JP2813430B2 - Method for producing aqueous emulsion type pressure-sensitive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to adhesiveness to various objects to be adhered, and humidity resistance deterioration when coated paper is used as a surface substrate. The present invention relates to a method for producing an aqueous emulsion type pressure-sensitive adhesive excellent in water resistance.

(Conventional technology) Conventionally, adhesives include adhesiveness, coating suitability, drying property,
So-called solution-type adhesives using organic solvents such as aromatics, esters, and ketones which are excellent in water resistance and the like have been the mainstay. In recent years, however, attention has been paid to aqueous emulsion-type pressure-sensitive adhesives in terms of resource saving, pollution-free, and safety and health aspects. In particular, the market share of aqueous emulsion-type pressure-sensitive adhesives containing polyacrylic acid alkyl ester copolymer as a main component is increasing year by year. doing.

The aqueous emulsion type adhesive is used for tapes, general labels, labels for frozen foods, stickers, seals, business forms, etc. The material to be adhered is plastic, metal, glass, paper, pottery, cardboard cases. And so on. In particular, plastic products continue to increase, and the proportion of polyolefin resins in particular is gradually increasing in terms of safety, hygiene, cost, and functionality.

In general, aqueous emulsion-type pressure-sensitive adhesives tend to be inferior in water resistance, moisture resistance, adhesiveness, drying property, stability, etc. as compared with solution-type pressure-sensitive adhesives. There is a demand for an improvement in the adhesive strength of the adhesive.

On the other hand, in recent years, the number of types of surface base materials for pressure-sensitive adhesive coatings has increased, and applications for coating paper base materials called coated papers typified by cast-coated paper, coated paper, and the like have been increasing. When these coated papers are used as a surface substrate and an aqueous emulsion-type adhesive is applied and the adhesive coated product is left under high temperature and high humidity, the adhesive properties such as adhesive strength and tack are significantly reduced (hereinafter referred to as "tackiness"). , Humidity resistance).

Conventionally, there are literatures on a method for improving the adhesion to various kinds of objects to be adhered and a method for improving the resistance to humidity deterioration, but there is no report on an improvement means for solving these problems at the same time. That is, the method of improving the adhesiveness to various kinds of objects to be adhered is structurally characterized by multi-stage polymerization represented by two-stage polymerization or three-stage polymerization,
There are many methods such as a method of mixing an ethylene-vinyl acetate resin and a method of mixing a tackifier represented by a rosin resin and a petroleum resin. Absent.

On the other hand, regarding humidity resistance, the addition of a sequestering agent or the like has been studied to suppress metal cross-linking between metal ions contained in the coated paper base and carboxyl groups in the adhesive. (Japanese Patent Application Laid-Open No. Sho 63-22884), this method has an effect on the humidity resistance deterioration, but has a drawback such as low adhesion to polyolefin-based objects to be adhered and rough surfaces such as cardboard. However, it is not a means for improving the adhesion and the resistance to humidity deterioration in a well-balanced manner.

(Problems to be Solved by the Invention) The present invention improves the above-mentioned various drawbacks, and improves the adhesiveness to various objects to be adhered and the resistance to humidity deterioration when coated paper is used as a surface substrate. An object of the present invention is to provide a method for producing an excellent aqueous emulsion-type pressure-sensitive adhesive.

[Configuration of the invention]

Means for Solving the Problems The present invention mainly comprises an alkyl acrylate having an alkyl group having 4 to 12 carbon atoms, and contains 0.5 to 5% by weight of an α, β-ethylenically unsaturated carboxylic acid. In obtaining an aqueous emulsion type pressure-sensitive adhesive by emulsion polymerization of a monomer,
Emulsion polymerize 50 to 99.8% by weight of a mixture of monomers which can contain up to 40% by weight of the α, β ethylenically unsaturated carboxylic acid to form an aqueous emulsion, and then in the presence of the emulsion This is a method for producing an aqueous emulsion-type pressure-sensitive adhesive obtained by subjecting the remaining amount of β-ethylenically unsaturated carboxylic acid to emulsion polymerization alone. The aqueous emulsion-type pressure-sensitive adhesive of the present invention is an emulsion of an acrylic resin containing an alkyl acrylate as a main component. Examples of the acrylate having an alkyl group having 4 to 12 carbon atoms used in the acrylic resin include butyl acrylate, hexyl acrylate, octyl acrylate, and acrylic acid 2.
-Acrylates of linear or branched fatty alcohols such as ethylhexyl, decyl acrylate and lauryl acrylate. Two or more types may be used in combination. These acrylates are used in an amount of 60 to 99.5% by weight, preferably 70 to 90% by weight, based on the total amount of the monomers forming the acrylic resin. Examples of the α, β-ethylenically unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid.

In addition to the above-mentioned monomers, the acrylic resin of the present invention contains a hydroxyl group-containing acrylate or methacrylate of β-hydroxyethyl acrylate, β-hydroxypropyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropyl methacrylate. Acrylates, acrylamide, acrylamide derivatives such as N-methylol acrylamide, N-butoxymethyl acrylamide, alkyl acrylates having an alkyl group having 3 or less carbon atoms, such as methyl acrylate, ethyl acrylate and propyl acrylate; It can be obtained by copolymerizing a monomer having 1 to 4 carbon atoms such as methacrylic acid ester, vinyl acetate, styrene, acrylonitrile and the like.

The emulsion type pressure-sensitive adhesive of the present invention is obtained by emulsion polymerization. For example, emulsion polymerization is carried out by continuously and dropwise supplying a monomer mixture containing a polymerization initiator into water containing an emulsifier. At this time, first, emulsion polymerization is carried out using a monomer mixture in which the α, β-ethylenically unsaturated carboxylic acid is used in an amount of 0 to 40% by weight, preferably 10 to 40% by weight of the amount used. Emulsion polymerization at this stage is 50% by weight of total monomer
The content is preferably at least 80% by weight, more preferably at least 90% by weight, and the upper limit is 99.8% by weight. The α, β-ethylenically unsaturated carboxylic acid need not be used, but is preferably blended in order to balance the humidity resistance and the holding power.

Then, the remaining amount of the α, β-ethylenically unsaturated carboxylic acid is dropped alone or as a mixture of other monomers to continue the emulsion polymerization. The emulsifier may be contained in the water to be dropped, or may be contained in the form of a pre-emulsion together with the monomer mixture.

Examples of the emulsifier include polyoxyethylene alkylphenol ether sulfate or sulfonate, alkylbenzene sulfonate, α-olefin sulfonate and the like, alone or in combination thereof, polyoxyethylene alkylphenol ether, polyoxyethylene stearate, polyoxyethylene-polyoxypropylene block. Copolymers and the like can be used.

Examples of the polymerization initiator include persulfates such as ammonium persulfate, potassium persulfate and sodium persulfate, and peroxides such as persulfuric acid or hydrogen peroxide and cumene hydroperoxide. Polymerization can also be carried out by a redox reaction using a reducing agent such as sodium, ersorbic acid or ammonium ferrous sulfate in combination.

It is also possible to use a polymerization control agent for mercaptans such as dodecyl mercaptan and, if necessary, a water-soluble salt as a buffer.

The present invention focuses on the method of adding an α, β-ethylenically unsaturated carboxylic acid during emulsion polymerization, wherein 60% to 100% by weight of the α, β-ethylenically unsaturated carboxylic acid is added in the latter half of the polymerization. Is what you do. The emulsion pressure-sensitive adhesive thus obtained shows good results in the adhesiveness to various objects to be adhered and the humidity resistance deterioration when a coated paper is used as the surface substrate. The α, β-ethylenically unsaturated carboxylic acid component is an indispensable component in the constitution of the pressure-sensitive adhesive, and at the same time, contributes greatly to various required physical properties. It is preferable that the α, β-ethylenically unsaturated carboxylic acid component has a small amount in terms of polarity with respect to the adhesive force to the polyolefin-type adhered object, and the holding force is reduced for the adhesive force to stainless steel, corrugated cardboard, and the like. As many as possible, more is better. Further, with respect to the cutting suitability required for post-processing suitability of the coated product and the cut-off property at the time of punching of labels and seals, etc., it is preferable that the adhesive has a high holding power, and α, β-ethylen It is necessary to introduce a large amount of a saturated carboxylic acid component. However, when coated paper is used as the surface base material, the moisture resistance deterioration resistance is α, β-
Defects are inversely proportional to the amount of the ethylenically unsaturated carboxylic acid component introduced. As described above, various required physical properties cannot be satisfied only by examining the type and amount of the α, β-ethylenically unsaturated carboxylic acid monomer.

α, β-ethylenically unsaturated carboxylic acid can be added directly to the reaction vessel, added to the dropping pre-emulsion or dropped monomer mixture, or added in two or more portions and added intermittently. Any of these methods may be used.

In the aqueous emulsion-type pressure-sensitive adhesive of the present invention, a portion having a large amount of carboxylic acid and a portion having a small amount of carboxylic acid are present in the emulsion component, and an emulsion having a wide polarity distribution can be obtained. As a result, it is considered that the balance between the leakage to various objects to be adhered is widened, and the adhesion to polyolefin-based objects and the objects to be adhered is particularly improved. In addition, regarding the humidity resistance deterioration, regarding the reactivity with metal ions in the coated paper base material, the portion with less carboxylic acid that is less likely to react with metal ions and the portion with less carboxylic acid that reacts preferentially with metal ions. When the physical properties of the adhesive as a whole are observed, the rate of deterioration is smaller than that of the emulsion synthesized by uniform dropping, and the adhesive coating is performed. It is probable that the humidity resistance of the work became better.

Hereinafter, the present invention will be described with reference to examples. In the examples, “parts” means “parts by weight” and “%” means “% by weight”.

Example 1 A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a dropping funnel was charged with 250 parts of ion-exchanged water, 2 parts of polyoxyethylene alkylphenol ether, and 2 parts of ammonium sulfate of polyoxyethylene alkylphenol ether. When heated to 80 ° C., 1 part of ammonium persulfate is added, and the following emulsified pre-emulsion is added dropwise.

2-ethylhexyl acrylate 790 parts Vinyl acetate 70 parts Methyl methacrylate 80 parts 2-hydroxyethyl methacrylate 30 parts Methacrylic acid 6 parts Polyoxyethylene alkyl phenol ether 13 parts Ammonium sulfate of polyoxyethylene alkyl phenol ether 13 parts Ion-exchanged water 441 parts Ammonium persulfate 4 parts Keep the temperature inside the reactor at 80 ° C, and add dropwise over 3 hours. Simultaneously with the addition, 24 parts of methacrylic acid are added to the reactor. Thereafter, ammonium persulfate is added twice, one part per hour, to complete the polymerization.

The resulting milky white emulsion had a solid content of 60% pH 3.0 and a viscosity of 1500 cps (BL viscometer, # 3 rotor, 30 rpm).

Preservative, defoamer, aqueous ammonia and thickener are added to this emulsion, and the viscosity is 15,000-20,000 cps (BL viscometer,
# 4 rotor, 12 rpm).

The aqueous emulsion type adhesive is 20-25 g / m ² coated on a dry weight in commercial polyethylene laminate quality paper separator,
The coating was dried at 100 ° C. for 2 minutes and turned over to a commercially available cast-coated paper to prepare a coated product. The coated product was measured for adhesive strength, holding power, and the like based on JIS-Z-0237. The coated product left at 23 ° C-65% is a normal coated product, left in an atmosphere of high temperature and high humidity of 50 ° C-98% for 2 days, and then the coated product left at 23 ° C-65% for 1 day is humidified. Aged coatings were evaluated, and the value of the adhesive strength of the humidified aged coating with respect to the adhesive strength of the normal coated product was defined as the retention of physical properties over time of the humidification, and the humidity resistance deterioration was evaluated. That is, if this value is 100
%, The lower the humidity resistance, the closer to 0%,
Great resistance to humidity degradation.

Example 2 After dropping 82% by weight of all the monomers constituting the emulsion in the same formulation as in Example 2, methacrylic acid was added to 8% by weight.
Parts are added all at once to the reaction kettle. After 15 minutes, 8 parts of methacrylic acid were intermittently added to the reactor after 15 minutes, and 8 minutes after 30 minutes (at the end of the dropping).

Thereafter, ammonium persulfate is added twice, one part per hour, to complete the polymerization.

The obtained milky white emulsion for aqueous pressure-sensitive adhesive has a solid content
59.9% pH 3.1, viscosity 1780 cps.

Comparative Example 1 The same raw material composition and quantity as in Example 1 were used, but 30 parts of methacrylic acid was mixed with another monomer and dropped.

Example 3 An aqueous emulsion was obtained in the same manner as in Example 1. However, the monomer composition dropped first is as follows.

Butyl acrylate 640 parts Lauryl acrylate 200 parts Ethyl acrylate 100 parts 2-hydroxyethyl methacrylate 40 parts Acrylic acid 4 parts Then, after dropping of the above monomer mixture, 16 parts of acrylic acid are added at a time. Same as Example 1.

The obtained milky white emulsion for aqueous pressure-sensitive adhesive has a solid content
59.8% pH 2.5 viscosity 1200 cps.

[Effects of the Invention] According to the present invention, it is possible to obtain an aqueous emulsion-type pressure-sensitive adhesive excellent in adhesiveness to various kinds of objects to be adhered and in resistance to humidity deterioration when coated paper is used as a surface substrate. Was.

Claims (1)

(57) [Claims] 1. An aqueous emulsion obtained by emulsion-polymerizing a monomer mainly comprising an alkyl acrylate having an alkyl group having 4 to 12 carbon atoms and containing 0.5 to 5% by weight of an α, β-ethylenically unsaturated carboxylic acid. In obtaining the mold adhesive,
Emulsion polymerize 50 to 99.8% by weight of a mixture of monomers which can contain up to 40% by weight of the α, β ethylenically unsaturated carboxylic acid to form an aqueous emulsion, and then in the presence of the emulsion And a method for producing an aqueous emulsion-type pressure-sensitive adhesive obtained by subjecting the remaining amount of β-ethylenically unsaturated carboxylic acid to emulsion polymerization alone.