JPS6345430B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a water-dispersed pressure-sensitive adhesive composition based on an acrylic polymer emulsion,
It is an object of the present invention to provide a pressure sensitive adhesive composition having improved rough surface adhesion. BACKGROUND ART Water-dispersible pressure-sensitive adhesives based on acrylic polymer emulsions obtained by emulsion polymerization of acrylic monomers in an aqueous medium have been known. Since this adhesive does not contain organic solvents, it has been developed as a resource-saving and pollution-hygienic solution, but it has poor adhesion compared to general organic solvent-soluble adhesives, especially rough surface adhesion. In other words, when the surface of the adherend is rough, the adhesion to the rough surface is extremely poor. In general, polymers formed by emulsion polymerization are
It is known that its molecular weight tends to be extremely high, usually 300,000 or more, and its molecular weight distribution is also narrow. Adhesives containing such polymers exhibit very high cohesive strength, but on the other hand, they tend to suffer from the adhesion problems described above. As a result of intensive studies to avoid these drawbacks, the inventors added water-soluble or water-dispersible polymers to the polymer emulsion obtained by emulsion polymerization of acrylic monomers in an aqueous medium. It has been found that when a low molecular weight acrylic polymer or its salt is blended, rough surface adhesion is greatly improved. This method can be considered as other means for improving adhesion, such as reducing the molecular weight of the polymer in an acrylic polymer emulsion as much as possible or adding a low molecular weight plasticizer such as dioctyl phthalate to the polymer emulsion. Compared to other methods, it is possible to suppress the decrease in cohesive force due to improved adhesion to a practically acceptable level, and there is no risk of impairing the stability of adhesive compositions based on polymer emulsion. It had many advantages, including a large improvement effect. The reason for this is that the low molecular weight acrylic polymer used is well compatible with the polymer formed by the emulsion polymerization method and exhibits the function of plasticizing this polymer, as well as being integrated with the polymer of the adhesive. This is thought to be because it functions effectively as an ingredient. Furthermore, it is known that certain low molecular weight acrylic polymers used in this method can themselves be used as solvent-free adhesives, but in this case, it takes a lot of effort to obtain the cohesive strength that is practically desired. It also had the disadvantage that it required a large amount of crosslinking agent and that it was difficult to obtain a stable product due to large changes in viscosity over time. On the other hand, since the above-mentioned adhesives are based on acrylic polymer emulsion, sufficient cohesive strength can be obtained even without the use of such cross-linking agents or even with a very small amount of cross-linking agents. It has also been found that it is possible to provide a pressure-sensitive adhesive that is essentially different from the above-mentioned known ones, such as a stable product with little viscosity change. On the other hand, the low molecular weight acrylic polymer used in this proposed method was required to have an average molecular weight (in this specification, average molecular weight means weight average molecular weight) in the range of 1,000 to 50,000. Here, the lower limit value is mainly set to obtain a practically acceptable minimum cohesive force, and the upper limit value is set mainly to a level of workability that does not hinder blending into an acrylic polymer emulsion. This was to obtain rough surface adhesion. However, according to subsequent research by the inventors, in this molecular weight range, when the average molecular weight is 10,000 or more, the viscosity becomes considerably high. It is better to mix in a state with increased fluidity, and in addition to the desired effect of improving mixing workability, this heating mixing method also improves rough surface adhesion without heating and requires a long time to mix. I found out that it is much better than when I did it. Therefore, as a result of further investigation based on this knowledge, we found that if such a heating mixing method is adopted,
It is now possible to use low molecular weight acrylic polymers with molecular weights even higher than the above-mentioned upper limit, and in this case, it is expected that the rough surface adhesion will be sufficiently improved, and it is also possible to suppress the cohesive force to a high level. I learned that this is convenient. This invention has been made based on the above knowledge, and uses a functional group-containing monomer that requires a carboxyl group-containing monomer for 100 parts by weight of the main monomer consisting of (meth)acrylic acid ester.
An acrylic polymer emulsion obtained by emulsion polymerization of an acrylic monomer containing 0.1 to 15 parts by weight in an aqueous medium contains a carboxyl group-containing monomer per 100 parts by weight of the main monomer consisting of (meth)acrylic acid ester. A water-soluble or water-dispersible low molecular weight acrylic polymer or its salt with an average molecular weight higher than 50,000 and 100,000 or less, which is obtained by polymerizing an acrylic monomer containing 0.5 to 20 parts by weight of a functional group-containing monomer, is used as an emulsion. A water-dispersed pressure-sensitive adhesive composition having improved rough surface adhesion obtained by heating and mixing a low molecular weight acrylic polymer in a proportion of 20 to 150 parts by weight based on 100 parts by weight of solid content. It is something. The acrylic polymer emulsion used in this invention is obtained by emulsion polymerization of acrylic monomers in an aqueous medium. ester is used as the main monomer. (In the formula, R ₁ is hydrogen or a methyl group, R ₂ is an alkyl group with 12 or less carbon atoms, a phenyl group, or

[Formula] means a group) In addition, a functional group-containing monomer is used, which essentially includes a carboxyl group-containing monomer that can be copolymerized with these main monomers. Examples of the carboxyl group-containing monomer as the essential monomer include acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid. Along with this carboxyl group-containing monomer, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate,
Acrylamide, methoxyethyl acrylate,
Other functional group-containing monomers such as acrylonitrile may also be used. These functional group-containing monomers are used in a proportion of 0.1 to 15 parts by weight based on 100 parts by weight of the main monomer. Furthermore, if necessary, vinyl monomers without functional groups such as vinyl acetate, styrene, and vinyl ether can also be used in combination as other monomers, and these are usually used in a proportion of 5 to 100 parts by weight per 100 parts by weight of the main monomer. used. Emulsion polymerization is carried out by adding an appropriate emulsifier or polymerization initiator to water together with an acrylic monomer according to a known method, adding a chain transfer agent if necessary, and reacting for 3 to 10 hours at 50 to 80°C under a nitrogen stream. Bye. Examples of the emulsifier used here include commercial products such as Nonion S40 and Pronone 208 manufactured by Nippon Oil & Fats Corporation, Emulgen 120 and 147 manufactured by Kao Atlas Co., Ltd., and Neocol P manufactured by Daiichi Kogyo Seiyaku Co., Ltd. The amount added is usually about 5 to 10 parts by weight per 100 parts by weight of the acrylic monomer. As the polymerization initiator, a water-soluble radical polymerization initiator such as ammonium persulfate or potassium persulfate is used. The amount added is usually about 0.1 to 10 parts by weight per 100 parts by weight of the acrylic monomer. In addition, the water used as the weight medium is generally ion-exchanged water, and it is usually 100 parts by weight per 100 parts by weight of the acrylic monomer.
~500 parts by weight. The acrylic polymer emulsion obtained in this way generally has an average molecular weight of 30.
This polymer is stably emulsified and dispersed in water. Of course, the molecular weight of the polymer does not necessarily need to be limited to the above-mentioned values, and may be made lower than the above-mentioned values by selecting polymerization conditions, etc., as long as the stability of the emulsion can be maintained. In this invention, as the low molecular weight acrylic polymer to be blended into such an acrylic polymer emulsion, one having an average molecular weight of more than 50,000 and less than 100,000 is used. The average molecular weight
When the molecular weight is lower than 50,000, it is essentially possible to prepare an adhesive composition without employing the heating mixing method according to the present invention. On the other hand, if it is higher than 100,000, it will not be possible to mix and disperse uniformly even with the heating mixing means of the present invention, and a stable adhesive will not be obtained. Next, such a low molecular weight acrylic polymer is selected to be either water-soluble or water-dispersible itself, or one that can be made water-soluble or water-dispersible by forming a salt with a basic compound. . This is because unless it is water-soluble or water-dispersible, it is difficult to mix uniformly into the acrylic polymer emulsion. The acrylic monomer used to obtain such a low molecular weight acrylic polymer is an ester of acrylic acid or methacrylic acid represented by the above general formula as the main monomer, and is copolymerizable with this monomer and can be copolymerized with itself or with methacrylic acid. A carboxyl group-containing monomer such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, etc., which can impart a water-soluble or water-dispersible function when converted into a salt, is used. In addition to this carboxyl group-containing monomer, other functional group-containing monomers such as 2-hydroxyethyl acrylate, 2-
Hydroxyethyl methacrylate, 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, etc. may also be used. The amount of these functional group-containing monomers is 0.5 to 100 parts by weight of the main monomer.
It is used in a proportion of 20 parts by weight. If necessary, a vinyl monomer having no functional group, such as vinyl acetate, styrene, or vinyl ether, can also be used in addition to the above-mentioned main monomer and functional group-containing monomer. The type and composition of the acrylic monomer may be the same as or different from the acrylic monomer used to synthesize the acrylic polymer emulsion. To obtain a low molecular weight acrylic polymer from such an acrylic monomer, a polymerization initiator and a chain transfer agent are generally added to the acrylic monomer by a bulk polymerization method, and the polymerization is generally carried out under a nitrogen stream for 50 to
The reaction may be carried out at 70°C for about 5 to 10 hours. Examples of the polymerization initiator used here include organic peroxides such as dibenzoyl peroxide and cumene hydroperoxide, and azo compounds such as azobisisobutyronitrile. The amount used is usually based on 100 parts by weight of acrylic monomer.
The amount may be about 0.05 to 5 parts by weight. In addition, as a chain transfer agent, thioglycolic acid,
Common chain transfer agents such as lauryl mercaptan can be widely used. The molecular weight of the polymer can be adjusted arbitrarily mainly by changing the amount of chain transfer agent used, so the amount to be used can be determined appropriately depending on the molecular weight of the required polymer, but in general, 100% of the weight of the acrylic monomer is used. The amount may be about 0.1 to 20 parts by weight. The low molecular weight acrylic polymers obtained in this way are generally viscous liquids in their normal state, and may themselves be water-soluble or water-dispersible; is further reacted with a basic compound to form a water-soluble or water-dispersible salt. A particularly suitable basic compound that can be used here is aqueous ammonia. This is because it can be easily volatilized when the resulting adhesive composition is applied to a tape-shaped substrate and dried by heating, which is desirable for maintaining the water and moisture resistance properties of the adhesive. Other basic compounds include propylamine,
Examples include nitrogen-containing compounds such as aniline and alkanolamines, and compounds containing metal ions such as potassium hydroxide and sodium hydroxide. Such a basic compound generally only needs to be added to the emulsion when the low molecular weight acrylic polymer is blended into the acrylic polymer emulsion. This addition turns the low molecular weight acrylic polymer into a salt, imparting water-soluble or water-dispersible characteristics. Of course, if desired, there is no problem in forming a polymer salt before compounding.
The amount of the basic compound to be used is usually about 0.05 to 1 equivalent relative to the acidic group contained in the polymer. In this invention, the blending ratio of the low molecular weight acrylic polymer or its salt to the acrylic polymer emulsion is such that the low molecular weight acrylic polymer is 20 to 150 parts by weight per 100 parts by weight of the solid content of the emulsion. It should be a percentage. If the amount is less than 20 parts by weight, sufficiently satisfactory rough surface adhesion cannot be obtained; conversely, if it is more than 150 parts by weight, the cohesive force decreases, and if it is too much, the rough surface adhesion also decreases. In the present invention, heating mixing means is employed to mix the low molecular weight acrylic polymer or its salt having such a blending ratio into the acrylic polymer emulsion. The heating mixing may be performed by heating the two after mixing them, but preferably at least one of the low molecular weight acrylic polymer or its salt or the acrylic polymer emulsion is mixed, particularly preferably both are heated in advance. It is better to do so. The heating temperature varies depending on the type and molecular weight of the low molecular weight acrylic polymer used, but is generally between 40 and
The temperature is preferably about 100°C; if the temperature is too high, the stability of the acrylic polymer emulsion may be impaired, which is not preferable. Further, during such heating and mixing, an appropriate organic solvent may be added in advance to the low molecular weight acrylic polymer or its salt in order to achieve more uniform mixing and dispersion. Examples of organic solvents include benzene, toluene, minesol, hexane, and methyl ethyl ketone. The amount used should be at most equal to or less than the amount of the low molecular weight acrylic polymer or its salt so as not to lose its value as a water-dispersed pressure-sensitive adhesive composition. As described above, the water-dispersed pressure-sensitive adhesive composition of the present invention substantially includes an acrylic polymer emulsion and a low molecular weight acrylic polymer blended therein in a heated state. If necessary, a conventionally known crosslinking agent or adhesion imparting resin may be added. The use of a crosslinking agent contributes to improving the cohesive force of the adhesive, but in this invention, the amount used can be very small due to the characteristics of the acrylic polymer emulsion. Usually, it is sufficient to add 1 part by weight or less per 100 parts by weight of the solid content of the polymer emulsion. There are two types of crosslinking agents: water-soluble ones and hydrophobic ones.If the cross-linking agent is water-soluble, it can be dissolved in an organic solvent and blended in the form of an emulsion. Water-soluble cross-linking agents include calcium chloride, polyvalent metal salts such as aluminum acetate, water-soluble glycidyl compounds, and water-soluble melamine, and hydrophobic cross-linking agents include organic peroxides such as benzoyl peroxide. and blocked isocyanate compounds. Next, as the adhesion imparting resin, xylene resin such as Nicanol manufactured by Nippon Gas Chemical Industry Co., Ltd.
HP100, rosin esters such as Ester Gum H (hydrogenated rosin) manufactured by Arakawa Forestry Co., Ltd., terpene-modified phenolic resins such as YS Polyster manufactured by Yasushi Oil Co., Ltd., and aliphatic or aromatic hydrocarbon resins are used. Generally, these adhesion-imparting resins are dissolved in an organic solvent, and then an emulsifier and a predetermined amount of water are added to form a resin emulsion, which is then incorporated into the acrylic polymer emulsion. The blending ratio is usually 10 to 100 parts by weight, preferably 20 to 50 parts by weight of the adhesion imparting resin per 100 parts by weight of the solid content of the emulsion. Incidentally, examples of the organic solvent used in preparing the resin emulsion include benzene, toluene, minesol, hexane, methyl ethyl ketone, etc., and both nonionic and anionic emulsifiers can be used as the emulsifier. It is preferable to use an emulsifier that is the same as or similar to that used in the synthesis of the acrylic polymer emulsion. The thus obtained water-dispersed pressure-sensitive adhesive composition of the present invention may further contain known compounding agents such as fillers, pigments, and thickeners, if necessary. The water-dispersed pressure-sensitive adhesive composition of the present invention can be used in the same way as adhesive compositions based on general acrylic polymer emulsions, such as plastic films, rubber sheets, and release-treated graft paper. The composition may be coated and dried on a base material such as plastic foam, or impregnated and dried on a base material such as cloth, nonwoven fabric, paper, etc., and used as various adhesive products such as adhesive films and adhesive sheets. As detailed above, according to the water-dispersed pressure-sensitive adhesive composition obtained by mixing the acrylic polymer emulsion of the present invention with a low molecular weight acrylic polymer or its salt under heating, the low molecular weight acrylic Since the average molecular weight of the polymer is relatively high, higher than 50,000 and lower than 100,000, the effect of greatly improving rough surface adhesion while maintaining a higher level of cohesive force can be achieved. Examples of the present invention will be described below, and will be explained more specifically in comparison with comparative examples. In addition, in the following, parts shall mean parts by weight. Comparative Example 1 70 parts of 2-ethylhexyl acrylate, 25 parts of vinyl acetate, 5 parts of acrylic acid, 208 parts of pronone (emulsifier:
A mixture consisting of 2 parts of the above), 0.5 parts of potassium persulfate, and 100 parts of ion-exchanged water was heated at 70°C under a nitrogen stream.
By reacting for 6 hours, an acrylic polymer emulsion was obtained. The solid content of this emulsion was 48% by weight, and the average molecular weight of the polymer was 1 million. This acrylic polymer emulsion was directly used as a water-dispersible pressure-sensitive adhesive composition. This composition was coated on a 25μm polyester film to a dry thickness.
It was applied to a thickness of 80 μm and dried at 130° C. for 10 minutes to form an adhesive film. The rough surface adhesion and holding power of this film were examined using the methods described below. As a result, the rough surface adhesion was 55 g/20 mm, and the holding power was over 1000 minutes. <Rough surface adhesion> Apply adhesive film to #200 sandpaper surface at 20℃.
Bonded with the load of one round trip of a 2Kg rubber roller.
The 180 degree peeling force was measured at 20° C. and at a peeling speed of 300 mm/min using a shovel type peel tester. <Holding power> Adhesive film pasting area is 1cm (width) x 2
After pasting it on a Bakelite board to a height of 1.5 cm, a load of 500 g was applied at 40°C and the time until it fell was measured. As is clear from the above test results, the adhesive composition consisting only of an acrylic polymer emulsion has a high cohesive force, but has a very low rough surface adhesion force. Comparative Example 2 The acrylic polymer emulsion obtained in Comparative Example 1 was blended with 30 parts of dioctyl tafrate based on 100 parts of the solid content of the emulsion to prepare a water-dispersed pressure-sensitive adhesive composition. An adhesive film was formed using this composition in the same manner as in Comparative Example 1, and the rough surface adhesion and holding power of this film were similarly examined. The rough surface adhesion was 75 g/20 mm, and the holding power was 1 minute or less. It was hot. As can be seen from this result, when a low molecular weight plasticizer such as dioctyl phthalate is incorporated into an acrylic polymer emulsion, it is recognized that the rough surface adhesion is improved to some extent, but it is still not fully satisfactory. However, this method significantly reduces the cohesive force. Example 1 A mixture consisting of 70 parts of butyl acrylate, 25 parts of vinyl acetate, 5 parts of acrylic acid, 0.5 part of thioglycolic acid and 0.5 part of azobisisobutyronitrile,
A low molecular weight acrylic polymer was obtained by reacting at 60° C. for 5 hours under a nitrogen stream. This polymer was a viscous liquid with an average molecular weight of 55,000. Next, 3 parts of 28% ammonia water was added to the acrylic polymer emulsion obtained by the method of Comparative Example 1, based on 100 parts of solid content of this emulsion.
After heating this to 70°C, 20 parts of the above-mentioned low molecular weight acrylic polymer heated to 80°C and 2 parts of benzoyl peroxide were blended and mixed with thorough stirring to form the water-dispersed pressure-sensitive adhesive of the present invention. I made it into a thing. An adhesive film was formed from this composition in the same manner as in Comparative Example 1, and the rough surface adhesion and holding power of this film were examined, and the rough surface adhesion was 390 g/20
mm, and the holding force was 430 minutes. As clearly understood from these results, the adhesive composition of the present invention can satisfy both rough surface adhesion and cohesive force. Example 2 The blending ratio of low molecular weight acrylic polymer was 80
A water-dispersed pressure-sensitive adhesive composition was obtained in exactly the same manner as in Example 1, except for changing the amount of water. An adhesive film was formed from this composition in the same manner as in Example 1,
The rough surface adhesion and holding power of this film were investigated.
The results show that the rough surface adhesion is 560g/20mm, and the holding force is 205.
It was hot in minutes. It is clear that by increasing the blending ratio of the low molecular weight acrylic polymer as described above, the rough surface adhesive strength can be further improved. For reference, if the above blending ratio is increased to more than 150 parts by weight, the retention strength will drop even if the rough surface adhesion is satisfied, and conversely, if it is decreased to less than 20 parts by weight, The rough surface adhesion could not be significantly improved. Example 3 85 parts of 2-ethylhexyl acrylate, styrene
A low molecular weight acrylic polymer with an average molecular weight of 81,000 was prepared in the same manner as in Example 1 using a mixture of 10 parts of acrylic acid, 10 parts of acrylic acid, and 0.2 parts of azobisisobutyronitrile, and an appropriate amount of thioglycolic acid. was synthesized. Next, 3 parts of 28% ammonia water was added to the acrylic polymer emulsion obtained by the method of Comparative Example 1, based on 100 parts of solid content of this emulsion.
After heating this to 70°C, 30 parts of the above polymer heated to 90°C, 20 parts of a 50% emulsion of Nicanol H-100 (tackifier resin: mentioned above) and 0.5 parts of zinc acetate.
The water-dispersed pressure-sensitive adhesive composition of the present invention was prepared by stirring and mixing thoroughly. An adhesive film was formed from this composition in the same manner as in Example 1, and the rough surface adhesion and holding power of this film were examined, and the rough surface adhesion was 380 g/20
mm, the holding force was 1218 minutes, and similar to Examples 1 and 2, good results were obtained. Further, in this example, even better results were obtained especially in terms of maintaining the holding force. For reference, we synthesized the above low molecular weight acrylic polymer with a higher average molecular weight, that is, the above polymer with an average molecular weight of 120,000, and used this polymer to create a water-dispersed pressure-sensitive adhesive in the same manner as above. An attempt was made to prepare a composition. However, in this case, when blending the above polymer into the acrylic polymer emulsion, even if the two are heated, uniform mixing and dispersion cannot be achieved, and uniform mixing is possible if a very large amount of organic solvent is used. The rough surface adhesion of the resulting pressure-sensitive adhesive was not significantly improved.

Claims (1)

[Claims] 1. 0.1 to 15 parts by weight of a functional group-containing monomer, which is essentially a carboxyl group-containing monomer, per 100 parts by weight of the main monomer consisting of (meth)acrylic acid ester.
An acrylic polymer emulsion obtained by emulsion polymerization of acrylic monomers containing parts by weight in an aqueous medium is added with a functional compound that requires a carboxyl group-containing monomer for 100 parts by weight of the main monomer consisting of (meth)acrylic acid ester. Group-containing monomer 0.5
A water-soluble or water-dispersible polymer with an average molecular weight obtained by polymerizing an acrylic monomer containing ~20 parts by weight.
An improved product obtained by heating and mixing a low molecular weight acrylic polymer or its salt with a molecular weight higher than 50,000 and less than 100,000 at a ratio of 20 to 150 parts by weight of the low molecular weight acrylic polymer to 100 parts by weight of the solid content of the emulsion. A water-dispersed pressure-sensitive adhesive composition having rough surface adhesion. 2. The water-dispersed pressure-sensitive adhesive composition according to claim 1, wherein the temperature during heating and mixing is 40 to 100°C. 3. The water-dispersed pressure-sensitive adhesive composition according to claim 1 or 2, which comprises a low molecular weight acrylic polymer or a salt thereof and an equal or less amount of an organic solvent. 4. The water-dispersed pressure-sensitive adhesive composition according to any one of claims 1 to 3, which contains a small amount of a crosslinking agent together with a low molecular weight acrylic polymer or a salt thereof. 5. The water-dispersed pressure-sensitive adhesive composition according to any one of claims 1 to 4, which comprises a low molecular weight acrylic polymer or a salt thereof and a tackifying resin.