JPH07281158A - Method for manufacturing liquid crystal light modulation element - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal light modulation element having a low driving voltage, high contrast, excellent heat resistance, and high reliability. In a method for manufacturing a liquid crystal light modulation device, a liquid crystal / polymer composite film in which liquid crystal is micron-sized and held in a polymer matrix is sandwiched by a pair of conductive substrates, at least one of which is transparent. A method for producing a liquid crystal light modulation element, comprising: a film forming step of applying and drying a liquid crystal dispersion on one conductive substrate surface; and a heating step of heat-treating the coating film.

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 which is responsive to electric fields and heat and which can display and record information.
The present invention relates to a liquid crystal light modulation device using a polymer composite film, and the liquid crystal light modulation device of the present invention can be widely applied to light control panels, displays, recording media and the like.

[0002]

2. Description of the Related Art Liquid crystal displays are widely used in wrist watches, calculators, personal computers, televisions, etc. as a display medium for characters and images because they have characteristics of low power consumption, light weight, thin film and the like. A general TN- and STN-liquid crystal display is one in which liquid crystal is enclosed in a liquid crystal cell in which a glass plate having transparent electrodes is provided with a predetermined seal or the like, and further sandwiched by polarizing plates from both sides.

However, the above liquid crystal display (1) requires a polarizing plate with a high power consumption because it has a narrow viewing angle because two polarizing plates are required and the brightness is insufficient. , (2) It is difficult to make a large area due to large cell thickness dependency, (3) There is a problem that the manufacturing cost is high because the structure is complicated and it is difficult to enclose the liquid crystal in the cell. There are limits to weight reduction, thinning, large area, low power consumption, and low cost.

As a liquid crystal display medium for solving such problems, application of a liquid crystal / polymer composite film in which liquid crystal is dispersed in a polymer matrix is expected, and research and development thereof have been activated. The following techniques have already been disclosed. The liquid crystal / polymer composite film production method can be mainly classified into an emulsion method and a phase separation method.

In the emulsion method, a composite film is prepared from an aqueous solution obtained by emulsifying a liquid crystal using polyvinyl alcohol (PVA) as a protective colloid (Japanese Patent Publication No. 58-50163).
No. 1), a method for preparing a composite film from an aqueous solution by mixing a liquid crystal emulsion with latex (Tokusho Sho-60-2).
No. 52687) and the like.

On the other hand, the phase separation method can be further classified into a method of fixing the phase separation state of the liquid crystal and the matrix resin and a method of phase separation of the liquid crystal from the matrix resin during film formation. As a method for fixing the phase-separated state, a method in which liquid crystal is dispersed in an epoxy resin and then cured (see Table 6)
1-502128), and a method of dispersing a liquid crystal in a UV curable resin and then curing the liquid crystal (see Japanese Patent Publication No. 62-2231).

[0007]

[Problems to be Solved] In the prior art relating to the above-mentioned conventional liquid crystal / polymer composite film, liquid crystal seepage from the composite film, high driving voltage of the device, low display contrast, and production of composite film At this time, there is a problem that the coating suitability of the liquid crystal dispersion is low. It is necessary to reduce the content of the polymer matrix in the composite film in order to reduce the low driving voltage of the device without the exudation of the liquid crystal, but in the conventional method, the polymer matrix in the composite film is used. The liquid crystal becomes a continuous phase as the content of is reduced, and the problem of seepage of the liquid crystal occurs. Further, in the method of lowering the driving voltage of the element by reducing the film thickness, there is a problem that it is difficult to obtain a display contrast.

Further, the conventional polymer matrix is poor in water resistance and thermal stability such as polyvinyl alcohol resin, epoxy resin, polyurethane resin, polycarbonate resin, and UV curable resin of polythiol, or has high molecular mobility, so that the device In addition to reducing the reliability and stability when used as, the electro-optical effect (eg, responsiveness) becomes a problem.

Regarding the coating suitability, since the liquid crystal particles are not completely included in the polymer, that is, they are not an emulsion, it is difficult to control the viscosity and a stable film cannot be formed. As a method of solving these problems, JP-A-1-203494 proposes encapsulation of liquid crystal. Further, Japanese Patent Laid-Open No. 4-179918 proposes a method of forming a liquid crystal / polymer composite film in a pattern on a substrate by electrodeposition coating a microcapsulated liquid crystal.

However, in order to apply and form a microcapsule containing a liquid crystal, a resin as a binder is required. Due to the voltage drop due to this binder, a high voltage is required to drive the obtained coating film.
When the amount of binder used is reduced, minute voids are generated in the obtained liquid crystal / polymer composite film,
This air gap causes a voltage drop. Furthermore, since light is scattered by the voids, there is a problem that the transparency is deteriorated when a voltage is applied. Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a liquid crystal light modulation element having a low driving voltage, high contrast, excellent heat resistance, and high reliability.

[0011]

The above object can be achieved by the present invention described below. That is, the present invention relates to a liquid crystal light modulation element in which a liquid crystal / polymer composite film in which a liquid crystal is micron-sized and held in a polymer matrix is sandwiched by a pair of conductive substrates, at least one of which is transparent. A method for producing a liquid crystal light modulation element, which comprises a film forming step of applying a liquid crystal dispersion on one conductive substrate surface and drying, and a heating step of heat-treating the coating film. .

[0012]

[Function] A liquid crystal / polymer composite film obtained by microencapsulating a liquid crystal with a thermosetting resin to prepare a dispersion liquid, coating and drying the dispersion liquid on the substrate, and heat-treating the coating film is used. As a result, a liquid crystal light modulation element having a low driving voltage, high contrast, excellent heat resistance, and high reliability is provided.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the preferred embodiments. The liquid crystal referred to in the present invention is an organic mixture showing a liquid crystal state at around room temperature, and includes nematic liquid crystal, cholesteric liquid crystal and smectic liquid crystal. Of these, nematic liquid crystal or nematic liquid crystal to which cholesteric liquid crystal is added is preferable in terms of characteristics when used as a display element.

When a memory function is required, it is desirable to use smectic liquid crystal. Incidentally, the liquid crystal may contain a dye in order to improve the contrast or the color tone. When a dichroic dye is added, it can be used not only as a scattering-transmissive composite film, but also as a composite film that switches in a light absorption (coloring) -transparent state by the guest-host effect of the dye. .

In the present invention, the above liquid crystal is preferably used in the form of microcapsules. The method of microencapsulation is not particularly limited, but it is particularly preferable to form the capsule wall with a thermosetting resin. The thermosetting capsule wall is formed by a method of emulsifying and dispersing liquid crystal particles in an aqueous medium using a surfactant or a protective colloid, and supplying a capsule wall material such as a thermosetting resin precursor from the aqueous phase side. Done.

The precursor is supplied from the aqueous phase side to perform in-situ
The following materials are preferably used as a combination of precursors used when forming microcapsule walls on the surface of liquid crystal particles by the u polymerization method, but the present invention is not particularly limited to these materials. Organic amine + acid amide + water-soluble epoxy resin Urea + formaldehyde prepolymer Urea + formaldehyde + polyacrylic acid aminoplast resin prepolymer + surfactant Heterocyclic amine + aldehyde, etc.

The polymerization reaction of these precursors proceeds by heating, but in some cases a catalyst is used. After the liquid crystal is microencapsulated, a reactive group remains in the wall material during microencapsulation because the capsule wall is cured by heat treatment after the liquid crystal / polymer composite film is formed using the matrix resin. Thus, it is preferable to terminate the polymerization reaction at an incomplete point. The formation of the capsule wall is in-s
The method is not limited to the in situ polymerization method, and a coacervation method, an in-liquid drying method, an in-liquid curing coating method, or the like can be used. Also when these methods are adopted, it is preferable that a functional group for thermosetting is introduced into the resin used as the capsule wall material.

The thickness of the capsule wall of the microencapsulated liquid crystal is preferably thin from the viewpoint of suppressing the increase of the driving voltage for driving the liquid crystal light modulation element as much as possible, and in the present invention, it is about 20 to 200 nm. good. Further, a material having high mechanical strength is preferably selected as the capsule wall material. When the liquid crystal particles are encapsulated under preferable conditions, the diameter of the obtained liquid crystal microcapsules can be made almost equal to the emulsion particle diameter when the liquid crystal is first emulsified and dispersed. Therefore, it is possible to optimize the particle size of the obtained capsules depending on the conditions for emulsifying and dispersing the liquid crystal in the aqueous medium. If the obtained microcapsules have a wide particle size distribution and capsules with an undesirable diameter are mixed, the capsules with an undesirable diameter can be removed by a method such as a centrifugal sedimentation method or a filtration method.
The average particle size of the liquid crystal microcapsules is preferably about 1 to 5 μm.

The electro-optical characteristics of the liquid crystal / polymer composite film are as follows.
It is known that the magnitude of the anchoring force of the polymer material, which is the matrix or capsule wall material, on the liquid crystal is important, but it can be obtained by the above method in order to control the anchoring force of the polymer material. It is also possible to provide a capsule wall made of a different resin inside the capsule wall. The inner capsule wall is formed by adding a monomer or oligomer to the liquid crystal, emulsifying and dispersing the liquid crystal in an aqueous medium, and then polymerizing the monomer or oligomer in the liquid crystal.

In order to suppress the voltage drop due to the capsule wall,
As described above, it is preferable to make the capsule wall as thin as possible. When the capsule wall is doubled, the inner capsule wall is not required to have strength, so that it can be made thinner, and the preferable amount of the monomer added is 0.5 to 5% by weight based on the liquid crystal. It is a degree. When a guest-host type display is performed by adding a dichroic dye to the liquid crystal, the dye added to the liquid crystal also colors the capsule wall,
Since it causes a color residue when a voltage is applied, it is desirable to make the addition rate of the monomer as small as possible in order to minimize the color residue.

Examples of the monomer used for forming the inner wall of the capsule include acrylic acid ester, methacrylic acid ester, vinyl acetate, styrene, polyisocyanate-polyol, polyisocyanate-polyamine and the like, but the anchoring force is weak. Acrylic acid ester, methacrylic acid ester, and styrenes are preferable as the polymer forming agent. Further, acrylic acid / methacrylic acid esters having a fluorine atom are also particularly preferably used. These monomers are easily polymerized to form the inner wall of the capsule when a radical generator is added and heated.
When the monomer does not dissolve in the liquid crystal at room temperature, the dye-containing liquid crystal in which the dye is dissolved at high temperature can be dispersed in the aqueous medium.

The inner wall of the capsule does not need to have high strength, but when a monomer having low solubility with the liquid crystal is used, the inner wall of the capsule formed by polymerization is composed of a polymer having a low molecular weight. In some cases, the inner capsule material is trapped in the outer capsule wall and does not form a double structure. In order to solve such a problem, a method of using a polyfunctional monomer together as a monomer for the inner wall is preferably used. If the proportion of polyfunctional monomer used is too high, gel-like walls will form and the liquid crystal will be taken into the gel, or the inner surface of the walls will have irregularities, increasing the drive voltage and lowering the contrast. Things happen. The preferred amount of the polyfunctional monomer used is usually 30% by weight or less based on the monofunctional monomer.

The liquid crystal-containing polymer microcapsules obtained as described above can be cast in the state of a dispersion liquid to form a liquid crystal / polymer composite film. Regardless of whether the film is formed as a cast or an electrodeposition coating, it is desirable to use a resin that serves as a binder in any case.

As the binder, for example, water-soluble polymer materials such as polyvinyl alcohol, acrylic acid copolymer, gelatin and water-soluble alkyd resin are preferably used. The amount of the binder used is preferably as small as possible in order to suppress the voltage drop due to the binder. The amount of binder used is, for example, polymer material / liquid crystal =
5/95 to 50/50, preferably 30/70 to 10 /
The ratio is 90 (weight ratio). In addition, in order to remove unnecessary surfactant, unreacted encapsulating agent, water, etc. in the dispersion liquid after microencapsulation, operations such as centrifugal sedimentation, atmosphere drying, solvent replacement, and dry concentration are performed. Then, the microcapsules may be once separated from the polymerization medium, and the separated microcapsules may be redispersed in an appropriate medium and used for forming the liquid crystal / polymer composite film.

The conductive substrate for forming the liquid crystal light modulating element of the present invention is generally used in a conventionally known liquid crystal display element. In the present invention, the conventionally known conductive substrate is Either can be used, and specifically, for example,
It is a pair of electrode substrates in which a transparent conductive material such as ITO, SnO ₂ or ZnO is attached to a transparent substrate such as glass or polymer film. At this time, when an opaque conductive substrate is used for the other side, its electrode is also required to function as a reflection plate, and therefore, for example, a substrate provided with an aluminum reflection electrode is preferable. The substrate itself may be glass, polymer film or others.

As a method for coating the coating liquid containing the liquid crystal-containing microcapsules on the element substrate, any conventionally known coating method such as a doctor coating method or a blade coating method can be used, but is preferable. One example is an electrodeposition coating method. In this coating method, since the liquid crystal content can be particularly increased, a film having excellent electro-optical characteristics can be formed with high film thickness accuracy. It is also possible to form the liquid crystal / polymer composite film in a fine pattern. The film thus obtained after coating and drying has minute voids in the film at this point.

In the present invention, the liquid crystal /
The feature is that the polymer composite film is subjected to heat treatment.
As the heat treatment conditions, it is preferable that the temperature is 50 ° C. or higher and the heating time is 24 hours or longer. By performing such heat treatment, shrinkage accompanying hardening of the thermosetting capsule wall, bridging between capsules, and flow of the binder resin eliminates minute voids in the film, resulting in a film having a dense structure. Become.

Comparing the film after the heat treatment with the film before and after the heat treatment, the film after the heat treatment has a low driving voltage when being constituted and driven as a liquid crystal light modulation element and has a good contrast, and at the same time, the film. The strength and smoothness of the surface are higher. Therefore, the other electrode substrate can be favorably laminated. In some cases, when good lamination cannot be achieved, good lamination can be achieved by providing an intermediate layer between the liquid crystal / polymer composite film and the counter electrode.

The thickness of the liquid crystal / polymer composite film formed between the pair of substrates is generally preferably about 3 to 23 μm. When the film thickness is less than the above range, it is not preferable in that the display contrast becomes low. On the other hand, when the film thickness exceeds the above range, the voltage (driving voltage) for erasing the display becomes high. Not preferable.

[0030]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 A liquid crystal emulsion having the following composition was obtained from a porous glass having a pore size of 0.35 μm using an MPE membrane emulsification small system manufactured by Ise Chemical Industry. Oil phase: nematic liquid crystal (E-31LV, manufactured by Merck) 100 g Water phase: modified polyvinyl alcohol (T-50, manufactured by Nippon Synthetic Chemical Industry) 5.5 g Ion-exchanged water 214.5 g

370 g of ion-exchanged water was added to the above dispersion, and 66 g (37 g) of a thermosetting resin precursor aqueous solution was added at 70.degree.
Melamine 1.5g in 4.5g% formaldehyde aqueous solution
Was added and reacted at 60 ° C for 15 minutes, and then ion-exchanged water 6
0 g was added) slowly. 80 g of a hydrochloric acid aqueous solution having a pH of 2.5 was dropped, and the mixture was further reacted at 70 ° C. for 3 hours to form liquid crystal microcapsules having a melamine resin wall. The microcapsules are sedimented by a centrifuge,
Liquid crystal microcapsules having a sharp particle size distribution with an average particle size of 2.0 μm were obtained.

Using the obtained microcapsules, an electrodeposition coating solution having the following composition was prepared. Microcapsules 48g Anionic acrylic resin 2.7g Triethylamine 0.5g Ethanol 5.5g Ion-exchanged water 340g

A stainless steel plate as a cathode and a glass substrate on which an ITO film was patterned as an anode were dipped in the above electrodeposition coating solution, and electricity was applied at 20 V for 30 seconds. The glass substrate was pulled up, washed with water, and then dried at room temperature for 20 hours. The obtained film was heat-treated at 60 ° C. for 2 days. ITO
The thickness of the liquid crystal / polymer composite film on the film was 8 μm. As a counter electrode, a PET film with ITO was sandwiched to prepare a liquid crystal light modulation element of the present invention.

Example 2 Using the liquid crystal microcapsules obtained in Example 1, a cast coating liquid having the following composition was prepared. Microcapsules 50 g PVA (KH-20 manufactured by Nippon Synthetic Chemical Industry) 7.2 g Ion-exchanged water 76.7 g The above coating liquid was applied onto a glass substrate with ITO using a blade coater. After drying at room temperature for 20 hours, 6
Heat treatment was performed at 0 ° C. for 2 days. The thickness of the liquid crystal / polymer composite film on the ITO film was 8 μm. ITO as counter electrode
A liquid crystal light modulator of the present invention was produced by sandwiching the coated PET film.

Example 3 A liquid crystal emulsion having the following composition was obtained from a porous glass having a pore size of 0.35 μm using a MPG membrane emulsification small system manufactured by Ise Chemical Industry. Oil phase: nematic liquid crystal (E-31LV, manufactured by Merck) 100 g Methyl methacrylate 2.2 g Azobisisobutyronitrile 0.04 g Water phase: Modified polyvinyl alcohol (T-50, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) 5.5 g Ion Exchanged water 214.5g

The liquid crystal was encapsulated with polymethylmethacrylate walls by heating the above liquid crystal emulsion at 70 ° C. for 15 hours. 370 g of deionized water in the dispersion
66 g of thermosetting resin precursor aqueous solution at 70 ° C.
(1.5 g of melamine was added to 4.5 g of 37% aqueous formaldehyde solution and reacted at 60 ° C. for 15 minutes, and then 60 g of ion-exchanged water was added) was slowly added dropwise. pH
80 g of 2.5 hydrochloric acid aqueous solution was added dropwise, and further at 70 ° C. for 4 hours.
The reaction was allowed to proceed for a period of time to form a melamine resin capsule wall on the outside of the PMMA wall. The microcapsules were settled with a centrifuge to obtain microcapsules with an average particle diameter of 2.1 μm.

Using the obtained microcapsules, an electrodeposition coating solution having the following composition was prepared. Microcapsules 48 g Anionic acrylic resin 2.7 g Triethylamine 0.5 g Ethanol 5.5 g Ion-exchanged water 340 g A glass substrate on which a stainless steel plate as a cathode and an ITO film as an anode are formed in a pattern in the above electrodeposition coating solution. Was soaked and energized at 15V for 40 seconds. The glass substrate was pulled up, washed with water, and then dried at room temperature for 20 hours. The obtained film was heat-treated at 60 ° C. for 2 days. Liquid crystal on ITO film /
The thickness of the polymer composite film was 8 μm. As a counter electrode, a PET film with ITO was sandwiched to prepare a liquid crystal light modulation element of the present invention.

Example 4 Using the capsule obtained in Example 3, a cast coating solution having the following composition was prepared. Microcapsules 50 g PVA (Nippon Gosei Kagaku Kogyo KH-20) 7.2 g Ion-exchanged water 76.7 g The above coating liquid was applied onto a glass substrate with ITO using a blade coater. After drying at room temperature for 20 hours, 6
Heat treatment was performed at 0 ° C. for 2 days. The thickness of the liquid crystal / polymer composite film on the ITO film was 8 μm. ITO as counter electrode
A liquid crystal light modulator of the present invention was produced by sandwiching the coated PET film.

Comparative Examples 1 to 4 Liquid crystal light modulating elements of Comparative Examples 1 to 4 were obtained in the same manner as in Examples 1 to 4 except that the heat treatment after coating was not performed. Evaluation Example Changes in parallel light transmittance with respect to voltage of the liquid crystal light modulation elements of Examples 1 to 4 and Comparative Examples 1 to 4 were measured and compared.
The measurement was performed by using a Fortal LCD-5000 manufactured by Otsuka Electronics Co., Ltd. and applying a rectangular wave of 1 kHz at F # = 4. The results are shown in FIGS. It was revealed that the liquid crystal light modulation elements of Examples 1 to 4 had lower drive voltage and good contrast than the liquid crystal light modulation elements of Comparative Examples 1 to 4. Further, when these liquid crystal light modulation elements were pressed from the film side with the back side of the nail, the liquid crystal light modulation elements of Comparative Examples 1 to 4 had a high transmittance at the time of being pressed, and there were marks, but There was no change in the liquid crystal light modulation elements of Examples 1 to 4.

[0040]

According to the present invention as described above, the following effects can be obtained. 1. A liquid crystal light modulator having a low driving voltage and a high contrast can be obtained. 2. Formation of liquid crystal / polymer composite film by coating
Realized with high processing accuracy. 3. A liquid crystal / polymer composite film with high uniformity and heat resistance can be produced without bleeding of liquid crystal. 4. Since the strength of the coating film of the liquid crystal / polymer composite film is high, even when a plastic film is used as the substrate, it is hardly affected by external stress and a reliable liquid crystal light modulation element can be supplied.

[0041]

[Brief description of drawings]

FIG. 1 is a diagram illustrating a relationship between an applied voltage and light transmittance.

FIG. 2 is a diagram illustrating a relationship between applied voltage and light transmittance.

FIG. 3 is a diagram illustrating a relationship between an applied voltage and a light transmittance.

FIG. 4 is a diagram illustrating a relationship between applied voltage and light transmittance.

Claims (7)

[Claims] 1. A liquid crystal light modulation device comprising a liquid crystal / polymer composite film in which a liquid crystal is micron-sized and held in a polymer matrix and is sandwiched by a pair of conductive substrates, at least one of which is transparent. A method for producing a liquid crystal light modulation element, which comprises a film forming step of applying and drying a liquid crystal dispersion on one conductive substrate surface, and a heating step of heat treating the applied film. 2. The method for producing a liquid crystal light modulation element according to claim 1, wherein the liquid crystal particles are microencapsulated. 3. The method for producing a liquid crystal light modulation element according to claim 2, wherein a dispersion liquid containing microencapsulated liquid crystals is electrodeposited on a conductive substrate. 4. The method for producing a liquid crystal light modulation element according to claim 2, wherein the partition walls of the microcapsules are made of a thermosetting resin. 5. The method for producing a liquid crystal light modulation element according to claim 1, wherein the heat treatment temperature is 50 ° C. or higher, and the heating time is 24 hours or longer. 6. A liquid crystal dispersion is applied and dried on one conductive substrate, and the coating film is sandwiched between the other conductive substrates,
The method for producing a liquid crystal light modulation element according to claim 1, wherein heat treatment is performed. 7. The method for producing a liquid crystal light modulation element according to claim 4, wherein the partition walls of the microcapsules are made of an incompletely cured thermosetting resin.