Ultraviolet curable silicone adhesive composition and silicone adhesive film

Abstract

This ultraviolet curable silicone adhesive composition that contains (A) an organopolysiloxane resin which contains (a) an R.sup.1.sub.3SiO.sub.1/2 unit (wherein R.sup.1 represents a monovalent hydrocarbon group) and (b) an SiO.sub.4/2 unit, and wherein the molar ratio of the unit (a) to the unit (b) is from 0.6:1 to 1.2:1, (B) a linear or branched organopolysiloxane which has a viscosity of more than 50 mPa.Math.s but 500,000 mPa.Math.s or less, while having 1-4 groups represented by formula (1) and/or (2) ##STR00001##
(wherein R.sup.2 represents H or Me, a represents a number of 1-3, and the broken line represents a bonding hand that is bonded with Si)
as Si-bonded groups, and wherein the main chain is composed of repeated diorganosiloxane units, and (C) a reactive diluent which is composed of an organo(poly)siloxane that has a viscosity of 1-50 mPa.Math.s, while having one group represented by formula (3) ##STR00002##
(wherein a is as defined above, and the broken line represents a bonding hand)
at an end of the molecular chain or in a molecular side chain as an Si-bonded group, is rapidly cured by means of irradiation of ultraviolet light, and exhibits good adhesion to a sheet-like substrate.

Claims

1. A UV-curable silicone pressure-sensitive adhesive composition comprising (A) 30 to 70 parts by weight of an organopolysiloxane resin (A) comprising (a) R.sup.1.sub.3SiO.sub.1/2 units wherein R.sup.1 is a substituted or unsubstituted C.sub.1-C.sub.10 monovalent hydrocarbon group and (b) SiO.sub.4/2 units, wherein a molar ratio of units (a) to units (b) is from 0.6:1 to 1.2:1, (B) 1 to 40 parts by weight of a linear or branched organopolysiloxane (B) having a backbone composed of repeating diorganosiloxane units and containing an average of 1 to 4 monovalent substituent groups per molecule, the monovalent substituent groups having the general formula (4): ##STR00025## wherein R.sup.2 is hydrogen or methyl, R.sup.3 is independently a substituted or unsubstituted C.sub.1-C.sub.10 monovalent hydrocarbon group, X is a C.sub.2-C.sub.6 alkylene group, a is an integer of 1 to 3, b is 1 or 2, and the broken line designates a valence bond to a silicon atom, the organopolysiloxane (B) having a viscosity at 25° C. of from more than 50 mPa.Math.s to 500,000 mPa.Math.s, and (C) 1 to 40 parts by weight of a reactive diluent, the reactive diluent being an organopolysiloxane (C) containing one monovalent group having the general formula (3): ##STR00026## wherein a is as defined above and the broken line designates a valence bond to a silicon atom at an end or on a side chain of the organopolysiloxane (C) molecular chain, the organopolysiloxane (C) having a viscosity at 25° C. of 1 to 50 mPa.Math.s, with the proviso that the total amount of organopolysiloxane resin (A), organopolysiloxane (B), and organopolysiloxane (C) is 100 parts by weight.

2. The silicone pressure-sensitive adhesive composition of claim 1 wherein the organopolysiloxane (B) contains monovalent substituent groups having the general formula (4) at both ends of the molecular chain.

3. The silicone pressure-sensitive adhesive composition of claim 1 or 2 wherein the backbone of the organopolysiloxane (B) consists of diphenylsiloxane repeating units having the general formula (6): ##STR00027## wherein Me is methyl, Ph is phenyl, c1 and c2 are integers in the range: c1≥0, c2≥1, and c1+c2=c, c is such a number that the organopolysiloxane (B) has a viscosity at 25° C. of from more than 50 mPa.Math.s to 500,000 mPa.Math.s, and the broken line designates a valence bond.

4. The silicone pressure-sensitive adhesive composition of claim 1 wherein the organopolysiloxane (C) has the general formula (7) or (8): ##STR00028## wherein R.sup.6 to R.sup.10 each are a substituted or unsubstituted C.sub.1-C.sub.12 monovalent hydrocarbon group, a is an integer of 1 to 3, the organo(poly)siloxane has a viscosity at 25° C. of 1 to 50 mPa.Math.s, d is an integer of 0 to 3, e and f are 0 or 1.

5. The silicone pressure-sensitive adhesive composition of claim 1, further comprising (D) 0.01 to 15 parts by weight of a photo-initiator per 100 parts by weight of the organopolysiloxane resin (A), the organopolysiloxane (B), and the organopolysiloxane (C) combined.

6. The silicone pressure-sensitive adhesive composition of claim 1 which forms a silicone pressure-sensitive adhesive having a storage elastic modulus of up to 1.0 MPa after curing, wherein the storage elastic modulus is measured at 1.0 Hz, an oscillation angle γ 4.0%, and a temperature of 25±0.5° C.

7. A silicone pressure-sensitive adhesive film comprising a substrate and a pressure-sensitive adhesive layer formed on at least one surface of the substrate, said pressure-sensitive adhesive layer being a UV-cured product of the silicone pressure-sensitive adhesive composition of claim 1.

8. The silicone pressure-sensitive adhesive film of claim 7 wherein the substrate is a plastic film.

Description

EXAMPLES

(1) Examples and Comparative Examples are given below for further illustrating the invention although the invention is not limited thereto. In Examples, parts are by weight. Me stands for methyl, Ph for phenyl, and tert-Bu for tert-butyl. The viscosity is as measured at 25° C. by a rotational viscometer.

(2) Component (A)

(3) (A-1) A 60 wt % toluene solution of an organopolysiloxane resin of three-dimensional network structure consisting of Me.sub.3SiO.sub.1/2 units and SiO.sub.2 units in a molar ratio (Me.sub.3SiO.sub.1/2 units)/(SiO.sub.2 units) of 1.15, viscosity 10 mPa.Math.s.
Component (B) (B-1) A linear diphenylsiloxane-dimethylsiloxane copolymer having a backbone consisting of repeating diphenylsiloxane units and dimethylsiloxane units wherein the diphenylsiloxane units and dimethylsiloxane units are randomly arranged in the backbone, and containing four acryloxyethyloxy groups in the molecule at both ends of the molecular chain (i.e., two groups at each molecular chain end), as represented by the following formula (10), viscosity 3,000 mPa.Math.s.

(4) ##STR00020## (B-2) A linear dimethylpolysiloxane having a backbone consisting of repeating dimethylsiloxane units and containing two acryloxymethyl groups in the molecule at both ends of the molecular chain (i.e., one group at each molecular chain end), as represented by the following formula (11), viscosity 100 mPa.Math.s.

(5) ##STR00021## (B-3) A linear dimethylpolysiloxane having a backbone consisting of repeating dimethylsiloxane units and containing per molecule one acryloxyethyloxy-dimethylsilylethyl group and one tert-butyl group at both ends of the molecular chain, as represented by the following formula (12), viscosity 80 mPa.Math.s.

(6) ##STR00022##
Component (C) (C-1) (acryloxypropyl)-pentamethyldisiloxane represented by the following formula (13), viscosity 2 mPa.Math.s.

(7) ##STR00023## (C-2) 3-(acryloxypropyl)-1,1,1,3,5,5,5-heptamethyltrisiloxane represented by the following formula (14), viscosity 6 mPa.Math.s.

(8) ##STR00024## (C-3) 3-acryloxypropyl-methyldimethoxysilane (KBM-5102 by Shin-Etsu Chemical Co., Ltd.) (C-4) 3-acryloxypropyl-trimethoxysilane (KBM-5103 by Shin-Etsu Chemical Co., Ltd.)
Component (D) (D-1) Darocur 1173 by BASF Japan

Examples 1 to 3 and Comparative Examples 1 to 3

(9) Silicone PSA compositions S1 to S6 were prepared by blending components (A) to (D) in accordance with the formulation in Table 1 and distilling off toluene at 100° C. in vacuum. The silicone PSA compositions were cured by exposure to UV of wavelength 365 nm from an Eye UV electronic control instrument (model: UBX0601-01, Eye Graphics Co., Ltd.) at room temperature (25° C.) in air atmosphere such that the exposure dose of UV light was 2,000 mJ/cm.sup.2.

(10) Notably, the amount of component (A) shown in Table 1 is the net amount (pbw) of solids with the solvent removed.

(11) The silicone PSA compositions and cured products thus obtained were evaluated with respect to the following items.

(12) [Measurement of Storage Elastic Modulus]

(13) The cured product of the silicone PSA composition was measured for storage elastic modulus by a viscoelasticity analyzer ARES-G2 (TA Instruments) under measurement conditions: frequency 1.0 Hz, oscillation angle γ 4.0%, and temperature 25±0.5° C. The results are shown in Table 1.

(14) [Measurement of Pressure-Sensitive Adhesion]

(15) Each of the silicone PSA compositions S1 to S6 was coated onto a support (sheet-like substrate) in the form of polyethylene terephthalate (PET) resin film so as to give a dry thickness of around 400 μm after curing, and cured by irradiating UV light of wavelength 365 nm in a dose of 2,000 mJ/cm.sup.2, whereby a PSA sheet was obtained. The PSA sheet was attached to a PET resin film of 25 mm wide, pressed by moving a pressing roller of 2 kg once back and forth, and allowed to stand for 24 hours in a 23° C. atmosphere, after which a 180° peeling force (bonding force) was measured at a pulling rate of 0.3 m/min. The test piece was also evaluated for breaking mode (CF: cohesive failure, AF: adhesive failure (interfacial peeling)). The results are also shown in Table 1.

(16) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 3 1 2 3 Silicone PSA composition S1 S2 S3 S4 S5 S6 Amount (pbw) (A-1) 60 60 50 60 60 50 (B-1) 20 20 25 20 20 — (B-2) — — — — — 15 (B-3) — — — — — 35 (C-1) 20 — 25 — — — (C-2) — 20 — — — — (C-3) — — — 20 — — (C-4) — — — — 20 — (D-1) 2.0 2.0 2.0 2.0 2.0 2.0 Storage elastic modulus (MPa) 0.08 0.3 0.05 2.0 12 0.07 Pressure-sensitive adhesion Bonding force 15 5.6 5.8 17 24 0.3 (to PET, N/25 mm) Breaking mode CF CF CF AF AF AF

(17) As seen from the results in Table 1, Examples 1 to 3 show a high bonding force to PET despite a relatively low storage modulus, demonstrating satisfactory pressure-sensitive adhesion. Because of a high storage modulus after curing, Comparative Examples 1 and 2 have a bonding force to PET, but show the breaking mode of interfacial peeling. Comparative Example 3 shows not only a low bonding force to PET, but also the breaking mode of interfacial peeling.