JPS5837070A - Aqueous adhesive - Google Patents

Abstract

PURPOSE:To provide an adhesive which does not emit volatile matter causing environmental pollution, has a long pot life and hence can be stably used, and gives products having excellent strength and resistance to water and heat, by mixing a water-emulsifiable polyisocyanate with a water-soluble masked polyisocyanate. CONSTITUTION:A water-emulsifiable polyisocyanate, pref. having a high effective NCO content, a low viscosity and a good water-dispersibility, is mixed with a water-soluble masked polyisocyanate such as a masked polyisocyanate derived from a polyisocyanate and/or a NCO-terminated prepolymer and a bisulfate salt. For example, spray coating, kneading or roll coating can be applied. Hot pressing must be conducted at 70 deg.C or higher. The adhesive is suitable for use in the production of chipboard, and also useful for plywood, corrugated board, metallic foil, paper or processing of fiber.

Description

[Detailed description of the invention] related.

More specifically, the present invention relates to a polyisocyanate water-based adhesive having excellent processing properties and physical properties for wood, especially for wood chips.

Conventionally, urea resin, urea resin, etc. have been used as adhesives for plywood or chipboard. Enol resins, urea/melamine cocondensation resins, etc. are mainly used. These resins are widely used because they are inexpensive and have relatively good performance, but
The disadvantage is that formalin is generated not only during use but also from the resulting product.

On the other hand, polyisocyanates have already been used in some cases as adhesives that do not generate formalin.

Although it is known to use polyisocyanate monomers and NGO-terminated prebolimers as wood adhesives in solvent-based systems, this method has the disadvantage that the solvent evaporates during use.

Furthermore, an example of using an aqueous incyanate emulsion is also found in Japanese Patent Publication No. 7472/1983.

However, this has disadvantages such as increased viscosity and decreased effective NCO group content due to its relatively short pot life after being made into an emulsion, resulting in insufficient adhesive strength. There is also.

The present invention improves the drawbacks of the polyisocyanate adhesives described above.

That is, the present invention relates to a water-based adhesive characterized by using a water-emulsified polyinsyanate and a water-soluble masked polyisocyanate in combination.

The greatest feature of the present invention is that there is no volatile matter that pollutes the environment.
As a water-based adhesive, it has a long pot life and can be used in a stable state.As a result, it has excellent applicability to the substrate and has sufficient adhesive strength, and the resulting product is water resistant. It has excellent properties such as hardness, heat resistance, and strength. Furthermore, it has been found that the adhesive of the present invention has an unexpected effect in that the amount of resin used can be smaller than when a water-emulsified polyisocyanate or a water-soluble masked polyisocyanate is used alone.

(The reason for this is not clear, but in the present invention, it is thought that the adhesion is mainly due to the formation of polyurea by the reaction between polyisocyanate and water, This is presumed to be due to the balance between scattering outside the body system and the dissociation rate of the masked polyisocyanate.) Many methods have already been disclosed for producing water-emulsified polyisocyanate, and the method used in the present invention is Any known water-emulsifying polyisocyanate can be used, but it is preferable to use one that has a high effective NGO content, low viscosity, and good water dispersibility. R O (CH2CH2
0) nCONHX (wherein R is an alkyl group having 1 to 4 carbon atoms, n is an integer such that the compound contains on average at least 5 oxyethylene groups, and X is di or The surfactant is a residue of a polyisocyanate and contains at least one free incyanate.

The water-soluble masked polyisocyanate and 12 that can be used in the present invention are those that dissociate at 100°C or lower to regenerate free NCO groups.
Polyisocyanate and/or as described in 879
Masked polyisocyanate made from NGO group-terminated prepolymer and bisulfite.

The adhesive of the present invention is a mixture of a water-emulsified polyisocyanate and a water-soluble masked polyisocyanate. It is obtained by dropping a water-emulsified polyisocyanate into an aqueous polyisocyanate solution with sufficient mixing. The mixing ratio of each of the above-mentioned components (A) is 89'20 to 2%0 (weight ratio)
is within the range of The mixing ratio of mixed polyisocyanate and water is appropriately determined depending on the water content of the adherend and the viscosity of the mixture.

In carrying out the present invention, a small amount of catalyst (such as a tertiary amine or an organic metal such as tin) or a low molecular weight active hydrogen-containing catalyst such as trimethylolpropane or triethanolamine may be used as necessary to accelerate the reaction. Compounds can be used in combination.

Furthermore, various fillers and additives may be used as necessary.

When using the adhesive of the present invention, conventional methods such as spraying, kneading, roll coating, etc. can be applied, and conventional equipment can be used, but in that case, heat pressure at 70° C. or higher is required.

This adhesive is particularly suitable for chipboard, but is also effective as an adhesive for plywood, corrugated poles, metal foil, paper, and textile processing.

Next, the present invention will be explained by examples, but the present invention is not limited thereto. All parts in the examples are parts by weight.

Example 1 In a glass four-eye flask equipped with a thermometer, stirrer, condenser and dropping funnel, 25 parts of hexamethylene diisocyanate (hereinafter referred to as HDI, manufactured by Nippon Polyurethane Industries) was heated at 40°C. 100 parts of polyether triol (manufactured by Sanyo Chemical Industries, hydroxyl value 83.8) with an average molecular weight of 2000 was added dropwise while stirring at 100°C.
The temperature was raised to 1, and the reaction was carried out for 2 hours in a nitrogen stream while maintaining the same temperature to obtain a prepolymer.

In a four-eye glass flask having the same shape as above, add 10 parts of sodium bisulfite to 90 parts of water, dissolve, add 150 ml of methanol, add 100 parts of the above prepolymer at room temperature with stirring, and then heat at 40°C. The reaction was carried out for 60 minutes to obtain a bisulfite masked isocyanate aqueous solution [1].

Using a stirrer in a beaker, stir [1] at room temperature.
When 20 parts of Coronate 3053 (manufactured by Nippon Polyurethane Industries, Ltd., trade name of water-emulsified polyisocyanate) was added to 380 parts, a good emulsion (2) was obtained. The pot life of this ailsion was 8 hours at room temperature.

Dry lauan chips 6 in the preng while stirring.
Spray 30g of Ailsion (494.5g as a binder), fill it to a uniform thickness in a wooden frame (300 x 300 mowing 50W+), remove the temporary compression grafting frame, and heat it at 150℃ with a pressurized heating plate. Particle board (300x300xlOm
m) was prepared.

The physical properties of the board are shown in Table 1.

In a four-day flask with the same shape as in Example 1, HD
While keeping 30 parts of I at 40°C and stirring, the average molecular weight was 20.
50 parts of polyether diol No. 00 (manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 56.3) and 5 parts of trimethylolpropane were added dropwise to the mixture, the temperature was raised to 120°C, and the mixture was reacted for 2 hours in a nitrogen stream while maintaining the same temperature. Dioxane 15 after cooling to room temperature
80 parts of a 20% aqueous sodium bisulfite solution were added and reacted at 40°C for 60 minutes.

After cooling to room temperature, 100 parts of water was added to the page to obtain a bisulfite masked isocyanate oil-in-water ailsion [11] with a solid content of 30%.

In the same manner as in Example 1, 60 parts of [n] and 30 parts of Coronate were added.
Emulsilon 0 was obtained from 5340 parts.

The pot life of this emulsion (■) was 6 hours at room temperature.

A particle board was produced from 630 g of dried lauan chips and 7063 g of emulsion under the same conditions as in Example-1. The physical properties of the board are shown in Table 1.

Comparative Example 1 A particle board was made under the same conditions as in Example 1 using 3189 g of the bisulfite masked isocyanate aqueous solution obtained in Example 1 and 630 g of dried lauan chips as a binder. The physical properties of the board are shown in Table 1.

Comparative Example 2 When 50.4 g of Coronate 3053 and 50.4 g of water were mixed, a potted product having a pot life of 3 hours at room temperature was obtained. A particle board was made under the same conditions as in Example 1 using this emulsilon as a binder and 630 g of dried lauan chips.

The physical properties of the board are shown in Table 1.

Table 1 ) 1) According to JIS A 5908.

Claims (1)

[Claims] A water-based adhesive characterized by the combined use of a water-emulsified polyisocyanate and a water-soluble masked polyinanate.