JPH0710901B2 - Method for producing synthetic resin emulsion - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a synthetic resin emulsion useful as a one-pack type pressure-sensitive adhesive, and more specifically, using a reactive emulsifier in the presence of a chain transfer agent,
Heat resistance and heat resistance, characterized by emulsion-polymerizing a vinyl-based monomer mixture containing an acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms as a main component and containing a specific amount of unsaturated carboxylic acid and vinyl acetate. The present invention relates to a method for producing a synthetic resin emulsion useful as a one-component pressure-sensitive adhesive having excellent tackiness.

[0002]

2. Description of the Related Art In recent years, acrylic pressure-sensitive adhesive emulsions have been widely used in place of conventional natural rubber-based and synthetic rubber-based pressure-sensitive adhesives because of their excellent adhesive properties and durability. There is. As the market needs become more sophisticated, functionalization of pressure-sensitive adhesives is required. However, the conventional acrylic pressure-sensitive adhesive emulsion has a drawback that it is inferior in heat resistance.

As a method for improving the drawbacks of the conventional acrylic pressure-sensitive adhesive emulsion, (a) a method of using a vinyl monomer having a polyfunctional group in combination to improve cohesive force by intra-particle crosslinking, ( b) functional groups in the polymer (-OH,
-COOH), a cross-linking agent is added later to cross-link the particles to improve cohesive force, (c) a glass transition polymer having a high glass transition temperature monomer such as acrylic amide is copolymerized. A method of increasing the cohesive force by increasing the temperature is known. However, in the above method (a) or (b), although the heat resistance can be imparted due to the improvement of the cohesive force of the polymer, the adhesiveness is lowered due to the increase in the molecular weight, and a strong adhesive force is obtained. Was impossible. Further, in the method (c), the wettability is deteriorated at the time of sticking to an adherend, and strong tackiness cannot be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the conventional acrylic pressure-sensitive adhesive emulsions described above and is excellent in heat resistance and tackiness and is useful as a one-component pressure-sensitive adhesive synthetic resin. It is another object of the present invention to provide a method for producing an emulsion in one step without using a crosslinking agent or the like.

[0005]

As a result of intensive studies to solve the above problems, the present inventors have found that a pressure-sensitive adhesive having a high heat-peelability, which is not found in conventional pressure-sensitive adhesive emulsions. Using a special reactive emulsifier having a reactive double bond in its structural formula in one step of the adhesive emulsion and using no crosslinking agent at all, in the presence of a chain transfer agent, A synthetic resin emulsion obtained by emulsion-polymerizing a vinyl-based monomer mixture containing an acrylic acid alkyl ester having 4 or more alkyl groups as a main component and containing an unsaturated carboxylic acid and vinyl acetate in a specific ratio has the above-mentioned problems. The inventors have come to complete the present invention by knowing that they can be solved.

That is, the present invention is mainly composed of an acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms, and contains 0.1 to 20% by weight of unsaturated carboxylic acid and 1 to 30% by weight of vinyl acetate. The vinyl-based monomer mixture contained is represented by the following general formulas (I) to (V) in the presence of 0.001 to 5% by weight of a chain transfer agent based on the total weight of the vinyl-based monomer mixture. The present invention relates to a method for producing a synthetic resin emulsion, which comprises performing emulsion polymerization using at least one selected from the reactive emulsifiers represented.

[0007]

[Chemical 6] (However, R ₁ is a hydrocarbon group which may have a substituent,
R ₂ is hydrogen or a methyl group, and M is Na or NH ₄ . )

[0008]

[Chemical 7] (However, R ₃ is a hydrocarbon group which may have a substituent,
R ₄ is hydrogen or a methyl group, and M is Na or NH ₄ . )

[0009]

[Chemical 8] (However, R ₅ is a hydrocarbon group which may have a substituent,
R ₆ is hydrogen or a methyl group, A is an alkylene group having 2 to 4 carbon atoms, m is a number of 0 to 100, and X is hydrogen, a nonionic hydrophilic group or an anionic hydrophilic group. )

[0010]

[Chemical 9] (However, R ₇ is an alkyl group having 4 to 18 carbon atoms, an alkenyl group or an aralkyl group, R ₈ is hydrogen, and having 4 to 18 carbon atoms.
An alkyl group, an alkenyl group or an aralkyl group, A is an alkylene group having 2 to 4 carbon atoms or a substituted alkylene group,
n is a number from 2 to 200, M is an alkali metal atom, N
H ₄ or an alkanolamine residue. )

[0011]

[Chemical 10] (However, A is an alkylene group having 2 to 4 carbon atoms, and n is a number of 0 to 100.) The present invention will be described in more detail below. The vinyl-based monomer mixture used in the present invention is mainly composed of an acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms, and contains 0.1 to 20 unsaturated carboxylic acid in the vinyl-based monomer mixture. % By weight and 1 to 30% by weight of vinyl acetate, respectively.

As the acrylic acid alkyl ester, one having an alkyl group having 4 or more carbon atoms, preferably 4 to 12 carbon atoms and having a relatively low glass transition temperature of the polymer when formed into a polymer is used. Typical examples thereof include n-butyl, iso-butyl or t-butyl acrylate, n-amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl or iso-octyl acrylate, nonyl acrylate and the like. These acrylic acid alkyl esters are used in at least 50% by weight in the vinyl monomer mixture. The amount of alkyl acrylate having an alkyl group having 4 or more carbon atoms is 5
If it is less than 0% by weight, the glass transition temperature of the polymer is high,
It has drawbacks such as tackiness at the time of drying, deterioration of wettability, and further deterioration of adhesiveness.

The unsaturated carboxylic acid is used for imparting the cohesive force required for obtaining heat resistance. The unsaturated carboxylic acid used is one containing a monovalent or divalent or higher carboxylic acid, and specifically, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid and the like. can give.

The amount of the unsaturated carboxylic acid used is 0.1 to 20% by weight, preferably 0.5, in the vinyl monomer mixture.
10 to 10% by weight. The amount of unsaturated carboxylic acid used is 0.
If it is less than 1% by weight, the cohesive force for obtaining heat resistance will be insufficient, and if it exceeds 20% by weight, the cohesive force of the polymer will be too strong and the adhesiveness will be deteriorated.

The vinyl acetate used in the present invention has a function of enhancing the cohesive force of the polymer, imparting heat resistance, and assisting in compatibility with the substrate / adherent. The amount of vinyl acetate used is 1 to 30% by weight, preferably 2 in the vinyl monomer mixture.
~ 15% by weight. When the amount of vinyl acetate used is less than 1% by weight, the cohesive strength is improved, and the base material of vinyl acetate,
It is not preferable because the adhesiveness to the adherend cannot be obtained, and when it exceeds 30% by weight, the glass transition temperature becomes too high and the adhesive strength decreases.

The vinyl-based monomer mixture may contain other vinyl-based monomers in addition to the alkyl acrylate having an alkyl group having 4 or more carbon atoms, the unsaturated carboxylic acid and vinyl acetate. For example, in order to impart cohesive force to the produced polymer, a monomer that exhibits a relatively high glass transition temperature when made into a polymer, such as methyl (meth), is used.
Acrylate, ethyl (meth) acrylate, propyl (meth) acrylate and the like can be added within a range that does not impair the object of the present invention. Other typical vinyl monomers that can be used include n-butyl and i
so-butyl or t-butyl methacrylate, n-
Amyl methacrylate, hexyl methacrylate,
2-ethylhexyl methacrylate, octyl or iso-octyl methacrylate, nonyl methacrylate, vinyl propionate, styrene, α-methylstyrene, acrylonitrile, ethylene, vinyl chloride, vinylidene chloride, and a suitable amount of hydrophilic vinyl monomer, Sodium vinyl sulfonate, sodium methallyl sulfonic acid, 2-acrylamide 2-methylpropane sulfonic acid, sodium p-styrene sulfonate, (meth) acrylamide, N-methylol (meth) acrylamide,
Examples thereof include hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate.

Typical examples of the chain transfer agent used in the present invention include mercaptans such as butyl mercaptan, lauryl mercaptan, dodecyl mercaptan, mercaptoacetic acid and 2-hydroxyethanethiol, alcohols such as methanol, ethanol and isopropyl alcohol. And halogenated carbons such as carbon tetrachloride. These chain transfer agents are used alone or in combination of two or more.

The amount of the chain transfer agent used is 0.001 to 5% by weight, preferably 0.05 to 2% by weight, based on the total weight of the vinyl monomer mixture. If it is less than 0.001% by weight, the cohesive force of the polymer is too high to obtain a strong adhesive force, and if it exceeds 5% by weight, the cohesive force of the polymer is too low and heat resistance cannot be maintained, which is preferable. Absent.

The reactive emulsifier used in the present invention is represented by the above general formulas (I), (II), (III), (IV) and (V), and these are mixed in two or more kinds. May be used. The amount of the reactive emulsifier used is preferably 0.1 to 5% by weight based on the total weight of the vinyl-based monomer mixture.

The synthetic resin emulsion of the present invention can be produced by a usual emulsion polymerization method. At the time of polymerization, a polymerization initiator is usually used, and any of those generally used for emulsion polymerization can be used. Typical examples are water-soluble inorganic peroxides or persulfates such as hydrogen peroxide and ammonium persulfate, organic peroxides such as cumene hydroperoxide and benzoyl peroxide, and azobisisobutyronitrile. Examples include azo compounds. The amount of the polymerization initiator used is preferably 0.1 to 2% by weight based on the total weight of the vinyl-based monomer mixture. It is needless to say that a method generally known as a redox polymerization method using these polymerization initiators in combination with a metal ion and a reducing agent may be used.

The above-mentioned various monomers may be added all at once, in a divided manner, or continuously by dropping. The polymerization is usually performed at a temperature of 60 to 85 ° C.

The glass transition temperature of the produced emulsion polymer is preferably in the range of -80 to -20 ° C as a theoretical glass transition temperature determined from the glass transition temperature of each component constituting the polymer. When the glass transition temperature is lower than −80 ° C., the cohesive force is generally too low and heat resistance is not obtained. If a high molecular weight polymer is used in order to increase the cohesive force, there is a drawback that the adhesiveness is lowered. On the other hand, when the glass transition temperature is higher than −20 ° C., the cohesive force and hardness of the polymer are too high, the tack and the wettability at the time of dry use are deteriorated, and the adhesion is deteriorated, which is not preferable as an adhesive. .

If desired, the synthetic resin emulsion of the present invention may contain additives such as tackifiers, preservatives, fungicides and pigments.

The synthetic resin emulsion of the present invention has excellent heat resistance and tackiness and is useful as a pressure-sensitive adhesive for general pressure-sensitive adhesive tapes, sheets and labels.

[0025]

In the present invention, a vinyl-based monomer mixture containing an alkyl acrylate having an alkyl group having 4 or more carbon atoms as a main component and containing a specific amount of unsaturated carboxylic acid and vinyl acetate is used as a chain transfer agent. Below, it is not clearly understood why the synthetic resin emulsion obtained by emulsion polymerization using a reactive emulsifier shows a very high heat-resistant peeling force. However, in the polymer composed of acrylic acid alkyl ester / unsaturated carboxylic acid / vinyl acetate, acid is localized on the particle surface, vinyl acetate is present underneath it, and acrylic acid alkyl ester with a low glass transition temperature is in the innermost shell. There may be some localization within the particles (the presence of a soft polymer in the hard shell), and the presence of a homopolymer of unsaturated carboxylic acid or vinyl acetate is also considered to be the theoretical value. It is considered that the glass transition temperature of the particle surface is higher than the glass transition temperature. In such a state, the effective use of the chain transfer agent improves the familiarity with the substrate / adherend, and the contact at a high glass transition temperature does not result in a higher heat resistance than expected. It is supposed.

[0026]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. In the examples, all parts and% are by weight.

Example 1 15 parts of ion-exchanged water was charged in a container having a stirrer, a thermometer, a reflux condenser, and a dropping funnel, and the temperature was raised to 80 ° C. 23.5 parts of ion-exchanged water, the general formula (III)
Reactive emulsifier represented by (wherein R ₅ is C ₉ H ₁₉ , R
₆ is H, A is ethylene group, m is 20, X is sulfonic acid group) 0.5 part, 2-ethylhexyl acrylate 50
Part, 5 parts of vinyl acetate, 3 parts of methacrylic acid, and 0.05 part of dodecyl mercaptan were added dropwise over 4 hours.

On the other hand, at the same time when the dropping of the mixed emulsion is started,
Emulsion polymerization was initiated by separately adding 0.2 part of a 5% aqueous solution of ammonium persulfate and 0.3 part of a 5% aqueous solution of acidic sodium sulfite. At the same time, 5% ammonium persulfate aqueous solution 1
Parts were added dropwise over 4 hours. During this time, the inside of the container was kept at 80 ° C., and was kept at 80 ° C. for 1.5 hours after completion of dropping. After that, cooling was started, and after cooling to 30 ° C. or lower, 1.5 parts of aqueous ammonia (28%) was added. The obtained synthetic resin emulsion has a solid content concentration of 58.4% and a viscosity of 2400 cp.
It was s.

Example 2 The same reaction as in Example 1 was carried out except that the amount of vinyl acetate used was reduced to 1 part and the amount of 2-ethylhexyl acrylate used was changed to 54 parts. The solid content concentration of the obtained synthetic resin emulsion is 58.4%,
The viscosity was 2000 cps.

Example 3 In Example 1, 0.05 g of dodecyl mercaptan
Was changed to 0.8 g of isopropyl alcohol (IPA), and the same reaction as in Example 1 was performed. The resulting synthetic resin emulsion had a solid content concentration of 58.3% and a viscosity of 1100 cps.

Example 4 The same reaction as in Example 1 was carried out except that the amount of methacrylic acid used was reduced to 1 part and the amount of 2-ethylhexyl acrylate used was increased to 52 parts. The solid content concentration of the obtained synthetic resin emulsion was 58.4.
%, The viscosity was 1400 cps.

Example 5 In Example 1, 1 part of IPA was further added to the charge,
The same reaction as in Example 1 was carried out except that the amount of ion-exchanged water was 14 parts and the amount of dodecyl mercaptan used was reduced to 0.02 part. The resulting synthetic resin emulsion had a solid content concentration of 58.3% and a viscosity of 900 cps.

Comparative Example 1 The same reaction as in Example 1 was carried out except that an equivalent amount of sodium dodecylbenzenesulfonate was used in place of the reactive emulsifier represented by the general formula (III). The solid content concentration of the obtained synthetic resin emulsion was 58.5.
%, The viscosity was 3900 cps.

Comparative Example 2 The same reaction as in Example 1 was carried out except that the same amount of methyl methacrylate was used in place of vinyl acetate in Example 1. The resulting synthetic resin emulsion had a solid content concentration of 58.5% and a viscosity of 3400 cps.

Comparative Example 3 A reaction was carried out in the same manner as in Example 1 except that dodecyl mercaptan was removed. The obtained synthetic resin emulsion has a solid content concentration of 58.4% and a viscosity of 460.
It was 0 cps.

Comparative Example 4 The reaction was carried out in the same manner as in Example 1 except that an equal amount of acrylate was used instead of methacrylic acid. The obtained synthetic resin emulsion had a solid content concentration of 58.3% and a viscosity of 8200 cps.

The synthetic resin emulsions obtained in the above Examples and Comparative Examples were treated with a polycarboxylic acid type thickener to obtain 1000
After thickening to 0 ± 1000 (cps), this was applied to a PET film so as to be 30 g / m ² (dry) to prepare an adhesive film. Using this adhesive film, 80
The 180 ° peeling force and holding force at ℃ were measured. The results are shown in Table 1.

[0038]

[Table 1]

As is clear from the results shown in Table 1, the synthetic resin emulsion of the present invention has both heat resistance and strong tackiness and is useful as a one-component pressure-sensitive adhesive.

[0040]

Since the present invention is constructed as described above,
A synthetic resin emulsion useful as a one-component pressure-sensitive adhesive with excellent heat resistance and tackiness can be produced in a single step in a simple process, and by utilizing the characteristics of the obtained synthetic resin emulsion, It can be used as a pressure-sensitive adhesive for adhesive tapes, sheets, labels and the like.

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Claims (1)

[Claims] 1. A main component is an alkyl acrylate ester having an alkyl group having 4 or more carbon atoms, and 0.1 to 20% by weight of an unsaturated carboxylic acid and 1 to 1 of vinyl acetate.
0.001 to 5% by weight of the vinyl-based monomer mixture containing 30% by weight, based on the total weight of the vinyl-based monomer mixture.
The method for producing a synthetic resin emulsion, which comprises emulsion-polymerizing in the presence of the chain transfer agent described above, using at least one selected from the reactive emulsifiers represented by the following general formulas (I) to (V). [Chemical 1] (However, R ₁ is a hydrocarbon group which may have a substituent,
R ₂ is hydrogen or a methyl group, and M is Na or NH ₄ . ) [Chemical 2] (However, R ₃ is a hydrocarbon group which may have a substituent,
R ₄ is hydrogen or a methyl group, and M is Na or NH ₄ . ) [Chemical 3] (However, R ₅ is a hydrocarbon group which may have a substituent,
R ₆ is hydrogen or a methyl group, A is an alkylene group having 2 to 4 carbon atoms, m is a number of 0 to 100, and X is hydrogen, a nonionic hydrophilic group or an anionic hydrophilic group. ) [Chemical 4] (However, R ₇ is an alkyl group having 4 to 18 carbon atoms, an alkenyl group or an aralkyl group, R ₈ is hydrogen, and having 4 to 18 carbon atoms.
An alkyl group, an alkenyl group or an aralkyl group, A is an alkylene group having 2 to 4 carbon atoms or a substituted alkylene group,
n is a number from 2 to 200, M is an alkali metal atom, N
H ₄ or an alkanolamine residue. ) [Chemical 5] (However, A is an alkylene group having 2 to 4 carbon atoms, and n is a number of 0 to 100.)