JP2000204335A - Adhesive composition with amino resin curability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject adhesive composition having such advantages that, in bonding operations for secondary processed plywoods such as sliced veneers, the setting time range until sliced veneer sheet laminating is wide; in this case, there is good workability enough to stand some corrections by handwork; adhesive force is developed quickly after bonding and enhanced with time; and even the highly severe requirements as specified in JAS Class I can be met. SOLUTION: This adhesive composition comprises (A) 60-98 wt.%, on a solid basis, of an ethylene-vinyl acetate copolymer resin emulsion and (B) 40-2 wt.%, on a solid basis, of an amino resin adhesive; wherein the component A to be preferably used is such one as to be 5-30 wt.% in ethylene content and prepared by a well-known method by emulsion polymerization under an autoclave pressure of 20-100 kg/cm2 using normally polyvinyl alcohol or the like as protective colloid in the presence or absence of nonionic and/or anionic surfactant(s); and the component B to be preferably used is e.g. a melamine-formaldehyde resin adhesive, urea-formaldehyde resin adhesive, being such one as to be prepared by a well-known method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amino resin-curable adhesive composition suitable for producing a secondary processed plywood such as a veneer.

[0002]

2. Description of the Related Art Secondary processed plywood such as a veneer is generally manufactured by the following method. That is, first, an adhesive compounded with a glue bat by a roll is applied onto a base plate, and then a veneer plate is bonded. A number of laminated veneer plywoods are stacked and put on a multi-stage press machine, but after the adhesive is applied to the base plate, several sheets are left and then the veneer sheets are laminated, and the number of The larger the number, the more advantageous in terms of workability, and the adhesive requires a certain open time (set time width). The finished veneer plywood is a special plywood Japanese Agricultural Standard (JA)
According to S), the adhesion performance is measured under various conditions such as normal conditions and boiling. Therefore, as the adhesive, together with the above-mentioned open time (set time width), the adhesive force is quickly developed after the veneer sheet is bonded, and the adhesive force increases with time, not to mention the normal state. Even in water and boiling resistance, the adhesive strength is strong enough and it must pass the standard.

As a conventional veneer adhesive, an amino resin is mixed with SBR latex as a curing agent, and a paste such as starch is used in combination with the amino resin to prevent bleeding. However, when SBR latex is used as the veneer adhesive, the adhesive is dried too quickly after the adhesive is applied to the base plate, and a sufficient open time (set time width) cannot be obtained. It is not possible to leave several coated boards, and the veneer sheet must be quickly bonded to the base plate each time one adhesive is applied, resulting in extremely poor workability. There was a point. Furthermore, in the case of SBR latex, the rate of increase in adhesive strength with time is slow, and the final adhesive performance does not pass the specifications under strict conditions, for example, boiling resistance (JAS class), and the commercial value is poor. there were.

[0004]

SUMMARY OF THE INVENTION According to the present invention, in the bonding of a secondary processed plywood such as a veneer, the open time after the adhesive is applied to the base plate can be lengthened, and therefore, the bonding time of the veneer sheet can be reduced. Set time width is wide. Even if adhesive is applied to the base plate and left for 5 or 6 sheets or more, and then the veneer sheet is pasted, sufficient drying is obtained without overdrying. In that case, it has good workability enough to withstand a slight manual correction, the adhesive strength is fast after bonding, and shows high strength adhesive strength over time,
It is an object of the present invention to provide an adhesive composition having amino resin curability that can pass extremely severe conditions such as JAS class.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present invention improves the open time (set time width) at the time of bonding the above-mentioned veneer, and the adhesive force under severe conditions after bonding the veneer. As a result of diligent studies for the purpose of improving the above, it was found that the above object was achieved by using an adhesive composition in which an amino resin was added at a specific ratio to an ethylene-vinyl acetate copolymer resin emulsion. Headings,
The present invention has been completed.

That is, the present invention has an amino resin curability comprising 60 to 98% by weight (solid content) of an ethylene-vinyl acetate copolymer resin emulsion and 40 to 2% by weight (solid content) of an amino resin adhesive. An adhesive composition is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The ethylene-vinyl acetate copolymer resin emulsion used in the present invention has an ethylene content of 5 to 3%.
0% by weight, 20 to 100 kg / cm by emulsion polymerization
^{In the second step} , those produced by a known method using polyvinyl alcohol or the like as a protective colloid under autoclave pressure in the presence or absence of a nonionic and / or anionic surfactant are preferably used. As monomers to be used, ethylene and vinyl acetate are essential components. In addition to these, well-known unsaturated carboxylic acids such as (meth) acrylic acid and (meth) acrylate which are generally used in emulsion polymerization are commonly used. , (Meth) acrylamides, N-methylol (meth) acrylamide, and the like may be copolymerized, and the resulting resin adhesive may be in the form of a multi-component copolymer. The solid content of the product is 3
It is desirably from 0 to 70% by weight.

The amino resin adhesive used in the present invention includes a melamine-formaldehyde resin adhesive, a urea-formaldehyde resin adhesive, a melamine-urea-formaldehyde co-condensation resin adhesive and the like. Manufactured products can be suitably used. Among these amino resin adhesives, the melamine-formaldehyde resin adhesive is obtained by reacting formaldehyde at a ratio of 1 to 6 moles with respect to 1 mole of melamine, and sodium hydroxide (NaOH), Potassium hydroxide (KOH), sodium carbonate (Na ₂ CO ₃ ),
An alkaline compound (alkali catalyst) such as aqueous ammonia (NH ₄ OH) and, if necessary, an acid (acid catalyst) such as hydrochloric acid, acetic acid, oxalic acid and formic acid are added. The reaction is usually 60-1
It is performed at a temperature of 00 ° C. The urea-formaldehyde resin adhesive contains 1 to 3 formaldehyde per mole of urea.
In the same manner as in the case of the production of the melamine-formaldehyde resin adhesive in a molar ratio, it can be obtained by adding and reacting an alkali catalyst and, if necessary, an acid catalyst.
The reaction temperature is from 60 to 100 ° C. The melamine-urea-formaldehyde co-condensation resin adhesive has a ratio of melamine of 0.01 to 1 mol with respect to 1 mol of formaldehyde, and a ratio of 0.01 to 1 mol of urea with respect to 1 mol of formaldehyde. And formaldehyde 1
It is obtained by reacting at a ratio such that the total number of moles of melamine and urea does not exceed 1 mole per mole. At the time of the reaction, the kind of the alkali and the acid to be added as the catalyst are the same as those in the production of the melamine-formaldehyde resin adhesive and the urea-formaldehyde resin adhesive. Also,
The reaction temperature is also in the range of 60 to 100 ° C.

The amino resin curable adhesive composition of the present invention contains the ethylene-vinyl acetate copolymer resin emulsion obtained by the above-mentioned method and one or more amino resin adhesives in a specific ratio. The solid content of the ethylene-vinyl acetate copolymer resin emulsion is 60 to 98% by weight (preferably 70 to 95% by weight) and the amino resin adhesive is 40 to 2% by weight ( Preferably, it is 30 to 5% by weight. Ethylene-
60% by weight of vinyl acetate copolymer resin emulsion
Below, the open time of the adhesive (set time width)
Is short, in the production by bonding of the veneer, the adhesive is dried too quickly after the adhesive is applied on the base plate, the surface is skinned, there is a risk of causing poor adhesion due to overdrying, It cannot be left for a long time with the adhesive applied to the base plate, and it is impossible to bond the veneer after leaving a plurality of the plates. Also, it is difficult to correct the bonded veneer. Conversely, when the proportion of the ethylene-vinyl acetate copolymer resin emulsion is more than 98% by weight, the drying of the adhesive is too slow to develop the initial adhesive strength, and the increase in the adhesive strength with time is limited. It has poor water resistance and does not pass the standard for adhesion under severe conditions such as boiling resistance. The composition of the present invention is produced by blending an ethylene-vinyl acetate copolymer resin emulsion and an amino resin adhesive in a specific ratio, and the properties thereof are relatively determined by the ratio of the two components depending on the blend ratio. When the proportion of the amino resin adhesive is too large or less than the specified proportion, the inconvenience that occurs when the proportion is too small is only opposite to the case of the above-mentioned ethylene-vinyl acetate copolymer resin emulsion. Needless to say.

Next, the process for producing the amino resin curable adhesive composition of the present invention will be described in more detail. That is, the ethylene-vinyl acetate copolymer resin emulsion obtained as described above is charged into a container equipped with a stirrer, and the amino resin adhesive obtained by the above-described method is added thereto while stirring. Or two or more of them are gradually added and mixed, and then, starch and water are added and stirring is continued to adjust the viscosity to an appropriate level for adhesion. As for the order of adding the ethylene-vinyl acetate copolymer resin emulsion and the amino resin adhesive to the mixing vessel, it is more convenient to add the higher one first depending on the viscosity because the more effective stirring can be obtained.

[0011]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. Example 1 An ethylene-vinyl acetate copolymer resin emulsion was synthesized according to the following procedure. The components shown in Table 1 below were charged into a stainless steel dissolving vessel equipped with a 60-liter internal light type stirrer, and stirred and dissolved at 50 ° C. for 2 hours to obtain a uniform aqueous solution.

[0012]

[Table 1] Water 10814 g (1) Polyvinyl alcohol trade name Kuraray PVA205 296 g (2) polyvinyl alcohol trade name Kuraray PVA217 296 g

Next, a second sodium phosphate 14.
3 g and 200 g of sodium metabisulfite were added and dissolved.
Cooled to below 0 ° C. Furthermore, vinyl acetate 1
2299 g was gradually added with stirring to obtain a vinyl acetate monomer emulsion. 25% of this monomer emulsion
Was charged into a stainless steel autoclave equipped with a 30-liter immersion type stirrer, and then the air in the autoclave was sufficiently replaced with nitrogen and ethylene. Then, while stirring, the monomer emulsion was heated to 72 ° C. After increasing the ethylene pressure to 50 kg / cm ² , the temperature was increased to 72 ° C.
The polymerization was carried out for 1 hour while controlling the ethylene pressure at 50 kg / cm ² . Next, the remaining 75% of the monomer emulsion
Was added uniformly over 7 hours to carry out polymerization. At this time, 1081 g of a 5.8% aqueous solution of ammonium persulfate was uniformly dropped as a polymerization catalyst over 10 hours from the beginning of the polymerization. From the 9th hour, the aging temperature was set to 8
The temperature was raised to 0 ° C., and aging was performed for 1 hour. Thereafter, it was cooled to obtain a product. The amino resin adhesive was synthesized as follows using the raw materials shown in Table 2 below.

[0014]

Table 2 Melamine 400g Formalin (37%) 860g Caustic soda (20% aqueous solution) 1.9ml Methanol 165g Hydrochloric acid (10% aqueous solution) 15ml Borax 0.6g

Was charged into a reaction vessel and adjusted to pH 9.2 to 9.4 (TB paper) with stirring.
Reaction at 30 ° C for 30 minutes. During that time, the pH drops naturally. Next, pH is adjusted to 6.2 to 6.4 (pH meter) by adding, and the reaction is performed at 60 ° C. 50 ~ after addition of
In 60 minutes, one drop of the reaction solution is dropped into water at 25 ° C. in a beaker, and the reaction is performed until the mixture becomes cloudy.

400 g of the ethylene-vinyl acetate copolymer resin emulsion thus obtained is charged into a container, and 140 g of the amino resin adhesive is added with stirring. Next, 260 g of flour is gradually added as it is, and
The viscosity was adjusted by adding 60 g to obtain an adhesive composition.

Next, using the adhesive composition obtained above, a veneer was prepared according to the processing conditions shown in Table 3 below.

[0018]

TABLE 3 bedplate 3mm thick coating weight 8 g / scale ² veneer red oak hot press ^{100 ℃, 6Kg / cm 2,} 1 minute curing 20 ℃ · 65% RH atmosphere for 24 hours under

In the performance test, the workability was measured in accordance with the set time width, and the adhesion performance was measured in accordance with the Japanese Agricultural and Forestry Standards (JAS class, especially boiling resistance) of special plywood. Table 4 shows the results.

[0020] (Example 2) Example 1 Ethylene - in the production of vinyl acetate copolymer resin emulsion, except that the polymerization pressure 50 kg / cm ² to 30kg / cm ² was performed in the same manner as in Example 1. Table 4 shows the results.

[0021] (Example 3) Example 1 of the ethylene - in the production of vinyl acetate copolymer emulsion, except that the polymerization pressure 50 kg / cm ² was changed to 70 kg / cm ² was performed in the same manner as in Example 1. Table 4 shows the results.

Example 4 In the production of the amino resin adhesive of Example 1, 400 g of melamine and 860 formalin were used.
The procedure was exactly the same as in Example 1 except that g was changed to 320 g of melamine and 720 g of formalin. Table 4 shows the results.

EXAMPLE 5 In the production of the amino resin curable adhesive composition of Example 1, 400 g of the ethylene-vinyl acetate copolymer resin emulsion and 160 g of the amino resin adhesive were mixed with the ethylene-vinyl acetate copolymer resin emulsion. The procedure was exactly the same as in Example 1, except that the amounts were changed to 500 g and amino resin adhesive 60 g, respectively. Table 4 shows the results.

Comparative Example 1 The procedure of Example 1 was repeated except that no amino resin adhesive was used and only an ethylene-vinyl acetate copolymer resin emulsion was used in the production of the amino resin curable adhesive composition. Performed exactly as in Example 1. Table 4 shows the results.

COMPARATIVE EXAMPLE 2 In the production of the amino resin curable adhesive composition of Example 1, 400 g of the ethylene-vinyl acetate copolymer resin emulsion and 160 g of the amino resin adhesive were mixed with the ethylene-vinyl acetate copolymer resin emulsion. The procedure was exactly the same as in Example 1 except that the amounts were changed to 160 g and amino resin adhesive 400 g, respectively.
Table 4 shows the results.

Comparative Example 3 The preparation of the adhesive composition having amino resin curability of Example 1 was carried out in exactly the same manner as in Example 1, except that no ethylene-vinyl acetate copolymer resin emulsion was used. . Table 4 shows the results.

(Comparative Example 4) In the production of the amino resin curable adhesive composition of Example 1, 400 g of an ethylene-vinyl acetate copolymer resin emulsion was added to a commercially available SBR.
Latex (solids concentration 50.4%, viscosity 1650 cp
s, pH 7.6), except that the amount was changed to 400 g. Table 4 shows the results.

[0028]

[Table 4]

[0029]

According to the present invention, an adhesive composition is prepared by blending a fixed ratio of an ethylene-vinyl acetate copolymer resin emulsion and an amino resin adhesive, and an effective amino resin which cannot be obtained by using each of them alone. Curability can be obtained. In other words, in the bonding of a secondary processed plywood such as a veneer, the open time after applying the adhesive to the base plate can be lengthened, so that the set time width until the bonding of the veneer sheet is wide, and the adhesive Even if the veneer sheet is pasted after leaving it for 5 or 6 sheets or more, sufficient adhesion is obtained without overdrying. It has good workability that can withstand even, and after the bonding, the adhesive strength is fast, and it shows high strength adhesive force over time, and it can pass extremely severe conditions like JAS class. It is possible to provide an adhesive composition having a curable amino resin.

Claims (1)

[Claims] 1. An amino resin curable adhesive composition comprising 60 to 98% by weight (solid content) of an ethylene-vinyl acetate copolymer resin emulsion and 40 to 2% by weight (solid content) of an amino resin adhesive. object.