JPH11100575A - Liquid crystal composition and high-molecular liquid crystal prepared by polymerizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photopolymerizable liq. crystal compsn. having an excel lent durability and a high refractive index anisotropy by incorporating an acrylic acid deriv. having a specific chemical structure into the same and to obtain a high-molecular liq. crystal by polymerizing the same. SOLUTION: This liq. crystal compsn. is prepd. by mixing a compd. of formula I (wherein X is 2-7C linear alkylene; and Ph is 1,4-phenylene) with a compd. of formula II or by mixing at least one compd. selected from among compds. of formulas I and II with another liq. crystal compd. The content of a compd. of formula I and/or a compd. of formula II in the compsn. is 30-99.9 wt.%. A component exhibiting liq. crystallinity at low temps., a low-viscosity component for low temp use, a component for adjusting refractive index anisotropy, a component for imparting cholesteric properties, a component for imparting crosslinkability. etc., are used suitably as another liq. crystal compd. according to required performances. The compsn. is polymerized by the irradiation with ultraviolet or visible rays in the presence of a photopolymn. initiator to give a high-molecular liq. crystal having a refractive index anisotropy of 0.1 or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal composition containing an acrylic acid derivative compound and a polymer liquid crystal obtained by polymerizing the composition.

[0002]

2. Description of the Related Art A photopolymerizable liquid crystal monomer obtained by adding a photopolymerizable functional group to a liquid crystal monomer has both properties as a monomer and a liquid crystal. Therefore, when light is irradiated in a state where the photopolymerizable liquid crystal monomer is oriented, it is polymerized while maintaining the orientation, and a polymer in which the orientation is fixed is obtained. The polymer liquid crystal thus obtained has an optical anisotropy based on the refractive index anisotropy of the liquid crystalline skeleton, and can provide special characteristics by controlling the liquid crystal alignment state. Applications to optical heads and the like are expected.

An optical head device converges light from a light source onto an optical disk to write information on the optical disk,
This is a device for reading information on an optical disk by receiving light reflected from the optical disk by a light receiving element, and an optical head used for the device functions as a beam splitter.

Conventionally, as an optical head, for example, a rectangular grating (relief type) formed on glass or plastic by forming an isotropic diffraction grating by dry etching or injection molding, or a crystal exhibiting refractive index anisotropy. It is known that an anisotropic diffraction grating is formed on the surface and has polarization selectivity in combination with a quarter-wave plate.

However, in the isotropic diffraction grating, the outgoing use efficiency is about 50%, and the return use efficiency is about 20%. There is a problem that cannot be solved.

On the other hand, in a method in which a flat plate of a crystal having a refractive index anisotropy such as LiNbO ₃ is used, an anisotropic diffraction grating is formed on the surface to provide polarization selectivity, and a high reciprocal efficiency is utilized, Crystals exhibiting anisotropy are expensive, and are difficult to apply to the consumer field. In addition, when the lattice is formed by the normal proton exchange method, there is also a problem that it is difficult to form a fine-pitch lattice because the protons in the proton exchange solution easily diffuse into the LiNbO ₃ substrate.

When a photopolymerizable liquid crystal monomer is used,
After the liquid crystal alignment state is controlled, high reciprocation efficiency equivalent to that of a crystal exhibiting refractive index anisotropy can be obtained by using a polymer liquid crystal. For example, there is a method of filling a polymer liquid crystal in a lattice to increase the efficiency. In a liquid crystal cell in which one side of the substrate surface is finely processed into a rectangular lattice shape, usually, the long axis of the liquid crystal monomer is parallel to the lattice. After orienting the direction, polymerization is performed to obtain a polymer liquid crystal. At this time, a high reciprocating efficiency can be obtained by optimizing the grating depth such that the ordinary light refractive index of the polymer liquid crystal matches the refractive index of the grating substrate.

Theoretically, when the lattice depth is d, the refractive index anisotropy of the polymer liquid crystal is △ n, and the wavelength is λ, λ / 2 = △
When n · d is satisfied, the reciprocation efficiency becomes maximum, and the efficiency of ± 1st-order diffracted light is about 40%, and a high light utilization efficiency of about 80% in total is obtained.

As another example, there is a method of filling a polymer liquid crystal into a liquid crystal cell having a transparent electrode patterned in a stripe shape to improve the efficiency. After orienting the long axis direction of the liquid crystal monomer in the substrate plane in the direction perpendicular to the stripe direction, a voltage is applied to orient the liquid crystal monomer sandwiched between the upper and lower transparent electrodes in the direction perpendicular to the substrate surface. . In this way, the alignment state is periodically controlled between the position where the electrode is and the position where the electrode is not, and then polymerized to obtain a polymer liquid crystal. Also in this case, when λ / 2 = △ nd is satisfied, the maximum reciprocating efficiency is obtained.

Since the liquid crystal polymer is inexpensive, it can be applied to the consumer field and is expected as an excellent optical head. The characteristics of the optical head include high durability and high reciprocating efficiency at a fine pitch (10 μm or less).

As the photopolymerizable liquid crystal monomer, for example, a compound represented by the formula (3), (4) or (5)
In the formulas 3, 4 and 5, Ph is a 1,4-phenylene group, and Cy is a trans-1,4-cyclohexylene group. ) Is known (Takatsu, Hasebe, 106th Photopolymer Meeting Regular Meeting Material, III-1).

[0012]

CH ₂ ＣＨCHCOO-Ph-C≡C-Ph- (CH ₂ ) ₅ H Formula 3 CH ₂ ＣＨCHCOO-Cy-Cy- (CH ₂ ) ₄ H Formula 4 CH ₂ ＣＨCHCOO-Ph-Cy — (CH ₂ ) ₃ H Formula 5

However, the compound represented by the formula 3 (hereinafter, also referred to as compound 3) has a problem that it has no durability since it has a tran group in the molecule. Also,
Compounds 4 and 5 have a problem that the refractive index anisotropy of the monomer alone is as small as 0.1 or less, and a liquid crystal composition containing the same cannot have a large refractive index anisotropy. Further, since the refractive index anisotropy of the polymer liquid crystal after the polymerization is reduced to about の of that before the polymerization, when a compound having a low refractive index anisotropy is used as a main component of the liquid crystal composition, There is a problem that it is difficult to make fine pitch while maintaining high reciprocating efficiency.

That is, when the polymer liquid crystal is filled in the lattice, if the wavelength is 0.65 μm and the refractive index anisotropy is less than 0.1, the lattice depth must be 3 μm or more.
It is very difficult to finely process a lattice having a large aspect ratio. In addition, when the alignment is controlled by an electric field using a patterned transparent electrode, the alignment of the liquid crystal in a portion where there is no electrode pattern is disturbed by the influence of the leakage electric field. Therefore, in order to achieve a fine pitch, the polymer liquid crystal had to have a refractive index anisotropy of 0.1 or more.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal composition having excellent durability and a large refractive index anisotropy and a polymer liquid crystal obtained by polymerizing the composition.

[0016]

The present invention provides a liquid crystal composition containing a compound represented by the following formula 1 and / or a compound represented by the following formula 2. However, in Formulas 1 and 2, X is an alkylene group, and Ph is a 1,4-phenylene group. In Formulas 7 to 10, Ph is a 1,4-phenylene group.

[0017]

Embedded image CH ₂ ＣＨCHCOO-XO-Ph-Ph-CN Formula 1 CH ₂ ＣＨCHCOO-Ph-Ph-CN Formula 2

Both Compound 1 and Compound 2 are durable liquid crystal monomers having no trans group in the molecule. In addition, the refractive index anisotropy of the monomer alone is 0.2 or more, and the photopolymerizable liquid crystal composition using these as a main component has a large refractive index anisotropy. Those having a rate anisotropy of 0.1 or more can be obtained.

In compound 1, if the number of carbon atoms in X is too large, the temperature at which liquid crystallinity is exhibited becomes too low.
It is preferably an alkylene group of from 7 to 7. In order to further broaden the temperature range exhibiting liquid crystallinity, X is desirably a linear alkylene group.

Compound 1 can be synthesized, for example, by the following method. The ω-bromoalkanol is reacted with 4-hydroxy-4′-cyanobiphenyl in the presence of an alkali to obtain 4- (ω-hydroxyalkoxy) -4′-cyanobiphenyl. This is reacted with acryloyl chloride in the presence of a base such as trimethylamine to give compound 1. Compound 2 is a known compound obtained by reacting hydroxycyanobiphenyl with acryloyl chloride. Table 1 shows the physical properties of the compound. Where T
_m represents a melting point (unit: ° C), and _Tc represents a nematic-isotropic phase transition temperature (unit: ° C).

[0021]

[Table 1]

Among F, A, B, C, D, E and F, only F is an enantiotropic liquid crystal, and F has a very high melting point of 103 ° C. That is, these liquid crystals do not themselves exhibit stable nematic liquid crystal properties at or near room temperature. However, the present inventor has found that this can be achieved only by mixing into a liquid crystal composition.

When used as a liquid crystal composition, compound 1
And a compound 2 or a mixture of at least one compound selected from the compounds 1 and 2 with another liquid crystal compound to obtain a liquid crystal composition having desired characteristics. The ratio of the compound 1 and / or the compound 2 in the liquid crystal composition is 30 to 99.9% by weight in total, particularly 50 to 9% by weight.
0% by weight is preferred.

The liquid crystal composition may contain another liquid crystal compound. Other liquid crystal compounds vary depending on the application, required performance, etc., but are components that exhibit liquid crystallinity at low temperatures, low-viscosity components for low temperatures, components that adjust refractive index anisotropy, and components that adjust dielectric anisotropy. A component that imparts cholesteric properties, a component that imparts crosslinkability, and various other additives may be appropriately used.

The liquid crystal composition may contain other compounds, and the proportion of the other compounds in the liquid crystal composition is preferably less than 50% by weight. The liquid crystal composition of the present invention,
It is preferable that two or more kinds of compound 1 and compound 2 are included.

In the case of photopolymerization, the reaction can be efficiently performed by using a photopolymerization initiator. Photopolymerization initiator is not particularly limited, acetophenones, benzophenones,
Benzoins, benzyls, Michler's ketones, benzoin alkyl ethers, benzyldimethyl ketals, thioxanthones, and the like can be preferably used. If necessary, two or more photopolymerization initiators may be mixed and used. The photopolymerization initiator is used in an amount of 0.1 to 1 based on the liquid crystal composition.
It is preferably contained at 0% by weight, particularly 0.5 to 2% by weight.

Using the composition thus prepared,
Photopolymerize to form a polymer liquid crystal. Radiation used for polymerization includes ultraviolet light or visible light. At this time, glass, plastic, or the like is used as a support.
An orientation treatment is performed on the support surface.

In the orientation treatment, the surface of the support may be directly rubbed with natural fibers such as cotton and wool, and synthetic fibers such as nylon and polyester, or rubbed with polyimide or polyamide or the like and rubbed with the above fibers or the like. May be. A spacer such as a glass bead is arranged, and the composition is injected and filled into a support which is controlled to a desired gap.

[0029] may be the ambient temperature in order to maintain the liquid crystal composition in a liquid crystal state in the range of T _m through T _c, but the refractive index anisotropy at a temperature close to T _c is extremely small, the upper limit of the ambient temperature Is preferably (T _c -10) ° C. or lower.

The polymer liquid crystal prepared according to the present invention is:
It may be used while being sandwiched between supports, or may be used after being separated from the support. The polymer liquid crystal of the present invention has a refractive index anisotropy of 0.1 or more.

The polymer liquid crystal thus produced is suitable for an optical element. Specifically, it can be used as a retardation film. In addition, a polymer liquid crystal whose alignment is controlled in a lattice shape and 1
By combining with a 波長 wavelength plate, or combining a 格子 wavelength plate with a polymer liquid crystal filled in a lattice recess, a polarization hologram beam splitter with high reciprocation efficiency having polarization dependence can be manufactured. An optical head having high light use efficiency can be manufactured by using the optical head. Further, a polarizing element having excellent temperature characteristics can be manufactured by the structure without the quarter wavelength plate.

[0032]

【Example】

Example 1 (Synthesis of Compound 1) 50 g of Compound 6 and 49.1 g of 4-hydroxy-4′-cyanobiphenyl were added to 400 ml of a methanol solution of 5.7% by weight of potassium hydroxide, and the mixture was refluxed. After sufficient reaction, water and dichloromethane were added, and the organic layer was extracted. Next, after adding a saturated sodium chloride aqueous solution, the organic layer was extracted and washed with water. After adding anhydrous magnesium sulfate, the mixture was filtered under reduced pressure and the filtrate was extracted. The filtrate was subjected to column chromatography using dichloromethane as a developing solution, and then dichloromethane was distilled off at 30 ° C. to obtain powder crystals. To this was added n-hexane and recrystallized to give compound 7, namely 4- (3-hydroxypropyloxy) -4'-cyanobiphenyl 40.0 g.
I got

Next, 500 ml of dichloromethane, 29.9 g of triethylamine and 40.0 g of the compound 7 were prepared as a mixture.
5 g were added. After sufficiently stirring and reacting, hydrochloric acid and water were added to the reaction solution to extract an organic layer. Next, after adding a saturated sodium chloride aqueous solution, the organic layer was extracted and washed with water. After adding anhydrous magnesium sulfate, filtration under reduced pressure was performed. The filtrate was subjected to column chromatography using dichloromethane as a developing solution, and then dichloromethane was distilled off at 30 ° C. to obtain powder crystals. To this was added n-hexane and recrystallized to obtain 18.0 g of white crystals of the compound of the above B, that is, 4- [3- (propenoyloxy) propyloxy] -4′-cyanobiphenyl (melting point: 70 ° C.). Was.

Using the same synthetic method, the compound of the above C (4- [4- (propenoyloxy) butyloxy]-
4′-cyanobiphenyl), the compound of D (4- [5
-(Propenoyloxy) pentyloxy] -4'-cyanobiphenyl), the compound of E (4- [6- (propenoyloxy) hexyloxy] -4'-cyanobiphenyl), and the compound of A (4 -[2- (propenoyloxy) ethyloxy] -4'-cyanobiphenyl) was obtained.

[0035]

Embedded image Br— (CH ₂ ) ₃ —OH Formula 6 HO— (CH ₂ ) ₃ —O-Ph-Ph-CN Formula 7

Example 2 17% by weight of compound 2 (4-propenoyloxy-4'-cyanobiphenyl), 36% by weight of compound B and 47% by weight of compound D were mixed. This liquid crystal composition has a T _m of 45 ° C. and a T _c of 52
It was a nematic liquid crystal having a temperature of ℃. The refractive index anisotropy was 0.245 at 589 nm at 46 ° C.

Example 3 Compound 2 (24% by weight) Compound D (27% by weight) Compound 8 (4- (4'-n-butylphenylcarbonyloxy) phenyl acrylate)
And 24% by weight of compound 9 and 4- (4'-n-pentylphenylcarbonyloxy) phenyl acrylate)
Each 5% by weight was mixed. This liquid crystal composition has a _Tm of 39.
It was a nematic liquid crystal having a C and a _Tc of 73C. The refractive index anisotropy is 0.2 at 589 nm at 40 ° C.
04.

[0038]

CH ₂ ＣＨCHCOO-Ph-OCO-Ph-C ₄ H ₉ Formula 8 CH ₂ ＣＨCHCOO-Ph-OCO-Ph-C ₅ H ₁₁ Formula 9

[Example 4] Polyimide as an aligning agent was applied by a spin coater, heat-treated, and rubbed in a certain direction with a nylon cloth as a support. Were bonded using an adhesive. At that time, glass beads were mixed in the adhesive, and the gap was adjusted so that the distance between the supports was 10 μm.

A cell prepared by adding 0.5% by weight of the liquid crystal composition of Example 3 to Irgacure 907 (manufactured by Ciba Geigy) as a photopolymerization initiator was injected into the cell thus prepared at 80 ° C. Next, ultraviolet light having a wavelength of 360 nm was irradiated at 40 ° C. to perform photopolymerization. After the polymerization, a film-like polymer was obtained. This polymer was a liquid crystal polymer which was horizontally oriented in the rubbing direction of the substrate and had a refractive index anisotropy of 0.124 at 589 nm. Further, this polymer was transparent in the visible region, and no scattering was observed.

Example 5 Polyimide as an aligning agent was applied on a glass substrate on which a rectangular lattice having a pitch of 6 μm and a depth of 2.9 μm was formed by a spin coater, heat-treated, and then parallelized with a nylon cloth in the lattice direction. The rubbed substrate was subjected to the rubbing process in the direction, and the glass plate substrate subjected to the orientation process in the same manner was bonded using an adhesive so that the orientation-treated surfaces faced each other. At that time, the orientation directions were made parallel.

A cell prepared by adding 0.5% by weight of the liquid crystal composition of Example 3 to Irgacure 907 (manufactured by Ciba Geigy) as a photopolymerization initiator at 80 ° C. was injected into the cell thus prepared. Was filled with the composition. Next, an ultraviolet ray having a wavelength of 360 nm was irradiated at 40 ° C. to perform photopolymerization. A quarter-wave plate was laminated on one side of this cell to produce a polarization hologram beam splitter. Figure 1
Shown in When this element was used for an optical head,
With a 0 nm laser light source, 60% light utilization efficiency was obtained in total of the efficiency of ± 1st order diffracted light.

Example 6 25% by weight of compound 2, 25% by weight of compound B, 25% by weight of compound 8, and 9% by weight of compound 9
Was mixed by 25% by weight. This liquid crystal composition has a _Tm of 3
It was a nematic liquid crystal showing 4 ° C and _Tc of 68 ° C. The refractive index anisotropy is 0.2 at 589 nm at 35 ° C.
00.

Example 7 A cell prepared in the same manner as in Example 4 was prepared by adding 1% by weight of Irgacure 907 (manufactured by Ciba Geigy) as a photopolymerization initiator to the liquid crystal composition of Example 6.
Injected at 0 ° C. Next, ultraviolet light having a wavelength of 360 nm was irradiated at 35 ° C. to perform photopolymerization. After the polymerization, a film-like polymer was obtained. This polymer was a polymer liquid crystal which was horizontally oriented in the rubbing direction of the substrate and had a refractive index anisotropy of 0.120 at 589 nm. This polymer liquid crystal was transparent in the visible region, and no scattering was observed.

[Example 8] IT processed to a pitch of 8 μm
On a glass plate having an O transparent electrode on the surface, polyimide as an aligning agent is applied by a spin coater, heat-treated, and then subjected to a rubbing treatment in a direction perpendicular to the lattice with a nylon cloth, and a glass subjected to the same orientation treatment. The flat plates were bonded using an adhesive such that the alignment treatment surfaces faced each other.
At that time, the grid electrode portions were made to overlap, and the cell gap was set to 3 μm using spacers.

In the liquid crystal composition of Example 6, 1% by weight of Irgacure 907 (manufactured by Ciba Geigy) as a photopolymerization initiator and 5% of compound 10 (4,4'-bis (acryloyloxy) biphenyl) as a crosslinking agent were added. The mixture with the weight% added was prepared, and the mixture was injected into the above-mentioned cell at 70 ° C. Next, while applying a voltage of 5 V _rms at 100 Hz, 35 V _rms is applied.
Photopolymerization by irradiating ultraviolet rays of 360 nm wavelength at ℃
Polymer liquid crystals that were periodically aligned horizontally and polymer liquid crystals that were vertically aligned were formed. A quarter-wave plate was laminated on one side of this cell to produce a polarization hologram beam splitter. This is shown in FIG. When this element was used for an optical head, a light use efficiency of 40% in total of the efficiency of ± 1st-order diffracted light was obtained with a laser light source having a wavelength of 650 nm.

[0047]

Embedded image CH ₂ ＣＨCHCOO-Ph-Ph-OCOCH ＝ CH ₂

[0048]

According to the present invention, a photopolymerizable liquid crystal composition and a polymer liquid crystal having excellent durability and a large value of refractive index anisotropy can be produced. The polymer liquid crystal obtained by photopolymerization can be used for a retardation film or an optical head. The present invention can be applied to various applications within a range that does not impair the effects of the present invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a polymer liquid crystal polarization hologram beam splitter using a grating substrate.

FIG. 2 is a cross-sectional view of a polymer liquid crystal polarization hologram beam splitter using a periodic electrode.

[Explanation of symbols]

 11: Glass plate substrate 12: Alignment film 13: Adhesive 14: Polymer liquid crystal 15: Glass lattice substrate 16: 1/4 wavelength plate 21: Glass plate substrate 22: Transparent electrode 23: Alignment film 24: Adhesive 25: Transparent Electrode 26: Glass plate substrate 27: Horizontally aligned polymer liquid crystal 28: Vertically aligned polymer liquid crystal 29: 1/4 wavelength plate

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiromasa Sato 1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Inside Asahi Glass Co., Ltd.

Claims (9)

[Claims] A liquid crystal composition comprising a compound represented by the following formula 1 and / or a compound represented by the following formula 2. In the formulas 1 and 2, X is an alkylene group, and Ph is 1,4-
It is a phenylene group. CH ₂ ＣＨCHCOO-X-Ph-Ph-CN Formula 1 CH ₂ ＣＨCHCOO-Ph-Ph-CN Formula 2 2. The liquid crystal composition according to claim 1, wherein X is a linear alkylene group having 2 to 7 carbon atoms. 3. The liquid crystal composition according to claim 1, wherein the total amount of the compound represented by Formula 1 and / or the compound represented by Formula 2 is 30 to 99.
3. The liquid crystal composition according to claim 1, wherein the content is 9% by weight. 4. The liquid crystal composition according to claim 1, comprising two or more compounds represented by the formula (1) and a compound represented by the formula (2). 5. A polymer liquid crystal obtained by polymerizing the liquid crystal composition according to claim 1, 2, 3 or 4. 6. The polymer liquid crystal according to claim 5, which is polymerized by irradiation with ultraviolet light or visible light. 7. The method according to claim 5, wherein the refractive index anisotropy is 0.1 or more.
Or a polymer liquid crystal according to 6. 8. An optical element using the polymer liquid crystal according to claim 5, 6, or 7. 9. An optical head using the optical element according to claim 8 as a polarization hologram element.