JP2670055B2 - Pressure sensitive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a pressure-sensitive adhesive comprising a graft copolymer. <Prior Art> Acrylic pressure-sensitive adhesives have been conventionally used, but for the purpose of imparting cohesive force and improving adhesive force, and for imparting functional groups for forming cross-linking points by a cross-linking agent. In addition, a means of copolymerizing a small amount of (meth) acrylic acid with a main component (meth) acrylic acid ester is adopted. However, while (meth) acrylic acid can achieve the above object, it tends to lower the adhesive properties under low temperature conditions and the adhesiveness to rough surfaces in order to raise the glass transition temperature of the pressure-sensitive adhesive obtained. It is a thing. Therefore, in order to reduce such a tendency, various means such as those shown below have been studied. By increasing the molecular weight of the acrylic pressure-sensitive adhesive without copolymerizing (meth) acrylic acid, the cohesive force is improved without increasing the glass transition temperature. A monomer containing a hydroxyl group is copolymerized in place of (meth) acrylic acid, and the hydroxyl group is used for a cross-linking reaction to suppress an increase in glass transition temperature and improve only a cohesive force. <Problems to be Solved by the Invention> However, in any of the above means, it has not been possible to exhibit adhesive properties to the same extent as when (meth) acrylic acid is copolymerized, and particularly in sticking to a curved surface. The reality is that the adhesive properties are insufficient and a satisfactory pressure-sensitive adhesive has not yet been obtained. It is an object of the present invention to obtain a pressure-sensitive adhesive having excellent cohesive strength, excellent adhesive properties, particularly under low temperature conditions, and adhesive properties at the time of sticking to a rough surface or a curved surface. <Means for Solving Problems> As a result of intensive studies conducted by the present inventors in order to achieve the above object, the use of a graft copolymer having a specific molecular design even when (meth) acrylic acid is used. Thus, the present inventors have found that the above-mentioned problems of the conventional pressure-sensitive adhesive can be solved, and have completed the present invention. That is, the pressure-sensitive adhesive of the present invention has a first carbon number of 14 or less.
Made by polymerizing 50% by weight or more of (meth) acrylic acid ester consisting of primary or secondary alcohol and (meth) acrylic acid, and having an acrylic polymer having a glass transition temperature of -10 ° C or lower as a main chain, It is a graft copolymer having an average molecular weight of 1,000 or more and having a side chain of a macromonomer obtained by polymerizing 5% by weight or more of (meth) acrylic acid. The pressure-sensitive adhesive of the present invention is characterized by a novel graft copolymer, and the acrylic polymer constituting the main chain of the graft copolymer has a glass transition temperature of −10 ° C. or lower, preferably − Adjust so that the temperature does not exceed 20 ° C. If the glass transition temperature exceeds -10 ° C, the pressure-sensitive adhesive obtained tends to have poor tack at low temperatures. The acrylic polymer is obtained by polymerizing a (meth) acrylic acid ester of a primary or secondary alcohol having 14 or less carbon atoms and (meth) acrylic acid. An ester using an alcohol having a carbon number of 15 or more or a tertiary alcohol tends to have poor molecular side chain flexibility, and the tack of the obtained pressure-sensitive adhesive tends to be insufficient. Examples of such (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isoamyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Isooctyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, and the like may be used alone or in combination of two or more. May be used. When two or more kinds are used in combination, by combining them so that the average carbon number of the alcohol part in the (meth) acrylic acid ester is 4 to 12, the flexibility of the acrylic polymer as the main chain obtained is good. Is preferable. Even when one type of (meth) acrylic acid ester is used, it is preferable to use one having 4 to 12 carbon atoms in the alcohol portion for the same reason. The acrylic polymer used as the main chain in the present invention, the (meth) acrylic acid ester is 50% by weight or more,
It is preferably obtained by polymerizing 70% by weight or more. If the polymerization amount is less than 50% by weight, the flexibility of the molecular chain and the heat resistance and weather resistance of the obtained pressure-sensitive adhesive will be poor, and it will be difficult to obtain satisfactory characteristics. The acrylic polymer may be formed only from the above (meth) acrylic acid ester, but it is preferably obtained by copolymerizing with another monomer in order to satisfy the conditions of the glass transition temperature. The monomer to be copolymerized is not particularly limited, but examples thereof include acid-based monomers such as (meth) acrylic acid, maleic acid, itaconic acid, crotonic acid, 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate. Hydroxyl group-containing monomer such as N, N-dimethylaminoethyl (meth)
Amino group-containing monomers such as acrylate and N-tert-butylaminoethyl acrylate; amide group-containing monomers such as (meth) acrylamide and N-methylol (meth) acrylamide; and oxirane ring-containing monomers such as glycidyl methacrylate Others (meth) acrylonitrile, vinyl acetate, vinyl chloride, etc. are used. The acrylic polymer preferably has a weight average molecular weight of 50,000 or more, particularly 100,000 to 2,000,000 in view of flexibility of the molecular chain and adhesive properties of the pressure-sensitive adhesive obtained. Is. In the present invention, the macromonomer constituting the side chain of the graft copolymer has a weight average molecular weight of 1,000 or more, preferably 3,000 or more, and (meth) acrylic acid is 5% by weight or more, preferably 20% by weight or more, further preferably Is obtained by polymerizing 50% by weight or more. Weight average molecular weight
If it is less than 1,000, entanglement and interaction between the side chain portions are unlikely to occur, so that it is difficult to obtain a pressure-sensitive adhesive having high cohesive force. If the amount of (meth) acrylic acid polymerized is less than 5% by weight, the effect of imparting adhesive properties, particularly cohesive properties, by (meth) acrylic acid cannot be expected. still,
The upper limit of the weight average molecular weight of the macromonomer is not particularly limited, but it is preferably adjusted to 200,000 or less, particularly 50,000 or less from the viewpoint of controlling the molecular weight during the graft copolymerization reaction. The graft copolymer constituting the pressure-sensitive adhesive of the present invention is composed of the main chain portion and the side chain portion as described above, and the content of the macromonomer of the graft copolymer is 2 to 50% by weight. By setting it in the range of preferably 3 to 20% by weight, a satisfactory cohesive force can be obtained. In order to prepare a graft copolymer having the above structure, a high molecular weight compound having a radically polymerizable double bond at at least one terminal (hereinafter referred to as macromonomer) is used as a polymer constituting a side chain, It is preferable to adopt a method in which the acrylic polymer as a chain is subjected to a grafting reaction because it facilitates the adjustment of the molecular weight of the side chain, the suppression of the amount of homopolymer produced, the design of the graft copolymer, and the like. Specific examples of the method for preparing such a graft copolymer include (meth) acrylic acid alkyl ester,
One or more α, β-ethylenically unsaturated monomers having no oxirane ring and no carboxyl group in the molecule, such as acid amides, acid nitriles, vinyl esters, and aromatic monoolefins, and a tertiary alcohol ( (Meth) acrylic acid ester composed of (meth) acrylic acid, for example, tert-butyl (meth) acrylate, 1,1-dimethylpropyl (meth) acrylate, 1,1-dimethylbutyl (meth) acrylate, 1,1-diethylpropyl Polymerization with (meth) acrylate etc. in an organic solvent in the presence of an azo polymerization initiator and a carboxyl group-containing chain transfer agent is performed to obtain a terminal carboxyl group controlled to have a weight average molecular weight of about 500 to 200,000. Having an oxirane ring such as glycidyl (meth) acrylate and a radically polymerizable unsaturated group The dimers are reacted to prepare a macromonomer. Next, this macromonomer is selectively hydrolyzed in the presence of a catalyst to a (meth) acrylic ester portion composed of a tertiary alcohol and (meth) acrylic acid to obtain a (meth) acrylic acid-containing macromonomer, The desired graft copolymer can be obtained by copolymerizing with a chain-forming acrylic monomer. The above hydrolysis reaction may be carried out at the time of preparing the macromonomer, but it may be carried out after obtaining the graft copolymer to introduce the acrylic acid moiety later. In any of the above methods, when acrylic acid is present in the macromonomer when a double bond is introduced into the terminal of the macromonomer, it becomes a reaction point and cannot be introduced into the terminal, and therefore, in the present invention. When preparing the graft copolymer, it is necessary to protect the acrylic acid moiety as an ester with a tertiary alcohol that is easily hydrolyzed until a double bond is introduced at the terminal of the macromonomer for the side chain polymer. When the pressure-sensitive adhesive of the present invention is prepared, various compounds can be blended, if necessary, in addition to the above graft copolymer. Typical examples of the optional compounding components include terpene-based, terpene-phenol-based, coumarone-indene-based, styrene-based, rosin-based, xylene-based, phenol-based, petroleum-based and other tackifiers at room temperature. A liquid softening agent such as tackifying resin, process oil, polyester-based plasticizer, polybutene, liquid rubber, cross-linking agent including polyisocyanate, melamine resin, amine-epoxy resin, peroxide, metal chelate compound, etc. I can give you. The total amount of the tackifier and the softening agent should be equal to or less than the graft copolymer, and the amount of the crosslinking agent should be approximately 10 parts by weight or less per 100 parts by weight of the graft copolymer. . Further, various polymers such as acrylic polymers may be blended for the purpose of finely adjusting the adhesive properties. Other optional components include, for example, additives commonly used in pressure-sensitive adhesives such as antioxidants, ultraviolet absorbers, fillers, pigments, and extenders. The blending amount may be a normal amount. The pressure-sensitive adhesive of the present invention can be applied by a usual method such as a method of coating the pressure-sensitive adhesive as a solution type with a solvent on a support and drying it. Further, it can be applied to a usual pressure-sensitive adhesive application such as an adhesive tape attached to a substrate made of plastic, paper, cloth, metal foil or the like. The thickness of the pressure-sensitive adhesive layer is generally 1 to 500 μm, but it is appropriately determined according to the purpose of use. <Effects of the Invention> As described above, since the pressure-sensitive adhesive of the present invention uses the graft copolymer having an acrylic acid component in the side chain,
It does not raise the glass transition temperature unlike conventional pressure-sensitive adhesives that are simply copolymerized with (meth) acrylic acid, and has excellent cohesive strength and adhesive properties, as well as low-temperature properties and excellent adhesion to rough surfaces and curved surfaces. It shows power. <Examples> Examples of the present invention will be shown and specifically described below. Reference Example 1 50 parts of methyl ethyl ketone (parts by weight, hereinafter the same), 50 parts of toluene, 50 parts of n-butyl acrylate, 50 parts of tert-butyl acrylate, in a reaction vessel equipped with a cooling pipe, a nitrogen introduction pipe, a thermometer, and a stirring bar. 4,4'-azobis (4-cyano)
1 part of valeric acid and 2 parts of thioglycolic acid were added and reacted at 60 ° C. for 3 hours under a nitrogen atmosphere, and the resulting reaction product was subjected to precipitation purification treatment with a water-methanol mixed solvent to obtain a terminal carboxylated prepolymer. It was The KOH equivalent weight of this prepolymer was 11.2 mg KOH / g polymer. Next, 100 parts of the prepolymer, 200 parts of xylene, 7.1 parts of glycidyl methacrylate, 0.5 part of hydroquinone and 0.5 part of triethylamine were placed in the same reaction vessel as above and reacted at 140 ° C. for 5 hours, and the resulting reaction product was added to water. -After precipitation purification with a mixed solvent of methanol, 48 ° C under 1 mgHg at 50 ° C.
It was dried under reduced pressure for an hour to obtain an n-butyl acrylate / tert-butyl acrylate macromonomer. This compound
From the KOH equivalent, the reaction rate of the terminal carboxyl groups of the prepolymer was 95%. Table 1 shows the physical properties of the macromonomer as the side chain forming compound. Reference Examples 2 to 3 In accordance with Reference Example 1, the reaction was performed according to the formulation shown in Table 1 to obtain a macromonomer. The physical properties of this macromonomer are shown in Table 1. Example 1 10 parts of the macromonomer obtained in Reference Example 1, 90 parts of n-butyl acrylate, 100 parts of ethyl acetate, and 1 part of azobisisobutyronitrile were placed in a reaction vessel equipped with a cooling tube, a nitrogen introducing tube, and a stirring rod. Put in nitrogen atmosphere at 60 ℃ for 5 hours, then 70
The reaction was carried out at 2 ° C. for 2 hours. After lowering the temperature of the reaction product to room temperature, 150 g of ethyl acetate, 50 g of water and 10 g of sulfuric acid were added,
The hydrolysis reaction was performed at 4 ° C. for 4 hours. Thereafter, the reaction product was sufficiently washed with water and further purified by precipitation with methanol to obtain a graft copolymer, which was used as the pressure-sensitive adhesive of the present invention. The content of acrylic acid in the macromonomer of Reference Example 1 separately hydrolyzed under the same conditions as above was measured by ¹³ C-NMR, and as a result, the molar ratio of n-butyl acrylate / acrylic acid was found to be
52/48, and it was confirmed that the tert-butyl acrylate moiety in the side chain was selectively hydrolyzed. The physical properties of the above graft polymer are shown in Table 2. Example 2 A pressure-sensitive adhesive was obtained according to Example 1, except that 5 parts of the macromonomer obtained in Reference Example 2 and 95 parts of n-butyl acrylate were used. The physical properties of the graft copolymer used as the pressure sensitive adhesive are shown in Table 2. Example 3 A pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that 10 parts of the macromonomer obtained in Reference Example 3 and 90 parts of 2-ethylhexyl acrylate were used. Comparative Example 1 95 parts of n-butyl acrylate, 5 parts of acrylic acid, 100 parts of ethyl acetate and 1 part of azobisisobutyronitrile were blended to obtain a pressure-sensitive adhesive. Comparative Example 2 2-Ethylhexyl acrylate 90 parts, acrylic acid 10
Parts and 1 part of azobisisobutyronitrile were mixed and polymerized to obtain a pressure-sensitive adhesive. Evaluation test The pressure-sensitive adhesive obtained in each of the examples and comparative examples was coated on a polyester film or release paper having a thickness of 50 μm and the thickness after drying was
The adhesive tape was uniformly applied so as to have a thickness of 50 μm and dried by heating to obtain an adhesive tape, and the following characteristics were examined. [Adhesive strength] Measured according to LIS Z 1522. [Holding power] Adhesive tape is adhered to one end of a phenolic resin plate with a mirror-finished surface (adhesive area: 20 mm x 10 mm), and after 30 minutes, this is heated to 40 ° C.
It was left to stand for 20 minutes under which it was aged. Next, hang the phenolic resin plate and attach it to the free end of the adhesive tape.
A uniform load of 400 g was applied to apply a tensile shear stress to the adhesive layer, and in this state, measurement was performed using a shift distance creep tester per hour. [Anti-rubber resistance test] 0.4mm thick aluminum plate with a mirror-like surface (10mm x 100mm)
Attach one side of the tape sample to. Next, place the other side of this tape sample into an ABS cylinder with a diameter of 200 mm.
Laminate under pressure of 5kg roll once reciprocating under ℃. The floating height of the test piece at the end (after 24 hours) was measured. [Cold Resistance, Rough Surface Adhesion Test] One side of the tape sample is attached to a slate plate (20 mm x 20 mm) having a thickness of 4 mm under the condition of 5 kg roll once reciprocating at 20 ° C. Next, the other surface of this sample is pressed on a 50 g × 150 mm metal plate with a 50 g surface by a single reciprocation of a 5 kg roll. Then, the test piece was left at -10 ° C for 2 hours,
Under the same conditions, it was dropped onto a concrete surface from a height of 2 m and examined for peeling. The results of the above evaluation test are shown in Table 2. The glass transition temperature of the main chain polymer is a value measured by differential thermal analysis by separately synthesizing a main chain forming polymer with a corresponding composition. As is clear from the results shown in Table 2, the pressure-sensitive adhesive according to the present invention is excellent in cohesiveness, and is sufficiently satisfactory in sticking to a curved surface and cold resistance.

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Claims (1)

(57) [Claims] It is made by polymerizing 50% by weight or more of a (meth) acrylic acid ester consisting of a primary or secondary alcohol having 14 or less carbon atoms and (meth) acrylic acid, and having a glass transition temperature of -10.
Pressure sensitivity consisting of a graft copolymer whose main chain is an acrylic polymer whose temperature is ℃ or less, whose weight average molecular weight is 1000 or more, and whose side chain is a macromonomer obtained by polymerizing 5% by weight or more of (meth) acrylic acid. adhesive. 2. The content of macromonomer in the graft copolymer is 2
The pressure-sensitive adhesive according to claim 1, which is -50% by weight. 3. The pressure-sensitive adhesive according to claim 1, wherein the weight average molecular weight of the graft copolymer is 100,000 or more.