Circular polarizer for improving light extraction efficiency, and display device

Abstract

The present invention belongs to the technical field of display. Disclosed are a circular polarizer for improving light extraction efficiency, and a display device. The circular polarizer for improving light extraction efficiency according to the present invention comprises a cholesteric liquid crystal film, a first phase difference film, a second phase difference film, a third phase difference film, and a linear polarizing film. The display device comprises a display substrate and the circular polarizer for improving light extraction efficiency. The cholesteric liquid crystal film is located between the display substrate and the first phase difference film, and the linear polarizing film is located on the side of the third phase difference film away from the cholesteric liquid crystal film. By adjusting an arrangement order of liquid crystal polymer layers with different pitches in the cholesteric liquid crystal film in the direction of thickness and adding an additional phase difference film, the present invention solves the problem of low light extraction efficiency of the cholesteric liquid crystal film in the circular polarizer for light with a large wavelength at a large viewing angle, greatly improves the light extraction efficiency of the display device at a viewing angle of 30°-80°, and enhances the display effect of the display device.

Description

A circular polarizer with improved light extraction efficiency and a display device Technical Field

[0001] This invention belongs to the field of display technology and relates to a circular polarizer and display device for improving light extraction efficiency. Background Technology

[0002] Organic light-emitting diodes (OLEDs) have become deeply integrated into display devices such as mobile phones, computers, and televisions due to their numerous advantages, including simple structure, self-illumination without the need for an external light source, high contrast, ultra-thinness, wide viewing angle, fast response, adaptability to flexible panels, and strong environmental adaptability. The circular polarizer built into an OLED screen, composed of a linear polarizing layer and a retardation layer, effectively blocks ambient light reflection, thereby optimizing display quality. However, the linear polarizing layer absorbs approximately 50% of the emitted light, resulting in light energy loss. Similarly, the lower polarizer in the backlight module of a liquid crystal display (LCD) also leads to approximately 50% loss of emitted light. To improve the light extraction efficiency of display devices, cholesteric liquid crystal layers have been introduced in existing technologies. Cholesteric liquid crystal molecules are arranged in a periodic helical pattern, forming a pitch structure with Bragg diffraction, and the pitch determines the center wavelength of the reflected light. Cholesteric liquid crystal layers can transmit circularly polarized light with the opposite rotation direction to their own and reflect circularly polarized light with the same rotation direction. Although the introduction of a cholesteric liquid crystal layer enhances light output to some extent (a phase retardation film needs to be laminated to the cholesteric liquid crystal film in an LCD), its brightening effect is significantly weakened under wide viewing angles. This directly leads to a deterioration in display performance at wide viewing angles (30°~80°). Therefore, there is an urgent need for a new circular polarizer design to compensate for the insufficient brightening efficiency of the cholesteric liquid crystal layer at wide viewing angles, ensuring that display devices can provide excellent visual performance at various viewing angles. Summary of the Invention

[0003] To address the aforementioned technical problems and defects, this invention provides a circular polarizer and display device with improved light extraction efficiency. This invention solves the problem of low light extraction efficiency of the cholesteric liquid crystal film for larger wavelengths of light at wide viewing angles by adjusting the arrangement order of liquid crystal polymer layers with different pitches in the cholesteric liquid crystal film in the thickness direction and adding a phase retardation film.

[0004] In a first aspect, the present invention provides a circular polarizer, which is placed on a display substrate and includes a cholesteric liquid crystal film, a first phase reversal film, a second phase reversal film, a third phase reversal film, and a linear polarizer film.

[0005] The cholesteric liquid crystal film is located between the display substrate and the first phase reversal film; the linear polarizing film is located on the side of the third phase reversal film away from the cholesteric liquid crystal film; the first phase reversal film, the second phase reversal film, and the third phase reversal film are located between the cholesteric liquid crystal film and the linear polarizing film.

[0006] Furthermore, in the circular polarizer provided by the present invention, the cholesteric liquid crystal film includes at least two of the following: a first liquid crystal polymer layer for controlling red light, a second liquid crystal polymer layer for controlling green light, and a third liquid crystal polymer layer for controlling blue light.

[0007] The pitch of the first liquid crystal polymer layer is P1, the pitch of the second liquid crystal polymer layer is P2, and the pitch of the third liquid crystal polymer layer is P3, where P1>P2>P3.

[0008] Furthermore, in the circular polarizer provided by the present invention, the red light refers to light with a wavelength of 600~680nm, the green light refers to light with a wavelength of 500~580nm, and the blue light refers to light with a wavelength of 440~480nm.

[0009] Furthermore, in the circular polarizer provided by the present invention, the first phase difference film is used to compensate for the negative phase difference value of the liquid crystal polymer layer with a smaller pitch in the cholesteric liquid crystal film in the thickness direction for a longer wavelength.

[0010] Furthermore, in the circular polarizer provided by the present invention, the second phase difference film is used for the conversion between circularly polarized light or elliptically polarized light and linearly polarized light;

[0011] The third phase difference film is used to compensate for the phase difference loss of the second phase difference film at a viewing angle of 30° to 80°.

[0012] Furthermore, in the circular polarizer provided by the present invention, the first phase difference film, the second phase difference film, and the third phase difference film can be arranged in any order.

[0013] Furthermore, in the circular polarizer provided by the present invention, the first liquid crystal polymer layer, the second liquid crystal polymer layer, and the third liquid crystal polymer layer in the cholesteric liquid crystal film are arranged in order of pitch.

[0014] Furthermore, in the circular polarizer provided by the present invention, the cholesteric liquid crystal film contains any two of a first liquid crystal polymer layer, a second liquid crystal polymer layer, and a third liquid crystal polymer layer, wherein the liquid crystal polymer layer with a smaller pitch is closer to the side of the first retardation film, and the liquid crystal polymer layer with a larger pitch is farther away from the side of the first retardation film.

[0015] Further, in the circular polarizing plate provided by the present invention, the cholesteric liquid crystal film comprises a first liquid crystal polymer layer, a second liquid crystal polymer layer and a third liquid crystal polymer layer, the second liquid crystal polymer layer is adjacent to the side of the first retardation film, the first liquid crystal polymer layer is away from the side of the first retardation film, and the third liquid crystal polymer layer is located between the second liquid crystal polymer layer and the first liquid crystal polymer layer.

[0016] In a second aspect, the present invention provides a display device, comprising the above-mentioned circular polarizing plate and a display substrate.

[0017] Compared with the prior art, the technical solution provided by the present invention at least has the following beneficial effects or advantages: the circular polarizing plate of the present invention comprises a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film and a linear polarizing film. The cholesteric liquid crystal film is used to improve the light extraction efficiency of the display device under normal emission. By reasonably arranging the liquid crystal polymer layers with different pitches, the present invention can realize graded reflection and regulation of light of different wavelengths, reduce light scattering and absorption, so as to optimize the display effect. The present invention additionally provides a first retardation film, which is used to compensate the phase difference value in the thickness direction of the small-pitch liquid crystal polymer layer in the cholesteric liquid crystal film for longer wavelengths (λ<n×P), so as to greatly improve the ellipticity of the outgoing light of the cholesteric liquid crystal film at a large viewing angle; the second retardation film is used for converting circularly polarized light (elliptically polarized light) into linearly polarized light; the third retardation film is used for compensating the phase difference loss of the second retardation film at a large viewing angle, so as to improve the conversion efficiency. The different arrangement order of the multiple retardation films in the structure of the circular polarizing plate of the present invention and the liquid crystal polymer layers with different pitches in the cholesteric liquid crystal film significantly improves the light extraction efficiency and display effect of the display device at different viewing angles, and has broad application prospects. Brief Description of the Drawings

[0018] Figure 1 is a schematic diagram of the brightness enhancement principle of a cholesteric liquid crystal film. Wherein, L is left-handed circularly polarized light; R is right-handed circularly polarized light; S00 is a display substrate; S100 is a cholesteric liquid crystal film.

[0019] Figure 2 is a schematic structural diagram of a circular polarizing plate. Wherein, P1 represents a liquid crystal polymer layer with a pitch of P1; P2 represents a liquid crystal polymer layer with a pitch of P2; S200 is a retardation film; S210 is a first retardation film; S220 is a second retardation film; S230 is a third retardation film; S300 is a linear polarizing film. Detailed Description of the Embodiments

[0020] Hereinafter, the technical solution of the present invention will be described with reference to the embodiments, but the present invention is not limited to the following embodiments. The experimental methods and detection methods described in each embodiment are conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified.

[0021] This invention provides a circular polarizer, which is placed on a display substrate. The circular polarizer includes a cholesteric liquid crystal film, a first phase reversal film, a second phase reversal film, a third phase reversal film, and a linear polarizing film.

[0022] The cholesteric liquid crystal film is located between the display substrate and the first phase reversal film, and the linear polarizing film is located on the side of the third phase reversal film away from the cholesteric liquid crystal film (the first, second and third phase reversal films are located between the cholesteric liquid crystal film and the linear polarizing film, and the arrangement order of the first, second and third phase reversal films can be arbitrary and is not limited).

[0023] The present invention also provides a display device, the display device comprising a display substrate and the aforementioned circular polarizer.

[0024] 1. This invention provides the basic principle of the circular polarizer composition described in this invention.

[0025] 1.1 Cholesteric phase liquid crystal film:

[0026] The cholesteric liquid crystal film modulates light in a wavelength range of at least 440–680 nm, and the cholesteric liquid crystal film is composed of multiple layers of liquid crystal polymers with different pitches. The cholesteric liquid crystal film modulates light in a wavelength range that includes at least two of the following: blue light (440–480 nm), green light (500–580 nm), and red light (600–680 nm). Specifically, the cholesteric liquid crystal film modulates light in a wavelength range that includes both red and green light, or blue and green light, or red, green, and blue light.

[0027] The relationship between the pitch of the liquid crystal polymer layer in the cholesteric liquid crystal film and the wavelength of the modulated light is as follows: n o ×P≤λ≤n e ×P. Where λ is the wavelength of the control light, P is the pitch, and n o n is the refractive index along the optical axis of the liquid crystal polymer layer surface. e denoted as , where is the refractive index of the liquid crystal polymer layer surface perpendicular to the optical axis.

[0028] The relationship between the pitch of the liquid crystal polymer layer in the cholesteric liquid crystal film and the bandwidth of the modulated light wave is as follows: ∆λ=(n e -n o )×P. Where ∆λ is the bandwidth of the controlled optical wave.

[0029] In cholesteric liquid crystal films, the liquid crystal polymer layers used to control a specific color of light have the same helical direction. For example, the liquid crystal polymer layer used to control red light in a cholesteric liquid crystal film is a levorotatory cholesteric liquid crystal polymer layer, while the liquid crystal polymer layer used to control green light can be either a levorotatory or dextrorotatory cholesteric liquid crystal polymer layer. A levorotatory cholesteric liquid crystal polymer layer can reflect levorotatory circularly polarized or elliptically polarized light, which can pass through it.

[0030] The emission optical path diagram of the cholesteric liquid crystal film-controlled display substrate is as follows:

[0031] As shown in Figure 1, the light emitted from the display substrate reaches the cholesteric liquid crystal film. About 50% of the light can pass through the cholesteric liquid crystal film and be converted into left-handed (right-handed) circularly polarized or elliptically polarized light, while the other about 50% of the light is reflected back to the display substrate by the cholesteric liquid crystal film. After being reflected again by the display substrate, it is converted into left-handed (right-handed) circularly polarized or elliptically polarized light, which can then pass through the cholesteric liquid crystal film.

[0032] In the cholesteric liquid crystal film, the pitches of the liquid crystal polymer layers used to control red, green, and blue light are P1, P2, and P3, respectively, where P1 > P2 > P3; the thickness of the liquid crystal polymer layers with different pitches used to control red, green, and blue light is greater than or equal to 3 pitches. For example, the thickness of the liquid crystal polymer layer used to control red light is greater than or equal to 3 * P1, and further, the thickness of the liquid crystal polymer layer is greater than or equal to 5 pitches.

[0033] 1.2 First phase retardation film, second phase retardation film, third phase retardation film

[0034] (1) The first phase difference film is used to compensate for the negative phase difference value in the thickness direction of the liquid crystal polymer layer with a smaller pitch in the cholesteric liquid crystal film for a longer wavelength.

[0035] For example, consider a cholesteric liquid crystal film comprising two liquid crystal polymer layers with pitches P1 and P2 for controlling red and green light. The liquid crystal polymer layer with pitch P2 acts as a negative C phase retardation film relative to red light with a wavelength of 600-680 nm. The thickness of the liquid crystal polymer layer with pitch P2 is d. In one possible application structure, the liquid crystal polymer layer with pitch P1 is closer to the display substrate, while the liquid crystal polymer layer with pitch P2 is located on the side of P1 away from the display substrate. The phase difference value R of the liquid crystal polymer layer with pitch P2 relative to red light in the thickness direction is... th The calculation formula is as follows:

[0036]

[0037] In the above formula, n z denoted as , where is the refractive index of the P2 liquid crystal polymer layer in the thickness direction.

[0038] In one possible application structure, P1 is 412 nm, P2 is 350 nm, the pitch is [missing information], the thickness of the P2 liquid crystal polymer layer is 3 μm, and n [missing information]. o For 1.5, n e It is 1.65, n z Taking a center wavelength of 650nm for red light as an example, with a pitch of 1.5, the phase difference in the thickness direction of the liquid crystal polymer layer with pitch P2 for 650nm red light can be calculated using the above formula as R. th1 It is 225nm.

[0039] The first phase difference film compensates for the aforementioned phase difference value R. th1 The compensation value of the first phase difference film is -225nm.

[0040] In one possible application structure, the liquid crystal polymer layer with pitch P2 is located closer to the display substrate, the liquid crystal polymer layer with pitch P1 is located on the side of P2 away from the display substrate, and the first retardation film is located between P1 and the display substrate. The first retardation film can be located between P1 and P2, or it can be located between P2 and the display substrate.

[0041] (2) The second phase difference film is used for the conversion between circularly polarized light (elliptically polarized light) and linearly polarized light, that is, the in-plane phase difference value R e =(n e -n o )×d=λ / 4. The phase difference value R in the thickness direction of the second phase difference film. th The absolute value is ≤50nm, and further, R th The absolute value is ≤20nm.

[0042] (3) The third phase difference film serves as the viewing angle compensation layer for the second phase difference film, compensating for the phase difference loss of the second phase difference film at large viewing angles.

[0043] In one possible application structure, the first phase difference film and the third phase difference film can be a single phase difference film, whose phase difference in the thickness direction is the sum of the phase difference values ​​of the original first phase difference film and the third phase difference film.

[0044] The in-plane phase difference R between the first and third phase difference films e The absolute value is ≤50nm, and further, R e The absolute value is ≤20nm.

[0045] For example, a cholesteric liquid crystal film structure includes liquid crystal polymer layers with pitches P1, P2, and P3. The arrangement order of P1, P2, and P3 in the thickness direction is not limited. In one possible application, the liquid crystal polymer layer with pitch P1 is closer to the display substrate, the liquid crystal polymer layer with pitch P2 is between P1 and P3, and the liquid crystal polymer layer with pitch P3 is located on the side of P1 away from the display substrate. P1 is 412 nm, P2 is 350 nm, P3 is 290 nm, and the thickness of the P2 liquid crystal polymer layer is 3 μm. o For 1.5, n e It is 1.65, n z Given a pitch of 1.5, a pitch of P3, a liquid crystal polymer layer thickness of 3 μm, and taking a red light center wavelength of 650 nm as an example, the phase difference in the thickness direction between liquid crystal polymer layers with pitches P2 and P3 for 650 nm red light can be calculated using the above formula as R. th1 +R th2 The wavelength is 450nm. Taking the center wavelength of green light as 550nm, the phase difference in the thickness direction of the liquid crystal polymer layer with pitch P3 relative to 550nm is 2×R. th2 The calculated value is 450nm, therefore the phase difference of the first phase difference film in the thickness direction needs to be -450nm.

[0046] 2. This invention also provides a method for preparing a circular polarizer.

[0047] 2.1 Preparation of cholesteric phase liquid crystal film

[0048] In the circular polarizer provided by this invention, the cholesteric liquid crystal film is prepared by coating a liquid crystal mixture onto a substrate layer and then curing it. By mass parts, the liquid crystal mixture comprises: 100-980 parts of a polymerizable liquid crystal monomer, 5-300 parts of a chiral compound, 1-50 parts of a photoinitiator, and 5-800 parts of an organic solvent. The substrate layer is an organic film with a thickness of 5-300 μm. 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 n polymerizable groups, where n ≥ 1. The polymerizable group is one of alkenyl, alkynyl, epoxy, and mercapto groups.

[0049] The specific preparation method of the cholesteric phase liquid crystal film is as follows:

[0050] The first step involves pretreating the substrate layer to improve the adhesion of the cholesteric liquid crystal coating. The pretreatment method can be corona treatment or plasma pretreatment. For example, the substrate layer can be corona treated with a power of 100V*2A and a corona velocity of 2m / min. The substrate layer is preferably an easily wound organic film layer, such as PMMA film, TAC (cellulose triacetate) film, COP film, etc., without specific limitations. The thickness of the substrate layer is 5~300μm, preferably 5~100μm.

[0051] The second step involves preparing a liquid crystal mixture for coating the cholesteric phase liquid crystal film. The raw materials for preparing the liquid crystal mixture are measured in proportion, and by mass fraction, the liquid crystal mixture comprises: 10–98% polymerizable liquid crystal monomers, 0.5–30% chiral compounds, 0.1–5% photoinitiator, and 0.5–80% organic solvent. In some applications, other functional additives such as surfactants and crosslinking agents may be added as needed. The measured liquid crystal mixture is heated to above the phase transition temperature of all polymerizable liquid crystal monomers while stirring until homogeneous. It is then cooled to 10–50°C for coating.

[0052] 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 one of alkenyl, alkynyl, epoxy, and mercapto groups.

[0053] For example, polymerizable liquid crystal monomers containing two or more polymerizable groups include:

[0054] L1: ;

[0055] L2: ;

[0056] L3: ;

[0057] L4: ;

[0058] L5: ;

[0059] L6: ;

[0060] L7: ;

[0061] L8: .

[0062] 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.

[0063] The structure of X1 is as follows: ;

[0064] The structure of X2 is as follows: ;

[0065] The structure of X3 is as follows: ;

[0066] The structure of X4 is as follows: ;

[0067] The structure of X5 is as follows: ;

[0068] The structure of X6 is as follows: ;

[0069] The structure of X7 is as follows: ;

[0070] The structure of X8 is as follows: ;

[0071] The structure of X9 is as follows: ;

[0072] The structure of X10 is as follows: ;

[0073] The structure of X11 is as follows: ;

[0074] The structure of X12 is as follows: ;

[0075] The structure of X13 is as follows: ;

[0076] The structure of X14 is as follows: ;

[0077] The structure of X15 is as follows: ;

[0078] The structure of X16 is as follows: ;

[0079] The structure of X17 is as follows: ;

[0080] The structure of X18 is as follows: ;

[0081] The structure of X19 is as follows: ;

[0082] The structure of X20 is as follows: ;

[0083] The structure of X21 is as follows: .

[0084] 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, 4- The following are one or more of the following: 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.

[0085] [Amended according to Rule 26, April 30, 2026] The solvents are 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, 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, ethylene glycol dimethyl ether, or one or more of the following.

[0086] The third step involves coating the liquid crystal mixture from the second step onto the pretreated substrate layer to a thickness of 100–5000 nm. The organic solvent is then removed by heating at 30–150 °C for 5–1000 s. Finally, the mixture is cured by irradiation at a wavelength of 300–400 nm and an irradiation dose of 1000–200000 J / m². 2 When a cholesteric liquid crystal film is composed of multiple layers of liquid crystal layers with a single pitch, after the first cholesteric liquid crystal coating is prepared and cured, the remaining cholesteric liquid crystal mixtures with different pitches are sequentially coated until all liquid crystal mixtures are coated.

[0087] 2.2 Phase Difference Layer:

[0088] The phase retardation layer can be a stretched phase retardation layer or a coated phase retardation layer. The stretched phase retardation layer can be made of PC or PET materials, while the coated phase retardation layer can be a liquid crystal coated phase retardation layer. For example, the first and third phase retardation films are vertically oriented nematic liquid crystal polymer layers, and the second phase retardation film is a horizontally oriented nematic liquid crystal polymer layer. The second phase retardation film preferably has a material or structure with reverse wavelength dispersibility, for example, it can be prepared by composite coating of multiple nematic liquid crystal polymer layers, where the optical axes of each nematic liquid crystal polymer layer have a certain angle, or the liquid crystal polymer coating is a second phase retardation film prepared by adding a chiral compound, forming an optical axis change in the thickness direction, thereby achieving reverse wavelength dispersibility. A coated liquid crystal second phase retardation film is an example of the reverse wavelength dispersibility phase retardation film prepared in CN117844494A.

[0089] 2.3 Linear polarizing layer:

[0090] The linear polarizing layer can be either an iodine-based polarizing layer or a dye-based polarizing layer, without specific limitations. Iodine-based polarizers include the commercially available SMV-TDA linear polarizing layer from Shengbo Optoelectronics, while dye-based polarizers include the linear polarizing layer prepared in CN117844494A.

[0091] The cholesteric liquid crystal film, the first phase retardation film, the second phase retardation film, the third phase retardation film, and the linear polarizing film can all be bonded together with optical adhesive.

[0092] The light-emitting side of the circular polarizer described in this invention may also include other functional layers, such as an anti-fingerprint layer, an anti-glare layer, and an anti-scratch layer. Example

[0093] This embodiment provides a method for preparing a circular polarizer.

[0094] As shown in Figure 2, the circular polarizer in this embodiment includes: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises two liquid crystal polymer layers with pitches P1 and P2. The liquid crystal polymer layer with pitch P2 is closer to the first retardation film, and the liquid crystal polymer layer with pitch P1 is located on the side of the liquid crystal polymer layer with pitch P2 away from the first retardation film. P1 is 412 nm, P2 is 350 nm, and the thickness of the liquid crystal polymer layer with pitch P2 is 3 μm. o For 1.5, n e It is 1.65, n z Given a pitch of 1.5 and a center wavelength of 650nm for red light, the phase difference in the thickness direction of the liquid crystal polymer layer with pitch P2 for 650nm red light can be calculated using the above formula as R. th1 The wavelength is 225 nm. The arrangement order of the first, second, and third retardation films can be arbitrary, and the R0 of the first retardation film is... th The value is -225nm, which is the in-plane phase difference value R of the second phase retardation film for 550nm light. e The thickness phase difference value R of the third phase retardation film for 550nm light is 137.5nm. th The linear polarizing film is -90nm and is selected from the commercially available Shengbo Optoelectronics SMV-TDA linear polarizing film. Example

[0095] This embodiment provides a method for preparing a circular polarizer.

[0096] This embodiment differs from Embodiment 1 in that the circular polarizer comprises: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises two liquid crystal polymer layers with pitches P2 and P3. The liquid crystal polymer layer with pitch P3 is closer to the first retardation film, and the liquid crystal polymer layer with pitch P2 is located on the side of the liquid crystal polymer layer with pitch P3 away from the first retardation film. P3 is 290 nm, and the thickness of the liquid crystal polymer layer with pitch P2 is 3 μm. o For 1.5, n e It is 1.65, n z Given a pitch of 1.5, a P3 liquid crystal polymer layer thickness of 3 μm, and a green light center wavelength of 550 nm, the phase difference in the thickness direction of the P3 liquid crystal polymer layer relative to 550 nm is 225 nm. The R0 of the first phase difference film... th The value is -225nm. Example

[0097] This embodiment provides a method for preparing a circular polarizer.

[0098] This embodiment differs from Embodiment 1 in that the circular polarizer comprises: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises two liquid crystal polymer layers with pitches P1 and P3. The liquid crystal polymer layer with pitch P3 is closer to the first retardation film, and the liquid crystal polymer layer with pitch P1 is located on the side of the liquid crystal polymer layer with pitch P3 away from the first retardation film. Therefore, the liquid crystal polymer layer with pitch P3 has a phase difference of 225 nm in the thickness direction for 450 nm, and the Ro of the first retardation film... th The value is -225nm. Example

[0099] This embodiment provides a method for preparing a circular polarizer.

[0100] This embodiment differs from Embodiment 1 in that the circular polarizer comprises: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises three liquid crystal polymer layers with pitches P1, P2, and P3. The liquid crystal polymer layer with pitch P2 is close to the first retardation film, the liquid crystal polymer layer with pitch P1 is located on the side of the liquid crystal polymer layer with pitch P2 away from the first retardation film, and the liquid crystal polymer layer with pitch P3 is located between the liquid crystal polymer layers with pitches P1 and P2. The phase difference value of the liquid crystal polymer layers with pitches P2 and P3 for 650nm red light in the thickness direction is calculated using the above formula, resulting in R. th1 +R th2 The wavelength is 450nm. Taking the center wavelength of green light as 550nm, the phase difference in the thickness direction of the liquid crystal polymer layer with pitch P3 relative to 550nm is 2×R. th2 The calculated value is 450nm, and the phase difference of the first phase difference film in the thickness direction is -450nm. Example

[0101] This embodiment provides a method for preparing a circular polarizer.

[0102] This embodiment differs from Embodiment 2 in that the circular polarizer comprises: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises two liquid crystal polymer layers with pitches P3 and P2. The liquid crystal polymer layer with pitch P2 is closer to the first retardation film, and the liquid crystal polymer layer with pitch P3 is located on the side of the liquid crystal polymer layer with pitch P2 away from the first retardation film. Therefore, the liquid crystal polymer layer with pitch P3 has a phase difference of 450 nm in the thickness direction for 550 nm, and the Ro of the first retardation film... th The value is -450nm. Example

[0103] This embodiment provides a method for preparing a circular polarizer.

[0104] This embodiment differs from Embodiment 3 in that the circular polarizer comprises: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises two liquid crystal polymer layers with pitches P3 and P1. The liquid crystal polymer layer with pitch P1 is closer to the first retardation film, and the liquid crystal polymer layer with pitch P3 is located on the side of the liquid crystal polymer layer with pitch P1 away from the first retardation film. Therefore, the liquid crystal polymer layer with pitch P3 has a phase difference of 450 nm in the thickness direction for 650 nm, and the Ro of the first retardation film... th The value is -450nm. Example

[0105] This embodiment provides a method for preparing a circular polarizer.

[0106] The difference between this embodiment and Embodiment 4 is that the circular polarizer includes: a cholesteric liquid crystal film, a first retardation film, a second retardation film, a third retardation film, and a linear polarizing film. The cholesteric liquid crystal film comprises three liquid crystal polymer layers with pitches P3, P2, and P1. The liquid crystal polymer layer with pitch P3 is close to the first retardation film, the liquid crystal polymer layer with pitch P1 is located on the side of the liquid crystal polymer layer with pitch P3 away from the first retardation film, and the liquid crystal polymer layer with pitch P2 is located between the liquid crystal polymer layers with pitches P1 and P3. The phase difference value of the liquid crystal polymer layers with pitches P2 and P3 for 650nm red light in the thickness direction is calculated using the above formula, resulting in R. th1 +R th2 The wavelength is 450nm. Taking the center wavelength of green light as 550nm, the phase difference in the thickness direction of the liquid crystal polymer layer with pitch P3 relative to 550nm is R. th2 The calculated value is 225 nm. The phase difference of the first phase retardation film in the thickness direction is -337 nm.

[0107] Comparative Example 1

[0108] This comparative example provides a circular polarizer.

[0109] The difference between this comparative example and Example 1 is that the circular polarizer includes: a cholesteric liquid crystal film, a second phase reversal film, a third phase reversal film, and a linear polarizing film. The cholesteric liquid crystal film includes two liquid crystal polymer layers with pitches of P1 and P2. The liquid crystal polymer layer with pitch P2 is closer to the second phase reversal film, and the liquid crystal polymer layer with pitch P1 is located on the side of the liquid crystal polymer layer with pitch P2 away from the second phase reversal film.

[0110] Comparative Example 2

[0111] This comparative example provides a circular polarizer.

[0112] The circular polarizer described in this comparative example includes: a cholesteric liquid crystal film, a second retardation film, a third retardation film and a linear polarizing film, wherein the cholesteric liquid crystal film comprises two layers of liquid crystal polymers with pitches of P2 and P1, the liquid crystal polymer layer with a pitch of P1 is adjacent to the second retardation film, and the liquid crystal polymer layer with a pitch of P2 is located on the side of the liquid crystal polymer layer with a pitch of P1 away from the second retardation film. Examples

[0113] This example provides a display device.

[0114] The display device described in this example includes a circular polarizer and a display substrate.

[0115] When measuring the light extraction efficiency of Examples 1 to 8 and Comparative Examples 1 to 2 at different viewing angles, the circular polarizer is attached to the display panel. The wavelengths of light emitted from the display substrate include blue light with a central wavelength of 450nm, green light with a central wavelength of 550nm, and red light with a central wavelength of 650nm. The light power and the light extraction brightness at different viewing angles are measured, with the unit being nit, and the test results are shown in Table 1.

[0116] Table 1 Light extraction efficiency of the display device at different viewing angles

[0117]

[0118] In the present invention, the first retardation film is used to compensate the retardation in the thickness direction of the cholesteric liquid crystal film, so as to improve the light transmittance and polarization state; the second retardation film is used for the conversion between linearly polarized light and circularly polarized light (elliptically polarized light); the third retardation film serves as a viewing angle compensation layer, which broadens the in-plane retardation value of the second retardation film at a large viewing angle, and improves the conversion efficiency between linearly polarized light and circularly polarized light (elliptically polarized light) at a large viewing angle. Since Example 1 includes the first retardation film, it can compensate the retardation value in the thickness direction of the small-pitch liquid crystal polymer layer in the cholesteric liquid crystal film for longer wavelengths (λ<n×P), that is, the first retardation film compensates the R in the thickness direction of the liquid crystal polymer layer with a pitch of P2 for light with a wavelength of 650nm th value, so as to maintain more stable light extraction brightness at different viewing angles. However, since Comparative Example 1 lacks the first retardation film, the cholesteric liquid crystal film has a large retardation variation for red light at a large viewing angle, which leads to a decrease in light extraction brightness.

[0119] In cholesteric liquid crystal films, liquid crystal molecules are arranged in a periodic helical pattern, and the pitch of these helical molecules determines the center wavelength of the reflected light. Liquid crystal polymer layers with different pitches can reflect light of different wavelengths. The different pitch arrangements of the liquid crystal polymers in Comparative Examples 1 and 2 result in different propagation paths and phase differences of light within the liquid crystal polymer layers, thus affecting the emitted brightness at different viewing angles. In Comparative Example 1, the P1 layer with a larger pitch is closer to the substrate, while the P2 layer with a smaller pitch is farther away. The emitted light first passes through the P1 layer and then through the P2 layer. The emitted red light only passes through the P2 layer once, resulting in a smaller phase difference in the thickness direction. In Comparative Example 2, the P2 layer with a smaller pitch is closer to the substrate, while the P1 layer with a larger pitch is farther away. The emitted light first passes through the P2 layer and then through the P1 layer. In this case, the thickness of the red light reflected back to the display substrate by the P1 layer and then reflected again is twice that of Comparative Example 1. The phase difference caused by the P2 layer is larger, resulting in lower light emission efficiency. Therefore, by rationally arranging liquid crystal polymer layers with different pitches, it is possible to achieve graded reflection and control of light of different wavelengths, reducing light scattering and absorption. In the cholesteric phase film with two pitches in this invention, the liquid crystal polymer layer with the smaller pitch is preferably located on the side closer to the first retardation film, and the liquid crystal polymer layer with the larger pitch is located on the side farther away from the first retardation film. In the cholesteric phase film with three pitches in this invention, considering the phase difference value in the thickness direction for different light wavelengths, it is preferred that the P1 pitch liquid crystal polymer layer is located on the side farther away from the first retardation film, the P2 pitch liquid crystal polymer layer is located on the side closer to the first retardation film, and the P3 pitch liquid crystal polymer layer is located between the P1 pitch liquid crystal polymer layer and the P2 pitch liquid crystal polymer layer.

[0120] The embodiments described above are some, but 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 selected embodiments of the invention. 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 circular polarizer, wherein the circular polarizer is disposed on a display substrate, characterized in that, The circular polarizer includes a cholesteric liquid crystal film, a first phase reversal film, a second phase reversal film, a third phase reversal film, and a linear polarizing film; The cholesteric liquid crystal film is located between the display substrate and the first phase reversal film; the linear polarizing film is located on the side of the third phase reversal film away from the cholesteric liquid crystal film. The first phase difference film, the second phase difference film, and the third phase difference film are located between the cholesteric liquid crystal film and the linear polarizing film.

2. The circular polarizer according to claim 1, characterized in that, The cholesteric liquid crystal film includes at least two of the following: a first liquid crystal polymer layer for regulating red light, a second liquid crystal polymer layer for regulating green light, and a third liquid crystal polymer layer for regulating blue light. The pitch of the first liquid crystal polymer layer is P1, the pitch of the second liquid crystal polymer layer is P2, and the pitch of the third liquid crystal polymer layer is P3, where P1>P2>P3.

3. The circular polarizer according to claim 2, characterized in that, The red light refers to light with a wavelength of 600~680nm, the green light refers to light with a wavelength of 500~580nm, and the blue light refers to light with a wavelength of 440~480nm.

4. The circular polarizer according to claim 3, characterized in that, The first phase difference film is used to compensate for the negative phase difference in the thickness direction of the liquid crystal polymer layer with a smaller pitch in the cholesteric liquid crystal film for a longer wavelength.

5. The circular polarizer according to claim 1, characterized in that, The second phase difference film is used for the conversion between circularly polarized or elliptically polarized light and linearly polarized light; The third phase difference film is used to compensate for the phase difference loss of the second phase difference film at a viewing angle of 30° to 80°.

6. The circular polarizer according to claim 1, characterized in that, The first phase difference film, the second phase difference film, and the third phase difference film can be arranged in any order.

7. The circular polarizer according to claim 2, characterized in that, The first liquid crystal polymer layer, the second liquid crystal polymer layer, and the third liquid crystal polymer layer in the cholesteric phase liquid crystal film are arranged in order of pitch.

8. The circular polarizer according to claim 7, characterized in that, The cholesteric liquid crystal film contains any two of the following: a first liquid crystal polymer layer, a second liquid crystal polymer layer, and a third liquid crystal polymer layer. The liquid crystal polymer layer with a smaller pitch is closer to the first phase reversal film, while the liquid crystal polymer layer with a larger pitch is farther away from the first phase reversal film.

9. The circular polarizer according to claim 7, characterized in that, The cholesteric liquid crystal film contains a first liquid crystal polymer layer, a second liquid crystal polymer layer and a third liquid crystal polymer layer. The second liquid crystal polymer layer is close to the first phase reversal film, the first liquid crystal polymer layer is far from the first phase reversal film, and the third liquid crystal polymer layer is located between the second liquid crystal polymer layer and the first liquid crystal polymer layer.

10. A display device, characterized in that, It includes the circular polarizer and display substrate as described in any one of claims 1 to 9.

Images