JP6066057B2 - Aligned phase separation structure of liquid crystal and polymer and production method thereof - Google Patents

Description

  The present invention relates to a technical field related to an alignment phase separation structure of a liquid crystal and a polymer used in fields such as an optical shutter, a light control window glass, a sensor, an amenity, a thermally driven optical switch, and a photothermal writing memory, and a manufacturing method thereof. Belongs.

  It is industrially important for light to transmit energy and information across space, and to control its propagation state, particularly the intensity and polarization of transmission, and various technologies have been developed and put into practical use. As the control method, there are various methods according to the state change such as temperature, electricity, pressure, humidity, chemical reaction and the like. Among them, temperature change is the most familiar phenomenon that occurs around us, so it is important that heat-responsive light transmission control materials or elements and devices based on them are used in various situations. ing. In particular, materials that respond to temperature changes near room temperature are expected to be applied to next-generation energy-saving environmental building materials, such as temperature-sensitive dimmable window glass that can be controlled by solar radiation automatically in response to the heat of the season. ing.

  There are various types of temperature change responsive materials. Among them, a light control technique for reversibly changing the state of transparency and light scattering depending on the temperature has been reported, and some have been put into practical use. For example, in a system in which a gel is dispersed in a solvent, the gel thermally swells and contracts and reversibly becomes transparent / light-scattering due to a uniform / non-uniform change in the refractive index distribution of the system. Hydrogels have been proposed (see, for example, Patent Document 1-2 and Non-Patent Document 1). More specifically, Affinity, for example, has already manufactured a window glass whose basic composition is an aqueous solution of an amphiphilic polysaccharide derivative and an amphiphile, and whose transparency / scattering state is controlled by temperature using the above transition phenomenon. It has become. As other materials using the swelling-shrinkage transition, many temperature-sensitive light-control materials using poly N-isopropylacrylamide gel (Poly-NIPAM) have been reported (for example, Patent Document 3, Non-Patent Document). 2).

Several heat-responsive light-control materials using the phase transition phenomenon of liquid crystals have been reported. For example, a structure in which a low-molecular liquid crystal and a photopolymerizable liquid-crystalline monomer are mixed with each other and the liquid-crystalline monomer is cross-linked by UV irradiation and the low-molecular liquid crystal is aligned and melted in this network structure has been reported. . This uses the transition between the smectic A (S _A ) -chiral nematic (N *) phase with temperature, uses the reflection characteristics in a specific wavelength region of the low temperature N * phase, and transmits and reflects light thermally. It is reported that switching is performed in a state (see, for example, Patent Document 4). In addition, a composition in which liquid crystal is added to a colloidal crystal composed of a polymer and fine particles has been proposed. This is because the arranged fine particles serve as a kind of photonic crystal and fill the gap between them. The refractive index distribution changes due to a decrease in the alignment order accompanying thermal transition to the isotropic phase of the aligned nematic liquid crystal, and a dimming function in a specific wavelength range due to the appearance / disappearance of Bragg reflection has also been proposed (for example, (See Patent Document 5).

  On the other hand, the present inventor has so far worked on research on holographic polymer dispersed liquid crystal (H-PDLC), and has developed a technique capable of efficiently switching the diffraction intensity thermally. More specifically, it has a refractive index change and an optical anisotropic-isotropic change due to a nematic isotropic phase transition in one phase of a (sub) micron pitch one-dimensional spatial periodic structure constituting the diffraction grating. Photopolymerization / phase separation process by holographic exposure or two-beam interference exposure using low molecular liquid crystal and anisotropic polymer phase that matches birefringence and refractive index of low molecular liquid crystal phase as the other phase In this technique, molecular orientation is induced by the formation of a periodic structure, and the diffraction intensity can be appropriately switched in a polarization-selective manner (Patent Documents 6 and 7).

H. Watanabe, Sol. Energy Mater. Sol. Cells, 54 (1998) 203. A. Szilagyi, Macromol. Symp. 227 (2005) 227.

JP 2000-155345 A JP 08-11256 JP 2003-113249 A JP 2002-265945 A JP 2009-235259 JP 2008-134628 A JP 2009-300629 Japanese Unexamined Patent Publication No. 08-286162

There are several problems with the prior art. First, the compatible structure of the low-molecular liquid crystal and the high-molecular liquid crystal described in Patent Document 4 enables switching to a light reflection / transmission state in a specific wavelength range with a change in temperature. In addition to preventing the expansion of the dimming fluctuation range, these wavelength ranges are characterized by changes depending on the angle, and handling is complicated. In addition, since this material is limited to a material having a phase transition of isotropic (I) -chiral nematic (N *)-smectic A (S _A ) phase, there is room for improvement in terms of ease of production. On the other hand, the liquid crystal-added colloidal crystal described in Patent Document 5 has the same defects as the contents described in Patent Document 4 in terms of the thermal switching of the reflection / transmission state. The above-mentioned thermosensitive hydrogel has already been commercialized as a heat-responsive dimming window glass due to the scattering / transparent state at high / low temperature due to the change in refractive index accompanying the swelling-shrinkage transition of the gel in the solution. . However, the structure that is basically in the liquid phase still has problems in general-purpose handling, such as the necessity of its encapsulation.

  From the background as described above, the present invention provides a solid phase that reversibly changes to a light scattering state at a temperature above the nematic-isotropic phase transition temperature and to a light transmission state at a temperature below the nematic-isotropic phase transition temperature. It is an object of the present invention to provide a system structure and a manufacturing method thereof.

In order to solve the above problems, the alignment phase separation structure of liquid crystal and polymer is an alignment phase separation structure of liquid crystal and polymer, which is dispersed as liquid crystal droplets in a state where liquid crystal material is aligned in anisotropic polymer. There,
The liquid crystal material in the liquid crystal droplets by the temperature change causes a phase transition of a nematic phase and an isotropic phase, the phase transition, the liquid crystal droplets, optically anisotropic - cause isotropic change,
At a predetermined temperature below the phase transition point, the refractive index of the liquid crystal droplets in a nematic state matches the refractive index of the anisotropic polymer for each independent polarization component,
It is possible to reversibly change to a light scattering state at a temperature exceeding the phase transition point and to a light transmission state at a temperature lower than the phase transition point .

  In this oriented phase separation structure of liquid crystal and polymer, the liquid crystal material is phase-separated in the anisotropic polymer and dispersed as liquid crystal droplets, and these liquid crystal droplets are irregular in the polymer phase. It is preferable that the liquid crystal molecules distributed in the positions and in the liquid crystal droplets are aligned in the same direction as the anisotropic polymer.

  In this aligned phase separation structure of liquid crystal and polymer, the light wave of the scattered light generated in the structure is polarized in one specific direction and is perpendicular to the specific direction in the temperature range exceeding the nematic-isotropic phase transition point. It is preferable that a light transmission state can be maintained with a directional polarization component.

  In this liquid crystal-polymer oriented phase separation structure, the size of the liquid crystal droplets is preferably in the range of 10 nm to 10 μm.

  In this oriented phase separation structure of liquid crystal and polymer, the liquid crystal material preferably has a nematic-isotropic phase transition point in the range of 20 ° C. or higher and 120 ° C. or lower.

  In this oriented phase separation structure of liquid crystal and polymer, the structure is preferably sandwiched between a pair of substrates having visible or near infrared transmittance.

  In the liquid crystal / polymer alignment phase separation structure, the pair of substrates is preferably formed of a soft material.

  In this liquid crystal / polymer oriented phase separation structure, the distance between the pair of substrates is preferably in the range of 5 μm to 500 μm.

  In this alignment phase separation structure of liquid crystal and polymer, it is preferable to have an alignment film for molecular alignment in a specific direction on the inner surface of the substrate.

  The light control window glass of the present invention is characterized by having an alignment phase separation structure of any one of the above liquid crystals and polymers.

  In the method for producing a liquid crystal and polymer oriented phase separation structure according to the present invention, a liquid mixture of a photopolymerizable liquid crystal monomer and a liquid crystal material is injected between a pair of substrates, and then the photopolymerizable liquid crystal is irradiated by light irradiation. A monomer is polymerized to phase-separate the liquid crystal material and disperse it as liquid crystal droplets.

  In this method for producing an alignment phase separation structure of liquid crystal and polymer, the light irradiation is preferably performed with the irradiation intensity distribution being nonuniform.

  In this method for producing an alignment phase separation structure of liquid crystal and polymer, light irradiation is preferably performed through a light diffusion plate.

  In this method for producing an alignment phase separation structure of liquid crystal and polymer, it is preferable to use a substrate that has been previously subjected to molecular alignment treatment as the substrate.

  In this method for producing an aligned phase separation structure of liquid crystal and polymer, the molecular blending process may be a process of aligning in a specific direction parallel to the substrate surface, or a process of aligning perpendicularly to the substrate surface. preferable.

  According to the present invention, a solid phase structure is obtained that reversibly changes to a light scattering state at a temperature above the nematic-isotropic phase transition temperature and to a light transmission state at a temperature below the nematic-isotropic phase transition temperature. be able to. Further, the light transmission state can be controlled with high efficiency over a wide range of wavelengths. Since the control method is temperature, a simple configuration that can operate autonomously without basically requiring a utility such as electric power can be achieved. Furthermore, since it has a solid-phase structure, it can be produced on a transparent flexible substrate such as a plastic film, and can be made into a more versatile product. Further, in this structure, by further adding a function of selectively controlling the light transmission state by polarization, more advanced light propagation control can be performed.

(a), (b) is a schematic cross-sectional view of a conventional PDLC, (c) is the temperature dependence of the refractive index n _e , n _o , n _i of the low-molecular liquid crystal and the temperature of the refractive index n _p of the polymer It is a schematic diagram of dependency. (a), (b) is a cross-sectional schematic view of a PDLC according to the present embodiment, (c) the refractive index n _e of the low-molecular liquid crystal, n _o, the temperature dependence and anisotropy polymer n _i It is a schematic diagram of the temperature dependence of refractive indexes n _pe and n _po . (a), (b) is the optical polarization microscope photograph of the sample produced in the Example, and the SEM photograph of a cell cross section, respectively. It is the behavior with respect to the temperature of the sample prepared with the transparent glass substrate with the horizontal alignment treatment polyimide film, (a) shows the behavior with respect to the temperature of the transmission spectrum with orthogonal polarization components (P, S), and (b) shows the temperature change. Shows how light is dimmed. The behavior of the transmission spectrum with respect to the temperature with orthogonal polarization components (P, S) in a sample made of a transparent glass substrate subjected to the glass surface vertical alignment treatment is shown. The behavior of the transmission spectrum with orthogonal polarization components (P, S) with respect to temperature is shown. The behavior of the transmission spectrum with orthogonal polarization components (P, S) with respect to temperature is shown. The behavior of the transmission spectrum with orthogonal polarization components (P, S) with respect to temperature is shown. A mode that the transmittance | permeability change width changes with selection of the mesh number, installation position, exposure temperature, exposure wavelength, and raw material of a light diffusing plate is shown. (a) is a photograph obtained by observing transmission and scattering changes of the PDLC of this example according to orthogonal polarized light (P, S), and (b) is a polarization component orthogonal to the relationship between turbidity (Haze) and temperature ( P, S) is a diagram shown separately.

  Hereinafter, a polymer-dispersed liquid crystal (hereinafter simply referred to as “PDLC”), which is an embodiment of the alignment phase separation structure of the liquid crystal and the polymer of the present invention, will be described.

  The conventional PDLC, which is a premise of the PDLC according to the present embodiment, is known as a solid phase material having a structure in which fine liquid crystal droplets are dispersed in a polymer phase. By utilizing the optical anisotropy and molecular dipole moment of the low-molecular liquid crystal that composes PDLC together with the polymer phase, and applying an electric field to this, the orientation direction of the liquid crystal molecules in the droplets is switched to develop a refractive index distribution. This is a technique that reversibly changes to an electric field to be in a light transmission state or a light scattering state. In recent years, application to electronic paper, privacy light control glass, optical shutters, etc. has been carried out, and some have been put to practical use. In particular, instantaneous light control glass has been commercialized as a product for automatic light control building materials, and is used for privacy protection indoors or between rooms by using it as an electronic curtain (Patent Document 8).

The present inventor changed the focus on the structure and optical behavior of the above-described conventional PDLC that has been developed as an electric field responsive dimming material, and uses the PDLC according to the present embodiment as a thermal responsive dimming material. Designed, developed, and solved problems. More specifically, the light scattering state, nematic-isotropic phase transition point (at a temperature exceeding the nematic-isotropic phase transition point (T _NI ) (hereinafter simply referred to as “high temperature”)) We have developed PDLC that becomes transparent (light transmission state) at temperatures below T _NI ) (hereinafter simply referred to as “low temperature”). In this PDLC, light waves of scattered light generated by the PDLC are polarized in one specific direction, and can maintain a transparent state with a polarization component perpendicular to the specific direction at a high temperature.

First, for comparison, schematic cross-sectional views of a conventional PDLC are shown in FIGS. FIGS. 1A and 1B show a low temperature (T <T _NI ) state and a high temperature (T> T _NI ) state, respectively. FIG. 1 (c) shows the temperature dependence of the refractive indexes n _e , n _o and n _i of the low molecular liquid crystal and the temperature dependence of the refractive index n _p of the polymer.

PDLC is generally produced by exposing a mixed raw material mainly composed of low-molecular liquid crystal (hereinafter also referred to as liquid crystal material) and a photopolymerizable monomer between a pair of transparent substrates, and phase separation induced with photopolymerization. Thus, a fine liquid crystal droplet has a two-phase structure dispersed in a polymer. The low molecular liquid crystal phase has an optical anisotropic-isotropic change due to a nematic-isotropic phase transition. During the production of PDLC, the low-molecular liquid crystal phase is in a specific direction in a nematic state at a low temperature in the absence of an electric field, depending on the alignment film treatment on the substrate surface, the combination and composition of raw materials, or the temperature during exposure. Can be naturally oriented. On the other hand, the polymer phase is optically isotropic, and as shown by the temperature dependence of the refractive index in Fig. 1 (c), this isotropic polymer (refractive index n _p ) and the nematic phase at low temperature in the liquid crystal droplets exhibited anisotropy (refractive index: n _e, n _o) and the to match the refractive index between the two phases can not be in principle.

Therefore, since conventional PDLC has a refractive index difference between two phases at low temperatures, light scattering occurs due to dispersed liquid crystal droplets, whereas both low-molecular liquid crystal and polymer phases are isotropic at high temperatures. As shown in the example shown in FIG. 1 (c), the liquid crystal droplets become transparent by designing and producing these refractive indexes to coincide (n _i = n _p ). Therefore, even the conventional PDLC can switch the light scattering state itself. However, with this structure, light scattering at low temperatures and switching to a transparent state at high temperatures are possible, but in reverse, operation in a transparent state at low temperatures and a light scattering state at high temperatures is impossible in principle.

  The PDLC according to this embodiment forms an anisotropic polymer phase by introducing an anisotropic polymer material instead of the isotropic polymer phase in the conventional PDLC.

2A and 2B are schematic cross-sectional views of the PDLC according to the present embodiment. 2 (a) and 2 (b) show a low temperature (T <T _NI ) state and a high temperature (T> T _NI ) state, respectively. FIG. 2 (c) shows the temperature dependence of the refractive indexes n _e , n _o and n _i of the low molecular liquid crystal and the temperature dependence of the refractive indices n _pe and n _po of the anisotropic polymer.

As shown in FIG. 2 (a), the PDLC according to this embodiment has a low molecular liquid crystal (indicated as “liquid crystal” in FIG. 2) in an anisotropic polymer (indicated as “anisotropic polymer” in FIG. 2). The phases are separated and dispersed as liquid crystal droplets. The liquid crystal droplets are distributed at irregular positions in the phase of the anisotropic polymer, and the liquid crystal molecules inside the liquid crystal droplet are oriented in the same direction as the orientation of the anisotropic polymer. Thus, the structure of the PDLC according to the present embodiment is in a state in which both phases of the low-molecular liquid crystal and the anisotropic polymer are molecularly oriented at a low temperature. As a result, as shown in FIG. 2 (c), the anisotropic polymer always maintains a state having a birefringence (n _pe , n _po ). For this reason, for example, the birefringence index (n of the anisotropic polymer) is set so that the refractive index difference between the phase of the anisotropic polymer and the phase of the low molecular liquid crystal in the nematic state matches each independent polarization component. _pe, n _po) and the low molecular birefringence of the liquid crystal of the nematic state (n _e, n _o) and is designed to meet, by manufacturing produced no refractive index difference in these two phases at a low temperature, while When the temperature becomes high and the low molecular liquid crystal transitions to the isotropic phase, a refractive index difference (n _{i ≠} n _pe and n _{i ≠} n _po ) can be generated. Here, the birefringence (n _pe , n _po ) of an anisotropic polymer and the birefringence (n _e , n _o ) of a low molecular liquid crystal in a nematic state match at least at one temperature in a low temperature state. This means that the birefringence (n _pe , n _po ) of the anisotropic polymer and the birefringence (n _e , n _o ) of the low-molecular liquid crystal match or substantially match. The present inventor succeeded in producing this structure and realized for the first time an operation of being in a transparent state at a low temperature and in a light scattering state at a high temperature.

  In the present embodiment, the liquid crystal droplets can be spherical. As the size of the liquid crystal droplets, for example, the particle size is preferably in the range of 10 nm to 10 μm. By setting the size of the liquid crystal droplets within such a range, light can be effectively scattered at high temperatures. The size of the liquid crystal droplets can be set to a desired size by changing the polymerization conditions such as the temperature at the time of polymerization of the liquid mixture of the photopolymerizable liquid crystal monomer and the liquid crystal material when preparing PDLC.

  In the present embodiment, the liquid crystal material forming the liquid crystal droplets preferably has a nematic-isotropic phase transition point within a range of 20 ° C. or higher and 120 ° C. or lower. The liquid crystal and polymer alignment phase separation structure of the present invention can be widely used for applications such as optical shutters, light control window glass, sensors, amenity, heat-driven optical switches, photothermal writing memories, etc. By having a nematic-isotropic phase transition point in the range, it can be used more effectively for these applications. Furthermore, a light control window that takes advantage of the polarization selectivity when light is incident obliquely at a high angle into the window glass, such as in summer solar radiation, etc. Application to materials is expected. Alternatively, by combining the element of the present invention and a polarizer, the contrast change in the scattered and transmissive state can be enlarged or reduced, so that it can be applied to a heat detection sheet with variable sensitivity. .

  The PDLC according to the present embodiment has a pair of transparent substrates as described above. The substrate is not particularly limited as long as it has visible or near-infrared transmittance, and can be formed of, for example, a glass substrate or a plastic film. The substrate can also be formed of a soft material such as having a flexible shape.

  The distance between the substrates can be in the range of 5 μm to 500 μm. By setting it within such a range, desired light scattering characteristics can be satisfied.

  The inner surface of the substrate may be subjected to an alignment (rubbing) process for aligning the liquid crystal material and the anisotropic polymer in a specific direction. In addition, a thin film (alignment film) such as polyimide subjected to alignment treatment can be provided.

  In the present embodiment, a viewing angle limited transmission film or a filter (polarizing plate) that transmits only linearly polarized light at a specific angle can be disposed on the light incident side or the light emitting side of the PDLC as necessary. . The amount of transmitted light can be made variable depending on the angle and polarization state of these films and filters, and more advanced light propagation control is possible. For example, the transmitted light amount of either P or S polarized light can be controlled with temperature preferentially.

  As described above, the present invention provides a fine low-molecular liquid crystal that has a high orientation order below the nematic-isotropic phase transition point in a polymer phase that is oriented in a specific direction and has optical anisotropy. It is a structure in which droplets are dispersed, and exhibits a characteristic that a light scattering / transparent state is switched with respect to a temperature change by the structure. Below, one Embodiment of the manufacturing method of the structure is described.

  The method for producing an alignment phase separation structure of liquid crystal and polymer according to the present embodiment uses a photopolymerizable liquid crystal monomer instead of the photopolymerizable monomer used in the conventional PDLC production. That is, a liquid mixture of a photopolymerizable liquid crystal monomer and a liquid crystal material is injected between a pair of substrates, the photopolymerizable liquid crystal monomer is polymerized by light irradiation, the liquid crystal material is phase-separated, and dispersed as liquid crystal droplets. Get the structure.

  The molecular alignment direction of the photopolymerizable liquid crystal monomer and the liquid crystal material is controlled by non-uniform exposure in the photopolymerization process of the photopolymerizable liquid crystal monomer when the polymer phase and the liquid crystal material phase are separated in the photopolymerization process. Thus, the polymer phase and the phase of the liquid crystal material can be aligned in a specific direction. In addition, nonuniform exposure is exposing in the state which made irradiation intensity distribution non-uniform through the light diffusing plate of various roughness. The light diffusing plate is disposed between an irradiation light source such as a laser and a substrate that is an irradiation target surface. For example, a light diffusing plate is disposed at a position about 10 mm to 500 mm away from the substrate. As the light diffusing plate, light diffusing plates having various surface roughness, for example, light diffusing plates having mesh numbers # 240 to # 1500 can be used. The position where the light diffusing plate is disposed and the surface roughness of the light diffusing plate are not limited to the above-mentioned ranges, but are appropriately set according to the type of photopolymerizable liquid crystal monomer or liquid crystal material, exposure temperature, light source wavelength, etc. Is done. Further, exposure (uniform exposure) can be performed without using a light diffusion plate.

  Further, as the substrate, a substrate that has been subjected to molecular orientation treatment in advance can be used. For example, by injecting a liquid mixture of a photopolymerizable liquid crystal monomer and a liquid crystal material between a pair of substrates having an inner surface subjected to alignment treatment or between a pair of substrates having an alignment film disposed in a specific direction. Thus, the polymer phase and the phase of the liquid crystal material can be oriented in a specific direction by photopolymerization and phase separation. The molecular compounding process may be any of a process that is oriented in parallel and in a specific direction with respect to the substrate surface, or a process that is oriented perpendicularly to the substrate surface.

  In addition, the raw material type, raw material mixing ratio, polymerization initiator, sensitizer, additive such as surfactant, surface alignment treatment method such as rubbing, or the temperature and exposure intensity of exposure and space, time It is possible to change the polarization / transparent state by temperature by changing the optical modulation and the combination thereof. Further, a glass or film for light diffusion can be additionally inserted at a specific position between the sandwich structure of the two-phase liquid crystal and the exposure light source.

The liquid crystal material is not particularly limited as long as it has an optical anisotropic-isotropic change due to a nematic-isotropic phase transition, and commercially available materials can be used. For example, a raw material having a nematic-isotropic phase transition temperature (T _NI ) in the range of 20 to 120 ° C., a raw material having a birefringence (Δn = n _e -n _o ) in the range of 0.06 to 0.29 can be used. . Specific examples include 4-cyano-4'-hexylbiphenyl (Merck: K18, T _NI : 29 ° C) and 4-cyano-4'-pentylbiphenyl (Merck: K15, T _NI : 35 ° C). a liquid crystal material system, and the like RDP-98487 of DIC Corporation having a T _NI to 48 ° C.. These are liquid crystal materials having a low nematic-isotropic phase transition temperature. Examples of liquid crystal materials having a nematic-isotropic phase transition temperature at a temperature of 80 ° C. or higher include Merck's product names BL024 and E44. Any of these liquid crystal materials can be used, and various switching temperatures of the light transmission state can be designed and manufactured.

Examples of the photopolymerizable liquid crystal monomer include azo, azoxy, biphenyl, terphenyl, ester, cyclohexane, and other examples include photopolymerizable groups such as acrylate, methacrylate, diene, cyanate, acryloyl, vinyl, and epoxy. The inclusion etc. can be mentioned. Specific examples include RM257 and RM82 manufactured by Merck, ULC-001, ULC-011 and ULC-008 manufactured by DIC Corporation. RM257 manufactured by Merck is a liquid crystalline diacrylate monomer: 1,4-di (4- (3-acryloyloxypropyloxy) benzoyloxy) -2-methylbenzene, and has a birefringence (Δn = n _pe -n _po ) is about 0.18. The liquid crystal material K18 made by Merck is also close to the value of the birefringence of RM257 made by Merck. By using both in combination, the intended effect of the present invention can be further enhanced.

  The photopolymerizable liquid crystal monomer can be contained in the liquid mixture of the photopolymerizable liquid crystal monomer and the liquid crystal material, for example, at a ratio of 20 wt% to 90 wt%.

  The liquid mixture can further contain a photopolymerization initiator, a sensitizer, and the like that match the liquid crystal material and the photopolymerizable liquid crystal monomer. The blending of these additives is an effective means for improving the characteristics. Specific examples include 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1 -One, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, 2,2'-azobis (isobutyronitrile), azobisisobutyronitrile (AIBN), rose bengal, rhodamine 6G, 3,3′-carbonylbis (7-diethylaminocoumarin) and the like can be mentioned. Furthermore, it may be effective to add a surfactant in order to assist the viscosity adjustment and uniform mixing of the raw material to be produced. Specific examples include octanoic acid and sodium lauryl sulfate. Further, a dye can be further added.

  The aligned phase separation structure of the liquid crystal and polymer prepared as described above is in a light scattering state at a temperature exceeding the nematic-isotropic phase transition temperature, and in a light transmitting state at a temperature below the nematic-isotropic phase transition temperature. Have reversibly changing characteristics.

  Hereinafter, examples will be shown and described in more detail. Of course, the present invention is not limited to the following examples.

  Table 1 shows the production conditions of the samples (PDLC) 1 to 5 produced in this example. Samples were prepared as follows.

  Nematic liquid crystal as liquid crystal material: 4-cyano-4'-hexylbiphenyl (Merck: K18), liquid crystal diacrylate monomer as photopolymerizable liquid crystal monomer: 1,4-di (4- (3-acryloyloxypropyloxy) benzoyl Oxy) -2-methylbenzene (Merck: RM257) was mixed at a weight ratio of 70:30, 60:40, or 50:50, and N-phenylglycine (NPG: Tokyo) as a photopolymerization initiator and pigment. Kasei) and dibromofluorescein (DBF: Tokyo Kasei) 0.1, 0.1 (wt%) or 1-hydroxycyclohexyl phenyl ketone (Wako Pure Chemicals: HCHPK) 1 (wt%), respectively, and stirring while maintaining at 80 ° C Thus, a uniform liquid mixed raw material was produced.

  The above liquid mixed raw material is injected into a gap fixed to about 10 or 30 μm with a pair of glass substrates, and is passed through a light diffusion plate of mesh number # 1500 arranged at a distance of 10 mm from the glass substrate that is the irradiation target surface. Then, a laser with a wavelength of 532 nm suitable for photopolymerization of this liquid mixed raw material was scattered in the plane of the glass substrate and exposed with a non-uniform intensity distribution at the in-plane position. (Wavelength: 351 nm)). By this non-uniform exposure, the photopolymerizable liquid crystal monomer is polymerized in the high strength portion, and the liquid crystal is aggregated in the low strength portion, resulting in phase separation into a liquid crystal phase and a polymer phase. The molecules in both phases of the polymer were oriented.

  Specifically, the above laser exposure was performed for about 5 minutes while adjusting the temperature to a constant temperature within a range of 20 to 60 ° C. Thereafter, irradiation with a UV lamp (wavelength 365 nm) for about 5 minutes fixed the structure formed by polymerization to obtain a sample (PDLC).

  In this embodiment, a sample (PDLC) is manufactured using a transparent raw glass substrate (without alignment treatment) as a glass substrate. In order to control the orientation of the material more effectively, a transparent glass substrate with a horizontal alignment treatment polyimide film (hereinafter also referred to as a horizontal alignment treatment substrate), and a transparent glass substrate (cetyltrimethylammonium that has been subjected to a glass surface vertical alignment treatment) Samples (PDLC) are also produced using each (with a bromide film) (hereinafter also referred to as a glass surface vertical alignment substrate).

FIGS. 3 (a) and 3 (b) show an optical micrograph of sample 1 and an SEM photograph of the sample cross section, respectively.

  Fig. 3 (a) shows a microscopic anisotropic structure in a crossed-Nicol arrangement with a polarization microscope mode. Random grayscale images can be seen on the micron order. These are slight alignments of low-molecular liquid crystals and liquid-crystal polymers. It seems that the difference in order appears. FIG. 3 (b) shows a cross-section obtained by breaking the prepared sample, and the polymer phase morphology remaining after rinsing the low-molecular liquid crystal near the cross-section exposed from the glass substrate with methanol is observed. This suggests that a phase-separated structure was formed due to the presence of aggregated droplets of low-molecular liquid crystals in the irregularities and fine holes and depressions at the top of the cross section.

  4 to 8 show spectral transmittances of Samples 1 to 5 measured at different temperatures by dividing them into P and S polarized light. The spectral transmittance is a transmittance measured at normal incidence / transmission of P and S polarized light (see FIG. 1 or FIG. 2), and is measured at two sample temperatures of 20 ° C. and 35 ° C.

  4A shows the spectral transmittance of Sample 1, and FIG. 5 shows the spectral transmittance of Sample 2. FIG. Sample 2 differs from Sample 1 in that a glass surface vertical alignment treatment substrate is used as the glass substrate, and the exposure temperature is 40 ° C.

  As shown in Fig. 4 (a), the orientation of the horizontally aligned substrate is the same as that of P-polarized light. As a result, both P and S-polarized light show high transmittance at low temperatures, and both polarized light are transmitted at high temperatures. The rate is lowered, and in particular, P-polarized light is selectively lowered. The state of this transmission change is shown in the photograph in FIG.

  On the other hand, when the alignment treatment is performed on the substrate surface in the vertical direction, the molecules are arranged along the direction to show a so-called homeotropic alignment tendency. As a result, as shown in FIG. 5, an element exhibiting high transmittance at a low temperature and low transmittance at a high temperature can be obtained without depending on P and S polarized light.

  FIG. 6 shows the spectral transmittance of Sample 3. In Sample 3, the composition ratio of K18 and RM257 differs by 10% by weight compared to Sample 1, but basically the effect is seen when exposed at a temperature (60 ° C) sufficiently higher than the phase transition point. .

  As shown in FIG. 6, the behavior with respect to temperature is reversed from the result of FIG. 4, and low transmittance is obtained at a low temperature and high transmittance is obtained at a high temperature. Although the thermal response characteristics in the light transmission state can be controlled by selecting the raw material species and mixing ratio, as shown in this result, changing the alignment treatment conditions and the preparation temperature does not significantly change the raw material used or its composition. Can also control various characteristics.

  FIG. 7 shows the spectral transmittance of Sample 4. As shown in FIG. 7, it was found that the function can be expressed to some extent even in a sample manufactured using a bare glass substrate without an alignment film.

  FIG. 8 shows the spectral transmittance of Sample 5. In this sample, HCHPK that responds more to ultraviolet rays was used as a polymerization initiator, the temperature was set to 30 ° C., and ultraviolet rays (center wavelength: 351 nm) were exposed. From the results of FIG. 8, it was confirmed that the function of controlling the light transmission state in a polarization selective manner can be exhibited also in this sample.

  Table 2 shows the production conditions of the samples (PDLC) 6 to 19 produced as this example. Samples were prepared as follows.

  In samples 6 to 19 shown in Table 2, nematic liquid crystal: 4-cyano-4'-hexylbiphenyl (Merck: K18) or 4-cyano-4'-pentylbiphenyl (Merck: K15) as a liquid crystal material, photopolymerization As the liquid crystal monomer, liquid crystal diacrylate monomer: 1,4-di (4- (3-acryloyloxypropyloxy) benzoyloxy) -2-methylbenzene (Merck: RM257) was used. This liquid crystal material and photopolymerizable liquid crystal monomer are mixed at a weight ratio of 50:50, and N-phenylglycine (NPG: Tokyo Kasei) and dibromofluorescein (DBF: Tokyo Kasei) are used as a photopolymerization initiator and pigment. Were added in 0.1, 0.1 (wt%) or 1 (wt%) 1-hydroxycyclohexyl phenyl ketone (Wako Pure Chemicals: HCHPK) and stirred while maintaining at 80 ° C to prepare a uniform liquid mixed raw material.

  A light diffusion plate of mesh numbers # 240 to # 1500, in which the above liquid mixed raw material is injected into a gap fixed to about 10 μm by a pair of glass substrates and arranged at a distance of 20 mm or 500 mm from the glass substrate as the irradiation target surface Then, in order to photopolymerize this liquid mixed raw material, a laser having a wavelength of 532 nm or 351 nm was scattered in the plane of the glass substrate and exposed with a non-uniform intensity distribution in the plane. By this exposure, the photopolymerizable liquid crystal monomer is polymerized in the high-strength portion, and the liquid crystal is aggregated in the low-strength portion, resulting in phase separation into a liquid crystal phase and a polymer phase. The molecules of both phases were oriented. Sample 6 was prepared by exposure without using a light diffusion plate.

  Specifically, the above laser exposure was performed for about 5 minutes while adjusting to a constant temperature within a range of 30 to 50 ° C. Thereafter, irradiation with a UV lamp (wavelength 365 nm) for about 5 minutes fixed the structure formed by polymerization to obtain a sample (PDLC).

  In Samples 6 to 19, in order to more effectively control the orientation of the material, a sample (PDLC) was prepared using a horizontal alignment substrate.

Depending on the combination of liquid crystal and photopolymerizable monomer, it may be difficult to control the phase separation structure in uniform exposure, in which case the light diffusion plate is placed at an appropriate position in the optical path between the irradiation light source and the irradiation target surface. It can be solved by inserting. FIG. 9 shows the width of the change in transmittance with respect to the temperature of the sample obtained in the embodiment when a light diffusing plate is inserted to form a non-uniform intensity distribution on the irradiated surface and exposure is performed. FIG. 9a shows the effect of the fineness (roughness) of the light diffusion plate on the width of the transmittance change. In this raw material system, the transmittance change does not appear without the light diffusing plate, but the width of the transmittance change increases as the light diffusing plate becomes finer (the number shown on the horizontal axis increases). On the other hand, when the effect of changing the distance between the light diffusing plate and the irradiation target surface was examined, as shown in FIG. 9b, the transmittance change width increased when the distance was close to 20 mm. In this raw material system, if the distance from the irradiation target surface is further reduced and irradiated, there is a high possibility that the width of the transmittance change will increase. About the influence of the exposure temperature at the time of irradiation through a light diffusing plate, as shown in FIG. 9c, it turned out that a suitable temperature exists and in this raw material system, 40 degreeC is a suitable temperature. In addition, as shown in Fig. 9d, matching between the raw material system and the exposure wavelength is also an item to be examined. By selecting a polymerization initiator according to the wavelength, the transmittance change width can be maximized. It is.
Scattered light generated by this phase separation structure can have high polarization selectivity, which is apparent from the spectral data of FIG. 4, but for each sample of orthogonal polarization components (P and Visual results are shown in (S-polarized component). As shown in the photograph in Fig. 10 (a), when the image is observed through the sample, the image observed is clear because the sample is transparent with both P and S polarized light at a lower temperature than the phase transition point. It is. When the temperature rises and the phase transition temperature is exceeded, the light is scattered in the P-polarized light and the image cannot be observed through the sample, but the image is observed through the sample because the S-polarized light maintains a certain degree of transparency. FIG. 10 (b) shows the relationship between turbidity (Haze) and temperature for each polarization component. In this figure, it changes to a transparent state or a light scattering state around 30 ° C., and the light scattering state varies depending on the polarization component.

Claims (15)

An alignment phase separation structure of a liquid crystal and a polymer, which is dispersed as liquid crystal droplets in a state where a liquid crystal material is aligned in an anisotropic polymer,
The liquid crystal material in the liquid crystal droplets causes a phase transition between a nematic phase and an isotropic phase due to a temperature change thereof, and the liquid crystal droplets undergo an optical anisotropy-isotropic change due to the phase transition,
At a predetermined temperature below the phase transition point, the refractive index of the liquid crystal droplets in a nematic state matches the refractive index of the anisotropic polymer for each independent polarization component,
An oriented phase separation structure of liquid crystal and polymer, which can reversibly change to a light scattering state at a temperature exceeding the phase transition point and to a light transmission state at a temperature lower than the phase transition point.   In the anisotropic polymer, the liquid crystal material is phase-separated and dispersed as liquid crystal droplets in an oriented state, the liquid crystal droplets are distributed at irregular positions in the polymer phase, and the inside of the liquid crystal droplets 2. The liquid crystal / polymer oriented phase separation structure according to claim 1, wherein the liquid crystal molecules are oriented in the same direction as the orientation of the anisotropic polymer.   The light wave of the scattered light generated in the structure is polarized in one specific direction, and maintains a light transmission state with a polarization component perpendicular to the specific direction in the temperature range exceeding the phase transition point between the nematic phase and the isotropic phase. 3. The alignment phase separation structure of liquid crystal and polymer according to claim 1 or 2, which is possible.   4. The liquid crystal and polymer oriented phase separation structure according to claim 1, wherein the size of the liquid crystal droplets is in the range of 10 nm to 10 μm.   The liquid crystal material according to any one of claims 1 to 4, wherein the liquid crystal material has a phase transition point between a nematic phase and an isotropic phase within a range of 20 ° C or higher and 120 ° C or lower. Oriented phase separation structure.   6. The liquid crystal and polymer alignment phase separation structure according to claim 1, wherein the structure is sandwiched between a pair of substrates having visible or near infrared transmittance.   The liquid crystal and polymer alignment phase separation structure according to claim 6, wherein the pair of substrates are made of a soft material.   8. The liquid crystal / polymer alignment phase separation structure according to claim 6, wherein a distance between the pair of substrates is in a range of 5 μm or more and 500 μm or less.   The liquid crystal and polymer alignment phase separation structure according to any one of claims 6 to 8, further comprising an alignment film for molecular alignment in a specific direction on an inner surface of the substrate.   10. A light control window glass comprising the liquid crystal and polymer alignment phase separation structure according to claim 1. A method for producing an aligned phase separation structure of a liquid crystal and a polymer according to any one of claims 1 to 9,
A liquid mixture of a photopolymerizable liquid crystal monomer and a liquid crystal material is injected between a pair of substrates, and then the photopolymerizable liquid crystal monomer is polymerized by light irradiation to phase-separate the liquid crystal material and disperse it as liquid crystal droplets. A method for producing an oriented phase separation structure of a liquid crystal and a polymer, characterized by comprising:   The method according to claim 11, wherein the light irradiation is performed in a state where the irradiation intensity distribution is nonuniform.   The method for producing an aligned phase separation structure of liquid crystal and polymer according to claim 12, wherein light is irradiated through a light diffusion plate.   14. The method for producing an aligned phase separation structure of liquid crystal and polymer according to any one of claims 11 to 13, wherein a substrate that has been subjected to a molecular alignment process in advance is used as the substrate.   15. The alignment phase of liquid crystal and polymer according to claim 14, wherein the molecular alignment treatment is a treatment that is aligned in a specific direction parallel to the substrate surface, or a treatment that is aligned perpendicularly to the substrate surface. A method for manufacturing a separation structure.