JPS61264077A - Water-dispersed type pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:The titled composition, obtained by polymerizing an unsaturated mono mer capable of giving a pressure-sensitive adhesive polymer with an aqueous dispersion of hydrosol particles consisting of a specific acrylic copolymer and having improved film-forming properties, water resistance, adhesive properties, etc. CONSTITUTION:An adhesive composition obtained by polymerizing (B) an unsaturated monomer capable of giving a pressure-sensitive adhesive polymer consisting essentially of an alkyl (meth)acrylate at 10-500 weight ratio, based on an acrylic copolymer constituting hydrosol particles, with (A) an aqueous dispersion of the above-mentioned hydrosol particles, prepared by adding an alkali and water to an acrylic copolymer, consisting of (i) 2-20wt% unsaturated monomer having an acidic group and (ii) 98-80wt% unsaturated monomer consisting essentially of an alkyl (meth)acrylate, copolymerizable therewith and having 10<4>-10<6> weight-average molecular weight and 0.01-0.1mu average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] This invention relates to an acrylic water-dispersed pressure-sensitive adhesive composition.

(Prior Art J) In recent years, acrylic pressure-sensitive adhesives have become widely used in place of conventional natural rubber-based 5 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.

Such water-dispersible pressure-sensitive adhesives are generally prepared by emulsion polymerization. That is, it is produced by emulsion polymerizing a (meth)acrylic acid alkyl ester together with a modifying monomer such as acrylic acid, styrene, or vinyl acetate as necessary in an aqueous medium in the presence of an emulsifier. It is known that the acrylic polymer obtained by this method has a relatively large molecular weight compared to the polymer obtained by solution polymerization, and therefore has a high cohesive force as a pressure-sensitive adhesive.

Problems to be Solved by the Invention] However, in the above conventional water-dispersed pressure-sensitive adhesives, the average particle diameter of the dispersed particles is usually as large as 0.1 to 0.5μ;
There was a problem that film forming properties were inferior to those of a solution type using an organic solvent. Moreover, in addition to the poor film-forming properties mentioned above, the adhesive contains the emulsifier used during emulsion polymerization, which deteriorates the water resistance of the adhesive coating, resulting in areas where water is used or usage conditions of high humidity. There was a problem that the adhesion strength decreased significantly under the lower part. Furthermore, this type of adhesive has the problem of low adhesion to rough surfaces, and there is also the problem that the emulsifier bleeds out onto the surface of the adhesive coating over time, causing a decrease in adhesive strength.

In order to avoid the above-mentioned problems caused by emulsifiers,
Water-dispersed adhesives that do not contain any emulsifiers are also being considered, but in this case the particle size of the dispersed particles becomes even larger.
There was a problem in that the film-forming property deteriorated significantly and a considerable amount of thermal energy was required for film-forming.

Therefore, the present invention makes it possible to obtain dispersed particles having a relatively small particle size that greatly contributes to improving film-forming properties without using an emulsifier that causes a decrease in water resistance.
Moreover, it is an object of the present invention to provide an acrylic water-dispersed adhesive composition that can improve adhesive properties such as adhesive strength to rough surfaces.

Means for Solving the U Problems J As a result of intensive studies to achieve the above object, the inventors found that hydrosol particles with an average particle diameter of 0.01 to 01 μm were produced by using an acrylic copolymer by a specific means. A pressure-sensitive adhesive polymer is attached to this aqueous dispersion by adding an unsaturated monomer mainly composed of (meth)acrylic acid alkyl ester and polymerizing it. In this case, it is possible to obtain a water-dispersed adhesive composition containing dispersed particles with a relatively small particle size that contributes to improving film-forming properties without using an emulsifier. After learning that it was possible to improve adhesive properties such as adhesive strength, the present invention was completed.

That is, this invention provides an unsaturated monomer 2 having an acidic group.
~20% by weight and an unsaturated monomer 98-8 whose main component is a (meth)acrylic acid alkyl ester copolymerizable with this
An acrylic copolymer with a weight average molecular weight of 10 to 10 and 0% by weight is mixed with an alkali and water to form an acrylic copolymer with an average particle size of 0.01 to 0.0% by weight.
In an aqueous dispersion of hydrosol particles of 01/ffi, (
Adding an unsaturated monomer capable of imparting a pressure-sensitive adhesive polymer containing meth)acrylic acid alkyl ester as a main component at a weight ratio of 10 to 500 times the weight of the acrylic copolymer constituting the particles, It relates to a water-dispersed pressure-sensitive adhesive composition obtained by polymerization.

In this invention, the unsaturated monomer mainly composed of (meth)acrylic acid alkyl ester to be involved in the polymerization is an acrylic copolymer composed of almost the same monomer as the unsaturated monomer, which is mixed with alkali and water. By adding it to an aqueous dispersion formed into hydrosol particles, it is impregnated into the inside of the particles, and polymerized in this state. Here, since the above-mentioned hydrosol particles are stably dispersed in water, a stable polymerization reaction can be carried out without using an emulsifier, and furthermore, the dispersed particles after polymerization contain 0% of the above-mentioned hydrosol particles.
Since it has a very small particle size of 0.01~0.1/'I, it has a smaller particle size (usually 0.Q5~03p) and is more stable than conventional emulsion polymerization type products. .

As described above, according to the present invention, it is possible to obtain stable dispersed particles with a small particle size without using an emulsifier, so that it is possible to improve the water resistance of the adhesive coating film as well as the film-forming property. There is an advantage. Further, the particle diameter of the dispersed particles can be arbitrarily controlled by the amount of unsaturated monomer to be polymerized, that is, the amount of impregnation into the inside of the hydrosol particles.

Moreover, the dispersed particles after polymerization have a structure in which the acrylic copolymer constituting the hydrosol and the polymer of the unsaturated monomer added thereto are integrally mixed, and the two are entangled at the intermolecular level. In addition, some of the above monomers may also contain a graft polymer obtained by graft polymerization to the above acrylic copolymer. It also avoids the problem of reduced adhesion to rough surfaces, which has been a drawback of conventional water-dispersed adhesives. In order to improve such adhesive properties, especially to adjust the cohesive force, adhesive force, and adhesive force, it is necessary to set the weight ratio of the unsaturated monomer to be added and polymerized to the acrylic copolymer constituting the hydrosol particles. It has the advantage of being easy to perform.

Furthermore, by using a polyfunctional unsaturated monomer containing two or more ethylenic double bonds as a part of the unsaturated monomer for polymerization, the dispersed particles can be composed of a crosslinked polymer. As a result, the cohesive force of the pressure-sensitive adhesive can be increased, and it becomes easier to prepare a pressure-sensitive adhesive composition that has high adhesive strength and high adhesive strength.

Structure and operation of the invention] In the present invention, the acrylic copolymer for forming the hydrosol particles mainly contains an unsaturated monomer having an acidic group and a (meth)acrylic acid alkyl ester copolymerizable with the unsaturated monomer. It is obtained by copolymerizing an unsaturated monomer as a component.

Examples of the unsaturated monomers having an acidic group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid, styrene sulfonic acid, allyl sulfonic acid, sulfopropylacrylate, and 2-acryloyl Examples include unsaturated sulfonic acids such as oxynaphthalene-2-sulfonic acid, 2-methacryloyloxynaphthalene-2-sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-acryloyloxybenzenesulfonic acid.

In addition, examples of the monomers containing the above-mentioned (meth)acrylic acid alkyl ester as a main component include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,
(where the alkyl group has 2 to 15 carbon atoms, such as isooctyl acrylate, ethyl methacrylate, and butyl methacrylate)
The main component is meth)acrylic acid alkyl ester, and if necessary, (meth)acrylic acid alkyl ester in which the number of carbon atoms in the alkyl group is outside the above range, such as methyl acrylate or methyl methacrylate, vinyl acetate, acrylonitrile, Those containing modifying monomers such as styrene, 2-methoxyethyl acrylate, vinyl ethers, glycidyl acrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, acrylamide, and N-methylolacrylamide are used. It is preferable that the amount of the above-mentioned modifying monomer is generally 40% by weight or less based on the total amount of the above-mentioned main components.

An unsaturated monomer having an acidic group and copolymerizable with it (
The proportion of the unsaturated monomer containing meth)acrylic acid alkyl ester as the main component should be 2 to 20% by weight of the former and 98 to 80% by weight of the latter. Particularly preferably, the former should be 3 to 80% by weight. It is preferable that the content is 10% by weight and the latter 97% to 90% by weight. The amount used of the former unsaturated monomer having an acidic group is 2
If it is less than % by weight, it will be difficult to form a hydrosol.
In addition, if it is used in an amount exceeding 20% by weight, water resistance may deteriorate, and both are inappropriate.

Copolymerization of these monomers can be carried out by conventionally known methods such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. Particularly preferred is the bulk polymerization method and 20% by weight
This is a solution polymerization method using the following organic solvents, and the acrylic copolymer obtained by these methods can be used as it is as a raw material for hydrosolization. In the solution polymerization method using 20% by weight or less of an organic solvent, as an organic solvent, alcohol-based hydrophilic alcohol such as methyl alcohol, ethyl alcohol, n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, 5ec-butyl alcohol, etc. Solvent or hydroxyl group,
It is desirable to use an oligomer or prepolymer having a hydrophilic group such as a carboxyl group or an amino group.

The above description of the amount and type of organic solvent to be used is based on the consideration that when the acrylic copolymer solution after solution polymerization is directly used as a raw material for hydrosolization, the hydrosolization can be carried out without any problems. be. Therefore, when part or all of the organic solvent is removed by distillation or the like after solution polymerization, the amount and type of organic solvent used are not particularly limited.

In the emulsion polymerization method, suspension polymerization method, etc., after copolymerization, the acrylic copolymer can be separated as a solid by an appropriate means such as a salting-out method, and this can be used as a raw material for hydrosolization. During the separation, the emulsifier used during polymerization is substantially removed by thorough washing such as water washing.

The weight average molecular weight of the acrylic copolymer thus obtained is required to be in the range of 10 to 10, particularly preferably in the range of 8 x 10 to 9 x 10. If the molecular weight is less than 10, the cohesive force as an adhesive will be poor, and if the molecular weight is higher than 10, the viscosity of the copolymer will become too high, which will impede hydrosolization, so both are unsuitable.

In this invention, the above-mentioned acrylic copolymer is made into hydrosol particles having an average particle diameter of 0.01-0.1 pn using an alkali and water. That is, alkali and water are added to the acrylic copolymer described in "-" while stirring to neutralize the acidic groups contained in the copolymer, and W2
An aqueous dispersion having the above hydrosol particles is prepared by inverting the phase from O type (water-in-oil type) to O/W type (oil-in-ice type).

In addition, prior to the above-mentioned hydrosolization, if the acrylic copolymer does not contain any organic solvent, if necessary, an organic solvent of 20% by weight or less based on the total amount of the copolymer, especially methyl alcohol, ethyl alcohol. , n-propyl alcohol, isopropyl alcohol, 5ec-butyl alcohol, and other alcohol-based aqueous solvents may be added. These solvents give good results in hydrosolization.

Examples of the alkali used in hydrosolization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, amines such as ethylamine and propylamine, ammonia, and α-amine ethyl alcohol. Among these, after hydrosolization as typified by ammonia, for example, coating on a tape support,
It is desirable to use an easily volatile material that can be easily volatilized during drying. This is because if alkali remains in the adhesive coating film, there is a risk of deterioration of adhesive properties. The amount of these alkalis to be used is approximately 0.02 to 2 equivalents relative to the acidic groups in the acrylic copolymer so that part or all of the acidic groups contained in the acrylic copolymer can be neutralized. Good.

The temperature during the neutralization treatment can be appropriately set depending on the type and properties of the acrylic copolymer, but is generally preferably in the range of 30 to 95°C. An example of a method for neutralization and hydrosolization is to add a predetermined amount of alkali or alkaline aqueous solution to the acrylic copolymer and thoroughly stir and mix for neutralization, followed by gradual addition of water and transfer. There is a method in which an O/W type dispersion, that is, a hydrosol, in which copolymer particles are finely separated, is produced by using water as a continuous phase by making them phase. Alternatively, a method may be adopted in which all the necessary amount of water is added during the above neutralization treatment to simultaneously advance hydrosolization while performing the neutralization treatment.

The solid concentration of the aqueous dispersion containing hydrosol particles obtained in this way, that is, the concentration of hydrosol particles, is generally adjusted to 1 to 40% by weight, preferably 2 to 30% by weight. This adjustment may be carried out by adjusting the amount of water added during the double hydrosolization, but it is generally desirable to further add water after the hydrosolization.

In this invention, an unsaturated monomer capable of imparting a pressure-sensitive adhesive polymer containing (meth)acrylic acid alkyl ester as a main component is added to the aqueous dispersion and polymerized.

The above unsaturated monomer used here is different from the raw material monomer of the acrylic copolymer constituting the hydrosol particles, except that the unsaturated monomer having an acidic group is not an essential component. There is no essential difference. Of course, the above-mentioned unsaturated monomer having an acidic group can also be used as an optional component if necessary.

That is, examples of unsaturated monomers capable of imparting the above-mentioned pressure-sensitive adhesive polymer include butyl acrylate, inoctyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, propyl methacrylate, etc. whose alkyl group has a large number of carbon atoms. The main component is 2-15 (DO) acrylic acid alkyl ester, and if necessary, functional groups such as acrylic acid, itaconic acid, maleic acid, fumaric acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, etc. Containing unsaturated monomers and other copolymerizable alkyl esters of (meth)acrylate other than the above-mentioned main components such as methyl acrylate and methyl methacrylate, styrene, acrylonitrile, methacrylonitrile, vinyl acetate, etc. A monomer containing △ is used.

The amount of the functional group-containing unsaturated monomer in the monomer mixture is generally 0 to 10% by weight, and the various copolymerizable unsaturated monomers are the main components. 50 out of the total amount of the above (meth)acrylic acid alkyl ester
It is preferable that the amount is less than % by weight. By using the amount in such a range, an adhesive polymer having pressure-sensitive adhesive properties and various functions depending on the purpose of use can be obtained.

In addition, in order to increase the cohesive force of the adhesive composition that is finally obtained by using this adhesive polymer as a crosslinked polymer, an ethylenic double bond is added in the molecule as a part of the unsaturated monomer. It is also possible to use polyfunctional unsaturated monomers having two or more.

Examples of such unsaturated monomers include polyvalent vinylbenzenes such as divinylbenzene, polyvalent esters of unsaturated carboxylic acids such as ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and polyvalent vinylbenzenes such as divinylbenzene. There are allyl compounds. The amount of this polyfunctional unsaturated monomer to be used is preferably up to 5% by weight in the monomer mixture; if it is used too much, problems such as a decrease in adhesive strength will occur, which is not preferred.

The method of adding the unsaturated monomer having such a structure to the aqueous dispersion containing hydrosol particles is not particularly limited, and for example, the entire amount thereof can be added to the dispersion at once. However, a more preferable method is to add the hydrosol particles little by little to the aqueous dispersion, and particularly by adjusting the amount and rate of addition, the stability of the hydrosol particles in the aqueous dispersion can be improved. It is desirable that the added monomer be uniformly diffused inside the hydrosol particles to uniformize the polymerization reaction.

Polymerization of the above unsaturated monomers added in this manner is carried out by using an appropriate polymerization initiator. Examples of the polymerization initiator include benzoyl peroxide,
Organic peroxides such as tert-butyl peroxide and halogenated benzoyl peroxide, azo compounds such as azobisisobutyronitrile, azobisisobutyramide, methylvaleronitrile, diazoaminoazobenzene, sodium persulfate, potassium persulfate , persulfates such as ammonium persulfate, redox initiators formed by combining these persulfates with reducing agents such as sulfites and bisulfites, and hydrogen peroxide. The amount of these polymerization initiators used is usually about 0.01 to 5 parts by weight, preferably about 0.1 to 3 parts by weight, based on 100 parts by weight of the unsaturated monomer.

The initiation of the polymerization reaction using the polymerization initiator is preferably carried out after the unsaturated monomer is uniformly impregnated into the hydrosol particles. When polymerization is carried out in a state where a large amount of unsaturated unsaturated monomer exists, that is, in the form of oil droplets in an aqueous dispersion, a large amount of polymer of the above monomer is generated outside the hydrosol particles. This is because the stability of the dispersed particles of the aqueous dispersion may be lowered.

One method for initiating polymerization as described above is to add an unsaturated monomer using the method described above, and then add a polymerization initiator to initiate polymerization.

In addition, if the polymerization initiator is added to the aqueous dispersion before adding the unsaturated monomer, or mixed with the unsaturated monomer and added together, the hydrosol of the added unsaturated monomer may be added. The temperature of the aqueous dispersion is maintained at a low temperature until the impregnation into the particles is almost completed, and after the impregnation is completed, if the polymerization initiator is a thermally cleavable type, it is generally heated to a temperature of 40 to 90 °C. In addition, in the case of a redox initiator, the polymerization reaction may be initiated by raising the temperature to a temperature higher than room temperature.

Of course, in the latter addition mode of the polymerization initiator,
If the unsaturated monomer is added in very small amounts and impregnation into the hydrosol particles is achieved relatively quickly by stirring, the temperature of the aqueous IPI liquid is kept high from the beginning to allow the monomer to There is no problem in starting the polymerization while adding and stirring.

In such a polymerization reaction, the amount of the unsaturated monomer, that is, the unsaturated monomer capable of imparting a pressure-sensitive adhesive polymer containing (meth)acrylic acid alkyl ester as a main component, added to the aqueous dispersion is as follows: The weight ratio must be set within a range of 10 to 500 times the weight of the acrylic copolymer constituting the hydrosol particles of the aqueous dispersion.

That is, when the above weight ratio is less than 10 times, the type of monomer described in 1. is selected to achieve desired pressure-sensitive adhesive properties, particularly improved cohesive force and adhesive force.
It is difficult to achieve the objective of the present invention, which is to obtain an adhesive composition with a good balance between adhesive strength and the like. On the other hand, if the above weight ratio exceeds 500 times, the stability of the hydrosol particles cannot be maintained, the stability of the dispersed particles of the resulting adhesive composition is impaired, and the particle size of the dispersed particles becomes larger. This results in a loss of film-forming properties.

On the other hand, by setting the above weight ratio within the above range, a water-dispersed adhesive composition with a smaller particle diameter of dispersed particles and excellent stable film-forming properties compared to conventional emulsion polymerization type adhesives. Moreover, the adhesive properties of this composition, such as adhesive strength, adhesive strength, and cohesive strength, can be fully satisfied. A particularly preferred weight ratio that satisfies these characteristics to a high degree is 15 to 200 times, and a more preferred weight ratio is 20 to 100 times.

The water-dispersed pressure-sensitive adhesive composition of the present invention obtained in this way contains the acrylic copolymer constituting the hydrosol particles in the dispersed particles produced by the above polymerization, and the unsaturated monomer impregnated into the acrylic copolymer and polymerized. It has a structure in which the acrylic copolymer is intertwined with the acrylic copolymer, and the latter polymer occupies the majority, and a part of it is intertwined with the acrylic copolymer. Because of the grafting, these dispersed particles can be stably dispersed in water even though no emulsifier is used, and the particle size is usually 0.05 to 0.
3 P, which is smaller than conventional emulsion polymerization type products, provides an adhesive coating that exhibits excellent film-forming properties and water resistance, and this coating is due to the unique polymer structure of the dispersed particles and exhibits good adhesive properties.

The water-dispersed pressure-sensitive adhesive composition of the present invention having such characteristics may optionally contain conventionally known additives, such as external crosslinking agents, colorants, fillers, tackifying resins, and anti-aging agents. , a rust preventive agent, an antibacterial agent, a leveling agent, etc. may be optionally added. These additives can also be added during any step in the production of the composition, such as the hydrosol preparation step or the subsequent step of adding and polymerizing the unsaturated monomer.

The water-dispersed pressure-sensitive adhesive composition of the present invention constructed in this way can be used to manufacture adhesive tapes and the like using conventional emulsion polymerization type adhesives within the range that does not impair the characteristics of the composition. In some cases, it is also possible to use it in combination with a composition.

In addition, as a special form of use, it can also be applied as a modifier for the above-mentioned conventional adhesive compositions.

[Effects of the Invention] As described above, in this invention, an aqueous dispersion in which an acrylic copolymer is made into hydrosol particles with an average particle diameter of 0.01 to 0.1 is used, and the water dispersion is By adding and polymerizing an unsaturated monomer mainly composed of (meth)acrylic acid alkyl ester that can impart a pressure-sensitive adhesive polymer to the dispersion, film-forming properties, water resistance, and roughness are improved. It is possible to provide an acrylic water-dispersed pressure-sensitive adhesive composition that has excellent adhesive properties such as adhesive force to surfaces and cohesive force.

[Real Male Side] Hereinafter, embodiments of the present invention will be described in more detail. In the following, parts shall mean parts by weight.

Example 1 10% by weight of a monomer mixture consisting of 75 parts of 2-ethylhexyl acrylate, 25 parts of methyl methacrylate, 5 parts of acrylonitrile, and 5 parts of acrylic acid and 10 parts of n-propertool were added to four The mixture was placed in a second flask and purged with nitrogen at 40°C for about 40 minutes while stirring. Next, 015 parts of azobisisobutyronitrile was added as a polymerization initiator, and after dissolving, the temperature of the bath was raised to 80°C to initiate polymerization, and the stirring speed, external bath temperature, and residual monomer content were adjusted. While controlling the reaction temperature at 80 to 90°C depending on the dropping rate of the mixture, dropwise polymerization of the remaining 11ii body mixture was carried out for 3 hours to obtain a weight average molecular weight of 4×1. An acrylic copolymer of O (according to GPC) was obtained.

Next, 0.5 equivalent of ammonia aqueous solution (
Neutralize by adding 10% by weight) and water.

Phase inversion was performed to obtain an aqueous dispersion containing hydrosol particles stably dispersed in water. The solid content concentration of this dispersion is 35%, the viscosity at 25°C is 140 poise, and the average particle diameter of the hydrosol particles (according to Nanosizer) is 0.05.
It was fi7n.

Add 10 parts of this aqueous dispersion and 90 parts of ion-exchanged water to four [''
After charging the mixture into a flask and diluting it, a monomer mixture consisting of 50 parts of n-butyl acrylate, 40 parts of ethyl acrylate, 3 parts of methacrylic acid, and 05 parts of divinylbenzene was gradually added dropwise and stirred for about 1 hour. Then, an aqueous solution of 02 parts of ammonium persulfate dissolved in 10 parts of water was added, and a polymerization reaction was carried out at 70° C. for 3 hours under a nitrogen stream to obtain a water-dispersed pressure-sensitive adhesive composition of the present invention.

Example 2 One of the monomer mixtures consisting of 80 parts of n-butyl acrylate, 20 parts of ethyl acrylate, and 10 parts of methacrylic acid
Pour 0% by weight into four flasks and add about 1% by weight while stirring.
Nitrogen replacement was performed for a period of time. Then, after raising the bath temperature to 65°C, 01 part of benzoyl peroxide was added as a polymerization initiator to initiate polymerization, and the reaction was controlled by stirring speed, external bath wetness, and dropping rate of the remaining monomer mixture. temperature to 70
Dropwise polymerization of the residual monomer mixture was carried out for 4 hours while controlling the temperature to 80°C. When no heat generation was observed, the bath temperature was raised to 80-90°C and aged for about 2 hours.
An acrylic copolymer having a weight average molecular weight of 5.2×10 (according to GPC) was obtained.

Next, 0.25 equivalent of ammonia water (10
(wt% concentration) was added with sufficient stirring while maintaining the bath temperature at 60°C to carry out neutralization treatment, and further water was added to invert the phase to form an aqueous dispersion containing hydrosol particles stably dispersed in water. I got the liquid.

The solid content concentration of this aqueous dispersion was 27% by weight, the viscosity at 25° C. was 32 poise, and the average particle diameter of the hydrosol particles (according to Nanosizer) was 0.006 fim.

After charging 10 parts of this aqueous dispersion into a fourth flask and diluting it with 90 parts of ion-exchanged water, 02 parts of potassium persulfate was added thereto, and then 95 parts of 2-ethylhexyl acrylate, 5 parts of acrylonitrile, and acrylic A monomer mixture consisting of 1 part of acid was gradually added dropwise over 4 hours at 70° C. in a nitrogen stream to cause polymerization. To this aqueous dispersion after polymerization, 3 parts of Super Beckamine MAS (trade name, melamine-based crosslinking agent) manufactured by Dainippon Ink Co., Ltd. is blended with respect to 100 parts of the solid content of the aqueous dispersion. A type pressure sensitive adhesive composition was obtained.

Comparative Example 1 A monomer mixture having exactly the same composition ratio as the final polymerization reaction product of Example 2 was prepared using thioglycolic acid as a chain transfer agent, potassium persulfate as a polymerization initiator, and Daiichi Kogyo Seiyaku Co., Ltd. as an emulsifier. A polymer emulsion was obtained by carrying out emulsion polymerization using each product under the trade name Hitenol N-17 (ammonium salt of polyethylene glycol sulfate).

The solid content concentration of this emulsion was 502% by weight at 25°C.
The viscosity was 75 poise, the average particle diameter of the dispersed particles (according to Nanosizer) was 04 μm, and the weight average molecular weight of the polymer constituting the dispersed particles was 35×10.

To this emulsion, 3 parts of Super Beckamine MASC (trade name, supra), manufactured by Dainippon Ink Co., Ltd., was added to 100 parts of the solid content to obtain a water-dispersed pressure-sensitive adhesive composition.

Comparative Example 2 In order to perform the second stage polymerization of Example 1 in a system that does not contain hydrosol particles, 100 parts of ion-exchanged water was charged into a four-hole flask, and then the corresponding monomer mixture was added, and the following Example 1 was carried out. When a polymerization reaction was carried out in the same manner as above, gelation occurred during the polymerization, the resulting polymer precipitated, and a uniform aqueous dispersion could not be obtained.

Each pressure-sensitive adhesive composition according to Examples 1 and 2 and Comparative Example 1 was coated on a 25p thick polyester film using a coating rod, and dried by heating at 130°C for 5 minutes to form a 50p thick adhesive. A pressure-sensitive adhesive tape having a coating film was prepared, and this tape was subjected to the following tests for adhesion, holding power (d Touhou), and water resistance. The test results were as shown in the table below.

<Adhesive Strength Test> The 180 degree peel adhesive strength (Cy/20 mm width) with respect to a stainless steel plate and cotton cloth was measured according to JIS Z-1528.

<Holding force test> Adhesive tape sample pasted on Bakelite board area 10
Paste it in mm width x 20 mm length, and attach 50 mm to the sample edge.
A load of 0y was suspended, and the time required for the sample to fall due to a-collection failure was measured in a thermostat at 40°C and 80°C.

<Water resistance test> The adhesive tape was immersed in ion-exchanged water at 40°C, and the whitening state of the adhesive layer was observed.

As is clear from the table above, the water-dispersed adhesive composition of the present invention has superior film-forming properties compared to conventional emulsion polymerization type adhesives, and since it does not contain an emulsifier, it has excellent water resistance. It can be seen that in addition to providing an adhesive coating film, the adhesive strength of this coating film, especially the adhesive strength to rough surfaces (cotton cloth), is high and the holding power is also high.

Claims (1)

[Claims] (1) Weight average of 2 to 20% by weight of an unsaturated monomer having an acidic group and 98 to 80% by weight of an unsaturated monomer whose main component is an alkyl (meth)acrylate copolymerizable with the unsaturated monomer An acrylic copolymer with a molecular weight of 10^4 to 10^6 is reduced to an average particle size of 0.01 to 0.1μ by using an alkali and water.
An unsaturated monomer capable of imparting a pressure-sensitive adhesive polymer containing an alkyl (meth)acrylic acid ester as a main component to an aqueous dispersion of hydrosol particles of m is added to the acrylic copolymer constituting the particles. A water-dispersible pressure-sensitive adhesive composition obtained by adding 10 to 500 times the weight of the water-dispersed pressure-sensitive adhesive composition.