JPS6329715B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-resistant adhesive, and is particularly suitable as an adhesive for wood. Currently, adhesives for plywood or plywood secondary processing include urea resin, melamine-urea cocondensation resin,
Phenol resin etc. are mainly used.
These adhesives are widely used because they are inexpensive and have good water resistance, but recently formaldehyde (hereinafter referred to as formalin) remaining in these adhesives has become a problem, making the environment for plywood work worse. Furniture and houses made with plywood using this material emit formalin, which has become a major problem in the world. Recently, various attempts have been made to reduce the release of formalin using urea resins, etc., and some have achieved considerable results. There is also a possibility that incomplete curing of the adhesive may occur due to variations in the rate or heat and pressure conditions, which may cause formalin release from the product. Therefore, the current situation is that formalin-based resins such as urea resins are not completely safe. Furthermore, there are adhesives for plywood that do not contain formalin at all, such as protein-based and vinyl acetate resin-based adhesives, but these are not generally used because of their poor water resistance. Furthermore, non-formalin-based polyvinyl alcohol (hereinafter referred to as PVA) is used as an adhesive for plywood.
Examples of using isocyanate adhesives can also be found in US Pat. No. 2,277,083. However, in this U.S. patent, PVA and isocyanate are used in a non-aqueous system. For example, in Example 2 of the U.S. patent, a PVA aqueous solution is applied to plywood, the water is evaporated, and then hexamethylene diisocyanate is applied on top of it. A toluene solution is applied and the layers are laminated together, but even if plywood is manufactured using this method, it is not possible to obtain plywood with sufficient adhesive strength. On the other hand, an aqueous solution containing polyvinyl alcohol is prepared by dissolving an isocyanate compound or isocyanate polymer in a solvent that has almost no mutual solubility with water and also has mutual solubility with the isocyanate compound or isocyanate polymer. Alternatively, a water-resistant adhesive made by dispersing it in an aqueous emulsion was developed (Special Publication No. 51-30577).
It is widely used as an adhesive for plywood, woodworking, and particle board. However, these water-based PVA-isocyanate adhesives may not have perfect water-resistant adhesive strength depending on the working conditions and structures, and there is a need for the development of even better adhesives. In view of this situation, the inventors of the present invention have conducted intensive studies to improve the adhesive strength of these water-based PVA-isocyanate adhesives.
By using modified PVA that has both hydrophobic and hydrophilic groups instead of PVA, it has excellent heat resistance and
It has been found that it exhibits water-resistant adhesive performance. That is, in the present invention, an isocyanate compound or an isocyanate polymer dissolved in a solvent that has almost no mutual solubility with water, and further has mutual solubility with the isocyanate compound or isocyanate polymer, is dissolved in a hydrophobic group. This is a water-resistant adhesive prepared by dispersing a modified polyvinyl alcohol having both a polyvinyl alcohol and a hydrophilic group in an aqueous solution or emulsion. The hydrophobic group in the modified PVA used in the present invention can be introduced by means such as copolymerization or graft polymerization, and the compounds used in this case include fatty acid vinyl esters, such as valeric acid vinyl ester, capric acid vinyl ester, etc. acid vinyl ester, myristate vinyl ester, stearic acid vinyl ester, etc., among others pivalic acid vinyl ester, 1,1,3,3 tetramethylbutyric acid vinyl ester or
More preferred are fatty acid vinyl esters having a branched alkyl group, such as saturated branched fatty acid vinyl esters. Also butyl vinyl ether, octyl vinyl ether, lauryl vinyl ether,
Vinyl ether compounds such as isocyanyl vinyl ether, α-olefins such as heptene-1, octene-1, and dodecene-1, CH ₂ =CHCH ₂ Cl,
Halogenated unsaturated hydrocarbons such as CH ₂ = CHF, CH ₂ = CH-OC ₈ F ₁₇ , or CH ₂ = CH-Si-
It may also be a silicone compound such as (OC ₂ H ₅ ) ₃ or CH ₂ =CH—O—Si(CH ₃ ) ₃ . Furthermore, hydrophobic groups may be introduced into PVA by methods such as acetalization and esterification using aldehydes, fatty acids, halogenated fatty acids (eg, perfluorooctanoic acid), higher alcohols, and the like. Although the mechanism of action of these hydrophobic groups on the water-resistant adhesive of the present invention is not clear, it is thought that the hydrophobic effect of these hydrophobic groups has a positive effect on the water-resistant adhesive strength. Furthermore, compounds capable of introducing hydrophilic groups into the modified PVA used in the present invention include ethylenically unsaturated carboxylic acids or lower alkyl esters or acid anhydrides thereof, such as acrylic acid,
Methacrylic acid, crotonic acid, maleic acid, itaconic acid, acrylic acid ethyl ester, methacrylic acid methyl ester, crotonic acid methyl ester, citraconic acid, citraconic acid diethyl ester, maleic acid, maleic acid monomethyl ester, maleic acid diethyl ester, itaconic acid Dimethyl ester, maleic anhydride, aconitic acid, etc. are used, but citraconic acid, maleic acid, itaconic acid, maleic acid monomethyl ester, maleic anhydride are preferably used, especially maleic acid, maleic anhydride, monomethyl maleate. More preferred are esters and itaconic acids. Furthermore, olefin sulfonic acid compounds such as ethylene sulfonic acid, allyl sulfonic acid, methalylsulfonic acid,
Acrylamide sulfonic acid compounds such as 2-acrylamide-2-methylpropanesulfonic acid, 2-acrylamide-1-methylpropanesulfonic acid, 2-methacrylamide 2-methylpropanesulfonic acid, acrylamide methacrylic acid,
It may also be an acrylamide compound such as N,N-dimethylacrylamide. In the present invention, it is necessary to use modified PVA that has both hydrophobic groups and hydrophilic groups, and PVA modified with only hydrophobic groups becomes difficult to dissolve in water due to the introduced hydrophobicity. It becomes difficult to prepare an aqueous solution of modified PVA, and sufficient water-resistant adhesive strength cannot be obtained with PVA modified only with hydrophilic groups. On the other hand, modified PVA having both hydrophobic groups and hydrophilic groups easily dissolves in water, and adhesives using this modified PVA have excellent water-resistant adhesive strength. This modified PVA has a polymerization degree of 100~
3500 and saponification degree of 50 to 100 mol% are suitable, but among them, polymerization degree of 300 to 2400 and saponification degree of 70 to 100% are suitable.
A range of 100 mol% is even more preferred. The proportion of hydrophobic groups contained in the modified PVA used in the present invention varies depending on the number of carbon atoms, but is suitably 0.01 to 10 mol%, with 0.1 to 10 mol% being appropriate.
-7 mol%% is more preferred. Although the proportion of hydrophilic groups contained in the modified PVA varies depending on the proportion of hydrophobic groups, a range of 0.01 to 10 mol% is appropriate, and a range of 0.1 to 7 mol% is particularly preferable. The adhesive of the present invention has excellent water resistance and initial adhesive strength, and furthermore, since it does not contain formalin, there is no need to worry about pollution. In the present invention, an isocyanate compound or a polymer thereof dissolved in a specific solvent as mentioned above is uniformly and sufficiently dispersed in an aqueous solution or aqueous emulsion containing modified PVA having both hydrophobic groups and hydrophilic groups. Only then can the desired water-resistant adhesive be obtained. Dissolving the isocyanate compound or its polymer in a solvent other than the specific solvents mentioned above,
Alternatively, it can be dispersed in an aqueous solution or emulsion containing PVA without being dissolved in any solvent.
The glue solution is unstable due to thickening and foaming, the working time is short, and the water resistance is low, so that it cannot be used as the water-resistant adhesive targeted by the present invention. In the present invention, the aqueous solution or aqueous emulsion containing modified PVA as described above refers to a modified PVA aqueous solution or a vinyl acetate polymer emulsion using modified PVA as a protective colloid, or a vinyl acetate polymer emulsion that does not use modified PVA as a protective colloid. Not only the combined emulsion mixed with a modified PVA aqueous solution and the emulsion of vinyl acetate homopolymer, but also the copolymer emulsion of vinyl acetate with unsaturated acids such as acrylic acid, maleic acid, fumaric acid, and crotonic acid, and their esters. Copolymer emulsions of vinyl acetate and other monomers that can be copolymerized with vinyl acetate, such as copolymer emulsions of vinyl acetate and ethylene, styrene-butadiene copolymer latexes, butadiene-acrylonitrile copolymer latexes,
Modified to chloroprene latex, polyacrylate latex, butyl rubber latex, polybutadiene latex, polyvinyl chloride emulsion, polyvinylidene chloride emulsion, etc.
These include those containing an aqueous PVA solution or those using modified PVA as a protective colloid. Modified PVA in these aqueous solutions or emulsions
The appropriate concentration is 0.5 to 20% by weight. Modified PVA
You can dissolve it in water by dissolving it in hot water, or if you use modified PVA that is soluble in cold water, you can mix it with an extender or filler in advance and dissolve it in water before use. Good too. In the present invention, the isocyanate compound or isocyanate polymer may be any compound containing two or more isocyanates in the molecule, such as tolylene diisocyanate (TDI, such as Bayer Desmodur T), hydrogenated TDI, and trimethylolpropane. (TMP) - TDI adduct (Desmodur L), triphenylmethane triisocyanate (TTI.Desmodur R), methylene bis-di-phenyl isocyanate (MDI
Desmodur44), hydrogenated MDI, hexamethylene diisocyanate (Desmodur N), xylene diisocyanate, 4,4' dicyclohexylmethane diisocyanate, etc. are typical isocyanate compounds or isocyanate polymers that can be used. Furthermore, blocks, adducts, etc. of these polyisocyanates can also be used as they have reactivity with hydroxyl groups. In addition, polyisocyanate and polyol mixing systems, such as polyols such as hydrous acid group polyester and polyether (Desmophe), are combined with the above Desmodur.
There is no problem even if a mixture of an excessive amount of polyisocyanate such as L is used. Furthermore, when using a prepolymer method, that is, an NCO-filled prepolymer prepolymerized with a polyol and an excess of polyisocyanate, or an OH-filled prepolymer prepolymerized with an excess of polyol, a polyester such as Desmodur L mentioned above may be used. There is no problem even if the isocyanate is added in excess. The blending ratio of isocyanate compounds or their polymers is 1 to 300% by weight based on the PVA (solid content) in the adhesive, and 10 to 200% for plywood adhesives.
Weight percent is preferred. Furthermore, the solvent used in the present invention, which has almost no mutual solubility with water and has mutual solubility with the isocyanate compound or the isocyanate polymer, is normally liquid, and
It means a solvent compound whose solubility in water at ~30°C and solubility in water in the solvent are both 5% by weight or less. Typical such solvents include aliphatic and aromatic hydrocarbons and mixed liquids containing these as main components (e.g. toluene, xylene, benzene, gasoline, kerosene, ligroin, tetralin, decalin, turpentine oil, pine oil, liquid paraffin, alkylbenzene, etc.), halogenated hydrocarbons (e.g. methylene chloride, chlorobenzene, chlorotoluene, bromobenzene chlorinated liquid paraffin, etc.), ketones (e.g. methyl isobutyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone) , ethyl-n-butyl ketone, di-
n-propyl ketone, acetophenone, etc.), ethers (e.g. isopropyl ether, methyl phenyl ether, ethyl benzyl ether, furan, etc.), esters (e.g. isopropyl acetate,
butyl acetate, butyl propionate, etc.), various phthalate esters (e.g. dibutyl phthalate, diotyl phthalate, butylbenzene phthalate, etc.),
Various oleic esters, various adipic esters, various azelaic esters, various sebacic esters, various stearic esters, various benzoic esters, various abietic esters, various oxalic esters, various phosphoric esters, various maleic esters ( (e.g. dibutyl maleate, dioctyl maleate, diethyl maleate, etc.)
Various fumaric acid esters (e.g., dibutyl fumarate, dioctyl fumarate, dimethyl fumarate, etc.), various succinic acid esters (e.g., dibutyl succinate, dibropyl succinate, dioctyl succinate, etc.), various tartaric acid esters (e.g., dibutyl tartrate, tartaric acid, etc.). dibropyl, dioctyl tartrate, etc.), various citric acid esters (e.g. tributyl citrate, acetyl tributyl citrate, triethyl citrate, acetyl tri-2-ethylhexyl citrate, acetyl triethyl citrate, etc.),
Various ricinoleic acid esters (e.g. methyl acetyl ricinoleate, butyl acetyl ricinoleate,
methoxyethyl acetyl ricinoleate, etc.), and other higher fatty acids (such as oleic acid,
linoleic acid, linolenic acid, enanthic acid, caproic acid), as well as oils mainly containing higher fatty acids (e.g. castor oil, soybean oil, rapeseed oil, coconut oil, cottonseed oil, linseed oil, tung oil, whale oil, palm oil, palm oil). Kernel oil, peanut oil, olive oil, corn oil,
Eno oil, pine oil, etc.) can also be used. When an isocyanate compound or a polymer thereof is dissolved in the above-mentioned solvent, if the solvent contains active hydrogen such as a carboxyl group, hydroxyl group, or amine group in its molecule, the isocyanate compound and its polymer may be dissolved through the active hydrogen. It is not appropriate to dilute it too thinly as it will react and reduce its effectiveness. However, since there is no particular dilution limit for such a solvent that does not have active hydrogen, it can be diluted to a limit value that allows the isocyanate compound or its polymer-solvent system to be uniformly dispersed in water. However, from the viewpoint of water resistance and dispersion effects, isocyanate compounds or their polymers are not suitable for solvents.
Add 10 to 400% by weight, preferably 50 to 300% by weight,
It is best to dissolve it. These solvents have various boiling points, and it is desirable to select a suitable solvent depending on the conditions of use of the adhesive. For example, when used as an adhesive for plywood, odorless properties are required because the adhesive can be heated and bonded in an open state during use, so dibutyl phthalate, dioctyl phthalate, methyl oleate, etc. with a boiling point of 200°C or higher must be used. It is better to use a high boiling point solvent that is difficult to clean. In this case, the solvent remains in the adhesive layer and acts as a plasticizer. On the other hand, if it is undesirable to leave the solvent in the adhesive layer, it is desirable to use a low boiling point solvent. These solvents have the function of uniformly dispersing the isocyanate compound in the aqueous solution or aqueous emulsion containing the modified PVA, and the function of protecting the isocyanate groups from water by reducing the contact between the isocyanate groups and water through an emulsifying effect. When an isocyanate compound or its polymer is dissolved in a solvent and then added to an aqueous solution or aqueous emulsion containing modified PVA, it is preferable to disperse it uniformly with a little vigorous stirring. Further, the adhesive of the present invention may further contain an extender. This extender not only acts as an extender, but also reacts with other components of the adhesive, particularly isocyanates, to impart additional water resistance and initial adhesion to the adhesive.
Usual bulking agents such as wheat flour, starches, defatted soybean flour, and blood meal can be used as bulking agents (for example, bulking agents used in urea resins, etc.), but wheat flour and starches are water-resistant due to isocyanates. It is more preferable because it imparts properties, and furthermore, it does not gelatinize in cold water but becomes gelatinized and viscous by heating during adhesion. Further, the adhesive of the present invention may contain a filler. Inorganic fillers such as clay, kaolin, talc, titanium oxide, calcium carbonate, calcium chloride, and lithium chloride are used as fillers, but organic fillers such as wood flour and walnut shell powder can also be used. The proportion of these extenders and/or fillers varies depending on the intended use of the adhesive, but
It is appropriate that the amount of the PVA-containing aqueous solution or aqueous emulsion be 10 to 100% by weight, especially the range of 15 to 50% by weight of the adhesive for plywood. Further, these extenders and fillers may be used alone or in combination, but it is also preferable to use the extenders and fillers at the same time. Furthermore, boric acid, aluminum sulfate, alum, chromium borate, etc. can be added to the adhesive of the present invention as a reaction accelerator. Furthermore, surfactants can be used simultaneously in the compositions of the invention. The use of a surfactant is effective in improving the stability of the adhesive, extending its pot life, preventing foaming, and improving mold releasability during use. As the surfactant to be used, anionic surfactants, nonionic surfactants, or a suitable combination of both systems (anion-anionic, anion-nonionic, nonionic-nonionic) are effective, but anionic surfactants are preferred. . The structural components of both systems are not particularly important. The adhesive of the present invention is particularly suitable as an adhesive for plywood or its secondary processing, but is also suitable for use in woodworking, particle board, corrugated board, metal foil, paper, film, etc. It is also effective as an adhesive for textile processing. Next, the present invention will be further explained by examples.
The present invention is not limited to these. still%
means weight % unless otherwise specified. Example 1 To 100 parts of a 10% aqueous solution of the various PVA shown in Table 1, 40 parts of "Millionate MR" (MDI isocyanate made by Nippon Polyurethane) diluted twice with dibutyl phthalate was added with thorough stirring. , 20 parts of clay was added to each to create an adhesive. Next, plywood was produced using lauan material with a veneer configuration of 0.7 mm + 1.4 mm + 0.7 mm under the following conditions. Adhesive application amount: 30g/shaku ² Cold press: 10Kg/cm ² -20 minutes Hot press: 120℃ - 1 minute - 10Kg/cm ³ The hot and cold water adhesive strength of the obtained plywood is shown in Table 1. Modified PVA It can be seen that the water-resistant adhesive strength of the adhesive using .

[Table] Example 2 Styrene-butadiene copolymer latex (JSR
0668 Japan Synthetic Rubber Co., Ltd.) 20 parts, Ravisol B-
30 (sodium dioctyl sulfosuccinate manufactured by Nippon Oil & Fats) was added, and an isocyanate (PaPi manufactured by Kasei Appdition Co., Ltd.) diluted twice as much as dioctyl phthalate was added with thorough stirring to prepare an adhesive. When the adhesive strength of the obtained plywood was measured, the results were shown in Table 2, and the adhesive strength was higher than that of the one using known PVA.

[Table] Example 3 To 100 parts of a 15% aqueous solution of each PVA shown in Table 3,
Add 50 parts of styrene-butadiene copolymer latex (DL612, manufactured by Asahi Dow Co., Ltd.) and 30 parts of charcoal, mix well, and then dilute isocyanate (PaPi manufactured by Kasei Appillon) twice with dibutyl phthalate. An adhesive was prepared by adding 50 parts while stirring well. Next, plywood (3mm type plywood) and slate board (4
After laminating under the following conditions using a flexible board (mm flexible board) and treating it under the same test conditions as similar plywood, a peel test was conducted and the state of material breakage was measured. Adhesive application amount: 20g/shaku ² Hot press: 120℃ - 5 minutes Kg/cm ³

[Table] As a comparative example, degree of polymerization is 1750, degree of saponification is 88.5 mol%
An adhesive using Kuraray's PVA-217 was also tested at the same time, but the adhesive of the present invention using modified PVA had a higher wood breakage rate. Example 4 To 100 parts of a 12% aqueous solution of PVA shown in Table 4, add 50 parts of vinegar beer emulsion (OM-4000 manufactured by Kuraray).
1 part, add 30 parts of Charcoal, and add Millionate MR
(Isocyanate manufactured by Nippon Polyurethane Co., Ltd.) was diluted twice with dibutyl phthalate and 45 parts of the solution was added with thorough stirring to prepare an adhesive. Next, plywood (3mm type plywood) and aluminum plate (0.5mm made by NLM)
and were laminated together under the following conditions and the plane tensile strength was measured. Adhesive application amount: 15g/cm ³ shaku ² cold press: 3Kg/cm ² -30 minutes

[Table] All adhesives using modified PVA have excellent adhesive strength. Example 5 To 100 parts of a 10% aqueous solution of various PVA shown in Table 5, 30 parts of clay, 0.5 part of phosphoric acid, and 1.0 part of Metrose (Methyl Cellulose, manufactured by Shin-Etsu Chemical) were added, and Millionate MR (Japan Polyurethane (Japan Polyurethane)) was added. An adhesive was prepared by adding 20 parts of a solution prepared by diluting Isocyanate (manufactured by Co., Ltd.) twice with dibutyl phthalate while stirring thoroughly. Next, using a silicon cal board (specific gravity 1.0) and Toughper (PE synthetic paper), apply amount 20g/ ^shaku2 , press 0.2Kg/ ^cm2
The adhesive strength was measured after 3 days.

[Table] As a comparative example, partially saponified polyvinyl alcohol PVA made by Kuraray with a degree of polymerization of 1750 and a degree of saponification of 88.5.
Adhesives using 217 were simultaneously tested, but denatured
The adhesive of the present invention using PVA had better adhesive strength.

Claims (1)

[Claims] 1. An isocyanate compound or an isocyanate polymer having almost no mutual solubility with water,
A water-resistant adhesive obtained by dispersing an isocyanate compound or an isocyanate polymer dissolved in a solvent mutually soluble in an aqueous solution or aqueous emulsion containing modified polyvinyl alcohol having both hydrophobic groups and hydrophilic groups. agent. 2 Claims in which the modified polyvinyl alcohol having both a hydrophobic group and a hydrophilic group is a modified polyvinyl alcohol having a hydrocarbon group having 3 or more carbon atoms as the hydrophobic group, and a carboxyl group or a sulfone group as the hydrophilic group. 1. The water-resistant adhesive according to item 1. 3 Modified polyvinyl alcohol having both a hydrophobic group and a hydrophilic group has a carboxyl group at the α-position relative to the tertiary or quaternary carbon atom, and a branched fatty acid vinyl ester and an ethylenically unsaturated dicarboxylic acid or its Claim 1: A modified polyvinyl alcohol comprising a saponified product of a copolymer of lower alkyl monoester or diester or acid anhydride and vinyl acetate ester.
Water-resistant adhesives listed in . 4. The water-resistant adhesive according to claim 3, wherein the ethylenically unsaturated dicarboxylic acid or its lower alkyl monoester or diester or acid anhydride is maleic acid monomethyl ester or maleic anhydride. 5. The water-resistant adhesive according to claim 3, wherein the ethylenically unsaturated dicarboxylic acid is itaconic acid. 6 Claim 1, wherein the aqueous emulsion is an aqueous emulsion of a vinyl acetate polymer or an aqueous emulsion of a butadiene polymer latex.
Water-resistant adhesives listed in . 7. The water-resistant adhesive according to claim 1, wherein the aqueous solution or aqueous emulsion containing modified polyvinyl alcohol contains an anionic surfactant.