JPS6117875B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wood adhesive composition with a high moisture content. Wood, including logs, is a finite resource, and the resource is decreasing year by year. Effective use of these resources and improvement of product yield are essential requirements. From this perspective, adhesives for wood with high moisture content have been developed. There is a huge demand for agents. Conventionally, as adhesives for wood, urea-formalin resin systems, melanin resin systems, phenol resin systems, urethane resin systems, and the like are often used. Adhesives based on urea-formalin resin, melanin resin, and phenol resin are thermosetting, so they have good adhesive strength and water resistance, but on the other hand, they require heating, and formalin remains even after bonding, causing odor, Unfavorable in terms of environmental stability and hygiene. Additionally, it has very weak adhesion to wood with high moisture content. In addition, regarding urethane resin adhesives,
No., Special Publication No. 31-8888, Special Publication No. 9586, Special Publication No. 32-35, Japanese Patent Publication No. 30429-1973, Japanese Patent Application Publication No. 1973-
No. 75704, JP-A-49-86506, JP-A-49-118807
The properties and compositions are detailed in the specifications of the publications such as No. 1, No. 118808/1983, and No. 118805/1983. These urethane resins have an isocyanate group at the end of the molecule and form a primary chemical bond with wood having an alcoholic hydroxyl group, so their adhesive strength is extremely excellent. However, when used on wood with a high moisture content, foaming occurs, the adhesion to the adhesive part is poor, the adhesive force is also poor, and the strength deteriorates, making it useless as an adhesive. The present inventor has conducted extensive research in order to improve the above-mentioned drawbacks, and as a result, has arrived at the present invention. That is, a polyoxyalkylene triol with a molecular weight of 3,000 to 9,000, obtained by random addition polymerization of an alkylene oxide containing 50 to 90% ethylene oxide, and an organic polyisocyanate are combined with NCO/
A wood adhesive composition with a high water content, characterized by being a urethane resin containing terminal isocyanate groups reacted at an OH equivalent ratio of 2 to 8, or a urethane resin blended with an inert solvent as necessary. It is. The wood adhesive composition with a high moisture content, that is, the urethane resin used in the present invention uses a special hydrophilic polyoxyalkylene triol as a polyol component. A special hydrophilic polyoxyalkylene triol is a starting material having three active hydrogen groups, such as glycerin, and an alkylene oxide (however, 50 to 90% ethylene oxide is added to the starting material, such as glycerin).
Random addition polymerization of molecular weight 3000~
9000 polyoxyalkylene triol. Regarding the number of hydroxyl groups, in the case of one hydroxyl group, adhesive strength and water resistance are poor. In the case of two pieces, workability is good, but floating occurs, which is not preferable. Also,
In the case of 4, 6, and 8, the reaction with the organic polyisocyanate is very fast and takes the form of a crosslinking reaction, resulting in thickening or gelation, making industrial production difficult, and even if urethane resin is obtained. However, it has a short pot life on wet surfaces made of wood with a high moisture content, hardens during the application process, and does not penetrate sufficiently into the adherend. Regarding the amount of ethylene oxide in polyoxyalkylene triol, if it is less than 50%,
The wet surface of wood with a high moisture content has poor compatibility with moisture, and the slicing yield is also poor. If it exceeds 90%, the freezing point and viscosity of the polyoxyalkylene triol will become extremely high, causing problems in the purification and filtration process in industrial production, making production virtually impossible. The organic polyisocyanate to be reacted with the polyoxyalkylene triol is toluene diisocyanate (2,4/2,6 isomer ratio 80/20),
When used, 4,4 or polydiphenylmethane diisocyanate, naphthalene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, etc. are used alone or in combination. The reaction ratio between the polyoxyalkylene triol and the organic polyisocyanate is an NCO/OH equivalent ratio of 2 to 8. If it is less than 2, the urethane resin will have high viscosity and poor storage stability. On the other hand, when it exceeds 8, foaming occurs when adhering wood with a high moisture content, and the adhesive strength is also poor. Furthermore, when toluene diisocyanate is used as the organic polyisocyanate component, the amount of free toluene diisocyanate is large, which is unfavorable in terms of the working environment. In order to improve workability, it is preferable that an inert solvent having no active hydrogen group can be added to these urethane resins. Examples of the inert solvent include methyl ethyl ketone, xylene, toluene, 1.1.1 torque chlorotin, dioxane, etc., and the amount added is preferably 5 to 30%. The wood with a high moisture content in the present invention refers to raw wood with a high moisture content or wood with a high moisture content. Specific adhesive application examples include wet lauan wood, plywood, birch, paulownia, rosewood, etc. Manufacture of plywood facing material to which sliced boards of 1 mm or less of high quality raw wood such as ebony are glued together.
These include gluing short lengths of raw wood for plywood, filling cracks in plywood raw wood, gluing frits of precious wood such as oak, etc. After gluing, rotary lace cutting, slicing with a sharp knife, or re-gluing are performed, followed by heating. It is dried and finished as a facing material or plywood. In reality, during processing, artificial immersion in water or hot water is performed to improve cutting workability, and heating and drying are performed to improve the adhesiveness that can withstand the force of shearing on the bonded surface, i.e. , compressive shear strength and water resistance are required. The adhesive composition of the present invention has a compressive shear strength (ASTMD905-49) of 15.0 kg/
cm ² or more, and no floatation is observed when boiling. Therefore, these requirements are fully satisfied. The urethane resin of the present invention satisfies the requirements required for adhesive applications for wood with a high moisture content as described above, namely: (1) It has excellent adhesion to wet surfaces, especially wood with a high moisture content. (2) Good compatibility with water and no foaming phenomenon occurs during curing. (3) Excellent water resistance; no swelling or peeling occurs even if boiled after adhesion. (4) The cured product is flexible, making it easy to process rotary races and slicing without damaging the cutting blade. (5) It has excellent heat resistance and does not suffer from inferior physical properties during heat drying. (6) It is one-component and has excellent workability. This fully satisfies the following. The present invention will be explained below with reference to Examples. However, in the examples and percentages are based on weight. Example (1) Method for producing urethane resin A predetermined amount of various polyoxyalkylene polyols was added to a 1-capacity four-necked flask equipped with a thermometer and a stirring device, and the temperature was increased in a nitrogen gas stream.
Raise the temperature to 120℃~130℃ and dehydrate for 60 minutes. Next, bring the temperature of the contents to 80 to 120℃, drop the organic polyisocyanate over 3 to 5 minutes, and then
React at 120°C for 1 to 2 hours. Then the temperature
Cool to 60°C, add an inert solvent, mix for 30 minutes, cool to 40°C, take out into a container, seal and store. (2) Workability of various urethane resins obtained in section (1),
Adhesion to wood and slice yield were evaluated. The results are shown in Table 1.

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Claims (1)

[Claims] 1 Random addition polymerization of alkylene oxide containing 50-90% ethylene oxide, molecular weight 3000~
9000 polyoxyalkylene triol and organic polyisocyanate at an NCO/OH equivalent ratio of 2 to 8.
1. An adhesive composition for wood having a high water content, characterized in that it is a urethane resin containing terminal isocyanate groups reacted with the urethane resin, or the urethane resin is blended with an inert solvent as required.