JPH0415270B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aqueous adhesive composition that not only has excellent water resistance, heat resistance, and stability, but also has improved yellowing over time.

Conventionally, urea resins, urea-melamine cocondensation resins, formalin resins such as phenolic resins, acrylic resins, epoxy resins, etc. have been used as connecting agents for processing wood materials, plastics, metal materials, etc., depending on the purpose. However, it has some drawbacks such as formaldehyde emission, resin cost, workability, water resistance, heat resistance, and chemical resistance. In addition, there are low-cost adhesives such as non-formalin-based protein-based, vinyl acetate-based, rubber latex-based, and polyvinyl alcohol-based adhesives, but they lack water resistance and are not practical.

However, although it is a well-known fact that adhesive compositions use the above substances alone or in combination with isocyanate for the purpose of improving water resistance, in general, systems using isocyanate are The use time is relatively short, which may have a negative effect on workability and adhesive properties. At the same time, aromatic isocyanates are often used, and their chemical structure prevents the adhesive layer from yellowing over time. I can't do that. It is a well-known fact that aliphatic isocyanates, hydrogenated isocyanates, etc. are resistant to yellowing, but when used in aqueous systems, they have poor dispersibility and also pose problems in terms of toxicity.

Based on the well-known fact that water resistance is improved by introducing isocyanate into an aqueous dispersion of an aqueous polymer as a result of extensive research, the present inventors have determined that the various drawbacks that occur in this state can be solved by containing isocyanurate rings. The inventors have discovered that the problem can be solved by using a hexamethylene diisocyanate polymer, and have arrived at the present invention.

That is, the present invention comprises: 1 an adhesive composition formed by mixing the following components 1 and 2; 2 an aqueous dispersion containing a water-soluble polymer, an aqueous emulsion, and a stabilizer and/or thickener and/or filler; Hexamethylene diisocyanate polymer containing isocyanurate rings and molecular weight 250-4000
A self-emulsifying prepolymer whose ends are isocyanate groups obtained by reacting alkoxy polyalkylene glycols.

It is related to.

The water-soluble polymer used in the present invention includes polyvinyl alcohol, water-soluble ethylene vinyl acetate copolymer,
polyethylene oxide, water-soluble acrylic resin,
water-soluble epoxy resin, water-soluble cellulose derivative,
Examples include water-soluble polyesters and water-soluble lignin derivatives.

In addition, the aqueous emulsion that can be used in the present invention includes all so-called latexes and emulsions. For example, styrene-butadiene copolymer latex, acrylonitrile
Rubber latexes such as butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, chlorobrene latex, polybutane diene latex, polyacrylate latex, polyvinylidene chloride latex,
Examples include polybutadiene latex and carboxyl-modified versions of these latexes, as well as polyvinyl chloride emulsion, urethane acrylic emulsion, silicone acrylic emulsion, vinyl acetate acrylic emulsion, urethane emulsion, acrylic emulsion, etc. are listed.

It is a well-known fact that isocyanate compounds are used for the purpose of imparting water resistance to the above composition, but in the present invention, not only water resistance but also extension of pot life and improvement of heat resistance of the adhesive composition can be achieved. A major feature of this adhesive composition is that it solves problems that have remained with adhesive compositions of this type until now, such as improvement in yellowing.

Polymers of hexamethylene diisocyanate containing isocyanurate rings are produced by adding tertiary amines, alkyl-substituted ethyleneimines, tertiary alkyl phosphines, acetylacene metal salts, and metals of various organic acids to hexamethylene diisocyanate as catalysts. It can be obtained by carrying out an isocyanurate reaction at 100° C. or lower, using salts or the like alone or in combination, and using a co-catalyst if necessary. As co-catalysts, phenolic hydroxy compounds,
The reaction can be further facilitated by using alcoholic hydroxy compounds, tertiary amines, etc. as necessary. The catalyst can be rendered inactive by using known strong acids such as phosphoric acid, sulfuric acid, etc. as terminators.

The molecular weight of the hexamethylene diisocyanate polymer containing an isocyanurate ring and the alkoxypolyalkylene glycol constituting the prepolymer used in the present invention is in the range of 250 to 4,000, particularly preferably in the range of 600 to 2,000. It is something. After this prepolymer is dispersed in water, a polyurethane protective film is formed on the surface of the prepolymer particles to maintain a state in which the reaction between the isocyanate groups of the prepolymer and water can be suppressed, thereby making it possible to obtain a stabilized isocyanate emulsion.

The general formula of the alkoxy polyalkylene glycol used in the present invention is represented by R ₁ O(-R ₂ O)- _o H,
Here, R ₁ is an alkyl group and R ₂ is an alkylene group, and since this alkoxy group as a whole acts like a nonionic surfactant, it is thought to exhibit self-emulsifying characteristics. When the molecular weight is 4,000 or more, water emulsification is good, but at the same time, stability in water deteriorates, and because compounds with a molecular weight of 4,000 or more have high crystallinity, the storage stability of the obtained prepolymer itself at low temperatures decreases. , turbidity, etc. occur. Polypolymers are produced by known methods, generally in the absence of solvents, and the residual NCO content is desirably adjusted to 15-24%. If it is less than 15%, during emulsification, the interfacial layer of the emulsified particles will have stronger hydrophilicity than necessary, resulting in poor stability, and high viscosity, resulting in poor dispersibility. If it exceeds 24%, the hydrophilicity in the interfacial layer will be insufficient, making it difficult to form a stable emulsion.

Stabilizers that can be used in the present invention include halogenated hydrocarbons such as chlorinated paraffin, ethers such as ethylene glycol monobutyl ether, phthalates, olefinic esters, adipic esters, and azelaic esters. esters such as stearate esters, benzoate esters, phosphate esters, trimellitate esters, maleate esters, fumarate esters, etc., cyclic alkylene carbonates, tertiary amines, Examples include ionic surfactants.

Examples of the thickener include wheat flour, celluloses such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose.

Examples of the filler include silica, talc, wood flour, clay, pentonite, starch, etc., and it is possible to adjust the hardness of the resin component in the adhesive layer.

The above-mentioned components may be added in any order except for the isocyanate component. This has almost no effect on viscosity or adhesive strength.
The isocyanate component is added as a water emulsion, but in some cases it may also be added directly.

Although the present adhesive composition exhibits sufficient adhesive strength even when bonded at room temperature, it is also significant to perform appropriate heat treatment in order to improve workability, adhesion, water resistance, and heat resistance.

According to the present invention, (a) By converting hexamethylene diisocyanate into isocyanurate and removing free hexamethylene diisocyanate, its toxicity can be extremely reduced, and by introducing an isocyanurate ring, it can be used as an adhesive. It has become possible to improve heat resistance.

(b) By modifying the above polymer with an alkoxypolyalkylene glycol having a molecular weight of 250 to 4000, it became a prepolymer with self-emulsifying properties, making it possible to significantly improve the dispersibility in aqueous systems.

(c) Due to its chemical structure, hexamethylene diisocyanate has extremely excellent performance against yellowing over time due to ultraviolet rays, so it has become possible to improve yellowing as an adhesive.

(d) The water emulsion of the self-emulsifying prepolymer used in the present invention is prepared at a liquid temperature of prepolymer:water=1:1.
At 20°C, it has a pot life of 10 hours or more, making it possible to obtain a size liquid with extremely excellent stability even when used as a crosslinking agent for adhesives.

(e) No formalin-based resin is used, and since it is water-based, there are no emissions that pollute the environment.

That is, there are no emissions that pollute the environment, and the pot life is long, so it can be used in a stable state, and as a result, it has excellent applicability to substrates and has sufficient adhesive strength. Molded products are water resistant, heat resistant,
It has excellent yellowing resistance and adhesive strength.

This adhesive composition is particularly suitable as an adhesive for processing wood materials, plastics, metal materials, etc., but is also effective for processing cardboard, paper, and fibers.

EXAMPLES Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples.

Parts and % in Examples and Comparative Examples indicate parts by weight and % by weight, respectively.

Production synthesis example of self-emulsifying prepolymer 1 Coronate EH (hexamethylene diisocyanate polymer with isocyanurate rings, manufactured by Nippon Polyurethane Industries, same NCO content of 21.0% or less)
In the infrared absorption spectrum of this liquid, strong absorption characteristic of the isocyanurate ring was observed at 1680 cm ^-1 , and absorption at 1780 cm ^-1 characteristic of the dimer was not observed at all.

100 parts of Coronate EH was placed in a 500 ml four-necked glass flask with a sliding lid equipped with a thermometer, stirrer, and nitrogen-sealed tube, and then 2 parts of methoxypolyethylene glycol (MPG-081, manufactured by Nippon Nyukazai Kogyo) were added. 3 while increasing the temperature and maintaining it at 70℃
After time reaction, NCO content 19.8%, viscosity
A pale yellow transparent isocyanate group-terminated prepolymer was obtained at 3200 cps/25°C. This prepolymer had self-emulsifying properties.

Synthesis Example 2 100 parts of Coronate EH was charged into a reactor equipped with the same equipment as in Synthesis Example 1, and then 2 parts of methoxypolyethylene glycol (MPG-038, manufactured by Nippon Nyukazai Kogyo) was added and the temperature was raised, maintaining the temperature at 70°C. After 3 hours of reaction, NCO content 19.5%, viscosity
A pale yellow transparent isocyanate group-terminated prepolymer was obtained at 3000 cps/25°C. This prepolymer had self-emulsifying properties.

Synthesis Example 3 500 parts of hexamethylene diisocyanate (HDI, manufactured by Nippon Polyurethane Industries) was charged into a 1-volume four-necked glass flask with a sliding lid equipped with a thermometer, stirrer, and nitrogen-sealed tube, and then the temperature was raised to 40°C. At this point, 38.5 parts of 1.3-butanediol was added, the temperature was further raised to 80°C, and the mixture was reacted for 3 hours.

The NCO content of the resulting colorless and transparent reaction solution was measured and found to be 39.8%. Free hexamethylene diisocyanate was removed using a molecular distillation apparatus. The resulting liquid is a pale yellow liquid with an NCO content of 17.5.
%, viscosity 2700 cps/25°C, and free hexamethylene diisocyanate 0.4%. In the infrared absorption spectrum of this liquid, no strong absorption at 1680 cm ^-1 characteristic of isocyanurate rings was observed.

100 parts of the hexamethylene diisocyanate modified product obtained in this way was charged into a reactor equipped with the same equipment as in Synthesis Example 1, and then 2 parts of methoxypolyethylene glycol (MPG-081, manufactured by Nippon Nyukazai Kogyo) was added. 3 while keeping the temperature at 70℃.
After time reaction, NCO content 16.3%, viscosity
A pale yellow transparent isocyanate group-terminated prepolymer was obtained at 3500 cps/25°C. This prepolymer had self-emulsifying properties.

Example 1 Vinyl acrylic copolymer latex (Haloflex) adjusted to pH5.0 with 28% ammonia water
208, manufactured by ICI) 40 parts, polyvinyl alcohol 10%
100 parts of aqueous solution (PA-18, manufactured by Shin-Etsu Chemical), styrene-butadiene copolymer latex (Nipole)
LX-209 (manufactured by Nippon Zeon) and 25 parts of talc were thoroughly mixed to obtain an aqueous dispersion.

When 15 parts of the self-emulsifying prepolymer obtained in Synthesis Example 1 was added to 100 parts of this aqueous dispersion and stirred and mixed with a glass rod, the mixture was easily dispersed. The pot life of this paste at 25°C was over 12 hours. Furthermore, this paste liquid was used as an adhesive for sawing boards, and an adhesion test (according to JISK6852, hereinafter the same) was conducted under the following conditions.

Adherent material: Cover/cover (10m/m) Clamping:
10Kg/cm ² × 2 hours Application amount: 300g/m ² Curing: 3 days or more Normal adhesive strength: 165Kg/cm ² Wood breakage rate 86% Repeated boiling adhesive strength: 66Kg/cm ² Wood breakage rate 95% Heat resistant adhesive strength ( 120℃ x 24 hours): 175Kg/ ^cm2
Wood breakage rate 95% Example 2 60 parts of acrylic emulsion (AE-942, manufactured by Japan Synthetic Rubber), 100 parts of 10% polyvinyl alcohol aqueous solution (PA-15, manufactured by Shin-Etsu Chemical), styrene-butadiene copolymer latex (Nipole) 2570X5,
(manufactured by Nippon Zeon) 20 parts, 3% aqueous solution of hydroxypropyl methylcellulose (Hymetrose 90SH-
4000 (manufactured by Shin-Etsu Chemical) and 25 parts of talc were thoroughly mixed to obtain an aqueous dispersion.

When 15 parts of the self-emulsifying prepolymer obtained in Synthesis Example 2 was added to 100 parts of this aqueous dispersion and stirred and mixed with a glass rod, the mixture was easily dispersed. The pot life of this paste at 25°C was over 12 hours. Furthermore, this paste liquid was used as an adhesive for sawing boards, and an adhesion test was conducted under the same conditions as in Example 1.

Normal adhesive strength: 158Kg/cm ² Wood breakage rate 90% Boiling repeated adhesive strength: 65Kg/cm ² Wood breakage rate 100% Heat resistant adhesive strength (120℃ x 24 hours): 170Kg/cm ²
Wood breakage rate: 98% Comparative Example 1 15 parts of the self-emulsifying prepolymer obtained in Synthesis Example 3 was added to 100 parts of the aqueous dispersion of Example 1, and the mixture was stirred and mixed with a glass rod, resulting in easy dispersion. The pot life of this paste at 25°C was over 12 hours. Furthermore, this paste liquid was used as an adhesive for sawing boards, and an adhesion test was conducted under the same conditions as in Example 1.

Normal adhesive strength: 162Kg/cm ² Wood breakage rate 84% Boiled repeated adhesive strength: 42Kg/cm ² Wood breakage rate 40% Heat resistant adhesive strength (120℃ x 24 hours): 75Kg/cm ²
Wood breakage rate: 48% Example 3 100 parts of acrylic emulsion (AE-942, manufactured by Japan Synthetic Rubber Co., Ltd.), 30 parts of a 5% aqueous solution of polyvinyl alcohol (PA-18, manufactured by Shin-Etsu Chemical Co., Ltd.), and a 1.5% aqueous solution of hydroxypropyl methylcellulose (Himetrose) 90SH-4000, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed well to obtain an aqueous dispersion. This aqueous dispersion 100
20 parts of the self-emulsifying prepolymer obtained in Synthesis Example 1 were added to the mixture and stirred and mixed with a glass rod, resulting in easy dispersion. The pot life of this paste at 25°C was over 12 hours. Further, a white nonwoven fabric was impregnated with this paste solution, dried at 80°C for 3 hours, and then exposed outdoors. No discoloration was observed even after 90 days.

Comparative Example 2 A glue solution was prepared using the same recipe as in Example 3. However, instead of the self-emulsifying prepolymer of Example 3, 20 parts of a trimethylolpropane adduct of tolylene diisocyanate (Coronate L, manufactured by Nippon Polyurethane Industries) was used. The pot life of this glue is 2
It took 20 minutes. When the same test as in Example 3 was conducted, the color changed to brown after 90 days.

Claims (1)

[Scope of Claims] 1. Adhesive composition formed by mixing the following components 1 and 2. 1. An aqueous dispersion containing a water-soluble polymer, an aqueous emulsion, and a stabilizer and/or thickener and/or filler. Solution 2 Hexamethylene diisocyanate polymer containing isocyanurate rings with a molecular weight of 250 to 4000
A self-emulsifying prepolymer with terminal isocyanate groups obtained by reacting alkoxy polyalkylene glycol.