JPH051314B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an adhesive mainly composed of an acrylic polymer that has excellent adhesive strength and excellent cutting processability, and more specifically relates to an adhesive having different elastic moduli. The present invention relates to a pressure-sensitive adhesive for tapes, labels, and seals, which is obtained by blending two types of acrylic polymers in a fixed ratio and has excellent adhesive strength and improved cutting processability. [Prior Art] Various pressure-sensitive adhesive products have been used for tapes, labels, and seals in printing, packaging, food, medical, and other industries.
It has been widely used in fields such as electronics and automobiles. Rubber-based and acrylic-based polymers are used as pressure-sensitive adhesives, and acrylic-based pressure-sensitive adhesives are particularly used for sealing and label processing. [Problems to be Solved by the Invention] However, the current situation is that the acrylic pressure-sensitive adhesive has poor adhesion, particularly to adherends such as films and molded articles made of polyolefin or polybutadiene resins. It is. Methods of improving adhesion to these adherends include softening the pressure-sensitive adhesive or reducing its molecular weight to lower its cohesive force and improve its adhesion;
Alternatively, there is a method of blending water dispersants such as tackifiers, plasticizers, and rubbers, but in either case, the pressure-sensitive adhesive may protrude from the support due to a decrease in cohesive force, penetrate or slit, or cause the blade to deteriorate during sealing. Disadvantages such as staining and reduced weather resistance occur. Furthermore, natural rubber-based pressure-sensitive adhesives have drawbacks such as poor weather resistance and staining of the blade during slitting and cutting. Conventional pressure-sensitive adhesives for stickers and labels are categorized according to their uses, such as those for frozen foods, those for measuring labels, strong adhesive types, and removable types. Pressure-sensitive adhesives, which are said to be highly adhesive, have a strong adhesive force and adhere well to non-polar adherends, but they are pressure-sensitive to the guillotine blade during the slitting, cutting, and punching processes of adhesive labels, stickers, tapes, etc. Adhesion of adhesive becomes a problem. In addition, many strong adhesive pressure sensitive adhesives are natural rubber emulsion type or natural rubber solvent type, and these have poor weather resistance. In addition, the quality of acrylic pressure-sensitive adhesives has conventionally been generally controlled by using a polymerization degree regulator, and those with a high degree of polymerization have weak adhesive strength but good cutting properties, while those with a low degree of polymerization have showed strong adhesive strength, but was thought to have poor cutting workability. Furthermore, even if a pressure-sensitive adhesive with a polymerization degree intermediate between the two was synthesized, a pressure-sensitive adhesive with excellent adhesive strength and cutting processability could not be obtained, and there was a demand for the development of such a pressure-sensitive adhesive. [Object of the present invention] An object of the present invention is to provide a pressure-sensitive adhesive having excellent adhesive strength and improved cutting workability. Another object of the present invention is to use two types of acrylic polymers to adhere to adherends such as films or molded products made of resins such as polyolefin and polybutadiene, which have higher adhesive properties than conventional pressure-sensitive adhesives that are said to have strong adhesive properties. The objective is to provide a pressure-sensitive adhesive that has excellent performance such as adhesive properties and is easy to process on a cutting machine.Another purpose is to provide a pressure-sensitive adhesive that has high adhesive strength and adheres well to non-polar adherends. To provide a pressure-sensitive adhesive which is excellent in weather resistance, has less blade stain when cutting with a guillotine, has less blade stain when cutting with a slit, and has good die-cutting properties when printing stickers. Still other objects will become clear from the description below. [Means for solving the problems] The present invention provides (A) (a) 0.5 to 10% by weight of acrylic acid, (b) 0 to 25% by weight of vinyl acetate, and (c) an alkyl group having 1 to 10 carbon atoms. 12
5 to 50% by weight of at least one monomer selected from the group consisting of alkyl acrylates having 1 to 12 carbon atoms and alkyl methacrylates having an alkyl group of 1 to 12 carbon atoms, and the amount of these monomers as necessary. 5% by weight or less of a monomer having a functional group that can be copolymerized with a monomer, and 0.1% of an alkyl mercaptan whose alkyl group has 1 to 12 carbon atoms as a chain transfer agent.
Low elasticity alkyl acrylate and/or alkyl methacrylate multi-component copolymer emulsion obtained by copolymerization using ~1% by weight 50-90
Parts by weight (based on solid content) and (B) (a) acrylic acid 0.5-10% by weight, (b) vinyl acetate 0-25% by weight, (c) alkyl group with carbon number of 1-12
(d) 70 to 95% by weight of at least one monomer selected from the group consisting of alkyl acrylates having 1 to 12 carbon atoms and alkyl methacrylates having an alkyl group of 1 to 12 carbon atoms; and (d) these monomers. 0.1 to 3% of a crosslinkable monomer copolymerizable with the monomer, and further 5% by weight or less of a monomer having a functional group that can be copolymerized with these monomers, as necessary. The number of carbon atoms in the alkyl group is 1 to 1% by weight or less
5 to 40 parts by weight (solid content basis) of a highly elastic alkyl acrylate and/or alkyl methacrylate multi-component copolymer emulsion obtained by copolymerizing 12 alkyl mercaptans as a chain transfer agent. This invention relates to an emulsion-type pressure-sensitive adhesive characterized in that it is a component of the present invention. The present inventors have pursued a pressure-sensitive adhesive with excellent adhesive strength and improved cutting processability, and as a result of repeated research, the following factors have been found to have a major influence on these properties:
It was discovered that the problem is not the degree of polymerization of the acrylic polymer, as previously thought, but its elastic modulus. The elastic modulus of the acrylic polymer was determined by creating a film with a length of 10 mm and a cross-sectional area of 0.25 mm ² and stretching it at 1000%/min.
Obtain by measuring the relationship between stress and elongation. maximum stress
Highly elastic copolymers are those with a breaking elongation of 2.0×10 ² dyne/cm ² or more and 2000% or less, and a maximum stress of 5.0×10 ¹
A low elasticity copolymer is defined as a copolymer exhibiting dyne/cm ² or less and elongation at break of 3000% or more. According to the present inventors, when a highly elastic copolymer is used, cutting workability is good, but adhesiveness is poor.
On the other hand, in the case of a copolymer with low elasticity, although the adhesive strength is excellent, the cutting processability cannot be said to be good. Therefore, in order to obtain an adhesive that has both properties, copolymers with an intermediate elastic modulus were manufactured and studied, but it was not possible to obtain a desirable product with a good balance of both properties. In order to be used in pressure-sensitive adhesives, acrylic copolymers must exhibit viscoelasticity within a specific range of elastic modulus, but as mentioned above, some intermediate elastic copolymers can be processed by cutting. It is not possible to obtain a product that maintains an appropriate balance between adhesive strength and adhesive strength. Therefore, the present inventors changed their point of view and tried blending the above-mentioned high elasticity copolymer and low elasticity copolymer in a specific ratio, and unexpectedly found a balance between both adhesive strength and cutting workability. They also discovered that an excellent pressure-sensitive adhesive can be obtained. The present invention provides an emulsion of a low elasticity alkyl acrylate and/or alkyl methacrylate multi-component copolymer shown in (A) and high elasticity shown in (B), in which the former is 50 to 90 parts by weight, the latter is The present invention relates to an emulsion-type pressure-sensitive adhesive obtained by blending 5 to 40 parts by weight of the above, but its effects are not necessarily clear. However, by mixing low- and high-elasticity copolymers at the molecular or particle level and creating an apparent distribution of elastic modulus, it is possible to control the balance between adhesive strength and cutting workability of pressure-sensitive adhesives. It is believed that we were able to provide a pressure-sensitive adhesive with adhesive strength and cutting workability that cannot be achieved with a single polymeric material that is excellent in both qualities. Acrylic polymers with low elasticity are used as polymerization degree regulators (chain transfer agents) during polymerization in order to lower the degree of polymerization and reduce the entanglement of polymer chains. It is necessary to use 0.1 to 1 part by weight of 12 alkyl mercaptans. In addition, highly elastic acrylic copolymers are crosslinked and the degree of polymerization is increased to increase the entanglement of polymer chains and to achieve high elasticity. It is necessary to contain monomers such as ethylene glycol dimethacrylate, glycidyl methacrylate, and cyvinylbenzene. 0.1% by weight or less of an alkylmercaptan in which the alkyl group has 1 to 12 carbon atoms may also be used. In the low elasticity and high elasticity alkyl acrylate and/or alkyl methacrylate multi-component copolymer used in the present invention, the alkyl group to be copolymerized with the acrylic acid or vinyl acetate monomer has 1 to 12 carbon atoms. Monomer (c) includes methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and (meth)acrylate.
Butyl acrylate, amyl (meth)acrylate,
(meth)hexyl acrylate, (meth)heptyl acrylate, (meth)octyl acrylate, (meth)
Examples include 2-ethylhexyl acrylate, decyl (meth)acrylate, and lauryl (meth)acrylate, but particularly preferred are those with 2 to 8 carbon atoms.
It is an alkyl (meth)acrylate having an alkyl group of In addition, in these multi-component copolymers, if necessary, a monomer having a functional group copolymerizable with the above-mentioned monomer can be used as a copolymerization component. α,β-unsaturated carboxylic acids such as methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid, (meth)
Monomers with hydroxyl groups such as hydroxyethyl acrylate and hydroxypropyl (meth)acrylate, monomers with glycidyl groups such as glycidyl (meth)acrylate, (meth)acrylamide, N-methylol (meth)acrylamide ,
There are unsaturated carboxylic acid amides having an amide group such as N-butoxymethyl (meth)acrylamide and diacetone (meth)acrylamide, and further monomers having an amino group such as melamine and vinylpyridine. (A) low elasticity acrylic copolymer in the present invention is
The above monomer mixture is mixed with a suitable emulsifier, a dispersant such as a protective colloid, a radical polymerization initiator, and the presence of 0.1 to 1% by weight of an alkyl mercaptan whose alkyl group has 1 to 12 carbon atoms (chain transfer agent). It can be produced by emulsion copolymerization as described below. (B) Highly elastic acrylic copolymer in the present invention is
It can likewise be produced as an emulsion copolymer or a solution copolymer. The polymerization initiator for emulsion polymerization is potassium persulfate, and other inorganic peroxides may be used. Polymerization initiators for solution polymerization include α,α'-azodiisobutyronitrile, benzoyl peroxide, acetyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, di-t-butyl peroxide, azodicyclohexyl carbonitrile α ，
Dimethyl α'-azodiisobutyrate, succinic peroxide, dicumene peroxide, benzoyl dichloroperoxide, etc. can be used. The solvent is preferably ethyl acetate, but other organic solvents such as butyl acetate, benzene, cyclohexane, carbon tetrachloride, methanol, and toluene may also be used. The pressure-sensitive adhesive composition of the present invention contains 50 to 90 parts by weight of the low modulus copolymer emulsion and 5 to 40 parts by weight of the high modulus copolymer emulsion (all based on solid content). It is obtained by mixing with
If the content of the high elastic copolymer exceeds 40 parts by weight, the adhesive strength will decrease. In order to maintain good adhesion to polyolefin films and molded articles, which are non-polar and difficult to adhere to, the content is desirably 30% by weight or less. On the other hand, if the amount of the low-elasticity copolymer is 90 parts by weight or more and the amount of the high-elasticity copolymer is less than 5 parts by weight, the cutting processability will deteriorate, such as increased adhesion to the blade during guillotine cutting. The emulsion-type pressure-sensitive adhesive of the present invention can be used as it is, or with the addition of plasticizers, tackifiers, thickeners, pH adjusters, wetting agents, antifungal agents, etc., as necessary. can. Normally, in order to apply an emulsion-type pressure-sensitive adhesive, it is necessary to increase the viscosity to about 10,000 to 20,000 cps. In this case, useful thickeners include celluloses, polyvinyl alcohol, polyacrylates, polymeric surfactants, and alkali thickening acrylic resins. Supports to which the emulsion-type pressure-sensitive adhesive of the present invention is coated include papers such as wood-free paper, art paper, coated paper, metallized paper, and kraft paper, polyethylene, polypropylene, polyester, acetate, and polychloride. Examples include films such as vinyl and composites thereof. [Effects of the Invention] The pressure-sensitive adhesive of the present invention, which is composed of a specific proportion of an acrylic low-elasticity copolymer and an acrylic high-elasticity copolymer, has excellent adhesive strength and excellent cutting processability. It is a pressure-sensitive adhesive that adheres particularly well to non-polar adherends, has excellent weather resistance, has minimal blade stains during guillotine and slit cutting, has good die-cutting properties when printing stickers, and has excellent adhesive strength. It has now become possible to provide a pressure-sensitive adhesive with excellent properties in both cutting and cutting processability. [Example] Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these in any way. Note that parts and % in the text mean parts by weight and % by weight, respectively. Example 1 2-ethylhexyl acrylate 80%, vinyl acetate 4%, methyl acrylate 15%, acrylic acid 1%
and dodecyl mercaptan 0.2% to water 100%
%, potassium persulfate 1% as a polymerization initiator, and 5% Emar NC (sodium polyoxyethylene alkyl phenol ether sulfate, manufactured by Kao Atlas Co., Ltd.) as an emulsifier were added, and the mixture was heated at 70°C for 20 hours in a flask equipped with a reflux condenser. By heating, a copolymer emulsion (A) was synthesized. Copolymer emulsion (A)
(Solid content 50%) 70 parts 2-ethylhexyl acrylate 79%, vinyl acetate 4 synthesized in the same manner
%, acrylic copolymer emulsion (B) consisting of 15% methyl methacrylate, 1% acrylic acid and 1% ethylene glycol dimethacrylate (solid content
50%) was added thereto and stirred for 30 minutes to obtain an emulsion-type pressure-sensitive adhesive. The resulting adhesive had a solid content of 50%, a pH of 3.5, and a viscosity of 750 cps. The results of the physical property evaluation described below for this adhesive are shown in the first table.
They are summarized in the table. Next, samples (length 10
Figure 1 shows the relationship between elongation and elongation stress when a material (mm) is elongated at 20°C and 1000%/min. Copolymer A has a large elongation at break, low tensile stress, low elasticity, and high adhesiveness, but poor cutting workability. Copolymer B has low elongation at break, high tensile stress, high elasticity, and low adhesiveness, but good cutting workability. The product of the present invention (A+B, blend) has the same elongation at break as copolymer B, has better cutting workability than copolymer A, has significantly lower elongation stress than copolymer B, has higher adhesive strength, and has both properties. A balanced pressure sensitive adhesive. Example 2 80% 2-ethylhexyl acrylate, 15% methyl methacrylate, 5% acrylic acid, and 0.5% dodecyl mercaptan were polymerized in the same manner as in Example 1,
Acrylic copolymer emulsion (A) (solid content
50%) 90 parts, 78% 2-ethylhexyl acrylate, 15% methyl methacrylate, 5% acrylic acid
% and 10 parts of an acrylic copolymer emulsion (B) (solid content 50%) consisting of 2% divinylbenzene and 0.05% dodecyl mercaptan to obtain an emulsion-type pressure-sensitive adhesive. The solid content of this thing is 50
%, pH was 4.0, and viscosity was 800 cps. The results of these physical property evaluations are summarized in Table 1. The physical properties of each emulsion-type pressure-sensitive adhesive obtained above were evaluated as follows. A thickener (manufactured by Nippon Acrylic Co., Ltd.,
Add Primal ASE-108) and use 25% ammonia water to obtain a viscosity of 15,000 to 20,000 cps (B-type viscometer,
6 rpm). This emulsion-type pressure-sensitive adhesive was coated on release paper at 25 to 30 g/m ² (after drying), and after drying at 110°C for 2 minutes, it was coated on high-quality paper (64 g/m ² ).
were pasted together to obtain adhesive paper. The adhesive strength (adhesive force) of this adhesive paper was determined according to JIS-Z-0237 using a 180-degree peeling method using a high-density polyethylene plate as an adherend at a peeling speed of 30 mm/min.
The measurement was carried out under the conditions of ℃ and pH 65%, and the cutting processability was evaluated by cutting 100 sheets of samples stacked on top of each other using an office guillotine cutting machine. In addition, for comparison, strong adhesive tack paper for rough surfaces (Modern Plastic Co., Ltd.) was used as control 1, strong adhesive tack paper (Fuji Paper Co., Ltd. PZ2) was used as control 2, and weighing label paper (Souken Kako Co., Ltd.) was used as control 1. ) PM−
700B) was used as Control 3, and similar tests were conducted on these as well. Table 1 shows the evaluation results of their physical properties. As is clear from Table 1, the pressure-sensitive adhesives of Examples 1 and 2 have a high adhesive strength, particularly excellent adhesive strength to adherends made of polyolefin, and also have excellent cutting workability. In contrast, control 1,
Sample No. 2 had excellent adhesion, but the guillotine blade was heavily stained, and Control 3 had good cutting workability, but the guillotine blade was poorly stained and the adhesive strength was insufficient. 【table】

[Brief explanation of the drawing]

Figure 1 shows copolymers A and B synthesized in Example 1,
and is a graph showing the relationship between elongation and extensional stress for the adhesive of the present invention obtained by mixing these.

Claims (1)

[Scope of Claims] 1 (A) (a) 0.5 to 10% by weight of acrylic acid, (b) 0 to 25% by weight of vinyl acetate, and (c) acrylic acid whose alkyl group has 1 to 12 carbon atoms. At least one member selected from the group consisting of alkyl and alkyl methacrylates whose alkyl group has 1 to 12 carbon atoms.
Alkyl acrylate type and/or obtained by copolymerizing 5 to 50% by weight of a seed monomer using 0.1 to 1% by weight of an alkyl mercaptan whose alkyl group has 1 to 12 carbon atoms as a chain transfer agent. or 50 to 90 parts by weight of an alkyl methacrylate multi-component copolymer emulsion (solid content basis) and (B) (a) 0.5 to 10% by weight of acrylic acid, (b) 0 to 25% by weight of vinyl acetate, (c) alkyl methacrylate. The number of carbon atoms in the group is 1 to 12
(d) 70 to 95% by weight of at least one monomer selected from the group consisting of alkyl acrylates having 1 to 12 carbon atoms and alkyl methacrylates having an alkyl group of 1 to 12 carbon atoms; and (d) these monomers. 5 to 40 parts by weight (based on solid content) of an alkyl acrylate and/or alkyl methacrylate multi-component copolymer emulsion obtained by copolymerizing 0.1 to 3% of a crosslinkable monomer copolymerizable with An emulsion-type pressure-sensitive adhesive characterized by comprising: 2 The multi-component copolymer of either (A) or (B) above, or both, further contains, as a copolymerization component, 5 weight monomers having a functional group copolymerizable with the above monomer component. % or less of the emulsion type pressure-sensitive adhesive according to claim 1. 3. Claim 1, wherein the multicomponent copolymer (B) further contains 0.1% by weight or less of an alkyl mercaptan whose alkyl group has 1 to 12 carbon atoms as a copolymerization component. The emulsion-type pressure-sensitive adhesive according to item 1 or 2.