JP4412802B2 - Color filter for reflective LCD - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color filter for a reflective liquid crystal display (hereinafter, reflective LCD).
[0002]
[Prior art]
For example, as disclosed in JP-A-10-282324, a liquid crystal using a cholesteric liquid crystal or a chiral nematic liquid crystal has been proposed as a color filter for a reflective LCD.
[0003]
This color filter has superior performance in brightness and color purity compared to conventional color filters using pigments and dyes. In particular, the selective reflection wavelength region changes depending on the temperature, and further, the liquid crystal is irradiated by ultraviolet irradiation. By using an ultraviolet curable cholesteric liquid crystal capable of maintaining the state, it can be easily produced as compared with the conventional case.
[0004]
The cholesteric liquid crystal and chiral nematic liquid crystal as described above have a characteristic that the director spirally changes in space in addition to the long-range alignment order of the liquid crystal molecular axes. That is, in the plane parallel to the liquid crystal molecule axis, each liquid crystal molecule has an alignment order similar to that of the nematic phase, but when moving to the adjacent plane, the local alignment direction is slightly rotated, so that the adjacent planes are sequentially changed. When stacked, a three-dimensional spiral structure is formed in which the direction perpendicular to the plane is the spiral central axis.
[0005]
When natural light is incident on the cholesteric liquid crystal or chiral nematic liquid crystal having such a spiral structure in parallel to the helical axis, the right-handed circularly polarized light and the left-handed circularly polarized light that form this natural light are Only one circularly polarized component in the same turning direction is reflected, and a circularly polarized component in a different turning direction is transmitted.
[0006]
The wavelength of the reflected light is proportional to the pitch of twist in the helical structure of cholesteric liquid crystal or chiral nematic liquid crystal.
[0007]
The pitch of the cholesteric liquid crystal or chiral nematic liquid crystal changes depending on the amount of chiral agent added to generate twisting force in the liquid crystal and an appropriate external field (for example, temperature, electric field, magnetic field). It can also be adjusted by adding an agent.
[0008]
For example, when a left-handed chiral agent is added to a right-handed spiral liquid crystal, the reflection wavelength is different from that when no liquid crystal is solidified at the same temperature.
[0009]
Therefore, by controlling the above parameters in the visible range, specifically, it is possible to configure a color filter that forms reflected light of red, green, and blue by setting the twist pitch of the liquid crystal to three stages. The reflectance can be set higher than that of the conventional color filter.
[0010]
Note that since the phase of the reflected light in the cholesteric liquid crystal or the chiral nematic liquid crystal does not change with respect to the incident light, the polarization direction before and after the incident of the reflected light remains unchanged.
[0011]
Here, the cholesteric liquid crystal or the chiral nematic liquid crystal as described above constitutes a cell in a state of being sandwiched between two substrates, and the surface on the liquid crystal side of the substrate in each cell is planarly aligned.
[0012]
In general, the gap between substrates in each cell, ie, the gap, is constant, and therefore the helical pitch of cholesteric liquid crystal or chiral nematic liquid crystal in each cell is constant. The area is also constant.
[0013]
Further, as a method for widening the selective reflection wavelength region of reflected light, that is, the wavelength bandwidth, for example, as in US Pat. No. 5,691,789, a graded pitch type in which the helical pitch of cholesteric liquid crystal molecules is changed, or for example, JP-A-9-304770 As disclosed in Japanese Laid-Open Patent Publication No. H. No. 1, a plurality of cholesteric liquid crystal layers having different helical pitches are stacked, and an extended reflection wavelength region is provided outside a central wavelength region which is a desired reflection spectral region for each color. There is a so-called selective reflection area enlargement type liquid crystal.
[0014]
[Problems to be solved by the invention]
However, when the reflective LCD having the color filter as described above is observed at an angle shifted from the front, that is, when the viewing angle changes, the wavelength of the reflected light is shorter than that observed from the front. There is a problem that the color tone (color eye) changes for this reason.
[0015]
In this case, if the selective reflection wavelength region is set only in the center wavelength region of each color, although the color purity of the reflected light can be set high, the reflected light intensity in the center wavelength region is lost due to the change in the viewing angle. Further, when the selective reflection area enlargement type liquid crystal is used, the loss of reflected light intensity in the central wavelength area due to the change of the viewing angle can be prevented, but the decrease in color purity is inevitable.
[0016]
The present invention has been made in view of the above-described conventional problems, and uses a cholesteric liquid crystal or a chiral nematic liquid crystal, and at a low cost, shifts the wavelength of reflected light to the short wavelength side when the viewing angle increases. An object of the present invention is to provide a color filter for a reflective LCD that can reliably display a target color without lowering the reflection intensity even if this occurs.
[0017]
[Means for Solving the Problems]
According to the present invention, as described in claim 1, for each of at least three color pixels, a liquid crystal layer composed of either a selective reflection area expansion type, photocurable cholesteric liquid crystal or chiral nematic liquid crystal is formed on a substrate. In the color filter for a reflective liquid crystal display, in which the twist pitch of the liquid crystal in the liquid crystal layer is adjusted corresponding to each color, the twist pitch of the liquid crystal in the pixel of each color is set to the central wavelength region of the color and In addition, the wavelength light in the extended reflection wavelength region adjacent to the longer wavelength side than this is reflected, and the liquid crystal layer in each color pixel has a longer wavelength side and a shorter wavelength side than the central wavelength region of the color. The above object is achieved by a color filter for a reflective liquid crystal display, which is characterized by mixing a dye that absorbs light in the wavelength region.
[0018]
According to a second aspect of the present invention, as described in claim 2, for each of the pixels of at least three colors, a liquid crystal layer composed of one of a selective reflection area expansion type, photocurable cholesteric liquid crystal or chiral nematic liquid crystal is formed on a substrate. In a color filter for a reflective liquid crystal display, wherein the twist pitch of the liquid crystal in the liquid crystal layer is adjusted corresponding to each color, and the twist pitch of the liquid crystal in the pixel of each color is determined from the central wavelength region of the color In addition, the wavelength light in the extended reflection wavelength region adjacent to the longer wavelength side than this is reflected, and the wavelength region on the longer wavelength side than the center wavelength region of the color in the liquid crystal layer in each color pixel, and A reflective liquid crystal display comprising a dye that absorbs light in a wavelength region shorter than a region shifted from a short wavelength side limit of the central wavelength region to a short wavelength side. The lay-color filter, is to achieve the above object.
[0019]
In the present invention, even if the viewing angle is increased and the wavelength shift of the reflected light to the short wavelength side occurs, the reflected light having the wavelength in the central wavelength region of the color is secured and the wavelength light outside the central wavelength region is secured. As a result, it is possible to display a clear color with no change in color tone.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0021]
As shown in FIG. 1, a reflective liquid crystal display (hereinafter, LCD) color filter 10 according to a first example of an embodiment of the present invention includes two substrates 12 and 14 made of glass plates, and It has a cell 16 composed of a cholesteric liquid crystal 20 sandwiched between them. FIG. 1 shows one pixel of the reflective LCD color filter 10.
[0022]
Of the two substrates 12, 14, the inner surface (lower surface) of the upper substrate 12 in FIG. 1 is a parallel alignment film 12A, and the inner surface of the lower substrate 14 facing the parallel alignment film 12A. The (upper side surface) is also a parallel alignment film 14A.
[0023]
Here, the parallel alignment film is a film formed by, for example, applying polyimide to a base material, baking it, and rubbing it in parallel with a cloth to perform parallel alignment treatment.
[0024]
In FIG. 1, reference numeral 18 denotes a liquid crystal layer thickness control bead for keeping the distance between the substrates 12 and 14 constant.
[0025]
The gap, that is, the cholesteric liquid crystal 20 in which the dye 22 is mixed is filled between the parallel alignment film 12A of the base material 12 and the parallel alignment film 14A of the base material 14, and red, blue, Solidified in green pattern.
[0026]
The cholesteric liquid crystal 20 sandwiched between the two substrates 12 and 14 is a selective wavelength region expansion type as disclosed in the above-mentioned US Pat. No. 5,691,789 or JP-A-9-304770, and each color of red, green and blue Are set so as to reflect the wavelength light in the central wavelength region of the color and the extended reflection wavelength region adjacent to the longer wavelength side thereof.
[0027]
As shown in FIGS. 2A to 2C, in the pixels of each color of red, green, and blue, the selective reflection wavelength regions A1, A2, and A3 enlarged by the cholesteric liquid crystal 20 are center wavelengths of the colors. The regions B1, B2, and B3 and the extended reflection wavelength regions C1, C2, and C3 adjacent to the longer wavelength side are set.
[0028]
Further, the dye 22 mixed in the cholesteric liquid crystal 20 has wavelength light in a wavelength region other than the central wavelength regions B1, B2, and B3 of the respective colors as shown by broken lines in FIGS. The non-absorption wavelength regions D1, D2, and D3 are set so as to absorb the light. In particular, the short wavelength side limit of the non-absorption wavelength regions D1, D2, and D3 is more than that of the central wavelength regions B1, B2, and B3. The wavelength is set so as to be shifted to the short wavelength side, and a part of the wavelength light in the short wavelength region is not absorbed slightly than the short wavelength side limit of the central wavelength regions B1, B2, and B3 of each color.
[0029]
The pigment 22 is composed of a pigment or a dye, such as a quinacridone pigment, a phthalocyanine pigment, or an anthraquinone pigment, and an azo dye, a phthalocyanine dye, an anthraquinone dye, or the like.
[0030]
In the reflective LCD color filter 10 according to the example of this embodiment, when the viewing angle is increased under external light, the selective reflection wavelength regions A1, A2, and A3 are shown in FIG. Although it is shifted to the short wavelength side as shown by the two-dot chain line, since the light having a shorter wavelength other than the non-absorption wavelength regions D1, D2, and D3 is absorbed by the dye 22, red, green, blue No component deviated from the central wavelength region B1, B2, B3 of each color to the short wavelength side by a certain amount or more is observed.
[0031]
Further, as described above, the liquid crystal 20 is a selective reflection region expansion type, and thereby, the center wavelength regions B1, B2, and B3 of the corresponding color and the expansion reflection wavelength region C1 adjacent to the longer wavelength side than this. , C2 and C3 are reflected, even if the reflected wavelength is shifted to the short wavelength side as a whole, the reflection intensity in the central wavelength regions B1, B2 and B3 does not decrease. Therefore, predetermined color light can be secured.
[0032]
Note that although cholesteric liquid crystal is used in all of the above embodiments, chiral nematic liquid crystal may be used.
[0033]
Further, the cholesteric liquid crystal 20 is sandwiched between two substrates 12 and 14, which, like the reflective LCD color filter 30 shown in FIG. The substrate, for example, the substrate 12, may be removed.
[0034]
【Example】
Next, examples of the present invention will be described in detail.
[0035]
This embodiment has the same configuration as that of the reflective LCD color filter 10 shown in FIG. 1. First, the manufacturing process will be described with reference to FIG.
[0036]
Appropriate cleaning treatment is performed, and a polyimide (for example, AL-1254 manufactured by JSR) is spin-coated as an alignment film on a glass substrate as a clean base material 12 or 14, and fired at 200 ° C. for 1 hour. The polyimide was rubbed with a cloth to form parallel alignment films 12A and 14A having a thickness of about 600 mm as shown in FIG.
[0037]
Next, the base materials (glass substrates) 12 and 14 on which the parallel alignment films 12A and 14A are formed are bonded together with the parallel alignment films 12A and 14A inside as shown in FIG. 4B. At this time, the gap between the parallel alignment films 12A and 14A is kept constant by spreading the liquid crystal thickness control beads 18 formed in advance between them.
[0038]
The cholesteric liquid crystal 20 is an ultraviolet curable type, and is a graded pitch type in which the chiral pitch continuously changes by adjusting the amount of ultraviolet irradiation. The cholesteric liquid crystal mixed with the dye 22 is heated to an isotropic phase on a hot plate and injected between the parallel alignment films 12A and 14A using a capillary phenomenon as shown in FIG. Fully fills the LCD. As the dye 22, Kayset Red G for red, Kayset Green AB for green, and Kayset Blue A-CR for blue (both trade names, manufactured by Nippon Kayaku Co., Ltd.) were used.
[0039]
Next, annealing was performed at room temperature in order to develop a planar alignment state of the cholesteric liquid crystal. After that, as shown in FIG. 4D, the chiral pitch in the cholesteric liquid crystal layer is adjusted by irradiating with ultraviolet rays to obtain a graded pitch type, and then through a photomask (not shown), FIG. As shown in E), the red part was cured by irradiating with ultraviolet rays (wavelength range different from the ultraviolet rays used for pitch adjustment).
[0040]
Thereafter, the same treatment is performed for green and blue, and as shown in FIG. 4 (F), the top substrate is removed, and an uncured portion is removed using an organic solvent (acetone, propylene glycol, monomethyl ether acetate, etc.). After removal, a color filter patterned on the substrate in red, green and blue was obtained.
[0041]
【The invention's effect】
Since the present invention is configured as described above, in a color filter using a cholesteric liquid crystal or a chiral nematic liquid crystal, good color reproducibility without a change in color and a decrease in reflection intensity is obtained even when the viewing angle changes. It has an excellent effect of being able to.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing a main part of a color filter for a reflective liquid crystal display according to an example of an embodiment of the present invention. FIG. 2 shows green, blue and red light in the color filter for the reflective liquid crystal display. FIG. 3 is a diagram showing the intensity distribution of reflected light by cholesteric liquid crystal and reflected light not absorbed by the dye. FIG. 3 is an enlarged cross-sectional view showing the main part of another embodiment of the color filter for the reflective liquid crystal display. 4] Expanded schematic cross-sectional view showing the manufacturing process of the color filter for the same reflective liquid crystal display [Explanation of symbols]
DESCRIPTION OF SYMBOLS 10, 30 ... Color filter 12 for reflection type liquid crystal displays, 14 ... Base material 12A, 14A ... Parallel alignment film 18 ... Liquid crystal layer thickness control bead 20 ... Cholesteric liquid crystal 22 ... Dye A1, A2, A3 ... Selective reflection wavelength range B1, B2, B3 ... central wavelength regions C1, C2, C3 ... expanded reflection wavelength regions D1, D2, D3 ... non-absorption wavelength regions

Claims (2)

For each of the pixels of at least three colors, a liquid crystal layer made of one of a selective reflection area expansion type, photocurable cholesteric liquid crystal or chiral nematic liquid crystal is formed on the substrate, and the twist of the liquid crystal in the liquid crystal layer In a color filter for a reflective liquid crystal display in which the pitch is adjusted corresponding to each color,
The twist pitch of the liquid crystal in the pixels of each color is set so as to reflect the wavelength light in the central wavelength region of the color and the extended reflection wavelength region adjacent to the longer wavelength side, and the liquid crystal in the pixel of each color A color filter for a reflective liquid crystal display, wherein a dye that absorbs light in a wavelength region on the longer wavelength side and shorter wavelength side than the central wavelength region of the color is mixed in the layer. For each of the pixels of at least three colors, a liquid crystal layer made of one of a selective reflection area expansion type, photocurable cholesteric liquid crystal or chiral nematic liquid crystal is formed on the substrate, and the twist of the liquid crystal in the liquid crystal layer In a color filter for a reflective liquid crystal display in which the pitch is adjusted corresponding to each color,
The twist pitch of the liquid crystal in the pixels of each color is set so as to reflect the wavelength light in the central wavelength region of the color and the extended reflection wavelength region adjacent to the longer wavelength side, and the liquid crystal in the pixel of each color In the layer, a dye that absorbs light in the wavelength region longer than the central wavelength region of the color and light in a wavelength region shorter than the region shifted from the short wavelength side limit of the central wavelength region to the short wavelength side is mixed. A reflective color filter for a liquid crystal display.

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