JPS63238180A - Water dispersion type pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To obtain the titled acrylic composition having high bond strength, high cohesive force and repulsion resistance, by dividing polymerization in a water medium without using an emulsifying agent into two stages, polymerizing an acrylic monomer and further polymerizing a monomer for post- polymerization. CONSTITUTION:(A) A monomer mixture which consists of (i) an acrylic acid 1-14C alkyl ester as a main component and (ii) a carboxyl group-containing ethylenic unsaturated monomer and can provide a copolymer showing pressure- sensitive adhesiveness and <=250 deg.C glass transition point is polymerized in (B) a water medium in the presence of (C) a persulfate to give a polymer emulsion containing polymer particles having 20-60wt.% gel fraction, to which (D) a monomer for post-polymerization consisting of an ethylenic unsaturated monomer capable of providing a (co)polymer having >=273 deg.k glass transition point is added and the monomer is polymerized to give a polymer emulsion. The pre pared polymer emulsion is used as a base to give the aimed composition.

Description

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

[Prior Art] 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 adhesive has the following problems:
This is still unsatisfactory when applied to applications where a high degree of cohesive force is desired, and when the bonded area is exposed to relatively high temperatures, the cohesive force is significantly reduced.
could hardly be put to use. 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 that cannot be ignored. becomes non-uniform, and 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 pressure sensitive adhesive compositions that have such strength.

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 the polymer particles during emulsion polymerization, and this emulsifier is mixed into the adhesive composition, resulting in poor moisture and water resistance. There was also the problem that the adhesive properties were adversely affected.

Therefore, the present invention provides a water-dispersed pressure-sensitive adhesive composition that does not contain any emulsifier that causes the deterioration of the adhesive properties, and that has high adhesive strength and high cohesive strength even without the addition of an external crosslinking agent. It is an object of the present invention to provide an acrylic water-dispersed pressure-sensitive adhesive composition that exhibits the above properties and also has excellent repulsion resistance.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors conducted two-step polymerization in an aqueous medium that eliminated the use of emulsifiers by using a specific polymerization initiator instead of conventional emulsion polymerization. In the first stage of polymerization, a specific acrylic monomer mixture, a part of which is an ethylenically unsaturated monomer containing a carboxyl group, is used to control the gel fraction of the polymer particles within a specific range. When a polymer emulsion is produced, and a specific ethylenically unsaturated monomer is added to carry out the second stage of polymerization, it has excellent moisture and water resistance because it does not contain an emulsifier. Moreover, an acrylic water-dispersed pressure-sensitive adhesive composition that exhibits high adhesive strength and high cohesive strength without adding an external crosslinking agent and has excellent repulsion resistance can be obtained. This led to the completion of this invention.

That is, in this invention, the alkyl group has 1 to 14 carbon atoms.
The copolymer, which is composed of a main monomer mainly composed of (meth)acrylic acid alkyl ester and an ethylenically unsaturated monomer containing a carboxyl group, exhibits pressure-sensitive adhesive properties and has a glass transition point of 250°K or less. The homopolymer is added to a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight, which is obtained by polymerizing a monomer mixture in an aqueous medium in the presence of a persulfate without using an emulsifier. Or water based on a polymer emulsion obtained by polymerization with the addition of a post-polymerization monomer consisting of one or more ethylenically unsaturated monomers whose copolymer has a glass transition point of 273°K or higher. This invention relates to a dispersed pressure-sensitive adhesive composition.

In this way, in this invention, polymerization in an aqueous medium is carried out without using an emulsifier by using a persulfate as a polymerization initiator, and the above persulfate produces ions by decomposition. This generates terminal groups that greatly contribute to polymerization stability and the stability of the emulsion after polymerization. Therefore, the pressure-sensitive adhesive composition based on the polymer emulsion obtained by this method has excellent moisture and water resistance because it does not contain an emulsifier. The stability of the emulsion is comparable to that of other emulsions.

In addition, in this invention, the polymerization in an aqueous medium as described above is divided into two stages, and an acrylic monomer mixture containing a carboxyl group-containing ethylenically unsaturated monomer is used as a monomer for polymerization in the first stage. By using this method, an emulsion containing specific polymer particles with a controlled gel fraction is produced, and a second-stage post-polymerization monomer is further added to this for post-polymerization. The above-mentioned first-stage polymer particles have an appropriate crosslinked structure, which not only contributes to the stability of the first-stage polymerization through particle surface energy stability, but also contributes to the mechanical stability of the first-stage polymer particles. The stability plays a very important role in allowing the monomer for post-polymerization to be uniformly absorbed and dispersed in the particles without undesirable agglomeration between the polymer particles during the second stage polymerization. For this reason,
The post-polymerization monomer is uniformly polymerized inside and near the surface of the crosslinked polymer particles while maintaining the crosslinked structure.

Therefore, the polymer particles finally obtained by this method are composed of an acrylic pressure-sensitive adhesive polymer with an appropriately crosslinked structure, and a polymer that exists inside and near the surface of the particle. It is composed of a homopolymer or copolymer of the monomer for polymerization, or a graft polymer in which these polymers are grafted onto the above-mentioned acrylic polymer. By using a monomer whose homopolymer or copolymer can have a glass transition temperature of 273°K or higher, which particularly contributes to improving the cohesive force, adhesives based on emulsions containing this polymer particle can be obtained. The agent composition exhibits high adhesive strength and high cohesive strength without intentionally incorporating an external crosslinking agent into it, and furthermore, it has excellent repulsion resistance.

Of course, the detailed reason why this invention achieves the above-mentioned special effects of having high adhesive strength, high cohesive force, and excellent repulsion resistance has not been clearly elucidated so far. No, no. However, if the monomer for post-polymerization in the second stage is polymerized together in the first stage polymerization, either adhesive strength, collective strength, or repulsion resistance will be extremely impaired. In addition, when a polymer emulsion obtained by polymerizing the second-stage post-polymerization monomer alone is mixed with the first-stage polymer emulsion, the cohesive force, especially at high temperatures, can be improved. It is less effective, tends to have lower adhesive strength, and is less likely to have good repulsion resistance. Furthermore, even if the monomer for post-polymerization in the second stage is added to a polymer emulsion in which the gel fraction of the first-stage polymer particles is O, the post-polymerization It is difficult to maintain particle stability at the time of use, and the resulting adhesive has a poor cohesive force improvement effect, and is also difficult to have good repulsion resistance.

Considering these facts, as in the present invention, post-polymerization consisting of a specific ethylenically unsaturated monomer in acrylic polymer particles having an appropriate crosslinked structure with a gel fraction regulated within a specific range. The properties of adhesion, cohesion, and repulsion resistance can be improved by polymerizing the polymer monomer to form a homopolymer or copolymer thereof, or a graft polymer in which these polymers are grafted onto the polymer particles. It is at least clear that this method also brings good results.

In addition, the gel fraction of polymer particles in this specification is
It serves as an index indicating the extent to which the polymer constituting the polymer particles is involved in crosslinking, and 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.

Furthermore, the weight average molecular weight of the polymer particles in this specification is the value measured by gel permeation chromatography (GPC) using polystyrene as a standard after extracting solvent-insoluble matter from the polymer constituting the particles. The surface tension of the polymer emulsion means the value measured with a CBVP surface tension meter (manufactured by Kyowa Kagakusha).

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

[Structure and operation of the invention] In this invention, first, a first-stage polymerization monomer is used and polymerized in an aqueous medium in the presence of a persulfate without using an emulsifier, thereby forming a gel. A polymer emulsion containing polymer particles whose fraction is regulated within a specific range is produced.

The above monomer for polymerization has an alkyl group having 1 to 14 carbon atoms.
It is a monomer mixture consisting of a main monomer mainly composed of (meth)acrylic acid alkyl ester and a carboxyl group-containing ethylenically unsaturated monomer. From the viewpoint of properties, alkyl groups having 1 to 14 carbon atoms are used, and particularly preferred examples include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, Examples include ethyl methacrylate, butyl methacrylate, and lauryl methacrylate. As the main monomer, various monomers such as styrene, acrylonitrile, vinyl acetate, etc., which can be copolymerized with the above-mentioned ester, are used in an amount of 25% by weight or less based on the main monomer. It may be something you have.

In addition, the carboxyl group-containing ethylenically unsaturated monomer is
(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.Why are crosslinks formed when such monomers are used? is not necessarily clear at present. It is speculated that when the above monomer is used, a chain transfer reaction by radicals occurs within the emulsion particles (polymer particles) during the polymerization process, and this is thought to be involved in the formation of crosslinks.

A monomer mixture consisting of a main monomer mainly composed of (meth)acrylic acid alkyl ester and a carboxyl group-containing ethylenically unsaturated monomer is such that the copolymer exhibits pressure-sensitive adhesive properties. It is necessary that the composition has a glass transition point of 250' or less. With such a composition, it is possible to prepare an adhesive composition that has both high cohesive strength and high adhesive strength.

Further, the proportion of the carboxyl group-containing ethylenically unsaturated monomer in the monomer mixture is generally 0.1 to 10
The amount is preferably about 0.5 to 7% by weight. If this ratio is too small, the gel fraction of the polymer particles cannot be set within the desired range, and if it is too large, the polymerization stability will deteriorate significantly, and the gel fraction of the polymer particles will become too high, resulting in poor adhesive strength. Also, problems tend to occur in terms of repulsion resistance.

In addition, it is also possible to further improve the cohesive force by using an internal crosslinking monomer such as di(meth)acrylate or divinylbenzene together with the above monomer mixture. However, the amount used is such that when the post-polymerization monomer is added to the first-stage polymer emulsion and polymerized, the post-polymerization monomer can be sufficiently diffused into the polymer particles. In addition, the amount should be so small (usually 0.5% by weight or less based on the total monomers) that it does not adversely affect the adhesive strength or rebound resistance of the final pressure-sensitive adhesive.

In the first stage of polymerization, persulfate as a polymerization initiator is added and dissolved in water, heated to a temperature of 60 to 90°C, and the above-mentioned monomer is added to this aqueous medium with stirring. The polymer mixture may be added dropwise at a predetermined dropping rate and allowed to react for a predetermined period of 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 affects the molecular weight and gel fraction of the produced polymer, and the ionic end groups produced by its decomposition improve polymerization stability in aqueous medium. It contributes to the stability of the emulsion after polymerization. In addition, this persulfate contributes to polymerization stability and emulsion stability during the second stage polymerization, and also plays a role as a polymerization initiator in the second stage polymerization. There is also.

Therefore, the amount of the persulfate used is desirably set within an appropriate range from the above-mentioned viewpoints, that is, from the viewpoints of the molecular weight, gel fraction, and stability of the produced polymer. Generally, the proportion of persulfate is preferably 0.1 to 5 parts by weight per 100 parts by weight of the monomer mixture used in the first stage polymerization.

It is important that the gel fraction of the polymer particles contained in the polymer emulsion thus obtained is set in the range of 20 to 60% by weight.

This setting can be easily achieved 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. It can be done.

By setting the gel fraction of the polymer particles within the above range, an adhesive composition with high adhesive strength, high cohesive strength, and excellent repulsion resistance can be obtained. If the ratio is less than 20% by weight, the cohesive force will decrease, and if it exceeds 60% by weight, the adhesive strength will decrease and it will be difficult to obtain an adhesive composition with excellent rebound resistance.

In addition, the molecular weight of the solvent-soluble portion of the polymer particles in the above polymer emulsion is such that the weight average molecular weight is 3.
It is desirable to set it to 00,000 or more. If this molecular weight becomes too low, it becomes difficult to obtain an adhesive with high cohesive strength, which is undesirable. The concentration is not particularly limited, but it should be selected so as to ensure the stability of the polymerization in the first and second stages and the stability of the emulsion, taking into account the amount of monomer used for the second stage polymerization. generally 20
It is preferable to adjust the amount to about 50% by weight.

In this invention, a monomer for post-polymerization is further added to the polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight obtained as described above to carry out the second stage polymerization. However, in this case, it is desirable that the surface tension of the polymer emulsion is set to an appropriate value. That is, according to the findings of the inventors, if the above-mentioned surface tension is too low, the monomer for post-polymerization will not effectively diffuse into the polymer particles, and the polymer particles will not be able to diffuse into the polymer particles. There is a risk that a homopolymer or copolymer of the monomer for post-polymerization may be formed in the field, and in this case, of course, the formation of the above-mentioned graft polymer is also suppressed, and it has been found that the effect of improving adhesive properties is reduced. Ta. The generally recommended surface tension is usually 43 dyne/cm or more, and particularly preferably one or two homopolymers or copolymers whose glass transition temperature is 273°K or more, preferably 300°K or more. More than one ethylenically unsaturated monomer. Here, if the glass transition point of the homopolymer or copolymer is lower than 273°K, a sufficient effect of improving the cohesive force cannot be obtained.

Note that among the two or more ethylenically unsaturated monomers that can make the copolymer have a glass transition point of 273°K or higher,
The glass transition point of the homopolymer of each monomer is 27.
In addition to monomer mixtures that can have a temperature of 3°K or higher, homopolymers and unsaturated monomers that can have a glass transition point above 273°KU and unsaturated monomers that can have a homopolymer glass transition point lower than 273°K. Also includes mixtures with the body. The latter monomer mixture may be one that exhibits a glass transition point of 273°K or higher when formed into a copolymer depending on its composition ratio.

The inventors found that homopolymers selected from the group of ethylenically unsaturated monomers such as styrene, vinyl acetate, tolyl, and methacrylonitrile all have a glass transition point of 300. The glass transition point of the homopolymer selected from the group of ethylenically unsaturated monomers or acrylic esters, methacrylic esters or styrene derivatives which can be higher than 27
Ethylenically unsaturated monomers (hereinafter referred to as
It has been found that unsaturated monomers belonging to both groups (referred to as component A monomers) are particularly suitable.

Specific examples of ethylenically unsaturated monomers belonging to the latter group include cyclohexyl acrylate (289°K), methyl acrylate (279°K), and butyl methacrylate (289°K).
293°K), N-N dimethylaminoethyl methacrylate (289°K), quinadecyl methacrylate (28
8° K), 2-methoxyethyl methacrylate (286°
K), unsaturated monomers whose homopolymers can have a glass transition temperature of 273°K or higher, such as 4-7'tylstyrene (279°K), and 2-butyl methacrylate (318°K).
K), 3,3-dimethylbutyl methacrylate (318
°K), 3,3-dimethyl-2-butyl methacrylate (381'K), ethyl methacrylate (338 °K)
, glycidyl methacrylate (319°K), isobornyl methacrylate (383°K), isobutyl methacrylate (326'K), isopropyl methacrylate (
354°K), methyl methacrylate (378°K), phenyl methacrylate (378”K), n-propyl methacrylate (308y), inbornyl acrylate (
367”K), 4-tert-butylstyrene (403
°K), 2,4-diisopropylstyrene (441 °K), 2,4-diisopropylstyrene (441 °K)
), 2,5-dimethylstyrene (416°K), 3,4
-diethylstyrene (382°K), 2-hydroxymethylstyrene (433°K), 4-methylstyrene (3
There are unsaturated monomers whose homopolymers have glass transition points of 300' or higher, such as 2-methylstyrene (366'K) and 2-methylstyrene (366'K).

Among these unsaturated monomers belonging to the latter group, those whose homopolymer glass transition point can be 300°K or higher are desirable, and among these, methyl methacrylate is the most preferred.

In this invention, one or both of these A component monomers are selected from one or both of the two groups, depending on the properties such as the monomer composition and gel fraction of the first-stage polymer particles. In addition, unsaturated monomers (hereinafter referred to as these) which can be copolymerized with these component A monomers and whose copolymer has a glass transition point of 273°K or higher are recommended. (referred to as component B monomer) may be used in combination.

Such component monomers include unsaturated monomers such as acrylic acid, methacrylic acid, and itaconic acid whose homopolymers can have a glass transition temperature of 273°K or higher, butyl acrylate, ethyl acrylate, and acrylic acid. The glass transition temperature of its homopolymers such as 2-ethylhexyl is 27
One or more monomers used in general acrylic pressure-sensitive adhesives, such as unsaturated monomers having a temperature lower than 3°K, are used. The amount of these component B monomers used is one of the factors that determines the glass transition point of the copolymer, so it may be determined appropriately depending on the types of both component A and B monomers, taking this point into consideration. However, if the amount used becomes too large,
Since it may interfere with the remarkable cohesive force improvement effect achieved by using the component monomers, the content should be 50% by weight or less, preferably 30% by weight or less, based on the total monomers.

The amount of the post-polymerization monomer consisting of ethylenically unsaturated monomers depends on the composition of the monomer mixture used in the first stage polymerization and the gel of polymer particles made from this mixture. Fraction, molecular weight of solvent soluble fraction.

It is determined as appropriate depending on the surface tension of the polymer emulsion and so that the final solid content concentration becomes an appropriate ratio, and usually the monomer mixture in the first stage is 100%
The proportion of the monomer for post-polymerization is preferably 3 to 200 parts by weight, preferably 5 to 100 parts by weight. If the amount used is too small, the effect of improving cohesive force will be poor, and if it is too large, there is a risk of impairing adhesive strength and repulsion resistance, so neither is preferable.

The second stage polymerization is carried out by adding the monomer for post-polymerization to the polymer emulsion produced in the first stage. The temperature may be heated to 60 to 90°C as in the first stage, and the monomer for post-polymerization may be added dropwise to this at a predetermined dropping rate while stirring, or the emulsion may be polymerized. The entire amount of the monomer for post-polymerization may be added first, stirred and mixed uniformly, and then polymerized at a predetermined temperature. In these methods, it is preferable to use the same persulfate as in the first stage as the polymerization initiator. However, other organic peroxides such as hydrogen peroxide and benzoyl peroxide, or redox catalysts such as sodium bisulfite, sodium ascorbate, metal salts, and amines can also be used together with these initiators. The amount of these polymerization initiators to be used is preferably about 0.01 to 5 parts by weight, preferably about 0.05 to 3 parts by weight, based on 100 parts by weight of the monomer for post-polymerization.

If the polymerization initiator used is a water-soluble one such as a persulfate, it can be added to the polymer emulsion as an aqueous solution, but if the polymerization initiator is a poorly water-soluble one such as benzoyl peroxide, it can be added to the polymer emulsion in the form of an aqueous solution. It is preferable to add it by dissolving it in an organic solvent or in a monomer for post-polymerization. Particularly in the latter case, it is preferable to uniformly stir and disperse the polymerization initiator solution in the polymer emulsion before the start of polymerization.

In the polymer emulsion obtained in this way, the concentration of the polymer particles, that is, the solid content concentration, is generally set in the range of 50 to 70% by weight from the viewpoint of emulsion stability and viscosity characteristics. is desirable.

The water-dispersed pressure-sensitive adhesive composition of the present invention is based on the polymer emulsion obtained in the second stage polymerization, and the polymer particles contained therein are as described above. By taking the configuration or particle configuration,
It has the characteristics of exhibiting excellent adhesive strength, cohesive force, and repulsion resistance, but in order to further improve these adhesive properties, various modifying ingredients such as those listed below may be appropriately blended into the above emulsion. do not have.

For example, if it is desired to increase the adhesive strength, up to 50 parts by weight of a tackifying resin with a softening point of 330°K or higher per 100 parts by weight of the polymer particles in the polymer emulsion can be used.
It can be blended preferably in a range of 5 to 40 parts by weight. If a tackifying resin with a softening point lower than 330' is used or if the blending ratio is too high, the cohesive force of the adhesive may be impaired and heat resistance and cold resistance are also adversely affected, which is not preferable.

Examples of such adhesion-imparting resins include Ester Gum H (softening point 345'K) manufactured by Arayo Kagaku Kogyo Co., Ltd., Bencel A (softening point 375'K) manufactured by Vercules, and Guimalex Resin (softening point 375'K) manufactured by Vercules. 418°K), pentaline C
(softening point 405°K), rosin-based adhesive auxiliary resin such as Mitsui Petrochemical's Hi-Resin C-110X (softening point 37
3°K), Pico Pail ll05F (softening point 3
80″K), Picodiene 2215 manufactured by Vercules (
petroleum resin-based adhesive auxiliary resins such as Kobe Yuka Co., Ltd.'s Coumaron Resin (softening point 389°K); coumaron-indene resin-based adhesive auxiliary resins such as Kobe Yuka Co., Ltd.'s Coumaron Resin (softening point 389°K); Examples include oil-soluble phenol resin-based adhesive force resins having a softening point of 378°K) and xylene resin-based adhesive force resins.

Further, in order to improve the initial adhesive strength (tack), a softener such as a liquid tackifying resin or a plasticizer used in general pressure-sensitive adhesives may be added.

The blending ratio is preferably up to 50 parts by weight per 100 parts by weight of the polymer particles in the polymer emulsion; if the amount is too large, properties such as cohesive force and heat resistance will be impaired.

In addition, the average molecular weight that is liquid at room temperature is 8,000 to 20
0. '000 low molecular weight polymers may also be included to improve initial adhesion (tack). As such a low molecular weight polymer, an acrylic low molecular weight polymer having a composition similar to that of the monomer mixture used in the first stage polymerization is preferable from the viewpoint of compatibility. The amount to be added varies depending on the composition, but it is generally recommended to add up to 200 parts by weight per 100 parts by weight of the polymer particles in the polymer emulsion, as too much will impair properties such as cohesive force and heat resistance. Undesirable.

Furthermore, if you wish to further increase the cohesive force,
An appropriate crosslinking agent may be added. It is sufficient that the blending ratio is usually up to 2 parts by weight, preferably within the range of 0.005 to 1 part by weight, based on 100 parts by weight of the polymer particles in the polymer emulsion. Specific examples of this crosslinking agent include triglycidyl isocyanurate, alicyclic glycidyl ester type, alicyclic glycidyl ether type, bisphenol type,
There are epoxy compounds such as aliphatic type low molecular weight epoxy compounds having a terminal 1,2-epoxy group, and commercially available products include Epikot #828 and Epicoat #1031 manufactured by Ciba Geigy, Epon #834 manufactured by Shell, and Ciba. ECN#1235 manufactured by Nippon Kagaku Co., Ltd., and TEP IC manufactured by Nichiryo Kagaku Co., Ltd. Also melamine or its derivatives such as mono,
Polymethylol melamine such as di-, tri-, tetra-, penta- or hexamethylol melamine, melamine compounds such as trimethoxymethyl melamine, tributoxymethyl melamine, commercially available Taquil #2 manufactured by Sumitomo Chemical Co., Ltd.
Examples include reactive phenol resins such as No. 01, polyvalent metal chelate compounds such as titanium acetylacetonate and ammonium titanium lactate, and various other isocyanate compounds and metal salts.

The water-dispersed pressure-sensitive adhesive composition of the present invention may further contain known compounding agents such as colorants, fillers, and anti-aging agents, if necessary. These compounding agents may be used in amounts commonly used in known adhesives.

〔Effect of the invention〕

As described above, since the water-dispersed pressure-sensitive adhesive composition of the present invention does not contain an emulsifier, there is no deterioration in adhesive properties due to deterioration in moisture resistance and water resistance caused by emulsifiers, and moreover, it does not contain an external crosslinking agent. It exhibits high adhesive strength and high cohesive strength even without being intentionally blended, and there is no decrease in cohesive strength especially at high temperatures.
Furthermore, it has the characteristic of being extremely resistant to repulsion, and can be used for general pressure-sensitive adhesive tapes, sheets, labels, etc., as well as applications that require particularly high repulsion resistance. is also very useful.

[Example 1] Examples of the present invention will be described below to explain more specifically. In addition, in the following, "part" means 1 part by weight, and "%" means % by 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 was applied to both sides of a 25μ thick polyester film so that the thickness after drying was 50 degrees 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/20 mm width) was measured according to JIS Z-1528.

Cohesion force〉 Make a double-sided adhesive tape similar to the adhesive strength test, and apply it to the
It was attached to two Bakelite plates with an adhesive area of 25 mm x 25 mm, and the time (minutes) until the Bakelite plate fell was measured by applying a load of I kg at 40°C and 80°C.

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, cut into 10 m x 80 m to make a test piece.The test piece was bent and attached to an aluminum cylinder with a diameter of 50 m, and then stored at 40 °C for 24 hours. At that time, the distance (rxrs) that the test piece rose from the cylinder was measured.

<Gel fraction> A polymer emulsion was applied to one side of a polyester film with a thickness of 25/ffi so that the thickness after drying was 50P, dried at 100°C for 3 minutes, and then 50m x 5
A test piece was prepared by cutting it into a size of Q g, 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 the test piece after immersion Ao; Weight of the test piece before immersion P; Weight of the polyester film constituting the test piece Example 1 500 m1 equipped with a thermometer, stirrer, nitrogen introduction tube and reflux condenser tube ? Into a reactor, 100 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 96 parts of 2-ethylhexyl acrylate and 4 parts of acrylic acid (copolymer glass transition point 210°K) was continuously heated for 5 hours while maintaining the above temperature. The mixture was added dropwise to obtain a first stage polymer emulsion. The solid concentration of this emulsion was 49.7%, the gel fraction of the polymer particles was 39.6%, the weight average molecular weight of the solvent-soluble component was 1 million, and the surface tension of the emulsion was 55 dyne/c+y+. .

Next, 30 parts of styrene (glass transition point of homopolymer: 370°K) and 20 parts of distilled water were added to this polymer emulsion based on 100 parts of the monomer mixture.
After stirring and mixing for 0 minutes, an aqueous polymerization initiator solution prepared by dissolving 0.5 parts of potassium persulfate in 10 parts of distilled water was added,
The reaction was carried out at 70° C. for 3 hours under a nitrogen stream to perform the second stage of polymerization.

The solid content concentration of the polymer emulsion thus obtained was 52%, and this emulsion was used as it was as the water-dispersed pressure-sensitive adhesive composition of the present invention.

Comparative Example 1 The first stage polymer emulsion of Example 1 was used as a comparative water-dispersed pressure-sensitive adhesive composition.

Comparative Example 2 A monomer mixture consisting of 96 parts of 2-ethylhexyl acrylate, 4 parts of acrylic acid, and 30 parts of styrene (glass transition point of the copolymer: 247°K), 0.5 part of potassium persulfate, and 130 parts of distilled water were added. A water-dispersed pressure-sensitive adhesive composition for comparison was obtained by reacting at 70° C. for 6 hours under a nitrogen stream according to the first-stage polymerization method of Example 1. Note that this composition corresponds to one in which the monomers for the first and second stages of Example 1 were simultaneously emulsion polymerized.

Comparative Example 3 A separately prepared polystyrene polymer emulsion was added to the first stage polymer emulsion of Example 1, and the latter polystyrene particles were added in an amount of 30 parts per 100 parts of the former polymer particles.
A comparative water-dispersed pressure-sensitive adhesive composition was prepared by mixing 100% of the water-dispersed pressure sensitive adhesive composition.

Comparative Example 4 100% of the monomer mixture used to produce the first stage polymer emulsion of Example 1
30 parts of ethyl acrylate (glass transition point of homopolymer 251'K) and 20 parts of distilled water were added to
After stirring and mixing for 0 minutes, an aqueous polymerization initiator solution prepared by dissolving 0.5 parts of potassium persulfate in 10 parts of distilled water was added,
A water-dispersed pressure-sensitive adhesive composition for comparison was prepared by performing a second stage polymerization by reacting at 70° C. under a nitrogen stream for 3 hours.

Comparative Example 5 Using 96 parts of 2-ethylhexyl acrylate, 0.5 parts of potassium persulfate, and 100 parts of distilled water, a reaction was carried out at 80°C for 5 hours under a nitrogen stream according to the first stage polymerization method of Example 1. By doing so, a first stage polymer emulsion in which the gel fraction of the polymer particles was 0% was obtained. To this emulsion, 3 parts of styrene was added to 96 parts of 2-ethylhexyl acrylate used to form the emulsion.
After stirring and mixing for about 30 minutes, an aqueous polymerization initiator solution prepared by dissolving 0.5 parts of potassium persulfate in 10 parts of distilled water was added, and the mixture was stirred for 70 minutes under a nitrogen stream.
A water-dispersed pressure-sensitive adhesive composition for comparison was prepared by reacting with C for 3 hours and performing second-stage polymerization.

Example 2 A monomer mixture consisting of 94 parts of 2-ethylhexyl acrylate, 4 parts of ethyl acrylate and 3 parts of acrylic acid (glass transition temperature of the copolymer 212°K), 0.5 part of potassium persulfate and distilled By reacting with 100 parts of water at 70°C for 6 hours under a nitrogen stream according to the first polymerization method of Example 1, a gel of polymer particles with a solid concentration of 49.8% was obtained. The fraction is 33.2%, the weight average molecular weight of the solvent soluble portion is 950,000, and the surface tension of the emulsion is 61 dy.
A first stage polymer emulsion having ne/σ was obtained.

Next, to this polymer emulsion, a monomer mixture of 20 parts of methyl methacrylate and 70 parts of vinyl acetate (glass transition point of the copolymer: 316°K) was added to 101 parts of the above monomer mixture. After stirring and mixing for a minute, an aqueous polymerization initiator solution prepared by dissolving 0.5 parts of ammonium persulfate in 10 parts of distilled water was added, and the mixture was heated at 70°C under a nitrogen stream for 3 minutes.
The reaction was carried out for a period of time to perform the second stage of polymerization.

The solid content concentration of the polymer emulsion thus obtained was 63%, and this emulsion was used as it was as the water-dispersed pressure-sensitive adhesive composition of the present invention.

Example 3 A monomer mixture consisting of 86 parts of n-butyl acrylate, 10 parts of ethyl acrylate and 4 parts of acrylic acid (glass transition temperature of the copolymer 226°K), 0.5 part of potassium persulfate and 100 parts of distilled water The solid concentration was 488% and the gel fraction of the polymer particles was 42. .2%, the weight average molecular weight of the solvent soluble portion is 1
0,000,000, the surface tension of the emulsion is 60 dyne/c
A first stage polymer emulsion of m was obtained.

Next, a monomer mixture of 10 parts of ethyl acrylate and 30 parts of styrene (glass transition point 3
After stirring and mixing for 30 minutes, an aqueous polymerization initiator solution prepared by dissolving 0.5 parts of ammonium persulfate in 10 parts of distilled water was added, and the mixture was reacted for 3 hours at 70°C under a nitrogen stream. , the second stage polymerization was carried out.

The solid content concentration of the polymer emulsion thus obtained was 54%, and this alesion was used as it was as the water-dispersed pressure-sensitive adhesive composition of the present invention.

Example 4 Monomer mixture 101 used to produce the first stage polymer emulsion of Example 2
Add 30 parts of styrene and 20 parts of distilled water to 30 parts of
After stirring and mixing for a minute, a polymerization initiator aqueous solution prepared by dissolving 0.5 parts of potassium persulfate in 10 parts of distilled water was added, and the mixture was reacted for 3 hours at 70°C under a nitrogen stream to carry out the second stage polymerization. By doing this, a polymer emulsion having a solid content concentration of 50% was obtained, and this emulsion was used as it was as the water-dispersed pressure-sensitive adhesive composition of the present invention.

The adhesive strength, cohesive force, and repulsion resistance of each of the adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 5 were investigated, and the results 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 a-gathering force,
Furthermore, it has very good rebound resistance, and since it does not contain an emulsifier, it has excellent moisture resistance and water resistance, and this together with the fact that it is an adhesive composition with extremely high practical value.

Claims (7)

[Claims] (1) A copolymer consisting of a main monomer mainly composed of an alkyl (meth)acrylic acid ester with an alkyl group having 1 to 14 carbon atoms and an ethylenically unsaturated monomer containing a carboxyl group is pressure-sensitive adhesive. The glass transition point showing the properties is 250°
A polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight, obtained by polymerizing a monomer mixture that can be less than K in an aqueous medium in the presence of a persulfate without using an emulsifier, Based on a polymer emulsion obtained by adding and polymerizing a post-polymerization monomer consisting of one or more ethylenically unsaturated monomers whose homopolymer or copolymer can have a glass transition point of 273°K or higher. A water-dispersed pressure-sensitive adhesive composition. (2) In a monomer mixture for obtaining a polymer emulsion containing polymer particles having a gel fraction of 20 to 60% by weight, the amount of carboxyl group-containing ethylenically unsaturated monomer in the mixture is 0.1 to 10%. Claim No. 1 (wt%)
) The water-dispersed pressure-sensitive adhesive composition described in item 1. (3) The polymerization temperature is 60 to 90% to obtain a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight.
The water-dispersed pressure-sensitive adhesive composition according to claim 1 or 2, wherein the temperature is .degree. (4) The amount of persulfate used to obtain a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight is 0.1 to 5 parts by weight based on 100 parts by weight of the monomer mixture. A water-dispersible pressure-sensitive adhesive composition according to any one of claims (1) to (3). (5) The surface tension of the polymer emulsion containing polymer particles having a gel fraction of 20 to 60% by weight is 43 dyne/cm or more, according to any one of claims (1) to (4). Water-dispersed pressure-sensitive adhesive composition. (6) The polymer particles according to any one of claims 1 to 5, wherein the weight average molecular weight of the solvent-soluble portion in the polymer particles having a gel fraction of 20 to 60% by weight is 300,000 or more. Water-dispersed pressure-sensitive adhesive composition. (7) A patent in which the amount of post-polymerization monomer is 3 to 200 parts by weight based on 100 parts by weight of a monomer mixture to obtain a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight. The water-dispersed pressure-sensitive adhesive composition according to any one of claims (1) to (6).