JPH0574633B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] This invention relates to an acrylic water-dispersed pressure-sensitive adhesive composition. [Prior Art] In recent years, acrylic pressure-sensitive adhesives have become widely used in place of conventional natural rubber-based and 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-dispersed adhesives are generally prepared by emulsion polymerization. That is, it is prepared by emulsion polymerization of a (meth)acrylic acid alkyl ester in an aqueous medium together with a modifying monomer such as acrylic acid, styrene, or vinyl acetate as necessary, and the room temperature obtained by this method is It is known that acrylic polymers with adhesive properties have a relatively large molecular weight compared to polymers obtained by solution polymerization, and therefore can provide relatively high cohesive strength as pressure-sensitive adhesives. [Problems to be Solved by the Invention] However, the above-mentioned conventional acrylic water-dispersed adhesives are still not satisfactory when applied to applications where a high degree of cohesion is desired.
Furthermore, when the bonded area was exposed to relatively high temperatures, the cohesive force was significantly reduced, making it 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 productivity problems such as the thermal energy for crosslinking which cannot be ignored. Due to the non-uniformity, the cohesive force is not so large compared to the degree of crosslinking, and even if the cohesive force can be increased, the adhesive force will decrease as a result, resulting in high adhesive force and high cohesive force. It has been difficult to obtain pressure-sensitive adhesive compositions having such properties. Furthermore, when the cohesive force is increased by the above-mentioned means, there is a problem in that, in addition to a decrease in adhesive strength, the adhesive also has poor anti-rebound properties.
In other words, for example, when 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 or plastic plate, so it is difficult to resist this restoring force. This repulsion resistance is expressed by the balance between adhesive strength and cohesive force. It was impossible to satisfy them. As described above, the conventional acrylic water-dispersed adhesive has the problem that it is difficult to obtain one that highly satisfies both adhesive force and cohesive force and also has excellent repulsion resistance. Moreover, this kind of adhesive is
Since an emulsifier is used to stabilize polymer particles during emulsion polymerization, this emulsifier mixes into the adhesive composition, resulting in poor moisture resistance and water resistance, which adversely affects adhesive properties. It also had problems. Therefore, the present invention provides a water-dispersed pressure-sensitive adhesive composition that does not contain any emulsifiers that cause the deterioration of the adhesive properties, and that has high adhesive strength and high adhesive strength even without the addition of an external crosslinking agent. Demonstrates cohesive power,
Furthermore, it is an object of the present invention to provide an acrylic water-dispersed pressure-sensitive adhesive composition that has excellent rebound resistance. [Means for Solving the Problems] As a result of intensive studies to achieve the above object, the inventors developed a new method instead of conventional emulsion polymerization.
A two-step polymerization in an aqueous medium that eliminates the use of emulsifiers by using a specific polymerization initiator is adopted, and the first step is a specific polymerization process in which a part of the component is a self-crosslinking monomer. A polymer emulsion in which the gel fraction of the polymer particles falls within a specific range is produced using a mixture of acrylic monomers, and a specific acrylic monomer is further added to this for the second stage of polymerization. When this process is carried out, it has excellent moisture resistance and water resistance because it does not contain an emulsifier, and also exhibits high adhesive strength and high cohesive strength even without the addition of an external crosslinking agent, and has excellent repulsion resistance. After learning that an acrylic water-dispersed pressure-sensitive adhesive composition can be obtained, the present invention was completed. That is, this invention is based on a (meth)acrylic acid alkyl ester having an alkyl group of 1 to 14 carbon atoms alone, or an unsaturated monomer having no functional group in the molecule that can be copolymerized with this ester. The main monomer, whose homopolymer or copolymer exhibits pressure-sensitive adhesive properties and whose glass transition point is 250°K or lower, is a self-crosslinking monomer containing unsaturated N-methylol or N-alkoxymethyl groups. A polymer containing polymer particles with a gel fraction of 20 to 60% by weight obtained by polymerizing a monomer mixture obtained by adding monomers in an aqueous medium in the presence of a persulfate without using an emulsifier. In the emulsion, a (meth)acrylic acid alkyl ester with an alkyl group having 1 to 14 carbon atoms alone, or a homopolymer or copolymer thereof consisting of this ester and an unsaturated monomer copolymerizable with the ester has pressure-sensitive adhesive properties. The glass transition point is
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 monomer for post-polymerization that can have a temperature of 250°K or less. In this way, in this invention, polymerization in an aqueous medium is carried out without using an emulsifier by specifically using a persulfate as a polymerization initiator, and the above persulfate is used for its decomposition. 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 resistance and water resistance because it does not contain an emulsifier. The stability of the emulsion is comparable to that of the seed composition. Further, in this invention, the polymerization in an aqueous medium as described above is divided into two stages, and an acrylic monomer mixture containing the above-mentioned specific self-crosslinking monomer is used as a monomer for the first stage polymerization. By using this method, an emulsion containing specific polymer particles with a controlled gel fraction is produced, and an acrylic monomer with excellent pressure-sensitive adhesive properties is added to this in the second stage for post-polymerization. In other words, it is assumed 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. ,
Due to this particle structure, the gel fraction of the entire polymer constituting the particles is regulated within a specific range, so adhesive compositions based on emulsions containing these polymer particles can be used without the addition of an external crosslinking agent. Even without blending, it exhibits high adhesive strength and high cohesive strength, and is also extremely resistant to rebounding. In this specification, the gel fraction of polymer particles is an indicator of how much the polymer constituting the polymer particles is involved in crosslinking, and this is an indicator of the solvent insolubility of the polymer. It is expressed by measuring minutes (% by weight). Specifically, it is actually measured by forming a polymer film from an emulsion containing polymer particles, immersing it in a solvent to elute the polymer that does not participate in crosslinking, and measuring the remaining solvent-insoluble content. . This measurement is as shown in Examples below. Furthermore, 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, and (meth)acrylic acid alkyl ester refers to acrylic acid alkyl ester and/or methacrylic acid alkyl ester. )
Acrylate means acrylate and/or methacrylate, respectively. [Structure and operation of the invention] In the present invention, a first-stage polymerization monomer is used and polymerized in an aqueous medium in the presence of a persulfate without using an emulsifier, thereby forming a gel. A polymer emulsion containing polymer particles whose fraction is regulated within a specific range is produced. The above monomer for polymerization is an unsaturated monomer having no functional group in the molecule that can be copolymerized with (meth)acrylic acid alkyl ester having an alkyl group of 1 to 14 carbon atoms alone or with this ester. A monomer mixture is used in which an unsaturated monomer containing an N-methylol group or an N-alkoxymethyl group is added as a self-crosslinking monomer to a main monomer consisting of a polyester and a polyester. As the (meth)acrylic acid alkyl ester as the main monomer, those having an alkyl group of 1 to 14 carbon atoms are used from the viewpoint of adhesive properties, and particularly preferred examples include ethyl acrylate, acrylic acid, etc. butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, and the like. In addition, examples of unsaturated monomers that do not have a copolymerizable group in the molecule include acrylonitrile, methacrylonitrile,
Examples include vinyl acetate, styrene, and derivatives thereof, and these monomers mainly contribute as components that increase the cohesive force of the polymer constituting the polymer particles. The main monomer consisting of such (meth)acrylic acid alkyl ester alone or with the above-mentioned copolymerizable unsaturated monomer has a glass transition point such that its homopolymer or copolymer exhibits pressure-sensitive adhesive properties. It is necessary that the composition is such that the temperature is 250°C or less. With such a composition, it is possible to prepare an adhesive composition that has both high cohesive strength and high adhesive strength. For this reason, the copolymerizable unsaturated monomer is preferably kept in a small amount relative to the (meth)acrylic acid alkyl ester, and generally the main monomer and self-crosslinking monomer are It is preferable that the amount of the copolymerizable unsaturated monomer in the monomer mixture consisting of the above-mentioned copolymerizable unsaturated monomer is usually 10% by weight or less. The self-crosslinking monomer used in combination with this main monomer is
This is an essential component for making polymer particles have a suitable gel fraction, and an unsaturated monomer containing an N-methylol group or an N-alkoxymel group is used. The amount of these monomers to be used is within the range of 1 to 10% by weight in the monomer mixture, and is appropriately determined depending on the type thereof and the desired gel fraction of the polymer particles. If the amount used is too small, the gel fraction of the polymer particles cannot be set within the desired range, and conversely, if it is too large, the gel fraction of the polymer particles becomes too high, resulting in poor adhesion and repulsion resistance. A difficulty arises. Specific examples of unsaturated monomers containing an N-methylol group or an N-alkoxymethyl group include N-methylol acrylamide, N-methylol methacrylamide, N-n-butoxymethyl acrylamide, and N-n-butoxymethyl methacrylamide. Examples include. The number of carbon atoms in the alkoxy group of the N-alkoxymethyl group is preferably about 5 or less from the viewpoint of reactivity. 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 produced polymer, and the ionic end groups produced by its decomposition improve polymerization stability in aqueous medium. It contributes to the stability of the emulsion after polymerization. In addition, this persulfate 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, it is desirable to set the amount of the persulfate used 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, for 100 parts by weight of the monomer mixture used in the first stage polymerization,
The proportion of persulfate is preferably 0.1 to 5 parts by weight. The polymer emulsion obtained in this way has a gel fraction of the polymer particles contained therein of 20 to 20.
It is important that the content is set within a range of 60% by weight. This setting can be easily achieved mainly by adjusting the type and amount of the self-crosslinking monomer, and in addition, by appropriately selecting the amount of persulfate used and polymerization conditions as described above. be. 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. When the ratio is less than 20% by weight, the cohesive force decreases, and when 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 consideration of the above, it is generally preferable to adjust the amount to about 20 to 50% by weight so as to ensure the polymerization stability of the first and second stages and the stability of the emulsion. In this invention, a monomer for post-polymerization is further added to the polymer emulsion containing polymer particles having 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 is composed of a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms alone, or this ester and an unsaturated monomer copolymerizable therewith. . As the (meth)acrylic acid alkyl ester, the same monomers as those in the first stage are used. In addition, unsaturated monomers that can be copolymerized with this include (meth)
Acrylic acid, itaconic acid, fumaric acid, maleic acid, 2-hydroxyethyl (meth)acrylate,
Examples include acrylonitrile, methacrylonitrile, styrene, and vinyl acetate. 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 main monomer in the first stage. 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 if an unsaturated monomer copolymerizable with the (meth)acrylic acid alkyl ester is used, the amount of the latter monomer used should be 10% by weight or less in the post-polymerization monomers. The usage ratio should be such that the above glass transition point is satisfied within the range. The amount of the monomer for subsequent polymerization to be used depends on the composition of the monomer mixture used in the first stage polymerization and the gel fraction of the polymer particles composed of this mixture.
In addition, to ensure that the final solid content concentration is at an appropriate ratio,
This can be determined as appropriate, and the ratio of the post-polymerization monomer to 100 parts by weight of the first-stage monomer mixture is usually 10 to 500 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 is 60 to 90℃ as in the first stage.
It may be within the range of . 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%, from the viewpoint of emulsion stability and viscosity characteristics.
It is desirable that the content be set in the range of ~70% 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 if necessary, a colorant and a filler are added to the composition. Conventionally known additives such as anti-aging agents, tackifiers and the like can be appropriately blended. The amount to be added may be a normal amount. Furthermore, although the above composition exhibits high adhesive strength and high cohesive strength by itself, 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 in combining them. [Effects 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 a decrease in moisture resistance and water resistance caused by an emulsifier. Moreover, it exhibits high adhesive strength and high cohesive strength even without the addition of an external crosslinking agent, shows no decline in cohesive strength especially at high temperatures, and has excellent rebound resistance. This characteristic makes it extremely useful not only for general pressure-sensitive adhesive tapes, sheets, labels, etc., but also for applications that particularly require rebound resistance. [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. Moreover, adhesive force, cohesive force, repulsion resistance, and gel fraction were measured by the following methods. <Adhesive strength> A pressure-sensitive adhesive composition was applied to both sides of a 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, and JIS Z- 1528 to measure the 180 degree peel adhesive strength (g/20 mm width). <Cohesive force> Make double-sided adhesive tape similar to the adhesive force test,
This was bonded to two Bakelite plates with an adhesive area of 25 mm x 25 mm, 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 a 0.3 mm thick aluminum plate so that the thickness after drying would be 50 μm, and after drying at 100°C for 3 minutes, a 10 mm x 80 mm
A test piece was made by cutting it to a size of (mm) was measured. <Gel fraction> Coat the polymer emulsion on one side of a 25 μm thick polyester film so that the thickness after drying is 50 μm, dry it at 100℃ for 3 minutes, and then
A test piece was prepared by cutting it into a size of 50 mm, and this test piece was immersed in heated acetone for 24 hours, and the gel fraction was determined by the following method. Gel fraction (%) = At-P/Ao-P×100 At: Dry weight of test piece after immersion Ao: Weight of test piece before immersion P: Weight of polyester film constituting the test piece Example 1 Temperature In a 500 ml reactor equipped with a meter, stirrer, nitrogen inlet tube and reflux condenser, add 0.5 potassium persulfate.
After dissolving 100 parts of distilled water and heating it to 80°C under a nitrogen stream, the main monomer (copolymer) consisting of 44 parts of n-butyl acrylate and 53 parts of 2-ethylhexyl acrylate was added. glass transition point of
A monomer mixture prepared by adding 3 parts of N-n-butoxymethylmethacrylamide to the mixture (210°K) was continuously added dropwise over 5 hours while maintaining the above temperature, and after the dropwise addition, the mixture was further held at 80° for 2 hours. A first stage polymer emulsion was obtained. The gel fraction of the polymer particles contained in this emulsion was 27.5%. Next, the above polymer emulsion was heated to 80° under a nitrogen stream, and then acrylic acid n
-21 parts of butyl, 27 parts of 2-ethylhexyl acrylate
A post-polymerization monomer (glass transition point of the copolymer: 213°K) consisting of 1.5 parts and 1.5 parts of methacrylic acid was continuously added dropwise over 3 hours while maintaining the above temperature.
After the dropwise addition, the mixture was further maintained at 80°C for 2 hours to carry out the second stage of polymerization. The solid content concentration of the polymer emulsion thus obtained was 59.8%, 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 N-n-butoxymethyl methacrylamide was omitted from the monomer mixture in the first stage. . Note that the gel fraction of the polymer particles of the emulsion obtained in the first stage polymerization is 0.
It was %. Comparative Example 2 As the first stage monomer mixture, acrylic acid n
-45.8 parts of butyl and 2-ethylhexyl acrylate
A water-dispersed pressure-sensitive adhesive composition was obtained in exactly the same manner as in Example 1, except that 0.2 parts of N-n-butoxymethylmethacrylamide was used as the main monomer consisting of 54 parts. Ta. Note that the gel fraction of the polymer particles of the emulsion obtained in the first stage polymerization was 11.5%. Comparative Example 3 As the first stage monomer mixture, acrylic acid n
-42 parts of butyl and 43 parts of 2-ethylhexyl acrylate
A water-dispersed pressure-sensitive adhesive composition was obtained in exactly the same manner as in Example 1, except that 15 parts of N-n-butoxymethylmethacrylamide was used as the main monomer consisting of . In addition, the polymer particle gel fraction of the emulsion obtained in the first stage polymerization is
It was 70.5%. Examples 2 to 6 A first-stage polymer emulsion was 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, A is the main monomer, B is the self-crosslinking monomer, and the glass transition point means the glass transition point of the copolymer consisting of the main monomer.

[Table] Next, a second polymer emulsion was prepared in the same manner as in Example 1, except that the monomers for post-polymerization shown in Table 2 below were used for the polymer emulsion in the first stage. A stage polymer emulsion was obtained. 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.

[Table] The results of examining 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 above were as shown in Table 3 below. .

[Table] As is clear from the results above, the water-dispersed pressure-sensitive adhesive composition of the present invention has high adhesive strength and high cohesive strength, and also has excellent rebound resistance. Since it does not contain an emulsifier, it has excellent moisture resistance and water resistance, and together with this, it is found that it is an adhesive composition with extremely high practical value.

Claims (1)

[Scope of Claims] 1. (Meth)acrylic acid alkyl ester having an alkyl group of 1 to 14 carbon atoms alone or this ester and an unsaturated monomer having no functional group in the molecule that can be copolymerized with the ester. The glass transition point at which the homopolymer or copolymer consisting of
A monomer mixture obtained by adding an unsaturated monomer containing an N-methylol group or an N-alkoxymethyl group as a self-crosslinking monomer to a main monomer that can have a temperature of 250°K or less is filtrated in an aqueous medium. The gel fraction obtained by polymerization in the presence of sulfate without using an emulsifier is
A (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms alone or an unsaturated monomer copolymerizable with the ester and this ester is added to a polymer emulsion containing 20 to 60% by weight of polymer particles. A water-dispersed polymer emulsion based on a polymer emulsion obtained by polymerization with the addition of a post-polymerization monomer whose homopolymer or copolymer exhibits pressure-sensitive adhesive properties and whose glass transition temperature can be 250°K or lower. Pressure adhesive composition. 2. In a monomer mixture for obtaining a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight, the self-crosslinking monomer is contained in the mixture in an amount of 1 to 10%.
% by weight of the water-dispersed pressure-sensitive adhesive composition according to claim 1. 3 Monomer mixture for obtaining a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight
3. The water-dispersed pressure-sensitive adhesive composition according to claim 1, wherein the persulfate is present in an amount of 0.1 to 5 parts by weight per 100 parts by weight. 4 Monomer mixture for obtaining a polymer emulsion containing polymer particles with a gel fraction of 20 to 60% by weight
4. The water-dispersed pressure-sensitive adhesive composition according to claim 1, wherein the post-polymerization monomer is present in an amount of 10 to 500 parts by weight per 100 parts by weight. 5. The polymerization temperature is 60-60% to obtain a polymer emulsion containing polymer particles with a gel fraction of 20-60% by weight.
The water-dispersed pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the temperature is 90°C. 6. A polymer emulsion obtained by adding and polymerizing a post-polymerization monomer, wherein the solid content concentration is 50 to 70% by weight in the emulsion, according to any one of claims 1 to 5. water-dispersible pressure-sensitive adhesive composition.