Optical film

Abstract

The present invention provides an optical film comprising a substrate including a photoluminescent material and an adhesive layer formed on one surface of the substrate. The optical film according to the present invention can not only enhance the visibility of a laser pointer when the laser pointer is pointed on a display having the optical film adhered thereto, but also suppresses the generation of bubbles when adhered to an antiglare-treated display having fine asperities on its surface to prevent the deterioration of visibility, and can also have an excellent transmissive clarity and be easily attached and detached.

Claims

1. An optical film comprising a substrate including a photoluminescent material and an adhesive layer formed on one surface of the substrate, wherein the refractive index of the adhesive layer is larger than the refractive index of the substrate, and the difference in refractive index between the adhesive layer and the substrate is within a range of 0.1 to 0.3.

2. The optical film of claim 1, wherein the photoluminescent material is a material emitting light by ultraviolet rays and the maximum excitation wavelength thereof is within a range of 300 to 450 nm.

3. The optical film of claim 1, wherein the photoluminescent material is a material discolored by ultraviolet rays and the maximum excitation wavelength thereof is within a range of 300 to 450 nm.

4. The optical film of claim 1, wherein the photoluminescent material is a material emitting light by infrared rays and the maximum excitation wavelength thereof is within a range of 700 to 1600 nm.

5. The optical film of claim 1, wherein the adhesive layer has a storage elastic modulus (G′) at 23° C. of 1.0×10.sup.3 Pa to 1.0×10.sup.6 Pa.

6. The optical film of claim 1, wherein the adhesive layer is formed of an adhesive composition comprising an adhesive resin, a crosslinking agent and an additive.

7. The optical film of claim 6, wherein the adhesive resin is an acryl-based copolymer, an urethane-based copolymer or a silicone rubber.

8. The optical film of claim 1, wherein an initial adhesive strength of the adhesive layer is 0.005 to 0.1 N/25 mm in a state where the adhesive layer is attached to an antiglare film.

9. The optical film of claim 1, wherein a heating adhesive strength of the adhesive layer is 0.005 to 1 N/25 mm in a state where the adhesive layer is attached to an antiglare film.

10. An image display device comprising the optical film according to claim 1.

11. The image display device of claim 10, wherein a transmissive clarity of the image display device is at least 240.

12. The optical film of claim 1 further comprising a release film on the adhesive layer.

Description

Preparation Example 1: Preparation of a Substrate Including a Material Emitting Light by the Ultraviolet Rays

(1) A casting stock solution composed of 18.5 wt. % of a solid content containing triacetyl cellulose (TAC) as a cellulose component and a small amount of triphenyl phosphate (TPP) as a plasticizer, 0.1 wt. % of a material emitting light by the ultraviolet rays (lanthanide complex (tris(dibenzoyl methane)mono(1,10-phenanthroline)europium (III))) and 81.4 wt. % of methylene chloride solvent was extruded in the form of a sheet with a thickness of 400 μm and a width of 600 mm on the surface of the metal belt. The metal belt was rotated and moved to evaporate the solvent and form a cellulose film having a thickness of 90 μm. Then, the resulting film was dried at 120° C. to prepare the desired cellulose film.

Preparation Example 2: Preparation of a Substrate Including a Material Discolored by Ultraviolet Rays

(2) A casting stock solution composed of 18.5 wt. % of a solid content containing triacetyl cellulose (TAC) as a cellulose component and a small amount of triphenyl phosphate (TPP) as a plasticizer, 0.5 wt. % of a material discolored by the ultraviolet rays (spiropyran-based compound (1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2′-(2H)-indole]) and 81 wt. % of methylene chloride solvent was extruded in the form of a sheet with a thickness of 400 μm and a width of 600 mm on the surface of the metal belt. The metal belt was rotated and moved to evaporate the solvent and form a cellulose film having a thickness of 90 μm. Then, the resulting film was dried at 120° C. to prepare the desired cellulose film.

Preparation Example 3: Preparation of a Substrate Including a Material Emitting Light by the Infrared Rays

(3) 2.06 mmol of CF.sub.3COONa, 0.75 mmol of Y(CF.sub.3COO).sub.3, 0.16 mmol of Yb(CF.sub.3COO).sub.3, 0.03 mmol of Er(CF.sub.3COO).sub.3, 60 mmol of oleic acid, and 60 mmol of 1-octadecan were added to a round-bottomed flask in which argon gas has been purged. The solution was maintained at 120° C. for 30 minutes, heated up to 330° C. at a rate of 8 degrees per minute and cooled down to a room temperature. The cooled solution was added to an excessive amount of acetone. The nanoparticles were deposited and then centrifuged to prepare a material emitting light by the infrared rays, i.e., NaYF.sub.4 nanoparticle in which 17 mol % of Yb.sup.3+ and 3 mol % of Er.sup.3+ were doped [see. J. Phys. Chem. C Vol. 114, No. 1, p 610-616].

(4) A casting stock solution composed of 18.5 wt. % of a solid content containing triacetyl cellulose (TAC) as a cellulose component and a small amount of triphenyl phosphate (TPP) as a plasticizer, 0.5 wt. % of a material emitting light by the infrared rays (NaYF.sub.4 nanoparticle in which 17 mol % of Yb.sup.3+ and 3 mol % of Er.sup.3+ were doped) and 81 wt. % of methylene chloride solvent was extruded in the form of a sheet with a thickness of 400 μm and a width of 600 mm on the surface of the metal belt. The metal belt was rotated and moved to evaporate the solvent and form a cellulose film having a thickness of 90 μm. Then, the resulting film was dried at 120° C. to prepare the desired cellulose film.

Comparative Examples 1-3

(5) An acryl-based adhesive layer having a storage elastic modulus (G′) of 1.4×10.sup.6 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1 and then attached to a surface-treated film used in the outside surface of the visible side of the image display device and having an outside haze of 0 to 19% by surface fine-asperities to measure an initial adhesive strength, a heating adhesive strength, an appearance and a transmissive clarity in the following manner, and the results thus obtained are shown in table 1 below.

(6) (1) Initial Adhesive Strength

(7) The prepared specimen was cut into a size of 25 mm×100 mm, left for one hour under the conditions of 23° C. and RH 50% and then peeled at a peeling rate of 300 mm/min and a peeling angle of 180° using an universal tensile testing machine (UTM, Instron) to measure the initial adhesive strength. At this time, the measurement was made under the conditions of 23° C. and RH 50%.

(8) (2) Heating Adhesive Strength

(9) The heating adhesive strength was measured in the same manner as in the measurement method of the initial adhesive strength, except that the cut specimen was left for 24 hours under the condition of 50° C.

(10) (3) Appearance

(11) The prepared specimen was adhered to an antiglare film and then reflected with a three-wavelength stand light to evaluate the appearance based on whether the shape of stand light is clearly seen as follows:

(12) Appearance ◯: the shape of the stand light is clearly visible

(13) Appearance X: the shape of the stand light is visually blurred (fine bubbles were generated)

(14) (4) Transmissive Clarity

(15) The transmissive clarity (%) of each film was measured using a transmissive clarity measuring device (ICM-1T, Suga Tester Instruments Co., Ltd.). The transmissive clarity represents an image clarity obtained by calculating the transmittance of the light which has transmitted through the film, in accordance with JIS K7105. The value of the transmissive clarity is the sum of the image clarity values measured using four types of optical lights having a slit spacing of 0.125 mm, 0.5 mm, 1.0 mm, and 2.0 mm.

Examples 1-2

(16) An acryl-based adhesive layer having a storage elastic modulus (G′) of 1.1×10.sup.5 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1 and then attached to a surface-treated film used in the outside surface of the visible side of the image display device and having an outside haze of 5 to 19% by surface fine-asperities to measure an initial adhesive strength, a heating adhesive strength, an appearance and a transmissive clarity in the same manner as in Comparative Example 1, and the results thus obtained are shown in table 1 below.

Examples 3-4

(17) The measurement was made out in the same manner as in Example 1, except that an acryl-based adhesive layer having a storage elastic modulus (G′) of 3.7×10.sup.4 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1, and the results thus obtained are shown in table 1 below.

Examples 5-6

(18) The measurement was made in the same manner as in Example 1, except that a silicone-based adhesive layer having a storage elastic modulus (G′) of 2.5×10.sup.3 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1, and the results thus obtained are shown in table 1 below.

Examples 7-8

(19) The measurement was made in the same manner as in Example 1, except that a silicone-based adhesive layer having a storage elastic modulus (G′) of 4.9×10.sup.5 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1, and the results thus obtained are shown in table 1 below.

Examples 9-10

(20) The measurement was made in the same manner as in Example 1, except that an urethane-based adhesive layer having a storage elastic modulus (G′) of 2.5×10.sup.5 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1, and the results thus obtained are shown in table 1 below.

(21) TABLE-US-00001 TABLE 1 Properties of surface treatment Properties of adhesive Trans- Elastic Intial Heating Trans- Outside missive Modulus adhesive adhesive Appear- mission haze clarity type (Pa) strength strength ance clarity Comparative 0 386 Acryl- 1.4 × 10.sup.6 0.11 0.23 ∘ 325 Example 1 based Comparative 5 230 0.21 0.48 x 202 Example 2 Comparative 19 26 0.44 1.0 x 96 Example 3 Example 1 5 230 1.1 × 10.sup.5 0.04 0.07 ∘ 326 Example 2 19 26 0.05 0.08 ∘ 278 Example 3 5 230 3.7 × 10.sup.4 0.04 0.08 ∘ 334 Example 4 19 26 0.05 0.08 ∘ 325 Example 5 5 230 Silicon 2.5 × 10.sup.3 0.07 0.09 ∘ 347 Example 6 19 26 e-based 0.07 0.09 ∘ 342 Example 7 5 230 4.9 × 10.sup.5 0.06 0.07 ∘ 338 Example 8 19 26 0.06 0.07 ∘ 336 Example 9 5 230 Urethane- 2.5 × 10.sup.5 0.08 0.09 ∘ 324 Example 10 19 26 based 0.05 0.07 ∘ 302

(22) As seen from Table 1 above, it could be confirmed that the optical film according to the present invention had a very excellent transmissive clarity without generation of bubbles even when adhered to an antiglare film. In addition, it could be confirmed that the optical film according to the present invention had low initial adhesive strength and heating adhesive strength and thus the re-peeling was easy.

Examples 11-13 and Comparative Examples 4-6

(23) When the refractive index of the substrate was within a range of 1.2 to 1.8, the refractive index of the adhesive layer was 1.5, and the refractive index of the antiglare layer used for the visible side surface of the image display device to which the adhesive layer was attached was 1.5, the intensity of the light which was emitted from the photoluminescent material included in the substrate and received in the front direction of the visible side was calculated, and the results thus obtained are shown in Table 2 below.

Comparative Example 7

(24) The calculation was made in the same manner as in Example 11, except that the refractive index of the substrate was 1.7, and the refractive index of the adhesive layer was 1.7.

(25) TABLE-US-00002 TABLE 2 Refractive Refractive Refractive index index of index of Light of substate adhesive layer antiglare layer intensity Example 11 1.2 1.5 1.5 24.5 Example 12 1.3 20.3 Example 13 1.4 16.5 Comparative 1.5 13.8 Example 4 Comparative 1.6 11.7 Example 5 Comparative 1.8 8.8 Example 6 Comparative 1.7 1.7 10.1 Example 7

(26) As seen from Table 2, the optical film according to the present invention could further improve the visibility of the laser pointer by making the refractive index of the adhesive layer to be higher than the refractive index of the substrate and making the difference in refractive index to be 0.1 to 0.3, thereby increasing the light intensity.

Example 14

(27) An acryl-based adhesive layer having a storage elastic modulus (G′) of 1.1×10.sup.5 and a thickness of 20 μm was formed by coating on the substrate obtained in Preparation Example 1 and then attached to the visible side of LCD (Liquid Crystal Display) to which a surface-treated film having an outside haze of 19% was attached to evaluate the visibility of point, and the results thus obtained are shown in table 3 below.

(28) (1) Evaluation of Visibility of Point

(29) For evaluating the visibility of the position to which ultraviolet or infrared light sources are pointed, the position visibility by the naked eye was evaluated under the following criteria.

(30) ∘: visually well recognized.

(31) X: never visually recognized.

Example 15

(32) The evaluation was made in the same manner as in Example 14, except that the adhesive was coated on the substrate obtained in Preparation Example 2, and the results thus obtained are shown in table 3 below.

Example 16

(33) The evaluation was made in the same manner as in Example 14, except that the adhesive was coated on the substrate obtained in Preparation Example 3, and the results thus obtained are shown in table 3 below.

Comparative Example 8

(34) The cellulose film was prepared in the same manner as in Preparation Example 1, except that a casting stock solution composed of 0.0005 wt. % of the material emitting light by the ultraviolet rays (lanthanide complex (tris(dibenzoyl methane)mono(1,10-phenanthroline)europium (III))) was used. The evaluation was made in the same manner in Example 14, and the results thus obtained are shown in Table 3 below.

(35) TABLE-US-00003 TABLE 3 Laser intensity (mW/mm.sup.2) 0.5 1 2 Example 14 ∘ ∘ ∘ Example 15 ∘ ∘ ∘ Example 16 ∘ ∘ ∘ Comparative x x x Example 8

(36) As seen from Table 3, it could be confirmed that in the case of Examples 14 to 16 using, as a photoluminescent material, the material emitting light by the ultraviolet rays, the material discolored by the ultraviolet rays and the material emitting light by the infrared rays, respectively, the visibility was excellent, but in the case of Comparative Example 8 in which a small amount of photoluminescent material was used, the point was not visually recognized.

(37) Although particular embodiments of the present invention have been described in detail, it will be obvious to those skilled in the art that these are only preferred embodiments and the scope of the present invention is not intended to be limited to thereto. Also, those skilled in the art will understand that various changes and modifications may be made to the invention without departing from the spirit and scope of the invention. The scope of the present invention, therefore, is to be defined by the appended claims and equivalents thereof.