JPS63238179A - Water dispersion type pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition useful as pressure-sensitive adhesive tape, etc., having low viscosity, excellent film-forming properties, high bond strength and high cohesive force, by blending specific amounts of two water dispersions containing specific polymers, respectively. CONSTITUTION:(A) A water dispersion containing polymer particles which comprise a copolymer consisting of (i) 90-99.5wt.% main monomer having 1-14C alkyl group-containing (meth)acrylic acid alkyl ester as a main component and (ii) 10-0.5wt.% ethylenic unsaturated carboxylic acid and having <=250 deg.k glass transition point and has 0.3-1.0mum average particle diameter is blended with (B) a water dispersion containing polymer particles which comprise a polymer having <=310 deg.k glass transition point and 0.01-0.3mum average particle diameter in the blending ratio of 60-95wt.% polymer particles of the component A and 40-5wt.% polymer particles of the component B in sum of the polymer particles of the components A and B to give the aimed composition.

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 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.

[Problem that the invention seeks to solve]

However, the conventional acrylic water-dispersed adhesive mentioned above is
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 non-negligible thermal energy for crosslinking. The crosslinking becomes non-uniform, and the cohesive force is not very large compared to the degree of crosslinking, and even if the cohesive force becomes thicker (even if it is possible, the adhesive force will decrease accordingly, and in the end, it will not be possible to achieve a high adhesive force). It has been difficult to obtain a pressure-sensitive adhesive composition that also has high cohesive strength.

In addition, this type of water-dispersed adhesive has the disadvantage that when it is coated on a support and dried to make adhesive tapes, etc., it has poor film-forming properties and is difficult to form a uniform adhesive coating. This was one of the causes of a decline in adhesive properties, especially cohesive strength. For this reason, attempts have been made to improve film-forming properties by raising the drying temperature or adding film-forming aids, but in this case, problems such as thermal energy and adhesion properties due to the remaining film-forming aids have been made. The problem of negative effects could not be avoided.

In addition, attempts have been made to reduce the particle size of polymer particles in water-dispersed adhesives in order to improve film-forming properties, but in this case, the viscosity of the adhesive becomes extremely high, and colorants and adhesives Drying after application may impair mixing workability when blending various additives such as imparting agents and workability during application, and the concentration of polymer particles in water, that is, the solid content concentration, must be lowered. It took a long time to complete the process, which resulted in a loss of workability.

Therefore, this invention can maintain a low viscosity that poses no practical problem even with a high solid content concentration that contributes to shortening drying time, and when making it into a tape, it is possible to raise the drying temperature or use a coating aid. The object of the present invention is to provide an acrylic water-dispersed pressure-sensitive adhesive composition that can obtain good film-forming properties even without the addition of additives and has highly satisfactory adhesion and cohesive strength.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors developed a relatively large particle size copolymer of an acrylic monomer mixture containing ethylenically unsaturated carboxylic acid as a part of the component. When a specific amount of an aqueous dispersion containing polymer particles having a specific glass transition point and having a particle size smaller than the above-mentioned particles is mixed into an aqueous dispersion containing polymer particles having a particle diameter of Even if the solid content concentration is increased, a water-dispersed pressure-sensitive adhesive composition with low viscosity can be obtained, and when it is made into a tape, etc., the drying temperature is particularly high or a film-forming agent is added. Knowing that good film-forming properties can be obtained without adding any auxiliary means, and excellent adhesive properties that highly satisfy both adhesive force and cohesive force, it was necessary to complete this invention. It's arrived.

That is, the present invention provides: a) a main monomer 90 to 9 containing a (meth)acrylic acid alkyl ester having an alkyl group of 1 to 14 carbon atoms;
9.5% by weight and 10-0% ethylenically unsaturated carboxylic acid.
5% by weight of a copolymer with a glass transition point of 250°K or less, and an aqueous dispersion containing polymer particles having an average particle diameter in the range of 0.3 to 1.0 μm; b) glass transition; The point is 310″ or less, and the average particle size is 0.01 μm or more and 0.3 μm.
An aqueous dispersion containing polymer particles in a range of less than 60% of the total amount of the polymer particles of the above component a and the polymer particles of the above component.
This relates to a water-dispersed pressure-sensitive adhesive composition formed by mixing polymer particles of the above-mentioned components in a proportion of 40 to 5% by weight.

As described above, in the present invention, a specific acrylic copolymer having a glass transition point of 250°K or less and exhibiting pressure-sensitive adhesive properties and having an average particle diameter of 0.3 to 1.0 μm is used.
For an aqueous dispersion containing relatively large polymer particles in the range of 0.3 to 310" or less, the average particle diameter is 0.01 μm or more.
An aqueous dispersion containing relatively small polymer particles in the range of less than μm is included in the total amount of polymer particles in both dispersions.
6 large polymer particles made of acrylic copolymer
It is characterized in that it is mixed in such a manner that the proportion of polymer particles of small particle size is 0 to 95% by weight, and the proportion of polymer particles of small particle size is 40 to 5% by weight, that is, the proportion of polymer particles of large particle size is relatively large.

In such a mixed system, since the relatively large acrylic polymer particles are present in greater numbers than the small polymer particles, there is no concern that the viscosity of the entire aqueous dispersion will increase, and Even if the concentration is as high as 50 to 70% by weight, the viscosity can be made low enough to cause no practical problems, and it can also have low thixotropy. Moreover, when this is made into tape, etc., a structure is created in which small-sized polymer particles are inserted into the gaps between large-sized acrylic polymer particles, and the small-sized polymer particles have a glass transition point. Since the temperature is kept below 310°K, the film forming property is very good, and a uniform adhesive coating can be formed without raising the drying temperature or adding a film forming aid as in the conventional method. Therefore, adverse effects on adhesive properties due to poor film-forming properties can be avoided.

In addition to this film-forming property improvement effect, the acrylic copolymer that makes up the large polymer particles has a structure that is moderately crosslinked through the use of ethylenically unsaturated carboxylic acid. The small-sized polymer particles mixed into this are composed of a polymer with a glass transition point of 310°K or less, and the amount used is set to be small, so that the cohesive force can be maintained without reducing the adhesive force. It has been greatly improved and exhibits excellent adhesive properties such as high adhesive strength and high cohesive strength.

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

[Structure and operation of the invention]

The monomer mixture used to obtain the aqueous dispersion of component a in this invention includes a main monomer containing an alkyl (meth)acrylic acid ester having an alkyl group of 1 to 14 carbon atoms; It consists of ethylenically unsaturated carboxylic acid.

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, butyl acrylate, acrylic acid 2-
Ethylhexyl, isononyl acrylate, isodecyl acrylate, ethyl methacrylate, butyl methacrylate,
Examples include lauryl methacrylate. In addition to the above-mentioned esters, the main monomers include acrylonitrile, methacrylate trile, vinyl acetate, styrene or its derivatives, etc., in an amount of 25% by weight based on the main monomers. It can be used in the following proportions.

Ethylenically unsaturated carboxylic acids used in combination with the above main monomers include acrylic acid, methacrylic acid, itaconic acid,
Maleic acid and the like are used. This carboxylic acid not only contributes to improving adhesive strength, but also plays a role in increasing cohesive strength by participating in the formation of crosslinks in polymer particles.

A particularly suitable carboxylic acid is acrylic acid.

The ratio of the main monomer and ethylenically unsaturated carboxylic acid used 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. Should be. When the latter carboxylic acid content is less than 0.5% by weight, adhesive strength and cohesive force decrease, and when it exceeds 10% by weight, polymerization stability is impaired and many aggregates are generated during polymerization. , is inappropriate.

Needless to say, a monomer mixture consisting of such a main monomer and an ethylenically unsaturated carboxylic acid has a glass transition point of 250°K so that the copolymer exhibits pressure-sensitive adhesive properties.
The composition is as follows.

With such a composition, it is possible to prepare a pressure-sensitive adhesive composition that has both high cohesive strength and high adhesive strength.

In this invention, using a monomer mixture consisting of such a main monomer and a tyrenically unsaturated carboxylic acid,
A copolymer having a glass transition point of 250°K or less and an average particle diameter of 0.3 to 1.0 μm, preferably 0.4 to 0.
．． An aqueous dispersion is prepared as component a containing relatively large polymer particles in the range of 8 μm. The concentration of polymer particles in water in this aqueous dispersion is generally 50 to 70.
It's about % heavy.

The method for preparing this aqueous dispersion is not particularly limited, and various conventionally known emulsion polymerization methods can be employed. It is desirable to reduce the amount or apply a seed polymerization method. If the average particle diameter of the produced polymer particles is less than 0.3 μm, the viscosity of the aqueous dispersion will be high, and if it exceeds 1.0 μm, the film forming property will be poor. Both of these methods are unsuitable because it becomes difficult to form a uniform adhesive coating.

In this invention, the aqueous dispersion of component b mixed with the aqueous dispersion of component a is made of a polymer having a glass transition point of 310°K or less, preferably 273°K or less, and has an average particle diameter of 0.01 μm or more. less than 0.3 μm, preferably 0.0
It is an aqueous dispersion containing relatively small polymer particles in the range of 2 to 0.2 μm, and the concentration of the polymer particles in water is usually about 30 to 55% by weight.

The polymer constituting the polymer particles of component b is not particularly limited as long as its glass transition point is 310°K or less, and may be an acrylic polymer similar to component a or any other polymer. It's okay. Specifically, (meth)acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, n-propyl methacrylate, n-butyl methacrylate, and lauryl methacrylate, and acetic acid. Examples include homopolymers or copolymers of monomers such as vinyl and vinyl propionate. Furthermore, the glass transition temperature of acrylonitrile, styrene, acrylic acid, methyl methacrylate, and other homopolymers thereof is 310.
Even if the monomer has a temperature exceeding 310 °K, it is a copolymer of this monomer with the above-mentioned monomer and its glass transition point is 310 °K.
It is sufficient if the temperature is below °K. Furthermore, various polymers such as polyurethane and styrene-butadiene copolymer having a glass transition point of 310°K or less can be used.

In addition, if the glass transition point of the above polymer exceeds 310°K, the effect of improving film-forming properties will be reduced, and there is a risk that the adhesive properties as a pressure-sensitive adhesive composition, especially the adhesive strength, will decrease. Not applicable to this invention.

The method for separately preparing the aqueous dispersion of such a component is not particularly limited as in the case of component a, and various conventionally known emulsion polymerization methods can be employed, but if the particle size of the produced polymer particles is within the above-mentioned range. For example, it is desirable to increase the amount of emulsifier used or to apply a phase inversion emulsification method, etc., so as to maintain the same temperature. The average particle diameter of the produced polymer particles is 0.01 μm
If it is less than 0.3μ, the viscosity of the aqueous dispersion becomes high.
If it is more than m, the film-forming properties will deteriorate and it will be difficult to form a uniform adhesive coating, so both are unsuitable.

In this invention, the aqueous dispersion of the component a and the aqueous dispersion of the component described above are combined with relatively large polymer particles of the component a and relatively small polymer particles of the component described above. 60 to 95 of the above large diameter polymer particles in the total amount of
% by weight, preferably 70-90% by weight, 40-5% by weight, preferably 30-10% by weight of the small-sized polymer particles.
Mix at a mixing ratio that gives . If the content of the small-sized polymer particles exceeds 40% by weight, the viscosity of the aqueous dispersion will increase, and depending on the type of polymer in the polymer particles, the characteristics as an acrylic adhesive may be impaired. Also, if it is less than 5% by weight, film forming properties will deteriorate and it will be difficult to form a uniform adhesive coating (because it will become difficult to form).
Both are inappropriate.

The mixed aqueous dispersion obtained in this way has a concentration of the entire polymer particles in water, that is, a solid content concentration of 50 to 70%.
It has a low viscosity even at such high concentrations, low thixotropy, and excellent film-forming properties when made into tapes, and has excellent adhesive strength and cohesive strength. Demonstrate characteristics.

Therefore, in this invention, the aqueous dispersion obtained by the above method can be used as it is as a water-dispersed pressure-sensitive adhesive composition, but this composition may be colored if necessary. Conventionally known additives such as additives, fillers, anti-aging agents, and tackifiers may be blended as appropriate, and the blending amount thereof may be a usual amount. Further, the above composition alone exhibits high adhesive strength and good cohesive strength, but if it is desired to further increase this cohesive strength, various conventionally known external crosslinking agents can be added.

〔Effect of the invention〕

As described above, in the present invention, water containing polymer particles having a relatively large particle size and made of a copolymer of an acrylic monomer mixture containing ethylenically unsaturated carboxylic acid as a part of the component is used. By mixing a specific amount of an aqueous dispersion containing polymer particles with a specific glass transition temperature with a particle size smaller than the above particles into the dispersion, the viscosity is low even if the concentration of the entire polymer particles in water is high. It is possible to provide a water-dispersed pressure-sensitive adhesive composition that has excellent film-forming properties when formed into a tape, etc., and can exhibit excellent adhesive properties such as high adhesive strength and high cohesive strength.

Therefore, the water-dispersed pressure-sensitive adhesive composition of the present invention is very useful for general pressure-sensitive adhesive tapes, sheets, labels, and the like.

〔Example〕

EXAMPLES Below, examples of the present invention will be described in more detail. In addition, in the following, "part" means part by weight, and "%" means weight %, respectively.

In addition, adhesive force and cohesive force were measured using the following methods, and viscosity was measured using a B-type rotational viscometer (rotation speed: 20 rpm).
) and the average particle diameter of the polymer particles are values measured using a submicron particle analyzer NASD type (Coulter Electronic Inc.).

Adhesive strength> A pressure-sensitive adhesive composition was applied to both sides of a 25 μm thick polyester film so that the thickness after drying was 50 μm on one side, and dried at 100°C for 3 minutes to make a double-sided adhesive tape. As a test piece, JIS Z-1528
The 180 degree peeling adhesive strength (g/20wm width) was measured.

Cohesive strength> Make double-sided adhesive tape similar to the adhesive strength test, and
It was pasted onto two Bakelite plates with an adhesion area of 25 parts m x 25 u+, and a load of 1 kg was applied at 40°C and 80°C, and the time (minutes) until the Bakelite plate fell was measured.

Example 1 An aqueous solution consisting of 66 parts of water, 0.3 parts of potassium persulfate, and 0.2 parts of sodium lauryl sulfate was charged into a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser. , heated to 70°C, n-butyl acrylate 97
By uniformly dropping 100 parts of a monomer mixture consisting of 3% and 3% acrylic acid over 4 hours and holding it at 80°C for 2 hours after the dropping, the glass transition point was 222°K and the average particle size was An aqueous dispersion AI containing 60% of 0.7 μm polymer particles was obtained.

Meanwhile, into a reactor similar to the above, polymerization raw materials consisting of 100 parts of water, 0.3 parts of potassium persulfate, 100 parts of n-hexyl methacrylate, and 1 part of sodium lauryl sulfate as an emulsifier were charged, and the polymerization temperature was 75°C. By carrying out the reaction for two polymerization times of 8 hours, an aqueous dispersion B containing 50% of polymer particles having a glass transition point of 268°K and an average particle diameter of 0.2 μm was obtained.

The above aqueous dispersion A and aqueous dispersion B were uniformly mixed so that the weight ratio of the former to the latter polymer particles was 70/30, and the concentration of the entire polymer particles in water was 57%. ,
An aqueous dispersion having a viscosity (25°C) of 70 centipoise was prepared, and this was used as the water-dispersible pressure-sensitive adhesive composition of the present invention.

Comparative Example 1 The aqueous dispersion A of Example 1 was used as a comparative water-dispersed pressure-sensitive adhesive composition. Note that the viscosity (25° C.) of this composition was 60 centipoise.

Comparative Example 2 In the preparation of aqueous dispersion B of Example 1, the amount of emulsifier used was changed to 0.5 part, and the polymerization temperature was changed to 70°C, and polymer particles consisting of polyn-hexyl methacrylate were prepared. Aqueous dispersion C was prepared in the same manner as in Example 1 except that the average particle diameter was 0.7 μm. A comparative water-dispersed pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, except that this aqueous dispersion C was used in place of the aqueous dispersion B.

The viscosity of this composition (at 25°C) was 55 centivoise.

Comparative Example 3 An aqueous dispersion containing 40% of polymer particles made of polystyrene having a glass transition point of 360°K and having an average particle diameter of 0.2 μm was prepared according to the method for preparing aqueous dispersion B of Example 1. A sample was prepared. A comparative water-dispersed pressure-sensitive adhesive composition was obtained in the same manner as in Example 1, except that this water dispersion was used in place of water dispersion B1. The overall concentration of polymer particles in this composition in water was 52%, and the viscosity (at 25°C) was 50 centivoise.

Example 2 A copolymer with a glass transition point of 200°K of 80% 2-ethylhexyl acrylate, 19% ethyl acrylate, and 1% acrylic acid was prepared according to the method for preparing aqueous dispersion A of Example 1. An aqueous dispersion A2 containing 60% of polymer particles having an average particle diameter of 0.4 μm was prepared.

In addition, according to the method for preparing aqueous dispersion B1 of Example 1, a copolymer of 70% 2-ethylhexyl acrylate and 30% methyl methacrylate with a glass transition point of 222°K was prepared, and the average particle size thereof was Eight rounds of aqueous dispersion B2 containing 35% of polymer particles having a diameter of 0.1 μm were prepared.

The above aqueous dispersion A2 and aqueous dispersion B2 are uniformly mixed so that the weight ratio of the former to the latter polymer particles is 90/l O, and the concentration of the entire polymer particles in water is 56%. An aqueous dispersion having a viscosity (25° C.) of 90 centipoise was prepared, and this was used as the water-dispersible pressure-sensitive adhesive composition of the present invention.

Example 3 According to the method for preparing aqueous dispersion A of Example 1, a copolymer of 90% n-butyl acrylate, 3% acrylonitrile, and 7% acrylic acid with a glass transition point of 230°K was prepared. , 5 polymer particles whose average particle diameter is 0.5 μm
An aqueous dispersion A3 containing 5% was prepared.

In addition, according to the method for preparing aqueous dispersion B of Example 1, 60% n-butyl acrylate and 40% n-butyl methacrylate were prepared.
% and a glass transition point of 245',
4 polymer particles whose average particle diameter is 0.16 μm
Aqueous dispersion B containing 0% was prepared once.

The above aqueous dispersion A3 and aqueous dispersion B are uniformly mixed so that the weight ratio of the former to the latter polymer particles is 80/20, and the concentration of the entire polymer particles in water is 51%.
An aqueous dispersion having a viscosity (25° C.) of 50 centivoids was prepared, and this was used as the water-dispersed pressure-sensitive adhesive composition of the present invention.

The adhesive force and cohesive force of each of the compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were examined, and the results were as shown in the table below. The water absorption rates listed in the same table are based on the double-sided adhesive tape prepared in the same way as the adhesive strength test.
The weight increase rate is shown when the sample is cut into pieces with a size of 0 (ltmXloomm) and immersed in water for 10 days at room temperature. The lower the water absorption rate, the better the film-forming properties and the ability to form a uniform adhesive coating.

As is clear from the results in the above table, the composition of the aqueous dispersion of the present invention provides a water-dispersed pressure-sensitive material that exhibits excellent adhesive properties such as excellent film-forming properties, high adhesive strength, and high cohesive strength. It can be seen that an adhesive composition is obtained. Furthermore, it is clear from the description of each example that this composition has a low viscosity even though it has a high solid content concentration.

Claims (2)

[Claims] (1)a) Alkyl group has 1 to 14 carbon atoms (meth)
Main monomer 9 whose main component is acrylic acid alkyl ester
0-99.5% by weight and 10% ethylenically unsaturated carboxylic acid
~0.5% by weight and a copolymer with a glass transition point of 250°K or less, and an average particle size of 0.3 to 1.0
an aqueous dispersion containing polymer particles in the μm range, and b) a polymer with a glass transition point of 310°K or less, and whose average particle diameter is 0.01 μm or more and 0.3 μm.
An aqueous dispersion containing polymer particles in a range of less than 60% of the total amount of the polymer particles of the component a and the polymer particles of the component b.
A water-dispersible pressure-sensitive adhesive composition comprising 95% by weight of the polymer particles and 40-5% by weight of the polymer particles of component b. (2) The water-dispersed pressure-sensitive adhesive composition according to claim (1), wherein the total concentration in water of the polymer particles of component a and the polymer particles of component b is 50 to 70% by weight.