A functional film capable of improving the viewing angle of liquid crystal display devices

Abstract

An optical functional film for improving the viewing angle of a liquid crystal display device, comprising a substrate layer and an optical structure layer formed on the substrate layer. By attaching the optical functional film to the front polarizer of a liquid crystal display using OCA tape, the problem of insufficient viewing angle of existing liquid crystal displays can be improved. At the same time, the problem of a significant decrease in the center contrast of the liquid crystal display at a normal viewing angle caused by attaching the optical functional film can also be suppressed.

Description

Technical Field

[0001] The present invention relates to the technical field of optical films, in particular to an optical functional film that can be attached to the outer side of a proximal polarizer of an existing liquid crystal display device to improve the viewing angle and picture effect of the liquid crystal display. Background Art

[0002] With the popularization of digital campuses and smart offices, the demand for interactive flat panels (IFPD) that integrate touch interaction and high-definition LCD displays is experiencing explosive growth. Different from home use environments (living rooms, bedrooms), LCD displays suitable for open use environments such as classrooms and conference rooms have differentiated performance requirements for optical indicators, such as center brightness and contrast, brightness viewing angle, etc. In response to classroom environments, the National Health Commission promulgated the national standard "Hygiene Requirements for Myopia Prevention and Control of Children and Adolescents' Learning Supplies" in 2021 and implemented it in 2022. It clarified the display technology requirements for teaching multimedia products (TV video display systems): 1. Horizontal brightness viewing angle > 120°, vertical brightness viewing angle > 60°; 2. Brightness contrast ≥ 1000:1; 3. The screen brightness range of teaching multimedia products is 300-400cd / m 2 For conference scenarios, as the number of viewers decreases, the IFPD does not need to have a 120° horizontal brightness viewing angle. It is necessary to improve the brightness at the side viewing angle while maintaining the center brightness contrast and chromaticity viewing angle as much as possible to maintain the image quality of the LCD display at the center and near-center viewing angles.

[0003] CN201910090524.7 discloses an optical film and display device. The refractive index of the isotropic optical layer of the optical film is lower than the ordinary light refractive index of the uniaxial anisotropic optical layer, and the width of the protrusion structure is within the wavelength range of the incident light. When light passes through the intersection of the groove and the protrusion structure, it will produce a diffraction effect, so that the energy distribution of the normal viewing angle light type is wide, and the color deviation of the viewing angle is improved.

[0004] CN201910090545.9 discloses an optical film and a display device. The optical film includes a first uniaxial optical layer and a second uniaxial optical layer, wherein the ordinary light refractive index of the second uniaxial optical layer is less than the extraordinary light refractive index of the first uniaxial optical layer, and the width of the raised structure is within the wavelength range of the incident light.

[0005] Although the above technologies can improve the color shift problem at lateral viewing angles to a certain extent, they cannot significantly increase the brightness of the liquid crystal display at a specific lateral viewing angle.

[0006] CN202222583913.3 discloses a wide-viewing angle functional film for VA panel polarizer, comprising a low-reflection surface treatment layer, a viewing angle expansion layer and an adhesive layer distributed layer by layer, wherein the low-reflection surface treatment layer and the viewing angle expansion layer are respectively formed on both sides of a first super retardation polyethylene terephthalate substrate, and one end of the adhesive layer facing away from the viewing angle expansion layer is attached to a second super retardation polyethylene terephthalate substrate, and a polyvinyl alcohol film and an optical compensation film are sequentially bonded to the side of the second super retardation polyethylene terephthalate substrate facing away from the adhesive layer, and a pressure-sensitive adhesive is coated on the side of the optical compensation film facing away from the polyvinyl alcohol film.

[0007] The above technology focuses on the integration of a wide-viewing angle functional film onto an outer polarizer. While it demonstrates that the addition of a wide-viewing angle film improves the brightness and chromaticity of the LCD display at lateral viewing angles, it does not provide actual data on the improvement in brightness, chromaticity, and contrast performance of the LCD display before and after viewing. Considering that the center brightness of the LCD display at normal viewing angles will be reduced after the wide-viewing angle film is applied, and that the contrast will be further attenuated due to the compensation of lateral viewing angle light to the normal viewing angle light, how to optimize the LCD display to have a more reasonable brightness viewing angle, chromaticity viewing angle, and contrast viewing angle, while suppressing the negative effects of integrating or applying a wide-viewing angle film on the LCD display, is an issue that needs to be considered and resolved urgently.

[0008] CN202210615752.3 discloses a wide-viewing angle polarizer, a manufacturing method thereof, and a display device. The manufacturing method of the wide-viewing angle polarizer includes: providing a polarizing film layer; forming a wide-viewing angle functional film layer on one side of the polarizing film layer, and a first light is incident from the polarizing film layer and then emitted through the wide-viewing angle functional film layer to obtain a second light, and the viewing angle of the second light is greater than that of the first light.

[0009] The above technology focuses on optimizing and improving the problem of thick thickness of thinned integrated wide-viewing angle functional polarizer, and does not optimize and improve the optical design of the wide-viewing angle film itself to improve the LCD display's more balanced optical performance, that is, to improve the LCD display's brightness viewing angle, contrast viewing angle and chromaticity viewing angle to adapt to scene requirements, while minimizing the negative effects on the LCD display caused by the wide-viewing angle film.

[0010] It is known that the solution to improve the brightness at side viewing angles can be achieved through special viewing angle improvement films. Its characteristics are a symmetrical unit optical structure with two layers of UV resin with different refractive indices. Figure 1As shown, when light 1 is refracted through the low-refractive index resin layer into the high-refractive index resin layer, and further refracted from the high-refractive index resin layer to the air layer, the light 1 emitted from the center is deflected twice and emitted toward the side viewing angle, thereby increasing the brightness at the side viewing angle and improving the chromaticity and viewing angle of the liquid crystal display. At the same time, light 2 originally emitted from the side viewing angle is refracted through the low-refractive index resin layer toward the center viewing angle, which will cause a decrease in the center brightness contrast. Further, as Figure 2 As shown, when light 3 is incident from the high refractive index resin layer to the low refractive index resin layer, the central light 3 greater than the critical incident angle will be totally reflected at the trapezoidal hypotenuse, and after reaching the upper platform of the trapezoid, it will be refracted toward the low refractive index resin and then emitted, and further emitted through the interface between the low refractive index resin and the air. Unlike light 1 that is incident from the low refractive index resin to the high refractive index resin and then emitted, light 3 that is incident from the low refractive index resin to the high refractive index resin and then emitted (1 total reflection, 2 refractions) will be deflected to a larger side viewing angle, thereby improving the brightness and chromaticity of the liquid crystal display at side viewing angles (the viewing angle is 20°). Figure 2 ). Furthermore, the color deviation inflection point appears at a more outer viewing angle in the color deviation viewing angle curve, so the color deviation value transition process is not easy to be perceived. However, in terms of center contrast, Figure 2 The figure shows that the light 4 originally deflected to a larger viewing angle is refracted by the high and low refractive index resin layers and then emitted to the normal viewing angle, causing a greater loss of central contrast. How to reduce the loss of central contrast is an urgent problem to be solved in this optical design solution. Summary of the Invention

[0011] In order to solve the problems of low brightness viewing angle and insufficient side viewing angle contrast ratio in existing liquid crystal displays, the present invention provides an optical functional film. By attaching the optical functional film to the front polarizer (Front Polarizer) of the liquid crystal display using OCA tape, the problem of insufficient viewing angle of the existing liquid crystal display can be improved. At the same time, the problem of a significant decrease in the center contrast ratio of the liquid crystal display at the front viewing angle due to the attachment of the optical functional film can be suppressed.

[0012] In order to solve the problems of the prior art, the present invention provides an optical functional film that can be used to improve the viewing angle of a liquid crystal display device, wherein the viewing angle of the liquid crystal display device includes brightness viewing angle, contrast viewing angle and chromaticity viewing angle.

[0013] The present invention first provides an optical functional film for improving the viewing angle of a liquid crystal display device, wherein the optical functional film comprises a substrate layer and an optical structure layer formed on the substrate layer;

[0014] The optical structure layer includes: a first resin layer 1 with a refractive index of N1 adjacent to the substrate layer, which includes a plurality of isosceles trapezoidal patterns and flat portions (Gap, in micrometers) between adjacent isosceles trapezoidal patterns, wherein the flat portions between a single isosceles trapezoidal pattern and its adjacent isosceles trapezoidal patterns constitute a unit period (Pitch, in micrometers); and a second resin layer 2 with a refractive index of N2, which is directly formed on the flat portions above the patterns and between adjacent patterns in the patterned resin layer 1;

[0015] The refractive index N1 of the first resin layer 1 is greater than the refractive index N2 of the second resin layer 2 .

[0016] Furthermore, the substrate layer is triacetate (TAC), super retardation film (SRF), cycloolefin (COP), polyethylene terephthalate (PET), etc.

[0017] Furthermore, the thickness of the substrate layer is 50-500um, or 450um, 300um, 250um, 188um, 125um, 100um, 80um, and more preferably 125um, 100um and 80um.

[0018] Furthermore, the first resin layer 1 is one or more of polyacrylic resin, polyester acrylate, polyurethane acrylate copolymer or curable polymers modified therefrom.

[0019] Furthermore, the first resin layer 2 is one or more of polyacrylic resin, polyester acrylate, polyurethane acrylate copolymer or curable polymers modified therefrom.

[0020] Furthermore, the base angle value of the isosceles trapezoidal pattern of the first resin layer 1 is θ, in degrees, preferably 70.0° to 80.0°, further, preferably the base angle is 73.0° to 75.0°, or 72.0°, 74.0°, 76.0°, or 78.0°.

[0021] Furthermore, the upper platform width of the isosceles trapezoidal pattern of the first resin layer 1 is a, and the lower platform width is b, both in micrometers, wherein the upper platform width is preferably 4.0-6.5um, further preferably 4.5-6.0um, or 4.3um, 4.8um, 5.0um, 5.5um, 5.8um; the depth of the trapezoid is h, in micrometers; the ratio of the depth of the trapezoid to the lower platform is defined as the aspect ratio h / b, preferably 0.8-1.2, further preferably 0.9-1.0, or 0.85, 0.95; the flat part between adjacent trapezoidal structures is defined as the spacing c, in micrometers; the width between adjacent repeating unit trapezoidal structures is defined as the period p, in micrometers; the aperture ratio represents the proportion of the flat part between adjacent trapezoidal structures in the entire unit period c / p, preferably 10.0% to 30.0%, further preferably 16.0% to 25.0%, or 14.0%, 18.0%, 20.0%, 28.0%.

[0022] Among them, the refractive index N1 of the resin layer 1 ranges from 1.60 to 1.69, further, preferably 1.60-1.65, or 1.63, 1.66, or 1.67; the refractive index N2 of the resin layer 2 ranges from 1.43 to 1.55, further, preferably 1.48-1.52, or 1.44, 1.49, or 1.50; the refractive index difference ΔN(N1-N2) between the resin layers 1 and 2 ranges from 0.05 to 0.21; further, preferably 0.10 to 0.15, or 0.08, 0.12, or 0.18.

[0023] The present invention also provides a method for preparing an optical functional film for improving the viewing angle of a liquid crystal display device, comprising:

[0024] Step 1, forming a mold structure on a substrate;

[0025] Step 2: Add the liquid resin of the first resin layer to the substrate, adhere it to the substrate, and form a sandwich sealing structure;

[0026] Step 3: solidifying the resin of the first resin layer and peeling off the substrate to obtain a semi-finished unit optical structure arranged along a two-dimensional anti-glare periodic pattern, wherein the unit optical structure is an isosceles trapezoid and a flat portion of an adjacent isosceles trapezoid;

[0027] Step 4, adding the resin of the liquid second resin layer onto the first resin layer of the semi-finished product, covering the release film or substrate to form a sandwich structure;

[0028] Step 5: solidify the second resin layer and the glass release film or substrate to obtain a functional film.

[0029] Furthermore, in step 1, a mold structure is formed by engraving, and the substrate is a nickel plate. Furthermore, a mold structure of a suitable size is engraved on the nickel plate using a diamond tool.

[0030] Furthermore, in step 2, the liquid resin of the first resin layer is dripped onto the substrate.

[0031] Furthermore, in step 2, the substrate is a sheet.

[0032] Furthermore, in step 3, the first resin layer is subjected to air bubble removal, and the curing is performed by UV ray irradiation curing.

[0033] Furthermore, in step 4, the liquid resin of the second resin layer is dripped onto the first resin layer.

[0034] Furthermore, in step 4, the release film or substrate is mirror-smooth.

[0035] Furthermore, in step 4, the release film is a frosted release film.

[0036] Furthermore, in step 4, the substrate is a nickel plate, and further, the substrate is a nickel plate polished with glass sand beads.

[0037] Furthermore, in step 5, the second resin layer is subjected to air bubble removal, and the curing is performed by UV ray irradiation curing.

[0038] Furthermore, in step 6, an OCA adhesive layer is prepared on the non-optical structure side of the functional film to obtain a functional film sample with adhesive backing.

[0039] According to another aspect of the present invention, a liquid crystal display device with improved viewing angle may include: a liquid crystal display device and an optical film fixed on its front end polarizer for improving viewing angle, and the fixing method may be full bonding using frame bonding, water glue (LOCA) or optical grade transparent glue (OCA).

[0040] The optical functional film provided by the present invention for improving the viewing angle can increase the brightness value of the liquid crystal display at the side viewing angle (the side viewing angle refers to the viewing angle corresponding to a deviation from the front viewing angle greater than or equal to 45°), thereby improving the brightness viewing angle of the liquid crystal display, while minimizing the decrease in the center brightness of the liquid crystal display at the front viewing angle caused by the bonding of the optical functional film.

[0041] The optical functional film for improving viewing angle of the present invention can improve the chromaticity value of a liquid crystal display at a side viewing angle, enhance the chromaticity viewing angle of the liquid crystal display, and further enhance the image quality of the liquid crystal display.

[0042] The optical functional film provided by the present invention for improving viewing angles can deflect central light rays with high brightness contrast toward side viewing angles through the optical microstructure layer, thereby improving the brightness contrast of a liquid crystal display at side viewing angles. Furthermore, it only allows a portion of light rays near the front viewing angle to be deflected toward the front viewing angle, thereby significantly reducing the reduction in the central contrast of the liquid crystal display at the front viewing angle caused by the application of the optical functional film. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 .The light path orientation when the light emitted from the liquid crystal display device passes through the low refractive index resin layer and enters the high refractive index resin layer.

[0044] Figure 2 .The light path orientation when the light emitted from the liquid crystal display device passes through the high refractive index resin layer and enters the low refractive index resin layer.

[0045] Figure 3A .Schematic diagram of semi-finished product (side view).

[0046] Figure 3B .Schematic diagram of semi-finished product (top view).

[0047] Figure 4A .A viewing angle-improving film with a low-refractive-index resin layer and a smooth surface.

[0048] Figure 4B .A viewing angle improving film having a low refractive index resin layer with a certain degree of roughness on its surface.

[0049] Figure 5A .Schematic diagram of a viewing angle improvement film with a low refractive index resin layer having a flat surface attached to a liquid crystal display device.

[0050] Figure 5B .Schematic diagram of a viewing angle improvement film with a low refractive index resin layer having a certain degree of roughness attached to a liquid crystal display device.

[0051] Figure 6A .Schematic diagram of a viewing angle improvement film with a low refractive index resin layer having a flat surface attached to a liquid crystal display device.

[0052] Figure 6B .Schematic diagram of a viewing angle improvement film with a low refractive index resin layer having a certain degree of roughness attached to a liquid crystal display device.

[0053] 01. Viewing angle improvement film

[0054] 01-a. A viewing angle improving film

[0055] 01-b. Another viewing angle improvement film

[0056] 03. High refractive index resin layer

[0057] 04. Low refractive index resin layer

[0058] 04-a, low refractive index resin layer with smooth surface

[0059] 04-b, low refractive index resin layer with a certain surface roughness

[0060] 05. Adhesive layer

[0061] 06. Liquid crystal display devices

[0062] 07. Release film

[0063] 101. Interface between high refractive index resin layer and air layer

[0064] 102. Trapezoidal inclined edge (interface between high and low refractive index resin layers)

[0065] 103. Flat portion between adjacent trapezoidal unit structures (interface between high and low refractive index resin layers)

[0066] 104. Interface between substrate and low refractive index resin layer

[0067] 105. Interface between low refractive index resin layer and air layer

[0068] 106. Trapezoidal upper platform (interface between high and low refractive index resin layers)

[0069] 107. Trapezoidal inclined edge (interface between high and low refractive index resin layers)

[0070] 108. Flat portion between adjacent trapezoidal unit structures (interface between high and low refractive index resin layers) 109. Interface between substrate and high refractive index resin layer

[0071] 110. Light emission interface

[0072] 111. Light incident interface

[0073] 112. The near side of the polarizer of the liquid crystal display device

[0074] a. Trapezoidal upper platform

[0075] b. Trapezoidal lower platform

[0076] c. Flat portion between adjacent trapezoidal unit structures

[0077] h. Trapezoidal depth

[0078] p. Period of ladder unit structure

[0079] θ. Bottom angle of the trapezoidal unit structure DETAILED DESCRIPTION

[0080] In order to make it easier to understand the structure of the present invention and the functional features and advantages that can be achieved, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings:

[0081] like Figure 1 As shown, when the light 1 is incident on the low-refractive index resin layer 2 and refracted to the high-refractive index resin layer 1, it will be refracted once on the interface 102 and the interface 101 in sequence, so that the light 1 originally emitted from the central viewing angle can be deflected to the wide viewing angle, thereby improving the brightness and contrast at the wide viewing angle. At the same time, this also causes the brightness at the central viewing angle to attenuate.

[0082] Furthermore, the light 2 originally emitted toward a wide viewing angle will be refracted once on interfaces 104 and 103 in turn, and after undergoing total reflection once on interface 102, it will be collimated and emitted through interface 101. This part of the light can be used to compensate for the central brightness attenuation caused by the deflection of the light 1 itself. However, since the brightness contrast of this part of the light itself is low, the contrast in the center of the LCD screen will be reduced.

[0083] like Figure 2 As shown, when the light 3 is refracted from the high-refractive index resin layer 1 to the low-refractive index resin layer 2, the collimated incident light 3 will undergo a total reflection on the interface 107, and then be refracted twice on the interface 106 and the interface 105 before being emitted at a wide viewing angle, thereby improving the brightness and contrast of the liquid crystal screen at a wide viewing angle. At the same time, this will cause the central brightness to attenuate.

[0084] Furthermore, light 4 originally emitted at a wide viewing angle undergoes two refractions at interfaces 109 and 107, before being collimated and emitted from interface 105 to compensate for some of the light 3 lost due to deflection, thus reducing central light loss. Similarly, because the original brightness contrast of the light emitted at a wide viewing angle is low, this portion of the emitted light causes a decrease in the contrast at the center of the LCD screen after the functional film is applied.

[0085] Regardless of whether the light is incident from the high-refractive-index resin layer to the low-refractive-index resin layer or from the low-refractive-index resin layer to the high-refractive-index resin layer, the light at a large viewing angle will be deflected and emitted toward the central viewing angle, thus causing a decrease in the center contrast of the LCD screen after the functional film is attached to varying degrees.

[0086] Table 1 shows the deflection pattern of light when it passes through high-refractive-index resin layer 1 and enters low-refractive-index resin layer 2. Specifically, the high- and low-refractive-index resins are composed of one or more of polyacrylic resins, polyester acrylates, polyurethane acrylate copolymers, or curable polymers modified therefrom. For example, with a high-refractive-index resin layer with a refractive index of RI1 = 1.67 and a low-refractive-index resin with a refractive index of RI2 = 1.50, as the lower base angle of the trapezoid decreases from 86.0° to 70.0°, the incident angle of light 2 gradually increases from 13.5° to total reflection, causing the contrast at the center of the screen to gradually decrease. Unlike the previous example, when light 4 passes through high-refractive-index resin layer 1 and enters low-refractive-index resin layer 2, as the lower base angle of the trapezoid decreases from 86.0° to 70.0°, the incident angle of light 4 gradually decreases from 39.3° to 21.1°. This means that the contrast reduction at the center of the LCD screen with the functional film applied will gradually decrease. Note that when the trapezoidal angle is greater than or equal to 81.0°, the light path preferably enters through the low-refractive-index resin layer and exits through the high-refractive-index resin layer, minimizing the adverse effect of reduced central contrast caused by the original wide-viewing angle light being deflected toward the center. When the trapezoidal angle is less than 80.0°, as the lower base angle of the trapezoid decreases, the incident angle of the light corresponding to the deflection toward the center gradually decreases, which helps improve the center contrast of the screen.

[0087] Furthermore, if Figure 1 As shown, when the optical light is incident from the low refractive index resin layer to the high refractive index resin layer, the collimated incident light 1 is deflected and emitted to the side angle through two refractions at the interfaces 102 and 101. Table 2 shows the change pattern of the emission angle of light 1 as the base angle of the trapezoid changes. When the trapezoid angle is 86.0°, the emission angle of the light emitted from the interface 101 is 39.4°. As the base angle of the trapezoid decreases to 81.0, the emission angle of the light emitted from the interface 101 decreases to 32.0°. Therefore, for the light incident from the low refractive index resin to the high refractive index resin layer, the trapezoid angle is in the range of 86.0 to 81.0°. As the trapezoid angle decreases, the emission angle of the collimated incident light 1 also decreases. As shown Figure 2As shown in Table 2, the collimated incident light 3 incident from the high-refractive-index resin layer to the low-refractive-index resin layer is totally reflected once by interface 107, and refracted twice by interface 106 and interface 105, so as to be deflected to a larger lateral viewing angle. As shown in Table 2, when the lower base angle of the trapezoid is 80.0°, the angle of exit of the light emitted from interface 105 is 33.6°. As the lower base angle of the trapezoid decreases from 80.0° to 71.0°, the angle of exit of light 3 gradually increases from 33.6° to 85.8°. When the bottom angle of the trapezoid decreases to 70.0°, light 3 is totally reflected at interface 105 (greater than the critical angle) and cannot be emitted from interface 105. Among them, the national standard "40070-2021 Hygiene Requirements for Myopia Prevention and Control of Children and Youth Learning Supplies" stipulates that liquid crystal display devices suitable for classroom environments must have a brightness viewing angle greater than 120° (1 / 3 of the center brightness is used as the threshold). In addition, considering that the light corresponding to the output angle greater than 70° is basically invalid light. Considering the actual use environment, the optimal output angle of the light that compensates for the side viewing angle is 50 to 70 degrees, and more preferably 55 to 65 degrees. Therefore, the preferred light path is incident from the high-refractive-index resin layer to the low-refractive-index resin layer, with the base angle of the trapezoid preferably being 73.0 to 75.0 degrees.

[0088] Table 1. Incident angles of light rays incident from resin layer 1 to resin layer 2 and incident from resin layer 2 to resin layer 1.

[0089]

[0090]

[0091] Note: The refractive index of resin layer 1 is 1.67, and the refractive index of resin layer 2 is 1.50

[0092] Table 2. Effect of the trapezoidal base angle on the angle of the incident collimated light from resin layer 2 to resin layer 1.

[0093] Trapezoid base angle (°) Incident angle at interface 1 (°) Outgoing angle of interface 1 (°) 86.0 22.4 39.4 85.0 21.5 37.8 84.0 20.7 36.2 83.0 19.9 34.7 82.0 19.2 33.3 81.0 18.5 32.0

[0094] Table 3. The influence of the trapezoidal base angle on the angle of the incident collimated light from resin layer 1 to resin layer 2.

[0095] Trapezoid base angle (°) Incident angle of interface 5 (°) Outgoing angle of interface 1 (°) 80.0 20.0 34.8 79.0 22.0 38.7 78.0 24.0 47.1 77.0 26.0 51.6 76.0 28.0 49.5 75.0 30.0 56.6 74.5 31.0 59.3 74.0 32.0 62.2 73.5 33.0 65.4 73.0 34.0 69.0 72.0 36.0 79.0 71.0 38.0 The incident angle is greater than the critical angle of interface 1 (41.8°) 70.0 40.0 The incident angle is greater than the critical angle of interface 1 (41.8°)

[0096] Note: The above experimental results show that the angle of incidence = arcsin[N RI1 *sin(α) / N air ], where N RI1 =1.67, N air =1.0, α=the incident angle of the interface 5.

[0097] As shown in Table 4, for different trapezoidal base angles, when light 3 is refracted into the low-refractive-index resin layer 2 through the high-refractive-index resin layer 1, light 3 will undergo one total internal reflection and two refractions in sequence, and will be deflected and emitted from the interface 105 toward the side viewing angle. For a fixed trapezoidal base angle, as the refractive index of the high-refractive-index resin layer increases, the angle of deflection toward the side viewing angle increases. For a high-refractive-index resin layer with a fixed refractive index, as the trapezoidal base angle decreases, the angle of deflection toward the side viewing angle increases. As mentioned above, considering practical applications, the optimal output viewing angle of the light compensating for the side viewing angle is 50 to 70°, and a viewing angle of 55 to 65° is further preferred.

[0098] Furthermore, as shown in Table 5, for different trapezoidal base angles, when light 4 enters the high-refractive-index resin layer 1 and exits the low-refractive-index resin layer, the incident angle of light 4 gradually decreases as the refractive index of the high-refractive-index resin layer 1 decreases. For high-refractive-index resin layers with the same refractive index, the incident angle of light also shows a consistent downward trend as the trapezoidal base angle decreases. Therefore, lowering the refractive index of the high-refractive-index resin layer 1 can help achieve higher contrast in liquid crystal display devices after laminating the functional film.

[0099] Table 4. Variation of the exit angle of the collimated incident light 3 with changes in the base angle of the trapezoid and the refractive index of the resin layer 1.

[0100]

[0101] Note: The angle of incidence of ray 3 = arcsin{N RI1 *sin[2*(90-θ)]}, where nRI is the refractive index of the resin layer 1, and θ is the base angle of the trapezoid.

[0102] Table 5. Incident angle requirements for the collimated light 4 emitted from the interface 1 as the refractive index of the resin layer 1 changes.

[0103]

[0104]

[0105] Based on the analysis of the results in Tables 4 and 5, it is known that when the refractive index of the high-refractive-index resin is in the range of 1.60 to 1.67, considering that the deflection viewing angle of light 3 is preferably in the range of 50.0 to 70.0°, the trapezoidal base angle is preferably in the range of 76.0 to 72.0°. Furthermore, considering that the deflection viewing angle of light 3 is preferably in the range of 55.0 to 65.0°, the trapezoidal base angle is preferably in the range of 75.0 to 73.0°. Furthermore, considering the incident angle of light 4, for the same trapezoidal base angle, it is preferred that resin layer 1 have a lower refractive index to prevent light with a larger side angle from being emitted from the center, resulting in a significant reduction in the center brightness contrast at a normal viewing angle of the LCD screen fitted with the viewing angle-enhancing functional film.

[0106] Sample preparation and testing steps:

[0107] Functional membrane sample preparation steps:

[0108] Step 1: Carve a mold structure of appropriate size on a nickel plate using a diamond cutter;

[0109] Step 2: Using a dropper, take a suitable amount of UV-curable liquid high-refractive index resin 1, drop it onto the nickel plate, and then attach it to the cut substrate sheet to form a sandwich sealing structure;

[0110] Step 3: After fully removing the bubbles in the resin, the liquid high-refractive-index resin 1 is irradiated with UV rays of a certain energy from one side of the substrate to complete the light-curing process. The nickel plate is then peeled off to obtain a semi-finished product with unit optical structures (isosceles trapezoids and flat portions between adjacent isosceles trapezoids) periodically arranged in two dimensions, as shown in FIG3 .

[0111] Step 4: Repeat step 2 and drop a suitable mass of light-curable liquid low-refractive-index resin 2 onto the semi-finished resin layer 1 obtained in step 3. Cover the semi-finished resin layer 1 with a mirror-smooth release film or nickel plate to form a sandwich structure. Furthermore, the flat release film can be replaced with a frosted release film with a certain haze, or a nickel plate polished with glass beads, so that the filled resin layer 2 has a certain haze, which helps to make the emitted light more uniform.

[0112] Step 5: After fully removing the bubbles between the release film or nickel plate and the resin layer, the resin is photocured with UV rays of a certain energy and then the release film or nickel plate is peeled off to obtain a functional film test sample without atomization effect on the surface ( Figure 4A ) and functional film test samples with atomization effect on the surface ( Figure 4B );

[0113] Step 6: In order to reduce the reflection loss of light between interfaces with different refractive indices, an OCA adhesive layer is prepared on the non-optical structure side of the functional film to obtain a functional film sample with adhesive backing ( Figure 5A and Figure 5B ), further, before testing, remove the heavy release film and attach one side of the OCA adhesive layer to the front polarizer of the liquid crystal display device ( Figure 6A and 6B ) to test.

[0114] The tested optical effects of the LCD modules are shown in Tables 6 and 7 below. The differences in optical effects between the LCD modules produced in different Examples and Comparative Examples are detailed in the table below. Depending on the orientation of the cell structures in the functional film, a vertical alignment can improve the LCD device's horizontal viewing angle (brightness viewing angle, contrast ratio at side viewing angles, and chromaticity viewing angles); a horizontal alignment can improve the LCD device's vertical viewing angle.

[0115] The following test only takes the horizontal viewing angle of an LCD device as an example.

[0116] The LCD display used was a commercially available Redmi A55 (with vertical alignment of the liquid crystal). The added functional film was bonded and fixed to the polarizer near the Redmi A55 using an optical fiber connector (OCA). The test platform and luminance colorimeter used were a Fushida FS-6500TL and a TOPCON BM-5AS, respectively. The horizontal viewing angle range was -80.0 to 80.0°, with a step size of 5.0°. The corresponding optical data was recorded.

[0117] (1) Center brightness and brightness viewing angle of the LCD device: The center brightness of the LCD device is measured at the front viewing angle and different side viewing angles in white mode and black mode. The center brightness attenuation caused by the application of the functional film is calculated by [(center brightness of the LCD device after the functional film is applied - center brightness of the LCD device before the functional film is applied) / center brightness of the LCD device before the functional film is applied * 100%]. The target brightness attenuation ratio is less than or equal to 10%.

[0118] Furthermore, the sum of the horizontal left and right viewing angles corresponding to 1 / 3 of the center brightness under the normal viewing angle is calculated as the brightness viewing angle of the liquid crystal display device. The target brightness viewing angle is greater than or equal to 115°.

[0119] (2) Center contrast and contrast viewing angle of liquid crystal display devices: Use Foster FS-6500TL and TOPCONBM-5AS to test and record the center brightness of the liquid crystal display devices before and after the functional film is attached at the front and side viewing angles in white and black modes. The center contrast of the liquid crystal display before and after the attachment at the front and side viewing angles is obtained by the calculation formula (center brightness of the front viewing angle in white mode / center brightness of the front viewing angle in black mode). Further, the attenuated center contrast ratio is calculated by [(center contrast of the liquid crystal display device after the functional film is attached - center contrast of the liquid crystal display device before the functional film is not attached) / center contrast of the liquid crystal display device before the functional film is not attached]. The target center contrast attenuation ratio is less than or equal to 60%.

[0120] (3) Chromaticity viewing angle of liquid crystal display device: Calculate the sum of the horizontal left and right color deviation viewing angles corresponding to the color deviation value Δu'v'<0.02 under the side viewing angle as the chromaticity viewing angle of the liquid crystal display device.

[0121] Target chromaticity viewing angle is greater than or equal to 140°

[0122] Test reference standards: Brightness and viewing angle test refer to "GB40070-2021 Hygiene requirements for myopia prevention and control of learning supplies for children and adolescents" and "SJ / T11348-2016 Flat-panel TV display performance measurement method", contrast and viewing angle test refer to "SJ / T11292-2016 General specification for liquid crystal displays for computers".

[0123] Example 1

[0124] High-refractive-index UV resin 1 (urethane acrylate, liquid refractive index = 1.61) was applied to a nickel plate, which had been previously engraved with a diamond cutter to form microstructures and flat areas between adjacent microstructures. PET was then placed over the nickel plate coated with the high-refractive-index resin layer 1. After fully removing any remaining bubbles, the plate was photocured to produce a semi-finished product with a high-refractive-index resin layer formed on the PET, including microstructure units and flat areas. The engraved patterns for the microstructure units and the flat areas between adjacent microstructure units are shown in Table 6.

[0125] Next, a low-refractive-index UV resin 2 (polyurethane acrylate, liquid refractive index = 1.50) was applied to the high-refractive-index resin layer 1. A mirrored or frosted release film or frosted nickel plate was placed over the low-refractive-index resin 2, ensuring that the low-refractive-index resin layer 2 fully covered the patterned surface of the high-refractive-index resin layer and the flat areas between adjacent patterns. After fully removing any remaining bubbles, UV curing was performed. The release film or nickel plate was peeled off to obtain a functional film for viewing angle improvement. Furthermore, the resulting functional film was attached to the proximal polarizer side of a liquid crystal display device using optical characterization (OCA) for optical performance evaluation.

[0126] Examples 2-9

[0127] A functional film for improving viewing angle was prepared in the same manner as in Example 1, wherein both the high and low refractive index resins adopted the above-designed refractive indexes, but the engraved pattern and the flat portion therebetween were different, as shown in Table 6. The evaluation method was similar to that in Example 1.

[0128] Comparative Example 1

[0129] High-refractive-index UV resin 1 (urethane acrylate, liquid refractive index = 1.62) was applied to a nickel plate, onto which microstructures and flat areas between adjacent microstructures had been engraved using a diamond cutter. PET was then placed on the nickel plate coated with the high-refractive-index resin layer 1. After fully removing any remaining bubbles, the plate was photocured, resulting in a semi-finished high-refractive-index resin layer with microstructure units and flat areas formed on the PET. The engraved patterns corresponding to the microstructure units and the flat areas formed between adjacent microstructure units are shown in Table 6. Furthermore, low-refractive-index UV resin 2 (homemade, liquid refractive index = 1.50) was applied to the high-refractive-index resin layer 1. A mirrored or frosted release film and a frosted nickel plate were placed over the low-refractive-index resin layer 2, ensuring that the low-refractive-index resin layer 2 fully covered the patterned surface of the high-refractive-index resin layer and the flat areas between adjacent patterns. After fully removing any remaining bubbles, the plate was UV-cured. The release film or nickel plate was peeled off to obtain a functional film for improving viewing angles. Furthermore, the prepared functional film was attached to the proximal polarizer side of the liquid crystal display device using OCA for optical performance evaluation.

[0130] Table 6. Structural details and optical performance evaluation results of Examples 1-9, Reference Example and Comparative Example 1.

[0131]

[0132]

[0133] The reference example is a liquid crystal display device without a functional film attached and the optical data obtained by testing the device.

[0134] Table 6. Structural details and optical performance evaluation results of Examples 1-9, Reference Example and Comparative Example 1.

[0135]

[0136]

[0137] The reference example is based on optical data obtained from testing a liquid crystal display device without a functional film attached.

[0138] Examples 10-17

[0139] Furthermore, in order to improve the brightness and chromaticity viewing angle of the liquid crystal display device, functional film Examples 10 to 17 that can be used for viewing angle improvement were prepared in the same manner as Example 1, wherein the high and low refractive index resins both adopted the refractive index designed as described above, but the engraved pattern and the flat portion therebetween were different, as shown in Table 7.

[0140] In addition to the differences in the specific engraving patterns, flat portions, and bottom angles, the refractive indices of the high-refractive index resins in Comparative Examples 2-3 are also different.

[0141] Table 7. Structural details and optical performance evaluation results of Examples 10-17, Reference Examples, and Comparative Examples 2-3.

[0142]

[0143]

[0144] Table 7. Structural details and optical performance evaluation results of Examples 10-17, Reference Examples, and Comparative Examples 2-3.

[0145]

[0146] The reference example is based on optical data obtained from testing a liquid crystal display device without a functional film attached.

[0147] Table 8. Structural details and optical performance evaluation results of Example 18 and Comparative Example 4.

[0148]

[0149]

[0150] Note: The haze of the mirror-treated low-refractive-index resin layer is about 1-3%, and the haze of the frosted low-refractive-index resin layer is about 20%. The test uses ordinary PET chemically treated substrate; the test standard is ISO14782.

[0151] Example 18

[0152] Furthermore, in order to evaluate the influence of the surface roughness of the low-refractive index resin layer on the optical effect of the viewing angle-enhancing film, the surface roughness of the low-refractive index resin layer of Example 18 was obtained by transferring the surface roughness onto a frosted release film or a frosted nickel plate. The other structural parameters were similar to those of Example 3.

[0153] Comparative Example 4

[0154] The other optical structural parameters and resin refractive index designs are similar to those of Example 18, except that the surface of the low-refractive resin layer is obtained by transfer printing using a smooth release film or a mirror nickel plate.

[0155] It has been confirmed that compared with a low-refractive-index resin layer with a certain roughness, a liquid crystal display device with a viewing angle improvement film bonded with a mirror-smooth refractive-index resin layer has smaller center brightness attenuation at the positive viewing angle and higher contrast at the positive and side viewing angles, but the chromatic viewing angle does not reach the target of greater than 140°.

[0156] It can be concluded from the test results of the above embodiments and comparative examples that embodiments 1-9 provided by the present invention can minimize the attenuation of the center brightness and center contrast under the positive viewing angle while improving the brightness viewing angle and side viewing angle brightness of the liquid crystal display device. Embodiments 10-17 can further improve the brightness viewing angle, chromaticity viewing angle and side viewing angle brightness of the liquid crystal display device. Compared with the mirror-smooth low-refractive index resin layer, it is preferred that the low-refractive index resin layer has a certain surface roughness in order to achieve excellent chromaticity viewing angle. In the present invention, the liquid crystal display used for the test is the Redmi A55 TV, whose brightness viewing angle is about 95°. By attaching a wide-viewing angle film, the brightness viewing angle can be increased to more than 120°. In addition, the original chromaticity viewing angle of about 75° can be increased to more than 140°.

[0157] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent changes and modifications made based on the content of the present invention are included in the patent scope of the present invention.

Claims

1. An optical functional film for improving the viewing angle of a liquid crystal display device, the optical functional film comprising a substrate layer and an optical structure layer formed on the substrate layer; in, The optical structure layer comprises: a first resin layer with a refractive index of N1 adjacent to the substrate layer, comprising a plurality of isosceles trapezoidal patterns and flat portions between adjacent isosceles trapezoidal patterns, wherein a single isosceles trapezoidal pattern and the flat portions between adjacent isosceles trapezoidal patterns constitute a unit period; and a second resin layer with a refractive index of N2, formed directly on the flat portions above the patterns in the patterned resin layer 1 and between adjacent patterns; wherein the refractive index N1 of the first resin layer is greater than the refractive index N2 of the second resin layer; The base angle value of the isosceles trapezoidal pattern of the first resin layer is θ, in degrees, and the base angle is 73.0° to 75.0°; The ratio of the flat portion between adjacent isosceles trapezoidal patterns to the entire unit period is the aperture ratio, and the aperture ratio is 10.0% to 28.0%.

2. The optical functional film according to claim 1, wherein The substrate layer is triacetate (TAC), super retardation film (SRF), cycloolefin (COP), polyethylene terephthalate (PET), etc.

3. The optical functional film according to claim 1 or 2, characterized in that: The thickness of the substrate layer is 50-500 μm.

4. The optical functional film according to claim 3, characterized in that The thickness of the substrate layer is 450um, 300um, 250um, 188um, 125um, 100um or 80um.

5. The optical functional film according to claim 1 or 2, characterized in that: The first resin layer is one or more of polyacrylic resin, polyester acrylate, polyurethane acrylate copolymer, or curable polymers modified therefrom.

6. The optical functional film according to claim 1 or 2, characterized in that: The optical functional film is characterized in that the first resin layer 2 is one or more of polyacrylic resin, polyester acrylate, polyurethane acrylate copolymer or curable polymers modified therefrom.

7. A method for preparing an optical functional film for improving the viewing angle of a liquid crystal display device, comprising: Step 1, forming a mold structure on a substrate; Step 2: Add the liquid resin of the first resin layer to the substrate, adhere it to the substrate, and form a sandwich sealing structure; Step 3: Curing the resin of the first resin layer and peeling off the substrate to obtain a semi-finished unit optical structure with a two-dimensional anti-glare periodic arrangement, wherein the unit optical structure is an isosceles trapezoid and a flat portion between adjacent isosceles trapezoids, the base angle of the isosceles trapezoid is 73.0° to 75.0°, and the proportion of the flat portion between adjacent isosceles trapezoids to the periodically arranged unit optical structure semi-finished product is an aperture ratio, and the aperture ratio is 10.0% to 28.0%; Step 4, adding the resin of the liquid second resin layer onto the first resin layer of the semi-finished product, covering the release film or substrate to form a sandwich structure; Step 5: solidify the second resin layer, peel off the release film or substrate, and obtain a functional film.

8. The preparation method according to claim 7, characterized in that In the step 1, a mold structure is formed by engraving. The substrate is a nickel plate. Furthermore, a mold structure of a suitable size is engraved on the nickel plate using a diamond tool.

9. The preparation method according to claim 7, characterized in that Step 2: dripping the liquid resin of the first resin layer onto the substrate.

10. The preparation method according to claim 7, characterized in that Step 2: The substrate is a sheet.

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