JPH11156820A - Production of particle board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase curing speed of a particle board excellent in water resistance and strength with the use of a melamine resin adhesive, and to improve productivity. SOLUTION: A urea resin and a liquid melamine urea resin adhesive obtained by reacting a mixture of formaldehyde/melamine/urea/methanol in a mole ratio of 2.2-6.0/1/0.1-1.0/0.05-1.0 are mixed in a ratio of 8/2-3/7, the mixture is added with wood chips to be hot-pressed. In this way, a particle board which indicates only a small variation of curing time in a blend ratio and does not require the change of press conditions and the amount of a curing agent.

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 a particle board by adding an adhesive made of a melamine resin and a urea resin to a wood chip and heating and compressing the chip.

[0002]

2. Description of the Related Art It is a well-known fact that woody boards such as particleboard, plywood, and wood fiberboard obtained by bonding thin boards, small pieces, fibers and the like of wood are useful for effective use of woody resources. . In particular, particle board is extremely useful because it recycles wood-based building waste, which is generated by about 10 million cubic meters per year, without incineration and effectively uses it. These wooden boards often use an amino adhesive, that is, a melamine resin, a melamine urea resin, a urea resin, or the like as the adhesive. As a method for producing a melamine urea-based adhesive, there are a method of producing melamine and urea by reacting them with formaldehyde simultaneously or sequentially in a reaction vessel, and a method of mixing melamine resin and urea resin separately prepared. According to the melamine urea adhesive manufactured by the latter method, for example, JIS A 59
08-1994 When manufacturing particle board that meets the M-type standard, it supports the mixing ratio of chips made of wood-based waste material and the specific gravity distribution of the waste material, as well as the user's unique required quality and water-resistant strength. Thus, the mixing ratio between the melamine resin and the urea resin can be arbitrarily changed.

[0003]

However, in order to efficiently manufacture boards satisfying various grades required by users, for example, in order to enhance water resistance,
It is a well-known fact that by increasing the blend ratio of the melamine-based adhesive, it is possible to correspond to various water-resistant grades.
Depending on the blend ratio, an unexplained phenomenon occurs in which the curing time after blending is delayed to nearly twice the original curing time, and the production conditions must be changed each time depending on the blend ratio. In addition, as a response to released formalin, which has become a social problem in recent years, resins with a reduced molar ratio of formalin have been manufactured, but the lower the molar ratio of this formalin, the longer the curing time after blending is significantly delayed. There is a problem.

As a countermeasure against the delay of the curing time, methods such as increasing the amount of the curing agent and extending the press time are adopted. However, even if the amount of the curing agent is increased by a certain amount or more, there is a limit in shortening the curing time. If the amount is extremely increased, the particle board is liable to be hydrolyzed, causing a problem in durability. Also, extending the press time reduces productivity,
Not realistic. Therefore, JIS A 5908
In the production of the M type board, a production method of arbitrarily changing the blend ratio of the melamine urea resin and the urea resin has not been established, and there is no melamine urea resin suitable for use.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to reduce the curing time in the mixed use of a melamine urea resin and a urea resin. It has been found that by blending, it is possible to obtain a melamine urea resin having excellent strength without prolonging the curing time, and the present invention for producing a particle board using the melamine urea resin has been completed. That is, the method for producing a particle board of the present invention comprises the steps of:
The molar ratio of formaldehyde: melamine: urea: methanol is (2.2-6.0) :( 1) :( 0.1-1.
0): The liquid melamine urea resin obtained by the reaction of (0.05 to 1.0) is mixed at a ratio of 8: 2 to 3: 7, added to the wood chips, and heated and pressed. It is assumed that.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. The liquid melamine urea resin adhesive according to the present invention is obtained by the following three-step reaction. First, formaldehyde, melamine, urea, and methanol were used as primary reactions at (2.2 to 6.0): (1.0): (0 to 1.
0): The reaction is performed at a molar ratio of (0.05 to 1.0). The reaction temperature is preferably from 65 to 90 ° C.
The reaction is performed for about 0 to 30 minutes. The initial pH of the primary reaction is preferably from 6.5 to 9, and if it is less than 6.5, it is difficult to control the reaction. The initial pH is the pH of formalin before adding urea and melamine.

[0007] The secondary reaction is carried out by adding urea and / or melamine to the reaction system all at once, dividedly or continuously. The reaction temperature is 65-85 ° C, and the reaction pH is 7.5-9.0. The reaction end point is determined by the cloudiness method. The end point of the secondary reaction is 20 to 35 ° C / 10 times. If the reaction is insufficient, the storage stability at 0 ° C. decreases. The reaction molar ratio after the addition of urea and / or melamine is as follows: formaldehyde, melamine, urea, methanol
3.5): (1.0): (0.1 to 1.0): (0.0
5 to 0.6).

In the subsequent tertiary reaction, the pH of the reaction system is adjusted to 10 to 1 with a catalyst such as NaOH or KOH while maintaining the reaction molar ratio.
Adjusted to 1.5. The end point of the tertiary reaction is 30 to 55 ° C / 5 times by the cloudiness method, preferably 40 to 50 ° C /
5 times. After the reaction has proceeded to a predetermined degree of condensation, the pH of the resin solution is adjusted to 9.5 to 11.0 and cooled to obtain the transparent liquid melamine urea resin of the present invention. The resin has a stability of more than 2 weeks throughout the year and has no abnormal thickening. The final pH adjustment greatly affects the storage stability in summer. The pH and reaction endpoint of each reaction step must be precisely controlled. The cloudiness method is a method of diluting a resin solution 5 or 10 times with water and then gradually cooling the solution to determine the degree of condensation of the resin at a temperature at which the resin solution starts clouding.

In the present invention, the liquid melamine urea resin obtained by the above reaction is mixed with a urea resin and used as an adhesive for wood chips. The urea resin used in the present invention is not particularly limited, and is an ordinary water-based urea resin adhesive, which is provided for the production of plywood and particle board. The mixing ratio of the liquid melamine urea resin and the urea resin is
If the weight ratio is 8: 2 to 3: 7, and the ratio of the liquid melamine urea resin exceeds 8, the cost increases,
If it is less than 3, the water resistance becomes insufficient, which is not preferable.
The liquid melamine urea resin is mixed with the urea resin immediately after the liquid melamine urea resin is manufactured and immediately before use by mixing while stirring in a regulating tank or tank equipped with a stirrer, or a line mixer installed in a pipe. And mix. After mixing, the particles can be sprayed onto chips in the blender, or mixed in such a manner that each resin is simultaneously sprayed into the blender through individual lines, and then heated and pressed to obtain a particle board. As described above, after mixing the liquid melamine urea resin adhesive and the isocyanate-based adhesive or separately attaching them to a wood chip, a wood fiber, a veneer or the like, they are heated and pressed to obtain a wood board.

In the method of the present invention, since the adhesive used has the same pot life and viscosity as the conventional amino resin, the step of adhering it to wood chips, wood fibers or veneers can be easily carried out with existing equipment. Can do things. Further, since the curability of the adhesive is equal to or higher than that of the conventional amino resin, an existing hot press can be used. As the curing conditions, almost the same conditions as those of a conventional melamine resin or the like can be adopted. The amount of the curing agent is 0.5 to 1 in the surface layer with respect to the adhesive.
wt%, about 1 to 3% for the core layer, and the addition amount of the adhesive is preferably 9 to 12 wt% for the surface layer and 3 to 9 wt% for the core layer with respect to the wood chip, wood fiber or veneer. . Furthermore, there is no problem even if paraffin wax or the like is added as a water repellent.

[0011]

(Production of melamine urea resin)

Production Example 1 (Production of New Melamine Urea Resin) First, the primary reaction was performed using formaldehyde, melamine, urea, and methanol as (7): (1.0): (1.13):
The reaction is performed at a molar ratio of (0.5). Reaction temperature is 80 ° C
And react for 20 minutes after the monomer is dissolved. The initial pH of the primary reaction is 8.0. In the secondary reaction, urea and melamine are further added to the reaction system by formaldehyde: melamine: urea (2.52) :( 1.0) :( 0.5) :( 0.5)
Melamine and urea are added all at once such that the molar ratio is as follows. The reaction temperature is 70 ° C, and the end point of the secondary reaction is 25 ° C / 10 times by the cloudiness method. In the subsequent tertiary reaction, the reaction system was adjusted to pH 11.5 using NaOH, and the reaction temperature was adjusted to 7
At 0 ° C, the reaction was advanced to 45 ° C / 5 times in the cloudiness method.
After adjusting H to 10.5 using formic acid, the mixture is cooled to obtain a transparent melamine urea resin adhesive. This resin is 0-3
It had good flowability at 5 ° C for more than 2 weeks. The resin characteristic values of this resin are as follows: solid content 65%, specific gravity 1.29, pH 1
0.5, viscosity 180 cp, free formalin value 0.3% or less.

Production Example 2 (Conventional Production of Melamine Urea Resin) Formaldehyde, melamine, urea and methanol are reacted in a molar ratio of (2.52) :( 1) :( 0.2) :( 1.33). Reaction temperature is 80 ° C. For the initial pH, a specified amount of NaOH is added, and the reaction proceeds at pH 12. The end point of the reaction was determined by water miscibility, and 7 to 8 times / 20 ° C by the cloudiness method.
It is. Thereafter, the pH of the resin solution was adjusted to 11.0 with formic acid.
After cooling, a transparent melamine urea resin adhesive is obtained.

[Measurement of Curing Time of Resin] Curing time was measured at each mixing ratio of each melamine urea resin and urea resin. Melamine urea resin and urea resin in a polycup 8:
It is added at a ratio of 2-2: 8 and mixed and stirred by a stirrer. 1 part of 25% ammonia water and 1 part of ammonium chloride are added to 100 parts of the resin after mixing, and mixed and stirred for 5 minutes. Weigh 5 g of the resin solution in a test tube,
Immersed in warm water and measured the time based on JIS.
The results are shown in FIG.

[Manufacture of Particle Board] Manufacturing conditions of particle board Board style: 3-layer board Chip used: (surface layer) Rawan, (core layer) Rawan Chip composition ratio: (surface layer: core layer = 1: 2) Resin spraying Before chip moisture content: Surface layer 4%, core layer 2% Resin sprayed chip moisture content: Surface layer 18%, core layer 8% Resin spray rate: surface layer 13%, core layer 7% Set board thickness; 16mm Set board specific gravity 0.76 hot-press temperature; 185 ° C hot-press time: 2 minutes 30 seconds, 3 minutes, 3 minutes 30 seconds, 4 minutes, 4 minutes 30 seconds Curing agent: appearance of adhesive prepared in Examples 1 and 2 10
One part of ammonium chloride and one part of 25% aqueous ammonia were added to 0 parts.

Under the above conditions as basic conditions, particle boards were manufactured at various mixing ratios of each melamine urea resin adhesive and urea resin, and the results of the tests are shown in FIGS. 2, 3 and 4. The residual ratio is the value of the wet bending strength expressed in% when the value of the normal bending strength is 100. The board test was performed according to JIS A5908-1994.

[0016]

According to the method of the present invention, the variation of the curing time in the blend ratio is small, and the particle board can be manufactured without changing the pressing conditions and the amount of the curing agent. It is possible to arbitrarily change the blend ratio of the adhesive in accordance with the manufacture of the standard, and as in the past, the curing time is delayed by the blend ratio, and the curing does not become insufficient even with the same amount of the curing agent and the same pressing time ,
Productivity is improved. In addition, the melamine resin used in the present invention has high reactivity and, compared with the conventional melamine urea resin, can obtain a high strength in terms of physical properties, so that the addition ratio of the melamine resin can be reduced, and the strength is maintained. The cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the mixing ratio of urea resin / melamine resin and the curing time.

FIG. 2 is a graph showing a comparison of normal bending strength according to a blend ratio of a current melamine urea resin and a urea resin.

FIG. 3 is a graph showing a comparison of a normal bending strength according to a blend ratio of a novel melamine urea resin and a urea resin.

FIG. 4 is a diagram showing a comparison of the residual ratio between a current melamine urea resin and a new melamine urea resin.

Claims (1)

[Claims] 1. A urea resin having a formaldehyde: melamine: urea: methanol molar ratio of (2.2 to 6.0):
(1): The liquid melamine urea resin adhesive obtained by reacting with (0.1-1.0) :( 0.05-1.0)
Mix at a ratio of 8: 2 to 3: 7 and add to the wood chips,
A method for producing a particle board, comprising heating and pressing.