JPS6152191B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pressure-sensitive adhesive composition that has excellent adhesive strength particularly to polyolefins such as polyethylene or polypropylene, and has excellent adhesive strength at low temperatures. In recent years, polyolefins such as polyethylene or polypropylene have been widely used as sheets and films for packaging materials such as frozen foods, so there is a strong demand for pressure-sensitive adhesives that have good adhesion to polyolefins and low-temperature adhesion. has been done. Rubber-based, silicone-based, and acrylic-based adhesives are conventionally known as pressure-sensitive adhesives, and are widely used in various adhesive tapes or adhesive sheets applied to base materials such as paper, plastic, cloth, and metal. There is. However, rubber-based or silicone-based adhesives do not have perfect adhesion to polyolefins, and have problems with weather resistance, cohesive strength, aging, etc.; Although it has a good adhesion performance than other pressure sensitive adhesives, it still has weak adhesion to polyolefins. In order to improve the above-mentioned problems, the present inventors have conducted intensive research and found that in addition to adhesive properties such as adhesive strength, cohesive force, and adhesive strength, polyethylene or polypropylene, especially polyethylene or polypropylene, has good weather resistance, water resistance, etc. We have discovered a pressure-sensitive adhesive composition that has outstanding adhesion to polyolefins and tackiness at low temperatures, and completed the present invention. The pressure-sensitive adhesive composition of the present invention has more than twice the adhesive strength to polyolefins than commercially available acrylic pressure-sensitive adhesives, and also has adhesive strength at 0°C compared to that at 20°C. There is no big difference,
It also has excellent suitability for coating on various substrates such as paper, plastic, cloth, and metal, and adhesive sheets for labels using this material also have excellent suitability for punching. That is, in the present invention, a copolymer having an average molecular weight of 3,000 to 50,000 and containing 5 to 30% by weight of an unsaturated carboxylic acid monomer as a constituent, an alkaline metal salt,
In the presence of a first-stage polymer dispersion that has been neutralized and dispersed in water with ammonia or amines to have a pH in the range of 6 to 10, 1 to 20% by weight of polybutadiene is mixed with (meth) alkyl groups having 4 to 12 carbon atoms. 2 dissolved in 80 to 99% by weight of a radically polymerizable vinyl monomer whose main component is an acrylic acid alkyl ester.
The present invention relates to an aqueous pressure-sensitive adhesive composition in which stage components are copolymerized using a hydrophilic catalyst. To explain the present invention in more detail, the first stage polymeric dispersant having surface-active ability includes 5 to 30% by weight of an unsaturated carboxylic acid monomer and other polymerizable monomers, particularly those having 1 to 4 carbon atoms. Acrylic acid or methacrylic acid ester with alkyl group50
A polymerizable monomer mixture containing ~70% by weight,
obtained by polymerization in the presence of one or more lower alcohols having 1 to 3 carbon atoms, or
An aqueous solution of one or a mixture of two or more nonionic, anionic, or cationic surfactants, such as polyoxyethylene condensates and polyethylene oxide-polypropylene oxide block copolymers used in ordinary emulsion polymerization methods. A copolymer with an average molecular weight of 3,000 to 50,000 obtained by polymerization in the presence of a copolymer is neutralized to a pH range of 6 to 10 with an alkali metal salt, ammonia, or amines, and the final pressure-sensitive adhesive is obtained. A stable dispersion with no aggregates can be obtained by adding water in an amount to achieve the desired solids content of the composition, usually about 40 to 60% by weight, and by using the above-mentioned polymeric dispersant. It will be done. Furthermore, the use of polymeric chain transfer agents such as alkyl mercaptans, carbon tetrachloride, and carbon tetrabromide is also an effective method. The amount of solid content of the polymer dispersant is preferably used in the range of several percent to 50% by weight of the total solid content in the final pressure-sensitive adhesive composition, and if it is too small, the dispersibility may deteriorate. If the amount is too large, problems may arise in water resistance. Examples of the unsaturated carboxylic acid monomer used in the first stage of the present invention include acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, or anhydrides thereof, and if the amount thereof is 5% by weight or less, , if a stable dispersion cannot be obtained in the second stage suspension polymerization, and if the amount exceeds 30% by weight,
The water resistance of the resulting dispersion composition will be adversely affected. As other polymerizable monomers, it is preferable to use 50 to 70% by weight of acrylic acid and methacrylic acid esters having alkyl groups such as methyl, ethyl, isopropyl, n-butyl, and isobutyl; However, if a large amount of acrylic acid or methacrylic acid ester is used, it is difficult to obtain a stable dispersion in the second stage of polymerization, and even if a stable dispersion is obtained, there are problems with adhesive performance, especially initial adhesive strength. . In addition, as the first-stage radical initiator, in the former case, an organic peroxide-based and azo-based oil-soluble catalyst is used, and in the latter case, a water-soluble catalyst such as ammonium persulfate and potassium persulfate is used. I can do it. In addition, as the second stage component polybutadiene,
The ratio of 1,2 bonds to 1,4 bonds is arbitrary, and in addition to unmodified polybutadiene, various modified polybutadienes having carboxyl groups, hydroxyl groups, epoxy groups, etc. can be used. Especially number average molecular weight 500~10000
The polybutadiene mainly in the oligomer region is
It has an appropriate viscosity and good workability, and when grafted with other vinyl monomers, it exhibits extremely good performance in terms of adhesive strength, adhesive strength at low temperatures, water resistance, etc. However, if the amount used is less than 1% by weight, satisfactory adhesion to polyolefins such as polyethylene or polypropylene cannot be obtained, and if it is more than 20% by weight, a stable dispersion may not be obtained. Even if it is added, the cohesive force will be significantly reduced, and a range of 2 to 10% by weight is particularly preferable. Furthermore, the vinyl monomer capable of second-stage radical polymerization that dissolves polybutadiene is
Alkyl esters of acrylic acid and methacrylic acid, styrene and its derivatives, nitrogen-containing monomers such as acrylonitrile and acrylamide, epoxy group-containing monomers such as glycidyl methacrylate, lower carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate, and 5 Within the range of % by weight or less, one type or a combination of two or more unsaturated carboxylic acid monomers are used, but in particular, alkyl esters of acrylic acid and methacrylic acid having an alkyl group having 4 to 12 carbon atoms. It is preferable that the main component is Further, it is also possible to introduce a crosslinking component having two or more unsaturated double bonds such as diallylphthalate, divinylbenzene, dicyclopentadiene, etc. As the second-stage polymerization catalyst, hydrophilic catalysts such as ammonium persulfate, potassium persulfate, and hydrogen peroxide are most suitable, because the polymerization time is shortened, and stable aqueous dispersion polymers without aggregates This is because it can be obtained. The adhesive composition of the present invention thus obtained has extremely good performance, particularly in terms of adhesion to polyolefins such as polyethylene and polypropylene, or adhesion at low temperatures, and is independently pressure sensitive. Although it can be used satisfactorily as an adhesive, ethylene-vinyl acetate copolymer,
There is no problem in using a mixture of acrylic polymers, ethylene-propylene copolymers, etc. In addition, other commonly used additives such as thickeners, tackifiers, pigments, fillers, stabilizers, plasticizers, etc. may be added as appropriate. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited only to these Examples. Note that all parts in the examples indicate parts by weight. Example 1

[Table] After charging (1) into a flask saturated with nitrogen gas and raising the temperature to 80-82℃, add the total amount of (2), 20 parts of (3), and (4) into the dropping funnel. Drop it for 2 hours, and then apply (3) immediately after the drop and 1 hour later.
The reaction was completed after adding 0.25 parts at a time and stirring for 1 hour. The temperature was lowered to 40°C, (5) was added, and after stirring well, (6) was added to obtain a water-soluble polymer dispersant.

[Table] After raising the temperature of the polymer dispersant obtained in 68 to 70℃, 4.0 parts of (8) was added, and the entire amount of (7) was added dropwise over 2 hours. After stirring for about 1 hour, the reaction was completed and the non-volatile content was 50
%, a stable opalescent pressure-sensitive adhesive with a viscosity of 9500 cps (25°C) was obtained. Example 2 First stage polymer powder Same as Example 1 except that isopropyl alcohol in Example 1 was replaced with ethanol and ethyl acrylate was replaced with methyl acrylate Second stage monomer mixture was 2-ethylhexyl acrylate 200 Part octyl acrylate 100 Butyl acrylate 75 Vinyl acetate 100 Nitsuso PB B-2000 25 (Unmodified polybutadiene manufactured by Nippon Soda) Polymerized in the same manner as in Example 1,
A stable milky-white pressure-sensitive adhesive with a non-volatile content of 50% and a viscosity of 11000 cps (25°C) was obtained. Example 3 First-stage polymer powder Ethyl acrylate 40.0 parts Butyl acrylate 40.0 Acrylic acid 20.0 Dodecyl mercaptan 1.0 Ethylene oxide adduct of alkylphenol (25%) 8.0 Alkylbenzene sulfonate (20%)
2.5 Water 500.0 Ammonium persulfate 1.0 Sodium bisulfite 0.5 Aqueous ammonia (25%) 18.0 After synthesizing the above compounding ratio by a normal emulsion polymerization method, it was neutralized with aqueous ammonia to obtain an aqueous polymer dispersant. The same procedure as in Example 1 was carried out using 2-ethylhexyl acrylate 350.0 parts, butyl acrylate 100.0, ethyl methacrylate 75.0, vinyl acetate 75.0, polybdR-45HT 15.0 (2w-polybutadiene diglycol manufactured by Idemitsu Petroleum) as the second-stage monomer mixture. polymerized by a method,
A pressure-sensitive adhesive with a non-volatile content of 58% and a viscosity of 12,000 cps (25°C) with few aggregates was obtained. Example 4 First-stage polymer powder Same as Example 3 Second-stage monomer mixture Polymerization was performed in the same manner except that 15.0 parts of R-45HT in Example 3 was changed to 100.0 parts, and the nonvolatile content was 60%. A stable pressure-sensitive adhesive with a viscosity of 11000 cps (25°C) was obtained. Comparative Example 1 First stage polymer dispersant Same as Example 1 Second stage monomer mixture 75.0 parts of Nitsuso PBC-1000 of Example 1
Changed to 150.0. Others are the same, non-volatile content 53
% and a viscosity of 12500 cps (25°C) was obtained. Comparative Example 2 First stage polymer dispersant Same as Example 3 Second stage monomer mixture 15.0 parts of the poly bdR-45HT of Example 3 was removed. Others are the same, non-volatile content 58%, viscosity
A pressure sensitive adhesive of 13000 cps (25°C) was obtained. Adhesive performance test method (1) Adhesive strength sample size: 15mm x 100mm Adherent: Stainless steel SUS27 (thickness 1mm), polyethylene, polypropylene film Lamination: 5Kg, 1 round trip, 20℃, 65%RH measurement : Immediately after lamination, tensile speed 300mm (2) Cohesive force sample size: 15mm x 100mm Lamination area: 15mm x 20mm (stainless steel SUS27) Lamination: 5Kg, 1 round trip, 20℃, 65%RH measurement :After lamination, after being left at 40℃ for 20 minutes, the sample and adherend completely separate under a load of 1 kg, and the sample is expressed as the number of seconds until the sample falls. (3) Adhesive force measurement: Glue surface 100mm, run-up 100mm, angle 30° - 20°C
Roll a 1/32 to 32/32 inch steel ball in an atmosphere of 65% RH and 0°C-90% RH, and indicate the maximum diameter that will stop on the adhesive surface. The pressure-sensitive adhesives obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were applied to release paper using an applicator so that the evaporation residue after drying was 30 g/m ² .
After drying at -2 minutes at -2 minutes, it was inverted onto high-quality paper to prepare a sample. The results of the test are shown in Table-1.

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Claims (1)

[Claims] 1. Neutralize and disperse a copolymer with an average molecular weight of 3,000 to 50,000 containing 5 to 30% by weight of unsaturated carboxylic acid monomer as a constituent in water to a pH range of 6 to 10 using an alkali metal salt, ammonia, or amines. In the presence of the first stage polymeric dispersant, 1 to 20% by weight of polybutadiene is mixed with a radically polymerizable vinyl monomer 80 whose main component is an alkyl (meth)acrylic acid ester having an alkyl group having 4 to 12 carbon atoms. An aqueous pressure-sensitive adhesive composition prepared by copolymerizing a second stage component dissolved in up to 99% by weight using a hydrophilic catalyst.