JP2008089970A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element which has a superior color balance by enhancing the reflection efficiency of a liquid crystal layer away from an observation side. <P>SOLUTION: The liquid crystal display element includes a first liquid crystal dimming layer showing a cholesteric phase and a second liquid crystal dimming layer showing a cholesteric phase layered in this order from the observation side, wherein the average diameter of liquid drops of the first liquid crystal is smaller than the average diameter of liquid drops of the second liquid crystal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display element.

  A liquid crystal display element using a chiral nematic liquid crystal composition that exhibits a cholesteric phase at room temperature by adding a chiral material to the nematic liquid crystal is known. In such a liquid crystal display device, the liquid crystal is in a planar (PL) alignment state and a focal conic (FC) alignment state by applying high and low pulse voltages (driving voltages) between a pair of electrodes sandwiching a chiral nematic liquid crystal composition. Alternatively, the display is switched to the homeotropic state. Since the two states of the PL alignment state and the FC alignment state can be maintained without a power source, it is not necessary to supply power except during display rewriting, and a display element with low power consumption can be provided. The chiral nematic liquid crystal in the PL alignment state has a structure in which rod-like liquid crystal molecules are arranged in parallel and spirally overlapped, and selectively reflects light of a specific wavelength determined by the helical pitch, and other wavelengths. Light has the property of transmitting. For this reason, a display can be switched between the color derived from selective reflection and black by providing a light absorption layer on the back surface of the liquid crystal display element. By laminating a liquid crystal display element sandwiching a chiral nematic liquid crystal composition with a spiral pitch adjusted to reflect light of wavelengths corresponding to red, green, and blue, a full color display and monochrome display can be achieved by additive color mixing. It becomes possible. However, when three layers of elements each having a liquid crystal sandwiched between a pair of substrates are stacked, there is a problem that the film lacks flexibility and cracks or peels when bent.

  In recent years, a light control layer formed by applying a coating liquid in which a chiral nematic liquid crystal is dispersed in a polymer resin on a substrate, as seen in Patent Document 1 and Patent Document 2, to solve such problems. A dispersion-coated chiral nematic liquid crystal display device having the above has been studied.

This coating-type chiral nematic liquid crystal display element can be formed by applying or vapor-depositing electrode layers or liquid crystal layers directly on a resin sheet substrate, making it flexible and resistant to bending. It has a feature that a plurality of liquid crystal layers can be directly stacked on a single substrate and is suitable for multicoloring. A liquid crystal display element having a light control layer formed by applying a microcapsule enclosing a chiral nematic liquid crystal on a substrate is also known.
US Pat. No. 6,585,849 US Pat. No. 6,690,447

  However, in the multilayer display element manufactured by the method shown in Patent Literature 1 and Patent Literature 2, the liquid crystal layer farther from the observation side has lower light utilization efficiency, and thus the reflectance becomes lower. Therefore, there arises a problem that the color balance is deteriorated when each layer is colored.

  Therefore, the technical problem to be solved by the present invention is to provide a liquid crystal display element with good color balance by increasing the reflection efficiency of the liquid crystal layer far from the observation side.

  This invention can achieve the said subject with the following structures.

1.
At least a first liquid crystal light control layer in which first liquid crystal droplets exhibiting a cholesteric phase at 20 ° C. are dispersed, and a second liquid crystal composition in which second liquid crystal droplets exhibiting a cholesteric phase at 20 ° C. are dispersed. A liquid crystal display element having an optical layer and stacked in this order from the observation side, wherein an average value of the diameter of the first liquid crystal droplet is an average value of the diameter of the second liquid crystal droplet A liquid crystal display element characterized by being smaller.

2.
2. The liquid crystal display element according to 1, wherein the first liquid crystal and the second liquid crystal have different selective reflection wavelengths.

3.
3. The liquid crystal display element according to 1 or 2, wherein the first liquid crystal and the second liquid crystal have different directions of spiral twist.

4).
4. The liquid crystal display element according to claim 1, wherein the selective reflection wavelength of the first liquid crystal is shorter than the selective reflection wavelength of the second liquid crystal.

5.
A third liquid crystal light control layer in which a third liquid crystal exhibiting a cholesteric phase at 20 ° C. is dispersed as droplets is provided between the first liquid crystal light control layer and the second liquid crystal light control layer. The average value of the diameters of the third liquid crystal droplets is not less than the average value of the diameters of the first liquid crystal droplets and not more than the average value of the diameters of the second liquid crystal droplets. 5. The liquid crystal display element according to any one of 1 to 4, wherein the liquid crystal display element is characterized.

6).
6. The liquid crystal display element according to 5, wherein the selective reflection wavelength of the third liquid crystal is longer than the selective reflection wavelength of the first liquid crystal and shorter than the selective reflection wavelength of the second liquid crystal.

7).
The first to third liquid crystals have a peak value of selective reflection wavelength in a blue reflective liquid crystal in 400 to 500 nm, a green reflective liquid crystal in 500 to 580 nm, a yellow reflective liquid crystal in 580 to 610 nm, and 610 to 700 nm. 7. The liquid crystal display element according to any one of 1 to 6, wherein the liquid crystal display element is selected from red reflective liquid crystals.

8).
8. The liquid crystal display element according to any one of 1 to 7, wherein the first to third liquid crystal droplets are covered with a microcapsule wall.

9.
The liquid crystal display element according to any one of 1 to 8, wherein the first to third liquid crystals are made of a nematic liquid crystal and a chiral material.

10.
10. The liquid crystal display element according to any one of 1 to 9, wherein an electrode for driving the first to third liquid crystals is provided.
Please change to.

  According to the present invention, there is provided a liquid crystal display element having a layer in which a first liquid crystal light control layer and a second liquid crystal light control layer are laminated in order from the observation side, and an average diameter of droplets of the first liquid crystal Since the value is smaller than the average value of the diameters of the droplets of the second liquid crystal, it becomes possible to adjust the reflectance from the first liquid crystal light control layer and the reflectance from the second liquid crystal light control layer, By increasing the reflection efficiency of the liquid crystal light control layer far from the observation side, a liquid crystal display element with good color balance can be provided.

  Embodiments of the present invention will now be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a liquid crystal display element according to an embodiment of the present invention. As shown in FIG. 1, in the liquid crystal display element 10, striped electrodes 32 are formed on a transparent substrate 42. On the electrode 32, a second liquid crystal light control layer 22 in which droplets of the second liquid crystal 2 are dispersed in a polymer is formed. On the second liquid crystal light control layer 22, a first liquid crystal light control layer 21 in which droplets of the first liquid crystal 1 are dispersed in a polymer is formed. A striped electrode 31 is formed on the first liquid crystal light control layer 21 so as to cross the electrode 32. A transparent substrate 41 is formed on the electrode 31, and the transparent substrate 41 side is an observation side. A power source 60 for driving the liquid crystal display element 10 is connected to the electrodes 31 and 32. A black light absorption layer 50 is formed on the surface of the transparent substrate 42 opposite to the surface on which the electrodes 32 are formed. The liquid crystal display element 10 can be used to perform black and white display.

  In the liquid crystal display element 10, the average value of the diameters of the droplets of the first liquid crystal 1 and the average value of the diameters of the droplets of the second liquid crystal 2 are different from each other. With this relationship, the light reflection efficiency of the first liquid crystal light control layer 21 and the second liquid crystal light control layer 22 can be controlled, and the color balance depending on the reflectance of each layer is adjusted. be able to.

  Further, the average value of the diameters of the droplets of the first liquid crystal 1 is smaller than the average value of the diameters of the droplets of the second liquid crystal 2. With such a relationship, the diameter of the droplets of the second liquid crystal 2 is reduced with respect to the problem that the light use efficiency decreases as the layer becomes farther from the observation side, and the reflectance of the layer decreases. By increasing the ratio, the reflectance of the second liquid crystal light control layer 22 can be brought close to the reflectance of the first liquid crystal light control layer 21, and color balance can be achieved. As a result, it can be close to pure white. The reason why such an effect can be obtained is that the efficiency of selective reflection of each liquid crystal layer increases as the diameter of the droplet or capsule increases. In addition, when the diameter of the capsule increases, the binder region between droplets or capsules that does not contribute to selective reflection, and the capsule coating and the liquid crystal region in the vicinity of the coating are relatively small, and there are regions that contribute to selective reflection. By increasing, the efficiency of selective reflection increases.

  Further, the selective reflection wavelengths of the first liquid crystal 1 and the second liquid crystal 2 are preferably different. In this way, white can be expressed, color balance can be achieved, and a purer white can be formed.

  Further, it is preferable that the first liquid crystal 1 and the second liquid crystal 2 have different spiral twist directions. By doing in this way, the other circularly polarized light which is not used for reflection in the first liquid crystal light control layer 21 can be used in the second liquid crystal light control layer 22, and the light utilization efficiency is improved. .

  Further, as one characteristic when the liquid crystal exhibiting a cholesteric phase selectively reflects, the light transmittance of a wavelength other than the selective reflection wavelength region can be mentioned. When light having a wavelength longer than the selective reflection wavelength region is compared with light having a short wavelength, the transmittance of light having a long wavelength is higher. Therefore, the use efficiency of light can be improved by arranging the liquid crystal light control layer having a shorter selective reflection wavelength closer to the observation side. Therefore, the selective reflection wavelength of the first liquid crystal 1 is preferably shorter than the selective reflection wavelength of the second liquid crystal 2. By doing in this way, the reflective efficiency in the 2nd liquid crystal light control layer 22 can be raised more, and white with a better color balance can be displayed.

  In this embodiment, an electrode is not formed between the first liquid crystal light control layer 21 and the second liquid crystal light control layer 22, but an electrode is formed between the first liquid crystal light control layer 22 and the first liquid crystal light control layer. 21 and the second liquid crystal light control layer 22 may be driven separately.

  FIG. 2 shows another embodiment of the present invention. The liquid crystal display element 11 shown in FIG. 2 has a third liquid crystal 3 having high droplets between the first liquid crystal dimming layer 21 and the second liquid crystal dimming layer 22 of the liquid crystal display element 10 shown in FIG. A third liquid crystal light control layer 23 dispersed in a molecular body is formed. Other configurations were the same as those of the liquid crystal display element 10. The liquid crystal display element 11 can perform white display or multicolor display.

  In this liquid crystal display element 11, the average value of the diameters of the droplets of the third liquid crystal 3 is equal to or greater than the average value of the diameters of the droplets of the first liquid crystal 1, and the average value of the diameters of the droplets of the second liquid crystal 2. The following is preferable. In this way, the problem that the light utilization efficiency decreases and the reflectance decreases as the liquid crystal light control layer farther from the observation side is solved, and the control is performed so that the reflectance of each liquid crystal light control layer becomes substantially equal. Can balance the colors.

  The selective reflection wavelength of the third liquid crystal 3 is preferably longer than the selective reflection wavelength of the first liquid crystal 1 and shorter than the selective reflection wavelength of the second liquid crystal. Thus, the use efficiency of light can be improved by arrange | positioning the liquid crystal light control layer with a short selective reflection wavelength nearer to an observation side.

  In the liquid crystal display element 11 shown in FIG. 2, each liquid crystal dimming layer is driven at once by the electrodes 31 and 32. However, an electrode is formed between each liquid crystal dimming layer, and each liquid crystal dimming layer is driven. You may make it drive a light control layer separately.

  By the way, in the liquid crystal display elements 10 and 11 of the two embodiments described above, liquid crystal droplets dispersed in a polymer are used, but dispersed liquid crystal droplets covered with microcapsule walls are used. May be. By using the droplets covering the microcapsule wall, handling during production becomes easier.

Next, details of each component of the liquid crystal display element according to the present invention will be described sequentially.
(Liquid crystal light control layer)
Each liquid crystal light control layer according to the present invention comprises at least liquid crystal droplets exhibiting a cholesteric phase at 20 ° C. or droplets coated with microcapsule walls dispersed in a binder. The average diameter of the droplets is preferably 1 μm to 100 μm. When the droplets are smaller than 1 μm, it becomes difficult to control the average diameter. On the other hand, if it exceeds 100 μm, it becomes difficult to control the reflectance by controlling the average diameter.

The components of the liquid crystal light control layer are shown below.
(binder)
As the binder according to the present invention, a water-soluble polymer binder is used, and specifically, the binders shown below are preferably used.

  Binders suitable in the present invention are transparent or translucent and generally colorless, such as gelatin, gum arabic, poly (vinyl alcohol), hydroxyethyl cellulose, cellulose acetate, cellulose acetate butyrate, casein, starch, cellulose esters, Is mentioned. Two or more of these binders may be used in combination.

  The binder according to the present invention may further contain a dye or / and an ultraviolet absorber. The added dye improves display contrast and color balance. Various conventionally known dyes such as azo compounds, quinone compounds, anthraquinone compounds, or dichroic dyes can be used. The added ultraviolet absorber prevents ultraviolet deterioration of the binder or the liquid crystal composition, for example, discoloration or responsiveness change with time. Materials such as a benzophenone compound, a benzotriazole compound, and a salicylate compound can be used. In addition, an antioxidant, a light stabilizer and the like may be added. The addition amount is 5% by mass or less, preferably 3% by mass or less, based on the mass of the binder resin.

  The binder according to the present invention is important for ensuring the film strength of the dispersed liquid crystal-containing layer, particularly when a counter electrode is used. In order to make the film thickness constant together with the binder, resin pillar structures and spacer particles are used. However, it is preferable not to use them because of simplification of the process.

  The polyvinyl alcohol preferably used in the embodiment according to the present invention includes, in addition to normal polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, cation-modified polyvinyl alcohol and anion-modified polyvinyl alcohol having an anionic group. Modified polyvinyl alcohol, polyvinyl alcohol derivatives, etc. are also included.

The polyvinyl alcohol obtained by hydrolyzing vinyl acetate preferably has an average degree of polymerization of 1000 or more, and particularly preferably has an average degree of polymerization of 1500 to 5000. The saponification degree is preferably 50 to 100%, particularly preferably 60 to 99.5%. It is desirable that the content of ionic substances such as sodium acetate is small, and it is preferably 2% or less, particularly 0.5% or less.
(liquid crystal)
The liquid crystal according to the present invention (hereinafter also referred to as a liquid crystal composition) preferably includes a liquid crystal composition exhibiting a cholesteric phase.

  A chiral nematic liquid crystal is a typical liquid crystal exhibiting a cholesteric phase, and can be obtained by adding a predetermined amount of a chiral material to a nematic liquid crystal.

  The nematic liquid crystal is not particularly limited, and a nematic liquid crystal conventionally known in the field of liquid crystal display elements can be used. Examples of such nematic liquid crystal materials include liquid crystal ester compounds, liquid crystal pyrimidine compounds, liquid crystal cyanobiphenyl compounds, liquid crystal tolan compounds, liquid crystal phenyl cyclohexane compounds, liquid crystal terphenyl compounds, fluorine atoms, and fluoroalkyls. Other liquid crystalline compounds having a polar group such as a cyano group and a cyano group, and mixtures thereof.

  As the chiral material, various materials conventionally known in the field of liquid crystal display elements can be used. For example, a cholesteric compound having a cholesteric ring, a biphenyl compound having a biphenyl skeleton, a terphenyl compound having a terphenyl skeleton, an ester compound having a skeleton in which two benzene rings are connected by an ester bond, and a cyclohexane ring directly on the benzene ring A cyclohexane compound having a skeleton formed by linking a ring, a pyrimidine compound having a skeleton formed by directly linking a pyrimidine ring to a benzene ring, and an azoxy having a skeleton formed by linking two benzene rings by an azoxy bond or an azo bond Or an azo compound etc. are mentioned.

  Examples of such a chiral material include compounds represented by the following chemical structural formulas (C1) to (C7).

  The content of the chiral material is not particularly limited, and is usually 3 to 40% by mass with respect to the total amount of the nematic liquid crystal and the chiral material.

  An additive such as an ultraviolet absorber may be further added to the liquid crystal composition. The ultraviolet absorber is for preventing ultraviolet deterioration of the liquid crystal composition, for example, fading or responsiveness change with time. For example, materials such as a benzophenone compound, a benzotriazole compound, and a salicylate compound can be used. The addition amount is 5% by mass or less, preferably 3% by mass or less with respect to the total amount of the nematic liquid crystal and the chiral material.

  Such a liquid crystal composition can be obtained by mixing each material at a predetermined ratio. If desired, the liquid crystal composition may be purified by contacting with an ion exchange resin, an adsorbent or the like to remove moisture and impurities, and then used for manufacturing the device.

  This chiral nematic liquid crystal generally has a twisted arrangement of rod-like liquid crystal molecules and exhibits a cholesteric phase. When light is incident on this liquid crystal, when light is incident from a direction parallel to the helical axis, light having a wavelength indicated by λ = np is selectively reflected (planar state). Here, λ is the wavelength, n is the average refractive index of the liquid crystal molecules, and p is the distance at which the liquid crystal molecules are twisted 360 °. On the other hand, when light is incident from a direction perpendicular to the helical axis, the light is transmitted without being reflected (focal conic state). Display is performed using this selective reflection and transmission.

  The operation mode of the reflective liquid crystal display having a memory property is disclosed in the technical paper SID International Symposium Digest of Technical Paper, Vol. 29, page 897. In this operation mode, the display is performed by switching the alignment state of the chiral nematic liquid crystal to one of a planar state (light selective reflection state) and a focal conic state (light transmission state). Since the planar state and the focal conic state are stable states, once the liquid crystal is set to any state, the state is maintained semipermanently unless an external force is applied. In other words, it is useful as a reflective liquid crystal display element having a memory property that once an image is displayed, the displayed image is maintained as it is even when the power is turned off. The liquid crystal composition used in the present invention can be used in a state of being encapsulated in microcapsules.

  As a method for producing a microcapsule that can be used in the present invention, a known method such as a coacervation method, an interfacial polymerization method, or an in-situ method can be used. Among these, the production method by the coacervation method can be preferably used with little chemical influence on the liquid crystal composition which is an oil phase.

  In addition, the interfacial polymerization method can form a microcapsule wall by polymerizing polyamine, polyhydric phenol and the like with a polybasic acid halide, polyisocyanate and the like at the interface between the aqueous phase and the oil phase.

  As an in-situ polymerization method, microcapsules can be formed by crosslinking amide resin, phenol resin alone or a copolymer thereof used for urea-melamine or the like with formaldehyde or glutaraldehyde.

  On the microcapsule wall, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, polyvinyl alcohol, polyethylene oxide, polypropylene oxide, ethylene-vinyl alcohol copolymer, polyacetal , Acrylic resin, methylcellulose, ethylcellulose, phenolic resin, fluororesin, silicone resin, diene resin, polystyrene-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyphenylene ether, polyphenylene sulfide, Polyethersulfone, polyetherketone, polyarylate, aramid, polyimide, poly- -Microcapsule wall strength is improved by coexisting -phenylene, poly-p-xylene, poly-p-phenylene vinylene, polyhydantoin, polyparabanic acid, polybenzimidazole, polybenzothiazole, polybenzoxadiazole, polyquinoxaline, etc. Can be improved.

The microcapsules according to the present invention can be prepared by a solution system and then dried and classified. Examples of the drying method include spray drying, rotary drying, and band drying. Examples of the classification method include a specific gravity method, a centrifugal method, an inertia method, and a sieving method.
(substrate)
The substrate that can be used for the liquid crystal display element preferably has a light-transmitting property. As the light-transmitting substrate, a glass substrate and a flexible substrate such as polycarbonate, polyethersulfone, polyarylate, and polyethylene terephthalate can be used. From the viewpoint of reducing the weight of the element, it is preferable to use a flexible substrate. When a flexible substrate is used as the substrate, a light and thin element can be produced, and damage (cracking) can be suppressed.
(electrode)
In the liquid crystal display element according to the present invention, an electrode having translucency is preferably used as the electrode positioned closer to the observation side than the liquid crystal layer. The translucent electrode is not particularly limited as long as it is transparent and conducts electricity. For example, indium tin oxide (ITO), indium zinc oxide (IZO), fluorine-added tin oxide (FTO), indium oxide, zinc oxide, bismuth silicon oxide (BSO), 3,4-ethylenedioxythiophene / polystyrene A sulfonic acid (PEDOT / PSS) etc. are mentioned. The surface resistance value is preferably 300Ω / □ or less. The thickness of the transparent electrode is not particularly limited, but is generally 0.1 to 20 μm.

  A metal electrode can also be preferably used for the back side electrode. As the metal electrode, for example, known metal species such as platinum, gold, silver, copper, aluminum, zinc, nickel, titanium, bismuth, and alloys thereof can be used.

  The electrode pattern is formed by a known method such as a vapor deposition method, a CVD method, an ink jet method, a dip coating method, a spin coating method, a spray method, a roll coater method, a flexographic printing method, a screen printing method, a lithography method, or a laser etching method. It can be formed by using alone or in combination.

Examples of the present invention are shown below.
(Measurement of liquid crystal droplet size)
The display layer coating solution is taken on a slide glass, observed under a crossed Nicol using an optical microscope with a CCD camera, and the observed image is taken into a personal computer and binarized with image processing software to determine the number of liquid crystal droplets and the area occupied The average particle size was determined.
(Measurement of element display characteristics)
The display element is driven by applying the pulse shown in FIG. 3 (in this driving waveform, the liquid crystal is once reset to the planar state at the previous stage pulse. The values of a and b are shown in each embodiment). The Y value indicating brightness in each of the focal conic state and the planar state was measured using a spectrocolorimeter (CM3700d; manufactured by Konica Minolta Sensing).

  At the same time, the spectral distribution curve in the planar state of the display element was measured to obtain the whiteness. That is, the chromaticity coordinates (x, y) of the CIE 1931 color system are obtained from the measured spectral distribution curve, and the distance (d) from the standard light D65 (x = 0.3127, y = 0.3290) is obtained by the following equation. Calculated.

  The distance (d) is one parameter representing whiteness, and the smaller the distance (d) is, the more white it is. The following knowledge is obtained about the distance (d).

d <0.02; can be considered pure white;
0 · 02 ≦ d <0.04; can be considered almost white;
0.04 ≦ d <0.05; may not be considered white due to light source; ×
0.05 ≦ d; apparently colored; XX
Therefore, it is preferable to set d <0.04, more preferably d <0.02.

The measurement temperature for each value was 25 ° C.
<Preparation of coating solution>
(Coating liquid 1: Preparation of display layer coating liquid Y1)
Nematic liquid crystal (BL035; manufactured by Merck & Co., Inc.) 81 parts by mass and chiral material (CNL611L; manufactured by ADEKA) 19 parts by mass are mixed, heated and stirred to be in a uniform state, and then cooled to obtain a chiral nematic liquid crystal composition ( A selective reflection wavelength of 590 nm) was obtained. This chiral agent induces a left helical twist.

Dissolve 10 parts by mass of this chiral nematic liquid crystal and 1 part by mass of an adduct of xylylene diisocyanate and trimethylolpropane in 75% ethyl acetate (Takenate D-110N; manufactured by Mitsui Chemicals Polyurethanes) in 100 parts by mass of ethyl acetate. Thus, an oil phase composition was prepared. This was put into 150 parts by mass of a 2% aqueous polyvinyl alcohol solution and emulsified by stirring for 2 minutes with a comb-type disperser. The emulsion was stirred at 60 ° C. for 3 hours and then cooled to room temperature to obtain a microcapsule dispersion having an average particle size of 15 μm. A display layer coating solution Y1 was obtained by adding 1 part by mass of a 10% aqueous polyvinyl alcohol solution to 5 parts by mass of the microcapsule dispersion.
(Coating liquid 2: Preparation of display layer coating liquid B1)
Chiral nematic liquid crystal composition (selective reflection wavelength 470 nm) obtained using 81 parts by weight of nematic liquid crystal (BL006; manufactured by Merck) and 19 parts by weight of chiral material (2: 1 mixture of MLC6248 and R1011; both manufactured by Merck). A display layer coating solution B1 was obtained in the same manner as the coating solution 1, except that a microcapsule dispersion with an average particle size of 10 μm was obtained by setting the stirring time in a comb-type disperser to 3 minutes. This chiral agent induces a right spiral twist.
(Coating liquid 3: Preparation of display layer coating liquid G1)
Chiral nematic liquid crystal composition (selective reflection wavelength 550 nm) obtained using 83 parts by weight of nematic liquid crystal (BL006; manufactured by Merck) and 17 parts by weight of chiral material (2: 1 mixture of MLC6247 and S1011; both manufactured by Merck). A display layer coating solution G1 having an average particle size of 10 μm was obtained in the same manner as in the coating solution 2 except that was used. This chiral agent induces a left helical twist.
(Coating liquid 4: Preparation of display layer coating liquid R1)
Chiral nematic liquid crystal composition (selective reflection wavelength 680 nm) obtained by using 86 parts by weight of nematic liquid crystal (BL006; manufactured by Merck) and 14 parts by weight of chiral material (2: 1 mixture of MLC6248 and R1011; both manufactured by Merck). A display layer coating solution R1 having an average particle size of 15 μm was obtained in the same manner as in the coating solution 1 except that was used. This chiral agent induces a right spiral twist.
(Coating liquid 5: Preparation of display layer coating liquid Y2)
A microcapsule dispersion was obtained in the same manner as coating solution 1.

  On the other hand, a microcapsule dispersion having an average particle size of 15 μm was prepared in the same manner as in the coating solution 1 except that a chiral material (CNL611R; manufactured by ADEKA) that induces a helical twist opposite to that of the chiral material used in the coating solution 1 was used. Obtained. This chiral agent induces a right spiral twist.

A display layer coating solution Y2 was obtained by adding 1 part by weight of a 10% polyvinyl alcohol aqueous solution to 2.5 parts by weight of each of these microcapsule dispersions.
(Coating liquid 6: Preparation of display layer coating liquid B2)
A microcapsule dispersion was obtained in the same manner as coating solution 2.

  On the other hand, an average was obtained in the same manner as in the coating solution 2 except that a chiral material (2: 1 mixture of MLC6247 and S1011; both manufactured by Merck) that induces a helical twist opposite to the chiral material used in the coating solution 2 was used. A microcapsule dispersion having a particle size of 10 μm was obtained. This chiral agent induces a left helical twist.

A display layer coating solution B2 was obtained by adding 1 part by mass of a 10% aqueous polyvinyl alcohol solution to 2.5 parts by mass of each of these microcapsule dispersions.
(Coating liquid 7: Preparation of display layer coating liquid Y3)
A microcapsule dispersion liquid having an average particle size of 15 μm was obtained in the same manner as in the coating liquid 1 except that a chiral material (CNL611R; manufactured by ADEKA) that induces a helical twist opposite to that of the chiral material used in the coating liquid 1 was used. . This chiral agent induces a right spiral twist.

A display layer coating solution Y3 was obtained by adding 1 part by mass of a 10% polyvinyl alcohol aqueous solution to 5 parts by mass of the microcapsule dispersion.
(Coating liquid 8: Preparation of display layer coating liquid B3)
The average particle diameter is the same as that of the coating solution 2 except that a chiral material (2: 1 mixture of MLC6247 and S1011; both manufactured by Merck) that induces a helical twist opposite to that of the chiral material used in the coating solution 2 is used. A 10 μm microcapsule dispersion was obtained. This chiral agent induces a left helical twist.

To 5 parts by mass of the microcapsule dispersion, 1 part by mass of a 10% polyvinyl alcohol aqueous solution was added to obtain a display layer coating liquid B3.
(Coating liquid 9: Preparation of display layer coating liquid B4)
A display layer coating solution B4 was obtained in the same manner as in the coating solution 2, except that the microcapsule dispersion having an average particle size of 15 μm was obtained by setting the stirring time in the comb-type disperser to 2 minutes. This chiral agent induces a right spiral twist.
(Coating liquid 10: Preparation of display layer coating liquid Y4)
A display layer coating solution Y4 was obtained in the same manner as in the coating solution 1, except that the microcapsule dispersion having an average particle size of 10 μm was obtained by setting the stirring time in the comb-type disperser to 3 minutes. This chiral agent induces a left helical twist.
(Coating liquid 11: Preparation of display layer coating liquid G2)
A display layer coating solution G2 was obtained in the same manner as in the coating solution 3, except that the microcapsule dispersion having an average particle size of 12 μm was obtained by setting the stirring time in the comb-type disperser to 2.5 minutes.
(Coating liquid 12: Preparation of display layer coating liquid G3)
A display layer coating solution G3 was obtained in the same manner as in the coating solution 3, except that the microcapsule dispersion having an average particle size of 15 μm was obtained by setting the stirring time in the comb-type disperser to 2 minutes.

  Table 1 shows a list of the above coating solutions.

<Examples and Comparative Examples>
(Examples 1-8, Comparative Examples 1-3)
The display layer coating liquid prepared in coating liquids 1 to 12 was applied to the polyethersulfone substrate on which the transparent electrode made of indium tin oxide was formed on the entire surface in order from the first layer with an applicator and dried. A liquid crystal light control layer was formed. The thickness of each layer was determined to be 6 μm (dry film thickness) from the film thickness measured using a stylus-type surface shape measuring device Dektak 3030 (manufactured by Becoin Instruments) every time one layer was applied and dried. Next, a conductive paste (DW-250H-5; manufactured by Toyobo Co., Ltd.) was applied and dried by a screen printing method to obtain an electrode. Further, a 1: 1 mixture of aqueous black pigment ink and 5% polyvinyl alcohol aqueous solution was applied and dried with an applicator to form a light absorption layer (thickness 2 μm), thereby completing a liquid crystal display element.

  In the liquid crystal display element, the voltage values of a and b in a focal conic state (black display state) were applied between the electrodes as the pulse voltage shown in FIG. 3, and the Y value at that time was measured. Moreover, the voltage value of a and b which will be a planar state (white display state) was applied between electrodes, and Y value was measured. The distance (d) at this time was measured.

  In Examples 1 to 8 and Comparative Examples 1 to 3, liquid crystal display elements were prepared using the coating liquids shown in Table 1 with the layer configurations shown in Table 2.

  In addition, Table 2 also shows measured values and evaluation results of Examples 1 to 8 and Comparative Examples 1 to 3.

  From the results of Table 2, in Example 1, the average value of the diameter of the first liquid crystal droplets is smaller than the average value of the diameter of the second liquid crystal droplets. Thus, a bright liquid crystal display element having a good white color balance and good color balance between the reflected light of the first liquid crystal and the reflected light of the first liquid crystal light control layer could be produced.

  In addition, it can be seen from the results of Example 1 and Example 5 that the first liquid crystal and the second liquid crystal preferably have different spiral twist directions.

  In addition, the results of Example 1 and Example 6 show that the selective reflection wavelength of the first liquid crystal is more preferably shorter than the selective reflection wavelength of the second liquid crystal.

  From the results of Example 2, Example 7, and Example 8, a third liquid crystal light control layer is provided between the first liquid crystal light control layer and the second liquid crystal light control layer, and the liquid crystal of the third liquid crystal is provided. It can be seen that the average value of the diameters of the droplets is preferably not less than the average value of the diameters of the first liquid crystal droplets and not more than the average value of the diameters of the second liquid crystal droplets. More preferably, it can be said that the average value of the diameter of the liquid crystal droplets in each light control layer is preferably increased in order from the observation side shown in Example 7.

  In addition, as in Example 4, the first layer and the second layer have the same average value of the selective reflection wavelength of the liquid crystal and the diameter of the liquid droplets, and the directions of the spiral twist are opposite. The third layer and the fourth layer also have the same liquid crystal selective reflection wavelength and the average value of the diameter of the droplets, and the spiral twist directions are opposite to each other. The selective reflection wavelengths of the first layer and the second layer are the third The average value of the liquid crystal droplet diameters of the first and second layers is shorter than the average value of the liquid crystal droplet diameters of the third and fourth layers. Therefore, a bright liquid crystal display element with good white purity can be obtained.

  In Comparative Examples 1 to 3, the average value of the diameter of the first liquid crystal droplet is not smaller than the average value of the diameter of the second liquid crystal droplet, and is equal to or larger than the average value. I understand.

  As described above, according to the present invention, it can be seen that a bright liquid crystal display element with high white purity and good color balance can be provided.

It is sectional drawing of the liquid crystal display element which is one Embodiment of this invention. It is sectional drawing of the liquid crystal display element which is another embodiment of this invention. It is a figure which shows the voltage drive waveform for driving a liquid crystal display element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st liquid crystal 2 2nd liquid crystal 3 3rd liquid crystal 10, 11 Liquid crystal display element 21 1st liquid crystal light control layer 22 2nd liquid crystal light control layer 23 3rd liquid crystal light control layer 31, 32 Electrode 41 42 substrate 50 light absorption layer 60 power supply

Claims (10)

At least a first liquid crystal light control layer in which first liquid crystal droplets exhibiting a cholesteric phase at 20 ° C. are dispersed, and a second liquid crystal composition in which second liquid crystal droplets exhibiting a cholesteric phase at 20 ° C. are dispersed. A liquid crystal display element having an optical layer and stacked in this order from the observation side, wherein an average value of the diameter of the first liquid crystal droplet is an average value of the diameter of the second liquid crystal droplet A liquid crystal display element characterized by being smaller. The liquid crystal display element according to claim 1, wherein the first liquid crystal and the second liquid crystal have different selective reflection wavelengths. The liquid crystal display element according to claim 1, wherein the first liquid crystal and the second liquid crystal have different directions of spiral twist. 4. The liquid crystal display element according to claim 1, wherein the selective reflection wavelength of the first liquid crystal is shorter than the selective reflection wavelength of the second liquid crystal. 5. A third liquid crystal light control layer in which a third liquid crystal exhibiting a cholesteric phase at 20 ° C. is dispersed as droplets is provided between the first liquid crystal light control layer and the second liquid crystal light control layer. The average value of the diameters of the third liquid crystal droplets is not less than the average value of the diameters of the first liquid crystal droplets and not more than the average value of the diameters of the second liquid crystal droplets. The liquid crystal display element according to claim 1, wherein the liquid crystal display element is a liquid crystal display element. 6. The liquid crystal display element according to claim 5, wherein the selective reflection wavelength of the third liquid crystal is longer than the selective reflection wavelength of the first liquid crystal and shorter than the selective reflection wavelength of the second liquid crystal. The first to third liquid crystals have a peak value of selective reflection wavelength in a blue reflective liquid crystal in 400 to 500 nm, a green reflective liquid crystal in 500 to 580 nm, a yellow reflective liquid crystal in 580 to 610 nm, and 610 to 700 nm. The liquid crystal display element according to claim 1, wherein the liquid crystal display element is selected from red reflective liquid crystals. 8. The liquid crystal display element according to claim 1, wherein the first to third liquid crystal droplets are covered with a microcapsule wall. The liquid crystal display element according to claim 1, wherein the first to third liquid crystals are made of a nematic liquid crystal and a chiral material. The liquid crystal display element according to claim 1, further comprising an electrode for driving the first to third liquid crystals.

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