JPH0867864A - Adhesive for sliced veneer - Google Patents

Abstract

PURPOSE: To obtain an adhesive for sliced veneer capable of preventing oozing contamination of adhesive to the surface of sliced veneer after bonding even if it is applied even to extremely thin sliced veneer and suppressing crack of the surface of sliced veneer after long-period passage. CONSTITUTION: The first adhesive for sliced veneer contains either one or both of an aqueous solution and an aqueous dispersion containing a polymer compound having an acetoacetyl group in the molecule and an amino based resin liquid and urea in an amount of 5-70wt.% based on the amino-based resin liquid. The second adhesive for sliced veneer contains further either one or both of a polyol compound having two or more hydroxyl groups in one molecule and its derivative in addition to the composition of the first adhesive for sliced veneer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive for a thin wood board having a grain pattern of natural wood. For more details, plywood, plywood, hardboard, MDF (Medium Density Fib)
er Board), a particle board, and the like, the present invention relates to a one-liquid coating type adhesive for a luck board. In the present specification, the term "wood board" refers to a natural wood-grained veneer obtained by thinly cutting a natural wood such as Japanese cypress, oak, beech, etc. into a thin slice of about 0.1 to 10 mm.

[0002]

2. Description of the Related Art As an ordinary wood adhesive, a wood adhesive made of a vinyl acetate polymer emulsion containing polyvinyl alcohol having an acetoacetate group (Japanese Patent Publication No. 59-43069) and an acetoacetyl group in the molecule. An aqueous solution and / or an aqueous emulsion of a polymer compound having the above is used as a first liquid, and an aqueous solution of an aldehyde compound is used as a second liquid. 202176) has been proposed. The former adhesive is characterized in that it cures at room temperature within a short time after being applied. In particular, when a curing agent such as a dimethylol compound of formaldehyde, a dimethylol compound of urea, a dimethylol compound of melamine is contained, the methylol group of the dimethylol compound promotes gelation, and is characterized in that it is cured in a shorter time. Also, the latter adhesive is the first liquid and the second
When mixed with a liquid, it is characterized by rapidly causing a gelling reaction at room temperature to cure. For this reason, there is a problem that it is not suitable as an adhesive for a wood board, which requires the wood board to be adhered after applying the adhesive thinly and uniformly.

For this reason, as a conventional adhesive for a wood board,
Generally, an adhesive is used in which a urea resin and a vinyl acetate resin emulsion are mixed and a small amount of a filler such as wheat flour is further mixed. However, when a glue board with a large number of pores such as conduit holes is hot-press bonded to the base board using this glue for glue board, the adhesive exudes to the surface of the glue board and contaminates the surface. There was a problem that coating unevenness occurs when the surface is further coated. In addition, after a long time has passed, natural wood decorative plywood, etc. with a wood board attached will have insufficient dimensional stability of the woody part of the adhesive surface between the wood board and the base board, which will cause cracks on the wood board surface, resulting in a beautiful appearance. The problem that spoils For this reason, the adhesive for the wood board is applied to the surface of the base board, then the wood boards are stacked, then left for a long time, and when the water content of the adhesive has dried to a certain degree, hot press bonding is performed to exude the adhesive. Measures have been taken to prevent pollution.

Further, since the above-mentioned adhesive for a wood board cannot sufficiently suppress cracks on the surface of the wood board, another adhesive for a wood board is used as another adhesive for wood board, which is carboxylated styrene-butadiene rubber, methacrylic acid-butadiene. An adhesive is used in which a synthetic rubber latex such as rubber is mixed with a melamine resin, and a large amount of a filler such as wheat flour is further mixed. According to this adhesive for wood board, the synthetic rubber latex improves the water resistant adhesive performance, prevents the exudation of the adhesive to the surface of the wood board and prevents contamination, and also reduces cracks on the surface of the base board to which the wood board is attached. You can

[0005]

In recent years, there has been a tendency to thin the wood board in order to suppress the manufacturing cost of the natural wood decorative plywood laminated with the wood board. Therefore, if the wood board is made very thin for this reason, the above-mentioned conventional wood board is used. The board adhesive has a problem that it is not possible to sufficiently prevent the exudation of the adhesive and the cracks on the surface of the wood board in the natural wood decorative plywood. An object of the present invention is to provide an adhesive for a wood board, which prevents the adhesive from seeping out and contaminating the surface of the wood board after adhesion even when used for a very thin wood board. Another object of the present invention is to provide an adhesive for a wood board, which suppresses cracks on the surface of the wood board after a long period of time has been adhered to a very thin wood board.

[0006]

In order to achieve the above object, the adhesive for the first woodpluck board of the present invention is either an aqueous solution or an aqueous emulsion containing a polymer compound having an acetoacetyl group in the molecule. One or both (hereinafter referred to as an aqueous solution of a polymer compound having an acetoacetyl group)
And the amino resin solution, and 5 for this amino resin solution
And 70% by weight of urea. In addition to the composition of the adhesive for the first wood board, the second adhesive for the wood board of the present invention is one or both of a polyol compound having two or more hydroxyl groups in one molecule and a derivative thereof (hereinafter , A polyol compound, etc.) are further included.

The present invention will be described in detail below. (a) Aqueous solution of polymer compound having acetoacetyl group, etc.As an aqueous solution containing a polymer compound having an acetoacetyl group in the molecule used in the method of the present invention,
Examples thereof include acetoacetylated polyvinyl alcohol obtained by reacting polyvinyl alcohol and diketene by a known method, a derivative thereof, an aqueous solution of a water-soluble polymer such as acetoacetylated hydroxyalkyl cellulose, and acetoacetylated starch. In addition, the aqueous emulsion containing a polymer compound having an acetoacetyl group in the molecule,
It can be prepared by emulsion-polymerizing a monomer containing an acetoacetyl group and α, β ethylenic monomers and the like. Examples of monomers containing an acetoacetyl group include allyl acetoacetate, vinyl acetoacetate, 2-acetoacetoxyethyl acrylate, 2-acetoacetoxyethyl methacrylate, 2-acetoacetoxypropyl acrylate, and 2-acetoacetoxypropyl methacrylate. Is mentioned. Examples of α and β ethylenic monomers are vinyl acetate, vinyl ester of saturated fatty acid branched at α position, methyl acrylate,
Acrylates or methacrylates such as methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, nonyl acrylate and nonyl methacrylate, and monovinyl polymers such as styrene, ethylene and vinyl chloride. . The aqueous solution and the aqueous emulsion of the polymer compound having an acetoacetyl group in the molecule may be used alone, or two or more kinds may be mixed and used.

(B) Amino Resin Solution The amino resin solution used in the present invention is a solution containing a melamine resin, a solution containing a cocondensate of melamine and urea, a solution containing a urea resin, or a solution containing these. It is preferably a mixture of the solutions of The amino-based resin liquid is prepared by reacting a compound containing an amino group with formaldehyde at a pH of 10 or higher in the presence of alcohols such as methanol and ethanol, or using an acidic catalyst in the presence of alcohols. What is obtained by reacting at pH 4 or less is preferable because the viscosity of the mixed solution becomes more stable when mixed with an aqueous solution of the above-mentioned polymer compound having an acetoacetyl group. This amino resin solution may be prepared by reacting melamine or urea with formaldehyde, or by reacting both melamine and urea with formaldehyde. In addition to melamine and urea, acetoguanamine, benzoguanamine, thiourea, phenol,
The amino resin solution of the present invention may be prepared by reacting resorcinol, furfuryl alcohol and the like with formaldehyde. The concentration of the amino resin solution is 30 to 7
0% by weight is preferred. The amino resin solution preferably contains free formaldehyde in an amount of 0.8% by weight or less. This is because free formaldehyde becomes a methylol group that promotes gelation of the adhesive. The amino resin solution is preferably mixed in the range of 5 to 100% by weight with respect to 100% by weight of an aqueous solution of a polymer compound having an acetoacetyl group. If the amount of the amino resin solution is less than 5% by weight, the water resistance is poor, and if it exceeds 100% by weight, the amount of exudation may increase.

(C) Urea In the present invention, urea is used in an amount of 5 to 7 relative to the amino resin solution.
0% by weight, preferably 5 to 50% by weight is added and mixed.
As a result, it becomes possible to remarkably improve the viscosity characteristics of the mixed liquid, and after mixing, an adhesive for a wood board that maintains good fluidity for 3 hours or more at room temperature is produced. When the amount of urea added to the amino resin solution is less than 5% by weight, the viscosity stability of the mixed solution is poor and uniform application is difficult. When the amount of urea is more than 70% by weight, the urea is not completely dissolved, and when the wood plate is directly adhered to the base plate as it is, residual urea may be decomposed and the wood plate may be discolored. This urea may be mixed in advance with the amino resin solution when preparing the amino resin solution.

(D) Filler, filler, thickener or curing agent The viscosity of a mixed solution of the above-mentioned polymer compound having an acetoacetyl group, an amino resin solution and urea is applied by a roll spreader or the like. In order to adjust the viscosity so that it is easy to add, flour, barley flour, low temperature defatted soybean flour and other fillers or fillers such as calcium carbonate, clay, talc, wood flour and coconut shell powder may be added to the mixture as appropriate. . If necessary, an ammonium salt such as ammonium chloride, an inorganic acid such as hydrochloric acid or an organic acid such as sulfamic acid may be used as a curing agent, or polyvinyl alcohol, starch, carboxy methyl cellulose, sodium polyacrylate may be used as a thickening agent. You may add each. These fillers, fillers, thickeners and curing agents may be used in combination as required.

(E) Polyol compound etc. The polyol compound etc. used in the present invention is a compound having two or more hydroxyl groups in one molecule. Examples of this include compounds such as ethylene glycol, glycerin, tetramethylolmethane, propylene glycol, polyethylene glycol, polypropylene glycol, glucose, sugar-tight, sucrose (sugar) and sorbitol, or derivatives of these compounds. These polyol compounds may be used alone or in combination of two or more. Among the polyol compounds, particularly preferred is polyerylene glycol having a degree of polymerization of 200 to 4000, and polyethylene glycols having a degree of polymerization in the above range can be used alone or as a mixture. The total amount of the polyol compound and the like is an aqueous solution of a polymer compound having an acetoacetyl group and the amino resin solution 1
It is preferable to add 5 to 50% by weight to 00% by weight. If the amount of the polyol compound or the like is less than 5% by weight, the cracks on the surface of the wood veneer in the natural wood decorative plywood will be insufficiently suppressed, and if it exceeds 50% by weight, the water-resistant adhesive performance will be deteriorated. The polyol compound and the like may be added in advance to the aqueous solution of the polymer compound having an acetoacetyl group or the like, or the amino resin solution, or may be added when preparing them or the filler.

[0012]

In the conventional adhesive, when the amino resin solution is added to the aqueous solution of the polymer compound having an acetoacetyl group, the mixed solution gels in a short time. This gelation is due to the reaction of free formaldehyde and methylol groups contained in the amino resin solution with acetoacetyl groups.
In the present invention, urea was added together with the amino resin solution to an aqueous solution of a polymer compound having an acetoacetyl group, so that this urea suppresses free formaldehyde and takes precedence over the reaction between a methylol group and an acetoacetyl group. Thus, the urea reacts with the methylol group to prevent gelation during mixing and acts to maintain the fluidity of the mixed solution. Further, gelling can be further delayed by using an amino resin solution having a low content of free formaldehyde. The adhesive for wood board mixed in this way is
It retains fluidity for more than time and becomes a one-liquid coating type adhesive. When this adhesive is applied to the surface of the base plate, a gradual reaction proceeds and the resin liquid gradually becomes a polymer. After applying the adhesive of the present invention to the base plate and stacking the wood plates on top of each other, 60 to ¹ under pressure of ² to 12 kg / cm ² by the upper and lower press plates.
When pressed at 50 ° C. for 10 to 300 seconds, the gelling reaction is rapidly performed by the heating temperature, the flow of the adhesive is significantly reduced, and the exudation of the adhesive on the surface of the wood board can be prevented. Furthermore, by blending a polyol compound in the adhesive of the present invention and bonding them by hot pressing, the polyol compound penetrates into the wood part of the adhesive surface of the wood board and the base plate during hot pressing, and the polyol compound remaining in the adhesive layer is Further, it migrates to the inside with the passage of time and imparts dimensional stability to the wood part near the bonding surface between the wood board and the base plate. This makes it possible to suppress cracks on the surface of the wood board even after a long period of time.

[0013]

As described above, according to the first adhesive for wood board of the present invention, by mixing an aqueous solution of a polymer compound having an acetoacetyl group, an amino resin solution and urea, Allows one-liquid application, delays gelation at room temperature, and causes rapid gelation during hot pressing, so even if the skid plate is very thin, the adhesive will seep to the surface of the skid plate adhered to the base plate. Pollution can be completely suppressed. This rapid gelation shortens the hot pressing time and does not require the deposition of the base plate after the adhesive is applied unlike the conventional method, so that the time required for the bonding process is significantly shortened and the productivity is improved. . In addition, in the conventional adhesive, when a wood board is bonded with a polyol, the exudation of the adhesive to the surface of the wood board is further promoted, and the surface contamination results in a marked loss of the appearance of the natural wood decorative plywood. However, according to the second adhesive for a wood board of the present invention,
When a polyol compound or the like is further added to the adhesive for a wood board and hot pressing is performed, gelation is rapidly promoted, and therefore the adhesive does not exude and contaminate the surface of the wood board. Also, with conventional adhesives, cracks have been generated on the surface of the wood board over a long period of time, but these cracks can be suppressed by the original action of the polyol compound and the like. As a result,
By using the adhesive for a wood board of the present invention to bond a wood board to a base board, a natural wood decorative plywood excellent in appearance and performance can be obtained.

[0014]

【Example】

<Example 1> A 12 mm-thick South Sea plywood plywood was prepared as a base plate, and a checkerboard-like oak wood plaque having a thickness of 0.3 mm was prepared as a wood plate. In adhering the wood board to the base board, 50% by weight of granular urea was added to 100% by weight of a melamine-urea resin adhesive (manufactured by Oshika Shinko Co., Ltd., trade name: PWP
-513) dissolved in a resin solution obtained in an amount of 30 kg, a polyvinyl alcohol having an acetoacetyl group (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: Gocefimer-Z) 40% by weight aqueous solution and ethylene.・ Vinyl acetate copolymer resin emulsion (Kuraray Co., Ltd., trade name: OM-420)
0) 10 k of an aqueous emulsion mixed with 60% by weight
15 g of wheat flour (Marusho Flour Milling Co., Ltd., trade name: Maru A)
kg, water 5 kg and ammonium chloride powder 0.15 k
and g were put in a paste mixer and stirred to uniformly mix them to prepare an adhesive for a wood board. 120 g per 1 square meter of this glue for wood board on the surface of Nanyo Plywood which is the base plate
The surface is covered with a Japanese oak lumber board, which is then inserted into a hot press maintained at a press temperature of 110 ° C., and a pressure of 6 kg / cm ² is applied for 45 seconds to heat press the natural wood makeup. Plywood was made.

As a result of examining the surface of the wood board of the natural wood decorative plywood thus obtained, no bleeding-out stain of the adhesive was observed. In addition, after coating the surface of the extracted sample with urethane resin paint,
The first class immersion peeling test specified for AS natural wood decorative plywood was performed. As a result, peeling of the wood board was not observed at all, and excellent water-resistant adhesiveness that passed the standard was exhibited. At the same time, J
Cold heat repeated A test (80 ° C ± 3 ° C) specified in AS standard
After being left in the incubator for 2 hours, the operation of leaving it in the incubator at −20 ° C. ± 3 ° C. for 2 hours is repeated twice. ), Cracks were seen in a very small part of the coated surface of the wood board.

<Example 2> A melamine-urea resin adhesive (manufactured by Honen Corporation, trade name: ML-0) in which a part of the bound methylol group is methyl etherified.
48) The first liquid was prepared by dissolving 10% by weight of granular urea in 100% by weight. The second liquid was a vinyl acetate resin emulsion (manufactured by Hoechst Synthesis Co., Ltd., trade name: Movinyl AD-100H) obtained by emulsion polymerization using polyvinyl alcohol having an acetoacetyl group as a protective colloid. First liquid 3 kg
20 kg of the second liquid, 8 kg of flour, and 2 kg of water,
4 kg of polyethylene glycol (# 1000) was agitated with a size-making mixer and uniformly mixed to prepare an adhesive for wood board. The prepared adhesive for a wood board was applied to one side of the same base plate as in Example 1 at a rate of 120 g per square meter, and the same wood board as in Example 1 was overlaid.
Immediately, hot pressing was performed under the same conditions as in Example 1 to produce a natural wood decorative plywood.

As a result of examining the surface of the wood plywood of the natural wood decorative plywood thus obtained, no bleeding and contamination of the adhesive was observed. In addition, after coating the surface of the extracted sample with urethane resin paint,
The first class immersion peeling test specified for AS natural wood decorative plywood was performed. As a result, peeling of the wood board was not observed at all, and excellent water-resistant adhesiveness that passed the standard was exhibited. At the same time, J
When the cold heat repeated A test specified in the AS standard was conducted, no cracks were observed on the coated surface of the wood board.

<Comparative Example 1> Styrene-butadiene rubber latex having a carboxyl group (Asahi Kasei
Co., Ltd., trade name: L-1151) 20 kg, melamine-urea resin adhesive (Honen Corporation Co., Ltd., trade name: ML-048) 3 kg, and flour 8 kg.
And 2 kg of water were stirred with a paste mixer to uniformly mix them, to prepare an adhesive for wood board. The prepared adhesive for wood chips was applied on one side of the same base plate as in Example 1 at a rate of 120 g per square meter, and the same wood plates as in Example 1 were overlaid, and immediately the same as in Example 1. Hot pressing was performed under the conditions to produce a natural wood decorative plywood.

As a result of examining the surface of the wood plywood of the natural wood decorative plywood thus obtained, the adhesive was found to bleed to the surface of the wood plywood through the holes of the wood ply conduit. After coating the surface of the sample taken with urethane resin paint,
A first-class immersion peeling test, the adhesiveness of which was defined by JAS natural wood decorative plywood, was performed. As a result, although peeling of the wood board was observed in part, it showed water-resistant adhesiveness that passed the standard. Further, at the same time, when a cold heat repeated A test specified in the JAS standard was conducted, fine cracks were found on the entire coated surface of the wood board.

Claims (7)

[Claims] 1. An aqueous solution and / or an aqueous emulsion containing a polymer compound having an acetoacetyl group in the molecule, an amino resin solution, and 5 to 70% by weight based on the amino resin solution. Adhesive for wood board containing urea. 2. One or both of an aqueous solution and an aqueous emulsion containing a polymer compound having an acetoacetyl group in the molecule, an amino resin solution, and 5 to 70% by weight based on the amino resin solution. An adhesive for a wood board, which comprises the urea of 1) and one or both of a polyol compound having two or more hydroxyl groups in one molecule and a derivative thereof. 3. An amino resin solution containing a melamine resin, a solution containing a cocondensation product of melamine and urea,
The adhesive for wood board according to claim 1 or 2, which is a solution containing a urea resin or a mixture of these solutions. 4. The adhesive for wood board according to claim 1, wherein the amino resin solution contains 0.8% by weight or less of free formaldehyde. 5. An amino-based resin liquid is reacted with a compound containing an amino group and formaldehyde in the presence of alcohols using an alkaline catalyst at a pH of 10 or more,
The adhesive for wood board according to claim 3, which is a resin obtained by reacting at a pH of 4 or less using an acidic catalyst in the presence of alcohols. 6. The amino resin solution comprises 5 to 100% by weight based on 100% by weight of either or both of an aqueous solution and an aqueous emulsion containing a polymer compound having an acetoacetyl group in the molecule. 2. An adhesive for a wood board according to 2. 7. Two or more per molecule based on 100% by weight of the total amount of one or both of an aqueous solution and an aqueous emulsion containing a polymer compound having an acetoacetyl group in the molecule and an amino resin solution. Either or both of the polyol compound having a hydroxyl group and its derivative are 5
The adhesive for wood board according to claim 2, wherein the adhesive is contained in an amount of -50% by weight.