TW200540450A - Optical film and preparation method thereof - Google Patents

Abstract

The present invention provides an optical film comprising a transparent substrate and at least one layer of cholesterol liquid crystalline (CLC) polymer coated on a surface of the substrate. The polymer is formed by polymerizing a mono-functional single-function nematic liquid crystalline monomer, a di-functional nematic liquid crystalline monomer, and a chiral compound monomer. The optical film can be used as a polarizing film, especially a brightness enhancement film, in a liquid crystal display (LCD), so as to raise the brightness of the LCD.

Description

200540450 发明 Description of the invention: [Technical field to which the invention belongs] The present invention relates to an optical film comprising a transparent substrate and at least one layer of a cholesteric liquid crystal polymer coated on the surface of the substrate as a polarizer for a liquid crystal display. . Since the optical film of the present invention can utilize multiple layers to adjust its reflected wave bandwidth, it can effectively increase the brightness of the liquid crystal display, and is suitable for liquid crystal displays with a wide bandwidth or a special bandwidth range. [Prior Art] A polarizer refers to an optical material that selectively allows light in a specific direction to pass through. It is mainly used to convert general unpolarized light into polarized light. Its mode of action is that when irradiating a non-polarized general light source, only one of the two orthogonal linear optical axes is allowed to pass, but the light in the other axis will be absorbed by a polarizer to control the polarization direction of a specific light wave. . In a general LCD display structure, two positive and negative polarizers must be attached to the front and back of the LCD panel. "Since the liquid crystal itself does not have the control function to allow light to pass through and block it," polarizers are required to achieve related functions in order to effectively control each element. Light and dark states. Standard polarizers use an adsorption method to filter the light source. The disadvantage of this polarizer is that in the best state, only the highest $ of incident light is converted into linear polarized light, which results in loss of light source and insufficient brightness of the liquid crystal display. Life of the lamp. Another disadvantage of this type of polarizer is the part of the light source that is not penetrated. This part of the absorbed light source will transform the polarizer into a large amount of thermal energy, which will cause unpredictable changes in polarizer properties, especially at high energy incidence. Under light, the structure of the polarizer may even be damaged.

O: \ 90 \ 90609.DOC 200540450 In order to solve the above problems, the industry has developed a cholesterol-based optical chirp to recover the light energy that must be lost. The so-called cholesteric liquid crystal system is a liquid crystal whose structure is similar to that of cholesterol molecules. Cholesterol liquid crystal is mainly formed by the accumulation of nematic liquid crystals. Adding a chiral compound to nematic liquid crystals will gradually rotate the nematic liquid crystal molecules by an angle of one angle. Spiral, this structure is similar to cholesterol molecules, so this type of liquid crystal is called cholesterol-type liquid crystal. FIG. 1 is a schematic diagram of a conventional conventional display (I) and a liquid crystal display (π) with a cholesteric optical film. As shown in Figure 丨, from bottom to top are the reflection plate 10, the light guide plate 12, the cholesteric liquid crystal optical film (CLC) 14 with a left-handed chemical structure, the λ / 4 retardation plate 16, the lower polarizer 18, and the liquid crystal layer 2. 〇 and upper polarizer 22. When the light source 24 is lit, the light diffuses through the light guide plate 12, and when the light passes through the cholesteric liquid crystal optical film 14, only right-handed light is allowed to pass through and the left chirped light is reflected back to the direction of the light source, while the right-handed light passes through The circular polarized aurora is transformed into an elliptical polarized aurora. Therefore, it is necessary to correct the light to a linear polarized aurora through the phase difference plate 16. This type of light can be applied to a liquid crystal display system. On the other hand, the left-handed light reflected to the direction of the light source is reflected by the reflecting plate 10 and converted into right-handed light. When it passes through the cholesterol liquid crystal optical film 14 again, the optical rotation can be passed smoothly. Therefore, when a cholesteric liquid crystal optical film exists, the light source has been fully converted into a linear polarized polarized light in a single direction before entering the liquid crystal panel, without causing a large loss of the light source. Therefore, this kind of cholesteric liquid crystal optical film is called a cholesteric polarizer, and it is expected to replace the traditional polarizer. But in fact, it is not easy to do, because the light passing through the bile polarizer can not get

O: \ 90 \ 90609.DOC 200540450 The same degree of linear polarization of traditional polarizers, that is, its polarization is insufficient. This light will cause serious light leakage after entering the LCD panel. Therefore, the current industry practice is to attach the cholesteric liquid crystal optical film, retardation plate and polarizer at the same time, which can not only ensure the polarization of the light source, but also greatly improve the effective utilization of the light source. This cholesteric liquid crystal optical film is currently called a brightness enhancement film. In addition, according to Maxwell's theory: λ == ηχρ, where is the reflection wavelength of liquid aa, η is the refractive index of the material, and ρ is the pitch. Because of the birefringent nature of liquid crystals, the above formula can be modified as: zU = (ne — η0) χρ = Δηχρ, where ^ is the frequency bandwidth of the reflected wave, ~ is the refractive index of the liquid crystal material, and η. Is the general refractive index. However, in terms of practicality, the visible light bandwidth is about 250 nm, but the Δη value of a general liquid crystal is about 0 "~ 0.2, so its bandwidth is about 50 ~ 100nm, which is much smaller than the visible light bandwidth. The brightness enhancement films made of different liquid crystal materials can be used for multi-layer stacking, making this process cumbersome and complicated. Therefore, how to solve the problem that the bandwidth of the brightness enhancement film is too small has become an important issue in the display industry.

Dreher in Solid State Communication (Vol. 12, 519-522, 1973), Mazkedian et al. In j. Physique c〇11〇q (ν〇: 36, PP · Ci-283, 1974) and Hajd0 et al. In j 〇 A study made in pt soc Am (ν〇ι_36, PP_1017, 1976) pointed out that a spiral structure with a spiral pitch with a gradient distribution change in the depth direction can effectively obtain a wide reflected wave ^. European patent EP 0 606 940 A2 has proposed the use of different monomers (palm and non-palm compounds) to polymerize, resulting in a continuous gradient distribution of spirals due to diffusion effects.

O: \ 90 \ 90609.DOC 200540450 2 value. However, if you want to obtain a product with a wide bandwidth, you must add external dye to cause the intensity of the light source to vary with the vertical depth of the film. The disadvantage of this method is that the long-term exposure with a low-energy light source to control the pitch distribution 'has extremely strict requirements for film thickness. In addition, Pmdak et al. In PhyS. Rev. Lett (v〇1 32, pp 43, 1974) θ does not control the change in the pitch of cholesterol-derived substances by controlling the temperature gradient. However, due to the good thermal conductivity of polymer films, It is extremely difficult to effectively control the temperature gradient in the production process, which has become an important disadvantage of this method. 2. The inventors of this case have found through extensive research that different reflected waves can be obtained for optical films made from cholesterol-type liquid crystal polymers. The multi-layer stack can make the reflected wave bandwidth cover the visible light bandwidth ', which can effectively solve the above disadvantages. SUMMARY OF THE INVENTION The object of the present invention is to provide an optical film, which comprises a transparent substrate including a polymer resin and at least one layer of a cholesteric liquid crystal polymer coated on the surface of the substrate. The optical film can be used as a polarizer in a liquid crystal display, especially a shell-enlarging film to improve the brightness of the liquid crystal display. Another object of the present invention is to provide a cholesteric liquid crystal formulation which can be used to form an optical film. Another object of the present invention is to provide a method for manufacturing an optical film. [Embodiment] There is no particular limitation on the polymer resin used in the optical film of the present invention, and it can be: ,,, κ-sun tree month (p0yyester resin), polycarbonate resin (p0yycarb〇nate resin) ) Or ♦ yurethane resin (p〇1yurethane resin) or its mixture

O: \ 90 \ 90609.DOC 200540450, preferably polyethylene terephthalate (PET). The cholesteric liquid crystal polymer of the present invention is polymerized from a cholesteric liquid crystal formulation, which comprises: (1) a monofunctional nematic liquid crystal monomer; (2) a bifunctional nematic liquid crystal monomer (3) Palm compound monomer; and (4) Photoinitiator. The monofunctional nematic liquid crystal monomer and the bifunctional nematic liquid crystal monomer that can be used to form a polymer in the present invention can be selected from the group consisting of the following structural formulas, respectively:

(1) Monofunctional nematic liquid crystal monomer CH2 = CH—C—0—R—Ar—X δ 〒η3

CH2 = C—C—〇—R—Ar——X O / 〇 \

CH2—CH—R—Ar——X (2) Bifunctional nematic liquid crystal monomer CH2 = CH—C—0—R—Ar—R—〇—C—ChNCH2 π 11 〇〇CH3 ch3 CH2 = CC —〇—R—Ar—R—〇—C—C = CH2 11 11 〇〇O: \ 90 \ 90609.DOC -10- 200540450

CH2—CH Bayi R—Ar—R—CH—CH2 where Ci is a Ci-Cn alkyl or Ci-Cw alkyl alkoxy group, and X is selected from the group consisting of aryl, Ci-Cio, and oxo A terminal group of a group consisting of a calcining group, and Ar is selected from the group consisting of the following groups having a liquid crystal phase: < 〇 ^ ~ n = n ~ < 〇 >-, -CH = CH ——

Or try ^ Qr,

and

A

A

Among them, A is another terminal group selected from the group consisting of a hydrogen atom, a Ci-C6 alkyl group, and a halogen atom O: \ 9O \ 906O9.DOC -11-200540450. The palm compound monomer that can be used to form a polymer in the present invention is a monofunctional palm compound monomer, and can be selected from the group consisting of the following structural formula: CH2 = Ch ^ C—0—R—Ar— Ya

II 〇 ch3

CH2 = C—c—Ο —R—Ar-Y

II 〇 〇 / \

CH2—CH2—R—Ar—Y, where 11 is 0: 1-(^ () alkylene and alkyleneoxy, and X is selected from the group consisting of cyano, Ci-Cioalkoxy, and cardio / fluorenyl One terminal group of the group, and Ar is selected from the group consisting of the following groups having a liquid crystal phase:

O: \ 90 \ 9O6O9.DOC -12- 200540450

Where 'A is another terminal group selected from the group consisting of a hydrogen atom, a Ci-C6 alkyl group, and a halogen atom; wherein Y is selected from the group consisting of cholesterol, 〇

II U-C—O 〇

It can form optically active group of liquid crystal phase. , Bromine or iodine atom. Monofunctional nematic liquid In the present invention, the halogen atom may be fluorine or gas. In addition, in a preferred embodiment of the present invention, the crystalline monomer may be one having the following structural formula:

Formula (A)

O: \ 90 \ 90609.DOC -13- 200540450 In a preferred embodiment of the present invention, the bifunctional nematic liquid crystal monomer may be selected from the following structural formulas: ch2 = ch -ο— (ch2 ) "O-

C2H5 ch = ch2 ^ -〇— (ch2) 6—o— 《Formula (B) CH2 = CHn C1 -co— ^ oc ch = ch2, -o— (CH2) 6-od Formula (C) In the present invention In a preferred embodiment, the monofunctional palm compound monomer may be selected from the following structural formulas: -

h2c = c- In the cholesterol type liquid crystal formulation of the present invention, the monofunctional nematic liquid crystal single system accounts for about 30 to 60 weight percent (wt%) of the cholesterol type liquid crystal formulation, preferably about 40 to 50 wt% ; Bifunctional nematic liquid crystal single system accounts for about 30 to 60 wt%, preferably about 40 to 50 wt% of cholesterol-based liquid crystal formulations; and palmitic compound single systems account for about 1 to about cholesterol-based liquid crystal formulations 20 wt%, preferably about 5 to 15 wt%. The photoinitiator useful in the present invention for forming polymers is well known to those skilled in the art, such as, but not limited to, 2,4,6-trimethylphenylphosphonium diphenylphosphine oxide (2,4 , 6_trimethyl benzoyl diphenyl phosphine oxide (TPO). In the cholesteric liquid crystal formulation of the present invention, the photoinitiator accounts for about 0.1 to 10 wt%, preferably about 1 to 5 wt% of the cholesterol liquid crystal formulation. O: \ 90 \ 90609.DOC -14- 200540450 The sterol-type liquid crystal formulation of the present invention may add various additives, such as a flattening agent, such as, but not limited to, an acrylate copolymer, Bγκ_36ΐ, as required. In the cholesteric liquid crystal formulation of the present invention, the amount of the additive is about 0.05 to 5 wt%, preferably about 0.00 to 2 wt%. The polymer prepared by the cholesteric liquid crystal formulation of the present invention can be used as a material for an optical film in a liquid crystal display, and the optical film can be used as a brightness enhancement film. In addition, the present invention further provides a method for preparing an optical film, which includes the following steps: (a) blending a nematic liquid crystal monomer and a palm compound monomer, and then adding a photoinitiator to form a cholesterol-type liquid crystal Formulation; (b) coating the cholesterol-type liquid crystal formula on a transparent substrate; (c) irradiating the cholesterol-type liquid crystal formula with energy rays at normal temperature or under heating for photopolymerization reaction. In the preparation method of the present invention, the energy ray used for photopolymerizing the cholesterol-type liquid crystal formulation generally refers to a light source with a certain range of wavelengths, such as ultraviolet light, infrared light, visible light, or hot rays (radiation or radiation), and preferably ultraviolet light. The light has a light intensity of about 0.1 to 10 watts per square centimeter (w / cm2), preferably 1 to 5 W / cm2. In the preparation method of the present invention, the temperature of the coating step or the polymerization reaction step is controlled at about 20 to 40 ° C, preferably about 300c. The thickness of the cholesteric liquid crystal formulation coated on the transparent substrate is about 2 to 25 μm, preferably about 3 to 10 μm. The above method can be repeated as needed to repeatedly increase the transparent substrate |

O: \ 90 \ 90609.DOC -15- 200540450 visible light bandwidth. The following examples will further modify the scope of the present invention. Anyone who is familiar with the scope of the present invention is not limited to the spirit of the present invention. Modifications and changes achieved by those who are not "Hi" in the two technical fields belong to Examples of the scope of the present invention Each monomer structure used in the examples of the present invention is, for example, a monofunctional nematic liquid crystal monomer (a):

Bifunctional nematic liquid crystal monomer (b)

-Ο— (CH2) 6—I

O— (CH2) 6 ~ 〇-C ^ CH2 == CH \, ch = ch2 (/ bifunctional nematic liquid crystal monomer (c) ch2 == ch) c-ο— (ch2) 6-0-

ίο- ^ oJ ch = ch2 Monofunctional palm monomer (d)

O plant-V H2C = C- C ~ ^ 〇

Η Example 1-3 Plane agent and photoinitiator Take the above monomers (a), (b) and (d),

O: \ 90 \ 90609.DOC -16- 200540450 to form cholesterol-type liquid crystal formulations 1, 2 and 3, as shown in Table 1: Table 1 Liquid crystal formulation 1 2 3 Monofunctional nematic liquid crystal monomer (a) 46 % 45% 44% Bifunctional nematic liquid crystal monomer (b) 46% 98 wt% 45% 98 wt% 44% 98 wt% Monofunctional palm monomer (d) ^ 8% 10% 12% Flat Agent (BYK_361) 1 wt% 1 wt% 1 ^ vt% Photoinitiator (TPO) 1 wt% 1 wt% 1 wt% The main condition that determines the reflected light color of the obtained formula is the blending ratio of palm monomers, Those with a small proportion can reflect the red light region with a short wavelength, and vice versa can obtain blue light, but the composition formula that exceeds the applicable content range reflects infrared or ultraviolet light outside the visible light region, which has no practical value. The liquid crystal formulations 1, 2 and 3 were respectively formed into an optical film 'by the manufacturing method of the present invention as a monochromatic anti-remission film. FIG. 2 is a spectrum of the reflection band widths of the cholesteric liquid crystal formulations 1 to 3 in Examples 1 to 3 of the present invention, which are represented by I, η, and III, respectively. Among them, Formula 1 is a red light enhancement film with an effective wavelength range of about 576 to 694 nanometers (nm), and Formula 2 is a green light enhancement film with an effective wavelength range of about 492 to 586 nm. Formula 3 is Blue light band brightening film, effective wavelength range is about 400 to 492 nm. According to the above data, the superimposed product of the three-layer brightness enhancement film prepared by using the cholesterol-type liquid crystal formulation of the present invention can effectively cover the entire visible light bandwidth (effective wavelength range is about 426 to 686 nm). Example 4-9 The above-mentioned monomers (a), (a) and (d), a flattening agent, and a photoinitiator were prepared in different proportions to form cholesterol-type liquid crystal formulations 4 to 9, as shown in Table 2: O: \ 90 \ 90609.DOC -17- 200540450 Table 2 Liquid crystal formulation 4 5 6 Monofunctional nematic liquid crystal monomer (a) 47.5% 98 wt% 47% 98wt% 46.5% 98wt% Bifunctional nematic liquid crystal monomer ( c) 47.5% 47% 46.5% Monofunctional Palm Monomer (d) 5% 6% 7% Planer (BYK-361) 1 wt% 1 wt% 1 wt% Photoinitiator (TPO) 1 wt% 1 wt% 1 wt% liquid crystal formulation 7 8 9 monofunctional nematic liquid crystal monomer (a) 46% 98wt% 45.5% 98wt% 45% 98wt% bifunctional nematic liquid crystal monomer (c) 46% 45.5 % 45% Monofunctional Palm Monomer (d) 8% 9% 10% Planar (BYK-361) 1 wt% 1 wt% 1 wt% Photoinitiator (TPO) 1 wt% 1 wt% 1 wt % Formulas 4 to 9 are bifunctional nematic liquid crystal monomers different from those of Formulas 1 to 3 of Examples 1 to 3. The main difference is that monomer (b) is a material with a high birefringence value, while the monomer (C) is a material with a low birefringence value. According to the aforementioned Maxwell theory, the birefringence value of the material can directly affect the reflection Therefore, the formulas prepared in Examples 4 to 9 all have a narrow reflection band bandwidth, as shown in FIG. 3, which is a cholesterol-type liquid crystal formula in Examples 4 to 9 of the present invention. The spectrum of the reflection band bandwidth of 4 to 9. Therefore, if the full visible light enhancement film is made with the formulas 4 to 9, it must be represented by the superposition of more optical films. For example, the embodiments 6 to 9 can be selected. Brightening film, using four layers of superposition to obtain the visible spectrum brightening film. In summary, the cholesterol-type liquid crystal formulation of the present invention can use a simple and easy-to-control process to flexibly make appropriate reflected waves from the composition. : \ 90 \ 90609.DOC -18-200540450 The brightening film can not only effectively increase the brightness of the LCD display, but also can use multiple layers to effectively cover the entire visible light bandwidth, and is used in general displays that require full-spectrum white light. Or the special display driving mode applied to the special bandwidth range. The following patent application scope is used to define the reasonable protection scope of the present invention. However, it should be clear that those skilled in the art can make use of the disclosure of the present invention. The various obvious improvements should also belong to the reasonable protection scope of the present invention. [Simplified illustration of the figure] Figure 1 shows the conventional LCD (I) and the liquid crystal display (II) with a cholesteric optical film. No intention. FIG. 2 is a spectrum of the reflection band width of the cholesteric liquid crystal formulations 1 to 3 in Examples 1 to 3 of the present invention. FIG. 3 is a spectrum of the reflection band width of the cholesteric liquid crystal formulations 1 to 3 in Examples 4 to 9 of the present invention. [Simplified description of the symbols of the diagram elements] 10 Reflective plate 12 Light guide plate 14 Cholesterol liquid crystal optical film 16 λ / 4 retardation plate 18 Lower polarizer 20 Liquid crystal layer 22 Upper polarizer 24 Light source 卩 8 1 ^ ¥ \ 新 案 \ 90609 \ 90609 € 5 Changxing-FINAL.DOC -19-

Claims (1)

200540450 Scope of patent application ... 1 An optical film comprising a transparent substrate and at least one layer of a cholesteric liquid crystal compound coated on the surface of the substrate, characterized in that the polymer is polymerized by the following monomers: Into: (a) a monofunctional nematic liquid crystal monomer; (b) a bifunctional nematic liquid crystal monomer; and (c) a palmitic compound monomer. 2. The optical film according to item 1 of the scope of patent application, which is used as a brightness enhancement film. 3. The optical film according to item 1 of the patent application range, wherein the substrate comprises a polymer resin. 4. The optical film according to item 3 of the patent application range, wherein the polymer resin is selected from the group consisting of a poly S resin, a polycarbonate resin, and a polyurethane resin. 5. The optical film according to item 3 of the application, wherein the polymer resin is polyethylene terephthalate. 6. A cholesterol-type liquid crystal formulation comprising: 0) a monofunctional nematic liquid crystal monomer; (b) a bifunctional nematic liquid crystal monomer; (c) a palmitic compound monomer; and (d) light Initiator. 7. The cholesteric liquid crystal formulation according to item 6 of the patent application, wherein the monofunctional nematic liquid crystal single system is selected from the group consisting of the following structural formula: O: \ 90 \ 90609.DOC 200540450 CH2 = CH—C—0—R—Ar—X 0, &lt; pH3 —C—O—R—A “—X 〇 and / 0 \ CH2—CH—R—A“ X, where the ruler is €: 1 -(: 1 () alkylene or (^-(: 1 () alkyleneoxy), x is one of the ends selected from the group consisting of aryl, Ci-Cio, and Cl-ClQ alkyl. And Ar is selected from the group consisting of the following groups having a liquid crystal phase: -QrQr, O: \ 90 \ 90609.DOC -2- 200540450 Among them, A is the other terminal group selected from the group consisting of a hydrogen atom, a Ci_C6 group, and a halo atom. 8. The cholesterol-type liquid crystal formulation according to item 7 of the application, wherein the monofunctional nematic liquid crystal single system has the formula (A) structure: Formula ㈧ 9. The cholesteric liquid crystal formulation according to item 6 of the patent application, wherein the bifunctional nematic liquid crystal single system is selected from the group consisting of the following structural formula: CH2 = CH-C-〇-R- —R—O—C—CH = CH2 〇δ ch3 = C—C— (CH3 CH2F = C—c —〇—r—Ar—R-0 ~ CC == CH2 A ii Δ 〇〇 and CH2—CH- Hachiman γ-R-CH-CH2 where 'R is Ci_Ci〇 thiocarbonate or C1-C1 〇 lactic acid group' and Ar is selected from the group consisting of the following groups with a liquid crystal phase: O: \ 9O \ 906O9.DOC 200540450 , Pu CH = CH and Among them, A is another terminal group selected from the group consisting of a hydrogen atom, an alkyl group, and a halogen atom. 10. The cholesteric liquid crystal formulation according to item 9 of the scope of patent application, wherein the bifunctional nematic liquid crystal single system is selected from the formula (B) or the formula (C) structure: CH2 == CH \ -o- (ch2 ) "0 CH = CH ^ 〇— (CH2) 6-〇-C ^ 0 Formula (B) O: \ 90 \ 90609.DOC 200540450 ch2 = chn o ' Formula (C) 〇 11 · The cholesteric liquid crystal formulation according to item 6 of the patent application range, wherein the palm compound single system is a monofunctional palm compound monomer. 12. The cholesteric liquid crystal formulation according to item 11 of the scope of patent application, wherein the palm compound single system is selected from the group consisting of the following structural formula: CH2 == CH—C—O—R—Ar—Y CH3 CH2 = C-〇-〇-R-Ar-Y 〇 and ο CH <-〇h2-R-Ar-Y, wherein R ^ Ci-Cio alkynyl or 匸 丨 / ⑺ alkynyloxy, and Ar To select a group consisting of the following groups with a liquid crystal phase: CH = CH O: \ 90 \ 90609.DOC 200540450 -c = c-^^ y ~ ^ A C three C A C ^ G O a And A Among them, A is another terminal group selected from the group consisting of a hydrogen atom, a group, and a halogen atom; wherein γ is selected from the group consisting of cholesterol, 0 II —0—〇 * 〇 · Ή _ ·· 〇-0 rO &gt;- 〇 ——c—〇 The composition can form an optically active group of a liquid crystal phase. 13. The cholesterol-type liquid crystal formulation according to item 12 of the patent application scope, wherein the palmitic compound has a system of formula (D): O: \ 90 \ 90609.DOC -6- 200540450 h2c = Formula (D) ο 14. The cholesteric liquid crystal formulation according to item 6 of the patent application, further comprising a flattening agent. 15 · A method for preparing an optical film, comprising the following steps: (a) blending a nematic liquid crystal monomer and a palmitic compound monomer, and then adding a photoinitiator to form a cholesteric liquid crystal formulation; ( b) coating the cholesteric liquid crystal formulation on a transparent substrate; and (c) irradiating the cholesteric liquid crystal formulation with energy rays at room temperature or under heating to perform a photopolymerization reaction. 16. The method according to item 15 of the patent application, wherein the energy ray is ultraviolet light. 17. The method according to item 15 of the patent application, wherein the photopolymerization temperature is about 20 to 40 ° C. 18. The method of claim 17 in the scope of patent application, wherein the photopolymerization reaction temperature is about 30oC. 1 9 · Shi declares patent | &amp; The method according to item 5, wherein the thickness of the cholesteric liquid crystal formulation is 2 to 25 m on the transparent substrate. 20. If the method of applying for a patent in the scope of 15jg is negative, these steps can be repeated several times. O: \ 90 \ 90609.DOC