Antireflection film

Abstract

The present invention relates to an antireflection film. The antireflection film includes a low refractive index layer having excellent alkali resistance and exhibiting remarkably improved mechanical properties such as scratch resistance and impact resistance as well as reduction of a glare phenomenon, and a base film exhibiting excellent mechanical strength and water resistance in spite of a thin thickness and having no fear of interference fringes occurring. Therefore, such antireflection film can be used as a protective film of a polarizing plate or used as any other component so as to provide a thin display device, and furthermore, can effectively prevent the glare phenomenon of the display device, and can more improve the durability and lifespan thereof.

Claims

1. An antireflection film comprising: a polyester film having an in-plane retardation value (Rin) of 3000 nm to 30,000 nm in which a ratio (Rin/Rth) of the in-plane retardation value (Rin) to a thickness-direction retardation value (Rth) is 0.2 to 1.2; a low refractive index layer which is disposed on the polyester film and which comprises a crosslinked polymer of a photocurable coating composition comprising a photopolymerizable compound comprising a monomer or oligomer containing a (meth)acryloyl group, a fluorine-based compound containing a photoreactive functional group, an inorganic particle, and a polyhedral oligomeric polysilsesquioxane (POSS) having a cage structure in which at least one reactive functional group is substituted; and a hard coating layer between the polyester film and the low refraction index layer, wherein the photocurable coating composition contains the POSS having a cage structure in which at least one reactive functional group is substituted, in an amount of 2 to 27 parts by weight based on 100 parts by weight of the photopolymerizable compound, and wherein the photopolymerizable compound is included in an amount of 13 wt % to 80 wt % with respect to the solid content of the photocurable coating composition, wherein the fluorine-based compound containing a photoreactive function group is not included in the photopolymerizable compound, and wherein the photocurable coating composition includes 1 to 75 parts by weight of the fluorine-based compound containing the photoreactive functional group based on 100 parts by weight of the photopolymerizable compound.

2. The antireflection film of claim 1, wherein the polyester film is a uniaxially stretched film or a biaxially stretched film of polyethylene terephthalate or polyethylene naphthalate.

3. The antireflection film of claim 1, wherein the reactive functional group substituted in the POSS comprises at least one functional group selected from the group consisting of an alcohol, an amine, a carboxylic acid, an epoxide, an imide, a (meth)acrylate, a nitrile, a norbornene, an olefin, a polyethylene glycol, a thiol, and a vinyl group.

4. The antireflection film of claim 1, wherein the photoreactive functional group of the fluorine-based compound is at least one functional group selected from the group consisting of a (meth)acryloyl group, an epoxy group, a vinyl group, and a mercapto group.

5. The antireflection film of claim 1, wherein the fluorine-based compound containing the photoreactive functional group has a weight average molecular weight of 2,000 to 200,000 g/mol.

6. The antireflection film of claim 1, wherein the inorganic particle includes a hollow silica particle having a number average particle diameter of 10 nm to 100 nm.

7. The antireflection film of claim 6, wherein the photocurable coating composition includes 10 to 350 parts by weight of the hollow silica nanoparticle based on 100 parts by weight of the photopolymerizable compound.

8. The antireflection film of claim 1, wherein the hard coating layer is provided with a function selected from the group consisting of an antiglare function, a scratch prevention function, an antistatic function, and any combination thereof.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The action and effect of the invention will be described in more detail through concrete examples of the invention below. However, these examples are given for illustrative purposes only, and these examples are not intended to limit the scope of the invention in any way.

Examples 1-4 and Comparative Examples 1-4: Preparation of Antireflection Film

(2) An antireflection film was prepared by the following method using the base film, the hard coating composition, and the photocurable coating composition listed in Table 1 below.

(3) Specifically, the hard coating composition was coated onto a base film with a #10 Mayer bar, dried at 90° C. for 1 minute, and then irradiated with ultraviolet light at 150 mJ/cm.sup.2 to form a hard coating layer having a thickness of 5 μm (antistatic hard coating layer or antiglare hard coating layer).

(4) Then, the photocurable coating composition was coated onto the hard coat layer with a #3 Mayer bar and dried at 60° C. for 1 minute. Then, ultraviolet light at 180 mJ/cm.sup.2 was irradiated to the dried material under a nitrogen purge to form a low refractive index layer having a thickness of 110 nm, thereby preparing an antireflection film.

(5) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Comparative Example Example Example Example Example Example Example Example 1 2 3 4 1 2 3 4 Base TA015 A015 A015 A015 4300 4300 Z TAC TA015 film (thickness: (thickness: (thickness: (thickness: (thickness: (thickness: (thickness: (thickness: 80 μm) 80 μm) 80 μm) 80 μm) 75 μm) 100 μm) 60 μm) 80 μm) ard HD1 HD2 HD1 HD2 HD1 HD1 HD1 HD1 coating composition Photo- LR1 LR1 LR2 LR2 LR1 LR1 LR1 LR3 curable coating composition

(6) The physical properties such as manufacturer, phase difference, and water vapor transmission rate of each base film in Table 1 are listed in Table 2 below. HD1 is a salt type of antistatic hard coating solution (manufactured by KYOEISHA Chemical, solid content: 50 wt %, product name: LJD-1000).

(7) HD2 is an antiglare hard coating composition prepared by mixing 13 g of pentaerythritol triacrylate (molecular weight: 298 g/mol), 10 g of a urethane acrylate oligomer (306I, KYOEISHA Chemical), 10 g of a urethane acrylate oligomer (306T, KYOEISHA Chemical), 20 g of isopropyl alcohol as a solvent, 2 g of a photoinitiator (Irgacure 184, Ciba), and 0.5 g of a leveling agent (Tego glide 410) and then adding 2.3 g of an acryl-styrene copolymer (Techpolymer, Sekisui Plastic) which is spherical organic fine particles having an average particle diameter of 3 μm and a refractive index of 1.555, and 0.01 g of a nanosilica dispersion (MA-ST, Nissan Chemical) having a volume average particle diameter of 12 nm, to the resulting composition. Specific components and compositions of LR1, LR2, and LR3 are listed in Table 3 below. LR1, LR2, and LR3 were used by mixing the components described in Table 3 below with the compositions described herein and diluting in a solvent in which MIBK (methyl isobutyl ketone) and PGME (propylene glycol monomethyl ether) were mixed at a weight ratio of 1:1 so that the solid content concentration became 3 wt %.

(8) TABLE-US-00002 TABLE 2 TA015 4300 4300 Z TAC (thickness: (thickness: (thickness: (thickness: Product name 80 μm) 75 μm) 100 μm) 60 μm) Manufacturer TOYOBO TOYOBO TOYOBO FUJI Rin [nm] 8400 2400 3200 3.3 Rth [nm] 9200 12750 17000 48.6 Rin/Rth 0.913 0.188 0.188 0.068 Water vapor 6.38 6.93 5.1 275 transmission rate [g/m.sup.2*day] Permeability 5.1 5.2 5.1 165 (1) The thickness of the base film was measured using ID-C112XBS (Mitutoyo). (2) The in-plane retardation value (Rin = |nx − ny| * d) and the thickness-direction retardation value (Rth = [(nx + ny)/2 − nz]d) of the base film were measured using RETS-100 (OTSUKA ELECTRONICS). However, the retardation value of the triacetylcellulose film (UZ TAC, FUJI) was measured using AxoScan (Axometrics). Then, Rin/Rth was determined by dividing the in-plane retardation value (Rin) by the thickness-direction retardation value (Rth). (3) The water vapor transmission rate (WVTS) of the base film was measured at a temperature of 40° C. and relative humidity of 90% using TSY-T3 (Labthink) which is a water vapor permeability tester. Since the water vapor transmission rate (WVTS) decreases as the thickness increases, the water vapor transmission rate per thickness of 100 μm is defined as permeability, and the permeability is determined by the formula of “thickness (unit: μm) * water vapor transmission rate/100” and shown in Table 2.

(9) TABLE-US-00003 TABLE 3 LR1 LR2 LR3 Hollow silica dispersion.sup.1) 250 220 250 Dipentaerythritol pentaacrylate 37 39 40 Polysilsesquioxane.sup.2) 3 3 0 Fluorine-containing compound containing a 13.3 26.7 13.3 photoreactive functional group.sup.3) Photoinitiator.sup.4) 6 6 6 (unit: g) .sup.1)Hollow silica dispersion: THRULYA 4320 (manufactured by Catalysts and Chemicals Ltd.) in which hollow silica particles having a number average diameter of 50 nm are dispersed to a solid content of 20% by weight in methyl isobutyl ketone. .sup.2)Polysilsesquioxane: MA0701 manufactured by Hybrid Plastics. .sup.3)Fluorine-based compound containing a photoreactive functional group: A fluorine compound containing a photoreactive functional group and containing a trace amount of silicon, and RS537 (manufactured by DIC) diluted to 30% by weight in methyl isobutyl ketone .sup.4)Photoinitiator: Irgacure-127 (manufactured by Ciba)

Experimental Examples: Measurement of Physical Properties of Antireflection Films

(10) 1. Measurement of Average Reflectivity

(11) The average reflectivity of the antireflection films obtained in the examples and comparative examples was measured using Solidspec 3700 (SHIMADZU) equipment.

(12) Specifically, a black tape was attached to the surface of the base film on which no hard coating layer was formed so that light would not be transmitted. The measurement conditions were set as a sampling interval 1 nm, a time constant of 0.1 s, a slit width 20 nm, and a medium scanning speed. Light of a wavelength region of 380 nm to 780 nm was irradiated to the low refractive index layer of the antireflection film at room temperature.

(13) When HD2 was used as the hard coating composition, a 100% T mode was applied, and when HD1 was used as the hard coating composition, a measure mode was applied. Thereby, the reflectance in the wavelength region of 380 nm to 780 nm was measured. The results are shown in Table 4 below.

(14) 2. Measurement of Scratch Resistance

(15) The surfaces of the antireflection films obtained in the examples and comparative examples were rubbed while applying a load to a steel wool (#0000) and reciprocating ten times at a speed of 24 rpm. When observed with the naked eye under ceiling illumination by a 50 W LED while increasing the load applied to the steel wool, the maximum load at which scratches were not generated was measured. The above load is defined as weight (g) per area (2*2 cm.sup.2) of 2 cm in width and 2 cm in height.

(16) 3. Evaluation of Occurrence of Interference Fringes

(17) A black PET film was attached to the surface of the base film on which the hard coating layer was not formed by using the antireflection film produced according to the examples and comparative examples, and it was evaluated with respect to whether interference fringes were observed with the naked eye. As a result of the evaluation, when no interference fringes were observed in the antireflection film, it was described as “good” in Table 4 below, and when interference fringes were clearly observed, it was described as “severe”.

(18) 4. Evaluation of Water Vapor Transmission Rate and Permeability

(19) The water vapor transmission rate (WVTS) of the antireflection films prepared according to the examples and comparative examples was measured at a temperature of 40° C. using TSY-T3 (Labthink), a water vapor permeability tester. At this time, the antireflection film was loaded so that the base film side of the antireflection film was placed under a relative humidity of 100%, and the low refractive index layer side was placed under a relative humidity of 10%. Since the water vapor transmission rate (WVTS) decreases as the thickness increases, the water vapor transmission rate per thickness of 100 μm is defined as permeability, and the permeability is determined by the formula “thickness (unit: μm)*water vapor transmission rate/100” and is shown in Table 4 below. Here, the thickness of the antireflection film was measured in the same manner as the method of measuring the thickness of the base film.

(20) TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Comparative Example Example Example Example Example Example Example Example 1 2 3 4 1 2 3 4 Average ~1.5% ~1.5% ~1.5% ~1.5% ~1.5% ~1.5% ~1.5% ~1.5% reflectivity Scratch 300 300 300 300 300 300 300 100 resistance [g/(2 * 2 cm.sup.2)] Interference Good Good Good Good Severe Severe Good Good fringes Water vapor 10.18 9.79 10.20 9.56 11.01 8.54 222.77 10.82 transmission rate [g/m.sup.2 * day] Total thickness 85.1 85.1 85.1 85.1 80.1 105.1 65.1 85.1 of film [μm] Permeability 8.66 8.33 8.68 8.14 8.82 8.98 145.02 9.21

(21) Referring to Table 4, it was confirmed that the antireflection film according to one embodiment of the present invention exhibited excellent water resistance while showing an excellent low reflective index and scratch resistance, and hardly any interference fringe was found. In contrast, when an optically anisotropic base film of which the phase difference was not adjusted to a specific range was used as in Comparative Examples 1 and 2, it was confirmed that interference fringes were severely generated, thereby being unsuitable for the antireflection film of the display. Moreover, when an existing cellulose base film was used as in Comparative Example 3, it was confirmed that the permeability was poor and there was a fear of shortening the lifespan of the display. In addition, even if an optically anisotropic base film of which the phase difference was adjusted to a specific range was used as the base film as in Comparative Example 3, it was confirmed that, when the low refractive index layer according to one embodiment of the present invention was not included, excellent scratch resistance could not be ensured.