WO2020078325A1

WO2020078325A1 - Polarizing backlight unit, method of manufacturing the same and liquid crystal display device using the same

Info

Publication number: WO2020078325A1
Application number: PCT/CN2019/111062
Authority: WO
Inventors: Hui Zhao; Danni WANG; Yuming DING; Yedan ZHAO; Jiuzhi Xue
Original assignee: Smart Liquid Crystal Technologies Co., Ltd.
Priority date: 2018-10-19
Filing date: 2019-10-14
Publication date: 2020-04-23
Also published as: CN111077605A

Abstract

A polarizing backlight unit for TFT LCDs, which comprises: a light source (10), a lightguide plate (20), a polarizing optical film (40) and an optically anisotropic layer (50). The polarizing optical film (40) is located above the light exiting surface (22) of the lightguide plate (20) and comprises a transparent substrate (41), a plurality of first microstructured prisms (42) and a plurality of second microstructured prisms (43). A gap is set between the polarizing optical film (40) and the lightguide plate (20). The optically anisotropic layer (50) covers one surface of the polarizing optical film (40). The polarizing backlight unit can significantly improve the light utilization, reduce the cost, and save the energy consumption.

Description

A polarizing backlight unit, method of manufacturing the same and liquid crystal display device using the same

Technical Field

The present invention relates to the liquid crystal display field, and more particularly, to a polarizing backlight unit and a liquid crystal display device.

Background of the Invention

Flat panel displays such as liquid crystal displays (LCDs) are an essential component of many types of electronic devices. As a passive type of light emitting device, one type of liquid crystal displays relies on a backlight at the back of the display to illuminate the screen. Due to the working principle of liquid crystal displays, only the light of specific polarization is effectively utilized. Generally, a conventional backlight unit is composed of a natural light source, a lightguide plate, a reflective film, a diffuser film, brightness enhancement films, and the like. In detail, the lightguide plate having dots and V-groove structures on the upper and lower surfaces converts point light sources into a planar light source where the light is narrowly longitudinal distributed at large glancing angles to the surface normal. Therefore, the light must be first scattered around through the diffuser film to be distributed widely and symmetrically around the surface normal, and then, it goes through two layers of mutually perpendicular brightness enhancement films where the brightness enhancement film transmits light of small angles and reflects light of large angles, resulting in half of the light is reflected back to the lightguide plate. After passing through the reflective film on the lower surface, the reflective light is directed to the brightness enhancement film again. The cycle will be repeated several times, and the horizontal/longitudinal angle of the emission light is controlled at -35°～35°, to achieve a uniform emission light of small angles. The final light utilization of such backlights tends to be less than 5%of the original illumination in LCD, and the optical loss is high. The lost part may further cause adverse effects, such as an increase in temperature. If the light emitted from the backlight unit is linearly polarized, it could significantly improve light utilization, reduce energy consumption, and alleviate adverse effects such as heat generation.

Summary of the Invention

The purpose of the present invention is to provide a polarizing backlight unit and a liquid crystal display device, in order to solve the above technical problems existing in the prior art.

One objective of the present invention is to provide a polarizing backlight unit, comprising : a light source; a lightguide plate configured with a light incident surface and a light exiting surface, wherein the light incident surface and the light existing surface are adjacent and perpendicular to each other, the light incident surface faces the light source; a reflective layer located on the side of the lightguide plate opposite to the light existing surface; a polarizing optical film located above the light exiting surface with a gap between the polarizing optical film and the lightguide plate, wherein the polarizing optical film comprises a transparent substrate, a plurality of first microstructured prisms on one surface of the transparent substrate and a plurality of second microstructured prisms on the other surface of the transparent substrate, wherein the second microstructured prisms are close to the lightguide plate, and the first microstructured prisms and the second microstructured prisms are arranged in parallel and extend in the direction parallel to the light incident surface; and an optically anisotropic layer covering completely the first microstructured prisms, wherein the surface of the optically anisotropic layer away from the first microstructured prisms is substantially smooth.

Preferably, the first microstructured prisms, the second microstructured prisms and the transparent substrate are integrally formed by a same material.

Preferably, the first microstructured prisms are arranged in an equal interval and the cross section of the first microstructured prisms is an isosceles triangle.

Preferably, the vertex angle of the isosceles triangle varies from 30 degrees to 120 degrees.

Preferably, the ratio of the distance between any two adjacent first microstructured prisms to the width of the isosceles triangle varies between 1 and 10.

Preferably, the height of the first microstructured prisms is not more than 50 microns.

Preferably, the cross section of the second microstructured prisms is an isosceles triangle, and the base angle of the isosceles triangle ranges varies from 28 degrees to 33 degrees.

Preferably, the second microstructured prisms are continuously arranged without an interval.

Preferably, the optically anisotropic layer is a polymer material made of liquid crystal compounds.

Preferably, the liquid crystal compounds comprise a polymerizable liquid crystal compound and a polymerization initiator.

Preferably, the liquid crystal compounds comprise a polymerization inhibitor.

Preferably, the refractive index of the transparent substrate is substantially the same as the ordinary refractive index of the optically anisotropic layer.

Preferably, the reflective layer comprises a substrate layer with microstructured prisms and a reflection layer, and the reflection layer is adjacent to the lightguide plate.

Another objective of the present invention is to provide a liquid crystal display device comprising the polarizing backlight unit as described above.

The polarizing backlight unit and the liquid crystal display device of the present invention can significantly improve the light utilization, spare the brightness enhancement films in the conventional backlight to reduce the backlight cost, and save the backlight energy consumption.

Brief Description of the drawings

The present invention will become more apparent by the description of embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a schematic view illustrating the structure of a polarizing backlight unit according to an embodiment of the present invention;

FIG. 2 is a partial enlargement of FIG. 1;

FIG. 3 (a) is a schematic view illustrating the first structure of a reflective layer in a polarizing backlight unit according to an embodiment of the present invention;

FIG. 3 (b) is a schematic view illustrating the second structure of a reflective layer in a polarizing backlight unit according to an embodiment of the present invention;

FIG. 3 (c) is a schematic view illustrating the third structure of a reflective layer in a polarizing backlight unit according to an embodiment of the present invention;

FIG. 4 is a schematic view illustrating the distribution of angle diagram of s-polarized light and p-polarized light in a polarizing backlight unit according to a specific embodiment of the present invention.

Detailed Description of the Invention

In the following description, for the purpose of explanation so as to have a comprehensive understanding of the invention, numerous specific details are disclosed, however, it is obvious to those skilled in the art, that the invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in block diagrams in the invention. The exemplary embodiments are merely illustrative of the invention, rather than limiting the scope of the present invention being defined by appended claims thereof.

The polarizing backlight unit and the liquid crystal display device of the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic view illustrating the structure of a polarizing backlight unit according to an embodiment of the present invention. As shown in FIG. 1, the polarizing backlight unit includes a light source 10, a lightguide plate 20, a reflective layer 30, a polarizing optical film 40 and an optically anisotropic layer 50. The lightguide plate 20 is configured with a light incident surface 21 and a light exiting surface 22, where the light incident surface 21 and the light existing surface 22 are adjacent and perpendicular to each other, and the light incident surface 21 faces the light source 10. The reflective layer 30 is located on the side of the lightguide plate which is opposite to the light exiting surface 22. The polarizing optical film 40 is located above the light exiting surface 22 and a gap is disposed between the polarizing optical film 40 and the lightguide plate 20 (the gap can be adjusted according to actual needs) . As shown in FIG. 2, the polarizing optical film 40 comprises a transparent substrate 41, a plurality of first microstructured prisms 42 on one surface of the transparent substrate 41 and a plurality of second microstructured prisms 43 on the other surface of the transparent substrate 41 where the second microstructured prisms 43 are close to the lightguide plate 20. The first microstructured prisms 42 and the second microstructured prisms 43 are arranged in parallel and extend in the direction parallel to the light incident surface 21 (as shown in FIG. 1 and FIG. 2, the

microstructured prisms

42 and 43 in the present invention are pointed away from the transparent substrate 41) . The optically anisotropic layer 50 covers completely the first microstructured prisms 42, wherein the first microstructured prisms 42 penetrate into the optically anisotropic layer 50. The height D1 of the first microstructured prisms 42 is not more than the thickness T of the optically anisotropic layer 50, so that the first microstructured prisms 42 are all embraced in the optically anisotropic layer 50. The surface of the optically anisotropic layer away from the first microstructured prisms 42 is substantially smooth.

In a specific embodiment of the present invention, the first microstructured prisms 42, the second microstructured prisms 43 and the transparent substrate 41 are integrally formed by a same material. The transparent substrate 41, the first microstructured prisms 42, and the second microstructured prisms 43 each have a refractive index of no more than 1.6. The transparent substrate 41, the first microstructured prisms 42 and the second microstructured prisms 43 can also be separately formed and assembled by a bonding process. The invention is not limited to it, the transparent substrate 41, the first microstructured prisms 42, and the second microstructured prisms 43 may also be formed by different materials. For example, the transparent substrate 41 is first formed by a material with a refractive index of no more than 1.6, and next the first microstructured prisms 42 and the second microstructured prisms 43 may be an isotropic material cured by an optical glue. The refractive index of the isotropic material is between 1.5 and 1.6.

In a specific embodiment of the present invention, the first microstructured prisms 42 are repeatedly arranged equidistantly, and the cross section of the first microstructured prisms 42 is an isosceles triangle. Preferably, the vertex angle α of the isosceles triangle varies from 30° to 120°. Preferably, the ratio of the distance H between any two adjacent of the first microstructured prisms to the width L1 of the isosceles triangle varies between 1 and 10. More preferably, the ratio is in the range of 1.2 to 3. More preferably, the ratio is in the range of 1.5 to 2. In the present invention, as shown in FIG. 2, the distance H between any two adjacent of the first microstructured prisms refers to the distance between the vertexes of two adjacent first microstructured prisms. Preferably, the height D1 of the first microstructured prisms 42 is no more than 50 microns.

In a specific embodiment of the present invention, the cross section of the second microstructured prisms 43 is an isosceles triangle. Preferably, the base angle β of the isosceles triangle varies from 28° to 33°, and the second microstructured prisms 43 are continuously arranged without an interval. The heights of the second microstructured prisms 43 may be the same, but are not limited thereto, and the second microstructured prisms 43 may also have different heights, such as in a high and low staggered arrangement and in an incremental or decreasing staggered arrangement, which enhances the scattering effect of the overall structure of the polarizing optical film 40.

In a specific embodiment of the present invention, the optically anisotropic layer 50 is a polymer material made of liquid crystal compounds. The liquid crystal compounds include a polymerizable liquid crystal compound and a polymerization initiator. Further, the liquid crystal compounds further include a polymerization inhibitor. The polymerizable liquid crystal compound may be selected from the group of compounds of formula P ₁-R ¹-MG-R ²-P ², wherein P ₁ and P ₂ each independently represent a polymerizable group or -CH ₃ and at least one of P ₁ and P ₂ is a polymerizable group; R ₁ and R ₂ each independently denote an alkyl group having 1 to 18 C atoms where one or more H atom may be independently substituted by F or Cl and one or more nonadjacent -CH ₂-may be independently replaced by -O-, -S-, -NH-, -CO-, -COO-, -OCO-, -OCOO-, -SCO-, -COS-, -CH=CH-, -CH= CF-, -CF=CF-, -C≡C-or -CH (CN) -in such a manner that two -O-are not directly adjacent to one another or any two groups selected from -OCO-, -SCO-, -OCOO-, -COS-, -COO-, and -CH=CH-are not directly adjacent to one another; MG denotes a mesogenic group. The polymerization initiator may be a photo-polymerization initiator, a thermal-polymerization initiator, or radiation-polymerization initiator. Preferably, the polymerization initiator is a free-radical polymerization initiator such as photoinitiator 184

photoinitiator 907

TPO (2, 4, 6-trimethylbenzoyl-diphenylphosphine oxide) Etc. The polymerization inhibitor can be selected from phenolic polymerization inhibitors, anthraquinone inhibitors, aromatic nitro compounds or the like. For example, the polymerization inhibitor can be

or the like. In the present invention, since the polymer material made of liquid crystal compounds used in the optically anisotropic layer 50 has a large phase transition temperature range and good optical anisotropy, the prepared optically anisotropic layer has good temperature adaptability and polarization separation effect. In a specific embodiment of the present invention, the refractive index of the transparent substrate 41 substantially coincides with the ordinary refractive index of the optically anisotropic layer 50. More preferably, the refractive index of the transparent substrate 41 is not more than 1.6, and the transparent substrate 41 is formed by curing of an optical adhesive.

Specifically, as shown in FIG. 1, the natural light emitted from the light source 10 enters the lightguide plate 20 from the light incident surface 21, propagates in the form of a waveguide through alternate reflection on the upper and lower surfaces, and exits through the light exiting surface 22. In the present invention, the angle between the direction of the exit light and the light exiting surface is not more than 25°. Next the light enters the second microstructured prisms 43 of the polarizing optical film 40 through the gap between the lightguide plate 20 and the polarizing optical film 40, and then is refracted at the boundary surface between the gap and the second microstructured prisms 43, which can adjust the large-angle light exiting from the lightguide plate 20 to close to the normal line of the light exiting surface. The angle of the exit light in the longitudinal direction are between -35° and 35°, which remarkably improves the forward light emission of the backlight. After that, the light enters the optically anisotropic layer 50 through the transparent substrate 41 and the first microstructured prism 42 and is divided into s-polarized light and p-polarized light, where the s-polarized light can be totally reflected on the interface between the first microstructured prism 42 and the optically anisotropic layer 50, is optically oriented and exits from the upper surface of the optically anisotropic layer 50. The p-polarized light is totally reflected at the upper surface of the optically anisotropic layer 50 and returned, thus achieving polarization separation of s-polarized light and p-polarized light. In the specific embodiment of the present invention, by introducing the first microstructured prism 42 and the second microstructured prism 43 on the upper and lower surfaces of the polarizing optical film 40, polarization separation of natural light can be realized, and the light utilization rate of the backlight is remarkably improved.

In a specific embodiment of the present invention, the upper surface of the optically anisotropic layer 50 is a substantially smooth plane, the extending directions of the first microstructured prisms 42 and the second microstructured prisms 43 are parallel to the light incident surface 21, and the optical axis of the optically anisotropic layer 50 is substantially parallel to the extending directions. The optically anisotropic layer 50 has an ordinary refractive index n _o and an extraordinary refractive index n _e, and the refractive index of the second microstructured prisms 43 is substantially equal to the ordinary refractive index n _o of the optically anisotropic layer 50. As described above, the light entering the optically anisotropic layer 50 is subjected to polarization separation under the action of the internal structure, wherein the s-polarized light will exit with a certain probability and the p-polarized light remains in the waveguide mode to propagate until converted into s-polarized light.

The reflective layer 30 is located on the side of the lightguide plate 20 facing away from the light exiting surface 22, and is used for recycling the light incident on the reflective layer 30, thereby further improving the light utilization of the backlight.

FIG. 3 (a) is a first structure of the reflective layer in a polarizing backlight unit according to an embodiment of the present invention. As shown in FIG. 3 (a) , the reflective layer includes a substrate layer and a reflective layer, where a plurality of microstructured prisms are formed on the substrate layer and the microstructured prisms are parallel arranged and extends in a direction parallel to the light incident surface of the lightguide plate. The cross section of the microstructured prisms is a triangular. The reflective layer (not shown) is located above the microstructured prisms (i.e., the side adjacent to the lightguide plate) , and the reflective layer may be, for example, an aluminum layer whose manufacturing process is a physical vapor deposition method such as vapor deposition or magnetron sputtering, or a chemical vapor deposition method used in material chemistry. In an embodiment, as shown in FIG. 3 (a) , the vertex angle θ1 of the triangle is 80°, and the base angles θ2 is 10°, and θ3 is 90°. The microstructured prisms are repeatedly arranged in an equal distance, and there is a gap between the adjacent microstructured prisms, where the width of the gap can be adjusted according to the angle of the incident light. In the embodiment, the reflective layer 30 only reflects the light having a larger incident angle, and according to the angle range of the incident light, different θ1, θ2, and θ3 may be selected. The reflective layer of the present invention is preferably a film which has a large-angle reflection function and no scattering, to ensure that light enter the polarizing optical film 40 at a specific angle.

FIG. 3 (b) is a second structure of the reflective layer in a polarizing backlight unit according to another embodiment of the present invention, where θ1 is 45°, θ2 is 45°, and θ3 is 90°.

FIG. 3 (c) is a third structure of the reflective layer in a polarizing backlight unit according to another embodiment of the present invention. In this embodiment, the microstructured prisms are arranged in series without a gap.

FIG. 4 is a schematic view illustrating the distribution of angle diagram of s-polarized light and p-polarized light in a polarizing backlight unit according to a specific embodiment of the present invention. The technical parameters of the polarizing backlight unit are: for the first microstructured prisms 42, the width L1 is 8 micron, and the height D1 is 10 microns, the vertex angle is 45°, and the distance H between two adjacent microstructured prisms is 15 microns; for the liquid crystal compounds in the optically anisotropic layer, n _o is around 1.5 and n _e is around 1.7; for the second microstructured prisms 43, the width L2 is 52 microns, the height D2 is 15 microns, the base angle β is 30°. In the simulation, the light exiting surface is uniformly planar plane which has an ideal even light output and the angle between the exit light and the light existing surface is not more than 25°. It can be shown from FIG. 4 that under such simulation conditions, the exit light is mainly s-polarized light and the photon flux of the s-polarized light to the p-polarized light in the exit light is greater than 10: 1. Moreover, the exit light is mainly concentrated in longitudinal direction, improving the forward exit light of the backlight.

In an embodiment of the present invention, the lightguide plate 20 includes a light incident surface and a light exiting surface. However, the present invention is not limited thereto, and the lightguide plate 20 may further include a light incident surface and two light exiting surfaces, where the two light exiting surfaces are parallel to each other and both are adjacent and perpendicular to the light incident surface. For example, one light exiting surface is the light exiting surface 22 as shown in FIG. 1 , and the other light exiting surface is opposite to the light exiting surface 22 and is disposed in parallel with the light exiting surface 22 and near the reflective surface of the reflective layer 30.

In a specific embodiment of the present invention, the material of the lightguide plate may be PC, PMMA, glass, PS, etc. The light source is preferably an LED light bar. The material of the transparent substrate 41, the first microstructured prism 42 and the second microstructured prism 43 is one or more selected from polyethylene terephthalate, polyethylene terephthalate, cellulose triacetate, polypropylene, polyethylene, acrylonitrile, butadiene, and styrene.

In addition, the present invention also provides a liquid crystal display device comprising the polarizing backlight unit described above and a liquid crystal display panel. The polarizing backlight unit and the liquid crystal display device of the invention not only can significantly improve the light utilization, but also spare the brightness enhancement film in the traditional backlight, thus reducing the backlight cost, and save the backlight energy consumption.

While the present invention has been described in connection with certain example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.

Claims

A polarizing backlight unit comprising:

a light source;

a lightguide plate configured with a light incident surface and a light exiting surface, wherein the light incident surface and the light existing surface are adjacent and perpendicular to each other, the light incident surface faces the light source;

a reflective layer located on the side of the lightguide plate opposite to the light existing surface;

a polarizing optical film located above the light exiting surface with a gap between the polarizing optical film and the lightguide plate, wherein the polarizing optical film comprises a transparent substrate, a plurality of first microstructured prisms on one surface of the transparent substrate and a plurality of second microstructured prisms on the other surface of the transparent substrate, wherein the second microstructured prisms are close to the lightguide plate, and the first microstructured prisms and the second microstructured prisms are arranged in parallel and extend in the direction parallel to the light incident surface; and

an optically anisotropic layer covering completely the first microstructured prisms, wherein the surface of the optically anisotropic layer away from the first microstructured prisms is substantially smooth.
The polarizing backlight unit of claim 1, wherein the first microstructured prisms, the second microstructured prisms and the transparent substrate are integrally formed by a same material.
The polarizing backlight unit of claim 1, wherein the first microstructured prisms are arranged in an equal interval and the cross section of the first microstructured prisms is an isosceles triangle.
The polarizing backlight unit of claim 3, wherein the vertex angle of the isosceles triangle varies from 30 degrees to 120 degrees.
The polarizing backlight unit of claim 3, wherein the ratio of the distance between any two adjacent first microstructured prisms to the width of the isosceles triangle varies between 1 and 10.
The polarizing backlight unit of claim 1, wherein the height of the first microstructured prisms is not more than 50 microns.
The polarizing backlight unit of claim 1, wherein the cross section of the second microstructured prisms is an isosceles triangle, and the base angle of the isosceles triangle varies from 28 degrees to 33 degrees.
The polarizing backlight unit of claim 1, wherein the second microstructured prisms are continuously arranged without an interval.
The polarizing backlight unit of claim 1, wherein the optically anisotropic layer is a polymer material made of liquid crystal compounds.
The polarizing backlight unit of claim 9, wherein the liquid crystal compounds comprise a polymerizable liquid crystal compound and a polymerization initiator.
The polarizing backlight unit of claim 10, wherein the liquid crystal compounds comprise a polymerization inhibitor.
The polarizing backlight unit of claim 1, wherein the refractive index of the transparent substrate is substantially the same as the ordinary refractive index of the optically anisotropic layer.
The polarizing backlight unit of claim 1, wherein the reflective layer comprises a substrate layer with microstructured prisms and a reflective layer, and the reflective layer is adjacent to the lightguide plate.
A liquid crystal display device, wherein the liquid crystal display device comprises the polarizing backlight unit of any one of claims 1-13.