JPH0717881B2 - Adhesive for veneer makeup processing - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive for veneer decorative processing.
More particularly, it relates to an adhesive for veneer decorative plywood, which has excellent resistance to cracking on the surface of the veneer and does not cause bleeding and contamination of the adhesive on the surface of the veneer.

[Prior Art and Problems Thereof] In a decorative plywood in which a veneer such as a thin decorative veneer is pasted on the surface of a base plywood, the resulting veneer is considerably thin because the veneer is extremely thin. After several hours, the veneer surface may be cracked, and the adhesive may seep out to the veneer surface during bonding, which causes a practical problem.

As an adhesive for veneer decorative plywood, an adhesive prepared by blending an amino resin with a vinyl acetate resin or a (homo) vinyl acetate emulsion is provided (Japanese Patent Publication No. 56-39829).

However, the adhesive causes cracking of the veneer and exudation of the adhesive to the surface of the veneer.

As an adhesive with which these cracks and bleeding of the adhesive onto the surface of the veneer are particularly improved, Japanese Patent Publication No. 56-34196 discloses a butadiene or isoprene conjugated diene, a vinyl monomer copolymerizable therewith, an amino group and an N group. A mixture adhesive of a modified synthetic rubber latex obtained by copolymerizing a reactive monomer that reacts with a methylol group and an amino resin has been proposed.

However, even with this mixture adhesive of the modified synthetic rubber latex and the amino resin, the cracking of the veneer cannot be sufficiently prevented.

On the other hand, in Japanese Examined Patent Publication No. 40-22480 and Japanese Examined Patent Publication No. 47-28291, interposing a woven fabric, paper, etc. between the veneer and the base plate, amino resin and (homo) vinyl acetate resin or emulsion and flour, and modified A patent was found to adhere with a mixture of synthetic rubber latex, flour and amino resin to prevent cracking of the veneer, and the product is actually marketed,
Has an excellent reputation.

However, in the method for manufacturing a veneer decorative plywood in which a fabric or paper is interposed between the veneer and the base plywood, an adhesive is applied to the surface of the base plywood to bond the fabric and the paper, and then the fabric (paper) Since the adhesive is applied again to the top and the veneer and the woven fabric (paper) are adhered to the base plywood, the adhesive must be applied twice in the process, and the adhesion process becomes complicated. It is clear that the use of woven fabrics and papers leads to a significant cost increase. In addition, when trying to bond the veneer and the fabric and the paper and the base plate plywood at the same time, in order to obtain stable adhesiveness, the amount of adhesive applied is increased, so the phenomenon of the adhesive seeping out to the surface of the veneer Occurs, which causes a problem in practical use.

Therefore, in order to prevent the adhesive from seeping out and contaminating the veneer surface, apply amino resin and (homo) vinyl acetate resin or emulsion adhesive, and modified synthetic rubber latex and amino resin mixture adhesive to the base plate plywood. After that, heat and pressure should be applied when the adhesive is in a semi-dried state. Compared with the amino resin alone or the amino resin and (homo) vinyl acetate emulsion mixed adhesive, the modified synthetic rubber latex and amino resin mixed adhesive has less oozing out of the adhesive to the surface of the veneer, and cracking does not occur. Although it is small, it is still not fully satisfactory in practical use.

An object of the present invention is to provide an adhesive for veneer decorative processing, which solves the problems of the prior art, and the improvement of the cracking resistance of the veneer can be solved only by the adhesive without the interposition of fabric or paper. Furthermore, it is an object of the present invention to provide a material in which the exudation of the adhesive on the surface of the veneer plate can be practically satisfied without performing a working step such as intentionally semidrying the adhesive.

[Means for Solving Problems] The present invention relates to vinyl acetate, N-methylolacrylamide, acrylic acid, acrylic acid ester, methacrylic acid ester, crotonic acid, itaconic acid, maleic acid and / or fumaric acid (hereinafter, these Are also collectively referred to as acrylic acid)) and an adhesive for veneer decorative processing composed of a copolymer emulsion with an amino resin.

A preferable example of the emulsion used in the present invention, which is obtained by copolymerizing vinyl acetate, N-methylolacrylamide and acrylic acid, is 0.5 to 20% by weight of N-methylolacrylamide and 0.1 to 8% by weight of acrylic acid. The rest is of vinyl acetate composition.

Examples of acrylic acid ester in the acrylic acid to be copolymerized include acrylic acid methyl ester, acrylic acid ethyl ester, acrylic acid butyl ester, acrylic acid amino ester and the like. Examples of the methacrylic acid ester include methacrylic acid methyl ester, methacrylic acid ethyl ester, methacrylic acid propyl ester, methacrylic acid butyl ester, methacrylic acid amino ester and the like. Further, the acrylic acids of the present invention include itaconic acid, crotonic acid, maleic acid and fumaric acid. These acrylic acids can be used alone or in combination. A suitable amount of acrylic acid is 0.1 to 8% by weight. When the amount of acrylic acid is less than 0.1, the elasticity of the adhesive layer becomes poor, the cracks on the veneer often occur, and it is difficult to obtain the copolymer emulsion with good storage stability (separation and generation of coarse particles). . On the other hand, when the amount of acrylic acid is more than 8% by weight, the adhesive easily exudes to the surface of the veneer and is likely to cause contamination.

A suitable amount of N-methylol acrylamide is 0.5 to 20% by weight. If the amount of N-methylolacrylamide is less than 0.5% by weight, the water resistance and heat resistance of the adhesive will be poor, and if bonding is performed under heat pressure (80 to 120 ° C) during the manufacturing process of the processed product, puncture, It causes defects such as blister. On the other hand, when the N-methylolacrylamide content exceeds 20% by weight, the elasticity of the adhesive layer becomes poor and cracking easily occurs, which is not practically sufficient.

As the amino resin used in the present invention, a condensation resin of formaldehyde with one or more known amino compounds such as urea, melamine and guanamine and formaldehyde, or these resins with phenols, polyvinyl alcohol , Modified resins partially modified with furfuryl alcohol and the like, in which the molar ratio of the resins is formaldehyde / amino compound = 1.5 to 3.0 and solid content is 35 to 100.
A weight percent of resin is illustrated as a preferred example.

The mixing ratio of the emulsion obtained by copolymerizing N-methylolacrylamide and acrylic acid of butyl acetate of the present invention and the amino resin is N-methylolacrylamide-acrylic acid-vinyl acetate copolymer emulsion / amino resin in terms of solid content. = 100 parts / 1 to 200 parts by weight, but in practice, this ratio is preferably 100 parts / 10 to 100 parts by weight (solid content conversion). If this ratio is less than 100/1 parts by weight of the amino resin, the water resistance and heat resistance are poor, and when bonding at hot pressure (80 to 120 ° C.), adhesion failure due to puncture or blistering is likely to occur. On the other hand, when the ratio is more than 100/200 parts of amino resin, the prevention of bleeding contamination and cracking on the surface of the veneer, which is the object of the present invention, becomes insufficient.

In the adhesive of the present invention, conventional plywood production, a filler to be mixed in the adhesive for veneer production, substances as extenders such as wheat flour, starches, defatted soybean flour, blood meal, organic systems such as walnut shells, Acidic inorganic substances such as clay, kaolin, and zeolide can be used. Among them, wheat flour and starches are more preferable because they are less gelatinized in cold water and are gelatinized and become a viscous liquid by heating during bonding.

The mixing ratio of the filler and the extender is usually such that the viscosity becomes 50 to 500 poise / 25 ° C.

Further, an aqueous thickener such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene oxide and alginic acid can be added to the composition of the present invention.

Further, in the present invention, a known curing agent such as ammonium chloride used for curing an amino resin, hydrochloric acid such as acids, oxalic acid, paratoluenesulphonic acid, tartaric acid, or phthalic anhydride may be used together with the adhesive. Good.

The emulsion in which the vinyl acetate of the present invention is copolymerized with N-methylol acrylamide and acrylic acids (shown in the examples using acrylic acid) can be obtained, for example, by the following method.

Polyvinyl alcohol Pure water Vinyl acetate monomer Ammonia water A mixture of ammonium ferrous sulfate is heated in nitrogen. Next, a catalyst is added to start polymerization. The following monomer liquids are separately and simultaneously added to the liquid mixture continuously.

Monomer liquid 1 N-methylol acrylamide Pure water Monomer liquid 2 Vinyl acetate monomer Acrylic acid tert-Butyl hydroxyl oxide After completion of addition of monomer liquids 1 and 2, vinyl acetate and N-methylol acrylamide and acrylic acid were aged and cooled. An emulsion obtained by copolymerizing

[Examples] Example 1 An emulsion obtained by copolymerizing vinyl acetate, N-methylolacrylamide and acrylic acid (92.1% by weight of vinyl acetate, 6.9% by weight of N-methylolacrylamide, 1.0% by weight of acrylic acid, hereinafter referred to as AA-N-MAM. A composition was obtained by adding 20 parts by weight of urea-melamine copolymer resin (molar ratio: formaldehyde / urea-melamine = 2.2% solid content 52% by weight) to 100 parts by weight of (-VAC). 23 parts by weight of Constarch was added to 100 parts by weight of this composition and mixed to obtain an adhesive for veneer decorative plywood having a viscosity of 110 voise / 25 ° C.

Example 2 Urea-melamine copolymer resin (molar ratio: formaldehyde / urea-melamine = 100 parts by weight of AA-N-MAM-VAC)
2.2, solid content 52% by weight) 30 parts by weight was added and mixed to obtain a composition.

To 100 parts by weight of this composition, 18 parts by weight of wheat flour and 7 parts by weight of water were added and mixed to obtain an adhesive for veneer decorative processing having a viscosity of 200 poise / 25 ° C.

Example 3 Emulsion obtained by copolymerizing vinyl acetate, N-methylolacrylamide and acrylic acid ethyl ester (100% by weight of vinyl acetate 92.1% by weight, N-methylolacrylamide 6.9% by weight, acrylic acid ethyl ester 1.0% by weight) and urea- A composition was obtained in which 30 parts by weight of a melamine copolymer resin (molar ratio: formaldehyde / urea-melamine = 2.2, solid content 52% by weight) were added and mixed.

To 100 parts by weight of this composition, 18 parts by weight of wheat flour and 7 parts by weight of water were added and mixed to obtain an adhesive for veneer decorative plywood having a viscosity of 200 poise / 25 ° C.

Example 4 The following 4-1 to 4 were added to 100 parts by weight of AA-N-MAM-VAC.
A urea resin and a urea-melamine copolymer resin having a molar ratio shown in -4 were added and mixed in the amounts shown below to obtain a composition.

4-1 Formaldehyde / urea = 1.3 30 parts by weight 4-2 Formaldehyde / urea = 1.9 30 parts by weight 4-3 Formaldehyde / urea / melamine = 2.2 30 parts by weight 4-4 Formaldehyde / urea / melamine = 2.5 30 parts by weight Each of these 18 parts by weight of flour with respect to 100 parts by weight of the composition of,
7 parts by weight of water was added and mixed to obtain an adhesive for veneer decorative plywood having a viscosity of 200 poise / 25 ° C.

Comparative Example 1 Homovinyl acetate emulsion (solid content 45% by weight, viscosity 60
An adhesive composition was obtained by adding 30 parts by weight of urea resin (molar ratio: formaldehyde / urea = 1.9, solid content 73% by weight, viscosity 25 poise / 25 ° C.) to 100 parts by weight of 0 poise / 30 ° C.). .

To 100 parts by weight of this composition, 18 parts by weight of flour and 10 parts by weight of water were added and mixed to obtain an adhesive for a veneer decorative plywood having a viscosity of 200 poise / 25 ° C.

Comparative Example 2 Carboxy-modified styrene-butadiene synthetic rubber latex [solid content 50% by weight, manufactured by Nippon Synthetic Rubber Co., Ltd.] 100
Urea resin (molar ratio: formaldehyde / urea =
50 parts by weight (1.8, solid content 54% by weight) were added and mixed to obtain an adhesive composition.

To 100 parts by weight of this composition, 28 parts by weight of wheat flour and 15 parts by weight of water were added and mixed to obtain an adhesive for veneer decorative plywood having a viscosity of 200 poise / 25 ° C.

The adhesives for veneer decorative plywood obtained in the above-mentioned Examples and Comparative Examples were treated with a thickness of 0.7 m / m 5
Plylawan plywood (12m / m thickness) coating amount 90g / m ² and 150
After coating with g / m ² and laminating four layers of 0.2m / m thick oak, Japanese zelkova, Yonematsu, and Tamo on the lauan plywood, and after taking the deposition time as shown in the working conditions below. , Hot pressure condition 110 ℃, 7
Bonded at ~ 8 kg / cm ² for 60 seconds.

The degree of dry cracking of the bonded veneer decorative plywood was determined by the cold repeated B test of the Japanese agricultural standard of special plywood, the dry and wet repeated test and the high temperature repeated test.

Further, the adhesion of the bonded veneer decorative plywood was evaluated by a two-class immersion peeling 5 cycle test of ordinary plywood of Japanese agricultural and forestry standard.

Furthermore, the degree of contamination of the adhered veneer decorative plywood was observed with the naked eye.

The test results are shown in Tables 1 and 2.

1 Working conditions Base plate: 12 m / m thickness, front and back 0.7 m / m, 5 ply lawan plywood Veneer veneer: 0.2 m / m thickness, 40-60% water content, oak, zelkova, pine tree, taro coating amount: 90 g / m ² and 150g / m ² deposition: Open deposition time within 30 seconds / 20 ℃ Closed deposition time 1 minute and 10 minutes Heat pressure: 110 ℃, 7-8kg / cm ² , 60 seconds 2 Test method 2-1 Drying test Method a> Cold heat repetition B test Fix 15 cm parallel test pieces around with a metal frame and leave them in an incubator at 80 ± 3 ° C for 2 hours, and then in an incubator at −20 ± 3 ° C for 2 hours. The process is defined as 1 cycle, and 12 cycles are repeated, and it is left to stand until it reaches room temperature, and the number of cracks is visually inspected.

b> Dry-wet repeated test A step of leaving a 2.5 x 20 cm ² test piece in a thermo-hygrostat at 20 ± 2 ° C and 90 to 98% RH for 6 hours, and then leaving it in a thermostat at 60 ± 3 ° C for 1 day. Repeat 5 cycles as a cycle, leave it until room temperature is reached, and visually inspect the number of cracks.

c> Repetitive high temperature test 2.5 x 20 cm ² test piece is left in an incubator at 40 ± 2 ° C for 30 minutes, and then left in an incubator at 80 ± 3 ° C for 150 minutes, which is repeated 4 cycles. Allow to reach room temperature and visually inspect for cracks.

2-2 Bleed-out test method Wiping coating is applied to a 30 x 30 cm test piece, and the bleeding of the coating visually determines the presence or absence of bleeding.

2-3 Adhesive performance Two-class immersion peeling 5-cycle test A square test piece of 75 mm was placed in 70 ± 3 ° C hot water for 2
After soaking for 5 hours, a step of drying for 3 hours in an incubator at 60 ± 3 ° C. is performed for 5 cycles, and the peel length of the adhesive layer is measured.

Comparative Example 3 Vinyl acetate emulsion (solid content 45% by weight, viscosity 600 poise / 30 ° C.) 100 parts by weight to urea resin (molar ratio = urea / formaldehyde = 1.9, solid content 73% by weight, viscosity 25 poise / 25)
(° C) 30 parts by weight were added and mixed to obtain an adhesive composition.

To 100 parts by weight of this composition, 18 parts by weight of wheat flour and 12 parts by weight of water were added and mixed to obtain an adhesive for veneer decorative plywood having a viscosity of 150 poise / 25 ° C.

Using the obtained adhesive for veneer decorative plywood, thickness 0.7m / m
After applying 120 g / m ^{2 of} this adhesive for veneer decorative plywood to 5 ply lauan plywood (12 m / m thick), 31 g / m ² of non-sized kraft paper is temporarily bonded with a rubber roll and dried at 40 ° C. Dry in 15 minutes.

Then, after the touch-drying is completed, 10 kg / cm ² by a flat plate press,
It was hot pressed at 100 ° C for 60 seconds.

Then the adhesive of the same composition kraft paper plywood 90 g / m ² and 150 g / m ² coated on Kraft paper of, 0.2 m / m thick oak,
For every 4 types of zelkova, pine, and veneer veneer, stack the veneer on the kraft paper plywood coated with the above adhesive and keep it at 20 ° C for 1 minute.
After taking 10 minutes of deposition time, heat and pressure conditions 110 ℃, 7-8kg
Bonding was performed with a flat plate press at / m ² for 60 seconds.

Based on the same test method as described above, Tables 1 and 2 show the test results of cracking, evaluation of adhesiveness and seepage contamination.

[Advantages of the Invention] (1) According to the present invention, as shown in the above-mentioned examples, it was possible to obtain an adhesive having excellent resistance to cracking of the veneer.

In veneer decorative plywood made by sticking veneer veneer to plywood for the purpose of aesthetics, the aesthetics of veneer surface is extremely important to enhance the high value of the product. Damage should be prevented. According to the present invention, it is possible to provide a veneer decorative plywood which prevents the phenomenon of dry cracking on the surface of the veneer not only immediately after hot pressing in the veneer decorative process, but also with the lapse of time after production.

(2) According to the present invention, the dry cracking can be solved by using only an adhesive without the need for interposing a woven fabric or paper, simplifying the manufacturing process of the veneer decorative plywood, and reducing the cost. I was able to.

(3) The adhesive of the present invention avoids bleeding and contamination on the surface of the veneer.

The veneer veneer tends to become thinner from the viewpoint of improving the retention of raw wood, etc., but according to the present invention, even when such a thin veneer veneer is used, the bleeding on the veneer surface is bleeding. Since it is possible to prevent the veneer from coming out, it is possible to avoid impairing the aesthetics that affect the commercial value of the veneer decorative plywood as described above.

(4) According to the present invention, it is possible to obtain a veneer decorative plywood which is practically satisfactory without necessarily requiring a work step of intentionally semidrying the adhesive in order to prevent the exudation as in the conventional case. did it.

(5) According to the present invention, it is possible to prevent the bleeding contamination and cracking even if the veneer veneer material is changed.

(6) According to the present invention, as described above, the adhesive of the present invention has excellent water resistance and heat resistance because it is excellent in resistance to cracking and is prevented from seeping out and contaminating the veneer surface. Moreover, it is possible to provide an adhesive for decorative veneer decorative processing, which is less likely to cause a puncture or blistering phenomenon when being bonded under heat pressure (particularly under high temperature).

In the above description, the invention mainly made by the present inventor is the background field of application, and the case where the invention is applied to the veneer decorative plywood for sticking the veneer veneer to the plywood is described, but is not limited thereto. Widely used in veneer decorative processing, such as when sticking a veneer single plate to a wood processing base plate such as particle board or fiber board instead of the plywood, or when adhering paper or fabric, which is not necessary. Can be applied to.

Claims (1)

[Claims] 1. A copolymer emulsion of vinyl acetate, N-methylolacrylamide, acrylic acid, acrylic acid ester, methacrylic acid ester, crotonic acid, itaconic acid, maleic acid and / or fumaric acid, and an amino resin. Adhesive for decorative veneer makeup.