JP4889327B2 - Liquid crystal light modulator, method for manufacturing the same, and liquid crystal display device - Google Patents

Description

  The present invention relates to a liquid crystal light modulator that modulates light using liquid crystal, a manufacturing method thereof, and a liquid crystal display device.

  In general, a liquid crystal light modulator is formed by sandwiching a liquid crystal, which is a liquid, between a pair of substrates, at least one of which is provided with an electrode layer and made of a transparent body. When a voltage is applied between the two electrodes to change the alignment state of the liquid crystal molecules, the optical properties of the liquid crystal change, so that a function of modulating incident light with voltage can be obtained. That is, an optical modulator can be easily realized by applying the electro-optic effect of liquid crystal. Since liquid crystal display elements operate at a lower voltage than optical crystals exhibiting other electro-optic effects, they are rapidly spreading in recent years as electro-optic elements for display devices.

  Among such liquid crystal display elements, an element formed by holding a cholesteric liquid crystal having a highly twisted molecular orientation between transparent substrates is useful as a reflective display element (for example, the following non-patent document) 1).

  In this case, in the state where no voltage is applied, this element is in a state called Grandian structure or planar orientation (the torsion axis of molecular orientation is perpendicular to the substrate surface). At this time, reflected light is generated by the wavelength selective reflection (scattering) effect of the planar alignment, and becomes display light (bright state). On the other hand, when a voltage is applied to this element, the twist axis of the liquid crystal rotates and changes uniformly into a focal conic structure (the twist axis of molecular orientation is parallel to the substrate surface). In this state, the effect of selective reflection is eliminated, so that the display light disappears (dark state).

K. Ochi, E. Yamakawa, K. Hashimoto and K. Kohriyama: “Full color display system using reflective memory type chiral nematic LCDs” Proc. International Display Workshops, PLC1-1, pp.281-284 (2000).

  However, in general, in cholesteric liquid crystals, the twist pitch of liquid crystal molecules fluctuates according to changes in temperature. Therefore, when applied to outdoor applications or when the operating environment temperature changes, the wavelength of the selectively reflected light is reduced. There is a problem that the display color changes due to the shift.

  The present invention has been made in view of the above circumstances, and when using a cholesteric liquid crystal in a twisted alignment state, the variation in the twist pitch of liquid crystal molecules accompanying a temperature change is suppressed, and when applied to outdoor applications, An object of the present invention is to provide a liquid crystal light modulator capable of preventing a change in display color even when the use environment temperature changes, a manufacturing method thereof, and a liquid crystal display device.

In the liquid crystal light modulator of the present invention, a pair of substrates provided with an electrode film is disposed so that the electrode films face each other, and a network-like synthetic resin whose surface is molecularly oriented between the pair of substrates and sandwiching the composite film comprising a cholesteric liquid crystal twisted orientation, the intensity of the reflected-display light is determined by the twist pitch of the twisted orientation of the cholesteric liquid crystal, is configured to be modulated by the voltage applied to the electrode film, the The molecular orientation direction of the surface of the reticulated synthetic resin and the twisted orientation direction of the cholesteric liquid crystal are configured to be the same and uniform directions .

  The method for producing a liquid crystal light modulator of the present invention is a method for producing the above-described liquid crystal light modulator, wherein the cholesteric liquid is mixed with the cholesteric liquid crystal and the raw material of the network synthetic resin. The composite film is formed by curing the raw material of the network synthetic resin in a state where the liquid crystal is in a twisted orientation.

  Here, when the raw material of the network synthetic resin is cured, it is preferable to form a network structure by irradiating the mixed solution with ultraviolet rays.

The liquid crystal display device of the present invention is characterized by comprising a liquid crystal light modulator described above.

  According to the liquid crystal light modulator and the liquid crystal display device of the present invention, the surface of the molecule-oriented synthetic resin is twisted and aligned by liquid crystal by dispersing and forming a network-like synthetic resin having a molecule-oriented surface inside the cholesteric liquid crystal. Since the fluctuation of the twist pitch inherent to the liquid crystal accompanying the temperature change can be suppressed, a stable display color can be obtained even if the temperature changes.

  In addition, according to the method for manufacturing a liquid crystal light modulator of the present invention, the twisted alignment of the liquid crystal is stabilized by curing the raw material of the network synthetic resin in a state where the cholesteric liquid crystal in the mixed solution is in the twisted alignment. Since the structure having the surface to be converted is obtained, the above-described liquid crystal light modulator can be easily manufactured.

  Hereinafter, a liquid crystal light modulator according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment of a reflective liquid crystal light modulator according to the present invention.

  This liquid crystal light modulator 20 is a composite film composed of a network structure 3 and a cholesteric liquid crystal 4 made of synthetic resin and having a molecular orientation between a pair of transparent substrates 2 each having a transparent electrode 1 attached thereto. 5 and a synthetic resin spacer structure 10 which is interposed between the two substrates 2 and maintains the thickness of the composite film 5 by adhering and holding these substrates 2 (in reality, only one but only one is present). Are arranged adjacent to each other. The molecular orientation of the synthetic resin surface in the composite film 5 has the same orientation as the liquid crystal orientation in contact with the resin surface.

Both electrodes 1 are connected to a voltage source 8 through lead wires 9.
As a result, when incident light 6 is incident on the liquid crystal light modulator 20, emitted light 7 having a predetermined wavelength is emitted from the liquid crystal light modulator 20 as reflected display light.

  By the way, the orientation of the liquid crystal molecules of the cholesteric liquid crystal 4 is such that the twist axis is perpendicular to the substrate surface in the initial state (Grandjean structure or planar orientation). In this case, a wavelength selective reflection effect is generated, and the incident light 6 is Bragg-reflected according to the periodic structure of the twisted orientation of the cholesteric liquid crystal, and becomes outgoing light 7, that is, display light. At this time, a bright display state is obtained.

  On the other hand, when a voltage higher than a predetermined value is applied between the electrodes 1 from the voltage source 8 via the lead wire 9, the torsion axis of the cholesteric liquid crystal 4 becomes horizontal with respect to the substrate surface. (Focal conic organization or fingerprint organization). In this case, the twisted orientation is laid down, the wavelength selective reflection effect does not occur, and the incident light 6 travels straight and transmits, so that the display light disappears and a black display state is obtained.

  When a higher voltage is applied, the twisted alignment is eliminated and all liquid crystal molecules are aligned in the direction perpendicular to the substrate surface (homeotropic alignment).

  In addition, the method for manufacturing a liquid crystal light modulator according to the embodiment of the present invention can be configured by a simple manufacturing process using phase separation. The specific manufacturing method is as follows.

  That is, a pair of substrates 2 each provided with a transparent electrode 1 is used, a mixed liquid of cholesteric liquid crystal 4 and a resin raw material is applied on one substrate 2, and the other substrate 2 is placed on the coating liquid. Match. At this time, in order to control the thickness of the mixed liquid (composite film 6) of the cholesteric liquid crystal 4 and the resin, a spacer resin structure is formed on the substrate by using a photolithography method, or a spherical spacer is formed in the liquid crystal / resin mixed liquid. To disperse.

  By the way, since the substrate 2 is provided with the alignment film, the molecules of the liquid crystal 4 and the resin raw material have a uniform twist axis in the plane. In such a state where the molecularly oriented mixed liquid is sandwiched between the substrates 2, ultraviolet rays are irradiated from the outside to induce polymerization or crosslinking reaction of the resin raw materials in the mixed liquid. As a result, the molecular weight of the synthetic resin increases rapidly, causing phase separation with the liquid crystal 4, and the resin network 3 is formed in the cholesteric liquid crystal 4. Since the resin surface is also aligned by manufacturing in this way, the effect of maintaining the twisted alignment of the liquid crystal 4 can be obtained.

  The mesh size of the mesh structure 3 becomes finer as the ultraviolet intensity is higher, that is, as the curing speed is higher. Further, the twist pitch of the liquid crystal finally stabilized can be controlled by changing at least one element among the intensity of ultraviolet rays, the blending ratio of the resin, and the curing temperature. That is, the wavelength of reflected light that is display light can be stably controlled to a desired value. In general, the liquid crystal has a smaller twist pitch in the process of separating the resin raw material, but on the other hand, depending on the curing conditions of the resin raw material, the amount of resin raw material remaining in the liquid crystal and the timing of curing of the resin raw material are different. The twist pitch of the finally fixed liquid crystal is greatly affected. Therefore, in the present embodiment, the twist pitch of the liquid crystal is adjusted by changing at least one of ultraviolet intensity, resin blending ratio, and curing temperature, and preferably all elements.

  In order to efficiently draw out the electro-optic effect of the liquid crystal, the content of the cholesteric liquid crystal 4 in the composite film 6 needs to be at least 70% or more. The thickness of the composite film 6 is preferably 100 μm or less from the viewpoint of suppressing the driving voltage, and is preferably 5 μm or more from the viewpoint of increasing the contrast ratio of display.

  As the resin raw material, monomers and oligomers are used. Monofunctional or polyfunctional monomers can be used because the resin is more likely to proceed and the resin is more likely to undergo phase separation from the liquid crystal as the molecular weight changes significantly after polymerization. Furthermore, a resin raw material excellent in solubility with a liquid crystal is desirable, and an organic material having a molecular skeleton similar to a liquid crystal such as a phenyl group or a cyclohexane group in the core is preferable. Such resin raw materials exhibit a spontaneous molecular alignment function (liquid crystallinity), and retain the molecular alignment function together with liquid crystal molecules even when dissolved in liquid crystal. By utilizing this property, after curing with ultraviolet rays, the polymer surface can exert a strong alignment regulating force on the liquid crystal molecules, and the twisted alignment of the liquid crystal can be stabilized. Specific resin raw materials include acrylic resin, methacrylic resin, urethane resin, polyethylene resin, polypropylene resin, polyolefin resin, epoxy resin, polystyrene resin, polyvinyl alcohol resin, fluorine-based resin (for example, polytetrafluoroethylene), or those Copolymers of the above can also be used.

  Also, as the cholesteric liquid crystal material to be used, in addition to a liquid crystal material containing an asymmetric carbon atom and having its own twisted orientation, a chiral agent that induces twist orientation is added to a nematic liquid crystal that does not contain an asymmetric carbon atom. can do. As the chiral additive, a material capable of obtaining a small helical pitch with a small amount is preferable, and a chiral compound containing an asymmetric carbon atom having optical activity or a cholesterol derivative exhibiting a cholesteric phase is suitable.

  The twist pitch generated in the liquid crystal is inversely proportional to the concentration of the chiral dopant. In order to develop the orientation (cholesteric phase) of the focal conic structure, it is desirable to control the twist pitch to be 1/2 or less of the substrate interval.

Also in the liquid crystal to obtain a high-speed responsiveness to the voltage application, and the low viscosity and high elasticity material suitable as the chemical structure, the liquid crystal refractive index anisotropy [Delta] n ([Delta] n = extraordinary refractive index n _e - Cyano, biphenyl, taphenyl, pyrimidine, tolan, and fluorine are suitable for which the ordinary refractive index n _o ) is large.

In order to make the twisted alignment of the liquid crystal molecules uniform in the element plane, an alignment film for aligning the alignment of the liquid crystal molecules on the surface of the transparent electrode is used. As the material of the alignment film, polyimide resin, polyvinyl alcohol resin, polyvinyl cinnamate resin, azo compound, and the like are suitable. As the alignment treatment method, rubbing alignment treatment in which the resin film surface is rubbed with rayon or nylon cloth, or exposure treatment by irradiation with polarized ultraviolet rays can be used. In addition to various existing printing methods such as flexographic printing and gravure printing, alignment film coating methods include roll coating, dipping, spin coating, casting, spraying, doctor blade coating, and wire bar coating. Other coating techniques can also be used. It is also possible to form an oblique vacuum deposited SiO film or SiO ₂ film on the substrate surface as the alignment film of the inorganic material. The alignment treatment of these alignment films may be performed on both of the two substrates or on one of them.

  As a method of applying the liquid crystal / resin raw material mixture onto the substrate 2, roll coating, dipping, spin coating, casting, spraying, doctor blade coating, wire bar coating, etc. are used as methods with excellent productivity and mass productivity. It is done. Various printing techniques such as flexographic printing, screen printing, and gravure printing can also be used.

  Further, as the ultraviolet light source for curing the resin raw material of the mixed liquid, a light source that efficiently emits long-wavelength ultraviolet light that does not decompose the liquid crystal is suitable, and a high-power mercury xenon lamp, an ultra-high pressure mercury lamp, an excimer lamp, A xenon lamp or the like is preferable, but is not limited thereto.

  The substrate 2 is not only a thin glass substrate with a thickness of 1 mm or less, which is often used in current liquid crystal display devices, but also a flexible plastic film such as polycarbonate, polyethylene terephthalate, polyethersulfone, and polyethylene terephthalate with a thickness of 0.4 mm or less. Can be used.

  As the transparent electrode 1 provided on the substrate 2, indium oxide doped with tin (ITO), indium oxide, tin oxide, zinc oxide and the like are suitable. Those transparent electrodes 1 can be formed by a method such as vacuum deposition, sputtering, or ion plating. Further, as the transparent electrode 1 other than the metal oxide, a transparent organic conductive material such as a polythiophene resin may be applied by spin coating or printing.

  In the present embodiment, since the wavelength selective reflection effect of cholesteric liquid crystal is used as a principle for display, it is desirable to dispose a light absorber on the back surface of the element. In addition, since light of a specific wavelength can be selectively reflected, color display is possible by adjusting the twist pitch of the cholesteric liquid crystal. Since this method does not use a backlight, a reflective display device with low power consumption can be configured. In the case of such a reflection type display device, it is possible to make the light non-incident side substrate opaque or to replace the light non-incident side electrode with a metal electrode.

  In addition, as described above, the effect of stabilizing the twisted alignment of the liquid crystal 4 is enhanced by miniaturizing the synthetic resin in the liquid crystal 4 (increasing the intensity of ultraviolet rays to be irradiated) and increasing the amount of dispersion (increasing the amount of monomer added). Can do. However, if the polymer structure is distorted due to its strong alignment regulating force, the twisted alignment of the liquid crystal 4 is also greatly distorted, so that the reflection effect is weakened (decrease in reflectivity), and the liquid crystal 4 varies with temperature fluctuations. There is also a phenomenon that the twisted orientation of the film is easily disturbed. Therefore, it is desirable to set the polymer dispersion amount and the ultraviolet intensity to appropriate values.

From this viewpoint, the amount of monomer added is suitably 30% by weight or less. As the intensity of ultraviolet rays used for curing monomers, even damage to the liquid crystal 4 by considering the range of 10mW / cm ² ~100mW / cm ² are suitable.

  The examination result of the optical modulator according to the embodiment of the present invention will be described below.

A glass substrate with a transparent electrode (ITO) coated with a polyimide alignment film (AL-1254, JSR) was superposed through 5 μm spacer particles, and the periphery was hardened with a photocurable resin. In this case, only one of the substrates was previously subjected to orientation treatment by rubbing (friction). On the other hand, nematic liquid crystal without twist (JB-1010XX, Chisso), chiral agent (CM-33, Chisso, 23% by weight), and liquid crystalline monofunctional monomer (UCL-001, DIC) that cures with ultraviolet rays. , 10 wt.%) Mixed solution (cholesteric phase) was injected between the glass substrates to induce torsional orientation in the mixed solution. In this state, an ultraviolet ray having a central wavelength of 365 nm was irradiated, and a network resin was precipitated and aggregated by phase separation to produce an example. At that time, the intensity and time of ultraviolet irradiation were set to 33 mW / cm ² and 5 minutes, respectively.

  On the other hand, a liquid mixture (cholesteric phase) in which only a chiral agent (CM-33, Chisso) is mixed with nematic liquid crystal (JB-1010XX, Chisso) without twisting is injected between the glass substrates, and the others are implemented above. Comparative examples were prepared in the same manner as the examples.

  The transmission spectrum was measured while heating the cholesteric liquid crystal elements (planar alignment) according to the optical modulators of Examples and Comparative Examples produced as described above. The results for the example are shown in FIG. 2, and the results for the comparative example are shown in FIG. 2 and 3, the reflected light wavelength component is represented as a drop in transmittance.

As is apparent from FIG. 2, in the example, the center wavelength of selective reflection is almost unchanged even when the temperature is changed.
On the other hand, as is clear from FIG. 3, in the comparative example, the center wavelength of the reflected light greatly changes due to the temperature change.

  From the above verification results, it is possible to stabilize the reflection wavelength against temperature change by dispersing the network resin in the liquid crystal having a cholesteric phase, that is, to stabilize the twist pitch of liquid crystal molecules against temperature change. I was able to confirm.

  In the above examples, as a result of evaluating a plurality of samples prepared by changing the intensity of the ultraviolet rays to be irradiated, the larger the intensity of the ultraviolet rays, the finer the structure of the network resin, and the more stable the twisted pitch of the liquid crystal. It has been clarified that the crystallization effect is enhanced.

1 is a schematic cross-sectional view showing a liquid crystal light modulator according to an embodiment of the present invention. The graph which shows the result of having measured the transmission spectrum about the liquid crystal light modulator of an Example (light transmission characteristic) The graph which shows the result of having measured the transmission spectrum about the liquid crystal light modulator of a comparative example (light transmission characteristic)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent electrode 2 Substrate 3 Network-like structure 4 Cholesteric liquid crystal 5 Composite film 6 Incident light 7 Reflected light (display light)
8 Voltage source 9 Lead wire 10 Spacer structure

Claims (4)

A pair of substrates provided with an electrode film is disposed so that the electrode films face each other, and a composite film composed of a network-like synthetic resin whose surface is molecularly oriented and a twisted cholesteric liquid crystal between the pair of substrates. And the intensity of the reflected / display light determined by the twist pitch of the twist orientation of the cholesteric liquid crystal is modulated by the voltage applied to the electrode film ,
A liquid crystal light modulator comprising: a molecular orientation direction of the surface of the mesh-like synthetic resin and a twist orientation direction of the cholesteric liquid crystal that are the same and uniform directions . 2. The method of manufacturing a liquid crystal light modulator according to claim 1 , wherein the cholesteric liquid crystal is mixed with the raw material of the network synthetic resin, and the network is in a state in which the cholesteric liquid crystal is twisted. A method for producing a liquid crystal light modulator, comprising: curing a synthetic resin raw material to form the composite film. 3. The method of manufacturing a liquid crystal light modulator according to claim 2 , wherein when the raw material of the network synthetic resin is cured, the mixed solution is irradiated with ultraviolet rays to form a network structure. A liquid crystal display device comprising the liquid crystal light modulator according to claim 1 .

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