JP4362148B2 - Method for producing water-dispersible acrylic pressure-sensitive adhesive - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a water-dispersed acrylic pressure-sensitive adhesive excellent in both adhesive properties and cohesive strength.
[0002]
[Prior art]
In recent years, acrylic pressure-sensitive adhesives have been widely used in place of conventional rubber-based pressure-sensitive adhesives because of their excellent adhesive properties and durability. In addition, from the viewpoint of environmental measures and resource saving, water-dispersed acrylic pressure-sensitive adhesives that do not use organic solvents have been researched and developed, and the amount of use is increasing.
[0003]
Such water-dispersed acrylic pressure-sensitive adhesives are generally prepared by an emulsion polymerization method. That is, a monomer containing (meth) acrylic acid alkyl ester as a main component and, if necessary, a modifying monomer such as acrylic acid, styrene or vinyl acetate, is added as an emulsifier and a polymerization initiator in an aqueous medium. It is prepared by emulsion polymerization using Since the water-dispersed acrylic pressure-sensitive adhesive obtained by this method has a relatively high molecular weight as compared with the acrylic pressure-sensitive adhesive obtained by solution polymerization, it is common to obtain a high cohesive force.
[0004]
[Problems to be solved by the invention]
However, the above conventional water-dispersed acrylic pressure-sensitive adhesive does not satisfy the cohesive force when used in applications requiring higher properties, for example, at high temperatures, and obtains a higher cohesive force. Therefore, a melamine compound, an epoxy compound, a metal salt, or the like is blended as an external cross-linking agent. In this case, the adhesiveness, particularly the adhesiveness to a rough surface, is often inferior.
[0005]
In order to make these adhesiveness and cohesive force compatible, use special monomers, use additives that act as softeners, mix tackifier resins, use special crosslinking agents, Many attempts have been made, such as changing the polymerization method. However, when special monomers are used, the adhesive properties are limited and the application range is narrowed. Also, when various additives are used, there are contrivances and pot life to achieve uniformity during mixing. There was a problem that occurred.
[0006]
The present invention solves these problems, and can easily produce a water-dispersed acrylic pressure-sensitive adhesive that can easily achieve both adhesion and cohesion, and can be applied to many applications by simply changing the composition of the monomer. It aims to provide a method.
[0007]
[Means for Solving the Problems]
As a result of intensive studies in order to achieve the above object, the inventors of the present invention dropwise added a means for emulsion polymerization of an acrylic monomer using a specific polymerization initiator and an emulsion of the same monomer as above. Thus, the present inventors have found that a water-dispersed acrylic pressure-sensitive adhesive capable of easily achieving both adhesiveness and cohesive force can be obtained by properly combining the means for emulsion polymerization while achieving the present invention.
[0009]
That is, the present invention provides a polymerization initiator having a 10-hour half-life temperature of 70 ° C. or less containing a monomer containing an alkyl group having 1 to 14 carbon atoms (meth) acrylic acid alkyl ester in a proportion of 50% by weight or more. a step by emulsion polymerization of Ru to obtain a first aqueous dispersion at once charged with, separately, water was added to the polymerization initiator the carbon number of this alkyl group is 1 to 14 (meth) acrylic the acid alkyl ester and a resulting Ru step a second aqueous dispersion by emulsion polymerization while dropping water emulsion of monomers in a proportion of more than 50 wt%, the first and second aqueous dispersion The present invention relates to a method for producing a water-dispersed acrylic pressure-sensitive adhesive comprising mixing liquids.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The (meth) acrylic acid alkyl ester used in the present invention is an alkyl ester of acrylic acid or methacrylic acid having 1 to 14 carbon atoms in the alkyl group, and one or more are used. Specific examples include butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and isooctyl acrylate. These monomers are used as a main component in a proportion of 50% by weight or more of the total monomers. If the amount is less than this, it is difficult to obtain a water-dispersed acrylic pressure-sensitive adhesive excellent in the adhesiveness and cohesive force of the present invention.
[0011]
As a monomer, you may use another monomer together with said main component as needed. For example, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, and acrylic acid ε-caprolactone are used to improve adhesion. Further, there are acrylonitrile, methacrylonitrile, vinyl acetate, styrene or derivatives thereof, vinyl pyrrolidone, acrylamide, N-methylol acrylamide, 2-hydroxyethyl acrylate, N, N-dimethylaminopropyl acrylamide, morpholino acrylate, and the like.
[0012]
The amount of these other monomers is appropriately selected depending on the type of each monomer within the range of 50% by weight or less of the total monomers. For example, in the case of an ethylenically unsaturated carboxylic acid, it is preferable to use it in the range of 10% by weight or less of the total monomer so that the polymerization stability is not impaired. In order to develop good pressure-sensitive adhesive properties, it is desirable to determine the composition of the main component and other monomers so that the glass transition point of the obtained acrylic copolymer is usually 250 K or less.
[0013]
In the present invention, by using the above monomer, that is, a monomer mainly composed of (meth) acrylic acid alkyl ester having 1 to 14 carbon atoms in the alkyl group, by a specific method described later, A water-dispersed acrylic pressure-sensitive adhesive is manufactured. This water-dispersed acrylic pressure-sensitive adhesive can also be produced by a method different from the present invention. Below, after explaining this another method first, the method of this invention is demonstrated. This another method is the first step in which the monomer is emulsion-polymerized using a polymerization initiator having a 10-hour half-life temperature of 70 ° C. or less, and the polymerization initiator is added to the polymerization system after this step. the second step of the emulsion polymerization while dropping water emulsion of similar monomers, are those to produce the water-dispersible acrylic pressure-sensitive adhesive.
[0014]
The polymerization initiator used in the first step has a 10-hour half-life temperature of 70 ° C. or lower, preferably 65 ° C. or lower. For example, 2,2-azobis [2-methyl-N- (phenylmethyl) -propionamidine ] Dihydrochloride, 2,2-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2-azobis [2- (2-imidazoline-2- Azo) initiators such as yl) propane], peroxide initiators such as 3,5,5-trimethylhexanoyl peroxycide, t-butylperoxypivalate, persulfates and sodium bisulfite There are redox initiators.
[0015]
By using such a specific polymerization initiator, it is possible to prevent an abrupt reaction during emulsion polymerization and facilitate reaction control, and to fully exhibit the effect of increasing the molecular weight that is characteristic of emulsion polymerization. . The amount of such a polymerization initiator used is not particularly limited, and is appropriately determined depending on the polymerization temperature. However, if used in a large amount, the reaction control becomes difficult and the molecular weight is lowered to reduce the cohesive force. Since it falls, it is not preferable. Preferably, the optimum amount of use may be determined in consideration of the polymerization temperature in the range of 0.001 to 0.2 parts by weight per 100 parts by weight of the monomer.
[0016]
In the first step, the above monomer is uniformly emulsified and dispersed in water using an emulsifier, and the above polymerization initiator is added thereto, followed by emulsion polymerization at a predetermined temperature. As the emulsifier, any nonionic or anionic emulsifier can be used, and generally it is used in the range of about 0.3 to 5 parts by weight per 100 parts by weight of the monomer. It is preferable to use a reactive emulsifier having an ethylenically unsaturated double bond as the emulsifier because good results are obtained in water resistance. The polymerization temperature is preferably a temperature at which the reaction can be easily controlled, specifically 30 to 60 ° C., and emulsion polymerization at such a temperature is preferable because a higher molecular weight can be obtained.
[0017]
In the second step, after the polymerization rate in the first step reaches 95% by weight or more, preferably 98% by weight or more, a polymerization initiator is further added to the polymerization system after the first step, and the first step is performed in advance. In this case, emulsion polymerization is carried out at a predetermined temperature while a water emulsion obtained by emulsifying and dispersing the same monomer as in the case of water is added dropwise. If the polymerization rate in the first step is less than 95% by weight and the process moves to the second step, it is difficult to achieve both adhesion and cohesion.
[0018]
The monomer composition in the second step is basically the same as that in the first step, but the adhesive properties may be improved by slightly changing the composition. For example, adhesion can be increased by increasing the amount of ethylenically unsaturated carboxylic acid. Furthermore, the same polymerization initiator as that used in the first step may be used, but in order to quickly polymerize the dropped monomer, the amount used should be increased as much as possible, and the polymerization temperature should be as high as possible. desirable. Specifically, a persulfate such as ammonium persulfate or potassium persulfate is selected as the polymerization initiator, and the polymerization initiator is added at a ratio of about 0.01 to 0.5 parts by weight per 100 parts by weight of the monomer. And emulsion polymerization may be performed at a temperature of 40 to 80 ° C.
[0019]
In the first step, the water-dispersed acrylic pressure-sensitive adhesive obtained in this way produces a large amount of high molecular weight components because of polymerization in a state where monomers are present excessively, so-called radicals are insufficient. In particular, this contributes to an increase in cohesive force, while in the second step, the polymerization is performed while dropping the monomer water emulsion, so-called radical-excess polymerization, so that a low molecular weight component. This acts to supplement the adhesiveness, particularly rough surface adhesiveness, which tends to be a problem in the first step, and as a result, it is possible to successfully achieve both the adhesiveness, particularly rough surface adhesiveness, and cohesive force.
[0020]
In order to achieve such an effect, the weight ratio of the monomer used in the first step and the monomer used in the second step is preferably in the range of 20:80 to 80:20, more preferably It is good to set it as the range of 30: 70-70: 30. If too much monomer is used in the first step, the adhesiveness, particularly the rough surface adhesion, becomes low, and if too much monomer is used in the second step, the cohesive force is impaired, which is not preferable.
[0021]
In the present invention, the emulsion polymerization in the first and second steps in a method different from that of the present invention is not continuously performed, but the water-dispersed acrylic pressure-sensitive adhesive is mixed by mixing emulsion polymerizations separately. An agent is manufactured. That is, a first aqueous dispersion obtained Ru steps by emulsion polymerization in the same manner as the first step of the above, alternatively, by emulsion polymerization as in the second step described above, i.e. the polymerization initiator in water It was added and a thereto Ru obtain a second aqueous dispersion by emulsion polymerization while dropping water emulsion of monomer process, by mixing the first and second aqueous dispersion, water Dispersed acrylic pressure sensitive adhesive is manufactured.
[0022]
At that time, the mixing ratio of the first aqueous dispersion and the second aqueous dispersion is the weight of the monomer used for the first aqueous dispersion and the monomer used for the second aqueous dispersion. The ratio is preferably in the range of 20:80 to 80:20, more preferably in the range of 30:70 to 70:30. By mixing at such a ratio, coexistence of adhesiveness, particularly rough surface adhesiveness, and cohesive force can be achieved. The emulsion polymerization method for obtaining the first aqueous dispersion and the emulsion polymerization method for obtaining the second aqueous dispersion are in accordance with the first step and the second step, respectively.
[0023]
The water-dispersed acrylic pressure-sensitive adhesive produced by the method of the present invention may optionally contain various additives such as tackifier resins, colorants, fillers, anti-aging agents and the like as necessary. Can do. Further, when a further increase in cohesive force is required, an external crosslinking agent may be added. The water-dispersed acrylic pressure-sensitive adhesive of the present invention has a feature that even when an external cross-linking agent is added, the cohesive force can be improved without causing a significant decrease in adhesiveness.
[0024]
The water-dispersed acrylic pressure-sensitive adhesive of the present invention was applied directly to one or both surfaces of any support such as plastic film, paper, metal foil, and dried, or applied to a separator and dried. Then, it can be set as adhesive sheets, such as a sheet form and a tape form, by transcribe | transferring to the single side | surface or both surfaces of the said support body. In this case, the thickness of the pressure-sensitive adhesive layer is appropriately determined according to the purpose of use, but is usually about 5 to 150 μm.
[0025]
【Example】
Next, in order to describe the present invention more specifically, examples and comparative examples are shown. The present invention is not limited to these examples. In the following, “part” means part by weight.
[0026]
Example 1
In a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser, 70 parts of 2-ethylhexyl acrylate, 27 parts of ethyl acrylate, 3 parts of acrylic acid, 1 part of sodium dodecylbenzenesulfonate, polyoxyethylene 1 part of nonyl phenyl ether (HLB: 14) and 150 parts of water were added, and the whole was uniformly emulsified while purging with nitrogen. The temperature was set at 50 ° C., 0.02 part of 2,2-azobis [2-methyl-N- (phenylmethyl) -propionamidine] dihydrochloride was added, and the emulsion was maintained at 50 ° C. for 8 hours to carry out emulsion polymerization. A first aqueous dispersion A was obtained. The polymerization rate was 99.4% by weight.
[0027]
Separately, 70 parts of 2-ethylhexyl acrylate, 27 parts of ethyl acrylate, 3 parts of acrylic acid, 1 part of sodium dodecylbenzenesulfonate, 1 part of polyoxyethylene nonylphenyl ether (HLB: 14) and 70 parts of water Was uniformly emulsified with a homomixer to prepare a water emulsion. Into the same reactor, 80 parts of water and 0.2 part of ammonium persulfate were added, dissolved uniformly, and set to 70 ° C. while purging with nitrogen. The monomer aqueous emulsion was added dropwise to the reactor over 3 hours, and after completion of the addition, the temperature was maintained at the above temperature for 2 hours to carry out emulsion polymerization to obtain a second aqueous dispersion B. The polymerization rate was 99.8% by weight.
[0028]
The first aqueous dispersion A and the second aqueous dispersion B thus obtained were mixed at a weight ratio of 50:50 to obtain a water-dispersed acrylic pressure-sensitive adhesive. This pressure-sensitive adhesive was applied onto a 25 μm polyester film so that the thickness after drying was 50 μm, and dried at 100 ° C. for 3 minutes to prepare an adhesive tape.
[0031]
Comparative Example 1
The first aqueous dispersion A of Example 1 alone was used as a water-dispersed acrylic pressure-sensitive adhesive. Using this water-dispersed acrylic pressure-sensitive adhesive, an adhesive tape was produced in the same manner as in Example 1.
[0032]
Comparative Example 2
The second aqueous dispersion B of Example 1 alone was used as a water-dispersed acrylic pressure-sensitive adhesive. Using this water-dispersed acrylic pressure-sensitive adhesive, an adhesive tape was produced in the same manner as in Example 1.
[0033]
Example 2
In a reactor equipped with a thermometer, stirrer, nitrogen inlet tube and reflux condenser, isononyl acrylate 80 parts, ethyl acrylate 10 parts, acrylonitrile 5 parts, methacrylic acid 5 parts, polyoxyethylene alkyl phenyl ether sulfate 3 parts of a reactive emulsifier obtained by adding a propenyl group to a phenyl group of an ammonium salt and 150 parts of water were added, and the whole was uniformly emulsified while purging with nitrogen. The temperature was set to 50 ° C., and the emulsion polymerization was carried out by maintaining at 50 ° C. for 8 hours using a redox initiator composed of 0.05 part of potassium persulfate and 0.05 part of sodium hydrogen sulfite. An aqueous dispersion C was obtained. The polymerization rate was 98.9% by weight.
[0034]
Separately, reactive emulsifier 3 in which propenyl group is added to phenyl group of polyoxyethylene alkylphenyl ether sulfate ammonium salt 80 parts isononyl acrylate 80 parts, ethyl acrylate 10 parts, acrylonitrile 5 parts, methacrylic acid 5 parts And 70 parts of water were uniformly emulsified with a homomixer to prepare a water emulsion. Into the same reactor, 80 parts of water and 0.2 part of ammonium persulfate were added, dissolved uniformly, and set to 70 ° C. while purging with nitrogen. The monomer aqueous emulsion was added dropwise to the reactor over 3 hours, and after completion of the addition, the temperature was maintained at the above temperature for 2 hours to carry out emulsion polymerization to obtain a second aqueous dispersion D. The polymerization rate was 99.4% by weight.
[0035]
The first aqueous dispersion C and the second aqueous dispersion D thus obtained were mixed at a weight ratio of 50:50 to obtain a water-dispersed acrylic pressure-sensitive adhesive. Using this pressure-sensitive adhesive, an adhesive tape was produced in the same manner as in Example 1.
[0037]
With respect to the adhesive tapes of Examples 1 and 2 and Comparative Examples 1 and 2, the adhesive force, rough surface adhesive force and cohesive force were measured in the following manner. The results were as shown in Table 1 below.
[0038]
<Measurement of adhesive strength>
A test piece having a size of 20 mm × 100 mm was prepared from the adhesive tape, and this test piece was pressure-bonded to a stainless steel plate sanded with # 280 sandpaper by reciprocating once with a 2 kg roller. After 30 minutes, The force required for 180 ° peeling was measured at a temperature of 23 ° C. and a relative humidity of 65% at a tensile speed of 300 mm / min.
[0039]
<Measurement of rough surface adhesion>
The rough surface adhesive force was measured by the same method as in the case of measuring the adhesive force except that # 100 sandpaper was used.
[0040]
<Measurement of cohesive force>
Affix the adhesive tape to the phenolic resin plate with an adhesive area of 10 mm x 20 mm, leave it at room temperature for 20 minutes, and then leave it at 80 ° C for 20 minutes, then lower the phenolic resin plate vertically and place 500 g on the free end of the adhesive tape. The load until the adhesive tape dropped was measured.
[0041]
Table 1
┌────┬────────┬────────┬┬───────┐
│ │ Adhesive strength │ Rough surface adhesion │ Aggregation power │
│ │ (g / 20mm width) │ (g / 20mm width) │ (minutes) │
├────┼────────┼────────┼┼───────┤
│Example 1│ 910 │ 350 │ 65 │
├────┼────────┼────────┼┼───────┤
│Comparative Example 1│ 850 │ 190 │ 80 │
│Comparative Example 2│ 930 │ 370 │ 15 │
├────┼────────┼────────┼┼───────┤
│Example 2 │ 1,050 │ 460 │ 55 │
└────┴────────┴────────┴┴───────┘
[0042]
From the results of Table 1 above, both adhesive tapes of Comparative Examples 1 and 2 are inferior in adhesive force, particularly rough surface adhesive force, or inferior in cohesive force, whereas in each adhesive tape of Examples 1 and 2 , It is clear that both the adhesive strength, particularly the rough surface adhesive strength and the cohesive strength are excellent.
[0043]
【The invention's effect】
As described above, according to the present invention, means for emulsion polymerization of an acrylic monomer using a specific polymerization initiator and means for emulsion polymerization while dropping an emulsion of the same monomer as described above are provided. By combining them well, it is possible to easily produce a water-dispersed acrylic pressure-sensitive adhesive that can be applied to many applications by simply changing the composition of the monomers used in both of the above means. be able to.

Claims (2)

By using a polymerization initiator having a 10-hour half-life temperature of 70 ° C. or less as a batch, a monomer containing an alkyl group having 1 to 14 carbon atoms (meth) acrylic acid alkyl ester in a proportion of 50% by weight or more. a first aqueous dispersion obtained Ru steps by emulsion polymerization, separately, the number of carbon atoms of the polymerization initiator was added alkyl to water is 1 to 14 (meth) 50 weight acrylic acid alkyl ester from this and a resulting Ru step a second aqueous dispersion by emulsion polymerization while dropping water emulsion of monomers containing% or more of the total, from mixing the first and second aqueous dispersion A method for producing a water-dispersed acrylic pressure-sensitive adhesive.   The mixing of the first and second aqueous dispersions was carried out so that the weight ratio of the monomer used to produce the first aqueous dispersion to the monomer used to produce the second aqueous dispersion was 20:80. The method for producing a water-dispersed acrylic pressure-sensitive adhesive according to claim 1, which is set to ˜80: 20.