JP3268917B2 - Liquid crystal display manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal display utilizing the wavelength selectivity of a cholesteric liquid crystal.

[0002]

2. Description of the Related Art Conventionally, a field-effect type liquid crystal display has an advantage that a power consumption is small and a thin display can be formed. Typical examples of such a display include a device in which a twisted nematic liquid crystal layer having a twist of 90 degrees is sandwiched by crossed Nicols, and a chiral nematic liquid crystal layer having a large twist angle as disclosed in JP-A-60-107020. Some are used for display by selecting the polarization axis. However, these have low light utilization efficiency and low contrast.

On the other hand, there has been proposed a cholesteric liquid crystal display having a short pitch, which utilizes a coloring phenomenon due to the temperature dependency of liquid crystal for display. It is known that the pitch of the cholesteric liquid crystal has wavelength dependency of transmitted light. It is displayed using. However, a liquid crystal capable of performing stable color control has not been developed and has not been put to practical use.

[0004]

Therefore, we have previously disclosed in Japanese Patent Application No. Hei 4-320720 a liquid crystal display utilizing the circularly polarized light reflectivity for a specific wavelength of a short pitch cholesteric liquid crystal in which no electric field is applied during display. Proposed. In this method, a cholesteric liquid crystal is used as a background, and a field-effect liquid crystal layer having birefringence is arranged on the front surface thereof. However, no method has been found for producing such a cholesteric liquid crystal layer of a liquid crystal display device with good mass productivity, and there is no other way but to form a liquid crystal cell for each color and combine them. It was inconvenient.

[0005]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention has been made in view of the fact that the pitch of a cholesteric liquid crystal has a temperature dependence in an uncured state. Applying a polymer liquid crystal layer and providing a protective film on the surface thereof, and forming a reflective liquid crystal layer by sequentially curing predetermined portions at a predetermined temperature while changing the temperature of the polymer liquid crystal film, A step of forming a substrate by laminating an electrode film and an alignment film above the cured polymer liquid crystal layer, and overlapping the substrate with another substrate having at least an electrode and an alignment film and filling the space between the substrates with liquid crystal And a manufacturing process.

[0006]

In this manner, the polymer liquid crystal layers of a plurality of colors can be formed sufficiently close to each other, so that the display can be constituted as a single liquid crystal cell, and the applied liquid crystal layers are partially cured in order, so that the liquid crystal layer is substantially cured. A plurality of polymer liquid crystal layers of the same color will be formed on the same plane, and even if an optical layer, for example, a phase layer or a liquid crystal layer is laminated thereon, its optical characteristics can be easily adjusted,
A thin, easy-to-handle display with good display quality can be provided with high productivity.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the structure and display principle of a liquid crystal display according to the present invention will be described.

FIG. 1 is a sectional view of a liquid crystal display according to the present invention. In the drawing, reference numeral 1 denotes a first substrate, on which an optical layer is laminated on a base 11 made of a sheet glass or the like. Reference numeral 2 denotes a reflective liquid crystal layer made of a hardened cholesteric liquid crystal that reflects circularly polarized light having a selected wavelength, and is sandwiched between an underlayer 12 and a protective layer 13 as necessary. The base layer 12 may also serve as a light absorbing film, or a light absorbing layer may be provided further below the base layer 12. Reference numeral 3 denotes a phase layer provided as necessary above the reflective liquid crystal layer 2, and is approximately 1/4.
It comprises a nematic liquid crystal layer obtained by curing a polymer liquid crystal so as to serve as a wave plate. Reference numeral 4 denotes an electrode film provided above the phase layer 3, which is a transparent electrode layer (ITO) in a stripe shape for forming a matrix with the electrodes of the second substrate.
Are provided in parallel. Reference numeral 5 denotes an alignment film for liquid crystal molecules provided above the electrode film 4.

Reference numeral 6 denotes a second substrate having an electrode film 64 and an alignment film 65. Reference numeral 7 denotes a liquid crystal layer filled between the first and second substrates 1 and 6 and aligned by the alignment films 5 and 65. The alignment of the liquid crystal molecules can be controlled by an electric field.
Accordingly, optical characteristics such as a retardation value change. As the liquid crystal layer 7, for example, a nematic liquid crystal layer (TN) having a 90 ° twist alignment, a nematic liquid crystal layer (STN) having a large twist alignment of 270 ° or the like,
Alternatively, a field effect type liquid crystal such as a ferroelectric liquid crystal layer can be used. Reference numeral 8 denotes a polarizing plate which is disposed on the opposite side of the liquid crystal layer 7 from the reflective liquid crystal layer 2 and may be disposed outside the substrate 6 as shown in FIG. Since it may be constituted by a substrate having a linear polarization characteristic, it may be called a polarizer.

In such a configuration, in principle, the reflective liquid crystal layer 2 is a clockwise (or left-handed) circularly polarized light generating means for a specific wavelength, the phase layer 3 is a quarter-wave plate for the light, and the liquid crystal layer 7 Can be considered as a half-wave plate for the wavelength, and the polarizer is a plate for selecting the vibration direction of light. Due to the nature of the cholesteric liquid crystal, the reflective liquid crystal layer 2 reflects only circularly polarized light in a specific direction of light in a specific wavelength range, and reflects circularly polarized light in the opposite direction and light in other wavelength ranges. It is assumed that the liquid crystal layer 2 reflects circularly polarized light having a specific wavelength, resulting in, for example, light traveling π / 2 to the right, and the liquid crystal layer 7 is an STN type nematic liquid crystal having a helical structure.

Therefore, the light is circularly polarized by the reflective liquid crystal layer 2 and π / 2
The traveling light is converted into linearly polarized light traveling by π in the phase layer 3,
The light travels 2π by the liquid crystal layer 7, and if this coincides with the polarization axis of the polarizer 8, light of a specific color selected by the reflective liquid crystal layer will be observed. On the other hand, the liquid crystal layer 7
When an electric field is applied to the substrate, the liquid crystal molecules having a helical structure are oriented substantially perpendicular to the substrate surface and do not function as a half-wave plate, so that the π-advanced light output from the phase layer 3 is At the phase of π, the light passes through the liquid crystal layer 7 and is orthogonal to the polarization axis of the polarizer 8, so that light does not pass through and black is observed.

The relationship between the observed color and black is determined by the polarizer 8
Is reversed by changing the polarization axis of. If the wavelengths to be selected are provided corresponding to red, green, and blue, respectively, as the reflective liquid crystal layer 2, color display can be performed, and each wavelength plate (the phase layer 3 and the liquid crystal layer 7) transmits light. Although it affects the speed, it hardly absorbs light, and the polarizer 8 does not select a part of the light but transmits all the light that matches the vibration direction, so that a bright and high-contrast display can be performed. When the phase layer 3 is not used, the retardation of the liquid crystal layer 7 may be adjusted to a value suitable for transmitting and blocking light by the polarizer 8, or a polarizer 8 having circular polarization selectivity may be used. .

Next, the present invention will be specifically described. First, the base 11 is made of sheet glass or the like, and a light-absorbing coating is provided as necessary. Before forming a reflective liquid crystal layer 2 composed of a cholesteric liquid crystal layer on the base 11, an alignment treatment is performed.
It is preferable to provide a base layer 12 of nm and rub it with a cotton cloth or the like. Next, the cholesteric polymer liquid crystal layer is dissolved in a solvent such as toluene or m-xylene, or is heated to 80 to 120 ° C. without being dissolved, and is coated on the underlayer 12. The cholesteric liquid crystal constituting the reflective liquid crystal layer 2 is disclosed in, for example, JP-A-57-165480 and JP-A-6-165480.
A cholesteric polymer liquid crystal material as disclosed in JP-A-137133 can be used. In this case, the cholesteric liquid crystal is applied after being subjected to the alignment treatment as described above because the cholesteric spiral direction must be along the optical axis even if no electric field is applied during display. Although it may be dried as it is, in order to stabilize the orientation, heat treatment is performed after covering with the protective film 13 and then crosslinking is performed. More preferably, the polymer liquid crystal layer is cured after performing an alignment treatment on the protective film.

More specifically, for example, a siloxane ring is used in which an acrylic group and a cholesteric liquid crystal are alternately bonded around the siloxane ring to bond with another ring. It shows a nematic phase in a wide range up to 100 ° C., and has a glass transition point of −0.6 ° C.
-780 nm (red) when the viscosity at 4.5 degrees C and 80 degrees C is 1.5 Pas and each reflection wavelength is 90 degrees C
And 370nm (blue) thermochromic cholesteric liquid crys
tal). When these two types of liquid crystal materials are mixed,
Depending on the mixing ratio, the reflection wavelength at 90 ° C. is 380 n
m to 780 nm. For example, 50% of both
If it is 50%, it reflects light of about 500 nm. On the other hand, if the temperature of such a mixed liquid crystal material is changed in an uncured state, the reflection wavelength changes. For example, the aforementioned 50% -5
When 0% was changed from 25 ° C. to 110 ° C., it changed almost linearly from 630 nm to 460 nm, and the rate of change was −2.0 nm / K. After such a mixed liquid crystal material is cured (polymerized), the temperature is reduced from 20 ° C to 1 ° C.
Even if it is changed up to 50 degrees C, the reflection wavelength hardly changes. For example, after curing at 90 ° C and storing at 120 ° C, 50
A reflected light of 0 nm is obtained.
When the range is changed to 485 nm, the range is from 485 nm to 492 nm, and there is almost no change in consideration of the relative luminous efficiency.

After preparing a desired ratio of the mixed liquid crystal material based on such an experiment, the base is subjected to an alignment treatment, a polymer liquid crystal layer is applied, a protective film is provided on the surface, and the polymer liquid crystal layer is provided. A color reflection layer is obtained by sequentially curing a predetermined portion at a predetermined temperature while changing the temperature of the film to form a reflective liquid crystal layer. As the protective film 13 used at this time, for example, polyvinyl alcohol having a thickness of 100 to 1000 nm is preferably used. 80 to 17 after applying such a protective film material
In each of the heating and heating processes at 0 ° C. or in the process of rubbing and lowering the temperature from a predetermined temperature of about 170 ° C., curing is performed sequentially. As the sequential curing, for example, through a through hole of a metal mask having 100 μm wide through holes at a pitch of 230 μm, ultraviolet rays are applied to the polymer liquid crystal layer and UV cured, and the position of the through hole of the mask is shifted at the next temperature. UV curing was carried out, and this was repeated once again to form a reflective liquid crystal layer 2 corresponding to three primary colors having a pitch of 110 μm and a width of 100 μm. FIG. 2 illustrates the relationship between the curing temperature and the chromaticity of the above-described materials. It was also confirmed that by increasing the red thermochromic cholesteric liquid crystal component of the mixed liquid crystal material, a stable reflective liquid crystal layer shifted to a higher temperature could be obtained.

In such a process, since the cholesteric liquid crystal layer reflects light in a specific direction at a wavelength selected by the specific pitch, the cross-linking cures the specific pitch, and the cholesteric liquid crystal layer fixes the specific pitch to light of the selected wavelength. The reflective liquid crystal layer 2 is formed. Such a reflective liquid crystal layer 2 has a thickness of 3 to 300 μm, and flatness is maintained because a single polymer liquid crystal film is sequentially cured. Although 10 μm of the stripe gap was not described in this example, it is preferable to cure under a wavelength condition other than the visible light range, but the cured polymer liquid crystal film may be removed only in the gap portion, or the gap may be removed. A stripe width that can be eliminated may be used. Further, a light-shielding film may be newly disposed at a portion corresponding to the gap.

Next, a substrate is formed by laminating at least a phase layer, an electrode film and an alignment film above the reflective liquid crystal layer 2. Similarly, the phase layer 3 has, for example, a polysiloxane as a main chain and a nematic liquid crystal in a side chain, and appropriately dilutes a nematic polymer liquid crystal having an active group which is cross-linked by ultraviolet light in a solvent, and forms the reflective liquid crystal layer 2 or its reflective liquid crystal layer 2 Upper protective layer 1
3 and cured by irradiating ultraviolet rays. Such a phase layer 3 has a characteristic as a polymer resin, and for example, if Δn as a nematic liquid crystal is 0.15, the thickness may be 1 μm. The electrode film 4 and the alignment film 5 are made of an ITO film,
An alignment agent for TN, an alignment agent for STN, an alignment agent for ferroelectric liquid crystal, or the like is used. The same applies to the alignment film 65 and the electrode film 64 on the other substrate 6. Then, the substrate 1 thus constructed and another substrate 6 are overlapped, and the periphery thereof is sealed with a sealing material 9 to form a liquid crystal cell. The distance between the substrates 1 and 6 is determined by a dropping method, a vacuum injection method, or the like. Is filled with liquid crystal, and the inlet is sealed. As described above, the liquid crystal layer 7 can be made of a ferroelectric liquid crystal, TN or STN in which liquid crystal molecules have a helical structure.

In the above-described manufacturing method, a protective film 13 intended for an alignment film can be used. In this case, it is preferable to select a solvent for the protective film that has extremely low compatibility with the polymer liquid crystal. For example, NMP is desirable for a siloxane-type polymer liquid crystal. When a polyimide film is used as the protective film for such orientation, the imidization reaction is preferably completed, and the film may be formed by a vacuum film forming method or the like. Rubbing after forming such a protective film is desirably formed in parallel with the rubbing direction of the underlayer 12. The orientation force can also be given by applying a shearing force from above the protective film 13. As for the shearing force, rubbing is performed using a rubbing puffing agent such as rayon cloth with a rubbing strength corresponding to the heated state of the base 11. The higher the temperature, the lower the rubbing strength. Further, although the above-described protective film has been described as being used as a part of the display as it is, it may be removed after the reflective liquid crystal layer 2 is formed.

[0019]

As described above, according to the present invention, when focusing on light in a specific wavelength range and effectively utilizing light in that wavelength range, it is necessary to form reflective liquid crystal layers of a plurality of colors that are sufficiently close to each other. The display can be configured as a single liquid crystal cell, and the applied liquid crystal layer is partially cured in order to form a polymer liquid crystal layer of a plurality of colors in substantially the same plane. Layer, such as a phase layer or a liquid crystal layer, the optical characteristics of the layer can be easily adjusted and easily manufactured.
A thin, easy-to-handle liquid crystal display with high light utilization and high display quality could be provided with high productivity.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a chromaticity diagram relating to a reflective liquid crystal layer in an example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first substrate 2 reflective liquid crystal layer 3 phase layer 4 electrode film 5 alignment film 6 second substrate 7 liquid crystal layer 8 polarizing plate (polarizer) 9 sealing material

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-117394 (JP, A) JP-A-51-7949 (JP, A) JP-A-61-32801 (JP, A) JP-A-57-1979 165480 (JP, A) JP-A-4-12317 (JP, A) JP-A-3-291626 (JP, A) JP-A-3-67219 (JP, A) JP-A-4-3021 (JP, A) JP-A-61-137133 (JP, A) JP-A-56-175816 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/137 G02F 1/1347

Claims (1)

(57) [Claims] 1. A step of applying an alignment treatment to a base, applying a polymer liquid crystal layer and providing a protective film on the surface thereof, and sequentially curing predetermined portions at a predetermined temperature while changing the temperature of the polymer liquid crystal film. Forming a reflective liquid crystal layer by laminating an electrode film and an alignment film above the reflective liquid crystal layer to form a substrate, and overlapping the substrate with another substrate having at least an electrode and an alignment film. Filling the gap between the substrates with liquid crystal.