Pressure-sensitive adhesive composition

Abstract

Provided is a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition may form a pressure-sensitive adhesive having a fine phase separation structure by a block copolymer including a hard segment and a soft segment, and also has a high elastic modulus and an excellent pressure-sensitive adhesive property. For example, although applied to a thin polarizing plate on at least one surface of which a polarizer protective film is not used, the pressure-sensitive adhesive may allow the polarizing plate to exhibit excellent durability, moisture resistance, workability, a pressure-sensitive adhesive property and a light leakage inhibiting ability.

Claims

1. A polarizing plate, comprising: a polarizer; and a pressure-sensitive adhesive layer that is on one surface of the polarizer and that comprises a pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition comprising: a block copolymer that comprises a first block, of which a glass transition temperature is 50 C. or more, and a second block, of which a glass transition temperature is 30 C. or less; a multifunctional crosslinking agent capable of forming a crosslinking structure via a reaction with the block copolymer; and a multifunctional acrylate, and the pressure-sensitive adhesive composition forming an interpenetrating polymer network after curing, wherein the block copolymer has a number average molecular weight in a range from 20,000 to 500,000 and a polydispersity index in a range from 1.0 to 3.5, and wherein a tensile modulus of the pressure sensitive adhesive composition is from 0.5 to 1,000 MPa at 25 C. after the interpenetrating polymer network is formed.

2. The polarizing plate according to claim 1, further comprising a polarizer protective film formed on only one surface of the polarizer, and the pressure-sensitive adhesive layer being formed on a surface of the polarizer, on which the protective film is not formed.

3. The polarizing plate according to claim 1, further comprising an adhesive layer between the pressure-sensitive adhesive layer and the polarizer.

4. A pressure-sensitive adhesive composition for an optical film, that forms an interpenetrating polymer network structure after being cured, and that comprises: a block copolymer comprising a first block, of which a glass transition temperature is 50 C. or more, and a second block, of which a glass transition temperature is 30 C. or less; a multifunctional crosslinking agent capable of forming a crosslinking structure via a reaction with the copolymer; and a multifunctional acrylate, wherein the block copolymer has a number average molecular weight in a range from 20,000 to 500,000 and a polydispersity index in a range from 1.0 to 3.5, and wherein a tensile modulus of the pressure sensitive adhesive composition is from 0.5 to 1,000 MPa at 25 C. after the interpenetrating polymer network is formed.

5. The pressure sensitive adhesive composition according to claim 4, wherein the block copolymer comprises a crosslinkable functional group in the second block.

6. The pressure sensitive adhesive composition according to claim 4, wherein the block copolymer is a diblock copolymer comprising a first block and a second block, or a triblock copolymer comprising a first block, a second block and a third block.

7. The pressure sensitive adhesive composition according to claim 4, wherein the first block comprises a methacrylic acid ester monomer.

8. The pressure sensitive adhesive composition according to claim 4, wherein the second block comprises an acrylic acid ester monomer.

9. The pressure sensitive adhesive composition according to claim 8, wherein the second block further comprises a copolymerizable monomer having a crosslinkable functional group.

10. The pressure sensitive adhesive composition according to claim 4, wherein the block copolymer comprises 25 to 1900 parts by weight of the second block relative to 100 parts by weight of the first block.

11. The pressure sensitive adhesive composition according to claim 4, which comprises the multifunctional crosslinking agent in an amount from 0.01 to 10 parts by weight relative to 100 parts by weight of the block copolymer.

12. The pressure sensitive adhesive composition according to claim 4, wherein the multifunctional acrylate has a molecular weight of 10,000 g/mol or less.

13. The pressure sensitive adhesive composition according to claim 4, which comprises the multifunctional acrylate in an amount from 5 to 300 parts by weight relative to 100 parts by weight of the block copolymer.

14. The pressure sensitive adhesive composition according to claim 4, further comprising: a radical initiator in an amount from 0.01 to 10 parts by weight relative to 100 parts by weight of the block copolymer.

15. The pressure sensitive adhesive composition according to claim 4, further comprising: a silane coupling agent having an acetoacetate group or a beta-cyanoacetyl group.

16. A display device, comprising a liquid crystal panel on one or both surfaces of which the polarizing plate of claim 1 is adhered.

Description

BRIEF DESCRIPTION OF DRAWING

(1) FIG. 1 shows an illustrative embodiment of a structure of a general polarizing plate.

(2) FIGS. 2 and 3 show illustrative embodiments of structures of different illustrative polarizing plates.

ILLUSTRATIVE EMBODIMENTS

(3) Hereinafter, a pressure-sensitive adhesive composition will be described in detail with reference to examples and comparative examples, but the scope of the pressure-sensitive adhesive composition is not limited to examples.

(4) 1. Evaluation of Molecular Weight

(5) A number average molecular weight (Mn) and a molecular weight distribution (PDI) were measured using GPC under the following conditions. To draw a calibration curve, standard polystyrene of an Agilent system was used, and measurement results were converted.

(6) <Measurement Conditions>

(7) Measuring Tool: Agilent GPC (Agilent 1200 series, U.S.)

(8) Column: two connected PLgel mixed B

(9) Column Temperature: 40 C.

(10) Eluent: Tetrahydrofuran (THF)

(11) Flow Rate: 1.0 mL/min

(12) Concentration: 1 mg/mL (100 L injection)

(13) 2. Calculation of glass transition temperature

(14) A glass transition temperature (Tg) of each block of a block copolymer was measured by the following formula:
1/Tg=Wn/Tn<Formula>

(15) In this formula, Wn is a weight fraction of a monomer used in each block, and Tn is a glass transition temperature when a homopolymer is formed of the used monomer.

(16) That is, the right side of the formula is a result obtained by calculating a value (Wn/Tn) by dividing a weight fraction of the used monomer by a glass transition temperature when a homopolymer is formed of the used monomer, and adding the values corresponding to all of the monomers.

(17) 3. Evaluation of Tensile Modulus

(18) A tensile modulus of a pressure-sensitive adhesive in the specification was measured through a stress-strain test method according to the method regulated in the ASTM D638, or obtained by measuring a storage modulus by the following method and calculating a value by the following conversion formula when a tensile modulus was difficult to be directly measured. Specifically, a sample having a stacked structure of a PET release film (thickness: 38 m, MRF-38), a pressure-sensitive adhesive layer and a PET release film (thickness: 38 m, MRF-38), which was manufactured in Examples or Comparative Examples, was cut into a dog bone-type specimen having a size of 7 cm1 cm (lengthwidth), both ends of the specimen were fixed with jigs for a tensile test, and a tensile modulus was measured according to the ASTM D638. Such a tensile modulus was measured under the following conditions:

(19) <Conditions for Measuring Tensile Modulus>

(20) Measuring tool: Universal Test Machine (UTM)

(21) Equipment Model: Model: Zwick Roell Z010, Instron

(22) Measuring conditions: Load cell: 500 N Tensile speed: 3 mm/sec

(23) 4. Method of Evaluating Peeling Strength

(24) A peeling strength was evaluated by adhering a pressure-sensitive adhesive, prepared in Examples or Comparative Examples, to a glass washed with ethyl acetate, and peeling the pressure-sensitive adhesive at a room temperature using a texture analyzer (TA) at a peeling angle of 180 degrees and a peeling speed of 0.3 m/min. The peeling strength was measured to the same pressure-sensitive adhesive twice, and an average was recorded.

(25) 5. Method of Evaluating Durability and Reliability

(26) A sample was manufactured by washing soda lime glass (1.1 T) with ethyl acetate, and adhering the pressure-sensitive adhesive, prepared in Examples or Comparative Examples, cut to have a size of 130 nm180 nm (widthlength) to the glass. Afterward, the adhered sample was autoclaved at 5 kgf/cm.sup.2 and 50 C. for approximately 30 minutes to remove bubbles, and then durability was evaluated under the following conditions.

(27) <Heat Resistance and Durability>

(28) Evaluated after stored at 110 C. for 500 hours

(29) <Heat and Moisture Resistance and Durability>

(30) Evaluated after stored at 60 C. and a relative humidity of 90% for 500 hours

(31) <Evaluation Criteria>

(32) A: bubbling, peeling, and lifting did not occur

(33) B: bubbling, peeling or little lifting occurred

(34) C: bubbling, peeling or lifting greatly occurred

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

(35) Appropriate amounts of ethyl 2-bromoisobutyrate (EBiB) and methylmethacrylate (MMA) were mixed with ethyl acetate (EAc), a flask containing the mixture was sealed with a rubber membrane, and purged with nitrogen and stirred at 25 C. for approximately 30 minutes to remove dissolved oxygen. Afterward, appropriate amounts of CuBr.sub.2, tris(2-pyridylmethyl)amine (TPMA) and tin(II) 2-ethylhexanoate (Sn(EH).sub.2) were added to the mixture from which oxygen was removed, and maintained in a reaction vessel at approximately 67 C., thereby initiating a reaction (polymerization of a first block). A mixture of butyl acrylate (BA) and hydroxyethyl acrylate (HEA) previously bubbled with nitrogen was added at the time when a conversion rate of the methyl methacrylate became approximately 70 to 95% to have a ratio of the final block copolymer as shown in Table 1. Afterward, CuBr.sub.2, TPMA and Sn(EH).sub.2 were added to the reaction flask to perform a chain extension reaction (polymerization of a second block). When a conversion rate of the monomer (BA) reaches 80% or more, the reaction mixture was exposed to oxygen, and diluted with a suitable solvent to terminate the reaction, and therefore a block copolymer was prepared.

Preparation of Examples 2 and 3. Preparation of Block Copolymers (B1 and C1)

(36) A block copolymer was prepared by the same method as described in Preparation Example 1, except that weight ratios of monomers of a first block and a second block were controlled as shown in Table 1.

(37) TABLE-US-00001 TABLE 1 Block copolymer A1 B1 C1 First MMA ratio 100 100 100 block Tg ( ) 110 110 110 Second BA ratio 80 80 80 block HEA ratio 20 20 10 EO2EA ratio 10 Tg ( ) 40 40 45 Block Mn (10000) 8 15 8.2 copolymer PDI 1.28 1.35 1.30 First 30:70 20:80 30:70 block:second block (weight ratio) Monomer ratio unit: parts by weight obtained by converting the sum of monomers of respective blocks into 100 MMA: methyl methacrylate (single polymer Tg: approx. 110) BA: butyl acrylate (single polymer Tg: approx. 45) HEA: 2-hydroxyethyl acrylate (single polymer Tg: approx. 15) EO2EA: 2-(2-ethoxyethoxy)ethyl acrylate(single polymer Tg: approx. 70) Tg: glass transition temperature Mn: number average molecular weight PDI: polydispersity index

Preparation of Example 4. Preparation of Random Copolymer (D1)

(38) A random copolymer was prepared by adding a monomer mixture including butyl acrylate (BA) and 2-hydroxyethyl acrylate (HEA) in a ratio of 80:20 (BA:HEA) in an 1 L reactor equipped with a cooling device to perform a reflux of a nitrogen gas and facilitate control of a temperature, adding an appropriate amount of n-dodecyl mercaptane at a controlled molecular weight and then ethyl acetate as a solvent, purging nitrogen gas for approximately 60 minutes to remove oxygen, adding azobisisobutyronitrile (AIBN) as an initiator while a temperature was maintained at 60 C., and performing a reaction for approximately 8 hours. A number average molecular weight (Mn) of the prepared random copolymer (B4) was approximately 220,000, and a polydispersity index (PDI) was approximately 5.0.

Example 1 Preparation of Pressure-Sensitive Adhesive Layer

(39) A pressure-sensitive adhesive coating solution was prepared by blending 30 parts by weight of a pentaerythritol triacrylate adduct of isoboron diisocyanate, 0.5 parts by weight of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator) and 0.1 parts by weight of a TDI/trimethylolpropane adduct (crosslinking agent) relative to 100 parts by weight of a solid content of the block copolymer (A1) prepared in Preparation Example 1, diluting the mixture with a solvent, and uniformly mixing the diluted result. Subsequently, the prepared pressure-sensitive adhesive composition was coated on a release-treated surface of a poly(ethylene terephthalate) (PET) film (thickness: 38 m, MRF-38, Mitsubishi) with a silicon compound to have a thickness of 25 m after drying, and then dried. A pressure-sensitive adhesive layer was formed by further laminating a release-treated surface of the PET film (thickness: 38 m, MRF-38, Mitsubishi) on the dried coating layer, and being irradiated with UV under the following conditions.

(40) <Conditions for UV Radiation>

(41) UV radiator: High-pressure mercury lamp

(42) Radiation conditions: Luminance: 1000 mW/cm.sup.2 Quantity of light: 350 mJ/cm.sup.2

(43) Manufacture of Polarizing Plate

(44) A sequence of manufacturing a polarizing plate is as follows. First, a polyvinyl alcohol-based resin film was stretched, stained with iodine, treated with a boric acid aqueous solution, thereby manufacturing a polarizer. Subsequently, a triacetyl cellulose (TAC) film having a thickness of 60 m was adhered to one surface of the polarizer using a water-based polyvinylalcohol-based adhesive. Subsequently, on the polyvinylalcohol-based polarizer, a water-based polyvinylalcohol-based adhesive composition was coated on a surface to which the TAC film was not adhered to have a thickness after drying of 400 nm. As the water-based polyvinylalcohol-based adhesive composition, an adhesive composition generally used for adhering a TAC protective film to the polarizer was used. Afterward, the manufactured pressure-sensitive adhesive layer was laminated onto the surface on which the adhesive composition was coated, and the adhesive composition was dried, thereby manufacturing a polarizing plate (a polarizing plate structure: TAC film.fwdarw.water-based polyvinylalohol-based adhesive.fwdarw.polarizer water-based polyvinylalcohol-based adhesive.fwdarw.pressure-sensitive adhesive layer PET release film).

Examples 2 and 3 and Comparative Examples 1 and 2

(45) A pressure-sensitive adhesive was prepared by the same method as described in Example 1, except that ratios of components in preparation of a pressure-sensitive adhesive composition were changed as follows.

(46) TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 1 2 Polymer A1 100 B1 100 C1 100 D1 100 100 MFA1 30 50 70 140 MFA2 50 NCO crosslinking agent 0.1 0.1 0.1 0.1 0.1 Radical initiator 0.5 0.5 0.5 0.5 0.5 Content unit: parts by weight MFA1: isophorone diisocyanate/pentaerythritol triacrylate adduct MFA2: pentaerythritol tetraacrylate NOC crosslinking agent: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide Radical initiator: TDI/trimethylolpropane adduct

(47) Results of evaluating physical properties measured with respect to Examples and Comparative Examples are summarized and listed in Table 3.

(48) TABLE-US-00003 TABLE 3 Comparative Example Example 1 2 3 1 2 Elastic modulus 150 170 200 110 220 (MPa) Pressure-sensitive 385 290 210 60 12 adhesive strength (gf) Heat resistance A A A C C and durability Moisture and heat A A A B C resistance and durability

DESCRIPTION OF THE MARKS IN THE DRAWINGS

(49) 100, 200, 300: the polarizing plate 1021, 1022: the polarizer protective film 101: the polarizer 103, 201: the pressure sensitive adhesive layer 104: the releasing film 301: the adhesive layer