JP4020391B2 - Adhesive composition for wood - Google Patents

Description

  The present invention relates to an adhesive composition, and in particular, it does not disperse formaldehyde, has high adhesive strength, excellent durability, water resistance and hot water adhesiveness, and has a long working life, so that workability is remarkable. It relates to an improved adhesive composition.

Conventionally, in the plywood market, thermosetting adhesives such as melamine-formaldehyde resin, urea-formaldehyde resin, and phenol resin are mainly used as adhesives. However, in recent years, with the close-up of health problems due to formaldehyde indoor contamination, ie, the problem of sick house syndrome, these thermosetting resins have been developed with low formaldehyde emission, but formaldehyde emission is reduced to zero. It is virtually impossible.
On the other hand, vinyl acetate resin emulsions and ethylene-vinyl acetate resin emulsions are partly used as adhesives that do not contain formaldehyde. However, these adhesives have extremely insufficient water resistance and hot water adhesive properties. For example, it cannot be put into practical use in applications that require a high degree of adhesiveness, such as structural adhesives.
Therefore, as a water-resistant adhesive not containing formaldehyde, an aqueous emulsion, an aqueous polymer, an adhesive comprising an isocyanate compound, a so-called aqueous polymer-isocyanate adhesive has been widely used. However, its performance is not always sufficient, and there is a problem in workability such as foaming of the paste after blending the isocyanate compound, thickening with time, and short working time, and improvement thereof is desired.
For this reason, resorcinol resins, resorcinol-phenol copolymer resins, and water-based polymer-isocyanate adhesives are used as structural adhesives that require a high level of adhesiveness. At present, there has been no development that can satisfy these requirements.
Moreover, these problems are not limited to plywood and wood adhesives, but have been pointed out in decorative plywood, fiber boards, and other various adhesives, and an immediate solution has been desired.

  Accordingly, an object of the present invention is to provide an adhesive which does not disperse formaldehyde, has high adhesive strength, excellent durability, water resistance and hot water resistance, and has a significantly improved workability due to a long pot life. It is to provide a composition.

  As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved only when a specific synthetic resin emulsion, polyvinyl alcohol, an inorganic pigment, and an isocyanate group-containing compound are blended, thereby completing the present invention. .

The invention of claim 1 includes (A) a synthetic resin emulsion using gum arabic as a protective colloid, (B) polyvinyl alcohol, (C) an inorganic pigment, and (D) a compound having two or more isocyanate groups in one molecule. It is the adhesive composition formed.
According to a second aspect of the present invention, the gum arabic as a protective colloid of the synthetic resin emulsion is in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the solid content of the synthetic resin emulsion. It is an adhesive composition.
The invention according to claim 3 is the adhesive composition according to claim 1, wherein the synthetic resin emulsion has a glass transition temperature (Tg) of -10 ° C to 50 ° C.
Invention of Claim 4 is an adhesive composition of Claim 1 whose solid content of (B) polyvinyl alcohol is a ratio of 2-300 weight part with respect to 100 weight part of solid content of the said synthetic resin emulsion. is there.
The invention according to claim 5 is the adhesive composition according to claim 1, wherein (C) the inorganic pigment is 50 to 300 parts by weight with respect to 100 parts by weight of the solid content of the synthetic resin emulsion.
The invention of claim 6 relates to (D) a solid content of a compound having two or more isocyanate groups in one molecule with respect to 100 parts by weight of the solid content of both (A) synthetic resin emulsion and (B) polyvinyl alcohol. It is a ratio of 2-100 weight part, It is an adhesive composition of Claim 1.
The invention of claim 7 is an adhesive composition for wood comprising the adhesive composition according to any one of claims 1 to 6.

  According to the present invention, an adhesive composition that does not disperse formaldehyde, has high adhesive strength, excellent durability, water resistance and hot water resistance, and has a significantly improved workability due to a long pot life. Things are provided.

Hereinafter, the present invention will be described in more detail.
(A) Synthetic resin emulsion The (A) synthetic resin emulsion used in the wood adhesive composition of the present invention is obtained by emulsion polymerization of a radically polymerizable unsaturated monomer using gum arabic as a protective colloid. Can do . Anionic, cationic, amphoteric, and nonionic surfactants used in normal emulsion polymerization only when gum arabic is used as a protective colloid, and other water-soluble materials other than gum arabic such as various polyvinyl alcohols and hydroxyethyl cellulose Compared with the one using a functional polymer, (B) polyvinyl alcohol, (C) an inorganic pigment, and (D) an adhesive composition in combination with a compound having two or more isocyanate groups in one molecule It becomes possible to dramatically increase the pot life of an object.

(A) When the synthetic resin emulsion is obtained by emulsion polymerization, the amount of gum arabic used as the protective colloid is 0.1 to 20 parts by weight, preferably 0.1 to 100 parts by weight of the solid content of the synthetic resin emulsion. 5 to 15 parts by weight. When the blending amount of gum arabic is 0.1 parts by weight or more, the stability of the obtained synthetic resin emulsion (A) can be improved, and aggregation and gelation can be prevented, and the amount is 20 parts by weight or less. As a result, the water resistance of the finally obtained adhesive can be further increased.
In addition, various polyvinyl alcohols, hydroxyethyl cellulose, and the like can be used in combination with gum arabic as protective colloids as long as the pot life and adhesion performance are not hindered.

  Furthermore, the glass transition temperature of the synthetic resin emulsion (A) in the present invention is preferably in the range of −10 ° C. to 50 ° C. When the glass transition temperature is higher than −10 ° C., the adhesive strength of the finally obtained adhesive can be further increased, and the water resistance can be increased. Moreover, when the glass transition temperature is 50 ° C. or lower, the film forming property of the adhesive is improved, and the adhesive strength and water resistance can be further increased.

The synthetic resin emulsion (A) in the present invention is a vinyl acetate polymer emulsion, vinyl acetate-ethylene copolymer emulsion, vinyl acetate-unsaturated acid copolymer emulsion, which can be polymerized using gum arabic as a protective colloid, (meth) Examples thereof include an acrylate copolymer emulsion, a styrene- (meth) acrylate copolymer emulsion, a styrene-butadiene copolymer latex, an acrylonitrile-butadiene copolymer latex, and a styrene-isoprene copolymer latex.

In the adhesive composition of the present invention, the (A) synthetic resin emulsion can be produced according to a usual emulsion polymerization method. In the polymerization, a generally used polymerization initiator is used. Specific examples include water-soluble inorganic peroxides or persulfates such as hydrogen peroxide, potassium persulfate, and ammonium persulfate, organic peroxides such as cumene hydroperoxide and benzoyl peroxide, and azo such as azobisisobutylnitrile. Compounds. The amount of the polymerization initiator used is preferably 0.1 to 2.0 parts by weight with respect to 100 parts by weight of the solid content of the synthetic resin emulsion. Further, the polymerization initiator is usually used in combination with a reducing agent such as tartaric acid, formic acid, oxalic acid, and acidic sodium sulfite. Moreover, the radically polymerizable unsaturated monomer used for synthesizing the synthetic resin emulsion can be subjected to the reaction by batch or divided or continuously dropwise. The polymerization temperature can be carried out at a normal temperature of 60 to 90 ° C.
In addition, it is naturally possible to use a molecular weight regulator that is generally used in emulsion polymerization, or a film-forming aid and other additives frequently used in the case of a synthetic resin emulsion can be added as necessary. .

(B) Polyvinyl alcohol (B) Polyvinyl alcohol used in the adhesive composition of the present invention can be either a normal fully saponified product or a partially saponified product, and a mercapto group-modified product or an acetoacetyl group-modified product. Modified polyvinyl alcohol such as products can be used as well.

Adhesive composition In the adhesive composition for wood of the present invention, a mixture of (A) a synthetic resin emulsion and (B) polyvinyl alcohol is used as a main agent, and the blending is 100 parts by weight of the solid content of the (A) synthetic resin emulsion. On the other hand, it is good to mix | blend so that the solid content of the said (B) polyvinyl alcohol may be in the range of 2-300 weight part, More preferably, it is 5-200 weight part. (B) By suppressing the viscosity increase of the finally obtained adhesive composition after adding the compound (D) which has an isocyanate group demonstrated below, when polyvinyl alcohol is 2 weight part or more. This is preferable. Moreover, the water resistance of the adhesive composition finally obtained can be further improved because (B) polyvinyl alcohol is 300 weight part or less.

(C) Inorganic pigment Examples of the inorganic pigment used in the adhesive composition of the present invention include calcium carbonate, barium sulfate, clay, talc, titanium oxide and the like, and the amount added is (A) the solid content of the synthetic resin emulsion is 100. The proportion of (C) inorganic pigment is preferably 50 to 300 parts by weight with respect to parts by weight. When the added amount of the inorganic pigment is 50 parts by weight or more, the cohesive force of the adhesive can be increased and sufficient adhesive strength can be provided. Moreover, when the addition amount of the inorganic pigment is 300 parts by weight or less, the film forming property, adhesive strength and water resistance of the adhesive can be further enhanced.
In the present invention, (C) two or more kinds of inorganic pigments may be used in combination, and organics such as wheat flour, starch and wood flour may be used in combination.

(D) Compound having isocyanate group (D) The compound having an isocyanate group used in the wood adhesive composition of the present invention is particularly suitable if it has two or more isocyanate groups in one molecule. Examples include aliphatic isocyanates such as hexamethylene diisocyanate, m- and p-phenylene diisocyanate, tolylene-2,4- and -2,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylene. Aromatic isocyanates such as -4,4'-diisocyanate, 4,4'-diisocyanate-3,3'-dimethyldiphenyl, 3-methyl-diphenylmethane-4,4'-diisocyanate, diphenyl ether diisocyanate, and cyclohexane-2, 4- and -2,3-Dii Cyanate, an alicyclic isocyanate such as isophorone diisocyanate. These can be used alone or in admixture of two or more. Also, isocyanate-terminated prepolymers formed by reaction of excess diisocyanate or polyfunctional polyisocyanate with hydroxyl-terminated polyester or hydroxyl-terminated polyether, and excess diisocyanate or polyfunctional polyisocyanate with ethylene glycol, trimethylolpropane or 1,3 Products obtained by reaction with monomeric polyols such as butanediol or mixtures thereof can also be used.

  (D) The compounding amount of the compound having an isocyanate group may be arbitrarily determined depending on the purpose of use, but preferably it is solid with respect to 100 parts by weight of solid content of (A) synthetic resin emulsion and (B) polyvinyl alcohol. It is good to mix | blend so that it may become the range of 2-100 weight part in minutes. (D) When the compounding quantity of the compound which has an isocyanate group is 2 weight part or more, sufficient adhesive force can be provided and it is preferable. Moreover, when the compounding quantity of the compound which has (D) isocyanate group is 100 weight part or less, while being able to make the pot life after a compounding further longer, a raise in a viscosity can also be suppressed.

  Furthermore, various additives, such as antiseptic | preservative and a rust preventive agent, can be suitably added to the adhesive composition of this invention as needed. Moreover, you may add general SBR latex, NBR latex, an acrylic emulsion, a styrene-acryl emulsion, EVA emulsion, and EVA acrylic emulsion in the range by which a physical property does not fall as needed.

  Moreover, there is no restriction | limiting in particular about the application | coating method in the case of using the adhesive composition of this invention, or an adhesion | attachment method, If it is what has been performed conventionally, it can carry out by what kind of method. For example, it can be used in a pressing method in which an adhesive composition is applied to an adhesive surface of wood or the like by brush coating, and the adhesive surface is bonded and fixed by applying pressure. In addition, the adhesive composition of the present invention can be dried by any of the heat pressing method and the room temperature pressing method to obtain sufficient adhesive strength.

  The adhesive composition of the present invention can provide excellent durability, water resistance and hot water adhesion, little increase in viscosity after addition of a compound having an isocyanate group, almost no foaming, and Workability has been improved by significantly extending the pot life. That is, the adhesive composition of the present invention has extremely great advantages and features as already described. In particular, it has a long pot life, can be cured at room temperature as well as heat-cured, has excellent strength and workability, does not contain formaldehyde, and can bond hardwood and softwood Therefore, it is useful as a wood adhesive for a wide range of applications such as laminated wood, plywood, decorative plywood, and fiber board.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these examples. In the examples and comparative examples, “parts” and “%” are based on weight unless otherwise specified.

Example 1
(A) Synthesis of synthetic resin emulsion A 1 liter separable flask equipped with a stirrer, thermometer, reflux condenser, and dropping funnel was charged with 250 parts of a 20% aqueous solution of gum arabic and 200 parts of ion-exchanged water, and nitrogen gas was sent. While entering, the temperature inside the reaction vessel was raised to 80 ° C. Thereafter, a monomer mixed solution of 225 parts of methyl methacrylate and 225 parts of butyl acrylate was dropped over 4 hours. Further, ion exchange water was added to 2 parts of ammonium persulfate, and an aqueous solution with a total amount of 50 g was added dropwise at the same time as the monomer mixture to perform emulsion polymerization. At this time, the external temperature was controlled so that the internal temperature of the flask was 80 to 85 ° C. After completion of dropping, the mixture was held at 80 to 85 ° C. for 1 hour, and then cooled to 30 ° C. or lower to obtain an emulsion. The obtained aqueous emulsion had a non-volatile content (dried at 105 ° C. for 1 hour) of 49.5% and a viscosity (BH viscometer, No. rotor, 10 rpm, 23 ° C.) of 9,000 mPa · s. The glass transition temperature (Tg) was 26 ° C.

  A blended emulsion is prepared by mixing a solid content of 100 parts of the synthetic resin emulsion obtained above with a 15% aqueous solution of polyvinyl alcohol PVA117 (manufactured by Kuraray, completely saponified) so that the solid content is 100 parts. A mixture obtained by adding 60 parts of calcium carbonate to 100 parts was used as a main agent. 10 parts of a compound having an isocyanate group, Millionate MR-100 (manufactured by Nippon Polyurethane, polymethylene polyphenyl isocyanate) was added to 100 parts of the main agent, and mixed sufficiently to evaluate the performance as an adhesive composition of Example 1. .

Example 2
In the synthesis of the synthetic resin emulsion of Example 1, exactly the same as Example 1 except that a monomer mixed solution of 25 parts of 2-hydroxyethyl acrylate, 255 parts of methyl methacrylate and 170 parts of butyl acrylate was used. Synthesis was performed in the same manner to obtain a synthetic resin emulsion. The obtained (acrylic) synthetic resin emulsion had a non-volatile content (dried at 105 ° C. for 1 hour) of 49.5% and a viscosity (BH viscometer, No. rotor, 10 rpm, 23 ° C.) of 15,000 mPa · s. It was. The glass transition temperature (Tg) was 38 ° C.
Except for the use of the synthetic resin emulsion, everything was performed in accordance with Example 1, and performance evaluation was performed as the adhesive composition of Example 2.

Example 3
Except for mixing emulsion of 15% aqueous solution of polyvinyl alcohol PVA117 (manufactured by Kuraray, completely saponified) with a solid content of 30 parts with respect to 100 parts of the solid content of the synthetic resin emulsion of Example 1, All were performed according to Example 1, and performance evaluation was performed as an adhesive composition of Example 3.

Example 4
Except for blending emulsion by mixing 15% aqueous solution of polyvinyl alcohol PVA217 (manufactured by Kuraray, partially saponified) with a solid content of 100 parts with respect to 100 parts of the solid content of the synthetic resin emulsion of Example 1, It carried out based on Example 1 and performed performance evaluation as an adhesive composition of Example 4.

Comparative Example 1
Except that only the synthetic resin emulsion of Example 1 was used to obtain a blended emulsion, the performance was evaluated as an adhesive composition of Comparative Example 1 according to Example 1.

Comparative Example 2
Except for adding the calcium carbonate of Example 1 above to a blended emulsion, all were carried out according to Example 1, and performance evaluation was performed as an adhesive composition of Comparative Example 2.

Comparative Example 3
Except for adding the polyvinyl alcohol of Example 1 above to a blended emulsion, all were carried out in accordance with Example 1, and performance evaluation was performed as an adhesive composition of Comparative Example 3.

Comparative Example 4
In the synthesis of the synthetic resin emulsion of Example 1 above, the synthesis was performed using a 20% aqueous solution of polyvinyl alcohol PVA M-205 (manufactured by Kuraray, modified with mercapto group) instead of the 20% aqueous solution of gum arabic. 1 was synthesized in the same manner as in 1 to obtain a synthetic resin emulsion. The resulting synthetic resin emulsion had a solid content concentration (dried at 105 ° C. for 1 hour) of 49.2% and a viscosity (BH viscometer, No. rotor, 10 rpm, 23 ° C.) of 11,000 mPa · s. The glass transition temperature (Tg) was 26 ° C.
Except for the use of the synthetic resin emulsion, everything was carried out in accordance with Example 1, and performance evaluation was performed as an adhesive composition of Comparative Example 4.

Comparative Example 5
Performance evaluation was performed using the main agent of Example 1 as an adhesive composition of Comparative Example 5.

Block Compression Shear Test Test pieces were prepared using the adhesives obtained in Examples and Comparative Examples, and the adhesive performance was measured. The measurement method and measurement conditions are described below. The measurement results are shown in Table 1.
(1) Adhesion condition base material: birch plate, moisture content 11%
Application amount: 250 g / m ² (double-sided application)
Clamping: room temperature 10kg / cm ² -30 minutes.
(2) Test method Compressive shear test according to JIS K-6852 (3) Measurement method Normal adhesive strength: measured in a standard state under 20 ° C. and 65% RH Repeated boiling adhesive strength: after immersion in boiling water for 4 hours, 60 ° C. Dried for 20 hours, then immersed in boiling water for 4 hours, further immersed in water left at room temperature, cooled and measured

Adhesion test using plywood A softwood veneer was bonded using the adhesives obtained in Examples and Comparative Examples, and the tensile shear strength of the plywood was measured. The measurement method and measurement conditions are described below. The measurement results are shown in Table 2.
(1) Adhesive conditions Base material: Larch veneer (thickness 2/3/2/3 / 2mm cloth pasted 5ply), moisture content 8%
Application amount: 250 g / m ² (single-sided application)
Clamping: room temperature 8kg / cm ² -30 minutes.
(2) Test method Tensile shear test by JAS (3) Measurement method Normal adhesion strength: Measurement measured under standard conditions at 20 ° C. and 65% RH Steaming repeated test (JAS special): Immersion in water at room temperature for 2 hours or more Then, steam for 2 hours at 130 ° C, soak in flowing water for 1 hour at room temperature, further steam for 2 hours at 130 ° C, then soak in water left at room temperature, cool, and then measure wet

  According to the present invention, an adhesive composition that does not disperse formaldehyde, has high adhesive strength, excellent durability, water resistance and hot water resistance, and has a significantly improved workability due to a long pot life. Things are provided.

Claims (7)

(A) Synthetic resin emulsion using gum arabic as protective colloid, (B) polyvinyl alcohol, (C) inorganic pigment, and (D) an adhesive composition comprising a compound having two or more isocyanate groups in one molecule object. The adhesive composition according to claim 1, wherein the gum arabic as a protective colloid of the synthetic resin emulsion is in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the solid content of the synthetic resin emulsion.   The adhesive composition according to claim 1, wherein the synthetic resin emulsion has a glass transition temperature (Tg) of -10 ° C to 50 ° C.   The adhesive composition according to claim 1, wherein the solid content of (B) polyvinyl alcohol is 2 to 300 parts by weight with respect to 100 parts by weight of the solid content of the synthetic resin emulsion.   The adhesive composition according to claim 1, wherein (C) the inorganic pigment is in a proportion of 50 to 300 parts by weight with respect to 100 parts by weight of the solid content of the synthetic resin emulsion. (A) The ratio of the solid content of the compound having two or more isocyanate groups in one molecule is 2 to 100 parts by weight with respect to 100 parts by weight of the solid content of both the synthetic resin emulsion and (B) polyvinyl alcohol. The adhesive composition according to claim 1.   The adhesive composition for wood which consists of an adhesive composition of any one of Claim 1 thru | or 6.