Optical laminate

Abstract

An optical laminate is provided where stable durability is secured even at a high temperature, particularly an ultra-high temperature of about 100° C. or higher, no white turbidity is caused, other physical properties required for the optical laminate are also excellent, and even in the case of being disposed adjacent to the electrode, corrosion of the relevant electrode or the like is not induced.

Claims

1. An optical laminate comprising an optical film; and a pressure-sensitive adhesive layer formed on a side of the optical film, wherein the pressure-sensitive adhesive layer comprises a pressure-sensitive adhesive polymer having an alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms, an alkyl (meth)acrylate unit having an alkyl group with 3 or less carbon atoms, an aromatic group-containing monomer unit and a polar group-containing monomer unit that has a carboxyl group and an organic salt, and the polar group-containing monomer unit is present in an amount of 1.5 to 4.5 parts by weight relative to 100 parts by weight of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms, the pressure-sensitive adhesive layer has a room temperature storage elastic modulus of 0.07 MPa or more and a gel fraction of 80 wt % or more according to Equation 1 below:
Gel fraction=B/A×100  [Equation 1] wherein, B/A is a ratio of a dry mass (B) (unit: g) of an insoluble fraction recovered after immersing the pressure-sensitive adhesive layer in ethyl acetate at room temperature for 24 hours to a mass (unit: g) (A) of the pressure-sensitive adhesive layer before immersing the pressure-sensitive adhesive layer in ethyl acetate, wherein an amount of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms in the pressure-sensitive adhesive polymer is in a range of 50 wt % to 70 wt %, wherein the alkyl (meth)acrylate unit having an alkyl group with 3 or less carbon atoms is included in the pressure-sensitive adhesive polymer in an amount of 30 to 65 parts by weight relative to 100 parts by weight of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms.

2. The optical laminate according to claim 1, wherein the optical film is a polarizer.

3. The optical laminate according to claim 1, wherein the optical film is a polyvinyl alcohol polarizer containing potassium component and zinc component.

4. The optical laminate according to claim 3, wherein a ratio of the potassium component and the zinc component contained in the polyvinyl alcohol polarizer is in a range of 0.2 to 6.

5. The optical laminate according to claim 4, wherein the potassium component is included in an amount of 0.1 to 2 wt % based on a total weight of the polyvinyl alcohol polarizer.

6. The optical laminate according to claim 4, wherein the zinc component is included in an amount of 0.1 to 0.5 wt % based on a total weight of the polyvinyl alcohol polarizer.

7. The optical laminate according to claim 1, wherein an amount of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms in the pressure-sensitive adhesive polymer is in a range of 50 wt % to 65 wt %.

8. The optical laminate according to claim 1, wherein the alkyl (meth)acrylate unit having an alkyl group with 3 or less carbon atoms is methyl acrylate.

9. The optical laminate according to claim 1, wherein the alkyl (meth)acrylate unit having an alkyl group with 3 or less carbon atoms is included in the pressure-sensitive adhesive polymer in an amount of 30 to 58 parts by weight relative to 100 parts by weight of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms.

10. The optical laminate according to claim 1, wherein the aromatic group-containing monomer forming the aromatic group-containing monomer unit is represented by Formula 1 below: ##STR00003## wherein, R.sub.1 represents hydrogen or alkyl, A represents alkylene, n represents an integer in a range of 0 to 3, Q represents a single bond, —O—, —S— or alkylene, and P represents an aromatic ring.

11. The optical laminate according to claim 1, wherein the aromatic group-containing monomer unit is included in the pressure-sensitive adhesive polymer in an amount of 20 to 45 parts by weight relative to 100 parts by weight of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms.

12. The optical laminate according to claim 1, wherein the polar group-containing monomer is selected from a group consisting of (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropyl acid, 4-(meth)acryloyloxybutyric acid, an acrylic acid dimer, itaconic acid, maleic acid and maleic anhydride.

13. The optical laminate according to claim 1, wherein the polar group-containing monomer unit is included in the pressure-sensitive adhesive polymer in an amount of 1.5 to 2 parts by weight relative to 100 parts by weight of the alkyl (meth)acrylate unit having an alkyl group with 4 or more carbon atoms.

14. The optical laminate according to claim 1, wherein the organic salt comprises a cation of Formula 2 below: ##STR00004## wherein, R.sub.1 is an alkyl group having 1 to 3 carbon atoms, and R.sub.2 to R.sub.4 are each independently an alkyl group having 4 to 20 carbon atoms.

15. The optical laminate according to claim 14, wherein the organic salt comprises an anion of Formula 3 below or bisfluorosulfonylimide:
[X(YO.sub.mR.sub.f).sub.n]  [Formula 3] wherein, X is a nitrogen atom or a carbon atom, Y is a carbon atom or a sulfur atom, R.sub.f is a perfluoroalkyl group, m is 1 or 2, and n is 2 or 3.

16. The optical laminate according to claim 1, wherein an amount of metal salt in the pressure-sensitive adhesive layer is less than 0.05 wt %.

17. The optical laminate according to claim 1, wherein the pressure-sensitive adhesive layer further comprises a crosslinking agent for crosslinking the pressure-sensitive adhesive polymer.

18. A display device comprising a display panel to which the optical laminate of claim 1 is attached via the pressure-sensitive adhesive layer of the optical laminate.

19. The display device according to claim 18, further comprising an electrode wherein the pressure-sensitive adhesive layer directly contacts the electrode.

20. The optical laminate according to claim 1, wherein the room temperature storage elastic modulus of the pressure-sensitive adhesive layer is 0.07 to 0.2 MPa and the gel fraction of the pressure-sensitive adhesive layer is 80 to 95%.

Description

MODE FOR INVENTION

(1) Hereinafter, the present application will be specifically described by way of examples, but the scope of the present application is not limited by the following examples.

(2) 1. Method of Measuring Peel Force

(3) The pressure-sensitive adhesive polarizing plates prepared in Examples or Comparative Examples were each cut to a width of 25 mm and a height of 200 mm to prepare a specimen, which was attached to a glass plate via the pressure-sensitive adhesive layer of the specimen. The peel force was measured while peeling off the pressure-sensitive adhesive polarizing plate at a peel angle of 90 degree and a peel rate of 300 mm/min at an elapsed time of 1 hour after attachment of the specimen.

(4) 2. Method of Measuring Gel Fraction

(5) After holding each of the pressure-sensitive adhesive layers prepared in Examples or Comparative Examples at a constant temperature and humidity room (23° C., 50% relative humidity) for 7 days, 0.2 g (=A in gel fraction measurement equation) was collected. The collected pressure-sensitive adhesive layer was completely immersed in 50 mL of ethyl acetate, and then stored in a dark room at room temperature for 1 day. Subsequently, a portion (insoluble fraction) not dissolved in ethyl acetate was collected in a #200 stainless steel wire net and dried at 150° C. for 30 minutes to measure the mass (dry mass of insoluble fraction=B in gel fraction measurement equation). Subsequently, the gel fraction (unit: %) was measured by substituting the measurement result into the following equation.

(6) <Gel Fraction Measurement Equation>
Gel fraction=B/A×100

(7) A: mass of the pressure-sensitive adhesive (0.2 g)

(8) B: dry mass of insoluble fraction (unit: g)

(9) 3. Method of Measuring Elastic Modulus

(10) The pressure-sensitive adhesive compositions prepared in Examples or Comparative Examples were each coated between two release films and aged for 7 days under a constant temperature and humidity condition (23° C., 50% R.H.) to prepare a pressure-sensitive adhesive layer having a thickness of about 22 μm. Subsequently, the pressure-sensitive adhesive between the release films was cut to prepare a circumferential specimen of 8 mm×1 mm (=diameter×thickness), and then using a dynamic rheometer (ARES, RDA, TA Instruments Inc.), the storage elastic modulus, loss elastic modulus and loss tangent at room temperature (23° C.) were measured while applying shear stress between parallel plates at a frequency of 1 Hz.

(11) 4. ITO Corrosion Test (Resistance Change Rate)

(12) The pressure-sensitive adhesive compositions prepared in Examples or Comparative Examples were each laminated on a TAC (triacetyl cellulose) film having a thickness of 40 μm and aged for 7 days under a constant temperature and humidity condition (23° C., 50% relative humidity) to prepare a specimen. A typical ITO (indium tin oxide) film was cut to have a width of about 50 mm or so and a height of about 30 mm, on which a silver paste was applied to both ends in the transverse direction at a width of 10 mm or so, respectively. Subsequently, the specimen was cut to have a width of about 40 mm or so and a height of about 30 mm or so, and the pressure-sensitive adhesive layer was attached to the ends on the silver paste at an interval of 5 mm or so to prepare a sample. The prepared sample was stored for 250 hours under a high temperature and humidity condition (85° C., 85% relative humidity), and then the change rate of resistance was evaluated with a linear resistance meter (Hioki 3244-60 card hitester) as compared with before initial introduction to determine whether or not the ITO was corroded.

(13) 5. High Temperature Durability (Lifting, Peeling and Foaming Evaluation)

(14) The pressure-sensitive adhesive polarizing plates of Examples or Comparative Examples were each cut to have a width of about 140 mm or so and a height of about 90 mm or so to prepare a specimen, which was attached to a glass substrate at a pressure of 5 kg/cm.sup.2. The attachment was performed in a clean room so that bubbles or foreign materials were not generated. Subsequently, the prepared sample was kept in an autoclave for 15 minutes under conditions of 50° C. and 5 kg/cm.sup.2.

(15) After maintaining the sample at a temperature of about 100° C. for about 500 hours, the durability was evaluated according to the following criteria.

(16) <Evaluation Criteria>

(17) O: no bubbling and peeling occurred

(18) Δ: bubbling and/or peeling occurred

(19) X: severe bubbling and/or peeling occurred

(20) 6. White Turbidity Evaluation

(21) Pressure-sensitive adhesive compositions of Examples or Comparative Examples are each applied on a release film and dried to form a pressure-sensitive adhesive layer, and another release film is attached on the formed pressure-sensitive adhesive layer to produce an NCF (non-carrier film) type pressure-sensitive adhesive film. The pressure-sensitive adhesive film was held in a constant temperature and humidity chamber (23° C., 50% relative humidity) for 7 days, and then one of the release films was peeled off, and a distilled water droplet was dropped onto the exposed pressure-sensitive adhesive layer and it was evaluated whether or not a white turbidity phenomenon, in which the dropped distilled water droplet became cloudy, occurred.

(22) <Evaluation Criteria>

(23) O: no white turbidity

(24) X: white turbidity occurred

PREPARATION EXAMPLE 1

Preparation of Pressure-Sensitive Adhesive Polymer (A)

(25) n-Butyl acrylate (n-BA), benzyl acrylate (BzA), methyl acrylate (MA) and hydroxybutyl acrylate (4-HBA) were introduced into an 1 L reactor equipped with a cooling device for nitrogen gas refluxing and easy temperature control in a weight ratio of 64:15:20:1 (n-BA:BzA:MA:4-HBA) and 100 parts by weight of ethyl acetate (EAc) was introduced as a solvent. Subsequently, nitrogen gas was purged for 1 hour to remove oxygen, and then, 0.03 parts by weight of azobisisobutyronitrile (AIBN) diluted to a concentration of 50 wt % in ethyl acetate was introduced as a reaction initiator and reacted for 8 hours to prepare a copolymer (A) having a molecular weight (Mw) of about 1,800,000 or so.

PREPARATION EXAMPLE 2

Preparation of Pressure-Sensitive Adhesive Polymers B to G

(26) Copolymers were prepared by the method according to Preparation Example 1 above, while adopting the compositions shown in Table 1 below.

(27) TABLE-US-00001 TABLE 1 Preparation Example 1 2 3 4 5 6 7 A B C D E F G n-BA 64 54 63 64 81 84 84 BzA 15 15 15 15 15 15 15 MA 20 30 20 20 4-HBA 1 1 2 1 AA 1 4 1 Mw 1,800,000 1,850,000 1,800,000 1,650,000 1,300,000 1,500,000 1,650,000 Content unit: part by weight, n-BA: n-butyl acrylate, BzA: benzyl acrylate, MA: methyl acrylate, 4-HBA: 4-hydroxybutyl acrylate, AA: acrylic acid, Mw: weight average molecular weight

EXAMPLE 1

(28) Preparation of Pressure-Sensitive Adhesive Composition

(29) An isocyanate crosslinking agent (T-39M, Japan Soken Co., Ltd.) was combined to the copolymer (A) of Preparation Example 1 in an amount of about 0.12 parts by weight relative to 100 parts by weight of the solid content of the copolymer (A), an organic salt (3M Co., FC-4400A) was also combined thereto in a ratio of about 1.0 part by weight relative to 100 parts by weight of the solid content of the copolymer (A), and the mixture was diluted to an appropriate concentration and uniformly mixed, and then coated on a release paper and dried to produce a uniform pressure-sensitive adhesive layer having a thickness of 22 μm.

(30) Production of Polarizing Plate

(31) A polyvinyl alcohol (PVA) film (Japan Synthetic Co., M2004) having a thickness of about 30 μm was immersed in a dyeing solution at 30° C. containing 0.05 wt % of iodine and 1.5 wt % of potassium iodide for 60 seconds to be subjected to dyeing. Subsequently, the dyed polyvinyl alcohol film was immersed in a crosslinking solution at 30° C. containing 0.5 wt % of boron and 3.0 wt % of potassium iodide for 60 seconds to be subjected to crosslinking. Thereafter, the crosslinked polyvinyl alcohol film was stretched at a draw ratio of 5.5 times using a roll-to-roll stretching method. The stretched polyvinyl alcohol film was washed with water by immersing it in ion-exchanged water at 30° C. for 20 seconds and immersed in a solution at 30° C. containing 1.5 wt % of zinc nitrate and 4.0 wt % of potassium iodide for 10 seconds. Thereafter, the polyvinyl alcohol film was dried at a temperature of 80° C. for 200 seconds to produce a polarizer. The potassium content in the produced polarizer was about 0.47 wt %, and the zinc content was about 0.17 wt %. Subsequently, a polarizing plate was prepared by attaching a known TAC (triacetyl cellulose) protective film to both sides of the prepared polarizer.

(32) Production of Optical Laminate (Pressure-Sensitive Adhesive Polarizing Plate)

(33) The polarizing plate was stuck and processed to one side of the prepared pressure-sensitive adhesive layer to produce a pressure-sensitive polarizing plate (optical laminate).

EXAMPLE 2

(34) A crosslinking agent (T-39M, Japan Soken Co., Ltd.) was combined to the copolymer (B) of Preparation Example 2 in an amount of about 0.12 parts by weight relative to 100 parts by weight of the solid content of the copolymer (B), the same organic salt as that of Example 1 was combined thereto in an amount of about 1.0 part by weight relative to 100 parts by weight of the solid content of the copolymer (B), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

EXAMPLE 3

(35) A crosslinking agent (T-39M, Japan Soken Co., Ltd.) was combined to the copolymer (C) of Preparation Example 3 in an amount of about 0.12 parts by weight relative to 100 parts by weight of the solid content of the copolymer (C), the same organic salt as that of Example 1 was combined thereto in an amount of about 1.0 part by weight relative to 100 parts by weight of the solid content of the copolymer (C), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

EXAMPLE 4

(36) A toluene diisocyanate crosslinking agent (T-706BB, Japan Soken Co., Ltd.) was combined to the copolymer (D) of Preparation Example 4 in an amount of about 1 part by weight relative to 100 parts by weight of the solid content of the copolymer (D), an epoxy crosslinking agent (T-743L, Japan Soken Co., Ltd.) was combined thereto in an amount of about 0.005 parts by weight relative to 100 parts by weight of the solid content of the copolymer (D), the same organic salt as that of Example 1 was combined thereto in an amount of about 1.0 part by weight relative to 100 parts by weight of the solid content of the copolymer (D), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

COMPARATIVE EXAMPLE 1

(37) A toluene diisocyanate crosslinking agent (T-706BB, Japan Soken Co., Ltd.) was combined to the copolymer (E) of Preparation Example 5 in an amount of about 1.7 parts by weight relative to 100 parts by weight of the solid content of the copolymer (E), an epoxy crosslinking agent (T-743L, Japan Soken Co., Ltd.) was combined thereto in an amount of about 0.005 parts by weight relative to 100 parts by weight of the solid content of the copolymer (E), an inorganic salt (3M Co., HQ-115A) was combined thereto in an amount of about 0.7 parts by weight relative to 100 parts by weight of the solid content of the copolymer (E), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

COMPARATIVE EXAMPLE 2

(38) A crosslinking agent (T-39M, Japan Soken Co., Ltd.) was combined to the copolymer (F) of Preparation Example 6 in an amount of about 0.08 part by weight relative to 100 parts by weight of the solid content of the copolymer (F), the same inorganic salt (3M Co., HQ-115A) as that of Comparative Example 1 was combined thereto in an amount of about 0.7 parts by weight relative to 100 parts by weight of the solid content of the copolymer (F), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

COMPARATIVE EXAMPLE 3

(39) A crosslinking agent (T-39M, Japan Soken Co., Ltd.) was combined to the copolymer (A) of Preparation Example 1 in an amount of about 0.08 parts by weight relative to 100 parts by weight of the solid content of the copolymer (A), the same organic salt as that of Example 1 was combined thereto in an amount of about 1.0 part by weight relative to 100 parts by weight of the solid content of the copolymer (A), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

COMPARATIVE EXAMPLE 4

(40) A toluene diisocyanate crosslinking agent (T-706BB, Japan Soken Co., Ltd.) was combined to the copolymer (G) of Preparation Example 7 in an amount of about 1 part by weight relative to 100 parts by weight of the solid content of the copolymer (G), an epoxy crosslinking agent (T-743L, Japan Soken Co., Ltd.) was combined thereto in an amount of about 0.005 parts by weight relative to 100 parts by weight of the solid content of the copolymer (G), the same organic salt as that of Example 1 was combined thereto in an amount of about 1.0 part by weight relative to 100 parts by weight of the solid content of the copolymer (G), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

COMPARATIVE EXAMPLE 5

(41) A toluene diisocyanate crosslinking agent (T-706BB, Japan Soken Co., Ltd.) was combined to the copolymer (A) of Preparation Example 1 in an amount of about 0.08 parts by weight relative to 100 parts by weight of the solid content of the copolymer (D), the same inorganic salt (3M Co., HQ-115A) as that of Comparative Example 1 was combined thereto in an amount of about 0.7 parts by weight relative to 100 parts by weight of the solid content of the copolymer (F), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1

COMPARATIVE EXAMPLE 6

(42) A toluene diisocyanate crosslinking agent (T-706BB, Japan Soken Co., Ltd.) was combined to the copolymer (E) of Preparation Example 5 in an amount of about 0.08 part by weight relative to 100 parts by weight of the solid content of the copolymer (E), the same organic salt as that of Example 1 was combined thereto in an amount of about 1.5 parts by weight relative to 100 parts by weight of the solid content of the copolymer (E), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

COMPARATIVE EXAMPLE 7

(43) A toluene diisocyanate crosslinking agent (T-706BB, Japan Soken Co., Ltd.) was combined to the copolymer (D) of Preparation Example 4 in an amount of about 0.8 parts by weight relative to 100 parts by weight of the solid content of the copolymer (D), the same organic salt as that of Example 1 was combined in an amount of about 1.5 parts by weight relative to 100 parts by weight of the solid content of the copolymer (D), and a pressure-sensitive adhesive composition and a pressure-sensitive polarizing plate were prepared in the same manner as in Example 1.

(44) The evaluation results of Examples and Comparative Examples above were summarized and described in Tables 2 and 3 below.

(45) TABLE-US-00002 TABLE 2 Example 1 2 3 4 Peel force (gf/25 mm) 850 1000 750 1000 Gel fraction (wt %) 82 83 83 85 Elastic modulus (MPa) 0.072 0.09 0.091 0.105 High temperature durability ◯ ◯ ◯ ◯ ITO corrosion (resistance 20% 15% 13% 80% change rate) White turbidity ◯ ◯ ◯ ◯

(46) TABLE-US-00003 TABLE 3 Comparative Example 1 2 3 4 5 6 7 Peel force (gf/25 mm) 900 500 900 700 800 450 950 Gel fraction (wt %) 80 72 76 76 73 72 72 Elastic modulus (MPa) 0.088 0.044 0.063 0.08 0.063 0.044 0.082 High temperature durability Δ X Δ X Δ X X ITO corrosion (resistance change rate) 349% 20% 18% 85% 30% 28% 80% White turbidity X ◯ ◯ ◯ X ◯ ◯