JPS63223080A - Water dispersion type pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition having high bond strength and high cohesive force, by adding a polyvalent metallic salt to a specific acrylic monomer mixture, radically polymerizing the monomer mixture in a water medium to give a water dispersion of polymer and adding a solvent having dielectric constant of >=a fixed value to the dispersion. CONSTITUTION:(A) A polymerization raw material obtained by blending a monomer mixture, consisting of (i) 90-99.5wt.% main monomer comprising (meth)acrylic acid 1-14C alkyl ester or a mixture of the ester and a vinyl monomer copolymerizable with the ester and (ii) 10-0.5wt.% carboxyl group- containing ethylenic unsaturated monomer, capable of providing a copolymer having <=250 deg.K glass transition temperature, with 0.005-0.5 equivalent based on 1 equivalent carboxyl group of the component (ii) is radically polymerized in (B) a sulfate-containing water medium to give a water dispersion of acrylic polymer, which is incorporated with (C) a solvent having >=80 dielectric constant.

Description

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

[Prior Art] In recent years, acrylic pressure-sensitive adhesives have become widely used in place of conventional natural rubber-based and synthetic rubber-based pressure-sensitive adhesives due to their excellent adhesive properties and durability. Among these types of adhesives, water-dispersible adhesives that do not use organic solvents have recently been researched and developed from the viewpoint of resource saving and environmental hygiene. The agent is generally prepared by an emulsion polymerization method. 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 have relatively high cohesive strength as pressure-sensitive adhesives. There is.

[Problems to be Solved by the Invention] However, when applying the above-mentioned conventional water-dispersed pressure-sensitive adhesives to applications that require a high degree of cohesive strength,
The cohesive force was still unsatisfactory, and when the bonded area was exposed to a relatively high temperature, the cohesive force was significantly reduced and could hardly be used.

Therefore, attempts have been made to improve the cohesive force by adding external crosslinking agents such as melamine compounds, epoxy compounds, and metal salts to the polymer emulsion after emulsion polymerization. In addition to being troublesome in selecting the amount used, crosslinking is generally non-uniform and the cohesive force is not very large compared to the degree of crosslinking, and even if the cohesive force could be increased, A decrease in adhesive strength was observed, and it was difficult to obtain a pressure-sensitive adhesive composition having high adhesive strength and high cohesive strength.

Furthermore, when the cohesive force is increased by the above-mentioned means, there is a problem that apart from a decrease in adhesive force, the adhesive also has poor repulsion resistance. In other words, in applications such as bonding a bent metal or plastic plate 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.

Furthermore, because the conventional water-dispersed pressure-sensitive adhesives mentioned above are water-dispersed, their properties change orally due to changes in temperature, etc.
There was a problem in terms of storage stability, in that some of the polymer particles sedimented, and as a result, adhesive properties, particularly adhesive strength and repulsion resistance, deteriorated.

Therefore, the present invention exhibits high adhesive strength and high cohesive strength without intentionally incorporating an external crosslinking agent, has excellent repulsion resistance, and has good storage stability. Of course, the object of the present invention is to provide an acrylic water-dispersed pressure-sensitive adhesive composition that can easily balance adhesive strength, cohesive strength, and repulsion resistance even after oral storage.

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the inventors have developed an acrylic monomer containing a carboxyl group-containing ethylenically unsaturated monomer as a partial component. A specific amount of polyvalent metal salt is blended into a polymer mixture to form a polymerization raw material, and this is radically polymerized in an aqueous medium containing a specific polymerization initiator. When it contains a solvent, it exhibits high adhesive strength and high cohesive strength without the need to add an external crosslinking agent.
In addition, a water-dispersed pressure-sensitive adhesive composition is obtained which has excellent repulsion resistance, good mechanical stability of an aqueous dispersion, excellent storage stability, and good adhesive properties both at the initial stage and after oral storage. After realizing that it was possible to achieve this goal, he completed this invention.

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 or a mixture of this ester and a vinyl monomer copolymerizable therewith, and a carboxyl group-containing ethylenically unsaturated monomer. The carboxyl group-containing ethylenically unsaturated monomer described above is added to a monomer mixture whose copolymer has a pressure-sensitive adhesive property and a glass transition point of 250°K or less. An acrylic polymer obtained by radical polymerizing a polymerization raw material prepared by adding a polyvalent metal salt in an amount of 0.005 to 0.5 equivalent to 1 equivalent of the group in an aqueous medium containing a persulfate. The present invention relates to a water-dispersed pressure-sensitive adhesive composition characterized in that the combined aqueous dispersion contains a solvent having a dielectric constant of 80 or more.

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 above radical polymerization is performed using this as a polymerization raw material. Since the aqueous dispersion of the acrylic polymer obtained in this process contains a solvent with a dielectric constant of 80 or more, the adhesive composition made of the aqueous polymer dispersion is prepared by adding an external crosslinking agent to the aqueous dispersion. It has high cohesive strength even without the addition of external cross-linking agents, and does not show a significant decrease in cohesive strength, especially at high temperatures, and has the same adhesion as found in conventional adhesive compositions that contain external cross-linking agents. There is no decrease in strength or repulsion resistance.

Although it is not necessarily clear why such an effect occurs, it is speculated that some polyvalent metal ions are present in the polymer particles obtained by the above method, and this is caused by the presence of polyvalent metal ions within the polymer molecules. As a result of participating in ionic bonds with the carboxyl groups contained, the polymer particles themselves become crosslinked, and metal ions are solvated by using the above-mentioned specific solvent, which has a dielectric constant higher than the dielectric constant of water, near 8.5. As a result, bond formation with carboxyl groups in polymer molecules progresses more easily and uniformly, and fusion between polymer particles progresses moderately and uniformly, resulting in higher cohesive strength. It is estimated that good results can be obtained in maintaining adhesive strength and repulsion resistance.

In addition, in this invention, the above-mentioned specific solvent selectively acts on the carboxyl group within the polymer molecule and the polyvalent metal ion moiety interacting with the carboxyl group in the aqueous dispersion of the acrylic polymer. It is presumed that this prevents the polymer particles from agglomerating and fusing together orally and greatly contributes to improving the storage stability of the aqueous dispersion. Therefore, the aqueous dispersion of an acrylic polymer according to the present invention avoids problems such as precipitation of some of the polymer particles and changes in adhesive properties after oral storage.

Furthermore, in the present invention, the presence of polyvalent metal ions in the aqueous polymer dispersion generally tends to reduce the mechanical stability of the polymer particles; Another advantage is that sufficient mechanical stability is maintained for this reason.

Moreover, in this invention, when radically polymerizing the acrylic monomer mixture containing the 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 this persulfate give very good results in polymerization stability and stability of the aqueous dispersion after polymerization, and the aqueous dispersion after polymerization has low thixotropy. It has the following characteristics.

Therefore, the aqueous dispersion of the acrylic polymer obtained by this method contains almost no aggregates, and there is no deterioration in adhesive properties caused by these aggregates. Since there are few items, there is no risk of problems with workability in removing them. Moreover, this aqueous dispersion has low titanium tropism even at a high solid content concentration of 50 to 70% by weight, making it easy to uniformly mix ingredients such as tackifiers, and Another advantage is that heating and drying can be performed in a short time after being applied to a base material.

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.

Structure and operation of the invention The monomer mixture used in this invention is an acrylic acid alkyl ester whose alkyl group has 1 to 14 carbon atoms (meth) or a vinyl monomer copolymerizable therewith. It is made by adding a carboxyl group-containing ethylenically unsaturated monomer to the main monomer consisting of a mixture of.

As the (meth)acrylic acid alkyl ester constituting the main monomer, from the viewpoint of adhesive properties, those having an alkyl group of 1 to 14 carbon atoms are used, as particularly preferred examples. , ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, and the like.

As the main monomer, the above (meth)acrylic acid alkyl ester may be used alone, or a vinyl monomer copolymerizable with this ester may be used in combination with this ester. Examples of the vinyl monomer include acrylonitrile, methacrylonitrile, vinyl acetate, styrene or derivatives thereof. The amount of these vinyl monomers used is desirably 50% by weight or less based on the main monomers. In addition, examples of carboxyl group-containing ethylenically unsaturated monomers include (meth)acrylic acid, crotonic acid, , itaconic acid,
Maleic acid, fumaric acid, etc. are used, and among these, acrylic acid is particularly preferred. This carboxyl group-containing ethylenically unsaturated monomer is an essential component for forming crosslinks in polymer particles.

A monomer mixture consisting of 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 adhesive properties. It is necessary that the composition be specified. By having such a composition, it becomes possible to prepare a pressure-sensitive adhesive composition that has high cohesive force, high adhesive strength, and good repulsion resistance.

In addition, the mixing ratio of the main monomer and the carboxyl group-containing ethylenically unsaturated monomer in the above monomer mixture is such that the main monomer is 90 to 99.5% by weight, and the carboxyl group-containing ethylenically unsaturated monomer is 90 to 99.5% by weight. The body weight should be 10-0.5%. If the latter monomer is less than 0.5% by weight, it will be difficult to improve the cohesive force, and if it exceeds 10% by weight, polymerization stability will be impaired and many aggregates will be formed during polymerization, making it unsuitable. It is.

In this invention, as the polyvalent metal salt added to such a monomer mixture, water-soluble salts such as acetates, hydrochlorides, and sulfates of metals such as magnesium, aluminum, copper, calcium, zinc, and iron are preferably used. It will be done. The amount of these polyvalent metal salts used is 0.005 to 0 per equivalent of carboxyl group of the carboxyl group-containing ethylenically unsaturated monomer.
．． The ratio should be such that there are 5 equivalents. o,oos
If the amount is less than equivalent, the desired cohesive force cannot be obtained, and if it exceeds 0.5 equivalents, the polymerization stability will be significantly deteriorated.

In this invention, the above monomer mixture and polyvalent metal salt are used as polymerization raw materials, and by radically polymerizing them in an aqueous medium containing persulfate as a polymerization initiator,
An aqueous dispersion of an acrylic polymer is obtained. As a polymerization method, water in which persulfate was added and dissolved was heated to a temperature of 60 to 90°C, and the above polymerization raw material was emulsified in water as it was or by using an appropriate emulsifier. The solution may be dropped at a predetermined dropping rate, and allowed to react for a predetermined time while maintaining the above temperature.

Examples of persulfates used here include potassium persulfate, ammonium persulfate, and sodium persulfate. This persulfate acts as a polymerization initiator and influences the molecular structure of the produced polymer, and the ionic end groups produced by its decomposition improve polymerization stability in an aqueous medium and water dispersion after polymerization. It contributes to the stability of the liquid. The amount of persulfate used is 100% of the monomer mixture.
Usually 0.1 to 5 parts by weight per part by weight of the color may be used.

The aqueous dispersion of an acrylic polymer obtained in this manner generally has a concentration of polymer particles, that is, a solid content concentration of 50 to 70% by weight from the viewpoint of stability and viscosity characteristics of the aqueous dispersion.
It is desirable to set it within the range of . In this invention, by being able to prepare such a high solid content concentration, there is an advantage that drying after application can be performed in a short time.

In this invention, the solvent contained in the aqueous dispersion includes a solvent having a dielectric constant of 80 or more, such as N-methylacetamide, N-methylformamide, formamide, and ethylene carbonate. Here, if the dielectric constant of the solvent is less than 80, that is, the same as or lower than that of water, the effects of the present invention as described above cannot be obtained.

The usage amount of the above specific solvent is as follows:
0.1 to 20 parts by weight, preferably 0.00 parts by weight
．． The amount is preferably 5 to 10 parts by weight. If the amount of this solvent is too small, the effect of this invention cannot be obtained, and if it is too large, the solvent will not be completely scattered when dried after being applied to the base material, which may impair the adhesive properties. It's inappropriate.

The above-mentioned solvent is generally added to the aqueous dispersion of the acrylic polymer while stirring, but when preparing the aqueous dispersion of the above-mentioned polymer, in other words, the When performing this, it may be added within a range that does not impede stability during polymerization.

The water-dispersed pressure-sensitive adhesive composition of the present invention exhibits high adhesive strength and high cohesive strength by itself, but it is also blended with various external crosslinking agents such as epoxy compounds, melamine compounds, and metal salts. By doing so, the cohesive force can be further improved without causing a decrease in adhesive force or repulsion resistance. It is presumed that this effect occurs because the specific solvent plays a role in uniformly promoting the crosslinking reaction between the carboxyl group contained in the polymer molecule and the external crosslinking agent. The amount of such external crosslinking agent to be blended is usually 5 parts by weight or less per 100 parts by weight of the acrylic polymer.

In addition, the water-dispersed pressure-sensitive adhesive composition of the present invention may contain colorants, fillers, anti-aging agents,
Conventionally known additives such as tackifiers can be appropriately blended. The blending amount may be a normal amount.

〔Effect of the invention〕

As described above, according to the present invention, high adhesive strength and high cohesive strength can be achieved without intentionally adding an external cross-linking agent, and there is no significant decrease in cohesive strength, especially at high temperatures. An acrylic water-dispersed pressure-sensitive material with excellent repulsion resistance, good mechanical stability of the aqueous dispersion, excellent storage stability, and good adhesive properties both initially and after long-term storage. An adhesive composition can be provided.

In addition, this adhesive composition can be prepared to have a high solid content concentration of 50 to 70% by weight and has low thixotropy, so it does not require a long time to dry after being applied to a substrate. The smoothness of the coated surface is also good and can contribute to an increase in the bonding area.

Therefore, the acrylic water-dispersed pressure-sensitive adhesive composition of the present invention can be used not only for general pressure-sensitive adhesive tapes, sheets, and labels, but also for applications that particularly require rebound resistance. It is useful for

〔Example〕

Examples of the present invention will be described below to explain it more specifically. In addition, in the following, parts refer to parts by weight.
% means weight %. Further, adhesive force, cohesive force, repulsion resistance, and mechanical stability were measured by the following methods.

<Adhesive strength> A pressure-sensitive adhesive composition was applied to both sides of a 25 μ thick polyester film so that the thickness after drying was 50 cm on each side, and dried at 100°C for 3 minutes to make a double-sided adhesive tape. The 180 degree peel adhesive strength (y/20am width) was measured according to JIS Z-1528.

<Cohesive strength> A double-sided adhesive tape similar to the adhesive strength test was made, and this was
Two Bakelite plates were bonded together with an adhesive area of 25w x 25w, 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 a 0.3 mm thick aluminum plate so that the thickness after drying was 50 μm.
After drying at °C for 3 minutes, a test piece was made by cutting it into a size of 10 mm x 80 mm. This test piece was bent and attached to a 50 m diameter aluminum cylinder, and then stored at 40 °C for 24 hours. , the distance (distance) that the test piece rose from the cylinder was measured.

<Mechanical Stability> The pressure-sensitive adhesive composition was treated using a Marlon stability tester under a load of 30 kg for 30 minutes, and the weight fraction of broken and agglomerated polymer particles was measured.

Example 1 60 parts of distilled water in which 0.4 parts of potassium persulfate was dissolved was placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and heated at 80° under a nitrogen stream. After heating to C, 100 parts of a monomer mixture (copolymer glass transition point 208°K) consisting of 85% 2-ethylhexyl acrylate, 14% ethyl acrylate, and 1% acrylic acid (copolymer glass transition point 208°K) was added with 0% ferrous sulfate. A polymerization raw material to which ゜0219 (corresponding to 0.01 equivalent to 1 equivalent of carboxyl group of acrylic acid) was added was continuously added dropwise over 3 hours to carry out a polymerization reaction, so that the solid content concentration decreased. A 62.5% aqueous dispersion of acrylic polymer was prepared.

To this aqueous dispersion, add 3 parts per 100 parts of the acrylic polymer.
of N-methylformamide (dielectric constant: 182.4) was added and stirred uniformly to obtain a water-dispersed pressure-sensitive adhesive composition according to the present invention.

Comparative Example 1 An aqueous dispersion of an acrylic polymer was obtained in the same manner as in Example 1, except that ferrous sulfate was not added to the monomer mixture, and the same amount of N-methylformamide as in Example 1 was added to this. In addition,
A water-dispersed pressure-sensitive adhesive composition was prepared for comparison.

Comparative Example 2 The aqueous dispersion of the acrylic polymer obtained in Example 1 was used as a comparative water-dispersed pressure-sensitive adhesive composition without adding N-methylformamide.

Example 2 100 parts of a mixture of 87% butyl acrylate, 10% vinyl acetate and 3% acrylic acid (glass transition point of the copolymer 232°K) was used as the monomer mixture, and sulfuric acid was added to the monomer mixture. The same procedure as in Example 1 was carried out except that the amount of iron used was 0.63 parts (corresponding to 0.1 equivalent to 1 equivalent of carboxyl group of acrylic acid). An aqueous dispersion of an acrylic polymer was obtained, 5 parts of N-methylformamide was added to 100 parts of the polymer, and the mixture was stirred uniformly to form a water-dispersed pressure-sensitive adhesive composition according to the present invention. did.

Example 3 2-ethylhexyl acrylate 8 as monomer mixture
8%, 10% methyl methacrylate and 2% acrylic acid (glass transition temperature of copolymer 220″K)
Example 1 except that 100 parts of ferrous sulfate was used, and the amount of ferrous sulfate added was 0.21 parts (corresponding to 0.05"l per 1 day of carboxyl group of acrylic acid).
In the same manner as above, an aqueous dispersion of an acrylic polymer with a solid concentration of 62.5% was obtained, and 1 part of N was added to this for 100 parts of the polymer.
- Methylformamide was added and stirred uniformly to obtain a water-dispersed pressure-sensitive adhesive composition according to the present invention.

Example 4 0.014 parts of calcium acetate (instead of ferrous sulfate)
0, equivalent to 1 O equivalent per 1 equivalent of carboxyl group of acrylic acid), and N-methylacetamide (dielectric constant: 191.3) was used instead of N-methylformamide.
A water-dispersed pressure-sensitive adhesive composition according to the present invention was obtained in the same manner as in Example 1, except that 2 parts of (2) were used.

Example 5 0.16 parts of ferrous acetate (corresponding to 1 equivalent of carboxyl group of acrylic acid) was used instead of ferrous sulfate, and formamide was used instead of N-methylformamide. Except for using 4 parts of (permittivity = 84),
A water-dispersed pressure-sensitive adhesive composition according to the present invention was obtained in the same manner as in Example 1.

The results of examining the adhesive strength, cohesive force, repulsion resistance, and mechanical stability of each of the adhesive compositions of Examples 1 to 5 and Comparative Examples 1 to 2 above were as shown in the table below. . In addition, after storing each composition at 40°C for 60 days, the properties of each composition were examined with the naked eye, and it was observed that only in Comparative Example 2, some of the polymer particles had settled; No such sedimentation phenomenon was observed.

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,
It can be seen that it has very good repulsion resistance, and also has good mechanical stability and storage stability.

Claims (6)

[Claims] (1) Main monomer consisting of a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 14 carbon atoms or a mixture of this ester and a vinyl monomer copolymerizable with the same, 90 to 99.5 % by weight and 10 to 0.5% by weight of the carboxyl group-containing ethylenically unsaturated monomer. 0.005 to 0.5 per equivalent of carboxyl group of monomer
A polymerization raw material obtained by adding an equivalent proportion of a polyvalent metal salt,
A water-dispersed pressure-sensitive adhesive characterized by containing a solvent having a dielectric constant of 80 or more in an aqueous dispersion of an acrylic polymer obtained by radical polymerization in an aqueous medium containing a persulfate. agent composition. (2) Persulfate is 0 per 100 parts by weight of the monomer mixture
．． 1 to 5 parts by weight of the water-dispersed pressure-sensitive adhesive composition according to claim (1). (3) The water-dispersed 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) A solvent with a dielectric constant of 80 or more is mixed with an acrylic polymer of 10
The water-dispersed pressure-sensitive adhesive composition according to any one of claims (1) to (3), which contains 0.1 to 20 parts by weight relative to 0 parts by weight. (5) Any of claims (1) to (4), wherein the solvent having a dielectric constant of 80 or more is at least one selected from N-methylacetamide, N-methylformamide, formamide, and ethylene carbonate. A water-dispersed pressure-sensitive adhesive composition according to claim 1. (6) The water-dispersed pressure-sensitive adhesive composition according to any one of claims (1) to (5), wherein the solid content concentration is in the range of 50 to 70% by weight.