TWI407225B - Cholesteric liquid crystal panel and liquid crystal composition thereof - Google Patents

Abstract

A cholesteric liquid crystal panel and its liquid crystal material thereof are provided. The cholesteric liquid crystal material is driven by an electric field. The cholesteric liquid crystal composition includes a low molecular weight cholesteric liquid crystal and a plurality of cholesteric liquid crystalline polymer scattered in the low molecular weight cholesteric liquid crystal. The optical handedness of the low molecular weight cholesteric liquid crystal and the cholesteric liquid crystalline polymer are different, so as to reflect opposite circular polarized lights in same time.

Description

Cholesterol liquid crystal display panel and liquid crystal material thereof

The present invention relates to a reflective cholesteric liquid crystal display panel, and more particularly to a cholesteric liquid crystal display panel having a liquid crystal material capable of simultaneously reflecting two opposite optically polarized polarized light.

In the current era of high energy-saving and trend, the light-weight and power-saving display has become the mainstream in the field of display, and the bistable liquid crystal display device has attracted attention. Among them, Cholesteric Liquid Crystal Display (CHLCD) has the advantages of high brightness, high contrast, power saving, memory, wide viewing angle, no flicker, etc., and can maintain continuous light in the case of removing electric field. Two different states, state and dark state, have become the focus of current bi-stable displays.

Cholesterol liquid crystal is a liquid crystal molecule with a helical structure. In a natural state, it has two stable states, a planar state and a focal conic state, wherein the planar state can reflect a specific wavelength. The color light and the focal conic state are scattered and can correspond to the bright state and the dark state of the cholesteric liquid crystal display respectively; the conversion between the two states can use the electric field: the electric field is raised to make the cholesteric liquid crystal vertically aligned (homeotropic State), if the electric field is completely stopped, the vertical alignment state will be converted into a planar state; if the electric field is first removed by a small electric field, the vertical alignment state will be converted into a focal conic state.

The cholesteric liquid crystal in the planar state can reflect the color light of a specific wavelength, and the reflection wavelength is related to the average refractive index and the pitch of the cholesteric liquid crystal. The cholesteric liquid crystal display can adjust the size of the cholesteric pitch according to the actual reflection requirement. Reflect different wavelengths to display multiple colors.

Practically, the cholesteric liquid crystal is incorporated into the nematic liquid crystal by an optically active substance to induce the generation of a helical structure, and thus the cholesteric liquid crystal is also called a chiral nematic liquid crystal. The molecular pitch of the cholesteric liquid crystal varies depending on the helical twisting power (HTP) of the optically active substance, the amount of the optically active substance added, and the temperature. Different optically active substances will produce optical destructive properties. Therefore, if different optically active substances are placed in the same layer, not only can not reflect different optically polarized light to improve the reflectivity, but the helical torsional energy can be offset. The spiral structure will cause a period to become larger or unwind, which in turn changes the position of the reflection wavelength of the cholesteric liquid crystal or causes no reflection. Therefore, in general, different optically active substances are not placed in the same layer.

However, the helical structure of the cholesteric liquid crystal can penetrate the oppositely polarized circularly polarized light and reflect the circularly polarized light of the same optical rotation. The maximum reflectance of the cholesteric liquid crystal in a specific wavelength range does not exceed 50%, so the contrast and light efficiency in the display application. There will be considerable impact on it.

In order to increase the reflectivity of cholesteric liquid crystals, U.S. Patent Nos. 5,548,422 and 6,532,052, the disclosure of which are incorporated herein by reference to each of the entire disclosures of each of the s. A half-wavelength phase retardation film is added between the liquid crystals to simultaneously reflect polarized light of different optical rotations.

However, in the lamination method disclosed in the above two patents, it is necessary to select a cholesteric liquid crystal having the same reflection wavelength range so that the light is smoothly refracted in the cholesteric liquid crystal of the laminated structure. Moreover, the laminate must have a two-layer liquid crystal structure. In driving the cholesteric liquid crystal, it is necessary to drive separately using two sets of driving circuits, and use too many glass substrates. This will cause a problem of superimposition and also result in a reduction in image quality.

The invention provides a cholesteric liquid crystal display panel and a liquid crystal material thereof, thereby improving the problem that the cholesteric liquid crystal structure of the prior art has poor reflectivity due to optical destructiveness, and the conventional cholesteric liquid crystal structure is too complicated.

The cholesteric liquid crystal display panel disclosed in the present invention comprises two transparent conductive substrates and a liquid crystal material sandwiched between the two transparent conductive substrates. The liquid crystal material of the present invention can be driven by an electric field, and comprises a small molecule of cholesteric liquid crystal material and a plurality of high molecular cholesteric liquid crystal materials dispersed in the small molecule cholesteric liquid crystal material. Among them, the small molecule cholesteric liquid crystal material and the high molecular cholesteric liquid crystal material have different optical rotation properties to reflect the opposite optical rotation of the polarized light.

The effect of the invention is that the heterochromatic optically small molecule cholesteric liquid crystal material and the high molecular cholesteric liquid crystal material are uniformly blended, and the obtained single layer liquid crystal material can simultaneously reflect different optically polarized light, thereby improving the reflectance. .

The above description of the present invention and the following description of the embodiments of the present invention are intended to illustrate and explain the principles of the invention.

As shown in FIG. 1 , the cholesteric liquid crystal display panel 300 disclosed in the present invention includes two opposite transparent conductive substrates 310 and a liquid crystal material 100. The liquid crystal material 100 is interposed between the two transparent conductive substrates 310. Since the cholesteric liquid crystal display panel 300 disclosed in the present invention is a technology known to those skilled in the relevant art, the focus of the present invention is to emphasize the liquid crystal material 100 of the present invention and conventional liquid crystal. Since the difference in layers, only the main structure of the cholesteric liquid crystal display panel is schematically illustrated in "Fig. 1".

Please refer to the schematic diagram of the liquid crystal materials shown in "Figure 2" and "Figure 3". The liquid crystal material 100 disclosed in the present invention is electrically connected to an electric field 200 and can be driven by the electric field 200.

The liquid crystal material 100 includes a low molecular weight cholesteric liquid crystal 110 and a plurality of cholesteric liquid crystalline polymers 120, wherein the small molecule cholesteric liquid crystal material 110 is a liquid crystal state, a high molecular cholesterol. The liquid crystal material 120 is solid, and the polymer cholesteric liquid crystal 120 material is non-aggregated in the small molecule cholesteric liquid crystal 110 material, and the small molecule cholesteric liquid crystal material 110 and the high molecular cholesteric liquid crystal material 120 are not compatible. The optical rotation of the polymer cholesteric liquid crystal material 120 of the present invention is not affected or altered by other optically active substances, and the optical rotation of the small molecule cholesteric liquid crystal material 110 is different from that of the high molecular cholesteric liquid crystal material 120 (for example, small). The optical rotation of the molecular cholesteric liquid crystal material 110 is left-handed, and the optical rotation of the high-molecular cholesteric liquid crystal material 120 is right-handed) to simultaneously reflect the opposite-rotational polarization, that is, the right-handed polarized light RH and the left-handed light are simultaneously reflected. The polarized light LH is used to increase the reflectivity of the liquid crystal material 100.

The high molecular weight cholesteric liquid crystal material 120 of the present invention is uniformly blended into the small molecule cholesteric liquid crystal material 110 in the form of a flake or a platelet. However, the high molecular cholesteric liquid crystal material 120 of the present invention can also be microcell type. The state or the microcapsule pattern is dispersed in the small molecule cholesteric liquid crystal material 110, and is not limited to the sheet structure disclosed in the embodiment.

The central reflection wavelengths of the small molecule cholesteric liquid crystal material 110 and the high molecular cholesteric liquid crystal material 120 may be the same or similar, so that the reflection wavelength ranges of the dicholesteric liquid crystal materials 110 and 120 overlap to achieve good light efficiency, and The central reflection wavelength range of the cholesteric liquid crystal materials 110, 120 falls within the range of visible light. In addition, the polymer cholesteric liquid crystal material 120 is a well-aligned helical structure, and the Helical Pitch of each of the high molecular cholesteric liquid crystal materials 120 may be the same pitch, or may be an increasing pitch or a decreasing pitch. A gradient pitch type of pitch is present in the small molecule cholesteric liquid crystal material 110.

As shown in FIG. 2, when the liquid crystal material 100 of the present invention is not driven by the electric field 200, the small molecule cholesteric liquid crystal material 110 has a planar state and a focal conic state. At the same time, different polarizations of polarized light are reflected.

As shown in "Fig. 3", when the liquid crystal material 100 is driven by the electric field 200, the small molecule cholesteric liquid crystal material 110 has a planar state, a focal conic state, and a vertical alignment state ( The homeotropic state, and the polymer cholesteric liquid crystal material 120 also has the property of being driven by the electric field 200, that is, when the polymer cholesteric liquid crystal material 120 is driven by the electric field 200, it has a planar state and a focal conic state. And the homeotropic state.

Please refer to "Fig. 4" for the graph of the reflectance of the liquid crystal material of the present invention. Taking the cholesteric liquid crystal of the present invention as an example, the blending system is 92.9 weight percent (wt%) of ZLI-1132 (by Merck, Germany) Based on the company (Merck Ltd.), 7.1 weight percent (wt%) of the left-handed optical agent -S1011 (manufactured by Merck Ltd., Germany) was mixed and stirred uniformly at 80 ° C to obtain a central reflective wavelength. A small molecule cholesterol liquid crystal material that reflects about 560 nanometers (nm) of green light. The polymer cholesteric liquid crystal material of the present invention adopts the right-handed polymer cholesteric liquid crystal chip type Jade of LCP company, and the reflectance results of different proportions of concentration are shown in the graph of "Fig. 4". The results show that the addition of different optically active polymer cholesteric liquid crystal fragments can make the reflectance of the liquid crystal material of the present invention greater than 50%, and the more the amount of the high molecular cholesteric liquid crystal added, the higher the reflectance. Wherein, the concentration ratio of the polymer cholesteric liquid crystal material of the present invention to the small molecule cholesteric liquid crystal material is up to 8%, but the spirit of the present invention lies in the mixing of the heterochromatic optically active small molecule cholesteric liquid crystal material and the high molecular cholesteric liquid crystal material. Moreover, the polymer cholesteric liquid crystal material can be formulated at different concentrations according to actual use requirements, and is not limited to the data of the embodiments disclosed in the present invention.

The ratio of the left-handed optical agent that changes the small-molecule cholesterol liquid crystal material can be adjusted to formulate 440 nm (nm) and 660 nm (nm) of blue and red light, respectively (9% and 6%, respectively). In addition, LCP company's right-handed polymer cholesteric liquid crystal chip fragments Sapphire and Maple were separately added as polymer cholesteric liquid crystal materials. As a result, as shown in "5A" and "5B", the central reflection wavelength of small-molecule cholesterol materials is more than 440 nm or 660 nm, which is more than 50% reflectance of the conventional cholesteric liquid crystal structure. Improve the reflectivity of liquid crystal materials.

In order to stabilize the dispersion state of the polymer cholesteric liquid crystal material, a polymer network structure can be formed in the small molecule cholesteric liquid crystal material of the present invention, so that the polymer cholesteric liquid crystal material is dispersed in the polymer network structure, and Achieve uniform distribution. The microcapsule liquid crystal material can also form a microcup structure or a wall structure, so that the polymer cholesterol liquid crystal material is evenly dispersed in the small molecule cholesterol liquid crystal material.

The liquid crystal material of the invention is characterized in that the polymer cholesteric liquid crystal material is uniformly blended into the heterochromatic optically small molecule cholesteric liquid crystal material to obtain a single layer of liquid crystal material, thereby simultaneously reflecting the polarized light of different optical rotations, thereby achieving improvement. The reflectivity of the liquid crystal material while greatly simplifying the structure of the liquid crystal material.

Although the embodiments of the present invention are disclosed above, it is not intended to limit the present invention, and those skilled in the art, regardless of the spirit and scope of the present invention, the shapes, structures, and features described in the scope of the present application. And the spirit of the invention is subject to change. Therefore, the scope of patent protection of the present invention is subject to the scope of the patent application attached to the specification.

100‧‧‧Liquid crystal materials

110‧‧‧Small molecule cholesterol liquid crystal material

120‧‧‧ polymer cholesterol liquid crystal material

200‧‧‧ electric field

300‧‧‧Cholesterol LCD panel

310‧‧‧Transparent conductive substrate

RH‧‧‧right-polar polarized light

LH‧‧‧Dial-light polarized light

1 is a schematic view of a cholesteric liquid crystal display panel of the present invention; FIG. 2 is a schematic view of a liquid crystal material of the present invention; FIG. 3 is a schematic view of the liquid crystal material of the present invention after being driven; A reflectance graph of the polymer cholesteric liquid crystal material; and 5A and 5B are graphs showing the reflectance versus the wavelength of the polarized light of the present invention.

100‧‧‧Liquid crystal materials

110‧‧‧Small molecule cholesterol liquid crystal material

120‧‧‧ polymer cholesterol liquid crystal material

RH‧‧‧right-polar polarized light

LH‧‧‧Dial-light polarized light

Claims (12)

A liquid crystal display panel comprising: a transparent conductive substrate; and a liquid crystal material sandwiched between the two transparent conductive substrates, the liquid crystal material being driven by an electric field, the liquid crystal material further comprising: a small molecule a low molecular weight cholesteric liquid crystal, the two transparent conductive substrates are respectively in contact with opposite sides of the small molecule cholesteric liquid crystal material; and a plurality of cholesteric liquid crystalline polymers are dispersed in the In the small molecule cholesteric liquid crystal material, the small molecule cholesteric liquid crystal material coats the plurality of polymer cholesteric liquid crystal materials, and the optical rotation of the polymer cholesteric liquid crystal material is different from the optical rotatory property of the small molecule cholesteric liquid crystal material; wherein The small molecule cholesteric liquid crystal material and the high molecular cholesteric liquid crystal material respectively reflect the polarization of the opposite optical rotation. The cholesteric liquid crystal display panel according to claim 1, wherein the small molecule cholesteric liquid crystal material is in a liquid crystal state, and the high molecular cholesteric liquid crystal material is in a solid state, and the small molecule cholesteric liquid crystal material and the polymer Cholesterol liquid crystal materials are not compatible. The cholesteric liquid crystal display panel of claim 1, wherein the small molecule cholesteric liquid crystal material has a two-state transition between a planar state and a focal conic state. The cholesteric liquid crystal display panel according to claim 1, wherein the electricity The field drives the liquid crystal material, which has a three-state transition of a planar state, a focal conic state, and a homeotropic state. The cholesteric liquid crystal display panel according to claim 1, wherein the electric field drives the liquid crystal material, and the polymer cholesteric liquid crystal material has a planar state. The cholesteric liquid crystal display panel according to claim 1, wherein the polymer cholesteric liquid crystal material has a helical molecular structure. The cholesteric liquid crystal display panel according to claim 1, wherein the polymer cholesteric liquid crystal material has a shape of a sheet. The cholesteric liquid crystal display panel according to claim 1, wherein the spiral pitch of each of the high molecular phenolic liquid crystal materials is substantially the same. The cholesteric liquid crystal display panel according to claim 1, wherein the spiral pitch of each of the high molecular phenolic liquid crystal materials is substantially increasing or decreasing. The cholesteric liquid crystal display panel according to claim 1, wherein the small molecule cholesteric liquid crystal material and the polymer cholesteric liquid crystal material have substantially the same or similar central reflection wavelength. The cholesteric liquid crystal display panel according to claim 1, wherein the small molecule cholesteric liquid crystal material and the high molecular cholesteric liquid crystal material have a central reflection wavelength range of visible light. A liquid crystal material that can be driven by an electric field, including: a low molecular weight cholesteric liquid crystal; a plurality of cholesteric liquid crystalline polymers are dispersed in the small molecule cholesteric liquid crystal material, the small molecule cholesteric liquid crystal material coating the plurality of high molecular cholesteric liquid crystal materials, and the optical cholesteric liquid crystal material is rotated The optical properties of the small molecule cholesteric liquid crystal material are different; wherein the small molecule cholesteric liquid crystal material and the high molecular cholesteric liquid crystal material respectively reflect opposite optically polarized light.