JPH09208957A - Production of optical isomer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical isomer slight in light scattering, excellent in optically anisotropic characteristics, suitable as an optically compensating film for a liquid crystal display apparatus having high-quality complicated optical anisotropy, by polymerizing and curing a mixture of specific polymerizable liquid crystal compounds in an orientated state of liquid crystal. SOLUTION: This optical isomer is obtained by polymerizing and curing a mixture (A) of polymerizable liquid crystal compounds comprising a a mixture of acrylic acid 6-[(4'-cyanobiphenyl-4-yl)oxy]hexyl ester of formula I (A1 ) and acrylic acid 4'-cyanobiphenyl-4-yl ester of formula II (A2 ) in the ratio of 45-80wt.% of the component A1 in the mixture. The component A contains a chiral liquid crystal in <=10wt.% blending ratio besides the composition A1 and A2 . A photoinitiator in an amount of <=3wt.% based on the component A is used in the polymerization and curing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an optically anisotropic substance by polymerizing and curing a polymerizable liquid crystal compound in a liquid crystal alignment state.

[0002]

2. Description of the Related Art Liquid crystal display devices have the great advantages of thinness, light weight and low power consumption, and are therefore actively used for display devices such as personal computers, word processors and portable electronic notebooks. Many principles of liquid crystal display elements have been proposed, but most of the liquid crystal display elements currently in widespread use use twisted nematic liquid crystals. The display system using such a liquid crystal is roughly classified into a birefringence mode and an optical rotation mode.

The super twisted nematic (STN) system, which is a birefringence mode, has steep electro-optical characteristics.
Since it can be driven by a simple matrix, it is supplied to the market at a relatively low price. However, in such a system, incident light linearly polarized through the polarizing plate becomes elliptically polarized light due to birefringence by the liquid crystal cell, and when it is further viewed through the polarizing plate, the display appears to be colored. is there.

Therefore, in order to return the elliptically polarized light after passing through the liquid crystal cell to a straight line and prevent coloring, an optical anisotropic body as a retardation plate is interposed between the liquid crystal cell and the polarizing plate.
A scheme has been proposed.

As the optically anisotropic body as such a retardation plate, a uniaxially oriented film obtained by uniaxially stretching a polycarbonate film or the like, or a twist using a polymer liquid crystal as described in JP-A-3-87720 is used. A nematic structure having a fixed orientation has already been proposed.

Alternatively, a polymerizable liquid crystal, which is an acrylate liquid crystal having a nematic state, is sandwiched between glass cells that have been subjected to an alignment treatment, and UV curing is performed in the aligned state, and after curing, at least one of the glass cells is peeled off to obtain an optical compensation film. The method of obtaining an optically anisotropic body as
Proceedings of the Annual Meeting of the Liquid Crystal Symposium p216-p219 (199
4).

[0007]

When an optically anisotropic substance is obtained by polymerizing and curing a polymerizable liquid crystal while keeping the liquid crystal in a liquid crystal alignment state, the characteristics of the polymerizable liquid crystal are very important and even after the polymerization. It is necessary that the alignment state before the polymerization is preserved to some extent, that the polymerizable liquid crystal has a liquid crystal state in the range of 10 ° C. to 90 ° C. in order to obtain a uniform alignment cured product, At present, there are very few polymerizable liquid crystals and mixtures thereof that satisfy the required characteristics, such as small light scattering that causes elimination.

The present invention has been made to solve the above problems, and an object thereof is to obtain an optical anisotropic body having a small light scattering and an excellent optical anisotropic property, which is suitable as an optical compensation plate in a liquid crystal display device. And

[0009]

The present invention is a method for producing an optically anisotropic substance by polymerizing and curing a polymerizable liquid crystal compound in a liquid crystal alignment state, wherein the polymerizable liquid crystal compound is represented by the chemical formula (1). Is a mixture of the polymerizable liquid crystal compound represented by the formula (2) and the polymerizable liquid crystal compound represented by the chemical formula (2), and the mixing ratio of the compound represented by the formula (1) in the mixture is 45 to 80% by weight. It is characterized by that.

[0010]

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[0011]

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As the polymerizable liquid crystal used in the present invention, it is preferable to use a liquid crystal that exhibits a liquid crystal state in the region of at least 10 to 90 ° C. A polymerizable liquid crystal mixture that takes a liquid crystal state only in a region of less than 10 ° C. requires a cooling step in production, and the viscosity of the polymerizable liquid crystal tends to increase in a low temperature region, so that a uniform alignment state is obtained. Is often difficult. On the other hand, in the case of a polymerizable liquid crystal that exhibits a liquid crystal phase only in a temperature range higher than 90 ° C., it is necessary to raise the temperature to higher than 90 ° C. in order to form a liquid crystal phase, and thermal polymerization proceeds while maintaining this temperature. In many cases, it is difficult to control the orientation. The temperature range is 1
It is more preferable that the temperature is 5 to 70 ° C.

As the polymerizable liquid crystal used in the present invention, it is preferable to use a polymerizable liquid crystal having a temperature range of 10 ° C. or more in a liquid crystal state in any temperature range where the liquid crystal state is exhibited. This is even more preferably 15 ° C
It has the above temperature range. It is preferable in manufacturing that the temperature range of the liquid crystal state is as wide as possible. The phase transition behavior of the liquid crystal may be different in the temperature rising process and the temperature lowering process, but the liquid crystal phase may be expressed in the above temperature range in either process.

Alternatively, the polymerizable liquid crystal used in the present invention is preferably in an isotropic state in a temperature range higher than the liquid crystal state.

Further, as the polymerization and curing method of the present invention,
Light curing is preferable. Although it is not impossible even by thermal polymerization, the polymerizable liquid crystal needs to be in a liquid crystal state at the polymerization temperature, and the film forming conditions are limited.

The liquid crystal state is not particularly limited, but is preferably a nematic state or a chiral nematic state. These are often superior to other liquid crystal states in terms of easy controllability of alignment. When it is in a crystalline state or an isotropic state before photo-curing, it is difficult to obtain a sufficiently aligned state as an optical compensator used as a liquid crystal display device after curing. Also, use a curable liquid crystal that has a good alignment state before photo-curing, but the alignment is largely disturbed after curing, and cannot retain the optical anisotropy necessary as an optical compensator for liquid crystal display devices. I can't.

To obtain the chiral nematic state,
It can also be obtained by mixing a chiral liquid crystal with a polymerizable liquid crystal having a nematic state. That is, the polymerizable liquid crystal compound contains a mixture of the polymerizable liquid crystal compound represented by the chemical formula (1) and the polymerizable liquid crystal compound represented by the chemical formula (2) as a main component and a chiral liquid crystal as a subcomponent. Use the mixture. In the main component, the mixing ratio of the compound represented by the chemical formula (1) is 45 to 80% by weight. The mixing ratio of the subcomponents to the main component is 10% by weight or less. If the mixing ratio of the chiral liquid crystal is 10% by weight or less with respect to the nematic liquid crystal, the chiral liquid crystal does not necessarily have to be polymerizable.

As the alignment state of the polymerizable liquid crystal mixture, homogeneous alignment, twisted alignment, homeotropic alignment, tilted alignment and a composite of these are considered. By selecting an appropriate polymerizable liquid crystal mixture, these alignment states are almost fixed after photocuring.

A photoinitiator is preferably added to the polymerizable liquid crystal mixture. When the photoinitiator is added, it may affect the orientation of the liquid crystal, the phase transition temperature and the like, so that it is preferably 3% by weight or less with respect to the polymerizable liquid crystal. It should be noted that since the reaction efficiency becomes poor even if the amount of the photoinitiator is too small, the lower limit of the amount of the photoinitiator is preferably 0.01% by weight or more, and more preferably 0.05% by weight or more.

As the photoinitiator, it is preferable to use a photoinitiator that does not change as much as possible as compared with the case where the orientation of the liquid crystal is not added. The photoinitiator may be any one as long as it can efficiently react at the light wavelength used for curing, and known ones can be used as long as the above conditions are satisfied.

As a method of curing the polymerizable liquid crystal mixture, a method of injecting the polymerizable liquid crystal mixture into a glass cell for liquid crystal display, which is already known as a means for aligning liquid crystals, and setting it and then curing, is preferable. Not limited to. Of course, it may be a film cell. After curing, heat treatment may be performed if necessary. Further, as a form to be used, it may be used as it is, or only one substrate may be peeled off and used.

The optical characteristics of the obtained optical anisotropic body are as follows:
The haze value is preferably 1.5% or less and the transmittance is 80% or more, more preferably 1.0% or less and the transmittance is 85% or more. It is preferable that the transmittance satisfies these in the visible light region. If the haze value is more than this value, the polarizing performance is affected, and if the transmittance is low, it is unacceptable in terms of brightness loss when used in a liquid crystal display device.

In Examples and Comparative Examples described later, the evaluation method of the optical characteristics was performed as follows. (1) Retardation was evaluated with a trade name “M-150”, which is a multi-wavelength birefringence measuring device manufactured by JASCO Corporation. At that time, the measurement wavelength was 590 nm. (2) The transmittance is
Product name "U-3", which is a spectrophotometer manufactured by Hitachi, Ltd.
It was evaluated using "500". At that time, the measurement wavelength is 550
nm. (3) The haze value was evaluated using "COH-300A", a trade name of Nippon Denshoku Industries Co., Ltd.

[0024]

Example 1 A polymerizable liquid crystal compound represented by the chemical formula (1) was synthesized by the following method. First, 17 g of potassium hydroxide was dissolved in 400 ml of methanol. To this solution, 50 g of 4-hydroxy-4'-cyanobiphenyl and 47 g of 6-bromo-1-hexanol were added. After heating under reflux for 13 hours, the mixture was poured into ice water and extracted with ethyl acetate. This extract was concentrated under reduced pressure using an evaporator. After that, column chromatography treatment was performed. This column treatment was performed using silica gel as the carrier and hexane / tetrahydrofuran as the developing solvent.
Thus 4- (6-hydroxyhexyloxy) -4 '
29 g of cyanobiphenyl were obtained.

29 g of this 4- (6-hydroxyhexyloxy) -4'-cyanobiphenyl and 14 g of triethylamine were dissolved in 300 ml of tetrahydrofuran. This solution is cooled to 5 ° C. and acrylic acid chloride 1 is added.
1 g of the solution was added dropwise over 20 minutes, reacted for 1 hour, poured into ice water and extracted with ethyl acetate. The solid obtained by concentrating the extract was recrystallized from a mixed solvent of hexane and tetrahydrofuran to obtain 20 g of a polymerizable liquid crystal compound represented by the chemical formula (1).

The polymerizable liquid crystal compound represented by the chemical formula (2) was synthesized by the following method. First, 4-hydroxy-4'-
40 g of cyanobiphenyl and 53 g of triethylamine,
It was dissolved in 400 ml of tetrahydrofuran. The solution was cooled to 5 ° C. 25g of acrylic acid chloride
200 ml of tetrahydrofuran solution of was added dropwise over 15 minutes and then reacted for 1 hour. After completion of the reaction, 1000 ml of ethyl acetate was added for extraction, the organic layer was washed with a dilute aqueous solution of sodium hydrogen carbonate, and then further washed with water. Then, the organic layer was dried using anhydrous sodium sulfate, and the solvent was further distilled off to obtain 45 g of a crude product. This is subjected to column chromatography (silica gel as a carrier, ethyl acetate: n-hexane = 1: 5 as a developing solvent), and recrystallized from methanol to obtain 20 g of a polymerizable liquid crystal compound represented by the chemical formula (2). It was

The polymerizable liquid crystal compounds having the chemical formulas (1) and (2) thus obtained were mixed at a ratio of 50:50 (% by weight). The polymerizable liquid crystal mixture thus obtained,
In the temperature rising process, it was a substance that transitioned from a crystal to a nematic phase at 57 ° C, and from a nematic phase to an isotropic phase at 80 ° C. On the contrary, in the temperature lowering process, it was a substance that was transformed from an isotropic phase to a nematic phase at 80 ° C. and was transformed from a nematic phase to a crystalline phase at 30 ° C.

A photoinitiator was added to the polymerizable liquid crystal mixture in a ratio of 0.5% by weight based on the polymerizable liquid crystal component. As the photoinitiator, 2,2-, which is commercially available under the trade name “Irgacure 651” manufactured by Ciba Geigy, Inc.
Dimethoxy-2-phenylacetophenone was used.

The polymerizable liquid crystal mixture containing the photoinitiator was poured into a glass cell having an antiparallel alignment treatment with a cell gap of 4 μm at a temperature at which it transforms to an isotropic phase (isotropic temperature) and cooled to 57 ° C. Then, it was uniaxially oriented. Then 57
Keeping the temperature at ℃, UV light intensity of 8mW / square cm 3
It was irradiated for minutes to polymerize and cure.

The uniaxially oriented polymerizable liquid crystal mixture before ultraviolet curing had a Δnd of 579.6 ° C. of 859.6 nm.
After the UV curing, Δn · d was 491.
The haze value was 9 nm, the light transmittance was 90%. The orientation state after curing was uniform. That is, an optical anisotropic body having a small light scattering and excellent optical anisotropic properties could be obtained.

[0031]

Example 2 In the same manner as in Example 1, the polymerizable liquid crystal compounds of the chemical formulas (1) and (2) were synthesized. The polymerizable liquid crystal compounds represented by the chemical formulas (1) and (2) are mixed at 80: 2.
It mixed in the ratio of 0 (weight%). The polymerizable liquid crystal mixture thus obtained was a substance which, in the temperature rising process, transitioned from a crystal to a nematic phase at 55 ° C., and from a nematic phase to an isotropic phase at 62 ° C. On the contrary, in the temperature decreasing process,
It was a substance that transitioned from an isotropic phase to a nematic phase at 61 ° C. and from a nematic phase to a crystalline phase at 32 ° C.

A photoinitiator was added to the polymerizable liquid crystal mixture at a ratio of 0.5% by weight based on the polymerizable liquid crystal component. As the photoinitiator, 2,2-, which is commercially available under the trade name “Irgacure 651” manufactured by Ciba Geigy, Inc.
Dimethoxy-2-phenylacetophenone was used.

The polymerizable liquid crystal mixture containing the photoinitiator was injected into an antiparallel alignment-treated glass cell having a cell gap of 4 μm at an isotropic temperature, cooled to 50 ° C., and then uniaxially aligned. Next, while maintaining the temperature at 50 ° C., ultraviolet rays were irradiated at a light intensity of 8 mW / square cm for 3 minutes to polymerize and cure.

The uniaxially oriented polymerizable liquid crystal mixture before UV curing had a Δnd of 669.8 nm at 50 ° C.
After UV curing, Δn · d was 650 at 25 ° C.
The thickness was 3 nm, the haze value was 0.3%, and the light transmittance was 89%. The orientation state after curing was uniform. That is, an optical anisotropic body having a small light scattering and excellent optical anisotropic properties could be obtained.

[0035]

Example 3 In the same manner as in Example 1, the polymerizable liquid crystal compounds of the chemical formulas (1) and (2) were synthesized. The polymerizable liquid crystal compounds represented by the chemical formulas (1) and (2) and the chiral liquid crystal were mixed at a ratio of 49.8: 49.8: 0.4 (% by weight). Here, as the chiral liquid crystal, a product name “S811” manufactured by Merck Ltd. was used. The polymerizable liquid crystal mixture thus obtained was a substance that, during the temperature rising process, transitioned from a crystal to a nematic phase at 57 ° C., and from a nematic phase to an isotropic phase at 80 ° C. On the contrary, in the temperature decreasing process, 80
It was a substance that transitioned from an isotropic phase to a nematic phase at ℃, and from a nematic phase to a crystalline phase at 29 ℃.

A photoinitiator was added to the polymerizable liquid crystal mixture in a ratio of 0.5% by weight based on the polymerizable liquid crystal component. As the photoinitiator, 2,2-, which is commercially available under the trade name “Irgacure 651” manufactured by Ciba Geigy, Inc.
Dimethoxy-2-phenylacetophenone was used.

The polymerizable liquid crystal mixture containing the photoinitiator was injected into an antiparallel alignment-treated glass cell having a cell gap of 8 μm at an isotropic temperature, cooled to 57 ° C., and then allowed to have a twist structure of 180 °. It was Next, while maintaining the temperature at 57 ° C., ultraviolet rays were irradiated at a light intensity of 8 mW / square cm for 3 minutes to polymerize and cure.

It retained the twisted structure even after being cured by ultraviolet rays, and had a haze value of 0.7% and a light transmittance of 89%. The orientation state after curing was uniform. That is, an optical anisotropic body having a small light scattering and excellent optical anisotropic properties could be obtained.

[0039]

Example 4 In the same manner as in Example 1, the polymerizable liquid crystal compounds represented by the chemical formulas (1) and (2) were mixed at a ratio of 50:50 (% by weight). Further, the polymerizable liquid crystal mixture added with the photoinitiator was injected into the antiparallel alignment cell with the transparent electrode in the isotropic state in the same manner as in Example 1, 57
After cooling to 0 ° C., UV curing was performed in the same manner as in Example 1 while applying 10 V at 60 Hz. The obtained cured product is Δ
From the angle dependence measurement of n · d, it was confirmed that the orientation was tilted. The haze value was 0.4% and the light transmittance was 90%. That is, an optical anisotropic body having a small light scattering and excellent optical anisotropic properties could be obtained.

[0040]

Comparative Example 1 In the same manner as in Example 1, the polymerizable liquid crystal compounds represented by the chemical formulas (1) and (2) were synthesized. The polymerizable liquid crystal compounds represented by the chemical formulas (1) and (2) were mixed at a ratio of 40:60 (% by weight). The polymerizable liquid crystal mixture thus obtained was a substance that, during the temperature rising process, transitioned from a crystal to a nematic phase at 70 ° C. and from a nematic phase to an isotropic phase at 88 ° C. On the contrary, in the temperature-decreasing process, it was a substance that transitioned from the isotropic phase to the nematic phase at 88 ° C and from the nematic phase to the crystalline phase at 47 ° C.

A photoinitiator was added to the polymerizable liquid crystal mixture in a ratio of 0.5% by weight based on the polymerizable liquid crystal component. As the photoinitiator, 2,2-, which is commercially available under the trade name “Irgacure 651” manufactured by Ciba Geigy, Inc.
Dimethoxy-2-phenylacetophenone was used.

The polymerizable liquid crystal mixture containing the photoinitiator was poured into an antiparallel alignment-treated glass cell having a cell gap of 4 μm at an isotropic temperature, cooled to 67 ° C., and then uniaxially aligned. Next, while maintaining the temperature at 67 ° C., ultraviolet rays were irradiated at a light intensity of 8 mW / square cm for 3 minutes to polymerize and cure.

The uniaxially oriented polymerizable liquid crystal mixture before ultraviolet curing had a Δn · d of 871.2 nm at 67 ° C.
However, after UV curing, Δn · d was 39.7 at 25 ° C.
was nm. As described above, Δn · d was greatly reduced after ultraviolet curing, and sufficient anisotropy could not be secured.

[0044]

Comparative Example 2 In the same manner as in Example 1, a polymerizable liquid crystal compound represented by the chemical formula (1) was synthesized. The polymerizable liquid crystal compound of the chemical formula (1) was a substance that, in the temperature rising process, transitioned from a crystal to a nematic phase at 55 ° C., and from a nematic phase to an isotropic phase at 67 ° C. On the contrary, in the temperature decreasing process, 5
It was a substance that transitioned from an isotropic phase to a nematic phase at 1 ° C. and a transition from a nematic phase to a crystalline phase at 43 ° C.

A photoinitiator was added to the polymerizable liquid crystal compound at a ratio of 0.5% by weight based on the polymerizable liquid crystal component. As the photoinitiator, 2,2-, which is commercially available under the trade name “Irgacure 651” manufactured by Ciba Geigy, Inc.
Dimethoxy-2-phenylacetophenone was used.

The polymerizable liquid crystal compound to which the photoinitiator was added was injected into an antiparallel alignment-treated glass cell having a cell gap of 4 μm at an isotropic temperature, and after cooling to 47 ° C., uniaxial alignment was attempted. It could not be oriented uniformly. Further, in that state, ultraviolet curing was performed as in Example 1, but uniform orientation curing could not be performed.

[0047]

INDUSTRIAL APPLICABILITY The present invention relates to an optical anisotropic body obtained by polymerizing and curing a polymerizable liquid crystal mixture having a specified chemical structure and a mixing ratio in an aligned state. It is possible to obtain an optical anisotropic body having small optical scattering and excellent optical anisotropic characteristics, which is suitable as an optical compensation film for a liquid crystal display device having complicated optical anisotropy.

Claims (3)

[Claims] 1. A method for producing an optically anisotropic substance by polymerizing and curing a polymerizable liquid crystal compound in a liquid crystal alignment state, wherein the polymerizable liquid crystal compound is a polymerizable liquid crystal compound represented by the chemical formula (1) and a chemical formula: (2) An optically anisotropic substance which is a mixture comprising a polymerizable liquid crystal compound represented by (2) and in which the mixture ratio of the compound represented by the chemical formula (1) is 45 to 80% by weight. Body manufacturing method. Embedded image Embedded image 2. A method for producing an optically anisotropic substance by polymerizing and curing a polymerizable liquid crystal compound in a liquid crystal alignment state, wherein the polymerizable liquid crystal compound is a polymerizable liquid crystal compound represented by the chemical formula (1) and a chemical formula: A mixture containing a polymerizable liquid crystal compound represented by (2) as a main component and a chiral liquid crystal as an auxiliary component, and the mixing ratio of the compound represented by the chemical formula (1) in the main component is 45. ~ 80% by weight
And the mixing ratio of the accessory component to the main component is 10
A method for producing an optically anisotropic body, characterized in that the content is at most% by weight. 3. A photoinitiator is added at a ratio of 3% by weight or less with respect to the polymerizable liquid crystal component when the polymerizable liquid crystal compound is polymerized and cured in a liquid crystal alignment state. 3. The method for producing an optically anisotropic body according to any one of 2 to 3.