JPH08143847A - Acrylic adhesive composition - Google Patents

Abstract

PURPOSE: To obtain an acrylic adhesive composition which has high adhesion to both high-polar substrate surfaces to be adhered and to low-polar substrate surface to be adhered with excellent cohesion. CONSTITUTION: This acrylic adhesive composition comprises an acrylic copolymer composed of a hydroxyl group-containing macromonomer and an alkyl (meth)acrylate, a tackifier resin and a polyisocyanate wherein the number- average molecular weight of the macromonomer is 3,000-20,000, the formulation rate of the macromonomer is 0.3-15.0wt.% based on the acrylic copolymer, the weight-average molecular weight of the acrylic copolymer is 200,000-1,500,000, the ratio of Mw/Mn (Mw is the weight-average molecular weight, Mn is the number-average molecular weight) is 2.0-4.0, the hydroxyl number (A) of the tackifier is 1.5-8.0, and the softening point number (B) is 4.5-6.5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an acrylic pressure-sensitive adhesive composition having high adhesiveness and cohesive strength.

[0002]

2. Description of the Related Art Conventionally, an adhesive processed product such as an adhesive tape or an adhesive sheet whose surface is processed with an adhesive has been widely used for applications such as building materials, home electric appliances, cushioning materials for automobiles, gap tapes and the like.

As a pressure-sensitive adhesive composition used for such an adhesive processed product, an acrylic pressure-sensitive adhesive composition is widely used because it is superior in weather resistance and solvent resistance as compared with a rubber-based pressure-sensitive adhesive composition. ing. In recent years, as the applications of these adhesive processed products have expanded, the required properties have tended to become more sophisticated.

[0004] For example, in home electric appliances and the like, it is necessary to stick an adhesive processed product to a curved surface of plastic or the like, and the adhesive force corresponding to this and the elasticity of the adhesive composition itself (hereinafter referred to as "curved surface adhesiveness") Is required. In addition, depending on the application, a load may occur perpendicularly to the end of the adhesive processed product attached to the plastic molded product, and the adhesiveness and elasticity of the adhesive composition itself (hereinafter "Constant load peel force") is required.

In order to satisfy the balance force between the curved surface adhesiveness of the pressure-sensitive adhesive composition, the adhesive force such as the constant force peeling force and the stress deformation followability, a polar monomer or a high cohesive force monomer is used in a large amount, Alternatively, some efforts have been made by increasing the addition amount of the tackifying resin or the curing agent amount.

[0006] The acrylic copolymer has a tackiness by itself and can be used as an adhesive without adding a tackifying resin, but for an adherend having a low polarity surface such as polyethylene or polypropylene. However, it was difficult to exhibit good adhesiveness by itself. In particular, when the copolymerization amount of the carboxyl group-containing monomer in the acrylic copolymer is increased for the purpose of improving the adhesive property to the polar surface of a metal plate or the like, the adhesive force to polyethylene or polypropylene is practically unacceptable. It is recognized that it will be lowered. Therefore, a tackifying resin is usually added in the same manner as other pressure-sensitive adhesives to improve the low-polar adherend adhesion.

However, the adhesive obtained by adding the tackifying resin to the acrylic copolymer improves the adhesive strength itself to the low-polar adherend at room temperature as desired, but particularly at low temperature. It had the drawback that the tack was significantly reduced.

[0008] In JP-A-3-281587, by setting the hydroxyl value of the resin acid esterified product as a tackifying resin to be contained to 50 to 100, peeling resistance and peeling resistance can be obtained without impairing adhesive properties such as cohesive force. A technique for producing an acrylic pressure-sensitive adhesive composition excellent in low-temperature tack is disclosed. However, although the above-mentioned technique improves the adhesiveness at low temperatures, it is not always satisfactory in terms of the adhesiveness to synthetic resin foams such as urethane foam and polyethylene foam and the cohesive force.

[0009]

SUMMARY OF THE INVENTION In view of the above, the present invention has an acrylic pressure-sensitive adhesive composition having a high adhesive force on both the high-polarity adherend surface and the low-polarity adherend surface and excellent cohesive force. The purpose is to provide.

[0010]

SUMMARY OF THE INVENTION The gist of the present invention is to provide an acrylic adhesive composition comprising an acrylic copolymer composed of a hydroxyl group-containing macromonomer and an alkyl (meth) acrylate, a tackifier resin, and a polyisocyanate compound. The number average molecular weight of the hydroxyl group-containing macromonomer is 3000 to 20,000, and the compounding ratio of the hydroxyl group-containing macromonomer is 0.3 to 15.0 with respect to the acrylic copolymer. % By weight, the acrylic copolymer has a weight average molecular weight (Mw) of 200,000 to 1.5 million, and the acrylic copolymer has a weight average molecular weight (Mw).
The ratio (Mw / Mn) of w) to the number average molecular weight (Mn) is
It is 2.0 to 4.0, the hydroxyl group index (A) of the tackifying resin is 1.5 to 8.0, and the softening point index (B) is 4.5 to 6.5. There is a place to do it.

The alkyl (meth) acrylate used in the present invention preferably has an alkyl group having 2 to 14 carbon atoms, more preferably 4 to 9 carbon atoms. Examples thereof include ethyl acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl acrylate, 2-ethylhexyl (meth) acrylate, isononyl acrylate,
Examples thereof include lauryl (meth) acrylate, which may be used alone or in combination of two or more kinds.

The hydroxyl group-containing macromonomer used in the present invention has a copolymerizable double bond at one end of the molecule, and has a copolymer of a hydroxyl group-containing monomer and a hydroxyl group-free monomer as the main chain. It is a thing. The terminal double bond group contained in the hydroxyl group-containing macromonomer,
Examples thereof include terminal double bond groups such as acryloyl group and methacryloyl group. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl acrylate, and 2-hydroxypropyl (meth) acrylate. Examples of the hydroxyl group-free monomer include styrene,
Examples thereof include monomers having a non-reactive side chain such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate.

The copolymerization ratio of the hydroxyl group-containing monomer in the hydroxyl group-containing macromonomer is preferably 5 to 30%. If it is less than 5%, the reaction with the crosslinking agent is lowered,
If it exceeds%, macromonomer synthesis becomes difficult. The number average molecular weight of the hydroxyl group-containing macromonomer is
It is 3000 to 20,000. If it is less than 3,000, the cohesive force is difficult to obtain, and if it exceeds 20,000, the solution viscosity of the acrylic copolymer increases and the productivity decreases, so the content is limited to the above range.

The mixing ratio of the hydroxyl group-containing macromonomer is 0.3 to 15.
0% by weight. If it is less than 0.3% by weight, cohesive force is difficult to obtain, and if it exceeds 15.0% by weight, cohesive force becomes too high and adhesiveness to uneven surface is difficult to be obtained, so that it is limited to the above range. It

Examples of the method for producing the hydroxyl group-containing macromonomer include solution polymerization, bulk polymerization, suspension polymerization and the like. Among them, solution polymerization is preferred. The hydroxyl group-containing macromonomer is charged in a reactor together with a polymerization initiator and a carboxyl group-containing chain transfer agent, polymerized in an inert gas atmosphere, and then charged with an acid-reactive monomer such as glycidyl (meth) acrylate, and then the terminal. It is obtained by adding a double bond group. Examples of the polymerization initiator include peroxide initiators such as benzoyl peroxide;
Examples thereof include azo initiators such as azobisisobutyronitrile. As the carboxyl group-containing chain transfer agent,
Examples thereof include mercaptoacetic acid and mercaptopropionic acid.

The acrylic copolymer used in the present invention may optionally contain a copolymerizable vinyl monomer in addition to the above monomers. Examples thereof include carboxyl group-containing vinyl monomers such as (meth) acrylic acid, itaconic acid, (anhydrous) maleic acid, (anhydrous) fumaric acid; (meth) acrylonitrile, N-
Vinyl monomers having a high polar group such as vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, (meth) acrylamide, dimethylamino (meth) acrylate, diethylamino (meth) acrylate and dimethylaminopropylacrylamide; methyl ester (meth) acrylate , Styrene, vinyl acetate and the like.

The blending amount of the vinyl monomer with respect to the acrylic copolymer is preferably 0.5 to 30% by weight. If it is less than 0.5% by weight, it becomes difficult to obtain the cohesive force. If it exceeds 30% by weight, the cohesive force becomes too high and it becomes difficult to obtain the adhesiveness to the uneven surface.

Examples of the method for producing the acrylic copolymer include solution polymerization, bulk polymerization, suspension polymerization, photopolymerization, etc., in which a polymerization initiator is added to the vinyl monomer. Dispersion point, viscosity adjustment point,
Solution polymerization is preferably used because it is easy to uniformly mix the tackifying resin. Examples of the polymerization initiator used in the solution polymerization include azoisobutyronitrile and benzoyl peroxide.

The weight average molecular weight (Mw) of the acrylic copolymer is 200,000 to 1,500,000. When it is less than 200,000, it becomes difficult to obtain the necessary cohesive force, and when it exceeds 1.5 million, the viscosity becomes high and the productivity in the mixing with the tackifying resin and the coating process deteriorates. It It is preferably 350,000 to 750,000.

The ratio (Mw / M) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the above acrylic copolymer.
n), that is, the molecular weight distribution is 2.0 to 4.0.
When it is less than 2.0, it is practically impossible to produce a polymer, and when it exceeds 4.0, the balance between cohesive force and adhesive force becomes poor, so the range is limited. It is preferably 2.0 to 3.5.

The tackifying resin used in the present invention is, for example, one having a hydroxyl group and mainly includes an esterified product of a rosin compound. Examples of the rosin-based compound include rosin monomer, polymerized rosin, disproportionated rosin, hydrogenated rosin, and a mixture thereof. Examples thereof include esterified products with polyhydric alcohols. Examples of the polyhydric alcohol include diethylene glycol, glycerin, pentaerythritol and the like, and among them, glycerin and pentaerythritol are preferably used.

In addition, as those not containing a hydroxyl group, for example, C5 (aliphatic) type and C9 (aromatic) type petroleum resins, terpene resins, xylene resins, styrene resins, modified phenol compounds thereof, and non-esterification The rosin compound and the like are mentioned.

The hydroxyl group index (A) of the tackifying resin is
It is 1.5 to 8.0. If it is less than 1.5, the adhesiveness to the uneven surface will be poor, and if it exceeds 8.0, a sufficient cohesive force will not be obtained, so it is limited to the above range. Also,
The softening point index (B) is 4.5 to 6.5. If it is less than 4.5, the adhesiveness to the polyolefin becomes low,
When it exceeds 6.5, the adhesiveness to the uneven surface and the adhesive strength at low temperature are deteriorated, so the content is limited to the above range.

The above-mentioned hydroxyl group index (A) is the sum of the products of (hydroxyl group value of each tackifying resin) and (wt% of each tackifying resin with respect to the total amount of acrylic copolymer and tackifying resin). Is a parameter showing the concentration of hydroxyl groups of the tackifying resin present in the pressure-sensitive adhesive system.
It is measured according to SK 0070 and calculated by the following formula. Hydroxyl group index (A) = Σ (OHV (i) × W (i)) OHV (i): hydroxyl value of i-th component, W (i): weight fraction of i-th component

The above-mentioned softening point index (B) is a parameter indicating the cohesive strength level of the whole pressure-sensitive adhesive, and is a weight fraction of each tackifying resin (each tackifying amount relative to the total amount of the acrylic copolymer and the tackifying resin). The value obtained by multiplying the total of the quotient of (wt% of resin) and the softening point by 10000 is shown. It is calculated by the following formula and can be obtained according to the formula for obtaining the glass transition point of the polymer mixed system. Correlation with the glass transition temperature of the whole agent (mechanical properties of polymers and composites, JEN
IELSEN, translated by Shigeharu Onoki, p. 16). Softening point index (B) = Σ (W (i) / Sp (i)) × 10
⁴ W (i): Weight fraction of i-th component, Sp (i): Softening point of i-th component The acrylic pressure-sensitive adhesive composition of the present invention has a hydroxyl group index (A).
If the value of the softening point index (B) is within the above range, the tackifying resin can be optionally used in combination.

Additives such as a plasticizer, a softening agent, a filler, a pigment and a dye may be used in the acrylic pressure-sensitive adhesive composition, if necessary.

The polyisocyanate compound used in the present invention is not particularly limited, and examples thereof include tolylene diisocyanate (TDI) and tolidine diisocyanate (T
ODI), xylylene diisocyanate, diphenylmethane diisocyanate (MDI) and other aromatic diisocyanate compounds; hexamethylene diisocyanate (HM
DI), an aliphatic or alicyclic diisocyanate compound such as isophorone diisocyanate (IPDI); a tolylene diisocyanate trimer adduct of trimethylolpropane, triphenylmethane triisocyanate, triethylene such as methylenebis (4-phenylmethane) triisocyanate. An isocyanate compound etc. are mentioned.

The polyisocyanate compound is added in an amount of 100 parts by weight of the acrylic copolymer.
0.05 to 2.00 parts by weight is preferable. If the amount is less than 0.05 parts by weight, the effect of improving the cohesive strength expected by blending the polyisocyanate compound is not sufficient,
If it exceeds 2.00 parts by weight, the degree of crosslinking of the pressure-sensitive adhesive becomes too high, and sufficient pressure-sensitive adhesive force cannot be obtained.

A pressure-sensitive adhesive tape is obtained by applying the acrylic pressure-sensitive adhesive composition of the present invention to one side or both sides of a substrate to form a pressure-sensitive adhesive layer. Examples of the base material include synthetic resin films such as paper, non-woven fabric, polyester resin and polyolefin resin; synthetic resin foams such as polyolefin resin, polyurethane resin, polychloroprene resin and acrylic resin. Furthermore, a non-support type double-sided adhesive tape having no substrate layer can be obtained by forming only the adhesive material itself into a sheet.

[0030]

The acrylic pressure-sensitive adhesive composition of the present invention has a limited molecular weight and molecular weight distribution, an acrylic copolymer of a specific composition containing a specific macromonomer, a hydroxyl group index and a softening point within a limited range. By combining a tackifying resin having an index with a polyisocyanate compound, it is possible to secure room-temperature adhesiveness and adhesiveness to low-polar adherends such as polyolefin, and excellent in adhesiveness to uneven surfaces, cohesive force, and holding power. There is.

[0031]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Reference Example 1 Preparation of Hydroxyl Group-Containing Macromonomer (1) Methyl methacrylate (hereinafter referred to as "MMA") was placed in a five-necked flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas inlet. 90 parts by weight, 2-hydroxyethyl methacrylate (hereinafter referred to as "HEMA") 1
0 part by weight, mercaptoacetic acid 0.5 part by weight, ethyl acetate 8
After charging 0 parts by weight and stirring to dissolve the mixture into a uniform mixture,
Purge with nitrogen gas for about 30 minutes to remove oxygen present in the monomer solution.

Then, the temperature was raised with stirring under a nitrogen gas atmosphere, and the temperature was maintained at 70 ° C. to prepare a solution prepared by dissolving 0.1 part by weight of azobisisobutyrovaleric acid in 1 part by weight of ethyl acetate. After dropping with a dropping funnel, a polymerization reaction was performed at the same temperature for 10 hours to obtain a solution of an MMA-HEMA copolymer. Add 0.1 part by weight of triethylamine and 1 part by weight of glycidyl methacrylate to the flask and add 5
Heated to reflux for hours. After cooling, it was precipitated in isopropyl alcohol and vacuum dried at 60 ° C. overnight to obtain a hydroxyl group-containing macromonomer (1) having a number average molecular weight (Mn) of 9400.

Reference Example 2 Preparation of Hydroxyl Group-Containing Macromonomer (2) Reaction was carried out in the same manner as in Reference Example 1 except that 80 parts by weight of butyl methacrylate, 20 parts by weight of 2-hydroxyethyl methacrylate and 0.8 parts by weight of mercaptoacetic acid were used. Then, purification was performed to obtain a hydroxyl group-containing macromonomer (2) having a number average molecular weight (Mn) of 12000.

Reference Example 3 Preparation of Acrylic Copolymers A to L According to the blending composition shown in Table 1, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, acrylic acid, hydroxyl group-containing macromonomer (1) , A hydroxyl group-containing macromonomer (2), and AA-714 as a macromonomer having a number average molecular weight (Mn)
S (MMA; 86%, 2HEMA; 14% terminal methacryloyl group, manufactured by Toagosei Co., Ltd.) and lauryl mercaptan, together with 80 parts by weight of ethyl acetate, were equipped with a stirrer, a reflux condenser, a thermometer, a dropping funnel, and a nitrogen gas inlet. The mixture was charged into a five-necked flask and dissolved by stirring to form a uniform mixture, which was then purged with nitrogen gas for about 30 minutes to remove oxygen existing in the monomer solution.

Thereafter, the air in the flask was replaced with nitrogen gas, the temperature was raised with stirring, and the temperature was maintained at 70 ° C. to prepare a solution prepared by dissolving 0.03 part by weight of benzoyl peroxide in 1 part by weight of ethyl acetate. After dropping with a dropping funnel,
Polymerization reaction was carried out at the same temperature for 10 hours to obtain a solution of an acrylic copolymer.

Measurement of Molecular Weight of Acrylic Copolymers A to L The weight average molecular weight (Mw) and number average molecular weight (Mn) of the acrylic copolymer solution obtained as described above, (Mw / M
n) was measured. The above molecular weight was measured by gel permeation chromatography using standard polystyrene as a reference, tetrahydrofuran as an eluent, and detection using a refraction system. The results are shown in Table 1. In addition,
For the acrylic copolymer H, toluene 80 was used as a solvent. In Table 1, M3 is AA-714S (MMA; 86
%, 2HEMA; 14% terminal methacryl group, manufactured by Toagosei Co., Ltd.).

[0038]

[Table 1]

Example 1 Preparation of Acrylic Pressure-Sensitive Adhesive Composition Acrylic copolymer B and various tackifying resins were uniformly mixed while diluted with toluene according to the composition shown in Table 2 to give an adhesive of 55% by weight. A solution of the agent composition was obtained. Table 2 shows the hydroxyl group index and the softening index of the obtained pressure-sensitive adhesive composition. The tackifying resins in Table 2 are as shown below. "OHV" indicates a hydroxyl value, and "Sp" indicates a softening point (absolute temperature).

Tackifying resin 1; glycerin esterified product of disproportionated rosin, "Super Ester A100" (OH
V = 10.1, Sp = 373, manufactured by Arakawa Chemical Industry Co., Ltd.) Tackifying resin 2; C9 petroleum resin, "Oligotec 14
0 "(OHV = 0, Sp = 393, manufactured by Mitsubishi Petroleum Corp.) Tackifying resin 3; C5 petroleum resin," FTR6100 "
(OHV = 0, Sp = 373, manufactured by Mitsubishi Petroleum Co., Ltd.) Tackifying resin 4; Esterified from a mixture of rosin monomer and polymerized rosin with a mixture of pentaerythritol and glycerin, "Pencel D125" (OHV =
30.5, Sp = 398, manufactured by Arakawa Chemical Industry Co., Ltd.) Tackifying resin 5; pentaerythritol esterification product of disproportionated rosin "Super Ester A125" (OHV =
10.4, Sp = 398, manufactured by Arakawa Chemical Industry Co., Ltd.) Tackifying resin 6; Mixture of rosin monomer and polymerized rosin, "Silbatak 140" (OHV = 0, Sp = 413, manufactured by Arakawa Chemical Industry Co., Ltd.) Tackifying resin 7; Esterified from a mixture of rosin monomer and polymerized rosin with a mixture of pentaerythritol and glycerin, “Pencel D160” (OHV =
41.0, Sp = 433, manufactured by Arakawa Chemical Industry Co., Ltd.)

Preparation of adhesive tape To the solution of the acrylic adhesive composition obtained above, an ethyl acetate solution of a tolylene diisocyanate adduct of trimethylolpropane (Coronate L55E, solid content 55% by weight, manufactured by Nippon Polyurethane Industry Co., Ltd.) 1.2 parts by weight was added to 100 parts by weight of the acrylic copolymer and uniformly mixed, and then the mixture was coated on a release sheet and dried to obtain a laminate having a pressure-sensitive adhesive layer of 65 μm formed. Basis weight 1 for the above laminate
After transferring by laminating on both sides of a non-woven fabric of 4 g / m ² , it was cured at 40 ° C. for 3 days to obtain a double-sided adhesive tape. One side of the obtained adhesive tape was lined with a 38 μm-thick polyester film to prepare a single-sided adhesive tape sample. Using the double-sided pressure-sensitive adhesive tape and the single-sided pressure-sensitive adhesive tape, the SP pressure-sensitive adhesive force, the polypropylene pressure-sensitive adhesive force, the holding force and the urethane foam adhesion were measured by the following methods. The results are shown in Table 3.

Measurement of SP Adhesive Strength The above-mentioned single-sided adhesive tape was adhered to a SUS304 plate with a width of 25 mm in accordance with JIS Z 0237, at 23 ° C.
After leaving for 20 minutes, 180 ° direction, pulling speed 30
The peel strength was measured under the condition of 0 mm / min.

Measurement of Adhesive Strength of Polypropylene The above-mentioned one-sided adhesive tape was stuck on a polypropylene plate with a width of 25 mm, left at 23 ° C. for 20 minutes, and then the peel strength was measured under the conditions of 180 ° direction and a pulling speed of 300 mm / min. .

Measurement of holding power The above single-sided adhesive tape was applied to a SUS304 plate in an area of 20 × 20 m.
Laminated in an area of m, 23 ° C, 20 minutes, then 80
After left at 1 ° C. for 1 hour, a load of 1 kgf was applied in the vertical direction and the shift length (or drop time) after 1 hour was measured.

Measurement of Urethane Foam Adhesion The above-mentioned double-sided adhesive tape was laminated on a SUS304 plate with a width of 25 mm, and a urethane having a density of 0.05 g / cm ³ cut into a width of 20 mm, a length of 100 mm and a thickness of 5 mm. The foam foam sheet was left in an atmosphere of 5 ° C. for 2 hours or more, then laminated using a 2 kgf roller so that the thickness of the urethane foam was 50%, left at 5 ° C. for 24 hours, and then stretched in 90 ° direction. Speed 300mm / m
The peel strength was measured under the condition of in.

Examples 2 to 9 and Comparative Examples 1 to 6 Acrylic copolymers A to I and various tackifying resins were uniformly mixed while diluting with toluene according to the compounding composition shown in Table 2, and 55% by weight. A solution of the adhesive composition of was obtained. The hydroxyl group index and the softening index of the obtained pressure-sensitive adhesive composition are shown in Table 2. The double-sided pressure-sensitive adhesive tape and the single-sided pressure-sensitive adhesive tape were measured for the physical properties of the solution of the pressure-sensitive adhesive composition shown in Table 2 in the same manner as in Example 1. The results are shown in Table 3.

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

Since the acrylic pressure-sensitive adhesive composition of the present invention has the above-mentioned constitution, it has high adhesiveness not only to the highly polar adherend surface but also to the low polar adherend surface.
Furthermore, it has a relatively high adhesiveness even at a high-temperature cohesive force and an uneven surface such as a resin foam, and thus it can be suitably used as an adhesive tape and a double-sided adhesive tape for various purposes.

Claims (1)

[Claims] 1. An acrylic copolymer comprising a hydroxyl group-containing macromonomer and an alkyl (meth) acrylate,
A tackifying resin, and an acrylic pressure-sensitive adhesive composition comprising a polyisocyanate compound, wherein the number average molecular weight of the hydroxyl group-containing macromonomer is 3000 to 20,000, and the compounding ratio of the hydroxyl group-containing macromonomer is the above. 0.3 to 15.0% by weight based on the acrylic copolymer
And the weight average molecular weight of the acrylic copolymer (M
w) is 200,000 to 1,500,000, and the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the acrylic copolymer are
(Mw / Mn) is 2.0 to 4.0 and the hydroxyl group index (A) of the tackifying resin is 1.5 to 4.0.
It is 8.0 and the softening point index (B) is 4.5-6.5, The acrylic adhesive composition characterized by the above-mentioned.