JPH11181388A - Adhesive composition for wooden board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wooded board that satisfied the E-O specification of JIS relating to the amt. of formaldehyde released from a boards which has not been achievable by conventional melamine resin adhesive. SOLUTION: The objective adhesive compsn. is based on a melamine- formaldehyde resin which is prepd. by the condensation of melamine and aldehydes in the presence of a basic phosphate (e.g. sodium secondary phosphate) provided the equivalent ratio of formaldehyde to amino group in the reaction is 0.44-0.52 and hexamethylenetetramine is added after the reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melamine / formaldehyde resin adhesive for wood (hereinafter referred to as "melamine resin adhesive"), and more particularly, to an adhesive for a wood board capable of producing a wood board with a low formaldehyde emission. Composition.

[0002]

2. Description of the Related Art In recent years, health problems caused by indoor contamination of formalin have been highlighted, and particle boards,
E-0 standard (0.5 mg / l or less) as a JIS standard of formaldehyde emission amount (hereinafter, referred to as F emission amount) with respect to a wood board represented by a fiberboard (hardboard, MDF) and oriented strand board. Is required.

In a conventional amino resin adhesive composition, the equivalent ratio of formaldehyde to amino groups (hereinafter referred to as F / -NH
_When the equivalent ratio is set to 0.40 to 0.46, the amount of F released from the wood-based boards becomes 0.5 mg / l or less.
Although it meets the IS E-0 standard, there is a limit to such a reduction in the F / -NH ₂ equivalent ratio due to limitations on resin viscosity, water solubility, solubility of melamine during the reaction, and curability. E
Meeting the −0 standard has been difficult.

In the condensation reaction of melamine and formaldehyde, usually, in a pH range of 7 to 8.5 using an alkali catalyst, if the F / -NH ₂ equivalent ratio is less than 0.7, the melting temperature of melamine is too high and long. It takes time, and
The apparent reaction proceeded quickly, and it was difficult to control the reaction.

[0005] Usually, a hydroxyl group such as a caustic catalyst or a barium hydroxide catalyst serves as a reaction catalyst in the condensation reaction of a melamine resin. In the condensation reaction of a melamine resin, F / -NH _{2 is used.}
When the equivalent ratio is less than 0.7, melamine is promoted to be methylene, and there is a disadvantage that storage stability at low temperature is inferior.

An organic alkali catalyst such as hexamethylenetetramine, triethanolamine, triethylenediamine, etc. does not provide sufficient water solubility of a melamine resin.

Next, as a method of reducing the amount of F emission,
When urea is added as a formaldehyde catcher, the amount of F released is reduced, but the adhesive strength is significantly reduced by the water-resistant treatment.

Further, polyallylamine is considered as a formaldehyde catcher. However, if it is added, it reacts immediately with formaldehyde to form a polyallylamine / formaldehyde resin, which is difficult to spray on wood chips.

Further, the F / -NH ₂ equivalent ratio is 1.0-3.
It is conceivable to add an ammonium compound such as ammonium sulfate or ammonium acetate, which is an amino-based compound, or aqueous ammonia to the melamine resin of No. 0 as a formalin catcher, but these compounds react with formaldehyde quickly and adhere to form a gel. It was unsuitable as an agent composition.

Next, hexamethylenetetramine (hereinafter, referred to as "hexamethylenetetramine")
Hexamine) is used as a curing agent, but F /
When added to the melamine resin in a region where the -NH ₂ equivalent ratio is higher than 0.7, the gel time of the mixed size liquid was prolonged and the curing tended to be inhibited.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a wood-based board, which has been difficult to meet the JIS E-0 standard for a conventional melamine resin adhesive, with less deterioration in bending strength due to water resistance treatment. , Meet 18 types of JIS standard,
It is still another object of the present invention to provide an adhesive composition for a melamine resin wood-based board which can produce a wood-based board having an E-0 standard, which is a JIS standard F release amount.

[0012]

The present invention relates to a melamine resin obtained by condensing melamine and aldehydes in the presence of a basic phosphate, wherein the equivalent ratio of formaldehyde to amine groups at the time of reaction is 0.44 to 0.44. 0.52, preferably, after the reaction, hexamine is added so that formaldehyde generated by decomposition thereof is 0.02 to 0.05 with respect to the equivalent of amino group of the melamine resin. And a wood-based board-like adhesive composition.

In order to reduce the amount of F released from the wood board, it is necessary to reduce the F / -NH ₂ equivalent ratio of the melamine resin adhesive. The present inventors have found that the F / -NH ₂ equivalent ratio is a range where the F release amount satisfies the E-0 standard of 0.44 to 0.52.
In the condensation reaction of the melamine resin in the range described above, if the reaction is carried out with a basic phosphate (hereinafter referred to as phosphate) in the range of 7.5 to 9.5 instead of the caustic catalyst, methylol is formed. The reaction and the methyleneation reaction occur in equilibrium due to the steric hindrance of the phosphate ion, and have good low-temperature storage properties.
He found that a melamine resin capable of shortening the gel time was obtained.Furthermore, hexamine was decomposed into formaldehyde and ammonia in the alkaline region, and when reacted in a low pH region, the gel time of the melamine resin adhesive could be reduced. I noticed that there is. And F / -NH ₂
An area having a low pH at an equivalent ratio of 0.44 to 0.52, that is,
The pH was adjusted to 7.5 to 9.5 with a phosphate, and melamine / formaldehyde was co-condensed to obtain a melamine resin adhesive. Then, hexamine was added, and F was decomposed by formaldehyde generated by decomposition. By increasing the / —NH ₂ equivalent ratio in the range of 0.02 to 0.05, there is no decrease in the adhesive strength due to the water resistance treatment (satisfies the P board standard), the F release amount satisfies the E-0 standard, Further, an adhesive composition capable of obtaining a JIS standard 18-type wood-based board has been obtained.

Preferred specific examples include F / -NH
_The pH of formaldehyde and melamine is adjusted to 6.8 to 7. with phosphate so that the _two equivalent ratio is in the range of 1.0 to 2.5.
5 and usually reacted under reflux or at a temperature of 90 ° C. or higher for 20 to 40 minutes, then melamine was added secondarily, and the F / —NH ₂ equivalent ratio was adjusted to 0.44 to 0.52. In addition, the temperature is usually 20 ° C. under reflux or at a temperature of 90 ° C. or more.
Incubate for ~ 40 minutes. Thereafter, the mixture is cooled to 70 to 85 ° C. and reacted until the cloudiness point of the resin (measuring method: the temperature at which the mixed solution of resin / water is 6/9 becomes cloudy) becomes 25 to 55 ° C. Get the agent. Further, hexamine is added, and the F / -NH ₂ equivalent ratio of formaldehyde generated by decomposition from hexamine is 0.02 to 0.2.
It is possible to obtain a wood board in which the amount of F release satisfies the E-0 standard without lowering the adhesive performance by increasing the size by 0.05.

That is, according to the present invention, the final F / -NH ₂ equivalent ratio is adjusted to 0.44 to 0.52, and no urea is applied at the time of producing a wood board, and the JIS E-0 standard is not used. The aim is to obtain a stable wooden board. The reason why the co-condensation reaction between formaldehyde and melamine is carried out as the primary reaction is that the condensation reaction proceeds in the range of an F / -NH ₂ equivalent ratio of 1.0 to 2.5 to produce a high-molecular-weight melamine resin. If the equivalent ratio is less than 1.0, a high molecular weight melamine resin cannot be obtained, and if the equivalent ratio exceeds 2.5, it is difficult to reduce the F / -NH ₂ equivalent ratio by adding secondary melamine.
If the F / -NH ₂ equivalent ratio is less than 0.44 in the secondary reaction, the adhesion reliability of the melamine resin is not sufficient,
If the value exceeds, the E-0 standard cannot be stably obtained.

Next, the amount of formaldehyde generated by the decomposition of hexamine with respect to the amino group is 0.02 in equivalent ratio.
The reason for setting it to 0.05 is that if it is less than 0.02, the amount of formaldehyde generated by decomposition is small, and sufficient adhesive strength cannot be obtained. If it exceeds 0.05, ammonia generated by decomposition degrades the curing. And sufficient bending strength cannot be obtained.

Further, in the co-condensation reaction of melamine and formaldehyde, the pH during the reaction is adjusted to 7.5 to 9.5. If the pH is lower than 7.5, the melamine solubility becomes poor,
Since the condensation reaction does not proceed sufficiently, if the pH exceeds 9.5, the gel time of the melamine resin adhesive is not sufficiently reduced, and the amount of F release from the plywood is not sufficiently reduced.

The reason why the reaction after the addition of the secondary melamine is terminated at 25 to 55 ° C. at the cloudiness point is that the condensation reaction is not sufficient at less than 25 ° C., the matte moldability is not good, and the melamine The water solubility of the resin adhesive is inferior, making it difficult to spray the wood chips.

The melamine resin adhesive used in the present invention is obtained by reacting melamine and formaldehyde. For the purpose of improving the mat formability and preventing drying, polyvinyl alcohol, ethylene glycol, diethylene glycol, polyvinyl butyral and the like are used. A resin using a partially modified modified resin may be used. These modifiers are preferably added when the condensation reaction of melamine and formaldehyde is completed and the mixture is cooled.

Hexamine of the melamine resin adhesive obtained as described above is usually decomposed into formaldehyde and ammonia by adding hexamine to the alkaline resin adhesive at the time of preparing the paste liquid.

The basic phosphate used in the present invention includes sodium phosphate, dibasic sodium phosphate, potassium phosphate, dibasic potassium phosphate, calcium phosphate and the like. Preferably, dibasic sodium phosphate is used. Optimal.

The adhesive composition of the present invention comprises a water repellent, water,
It is also possible to add and mix a curing accelerator and the like as needed.

[0023]

Next, the present invention will be described based on embodiments.

Adhesive Preparation Example 1 42 parts by weight of melamine, 162.2 parts by weight of 37% formalin (F / -NH ₂ equivalent ratio: 2.0) and dibasic sodium phosphate were adjusted to a pH of about 7.5. And reacted under reflux conditions for 30 minutes. Thereafter, 148.9 parts by weight of melamine was added (F / -NH ₂ equivalent ratio: 0.44), the pH was adjusted to about 8.1 with sodium phosphate dibasic, and about 80 ° C.
The white turbid point was measured at a resin adhesive / water ratio of 6/9. When the white turbid point reached about 30 ° C., heating was terminated and cooling was performed.

Adhesive Production Example 2 42 parts by weight of melamine, 64.8 parts by weight of 37% formalin (F / -NH ₂ equivalent ratio: 0.8) and caustic soda were pH adjusted.
Was added at about 11.0 and reacted at a temperature of 90 ° C. When the white turbidity reached 30 ° C., the heating was terminated and cooled. The solid content of the resin adhesive obtained in each of the above production examples was adjusted to be about 48%.

Example 1 The melamine resin adhesive (A) 1 obtained in Adhesive Production Example 1
1 part by weight of ammonium chloride and 1.5 parts by weight of hexamine were added to 00 parts by weight, and 3 parts by weight of a water repellent (Cerogol A, manufactured by Chukyo Yushi) was added and stirred to obtain a size liquid.
%, A design thickness: 15 mm, a design specific gravity: 0.75, an adhesive is sprayed such that the solid content of the melamine resin is 9% or less, and after forming the mat, 170 ° C., 30 kg / cm. Heating and pressing was performed for 3 minutes and 45 seconds in ² to obtain a single-layer particle board.

Comparative Example 1 A single-layer particle board was prepared in exactly the same manner as in Example except that hexamine was not added to the melamine resin adhesive (A) obtained in Adhesive Production Example 1.

Comparative Example 2 Using the melamine adhesive (B) obtained in Adhesive Production Example 2, a single-layer particle board was prepared in exactly the same manner as in Example except that hexamine was not added.

The formulations for adjusting the size liquid are summarized in Table 1. Table 1 ─────────────────────────────── Example 1 Comparative Example 1 Comparative Example 2 ──────── ─────────────────────── Melamine resin adhesive (A) 100 100 Melamine resin adhesive (B) 100 Ammonium chloride 111 Hexamethylenetetramine 1. 5 Water generating agent 3 3 3 ───────────────────────────────

With respect to each of the obtained single-layer particle boards, evaluation was made of the normal state bending strength, the bending strength after wetting, the water absorption thickness expansion coefficient, and the amount of formaldehyde release. Table 2 shows the results. Table 2 ──────────────────────────────── Normal bending strength Wet bending strength Water absorption thickness expansion coefficient F emission unit N / Mm ² N / mm ² % mg / l {Example 1 29 16 5. 6 0.3 Comparative Example 1 18 10 8.8 0.8 Comparative Example 2 27 15 5.8 1.2 ────────

[0031]

Industrial Applicability The adhesive composition for wood-based boards of the present invention relates to JIS which relates to the amount of formaldehyde released from wood-based boards which could not be achieved by the conventional melamine resin adhesive.
A wood board satisfying the E-0 standard can be obtained. The obtained wooden board satisfies the P board standard in the water resistance standard and the 18 types of the JIS standard in the adhesive strength.

Claims (3)

[Claims] 1. A melamine-formaldehyde resin obtained by condensing melamine and aldehydes in the presence of a basic phosphate, wherein the equivalent ratio of formaldehyde to amino groups at the time of the reaction is 0.44 to 0.52. An adhesive composition for wood-based boards, wherein hexamethylenetetramine is added after the reaction. 2. The method according to claim 1, wherein formaldehyde decomposed from said hexamethylenetetramine is present in an amount of from 0.02 to 0.0 with respect to an equivalent ratio of amino groups of the melamine / formaldehyde resin.
The adhesive composition according to claim 1, wherein the adhesive composition is 5. 3. The adhesive composition for wood-based boards according to claim 1, wherein the pH of the solution in the melamine-formaldehyde resin co-condensation reaction is from 7 to 8.5.