JP3414189B2 - Reflection type color filter and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective color filter used in a reflective color liquid crystal display device and a manufacturing method thereof.

[0002]

2. Description of the Related Art Reflective liquid crystal display devices are thinner, lighter, and lighter than conventional transmissive liquid crystal display devices using a backlight.
It is an excellent and expected technology in terms of low power consumption. However, if a color filter is inserted for color display as in the case of the transmissive type, the light absorption of the coloring material lowers the reflectance, resulting in insufficient brightness as a display device, which causes a problem.

As a countermeasure against this, a method of lowering the color material concentration of the color filter to improve the brightness has been studied, but in this method, the color purity of the color filter is lowered and the color reproducibility of the liquid crystal display device is lowered. Resulting in.

Therefore, as a method of improving the brightness without deteriorating the color reproducibility, a reflective color filter is utilized by utilizing the wavelength selective reflection characteristic of the cholesteric liquid crystal without using coloring materials such as pigments and dyes. A method of forming is proposed. Among them, a UV-curable cholesteric liquid crystal or chiral nematic liquid crystal that can change the selective reflection wavelength depending on the temperature and can fix the selective reflection wavelength by exposing to ultraviolet light at a desired temperature has a plurality of layers in a single layer. It is possible to form a reflection color pattern of the above, and studies are being conducted as a material for forming a reflection type color filter. (SID '94 Choleste
ric Reflectors withaColor
Pattern)

The ultraviolet-curable cholesteric liquid crystal or chiral nematic liquid crystal can obtain a high reflectance by aligning the orientation directions of the individual molecules, and the temperature can be controlled to change the twist pitch of the liquid crystal molecules to change the selective reflection wavelength. Since it is a material that can be controlled, it is important to control these characteristics in order to form a reflective color filter.

[0006] As a method currently proposed, firstly, an ultraviolet-curable cholesteric liquid crystal or a chiral nematic liquid crystal is sandwiched between two glass substrates on which an alignment film such as polyimide is formed in order to align the alignment directions, and heating is performed. While applying pressure, the whole is uniformly oriented. Subsequently, while being heated to a temperature at which a required wavelength is reflected, it is exposed to ultraviolet light through a photomask having a required pattern to fix the pitch of the liquid crystal only in the exposed portion to obtain a reflective layer pattern. By repeating this process, a reflective color filter of a plurality of colors is formed.

Further, in the case of this system, since the liquid crystal layer itself is a reflection layer, it is not necessary to provide a reflection layer separately,
On the contrary, a light absorption layer is required to remove the light transmitted through the liquid crystal layer (the light other than the selective reflection wavelength is reflected. This light absorption layer is usually provided below the alignment film.

The problem in this step is that, firstly, since the glass substrate is sandwiched and pressure is applied to develop the film, the film is exposed through the glass substrate during ultraviolet exposure. Even if a photomask having a predetermined pattern is used, a gap between the mask and the liquid crystal layer occurs due to the thickness of the glass substrate, and resolution cannot be obtained.

The second problem is that so-called exposure fog occurs due to diffused reflection in the liquid crystal layer during exposure to ultraviolet light. That is, although the liquid crystal molecules are uniformly aligned by using the alignment film, they are not completely oriented in the same direction, but are oriented in a random direction to some extent. As a result, the ultraviolet light is scattered in random directions, the portion other than the predetermined pattern portion is also exposed, the liquid crystal pitch is fixed, and the patterning of the next color becomes impossible.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and it is an object of the present invention to use a UV-curable cholesteric liquid crystal or chiral nematic liquid crystal to display characteristics. To provide an excellent reflective color filter and its manufacturing method.

[0011]

In order to solve the above problems, the present invention provides a light absorbing layer on a substrate, and a recess is provided from the surface to the inside of the light absorbing layer, and the wavelength and polarization selective reflection layer is provided in the recess. A reflective color filter is provided. Further, in particular, there is provided a reflective color filter, wherein the wavelength and polarization selective reflection layer is an ultraviolet curable cholesteric liquid crystal or an ultraviolet curable chiral nematic liquid crystal.

As the manufacturing method thereof, 1) a photosensitive black resin composition is applied onto a substrate, and 2) exposure is performed using a photomask having a desired pattern to expose the unexposed portion of the light absorbing layer to a required depth. After development, a recess is formed in the light absorption layer to provide a recess. 3) A UV-curable cholesteric liquid crystal or a UV-curable chiral nematic liquid crystal is filled in the recess while applying pressure, and 4) a substrate is required. By heating to a temperature for controlling the UV-curable cholesteric liquid crystal or the UV-curable chiral nematic liquid crystal, a desired portion is cured by exposure using a photomask having a desired pattern, 5) 3) and 4 The present invention provides a method for manufacturing a reflective color filter, which is characterized in that the number of colors required is repeated.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The detailed contents of the present invention will be described below with reference to the drawings. First, the light absorption layer 2 is formed on the substrate 1, but the substrate material at this time can be arbitrarily selected as long as it is a material used for a liquid crystal display device. Usually, a glass substrate is used.

Light absorbing layer 2 provided on this glass substrate
Is formed of a black resin composition having the following composition. That is, it is a photosensitive black resin composition obtained by diluting a black pigment, a binder, a photosensitive resin, and a photosensitizer with a diluting solvent, and a black resist used for forming a black matrix of a transmission type color filter can be used. .

The black resist is uniformly applied on the substrate by a spin coating method, a roll coating method or the like, and dried by using a clean oven, a hot plate or the like. At this time, it is necessary to set the film thickness to be applied to be larger than the film thickness of the selective reflection layer to be formed in the subsequent steps, and usually 10 to 20 μm is applied.

Next, the film is exposed to ultraviolet rays using a predetermined photomask 3 and then developed using a predetermined developing solution. At this time, in the present invention, the light absorption layer is not completely developed by controlling the development time, and the development is stopped when a residual film is left to the extent that the function as the light absorption layer is not impaired.

Here, the light absorption layer becomes a layer 2'having a recess (rib shape) having a predetermined shape. The depth of the recessed portion is the depth of the selective reflection layer formed in the next step, and is 8 to 18
About μm is appropriate.

Subsequently, while heating the substrate provided with the light absorbing layer, a predetermined amount of ultraviolet-curable cholesteric liquid crystal or chiral nematic liquid crystal is dropped on the light absorbing layer, and a squeegee or the like is used to apply a shear to the recessed portion. A buried and selective reflection layer 5 is formed. At this time, as a material of the squeegee, a sufficiently flexible material such as urethane rubber or silicon rubber is used so as not to damage the light absorption layer.
By coating with a squeegee, the ultraviolet-curable cholesteric liquid crystal or chiral nematic liquid crystal has a share in the processing direction of the squeegee, and the liquid crystal molecules are aligned in the same alignment direction, and good reflection characteristics can be obtained.

When it is desired to make the orientation uniform,
It is also possible to form an alignment film on the light absorption layer in advance before coating the ultraviolet-curable cholesteric liquid crystal or chiral nematic liquid crystal and rub the alignment film according to the processing direction of the squeegee to provide the alignment layer.

Through the steps up to this point, the shape of the reflective color filter according to the present invention is formed as shown in FIG. Subsequently, a step of giving the selective reflection layer a selective reflection characteristic of a desired wavelength is performed. First, the substrate on which the light absorption layer and the selective reflection layer are formed is heated to a desired temperature. The temperature at this time is determined by the characteristics of the UV-curable cholesteric liquid crystal or chiral nematic liquid crystal used and the required reflection wavelength.

Next, while maintaining this temperature, UV exposure is carried out using a photomask adapted to the shape of the selective reflection layer. In the portion exposed to ultraviolet rays, the pitch of the liquid crystal is fixed by the polymerization reaction by the radicals generated by the initiator, and the reflection wavelength does not change even if the temperature is changed thereafter. Since the polymerization reaction does not occur in the unexposed portion, it is possible to change the selective reflection wavelength by changing the temperature.

Further, in the present invention, since the selective reflection layer is surrounded by the rib formed of the same material as the light absorption layer, the ultraviolet light scattered at the exposed portion is absorbed by the rib and the ultraviolet light other than the pattern is absorbed. There is no light scattering and so-called fog does not occur.

Subsequently, the number of colors required for the above steps is repeated to form a reflective color filter.

[0024]

EXAMPLE A 300 mm × 300 mm non-alkali glass substrate with a thickness of 1.1 mm (manufactured by Corning: “# 705
9 ”) on top of which a black resist (manufactured by Fuji Hunt:“ CK
7000 ") was spin-coated at 300 rpm and dried in a clean oven at 70 ° C for 20 minutes. Further, this step was repeated three times to obtain a black resist film having a thickness of 12 μm. This black resist film, line width 20μ
Ultraviolet light exposure was performed at 300 mJ using an ultrahigh pressure mercury lamp through a photomask having a pitch of 100 m and a pitch of 100 μm. Then, it was immersed in a developing solution (manufactured by Fuji Hunt: “CD”) for 10 minutes and developed, and rinsed with pure water spray. At this time, the unexposed portion of the black resist film was developed by 10 μm to form a rib-shaped light absorbing layer.

This substrate is heated to 100 using a hot plate.
While heating to ℃, stripes (WA
5 g of "TC3947L" manufactured by CKER Co., Ltd.) was dropped and a squeegee made of urethane rubber was used for coating while applying pressure. This became a form of being embedded in the rib shape of the light absorption layer to form a selective reflection layer. Then, the substrate 95
With heating to ℃ and peak reflection wavelength of 465 nm,
Of the selective reflection layer, only the pixels to be displayed in blue were exposed to ultraviolet light at 900 mJ through a photomask. Next, the substrate temperature was set to 70 ° C., and the selective reflection layer other than the pitch which was exposed in the previous step was fixed so as to reflect 545 nm, and only the green display pixel was similarly exposed. Furthermore, the substrate temperature is set to 45
After making it reflect at 620 nm as the temperature, the same exposure was carried out to form a red display pixel. At this time, the reflection characteristics of each pixel were good. Moreover, there was no problem such as color mixing in each pixel at a pitch of 100 μm.

[0026]

The present invention having the above-mentioned constitution has the following effects. That is, the light absorption layer is developed to a predetermined thickness to form a concave portion (rib shape), and the concave portion is filled with an ultraviolet curable cholesteric liquid crystal or a chiral nematic liquid crystal, so that a pattern is formed by the ultraviolet light. It is possible to obtain a pattern having a good resolution by preventing the scattering of light on the unexposed portion. In addition, uniform alignment is realized by inserting a UV-curable cholesteric liquid crystal or chiral nematic liquid crystal into the rib shape of the light absorption layer using a doctor, and a reflective color filter with high reflectance can be manufactured by a simple method. Is possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a cross-sectional structure of an example of a reflective color filter of the present invention.

FIG. 2 is an explanatory view showing steps of a method of manufacturing a reflective color filter of the present invention.

[Explanation of symbols]

1 ... Substrate 2, 2 '... Light absorbing layer 3 ... Photomask 4
... Doctor 5 ... Selective reflection layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-136602 (JP, A) JP 61-128205 (JP, A) JP 59-83112 (JP, A) JP 7- 287115 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 5/20 101 G02B 5/20 G02F 1/1335 505

Claims (3)

(57) [Claims] 1. A reflective color filter comprising a light absorbing layer provided on a substrate, a recess extending from the surface to the inside of the light absorbing layer, and a wavelength and polarization selective reflection layer provided in the recess. 2. The reflection type color filter according to claim 1, wherein the wavelength and polarization selective reflection layer is an ultraviolet ray curable cholesteric liquid crystal or an ultraviolet ray curable chiral nematic liquid crystal. 3. A photosensitive black resin composition is applied onto a substrate, and 2) is exposed using a photomask having a desired pattern to develop and remove the unexposed portion of the light absorbing layer to a required depth. The concave portion is provided in the light absorbing layer, 3) the ultraviolet absorbing cholesteric liquid crystal or the ultraviolet curable chiral nematic liquid crystal is filled in the concave portion of the light absorbing layer while applying pressure, and 4) the substrate is heated to a required temperature Then, while controlling the reflection wavelength of the UV-curable cholesteric liquid crystal or the UV-curable chiral nematic liquid crystal, light exposure is performed using a photomask having a desired pattern to cure necessary portions, and the steps 5) 3) and 4) are performed. A method of manufacturing a reflective color filter, characterized in that the required number of colors is repeated.