JPS6123954B2 - - Google Patents

Description

[Detailed description of the invention]

An object of the present invention is to provide a method for producing a urea resin adhesive that is highly condensed, exhibits excellent water solubility, and has little formalin odor. Conventionally, urea resin adhesives commonly used for wood use resins with a low degree of condensation. When a urea resin adhesive with a low degree of condensation is applied to wood, the adhesive penetrates into the wood, resulting in poor adhesive efficiency. In order to prevent adhesive penetration, thickeners, fillers, etc. are used to increase the viscosity. Increasing the degree of condensation is also thought to be effective in preventing penetration, but increasing the degree of condensation deteriorates stability and water solubility, so it has not been put to practical use. Also, when applying urea resin adhesive to wood chips for particle board, ideally the surface of the wood chips should be coated with the adhesive, but if the adhesive becomes highly viscous, the adhesive may be applied evenly. I can't do that. When a urea resin adhesive with a low degree of condensation is applied to wood chips, the adhesive penetrates into the wood chips. Furthermore, when wood chips coated with adhesive are hot-pressed, the adhesive penetrates into the wood chips, reducing the efficiency of the adhesive. In the present invention, after producing a urea resin with a high degree of condensation, formalin is further added, the reaction is continued, methylol groups are introduced, and then urea is added to remove excess formalin. Although the urea resin adhesive thus produced is highly condensed, it exhibits excellent water solubility and has little formalin odor. The method of the present invention is as follows. That is, formalin and urea are reacted at pH 6.6 to 7.6, then adjusted to pH 4.4 to 5.0 with acid, reacted under heating, and heated at 40°C.
A urea resin characterized in that when the above reaction solution becomes cloudy when dropped into the above water, it is neutralized with an alkali, then further formalin is added and reacted, and then urea is added and reacted, and then dehydrated and concentrated. The gist of this article is a method for manufacturing adhesives. The present invention will be explained in more detail below. In the present invention, the point at which the above reaction solution becomes cloudy when dropped into water at 40°C or higher is generally the point at which the reaction solution becomes cloudy when dropped into water at 20 to 30°C, the reaction is stopped and the reaction is neutralized with alkali. do. This is because if the reaction is stopped at a higher temperature, the degree of condensation increases, resulting in poor stability and water solubility. The initial molar ratio of formalin and urea in the present invention is preferably 1.7 to 2.4 for formalin to 1 for urea. If it exceeds 2.4, the reaction is too slow, and if it is less than 1.7, turbidity will occur during the reaction. The final molar ratio of formalin and urea in the present invention is preferably 1.15 to 1.6 for formalin to 1 for urea. If it exceeds 1.6, the formalin smell becomes strong.
If it is less than 1.15, the adhesive is unstable. Neutralization in the present invention does not have a strict meaning;
You can make acidic things closer to neutrality or even more than neutrality (PH7.0). This invention refers to the range of pH 6.6 to 7.6. The present invention will be explained by giving examples. Example 1 324g of 37% formalin and 120g of urea at pH7.0-7.2
After adjusting the pH to 4.6-4.8 with 20% acetic acid, the reaction was continued at 90°C. When the water temperature becomes cloudy at 60°C (when one drop of the reaction solution is dropped into water at 60°C, it becomes slightly cloudy), add 20% caustic soda to PH.
After adjusting the temperature to 6.8-7.0, 62g of 37% formalin was added and the reaction was continued at 90℃ for 1 hour.
g was added and reacted at 80°C for 30 minutes, followed by dehydration and concentration to obtain a urea resin adhesive with a solid content of 60%. This resin became cloudy at a water temperature of 30°C. Example 2 316g of 37% formalin and 120g of urea at pH7.0-7.2
After adjusting the pH to 4.6-4.8 with 20% formic acid, the reaction was continued at 90°C. When the water temperature becomes cloudy at 50℃ (it becomes slightly cloudy when one drop of the reaction solution is dropped into water at 50℃), the pH becomes 7.2 with 20% caustic soda.
After adjusting to -7.4, 70g of 37% formalin was added, the reaction was continued at 90℃ for 1 hour, 100g of urea was added, the reaction was continued at 80℃ for 10 minutes, and the solid content was dehydrated and concentrated.
A 60% urea resin adhesive was obtained. This resin has a water temperature of 25
It became cloudy at ℃. Example 3 550g of 37% formalin and 204g of urea at pH7.0-7.2
After adjusting the pH to 4.6-4.8 with 20% acetic acid, the reaction was continued at 90°C. When the water temperature becomes cloudy at 60°C, adjust the pH to 7.0-7.2 with 20% caustic soda, then add 163g of 37% formalin and boil at 90°C.
After continuing the reaction for 20 minutes, 204 g of urea was added.
The reaction was continued at 80°C until the system became cloudy and then dehydrated and concentrated to obtain a urea resin adhesive with a solid content of 60%. This resin became cloudy at a water temperature of 40°C. Comparative example 1 324g of 37% formalin and 120g of urea at pH7.0-7.2
After adjusting the pH to 4.6-4.8 with 20% formic acid, the reaction was continued at 90°C. When the water temperature is 30℃ and becomes cloudy, adjust the pH to 6.8-7.0 with 20% caustic soda.
After adding 64 g of urea and reacting at 80° C. for 15 minutes, the mixture was dehydrated and concentrated to obtain a urea resin adhesive with a solid content of 60%. The adhesives of Examples and Comparative Examples were applied to rawan chips at a solid content of 10% (hardening agent addition amount, resin liquid
(1 part by weight per 100 parts by weight). Using this chip, the temperature was 165℃ and the pressure was 20Kg/cm ² . Specific gravity in 4 minutes
0.70, 12mm thick particle board was manufactured. The test results are shown in the table below.

[Table] The test was conducted in accordance with JIS A-5908. The present invention has the following effects based on the above-mentioned constituent elements. Although the urea resin adhesive obtained by the production method of the present invention is highly condensed, it exhibits excellent water solubility and has the effect of having little formalin odor. The manufactured particle board is resistant to swelling and has high bending strength and peel strength.

Claims (1)

[Claims] 1. React formalin and urea at a pH of 8.6 to 7.6 by adjusting the molar ratio of formalin and urea to 1 urea to 1.7 to 2.4 formalin, and then reduce the pH with acid.
Adjust the temperature to 4.4 to 5.0 and react under heat. When the above reaction solution becomes cloudy when dropped into water at 40℃ or higher, neutralize with alkali. After that, formalin is further added and reacted, and then formalin and urea are mixed. A method for producing a urea resin adhesive, which comprises adding and reacting urea such that the final molar ratio of formalin to 1 urea is 1.15 to 1.6, followed by dehydration and concentration.