JPS6143394B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an adhesive for use in adhesive sheets or adhesive tapes. More specifically, the present invention relates to a removable adhesive having adhesive microspheres and polymer particles that can be repeatedly applied to and peeled off from a wide variety of adherends. Such adhesives have many desirable properties. For example, conventional adhesive sheets can be easily applied to adherends such as paper, plastic, metal, and glass, but when peeled off, the adherend or the adhesive sheet or tape may break. Occurs often. By using the removable adhesive obtained in the present invention in adhesive sheets etc., it can be pasted repeatedly,
It becomes possible to peel it off. Such a microsphere adhesive is disclosed in U.S. Pat. No. 3,691,140 to Silver, dated September 12, 1972. The US patent discloses that copolymer microspheres obtained by aqueous suspension polymerization of a monomer consisting of an acrylic acid alkyl ester, a water-soluble ionic monomer, and maleic anhydride in the absence of a protective colloid or anything belonging thereto are used to form various copolymer microspheres. It is said that it can be used as an aerosol spray adhesive by dispersing it in a solvent, and can be applied and peeled off many times on the surface of an adherend such as paper. However, since the polymerization reaction is carried out without using a protective colloid, particles tend to aggregate, making it difficult to obtain the desired aqueous suspension. Furthermore, it is extremely difficult to arbitrarily change the particle size to a desired size or to make the particle size uniform. In particular, when the adhesive is applied and dried, the adhesive strength, cohesive strength, adhesion strength, and anchorage properties are not balanced, making it impossible to repeat pasting and peeling. Also,
The adhesive polymer microspheres described in JP-A No. 54-41988 are similar to those in Silver's U.S. patent mentioned above, but the feature is that the microspheres are nonionic acrylic microspheres made from nonionic monomers. It must be made of a copolymer, and its manufacturing method uses polyacrylate, carboxy-modified polyacrylamide, acrylic acid-dimethylaminoethyl methacrylate copolymer, and quaternized polyvinyl-pyrrolidone copolymer as stabilizers. Suspension polymerization is carried out using ionic suspension stabilizers and emulsifiers such as , quaternized amine-substituted cellulose, carboxy-modified cellulose, and sodium carboxymethyl cellulose. However, in suspension polymerization of the adhesive composition, if an ionic monomer is not used, particles tend to aggregate during polymerization, and there is a risk that the suspension will aggregate. In order to prevent this, if a large amount of the above-mentioned stabilizer is used, the balance between cohesive force and adhesive force will be disrupted, and the physical properties will be adversely affected. This is because the suspension stabilizer made of an ionic polymer as mentioned above has a strong film and weak adhesive strength, so an increase in the amount used will significantly affect the physical properties of the adhesive. There is a flaw. Also, U.S. Patent No. 3691140 and Japanese Patent Application Publication No. 54-41988
The issue has a major flaw in practical use. Suspensions for these uses are said to have an average particle size in the range of 5 to 150 microns. However, if one tries to obtain the desired particle size in this range from 5 to 150μ, the smaller microspheres in the aqueous suspension will float to the top and become creamy, and the particles with an average size of 50 to 150μ If you try to get something, it will sink. When the desired adhesive is obtained by washing microspheres obtained by aqueous suspension polymerization with water, drying them, and dispersing them in a solvent, it is preferable that the microspheres are separated. Therefore, even if you try to use the obtained aqueous suspension as it is, it will have very poor coating suitability.
In addition, it cannot be commercialized in practical use because of its poor storage stability. As a result of research to eliminate the above-mentioned defects, the present inventors have found that an aqueous adhesive polymer that is extremely easy to manufacture industrially and has excellent storage stability, adhesion to substrates, and coating properties. It was discovered that a suspension can be obtained, leading to the present invention. That is, the present invention provides: 1 (A) (a) an alkyl ester of (meth)acrylic acid having an alkyl group having 4 to 12 carbon atoms;
99.9% by weight (hereinafter referred to as % and parts by weight), (b) 0.1 to 10% of α-monoolefincarboxylic acid, and (c) vinyl compounds other than both components (a) and (b) above. of monomer components consisting of 0 to 29.9%.
Adhesive polymer microspheres with an average particle diameter of 10 to 100 μ obtained by aqueous suspension polymerization of 100 parts and 20 to 300 parts of (B) vinyl monomer are polymerized in an aqueous medium. A removable pressure-sensitive adhesive composition containing fine polymer particles having an average particle diameter of 0.1 to 4 μm. 2 In the first reaction step, adhesive polymer microspheres of the above component (A) with an average particle diameter of 10 to 100 μ are produced by aqueous suspension polymerization, and then in the second and subsequent reaction steps, A removable pressure-sensitive adhesive composition comprising polymerizing (B) a vinyl monomer in an aqueous suspension obtained in a one-step reaction to produce fine polymer particles having an average particle size of 0.1 to 4μ. This invention consists of two manufacturing method inventions. Examples of the (meth)acrylic acid alkyl ester as component (a) used in the present invention include butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, lauryl acrylate, butyl methacrylate, lauryl methacrylate, and the like. The α-monoolefincarboxylic acids of component (b) include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and crotonic acid. In addition, the vinyl monopolymers of component (c) are used to adjust adhesive strength and cohesive force, and include methyl (meth)acrylate, ethyl (meth)acrylate, vinyl acetate, vinyl propionate, styrene, acrylonitrile, ( Hydroxyethyl meth)acrylate, hydroxypropyl (meth)acrylate, N,N-dimethylaminoethyl acrylate, acrylic acid amide, diacetone acrylamide, N-methylolacrylamide, N-methoxymethylacrylamide, N-n-butoxymethylacrylamide up to 29.9%, preferably 0.5 to 10%, alone or in combination. The (meth)acrylate component (a) is a component that provides adhesive strength and internal cohesive force, and in order to obtain a high elasticity, at least 70%
is required, preferably 80-99%. (b) The amount of α-monoolefincarboxylic acid used is 10
If it exceeds %, the polymerization reaction will be difficult and the internal cohesive force will become too high, resulting in weak adhesive strength and failure to adhere to the adherend. Furthermore, if the amount used is less than 0.1%, particles tend to coagulate during the polymerization reaction.
The preferred amount used is 1-5%. As the vinyl monomer of component (B), various (meth)acrylates, vinyl esters, vinyl ethers, styrene, acrylonitrile, and other monomers may be used alone or in appropriate combinations to form adhesive polymer microspheres. It is not particularly limited as long as it can be. Although a protective colloid is not an essential component in performing the aqueous suspension polymerization of the present invention, depending on the monomer components, it may be effective to use casein, polyacrylamide, polyethylene glycol derivatives, etc. alone or in combination. be. In particular, by using casein as a protective colloid, it is possible to obtain aqueous suspensions that are extremely easy to produce industrially and have high quality characteristics. The amount used varies depending on the required physical properties, but 2 parts per 100 parts of monomer.
~8 parts is sufficient. When using casein, it is best to make it a completely stable solution with an aqueous solution of ammonia or amine. Further, as the surfactant, anionic, nonionic or amphoteric surfactants are used, and particularly anionic surfactants can provide characteristic physical properties. In producing the removable pressure-sensitive adhesive composition of the present invention, an aqueous suspension containing adhesive polymer microspheres as component (A) and an aqueous suspension containing polymer fine particles as component (B) are used. Although it is possible to prepare the suspension or aqueous dispersion separately in advance and then blend them, it is preferable to manufacture the suspension by a series of stepwise polymerization methods in order to simplify the manufacturing process and reduce manufacturing costs. . In the case of a stepwise polymerization method, first, in the first step reaction step, the above monomer components (a), (b) and (c) are treated with a protective colloid in the presence of an oil-soluble polymerization initiator such as benzoyl peroxide. Alternatively, a suspension polymerization reaction is carried out in an aqueous medium using a surfactant or the like to obtain a suspension of microspheres with an average particle size of 10 to 100 μm. In this suspension polymerization reaction, a multilayer polymerization method may be adopted in which each monomer component is divided according to its properties and the polymerization reaction is proceeded in stages. Next, in the aqueous suspension obtained in the first step reaction, the monomer of the component (B) is added using a monomer addition method or an emulsion addition method in which a pseudo-emulsion that has been previously formed by high-speed stirring is added. Then, add it and cause a polymerization reaction, and the average particle size is 0.1 to 4μ.
of polymer fine particles. The larger the particle size of the adhesive polymer microspheres obtained by the aqueous suspension polymerization of the present invention, the better the re-peelability, but the worse the adhesive strength, anchoring ability, storage stability, and coating properties. 10-100 considering these
Those having a particle size of μ are preferred. but,
Even aqueous suspensions containing microspheres with a particle size of 10 to 100 μm do not have sufficient long-term storage stability, and sedimentation of the microspheres is unavoidable. Therefore, in order to prevent this sedimentation phenomenon, in the present invention, polymer fine particles with a particle size of 0.1 to 4μ, which are difficult to sediment or float due to Brownian motion, are included between microspheres with a particle size of 10 to 100μ. It is something that makes you Also, this particle size
The fine particles having a size of 0.1 to 4 μm have the feature of improving the anchoring property and adhesion effect after coating the aqueous suspension obtained in the present invention. If the microspheres are separated from the aqueous suspension, washed out once, and further dried, and only microspheres of the same size are used, the particles can be coated in a uniformly arranged state after coating.
However, if particles with a particle size of 10 to 100 μm are applied directly, the coated surface will become uneven. Therefore, from a microscopic perspective, there are areas where the adhesive microspheres are not coated, which causes poor anchoring performance. The ideal coated surface is one in which the microspheres are spaced evenly apart with gaps of 5 to 10μ, so that when pressure is applied, the microspheres will spread laterally more easily and will be in even contact, increasing adhesive strength. It restores its original shape when removed and can be used repeatedly. On the other hand, if the space between the fine spheres is too large, the fine spheres are elastic bodies with restoring force, so the contact area with the adherend and the base material decreases, resulting in an extremely low anchoring ability and adhesive force. Therefore, a bonding layer is required to provide these anchoring effects and adhesion. This function is performed by polymer fine particles having a particle size of 0.1 to 4 μm. The polymer fine particles act as an adhesive to the substrate and at the same time play an important role in fixing the microspheres. The content ratio is such that polymer fine particles consisting of 20 to 300 parts of component (B) monomer are included in adhesive microspheres consisting of 100 parts of component (A) monomer. Good. The pressure-sensitive adhesive composition of the present invention can be made into an aqueous suspension containing 74% or more of solids as per theory, but this will cause problems in terms of stability and coating suitability.
It is also preferable to manufacture the product so that the active ingredient content is around 10%. Examples will be described below. It should be noted that "middle part" in the examples refers to parts by weight, and "%" refers to % by weight. Example 1 Using a three-necked flask equipped with a thermometer, a reflux condenser, and a variable speed stirrer, the following (A) was prepared.
The polymerization reaction of each component (B) and (C) was carried out stepwise.

[Table] Pour the entire amount of ingredient (A) into a three-necked flask. _N2 after dissolving or mixing at a stirring speed of around 300 rpm
Purge gas. After that, when the temperature is gradually increased, it becomes 70~
The polymerization reaction begins at 75°C and suddenly becomes more intense at around 80-82°C, generating heat up to 85-88°C. Then cool down 81
The temperature is maintained at ~82°C and the polymerization reaction is carried out for 2 hours. An aqueous suspension of polymer microspheres with a particle size of 20-60 microns is formed in the flask. Next, the next polymerization step begins. Component (B) dissolved or mixed in a separate container is made into a pseudo-emulsion by high-speed stirring. The component (B) thus obtained was added dropwise to the previously produced aqueous suspension over 60 minutes, followed by reaction at 81-82°C for 1 hour. Subsequently, component (C) was added dropwise over 30 minutes, and the same stepwise polymerization reaction was continued for 3 hours. The resulting aqueous suspension was then cooled to 30°C, and its evaporation residue, viscosity, and particle size were confirmed. Evaporation residue
40.0%, viscosity 1400cp/20℃ Particle size is smaller
The diameter was 0.5 to 2μ, and the larger one was 20 to 60μ. Example 2 Using the apparatus and procedure described in Example 1
Components (A) and (B) were subjected to a stepwise polymerization reaction in the same manner as in Example 1. However, the reaction temperature was 75 to 78°C, the reaction time for component (A) was 4 hours, the time for dropping component (B) was 1 hour, and the subsequent reaction time was 2 hours.

[Table] The obtained aqueous suspension has an evaporation residue of 51.5% and a viscosity of
1500cp/20℃, particle size is small particles 0.3~1
μ, the large microspheres were an aqueous suspension with a particle size distribution of 10 to 40 μ. Example 3 Using the apparatus and procedure described in Example 1,
20 parts of a pre-dissolved 15% casein ammonia aqueous solution, 2 parts of polyethylene oxide (PEO-1, manufactured by Seitetsu Kagaku Kogyo) with a molecular weight of 100,000 to 150,000,
Add 1 part of anionic surfactant and 250 parts of water and stir thoroughly to form an aqueous solution. Next, 100 parts of 2-ethylhexyl acrylate,
90 parts of butyl acrylate, 10 parts of ethyl acrylate
1 part, 1.5 parts of crotonic acid, and 0.5 part of benzoyl peroxide in a separate container. Next, this monomer mixture is added to the previously prepared aqueous solution and stirred. Aqueous suspension polymerization was carried out for 2 hours at a stirring speed of around 200 revolutions and a reaction temperature of 80 to 82°C. An aqueous suspension containing microspheres with a particle size of 25-70 microns was formed in the flask. The evaporation residue is
43.0%, and the viscosity was 1800 cp/20°C. Next, in a separate container, add 1 part of anionic surfactant, 4 parts of nonionic surfactant, 300 parts of water, and 1 part of potassium persulfate.
parts, dibasic sodium phosphate 2 parts, sodium bisulfite 0.5 parts, acrylic acid 5 parts, butyl acrylate
100 parts of ethyl acrylate using the usual emulsion polymerization method, evaporation residue: 41.0%, viscosity: 100 cp/20
An emulsion liquid with a particle size of 0.1 to 0.5 μm was obtained.
This emulsion was previously produced as an aqueous suspension10
20 parts per part was added to obtain a mixed solution. The resulting mixed solution had an evaporation residue of 43.0% and a viscosity of 1650 cp/20°C. The removable adhesives obtained in Examples 1, 2, and 3 were directly coated onto high-quality paper (55K) using a tabletop applicator to a drying weight of 10 to 15 gr/m ² and allowed to dry. The pressure-sensitive adhesive sheet prepared in this manner was bonded to a stainless steel plate, and its adhesive strength, holding power, and tack were examined in accordance with JIS Z 0237-1980. The results are shown in the table below.

【table】

【table】

Claims (1)

[Scope of Claims] 1 (A) (a) Alkyl ester of (meth)acrylic acid having an alkyl group having 4 to 12 carbon atoms 70 to
99.9% by weight, (b) α-monoolefincarboxylic acid
100 parts by weight of a monomer component consisting of 0.1 to 10% by weight and (c) 0 to 29.9% by weight of a vinyl monomer other than both components (a) and (b) above are subjected to aqueous suspension polymerization. The average particle size obtained by polymerizing the thus obtained adhesive polymer microspheres with an average particle diameter of 10 to 100μ and (B) 20 to 300 parts by weight of vinyl monomer in an aqueous medium. A removable pressure-sensitive adhesive composition containing fine polymer particles having a particle size of 0.1 to 4μ. 2 In the first stage reaction step, (A) (a) 70 to 99.9% by weight of an alkyl ester of (meth)acrylic acid having an alkyl group having 4 to 12 carbon atoms, (b) 0.1 to 0.1 to 99.9% by weight of α-monoolefincarboxylic acid; 10% by weight and (c) above
(a) and (b) 100 parts by weight of a monomer component consisting of 0 to 29.9% by weight of vinyl monomers other than both components are subjected to aqueous suspension polymerization to form a sticky polymer with an average particle size of 10 to 100μ. Coalesced microspheres are produced, and then in the second and subsequent reaction steps, 20 to 300 parts by weight of the vinyl monomer (B) is polymerized in the aqueous suspension obtained in the first step reaction. 1. A method for producing a removable pressure-sensitive adhesive composition, which comprises producing fine polymer particles having an average particle diameter of 0.1 to 4 μm. 3. The method for producing a removable pressure-sensitive adhesive composition according to claim 2, characterized in that casein is used as a protective colloid during aqueous suspension polymerization.