Low refractive layer and anti-reflective film comprising the same

Abstract

The present invention relates to a low refractive layer and an anti-reflective film comprising the same. The low refractive layer can exhibit excellent optical properties such as a low reflectance and a high light transmittance, and excellent mechanical properties such as high wear resistance and scratch resistance at the same time. In particular, due to the excellent alkali resistance, the low refractive layer can maintain excellent physical properties even after alkali treatment. Therefore, when introducing a low refractive layer to the display device, it is expected that the production process can be simplified and further the production rate and the productivity can significantly increase.

Claims

1. A low refractive layer comprising a photo-cured product obtained by photo-curing a photocurable coating composition comprising: 100 parts by weight of a photopolymerizable compound, 1 to 75 parts by weight of a fluorine-based compound, 10 to 320 parts by weight of an inorganic particle, 0.5 to 2.5 parts by weight of a polysilsesquioxane substituted with at least one reactive functional group and at least one non-reactive functional group, and 1 to 100 parts by weight of a photopolymerization initiator wherein the fluorine-based compound contains —O—CF.sub.2CF.sub.2—O—CF.sub.3 and one or more photoreactive functional groups, wherein the low refractive layer satisfies the following formula 1:
30%≥ΔS=[(S.sub.0−S.sub.1)/S.sub.0]×100  [Formula 1] in the formula 1, S.sub.0 is the maximum load that scratches are not generated, when rubbing the surface of the low refractive layer while applying a load to a grade #0000 steel wool and reciprocating ten times at a speed of 24 rpm; and S.sub.1 is the maximum load that scratches are not generated, as measured in the same manner as a method of measuring So as to the film prepared by immersing the low refractive layer for 2 minutes in 10 wt % sodium hydroxide aqueous solution heated to 30° C., washing the immersed layer with water, wiping moisture off, followed by immersing the low refractive layer for 30 seconds in 10 wt % sodium hydroxide aqueous solution heated to 55° C., and then washing the immersed layer with water and wiping moisture off.

2. The low refractive layer according to claim 1, satisfying the following formula 2:
0.5≥Δb*=|b*.sub.1−b*.sub.0|  [Formula 2] in the formula 2, b*.sub.0 is a b* value in a L*a*b* color coordinate system as defined by the International Commission on Illumination as to the low refractive layer; and b*.sub.1 is a b* value in a L*a*b* color coordinate system as measured in the same manner as a method for measuring b*.sub.0 as to a film prepared by the order of: (1) immersing the low refractive layer for 2 minutes in 10 wt % sodium hydroxide aqueous solution heated to 30° C., (2) washing the low refractive layer with water after immersing, (3) wiping moisture off, followed by (4) immersing the low refractive layer for 30 seconds in 10 wt % sodium hydroxide aqueous solution heated to 55° C., (5) washing the low refractive layer with water and (6) wiping off moisture.

3. The low refractive layer according to claim 2 wherein the b*.sub.0 value in the formula 2 is from 1 to −8.

4. The low refractive layer according to claim 1 wherein the low refractive layer exhibits a minimum reflectance in the wavelength range of 480 to 680 nm wherein reflectance is measured over a wavelength range of 380 to 780 nm.

5. The low refractive layer according to claim 1 wherein an average reflectance for light in the wavelength range of 380 to 780 nm is from 0.9 to 2.5%.

6. The low refractive layer according to claim 1, wherein the at least one reactive functional group is selected from the group consisting of alcohol, amine, carboxylic acid, epoxide, imide, (meth)acrylate, nitrile, norbornene, olefin, polyethylene glycol, thiol and vinyl groups.

7. An anti-reflective film comprising a low refractive layer of claim 1; and a hard coating layer formed on one surface of the low refractive layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Example 1.

(2) FIG. 2 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Example 2.

(3) FIG. 3 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Example 3.

(4) FIG. 4 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Comparative Example 1.

(5) FIG. 5 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Comparative Example 2.

(6) FIG. 6 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Comparative Example 3.

(7) FIG. 7 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Comparative Example 4.

(8) FIG. 8 is a graph showing the reflectance according to the wavelength of the anti-reflective film prepared in Comparative Example 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) Hereinafter, the action and effect of the invention will be described in detail, through specific examples of the invention. However, the examples are provided only to illustrate the present invention, and the scope of the invention is not limited thereto.

Preparation Example

Preparation Example 1: Preparation of Hard Coating Film 1 (HD1)

(10) A salt type of antistatic hard coating solution (manufactured by KYOEISHA Chemical Co., Ltd., solid content: 50 wt %, product name: LJD-1000) was coated onto triacetylcellulose film with #10 layer bar and dried at 90° C. for one minute, followed by irradiation with ultraviolet light of 150 mJ/c to prepare a hard coating film (HD1) having a thickness of 5 μm.

Preparation Example 2: Preparation of Hard Coating Film 2 (HD2)

(11) 30 g of pentaerythritol triacrylate, 2.5 g of high molecular weight copolymer (BEAMSET 371, Arakawa Corporation, Epoxy Acrylate, molecular weight: 40,000), 20 g of methyl ethyl ketone and 0.5 g of leveling agent (Tego wet 270) were uniformly mixed. Then, 2 g of acrylic-styrene copolymer (volume average particle size: 2 μm, manufactured by Sekisui Plastic) with a refractive index of 1.525 as a fine particle was added to the mixture to prepare a hard coating composition. The hard coating composition thus obtained was coated onto triacetylcellulose film with a #10 mayer bar and dried at 90° C. for one minute. The dried product was irradiated with ultraviolet light of 150 mJ/ca to prepare a hard coating film (HD2) having a thickness of 5 mm.

Preparation Example 3: Preparation of Polysilsesquioxane 1

(12) 36.57 g (0.156 mol) of isooctyltrimethoxy silane, 23.34 g (0.094 mol) of 3-methacryloxypropyl trimethoxysilane and 500 mL of methanol were added to a 1 L reactor equipped with a nitrogen gas inlet tube, a condenser and a stirrer, and stirred at room temperature for 10 minutes. Then, tetramethylammonium hydroxide (280 g, 0.77 mol, 25 wt % in methanol) was added thereto, and the reaction was carried out for 8 hours by raising the reactor temperature under a nitrogen atmosphere to 60° C. After completion of the reaction, g of polyhedral oligomeric silsesquioxane (POSS) substituted by an isooctyl group and a methacryloxypropyl group was obtained through column chromatography and recrystallization. The confirmation result of GP Chromatography showed that the molar ratio of a methacryloxypropyl group to an isooctyl group (mole number of methacryloxypropyl group/mole number of isooctyl group) which is substituted at silicon of polysilsesquioxane is about 0.6 to 1.67.

Preparation Example 4: Preparation of Fluorine-Based Compound 2

(13) After sufficiently replacing with nitrogen gas, a 2.0 L stainless steel autoclave equipped with an electronic stirrer was charged with 400 g of ethyl acetate, 53.2 g of perfluoro(propyl vinyl ether), 36.1 g of ethyl vinyl ether, 44.0 g of hydroxyethyl vinyl ether, 1.00 g of lauroyl peroxide, 6.0 g of an azo group-containing polydimethylsiloxane represented by the following formula 1 (VPS1001 (trade name), Wako Pure Chemical industries, Ltd.) and 20.0 g of nonionic reactive emulsifier (NE-30 (trade name), manufactured by Asahi Denka Co., Ltd.) and cooled to −50° C. in methanol dry-ice bath, and then oxygen within the system was again removed with nitrogen gas.

(14) ##STR00001##

(15) Then, 120.0 g of hexafluoropropylene was added thereto and the temperature stated to rise. The pressure at a time point when the temperature in the autoclave reached 60° C. exhibited 5.3×10.sup.5 Pa. Thereafter, the reaction was continued while stirring at 70° C. for 20 hours, and the reaction was stopped by cooling the autoclave at a time point when the pressure was reduced to 1.7×10.sup.5 Pa. After reaching the room temperature, the unreacted monomers were released, and the autoclave was opened to obtain a polymer solution with a solid content concentration of 26.4%. The resulting polymer solution was added to methanol to precipitate a polymer, and then washed with methanol and dried in vacuum at 50° C. to obtain 220 g of a hydroxyl group-containing fluoropolymer.

(16) 50.0 g of a hydroxyl group-containing fluoropolymer prepared previously, 0.01 g of 2,6-di-t-butylmethylphenol as a polymerization inhibitor and 370 g of methyl isobutyl ketone (MIBK) were added to a 1 L flask equipped with an electronic stirrer, a cooling tube made of glass and a thermometer, and then stirred until the hydroxyl group-containing fluoropolymer was dissolved in MIBK at 20° C. and the solution became transparent.

(17) Then, 13.7 g of 2-acryloxyethyl isocyanate was added to the system and stirred until the solution became homogeneous. Thereafter, 0.1 g of dibutyltin dilaurate was added thereto and then stirred for 5 hours while maintaining the temperature in the system to 55 to 65° C., thereby obtaining a MIBK solution of the ethylenically unsaturated group-containing fluoropolymer (acrylic modified fluoropolymer). 2 g of this solution was weighed and dropped into an aluminum plate, dried for 5 minutes on a hot plate at 150° C. and re-weighed to calculate the amount of the solid content. As a result, the amount of the solid content was 15.0 wt %.

Examples and Comparative Example, Preparation of Anti-Reflective Film

(18) (1) Preparation of the Photocurable Coating Composition for the Production of a Low Refractive Layer

(19) The ingredients shown in Table 1 were mixed and diluted so that the solid content in MIBK (methyl isobutyl ketone) solvent became 3 wt %.

(20) TABLE-US-00001 TABLE 1 LR1 LR2 LR3 LR4 LR5 LR6 Hollow silica dispersion.sup.1) 220 (44)  130 (26)  220 (44)  130 (26)  220 (44)  40 (8)  Trimethylolpropane 41 (41) 62 (62) 47 (47) 67 (67) 41 (41) 0 (0) triacrylate Polysilsesquioxane 1.sup.2) 6 (6) 5 (5) 0 (0) 0 (0) 0 (0) 0 (0) Polysilsesquioxane 2.sup.3) 0 (0) 0 (0) 0 (0) 0 (0) 6 (6) 30 (30) Fluorine-based 13.333 (4)    6.667 (2)    13.333 (4)    6.667 (2)    0 (0) 0 (0) compound 1.sup.4) Fluorine-based 0 (0) 0 (0) 0 (0) 0 (0) 26.667 (4)    400 (60)  compound 2.sup.5) Photoinitiator (Irgacure-127, 5 (5) 5 (5) 5 (5) 5 (5) 5 (5) 2 (2) Ciba Specialty Chemicals Inc.) (Unit: g; the number in parentheses refers to the amount of the solid content) .sup.1)Hollow silica dispersion: THRULYA 4320 in which hollow silica particles with a number average diameter of 50 nm were dispersed at 20 wt % in MIBK (manufactured by Catalysts & Chemicals Ind. Co., Ltd.) .sup.2)Polysilsesquioxane 1: Polysilsesquioxane 1 prepared according to Preparation Example 3 .sup.3)Polysilsesquioxane 2: MAC-SQ-F (manufactured by TOAGOSEI CO., Ltd.) .sup.4)Fluorine-based compound 1: Fluorine-based compound containing a photoreactive functional group, —O—CF.sub.2CF.sub.2—O—CF.sub.3, —O—(CF.sub.2).sub.3—O— and —O—CF.sub.2CF.sub.2CF.sub.3; RS907 (manufactured by DIC Corporation) diluted at 30 wt % in MIBK. .sup.5)Fluorine-based compound 2: Fluorine-based compound 2 in which 15 wt % of the solid content was dispersed in MIBK, which was prepared according to Preparation Example 4.

(21) (2) Preparation of Low Refractive Layer and Anti-Reflective Film (Examples 1 to 3 and Comparative Examples 1 to 5)

(22) The respective photocurable coating compositions obtained in Table 1 were coated onto the hard coating layer of the hard coating film described in Table 2 below by #3 mayer bar and dried at 60° C. for one minute. Then, the dried product was irradiated with ultraviolet light of 180 mJ/cm.sup.2 while purging the nitrogen gas to form a low refractive layer having a thickness of 110 m, thereby preparing a desired anti-reflective film.

Experimental Example: Measurement of Physical Properties of Anti-Reflective Film

(23) The experiments given in the following items were carried out for the anti-reflective films obtained in Examples and Comparative Examples.

(24) 1. Alkaline Pretreatment

(25) The respective anti-reflective films obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were immersed in NaOH aqueous solution (solution in which 10 wt % of NaOH was diluted in distilled water) at 30° C. for two minutes and washed with flowing water, and then moisture was wiped off. The anti-reflective films in which moisture has been wiped off was again immersed in NaOH aqueous solution (solution in which NaOH was diluted at 10 wt % in distilled water) at 55° C. for 30 seconds and washed with flowing water, and then moisture was wiped off.

(26) 2. Measurement of Reflectance and Color Coordinate Value (b*)

(27) The average reflectance and the color coordinate value of the anti-reflective films prepared in Examples and Comparative Examples were measured using SolidSpec 3700 (SHIMADZU) before and after alkaline pretreatment.

(28) Specifically, to the surface in which the hard coating layer of the substrate film was not formed, a black tape was attached so as to prevent transmission of light, and the measurement conditions were set as follows: sampling interval 1 nm, time constant 0.1 sec, slit width 20 nm, medium scanning speed. Then, the low refractive layer of the anti-reflective film was irradiated with a light in the wavelength range of 380 nm to 780 nm at room temperature.

(29) When using HD2 as a hard coating layer, a 100% T mode was applied. When using HD1 as a hard coating layer, a Measure mode was applied. Then, the reflectance in the wavelength range of 380 nm to 780 nm was measured. The measurement results of the reflectance in the wavelength range of 380 nm to 780 nm of the anti-reflective films prepared in Examples and Comparative Examples were shown in FIGS. 1-8. In FIGS. 1 to 8, the dotted lines (----) are graphs showing the reflectance (y-axis) according to the wavelength (x-axis) of the anti-reflective film before alkali treatment, and solid lines () are graphs showing the reflectance (y-axis) according to the wavelength (x-axis) of the anti-reflective film after alkali treatment.

(30) The average reflectance and the color coordinate value (b*) in wavelength range of 380 nm to 780 nm of the anti-reflective films prepared in Examples and Comparative Examples were derived from the above reflectance through UV-2401PC color analysis program and shown in Table 2 below.

(31) 3. Measurement of Scratch Resistance

(32) The surfaces of the low refractive layers obtained in Examples and Comparative Examples were rubbed while applying a load to a grade #0000 steel wool and reciprocating ten times at a speed of 24 rpm. The maximum load that scratches are not generated, as observed with the naked eye under a LED 50 W ceiling illumination, was measured. The load is defined as weight (g) per area(2*2 cm.sup.2) having a width of 2 cm and a length of 2 cm

(33) TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Comparative Example 1 Example 1 Example 2 Example 2 Example 3 Example 3 Example 4 Example 5 Hard coating layer HD2 HD2 HD1 HD1 HD1 HD2 HD2 HD2 Low refractive LR1 LR3 LR1 LR3 LR5 LR2 LR4 LR6 layer Wavelength range 540~550 480~530 510~540 510~530 550~610 510~520 540~590 560~610 showing the minimum reflectance [nm] Average Before 1.23% 1.32% 1.07% 1.20% 1.19% 2.09% 2.00% 2.28% reflectance pretreatment After 1.24% 1.33% 1.01% 1.18% 1.24% 2.15% 2.02% 2.25% pretreatment color Before −3.48 −1.05 −2.27 −2.78 −6.92 −1.04 −2.62 −2.30 coordinate pretreatment value (b*.sub.0) (b*) After −3.04 −0.15 −1.84 −1.93 −5.87 −0.74 −1.54 −0.86 pretreatment (b*.sub.1) Δb* = b*.sub.1 − b*.sub.0 0.44 0.9 0.43 0.85 1.05 0.3 1.08 1.44 Scratch Before 350 200 400 150 200 600 500 450 resistance pretreatment [unit: g/(2*2 cm.sup.2)] After 250 50 350 50 100 600 300 250 pretreatment [unit: g/(2*2 cm.sup.2)] ΔS = [(S.sub.0 − S.sub.1)/ 28.57% 75.00% 12.50% 66.67% 50.00% 0.00% 40.00% 44.44% S.sub.0] × 100

(34) Referring to Table 2 and FIGS. 1 to 8, it was confirmed that the anti-reflective films of Examples 1 and 2 exhibited a significantly low reflectance and a high scratch resistance in the visible light range (480 to 680 nm) and these characteristics maintained superior levels even after the alkali treatment. In contrast, the anti-reflective films of Comparative Examples 1 to 3 exhibited poor scratch resistance, in particular, the scratch resistance was remarkably degraded after the alkali treatment.

(35) On the other hand, it was confirmed that the anti-reflective films of Example 3 and Comparative Examples 4 and 5 have achieved high scratch resistance by reducing the content of the hollow silica contained in the low refractive layer, but similarly, the anti-reflective films of Comparative Examples 4 and 5 exhibited a remarkably degraded scratch resistance even after the alkali treatment.

(36) Accordingly, it was confirmed that only when using the low refractive layer satisfying the specific conditions of the present invention, the low refractive layer exhibited excellent alkali resistance, thus providing the anti-reflective films showing little change in physical properties before and after the alkali treatment. In particular, although such a low refractive layer was exposed to an alkali according to the preparation process of the polarizing plate, there was less reduction in optical properties such as reflectance and transmittance or in mechanical properties such as wear resistance or scratch resistance. Therefore, it was possible to omit the application of additional protective films for the outer surface protection, and thus the production process was simplified and production costs were reduced. In addition, since the low refractive layer maintained excellent optical and mechanical properties even in the alkali treatment at high temperature, they are expected to contribute greatly to the improvement of productivity and production rate.