Antireflection film and method for preparing same

Abstract

The present invention relates to an antireflection film being capable of realizing high scratch resistance and antifouling property while simultaneously having low reflectivity and high light transmittance, and further being capable of enhancing screen sharpness of a display device, and a method for preparing the antireflection film.

Claims

1. An antireflection film comprising: a hard coating layer or an antiglare layer; and a low refractive index layer formed on one side of the hard coating layer or the antiglare layer and including a binder resin, and hollow silica nanoparticles, metal oxide nanoparticles, and inorganic nanoparticles dispersed in the binder resin, wherein a first region containing the hollow silica nanoparticles, a second region containing the metal oxide nanoparticles, and a third region containing the inorganic nanoparticles are present in the low reflective index layer, the first region, the second region, and the third region satisfy the following Equation 1:
Refractive Index (n1) of First Region<Refractive Index (n3) of Third Region<Refractive Index (n2) of Second Region[Equation 1] wherein n1, n2, and n3 are refractive indexes obtained by carrying out Ellipsometry measurement at an incident angle of 70 over a wavelength range of 380 nm to 1000 nm, and wherein average diameters of the hollow silica nanoparticle, the metal oxide nanoparticle, and the inorganic nanoparticle satisfy the following Equation 2:
Average Diameter of Inorganic Nanoparticles<Average Diameter of Metal Oxide Nanoparticles<Average Diameter of Hollow Silica Nanoparticles[Equation 2].

2. The antireflection film of claim 1, wherein the first region includes 70% by volume or more of the entire hollow silica nanoparticles, the second region includes 70% by volume or more of the entire metal oxide nanoparticles, and the third region includes 70% by volume or more of the entire inorganic nanoparticles.

3. The antireflection film of claim 1, wherein in the low refractive index layer, the third region is located closer to the interface between the hard coating layer or the antiglare layer and the low refractive index layer, compared to the second region, and the second region is located closer to the interface between the hard coating layer or the antiglare layer and the low refractive layer, compared to the first region.

4. The antireflection film of claim 1, wherein the first region, the second region, and the third region in the low refractive index layer are present in a continuous phase by one binder resin.

5. The antireflection film of claim 1, wherein the low refractive index layer is obtained by coating with a resin composition comprising a binder resin, a hollow silica nanoparticle, a metal oxide nanoparticle, and an inorganic nanoparticle.

6. The antireflection film of claim 1, wherein a ratio of the average diameter of the inorganic nanoparticles to the average diameter of the metal oxide nanoparticles is 0.5 to 0.9.

7. The antireflection film of claim 1, wherein a ratio of the average diameter of the inorganic nanoparticles to the average diameter of the hollow silica nanoparticles is 0.01 to 0.5.

8. The antireflection film of claim 1, wherein the refractive index of the first region is less than 1.4, the refractive index of the second region is more than 1.55, and the refractive index of the third region is more than 1.4 and less than 1.55.

9. The antireflection film of claim 1, wherein thicknesses of the first region, the second region, and the third region are respectively 10 nm to 200 nm.

10. The antireflection film of claim 1, wherein each of the inorganic nanoparticles, the metal oxide nanoparticles, and the hollow silica nanoparticles has on the surface thereof at least one reactive functional group selected from the group consisting of a (meth)acrylate group, an epoxide group, a vinyl group, and a thiol group.

11. The antireflection film of claim 1, wherein the inorganic nanoparticles include solid-type silica nanoparticles or antimony-doped tin oxide nanoparticles.

12. The antireflection film of claim 1, wherein the antireflection film exhibits an average reflectivity of 0.3% or less in the visible light wavelength band of 380 nm to 780 nm.

13. The antireflection film of claim 1, wherein the binder resin contained in the low refractive index layer includes a crosslinked (co)polymer between a (co)polymer of a photopolymerizable compound and a fluorine-containing compound containing a photoreactive functional group.

14. The antireflection film of claim 13, wherein the binder resin includes 20 parts by weight to 300 parts by weight of the fluorine-containing compound containing a photoreactive functional group based on 100 parts by weight of the (co)polymer of a photopolymerizable compound.

15. A method for preparing an antireflection film, comprising steps of: coating a resin composition for forming a low refractive index layer containing a photocurable compound or its (co)polymer, a fluorine-containing compound containing a photoreactive functional group, a photoinitiator, hollow silica nanoparticles, metal oxide nanoparticles, and inorganic nanoparticles on a hard coating layer or an antiglare layer, and drying the coated product at a temperature of 35 C. to 100 C.; and photocuring the dried product of the resin composition, wherein an average diameter of the hollow silica nanoparticles, the metal oxide nanoparticles, and the inorganic nanoparticles satisfy the following Equation 2:
Average Diameter of Inorganic Nanoparticles<Average Diameter of Metal Oxide Nanoparticles<Average Diameter of Hollow Silica Nanoparticles[Equation 2].

16. The method for preparing an antireflection film of claim 15, wherein the step of drying the resin composition for forming a low refractive index layer coated on the hard coating layer or the antiglare layer at a temperature of 35 C. to 100 C. is carried out for 10 seconds to 5 minutes.

17. The method for preparing an antireflection film of claim 15, wherein a ratio of the average diameter of the inorganic nanoparticles to the average diameter of the metal oxide nanoparticles is 0.5 to 0.9.

18. The method for preparing an antireflection film of claim 15, wherein a ratio of the average diameter of the inorganic nanoparticles to the average diameter of the hollow silica nanoparticles is 0.01 to 0.5.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The present invention will be described by way of examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention thereto.

PREPARATION EXAMPLE

Preparation Example: Preparation of Hard Coating Layer

(2) A salt type of antistatic hard coating solution (manufactured by KYOEISHA Chemical, solid content: 50 wt %, product name: LJD-1000) was coated onto a triacetyl cellulose (TAC) film with a #10 Meyer bar, dried at 90 C. for 1 minute, and then irradiated with ultraviolet light of 150 mJ/cm.sup.2 to prepare a hard coating film having a thickness of about 5 to 6 m.

Examples 1 to 5: Preparation of Antireflection Film

Examples 1 to 3

(3) (1) Preparation of a Photocurable Coating Composition for Preparing a Low Refractive Index Layer

(4) 35 wt % of hollow silica nanoparticles (average particle diameter: about 50 to 60 nm), 10 wt % of TiO.sub.2 nanoparticles (average particle diameter: about 17 nm, average length: about 30 nm), 10 wt % of solid-type silica nanoparticles (average particle diameter: about 12 nm), 5 wt % of a first fluorine-containing compound (X-71-1203M, Shin-Etsu Chemical), 10 wt % of a second fluorine-containing compound (RS-537, DIC Corporation), 25 wt % of pentaerythritol triacrylate (PETA), and 5 wt % of an initiator (Irgacure 127, Ciba) were diluted in an MIBK (methyl isobutyl ketone) solvent so that the solid content concentration became 4 wt %.

(5) (2) Preparation of Low Refractive Index Layer and Antireflection Film

(6) The photocurable coating composition obtained as described above was coated on the hard coating film of the above preparation example to a thickness of about 180 nm to 200 nm with a #4 Meyer bar, and dried and cured at the pressure, temperature, and time shown in Table 1 below, respectively. At the time of curing, ultraviolet light of 252 mJ/cm.sup.2 was irradiated to the dried coating under a nitrogen purge.

Examples 4 to 5

(7) (1) Preparation of a Photocurable Coating Composition for Preparing a Low Refractive Index Layer

(8) 30 wt % of hollow silica nanoparticles (average particle diameter: about 60 to 70 nm), 15 wt % of TiO.sub.2 nanoparticles (average particle diameter: about 17 nm, average length: about 30 nm), 10 wt % of solid-type silica nanoparticles (average particle diameter: about 12 nm), 3 wt % of a first fluorine-containing compound (X-71-1203M, Shin-Etsu Chemical), 17 wt % of a second fluorine-containing compound (RS-537, DIC Corporation), 20 wt % of pentaerythritol triacrylate (PETA), and 5 wt % of an initiator (Irgacure 127, Ciba) were diluted in an MIBK (methyl isobutyl ketone) solvent so that the solid content concentration became 4 wt %.

(9) (2) Preparation of Low Refractive Index Layer and Antireflection Film

(10) The photocurable coating composition obtained as described above was coated onto the hard coating film of the above preparation example to a thickness of about 180 nm to 200 nm with a #4 Meyer bar, and dried and cured at the pressure, temperature, and time shown in Table 1 below, respectively. At the time of curing, ultraviolet light of 252 mJ/cm.sup.2 was irradiated to the dried coating under a nitrogen purge.

(11) TABLE-US-00001 TABLE 1 Preparation conditions of antireflection film of Examples Category Drying temperature ( C.) Drying time Example 1 60 1 min Example 2 90 1 min Example 3 60 2 min Example 4 60 1 min Example 5 90 1 min

Comparative Examples 1 to 3: Preparation of Antireflection Film

Comparative Example 1

(12) The antireflection film was prepared in the same manner as in Example 1, except that a composition in which 65 wt % of hollow silica nanoparticles (average diameter: about 60 to 70 nm), 5 wt % of a first fluorine-containing compound (X-71-1203M, Shin-Etsu Chemical), 10 wt % of a second fluorine-containing compound (RS-537, DIC Corporation), 15 wt % of pentaerythritol triacrylate (PETA), and 5 wt % of an initiator (Irgacure 127, Ciba) were diluted in an MIBK (methyl isobutyl ketone) solvent so that the solid content concentration became 3%, and was used as a photocurable coating composition for preparing a low refractive index layer.

Comparative Example 2

(13) The antireflection film was prepared in the same manner as in Example 1, except that a composition in which 50 wt % of hollow silica nanoparticles (average diameter: about 50 to 60 nm), 10 wt % of solid-type silica nanoparticles (average particle diameter: about 12 nm), 3 wt % of a first fluorine-containing compound (X-71-1203M, Shin-Etsu Chemical), 15 wt % of a second fluorine-containing compound (RS-537, DIC Corporation), 17 wt % of pentaerythritol triacrylate (PETA), and 5 wt % of an initiator (Irgacure 127, Ciba) were diluted in an MIBK (methyl isobutyl ketone) solvent so that the solid content concentration became 3 wt %, and was used as a photocurable coating composition for preparing a low refractive index layer.

Comparative Example 3

(14) The antireflection film was prepared in the same manner as in Example 2, except that a composition in which 50 wt % of hollow silica nanoparticles (average diameter: about 50 to 60 nm), 10 wt % of solid-type silica nanoparticles (average particle diameter: about 12 nm), 5 wt % of a first fluorine-containing compound (X-71-1203M, Shin-Etsu Chemical), 13 wt % of a second fluorine-containing compound (RS-537, DIC Corporation), 17 wt % of pentaerythritol triacrylate (PETA), and 5 wt % of an initiator (Irgacure 127, Ciba) were diluted in an MIBK (methyl isobutyl ketone) solvent so that the solid content concentration became 3 wt %, and was used as a photocurable coating composition for preparing a low refractive index layer.

Experimental Examples: Measurement of Physical Properties of Antireflection Films

(15) The following experiments were conducted for the antireflection films obtained in Examples and Comparative Examples.

(16) 1. Measurement of Average Reflectivity

(17) The average reflectivity of the antireflection films obtained in the examples and comparative examples shown in a visible light region (380 to 780 nm) was measured using a Solidspec 3700 (SHIMADZU) apparatus, and the results are shown in Table 2 below.

(18) 2. Measurement of Scratch Resistance

(19) The surfaces of the antireflection films obtained in the examples and comparative examples were rubbed while applying a load to steel wool (area of 2 cm.sup.2) and reciprocating ten times at a speed of 27 rpm. The maximum load at which one or less scratches with a size of 1 cm or less were generated, as observed with the naked eye, was measured, and the results are shown in Table 2 below.

(20) 3. Measurement of Antifouling Property

(21) Straight lines with a length of 5 cm were drawn with a red permanent marker on the surface of the antireflection films obtained in the examples and comparative examples. Then, the antifouling property was measured by confirming the number of times of erasing when rubbed with a nonwoven cloth. The results are shown in Table 2 below.

(22) <Measurement Standard>

(23) : Erase when rubbing 10 times or less

(24) : Erase when rubbing 11 to 20 times

(25) X: Erase when rubbing 20 times or more

(26) TABLE-US-00002 TABLE 2 Results of Experiments for Examples and Comparative Examples Average Scratch Antifouling Category Reflectivity (%) Resistance (g) Property Example 1 0.27 300 O Example 2 0.25 300 O Example 3 0.26 300 O Example 4 0.21 300 O Example 5 0.23 300 O Comparative 0.28 100 X Example 1 Comparative 0.65 400 O Example 2 Comparative 0.62 400 O Example 3

(27) As shown in Table 2, the antireflection films of Examples 1 to 5, in which three kinds of particles (hollow silica nanoparticles, TiO.sub.2 nanoparticles, and solid-type silica nanoparticles) were contained in the low refractive index layer could realize high scratch resistance and antifouling property while simultaneously exhibiting low reflectivity of 0.30% or less in the visible light range.

(28) In contrast, it was confirmed that the low refractive index layer of the antireflection film of Comparative Example 1 containing only hollow silica nanoparticles exhibited lower scratch resistance as compared with the examples, and the antifouling property was also decreased.

(29) Further, it was confirmed that, in the low refractive index layers of the antireflection films of Comparative Examples 2 and 3, the hollow silica nanoparticles and the solid silica nanoparticles were included so that the scratch resistance and antifouling properties were high. However, the average reflectivity was measured to be higher than 0.6% and it was difficult to realize ultra-low reflectivity.

(30) That is, in the case of the examples, as three kinds of particles were dispersed in the low refractive index layer, it was confirmed that the ultra-low reflectivity of 0.30% or less could be achieved, and at the same time, the scratch resistance and antifouling property could be maintained at an appropriate level.

(31) 4. Phase Separation

(32) The polarization ellipticity of the low refractive index layer obtained in each of the examples and comparative examples was measured by an ellipsometry method.

(33) Specifically, the ellipticity measurement of the low refractive index layer obtained in each of the examples and comparative examples was carried out at an incident angle of 70 over a wavelength range of 380 nm to 1000 nm by using a J. A. Woollam Co. M-2000 apparatus. The measured ellipsometry data (, ) was fitted to a Cauchy model of the following General Formula 1 using CompleteEASE software so that the MSE became 5 or less. The values of Cauchy parameter A, substantially matching the refractive index values, are shown in Table 3 below.

(34) $\begin{array}{cc}n\left(\right)=A+\frac{B}{{}^2}+\frac{C}{{}^4}& \left[\mathrm{General}\mathrm{Formula}1\right]\end{array}$

(35) In the above General Formula 1, n() is a refractive index at a wavelength , is in a range of 300 nm to 1800 nm, and A, B, and C are Cauchy parameters.

(36) TABLE-US-00003 TABLE 3 Results of Experiments for Examples and Comparative Examples Comparative Comparative Comparative Category Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Example 2 Example 3 First region 1.356 1.314 1.303 1.238 1.277 1.315 1.338 1.395 Second region 1.603 1.620 1.547 1.558 1.583 (not (not (not analyzed) analyzed) analyzed) Third region 1.525 1.520 1.516 1.503 1.507 1.521 1.510

(37) As shown in Table 3, it was confirmed that in the low refractive index layer of the antireflection film of Examples 1 to 5, the values of Cauchy parameter A were analyzed as the distinguishable three regions by the ellipsometry method, and three regions having different refractive indexes were formed in the low refractive index layer.

(38) Specifically, it was confirmed through the refractive index data of each region and the refractive index of each of the solid-type silica nanoparticles (refractive index: 1.45 to 1.6), metal oxide nanoparticles (refractive index: 1.7 or more), and hollow silica nanoparticles (refractive index: 1.2 to 1.45) that the phase separation occurred into three regions where each of solid-type silica nanoparticles, metal oxide nanoparticles, and hollow silica nanoparticles was mainly distributed.

(39) In addition, depending on the particle size of the solid-type silica nanoparticles, the metal oxide nanoparticles, and the hollow silica nanoparticles, for the larger particle size, the phase separation occurred at the upper part of the low refractive index layer, and for the smaller particle size, the phase separation occurred at the lower part of the low refractive index layer. In consideration of this, it was confirmed that three regions were formed from the top to the bottom of the low refractive index layer in the order of the hollow silica nanoparticles, the metal oxide nanoparticles, and the solid-type silica nanoparticles.

(40) Meanwhile, in the case of Comparative Example 1, it was confirmed by the ellipsometry method that only one region was formed, and thus only a single region in which hollow silica nanoparticles were mainly distributed in the low refractive index layer was formed. In the case of Comparative Examples 2 and 3, it was confirmed by the ellipsometry method that two regions were formed, and thus hollow silica nanoparticles and solid-type silica nanoparticles contained in the low refractive index layer were phase-separated into two regions, thereby forming two regions having different reflective indexes.

(41) That is, in the case of the examples, it was confirmed that three kinds of particles were phase-separated into three regions in the low refractive index layer, thereby forming three regions having different refractive indexes, whereby ultra-low reflectivity of 0.30% or less could be realized and at the same time the scratch resistance and antifouling property could be maintained at appropriate levels.