JPH0513191B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a water-resistant resin emulsion containing vinyl acetate as a main component, and an object of the present invention is to provide an emulsion that is particularly suitable for bonding wood, paper, and the like. [Conventional technology] Conventionally, vinyl acetate resin emulsion has been widely used as an adhesive for wood, paper, etc. due to its excellent characteristics such as good adhesive strength development (initial adhesion) and ease of use. . However, they have drawbacks such as poor water resistance, and to compensate for these drawbacks, it is common practice to mix and use amine resin liquid adhesives such as urea resins and melamine resins. [Problems to be Solved by the Invention] However, in this method, the steps of preparing the size liquid and the size are troublesome, and by mixing the amino resin liquid adhesive, the excellent characteristics of vinyl acetate resin emulsion can be achieved. This has caused problems such as deterioration of initial adhesion performance. [Means and effects for solving the problem] In order to solve the above problem, the inventors of the present invention have conducted extensive research and found that vinyl acetate is produced by emulsifying amino resins such as urea resin and melamine resin in advance. By mixing it with a resin emulsion, it is possible to improve the water-resistant adhesive performance, which is a drawback of vinyl acetate resin emulsion, without reducing the initial adhesive performance. Organic amine and/or basic salt are added to the mixture of liquid and vinyl acetate resin emulsion to adjust the pH of the mixture to 7.0.
By making the above adjustments, a mixed solution with extremely excellent storage stability can be obtained without separation regardless of the mixing ratio of the amino resin emulsion and the vinyl acetate resin emulsion, and the mixed solution can be kept for a long time. They found that it can withstand storage for a long period of time, and completed the present invention. That is, the present invention is a water-resistant resin emulsion containing vinyl acetate as a main component, blended with an amino resin that has been emulsionized in advance, an organic amine and/or a basic salt, and adjusted to have a pH of 7.0 or higher. It is an emulsion adhesive. When an amino resin aqueous solution is mixed with a vinyl acetate resin emulsion, even if the pH of the mixture is adjusted to 7.0 or higher, if the mixing ratio of the amino resin aqueous solution is low (less than 50%), it will separate during storage. will occur. On the other hand, the amino resin emulsion used in the present invention can be mixed in any ratio, and this difference is a new finding that cannot be predicted at all. In addition, if a normal alkaline substance such as caustic soda is used to raise the pH of the mixture to 7.0 or higher, the PHH will immediately decrease due to the influence of the acid liberated from the vinyl acetate resin, resulting in poor storage stability. It will drop. However, if an alkaline substance such as an organic amine and/or a basic salt is used, it becomes possible to suppress changes in the pH of the mixture over time. When one or more compounds selected from the group of alkaline compounds having buffering properties such as organic amines, ammonia, potassium carbonate, soda carbonate, ammonium carbonate, and dibasic and tertiary sodium phosphates are used, This compound captures and buffers the acid produced from the vinyl acetate resin, suppresses the PH change of the adhesive over time, and exhibits the effect of preventing a decrease in storage stability. Examples of the organic amine mentioned here include ethylenediamine, diethylenetriamine, hexamethylenetetramine, and triethanolamine. The amino resin used in the amino resin emulsion of the present invention is obtained by reacting one or more selected from urea, thiourea, ethylene urea, melamine, acetoguanamine, benzoguanamine, etc. with formaldehyde. One or two resins selected from phenol, resorcinol, cresol, naphthalene, alkylresorcinol, xylenol, paratoluenesulfonamide, acetone, methyl ethyl ketone, cyclohexanone, etc.
Even if more than one species is co-condensed, the effects of the present invention will not change. In addition, vinyl acetate resin emulsion or vinyl acetate-based
Copolymer emulsions containing mol% or more include not only homopolymers thereof, but also vinyl acetate, acrylic acid and its derivatives, methacrylic acid and its derivatives, ethylene, vinyl chloride, vinylidene chloride, maleic acid, and N-methylol. A co-condensed resin emulsion with one or more selected from copolymerizable substances such as acrylamide, allyl alcohol, allyl glycidyl ether, allyl aldehyde, crotonic acid, itaconic acid, etc. is used. [Effects of the Invention] The adhesive obtained by the method of the present invention has excellent initial adhesion performance, waterproof adhesion performance, storage stability, etc., and is therefore suitable for bonding printed paper and decorative veneer to plywood. It is also suitable for adhesion of flash panels, laminated wood, finger joints, furniture assembly, etc., and for adhesion of paperboard, paper tubes, corrugated cardboard, etc. [Example] The effects of the present invention will be explained below with reference to Examples. Example 1 210 g of 37% formalin, 30 g of urea, and 48 g of melamine were weighed into a 500 ml three-necked flask, dibasic sodium phosphate was added to adjust the pH to 9.6, and the temperature was raised to 90° C. with stirring. After reacting at 90℃ for 30 minutes, add 20% formic acid aqueous solution to adjust the pH of the reaction solution.
5.0, and the condensation reaction was continued. Cool the reaction solution to 20°C, and when it becomes cloudy, add tribasic sodium phosphate to bring the pH of the reaction solution to 9.0, and at the same time lower the temperature of the reaction solution.
Cooled to 50°C. Next, 10g of acetone and 2.0g of polyvinyl alcohol (△Kuraray #205)
and 0.7 g of a nonionic surfactant (Lion△, Liponox), reacted for 20 minutes, and then heated to 80°C.
The temperature was raised to 1, and the reaction was continued for an additional 30 minutes. after that,
Add 20% formic acid aqueous solution to adjust the pH of the reaction solution to 5.0.
The reaction continued for about 60 minutes, and when the reaction solution became an emulsion, tertiary sodium phosphate was added to adjust the pH to 7.5, and the mixture was cooled. The amino resin emulsion thus obtained and the commercially available vinyl acetate resin emulsion (Hounen Oil △
(manufactured by: VW-415) in various ratios,
Triethanolamine was added to these mixed resins to adjust the PHH to 8.5 to obtain a water-resistant emulsion adhesive of the present invention. In order to clarify the characteristics of this adhesive, the adhesive was stored in a constant temperature chamber at 30° C., and its storage stability was investigated by measuring changes in viscosity over time. In addition, after adjusting the size liquid by adding 6 parts by weight of a 53% concentration para-toluenesulfonic acid aqueous solution to 100 parts by weight of this adhesive, 330 g/m ² (both sides) was applied to both sides of a 2.0 m/m thick lauan veneer ), stack lauan veneers of the same thickness one on top of the other so that their maintenance directions are perpendicular, and apply a pressure of 8 kg/cm ² .
Time was tight. After leaving it for one week, the adhesive strength was measured using the JAS ordinary plywood class 2 test method. Furthermore, using the same glue, the thickness of 2.5m/m, the width of 25m/m, and the length of
Apply lauan plywood of the same shape to one side of 75 m/m lauan plywood at a ratio of 160 g/m ² to the 25 m/m long part, and overlap the 25 m/m long part so that it overlaps. In total, pressure 10Kg/cm ²
I tightened it with The test piece thus obtained was taken out at predetermined time intervals at room temperature, and the tensile adhesive strength was immediately measured to examine adhesive strength development. Comparative Example 1 Instead of the amino resin emulsion used in Example 1, a commercially available urea resin adhesive (Honen Oil △
A control adhesive was obtained in the same manner as in Example 1 except that UW-062) was used. This adhesive was examined for storage stability, water resistance, and adhesive strength development in the same manner as in Example 1. These test results of Example 1 and Control Example 1 and vinyl acetate resin emulsion (manufactured by Honen Oil △:
The following table compares the test results when VW-415) was used alone.

[Table] Comparative Example 2 The amino resin emulsion synthesized in Example 1 and a commercially available vinyl acetate resin emulsion (VW-415 manufactured by Honen Oil △) were mixed in the same ratio as in Example 1, and the pH was adjusted. It was used as an adhesive. Then, it was subjected to an adhesive performance test in the same manner as in Example 1. Furthermore, in order to clarify the characteristics of the adhesive according to the present invention, each adhesive prepared in Control Example 2 was stored in a thermostat at 30°C.
Changes in viscosity and pH over time were investigated. Control Example 3 In addition to triethanolamine used as an alkaline compound with buffering properties in Example 1,
A control adhesive was obtained in the same manner as in Example 1, except that caustic soda was used for pH adjustment. Then, it was subjected to an adhesive performance test in the same manner as in Example 1. Furthermore, in order to clarify the characteristics of the adhesive according to the present invention, each adhesive prepared in Control Example 3 was
It was stored in a constant temperature chamber at 30°C, and changes in viscosity and pH over time were examined. The results are shown in the table below.

【table】

[Table] Example 2 Weighed 1200 g of 37% formalin, 250 g of urea, 400 g of melamine, 450 g of water, 2 g of hexamethylenetetramine, and 50 g of a water-soluble copolymer of acrylamide and acrylic acid into a three-necked flask, and added 80 g of water while stirring. The temperature was raised to ℃. After reacting at 80°C for 230 minutes, 5 g of 25% caustic soda was added and cooled to 30°C to obtain an amino resin emulsion. Example 1 Using this amino resin emulsion
After mixing with vinyl acetate resin emulsion (VW-415 manufactured by Hounen Oil △) in the same manner as above, tertiary sodium phosphate was added to these mixed resins to adjust the pH.
7.5 to obtain a water-resistant emulsion adhesive of the present invention. In order to clarify the characteristics of this adhesive, storage stability, water resistant adhesiveness, and adhesive strength development were investigated in the same manner as in Example 1. The results are shown in the table below.

[Table] From the above examples, it is clear that the method of the present invention has excellent effects.

Claims (1)

[Claims] 1. Mix vinyl acetate resin emulsion or vinyl acetate-based copolymer emulsion with amino resin that has been emulsionized in advance, and add organic amine, ammonia, potassium carbonate, soda carbonate, ammonium carbonate, secondary and tertiary sodium phosphate. A water-resistant emulsion adhesive made by blending one or more compounds selected from the group of alkaline compounds with buffering properties and adjusting the pH to 7.0 or higher.