Pressure-sensitive adhesive composition

Abstract

The present invention relates to a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition of the present invention can provide a pressure-sensitive adhesive having low time-dependency of dependability and adhesion strength and having excellent interfacial adhesion strength. After being applied to an optical member such as a polarizing plate, the pressure-sensitive adhesive composition exhibits excellent interfacial adhesion strength and maintains excellent dependability without time-dependency.

Claims

1. A pressure-sensitive adhesive composition comprising: a block copolymer including a first block having a glass transition temperature of 50° C. or more, and a second block having a glass transition temperature of −10° C. or less and including a radical polymerization group and a thermosetting functional group; and a multifunctional cross-linker, wherein the block copolymer is a diblock copolymer including the first block and the second block, and the first block comprises a polymerized unit induced from a methacrylic acid ester monomer, and the second block comprises: a main chain comprising a polymerized unit including an acrylic acid ester monomer and a copolymerizable monomer having the thermosetting functional group in the form of a polymer; and a radical polymerization compound which is bonded to the thermosetting functional group of the main chain and provides the radical polymerization group, wherein the radical polymerization compound comprises at least one selected from the group consisting of a compound expressed by the following Chemical Formula 1; a compound expressed by the following Chemical Formula 2; a compound expressed by the following Chemical Formula 3, a reaction product of a multifunctional isocyanate compound and a compound expressed by the following Chemical Formula 4; a reaction product of a multifunctional isocyanate compound, a polyol compound, and a compound expressed by the following Chemical Formula 4, and a compound expressed by the following Chemical Formula 5: ##STR00002## wherein in the above Chemical Formulas 1 to 5, R.sub.1 represents an alkyl group substituted with a (meth)acryloxy group; an alkyl group substituted with a (meth)acryloxyalkyl group; an alkyl group substituted with an alkenylphenyl group; a (meth)acryloyl group; a (meth)acryloxy group; or an alkenyl group, R.sub.2 represents hydrogen or an alkyl group, R.sub.3 represents hydrogen; an alkyl group substituted with an aziridinyl group; or a glycidyl group, R.sub.4 represents a (meth)acryloxyalkyl group, R.sub.5 represents a halogen atom, R.sub.6 represents an alkyl group, R.sub.7 represents a hydroxyalkyl group, R.sub.8 represents an alkenyl group, n+m+1 represents 4, and n and m independently represent 1 to 3.

2. The pressure-sensitive adhesive composition of claim 1, wherein the main chain includes 90 parts by weight to 99.9 parts by weight of the acrylic acid ester monomer and 0.01 part by weight to 10 parts by weight of the copolymerizable monomer having the thermosetting functional group in the form of a polymer, and a molar amount of the radical polymerization compound bonded to the main chain is 0.01 time to 1 time, relative to a molar amount of 1 part by weight of the copolymerizable monomer.

3. The pressure-sensitive adhesive composition of claim 1, wherein the thermosetting functional group is a hydroxyl group, a carboxyl group, an amino group, an isocyanate group or an epoxy group.

4. The pressure-sensitive adhesive composition of claim 1, wherein the block copolymer has a number average molecular weight of 50,000 to 300,000.

5. The pressure-sensitive adhesive composition of claim 1, wherein the block copolymer has a molecular weight distribution (PDI) of 1.0 to 2.5.

6. The pressure-sensitive adhesive composition of claim 1, wherein the block copolymer comprises 10 parts by weight to 50 parts by weight of the first block and 50 parts by weight to 95 parts by weight of the second block.

7. The pressure-sensitive adhesive composition of claim 1, wherein the multifunctional cross-linker is an isocyanate cross-linker, an epoxy cross-linker, an aziridine cross-linker or a metal chelate cross-linker.

8. The pressure-sensitive adhesive composition of claim 1, wherein the multifunctional cross-linker 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.

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

10. The pressure-sensitive adhesive composition of claim 9, wherein the radical polymerization initiator is comprised in an amount of 0.1 part by weight to 5 parts by weight, relative to 100 parts by weight of the (meth)acryl-based block.

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

12. 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.

13. 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.

14. A display device comprising: the pressure-sensitive adhesive optical laminate of claim 12, which is attached to one or both surfaces of a liquid crystal panel.

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

16. The pressure-sensitive adhesive composition of claim 1, wherein the first block has a glass transition temperature of about 50° C. to about 150° C., and the second block has a glass transition temperature of about −10° C. to about −100° C.

17. The pressure-sensitive adhesive composition of claim 1, wherein the first block has a glass transition temperature of about 60° C. to about 140° C., and the second block has a glass transition temperature of about −40° C. to about −90° C.

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 μL injection)

(12) 2. Time-Dependency Evaluation of Adhesion Strength

(13) The pressure-sensitive adhesive polarizing plate was cut into a size of 25 mm×100 mm (width×length) to prepare a sample, and then attached to an alkali-free glass using a laminator after removing a peeling sheet. Then, the resultant product was pressed in an autoclave (50° C., 0.5 atm) for about 20 minutes, and stored under constant temperature/humidity conditions (23° C., 50% RH) for 4 hours. Then, adhesion strength was measured under a condition in a peeling speed of 300 mm/min and a peeling angle of 180 degrees using Texture analyzer (Stable Micro Systems Ltd., U.K.), and time-dependency of the adhesion strength was evaluated according to the following criteria:

(14) <Evaluation Criteria> ◯: after 1 day, adhesion strength being 1,000 or less Δ: after 3 days, adhesion strength being 1,000 or less X: after 6 days, adhesion strength being 1,000 or less

(15) 3. Evaluation of Heat-Resistant and Moisture-Resistant Durability

(16) 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, and the moisture-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:

(17) <Evaluation Criteria>

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

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

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

(21) 4. Measurement of Interfacial Adhesion Strength

(22) The pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples were coated and attached to a polarizing plate, and the polarizing plate was cut into a size of 50 mm×100 mm to prepare a sample. 3 days after the sample was prepared, a release film of the sample was removed, and an adhesive tape was laminated. 30 minutes after lamination, the adhesive tape was peeled at an adequate speed, and then, an amount of the pressure-sensitive adhesive remaining on the polarizing plate was measured.

(23) <Evaluation Criteria> ◯: Pressure-sensitive adhesive residue of 80% or more Δ: Pressure-sensitive adhesive residue of 30% or more to 80% or less X: Pressure-sensitive adhesive residue of 30% or less

(24) 5. Calculation of Glass Transition Temperature

(25) Glass transition temperatures Tg of the respective blocks of the block copolymer were calculated according to the following Equation:

(26) <Equation>
1/Tg=ΣWn/Tn

(27) 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.

(28) 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.

(29) 6. Measurement of Conversion Rate and Composition Ratio of Monomer

(30) 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.

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

(32) 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.

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

(34) 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.

(35) <Calculation of Composition Ratio>

(36) 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.

(37) <Equation>
MMA Content(%) in Block Copolymer=100×MMA Peak Area/BA Peak Area

(38) 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.

(39) 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.

(40) 7. Evaluation of Transparency

(41) Each of the pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples was coated onto a release-treated surface of a 38 μm-thick PET (poly(ethyleneterephthalate)) film (MRF-38 manufactured by Mitsubishi Corporation) release-treated so that a thickness after drying could be about 40 μm, 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.

(42) <Evaluation Criteria>

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

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

PREPARATION EXAMPLE 1

Preparation of Block Copolymer (A1)

(45) 0.1 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, 0.002 g of CuBr.sub.2, 0.005 g of TPMA (tris(2-pyridylmethyl)amine), and 0.017 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 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.). 1.2 g of methacryloyl isocyanate was added to the polymerized block copolymer, and the resultant mixture was nitrogen-purged and stirred at a reaction temperature of about 50° C. for about 5 hours to carry out a reaction.

PREPARATION EXAMPLES 2 to 4

Preparation of Block Copolymers (A2 and B1 to B2)

(46) Block copolymers were prepared in the same manner as Preparation Example 1 except that kinds of materials and additives used in polymerizing a first block were controlled as shown in the following Table 1, and kinds of materials and additives used in polymerizing a second block were controlled as shown in the following Table 2.

(47) TABLE-US-00001 TABLE 1 Material MMA BMA EBiB EA CuBr.sub.2 TPMA V-65 Block A1 90 10 0.1 6.2 0.002 0.005 0.017 copolymer A2 90 10 0.1 6.2 0.002 0.005 0.017 B1 90 10 0.1 6.2 0.002 0.005 0.017 B2 90 10 0.1 6.2 0.002 0.005 0.017 Content unit: g MMA: methyl methacrylate (Homopolymer Tg: about 110° C.) BMA: butyl methacrylate (Homopolymer Tg: about 27° C.) EBiB: ethyl 2-bromoisobutyrate EA: ethyl acetate TPMA: tris(2-pyridylmethyl)amine V-65: 2,2′-azobis(2,4-dimethyl valeronitrile)

(48) TABLE-US-00002 TABLE 2 Material BA HBA MOI EA CuBr.sub.2 TPMA V-65 Block A1 97 1.5 1.2 250 0.006 0.01 0.05 copolymer A2 97 3 2.5 250 0.006 0.01 0.05 B1 97 1.5 — 250 0.006 0.01 0.05 B2 97 3 — 250 0.006 0.01 0.05 Content unit: g BA: butyl acrylate (Homopolymer Tg: about −45° C.) HBA: 4-hydroxybutyl acrylate (Homopolymer Tg: about −80° C.) MOI: methacryloyloxyethyl isocyanate EA: ethyl acetate TPMA: tris(2-pyridylmethyl)amine V-65: 2,2′-azobis(2,4-dimethyl valeronitrile)

(49) Properties of the respective block copolymers prepared by the above method are as shown in the following Table 3.

(50) TABLE-US-00003 TABLE 3 Block copolymer A1 A2 B1 B2 First MMA ratio 90 90 90 90 block BMA ratio 10 10 10 10 Tg (° C.) 90 90 90 90 Mn (×10000) 3.5 3.6 3.5 3.6 PDI 1.34 1.34 1.34 1.34 Second BA ratio 97 97 97 97 block HBA ratio 1.5 3 1.5 3 MOI ratio 1.2 1.5 — — Tg (° C.) −45 −45 −45 −45 Block Mn (×10000) 10.6 10.6 10.6 10.6 copoly- PDI 1.8 1.8 1.8 1.8 mer First block: 10.1:89.9 10.1:89.9 10.1:89.9 10.1:89.9 Second 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.) MOI: methacryloyloxyethyl isocyanate Tg: glass transition temperature Mn: number average molecular weight PDI: molecular weight distribution

EXAMPLE 1

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

(52) A coating solution (pressure-sensitive adhesive composition) was prepared by mixing 0.04 parts by weight of a cross-linker (Coronate L, produced by NPU, Japan), 0.1 part by weight of DBTDL (Dibutyltin dilaurate), and 0.2 parts by weight of a silane coupling agent having a β-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.

(53) Preparation of Pressure-Sensitive Adhesive Polarizing Plate

(54) The prepared coating solution was coated onto a release-treated surface of a 38 μm-thick PET (poly(ethyleneterephthalate)) film (MRF-38 manufactured by Mitsubishi Corporation) release-treated so that a thickness after drying could be about 23 μm, 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 3

(55) 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 4 when the pressure-sensitive adhesive composition (coating solution) was prepared.

(56) TABLE-US-00004 TABLE 4 Example Comparative Example 1 2 1 2 3 Block Kind A1 A2 B1 B2 A1 copolymer Content 100 100 100 100 100 Cross-linker 0.04 0.03 0.04 0.04 — content DBTDL content 0.1 0.1 0.1 0.1 0.1 SCA content 0.2 0.2 0.2 0.2 0.2 Content unit: part by weight Cross-linker: Coronate L, produced by NPU, Japan DBTDL: dibutyltin dilaurate SCA: silane coupling agent having a β-cyanoacetyl group (M812, produced by LG Chem.)

(57) Property evaluation results of the respective Examples and Comparative Examples are as shown in the following Table 5.

(58) TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 1 2 3 Time-dependency of ∘ ∘ x x ∘ adhesion strength Heat-resistant durability A A A A A Humidity-resistant A A A A B durability Interfacial adhesion ∘ ∘ ∘ ∘ x strength Transparency ∘ ∘ ∘ ∘ ∘

(59) The pressure-sensitive adhesive composition of the present invention can provide a pressure-sensitive adhesive having low time-dependency of dependability and adhesion strength and having excellent interfacial adhesion strength. After being applied to an optical member such as a polarizing plate, the pressure-sensitive adhesive composition exhibits excellent interfacial adhesion strength and maintains excellent dependability without time-dependency.

(60) It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers all such modifications provided they come within the scope of the appended claims and their equivalents.