JPH0158232B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an adhesive having excellent water resistance and heat resistance. More specifically, the present invention relates to a water-based polyisocyanate adhesive having excellent processing properties and physical properties for wood, especially wood chips. [Prior Art and its Problems] Conventionally, urea resins, phenol resins, urea/melamine cocondensation resins, etc. have been mainly used as synthetic or chipboard adhesives. Although these resins are widely used because they are inexpensive and have relatively good performance, they have the disadvantage that formalin is generated not only during use but also from the resulting products. 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 or NCO-terminated prepolymers 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 isocyanate emulsion is also found in Japanese Patent Publication No. 55-7472. However, since this emulsion has a relatively short pot life after being made into an emulsion, it may exhibit drawbacks such as increased viscosity and decreased effective NCO group content, resulting in insufficient adhesive strength. be. [Means for Solving the Problems] The present invention improves the drawbacks of the above-mentioned polyisocyanate adhesives. That is, the present invention provides a combination of a water-emulsified polyisocyanate and a water-soluble masked polyisocyanate, in which the water-emulsified polyisocyanate has a molecular weight of
A mixture of a nonionic surfactant having an isocyanate end group obtained by reacting an alkoxy polyalkylene glycol of 250 to 4000 and an organic polyisocyanate with an organic polyisocyanate, and the water-soluble masked polyisocyanate.
The present invention relates to a water-based adhesive characterized by using a bisulfite masked polyisocyanate. The most important feature of the present invention is that there are no volatile substances that pollute the environment, and the pot life is long as a water-based adhesive.
It becomes possible to use it in a stable state, and as a result,
It has excellent applicability to substrates and provides sufficient adhesive strength, and the resulting product has excellent water resistance, heat resistance, and strength. Furthermore, it has been found that the adhesive of the present invention has an unexpected effect in that a smaller amount of resin can be used 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 through the reaction between polyisocyanate and water, but it is believed that the bonding is mainly due to the formation of polyurea through the reaction between polyisocyanate and water. This is presumed to be due to the balance between scattering out of the system and the dissociation rate of the masked polyisocyanate.) Many methods have already been disclosed for producing water-emulsified polyisocyanates, and the water used in the present invention Any known emulsified polyisocyanate can be used, but it is preferable to use one that has a high effective NCO group content, low viscosity, and good water dispersibility. RO(CH ₂ CH ₂ O)nCONHX (R in the formula
is an alkyl group having 1 to 4 carbon atoms, and n
is an integer such that the compound contains on average at least 5 oxyethylene groups, and X is the residue of a di- or polyisocyanate and contains at least one free isocyanate. It contains an ionic surfactant and a nonionic surfactant which is a reaction product of an alkoxy polyalkylene glycol having a molecular weight of 250 to 4000, preferably 400 to 2000, and polyphenylmethane polyisocyanate, and polyphenylmethane polyisocyanate. It consists of isocyanate. An example is Coronate 3053 manufactured by Nippon Polyurethane Industries. The water-soluble masked polyisocyanate that can be used in the present invention is one that dissociates at 100°C or lower to regenerate free NCO groups. And/or a water-soluble masked polyisocyanate can be obtained by reacting a polyisocyanate prepolymer obtained by reacting a polyisocyanate with a polyhydroxy compound and a bisulfite. The adhesive of the present invention is a water emulsified polyisocyanate.
It is a mixture of (A) and a water-soluble masked polyisocyanate (B), and is obtained by dropping a water-emulsified polyisocyanate into an aqueous solution of a water-soluble masked polyisocyanate while thoroughly mixing. The mixing ratio of each of the above-mentioned components (A) and (B) is in the range of 80/20 to 20/80 (weight ratio). 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. Examples of polyisocyanates that can be used in the water-emulsified polyisocyanate and water-soluble masked polyisocyanate of the present invention include hexamethylene diisocyanate, phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, chlorphenylene diisocyanate, naphthalene diisocyanate, Diphenylene diisocyanate, isophorone diisocyanate, polyphenylmethane polyisocyanate, etc. are mentioned, and these isocyanate derivatives include Coronate L, Coronate HL, Coronate EH, Millionate MTL (all manufactured by Nippon Polyurethane Industries), etc., and compounds similar to these. They may be used alone or in a mixture of two or more. The polyhydroxy compound used in the water-soluble masked polyisocyanate of the present invention is polyether, polyester, polythioether, mixed polyester polyol or mixed polyether polythioether. Preferred polyhydroxy compounds are polyether polyols. 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. [Effects] 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 and pressure of 70° C. or higher are required. This adhesive is particularly suitable for chipboard, but also for plywood, cardboard, metal foil, etc.
Furthermore, it is effective as an adhesive for paper and fiber processing. [Example] Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto. All parts in the examples are parts by weight. Example 1 Hexamethylene diisocyanate (hereinafter referred to as HDI,
25 parts (manufactured by Nippon Polyurethane Industries) were kept at 40°C, and while stirring, 100 parts of polyether triol with an average molecular weight of 2000 (manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 83.8) was added dropwise, and the temperature was raised to 100°C and kept at the same temperature. The mixture was reacted for 2 hours in a nitrogen stream to obtain a prepolymer. In a glass four-neck flask of the same shape as above, add 10 parts of sodium bisulfite to 90 parts of water, dissolve it, 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 allowed to proceed for 60 minutes to obtain an aqueous bisulfite masked isocyanate solution. A good emulsion (A) is obtained by adding 20 parts of Coronate 3053 (manufactured by Nippon Polyurethane Industries, Ltd., trade name of water-emulsified polyisocyanate) to 80 parts of [] at room temperature while stirring using a stirrer in a beaker. Ta. The pot life of this emulsion (A) was 8 hours. In a blender, spray 94.5 g of emulsion (A) as a binder onto 630 g of dried lauan chips while stirring, and place in a wooden frame (300 x 300 x 150 mm).
Fill the inside to a uniform thickness, remove the wooden frame after temporary compression, and mold it on a pressurized heating plate at 150℃, 30Kg/cm ² , and 15 seconds/mm (time per 1 mm of board, the same applies hereinafter). Heat pressed and particle board (300×300×10mm)
was created. The physical properties of the board are shown in Table 1. Example 2 In a four-necked flask having the same shape as in Example 1, 30 parts of HDI was mixed with 50 parts of polyether diol having an average molecular weight of 2000 (manufactured by Sanyo Chemical Industries, hydroxyl value 56.3) while stirring at 40°C. 5 parts of trimethylolpropane was added dropwise, the temperature was raised to 120°C, and the mixture was reacted for 2 hours in a nitrogen stream while maintaining the same temperature. After cooling to room temperature, 15 parts of dioxane was added, followed by 80 parts of a 20% aqueous sodium bisulfite solution, and the mixture was reacted at 40°C for 60 minutes. After cooling to room temperature, add 100 parts of water,
A bisulfite masked isocyanate oil-in-water emulsion with a solid content of 30% was obtained. Emulsion (B) was obtained from 60 parts of Coronate 3053 and 40 parts of Coronate 3053 in the same manner as in Example 1. The pot life of this emulsion (B) was 6 hours at room temperature. 630g of dried lauan chips and 63g of emulsion (B)
A particle board was produced under the same conditions as in Example 1. The physical properties of the board are shown in Table 1. Comparative Example 1 189 g of the bisulfite masked isocyanate aqueous solution obtained in Example 1 was used as a binder,
A particle board was made using 630 g of dried lauan chips under the same conditions as in Example 1. 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, an emulsion with 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 emulsion as a binder and 630 g of dried lauan chips. The physical properties of the board are shown in Table 1. 【table】

Claims (1)

[Claims] 1. In the combination of a water-emulsified polyisocyanate and a water-soluble masked polyisocyanate, the water-emulsified polyisocyanate has a molecular weight of
A mixture of an organic polyisocyanate and a nonionic surfactant whose end group is an isocyanate group obtained by reacting an alkoxy polyalkylene glycol of 250 to 4000 with an organic polyisocyanate, and the water-soluble masked polyisocyanate.
A water-based adhesive characterized by using bisulfite masked polyisocyanate.