JPH04345125A - Liquid crystal film - Google Patents

Abstract

PURPOSE:To facilitate the production of a liquid crystal dispersion of the resin dispersed liquid crystal film. CONSTITUTION:This liquid crystal film has a liquid crystal film 30 which is provided between electrodes by crimping a liquid mixture mixed with a high- polymer resin and a liquid crystal between two sheets of conductive electrode substrates 20 by using suitable spacers at a specified thickness, then curing the high-polymer resin by using heat or UV rays and can attain a light scattering state and a transparent state according to the presence or absence of voltage impression. The phase sepn. of the liquid crystal phase of the above-mentioned liquid crystal film is accelerated at the time of curing the resin by adding <=0.5 micron superfine particles of an inorg. or org. material into the liquid mixture composed of the high-polymer resin and the liquid crystal.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a liquid crystal film.
More specifically, a liquid crystal film consisting of liquid crystal droplets dispersed in a polymer resin, their aggregates, and/or a three-dimensional network continuous phase of liquid crystal is sandwiched between two conductive electrodes, and a voltage is applied between the electrodes. This is a liquid crystal film having an optical switching function that allows the liquid crystal layer to take on a light scattering state and a transparent state.

0002

[Prior Art] In a liquid crystal film in which liquid crystal molecules are microencapsulated and the capsules are dispersed as liquid crystal droplets in a resin film, opacity is caused by scattering of light by the liquid crystal droplets, and liquid crystals within the liquid crystal droplets are created by applying an electric field. A liquid crystal film that utilizes transparency due to molecular orientation has already been proposed by Ferguson et al. (US Pat. No. 4,435,047), and some of them are in practical use. However, this method is complicated in terms of production process because it includes a step of microencapsulation. Further, in order to obtain a transparent/opaque shutter function, a high voltage of about 100V is required.

On the other hand, at the University of Kent,
-502128 Publication and Special Publication No. 1983-501512
In the publication, it is proposed to create a liquid crystal layer by dispersing liquid crystal microdroplets in a thermosetting resin transparent matrix by phase separation from a mixed solution of a thermosetting resin and liquid crystal molecules. However, even the above-mentioned liquid crystal film requires an AC voltage of about 100V to orient the liquid crystal, and has the disadvantage of high voltage consumption.When used not only for dimming purposes but also as a display element, the drive circuit In terms of design, a liquid crystal film that can be driven at low voltage is desired.

Furthermore, a method for producing a liquid crystal film by a phase separation method using an ultraviolet curable resin is also disclosed in JP-A-62-2231.

However, in order to use any of them as a display element, a driving voltage (voltage required to change from a light scattering state to a transparent state) is high, making them unsuitable for display using current general integrated circuits.

Furthermore, in the phase separation method, a good film can be obtained only within a limited range of optimal curing conditions depending on the combination of resin and liquid crystal, and it is difficult to control the production process.

[0007]

OBJECTS OF THE INVENTION The present invention provides a liquid crystal film which has a simple structure, low driving voltage, and is excellent as a display element.
Furthermore, it is a liquid crystal film obtained by controlling the phase separation process by curing a liquid mixture with ultrafine particles of an inorganic or organic substance using ultraviolet light.

[0008]

[Means for Solving the Problems] The present invention involves sandwiching a liquid mixture of a polymer resin and liquid crystal between two conductive electrode substrates at a constant thickness using an appropriate spacer, and then heating or A light scattering state is created between the electrodes by curing the polymer resin using ultraviolet rays, depending on whether or not a voltage is applied.
A liquid crystal film that has a liquid crystal film that can take a transparent state, and is made by adding ultrafine particles of inorganic or organic substances of 0.5 microns or less to a liquid mixture of polymer resin and liquid crystal, and then curing the resin. .

The present invention will be explained below based on the drawings.

The overall structure of the liquid crystal film of the present invention is shown in FIG.
As shown in FIG. 2, transparent substrates 10,
Transparent conductive electrode layers 20 and 2 respectively provided on 10
A liquid crystal film 30 made of transparent resin in which liquid crystal molecules are dispersed at
It is sandwiched between.

As the transparent substrate 10 of the present invention, a polyester film with excellent transparency is suitably used, but a glass plate or other transparent polymer film can also be used.

Further, as the transparent conductive electrode layer 20 provided on the substrate 10, an indium oxide film made of indium, which may contain a small amount of impurities such as tin, is preferable, but an inorganic oxide film such as zinc oxide, titanium oxide, etc. Material layer: A thin film of metal such as gold or platinum; A laminate in which a thin metal film is sandwiched between transparent conductive films can also be used.

[0013] One of the electrode layers 20 may be made of a thick metal film to form a non-transparent film with high reflectance, but in this case, the substrate 10 does not need to be transparent either.

A resistance of 500 Ω/□ or less is formed on the transparent substrate 10 using a known physical method such as a sputtering method.
A transparent conductive electrode layer 20 preferably having a resistance of 300Ω/□ or less can be provided.

In order to display characters and figures using the liquid crystal film of the present invention, it is necessary to pattern the transparent conductive electrode using a known method such as etching. Furthermore, in order to improve the display quality, it is possible to use a so-called active matrix type transparent electrode in which each display pixel is provided with a switching function.

Furthermore, by stacking red, blue, and green color filters in each pixel portion, color display in which transmitted light is colored is also possible.

The liquid crystal layer of the present invention comprises O dispersed in a polymer resin.
．． The liquid crystal layer is composed of liquid crystal droplets with a diameter of 5 to 5 μm, their aggregates, and/or a three-dimensional network continuous phase of liquid crystals.As the polymer resin, various types such as thermoplastic resins, thermosetting resins, and ultraviolet curing resins are used. A resin that is transparent and has good light resistance is selected. In order to improve the transparency when a voltage is applied to the liquid crystal film, it is preferable that the refractive index of the liquid crystal dispersed in the resin matches the refractive index of the resin. A resin having a refractive index difference of 0.1 or less is selected.

Suitable resins include ultraviolet curable resins and transparent acrylate resins. Further, it is a transparent resin containing 1 to 10 at% of fluorine atoms due to its optical properties.

By using an ultraviolet curable resin, the resin can be cured through a transparent substrate, and there is an advantage that the shape of the liquid crystal dispersed in the resin can be controlled by adjusting the intensity of the irradiated light. Furthermore, by incorporating fluorine atoms, it is possible to adjust the refractive index of the resin and control the precipitation state of the liquid crystal phase.

Of course, the resin is selected depending on the relationship with the liquid crystal, and the resin is not limited thereto.

The liquid crystal film of the present invention has a resin film containing 1 to 10%, preferably 1 to 5% (based on the number of atoms) of fluorine atoms, in which liquid crystal droplets with a diameter of 0.8 to 5 μm are arranged. It contains dispersed three-dimensional network continuous phases of aggregates and/or liquid crystals. The thickness of the resin film (which eventually becomes the thickness of the liquid crystal layer) is not particularly limited, but when considering applications that require driving at the lowest possible voltage, it is generally 50 μm or less, preferably 2 to 2 μm.
It is 30 μm.

[0022] Fluorine atoms are contained in an amount of 1 to 10%, preferably 1 to 10%.
The material for the liquid crystal layer containing 5% (based on the number of atoms) is not particularly limited as long as the liquid crystal phase stably exists therein and the resin does not have an adverse effect on the liquid crystal. A preferred example that can be most easily produced is acrylate resin.

A convenient means for incorporating fluorine into the acrylate resin is to use a fluorine-substituted (meth)acrylate compound which is a raw material for the acrylate resin.

At this time, all of the raw materials may be substituted with a predetermined amount of fluorine, but if an appropriate amount of fluorine is substituted (
It is convenient to use a mixture of a meth)acrylate compound and a (meth)acrylate compound that does not contain a fluorine atom. In addition, in this specification, "(meth)acrylic...
“…” means “acrylic… and/or metaacry…”
means. These can be monofunctional or polyfunctional monomers or oligomers thereof.

Among these resins, cured resins made from monofunctional monomer compounds are preferably used as resins suitable for liquid crystal constituents that can operate at low voltages. More preferred monomers include the following general formula (I):

[0026]

Phenoxyoligoethylene oxide acrylate monomer (hereinafter referred to as "EOA") represented by [Formula, R1 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n represents an integer of 1 to 14] ).

As the alkyl group having 1 to 10 carbon atoms represented by R1, nonyl group, methyl group, ethyl group, propyl group, butyl group, isopropyl group, isobutyl group, and isopentyl group are preferably used.

[0028] More preferably, n is 1 to 8.

Specific examples of the EOA represented by the general formula (I) include:

[0030]

[Chemical formula 2] etc. In addition to the compound represented by the general formula (I), the EOA may contain 20% by weight or less of a monofunctional or polyfunctional acrylate monomer that does not contain a fluorine atom other than the compound.

Monofunctional monomers that can be contained in this EOA include ethyl carbitol acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxypentyl acrylate, and 2-hydroxypropyl acrylate.
-hydroxy-3-phenoxypropyl acrylate,
Mention may be made of tetrahydrofurfuryl acrylate. Further, as the polyfunctional monomer, polypropylene glycol diacrylate, polyethylene glycol diacrylate, etc. are preferably used.

In the present invention, (meth)acrylate containing a fluorine atom is used as a promoting material for precipitating liquid crystal molecules as a liquid crystal phase, and as a material for adjusting the matching of optical properties between the liquid crystal phase and the polymer resin phase. A compound is further mixed into the acrylate compound. As a (meth)acrylate compound containing a fluorine atom, the general formula (
A (meth)acrylate compound represented by II) is exemplified.

[0033]

[In the formula, R represents -H or -CH3, n represents 1 to 10, x represents 0 to 2n, and y represents (2n+1)-x. ] Specific examples include trifluoroethyl acrylate,
Tetrafluoropropyl acrylate, hexafluorobutyl acrylate, octafluoropentyl acrylate,
Mention may be made of perfluorooctylethyl acrylate and their methacrylates. Of course, polyfunctional acrylates other than those exemplified may also be used. Fluorine atom-containing acrylate compounds are difficult to dissolve mutually with liquid crystal molecules, so when mixed with other acrylate compounds, it is necessary to use them within a range that does not cause unnecessary precipitation of liquid crystals.

For this purpose, the fluorine atom content is selected from the range of 2 to 50% by weight based on the total acrylate compound, and the content of fluorine atoms after curing is 1 to 10%, preferably 1 to 5%.
adjusted to %.

As a curing agent for curing the EOA and other monofunctional and/or polyfunctional acrylate compounds and acrylate compounds such as fluorine-containing acrylates by irradiating ultraviolet rays, for example, an acetophenone photoinitiator (manufactured by Merck & Co., Ltd. Darocure 1173 or "Irgacure" manufactured by Ciba Geigy, etc.).

[0036] Of course, without being limited to this,
Sensitizers, chain transfer agents, dyes, etc. can also be added.

The amount of the curing agent used is preferably about 1 to 5% by weight based on the total amount of the acrylate compound.

As the liquid crystal component constituting the liquid crystal phase, a cyanobiphenyl liquid crystal component that has high dielectric anisotropy and a refractive index difference between the normal light refractive index and the extraordinary light refractive index of 0.2 or more is preferably used. It will be done. Of course, the liquid crystal components are not limited to these, and depending on the application, nematic liquid crystals such as phenylcyclohexane, phenylpyrimidine, and benzoic acid esters, and not only positive dielectric anisotropy but also negative dielectric anisotropy can be used. A single liquid crystal or a mixture of smectic liquid crystals and the like are used.

[0039] Since the liquid crystal composition appears in an opaque state through the scattering of light by minute liquid crystal phases dispersed in the cured resin and the random orientation of liquid crystal molecules, liquid crystal droplets in the liquid crystal film and their aggregates and/or LCD 3
The average size of the dimensional network continuous phase has an average diameter of 0.8 μm or more, which is larger than the wavelength of visible light, and 10 μm.
The thickness is more preferably 5 μm or less. Furthermore, in order to obtain opacity due to the randomness of liquid crystal molecules, the larger the refractive index difference between the normal light refractive index and the extraordinary light refractive index, the better.

In general, even a liquid crystal film coated with an appropriate mixture of resin and liquid crystal can exhibit some optical change depending on whether or not a voltage is applied. However, good ON-O
FF characteristics, that is, the haze value when voltage is applied is small, for example, when a low potential such as 20V is applied, the haze value is 20%
In order to obtain a liquid crystal film that exhibits the following and also has a large haze value when no voltage is applied, for example, a haze value of 80% or more, an optimal combination of liquid crystal and resin is required.

[0041] A monofunctional or polyfunctional (meth)acrylate compound containing a fluorine atom of the present invention is mixed.
As the cyanobiphenyl (cyanoterphenyl) liquid crystal droplets dispersed in the resin made from the meth)acrylate compound, general formula (III) is used.

[0042]

Cyanobiphenyl (wherein X represents an alkyl or alkoxy group having 1 to 12 carbon atoms)
Cyanoterphenyl) type compounds are most suitable. These compounds may be used in combination of two or more.

[0043] As this liquid crystal, for example, E
-8 liquid crystal can be mentioned.

A coating liquid is prepared by mixing appropriate amounts of the above-mentioned UV curing resin and liquid crystal. At this time, inorganic or organic ultrafine particles are added to the coating liquid in order to promote and control phase separation. In order not to impair the transparency of the completed liquid crystal film, the ultrafine particles preferably have a particle size within a range that does not scatter visible light, and are 0.5 μm or less. The material for the ultrafine particles can be selected from either inorganic or organic materials.

[0045] As the inorganic fine particles, metal oxide particles such as silicon oxide and titanium oxide are used. The metal oxide fine particles may be subjected to a surface treatment to prevent agglomeration.
Further, a surface treatment may be applied to improve adhesive strength with the liquid crystal layer composition.

For example, particles whose surfaces are modified with alkyl groups, carbonyl groups, cyano groups, amino groups, hydroxyl groups, etc. are preferably used.

The ultrafine particles added to the mixed coating liquid of liquid crystal and resin are selected from a range of 0.1 to 20% by weight based on the resin component.

By mixing ultrafine particles, it becomes easier to precipitate liquid crystal during ultraviolet curing, and it becomes easier to control the liquid crystal droplet diameter uniformly.

[0049] Ultrafine particles are produced by further reducing particles, which have been previously refined to a size of several tens of micrometers, into ultrafine particles using a known pulverization technique. Known techniques include pulverization methods using pin mills, attrition mills, etc., and pulverization methods using thermal shock, pressure changes, and the like.

Chemical methods such as the CVD method and liquid phase precipitation method, and physical methods such as the evaporation method in gas, the ultrasonic pulverization method, and the freeze-drying method are also used as methods for producing ultrafine particles.

The steps for producing the liquid crystal film of the present invention include (1) spacer particles for defining the thickness of the liquid crystal layer, which are optionally contained on a substrate provided with a (patterned) transparent conductive electrode; Step of coating a resin/liquid crystal mixture containing a small amount of ultrafine particles (2) Step of superimposing another (patterned) transparent conductive electrode-attached substrate on the above coating film (3) The process consists of the steps of irradiating the laminate with ultraviolet light through the transparent substrate to cure the resin and create a liquid crystal film in which the liquid crystal phase is dispersed.

In the third step, the ultraviolet light intensity and curing temperature are one of the important factors that influence the characteristics of the liquid crystal film (ON/OFF characteristics when voltage is applied).

The curing temperature is important, and it is preferable to cure at a temperature higher than the phase transition temperature of the nematic phase or isotropic phase of the liquid crystal used, preferably 5 to 20°C higher.

[0054] By depositing the liquid crystal in an isotropic phase state, the orientation of the liquid crystal molecules at the resin/liquid crystal interface is improved, and good ON/OFF characteristics, especially fast operation characteristics when the voltage is turned off, can be obtained. . Of course, the optimum curing temperature is
It is selected depending on the combination of resins, and is not limited to the above temperature range.

The cyanobiphenyl liquid crystal phase in the liquid crystal film of the present invention comprises cyanobiphenyl liquid crystal in an acrylate monomer mixture, and the liquid crystal component is preferably 50% by weight or more, 7
By mixing to a concentration of 5% by weight or less and using this as a coating liquid, liquid crystal droplets, aggregates thereof, and/or three-dimensional network continuous phase of liquid crystals having an average diameter of 0.8 μm or more and 5 μm or less are obtained. be able to.

If the liquid crystal component is less than 50% by weight, the liquid crystal phase generated by phase separation from the liquid crystal component dissolved in the raw material acrylate compound mixture during resin formation becomes small, so that good opacity, that is, light shielding property is obtained. The disadvantage is that it may not be possible to obtain Furthermore, during the durability test, bubble-like portions that did not respond to voltage application were sometimes observed in the liquid crystal film.

On the other hand, if it exceeds 75% by weight, the liquid crystal component cannot be completely dissolved in the raw material (meth)acrylate, forming microdroplets from the time of monomer mixing, and the liquid crystal component cannot be further contained in the resin due to curing. will seep out. As a result, inconveniences such as a decrease in adhesiveness with the transparent conductive electrode and a decrease in workability occur.

As described above, in order to create a liquid crystal film having good light shielding properties, workability, and durability, it is preferable that the liquid crystal component is 50% by weight or more and 75% by weight or less. In order to obtain even more preferable light-shielding properties, the liquid crystal component should be added to 5
5 to 75% by weight.

The liquid crystal film thus obtained was 1
The film can be driven at a low voltage of 0 V or less and exhibits fast response characteristics, so it can be suitably used as a display panel.

[0060]

[Examples] The present invention will be explained in more detail with reference to Examples below.

[0061]

Example 1 A polyester film with a thickness of 125 μm was used as a transparent substrate, and an indium oxide film containing a small amount of tin was deposited as a transparent conductive layer thereon to a thickness of about 200 angstroms by sputtering.

E-8 manufactured by BDH Co., Ltd. was used as the cyanobiphenyl liquid crystal, and M113 (norylphenoltetraethylene oxide acrylate) manufactured by Toagosei Co., Ltd. was used as the acrylate monomer. As a fluorine-based acrylate compound, F-8 manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.
(octafluoropentyl acrylate) was used. These compounds have a weight mixing ratio of M113:HOPA:F-
They were mixed at a ratio of 8=64:16:20. As a curing agent, 3% by weight of Irgacure manufactured by Ciba Geigy was added and mixed. As a spacer, a 12 μ diameter “ made by Sekisui Chemical Co., Ltd.
0.3% of "Micropearl" was added to the resin.

As the ultrafine particles, OSCAP, manufactured by Catalysts Kasei Kagaku Kogyo Co., Ltd., which is a silicon oxide fine particle, was used. OSCAP microparticles having a diameter of about 800 angstroms were added at 5% by weight to the resin mixture. Liquid crystal component is 60% by weight
After mixing the mixture, the mixture was thoroughly stirred and degassed to obtain a coating liquid.

Next, the coating solution was applied onto the transparent conductive layer. Next, another polyester film with a transparent conductive layer was superimposed so that the transparent conductive layer was in contact with the liquid crystal coating film. This structure is heated to 75°C, which has a phase transition temperature higher than that of E-8 liquid crystal.
℃, and when equilibrium was reached, 6 mW/cm 2 of ultraviolet light was irradiated for about 5 minutes using an ultraviolet irradiator using a mercury lamp as a light source. The liquid crystal coating layer was cured between the transparent conductive layers by ultraviolet light to form a liquid crystal film with a thickness of about 12 μm, thereby obtaining a liquid crystal film.

0 between the two electrodes of the obtained liquid crystal film
A voltage from V to 10V was applied and the transmittance was measured (
Table 1 shows the change in transmittance (0V, 10V) of this liquid crystal film.
It was shown to). It can be seen that the liquid crystal composition of the present invention causes a wide change in transmittance from 0V to 10V when the liquid crystal concentration is 60%.

The transmittance of the liquid crystal film was measured using a multi-photometering system MCPD-1000 manufactured by Otsuka Electronics.

[0067]

Example 2 A liquid crystal film was prepared using the same resin and the same method as in Example 1. The ultrafine particles used at this time were made by further refining the fine powder of barium titanate (BaTiO3) manufactured by Sumitomo Cement using an attrition mill, and had a particle size of about 0.3 μm.

Approximately 5% by weight based on resin concentration was added. The liquid crystal concentration used was 60% by weight of E-8 liquid crystal.

Table 1 shows the transmittance of this liquid crystal film when 0V and 10V were applied.

[0070]

[Comparative Examples 1 and 2] A liquid crystal film was prepared using the same resin and the same method as in Example 1 without adding ultrafine particles.

Two types of liquid crystal concentrations were prepared: 60% by weight and 67% by weight of E-8. Table 1 shows the transmittance when 0V and 10V were applied at this time.

[0072]

Example 3 A liquid crystal film was prepared using the same resin and the same method as in Example 1.

The fine particles used at this time were pulverized silica gel (approximately 7 μm
) (Licrosolve CN) was further refined using an attrition mill, and the particle size was about 0.3 μm.

Approximately 5% by weight was added relative to the resin concentration. The liquid crystal concentration used was 60% by weight of E-8 liquid crystal.

Table 1 shows the transmittance of this liquid crystal film when 0V and 10V were applied.

[0076]

[Table 1] As described above, the ultrafine particle-added film of the present invention exhibits high transparency at the same liquid crystal concentration. In other words, this shows that it can be driven at low voltage. Furthermore, the film of the present invention exhibits the same performance at a lower liquid crystal concentration as compared to a product without the addition of ultrafine particles, and has the advantage that expensive liquid crystals can be saved.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a liquid crystal film of the present invention.

[Explanation of symbols]

10 Transparent substrate 20 Transparent conductive electrode layer 30 Liquid crystal film

Claims (5)

[Claims] Claim 1: A liquid mixture of polymer resin and liquid crystal is sandwiched between two conductive electrode substrates at a constant thickness using an appropriate spacer, and then the polymer resin is removed using heat or ultraviolet light. In a liquid crystal film having a liquid crystal film provided between electrodes by curing, which can change to a light scattering state or a transparent state depending on whether or not a voltage is applied, an inorganic material of 0.5 micron or less is added to a mixed liquid of a polymer resin and a liquid crystal. , or a liquid crystal film characterized by adding ultrafine particles of an organic substance. 2. The liquid crystal film according to claim 1, wherein the inorganic ultrafine particles of 0.5 microns or less added to the mixture of polymer resin and liquid crystal are oxides of metals such as silicon, titanium, and aluminum. 3. The surface of the inorganic ultrafine particles contains an alkyl group,
3. The liquid crystal film according to claim 2, which is chemically modified with a carbonyl group, a cyano group, an amino group, or the like. 4. The liquid crystal film is made of a cured resin of an ultraviolet curing type acrylate resin, in which 0.5
2. The liquid crystal film according to claim 1, comprising liquid crystal droplets having a diameter of ~5 microns, aggregates thereof, and/or a three-dimensional network continuous phase of liquid crystal. [Claim 5] The ultraviolet curable acrylate resin contains 1
5. The liquid crystal film according to claim 4, which is an acrylate compound containing ~10% (based on the number of atoms) of fluorine atoms.