ADHESIVE COMPOSITION

Abstract

An adhesive composition of one aspect of the present invention contains a block copolymer composed of a polymer block A which includes a (meth)acrylate ester unit having a linear or branched side chain of 1 to 8 carbon atoms and has a number average molecular weight of 2,000 to 10,000, a polymer block B which includes at least one of an aromatic vinyl compound unit and a (meth)acrylate ester unit having a cyclic structure, and a polymer block C which includes a (meth)acrylate ester unit having a linear or branched side chain of 1 to 8 carbon atoms, wherein the mass ratio (B/C) between the polymer block B and the polymer block C is within a range from 5.0/95.0 to 30.0/70.0, the mass ratio (A/(B+C)) between the polymer block A and the total of the polymer block B and the polymer block C is within a range from 0.1/99.9 to 5.0/95.0, and the acid value of the block copolymer is at least 8 mgKOH/g.

Claims

1. An adhesive composition comprising a block copolymer composed of a polymer block A which includes a (meth)acrylate ester unit having a linear or branched side chain of 1 to 8 carbon atoms and has a number average molecular weight of 2,000 to 10,000, a polymer block B which includes at least one of an aromatic vinyl compound unit and a (meth)acrylate ester unit having a cyclic structure, and a polymer block C which includes a (meth)acrylate ester unit having a linear or branched side chain of 1 to 8 carbon atoms, wherein a mass ratio (B/C) between the polymer block B and the polymer block C is within a range from 5.0/95.0 to 30.0/70.0, a mass ratio (A/(B+C)) between the polymer block A and a total of the polymer block B and the polymer block C is within a range from 0.1/99.9 to 5.0/95.0, and an acid value of the block copolymer is at least 8 mgKOH/g.

2. The adhesive composition according to claim 1, wherein the block copolymer is represented by A-B-C-B-A or A-B-C-B (wherein A represents the polymer block A, B represents the polymer block B, and C represents the polymer block C).

3. The adhesive composition according to claim 1, wherein the polymer block B includes a carboxyl group-containing monomer unit.

4. The adhesive composition according to claim 2, wherein the polymer block B includes a carboxyl group-containing monomer unit.

Description

EXAMPLES

[0125] The present invention is described below in further detail using a series of examples, but the present invention is not limited to these examples.

<Measurements, Evaluations>

(Calculation of Tg)

[0126] The Tg values for the polymer blocks A, B and C, and the block copolymer were determined from the Fox equation represented by formula (i) shown above.

(Measurement of Molecular Weight)

[0127] The Mn and Mw values for the polymer block A and the block copolymer were measured by gel permeation chromatography (GPC) under the conditions listed below. The Mn and Mw values refer to polystyrene-equivalent values.

[0128] GPC Measurement Conditions:

[0129] GPC apparatus: GPC-101 (manufactured by Shoko Co., Ltd.)

[0130] Columns: Shodex A-806M columns×2, connected in series (manufactured by Showa Denko K.K.)

[0131] Detector: Shodex RI-71 (manufactured by Showa Denko K.K.)

[0132] Mobile phase: tetrahydrofuran

[0133] Flow rate: 1 mL/minute

(Measurement of Acid Value)

[0134] The acid value was measured in accordance with JIS K 2501:2003. Specifically, the acid value was measured by titration using a solution prepared by dissolving potassium hydroxide in methanol to achieve a concentration of 0.1 N.

(Measurement of Adhesive Strength)

[0135] The adhesive composition was applied to a polyethylene terephthalate (PET) film in an amount sufficient to yield a dried film thickness of 50 μm, and the composition was dried at 100° C. for 5 minutes to obtain a test piece having an adhesive layer on the PET film. The test piece was cut to a width of 25 mm. A plurality of the cut test pieces were placed on a stainless steel sheet with dimensions of 50 mm×150 mm with the surface of the adhesive layer facing the stainless steel sheet, and a 2 kg roller was rolled once back and forth across the test pieces to effect bonding. Subsequently, following standing at room temperature (23° C.) and 50%RH for 20 minutes, or following standing at 60° C. for either one day or three days, the PET films of the test pieces bonded to the stainless steel sheet were measured for adhesive strength (N/25 mm), under an atmosphere at 23° C. and 50%RH, in accordance with section 8.3.1 “180° Peeling Method” of JIS Z 0237:2009. The adhesive strength is preferably at least 15 N/25 mm.

[0136] Based on the measured adhesive strength values, the adhesion increase (1 day, 3 days) was calculated using the formula shown below. A smaller adhesion increase indicates a smaller rise in the adhesive strength. The adhesion increase is preferably not more than 1.5.

[0137] Adhesion Increase (1 day)=Q.sup.2/Q.sup.1

[0138] Adhesion Increase (3 days)=Q.sup.3/Q.sup.1

[0139] Q.sup.1 represents the adhesive strength (N/25 mm) measured after standing for 20 minutes, Q.sup.2 represents the adhesive strength (N/25 mm) measured after standing for 1 day at 60° C., and Q.sup.3 represents the adhesive strength (N/25 mm) measured after standing for 3 days at 60° C.

(Measurement of Shear Adhesive Strength)

[0140] The adhesive composition was applied, in an amount sufficient to yield a dried film thickness of 50 μm, to a PET film that had been surface-treated with a silicone, and the composition was dried at 100° C. for 5 minutes to obtain a test piece having an adhesive layer on the PET film. The test piece was cut to pieces having dimensions of 1 cm×1 cm. A plurality of the cut test pieces were placed on an aluminum foil sheet with dimensions of 30 mm×150 mm with the surface of the adhesive layer facing the aluminum foil sheet. The PET film was then peeled off each of the test pieces to expose the adhesive layer, a separate aluminum foil sheet with dimensions of 30 mm×150 mm was placed on top of the exposed adhesive layer, and a 2 kg roller was rolled once back and forth across the test pieces to effect bonding. Subsequently, under an atmosphere at 23° C. and 50% RH, a tension tester was used to pull the aluminum foil at a pull speed of 50 mm/min, and the maximum stress value was recorded as the shear adhesive strength (N/cm.sup.2). The shear adhesive strength is preferably at least 100 N/cm.sup.2.

(Evaluation of Heat-Resistant Creep Characteristics)

[0141] Test pieces were prepared in the same manner as that described for measurement of the adhesive strength.

[0142] In accordance with JIS Z 0237:2009, the test pieces were rolled once back and forth with a pressure roller from the side of the PET film, and then installed in a creep tester that had been adjusted to 40° C. Under an atmosphere at either 100° or 150° C., a 1 kg weight was affixed to the PET film, and the time taken for the PET film to drop from the stainless steel sheet was measured. In those cases where the PET film had not fallen from the stainless steel sheet even after one hour had elapsed, the displacement of the PET film (the distance moved from the position prior to starting the test) after one hour was measured. The drop time (minutes) or the displacement (mm) was used as an indicator of the heat-resistance creep characteristics, with a smaller displacement (mm) meaning superior heat-resistance creep characteristics. In those cases where the PET dropped from the stainless steel sheet, a longer drop time (minutes) means superior heat-resistance creep characteristics.

[0143] A displacement of not more than 1 mm was deemed a passing grade, and an evaluation was made against the following evaluation criteria.

[0144] ∘: passing grade achieved under atmospheres at 100° C. and 150° C.

[0145] Δ: passing grade achieved under atmosphere at 100° C., but failing grade at 150° C.

[0146] ×: failing grade under atmosphere at 100° C.

Example 1

(1-1. Production of Polymer Block A)

[0147] A two-neck flask was charged with 100.0 g of n-butyl acrylate (BA), 4.54 g of the RAFT agent (1) and 0.05 g of 2,2′-azobis(2-methylbutyronitrile) (ABN-E), and the inside of the flask was flushed with nitrogen gas while the temperature was raised to 80° C. Subsequently, a polymerization reaction was conducted by stirring the contents at 80° C. for two hours (first stage reaction).

[0148] Following completion of the reaction, 4,000 g of n-hexane was added to the flask and stirred to precipitate the reaction product, the unreacted monomer (BA) and RAFT agent (1) were removed by filtration, and the reaction product was dried under reduced pressure at 70° C. to obtain a copolymer (polymer block A).

[0149] The Tg, Mn, Mw and Mw/Mn values for the thus obtained copolymer (polymer block A) are shown in Table 1.

(1-2. Production of Block Copolymer Z1)

[0150] A two-neck flask was charged with a mixture composed of 87.0 g of styrene (St), 1.0 g of 2-hydroxyethyl acrylate (HEA), 12.0 g of acrylic acid (AA), 0.19 g of ABN-E and 26.3 g of ethyl acetate, together with the copolymer (polymer block A) obtained above, and the inside of the flask was flushed with nitrogen gas while the temperature was raised to 85° C. Subsequently, a polymerization reaction was conducted by stirring the contents at 85° C. for 15 hours (second stage reaction), thus obtaining a reaction solution containing a block copolymer Z1 formed from a polymer block A and a polymer block B. The blend amounts of the mixture and the copolymer (polymer block A) were adjusted so that the mass ratio between the polymer block A and the polymer block B in the obtained block copolymer Z1 was 1/10.

[0151] Following completion of the reaction, 4,000 g of n-hexane was added to the flask and stirred to precipitate the reaction product, the unreacted monomers (St, HEA, AA) and the solvent were removed by filtration, and the reaction product was dried under reduced pressure at 70° C. to obtain the block copolymer Z1.

[0152] The Tg value for the polymer block B of the thus obtained block copolymer Z1 is shown in Table 1.

(1-3. Production of Block Copolymer X1)

[0153] A two-neck flask was charged with a mixture composed of 48.5 g of butyl acrylate (BA), 48.5 g of 2-ethylhexyl acrylate (2-EHA), 3.0 g of acrylic acid (AA), 0.05 g of ABN-E and 73.2 g of ethyl acetate, together with the block copolymer Z1 obtained above, and the inside of the flask was flushed with nitrogen gas while the temperature was raised to 85° C. Subsequently, a polymerization reaction was conducted by stirring the contents at 85° C. for 6 hours (third stage reaction), thus obtaining a reaction solution containing a block copolymer X1 formed from a polymer block A, a polymer block B and a polymer block C. The blend amounts of the mixture and the block copolymer Z1 were adjusted so that the mass ratio between the polymer block A, the polymer block B and the polymer block C in the obtained block copolymer X1 was 1/10/89.

[0154] A portion of the reaction solution was sampled, 4,000 g of n-hexane was added to the sample and stirred to precipitate the reaction product, the unreacted monomers (BA, 2-EHA, AA) and the solvent were removed by filtration, and the reaction product was dried under reduced pressure at 70° C. to obtain the block copolymer X1.

[0155] The Tg value for the polymer block C of the thus obtained block copolymer X1, and the Mn, Mw, Mw/Mn and acid value for the block copolymer Z1 are shown in Table 1.

[0156] Further, using the obtained reaction solution containing the block copolymer X1 as an adhesive composition, the adhesive strength, the shear adhesive strength and the heat-resistant creep characteristics were evaluated. The results are shown in Table 1. In Table 1, the entry “Creep” means the heat-resistant creep characteristics (this also applies to subsequent tables).

Examples 2 to 9, Comparative Examples 1 to 3

[0157] With the exceptions of altering the monomer compositions that constitute the polymer block A, the polymer block B and the polymer block C as shown in Tables 1 to 3, altering the polymerization conditions for the first stage reaction, the second stage reaction and the third stage reaction as shown in Tables 1 to 3, and altering the mass ratio (A/B/C) between the polymer block A, the polymer block B and the polymer block C as shown in Tables 1 to 3, block copolymers X2 to X12 were produced in the same manner as Example 1, and the various measurements were performed. The results are shown in Tables 1 to 3.

Comparative Example 4

(4-1. Production of Polymer Block B)

[0158] A two-neck flask was charged with 87.0 g of styrene (St), 1.0 g of 2-hydroxyethyl acrylate (HEA), 12.0 g of acrylic acid (AA), 0.5 g of the RAFT agent (1) and 0.2 g of 2,2′-azobis(2-methylbutyronitrile) (ABN-E), and the inside of the flask was flushed with nitrogen gas while the temperature was raised to 80° C. Subsequently, a polymerization reaction was conducted by stirring the contents at 80° C. for 6 hours (first stage reaction).

[0159] Following completion of the reaction, 4,000 g of n-hexane was added to the flask and stirred to precipitate the reaction product, the unreacted monomers (St, HEA, AA) and RAFT agent (1) were removed by filtration, and the reaction product was dried under reduced pressure at 70° C. to obtain a copolymer (polymer block B).

[0160] The Tg value for the thus obtained copolymer (polymer block B) is shown in Table 4.

(4-2. Production of Block Copolymer X13)

[0161] A two-neck flask was charged with a mixture composed of 48.5 g of butyl acrylate (BA), 48.5 g of 2-ethylhexyl acrylate (2-EHA), 3.0 g of acrylic acid (AA), 0.0282 g of ABN-E and 73.5 g of ethyl acetate, together with the copolymer (polymer block B) obtained above, and the inside of the flask was flushed with nitrogen gas while the temperature was raised to 85° C. Subsequently, a polymerization reaction was conducted by stirring the contents at 85° C. for 15 hours (second stage reaction), thus obtaining a reaction solution containing a block copolymer X13 formed from a polymer block B and a polymer block C. The blend amounts of the mixture and the copolymer (polymer block B) were adjusted so that the mass ratio between the polymer block B and the polymer block C in the obtained block copolymer X13 was 11/89.

[0162] A portion of the reaction solution was sampled, 4,000 g of n-hexane was added to the sample and stirred to precipitate the reaction product, the unreacted monomers (BA, 2-EHA, AA) and the solvent were removed by filtration, and the reaction product was dried under reduced pressure at 70° C. to obtain the block copolymer X13.

[0163] The Tg value for the polymer block C of the thus obtained block copolymer X13, and the Mn, Mw, Mw/Mn and acid value for the block copolymer X13 are shown in Table 4.

[0164] Further, using the obtained reaction solution containing the block copolymer X13 as an adhesive composition, the adhesive strength, the shear adhesive strength and the heat-resistant creep characteristics were evaluated. The results are shown in Table 4.

Comparative Examples 5 to 7

[0165] With the exceptions of altering the monomer compositions that constitute the polymer block B and the polymer block C as shown in Table 4, altering the polymerization conditions for the first stage reaction and the second stage reaction as shown in Table 4, and altering the mass ratio (B/C) between the polymer block B and the polymer block C as shown in Table 4, block copolymers X14 to X16 were produced in the same manner as Comparative Example 4, and the various measurements were performed. The results are shown in Table 4.

Comparative Example 8

[0166] A two-neck flask was charged 8.8 g of styrene (St), 44.1 g of 2-ethylhexyl acrylate (2-EHA), 3.0 g of acrylic acid (AA), 0.05 g of 2,2′-azobis(2-methylbutyronitrile) (ABN-E) and 40 g of ethyl acetate, and the inside of the flask was flushed with nitrogen gas while the temperature was raised to 85° C. Subsequently, a polymerization reaction was conducted by stirring the contents at 85° C. for 10 hours, thus obtaining a reaction solution containing a random copolymer.

[0167] A portion of the reaction solution was sampled, 4,000 g of n-hexane was added to the sample in a flask and stirred to precipitate the reaction product, and the random copolymer was extracted from the reaction solution by removing the unreacted monomers (St, 2-EHA, AA) and the solvent by filtration, and then drying the reaction product under reduced pressure at 70° C.

[0168] The Mn, Mw, Mw/Mn and acid value for the obtained random copolymer are shown in Table 4.

[0169] Further, using the obtained reaction solution containing the random copolymer as an adhesive composition, the adhesive strength, the shear adhesive strength and the heat-resistant creep characteristics were evaluated. The results are shown in Table 4.

TABLE-US-00001 TABLE 1 Example Example Example Example 1 2 3 4 Polymer Monomer BA 100 100 100 100 block A composition [g] 2-EHA Polymerization ABN-E 0.05 0.05 0.05 0.075 conditions [g] RAFT agent (1) 4.54 4.54 4.54 11.32 RAFT agent (2) Tg [° C.] −54 −54 −54 −54 Mn 5,000 5,000 5,000 1,700 Mw 6,000 6,000 6,000 2,260 Mw/Mn 1.19 1.19 1.19 1.33 Polymer Monomer St 87 87 87 87 block B composition [g] HEA 1 1 1 1 AA 12 12 12 12 BA 2-EHA Polymerization Ethyl acetate 26.3 26.3 26.3 11.3 conditions [g] RAFT agent (1) 4.54 4.54 4.54 2.03 RAFT agent (2) ABN-E 0.19 0.19 0.19 0.19 St/AA 87.9/12.1 87.9/12.1 87.9/12.1 87.9/12.1 Tg [° C.] 103.7 103.7 103.7 103.7 Polymer Monomer BA 48.5 40 48.5 40 block C composition [g] 2-EHA 48.5 40 48.5 40 MA 20 20 St HEA AA 3 3 Polymerization Ethyl acetate 73.2 76.5 73.2 82.9 conditions [g] ABN-E 0.05 0.05 0.0118 0.0232 Tg [° C.] −62.5 −57 −57 −57 Block A/B/C 0.5/10.4/89.1 0.7/14.3/85.0 1.3/25.1/73.6 0.3/13.6/86.2 copolymer X A/B + C 0.5/99.5 0.7/99.3 1.3/98.7 0.3/99.7 B/C 10/90 14/86 25/75 14/86 Mn 100,000 160,000 150,000 112,000 Mw 530,000 500,000 485,000 354,000 Mw/Mn 5.3 3.1 3.2 3.2 Acid value [mgKOH/g] 30.1 13.1 40.7 13.1 Evaluations Adhesive 20 min [N/25 mm] 16.7 21.2 15.1 16.5 strength 60° C. 1 day [N/25 mm] 18.0 23.8 15.5 18.2 60° C. 3 days [N/25 mm] 20.2 27.5 15.8 19.8 Adhesion increase (1 day) 1.1 1.1 1.0 1.1 Adhesion increase (3 days) 1.2 1.3 1.0 1.2 Shear adhesive strength 100.8 130.0 114.9 115.9 Creep 100° C. × 1 kg o o o o

TABLE-US-00002 TABLE 2 Example Example Example Example 5 6 7 8 Polymer Monomer BA 100 100 100 100 block A composition [g] 2-EHA Polymerization ABN-E 0.05 0.05 0.05 0.05 conditions [g] RAFT agent (1) 2.26 4.54 4.54 4.54 RAFT agent (2) Tg [° C.] −54 −54 −54 −54 Mn 8,000 7,500 5,000 5,000 Mw 9,040 9,600 6,000 6,000 Mw/Mn 1.13 1.28 1.19 1.19 Polymer Monomer St 87 87 87 87 block B composition [g] HEA 1 1 1 1 AA 12 12 12 12 BA 2-EHA Polymerization Ethyl acetate 19.4 26.3 26.3 26.3 conditions [g] RAFT agent (1) 10.11 4.54 4.54 4.54 RAFT agent (2) ABN-E 0.19 0.19 0.19 0.19 St/AA 87.9/12.1 87.9/12.1 87.9/12.1 87.9/12.1 Tg [° C.] 103.7 103.7 103.7 103.7 Polymer Monomer BA 40 48.5 48.5 40 block C composition [g] 2-EHA 40 48.5 48.5 40 MA 20 20 St HEA AA 3 3 Polymerization Ethyl acetate 76.3 73.2 76.3 76.3 conditions [g] ABN-E 0.0232 0.05 0.05 0.0232 Tg [° C.] −57 −62.5 −62.5 −57 Block A/B/C 1.5/15.3/83.1 4.8/14.0/81.2 0.8/5.5/93.7 1.4/27.7/70.9 copolymer X A/B + C 1.5/98.5 4.8/95.2 0.8/99.2 1.4/98.6 B/C 15/85 15/85 5/95 28/72 Mn 169,000 150,000 182,000 106,000 Mw 453,000 400,000 550,000 227,000 Mw/Mn 2.7 2.7 3.0 2.1 Acid value [mgKOH/g] 14.0 30.1 26.6 26.2 Evaluations Adhesive 20 min [N/25 mm] 16.4 15.5 16.2 16.4 strength 60° C. 1 day [N/25 mm] 16.9 16.1 17.0 17.1 60° C. 3 days [N/25 mm] 17.3 16.2 17.3 17.3 Adhesion increase (1 day) 1.0 1.0 1.0 1.0 Adhesion increase (3 days) 1.1 1.0 1.1 1.1 Shear adhesive strength 149.8 105.0 109.2 102.0 Creep 100° C. × 1 kg o o o o

TABLE-US-00003 TABLE 3 Example Comparative Comparative Comparative 9 Example 1 Example 2 Example 3 Polymer Monomer BA 100 100 100 block A composition [g] 2-EHA 100 Polymerization ABN-E 0.05 0.05 0.05 0.05 conditions [g] RAFT agent (1) 4.54 4.54 4.54 4.54 RAFT agent (2) Tg [° C.] −70 −54 −54 −54 Mn 5,000 35,000 5,000 5,000 Mw 6,000 40,000 6,000 6,000 Mw/Mn 1.19 1.28 1.19 1.19 Polymer Monomer St 87 87 87 87 block B composition [g] HEA 1 1 1 1 AA 12 12 12 12 BA 2-EHA Polymerization Ethyl acetate 26.3 26.3 26.3 26.3 conditions [g] RAFT agent (1) 4.54 4.54 4.54 4.54 RAFT agent (2) ABN-E 0.19 0.19 0.19 0.19 St/AA 87.9/12.1 87.9/12.1 87.9/12.2 87.9/12.3 Tg [° C.] 103.7 103.7 103.7 103.7 Polymer Monomer BA 40 48.5 40 48.5 block C composition [g] 2-EHA 40 48.5 40 48.5 MA 20 20 St HEA AA 3 3 Polymerization Ethyl acetate 76.3 73.2 73.2 73.2 conditions [g] ABN-E 0.0232 0.05 0.05 0.05 Tg [° C.] −57 −62.5 −62.5 −62.5 Block A/B/C 0.8/15.3/83.9 6.5/13.0/80.8 1.1/3.9/95.0 0.7/31.1/68.2 copolymer X A/B + C 0.8/99.2 6.5/93.5 1.1/98.9 0.7/99.3 B/C 15/85 15/85 4/96 32/68 Mn 164,000 160,000 283,000 160,000 Mw 498,000 425,000 530,000 360,000 Mw/Mn 3.0 2.7 1.9 2.3 Acid value [mgKOH/g] 14.0 30.1 3.7 45.6 Evaluations Adhesive 20 min [N/25 mm] 19.7 13.2 14.8 11.3 strength 60° C. 1 day [N/25 mm] 21.9 14.4 15.8 18.2 60° C. 3 days [N/25 mm] 22.6 15.4 16.3 20.8 Adhesion increase (1 day) 1.1 1.1 1.1 1.6 Adhesion increase (3 days) 1.1 1.2 1.1 1.8 Shear adhesive strength 109.0 84.0 53.2 256.2 Creep 100° C. × 1 kg o × o o

TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Comparative Comparative Example 4 Example 5 Example 6 Example 7 Example 8 Polymer Monomer BA block A composition [g] 2-EHA Polymerization ABN-E conditions [g] RAFT agent (1) RAFT agent (2) Tg [° C.] Mn Mw Mw/Mn Polymer Monomer St 87 87 87 block B composition [g] HEA 1 1 1 AA 12 12 3 12 BA 48.5 2-EHA 48.5 Polymerization Ethyl acetate 11.2 10 conditions [g] RAFT agent (1) 0.5 0.5 0.56 RAFT agent (2) 0.5 ABN-E 0.2 0.2 0.16 0.1 St/AA 87.9/12.4 87.9/12.5 87.9/12.5 Tg [° C.] 103.7 103.7 −54 103.7 Polymer Monomer BA 48.5 48.5 48.5 44.1 block C composition [g] 2-EHA 48.5 48.5 48.5 44.1 MA St 87 8.8 HEA 1 AA 3 3 12 3 3 Polymerization Ethyl acetate 73.5 73.9 72.7 47 40 conditions [g] ABN-E 0.0282 0.0148 0.015 0.0236 0.05 Tg [° C.] −62.5 −62.5 103.7 −57 −56.4 Block A/B/C copolymer A/B + C X B/C 11/89 15/85 11/89 12/88 Mn 170,000 78,400 203,000 200,000 120,000 Mw 530,000 189,000 750,000 570,000 490,000 Mw/Mn 3.1 2.4 3.7 2.9 4.1 Acid value [mgKOH/g] 31.1 33.9 31.1 31.8 23.4 Evaluations Adhesive 20 min [N/25 mm] 10.9 13.0 16.8 11.2 19.9 strength 60° C. 1 day [N/25 mm] 18 22.4 39.8 18.1 43.5 60° C. 3 days [N/25 mm] 22.2 27.0 52.3 19.2 51.7 Adhesion increase (1 day) 1.7 1.7 2.4 1.6 2.2 Adhesion increase (3 days) 2.0 2.1 3.1 1.7 2.6 Shear adhesive strength 112.0 252.0 27.2 33.6 44.8 Creep 100° C. × 1 kg o o × o ×

[0170] The abbreviations used in Tables 1 to 4 represent the compounds listed below. Further, the Tg value shown below inside the parentheses for each monomer represents the Tg value for the homopolymer.

[0171] St: styrene (Tg: 100° C.)

[0172] MA: methyl acrylate (Tg: 10° C.)

[0173] HEA: 2-hydroxyethyl acrylate (Tg: −15° C.)

[0174] AA: acrylic acid (Tg: 106° C.)

[0175] BA: n-butyl acrylate (Tg: −54° C.)

[0176] 2-EHA: 2-ethylhexyl acrylate (Tg: −70° C.)

[0177] RAFT agent (1): a compound represented by formula (2) shown below. The RAFT agent (1) was produced using the procedure disclosed in Production Example 1 of Japanese Unexamined Patent Application, First Publication No. 2014-133801.

[0178] RAFT agent (2): a compound represented by formula (3) shown below. The RAFT agent (2) was produced using the procedure disclosed in Production Example 2 of Japanese Unexamined Patent Application, First Publication No. 2014-133801.

##STR00002##

[0179] It is thought that because the RAFT agent (1) is a trithiocarbonate dimer, the block copolymers X1 to X12 obtained in Examples 1 to 9 and Comparative Examples 1 to 3 are penta-block copolymers represented by A-B-C-B-A. Further, it is thought that the block copolymers X13 to X15 obtained in Comparative Examples 4 to 6 are tri-block copolymers represented by B-C-B.

[0180] On the other hand, it is thought that because the RAFT agent (2) is a trithiocarbonate monomer, the block copolymer X16 obtained in Comparative Example 7 is a di-block copolymer represented by B-C.

[0181] As indicated by the above results, the adhesive compositions of the various examples each exhibited little rise in adhesive strength. The adhesive strength and the creep characteristics were also favorable.

[0182] In contrast, in the case of the adhesive composition of Comparative Example 1, because the Mn value of the polymer block A exceeded 10,000 and A/(B+C) exceeded 5.0/95.0, the adhesive strength and the creep characteristics were inferior.

[0183] In the case of the adhesive composition of Comparative Example 2, because B/C was less than 5.0/95.0 and the acid value was less than 8 mgKOH/g, the adhesive strength was inferior.

[0184] In the case of the adhesive composition of Comparative Example 3, because B/C exceeded 30.0/70.0, the rise in adhesive strength was large.

[0185] The adhesive compositions of Comparative Examples 4 to 8 did not include a polymer block A, and therefore the rise in adhesive strength was large.

INDUSTRIAL APPLICABILITY

[0186] The adhesive composition of the present invention exhibits little rise in adhesive strength following bonding, making bonding adjustment easy.

[0187] The adhesive composition of the present invention can be used in various applications. For example, as outlined above, the adhesive composition may be used in applications in which the adherends are not peeled apart after bonding, and also in applications in which peeling of the adherends is necessary.