JP2000119655A - Liquid crystal optical element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an element which shows high contrast with a low driving voltage by placing a mixture of a liquid crystal and plural uncured hardenable compounds having extremely different molecular weight between substrates with a pair of electrodes and curing thereof to form a liquid crystal/hardened material composite layer. SOLUTION: A mixture of a liquid crystal and two uncured hardenable compounds represented by the formula having different molecular weight, one having molecular weight not less than two times larger than the other, is placed between substrates with a pair of electrodes keeping a clearance of 4-50 μm, at least one of substrates being transparent, and is hardened by photo irradiation or heating to form a liquid crystal/hardened material composite layer and then give a liquid crystal photo element. A catalyst for photo hardening or thermosetting reaction is mixed with a mixture of the uncured hardenable compounds having molecular weight of not less than 1,000 and the liquid crystal, the amount thereof being not more than 20 wt.% of the hardenable compounds and a chiral agent is also mixed therewith such that a helical pitch is not less than 5 μm. In the formula, A1 and A2 are each acryloyl, glycidyl or the like; R1 and R2 are each a 2-6C alkylene; Z is a portion of a mesogen structure having two valences; and (n) and (m) are each integers of 1-10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical element which can be used for a light control element, a display element, an optical shutter and the like by controlling the transmission, scattering and reflection states of the element by application / non-application of an electric field.

[0002]

2. Description of the Related Art There has been proposed a transmission-scattering type optical element in which a liquid crystal and a transparent polymer are combined to produce a difference in refractive index between the polymer and the liquid crystal or between the liquid crystals (between minute regions). It is called a liquid crystal / polymer composite element, a liquid crystal / resin composite element, or a dispersion type liquid crystal element. Since this element does not require a polarizing plate in principle, it has low light absorption loss,
A great advantage is that high scattering performance is obtained and the light use efficiency of the entire device is high.

Utilizing this characteristic, it is used for light control glass, optical shutters, laser devices, display devices, and the like. Those in a scattering state when no voltage is applied and in a transparent state when a voltage is applied have been commercialized.

Further, a conventional example 1 (USP 518,876)
0) discloses an element using a liquid crystal and a polymerizable liquid crystal. In Conventional Example 1, since the liquid crystal in the device and the polymerized liquid crystal have the same orientation direction when no voltage is applied, the device exhibits a transparent state when viewed from any direction. When a voltage is applied, the orientation of the liquid crystal in the device is controlled by the electric field, and the orientation of the liquid crystal molecules changes in a minute area in various ways, so that the device exhibits a scattering state.

It has also been disclosed that the contrast ratio is improved by providing a helical structure in the initial alignment by adding a chiral agent. This device is called "anisotropic gel" or "liquid crystal gel". In this conventional example 1, a mesogen monomer having an acryloyl group at the terminal was used.

Further, a conventional example 2 (International Patent Publication WO92 /
19695) also disclosed an element having a similar configuration.
This is an operation mode similar to that of Conventional Example 1, in which a very small amount of polymer is dispersed in a chiral nematic liquid crystal to obtain a transparent state when no voltage is applied and a scattering state when a voltage is applied. This element is P
SCT (Polymer Stabilized Cholesteric
Texture). This Conventional Example 2 also discloses a mesogen monomer having an acryloyl group at the terminal.

[0007]

As the structure of the uncured curable compound, the compound of the formula (2) is exemplified in the conventional example 1, and the compound of the formula (3) is exemplified in the conventional example 2.

[0008]

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[0009]

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[0010] However, cured products formed by using these compounds alone have characteristics due to the molecular structure. That is, since the mesogen structure portion having high crystallinity is included, and the distance between the cured sites (acryloyl group in this case) in the molecule is short, the molecular weight between cross-linking points is reduced, and the obtained cured product is hard and brittle. Become. In addition, since the mobility of the uncured portion is significantly impaired during the curing, there is a problem that a considerably long curing time is required for sufficient curing.

The properties of the liquid crystal optical element obtained by curing the curable compound in the mixture largely depend on the structure of the liquid crystal / cured product composite layer. The structure is greatly affected by the molecular structure of the uncured curable compound used. In general, it is reported that a curable compound containing a mesogen structure such as a biphenyl structure has a large elastic modulus after curing at both curing sites, and a high glass transition temperature of the obtained polymer. .

On the other hand, this limits the molecular motion and free volume of the curable compound during curing. In the later stage of the curing process, there is a possibility that the reactivity of the cured site may be suppressed. A problem arises in that the reaction is not sufficiently performed or a very long curing time is required.

It has also been found that the physical properties of the resin which is a cured product of the liquid crystal / cured product composite layer contributes to the electro-optical characteristics of the liquid crystal optical element. If the elastic modulus of the resin is too high or brittle, the required driving voltage increases, and in a relatively low driving voltage range, a sufficient contrast ratio is obtained in a change in transmittance or a change in reflectance with / without voltage application. Sometimes it was not possible.

An object of the present invention is to solve the above-mentioned problems, and to provide, for example, a liquid crystal optical element which can be manufactured with a short curing time and has a high contrast ratio even at a low driving voltage.

[0015]

That is, the present invention provides a liquid crystal display device in which a mixture of a liquid crystal and an uncured curable compound is interposed between a pair of electrodes having at least one transparent electrode, and the curable compound is cured. A method for producing a liquid crystal optical element, wherein a liquid crystal / cured product composite layer is formed by heating, wherein the curable compound contains two types of curable compounds having a molecular weight different from each other by a factor of 2 or more. Provide a way.

Further, the present invention provides a method for producing a liquid crystal optical element, wherein the curable compound contains the compound of the formula (1). Further, in the above manufacturing method,
Three or more compounds having different molecular weights can be used,
Among them, at least two kinds of compounds should satisfy the above conditions.

[0017]

Embedded image A _1- (OR ₁ ) _n -OZO- (R ₂ O) _m -A ₂ Formula (1)

A ₁ , A ₂ : independently acryloyl, methacryloyl, glycidyl, allyl R ₁ , R ₂ : independently alkylene having 2 to 6 carbons Z: divalent mesogenic structure n, m: each independently an integer of 1 to 10

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the uncured curable compound contains two curable compounds whose molecular weights are different from each other by a factor of two or more. Can be changed. Or
The crystallinity of the resin can be controlled. It has been found that by these, the curability in the curing process can be improved and the elastic modulus of the cured resin can be adjusted, so that a liquid crystal optical element that can exhibit high contrast even at a low driving voltage can be obtained.

Further, the uncured curable compound has the formula (1)
When the curable compound is contained, the compatibility with the liquid crystal when not cured can be improved. In addition, by introducing an oxyalkylene structure with high molecular mobility between the mesogen structure and the curing site, the molecular mobility of the curing site in the curing process is improved, and an electric field is applied even during a short curing reaction. / It has been found that a liquid crystal optical element having a stable state when no voltage is applied, high reliability and high contrast can be obtained.

The curing site (A ₁ , A ₂ ) in the formula (1) may be any of the above-mentioned functional groups which can be generally photo-cured and heat-cured together with a curing catalyst. Acryloyl group and methacryloyl group which are suitable for photo-curing are preferred because they can control the temperature.

The number of carbon atoms of R ₁ and R _{2 in} the oxyalkylene moiety of the formula (1) is preferably 2 to 6 in view of its mobility, and more preferably an ethylene group having 2 carbon atoms and a propylene group having 3 carbon atoms.

As the mesogen structure (Z) in the formula (1), divalent polyphenylene in which two or more 1,4-phenylene groups are linked is preferable. Further, a divalent organic group in which a part of the 1,4-phenylene group in the polyphenylene group is substituted with a 1,4-cyclohexylene group may be used.

Some or all of the hydrogen atoms of these polyphenylene groups and divalent organic groups may be substituted with substituents such as alkyl groups having 1 to 2 carbon atoms, halogen atoms, carboxyl groups, alkoxycarbonyl groups and the like. . Desirable Z is a biphenylene group in which two 1,4-phenylene groups are linked (hereinafter, referred to as a 4,4′-biphenylene group), 3
A terphenylene group linked to each other, and a divalent organic group in which 1 to 4 of these hydrogen atoms are substituted with an alkyl group having 1 to 2 carbon atoms, a fluorine atom, a chlorine atom or a carboxyl group. Most preferred Z is unsubstituted 4,
4′-biphenylene group.

If n and m in the formula (1) are too large, the compatibility with the liquid crystal is reduced. Therefore, they are each independently 1 to 10, and more preferably 1 to 4 in consideration of the cured device characteristics.

In order to adjust the compatibility with the uncured liquid crystal and the elasticity of the cured resin, the uncured curable compound does not include the curable compound having a mesogen structure in the molecule. It is preferable to contain a curable compound together. This is because the mesogen structure part increases the elastic modulus of the cured resin more than necessary while improving the compatibility with the uncured liquid crystal.

The two uncured curable compounds contained are:
It is preferable that they can be bonded to each other in the resin formed by curing without causing phase separation between the resins and increasing the haze at the time of transmission or reflection.

In order to increase the molecular weight between cross-linking points to improve the curability at the time of curing and to lower the elasticity of the cured resin, a curable compound having a relatively large molecular weight is used as the uncured curable compound. Is preferred. Specifically, a curable compound having a molecular weight of 1,000 or more is preferable.

The mixture of the liquid crystal and the uncured curable compound may contain a curing catalyst. In the case of photo-curing, a benzoin ether-based, acetophenone-based, phosphine oxide-based photo-curable resin, etc. A polymerization initiator can be used. In the case of thermal curing, a curing catalyst such as a peroxide-based, thiol-based, amine-based, or acid anhydride-based curing catalyst can be used depending on the type of the curing site, and a curing aid such as an amine can be used if necessary. Can be used.

The content of the curing catalyst is preferably 20% by weight or less of the contained uncured curable compound. When a high molecular weight or a high specific resistance of the cured product after curing is required, it is 1 to 1%.
0 wt% is more preferable.

In order to improve the contrast of the device when an electric field is applied / not applied, a chiral agent can be added to a mixture of a liquid crystal and an uncured curable compound. If the voltage is too small, the driving voltage increases. If the voltage is too large, sufficient contrast cannot be obtained. Therefore, it is preferable that the voltage is 5 μm or more and twice or less the electrode gap.

On the other hand, the mixture of the liquid crystal and the uncured curable compound is preferably a homogeneous solution after mixing. The mixture of the liquid crystal and the uncured curable compound may exhibit a liquid crystal phase when sandwiched between the substrate with electrodes. The mixture of the liquid crystal and the uncured curable compound may exhibit a liquid crystal phase when cured.

The function of aligning the liquid crystal on the electrode surface by directly polishing the electrode surface of the substrate with electrodes sandwiching the mixture of the liquid crystal and the uncured curable compound, or by rubbing a resin thin film. Can be imparted, whereby the unevenness in holding the mixture of the liquid crystal and the uncured curable compound can be reduced. The combination of the orientation directions of the pair of orientation-treated substrates may be parallel or orthogonal, and the angle may be set so as to minimize unevenness when the mixture is held.

The electrode gap can be held by a spacer or the like, preferably 4 to 50 μm, more preferably 5 to 30 μm.
m is preferred. If the electrode gap is too small, the contrast ratio decreases, and if it is too large, the driving voltage increases. The substrate supporting the electrodes may be a glass substrate or a resin substrate, or may be a combination of a glass substrate and a resin substrate. Also,
One of them may be a reflective electrode of aluminum or a dielectric multilayer film.

In the case of a film substrate, a substrate with electrodes supplied continuously is sandwiched between two rubber rolls or the like, and a mixture of a liquid crystal containing a spacer and dispersed therein and an uncured curable compound is supplied between them. After that, it can be cured continuously, and the productivity is high.

In the case of a glass substrate, a small amount of spacers are scattered in the electrode surface, and four sides of the opposed substrate are sealed with sealing agents such as epoxy resin to form sealing cells at two or more locations. One is immersed in a mixture of a liquid crystal and an uncured curable compound, and the other is sucked from the other to fill the mixture in the cell and cure to obtain a liquid crystal optical element. Also, a normal vacuum injection method can be used. Hereinafter, examples will be described.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION

[0038]

(Example 1) 94.6 parts of a cyano-based nematic liquid crystal (BL-009 manufactured by Merck) and a chiral agent (a mixture of S-811 manufactured by Merck and C15 manufactured by Merck at a weight ratio of 1: 1) 2 .4 parts, 2.5 parts of a curable compound of the formula (4) having a molecular weight of 382, and a urethane acrylate oligomer having a molecular weight of 1500 or more (E, manufactured by UCB)
B-270) was prepared as a mixture (mixture A) of 0.5 part and benzoin isopropyl ether 0.09 part.

[0039]

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A mixture of the mixture A and a pair of substrates obtained by rubbing a polyimide thin film formed on a transparent electrode in one direction are opposed to each other so that the rubbing directions are orthogonal to each other.
The resin was injected into a liquid crystal cell manufactured by laminating epoxy resin printed on four sides with a width of about 1 mm through resin beads of m.

With the liquid crystal cell kept at 25 ° C.,
The dominant wavelength of about 365nm of HgXe lamp, 3 mW / cm ² from the upper side, the same about 3 mW / cm ² UV than the lower irradiation 10 minutes to obtain a liquid crystal optical element.

This liquid crystal optical element has a rectangular wave of 50 Hz, 20 Hz.
An operation of removing the voltage after applying the voltage of Vrms for 10 minutes
Repeated 0 times. Thereafter, when the transmittance was measured by a transmittance measuring system (F value of optical system: 11.5) using a measuring light source having a half value width of about 20 nm with a center wavelength of 530 nm, 83% was obtained without applying a voltage. The value of the contrast ratio obtained by dividing the value by the transmittance when 20 Vrms was applied was 31.

Comparative Example 1 A liquid crystal optical element was obtained in the same manner as in Example 1 except that only the compound of the formula (4) was used as an uncured curable compound. Example 1 was applied to this liquid crystal optical element.
After applying a voltage in the same manner as in the above, the transmittance was measured by the same measuring system.
The value of the contrast ratio divided by the transmittance when Vrms was applied was 11.

Example 2 Mixture A prepared in Example 1
Was injected into the same liquid crystal cell as in Example 1, and kept at 25 ° C., and irradiated with ultraviolet rays for 3 minutes in the same manner as in Example 1.
A liquid crystal optical element was obtained.

This liquid crystal optical element has a rectangular wave of 50 Hz, 20 Hz.
After applying the voltage of Vrms for 10 minutes, the operation of removing the voltage was repeated 10 times. Thereafter, the transmittance was measured by a transmittance measurement system (F value of optical system: 11.5) using a measurement light source having a half-width of about 20 nm with a center wavelength of 530 nm.
79% when no voltage is applied, this value is 20 Vrms
The value of the contrast ratio divided by the transmittance when applied is 4
It was 3.

Comparative Example 2 A liquid crystal optical element was obtained in the same manner as in Example 2 except that only the compound of the formula (2) was used as the uncured curable compound. Example 2 is applied to this liquid crystal optical element.
After applying a voltage in the same manner as in the above, the transmittance was measured using the same measurement system.
The value of the contrast ratio divided by the transmittance when Vrms was applied was 12.

[0047]

According to the liquid crystal optical element of the present invention, the curability of the curable compound used is high. High productivity because it can be manufactured.

Further, since the molecular weight between the crosslinking points and the elastic modulus of the cured resin can be controlled, a liquid crystal optical element having a high contrast ratio even at a low driving voltage can be obtained. It is suitable for an optical shutter or the like.

Claims (7)

[Claims] 1. A liquid crystal / cured product composite layer is formed by sandwiching a mixture of a liquid crystal and an uncured curable compound between a pair of substrates with electrodes, at least one of which is transparent, and curing the curable compound. The method for producing a liquid crystal optical element described above, wherein the curable compound contains two kinds of curable compounds whose molecular weights are different from each other by two times or more. 2. A method for producing a liquid crystal optical element, wherein the curable compound contains a compound of the formula (1). Embedded image A _1- (OR ₁ ) _n -O—Z—O— (R ₂ O) _m -A ₂ Formula (1) A ₁ and A ₂ : each independently an acryloyl group, a methacryloyl group, Glycidyl group, allyl group R ₁ , R ₂ : each independently an alkylene group having 2 to 6 carbon atoms Z: divalent mesogen structure part n, m: each independently an integer of 1 to 10 3. The liquid crystal optical element according to claim 1, wherein the curable compound contains both a curable compound having a mesogen structure in the molecule and a curable compound not having a mesogen structure in the molecule. Method. 4. The method for producing a liquid crystal optical element according to claim 1, wherein said two kinds of curable compounds have cured sites that can be bonded to each other. 5. The method for producing a liquid crystal optical element according to claim 1, comprising a curable compound having a molecular weight of 1,000 or more. 6. The method for producing a liquid crystal optical element according to claim 1, wherein said mixture contains a trace amount of a curing catalyst. 7. A liquid crystal optical element manufactured by the manufacturing method according to claim 1.