JPH0535749B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an adhesive composition with excellent water resistance, self-emulsifying properties, etc. More specifically, the present invention relates to a resin composition for thermosetting adhesives that has excellent working properties and physical properties for molding wood, plastics, etc. Conventionally, vinyl acetate resin, urea resin, phenol resin, urea/melamine cocondensation resin, etc. have been mainly used as adhesives for plywood, particle board, fiber board, etc. In recent years, boards obtained by compression molding wood chips or wood fibers with adhesives have been used for furniture, electrical products, building materials, etc. As adhesives, urea resins are mainly used for furniture and electrical products, and melamine resins and phenolic resins are used for building materials. However, although phenolic resins have excellent boiling resistance, they are susceptible to immersion in water at room temperature, and require high temperatures and long periods of time for curing, resulting in problems in terms of productivity. Moreover, urea resin and melamine resin have no problem in productivity, but are insufficient in terms of water resistance. Moreover, these adhesives have the disadvantage of emitting formaldehyde not only during use but also from the final product obtained. To overcome these drawbacks, wood chips, wood fibers, planer waste, veneer, wood wool, cork, leather, sawdust are used in the production of sheets or molded bodies, such as particleboard, fiberboard and composites. It is also a known practice to use organic polyisocyanates as adhesives for lignocellulosic materials such as straw, flax, hemp, rushes, etc. A typical method involves applying organic polyisocyanates in solution or aqueous emulsion to these lignocellulosic materials, which are then heated and compression molded. The resulting product is of high quality due to the excellent adhesive properties of the organic polyisocyanate. However, organic polyisocyanates generally have poor compatibility with water, and various problems arise when they are directly applied to the current production process of particle boards and the like. The object of the present invention is to eliminate such drawbacks and to provide a self-emulsifying polyisocyanate adhesive composition that can be applied to current processes. As a result of extensive research and study in line with this objective, the present inventors have obtained excellent results by adding a mixture of ethylene carbonate and propylene carbonate to a self-emulsifying prepolymer whose terminal group is an isocyanate group. The present inventors have discovered that the following can be obtained, and have completed the present invention. That is, the present invention provides a heat treatment system comprising a self-emulsifying prepolymer whose end group is an isocyanate group, which is a reaction product of an alkoxy polyalkylene glycol having a molecular weight of 250 to 4,000, and an organic polyisocyanate, and a mixture of ethylene carbonate and propylene carbonate. The present invention relates to a resin composition for curable adhesives. Examples of organic polyisocyanates that can be used in the synthesis of the self-emulsifying isocyanate group-terminated prepolymer of the present invention include tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4.4' methylene bis(cyclohexyl isocyanate),
xylylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate,
Examples of these isocyanate derivatives include Coronate L (manufactured by Nippon Polyurethane Industries), Coronate HL (manufactured by Nippon Polyurethane Industries), and similar compounds thereof alone or in mixtures of two or more. . Also useful are organic polyisocyanate prepolymers produced by the reaction of the above-mentioned organic polyisocyanate compounds and polyols containing active hydrogen. In this case, as the polyol having active hydrogen, any polyol having at least two or more hydroxyl groups in one molecule can be used, but typical examples include polyester polyol, polyether polyol, epoxy polyol, etc. It is also possible to use one type or a combination of two or more of these polyols. Examples of polyester polyols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol,
One or more compounds having at least two hydroxyl groups, such as trimethylene glycol, 1,3-butylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, etc. One of two or more compounds having at least two carboxyl groups, such as malonic acid, maleic acid, succinic acid, adipic acid, tartaric acid, sebacic acid, oxalic acid, phthalic acid, terephthalic acid, azelaic acid, trimellitic acid, etc. Using a species or two or more species,
It can be manufactured by a known method. or,
Also included are lactone-based polyesters obtained by ring-opening polymerization of monomers having a lactone ring, such as ε-caprolactone and ε-parellolactone. Examples of polyether polyols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol,
One or more compounds having at least two active hydrogen atoms such as trimethylene glycol, 1,3-butylene glycol, tetramethylene glycol, hexamethylene glycol, glycerin, sorbitol, sucrose, bisphenol A, ethylenediamine, etc. Ethylene oxide, propylene oxide, butylene oxide as an initiator,
It is produced by addition polymerizing one or more monomers such as styrene oxide and epichlorohydrin by a known method. The organic polyisocyanate and the alkoxypolyalkylene glycol constituting the self-emulsifying prepolymer used in the present invention have a molecular weight of 250 to
4000 range is used, particularly preferably
It is in the range of 600-2000. After dispersion in water, this prepolymer forms a polyurea protective film on the surface of the prepolymer particles and maintains a state in which reaction between the isocyanate groups of the prepolymer and water can be suppressed, so it has self-emulsifying characteristics. The general formula of the alkoxy polyalkylene glycol used in the present invention is R ₁ O(-R ₂ O)- _o H, where R ₁ is an alkyl group, R ₂ is an alkylene group, and this alkoxy group It is thought that it exhibits self-emulsifying characteristics because the whole acts like a nonionic surfactant. The molecular weight of alkoxy polyalkylene glycol that can be emulsified in water is
If the molecular weight is 250 or more, but the molecular weight is 4000 or more, the emulsifying property in water is good, but at the same time, the stability in water becomes poor, and at the same time, compounds with a molecular weight of 4000 or more have high crystallinity, so the storage stability at low temperatures of the prepolymer obtained is poor. The concentration decreases and turbidity occurs. The prepolymer is produced by a known method, generally in the absence of a solvent, and the residual isocyanate group content is preferably adjusted to 20 to 30%. If it is less than 20%, the hydrophilicity will be greater than necessary, resulting in poor stability of the emulsion and high viscosity, resulting in problems with dispersibility. If it exceeds 30%, the hydrophilicity in the interfacial layer with water is insufficient, making it difficult to form a stable emulsion. The purity of the ethylene carbonate or propylene carbonate added to the prepolymer thus obtained is not particularly limited, but may be 95% or more of the commercially available purity. If it is less than 95%, the storage stability will be poor when made into an aqueous emulsion. A method of mixing propylene carbonate or butylene carbonate with organic polyisocyanate and using it as an adhesive is disclosed in JP-A-58
However, the hydrophilicity of the carbonate is too low to mix it with the organic polyisocyanate in the form of an aqueous emulsion. On the other hand, if ethylene carbonate, which is highly hydrophilic, is used alone, the stability of the adhesive composition becomes extremely unstable due to its crystallinity. For these reasons, the present inventors came to use ethylene carbonate and propylene carbonate in a mixed system. The proportion of this mixture added to the adhesive composition is 3% by weight or more, and is particularly preferably in the range of 5 to 50% by weight. If the amount is less than 3% by weight, the effect of addition will not be expressed or
If it exceeds 50% by weight, the content of isocyanate groups in the adhesive composition decreases, resulting in decreased adhesion, which may affect the physical properties of the molded product. Although the mixing ratio of ethylene carbonate and propylene carbonate is not particularly limited, it is desirable that the ratio of ethylene carbonate in the mixture is 5 to 70% by weight. If it is less than 5% by weight, the hydrophilicity of ethylene carbonate will not be exhibited and the effect of the mixture system will not be noticeable, and if it is more than 70% by weight, the stability of the adhesive composition will decrease due to the crystallinity of ethylene carbonate, and crystals will precipitate. There is a risk that The effect of adding a mixture of ethylene carbonate and propylene carbonate is that it further improves the self-emulsifying property of the prepolymer itself and extends the pot life of the aqueous emulsion.
Since the effect of lowering the viscosity of the prepolymer is remarkable, workability is greatly improved. Moreover, it also has the effect of providing economical efficiency without deteriorating adhesive performance. Since the adhesive composition of the present invention has an extremely low viscosity, it can be used as it is without any special modification, or it can be emulsified in water and used as an emulsion. It is possible. This composition is suitable for use as a sheet or a molded body, and the method includes removing the resin composition or emulsion from a lignocellulosic material, usually at a resin content of 1 to 30 percent by weight, and then compressing the resin composition or emulsion. A desired product can be easily obtained by heating. This method is particularly suitable for the production of particle board, but is not limited thereto, and can also be used for the production of molded articles and plywood made of medium density fiberboard, wafer board, etc. The composition obtained by the present invention has excellent self-emulsifying properties, stability, working characteristics, economic efficiency, etc., and the obtained boards exhibit good results in both water resistance and strength. EXAMPLES Hereinafter, the present invention will be further explained in detail with reference to Examples, but the present invention is not limited to these Examples. Parts and percentages in Examples and Comparative Examples refer to parts by weight and percentages by weight, respectively. Examples 1 to 9, Comparative Example 1 In a 2-volume reactor equipped with a thermometer, a stirrer, and an inert gas inlet tube, the raw materials for synthesizing the isocyanate group-terminated prepolymer in the proportions shown in Table 1 were added as polyisocyanate components, The alkoxy polyalkylene glycols were charged in this order, stirred while blowing nitrogen gas, and reacted under the reaction conditions shown in Table 1 to obtain an isocyanate group-terminated prepolymer. Next, a mixture of ethylene carbonate and propylene carbonate in the proportions shown in Table 1 was added to obtain an adhesive composition. Application Examples 1 to 9, Application Comparative Example 1 The adhesive compositions were emulsified in water using a homomixer (rotation speed: 1000 rpm) at the ratios shown in Table 2 to form aqueous emulsions. Next, an aqueous emulsion was sprayed into the chips using an air spray gun while stirring the chips in a blender at the ratio shown in Table 2 to prepare the surface layer material and the core layer material. Place release paper on a cold-rolled steel plate, set a wooden frame (450 x 450 mm) on top of it, spread 593 parts of the surface layer material, then spread 1185 parts of the core layer material.
A further 593 parts of the surface material was laid down and shaped to make the thickness as uniform as possible, then the wooden frame was removed. Place a cold-rolled steel plate with release paper on top of this, then add the thickness of the finished particle board (16
A spacer corresponding to mm) was set, pressure was applied until the two cold rolled steel plates came into contact with the spacer, and compression heating was performed under the board making conditions shown below to produce a three-layer particle board, and the board physical properties were was measured. The board making conditions were as follows: Place temperature (°C) 160 Press pressure (Kg/cm ² ) 25.0 Press time (minutes) 4.5 Table 3 shows the physical properties of the board measured according to JAS A 5908.

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[Table] Comparative Example 2 Weigh out 100 parts of water in a 500ml polyethylene beaker, add 80 parts of Millionate MR-200 and 20 parts of a mixture of equal amounts of ethylene carbonate and propylene carbonate, stirred in advance, and mix with a homomixer. I tried to emulsify it at 1000rpm using the following, but it was not possible to emulsify it.

Claims (1)

[Claims] 1. Containing a mixture of ethylene carbonate and propylene carbonate in an amount of 3% by weight or more in a self-emulsifying prepolymer having an isocyanate end group, which is a reaction product of an alkoxypolyalkylene glycol having a molecular weight of 250 to 4000 and an organic polyisocyanate. Characteristic adhesive composition.