JP2006348226A - Liquid crystal/polymer composite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal/polymer composite capable of developing a polymer-stabilized blue phase within a wide temperature range, wherein the blue phase achieves a scattering state by electric field application. <P>SOLUTION: The liquid crystal/polymer composite is obtained by polymerizing a liquid crystal composition within a temperature range represented by formula [1]: from T<SB>BP1</SB>to [(T<SB>BP2</SB>-T<SB>BP1</SB>)/2] (wherein T<SB>BP1</SB>and T<SB>BP2</SB>are the lowest and highest temperatures, respectively, at which the liquid crystal composition develops the blue phase), wherein the liquid crystal composition contains a liquid crystal compound, a chiral agent, a monofunctional polymerizable monomer and a polyfunctional polymerizable monomer. The combination of the liquid crystal compound and the chiral agent in the composite develops the blue phase whose light transmittance can be modified by adjusting the voltage applied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal / polymer composite exhibiting a blue phase, wherein the amount of emitted light can be adjusted by adjusting the transmission and scattering of incident light by applying a voltage. About the body.

The optical information processing technology is a promising information processing technology that can utilize the characteristics of light, such as high-speed signal transmission, spatial parallelism of transmission and processing, and a wide frequency band. For practical application of this technology, an element (light modulation element) that controls light intensity, polarization state, etc. at high speed and high accuracy is indispensable, and a small and inexpensive light modulation element using liquid crystal has been attracting attention.
On the other hand, it is known that when the temperature of a chiral nematic liquid crystal is raised, a blue phase, which is one of the liquid crystal phases, appears immediately before the transition from the nematic phase to the isotropic phase. The blue phase is considered to be a state where a double-twisted structure in which liquid crystals are twisted and arranged and a linear defect in a state close to an isotropic phase coexist, and a body-centered cubic lattice with a lattice constant on the order of several hundred nm. It is known to form a three-dimensional periodic structure such as (blue phase I) or simple cubic lattice (blue phase II).

Therefore, the liquid crystal in the blue phase has both the property as a cubic crystal and the property as a chiral nematic liquid crystal, and exhibits optical rotation with respect to visible light and Bragg reflection is observed. Further, by changing the external field environment such as an electric field and a magnetic field, the diffraction angle of incident light, the polarization state, and the like can be changed with a response time on the order of microseconds. Therefore, a liquid crystal light modulation element using a liquid crystal in a blue phase can be expected to have a response speed far exceeding that of a conventional liquid crystal light modulation element and various light modulation functions. However, since the blue phase appears only within a temperature range (temperature range) of several degrees C (generally 1 to 3 C) just below the isotropic phase, extremely precise temperature control is required and practical application is difficult. there were. As a technique that can solve this problem, it has been reported that the temperature range (temperature range) of the blue phase can be greatly expanded by polymerizing a liquid crystal composition containing a liquid crystal exhibiting a blue phase and a polymerizable monomer. (See Patent Document 1).
JP 2003-327966 A

  Various studies have been made on liquid crystal materials exhibiting a blue phase, but liquid crystal / polymer composites have so far been adjusted by adjusting the transmission and scattering states of incident light by adjusting the applied voltage. No materials that can be adjusted in quantity have been reported.

  The present invention has been made to solve the above problems, and is a liquid crystal / polymer composite exhibiting a blue phase, which can adjust transmission and scattering of incident light by adjusting an applied electric field. Provide a complex. That is, the present invention provides the following inventions.

1. A liquid crystal / liquid crystal obtained by polymerizing a liquid crystal composition containing a liquid crystal compound, a chiral agent, a monofunctional polymerizable monomer, and a polyfunctional polymerizable monomer in a temperature range represented by the following formula [1] A liquid crystal composite, characterized in that the combination of the liquid crystal compound and the chiral agent in the composite has a blue phase, and the light transmittance is changed by adjusting the applied voltage. / Polymer composite.
_TBP1 to [( _TBP2 - _TBP1 ) / 2] [1]
However, _TBP1 represents the minimum temperature at which the liquid crystal composition exhibits a blue phase, and _TBP2 represents the maximum temperature at which the liquid crystal composition exhibits a blue phase.

2. 2. The liquid crystal / polymer composite according to 1, wherein the liquid crystal in the liquid crystal / polymer composite exhibits a blue phase in a range of at least −10 to 30 ° C.

3. 3. The liquid crystal / polymer composite according to 1 or 2, wherein the liquid crystal / polymer composite has a selective reflection wavelength of 0.85 to 0.95 times the blue phase selective reflection wavelength of the liquid crystal composition.

  According to the liquid crystal / polymer composite of the present invention, it is possible to adjust the state of transmission and scattering with respect to incident light while maintaining the three-dimensional periodic structure of the blue phase, that is, in a state where the blue phase is developed. Therefore, it is useful for an element to be used with a large change in light transmittance, and a light modulation element such as a liquid crystal shutter can be obtained by utilizing the characteristics of the blue phase.

In the present specification, the compound represented by the formula (1) is also referred to as the compound (1). A group represented by the formula (Q) is also referred to as a group (Q). The same applies to other compounds and groups. Further, hereinafter, dielectric anisotropy is abbreviated as Δε and refractive index anisotropy as Δn. The oscillation wavelength from the light source includes the range of the described value ± 10 nm even if it is described as a single point value.
The liquid crystal composition in the present invention is a composition containing a liquid crystal compound, a chiral agent, a monofunctional polymerizable monomer, and a polyfunctional polymerizable monomer. The combination of the liquid crystal compound and the chiral agent in the present invention is a combination consisting of only the liquid crystal compound and the chiral agent.
In the present invention, a combination of a liquid crystal compound and a chiral agent is treated as a cholesteric liquid crystal in a broad sense, and a liquid crystal phase represented by the combination is referred to as a cholesteric liquid crystal phase. The physical properties (Δε and Δn) of the combination of a liquid crystal compound and a chiral agent refer to the physical properties of the mixture when a mixture of only the liquid crystal compound and the chiral agent is prepared. The combination of the liquid crystal compound and the chiral agent is also simply referred to as “liquid crystal” hereinafter.

Examples of the liquid crystalline compound that can be used in the present invention include nematic liquid crystals, smectic liquid crystals, discotic liquid crystals, and the like, and nematic liquid crystals are preferable.
The combination of the liquid crystalline compound and the chiral agent is preferably a combination exhibiting a cholesteric liquid crystal phase (chiral nematic liquid crystal phase). In addition, 1 type may be used for a liquid crystalline compound and a chiral agent, respectively, and 2 or more types may be used for it.
In order for the combination of the liquid crystal compound and the chiral agent to stably develop the blue phase, the helical pitch in the cholesteric liquid crystal phase is preferably 500 nm or less. When the helical pitch is more than 500 nm, the blue phase does not appear or even if it appears. The expression of the blue phase can be confirmed by observation with a polarizing microscope and measurement of the reflection spectrum. That is, when the blue phase is expressed, platelets (platelet-like structures) characteristic of the blue phase are observed with a polarizing microscope. Further, when the reflection spectrum is measured, a peak is recognized in the vicinity of the wavelength corresponding to the platelet.

The liquid crystalline compound in the present invention is not particularly limited, and examples thereof include molecular structures such as a biphenyl structure, a terphenyl structure, a biphenyl cyclohexyl structure, an azomethine structure, an azo and azooxy structure, a stilbene structure, a bicyclohexyl structure, and a pyrimidine structure. For example, a cyanobiphenyl-based nematic liquid crystal (manufactured by Aldrich, product number: 5CB) can be preferably used.
In consideration of application to optical elements, it is preferable that the driving voltage of the element can be lowered and that the phase difference can be increased and the cell gap can be reduced. Therefore, the liquid crystalline compound preferably has a large dielectric anisotropy (Δε) and refractive index anisotropy (Δn). In this respect, the liquid crystal compound is preferably a compound represented by the following formula (1).

In the compound of the formula (1), R ¹ is an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms.
As the alkyl group having 1 to 8 carbon atoms, a linear alkyl group having 3 to 6 carbon atoms is preferable.
As a C2-C8 alkenyl group, a C2-C6 linear alkenyl group is preferable.
Among these, since the elastic constant ratio (K ₃₃ / K ₁₁ ) is large, when the number of carbon atoms is an even number, a group having a double bond from the carbon atom at the end of the alkenyl chain toward the cyclic group is preferable. In the case of an odd number, a group having a double bond from the second carbon atom from the end of the alkenyl chain toward the cyclic group is preferred, and CH ₃ —CH═CH—CH ₂ —CH—, CH ₂ = CH—CH ₂ —CH— or CH ₃ —CH═CH— is particularly preferable.
As a C1-C8 alkoxy group, a C2-C6 linear alkoxy group is preferable, and an ethoxy group, n-propyloxy group, n-butyloxy group, or n-pentyloxy group is especially preferable.

R ¹ includes n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, ethoxy group, n-propyloxy group, n-butyloxy group, or CH ₃ —CH═CH—CH ₂ —. CH- is preferred.
A ¹ is a 1,4-phenylene group or a trans-1,4-cyclohexylene group. These groups may be unsubstituted groups, and the hydrogen atom bonded to the carbon atom in the group may be substituted with a fluorine atom, and is preferably an unsubstituted group. A ¹ is preferably an unsubstituted trans-1,4-cyclohexylene group.
Y ¹ is —COO—, —OCO—, a single bond, —CH ₂ CH ₂ —, or —C≡C—, and preferably a single bond. Y ² represents —COO—, —OCO—, a single bond, or —C≡C—, preferably —COO— or a single bond.
X ¹ , X ² , X ³ , and X ⁴ are each independently a hydrogen atom or a fluorine atom, and at least one of X ³ and X ⁴ is a fluorine atom. As X ^{1 to} X ⁴ , X ³ is preferably a fluorine atom, and all of X ¹ , X ² , and X ⁴ are preferably hydrogen atoms.
n is 0 or 1.

  As the compound (1), the following compounds are preferable, and the following compounds (1A), the following compounds (1B-2) to (1B-4), and the following compounds (1C-2) to (1C-4) are particularly preferable.

Specifically, the compound (1A), the compound (1B-2), and the compound (1C-4) represented by the above formula are preferable.
1 type may be used for a liquid crystalline compound and 2 or more types may be used for it. When using 2 or more types, it is preferable that a mixture shows a nematic liquid crystal phase. When a plurality of liquid crystal compounds are used in combination, a commercially available mixed liquid crystal may be used. Examples of the composition include fluorine-based nematic mixed liquid crystal (manufactured by Chisso Corporation, product number: JC-1041XX).

The chiral agent in the present invention may be a liquid crystal compound or a non-liquid crystal compound. In addition, the configuration of the chiral carbon atom present in the structure of the chiral agent may be either R or S. When two or more chiral agents are used, they are induced when added to the liquid crystal. It is preferable to use a combination of chiral agents having the same direction. Furthermore, the chiral agent preferably has a similar structure to the liquid crystal. Thereby, the compatibility between the liquid crystal and the chiral agent can be improved, the phenomenon that the chiral agent is precipitated after the liquid crystal / polymer composite is formed can be prevented, and as a result, the blue phase can be further stabilized.
The chiral agent in the present invention is not particularly limited, but a chiral agent having a mesogenic structure is preferable because it is preferably compatible with a liquid crystal compound. Furthermore, since a driving voltage can be lowered and a phase difference can be increased, a chiral agent having a large Δε and a large Δn is preferable. As such a chiral agent, a compound represented by the following formula (2) is preferable.

In the compound (2), R ² is an alkyl group having 4 to 8 carbon atoms having an asymmetric carbon atom, an alkyl group having 2 to 8 carbon atoms having an asymmetric carbon atom substituted with an aryl group, or an asymmetric carbon atom. And an alkoxy group having 4 to 8 carbon atoms.
As a C4-C8 alkyl group which has an asymmetric carbon atom, a C4-C6 alkyl group of a branched structure is preferable, and the following group (W1) is especially preferable. In the following, the carbon atom to which the symbol “*” in the formula is attached means an asymmetric carbon atom.

When R ² is an alkyl group having 2 to 8 carbon atoms having an asymmetric carbon atom substituted with an aryl group, “2 to 8 carbon atoms” means that the alkyl group portion has 2 to 8 carbon atoms. Means. Further, the alkyl group portion preferably has a linear structure, and an n-propyl group is particularly preferable. As the aryl group, a phenyl group or an m-tolyl group is preferable. The number of substituted aryl groups is preferably one. As the C2-C8 alkyl group having an asymmetric carbon atom substituted with an aryl group, a group represented by the following formula (W2) is preferable.

  As a C4-C8 alkoxy group which has an asymmetric carbon atom, a C4-C6 branched alkoxy group is preferable, and the following group (W3) is especially preferable.

R ² is preferably a group represented by the formula (W1) or a group represented by the formula (W2).
A ² is the same group as A ^1, and an unsubstituted 1,4-phenylene group is preferable. Y ³ is the same group as Y ¹ and is preferably a single bond. Y ⁴ is the same group as Y ^2, and —COO— or a single bond is preferable.
X ⁵ , X ⁶ , X ⁷ , and X ⁸ are each independently a hydrogen atom or a fluorine atom, and at least one of X ⁷ and X ⁸ is a fluorine atom. As X ^{5 to} X ⁸ , X ⁵ and X ⁶ are preferably hydrogen atoms, and X ⁷ and X ⁸ are preferably fluorine atoms.
m is 0 or 1.

  As the compound (2), the following compounds (2K) to (2N) are preferable. It is preferable to use 2 or more types of compound (2) together, for example, the example which uses a compound (2K) and a compound (2L) or a compound (2K) and a compound (2M) together is mentioned.

  In general, it is known that the response speed becomes slow when the viscosity of the liquid crystal is high. The compound (1) and the compound (2) in the present invention have the following group (T3) or the following group (T4), so that the viscosity is low and the response speed can be increased. In addition, the compound having the following group (T1) is effective for reducing the driving voltage when the content in the liquid crystal composition is small, but the compound cancels the dipole moment when the content is increased. Since the dimer is formed, the driving voltage reduction effect tends to be small. However, since the compound of the formula (1) and the compound of the formula (2) have the group (T3) or the group (T4) containing a fluorine atom, it is difficult to form the dimer, and the content is increased. However, since Δε is difficult to saturate, it is effective in reducing the drive voltage.

  In the present invention, it is preferable to use the compound (1) as the liquid crystalline compound and the compound (2) as the chiral agent. By using the compound (1) and the compound (2) in combination, Δε and Δn are large (for example, Δε is preferably 30 to 80, particularly preferably 30 to 70. Δn is preferably 0.15 to 0.40, 0 .15 to 0.25 is particularly preferable, and 0.15 to 0.2 is particularly preferable.) Since a liquid crystal is obtained, it is preferable. Furthermore, since the structures of the liquid crystal compound and the chiral agent are similar, a liquid crystal having good compatibility between them can be obtained. Therefore, when a liquid crystal / polymer composite is used, the driving voltage can be lowered and the cell gap can be reduced. Furthermore, since the phase separation of the liquid crystal compound and the chiral agent can be suppressed, the blue phase can be stably expressed over a long period of time.

  The ratio of the liquid crystal compound such as the compound (1) contained in the liquid crystal composition of the present invention is preferably 45 to 75% by mass with respect to the liquid crystal composition. The ratio of the chiral agent such as the compound of the formula (2) is preferably 17 to 50% by mass with respect to the liquid crystal composition.

  Moreover, it is preferable that the ratio of the liquid crystalline compound in the combination of the liquid crystalline compound such as the compound (1) and the chiral agent such as the compound (2) is 20 to 80 mol% with respect to the total of both. It is preferable that the ratio of a chiral agent is 20-80 mol% with respect to the sum total of both. Moreover, it is preferable that both total amount is 85-96 mol% with respect to the total amount of a liquid crystalline compound, a chiral agent, the monofunctional polymerizable monomer mentioned later, and a polyfunctional polymerizable monomer. . In addition, the total amount of the liquid crystal compound and the chiral agent is preferably 85 to 95% by mass, and particularly preferably 92 to 95% by mass with respect to the liquid crystal composition.

  The liquid crystal composition of the present invention contains a monofunctional polymerizable monomer and a polyfunctional polymerizable monomer described later in addition to the liquid crystal compound and the chiral agent. By adding a monofunctional polymerizable monomer together with a polyfunctional polymerizable monomer in a liquid crystal composition and conducting a polymerization reaction to obtain a liquid crystal / polymer composite, the temperature range in which the liquid crystal exhibits a blue phase is several degrees. Can be greatly expanded to several tens of degrees.

  The temperature range of the blue phase of the liquid crystal composition in the present invention is preferably 3 to 7 ° C. When the temperature range of the blue phase of the liquid crystal composition is 3 to 7 ° C., the blue phase can be stably maintained during the polymerization reaction described later from the start to the end of the polymerization reaction. The structural change of the complex can be suppressed.

In particular, when the compound (3) described later is used as the monofunctional polymerizable monomer, the difference (ΔTc) between the clearing point (Tc ¹ ) of the liquid crystal and the clearing point (Tc) of the liquid crystal composition is 4 ° C. or higher. The temperature range (ΔBP) in which the liquid crystal composition exhibits a blue phase is preferably 3 ° C. or more and 6 ° C. or less. The clearing point (Tc ¹ ) of the liquid crystal means the blue phase-isotropic phase transition point of the liquid crystal, and the clearing point (Tc) of the liquid crystal composition means the blue phase-isotropic phase transition point of the liquid crystal composition. Means.

  When the values of ΔTc and ΔBP are in the above ranges, appropriate compatibility between the liquid crystal and the compound (3) can be obtained, and the blue phase can be stabilized. When ΔTc is narrower than 4 ° C., it is considered that the amount of compound (3) necessary for stabilizing the blue phase does not reach the defective portion, and when ΔTc is larger than 10 ° C., compound (3 ) And the liquid crystal are considered to be reduced in compatibility, and in any case, the blue phase stabilization effect is reduced. When ΔBP is narrower than 3 ° C., the blue phase may not be stabilized even when a polymerization reaction is performed. When ΔBP is wider than 6 ° C., the compound (3) is in a state where it is concentrated in the defect portion. The interface scattering between the compound (3) present in the defect portion and the liquid crystal occurs, which may cause a decrease in transmittance when no voltage is applied.

  In addition, when the liquid crystal composition is polymerized to obtain a liquid crystal / polymer composite, the upper limit temperature at which the blue phase of the liquid crystal in the composite disappears is almost the same as Tc of the liquid crystal composition. The Tc of the product is preferably higher by 5 ° C. or higher than the temperature used as the optical element, and particularly preferably higher by 10 ° C. or higher. Moreover, the standard of the minimum temperature at which the blue phase disappears is (Tc−60) ° C., and it is preferable to set the Tc of the liquid crystal composition so that this temperature is 10 ° C. or more lower than the minimum use temperature of the optical element. . Furthermore, when the liquid crystal composition is stored under low temperature conditions, if crystal precipitation occurs, the characteristics of the device may be deteriorated when it is used as an optical device, so that it has excellent storage stability at low temperatures. preferable.

The monofunctional polymerizable monomer in the present invention is a non-liquid crystalline or liquid crystalline compound having one polymerizable functional group. As the polymerizable functional group, an acryloyl group or a methacryloyl group is preferable. As the monofunctional polymerizable monomer, acrylic acid esters or methacrylic acid esters are preferable, and acrylic acid alkyl esters are particularly preferable. Furthermore, when it is desired to increase the effect of improving the light transmittance to be used, it is preferable to use a compound represented by the following formula (3) as a monofunctional polymerizable monomer.
_{CH 2 = CH-COOR (3} )
R in Formula (3) is a linear alkyl group having 10 to 30 carbon atoms in which an etheric oxygen atom may be inserted between carbon-carbon bonds, and R is a group having 12 to 24 carbon atoms. preferable. When the carbon number of the group is in the range of 10 to 30, more appropriate compatibility with the liquid crystal for stabilizing the blue phase can be realized. When the number of carbon atoms of the group is more than 30, the compatibility with the liquid crystal is insufficient, and there is a possibility that the light transmittance is lowered when an optical element is obtained.

  Further, in the production of the optical element, the step of injecting the liquid crystal composition into the cell is preferably performed by injection under reduced pressure in order to avoid adverse effects such as oxygen and moisture on the liquid crystal composition. In this case, it is necessary that the liquid crystal composition does not volatilize at the time of injection under reduced pressure. Since the compound (3) has 10 or more carbon atoms, there is an advantage that it does not volatilize at the time of injection under reduced pressure and the effect of stabilizing the blue phase is not impaired.

  R may have an etheric oxygen atom, and in this case, the number of oxygen atoms is preferably 1 to 4. The number of carbon atoms present between the etheric oxygen atom and the etheric oxygen atom is preferably 1 to 5, particularly preferably 2 or 4. R particularly preferably does not have an etheric oxygen atom.

As the compound (3), the following compound (3A) is preferable.
_{CH 2 = CH-COO - [} (CH 2 CH 2 O) p · (CH 2 CH 2 CH 2 CH 2 O) q] r - (CH 2) s -H (3A)
p, q, r, and s respectively have the following meanings, and the value of [((2p + 4q) × r) + s] is an integer of 10 to 30.
p is _{- (CH 2 CH 2 O)} - the number of units is an integer of 0 to 15, preferably an integer of 0 to 5. q is _{- (CH 2 CH 2 CH 2} CH 2 O) - the number of units is an integer of 0-7, preferably an integer of 0 to 5. r represents the number of — [(CH ₂ CH ₂ O) _p · (CH ₂ CH ₂ CH ₂ CH ₂ O) _q ] — units, which is 0 or 1, with 0 being preferred. s is - (CH ₂₎ - the number of units, is an integer of 0 to 30. When r is 0, s is preferably an integer of 12 to 24, particularly preferably an integer of 12 to 20. The values of p, q, and s when r is 1 can be appropriately changed within the range where the value of [((2p + 4q) × r) + s] is an integer of 10-30.
In addition, when p, q, r, and s are each 0, it means that there is no corresponding unit.

In addition, the notation of the “— (CH ₂ CH ₂ O) _p · (CH ₂ CH ₂ CH ₂ CH ₂ O) _q —” moiety in the formula (3A) is a — (CH ₂ CH ₂ O) — unit and — ( When there are one or more units each of (CH ₂ CH ₂ CH ₂ CH ₂ O) -units, it means that the arrangement of the two units is not limited. That is, when one — (CH ₂ CH ₂ O) — unit and one — (CH ₂ CH ₂ CH ₂ CH ₂ O) — unit exist, the unit bonded to CH ₂ ═CH—COO— is , — (CH ₂ CH ₂ O) — units or — (CH ₂ CH ₂ CH ₂ CH ₂ O) — units may be used. _{- (CH 2 CH 2 O)} - units and _{- (CH 2 CH 2 CH 2} CH 2 O) - units are present more than one unit, respectively, and, when at least one of the units are present or 2 units, 2 The arrangement of the two units may be block or random, and is preferably block.

Examples of the compound (3A) include the following compounds (3Aa) to (3Ap). From the viewpoint of compatibility with the liquid crystal, the following compounds (3Aa) to (3Ae), the following compounds (3Ah) to (3Aj), And the following compound (3Am) is preferable.
_{CH 2 = CH-COO- (CH} 2) 12 H (3Aa),
_{CH 2 = CH-COO- (CH} 2) 13 H (3Ab),
_{CH 2 = CH-COO- (CH} 2) 16 H (3Ac),
_{CH 2 = CH-COO- (CH} 2) 18 H (3Ad),
_{CH 2 = CH-COO- (CH} 2) 22 H (3Ae),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 8 H (3Af),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 10 H (3Ag),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 8 CH 3 (3Ah),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 9 CH 3 (3Ai),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 12 CH 3 (3Aj),
_{CH 2 = CH-COO- (CH} 2 CH 2 CH 2 CH 2 O) 3 H (3Ak),
_{CH 2 = CH-COO- (CH} 2 CH 2 CH 2 CH 2 O) 3 CH 3 (3Am),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 4 - (CH 2) 12 H (3An),
_{CH 2 = CH-COO- (CH} 2 CH 2 O) 5 · (CH 2 CH 2 CH 2 CH 2 O) 2 H
(3 Ap).

  The proportion of the monofunctional polymerizable monomer such as the compound (3) contained in the liquid crystal composition is preferably 1 to 4% by mass with respect to the liquid crystal composition, since it is excellent in the effect of stabilizing the blue phase. 5-3.5 mass% is especially preferable, and 2-3 mass% is especially preferable. When the amount of the compound (3) is less than 1% by mass with respect to the liquid crystal composition, the effect of stabilizing the blue phase is poor when a liquid crystal / polymer composite is obtained by performing a polymerization reaction described later, and 4% by mass. If the amount is larger than that, the blue phase does not appear, or even if it appears, the regularity of the three-dimensional periodic structure is disturbed at the time of polymerization, and a phenomenon such as scattering may occur.

  The polyfunctional polymerizable monomer in the present invention is a compound capable of forming a network structure by bonding molecules of a monofunctional polymerizable monomer such as the compound (3), and two or more, preferably two. A compound having a polymerizable functional group. Examples of the polymerizable functional group include the same groups as the polymerizable functional group in the monofunctional polymerizable monomer.

  Examples of the polyfunctional polymerizable monomer include diacrylate and dimethacrylate, and it is preferable to select the polyfunctional polymerizable monomer according to the structure of the monofunctional polymerizable monomer, the strength and characteristics required for the liquid crystal / polymer composite. Moreover, it is preferable that the polymerizable functional group in both is the same.

  The polyfunctional polymerizable monomer may be either a liquid crystalline compound or a non-liquid crystalline compound, and preferably has a mesogenic structure because it needs to have good compatibility with the liquid crystal. As the polyfunctional polymerizable monomer, diacrylates such as liquid crystalline diacrylate (manufactured by Merck, product number: RM-257) are preferable.

    In order to widen the temperature range of the blue phase in the liquid crystal / polymer composite, the crosslink density of the polymer portion obtained by polymerizing the monofunctional polymerizable monomer such as compound (3) and the polyfunctional polymerizable monomer is is important. When the crosslinking density is low, the blue phase does not appear, or even if the blue phase appears, the expression temperature range becomes narrow. Therefore, it is necessary to form a highly continuous network structure by using appropriate amounts of monofunctional polymerizable monomer and polyfunctional polymerizable monomer. Therefore, the total amount of the monofunctional polymerizable monomer and the polyfunctional polymerizable monomer is 4 to 15 mol% with respect to the total amount of the liquid crystal compound, the chiral agent, the monofunctional and polyfunctional polymerizable monomer. It is preferable that Moreover, it is preferable that the total amount of a monofunctional polymerizable monomer and a polyfunctional polymerizable monomer is 5-8 mass% with respect to a liquid-crystal composition.

    The mixing ratio of the monofunctional polymerizable monomer and the polyfunctional polymerizable monomer can be appropriately adjusted depending on the structure of each, the liquid crystal compound, the structure of the chiral agent, etc., but the monofunctional polymerizable monomer / polyfunctional The polymerizable monomer (mass ratio) is preferably 1/1 to 1/4.

  The monofunctional polymerizable monomer of the present invention is present in a large amount in the defective portion of the blue phase before polymerization, and plays a role of widening the stability of the blue phase, that is, the temperature range of the blue phase. The compatibility between the liquid crystal compound capable of expressing the blue phase of the present invention and the monofunctional polymerizable monomer is appropriate, and the content of the monofunctional polymerizable monomer in the liquid crystal composition is appropriate. is necessary.

Since the upper limit temperature at which the blue phase disappears is substantially the same as the nematic phase-isotropic phase transition temperature (Tc) of the liquid crystal composition, the Tc of the liquid crystal composition is higher by 5 ° C. or more than the temperature used as the light modulation element. It is preferable to increase the temperature by 10 ° C. or higher. The lower limit temperature at which the blue phase disappears is (Tc-60) ° C., and the Tc of the liquid crystal composition may be set so that this temperature is 10 ° C. lower than the lower limit temperature of use of the light modulation element. preferable.
In addition, the liquid crystal composition preferably has excellent storage stability at low temperatures because the characteristics of the device deteriorate when it is used as a light modulation device when precipitation occurs at low temperature storage.

In the present invention, a liquid crystal / polymer composite is obtained by polymerizing the liquid crystal composition in a temperature range represented by the following formula [1].
_TBP1 to [( _TBP2 - _TBP1 ) / 2] [1]
However, _TBP1 represents the minimum temperature at which the liquid crystal composition exhibits a blue phase, and _TBP2 represents the maximum temperature at which the liquid crystal composition exhibits a blue phase.
By performing the polymerization reaction within the temperature range represented by the formula [1], a liquid crystal / polymer composite that expresses a blue phase and whose transmittance is reduced by voltage application can be obtained.
The decrease in transmittance varies depending on the type of liquid crystal composition used for preparing the liquid crystal / polymer composite, but usually the lowest transmittance value is about half of the transmittance when no voltage is applied. Even when the same liquid crystal composition is used, when the polymerization reaction is performed in a temperature range exceeding the temperature represented by the formula [1], a liquid crystal / polymer that stably develops a blue phase. Although a composite can be obtained, in this composite, even when a voltage is applied, the light transmittance is kept almost constant.

  As the polymerization reaction, a photopolymerization reaction is preferable, and a photopolymerization reaction using ultraviolet rays is particularly preferable. When the thermal polymerization reaction is employed, the temperature at which the blue phase is maintained does not necessarily match the polymerization temperature (heating temperature), and thus it may be difficult to carry out the polymerization reaction while maintaining the blue phase. In addition, the structure of the liquid crystal / polymer composite may be changed by heating.

  In the photopolymerization reaction, it is preferable to use a photopolymerization initiator. As the photopolymerization initiator, acetophenones, benzophenones, benzoins, benzyls, Michler's ketones, benzoin alkyl ethers, benzyl dimethyl ketals, thioxanthones, and the like can be used as appropriate. The amount of the photopolymerization initiator is preferably from 0.05 to 1 mol%, particularly preferably from 0.1 to 0.5 mol%, based on the liquid crystal composition.

  The selective reflection wavelength of the blue phase of the liquid crystal composition in the liquid crystal / polymer composite of the present invention is usually 0.85 to 0. 0 of the selective reflection wavelength of the blue phase of the liquid crystal composition before the polymerization reaction. 95 times.

  In the liquid crystal / polymer composite of the present invention, when circularly polarized light in a wavelength region other than the selective reflection wavelength is incident upon application of a voltage, the difference between the transmittance of clockwise circularly polarized light and the transmittance of counterclockwise circularly polarized light is 5 % Or less is preferable. If the difference in transmittance is more than 5%, the amount of transmitted light varies greatly due to the difference in the direction of deflection of the incident circularly polarized light, which is not preferable.

The liquid crystal / polymer composite of the present invention exhibits a blue phase at least in the range of −10 to + 30 ° C. Since the blue phase is stably expressed in a temperature range suitable for practical use, it is useful for a light modulation element.
Further, when the liquid crystal / polymer composite of the present invention is used for a light modulation element, it is preferable that the light transmittance is good when no voltage is applied, and that the light transmittance is reduced when a voltage is applied. . Specifically, it is preferable that the transmittance of light having a working wavelength is 80% or more when no electric field is applied, and the transmittance is 40% or less when an electric field is applied. The liquid crystal / polymer composite of the present invention is preferably used for laser light having a wavelength of 400 to 420 nm, and the transmittance of the laser light is 80% or more when no electric field is applied, and 40% or less when an electric field is applied. It is useful for optical elements used for laser light.

  The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Examples 1 to 3 are examples, and example 4 is a comparative example. In the table, the blue phase is denoted as BP.

[1] Preparation of Liquid Crystal Composition Liquid crystal compounds, chiral agents, monofunctional polymerizable monomers, polyfunctional polymerizable monomers, and polymerization initiators are mixed at the ratio shown in Table 1, and liquid crystal compositions 1 to 4 are mixed. Was prepared. Each liquid crystal composition is observed using a small-sized multi-channel spectroscopic system (HR-2000, manufactured by Ocean Optics Co., Ltd.) and a polarizing microscope equipped with a light source (xenon lamp and halogen lamp) to develop a blue phase. The temperature range and reflection spectrum were examined.
The ratio of each component is represented by mass% with respect to the whole liquid crystal composition. Table 1 shows the lower limit temperature (T _BP1 ) indicating the blue phase, the upper limit temperature (T _BP2 ) indicating the blue phase, the temperature range (ΔBP) indicating the blue phase, and the inner phase of the blue phase of each liquid crystal composition. Represents the transition temperature. The liquid crystal composition used in the present embodiment, in the approximate middle of the temperature of the T _BP1 and T _BP2, motifs of crystal-like or particle-like is observed. This phenomenon is presumed to be a phase transition in the blue phase, and the temperature at which this phenomenon was observed is shown in Table 1 as the “blue phase transition temperature”.

The components used for the preparation of the liquid crystal composition are shown below.
Liquid crystalline compounds: the following compounds (1A) and (1C-4)

Chiral agent: the following compound (2K), compound (2L)

Monofunctional polymerizable monomer: (All of the following monofunctional polymerizable monomers are non-liquid crystalline.)
_{CH 2 = COO- (CH 2)} 12 CH 3 (Aldrich Corp., _hereinafter abbreviated as _{C 12} acrylate.),
BLEMMER CA (manufactured by NOF _Corporation, a mixture of _{CH 2 = COO- (CH 2)} 16 CH 3 and _{CH 2 = COO- (CH 2)} 18 CH 3),
Blemmer B-18A (manufactured by NOF _{Corp., CH 2 = COO-CH 2} CH (C 8 H 17) 2).

Multifunctional polymerizable monomer:
Liquid crystalline diacrylate (Merck, product number: RM257)

Polymerization initiator:
2,2-dimethoxy-2-phenylacetophenone (manufactured by Aldrich, hereinafter abbreviated as DMPAP).

[2] Preparation of Liquid Crystal / Polymer Composite The liquid crystal compositions 1 to 4 obtained in [1] were injected into sandwich cells having a cell gap of 10 μm with electrodes and alignment films, respectively, in an isotropic phase state. did. Obtained from a metal halide lamp (trade name: LIGHTNINGCURE LC6, manufactured by Hamamatsu Photonics Co., Ltd.) while observing the cell into which each liquid crystal composition was injected with a polarizing microscope under crossed Nicols and confirming that the blue phase was maintained. Polymerization was performed by irradiating ultraviolet rays having an irradiation intensity of 1.5 mW · cm ⁻² for 1 hour to prepare a liquid crystal / polymer composite. The liquid crystal in each liquid crystal / polymer composite was examined for blue phase expression temperature and reflection spectrum in the same manner as described above. Further, the light transmittance was examined by the following procedure.

[Measurement of transmittance of linearly polarized light]
For each liquid crystal / polymer composite, voltage was applied using a sine wave, 1 kHz AC power source at room temperature (25 ° C.) using an electro-optical property evaluation apparatus, and the change in transmittance before and after voltage application was measured. . The transmittance is measured by irradiating laser light (wavelength 407 nm) using a semiconductor laser diode (manufactured by Nichia Corporation, product number: NDHV310APC), and Si photodiode (manufactured by Hamamatsu Photonics, product number) is used for detection. : S2281).

[Transmittance of circularly polarized light]
The circularly polarized light transmittance was measured in the same manner as the linearly polarized light transmittance measurement except that a λ / 4 plate was placed between the laser beam and the liquid crystal / polymer composite.
Table 2 shows measured values before polymerization, measured values after polymerization, and transmittance of light after polymerization (linearly polarized light and circularly polarized light). As for the transmittance of linearly polarized light, the values before voltage pressure application (0 V) and the point at which the transmittance becomes minimum (when 20 V is applied) and the difference thereof are shown. Regarding the transmittance of circularly polarized light, the difference between the transmittance of right-handed circularly polarized light when 20 V was applied and the transmittance of left-handed circularly polarized light was shown.

  As shown in Table 2, when a liquid crystal / polymer composite is prepared by polymerization, the blue phase expression temperature range (ΔBP) covers a range of at least −10 to 30 ° C. in all the liquid crystal / polymer composites 50 Magnified above ℃. In all of Examples 1 to 4, a selective reflection peak derived from the blue phase was observed, and a peak corresponding to the pitch length of the cholesteric phase was not observed. Further, comparing Example 1 and Example 4, when each liquid crystal / polymer composite was observed with a polarizing microscope, a cossel pattern indicating a blue phase was observed. When linearly polarized light was incident, The state of transmittance change due to the applied voltage was different. The difference is shown in FIG.

  The liquid crystal / polymer composite of the present invention is a material that stably develops a blue phase over a practical temperature range, has high light transmittance when no voltage is applied, and decreases transmittance when a voltage is applied. It is. Therefore, it is useful for an element (light quantity adjusting element, liquid crystal shutter, etc.) used by adjusting the light transmittance.

It is a graph which shows the transmittance | permeability change accompanying the voltage application of the liquid crystal / polymer composite of Example 1 and Example 4.

Claims (3)

A liquid crystal / liquid crystal obtained by polymerizing a liquid crystal composition containing a liquid crystal compound, a chiral agent, a monofunctional polymerizable monomer, and a polyfunctional polymerizable monomer in a temperature range represented by the following formula [1] A liquid crystal composite, characterized in that the combination of the liquid crystal compound and the chiral agent in the composite has a blue phase, and the light transmittance is changed by adjusting the applied voltage. / Polymer composite.
_TBP1 to [( _TBP2 - _TBP1 ) / 2] [1]
However, _TBP1 represents the minimum temperature at which the liquid crystal composition exhibits a blue phase, and _TBP2 represents the maximum temperature at which the liquid crystal composition exhibits a blue phase.   The liquid crystal / polymer composite according to claim 1, wherein the liquid crystal in the liquid crystal / polymer composite exhibits a blue phase in a range of at least -10 to 30 ° C.   The liquid crystal / polymer composite according to claim 1 or 2, wherein a selective reflection wavelength of the liquid crystal / polymer composite is 0.85 to 0.95 times a selective reflection wavelength of a blue phase exhibited by the liquid crystal composition. .

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