JPS6313464B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an acrylic pressure-sensitive adhesive composition that has excellent tackiness and cohesiveness at room temperature, has excellent weather resistance, aging resistance, and water resistance, and also has excellent coating processability by heating and melting. It is. Adhesives include solvent-based adhesives, water-based adhesives, and 100%
% solids adhesives can be classified into three types.
The first two are very uneconomical in terms of energy and time consumption during the coating operation. Also, in the case of solvent-based adhesives, there is a risk of environmental pollution, fire and explosion. For hot melt adhesives, essentially
It is 100% solid, so no solvent removal step is required. Hot melt adhesives are applied in a molten state and then rapidly cooled with cooling rollers. Therefore, compared to solvent-based or water-based adhesives, it can be performed at higher speeds with less equipment, less energy consumption and greater safety. Hot melt pressure-sensitive adhesives are generally classified into two types: rubber-based and acrylic-based. Conventionally, rubber-based hot melt pressure sensitive adhesive compositions include SIS,
It is composed of a block copolymer such as SBS mixed with a large amount of tackifying resin, plasticizer, and liquid resin, which lowers the melt viscosity and enables melt coating, and also balances adhesive properties. However, these known modifiers have insufficient compatibility with the block copolymer, resulting in a decrease in the adhesive strength of the resulting adhesive, and even when the compatibility is good, the melt viscosity decreases in a short period of time during heating and melting. This increases the number of particles and makes coating work difficult. In addition, they have disadvantages such as coloration during melting, which significantly lowers commercial value, easy deterioration due to ultraviolet rays, ozone, etc., and insufficient weather resistance and aging resistance. On the other hand, acrylic hot-melt pressure-sensitive adhesives have excellent weather resistance, durability, and transparency, but it is extremely difficult to achieve both viscosity when melted by heating and cohesive strength at room temperature. That is, when the heated melt viscosity is set to a suitable value, the cohesive force becomes small, and when the cohesive force is increased, the melt viscosity also becomes high. In order to solve this problem, U.S. Patent No. 4,045,517 proposes a multi-step polymerization or blending of an acrylic copolymer containing acidic groups and an acrylic copolymer containing basic groups to eliminate ionic bonds between polymers. Japanese Patent Publication No. 52-26765 proposes methods such as metal ion crosslinking in which an alkali metal compound is added to an acrylic copolymer containing an acidic group. However, even if these methods are used, it is not possible to fully satisfy both melt viscosity and adhesive properties (especially cohesion) during coating, and these adhesives are usually used for packaging, masking, and medical bandages. It could only be applied to relatively low-grade products such as adhesive tapes and adhesive sheets for labels and wallpaper. Taking these drawbacks into consideration, the present inventors developed an acrylic pressure-sensitive adhesive that has excellent weather resistance and stress resistance, has the desired adhesive properties, and has excellent coating processability by heating and melting. As a result of extensive research in order to obtain this, we have arrived at this invention. That is, the present invention provides (a) in the presence of a mercaptan containing a nitrogen atom capable of forming an ionic bond with a carboxyl group or a sulfone group in the molecule,
(b) at least 50% by weight of esters of acrylic or methacrylic acid and alcohols having up to 18 carbon atoms;
A product obtained by copolymerizing the main monomer containing the above and (c) an α/β-olefin type unsaturated carboxylic acid or sulfonic acid, which has a carboxyl group or a sulfone group in the molecule, and has the above group at the end of the molecule. The present invention relates to a heat-melting type pressure-sensitive adhesive composition containing as a main component an acrylic polymer having an organic group containing a nitrogen atom capable of forming an ionic bond with the acrylic polymer. According to the above-mentioned composition of the present invention, it is possible to exhibit excellent performance such as durability and transparency such as weather resistance, aging resistance, and water resistance as the inherent properties of acrylic polymer, and also to exhibit excellent performance at low temperatures such as room temperature. In this case, the carboxyl group or sulfone group in the polymer chain of this polymer and the reactive nitrogen atom at the end of the polymer form ionic bonds due to positive and negative electrical attraction between or within the molecule, and the desired high cohesive force is achieved. can get. Moreover, this is heated at high temperature (100~
When heated to 200°C), the ionic bonds are loosened and the melt viscosity decreases rapidly, resulting in a low viscosity suitable for hot melt coating. Furthermore, this bond is reversible, and when it is cooled, a strong ionic bond is formed again, reproducing the high cohesive force. Since the pressure-sensitive adhesive composition of the present invention has such characteristics, it is particularly suitable as an adhesive to be used in a hot melt coating method. In this invention, it is not necessarily clear why the above-mentioned polymer exhibits the characteristic properties, but it is considered as follows.
In other words, when acid groups or basic groups are simply randomly introduced into polymer molecules, a network structure is formed by ionic bonds between the acid groups and basic groups, as shown in Figure 1. However, according to this invention, carboxylic acid or sulfonic acid (acid group) is present at the terminal.
As shown in Figure 2, polymers with organic groups (basic groups) containing nitrogen atoms that react with the polymer do not essentially form a network structure, but instead form extended molecular chains or branched structures. It becomes a highly branched polymer. For this reason, the product in Figure 1 becomes a hard polymer with strength but low elongation, which causes problems such as end peeling when used in adhesive tapes, etc., whereas the product of the present invention has high strength and elongation. Both are excellent, with low melt viscosity at high temperatures and improved adhesive properties. The above-mentioned acrylic polymer used in this invention is produced by (b) acrylic acid or methacrylic acid in the presence of (a) a mercaptan containing a nitrogen atom capable of forming an ionic bond with a carboxyl group or a sulfone group in the molecule. It can be produced by copolymerizing a main monomer containing at least 50% by weight of an ester of an acid and an alcohol having up to 18 carbon atoms, and (c) an α/β-olefin type unsaturated carboxylic acid or sulfonic acid. . Mercaptans, component a, function as a chain transfer agent to introduce an organic group containing a nitrogen atom that can form an ionic bond with a carboxyl group or a sulfone group into the molecular terminal of the acrylic polymer. It broadly includes aliphatic, aromatic, and alicyclic mercaptans represented by the general formula RSH. Specific examples include 2-aminoethanethiol, 2-mercaptobenzimidazole, 2-mercaptopyridine, and 4-mercaptopyridine. The usage ratio of these mercaptans is component b and component c.
The amount is usually 0.001 to 10 parts by weight per 100 parts by weight of the monomer mixture consisting of the following components. In addition,
Along with the above mercaptans, general chain transfer mercaptans such as mercaptans that do not contain a nitrogen atom capable of ionically bonding with a carboxyl group or sulfonic group in the molecule, such as 2-hydroxyethanethiol, dodecyl mercaptan, mercaptoacetic acid, and 3-mercaptopropionic acid There is no problem in using drugs together. By using these other chain transfer agents, it is possible to control the amount of nitrogen atom-containing organic groups introduced at the ends of the polymer molecules. The main monomer as component b may be an acrylic ester or a methacrylic ester alone, or may be a combination of these esters and other copolymerizable vinyl monomers.
The type and amount of the above-mentioned vinyl monomer is selected depending on the purpose of use of the pressure-sensitive adhesive composition, but if the amount exceeds 50% by weight, it is not preferable because it becomes too hard and the adhesive properties are impaired. Specific examples of acrylic esters or methacrylic esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 1-ethylpropyl (meth)acrylate, and 1-methyl. Pentyl (meth)acrylate, 2-methylpentyl (meth)acrylate,
3-methylpentyl (meth)acrylate, 1-
Examples include ethylbutyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, isooctyl (meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate. These esters have an alcohol with 18 carbon atoms.
It is desirable that the number of carbon atoms is as high as possible; if the number of carbon atoms is increased, the adhesive becomes too hard and tends to impair its adhesive properties. Specific examples of other copolymerizable vinyl monomers include vinyl ester, acrylonitrile, methacrylonitrile, acrylamide, diacetone acrylamide, and styrene. The α/β-olefinic unsaturated carboxylic acid or sulfonic acid as component c is a monomer that serves as an ionic bonding group and contributes to improving adhesive strength, and is used in varying amounts depending on the purpose of use. Specific examples of monomers belonging to this category include acrylic acid, methacrylic acid, maleic acid, itaconic acid, allyl acetic acid, and 2-sulfoethyl (meth)acrylate. Generally, the proportions of the b-component monomer and c-component monomer used are preferably 85 to 99.95% by weight for the b component and 0.05 to 15% by weight for the c component. If the c-component monomer increases too much, water resistance and other properties will be adversely affected, making it impossible to obtain good results. The copolymerization reaction can be carried out according to conventional methods, and can be carried out by bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc. using a polymerization initiator used in general radical polymerization. . The above polymerization initiators include benzoyl peroxide,
Examples include organic peroxides such as tert-butyl hydroperoxide and azo initiators such as azobisisobutyronitrile. The amount of initiator used is usually about 0.01 to 3 parts by weight, and the preferred range is about 0.02 to 1.0 parts by weight, based on 100 parts by weight of the monomer mixture. The optimum amount of initiator is determined in large part by the nature of the particular monomers used, including any impurities associated with the particular monomers. In the case of solution polymerization, solvents that can be used include known inert organic solvents such as benzene, toluene, xylene, mesitylene, butane, pentane, hexane, heptane, isooctane, methyl ethyl ketone, isobutyl ketone, ethyl acetate, propyl acetate, and butyl acetate. Both can be used. The acrylic polymer synthesized in this way contains a predetermined amount of carboxyl groups or sulfone groups derived from component c in the polymer molecule, while carboxyl groups or sulfone groups are present in the molecule as residues of the chain transfer agent in component a at the end of the molecule. It has an organic group (RS-) containing a nitrogen atom that can form an ionic bond with a group or a sulfone group. The molecular weight of this polymer is preferably about 10,000 to 800,000. The pressure-sensitive adhesive composition of the present invention has the above-mentioned acrylic polymer as a main component, and if necessary, a general acrylic polymer different from the above-mentioned one according to the present invention, such as an intramolecular acrylic polymers that have a carboxyl group or sulfone group on the molecule but do not have an organic group containing a nitrogen atom that can form an ionic bond with the above group at the end of the molecule, other phenolic resins, natural resins, etc.
Tackifiers such as petroleum resins, coumaron-indene resins, rosin esters, and hydrated rosin resin derivatives, as well as known additives such as antioxidants, ultraviolet absorbers, plasticizers, and pigments, can be blended. . As detailed above, the pressure-sensitive adhesive composition of the present invention has the inherent properties of an acrylic polymer, has excellent adhesive properties such as cohesive strength at room temperature, and can be applied by heating and melting. It also has excellent processability and can avoid the drawbacks of conventional pressure-sensitive adhesive compositions. Moreover, the adhesive composition of the present invention exhibits excellent performance as a hot-melt adhesive, in particular, due to the above-mentioned properties. Next, examples of this invention will be described. In the following, parts shall mean parts by weight. Example 1 A monomer mixture consisting of 95 parts of 2-ethylhexyl acrylate, 5 parts of methacrylic acid, 0.2 parts of 2-aminoethanethiol and 25 parts of ethyl acetate was
The mixture was placed in a flask and stirred at 40°C for 1 hour while introducing dry nitrogen. Then, an initiator solution containing 0.05 parts of azobisisobutyronitrile dissolved in 5 parts of ethyl acetate was added, the temperature of the contents was raised to 65°C, and 200 parts of ethyl acetate was gradually added dropwise over 2 hours. death,
The content temperature was controlled and kept at 65°C for an additional hour.
In order to completely polymerize the remaining monomer, the temperature of the contents was raised to 80°C and maintained for 1 hour. The homogeneous solution of the acrylic polymer thus obtained was
The mixture was heated to ~120°C, and the solvent was distilled off under reduced pressure to obtain a solid hot-melt pressure-sensitive adhesive. Apply the above adhesive using a hot melt applicator.
It was coated to a thickness of 30μ on a 25μ thick polyester film. The pressure-sensitive adhesive sheet thus obtained was cut into a predetermined size to obtain a pressure-sensitive adhesive tape. Example 2 2-ethylhexyl acrylate 70 parts Vinyl acetate 25 parts Methacrylic acid 5 parts 2-aminoethanethiol 0.2 parts Azobisisobutyronitrile 0.05 parts Ethyl acetate 225 parts The same procedure as in Example 1 was carried out using each of the above components. An acrylic polymer was synthesized using this as a solid heat-melting pressure-sensitive adhesive, and a pressure-sensitive adhesive tape was produced in the same manner as in Example 1. Example 3 N-butyl acrylate 95 parts Acrylic acid 5 parts 2-aminoethanethiol 0.2 parts Azobisisobutyronitrile 0.05 parts Ethyl acetate 225 parts An acrylic polymer was prepared in the same manner as in Example 1 using each of the above components. was synthesized, and a pressure-sensitive adhesive tape was produced in the same manner as in Example 1 using this as a solid heat-melting pressure-sensitive adhesive. Example 4 2-Ethylhexyl acrylate 95 parts Methacrylic acid 5 parts 2-aminoethanethiol 0.1 part 2-hydroxyethanethiol 0.05 part Azobisisobutyronitrile 0.05 part Ethyl acetate 225 parts Example 1 An acrylic polymer was synthesized in the same manner as in Example 1, and a pressure-sensitive adhesive tape was produced using this as a solid heat-melting pressure-sensitive adhesive in the same manner as in Example 1. Example 5 2-Ethylhexyl acrylate 95 parts Methacrylic acid 5 parts 2-hydroxyethanethiol 0.2 parts Azobisisobutyronitrile 0.05 parts Ethyl acetate 225 parts An acrylic polymer was prepared in the same manner as in Example 1 using each of the above components. Synthesized. After 40 parts of this polymer and 60 parts of the acrylic polymer obtained in Example 1 were dissolved and mixed in ethyl acetate, the ethyl acetate was distilled off by heating and vacuum treatment to form a solid hot-melt pressure-sensitive adhesive. Using this, a pressure-sensitive adhesive tape was produced in the same manner as in Example 1. Comparative Example 1 2-Ethylhexyl acrylate 95 parts Methacrylic acid 5 parts 2-hydroxyethanethiol 0.2 parts Azobisisobutyronitrile 0.05 parts Ethyl acetate 225 parts An acrylic polymer was prepared in the same manner as in Example 1 using each of the above components. This was synthesized and used as a solid heat-melting pressure-sensitive adhesive to produce a pressure-sensitive adhesive tape in the same manner as in Example 1. Comparative Example 2 An acrylic polymer was prepared in the same manner as in Example 1 using the above components. This was synthesized and used as a solid heat-melting pressure-sensitive adhesive to produce a pressure-sensitive adhesive tape in the same manner as in Example 1. Example 6 2-ethylhexyl acrylate 95 parts 2-acrylamido-2-methylpropanesulfonic acid 5 parts 2-aminoethanethiol 0.1 part 2-hydroxyethanethiol 0.1 part azobisisobutyronitrile 0.05 part N.N-dimethylformamide 200 An acrylic polymer was synthesized in the same manner as in Example 1 using each of the above components, and a pressure-sensitive adhesive tape was produced using this as a solid heat-melting pressure-sensitive adhesive in the same manner as in Example 1. Comparative Example 3 2-Ethylhexyl acrylate 95 parts 2-acrylamido-2-methylpropanesulfonic acid 5 parts 2-hydroxyethanethiol 0.2 parts Azobisisobutyronitrile 0.05 parts N.N-dimethylformamide 200 parts Using each of the above components An acrylic polymer was synthesized in the same manner as in Example 1, and this was used as a solid heat-melting pressure-sensitive adhesive to produce a pressure-sensitive adhesive tape in the same manner as in Example 1. The pressure-sensitive adhesive properties of each of the tapes of Examples 1 to 6 and Comparative Examples 1 to 3 were examined and found to be as shown in the following table. The table also lists the amino group/carboxyl group (or sulfone group) molar ratio in the acrylic polymer and the melt viscosity of the pressure-sensitive adhesives of each example and comparative example.

【table】

[Table] As is clear from the above test results, the pressure-sensitive adhesive composition of the present invention has a melt viscosity suitable for coating, and also satisfies adhesive strength, adhesive strength, and cohesive strength. It turns out that it can be done.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram regarding the characteristics of an acrylic polymer different from that of the present invention, and FIG. 2 is an explanatory diagram regarding the characteristics of the acrylic polymer of the present invention.

Claims (1)

[Scope of Claims] 1 (a) In the presence of a mercaptan containing a nitrogen atom capable of forming an ionic bond with a carboxyl group or a sulfone group in the molecule, (b) with acrylic acid or methacrylic acid and having a carbon number of 18 A carboxyl group or sulfone group in the molecule obtained by copolymerizing a main monomer containing at least 50% by weight or more of an ester with an alcohol, and (c) an α/β-olefin type unsaturated carboxylic acid or sulfonic acid. A heat-melting type pressure-sensitive adhesive composition containing as a main component an acrylic polymer having an organic group containing a nitrogen atom capable of forming an ionic bond with the above-mentioned group at the end of the molecule. 2 The ratio of component a to 100 parts by weight of the total amount of components b and c is 0.001 to 10 parts by weight, and component b is 85 to 99.95 parts by weight in the total amount of components b and c.
The heat-melting type pressure-sensitive adhesive composition according to claim 1, wherein the component c is 0.05 to 15% by weight. 3 The average molecular weight of the acrylic polymer is 10,000 to 80
3. The hot-melt pressure-sensitive adhesive composition according to claim 1 or 2, wherein the pressure-sensitive adhesive composition is