Optical film and image display device including same

Abstract

The present invention relates to an optical film exhibiting excellent optical properties such as low gloss value and reflectance, and an appropriate level of haze properties, and to an image display device including the same. The optical film comprises: a light-transmitting substrate film; an antiglare layer including a binder containing a (meth)acrylate-based crosslinked polymer, and organic fine particles of a micron (μm) scale dispersed on the binder and inorganic fine particles of a nanometer (nm) scale dispersed on the binder; and a low refractive index layer which is formed on the antiglare layer and includes a binder resin containing a (co)polymer of a photopolymerizable compound, and hollow silica particles dispersed in the binder resin, wherein the organic and inorganic fine particles exhibit a predetermined particle size distribution, refractive index difference, and content range.

Claims

1. An optical film comprising: a light-transmitting substrate film; an antiglare layer including a binder containing a (meth)acrylate-based crosslinked polymer, and organic fine particles of a micron (μm) scale dispersed in the binder and inorganic fine particles of a nanometer (nm) scale dispersed in the binder; a low refractive index layer which is directly formed on the antiglare layer and includes a binder resin containing a (co)polymer of a photopolymerizable compound, and hollow silica particles dispersed in the binder resin, wherein (D75-D25)/D average is 0.25 or less, wherein the total average particle size of the organic and inorganic fine particles is defined as D average, and where the organic and inorganic fine particles are arranged in order from the smallest particle size to the largest size, the particle size of the fine particles corresponding to the cumulative 25% is defined as D25 and the particle size of the fine particles corresponding to the cumulative number of 75% is defined as D75, wherein the absolute value of the refractive index difference between the organic and inorganic fine particles and the binder is 0.01 to 0.25, wherein the total content of the organic and inorganic fine particles is 1 to 30% by weight of the total content of the antiglare layer, wherein the (meth)acrylate-based crosslinked polymer includes a monomolecular (meth)acrylate-based compound with three to six (meth)acrylate functionalities, and a crosslinked (co)polymer of a polyfunctional (meth)acrylate-based compound including a polyurethane-based polymer, a poly(meth)acryl-based polymer, or a polyester-based polymer, having a (meth)acrylate-based functional group with ten or more (meth)acrylate functionalities; wherein the monomolecular (meth)acrylate-based compound with three to six functionalities and the crosslinked (co)polymer of a polyfunctional (meth)acrylate-based compound having a (meth)acrylate-based functional group with ten or more (meth)acrylate functionalities are in a weight ratio of 3:1 to 5:1, wherein the optical film has a deviation of the 60-degree gloss value of 3% to 10%, and a total haze value of 1 to 5%, and wherein the antiglare layer is a single layer.

2. The optical film of claim 1, wherein the light-transmitting substrate film is a cellulose ester-based substrate film, a polyester-based substrate film, a poly(meth)acrylate-based substrate film or a polycarbonate-based substrate film, having a thickness of 20 to 500 μM.

3. The optical film of claim 1, wherein the binder in the antiglare layer has a refractive index of 1.50 to 1.60.

4. The optical film of claim 1, wherein the organic fine particles include polystyrene-based resin, poly(meth)acrylate-based resin or poly(meth)acrylate-co-styrene copolymer resin.

5. The optical film of claim 1, wherein the organic fine particles are spherical particles having a particle size of 1 to 5 μm and have a refractive index of 1.5 to 1.57.

6. The optical film of claim 1, wherein the inorganic fine particles are metal oxide fine particles including silica, alumina, zirconia or titania.

7. The optical film of claim 1, wherein the inorganic fine particles are spherical particles having a particle size of 10 nm to 300 nm, and have a refractive index of 1.4 to 1.75.

8. The optical film of claim 1, wherein the D average is 1.7 μm to 2.3 μm, the D25 is 1.5 μm to 2.1 μm, and the D75 is 1.9 μm to 2.5 μm.

9. The optical film of claim 1, wherein the antiglare layer has a thickness of 1 to 10 μM.

10. The optical film of claim 1, wherein the low refractive index layer has a refractive index of 1.3 to 1.5 and a thickness of 1 to 300 nm.

11. An image display device comprising the optical film of claim 1.

12. An optical film comprising: a light-transmitting substrate film; an antiglare layer including a binder containing a (meth)acrylate-based crosslinked polymer, and plural types of light-transmitting fine particles having a sub-micron (sub-μm) scale dispersed in the binder; a low refractive index layer which is formed directly on the antiglare layer and includes a binder resin containing a (co)polymer of a photopolymerizable compound, and hollow silica particles dispersed in the binder resin, wherein (D75-D25)/D average is 0.04 to 0.15, wherein the total average particle size of the light-transmitting fine particles is defined as D average, and where the light-transmitting fine particles are arranged in order from the smallest particle size to the largest size, the particle size of the fine particles corresponding to the cumulative 25% is defined as D25 and the particle size of the fine particles corresponding to the cumulative number of 75% is defined as D75, wherein the absolute value of the refractive index difference between the light-transmitting fine particles and the binder is 0.02 to 0.25, wherein the total content of the light-transmitting fine particles is 1 to 30% by weight of the total content of the antiglare layer, wherein the (meth)acrylate-based crosslinked polymer includes a monomolecular (meth)acrylate-based compound with three to six (meth)acrylate functionalities, and a crosslinked (co)polymer of a polyfunctional (meth)acrylate-based compound including a polyurethane-based polymer, a poly(meth)acryl-based polymer, or a polyester-based polymer, having a (meth)acrylate-based functional group with ten or more (meth)acrylate functionalities; wherein the monomolecular (meth)acrylate-based compound with three to six functionalities and the crosslinked (co)polymer of a polyfunctional (meth)acrylate-based compound having a (meth)acrylate-based functional group with ten or more (meth)acrylate functionalities are in a weight ratio of 3:1 to 5:1, wherein a reflectance is 0.5% to 2.5%, wherein the optical film has a deviation of the 60-degree gloss value of 3% to 10%, and a total haze value of 1 to 5%, and wherein the antiglare layer is a single layer.

13. An image display device comprising the optical film of claim 12.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Specific embodiments of the present invention are now described in more detail by way of the following examples. However, these examples are given for illustrative purposes only, and the scope of the present invention is not intended to be limited to or by the examples.

Preparation Example: Preparation of Composition for Forming an Antiglare Layer, and Photo-Curable Coating Composition for Forming Low Refractive Index Layer

(2) (1) Preparation of Composition for Forming an Antiglare Layer

(3) The components shown in Table 1 below were uniformly mixed to prepare a composition for forming an antiglare layer. The contents of all components used in Table 1 are shown in parts by weight.

(4) TABLE-US-00001 TABLE 1 Preparation Preparation Preparation Preparation Preparation Example 1 Example 2 Example 3 Example 4 Example 5 Binder UA-306T 4.804 4.426 4.434 5.103 4.804 8BR-500 8.948 8.223 6.771 6.241 8.948 TMPTA 22.161 12.313 14.180 22.161 PETA 20.234 11.084 6.241 Organic 113BQ 0.999 1.266 0.739 0.849 0.999 fine (1.555) particles 97BQ (refractive (1.525) index) Inorganic 9600A (100 nm) 0.310 0.359 fine (1.430) particles MA-ST 0.200 0.087 0.200 0.220 0.200 (refractive (12 nm) index) (1.430) Initiator I184 2.537 2.278 2.337 2.697 2.537 Dispersant BYK300 0.269 0.253 0.250 0.280 0.269 Solvent IPA 40.058 63.233 61.562 42.550 40.058 EtOH 20.024 21.280 20.024 Total 100 100 100 100 100 Total content of antiglare 37.11 34.24 35.85 33.19 37.11 layer.sup.1) (part by weight) Fine particle 3.231 3.95 3.48 4.30 3.231 content/antiglare layer content (wt %) Refractive Binder 1.517 1.526 1.521 1.520 1.517 index Organic fine 1.555 1.555 1.555 1.555 1.555 particles (average) Inorganic fine 1.430 1.430 1.430 1.430 1.43 particles (average) Absolute 0.038 0.029 0.034 0.035 0.038 value of refractive index difference (binder & organic fine particle) Absolute 0.087 0.096 0.091 0.09 0.087 value of refractive index difference (binder & inorganic fine particle) Comparative Comparative Comparative Comparative Comparative Preparation Preparation Preparation Preparation Preparation Example 1 Example 2 Example 3 Example 4 Example 5 Binder UA-306T 4.804 4.426 3.426 4.804 8BR-500 8.948 4.40 8.223 6.223 TMPTA 22.161 26.316 22.161 PETA 20.234 15.044 8.948 Organic 113BQ 0.999 0.202 11.000 0.999 fine (1.555) particles 97BQ 1.266 (refractive (1.525) index) Inorganic 9600A (100 nm) fine (1.430) particles MA-ST 0.200 0.03 0.03 0.200 (refractive (12 nm) index) (1.430) Initiator I184 2.536 2.024 2.278 2.024 2.537 Dispersant BYK300 0.270 0.506 0.253 0.253 0.269 Solvent IPA 40.058 66.522 63.320 62.000 40.058 EtOH 20.024 20.024 Total 100 100 100 100 100 Total content of antiglare 37.12 30.95 34.12 35.72 37.11 layer.sup.1) (part by weight) Fine particle 3.23 0.75 3.71 30.88 3.231 content/antiglare layer content (wt %) Refractive Binder 1.517 1.512 1.526 1.526 1.517 index Organic fine 1.555 1.555 1.525 1.555 1.555 particles (average) Inorganic fine 1.430 1.430 1.430 1.430 1.430 particles (average) Absolute 0.038 0.043 0.001 0.029 0.038 value of refractive index difference (binder & organic fine particle) Absolute 0.087 0.082 0.096 0.096 0.087 value of refractive index difference (binder & inorganic fine particle)

(5) 1) The total content of the antiglare layer is calculated by the total content of the binder and the organic/inorganic fine particles, except for the dispersant, solvent, and initiator that are removed during the formation process, in the composition for forming an antiglare layer.

(6) 2) The refractive index of the binder is measured after crosslinking (co)polymerization according to the above compositions and preparation examples described hereinafter, and the refractive index of the organic/inorganic fine particles is derived from an average value when two or more kinds are used.

(7) 1) UA-306T: (Kyoeisha): hexafunctional acrylate-based compound formed by reacting toluene diisocyanate with two pentaerythritol triacrylates

(8) 2) 8BR-500 (TAISEI FINE CHEMICAL): polymer to which a urethane acrylate functional group with about 40 functionalities is bonded to a polyacryl backbone

(9) 3) TMPTA: trimethylolpropane triacrylate

(10) 4) PETA: Pentaerythritol triacrylate

(11) 5) 1184 (Irgacure 184): photoinitiator, manufactured by Ciba

(12) 6) BYK 300: PDMS dispersant

(13) 7) 113BQ (XX-113BQ, manufactured by Sekisui Plastic): PMMA-PS crosslinked copolymer fine particles having a refractive index of 1.555 and an average particle size of 2 μm

(14) 8) 97BQ(XX-97, manufactured by Sekisui Plastic):

(15) PMMA-PS crosslinked copolymer fine particles having a refractive index of 1.525 (about 1.53) and an average particle size of 2 μm

(16) 9) 9600A: spherical silica fine particles (X24-9600A; Shin-Etsu) having a volume average particle size of 100 nm and a refractive index of 1.43) MA-ST: dispersion solution in which spherical silica fine particles having a volume average particle size of 12 nm and a refractive index of 1.43 (manufactured by Nissan Chemical) is dispersed in methanol at a concentration of 30%

(17) (2) Preparation of Photo-Curable Coating Composition for Forming Low Refractive Layer

(18) The remaining components of Table 2 below were mixed and then diluted in a mixed solution of MIBK (methyl isobutyl ketone) and IPA (weight ratio=1:1) to prepare a photo-curable coating composition for forming a low refractive layer. The contents of all components used in Table 2 are shown in parts by weight.

(19) TABLE-US-00002 TABLE 2 Preparation Example 6 DPHA 1.38 THRULYA 4320 4.56 Irgacure-127 0.55 RS-907 0.51 IPA 46.50 MIBK 46.50 Total 100

(20) 1) DPHA: dipentaerythritol hexaacrylate, molecular weight of 524.51 g/mol, manufactured by Kyoeisha.

(21) 2) THRULIA 4320: hollow silica dispersion, solid content 20 wt % in MIBK solvent, manufactured by JGC Catalyst and Chemicals.

(22) 3) Irgacure-127: photoinitiator manufactured by BASF.

(23) 4) RS-907: fluorine-based compound containing photoreactive functional group, solid content 30 wt % in MIBK solvent, manufactured by DIC.

Examples 1 to 5 and Comparative Examples 1 to 6: Preparation of Optical Film

(24) As shown in Table 3 below, the antiglare layer compositions respectively prepared in Preparation Examples 1 to 5 or Comparative Preparation Examples 1 to 5 were coated onto a PET substrate film having a thickness of 100 μm and a refractive index of 1.6 to 1.7, dried at 90° C. for 1 minute, and then irradiated with ultraviolet rays of 150 mJ/cm.sup.2 to prepare an antiglare layer.

(25) Then, in Examples 1 to 5 and Comparative Examples 1 to 6, the low refractive layer on the antiglare layer was formed as follows.

(26) The composition prepared in Preparation Example 6 was coated on the antiglare layer with Meyer Bar #3 and dried at 90° C. for 1 minute. Then, the dried material was irradiated with ultraviolet rays of 180 mJ/cm.sup.2 under a nitrogen purge to form a low refractive index layer having a thickness of 100 nm, thereby forming an optical film.

Experimental Example: Measurement of Physical Properties of Optical Film

(27) The physical properties of the optical films prepared above were measured according to the following methods, and the results are shown in Table 3 below.

(28) 1. Measurement of Particle Size Distribution of Light-Transmitting (Organic/Inorganic) Fine Particles

(29) The particle diameters of the light-transmitting fine particles (organic/inorganic fine particles) contained in Preparation Examples 1 to 5 and Comparative Preparation Examples 1 to 5 were measured in a COULTER PARTICLE SIZE ANALYZER, and the fine particles were arranged in order from the smallest particle size to the largest size. From this, a particle size distribution curve of the light transmitting fine particles was derived. The organic fine particles were mixed with a solvent such as ethanol, methanol, and isopropyl alcohol to prepare a dispersion solution, and then the measurement was performed. In the case of the inorganic fine particles supplied in the form of a dispersion, the solution was diluted with the same solvent as the dispersion solvent and analyzed.

(30) From the particle size distribution curves, the average total particle diameter of the light-transmitting fine particles was determined as D average. The particle size of the fine particles corresponding to the cumulative 25% when the organic and inorganic fine particles were arranged in the order from the smallest particle size to the largest size was determined as D25, and the particle size of the fine particles corresponding to the cumulative number of 75% was determined as D75. From these measured values, the average value of (D75−D25)/D was calculated.

(31) 2. Measurement of Refractive Index

(32) The refractive indexes of the binder, the antiglare layer, the low refractive index layer and the like contained in the optical film were measured in a state of being coated on the wafer using an ellipsometer. More specifically, the refractive indexes of the binder, the antiglare layer, and the low refractive index layer were measured by a method in which each composition was applied to a 3 cm×3 cm wafer, coated using a spin coater (coating condition: 1500 rpm, 30 seconds), dried at 90° C. for 2 minutes and irradiated with ultraviolet rays under the condition of 180 mJ/cm.sup.2 under nitrogen purge. Thereby, each coating layer having a thickness of 100 nm was formed.

(33) The ellipsometry was measured for the coating layer at an incidence angle of 70° over a wavelength range of 380 nm to 1000 nm by using J. A. Woollam Co. M-2000 apparatus. The measured ellipsometry data (Ψ, Δ) was fitted to a Cauchy model of the following general formula 1 using Complete EASE software so that MSE became 3 or less.

(34) $n\left(\lambda \right)=A+\frac{B}{{\lambda }^2}+\frac{C}{{\lambda }^4}$

(35) Wherein, n(λ) is a refractive index at a wavelength λ (300 nm to 1800 nm), and A, B and C are Cauchy parameters.

(36) Meanwhile, the refractive indexes of the substrate film and the respective fine particles used information provided on the commercially available product.

(37) 3. Evaluation of Total/Internal/External Haze Value

(38) A 4 cm×4 cm optical film specimen was prepared. the average value was calculated by measuring three times with a haze meter (HM-150, A light source, Murakami Color Research Laboratory), which was calculated as a total haze value. In the measurement, the transmittance was measured according to JIS K 7361, and the haze value was measured according to JIS K 7105. In measuring the internal haze value, an adhesive film having a total haze value of 0 was bonded to the coated surface of the optical film to be measured to make the irregularities of the surface smooth, and an internal haze value was measured in the same manner as that of the total haze value.

(39) The external haze value was calculated as the average of the values obtained by calculating the difference between the total haze value and the measured value of the internal haze.

(40) 4. Evaluation of the 20°/60° Gloss Value and the Deviation Value Thereof

(41) The 20°/60° gloss value was measured using the micro-TRI-gloss manufactured by BYK Gardner Co., Ltd. At the time of measurement, a black tape (3M) was attached to the surface of the substrate film on which the coating layer was not formed so as not to transmit light. The 20°/60° gloss value was measured by varying the incidence angle of light to 20°/60°, and the average value measured five or more times was calculated as the gloss value.

(42) The deviation of the 60-degree gloss value was calculated by measuring the gloss value over 10 times by the above method and calculating the deviation from the data.

(43) 5. Reflectance

(44) The reflectance was measured as an average reflectance using a SolidSpec 3700 manufactured by SHIMADZU.

(45) Specifically, a black tape (Vinyl tape 472 Black, manufactured by 3M) was attached to the surface of the optical film on which the coating layer was not formed so as not to transmit light. After fixing the measurement conditions with sampling interval 1 mm, time constant 0.1 sec, slit width 20 nm and medium scanning speed, the optical film was irradiated with light having a wavelength of 380 nm to 780 nm by applying the 100T mode. Thereby, the reflectance was measured.

(46) TABLE-US-00003 TABLE 3 Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 1 Substrate PET PET PET PET PET PET film Refractive 1.6~1.7 1.6~1.7 1.6~1.7 1.6~1.7 1.6~1.7 1.6~1.7 index of (birefringence) (birefringence) (birefringence) (birefringence) (birefringence) (birefringence) substrate film Constitution Preparation Preparation Preparation Preparation Preparation Comparative of antiglare Example 1 Example 2 Example 3 Example 4 Example 5 Preparation layer Example 1 Thickness of 4.5 5.0 4.5 4.0 5.0 4.0 antiglare layer (μm) D average 2.1 1.98 2.1 1.98 2.03 2.02 (μm) D25 1.96 1.84 1.96 1.84 1.96 1.76 (μm) D75 2.15 2.02 2.15 2.02 2.09 2.29 (μm) (D75 − D25)/D 0.090 0.091 0.090 0.091 0.064 0.262 average Low formed formed formed formed formed formed refractive layer Thickness of 100 100 100 100 100 100 low refractive layer(nm) Refractive 1.41 1.41 1.41 1.41 1.41 1.41 index of low refractive layer Total haze 3.4 3.3 3.3 3.5 3.5 3.1 value Internal haze 3.1 2.9 3.1 3.1 3.2 2.8 value External 0.3 0.4 0.3 0.4 0.3 0.3 haze value Gloss 27.3 28.1 27.6 28.5 28.2 27.8 value(20- degree) Gloss 53.2 52.8 52.6 52.3 53.2 53 value(60- degree) 60-degree 6.5 6.6 6.5 6.7 6.2 15.1 gloss deviation (%) Reflectance 1.5 1.5 1.5 1.5 1.5 1.5 (%) Comparative Comparative Comparative Comparative Comparative Example 2 Example 3 Example 4 Example 5 Example 6 Substrate PET PET PET PET PET film Refractive 1.6~1.7 1.6~1.7 1.6~1.7 1.6~1.7 1.6~1.7 index of (birefringence) (birefringence) (birefringence) (birefringence) (birefringence) substrate film Constitution Comparative Comparative Comparative Preparation Comparative of antiglare Preparation Preparation Preparation Example 1 Preparation layer Example 2 Example 3 Example 4 Example 5 Thickness of 4.5 5.0 4.5 4.5 5.0 antiglare layer (μm) D average 1.98 2.01 1.98 2.1 2.03 (μm) D25 1.84 1.85 1.84 1.96 1..96 (μm) D75 2.02 2.03 2.02 2.15 2.09 (μm) (D75 − D25)/D 0.091 0.090 0.091 0.090 0.064 average Low formed formed formed uniformed formed refractive layer Thickness of 100 100 100 X 100 low refractive layer(nm) Refractive 1.41 1.41 1.41 X 1.41 index of low refractive layer Total haze 0.9 0.6 11.5 3.4 5.4 value Internal haze 0.8 0.1 9.2 3.1 5.0 value External 0.1 0.5 2.3 0.3 0.4 haze value Gloss 26.3 27.2 12.4 68.7 23.1 value(20- degree) Gloss 51.5 52 48.8 86.6 52.4 value(60- degree) 60-degree 5.8 8.6 14.3 5.7 7.2 gloss deviation (%) Reflectance 1.5 1.5 1.5 3.9 1.5 (%)

(47) Referring to Table 3, it was confirmed that the optical films of Examples 1-5 can exhibit excellent optical properties, such as low gloss value and reflectance, and an appropriate level of haze properties. On the other hand, it was confirmed that in Comparative Examples 1 and 4, since the gloss deviation value is too high the uniformity of the optical properties is greatly lowered. In addition, it was confirmed that in Comparative Example 5, the reflection of external light cannot be properly suppressed because the gloss value is too high and the reflectance is high.

(48) Further, it was confirmed that in Comparative Examples 2 and 3, the haze value is too low, and thus the external reflection image is not scattered and is visible, and therefore, the visibility and image sharpness of the screen are poor. In contrast, it was confirmed that in Comparative Example 6, since the internal haze value and the total haze value are too high, the optical properties are not sufficient and the visibility of the screen is poor.