JPS63234077A - Water-dispersed type pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition without any adverse effect of an emulsifying agent on bonding characteristics even with a high solid concentration, by adding an emulsion prepared by emulsifying a specific acrylic monomer mixture with a specific emulsifying agent into water containing a persulfate dissolved therein and carrying out polymerization. CONSTITUTION:The aimed composition obtained by initially blending (A) 100pts. wt. monomeric mixture, consisting of (A) 90-99.5wt.% main monomer consisting of an alkyl (meth)acrylate having 1-4C alkyl and (B) 10-0.5wt.% carboxyl- containing ethylenically unsaturated monomer and capable of providing a copolymer thereof, exhibiting pressure-sensitive adhesive property and having <=250 deg.K glass transition point with (B) 0.1-1pt.wt. sulfonic acid group-containing emulsifying agent soluble in the above-mentioned monomeric mixture and (D) water to provide a monomeric emulsion, adding the afore-mentioned emulsion into water containing a persulfate which is a polymerization initiator dissolved therein and carrying out polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to an acrylic water-dispersed pressure-sensitive adhesive composition.

[Conventional technology]

In recent years, acrylic pressure-sensitive adhesives have replaced conventional natural rubber-based adhesives due to their superior adhesive properties and durability.

It has become widely used as an alternative to synthetic rubber-based pressure-sensitive adhesives. Also, among this type of adhesive, recently water-dispersible adhesives that do not use organic solvents are resource-saving.

It is being researched and developed from the perspective of environmental hygiene.

Such water-dispersed adhesives are generally prepared by emulsion polymerization. That is, it is prepared by emulsion polymerization of a (meth)acrylic acid alkyl ester in an aqueous medium together with a modifying monomer such as acrylic acid, styrene, or vinyl acetate as necessary, and the room temperature obtained by this method is It is known that acrylic polymers with adhesive properties have a relatively large molecular weight compared to polymers obtained by solution polymerization, and therefore can provide relatively high cohesive strength as pressure-sensitive adhesives.

[Problems to be solved by the invention] -However, the above-mentioned conventional acrylic water-dispersed adhesives are still not satisfactory when applied to applications where a high degree of cohesive strength is desired. Furthermore, when the bonded area is exposed to relatively high temperatures, the cohesive force is significantly reduced, making it almost unusable. Therefore, in order to further improve the cohesive force of this type of adhesive, external crosslinking agents similar to those used in organic solvent types, such as melamine compounds, epoxy compounds, metal salts, etc., are added to the polymer emulsion after emulsion polymerization. Attempts have been made.

However, with these improvement measures, it is difficult to select the type and amount of crosslinking agent to be used, and there are productivity problems such as the thermal energy for crosslinking which cannot be ignored. Due to the non-uniformity, the cohesive force is not very large compared to the degree of crosslinking, and even if the cohesive force can be increased, the adhesive force will decrease accordingly, resulting in high adhesive force and high cohesive force. It has been difficult to obtain such pressure-sensitive adhesive compositions.

Furthermore, when the cohesive force is increased by the above-mentioned means,
Apart from the decrease in adhesive strength, there was also the problem that the adhesive had poor repulsion resistance.

In other words, in applications such as bonding a metal plate or plastic plate in a bent state to an adherend with a curved surface, a restoring force acts on the bent metal or plastic plate, so it is difficult to resist this restoring force. This repulsion resistance is expressed by the balance between adhesive strength and cohesive force. It was not possible to satisfy them.

As described above, the conventional acrylic water-dispersed adhesive has a problem in that it is difficult to obtain one that highly satisfies both adhesive strength and cohesive force and also has excellent repulsion resistance. Moreover, this type of adhesive uses an emulsifier to stabilize polymer particles during emulsion polymerization;
There is also a problem in that the adhesive composition is mixed with the adhesive composition, resulting in poor moisture resistance and water resistance, which adversely affects the adhesive properties.

In particular, in recent years, water-dispersed adhesives with a high solids concentration have been used to increase the drying speed and reduce manufacturing costs when manufacturing adhesive tapes and other products by coating and drying on a support. However, in this case, a large amount of emulsifier is required to stabilize the polymer particles, and the adverse effect on water resistance and, ultimately, adhesive properties cannot be ignored.

For example, JP-A No. 61-23614 describes a method for obtaining a water-dispersed adhesive with a high solid content concentration, in which a specific acrylic monomer mixture is emulsified in water using an emulsifier. A method of polymerizing while adding to the polymerization system is disclosed, but in order to perform stable emulsion polymerization by this method, anionic emulsifier and nonionic emulsifier are used together in a specific ratio and the monomer mixture is It is said that it is necessary to use a large amount of 2% by weight or more, usually 3 to 10% by weight. Use of such a large amount of emulsifier results in a significant loss of adhesive properties, making it extremely difficult to obtain a water-dispersed adhesive with excellent adhesive strength, cohesive force, and repulsion resistance.

Based on the above, this invention has no adverse effect on adhesive properties due to the use of emulsifiers even when using a high solids concentration, and does not intentionally use an external crosslinking agent (although it exhibits high cohesive force, The object of the present invention is to provide an acrylic water-dispersed pressure-sensitive adhesive composition that also has excellent adhesive strength and repulsion resistance.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors emulsified a specific acrylic monomer mixture using a specific emulsifier and used this emulsion as a water-soluble polymerization initiator. When emulsion polymerization is carried out while adding a sulfate solution to water, stable emulsion polymerization can be carried out even if the amount of the emulsion used is as small as 1% by weight or less based on the monomer mixture. Due to the effect of reducing the amount of emulsifier used and the properties of the emulsifier itself, adverse effects on adhesive properties caused by the use of emulsifiers can be avoided, and high cohesive strength can be achieved without using an external crosslinking agent. The present invention was completed based on the knowledge that an extremely high-performance water-dispersed pressure-sensitive adhesive composition with excellent adhesive strength and repulsion resistance can be obtained.

That is, in this invention, the alkyl group has 1 to 14 carbon atoms.
90 to 99.5% by weight of a main monomer consisting of a (meth)acrylic acid alkyl ester alone or this ester and a vinyl monomer copolymerizable therewith, and an ethylenically unsaturated monomer containing a carboxyl group. The copolymer consisting of ~0.5% by weight of IO exhibits pressure-sensitive adhesive properties and has a glass transition point of 2.
50" or less, an emulsifier having a sulfonic acid group in the molecule and being soluble in the monomer mixture, and water, and the emulsifier is based on 100 parts by weight of the monomer mixture. A water-dispersed pressure-sensitive adhesive composition based on a polymer emulsion obtained by adding 0.1 to 1 part by weight of a monomer emulsion to water in which a persulfate is dissolved and polymerizing it. It is related to things.

In this specification, (meth)acrylic acid refers to acrylic acid and/or methacrylic acid.
Acrylic acid alkyl ester means acrylic acid alkyl ester and/or methacrylic acid alkyl ester, and (meth)acrylate means acrylate and/or methacrylate, respectively.

Furthermore, the gel fraction of the polymer particles in this specification is an index indicating how much the polymer constituting the polymer particles is involved in crosslinking.
This is expressed by measuring the solvent insoluble content (% by weight) of the polymer.

Specifically, it is actually measured by forming a polymer film from an emulsion containing polymer particles, immersing it in a solvent to elute the polymer that does not participate in crosslinking, and measuring the remaining solvent-insoluble content. . This measurement is as shown in Examples below.

[Structure and operation of the invention]

The monomer mixture used in this invention is a main monomer consisting of a (meth)acrylic acid alkyl ester having an alkyl group of 1 to 14 carbon atoms alone, or this ester and a vinyl monomer copolymerizable therewith. and a carboxyl group-containing ethylenically unsaturated monomer.

In the above (meth)acrylic acid alkyl ester, the number of carbon atoms in the alkyl group is limited to 1 to 14 from the viewpoint of adhesive properties, and particularly preferred examples of such esters include Examples include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, ethyl methacrylate, butyl methacrylate, and lauryl methacrylate. In addition, as the main monomer, a vinyl monomer that can be copolymerized with the above ester may be used,
Specific examples thereof include acrylonitrile, methacrylaterile, vinyl acetate, styrene or derivatives thereof. The content of these copolymerizable vinyl monomers is preferably 25% by weight or less in the main monomers.

The carboxyl group-containing ethylenically unsaturated monomer used in combination with such a main monomer includes (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc., and among these, particularly preferred are The substance is acrylic acid.

This carboxyl group-containing ethylenically unsaturated monomer is a component that causes crosslinking in the polymer particles, increases the gel fraction of the polymer particles, and greatly contributes to improving the cohesive force. The reason why crosslinks are formed when such monomers are used is not necessarily clear at present, but it is speculated that when the above monomers are used, emulsion particles (polymer particles form) during the polymerization process. ), a chain transfer reaction by radicals occurs, which is thought to be involved in the formation of crosslinks.

The monomer mixture consisting of the main monomer and the carboxyl group-containing ethylenically unsaturated monomer has a composition such that the copolymer exhibits pressure-sensitive adhesive properties and has a glass transition point of 250°K or less. It is necessary that the With such a composition, it is possible to prepare an adhesive composition that has both high cohesive force and high adhesive strength, and has excellent repulsion resistance.

In addition, the ratio of the main monomer to the ethylenically unsaturated monomer containing a carboxyl group is 90 to 99.5% by weight of the main monomer and 1% by weight of the ethylenically unsaturated monomer containing a carboxyl group.
It should be between 0 and 0.5% by weight. If the amount of the carboxyl group-containing ethylenically unsaturated monomer is less than 0.5% by weight, the gel fraction of the polymer particles cannot be set within the desired range, resulting in poor cohesive force, and if it is more than 10% by weight, polymerization will occur. The stability becomes extremely poor, and the gel fraction of the polymer particles becomes too high, which tends to cause problems in terms of adhesive strength and repulsion resistance.

In this invention, before emulsion polymerization of such a monomer mixture, a monomer emulsion is prepared by previously emulsifying this mixture in water using an emulsifier. The emulsifier used here has a sulfonic acid group in its molecule and is soluble in the monomer mixture. Specific examples include polyoxyethylene alkyl ether sulfonate, polyoxyethylene alkylphenol ether sulfonate, and sulfosuccinate. Examples include sulfosuccinic acid derivatives such as sodium salts of acid dialkyl esters and sodium salts of alkyl alkenyl sulfosuccinate esters.

Since such specific emulsifiers have excellent emulsifying power for monomer mixtures, the amount used is 0.1 to 1 part by weight per 100 parts by weight of the monomer mixture to obtain a stable monomer emulsion. This small amount can greatly contribute to the stability of emulsion polymerization and the stability of the emulsion after polymerization. Moreover, since this emulsifier is soluble in the monomer mixture, it has excellent compatibility with the polymer particles, and even if it is mixed into the polymer emulsion, the amount used is small, and together with this, it is effective for adhesion. It has very little adverse effect on properties and gives very good results in improving adhesive properties.

On the other hand, if an emulsifier that does not have a sulfonic acid group in its molecule is used, a stable monomer emulsion cannot be obtained unless the amount used is considerably large, and in this case, the adverse effect on adhesive properties is large. Become. Furthermore, if a substance having a sulfonic acid group is insoluble in the monomer mixture, even if a stable monomer emulsion can be obtained with a small amount, it will be mixed into the polymer emulsion and form polymer particles. The poor compatibility with the adhesive also has an adverse effect on the adhesive properties.

In the present invention, as described above, a monomer emulsion is prepared consisting of the monomer mixture, the specific emulsifier in a proportion of 0.1 to 1 part by weight per 100 parts by weight of this mixture, and water. However, the amount of water used in this emulsion is preferably about 15 to 40 parts by weight per 100 parts by weight of the monomer mixture.

Such a monomer emulsion is then processed into a polymerization system containing a predetermined amount of water such that the final solid content concentration falls within an appropriate range, and a persulfate salt as a water-soluble polymerization initiator dissolved therein. To,
Polymerize with continuous addition. The polymerization temperature at this time is generally preferably in the range of 60 to 90°C.

Examples of the above persulfates include potassium persulfate, ammonium persulfate, and sodium persulfate.

This persulfate acts as a polymerization initiator and affects the molecular weight of the produced polymer, and the ionic end groups produced by its decomposition improve the polymerization stability in an aqueous medium and the stability of the emulsion after polymerization. Since it also contributes to stability, it is desirable to set the amount used within an appropriate range taking these factors into account. Generally, a monomer mixture of 10
A suitable ratio is 0.1 to 2 parts by weight to 0 parts by weight.

In the polymer emulsion thus obtained, the gel fraction of the polymer particles contained therein is preferably in the range of 20 to 60% by weight, and by setting such a gel fraction, adhesive strength, Good results can be obtained in both cohesive force and repulsion resistance properties. The above gel fraction can be set mainly by adjusting the type and amount of the carboxyl group-containing ethylenically unsaturated monomer, and in addition, by appropriately selecting the amount of persulfate used and polymerization conditions as described above. This can be done easily by doing this.

In addition, this polymer emulsion contains a moderate concentration of polymer particles having a crosslinked structure.

That is, from the viewpoint of emulsion stability, viscosity characteristics, etc., it is generally desirable that the solid content concentration be set in the range of 60 to 65% by weight.

The water-dispersed pressure-sensitive adhesive composition of the present invention is based on the above-mentioned polymer emulsion, and the composition may optionally contain a colorant, filler, anti-aging agent, tackifier, etc. Conventionally known additives may be appropriately blended. The amount added may be a normal amount, and the above composition alone exhibits high adhesive strength and high cohesive strength, but if it is desired to further increase the cohesive strength, it is within the range that does not impair the characteristics of the present invention. Various conventionally known external crosslinking agents may be blended within the composition.

〔Effect of the invention〕

As described above, in this invention, a specific acrylic monomer mixture is emulsified in water using a specific emulsifier, and this emulsion is added to water in which persulfate is dissolved and polymerized. As a result, stable emulsion polymerization can be carried out even with a small amount of emulsifier used, and due to the effect of reducing the amount of emulsifier used and the properties of the emulsifier itself, it is possible to carry out stable emulsion polymerization even when using a high solids concentration. To obtain an acrylic-based water-dispersed pressure-sensitive adhesive composition that has no adverse effect on adhesive properties, exhibits high cohesive strength without intentionally adding an external cross-linking agent, and has excellent adhesive strength and repulsion resistance. becomes possible. Therefore, the composition of the present invention is very useful not only for general pressure-sensitive adhesive tapes, sheets, labels, etc., but also for applications where rebound resistance is particularly required.

〔Example〕

EXAMPLES Below, examples of the present invention will be described in more detail. In addition, in the following, "part" means part by weight, and "%" means weight %, respectively.

Moreover, adhesive force, cohesive force, repulsion resistance, and gel fraction were measured by the following methods.

Adhesive strength> A pressure-sensitive adhesive composition is applied to both sides of a 25 μm thick polyester film so that the thickness after drying is 50 μm on one side, and dried at 100°C for 3 minutes to make a double-sided adhesive tape, and JIS Z- 1528, the 180 degree peeling adhesive strength (g/20w width) was measured.

Cohesive strength> Make double-sided adhesive tape similar to the adhesive strength test, and
It was attached to two Bakelite plates with an adhesive area of 25 m x 25 m, and a load of 1 kg was applied at 40° C. and 80° C., and the time (minutes) until the Bakelite plate fell was measured.

Repulsion resistance> A pressure-sensitive adhesive composition was applied to one side of an aluminum plate with a thickness of 0.3 to 50 μm after drying.
After drying at 0℃ for 3 minutes, cut into 10m x 80 pieces to make a test piece.The test piece was bent and attached to an aluminum cylinder with a diameter of 50 days, and then dried at 40℃ for 2 minutes.
When the test piece was stored for 4 hours, the distance (crane) that the test piece rose from the cylinder was measured.

Gel fraction> A pressure-sensitive adhesive composition was applied to one side of a 25 μm thick polyester film so that the thickness after drying was 50 crm, and after drying at 100°C for 3 minutes, 50fiX50M was applied.
A test piece was prepared by cutting it into a size of , and this test piece was immersed in heated acetone for 24 hours, and the gel fraction was determined by the following method.

At: Dry weight of test piece after immersion AO: Weight of test piece before immersion Example 1 50.0 mj equipped with thermometer, stirrer, nitrogen introduction tube and reflux condenser tube! Into a reactor, 30 parts of distilled water containing 0.5 part of potassium persulfate was added, and 8 parts of distilled water was added under a nitrogen stream.
After heating to 0°C, a monomer mixture consisting of 83% n-butyl acrylate, 15% ethyl acrylate, and 2% acrylic acid (glass transition point of copolymer 224°K) 10
0 parts, 0.25 parts of ammonium salt of polyoxyethylene alkyl ether sulfonic acid (trade name Hitenol N-17, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 25 parts of distilled water. 5 while maintaining the above temperature.
Polymerization was carried out by continuous addition over time.

The solid content concentration of the polymer emulsion thus obtained was 64.0%, and the gel fraction of the polymer particles was 48.5%. It was made into a composition.

Comparative Example 1 The same procedure as in Example 1 was carried out except that 0.25 parts of sodium lauryl sulfate (insoluble in the monomer mixture) was used as an emulsifier, the solid content concentration was 64.5%, and the gel content of the polymer particles was rate is 5
A 0.5% water-dispersed pressure sensitive adhesive composition was obtained.

Comparative Example 2 Polyethylene glycol nonylphenyl ether (which does not have a sulfonic acid group in the molecule) was used as an emulsifier at 0.
An attempt was made to prepare a water-dispersed pressure-sensitive adhesive composition in the same manner as in Example 1, except that 25 parts were used, but a stable monomer emulsion could not be obtained and the polymerization system became unstable. This caused problems with emulsion polymerization.

Comparative Example 3 The solid content concentration was 64.8% in the same manner as in Example 1, except that the amount of emulsifier made of ammonium salt of polyoxyethylene alkyl ether sulfonic acid was changed to 2 parts.
A water-dispersed pressure-sensitive adhesive composition was obtained in which the gel fraction of polymer particles was 47.5%.

Example 2 2-ethylhexyl acrylate 8 as a monomer emulsion
A monomer mixture consisting of 7% methyl acrylate, 10% methyl acrylate and 3% methacrylic acid (glass transition point of the copolymer 212
°K), 0.5 parts of ammonium salt of polyoxyethylene alkyl ether sulfonic acid (same as used in Example 1) and 25 parts of water, otherwise the method of Example 1. According to the solid content concentration is 64.2
%, and a water-dispersed pressure-sensitive adhesive composition having a gel fraction of polymer particles of 51.5% was obtained.

Example 3 As a monomer emulsion, a monomer mixture consisting of 83% n-butyl acrylate, 15% methyl methacrylate, and 2% acrylic acid (glass transition point of copolymer 235"K) 1
00 parts, sodium salt of alkyl alkenyl sulfosuccinate (trade name: Reminol JS, manufactured by Sanyo Chemical Co., Ltd.)
-2; having a sulfonic acid group in the molecule and also having an olefinic double bond) and 25 parts of water were used, and the other parts were as follows according to the method of Example 1. Concentration is 64.5%, gel fraction of polymer particles is 50.5
% of the water-dispersed pressure-sensitive adhesive composition was obtained.

Example 4 As a monomer emulsion, a monomer mixture consisting of 68% isononyl acrylate, 30% ethyl acrylate, and 2% methacrylic acid (glass transition point of copolymer 211 °K) 1
00 parts, sodium salt of sulfosuccinic acid alkyl alkenyl ester (same as used in Example 3) 0.5
A water-dispersed pressure-sensitive adhesive was used in which the solid content concentration was 63.8% and the gel fraction of the polymer particles was 52.3%. A drug composition was obtained.

The results of examining the adhesive strength, cohesive force, and repulsion resistance of each of the adhesive compositions of Examples 1 to 4 and Comparative Examples 1.3 above were as shown in the table below.

As is clear from the above results, the water-dispersed pressure-sensitive adhesive composition of the present invention has high adhesive strength and high cohesive strength,
Moreover, it has very good rebound resistance, no deterioration in adhesive properties due to the use of emulsifiers is observed, and high cohesive strength can be obtained even without the use of external crosslinking agents. .

Claims (4)

[Claims] (1) Main monomer 90 consisting of a (meth)acrylic acid alkyl ester with an alkyl group having 1 to 14 carbon atoms alone or this ester and a vinyl monomer copolymerizable with the ester
~99.5% by weight and 10 to 0.5% by weight of a carboxyl group-containing ethylenically unsaturated monomer, a monomer mixture whose copolymer exhibits pressure-sensitive adhesive properties and can have a glass transition point of 250°K or less , consisting of an emulsifier that has a sulfonic acid group in its molecule and is soluble in the monomer mixture, and water, and the emulsifier is in a proportion of 0.1 to 1 part by weight per 100 parts by weight of the monomer mixture. A water-dispersed pressure-sensitive adhesive composition based on a polymer emulsion obtained by adding and polymerizing the monomer emulsion obtained above into water in which a persulfate is dissolved. (2) The emulsifier that has a sulfonic acid group in its molecule and is soluble in the monomer mixture is polyoxyethylene alkyl ether sulfonate, polyoxyethylene alkylphenol ether sulfonate, sodium salt of sulfosuccinic acid dialkyl ester, and sulfosuccinic acid. The water-dispersed pressure-sensitive adhesive composition according to claim 1, which is at least one selected from sulfosuccinic acid derivatives such as sodium salts of alkyl alkenyl esters. (3) The water-dispersed pressure-sensitive adhesive composition according to claim (1) or (2), wherein the polymerization temperature is 60 to 90°C. (4) The water-dispersed pressure-sensitive adhesive composition according to any one of claims (1) to (3), which has a solid content concentration of 60 to 65% by weight.