JPS5939474B2 - adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive solution with excellent water resistance and stability, and is particularly suitable as an adhesive for wood.

Currently, urea resins, urea-melamine cocondensation resins, phenolic resins, and the like are mainly used as adhesives for plywood or secondary processing of plywood, for example.

These &A are widely used because they are cheap and have good water resistance, but recently the formaldehyde (hereinafter referred to as formalin) that remains in them has become a problem, making the environment for plywood work worse. Formalin is released from manufactured furniture and houses, and it 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 although some results have been reported, it is essentially impossible to eliminate formalin, and the water content of the veneer veneer during the manufacturing process 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, at present, formalin-based resins such as urea resin cannot be said to be completely safe. Furthermore, there are plywood adhesives that do not contain formalin, such as protein-based and vinyl acetate resin-based adhesives, but these are not generally used because of their poor water resistance. Furthermore, there is also an example of using a non-formalin-based polyvinyl alcohol (hereinafter referred to as PVA)-isocyanate adhesive as a plywood adhesive in US Pat. No. 2,277.
This can be seen in the specification of No. 083. However, in this US patent, PVA and isocyanate are used in a non-aqueous system. For example, in Example 2 of the US 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 of
Even if plywood is manufactured by such a method, it is not possible to obtain plywood with excellent adhesive strength, especially water-resistant adhesive strength. Furthermore, aqueous emulsions of vinyl acetate polymers have been used in various adhesives, but they are not always sufficient in terms of water-resistant adhesive strength.

Furthermore, if an isocyanate compound or isocyanate polymer is simply blended into an aqueous solution containing PVA, the water resistance will rapidly decrease within 2 to 3 hours due to the reaction between the isocyanate and water, and significant foaming and viscosity increase will occur. This causes problems such as gelation in a short period of time. The present invention eliminates these drawbacks, and consists of an aqueous vinyl acetate polymer emulsion, (1) PVAl, (2) a compound having an isocyanate group dissolved in a hydrophobic solvent, and (3) a formalin condensation resin. This is an adhesive composition comprising:

The adhesive composition of the present invention has excellent water resistance and various adhesive strengths, and is also stable.

The formalin condensation resin used in the present invention includes urea-formalin condensation resin, melamine-formalin condensation resin, urea-melamine-formalin copolymer resin, phenol-formalin condensation resin, etc. Amino condensation resins are preferred.

The amount of formalin-based condensation resin blended is arbitrary. Further, the compound having an isocyanate group used in the present invention exhibits a unique behavior in an aqueous emulsion of a vinyl acetate polymer containing PVA, and acts to impart water resistance to the composition.

The compound or isocyanate polymer having an isocyanate group may be any compound containing two or more isocyanate groups in the molecule, such as tolylene diisocyanate (TDI, such as Bayer DesmO
durT), hydrogenated TDIl trimethylolpropane (
TMP)-TDI adduct (DesmOdurL), triphenylmethane triisocyanate (TTIDesm
OdurR), methylene bis-diphenyl isocyanate (MDIDesmOdur44), hydrogenated MDI,
Hexamethylene diisocyanate (DesmOdurN
), xylene diisocyanate, 4,4' synchrohexylmethane diisocyanate, polymethylene polyphenylisocyanate, etc. are typical examples that can be used.

However, it is possible to temporarily block isocyanate groups with ketokims, phenols, etc., but using such blocked isocyanate compounds requires at least 140 ℃, and the need for such high-temperature heating itself makes cold pressing impossible, and is not only undesirable from a thermal energy perspective, but also particularly difficult to cover materials such as wood. This is not desirable because it is necessary to take care of the problems of damage and warpage caused by such high temperatures when attaching the adhesive, and furthermore, there are problems such as deterioration of the working environment due to the generation of toxic gases due to the decomposition of the adhesive components. It's not a thing.

The compounding ratio of the compound having an isocyanate group is PVA (
It is preferably 1 to 300% by weight based on the solid content (solid content), and 10 to 150% by weight when used as a plywood adhesive. In the present invention, the compound having an isocyanate group is used in a hydrophobic solvent (that is, a solvent that has almost no mutual solubility with water and also has mutual solubility with the compound having an isocyanate group) (hereinafter, this solvent is simply referred to as a "solvent"). It is written as

) and then blended. like this"
By using a solvent, a compound having an isocyanate group can be uniformly dispersed in an aqueous solution containing PVA, and furthermore, contact between the isocyanate group and water can be reduced by emulsifying action, and the isocyanate group can be protected from water. You can also do it. Furthermore, by using a compound having an isocyanate group dissolved in the above-mentioned [solvent], an adhesive solution that is stable and has excellent water resistance can be obtained.

A [solvent] that dissolves an isocyanate compound or an isocyanate polymer is normally liquid, and
It means a solvent compound whose solubility in water at 0 to 30°C and solubility in water in a solvent are both 5 wt% or less. Typical 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, pine oil,
liquid paraffin, alkylbenzene, etc.) halogenated hydrocarbons (e.g. methylene chloride, chlorobenzene, chlorotoluene, bromobenzene, fluorinated 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 pen shell ether, furan, etc.), esters (e.g. isopropyl acetate, butynole acetate, butyl propionate, ester citrate, ricinoleate, etc.), various phthalate esters (e.g. dibutyl phthalate, dioctyl phthalate, butyl benzyl phthalate, etc.), various oleate esters, various esters adipic acid, various azerai esters. , various sebacic acid esters, various stearic acid esters, various benzoic acid esters, various abietic acid esters, various oxalic acid esters, various phosphoric acid esters, etc.), as well as oils containing higher fatty acids as main components, such as castor oil, etc. Available for use.

When dissolving an isocyanate compound or its polymer in a "solvent", if the "solvent" contains active hydrogen such as a carboxyl group, hydroxyl group, or amine group in its molecule, it will react with the isocyanate compound via the active hydrogen. It is not appropriate to dilute it too thinly as the effectiveness will be reduced.

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 effect and dispersion effect, the isocyanate compound or its polymer should be added in an amount of 10 to 1000% by weight, preferably 5% by weight based on the "solvent".
It is preferable to add and dissolve 0 to 400% by weight. These "solvents" have various boiling points, and it is desirable to select an appropriate solvent depending on the intended use or usage conditions of the composition.

For example, when used as an adhesive for plywood, odorless properties are required since the adhesive can be heated and bonded in an open state during use, so dibutyl chloride, dioctyl phthalate, methyl oleate, etc., with a boiling point of 200°C or higher, are required. It is best to use a high boiling point solvent that does not easily evaporate.

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 solvent with a low boiling point.

When an isocyanate compound or a polymer thereof is dissolved in a "solvent" and then added to an aqueous vinyl acetate copolymer emulsion, it is preferable to disperse it uniformly with somewhat vigorous stirring.

In this case, since the surfactant contained in the aqueous emulsion or the surfactant added separately in advance stabilizes the adhesive solution, it is preferable to incorporate a surfactant in some form. In the present invention, PVA is conventional partially or fully saponified PVA, or PVAl derivatives.

The degree of polymerization and degree of saponification are not particularly limited, but in particular, the degree of polymerization is 300 to 25,001 and the degree of saponification is 80.
~100 mol% is preferable. P in aqueous emulsion
The appropriate concentration of VA is 5 to 20% by weight. In the present invention, vinyl acetate polymer aqueous emulsion refers to polyvinyl acetate emulsion, vinyl acetate and unsaturated acids such as ethylene, acrylic acid, maleic acid, fumaric acid and crotonic acid, and one or more monomers of these esters. These are an aqueous copolymer emulsion of vinyl acetate and other monomers that can be copolymerized with vinyl acetate.

Further, among these, an aqueous emulsion containing PVA as a protective colloid in advance is preferable since it is not necessary to further incorporate PVA later. The blending ratio of PVA and vinyl acetate polymer aqueous emulsion is arbitrary, but preferably PVA (solid content) is 10 to 400% by weight, more preferably 50% by weight based on the solid content of the vinyl acetate polymer aqueous emulsion. ~200%.

Further, when the composition of the present invention is used as an adhesive, an extender can be further added.

This extender not only acts as an extender, but also reacts with other components of the adhesive, particularly isocyanates, to provide the adhesive with additional water resistance and initial adhesion. 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, fillers can also be added to the composition of the present invention. This filler not only acts to prevent excessive penetration of the adhesive into the wood, but also reacts with other adhesive components, particularly isocyanates, to provide the adhesive with additional water resistance and initial adhesion. will also be done. Inorganic fillers such as clay, kaolin, and talc are used as fillers, but organic fillers such as wood flour and walnut shell powder can also be used.

The blending ratio of these extenders and fillers varies depending on the composition, especially the intended use of the adhesive, but is 10 to 100% by weight based on the vinyl acetate polymer aqueous emulsion containing PVA.
In particular, the appropriate proportion of the adhesive for plywood is 15 to 50% by weight. 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, reaction accelerators such as boric acid, aluminum sulfate, alum, chromium borate, and water glass can also be added to the adhesive composition of the present invention.

When the composition of the present invention is used as an adhesive, it is possible to achieve sufficient adhesion by just adhesion at room temperature (cold pressing), but in order to further improve adhesive strength and water resistance, adhesion by hot pressing is preferable. The composition of the present invention is suitable as an adhesive, particularly for plywood or its secondary processing, but is also suitable for use in woodworking, particle board, corrugated board, etc., as well as for adhesion of metal foil, as well as for paper and cloth. , adhesives for textile processing, or ceramics, inorganic boards {cemen. Mineral inorganic boards (asbestos, rock wool, etc.)
It can also be applied to bonding plastic sheets (e.g. PVC tiles, asphalt tiles), glass plates, etc. Can be used as a pigment binder in clay coatings, paints, etc.

Next, the present invention will be further explained by examples (the present invention is not limited to these).

Example 1 PVA (
Polymerization degree 1700, saponification degree 98 mol%) 10% aqueous solution 1
00 parts, and 100 parts of a urea-formalin resin with a non-volatile content of 50% were added to the mixture, 10 parts of various isocyanate solutions (75% isocyanate) were added, and further 10 parts of urea, 50 parts of wheat flour, and 10 parts of clay were added. was added, and the pH was adjusted to 5.8 with ammonium chloride.

Veneer configuration using this adhesive: Lauan 1.0+1.0+
1.0mm, coating amount 25y/900cd, cold pressure 10k9
/Cd for 15 minutes and heat pressure at 120°C at 10 kg/Criil to bond the plywood. The following three types of isocyanate solutions were used. A: A dioctyl phthalate solution of polymethylene polyphenyl isocyanate ("PAPi9Ol" manufactured by Kasei Appdition Co., Ltd.) B: An ethyl acetate solution of trimethylolpropane-tolylene diisocyanate ("Coronate LU" manufactured by Nippon Polyurethane) C: Polymethylene polyphenyl isocyanate ("PAPi9Ol" manufactured by Nippon Polyurethane Co., Ltd.) Adhesion test 1 using toluene solution JAS method of "Millionate MR"
The test results are shown in Table 1.

Example 2 Various ethylene monovinyl acetate copolymer aqueous emulsions 1
00 parts, 30 parts of a 10% solution of PVA (polymerization degree 17001 saponification degree 98 mol%) was mixed, and to this, 5 parts of non-volatile matter was added.
Add 20 parts of 0% melamine-urea cocondensation resin, 5 parts of wheat flour, 5 parts of wood flour, anionic surfactant, sodium dodecylbenzenesulfonate (NOF Corporation "Nitsun Yurex Powder I W") 0 To the mixture, 30 parts of a xylene solution (isocyanate 75%) of polymethylene polyphenynolysocyanate (Millionate MR manufactured by Nippon Polyurethane) was added and thoroughly mixed, and the pH was adjusted to 5.8 with ammonium chloride.

Using this adhesive, 1.4mm+1.4mm+1.4m
Thick lauan plywood with veneer structure of m, coated amount 30y/900c
d. Plywood bonding was performed using cold pressure of 10k9/Cd time of 15 minutes and hot pressure of 12'C for 1 minute. Table 2 shows the results of the adhesion test according to JAS. The following three types of ethylene monovinyl acetate copolymer aqueous emulsions were used.

Claims (1)

[Claims] 1. An adhesive composition prepared by blending (1) polyvinyl alcohol, (2) a compound having an isocyanate group dissolved in a hydrophobic solvent, and (3) a formalin-based condensation resin into a vinyl acetate-based polymer aqueous emulsion. .