JPS62104887A - Pressure-sensitive adhesive composition dispersed in water - Google Patents

Abstract

PURPOSE:To obtain the titled composition having low thixotropic index, easily and uniformly miscible with a tackifier, etc., transportable through a pipe without trouble and useful for label, etc., by adding an acrylic monomer mixture dropwise to a specific aqueous dispersion and polymerizing the monomer. CONSTITUTION:The objective composition having a polymer particle diameter of 0.2-0.6mum and a polymer concentration of 50-65(wt)% can be produced by dripping and polymerizing (A) a monomer mixture composed of (i) 90-99.5% main monomer composed mainly of a 1-14C alkyl (meth)acrylate and (ii) 10-0.5% ethylenic unsaturated carboxylic acid giving a copolymer having a glass transition point of <=250 deg.K to (B) an aqueous dispersion of a polymer having a polymer particle diameter of 0.03-0.05mum and a polymer concentration of 0.5-2%. The dripping and polymerization are carried out in the absence of a dispersion stabilizer.

Description

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

[Conventional technology]

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

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

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

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

By the way, this type of acrylic-based water-dispersed pressure-sensitive adhesive can be used as pressure-sensitive adhesive sheets, labels, etc. by applying it directly to a base material or separator after it is prepared by the above method. However, in order to improve adhesive strength, cohesive strength, and adhesive strength, tackifiers, crosslinking agents, plasticizers, pigments, fungicides, viscosity modifiers, etc. are further added after the above preparation.
Thereafter, it is often used in the manner described above. In this case, it is very important that the above-mentioned ingredients are mixed uniformly in order to obtain the desired adhesive properties.

[Problem that the invention seeks to solve]

However, water-dispersed pressure-sensitive adhesives prepared by the conventional emulsion polymerization method have high thixotropy, so it takes a considerable amount of mixing time to uniformly mix the above-mentioned ingredients, and solvent-based It is complicated to use a mixing method different from that used for adhesives, and there is also a risk that the water-dispersed particles will be destroyed if a stronger mixing method is used. Furthermore, due to its high thixotropy, it remains attached to the inner surface of the pipe during pipe transportation, which requires frequent removal.

Therefore, in order to solve the above problems, attempts have been made to dilute water-dispersed pressure-sensitive adhesives with water to a low concentration to achieve low thixotropy, but in this case, pressure-sensitive adhesive sheets, labels, etc. It takes a long time to dry the coating after it has been applied to the substrate, which is disadvantageous in terms of heat energy and productivity of the sheets, labels, etc.

Therefore, the present invention provides a water-dispersed pressure-sensitive adhesive composition with a high polymer concentration that does not require a long time to dry after being applied to a substrate, and which is different from the conventional one. Compared to other products, it has low thixotropy, which makes it easy to uniformly mix various ingredients such as tackifiers, and it is industrially advantageous since it does not cause transportation problems such as adhesion remaining on the inner surface of pipes during pipe transportation. It is an object of the present invention to provide a water-dispersed pressure-sensitive adhesive composition.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors used as starting materials an aqueous dispersion of various polymers with a small polymer particle size and a very low polymer concentration, and in this aqueous dispersion, , an acrylic monomer mixture,
A water-dispersed pressure-sensitive adhesive composition whose polymer particle size falls within a specific range, obtained by continuously dropping the polymer without adding a dispersion stabilizer such as an emulsifier and polymerizing the polymer to a concentration of 50 to 65% by weight. As a product, it has low thixotropy, allows for easy and uniform mixing of various compounding ingredients, does not cause the above-mentioned transportation problems, and, moreover, this composition has a high polymer concentration as mentioned above, so it can be used as a base material. This invention was completed after learning that this method does not pose the problem of requiring a long time to dry after application.

That is, in this invention, the polymer particle size is 0.03 to 0.
05P with a polymer concentration of 0.5 to 2% by weight, an alkyl group having 1 to 14 carbon atoms (7
) The glass transition point of a copolymer consisting of 90 to 99.5% by weight of a main monomer mainly composed of (meth)acrylic acid alkyl ester and 10 to 0.5% by weight of ethylenically unsaturated carboxylic acid is 250°. The monomer mixture that follows is
The polymer particle size obtained by dropwise polymerization without adding a dispersion stabilizer is 0.2 to 0.6μ and the polymer concentration is 50.
65% by weight of a low thixotropic water-dispersed pressure sensitive adhesive composition.

By the way, as in this invention, the method of polymerizing an aqueous dispersion of a specific polymer as a starting material and adding monomers thereto is called a seed polymerization method, in which the composition of the polymer and monomer is changed. , is used as a means to modify various polymers. However, in the known seed polymerization method, a dispersion stabilizer such as an emulsifier is added to the polymerization system to prevent the polymer particles from agglomerating and to prevent the formation of new polymer particles other than the seed particles, thereby increasing the size of the seed particles. In contrast, the present invention is characterized by not adding a dispersion stabilizer as described above, and in this case, seed polymerization cannot be completed completely, resulting in some agglomeration of particles. , with this partial aggregation, the final particle size becomes 0.2 to 0.6/'' (7), l?lJ mer particle size.

On the other hand, an aqueous dispersion having such a polymer particle size can be obtained by simply adding monomers into an aqueous medium without using a polymer dispersion as a starting material as in the present invention and without adding a dispersion stabilizer. Depending on the conditions, it may also be obtained by a method of continuous dropwise addition and polymerization. but,
In this case, since the polymer particles cannot be stabilized during polymerization, particle aggregation becomes significant, resulting in a large amount of aggregates and extremely poor reproducibility for obtaining the desired aqueous dispersion.

In contrast, in this invention, the starting material has a polymer particle size of 0.03 to 0.05F and a polymer concentration of 0.5 to 0.05F.
Using a dilute aqueous dispersion with a small particle size of 2% by weight, monomers are continuously added dropwise to this to polymerize the polymer to a concentration of 50 to 65% by weight. Therefore, as mentioned above, even if some polymer particles agglomerate, there is no particular problem in that large amounts of large aggregates are formed, and the polymer particles are sufficiently stabilized during polymerization, resulting in a final It becomes possible to obtain with good reproducibility a stable aqueous dispersion having a polymer particle size in the range of 0.2 to 0.64 and containing almost no aggregates.

This aqueous dispersion has a polymer particle size within the above range, and in particular has no polymer particles smaller than 0.2P, so that it has lower thixotropy than the conventional dispersion. Moreover, since the concentration of the polymer in the aqueous dispersion as a starting material is dilute, the polymer constituting the particles is essentially a monomer that is added later, that is, a monomer mainly composed of (meth)acrylic acid alkyl ester. It consists of a mixture, and by arbitrarily changing the monomer composition of this mixture, desired adhesive properties can be obtained as an acrylic pressure-sensitive adhesive.

As described above, the acrylic water-dispersed pressure-sensitive adhesive composition of the present invention has low thixotropy even though the polymer concentration is as high as 50 to 65% by weight. Therefore, when adding various compounding agents such as tackifiers to this product, it is easy to mix them uniformly.
Furthermore, the problem of sticking and remaining on the inner surface of the pipe during pipe transportation is suppressed.

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 aqueous dispersion of the polymer used as a starting material in this invention is prepared by dispersing appropriate monomers in an aqueous medium, and dispersing potassium persulfate, ammonium perstatate, hydrogen peroxide, etc. It can be prepared by adding a polymerization initiator and polymerizing it. The type of the above-mentioned monomer used here is not limited at all, but it is preferably the same as the acrylic monomer mixture to be added dropwise and polymerized later.

Of course, it is not particularly necessary that the above mixture and its composition ratio be the same.

In addition, in the above preparation, anionic emulsifiers, nonionic emulsifiers, etc. may or may not be used. When using the above-mentioned polymerization initiators, polymerization stability can be ensured by the ionic terminal groups produced by decomposition of the initiator. Not using an emulsifier is desirable because the ultimately obtained water-dispersed pressure-sensitive adhesive composition has better moisture resistance and water resistance.

The aqueous dispersion of the polymer prepared by the above method has a polymer particle size of 0.03 to 0.05P, a polymer particle size of less than 0.03F, or a polymer concentration of 0.5% by weight.
If it is less than that, when an acrylic monomer mixture is added dropwise thereto and polymerized, many polymer particles having a particle size of less than 0.2 mm will be produced, making it difficult to achieve low thixotropy. In addition, if the polymer particle size of the aqueous dispersion exceeds 0.0 SP, there is a risk that a large amount of aggregates will be formed when the acrylic monomer mixture is dropped into the aqueous dispersion and polymerized.
Furthermore, if the polymer concentration exceeds 2% by weight, many polymer particles with a particle size exceeding 0.6μ will be produced when polymerized in the same manner as above, which will impair the stability of the aqueous dispersion, and will also cause problems such as tackifiers, etc. Even if such compounding agents are added and mixed uniformly, there is a risk that the effects of the compounding agents will not be fully expressed.

In this invention, an acrylic monomer mixture is continuously dropped into an aqueous dispersion having a specific polymer particle size and polymer concentration as described above without adding a dispersion stabilizer such as an emulsifier. Allow a polymerization reaction to occur. The above-mentioned acrylic monomer mixture used here refers to a main monomer whose main component is a (meth)acrylic acid alkyl ester whose alkyl group has 1 to 14 carbon atoms, and an ethylenically unsaturated carboxylic acid. It consists of.

As the (meth)acrylic acid alkyl ester as the main monomer, from the viewpoint of adhesive properties, those in which the alkyl group has 1 to 14 carbon atoms are used, and particularly preferred examples include:
Ethyl acrylate, phthyl acrylate, acrylic acid 2-
Ethylhexyl, innonyl acrylate, isodecyl acrylate, ethyl methacrylate, butyl methacrylate,
Examples include lauryl methacrylate. In addition to the above-mentioned esters, the main monomers include acrylonitrile, methacrylonitrile, vinyl acetate, styrene or derivatives thereof, etc., as unsaturated monomers copolymerizable with the above esters. It can be used in a proportion of up to % by weight. As the ethylenically unsaturated carboxylic acid, acrylic acid, methacrylic acid, itaconic acid, maleic acid, etc. are used.

This carboxylic acid contributes to improving adhesive strength.

The ratio of the main monomer to the ethylenically unsaturated carboxylic acid is such that the main monomer is 90 to 99.5% by weight and the ethylenically unsaturated carboxylic acid is 10 to 0.5% by weight. It should be a percentage. If the latter carboxylic acid is less than 0.5% by weight, the adhesive strength will decrease, and if it exceeds 10% by weight, polymerization stability will be impaired and many aggregates will be formed during polymerization, so it is unsuitable. It is. In addition, the monomer mixture consisting of such a main monomer and ethylenically unsaturated carboxylic acid has a composition such that the glass transition point is 250°K or less so that the copolymer exhibits pressure-sensitive adhesive properties. must have been done.

In this dropwise polymerization of the monomer mixture, the aqueous dispersion of the polymer is generally heated to about 60 to 80°C, and then added to the water, usually about 0.1 to 5 parts by weight per 100 parts by weight of the monomer mixture. A polymerization initiator, such as potassium persulfate or ammonium persulfate, is added and dissolved therein, and the monomer mixture is continuously added dropwise thereto at a predetermined dropping rate to cause the reaction to occur while maintaining the above temperature.

In such a reaction, dropwise polymerization is performed on an aqueous dispersion of the polymer, so the heat generation during polymerization is milder and reaction control is easier than when such an aqueous dispersion is not used. This has the advantage of preventing the formation of large amounts of aggregates during polymerization.

Further, a dispersion stabilizer such as an emulsifier is not added to the above polymerization reaction system. When added, good results can be obtained in preventing the formation of aggregates, but the particle size of the resulting polymer particles becomes small, making it impossible to achieve low thixotropy. On the other hand, in the case of no additive, some particle aggregation is observed, but due to this aggregation, the particle size increases and moderate polymer particles contributing to low thixotropy are produced.

In this invention, an aqueous dispersion having a polymer concentration of 50 to 65% by weight is obtained by appropriately setting the amount of the monomer mixture to be drop-polymerized in this manner. In this case, if the polymer concentration is less than 50% by weight, it will take a long time to coat and dry the coating on the substrate, and if it exceeds 65% by weight, polymerization stability will be affected, so it is not suitable.

The aqueous dispersion with such a polymer concentration is
Since the polymer particles have a particle size in the range of 0.2 to 0.6 microns, they have low thixotropy.

The water-dispersed pressure-sensitive adhesive composition of the present invention consists essentially of the aqueous dispersion obtained as described above,
When using this, various known compounding agents such as tackifiers, colorants, fillers, anti-aging agents, and crosslinking agents can be easily and uniformly mixed by utilizing its low thixotropy. This allows desired adhesive properties to be exhibited.

[Effects of the Invention] As described above, according to the present invention, the polymer concentration is as high as 50 to 65% by weight, which does not require a long time to dry after being applied to a substrate, etc., and is low. It is thixotropic, makes it easy to uniformly mix ingredients such as tackifiers, and makes it easy to produce a water-dispersed pressure-sensitive adhesive composition that does not cause transport problems such as remaining adhesion on the inner surface of pipes during pipe transportation. can be provided to

In addition, during the polymerization of the acrylic monomer mixture to obtain this type of composition, the heat generation is small, making it easy to control the polymerization and advantageous in terms of production management.Furthermore, since no emulsifier is used during the polymerization, An adhesive composition with good moisture resistance and water resistance can be provided.

Furthermore, since this composition has low thixotropy as described above, the smoothness of the coated surface when applied to a substrate etc. is good, which contributes to an increase in the adhesive area and, in turn, to an increase in adhesive strength. You can also do it.

[Examples] Examples of the present invention will be described below. In the following,
Parts and percentages refer to parts by weight and percentages by weight.

Example 1 A monomer mixture consisting of 50% 2-ethylhexyl acrylate, 45% ethyl acrylate, and 5% acrylic acid ( Add 1 part of the copolymer (glass transition point 227°K) and 100 parts of distilled water, mix with stirring, add 0.1 part of potassium persulfate, and react for 5 hours at 70°C under a nitrogen stream. By this, the polymer particle size is 0.03
An aqueous dispersion of the polymer was prepared with μ and a polymer concentration of 1.18%.

Next, 0.5 parts of potassium persulfate was added to this aqueous dispersion while maintaining it at 70'C, and then 150 parts of the same monomer mixture as above was added continuously for 5 hours. After the dropwise addition, the temperature was further raised to 80°C and maintained for 2 hours to complete the reaction.

The aqueous dispersion thus obtained has a polymer particle size of 0.
．． 4-, the polymer concentration was 60%.

Further, the ratio of viscosity at 2 rpm and 2 Orpm (viscosity at 20 rpm/viscosity at 2 rpm) measured by a B-type viscometer, which is a measure of the thixotropic property, was 0.45.

To 100 parts of this aqueous dispersion, 2 parts of a tackifier resin (trade name Pentaline c-so manufactured by Bercules; so% aqueous dispersion)
When 0 parts were added and mixed, uniform mixing was easily possible without impairing the stability of the aqueous dispersion. This mixture (
(mixing time: 10 minutes) was used as a water-dispersible pressure-sensitive adhesive composition according to the present invention.

Comparative Example 1 Into the same reactor as in Example 1, 100 parts of distilled water in which 06 parts of potassium persulfate was dissolved was charged, and 151 parts of the same monomer mixture as in Example 1 was added thereto for 70 minutes under a nitrogen stream. The mixture was continuously added dropwise over 5 hours at ℃, and after the dropwise addition, the temperature was further raised to 80℃ and maintained for 2 hours to complete the reaction.

The aqueous dispersion thus obtained contained a large amount of aggregates (6% based on the total polymer), the average particle size of the polymer particles was 0.25/ffi, and the distribution width was Wide <
It had spread to 0.06P. In addition, the ratio of viscosity between 2 rpm and 2 Orpm (viscosity at 2 Orpm/viscosity at 2 rpm) of a B-type viscometer, which is a measure of titanium tropism, is 0.
．． It was 2.

After removing the aggregates, the same tackifier as in Example 1 was added and mixed in the same proportion as in Example 1. Due to the high thixotropy of the aqueous dispersion, uniform mixing took a very long time. It took time.

A mixture obtained by mixing for 1 hour was used as a water-dispersed pressure-sensitive adhesive composition for comparison.

Example 2 In a reactor similar to Example 1, 8 n-butyl acrylate was added.
A monomer mixture consisting of 8% vinyl acetate, 10% vinyl acetate and 2% acrylic acid (glass transition temperature of the copolymer 231 °K) 1
and 100 parts of distilled water, stirred and mixed, added 0.1 part of ammonium persulfate, and heated to 80% under a nitrogen stream.
By reacting for 5 hours at °C, the polymer particle size was reduced to 0.
．． Next, 0.4 part of ammonium persulfate was added to this aqueous dispersion while keeping it at 80°C, and then the above procedure was carried out. 150 parts of the same monomer mixture as above was continuously added dropwise over 5 hours, and after the addition, the reaction was further maintained at 80°C for 2 hours to complete the reaction.

The aqueous dispersion thus obtained has a polymer particle size of 0.
．． At 45μ, the polymer concentration was 60%.

Further, the ratio of the viscosity at 2 rpm and 2 Orpm (viscosity at 20 rpm/viscosity at 2 rpm) measured by the B total viscometer, which is a measure of the thixotropic property, was 0.46.

To 100 parts of this aqueous dispersion, add 0.05 parts of a crosslinking agent (trade name: TEPIC, manufactured by Yasan Kagaku Co., Ltd.; an epoxy crosslinking agent) to 1 part of water.
When I mixed an aqueous solution prepared by dissolving the two parts, it was easy to mix uniformly. The composition after this mixing was used as a water-dispersible pressure-sensitive adhesive composition according to the present invention.

As the adhesive properties of the adhesive compositions of Examples 1 and 2 and Comparative Example 1, the adhesive force and cohesive force were investigated for reference, and the results were as shown in Table 1 below.

Note that the adhesive properties were measured by the following method.

Adhesive strength> A pressure-sensitive adhesive composition was applied to both sides of a 25pn thick polyester film so that the thickness after drying was 50μ on one side, and dried at 100°C for 3 minutes to make a double-sided adhesive tape. -1528, the 180 degree peeling adhesive strength (Cy720mm width) was measured.

Cohesive strength> Make double-sided adhesive tape similar to the adhesive strength test, and
It was bonded to two Bakelite plates with an adhesive area of 25 rxm x 25 mm, and a load of Ikg was applied at 40°C and 8o°C, and the time (minutes) until the Bakelite plate fell was measured.

As is clear from the results shown in Table 1, according to the present invention, a water-dispersed pressure-sensitive adhesive composition with low thixotropy can be easily produced, and because of the low thixotropy, the tackifier and crosslinking agent can be uniformly distributed. It can be seen that the mixture is easy to mix and that appropriate adhesive properties can be obtained by this mixing.

Claims (1)

[Claims] (1) Add (meth)acrylic acid whose alkyl group has 1 to 14 carbon atoms to an aqueous dispersion of a polymer having a polymer particle size of 0.03 to 0.05 μm and a polymer concentration of 0.5 to 2% by weight. Main monomer mainly composed of alkyl ester 90-99
．． 5% by weight and 10-0.5 ethylenically unsaturated carboxylic acid
The glass transition point of the copolymer consisting of 250° by weight
The polymer particle size obtained by dropping and polymerizing a monomer mixture that can be less than K without adding a dispersion stabilizer is 0.
A low thixotropic water-dispersible pressure sensitive adhesive composition having a diameter of 2 to 0.6 μm and a polymer concentration of 50 to 65% by weight.