JP2009242512A - Adhesive composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive composition which can prevent a dry crack of a sliced veneer even when it is a sliced veneer which is liable to cause a dry crack and is suitable for adhesion of a sliced veneer. <P>SOLUTION: The adhesive composition comprises a vinyl acetate resin emulsion (a), polyvinyl alcohol (b), and an aqueous epoxy compound (c). The adhesive composition preferably further comprises an isocyanate compound (d), and the polyvinyl alcohol (b) preferably contains an acetoacetyl group. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an adhesive composition that can prevent dry cracking even if it is a veneer that is prone to dry cracking without using a formaldehyde-containing resin, and is suitable for adhesion of the veneer.

  Conventionally, when a decorative paper or a veneer is bonded to a woody substrate such as plywood, an adhesive obtained by mixing an amino resin obtained by condensation polymerization of urea, melamine and formaldehyde and a vinyl acetate resin has been used. However, due to the problem of so-called sick house syndrome, building materials that dissipate more than a certain amount of formaldehyde have a limited use area. For example, building materials and adhesives used in these materials are required to be of a type that does not use formaldehyde. .

The present inventors have already proposed a type of adhesive that does not use an amino resin. However, when a veneer that is prone to dry cracking such as maple, pine or zelkova was bonded, dry cracking occurred.
JP 2006-28316 A

  This invention provides the adhesive composition which can prevent a dry crack even if it is a veneer which is easy to dry without using formaldehyde containing resin like an amino-type resin.

  As a result of intensive studies by the present inventors, the above problem is solved by an adhesive composition comprising a vinyl acetate resin emulsion (a), polyvinyl alcohol (b), and an aqueous epoxy compound (c). I found out that Moreover, it was found that the isocyanate compound (d) was further contained, and that the polyvinyl alcohol (b) preferably contained an acetoacetyl group.

  Although the reason why the adhesive composition of the present invention can prevent dry cracking even if it is a veneer that is prone to dry cracks is not necessarily clear, it has a sufficiently strong adhesive force to the veneer, while it moves due to dry shrinkage of the veneer. This is thought to be due to having the flexibility to alleviate the problem.

  Since the adhesive composition of the present invention can prevent dry cracking even if it is a veneer that is prone to dry cracking, it can be bonded without problems even if it is a dry veneer such as maple, pine or zelkova. In addition, since no amino-based resin, which is a formaldehyde emission source, is used, it can be used without problems in the production of building materials used in houses and the like.

  Hereinafter, the present invention will be described in detail.

  The vinyl acetate resin emulsion (a) used in the present invention usually has a water-soluble polymer such as polyvinyl alcohol having a saponification degree of 75 to 99.5% and an average polymerization degree of 300 to 4000 as a protective colloid. It is synthesized by emulsion polymerization of vinyl acetate alone or a monomer copolymerizable with vinyl acetate in combination with an emulsifier such as a surfactant. Examples of monomers copolymerizable with vinyl acetate include ethylene, acrylic acid, acrylic esters, and vinyl versatate. An ethylene-vinyl acetate copolymer resin copolymerized with ethylene has a low glass transition temperature and is flexible and is preferably used. In addition, by polymerizing vinyl acetate alone or a monomer copolymerizable with vinyl acetate in the presence of a resin emulsion having a low glass transition temperature such as an ethylene-vinyl acetate copolymer resin emulsion or an acrylic resin emulsion, A flexible vinyl acetate resin emulsion can be obtained and used. Furthermore, water resistance can be improved by using a vinyl acetate resin emulsion copolymerized with a carboxyl group-containing monomer or an acetoacetyl group-containing monomer.

  Polyvinyl alcohol (b), which is also contained in the vinyl acetate resin emulsion, is consumed as a protective colloid during the polymerization of vinyl acetate or the like, and thus indicates polyvinyl alcohol added separately after polymerization. It is. Moreover, water resistance can be improved by using acetoacetyl group containing polyvinyl alcohol.

  The aqueous epoxy compound (c) is added for the purpose of preventing dry cracking of the veneer. The aqueous epoxy compound is a compound obtained by glycidyl etherification of a polyhydric alcohol such as ethylene glycol, propylene glycol, or glycerin. Note that it is not necessary that all alcohol groups of the polyhydric alcohol are glycidyl etherified. A preferable addition amount of the aqueous epoxy compound is 5 to 30 parts by weight with respect to 100 parts by weight of (a) the vinyl acetate resin emulsion.

  Since the water resistance can be improved by adding the isocyanate compound (d), it is preferable to add an isocyanate compound, for example, when the water resistance is required to pass the type 1 immersion peel test. Specific examples of the isocyanate compound include aromatic isocyanates such as 2,4′-diphenylmethane diisocyanate (2,4′-MDI), 4,4′-diphenylmethane diisocyanate (4,4′-MDI), tolylene diisocyanate, and naphthalene diisocyanate. And aliphatic polyisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate. By using 1 part by weight or more of the isocyanate compound with respect to 100 parts by weight of the solid content of the vinyl acetate resin emulsion (a), the water resistance is remarkably improved. On the other hand, even if it is used in an amount of 30 parts by weight or more, the water resistance reaches a peak, and the viscosity increases after mixing, so workability decreases.

  In the adhesive composition of the present invention, known additives can be used in addition to the above components. For example, a thickener, a filler, a pH adjuster, a tackifier resin, a surfactant, an antiseptic, an antifoaming agent, an antirust agent, and the like can be given.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited to an Example.

  10 parts by weight of Goosephimer Z-320 (trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), which is an acetoacetyl group-containing polyvinyl alcohol, is dispersed in 90 parts by weight of water, heated and stirred at 90 ° C. for 3 hours, and then cooled. AA-PVA aqueous solution (1) was obtained by mixing 0.1 part of sodium bisulfite.

  60 parts by weight of AE-156 (manufactured by Aika Kogyo Co., Ltd.) which is an ethylene-vinyl acetate copolymer resin emulsion, 20 parts by weight of the AA-PVA aqueous solution (1), 15 parts by weight of flour, and AUH-1 (Aika) which is an isocyanate compound 1 part by weight manufactured by Kogyo Co., Ltd. and 7 parts by weight of glycerin polyglycidyl ether which is an aqueous epoxy compound were mixed to obtain an adhesive composition of Example 1.

  Each adhesive composition of Examples and Comparative Examples was prepared in the same manner as in Example 1 with the formulation shown in Table 1.

Each adhesive composition was applied to JAS1 plywood (12 mm thick, F ☆☆☆☆) at 100 g / m ^2, and a maple veneer (0.25 mm thick) was bonded together at 105 ° C. and 0.7 MPa. A veneer plywood was prepared by pressing for 60 seconds. Each veneer plywood was subjected to a type 1 immersion peel test and a type 2 immersion peel test, and the case of conforming to the standard was evaluated as ◯, and the case of not conforming was evaluated as ×. Moreover, the state of the veneer of each veneer decorative plywood was confirmed, and the case where there was no remarkable crack was evaluated as ○, and the case where the significant crack was conspicuous was evaluated as ×.

  When each adhesive composition of an Example was used, there was no remarkable crack in the obtained veneer decorative plywood. Moreover, high water resistance can be obtained by using an isocyanate compound like Example 1,2. On the other hand, when each adhesive composition of a comparative example was used, the remarkable crack was a result, and the crack also generate | occur | produced also in the comparative example 2 which is excellent in water resistance by using an isocyanate compound. Therefore, it turns out that water resistance and the evaluation of a crack do not necessarily correspond.

Claims (3)

  An adhesive composition comprising a vinyl acetate resin emulsion (a), polyvinyl alcohol (b), and an aqueous epoxy compound (c).   The adhesive composition according to claim 1, further comprising an isocyanate compound (d).   The adhesive composition according to claim 1 or 2, wherein the polyvinyl alcohol (b) contains an acetoacetyl group.