JP2986201B2 - Wood bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for bonding wood in which at least one of the adherends is wood, and mainly aims at improving the bonding strength, durability and the like. It is. Wood articles bonded using the bonding method of the present invention are, for example, Japanese Agricultural Standards (JS
It can fully pass the special test of A) plywood standard (continuous boiling for 72 hours).

[Conventional technology]

2. Description of the Related Art Conventionally, a phenol resin adhesive obtained by condensing phenol and formaldehyde, which are thermosetting resins, and a urea resin adhesive obtained by condensing urea and formaldehyde, have been widely used as wood adhesives.

In general, phenolic resin adhesives have the characteristics of low formaldehyde odor generated from products such as plywood and excellent durability.Therefore, phenolic resin is used in applications requiring high durability, such as JAS special plywood. Has been used. However, phenolic resin adhesives have the drawback that they have poor storage stability and are expensive, and furthermore, they cannot exhibit sufficient adhesive durability unless the water content of the adherend is reduced to a low level.

On the other hand, urea resin adhesives are inexpensive, have better storage stability than phenolic resin adhesives, and are more tolerant to the moisture content of adherends than phenolic resin adhesives, but have durability and hydrolysis resistance. Is insufficient, for example, plywood bonded with urea resin adhesive does not withstand long-term outdoor use,
Also, it cannot pass the JAS boiling repetition test (4 hours boiling, 20 hours drying, 4 hours boiling). Also, the formaldehyde odor generated from the product is relatively large.

In addition, based on the demand for an adhesive having only the advantages of both, attempts to mix phenolic resin and amino resin in various ratios and use them as an adhesive have been made.
There are many examples, as in 52-711. However, the amino compound used in these adhesive mixtures contains an amino compound such as expensive melamine as an essential component,
In addition, the durability can be exhibited only when the amount of the amino compound is small. Furthermore, even if phenol resin and urea resin are simply used together, the result is durability,
The hydrolysis resistance was insufficient. For example, even when the amount of phenolic resin was large, it could not pass the special test at best because it passed the repeated boiling test of JAS, and the improvement was insufficient. This was to be expected, since the inclusion of the urea resin means that the proportion of the phenol resin is substantially reduced.

Furthermore, with the recent changes in the log situation, the import of hard-to-bond species has increased, and regulations on the formalin odor of wood products have been examined. Further improvements in durability, adhesive strength, economy, storage stability, formalin odor and the like of the adhesive have been desired.

[Means for solving the problem]

The present inventors have found that the curing behavior of phenolic resin adhesives and urea resin adhesives and mixtures thereof, reaction rates, heat resistance,
As a result of intensive studies on hydrolysis resistance, the effects of pH and temperature on the condensation reaction of phenol, urea, and formaldehyde were clarified, and by curing phenol-urea resin adhesive at a specific pH under specific heating conditions, Surprisingly, it has been found that even a phenol urea-based resin in which a large amount of a urea resin is mixed exhibits extremely good adhesion durability, and the present invention has been completed.

That is, the present invention provides: (1) a phenol-urea-based resin which is a mixture of a thermosetting phenolic resin and a urea-based resin, wherein a molar ratio of phenol in the phenolic resin to urea in the urea-based resin is used as an adhesive; However, when heating and curing with a resin having a ratio of 1: 0.5 to 1: 2.6 and a pH of 7 to 13, the highest temperature of the adhesive layer is 110 ° C. or higher, and after the highest temperature, the highest temperature is reached. A method for bonding wood, comprising curing and bonding under curing conditions with Ti being a time required for cooling down to 90% or more of the value obtained by the following equation (1).

Formula 1: Ti = 0.241 × exp (198.6 ÷ (Te−52)) where Te: Maximum temperature reached (110 <Te) (° C) Ti: Required heating time (minutes) (The temperature reaches 90% of the maximum temperature reached (From the time when the temperature reaches the maximum temperature to the time when the temperature reaches 90% of the maximum temperature) and (2) When the maximum temperature at which the phenol urea resin is cured by heating is higher than the temperature Te represented by the following formula 2, The method for bonding wood according to the above (1), wherein

Formula 2: Te = 110 + R × 13.5 where Te: Maximum temperature reached (110 <Te) (° C.) R: Mole ratio of urea / phenol in phenol urea resin (U / P = 0.5-2.6) According to the bonding method, not only the bonding strength and durability can be improved, but also the adhesion of hardly bonded wood, the tolerance of the moisture content of the adherend can be improved, and the cost can be reduced.

The phenol urea resin used in the present invention is a mixture of a phenol resin and a urea resin, and the mixing ratio is a molar ratio of phenol in the phenol resin of the phenol urea resin adhesive and urea in the urea resin. But 1: 0.5 ~
1: 2.6, and the pH is 7-13, more preferably 10-12.

The phenol resin used for preparing the phenol urea resin is, for example, an aldehyde and a phenol in a molar ratio of 1.
It is obtained by reacting at 3-2.5. When the reaction molar ratio is less than 1.3, the curing time of the phenol urea resin becomes long.
If it exceeds 2.5, the product will have a formaldehyde odor. The reaction pH is desirably 8.0 to 13.0. As the basic catalyst,
Alkali metal compounds such as hydroxides and oxides of alkali metals, alkaline earth metal compounds such as hydroxides and oxides of alkaline earth metals, and amine compounds are used. For example
Examples include NaOH, KOH, Ca (OH) ₂ , CaO, and ammonia.

Aldehydes are formaldehyde, acetaldehyde, n-butyraldehyde, paraformaldehyde,
And trioxane.

The urea resin used for preparing the phenol urea resin is, for example, a aldehyde and urea molar ratio of 1.0 to 1.8, pH 4.
It is obtained by reacting at 0 to 8.0. When the molar ratio is less than 1.0, the adhesive strength becomes insufficient. If the molar ratio exceeds 1.8, the formaldehyde odor of the product becomes severe.

It is possible to partially replace urea with a compound having an amino group such as melamine or thiourea.

The mixing ratio of phenolic resin and urea-based resin is the molar ratio of phenol in phenolic resin and urea in urea resin,
It is usually 1: 0.5 to 1: 2.6, preferably 1: 1 to 1: 1.5. When the amount of urea is less than 0.5 mole per mole of phenol, the proportion of expensive phenol resin is large, which is economically disadvantageous, and when the moisture content of the adherend is high, the adhesive strength is reduced. When the amount of urea exceeds 2.6 moles, the durability becomes insufficient even with heating at a high temperature for a long time.

In the case of a phenol resin and a urea resin, they may be performed in advance or immediately before use. When mixing the phenolic resin and the urea-based resin, any method and apparatus can be adopted as long as both are sufficiently mixed.

In the present invention, the pH of the phenol urea resin adhesive is
The pH is adjusted to 7 to 13, preferably pH 10 to 13. Adjustment of the pH to this range is realized by a method such as addition of a basic compound or an acidic compound. As the basic compound,
Alkali metal compounds such as hydroxides and oxides of alkali metals, alkaline earth metal compounds such as hydroxides and oxides of alkaline earth metals, and amine compounds are used. For example
Examples include NaOH, KOH, Ca (OH) ₂ , CaO, and ammonia.
In particular, an alkali metal hydroxide is desirable. Examples of the acidic substance include mineral acids such as hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid and maleic acid.

The basic compound or the acidic compound may be added after mixing, or may be added to the phenol resin and / or the urea resin in advance.

When the pH of the phenol urea resin is lower than 7, the durability of the cured product becomes insufficient even with sufficient heating, and when it exceeds 13, a large amount of a basic catalyst is required, which is economically disadvantageous. Hydrolysis resistance decreases due to the effect of a large amount of salts.

In the present invention, the heating conditions during bonding are important. That is, the maximum temperature of the phenol urea resin adhesive at the time of thermal curing is at least 110 ° C. or more, and it is necessary to perform heating for the heating time obtained from Equation 1. The heating time is the time from when the temperature reaches 90% of the maximum attained temperature to when the temperature reaches the maximum attained temperature and cools down to 90% of the maximum attained temperature.

If the maximum temperature of the adhesive layer is less than 110 ℃,
If the heating time is less than the required time, apparent curing occurs, but durability cannot be expected.

Still more desirably, the maximum temperature is appropriately set in the above range according to the ratio of urea to phenol in the phenol urea resin. The preferred maximum temperature in this case is obtained by Equation 2. The theoretical support of the relationship between the urea / phenol ratio and the highest temperature is not clear, but it is considered that the reaction between the ortho-methylol group in the phenol resin and urea is related. In a mixed system of phenolic resin and urea resin, as the ratio of urea resin increases within a certain range, it can easily pass the JAS specialty by strictly controlling the thermosetting conditions, that is, the maximum temperature and heating time That was completely unexpected with the prior art.

If the heating temperature is too high, there is a risk that the wood will be thermally degraded.

Further, the temperature obtained by Expressions 1 and 2 indicates the temperature of the adhesive itself, and does not mean the temperature of a hot plate press or the like.

The method of heating may be arbitrary. If the temperature change of the adhesive layer satisfies the conditions of Expressions 1 and 2, for example, a method such as hot pressing, high-frequency heating, or steam injection can be used. That is, the gist of the present invention is that the temperature of the adhesive itself is a problem. For example, when heating with a hot press, the temperature of the press needs to be set higher than desired.

Since the temperature of the adhesive layer can be easily measured using a thermocouple or the like, a preliminary experiment may be performed to determine a heating schedule based on the result.

When blended as an adhesive paste liquid, wood powder, coconut shell powder, inorganic powder and the like may be added as an extender. As a bulking agent, coconut shell powder can be particularly preferably used.

A paste liquid having an appropriate viscosity may be obtained by adding an extender and water to the phenol urea resin adhesive. Additives such as fillers, preservatives, coloring agents, insect repellents, and flame retardants can be added as needed.

[Action]

According to the present invention, it is possible to obtain a bonding method that is inexpensive, durable, has excellent hydrolysis resistance, and is less likely to be affected by the moisture content of an adherend, using a phenol urea-based resin, which could not be predicted by the prior art. it can. Further difficult with conventional adhesives,
It is also suitable for adhesion of Kapur, Apithon and the like.

Furthermore, the tolerance of wood to moisture is better than that of phenol and at the same time or better than that of urea resins.

〔Example〕

The following examples are provided to illustrate the present invention more specifically, but the present invention is not limited by these examples.

Reference Example 1 (Production of phenolic resin) 200 g of phenol, 350 g of 37% formalin, and 25 g of reaction placo equipped with a reflux condenser, thermometer, stirrer, and dropping funnel
30 g of NaOH was dissolved while cooling, and then reacted at 80 ° C. for 3 hours and cooled. Transparent reddish brown, non-volatile content is 52
%was.

Reference Example 2 (Production of urea resin 1) A reaction flask equipped with a reflux condenser, a thermometer, a stirrer, and a dropping funnel was charged with 90 g of urea and 232 g of 37% formalin.
Adjust H to 8.6. After reacting at 85 ° C for 15 minutes, 1N acetic acid is added to adjust the pH to 5.0. After the reaction at 80 ° C. for 1 hour, the pH is adjusted to 8.0 and cooled to 60 ° C. Further, 30 g of urea was added and reacted at 60 ° C. for 1 hour, followed by cooling to obtain a urea resin.

Reference Example 3 (Production of Urea Resin 2) A reaction flask equipped with a reflux condenser, a thermometer, a stirrer, and a dropping funnel was charged with 90 g of urea and 253 g of 37% formalin.
Adjust H to 8.6. After reacting at 85 ° C. for 15 minutes, 1N acetic acid is added to adjust the pH to 5.0. After the reaction at 80 ° C. for 1 hour, the pH is adjusted to 8.0 and cooled to 60 ° C. Further, 60 g of urea was added and reacted at 60 ° C. for 30 minutes, and then cooled to obtain a urea resin.

(Mixing of resin)

After mixing the phenol resin and the urea resin obtained in Reference Example 1, 2 or 3 at the ratios shown in Tables 3 and 4, the pH was adjusted using 30% NaOH. The obtained resin solution is a reddish-brown emulsion, is acidic and changes to a pale red-yellow, and does not produce a precipitate.

(Storage stability of mixed resin)

Each resin was stored at 25 ° C. and the storage stability was measured. As shown in Tables 3 and 4, the storage stability of the phenol urea resin of the present invention was good.

[Manufacture of plywood]

A three-ply plywood was prepared using a Lauan 1.7 mm veneer. The moisture content of the veneer was 10 to 12% for the high moisture content, and 0 to 2% for the low moisture content.

Tables 3 and 4 show the results of measuring the adhesive strength of these resin liquids based on JAS plywood standards (special class). This exam is
The strength after continuous boiling for 72 hours was measured in accordance with the JAS structural plywood standard.

As shown in Table 2, according to the present invention, excellent plywood strength and xylem fracture rate can be obtained. Further, as shown in Table 4, if a heat-pressure condition satisfying the expression 2 was selected, further excellent plywood strength could be obtained.

The passing strength of the special type is 7 kgf / cm ² in the case of Lauan.

a Adhesive composition 100 parts by weight of resin mixture 10 parts by weight of coconut husk powder 10 parts by weight of water b Adhesion conditions Coating amount 34 g / 900 cm ² Cold pressure 10 kg / cm ² , 20 minutes Heat pressure 10 kg / cm ² Maximum reached by reference example The heating time at the temperature is given by Equation 1.
Table 1 shows the results calculated from.

For reference, Table 2 shows the results of calculating the highest temperature at each urea / phenol molar ratio from Equation 2.

[Effects of the Invention] According to the bonding method of the present invention, bonding durability, bonding strength,
The tolerance in the case of a hydrated adherend can be remarkably improved as compared with the conventional bonding method. Further, according to the method for bonding wood of the present invention, the storage stability of the adhesive is excellent, economical,
Excellent prevention of formalin odor and the like can also achieve excellent wood adhesion.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C09J 5/00-5/06 B27D 1/04 C09J 161/34

Claims (2)

(57) [Claims] An adhesive is a phenol urea resin which is a mixture of a thermosetting phenol resin and a urea resin, wherein the molar ratio of phenol in the phenol resin to urea in the urea resin is 1 : 0.5 to 1: 2.6 and a resin having a pH of 7 to 13 when heat-cured, the highest temperature of the adhesive layer is 110 ° C. or higher, and after the highest temperature, the highest temperature reaches 90 ° C. %. The method of bonding wood, wherein the hardening and bonding are performed under the hardening condition in which the time Ti until the cooling to% is equal to or more than the value determined by the following formula 1. Formula 1: Ti = 0.241 × exp (198.6 ÷ (Te−52)) where Te: Maximum temperature reached (110 <Te) (° C) Ti: Required heating time (minutes) (The temperature reaches 90% of the maximum temperature reached From the time when the temperature reaches the maximum temperature, it cools down to 90% of the maximum temperature) 2. The method for bonding wood according to claim 1, wherein the maximum temperature when the phenol urea resin is cured by heating is a temperature Te or more represented by the following equation (2). Formula 2: Te = 110 + R x 13.5 where Te: Maximum temperature reached (110 <Te) (° C) R: Molar ratio of urea / phenol in phenol-urea resin (U / P = 0.5 to 2.6)