JPS6117876B2 - - 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 prepolymer 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.
Requires heating, formalin remains even after bonding,
Unfavorable in terms of odor, environmental stability, and hygiene. Additionally, it has very weak adhesion to wood with high moisture content.
Regarding urethane prepolymer adhesives, please refer to Japanese Patent Publication No. 31-2691, Japanese Patent Publication No. 8888-1988, Japanese Patent Publication No. 9586-1986, Japanese Patent Publication No. 32-35, and Japanese Patent Publication No. 49-1988.
No. 30429, JP-A-49-75704, JP-A-49-86506
No., JP-A-49-118807, JP-A-49-118808,
The characteristics and composition are detailed in publications such as JP-A-49-118805. These urethane prepolymers 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, an uncut EO-tipped polyoxyalkylene triol with an average molecular weight of 1,500 to 10,000 and a molecular terminal EO content of 5 to 30% obtained by addition polymerizing ethylene oxide (hereinafter referred to as EO) to the molecular terminal of polyoxypropylene triol. and an organic polyisocyanate at an NCO/OH equivalent ratio of 2 to 8 to form a terminal isocyanate group-containing urethane prepolymer, or the urethane prepolymer is blended with an inert solvent as necessary. An improved high moisture content wood adhesive composition. The wood adhesive composition with a high moisture content, that is, the urethane prepolymer used in the present invention uses, as a polyol component, an EO-terminated polyoxyalkylene triol with excellent wood adsorption properties. The terminal EO-tipped polyoxyalkylene triol used in the present invention is a polyoxypropylene triol obtained by addition-polymerizing PO to an active hydrogen group, and further has EO added to the molecular terminal, and has an average molecular weight of is from 1500
10000, and the molecular terminal EO content is 5 to 5.
30%. These are manufactured using known techniques. Next, regarding the number of hydroxyl groups regarding the terminal EO chipped polyoxyalkylene triol, if it has 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, 4,6
And in the case of 8, the reaction with the organic polyisocyanate is very fast and cross-linked, resulting in thickening or gelling phenomena, making industrial production difficult. For example, even if a urethane prepolymer is obtained, 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. Next, regarding the average molecular weight of terminal EO chipped polyoxyalkylene triol,
In the case of less than 1500, the content of urethane groups in the polymer increases, and the viscosity of the obtained urethane prepolymer is extremely high. If it exceeds 10,000, the viscosity of the terminal EO-tipped polyoxyalkylene triol itself is high, making industrial production difficult. Next, regarding the formation of alkylene oxide addition polymerization of terminal EO-tipped polyoxyalkylene triol, when alkylene oxide is addition-polymerized to terminal EO-tipped polyoxyalkylene triol, the obtained urethane prepolymer has excellent surfactant ability, and therefore has excellent wettability. It has excellent permeability to surfaces and good adhesion. As in the present invention, the average molecular weight is 1500 to 10000,
Only the terminal EO chipped polyoxyalkylene triol containing 5 to 30 molecules of EO at the end and forming a polyoxyethylene chain at the end of the molecule can be used as an excellent wood adhesive composition with a high moisture content without the above drawbacks. Become. The organic polyisocyanate to be reacted with the terminal EO-tipped polyoxyalkylene triol is toluene diisocyanate (2,4/2,
6 isomer ratio 80/20), 4,4 or polydiphenylmethane diisocyanate, naphthalene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, etc. When used, they are used alone or in combination. The reaction ratio between the terminal EO chipped polyoxyalkylene triol and the organic polyisocyanate is
If the NCO/OH equivalent ratio is 2 to 8, but less than 2, the viscosity of the urethane resin will be high and the storage stability will be poor. 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 to add an inert solvent having no active hydrogen groups to these urethane resins. The inert solvent is methyl ethyl ketone, xylene, toluene, 1.1.1 trichloroethane, 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, and specific adhesive application examples include wet lauan wood, plywood, birch wood, etc.
Manufacture of plywood facing materials for gluing sliced boards of 1 mm or less of high-quality raw wood such as paulownia, rosewood, and ebony, gluing of short lengths of raw wood for plywood, filling and adhesion of cracks of raw wood for plywood, and fritting of precious wood such as oak. Adhesion etc.
After adhesion, the material is rotary lace cut, sliced with a sharp knife, or re-adhered, and then heated and dried to form 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 (ASTMD 905-49) of 19.0 kg/
cm ² or more, and no floatation is observed when boiling. Therefore, these requirements are fully satisfied. The urethane prepolymer of the present invention satisfies the requirements required for adhesive application of 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, has a long pot life, and is easy to work with. 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 prepolymer 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, the content temperature is set to 80 to 120℃, organic polyisocyanate is added dropwise for 3 to 5 minutes, and 80℃ to 120℃ is added.
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) The workability, adhesion to wood, and slice yield of the various urethane prepolymers obtained in section (1) were evaluated. The results are shown in Table 1.

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【table】

【table】

Claims (1)

[Claims] 1 EO-tip polyoxyalkylene triol with an average molecular weight of 1,500 to 10,000 and an EO content of 5 to 30% at the molecular terminal obtained by addition polymerizing ethylene oxide (hereinafter referred to as EO) to the molecular terminal of polyoxypropylene triol and an organic polyol. A urethane prepolymer containing terminal isocyanate groups, which is obtained by reacting isocyanate with an NCO/OH equivalent ratio of 2 to 8.
Or an improved wood adhesive composition with a high water content, characterized in that the urethane polymer is blended with an inert solvent as required.