JP2007002083A - Liquid crystal optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal optical element having improved light resistance. <P>SOLUTION: For example, the liquid crystal optical element 100 is a liquid crystal optical element 100 having substrates 101 with a pair of electrodes 102 in which one is at least transparent. The liquid crystal optical element 100 is provided with a liquid crystal polymer composite 107 which is sandwiched between the pair of the substrates 101 and changes from a transparent state to a scattering state by applying a voltage across the electrodes 102 and a light stabilizer contained in the liquid crystal polymer composite 107. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal optical element, and more particularly to a liquid crystal optical element including a liquid crystal / polymer composite.

  Conventionally, a liquid crystal / polymer composite liquid crystal optical element having a transmission-scattering type operation mode is known. In the liquid crystal / polymer composite, light is controlled by a difference in refractive index between the polymer and the liquid crystal or in a domain inside the liquid crystal. Exclusively, a voltage can be applied between the counter electrodes to change the optical characteristics. It is also called a polymer dispersed liquid crystal element (PDLC) or a dispersed liquid crystal.

  Unlike the TN and STN liquid crystal optical elements, the transmission-scattering type liquid crystal optical element does not require a polarizing plate in principle. Therefore, the light transmittance is basically high, combined with scattering characteristics, and used for light control glass, optical shutters, laser devices, and the like.

  The basic techniques of a liquid crystal optical element provided with a liquid crystal / polymer composite are as follows. Patent Document 1 discloses that a liquid crystal optical element is formed from a mixture of a liquid crystal and a polymerizable liquid crystal. The mixture is placed in an aligned state in the liquid crystal cell and irradiated with ultraviolet rays to form a gel from the mixture. In Patent Document 1, this gel is particularly called an anisotropic gel.

  Further, in the liquid crystal optical element disclosed in Patent Document 1, the refractive index of the liquid crystal in a state where no voltage is applied substantially matches the refractive index of the anisotropic gel (polymerized polymer). Therefore, an optical element with high transparency can be obtained regardless of the viewing direction. In addition, when the voltage is applied, the orientation of the liquid crystal changes due to the dielectric anisotropy of the liquid crystal, and the refractive index of the liquid crystal and the refractive index of the anisotropic gel become different, resulting in a scattering state as an optical element.

  Patent Document 2 discloses a liquid in which a small amount of polymer is dispersed in a chiral nematic liquid crystal having a positive dielectric anisotropy. The basic configuration is the same as that of Patent Document 1. A transparent state is exhibited when no voltage is applied, and a scattering state is exhibited when a voltage is applied. The liquid crystal optical element of Patent Document 2 is called PSCT (Polymer Stabilized Cholesteric Texture).

Further, Patent Document 3 discloses a liquid crystal / polymer composite formed by polymer phase separation in which a mixture of a polymer and a liquid crystal having negative dielectric anisotropy is sandwiched between vertical alignment films.
US Pat. No. 5,188,760 International Patent Publication WO 92/19695 European Patent Publication EP1154006A1 (Example 7)

  By the way, it is known that a liquid crystal / polymer composite is deteriorated or discolored by heat or light under actual use conditions. Thereby, there existed a problem that a haze value will raise. For this reason, the transparency of the liquid crystal optical element itself is deteriorated.

  The present invention has been made against the background of the above problems, and an object of the present invention is to improve the durability (light resistance) of a liquid crystal display device.

  A liquid crystal optical element according to the first aspect of the present invention is a liquid crystal optical element having at least one pair of transparent substrates with electrodes, and is a liquid crystal / polymer composite sandwiched between the pair of substrates. And a liquid crystal / polymer composite that switches from a transparent state to a scattering state by applying a voltage between the electrodes, and a light stabilizer contained in the liquid crystal polymer composite. By having such a configuration, the light resistance of the liquid crystal optical element can be improved.

  The liquid crystal optical element according to a second aspect of the present invention is the above-described liquid crystal optical element, wherein the light stabilizer has a molecular weight of 500 or more. By having such a configuration, the volatility of the light stabilizer is reduced, the content of the light stabilizer can be appropriately controlled, and the light resistance of the liquid crystal optical element can be improved more reliably. it can.

  The liquid crystal optical element according to a third aspect of the present invention is the above liquid crystal optical element, wherein the light stabilizer does not contain a hydroxyl group in its structure. By having such a configuration, the light resistance of the liquid crystal optical element can be improved more reliably.

  In the liquid crystal optical element according to the fourth aspect of the present invention, in the liquid crystal optical element described above, the light stabilizer is highly compatible with the mixture forming the liquid crystal / polymer composite. As a result, the light resistance can be improved more reliably.

  The liquid crystal optical element according to a fifth aspect of the present invention is the liquid crystal optical element described above, wherein the light stabilizer is a hindered amine system. In such a case, the light resistance can be improved particularly effectively.

  Preferably, in the liquid crystal optical element, the liquid crystal has negative dielectric anisotropy, and an alignment film for aligning the liquid crystal perpendicular to the substrate surface is provided on at least one substrate. Thereby, the display characteristics of the liquid crystal optical element can be improved.

  Preferably, the liquid crystal optical element includes a columnar structure of a thermoplastic resin disposed in a space formed by the pair of substrates and the adhesive and having a height equal to the substrate interval. Thereby, impact resistance can be improved and durability can be improved.

  Further preferably, in the above-described liquid crystal optical element, the pair of substrates and the column structure are bonded to each other. Thereby, the impact resistance can be further improved and the durability can be improved.

  According to the present invention, a liquid crystal optical element with improved durability can be provided.

  Embodiments to which the present invention can be applied will be described below. For clarity of explanation, the following description is omitted and simplified as appropriate. In addition, what attached | subjected the same code | symbol in each figure or chemical formula has shown the same element, and abbreviate | omits description suitably.

  The liquid crystal optical element according to the embodiment of the present invention can reversibly and repeatedly take a transmission state and a scattering state by applying a driving voltage. The transmission state and the scattering state are applied to visible light. In the present embodiment, a reverse mode liquid crystal optical element that takes a scattering state when a voltage is applied and takes a transmission state when no voltage is applied will be described.

  In the reverse mode, when the liquid crystal optical element is not used (when no voltage is applied), it is transparent, and the presence of the liquid crystal optical element is less disturbing to the user and does not give a feeling of pressure, and feels open. A liquid crystal optical element that provides

  As the transmission-scattering mode of the liquid crystal optical element, it is possible to use a transmission mode (normal mode) that takes a transmission state when a voltage is applied and takes a scattering state when no voltage is applied.

  In the liquid crystal optical element of the present embodiment, a liquid crystal / polymer composite formed by phase separation of a liquid crystal and a polymer is a main component for developing an optical function. It is known that a liquid crystal / polymer composite is deteriorated or discolored by heat or light, and its transparency is lowered. In order to improve this, a light stabilizer that captures radicals is mixed in a mixture containing a liquid crystal and a polymerizable compound that is a material of the liquid crystal / polymer composite. Thereby, the light resistance of the liquid crystal optical element can be improved.

  As an effective means for preventing deterioration and discoloration of the liquid crystal / polymer composite layer, there are the above-mentioned light stabilizer for capturing radicals and a light absorber for absorbing ultraviolet rays. Among these, it is preferable to use a light stabilizer that traps radicals. When UV light is irradiated when forming the liquid crystal / polymer composite, the use of a light absorber may increase the amount of UV light irradiation necessary for forming the liquid crystal / polymer composite. In addition, the characteristics of the liquid crystal / polymer composite may change locally, and the drive voltage of the liquid crystal optical element may change.

  The light stabilizer is preferably a hindered amine. Since the hindered amine light stabilizer has high compatibility with the above mixture and low volatility, the light resistance can be improved by adding a small amount.

  In the present embodiment, two types of light stabilizers, N—OR and N—R, were studied as hindered amine functional groups. Specifically, TINUVIN (registered trademark) 123 having an N-OR molecular structure and TINUVIN (registered trademark) 144 having an N-R molecular structure can be used.

  The light stabilizer is preferably low in volatility. The above mixture containing the light stabilizer is injected into the liquid crystal cell after mixing. However, if the volatility is high, it volatilizes before being injected into the liquid crystal cell, and the function of improving the light resistance of the liquid crystal optical element cannot be exhibited. Therefore, it is required that the volatility is low so that the light stabilizer is contained in the mixture after the liquid crystal cell is injected. Volatility is determined by molecular weight, polarity, intermolecular force, and the like. Therefore, for example, since a light stabilizer having a molecular weight of 500 or more generally has low volatility, it can be preferably used. Thereby, light resistance can be improved more reliably.

  Moreover, it is preferable that the light stabilizer has high compatibility with the mixture of the liquid crystal and the photocuring agent compound. This is because it is important that a good structure capable of optically functioning is formed from the state of the mixture through a phase separation process. If the phase separation is not sufficient, the drive voltage for operating the liquid crystal rises, or problems such as the inability to operate as a liquid crystal optical element occur. In addition, in order to obtain a high-quality liquid crystal / polymer composite having uniform transmission-scattering electro-optical characteristics, the mixture containing the light stabilizer is preferably a homogeneous solution after mixing.

  Moreover, what does not contain a hydroxyl group in the molecular structure of a light stabilizer is preferable. Comparing a light stabilizer containing a hydroxyl group in the molecular structure (TINUVIN® 144) and a light stabilizer not containing a hydroxyl group (TINUVIN® 123) The specific resistance of the agent (TINUVIN (registered trademark) 144) is lower. If the specific resistance of the liquid crystal / polymer composite is lowered, display unevenness is likely to occur in a durability test or the like, which is not preferable. Therefore, when the two types of light stabilizers studied in the present embodiment are compared, it is preferable to use TINUVIN (registered trademark) 123 having a high specific resistance. However, the present invention is not limited to this, and any other light stabilizer can be used as long as it has a high specific resistance.

  Moreover, when mix | blending a mixture, when there is much content of a light stabilizer, a mixture will isolate | separate. Therefore, it becomes difficult to obtain a good phase separation structure. Further, since the Tc (phase transition temperature) of the liquid crystal is lowered, the temperature range in which the mixture can exhibit the liquid crystal layer is narrowed. Further, when the liquid crystal / polymer composite is formed, the mixture is irradiated with UV light. However, since the light stabilizer captures radicals, if the content of the light stabilizer is large, the driving voltage of the liquid crystal optical element is increased. May increase. On the other hand, when the content of the light stabilizer is small, the light resistance of the liquid crystal optical element cannot be improved. Therefore, it is preferable to appropriately select the mixing ratio of the light stabilizer. In the present embodiment, the light stabilizer can be mixed with about 1% to 2% of the liquid crystal compound (C) described later, that is, about 0.85% to 1.7% of the entire mixture.

  In addition, even if it does not use a hindered amine type | system | group light stabilizer, as long as the above-mentioned conditions are satisfy | filled, what kind of light stabilizer may be used.

  Here, an example of the configuration of the liquid crystal optical element according to the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an example of the configuration of the liquid crystal optical element 100 according to the present embodiment. The liquid crystal optical element 100 includes a substrate 101, an electrode 102, an alignment film 103, an adhesive 104, a spacer 105, a column structure 106, and a liquid crystal / polymer composite 107.

  The pair of substrates 101 each support the electrode 102. For example, the pair of substrates 101 may be a transparent glass substrate or a film substrate, or a combination of a glass substrate and a film substrate. In the case of a film substrate, since the substrate on which the electrode 102 that is continuously supplied is formed can be sandwiched between two rubber rolls and the like, it can be manufactured continuously, so that productivity is high.

  In the case of a glass substrate, a small amount of spacer 105 is dispersed in the electrode surface, and the four sides of the opposed substrate are sealed with an adhesive material 104 such as an epoxy resin, and two or more seal cutouts are provided. One of the above is immersed in a mixture of liquid crystal and a curable compound and sucked from the other, so that the mixture is filled in the cell and cured to obtain a desired liquid crystal optical element. A vacuum injection method can also be used.

The electrode 102 is made of a transparent conductive film such as ITO. The electrode 102 has a predetermined pattern corresponding to the display screen. One of the electrodes 102 may be a reflective electrode made of aluminum or a dielectric multilayer film.

  An alignment film 103 is formed on each electrode 102 provided on each substrate 101. The alignment film 103 is formed in contact with the liquid crystal in order to align a liquid crystal described later in a predetermined direction. At least one of the alignment films 103 formed on both substrates 101 preferably aligns the liquid crystal perpendicular to the substrate surfaces. Thereby, display characteristics can be improved. In addition, the combination of the alignment directions of the pair of substrates 101 obtained by performing a predetermined alignment process on the alignment film 103 may be either parallel or orthogonal, and the angle is set so that the unevenness of the display surface of the liquid crystal optical element 100 is minimized. do it. The surface of the electrode 102 of the substrate 101 with the electrode 102 sandwiching the mixture can be directly polished, or a resin thin film can be provided and rubbed to give a function of aligning liquid crystals on the surface of the electrode 102. Thereby, the nonuniformity at the time of pinching a mixture can also be reduced.

  The adhesive material 104 bonds the two substrates 101 together. The adhesive material 104 is disposed along the periphery of both the substrates 101. A spacer 105 is disposed in a space formed by both the substrates 101 and the adhesive material 104. The spacer 105 defines the height of a column structure 106 to be described later. The thickness of the liquid crystal / polymer composite 107 between the electrodes 102 is preferably held by the spacer 105. As a material of the spacer 105, conventionally used materials such as glass particles, resin particles, alumina particles, glass fibers, and films can be used. In addition, a columnar spacer may be used instead of a spherical spacer or a fiber-type spacer generally used in a liquid crystal display device. The thickness of the liquid crystal / polymer composite 107 is usually 1 to 50 μm, preferably 5 to 30 μm. When the electrode interval is too small, the contrast is lowered, and when it is too large, the drive voltage is increased.

  A column structure 106 made of an adhesive thermoplastic resin is disposed in a space formed by both the substrates 101 and the adhesive material 104. The column structure 106 is made of a thermoplastic resin such as an acrylic resin or an epoxy resin. The column structure 106 improves the impact resistance of the liquid crystal optical element 100. The pillar structure 106 is bonded to both the substrates 101, and the height of the pillar structure 106 is equal to the distance between the two substrates 101. In other words, the distance between the substrates 101 coincides with the height of the column structure 106.

  The space formed by both the substrates 101 and the adhesive 104 encloses a liquid crystal / polymer composite 107 formed by irradiating a mixture of liquid crystal, a polymerizable compound, a light stabilizer and the like with light. . The liquid crystal / polymer composite 107 includes a resin structure formed between the substrates 101 and a vertically aligned liquid crystal. Further, as described above, the liquid crystal / polymer composite 107 contains a light stabilizer. Since the liquid crystal has a domain structure exclusively and scatters when a voltage is applied, it is called a scattering display portion. The scattering display portion is in a transparent state when no voltage is applied, but is changed in a transmittance state when a voltage is applied. Therefore, the scattering display unit becomes an operation region in which the liquid crystal operates by voltage.

  Here, a preferred example of the mixture used for forming the liquid crystal / polymer composite 107 according to the present embodiment will be described. The fine shape of the phase separation structure of the liquid crystal / polymer composite in the liquid crystal optical element of the present embodiment can be variously changed depending on the type, properties, mixing ratio, etc. of the liquid crystal compound and the polymerizable compound and the non-polymerizable compound to be used. Can do. The combination and mixing ratio of the materials to be used are determined in consideration of optical characteristics such as transmission-scattering characteristics, the magnitude of drive voltage, and the degree of reliability required as an electro-optical element. The phase separation structure means a structure inside the liquid crystal cell that is formed through a phase separation process and can exhibit electro-optical characteristics and functions.

In the present embodiment, the mixture (D) forming the liquid crystal / polymer complex is represented by the chemical formula (2), at least one of the bifunctional polymerizable compounds (A) represented by the following chemical formula (1). It is a polymer derived from a mixture containing at least one bifunctional polymerizable compound (B) and a non-polymerizable liquid crystalline composition (C).

  The bifunctional polymerizable compound (A) forms a main skeleton component having rigidity in the polymer compound. On the other hand, the bifunctional polymerizable compound (B) forms a flexible component that can play a role of shock absorption among the polymer compounds. By combining such compounds having different physical properties, a liquid crystal / polymer composite having good impact resistance can be formed as an electro-optical element.

  In the present embodiment, when the mixture (D) is held between the alignment films in a liquid crystal state, the mixture (D) is in a horizontal alignment, twist alignment, hybrid alignment, vertical alignment, etc. depending on the type of alignment film (alignment ability). The orientation state is taken. In this orientation state, the polymerizable compound in the mixture (D) is polymerized to form a polymer.

  By adopting such a method, the polymer and the liquid crystal composition (C) are phase-separated to form a liquid crystal / polymer composite. At this time, the bifunctional polymerizable compound (A) is selected so that the molecular arrangement in the polymer can maintain the orientation before polymerization. In order to maintain the alignment before and after the polymerization phase separation process, it is preferable that the compatibility between the liquid crystalline composition (C) and the bifunctional polymerizable compound (A) is good.

  On the other hand, in order for the polymer formed after polymerization to phase-separate well from the liquid crystalline composition (C), the bifunctional polymerizable compound (A) preferably has no liquid crystallinity. Any of the above alignment states can be used as the alignment state. In the completed liquid crystal optical element, it is preferable to use vertical alignment in order to improve transparency when no voltage is applied. In the case of vertical alignment, alignment defects due to the spacer can be reduced. This is because the transparency of the liquid crystal optical element is further improved. In producing the liquid crystal optical element of the present invention, the polarity of dielectric anisotropy of the liquid crystal composition may be positive or negative, but negative in the case of vertical alignment. Otherwise, positive is preferred.

  Hereinafter, the bifunctional polymerizable compound (B) used in the present invention will be further described. The bifunctional polymerizable compound (B) is not particularly limited as long as it is a compound of the chemical formula (2). For example, it is a compound that satisfies the following conditions.

A ₃ and A ₄ are each independently an acryloyloxy group, a methacryloyloxy group, or a vinyl ether group.
R ₃ is —R ₄ — or — (R ₅ —O) _n —R ₅ —.
However, R ₄ is a linear or branched alkylene group having 2 to 20 carbon atoms, R ₅ is a linear or branched alkylene group having 2 to 8 carbon atoms, n represents 1-10 integer is there.

Or
R ₄ is a linear alkylene group having 2 to 20 carbon atoms, and R ₅ is — (CH ₂ ) r—, —CH ₂ —CH (CH ₃ ) —, —CH ₂ —CH ₂ —CH (CH ₃ ). - or _{-CH 2 -CH 2 -C (CH 3} ) 2 - a is (where, r is integer from 2 to 5), n is an integer from 1 to 6 is a compound.

Liquid crystal optical elements using these bifunctional polymerizable compounds (B) are preferable because of high impact resistance. The bifunctional polymerizable compound (B) can be used alone or in combination of two or more. Specific examples are shown in the following chemical formulas (3) to (7).

The bifunctional polymerizable compound (B) has polymerizable groups A ₃ and A ₄ and R ₃ that connects the polymerizable groups. R ₃ is selected from groups having a single bond between atoms and having a high degree of freedom of intramolecular rotation. By comprising in this way, the softness | flexibility of the polymerized polymer can be improved. It also contributes to increasing the reactivity of the polymerization phase separation.

Flexibility improves as the number of carbon atoms between A ₃ and A ₄ and the number of etheric oxygen atoms increase. On the other hand, the compatibility with the liquid crystalline composition (C) tends to decrease as the number of atoms increases. Therefore, the number of atoms is selected appropriately. In addition, in the case of adopting a manufacturing method in which the mixture is vacuum-injected into the liquid crystal cell, the number of carbon atoms is 8 or more, preferably 11 or more in consideration of scattering of volatile components from the mixture. An etheric oxygen atom may or may not be included. When it contains an etheric oxygen atom, the flexibility of the polymer is improved, which is preferable.

Since the bifunctional polymerizable compound (B) does not contain a group such as Q _{1 in} the molecule, it is relatively easy to increase the number of carbon atoms contained in R ₃ . Adoption of this structure greatly contributes to the improvement of the flexibility of the polymer.

  Next, the bifunctional polymerizable compound (A) will be described. The bifunctional polymerizable compound (A) is not particularly limited as long as it satisfies the condition of the chemical formula (1). Such a compound may be referred to by a name such as a mesogenic monomer, a liquid crystal monomer, or a polymerizable liquid crystal, but is not necessarily limited to such a compound, and to the non-polymerizable liquid crystalline composition (C). Those having good solubility can be selected and used.

  For example, known compounds described in JP-A-4-227684 can be appropriately selected and used. This is because by having such a structure, the solubility in the liquid crystal composition (C) is improved. Furthermore, the bifunctional polymerizable compound (A) preferably has the following structure.

The bifunctional polymerizable compound (A) represented by the chemical formula (1) is preferably a compound that satisfies the following conditions.
A ₁ and A ₂ are each independently an acryloyloxy group, a methacryloyloxy group, or a vinyl ether group.
Q ₁ , Q ₂ , Q ₃ and Q ₄ are each independently a 1,4-phenylene group or a 1,4-cyclohexylene group which may have a substituent.
X ₁ and X ₂ are each independently a single bond, an oxygen atom or an ester bond.
R ₁ and R ₂ are each independently a single bond or a linear or branched alkylene group having 2 to 20 carbon atoms which may have one or more etheric oxygen atoms between carbon atoms. .
Z _{1, Z} 2, _{Z 3} are each independently a single bond, -C (= O) -O - , - O-C (= O) -, - CH 2 -CH 2 -, - C≡C- , —CH ₂ —O—, —O—CH ₂ —.
p and q are both 0 or one is 0 and the other is 1.

Moreover, it is preferable that the bifunctional polymerizable compound (A) represented by the chemical formula (1) is a compound that satisfies the following conditions.
A ₁ and A ₂ are each independently an acryloyloxy group or a methacryloyloxy group.
Q ₁ and Q ₂ are both 1,4-phenylene groups which may have a substituent, and Q ₃ and Q ₄ may each independently have a substituent. A phenylene group or a 1,4-cyclohexylene group.
Z _{1, Z} 2, _{Z 3} are each independently a single bond, -C (= O) -O - , - O-C (= O) -, - CH 2 -CH 2 - or -C≡C- It is.
p and q are both 0 or one is 0 and the other is 1.

Moreover, it is preferable that the bifunctional polymerizable compound (A) represented by the chemical formula (1) is a compound that satisfies the following conditions.
A ₁ and A ₂ are both acryloyloxy groups.
Q ₁ and Q ₂ are both 1,4-phenylene groups which may have a substituent, and Q ₃ and Q ₄ may each independently have a substituent. A phenylene group or a 1,4-cyclohexylene group.
R ₁ and R ₂ are each independently a linear or branched alkylene group having 2 to 20 carbon atoms.
Z ₁ is a single bond, -C (= O) -O - , - O-C (= O) -, - CH 2 -CH 2 - or a _-C≡C-, one is Z 2, _{Z 3} Is also a single bond.
p and q are both 0 or one is 0 and the other is 1.

Specific examples of the bifunctional polymerizable compound (A) for forming the liquid crystal / polymer composite used in the liquid crystal optical element of the present invention include compounds represented by the following chemical formulas (8) to (11). it can.

  The bifunctional polymerizable compound (A) is classified into a compound having liquid crystallinity and a compound having no liquid crystallinity based on its properties. In the present invention, the mixture is preferably placed in a stable liquid crystal phase, and a liquid crystal / polymer composite is formed by phase separation from the state of the liquid crystal phase. In order to facilitate the phase separation process, it is preferable to use the non-liquid crystalline bifunctional polymerizable compound (A) in a state of being included in a mixture exhibiting a liquid crystal phase. Examples of the non-liquid crystalline bifunctional polymerizable compound (A) include compounds represented by the chemical formulas (8) to (11). Examples of the compound having good compatibility of the mixture include acrylate compounds of the chemical formula (8) and the chemical formula (10).

As explained above, the bifunctional polymerizable compound (A) can be used alone or in combination of two or more. The bifunctional polymerizable compound (A) having liquid crystallinity is a material that hardly causes phase separation from the viewpoint of the phase separation process, but from the viewpoint of controlling the state of the mixture, in order to widen the temperature range of the liquid crystal phase, Handling of the mixture can be facilitated. Specific compounds satisfying such conditions include the following chemical formulas (12) and (13).

  In the present invention, the bifunctional polymerizable compound (A) having liquid crystallinity can be used as one component of the mixture. That is, in addition to the case where only the bifunctional polymerizable compound (A) having no liquid crystallinity is used, the bifunctional polymerizable compound (A) having no liquid crystallinity and the bifunctional polymerizable compound (A) having liquid crystallinity are combined. Or a bifunctional polymerizable compound (A) having liquid crystallinity can be used alone.

In addition, the bifunctional polymerizable compound (A) has an organic group in which Q ₁ , Q ₂ , Q ₃ , and Q ₄ are bonded as a skeleton with linking groups Z ₁ , Z ₂ , and Z ₃ . The organic group improves the compatibility between the bifunctional polymerizable compound (A) and the liquid crystal composition (C), and the liquid crystal mixture (D) exhibits a liquid crystallinity (hereinafter referred to as a liquid crystal temperature range). .) To help spread.

In addition, p and q are each independently 0 or 1, but when both are 0, when adjusting the liquid crystalline mixture (D), the mixing temperature can be lowered, and A ₁ , A ₂ , A ₃ It is preferable because it reduces that polymerizable moiety represented by a ₄ are thus polymerized unnecessarily.

The organic group has an optical anisotropy of 0.01 or more. When the 1,4-phenylene group or pyrimidine-2,5-diyl group which may have a substituent is used, the optical anisotropy is increased. When 1,4-cyclohexylene group is used, the optical anisotropy becomes small. When the linking groups Z ₁ , Z ₂ , and Z ₃ are —C≡C—, the optical anisotropy can be particularly increased.

Further, the optical anisotropy is a portion other than the skeleton in the molecule of the bifunctional polymerizable compound (A), that is, the larger the size of A ₁ , A ₂ , R ₁ , R ₂ , X ₁ , X ₂ , There is a tendency to decrease. The optical anisotropy can be controlled as described above. However, the magnitude is determined by the magnitude of optical anisotropy of the liquid crystal composition (C) to be combined. For example, when the optical anisotropy of the liquid crystal composition (C) is large, the optical anisotropy of the bifunctional polymerizable compound (A) is increased. Conversely, when the optical anisotropy of the liquid crystal composition (C) is small, the optical anisotropy of the bifunctional polymerizable compound (A) is decreased.

  This is because the transparency of the liquid crystal optical element when no voltage is applied is improved. Moreover, since a bifunctional polymerizable compound (B) is a compound which does not have said organic group, it has the effect of reducing the optical anisotropy of a bifunctional polymerizable compound (A). Therefore, the compound is selected in consideration of the optical anisotropy of the bifunctional polymerizable compound (A) according to the addition amount of the bifunctional polymerizable compound (B).

In addition, the linking groups R ₁ , R ₂ , X ₁ and X ₂ play a role of linking the polymerizable groups A ₁ and A ₂ and the organic group. The linking group is selected from groups having a single bond between atoms and a high degree of freedom of intramolecular rotation. This is because the collision probability between the intermolecular polymerizable groups A ₁ , A ₂ , A ₃ , and A ₄ is increased, the reactivity is increased, and a highly reliable polymer can be formed.

Further, the flexibility of the bifunctional polymerizable compound can be improved by increasing the number of carbon atoms and the number of etheric oxygen atoms of R ₁ , R ₂ , X ₁ and X ₂ . However, there is a limit because it becomes difficult to synthesize compounds and to purify and isolate compounds with increasing molecular weight.

  As described above, the bifunctional polymerizable compound (A) improves the compatibility with the liquid crystalline composition (C) and adjusts the optical characteristics of the liquid crystal / polymer composite. On the other hand, the polymer formed from the bifunctional polymerizable compound (A) has low flexibility, and the formed liquid crystal / polymer composite tends to be weak against impact.

  The liquid crystal compounds that can be used in the present invention include various liquid crystal compounds that are used as general display materials such as nematic liquid crystals, cholesteric liquid crystals, smectic liquid crystals, and ferroelectric liquid crystals, or as materials for electric field driven display elements. Can be used. Specifically, biphenyl, phenylbenzoate, cyclohexylbenzene, azoxybenzene, azobenzene, azomethine, terphenyl, biphenylbenzoate, cyclohexylbiphenyl, phenylpyridine, cyclohexylpyrimidine, cholesterol, etc. And various liquid crystal compounds.

  These liquid crystal compounds do not need to be used alone as in the case of generally used liquid crystal compounds, and may be used in combination of two or more kinds of liquid crystal compounds. For the purpose of display by an electric field, it is preferable to use a liquid crystal compound having a negative dielectric anisotropy among the above liquid crystal compounds. In order to reduce the driving voltage, it is preferable that the dielectric anisotropy is large.

  In the present invention, the compounding ratio of the bifunctional polymerizable compound (A), the bifunctional polymerizable compound (B) and the liquid crystal composition (C) is 75 to 94.5% for the liquid crystal composition (C), It is preferable that the bifunctional polymerizable compound (A) is 5 to 15% and the bifunctional polymerizable compound (B) is 0.5 to 10%.

  Such blending makes it easy to control the mixture as a stable liquid crystal phase during the production process. When the relative amount of the polymerizable monomer is larger than the above range, the liquid crystalline composition and the polymerizable monomer tend to be separated into two layers. Therefore, it is preferable to satisfy the above range.

  On the other hand, when the relative amount of the polymerizable monomer is large, the temperature at which the mixture is separated into two layers increases, and the temperature at which the phase transition from the liquid crystal phase to the isotropic phase decreases. Therefore, the liquid crystal temperature range in which the mixture can exhibit a liquid crystal phase is narrowed. Therefore, it is preferable to satisfy the above range.

The above-mentioned mixture containing a liquid crystal compound, a polymerizable monomer and a light stabilizer is preferably a homogeneous mixed solution after mixing. In order for the mixed solution to exhibit a liquid crystal phase, the type and mixing ratio of each compound or composition described above may be selected as appropriate. The mixed solution only needs to exhibit a liquid crystal phase as a whole when the polymerizable compound is polymerized at least in the phase separation step.

  In the present invention, it is preferable to use a polymerization initiator in order to polymerize the polymerizable monomer. Such a polymerization initiator can be appropriately selected from known polymerization catalysts. However, when a photopolymerization phase separation method is used, a photopolymerization generally used for photopolymerization such as a benzoin ether type, an acetophenone type, or a phosphine oxide type is used. Initiators can be used.

  In the case of thermal polymerization, thermal polymerization initiators such as peroxides, thiols, amines, and acid anhydrides can be used depending on the type of polymerization site, and if necessary, curing aids such as amines can be used. Agents can also be used.

  Content of a polymerization initiator is 0.1-20 weight part normally with respect to 100 weight part of total amounts of a polymerizable monomer, and 0.1-10 weight part or less is preferable. In the polymer (polymer) after polymerization, when a high molecular weight and a high specific resistance are required, it is more preferably 0.1 to 5 parts by weight. When the content of the polymerization initiator exceeds 20 parts by weight, the compatibility of the mixture is inhibited, which is not preferable. Moreover, when content of a polymerization initiator is less than 0.1 weight part, even if it polymerizes the polymerizable monomer contained in a mixed solution, a polymerizable monomer cannot fully superpose | polymerize. A desired phase separation structure cannot be formed. Therefore, it is preferable to satisfy the above range. Moreover, in order to improve the contrast ratio of the liquid crystal optical element when an electric field is applied / not applied, a known chiral agent can be added to the mixed solution.

  The liquid crystal optical element according to the present invention includes a liquid crystal / polymer composite as an essential component. Even when the liquid crystal / polymer composite is composed of only three components of the liquid crystal compound, the bifunctional polymerizable compound (A), and the bifunctional polymerizable compound (B), as a display device or a light modulator. Can be used.

  Furthermore, various compounds can be added for the purpose of improving the contrast ratio and stability. For example, various dichroic dyes such as anthraquinone, styryl, azomethine, and azo can be used for the purpose of improving contrast. In that case, it is preferable that the dichroic dye is basically compatible with the liquid crystal compound and incompatible with the polymer compound. In addition, antioxidants, ultraviolet absorbers and various plasticizers are also preferably used from the viewpoint of stability and durability improvement.

  Below, the manufacturing method of the liquid crystal optical element concerning this Embodiment is demonstrated. First, a polymerizable monomer containing the bifunctional polymerizable compound (A) and the bifunctional polymerizable compound (B), a liquid crystal compound, a polymerization initiator, and a light stabilizer are mixed to form a mixture. Next, the temperature of the mixture is raised so that the mixture is uniformly mixed as an isotropic phase. Thereafter, the temperature of the mixture is lowered to confirm that the mixture has become a liquid crystal phase, and the mixture is adjusted.

  Next, the mixture is sandwiched between the pair of substrates 101 with electrodes 102. As a sandwiching method, for example, there is a method in which the mixture is applied to a certain thickness on one substrate with electrodes and the other substrate with electrodes is overlapped. Alternatively, the substrate 101 with the pair of electrodes 102 may be sandwiched by using a vacuum injection method or the like.

  Thereafter, the mixture is polymerized by heating or irradiating light or an electron beam under a constant temperature condition using a constant temperature bath or the like. Thereby, a liquid crystal / polymer composite containing a light stabilizer can be formed. Especially, since the temperature at the time of superposition | polymerization can be controlled easily, it is preferable to use the photopolymerization phase separation method which irradiates light, such as ultraviolet light and visible light.

  When the liquid crystal / polymer composite 107 is formed from the mixture by the photopolymerization phase separation method, light irradiation may be performed so that predetermined polymerization phase separation occurs, and the conditions are not particularly limited. A light source containing light having a wavelength of 400 nm or less is preferable under normal manufacturing conditions. For example, a high pressure mercury lamp, a low pressure mercury lamp, a metal halide lamp, or the like can be used.

The light irradiation conditions are preferably set according to the type of polymerizable monomer. The intensity of irradiation light when directly irradiating the mixture is preferably 1 to 400 mW / cm ² (measured at a wavelength of 365 nm). If it is less than 1 mW / cm ² , the phase separation rate becomes slow, and the scattering intensity decreases. ^{On the other hand} , when it exceeds 400 mW / cm ² , a decomposition reaction occurs due to a photoreaction, and a retention rate decreases.

  The temperature during irradiation is appropriately selected and set from the liquid crystal temperature range of the mixture. The liquid crystal temperature range in which the mixture can exhibit a liquid crystal phase varies depending on the type and the mixing ratio of each compound in the mixture. For example, 10-60 degreeC is preferable in implementing this invention. Furthermore, it is preferable that it is 30-50 degreeC. Below the miscibility temperature at which the mixture exhibits a compatible state, phase separation occurs before photopolymerization, resulting in a liquid crystal / polymer composite in which the liquid crystal is in a non-uniform state. Conversely, if the temperature is too high, the mixture undergoes a phase transition from the liquid crystal phase to the isotropic phase, and the scattering-transmission electro-optical characteristics of the liquid crystal optical element cannot be ensured.

  When polymerizing the mixture by exposure, a method such as exposure in air, exposure in nitrogen, or exposure in water is used to polymerize the entire surface of the liquid crystal optical element 10 under uniform conditions (light irradiation and polymerization temperature). Is preferred.

Examples will be described below. “Parts” in this example means parts by weight. In the embodiment of the present invention, nematic liquid crystal the dielectric anisotropy is negative _{(T C = 98 ℃, Δε} = -5.6, Δn = 0.220) and 85 parts of bifunctional polymerizable compound (A) 13 parts of the compound of the chemical formula (8) contained in the above, 2 parts of the compound of the chemical formula (7) contained in the bifunctional polymerizable compound (B) and benzoin isopropyl ether as a photopolymerization initiator in the total amount of the polymerizable monomer When 100 parts of (the compound of the chemical formula (8) and the compound of the chemical formula (7)) were mixed, they were mixed so as to be 3 parts. Further, the light stabilizer was mixed so as to be 1 part when the total amount of the polymerizable monomer (the compound of the chemical formula (8) and the compound of the chemical formula (7)) was 100 parts.

  In order to make this mixture into a liquid crystal phase, the mixture was heated to 90 ° C. with stirring to make the mixture uniform, and the temperature was lowered to 60 ° C. Thereafter, it was confirmed that the mixture became a liquid crystal phase, and a mixture was prepared.

  The liquid crystal cell was produced as follows. A pair of substrates having a vertically aligned polyimide thin film formed on a transparent electrode was prepared. A liquid crystal cell was formed by pasting together a small amount of dispersed resin beads (diameter 6 μm) with an epoxy resin (peripheral seal) printed with a width of about 1 mm so that the polyimide thin films face each other. The above mixture was then poured into the liquid crystal cell.

The liquid crystal cell was irradiated with ultraviolet rays of 10 mW / cm ² from the upper side and also about 10 mW / cm ² from the lower side for 10 minutes with a HgXe lamp having a dominant wavelength of about 365 nm while being kept at 33 ° C. A liquid crystal / polymer composite was formed between the substrates by the method to form a liquid crystal optical element having reverse mode transmission-scattering characteristics. In addition, as a comparative example, a liquid crystal optical element was formed in the same manner as in the above method by adjusting a mixture in which the light stabilizer was not mixed.

  An evaluation test regarding light resistance was performed on the above two types of liquid crystal optical elements. As an evaluation method, an exposure test using a sunshine weather meter was performed to examine changes in the haze value of the liquid crystal optical element. The haze value is a value indicating transparency, and the lower the haze value, the higher the transparency.

  When the haze value was measured after exposure for 500 hours, the haze value of a liquid crystal optical element not using a conventional light stabilizer increased from 3% to 8%. On the other hand, although the haze value of the liquid crystal optical element using the light stabilizer according to the present invention changed from 3% to 5%, the increase amount could be suppressed. From the above, it can be seen that the liquid crystal optical element of the present invention is superior in light resistance to that of the comparative example.

  Such a liquid crystal optical element of the present invention basically can reversibly switch between two optical states of transmission and scattering, and includes a liquid crystal shutter, a privacy glass, a partition, a high-speed optical shutter, a measuring device, and a screen. It is preferably used for optical communication, light flux control devices, touch-type display devices, automobile instrument panel display devices, and the like.

  In addition, display devices for store fronts such as car head-up displays, show windows, information display devices installed near receptions in offices, factories, exhibition halls, etc., information installed near registers in convenience stores It can also be used as a display device, a display device of an arcade game machine, or the like. The liquid crystal optical element of the present invention can be used as a lighting device as well as a display device.

It is sectional drawing of an example of the liquid crystal optical element concerning this Embodiment.

Explanation of symbols

101 Substrate 102 Electrode 103 Alignment Film 104 Adhesive Material 105 Spacer 106 Column Structure 107 Composite

Claims (5)

One is a liquid crystal optical element having at least a pair of transparent substrates with electrodes,
A liquid crystal / polymer composite sandwiched between the pair of substrates, wherein the liquid crystal / polymer composite is switched from a transparent state to a scattering state by applying a voltage between the electrodes;
A liquid crystal optical element comprising a light stabilizer contained in the liquid crystal / polymer composite.   The liquid crystal optical element according to claim 1, wherein the light stabilizer has a molecular weight of 500 or more.   The liquid crystal optical element according to claim 1, wherein the light stabilizer does not contain a hydroxyl group in its molecular structure.   The liquid crystal optical element according to claim 1, wherein the light stabilizer has high compatibility with the mixture forming the liquid crystal / polymer composite.   The liquid crystal optical element according to claim 1, wherein the light stabilizer is a hindered amine type.

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