JP5136597B2 - Liquid crystal optical element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a liquid crystal optical element that can be used for a light control element, a display element, an optical shutter, and the like by controlling transmission, scattering, and reflection states of the element by applying / not applying an electric field.

  A transmission-scattering type optical element has been proposed in which a liquid crystal and a transparent polymer are combined to cause a difference in refractive index between the polymer and the liquid crystal, or inside the liquid crystal (between microregions). It is called a liquid crystal / polymer composite element, a liquid crystal / resin composite element, or a dispersed liquid crystal element. Since this element does not require a polarizing plate in principle, it has a great advantage that light absorption loss is small, high scattering performance is obtained, and light use efficiency in the entire element is high.

  Taking advantage of 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 was applied and in a transparent state when a voltage was applied were commercialized.

  Further, Patent Document 1 discloses an element using a liquid crystal and a polymerizable liquid crystal. In Patent Document 1, since the liquid crystal in the element and the polymerized liquid crystal have the same alignment direction when no voltage is applied, the element is transparent when viewed from any direction. When a voltage is applied, the orientation of the liquid crystal in the element is controlled by an electric field, and the arrangement direction of the liquid crystal molecules changes variously in a minute region, whereby the element exhibits a scattering state.

  It has also been disclosed that the contrast ratio is improved by adding a chiral agent to provide a helical structure in the initial orientation. This element is called “anisotropic gel” or “liquid crystal gel”. In this Patent Document 1, a mesogenic monomer having an acryloyl group at the terminal is used.

  Patent Document 2 also discloses an element having a similar configuration. The operation mode is the same as in Patent Document 1, and a 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 called PSCT (Polymer Stabilized Cholesteric Texture). This Patent Document 2 also discloses a mesogenic monomer having an acryloyl group at the terminal.

US Pat. No. 5,188,760 International Publication No. 92/19695

  As the structure of the uncured curable compound, Patent Document 1 exemplifies the compound of Formula (2), and Patent Document 2 exemplifies the compound of Formula (3).

  However, a cured product formed by using these compounds alone had characteristics resulting from the molecular structure. That is, since it contains a highly crystalline mesogenic structure and the distance between the cured sites in the molecule (in this case, acryloyl groups) is short, the molecular weight between the crosslinking points is reduced, and the resulting cured product is hard and brittle. Become. For this reason, the motility of the uncured part is remarkably impaired during the curing, so that a considerably long curing time is required for sufficient curing.

The characteristics 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 influenced by the molecular structure of the uncured curable compound to be used.
In general, it is reported that a curable compound containing a mesogen structure such as a biphenyl structure has a cured portion bonded at both ends, has a large elastic modulus after curing, and a high glass transition temperature of the resulting polymer. .

  On the other hand, this restricts the molecular motion and free volume of the curable compound in the middle of curing, and in the latter stage of the curing process, the reactivity of the cured site may be suppressed, and the curing reaction is sufficient. There is a problem that it is not performed or a very long curing time is required.

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

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

  That is, in the present invention, a liquid crystal / cured material 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. In the method for producing a liquid crystal optical element, the curable compound does not include the first curable compound represented by the formula (1) and the mesogenic structure and can be bonded to the first curable compound. And a second curable compound having an acryloyl group and / or a methacryloyl group as a curing site, wherein the molecular weight of the second curable compound is at least twice that of the first curable compound. A method of manufacturing a liquid crystal optical element is provided.

A ₁ , A ₂ : each independently an acryloyl group, methacryloyl group R ₁ , R ₂ : each independently an alkylene group having 2 to 6 carbon atoms Z: a 4,4′-biphenylene group n which is a divalent mesogen structure part, m: each independently an integer of 1 to 4

  In the present invention, the uncured curable compound contains two kinds of curable compounds having different molecular weights by 2 times or more, so that the curing process and the molecular weight between crosslinking points of the cured resin can be changed. Alternatively, the crystallinity of the resin can be controlled. As a result, the present inventors have found that a liquid crystal optical element capable of producing a high contrast even at a low driving voltage can be obtained because the curability of the curing process can be improved and the elastic modulus of the cured resin can be adjusted.

  Furthermore, when an uncured curable compound contains the curable compound of Formula (1), compatibility with the liquid crystal when uncured can be improved. In addition, by introducing an oxyalkylene structure with high molecular mobility between the mesogenic structure and the curing site, the molecular mobility of the curing site in the curing process is improved, so that an electric field can be applied even in a short curing reaction. It has been found that a liquid crystal optical element having a stable state when not applied, high reliability, and high contrast can be obtained.

The curing site (A ₁ , A ₂ ) of the formula (1) may be any of the above functional groups that can be photocured and thermally cured together with a curing catalyst. In particular, the temperature during curing can be controlled. To acryloyl group and methacryloyl group suitable for photocuring.

About carbon number of R < ₁ > and R < ₂ > of the oxyalkylene part of Formula (1), 2-6 are preferable from the mobility, and also a C2-ethylene group and a C3-propylene group are preferable.

  As the mesogen structure part (Z) of 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, and alkoxycarbonyl groups. Preferred Z is a biphenylene group in which two 1,4-phenylene groups are linked (hereinafter referred to as 4,4′-biphenylene group), a terphenylene group in which three 1,4-phenylene groups are linked, and 1 to 4 of these hydrogen atoms. It is a divalent organic group substituted by an alkyl group having 1 to 2 carbon atoms, a fluorine atom, a chlorine atom or a carboxyl group. Most preferred Z is a 4,4′-biphenylene group having no substituent.

  If n and m in the formula (1) are too large, the compatibility with the liquid crystal is lowered. Therefore, each is independently 1 to 10, and 1 to 4 is more preferable in consideration of element characteristics after curing.

  In order to adjust the compatibility with the uncured liquid crystal and the elastic modulus of the cured resin, the uncured curable compound does not contain the curable compound containing a mesogen structure in the molecule Are preferably contained together. This is because the mesogen structure part improves the compatibility with the liquid crystal when it is uncured, but increases the elastic modulus of the cured resin more than necessary.

  The two uncured curable compounds to be contained are phase-separated with each other within the resin formed by curing when the two uncured curable compounds can be bonded to each other, thereby increasing the haze at the time of transmission or reflection. It is preferable without any problem.

  In order to increase the molecular weight between crosslinking points to improve the curability at the time of curing and to lower the elastic modulus of the resin after curing, it is necessary to use a curable compound having a relatively high molecular weight as the uncured curable compound. preferable. Specifically, a curable compound having a molecular weight of 1000 or more is preferable.

  A mixture of liquid crystal and an uncured curable compound may contain a curing catalyst. In the case of photocuring, a photopolymerization initiator generally used for photocuring resins such as benzoin ether, acetophenone, and phosphine oxide. Can be used. In the case of thermosetting, a curing catalyst such as peroxide, thiol, amine, or acid anhydride can be used depending on the type of curing site, and if necessary, curing aids such as amines can also be used. Can be used.

  The content of the curing catalyst is preferably 20 wt% or less of the uncured curable compound to be contained, and more preferably 1 to 10 wt% when a high molecular weight or high specific resistance of the cured product after curing is required.

  In addition, a chiral agent can be added to a mixture of liquid crystal and an uncured curable compound in order to improve the contrast of the device when an electric field is applied / not applied, and the helical pitch induced thereby is too small. If the driving voltage rises and is too large, sufficient contrast cannot be obtained. Therefore, the driving voltage is preferably 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. A mixture of liquid crystal and an uncured curable compound may exhibit a liquid crystal phase when sandwiched between substrates with electrodes. The mixture of liquid crystal and uncured curable compound may exhibit a liquid crystal phase when cured.

Giving a function to orient the liquid crystal on the electrode surface by directly polishing the electrode surface of the substrate with the electrode that sandwiches the mixture of liquid crystal and uncured curable compound, or by rubbing it with a resin thin film. It is also possible to reduce unevenness when sandwiching the mixture of the liquid crystal and the uncured curable compound.
Further, the combination of the alignment directions of the pair of alignment-treated substrates may be either parallel or orthogonal, and the angle may be set so as to minimize the unevenness when the mixture is sandwiched.

The electrode gap can be held by a spacer or the like, and is preferably 4 to 50 μm, more preferably 5 to 30 μm. If the electrode gap is too small, the contrast ratio decreases, and if it is too large, the drive voltage increases.
The substrate that supports the electrodes may be a glass substrate or a resin substrate, or a combination of a glass substrate and a resin substrate. Alternatively, one may be a reflective electrode made of aluminum or a dielectric multilayer film.

  In the case of a film substrate, a substrate with electrodes to be continuously supplied is sandwiched between two rubber rolls, and a mixture of a liquid crystal containing a spacer and dispersed therein and an uncured curable compound is interposed between the substrates, and then continuously inserted. Can be cured with high productivity.

  In the case of a glass substrate, a small amount of spacers are scattered on the electrode surface, and the four sides of the opposed substrate are sealed with a sealing agent such as epoxy resin, and one of the cutouts of the seals provided at two or more locations is liquid crystal A liquid crystal optical element can be obtained by immersing in a mixture of curable compound and uncured curable compound and sucking from the other to fill the cell with the mixture and cure. Also, a normal vacuum injection method can be used. Examples will be described below.

Example 1
94.6 parts of cyano nematic liquid crystal (BL-009 manufactured by Merck & Co.), 2.4 parts of chiral agent (mixture of S-811 manufactured by Merck & C15 manufactured by Merck & Co., weight ratio of 1: 1), and a molecular weight of 382. A mixture (mixture A) of 2.5 parts of the curable compound (4), 0.5 part of urethane acrylate oligomer (EB-270 manufactured by UCB) having a molecular weight of 1500 or more and 0.09 part of benzoin isopropyl ether was prepared.

  A pair of substrates obtained by rubbing this mixture A on a polyimide thin film formed on a transparent electrode in one direction are opposed so that the rubbing directions are orthogonal to each other, and a width of about 1 mm is provided on four sides through a small amount of resin beads having a diameter of 13 μm. It injected into the liquid crystal cell produced by bonding together with the printed epoxy resin.

While maintaining the liquid crystal cell 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 for 10 minutes, the liquid crystal optical element Obtained.

  The operation of removing the voltage after applying a rectangular wave of 50 Hz and a voltage of 20 Vrms for 10 minutes to this liquid crystal optical element was repeated 10 times. Thereafter, the transmittance was measured with a transmittance measurement system (F value 11.5 of the optical system) using a measurement light source with a center wavelength of 530 nm and a half-value width of about 20 nm. The value of the contrast ratio divided by the transmittance when the value was applied at 20 Vrms 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 formula (4) was used as the uncured curable compound. After applying a voltage to this liquid crystal optical element in the same manner as in Example 1, the transmittance was measured with the same measurement system. As a result, 83% was obtained when no voltage was applied, and this value was divided by the transmittance when 20 Vrms was applied. The ratio value was 11.

(Example 2)
The mixture A prepared in Example 1 was poured into the same liquid crystal cell as in Example 1, and irradiated with ultraviolet rays for 3 minutes in the same manner as in Example 1 while being kept at 25 ° C., to obtain a liquid crystal optical element.

  The operation of removing the voltage was repeated 10 times after applying a rectangular wave of 50 Hz and a voltage of 20 Vrms to the liquid crystal optical element for 10 minutes. Thereafter, the transmittance was measured with a transmittance measurement system (F value 11.5 of the optical system) using a measurement light source with a center wavelength of 530 nm and a half-value width of about 20 nm. The contrast ratio obtained by dividing the value by the transmittance when 20 Vrms was applied was 43.

(Comparative Example 2)
A liquid crystal optical element was obtained in the same manner as in Example 2 except that only the compound of formula (2) was used as the uncured curable compound.
After applying a voltage to this liquid crystal optical element in the same manner as in Example 2, the transmittance was measured with the same measurement system. As a result, 81% with no voltage applied, and this value divided by the transmittance when 20 Vrms was applied. The value of the ratio was 12.

  Since the liquid crystal optical element of the present invention has high curability of the curable compound to be used, a liquid crystal optical element having a high contrast in transmittance and reflectance at the time of application / non-application of an electric field can be produced in a short curing time. So productivity is high.

  In addition, since the molecular weight and elastic modulus between the crosslinking points of the cured resin can be controlled, a liquid crystal optical element that exhibits a high contrast ratio even at a low driving voltage can be obtained, and a light control glass, display, optical shutter, etc. with a limited driving voltage. It is suitable for.

Claims (4)

Production of a liquid crystal optical element in which a mixture of a liquid crystal and an uncured curable compound is sandwiched between a pair of substrates with electrodes at least one of which is transparent, and the curable compound is cured to form a liquid crystal / cured material composite layer In the method
The curable compound is
A first curable compound represented by formula (1);
Including no mesogenic structure and having a acryloyl group and / or a methacryloyl group as a curing site capable of binding to the first curable compound, and a second curable compound,
A method for producing a liquid crystal optical element, wherein the molecular weight of the second curable compound is twice or more that of the first curable compound.
_{A 1 - (OR 1) n} -O-Z-O- (R 2 O) m -A 2 ··· Equation (1)
A ₁ , A ₂ : each independently an acryloyl group, methacryloyl group R ₁ , R ₂ : each independently an alkylene group having 2 to 6 carbon atoms Z: a 4,4′-biphenylene group n which is a divalent mesogen structure part, m: each independently an integer of 1 to 4   The method for producing a liquid crystal optical element according to claim 1, wherein the molecular weight of the second curable compound is 1000 or more.   The method for producing a liquid crystal optical element according to claim 1, wherein the mixture contains a curing catalyst of 20 wt% or less.   The liquid crystal optical element manufactured with the manufacturing method of any one of Claims 1-3.