JPH0321586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a plywood adhesive. Conventionally, urea-formalin resin, melamine-
Formalin resin is used in large quantities as an adhesive for plywood, but polyvinyl alcohol and starch are generally added as temporary adhesion improvers, and carboxymethyl cellulose is usually added as a thickener. In this case, in order to further improve the temporary adhesion, it is necessary to increase the amount of polyvinyl alcohol and starch, but it lacks stability and cannot be stored for a long time. Therefore, at present, polyvinyl alcohol and carboxymethyl cellulose are used in combination, with the blending ratio appropriately changed. With this, a large temporary bond cannot be expected, the formulation is complicated, and it cannot be a useful and inexpensive adhesive. In addition, in the case of starch, it is an inexpensive additive that has a certain degree of temporary adhesive strength and thickening effect, but because it has aging properties, which is a characteristic of starch, it lacks storage stability and seems to deteriorate temporary adhesiveness. be. Etherified starch eliminates the drawbacks caused by starch, but although its storage stability has been improved by eliminating starch aging, it requires a large amount for temporary adhesion and needs to be used in combination with polyvinyl alcohol. Therefore, it could not be an inexpensive adhesive with excellent temporary adhesion. In order to overcome the above-mentioned drawbacks, the present inventors conducted extensive research in search of a thickening stabilizer with high temporary adhesion, and discovered that a certain type of graft-modified starch is suitable for such uses. The invention was completed. In other words, when producing urea or melamine and formaldehyde resin according to the conventional method, if a stable graft-modified starch is added, it will have good storage stability and fluidity for workability, and will have a temporary stability during cold pressing. It has excellent adhesion, does not form a gel when heated, has a favorable affinity for wood, provides excellent water resistance upon heat curing, and can be used as an inexpensive plywood adhesive. Furthermore, the resin solution using this graft-modified starch had excellent effects. That is, since the graft-modified starch has an aggregating effect, adding a small amount of water produces water-insoluble flocculated precipitated starch. Therefore, when mechanically cleaning the coating roller, etc., adding a small amount of water to the remaining resin liquid creates a cloudy precipitate, which can be easily separated from the liquid, so the precipitate can be reused by adding it to new resin liquid. At the same time, the liquid can also be used again as a cleaning liquid. In this way, the amount of industrial wastewater is extremely reduced or almost eliminated, and since the precipitate can be recovered and reused, costs can be further reduced and it is also advantageous in terms of pollution control. Therefore, the object of the present invention is to produce various advantages obtained by co-condensing urea and/or melamine with formaldehyde, or by adding graft-modified starch after co-condensation. The material to be co-condensed to produce the resin liquid may be urea and formaldehyde, melamine and formaldehyde, or urea, melamine and formaldehyde, and the co-condensation is carried out in an appropriate molar ratio according to a known method. Heat to 90°C to conduct addition and condensation reactions. The starch that becomes the backbone polymer of the graft-modified starch to be used for this purpose includes natural starches such as potato starch, sweet potato starch, wheat starch, corn starch, waxy corn starch, rice starch, tapioca starch, and sago starch, and their decomposition products. , amylose and amylopectin fractions, cross-linked starch, etherified starch, esterified starch, oxidized starch, dextrin, modified starch such as acid-treated starch, and starch-containing substances such as wheat flour, corn flour, dried sweet potato, and dried tapioca. . As the water-soluble monomer forming the graft side chain, a monoethylenic monomer having at least one hydrophilic group can be used. Examples of such monomers include the following. (1) Monoethylenic mono- or polycarboxylic acids such as acrylic acid, methacrylic acid (hereinafter, acrylic and methacrylic are collectively referred to as (meth)acrylic), maleic acid, and fumaric acid. (2) Carboxylic acid anhydrides such as maleic anhydride. (3) alkali metal salts, ammonium salts of monoethylenically unsaturated mono- or polycarboxylic acids, such as sodium (meth)acrylate, triethanolamine (meth)acrylate, sodium maleate, methylamine maleate; Water-soluble salts such as amine salts. (4) Vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid,
aliphatic or aromatic vinyl sulfonic acids such as (meth), acrylsulfonic acids (for example, sulfopropyl (meth)acrylate, 2-hydroxy-3-(meth)acryloxypropylsulfonic acid, etc.); (5) Water-soluble salts such as alkali metal salts, ammonium salts, and amine salts of the aliphatic or aromatic vinyl sulfonic acids. (6) Monoethylenically unsaturated alcohols such as allyl alcohol and meta-allyl alcohol (hereinafter allyl and meta-allyl groups are collectively referred to as (meth)allyl). (7) Hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, polyethylene glycol (meth)acrylate (e.g., triethylene glycol (meth)acrylate), polyoxyethyleneoxypropylene glycol mono(meth)allyl ether (random monoethylenically unsaturated esters or ethers of polyols (e.g. alkylene glycols, glycerin, polyoxyalkylene glycols, etc.), which may be blocked and the terminal hydroxy groups may be etherified or esterified. (8) (meth)acrylamide, N-alkyl (meth)acrylamide (e.g., N-methylacrylamide, N-hexylacrylamide),
N,N-dialkyl(meth)acrylamide (e.g. N,N-dimethylacrylamide,
N, N-di-n-propylacrylamide,
N, N-diisopropylacrylamide), N
-Hydroxyalkyl (meth)acrylamide (e.g. N-methylol (meth)acrylamide, N-hydroxyethyl (meth)acrylamide), N,N-dihydroxyalkyl (meth)acrylamide (e.g. N,N-dihydroxyethyl ( amide group-containing monomers such as (meth)acrylamide), vinyl lactams (for example, N-vinylpyrrolidone, etc.). Monomers that become water-soluble through hydrolysis include:
Alkyl esters of monoethylenically unsaturated carboxylic acids such as methyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, vinyl acetate, acetic acid (meth)acrylate
Monomers having at least one ester group, a hydrolyzable group such as a nitrile group, such as esters of monoethylenically unsaturated alcohols such as allyl, and nitrile group-containing monomers such as (meth)acrylonitrile. One example is the body. In the graft modified starch used in the present invention,
The grafting rate can be selected as appropriate, but from the viewpoint of temporary adhesion effect, water-soluble monomers forming graft side chains and/or water-soluble monomers due to hydrolysis are It is preferable to graft-polymerize the monomers in a weight ratio of 0.5 to 100. The graft-modified starch is prepared by adding a conventional graft polymerization initiator such as ceric salt, persulfate, persulfate-sulfite, persulfate, etc. in an organic solvent such as methanol, acetone, or water or a mixed solvent thereof. 10 to 100 using hydrogen oxide or hydrogen peroxide-Mohr's salt according to a conventional method.
℃, preferably 15 to 75℃. The amount of graftable starch added is usually based on the resin.
It is within the range of 0.2 to 3.0% by weight, preferably 0.5 to 2.0% by weight. Next, specific embodiments of the present invention will be described with reference to Examples. Reference example 1 Uniformly suspend 100 parts of untreated potato starch in 150 parts of water, add 0.1 part of Mohr's salt and acrylic acid while stirring.
10 parts and 0.1 part of hydrogen peroxide solution (35% solution) were added one after another, and the reaction was carried out at room temperature for 4 hours. After completion, the mixture was washed with water and dried to obtain a powdered starch-polyacrylic acid graft copolymer. Example 1 120 g (2 moles) of urea and 37% formaldehyde
308 g (3.8 mol) was mixed with 2 g of the potato starch-polyacrylic acid graft copolymer obtained in the reference example, and after stirring, the pH was adjusted to 8.5, reacted at 90°C for 60 minutes, and the temperature was lowered to 70°C. Adjust the pH to 5.5 and carry out the reaction for 60 minutes. After completion, it was neutralized and cooled to 30°C. The viscosity of this resin was 90 cps. Example 2 In the same manner as in Example 1, 3 g of potato starch-polyacrylic acid graft copolymer was added and the same reaction was carried out. The viscosity of the resin liquid was 220 cps. Example 3 The product from which 2 g of potato starch-polyacrylic acid graft copolymer was removed in Example 1 was reacted, and after neutralization, 5 g of potato starch-polyacrylic acid graft copolymer of Reference Example was added and reacted for 30 minutes. Stir and cool to 30°C. The viscosity of the resin liquid was 290 cps. Comparative Example 1 In Example 1, untreated potato starch was used instead of 2 g of potato starch-polyacrylic acid graft copolymer.
4g was added and the same reaction was carried out. The viscosity at 30°C was 210 cps. Comparative Example 2 The same reaction as in Example 1 was carried out by adding 5 g of polyvinyl alcohol (manufactured by Nippon Gosei Co., Ltd., completely saponified, degree of polymerization 1700) instead of the potato starch-polyacrylic acid graft copolymer. The viscosity at 30°C was 50 cps. Comparative Example 3 The same reaction as in Example 1 was carried out except that 2 g of carboxymethyl cellulose (manufactured by Daicel Corporation) was added instead of the potato starch-polyacrylic acid graft copolymer. The following tests were conducted on the resin liquids obtained in the above Examples and Comparative Examples. (1) Storage test The viscosity changes over time of the resin liquids of Examples 1 to 3 and Comparative Examples 1 to 3 were measured at a storage temperature of 30° C. using a BN-type rotational viscometer (30 rpm), and the results are shown in FIG. (2) Thickening test The viscosity of the resin liquid was measured at 30° C. using a BM type rotational viscometer (30 rpm) when the amount of additives added was varied in Example 1 and Comparative Examples 1, 2, and 3. The results are shown in FIG. Examples 1 to 3 Resin liquids obtained in Comparative Examples 1 to 3
100g, flour 20g, water 13g, ammonium chloride 1g
A glue material for plywood was prepared and the following tests were conducted. (A) Temporary adhesive strength test 300 x 300 x 2 mm red lauan material (water content 8-10%)
Apply 14g of the above glue evenly on one side and apply it on both sides.
300 x 300 x 1 mm pieces of red lauan wood were aligned perpendicular to the wood grain at 10 kg/cm ² and pressed at 30°C for 5 minutes, then tested using a tensile tester to measure adhesive strength. (B) Normal adhesion test and wood breakage rate Normal adhesion was determined using the plywood standard test method for ordinary plywood stipulated by JAS, using 0.7 x 1.5 x 0.7 mm lauan material in a three-layer board configuration, and applying 260g/g of the above glue material. m ² and apply this at 10Kg/cm ² , cold pressure at 30℃ for 15 minutes, 8
Kg/cm ² , heat-pressed at 120°C for 60 seconds, and its adhesive strength is measured. The xylem breakage rate is shown in parentheses in Table 1, which represents the percentage of parts of the adhesion layer where the coated surface cannot be peeled off and the xylem is destroyed. (C) Adhesion test and wood breakage rate after immersion in cold water After immersing the lauan material in hot and cold water, the adhesion strength is tested under the same conditions as the normal adhesion test. The method of expressing the wood breakage rate is the same as that for the normal adhesion test. (D) Insoluble white precipitate test by dilution with water Take 10 ml of sample resin solution in a 1000 ml measuring cylinder, add a small amount of water, read the number of ml at the point where a cloudy coagulated precipitate starts to form, and The value obtained by dividing the number of ml by 10 ml is the double amount of water. Use distilled water at a temperature of 25°C. The results of Examples 1 to 3 and Comparative Examples 1 to 3 are first displayed. (E) BOD test of waste liquid The value of the liquid obtained in the above test (D) from which the white precipitate had been removed was measured by a conventional BOD measurement method. The results are shown in Table 1. The test results for A-E above are shown in Table 1. 【table】

[Brief explanation of the drawing]

The drawings show test results regarding various properties of resin liquids obtained by the method of the present invention and the conventional method.
is a graph showing the results of the storage test, and FIG. 2 is a graph showing the results of the thickening test.

Claims (1)

[Claims] 1. Production of a plywood adhesive characterized by adding graft-modified starch of an anionic or nonionic polymer during or after co-condensation of urea and/or melamine with formaldehyde. Method. 2 The graft-modified starch contains 100 parts by weight of the raw material starch and/or modified starch that will become the backbone polymer,
The water-soluble monomer that forms the graft side chain and/or the monomer that becomes water-soluble upon hydrolysis is 0.5
1. The method for producing a plywood adhesive according to item 1 above, wherein graft-modified starch obtained by graft polymerization and, if necessary, hydrolysis, is added in an amount of 100 parts by weight. 3 The monomer is acrylic acid, methacrylic acid, sodium acrylate, sodium methacrylate,
One or more monomers selected from the group consisting of acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, polyethylene glycol methacrylate (the terminal hydroxy group may be etherified or esterified), and vinyl acetate The method for producing a plywood adhesive according to items 1 and 2 above, in which a graft-modified starch is added.