JP3758634B2 - Liquid crystal display element - Google Patents

Description

【０１０６】
【発明の効果】
以上説明したように本発明によると、コレステリック液晶を用いた液晶表示素子であって、双安定性に優れるとともに、高分子安定型液晶表示素子と比べると低電圧駆動可能で、明るく視認性に優れた画像表示ができ、黒色背景色を利用して白黒画像表示を行う場合、良好な白色純度、明るさの特性を得ることができる液晶表示素子を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る液晶表示素子の１例の概略断面図である。
【図２】本発明に係る液晶表示素子の他の例の概略断面図である。
【図３】本発明に係る液晶表示素子のさらに他の例の概略断面図である。
【図４】関数ｆ₁ （λ）で表される光反射率（％）が３６０（ｎｍ）≦λ_t ＜λ_P となる波長λ_t （ｎｍ）で極大となる例を示す図である。
【図５】式｛ｅｘｐ−［２（λ−ｎＰ）² ／Δｎ² Ｐ² ］｝Ｒの可視波長域における積分値Ｓａ及び関数ｆ₂ （λ）の可視波長域における積分値Ｓｂの関係を示す図である。
【図６】実験結果であるｆ₁ （λ_t ）、ピーク反射率等を示す図である。
【符号の説明】
ＬＣＤ１、ＬＣＤ２、ＬＣＤ３ 液晶表示素子
１１、１２、１３ 基板
２１、２２ 電極
３１、３２ 絶縁性膜
４１、４２ 配向膜
５ 液晶層
６ スペーサ
７ シール壁
８ 黒色層
９、９’ 光散乱層
ＣＬ 柱状構造物
Ｄ 駆動部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display element (in other words, a liquid crystal light modulation element). In particular, the present invention relates to a liquid crystal display element using two stable state switching (bistable switching) using a liquid crystal exhibiting a cholesteric phase at room temperature.
[0002]
[Prior art]
The liquid crystal display element basically includes a pair of substrates having transparent electrodes and a liquid crystal layer sandwiched between the substrates. By applying a driving voltage to the liquid crystal layer, the arrangement of liquid crystal molecules is controlled, and external light incident on the element is modulated to display a target image.
[0003]
Various liquid crystal display elements have been proposed. Recently, various liquid crystal display elements using chiral nematic liquid crystals that exhibit a cholesteric phase at room temperature by adding a chiral material to nematic liquid crystals have been studied. Yes. It is known that such a liquid crystal display element can be used, for example, as a reflective liquid crystal display element characterized by low power consumption utilizing selective reflection of chiral nematic liquid crystal.
[0004]
In this reflection type display element, by applying high and low pulse voltages, the liquid crystal is switched between a planar state (colored state) and a focal conic state (transparent state) for display. In addition, the area that was in the planar state after applying the pulse voltage is maintained in the planar state, and the area that was in the focal conic state is maintained in the focal conic state, so that the display is possible even after the voltage application is stopped. It is possible to keep it. Such retention of each state of the planar and focal connection is generally called bistability or memory property.
[0005]
Some of such reflective liquid crystal display elements perform monochrome (monocolor) image display using a whitish color and a background color such as black for the purpose of replacing paper or books.
[0006]
However, in a liquid crystal display device using selective reflection of chiral nematic liquid crystal, in general, the peak of selective reflection in the wavelength-light reflectance spectrum is concentrated in the vicinity of the selective reflection wavelength in the colored state. Since the spectrum waveform is sharp, when the liquid crystal layer is a single layer, it is possible to display only vivid colors with high color purity, in other words, with low white purity, which is not satisfactory in terms of image visibility.
[0007]
In this regard, a polymer-stable liquid crystal display element in which a polymer precursor is mixed in a chiral nematic liquid crystal and a liquid crystal cell is formed using the polymer precursor and then polymerized to form a polymer network is disclosed in the United States. Many proposals have been made in Japanese Patent No. 5,847,798. According to this type of liquid crystal display element, it is said that monochrome display can be performed with a single liquid crystal layer by broadening the reflection spectrum in the selective reflection state.
[0008]
In addition, a liquid crystal display element that does not employ a polymer network in which a polymer precursor is polymerized, such as a polymer-stable liquid crystal display element, uses a liquid crystal that exhibits a cholesteric phase at room temperature, and in a selective reflection state of the liquid crystal In other words, in a colored state, a favorable monochrome image display can be performed by broadening the peak of the selective reflection light reflectance in the wavelength-light reflectance spectrum (widening it to a wider visible wavelength range). A liquid crystal display element has also been proposed (Japanese Patent Laid-Open No. 2001-311967).
[0009]
A liquid crystal display element that does not use a polymer network in which a polymer precursor is polymerized, such as a polymer stable liquid crystal display element, and uses a chiral nematic liquid crystal that exhibits a cholesteric phase at room temperature, and has a light reflectance of selective reflection. A liquid crystal display element having a broad peak and a wide temperature compensation range has also been proposed (Japanese Patent Laid-Open No. 2001-311968).
[0010]
[Patent Document 1]
US Pat. No. 5,847,798
[Patent Document 2]
JP 2001-31967 A
[Patent Document 3]
JP 2001-31968 A
[0011]
[Problems to be solved by the invention]
However, since the polymer-stable liquid crystal display element includes a networked polymer in the liquid crystal, the driving voltage for image display is relatively high, and background display characteristics (for example, black display characteristics) Is not enough to be satisfied.
[0012]
In addition, when the liquid crystal display elements disclosed in Japanese Patent Laid-Open Nos. 2001-311967 and 2001-31968 are liquid crystal display elements that perform black and white display, white purity and brightness in the white display portion are as much as possible. It is desirable to improve.
[0013]
Therefore, the present invention is a liquid crystal display element using cholesteric liquid crystal, which is excellent in bistability, can be driven at a lower voltage than a polymer stable liquid crystal display element, and can display a bright and excellent image display. It is an object of the present invention to provide a liquid crystal display element capable of obtaining good white purity and brightness characteristics when performing black and white image display using a black background color.
[0014]
[Means for Solving the Problems]
The present inventor has conducted research to solve the above problems and has obtained the following knowledge.
The liquid crystal display element is basically sandwiched between a pair of substrates having a translucent substrate disposed on at least the image observation side, a transparent electrode provided on the element observation side substrate, and the pair of substrates. Liquid crystal layer.
[0015]
In such a liquid crystal display element, at least one substrate is formed with an insulating film for preventing an electrical short circuit between the two substrates and a stabilizing film for controlling the alignment of liquid crystal molecules, and the liquid crystal layer is formed as such. May be sandwiched between the substrates via a thin film.
[0016]
In this way, when multiple layers of films are arranged at a very close distance between the liquid crystal layer and the substrate, the light passing through the element may cause multiple reflection or scattering between the layers. However, since such multiple reflection and scattering depend on the refractive index of each layer, the influence of the transparent electrode, which is an inorganic thin film having a high refractive index, is large.
[0017]
Therefore, white purity and brightness in black and white display can be improved by using the scattering peak in the visible short wavelength region that appears due to the interference between the substrate and the transparent electrode. Furthermore, the thickness of at least the electrode on the device observation side of the electrodes on both the substrates is set so as to increase the effect of strengthening the interference by utilizing interference of reflected light occurring at the interface of the transparent electrode. By making it relatively thin (however, it is thin as long as the surface resistance of the electrode does not become too large), increasing the influence of the film characteristics of the electrode, and increasing interference of light in the visible short wavelength region, it is possible to display black and white images When performed, good white purity and brightness can be obtained.
[0018]
In particular, when the thickness d (nm) of the transparent electrode is less than 80 nm, strengthening due to interference of reflected light increases, and the function of the light wavelength λ (nm) of the device when the liquid crystal layer is in a focal conic state f ₁ The light reflectance (%) represented by (λ) is the selective reflection wavelength λ in the planar state of the liquid crystal layer. _P (Nm) 360 (nm) ≦ λ _t <Λ _P Wavelength λ _t (Nm) is maximized and f ₁ (Λ _t )> F ₁ (Λ _P ) Appears when the liquid crystal layer is in the focal conic state, and the spectral waveform of the wavelength-one-light reflectance spectrum in the colored state can be expanded to a wide visible range, and the background color is black. In this case, it is possible to display a monochrome image with excellent white purity.
[0019]
Based on such knowledge, the present invention is sandwiched between the pair of substrates, at least a pair of substrates in which the substrate arranged on the element observation side has translucency, a transparent electrode provided on the element observation side substrate, and the pair of substrates. And a liquid crystal layer containing a cholesteric liquid crystal (liquid crystal exhibiting a cholesteric phase at room temperature), the substrate opposite to the element observation side is colored black, and the thickness d (nm) of the transparent electrode is less than 80 nm And the function f of the light wavelength λ (nm) of the device when the liquid crystal layer is in a focal conic state. ₁ The light reflectance (%) represented by (λ) is the selective reflection wavelength λ in the planar state of the liquid crystal layer. _P (Nm) 360 (nm) ≦ λ _t <Λ _P Wavelength λ _t (Nm) is maximized and f ₁ (Λ _t )> F ₁ (Λ _P A liquid crystal display element in which a reflection peak that satisfies the relationship (1) exists in a focal conic state is provided.
[0020]
In addition, the black coloring of the substrate opposite to the element observation side may be that the substrate itself may be colored black, but as the black colored substrate, for example, a light absorbing layer such as a black layer on the outer surface (back surface) of the transparent substrate. You may employ | adopt what provided (black display layer).
[0021]
When reducing the thickness of the electrode, it is desirable to do so as long as the surface resistance of the electrode does not become too large. Although it depends on the electrode material and the electrode forming method, generally, when the electrode thickness d is reduced to 0 <d <50 (nm), the strengthening due to interference of reflected light becomes larger, but the electrode surface resistance is 500 Ω / □. The electrode thickness d [nm] is preferably 50 nm ≦ d <80 nm because there is a fear that it will be very large as described above.
[0022]
In obtaining good white purity and brightness, the reflection peak is f ₁ (Λ _t )> F ₁ (Λ _P ) + 5% is more desirable. Further, when the liquid crystal layer is in a focal conic state, the reflectance of the element is the wavelength λ. _t It is preferable that the maximum is obtained.
[0023]
In order to obtain good white purity and brightness, the selective reflection wavelength nP (n is the average refractive index of the cholesteric liquid crystal and P is the cholesteric liquid crystal) when the cholesteric liquid crystal contained in the liquid crystal display element is in a colored state (planar state). When the optical reflectance at the helical pitch of the liquid crystal is R and the refractive index anisotropy of the cholesteric liquid crystal is Δn, an expression expressed as a function of the wavelength λ
{Exp- [2 (λ-nP) ² / Δn ² P ² ] The integral value Sa in the visible wavelength region of R represents a function f representing the wavelength-light reflectance spectrum of the device when the liquid crystal layer is in the planar state. ₂ It is preferable that the integral value Sb in the visible wavelength region of (λ) is 40% or more and 55% or less.
[0024]
The visible wavelength range here means a wavelength range of 360 nm to 740 nm. Formula {exp- [2 (λ-nP) ² / Δn ² P ² ] R is reflectivity R at the center wavelength (selective reflection wavelength nP), and dispersion is (ΔnP / 2) ² Represents a normal distribution function. Since Sb is the total integral value of the spectrum in the visible light region and Sa is the integral value of the spectrum excluding the scattered portion, the smaller the Sa / Sb value, the more white display can be made.
[0025]
However, if it falls below 40%, it becomes difficult to generate a light reflectance peak of selective reflection in a wavelength region where the luminous reflectance is large, and the visibility of the element is lowered. % Or more is desirable.
[0026]
From the viewpoint of obtaining good white purity and brightness, the selective reflection wavelength nP in the planar state of the cholesteric liquid crystal contained in the liquid crystal layer may be 500 nm or more and 800 nm or less. Examples of the refractive index anisotropy Δn of the cholesteric liquid crystal contained in the liquid crystal layer include 0.18 to 0.32.
[0027]
A functional surface having light scattering ability may be arranged in the light incident direction of the liquid crystal display element. Furthermore, for example, the outermost surface of the substrate on the element observation side of the pair of substrates may be a functional surface having light scattering ability. By doing so, interference of the reflected light at the electrode interface appears more effectively, and the wavelength-one-light reflectance spectrum in the colored state can be extended to a wider visible region.
[0028]
When a transparent substrate is adopted as the substrate opposite to the element observation side and a light absorption layer (black display layer) such as a black layer is provided on the outer surface (back surface), the substrate surface facing the black display layer is also It may be a functional surface having light scattering ability, and by doing so, the white purity in the colored state of the liquid crystal layer is remarkably improved, and the light scattering functional surface does not affect the black display, so this is not provided. Since a black display similar to the case can be obtained, the contrast is also improved.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
[0030]
1 is a cross-sectional view of the liquid crystal display element of the first embodiment, FIG. 2 is a cross-sectional view of the liquid crystal display element of the second embodiment, and FIG. 3 is a cross-sectional view of the liquid crystal display element of the third embodiment.
[0031]
1 has a liquid crystal layer 5 sandwiched between a pair of substrates 11 and 12. The light incident side (image viewing side) substrate 11 is a transparent substrate, and the opposite substrate 12 is a visible light absorbing black substrate. The substrate 12 may be a transparent substrate. In that case, a black layer may be provided on the back surface (outer surface) of the substrate.
[0032]
A large number of narrow strip-like transparent electrodes 21 are formed in parallel on the substrate 11. A large number of narrow strip-shaped transparent electrodes 22 are also formed in parallel on the substrate 12. The two substrates 11 and 12 face each other so that these electrodes face each other, and when viewed from the substrate surface side, the electrodes 21 and 22 are orthogonal to each other. That is, a matrix electrode structure is formed. A portion where the electrodes 21 and 22 intersect as seen from the substrate surface side is a pixel.
[0033]
An insulating film 31 for preventing a short circuit between the electrodes is formed on the surface of the substrate 11 having the electrodes 21, and an alignment film (alignment stabilizing film) 41 for aligning liquid crystal molecules is formed thereon. An insulating film 32 is also formed on the surface of the other substrate 12 having the electrodes 22, and an alignment film (alignment stabilizing film) 42 is further formed thereon. Note that an insulating film and an alignment film are not necessarily provided, and may be provided as necessary.
[0034]
In addition, spacers 6 for defining the thickness of the liquid crystal layer 5 are distributed between the substrates 11 and 12, and the liquid crystal layer 5 is surrounded by a seal wall 7 formed between the substrates, thereby leaking liquid crystal. Is prevented. The liquid crystal layer 5 includes cholesteric liquid crystal exhibiting a cholesteric phase at room temperature.
[0035]
Appropriate columnar structures CL for satisfying one or more of the maintenance of the distance between the two substrates and the self-holding property (mutual coupling of the two substrates, the maintenance of the element strength, etc.) between the substrates. May be provided.
[0036]
The electrodes 21 and 22 are connected to an element driving unit D for matrix driving. In each pixel, a predetermined pulse voltage is applied between the electrodes 21 and 22 by the driving unit, so that the liquid crystal layer in the pixel is in a planar state (colored state) or a focal conic state (transparent state, and hence a black display layer). Black display state), thereby enabling image display. The liquid crystal display element LCD1 has a memory property. That is, the planar state or focal connection state is maintained even after the pulse voltage is applied.
[0037]
The liquid crystal display element LCD2 of FIG. 2 employs a transparent substrate 13 instead of the black substrate 12 in the element of FIG. 1, and has a black layer 8 provided on the back surface thereof and a light scattering layer on the surface (outer surface) of the image observation side substrate 11. 9 is provided. The substrate 11 and the light scattering layer 9 may be combined to be regarded as an image observation side substrate. In this case, the substrate is a substrate having a functional surface having light scattering ability on the surface. The surface of the substrate 11 itself may be a surface having light scattering ability. The other points are the same as those of the element shown in FIG. Parts similar to those of the element of FIG. 1 are denoted by the same reference numerals as in FIG.
[0038]
The liquid crystal display element LCD3 of FIG. 3 is obtained by further providing a light scattering layer 9 ′ between the substrate 13 and the black layer 8 in the element of FIG. Substrate 13 and light scattering layer 9 ' Can be viewed as a substrate opposite to the image observation side, in which case the substrate is a substrate having a functional surface having light scattering ability on the surface (outer surface). The surface of the substrate 13 itself may be a surface having light scattering ability. The other points are the same as those of the element shown in FIG. Parts similar to those of the element of FIG. 2 are denoted by the same reference numerals as in FIG.
[0039]
Next, each part of the liquid crystal display elements LCD1 to LCD3 will be described.
<Substrate 11, 12, 13>
At least one of the pair of substrates needs to have translucency. As a substrate having translucency, a glass substrate can be given as a typical example. In addition to a glass substrate, for example, polycarbonate (PC), polyethersulfone (PES), polyarylate (PAr), polyethylene terephthalate (PET). A flexible substrate made of, for example, can be used.
<Electrodes 21 and 22>
As the electrode, for example, a transparent conductive film such as Indium Tin Oxide (ITO: Indium Tin Oxide) or Indium Zinc Oxide (IZO: Indium Zinc Oxide) can be employed. A metal electrode such as aluminum or silicon, or a photoconductive film such as amorphous silicon or BSO (Bismuth Silicon Oxide) can also be used.
[0040]
In order to form the electrodes in a matrix, for example, a transparent electrode film such as ITO is vapor-deposited on the substrate by a sputtering method or the like, or a transparent electrode film such as ITO is formed on the entire surface of the substrate, and then the photolithographic method is used. What is necessary is just to pattern. Further, a plurality of TFTs may be used as switching elements.
<Insulating films 31, 32>
The insulating film may also serve as a gas barrier layer for improving the reliability of the liquid crystal display element.
[0041]
Examples of the insulating film include inorganic material films made of silicon oxide, titanium oxide, zirconium oxide and alkoxides thereof, and organic films made of polyimide resin, acrylic resin, urethane resin, and the like. It can form by well-known methods, such as a vapor deposition method, a spin coat method, and a roll coat method, using such materials.
[0042]
The insulating film also functions as a color filter if a dye is added to the above material. Furthermore, the insulating film can be formed using the same material as the polymer resin used for the columnar structure CL.
<Alignment stabilizing films 41 and 42>
Examples of the material for the alignment stabilizing film include organic films such as polyimide resin, polyamideimide resin, polyetherimide resin, polyvinyl butyral resin, and acrylic resin, and inorganic materials such as silicon oxide and aluminum oxide. The alignment film formed using these materials may be subjected to a rubbing treatment or the like.
<Spacer 6>
The spacer is for determining a gap between the pair of substrates and maintaining the gap uniformly. Examples of the spacer include a sphere made of an organic material such as a resin or an inorganic oxide (glass, ceramic, etc.). In addition, a spacer having a fixing / adhesion performance in which a thermoplastic resin is coated on the surface is also preferably used.
[0043]
When adopting the columnar structure CL, a spacer having a size smaller than the thickness (height) of the columnar structure is arranged, and the gap accuracy between substrates is reduced by compressing the columnar structure to the spacer size under heating or pressurization. As a result, voltage application unevenness, display unevenness, and the like can be reduced accordingly.
<Cholesteric liquid crystal layer 5>
The liquid crystal layer 5 includes cholesteric liquid crystal. Examples of such cholesteric liquid crystal include chiral nematic liquid crystal obtained by adding an appropriate amount of a chiral material described below to nematic liquid crystal. Chiral nematic liquid crystals exhibit a cholesteric phase at room temperature. In addition, the selective reflection wavelength can be adjusted by the amount of the chiral material added.
[0044]
Examples of nematic liquid crystal include conventionally known liquid crystal ester compounds, liquid crystal pyrimidine compounds, liquid crystal cyanobiphenyl compounds, and liquid crystal compounds having a polar group such as a fluorine atom, a fluoroalkyl group, and a cyano group. One or a mixture thereof may be mentioned, and a liquid crystal compound having a positive dielectric anisotropy as a main component is preferable. Furthermore, you may add a pigment | dye and / or a ultraviolet absorber.
[0045]
The chiral nematic liquid crystal has the advantage that the pitch of the spiral structure of the chiral nematic liquid crystal can be changed by changing the amount of the chiral dopant to be added, thereby controlling the selective reflection wavelength of the liquid crystal. In general, as a term representing the pitch of the helical structure of the liquid crystal molecules, a helical bitch defined by the distance between the molecules when the liquid crystal molecules rotate 360 ° along the helical structure of the liquid crystal molecules is used.
[0046]
As the chiral material to be added, a cholesteric liquid crystal having a cholesteric ring, a chiral nematic liquid crystal, or an organic compound that does not exhibit liquid crystallinity but has a function of twisting nematic liquid crystal molecules can be used.
[0047]
For example, biphenyl compounds, terphenyl compounds, ester compounds, pyrimidine compounds, azoxy compounds, etc. that give nematic liquid crystal molecules a layered helical structure (a molecular structure in which liquid crystal molecules rotate 360 ° along the helical structure of liquid crystal molecules) it can.
[0048]
A commercially available chiral material having an optically active group at the terminal group of the compound can also be used. A cholesteric liquid crystal having a cholesteric ring typified by cholesteric nanolates can also be used.
[0049]
The addition amount of the chiral material can be about 7 wt% to about 45 wt% based on the total weight of the nematic liquid crystal and the chiral material. If the amount is less than 7 wt%, sufficient memory properties may not be obtained. If the amount exceeds 45 wt%, the cholesteric phase is not exhibited or solidified at room temperature. Case There is. The type of chiral material to be added may be one type or a plurality of types, but there are some advantages in terms of temperature compensation and stability when using a plurality of types of materials depending on the type of liquid crystal.
[0050]
Further, in order to realize the favorable device characteristics aimed by the present invention, it is desirable to use a liquid crystal composition having a high refractive index anisotropy. That is, the refractive index anisotropy is desirably about 0.18 to 0.32. If the refractive index anisotropy is too small, the reflectance is lowered and the scattering component is also reduced, so that it is difficult to obtain a broad selective reflection peak.
[0051]
The dielectric anisotropy is desirably 5 to 40. If the dielectric anisotropy is too low, the driving voltage becomes high. On the other hand, if the dielectric anisotropy is too high, the stability and reliability of the device deteriorates, and image defects and image noise are likely to occur.
[0052]
If the selective reflection wavelength of the cholesteric liquid crystal (cholesteric liquid crystal composition) is adjusted to selectively reflect visible light, brighter reflection can be obtained. Furthermore, by adjusting to 500 nm to 800 nm, more preferably 570 nm to 630 nm, both brightness and color can be achieved.
<Columnar structure CL>
Examples of the columnar structure include those made of a polymer composition (particularly a resin material). First, the structure surface of the columnar structure will be described.
[0053]
Examples of the columnar structure include columnar structures such as a columnar body, a quadrangular columnar body, an elliptical columnar body, a trapezoidal columnar body, and a conical columnar body, which are arranged in a predetermined pattern such as a lattice arrangement. be able to. Alternatively, stripes arranged at predetermined intervals may be used. The arrangement of the columnar structures is not a random arrangement, and can appropriately hold the gaps of the substrate, such as an equidistant arrangement, an arrangement in which the interval gradually changes, and an arrangement in which a predetermined arrangement pattern is repeated at a constant period. In addition, the arrangement is preferably considered so as not to disturb the image display. If the ratio of the area occupied in the display area of the liquid crystal display element is 1% to 40%, the columnar structure can give practically satisfactory characteristics to the liquid crystal display element while maintaining an appropriate strength.
[0054]
As a resin material, any general resin such as an epoxy resin, an acrylic resin, a polyester resin, a polyether resin, a polyethylene resin, or a polyimide resin can be used.
[0055]
A method for manufacturing a columnar structure using a polyester resin will be described. For example, a polyester resin solution may be printed on a substrate on which an ITO electrode having a predetermined pattern is formed using a printing machine such as a roll coater or a gravure coater, and then dried and cured.
[0056]
When a liquid crystal display element is formed, a liquid crystal composition may be injected between the substrates sandwiching the columnar structures by a vacuum injection method or the like. Alternatively, the liquid crystal composition may be dropped when the pair of substrates are bonded, and the liquid crystal composition may be sealed simultaneously with the bonding of the substrates.
<Seal wall 7>
As the material of the seal wall, a thermosetting type or a photosetting type adhesive such as an epoxy resin or an acrylic resin can be used.
<Light scattering layer>
Typical examples of the light scattering layer include those in which transparent fine particles are dispersed in a plastic film, and plastic films having a roughened surface. Moreover, as a position which arrange | positions a light-scattering layer, the outermost surface side of the board | substrate by the side of element observation and the space between the board | substrate on the opposite side to an element observation side and a light absorption layer can be mentioned, for example. The substrate itself may also serve as the light scattering layer.
<Others: UV absorbing layer>
In general, it is known that the characteristics of liquid crystals change due to light components of 380 nm or less. The change in characteristics occurs in the form of display unevenness or drive voltage deterioration. In order to prevent this, an ultraviolet cut filter or an ultraviolet cut resin film may be provided.
[0057]
When a deflection plate or a phase difference plate is employed, an ultraviolet absorbing layer may be formed thereon as a protective film containing an ultraviolet absorber. Further, an ultraviolet absorbing layer may be formed on the transparent substrate.
[0058]
The ultraviolet absorbing layer is not particularly limited and may be formed by any method. As a typical method, a method in which an ultraviolet absorbent is mixed in an acrylic resin, a silicon resin, or the like and applied to a substrate or the like and cured, or a method in which a filter in which an ultraviolet absorbent material is added to a material such as triacetate is sandwiched may be used.
Representative ultraviolet absorbing materials include, but are not limited to, benzophenone and benzotriazole.
[0059]
In any of the elements LCD1 to LCD3, the thickness of the electrodes 21 and 22 (particularly the electrode 21 on the image observation side) is set to be less than 80 nm and 50 nm or more. The function f of the light wavelength λ (nm) of the element when the thickness of the electrode is in such a range and the liquid crystal layer 5 is in the focal conic state. ₁ The light reflectance (%) represented by (λ) is the selective reflection wavelength λ in the planar state of the liquid crystal layer 5. _P (Nm) 360 (nm) ≦ λ _t <Λ _P Wavelength λ _t (Nm) is maximized and f ₁ (Λ _t )> F ₁ (Λ _P The whole is prepared so that the reflection peak that satisfies the relationship (1) exists in the focal conic state.
[0060]
FIG. 4 shows that when the liquid crystal layer 5 is in the focal conic state, the light reflectance of the element is 360 (nm) ≦ λ. _t <Λ _P Wavelength λ _t (Nm) is the maximum, and f ₁ (Λ _t )> F ₁ (Λ _P ), Or f ₁ (Λ _t )> F ₁ (Λ _P ) + 5% relationship is established.
[0061]
Further, as a cholesteric liquid crystal that provides the liquid crystal layer 5, the light reflectance at a selective reflection wavelength nP (n is an average refractive index of the cholesteric liquid crystal and P is a helical pitch of the cholesteric liquid crystal) in a colored state (planar state). R, an equation expressed as a function of wavelength λ, where Δn is the refractive index anisotropy of the cholesteric liquid crystal
{Exp- [2 (λ-nP) ² / Δn ² P ² ] The integral value Sa in the visible wavelength region of R is a function f representing the wavelength-light reflectance spectrum of the element when the liquid crystal is in the planar state. ₂ A value that is 40% to 55% of the integrated value Sb in the visible wavelength range of (λ) is employed. The visible wavelength range here is a wavelength range of 360 nm to 740 nm. Since Sb is the total integral value of the spectrum in the visible light region, and Sa is the integral value of the spectrum excluding the scattered portion, the smaller the Sa / Sb value, the whiter it is. FIG. 5 is a diagram showing the relationship between Sa and Sb.
[0062]
Each of the liquid crystal display elements LCD1 to LCD3 can spread the spectrum waveform of the wavelength-light reflectance spectrum in a colored state (liquid crystal is in a focal conic state) to a wide visible region, and has excellent white purity with black as a background color. Therefore, it is possible to display a bright black and white image with good visibility. Further, the driving voltage is lower than that of the polymer stable liquid crystal display element.
[0063]
In the element LCD 2 of FIG. 2, since the light scattering layer 9 is provided on the light incident side (image observation side) of the element, interference of reflected light at the interface of the electrode (particularly the electrode 21) appears more effectively and is colored. The spectrum waveform of the wavelength-light reflectance spectrum in the state can be expanded to a wider visible region, and a black and white image display with excellent white purity can be performed with black as a background color.
[0064]
In the element LCD 2 of FIG. 3, since the light scattering layer 9 ′ is also provided between the substrate 13 opposite to the light incident side of the element and the black layer 8, the white purity in the colored state is remarkably improved. Further, since the light scattering layer 9 ′ between the black layer 8 and the substrate 13 does not affect the black display, a black display similar to the case where it is not provided can be obtained, and the contrast is also improved.
[0065]
Next, since the performance evaluation experiment of the liquid crystal display element which concerns on this invention was performed, it demonstrates with a comparative experiment example, However, This invention is not limited to those experiment examples.
[0066]
Spectral reflection characteristics and Y value (luminous reflectance) of the element were measured with a spectrocolorimeter CM3700d manufactured by Minolta Co., Ltd. White purity is a value indicating the distance from the white coordinate of the white calibration plate when the color is displayed in XY coordinates. In other words, the smaller the value, the more white it can be said. 0.08 or less is preferable.
<Experimental example 1>
Nematic liquid crystal (refractive index anisotropy Δn: 0.286, dielectric anisotropy Δε: 17.3, NI point: 113 ° C., viscosity η: 71) 86.09 wt /% chiral material (CB15 manufactured by Merck) A chiral nematic liquid crystal A was prepared by adding 11.23 wt% and 2.68% of a chiral material (R1011 manufactured by Merck). This chiral nematic liquid crystal A exhibits a cholesteric phase and has a selective reflection wavelength λ. _P Was around 580 nm.
[0067]
As each of the pair of substrates sandwiching the liquid crystal layer, a glass substrate (thickness 1 mm) on which a planar transparent electrode was formed was employed. The transparent electrode is an ITO (indium tin oxide) transparent electrode having a thickness of 73 nm and a surface resistance of 320 Ω / □.
[0068]
For any of the substrates, an alignment film having a thickness of 800 mm was formed on the surface provided with the transparent electrode using an alignment film material JALS-204 (manufactured by JSR).
[0069]
One substrate was sprayed with a 9 μm diameter spacer (manufactured by Sekisui Fine Chemical Co., Ltd.) on the alignment film, followed by screen printing of a sealing material XN21S (manufactured by Mitsui Chemicals) on the periphery of the substrate, and partly for liquid crystal injection A sealing wall having a predetermined height was formed leaving the opening. Thereafter, the two substrates were bonded so that their electrodes face each other and orthogonal to each other when seen from the plane, and the sealing wall was heat-cured.
[0070]
The liquid crystal A was injected between the substrates in the cholesteric phase state by vacuum injection through the seal wall opening into the empty cell thus formed, and then the seal wall opening was closed with a photocurable resin. . Further, a black light absorption film was provided on the back surface of the cell (the substrate outer surface opposite to the light incident side (image observation side)).
[0071]
The device characteristics measured by driving the liquid crystal display device thus formed were as follows.
[0072]
Apply 70V, 5msec pulse voltage between the electrodes, apply 2msec 50V, 2msec pulse voltage, and apply 2msec 50V, 2msec pulse voltage to bring liquid crystal A into the focal conic state, and then between the electrodes Then, 70 V, 5 msec pulse voltage was applied to the liquid crystal, 2 msec apart, 70 V, 2 msec pulse voltage was applied, and 2 msec apart, 70 V, 2 msec pulse voltage was applied, and the liquid crystal A was brought into the planar state.
[0073]
λ _t : 380 nm, f ₁ (Λ _t ): 7.6%, f ₁ (Λ _P ): 1.9% Black Y value: 1.7 (threshold voltage 50V), Colored Y value: 17.4 (threshold voltage 70V)
Peak reflectance: 21.2%, Sa / Sb: 50.3%
White purity: 0.054
Here, the peak reflectance is the selective reflection wavelength (λ in the planar state). _P ). The spectral characteristic in the selective reflection state has a broad peak or a plurality of peaks as compared with an element displaying a single color such as R, B, and G, and therefore corresponds to the peak showing the highest reflectance here. The reflection wavelength was determined as the selective reflection wavelength.
[0074]
FIG. 6 shows f in Experimental Example 1. ₁ (Λ _t ), Peak reflectance and the like.
<Comparative Experimental Example 1>
A liquid crystal composition A prepared in the same manner as in Experimental Example 1 was used.
[0075]
As each of the pair of substrates sandwiching the liquid crystal layer, a glass substrate (thickness 0.7 mm) on which a planar transparent electrode was formed was employed. The transparent electrode is an ITO transparent electrode having a thickness of 230 nm and a surface resistance of 7Ω / □.
[0076]
For one substrate, an alignment film having a thickness of 800 mm was formed on the surface provided with the transparent electrode using an alignment film material JALS-204 (manufactured by JSR). About the other board | substrate, the 800-thick thickness vertical alignment film was formed on the surface in which the transparent electrode was provided using alignment film material JALS-204 (made by JSR).
[0077]
A spacer of 9 μm diameter (manufactured by Sekisui Fine Chemical Co., Ltd.) is sprayed on the alignment film on the one substrate, and then a sealant XN21S (manufactured by Mitsui Chemicals Co., Ltd.) is screen-printed on the periphery of the substrate, and a liquid crystal is injected in part. A sealing wall having a predetermined height was formed leaving an opening for use. Thereafter, the two substrates were bonded so that their electrodes face each other and orthogonal to each other when seen from the plane, and the sealing wall was heat-cured.
[0078]
The liquid crystal A was injected between the substrates in the cholesteric phase state by vacuum injection through the seal wall opening into the empty cell thus formed, and then the seal wall opening was closed with a photocurable resin. . Further, a black light absorption film was provided on the back surface of the cell.
[0079]
The device characteristics measured by driving the liquid crystal display device thus formed were as follows.
[0080]
After applying 60V, 5msec pulse voltage between the electrodes, 2msec apart, 40V, 2msec pulse voltage is applied, and 2msec apart, 40V, 2msec pulse voltage is applied to bring liquid crystal A into a focal conic state, and then between the electrodes 60 V, 5 msec pulse voltage was applied to the liquid crystal, 2 msec apart, 60 V, 2 msec pulse voltage was applied, and 2 msec apart, 60 V, 2 msec pulse voltage was applied, and the liquid crystal A was brought into the planar state.
[0081]
λ _t : 380 nm, f ₁ (Λ _t ): 4.7%, f ₁ (Λ _P ): 1.5%
Black Y value: 1.2 (threshold voltage 40V), coloring Y value: 17.4 (threshold voltage 60V)
Peak reflectance: 22.0%, Sa / Sb: 58.2%
White purity: 0.094
It can be seen that the Sa / Sb value increases when the transparent electrode is formed thick. That is, the scattered component of the spectrum waveform is reduced (see FIG. 6), and the white purity value is also increased.
[0082]
FIG. 6 shows f in Comparative Experimental Example 1. ₁ (Λ _t ), Peak reflectance and the like.
<Experimental example 2>
A liquid crystal composition A prepared in the same manner as in Experimental Example 1 was used, and the same procedure as in Experimental Example 1 was adopted up to the procedure of providing a black light absorption film to form a display element.
[0083]
Furthermore, the functional layer P (Dai Nippon Printing Co., Ltd. light-scattering film IDS21K) which has light-scattering ability was arrange | positioned on the light-incidence side surface (image observation side surface) of this element.
[0084]
The device characteristics measured by driving the liquid crystal display device thus formed were as follows.
[0085]
Apply 70V, 5msec pulse voltage between the electrodes, apply 2msec 50V, 2msec pulse voltage, and apply 2msec 50V, 2msec pulse voltage to bring liquid crystal A into the focal conic state, and then between the electrodes Then, 70 V, 5 msec pulse voltage was applied to the liquid crystal, 2 msec apart, 70 V, 2 msec pulse voltage was applied, and 2 msec apart, 70 V, 2 msec pulse voltage was applied, and the liquid crystal A was brought into the planar state.
[0086]
λ _t : 410 nm, f ₁ (Λ _t ): 10.3%, f ₁ (Λ _P ): 2.8% black Y value: 3.6 (threshold voltage 50 V), coloring Y value: 19.9 (threshold voltage 70 V)
Peak reflectance: 23.4%, Sa / Sb: 50.7%
White purity: 0.048
Compared with Experimental Example 1, the Sa / Sb value is large because the light scattering layer also has ultraviolet absorption ability, so light up to around 400 nm is cut, and the entire spectrum area is reduced accordingly. However, as shown in FIG. 6, the scattering component is greatly increased.
[0087]
FIG. 6 shows f in Experimental Example 2. ₁ (Λ _t ), Peak reflectance and the like.
<Experimental example 3>
A liquid crystal composition A prepared in the same manner as in Experimental Example 1 was used, and the same procedure as in Experimental Example 1 was adopted up to the procedure of providing a black light absorption film to form a display element.
[0088]
Further, a light scattering layer P similar to that in Experimental Example 3 was provided between the black light absorption film and the glass substrate and on both sides of the light incident side of the element.
[0089]
The device characteristics measured by driving the liquid crystal display device thus formed were as follows.
[0090]
Apply 70V, 5msec pulse voltage between the electrodes, apply 2msec 50V, 2msec pulse voltage, and apply 2msec 50V, 2msec pulse voltage to bring liquid crystal A into the focal conic state, and then between the electrodes Then, 70 V, 5 msec pulse voltage was applied to the liquid crystal, 2 msec apart, 70 V, 2 msec pulse voltage was applied, and 2 msec apart, 70 V, 2 msec pulse voltage was applied, and the liquid crystal A was brought into the planar state.
[0091]
λ _t : 420 nm, f ₁ (Λ _t ): 11.4%, f ₁ (Λ _P ): 3.8%
Black Y value: 3.7 (threshold voltage 50V), coloring Y value: 21.5 (threshold voltage 70V)
Peak reflectance: 24.1%, Sa / Sb: 45.2%
White purity: 0.030
<Experimental example 4>
A liquid crystal composition A prepared in the same manner as in Experimental Example 1 was used.
[0092]
A glass substrate (thickness 1 mm) on which a planar transparent electrode was formed was adopted as each of the pair of substrates sandwiching the liquid crystal layer. The transparent electrode is an ITO transparent electrode having a thickness of 45 nm and a surface resistance of 550 Ω / □.
[0093]
For any of the substrates, an alignment film having a thickness of 800 mm was formed on the surface provided with the transparent electrode using an alignment film material JALS-204 (manufactured by JSR).
[0094]
One substrate was sprayed with a 9 μm diameter spacer (manufactured by Sekisui Fine Chemical Co., Ltd.) on the alignment film, followed by screen printing of a sealing material XN21S (manufactured by Mitsui Chemicals) on the periphery of the substrate, and partly for liquid crystal injection A sealing wall having a predetermined height was formed leaving the opening. Thereafter, the two substrates were bonded so that their electrodes face each other and orthogonal to each other when seen from the plane, and the sealing wall was heat-cured.
[0095]
The liquid crystal A was injected between the substrates in the cholesteric phase state by vacuum injection through the seal wall opening into the empty cell thus formed, and then the seal wall opening was closed with a photocurable resin. . Further, a black light absorption film was provided on the back surface of the cell.
[0096]
The device characteristics measured by driving the liquid crystal display device thus formed were as follows.
[0097]
Apply 100V, 5msec pulse voltage between electrodes, apply 2msec pulse voltage, 70V, 2msec pulse voltage, apply 2msec pulse voltage, 70V, 2msec pulse voltage to bring liquid crystal A into a focal conic state, and then between electrodes 100 V, 5 msec pulse voltage was applied to the liquid crystal, 2 msec apart, 100 V, 2 msec pulse voltage was applied, and 2 msec apart, 100 V, 2 msec pulse voltage was applied, and the liquid crystal A was brought into the planar state.
[0098]
λ _t : 380 nm, f ₁ (Λ _t ): 9.7%, f ₁ (Λ _P ): 2.4%
Black Y value: 2.2 (threshold voltage 70V), coloring Y value: 17.5 (threshold voltage 100V)
Peak reflectance: 20.9%, Sa / Sb: 46.4%
White purity: 0.049
As can be seen from this experiment, the thinner the transparent electrode, the more the white purity of the colored state can be improved. However, the surface resistance of the electrode increases and the threshold voltage increases.
<Comparative Experiment Example 2>
A liquid crystal composition A prepared in the same manner as in Experimental Example 1 was used.
[0099]
A glass substrate (thickness 1 mm) on which a planar transparent electrode was formed was adopted as each of the pair of substrates sandwiching the liquid crystal layer. The transparent electrode is an ITO transparent electrode having a thickness of 100 nm and a surface resistance of 230Ω / □.
[0100]
For any of the substrates, an alignment film having a thickness of 800 mm was formed on the surface provided with the transparent electrode using an alignment film material JALS-204 (manufactured by JSR).
[0101]
One substrate was sprayed with a 9 μm diameter spacer (manufactured by Sekisui Fine Chemical Co., Ltd.) on the alignment film, followed by screen printing of a sealing material XN21S (manufactured by Mitsui Chemicals) on the periphery of the substrate, and partly for liquid crystal injection A sealing wall having a predetermined height was formed leaving the opening. Thereafter, the two substrates were bonded so that their electrodes face each other and orthogonal to each other when seen from the plane, and the sealing wall was heat-cured.
[0102]
The liquid crystal A was injected between the substrates in the cholesteric phase state by vacuum injection through the seal wall opening into the empty cell thus formed, and then the seal wall opening was closed with a photocurable resin. . Further, a black light absorption film was provided on the back surface of the cell.
[0103]
The device characteristics measured by driving the liquid crystal display device thus formed were as follows.
After applying 60V, 5msec pulse voltage between the electrodes, 2msec apart, 40V, 2msec pulse voltage is applied, and 2msec apart, 40V, 2msec pulse voltage is applied to bring liquid crystal A into a focal conic state, and then between the electrodes 60 V, 5 msec pulse voltage was applied to the liquid crystal, 2 msec apart, 60 V, 2 msec pulse voltage was applied, and 2 msec apart, 60 V, 2 msec pulse voltage was applied, and the liquid crystal A was brought into the planar state.
[0104]
λ _t : 380 nm, f ₁ (Λ _t ): 5.8%, f ₁ (Λ _P ): 1.5%
Black Y value: 1.3 (threshold voltage 40V), coloring Y value: 17.4 (threshold voltage 60V)
Peak reflectance: 21.5%, Sa / Sb: 57.5%
White purity: 0.091
When the thickness of the electrode exceeds 80 nm, both the white purity and the Sa / Sb value increase, and the effect due to the interference of the reflected light cannot be seen.
[0105]
Table 1 summarizes the experimental examples and comparative experimental examples described above.
[Table 1]

[0106]
【The invention's effect】
As described above, according to the present invention, a liquid crystal display element using cholesteric liquid crystal has excellent bistability, can be driven at a lower voltage than a polymer stable liquid crystal display element, and is bright and excellent in visibility. When a black and white image is displayed using a black background color, a liquid crystal display element capable of obtaining good white purity and brightness characteristics can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of a liquid crystal display element according to the present invention.
FIG. 2 is a schematic cross-sectional view of another example of the liquid crystal display element according to the present invention.
FIG. 3 is a schematic cross-sectional view of still another example of the liquid crystal display element according to the present invention.
FIG. 4 is a function f. ₁ The light reflectance (%) represented by (λ) is 360 (nm) ≦ λ _t <Λ _P Wavelength λ _t It is a figure which shows the example which becomes maximum in (nm).
FIG. 5 shows an expression {exp− [2 (λ−nP) ² / Δn ² P ² ]} Integral value Sa and function f in the visible wavelength range of R ₂ It is a figure which shows the relationship of the integral value Sb in the visible wavelength range of ((lambda)).
FIG. 6 shows the experimental result f ₁ (Λ _t ) And peak reflectivity and the like.
[Explanation of symbols]
LCD1, LCD2, LCD3 Liquid crystal display element
11, 12, 13 substrate
21 and 22 electrodes
31, 32 Insulating film
41, 42 Alignment film
5 Liquid crystal layer
6 Spacer
7 Seal wall
8 Black layer
9, 9 'Light scattering layer
CL Columnar structure
D drive unit

Claims (7)

A pair of substrates in which at least a substrate disposed on the element observation side has translucency; a transparent electrode provided on the element observation side substrate; and a liquid crystal layer including a cholesteric liquid crystal sandwiched between the pair of substrates; The substrate opposite to the element observation side is colored black, the transparent electrode has a thickness d (nm) of less than 80 nm, and the liquid crystal layer is in a focal conic state. The light reflectance (%) represented by the function f ₁ (λ) of the light wavelength λ (nm) is 360 (nm) with respect to the selective reflection wavelength λ _P (nm) in the planar state of the liquid crystal layer. ≦ λ _t <λ _P , which is a maximum at a wavelength λ _t (nm), and a reflection peak that satisfies the relationship of f ₁ (λ _t )> f ₁ (λ _P ) exists in a focal conic state. A liquid crystal display element. The liquid crystal display element according to claim 1, wherein the reflection peak satisfies f ₁ (λ _t )> f ₁ (λ _P ) + 5%. The light reflectance at the selective reflection wavelength nP of the cholesteric liquid crystal in the planar state (where n is the average refractive index of the cholesteric liquid crystal and P is the helical pitch of the cholesteric liquid crystal) is R, and the refractive index anisotropy of the cholesteric liquid crystal is Δn. Then, the integral value Sa in the visible wavelength region of the expression {exp− [2 (λ−nP) ² / Δn ² P ² ]} R expressed as a function of the wavelength λ is obtained when the liquid crystal layer is in a planar state. 3. The liquid crystal display element according to claim 1, wherein the function value f ₂ (λ) representing the wavelength-light reflectance spectrum of the element is not less than 40% and not more than 55% of the integrated value Sb in the visible wavelength region.   The liquid crystal display element according to claim 1, wherein a thickness d of the transparent electrode is 50 nm or more. Wherein when the liquid crystal layer in the focal conic state, the liquid crystal display device according to any one reflectivity of 4 claims 1 to a maximum at the wavelength lambda _t of the element. The liquid crystal display element according to claim 1, wherein the substrate on the element observation side has a functional surface having light scattering ability on an outer surface. The substrate opposite to the element observation side is a transparent substrate having a light absorption layer provided on an outer surface, and the substrate outer surface provided with the light absorption layer has a functional surface having light scattering ability. 7. A liquid crystal display element according to any one of items 1 to 6.

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