JPH0957716A - Particle board with less amount of formalin released - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the amt. of formalin released by a method wherein chips for the surface layer are coated with a phenol resin adhesive with a pH in a specified range and chips for the core layer are coated with a methylene diphenyldiisocyanate(MDI) resin adhesive and after forming, they are molded into a sheet by heat pressing. SOLUTION: At first, wooden waste materials are ground and sifted by an ordinary means to obtain fine particle chips for the surface layer and wood piece chips for the core layer. A phenol resin with a pH of 4-9 as an adhesive for the surface layer and an MDI resin for an adhesive for the core resin are respectively applied. Thereafter, the chips for the surface layer on the bottom part, the chips for the core layer and finally, the chips for the surface layer again are formed into three layers. Then, they are heat-pressed into a sheet from both sides. As the amt. of formalin released as the adhesive is small, there exists no possibility to feel pains in eyes and throat and to feel ill caused by odor. As there exists no decrease in productivity, it is possible to manufacture it by the same method as the ordinary method for manufacturing the particle board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing particle board which releases a small amount of formalin.

[0002]

2. Description of the Related Art In the manufacture of particle boards, wood chips that are subdivided into small pieces
It is manufactured by applying a thermosetting resin of melamine co-condensation system, melamine system, or phenol system, forming and hot pressing into a plate shape from both sides. In addition, since the wood chip, which is a raw material for particleboard, is usually made of wood waste material as a main raw material, it is inexpensive and has uniform quality, and is therefore widely used for furniture and building members.

[0003]

The adhesive for particle board is produced by condensation and addition reaction of the thermosetting resin and formalin (formaldehyde) in order to improve the adhesive performance and shorten the heat pressing time. . When using the manufactured particle board for furniture and building materials,
Depending on the place of use and conditions of use, formalin may be released and released, which may hurt the eyes, the throat, or the odor may make you feel unwell. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a particle board that releases a small amount of formalin.

[0004]

[Means for Solving the Problems] As means for solving the problems, methylenediphenyl diisocyanate resin (hereinafter referred to as MDI resin), which is known not to release formalin to an adhesive, and acidity of PH3 or less have been known. Attempts have been made to use phenolic resins, alkali phenolic resins with a pH of 10 or above, but MDI resins adhere to the metal because they adhere to the metal, and adhesion to the press hot platen is a problem. There was a problem in productivity reduction such that the storage time (pot life) of the subsequent wood chips was shortened and it was necessary to extend the heat pressing time. When MDI resin is used for the core layer adhesive and acidic phenol resin is used for the surface layer adhesive to shorten the heat pressing time, there is a risk of curing inhibition between the layers of the particle board and peeling. It was If MDI resin is used for the core layer adhesive and alkali phenol resin is used for the surface layer adhesive, the reaction may be abnormally promoted and there is a risk of peeling between the layers of the particle board, or for building materials. When used as, reddish-brown drips were sometimes generated by rainwater. Therefore, according to the method for producing a particle board having a small amount of formalin released according to claim 1, the surface chip is provided with a PH.
4 to 9 of a phenol resin adhesive is applied, the core layer chip is coated with the MDI resin adhesive and formed, and then heat-pressed into a plate shape.

[0005]

In the method of manufacturing a particle board according to the first aspect, the heat pressing time is almost the same as that of the particle board manufactured by the ordinary method, and the productivity is not deteriorated. And since there is almost no formalin released, it does not hurt the eyes, the throat, and the odor does not cause sickness. It is a known fact that the phenol resin used as the adhesive for the surface layer has a smaller amount of formalin released than other thermosetting resins such as urea and melamine. In addition, in the case of phenol resin, the carbon that constitutes the benzene ring and the nitrogen that constitutes the amino group in the case of urea and melamine and formalin condense and add, but since carbon has a stronger binding force than nitrogen, it is released. It is believed that less formalin is released. In the case of the MDI resin used as the adhesive for the core layer, formalin is unnecessary and is not used, and formalin is not necessarily released. Further, the reason why the phenol resin is limited to the range of PH4 to 9 is that there is no problem such as peeling between layers, which is observed when an acidic phenol resin having a pH of 3 or less and an alkaline phenol resin having a pH of 10 or more is used.

[0006]

Embodiments of the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is a cross-sectional view of a particle board according to an embodiment of the present invention, which releases a small amount of formalin.

First, a wood waste material or the like is crushed and sieved by an ordinary means to obtain fine particle chips for the surface layer and wood chip chips for the core layer having a thickness of 0.2 to 0.8 mm and a length of 5 to 20 mm. . After applying a phenol resin having a pH of 4 to 9 as a surface layer adhesive in an amount of about 3 to 5 kg / m3 and an MDI resin as an adhesive for a core layer in an amount of about 1 to 3 kg / m3, a surface layer chip at the bottom as shown in FIG. The core chip and finally the surface chip were formed into three layers. Then, the plate was heat-pressed from both sides. The hot pressing conditions are a temperature of 150 to 170 ° C. and a pressure of 20 to 30 kgf /
It is about cm2.

Next, a method for producing a phenol resin having a pH of 4 to 9 will be described. The formalin and phenol are mixed at a molar ratio of 1 to 1.6 to 1 and reacted at a temperature of 60 to 95 ° C. with caustic soda or hydrochloric acid as a catalyst. Reaction progresses,
When the resin and water are separated, the reaction end point is determined, and the nonionic surfactant is added in an amount of 0.1 to 0.1 at a temperature of 60 to 95 ° C.
5% was added, and the mixture was vigorously stirred and dispersed in water to prepare an emulsion type. A protective colloid agent such as polyvinyl alcohol (PVA) may be added to stabilize the emulsion. The end point of the reaction is when the ratio of resin to water is about 3 to 5 to 1 at 25 ° C.

It should be noted that the phenol resins having a pH of 3 or less and the pH of 10 or more are water-soluble, but the phenol resins having a pH of 4 to 9 cannot be water-soluble and must be dissolved in a solvent such as methanol, which makes cleaning difficult. However, use of a solvent causes problems such as attention to fire, workability such as use of explosion-proof equipment, and cost, so it should be an emulsion type so that it does not interfere with work.

[0010]

As is apparent from the above description, the method for producing a particle board having a small amount of formalin released according to claim 1 is a phenol resin having a pH of 4 to 9 for the surface layer as an adhesive having a small amount of formalin released. And MDI resin system is used for the core layer. Since the amount of formalin released as an adhesive is small, not only does it hurt the eyes, the throat, and the odor does not make you feel uncomfortable. It can be manufactured by the method.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a particle board obtained by a method for manufacturing a particle board according to an embodiment of the present invention.

[Explanation of symbols]

10 Three-layer structure particle board 11 Surface layer formed using a phenol resin of PH4 to 9 as an adhesive 12 Core layer formed using an MDI resin system as an adhesive

Claims (1)

[Claims] 1. A surface layer wood chip chip is coated with a PH4-9 phenol resin adhesive, a core layer wood chip chip is coated with methylenediphenyldiisocyanate resin adhesive, and then formed into a plate, followed by heat pressing. A method for producing a three-layer structure particle board which releases a small amount of formalin, characterized by being molded.