Pressure-Sensitive Adhesive Composition

Abstract

A pressure-sensitive adhesive composition, an optical laminate, a polarizing plate and a display device are provided. The pressure-sensitive adhesive composition includes a block copolymer containing a first block having a glass transition temperature of 50° C. or more and having a cross-linkable functional group, a second block having a glass transition temperature of −10° C. or less, and an epoxysilane compound. The pressure-sensitive adhesive composition according to the present application can provide excellent durability and excellent optical characteristics with respect to the pressure-sensitive adhesive polarizing plate.

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 having a cross-linkable functional group; a second block having a glass transition temperature of −10° C. or less; and an epoxysilane compound, wherein a refractive index (R.I..sub.1) of the first block and a refractive index (R.I..sub.2) of the second block are calculated through the following equation and satisfy the following relational expression:
R.I.=Σ{Rn×(Wn/100)}  [Equation] wherein, R.I. is the refractive index of the first block or the second block, Wn/100 is the weight fraction of the monomer component used to form the first block or the second block, and Rn is a refractive index of the homopolymer of each monomer:
|ΔR.I.|=|R.I..sub.1−R.I..sub.2|<0.011   Relational Expression] wherein, ΔR.I. is an absolute value of the difference between the refractive index (R.I..sub.1) of the first block and the refractive index (R.I..sub.2) of the second block.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the second block comprises a cross-linkable functional group.

3. The pressure-sensitive adhesive composition according to claim 2, wherein the first block or the second block comprises an aromatic group.

4. The pressure-sensitive adhesive composition according to claim 3, wherein the first block or the second block has a polymerized unit derived from a compound of Formula 1 below capable of providing the cross-linkable functional group: ##STR00004## wherein, Q is hydrogen or an alkyl group, A and B are each independently an alkylene group or an alkylidene group, and n is an integer in a range of 0 to 10.

5. The pressure-sensitive adhesive composition according to claim 4, wherein the second block comprises a unit derived from a compound capable of providing an aromatic group, and the compound capable of providing the aromatic group comprises an aromatic group and a vinyl group.

6. The pressure-sensitive adhesive composition according to claim 5, wherein the compound capable of providing an aromatic group is represented by Formula 2 below: ##STR00005## wherein, R1 is hydrogen or an alkyl group, R2 is an alkylene group or an alkylidene group, m is an integer of 0 to 5, X is a single bond, an oxygen atom or a sulfur atom, and Ar is an aryl group.

7. The pressure-sensitive adhesive composition according to claim 6, wherein the second block comprises a cross-linkable functional group and an aromatic group.

8. The pressure-sensitive adhesive composition according to claim 7, wherein the second block comprises a polymerized unit derived from 20 to 98 parts by weight of (meth)acrylic acid ester, a polymerized unit derived from 1 to 40 parts by weight of a compound capable of providing a cross-linkable functional group, and a polymerized unit derived from 1 to 40 parts by weight of a compound capable of providing an aromatic group.

9. The pressure-sensitive adhesive composition according to claim 8, wherein the second block comprises two or more polymerized units derived from the compound represented by Formula 1.

10. The pressure-sensitive adhesive composition according to claim 9, wherein the second block comprises a polymerized unit derived from a monomer (M1), in which the carbon number of A, the carbon number of B or the carbon number combining the carbon numbers of A and B in the compound represented by Formula 1 is larger, in an amount less than that of a polymerized unit derived from a monomer (M2) having the low carbon number.

11. The pressure-sensitive adhesive composition according to claim 10, wherein the second block comprises the polymerized unit derived from 0.5 to 5 parts by weight of the monomer (M1) and the polymerized unit derived from 1 to 10 parts by weight of the monomer (M2).

12. The pressure-sensitive adhesive composition according to claim 7, wherein the first block comprises a polymerized unit derived from 80 to 99 parts by weight of (meth)acrylic acid ester and a polymerized unit derived from 1 to 20 parts by weight of a compound capable of providing a cross-linkable functional group.

13. The pressure-sensitive adhesive composition according to claim 1, wherein the first block has a number average molecular weight (Mn) in a range of 10,000 to 250,000, and the first block has a molecular weight distribution in a range of 1.0 to 3.0.

14. The pressure-sensitive adhesive composition according to claim 10, wherein the block copolymer has a number average molecular weight (Mn) in a range of 100,000 to 500,000, and a molecular weight distribution in a range of 2.0 to 5.0.

15. The pressure-sensitive adhesive composition according to claim 1, wherein the block copolymer is a diblock copolymer.

16. The pressure-sensitive adhesive composition according to claim 1, wherein the block copolymer is a diblock copolymer comprising 5 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.

17. The pressure-sensitive adhesive composition according to claim 16, further comprising 0.01 to 20 parts by weight of a cross-linking agent relative to 100 parts by weight of the block copolymer.

18. A pressure-sensitive adhesive optical laminate comprising: an optical film; and a pressure-sensitive adhesive layer formed on at least one side of the optical film, wherein the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition according to claim 1.

19. The pressure-sensitive adhesive optical laminate according to claim 18, wherein the pressure-sensitive adhesive optical laminate is a pressure-sensitive adhesive polarizing plate comprising: one or more films selected from a protective film and an optical functional film; and a polarizer.

20. The pressure-sensitive adhesive optical laminate according to claim 19, wherein the pressure-sensitive adhesive polarizing plate has crossed nicol transmittance (Tc) of less than 0.002% and satisfies a polarization degree (P.E) in a range of 99.996 to 99.998%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0138] The FIGURE is a view for explaining a light leakage measurement method in Examples and Comparative Examples.

BEST MODE

[0139] Hereinafter, the present application will be described in detail through examples. However, the protection scope of the present application is not limited by examples described below.

<Measurement or Evaluation Items>

1. Molecular Weight

[0140] The number average molecular weight (Mn) and the molecular weight distribution (PDI) of the block or block copolymer were measured using GPC (gel permeation chromatograph), and the GPC measurement conditions were as follows. The measurement results were converted using standard polystyrene (manufactured by Aglient system) for preparing the calibration curve.

[0141] <GPC measurement conditions>

[0142] Measuring instrument: Aglient GPC (Aglient 1200 series, U.S.)

[0143] Column: Two PL Mixed B connected

[0144] Column temperature: 40° C.

[0145] Eluent: THF (tetrahydrofuran)

[0146] Flow rate: 1.0 mL/min

[0147] Concentration: ˜1 mg/mL (100 μl injection)

2. Durability

[0148] The polarizing plates prepared in Examples and Comparative Examples were each tailored to have a width of about 106 mm and a length of about 142 mm, and attached to a 7-inch commercial liquid crystal panel. Thereafter, the panel with the attached polarizing plate is stored for about 20 minutes in an autoclave (50° C., 5 atm) to prepare a sample. In the case of the moist-heat resistant durability of the prepared sample, it was evaluated according to the following criteria by observing occurrence of bubbles and peeling at the pressure-sensitive adhesive interface after leaving the sample to stand at 65° C. and 95% relative humidity for 500 hours. In the case of the heat resistant durability, it was evaluated according to the following criteria by also observing occurrence of bubbles and peeling after maintaining the sample at 100° C. for 500 hours.

[0149] <Heat resistant and moist-heat resistant durability evaluation criteria>

[0150] A: no bubbles and peeling occurred

[0151] B: slight bubbles and/or peeling occurred

[0152] C: large amount of bubbles and/or peeling occurred

3. Glass Transition Temperature

[0153] The glass transition temperature (Tg) of a block copolymer or each block of the block copolymer was calculated according to Equation A below.

1/Tg=ΣWn/Tn   [Equation A]

[0154] In Equation above, Wn is a weight fraction of the monomer applied to a block copolymer or each block of the block copolymer, and Tn represents a glass transition temperature when each of the corresponding monomers has formed a homopolymer. That is, in Equation A, the right side is a result of summing up the calculated values after calculating all the values (Wn/Tn) obtained by dividing the weight fraction of the used monomer by the glass transition temperature appearing when the monomer has formed the homopolymer for each monomer.

4. Refractive Index (R.I.) and Optical Characteristic of Each Block

[0155] (1) Refractive Index

[0156] The refractive index of each block included in the copolymers of Examples and Comparative Examples was calculated according to the above-described relational expressions and equations.

[0157] (2) Optical Characteristic

[0158] The pressure-sensitive adhesive polarizing plates prepared in Examples or Comparative Examples were each cut so as to have a width of 40 mm and a length of 40 mm to prepare a specimen. Subsequently, it is attached to a jig having a width of 40 mm and a length of 40 mm. Then, using UV-VIS Spectrophotometer (JASCO, model name V-7100) equipment, the single transmittance (%, Ts), parallel transmittance (%, Tp), crossed nicol transmittance (%, Tc, orthogonal transmittance) and polarization degree (%, P.E.) for the TD and MD directions of the polarizing plate were each measured after the pressure-sensitive adhesive side was placed toward the light source.

5. Light leakage

[0159] In order to investigate uniformity of light transmittance, it was observed using a backlight whether there was a light leakage portion in the dark room.

[0160] Panel type: LCD module for TN

[0161] Specimen: 2 polarizing plates to which the pressure-sensitive adhesive fitting LCD module size is attached

[0162] Polarizing plate check: polarizing plate tailored in the 45 degree direction with respect to the stretching direction

[0163] Wide view liquid crystal direction check of polarizing plate: The long side of the polarizing plate is held with both hands and shone vertically on the LCD monitor so that light is not transmitted, and then the long side of the polarizing plate is bent toward the body to check which light of the left and right leaks, where if the light leaking direction is to the right, the down right direction is the liquid crystal direction.

[0164] (1) The LCD module is disassembled, the polarizing plate attached to the LCD cell is removed and the cell surface is wiped with EAc.

[0165] (2) After checking the wide view liquid crystal coating direction of the polarizing plate, the polarizing plate is attached so that the liquid crystal direction faces away from the side tap, as shown in the FIGURE. Two upper and lower specimens are attached to both sides of the cell in the state that the polarized light is crossed, and the direction is aligned so that the top and bottom of the liquid crystal direction cross.

[0166] (3) The cell is stored for 240 hours under aging conditions (moist-heat resistant condition: a temperature of 65° C. and 95% relative humidity, heat resistant condition: a temperature of 100° C.), and then left to stand at room temperature for 2 hours to observe the light leakage.

[0167] Method of observing light leakage: it was evaluated according to the following criteria by observing the LCD module with the naked eye while driving it.

[0168] <Evaluation criteria>

[0169] A: it is difficult to determine the light leakage with the naked eye.

[0170] B: slight light leakage

[0171] C: some light leakage

[0172] D: large amount of light leakage

6. Peel Force

[0173] The release pressure-sensitive adhesive laminates prepared in Examples or Comparative Examples were each tailored so as to have a width of 25 mm and a height of 100 mm to prepare specimens. Subsequently, the release PET film attached to the pressure-sensitive adhesive layer is peeled off and the pressure-sensitive polarizing plate is attached to glass (soda lime glass) using a roller of 2 kg in accordance with the provision of JIS Z 0237. The glass with the attached polarizing plate is squeezed in an autoclave (50° C., 5 atm) for about 20 minutes and stored under constant temperature and humidity conditions (23° C., 50% relative humidity) for 24 hours to prepare a sample. Thereafter, the peel force is measured while peeling the polarizing plate from the glass at a peel rate of 0.3 m/min and a peel angle of 180° , using TA equipment (Texture Analyzer, manufactured by Stable Micro Systems, UK).

7. Interface Adhesive Force

[0174] The pressure-sensitive adhesive polarizing plates prepared in Examples and Comparative Examples were tailored so as to have a width of 25 mm and a height of 100 mm to prepare specimens. Thereafter, the specimen is attached to a PET (poly(ethylene terephthalate)) film via the pressure-sensitive adhesive layer to prepare a laminate, and after maintaining the laminate at room temperature for 3 days, the laminate is attached to a glass substrate with a double-sided tape so that the PET film comes to the top, and then the interface adhesive force is evaluated by measuring the adhesive force between the polarizing plate and the PET film while peeling the PET film at room temperature at a peel rate of 10 mm/sec and a peel angle of 180°.

<Preparation Examples of Copolymers>

PREPARATION EXAMPLE 1

Preparation of Block Copolymer (A1)

[0175] 0.098 g of EBiB (ethyl 2-bromoisobutyrate), 160 g of methyl methacrylate (MMA), 30 g of butyl methacrylate (BMA) and 10 g of hydroxyethyl methacrylate (HEMA) were mixed in 370 g of ethyl acetate (EAc). The reactor containing the mixture was sealed, purged with nitrogen and stirred at about 25° C. for about 30 minutes, and dissolved oxygen was removed through bubbling. Thereafter, 0.0338 g of CuBr.sub.2, 0.0876 g of TPMA (tris(2-pyridylmethyl)amine) and 0.226 g of V-65 (2,2′-azobis(2,4-dimethyl valeronitrile)) were introduced to the mixture in which oxygen was removed and the mixture was immersed in a reaction tank at about 67° C. to initiate the reaction (polymerization of the first block). When the conversion of methyl methacrylate was about 70%, a mixture of 829 g of n-butyl acrylate (BA), 15 g of hydroxybutyl acrylate (HBA), 100 g of benzyl acrylate (BzA), 60 g of hydroxyethyl acrylate (HEA) and 411 g of ethyl acetate (EAc), which had been previously bubbled with nitrogen, was introduced thereto in the presence of nitrogen. Then, 0.0264 g of CuBr.sub.2, 0.0685 g of TPMA and 0.335 g of V-65 were added to the reactor, and a chain extension reaction was carried out (polymerization of the second block). If the conversion of the monomer (BA) reached 80% or more, the reaction mixture was exposed to oxygen and diluted with an appropriate solvent to terminate the reaction, thereby preparing the block copolymer (in the above process, V-65 was appropriately divided and introduced until the end of the reaction in consideration of its half-life).

PREPARATION EXAMPLES 2 TO 6

Preparation of Block Copolymers (A2 to A3 and B1 to B3)

[0176] Block copolymers were prepared in the same manner as in Preparation Example 1, except that the raw materials used in the polymerization of the first block and the second block were controlled as in Table 1 below.

TABLE-US-00001 TABLE 1 Preparation Example of diblock copolymer 1 2 3 4 5 6 A1 A2 A3 B1 B2 B3 First block MMA ratio 80 77 77 80 70 95 BMA ratio 15 20 20 15 30 — HEMA ratio 5 3 3 5 — 5 Tg(° C.) 92 83 83 92 80 107 Mn(×10,000) 8.7 6.1 5.8 8.7 5.5 8.5 PDI 2.01 2.05 2.05 2.01 2.1 2.1 R.I.sub.1 1.482 1.478 1.478 1.482 1.470 1.492 Second block BzA ratio 10 20 10 10 10 10 BA ratio 82.5 75.5 82.5 88.5 88.5 88.5 HBA ratio 1.5 1.5 1.5 1.5 1.5 1.5 HEA ratio 6 3 6 — — — Tg(° C.) −35.1 −44.8 −35.1 −50 −50 −50 R.I.sub.2 1.473 1.476 1.472 1.470 1.470 1.470 Block copolymer Mn(×10,000) 23.3 21.5 21.7 23.0 29.2 22.3 PDI 3.0 3.3 3.1 3.0 3.2 3.2 First block:Second 20:80 15:85 15:85 20:80 11:89 20:80 block (weight ratio) ΔR.I. 0.009 0.002 0.006 0.012 0 0.022 Monomer ratio unit: part by weight MMA: methyl methacrylate (homopolymer Tg: about 110° C./homopolymer R.I.: 1.491) BMA: butyl methacrylate (homopolymer Tg: about 26° C./homopolymer R.I. 1.422) HEMA: hydroxyethyl methacrylate (homopolymer Tg: about 57° C./homopolymer R.I. 1.512) BzA: benzyl acrylate (homopolymer Tg: about 6° C./homopolymer R.I. 1.514) BA: n-butyl acrylate (homopolymer Tg: about −54° C./homopolymer R.I. 1.465) HBA: 4-hydroxybutyl acylate (homopolymer Tg: about −80° C./homopolymer R.I. 1.452) HEA: 2-hydroxylethyl acrylate (homopolymer Tg: about −15° C./homopolymer R.I. 1.507) Mn: number average molecular weight PDI: molecular weight distribution Tg: glass transition temperature R.I.: refractive index

EXAMPLES AND COMPARATIVE EXAMPLES

EXAMPLE 1

[0177] 0.15 parts by weight of a TDI-based cross-linking agent (Coronate L, manufactured by Japan NPU), 0.01 parts by weight of DBTDL (dibutyltin dilaurate) and 0.5 parts by weight of an epoxy group-containing silane coupling agent (KBM-403, 3-glycidoxypropyl trimethoxysilane), relative to 100 parts by weight of the block copolymer (A1) prepared in Preparation Example 1, were mixed and ethyl acetate as a solvent was blended and controlled so as to have a coating solid content of about 25 wt % to prepare a coating liquid (pressure-sensitive adhesive composition).

[0178] The prepared coating solution was coated on the release-treated surface of a release PET (poly(ethylene terephthalate)) (MRF-38, manufactured by Mitsubishi) having a thickness of 38 μm so as to have a thickness after drying of about 23 μm, and maintained in an oven at 80° C. for about 3 minutes (production of a release pressure-sensitive adhesive laminate).

[0179] After drying, the coating layer formed on the release PET was laminated on one side of a polarizing plate (laminated structure of COP/PVA/COP: COP =cyclopolyolefin, PVA=polyvinyl alcohol-based polarizing film) to produce a pressure-sensitive polarizing plate. At this time, the crossed nicol transmittance (Tc) of the used polarizing plate is about 0.001%, the polarization degree (P.E.) is a level of 99.997 to 99.998%.

EXAMPLES 2 TO 3 AND COMPARATIVE EXAMPLES 1 TO 9

[0180] A pressure-sensitive adhesive composition (coating liquid) and a pressure-sensitive adhesive polarizing plate were prepared in the same manner as in Example 1, except that upon preparing the pressure-sensitive adhesive composition (coating liquid), components and ratios were each adjusted as in Table 2 below.

TABLE-US-00002 TABLE 2 Polymer Cross-linking Epoxysilane Non-epoxysilane Type Content agent content DBTDL compound compound* Example 1 A1 100 0.15 0.01 0.5 — 2 A2 100 0.15 0.01 0.5 — 3 A3 100 0.15 0.01 0.5 — Comparative 1 B1 100 0.15 0.01 0.5 — Example 2 B2 100 0.15 0.01 0.5 — 3 B3 100 0.15 0.01 0.5 — 4 B1 100 0.15 0.01 — 0.5 5 B2 100 0.15 0.01 — 0.5 6 B3 100 0.15 0.01 — 0.5 Content unit: part by weight Non-epoxysilane compound*: a silane coupling agent with a beta-cyanoacetyl group (M812, LG Chemical)

[0181] Physical property measurement results are as shown in Table 3.

TABLE-US-00003 TABLE 3 Light Light Moist- leakage leakage Heat heat (heat (moist-heat Interface resistant resistant resistant resistant Peel adhesive durability durability condition condition force force Tc P.E. at at 65° C., at at 65° C., (gf/25 (gf/25 |ΔR.I.| (%) (%) 100° C. 95% 100° C.) 95%) mm) mm) Example 1 0.009 0.001 99.997 A A A A 380 3,450 2 0.002 0.001 99.998 A A A A 450 3,320 3 0.006 0.001 99.998 A A A A 420 3,210 Comparative 1 0.012 0.002 99.993 B B C C 340 2,600 Example 2 0.0 0.001 99.998 C C C C 2,800* 780 3 0.022 0.002 99.993 B B C C 220 3,130 4 0.012 0.002 99.993 B C C C 360 800 5 0.0 0.001 99.998 C C C C 3,100* 760 6 0.022 0.002 99.993 B C C C 210 2,190 *pressure-sensitive adhesive residue occurs on glass

[0182] As confirmed in Tables 1 to 3 above, in the case of the pressure-sensitive adhesive polarizing plates having the block copolymers of Examples, the optical characteristics are maintained, and at the same time, the durability, peel force and interface adhesive force are excellent. On the other hand, in the case of Comparative Examples 1, 3, 4 and 6 using block copolymers that do not satisfy the above relational expression (|ΔR.I.|<0.011), the optical characteristics of the pressure-sensitive adhesive polarizing plates are not good. In the case of Comparative Examples 2 and 5, they have not secured the sufficient degree of cross-linking as in Examples, and the durability is not good because the content of hard blocks is small.