Brightness enhancement film, circular polarizer, and display device

Abstract

The application relates to the technical field of display, and discloses a brightness enhancement film, a circular polarizer and a display device. The brightness enhancement film comprises a first cholesteric liquid crystal film layer, a second cholesteric liquid crystal film layer, a third cholesteric liquid crystal film layer and at least one substrate layer. The material of the substrate layer is an organic transparent material without birefringence, the thickness of the substrate layer is preferably 5-100 microns, and the light transmittance is preferably greater than 90%. By adding the substrate layer in the brightness enhancement film, the function of fixing the helical axis of the cholesteric liquid crystal film can be achieved, the problem that the helical axis is tilted when the cholesteric liquid crystal film is subjected to external tension and the problem that the brightness enhancement film is seriously scattered and the display effect is poor are effectively avoided. The brightness enhancement film provided by the application has a haze of 0.5% and a tensile strength of 3210 kPa, which are better than those of ordinary brightness enhancement films. The display device provided by the application has an outlight efficiency of 84.5%, which is better than that of ordinary display devices.

Description

Technical Field

[0001] This invention belongs to the field of display technology, specifically relating to a brightness enhancement film, a circular polarizer, and a display device. Background Technology

[0002] With the continuous improvement of social informatization, organic light-emitting diode (OLED) display technology has made significant progress. OLEDs possess advantages such as simple structure, self-illumination without backlighting, high contrast, thinness, wide viewing angle, fast response speed, applicability to flexible panels, and strong adaptability to ambient temperature. Therefore, they are widely used in displays for mobile phones, computers, televisions, and other devices. OLEDs contain a circular polarizer composed of a linear polarizer and a phase retardation layer. The circular polarizer is used to shield ambient light reflection, improving display performance. However, the circular polarizer causes approximately 50% of the emitted light from the display to be absorbed.

[0003] In existing technologies, multilayer cholesteric liquid crystal films are bonded together to broaden the bandwidth of the tunable light wavelength of the brightness enhancement film. However, during the bonding process, the spiral axis of the cholesteric liquid crystal film deflects, resulting in severe scattering and increased haze in the composite brightness enhancement film, which in turn affects the display effect.

[0004] Therefore, there is an urgent need for a brightness enhancement film with adjustable wavelength bandwidth and no increase in haze, in order to improve light extraction efficiency and ensure display effect. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an optical adhesive, a circular polarizer, and a display device to solve the problems of high haze and poor display effect caused by scattering in the brightness enhancement film. To achieve the above technical effects, this invention adopts the following technical solution.

[0006] This invention first provides a brightness enhancement film, comprising: a first cholesteric liquid crystal film layer, a second cholesteric liquid crystal film layer, a third cholesteric liquid crystal film layer, and at least one substrate layer. The substrate layer is made of a transparent organic material with no birefringence. When the number of substrate layers in the brightness enhancement film is ≥2, the substrate layers may be made of the same or different materials, and there is at least one cholesteric liquid crystal film layer between the two substrate layers. The cholesteric liquid crystal film layers are bonded together using optical adhesive, or the cholesteric liquid crystal film layers are composited during the preparation process through a one-time or step-by-step coating process.

[0007] Furthermore, in the brightening film, the substrate layer material includes: PMMA film, TAC film, and COP film.

[0008] Furthermore, in the brightening film, the thickness of the substrate layer is 5–300 μm, preferably 5–100 μm. The light transmittance of the substrate layer is greater than 80%, preferably greater than 90%.

[0009] Furthermore, in the brightness enhancement film, the first cholesteric liquid crystal film layer is used to control blue light, the second cholesteric liquid crystal film layer is used to control green light, and the third cholesteric liquid crystal film layer is used to control red light. The blue light refers to light with a wavelength of 450–480 nm, the green light refers to light with a wavelength of 500–580 nm, and the red light refers to light with a wavelength of 600–680 nm.

[0010] In addition, the present invention also provides a method for preparing the brightness enhancement film, comprising: pretreatment of a substrate layer, preparation of a first, second, and third liquid crystal mixture, and coating of the first, second, and third liquid crystal mixture.

[0011] Furthermore, in the above preparation method, the pretreatment method of the substrate layer is as follows: the substrate layer is subjected to corona treatment with a corona power of 100V*2A and a corona velocity of 2m / min.

[0012] Furthermore, in the above preparation method, the preparation method of the first, second, and third liquid crystal mixtures is as follows: The raw materials for preparing the liquid crystal mixture are measured in proportion, by mass percentage, and the raw materials include: 10-98% polymerizable liquid crystal monomers, 0.5-30% chiral compounds, 0.1-5% photoinitiator, and 0.5-80% organic solvent. The measured raw materials are heated to above the phase transition temperature of all polymerizable liquid crystal monomers, while stirring until uniformly mixed, and then cooled to 10-50°C for coating.

[0013] Furthermore, in the above preparation method, the polymerizable liquid crystal monomer is selected from one or more of nematic liquid crystals, disk-shaped liquid crystals, and disc-shaped liquid crystals. The polymerizable liquid crystal monomer contains at least one polymerizable group, preferably two or more polymerizable groups. The polymerizable group is alkenyl, alkynyl, epoxy, or mercapto.

[0014] Among them, polymerizable liquid crystal monomers containing two or more polymerizable groups include:

[0015] L1:

[0016]

[0017] L2:

[0018]

[0019] L3:

[0020]

[0021] L4:

[0022]

[0023] L5:

[0024]

[0025] L6:

[0026]

[0027] L7:

[0028]

[0029] L8:

[0030]

[0031] Furthermore, in the above preparation method, the chiral compound is selected from one or more of X1, X2, X3, X4, X5, X6, X7, X8, X9, X10, X11, X12, X13, X14, X15, X16, X17, X18, X19, X20, and X21;

[0032] Wherein, X1:

[0033]

[0034] X2:

[0035] X3:

[0036] X4:

[0037] X5:

[0038]

[0039] X6:

[0040]

[0041] X7:

[0042]

[0043] X8:

[0044]

[0045] X9:

[0046] X10:

[0047] X11:

[0048] X12:

[0049] X13:

[0050] X14:

[0051] X15:

[0052] X16:

[0053] X17:

[0054]

[0055] X18:

[0056]

[0057] X19:

[0058]

[0059] X20:

[0060]

[0061] X21:

[0062]

[0063] Furthermore, in the above preparation method, the photoinitiator is selected from: benzoyl peroxide, azobisisobutyronitrile, benzoin ethers, benzophenones, acetophenones, benzoylacetyl ketals, diaryliodomonium salts, triarylthionium salts, diphenyliodomonium tetrafluoroborate, diphenyliodomonium hexafluorophosphate, diphenyliodomonium arsenate, diphenyliodomonium tetrafluoroborate, 4-methoxyphenyliodomonium tetrafluoroborate, 4-methoxyphenyliodomonium hexafluorophosphate, 4-methoxyphenyliodomonium hexafluoroarsenate, 4-tert-butylphenyliodomonium diphenyliodomonium tetrafluoroborate, 4-tert-butylphenyliodomonium diphenyliodomonium hexafluorophosphate. Phosphate, 4-tert-butylphenyliodonium diphenyliodonium trifluoromethane sulfonate, triphenylthionium hexafluorophosphate, triphenylthionium hexafluoroarsenate, triphenylthionium tetraborate, 4-methoxyphenyl diphenylthionium tetrahydroborate, 4-methoxyphenyl diphenylthionium tetrahydrophosphate, 4-methoxyphenyl diphenylthionium tetrahydroarsenate, 4-methoxyphenyl diphenylthionium trifluoromethane sulfonate, 4-methoxyphenyl diphenylthionium triphenylthionium tetraborate, 4-phenylphenylthiodiphenylthionium hexafluoroarsenate, benzoyl dimethyl ketal, and bis-phenylphosphine oxides, one or more of these.

[0064] Furthermore, in the above preparation method, the solvent is selected from: benzene, toluene, xylene, mesitylene, n-butylbenzene, diethylbenzene, tetrahydronaphthalene, methoxybenzene, 1,2-dimethoxybenzene, cyclohexanone, ethyl acetate, methyl lactate, ethyl lactate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, 2-pyrrolidone, chloroform, dichloromethane, carbon methyl chloride, dichloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, tert-butanol, diacetone alcohol, glycerol, glyceryl monoacetate, triethylene glycol monoethyl ether acetate, etc. One or more of the following: alcohol, ethyl cellosolve and butyl cellosolve, N-methyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, diethylene glycol monomethyl ether ethyl ester, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, tetrahydrofuran, dichloromethane, chlorobenzene, 1,2-dichloroethane, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclobutanone, methyl acetate, ethyl acetate, diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol methyl ethyl ether, and ethylene glycol dimethyl ether.

[0065] Furthermore, in the above preparation method, the coating method for the first, second, and third liquid crystal mixtures is as follows:

[0066] The first liquid crystal mixture is coated onto a pretreated substrate layer to a thickness of 500–5000 nm. The organic solvent is removed by heating at 30–150 °C for 5–1000 s. Curing is then performed by irradiation at a wavelength of 300–400 nm and an irradiation dose of 1000–200000 J / m². 2 The second and third liquid crystal mixtures are coated using the same method to obtain the brightness enhancement film.

[0067] The present invention also claims protection for a circular polarizer, the circular polarizer comprising: a linear polarizer, the above-mentioned brightness enhancement film and a phase retardation layer; the linear polarizer and the phase retardation layer are bonded together by the above-mentioned brightness enhancement film.

[0068] The present invention also claims protection for a display device comprising the circular polarizer.

[0069] Compared with the prior art, the present invention, "a brightness enhancement film, a circular polarizer, and a display device," has at least the following technical effects:

[0070] In the preparation of the brightness enhancement film, this invention adds at least one substrate layer. The substrate layer is a transparent organic material with no birefringence and a light transmittance greater than 90%, such as PMMA film, TAC film, or COP film. On one hand, the use of the substrate in the brightness enhancement film can significantly reduce the haze of the film, improve the light extraction efficiency, and enhance the display effect. Testing showed that the haze of the brightness enhancement film prepared in Comparative Example 1 was 8.5%, while the haze of the brightness enhancement film prepared in Example 4 of this invention was 0.5%, significantly lower than that of Comparative Example 1. The display device prepared using the brightness enhancement film provided by this invention can achieve a light extraction efficiency of 84.5% (Example 11-1), significantly higher than the 75% of Comparative Example 2.

[0071] On the other hand, the use of a substrate in the brightness enhancement film can significantly improve its mechanical strength, making it less prone to tilting or deflection of the helical optical axis of the cholesteric liquid crystal film in the brightness enhancement film, thus ensuring the stability of the brightness enhancement film. Tests showed that the tensile strength of the brightness enhancement film prepared in Comparative Example 1 was 220 kPa, and the tensile strength of the brightness enhancement film prepared in Example 8 was 3210 kPa, significantly higher than that of Comparative Example 1. Attached Figure Description

[0072] Figure 1 This is a schematic diagram of the brightness enhancement film structure in Example 1.

[0073] Figure 2 This is a schematic diagram of the brightness enhancement film structure in Example 2.

[0074] Figure 3 This is a schematic diagram of the brightness enhancement film structure in Example 3.

[0075] Figure 4 This is a schematic diagram of the brightness enhancement film structure in Example 4.

[0076] Figure 5 This is a schematic diagram of the brightness enhancement film structure in Example 5.

[0077] Figure 6 This is a schematic diagram of the brightness enhancement film structure in Example 6.

[0078] Figure 7 This is a schematic diagram of the brightness enhancement film structure in Example 7.

[0079] Figure 8 This is a schematic diagram of the brightness enhancement film structure in Example 8.

[0080] Figure 9 This is a schematic diagram of the brightness enhancement film structure in Example 9.

[0081] Explanation of reference numerals in the attached figures: M1 represents TAC substrate, M2 represents PMMA substrate, and S1, S2, and S3 represent the first cholesteric liquid crystal film, the second cholesteric liquid crystal film, and the third cholesteric liquid crystal film, respectively. Detailed Implementation

[0082] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0083] This invention provides a brightness enhancement film, comprising: a first cholesteric liquid crystal film layer, a second cholesteric liquid crystal film layer, a third cholesteric liquid crystal film layer, and at least one substrate layer. The substrate layer is made of a transparent organic material with no birefringence. When the number of substrate layers in the brightness enhancement film is ≥2, the substrate layers may be made of the same or different materials, and there is at least one cholesteric liquid crystal film layer between each substrate layer. The cholesteric liquid crystal film layers are bonded together using optical adhesive, or the cholesteric liquid crystal film layers are composited during the preparation process through a one-time or step-by-step coating process.

[0084] For example, in the brightening film, the substrate layer material includes: PMMA film, TAC film, and COP film.

[0085] For example, in the brightening film, the thickness of the substrate layer is 5 to 300 μm, preferably 5 to 100 μm; the light transmittance of the substrate layer is greater than 80%, preferably greater than 90%.

[0086] For example, in the brightness enhancement film, the first cholesteric liquid crystal film layer is used to control blue light, the second cholesteric liquid crystal film layer is used to control green light, and the third cholesteric liquid crystal film layer is used to control red light. The blue light refers to light with a wavelength of 450–480 nm, the green light refers to light with a wavelength of 500–580 nm, and the red light refers to light with a wavelength of 600–680 nm.

[0087] In addition, the present invention also provides a method for preparing the brightness enhancement film, comprising: pretreatment of a substrate layer, preparation of a first, second, and third liquid crystal mixture, and coating of the first, second, and third liquid crystal mixture.

[0088] For example, in the above preparation method, the pretreatment method of the substrate layer is: to subject the substrate layer to corona treatment, with a corona power of 100V*2A and a corona velocity of 2m / min.

[0089] For example, in the above preparation method, the preparation method of the first, second, and third liquid crystal mixtures is as follows:

[0090] The raw materials for preparing the liquid crystal mixture are measured in proportion, by mass percentage, comprising: 10–98% polymerizable liquid crystal monomers, 0.5–30% chiral compounds, 0.1–5% photoinitiator, and 0.5–80% organic solvent. The measured raw materials are heated to above the phase transition temperature of all polymerizable liquid crystal monomers while stirring until homogeneous. The mixture is then cooled to 10–50°C for coating.

[0091] For example, in the above preparation method, the polymerizable liquid crystal monomer is selected from one or more of nematic liquid crystals, disk-shaped liquid crystals, and disc-shaped liquid crystals. The polymerizable liquid crystal monomer contains at least one polymerizable group, preferably two or more polymerizable groups. The polymerizable group is alkenyl, alkynyl, epoxy, or mercapto.

[0092] For example, a polymerizable liquid crystal monomer containing two or more polymerizable groups includes:

[0093] L1:

[0094]

[0095] L2:

[0096]

[0097] L3:

[0098]

[0099] L4:

[0100]

[0101] L5:

[0102]

[0103] L6:

[0104]

[0105] L7:

[0106]

[0107] L8:

[0108]

[0109] For example, in the above preparation method, the chiral compound is selected from one or more of X1, X2, X3, X4, X5, X6, X7, X8, X9, X10, X11, X12, X13, X14, X15, X16, X17, X18, X19, X20, and X21.

[0110] Wherein, X1:

[0111]

[0112] X2:

[0113]

[0114] X3:

[0115]

[0116] X4:

[0117]

[0118] X5:

[0119]

[0120] X6:

[0121]

[0122] X7:

[0123]

[0124] X8:

[0125]

[0126] X9:

[0127] X10:

[0128] X11:

[0129] X12:

[0130] X13:

[0131] X14:

[0132] X15:

[0133] X16:

[0134] X17:

[0135]

[0136] X18:

[0137]

[0138] X19:

[0139]

[0140] X20:

[0141]

[0142] X21:

[0143]

[0144] Exemplarily, in the above preparation method, the photoinitiator is selected from: benzoyl peroxide, azobisisobutyronitrile, benzoin ethers, benzophenones, acetophenones, benzoylayl ketals, diaryliodomonium salts, triarylthionium salts, diphenyliodomonium tetrafluoroborate, diphenyliodomonium hexafluorophosphate, diphenyliodomonium arsenate, diphenyliodomonium tetrafluoroborate, 4-methoxyphenyliodomonium tetrafluoroborate, 4-methoxyphenyliodomonium hexafluorophosphate, 4-methoxyphenyliodomonium hexafluoroarsenate, 4-tert-butylphenyliodomonium diphenyliodomonium tetrafluoroborate, 4-tert-butylphenyliodomonium diphenyliodomonium hexafluorophosphate. One or more of the following: fluorophosphate, 4-tert-butylphenyliodonium diphenyliodonium trifluoromethane sulfonate, triphenylthionium hexafluorophosphate, triphenylthionium hexafluoroarsenate, triphenylthionium tetraborate, 4-methoxyphenyl diphenylthionium tetrahydroborate, 4-methoxyphenyl diphenylthionium tetrahydrophosphate, 4-methoxyphenyl diphenylthionium tetrahydroarsenate, 4-methoxyphenyl diphenylthionium trifluoromethane sulfonate, 4-methoxyphenyl diphenylthionium triphenylthionium tetraborate, 4-phenylphenylthiodiphenylthionium hexafluoroarsenate, benzoyl dimethyl ketal, and bis-phenylphosphine oxide.

[0145] For example, in the above preparation method, the solvent is selected from: benzene, toluene, xylene, mesitylene, n-butylbenzene, diethylbenzene, tetrahydronaphthalene, methoxybenzene, 1,2-dimethoxybenzene, cyclohexanone, ethyl acetate, methyl lactate, ethyl lactate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, 2-pyrrolidone, chloroform, dichloromethane, carbon methyl chloride, dichloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, tert-butanol, diacetone alcohol, glycerol, glyceryl monoacetate, triethylene glycol monoethyl ether acetate, etc. One or more of the following: alcohol, ethyl cellosolve and butyl cellosolve, N-methyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, diethylene glycol monomethyl ether ethyl ester, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol, tetrahydrofuran, dichloromethane, chlorobenzene, 1,2-dichloroethane, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclobutanone, methyl acetate, ethyl acetate, diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol methyl ethyl ether, and ethylene glycol dimethyl ether.

[0146] For example, in the above preparation method, the coating method for the first, second, and third liquid crystal mixtures is as follows: the first liquid crystal mixture is coated onto a pretreated substrate layer with a coating thickness of 500–5000 nm; the organic solvent is removed by heating at a temperature of 30–150 °C for 5–1000 s; and then cured by irradiation at a wavelength of 300–400 nm and an irradiation dose of 1000–200000 J / m². 2 The second and third liquid crystal mixtures are coated using the same method to obtain the brightness enhancement film.

[0147] Example 1

[0148] This embodiment provides a method for preparing a brightness enhancement film. The brightness enhancement film includes three cholesteric liquid crystal film layers for controlling red, green, and blue light, and a substrate layer. Each cholesteric liquid crystal film layer has a uniform pitch distribution, and the three cholesteric liquid crystal film layers are located on one side of the substrate layer. Figure 1 As shown. The arrangement order of the three cholesteric phase liquid crystal films S1, S2, and S3 in the thickness direction is not limited. The thickness of the three cholesteric phase liquid crystal films is 10 μm. The substrate is a TAC film material with a thickness of 25 μm. The total thickness of the brightness enhancement film is 35 μm.

[0149] 1. Pretreatment of the substrate layer

[0150] One side of the TAC membrane was subjected to corona treatment with a corona power of 100V*2A and a corona velocity of 2m / min.

[0151] 2. Preparation of liquid crystal mixtures

[0152] The polymerizable liquid crystal monomer, chiral compound, photoinitiator, and solvent are measured in the specified proportions. The measured raw materials are heated to 180°C while stirring continuously until the raw materials are uniformly mixed. The mixture is then cooled to 30°C for later use.

[0153] In the above steps, the raw materials for preparing the first liquid crystal mixture, by mass percentage, include: 80% polymerizable liquid crystal monomer, 2% X13 compound (chiral compound), 2% 4-tert-butylphenyliodonium diphenyliodonium tetrafluoroborate (photoinitiator), and 16% propylene glycol monomethyl ether acetate (organic solvent).

[0154] The polymerizable liquid crystal monomer is composed of a mixture of multiple polymerizable liquid crystal monomers, comprising, by mass percentage: 30% L1 compound, 33% L2 compound, 25% L3 compound, and 12% L6 compound.

[0155] The difference between the raw materials for preparing the second liquid crystal mixture and those for the first liquid crystal mixture is that the content of X13 compound (chiral compound) is 1.7%, and the content of propylene glycol monomethyl ether acetate (organic solvent) is 16.3%.

[0156] The difference between the raw materials for preparing the third liquid crystal mixture and those for the second liquid crystal mixture is that the content of X13 compound (chiral compound) is 1.4%, and the content of propylene glycol monomethyl ether acetate (organic solvent) is 16.6%.

[0157] 3. Coating of liquid crystal mixtures

[0158] The first liquid crystal mixture obtained in step 2 was coated onto the substrate layer that had undergone corona treatment in step 1 using a slit coating process. The coating thickness was 3 μm. The mixture was heated to 80°C and held for 1 min to remove the solvent. It was then cured by ultraviolet (UV) irradiation at a wavelength of 365 nm and an irradiation dose of 5000 J / m². 2 This forms the first cholesteric phase liquid crystal film layer.

[0159] A second and third cholesteric liquid crystal mixture were coated onto the first cholesteric liquid crystal film layer using the same method to obtain the second and third cholesteric liquid crystal film layers. The coating thickness of both the second and third liquid crystal mixtures was 4.5 μm.

[0160] The first cholesteric phase liquid crystal film is used to regulate blue light, the second cholesteric phase liquid crystal film is used to regulate green light, and the third cholesteric phase liquid crystal film is used to regulate red light.

[0161] Example 2

[0162] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the three cholesteric liquid crystal films are located on both sides of the substrate; that is, one layer of the three cholesteric liquid crystal films is located on one side of the substrate layer, and the other two cholesteric liquid crystal films are located on the other side of the substrate layer, as shown below. Figure 2 As shown. The arrangement order of the three-layer cholesteric liquid crystal film S1, S2, and S3 in the thickness direction is not limited. The substrate is subjected to double-sided corona treatment under the same conditions as in Example 1.

[0163] Example 3

[0164] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains two substrate layers, and the three cholesteric liquid crystal layers are all located between the two substrate layers, as shown below. Figure 3 As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited. The materials and thicknesses of the two substrate layers are the same as in Example 1, and the total thickness of the brightness enhancement film is 60 μm.

[0165] Example 4

[0166] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains two substrate layers, a cholesteric liquid crystal film located between the two substrate layers, and two other cholesteric liquid crystal films distributed on opposite sides of the two substrate layers that are not adjacent to the cholesteric liquid crystal film. Figure 4 As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited. The materials and thicknesses of the two substrate layers are the same as in Example 1, and the total thickness of the brightness enhancement film is 60 μm.

[0167] Example 5

[0168] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains two substrate layers, a cholesteric liquid crystal film located between the two substrate layers, and the remaining two cholesteric liquid crystal films located on the side of either substrate layer that is not adjacent to the cholesteric liquid crystal film, such as... Figure 5 As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited. The materials and thicknesses of the two substrate layers are the same as in Example 1, and the total thickness of the brightness enhancement film is 60 μm.

[0169] Example 6

[0170] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains two substrate layers, two cholesteric liquid crystal films are located between the two substrate layers, and another cholesteric liquid crystal film is located on the side of either substrate layer that is not adjacent to a cholesteric liquid crystal film. Figure 6As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited. The materials and thicknesses of the two substrate layers are the same as in Example 1, and the total thickness of the brightness enhancement film is 60 μm.

[0171] Example 7

[0172] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains three substrate layers. Between any two adjacent substrate layers, there is a cholesteric liquid crystal film. Another cholesteric liquid crystal film is located on the side of either of the two outermost substrate layers that is not adjacent to the cholesteric liquid crystal film. Figure 7 As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited.

[0173] Example 8

[0174] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains four substrate layers, and three cholesteric liquid crystal layers are respectively located between any two adjacent substrate layers among the four substrate layers, such as... Figure 8 As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited.

[0175] Example 9

[0176] This embodiment provides a method for preparing a brightness enhancement film. The difference between this embodiment and Embodiment 1 is that the brightness enhancement film contains two substrate layers, and three cholesteric liquid crystal films are all located between the two substrate layers. The two substrate layers are made of different materials: one is a TAC film material, and the other is a PMMA film material. The PMMA film thickness is 30 μm. Figure 9 As shown. The arrangement order of the three cholesteric liquid crystal films S1, S2, and S3 in the thickness direction is not limited.

[0177] Comparative Example 1

[0178] This comparative example provides a method for preparing a brightness enhancement film. The brightness enhancement film comprises a three-layer cholesteric liquid crystal film.

[0179] 1. PET release film is used as the substrate, with a substrate thickness of 50μm and a release force of 50g / 25mm.

[0180] 2. The preparation method of the liquid crystal mixture is the same as in Example 1.

[0181] 3. The first liquid crystal mixture obtained in step 2 is coated onto a PET release film. The coating process, coating thickness, heating temperature, heating time, and curing conditions are the same as in Example 1. After curing, a first cholesteric liquid crystal film layer is formed.

[0182] 4. On the first cholesteric liquid crystal film layer, the second and third liquid crystal mixtures are coated in the same way to obtain the second and third cholesteric liquid crystal film layers.

[0183] 5. The first, second, and third cholesteric liquid crystal films were bonded together using optical adhesive. After bonding, the brightness enhancement film was separated from the substrate layer. The optical adhesive was selected from commercially available commonly used optical adhesives, and its thickness was 25 μm. The resulting brightness enhancement film had a thickness of 60 μm.

[0184] The brightness enhancement film prepared in this comparative example was compared with the brightness enhancement films prepared in Examples 1-9 (Table 1). The test indicators included thickness, haze, and tensile strength. The thickness was measured using a micrometer; the haze was measured using a haze meter (TH-09 haze meter, ColorSpectrum Technology); and the light extraction efficiency was measured using a luminance meter (PR-670SpectraScan).

[0185] Table 1. Comparison of the brightening films prepared in Examples 1-9 with those prepared in Comparative Example 1

[0186] Example 1 35 0.8 1180 Example 2 35 0.6 1180 Example 3 60 0.8 2150 Example 4 60 0.5 2150 Example 5 60 0.6 2150 Example 6 60 0.8 2150 Example 7 85 0.8 3210 Example 8 110 0.9 3210 Example 9 65 0.8 2440 Comparative Example 1 60 8.5 220

[0187] As shown in Table 1, the haze of the brightness enhancement films in Examples 1-9 is significantly lower than that in Comparative Example 1. In Comparative Example 1, the tensile tension during the separation process of the brightness enhancement film from the substrate layer after being bonded with optical adhesive caused the helical optical axis of the cholesteric liquid crystal film to tilt and deflect, thereby increasing the haze of the brightness enhancement film. In the preparation process of the brightness enhancement film in this invention, the use of a substrate can significantly reduce the haze of the brightness enhancement film and improve the display effect. In addition, the use of a substrate can also significantly improve the tensile strength of the brightness enhancement film, making it less likely for the helical optical axis of the cholesteric liquid crystal film in the brightness enhancement film to tilt and deflect, thus ensuring the stability of the brightness enhancement film in actual use.

[0188] Example 10

[0189] This embodiment provides a circular polarizer, including the brightness enhancement film, phase retardation layer, linear polarizing layer and optical adhesive layer prepared in Examples 1 to 9.

[0190] Example 11

[0191] This embodiment provides a display device, including the circular polarizer prepared in Embodiment 10.

[0192] Comparative Example 2

[0193] This comparative example provides a display device, which differs from Example 11 in that the brightness enhancement film of the display device is selected from Comparative Example 1.

[0194] The light emission efficiency of the display device provided in this comparative example is compared with that of the display device provided in Example 11 (Table 2).

[0195] Table 2. Comparison of light output efficiency between Example 11 and Comparative Example 2

[0196]

[0197]

[0198] Note: In Table 2, “Example 11-1” refers to a display device prepared using the brightness enhancement film in Example 1, and so on.

[0199] As can be seen from Table 2, the light extraction efficiency of the display devices in Examples 11-1 to 11-9 is higher than that in Comparative Example 2. This is because the brightness enhancement film in Comparative Example 2 experiences more severe scattering, resulting in increased haze. Scattering causes some of the light emitted by the display device to be absorbed by the black matrix material outside the pixels, thus reducing the light extraction efficiency.

[0200] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A brightness enhancement film, characterized in that, The brightness enhancement film comprises: a first cholesteric liquid crystal film layer, a second cholesteric liquid crystal film layer, a third cholesteric liquid crystal film layer, and at least one substrate layer; The first cholesteric liquid crystal film layer is used to control blue light with a wavelength of 450~480nm, the second cholesteric liquid crystal film layer is used to control green light with a wavelength of 500~580nm, and the third cholesteric liquid crystal film layer is used to control red light with a wavelength of 600~680nm. The substrate layer is made of a non-birefringent organic transparent material, including PMMA film, TAC film, and COP film; the substrate layer has a thickness of 5~100μm and a light transmittance of greater than 90%; the substrate layer is used to improve mechanical strength, making it less likely for the spiral optical axis of the cholesteric liquid crystal film in the brightness enhancement film to tilt or deflect, while reducing the haze of the brightness enhancement film and improving the display effect. When the number of substrate layers in the brightening film is ≥2, the materials of each substrate layer are the same or different, and there is at least one cholesteric liquid crystal film between the two substrate layers. The cholesteric phase liquid crystal film layers are bonded together using optical adhesive, or the cholesteric phase liquid crystal film layers are composited during the preparation process through a one-time or step-by-step coating process.

2. The method for preparing the brightening film according to claim 1, characterized in that, include: Pretreatment of the substrate layer, preparation of the first, second, and third liquid crystal mixtures, and coating of the first, second, and third liquid crystal mixtures; The pretreatment method for the substrate layer is as follows: The substrate layer is subjected to corona treatment with a corona power of 100V. 2A, corona velocity is 2m / min; The preparation methods for the first, second, and third liquid crystal mixtures are as follows: The raw materials for preparing the liquid crystal mixture are measured in proportion, by mass percentage, comprising: 10-98% polymerizable liquid crystal monomers, 0.5-30% chiral compounds, 0.1-5% photoinitiators, and 0.5-80% organic solvents; wherein the polymerizable liquid crystal monomers are selected from one or more of nematic liquid crystals, disc-shaped liquid crystals, and dish-shaped liquid crystals, and each polymerizable liquid crystal monomer contains at least two polymerizable groups; the polymerizable groups are alkenyl, alkynyl, epoxy, or mercapto groups; the measured raw materials are heated to above the phase transition temperature of all polymerizable liquid crystal monomers, while stirring until uniformly mixed, and then cooled to 10-50°C for coating; The coating methods for the first, second, and third liquid crystal mixtures are as follows: The first liquid crystal mixture is coated onto a pretreated substrate layer with a coating thickness of 500-5000 nm. The organic solvent is removed by heating at 30-150°C for 5-1000 s. Curing is then performed by irradiation with a wavelength of 300-400 nm and an irradiation dose of 1000-200000 J / m². 2 The second and third liquid crystal mixtures are coated in the same way to obtain the brightness enhancement film.

3. A circular polarizer, characterized in that, The circular polarizer comprises: a linear polarizer, a brightness enhancement film as described in claim 1, and a phase retardation layer; the linear polarizer and the phase retardation layer are bonded together by the brightness enhancement film as described in claim 1.

4. A display device, characterized in that, Includes the circular polarizer as described in claim 3.

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