JPH11326911A - Reflection type liquid crystal display element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to sufficiently increase refractive index differences between polymer layers and liquid crystal layers in the state of not impressing an electric field on reflection layers alternately laminated with the polymer layers and the liquid crystal layers and to obtain sufficient reflected light intensity. SOLUTION: This process for production consists in forming a polyimide film 21b by applying photodecomposable polyimide on an electrode 12 of a substrate 11 then, heating the coating. Liquid crystals and a liquid mixture composed of a photodimerization material, such as polyvinyl cinnamate, and a photopolymerizable monomer are applied on the polyimide film 21b and is irradiated with polarizing UV rays having a polarization direction in a direction perpendicular to the substrate surface. As a result, the liquid crystal layer 22b of a PDLC structure is formed on the polyimide film 21b and the photodimerization material 4 in the liquid crystal layer 22b induces a photodimerization reaction. In the polyimide film 21b, the polyimide chains 1a of the same direction as the polarizer direction of the polarizing UV rays are decomposed and only the polyimide chains 1b of the direction perpendicular to the polarization direction remain and the liquid crystal molecules 3a in the liquid crystal layer 22b are aligned in the substrate surface direction. The reflection layers are obtd. by alternately laminating and forming the polyimide films 21b and liquid crystal layers 22b described above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device capable of color display and a method for manufacturing the same.

[0002]

2. Description of the Related Art A reflection type liquid crystal display element does not require a dedicated light source such as a backlight unlike a transmission type liquid crystal display element, consumes less power, and can be configured to be thin and light. Suitable for display devices such as portable information terminals.

Conventionally, as a reflection type liquid crystal display device capable of color display, a polarizing plate is arranged on both sides of a TN liquid crystal or STN liquid crystal cell to constitute an optical shutter, and incident light as external light is filtered by a color filter. There is a known colorant which is colored, transmitted through an optical shutter, and reflected by a reflector. However, since this reflection type liquid crystal display element uses a polarizing plate and a color filter, there is a disadvantage that light loss is large, reflected light of output is weak, and luminance is low.

Therefore, as a reflection type liquid crystal display element not using a polarizing plate or a color filter, a liquid crystal layer and a polymer layer are alternately formed in a multilayer between two electrodes on which electrodes are respectively formed. It is considered that a reflective layer is formed by laminating the layers to reflect light of a specific wavelength in visible light by a periodic change in refractive index.

For example, Japanese Patent Application Laid-Open Nos. 4-355424 and 5-134266 disclose between electrodes 12, 14 of substrates 11, 13 on which electrodes 12, 14 are formed, as shown in FIG. In the figure, a reflective layer in which a polymer layer 17 and a liquid crystal layer 18 are alternately laminated is sandwiched.

This display element has a periodic refractive index between a liquid crystal layer 18 whose refractive index changes according to a voltage applied between the electrodes 12 and 14 and a polymer layer 17 whose refractive index does not change. According to the principle of the interference filter, the light of a specific wavelength in the incident light is reflected and the light of another wavelength region is transmitted according to the principle of the interference filter.

For example, when no voltage is applied between the electrodes 12 and 14, the liquid crystal is oriented in a random direction, causing a difference in the refractive index between the polymer layer 17 and the liquid crystal layer 18. , 14 periodically changes in the refractive index, and as shown in FIG. 10C, the light 56 of the specific wavelength in the incident light 55 is reflected. The reflection wavelength is determined by the period of change in the refractive index, that is, the thickness of the polymer layer 17 and the liquid crystal layer 18.

On the other hand, when a sufficient voltage is applied between the electrodes 12 and 14, the liquid crystal is arranged in a direction perpendicular to the substrates 11 and 13, so that the polymer layer 17 and the liquid crystal layer 18 are refracted. As the refractive index becomes closer, the periodic change in the refractive index between the electrodes 12 and 14 becomes smaller, and most of the incident light 55 passes through the display element.

This reflective liquid crystal display element does not use a polarizing plate or a color filter, so that a light loss is small and a high reflectance is obtained, so that a high-luminance display is obtained.

As a method of manufacturing the reflection type liquid crystal display device, conventionally, a liquid mixture of a liquid crystal and a photopolymerizable monomer is injected between the electrodes 12 and 14, and a laser beam having a predetermined wavelength and the same phase is injected into the liquid mixture. A method of forming a polymer layer 17 by polymerizing a photopolymerizable monomer by interference of light from both directions to form a polymer layer 17 and depositing liquid crystal in a region other than the polymer layer 17 to form a liquid crystal layer 18 Is considered.

[0011] For example, SPIE Vol.2152 / 303 ('94) "Develo
pment of photopolymer-liquid crystal composite mat
In the “erials for dynamic hologram applications”, the mixed solution 16 as described above is injected between the electrodes 12 and 14 as shown in FIGS. 10A and 10B, and the substrate 13 is formed as shown in FIG. , 11 or by irradiating laser beams 53, 54 from the substrate 13 side as shown in FIG. 3B, thereby increasing the height as shown in FIG. It is shown that a reflective layer in which molecular layers 17 and liquid crystal layers 18 are alternately formed is obtained.

[0012]

In the reflection type liquid crystal display device shown in FIG. 10C, the refraction is caused between the polymer layer 17 and the liquid crystal layer 18 without applying a voltage between the electrodes 12 and 14. A difference in rate causes light 56 of a specific wavelength in the incident light 55.
Is reflected.

However, at this time, the liquid crystal in the liquid crystal layer 18 is not controlled in orientation and is oriented in a random direction, so that the difference in the refractive index between the polymer layer 17 and the liquid crystal layer 18 is increased. Can not do. Therefore, reflected light with sufficient intensity cannot be obtained.

If the liquid crystal in the liquid crystal layer 18 can be oriented in a specific direction without applying a voltage between the electrodes 12 and 14, the difference in the refractive index between the polymer layer 17 and the liquid crystal layer 18 can be sufficiently reduced. The intensity can be increased, and a sufficient reflected light intensity can be obtained.

A liquid crystal alignment material such as photodegradable polyimide has an effect of aligning the liquid crystal in a certain direction. For example,
As shown in Oplus E No. 207 ('97) p81-87, "Current and Future of Liquid Crystal Alignment Films,"
When irradiated with polarized ultraviolet light, the polyimide chain in the same direction as the polarization direction is decomposed, and only the polyimide chain in the direction perpendicular to the polarization direction remains, and the liquid crystal molecules can be oriented in the direction of the remaining polyimide chain. .

Further, polyvinyl cinnamate (PVC)
i) and cinnamate ethyl methacrylate (CEMA)
A light dimerization material such as described above is also effective in orienting the liquid crystal in a certain direction. For example, Applied Physics Vol. 64, No. 10, ('95) p1007-
1012 `` Control of liquid crystal alignment using photodimerization reactive polymer film ''
As shown in the above, the polyvinyl cinnamate film is
By irradiating polarized ultraviolet light, polyvinyl cinnamate molecules having side chains parallel to the polarization direction preferentially cause a photodimerization reaction, develop optical anisotropy, and align liquid crystal molecules in a certain direction. be able to. In addition, when cinnamate ethyl methacrylate film is irradiated with polarized ultraviolet light, the cinnamate ethyl methacrylate itself, which is parallel to the polarization direction, preferentially causes a light dimerization reaction, and develops optical anisotropy, and the liquid crystal molecules Can be oriented in a certain direction.

Thus, the polyimide chain in a certain direction is
The liquid crystal can be oriented in that direction. Light 2
Polyvinyl cinnamate and cinnamate ethyl methacrylate after the quantification reaction can also orient the liquid crystal in a certain direction.

However, the liquid crystal alignment force of a liquid crystal alignment material such as a certain direction of a polyimide chain is weak. Similarly, the photo-dimerization material such as polyvinyl cinnamate and cinnamate ethyl methacrylate after the photo-dimerization reaction has a weak liquid crystal alignment force.

For this reason, in the reflection type liquid crystal display device shown in FIG. 10C, the liquid crystal in the liquid crystal layer 18 is kept in a state where no voltage is applied between the electrodes 12 and 14 by the liquid crystal alignment material or the light dimerization material. Is oriented in a specific direction, it cannot be reliably and sufficiently oriented, and it is difficult to sufficiently increase the refractive index difference between the polymer layer 17 and the liquid crystal layer 18.

Further, in this case, the liquid crystal display element is provided with a certain direction on the surface of the substrates 11 and 13 on which the electrodes 12 and 14 are formed, similarly to the method of orienting the liquid crystal in a specific direction. When a liquid crystal alignment material such as a polyimide chain or a photodimerization material such as polyvinyl cinnamate or cinnamate ethyl methacrylate after a photodimerization reaction is formed as an alignment film, a liquid crystal alignment material or a photodimerization material The liquid crystal alignment force of only reaches the liquid crystal layer in the large number of liquid crystal layers 18 which is close to the alignment film. In particular, in the reflection type liquid crystal display element shown in FIG. 10C, since the polymer layers 17 and the liquid crystal layers 18 are alternately provided in the thickness direction of the reflection layer, the liquid crystal layer in the central portion of the reflection layer in the thickness direction is provided. On the other hand, the liquid crystal alignment force of the alignment film on the substrates 11 and 13 is less affected.

Accordingly, the present invention provides a reflective liquid crystal display device having a reflective layer in which a polymer layer and a liquid crystal layer are alternately laminated between two substrates, in a state where no electric field is applied to the reflective layer. In addition, the difference in the refractive index between the polymer layer and the liquid crystal layer can be made sufficiently large, and sufficient reflected light intensity can be obtained.

[0022]

According to the reflection type liquid crystal display device of the present invention, a polymer layer made of a liquid crystal alignment material and a liquid crystal layer containing a light dimerization material are alternately provided between two substrates. A laminated reflective layer is formed, and the liquid crystal in each of the liquid crystal layers is oriented in a specific direction by the light dimerization material in the liquid crystal layer and the liquid crystal alignment material forming the adjacent polymer layer. It is assumed that

[0023]

As described above, a liquid crystal alignment material such as a polyimide chain in a certain direction and a photodimerization material such as polyvinyl cinnamate and cinnamate ethyl methacrylate after a photodimerization reaction align a liquid crystal in a certain direction. However, each liquid crystal alignment force is weak.

On the other hand, in the present invention, each polymer layer of the reflective layer in which the polymer layer and the liquid crystal layer are alternately laminated is formed by a liquid crystal alignment material such as a polyimide chain in a certain direction, Since each liquid crystal layer contains a light dimerization material such as polyvinyl cinnamate and cinnamate ethyl methacrylate after the light dimerization reaction, the central part of the reflective layer in the thickness direction without applying an electric field to the reflective layer. The liquid crystal in all the liquid crystal layers, including the liquid crystal layer, has the liquid crystal alignment force of the photo-dimerizing material in each liquid crystal layer and the liquid crystal alignment force of the liquid crystal alignment material forming the adjacent polymer layer, At the same time, it is surely and sufficiently oriented in a specific direction, for example, a direction parallel to the substrate surface.

Therefore, the refractive index difference between the polymer layer and the liquid crystal layer can be made sufficiently large over the entire area in the thickness direction of the reflection layer without applying an electric field to the reflection layer, and sufficient reflection can be obtained. Light intensity can be obtained.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment as Manufacturing Method FIGS. 1 to 3 show a first example of a manufacturing method according to the present invention.

In this example, first, as shown in FIG. 1A, the electrode 12 of the substrate 11 having the electrode 12 formed on one side is formed.
The photodegradable polyimide 21a is applied thereon with a thickness of about 70 to 110 nm by a printing method, a transfer method, a spin coating method, or the like. As the photodegradable polyimide 21a, for example, Optmer AL125 manufactured by Nippon Synthetic Rubber Co., Ltd.
4 can be used.

Next, heat is applied to the photodegradable polyimide 21a to polymerize the photodegradable polyimide 21a, thereby forming a polyimide film 21b on the electrode 12 as shown in FIG. 1B. At this time, as shown in FIG. 2A, the polyimide chains 1 in the polyimide film 21b are oriented in random directions.

Next, as shown in FIG. 1C, a mixed solution 22a obtained by further dissolving a photo-dimerizing material in a mixed solution of a liquid crystal and a photopolymerizable monomer is formed on the polyimide film 21b.
7 by printing, transfer or spin coating
It is applied with a film thickness of about 0 to 110 nm. As the photopolymerizable monomer, one having compatibility with liquid crystal, transparency, and being polymerized and cured in an ultraviolet region described later is used.

As the light dimerization material, for example, polyvinyl cinnamate having a molecular structure as shown in FIG. 5 and causing a light dimerization reaction by irradiation with polarized ultraviolet rays as described later, or a material as shown in FIG. Cinnamate ethyl methacrylate having a molecular structure and causing a photodimerization reaction by irradiation with polarized ultraviolet rays as described later is used.

Next, as shown in FIG.
2a and the polyimide film 21b are irradiated with polarized ultraviolet rays 25 whose polarization direction is the polarization direction in these thickness directions.

As a result, the photopolymerizable monomer in the mixed solution 22a is polymerized, and as shown in FIGS. 1D and 2B, the liquid crystal droplet is formed on the polyimide film 21b and in the polymer 2. Liquid crystal layer 2 having PDLC structure 3 dispersed therein
2b is formed, and the photo-dimerization material 4 in the polymer 2 causes a photo-dimerization reaction to exhibit optical anisotropy.

That is, when polyvinyl cinnamate is used as the light dimerization material 4, a polyvinyl cinnamate molecule having a side chain parallel to the polarization direction of the polarized ultraviolet light 25 preferentially causes a light dimerization reaction, When cinnamate ethyl methacrylate is used as the dimerization material 4, the cinnamate ethyl methacrylate itself parallel to the polarization direction of the polarized ultraviolet light 25 causes a photo-dimerization reaction preferentially, and each of the photo-dimerization materials 4 Optical anisotropy that causes the liquid crystal molecules 3a in the liquid crystal droplet 3 to be oriented in the plane direction of the substrate 11 is developed.

At the same time, the irradiation of the polarized ultraviolet rays 25
In the polyimide film 21b, as shown in FIG. 2B, the polyimide chain 1a in the same direction as the polarization direction of the polarized ultraviolet light 25 of the polyimide chain 1 shown in FIG. Polyimide chain 1b in the direction perpendicular to the direction
Only remains, the direction of the remaining polyimide chain 1b,
That is, the effect of aligning the liquid crystal molecules 3a in the plane direction of the substrate 11 is generated.

The liquid crystal layer 22b does not lose the switching property of the liquid crystal molecules 3a due to the polymerization of the photopolymerizable monomer, but is fixed on the polyimide film 21b as a whole. Can be applied.

Thereafter, the steps shown in FIGS. 1A to 1D are repeated a predetermined number of times, and the polyimide film 21b and the liquid crystal layer 22b are alternately formed on the electrode 12 as shown in FIG. Then, a reflective layer is obtained by laminating a predetermined number of layers.

In this case, in each of the liquid crystal layers 22b constituting the reflection layer, as shown in FIG. 2B, the liquid crystal molecules 3a are formed by the light dimerization material 4 after the light dimerization reaction.
2B in the plane direction of the substrate 11, and in each of the polyimide films 21b constituting the reflection layer, as shown in FIG. 2B, the liquid crystal molecules 3a are formed by the remaining polyimide chains 1b. 11 has an effect of orienting in the plane direction of each liquid crystal layer 22.
In FIG. 2B, as shown in FIG.
Are reliably and sufficiently oriented in the plane direction of the substrate 11.

Next, as shown in FIG. 3 (B), the electrode 14 side of the substrate 13 having the electrode 14 formed on one surface side is adhered to the reflective layer to obtain a reflective liquid crystal display device.

[Second Embodiment as Manufacturing Method] FIG. 4
Shows a second example of the manufacturing method of the present invention.

In this example, as shown in FIG. 4A, the steps shown in FIGS. 1A to 1D are repeated on the electrode 12 on the substrate 11 so that the polyimide film 21b and the liquid crystal layer 22b are formed.
4 are alternately laminated to form a multilayer film.
As shown in FIG. 1B, on the electrode 14 on the substrate 13, FIG.
The steps shown in (A) to (D) are repeated to form a multilayer film in which the polyimide film 21b and the liquid crystal layer 22b are alternately laminated, and then, as shown in FIG. Is bonded to the multilayer film on the substrate 12.

[Embodiment as Reflection Type Liquid Crystal Display Element]
In the reflective liquid crystal display device obtained by the above method, as shown in FIG. 7A, when no voltage is applied between the electrodes 12 and 14, the liquid crystal layer 22b having the refractive index n1 and the polyimide having the refractive index n3 are formed. The refractive index difference (n1
To n3), that is, due to the periodic change of the refractive index in the reflective layer, the light 57 of the specific wavelength in the incident light 55
Is reflected, and the other light is transmitted.

At this time, each liquid crystal layer 22
The liquid crystal in FIG. 2B shows the liquid crystal alignment force of the photodimerizing material 4 in the liquid crystal layer 22b after the photodimerization reaction shown in FIG. 2B and the adjacent polyimide film 21b in FIG. Due to the remaining liquid crystal alignment force of the remaining polyimide chains 1b, the substrate 1
1 and 13 are reliably and sufficiently aligned in the plane direction, so that the difference in the refractive index between the liquid crystal layer 22b and the polyimide film 21b (n
1 to n3) are sufficiently large, and a sufficient reflected light intensity is obtained.

Curve 6 in FIG. 8 shows the case where a polyimide film composed of the above-mentioned remaining polyimide chains was formed as a polymer layer, and the liquid crystal layer did not contain a photodimerizing material. In the case where the layer is formed of a material having no liquid crystal orientation and the liquid crystal layer contains the photodimerized material after the photodimerization reaction, the curve 8 further shows, as in the above embodiment of the present invention, When a polyimide film composed of polyimide chains remaining as a polymer layer is formed, and the liquid crystal layer also contains a photodimerization material after the photodimerization reaction,
The change in reflectance of one layer of the polymer layer and the liquid crystal layer with respect to the incident angle of incident light is measured. The measurement was performed by setting the polarizing microscope to the crossed Nicols state and setting the sample to 0.
The rotation was performed from ° to 90 °.

As is apparent from the above, according to the present invention, the light-dimerizing material in the liquid crystal layer after the photo-dimerization reaction and the liquid crystal alignment material forming the adjacent polymer layer have a synergistic effect. The rate increases significantly.

FIG. 9 is a graph showing the maximum reflectance (reflectance when the angle is 45 ° in FIG. 8) with respect to the number of polymer layers and liquid crystal layers in the reflection type liquid crystal display device according to the above embodiment of the present invention. The relationship was shown, and the polarization microscope was set in a crossed Nicols state as described above, and the sample was turned from 0 ° to 90 °.
This is the result of measurement by rotating the sample up to. As is clear from this, the maximum reflectance can be significantly increased by setting the number of layers to be equal to or more than a certain value.

In the reflection type liquid crystal display device of the above embodiment, when a sufficient voltage is applied between the electrodes 12 and 14 as shown in FIG.
The liquid crystal layer 22b has a refractive index to the incident light 55 by being oriented in a direction perpendicular to
1b to a refractive index n2 close to the refractive index n3, and the difference in the refractive index between the liquid crystal layer 22b and the polyimide film 21b (n2-n2).
n3) is small, and most of the incident light 55
Transmit 0.

[0047]

As described above, according to the reflection-type liquid crystal display device of the present invention, when no electric field is applied to the reflection layer,
The refractive index difference between the polymer layer and the liquid crystal layer can be made sufficiently large, and a sufficient reflected light intensity can be obtained. Further, since a high luminance is obtained, the luminance is slightly lowered, but the viewing angle can be widened by disposing a scattering plate.

According to the manufacturing method of the present invention, the above-mentioned reflective liquid crystal display device can be obtained reliably and easily.

[Brief description of the drawings]

FIG. 1 is a view showing some steps of a first example of a manufacturing method of the present invention.

FIG. 2 is a diagram showing a state of a polyimide film and a liquid crystal layer.

FIG. 3 is a view showing a subsequent step of the first example of the manufacturing method of the present invention.

FIG. 4 is a view showing a second example of the manufacturing method of the present invention.

FIG. 5 is a diagram showing a molecular structure of polyvinyl cinnamate and a photodimerization reaction process.

FIG. 6 is a diagram showing the molecular structure of cinnamate ethyl methacrylate and the process of photodimerization reaction.

FIG. 7 is a diagram for explaining the operation of an example of the reflection type liquid crystal display device of the present invention.

FIG. 8 is a diagram showing a comparison of reflectance characteristics between the reflective liquid crystal display device of the present invention and a reflective liquid crystal display device using only a liquid crystal alignment material or a light dimerization material.

FIG. 9 is a diagram showing the relationship between the number of layers and the maximum reflectance in the reflective liquid crystal display device of the present invention.

FIG. 10 is a diagram showing an example of a conventional manufacturing method and a reflective liquid crystal display device obtained by the method.

[Explanation of symbols]

 11, 13 Substrate 12, 14 Electrode 21a Photodegradable polyimide 21b Polyimide film 22a Mixed solution 22b Liquid crystal layer 25 Polarized ultraviolet light 1,1a, 1b Polyimide chain 2 Polymer 3 Liquid crystal droplet 3a Liquid crystal molecule 4 Photodimerizing material

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Taketo Hikiji 430 Sakai Nakaicho, Ashigara-gun, Kanagawa Prefecture Inside Green Tech Nakai Fuji Xerox Co., Ltd. Inside the company (72) Inventor Masanobu Ninomiya 1600 Takematsu, Minamiashigara-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (6)

[Claims] A reflective layer in which a polymer layer made of a liquid crystal aligning material and a liquid crystal layer containing a photo-dimerizing material are alternately laminated between two substrates. A reflective liquid crystal display device, wherein the liquid crystal therein is oriented in a specific direction by a light dimerization material in the liquid crystal layer and a liquid crystal alignment material forming an adjacent polymer layer. 2. The reflective liquid crystal display element according to claim 1, wherein the liquid crystal aligning material remains after the photodegradable polyimide is cured by heat and further partially decomposed by irradiation with polarized ultraviolet rays. A reflective liquid crystal display device comprising a polyimide chain. 3. A reflection type liquid crystal display device according to claim 1, wherein said light dimerization material is polyvinyl cinnamate or cinnamate ethyl methacrylate after a light dimerization reaction by irradiation with polarized ultraviolet rays. Liquid crystal display device. 4. The reflection type liquid crystal display device according to claim 1, wherein the liquid crystal alignment material is a photodegradable material, and a photolysis reaction of the liquid crystal alignment material forming the polymer layer and an adjacent liquid crystal layer. A reflection type liquid crystal display device, wherein the light dimerization reaction of the light dimerization material therein is simultaneously caused by irradiation of a polymer layer and a liquid crystal layer adjacent thereto with polarized ultraviolet rays. 5. A polymer layer made of a liquid crystal alignment material is formed on the electrode side of the first substrate on which the electrodes are formed, and after thermosetting, a photodimerizing material is contained on the polymer layer. Forming a liquid crystal layer, and then irradiating the liquid crystal layer and the polymer layer with polarized ultraviolet light to cause a photodimerization material in the liquid crystal layer to undergo a photodimerization reaction; By repeating the step of decomposing the polymer chain in the same direction as the polarization direction of the polarized ultraviolet light of the alignment material, to form a multilayer film,
A method of manufacturing a reflection type liquid crystal display device, comprising bonding an electrode side of a second substrate on which an electrode is formed on the multilayer film. 6. A polymer layer made of a liquid crystal alignment material is formed on the electrode side of the first substrate on which the electrode is formed, and after thermosetting, the polymer layer contains a light dimerization material. Forming a liquid crystal layer, and then irradiating the liquid crystal layer and the polymer layer with polarized ultraviolet light to cause a photodimerization material in the liquid crystal layer to undergo a photodimerization reaction; Repeating the step of decomposing the polymer chains of the alignment material in the same direction as the polarization direction of the polarized ultraviolet light to form a multilayer film, and repeating the above steps on the electrode side of the second substrate on which the electrodes are formed. , A multilayer film is formed, and then the first
A method of manufacturing a reflective liquid crystal display device, comprising: bonding a multilayer film on a substrate to the multilayer film on the second substrate.