JPH0251949B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a wood adhesive having moisture content tolerance and high wood type tolerance, which is made by blending a melamine-phenol cocondensation resin (hereinafter abbreviated as FMPF) with an aqueous latex and an isocyanate. Traditionally, melamine-urea co-condensation resin (hereinafter referred to as
(abbreviated as MUF) and MPF have been used. However, in order to obtain a sufficient adhesive effect using these resins, it is necessary to dry the veneer thoroughly, and the moisture content is usually kept below 10% by weight, and at most 12 to 14% by weight. It was necessary to control it. However, in recent years, in order to improve log yield, it has become necessary to increase the moisture content of the veneer, and as a countermeasure, methods include reducing the amount of fillers such as wheat flour and water when using the resin; At the same time, methods using soybean flour, blood meal, corn starch, etc., or methods such as extending the heat-pressing time have been adopted, but no satisfactory method has been found. Additionally, due to the depletion of lauan wood in recent years, consideration has been given to using other South Sea woods such as apiton and cruin, and softwoods such as Douglas fir and hemlock, but these woods have a high resin content and are not sufficient. In order to obtain an adhesive effect, methods are being considered such as lowering the moisture content of the veneer, increasing the amount of adhesive applied, extending the heat-pressing time, and adding resorcinol when using the resin. However, a sufficient adhesion effect cannot be obtained by any of the methods. Furthermore, Japanese Patent Publication No. 57-19148 provided an adhesive comprising an aqueous emulsion mixed with a compound having an isocyanate group dissolved in a hydrophobic organic solvent and a surfactant, and in some cases, a formalin-based condensation resin was also used. It has been disclosed that this can also be done. The formalin-based condensation resins used at this time include urea-formalin (hereinafter abbreviated as UF), melamine-formalin (hereinafter abbreviated as MF),
It has been shown that MDF and phenol-formalin (hereinafter abbreviated as PF) based condensation resins are used. However, when using UF, MF, and DMF among the formalin-based condensation resins mentioned above, the tolerance of the moisture content of the veneer and the tolerance of the veneer material used is narrow, and the moisture content is high at 20% by weight or more. When using a veneer, it is difficult to use due to punctures, and when using Apitone material with a large resin content, sufficient adhesive strength cannot be obtained. Also, when using PF,
The blended adhesive becomes abnormally thick or gels in a short period of time, resulting in a short pot life and poor workability. In view of the above-mentioned circumstances, the present invention has been developed to produce plywood that has sufficient adhesive strength even when using a veneer with a high moisture content such as 20 to 30% by weight, or even when using a veneer of a wood with a high resin content. The object of the present invention is to provide an adhesive that is easy to peel, exhibits no abnormal thickening, and has a long pot life. Accordingly, in the present invention, the molar ratio of formaldehyde to melamine/phenol is 1.5 to 3.5, the melamine content is 10% by weight or more, and the phenol content is 3% by weight.
% by weight or more and methanol content 5-20% by weight
The melamine/phenol cocondensation resin is blended with an aqueous latex and a compound having an isocyanate group, and the weight ratio of the melamine/phenol cocondensation resin and the aqueous latex is 5/95 to 95/5. The compound having the following formula is an adhesive in an amount of 1 to 30 parts by weight based on 100 parts by weight of the total amount of the melamine-phenol cocondensation resin and the aqueous latex. The melamine/phenol co-condensation resin used in the present invention may be one in which melamine resin is co-condensed with phenol, a phenol resin and melamine in co-condensation, or a co-condensation of melamine, phenol and formaldehyde all at once. It may be a mixture or co-condensation of a phenolic resin and a melamine resin. Furthermore, these resins may be co-condensed with urea or resorcinol. The molar ratio of formaldehyde to melamine/phenol is required to be 1.5 to 3.5. If it is lower than 1.5, there are few methylol groups in the resin, and reaction with isocyanate groups is insufficient, making it impossible to obtain sufficient adhesive strength. If the molar ratio is 3.5 or more, the reactivity with isocyanate groups is too rapid and the pot life is short, making it impractical. The melamine content in the melamine-phenol cocondensation resin must be 10% by weight or more, and the phenol content must be 3% by weight or more. If the content of either melamine or phenol does not reach this value, the desired water resistance cannot be obtained. On the other hand, there is no particular upper limit on the content, but in order to avoid increases in manufacturing costs, the melamine content should be 30% by weight or less, and the phenol content should be 30% by weight or less.
The content is preferably 15% by weight or less. Furthermore, the menol content is preferably in the range of 5 to 20% by weight. If the amount is less than 5% by weight, the adhesive compounded will thicken rapidly over time, resulting in a shortened pot life. Moreover, if the amount is more than 20% by weight, the isocyanate groups are consumed by free methanol, and the desired water resistance cannot be obtained. The aqueous latex in the present invention refers to conjugated dienes such as butadiene and isoprene copolymerized with monomers copolymerized with these, such as various vinyl monomers such as styrene, methyl methacrylate, and acrylonitrile, chloroprene latex, butyl rubber latex, etc. Carboxyl group, N-methylol group, N-alkoxy A reactive monomer having at least one crosslinking reactive group selected from the group consisting of a methyl group, a glycidyl group, a β-methylglycidyl group, a hydroxyl group, an amino group, an amide group, and an acid anhydride group in its side chain. It is a so-called modified latex made by emulsion copolymerization of at least one type of latex. The ratio of aqueous latex to melamine phenolic resin ranges from 5/95 to 95/5 by weight. More preferably, it is in the range of 30/70 to 70/30. The compound having an isocyanate group in the present invention may be any compound containing two or more isocyanate groups in the molecule, such as tolylene diisocyanate (TDI), 4-4'-diphenylmethane isocyanate (MDI), Examples include hexamethylene diisocyanate (HMDI), xylylene diisocyanate (XDI), and isopone diisocyanate (IDI). In addition, as a compound having an isocyanate group,
The polymers, such as mixtures of polyisocyanates and polyols, prepolymers, i.e. NCO-terminated prepolymers prepolymerized with polyol and excess polyisocyanate, or OH-terminated prepolymers prepolymerized with excess polyol. A polymer obtained by adding an excessive amount of polyisocyanate at the time of use may be used. The blending ratio of the isocyanate compound or polymer is in the range of 1 to 30 parts by weight based on 100 parts by weight of the total amount of MPF and aqueous latex. If the blending ratio is lower than 1 part, it will be difficult to obtain the desired water-resistant adhesive strength.
Moreover, if the amount is more than 30 parts by weight, the viscosity increases over time and the pot life is shortened. In carrying out the present invention, a compound having an isocyanate group is dissolved in a hydrophobic solvent, that is, a solvent that has almost no mutual solubility with water and has mutual solubility with the isocyanate compound or its polymer. However, even if it is not dissolved in a hydrophobic solvent, the adhesive thickens over time and has a long pot life, so sufficient performance can be obtained even without the addition of a hydrophobic solvent. It will be done. Further, in the practice of the present invention, a surfactant may be blended, but even without blending, sufficient water resistance is exhibited, viscosity increases little over time, and viscosity stability is good. In carrying out the present invention, barley flour, rice flour, wood flour, talc, clay, etc. may be used in addition to wheat flour as a bulking agent that has been conventionally used in plywood manufacturing, and other additives may be used for the purpose of improving temporary adhesion. It is permissible to use compounds such as polyvinyl alcohol together with blood powder, soybean powder, corn powder, etc., which have been conventionally used as measures to improve adhesive strength. When the adhesive of the present invention is used, it is possible to produce plywood with practically sufficient adhesive strength even when using veneers with a high moisture content of 20 to 30% by weight, which could not be used with the prior art. In addition, plywood with sufficient adhesive strength can be manufactured even by using apitone wood or softwood veneer with a high tar content, and it is extremely easy to implement and has a high practical value. Moreover, the adhesive solution does not thicken abnormally and has a long pot life.
It is stable. Next, the present invention will be specifically explained with reference to Examples. In the examples, % indicates weight %, and parts indicate parts by weight. Example 1 Melamine/phenol cocondensation resin (molar ratio; formaldehyde/(melamine + phenol) =
2.5, melamine content 20%, phenol content 10
%, methanol content 12%), 50 parts of N-methylol group-modified styrene-butadiene emulsion polymer (manufactured by Mitsui Toatsu Chemical KK, trade name Polylac-750) and crude MDI (manufactured by Mitsui Nisso Urethane Co., Ltd.). , trade name: MDI-CR200) were mixed with a mixer while stirring to obtain an adhesive. 100 parts of this adhesive was stirred and mixed with 13 parts of wheat flour as a bulking agent, 19 parts of water as a bulking agent, and 0.5 parts of powdered ammonium chloride as a hardening agent to form a plywood adhesive compound paste, in the same way as is normally done in plywood factories. A plywood was produced using the blended paste under the following bonding conditions, and its performance is shown in Table 1. - Bonding conditions - Veneer composition 5-layer veneer composition with each thickness of 1.6 + 3.6 + 1.6 + 3.6 + 1.6m/m Veneer material Veneer moisture content Lauan 23-27% Apitone, softwood 8-10% Coating Amount applied 35g/900cm ² Deposition time 20 minutes Cold pressure condition 12Kg/cm ² 15 minutes Hot pressure condition 10Kg/cm ² 120℃ 4 minutes/sheet Examples 2 to 7 Melamine-phenol co-condensation resin as shown in Table 1 and An aqueous latex and a compound having an isocyanate group were blended in the proportions shown in Table 1 to obtain an adhesive. In the same way as in Example 1, add flour, water,
Plywood was manufactured using the compounded glue obtained by stirring and mixing the hardening agent under the same bonding conditions as in Example 1, and its performance is shown in Table 1. Comparative Examples 1 to 14 Adhesives were prepared by blending a formalin-based resin and a melamine-phenol cocondensation resin as shown in Table 2, an aqueous latex, and a compound having an isocyanate group in the proportions shown in Table 1. Example 1 for this adhesive
Plywood was manufactured under the same bonding conditions as in Example 1 using a blended glue obtained by stirring and mixing wheat flour, water, and a hardening agent in the same manner as in Example 1, and its performance is shown in Table 2.

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Claims (1)

[Claims] 1 Melamine/phenol having a molar ratio of formaldehyde and melamine/phenol of 1.5 to 3.5, with a melamine content of 10% by weight or more, a phenol content of 3% by weight or more, and a methanol content of 5 to 20% by weight.
It is made by blending a phenol cocondensation resin with an aqueous latex and a compound having an isocyanate group,
The weight ratio of the melamine/phenol cocondensation resin and the aqueous latex is 5/95 to 95/5, and the compound having an isocyanate group is 1 part by weight per 100 parts by weight of the melamine/phenol cocondensation resin and the aqueous latex. ~30 parts by weight adhesive.