JPS5933602B2 - Method of manufacturing pressure sensitive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an emulsion type pressure sensitive adhesive.

In recent years, demand for solvent-free adhesives has increased even in the field of pressure-sensitive adhesives.
Organic solvent-based pressure-sensitive adhesives, which have traditionally dominated the market, are being replaced by aqueous emulsion-based adhesives.

However, conventional emulsion type resins have the disadvantage that their adhesion to polyolefin resins with low surface energy, such as containers and films made of polyethylene or polypropylene, is insufficient for practical use, and there is a strong demand for improvement. was. In general, there are three main performance requirements for pressure-sensitive adhesives: adhesive strength, cohesive strength, and adhesive strength.

Adhesion is an element that indicates instantaneous wetness to the adherend.
Cohesive force is an element that indicates creep resistance, and adhesive force is an element that indicates peeling resistance. Among these, in order to exhibit practically sufficient adhesiveness, adhesive force and cohesive force must be sufficiently large.

Even if the adhesive force is high, if the cohesive force is low, the adhesive may naturally peel off from the adherend if left for a long period of time, making it unsatisfactory for practical use. Acrylic emulsion type pressure-sensitive adhesives can achieve the above-mentioned performance, that is, adhesive strength,
The balance between cohesive force and adhesive force can be adjusted to some extent.

However, it is difficult to obtain a material with sufficiently large cohesive force and adhesive force using acrylic copolymer resin alone, and in order to improve adhesive force, for example,
As shown in No. 6, etc., it has been known to blend tackifier resins and elastomers.

This product uses an acrylic copolymer resin base to wet the adherend, and a blend of adhesion agent resin and elastomer improves the tensile stress of the pressure-sensitive adhesive layer, reducing the breaking energy of the pressure-sensitive adhesive. The purpose is to increase the peel strength by increasing the peel strength. However, in the case of such conventional blending technology, particles of acrylic copolymer and particles of blended resin exist independently in the emulsion, and acrylic copolymer particles and blended resin particles exist independently on the adhesive surface of the pressure-sensitive adhesive resin layer after drying. The particles of the system polymer and the particles of the blend resin exist independently, and the poor wettability of the blend resin leads to a decrease in the wettability of the pressure-sensitive adhesive. Even if the tensile stress of the layer is improved, the adhesive strength is not sufficiently improved.

However, as a result of intensive research into this problem, the inventors of the present invention discovered that by performing two-stage polymerization of an acrylic monomer in an ethylene monovinyl acetate copolymer emulsion, a solution that could not be obtained using conventional blending techniques was obtained. The inventors have discovered that it is possible to obtain a pressure-sensitive adhesive having excellent adhesive strength and sufficiently large cohesive strength, and have thus completed the present invention.

That is, the present invention provides one or more aqueous emulsions selected from the group consisting of ethylene monoacetate pinyl copolymer, ethylene monovinyl acetate vinyl monochloride copolymer, and ethylene monovinyl acetate-acrylic acid ester copolymer. 200 parts by weight per 100 parts by weight of the solid content of the aqueous emulsion.
1 of the acrylic monomer in an amount corresponding to ~1000 parts by weight
The present invention relates to a method for producing an emulsion-type pressure-sensitive adhesive, which comprises dropping an emulsifying monomer consisting of a species or two or more species and an emulsifier, and carrying out two-stage polymerization in the presence of a radical polymerization initiator.

In the pressure-sensitive adhesive of the present invention, an acrylic monomer is dissolved in ethylene monovinyl acetate copolymer emulsion particles, and the acrylic monomer is dissolved in the particles using an ethylene monovinyl acetate copolymer resin as a core. Polymerization has progressed, and the ethylene monovinyl acetate copolymer emulsion particles that existed before polymerization have become a two-stage polymer emulsion wrapped in the acrylic polymer.

To this end, as the two-stage polymer emulsion, which is the pressure-sensitive adhesive of the present invention, dries, the ethylene monovinyl acetate copolymer is incorporated into the acrylic polymer and dispersed uniformly. , a pressure-sensitive adhesive having a suitably high tensile stress can be obtained.

Even if the tensile stress of a pressure-sensitive adhesive is high, high adhesive strength cannot be obtained if the wetting to the adherend is poor. Since it is included in the polymer and forms the surface to which the acrylic polymer adheres, it is thought that wetting is good and extremely high adhesive strength can be obtained.

Furthermore, according to the production method of the present invention, the ethylene monovinyl acetate copolymer emulsion particles polymerized in the first stage are provided as a site for the polymerization reaction of the acrylic monomer to be reacted in the second stage, so the emulsifier The number of micelles required to initiate emulsion polymerization can be adjusted by the type, amount, and type of catalyst, and the number of particles at the end of emulsion polymerization can be adjusted. It is possible to produce emulsions with higher concentrations than acid ester copolymer emulsions.

Furthermore, as shown in Japanese Patent Publication No. 54-44034, it has conventionally been thought that in two-stage polymerization, it is not possible to polymerize a large amount of acrylic monomer in the second stage polymerization.

However, the present inventor believes that this conventional way of thinking arose because the second stage polymerization was carried out by adding only monomers, and that monomers were mixed in advance with an emulsifier as in the present invention. It has also been found that by using the above emulsifying monomer, a large amount of 200 to 1000 parts by weight of an acrylic monomer can be stably subjected to two-stage polymerization with respect to 100 parts by weight of a first-stage polymer.

Therefore, unless the acrylic monomer within this range is subjected to two-stage polymerization, a pressure-sensitive adhesive with excellent performance such as that of the present invention cannot be obtained. Ethylene monovinyl acetate used in the present invention As the emulsion, an aqueous emulsion containing 10 to 30% by weight of ethylene, 90 to 20% by weight of vinyl acetate, and 0 to 50% by weight of vinyl chloride, acrylic ester or methacrylic ester is suitable.

In addition, the acrylic monomers used in the present invention include acrylic esters, methacrylic esters, acrylic acid,
Methacrylic acid, acrylamide, methacrylamide, N
Examples include -methylol acrylamide, acrylol nitrile, hydroxyalkyl acrylate, glycidyl methacrylate, and in addition to these, a small amount of a copolymerizable α-ethylene monomer is preferred.

Examples of emulsifiers used in the present invention include alkylbenzene sulfonates, higher alcohol sulfates, polyoxyethylene alkyl phenyl sulfates, dialkyl sulfosuccinates, etc. Anionic emulsifiers such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether, oxyethylene-oxypropylene polymer copolymers, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, hydroxyethyl cellulose, starch One or more types of protective colloids such as these are used.

As the emulsifier for producing the acrylic emulsified monomer used in the second stage polymerization, a mixed emulsifier containing the above-mentioned nonionic emulsifier or, depending on the case, an anionic emulsifier is used.

To make an emulsifying monomer, the acrylic monomer 100
Adding 0.5 to 6 parts by weight of the emulsifier to parts by weight,
Stir thoroughly to emulsify.

As the radical polymerization initiator, water-soluble radical polymerization initiators such as potassium persulfate, ammonium persulfate, and hydrogen peroxide are used in the first stage polymerization. Depending on the case, reducing agents such as sodium sulfite, sodium hydrogen sulfite, and 1-ascorbic acid may be used in combination. In the second stage polymerization, oil-soluble radical polymerization initiators such as benzoyl peroxide, tert-butyl peroxide, and azobisisobutyronitrile can also be used in addition to those mentioned above.

The aqueous emulsion obtained in the present invention can be used as a pressure-sensitive adhesive as it is, but various agents such as a tackifying agent, a plasticizer, and titanium oxide may be added thereto. Next, the method of the present invention will be explained in detail with reference to production examples and examples.

Note that parts and % represent parts by weight and % by weight, respectively.

Example of manufacturing the first stage copolymer emulsion [Production method of ethylene monovinyl acetate copolymer emulsion] In an autoclave equipped with a stirrer, 100 parts of total monomers, 64 parts of ion-exchanged water, and sodium dodecylbenzenesulfonate were added at room temperature. 0
, 9 parts, polyoxyethylene nonylphenol ether emulsifier 0.54 part, Gohsenol GM-14 (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., partially saponified polyvinyl alcohol) 0.18 part, acetic acid 0.06 part, sodium acetate 0.3
An aqueous solution consisting of 0.58 parts of Rongalit and 0.58 parts of Rongalit was charged, and nitrogen and ethylene substitution was carried out under stirring.

Next, the temperature inside the system was heated to 50°C, and 19.4 parts of a 6.26% ammonium persulfate aqueous solution and the monomers other than ethylene in the monomers listed in Table 1 were uniformly added dropwise over a period of 4 hours. .

During this time, the reaction temperature was adjusted to 50°C, and ethylene was supplied. During the polymerization, the ethylene pressure was adjusted to 30 to 60 kgf/Cd depending on the ethylene copolymerization ratio.

After the polymerization was completed, the pH was neutralized to 5.5 using aqueous ammonia. The solids content of the resulting emulsion was approximately 54%.
Examples 1 to 4 185 parts of an ethylene monovinyl acetate copolymer emulsion having the composition ratio shown in Table 1 prepared by the method of the production example was placed in a container equipped with a stirrer, a thermometer, a reflux condenser, and a dropping load. When the temperature reaches 60℃ while stirring, 2
-200 parts of ethylhexyl acrylate, 186 parts of butyl acrylate, 12 parts of acrylic acid, 2 parts of N-methylol acrylamide, 7 parts of polyoxyethylene alkyl phenol sulfate emulsifier, 7 parts of polyoxyethylene nonyl phenol ether emulsifier, 1 part of ion-exchanged water
10% of the emulsified monomer mixture consisting of 75 parts was added.

Tertiary butyl peroxide after 10 minutes 2.
4 parts, 10% of the radical polymerization initiator dispersion consisting of 0.5 parts of polyoxyethylene nonylphenol ether emulsifier and 25 parts of ion-exchanged water, and 10% of 24 parts of 10% sodium bisulfite aqueous solution. The second stage polymerization was started by adding the same amount dropwise.

After 30 minutes, the remaining 90% of the emulsified monomer mixture, the remaining 90% of the radical polymerization initiator dispersion, and the remaining 90% of the 10% sodium hydrogen sulfite aqueous solution were added for 15 minutes. It was fed evenly over a 4 hour period at minute intervals.

difference. Stirring was continued for another 1 hour to complete the polymerization.

The solid content of the emulsion obtained was approximately 62%, and the viscosity was 18%.
It was between 000 and 20,000 centipoise. Example 5
185 parts of the ethylene monovinyl acetate copolymer emulsion used in Example 1 was charged into a container equipped with a stirrer, a thermometer, a reflux condenser, and a dropping load, and heated while stirring until the temperature reached 70°C. -450 parts of nitylhexyl acrylate, 383 parts of butyl acrylate, 54 parts of methyl methacrylate, 13 parts of itaconic acid, 15 parts of polyoxyethylene alkylphenol sulfate emulsifier, 1 part of polyoxyethylene nonylphenol ether emulsifier
10% of the emulsified monomer mixture consisting of 5 parts and 900 parts of ion-exchanged water was added, and then 27 parts of a 4% potassium persulfate aqueous solution was added dropwise to initiate the second stage polymerization.

After 30 minutes, the remaining 90% of the emulsified monomer mixture and 108 parts of a 4% potassium persulfate aqueous solution were uniformly supplied over a period of 4 hours, and stirring was continued for an additional hour to complete the polymerization. .

The solid content of the emulsion obtained was 48% and the viscosity was 300.
The temperature was 0 centipoise.

Comparative Example 1 Using the acrylic monomer used in the two-stage polymerization in Example 1, an acrylic ester copolymer emulsion was produced in a conventional manner.

Comparative Example 2 The ethylene monovinyl acetate copolymer emulsion obtained by one-stage polymerization in Example 1 and the acrylic acid ester copolymer emulsion obtained in Comparative Example 1 were combined in a resin composition ratio similar to that of Example 1.
The emulsions were mixed uniformly in the same ratio of 1:4.

The results of these Examples and Comparative Examples are shown in Table 1.

The test method was performed as follows.

(Toray Industries, Inc. Lumira #30) was coated with the adhesives obtained in the Examples and Comparative Examples so that the dry coating thickness was 25μm and 5μm, and the samples were dried at 110°C for 3 minutes with hot air circulation. Created.

Measurement of adhesion: J. According to the DOw method, a sample of length 10 (V7l) is pasted on a slope with an inclination angle of 300, and
A steel ball having a diameter of x/32 inch was rolled from the 0CTrL position, and the size of the ball with the largest diameter that stopped on the sample was indicated by the size of X.

Measurement of adhesive strength: SUS3O4 stainless steel plate polished with #280 water-resistant abrasive paper specified in JISR6253,
and polyethylene plate (1804 for γc = 43dyn/(V7l) by the method specified in JISK6768)
Peeling force: 200C) 65%RH) Peeling speed: 300mm
/Min.

Claims (1)

[Claims] 1 One or more selected from aqueous emulsions of ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, or ethylene-vinyl acetate-acrylic ester copolymer, and the aqueous emulsion An emulsifying monomer consisting of one or more acrylic monomers and an emulsifier in an amount equivalent to 200 to 1000 parts by weight per 100 parts by weight of the solid content is added dropwise, and in the presence of a radical polymerization initiator. A method for producing an emulsion-type pressure-sensitive adhesive characterized by two-stage polymerization.