Pressure-sensitive adhesive tape, pressure-sensitive adhesive tape for affixing component for electronic appliance, and transparent pressure-sensitive adhesive tape for optical use

Abstract

The present invention aims to provide an adhesive tape excellent in resistance against sebum to be able to maintain its adhesive force even when applied to a part frequently touched with human hands, and an adhesive tape for fixing electronic device component and a transparent adhesive tape for optical use each provided with the adhesive tape. The present invention relates to an adhesive tape including an adhesive layer containing an acrylic adhesive, the adhesive layer having a swelling ratio of 100% or more and 130% or less after immersion in oleic acid under the conditions of a temperature of 60° C. and a humidity of 90% for 24 hours.

Claims

1. An adhesive tape comprising an adhesive layer comprising an acrylic adhesive comprising a (meth)acrylate copolymer comprising 30% by weight or more and 60% by weight or less of a constitutional unit derived from a fluorine-containing (meth)acrylate and 15% by weight or more and 40% by weight or less of a constitutional unit derived from an acrylate having an alkyl group with a carbon number of 2 or less, wherein the fluorine-containing (meth)acrylate is at least one selected from the group consisting of 2,2,2-trifluoroethylacrylate, 2-(perfluorohexyl)ethylacrylate, 2,2,3,3,3-pentafluoropropylacrylate, 2-(perfluorobutyl)ethylacrylate, 3-perfluorobutyl-2-hydroxypropylacrylate, 3-perfluorohexyl-2-hydroxypropylacrylate, 3-(perfluoro-3-methylbutyl)-2-hydroxypropylacrylate, 1H,1H,3H-tetrafluoropropylacrylate, 1H,1H,5H-octafluoropentylacrylate, 1H,1H,7H-dodecafluoroheptylacrylate, 1H-1-(trifluoromethyl)trifluoroethylacrylate, 1H,1H,3H-hexafluorobutylacrylate, and 1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethylacrylate, wherein the copolymer excludes a methyl methacrylate constitutional unit, and wherein the adhesive layer has a swelling ratio of 100% or more and 130% or less after immersion in oleic acid under the conditions of a temperature of 60° C. and a humidity of 90% for 24 hours.

2. The adhesive tape according to claim 1, wherein the amount of the constitutional unit derived from a fluorine-containing (meth)acrylate in the (meth)acrylate copolymer is 40% by weight or more.

3. The adhesive tape according to claim 1, wherein the (meth)acrylate copolymer has a weight average molecular weight of 250,000 or more.

4. The adhesive tape according to claim 1, wherein the adhesive layer has a gel fraction of 30% or more.

5. An adhesive tape for fixing an electronic device component comprising the adhesive tape according to claim 1.

6. A transparent adhesive tape for optical use comprising the adhesive tape according to claim 1.

7. The adhesive tape according to claim 1, wherein the fluorine-containing (meth)acrylate is at least one selected from the group consisting of 2,2,2-trifluoroethylacrylate and 2-(perfluorohexyl)ethylacrylate.

Description

DESCRIPTION OF EMBODIMENTS

(1) The present invention is more specifically described in the following with reference to, but not limited to, examples.

Example 1

(2) (1) Production of a (Meth)Acrylate Copolymer

(3) A reaction vessel was charged with ethyl acetate as a polymerization solvent, and the ethyl acetate was bubbled with nitrogen. The reaction vessel was heated while nitrogen was flowed thereinto, thereby starting reflux. Subsequently, to the reaction vessel was charged a polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile, as a polymerization initiator, 10 times with ethyl acetate. Then, 63.5 parts by weight of butyl acrylate, 33.5 parts by weight of 2,2,2-trifluoroethylacrylate, and 3 parts by weight of acrylic acid were dropwise added over two hours. After the dropwise addition, the polymerization initiator solution prepared by diluting 0.1 parts by weight of azobisisobutyronitrile, as a polymerization initiator, 10 times with ethyl acetate was again added to the reaction vessel, and the polymerization reaction was allowed to proceed for four hours. Thus, a (meth)acrylate copolymer-containing solution was obtained.

(4) (2) Production of an Adhesive Tape

(5) To the obtained (meth)acrylate copolymer-containing solution was added TETRAD-C (Mitsubishi Gas Chemical Company), as an epoxy crosslinking agent, in an amount of 1 part by weight relative to 100 parts by weight of the (meth)acrylate copolymer-containing solution. The mixed solution was applied to a release-treated PET film having a thickness of 75 μm such that the dried adhesive layer had a thickness of 35 μm, followed by drying at 110° C. for five minutes. This adhesive layer was transferred to a corona-treated PET film having a thickness of 50 μm as a substrate, and then allowed to stand at 40° C. for 48 hours. Thus, an adhesive tape was obtained.

(6) (3) Measurement of Gel Fraction

(7) A plane rectangular test piece (20 mm×40 mm) was cut out from the obtained adhesive tape, and the weight thereof was measured. The test piece was immersed in ethyl acetate at 23° C. for 24 hours, taken out from the ethyl acetate, and dried at 110° C. for one hour. The weight of the dried test piece was measured, and the gel fraction was calculated using the following equation (1):
Gel fraction (% by weight)=100×(W2−W0)/(W1−W0)  (1)
(W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying).
(4) Measurement of Oleic Acid Swelling Ratio

(8) A plane rectangular test piece (20 mm×40 mm) was cut out from the obtained adhesive tape, and the weight thereof was measured. The test piece was immersed in oleic acid under the conditions of a temperature of 60° C. and a humidity of 90% for 24 hours, and taken out from the oleic acid. The surface of the test piece was washed with ethanol. Then, the test piece was dried at 110° C. for three hours. The weight of the dried test piece was measured, and the oleic acid swelling ratio of the acrylic adhesive was calculated using the following equation (2):
Swelling ratio (% by weight)=100×(W5−W3)/(W4−W3)  (2)
(W3: weight of substrate, W4: weight of test piece before immersion in oleic acid, W5: weight of test piece after immersion in oleic acid and drying).

Examples 2 to 20, Comparative Examples 1 to 5

(9) Adhesive tapes were obtained in the same manner as in Example 1, except that the types and amounts of the monomer and crosslinking agent to be used were changed as shown in Tables 1 to 4, and the gel fraction and the oleic acid swelling ratio of each were measured.

(10) Coronate L-45 in the tables is an isocyanate crosslinking agent available from Tosoh Corporation.

Example 21

(11) A reaction vessel was charged with 99 parts by weight of 2,2,3,3,3-pentafluoropropylacrylate, 0.5 parts by weight of acrylic acid, and 0.1 parts by weight of product name “IRGACURE 651” available from Ciba Specialty Chemicals Inc. as a photopolymerization initiator. The contents were bubbled with nitrogen, and then irradiated with UV light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature of 30° C.) reached about 8,000 mPa.Math.s, while nitrogen was flowed into the reaction vessel. Then, 0.5 parts by weight of trimethylolpropanetriacrylate (Tokyo Chemical Industry Co., Ltd.) was added thereto. Thus, a composition for forming an adhesive layer was prepared.

(12) The obtained composition for forming an adhesive layer was applied to a polyethylene terephthalate (PET) film having a thickness of 75 μm such that the dried adhesive layer had a thickness of 35 μm, and attached to a corona-treated PET film having a thickness of 50 μm serving as a substrate, thereby preparing a laminated sheet. The obtained laminated sheet was irradiated with UV light at an illuminance of 5 mW/cm.sup.2 from the substrate PET film side for five minutes using a black light (Toshiba Corporation). Thus, an adhesive tape was obtained.

(13) The gel fraction and the oleic acid swelling ratio of the obtained adhesive tape were measured in the same manner as in Example 1.

Example 22

(14) A (meth)acrylate copolymer-containing solution was obtained in the same manner as in Example 1, except that the types and amounts of the monomer and crosslinking agent used were set as shown in Table 5.

(15) To the obtained (meth)acrylate copolymer-containing solution were added TETRAD-C (Mitsubishi Gas Chemical Company) as an epoxy crosslinking agent in an amount of 0.1 parts by weight relative to 100 parts by weight of the (meth)acrylate copolymer-containing solution. The resulting solution was applied to a release-treated PET film having a thickness of 75 μm such that the dried adhesive layer had a thickness of 15 μm, and dried at 110° C. for five minutes. Another release-treated PET film having a thickness of 75 μm was attached to sandwich the adhesive layer, and the resulting laminate was allowed to stand at 40° C. for 48 hours. Thus, a non-supported type adhesive tape including no substrate was obtained.

(16) The gel fraction and the oleic acid swelling ratio of the obtained adhesive tape were measured in the same manner as in Example 1.

(17) A 15 mm×15 mm piece was cut out from the obtained adhesive tape, and the release film on each surface was peeled. The one surface of the adhesive tape was attached to a glass plate, thereby obtaining a measurement sample. The total light transmittance of the obtained measurement sample was measured with “Haze Meter NDH4000” available from Nippon Denshoku Industries Co., Ltd., and was 99%. The Haze value was 0.23%. The Y value of the sample was measured with “SPECTROPHOTOMETER CM-3700d” available from Konica Minolta, Inc., and was 0.245. The L* coordinate was 99.7, the a* coordinate was 0, and the b* coordinate was 0.02. These optical properties show that the obtained adhesive tape exhibits sufficient performance as a transparent adhesive tape for optical use.

(18) (Evaluation)

(19) The adhesive tapes obtained in the examples and comparative examples were evaluated for the following parameters. Tables 1 to 5 show the results.

(20) (1) Measurement of 180° Peel Adhesive Force

(21) A rectangular test piece having a width of 10 mm was cut out from the obtained adhesive tape, and one release film was peeled from the test piece to expose the adhesive layer. The test piece was placed on a stainless-steel plate in such a manner that the adhesive layer faces the stainless-steel plate. The test piece was bonded to the stainless-steel plate by one reciprocating motion of a 2-kg rubber roller on the test piece at a rate of 300 mm/min, and then allowed to stand at 23° C. for 24 hours. Thus, a test sample was prepared. The test sample was heated in an oven under the conditions of a temperature of 60° C. and a humidity of 90% for 100 hours, allowed to stand at 23° C. for 24 hours, and subjected to a tensile test in a 180° direction at a peel rate of 300 mm/min in conformity with JIS 20237. Thus, the 180° peel adhesive force (N/mm) before immersion in oleic acid was measured.

(22) In Example 22, after bonding of the test piece to the stainless-steel plate, the other release film was peeled off to expose the adhesive layer, and a PET film having a thickness of 50 μm was attached thereto. The laminate was allowed to stand at 23° C. for 24 hours, thereby preparing a test sample.

(23) The test sample was immersed in an oleic acid bath under the conditions of a temperature of 60° C. and a humidity of 90% for 100 hours, taken out from the bath, washed with water, and allowed to stand for 24 hours. The resulting test sample was subjected to the above peel test. Thus, the 180° peel adhesive force after immersion in oleic acid was measured.

(24) Based on the 180° peel adhesive force of a blank test sample and the 180° peel adhesive force of the test sample after immersion in oleic acid, the residual adhesive force ratio (%) was calculated using the following equation (3). The case where the residual adhesive force ratio was 20% or higher or the 180° peel adhesive force after immersion in oleic acid was 0.2 N/mm or more was rated “∘∘ (Excellent)”. The case where the residual adhesive force ratio was 5% or higher or the 180° peel adhesive force after immersion in oleic acid was 0.04 N/mm or more was rated “∘ (Good)”. The case where the residual adhesive force ratio was lower than 5% was rated “x (Poor)”.
Residual adhesive force ratio (%)=(180° peel adhesive force after immersion in oleic acid/180° peel adhesive force before immersion in oleic acid)×100  (3)
(2) Evaluation of Tackiness

(25) The adhesive surface of the produced adhesive tape was touched with a hand, and tackiness of the adhesive tape was evaluated by sensory evaluation. The tackiness was evaluated on a four-point scale where the tackiness of Example 18 was taken as “slight tackiness” and the tackiness of Comparative Example 1 was taken as “high tackiness”.

(26) 1: slight tackiness, 2: low tackiness, 3: medium tackiness, 4: high tackiness

(27) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Acrylic Monomer Methyl acrylate 0 0 0 0 adhesive composition of Ethyl acrylate 0 0 33.5 23.5 (meth)acrylate Butyl acrylate 63.5 47 33.5 23.5 copolymer 2-Ethylhexylacrylate 0 0 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 33.5 50 30 50 2-(perfluorohexyl)ethylacrylate 0 0 0 0 2,2,3,3,3-pentafluoropropylacrylate 0 0 0 0 Acrylic acid 3 3 3 3 Weight average molecular weight 1020000 1040000 1200000 1090000 Crosslinking agent TETRAD-C 1 1 1 1 [parts by weight] Coronate L-45 0 0 0 0 Thickness of adhesive layer [μm] 35 35 35 35 Gel fraction [%] 88 92 92 93 Oleic acid swelling ratio [%] 125 118 106 108 Evaluation 180° peel Before immersion in oleic acid [N/mm] 0.93 0.99 0.92 1.19 adhesive force After immersion in oleic acid [N/mm] 0.05 0.09 0.21 0.40 Residual adhesive force ratio [%] 5.4 8.8 22.8 34.0 Judgement ∘∘ ∘∘ ∘∘ ∘∘ Tackiness 3 3 2 2 Example 5 Example 6 Example 7 Example 8 Acrylic Monomer Methyl acrylate 0 0 0 0 adhesive composition of Ethyl acrylate 0 23.5 23.5 0 (meth)acrylate Butyl acrylate 47 23.5 23.5 17 copolymer 2-Ethylhexylacrylate 0 0 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 0 0 0 0 2-(perfluorohexyl)ethylacrylate 50 50 50 0 2,2,3,3,3-pentafluoropropylacrylate 0 0 0 80 Acrylic acid 3 3 3 3 Weight average molecular weight 690000 960000 750000 950000 Crosslinking agent TETRAD-C 0.2 0.2 0.2 0.2 [parts by weight] Coronate L-45 0 0 0 0 Thickness of adhesive layer [μm] 35 35 35 35 Gel fraction [%] 66 82 42 91 Oleic acid swelling ratio [%] 112 102 105 102 Evaluation 180° peel Before immersion in oleic acid [N/mm] 0.88 1.21 1.24 0.84 adhesive force After immersion in oleic acid [N/mm] 0.13 0.33 0.33 0.16 Residual adhesive force ratio [%] 14.7 27.6 26.7 18.5 Judgement ∘∘ ∘∘ ∘∘ ∘∘ Tackiness 3 2 2 2

(28) TABLE-US-00002 TABLE 2 Example 9 Example 10 Example 11 Example 12 Example 13 Acrylic Monomer Methyl acrylate 0 0 0 0 0 adhesive composition of Ethyl acrylate 0 0 0 0 0 (meth)acrylate Butyl acrylate 67 67 59 57 57 copolymer 2-Ethylhexylacrylate 0 0 0 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 30 30 38 40 40 2-(perfluorohexyl)ethylacrylate 0 0 0 0 0 2,2,3,3,3-pentafluoropropylacrylate 0 0 0 0 0 Acrylic acid 3 3 3 3 3 Weight average molecular weight 1100000 1100000 1000000 1120000 1120000 Crosslinking agent TETRAD-C 1 0.05 0.3 1 0.1 [parts by weight] Coronate L-45 0 0 0 0 0 Thickness of adhesive layer [μm] 35 35 35 35 35 Gel fraction [%] 89 12 35 91 18 Oleic acid swelling ratio [%] 128 129 122 119 120 Evaluation 180° peel adhesive Before immersion in oleic acid [N/mm] 0.74 0.80 0.88 0.90 0.96 force After immersion in oleic acid [N/mm] 0.05 0.04 0.06 0.08 0.12 Residual adhesive force ratio [%] 6.8 5.0 6.8 8.9 12.5 Judgement ∘∘ ∘∘ ∘∘ ∘∘ ∘∘ Tackiness 3 3 3 3 3 Example 14 Example 15 Example 16 Example 17 Acrylic Monomer Methyl acrylate 0 0 0 0 adhesive composition of Ethyl acrylate 0 0 0 0 (meth)acrylate Butyl acrylate 57 57 47 17 copolymer 2-Ethylhexylacrylate 0 0 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 40 0 0 0 2-(perfluorohexyl)ethylacrylate 0 40 50 0 2,2,3,3,3-pentafluoropropylacrylate 0 0 0 80 Acrylic acid 3 3 3 3 Weight average molecular weight 250000 280000 450000 950000 Crosslinking agent TETRAD-C 1 0.1 0.1 0 [parts by weight] Coronate L-45 0 0 0 1 Thickness of adhesive layer [μm] 35 35 35 35 Gel fraction [%] 45 12 15 60 Oleic acid swelling ratio [%] 126 128 122 102 Evaluation 180° peel adhesive Before immersion in oleic acid [N/mm] 0.96 0.79 0.85 0.88 force After immersion in oleic acid [N/mm] 0.05 0.04 0.11 0.20 Residual adhesive force ratio [%] 5.2 5.1 12.9 22.7 Judgement ∘∘ ∘∘ ∘∘ ∘∘ Tackiness 3 3 3 2

(29) TABLE-US-00003 TABLE 3 Example 18 Example 19 Example 20 Acrylic Monomer Methyl acrylate 0 0 60 adhesive composition of Ethyl acrylate 97 90 20 (meth)acrylate Butyl acrylate 0 7 17 copolymer 2-Ethylhexylacrylate 0 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 0 0 0 2-(perfluorohexyl)ethylacrylate 0 0 0 2,2,3,3,3-pentafluoropropylacrylate 0 0 0 Acrylic acid 3 3 3 Weight average molecular weight 280000 510000 580000 Crosslinking agent TETRAD-C 1 1 1 [parts by weight] Coronate L-45 0 0 0 Thickness of adhesive layer [μm] 35 35 35 Gel fraction [%] 96 92 85 Oleic acid swelling ratio [%] 125 129 125 Evaluation 180° peel adhesive Before immersion in oleic acid [N/mm] 1.09 1.02 0.82 force After immersion in oleic acid [N/mm] 0.31 0.29 0.22 Residual adhesive force ratio [%] 28.1 28.4 26.9 Judgement ∘∘ ∘∘ ∘∘ Tackiness 1 1 1

(30) TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Acrylic Monomer Methyl acrylate 0 0 0 0 0 adhesive composition of Ethyl acrylate 0 0 58.5 0 0 (meth)acrylate Butyl acrylate 97 0 38.5 68.5 47 copolymer 2-Ethylhexylacrylate 0 97 0 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 0 0 0 28.5 0 2-(perfluorohexyl)ethylacrylate 0 0 0 0 50 2,2,3,3,3-pentafluoropropylacrylate 0 0 0 0 0 Acrylic acid 3 3 3 3 3 Weight average molecular weight 1040000 1070000 670000 1120000 100000 Crosslinking agent TETRAD-C 1 1 1 1 0.1 [parts by weight] Coronate L-45 0 0 0 0 — Thickness of adhesive layer [μm] 35 35 35 35 35 Gel fraction [%] 97 93 92 92 10 Oleic acid swelling ratio [%] 238 215 160 134 180 Evaluation 180° peel adhesive Before immersion in oleic acid [N/mm] 0.67 0.76 0.78 0.80 0.51 force After immersion in oleic acid [N/mm] 0.001 0.001 0.001 0.003 0.001 Residual adhesive force ratio [%] 0.2 0.1 0.2 0.3 0.2 Judgement x x x x x Tackiness 4 4 3 2 3

(31) TABLE-US-00005 TABLE 5 Example 21 Example 22 Acrylic Monomer Methyl acrylate 0 0 adhesive composition of Ethyl acrylate 0 23.5 (meth)acrylate Butyl acrylate 0 23.5 copolymer 2-Ethylhexylacrylate 0 0 [parts by weight] 2,2,2-trifluoroethylacrylate 0 0 2-(perfluorohexyl)ethylacrylate 0 50 2,2,3,3,3-pentafluoropropylacrylate 99 0 Acrylic acid 0.5 3 Trimethyrolpropane triacrylate 0.5 0 Weight average molecular weight 1800000 960000 Crosslinking agent TETRAD-C 0 0.1 [parts by weight] Coronate L-45 0 0 Thickness of adhesive layer [μm] 35 15 Gel fraction [%] 98 60 Oleic acid swelling ratio [%] 100 103 Evaluation 180° peel adhesive Before immersion in oleic acid [N/mm] 0.25 0.89 force After immersion in oleic acid [N/mm] 0.18 0.26 Residual adhesive force ratio [%] 72.0 29.2 Judgement ∘∘ ∘∘ Tackiness 2 2

INDUSTRIAL APPLICABILITY

(32) The present invention can provide an adhesive tape excellent in resistance against sebum to be able to maintain its adhesive force even when applied to a part frequently touched with human hands, and an adhesive tape for fixing electronic device component and a transparent adhesive tape for optical use each provided with the adhesive tape.