JPH0667165A - Liquid crystal display element and its production - Google Patents

Abstract

PURPOSE:To quicken a response speed and to improve the stability and reproducibility of a response speed by incorporating an ionic group into a molecule of side chain type high-molecular liquid crystal. CONSTITUTION:In a liquid crystal display element in which a mixed film containing side chain type high-molecular liquid crystal and low molecular liquid crystal is interposed between electrodes at least one of which is transparent, the ionic group is incorporated into the molecule of the side chain type high-molecular liquid crystal. In this case, a coating liquid in which the side chain type high-molecular liquid crystal and an electrolyte are dissolved in a respective common solvent is applied on a surface of one electrode in a pair of transparent electrodes, is dried and solidified to form the mixed film and then another transparent electrode is laminated on the mixed film to obtain the liquid crystal display element with a structure in which the mixed film is interposed between a pair of transparent electrodes. Thus movement of ions at the time of directly impressing is efficiently transmitted into molecules of main chains by incorporating the ionic group into the main chain or the side chain liquid crystal group (methogenic group, etc.) of the high-molecular liquid crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display element used in general OA equipment such as TV and CPU, and other liquid crystal display devices, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A conventional liquid crystal display element is formed by injecting a liquid crystal material between a pair of transparent electrode plates fixed at intervals of several μm. However, with the above configuration, it is difficult to create a large-area display, and since a pair of transparent electrode plates enclosing liquid crystals need to be equipped with polarizing plates whose polarization axes are orthogonal to each other, the brightness of the screen and the field of view are reduced. The corners were insufficient.

Further, in the conventional liquid crystal display device, except for the case where the ferroelectric liquid crystal is used, since the alignment state has no memory property, the TF having a low manufacturing yield is used for a display screen having a large number of pixels.
Active matrix drive using T etc. is required,
There was a problem of becoming expensive. Further, when a ferroelectric liquid crystal is used, it is difficult to obtain a satisfactory display even with a small area, because it is necessary to control the cell gap to be extremely thin at 1 to 2 μm and to control the uniform alignment of the liquid crystal.

On the other hand, recently, a side chain type polymer liquid crystal having a side chain in which a portion corresponding to a liquid crystal compound is bonded to a polymer skeleton through a flexible carbon skeleton and a normal low molecular weight liquid crystal A solution prepared by dissolving a material and a solvent in a solvent is cast and applied on a plate-shaped body such as a transparent electrode plate or a film-shaped support, dried and solidified to form a polymer liquid crystal / low-molecular liquid crystal mixed film, A liquid crystal display device has been proposed in which another support is superposed on this polymer liquid crystal / low molecular weight liquid crystal mixed film (Japanese Patent Laid-Open Nos. 2-193115 and 2-1).
27494, Chem. Lett., Pp817, 1989, Polym.
Preprints, Japan 39 (8) 2373 (1990) etc.).

In this liquid crystal display element, when a low-frequency or direct-current electric field is applied to a polymer liquid crystal / low-molecular liquid crystal mixed film, the ions are moved in the film along with the electric field, so that the alignment of the liquid crystal is disturbed. Then, the incident light is strongly scattered and becomes opaque. When a high-frequency electric field is applied, the liquid crystal molecules in the polymer liquid crystal / low molecular weight liquid crystal mixed film are homeotropically aligned in the electric field direction by the electro-optical effect, and incident light can pass without being scattered. , Switch to a transparent state. In addition, this liquid crystal display element has a memory property of stably holding the light scattering state or the non-scattering state when the electric field is removed in both of the above states.

On the other hand, in recent years, a polymer liquid crystal having an ionic group in the molecule has been proposed (Chem. Lett., Pp411-41.
4, 1991, Chem Lett pp995-998, 1990).

[0007]

In a conventional polymer liquid crystal / low molecular weight liquid crystal mixed film, the change from transparent to cloudy is caused by the presence of a very small amount of ions moving in the mixed film according to a direct current or a low frequency electric field. It is caused by disturbing the alignment of liquid crystals.
That is, in the conventional mixed film, the electrolyte added to the liquid crystal was used as a driving source at the time of [transparent → scattering], so that there was the following problem. (1) Ion polarization occurs on the electrode surface, and the display element lacks long-term stability. (2) Since ions move in all directions, effective ion movement to disturb the alignment of the polymer liquid crystal main chain cannot be obtained,
The response speed is slow.

The main object of the present invention is that the response speed is high,
Another object of the present invention is to provide a liquid crystal display device having excellent stability and reproducibility in response speed. Another object of the present invention is to provide a liquid crystal display device that can be used in a wide temperature range including room temperature. Still another object of the present invention is to
An object of the present invention is to provide a method for manufacturing a liquid crystal display element, which can reduce the number of steps in manufacturing the liquid crystal display element.

[0009]

A liquid crystal display device of the present invention is a liquid crystal display in which a mixed film containing a side chain type polymer liquid crystal and a low molecular weight liquid crystal is sandwiched between electrodes, at least one of which is transparent. In the device, the side chain type polymer liquid crystal has an ionic group in the molecule. Further, the method for producing a liquid crystal display element of the present invention, a side chain type polymer liquid crystal and a low molecular weight liquid crystal are applied to one surface of a pair of transparent electrodes with a coating solution in which a common solvent is dissolved together with an electrolyte, After being dried and solidified to form a mixed film, the other transparent electrode is laminated on the mixed film to obtain a liquid crystal display device having a structure in which the mixed film is sandwiched between a pair of transparent electrodes.

Another manufacturing method of the liquid crystal display element of the present invention is
A side chain type polymer liquid crystal containing an ionic group in the molecule, a mixed liquid crystal containing two or more kinds of low molecular weight liquid crystals, and a mixture containing a spacer are placed on one side of one transparent electrode, and then at least one pressure bonding is performed. One of the transparent electrodes is bonded to the other transparent electrode by using a roller.

That is, the inventors of the present invention have conducted intensive studies as a result of paying attention to the fact that the change of transparency → scattering is the random orientation state of the polymer main chain accompanying the ion movement under direct current.
We obtained new knowledge that random orientation of the polymer main chain can be caused faster by ions, and based on this finding, by introducing an ionic group into the side chain type polymer liquid crystal molecule, the response speed can be improved. The present inventors have completed the present invention by finding the fact that a liquid crystal display device which is fast and has excellent response speed stability and reproducibility can be obtained.

That is, according to the present invention, by introducing an ionic group into the main chain of a polymer liquid crystal or into a side chain liquid crystal group (mesogenic group, etc.), ions can be efficiently moved when a direct current is applied. It is intended to be transmitted inside. Further, in the present invention, by introducing an ionic group into the polymer liquid crystal, there is no fear of deterioration of the electrode surface of the liquid crystal display element due to excess ions, and a stable liquid crystal display element can be obtained.

The low-molecular liquid crystal is preferably a mixed liquid crystal containing two or more kinds of liquid crystals, which makes it possible to operate in a wide temperature range. Further, the low-molecular liquid crystal may be a mixed liquid crystal containing a low-molecular liquid crystal that can substitute for the side-chain liquid crystal group of the side-chain polymer liquid crystal. The side chain type polymer liquid crystal main chain is not particularly limited, for example, polyoxirane main chain, polysiloxane main chain,
A polyoxetane main chain, a polyacrylic main chain, a polyester main chain, a polyether main chain, a polybutadiene main chain, etc. can be used.

Further, the liquid crystal group is preferably bonded to the main chain of the side chain type polymer liquid crystal through a spacer portion in order to impart flexibility. As such a spacer part,
There is no particular limitation, and for example, in addition to an alkylene group, a siloxane chain, an ester chain, an ether chain, an oxetane chain, a butadiene chain, etc. can be used. The liquid crystal group is not particularly limited, and various commonly used liquid crystal groups can be used. In addition,
The polymer liquid crystal may be a cross-linked polymer liquid crystal. Furthermore, the liquid crystal group is not particularly limited, and various commonly used liquid crystal groups can be used.

The ratio of high-molecular liquid crystal / low-molecular liquid crystal is usually
It is preferably 0.1 / 9.9 to 6/4. When the amount of the polymer liquid crystal is more than the above proportion, the response speed becomes slow, and when the amount of the low molecular liquid crystal is more than the above proportion, light scattering becomes insufficient. Although the kind of the ionic groups introduced into the molecule of the polymer liquid crystal is not particularly limited, for example, cationic group, the nitrogen atom-containing groups such as pyridinyl group, and in anionic group sulfonato group SO ₃ ^- And a sulfur atom-containing group.

The site of introduction of the ionic group into the polymer liquid crystal may be in either the main chain structure or the side chain structure. Specific examples of the side chain type polymer liquid crystal having an ionic group introduced include those shown below. However, in the following model, 1 is a main chain, 2 is a spacer part, 3 is a liquid crystal group,
4 is a spacer portion or a rigid portion (for example, a spacer portion such as a methylene chain or a siloxane chain, a rigid portion such as a benzene ring or biphenyl), X ⁻ represents an anion such as a halogen ion,

[0017]

[Chemical 1]

## STR3 ## represents a cationic group and an anionic group, respectively.

[0019]

[Chemical 2]

Specific structural formulas of the side chain type polymer liquid crystals in the present invention are shown below, but the side chain type polymer liquid crystals usable in the present invention are not limited to these.

[0021]

[Chemical 3]

(In each formula, R is an alkyl group having 1 to 20 carbon atoms, Y is a cyano group, an alkyl group having 1 to 20 carbon atoms,
A halogen atom, an alkoxy group having 1 to 20 carbon atoms, a nitro group or an amino group, n is 3 to 100, and m is an integer of 1 to 20. Although these polymer liquid crystals show examples in which a cationic group is introduced, examples of the one in which an anionic group is introduced include the following.

[0023]

[Chemical 4]

[In each formula, R, Y, m and n are the same as defined above.
It is the same. R¹, R²And R³Is C _nH_{2n + 1}, (C
H₂)_n-OH (where n is an integer of 1 to 10)
Show. As the low-molecular liquid crystal, various well-known compounds can be used.
Can be used, but side chains in polymer liquid crystals
Small molecule that can replace liquid crystal group (mesogen group etc.)
Liquid crystal group that may contain liquid crystal
Is similar to a liquid crystal group bonded to the side chain of a side chain type polymer liquid crystal.
It is necessary to have a structure such as the formula:

[0025]

[Chemical 5]

[In the formula, R is the same as defined above. ] For the liquid crystal group represented by the above, it is necessary to use a low molecular weight liquid crystal having the following structure.

[0027]

[Chemical 6]

(In each formula, R is the same as above, R ⁵ is a carbon number 1
An alkyl group having 20 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or a cyano group. ) Also the formula:

[0029]

[Chemical 7]

For the liquid crystal group represented by the formula (Y is the same as above), it is necessary to use a low-molecular liquid crystal having the following structure.

[0031]

[Chemical 8]

(In each formula, Y ¹ and Y ² are the same or different and are the same as the above Y.)

As the low-molecular liquid crystal that does not substitute for the liquid crystal group of the side chain type high-molecular liquid crystal, various low-molecular liquid crystals that are commonly used can be used. Further, as the side chain type polymer liquid crystal in the present invention, both of those exhibiting a smectic phase and those exhibiting a nematic phase can be used. When both the high-molecular liquid crystal and the low-molecular liquid crystal exhibit a nematic phase, it is necessary to select a mixed system in which a smectic phase is induced by mixing.

The main chain of the side chain type polymer liquid crystal is not particularly limited, and for example, a siloxane main chain, a polyether main chain, a polyethylene main chain or the like can be used. Further, the spacer portion connecting the main chain of the side chain type polymer liquid crystal and the liquid crystal group is not particularly limited, and for example, an alkylene chain (ethylene group or the like), a siloxane chain, a polyether chain or the like can be used. Furthermore, the liquid crystal group is not particularly limited, and various commonly used liquid crystal groups can be used.

When a low-molecular liquid crystal that substitutes for the liquid crystal group of the side-chain type polymer liquid crystal is used in combination, (side-chain type polymer liquid crystal +
Low-molecular liquid crystal that replaces the liquid crystal group of side-chain polymer liquid crystal) /
It is preferable to use (low-molecular liquid crystal that does not substitute for the liquid crystal group) in the range of 3/7 to 6/4. In addition, the mixed film,
The electrolyte may be contained in a proportion of 0.005 to 1% by weight, and the ion derived from this electrolyte enhances the response speed and surely and reproducibly changes the state from transparent to cloudy.

Any of the above-mentioned electrolytes can be used as long as it can be dissolved in the coating liquid.
The following general formula:

[0037]

[Chemical 9]

A quaternary ammonium salt represented by the following is mentioned. In the formula, R ⁶ , R ⁷ , R ⁸ and R ⁹ are the same or different and each represents an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, pentyl or hexyl group, and X is F, Cl, Br, I, Cl
O ₄ , PF _4, BF _4, etc. are shown.

The electrolyte may be composed of one kind of electrolyte or a mixture thereof. It should be noted that various conventionally known dichroic dyes can be blended in the mixed film in order to make the liquid crystal display element a color display type. Also,
As the spacer used in the method of the present invention, the one used in a normal liquid crystal display element can be used, the shape is a sphere, a rod or the like, and the material is a resin,
Glass, silica, etc. can be used.

As a pair of electrodes, at least one of which is transparent for sandwiching the mixed film, a glass or plastic film [eg polyethylene terephthalate (PE
T), polyether sulfone (PES)] or the like on the surface of a transparent support such as ITO (indium tin oxide) or Sn.
Examples thereof include those obtained by forming a conductive film such as O ₂ by vapor deposition or sputtering, and also include transparent conductive glass and films used for ordinary liquid crystal display elements.

In the method of the present invention, the above-mentioned coating solution is applied onto one transparent electrode, dried and solidified to form a mixed film, and then the other transparent electrode is superposed on the mixed film to form a liquid crystal display device. Therefore, it is not necessary to perform extra steps as compared with the conventional manufacturing process of a liquid crystal display element. The mixing ratio of each component contained in the coating liquid can be appropriately set according to the type of coating method for coating the coating liquid on the transparent electrode and the film thickness of the mixed film to be formed.

As a method for applying the above-mentioned coating liquid on the transparent electrode, a conventionally known coating method such as a bar coating method, a spin coating method, a spray coating method or a roller coating method can be adopted. Further, in the method of the present invention, a mixture of the above mixture and a spacer is placed on one transparent electrode,
Since one transparent electrode is pressure-bonded onto the other transparent electrode by using one or two pressure rollers (that is, pressure is applied from the coating side of the mixture), compared with the conventional liquid crystal display device manufacturing method. There is no need to perform extra steps such as cell manufacturing, and liquid crystal injection into the cell.

As a method for producing a mixture, (1) a spacer is mixed and stirred in a solution in which a polymer liquid crystal, a low molecular liquid crystal and an electrolyte are dissolved in a solvent, and the spacer is dried to dry the solution. How to remove the (2)
It can be carried out by a method of directly mixing a polymer liquid crystal, a low molecular liquid crystal, an electrolyte and a spacer without using a solvent to prepare a mixture.

[0044]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. In the examples, all "parts" are parts by weight. Example formula:

[0045]

[Chemical 10]

30 parts of a side chain type polymer liquid crystal having a repeating unit represented by: and 20 parts of low molecular weight liquid crystal E63 (estimated to contain a low molecular weight liquid crystal of 5 components or more, manufactured by Merck Japan Ltd.) are acetone. / Dichloromethane was dissolved in a mixed solvent of 1/1 to obtain a coating liquid. This was applied onto an ITO film by a bar coating method, dried at room temperature for 30 minutes to form a mixed film, and then another ITO film was laminated to obtain a liquid crystal display element. Comparative Example As a side chain type polymer liquid crystal, 14 parts shown in the following formula,
Tetraethylammonium bromide (TE
A liquid crystal display device was obtained in the same manner as in Example except that 0.05% by weight of AB) was added to the whole.

[0047]

[Chemical 11]

Evaluation Test For each of the liquid crystal display devices obtained in Examples and Comparative Examples, the response time from transparent to white turbidity and white turbidity to transparent at room temperature with an alternating current of 1 kHz applied was measured by using a He-Ne laser beam (wavelength 633 μm). ). In addition, the temperature range in which the mixed film was in the smectic phase was examined by observing with a polarizing microscope. The results are shown in Table 1.

[0049]

[Table 1]

It can be seen from Table 1 that the liquid crystal display elements obtained in the examples have a short response time from transparent to white turbidity, and have a smectic phase in a wide range including room temperature, and have an alignment state with a memory property.

[0051]

As described above, the liquid crystal display element of the present invention comprises a mixed film containing a side chain type polymer liquid crystal and a low molecular weight liquid crystal,
At least one is sandwiched between transparent electrodes, and since the side chain type polymer liquid crystal has an ionic group, the response speed is fast, and the stability and reproducibility of the response speed are improved. It is excellent.

By using a mixed liquid crystal of two or more kinds as the low molecular weight liquid crystal, it becomes possible to use the liquid crystal in a wide temperature range including room temperature. Further, according to the method of the present invention, the liquid crystal display element according to the present invention can be easily obtained without performing extra steps.

Further, since the liquid crystal display device of the present invention does not use a polarizing plate, it has a high light utilization efficiency and is particularly suitable for reflection type and projection type displays.

Claims (4)

[Claims] 1. A liquid crystal display device comprising a liquid crystal display device comprising a mixed film containing a side chain type polymer liquid crystal and a low molecular weight liquid crystal sandwiched between electrodes, at least one of which is transparent. A liquid crystal display device having an ionic group. 2. The liquid crystal display device according to claim 1, wherein the low-molecular liquid crystal is a mixed liquid crystal containing two or more kinds of liquid crystals. 3. A mixed film is formed by applying a coating solution prepared by dissolving a side chain type polymer liquid crystal and a low molecular weight liquid crystal together with an electrolyte in a common solvent thereof to one surface of a pair of transparent electrodes and drying and solidifying. After that, the other transparent electrode is laminated on the mixed film to obtain a liquid crystal display device having a structure in which the mixed film is sandwiched by a pair of transparent electrodes. 4. A side chain type polymer liquid crystal containing an ionic group in a molecule, a mixed liquid crystal containing two or more kinds of low molecular weight liquid crystals, and a mixture containing a spacer are placed on one side of one transparent electrode, A method for manufacturing a liquid crystal display device, characterized in that the one transparent electrode is attached to the other transparent electrode by using at least one pressure roller.