Pressure-sensitive adhesive composition

Abstract

The present invention relates to a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition of the present invention exhibits excellent dependability under a high temperature or high humidity condition, and also has excellent stress relaxation property and reworkability when being applied to a polarizing plate, and thus, it can effectively prevent warpage. Accordingly, the pressure-sensitive adhesive composition can be usefully applied for an optical film.

Claims

1. A pressure-sensitive adhesive composition comprising: a block copolymer including 5 parts by weight to 40 parts by weight of a first block having a glass transition temperature of 50 C. or more, and 60 parts by weight to 95 parts by weight of a second block having a glass transition temperature of 10 C. or less; and a multifunctional compound having two or more radical polymerization groups, wherein the first block consists of an alkyl (meth)acrylate monomer as a polymerization unit, and the second block comprises 90 to 99.9 parts by weight of an acrylic acid ester monomer and 0.1 to 10 parts by weight of a copolymerizable monomer having a thermosetting functional group as a polymerization unit, and wherein the multifunctional compound is a multifunctional acrylate comprising a cyclic structure.

2. The pressure-sensitive adhesive composition of claim 1, wherein the block copolymer is a diblock copolymer including the first block and the second block.

3. The pressure-sensitive adhesive composition of claim 1, further comprising a multifunctional cross-linker having two or more functional groups capable of reacting with a thermosetting functional group.

4. The pressure-sensitive adhesive composition of claim 3, wherein the multifunctional cross-linker is an isocyanate cross-linker, an epoxy cross-linker, an aziridine cross-linker or a metal chelate cross-linker.

5. The pressure-sensitive adhesive composition of claim 3, wherein the multifunctional cross-linker is comprised in an amount of 0.01 part by weight to 20 parts by weight, relative to 100 parts by weight of the block copolymer.

6. The pressure-sensitive adhesive composition of claim 1, further comprising a radical polymerization initiator.

7. The pressure-sensitive adhesive composition of claim 6, wherein the radical polymerization initiator is comprised in an amount of 0.01 part by weight to 10 parts by weight, relative to 100 parts by weight of the block copolymer.

8. The pressure-sensitive adhesive composition of claim 1, wherein the multifunctional compound is comprised in an amount of 1 part by weight to 20 parts by weight, relative to 100 parts by weight of the block copolymer.

9. The pressure-sensitive adhesive composition of claim 1, wherein after a cross-linked structure is realized, a gel fraction is 80 weight % or less.

10. A pressure-sensitive adhesive optical laminate comprising: an optical film; and a pressure-sensitive adhesive layer which is formed on one or both surfaces of the optical film, and comprises the cross-linked pressure-sensitive adhesive composition of claim 1.

11. A display device comprising the pressure-sensitive adhesive optical laminate of claim 10.

12. A pressure-sensitive adhesive polarizing plate comprising: a polarizing film; and a pressure-sensitive adhesive layer which is formed on one or both surfaces of the polarizing film, and comprises the cross-linked pressure-sensitive adhesive composition of claim 1.

13. A display device comprising the pressure-sensitive adhesive polarizing plate of claim 12, which is attached to one or both surfaces of a liquid crystal panel.

Description

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(1) Exemplary embodiments of the present invention will be described in detail below with reference to the accompanying drawings. While the present invention is shown and described in connection with exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.

(2) Hereinafter, a pressure-sensitive adhesive composition will be described in detail with reference to Examples and Comparative Examples, but a range of the pressure-sensitive adhesive composition is not limited by the following Examples and Comparative Examples.

(3) 1. Evaluation of Molecular Weight

(4) A number average molecular weight (Mn) and a molecular weight distribution (PDI) were measured using a GPC under the following conditions. To prepare a calibration curve, measurement results were converted using standard polystyrene produced by Agilent System.

(5) <Measurement Conditions>

(6) Gauge: Agilent GPC (Agilent 1200 series, U.S.)

(7) Column: Two PL Mixed Bs connected

(8) Column Temperature: 40 C.

(9) Eluent: THF (Tetrahydrofuran)

(10) Flow Rate: 1.0 mL/min

(11) Concentration: About 1 mg/mL (100 L injection)

(12) 2. Measurement of Storage Modulus of Elasticity

(13) A pressure-sensitive adhesive layer having a thickness of about 25 m was obtained by irradiating UV to a pressure-sensitive adhesive between release films and aging the pressure-sensitive adhesive under constant temperature/humidity conditions (23 C., 50% RH) for 7 days. The pressure-sensitive adhesive between release films was prepared as a columnar sample having a size of 8 mm1 mm, and a storage modulus of elasticity of the sample between parallel plates was measured using a dynamic rheometer (ARES, RDA, manufactured by TA Instruments) at a frequency of 1 Hz while applying a shear stress.

(14) 3. Evaluation of Heat-Resistant, High Temperature-Resistant and Wet Heat-Resistant Durability

(15) Polarizing plates prepared in Examples and Comparative Examples were cut into pieces having a width of about 180 mm and a length of about 320 mm to prepare samples. The samples were attached to a 19-inch commercially available panel. Then, the panel was kept in an autoclave (50 C., 5 atm) for about 20 minutes to prepare samples. The heat-resistant durability of the prepared samples was evaluated according to the following evaluation criteria after the samples were kept at 80 C. for 500 hours and appearance of bubbles and peels were observed, the high temperature-resistant durability was evaluated according to the following evaluation criteria after the samples were kept at 100 C. for 500 hours and appearance of bubbles and peels were observed, and the wet heat-resistant durability was evaluated according to the following evaluation criteria after the samples were left at 60 C. with a relative humidity of 90% for 500 hours and then appearance of bubbles and peels at a pressure-sensitive adhesive interface were observed:

(16) <Evaluation Criteria>

(17) A: Bubbles and peels are not generated.

(18) B: Bubbles and/or peels are slightly generated.

(19) C: Bubbles and/or peels are highly generated.

(20) 4. Calculation of Glass Transition Temperature

(21) Glass transition temperatures Tg of the respective blocks of the block copolymer were calculated according to the following Equation:
1/Tg=Wn/Tn<Equation>

(22) In the above Equation, Wn represents a weight fraction of a monomer used in each block, and Tn represents a glass transition temperature when the monomer used forms a homopolymer.

(23) That is, the right hand side in the above Equation is the sum of values (Wn/Tn) of respective monomers calculated by dividing a weight fraction of a monomer used by a glass transition temperature when the monomer forms a homopolymer.

(24) 5. Measurement of Conversion Rate and Composition Ratio of Monomer

(25) Conversion rates of methyl methacrylate (MMA) as a main monomer constituting a first block and butyl acrylate (BA) as a main monomer constituting a second block during polymerization in block copolymers of Examples and Comparative Examples and composition contents thereof in the block copolymers were calculated according to the following Equation based on a result of 1H-NMR.

(26) <MMA Conversion Rate>
MMA Conversion Rate(%)=100B/(A+B)

(27) In the above Equation, A represents an area of a peak (around 3.4 ppm to 3.7 ppm) derived from a methyl group induced from MMA included in the polymer in the 1H-NMR spectrum, and B represents an area of a peak (around 3.7 ppm) derived from a methyl group of unpolymerized MMA. That is, a conversion rate of the monomer was calculated in consideration of a movement position of the methyl group peak in the MMA structure.

(28) <BA Conversion Rate>
BA Conversion Rate(%)=100C/(C+D)

(29) In the above Equation, D represents an area of a peak (around 5.7 ppm to 6.4 ppm) derived from CH.sub.2 at a double bond terminal of BA in the 1H-NMR spectrum, and C represents an area of a peak (around 3.8 ppm to 4.2 ppm) derived from OCH.sub.2 present in the polymer formed by polymerization of BA. That is, a conversion ratio of BA was measured by calculating relative values of the CH.sub.2 peak of BA and the OCH.sub.2 peak of the polymer.

(30) <Calculation of Composition Ratio>

(31) A ratio between a first block and a second block in a block copolymer was calculated according to the following Equation based on a ratio between methyl methacrylate (MMA) and butyl acrylate (BA) as main monomers constituting the first block and the second block, respectively.
MMA Content(%) in Block Copolymer=100MMA Peak Area/BA Peak Area<Equation>

(32) In the above Equation, the MMA peak area is an area per 1H proton of the peak (peak observed due to CH.sub.3 derived from MMA) around 3.4 ppm to 3.7 ppm in the 1H-NMR, and the BA peak area is an area per 1H proton of the peak (peak observed due to OCH.sub.2 present in the polymer formed of BA) around 3.8 ppm to 4.2 ppm in the 1H-NMR.

(33) That is, a weight ratio between the first and second blocks was calculated by calculating relative values of the CH.sub.3 peak of the MMA structure and the OCH.sub.2 peak of the polymer formed of BA.

(34) 6. Evaluation of Transparency

(35) Each of the pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples was coated onto a release-treated surface of a 38 m-thick PET (poly(ethyleneterephthalate)) film (MRF-38 manufactured by Mitsubishi Corporation) release-treated so that a thickness after drying could be about 40 m, and kept at 110 C. for about 3 minutes in an oven. Then, transparency of the coated pressure-sensitive adhesive layer was observed with the naked eye and evaluated according to the following evaluation criteria.

(36) <Evaluation Criteria>

(37) A: A coated layer is very transparent.

(38) B: A coated layer is slightly transparent, opaque, or extremely opaque.

(39) Preparation Example 1. Preparation of Block Copolymer (A1)

(40) 0.12 g of EBiB (ethyl 2-bromoisobutyrate) and 14.2 g of methyl methacrylate (MMA) were mixed with 6.2 g of ethyl acetate (EAc). A flask of the mixture was sealed with a rubber film, and the mixture was nitrogen-purged and stirred at about 25 C. for about 30 minutes. Then, dissolved oxygen was removed by bubbling. Then, 0.0025 g of CuBr.sub.2, 0.006 g of TPMA (tris(2-pyridylmethyl)amine), and 0.019 g of V-65 (2,2-azobis(2,4-dimethyl valeronitrile)) were added to the mixture from which oxygen was removed, and the resultant mixture was immersed in a reactor at about 67 C. to initiate a reaction (polymerization of a first block). At the time when a conversion rate of methyl methacrylate was about 75%, a mixture of 115 g of butyl acrylate (BA) previously undergoing bubbling with nitrogen, 0.8 g of hydroxybutyl acrylate (HBA), and 250 g of ethyl acetate (EAc) was added thereto in the presence of nitrogen. Then, 0.006 g of CuBr.sub.2, 0.01 g of TPMA, and 0.05 g of V-65 were put into the reaction flask to carry out a chain extension reaction (polymerization of a second block). When a conversion rate of the monomer (BA) reached 80% or more, the reaction mixture was exposed to oxygen and diluted in an adequate solvent to terminate the reaction, thereby preparing a block copolymer (In the above process, V-65 was appropriately added in installments in consideration of its half-life until the reaction was terminated.).

Preparation Example 2. Preparation of Block Copolymer (B1)

(41) A block copolymer was prepared in the same manner as Preparation Example 1 except that a weight ratio of a first block and a second block was controlled as shown in the following Table 1.

(42) TABLE-US-00001 TABLE 1 Block copolymer A1 B1 First MMA ratio 90 90 block BMA ratio 10 10 Tg ( C.) 90 90 Mn (10000) 3.5 3.5 PDI 1.34 1.34 Second BA ratio 97 97 block HBA ratio 1.5 1.5 Tg ( C.) 45 45 Block Mn (10000) 10.6 12.2 copolymer PDI 1.8 1.9 First block:Second 10.1:89.9 40.5:59.5 block (Weight ratio) Monomer ratio unit: part by weight MMA: methyl methacrylate (Homopolymer Tg: about 110 C.) BMA: butyl methacrylate (Homopolymer Tg: about 27 C.) BA: butyl acrylate (Homopolymer Tg: about 45 C.) HBA: 4-hydroxybutyl acrylate (Homopolymer Tg: about 80 C.) Tg: glass transition temperature Mn: number average molecular weight PDI: molecular weight distribution

Example 1

(43) Preparation of Coating Solution (Pressure-Sensitive Adhesive Composition)

(44) A coating solution (pressure-sensitive adhesive composition) was prepared by mixing 7 parts by weight of tris methacryloxy ethylisocyanurate as a multifunctional compound, 0.2 parts by weight of hydroxycyclohexyl phenyl ketone (Irgacure 184, produced by BASF) as a photoinitiator, 0.04 parts by weight of a cross-linker (Coronate L, produced by NPU, Japan), 0.1 parts by weight of DBTDL (Dibutyltin dilaurate), and 0.2 parts by weight of a silane coupling agent having a -cyanoacetyl group with respect to 100 parts by weight of the block copolymer (A1) prepared in Preparation Example 1, and mixing the resultant mixture with ethyl acetate as a solvent.

(45) Preparation of Pressure-Sensitive Adhesive Polarizing Plate

(46) The prepared coating solution was coated onto a release-treated surface of a 38 m-thick PET (poly(ethyleneterephthalate)) film (MRF-38 manufactured by Mitsubishi Corporation) release-treated so that a thickness after drying could be about 23 m, and kept at 110 C. for about 3 minutes in an oven. A pressure-sensitive adhesive polarizing plate was prepared by laminating the coating layer formed on the release-treated PET film on a WV (Wide View) liquid crystal layer of a polarizing plate (TAC/PVA/TAC-laminated structure: TAC=triacetylcellulose, PVA=polyvinylalcohol-based polarizing film), of which one surface was coated with the WV liquid crystal layer, after drying.

Example 2 and Comparative Examples 1 to 4

(47) A pressure-sensitive adhesive composition (coating solution) and a pressure-sensitive adhesive polarizing plate were prepared in the same manner as Example 1 except that each component and a ratio were regulated as shown in the following Table 2 when the pressure-sensitive adhesive composition (coating solution) was prepared.

(48) TABLE-US-00002 TABLE 2 Example Comparative Examples 1 2 1 2 3 4 Block Kind A1 A1 A1 B1 B1 B1 copolymer Content 100 100 100 100 100 100 MFA content 7 10 20 15 Photoinitiator 0.2 0.2 0.2 1.0 content Cross-linker content 0.04 0.03 0.04 0.04 0.04 0.03 DBTDL content 0.1 0.1 0.1 0.1 0.1 0.1 SCA content 0.2 0.2 0.2 0.2 0.2 0.2 Content unit: part by weight MFA: tris(meth)acryloxy ethyl isocyanurate Photoinitiator: hydroxycyclohexyl phenyl ketone (Irgacure 184, produced by BASF) Cross-linker: Coronate L, produced by NPU, Japan DBTDL: dibutyltin dilaurate SCA: silane coupling agent having a -cyanoacetyl group (M812, produced by LG Chem.)

(49) Property evaluation results of the respective Examples and Comparative Examples are as shown in the following Table 3.

(50) TABLE-US-00003 TABLE 3 Example Comparative Examples 1 2 1 2 3 4 Storage modulus of 0.07 0.09 0.04 0.21 0.17 0.10 elasticity (unit: MPa) Heat-resistant durability A A A A A A High temperature- A A C C C A resistant durability Humidity-resistant A A A C B C durability Transparency