JPS6162573A - Tannin adhesive composition - Google Patents

Abstract

PURPOSE:The titled composition useful for wood, etc., comprising an adhesive as tannin, curing the composition by oxidation reaction of plant tannin, not containing formaldehyde. CONSTITUTION:The aimed composition wherein an acidic group of plant tannin (e.g., mimosa tannin, quebracho-tannin, chestnut tannin, etc.) is made into a free type, or plant tannin having an acidic group of salt type is mixed with an acid, and it is cured by oxidation reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive composition characterized in that vegetable tannin is cured by an oxidative reaction.

Today, urea formaldehyde resin, melamine formaldehyde resin, and phenol formaldehyde resin, which are used as wood adhesives, all depend on petroleum resources for their raw materials. There are concerns about its future due to its instability, and the conversion of adhesive raw materials to renewable natural resources other than petroleum has become an important issue.

For this reason, various studies have recently begun on adhesives that use vegetable tannins, which are natural phenols that can be collected from plants, but most of them are formaldehyde resins that become polymeric through reaction with formaldehyde; However, the possibility of emitting formaldehyde from adhesive products, which has become a social problem in recent years, remains as a drawback, and its performance is beyond the level of a substitute. Not yet.

From this point of view, the present inventors have conducted intensive studies on adhesive compositions that use tannins extracted from plants as an adhesive base and harden them through oxidative reactions without using formaldehyde, and have developed the present invention. Completed the invention.

The vegetable tannins used in the present invention are not limited to the tree species from which they are collected or the extraction method, and any known vegetable tannins can be used. Typical vegetable tannins include, for example, mimosa tannin, keflaco tannin, mangrove tannin, coconut tannin, chamatil tannin natono-condensed tannin, and chestnut tannin nato hydrolyzed tannin.

The aqueous solution of vegetable tannins mentioned above includes hydrogen peroxide, hydrogen peroxide and ferrous sulfate, hydrogen peroxide and copper sulfate, hydrogen peroxide and potassium ferrocyanide, hydrogen peroxide and potassium ferricyanide,
Add oxidizing agents such as ammonium persulfate, ammonium persulfate and ferrous sulfate, ammonium persulfate and steel sulfate, potassium dichromate, potassium dichromate and manganese sulfate, or sodium hypochlorite to 100 g of vegetable tannin solids.
By adding 2 to 0.001 oxidation equivalent per
An oxidative coupling reaction occurs to form a polymer, producing a gelled product or a precipitated cured product. The concentration of the vegetable tannin aqueous solution used as the adhesive composition is 20 to 70%, preferably 40 to 55% (all percentages by weight).

As a pretreatment for vegetable tannins, molecular weight 50
When an operation is performed to remove the low molecular weight category of 0 to 2Q, 000 or less, compared to vegetable tannins that do not remove the low molecular weight category,
A cured product is easily produced by an oxidative reaction, and the water resistance of the cured product is also improved.

(a) Acidic groups such as carboxyl groups and phenolic hydroxyl groups possessed by naturally occurring vegetable tannins.

Alternatively, vegetable tannins can be dissolved in water containing sulfites.

If acidic groups such as sulfone groups and carboxyl groups introduced during extraction or treatment are made into a free state (hydrogen form) by a pretreatment operation such as ion exchange, (b) or these acidic groups are When 15 to 150 mmol of acid such as sulfuric acid or nitric acid is added to vegetable tannin in the salt form such as salt, calcium salt, or ammonium salt per 100 fi of vegetable tannin, in either case (a) or (b), Also, adhesive compositions with improved water resistance can be produced by promoting oxidative reactions by the acids present, or by adding further oxidizing agents to these acidic vegetable tannins. Become a thing.

An adhesive composition based on acidified vegetable tannins or vegetable tannins to which an oxidizing agent has been added, or vegetable tannins to which an oxidizing agent has been added in an acidic state, is treated with an acid or an oxidizing agent. An adhesive in which the water resistance of the cured product is significantly improved by adding an additive such as polyvinyl alcohol or furfuryl alcohol that forms an insoluble crosslinked polymer gel in an amount of 1 to 30% of the weight of vegetable tannin. It becomes a composition.

Next, examples using mimosa tannin and quebraco tannin as vegetable tannins will be shown to explain the present invention in further detail.

Example 1 An aqueous solution of mimosa tannin or quebraco tannin with a solid content concentration of 50% was poured into a test tube at 1O! ! It was weighed out, and aqueous solutions of various oxidizing agents were added to it in varying amounts.

The reaction was carried out at 30°C and the gel formation status was examined. As a result, the amount of oxidizing agent required to react with 100 g of mimosa tannin to obtain a gelled or precipitated cured product is 0.3 oxidation equivalent or more in the case of hydrogen peroxide, and 0.1 oxidation equivalent or more in the case of ammonium persulfate. , 0.05 for potassium dichromate
It was more than the oxidation equivalent.

In addition, 120 parts of a 20% sodium sulfite aqueous solution was added to 100 parts of Mimosa tannin, and the mixture was reacted at 90°C for 120 minutes to form a sulfonate. The sulfonated Mimosa tannin was then dialyzed using a cellophane tube to remove the low molecular weight fraction. In this case, the amount of oxidizing agent required to react with too g to obtain a gelled product or a precipitated cured product is 3/4 to V2 of that for sulfonated mimosa tannin that does not remove the low molecular weight segment.
When the amount of oxidizing agent is the same, the time to reaction product formation is shortened to V2o~2 for the same amount of oxidant, and the reaction product is more gel-like than precipitate cured product.

Example 2 After dialysis using cellophane cheese.

Sulfonated mimosa tannin, in which the sulfone group is made into a free form (hydrogen form) by cation exchange using a cation exchange resin (Amberlite IR-120B>), or sulfonate, in which the sulfone group is made into a free form without dialysis. A solid solution of 950% of Keplako tannin is used as it is, respectively.
Alternatively, an adhesive liquid with a solid content concentration of 50% was prepared by adding 6.89% (based on tannin) of hydrogen peroxide as an oxidizing agent. These adhesive liquids were sprayed at 15% (solid content weight %) on flaky particles made from cedar wood, molded and heat-pressed at 150°C for 7 minutes to produce particle boards. Cured for over 7 days (23℃, 55%
R, H,) 1. Its strength properties were measured according to JIS A 5908. The results are shown in Table 1. Note that the values shown as a control are for a board manufactured using an area resin adhesive commercially available for particle boards, but this board completely disintegrated after being boiled for 2 hours.

Example 3 A 50% solids solution of Mimosa tannin, a 50% solids solution of Mimosa tannin and sulfonated Keplacota/J2 with the addition of 55 mmol sulfuric acid per 100g tannin solids, and a cation exchange resin. The sulfone group is converted into free form (hydrogen form) by ion exchange using
Solutions of sulfonated kepracotanni with a solid content of 50% were prepared respectively. After weighing these melts into a 20 gt sample pin, hydrogen peroxide was added as an oxidizing agent.
The proportion of polyvinyl alcohol as an additive shown in Table 2 (
After adding (wt% of chemical to tannin solids),
The adhesive was cured by heating at 110°C for 200 minutes to obtain a cured adhesive. After adding 20 times its weight of water to this cured product, 2 hours? 3 was dissolved, cooled, and filtered to obtain an undissolved substance. The ratio of the weight of the insoluble matter to the weight of the initially cured material was determined as the insolubilization rate, and was used as a measure of the water resistance of the cured adhesive material.

The results are shown in Table 2. In the case of a control sample that was not pretreated or added with any additives, it was completely dissolved by boiling for 2 hours (insolubilization rate was 0).
H) It is clear that the cured adhesive of the present invention has excellent water resistance.Example 4 Mimosa tannin and sulfonated kepraco tannin solids to which 55 mmol of sulfuric acid was added per 100 g of tannin solid content A solution with a concentration of 50%, and sulfonated mimosa tannin dialyzed using a cellophane tube after sulfonation, or keplaco tannin that had only been sulfonated, were cation-exchanged to convert the sulfone group into a free form (hydrogen form). A solution with a solid content concentration of 50% was prepared. An adhesive liquid was prepared by adding hydrogen peroxide as an oxidizing agent and polyvinyl alcohol or furfuryl alcohol as an additive to these solutions in the proportions shown in Table 8 (expressed as the weight percent of the chemical relative to the tannin solid content). Particle boards were manufactured using these materials in the same manner as in Example 2, and their properties were investigated. The results are shown in Table 4. Control example (Example 2
Table 3 Table 4 (Good) Board density is 0.78±0.02 (j+
/z is.

It is clear that the adhesive composition of the present invention has excellent adhesive performance in all cases.

Claims (4)

[Claims] (1) An adhesive composition in which vegetable tannin is cured by an oxidative reaction. (2) An adhesive composition in which vegetable tannins are pretreated to remove low molecular weight fractions and then cured by an oxidative reaction in the method according to claim 1. (3) In the method according to claims 1 and 2, the acidic groups of vegetable tannins are made into a free form,
Alternatively, adhesive compositions are made by adding acid to vegetable tannins having salt-type acidic groups and curing them through oxidative reactions. (4) In the method according to claims 1, 2, and 3, an additive that imparts water resistance to the cured product is added to the vegetable tannin, and the cured product is cured by an oxidative reaction. Adhesive composition with improved water resistance.