JP2001294832A - Adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the water resistance of an adhesive where a vinyl ester- based copolymer emulsion is used. SOLUTION: The adhesive is prepared by compounding a crosslinking agent with a principal ingredient composed mainly of an emulsion of a copolymer consisting of a vinyl pivalate unit, a primary hydroxyl group-containing vinyl compound unit and an ethylenic unsaturated monomer unit, and having a glass transition temperature of >=-10 deg.C. A polyvalent isocyanate compound, a metallic salt, a polyvalent aldehyde, a polyamidoepichlorohydrin or the like is suitable as the crosslinking agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive, and more particularly, to an adhesive having excellent water resistance and heat resistance and good initial adhesion.

[0002]

2. Description of the Related Art Vinyl ester (co) polymer emulsions typified by polyvinyl acetate (co) polymer emulsions are used as adhesives for woodworking, etc.
Water resistance and the like are poor, and improvement of this point is strongly demanded in the industry. In recent years, higher levels of quality have been required, and various modifications and modifications have been made to emulsions in order to respond to the demand. For example, one of the reasons why conventional adhesives using vinyl ester (co) polymer emulsions are inferior in water resistance is that the resin itself is hydrophilic, so that even if the crosslink density is considerably increased, it can absorb water if soaked in water. It is considered that the elastic modulus of the adhesive is remarkably reduced, which leads to a decrease in the adhesive strength. From such a viewpoint, attempts have been made to copolymerize a hydrophobic monomer in order to improve the water resistance of the resin itself. For example, Japanese Patent Publication No. 51-12653 proposes copolymerizing a specific amount of a higher carboxylic acid vinyl ester having 5 to 12 carbon atoms. Also, Japanese Patent Application Laid-Open No. 52-47
No. 833 also proposes a similar copolymerization. These are all proposals for pressure-sensitive adhesives. Furthermore, the research group of the present inventors has proposed that an isocyanate compound or the like be blended with the above-mentioned higher carboxylic acid vinyl ester copolymer emulsion and used as a contact-type adhesive (Japanese Patent Publication No. Sho 62-31755, No. 63-18634). However, these are all proposals as adhesives (adhesives) having a low elastic modulus, and cannot be applied to woodworking adhesives that require a high elastic modulus.

[0003]

An object of the present invention is to further improve the water resistance of an adhesive using a vinyl ester copolymer emulsion.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above-mentioned objects, and as a result, have completed the present invention. That is, the present invention relates to a main ingredient comprising a copolymer emulsion comprising a vinyl pivalate unit, a primary hydroxyl group-containing vinyl compound unit and an ethylenically unsaturated monomer unit and having a glass transition temperature of -10 ° C or higher. And a cross-linking agent.

[0005] The adhesive in the present invention is obtained by blending a crosslinking agent with a main component containing a copolymer emulsion as a main component. Here, the copolymer emulsion is composed of a vinyl compound having a pivalate unit and a vinyl compound having a primary hydroxyl group. A copolymer comprising a monomer unit and an ethylenically unsaturated monomer unit and having a glass transition temperature of −10 ° C. or higher is used as a dispersoid. Among them, the primary hydroxyl group-containing vinyl compound unit is various, but preferred are hydroxyethyl acrylate, hydroxyethyl methacrylate or caprolactone-modified (meth) acrylate, α, β having 3 to 10 carbon atoms. -N- of ethylenically unsaturated carboxylic acid
Alkylamides (N-methylolacrylamide, N-ethanolacrylamide, N-propanolacrylamide, N-methylolmethacrylamide, N
-Ethanol methacrylamide, N-methanol maleamide, etc.) and further a primary hydroxyl group-containing vinyl compound unit such as allyl alcohol.

[0006] The ethylenically unsaturated monomer unit may be of various types, but a unit derived from an ethylenically unsaturated monomer copolymerizable with vinyl pivalate is particularly preferred. Specifically, a unit of at least one monomer selected from the group consisting of ethylene, vinyl acetate and acrylate is preferred. Here, examples of the acrylate include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like.

[0007] The composition of these monomers in the above copolymer is not particularly limited as long as the glass transition temperature of the copolymer is -10 ° C or higher, preferably 5 ° C or higher, and is appropriately determined according to the situation. Just do it. Usually, the content of the vinyl pivalate unit is 5 to 90% by weight, preferably 10 to 80% by weight, and the content of the primary hydroxyl group-containing vinyl compound unit is 0.2 to 15% by weight, preferably 0.5 to 50% by weight. 10% by weight. The content of the ethylenically unsaturated monomer unit is not particularly limited, but contains 5 to 80% by weight, preferably 10 to 80% by weight of a vinyl acetate unit, and 50% by weight or less, preferably 5 to 50% by weight of an ethylene unit. 50% by weight, more preferably 5 to 40% by weight, and 50 units of acrylate units.
% By weight, preferably 5 to 50% by weight.

If the copolymer contains less than 5% by weight of vinyl pivalate units, the water resistance is not sufficiently improved.
When the content exceeds 0% by weight, the film-forming property becomes poor even when the content of the ethylene unit or the acrylate unit is large, and it may not function as an adhesive. If the amount of vinyl ester units other than vinyl pivalate units is less than 5% by weight, the adhesion to polar substances may be impaired, and if it exceeds 80% by weight, water resistance may decrease. The ethylene unit and the acrylate unit are components for imparting hydrophobicity to the vinyl ester resin, but are components for effectively internalizing the vinyl ester resin having insufficient film-forming properties by itself. . Therefore, an ethylene unit and an acrylate unit may be used in combination, but any one of them may be included. When mainly using ethylene units, the content of ethylene units is preferably 5 to 50% by weight. If it is less than 5% by weight, the film-forming property is not sufficient, and if it exceeds 50% by weight, the cohesive strength is reduced, and the adhesive strength is reduced. When the acrylate unit is mainly used, the optimum amount of the acrylate unit varies depending on the carbon number of the alkyl group, but is preferably about 5 to 50% by weight. If the content is less than 5% by weight, the film-forming property is not sufficient, and if it exceeds 50% by weight, the cohesive strength is reduced, and the adhesive strength is reduced.

The composition of the copolymer in the present invention is based on the above-mentioned composition, but within the range not impairing the object of the present invention.
A monomer copolymerizable with vinyl pivalate or vinyl acetate may be copolymerized. For example, acrylic acid, methacrylic acid,
Unsaturated carboxylic acids such as itaconic acid, maleic acid and fumaric acid; methacrylic esters such as methyl methacrylate and ethyl methacrylate; and N-methylolacrylamide, acrylamide, vinyl propionate, vinyl versatate (manufactured by Shell Chemical Co., Ltd. Product Name: Veov
a10), vinyl chloride and the like.

[0010] The copolymer emulsion of the present invention comprises:
This is an aggregate using the above-described copolymer as a dispersoid, but the dispersant used in this case is not particularly limited. For example, conventionally known surfactants, PVA or hydroxycellulose, and PVA having at least one kind of functional group selected from primary hydroxyl group, primary amino group and secondary amino group can be used. Especially PVA
And PVA having the functional group are preferable. As the dispersant used here, PVA which has been widely used may be used. For example, PVA having a degree of saponification of 80 to 99 mol% and a degree of polymerization of 200 to 8000 may be used.
Also, a so-called modified PVA in which a functional group is introduced into a main chain, a side chain or a molecular terminal is suitably used. The amount to be used is 0.2 to 20% by weight, preferably 0.3 to 20% by weight based on the whole copolymer.
It may be appropriately determined within the range of 15 to 15% by weight.

This copolymer emulsion can be produced by various methods. Preferably, the copolymer emulsion is prepared by adding vinyl pivalate, a vinyl compound containing a primary hydroxyl group and an ethylenically unsaturated monomer in the presence of a dispersant as described above. It is obtained by emulsion copolymerization of a monomer mainly composed of a body. The respective proportions of the vinyl pivalate, the vinyl compound containing a primary hydroxyl group and the ethylenically unsaturated monomer used in the emulsion copolymerization may be selected so as to correspond to the constitutional units of the copolymer emulsion. Further, the ratio of the monomer and the dispersant used may be determined so as to correspond to the ratio of the dispersoid and the dispersant of the copolymer described above. In the above emulsion copolymerization, a vinyl monomer other than the above-mentioned vinyl pivalate, a vinyl compound having a primary hydroxyl group and an ethylenically unsaturated monomer may be added as necessary.

The emulsion copolymerization reaction is usually carried out in an aqueous medium,
It is carried out in the presence of a radical polymerization initiator. Hydrogen peroxide, benzoyl peroxide, dicumyl peroxide, cumene hydroperoxide, t-
Butyl hydroperoxide, azobisisobutyronitrile, persulfate (potassium, sodium or ammonium salt), t-butyl peracetate, t-butyl perbenzoate alone or sodium sulfite, triethanolamine, Rongalit, L -Used by forming a redox system with ascorbic acid, tartaric acid, etc.

The copolymerization method includes a method in which a dispersant, a monomer mainly composed of vinyl pivalate, a vinyl compound having a primary hydroxyl group and an ethylenically unsaturated monomer and water are charged at once and copolymerized. A method in which a part of the monomer is charged and the copolymerization is started, and then the remainder is sequentially added to the polymerization system,
A method in which water, the dispersant, and the monomer are mixed in advance, a part thereof is charged to start copolymerization, and the remainder is sequentially added to the polymerization system. A multi-stage copolymerization method is also possible in which a monomer mainly composed of vinyl pivalate, a vinyl compound containing a primary hydroxyl group and an ethylenically unsaturated monomer is divided into two or more stages and sequentially added to the polymerization system. In addition, an aqueous solution of a dispersant can be additionally added to the produced copolymer emulsion as long as the initial adhesiveness and other properties are not impaired.

The adhesive of the present invention is obtained by blending a crosslinking agent with a main component containing the above-mentioned copolymer emulsion as a main component, wherein the crosslinking agent includes a polyvalent isocyanate compound, a metal salt, Polyhydric aldehydes, polyamide epichlorohydrin and the like are suitable, and these can be used alone or in combination of two or more. First,
Examples of the polyvalent isocyanate compound include tolylene diisocyanate (TDI); hydrogenated TDI; trimethylolpropane-TDI adduct (for example, manufactured by Bayer, trade name: Desmodur L); MDI); hydrogenated MDI; polymerized MDI; hexamethylene diisocyanate; xylylene diisocyanate; 4,4-dicyclohexylmethane diisocyanate; isocyanates such as isophorone diisocyanate or a blocked product thereof. In addition, a prepolymer having a terminal group having an isocyanate group, which is previously polymerized with an excess of polyisocyanate in a polyol, may be used. Further, a so-called blocked isocyanate shielded with phenol, oxime, ethyleneimine or the like can also be used. Examples of the metal salt include salts of metals having an atomic weight of 26 or more, such as aluminum, chromium, iron, zirconium,
Chloride such as tin and nitrate are preferred. Next, as the polyhydric aldehyde, those represented by glyoxal, adipindialdehyde, and the like are preferable. As the polyamide epichlorohydrin, a water-soluble resin obtained by quaternizing a polyamide synthesized from adipic acid and diethylenetriamine with epichlorohydrin is preferable.

The proportion of the crosslinking agent in the adhesive of the present invention is as follows:
There is no particular limitation, and it may be determined according to various situations.
Usually, the amount should be selected in the range of 10 to 150 polymerization parts, preferably 20 to 100 parts by weight, based on 100 parts by weight of the main ingredient mainly composed of the above-mentioned copolymer emulsion. The adhesive of the present invention contains a dispersant such as PVA used in producing an emulsion,
It may be added additionally. Further, the adhesive of the present invention includes fillers such as clay, kaolin, talc, calcium carbonate, and wood flour; fillers such as flour and starch; reaction accelerators such as boric acid and aluminum sulfate; Pigments and others,
Various additives such as a preservative and a rust inhibitor can be added as needed.

[0016]

EXAMPLES The present invention will now be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, in an Example, all parts and% mean a weight basis. Example 1 In a pressure-resistant autoclave equipped with a stirrer, a nitrogen inlet tube and various chemical injection pumps, 5 parts of partially saponified PVA having an average degree of polymerization of 1000 and a saponification degree of 88 mol% were heated and dissolved with 85 parts of ion-exchanged water, and then vinyl acetate was added. 6 parts and 10 parts of vinyl pivalate were added, and the temperature was raised to 60 ° C. after the replacement with nitrogen.
Ethylene was injected to 45 kg / cm ² . Copolymerization was started using 1% hydrogen peroxide solution and 5% Rongalit aqueous solution,
Subsequently, 25 parts of vinyl acetate, 2 parts of 2-hydroxyethyl acrylate and 40 parts of vinyl pivalate were taken over 3 hours.
Parts were added continuously. The obtained copolymer emulsion had a solid content of 53.8%, a viscosity of 1900 mPa · s (millipascal second) (30 ° C.), and the copolymer composition determined by nuclear magnetic resonance (NMR) was a vinyl pivalate unit: Vinyl acetate unit: ethylene unit: 2-hydroxyethyl acrylate unit = 48: 30: 20: 2 (weight ratio). The glass transition temperature (Tg) determined by a differential scanning calorimeter (DSC) was -2 ° C. Next, an adhesion test was performed using the above emulsion under the following conditions.
The results are shown in Table 1.

(Adhesion test) (a) adherend: birch / birch (masa) (b) adhesive composition: PV of 45 parts of emulsion
A117 (manufactured by Kuraray, polymerization degree 1700, saponification degree 98 mol%) 45 parts of 10% aqueous solution and 10 parts of calcium carbonate were added, and polymethylene polyphenylisocyanate (manufactured by Nippon Polyurethane, trade name: Millionate MR10)
0) was added and mixed. (C) Coating amount: 125 g / m ² applied to one side (d) Pressing condition: 24 hours at 15 kg / cm ² (e) Adhesive force measuring condition: By compression shear method. Normal condition: measured immediately after preparing the adhesive test piece. Repeat boiling, immerse test specimen in boiling water for 4 hours,
The sample is dried in air at 20 ° C. for 20 hours, further immersed in boiling water for 4 hours, immersed in water at room temperature until immersed, and subjected to the test in a wet state.

Example 2 The autoclave used in Example 1 was charged with an average degree of polymerization of 100.
0, 5 parts of saponified PVA having a saponification degree of 88 mol% and 20 mol of polyoxyethylene added nonyl phenyl ether 2
Was dissolved in 95 parts of ion-exchanged water, and then 39 parts of vinyl acetate,
10% of a mixture (mixed monomer) of 31 parts of vinyl pivalate and 30 parts of butyl acrylate was added, the temperature was increased to 70 ° C. after replacement with nitrogen, copolymerization was started using a 2% aqueous solution of ammonium persulfate, and then 3%. The mixture obtained by adding 2 parts of 2-hydroxyethyl acrylate to the remaining mixed monomer was continuously added over time. The obtained copolymer emulsion had a solid content of 54.5% and a viscosity of 1,100 mPa · s (3
0 ° C.) and determined by NMR: vinyl pivalate units: vinyl acetate units: butyl acrylate units: 2-hydroxyethyl acrylate units = 33: 37: 28: 2
And the Tg determined by DSC was -1 ° C. Next, the above emulsion was subjected to an adhesion test in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 The same operation as in Example 1 was carried out except that 2-hydroxyethyl acrylate was not used, to obtain a copolymer emulsion. The obtained copolymer emulsion had a solid content of 53.1% and a viscosity of 1,600 mPa · s (30 ° C.).
The copolymer composition determined by NMR was as follows: vinyl pivalate units: vinyl acetate units: ethylene units = 49: 31: 20
(Weight ratio). Further, Tg determined by DSC was -4 ° C. Next, the above emulsion was subjected to an adhesion test in the same manner as in Example 1. The results are shown in Table 1.

Example 3 Partially saponified P having an average degree of polymerization of 800 and a saponification degree of 88 mol%
5 parts of VA were dissolved in 85 parts of ion-exchanged water, 65 parts of vinyl pivalate, 21 parts of vinyl acetate and 2 parts of 2-hydroxyethyl acrylate were added, and ethylene was added at 40 kg / cm ^2.
Under pressure, copolymerization was carried out at 55 ° C. using the same hydrogen peroxide solution and Rongalit aqueous solution as in Example 1. The obtained copolymer emulsion had a solid content of 55.4% and a viscosity of 2,200 m.
Pa · s (30 ° C.), and the copolymer composition determined by NMR was as follows: vinyl pivalate unit: vinyl acetate unit: ethylene unit: 2-hydroxyethyl acrylate unit = 6
4: 20: 14: 2 (weight ratio). Also, DSC
Was 4 ° C. This emulsion 1
10 parts of dibutyl phthalate was added to 00 parts and subjected to the same adhesion test as in Example 1. The results are shown in Table 1.

Comparative Example 2 5 parts of partially saponified PVA having an average degree of polymerization of 1000 and a degree of saponification of 88 mol% were dissolved in 85 parts of ion-exchanged water, and 72 parts of vinyl acetate and Veova 10 (trade name, manufactured by Shell Chemical Co., Ltd.) 2
1 part and 2 parts of 2-hydroxyethyl acrylate were added, and the mixture was heated to 60 ° C. under the pressure of 30 kg / cm ^{2 of} ethylene using the same hydrogen peroxide solution and Rongalit aqueous solution as in Example 1.
Was copolymerized. The obtained copolymer emulsion had a solid content of 53.6% and a viscosity of 1,350 mPa · s (30 ° C.).
The copolymer composition determined by NMR was a vinyl acetate unit: Ve
ova 10 units: ethylene units: 2-hydroxyethyl acrylate units = 68: 20: 10: 2 (weight ratio). The emulsion was subjected to an adhesion test in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 Partially saponified P having an average degree of polymerization of 800 and a degree of saponification of 88 mol%
5 parts of VA was dissolved in 85 parts of ion-exchanged water, and 30 parts of vinyl pivalate, 45 parts of vinyl acetate and 2 parts of 2-hydroxyethyl acrylate were added, and ethylene was added at 55 kg / cm ^2.
Under pressure, copolymerization was carried out at 50 ° C. using the same hydrogen peroxide solution and Rongalit aqueous solution as in Example 1. The obtained copolymer emulsion had a solid content of 54.9% and a viscosity of 2,300 mP.
a · s (30 ° C.), and the copolymer composition determined by NMR was as follows: vinyl pivalate unit: vinyl acetate unit: ethylene unit: 2-hydroxyethyl acrylate unit = 29:
39: 30: 2 (weight ratio). Further, Tg determined by DSC was -14 ° C. The emulsion was subjected to an adhesion test in the same manner as in Example 1. The results are shown in Table 1.

[0023]

[Table 1]

* Veova10 VPi; vinyl pivalate, VAc; vinyl acetate, E
t; ethylene, BA; butyl acrylate, HEA;
-Hydroxyethyl acrylate

[0025]

[Table 2]

[0026]

As described above, the adhesive of the present invention has remarkably improved water resistance. Therefore, the adhesive of the present invention can be adapted to the bonding of various materials, but can be particularly suitably used as an adhesive for wood. It can also be used to bond wood to paper, textiles, inorganic plates, films, etc., in addition to bonding between woods. It can also be used effectively for sealers such as wood panels.

Continued on the front page (72) Inventor Hitoshi Maruyama 1621 Sazu, Kurashiki-shi, Okayama Pref. Kuraray Co., Ltd. (72) Inventor Tatsuaki Hattori 3-8-2 Nihonbashi, Chuo-ku, Tokyo Kuraray Co., Ltd.

Claims (1)

[Claims] 1. A main component comprising a copolymer emulsion comprising a vinyl pivalate unit, a vinyl compound containing a primary hydroxyl group and an ethylenically unsaturated monomer unit and having a glass transition temperature of -10 ° C. or higher. An adhesive obtained by blending a crosslinking agent with the adhesive.