Pressure-sensitive adhesive composition

Abstract

Provided are a pressure-sensitive adhesive composition, an optical member, a polarizing plate and a display device. The pressure-sensitive adhesive composition having physical properties required for an optical member using a particular block copolymer and an antioxidant or a photostabilizer, which forms a fine phase change region in a crosslinking structure, and particularly having excellent bending preventability and storage stability may be provided. Such a pressure-sensitive adhesive composition may be used for optical uses, for example, to laminate various optical members, or apply an optical member to a display device.

Claims

1. A pressure-sensitive adhesive polarizing plate, comprising: a polarizer; and a pressure-sensitive adhesive layer formed on one or both surfaces of the polarizer, and including a pressure-sensitive adhesive composition which is crosslinked, wherein the pressure-sensitive adhesive composition prior to crosslinking comprises: a block copolymer, which is a diblock copolymer including a first block having a glass transition temperature of 70 to 95° C. and a second block having a glass transition temperature of −55 to −45° C. and a crosslinkable functional group; and an antioxidant, wherein the first block has a polymerization unit of an alkyl methacrylate, and the second block has a polymerization unit of an alkyl acrylate and a crosslinkable monomer, wherein the block copolymer includes 100 to 1,500 parts by weight of the second block with respect to 100 parts by weight of the first block, and wherein the antioxidant is at least one selected from the group consisting of a phenol-based antioxidant and a thioether-based antioxidant, wherein the antioxidant is included at 0.01 to 3 parts by weight with respect to 100 parts by weight of the block copolymer, and wherein a viscosity change of the pressure-sensitive adhesive composition prior to crosslinking after being maintained at 60° C. for 30 days is 5% or less.

2. The pressure-sensitive adhesive polarizing plate of claim 1, wherein a difference in glass transition temperature between the first and second blocks of the block copolymer is 80 to 150° C.

3. The pressure-sensitive adhesive polarizing plate of claim 1, wherein the first block has a number average molecular weight of 3,000 to 200,000.

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

5. The pressure-sensitive adhesive polarizing plate of claim 1, wherein the block copolymer has a polydispersity index (Mw/Mn) of 1.0 to 3.0.

6. The pressure-sensitive adhesive polarizing plate of claim 1, further comprising a multifunctional crosslinking agent.

7. A pressure-sensitive adhesive optical laminate, comprising: an optical film; and a pressure-sensitive adhesive layer formed on one or both surfaces of the optical film and including a pressure-sensitive adhesive composition, which is crosslinked, wherein the pressure-sensitive adhesive composition prior to crosslinking comprises: a block copolymer, which is a diblock copolymer including a first block having a glass transition temperature of 70 to 95° C. and a second block having a glass transition temperature of −55 to −45° C. and a crosslinkable functional group; and an antioxidant, wherein the first block has a polymerization unit of an alkyl methacrylate, and the second block has a polymerization unit of an alkyl acrylate and a crosslinkable monomer, wherein the block copolymer includes 100 to 1,500 parts by weight of the second block with respect to 100 parts by weight of the first block, and wherein the antioxidant is at least one selected from the group consisting of a phenol-based antioxidant and a thioether-based antioxidant, wherein the antioxidant is included at 0.01 to 3 parts by weight with respect to 100 parts by weight of the block copolymer, and wherein a viscosity change of the pressure-sensitive adhesive composition prior to crosslinking after being maintained at 60° C. for 30 days is 5% or less.

8. A display device comprising the pressure-sensitive adhesive optical laminate of claim 7.

9. A display device comprising the pressure-sensitive adhesive polarizing plate of claim 1.

Description

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(1) 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 the following examples.

(2) 1. Evaluation of Molecular Weight

(3) A number average molecular weight (Mn) and a polydispersity index (PDI) were measured under the following conditions using GPC, standard polystyrene produced by Agilent System was used to draw a calibration curve, and measurement results were converted.

(4) <Measurement Conditions>

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

(6) Column: Two connected PL mixed B

(7) Column Temperature: 40° C.

(8) Eluent: Tetrahydrofuran (THF)

(9) Flow Rate: 1.0 mL/min

(10) Concentration: ˜1 mg/mL (100 μL injection)

(11) 2. Evaluation of Viscosity

(12) Viscosity was evaluated by the following method using a Brookfield digital viscometer (DV-I+, DV-II+Pro).

(13) <Sequence of Measuring Viscosity>

(14) 1) 180 mL of a sample was put in a beaker, and maintained under a constant temperature/constant humidity (23° C./50% relative humidity) condition for approximately 1 hour to remove bubbles.

(15) 2) A spindle was put in the sample at an angle not to have bubbles such that a liquid surface of the sample was not lower than a groove of the spindle.

(16) 3) The spindle was connected to a viscometer, and adjusted such that the groove of the spindle matched the liquid surface of the sample.

(17) 4) A set speed key was pressed to choose RPM of the spindle.

(18) 5) A motor on/off key was pressed to operate the viscometer.

(19) After a viscosity shown on a screen was stabilized, a value was obtained. RPM at which a confidence interval was approximately 10% or more was detected on the display and fixed, thereby measuring a viscosity.

(20) 3. Evaluation of Durability

(21) A polarizing plate formed in Example or Comparative Example was cut to a size of approximately 180 mm×320 mm (width×length) to prepare a specimen, and then the specimen was adhered to a commercially available 19-inch panel. Afterward, the panel was stored in an autoclave (50° C., 5 atm) for approximately 20 minutes, thereby preparing a sample. Humidity, heat resistance and durability of the prepared sample were evaluated under the following criteria by maintaining the sample at 60° C. and a relative humidity of 90% for 500 hours, and observing generation of bubbles and peel-off at a pressure-sensitive adhesive interface. Heat resistance and durability were evaluated under the following criteria by maintaining the sample at 90° C. for 300 hours, and observing generation of bubbles and peel-off.

(22) <Evaluation Criteria>

(23) A: There were no bubbles or peel-off.

(24) B: There were some bubbles and/or peel-off.

(25) C: There was a great amount of bubbles and/or peel-off.

(26) 4. Calculation of Glass Transition Temperature

(27) A glass transition temperature (Tg) of each block of a block copolymer was calculated according to the following equation.
1/Tg=ΣWn/Tn  <Equation>

(28) In the equation, Wn was a weight fraction of a monomer used in each block, and Tn was a glass transition temperature detected when the used monomer formed a homopolymer.

(29) That is, in the equation, the right side was a result obtained by summarizing values (Wn/Tn) obtained by dividing a weight fraction of the used monomer by a glass transition temperature detected when each monomer formed a homopolymer.

(30) 5. Measurement of Conversion Ratio and Component Ratio of Monomer

(31) A conversion ratio in a polymerization process of a main monomer for forming a first block, methyl methacrylate (MMA), and a main monomer for forming a second block, butyl acrylate (BA), in a block copolymer of Example or Comparative Example and component contents in the block copolymer were calculated by the following equation according to the 1H-NMR result.
MMA conversion ratio (%)=100×B/(A+B)  <MMA Conversion Ratio>

(32) Here, A was an area of a peak (approximately 3.4 to 3.7 ppm) derived from a methyl group induced from MMA included in a polymer in a 1H-NMR spectrum, and B was an area of a peak (approximately 3.7 ppm) derived from a methyl group of MMA which was not polymerized. That is, in consideration of a migration position of a methyl group peak in the MMA structure, a conversion ratio of the monomer was calculated.
BA conversion ratio (%)=100×C/(C+D)  <BA Conversion Ratio>

(33) Here, D was an area of a peak (approximately 5.7 to 6.4 ppm) derived from ═CH.sub.2 at a double bonded terminal end of BA in the 1H-NMR spectrum, and C was an area of a peak (approximately 3.8 to 4.2 ppm) derived from —OCH.sub.2— present in a polymer formed by polymerization of BA. That is, the BA conversion ratio was measured by calculating relative values of ═CH.sub.2 peak formed by a double bond of BA and —OCH.sub.2— peak of the polymer.

(34) <Estimation of Component Ratio>

(35) Ratios of the first block and the second block of the block copolymer were calculated by the following equation based on ratios of MMA and BA, which were main monomers used to form the first and second blocks.
Content ratio (%) of MMA in block copolymer=100×MMA peak area/BA peak area  <Equation>

(36) Here, the MMA peak area was an area value per 1H proton of a peak detected at approximately 3.4 to 3.7 ppm in 1H NMR (the peak observed by —CH.sub.3 derived from MMA), and the BA peak area was an area value per 1H proton of a peak detected at approximately 3.8 to 4.2 ppm in 1H NMR (the peak observed by —OCH.sub.2— present in a polymer formed by BA).

(37) That is, the weight ratios of the first block and the second block were estimated by calculating relative values of the —CH.sub.3 peak of the MMA structure and the —OCH.sub.2— peak of the polymer formed from BA.

(38) 6. Evaluation of Degree of Bending

(39) A polarizing plate formed in Example or Comparative Example was cut to a size of 240 mm×410 mm (width×length), thereby preparing a specimen, and the specimen was adhered to a glass substrate (0.4t glass), thereby forming a laminate. Afterward, the formed laminate was disposed on a flat bottom and maintained at 60° C. for 72 hours, and then a degree of bending was evaluated by measuring a height of the laminate from the bottom.

Preparation Example 1. Preparation of Block Copolymer (A)

(40) A monomer mixture including MMA and butyl methacrylate (BMA) in a weight ratio of 7:3 (MMA:BMA) as a monomer for forming a first block was mixed with suitable amounts of ethyl 2-bromoisobutyrate (EBiB) and ethyl acetate (EAc). A flask containing the mixture was sealed with a rubber membrane, nitrogen purging and stiffing were performed at approximately 25° C. for approximately 30 minutes, and remaining oxygen was removed by bubbling. Afterward, the mixture of CuBr.sub.2, tris(2-pyridylmethyl)amine (TPMA) and 2,2′-azobis(2,4-dimethyl valeronitrile) (V-65), from which the suitable amount of oxygen was removed, was added and dipped in a reaction vessel at approximately 67° C. to initiate a reaction (polymerization of the first block). When a conversion ratio of MMA approached approximately 75%, a mixture for forming a second block previously bubbled with nitrogen was added in the presence of nitrogen. The mixture for forming the second block was prepared by dissolving butyl acrylate (BA) and hydroxybutyl acrylate (HBA) in a solvent such as ethyl acetate (EAc) in a weight ratio of 99.5:0.5 (BA:HBA) as a monomer mixture. Afterward, suitable amounts of CuBr.sub.2, TPMA and V-65 were further added in a reaction flask, and a chain extension reaction was performed (polymerization of second block). When a conversion ratio of the monomer (BA) approached 80% or more, the reaction mixture was exposed to oxygen and diluted in a suitable solvent to terminate the reaction, resulting in a block copolymer (in this process, V-65 was divided into suitable portions and added until the time at which the reaction was terminated in consideration of a half life of V-65).

Preparation Examples 2 to 7. Preparation of Block Copolymers (A2 to 4A and B1 to B3)

(41) Block copolymers were prepared by the same method as described in Preparation Example 1, except that monomers used in polymerization of first and second blocks and ratios thereof were controlled as shown in Table 1. EbiB, EA, CuBr.sub.2, TPMA and V-65 corresponding to a catalyst, a solvent, and an initiator in the preparation of the block copolymer, respectively, were added at a suitable amount in consideration of polymerization efficiency.

(42) TABLE-US-00001 TABLE 1 Ingredients of first block Ingredients of second (weight ratio) block (weight ratio) MMA BMA HPMA BA HBA B A1 70 30 — 99.5 0.5 C A2 80 20 — 97 3 P A3 60 40 — 94 6 A4 70 30 — 95 5 B1 10 — 99.5 0.5 B2 81 16 3 100 — B3 81 16 3 97 3 Weight ratio: ratio when total of weights of monomers was set to 100 MMA: methyl methacrylate (homopolymer Tg: approximately 110° C.) BMA: butyl methacrylate(homopolymer Tg: approximately 27° C.) HPMA: 2-hydroxypropyl methacrylate (homopolymer Tg: approximately 26° C.) BA: butyl acrylate (homopolymer Tg: approximately −45° C.) HBA: 4-hydroxybutyl acrylate (homopolymer Tg: approximately −80° C.)

(43) Characteristics of the block copolymer prepared by the above method are shown in Table 2.

(44) TABLE-US-00002 TABLE 2 block copolymer A1 A2 A3 A4 B1 B2 B3 First MMA ratio 70 80 60 70 100 81 81 block BMA ratio 30 20 40 30 0 16 16 HPMA ratio 0 0 0 0 0 3 3 Tg (° C.) 80 90 72 80 110 90 90 Mn(× 10.sup.4) 2.9 2.3 2.9 3.8 2.3 2.3 2.3 PDI 1.38 1.34 1.38 1.41 1.36 1.36 1.36 Second block BA ratio 99.5 97 94 95 97.0 100.0 97.0 HBA ratio 0.5 3 6 5 3.0 0.0 3.0 Tg (° C.) −45 −46.2 −47.5 −47 −46.2 −45 −46.2 Block Mn(× 10.sup.4) 12.3 12.3 14.1 10.4 12.4 12.4 12.2 copolymer PDI 2.2 1.8 2.1 2.1 1.9 1.8 1.8 Weight ratio of 10:90 10:90 11.2:88.8 34.7:65.3 10:90 10:90 10:90 block Monomer ratio unit: parts by weight (based on total of 100) BA: butyl acrylate (homopolymer Tg: approximately −45° C.) HBA: 4-hydroxybutyl acrylate (homopolymer Tg: approximately −80° C.) MMA: methyl methacrylate (homopolymer Tg: approximately 110° C.) BMA: butyl methacrylate(homopolymer Tg: approximately 27° C.) HPMA: 2-hydroxypropyl methacrylate (homopolymer Tg: approximately 26° C.) Tg: glass transition temperature Mn: number average molecular weight PDI: polydispersity index Block weight ratio: first block: second block(weight ratio)

Preparation Example 8. Preparation of Random Copolymer (B4)

(45) 10 parts by weight of MMA, 87.3 parts by weight of n-butyl acrylate, and 2.7 parts by weight of 4-hydroxybutyl acrylate were added in a 1 L reaction vessel equipped with a cooling device to perform a reflux of nitrogen gas and facilitate temperature control, 200 ppm of n-dodecyl mercaptanol was added as a molecular weight controller, and then 120 parts by weight of ethyl acetate was added as a solvent. Subsequently, nitrogen gas was purged for approximately 60 minutes to remove oxygen, 0.05 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator at 60° C., and a reaction was performed for approximately 8 hours, thereby preparing a random copolymer. A number average molecular weight (Mn) of the prepared random copolymer (B4) was approximately 132000, and a polydispersity index (PDI) was approximately 4.6.

Example 1

Preparation of Coating Solution (Pressure-Sensitive Adhesive Composition)

(46) A coating solution (pressure-sensitive adhesive composition) was prepared by mixing 0.1 parts by weight of a crosslinking agent (Coronate L, NPU, Japan), 0.1 parts by weight of dibutyltin dilaurate (DBTDL) and 0.2 parts by weight of a phenol-based antioxidant (Irganox1010, Ciba), and blending ethyl acetate as a solvent.

(47) Preparation of Pressure-Sensitive Adhesive Polarizing Plate

(48) The prepared coating solution was coated on a release-treated surface of a release-treated release poly(ethylene terephthalate) (PET) (MRF-38, Mitsubishi) having a thickness of 38 μm such that a thickness after drying became approximately 23 μm, and maintained in an oven at 110° C. for approximately 3 minutes. After drying, a coating layer formed on the release PET was laminated on a WV liquid crystal layer of a polarizing plate (laminate of TAC/PVA/TAC; TAC=triacetylcellulose, PVA=polyvinylalcohol-based polarizing film) on one side of which a wide view (WV) liquid crystal layer was coated, thereby preparing a pressure-sensitive adhesive polarizing plate.

Examples 2 to 5 and Comparative Examples 1 to 5

(49) A pressure-sensitive adhesive composition (coating solution) and a pressure-sensitive adhesive polarizing plate were formed by the same method as described in Example 1, except that components and ratios in preparation of the pressure-sensitive adhesive composition (coating solution) were controlled as shown in Table 3 or 4.

(50) TABLE-US-00003 TABLE 3 Examples 1 2 3 4 5 6 7 Acrylic Type A1 A1 A2 A3 A4 A1 A2 polymer Content 100 100 100 100 100 100 100 Content of crosslinking 0.1 0.1 0.07 0.2 0.2 0.1 0.07 agent Content of DBTDL 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Content of antioxidant 0.2 1 0.2 0.2 0.2 Photostabilizer 0.2 1 Content unit: parts by weight Crosslinking agent: Coronate L, NPU, Japan) DBTDL: dibutyltin dilaurate Antioxidant: phenol-based antioxidant (Irganox1010, Ciba)

(51) TABLE-US-00004 TABLE 4 Comparative Examples 1 2 3 4 5 Acrylic Type B1 A1 B2 B3 B4 polymer Content 100 100 100 100 100 Content of 0.1 0.1 0.07 0.07 0.07 crosslinking agent Content of 0.1 0.1 0.1 0.1 0.1 DBTDL Content of 0.2 0 0.2 0.2 0.2 antioxidant Content unit: parts by weight Crosslinking agent: Coronate L, NPU, Japan) DBTDL: dibutyltin dilaurate Antioxidant: phenol-based antioxidant (Irganox1010, Ciba) Viscosity unit of coating solution: cP

(52) Results of evaluating physical properties with respect to Examples and Comparative Examples are shown in Tables 5 and 6.

(53) TABLE-US-00005 TABLE 5 Examples 1 2 3 4 5 6 7 Initial 1750 1730 1760 1700 1690 1740 1755 viscosity (cP) Late viscosity 1750 1730 1760 1700 1690 1745 1760 (cP) Viscosity 0 0 0 0 0 approxi- approxi- change (%) mately mately 0.29 0.29 Degree of 37 37 38 36 37 36 35 bending (mm) Heat resistance A A A A A A A and reliability Humidity and A A A A A A A heat resistance and reliability Initial viscosity: the viscosity measured with respect to a coating solution of a block copolymer and an antioxidant (a crosslinking agent was not blended) Late viscosity: the viscosity measured immediately after a coating solution whose initial viscosity was measured at 60° C. for 30 minutes

(54) TABLE-US-00006 TABLE 6 Comparative Examples 1 2 3 4 5 Initial viscosity 1820 1760 1760 1730 1900 (cP) Late viscosity 1880 2530 1770 1750 1900 (cP) Viscosity change approximately approximately approximately approximately 0 (%) 3.3 43.8 5.7 1.16 Degree of  49  37  39  39 50 blending (mm) Heat resistance A C C B C and reliability Humidity and A A C B B heat resistance and reliability Initial viscosity: the viscosity measured with respect to a coating solution of a block copolymer and an antioxidant (a crosslinking agent was not blended) Late viscosity: the viscosity measured immediately after a coating solution whose initial viscosity was measured at 60° C. for 30 minutes

(55) In the present invention, a pressure-sensitive adhesive composition having physical properties required for an optical member using a particular block copolymer and an antioxidant or a photostabilizer, which forms a fine phase change region in a crosslinking structure, and particularly having excellent bending preventability and storage stability can be provided. Such a pressure-sensitive adhesive composition can be used for optical uses, for example, to laminate various optical members, or apply an optical member to a display device.

(56) While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.