate, polynaphthalene terephthalate,
Polyethylene resin film, polypropylene resin film, polyvinyl chloride resin film, polycarbonate resin film, polysulfone resin film, poly (meth) acrylic resin film,
Fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, polyethylene tetrafluoroethylene, polytetrafluoroethylene, tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer A film etc. are mentioned.
A film in which these plastic films are used as a support and are coated with an acrylic or fluorine-based paint, a multilayer film in which polyvinylidene fluoride, an acrylic resin, or the like is laminated by coextrusion can be used. Furthermore, you may use the sheet-like member by which multiple said plastic films were laminated | stacked through the urethane type adhesive bond layer.

An example of the metal foil is aluminum foil.
Examples of the metal oxide or nonmetal inorganic oxide to be deposited include oxides such as silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, and yttrium.

Among these, polyethylene terephthalate, polynaphthalene terephthalate, etc. that have resistance to temperature in order to satisfy performance such as weather resistance, water vapor permeability, electrical insulation, mechanical properties, mounting workability when used as a solar cell module Polyester resin film, polycarbonate resin film,
A metal foil such as a plastic film or an aluminum foil on which a metal oxide or a non-metal inorganic oxide having a water vapor barrier property is deposited in order to prevent a decrease in output due to the influence of water of the solar battery cell;
In order to prevent appearance defects due to photodegradation, a back protective sheet for solar cells in which a fluorine resin film having good weather resistance is laminated is preferable.

  In addition, the back surface protection sheet of the solar cell is required to have a partial discharge voltage of 700 V or 1000 V in combination with the power generation capacity of the cell in order to protect the solar cell module from damage due to voltage application, and includes an electrical insulating property and a foam layer. Many configurations have been proposed to improve the partial discharge voltage. Electrical insulation as a method for improving the partial discharge voltage tends to be a pressure film because it depends on the thickness of the film or foamed layer, and recently, a configuration using about 100 μm to 300 μm is preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, a following example does not restrict | limit the right range of this invention at all. In addition, each evaluation in an Example followed the following method. In the examples, parts are parts by weight,% is% by weight, hydroxyl value is KOH mg / g, and acid value is KOH mg / g. The number average molecular weight, glass transition temperature, hydroxyl value, and acid value were determined as follows.

<Number average molecular weight>
For the measurement of the number average molecular weight, GPC (gel permeation chromatography) “HPC-8020” manufactured by Tosoh Corporation was used, and tetrahydrofuran was used as the solvent. The number average molecular weight was calculated in terms of standard polystyrene.

<Glass transition temperature>
The glass transition temperature was measured using DSC “RDC220” manufactured by Seiko Instruments Inc. A sample obtained by drying the polycarbonate urethane polyol A-1 to A-14 solution synthesized by the following method, about 10 mg was weighed into an aluminum pan, set in a DSC apparatus, cooled to −100 ° C. with liquid nitrogen, and then 10 ° C. / The glass transition temperature was determined from the DSC chart obtained by raising the temperature in min.

<Hydroxyl value, acid value>
The acid value was determined by taking 0.2 g of a sample in an Erlenmeyer flask and dissolving it in 20 ml of ethanol, followed by titration with 0.01 N potassium hydroxide (ethanol solution). Phenolphthalein was used as an indicator.
Regarding the hydroxyl value, about 2 g of a sample was dissolved in about 10 ml of pyridine, 5 ml of a mixed solution having a previously prepared volume ratio of acetic anhydride / pyridine of 15/85 was added, and the mixture was allowed to stand for 20 hours. Thereafter, 1 ml of water and 10 ml of ethanol were added, and titration was performed with 0.1 N potassium hydroxide (ethanol solution). Phenolphthalein was used as an indicator.

Synthesis Example of Polycarbonate Urethane Polyol (A) <Synthesis Example 1>
140.58 g of “Kuraray polyol C-1090”, 25.00 g of isophorone diisocyanate, and 0.47 g of trimer of hexamethylene diisocyanate were charged into a reaction vessel and gradually stirred to 140 to 160 ° C. while stirring under a nitrogen stream. The urethanization reaction was carried out. After reacting at 160 ° C. for 3 hours and confirming that there was no NCO peak by IR measurement, ethyl acetate was added to obtain a polycarbonate urethane polyol (A1) solution having a solid content of 50% by weight.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 9.5, a glass transition temperature of −20 ° C., and an average of 2.2 hydroxyl groups in one molecule.

<Synthesis Example 2>
A polycarbonate urethane polyol having a solid content of 50 wt% (same as in Synthesis Example 1) except that “Kuraray polyol C-1090” was changed to 144.19 g and the trimer of hexamethylene diisocyanate was changed to 0.97 g. A2) A solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of −20 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 3>
A polycarbonate urethane polyol having a solid content of 50% by weight (same as in Synthesis Example 1) except that “Kuraray polyol C-1090” was changed to 151.98 g and the trimer of hexamethylene diisocyanate was changed to 2.04 g. A3) A solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 12.1, a glass transition temperature of −20 ° C., and an average of 2.8 hydroxyl groups in one molecule.

<Synthesis Example 4>
A polycarbonate urethane polyol having a solid content of 50% by weight (same as in Synthesis Example 1) except that “Kuraray polyol C-1090” was changed to 160.67 g and the trimer of hexamethylene diisocyanate was changed to 1.08 g. A4) A solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 8,000, a hydroxyl value of 17.5, a glass transition temperature of −20 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 5>
A polycarbonate urethane polyol having a solid content of 50% by weight (same as in Synthesis Example 1) except that “Kuraray polyol C-1090” was changed to 124.96 g and the trimer of hexamethylene diisocyanate was changed to 0.84 g. A5) A solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 20,000, a hydroxyl value of 7.0, a glass transition temperature of −20 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 6>
66.16 g of “Kuraray polyol C-1090”, 7.82 g of methylpentanediol, 25.00 g of isophorone diisocyanate, and 0.67 g of trimer of hexamethylene diisocyanate were charged into a reaction can. In the same manner as in the case, a polycarbonate urethane polyol (A6) solution having a solid content of 50% by weight was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of 0 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 7>
50 wt.% Solid content in the same manner as in Synthesis Example 6 except that 262.42 g of “Kuraray polyol C-3090”, 6.65 g of methylpentanediol, and 6.30 g of trimer of hexamethylene diisocyanate were used. % Polycarbonate urethane polyol (A7) solution.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of −30 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 8>
72.30 g of “Kuraray polyol C-2090”, 10.44 g of methylpentanediol, 0.72 g of trimethylolpropane, and 25.00 g of isophorone diisocyanate were charged into a reaction can. Thus, a polycarbonate urethane polyol (A8) solution having a solid content of 50% by weight was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of −20 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 9>
Synthesis except that Kuraray polyol C-2090 was changed to 30.79 g, methylpentanediol was changed to 5.00 g, trimethylolpropane was changed to 0.34 g, and hexamethylene diisocyanate was changed to 25.00 g instead of isophorone diisocyanate. In the same manner as in Example 8, a polycarbonate urethane polyol (A9) solution having a solid content of 50% by weight was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of −20 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 10>
“Kuraray polyol P-3010” 93.72 g, methylpentanediol 11.08 g, isophorone diisocyanate 25.00 g, hexamethylene diisocyanate trimer 2.52 g, charged into a reaction can. In the same manner as in the case, a polycarbonate urethane polyol (A10) solution having a solid content of 50% by weight was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of −30 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 11>
A polycarbonate urethane polyol (A11) solution having a solid content of 50% by weight was obtained in the same manner as in Synthesis Example 1 except that the trimer of hexamethylene diisocyanate was not used.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 8.6, a glass transition temperature of −20 ° C., and an average of 2.0 hydroxyl groups in one molecule.
<Synthesis Example 12>
A polycarbonate urethane polyol having a solid content of 50 wt% (same as in Synthesis Example 1) except that “Kuraray polyol C-1090” was changed to 281.16 g and hexamethylene diisocyanate trimer was changed to 28.34 g. A12) A solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 25.9, a glass transition temperature of −20 ° C., and an average of 6.0 hydroxyl groups in one molecule.

<Synthesis Example 13>
50% by weight of solid content in the same manner as in Synthesis Example 1 except that 122.25 g of “Kuraray polyol C-2090”, 25.00 g of isophorone diisocyanate, and 1.23 g of trimer of hexamethylene diisocyanate were used. A polycarbonate urethane polyol (A13) solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 30,000, a hydroxyl value of 4.7, a glass transition temperature of −28 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 14>
A polycarbonate urethane polyol having a solid content of 50 wt% (same as in Synthesis Example 1) except that “Kuraray polyol C-1090” was changed to 224.93 g and the trimer of hexamethylene diisocyanate was changed to 1.51 g. A14) A solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 4,000, a hydroxyl value of 35.1, a glass transition temperature of −20 ° C., and an average of 2.5 hydroxyl groups in one molecule.

<Synthesis Example 15>
Synthesis Example 1 except that polycarbonate diol (CD-205PL, manufactured by Daicel Chemical Industries, Ltd., number average molecular weight 500) is 14.06 g, isophorone diisocyanate is 25.00 g, and hexamethylene diisocyanate trimer is 0.47 g. In the same manner as above, a polycarbonate urethane polyol (A15) solution having a solid content of 50% by weight was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 8,000, a hydroxyl value of 19.6, a glass transition temperature of 20 ° C., and an average of 2.8 hydroxyl groups in one molecule.

<Synthesis Example 16>
50% by weight of solid content in the same manner as in Synthesis Example 1 except that 374.89 g of “Kuraray polyol C-3090”, 25.00 g of isophorone diisocyanate, and 0.63 g of hexamethylene diisocyanate trimer were used. A polycarbonate urethane polyol (A16) solution was obtained.
This polycarbonate urethane polyol has a number average molecular weight of 13,000, a hydroxyl value of 10.8, a glass transition temperature of −60 ° C., and an average of 2.5 hydroxyl groups in one molecule.

Abbreviations shown in Tables 1 to 3 are as follows.
<Diol (A)>
C-1090: Kuraray Co., Ltd. Kuraray polyol (polycarbonate diol)
-C-2090: Kuraray Co., Ltd. Kuraray polyol (polycarbonate diol)
C-3090: Kuraray Co., Ltd. Kuraray polyol (polycarbonate diol)
-P-3010: Kuraray polyol (polyester diol) manufactured by Kuraray Co., Ltd.
・ CD205PL: Daicel Chemical (polycarbonate diol)

<Curing agent 1>
Curing agent 1 is obtained by diluting a trimer of isophorone diisocyanate with ethyl acetate to obtain a solution having a solid content of 70%. The isocyanate group contained in 100 g of curing agent 1 is about 12 g.
<Curing agent 2>
Curing agent 2 is obtained by diluting hexamethylene diisocyanate with ethyl acetate to give a solution having a solid content of 70%. The isocyanate group contained in 100 g of curing agent 2 is about 19.4 g.
<Curing agent 3>
Curing agent 3 is obtained by mixing isophorone diisocyanate trimer and hexamethylene diisocyanate at a weight ratio of 8: 2 and diluting with ethyl acetate to give a solution having a solid content of 70%. The isocyanate group contained in 100 g of curing agent 3 is about 17.9 g.
<Curing agent 4>
Curing agent 3 is a solution in which a trimer of isophorone diisocyanate and hexamethylene diisocyanate are mixed at a weight ratio of 5: 5 and diluted with ethyl acetate to give a solution having a solid content of 70%. The isocyanate group contained in 100 g of curing agent 4 is about 15.7 g.
<Hardening agent 5>
Curing agent 3 is obtained by mixing a trimer of isophorone diisocyanate and hexamethylene diisocyanate at a weight ratio of 2: 8 and diluting with ethyl acetate to obtain a solution having a solid content of 70%. The isocyanate group contained in 100 g of curing agent 5 is about 13.5 g.
<Curing agent 6>
A curing agent 6 is obtained by diluting an adduct of hexafunctional isocyanate (Duranate MHG-80, manufactured by Asahi Kasei Co., Ltd.) with ethyl acetate to obtain a solution having a solid content of 70%. The isocyanate group contained in 100 g of curing agent 6 is about 15.5 g.

<Example 1>
With respect to the polycarbonate urethane polyol (A1) solution obtained in Synthesis Example 1 (solid content: 100 parts by weight), the curing agent 1 is 1.5 parts by weight in solid content, and an epoxy group-containing silane coupling agent (“KBM-403”). 1 part by weight of Shin-Etsu Chemical Co., Ltd.) and 0.01 part by weight of dioctyltin dilaurate (“Neostan U-810”, manufactured by Nitto Kasei Co., Ltd.) as a reaction accelerator are diluted with ethyl acetate. Thus, an adhesive solution having a solid content of 30% was obtained.

<Examples 2 to 12>, <Comparative Examples 1 to 8>
In the same manner as in Example 1, each polycarbonate urethane polyol solution and a curing agent solution were blended in the composition shown in Table 2, and diluted with ethyl acetate to obtain an adhesive solution having a solid content of 30%. The initial adhesive strength when the PET films having different foaming properties and thicknesses were bonded together, the initial adhesive strength when the fluororesin films were bonded together, and the adhesive strength after the wet heat resistance test were evaluated. The results are shown in Table 4.

[Foaming test evaluation] (deposition PET film / adhesive layer / deposition PET film)
A vapor-deposited layer of silicon oxide on one side of the polyethylene terephthalate film, and a single-side vapor-deposited polyethylene terephthalate film (Tech Barrier LX, thickness 12 μm, manufactured by Mitsubishi Plastics, Inc.) formed by corona treatment on the other side is used as vapor-deposited PET It was.
The adhesives of Examples and Comparative Examples were applied to the vapor deposition surface of the vapor deposited PET, and dried at 80 ° C. for 1 minute to form an adhesive layer having a dry adhesive amount of 4 to 5 g / m ^2. The vapor-deposited surfaces of the vapor-deposited PET and the same type of vapor-deposited PET were superimposed on the adhesive layer, and laminated by passing between two rolls set at 60 ° C. Then, the obtained laminate of deposited PET / adhesive layer / deposited PET was aged for 3 days in an environment of 50 ° C. and 80% RH to sufficiently cure the adhesive layer. The laminated bodies after aging were each cut into a size of 100 mm × 100 mm, and the state of generation of bubbles at the laminated interface was visually observed through PET and evaluated according to the following criteria.
◎: No foaming (diameter 0.5 mm or more) that can be visually confirmed ○: Foaming is present in an area of less than 10% of the deposited area of the deposited PET film △: Foamed in an area of less than 20% of the adhered area of the deposited PET film Yes ×: Foaming is present in an area of less than 40% of the area where the deposited PET film is attached

[Evaluation of initial adhesive strength]
(Creation of thin PET film / adhesive layer / thin PET film)
The adhesives of Examples and Comparative Examples were applied to a stretched polyester film having a thickness of 50 μm (manufactured by Toray: product name X10S) and a stretched polyester film having a thickness of 50 μm (manufactured by Toray: product name X10S) at 80 ° C. for 1 minute. Dry and dry adhesive amount: 4 to 5 g / m ² of adhesive layer is formed, respectively, and stretched polyester film of 50 μm thickness (manufactured by Toray Industries, Inc. on two types of PET films having different thicknesses). The product name X10S) was superposed and laminated by passing between two rolls set at 60 ° C. Thereafter, the resulting thick PET / adhesive layer / thin PET laminate was aged for 3 days in an environment of 50 ° C. and 40% RH to sufficiently cure the adhesive layer.
The laminated body after aging is allowed to stand for 6 hours in an environment of 25 ° C. and a humidity of 65%, and then cut into a size of 200 mm × 15 mm, and a tensile tester is applied according to the test method of ASTM-D1876-61. The T-type peel test was performed at a load speed of 300 mm / min in an environment of 25 ° C. and 65% humidity. The peel strength (N / 15 mm width) between the polyester films is shown as an average value of five test pieces.
◎ Excellent in practical use: 5N / 15mm or more ○ Practical range: 4-5N / 15mm
△ Practical lower limit: 2-4N / 15mm
× Not practical: Less than 2N / 15mm

(Creation of thick PET film / adhesive layer / thin PET film)
The adhesives of Examples and Comparative Examples were applied to a stretched polyester film having a thickness of 50 μm (manufactured by Toray: product name X10S) and a stretched polyester film having a thickness of 188 μm (manufactured by Toray: product name X10S) at 80 ° C. for 1 minute. Dry and dry adhesive amount: 4 to 5 g / m ² of adhesive layer is formed, respectively, and stretched polyester film of 50 μm thickness (manufactured by Toray Industries, Inc. on two types of PET films having different thicknesses). The product name X10S) was superposed and laminated by passing between two rolls set at 60 ° C. Thereafter, the resulting thick PET / adhesive layer / thin PET laminate was aged for 3 days in an environment of 50 ° C. and 40% RH to sufficiently cure the adhesive layer.
The laminated body after aging is allowed to stand for 6 hours in an environment of 25 ° C. and a humidity of 65%, and then cut into a size of 200 mm × 15 mm, and a tensile tester is applied according to the test method of ASTM-D1876-61. The T-type peel test was performed at a load rate of 300 mm / min in an environment of 25 ° C. and 65% humidity. The peel strength (N / 15 mm width) between the polyester films is shown as an average value of five test pieces.
◎ Excellent in practical use: 5N / 15mm or more ○ Practical range: 4-5N / 15mm
△ Practical lower limit: 2-4N / 15mm
× Not practical: Less than 2N / 15mm

[Adhesive strength after initial adhesive strength evaluation and wet heat resistance test]
(Creation of fluorine resin film / adhesive layer / fluorine resin film)
Each adhesive of Examples and Comparative Examples was applied to a fluorine film (Kynar Film302-PGM-TR, PVDF manufactured by Arkema Co., Ltd., thickness 30 μm), dried at 80 ° C. for 1 minute, and the amount of adhesive when dried: 4 to An adhesive layer of 5 g / m ² was formed, and a fluorine film (Kynar Film 302-PGM-TR) was superposed on the adhesive layer and laminated by passing between two rolls set at 60 ° C. Then, the obtained fluororesin film / adhesive layer / fluororesin film laminate was aged at 50 ° C. for 3 days to sufficiently cure the adhesive layer.
In the same manner as in the case of thick PET film / adhesive layer / thin PET film, the initial adhesive force between the fluororesin films was determined for the laminate after aging.
Separately, the laminate after aging was allowed to stand in an environment of 121 ° C. and 100% RH for 24 hours, 48 hours, 72 hours, 96 hours, 120 hours, and 144 hours, respectively.
Thereafter, as in the initial stage, the adhesive force between the fluororesin films was determined.
In addition, since PET film easily deteriorates in an environment of 121 ° C. and 100% RH, it is inappropriate when evaluating the heat-and-moisture resistance of the adhesive layer. A difficult fluorine-based resin film was used.

As shown in Table 4, since Comparative Example 1 used polyester urethane polyol as the main agent, hydrolysis could not be suppressed, and the adhesive strength after the wet heat resistance test was greatly deteriorated.
In Comparative Example 2, polycarbonate urethane having a hydroxyl group is used as the main agent, but since the average number of hydroxyl groups contained in one molecule is 2, the curing rate during aging is slow, and foaming is remarkably caused in the foaming test. It was.
On the other hand, Comparative Example 3 uses a polycarbonate urethane having a hydroxyl group as the main agent, but the average number of hydroxyl groups contained in one molecule is 6.0 and many branches, so that the adhesive layer becomes too hard and cured. Stress also increases.
In the case of bonding PET with extremely different thicknesses, too large curing stress occurs non-uniformly in the adhesive layer, so even the initial adhesive force could not be ensured.
On the other hand, when the sheet-like members having the same thickness are bonded, the curing stress itself is large, but the curing stress itself is uniform, and no large deflection occurs during the peel test, so that the initial adhesive force can be secured. Considered.
In addition, it is considered that the curing stress was relaxed and the adhesive strength could be maintained at a high level by placing the sample in a high temperature environment in the wet heat aging test.

In Comparative Example 4, the number average molecular weight of the polycarbonate urethane polyol is 30,000, which is larger than 25,000, so that the wettability with the sheet-like member is low in the first place, but on the other hand, the bulk cohesive force of the adhesive layer itself is large. Therefore, when the sheet-like members having the same thickness are bonded, the initial adhesive force can be secured.
However, when the sheet-like members having significantly different thicknesses are bonded together, the initial adhesive force cannot be ensured. When sheet-like members with significantly different thicknesses are pasted together, the curing stress generated in the adhesive layer becomes non-uniform and a greater deflection occurs when measuring the adhesive strength. Easier to peel than when combined. In addition, when the molecular weight of the polycarbonate urethane polyol (A) is too large, the poor wettability and the cohesive force act as a kind of repulsive force, so the initial adhesive force cannot be ensured.
In addition, the poor wettability of the adhesive layer to the sheet-like member is eliminated by placing the sample in a high temperature environment in the wet heat aging test, and the magnitude of the cohesive force of the adhesive layer due to the size of the molecular weight It is considered that the adhesive strength could be maintained at a high level.
So

In Comparative Example 5, the number average molecular weight of the polycarbonate urethane polyol is 4,000, and the cohesive force is insufficient because it is less than 5,000. It was not obtained.
When the sheet-like members having the same thickness were bonded, the initial adhesive force could barely be ensured, but due to insufficient cohesive force, the adhesive force was reduced by the moist heat resistance test.
Moreover, since the number average molecular weight was small, the elasticity at the initial stage of curing was small, and the generated bubbles could not escape from the deposited PET and the adhesive layer, and foaming was observed a little.

  In Comparative Example 6, the glass transition temperature is 20 ° C., which is higher than 10 ° C., and therefore, when the sheet-like portions having significantly different thicknesses are bonded to each other, the elasticity at the time of curing is large and the adhesive layer is largely non-uniform. Since a curing stress was generated and the deflection at the time of peeling was large, a sufficient initial adhesive force could not be secured.

  In Comparative Example 7, since the glass transition temperature is −60 ° C. and lower than −50 ° C., bubbles generated due to low initial elasticity cannot be released from the layer between the vapor-deposited PET and the adhesive layer, and are slightly foamed. Was observed. Furthermore, since the cohesive force after curing is not high due to the low glass transition temperature, the adhesive layer is softened by the temperature of the moist heat resistance test, and the adhesive strength is significantly reduced.

  In Comparative Example 8, since the blending amount of the polyisocyanate (B) was small, a sufficient cross-linking structure was not formed in the adhesive layer, and the initial adhesive strength between PETs having significantly different thicknesses could not be ensured. When the sheet-like members having the same thickness were bonded, the initial adhesive force could be secured, but due to the lack of the crosslinked structure, the adhesive layer was deteriorated by the heat and humidity resistance test, and the adhesive force was greatly deteriorated.

  Since the comparative example 9 has many compounding quantities of polyisocyanate (B), an adhesive bond layer becomes too hard and a cure distortion also becomes large. As a result, in the case of bonding PET with remarkably different thicknesses, it was not possible to ensure even the initial adhesive force due to excessive curing strain. In addition, when the sheet-like member with the same thickness was bonded, it was difficult to be affected by the curing strain, and the adhesive strength was secured.

  On the other hand, in Examples 1 to 12 shown in Table 4, the main agent has a number average molecular weight of 5,000 to 25,000, a glass transition temperature of −50 to 10 ° C., and an average hydroxyl group contained in one molecule is 2. 1 to 5 polycarbonate urethane polyol (A), which contains all isocyanate groups of polyisocyanate (B) in an equivalent ratio of 0.5 to 10 with respect to the hydroxyl groups of polyol (A). Even when aged in a humidity environment, foam was hardly generated, and the initial adhesive strength and the adhesive strength after the wet heat resistance test were all well-balanced.

  Among them, Examples 2, 5, and 7 shown in Table 4 are more excellent because the number average molecular weight, glass transition temperature, and average number of hydroxyl groups in one molecule are more suitable for the polycarbonate urethane polyol (A).

If the adhesive agent of this invention is used, the solar cell back surface protection sheet excellent in durability can be formed.
For example, in JIS C 8917 (environmental test method and durability test method for crystalline solar cell module), a durability test of 1000 hours at 85 ° C. and 85% RH is imposed as a moisture resistance test B-2. It is known as a particularly harsh test method. This time, a heat and humidity resistance test was performed at 121 ° C. and 100% RH, but this test is more severe than JIS C 8917 and can withstand this heat and heat resistance test at 121 ° C. and 100% RH. This suggests that it can sufficiently withstand the long-term moisture resistance test B-2.
The solar cell back surface protective sheet using the adhesive of the present invention maintains sufficient interlayer adhesive strength (laminate strength) in such a long-term moisture and heat resistance test, and does not generate delamination between the sheet layers. It can contribute to protection of battery elements, maintenance of power generation efficiency, and extension of the life of solar cells. Extending the lifetime of solar cells leads to the spread of solar cell systems and contributes to environmental conservation from the viewpoint of securing energy other than fossil fuels.

  The adhesive according to the present invention is a multilayer laminated material for outdoor industrial applications such as a solar cell back surface protection sheet and a building that requires long-term moisture and heat resistance (wall barrier agent, roofing material, window material, outdoor flooring material, certification protection) It is suitable as an adhesive for materials, automobile members, and the like.

Claims (7)

An adhesive composition for laminated sheets using a main agent and a curing agent,
A polycarbonate urethane polyol (A) having a number average molecular weight of 5,000 to 25,000 and a glass transition temperature of −50 to 10 ° C.
The curing agent comprises polyisocyanate (B);
The total isocyanate group of the polyisocyanate (B) is 0.5 to 10 in equivalent ratio with respect to the hydroxyl group of the polyol (A),
The polyol (A) has an OH terminal functional group number contained in one molecule of 2.1 to 5, and is an adhesive composition for laminated sheets. The total isocyanate group of the polyisocyanate (B) is 1.0 to 2.5 in an equivalent ratio with respect to the hydroxyl group of the polyol (A),
The polyol composition (A) has an OH terminal functional group number contained in one molecule of 2.1 to 2.5, and an adhesive composition for laminated sheets.   The polyol (A) is a polycarbonate diol (A-1), a diisocyanate (A-2), a polyfunctional polyol having three or more hydroxyl groups, or a polyfunctional having three or more isocyanate groups. It is a polycarbonate urethane polyol obtained by reaction with a polyisocyanate (A-3), The adhesive composition for laminated sheets of Claim 1 or 2 characterized by the above-mentioned.   The solar cell which comprised the adhesive bond layer formed from the adhesive composition for lamination | stacking of any one of Claims 1-3, and two or more sheet-like members laminated | stacked through the said adhesive bond layer. Back surface protection sheet.   5. One of the sheet-like members is a metal foil or a plastic film with a vapor deposition layer formed by depositing a metal oxide or a non-metal inorganic oxide on at least one surface of a plastic film. The back surface protection sheet for solar cells as described. Solar cell surface protective material (I) located on the light receiving surface side of the solar cell, solar cell (III), ethylene-vinyl acetate copolymer filler layer (IV) located on the non-light receiving surface side of the solar cell, and A solar cell module comprising the solar cell back surface sealing sheet (V) in contact with a non-light-receiving surface side ethylene-vinyl acetate copolymer filler layer,
The said solar cell back surface sealing sheet (V) uses the back surface protection sheet (V ') for solar cells of Claim 4 or 5, The solar cell module characterized by the above-mentioned.   The light receiving surface side ethylene-vinyl acetate copolymer system filler layer (II) is further provided between the solar cell surface protective material (I) and the solar cell (III). Solar cell module.