Composition, adhesive and aqueous emulsion

Abstract: There is disclosed a composition which comprises an (A) aqueous emulsion comprising a dispersoid which comprises a copolymer of a hydrophobic unsaturated monomer such as (meth)acrylic ester and a primary hydroxyl group-containing ethylenically unsaturated monomer; and a dispersant comprising a vinyl alcohol polymer having a mercapto group at an end thereof and a (B) polyvalent isocyanate compound. Disclosed also are an adhesive comprising the aforementioned composition and a wooden product which is joined by the use of the adhesive. The above-disclosed adhesive is excellent in initial adhesivity, adhesive strength, water resistance and so forth.

Description: The present invention relates to a composition, an adhesive and an aqueous emulsion. More particularly, it pertains to a composition useful for a variety of uses especially as an adhesive, an adhesive excellent in initial adhesivity, adhesive strength and water resistance which comprises said composition, and an aqueous emulsion as the material for said adhesive and the like. Differing from the conventional aminoplast adhesive, an adhesive which comprises as principal ingredients, a water-soluble high molecular compound, an aqueous emulsion and an isocyanate compound is free from the generation of formalin and develops an extremely high adhesive strength and water resistance only by press bonding at ordinary temperature for a relatively short time and therefore, is admirably used as an adhesive for wood (refer to, for example (JP-A-94739/1973 and 69139/1975). There have been proposed also as the similar adhesives, an aqueous adhesive composition which comprises the emulsion of a copolymer of a hydroxyl group-containing monomer such as allyl alcohol, 2-hydroxyethyl acrylate, N-methylolacrylamide or the like and vinyl acetate or the like; and a divalent isocyanate compound (JP-A-26346/1974) and water-resistant adhesive composition comprising a polyvinyl acetate emulsion using a polyvinyl alcohol as a dispersant (protective colloid) and a polyvalent isocyanate compound (JP-A-33178/1991). There is reported an adhesive comprising a polymer emulsion stabilized by polyvinyl alcohol, said polymer emulsion being produced by two-stage polymerization process wherein in the first stage is produced a vinyl acetate copolymer having a glass transition temperature of 10 to 40°C and in the second stage is produced a methyl methacrylate copolymer having a glass transition temperature of 50 to 120°C at a ratio of the vinyl acetate copolymer to the methyl methacrylate copolymer being 10:1 to 10:6 (Japanese Patent Application Laid-Open No. 302485/1990). Moreover, there is disclosed an aqueous emulsion usable for an adhesive comprising as the dispersoid, polystyrene, polymethyl methacrylate, polymethyl acrylate, methyl methacrylate/butadiene copolymer, polyvinyl chloride or polyvinyl acetate and as the suspending agent, polyvinyl alcohol having a mercapto group at an end thereof (Japanese Patent Application Laid-Open No. 197229/1985). Under such circumstances, there has recently been established Japanese Industrial Standard (JIS) regarding adhesives for wood comprising an aqueous high molecular compound and an isocyanate compound. With increase in the objects to be bonded, however, there has arisen the necessity for further enhancing the present adhesivity level as the case may be. Specifically, an adhesive is sometimes required to have higher durability as the structural adhesive or further enhanced initial adhesivity as ordinary adhesive for individual use. In the case of the latter, the versatile application of an aqueous emulsion of a vinyl acetate resin using polyvinyl alcohol (hereinafter sometimes abbreviated to "PVA") as the dispersant has enhanced initial adhesivity but has caused the problem of water resistance being insufficient. For the requirement of high durability and/or high water resistance there have heretofore been admirably employed an aqueous emulsion of acrylic series and that of styrene/butadiene rubber (SBR). However, since in the above-mentioned aqueous emulsions has been used an anionic surfactant or a nonionic surfactant alone or in combination with each other as the dispersant at the time of emulsion polymerization, the aqueous emulsions have involved the problem that they could not develop such initial adhesivity like the aqueous emulsion of vinyl acetate resin obtained by using PVA as the dispersant and the problem of inferior operation efficiency. It is the present state of the aforementioned conventional adhesives that in spite of their performance being recognized to some extent, an adhesive having satisfactory performance in all respects of initial adhesivity, adhesive strength and water resistance still remains undeveloped. It is an object of the present invention to solve the problems of the prior arts as described hereinbefore and thereby provide a composition well suited for use in an adhesive having satisfactory initial adhesivity as well as excellent adhesive strength and water resistance. It is another object of the present invention to provide an adhesive having satisfactory initial adhesivity as well as excellent adhesive strength and water resistance which adhesive is obtained by the use of the above-mentioned composition. It is still another object of the present invention to provide a wooden product excellent in adhesive strength and water resistance which is obtained by the use of the above-mentioned adhesive. It is a further object of the present invention to provide an aqueous emulsion which constitutes a component of the above-mentioned composition. It is a still further object of the present invention to provide a process for efficiently producing the above-mentioned aqueous emulsion. Other objects of the present invention will be obvious from the text of the specification hereinafter disclosed. The composition according to the present invention comprises an (A) aqueous emulsion comprising a dispersoid which comprises a copolymer containing at least one hydrophobic unsaturated monomer unit selected from a methacrylic ester monomer unit, acrylic ester monomer unit, styrenic monomer unit, diene monomer unit and halogenated unsaturated monomer unit; and a primary hydroxyl group-containing ethylenically unsaturated monomer unit in an amount of 0.1 to 50% by weight based on said copolymer; and a dispersant comprising a vinyl alcohol polymer having a mercapto group at an end thereof and a (B) polyvalent isocyanate compound. The composition according to the present invention comprises (A) an aqueous emulsion and (B) a polyvalent isocyanate compound. The aqueous emulsion comprises the dispersoid and the dispersant described hereinbefore. The aforementioned dispersoid comprises a copolymer containing as constitutional units, at least one hydrophobic unsaturated monomer unit selected from a methacrylic ester monomer unit, acrylic ester monomer unit, styrenic monomer unit, diene monomer unit and halogenated unsaturated monomer unit; and a primary hydroxyl group-containing ethylenically unsaturated monomer unit. The methacrylic ester monomer unit includes a variety of species and is preferably exemplified by a monomer unit having an alkyl group of 1 to 12 carbon atoms such as those derived from methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate and dimethylaminoethyl methacrylate; the units each derived from a quaternary compound of any of the aforestated 7 monomer units; and the units each derived from any of methacrylamide and ethylene glycol dimethacrylate, among which is preferable a methacrylic ester unit having an alkyl group of 1 to 4 carbon atoms. As is the case with the above, the acrylic ester monomer unit includes a variety of species and is exemplified by a monomer unit having an alkyl group of 1 to 12 carbon atoms such as those derived from methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate and dimethylaminoethyl acrylate; the units each derived from a quaternary compound of any of the aforesaid 8 monomer units; and the units each derived from any of acrylamide, N,N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid and sodium salt thereof, among which is preferable an acrylic ester unit having an alkyl group of 1 to 4 carbon atoms. Examples of the styrenic monomer unit include a wide diversity of species, among which are preferably units derived from styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, p-styrenesulfonic acid and an alkali salt thereof such as sodium salt and potassium salt. Examples of the diene monomer unit include a large variety of species, among which are preferably units derived from butadiene, isoprene, chloroprene and neoprene. Examples of the halogenated unsaturated monomer unit include a variety of species, among which are preferably units derived from vinyl chloride, vinylidene chloride, vinyl bromide and vinylidene bromide. The primary hydroxyl group-containing ethylenically unsaturated monomer unit in the aqueous emulsion includes a variety of species and is preferably exemplified by those derived from hydroxyethyl acrylate, hydroxyethyl methacrylate, caprolactone-modified (meth)acrylic ester, N-alkylolamide from α,β-ethylenically unsaturated carboxylic acid having 3 to 10 carbon atoms such as N-methylolacrylamide, N-ethanolacrylamide, N-propanolacrylamide, N-methylolmethacrylamide, N-ethanolmethacrylamide and N-methanolmaleamide, and allyl alcohol. The aforementioned at least one hydrophobic unsaturated monomer unit selected from a methacrylic ester monomer unit, acrylic ester monomer unit, styrenic monomer unit, diene monomer unit and halogenated unsaturated monomer unit, and primary hydroxyl group-containing ethylenically unsaturated monomer unit may contain one member or at least two members in combination, respectively. The above-mentioned copolymer which constitutes the dispersoid of the aqueous emulsion of the present invention indispensably comprises the aforesaid hydrophobic unsaturated monomer unit and primary hydroxyl group-containing ethylenically unsaturated monomer unit, and may contain, in addition to the aforestated monomer units, a copolymerized monomer unit exemplified by vinyl ester monomer unit such as those derived from vinyl acetate, vinyl formate, vinyl versate and vinyl pivalate, mono-olefinic monomer unit such as ethylene and propylene and nitrile monomer unit such a acrylonitrile and methacrylonitrile to the extent that the addition thereof does not impair the effect of the present invention. The content of the above-mentioned copolymerized monomer unit in the copolymer is desirably 20% or less by weight, more desirably 10% or less by weight. The content of the primary hydroxyl group-containing ethylenically unsaturated monomer unit in the copolymer constituting the dispersoid in the aqueous emulsion according to the present invention is indispensably 0.1 to 50% by weight, desirably 0.2 to 15% by weight, more desirably 0.5 to 10% by weight. An unreasonably low content of the primary hydroxyl group-containing ethylenically unsaturated monomer unit decreases the effect on the crosslinkage with the polyvalent isocyanate compound as the component (B), thus failing to sufficiently develop water resistance required for the adhesive obtained therefrom. Conversely, an excessively high content thereof unreasonably increases the hydrophilic nature of the copolymer constituting the dispersoid, thereby decreases the polymerization stability at the time of emulsion polymerization and water resistance of the aqueous emulsion itself, resulting in failure to sufficiently develop water resistance required for the adhesive to be made from the aqueous emulsion. The content of the hydrophobic unsaturated monomer unit in the copolymer is desirably 50 to 99.9% by weight, more desirably 85 to 99.8% by weight, furthermore desirably 90 to 99.5% by weight. The glass transition temperature (Tg) of the copolymer which constitutes the dispersoid in the aqueous emulsion according to the present invention is not specifically limited, but is desirably not lower than -10°C to lower than 50°C, more desirably from -10°C to 40°C. A Tg of lower than -10°C may decrease the adhesive strength on account of insufficient cohesive force, while a Tg of 50°C or higher may deteriorate the film-forming properties resulting in decrease in the adhesive strength. The aqueous emulsion according to the present invention, as described hereinbefore, comprises the aforestated dispersoid and dispersant, which comprises PVA having a mercapto group at an end thereof. Such PVA as above may be chemically bonded to the copolymer of the dispersoid by graft reaction or may be physically adsorbed on the copolymer of the dispersoid, but the former chemical bonding is preferable. Although the use of a PVA having a mercapto group in the main chain thereof instead of at an end thereof can develop the effect to some extent, the use thereof is not desirable because of possibility of insolubilization due to the formation of disulfide bond by the oxidation of PVA itself. Therefore, in the aqueous emulsion according to the present invention, there should be used the PVA having a mercapto group at an end thereof, preferably the PVA having a mercapto group at one end only thereof, since the use of the latter can eliminate the fear of insolubilization and facilitate the handling thereof. The PVA having a mercapto group at an end thereof to be used in the present invention may have a different functional group in the main or side chain of the PVA in addition to the mercapto group at an end thereof. The aforesaid PVA having a mercapto group at one end only thereof can be prepared for example, by hydrolyzing a vinyl ester polymer obtained by polymerizing, in the presence of a thiolic acid, a vinyl monomer comprising a vinyl ester monomer as primary component. The degree of polymerization of the PVA having a mercapto group at an end thereof to be used in the present invention may be determined according to respective situations without specific limitation, but is desirably 3500 or less, more desirably 1500 or less. The degree of hydrolysis thereof depends on the type of the other modifying group and can not be unequivocally determined, but is desirably not less than 70 mol% from the viewpoint of water-solubility. The dispersant may be composed of the PVA having a mercapto group at an end thereof alone but may contain, in addition to the above, a known PVA or an emulsifying agent other than PVA to the extent that the addition thereof does not injure the emulsion polymerization stability or initial adhesivity. By virtue of the high activity of the mercapto group in radical reaction, the PVA having a mercapto group at an end thereof can be highly reactive even with a monomer having a relatively low radical reactivity such as methacrylic ester monomer, acrylic ester monomer, styrenic monomer, diene monomer and halogenated unsaturated monomer which have been extremely difficult to be made into a stable emulsion by the use of the conventional PVA not having a mercapto group at an end thereof as the dispersant. As a result, the PVA having a mercapto group at an end thereof can be chemically bonded to the particles of the dispersoid composed of the copolymer comprising any of the aforementioned monomers as the constitutional unit, thereby providing an exceptionally stable aqueous emulsion. The average particle diameter of the dispersoid in the aqueous emulsion according to the present invention is not specifically limited but is desirably 0.2 to 2.0 µm, more desirably 0.3 to 1.5 µm. The concentration of the dispersoid in the aqueous emulsion may be suitably determined according to the various situations, but is desirably 30 to 70% by weight, more desirably 40 to 60% by weight. The concentration of the dispersant in the aqueous emulsion is not specifically limited as well but is desirably 0.5 to 30 parts by weight, more desirably 1 to 10 parts by weight per 100 parts by weight of the dispersoid. In the case where the average particle diameter, concentration of the dispersoid or the concentration of the dispersant departs from the foregoing desirable range in the aqueous emulsion of the present invention, polymerization stability at the time of emulsion polymerization and water resistance, durability and initial adhesivity of the adhesive obtained from the aqueous emulsion may not be developed with favorable balance among them. To the aqueous emulsion of the present invention, if necessary, different types of aqueous emulsions may be added to the extent that the addition thereof does not impair the performance such as water resistance and initial adhesivity, which emulsions are exemplified by vinyl acetate, ethylene/vinyl acetate copolymer, polychloroprene, polybutadiene, styrene/butadiene copolymer, butadiene/acrylonitrile copolymer, butyl rubber, polyacrylic acid ester, polyvinyl chloride and polyvinylidene each in the form of emulsion. As described hereinbefore, the composition according to the present invention comprises an (A) aqueous emulsion and a (B) polyvalent isocyanate compound, which possesses at least two isocyanate groups in a molecule and is enumerated by toluylene diisocyanate (TDI); hydrogenated TDI; trimethylol ) propane-TDI adduct (e.g. produced by Bayer AG under the tradename "Desmodur L"); triphenylmethane triisocyanate; methylenebis(diphenyl isocyanate) (MDI); hydrogenated MDI; polymerized MDI; hexamethylene diisocyanate; xylylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate; and isophorone diisocyanate. There may be also used a prepolymer having an isocyanate group at an end thereof which is obtained by preliminarily polymerizing a polyol with excessive polyisocyanate. The compounding ratio of the (A) aqueous emulsion to the (B) polyvalent isocyanate compound, together constituting the foregoing composition of the present invention, may be suitably determined according to the various conditions, but is desirably 10 to 150 parts by weight, more desirably 20 to 100 parts by weight of polyvalent isocyanate compound per 100 parts by weight of aqueous emulsion expressed in terms of solid content. The composition according to the present invention comprises the aqueous emulsion in which is contained PVA having a mercapto group at an end thereof as the dispersant, and according to the demand, a known PVA may be added to the PVA in the aqueous emulsion. The composition according to the present invention may be incorporated, if necessary, with starch, denatured starch, oxidized starch, sodium alginate, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, maleic anhydride/isobutene copolymer, maleic anhydride/styrene copolymer, water-soluble high molecular compound such as maleic anhydride/methylvinyl ether copolymer and a thermosetting resin such as urea/formalin resin, urea/melamine/formalin resin and phenol/formalin resin, each resin being generally used in an adhesive. In addition, the composition according to the present invention may be incorporated as required with a filler such as clay, kaoline, talc, calcium carbonate and wood powder; extender such as wheat flour; reaction accelerator such as boric acid and aluminum sulfate; pigment such as titanium oxide; and various additives such as preservative and rust preventive. The adhesive of the present invention is used for joining a variety of objects and above all for joining wood and lumber. The coating amount of the adhesive of the present invention is desirably 20 to 300 g/m 2 , more desirably 30 to 200 g/m 2 expressed in terms of solid content. As the method for coating, brush coating, roll coating and the like are available. As the method for drying after coating of the adhesive, drying at room temperature to 200°C is acceptable, but the adhesive of the present invention develops a sufficient adhesive force even after drying at room temperature. The adhesive of the present invention is characterized in that it is excellent in both initial adhesivity and water resistance in boiling water. The drying time after coating is desirably 30 minutes to 5 hours, preferably under press bonding. The pressure required for the press bonding is determined in the range of 5 to 20 kg/cm 2 , preferably higher in the case where the object to be joined is a hard wood or lumber and preferably higher, so far as the object is not broken, in the case where the object to be joined is a soft wood or lumber. The wooden product according to the present invention is a wooden product joined with the above-described adhesive, including plywood, furniture and the like, each joined with the adhesive. The kinds of wood in the wooden product is not specifically limited and is exemplified by birch, (Japanese) hemlock, (Japanese) cedar, lauan, zelkova tree and the like. For the production of the above-described aqueous emulsion according to the present invention, various processes are taken into consideration, among which a process for efficiently producing a high quality aqueous emulsion will be described as follows: The desirable process for producing the aqueous emulsion is the process which comprises emulsion-polymerizing at least one hydrophobic unsaturated monomer selected from the group consisting of methacrylic ester monomer, acrylic ester monomer, styrenic monomer, diene monomer and halogenated unsaturated monomer and 0.1 to 50% by weight of a primary hydroxyl group-containing ethylenically unsaturated monomer based on the total amount of the aforementioned monomer in the presence of PVA having a mercapto group at an end thereof. In putting the above-mentioned process into practice, there is available the conventional emulsion polymerization method in which the aforesaid monomer is added to the reaction system at a time or continuously followed by heating and stirring in the presence of water, said PVA and a polymerization initiator. There is also available the method in which a preliminarily emulsified mixture of a monomer and the aqueous solution of said PVA is continuously added to the reaction system. As the polymerization initiator to be used in the aforesaid process, there is available a Redox system comprising the terminal mercapto group of a PVA having a mercapto group at an end thereof and a water-soluble oxidizing agent such as potassium bromate, potassium persulfate, ammonium persulfate and hydrogen peroxide. Among them potassium bromate is a particularly desirable polymerizaticn initiator since it does not generate a radical independently under usual polymerization conditions, but is decomposed only by the Redox reaction with the terminal mercapto group of a PVA having a mercapto group at an end thereof to generate a radical, thereby effectively producing a block copolymer with the PVA having a mercapto group at an end thereof with the result that the stability of the aqueous emulsion is enhanced. It is also possible to use an oxidizing agent in combination, that is, to use potassium bromate at the start of polymerization and thereafter add another oxidizing agent. It is particularly desirable that the polymerization system is acid in the case of emulsion (co)polymerization in the presence of the PVA having a mercapto group at an end thereof. The reason for the above is that under alkaline condition, the mercapto group which exhibits an extremely active reactivity at the time of radical polymerization increases the velocity of ionically adding to the double bond of a hydrophobic unsaturated monomer, resulting in a marked decrease in polymerization efficiency. Accordingly, the pH in the polymerization system depends on the type of the hydrophobic unsaturated monomer, but is desirably 6 or less, particularly desirably 4 or less for all of the emulsion polymerization operations to be carried out according to the process of the present invention. The composition of the present invention finds a wide diversity of use typified by adhesive. The use of the composition as an adhesive can drastically improve initial adhesivity as well as adhesive strength and water resistance. The adhesive according to the present invention is applicable for joining miscellaneous objects, particularly favorably for joining wooden products, and also can be used for joining not only two or more woods but also wood to paper, fiber product, inorganic board, and the like. By virtue of its adhesive film excellent in water resistance, the composition of the present invention can find effective use in the field of inorganic binder, primer for inorganic board, wooden panel and the like. In the following, the present invention will be described in more detail with reference to the examples and comparative examples, wherein "part(s)" and "%" denote part(s) by weight and % by weight, respectively, unless otherwise specified. Example 1 (1) Preparation of aqueous emulsion In a glass-made polymerization reactor equipped with a reflux condenser, a dropping funnel, a thermometer and a nitrogen injection nozzle were placed 5 parts of PVA having a mercapto group at an end thereof (average degree of polymerization of 550, degree of hydrolysis of 88.0 mol% and mercapto group (SH) content of 3.2 x 10 -5 equivalent/g) and 100 parts of ion-exchanged water, in which the PVA was completely dissolved at 95°C. The solution was adjusted to pH 3.0 with sulfuric acid, incorporated with 10 parts of methyl methacrylate and 10 parts of n-butyl acrylate, heated to 65°C after atmosphere in the reactor was replaced with nitrogen, incorporated with 1.3 part of 2% potassium bromate aqueous solution to initiate polymerization and to the mixture were continuously added 40 parts of methyl methacrylate, 38 parts of n-butyl acrylate and 2 parts of 2-hydroxyethyl acrylate over a period of 2 hours. The polymerization was completed after 3 hours from the start thereof, producing a stable copolymer emulsion (I) of methyl methacrylate/n-butyl acrylate/2-hydroxyethyl acrylate having a solid concentration of 50.9%, a viscosity of 750 mPa·s and an average particle diameter of 0.9 µm. (2) Adhesion test By the use of the aforesaid aqueous emulsion, adhesion test was carried out under the following conditions. The result are given in Table 1. Conditions of adhesion test [Adhesive composition] The adhesive to be tested was obtained by adding 45 parts of 10% PVA aqueous solution having a degree of polymerization of 1700 and a degree of hydrolysis of 98 mol% (produced by Kuraray Co., Ltd. under the tradename "PVA 117") and 10 parts of calcium carbonate to 45 parts of said aqueous emulsion, and to the resultant mixture further adding 15 parts of polymethylene polyphenyl isocyanate (produced by Nippon Polyurethane Industry Co., Ltd. under the tradename "Millionate MR-100") followed by mixing. [Adhesion conditions] Object to be joined: birch/birch (grain face) with 8% water content Coating amount : 250 g/m 2 (for both sides) Open time : 1 min. Pressure bonding condition: 20°C, 24 hours, 10 kg/cm 2 pressure (only for test pieces for dry strength and for ones for repeated boiling) [Measuring condition] Compression-shear adhesive strength was measured according to JIS K-6852 Dry strength: After curing at 20°C for 7 days, measured as such. Repeated boiling: after curing at 20°C for 7 days, a test piece was immersed in boiling water for 4 hours, then dried in the air at 60°C for 20 hours, again immersed in boiling water for 4 hours, allowed to stand in the water until the boiling water cools to room temperature and subjected to the test as such under wet condition. Initial adhesivity: A pair of test pieces was stuck together, subjected to press bonding at 20°C and 10 kg/cm 2 and immediately thereafter measured for compression-shear adhesive strength. Example 2 (1) Preparation of aqueous emulsion In a glass-made polymerization reactor equipped with a reflux condenser, a dropping funnel, a thermometer and a nitrogen injection nozzle were placed 5 parts of PVA having a mercapto group at an end thereof and a carboxyl group in the side chain thereof (average degree of polymerization of 700, degree of hydrolysis of 89.2 mol%, content of carboxyl group of 1.0 mol% and mercapto group (SH) content of 2.3 x 10 -5 equivalent/g) and 105 parts of ion-exchanged water, in which the PVA was completely dissolved at 95°C. The solution was adjusted to pH 3.0 with sulfuric acid, incorporated with 8 parts of styrene and 12 parts of 2-ethylhexyl acrylate, heated to 60°C after atmosphere in the reactor was replaced with nitrogen, incorporated with 1.0 part of 2% potassium bromate aqueous solution to initiate polymerization and to the mixture were continuously added 32 parts of styrene, 45 parts of 2-ethylhexyl acrylate and 3 part of 2-hydroxyethyl methacrylate over a period of 2 hours. The polymerization was completed after 3 hours from the start thereof, producing a stable copolymer emulsion (II) of styrene/2-ethylhexyl acrylate/2-hydroxyethyl methacrylate having a solid concentration of 49.7%, a viscosity of 2800 mPa·s and an average particle diameter of 0.8 µm. (2) Adhesion test By the use of the aforestated aqueous emulsion (II), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Example 3 (1) Preparation of aqueous emulsion In a pressure resistant autoclave equipped with a nitrogen injection nozzle and a thermometer was placed 120 parts of 5% PVA aqueous solution having a mercapto group at an end thereof, said PVA being the same as that used in Example 1. By the use of sulfuric acid, the solution was adjusted to pH 4.0 and thereafter incorporated with 53 parts of styrene and 2 parts of 2-hydroxyethyl methacrylate. Subsequently, the autoclave was pressurized with 45 parts of butadiene through a metering pressure bottle. After raising the temperature of the contents in the autoclave to 70°C, 25 parts of 2% potassium persulfate aqueous solution was added into the autoclave to initiate polymerization. An internal pressure of 4.8 kg/cm 2 decreased with the progress of reaction and dropped to 0.5 kg/cm 2 after 20 hours. The conversion to polymer was obtained as 98.5%. The resultant copolymer emulsion (III) of styrene/butadiene/2-hydroxyethyl methacrylate was stable and had a solid concentration of 42.9%, a viscosity of 850 mPa·s and an average particle diameter of 1.1 µm. (2) Adhesion test By the use of the aforestated aqueous emulsion (III), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Example 4 (1) Preparaticn of aqueous emulsion In a pressure resistant autoclave equipped with a nitrogen injection nozzle and a thermometer was placed 120 parts of 5% PVA aqueous solution having a mercapto group at an end thereof, said PVA being the same as that used in Example 1. By the use of sulfuric acid, the solution was adjusted to pH 4.0 then after atmosphere in the autoclave was replaced with nitrogen, incorporated with 3 parts of 2-hydroxyethyl methacrylate. Subsequently, the autoclave was pressurized with 80 parts of vinyl chloride monomer through a metering pressure bottle. Thereafter the autoclave was pressurized with ethylene up to show the pressure of 30 kg/cm 2 and, after temperature raising to 60°C, 25 parts of 2% potassium persulfate aqueous solution was added. After 6 hours from the start of polymerization, the concentration of the residual vinyl chloride monomer dropped to 0.01% or lower, indicating the completion of polymerization. The vinyl chloride/ethylene copolymer emulsion (IV) thus obtained was stable and had a solid concentration of 43.3%, viscosity of 1000 mPa·s and an average particle diameter of 1.0 µm. (2) Adhesion test By the use of the aforementioned aqueous emulsion (IV), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Comparative Example 1 The procedure in Example 1 was repeated to produce methyl methacrylate/n-butyl acrylate copolymer emulsion (V) except that the use of 2-hydroxyethyl acrylate containing primary hydroxy group was omitted. The aqueous emulsion thus obtained was stable and had a solid concentration of 50%, viscosity of 700 mPa·s and an average particle diameter of 0.9 µm. By the use of the aforementioned aqueous emulsion (V), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Comparative Example 2 The procedure in Example 1 was repeated except that an unmodified PVA having an average degree of polymerization of 500 and a degree of hydrolysis of 88 mol% (produced by Kuraray Co., Ltd. under the tradename "PVA 205") was used in place of the PVA having an mercapto group at an end thereof to try to effect emulsion polymerization of methyl methacrylate, n-butyl acrylate and 2-hydroxyethyl acrylate. However, after 30 minutes from the start of the trial coarse particles of several mm in size were formed at a conversion to polymer of 15.5%, thus failing to afford a stable aqueous emulsion. Comparative Example 3 The procedure in Example 3 was repeated except that an unmodified PVA having an average degree of polymerization of 500 and a degree of hydrolysis of 88 mol% (produced by Kuraray Co., Ltd. under the tradename "PVA 205") and an unmodified PVA having an average degree of polymerization of 1700 and an average degree of hydrolysis of 88 mol% (also produced by Kuraray Co., Ltd. under the tradename "PVA 217") in a ratio by weight of 8:2 were used in place of the PVA having an mercapto group at an end thereof to try to conduct emulsion polymerization of styrene, butadiene and 2-hydroxyethyl acrylate. However, after 2 hours from the start of the trial, blocking took place at a conversion to polymer of 25.3% thus failing to afford a stable aqueous emulsion. Comparative Example 4 The procedure in Example 2 was repeated except that a polyoxyethylene nonylphenyl ether having 40 mol of oxyethylene units (produced by Sanyo Chemical Industries, Ltd. under the tradename "Nonipol 400") was used in place of the PVA having a mercapto group at an end thereof and a carboxyl group in the side chain to obtain a styrene/2-ethylhexyl acrylate/2-hydroxyethyl methacrylate copolymer emulsion (VI). The emulsion thus obtained was stable and had a solid concentration of 49.8%, viscosity of 110 mPa·s and an average particle diameter of 0.15 µm. By the use of the aqueous emulsion (VI), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Comparative Example 5 The procedure in Example 3 was repeated except that a sodium salt of alkyldiphenyl ether disulfonic acid (produced by Sanyo Chemical Industries, Ltd. under the tradename "Sundet BL") was used in place of the PVA having a mercapto group at an end thereof to obtain a styrene/butadiene/2-hydroxyethyl methacrylate copolymer emulsion (VII). The emulsion thus obtained was stable and had a solid concentration of 42.5%, viscosity of 85 mPa·s and an average particle diameter of 0.1 µm. By the use of the aqueous emulsion (VII), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Comparative Example 6 In a pressure resistant autoclave equipped with a nitrogen injection nozzle and a thermometer was placed 100 parts of 6% PVA aqueous solution having a mercapto group at an end thereof, said PVA being the same as that used in Example 1. By the use of sulfuric acid, the solution was adjusted to pH 4.0 and thereafter incorporated with 80 parts of vinyl acetate and 2 parts of 2-hydroxyethyl acrylate. After raising the temperature of the contents in the autoclave to 60°C and replacing atmosphere therein with nitrogen, the autoclave was pressurized with ethylene to show the pressure of 40 kg/cm 2 and polymerization was initiated by the use of a redox initiator of hydrogen peroxide/Rongalite system. After 4 hours from the start of polymerization, the concentration of the residual vinyl acetate monomer dropped to 0.5%. The ethylene/vinyl acetate/2-hydroxyethyl acrylate copolymer emulsion (VIII) thus obtained was stable and had a solid concentration of 50.0%, viscosity of 900 mPa·s and an average particle diameter of 0.7 µm. By the use of the aforementioned aqueous emulsion (VIII), adhesion test was carried out in the same manner as in Example 1. The results are given in Table 1. Comparative Examples 7 to 10 In the same manner as in Example 1, adhesion test was carried out for aqueous emulsions (I) to (IV) obtained in Examples 1 to 4, respectively except that polymethylene polyphenyl isocyanate was not used. The results are given in Table 1.

Claims: A composition which comprises an (A) aqueous emulsion comprising a dispersoid which comprises a copolymer containing at least one hydrophobic unsaturated monomer unit selected from a methacrylic ester monomer unit, acrylic ester monomer unit, styrenic monomer unit, diene monomer unit and halogenated unsaturated monomer unit; and a primary hydroxyl group-containing ethylenically unsaturated monomer unit in an amount of 0.1 to 50% by weight based on said copolymer; and a dispersant comprising a vinyl alcohol polymer having a mercapto group at an end thereof and a (B) polyvalent isocyanate compound. The composition according to claim 1, wherein said (B) polyvalent isocyanate compound is compounded in an amount of 10 to 150 parts by weight per 100 parts by weight of said (A) aqueous emulsion expressed in terms of solid content. Use of the composition according to any of claims 1 to 2 for the production of an adhesive. An adhesive which comprises the composition set forth in any of claims 1 to 2. Use of the adhesive according to claim 4 for joining objects, particularly wood and lumber. A wooden product characterized in that the wooden product is joined by the adhesive as set forth in claim 4. An aqueous emulsion (A) comprising a dispersoid which comprises a copolymer containing at least one hydrophobic unsaturated monomer unit selected from a methacrylic ester monomer unit, acrylic ester monomer unit, styrenic monomer unit, diene monomer unit and halogenated unsaturated monomer unit; and a primary hydroxyl group-containing ethylenically unsaturated monomer unit in an amount of 0.1 to 50% by weight based on said copolymer; and a dispersant comprising a vinyl alcohol polymer having a mercapto group at an end thereof. A process for producing an (A) aqueous emulsion as set forth in claim 7 which comprises subjecting at least one hydrophobic unsaturated monomer selected from a methacrylic ester monomer, acrylic ester monomer, styrenic monomer, diene monomer and halogenated unsaturated monomer; and a primary hydroxyl group-containing ethylenically unsaturated monomer in an amount of 0.1 to 50% by weight based on the total amount of the monomers to emulsion polymerization in the presence of a dispersant comprising a vinyl alcohol polymer having a mercapto group at an end thereof.

Inventors: HATTORI TATSUAKI, MARUYAMA HITOSHI, NAKAMAE MASATO, YUKI KEN, HATTORI, TATSUAKI, MARUYAMA, HITOSHI, NAKAMAE, MASATO, YUKI, KEN
Applicants: KURARAY CO, KURARAY CO., LTD.
Application year: 1992
Main classification: C08G18
IPC codes: C08G18, C09J175