JP2016222741A - Adhesive composition and re-peelable adhesive double-sided tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition capable of being suitably used for a re-peelable adhesive double-sided tape excellent in adhesiveness and retention power, good in stain into nonwoven core material, especially nonwoven core material with high basis weight, and capable of being peeled without contaminating an adherend when peeling.SOLUTION: There is provided an adhesive composition containing a vinylester (meth)acrylic acid alkylester copolymer (A) obtained by copolymerizing a (meth)acrylic acid alkylester monomer (a1), a (meth)acrylate monomer having a hydroxyl group (a2), vinyl acetate (a3) and a maleic acid ester monomer (a4) and an isocyanate crosslinking agent (B) having two or more isocyanate groups and having an acid value of the vinylester (meth)acrylic acid alkylester copolymer (A) of less than 1 mgKOH/g and weight average molecular weight of 150,000 to 500,000.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive composition and a re-peelable double-sided adhesive tape using the same.

  Double-sided tape is used in various fields such as daily necessities to fixing industrial parts. As market needs, there is a great demand for those having excellent adhesive strength, little change in adhesive strength with time, and good removability. Normally, strong adhesiveness is imparted by introducing a large amount of acid into the adhesive, but when such a strong adhesive adhesive is adhered to a polar adherend such as metal, the adhesive strength increases over time. However, there is a problem that adhesive residue is easily left during peeling.

  On the other hand, a nonwoven fabric is generally used for the core material of the double-sided tape. For double-sided tapes that require strong adhesiveness, a nonwoven fabric core material with high mechanical strength is used. However, since the nonwoven fabric core material with high mechanical strength usually has a large basis weight and poor penetration of the pressure-sensitive adhesive, when peeled, the breakage occurs between the core layers where the pressure-sensitive adhesive has not sufficiently penetrated. As a result, there was a problem that good removability could not be obtained.

  For example, Patent Document 1 proposes a releasable pressure-sensitive adhesive tape in which a pressure-sensitive adhesive layer mainly comprising a (meth) acrylic resin composition containing substantially no carboxyl group is provided on a base film. . Patent Document 2 discloses an acrylic resin and a crosslinking agent obtained by polymerizing a (meth) acrylic acid alkyl ester monomer and a monomer having a functional group other than an acidic group in the presence of a functional group-containing polymerization initiator. Containing pressure-sensitive adhesive compositions have been proposed.

JP 2009-209223 A JP 2011-202125 A

  However, when the present inventors examined the removable adhesive tape described in Patent Document 1, it was found that the adhesive strength was insufficient. Moreover, when the pressure-sensitive adhesive composition described in Patent Document 2 was also examined, it was found that although a certain level of pressure-sensitive adhesive force was obtained, the pressure-sensitive adhesive holding power was insufficient.

  Accordingly, the present invention has been made to solve the above-described problems, and has excellent adhesive strength and holding power, good penetration into a nonwoven fabric core material, particularly a high basis weight nonwoven fabric core material, and release. It is an object of the present invention to provide a pressure-sensitive adhesive composition that can be suitably used for a re-peelable double-sided adhesive tape that can be peeled without contaminating the adherend.

Therefore, as a result of intensive studies to solve the above problems, the present inventors have obtained a copolymer obtained by copolymerizing a specific monomer component, having a hydroxyl group and substantially having a carboxyl group. The pressure-sensitive adhesive composition comprising a copolymer having a weight average molecular weight of 150,000 to 500,000 and an isocyanate crosslinking agent having two or more isocyanato groups can be found to solve the above-mentioned problems. It came to complete.
That is, this invention is shown by the following [1]-[8].
[1] Vinyl ester obtained by copolymerizing (meth) acrylic acid alkyl ester monomer (a1), (meth) acrylate monomer (a2) having hydroxyl group, vinyl acetate (a3) and maleic acid ester monomer (a4) A pressure-sensitive adhesive composition comprising a (meth) acrylic acid alkyl ester copolymer (A) and an isocyanate crosslinking agent (B) having two or more isocyanate groups,
The pressure-sensitive adhesive composition, wherein the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) has an acid value of less than 1 mgKOH / g and a weight average molecular weight of 150,000 to 500,000.
[2] In the above [1], the (meth) acrylate monomer (a2) having a hydroxyl group is at least one selected from the group consisting of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The pressure-sensitive adhesive composition described.
[3] The vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) is 40% by mass to 99.7% by mass of (meth) acrylic acid alkyl ester monomer (a1), 0.1% by mass to (Meth) acrylate monomer (a2) having 30% by mass of hydroxyl group, 0.1% by mass to 50% by mass of vinyl acetate (a3) and 0.1% by mass to 30% by mass of maleate ester monomer (a4) The pressure-sensitive adhesive composition according to [1] or [2], which is obtained by copolymerization.
[4] The isocyanate crosslinker (B) is included in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A). 1]-[3] The adhesive composition in any one of.
[5] A pressure-sensitive adhesive composition for a releasable pressure-sensitive adhesive tape, comprising the pressure-sensitive adhesive composition according to any one of [1] to [4].
[6] A releasable pressure-sensitive adhesive tape, wherein a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition for a releasable pressure-sensitive adhesive tape according to [5] is formed on at least one surface of a nonwoven fabric core material. .
[7] A releasable pressure-sensitive adhesive double-sided tape, wherein a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition for re-peelable pressure-sensitive adhesive tape according to [5] is formed on both surfaces of a nonwoven fabric core material.
[8] The basis weight of the nonwoven core ^material, the removable pressure-sensitive double-sided tape according to characterized in that it is a ^{10g / m 2 ~30g / m 2} [7].

  According to the present invention, the adhesive strength and holding power are excellent, the penetration into a nonwoven fabric core material, in particular, a high basis weight nonwoven fabric core material is good, and it is possible to peel the substrate without contaminating the adherend. An adhesive composition that can be suitably used for a peelable double-sided adhesive tape can be provided.

The present invention is described in detail below.
The pressure-sensitive adhesive composition of the present invention comprises a vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) having an acid value of less than 1 mgKOH / g and an isocyanate crosslinking agent (B) as main components. . In the present invention, (meth) acryl means methacryl or acryl.

  The vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) comprises a (meth) acrylic acid alkyl ester monomer (a1), a (meth) acrylate monomer (a2) having a hydroxyl group, vinyl acetate (a3), And a maleic ester monomer (a4). In the present invention, (meth) acrylate means acrylate or methacrylate.

  The (meth) acrylic acid alkyl ester monomer (a1) is an alkyl ester of (meth) acrylic acid containing no hydroxyl group, and the alkyl group usually has 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms. More preferably 1-8, most preferably 4-8. Specific examples of the (meth) acrylic acid alkyl ester monomer (a1) include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meta ) Acrylate, n-propyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, cetyl (meth) ) Acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate and the like. These monomers can be used alone or in combination of two or more.

  Among the (meth) acrylic acid alkyl ester monomers (a1), n-butyl (meth) acrylate and 2-ethylhexyl (meth) acrylate are copolymerizable, adhesive properties, easy handling and easy availability of raw materials. And methyl methacrylate are preferable, and n-butyl (meth) acrylate and methyl methacrylate are more preferable in terms of excellent heat resistance.

  The (meth) acrylate monomer (a2) having a hydroxyl group is a monomer having a hydroxyl group and an acryloyl group. For example, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) Acrylic acid hydroxyalkyl esters such as acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, diethylene glycol (meth) acrylate, polyethylene Oxyalkylene-modified monomers such as glycol (meth) acrylate, 2-acryloyloxyethyl 2-hydroxyethylphthalic acid, N-methylol (meth) acrylic Primary hydroxyl group-containing monomers such as amide, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 3-chloro 2-hydroxypropyl (meth) acrylate Secondary hydroxyl group-containing monomers such as 2-hydroxy-3-phenoxypropyl (meth) acrylate, and tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth) acrylate. These monomers can be used alone or in combination of two or more.

  Among the (meth) acrylate monomers (a2) having a hydroxyl group, a primary hydroxyl group-containing monomer is preferable because it is excellent in reactivity with a crosslinking agent, and there are few impurities, and 2-hydroxyethyl (meta) is easy to manufacture. ) Acrylate is more preferred.

  Specific examples of the maleate monomer (a4) include dimethyl maleate, diethyl maleate, diisopropyl maleate, dibutyl maleate, di-2-ethylhexyl maleate, diallyl maleate, monomethyl maleate, monoethyl maleate, maleic acid Examples thereof include monobutyl and mono-2-ethylhexyl maleate. These monomers can be used alone or in combination of two or more.

  Among the maleic acid ester monomers (a4), dimethyl maleate, diethyl maleate, dibutyl maleate, di-2-ethylhexyl maleate and diallyl maleate are preferable in terms of reactivity and pressure-sensitive adhesive properties. From the viewpoint of releasability, di-2-ethylhexyl maleate is more preferable.

  The vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) includes 40% by mass to 99.7% by mass of the monomer (a1), 0.1% by mass to 30% by mass of the monomer (a2), It is preferable that 0.1% by mass to 50% by mass of vinyl acetate (a3) and 0.1% by mass to 30% by mass of monomer (a4) are copolymerized, and 50% by mass to 90% by mass. % Monomer (a1), 0.2% to 20% by weight monomer (a2), 0.2% to 40% by weight vinyl acetate (a3), and 0.2% to 20% by weight. More preferably, the monomer (a4) is copolymerized with 50% by mass to 80% by mass of the monomer (a1), 0.3% by mass to 10% by mass of the monomer (a2), and 0% by mass. .2% to 35% by weight of vinyl acetate (a3) and 0.2 It is still more preferable that the monomer (a4) is copolymerized in an amount of from 10% to 10% by weight, the monomer (a1) from 55% to 70% by weight, and the monomer from 0.4% to 5% by weight. Most preferably, (a2), 10% by mass to 35% by mass vinyl acetate (a3) and 5% by mass to 10% by mass monomer (a4) are copolymerized.

When the amount of the (meth) acrylic acid alkyl ester monomer (a1) used is 99.7% by mass or less, the cohesive strength of the copolymer is improved, and better removability can be obtained. On the other hand, when the amount of the (meth) acrylic acid alkyl ester monomer (a1) used is 40% by mass or more, the cohesive strength of the copolymer becomes appropriate, and the decrease in adhesive strength is small.
If the usage-amount of the (meth) acrylate monomer (a2) which has a hydroxyl group is 30 mass% or less, the penetration property to a core material will become suitable, and more favorable removability can be obtained. On the other hand, when the amount of the (meth) acrylate monomer (a2) having a hydroxyl group is 0.1% by mass or more, the introduction amount of the hydroxyl group becomes appropriate, and a sufficient crosslinking point is secured. Can be obtained.
If the usage-amount of vinyl acetate (a3) is 50 mass% or less, the penetration property to a core material becomes appropriate, and more favorable removability can be obtained. On the other hand, if the usage-amount of vinyl acetate (a3) is 0.1 mass% or more, the cohesive force of a copolymer will improve and better removability can be obtained.
When the amount of the maleic ester monomer (a4) used is 30% by mass or less, the cohesive strength of the copolymer becomes appropriate and the decrease in adhesive strength is small. On the other hand, when the amount of the maleic ester monomer (a4) used is 0.1% by mass or more, the cohesive strength of the copolymer is improved, and better removability can be obtained.

The vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) contains substantially no carboxyl group, that is, has an acid value of less than 1 mgKOH / g. The vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) preferably contains no carboxyl group.
In the present invention, the acid value of the copolymer (A) is a value measured according to JIS K0070, and is measured, for example, as follows.
About 2 g of a sample is precisely weighed into a 100 ml Erlenmeyer flask with a precision balance, and 10 ml of a mixed solvent of ethanol / diethyl ether = 1/1 (mass ratio) is added and dissolved therein. Further, 1 to 3 drops of phenolphthalein ethanol solution is added to this container as an indicator, and the mixture is sufficiently stirred until the sample becomes uniform. This is titrated with a 0.1N potassium hydroxide-ethanol solution, and the end point of neutralization is taken when the indicator is light red for 30 seconds. The value obtained from the result using the following formula (1) is defined as the acid value of the resin.
Acid value (mgKOH / g) = [B × f × 5.611] / S (1)
In the calculation formula (1), B is the amount of 0.1N potassium hydroxide-ethanol solution used (ml), f is the factor of 0.1N potassium hydroxide-ethanol solution, and S is the sample The amount collected (g).

  The weight average molecular weight of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) needs to be 150,000 to 500,000, preferably 200,000 to 400,000. When the weight average molecular weight is less than 150,000, excellent holding power cannot be obtained. On the other hand, when the weight average molecular weight exceeds 500,000, the penetrability into the core material is lowered and good removability is obtained. Absent.

In the present invention, the weight average molecular weight of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) is determined by gel permeation chromatography (“Showex (trademark) GPC SYSTEM- manufactured by Showa Denko KK). 11 ”, column: Shodex (trademark) GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical plate number: 10,000 plates / line, packing material: average particle Styrene-divinylbenzene copolymer having a diameter of 10 μm), sample: 0.5% by mass tetrahydrofuran solution of copolymer, developing solvent: tetrahydrofuran, column temperature: 40 ° C., flow rate: 2 mL / min. It is a weight average molecular weight in terms of standard polystyrene molecular weight.

  The copolymerization reaction for obtaining the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) is not particularly limited, and a normal radical polymerization method can be applied. For example, a monomer in which a polymerization initiator such as 2,2′-azobis (isobutyronitrile) or benzoyl peroxide is dissolved in the monomer (a1), the monomer (a2), the vinyl acetate (a3) and the monomer (a4) By dropping into an organic solvent and polymerizing at 60 to 100 ° C. for 2 to 10 hours, an organic solvent solution of the copolymer comprising (a1) to (a4) is obtained. The amount of the polymerization initiator used is usually 0.01 parts by weight to 1.0 parts by weight, preferably 0.05 parts by weight to 0.5 parts by weight with respect to 100 parts by weight as the total amount of (a1) to (a4). Part by mass.

  Examples of the organic solvent used for polymerization include ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate and ethyl acetoacetate, aromatic hydrocarbons such as toluene and xylene, n-propyl alcohol, and iso-propyl alcohol. And aliphatic alcohols such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These organic solvents can be used alone or in combination of two or more. Among these organic solvents, ethyl acetate is preferable in terms of solubility, drying properties, environmental aspects, price, and the like.

  By mixing the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) thus obtained with the isocyanate crosslinking agent (B), the pressure-sensitive adhesive composition of the present invention is obtained. Although the crosslinking reaction starts after mixing, it takes some time for crosslinking to proceed sufficiently at room temperature.

  The isocyanate crosslinking agent (B) is a compound having two or more isocyanato groups capable of reacting with a hydroxyl group in one molecule. Specific examples of the isocyanate crosslinking agent (B) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, Hexamethylene diisocyanate, diphenylmethane-4,4-diisocyanate, isophorone diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, and their poly Examples include adducts of isocyanate compounds and polyol compounds such as trimethylolpropane, burettes and isocyanurates of these polyisocyanate compounds.

  Among the isocyanate crosslinking agents (B), 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and hexamethylene diisocyanate are preferable in terms of reactivity, and 2,4-tolylene diisocyanate in terms of pressure-sensitive adhesive properties. 2,6-tolylene diisocyanate is more preferred.

  The amount of the isocyanate crosslinking agent (B) used is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A). More preferably, it is 5 to 5 parts by mass, and most preferably 1.0 to 2.5 parts by mass. If the amount of the isocyanate crosslinking agent (B) used is 0.1 parts by mass or more with respect to 100 parts by mass of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A), the holding power becomes sufficient and better Heat resistance and removability can be obtained. On the other hand, if the amount of the isocyanate crosslinking agent (B) used is 10 parts by mass or less with respect to 100 parts by mass of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A), the flexibility of the resin is ensured, Impregnation into the core material is improved and better removability can be obtained.

The pressure-sensitive adhesive composition of the present invention usually preferably contains 40% by mass to 99.9% by mass of a nonvolatile content.
In the present invention, the non-volatile content is a value calculated from the following formula by weighing about 1 g of the pressure-sensitive adhesive composition on an aluminum dish having a diameter of 5 cm and then drying the residue at 110 ° C. for 5 hours and weighing the residue. It is. The volatile matter here is ethyl acetate or the like.
Nonvolatile content (mass%) = (mass of residual) / (initial mass) × 100

  In addition, the pressure-sensitive adhesive composition of the present invention includes an antistatic agent, other acrylic pressure-sensitive adhesives, rosin, rosin ester, hydrogenated rosin ester, aromatic modified terpene resin, phenol as long as the effects of the present invention are not impaired. Various additives such as tackifiers such as resins, xylene resins, styrene resins, coumarone resins, aliphatic petroleum resins, alicyclic petroleum resins, coloring agents, fillers, anti-aging agents, and UV absorbers are added. May be.

The nonwoven fabric core material for applying the pressure-sensitive adhesive composition of the present invention to provide a pressure-sensitive adhesive layer includes wet nonwoven fabrics using fibers such as rayon, pulp, hemp, and vinylon, polyesters that are long fibers, polypropylene, polyethylene, and nylon. Examples thereof include dry nonwoven fabrics, spunbonds, needle punches, water punches, and spunlaces that mainly use synthetic resin fibers such as. The nonwoven fabric core material may be composed of one type of fiber, or may be composed of two or more types of fibers. The basis weight of the nonwoven core material, ensures sufficient strength, in terms of suppressing the interlaminar ^fracture, it is ^{preferably, 12g / m 2 ~28g / m} 2 is a 10g / ^{m 2} ~30g / m 2 it is more ^preferable, and most preferably ^{14g / m 2 ~26g / m 2} . Moreover, the thickness of the nonwoven fabric core is appropriately set in the range of 15 μm to 125 μm depending on the application.

  As a method for forming the pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition of the present invention, a direct method in which the pressure-sensitive adhesive composition is directly coated on a nonwoven fabric core and dried, paper that has been subjected to mold release treatment with silicone or the like Or, after coating the pressure-sensitive adhesive composition on a release material such as a plastic film, after forming a pressure-sensitive adhesive layer by cross-linking by drying, and then pressurizing the nonwoven fabric core material on the pressure-sensitive adhesive layer, Examples thereof include a transfer method in which the pressure-sensitive adhesive layer is transferred onto the nonwoven fabric core material. After forming the pressure-sensitive adhesive layer on both surfaces of the nonwoven fabric core material, an aging treatment may be performed as necessary.

  As a coating method, if it is a general coating method, it will not specifically limit, For example, the method of using roll coating, die coating, gravure coating, comma coating, screen printing etc. is mentioned.

  Furthermore, as said mold release material, what performed the mold release process to various synthetic resin sheets, paper, cloth, a nonwoven fabric, etc. can be used, for example.

  As drying conditions after coating, it is only necessary that the pressure-sensitive adhesive composition can be dried and cross-linked. For example, the drying condition is 50 to 150 ° C. for 1 to 5 minutes.

  The aging treatment is performed in order to balance the physical properties of the adhesive. The aging conditions are usually from room temperature (25 ° C. ± 5 ° C.) to 70 ° C. for 1 day to 30 days. What is necessary is just to carry out on conditions, such as 1 day-20 days at 40 degreeC, or 1 day-7 days at 40 degreeC.

  The pressure-sensitive adhesive composition of the present invention can be used for a re-peelable pressure-sensitive adhesive tape, and is particularly suitable for a re-peelable pressure-sensitive adhesive double-sided tape. The thickness of the pressure-sensitive adhesive layer in the re-peelable pressure-sensitive adhesive tape or the re-peelable pressure-sensitive adhesive double-sided tape of the present invention is preferably 5 μm to 250 μm, more preferably 5 μm to 150 μm, and most preferably 5 μm to 100 μm. When the thickness of the pressure-sensitive adhesive layer is 5 μm or more, the physical properties of the pressure-sensitive adhesive are stabilized, and a better adhesive force can be obtained. On the other hand, if the thickness of the pressure-sensitive adhesive layer is 250 μm or less, the pressure-sensitive adhesive composition can be easily dried.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these.

<Synthesis Example 1>
In a reactor equipped with a thermometer, a stirrer, a dropping funnel and a reflux condenser, 170 parts by mass of ethyl acetate was charged and heated to 78 ° C. while stirring. Next, 176 parts by mass of 2-ethylhexyl acrylate, 4 parts by mass of 2-hydroxyethyl methacrylate, 93 parts by mass of vinyl acetate and 30 parts by mass of di-2-ethylhexyl maleate were added to 2,2′-azobis (isobutyronitrile) The mixture in which 0.6 part by mass was dissolved (may be abbreviated as AIBN) was dropped into the reactor over 2 hours. Further, during the polymerization, the polymerization catalyst solution in which 0.2 parts by mass of AIBN was dissolved in 10 parts by mass of ethyl acetate was successively added for 7 hours, diluted with ethyl acetate, cooled, and then discharged from the reactor. The ester / (meth) acrylic acid alkyl ester copolymer solution was taken out. The weight average molecular weight of the vinyl ester / (meth) acrylic acid alkyl ester copolymer was 360,000. The nonvolatile content of the vinyl ester / (meth) acrylic acid alkyl ester copolymer solution was 51% by mass. The acid value of the vinyl ester / (meth) acrylic acid alkyl ester copolymer is 0 mgKOH / g.

<Synthesis Examples 2-8>
A copolymer solution was obtained in the same manner as in Synthesis Example 1 with the components and blending amounts shown in Table 1. The nonvolatile content and weight average molecular weight of the obtained copolymer solution are also shown in Table 1. The acid value of the copolymer of Synthesis Example 3 is 1 mgKOH / g or more, but the other is 0 mgKOH / g.

<Examples 1-4 and Comparative Examples 1-5>
Next, 45% isocyanate cross-linking agent (Coronate (registered trademark) L-45E manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the copolymer solutions of Synthesis Examples 1 to 8 in the blending amounts shown in Table 2, and pressure-sensitive adhesive composition A product was prepared.

  Using the pressure-sensitive adhesive composition thus obtained, a double-sided tape was prepared according to the following method, and the characteristics were evaluated (initial adhesive strength, removability, holding power and ball tack). The results are shown in Tables 3 and 4.

<Characteristic evaluation>
The pressure-sensitive adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 5 were coated on a release paper so that the thickness after drying was 70 μm to 80 μm, and then dried at 105 ° C. for 3 minutes for crosslinking. It was. Next, the pressure-sensitive adhesive composition on the release paper was stacked on a rayon nonwoven fabric core (basis weight 14 g / m ² or 27 g / m ² ) and then pressure-bonded with a roll. This operation was also performed on the other side of the rayon nonwoven core. Thereafter, a 25 μm PET film was bonded to one side and cured at 40 ° C. for 3 days to obtain a double-sided tape having a rayon nonwoven fabric as a core material.

[Initial adhesive strength]
The obtained double-sided tape was bonded to a SUS304 polishing plate at 23 ° C. and 50% RH by reciprocating a 2 kg roller once and then peeled off at 300 mm / min in an atmosphere of 23 ° C. and 50% RH. The 180 degree peel strength (N / 10 mm) at the speed was measured.

[Removability]
The obtained double-sided tape was bonded to a SUS304 polishing plate by reciprocating a 2 kg roller at 23 ° C. and 50% RH and left in a constant temperature bath at 60 ° C. and 90% RH for 1 day, and then 23 ° C. , Left in an atmosphere of 50% RH for 1 hour, and peeled off at an angle of 90 ° at a peeling speed of 300 mm / min. The degree of contamination on the adherend surface was visually observed and evaluated according to the following criteria.
○: No contamination was observed CF: Adhesive residue was observed BF: Core material interlayer fracture was observed

[Retention force]
The obtained double-sided tape was affixed to a stainless steel plate so that the area was 25 mm × 25 mm, and a load of 1 kg was applied under the condition of 80 ° C., according to the holding power measurement method of JIS Z 0237, The falling time was measured, and the deviation after 24 hours was measured for those whose dropping time exceeded 24 hours.

[Ball tack]
In the obtained double-sided tape, J.M. Using a dow ball tack measuring machine, the ball number of the maximum diameter that stops on the test piece (adhesive surface) was measured at a test piece 25 mm × 100 mm and an angle of 30 degrees under the conditions of 23 ° C. and 50% RH. . It can be said that the larger the maximum diameter of the ball number, the greater the initial adhesion to the adherend.

  From the above results, when the appropriate amount of the isocyanate cross-linking agent was blended, the example products had excellent removability while having excellent adhesive strength. Furthermore, there was no problem with respect to the cohesive force without any deviation.

Claims (8)

(Meth) acrylic acid alkyl ester monomer (a1), vinyl ester (meth) obtained by copolymerizing (meth) acrylate monomer (a2), vinyl acetate (a3) and maleic acid ester monomer (a4) having a hydroxyl group An adhesive composition comprising an alkyl acrylate copolymer (A) and an isocyanate crosslinking agent (B) having two or more isocyanate groups,
The pressure-sensitive adhesive composition, wherein the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) has an acid value of less than 1 mgKOH / g and a weight average molecular weight of 150,000 to 500,000.   The pressure-sensitive adhesive according to claim 1, wherein the (meth) acrylate monomer (a2) having a hydroxyl group is at least one selected from the group consisting of 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. Agent composition.   The vinyl ester / (meth) acrylic acid alkyl ester copolymer (A) is 40% by mass to 99.7% by mass of (meth) acrylic acid alkyl ester monomer (a1), 0.1% by mass to 30% by mass. (Meth) acrylate monomer (a2) having a hydroxyl group of 0.1% by mass to 50% by mass of vinyl acetate (a3) and 0.1% by mass to 30% by mass of maleic ester monomer (a4) The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition is obtained.   The isocyanate cross-linking agent (B) is included in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester / (meth) acrylic acid alkyl ester copolymer (A). 4. The pressure-sensitive adhesive composition according to any one of 3.   It consists of the adhesive composition as described in any one of Claims 1-4, The adhesive composition for re-peelable adhesive tapes characterized by the above-mentioned.   A re-peelable pressure-sensitive adhesive tape, wherein a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition for re-peelable pressure-sensitive adhesive tape according to claim 5 is formed on at least one surface of a nonwoven fabric core material.   A re-peelable pressure-sensitive adhesive double-sided tape, wherein a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition for a re-peelable pressure-sensitive adhesive tape according to claim 5 is formed on both surfaces of a nonwoven fabric core material. The basis weight of the nonwoven fabric core material is 10 g / m ^{2 to} 30 g / m ² , The re-peelable double-sided adhesive tape according to claim 7.