Adhesive composition, adhesive, and method for producing adhesive composition

Abstract

To provide an adhesive composition with excellent adhesive strength.SOLUTION: An adhesive composition comprises two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, and an isocyanate compound (B).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an adhesive composition and an adhesive containing the adhesive composition, and more particularly to the technology of aqueous vinyl polymer solution isocyanate adhesives (API). [Background technology]

[0002] Water-based resin adhesives are adhesives that use water as a medium. Compared to adhesives that use organic solvents as a medium, they do not emit toxic gases, are not flammable, and have a low environmental impact, making them safer adhesives. As such, they are used in a variety of applications, including automobiles, electronic parts, and woodworking products.

[0003] Known examples of water-based resin adhesives include aqueous polymer-isocyanate adhesives (APIs). APIs are compositions consisting of a base agent whose main component is an aqueous polymer solution or dispersion, and a crosslinker whose main component is an isocyanate compound. Examples of the API's main component include polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), and ethylene-vinyl acetate copolymer (EVA), and the cross-linking agent component is polymeric diphenylmethane diisocyanate (pMDI).

[0004] Various APIs containing polyvinyl alcohol (PVA) as a main component have been proposed. For example, Patent Document 1 proposes an adhesive comprising a plurality of partially saponified polyvinyl alcohols with different polymerization degrees as main components, and a polyisocyanate blended into the aqueous composition solution to form an adhesive comprising the partially saponified polyvinyl alcohols and water. Patent Document 2 also proposes an easily peelable adhesive composition comprising an A component made of 15-25 parts by weight of polyvinyl alcohol, 1-5 parts by weight of dextrin, 70-80 parts by weight of water, and an appropriate amount of a dispersing aid, and an A component made of polyisocyanate blended in an amount of 3-10% by weight relative to the A component. Patent Document 2 describes that the polyvinyl alcohol contains a combination of a high polymer with a polymerization degree of 1000-2000 and a low polymer with a polymerization degree of 200-700. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-063785 A [Patent Document 2] Japanese Patent Application Publication No. 11-256129 Summary of the Invention [Problem to be solved by the invention]

[0006] Water-based resin adhesives do not contain organic solvents, so they are easy to use and have no effect on the human body or the environment, but they tend to have low adhesive performance, which has been an issue. In particular, conventional APIs that use PVA, a hydrophilic resin, as the base component and isocyanate compounds, a lipophilic resin, as the crosslinking agent component have difficulty dispersing the crosslinking agent in the base component due to the difference in polarity, and the poor dispersibility of the crosslinking agent results in insufficient adhesive strength.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an adhesive composition having excellent adhesive strength and an adhesive containing the adhesive composition. [Means for solving the problem]

[0008] The present inventors have found that by using two or more types of PVA-based resins having different degrees of saponification, pre-emulsifying the PVA-based resin with a low degree of saponification with an isocyanate compound, and then mixing it with a PVA-based resin with a high degree of saponification, the dispersibility of the isocyanate compound is improved and the adhesive strength is increased, leading to the completion of the present invention.

[0009] A first aspect of the present invention is an adhesive composition containing two or more types of polyvinyl alcohol resins (A) having different degrees of saponification, and an isocyanate compound (B).

[0010] A second aspect of the present invention is an adhesive composition according to the first aspect, in which, among two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the difference in degree of saponification between the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification is 3 mol % or more.

[0011] A third aspect of the present invention is an adhesive composition according to the first or second aspect, wherein, among two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification has a degree of saponification of 65 to 85 mol %, and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification has a degree of saponification of 80 to 99.9 mol %.

[0012] A fourth aspect of the present invention is the adhesive composition according to any one of the first to third aspects, wherein the isocyanate compound (B) is a compound having a structural unit derived from an aromatic compound.

[0013] A fifth aspect of the present invention is the adhesive composition of the fourth aspect, wherein the compound having a structural unit derived from an aromatic compound has a structural unit derived from an alkylene oxide group.

[0014] A sixth aspect of the present invention is the adhesive composition according to any one of the first to fifth aspects, wherein the content ratio (A) / (B) of the polyvinyl alcohol resin (A) to the isocyanate compound (B) is 15 / 85 to 80 / 20 by mass in terms of solid content.

[0015] A seventh aspect of the present invention is the adhesive composition according to any one of the first to sixth aspects, wherein the particle dispersion diameter of the isocyanate compound (B) in the adhesive composition is less than 1.0 μm.

[0016] An eighth aspect of the present invention is an adhesive comprising the adhesive composition of any one of the first to seventh aspects.

[0017] A ninth aspect of the present invention is a method for producing an adhesive composition, which comprises using two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, mixing the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification with an isocyanate compound (B) to obtain a pre-emulsion, and then mixing it with the polyvinyl alcohol-based resin (A2) having the highest degree of saponification.

[0018] A tenth aspect of the present invention relates to a method for producing an adhesive composition according to a ninth aspect, wherein, among two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the difference in degree of saponification between the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification is 3 mol % or more.

[0019] An eleventh aspect of the present invention relates to a method for producing an adhesive composition according to the ninth or tenth aspect, wherein, among two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification has a degree of saponification of 65 to 85 mol %, and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification has a degree of saponification of 80 to 99.9 mol %.

[0020] A twelfth aspect of the present invention is a method for producing an adhesive composition according to any one of Aspects 9 to 11, wherein the isocyanate compound (B) is a compound having a structural unit derived from an aromatic compound.

[0021] A thirteenth aspect of the present invention is the method for producing an adhesive composition according to the twelfth aspect, wherein the compound having a structural unit derived from an aromatic compound has a structural unit derived from an alkylene oxide group.

[0022] A fourteenth aspect of the present invention relates to a method for producing an adhesive composition according to any one of the ninth to thirteenth aspects, wherein a content ratio (A) / (B) of the polyvinyl alcohol resin (A) to the isocyanate compound (B) is a mass ratio of 15 / 85 to 80 / 20 in terms of solid content. Effect of the Invention

[0023] The adhesive composition of the present invention contains at least two types of PVA resins with different degrees of saponification, and is obtained by mixing the PVA resin with the lowest degree of saponification with an isocyanate compound in advance, and then mixing with the PVA resin with the highest degree of saponification. In the adhesive composition obtained by this method, the PVA resin with the lowest degree of saponification acts as a dispersant to disperse the isocyanate compound well, and then it is mixed with the PVA resin with the highest degree of saponification (base resin), so that the reaction between the isocyanate compound (crosslinking agent) and the PVA resin with the highest degree of saponification (base resin) proceeds efficiently, thereby improving the adhesive strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] [Adhesive Composition] The adhesive composition according to the present invention contains two or more polyvinyl alcohol (PVA) resins (A) having different degrees of saponification, and an isocyanate compound (B). Each component of the adhesive composition according to the present invention will be described below in order.

[0025] <Polyvinyl alcohol resin (A)> Polyvinyl alcohol (PVA) resins are obtained by saponifying polyvinyl esters obtained by polymerizing vinyl ester monomers. PVA resins include unmodified PVA resins, copolymer-modified PVA resins obtained by saponifying copolymers obtained by copolymerizing modifying monomers to impart desired properties, and post-modified PVA resins obtained by post-modifying PVA resins. In this specification, unless otherwise specified, the term "PVA-based resin" is a general term for unmodified PVA-based resin, copolymer-modified PVA-based resin, and post-modified PVA-based resin. When copolymer-modified PVA-based resin and post-modified PVA-based resin are collectively referred to, they are called "modified PVA-based resin".

[0026] 1. Unmodified PVA resin Unmodified PVA resins are obtained by saponifying polyvinyl ester obtained by polymerizing vinyl ester monomers, and contain vinyl alcohol units represented by the following formula (1) and vinyl ester units (the following formula (2)) which are unsaponified portions. The vinyl ester units are included when the degree of saponification is less than 100%.

[0027] [ka]

[0028] [ka]

[0029] (2) In the formula, R a depends on the type of vinyl ester monomer used, and for example, when vinyl acetate monomer is used, it becomes a methyl group.

[0030] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate, with vinyl acetate being economically preferred.

[0031] The degree of saponification of the unmodified PVA resin is preferably in the range of 65 to 99.9 mol %. When the degree of saponification is in the above range, the resin has excellent water dispersibility, and since an acetate group (hydrophobic group) is present in addition to a hydroxyl group (hydrophilic group) in the molecule, the resin has surface activity and can be uniformly dispersed in water (dispersion medium). The saponification degree is an average saponification degree measured in accordance with JIS K6726.

[0032] The number average degree of polymerization of the unmodified PVA resin (measured in accordance with JIS K6726) is preferably 150 to 4000, more preferably 500 to 3000, and further preferably 700 to 2500. When the number average degree of polymerization is within the above range, the surface activity and protective colloid performance are high, the resin can be uniformly dispersed in water (dispersion medium), and stable micelles can be formed.

[0033] The viscosity of an aqueous solution may be used as an index of the average degree of polymerization of the unmodified PVA resin. The viscosity of a 4% by mass aqueous solution at 20°C measured in accordance with JIS K6726 is preferably 1.5 to 80 mPa·s, more preferably 3 to 70 mPa·s, and even more preferably 5 to 50 mPa·s. When the viscosity of the 4% by mass aqueous solution is within the above range, the handling property is improved, and the coatability and productivity can be improved.

[0034] The unmodified PVA resin preferably has a melting point of 160 to 230°C and a decomposition temperature of 250 to 350°C, although this depends on the degree of saponification and polymerization.

[0035] In the case of a typical PVA resin, the main chain bond is mainly 1,3-diol bond, and the content of 1,2-diol bond is about 1.5 to 1.7 mol %. However, the content of 1,2-diol bond can be increased by increasing the polymerization temperature when polymerizing the vinyl ester monomer.

[0036] 2. Modified PVA resin Examples of copolymerization monomers used in the copolymerized modified PVA resin include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or their salts or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, or their salts; alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth)allyl ether, polyoxypropylene polyoxyalkylene (meth)allyl ethers such as polyoxyalkylene (meth)acrylate and polyoxypropylene (meth)acrylate; polyoxyalkylene (meth)acrylamides such as polyoxyethylene (meth)acrylamide and polyoxypropylene (meth)acrylamide; hydroxyl group-containing α-olefins such as polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, and derivatives thereof, such as acylated products.

[0037] Examples of post-modified PVA-based resins include those having an acetoacetyl group by reaction with diketene, those having a polyalkylene oxide group by reaction with ethylene oxide, those having a hydroxyalkyl group by reaction with an epoxy compound or the like, and those obtained by reacting an aldehyde compound having various functional groups with a PVA-based resin.

[0038] The amount of modification in the modified PVA-based resin, i.e., the content of structural units derived from various monomers in the copolymer or functional groups introduced by a post-reaction, cannot be generally determined because the characteristics vary greatly depending on the type of modification, but is preferably in the range of 0.1 to 20 mol %, and particularly preferably in the range of 0.5 to 15 mol %.

[0039] Among these various modified PVA resins, in the present embodiment, a PVA resin having a hydrophilic modified group is preferably used. Examples of the hydrophilic modified group include a hydroxyl group, a carboxyl group, and an amino group. In particular, from the viewpoint of water solubility, a PVA resin containing a structural unit having a 1,2 diol modified group is preferred.

[0040] The modified PVA resin containing a structural unit having a 1,2-diol modifying group contains a structural unit having a 1,2-diol modifying group in a side chain in addition to the vinyl alcohol unit represented by the following formula (1) constituting polyvinyl alcohol and the vinyl ester unit (the following formula (2)) which is an unsaponified portion. The vinyl ester unit is included when the saponification degree is less than 100%.

[0041] [ka]

[0042] [ka]

[0043] (2) In the formula, R a depends on the type of vinyl ester monomer used, and for example, when vinyl acetate monomer is used, it becomes a methyl group.

[0044] As the structural unit having a 1,2-diol modifying group in the side chain, a 1,2-diol-containing unit in the side chain represented by the following formula (3) is preferred.

[0045] [ka]

[0046] In formula (3), R 1 ~R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X represents a single bond or a bonding chain.

[0047] In the general formula (3), R 1 ~R 6 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, etc., which may have a substituent such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group). A hydrogen atom is more preferable. R 1 ~R 6 may all be the same or different, but are preferably all hydrogen atoms.

[0048] In formula (3), X is a single bond or a bonding chain. Examples of the bonding chain (X) include hydrocarbon groups such as alkylene groups, alkenylene groups, alkynylene groups, phenylene groups, and naphthylene groups (these hydrocarbon groups may be substituted with halogen atoms such as fluorine atoms, chlorine atoms, and bromine atoms), -O-, -(CHO) m -, -(OCH2) m -, -(CH2O) m CH2-, -CO-, -COCO-, -CO(CH2) m Examples thereof include CO-, -CO(CH)CO-, -S-, -CS-, -SO-, -SO-, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO-, -Si(OR)-, -OSi(OR)-, -OSi(OR)O-, -Ti(OR)-, -OTi(OR)-, -OTi(OR)O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O-, and the like (each R is independently any substituent, preferably a hydrogen atom or an alkyl group, and m is an integer of 1 to 5). From the viewpoint of stability during production or use, X is preferably a single bond, an alkylene group having 6 or less carbon atoms (particularly a methylene group), or -CH2OCH2-, and among these, a single bond is most preferable from the viewpoint of thermal stability and stability under high temperatures or acidic conditions.

[0049] The structural unit represented by the above formula (3) is R 5 and R 6 A structural unit having a primary hydroxyl group in a side chain in which R is a hydrogen atom is particularly preferred, and the most preferred structural unit is 1 ~R 6 are all hydrogen atoms and X is a single bond,

[0050] [ka]

[0051] The saponification degree of the modified PVA resin (average saponification degree measured according to JIS K6726) is preferably in the range of 65 to 99.9 mol %. When the saponification degree is in the above range, the resin has excellent water dispersibility, and since acetate groups (hydrophobic groups) are present in addition to hydroxyl groups (hydrophilic groups) in the molecule, the resin has surface activity and can be uniformly dispersed in water (dispersion medium).

[0052] The number average degree of polymerization of the modified PVA resin (measured in accordance with JIS K6726) is preferably 150 to 4000, more preferably 500 to 3000, and further preferably 700 to 2500. When the number average degree of polymerization is within the above range, the surface activity and protective colloid performance are high, the resin can be uniformly dispersed in water (dispersion medium), and stable micelles can be formed.

[0053] The viscosity of a 4% by mass aqueous solution of the modified PVA resin at 20°C measured in accordance with JIS K6726 is preferably 1.5 to 80 mPa s, more preferably 3 to 70 mPa s, and even more preferably 5 to 50 mPa s. When the viscosity of the 4% by mass aqueous solution is within the above range, the handling property is improved, and the coatability and productivity can be improved.

[0054] The melting point of the modified PVA resin is preferably 160 to 230°C, and the decomposition temperature is preferably 250 to 350°C, although this depends on the degree of saponification and the degree of polymerization.

[0055] 3. Low saponification degree PVA resin (A1) and high saponification degree PVA resin (A2) The adhesive composition of the present invention contains two or more PVA-based resins having different degrees of saponification. The PVA-based resin having the lowest degree of saponification among the two or more PVA-based resins forms a pre-emulsion with an isocyanate compound to increase the dispersibility of the isocyanate compound in water, and can increase adhesive strength by reacting with other PVA-based resins.

[0056] Examples of the two or more types of PVA-based resins include combinations of the above-mentioned unmodified PVA-based resins, combinations of an unmodified PVA-based resin and various modified PVA-based resins, and combinations of different types of modified PVA-based resins. Also included are combinations of modified PVA-based resins of the same type but different in polymerization degree, modification rate, melting point, etc. From the viewpoints of compatibility between the PVA-based resins and dispersibility of the isocyanate compound, it is preferable that the PVA-based resins are included in a range of 2 to 4 types, more preferably 2 to 3 types.

[0057] Of the two or more PVA resins with different degrees of saponification contained in the adhesive composition, the PVA resin (A1) with the lowest degree of saponification (also referred to as low-saponification PVA resin (A1)) preferably has a degree of saponification of 65 to 85 mol %. When the low-saponification PVA resin (A1) has a degree of saponification of 65 mol % or more, the PVA resin can be dispersed in water and handled as an aqueous solution, and when it is 85 mol % or less, the adsorption to isocyanate compounds can be increased. The saponification degree of the low saponification degree PVA resin (A1) is more preferably from 68 to 84 mol %, further preferably from 72 to 82 mol %.

[0058] Of the two or more PVA resins having different degrees of saponification contained in the adhesive composition, the PVA resin (A2) having the highest degree of saponification (also referred to as the high-saponification PVA resin (A2)) preferably has a degree of saponification of 80 to 99.9 mol %. When the high-saponification PVA resin (A2) has a degree of saponification of 80 mol % or more, it has high affinity for water and can form a strong protective colloid at the interface between the isocyanate compound and the water, which is the dispersion medium, and when it is 99.9 mol % or less, it has excellent water dispersibility and has an acetate group (hydrophobic group) in addition to a hydroxyl group (hydrophilic group) in the molecule, so it has surface activity and can be uniformly dispersed in the dispersion medium. The saponification degree of the highly saponified PVA resin (A2) is more preferably from more than 85 mol % to 99 mol % or less, and further preferably from 86 to 98 mol %.

[0059] In addition, among the two or more PVA resins having different degrees of saponification contained in the adhesive composition, the difference in the degree of saponification between the PVA resin (A1) with the lowest degree of saponification (low saponification degree PVA resin (A1)) and the PVA resin (A2) with the highest degree of saponification (high saponification degree PVA resin (A2)) is preferably 3 mol% or more. When the difference in the degree of saponification between the low saponification degree PVA resin (A1) and the high saponification degree PVA resin (A2) is 3 mol% or more, the dispersibility of the isocyanate compound (B) due to the low saponification degree PVA resin (A1) can be increased, and the affinity to water, which is the dispersion medium of the pre-emulsion formed by the low saponification degree PVA resin (A1) and the isocyanate compound (B), can be increased due to the high saponification degree PVA resin (A2), and a high protective colloid can be formed. The difference in the saponification degree is preferably 3 mol% or more, more preferably 5 mol% or more. From the viewpoint of compatibility between the PVA resins, the difference between the low saponification degree PVA resin (A1) and the high saponification degree PVA resin (A2) is preferably 34 mol% or less, more preferably 30 mol% or less, and even more preferably 25 mol% or less. That is, the difference in the saponification degree is preferably in the range of 3 to 34 mol%.

[0060] In the adhesive composition of the present invention, the low saponification degree PVA resin (A1) is a component for uniformly dispersing the isocyanate compound (B) as described above. The content of the low saponification degree PVA resin (A1) in the adhesive composition is preferably 10 to 80 parts by mass, calculated as solid content, per 100 parts by mass of the total of the PVA resins contained in the adhesive composition. By including 10 parts by mass or more of the low saponification degree PVA resin (A1), a uniform pre-emulsion can be formed, and by including 80 parts by mass or less, a stable pre-emulsion can be formed. The content of such low saponification degree PVA-based resin (A1) is more preferably 12 parts by mass or more, even more preferably 15 parts by mass or more, and more preferably 70 parts by mass or less, even more preferably 60 parts by mass or less, based on 100 parts by mass of the total PVA-based resins.

[0061] On the other hand, the highly saponified PVA resin (A2) is used as the main agent in the adhesive composition. When there are two types of PVA resins, the main agent refers to the highly saponified PVA resin (A2), and when there are three or more types of PVA resins, the main agent refers to the PVA resins other than the low saponification PVA resin (A1), including the highly saponified PVA resin (A2).

[0062] The PVA resin as the base is preferably 20 to 90 parts by mass, calculated as solid content, per 100 parts by mass of the total PVA resin contained in the adhesive composition. By including 20 parts by mass or more of the PVA resin as the base, a strong protective colloid can be formed at the interface of the pre-emulsion, and by including 90 parts by mass or less, the pre-emulsion can be uniformly dispersed in water. The content of the PVA-based resin as the main component is more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, and more preferably 88 parts by mass or less, and even more preferably 85 parts by mass or less, per 100 parts by mass of the total PVA-based resin.

[0063] <Isocyanate compound (B)> The isocyanate compound is a crosslinking agent for the adhesive composition. The isocyanate compound is not particularly limited as long as it is a compound having an isocyanate group that is usually used in the production of polyurethane, etc. Examples thereof include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives and modified products of these isocyanates.

[0064] Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate, and the like. aliphatic diisocyanates such as ethyl acetate methyl caproate; and aliphatic triisocyanates such as lysine ester triisocyanate, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 3,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0065] Examples of alicyclic polyisocyanates include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate (hereinafter also referred to as isophorone diisocyanate), 4,4'-methylenebis(cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl- Alicyclic diisocyanates such as 2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatemethyl)cyclohexane (hereinafter also referred to as hydrogenated xylylene diisocyanate) or mixtures thereof, and norbornane diisocyanate; 1,3,5-triisocyanate cyclohexane, 1,3,5-trimethylisocyanate cyclohexane, 2-(3-isocyanatepropyl)-2,5-di(isocyanatemethyl) -Bicyclo(2,2,1)heptane, 2-(3-isocyanatepropyl)-2,6-di(isocyanatemethyl)-bicyclo(2,2,1)heptane, 3-(3-isocyanatepropyl)-2,5-di(isocyanatemethyl)-bicyclo(2,2,1)heptane, 5-(2-isocyanateethyl)-2-isocyanatemethyl-3-(3-isocyanatepropyl)-bicyclo(2,2,1)heptane, 6-(2-isocyanateethyl) alicyclic triisocyanates such as 2-isocyanateethyl-3-(3-isocyanatepropyl)-bicyclo(2,2,1)heptane, 5-(2-isocyanateethyl)-2-isocyanatemethyl-2-(3-isocyanatepropyl)-bicyclo(2,2,1)heptane, and 6-(2-isocyanateethyl)-2-isocyanatemethyl-2-(3-isocyanatepropyl)-bicyclo(2,2,1)heptane.

[0066] Examples of the aromatic aliphatic polyisocyanate include aromatic aliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (hereinafter also referred to as tetramethylxylylene diisocyanate) or a mixture thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0067] Examples of aromatic polyisocyanates include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4- or 4,4'-diphenylmethane diisocyanate (hereinafter also referred to as MDI) or a mixture thereof, 2,4- or 2,6-tolylene diisocyanate (hereinafter also referred to as TDI) or a mixture thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenylether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzene, and 2,4,6-triisocyanate toluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0068] In addition, examples of derivatives of these polyisocyanates include dimers, trimers, biurets, allophanates, carbodiimides, uretdione, oxadiazinetrione, polymethylene polyphenyl polyisocyanate (hereinafter also referred to as crude MDI or polymeric MDI (pMDI)), and crude TDI.

[0069] Examples of the modified polyisocyanate include polyol modified products and polyamine modified products of isocyanates obtained by reacting the polyisocyanate or a derivative of the polyisocyanate with a low-molecular-weight polyol or low-molecular-weight polyamine described below so that an isocyanate group remains, i.e., in a ratio in which the isocyanate group of the polyisocyanate or its derivative is in excess of the hydroxyl group of the low-molecular-weight polyol or the amino group of the low-molecular-weight polyamine.

[0070] These isocyanate compounds may be used alone or in combination of two or more. The isocyanate compound is preferably a compound having a structural unit derived from an aromatic compound, and among the above-listed isocyanate compounds, aromatic polyisocyanates, derivatives and modified products of aromatic polyisocyanates are preferred, and in particular, a compound having a structural unit derived from an aromatic compound and a structural unit derived from an alkylene oxide group is preferred, and a compound having a structural unit derived from an aromatic compound and a structural unit derived from an ethylene oxide group is most preferred. Specifically, polymeric MDI (pMDI) is preferred from the viewpoint of high crosslinkability with PVA resins and high strength properties as a wood adhesive.

[0071] In the adhesive composition of the present invention, the content of the isocyanate compound (B) is preferably 20 to 200 parts by mass, calculated as solid content, per 100 parts by mass of the total of the PVA resin (A). By containing 20 parts by mass or more of the isocyanate compound, the effect as an adhesive can be exhibited, and by containing 200 parts by mass or less, the crosslinking density is optimized and the adhesive strength can be improved. The amount of such an isocyanate compound, calculated as solid content, per 100 parts by mass of the PVA-based resin (A) in total is more preferably 25 parts by mass or more, even more preferably 30 parts by mass or more, and is more preferably 150 parts by mass or less, even more preferably 180 parts by mass or less.

[0072] The content ratio (A) / (B) of the PVA resin (A) and the isocyanate compound (B) is preferably 15 / 85 to 80 / 20 by mass in terms of solid content. When the ratio (A) / (B) is within the above range, the crosslink density is optimized and the adhesive can be effective. The ratio (A) / (B) is more preferably from 20 / 80 to 75 / 25, and further preferably from 25 / 75 to 70 / 30.

[0073] The adhesive composition of the present invention is used in water-based resin adhesives and contains water. Examples of water include purified water, distilled water, ion-exchanged water, and tap water.

[0074] The content of water is preferably 200 to 10,000 parts by mass relative to 100 parts by mass of the total PVA resin (A). When the content of water is 200 parts by mass or more, the viscosity of the adhesive composition and the adhesive can be easily adjusted, and the adhesive has excellent handleability. When the content of water is 10,000 parts by mass or less, the adhesive strength can be prevented from decreasing. The content of such water is more preferably 250 parts by mass or more, and even more preferably 300 parts by mass or more, and more preferably 5000 parts by mass or less, and even more preferably 1000 parts by mass or less, per 100 parts by mass of the total PVA-based resin (A).

[0075] [Method for producing adhesive composition] The adhesive composition of the present invention is prepared by mixing the PVA resin (A) and the isocyanate compound (B).

[0076] The components may be mixed all at once or sequentially, and the method of sequentially mixing the components is preferred because it is easy to improve the dispersibility of the isocyanate compound (B) in the low saponification degree PVA resin (A1).

[0077] A method for producing the adhesive composition by sequentially mixing the components will now be described. The method for producing an adhesive composition of the present invention includes using two or more types of PVA-based resins (A) having different degrees of saponification, mixing the PVA-based resin (A1) with the lowest degree of saponification (low saponification degree PVA-based resin (A1)) with an isocyanate compound (B) to obtain a pre-emulsion, and then mixing it with the PVA-based resin (A2) with the highest degree of saponification (high saponification degree PVA-based resin (A2)).

[0078] The PVA resin (A) is as described above, and the preferred PVA resin and the preferred range of the content are also the same. The isocyanate compound (B) is also as described above, and the preferred isocyanate compound and the preferred range of the content are also the same.

[0079] First, a low saponification degree PVA resin (A1) and an isocyanate compound (B) are mixed to prepare a pre-emulsion. The low saponification degree PVA resin (A1) is preferably used in the form of an aqueous solution. In the mixed solution, the low saponification degree PVA resin (A1) surrounds the isocyanate compound (B), dispersing the isocyanate compound (B) in the form of small particles.

[0080] The mixing means may be a conventionally known method, such as mixing by shaking the mixture by hand, mixing with a stirring rod, mixing with a stirrer, or using a homogenizer.

[0081] As for the mixing conditions, it is sufficient to mix until the isocyanate compound and the PVA resin are uniformly dispersed, for example, when mixing by shaking by hand, it is sufficient to stir about 200 to 300 times. The temperature during mixing is preferably in the range of 20 to 40°C.

[0082] Next, the highly saponified PVA resin (A2) is added to the obtained pre-emulsion and mixed. The highly saponified PVA resin (A2) is preferably used in the form of an aqueous solution. When three or more types of PVA-based resins (A) are used, the remaining PVA-based resins may be added simultaneously with the highly saponified PVA-based resin (A2) and mixed at once, or the highly saponified PVA-based resin (A2) and the remaining PVA-based resins may be added separately and mixed.

[0083] As for the mixing conditions, the components should be mixed until they become uniform, for example, when mixing by shaking by hand, about 200 to 300 times should be sufficient. The temperature during mixing is preferably in the range of 20 to 40°C.

[0084] If foaming is observed in the mixed liquid after mixing, it is preferable to eliminate the foaming using, for example, an automatic revolution type mixer.

[0085] The adhesive composition obtained as described above has the isocyanate compound (B) uniformly dispersed therein.

[0086] [Physical Properties of Adhesive Composition] In the adhesive composition of the present invention, the isocyanate compound (B) preferably has a particle dispersion diameter of less than 1.0 μm. When the particle dispersion diameter of the isocyanate compound (B) is less than 1.0 μm, the isocyanate compound (B) is uniformly dispersed in the PVA resin, thereby increasing the adhesive strength. The particle dispersion diameter is more preferably 0.9 μm or less, and even more preferably 0.8 μm or less, and from the viewpoint of adhesive strength expression, the particle dispersion diameter is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more.

[0087] 〔glue〕 The adhesive of the present invention comprises the adhesive composition of the present invention. The content of the adhesive composition in the adhesive is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and the adhesive may consist of the adhesive composition (100% by mass).

[0088] The adhesive of the present invention may contain any optional components other than the adhesive composition of the present invention, so long as the components do not impair the effects of the present invention. Examples of optional components contained in the adhesive include extenders such as wheat flour, starches, defatted soybean flour, clay, kaolin, talc, calcium carbonate, and titanium oxide; antifreeze agents such as ethylene glycol and propylene glycol; nonionic surfactant-based dispersion aids; antifoaming agents; preservatives; antifungal agents; colorants; solvents; and thickeners.

[0089] The adhesive can be prepared by homogeneously mixing the adhesive composition of the present invention with any optional ingredients.

[0090] The adhesive of the present invention has excellent adhesive strength and is therefore particularly suitable as a wood / wood adhesive (plywood adhesive, woodworking adhesive, particle board adhesive, MDF adhesive, etc.), wood / plastic material adhesive (PVC plywood adhesive, foamed resin / wood adhesive, etc.), etc. Furthermore, it can be used as a packaging adhesive (paper / paper adhesive, paper / plastic adhesive, paper / aluminum foil adhesive, etc.), cloth adhesive (cloth / plastic adhesive, cloth / paper adhesive, cloth / wood adhesive, etc.), and building material adhesive (concrete / wood adhesive, wood / various board adhesive, etc.). EXAMPLES

[0091] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0092] The components used in the following examples and comparative examples are as follows. <Polyvinyl alcohol (PVA) resin> The PVA-based resin was prepared as follows. (Preparation of PVA (A1-1)) In a polymerization vessel equipped with a reflux condenser, a dropping funnel, and a stirrer, 100 parts by mass of vinyl acetate, 14.4 parts by mass of methanol, and 0.0044 mol% of azobisisobutyronitrile relative to vinyl acetate were charged, and polymerization was carried out at the boiling point for 5.8 hours while stirring under a nitrogen stream (polymerization rate: 65 mol%). Next, unreacted vinyl acetate was removed from the system to obtain a methanol solution of the polymer (resin content: 30 mass%). The resulting solution (dielectric constant of methanol is 31.2) was then charged into a kneader, and neutralized by adding sodium hydroxide while maintaining the solution temperature at 35°C. Furthermore, 7 mmol of sodium hydroxide was added relative to the vinyl acetate unit in the polymer to perform saponification. The precipitate was filtered off, thoroughly washed with methanol, and dried in a hot air dryer to obtain PVA (A1-1). The resulting PVA (A1-1) had a degree of saponification of 79 mol % and a number average degree of polymerization of 2,000.

[0093] (Preparation of PVA(A1-2), PVA(A2-1) and PVA(A2-2)) PVA having the following saponification degrees and number average polymerization degrees was prepared in the same manner as in the production of the above PVA (A1-1), except that the saponification time was changed. PVA (A1-2): Saponification degree 87 mol%, number average polymerization degree 500 PVA (A2-1): Saponification degree 98 mol%, number average polymerization degree 1800 PVA (A2-2): Saponification degree 87 mol%, number average polymerization degree 1750

[0094] <Isocyanate compounds> The following isocyanate compounds were used: Isocyanate compound (B-1): "Cosmonate M-200" (pMDI) manufactured by Mitsui Chemicals, Inc. Isocyanate compound (B-2): "Cosmonate M-200W" (E-pMDI) manufactured by Mitsui Chemicals, Inc.

[0095] Example 1 An adhesive composition was prepared by the pre-emulsion method (I). 20 parts by mass of a 15 wt % aqueous solution of PVA (A1-1) and 15 parts by mass of the isocyanate compound (B-2) were weighed out and placed in a container, and the mixture was stirred by hand 200 times to obtain a pre-emulsion. Then, 80 parts by mass of a 15 wt % aqueous solution of PVA (A2-2) was added to the obtained pre-emulsion, and the mixture was stirred by hand 200 times, and then treated with an automatic orbital mixer (Thinky Corporation's "AER-310") at 2200 rpm for 1 minute to defoam the mixture, thereby obtaining the adhesive of Example 1.

[0096] (Examples 2 to 3) The adhesives of Examples 2 and 3 were prepared in the same manner as in Example 1, except that the blending amounts of each component were changed as shown in Table 1.

[0097] Example 4 An adhesive composition was prepared by the blending method (II). 20 parts by mass of a 15 wt % aqueous solution of PVA (A1-1), 80 parts by mass of a 15 wt % aqueous solution of PVA (A2-2), and 15 parts by mass of an isocyanate compound (B-2) were weighed out and placed in a container, and the mixture was stirred by hand 200 times, and then treated with an automatic orbital mixer (Thinky Corporation, "AER-310") at 2200 rpm for 1 minute to defoam the mixture, thereby obtaining the adhesive of Example 4.

[0098] (Comparative Examples 1 to 2) Adhesives of Comparative Examples 1 and 2 were prepared in the same manner as in Example 4, except that the blending amounts of each component were changed as shown in Table 1.

[0099] Comparative Example 3 An adhesive of Comparative Example 3 was prepared in the same manner as in Example 1, except that the blending amounts of each component were changed as shown in Table 1.

[0100] [Measurement and evaluation method] 1.Particle dispersion diameter The adhesive thus prepared was poured into a Teflon (registered trademark) mold with a depth of 1 mm and left to stand at 20°C and 65% RH for 24 hours to form a film. After that, it was aged at 20°C for 2 weeks to obtain an adhesive film. The obtained adhesive film was cut, and the cross section of the film was observed under a scanning electron microscope ("S-3000N" manufactured by Hitachi, Ltd.) to confirm the particle size. The length in the major axis direction of 30 randomly selected isocyanate compound particles was measured, and the average value was taken as the particle dispersion diameter.

[0101] 2.Average shear strength 2-1.Normal state Two pieces of wood (beech, 300mm (L) x 120mm (R) x 10mm (T)) were left in a constant temperature and humidity room at 20℃ and 65%RH for more than two months, after which adhesive was applied to one side of each piece at a rate of 300g / m 2 The adhesive was applied so that the adhesive was applied as described above, and the pressure was 1 MPa, the pressure was 24 hours, and the adhesive was bonded at room temperature (20°C) to obtain a laminated timber. The decompressed laminated timber was then cured at 20°C and 65% RH for two weeks. After curing, the laminated timber was cut into block shear test pieces with a bonding area of ​​25 x 25 mm in accordance with JAS 3079, and a block shear test was performed at a load rate of 9.8 kN / min in accordance with JIS K 6851 (1994). The shear strength was calculated according to the following formula. Shear strength (MPa) = 9.8 x (maximum load (kgf) / adhesive area (mm 2 ))

[0102] 2-2.Water resistance The laminated timber was prepared in the same manner as in "2-1. Normal condition", and the decompressed laminated timber was immersed in room temperature water for 24 hours in a constant temperature and humidity room at 20℃. Then, in accordance with JAS 3079, it was cut into a block shear test piece with a bonding area of ​​25 x 25 mm, and while still wet, a block shear test was performed at a load rate of 9.8 kN / min in accordance with JIS K 6857 (1973).

[0103] 2-3.Boiling resistance A laminated timber was prepared in the same manner as in "2-1. Normal condition", and the decompressed laminated timber was immersed in boiling water for 4 hours, then dried at 70℃ for 20 hours, immersed in boiling water for another 4 hours, and immersed in room temperature water until it cooled. After that, in accordance with JAS 3079, a block shear test piece with a bonding area of ​​25 x 25 mm was cut out, and while still wet, a block shear test was performed at a load rate of 9.8 kN / min in accordance with JIS K 6857 (1994).

[0104] 3.Average wood breakage rate The wood pieces after the test in "2-1. Normal condition" were visually inspected, and the average wood breakage rate was calculated from the percentage of the total adhesive area where peeling between pieces of wood was observed.

[0105] The evaluation results for Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1.

[0106] [Table 1]

[0107] As shown in Table 1, a comparison of Examples 1 to 3 with Comparative Example 3 reveals that the adhesives of Examples 1 to 3 have a high average wood breakage rate, a high average shear strength in the normal test, the water resistance test, and the boiling resistance test, and have high adhesive strength. Similarly, a comparison of Example 4 with Comparative Examples 1 and 2 reveals that the adhesive of Example 4 has high adhesive strength.

Claims

1. An adhesive composition comprising two or more polyvinyl alcohol resins (A) having different degrees of saponification, and an isocyanate compound (B).

2. 2. The adhesive composition according to claim 1, wherein, among the two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the difference in the degree of saponification between the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification is 3 mol % or more.

3. The adhesive composition according to claim 1, wherein, among the two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification is 65 to 85 mol %, and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification is 80 to 99.9 mol %.

4. The adhesive composition according to claim 1 , wherein the isocyanate compound (B) is a compound having a structural unit derived from an aromatic compound.

5. The adhesive composition according to claim 4 , wherein the compound having a structural unit derived from an aromatic compound has a structural unit derived from an alkylene oxide group.

6. The adhesive composition according to claim 1, wherein a content ratio (A) / (B) of the polyvinyl alcohol-based resin (A) to the isocyanate compound (B) is a mass ratio of 15 / 85 to 80 / 20 in terms of solid content.

7. The adhesive composition according to claim 1 , wherein the particle dispersion diameter of the isocyanate compound (B) in the adhesive composition is less than 1.0 μm.

8. An adhesive comprising the adhesive composition according to any one of claims 1 to 7.

9. A method for producing an adhesive composition comprising using two or more types of polyvinyl alcohol-based resins (A) having different degrees of saponification, mixing the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification with an isocyanate compound (B) to obtain a pre-emulsion, and then mixing the pre-emulsion with the polyvinyl alcohol-based resin (A2) having the highest degree of saponification.

10. 10. The method for producing an adhesive composition according to claim 9, wherein, among the two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the difference in the degree of saponification between the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification is 3 mol % or more.

11. The method for producing an adhesive composition according to claim 9, wherein, among the two or more polyvinyl alcohol-based resins (A) having different degrees of saponification, the polyvinyl alcohol-based resin (A1) having the lowest degree of saponification has a degree of saponification of 65 to 85 mol %, and the polyvinyl alcohol-based resin (A2) having the highest degree of saponification has a degree of saponification of 80 to 99.9 mol %.

12. The method for producing an adhesive composition according to claim 9 , wherein the isocyanate compound (B) is a compound having a structural unit derived from an aromatic compound.

13. The method for producing an adhesive composition according to claim 12 , wherein the compound having a structural unit derived from an aromatic compound has a structural unit derived from an alkylene oxide group.

14. The method for producing an adhesive composition according to claim 9, wherein a content ratio (A) / (B) of the polyvinyl alcohol-based resin (A) to the isocyanate compound (B) is a mass ratio of 15 / 85 to 80 / 20 in terms of solid content.

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