Optical film

Abstract

The present application relates to an optical film and a use of the optical film, and can provide an optical film exhibiting selective transmission and blocking characteristics according to viewing angles, and such an optical film can be usefully used as a security film for a display device such as LCD, a smart window, sunglasses and the like.

Claims

1. An optical film comprising: a first linear polarizer; first and second spray orientation liquid crystal films sequentially formed on the first linear polarizer; and a second linear polarizer adjacent to the second spray orientation liquid crystal film, wherein absorption axes of the second linear polarizer and the first linear polarizer are parallel to each other; and wherein projections of the average optical axes of the first and second spray orientation liquid crystal films onto planes of the first and second spray orientation liquid crystal films are each parallel to the absorption axis of the first linear polarizer.

2. The optical film according to claim 1, wherein the first and second spray orientation liquid crystal films are each a liquid crystal layer comprising a linearly spray-oriented liquid crystal compound.

3. The optical film according to claim 1, wherein the first and second spray orientation liquid crystal films are each a liquid crystal layer comprising a non-linearly spray-oriented liquid crystal compound.

4. The optical film according to claim 1, wherein the first and second spray orientation liquid crystal films each comprise a liquid crystal layer comprising a linearly spray-oriented liquid crystal compound, and a positive C plate.

5. The optical film according to claim 1, exhibiting transmittance of 30% or less for light incident to an inclined angle of 50 degrees in an azimuth angles of 85 to 95 degrees and light incident to an inclined angle of 50 degrees in an azimuth angles of 265 to 275 degrees provided that azimuth angles of 0 degrees and 180 degrees are an angle of the absorption axis in the first linear polarizer.

6. The optical film according to claim 1, wherein the first and second spray orientation liquid crystal films have rotation directions of spray orientation equal to each other.

7. The optical film according to claim 1, wherein tilt angles at the interface between the first spray orientation liquid crystal film and the second spray orientation liquid crystal film form 0 degrees to 10 degrees to each other.

8. The optical film according to claim 1, wherein the first and second spray orientation liquid crystal films have rotation directions of spray orientation different from each other.

9. The optical film according to claim 1, wherein tilt angles at the interface between the first and second spray orientation liquid crystal films form 80 degrees to 90 degrees to each other.

10. The optical film according to claim 1, further comprising a third spray orientation liquid crystal film disposed between the first and second spray orientation liquid crystal films.

11. The optical film according to claim 1, further comprising a twisted nematic liquid crystal layer or a half-wave phase delay layer existing between the first linear polarizer and the first spray orientation liquid crystal film.

12. The optical film according to claim 1, further comprising a base material layer existing between the first linear polarizer and the first spray orientation liquid crystal film or adjacent to the second spray orientation liquid crystal film.

13. A liquid crystal display device comprising a light source, a lower polarization plate, a liquid crystal panel, an upper polarization plate and the optical film of claim 1 in sequence.

14. The liquid crystal display device according to claim 13, wherein the upper polarization plate and the second spray orientation liquid crystal film of the optical film exist in a state attached to each other, and the absorption axis of the upper polarization plate and the absorption axis of the first linear polarizer of the optical film are parallel to each other.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of an optical film of the present application.

(2) FIG. 2 is a schematic diagram for explaining spray orientation.

(3) FIG. 3 is a schematic diagram for explaining an inclined angle and an azimuth angle.

(4) FIGS. 4 to 7 are schematic diagrams of spray orientation of the first and second spray orientation liquid crystal films.

(5) FIGS. 8 to 12 are schematic diagrams of optical films of the present application.

(6) FIG. 13 is a schematic diagram of a liquid crystal display device of the present application.

(7) FIG. 14 is a schematic diagram for explaining selective transmission and blocking characteristics depending on viewing angles in a smart window or sunglass of the present application.

(8) FIG. 15 is a structure of the optical film of Example A1.

(9) FIG. 16 is a structure of the optical film of Example A4.

(10) FIGS. 17 to 24 show results evaluating transmittance.

(11) FIG. 25 is a structure of the optical film of Example B 1.

MODE FOR INVENTION

(12) Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the scope of the present application is not limited by the contents set forth below.

(13) <Linear Spray Orientation Liquid Crystal Film>

Example A1

(14) An optical film of Example A1 having the structure of FIG. 15 was prepared. Specifically, after a photo-alignment film was formed on an NRT base material film (Fuji Co.) (301A, 301B), a spray orientation liquid crystal composition, which was prepared by dissolving a mixed solid content of 95% by weight of a spray orientable polymerizable liquid crystal compound (manufactured by Merck Co.) consisting of cyanobiphenyl-based acrylate, cyanophenylcyclohexane-based acrylate and cyanophenyl ester-based acrylate, and 5% by weigh of IGACURE 907 (manufactured by Ciba-Geigy Co., Switzerland)) as a photo initiator, in a solvent of toluene to be 25% by weight of the total solution, was coated on the photo-alignment film via bar coating to be a thickness of about 2 m after drying, and then the coating layer was left to stand in an oven at about 80 C. for 2 minutes and dried.

(15) Subsequently, the dried coating layer was irradiated with ultraviolet (300 mW/cm.sup.2) for about 10 seconds while maintaining the temperature at about 80 C. to form a liquid crystal layer, thereby preparing a first linear spray orientation liquid crystal film (102). Next, a second linear spray orientation liquid crystal film (103) was prepared in the same method as the method of preparing the first linear spray orientation liquid crystal film. The lowest tilt angle of the base material surfaces of the first and second linear spray orientation liquid crystal films is about 16 degrees, the uppermost tilt angle of the air surfaces is about 73 degrees, the average tilt angle is about 45 degrees, and the tilt factor is in the range of about 0.95 to 1.05.

(16) Subsequently, the first and second linear spray orientation liquid crystal films produced by the above-described method were bonded to each other through a pressure sensitive adhesive (301) such that the air surfaces face each other and the tilt angles at the interface are equal to each other. Next, a first absorptive linear polarizer (101) was disposed on the opposite side of the base material film (301A) on which the liquid crystal film (102) was formed, and a second absorptive linear polarizer (601) functioning as an upper polarization plate of an LCD was disposed on the opposite side of the base material film (301B) on which the liquid crystal film (103) was formed. The optical film of Example 1 is disposed such that the projections of the average optical axes of the first and second liquid crystal films (102, 103) onto the planes of the liquid crystal films are each parallel to the absorption axis (P.sub.1) of the first linear polarizer and the absorption axis (P.sub.2) of the second linear polarizer is also parallel to the absorption axis (P.sub.1) of the first linear polarizer.

Example A2

(17) An optical film was prepared in the same manner as Example A1, except that the first and second linear spray orientation liquid crystal films were formed to have a thickness of 3.5 m, respectively. The lowest tilt angle of the base material surfaces of the first and second linear spray orientation liquid crystal films in Example A2 is about 3 degrees, the uppermost tilt angle of the air surfaces is about 85 degrees, the average tilt angle is about 50 degrees, and the tilt factor is in the range of about 0.95 to 1.05.

Example A3

(18) An optical film was prepared in the same manner as Example A1, except that the first and second linear spray orientation liquid crystal films were formed to have a thickness of 4.5 m, respectively. The lowest tilt angle of the base material surfaces of the first and second linear spray orientation liquid crystal films in Example A3 is about 2 degrees, the uppermost tilt angle of the air surfaces is about 86 degrees, the average tilt angle is about 51 degrees, and the tilt factor is in the range of about 0.95 to 1.05.

Example A4

(19) An optical film of Example A4 having the continuous (cascade) structure of FIG. 16 was prepared. Specifically, in the optical film of Example A2, structures other than the second linear polarizer (601) were further laminated on the side of the first linear polarizer (101) in the optical film of Example A2 to obtain the optical film of Example A4.

Example A5

(20) An optical film was prepared in the same manner as Example A1, except that the projections of the average optical axes of the first and second linear spray orientation liquid crystal films onto the planes of the first and second linear alignment liquid crystal films were disposed to form about 5 degrees with the absorption axis of the first polarizer.

Example A6

(21) An optical film was prepared in the same manner as Example A1, except that the projections of the average optical axes of the first and second linear spray orientation liquid crystal films onto the planes of the first and second linear alignment liquid crystal films were disposed to form about 10 degrees with the absorption axis of the first polarizer.

Example A7

(22) An optical film was prepared in the same manner as Example A1, except that the projections of the average optical axes of the first and second linear spray orientation liquid crystal films onto the planes of the first and second linear alignment liquid crystal films were disposed to form about 15 degrees with the absorption axis of the first polarizer.

Comparative Example A1

(23) Comparative Example A1 was prepared, except for using an automotive louver film from 3M Co. (LCF: Light Control Film) (having a structure in which a DBEF and a louver film are laminated) instead of the laminate of the first and second linear spray orientation liquid crystal films in Example A1.

Evaluation Example A1 Evaluation of Transmittance

(24) For the optical film prepared in Example A1, the transmittances depending on an azimuth angles of 0 to 360 degrees were evaluated using Axoscan (Axometrix, Inc.) at inclined angles of 30 degrees, 40 degrees and 50 degrees, respectively, and the results were shown in FIG. 17 and Table 1.

(25) TABLE-US-00001 TABLE 1 Transmittance depending on azimuth angles (%) 0 degrees 90 180 270 (360 degrees) degrees degrees degrees Inclined angle 30 degrees 91.68 60.99 83.2 24.8 40 degrees 91.91 42.39 80.7 5.8 50 degrees 91.72 23.47 90.58 27.68

(26) For the optical films prepared in Examples A1 to A3, the transmittances depending on the azimuth angles of 0 to 360 degrees were evaluated using Axoscan (Axometrix, Inc.) at an inclined angle of about 50 degrees, and the results were shown in FIG. 18 and Table 2. In addition, for the optical films prepared in Examples A1 to A3, the transmittances depending on up-and-down (azimuth angle 80 degrees and 270 degrees) and left-and-right (azimuth angle 0 degrees (360 degrees) and 180 degrees) inclined angles were evaluated, and the results were shown in FIGS. 19 to 21.

(27) TABLE-US-00002 TABLE 2 Transmittance depending on azimuth angles (%) 0 degrees 90 180 270 (360 degrees) degrees degrees degrees Example A1 91.72 23.47 90.58 27.68 (thickness 2 m) Example A2 95.32 4.62 94.01 7.63 (thickness 3.5 m) Example A3 94.33 14.49 91.87 25.12 (thickness 4.5 m)

(28) For the optical films prepared in Examples A2 and A4, the transmittances depending on the azimuth angles of 0 to 360 degrees were evaluated using Axoscan (Axometrix, Inc.) at an inclined angle of about 50 degrees, and the results were shown in Table 3.

(29) TABLE-US-00003 TABLE 3 Transmittance depending on azimuth angles (%) Example 2 Example 4 0 degrees 90 0 degrees 90 (360 degrees) degrees (360 degrees) degrees Inclined 30 degrees 94.67 44.25 82.22 17.5 angle 40 degrees 93.53 20.48 82.92 4.16 50 degrees 95.32 4.62 83.37 1.48

(30) For the optical films prepared in Examples A1 and A5 through A7, the transmittances depending on the azimuth angles of 0 to 360 degrees were simulated and evaluated using Axoscan (Axometrix, Inc.) at an inclined angle of about 50 degrees, and the results were shown in FIG. 22 (depicting Examples A1 and A5 to A7), FIG. 23 (depicting Example A7), and Table 4.

(31) TABLE-US-00004 TABLE 4 Transmittance depending on azimuth angles (%) 0 degrees 90 180 270 Contrast (360 degrees) degrees degrees degrees ratio Example A1 92 17.8 90 17.8 5.1:1 (=0) Example A5 90 9 90 29 10:1 (=5) Example A6 87 3.7 90 42 24:1 (=10) Example A7 86 2 90 55 44:1 (=15)

(32) For the optical film of Example A1 and the micro louver film of Comparative Example A1, the transmittances depending on up-and-down (azimuth angle 80 degrees and 270 degrees) and left-and-right (azimuth angle 0 degrees (360 degrees) and 180 degrees) inclined angles were evaluated using Axoscan (Axometrix, Inc.), and the results were shown in FIG. 23. As shown in FIG. 24, it can be confirmed that in the optical film of Example A1 the effect of increasing the front transmittance as a whole is greater compared to the micro louver film of Comparative Example A1.

(33) <Non-Linear Spray Orientation Liquid Crystal Film>

Example B1

(34) An optical film of Example B1 having the structure shown in FIG. 25 was prepared. Specifically, after a photo-alignment film was formed on an NRT base material film (Fuji Co.) (301A, 301B), a spray orientation liquid crystal composition, which was prepared by dissolving a mixed solid content of 95% by weight of a spray orientable polymerizable liquid crystal compound (manufactured by Merck Co.) consisting of cyanobiphenyl-based acrylate, cyanophenylcyclohexane-based acrylate and cyanophenyl ester-based acrylate, and 5% by weigh of IGACURE 907 (manufactured by Ciba-Geigy Co., Switzerland)) as a photo initiator, in a solvent of toluene to be 25% by weight of the total solution, was coated on the photo-alignment film via bar coating, and then the coating layer was left to stand in an oven at about 80 C. for 2 minutes and dried.

(35) Subsequently, the dried coating layer was irradiated with ultraviolet (300 mW/cm.sup.2) for about 10 seconds while maintaining the temperature at about 80 C. to form a first linear spray orientation liquid crystal film (106A) having a thickness of about 3.5 m. Next, a second linear spray orientation liquid crystal film (106B) was prepared in the same method as the method of preparing the first linear spray orientation liquid crystal film. They were linear spray orientation liquid crystal films in which the lowest tilt angle of the base material surface of the first and second linear spray orientation liquid crystal films is about 0 degrees, the uppermost tilt angle of the air surface is about 90 degrees, and the tilt factor is about 1.0.

(36) Subsequently, a +C plate (105) having a thickness of about 3.3 m, an Rin value of about 10 nm or less and an Rth value of about 400 nm was attached between the surfaces of the first and second linear spray orientation liquid crystal films, thereby preparing a laminate of a non-linear spray orientation liquid crystal film such as one in which two non-linear spray orientation liquid crystal films having a tilt factor of less than about 0.95 were laminated. Here, the first and second linear spray orientation liquid crystal films were attached so that the tilt angles in their air surfaces are equal to each other.

(37) Subsequently, a first absorptive linear polarizer (101) was disposed on the opposite side of the base material film (301A) on which the liquid crystal film (106A) was formed, and a second absorptive linear polarizer (601) functioning as an upper polarization plate of an LCD was disposed on the opposite side of the base material film (301B) on which the liquid crystal film (106B) was formed. The optical film of Example 1 is disposed such that the projections of the average optical axes of the first and second liquid crystal films (106A, 106B) onto the planes of the liquid crystal films are each parallel to the absorption axis (P.sub.1) of the first linear polarizer and the absorption axis (P.sub.2) of the second linear polarizer is also parallel to the absorption axis (P.sub.1) of the first linear polarizer.

Example B2

(38) The first and second spray orientation liquid crystal films were prepared in the same manner as Example 1, except that in the step of preparing the first and second spray orientation liquid crystal films the temperature of the coating layer of the spray orientation liquid crystal composition was maintained at 40 C. The tilt factors of the prepared first and second spray orientation liquid crystal films were about 0.7, respectively.

(39) Subsequently, the first and second linear spray orientation liquid crystal films were attached so that the tilt angles in the air surfaces are equal to each other.

(40) Next, the first and second absorptive linear polarizers were disposed in the same manner as Example B1 to prepare the optical film of Example B2.

Comparative Example B1

(41) Comparative Example B1 was prepared, except for using an automotive louver film from 3M Co. (LCF: Light Control Film) (having a structure in which a DBEF and a louver film are laminated) instead of the laminate of the non-linear spray orientation liquid crystal film in Example B1.

Evaluation Example B1 Evaluation of Front Brightness and Transmittance at Up- and Down Inclined Angles

(42) For Example B1 and Comparative Example B1-B2, the transmittances depending on up-and-down (azimuth angle 90 degrees and 270 degrees) inclined angles of 30 degrees and 50 degrees were evaluated using Axoscan (Axometrix Co.), and the results were shown in Table 5 below.

(43) TABLE-US-00005 TABLE 5 Comparative Example B1 Example B1 Front brightness 91% 83% Up and down 30 degrees inclined angle 23% 20% Up and down 50 degrees inclined angle 10% 10%

DESCRIPTION OF REFERENCE NUMERALS

(44) 101: first linear polarizer 102: first spray orientation liquid crystal film 103: second spray orientation liquid crystal film 104: third spray orientation liquid crystal film 105: retardation film 106A and 106B: first and second linear spray orientation liquid crystal films 201: twisted nematic liquid crystal layer or half-wave phase delay layer 301: pressure-sensitive adhesive layer 401A, 401B: base material layer 501A, 501B: alignment film 601: second polarizer 701: upper polarization plate