JPH09235539A - Tacky agent composition and tacky sheets - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tacky agent composition useful as a tacky sheet, using a small amount of an organic solvent, high in concentration, excellent in adhesion characteristics and high in reliability, by blending a specific acrylic prepolymer by copolymerization with a prescribed chain extender. SOLUTION: This composition is obtained by blending (A) an acrylic prepolymer containing a highly active OH in the molecule and having 5,000-300,000 weight-average molecular weight obtained by copolymerizing 75-99.95wt.% of a monomer (A1 ) of the formula CH2 =CH(R1 )COOR2 (R1 is H or methyl; R2 is a 2-14C alkyl) with 0.05-25wt.% of a monomer (A2 ) of the formula CH2 =CH(R1 )COOR3 [R3 is an OH-substituted 3-14C and the number (m) of the order of the carbon position of the alkyl chain to which OH at the longest tip end is bonded satisfies the relation m>=n-1 to the number (n) of the order of the carbon position of the longest tip end of the alkyl chain of the component A1 with (B) a polyfunctional isocyanate consisting essentially of bifunctional isocyanates as a chain extender.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet, such as a pressure-sensitive adhesive sheet or a pressure-sensitive adhesive tape, using the same.

[0002]

2. Description of the Related Art Conventionally, paper and plastic films,
BACKGROUND ART Adhesive sheets or adhesive tapes (hereinafter, referred to as adhesive sheets) in which an adhesive layer is provided on one or both sides of a support such as a woven fabric or a nonwoven fabric have been used for various applications. The type of the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer is various depending on the application, and rubber-based, natural, synthetic rubber-based, acrylic, vinyl ether-based, and silicone-based are commonly used. ing. Among these pressure-sensitive adhesives, acrylic pressure-sensitive adhesives are essentially excellent in weather resistance, solvent resistance, deterioration resistance properties such as heat resistance, and
Since it is easy to balance the adhesive properties such as adhesive strength, initial adhesive strength (tack) and cohesive strength, it is widely used in various fields. Acrylic pressure-sensitive adhesives generally have a low glass transition temperature (meth) acrylic acid alkyl ester as the main monomer in order to impart adhesive force and initial tackiness (tack). An acrylic polymer obtained by copolymerizing a small amount of a polar monomer having a functional group with an external cross-linking agent such as peroxide cross-linking or trifunctional polyisocyanate in order to improve cohesive strength, if necessary, The adhesive properties are balanced by preliminarily copolymerizing a small amount of a monomer for internal crosslinking such as glycidyl (meth) acrylate with the above polymer, or by means such as electron beam irradiation.

However, conventional acrylic copolymers for acrylic pressure-sensitive adhesives are themselves high-molecular weight substances, and therefore, in order to adjust the viscosity to an appropriate level for coating during production of pressure-sensitive adhesive sheets, a large amount is required. There is a problem that requires the organic solvent. In addition, the functional groups such as carboxyl groups and hydroxyl groups contained in the acrylic copolymer have low reactivity and require a long time to react with a crosslinking agent during the production of pressure-sensitive adhesive sheets, Alternatively, there is a drawback that the support is damaged when dried at a high temperature.

[0004]

SUMMARY OF THE INVENTION The present invention provides a novel pressure-sensitive adhesive composition using an acrylic copolymerized prepolymer having high reactivity while reducing the amount of an organic solvent used, and a pressure-sensitive adhesive sheet thereof. The purpose is to:

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the problems of the prior art, and as a result, an acrylic copolymer for an acrylic pressure-sensitive adhesive conventionally used generally has been used. In a polymer, a functional group in the polymer to be a reaction point is incorporated into a molecular side chain of the polymer, and it is difficult for a quick reaction to occur. It is considered that there are problems such as cost, and the functional groups (hydroxyl groups) contained in the prepolymer
By using an acrylic copolymer prepolymer with a relatively low molecular weight, which is designed to highly exhibit the reactivity of the polymer, a high molecular weight suitable for forming an adhesive layer by easily reacting with an isocyanate group can be obtained. The present invention has been completed by discovering that the chain can be extended.

That is, the present invention provides the following monomer (a)
An acrylic copolymer prepolymer having a highly reactive hydroxyl group in the molecule and having a weight average molecular weight of 5,000 to 300,000, which is obtained by copolymerizing (b) and (b) as an essential component, and mainly contains a bifunctional chain extender. The present invention relates to a pressure-sensitive adhesive composition containing a polyfunctional isocyanate. (A) General formula; CH ₂ ═CH (R ₁ ) COOR ₂ (R ₁
Is hydrogen or a methyl group, and R ₂ is an alkyl group having 2 to 14 carbon atoms). 75-99.
95% by weight (b) General formula; CH ₂ = CH (R ₁ ) COOR ₃ (R ₁
Is a hydrogen or methyl group, and R ₃ is a C 3-14 monovalent alkyl group having at least one hydroxyl group). 0.05 to 25% by weight (however, the monomers (a) and (b) used are based on the ester bond part, based on the order number n of the carbon position at the longest tip of the alkyl chain of (a)). Then, the rank number m of the carbon position of the alkyl chain to which the hydroxyl group at the longest tip in (b) is bonded is m
It is assumed that the relationship of ≧ n−1 is satisfied. )

In the present invention, the above-mentioned acrylic copolymer prepolymer having an average of 0.5 to 10 hydroxyl groups with high reaction activity in one molecule easily reacts with an isocyanate group. It is preferable in that the chain is extended to a high molecular weight suitable for forming the pressure-sensitive adhesive layer, and the polyfunctional isocyanate is such that the isocyanate group is 0.1 to 10 equivalents per 1 equivalent of the hydroxyl group of the acrylic copolymer prepolymer. It is preferable to mix them. Further, in the present invention, it is possible to satisfy the economical and environmental reasons for reducing the amount of the organic solvent used as much as possible, and the pressure-sensitive adhesive component containing the acrylic copolymer prepolymer and the polyfunctional isocyanate is a small amount of organic solvent. Since it can be uniformly dissolved in a solvent, it can be provided at a high concentration of 40 to 90% by weight. Furthermore, the pressure-sensitive adhesive composition of the present invention has a good pressure-sensitive adhesive layer that reacts rapidly and is heated at a normal drying temperature after being applied to one or both sides of a support such as plastic or paper. Adhesive sheets can be manufactured.

The monomer (a) used in the present invention is a (meth) acrylic acid alkyl ester having an alkyl group having 2 to 14 carbon atoms represented by the above general formula,
It is a component that mainly imparts adhesive properties. The carbon number of the alkyl group as the ester side chain depends on the initial adhesion (tack)
From the viewpoint of adhesiveness, it is necessary to set it to 2 to 14. The monomer (a) is copolymerized as an essential component in the range of 75 to 99.95% by weight, preferably 90 to 99.5% by weight of the total monomer from the viewpoint of the properties as an adhesive. You.
When the amount of the component (a) is less than 75% by weight, the amount of the component (b) is inevitably increased, and it is difficult to achieve chain extension by an isocyanate group. That is, the pressure-sensitive adhesive requires an appropriate gel, but it is not preferable because the gelation proceeds too much and, on the other hand, the formation of the required high-molecular-weight polymer is inhibited. (A)
When the amount of the component exceeds 99.95% by weight, the absolute amount of the component (b) described later becomes insufficient, and in this case, it is also difficult to achieve the intended chain extension of the present invention.

As the monomer as the component (a) in the present invention, one satisfying a certain relationship with the monomer (b) described later is used. Examples of the monomer (a) that can be used include (meth) acrylic acid ethyl ester, (meth) acrylic acid propyl ester, (meth) acrylic acid butyl ester, (meth) acrylic acid pentyl ester, (meth) acrylic acid. Hexyl ester, (meth) acrylic acid 2-ethylhexyl ester, (meth) acrylic acid heptyl ester, (meth) acrylic acid octyl ester, (meth) acrylic acid isooctyl ester, (meth) acrylic acid nonyl ester, (meth) acrylic Examples thereof include acid decyl ester and the like, which may be a linear ester or a branched chain ester as a structural isomer thereof, and one kind or two or more kinds are used.

The monomer (b) used in the present invention is a (meth) acrylic acid alkyl ester represented by the above general formula and having at least one hydroxyl group in the alkyl chain having 3 to 14 carbon atoms. , The number of carbons in the alkyl chain of the hydroxyl group as the reaction point is m based on the ester bond
At the position of. Examples of the monomer (b) that can be used include (meth) acrylic acid 3-hydroxypropyl ester, (meth) acrylic acid 2-methyl 3-hydroxypropyl ester, (meth) acrylic acid 4-hydroxybutyl ester, and ( (Meth) acrylic acid 6
-Hydroxyhexyl ester, (meth) acrylic acid 8
-Hydroxyoctyl ester, (meth) acrylic acid 1
0-hydroxydecyl ester and the like. One or more of the monomers (b) are used in the range of 0.05 to 25% by weight, preferably 0.1 to 10% by weight of the total monomers.

The above-mentioned monomer (a) and monomer (b)
Must be used in combination to satisfy the following certain conditions. That is, the monomers (a) and (b) used are based on the ester bond, with respect to the rank number n of the carbon position at the longest end of the alkyl chain in (a).
In (b), the rank number m of the carbon position of the alkyl chain to which the longest hydroxyl group is bonded must satisfy the relationship of m ≧ n−1. In the above conditions, the alkyl group of the monomer (a) may be a straight chain alkyl group or a branched chain alkyl group, and the order of the carbon position at the longest tip of the alkyl chain is based on the ester bond part. A few n of monomer (a)
In the case of using, as the monomer (b), the order number m of the carbon position of the alkyl chain to which the most extreme hydroxyl group is bonded is similarly m ≧ m based on the ester bond part. n
It means that the relationship of -1 is satisfied. For example, when butyl acrylate (n = 4) is used as the monomer (a), 2-methyl-3-hydroxypropyl (meth) acrylate is used as the monomer (b),
Those having m ≧ 3 such as (meth) acrylic acid 4-hydroxybutyl ester are used.

When the above relationship is satisfied, in the acrylic copolymer prepolymer comprising the monomers (a) and (b), the hydroxyl group present in the alkyl chain of the monomer (b) is a monomer ( Since it is pending at the same position as the carbon position at the longest tip of the alkyl chain of a) or at a position higher than that, the amount of hydroxyl groups incorporated into the molecular side chain of the copolymerization prepolymer is reduced, and The inherent high reactivity can be exhibited, and the chain extension effect and the crosslinking effect can be effectively achieved.

In the present invention, the monomer (a) is used within a range that does not impair the characteristics of the above-mentioned monomers (a) and (b) and for the purpose of imparting or modifying delicate characteristics as an adhesive. ) And (b) and the copolymerizable monomer (c) can be substituted in the range of 30% by weight or less, preferably 25% by weight or less based on the total monomers. Examples of these monomers (c) include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid, and sulfonic acid group-containing monomers such as 2-acrylamido-2-methylpropanesulfonic acid. Monomers, phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate, 2-hydroxypropyl acryloyl phosphate, (meth) acrylamide, N-substituted (meth) acrylamide, 3-acryloyloxypropyl amide, 4-acryloyloxy Butylamide, 5-acryloyloxyhexylamide, amide-based monomers such as N-vinylpyrrolidone, vinyl-based monomers such as vinyl acetate, styrene and α-methylstyrene, glycidyl (meth) acrylate, fluorine-containing (meth ) Acrylate, Silicon-containing (meth) acrylate Other (meth) acrylic ester monomers such bets, and the like. In some cases, a monomer copolymerizable with the monomers (a) and (b) and capable of introducing an unsaturated bond into the copolymerized prepolymer is also included, and a polyfunctional (meth) acrylate or the like is also required. Used accordingly. For example, it may be a cross-linking point when post-cross-linking is desired to be performed under a non-cross-linking agent by an electron beam or the like. Examples of such crosslinking agents include hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and neopentyl glycol di (meth) acrylate. Pentaerythritol di (meth) acrylate, trimethylolpropane di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, other epoxy acrylates, polyester acrylates, urethane acrylates, and the like.

The acrylic copolymer prepolymer used in the present invention contains the above-mentioned monomer (a) and monomer (b) as essential components, and further contains the monomer (c) if necessary. It is obtained by copolymerization, and its polymerization method is not particularly limited. A known polymerization method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method or a suspension polymerization method can be adopted, and in the bulk polymerization method which is a solventless polymerization method, polymerization by irradiation with radiation such as ultraviolet rays must be adopted. You can also As the polymerization initiator in each of the above polymerization methods, an azo-based or peroxide-based thermal polymerization initiator, an acetone phenone-based, benzoin ether-based, or ketal-based photopolymerization initiator can be used. Specific examples of these include benzoyl peroxide, azobisisobutyronitrile, tert-butyl perbenzoate, cumene hydroxyperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate as thermal polymerization initiators. , Di (2-ethoxyethyl) peroxydicarbonate, tert-butylperoxydecanoate, ter
Examples thereof include t-butyl peroxybibalate, di (3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, dipropionyl peroxide, diacetyl peroxide, ammonium or potassium persulfate, and the like. Examples of the photopolymerization initiator include 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, methoxyacetophenone, α-hydroxy-α, α′-dimethylacetophenone, Examples include acetophenone initiators such as 2-dimethoxy-2-phenylacetophenone, benzoin ether initiators such as benzoin ethyl ether and benzoin isopropyl ether, and other halogenated ketones, acylphosphinoxides, acylphosphonates, and the like. Can be.

In the polymerization, the acrylic copolymer prepolymer used in the present invention can be prepared by using an appropriate amount of a chain transfer agent in order to obtain a desired molecular weight. The chain transfer agent to be used is not particularly limited, and an appropriate one can be selected, and a mercaptan-based one is most commonly used. The weight average molecular weight of the prepolymer is adjusted to 5,000 to 300,000. If it is 300,000 or more, the effect of reducing the organic solvent at the time of solution coating, which is one of the objects of the present invention, is small, and if it is 5,000 or less, the molecular weight is too low, and it is necessary for increasing the molecular weight for forming an adhesive. Chain extension becomes difficult. The acrylic copolymer prepolymer thus obtained has an active hydroxyl group based on the monomer (b) in the molecule. As the amount of hydroxyl groups in the molecule, the above-mentioned monomers (a) and (b),
It is desirable to have an average of 0.5 to 10, preferably 0.5 to 5, in one molecule, together with the quantitative relationship including (c) in some cases. If the amount of the hydroxyl groups is out of the range of 0.5 to 10 on average, it is difficult to obtain the best high molecular weight, which is not desirable.

The pressure-sensitive adhesive composition of the present invention can be obtained by blending the acrylic copolymer prepolymer with a polyfunctional isocyanate mainly containing difunctional as a chain extender. The polyfunctional isocyanate reacts with the active hydroxyl group of the prepolymer to extend the chain, thereby giving a polymer which is desirable as an adhesive. The polyfunctional isocyanate that can be used in the present invention includes aromatic, alicyclic and aliphatic isocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 4,4'-methylene dibiphenyl diisocyanate, polymethylene polyphenylene diisocyanate, xylene diisocyanate, xylylene diisocyanate, methylene dicyclohexyl diisocyanate, hexamethylene diisocyanate,
4,4 ', 4 "-triphenylene methane triisocyanate, or trimerized and polymerized isocyanate such as an adduct of trimethylolpropane and toluene diisocyanate or hexamethylene diisocyanate, and liberating an isocyanate group by heating. For example, a so-called blocked polyisocyanate such as a reaction product of polyisocyanate with phenol or cresol may be mentioned, and one kind or two or more kinds may be used in combination.

The proportion of these polyfunctional isocyanates is preferably such that the isocyanate group is 0.1 to 10 equivalents relative to 1 active hydroxyl group of the copolymerization prepolymer. When the amount of isocyanate groups is 0.1 equivalent or less, it becomes difficult to secure the chain extension efficiency or the required gel amount when the amount of hydroxyl groups introduced into the copolymerized prepolymer is small. On the other hand, if the amount is more than 10 equivalents, the isocyanate group becomes excessive. In this case, too, the efficiency of chain elongation is lowered, and it becomes difficult to obtain good pressure-sensitive adhesive properties. In the pressure-sensitive adhesive composition of the present invention, an external cross-linking agent as an additional cross-linking treatment for improving cohesion, for example, additional use of a polyfunctional isocyanate, a melamine resin, an epoxy resin, an aziridine compound, a peroxide, a metal chelate, etc. Can be blended. In the pressure-sensitive adhesive composition of the present invention, further, if necessary, various fillers such as natural or synthetic resins, oils and fats, surfactants, glass fibers, glass beads, metal powders, inorganic powders, pigments, dyes, etc. It is also possible to mix the various additives in the range of 200 parts by weight or less with respect to 100 parts by weight of the copolymerization prepolymer.

Further, the present invention relates to a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer obtained from the above-mentioned pressure-sensitive adhesive composition formed on one surface or both surfaces of a support. The pressure-sensitive adhesive composition of the present invention includes various plastic films and sheets, paper,
On one or both sides of a support made of woven cloth, non-woven cloth, foam film or sheet, metal foil, or a laminate of these, 5 to
A pressure-sensitive adhesive sheet such as a pressure-sensitive adhesive tape or a pressure-sensitive adhesive sheet can be formed into a layer with a thickness of about 2000 μm.
The pressure-sensitive adhesive sheets of the present invention may be formed by forming a film of a known release agent such as a silicone-based resin, a fluorine-based resin, or a long-chain alkyl-based resin on the back surface of the support, winding the film into a roll shape, or forming the formed pressure-sensitive adhesive. The exposed surface of the agent layer may be covered with a separator having a known release agent film formed thereon.

[0019]

The pressure-sensitive adhesive composition of the present invention comprises an acrylic copolymer prepolymer having a highly reactive hydroxyl group in the molecule and having a weight average molecular weight of 5,000 to 300,000, which is mainly bifunctional as a chain extender. A polyfunctional isocyanate is added as an essential component to avoid the steric hindrance of the side chain of the prepolymer which affects the reactivity of the hydroxyl group contained in the prepolymer, and ensures the original reactivity of the hydroxyl group. By doing so, a relatively low molecular weight prepolymer can be efficiently chain-extended to form a high molecular weight compound, and thus a pressure-sensitive adhesive composition with a small amount of organic solvent used, that is, a high concentration can be provided. In addition, highly reliable pressure-sensitive adhesive sheets exhibiting good pressure-sensitive adhesive properties can be provided from this pressure-sensitive adhesive composition.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The production examples, examples, and
The present invention will be described more specifically with reference to Comparative Examples, but the present invention is not limited to these, and various modifications can be made without departing from the technical idea of the present invention. In the text, “parts” means “parts by weight”. The test items in Examples and Comparative Examples were measured by the following test methods. [Adhesive force] The prepared pressure-sensitive adhesive sheet was cut into a tape having a width of 20 mm, adhered to a stainless steel plate (SUS-304) polished with a sandpaper (# 280), reciprocated with a 2 kg rubber roll once, and left for 30 minutes. After the adhesive tape was folded at 180 ° against the stainless steel plate, the adhesive tape was peeled off at a speed of 300 mm / min, and the peeling force at this time was measured (JIS).
-C-2107). [Cohesive power] A 10 mm × 20 mm adhesive tape sample was attached on a Bakelite plate so that the attachment area would be 10 mm × 10 mm, and a weight of 500 g was dropped on the other end to 40 ° C.
And the amount of shift (shift distance m per hour)
m) was measured.

Production Example 1 300 parts of n-butyl acrylate (BA) and 6-hydroxyhexyl acrylate (HHA) 2.085 were placed in a reaction vessel equipped with a cooling tube, a nitrogen introducing tube and a stirrer.
Part, lauryl mercaptan (LSH) as chain transfer agent
0.580 parts, 0.3 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator and 200 parts of ethyl acetate were added, and the mixture was polymerized at 60 ° C. for 4 hours and then at 70 ° C. for 2 hours to give a polymerization rate of 99. % Acrylic acid-containing prepolymer solution containing hydroxyl groups was obtained. This solution has a viscosity of 130 poise at 25 ° C., and is a high-concentration solution containing 62.8% by weight of an acrylic copolymer prepolymer as a solid content after drying at 120 ° C. for 2 hours. GPC of this copolymerized prepolymer
The weight average molecular weight in terms of styrene by gel permeation chromatography was 189,000, and the number average molecular weight was 636,000. When calculated from this number average molecular weight, this copolymerized prepolymer has an average of 2.55 hydroxyl groups per molecule.

Production Example 2 Polymerization was conducted in the same manner as in Production Example 1 except that 1.406 parts of 2-hydroxyethyl acrylate (HEA) was added to the same reaction vessel as in Production Example 1 instead of HHA, and the polymerization rate was changed. 99
% Of a hydroxyl group-containing acrylic copolymer prepolymer solution was obtained. The properties of this solution and the acrylic copolymer prepolymer were almost the same as in Production Example 1. However, this acrylic copolymer prepolymer does not satisfy the relationship of m ≧ n−1 since the mutual relationship between the monomers (a) and (b) is n = 4 and m = 2. .

Production Examples 3 to 5 Polymerization was conducted in the same manner as in Example 1 except that the amounts of HHA and LSH were changed in the same reaction vessel as in Production Example 1 to give hydroxyl groups having different properties as shown in Table 1. An acrylic copolymer prepolymer solution containing was obtained.

[0024]

[Table 1]

Production Example 6 300 parts of 2-ethylhexyl acrylate (2-EHA), 1.450 parts of 6-hydroxyhexyl acrylate (HHA), 0.403 parts of lauryl mercaptan (LSH) were placed in the same reaction vessel as in the production example. , Azobisisobutyronitrile (AIBN) 0.3 parts and ethyl acetate 20
0 part was added, and the mixture was polymerized at 60 ° C. for 4 hours and then at 70 ° C. for 2 hours to obtain a hydroxyl group-containing acrylic copolymer prepolymer solution having a polymerization rate of 98.5%. This solution is 1
A highly concentrated solution having a viscosity of 35 poise and containing 62.5% by weight of an acrylic copolymer prepolymer as a solid content after drying at 120 ° C. for 2 hours. The weight average molecular weight of this copolymerized prepolymer in terms of styrene by GPC was 18.
It was 50,000 and the number average molecular weight was 60,000. When calculated from this number average molecular weight, this copolymerized prepolymer has an average of 1.7 hydroxyl groups per molecule.

Example 1 0.315 parts of 4,4'-diphenylmethane diisocyanate (MDI) based on 100 parts of the acrylic copolymer prepolymer solution obtained in Production Example 1 (equivalent to the hydroxyl groups of the prepolymer) (Relationship) was added to obtain a solution of the pressure-sensitive adhesive composition. This solution was applied on a polyester film having a thickness of 25 μm and dried at 120 ° C. for 5 minutes to prepare an adhesive sheet having an adhesive layer having a thickness of 50 μm. The adhesive strength of this pressure-sensitive adhesive sheet was 650 g / 20 mm, and the cohesive strength was 0.2 mm / hour or less.

Comparative Example 1 0.315 parts of 4,4'-diphenylmethane diisocyanate (MDI) per 100 parts of the acrylic copolymer prepolymer solution obtained in Preparation Example 2 (equivalent to the hydroxyl groups of the prepolymer) (Relationship) was added to obtain a solution of the pressure-sensitive adhesive composition. As described in Production Example 2, this copolymerized prepolymer does not satisfy the relationship of m ≧ n−1. Therefore, this solution was applied onto a polyester film having a thickness of 25 μm and dried at 120 ° C. for 5 minutes to prepare a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a thickness of 50 μm. However, the polymerization of the prepolymer was insufficient. The physical properties could not be evaluated. Further aging was carried out at 50 ° C. for 3 days, and the physical properties were evaluated.

Examples 2 to 5 For each 100 parts of the acrylic copolymer prepolymer solution obtained in Production Examples 3 to 6, as shown in Table 2, 4,4
A predetermined number of parts of'-diphenylmethane diisocyanate (MDI) was added so as to have an equivalence relationship with the hydroxyl group of each prepolymer to obtain a solution of the pressure-sensitive adhesive composition. For each of these solutions, a pressure-sensitive adhesive sheet was prepared in the same manner as in Example 1, and the results of tests of the adhesive force and the cohesive force were performed. Table 2 shows the results.

[0029]

[Table 2]

Example 6 To 100 parts of the acrylic copolymer prepolymer solution obtained in Production Example 5, a trimethylolpropane-tolylene diisocyanate adduct (manufactured by Nippon Polyurethane Company, trade name Coronate L, NCO content: 13. 8%), as shown in Table 3, with respect to the hydroxyl group of the copolymerization prepolymer,
An appropriate amount was added as in 3 to obtain a solution of the pressure-sensitive adhesive composition. This solution was applied on a polyester film and dried in the same manner as in Example 1 to produce an adhesive sheet. The gel fractions of the adhesive layers after drying were all about 100%. When the adhesive strength was measured in the same manner as in Example 1, as shown in Table 3, good low adhesive strength for re-peeling was shown. The above-mentioned gel fraction means that at room temperature, the pressure-sensitive adhesive layer is placed in a bag made of a fluororesin film having a pore size of 0.1 μm and immersed in ethyl acetate having a strong dissolving power for 1 week,
The dissolved content was determined from the residual amount after extraction, and is shown by the ratio of the undissolved adhesive (residual content) to the original adhesive. For re-peeling, the gel fraction is preferably 60% or more.

[0031]

[Table 3]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhide Kojima 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (6)

[Claims] 1. An acrylic copolymer having a weight average molecular weight of 5,000 to 300,000, which has a highly reactive hydroxyl group in the molecule and is obtained by copolymerizing the following monomers (a) and (b) as essential components. A pressure-sensitive adhesive composition comprising a polymerized prepolymer and a polyfunctional isocyanate mainly composed of difunctional as a chain extender. (A) General formula; CH ₂ ═CH (R ₁ ) COOR ₂ (R ₁
Is hydrogen or a methyl group, and R ₂ is an alkyl group having 2 to 14 carbon atoms). 75-99.
95% by weight (b) General formula; CH ₂ = CH (R ₁ ) COOR ₃ (R ₁
Is a hydrogen or methyl group, and R ₃ is a C 3-14 monovalent alkyl group having at least one hydroxyl group). 0.05 to 25% by weight (however, the monomers (a) and (b) used are based on the ester bond part, based on the order number n of the carbon position at the longest tip of the alkyl chain of (a)). Then, the rank number m of the carbon position of the alkyl chain to which the hydroxyl group at the longest tip in (b) is bonded is m
It is assumed that the relationship of ≧ n−1 is satisfied. ) 2. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic copolymer prepolymer has an average of 0.5 to 10 highly reactive hydroxyl groups in one molecule. 3. The pressure-sensitive adhesive composition according to claim 1, wherein the polyfunctional isocyanate is blended so that the isocyanate group is 0.1 to 10 equivalents to 1 equivalent of the hydroxyl group of the acrylic copolymer prepolymer. 4. The acrylic copolymerized prepolymer is prepared by copolymerizing other copolymerizable monomers in addition to the monomers (a) and (b) in a range of 30% by weight or less of all monomers. The pressure-sensitive adhesive composition according to claim 1, which is obtained by the above method. 5. The pressure-sensitive adhesive component containing an acrylic copolymer prepolymer and a polyfunctional isocyanate is dissolved in an organic solvent, and the pressure-sensitive adhesive component can be provided at a high concentration of 40 to 90% by weight. Adhesive composition. 6. A pressure-sensitive adhesive sheet comprising a support, on one or both sides of which a pressure-sensitive adhesive layer obtained from the pressure-sensitive adhesive composition according to claim 1 is formed.