JPS5952916B2 - Odorless plywood adhesive - Google Patents

Description

Detailed Description of the Invention The present invention provides an odorless plywood adhesive characterized in that glyoxal is used as a curing agent in a water-soluble resorcinol resin alone, a resin emulsion, and/or a mixture with a water-soluble polymer compound. It is related to.

Conventionally, water-soluble urea resins, melamine resins, and phenolic resins have been widely used as adhesives for plywood.

However, these resins contain free formaldehyde, and in the case of phenolic resins, paraformaldehyde or formalin may be added to speed up curing, resulting in a strong formaldehyde odor during use.
In addition, free formaldehyde remains in the product plywood, and formaldehyde is generated by hydrolysis of the resin, so formaldehyde gas is released from the product plywood. For this reason, when used for interior materials, cupboards, furniture, etc., formaldehyde odor becomes a problem. Formaldehyde is highly irritating and poses a major hygiene problem. An object of the present invention is to provide an odorless plywood adhesive with good workability, which releases extremely little formaldehyde from product plywood.

Odorless plywood adhesives are mainly made of amino resins such as water-soluble urea resins, melamine resins, and co-condensed resins of these resins, and formaldehyde scavengers such as urea, melamine, resorcinol, hydrogen peroxide, sodium sulfite, and various amines. (Japanese Patent Publication No. 53-28482), so-called low molar ratio resins in which the amount of formaldehyde to amino groups during amino resin reaction is reduced, and water-soluble phenol resins are used. . Regulation values for formaldehyde released from plywood include industry voluntary standards: IPPM or less for odorless plywood, and 5PIM or less for quasi-odorless plywood (desiccator method).

The amount of formaldehyde emitted from plywood is greatly influenced by factors that are difficult to control in plywood manufacturing, such as veneer resin, so it is not easy to completely maintain the odorless regulation value IPIM or less. When a formaldehyde scavenger is added to an amino resin or when plywood is manufactured using a low molar ratio resin, the crosslinking density after curing decreases, resulting in a decrease in adhesive strength, and there is a limit to suppressing the amount of formaldehyde released. .

For example, Table 1 shows the case where urea is added to a commercially available urea resin adhesive to make it odorless during use, and when the amount of formaldehyde released is O, 6 PIM, the adhesive strength is less than the JAS Class 2 standard value of 7 kg/cm2. Not practical. On the other hand, in the case of water-soluble phenolic resin, the formaldehyde test conditions for phenol were used for odorless plywood. Flour and water were added to a commercially available urea resin adhesive to increase the resin concentration to 36%, and the specified amount of urea and 0.5% ammonium chloride adhesive were added as a hardening agent.

Odor during use: Measured using a Kitagawa test tube at a position 10 cm above the center of the Spretsuda.

Initial adhesion force: Lilawan veneer 0.9m/m (surface), 1.8
m/m (two pieces of core 1 are overlapped with the fiber directions perpendicular to each other.

Veneer moisture content 8-10%, coating amount 240g/m, cold pressure 10
kg/CmI. After 15 minutes, a peeling test is performed.

Plywood creation conditions: Single board composition lauan 0.9x1.8x0.9
m/m (water content 8-10%), coating amount 260g/M2,
Cold pressure 10kg/CIll2, 15 minutes, hot pressure 120℃, 1
0kg/CIn290 seconds.

Amount of formaldehyde released: Put 10 sheets of plywood with a size of 5 x 15 cm into a desiccator with a capacity of 131 containing 300 ml of absorbed water, and after leaving it at 20°C for 24 hours, measure the amount of formaldehyde contained in the absorbed water using the acetylacetone method. , colorimetrically.

By using a resin reacted with a low molar ratio of , it is possible to produce plywood that has both formaldehyde release and adhesive strength.
In addition to increasing the heat-pressing temperature (over 130°C) and lengthening the heat-pressing time, it is necessary to use veneer with a moisture content of 5% or less, which reduces productivity and causes warpage in the product plywood. This will cause a problem during the next processing.

The present inventors have developed a water-soluble resorcinol resin, a water-soluble resorcinol resin and a resin-modified multilayer resin, and/or By using glyoxal as a curing agent in a mixture with a water-soluble polymer compound, it releases extremely little formaldehyde (0.5 PI), which can be used under the conditions of use of amino resins.
It has been discovered that an odorless adhesive for plywood can be obtained. Water-soluble resorcinol resin is usually used as a woodworking adhesive using paraformaldehyde or formaldehyde as a hardening agent, and is mainly used for cold pressure bonding.

The present inventors have discovered that by using glyoxal as a curing agent, a water-soluble resorcinol resin can be used as a thermopressure adhesive for plywood, and the amount of formaldehyde released from product plywood can be suppressed to an extremely low level.

In addition, when glyoxal is used, the pot life is longer than when paraformaldehyde is used as a hardening agent, and the pot life problem, which has traditionally been considered a drawback of water-soluble resorcinol resins, can be solved. Ta. Table 2 shows the cases in which paraformaldehyde and glyoxal were used as a curing agent in water-soluble resorcinol resin, ethylene-sac copolymer emulsion (EVA) as a resin emulsion, and polyvinyl alcohol (PVA) as a water-soluble polymer. The characteristics of the adhesive for plywood according to the present invention when used are compared.

When paraformaldehyde is used, the pot life is short and the amount of formaldehyde released is large, but when glyoxal is used, the pot life is extended and the amount of formaldehyde released is extremely small. When using a mixture of EVA emulsion or PVA aqueous solution, it is inevitable that the boiling resistance will be lower than when using resorcinol resin alone, but by changing the formulation, resorcinol resin and EVA emulsion or PVA aqueous solution By adjusting the blending ratio, adhesives of various grades from Class 2 to Special class can be obtained. For interior plywood applications where formaldehyde odor is the most problematic, a ratio of resorcinol resin to EVA emulsion of 5:100 is sufficient. Test conditions: Same as Table 1 *1. ．． : PR-150 manufactured by Sumitomo Durez *2. ．． : Manufactured by Sumitomo Chemical Co., Ltd. Sumikaflex #400*3. ．． : K-17, manufactured by Denki Kagaku Co., Ltd., 10% aqueous solution () Wood breakage percentage% The water-soluble resorcinol resin referred to here includes resorcinol, tannins, and polyhydric phenols such as high-value phenols produced by dry distillation of oil shale. , or phenol,
A condensate or co-condensate of one or more phenols such as cresol and xylenol with formaldehyde can be used.

It is also possible to modify a part of the phenols by replacing them with an amino compound such as eria, melamine, etc., but in this case, the adhesive strength, especially the water resistance, decreases and the amount of formaldehyde released increases. The resin emulsion to be mixed with the water-soluble resorcinol resin may be one or two of vinyl acetate, acrylic ester, meta-acrylic ester, ethylene, vinyl chloride, styrene, butadiene, acrylonitrile, taloloprene, isoprene, vinylidene chloride, etc. An emulsion of a copolymer consisting of the above copolymerizable monomers (e.g., polyvinyl acetate emulsion,
Ethylene-vinyl acetate copolymer emulsion, styrene-
Butadiene copolymer latex, vinyl acetate-methyl methacrylate copolymer emulsion) or natural rubber latex can be used.

On the other hand, water-soluble polymers include PVA, polyethylene oxide, CMC, sodium alginate, proteins, natural gums, starches, and one type of styrene, isobutene, isobutylene, atarylonitrile, acrylic ester, and methacrylic ester. A copolymer of the above monomer and one or more monomers selected from maleic anhydride, acrylamide, acrylonitrile, acrylic ester, and methacrylic ester can be used. For emulsions and water-soluble polymers that have poor miscibility with resorcinol resin, better results can be obtained by adjusting the pH to 7.0 or higher using an alkaline substance such as caustic soda or amine before mixing. It will be done. The adhesive of the present invention can be used with powder extenders such as grain powders such as wheat flour, barley flour, rice flour, and soybean flour, wood and fruit grain powders such as wood flour and walnut flour, and inorganic powders such as clay, talc, and calcium carbonate. It can be increased in volume with water and used in the same way as conventional plywood adhesives.

It goes without saying that when used as a plywood adhesive, the amount of formaldehyde released is extremely small, but it also has the characteristic of good adhesion to difficult-to-adhesive trees with a lot of poison, which have recently become a problem. The adhesive according to the present invention can also be used for bonding wooden products by hot pressing, such as laminated wood and particle board other than plywood.

Examples will be described below.

Example 1 To 100 parts of a commercially available water-soluble resorcinol resin adhesive (Sumilight Resin PR-200 manufactured by Sumitomo Durez), 20 parts of walnut powder was added as an extender, and 1 part of glyoxal was added as a hardening agent.
7 parts were mixed to obtain a plywood adhesive formulation, and plywood was prepared under the test conditions shown in Table 1 to obtain special plywood with a low amount of formaldehyde released.

Example 2 To 20 parts of the resorcinol resin adhesive used in Example 1,
Commercially available SBR latex whose pH was adjusted to 8.0 with triethanolamine in advance (4) LX-4 manufactured by Zeon Corporation
30) After mixing 100 parts, add 2 parts of walnut powder as a bulking agent.
0 parts and 4 parts of glyoxal as a hardening agent were added and stirred to obtain an adhesive composition for plywood, and plywood was prepared under the test conditions in Table 1 to obtain Type 1 plywood with a small amount of formaldehyde released.

Example 3 Commercially available water-soluble resorcinol resin adhesive (Table 2 *l)
Adjust the pH of 10 parts to 8.0 with triethanolamine in advance.
EVA emulsion adjusted to 0 (Table 2 *2)) 10
After mixing 0 parts, 30 parts of wheat flour as a bulking agent, 3 parts of glyoxal as a hardening agent, and 80 parts of water were added and stirred to obtain a plywood adhesive formulation, and plywood was made under the test conditions in Table 1. A Type 2 plywood with a small amount of formaldehyde released was obtained.

Example 4 Commercially available water-soluble resorcinol resin adhesive (Table 2 *1))
50 parts, adjust the pH to 8 with triethanolamine in advance.
．． Commercially available vinyl acetate resin emulsion (Sumito Bakelite Co., Ltd., Sumitaku VA-245-05) adjusted to 0
After mixing 0 parts, 15 parts of wheat flour and 8 parts of walnut flour as a bulking agent, 9 parts of glyoxal as a hardening agent, and 50 parts of water.
A plywood adhesive composition was obtained, and plywood was prepared under the test conditions shown in Table 1 to obtain special plywood with a small amount of formaldehyde released.

Example 5 100 parts of the resorcinol resin adhesive used in Example 1 was mixed with 20 parts of a styrene-maleic acid copolymer aqueous solution (Sumilettes Resin KL-1137 manufactured by Sumitomo Chemical Co., Ltd.), and then 10 parts of walnut powder was added as an extender. 1 part and calcium carbonate powder
0 parts and 20 parts of glyoxal as a hardening agent were added and stirred to obtain an adhesive composition for plywood, and plywood was prepared under the test conditions in Table 1 to obtain special plywood with a small amount of formaldehyde released.

Example 6 To 30 parts of the resorcinol resin adhesive used in Example 1,
Adjust the pH to 8 with caustic soda in advance. Commercially available SB adjusted to O
10 parts of R-latex (same as Example 2), 80 parts of commercially available vinyl acetate resin emulsion (same as Example 4), and
20 parts of PVA aqueous solution (same as in Table 2), 40 parts of wheat flour as a bulking agent, 6 parts of glyoxal and 60 parts of water as a hardening agent.
% and stirred to obtain a plywood adhesive formulation.
Plywood was prepared under the table test conditions, and a Type 2 plywood with a small amount of formaldehyde released was obtained.

Claims (1)

[Claims] 1. An odorless plywood adhesive characterized by using glyoxal as a curing agent in a water-soluble resorcinol resin. 2. An odorless plywood adhesive characterized in that glyoxal is used as a curing agent in a mixture of a water-soluble resorcinol resin, a resin emulsion, and/or a water-soluble polymer compound.