JP2009237584A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device which has high stability of the Kerr effect and can be easily manufactured. <P>SOLUTION: The display device includes a pair of substrates 1, 2 at least one of which is transparent and a medium layer 3 which is interposed between the pair of substrates 1, 2, exhibits optical isotropy when no electric field is applied and exhibits optical anisotropy when an electric field is applied, and the medium layer 3 contains a chiral agent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display element having high-speed response and wide-field display performance.

  Liquid crystal display elements have the advantage of being thin, light and low in power consumption among various display elements, and can be used for OA (Office Automation) devices such as TV, video, and other image display devices, monitors, word processors and personal computers. Widely used.

  Conventionally, as a liquid crystal display method of a liquid crystal display element, for example, a display mode using a TN (twisted nematic) mode using a nematic liquid crystal, a ferroelectric liquid crystal (FLC), or an antiferroelectric liquid crystal (AFLC). A polymer dispersion type liquid crystal display mode is known.

  Among them, conventionally used liquid crystal display elements include, for example, TN (twisted nematic) mode liquid crystal display elements using nematic liquid crystal, and the liquid crystal display elements using the TN mode. Have drawbacks such as a slow response and a narrow viewing angle. These disadvantages greatly hinder CRT (cathode ray tube) from surpassing.

  In addition, the display mode using FLC or AFLC has advantages such as quick response and wide viewing angle, but it has major drawbacks in terms of shock resistance, temperature characteristics, etc. It has not yet been realized.

  Furthermore, the polymer dispersion type liquid crystal display mode using light scattering does not require a polarizing plate and can display a high luminance, but the viewing angle cannot be controlled by the phase plate, and the response characteristic is not necessary. There is little advantage over the TN mode.

  In any of these display methods, the liquid crystal molecules are aligned in a certain direction, and the appearance differs depending on the angle with respect to the liquid crystal molecules. Each of these display systems uses rotation of liquid crystal molecules due to application of an electric field, and the liquid crystal molecules rotate in an aligned manner, so that it takes time to respond. In the case of a display mode using FLC or AFLC, although it is advantageous in terms of response speed and viewing angle, irreversible alignment breakage due to external force becomes a problem.

  On the other hand, a display method based on electronic polarization using a secondary electro-optic effect has been proposed in contrast to these display methods utilizing the rotation of molecules by applying an electric field.

  The electro-optic effect is a phenomenon in which the refractive index of a substance is changed by an external electric field. The electro-optic effect has an effect in which the refractive index of a substance is proportional to the first order of the electric field and an effect that is proportional to the second order, which are called the Pockels effect and the Kerr effect, respectively. In particular, the secondary electro-optic effect called the Kerr effect has been applied to high-speed optical shutters from an early stage, and has been put to practical use in special measuring instruments. The Kerr effect was discovered by J. Kerr in 1875. So far, materials such as organic liquids such as nitrobenzene and carbon disulfide have been known as materials showing the Kerr effect. These materials are used for, for example, high electric field strength measurement of power cables and the like in addition to the optical shutter described above.

  After that, it was shown that the liquid crystal material has a large Kerr constant, and a basic study for application to a light modulation element, a light polarization element, and an optical integrated circuit was performed, and the Kerr constant exceeding 200 times that of the nitrobenzene was shown. Liquid crystal compounds have also been reported.

  In such a situation, application to a display device of the Kerr effect is being studied. Since the refractive index of a material exhibiting the Kerr effect is proportional to the second order of the electric field, when a material exhibiting the Kerr effect is used for orientation polarization, a lower voltage drive is expected than when a material exhibiting the Pockels effect is used for orientation polarization. be able to. Furthermore, since a substance exhibiting the Kerr effect exhibits a response characteristic of several microseconds to several milliseconds, it is expected to be used for causing a display by a display device to respond to an input voltage at a high speed.

  However, there is a stability of the Kerr effect as a problem when a substance exhibiting the Kerr effect is applied to a display element. That is, it is known that the Kerr effect (which is itself observed in the isotropic phase state) becomes maximum near the liquid crystal phase-isotropic phase transition temperature and rapidly decreases as the temperature rises. For this reason, the stability of the Kerr effect is poor, which is a serious problem in practical use.

  On the other hand, an approach has been proposed in which liquid crystal molecules exhibiting the Kerr effect are confined in a polymer to increase the stability of the Kerr effect (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-183937 (published July 9, 1999)

Kazuya Saito, 1 other person, “Thermodynamics of unusual thermotropic liquid crystals that are optically isotropic”, Liquid Crystals, 2001, Vol. 5, No. 1. p.20-27 Jun Yamamoto, “Liquid Crystal Microemulsion”, Liquid Crystal, 2000, Vol. 3, No. 3, p.248-254 D. Demus, 3 others, "Handbook of Liquid Crystals Low Molecular Weight Liquid Crystal", Wiley-VCH, 1998, vol. 2B, p. 887-900 Jun Yamamoto, "Liquid Crystal Science Laboratory 1st: Identification of Liquid Crystal Phase: (4) Lyotropic Liquid Crystal", Liquid Crystal, 2002, Vol. 6, No. 1, p.72-83 Eric Grelet, 3 others, “Structural Investigations on Smectic Blue Phases”, PHYSICAL REVIEW LETTERS, The American Physical Society, April 23, 2001, vol. 86, no. 17, p3791-3794 Makoto Yoneya, “Searching for Nanostructured Liquid Crystal Phases by Molecular Simulation”, Liquid Crystals, 2003, Vol. 7, No. 3, p.238-245

  However, although Patent Document 1 is an effective method in terms of maintaining the stability of the Kerr effect, it is necessary to polymerize a reactive monomer by photopolymerization or the like, and the liquid crystal region size is set to 0.1 μm or less. There is a need to. For this reason, it is not easy to manufacture a display element using the liquid crystal material described in Patent Document 1. Further, since the area where the liquid crystal material and the polymer are in contact with each other is large, impurities such as ions in the polymer are dissolved in the liquid crystal material, thereby reducing reliability. For this reason, it is difficult to obtain high reliability as a display element.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a display element that has high Kerr effect and can be easily manufactured.

  In order to solve the above problems, a display element according to the present invention is sandwiched between a pair of substrates, at least one of which is transparent, and exhibits optical isotropy when no electric field is applied. A display element including a medium that sometimes exhibits optical anisotropy, wherein the medium includes a chiral agent.

  According to said structure, the chiral agent as a chiral substance contains in the medium. A chiral agent has a structure twisted with an adjacent molecule. In this case, the energy of interaction between molecules is reduced. For this reason, by including a chiral agent in the medium, the medium and the chiral agent spontaneously take a twisted structure, and the structure is stabilized. Therefore, the medium containing the chiral agent is stable in the original structure even in the vicinity of the isotropic phase-liquid crystal phase transition temperature, for example, so that abrupt structural change does not occur, and as a result, the Kerr effect is stabilized. Can do. Here, the stabilization of the Kerr effect means that the change in the Kerr constant is small.

  That is, a large amount of energy is required to change the state stabilized by the twisted structure. In other words, the twisted structure will not be broken unless large energy is applied. Therefore, in order for a system stabilized by a twisted structure to have a certain Kerr constant, to change its state, an energy larger than the energy required to change the state not stabilized by the twisted structure. Is considered necessary. That is, when there is a twisted structure, the Kerr constant does not change much. Therefore, the Kerr effect can be stabilized.

  Therefore, it is possible to easily realize a display element in which the Kerr effect is stabilized by a simple method of adding a chiral agent.

  In order to solve the above problems, a display element according to the present invention is sandwiched between a pair of substrates, at least one of which is transparent, and exhibits optical isotropy when no electric field is applied. A display device including a medium that sometimes exhibits optical anisotropy, wherein the medium is a chiral substance. That is, the display element is characterized in that the medium is a chiral substance.

  According to said structure, the medium itself consists of a chiral substance. The chiral substance is a substance having chirality (an optically active substance). A chiral substance has a twisted structure, so that the energy of intermolecular interaction is lowered. For this reason, the medium itself spontaneously takes a twisted structure, and the structure is stabilized. Therefore, a medium composed of a chiral substance has a stable original structure even in the vicinity of an isotropic phase-liquid crystal phase transition temperature, for example, and therefore does not undergo a sudden structural change, and as a result, stabilizes the Kerr effect. Can do. That is, similarly to the above, the Kerr constant does not change much when there is a twisted structure, so that the Kerr effect can be stabilized.

  Therefore, it is possible to easily realize a display element in which the Kerr effect is stabilized only by using a chiral substance as a medium.

  In the display element related to the present invention, it is preferable that a polarizing plate is disposed on the opposite side of the pair of substrates from the surface facing the medium in at least one of the substrates. According to said structure, it becomes possible to modulate a transmittance | permeability by applying an electric field to a medium and expressing birefringence.

  In the display element according to the present invention, it is preferable that one of the pair of substrates includes an electric field applying unit that applies an electric field substantially parallel to the substrate surface to the medium. According to the above configuration, an electric field can be easily applied in a direction substantially perpendicular to light passing in a direction perpendicular to the substrate, that is, a direction parallel to the substrate surface. Refractive anisotropy can be easily extracted as a change in the optical signal.

  In the display element according to the present invention, the electric field applying means includes at least a pair of comb-shaped electrodes provided on the medium side of the pair of substrates and arranged to face each other in a direction in which the comb-tooth portions are engaged with each other. It is preferable.

  According to said structure, the said electric field application means is at least 1 pair of comb-shaped electrodes, Comprising: It is provided in the medium side in the said pair of board | substrate, and is opposingly arranged in the direction which a comb-tooth part mutually meshes | engages . Since the comb-tooth portions of the comb-shaped electrode are arranged so as to mesh with each other, the electric field generated by the comb-shaped electrode becomes an electric field substantially parallel to the substrate. Therefore, according to the above configuration, since the comb-shaped electrode applies an electric field substantially parallel to the substrate to the medium, a display element with a reduced driving voltage can be realized. The “comb-shaped electrode” refers to an electrode in which a plurality of electrodes (comb tooth portions) are extended from one electrode (comb root portion) in a predetermined direction with respect to the longitudinal direction.

  In the display element according to the present invention, the comb tooth portion preferably has a wedge shape. The “wedge shape” refers to a shape in which the comb tooth portion is bent at a predetermined angle. According to the above configuration, the wedge-shaped comb teeth of the comb-shaped electrode are disposed so as to be engaged with each other, so that the electric field generated by the comb-shaped electrode has an electric field application direction of at least 2 Become a direction.

  Therefore, according to the above configuration, there are medium domains in which the direction of optical anisotropy of the medium is different because there are at least two electric field application directions. For this reason, viewing angle characteristics can be improved in the display element.

  In the display element according to the present invention, the angle formed by the wedge-shaped bent portion is preferably less than 90 ° ± 10 °. “An angle formed by a wedge-shaped bent portion” refers to an angle at which a comb-tooth portion is bent. Therefore, according to the above configuration, since the angle formed by the wedge-shaped bent portion is less than 90 degrees ± 10 degrees, the directions of the optical anisotropy of the medium are substantially orthogonal to each other (approximately 90 degrees). There is a medium domain that forms an angle. Therefore, it becomes possible to compensate each other for the coloring phenomenon of the oblique viewing angle in each medium domain. Therefore, it is possible to realize a display element that can further improve the viewing angle characteristics without impairing the transmittance.

  In the display element related to the present invention, it is preferable that an alignment film is disposed on a surface of at least one of the pair of substrates facing the medium. The alignment film is preferably an organic thin film, and the alignment film is particularly preferably made of polyimide.

  According to said structure, the orientation direction of a medium in the vicinity of the interface with the said alignment film of the said medium can be prescribed | regulated reliably in a desired direction. In addition, in a state where the liquid crystal phase is developed in the medium, the molecules constituting the medium can be reliably aligned in a desired direction.

  In the display element related to the present invention, the alignment film is preferably subjected to a horizontal alignment process in parallel or antiparallel to the substrate. Since the horizontal alignment process is performed in parallel or anti-parallel to the substrate, the contrast can be maximized, and for example, the black luminance can be further reduced. In the present invention, “parallel” means that the alignment treatment directions are parallel and the same direction, and “anti-parallel” means that the alignment treatment directions are parallel and opposite (reverse). This case shall be shown.

  In the display element according to the present invention, it is preferable that the medium has an alignment order equal to or less than the wavelength of light when no electric field is applied. If the alignment order is less than the wavelength of light, it is optically isotropic. Therefore, by using a medium in which the alignment order is equal to or less than the wavelength of light when no electric field is applied, it is possible to reliably change the display state when no voltage is applied and when a voltage is applied.

  In the display element according to the present invention, the medium preferably contains a liquid crystal substance. By applying an electric field to the liquid crystalline substance, the fine structure is distorted and optical modulation can be induced.

  In the display device related to the present invention, the medium may have an ordered structure exhibiting cubic symmetry.

  The medium may be composed of molecules exhibiting a cubic phase or a smectic D phase.

  The medium may be made of a liquid crystal microemulsion.

  The medium may be composed of a lyotropic liquid crystal exhibiting a micelle phase, a reverse micelle phase, a sponge phase, or a cubic phase.

  The medium may be composed of a liquid crystal fine particle dispersion system exhibiting a micelle phase, reverse micelle phase, sponge phase, or cubic phase.

  The medium may be a dendrimer.

  The medium may be composed of molecules exhibiting a cholesteric blue phase.

  The medium may be composed of molecules exhibiting a smectic blue phase.

  In any of the above substances, the optical anisotropy changes when an electric field is applied. Therefore, any of the above substances can be used as the medium.

  As described above, the display element according to the present invention is sandwiched between a pair of substrates, at least one of which is transparent, and exhibits optical isotropy when no electric field is applied, and optically when an electric field is applied. The display element includes a medium exhibiting anisotropy, and the medium includes a chiral agent as a chiral substance. Further, the medium has an alignment order that is equal to or less than the optical wavelength of light when no electric field is applied. By including a chiral agent in the medium, the medium and the chiral agent spontaneously take a twisted structure, and the structure is stabilized. As a result, it is possible to realize a display element in which the Kerr effect is stabilized.

(A) is sectional drawing which shows typically schematic structure of the principal part of the display element concerning one Embodiment of this invention in a voltage no application state, (b) is the said display element in a voltage application state. It is sectional drawing which shows the schematic structure of the principal part typically. It is a figure explaining an example of the electrode structure in the said display element, and the relationship between this electrode structure and a polarizing plate absorption axis. It is a schematic diagram which shows an example of the reverse micelle phase mixing system of liquid crystal microemulsion. It is a schematic diagram which shows the other example of the reverse micelle phase mixing system of liquid crystal microemulsion. It is a classification diagram of a lyotropic liquid crystal phase. It is a schematic diagram which shows the various structures of the medium of the display element of this invention. (A) is principal part sectional drawing which shows typically the structure of the said display element in an electric field no application state, (b) is principal part sectional drawing which shows typically the structure of the said display element in a voltage application state. (C) is a graph which shows the relationship between the applied voltage and the transmittance | permeability in the display element shown to (a) * (b). The difference in display principle between a display element that displays using the change in optical anisotropy due to the application of an electric field and a conventional liquid crystal display element is described as the average refractive index of the medium when no voltage is applied and when a voltage is applied. It is sectional drawing typically shown in the shape of an ellipsoid and the principal axis direction, (a) is a cross section at the time of no voltage application of the display element which displays using the change of the optical anisotropy by the application of an electric field (B) is a cross-sectional view when a voltage is applied to the display element shown in (a), (c) is a cross-sectional view when no voltage is applied to a TN liquid crystal display element, and (d) is a cross-sectional view. It is sectional drawing at the time of the voltage application of the liquid crystal display element shown to (c), (e) is sectional drawing at the time of no voltage application of the VA-type liquid crystal display element, (f) is the liquid crystal display shown to (e). It is sectional drawing at the time of the voltage application of an element, (g) is the interruption at the time of no voltage application of the liquid crystal display element of an IPS system. A diagram, (h) is a cross-sectional view of when a voltage is applied the liquid crystal display device shown in (g).

  An embodiment of the present invention, including a reference embodiment related to the present invention, will be described with reference to FIGS. 1 to 8 as follows.

  FIG. 1A is a cross-sectional view schematically showing a schematic configuration of a main part of the display element according to the present embodiment in a voltage non-application state (OFF state), and FIG. It is sectional drawing which shows typically schematic structure of the principal part of the display element concerning this Embodiment in an ON state.

  As shown in FIGS. 1 (a) and 1 (b), the display element according to the present embodiment includes a pair of substrates (hereinafter referred to as a pixel substrate 11 and a counter substrate 12) that are arranged to face each other and at least one of them is transparent. And a cell structure in which a medium layer 3 made of a medium that is optically modulated by applying an electric field (hereinafter referred to as medium A) is sandwiched between the pair of substrates as an optical modulation layer. Yes.

  Further, as shown in FIGS. 1A and 1B, the pixel substrate 11 and the counter substrate 12 have substrates 1 and 2 as medium holding means (optical modulation layer holding means), respectively. A configuration in which polarizing plates 6 and 7 are respectively provided on the outside of the substrates 1 and 2 (outside of the pixel substrate 11 and the counter substrate 12), that is, on the surface opposite to the facing surfaces of both the substrates 1 and 2. Have.

  Of the pair of substrates 1 and 2, at least one substrate is made of a transparent substrate such as a glass substrate having translucency, and the other substrate of the pair of substrates 1 and 2 is the other substrate. 2 is an electric field applying means for applying an electric field (lateral electric field) substantially parallel to the substrate 1 to the medium layer 3 as shown in FIGS. 1 (a) and 1 (b). The electrodes 4 and 5 are arranged to face each other.

  The electrodes 4 and 5 are made of an electrode material such as a transparent electrode material such as ITO (indium tin oxide). In the present embodiment, for example, the line width is 5 μm, the distance between electrodes (electrode interval) is 5 μm, and the thickness is 0. It is set to 6 μm. However, the electrode material, the line width, the distance between the electrodes, and the thickness are merely examples, and are not limited thereto. An example of the electrodes 4 and 5 is not particularly limited as long as the medium layer 3 can be applied and the medium A of the medium layer 3 can be optically modulated. For example, the substrate 1 And an electrode for applying an electric field (transverse electric field) substantially parallel to the medium layer 3 to the medium layer 3.

  Hereinafter, an example of the electrode structure of the electrodes 4 and 5 will be described with reference to FIG. FIG. 2 is a diagram for explaining the relationship between the structure of the electrodes 4 and 5 and the polarizing plate absorption axis in the display element of the present invention.

  The electrodes 4 and 5 are comb-shaped electrodes in which the comb-tooth portions 4a and 5a have a wedge shape and are arranged so as to face each other. The “wedge shape” refers to a shape in which the comb tooth portions 4a and 5a are bent at a predetermined angle α. Further, the comb-tooth portions 4a and 5a may have a shape having a plurality of wedge shapes as shown in FIG. Thus, an example of a shape having a plurality of wedge-shaped shapes is a sawtooth shape.

  Here, the “comb-shaped electrode” refers to an electrode in which a plurality of electrodes (comb tooth portions) 4a extend from one electrode (comb root portion) 4b in a predetermined direction with respect to the longitudinal direction. Further, as shown in FIG. 2, the “sawtooth shape” refers to a shape in which the comb tooth portion is extended while being alternately bent at an angle α in a direction away from the longitudinal direction of the comb root portion 4b.

  As shown in FIG. 2, the electrode 4 includes a comb tooth portion 4a and a comb root portion 4b. The comb tooth portions 4a extend while being alternately bent in a direction away from the longitudinal direction of the comb root portion 4b. The comb-tooth portion 4a has a configuration in which the saw-tooth unit 4e formed by the saw-tooth component 4c and the saw-tooth component 4d is continuously extended. The sawtooth unit 4e has a configuration in which the sawtooth component 4c and the sawtooth component 4d are bent so as to form an angle α. The comb-teeth portion 4a of the electrode 4 has a configuration in which it is extended while being alternately bent at equal intervals in a direction away from the longitudinal direction of the comb root portion 4b.

  Similarly to the comb-tooth portion 4a of the electrode 4, the comb-tooth portion 5a of the electrode 5 has a configuration in which the saw-tooth unit 5e formed by the saw-tooth component 5c and the saw-tooth component 5d is continuously extended, and the saw-tooth unit 5e. The sawtooth component 5c and the sawtooth component 5d are bent so as to form an angle α.

  The angle α in the electrodes 4 and 5 is preferably less than 90 ° ± 10 °, more preferably less than 90 ° ± 5 °, and most preferably 90 °.

  Further, as shown in FIG. 2, the electrode 4 and the electrode 5 are disposed to face each other so that the respective comb tooth portions 4a and the comb tooth portions 5a are engaged with each other. That is, the electrode 4 and the electrode 5 are disposed to face each other so that the sawtooth component 4c and the sawtooth component 4d in the comb tooth portion 4a are parallel to the saw tooth component 5c and the saw tooth component 5d in the comb tooth portion 5a, respectively. Therefore, when a voltage is applied to the electrodes 4 and 5, two electric fields having different electric field application directions are formed. That is, an electric field between the sawtooth component 4c and the sawtooth component 5c (electric field application direction 45c in FIG. 2) and an electric field between the sawtooth component 4d and the sawtooth component 5d (electric field application direction 45d in FIG. 2) are formed. The

  In addition, it can be said that the sawtooth unit 4e and the sawtooth unit 5e have a "<" shape. Therefore, it can be said that the “sawtooth shape” is a shape in which a “<” shape component corresponding to a sawtooth unit extends in a direction away from the longitudinal direction of the comb root portion. Moreover, it can be said that the “comb portion is a sawtooth shape” is a zigzag line shape in which the comb portion has a “<” shape.

  Further, it can be said that the sawtooth unit 4e and the sawtooth unit 5e have a shape of “v” from the shape thereof. Therefore, the “sawtooth shape” can be said to be a shape in which the “v” -shaped component corresponding to the sawtooth unit extends in a direction away from the longitudinal direction of the comb root portion. Moreover, it can be said that the “comb portion is a sawtooth shape” is a zigzag line shape in which the comb portion has a “v” shape.

  As shown in FIG. 2, the electric field application direction 45c and the electric field application direction 45d are perpendicular to each other. For this reason, there are medium domains in which the directions of optical anisotropy of the medium A are orthogonal to each other (at an angle of 90 degrees), and the display element compensates for the coloring phenomenon of the oblique viewing angle in each medium domain. Is possible.

  In the present embodiment, the polarizing plates 6 and 7 respectively provided on the substrates 1 and 2 are arranged so that the polarizing plate absorption axis directions are orthogonal to each other, as shown in FIG. The polarizing plate absorption axes 6a and 7a in the polarizing plates 6 and 7 form an angle of 45 degrees with respect to the above-described two electric field application directions 45c and 45d formed by the electrodes 4 and 5, respectively.

  Thus, the electrodes 4 and 5 provided on the substrate 1 are provided so that the electric field application direction is at least two directions. Since there are at least two electric field application directions, there are medium domains in the medium layer 3 in which the direction of optical anisotropy of the medium A is different. For this reason, the viewing angle characteristic is improved in the display element. When the electrodes 4 and 5 are provided so that the at least two electric field application directions are perpendicular to each other, the directions of the optical anisotropy of the medium A are orthogonal to each other (make an angle of 90 degrees). There is a medium domain. For this reason, in the display element, it becomes possible to compensate each other for the coloring phenomenon of the oblique viewing angle in each medium domain. Therefore, it is possible to realize a display element that can further improve the viewing angle characteristics without impairing the transmittance. When the direction of optical anisotropy of the medium A is orthogonal to each other and the angle between the polarizing plates 6 and 7 and the polarizing plate absorption axes 6a and 7a is 45 degrees, The degree of compensation for the coloring phenomenon of the oblique viewing angle is increased, and a display element that further improves the viewing angle characteristics can be realized.

  Further, on the surface of the substrate 1 facing the substrate 2, that is, on the surface of the pixel substrate 11 facing the counter substrate 12, a rubbing alignment film 8 (dielectric thin film) is provided on the electrode. 4 and 5 so as to cover the entire surface of the substrate 1 facing the substrate 2.

  An alignment film 9 (dielectric thin film) that has been subjected to rubbing treatment on the surface of the substrate 2 facing the substrate 1, that is, on the surface of the counter substrate 12 facing the pixel substrate 11, also has the substrate. 2 over the entire surface facing the substrate 1.

  As the rubbing treatment, the alignment treatment direction of the alignment films 8 and 9 is such that the rubbing direction thereof coincides with one of the absorption axes 6a and 7a of the polarizing plates 6 and 7. A horizontal rubbing process (horizontal alignment process) in the in-plane direction of the substrate is performed.

In the display element according to the present embodiment, as shown in FIG. 1B, the medium layer 3 exhibits optical anisotropy due to an increase in the degree of orientational order in the direction of electric field application, and the transmittance changes. It can function as a shutter-type display element. Therefore, with respect to the polarizing plate absorption axis directions orthogonal to each other, the anisotropic direction gives the maximum transmittance when forming an angle of 45 degrees. Note that the transmittance (P) when the orientation in which the optical anisotropy of the medium A develops exists at an angle of ± θ (degrees) with respect to the polarizing plate absorption axis is P (%) = Sin ² ( 2θ). If the transmittance when θ is 45 degrees is 100%, it is felt that the human eye has the maximum luminance when the transmittance is approximately 90% or more. If θ is 35 degrees <θ <55 degrees, it is felt that the human eye has the maximum luminance. That is, as shown in the present embodiment, in a display element in which an electric field is applied, for example, substantially parallel to the substrate 1, the polarizing plate absorption axis direction, in other words, the alignment treatment direction (rubbing direction) in the horizontal alignment treatment is The transmittance can be maximized by forming an angle of less than 45 degrees ± 10 degrees, more preferably less than 45 degrees ± 5 degrees, and most preferably 45 degrees with respect to the direction of electric field application by the electrodes 4 and 5. it can.

  In the present embodiment, as shown in FIG. 2, the polarizing plates 6 and 7 provided on both the substrates 1 and 2 are polarized in the polarizing plates 6 and 7, respectively, while the polarizing plate absorption axis directions are orthogonal to each other. The plate absorption axis and the electrode extending direction of the electrodes 4 and 5 (comb portions 4a and 5a) are formed so as to form an angle of 45 degrees.

  Therefore, in the display element, the electric field application direction by the electrodes 4 and 5 forms an angle of 45 degrees with the polarizing plate absorption axis direction of the polarizing plates 6 and 7 and the rubbing direction of the alignment films 8 and 9.

  In the present embodiment, as shown in FIG. 2, the rubbing directions in the alignment films 8 and 9 are parallel to each other as long as they coincide with the polarizing plate absorption axis of the polarizing plates 6 and 7 ( The orientation (treatment) directions of each other may be parallel and the same direction), and anti-parallel (anti-parallel), that is, the orientation (treatment) directions of each other are parallel and opposite (reverse). It may be present or orthogonal.

  Each of the alignment films 8 and 9 used in the present embodiment may be an organic film or an inorganic film, and improves the degree of alignment order of the molecules 10 constituting the medium A. As long as the molecules 10 can be aligned in a desired direction, the alignment is not particularly limited. However, when the alignment films 8 and 9 are formed of an organic thin film, a good alignment effect is exhibited. Therefore, it is more desirable to use an organic thin film as the alignment films 8 and 9. Among such organic thin films, polyimide has high stability and reliability, and exhibits an extremely excellent alignment effect. Therefore, by using polyimide as an alignment film material, a display element having better display performance is provided. be able to.

  A commercially available horizontal alignment film can be used as the alignment films 8 and 9. Further, the alignment films 8 and 9 may have a functional group having photosensitivity (hereinafter referred to as a photofunctional group) because the alignment control is easy. Examples of the photofunctional group include a cinnamate system and a chalcone system that perform a dimerization reaction, and an azo system that performs an isomerization reaction, but the present invention is not limited thereto.

  When the alignment films 8 and 9 have a photofunctional group, the surfaces of the pixel substrate 11 and the counter substrate 12, that is, the surfaces of the alignment films 8 and 9 are irradiated with polarized ultraviolet rays (hereinafter referred to as polarized ultraviolet light irradiation). ) To develop the alignment regulating force, the desired alignment treatment can be easily performed.

  In the display element, for example, the pixel substrate 11 and the counter substrate 12 are bonded to each other with a sealing agent (not shown) through a spacer such as a plastic bead or a glass fiber spacer (not shown) as necessary. The medium A is encapsulated.

The medium A used in the present embodiment is a medium whose optical anisotropy changes when an electric field is applied. When an electric field E _j is applied to the material from the outside, an electric displacement D _ij = ε _ij · E _j is generated, and at that time, a slight change is also seen in the dielectric constant (ε _ij ). Since the square of the refractive index (n) is equivalent to the dielectric constant at the frequency of light, the medium A can also be said to be a substance whose refractive index changes when an electric field is applied.

  As described above, the display element according to the present embodiment performs display using a phenomenon (electro-optic effect) in which the refractive index of a substance is changed by an external electric field. Unlike liquid crystal display elements that utilize the fact that they rotate together, the direction of optical anisotropy hardly changes, and the degree of optical anisotropy changes (mainly electronic polarization and orientation polarization). Is displayed.

  As the medium A, a substance exhibiting the Pockels effect or the Kerr effect is optically isotropic when the electric field is not applied. Therefore, it is desirable that the birefringence be increased.

  The Pockels effect and the Kerr effect (which are themselves observed in the isotropic phase state) are electro-optic effects that are proportional to the primary or secondary electric field, respectively, and are in the isotropic phase when no voltage is applied. Although optically isotropic, in the voltage application state, in the region where an electric field is applied, the long axis direction of the compound molecules is oriented in the electric field direction, and birefringence is expressed, thereby modulating the transmittance. be able to. For example, in the case of a display method using a substance exhibiting the Kerr effect, by controlling the bias of electrons within one molecule by applying an electric field, each randomly arranged individual molecule rotates and becomes oriented. Is advantageous in that the response speed is very fast and the molecules are arranged randomly, and there is no viewing angle limitation. The medium A that is roughly proportional to the primary or secondary electric field can be treated as a substance exhibiting the Pockels effect or the Kerr effect.

  Examples of the substance exhibiting the Pockels effect include, but are not limited to, organic solid materials such as hexamine. As the medium A, various organic materials and inorganic materials exhibiting the Pockels effect can be used.

  Moreover, as a substance which shows a Kerr effect, following structural formula (1)-(7)

Although the liquid crystalline substance shown by these is mentioned, it does not specifically limit.

  The Kerr effect is observed in a medium transparent to incident light. For this reason, the substance showing the Kerr effect is used as a transparent medium. Usually, a liquid crystalline substance shifts from a liquid crystal phase having a short-range order to an isotropic phase having random orientation at a molecular level as the temperature rises. In other words, the Kerr effect of liquid crystalline substances is not a nematic phase, but a phenomenon seen in liquids in the isotropic phase state above the liquid crystal phase-isotropic phase temperature. The liquid crystalline substance is used as a transparent dielectric liquid. Is done.

  A dielectric liquid such as a liquid crystal substance is in an isotropic phase state as the use environment temperature (heating temperature) by heating is higher. Therefore, when a dielectric liquid such as a liquid crystal substance is used as the medium, in order to use the dielectric liquid in a liquid state that is transparent, that is, transparent to visible light, for example, (1) medium layer 3 may be provided with heating means such as a heater (not shown), and the dielectric liquid may be heated to the clearing point or higher by the heating means. (2) Thermal radiation from the backlight, The dielectric liquid may be used by heating it above its clearing point by light conduction and / or heat conduction from the peripheral driving circuit (in this case, the backlight or the peripheral driving circuit functions as a heating means). (3) A sheet heater (heating means) may be bonded to at least one of the substrates 1 and 2 as a heater and heated to a predetermined temperature. Furthermore, in order to use the dielectric liquid in a transparent state, a material having a clearing point lower than the lower limit of the operating temperature range of the display element may be used.

  The medium A preferably contains a liquid crystalline substance. When a liquid crystalline substance is used as the medium A, the liquid crystalline substance is a transparent liquid that shows a macroscopic isotropic phase. However, microscopically, it is desirable to include a cluster which is a molecular group having a short-range order arranged in a certain direction. Since the liquid crystalline substance is used in a state transparent to visible light, the cluster is also used in a state transparent (optically isotropic) to visible light. Further, the liquid crystalline substance may be a single substance exhibiting liquid crystallinity, or may exhibit liquid crystallinity by mixing a plurality of substances, and other non-liquid crystalline substances may be included in these substances. May be mixed.

  For this purpose, as described above, the display element may be temperature-controlled using a heating means such as a heater, or the medium layer 3 may be divided into small areas using a polymer material or the like. The liquid crystalline substance may be a fine droplet having a diameter smaller than the wavelength of light, for example, the diameter of the liquid crystalline substance is 0.1 μm or less, and the transparent state is suppressed by suppressing light scattering. Alternatively, a liquid crystalline compound exhibiting a transparent isotropic phase at the use environment temperature (room temperature) may be used. Light scattering can be ignored when the diameter of the liquid crystalline substance, and further, the diameter (major axis) of the cluster is 0.1 μm or less, that is, smaller than the wavelength of light (incident light wavelength). Therefore, for example, if the diameter of the cluster is 0.1 μm or less, the cluster is also transparent to visible light.

  The medium A is not limited to a substance exhibiting the Pockels effect or the Kerr effect as described above. For this reason, the medium A has an ordered structure in which the molecular arrangement has cubic symmetry of a scale equal to or smaller than the wavelength of light (for example, nanoscale), and is optically isotropic cubic phase (non-patent document) Reference 1/3/6) may be included. The cubic phase is one of the liquid crystal phases of the liquid crystalline substance that can be used as the medium A. As the liquid crystalline substance exhibiting the cubic phase, for example, the following structural formula (8)

BABH8 etc. which are shown by these. When an electric field is applied to such a liquid crystalline substance, the fine structure is distorted and optical modulation can be induced.

  BABH8 shows a cubic phase composed of an ordered structure having cubic symmetry of a scale below the wavelength of light in a temperature range of 136.7 ° C. or more and 161 ° C. or less. The BABH 8 has an ordered structure equal to or less than the wavelength of light, and exhibits optical isotropy when no voltage is applied in the above temperature range, whereby good black display can be performed under crossed Nicols.

  On the other hand, when a voltage is applied between the electrodes 4 and 5 (comb-shaped electrodes) while controlling the temperature of the BABH 8 to 136.7 ° C. or more and 161 ° C. or less using, for example, the heating means described above, cubic symmetry is obtained. Distortion occurs in the structure (ordered structure). That is, the BABH8 is isotropic in the above temperature range when no voltage is applied, and anisotropy is exhibited when a voltage is applied.

  As a result, birefringence occurs in the medium layer 3, so that the display element can perform good white display. Note that the direction in which birefringence occurs is constant, and its magnitude changes with voltage application. The voltage transmittance curve showing the relationship between the voltage applied between the electrodes 4 and 5 (comb electrodes) and the transmittance is a temperature range of 136.7 ° C. or higher and 161 ° C. or lower, that is, a wide temperature range of about 20K. Becomes a stable curve. For this reason, when the BABH 8 is used as the medium A, temperature control can be performed very easily. That is, since the medium layer 3 made of BABH8 is a thermally stable phase, it does not exhibit abrupt temperature dependence, and temperature control is extremely easy.

  Further, as the medium A, it is also possible to realize a system that is optically isotropic, in which liquid crystal molecules are filled with aggregates that are radially aligned with a size equal to or smaller than the wavelength of light. As a technique, a liquid crystal microemulsion described in Non-Patent Document 2 or a liquid crystal / fine particle dispersion system (a mixed system in which fine particles are mixed in a solvent (liquid crystal), hereinafter simply referred to as a liquid crystal fine particle dispersion system) is applied. It is also possible. When an electric field is applied to these, a set of radial orientations is distorted, and optical modulation can be induced.

  Any of these liquid crystalline substances may be liquid crystalline as a single substance, or may be liquid crystalline by mixing a plurality of substances. Other non-liquid crystalline substances may be mixed. Furthermore, a polymer / liquid crystal dispersion material can also be applied. Moreover, you may add a gelatinizer.

  The medium A preferably contains a polar molecule. For example, nitrobenzene or the like is suitable as the medium A. Nitrobenzene is also a type of medium that exhibits the Kerr effect.

  Hereinafter, examples of the substance or the form of the substance that can be used as the medium A will be shown, but the present invention is not limited to the following examples.

[Smectic D phase (SmD)]
The smectic D phase (SmD) is one of liquid crystal phases of a liquid crystalline material that can be used as the medium A, has a three-dimensional lattice structure, and has a lattice constant equal to or less than the wavelength of light. For this reason, the smectic D phase is optically isotropic.

  Examples of liquid crystalline substances exhibiting a smectic D phase include the following general formulas (9) and (10) described in Non-Patent Document 1 or Non-Patent Document 3.

ANBC16 represented by the following. In the general formulas (6) and (7), m represents an arbitrary integer, specifically, m = 16 in the general formula (6), m = 15 in the general formula (7), and X Represents a —NO ₂ group.

  The ANBC16 exhibits a smectic D phase in a temperature range of 171.0 ° C. to 197.2 ° C. In the smectic D phase, a plurality of molecules form a three-dimensional lattice such as jungle gym (registered trademark), and the lattice constant is equal to or less than the optical wavelength. For this reason, the smectic D phase is optically isotropic.

  In addition, when an electric field is applied to the ANBC 16 in the above temperature range in which the ANBC 16 exhibits a smectic D phase, the ANBC 16 molecules themselves have dielectric anisotropy, so that the molecules are distorted in the lattice structure as the molecules move in the direction of the electric field. . That is, the optical anisotropy appears in ANBC16. Note that the material is not limited to ANBC16, and any material exhibiting a smectic D phase can be applied as the medium A of the display element according to the present embodiment.

[Liquid crystal microemulsion]
A liquid crystal microemulsion is an O / W type microemulsion proposed in Non-Patent Document 2 (a system in which water is dissolved in oil in the form of water droplets in an oil, and the oil becomes a continuous phase). A generic term for a system (mixed system) in which oil molecules are replaced with thermotropic liquid crystal molecules.

  Specific examples of the liquid crystal microemulsion include, for example, pentylcyanobiphenyl (5CB), which is a thermotropic liquid crystal showing a nematic liquid crystal phase, and a lyotropic (lyotropic) liquid crystal showing a reverse micelle phase described in Non-Patent Document 2. There is a mixed system with an aqueous solution of didodecyl ammonium bromide (DDAB). This mixed system has a structure represented by schematic views as shown in FIGS.

  In this mixed system, the diameter of reverse micelles is typically about 5 nm (50 mm), and the distance between the reverse micelles is about 20 nm (200 mm). These scales are about an order of magnitude smaller than the wavelength of light. In addition, reverse micelles exist randomly in three-dimensional space, and 5CB are radially oriented around each reverse micelle. Therefore, this mixed system is optically isotropic.

  When an electric field is applied to a medium composed of this mixed system, the molecule itself tends to move in the direction of the electric field because there is dielectric anisotropy in 5CB. That is, orientation anisotropy appears in a system that is optically isotropic because it is oriented radially around a reverse micelle, and optical anisotropy appears. The liquid crystal microemulsion is not limited to the above-described mixed system, and is optically isotropic when no voltage is applied, and exhibits optical anisotropy when voltage is applied. It can be applied as the medium A.

[Lyotropic LCD]
As the medium A, a lyotropic liquid crystal having a specific phase can be applied. The lyotropic liquid crystal means a liquid crystal of another component system in which main molecules forming the liquid crystal are dissolved in a solvent having other properties (such as water or an organic solvent). The specific phase is a phase that is optically isotropic when no electric field is applied. Examples of such a specific phase include a micelle phase, a sponge phase, a cubic phase, and a reverse micelle phase described in Non-Patent Document 4. FIG. 5 shows a classification diagram of the lyotropic liquid crystal phase.

  Surfactants that are amphiphilic substances include substances that develop a micelle phase. For example, an aqueous solution of sodium decyl sulfate, which is an ionic surfactant, an aqueous solution of potassium palmitate, and the like form spherical micelles. Further, in a mixed solution of polyoxyethylene nonylphenyl ether, which is a nonionic surfactant, and water, micelles are formed by the nonylphenyl group acting as a hydrophobic group and the oxyethylene chain acting as a hydrophilic group. In addition, micelles are formed even in an aqueous solution of a styrene-ethylene oxide block copolymer.

  For example, spherical micelles exhibit a spherical shape by packing molecules (forming molecular aggregates) in all spatial directions. In addition, since the size of the spherical micelle is equal to or smaller than the optical wavelength, it appears isotropic without showing anisotropy in the optical wavelength region. However, when an electric field is applied to such spherical micelles, the spherical micelles are distorted, so that anisotropy is expressed. Therefore, a lyotropic liquid crystal having a spherical micelle phase can be applied as the medium A of the display element. In addition, not only the spherical micelle phase but also a micelle phase having other shapes, that is, a string-like micelle phase, an elliptical micelle phase, a rod-like micelle phase, and the like can be used to obtain substantially the same effect.

  Further, it is generally known that reverse micelles in which a hydrophilic group and a hydrophobic group are exchanged are formed depending on the conditions of concentration, temperature, and surfactant. Such reverse micelles optically show the same effects as micelles. Therefore, by applying the reverse micelle phase as the medium A, an effect equivalent to that obtained when the micelle phase is used is obtained. The liquid crystal microemulsion described above is an example of a lyotropic liquid crystal having a reverse micelle phase (reverse micelle structure).

  In addition, the aqueous solution of pentaethylene glycol-dodecyl ether, which is a nonionic surfactant, has a concentration and temperature range showing a sponge phase and a cubic phase as shown in FIG. Such a sponge phase or cubic phase has an order equal to or less than the optical wavelength, and is therefore a transparent material in the optical wavelength region. That is, a medium composed of these phases is optically isotropic. When a voltage is applied to a medium composed of these phases, the orientation order changes and optical anisotropy appears. Therefore, a lyotropic liquid crystal having a sponge phase or a cubic phase can be applied as the medium A of the display element.

[Liquid crystal fine particle dispersion]
The medium A is, for example, a liquid crystal fine particle dispersion system in which latex particles having a diameter of about 10 nm (100 mm) whose surface is modified with a sulfate group are mixed in an aqueous solution of a nonionic surfactant pentaethylene glycol-dodecyl ether. There may be. In the liquid crystal fine particle dispersion system, a sponge phase is expressed. However, the medium A used in the present embodiment may be a liquid crystal fine particle dispersion system that expresses the aforementioned micelle phase, cubic phase, reverse micelle phase, or the like. In addition, by using the DDAB in place of the latex particles, an alignment structure similar to the liquid crystal microemulsion described above can be obtained.

[Dendrimer]
A dendrimer is a three-dimensional hyperbranched polymer having a branch for each monomer unit. Since dendrimers have many branches, they have a spherical structure when the molecular weight exceeds a certain level. Since this spherical structure has an order equal to or less than the optical wavelength, the spherical structure is a transparent material in the optical wavelength region, and the orientation order is changed by application of a voltage to exhibit optical anisotropy. Therefore, a dendrimer can also be applied as the medium A of the display element according to this embodiment. Further, by using the dendrimer in place of DDAB in the liquid crystal microemulsion described above, an alignment structure similar to that of the liquid crystal microemulsion described above can be obtained. The medium thus obtained can also be applied as the medium A.

[Cholesteric blue phase]
A cholesteric blue phase can be used as the liquid crystalline substance. FIG. 6 shows a schematic configuration of the cholesteric blue phase.

  As shown in FIG. 6, the cholesteric blue phase is known to have a three-dimensional periodic structure in the helical axis, and the structure has high symmetry (for example, non-patent Reference 6). Since the cholesteric blue phase has an order equal to or less than the optical wavelength, the cholesteric blue phase is a substantially transparent substance in the optical wavelength region, and the orientation order is changed by application of a voltage to exhibit optical anisotropy. That is, the cholesteric blue phase is optically substantially isotropic, and the liquid crystal molecules tend to move in the electric field direction when an electric field is applied, so that the lattice is distorted and anisotropy is expressed. Therefore, a cholesteric blue phase can be applied as the medium A.

  In addition, as a substance showing a cholesteric blue phase, for example, “JC1041” (trade name, mixed liquid crystal manufactured by Chisso Corporation) is 48.2 wt%, “5CB” (4-cyano-4′-pentylbiphenyl, nematic liquid crystal). Is a composition obtained by mixing 47.4% by weight of a chiral agent “ZLI-4572” (trade name, manufactured by Merck & Co., Inc.) at a ratio of 4.4% by weight. The composition exhibits a cholesteric blue phase in the temperature range of 330.7K to 331.8K.

[Smectic blue phase]
In addition, a smectic blue phase can be applied as the liquid crystalline substance. FIG. 6 shows a schematic configuration of the smectic blue phase.

As shown in FIG. 6, the smectic blue (BP _Sm ) phase has a highly symmetric structure as in the case of the costic blue phase (see, for example, Non-Patent Documents 5 and 6). Further, since it has an order equal to or less than the optical wavelength, it is a substantially transparent substance in the optical wavelength region, and the orientation order is changed by application of a voltage, and optical anisotropy is exhibited. That is, the smectic blue phase is optically substantially isotropic, and the liquid crystal molecules tend to move in the direction of the electric field when an electric field is applied, so that the lattice is distorted and anisotropy is expressed. Therefore, a smectic blue phase can be applied as the medium A.

In addition, as a substance which shows a smectic blue phase, FH / FH / HH-14BTMHC etc. which are described in the nonpatent literature 5 are mentioned, for example. The material exhibits a BP _Sm 3 phase at 74.4 ° C. to 73.2 ° C., a BP _Sm 2 phase at 73.2 ° C. to 72.3 ° C., and a BP _Sm 1 phase at 72.3 ° C. to 72.1 ° C. . Since the BP _Sm phase has a highly symmetric structure as shown in Non-Patent Document 6, it generally exhibits optical isotropy. Further, when an electric field is applied to the substance FH / FH / HH-14BTMHC, the lattice is distorted by the liquid crystal molecules moving in the direction of the electric field, and the substance exhibits anisotropy. Therefore, the same substance can be used as the medium A of the display element according to this embodiment.

  As described above, the substance that can be used as the medium A in the display element according to the present embodiment may be any substance that changes in optical anisotropy (refractive index, degree of orientation order) by application of an electric field. , A cubic phase, a smectic D phase, a cholesteric blue phase, a smectic blue phase, or a lyotropic liquid crystal exhibiting any of a micelle phase, a reverse micelle phase, a sponge phase, a cubic phase, or A liquid crystal fine particle dispersion may be used. The medium A may be a liquid crystal microemulsion, a dendrimer (dendrimer molecule), an amphiphilic molecule, a copolymer, or a polar molecule other than the above.

  The medium is not limited to a liquid crystalline substance, and preferably has an ordered structure (alignment order) that is equal to or less than the wavelength of light when no voltage is applied. If the ordered structure is less than the wavelength of light, it is optically isotropic. Therefore, by using a medium whose ordered structure is equal to or less than the wavelength of light when no voltage is applied, it is possible to reliably change the display state when no voltage is applied and when a voltage is applied.

  The medium A of the present invention further contains a chiral agent. The chiral agent has a twisted structure with adjacent molecules in the liquid crystal substance. Then, the energy of interaction between molecules in the liquid crystal material is lowered, and the liquid crystal material spontaneously takes a twisted structure, and the structure is stabilized. Therefore, in the medium A containing a chiral agent, a sudden structural change does not occur in the vicinity of the isotropic phase-liquid crystal phase transition temperature, and a liquid crystal phase having optical isotropy appears and the phase transition temperature is lowered. There is an effect. Examples of such a chiral agent include ZLI-4572 (manufactured by Merck), C15 (manufactured by Merck), CN (manufactured by Merck), or CB15 (manufactured by Merck). However, it is not limited to these.

  The concentration of the chiral agent in the medium A is not particularly limited as long as it can stabilize the structure of the liquid crystalline substance in the medium A. For example, the concentration is preferably 1 to 15% by weight, 3 to 10% by weight is particularly preferred. However, the concentration of the chiral agent in the medium A can be appropriately set according to the type of the chiral agent, the configuration of the display element, the design, or the like.

  In the present invention, the chiral agent is not added to the medium A, and the medium A itself may be made of a chiral substance having chirality (optically active). In this case, since the medium A is optically active, the medium A itself spontaneously takes a twisted structure and becomes stable. The chiral substance having chirality may be a compound having optically active carbon in the molecule. Specifically, the following structural formula (11)

4- (2-methylbutyl) phenyl-4'-octylbiphenyl-4-carboxylate (abbreviation: 8SI *) represented by That is, the medium A of the present invention only needs to have chirality and may be optically active.

  Here, as shown in FIG. 7A, when no voltage is applied, the twisted structure fills the space isotropically, so that the display element is optically isotropic. On the other hand, as shown in FIG. 7B, when a voltage is applied, the major axis direction of the molecules gradually turns to the direction of the electric field. In accordance with this, the twisted structure is also unwound. That is, the structure is changed by application of a voltage, thereby causing optical anisotropy.

  Thus, the medium A has a twisted structure by adding a chiral agent to the medium A or using a chiral substance as the medium A. As a result, the Kerr constant does not change so much and the stability of the Kerr effect increases. By adding a chiral agent, the medium A can also induce either a left-handed twist or a right-handed twisted structure. In this case, the transmittance can be further improved.

  Next, the display principle of the display element according to this embodiment will be described with reference to FIGS. 1A and 1B, FIGS. 7A to 7C, and FIGS. 8A to 8G. This will be described below. In the following description, a transmissive display element is mainly used as the display element, which is optically isotropic and preferably isotropic when no electric field is applied. The case where a substance exhibiting sex is used will be described as an example, but the present invention is not limited to this.

  FIG. 7A is a main part plan view schematically showing the configuration of the display element according to the present embodiment in an electric field non-application state (OFF state), and FIG. 7B is a voltage application state (ON). It is a principal part top view which shows typically the structure of the said display element in a state. 7A and 7B show the configuration of one pixel in the display element, and the illustration of the configuration of the counter substrate 12 is omitted for convenience of explanation. The electrodes 4 and 5 may be comb-shaped electrodes as shown in FIG. 2, and are particularly limited as long as they can apply an electric field substantially parallel to the substrates 1 and 2. Is not to be done.

  Further, FIG. 7C is a graph showing the relationship between the applied voltage and the transmittance in the display elements shown in FIGS. 7A and 7B, and FIGS. The difference in display principle between a display element that performs display using a change in optical anisotropy due to application and a conventional liquid crystal display element is described as a medium when no voltage is applied (OFF state) and when a voltage is applied (ON state). 8 is a cross-sectional view schematically showing the shape of the average refractive index ellipsoid (shown by the shape of the cut surface of the refractive index ellipsoid) and the principal axis direction thereof, and FIGS. , A cross-sectional view of a display element that performs display using a change in optical anisotropy due to application of an electric field when no voltage is applied (OFF state), a cross-sectional view of the display element when a voltage is applied (ON state), TN Sectional view when no voltage is applied to (Twisted Nematic) type liquid crystal display element, TN type liquid crystal display element Sectional view when voltage is applied, sectional view of liquid crystal display element of VA (Vertical Alignment) mode when no voltage is applied, sectional view of liquid crystal display element of VA mode when voltage is applied, IPS (In Plane Switching) liquid crystal A cross-sectional view of the display element when no voltage is applied and a cross-sectional view of the IPS liquid crystal display element when a voltage is applied are shown.

In general, the refractive index in a material is not isotropic and varies depending on the direction. This anisotropy of the refractive index is in a direction parallel to the substrate surface (in-plane direction), the opposing direction of the electrodes 4 and 5, the direction perpendicular to the substrate surface (substrate normal direction), and parallel to the substrate surface. An arbitrary orthogonal coordinate system (X ₁ , X ₂ , X ₃ ) is used where the direction (in-plane direction of the substrate) and the direction perpendicular to the opposing direction of the electrodes 4 and 5 are x, y, and z directions, respectively. The following relational expression (1)

(N _ji = n _ij , i, j = 1,2,3)
It is shown by the ellipsoid (refractive index ellipsoid) represented by these. Here, when the above relational expression (1) is rewritten using the coordinate system (Y ₁ , Y ₂ , Y ₃ ) in the principal axis direction of the ellipsoid, the following relational expression (2)

Indicated by n ₁ , n ₂ , n ₃ (hereinafter referred to as nx, ny, nz) are called main refractive indexes, and correspond to half the length of the three main axes in the ellipsoid. Considering a light wave traveling in a direction perpendicular to the Y ₃ = 0 plane from the origin, this light wave has polarization components in the directions of Y ₁ and Y _2, and the refractive indexes of the respective components are nx and ny, respectively. . In general, for light traveling in an arbitrary direction, the plane that passes through the origin and is perpendicular to the traveling direction of the light wave is considered to be the cut surface of the refractive index ellipsoid, and the principal axis direction of this ellipse is the component direction of the polarization of the light wave. Yes, half the length of the main axis corresponds to the refractive index in that direction.

  First, regarding a difference in display principle between a display element that performs display using a change in optical anisotropy due to application of an electric field and a conventional liquid crystal display element, a TN system, a VA system, and an IPS are used as conventional liquid crystal display elements. The method will be described as an example.

  As shown in FIGS. 8C and 8D, in the TN liquid crystal display element, a liquid crystal layer 105 is sandwiched between a pair of opposed substrates 101 and 102, and the two substrates 101 and 102 are respectively disposed. It has a configuration in which transparent electrodes 103 and 104 (electrodes) are provided, and when no voltage is applied, the major axis direction of the liquid crystal molecules in the liquid crystal layer 105 is twisted and aligned, but when a voltage is applied, The major axis direction of the liquid crystal molecules is aligned along the electric field direction. In this case, when no voltage is applied, the average refractive index ellipsoid 105a has a direction in which the principal axis direction (major axis direction) is parallel to the substrate surface (in-plane direction) as shown in FIG. 8C. When the direction and voltage are applied, as shown in FIG. 8D, the principal axis direction is the normal direction of the substrate surface. That is, the shape of the refractive index ellipsoid 105a does not change between when no voltage is applied and when the voltage is applied, and the principal axis direction changes (the refractive index ellipsoid 105a rotates).

  As shown in FIGS. 8E and 8F, the VA liquid crystal display element has a liquid crystal layer 205 sandwiched between a pair of substrates 201 and 202 arranged in opposition to each other. It has a configuration in which transparent electrodes (electrodes) 203 and 204 are provided, and when no voltage is applied, the major axis direction of the liquid crystal molecules in the liquid crystal layer 205 is aligned in a direction substantially perpendicular to the substrate surface. When a voltage is applied, the major axis direction of the liquid crystal molecules is aligned in a direction perpendicular to the electric field. As shown in FIG. 8E, the average refractive index ellipsoid 205a in this case has its principal axis direction (major axis direction) oriented in the normal direction of the substrate surface when no voltage is applied, and FIG. As shown in FIG. 5, when a voltage is applied, the principal axis direction is in a direction parallel to the substrate surface (in-plane direction of the substrate). In other words, in the case of a VA liquid crystal display element, as in the case of a TN liquid crystal display element, the shape of the refractive index ellipsoid 205a does not change between when no voltage is applied and when a voltage is applied, and the principal axis direction changes. (Refractive index ellipsoid 205a rotates).

  In addition, as shown in FIGS. 8F and 8G, the IPS liquid crystal display element has a configuration in which a pair of electrodes 302 and 303 are arranged to face each other on the same substrate 301, and is not shown. By applying a voltage to the liquid crystal layer sandwiched between the counter substrate and the electrodes 302 and 303, the orientation direction of the liquid crystal molecules in the liquid crystal layer (the principal axis direction (major axis direction) of the refractive index ellipsoid 305a) ), And different display states can be realized when no voltage is applied and when a voltage is applied. That is, in the case of the IPS mode liquid crystal display element, similarly to the TN mode and VA mode liquid crystal display elements, when no voltage is applied as shown in FIG. 8 (f) and when a voltage is applied as shown in FIG. The shape of the refractive index ellipsoid 305a does not change, but its principal axis direction changes (the refractive index ellipsoid 305a rotates).

  Thus, in the conventional liquid crystal display element, the liquid crystal molecules are aligned in some direction even when no voltage is applied, and display is performed by changing the alignment direction by applying a voltage (modulation of transmittance). Yes. That is, although the shape of the refractive index ellipsoid does not change, the display is performed by utilizing the fact that the principal axis direction of the refractive index ellipsoid is rotated (changed) by voltage application. That is, in the conventional liquid crystal display element, the degree of alignment order of liquid crystal molecules is constant, and display (modulation of transmittance) is performed by changing the alignment direction.

  On the other hand, a display element that performs display using a change in optical anisotropy due to the application of an electric field, including the display element according to this embodiment, is as shown in FIGS. The shape of the refractive index ellipsoid 3a when no voltage is applied is spherical, that is, optically isotropic (nx = ny = nz, orientation order = 0), and anisotropy (nx by applying a voltage) > Ny, orientational order> 0). Note that nx, ny, and nz are the main refractive index in the direction parallel to the substrate surface (in-plane direction of the substrate) and the opposing direction of the electrodes 4 and 5, and the direction perpendicular to the substrate surface (substrate normal direction ), The main refractive index in the direction parallel to the substrate surface (in-plane direction of the substrate) and perpendicular to the opposing direction of the electrodes 4 and 5.

  As described above, the display element according to the present embodiment performs display by modulating the degree of orientation order, for example, while the direction of optical anisotropy is constant (the voltage application direction does not change). The display principle is greatly different from that of a liquid crystal display element.

  As shown in FIG. 1A, the display element according to the present embodiment has a medium A (medium layer 3) sealed between the substrates 1 and 2 when no voltage is applied to the electrodes 4 and 5. Indicates an isotropic phase. Further, the medium A has a twisted structure, and since this twisted structure fills the space isotropically, the medium A is optically isotropic, so that black display is performed.

  On the other hand, as shown in FIG. 1 (b), when a voltage is applied to the electrodes 4 and 5, each molecule 10 of the medium A has its long axis direction along the electric field formed between the electrodes 4 and 5. The birefringence phenomenon appears because the twisted structure is unwound. By this birefringence phenomenon, the transmittance of the display element can be modulated in accordance with the voltage between the electrodes 4 and 5.

  Note that the voltage required to modulate the transmittance of the display element increases at a temperature sufficiently far from the phase transition temperature (transition point), but a voltage of about 0 to 100 V is sufficient at a temperature immediately above the transition point. It is possible to modulate the transmittance.

For example, if the refractive index in the electric field direction and the refractive index in the direction perpendicular to the electric field direction are n // and n⊥, respectively, the birefringence change (Δn = n // − n⊥) and the external electric field, that is, The relationship with the electric field E (V / m) is as follows:
Δn = λ · B _k · E ² (3)
It is represented by Here, λ is the wavelength (m) of incident light in vacuum, B _k is the Kerr constant (m / V ² ), and E is the applied electric field strength (V / m).

  The Kerr constant B is known to decrease with a function proportional to 1 / (T-Tni) as the temperature (T) increases, and even if it can be driven with a weak electric field strength near the transition point (Tni). As the temperature (T) rises, the required electric field strength increases rapidly. For this reason, the voltage necessary for modulating the transmittance increases at a temperature sufficiently far from the transition point (a temperature sufficiently higher than the transition point), but at a temperature immediately above the phase transition, the transmission is performed at a voltage of about 100 V or less. The rate can be modulated sufficiently.

  However, as a result of studies by the inventors of the present application, it has been found that when display is performed by modulating the degree of orientation order, the contrast may be lowered in some cases.

  According to the study by the inventors of the present application, the following two factors can be cited as factors that cause the contrast to decrease.

  First, when power is turned on in a conventional display element using a medium A that exhibits optical anisotropy by application of an electric field as a display medium or a display device including the display element, the ambient temperature If the temperature of the medium A is low, the temperature at which the medium A is originally driven has not been reached, and the physical state of the medium A may be different from the state that the medium A should originally have at the time of driving the element. Is mentioned. For example, when the medium A is in an isotropic phase state just above the nematic-isotropic phase transition temperature and must be driven originally, the medium A is in a nematic state lower than the phase transition temperature when the power is turned on. There is. In this case, when nematics that have optical anisotropy even when no electric field is applied must transmit black due to the optical anisotropy when black display must be achieved in an isotropic state when no electric field is applied. Will end up. Therefore, in such a case, good black display cannot be performed and the contrast is lowered. Of course, the display element can be overheated by a heater or a light source (backlight) to obtain a good display, but it is not easy to raise the temperature and stabilize it instantaneously.

  The other is that even if the medium A (display medium) realizes an optically isotropic state in a region away from the substrate interface, the molecules constituting the medium A by the substrate 1 at the substrate interface, particularly the substrate 1 interface. For example, since 10 is firmly adsorbed, an optically isotropic state may not be realized. For example, when driving at a temperature of 0.1 K just above the nematic-isotropic phase transition temperature, the vicinity of the substrate interface is in a nematic state.

  In any case, near the substrate interface, due to the adsorption phenomenon, the physical state of the medium A is different from the state that should originally have at the time of driving the element, and is different from the bulk region in the cell away from the substrate interface. The medium A in the vicinity of the substrate interface causes a phenomenon that light is transmitted even during black display, resulting in a problem that the contrast is lowered.

  Even in the display element according to the present embodiment, the nematic liquid crystal phase is precipitated at a temperature lower than the transition point in the same manner as the conventional display element. However, according to the display element according to the present embodiment, for example, when the ambient temperature is lower than the transition point when the power is turned on and the medium A does not reach the temperature that should be driven, the deposited nematic liquid crystal phase Is a medium in which the nematic liquid crystal phase, that is, the physical state is different from the original driving state in order to align in the alignment (treatment) direction in the alignment films 8 and 9, in this case, the polarizing plate absorption axis direction. There is no optical contribution. As a result, it was possible to realize a good black display until the temperature of the display element rose due to the heater and the backlight.

  That is, according to the present embodiment, even if optical anisotropy is manifested when no voltage is applied, the opposing surfaces of the pixel substrate 11 and the counter substrate 2 are parallel or orthogonal to one polarizing plate absorption axis. The optical contribution can be eliminated by applying a horizontal alignment treatment in the direction to be performed and keeping the direction of optical anisotropy, that is, the alignment direction parallel or orthogonal to the polarizing plate absorption axis. . That is, in the present embodiment, the surfaces of the pixel substrate 11 and the counter substrate 12 facing each other are subjected to a horizontal alignment process, so that the medium A at the substrate interface, strictly speaking, the molecules constituting the medium A 10 is a temperature lower than the element driving temperature and is oriented along the orientation (treatment) direction in the orientation treatment.

  In addition, according to the display element according to the present embodiment, even when the desired driving temperature range is reached, light leakage during black display due to molecules adsorbed on the substrate interface is not observed, and high contrast is realized. I was able to. As a result, a display element excellent in high-speed response and viewing angle characteristics could be obtained without reducing the contrast.

  As described above, the rubbing directions of the substrates 1 and 2 are preferably orthogonal, parallel or antiparallel, but more preferably parallel or antiparallel. Contrast can be maximized by performing horizontal alignment treatment on both the substrates 1 and 2 and making the horizontal alignment directions parallel or anti-parallel to each other. As a result, the black luminance can be further reduced. It was.

  In this embodiment, the alignment films 8 and 9 and the rubbing process are performed on both the substrates 1 and 2 (the pixel substrate 11 and the counter substrate 12). Even when rubbing is performed, it can be obtained. In this case, when the alignment films 8 and 9 are formed on both the substrates 1 and 2, that is, the effect as the alignment treatment is not performed on both the substrates 1 and 2, the electrodes 4 and 5 are formed. If the alignment film (alignment film 9) is formed only on the substrate 2 on the side opposite to the substrate 1, a voltage drop derived from the alignment film 8 on the substrate 1 side does not occur, and the drive voltage of the element increases. There are no practical advantages. Even when the desired driving temperature was reached, light leakage due to molecules adsorbed on the substrate interface did not occur, and high contrast could be obtained. Even when the desired driving temperature was reached, light leakage due to molecules adsorbed on the substrate interface did not occur, and high contrast could be obtained.

  Note that in this embodiment mode, the description has been mainly given of the transmissive display element as an example, but the present invention is not limited to this, and may be a reflective display element.

  Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but the present invention is not limited thereto.

[Example 1]
The following description describes a display element including a chiral agent in a medium according to the present embodiment. In addition, as a [Comparative Example], a display element in which a medium does not contain a chiral agent will be described.

  ITO was used as the electrodes 4 and 5 as the display element having the configuration shown in FIG. Specifically, the line width is 5 μm, the distance between the electrodes is 5 μm, and the electrode thickness is 0.6 μm. As described above, the electrode having a wedge-shaped structure of less than 90 ° ± 10 ° is comb-like on the substrate surface. Formed. A glass substrate was used as the substrate. As the medium, structural formulas (1) to (3)

A mixture obtained by adding an equal amount of the compound represented by the formula (7) to which 7% by weight of a chiral agent “ZLI-4572” (trade name, manufactured by Merck & Co., Inc.) was further added was used.

  The layer thickness of the medium layer 3 (that is, the distance between the substrates 1 and 2) was 10 μm. Further, a polarizing plate was disposed outside both the glass substrates, and an alignment film made of polyimide was formed inside both the glass substrates. The alignment film was previously subjected to a horizontal rubbing treatment.

  The mixture (medium) was maintained at a temperature in the vicinity of the nematic-isotropic phase transition immediately by an external heating device (heating means), and voltage was applied. The isotropic phase-liquid crystal phase transition temperature was 63 ° C. The maximum transmittance was obtained at 49 V, and the voltage holding ratio one month after the display element was 98%.

[Comparative example]
As a medium, nematic liquid crystal 5CB (90 wt%) and polymerizable monomer 1,4-di (4- (6-acryloyloxy) hexyloxy) benzoyloxy) -2-methylbenzene (10 wt%). After mixing, Irgacure (manufactured by Ciba Specialty Chemicals) as a polymerization initiator was added at 0.5 wt% with respect to the polymerizable monomer to prepare a mixture. After this mixture was injected between two glass substrates, a display element was produced by irradiating with ultraviolet rays near 365 nm using a high-pressure mercury lamp in an isotropic phase.

  The above mixture was kept at a temperature just above the nematic-isotropic phase transition by an external heating device, and voltage was applied. The isotropic phase-liquid crystal phase transition temperature was 28 ° C. The maximum transmittance was obtained at 66 V, and the voltage holding ratio one month after the display element was 89%.

  From the above results, it can be seen that the medium used in the display element according to the present invention has a smaller applied voltage for obtaining the maximum transmittance than the comparative example. That is, by adding a chiral agent to the medium, a medium with improved Kerr effect stability can be realized.

  That is, in the comparative example, unreacted polymerizable monomer and polymerization initiator remain in the monomer polymerization process. For this reason, the stability of the Kerr effect is improved by irradiating the polymerizable monomer with light to form a network polymer, but the residue deteriorates the voltage holding ratio of the liquid crystal.

  On the other hand, in the present Example 1, a chiral agent is added. For this reason, the medium spontaneously takes a twisted structure, and as a result, the Kerr effect is also stabilized. Moreover, since it is not necessary to stabilize with a polymer etc., the cause of deteriorating the voltage holding ratio of the liquid crystal such as residue can be eliminated. That is, the reliability problem can be solved. Further, in the comparative example, an ultraviolet light irradiation process for photopolymerization is essential, but in the present Example 1, this is not necessary, and the manufacturing problem can be solved at the same time.

[Example 2]
In this embodiment, the structural formulas (5) to (7) are used as the medium.

The same thing as Example 1 including a chiral agent was used except having used the mixture which mixed the compound shown by. The mixing ratio of the compounds represented by the structural formulas (5) to (7) is 30 wt% for the compound represented by the structural formula (5), 40 wt% for the compound represented by the structural formula (6), and the structural formula (7). The compound shown was 30 wt%.

  In Example 1, a medium made of a compound having a positive dielectric anisotropy was used, but in this example, a medium made of a compound having a negative dielectric anisotropy was used. Even in this case, the same effect as in Example 1 could be obtained. That is, in the present invention, not only a medium having positive dielectric anisotropy but also a medium having negative dielectric anisotropy can be used.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  Note that in the display device related to the present invention, a polarizing plate can be disposed on the opposite side of the pair of substrates from the surface facing the medium in at least one of the substrates.

  In the display device according to the present invention, an alignment film can be disposed on a surface of the at least one of the pair of substrates facing the medium.

  In the display device related to the present invention, the alignment film can be an organic thin film.

  In the display device related to the present invention, the alignment film can be polyimide.

  In the display device related to the present invention, the alignment film can be subjected to a horizontal alignment process parallel or antiparallel to the substrate.

  In the display device according to the present invention, the medium can have an alignment order equal to or less than the wavelength of light when a voltage is applied.

  In the display device related to the present invention, the medium can contain a liquid crystalline substance.

  In the display device related to the present invention, the medium may have an ordered structure exhibiting cubic symmetry.

  In the display device related to the present invention, the medium may be composed of molecules exhibiting a cubic phase or a smectic D phase.

  In the display device related to the present invention, the medium can be made of a liquid crystal microemulsion.

  In the display device related to the present invention, the medium may be composed of a lyotropic liquid crystal exhibiting a micelle phase, a reverse micelle phase, a sponge phase, or a cubic phase.

  In the display device related to the present invention, the medium may be a liquid crystal fine particle dispersion system exhibiting a micelle phase, a reverse micelle phase, a sponge phase, or a cubic phase.

  In the display device related to the present invention, the medium can be a dendrimer.

  In the display device related to the present invention, the medium can be made of molecules exhibiting a cholesteric blue phase.

  In the display device related to the present invention, the medium may be composed of molecules exhibiting a smectic blue phase.

  The display element of the present invention is a display element having excellent wide viewing angle characteristics and high-speed response characteristics. For example, an image display device such as a television or a monitor, an OA device such as a word processor (word processor) or a personal computer, or a video The present invention can be widely applied to image display devices provided in information terminals such as cameras, digital cameras, and mobile phones. In addition, as described above, the display element of the present invention has a wide viewing angle characteristic and a high-speed response characteristic, and also stabilizes the Kerr effect by reducing the liquid crystal phase-isotropic phase transition temperature and driving. Since the voltage can be reduced, it is also suitable for large screen display and moving image display.

1 Substrate 2 Substrate 3 Medium layer 4 Electrode (electric field applying means)
4a Comb tooth part 5 Electrode (electric field applying means)
5a Comb portion 6 Polarizing plate 7 Polarizing plate 11 Pixel substrate (substrate)
12 Counter substrate (substrate)
45c, 45d Electric field application direction A Medium

Claims (7)

A display element comprising a pair of substrates at least one of which is transparent and a medium sandwiched between the pair of substrates and exhibiting optical isotropy when no electric field is applied and exhibiting optical anisotropy when applying an electric field There,
The medium has an alignment order equal to or less than the optical wavelength of light when no electric field is applied,
A display element, wherein the medium contains a chiral agent as a chiral substance.   The display element according to claim 1, wherein the medium is a chiral substance.   The display element according to claim 1, wherein the medium contains a liquid crystalline substance.   4. The electric field applying means for applying an electric field substantially parallel to the substrate surface to the medium is provided on one of the pair of substrates. 5. Display element.   5. The electric field applying means includes at least a pair of comb-shaped electrodes that are provided on the medium side of the pair of substrates and are arranged to face each other in a direction in which comb-tooth portions are engaged with each other. The display element as described in.   The display element according to claim 5, wherein the comb-tooth portion has a wedge shape.   The display element according to claim 6, wherein an angle formed by the wedge-shaped bent portion is less than 90 ° ± 10 °.

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