JPS62100571A - Water-dispersed pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:The titled composition, consisting essentially of an emulsion obtained by polymerizing a raw material consisting of a specific acrylic monomer and specific unsaturated monomer in two stages by a special method and having high adhesive and cohesive force and improved rebound and moisture and water resistance. CONSTITUTION:A composition obtained by initially polymerizing a monomer mixture of (A) a 1-14C alkyl ester of (meth)acrylic acid with (B) a COOH group-containing ethylenically unsaturated monomer to give the resultant copoly mer of the components (A) with (B) exhibiting pressure-sensitive adhesive prop erty and <=250 deg.K glass transition point in an aqueous medium in the presence of a persulfate as a polymerization initiator without using an emulsifying agent to afford a polymer emulsion containing 20-60wt% gel fraction of polymer particles and adding and polymerizing a monomer, consisting of the component (A) and capable of giving the homopolymer exhibiting <=250 deg.K glass transition point so as to show pressure-sensitive adhesive property and used for post polymerization and finally using the above-mentioned resultant emulsion as a base.

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, Al1 is produced by emulsion polymerizing 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. Acrylic polymers, which are sticky at room temperature, have a relatively large molecular weight compared to polymers obtained by solution polymerization, and are therefore known to have relatively high cohesive strength when used as pressure-sensitive adhesives. ing.

[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 and It was almost unusable. 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 problems in terms of technical efficiency, such as the thermal energy for crosslinking that cannot be ignored. Due to the non-uniformity, 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 such pressure-sensitive adhesive compositions.

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, for example, in applications where a metal plate or plastic plate is bonded to an adherend with a curved surface in a bent state, a restoring force acts on the bent metal plate or plastic, so it is difficult to resist this restoring force. It is required to have excellent repulsion resistance, and this repulsion resistance is expressed by the balance between adhesive strength and cohesive force. I couldn't satisfy them.

As described above, conventional acrylic water-dispersed adhesives have had the problem of not being able to obtain adhesives that have a high degree of cohesive strength as well as adhesive strength, and that also have 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 a 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 whose - part is an ethylenically unsaturated monomer containing a carboxyl group is used so that the gel fraction of the polymer particles falls within a specific range. When a polymer emulsion such as
Acrylic-based water-dispersed pressure-sensitive material with excellent moisture and water resistance as it does not contain emulsifiers, exhibits high adhesion and cohesive strength without the need for external cross-linking agents, and has excellent repulsion resistance. Knowing that the adhesive composition is obtainable,
This invention was completed.

That is, in this invention, the alkyl group has 1 to 14 carbon atoms.
A monomer mixture of which the copolymer consisting of a (meth)acrylic acid alkyl ester and a carboxyl group-containing ethylenically unsaturated monomer exhibits pressure-sensitive adhesiveness and has a glass transition temperature of 250°K or less is added to an aqueous medium. A polymer emulsion containing polymer particles having a gel fraction of 20 to 60% by weight obtained by polymerization in the presence of a medium persulfate without using an emulsifier is added to a polymer emulsion containing polymer particles having an alkyl group of 1 to 14 carbon atoms ( The heptamodrimer or copolymer consisting of two or this]-ester in a meth)acrylic acid alkyl ester and an unsaturated monomer having no functional or νN in the molecule that can be copolymerized with the ester has pressure-sensitive adhesive properties. The present invention relates to a water-dispersed pressure-sensitive adhesive composition based on a polymer emulsion obtained by polymerization with the addition of a post-polymerization target having a glass transition point of 250' or less.

As described above, in this invention, polymerization in an aqueous medium is carried out without using an emulsifier by specifically using a persulfate as a polymerization initiator. This produces ionic end groups, which greatly contribute to polymerization stability and further to 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 generated, and a second acrylic material with excellent pressure-sensitive adhesive properties is added to this for post-polymerization. Therefore, it is presumed that the polymer particles produced by this method have a crosslinked structure inside and a structure made of acrylic pressure-sensitive adhesive polymer in the surrounding area. Because the gel fraction of the entire polymer that makes up these particles is regulated within a specific range due to the particle structure, adhesive compositions based on emulsions containing these polymer particles are intentionally formulated with an external crosslinking agent. Even without this, it exhibits high adhesive strength and high cohesive strength, and also has excellent repulsion resistance.

In addition, the gel fraction of polymer particles in this specification is
This is an indicator of how much the polymer constituting the polymer particles is involved in crosslinking, and this is expressed by measuring the insoluble content (wt%) of the above polymer. . Specifically, a polymer film is formed from an emulsion containing polymer particles, and this is immersed in a solvent for 7 days to expel the polymer that does not participate in crosslinking, and the remaining solvent-insoluble matter is measured. , actually measured.

This measurement is as shown in Examples below.

Furthermore, 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, ( The term meth)acrylate means acrylate and/or methacrylate, respectively.

[Structure and operation of the invention]

In this invention, the gel fraction is regulated within a specific range by first using the first-stage polymerization monomer and polymerizing it in the presence of persulfate in an aqueous medium without using an emulsifier. A polymer emulsion containing polymer particles is produced.

The above monomer for polymerization has an argyl group having 1 to 14 carbon atoms.
It is a monomer mixture consisting of (meth)acrylic acid alkyl ester and a carboxyl group-containing ethylenically unsaturated monomer. number 1-1
Four are used, and particularly preferred examples include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, ethyl methacrylate, butyl methacrylate, and lauryl methacrylate. Can be mentioned.

In addition, the carboxyl group-containing ethylenically unsaturated monomer is
(Meth)acrylic acid, crotonic acid, idaconic 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-mentioned jlj 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 crosslinking bonds.

A monomer mixture consisting of such a (meth)acrylic acid alkyl ester and an ethylenically unsaturated monomer containing a carboxyl group has a glass transition point of 250" or less at which the copolymer exhibits pressure-sensitive adhesive properties. By having 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 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 monomers are added to the aqueous medium with stirring. The reaction 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 resulting polymer, and the ionic end groups produced by its decomposition improve the polymerization stability in an aqueous medium. and contributes to the stability of the emulsion after polymerization. In addition, this persulfate usually plays a role as a polymerization initiator in the second stage of polymerization in the subsequent step, and also plays a role in polymerization stability and emulsion stability.

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%. 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 decreases, and if it exceeds 60% by weight, the adhesive strength decreases and it becomes difficult to obtain an adhesive composition with excellent rebound resistance.

Note that the solid content concentration of the polymer emulsion obtained in this first stage polymerization, that is, the concentration of polymer particles, is not particularly limited, but the amount of the monomer used for the second stage polymerization is In order to ensure the polymerization stability of the first and second stages and the stability of the emulsion, -In is
It is preferable to adjust the content to about 0 to 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. This produces a polymer emulsion containing polymer particles with a suitably crosslinked structure.

The above monomer for post-polymerization has an alkyl group having 1 to 1 carbon atoms.
It consists of four (meth)acrylic acid alkyl esters alone or this ester and an unsaturated monomer having no functional group in the molecule that can be copolymerized therewith. As the (meth)acrylic acid alkyl ester, the same monomers as those in the first stage are used. In addition, unsaturated monomers that do not have functional groups in their molecules that can be copolymerized with this are:
Examples include acrylonitrile, methallylonitrile, vinyl acetate, styrene or its HM i form.

These copolymerizable monomers are used as necessary components for modifying adhesive properties.

Such a monomer for post-polymerization has a glass transition point of 250°K or less at which the homopolymer or copolymer exhibits pressure-sensitive adhesive properties, as in the case of the first-stage monomer mixture. The composition must be such that a polymer having a higher glass transition point than the above is likely to cause problems in terms of adhesive strength. Therefore, even when using an unsaturated monomer that does not have a functional group in the molecule that can be copolymerized with the (meth)acrylic acid alkyl ester,
The amount of the latter monomer to be used should be within a range of 10% by weight or less in the monomer for post-polymerization, and should be used in a proportion that satisfies the above-mentioned glass transition point.

The amount of monomer used for the subsequent polymerization depends on the composition of the monomer mixture used in the first stage polymerization, the gel fraction of the polymer particles composed of this mixture, and the final solid state. It is determined appropriately so that the concentration of the components is at an appropriate ratio,
Usually, the amount of monomer for post-polymerization is 10 to 500 parts by weight, preferably 20 parts by weight, based on 100 parts by weight of the monomer mixture in the first stage.
It is preferable to set the proportion to 250 parts by weight.

The second stage polymerization is carried out by dropping the above monomer for post-polymerization into the polymer emulsion produced in the first stage at a predetermined dropping rate while stirring. The polymerization temperature at this time may be in the range of 60 to 90°C as in the case of the first stage. Incidentally, during this second stage polymerization, it is not necessary to intentionally add a persulfate as a polymerization initiator. However, they may be added if specifically desired.

The polymer emulsion obtained in this manner generally has a concentration of polymer particles having an appropriate crosslinked structure, that is, a solid content concentration of 50 to 70, from the viewpoint of emulsion stability and viscosity characteristics. It is desirable to set it within a range of % by weight.

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 composition may contain colorants and fillers as necessary. Conventionally known additives such as , anti-aging agents, and tackifiers can be appropriately blended. The blending amount may be a normal amount. Furthermore, although the above composition alone exhibits high adhesive strength and high a cohesive strength, if it is desired to further increase the cohesive strength, various conventionally known external crosslinking agents may be used within a range that does not impair the characteristics of the present invention. There is no problem even if it is mixed.

〔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〕

EXAMPLES Below, examples of the present invention will be described and explained in more detail. In addition, in the following, "part" means part by weight, and "%" means 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 is applied to both sides of a 25 μm thick polyester film so that the thickness after drying is 50 μm on one side, and dried at 100°C for 3 minutes to make a double-sided adhesive tape, and JIS Z- 1528, the 180 degree peeling adhesive strength (g/20 m width) was measured.

<Cohesive force> Make double-sided adhesive tape similar to the adhesive force test, and
It was attached to two Bakelite plates with an adhesive area of 251) x 25 tm, 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.

Repulsion resistance> A pressure-sensitive adhesive composition was applied to one side of an aluminum plate with a thickness of 0, 3 + U so that the thickness after drying was 5 Q ) t m, and it was dried at 100°C for 3 minutes (7) t3, lQm
Make a test piece by cutting it into a size of +m x 80 cranes.
When the test piece was bent and attached to a 50mm diameter aluminum cylinder and then stored at 40℃ for 24 hours,
The distance that the test piece rose from the cylinder (dragon) was measured.

Gel fraction> Coat the polymer emulsion on one side of a 25 μml”J polyester film so that the thickness after drying is 50 μm, dry it at 100°C for 3 minutes, and then
A test piece was prepared by cutting it into the size of a dragon, 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 test piece after immersion Ao: Weight of test piece before immersion Example 1 Potassium persulfate 0 After adding 100 parts of distilled water prepared by dissolving .5 parts of acrylic acid and heating it to 80°C under a nitrogen stream, a tetramer mixture (copolymer) consisting of 98 parts of 2-ethylhexyl acrylate and 2 parts of acrylic acid was added. (glass transition point: 225°K) was continuously added dropwise over 5 hours while maintaining the above temperature to obtain a first stage polymer emulsion. The solid content concentration of this emulsion was 49.8%, and the gel fraction of the polymer particles was 38.5%.
Met.

Next, the above polymer emulsion was heated to 80'C under a nitrogen stream, and then the isobutyl acrylate 9
．． The glass transition point of a copolymer consisting of 5 parts of 2-ethylhexyl acrylate and 40 parts of 2-ethylhexyl acrylate is 225".
K) was continuously added dropwise over a period of 3 hours while maintaining the above temperature, and after the addition, the temperature was further maintained at 80°C for 2 hours to carry out the second stage polymerization.

The solid content concentration of the polymer emulsion thus obtained was 59.5%, and this emulsion was used as it was as the water-dispersed pressure-sensitive adhesive composition of the present invention.

Comparative Example 1 A water-dispersed pressure-sensitive adhesive composition was obtained in exactly the same manner as in Example 1, except that 100 parts of 2-ethylhexyl acrylate was used instead of the first monomer mixture. In addition,
The gel fraction of the polymer particles of the emulsion obtained in the first stage polymerization was 0%.

Comparative Example 2 100 parts of n-butyl acrylate was used instead of the monomer mixture in the first stage, and 40 parts of n-butyl acrylate and 9 parts of acrylonitrile were used as monomers for post-polymerization in the second stage. A water-dispersed pressure-sensitive adhesive composition was obtained in exactly the same manner as in Example 1, except that . Note that the gel fraction of the polymer particles of the emulsion obtained in the first stage polymerization was 0%.

Comparative Example 3 Completely the same as Example 1 except that a monomer mixture of 99.98 parts of 2-ethylhexyl acrylate and 0.02 parts of acrylic acid was used as the first stage monomer mixture. A water-dispersed pressure-sensitive adhesive composition was obtained. Incidentally, the gel content of the polymer particles of the emulsion obtained in the first stage polymerization was 9.5%.

Examples 2 to 6 First-stage polymer emulsions were obtained in exactly the same manner as in Example 1, except that the monomer mixture shown in Table 1 below was used as the first-stage monomer mixture. .

The gel fraction of the polymer particles contained in this emulsion was as shown in Table 1. In Table 1, the glass transition point means the glass transition point of a copolymer made of a monomer mixture.

Next, for the first stage polymer emulsion,
A second stage polymer emulsion was obtained in the same manner as in Example 1, except that the monomers for post-polymerization shown in Table 2 below were used. This emulsion was directly used as the water-dispersed pressure-sensitive adhesive composition of the present invention. The solid content concentration in the second stage polymer emulsion was as shown in Table 2. Moreover, the glass transition point in Table 2 means the glass transition point of the copolymer composed of the monomer for post-polymerization.

The adhesive strength, cohesive force, and repulsion resistance of each of the adhesive compositions of Examples 1 to 6 and Comparative Examples 1 to 3 were investigated, and the results were as shown in Table 3 below.

Table 3 As is clear from the above results, the water-dispersed pressure-sensitive adhesive composition of the present invention has high adhesive strength and high cohesive strength,
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.

Patent applicant: Nitto Electric Industry Co., Ltd. Procedural amendment filed on December 21, 1985, Japanese Patent Application No. 60-239790 2, Title of invention: Water-dispersed pressure-sensitive adhesive composition 3, vg & patent with amendment person case Applicant Address: 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture
f'! (396) Representative of Nitto Electric Industry Co., Ltd.
Goro Kamai 4, agent mail (! number 530 "Detailed description of the invention" in the specification r, content of amendment A, specification (1) page 4, lines 8-9; "Water-dispersed adhesive "Water-dispersed pressure-sensitive adhesive"
I would like to correct this.

(2) Glass transition point (K) column in Table 1 on page 24; The text r226J in Example 2 will be corrected to r207J, and the text r218J in Example 5 will be corrected to r204J.

(3) Glass transition point (°K) column in Table 2 on page 26; Example 2 is r220J, r212J, Example 3 is r223J, and Example 4 is r226J.
The name is r207j, and the example 6 is r231J.
212j will be corrected.

Claims (6)

[Claims] (1) The copolymer consisting of a (meth)acrylic acid alkyl ester whose alkyl group has 1 to 14 carbon atoms and a carboxyl group-containing ethylenically unsaturated monomer exhibits pressure-sensitive adhesiveness and has a glass transition point of 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, A (meth)acrylic acid alkyl ester having an alkyl group of 1 to 14 carbon atoms alone, or a homopolymer or copolymer thereof consisting of this ester and an unsaturated monomer having no functional group in the molecule that can be copolymerized with the ester A water-dispersed pressure-sensitive adhesive composition based on a polymer emulsion obtained by polymerization with the addition of a post-polymerization monomer that exhibits pressure-sensitive adhesive properties and can have a glass transition point of 250°K or less. (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) A patent claim in which the amount of persulfate is 0.1 to 5 parts by weight per 100 parts by weight of a monomer mixture for obtaining 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 item (1) or item (2). (4) A patent in which the amount of the monomer for post-polymerization is 10 to 500 parts by weight based on 100 parts by weight of the 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 (3). (5) 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 any one of claims (1) to (4), which has a temperature of .degree. (6) In a polymer emulsion obtained by adding a monomer for post-polymerization and polymerizing the emulsion, the concentration of the solid content in the emulsion is 50 to 70% by weight.
The water-dispersible pressure-sensitive adhesive composition according to any one of items 1) to (5).