WO2017204014A1

WO2017204014A1 - Adhesive for laminated sheets

Info

Publication number: WO2017204014A1
Application number: PCT/JP2017/018177
Authority: WO
Inventors: Shouko Ito; Hitoshi Ikeda
Original assignee: Henkel Ag & Co. Kgaa
Priority date: 2016-05-26
Filing date: 2017-05-15
Publication date: 2017-11-30
Also published as: CN108779226B; KR102351304B1; CN108779226A; JP2017210564A; JP6726027B2; KR20190011230A

Abstract

Disclosed is an adhesive for laminated sheets, which adhesive is applied to a film to bond a plurality of films, and is a mixture comprising: (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxylic anhydrides; and (C) an isocyanate compound, wherein the (B) is mixed in an amount of 0.01 to 8.0 parts by weight per 100 parts by weight of the total of the (A)-(C), and wherein the (A) is obtainable by polymerizing a polymerizable monomer, and is a polymer having a weight average molecular weight of 10,000 to 100,000 and a hydroxyl value of 0.5 to 40 mgKOH/g. The adhesive for laminated sheets is excellent in coatability, peel strength after curing and hydrolysis resistance for a long time under high temperature when a laminated sheet is produced, and wherein the adhesive for laminated sheets does not impart an adverse effect to the appearance of the laminated sheet while improving the curability. A laminated sheet is suitably prepared using the adhesive for laminated sheets.

Description

ADHESIVE FOR LAMINATED SHEETS

Cross-Reference to Related Application

This application claims priority under Article 4 of the Paris Convention based on Japanese Patent Application No. 2016-105473 filed on May 26, 2016 in Japan. This priority patent application is incorporated herein by reference in its entirety.

The present invention relates to an adhesive for laminated sheets. Moreover, the present invention also relates to a laminated sheet obtainable by using the adhesive, and an article (or a material), for example packaging bags (packaging bags for shampoo, detergents, food staffs and the like) and outdoor materials (solar battery modules and the like), obtainable by using the laminated sheet.

Outdoor materials such as barrier materials, roof materials, solar battery modules (or panels), window materials, outdoor flooring materials, illumination protective materials, automobile members and signboards, and packaging bags and the like comprise, as a constituent material, a laminated sheet (or laminate) obtainable by laminating plural films using an adhesive. Examples of the film composing the laminated sheet include metal foils made of metals such as aluminum, copper, and steel; metal plates and metal deposited films; and films made of plastics such as polypropylenes, polyvinyl chlorides, polyesters, fluororesins, and acrylic resins.

As shown in Fig. 1, a laminated sheet 10 is a laminate of a plurality of

films

11 and 12, and the

films

11 and 12 are laminated by interposing an adhesive 13 therebetween. Since the laminate is exposed outdoors over a long term, it is required for the adhesive for laminated sheets (adhesive layer formed therefrom) to have excellent durability. It is required for adhesives for laminated sheets, particularly adhesives for solar battery applications, which convert sunlight into electricity, to have a higher level of durability than a conventional adhesive for laminated sheets.

As shown in Fig. 3, in the case of solar battery applications, the laminated sheet 10 referred to as a backsheet is comprised in a solar battery module 1, together with a sealing material 20, a solar battery cell 30, and a glass plate 40.
Since the solar battery module 1 is exposed outdoors over a long term, sufficient durability against sunlight is required under conditions of high temperature and high humidity. Particularly, when the adhesive 13 has poor performance, the film 11 can peel from the film 12, and thus appearance of the laminated sheet 10 deteriorates. Therefore, it is required that the adhesive for laminated sheets for the production of the solar battery module does not undergo peeling of the film of the laminated sheet even though the adhesive is exposed to high temperature over a long term.

Patent Documents 1 to 2 disclose, as examples of adhesives for laminated sheets, urethane based adhesives for producing solar battery protection sheets.
Patent Document 1 discloses an adhesive for laminated sheets which is used for producing solar battery backsheets, which adhesive for laminated sheets comprises an acrylic polyol and a polyisocyanate (refer to [Claim 1] of Patent Document 1). The acrylic polyol is adjusted to have a glass transition temperature in a specific range and to have a hydroxyl value in a specific range, and the polyisocyanate is limited to have a specific structure, so that the adhesive has improved environmental resistance (various durability under environment, for example adhesive strength before and after aging, heat and humidity resistance and the like) (refer to [Table 1] to [Table 5] of Patent Document 1).

Patent Document 2 also discloses an adhesive for solar battery backsheets comprising a urethane resin obtainable by a reaction of an acrylic polyol with an isocyanate compound, and a solar battery backsheet and a solar battery module obtainable by using the adhesive (refer to [Claim 1] and [Claim 5] of Patent Document 2). The adhesive for solar battery backsheets of Patent Document 2 is excellent in hydrolysis resistance, film peel strength after aging, and yellowing by UV radiation (refer to [Table 1] to [Table 5] of Patent Document 2).

In recent years, performance required to the adhesives for solar battery backsheets increases year by year. The adhesive for solar battery backsheets should be excellent in not only durability (hydrolysis resistance), but also handling (or handiness) when a solar battery backsheet is produced.
The adhesives of Patent Documents 1 and 2 are excellent in hydrolysis resistance, but the curability (or hardenability) of the adhesives does not completely satisfy a high level request of consumers. It is necessary for the adhesive to have more improved curability so as to produce solar battery backsheets efficiently.

One of methods to improve the curability is to add a catalyst to the adhesive. The addition of the catalyst improves the curability, but the pot life may be too short, leading to some difficulty in a laminating process of films and in appearance of obtainable laminated sheets.

[PTL 1] JP 5003849 B
[PTL 2] JP 2012-142349 A

The present invention has been made so as to solve such a problem and an object thereof is to provide an adhesive for laminated sheets, which is excellent in coatability in the case of producing a laminated sheet (or laminate), peel strength after aging (or curing), and hydrolysis resistance over a long term at high temperature, and also does not exert an adverse influence on appearance of the laminated sheet while improving the curability. Moreover, an object of the present invention is to provide a laminated sheet (such as solar battery backsheets and the like) obtainable using the adhesive, and an article (or a material) (such as packaging bags and outdoor materials (for example solar battery module) and the like) obtainable using the laminated sheet.

The present inventors intensively studied, and surprisingly found that use of a specific polyol as a raw material of a urethane resin and further addition of a specific compound lead an adhesive for laminated sheets, which is excellent in coatability in producing a laminated sheet, in peel strength after aging, and in hydrolysis resistance over a long term at high temperature, and wherein the adhesive does not exert an adverse influence on appearance of the laminated sheet while improving the curability. Thus, the present invention has been completed.

The present invention provides, in an aspect, a novel adhesive for laminated sheets, which is applied on a film to bond (or laminate) a plurality of films, the adhesive being a mixture comprising: (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxylic anhydrides, and (C) an isocyanate compound, wherein
the at least one selected from carboxylic acids and carboxylic anhydrides (B) is mixed (or comprised) in an amount of 0.01 to 8.0 parts by weight based on 100 parts by weight of the total weight of the components (A) to (C), and
the acrylic polyol (A) is obtainable by polymerizing a polymerizable monomer, and is a polymer having a weight average molecular weight of 10,000 to 100,000 and a hydroxyl value of 0.5 to 40 mgKOH/g.

The present invention provides, in an embodiment, an adhesive for laminated sheets, wherein at least one selected from carboxylic acids and carboxylic anhydrides (B) has a melting point of 280°C or lower.
The present invention provides, in another embodiment, an adhesive for laminated sheets, further comprising (D) a silane compound.
The present invention provides, in a further embodiment, an adhesive for laminated sheets, wherein the polymerizable monomer comprises a monomer having a hydroxyl group and the other monomer, and the other monomer comprises acrylonitrile and a (meth)acrylic ester.

The present invention provides, in a preferable embodiment, an adhesive for laminated sheets, wherein the acrylic polyol (A) has a glass transition temperature of -35°C to 20°C.
The present invention provides, in a further other embodiment, an adhesive for laminated sheets, wherein the silane compound (D) is comprised in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total weight of the components (A) to (C).
The present invention provides, in another aspect, a laminated sheet obtainable by laminating a plurality of films through interposing the adhesive for laminated sheets therebetween.
The present invention provides, in a further aspect, an article (an outdoor material, a packaging bag and the like) obtainable by using the laminated sheet.

The present invention provides, in a preferable aspect,
a method for producing an adhesive for laminated sheets, which comprises mixing (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxylic anhydrides, and (C) an isocyanate compound in an organic solvent, wherein
the at least one selected from carboxylic acids and carboxylic anhydrides (B) is mixed (or comprised) in an amount of 0.01 to 8.0 parts by weight based on 100 parts by weight of the total weight of the components (A) to (C), and
the acrylic polyol (A) is obtainable by polymerizing a polymerizable monomer, and is a polymer having a weight average molecular weight of 10,000 to 100,000 and a hydroxyl value of 0.5 to 40 mgKOH/g.

The present invention provides, in a more preferable aspect,
a method for producing an adhesive for laminated sheets, which comprises mixing (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxylic anhydrides, and (C) an isocyanate compound in an organic solvent to obtain a mixed solution, and applying the mixed solution on a film to bond (or laminate) a plurality of films, wherein
the at least one selected from carboxylic acids and carboxylic anhydrides (B) is mixed (or comprised) in an amount of 0.01 to 8.0 parts by weight based on 100 parts by weight of the total weight of the components (A) to (C), and
the acrylic polyol (A) is obtainable by polymerizing a polymerizable monomer, and is a polymer having a weight average molecular weight of 10,000 to 100,000 and a hydroxyl value of 0.5 to 40 mgKOH/g.

An adhesive for laminated sheets according to an aspect of the present invention is applied on a film to bond (or laminate) a plurality of films, the adhesive being a mixture comprising: (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxylic anhydrides, and (C) an isocyanate compound, where
the at least one selected from carboxylic acids and carboxylic anhydrides (B) is mixed (or comprised) in an amount of 0.01 to 8.0 parts by weight based on 100 parts by weight of the total weight of the components (A) to (C), and
the acrylic polyol (A) is obtainable by polymerizing a polymerizable monomer, and is a polymer having a weight average molecular weight of 10,000 to 100,000 and a hydroxyl value of 0.5 to 40 mgKOH/g.
Therefore, when a laminated sheet (or a laminate) is produced, the adhesive is excellent in coatability, peel strength after aging, and hydrolysis resistance over a long term at high temperature, so that the adhesive does not exert an adverse influence on appearance of the laminated sheet while improving the curability.
Therefore, the laminated sheet can be suitably produced using such an adhesive for laminated sheets, and an article can be produced using the laminated sheet.

Fig. 1 is a sectional view showing an embodiment of a solar battery backsheet of the present invention. Fig. 2 is a sectional view showing another embodiment of a solar battery backsheet of the present invention. Fig. 3 is a sectional view showing an embodiment of a solar battery module of the present invention.

An adhesive for laminated sheets of the present invention is a mixture comprising: (A) an acrylic polyol, (B) at least one carboxyl group-containing compound selected from carboxylic acids and carboxylic anhydrides, and (C) an isocyanate compound.
The order and method of blending the components (A) to (C) are not limited as long as the objective adhesive for laminated sheets of an embodiment of the present invention is obtainable. For example, the three components: the components (A) to (C) may be blended at one time. Moreover, the component (B) may be blended with the component (A) and then the component (C) may be added. Furthermore, the component (B) may be blended with the component (C) and then the component (A) may be added.

(A) The acrylic polyol is obtainable by the addition polymerization of a polymerizable monomer, and the polymerizable monomer comprises a “monomer having a hydroxyl group” and the “other monomer”.
The “monomer having a hydroxyl group” is a radical polymerizable monomer having a hydroxyl group and an ethylenic double bond, and is not particularly limited as long as the objective adhesive for laminated sheets of the present invention can be obtained. The monomer having a hydroxyl group comprises for example, a hydroxyalkyl (meth)acrylate, and the hydroxyalkyl (meth)acrylate may be used alone, or two or more hydroxyalkyl (meth)acrylates may be used in combination. The hydroxyalkyl (meth)acrylate may also be used in combination with a monomer having a hydroxyl group, except for the hydroxyalkyl (meth)acrylate.

Examples of the “hydroxyalkyl (meth)acrylate” include, but are not limited to, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and the like.
Examples of the “polymerizable monomer having a hydroxyl group, except for the hydroxylalkyl (meth)acrylates” include a polyethylene glycol mono(meth)acrylate, a polypropylene glycol mono(meth)acrylate and the like.

The “other monomer” is a “radical polymerizable monomer having an ethylenic double bond” except for the monomer having a hydroxyl group, and is not particularly limited as long as the objective adhesive for laminated sheets of the present invention can be obtained. The other monomers preferably comprise acrylonitrile and a (meth)acrylic ester, and may further comprise a radical polymerizable monomer having an ethylenic double bond, except for acrylonitrile and (meth)acrylic esters. The adhesive for laminated sheets of the present invention is preferably excellent in peel strength after aging and may provide a laminated sheet having further improved appearance, when the other monomers comprise acrylonitrile and a (meth)acrylic ester.

The “acrylonitrile” is a compound represented by the general formula: CH₂=CH-CN, and is also called acrylic nitrile, acrylic acid nitrile or vinyl cyanide.
The acrylonitrile is preferably comprised in an amount of 1 to 40 parts by weight, more preferably 5 to 35 parts by weight, and particularly preferably 5 to 25 parts by weight, based on 100 parts by weight of the polymerizable monomers. When the acrylonitrile is comprised in an amount of the above range, coatability of an adhesive may be further improved, and an adhesive for laminated sheet excellent in balance between peel strength after aging and hydrolysis resistance may be provided.

The “(meth)acrylic ester” is obtainable, for example, by the condensation reaction of (meth)acrylic acid with a monoalcohol, and has an ester bond. Even though it has an ester bond, a monomer having a hydroxyl group is not comprised in the (meth)acrylic esters. Specific examples thereof include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate and the like; glycidyl (meth)acrylate and the like. Both linear alkyl group and cyclic alkyl group are comprised in this “alkyl group”.

The “(meth)acrylic ester” preferably comprises at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate, more preferably comprises at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate, and most preferably comprises both methyl methacrylate and n-butyl acrylate.

In the present description, acrylic acid and methacrylic acid are collectively referred to as “(meth)acrylic acid”, and “an acrylic ester and a methacrylic ester” are collectively referred to as a “(meth)acrylic ester” or a “(meth)acrylate”.
Examples of the “radical polymerizable monomer having an ethylenic double bond, except for acrylonitrile and (meth)acrylic esters” include, but are not limited to, (meth)acrylic acid, styrene, vinyltoluene and the like. The radical polymerizable monomer is not limited to these compounds as long as an adhesive for laminated sheets of the present invention can be obtained.

As long as an objective adhesive for laminated sheets of the present invention can be obtained, there is no particular limitation on the polymerization method of the polymerizable monomer. For example, the polymerizable monomer can be polymerized by the radical polymerization of the polymerizable monomer with a suitable catalyst etc. in an organic solvent using a general solvent polymerization method. Herein, there is no particular limitation on the organic solvent as long as it can be used to polymerize the polymerizable monomer, and it does not substantially exert an adverse influence on the properties of the adhesive for laminated sheets after the polymerization reaction. Examples of such solvent include aromatic solvents such as toluene, xylene and the like; ester based solvents such as ethyl acetate, butyl acetate and the like; and combinations thereof.
The acrylic polyol (A) is preferably obtained in a form of a solution of an organic solvent or a mixture comprising the organic solvent, and can be used as a raw material of an adhesive without removing the organic solvent.

The polymerization reaction conditions such as reaction temperature, reaction time, type of organic solvents, type and concentration of monomers, stirring rate, as well as type and concentration of polymerization initiators in the polymerization of the polymerizable monomers can be appropriately selected according to characteristics and the like of the objective adhesive.
The polymerization initiator is preferably a compound which can accelerate the polymerization of the polymerizable monomer when added in a small amount and can be used in an organic solvent. Examples of the polymerization initiator include ammonium persulfate, t-butyl peroxybenzoate, 2,2-azobisisobutyronitrile (AIBN), and 2,2-azobis(2,4-dimethylvarelonitrile).

A chain transfer agent can be appropriately used for the polymerization in the present invention so as to adjust the molecular weight. It is possible to use compounds well-known to those skilled in the art as the “chain transfer agent”. Examples thereof include mercaptans such as n-dodecylmercaptan (nDM), laurylmethylmercaptan, mercaptoethanol and the like.

As mentioned above, the acrylic polyol is obtainable by polymerizing the polymerizable monomers. Considering the coatability of the adhesive and appearance of the laminated sheet, the weight average molecular weight (Mw) of the acrylic polyol is 10,000 to 100,000, preferably 10,000 to 90,000, and most preferably 30,000 to 80,000. The weight average molecular weight is a value obtained by gel permeation chromatography (GPC) in terms of polystyrene standard. Specifically, the value can be obtained using the following GPC apparatus and measuring method. HCL-8220GPC manufactured by TOSOH CORPORATION is used as a GPC apparatus, and RI is used as a detector. Two TSK gel SuperMultipore HZ-M manufactured by TOSOH CORPORATION are used as a GPC column. A sample is dissolved in tetrahydrofuran and the obtained solution is allowed to flow at a flow rate of 0.35 ml/min and a column temperature of 40°C, and then Mw is determined by conversion of the measured molecular weight based on a calibration curve which is obtained by using polystyrene having a monodisperse molecular weight as a standard reference material.

A hydroxyl value of the acrylic polyol is preferably 0.5 to 40 mgKOH/g, more preferably 1 to 30 mgKOH/g, and particularly preferably 4 to 20 mgKOH/g. The hydroxyl value of the acrylic polyol is not in the above range, an adhesive for laminated sheets cannot have sufficient properties with regard to peel strength after aging and hydrolysis resistance, and it would be difficult to use the adhesive as an adhesive for laminated sheets.

In the present description, the hydroxyl value is a number of mg of potassium hydroxide required to neutralize acetic acid combined with hydroxyl groups in case of acetylating 1 g of a resin.
In the present invention, the hydroxyl value is specifically calculated by the following formula (ii).
(ii): Hydroxyl value = (Weight of monomer having a hydroxyl group / Molecular weight of monomer having a hydroxyl group) × Mole number of hydroxyl groups contained in 1 mol of monomer having a hydroxyl group × Formula weight of KOH × 1,000/Weight of the acrylic polyol

A glass transition temperature of the acrylic polyol can be set by adjusting a mass fraction of a monomer to be used. The glass transition temperature of the acrylic polyol can be determined based on a glass transition temperature of a homopolymer obtainable from each monomer and a mass fraction of the homopolymer used in the acrylic polyol using the following calculation formula (i). It is preferred to determine a composition of the monomer of the adhesive using the glass transition temperature determined by the calculation:
(i): 1/Tg = W1/Tg1 + W2/Tg2 + ... + Wn/Tgn
where, in the above formula (i), Tg denotes the glass transition temperature of the acrylic polyol, each of W1, W2, ... , Wn denotes the mass fraction of each monomer, and each of Tg1, Tg2, ... , and Tgn denotes the glass transition temperature of the homopolymer corresponding to each monomer.

A value described in the document can be used as Tg of the homopolymer. It is possible to refer, as such a document, for example, the following documents: Acrylic Ester Catalog of Mitsubishi Rayon Co., Ltd. (1997 Version); edited by Kyozo Kitaoka, “Shin Kobunshi Bunko 7, Guide to Synthetic Resin for Coating Material”, Kobunshi Kankokai, published in 1997, pp.168-169; and “POLYMER HANDBOOK”, 3rd Edition, pp.209-277, John Wiley & Sons, Inc. published in 1989.

In the present specification, glass transition temperatures of homopolymers of the following monomers are as follows.
Methyl methacrylate: 105°C
2-Ethylhexyl acrylate: -70°C
n-Butyl acrylate: -54°C
Ethyl acrylate: -20°C
2-Hydroxyethyl methacrylate: 55°C
2-Hydroxyethyl acrylate: -15°C
Glycidyl methacrylate: 41°C
Acrylonitrile: 130°C
Styrene: 105°C
Cyclohexyl methacrylate: 83°C
Acrylic acid: 106°C

In the present invention, the acrylic polyol preferably has a glass transition temperature of -35°C to 20°C. Considering peel strength after aging and hydrolysis resistance, the acrylic polyol more preferably has a glass transition temperature of -30°C to 20°C, and particularly preferably has a glass transition temperature of -20°C to 15°C.
When the acrylic polyol has a glass transition temperature of -35°C to 20°C, a cohesive force of the adhesive for laminated sheets is maintained, leading to improved peel strength after aging and hydrolysis resistance.

In the present description, (B) at least one selected from carboxylic acids and carboxylic anhydrides means that any one of the carboxylic acids and carboxylic anhydrides may be used alone and a mixture (or combination) of the both may be used.
Since the adhesive for laminated sheets of the present invention comprises the component (B), it is excellent in curability while maintaining suitable pot life.
The "carboxylic acid" means an organic acid having at least one carboxyl group, and the "carboxyl anhydride" means a compound having a structure (carboxylic anhydride group) in which two carboxyl groups are dehydrated and condensed.

Examples of the carboxylic acid include formic acid, acrylic acid, methacrylic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, stearic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimeric acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, eicosapentaenoic acid, sorbic acid, 2-hydroxypropanoic acid, 2-hydroxybutanoic acid, 2-hydroxypropanetricarboxylic acid, 3-hydroxyphenylacetic acid, glycolic acid, diphenolic acid, benzoic acid, 4-hydroxybenzoic acid, salicylic acid, gallic acid, cinnamic acid, phthalic acid, isophthalic acid, 2-oxopropanoic acid, dimer acid, trimer acid, 1,2,3-propanetricarboxylic acid, melitic acid, pyromelitic acid, trimelitic acid and the like.

Examples of the carboxylic anhydride include acetic anhydride, phthalic anhydride, 4-methylhexahydrophthalic anhydride, benzoic anhydride, 4,4-oxyphthalic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, trimelitic anhydride, cyclohexane-1,2,4-tricarboxylic anhydride and the like.

In the present invention, at least one selected from carboxylic acids and carboxylic anhydrides (B) preferably comprises a compound having a melting point of 280°C or lower. The component (B) more preferably comprises a compound having a melting point of 250°C or lower, and most preferably comprises a compound having a melting point of 200°C or lower. When the melting point of the component (B) is in the above range, the adhesive of the present invention has an improved curability, and appearance of the obtainable laminated sheet would be more preferable.

In the present description, the melting point refers to a value measured by differential scanning calorimetry (DSC). Specifically, after weighing 10 mg of a sample in an aluminum container, the measurement is carried out at temperature rise rate of 10°C/minute using DSC6220 (trade name) manufactured by SII NanoTechnology Inc, and the temperature of a top of a fusion peak refers to the melting point.

In the present invention, at least one selected from carboxylic acids and carboxylic anhydrides (B) is preferably blended in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the acrylic polyol (A). When the component (B) is blended in an amount of the above range, the adhesive for laminated sheets of the present invention has an improved curability, but the pot life would not become too short, and as a result, it would be easier to apply the adhesive.

In the present invention, the component (B) is blended in an amount of 0.01 to 8.0 parts by weight per 100 parts by weight of the total of the components (A) to (C). When the component (B) is blended in an amount of the above range, the adhesive for laminated sheets of the present invention has an improved curability, but the pot life would not become too short, and as a result, it would be easier to apply the adhesive.

In the present invention, the component (B) preferably comprises at least one selected from adipic acid, benzoic acid, dimer acid, azelaic acid and trimelitic anhydride.
When the component (B) comprises the at least one selected from adipic acid, benzoic acid, dimer acid, azelaic acid and trimelitic anhydride, the adhesive for laminated sheets of the present invention not only has an improved curability, but also is excellent in both peel strength after aging and hydrolysis resistance.

In the present invention, examples of the isocyanate compound (C) include an aliphatic isocyanate, an alicyclic isocyanate and an aromatic isocyanate, and there is no particular limitation on the isocyanate compound as long as the objective adhesive for laminated sheets of the present invention can be obtained.
In the present specification, the “aliphatic isocyanate” refers to a compound which has a chain-like hydrocarbon chain in which isocyanate groups are directly combined to the hydrocarbon chain, and also has no cyclic hydrocarbon chain. Although the “aliphatic isocyanate” may have an aromatic ring, the aromatic ring is not directly combined with the isocyanate groups.
In the present specification, the aromatic ring is not comprised in the cyclic hydrocarbon chain.

The “alicyclic isocyanate” is a compound which has a cyclic hydrocarbon chain and may have a chain-like hydrocarbon chain. The isocyanate group may be either directly combined with the cyclic hydrocarbon chain, or may be directly combined with the obtainable chain-like hydrocarbon chain. Although the “alicyclic isocyanate” may have an aromatic ring, the aromatic ring is not directly combined with the isocyanate groups.
The “aromatic isocyanate” refers to a compound which has an aromatic ring, in which isocyanate groups are directly combined with the aromatic ring. Therefore, a compound, in which isocyanate groups are not directly combined with an aromatic ring, is classified into the aliphatic isocyanate or the alicyclic isocyanate even though it has the aromatic ring in the molecule.

Therefore, for example, 4,4’-diphenylmethane diisocyanate (OCN-C₆H₄-CH₂-C₆H₄-NCO) corresponds to the aromatic isocyanate, since the isocyanate groups are directly combined with the aromatic ring. On the other hand, for example, xylylene diisocyanate (OCN-CH₂-C₆H₄-CH₂-NCO) corresponds to the aliphatic isocyanate since the isocyanate groups are not directly combined with the aromatic ring and are combined with methylene groups even though it has an aromatic ring.
The aromatic ring may be fused with two or more benzene rings.

Examples of the aliphatic isocyanate include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane (hereinafter also referred to as HDI), 1,6-diisocyanato-2,2,4-trimethylhexane, 2,6-diisocyanatohexanoic acid methyl ester (lysine diisocyanate), 1,3-bis(isocyanatomethyl)benzene (xylylene diisocyanate) and the like.
Examples of the alicyclic isocyanate include 5-isocyanato-1-isocyanatomethyl-1,3,3-trimethylcyclohexane (isophorone diisocyanate), 1,3-bis(isocyanatomethyl)cyclohexane (hydrogenated xylylene diisocyanate), bis(4-isocyanatocyclohexyl)methane (hydrogenated diphenylmethane diisocyanate), 1,4-diisocyanatocyclohexane and the like.

Examples of the aromatic isocyanate include 4,4’-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate and the like. These isocyanate compounds can be used alone, or in combination.
In the present invention, there is no particular limitation on the isocyanate compound as long as the objective adhesive for laminated sheets of the present invention can be obtained. From the viewpoint of weatherability, it is preferred to select from aliphatic isocyanates and alicyclic isocyanates. It is particularly preferred to select from HDI, isophorone diisocyanate, xylylene diisocyanate, and derivatives thereof.

In the present invention, an equivalent ratio (NCO/OH) of isocyanate groups based on (C) the isocyanate to hydroxyl groups based on (A) the acrylic polyol is preferably 0.5 to 4.5, more preferably 1.0 to 4.0, and particularly preferably 1.5 to 3.5. When the equivalent ratio is in the above range, the adhesive for laminated sheets is excellent in curability, peel strength after aging and hydrolysis resistance.
In the present specification, the NCO/OH equivalent ratio is calculated according to the following equation (iii):
(iii): NCO/OH ratio = Amount of isocyanate (parts by weight) × (561/Hydroxyl value of the acrylic polyol) × (NCO %/(42 × 100) × (100/Amount of the polyol (weight of solid content))

The adhesive for laminated sheet of the present invention preferably further comprises (D) a silane compound.
It is possible to use, as the silane compound, for example, (meth)acryloxyalkyltrialkoxysilanes, (meth)acryloxyalkylalkylalkoxysilanes, vinyltrialkoxysilanes, vinylalkylalkoxysilanes, epoxysilanes, mercaptosilanes and isocyanuratesilanes. However, the silane compound is not limited to only these silane compounds.

Examples of the “(meth)acryloxyalkyltrialkoxysilanes” include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 4-(meth)acryloxyethyltrimethoxysilane and the like.
Examples of the “(meth)acryloxyalkylalkylalkoxysilanes” include 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropylethyldiethoxysilane, 3-(meth)acryloxyethylmethyldimethoxysilane and the like.

Examples of the “vinyltrialkoxysilanes” include vinyltrimethoxysilane, vinyltriethoxysilane, vinyldimethoxyethoxysilane, vinyltri(methoxyethoxy)silane, vinyltri(ethoxymethoxy)silane and the like.
Examples of the “vinylalkylalkoxysilanes” include vinylmethyldimethoxysilane, vinylethyldi(methoxyethoxy)silane, vinyldimethylmethoxysilane, vinyldiethyl(methoxyethoxy)silane and the like.

For example, the “epoxysilanes” can be classified into glycidyl-based silanes and epoxycyclohexyl-based silanes. The “glycidyl based silanes” have a glycidoxy group, and specific examples thereof include 3-glycidoxypropylmethyldiisopropenoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyldiethoxysilane and the like.
The “epoxycyclohexyl based silanes” have a 3,4-epoxycyclohexyl group, and specific examples thereof include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane and the like.

Examples of the “mercaptosilanes” include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane and the like.
Examples of the “isocyanuratesilanes” include tris(3-(trimethoxysilyl)propyl)isocyanurate and the like.

The silane compound (D) is preferably comprised in an amount of 1 to 10 parts by weight, more preferably 2 to 6 parts by weight, and most preferably 2.5 to 5 parts by weight, based on 100 parts by weight of the total weight of the components (A) to (C). When the adhesive for laminated sheets of the present invention comprises the silane compound (D) in an amount in the above range, the adhesive for laminated sheets of the present invention is more excellent in balance between adhesion after aging and hydrolysis resistance.

In the present invention, the silane compound (D) preferably comprises a glycidyl-based silane compound which is classified into epoxysilanes. Examples of the glycidyl-based silane compound include a functional group represented by the chemical formula (1).
Chemical Formula (1):

The functional group represented by the chemical formula (1) is a glycidoxy group.

In these glycidyl-based silane compounds, 3-glycidoxypropyltrialkoxysilane is particularly preferable. To improve hydrolysis resistance and adhesion after aging of the adhesive for laminated sheet, a 3-glycidoxypropyltrialkoxysilane compound is most suitable.

The silane compound (D) preferably acts as a silane coupling agent. The silane coupling agent refers to a compound which is composed of an organic element (or substance) and silicon, and also has both of an organic functional group “Y” such as an amino group, an epoxy group, a methacrylic group, a vinyl group and a mercapto group, which can be expected to react or interact with an organic substance, and a hydrolyzable group “OR” such as a methoxy group, an ethoxy group and a methylcarbonyloxy group in one molecule, thus enabling linking between an organic material and an inorganic material, which is not easy to be bonded in an ordinary way.

Therefore, a compound, which is a glycidyl-based silane compound and acts as a silane coupling agent, means a silane coupling agent which comprises a functional group having a glycidoxy group as the organic functional group “Y”. The adhesive for laminated sheets of the present invention exhibits further improved initial adhesion and hydrolysis resistance by comprising the glycidyl-based silane compound, and is particularly excellent in initial adhesion between polyvinylidene fluoride (PVDF) and polyethylene terephthalate (PET).

The method of blending the silane compound (D) is not particularly limited as long as the objective adhesive can be obtained and, for example, the silane compound (D) may be blended with the acrylic polyol (A), and preferably a solution and/or a mixture of the component (A) in an organic solvent in advance, or may be added to a mixed solution of the acrylic polyol (A) and the isocyanate compound (C) in advance.

The adhesive for laminated sheets of the present invention may comprise an ultraviolet absorber for the purpose of improving long-term weatherability. It is possible to use, as the ultraviolet absorber, a hydroxyphenyltriazine-based compound and other commercially available ultraviolet absorbers. The “hydroxyphenyltriazine-based compound” is a kind of triazine derivatives in which a hydroxyphenyl derivative is combined with a carbon atom of a triazine derivative, and examples thereof include TINUVIN 400, TINUVIN 405, TINUVIN 479, TINUVIN 477 and TINUVIN 460 (all of which are trade names) and the like which are commercially available from BASF Corp.

The adhesive for laminated sheets may further comprise a hindered phenol-based compound. The “hindered phenol-based compound” is commonly referred to as a hindered phenol-based compound, and there is no particular limitation as long as the objective adhesive for laminated sheets of the present invention can be obtained.
Commercially available products can be used as the hindered phenol-based compound. The hindered phenol-based compound is, for example, commercially available from BASF Corp. Examples thereof include IRGANOX1010, IRGANOX1035, IRGANOX1076, IRGANOX1135, IRGANOX1330 and IRGANOX1520 (all of which are trade names) and the like. The hindered phenol-based compound is added to the adhesive as an antioxidant and may be used, for example, in combination with a phosphite-based antioxidant, a thioether-based antioxidant, an amine-based antioxidant and the like.

The adhesive for laminated sheets of the present invention may further comprise a hindered amine-based compound. The “hindered amine-based compound” is commonly referred to as a hindered amine-based compound, and there is no particular limitation as long as the objective adhesive for laminated sheets of the present invention can be obtained.
Commercially available products can be used as the hindered amine-based compound. Examples of the hindered amine-based compound include TINUVIN 765, TINUVIN 111FDL, TINUVIN 123, TINUVIN 144, TINUVIN 152, TINUVIN 292 and TINUVIN 5100 (all of which are trade names) and the like which are commercially available from BASF Corp. The hindered amine-based compound is added to the adhesive as a light stabilizer and may be used, for example, in combination with a benzotriazole-based compound, a benzoate-based compound and the like.

The adhesive for laminated sheets of the present invention can further comprise the other components as long as the objective adhesive for laminated sheets can be obtained.
There is no particular limitation on timing of the addition of the “other components” to the adhesive for laminated sheets as long as the objective adhesive for laminated sheets of the present invention can be obtained. For example, the other components may be mixed with the component (A) in advance, or may be added to a mixture obtained by mixing the components (A) to (C).

Examples of the “other components” include a catalyst, a tackifier resin, a pigment, a plasticizer, a flame retardant, a wax and the like.
Examples of the “catalyst” include metal catalysts and non-metal catalysts.
Examples of the “metal catalysts” include tin catalysts (trimethyltin laurate, trimethyltin hydroxide, stannous octoate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin maleate and the like), lead based catalysts (lead oleate, lead naphthenate, lead octenoate and the like), and other metal catalysts (naphthenic acid metal salts such as cobalt naphthenate), bismuth octoate, sodium persulfate, potassium persulfate and the like.
Examples of the “non-metal catalysts” preferably include amine-based catalysts. Examples of the “amine-based catalysts” include triethylenediamine, tetramethylethylenediamine, tetramethylhexylenediamine, diazabicycloalkenes, dialkylaminoalkylamines and the like.

Examples of the “tackifier resin” include a styrene-based resin, a terpene-based resin, an aliphatic petroleum resin, an aromatic petroleum resin, a rosin ester, an acrylic resin, a polyester resin (excluding polyesterpolyols) and the like.
Examples of the “pigment” include titanium oxide, carbon black and the like.
Examples of the “plasticizer” include dioctyl phthalate, dibutyl phthalate, diisononyl adipate, dioctyl adipate, mineral spirit and the like.
Examples of the “flame retardant” include a halogen-based flame retardant, a phosphorous-based flame retardant, an antimony-based flame retardant, metal hydroxide-based flame retardant and the like.
The “wax” is preferably a wax such as a paraffin wax and a microcrystalline wax.

The adhesive for laminated sheets of the present invention comprises the above-mentioned components (A) to (C) and optionally comprises the component (D), and the adhesive for laminated sheets of the present invention can be obtained by mixing these components. The method of mixing the respective components is not particularly limited as long as the objective adhesive for laminated sheet of the present invention can be obtained. The order of mixing the components is not also particularly limited. The adhesive for laminated sheets of the present invention can be produced without using a special mixing method and a special mixing order.

Commonly, the adhesive for laminated sheets of the present invention preferably has a form of a mixture containing an organic solvent, and may be either in a form of a solution or a suspension.
The adhesive for laminated sheets of the present invention preferably has a concentration (solid component concentration) of 30% by weight or more, and more preferably has a concentration (solid component concentration) of 30 to 40% by weight.
The adhesive for laminated sheets of the present invention preferably has long pot life, and is preferably excellent in coatability in the case of coating a base material (film) for laminated sheets.

The pot life of the adhesive for laminated sheets of the present invention is evaluated by mixing the components (A) to (C) and optionally mixing additive(s) (D) to obtain an adhesive, measuring viscosity of the adhesive at 25°C for several hours, and determining a degree of increase in viscosity of the adhesive. The viscosity of the adhesive for laminated sheets is measured by using a rotational viscometer (Model BM, manufactured by TOKIMEC Inc.). If the viscosity of the adhesive rapidly increases, coatability of the adhesive for laminated sheets of the present invention may deteriorate, and thus there may be some difficulties on the productivity of a laminated sheet.

The adhesive for laminated sheets of the present invention is preferably applied onto a film constituting the laminated sheet, and is excellent in coatability. If the adhesive has poor coatability, there may arise poor coating such as stringiness or lineation. To prevent poor coating of the adhesive for laminated sheets, if an organic solvent is further added to reduce the viscosity of the adhesive, there may arise an increase in production cost of the laminated sheet.

The present invention further provides a kit for obtaining an adhesive for laminated sheet. The kit comprises, for example, a first component comprising the above-mentioned component (A) and a second component comprising the above-mentioned component (C). The component (B) may be comprised in the first or second component and the component (B) may be comprised in a third component which is different from the first and second components, and the third component is comprised in the kit. Furthermore, the first component, the second component and, if possible, the third component can optionally comprise at least one selected from the component (D) and other components. It is possible to obtain the adhesive for laminated sheets of the present invention by mixing these components.

The kit is preferably a two-part adhesive. The two-part adhesive comprises a first component and a second component and, for example, the first component comprises the above-mentioned component (A) and the second component comprises the above-mentioned component (C), and the component (B) and, optionally, the component (D) and other component are comprised in either the first or second component. However, it is not necessarily that all components are comprised in one component.

The adhesive for laminated sheets of the present invention is commonly applied on a film constituting the laminated sheet at room temperature and heated, if necessary, to remove the solvent, thus forming an adhesive layer. A film is applied on the adhesive layer, and then pressed and heated while being optionally evacuated, and thus curing proceeds to produce a laminated sheet.

The adhesive for laminated sheets of the present invention has long pot life and excellent coatability, and an adhesive layer thereof maintains hydrolysis resistance over a long term at high temperature and is excellent in curability, and is also excellent in total balance among various properties, for example, adhesion to a film after aging.
Therefore, a laminated sheet is manufactured by laminating (or bonding) a plurality of adherends using the adhesive of the present invention, and the obtained laminated sheet is used for producing various packaging bags and various outdoor materials.

The packaging bag of the present invention means a bag like article (or material) obtained by processing the laminated sheet so as to enclose foods, detergents, shampoo, rinse and the like. Examples of the outdoor materials of the present invention include barrier materials, roof materials, solar battery modules, window materials, outdoor flooring materials, illumination protective materials, automobile members, signboards and the like.
These packaging bags and outdoor materials comprise the laminated sheet obtainable by laminating plural films as an adherend. Examples of the films include a film (metal deposited film) in which metal is deposited on a plastic base material, and a film (plastic film) in which metal is not deposited.

It is required for an adhesive for producing a solar battery module to have initial adhesion to a film and curability in a particularly high level, and further hydrolysis resistance at a high temperature for a long term. The adhesive for laminated sheets of the present invention is excellent in hydrolysis resistance at a high temperature for a long term, and thus the adhesive is suitable as an adhesive for solar battery backsheets.
When the laminated sheet is produced, the adhesive for laminated sheets of the present invention is applied on a film. The application can be performed by various methods such as gravure coating, wire bar coating, air knife coating, die coating, lip coating, comma coating and the like. The adhesive for laminated sheets of the present invention is applied to form an adhesive layer, thus laminating (or bonding) a plurality of films, leading to completion of a laminated sheet.

Embodiments of the laminated sheet of the present invention are shown in Figs. 1 to 3, but the present invention is not limited to these embodiments.
Fig. 1 is a sectional view showing an embodiment of the laminated sheet of the present invention. The laminated sheet 10 is formed of two films and an adhesive layer 13 interposed therebetween, and the two

films

11 and 12 are laminated each other by the adhesive layer 13. The

films

11 and 12 may be made of either the same or different material. In Fig. 1, the two

films

11 and 12 are laminated each other, or three or more films may be laminated one another.

Another embodiment of the laminated sheet of the present invention is shown in Fig. 2. In Fig. 2, a thin film 11a is formed between the film 11 and the adhesive layer 13. For example, the drawing shows an embodiment in which a metal thin film 11a is formed on the surface of the film 11 when the film 11 is a plastic film. The metal thin film 11a can be formed on the surface of the plastic film 11 by vapor deposition, and the laminated sheet of Fig. 2 can be obtained by laminating the film 11 (on which surface the metal thin film 11a is formed) with the film 12 by interposing the adhesive layer 13 therebetween.

Examples of the metal to be deposited on the plastic film include aluminum, steel, copper and the like. It is possible to impart barrier properties to the plastic film by subjecting the film to vapor deposition. Silicon oxide or aluminum oxide is used as a vapor deposition material. The plastic film 11 as a base material may be either transparent, or white- or black-colored.

A plastic film made of a plastic selected from such as polyvinyl chloride, polyester, a fluorine resin and an acrylic resin is used as the film 12. In order to impart heat resistance, weatherability, rigidity, and insulating properties, a polyethylene terephthalate film and/or a polybutylene terephthalate film is preferably used. The

films

11 and 12 may be either transparent, or may be colored.
The deposited thin film 11a of the film 11 and the film 12 are laminated (or bonded) each other using the adhesive layer 13 of the present invention, and the

films

11 and 12 are often laminated each other by a dry lamination method.

Fig. 3 shows a sectional view of an example of a solar battery module as an embodiment of outdoor materials of the present invention. In Fig. 3, it is possible to obtain a solar battery module 1 by overlaying a glass plate 40, a sealing material 20 such as an ethylene-vinyl acetate resin (EVA), plural solar battery cells 30 which are commonly connected with each other to generate a desired voltage, and a backsheet 10 one another, and then fixing these

members

10, 20, 30 and 40 using a spacer 50.
As mentioned above, since the backsheet 10 is a laminate of

plural films

11 and 12, it is required for the adhesive layer 13 to cause no peeling of the

films

11 and 12 even if the backsheet 10 is exposed to outdoor over a long period.

The solar battery cell 30 is often manufactured by using silicon, and is sometimes manufactured by using an organic resin comprising a dye. In that case, the solar battery module 1 becomes an organic-based (dye-sensitization) solar battery module. Since colorability is required to the organic-based (dye-sensitization) solar battery, a transparent film is often used as the

films

11 and 12 which constitute the solar battery backsheet 10. Therefore, it is required for the adhesive layer 13 to cause very little change in color difference even though exposed to outdoor over a long period, and to have excellent weatherability.
In the present invention, when the sealing material 20 is integrated with the backsheet 10, the adhesive layer 13 is not released form the film 11.

The present invention is illustrated with reference to Examples and Comparative Examples, but these examples are for explaining the present invention and do not limit the present invention at all.

<Synthesis of acrylic polyol>
Synthetic Example 1 ((A1) Acrylic polyol (Polymer 1))
In a four-necked flask equipped with a stirring blade, a thermometer and a reflux condenser tube, 100 parts by weight of ethyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was charged and refluxed at about 80°C. In the flask, 1.0 parts by weight of 2,2-azobisisobutyronitrile was added as a polymerization initiator, and a mixture of monomers in each amount shown in Table 1 was continuously added dropwise over 1 hour and 30 minutes. After further heating for one hour, a step in which 0.2 part by weight of 2,2-azobisisobutyronitrile was added to the mixture and then the mixture was reacted for one hour was repeated four times. A solution comprising 50% by weight of non-volatile components (solid content) of an acrylic polyol (polymer 1) (A1) was obtained.
The composition of the polymerizable monomer components of the acrylic polyol (polymer 1) (A1) and physical properties of the obtained polymer 1 are shown in Table 1.

Synthetic Examples 2 to 19
A polymer 2 (A2) to a polymer 19 (A’19) were prepared by using a method similar to that of Synthetic Example 1 except for adjusting the molecular weight of each of the polymers by modifying the amount of 2,2-azobisisobutyronitrile to be added and except for changing the composition of the monomers and the like to be used so as to synthesize each of the polymers (or polyols) as shown in Tables 1 and 2. Physical properties of the obtained polymers 2 to 19 are shown in Tables 1 and 2.

The polymerizable monomers shown in Tables 1 and 2, and other components thereof are shown below.
Methyl methacrylate (MMA): manufactured by Wako Pure Chemical Industries, Ltd.
2-Ethylhexyl acrylate (2EHA): manufactured by Wako Pure Chemical Industries, Ltd.
Butyl acrylate (BA): manufactured by Wako Pure Chemical Industries, Ltd.
Ethyl acrylate (EA): manufactured by Wako Pure Chemical Industries, Ltd.
Glycidyl methacrylate (GMA): manufactured by Wako Pure Chemical Industries, Ltd.
Acrylonitrile (AN): manufactured by Wako Pure Chemical Industries, Ltd.
2-Hydroxyethyl methacrylate (HEMA): manufactured by Wako Pure Chemical Industries, Ltd.
2-Hydroxyethyl acrylate (HEA): manufactured by Wako Pure Chemical Industries, Ltd.
Styrene (St): manufactured by Wako Pure Chemical Industries, Ltd.
Cyclohexyl methacrylate (CHMA): manufactured by Wako Pure Chemical Industries, Ltd.
Acrylic acid (AA): manufactured by Wako Pure Chemical Industries, Ltd.

<Calculation of glass transition temperatures (Tg) of polymers>
Tg of each of the polymer 1 (A1) to the polymer 19 (A’19) was calculated by the above-mentioned formula (i) using the glass transition temperatures of homopolymers of the “polymerizable monomers” as a raw material of each polymer. A document value was used as the Tg of each homopolymer of methyl methacrylate and the like.

<Production of adhesive for laminated sheets>
Each of adhesives for laminated sheets was manufactured by blending a component (A) shown Tables 1 and 2 with components (B) and (C) as shown below.

(B) At least one selected from carboxylic acids and carboxylic anhydrides
(B1) Acetic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: -8°C)
(B2) Hexanoic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: -6°C)
(B3) Stearic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 63°C)
(B4) Adipic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 156°C)
(B5) Azelaic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 104°C)
(B6) Oleic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 2°C)
(B7) Maleic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 143°C)
(B8) Benzoic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 125°C)
(B9) Isophthalic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 351°C)
(B10) Trimelitic anhydride (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 169°C)
(B11) 4,4-oxydiphthalic anhydride (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 229°C)
(B12) Dimer acid (Pripol 1013 (trade name) manufactured by Croda International Plc., melting point: -47°C)
(B’13) Methanesulfonic acid (manufactured by Wako Pure Chemical Industries, Ltd., melting point: 21°C)

Using a differential scanning calorimeter (DSC) (manufactured by SII NanoTechnology Inc. under the trade name of DSC6620), the melting point of the component (B) was measured. A sample (ca. 10 mg) of each of (B) the carboxylic and carboxylic anhydride was weighed in an aluminum container, and the container was placed in the DSC apparatus and cooled to -70°C. Then, a DSC curve was measured at a rate of temperature increase of 10°C/min. A temperature of an endothermic peak top exhibited on the obtained DSC curve was referred to as the melting point.

(C) Isocyanate compound
(C1) Isocyanate compound 1 (Hexamethylene diisocyanate trimer: SUMIDULE N3300 (trade name), manufactured by Sumika Bayer Urethane Co., Ltd.: Isocyanurate)
(C2) Isocyanate compound 2 (Hexamethylene diisocyanate trimer: SUMIDULE HT (trade name), manufactured by Sumika Bayer Urethane Co., Ltd.: Adduct of trimethylolpropane)
(C3) Isocyanate compound 3 (Xylylene diisocyanate: TAKENATE 500 (trade name) manufactured by Mitsui Chemicals, Inc.)

Example 1
As shown in Table 3, 90.1 g of a polymer 1 (A1) [180.2 g of an ethyl acetate solution (50.0 wt% of solid content) of the polymer 1], 4.5 g of oleic acid (B6), 3.9 g of an isocyanate compound 1 (C1), 1.5 g of an isocyanate compound 3 (C3) and 0.5 g of 3-glycidoxypropyltriethoxysilane (D2) manufactured by EVONIK Industries AG were weighed and mixed, and then ethyl acetate was added so that the solid content was 40% by weight to obtain an adhesive for laminated sheets of Example 1.

Examples 2 to 19 and Comparative Examples 1 to 8
Each of adhesives for laminated sheets was obtained by blending the components (A) to (C) in each of the amounts shown in Tables 3 to 5 by using a method similar with that of Example 1. In Tables 3 to 5, a silane compound as a component (D) is optionally blended, and (D1) is 3-glycidoxypropyltrimethoxysilane manufactured by EVONIK Industries AG and (D2) is 3-glycidoxypropyltriethoxysilane manufactured by EVONIK Industries AG, as mentioned above.

These adhesives for laminated sheets were evaluated by the following tests.
<Production of laminated sheet 1>
Each of the adhesives for laminated sheets of Examples and Comparative Examples was applied on a transparent polyethylene terephthalate (PET) sheet (O300EW36 (trade name) manufactured by Mitsubishi Polyester Film Corporation) using a bar coater so that the weight of the solid content becomes 10 g/m², and then dried at 80°C for 5 minutes to form an adhesive layer. Then, a surface-treated transparent polyolefin film (linear low-density polyethylene film manufactured by Futamura Chemical Co., Ltd. under the trade name of LL-XUMN #30) was laid on the surface of the PET sheet, on which the adhesive layer was formed, so that the treated surface of the polyolefin film contacted with the surface of the PET sheet, and then the polyolefin film and the PET sheet were pressed using a heat (or hot) roll press machine at 80°C under a pressing pressure of 0.9 MPa and 5 m/min to obtain each of laminated sheets 1 of Examples and Comparative Examples.

<Production of laminated sheet 2>
Each of the adhesives for laminated sheets of Examples and Comparative Examples was applied on a transparent polyethylene terephthalate (PET) sheet (O300EW36 (trade name) manufactured by Mitsubishi Polyester Film Corporation) using a bar coater so that the weight of the solid content becomes 10 g/m², and then dried at 80°C for 5 minutes to form an adhesive layer. Then, a surface-treated PET film (Shinebeam (trade name) manufactured by TOYOBO Co., Ltd.) was laid on the surface of the PET sheet, on which the adhesive layer was formed, so that the treated surface of the PET film contacted with the surface of the PET sheet, and then the PET film and the PET sheet were pressed using a heat (or hot) roll press machine at 80°C under a pressing pressure of 0.9 MPa and 5 m/min to obtain each of laminated sheets 2 of Examples and Comparative Examples.

<Evaluation>
The adhesives for laminated sheets were evaluated by the following method. The evaluation results are shown in Tables 3 to 5.
1. Evaluation of appearance of laminated sheet
After aging the laminated sheet 1 at 50°C for 5 days, the surface of the laminated sheet 1 was visually observed and evaluated. Evaluation criteria are as follows.
B (Good): The surface of a film of the laminated sheet 1 is smooth.
C (Normal): Wrinkles or foams due to shrink of the laminated sheet 1 are observed on a part of the surface of the laminated sheet 1.
D (Bad): Wrinkles or foams due to shrink of the laminated sheet 1 are observed on most of the surface film of the laminated sheet 1.

2. Evaluation of reaction rate (Curability)
A reaction rate of each adhesive layer (adhesive for laminated sheets) of the laminated sheet 1 was evaluated by measuring infrared absorption (IR) immediately after press using a hot rolling press of the laminated sheet 1, and after aging at 50°C for 72 hours and 120 hours. The IR measurement was carried out using Nicolet 380 manufactured by Thermo Electron, a ratio of peak (2,270 cm^-1 to 2,250 cm^-1) height of isocyanate groups to peak (2,970 cm^-1 to 2,940 cm^-1) height of C-H stretching vibration of hydrocarbon groups was obtained at each aging time. The reaction rate can be calculated by the following equation (v).
(v): Reaction rate (%) = [1 - (Peak height of isocyanate groups after aging for 72 hours or 120 hours/Peak height of C-H stretching vibration of hydrocarbon groups after aging for 72 hours or 120 hours)/(Peak height of isocyanate groups immediately after press/Peak height of C-H stretching vibration of hydrocarbon groups immediately after press)] × 100
Evaluation criteria are as follows.
A (Excellent): Reaction rate is 95% or more after aging at 50°C for 72 hours.
B (Good): Reaction rate is 80% or more and less than 95% after aging at 50°C for 72 hours.
C (Normal): Reaction rate is less than 80% after aging at 50°C for 72 hours, and is 80% or more after aging for 120 hours.
D (Bad): Reaction rate is less than 80% after aging at 50°C for 120 hours.

3. Evaluation of adhesion to film after aging
The laminated sheet 2 after aging at 50°C for 120 hours was cut into pieces of 15 mm in width to obtain a sample for evaluation. Using a tensile strength testing machine (manufactured by ORIENTEC Co., Ltd. under the trade name of TENSILON RTM-250), a 180° peel test was carried out under a room temperature environment at a testing speed of 100 mm/min. Evaluation criteria are as follows.
A (Excellent): Peel strength is 12 N/15 mm or more.
B (Good): Peel strength is 9 N/15 mm or more and less than 12 N/15 mm.
C (Normal): Peel strength is 6 N/15 mm or more and less than 9 N/15 mm.
D (Bad): Peel strength is 1 N/15 mm or more and less than 6 N/15 mm.

4. Evaluation of hydrolysis resistance
Evaluation of hydrolysis resistance was carried out by an accelerated evaluation method using pressurized steam. The laminated sheet 2 after aging at 50°C for 120 hours was cut out into pieces of 15 mm in width to obtain a sample for evaluation. The sample was left to stand under a pressurizing environment at 121°C under 0.1 MPa for 48 hours using a high-pressure cooker (manufactured by Yamato Scientific Co., Ltd. under the trade name of Autoclave SP300), and then aged under a room temperature environment for one day. Then, the sample was cut out into pieces of 8 cm long to obtain test pieces. Hand peel test was carried out with regard to the test pieces.

The hand peel test is a test in which each test piece is peeled into a base material and an adherend (or two adherends, specifically PET sheet and PET film in this test piece) by hands of the same measurer without using a machine, and an adhesive is evaluated considering its peeled state. When adhesion of the adhesive is satisfactorily kept, the adherend or the base material is fractured (that is, material fracture occurs) on peeling the adherend. When adhesion of the adhesive deteriorates, the adhesive itself is fractured without causing material fracture of the adherend or the base material, or peeling occurs between the adhesive and the adherend or the base material. The peel length of the adherend and the state of material fracture were visually observed by the measurer, and hydrolysis resistance of the adhesive for laminated sheets was evaluated. The evaluation criteria are as follows.
A (Excellent): Material fracture is observed when peel length of adherend is less than 0.5 cm.
B (Good): Material fracture is observed when peel length of adherend is 0.5 cm or more and less than 1.5 cm.
C (Normal): Material fracture is observed when peel length of adherend is 1.5 cm or more and less than 3 cm.
D (Bad): Material fracture is not observed even when peel length of adherend is 3 cm or more.

5. Evaluation of pot life
The components (A) to (C) and, optionally, the component (D) were mixed to obtain adhesives for laminated sheets. Immediately thereafter, each adhesive for laminated sheets was stored at 25°C for 5 hours and 24 hours. Then, pot life was evaluated after measuring solution viscosity of each adhesives for laminated sheets. The solution viscosity was measured at 25°C and at a rotation speed of 30 rpm using a rotational viscometer (Model BM, manufactured by TOKIMEC Inc.). Evaluation criteria are as follows.
A (Excellent): Ratio of increase in viscosity after storage for 24 hours is less than 2.
B (Good): Ratio of increase in viscosity after storage for 5 hours is less than 2.
C (Normal
): Ratio of increase in viscosity after storage for 5 hours is 2 or more.
“Ratio of increase in viscosity” can be calculated by the following equation (iv).
(iv): Ratio of increase in viscosity = (Viscosity after storage for 5 or 24 hours)/(Viscosity immediately after mixing the components)

6. Evaluation of coatability
In the case of producing the above-mentioned laminated sheet 1, each adhesive for laminated sheets was applied on a transparent polyethylene terephthalate sheet using a bar coater. Before drying at 80°C for 5 minutes to form an adhesive layer, it was confirmed whether or not lineation is observed on the coated surface.
B (Good): The coated surface is free from lineation and is smooth.
C (Fair): Area where lineation was observed accounts for 20% or less of the surface area of the coated surface.
D (Bad): Area where lineation was observed accounts for more than 20% of the surface area of the coated surface.

As shown in Tables 3 to 5, since the adhesives for laminated sheets of Examples 1 to 19 comprise the components (A) to (C), they are excellent in balance among the above evaluations 1 to 6, and are suitable as an adhesive for laminated sheets.
Meanwhile, the adhesives for laminated sheets of Comparative Examples 1 to 8 receive a rating of "Bad" with regard to any one of the evaluations 1 to 6. The adhesives for laminated sheets of Comparative Examples 1, 7 and 8 comprise no component (B), and the adhesives for laminated sheets of Comparative Examples 2 to 5 comprise no component (A). In the adhesive for laminated sheets of Comparative Example 6, the amount of the component (B) is excessive.
It has been proved that the mixture which does not comprise either the component (A) or (B), and the mixture comprising excessive amount of the component (B) are not useful as the adhesive for laminated sheets.

Particularly, Comparative Example 1 is inferior in three items of hydrolysis resistance, appearance of the laminated sheet and coatability, although the acrylic polyol (A15) synthesized from acrylic acid as a polymerizable monomer was used and the component (A15) has a carboxyl group.
These results revealed that a mixture, which is not obtained by introducing a carboxyl group into (A) an acrylic polyol, but blending (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxyl anhydrides, and (C) an isocyanate compound, is excellent as an adhesive for laminated sheets.

The present invention provides an adhesive for laminated sheets. The adhesive for laminated sheets of the present invention maintains suitable pot life, and an adhesive layer formed therefrom is excellent in reaction rate and is also excellent in adhesion to a film after aging. The adhesive layer is also excellent in hydrolysis resistance over a long term at high temperature, leading to remarkably enhanced durability against a severe environment, and thus the adhesive for laminated sheets of the present invention is suited as an adhesive for packaging bags such as shampoo, rinses and the like, and for outdoor materials such as solar battery modules.

Description of Reference Numerals

1: Solar battery module
10: Laminated sheet (backsheet)
11: Film
11a: Deposited thin film
12: Film
13: Adhesive layer
20: Sealing material (EVA)
30: Solar battery cell
40: Glass plate
50: Spacer

Claims

An adhesive for laminated sheets, which adhesive is applied to a film to bond a plurality of films, and is a mixture comprising: (A) an acrylic polyol, (B) at least one selected from carboxylic acids and carboxylic anhydrides; and (C) an isocyanate compound, wherein
the at least one selected from carboxylic acids and carboxylic anhydrides (B) is mixed in an amount of 0.01 to 8.0 parts by weight per 100 parts by weight of the total of the components (A)-(C),
the acrylic polyol (A) is obtainable by polymerizing a polymerizable monomer, and is a polymer having a weight average molecular weight of from 10,000 to 100,000 and a hydroxyl value of from 0.5 to 40 mgKOH/g.
The adhesive for laminated sheets according to claim 1, wherein the at least one selected from carboxylic acids and carboxylic anhydrides (B) has a melting point not more than 280 °C.
The adhesive for laminated sheets according to claim 1 or 2, wherein the adhesive further comprises (D) a silane compound.
The adhesive for laminated sheets according to any one of claims 1-3, wherein the polymerizable monomer comprises a monomer having a hydroxyl group and the other monomer; and the other monomer comprises acrylonitrile and a (meth)acrylic ester.