Water-based emulsion adhesive mainly composed of vinyl acetate-based polymer

Abstract

To provide a water-based emulsion adhesive mainly composed of a vinyl acetate-based polymer exhibiting good adhesiveness to water-repellent paper.SOLUTION: There is provided a water-based emulsion adhesive which comprises 0.3 to 5.0 pts.mass of an acrylic polymer containing an amino group, 5 to 20 pts.mass of a polyvinyl alcohol and 10 to 30 pts.mass of a plasticizer selected from the group consisting of triacetin, a diethylene glycol butyl ether acetate, diethylene glycol monoethyl ether acetate, an ethylene glycol monobutyl ether acetate, 3-methoxybutyl acetate and a propylene glycol monomethyl ether acetate, based on 100 pts.mass of a vinyl acetate-based polymer containing no ethylene group as a structural unit.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous emulsion adhesive mainly composed of a vinyl acetate polymer, and in particular to an aqueous emulsion adhesive that can be suitably used for water-repellent paper. [Background technology]

[0002] The adhesive described in Patent Document 1 has been known as an aqueous emulsion adhesive that can be used for water-repellent paper. Specifically, this adhesive is known to be made by blending 30 to 200 parts by weight of an organic solvent with a boiling point of 50 to 150°C, 3 to 30 parts by weight of a plasticizer, and 0.1 to 10 parts by weight of a nonionic or anionic surfactant with 100 parts by weight of a vinyl acetate-based aqueous emulsion resin that does not contain ethylene as a constituent monomer (Patent Document 1, claim 1). Xylene or hexane is used as the organic solvent, and dibutyl phthalate is used as the plasticizer (Patent Document 1, Example).

[0003] However, the use of organic solvents such as xylene and hexane has the drawback of worsening the working and use environment. In addition, phthalate plasticizers such as dibutyl phthalate may have adverse effects on the human body, and there are moves to restrict their use.

[0004] [Patent Document 1] Special Publication No. 4-52311 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an aqueous emulsion adhesive containing a vinyl acetate polymer as a main component, which does not deteriorate the working environment or the environment of use and is unlikely to have adverse effects on the human body. [Means for solving the problem]

[0006] The present invention solves the above-mentioned problems by blending a specific plasticizer having an acetyl group and a specific acrylic polymer having an amino group into an aqueous emulsion adhesive mainly composed of a vinyl acetate polymer. That is, the present invention relates to an aqueous emulsion adhesive mainly composed of a vinyl acetate polymer, which contains a vinyl acetate polymer that does not contain an ethylene group as a structural unit, an acrylic polymer having an amino group, polyvinyl alcohol, and a plasticizer selected from the group consisting of triacetin, diethylene glycol butyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, 3-methoxybutyl acetate, and propylene glycol monomethyl ether acetate.

[0007] The vinyl acetate polymer used in the present invention does not contain an ethylene group as a constituent unit and generally consists only of constituent units derived from vinyl acetate monomers. However, as long as it does not contain an ethylene group, it may contain a small amount of such a constituent unit. For example, it may be a vinyl acetate copolymer containing constituent units derived from (meth)acrylic acid monomers or (meth)acrylate monomers.

[0008] The polyvinyl alcohol used in the present invention is used as a protective colloid during emulsion polymerization of a vinyl acetate polymer. Conventionally known polyvinyl alcohols can be used, but in the present invention, it is preferable to use one with a saponification degree of 85 mol% or less. If polyvinyl alcohol with a saponification degree of more than 85 mol% is used, the coating obtained by applying the aqueous emulsion adhesive tends to be highly hydrophilic, and adhesion to water-repellent paper tends to be reduced. The polyvinyl alcohol is preferably blended in an amount of 5 to 20 parts by mass per 100 parts by mass of the vinyl acetate polymer that does not contain an ethylene group as a structural unit. If the blending amount of polyvinyl alcohol is less than 5 parts by mass, the stability of the aqueous emulsion tends to be reduced. On the other hand, if the blending amount of polyvinyl alcohol is more than 20 parts by mass, adhesion to water-repellent paper tends to be reduced.

[0009] The amino-containing acrylic polymer used in the present invention has a main chain made of polyacrylate or polymethacrylate or the like, with aminoalkyl groups such as aminoethyl groups attached to the side chains. The amino-containing acrylic polymer is intended to improve adhesion to water-repellent paper. The amino-containing acrylic polymer is commercially available in the form of an aqueous emulsion, and examples of such products include "Polyment EK-100R" and "Polyment EK-350R" manufactured by Nippon Shokubai Co., Ltd.

[0010] The acrylic polymer having amino groups is preferably blended in an amount of 0.3 to 5.0 parts by mass per 100 parts by mass of the vinyl acetate polymer that does not contain ethylene groups as a structural unit. If the blending amount of the acrylic polymer having amino groups is less than 0.3 parts by mass, adhesion to water-repellent paper tends to decrease. On the other hand, if the blending amount of the acrylic polymer having amino groups is more than 5.0 parts by mass, the storage stability of the aqueous emulsion adhesive tends to deteriorate.

[0011] The plasticizers used in the present invention are compounds containing an acetyl group, and include triacetin, diethylene glycol butyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, 3-methoxybutyl acetate, and propylene glycol monomethyl ether acetate, used alone or in combination. These six plasticizers are less likely to have adverse effects on the human body than phthalate-based plasticizers and the like. Among these plasticizers, triacetin, diethylene glycol butyl ether acetate, and diethylene glycol monoethyl ether acetate are preferred, either alone or in combination. This is because these three plasticizers can further improve adhesion to water-repellent paper.

[0012] The blending amount of the six types of plasticizers is preferably 10 to 30 parts by mass per 100 parts by mass of the vinyl acetate polymer that does not contain an ethylene group as a structural unit. If the blending amount of the plasticizer is less than 10 parts by mass, low-temperature film-forming properties and adhesion to water-repellent paper tend to decrease. On the other hand, if the blending amount of the plasticizer is more than 30 parts by mass, adhesion to water-repellent paper tends to decrease. In particular, in the case of the three types of plasticizers mentioned above, the blending amount may be small, preferably 3 to 20 parts by mass.

[0013] The method for producing the aqueous emulsion adhesive of the present invention is similar to the known procedure for producing conventional polyvinyl acetate aqueous emulsion adhesives. Specifically, a dispersion in which polyvinyl alcohol, a protective colloid, is dissolved or dispersed is first prepared. A monomer solution containing vinyl acetate monomer and a polymerization initiator are then added to the dispersion, followed by emulsion polymerization. An acrylic polymer having an amino group and a plasticizer are added during or after the emulsion polymerization is completed, thereby obtaining an aqueous emulsion adhesive.

[0014] The aqueous emulsion adhesive of the present invention can be used in conventionally known applications such as woodworking, paper processing, fiber processing, etc. In particular, the aqueous emulsion adhesive of the present invention has good adhesion to water-repellent paper, and is therefore suitable for use in bonding liners together when assembling cardboard boxes using water-repellent cardboard. [Effects of the Invention]

[0015] The aqueous emulsion adhesive of the present invention contains substantially no organic solvents, which prevents deterioration of the working environment during production of the aqueous emulsion adhesive and the environment during use of the aqueous emulsion adhesive. Furthermore, the use of a specific plasticizer prevents adverse effects on the human body. Furthermore, the aqueous emulsion adhesive of the present invention also exhibits the advantages of low-temperature film-forming properties and excellent adhesion to water-repellent paper. [Example]

[0016] Example 1 An aqueous emulsion adhesive containing a vinyl acetate polymer as a main component and having the following composition was obtained. Vinyl acetate polymer not containing ethylene groups as a structural unit: 450 parts by mass Acrylic polymer having amino groups: 15 parts by mass (Nippon Shokubai Co., Ltd. "Polyment EK-350R": solids concentration 30% by mass) Polyvinyl alcohol (saponification degree 82 mol%, polymerization degree 500) 40 parts by mass ("JL-05E" manufactured by Japan Vinyl Acetate & Poval Co., Ltd.) Diethylene glycol butyl ether acetate 100 parts by mass 400 parts by mass of water Other substances such as antifoaming agents, small amounts

[0017] This aqueous emulsion adhesive was prepared by the following method. A 2-liter glass polymerization vessel equipped with a reflux condenser, dropping funnel, thermometer, and polymerization initiator dropping inlet was charged with 400 parts by mass of ion-exchanged water and 0.2 parts by mass of antifoaming agent [Noptam 8034F manufactured by Sannobuco Co., Ltd. (a mixture of mineral oil, silica, and a polyoxyalkylene-type nonionic surfactant)], followed by 40 parts by mass of polyvinyl alcohol (JL-05E manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree 82 mol%, polymerization degree 500). The mixture was heated to approximately 90°C while stirring to obtain a uniform dispersion. This dispersion was then heated to 85°C, and 450 parts by mass of vinyl acetate monomer solution and polymerization initiator (a uniform mixture of 1 part by mass of ammonium peroxodisulfate, 0.5 parts by mass of sodium bicarbonate, and 10 parts by mass of ion-exchanged water) were separately added dropwise over 2 hours and 35 minutes using the following method to carry out emulsion polymerization. Specifically, 45 parts by weight of vinyl acetate monomer liquid and a polymerization initiator were added dropwise separately over 30 minutes, and after 5 minutes of stopping each addition, 405 parts by weight of vinyl acetate monomer liquid and a polymerization initiator were added dropwise separately over 2 hours to carry out emulsion polymerization. After emulsion polymerization, 15 parts by weight of an amino group-containing acrylic polymer (Nippon Shokubai Co., Ltd.'s "Polyment EK-350R": solids concentration 30% by weight), 20 parts by weight of diethylene glycol butyl ether acetate, and 0.5 parts by weight of a preservative (Union Chemical Co., Ltd.'s "Unichemflex WB-200") were added to obtain an aqueous emulsion adhesive.

[0018] Example 2 An aqueous emulsion adhesive was obtained in the same manner as in Example 1, except that the amount of the acrylic polymer having an amino group ("Polyment EK-350R" manufactured by Nippon Shokubai Co., Ltd.: solid content concentration 30% by mass) was changed to 10 parts by mass.

[0019] Example 3 An aqueous emulsion adhesive was obtained in the same manner as in Example 1, except that the parts by mass of diethylene glycol butyl ether acetate was changed to 90 parts by mass.

[0020] Example 4 An aqueous emulsion adhesive was obtained in the same manner as in Example 1, except that the parts by mass of diethylene glycol butyl ether acetate was changed to 45 parts by mass and 45 parts by mass of propylene glycol monomethyl ether acetate was added.

[0021] Example 5 An aqueous emulsion adhesive was obtained in the same manner as in Example 4, except that the parts by mass of propylene glycol monomethyl ether acetate was changed to 22.5 parts by mass.

[0022] Example 6 An aqueous emulsion adhesive was obtained in the same manner as in Example 4, except that 45 parts by mass of 3-methoxybutyl acetate was added instead of 45 parts by mass of propylene glycol monomethyl ether acetate.

[0023] Example 7 An aqueous emulsion adhesive was obtained in the same manner as in Example 6, except that the parts by mass of 3-methoxybutyl acetate was changed to 22.5 parts by mass.

[0024] Example 8 An aqueous emulsion adhesive was obtained in the same manner as in Example 4, except that 45 parts by mass of triacetin was added instead of 45 parts by mass of diethylene glycol butyl ether acetate.

[0025] Example 9 An aqueous emulsion adhesive was obtained in the same manner as in Example 5, except that 45 parts by mass of triacetin was added instead of 45 parts by mass of diethylene glycol butyl ether acetate.

[0026] Example 10 An aqueous emulsion adhesive was obtained in the same manner as in Example 8, except that 45 parts by mass of 3-methoxybutyl acetate was added instead of 45 parts by mass of propylene glycol monomethyl ether acetate.

[0027] Example 11 An aqueous emulsion adhesive was obtained in the same manner as in Example 10, except that the parts by mass of 3-methoxybutyl acetate was changed to 22.5 parts by mass.

[0028] Comparative Example 1 An aqueous emulsion adhesive was obtained in the same manner as in Example 1, except that the acrylic polymer having an amino group and diethylene glycol butyl ether acetate were not added.

[0029] Comparative Example 2 An aqueous emulsion adhesive was obtained in the same manner as in Example 3, except that the acrylic polymer having an amino group was not added.

[0030] Comparative Example 3 An aqueous emulsion adhesive was obtained in the same manner as in Example 1, except that 100 parts by mass of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate was added instead of 100 parts by mass of diethylene glycol butyl ether acetate.

[0031] Comparative Example 4 An aqueous emulsion adhesive was obtained in the same manner as in Example 1, except that 100 parts by mass of 2,2,4-trimethyl-1,3-pentanediol diisobutyrate was added instead of 100 parts by mass of diethylene glycol butyl ether acetate.

[0032] The aqueous emulsion adhesives of Examples 1 to 11 and Comparative Examples 1 to 4 were evaluated for low-temperature film-forming ability and adhesion to water-repellent paper by the following methods.

[0033] [Low temperature film formation] In an environment of 23°C and 50% RH, the aqueous emulsion adhesives according to Examples 1 to 11 and Comparative Examples 1 to 4 were applied to a non-water-repellent cardboard liner at a rate of approximately 30 g / m using a bar coater. 2 The adhesive film was then exposed to a 0°C environment for 60 minutes, after which the degree of whitening of the surface of the adhesive film was visually observed and evaluated according to the following criteria. The results are shown in Table 1. 〇: Good film-forming properties (the film is colorless and transparent) △: Poor film formation (part of the film is whitened) ×: Poor film formation (whole surface of film is whitened)

[0034] [Adhesion to water-repellent paper] Two sheets (A and B) of water-repellent cardboard liners with a water-repellency equivalent to R7 were prepared as water-repellent paper. Each of the aqueous emulsion adhesives according to Examples 1 to 11 and Comparative Examples 1 to 4 was applied to the water-repellent surface of one sheet of liner A at a rate of approximately 60 g / m using a bar coater in an environment of 5°C. 2 After applying the coating amount, the water-repellent surface of Liner B was immediately attached to the other side and pressed down with a weight of approximately 2 kg for 5 minutes. Liners A and B were then held with the fingers and peeled off in a 180° direction, and the state of breakage (paper breakage rate) of Liners A and B was evaluated according to the following criteria. The results are shown in Table 1. 〇: Good (paper tear rate over 70%) △: Normal (paper break rate 20-70%) ×: Poor (paper breakage rate less than 20%)

[0035] [Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━ Low temperature film formation, adhesion to water-repellent paper ━━━━━━━━━━━━━━━━━━━━━━━━ Example 1 ○ ○ Example 2 ○ △ Example 3 ○ △ Example 4 ○ ○ Example 5 ○ △ Example 6 ○ ○ Example 7 ○ △ Example 8 ○ ○ Example 9 ○ △ Example 10 ○ ○ Example 11 ○ △ Comparative Example 1 × × Comparative Example 2 ○ ×~△ Comparative Example 3 ○ × Comparative Example 4 ○ × ━━━━━━━━━━━━━━━━━━━━━━━━

[0036] As can be seen from Table 1, the aqueous emulsion adhesives according to Examples 1 to 11 have good film-forming properties even at low temperatures, and generally good adhesion to water-repellent paper.

Claims

1. The aqueous emulsion adhesive is primarily composed of a vinyl acetate polymer, which includes a vinyl acetate polymer that does not contain an ethylene group as a constituent unit, an acrylic polymer having an amino group, polyvinyl alcohol, and a plasticizer selected from the group consisting of triacetin, diethylene glycol butyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, 3-methoxybutyl acetate, and propylene glycol monomethyl ether acetate.

2. The aqueous emulsion adhesive is primarily made of a vinyl acetate polymer, and contains, relative to 100 parts by mass of a vinyl acetate polymer that does not contain an ethylene group as a constituent unit, 0.3 to 5.0 parts by mass of an acrylic polymer having an amino group, 5 to 20 parts by mass of polyvinyl alcohol, and 10 to 30 parts by mass of a plasticizer selected from the group consisting of triacetin, diethylene glycol butyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, 3-methoxybutyl acetate, and propylene glycol monomethyl ether acetate.

3. 3. The aqueous emulsion adhesive mainly comprising a vinyl acetate polymer according to claim 2, wherein at least 3 to 20 parts by mass of a plasticizer selected from the group consisting of triacetin, diethylene glycol butyl ether acetate, and diethylene glycol monoethyl ether acetate is contained per 100 parts by mass of the vinyl acetate polymer not containing an ethylene group as a constituent unit.

4. 3. The aqueous emulsion adhesive mainly comprising a vinyl acetate polymer according to claim 1, wherein the polyvinyl alcohol has a degree of saponification of 85 mol % or less.

5. 3. The aqueous emulsion adhesive comprising a vinyl acetate polymer as claimed in claim 1 or 2, which is used for water-repellent paper.

6. 6. The aqueous emulsion adhesive based on a vinyl acetate polymer according to claim 5, wherein the water-repellent paper is a liner for cardboard.