JPS62260854A - Reagent composition for repairing surface of plywood - Google Patents

Abstract

PURPOSE:To provide the title compsn. having excellent surface strength, durability, smoothness and adhesion to plywood, containing alpha- or beta-type hemihydrate gypsum, an aq. melamine(/urea co-condensate) resin and a natural high-molecular gypsum coagulation retarder. CONSTITUTION:100pts.wt. alpha- or beta-type hemihydrate gypsum (A) having a particle size passing through a 100-mesh sieve or mixture thereof with a pigment (A) is blended with 20-100pts.wt. (on a solid basis) aq. melamine resin (B-a) obtd. by reacting formaldehyde with melamine in a molar ratio of 1.5-3 at a pH of 6-9 and at 50-98 deg.C or melamine/urea co-condensation resin (B-b) obtd. from urea and melamine in a molar ratio of 0.2-4, 0.25-1pt.wt. (on a solid basis) natural high-molecular gypsum coagulation retarder (C) and optionally water (D) in such an amount as to give a viscosity of 20-100P.

Description

[Detailed Description of the Invention] The present invention relates to (1) a gypsum-based repair agent, and is aimed at smoothing and repairing defects on the surface of wood-based materials, especially plywood; The present invention relates to a plywood surface repair agent composition with improved strength.

BACKGROUND OF THE INVENTION Plywood has been praised for its light weight, ease of cutting, and excellent economic efficiency for use in concrete formwork, and has been used in large quantities.

Logs for plywood are mainly South Sea lauan, but due to the depletion of high-quality logs for plywood, and due to resource protection in countries of origin, it has become increasingly difficult to obtain high-quality and inexpensive logs in recent years, forcing the use of inferior logs. It has become. In particular, defects such as cracks and knot holes on the surface of the plywood reduce its useful value by half.

Therefore, several methods have been proposed as methods for repairing such surface defects.

For example, repair agents that combine resin emulsions and fillers (Japanese Patent Publication No. 45-8670, Special Publication No. 46-3280)
etc.) Repair agents that combine a thermosetting resin and a filler (Japanese Patent Publication No. 45-38151, Japanese Patent Publication No. 51-16923, etc.) have been proposed.

Problems to be solved by 1. Conventionally proposed repair agents are often used to repair defects on the surface of plywood after hot-press forming, and in that case they have an excellent repair effect, but - force plate pressing When applied to the defective surface of plywood that has not yet been hot-pressed, the smoothing effect is poor due to volumetric shrinkage due to the volatilization of the volatile content (water or solvent) of the repair agent after molding, and the plywood In many cases, the adhesion was poor. In particular, repair agents based on resin emulsions have the disadvantage of poor adhesion to plywood.

Furthermore, the durability of the repair agent itself, such as resistance to hot water, was often poor.

In view of the problems of conventional repair agents, the present invention has been developed by applying it to plywood surface defects that have not yet been hot-pressed after temporary pressing and do not cause volumetric shrinkage during hot-pressing, and therefore have an excellent smoothing effect (2) ), and the purpose is to provide a repair agent that has excellent adhesion to plywood and the durability of the repair agent itself.

. A method for determining fortune-telling The present invention uses 20 to 100 parts by weight of melamine resin or melamine-urea cocondensation resin as a solid content to 100 parts by weight of α-type or β-type hemihydrate gypsum to retard gypsum setting. This repair agent is characterized in that it contains a natural polymer type setting retarder as a solid content of 0.05 to 1 part by weight.

The gypsum used in the present invention is hemihydrate gypsum, α type, β type
Either natural, phosphoric acid or flue gas desulphurization gypsum can be used.

The material used in the present invention does not contain coarse particles and contains 10
0 mesh bath products are preferable.

A pigment for coloring may be optionally added if necessary.

As the melamine resin or the melamine-urea cocondensation resin, a general aqueous resin is used. For example, formaldehyde/
Melamine molar ratio 1.5-3. pH6-9. Temperature 50~
An aqueous melamine resin made under standard manufacturing conditions at 98° C. or a resin with various modifiers added thereto as required is preferable.

The melamine-urea cocondensation resin has a urea/melamine molar ratio of about 0.2 to 4, and a commonly used resin can be used for the nine resins.

When a urea resin is used alone, it is not suitable for the present invention because the repair agent itself lacks durability such as hot water resistance.

Next, regarding the amount of melamine resin or melamine-urea cocondensation resin relative to plaster, the resin solid content is 20 parts by weight to 100 parts by weight relative to 100 parts by weight of plaster.

If it is less than 20 parts by weight, the strength as a repair agent will be insufficient due to the lack of resin content, and if the defect is deep and large, it will be easy for the crank to enter.

On the other hand, if the amount is 100 parts by weight or more, the strength as a repair agent is sufficient, but the ratio of gypsum in the repair agent decreases, resulting in insufficient 1 volume expansion, resulting in poor smoothing effect. It is also economically unfavorable.

When α-type or β-type hemihydrate gypsum and aqueous melamine resin or aqueous melamine-urea cocondensation resin are mixed, hydration of hemihydrate gypsum begins and the blended system begins to thicken. In some cases,
The pot life is less than 1 hour, making it unsuitable for practical use and requiring the addition of a gypsum setting retarder.

There are various conventionally known setting retarders for gypsum, such as low molecular weight ones such as sodium gluconate and sodium citrate, and natural polymer type ones such as amino acid derivatives and starch. is used.

Low-molecular-weight products such as sodium gluconate and sodium citrate have a sufficient delay effect, but when used as a main repair agent, they tend to bleed out onto the surface when hot-pressing after filling the defective part, resulting in a single repair plywood. When used for concrete formwork, it affects the hydration reaction of cement, resulting in inhibition of the hydration reaction.

This is undesirable because it weakens the concrete surface.

On the other hand, natural polymer type gypsum retarders do not bleed out.
＜Even when used to repair concrete formwork plywood, it does not cause weakening of the concrete surface.

The amount added is from 0.05 part by weight to 1 part by weight as a solid content of the retarder.

If it is less than 0.05 part by weight, the retardation effect will be insufficient and the pot life will be shortened, and if it is more than 1 part per ft, the pot life will be shortened.

For the production of the present repair agent composition, 9 conventional kneading machines, such as propeller type stirrers, roll type.

A general-purpose kneader type is used.

There are no particular restrictions on the manufacturing method, and a predetermined amount of aqueous melamine resin or aqueous melamine-urea cocondensate resin, α-type or β-type hemihydrate gypsum, and a natural polymer-type setting retarder are charged all at once into a kneading machine. , may be kneaded, or may be added individually and kneaded one after another. It is desirable to add water as necessary to set the viscosity of the system from 20 poise to 100 poise.

There are no particular restrictions on the method of applying the plywood surface repair agent to defects on the plywood surface, but for example, the necessary amount of repair agent may be applied to the defect by hand, or it may be applied continuously onto the plywood surface using a roll spreader, etc. A method is used in which the repair agent is applied uniformly to the surface, and then the repair agent is scraped off from the smooth areas using a scraping bar or roll and filled into the four defective areas.

After that, the product is manufactured by hot pressing using a flat press machine, but the hot pressing conditions are: 1. Conditions normally used for plywood production;
For example, heat pressure temperature 110℃ to 140℃, pressure 5k
g/co! From 15 kg/cni, heat pressure time 3
About 20 minutes is sufficient, and the heat pressing time is mainly determined depending on the thickness of the plywood.

Furthermore, after applying 1 plywood surface repair agent to the defective parts of the plywood surface, a base material such as paper or cloth was impregnated with water-based melamine resin, and an impregnated resin sheet obtained by drying was loaded and finished under the above heat-pressing conditions. Plywood is particularly suitable as plywood for concrete formwork because of its smoothness and alkali resistance.

parts, 50 parts of aqueous melamine resin (Nissan Chemical Industry ■Su■■ Ntosopro M 700 solid content 58%) and amino components were kneaded and the viscosity at 20°C was 30 poise (β-type viscometer, ■
A plywood surface repair agent composition was prepared with the following: (manufactured by Tokyo Keiki).

I also made a box with a fence around it using repaired plywood as the bottom. In this, cement/sand/water = 1/210.6
A mortar having a weight ratio of 100 to 100% was poured and cured at room temperature for one week.

Thereafter, nine mortar blocks were taken out and the hardening status of the mortar surface corresponding to the repaired area was mainly observed.

Medium 5 m/m, depth 1 m/m, length 5 on surface veneer
In a five-veneer structure with artificially created surface defects at 0 m/m, the plywood after temporary pressing was used, and the above repair agent was applied and filled into the defective parts by hand.

After that, it was hot-pressed using a flat press machine at a temperature of 130℃, a pressure of 8kg/ctl, and a time of 7 minutes to a size of 12m/m.
Manufactured plywood.

Measure the repaired area using a surface roughness measuring device (■ Koita Research Institute 5E-4A). The average depression depth was measured.

Also JAS cold and hot relapse A test, JAS water resistance A test.

And JAS I cervical immersion peeling test was conducted.

The results are shown in Table 1.

Examples 2, 3.4.5 Comparative Examples 1, 2, 3.4 and 5 The same gypsum, aqueous melamine resin and set retarder as in Example 1 were used, and the surface finish was formulated in the same manner as in Example I. Adjusted the repair agent.

A repair agent was filled into the surface defects using the same method as in Example 1, followed by hot-press molding in the same manner as in Example 1 to produce a 12 m/m plywood.

It was evaluated using the same method as in Example 1, and the results are shown in Table 1.

Example 6 A repair agent was prepared in the same manner as in Example 1. 20 g/l m of repair agent was applied to the plywood after pre-pressing and having the same artificially created defects as in Example 1 after application of the rd crawler.
/ m The entire surface was squeegeeed using the edges of the steel plate to remove the repair agent from areas other than the defective areas. Thereafter, it was hot-pressed in the same manner as in Example 1 and evaluated in the same manner as in Example 8.

The results are shown in Table 1.

Below, remaining white

Claims (1)

[Claims] 100 parts by weight of α-type or β-type hemihydrate gypsum and aqueous melamine resin or melamine-urea cocondensation resin as solid content,
A plywood surface repair agent composition comprising 20 to 100 parts by weight of a natural polymer type gypsum setting retarder and 0.25 to 1 part by weight as a solid content.