JPH0730296B2 - Water dispersion type pressure sensitive adhesive composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an acrylic water-dispersed pressure-sensitive adhesive composition.

[Conventional technology]

In recent years, acrylic pressure-sensitive adhesives 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. In addition, among these types of adhesives, recently, water-dispersible adhesives that do not use organic solvents have been researched and developed from the viewpoints of resource saving and environmental hygiene.

Such a water-dispersed adhesive is generally prepared by an emulsion polymerization method. That is, it is prepared by emulsion-polymerizing (meth) acrylic acid alkyl ester in an aqueous medium together with a modifying monomer such as acrylic acid, styrene or vinyl acetate, if necessary. Since the acrylic polymer having tackiness has a relatively large molecular weight as compared with a polymer obtained by solution polymerization, it is known that a relatively high cohesive force can be obtained as a pressure-sensitive adhesive.

[Problems to be solved by the invention]

However, when this type of conventional adhesive is applied to applications where a high degree of cohesive strength is desired, it cannot be said that cohesive strength is still satisfactory, and the adhesive spots are exposed to relatively high temperatures. At times, the cohesive force was significantly reduced, and it was almost unusable.

Therefore, in order to improve the cohesive force, an improved means of incorporating an external cross-linking agent such as a melamine compound, an epoxy compound, and a metal salt into the polymer emulsion after emulsion polymerization has been tried, but the type of cross-linking agent to be blended Also, in addition to being cumbersome to select the amount to be used, generally the crosslinking is non-uniform and the cohesive force is not so large compared to the degree of crosslinking,
Further, even if the cohesive force could be increased, the adhesive force was reduced accordingly, which made it difficult to obtain a pressure-sensitive adhesive composition having high adhesive force and high cohesive force.

Furthermore, when the cohesive force is increased by the above-mentioned means, there is a problem that the repulsion resistance as an adhesive becomes poor in addition to the decrease in the adhesive force. That is, for example, in a case where a metal plate or a plastic plate is adhered in a bent state to an adherend having a curved surface, a restoring force acts on the bent metal plate or the plastic plate, so that the restoring force is not affected. It is required to have excellent repulsion resistance, and this repulsion resistance is represented by a balance characteristic of adhesive force and cohesive force. Could not be satisfied with.

Therefore, the present invention provides an acrylic water-dispersible pressure-sensitive adhesive composition that exhibits high adhesive strength and high cohesive strength without intentionally blending an external cross-linking agent and has excellent repulsion resistance. The purpose is to provide.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the present inventors have found that a specific amount of a polyvalent metal salt is added to an acrylic monomer mixture containing a carboxyl group-containing ethylenically unsaturated monomer as a component. A water-dispersible pressure-sensitive adhesive composition based on a polymer emulsion obtained by radical polymerization in an aqueous medium containing a specific polymerization initiator by blending it as a polymerization raw material. The inventors have found that they can exhibit high adhesiveness and high cohesive force without intentionally blending an external cross-linking agent, and have excellent repulsion resistance, and have completed the present invention.

That is, the present invention is a main monomer 95-containing a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms or a mixture of this ester and a vinyl monomer copolymerizable therewith. The copolymer consisting of 99.5% by weight and 5 to 0.5% by weight of a carboxyl group-containing ethylenically unsaturated monomer shows pressure-sensitive adhesive properties. Radical polymerization of a polymerization raw material obtained by adding a polyvalent metal salt in an amount of 0.005 to 0.5 equivalents to 1 equivalent of a carboxyl group of a group-containing ethylenically unsaturated monomer in an aqueous medium containing persulfate. The present invention relates to a water-dispersed pressure-sensitive adhesive composition based on the polymer emulsion obtained as described above.

As described above, in the present invention, a polyvalent metal salt is added to a specific acrylic monomer mixture to be subjected to radical polymerization in an aqueous medium, and the radical polymerization is performed using this as a polymerization raw material. Therefore, some of the polyvalent metal ions are present in the polymer particles produced by this method, and as a result of this being involved in the ionic bond with the carboxyl group contained in the polymer molecule, the polymer particles themselves are It is presumed to form a crosslinked structure. Therefore, the adhesive composition based on emulsion containing the polymer particles has a high cohesive force without intentionally blending an external crosslinking agent into the adhesive composition, and the conventional adhesive composition containing an external crosslinking agent was used. The adhesive strength and repulsion resistance, which are observed in the adhesive composition, are not deteriorated. That is, according to the present invention, a water-dispersible pressure-sensitive adhesive composition that exhibits a high adhesive force and a high cohesive force without intentionally blending an external cross-linking agent, and further has very excellent repulsion resistance. Is what you get.

Further, in the present invention, when radically polymerizing an acrylic monomer mixture containing a polyvalent metal salt as described above in an aqueous medium, a persulfate is particularly used as a polymerization initiator. , The ionic end groups generated by the decomposition of the persulfate give very good results in terms of polymerization stability and stability of the emulsion after polymerization, and the emulsion after polymerization has low thixotropy. It has the characteristics of

Therefore, the polymer emulsion obtained by this method contains almost no agglomerates, no deterioration in the adhesive properties due to the agglomerates is observed, and there are few agglomerates adhering to the polymerization kettle or stirring blades. Therefore, there is no possibility of causing a problem of workability for removing this. Moreover, this emulsion has low thixotropy even at a high solid content concentration of 50 to 70% by weight of the solid content, so that it is easy to uniformly mix the components such as the tackifier and the substrate. There is also an advantage that heating and drying after application to can be performed in a short time.

In this specification, “(meth) acrylic acid” means 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.

[Constitution / Operation of Invention]

The monomer mixture used in the present invention is a main monomer composed of a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms or a mixture with a vinyl monomer copolymerizable therewith. In addition, a carboxyl group-containing ethylenically unsaturated monomer is added.

As the (meth) acrylic acid alkyl ester constituting the main monomer, from the viewpoint of adhesiveness, as described above, those having 1 to 14 carbon atoms in the alkyl group are used, and particularly preferable examples include: Ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate,
Examples thereof include isodecyl acrylate, ethyl methacrylate, butyl methacrylate, and lauryl methacrylate.

As the main monomer, the above-mentioned (meth) acrylic acid alkyl ester may be used alone, or a vinyl-based monomer copolymerizable therewith may be used together with this ester. As this vinyl-based monomer, acrylonitrile,
Examples thereof include methacrylonitrile, vinyl acetate, styrene and derivatives thereof. The amount of these vinyl monomers used is preferably 50% by weight or less in the main monomer.

Further, as the carboxyl group-containing ethylenically unsaturated monomer, (meth) acrylic acid, crotonic acid, itaconic acid,
Maleic acid, fumaric acid and the like are used, and of these, acrylic acid is particularly preferable. This carboxyl group-containing ethylenically unsaturated monomer is an indispensable component for causing cross-linking in polymer particles.

A monomer mixture comprising such a main monomer and a carboxyl group-containing ethylenically unsaturated monomer has a glass transition point of 250 ° K or less so that the copolymer exhibits pressure-sensitive adhesiveness. It must be a composition. With such a composition, it is possible to prepare an adhesive composition having a high cohesive force and a high adhesive force.

Further, the mixing ratio of the main monomer and the carboxyl group-containing ethylenically unsaturated monomer in the monomer mixture, the main monomer is 95 to 99.5 wt%, the carboxyl group-containing ethylenically unsaturated monomer Should be 5 to 0.5% by weight. If the amount of the latter monomer is less than 0.5% by weight, it is difficult to improve the cohesive force, and if it is more than 5% by weight, the cohesive force becomes too high and problems in terms of adhesion and repulsion resistance are likely to occur.

In the present invention, as the polyvalent metal salt added to such a monomer mixture, water-soluble salts such as acetate, hydrochloride and sulfate of metals such as magnesium, aluminum, copper, calcium, zinc and iron are preferably used. To be The amount of the polyvalent metal salt used should be 0.005 to 0.5 equivalent per 1 equivalent of the carboxyl group of the carboxyl group-containing ethylenically unsaturated monomer. If it is less than 0.005 equivalents, the desired cohesive force cannot be obtained, and if it exceeds 0.5 equivalents, the polymerization stability is significantly deteriorated.

In the present invention, a polymer emulsion is obtained by radical polymerization of the above-mentioned monomer mixture and polyvalent metal salt as polymerization raw materials in an aqueous medium containing a persulfate. As a method of radical polymerization, water in which persulfate is added and dissolved is heated to a temperature of 60 to 90 ° C., and the above polymerization raw material is emulsified in water as it is or using an appropriate emulsifier. In this state, the mixture may be dropped at a predetermined dropping speed, and the reaction may be performed for a predetermined time while maintaining the above temperature.

Examples of the persulfate used here include potassium persulfate, ammonium persulfate, and sodium persulfate. This persulfate has a function as a polymerization initiator to influence the molecular weight of the produced polymer, and the ionic terminal group produced by the decomposition thereof has stability in polymerization in an aqueous medium and of emulsion after polymerization. This contributes to stability.

Therefore, the amount of the persulfate used is preferably set in an appropriate range from the above-mentioned viewpoint, that is, from the viewpoint of the molecular weight of the produced polymer and the stability. In general,
Persulfate is 0.1 to 100 parts by weight of the monomer mixture in the previous period.
The proportion is preferably 5 parts by weight.

The polymer emulsion obtained in this manner generally has a concentration of polymer particles having an appropriate crosslinked structure contained therein, that is, a solid content concentration of 50 to 70 in terms of stability and viscosity characteristics of the emulsion. It is desirable to set it in the range of weight%. In the present invention, by adjusting to such a high solid content, it is possible to obtain an advantage that drying after coating can be performed in a short time.

The water-dispersible pressure-sensitive adhesive composition of the present invention is based on the above-mentioned polymer emulsion, and when it is used, a tackifier, a coloring agent, a filler, and an antiaging agent are used if necessary. Various compounding agents such as the above can be arbitrarily mixed. Further, this composition alone exhibits a high adhesive force and a high cohesive force, but if it is desired to further increase the cohesive force, various conventionally known external cross-linking agents can be used within a range not impairing the features of the present invention. There is no problem even if it is mixed.

〔The invention's effect〕

As described above, the water-dispersible pressure-sensitive adhesive composition of the present invention is adjusted to a high solid content of about 50 to 70% by weight, which does not require a long time for drying after being applied to a substrate or the like. In addition to the advantages such as being able to do, it exhibits high adhesive strength and high cohesive strength without the need to mix external cross-linking agent, and the cohesive strength is not significantly reduced especially at high temperature. It has excellent repulsion properties and is extremely useful not only for general pressure-sensitive adhesive tapes, sheets, labels, etc., but also for applications where repulsion resistance is particularly required. It is useful.

〔Example〕

Hereinafter, examples of the present invention will be described to more specifically describe. In the following, “part” means “part by weight” and “%” means “% by weight”. The adhesive strength, cohesive strength, and repulsion resistance are measured by the following methods.

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

<Cohesive strength> Make a double-sided adhesive tape similar to the adhesive strength test and
The pieces were attached to a piece of Bakelite plate with an adhesive area of 25 mm × 25 mm, and a load (1 kg) was applied at 40 ° C. and 80 ° C. to measure the time (minutes) until the Bakelite plate dropped.

<Repulsion resistance> A pressure-sensitive adhesive composition is applied to one side of an aluminum plate having a thickness of 0.3 mm so that the thickness after drying becomes 50 μm, and after drying at 100 ° C. for 3 minutes, it has a size of 10 mm × 80 mm. Cut to make a test piece, bend and stick this test piece to an aluminum cylinder with a diameter of 50 mm, and then store it at 40 ° C for 24 hours, and then measure the distance (mm) that the test piece floated from the cylinder. It was measured.

Example 1 20 parts of distilled water was put into a reactor equipped with a thermometer, a stirrer, a nitrogen introducing pipe and a reflux cooling pipe to raise the internal temperature to 80 ° C., and then the inside of the container was put under a nitrogen stream. Potassium persulfate 0.4
Parts were added. Thereafter, a monomer mixture consisting of 75 parts of 2-ethylhexyl acrylate, 23 parts of ethyl acrylate and 2 parts of acrylic acid (glass transition point of the copolymer 214
Emulsified by adding 0.042 parts of ferrous sulfate (corresponding to 0.01 equivalent to 1 equivalent of carboxyl group of acrylic acid), 0.2 parts of sodium dodecylbenzenesulfonate and 42.5 parts of distilled water to (° K) The liquid was continuously added dropwise over about 4 hours, and after completion of the addition, the temperature was kept at 80 ° C. for 2 hours to complete the polymerization.

The polymer emulsion thus obtained had a solid content of 61.0%. This emulsion was directly used as the water-dispersed pressure-sensitive adhesive composition according to the present invention.

Comparative Example 1 A polymer emulsion was obtained in the same manner as in Example 1 except that ferrous sulfate was not added to the monomer mixture, which was directly used as a water-dispersible pressure-sensitive adhesive composition for comparison.

Comparative Example 2 2-ethylhexyl acrylate 72.5 as a monomer mixture
Parts, 20 parts of ethyl acrylate and 7.5 parts of acrylic acid were used, and the solid content concentration was 60.5 in the same manner as in Example 1 except that the amount of ferrous sulfate added was 0.16 parts. % Polymer emulsion was obtained. This emulsion was directly used as a water-dispersible pressure-sensitive adhesive composition for comparison.

Comparative Example 3 To the polymer emulsion obtained in Comparative Example 1, 0.045 parts of ferrous sulfate was dissolved in 1 part of distilled water, added, and mixed by stirring to obtain a water-dispersible pressure-sensitive adhesive composition for comparison. did.

Example 2 2-Ethylhexyl Acrylate 73 as Monomer Mixture
Part, 25 parts of methyl acrylate and 2 parts of acrylic acid (glass transition temperature of the copolymer 220 ° K) are used, and 0.028 parts of calcium acetate (carboxyl group of acrylic acid 1 as a polyvalent metal salt to be added thereto. A polymer emulsion having a solid content of 60.8% was obtained in the same manner as in Example 1 except that the water-dispersible pressure-sensitive adhesive composition according to the present invention was used as it was. It was a thing.

Example 3 As a monomer mixture, a mixture of 94 parts of n-butyl acrylate, 5 parts of methyl methacrylate and 1 part of acrylic acid (copolymer glass transition point 242 ° K) was used, and polyvalent metal was added thereto. A polymer emulsion having a solid content concentration of 60.0% was obtained in the same manner as in Example 1 except that 0.019 part of cupric chloride (corresponding to 0.01 equivalent to 1 equivalent of a carboxyl group of acrylic acid) was used as a salt. This was directly used as the water-dispersed pressure-sensitive adhesive composition according to the present invention.

Example 4 As a monomer mixture, a mixture of 70 parts of isononyl acrylate, 27 parts of ethyl acrylate and 3 parts of acrylic acid (copolymer glass transition point 210 ° K) was used, and as a polyvalent metal salt to be added thereto. A polymer emulsion having a solid content concentration of 59.8% was obtained in the same manner as in Example 1 except that 0.068 parts of ferrous sulfate (corresponding to 0.01 equivalent to 1 equivalent of a carboxyl group of acrylic acid) was used. Was directly used as the water-dispersible pressure-sensitive adhesive composition according to the present invention.

The adhesive strength, cohesive strength, and repulsion resistance of the adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 3 were examined, and the results are shown in the table below.

As is clear from the above results, the water-dispersed pressure-sensitive adhesive composition of the present invention has a high adhesive force and a high cohesive force,
In addition, it can be seen that it has excellent repulsion resistance.

Claims (4)

[Claims] 1. An alkyl group having 1 to 14 carbon atoms (meth).
95-99.5% by weight of a main monomer composed of an acrylic acid alkyl ester or a mixture of this ester and a vinyl monomer copolymerizable therewith, and 5 to 0.5% by weight of a carboxyl group-containing ethylenically unsaturated monomer The copolymer consisting of 0.001 to 0.005 to 1 equivalent of the carboxyl group of the above-mentioned carboxyl group-containing ethylenically unsaturated monomer has a glass transition temperature of 250 ° K or less, in which the copolymer exhibits pressure-sensitive adhesiveness.
A water-dispersible pressure-sensitive adhesive composition based on a polymer emulsion obtained by radically polymerizing a polymerization raw material obtained by adding a polyvalent metal salt in a ratio of 0.5 equivalents in an aqueous medium containing a persulfate salt. object. 2. The water-dispersible pressure-sensitive adhesive composition according to claim 1, wherein the persulfate is 0.1 to 5 parts by weight per 100 parts by weight of the monomer mixture. 3. The water-dispersible pressure-sensitive adhesive composition according to claim 1 or 2, wherein the radical polymerization temperature is in the range of 60 to 90 ° C. 4. The solid content of the polymer emulsion is 50 to 70.
The water-dispersed pressure-sensitive adhesive composition according to any one of claims (1) to (3), which is in the range of wt%.