KR20150140000A - The LCD Light Modulation Apparatus - Google Patents

Abstract

The present invention relates to an LCD light attenuation device and a smart mirror for a vehicle using the same, wherein the LCD light attenuation device is applied to a smart glass window, a light shutter for a camera, and a room mirror or side mirror of a vehicle. The LCD light attenuation device according to the present invention comprises: an LCD panel including one or more liquid crystal cells; and an electric power supply device for supplying an electrical field to the LCD panel. The liquid crystal cell includes: a liquid crystal layer restricted within a cell gap having a particular range; and two substrate layers facing each other based on the liquid crystal layer. The liquid crystal layer is filled with a mixture of: a nematic liquid crystal having a negative dielectric constant aeolotropy; a chiral material having a content of 60-99% of a maximum content c_(th), wherein a nematic liquid crystal phase induced while an electric field is not applied under the predetermined cell gap d may be included; and a dichromatic dye having an amount of penetrating or absorbing light by being rearranged with the nematic liquid crystal according to a supply of the electric filed. The substrate layer comprises: a vertical aligning layer for firstly arranging the nematic liquid crystal in a vertical direction of a plane of the substrate layer; and an electrode for generating an electrical field passing through the liquid crystal layer, and secondly arranging the nematic liquid crystal and dichromatic dye differently from the firstly arranged order.

Description

The LCD Light Modulation Apparatus < RTI ID = 0.0 >

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection-type LCD light attenuator for use in a smart window, a camera-use optical shutter and the like, and a smart mirror for a vehicle, and more particularly to a smart window glass for electrically controlling the visible light transmittance of a window glass A transmissive type LCD light attenuating device applied to the LCD; A transmission type LCD light attenuator applied to an optical shutter for electrically controlling an amount of light incident on a camera image sensor; And a reflective type LCD light attenuating device applied to a room mirror or a side mirror of a vehicle to protect the eyesight of a driver from a strong light projected from the rear at night and to prevent glare, and a smart mirror for a vehicle using the same.

Recently, a special film for controlling the light transmittance is attached to the glass of the building or the glass of the vehicle for energy saving and privacy protection. Since such special films generally maintain a constant light transmittance, there is a need for a smart window that can artificially control the light transmittance when necessary.

In addition, as the smartphone camera becomes more high resolution with more than 10 million pixels, the size of each pixel becomes relatively small, and the sensitivity of the CMOS image sensor has been improved so as to minimize the noise of the reduced pixel. However, such a high-sensitivity image sensor has a problem in that too much light is incident under a bright environment, which exceeds the normal photosensitive limit. Therefore, in order to expand the normal operating range of the high-sensitivity image sensor, that is, the dynamic range, the need for an optical shutter capable of adjusting the amount of light incident on the image sensor has been highlighted.

In order to solve these problems, electro-optical optical shutters and light transmittance control methods using a liquid crystal display (LCD) technique have been proposed (Patent Documents 1 to 12). There has been proposed a technique of applying an LCD shutter to an image recognition apparatus by using an optical shutter. However, due to the polarizing plate applied to LCD, the light transmittance in a state where the shutter is open is lowered, and when polarized light is incident, There are disadvantages [Patent Documents 1, 2, 3, 5, 11]. There has been proposed a technique of electrically adjusting the size or shape of a diaphragm by using an LCD having a polarizing plate applied to an optical system of an image recognition apparatus. However, there is a problem that a loss of light transmittance caused by applying a polarizing plate, Due to problems such as image alteration due to strong interaction with the liquid crystal layer, improvement of the reaction speed of the LCD, and difficulty in maintaining uniformity of the iris light transmittance due to optical nonuniformity of the electrode pattern portion formed for driving plural pixels of the LCD It has not been practically used [Patent Literatures 7 and 11].

Generally, a reflection type optical attenuator is applied to a smart mirror which prevents a driver's glare. Since the reflection type optical attenuator of a vehicle smart mirror is mainly implemented by ECM (Electrochromic material) technology, since the reaction speed in the use temperature range is relatively low, which is several seconds to several tens of seconds, And the like.

In order to improve the reaction rate, a reflection type optical attenuator implemented by a reflection type LCD is proposed [Patent Documents 13-16, 19], and a reflection type optical attenuator is mainly implemented using a reflection type LCD including a polarizing plate [Patent Literatures 14 and 19]. However, existing LCDs including a polarizing plate have a different light transmittance depending on the polarization direction of incident light, and the light transmittance and the light reflectance are lowered, so that the maximum reflectance is 35% or the maximum transmittance or maximum reflectance is 44% [Patent Literatures 14 and 19]. Also disclosed is a technique of controlling the light transmittance by adding a dichroic dye to a nematic liquid crystal (NLC) having a positive dielectric anisotropy (Patent Document 13). The optical attenuator to which this technique is applied has a lower light transmittance when the electric field is not applied because the light transmittance in a state in which the electric field is not applied is lower than that in the state where the electric field is applied. Therefore, when applied to a smart mirror of a vehicle, the smart mirror is dark in an emergency in which electricity supply is interrupted, thereby interfering with the safety operation of the driver, which in turn violates the international safety regulations of the vehicle mirror.

In US Pat. No. 6,201,588 and US Pat. No. 6,239,778, a liquid crystal layer is formed by mixing a nematic liquid crystal having a negative dielectric anisotropy and a small amount of a dichroic dye between two substrates coated with a vertical alignment layer A guest-host LCD is created to implement a transmissive optical attenuator. This is because the dichroism dye molecules are arranged anisotropically on the plane of the substrate with the pitch of the cholesteric phase being four times or more of the thickness of the liquid crystal cell in the state of voltage application and when the polarized light is incident, . When the pitch in the cholesteric phase is four times the thickness of the liquid crystal cell, the liquid crystal molecules have a structure twisted up to 90 degrees on the plane of the substrate and the dichroic dye molecules absorbing light are arranged in parallel with the liquid crystal molecules. Lt; RTI ID = 0.0 > 90 < / RTI > That is, since almost all of the dichroic dye molecules are arranged only in the azimuthal direction within the range of 180 degrees, the light having the polarization direction parallel to the liquid crystal molecules is absorbed well, but the light having the polarization direction perpendicular to the liquid crystal molecules has the light absorption . That is, the anisotropic arrangement of dye molecules can not maximize the absorption of isotropically polarized incident light when using the same amount of dye molecules. Therefore, it is difficult to sufficiently reduce the minimum reflectance of the mirror, and it is also possible to obtain a reference value for the pitch value on the cholesteric phase in which the liquid crystal molecules can be stably vertically aligned in a state where no voltage is applied at a given cell thickness . In other words, the range of the pitch on the cholesteric phase which can maximize the light absorption in a state where a sufficient voltage is applied under the assumption that the liquid crystal molecules maintain a stable vertical alignment under a given average cell thickness without voltage application is not determined .

US 6,621,550 discloses a technique of incorporating a dichroic dye into a nematic liquid crystal having a negative dielectric anisotropy in the structure of a reflection type LCD and injecting the dichroic dye into a vertically aligned cell. In order to improve the light absorptivity of the dichroic dye, a 1/4 wavelength film is formed between the liquid crystal layer and the reflector. When the light is incident from the outside, the light passes through the LCD and is reflected by the reflector, the polarization direction of the incident light is rotated 90 degrees And then passes through the liquid crystal layer again to improve the light absorption rate by the dichroic dye. However, in order to form a 1/4 wavelength polymer liquid crystal film in the cell, a more complicated process is required, and the light absorption rate is not constant depending on the polarization direction of the incident light.

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SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and provides a light attenuator which does not depend as much on the polarization direction of incident light as possible. Providing an optical attenuator having an LCD design condition capable of stably maximizing a light absorption rate even under various environments; It is also an object of the present invention to provide a transmission type LCD light attenuating device and a reflection type LCD light attenuating device which have a fast reaction rate of light reflectance change and are low in power consumption.

It is another object of the present invention to provide a smart mirror for a vehicle using the reflective LCD light attenuator described above.

Other objects of the present invention will become readily apparent from the following description.

According to an aspect of the present invention, there is provided a transmissive LCD optical attenuator,

A liquid crystal display device comprising: a transmissive LCD panel including at least one liquid crystal cell; and a power supply device supplying an electric field to the LCD panel, wherein the liquid crystal cell has a liquid crystal layer maintaining a constant cell gap, In a transmission type LCD light attenuator including a substrate layer,

Wherein the liquid crystal layer comprises a nematic liquid crystal having negative anisotropy of dielectric anisotropy, a chiral material having a stable vertical alignment in a state in which the nematic liquid crystal is not applied with an electric field, And is filled with a mixture of dichroic dyes that are rearranged and transmit or absorb light; Wherein the substrate layer comprises a vertical alignment layer in which the nematic liquid crystal and the dichroic dye are arranged in a first array perpendicular to the plane of the substrate layer, and an electric field passing through the liquid crystal layer, And an electrode for rearranging the sex dyes in a second arrangement different from the first arrangement.

According to another aspect of the present invention, there is provided a reflective type LCD light attenuator,

1. A liquid crystal display device comprising: a reflective LCD panel including at least one liquid crystal cell; and a power supply device for supplying an electric field to the LCD panel, wherein the liquid crystal cell has a liquid crystal layer maintaining a constant cell gap, In a reflective type LCD light attenuator including two substrate layers,

Wherein the liquid crystal layer comprises a nematic liquid crystal having negative anisotropy of dielectric anisotropy, a chiral material having a stable vertical alignment in a state in which the nematic liquid crystal is not applied with an electric field, And is filled with a mixture of dichroic dyes that are rearranged and transmit or absorb light; Wherein the substrate layer comprises a vertical alignment layer in which the nematic liquid crystal and the dichroic dye are arranged in a first array perpendicular to the plane of the substrate layer, and an electric field passing through the liquid crystal layer, And an electrode for rearranging the sex dyes in a second arrangement different from the first arrangement; Wherein one electrode of the substrate layer is transparent and another substrate layer comprises an electrode and a reflective layer.

According to another aspect of the present invention, there is provided a smart mirror for a vehicle,

A reflection type LCD panel including at least one liquid crystal cell and a light reflection layer, a power supply unit for supplying an electric field to the reflection type LCD panel, an incident light detection unit for sensing the brightness of the surroundings, And an operation analysis unit operable to control the power supply unit according to brightness of the surroundings to operate the LCD panel;

Wherein the liquid crystal cell has a liquid crystal layer maintaining a constant cell gap and two substrate layers facing the liquid crystal layer,

Wherein the liquid crystal layer comprises a nematic liquid crystal having negative anisotropy of dielectric anisotropy, a chiral material having a stable vertical alignment in a state in which the nematic liquid crystal is not applied with an electric field, And is filled with a mixture of dichroic dyes that are rearranged and transmit or absorb light; Wherein the substrate layer comprises a vertical alignment layer in which the nematic liquid crystal and the dichroic dye are arranged in a first array perpendicular to the plane of the substrate layer, and an electric field passing through the liquid crystal layer to generate the nematic liquid crystal and the dichroic And an electrode for rearranging the dye in a second arrangement different from the first arrangement.

Other technical aspects, features and advantages other than those described above will become apparent from the following drawings, claims, and detailed description of the invention.

The present invention has the following effects.

First, a light-attenuating device capable of adjusting the light transmittance and the light reflectance can be constituted by a transmissive or reflective LCD panel which does not use a polarizing plate.

Second, an optical attenuator capable of uniformly and fully controlling both polarized light and unpolarized light can be constructed.

Third, since the power consumption of the LCD panel is small, an energy saving type optical attenuator can be constructed.

Fourth, the light transmittance and the light reflectance can be adjusted to an arbitrary reaction rate according to the change in ambient brightness using the quick reaction rate and the halftone of the LCD.

Fifth, even when the power supply is cut off, the optical attenuator can stably maintain a high light transmittance and a high light reflectance.

Sixth, depending on the characteristics of the dichroic dye to be used, it is possible to arbitrarily select a region capable of controlling the light transmittance and the light reflectance in the wavelength region of the visible light ray and the infrared ray.

Seventh, a flat or curved glass or plastic can be used as the LCD substrate.

1 is a view illustrating a structure of a transmissive LCD light attenuator including a vertically aligned twisted nematic (VATN) GH (Guest-Host) LCD panel in a state in which no voltage is applied, according to an example of the present invention.
FIG. 2 is a structure of a transmission type LCD light attenuator composed of a VATN GH LCD panel with a sufficient voltage applied to a liquid crystal layer, according to one example of the present invention. FIG.
3 is a graph showing a change in the visible light transmittance of a Normally White Mode VATN GH LCD panel according to an average applied voltage.
FIG. 4 is a graph of the rate of change of light transmittance when a voltage is applied to a Normally White Mode VATN GH LCD panel by a single pulse of 10 V and 10 ms.
FIG. 5 is a graph showing the relationship between the case where the voltage of the LCD device in which the helical twisting power (HTP) is changed and the voltage of the LCD device in which the voltage of the LCD device is not applied is adjusted by adjusting the content of the chiral material contained in the liquid crystal of the Normally White Mode VATN GH LCD It is also a change in visible light transmittance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Hereinafter, an LCD optical attenuator according to an embodiment of the present invention and a smart mirror for a vehicle using the same will be described in detail with reference to the accompanying drawings.

1 and 2 show a structure of a transmission type LCD optical attenuator according to an embodiment of the present invention. FIG. 1 shows a state in which no power is supplied, and FIG. 2 shows a state in which power is supplied.

The LCD optical attenuator according to the present invention comprises a guest-host LCD panel including at least one liquid crystal cell 100 and a power supply unit 200 for supplying an electric field to each liquid crystal cell 100 of the LCD panel. The liquid crystal cell 100 includes a liquid crystal layer 110 and two substrate layers 120 and 130 stacked on both sides of the liquid crystal layer 110. [

The liquid crystal layer 110 includes spacers 111 for maintaining the spacing between the two substrate layers 120 and 130 within a predetermined range and can be rearranged according to the intensity of the electric field and is transparent and dielectric anisotropy. A negative nematic liquid crystal 112 and a positive dichroic dye 113 which is mixed with the nematic liquid crystal 112 and absorbs light of a certain wavelength band, And a chiral material 114 that causes the nematic liquid crystals 112 to have a twisted structure. In addition, the liquid crystal layer 110 is sealed by the sealant 115. Here, positive dichroism refers to a property of mainly absorbing light that oscillates in the longitudinal direction of a dye molecule. Each of the substrate layers 120 and 130 is made up of an antireflection layer 121 and 131, transparent substrates 122 and 132, transparent electrode layers 123 and 133, transparent protective layers 124 and 134, The alignment layers 125 and 135 are laminated and a liquid crystal layer 110 is formed between the two liquid crystal alignment layers 125 and 135. The nonreflective layers 121 and 131 are located at the outermost portions of the LCD panel and include light incident on the interface between the transparent substrates 122 and 132 and air or other optical components,

It has the function of minimizing the reflectance of light, and is generally designed to have a reflectance of 1% or less on the visible light line. The transparent substrates 122 and 132 are made of glass or plastic and have a flat or curved shape. In the case of a well-bent plastic substrate, it may be attached to glass or solid plastic to maintain a flatness or curvature constant. The transparent electrode layers 123 and 133 are generally formed of an ITO (indium tin oxide) thin film having a thickness of 300 nm or less. The transparent electrode layers 123 and 133 may be formed by coating the transparent electrodes 122 and 132 to a thickness of about 1500 Å, It can also be used as a very thin coating. However, there is a problem that the loss of light transmittance increases when the metal is coated and used. The transparent protective layers 124 and 134 are silicon nitride thin films or silicon oxide thin films and block various impurities introduced into the liquid crystal layer 110 from the transparent substrates 122 and 132 and the transparent electrode layers 123 and 133.

The liquid crystal alignment layers 125 and 135 allow the nematic liquid crystal molecules 112 of the liquid crystal layer 110 to be arranged in a direction perpendicular to the substrate layer plane. Generally, the liquid crystal molecules are arranged at an angle of 80 to 90 degrees with respect to the substrate. A silane surfactant is mainly used as a vertical alignment agent for such a function, and rubbing is performed with a soft cloth when tilted homeotropic alignment is required. The spacers 111 are used as means for maintaining the gap between the two substrate layers 120 and 130 within a certain range and even if the two substrate layers 120 and 130 are curved in a curved shape, , And the cell gap (d) within a certain range. The spacer 111 may be formed by dispersing a micro-pearl in a generally spherical shape or a round bar shape and a method of forming a partition or a column using polyimide (PI) on the substrate layers 120 and 130 And the like.

The liquid crystal layer 110 is filled with a mixture of the nematic liquid crystal 112, the dichroic dye 113, and the chiral material 114 while keeping the cell gap d within a certain range by the spacer 111. [ The cell gap d of the liquid crystal layer 110 is several μm to several tens of μm and is formed in a VATN (Vertically Aligned Twisted Nematic) mode. The liquid crystal molecules 112 are vertically arranged in the direction of 80 degrees to 90 degrees with respect to the plane of the substrate by the liquid crystal alignment layers 125 and 135. [ This vertical alignment state is enlarged to the inside of the cell due to the interaction between the liquid crystal molecules, resulting in an induced nematic phase induced across the entire liquid crystal layer 110. According to GW Gray and DG McDonnell (Mol. Cryst. Liq. Cryst., 37, 189, 1976), when a small amount of chiral material 114 is added to a nematic liquid crystal in a bulk state, The liquid crystal molecules have a twisted arrangement and have a cholesteric phase. Typical chiral materials include conventional cholesteric liquid crystal materials and C15, CB15, S811, R811, S1011 and R1011 commercialized by Merck.

In Equation (1), HTP (helical twisting power) is a force for arranging the liquid crystal molecules in a twisted structure per unit chiral substance content, c is a weight percentage of the chiral substance of the liquid crystal contrast, P ₀ Is a unit value of a cholesteric pitch in a bulk state that is not influenced by the outside. HTP is an experimentally determined proportional constant that depends on the correlation between the given liquid crystal material and the chiral material and shows a very good linear correlation when the content of the chiral material is as small as several percent or less. THTP (Total Helical Twisting Power) is a value obtained by multiplying HTP by a chiral substance content c, and means a force for causing a nematic liquid crystal having an arbitrary amount c of a chiral substance to have a twisted structure And is inversely proportional to the pitch P ₀ of the cholesteric liquid crystals. That is, when the content of the chiral substance is increased in the nematic liquid crystal in a bulk state which is not influenced by the outside, it becomes more and more twisted and the pitch of the cholesteric structure gradually becomes smaller. The cholesteric phase is a spiral structure whose pitch P ₀ is proportional to the reciprocal of the chiral material weight content and thus can be adjusted relatively precisely. The pitch P ₀ is a pitch in a cholesteric phase when the liquid crystal is not affected by the outside in a bulk state, and is strongly influenced by the liquid crystal alignment layer in the thin film thin film liquid crystal cell as in the present invention. That is, in a thin cell that is vertically aligned as in the present invention, the vertical orientation force of the liquid crystal alignment layer is stronger than THTP, and the helical structure of cholesteric phase is transformed into an induced nematic phase. That is, under the condition that the cell gap of a given liquid crystal layer is d, the larger the pitch P ₀ on the cholesteric phase or the smaller the THTP, the better the induced nematic phase is formed. When the content c of the chiral substance is gradually increased at a given cell gap d of the liquid crystal, the THTP increases and the induced nematic phase due to the vertical orientation becomes gradually unstable. At the threshold THTP _th value, The twisting power THTP _th by the substance content c _th becomes similar, and if the chiral substance content (c> c _th ) of the THTP _th value or more is included, the induced nematic phase is transformed into cholesteric phase or phase It becomes a phase transition.

The limit of the nematic phase in which the cholesteric phase is induced by merely the vertical orientation force in the thin film state largely depends on the physical characteristics of the liquid crystal itself and the cell gap. PR Gerber, Z. (Naturforsch., 36A, 718, 1981) reported that ( P ₀ / d) = 0.98 and Jong cheon Lee (KENT STATE UNIVERSITY Ph.D. Thesis, 1990) (D / P ₀ ) = 0.74. Wherein a document in common, the 180 ° twisted cholesteric liquid crystal phase or d = P _0/2 means that the cholesteric liquid crystal phase of stably present in the nematic liquid crystal induced when positioned between a vertically oriented substrate having a thickness of do. In the present invention, when the content of the chiral material 114 is mixed so that the pitch Po on the cholesteric phase of the nematic liquid crystal has a value smaller than 2d, and when a sufficient external voltage is applied, the nematic liquid crystal molecules Have a helical structure that is warped about 180 degrees or more.

The dichroic dye (113) has a rectangular shape similar to a nematic liquid crystal molecule, and the nematic liquid crystal molecules and the dichroic dye molecules are well mixed with each other. Representative dichroic dyes include the azo base dye G165, G205, G232, G239, SI-486, Si-426, M-137, S-428 and anthraquinone dye commercialized by Mitsui Chemical. Dichroic dye molecules strongly absorb light at a specific wavelength band of the visible light band and display a specific color. Thus, mixing dichroic dyes that display multiple colors can produce a black dye mixture that absorbs light from the visible light line relatively evenly.

In general, the liquid crystal layer of the present invention is mixed with a negative dielectric anisotropy nematic liquid crystal 90% ~ 99.8%, 0.1% ~ 5% of the amount of the dichroic dye, and a chiral material content within 0.6c _th <c <0.99c _th . The nematic liquid crystal composing the liquid crystal layer, the mixture of the dichroic dye and the chiral material has a nematic phase by the liquid crystal alignment layer in the state where no electric field is applied from the outside, and when the electric field is not applied from the outside, And has a steric image.

The sealant 115 protects the liquid crystal mixture filled in the liquid crystal layer 110 from external air or impurities and defines a region of the liquid crystal layer 110. The power supply unit 200 includes a power source 210 connected between the transparent electrode layers 123 and 133 of the two substrate layers 120 and 130 and a switch 220 located between the power source 210 and the transparent electrode layers 123 and 133 ).

Referring to FIG. 1, the operation of the LCD light-attenuating device according to the present invention in a state where power is not applied to the LCD panel by opening a switch of a voltage supply unit will be described. When power is not supplied from the power supply unit 200 to the LCD panel, nematic liquid crystal molecules are vertically aligned by the liquid crystal orientation layers 125 and 135, and are aligned in a direction perpendicular to the substrate plane, Are arranged in a direction perpendicular to the plane. In this state, the incident light Oin proceeds in parallel with the long axis of the positive dichroic dye molecules in the liquid crystal layer, so that the light oscillation direction is orthogonal to the long axis of the dye molecules, so that the light absorption is minimized and transmitted through the liquid crystal layer The light Oout becomes a maximum value and therefore becomes a bright state. According to the experiment, the maximum light transmittance of the LCD light attenuator according to the present invention reaches 50 to 90%.

Referring to FIG. 2, the operation of the transmission type LCD light attenuator according to the present invention will be described in a state in which the switch of the voltage supply unit is turned on to apply power to the LCD panel.

An electric field is formed in the liquid crystal layer 110 when a sufficient potential difference equal to or greater than the threshold voltage is applied between the transparent electrode layers 123 and 133 of the two substrate layers 120 and 130. Then, the nematic liquid crystal molecules having negative dielectric anisotropy are rearranged in a direction parallel to the substrate plane.

The pitch P ₀ of the nematic liquid crystal molecules on the cholesteric phase Describing as a specific case of mixing a specific amount of chiral material 114 into a nematic liquid crystal such that the specific amount of chiral material 114 is 2d, the nematic liquid crystal molecules have a helical arrangement warped about 180 degrees between both substrate layers. That is, the liquid crystal molecules adjacent to one substrate layer are arranged in parallel to the substrate plane and parallel to the vertical direction of the substrate. Twisted in a helical shape toward the opposite substrate layer, liquid crystal molecules located at the center of the liquid crystal layer are parallel And the liquid crystal molecules adjacent to the opposite substrate layer are rotated 180 degrees so as to be aligned horizontally with the vertical direction of the substrate. That is, the nematic liquid crystal molecules 112 are arranged in a 180-degree helical structure corresponding to a half pitch of the cholesteric phase over the entire liquid crystal layer 110, and the positive dichroic dye molecules 113 are arranged in a Since the nematic liquid crystal molecules 112 are arranged in parallel with the nematic liquid crystal molecules 112, the rectangular nematic liquid crystal molecules and the positive dichroic dye molecules are uniformly arranged at an azimuth angle of 360 degrees on the plane parallel to the substrate due to the symmetry of the head and tail portions . Therefore, the light is transmitted at a uniform intensity irrespective of the polarization direction of the incident light Oin. In addition, the incident light Oin proceeds in a direction orthogonal to the positive dichroic dye molecules, so that the light absorption rate has a maximum value and the transmitted light Oout has a minimum value.

At this time, if a nematic liquid crystal and a dichroic dye have a cholesteric phase by applying an electric field of a sufficient intensity to the liquid crystal layer, the light of all the azimuthal angles is uniformly absorbed regardless of whether the light is polarized or not, thereby having a uniform transmittance.

The reflection type optical attenuator according to the present invention is composed of a transparent electrode layer 123 and a reflective electrode layer 133 of two substrate layers 120 and 130 in FIG. 2. In the transmission type optical attenuator, only the transparent electrode layer 133, And the remaining part has the same role and function as that of the above-mentioned transmission type optical attenuator. That is, the incident light Oin passes through the liquid crystal layer 110, is reflected by the reflective electrode layer 133, and then is reflected through the liquid crystal layer 110 in the incident direction.

FIG. 3 illustrates the electro-optical characteristic curve of the Normally White mode of the VATN Guest-Host LCD. That is, when the electric field is not applied to the LCD panel or the liquid crystal cell 100, the light transmittance is maintained at a high level. When the voltage is applied at a voltage higher than a predetermined voltage V th, the light transmittance gradually decreases. It becomes gradually closer to the minimum light transmittance. Also, by applying an average voltage between V (th) and V (sat), the light transmittance of the intermediate group can be obtained. Also, when the content c of the chiral substance gradually increases, V (th) and V (sat) gradually decrease.

4 shows an example of a light transmittance change degree when a pulse voltage of 10 volts is applied to the VATN GH LCD 100 of Normally White Mode for 0 to 10 ms for 10 msec. In the initial state, the LCD panel 100 or the liquid crystal cell 100 has the maximum light transmittance. When the voltage of 10 volts is applied, the minimum light transmittance is shown after about 1 msec. When the applied voltage is decreased to 0 volt, And is restored to the original state by the light transmittance. That is, the reaction speed t (on) of the LCD panel 100 is about 1 msec, and t (off) is about 5 msec. Generally, the reaction speed of an LCD panel is related to various factors such as cell gap, physical characteristics of a liquid crystal material, measurement temperature, intensity of an applied electric field, voltage waveform, structure of a liquid crystal panel, surface orientation force and orientation angle. Also, as illustrated in Fig. 4, the electro-optical response speed of the LCD panel 100 is generally t (on) ≠ t (off), and usually t (on) is shorter than t (off). In other words, the electro-optical rising time occurring when the intensity of the electric field applied to the LCD panel is sufficiently large is faster than the electro-optical relaxation time occurring when the electric field intensity is reduced. Also, when the content c of the chiral substance increases gradually, t (on) is hardly affected, but t (off) becomes larger and when c approaches c _th , t (off) becomes almost infinite. Consequently, to achieve a fast response time t (off) values are somewhat finite, it is necessary to limit the content of the chiral material in c <0.99 c _th.

FIG. 5 shows that the optical characteristics of the optical shutters made of a transmissive VATN guest-host LCD of Normally White Mode are changed according to the content c or THTP of the chiral material. Under the given liquid crystal cell gap, the maximum light transmittance T (OFF) does not change as the THTP increases, but the minimum light transmittance T (ON) decreases rapidly to about 50% of THTP _th , . That is, as the THTP increases, the amount of light to be switched increases, which means that the contrast ratio is improved during operation of the optical shutter. On the other hand, as the THTP increases, the force to twist the nematic liquid crystal increases, and thus the induced nematic phase in the state where no voltage is applied to the liquid crystal layer 110 becomes gradually unstable Phase transitions occur in a cholesteric phase on the nematic side at a threshold THTP _th or more. The threshold THTP _th value is determined by experimental measurement results of liquid crystal cells manufactured under a certain condition, such as cell gap d, anchoring strength, an angle of orientation (Pretilt Angle), temperature, do. PR Gerber, Z. (Naturforsch., 36A, 718, 1981 years) and LEE JONG CHEON As is mentioned (KENT STATE UNIVERSITY Ph.D. Thesis, 1990 years) if the threshold value for the key parameters of the liquid crystal cell gap d only THTP _th When the cell gap d of the liquid crystal has an error by? D under a given chiral material content, the influence of the vertical orientation force is changed. When the chiral substance content c approaches c _th (d), the liquid crystal cell gap d The error of the value seriously affects the stability of the liquid crystal array. When the value of the change amount? C (? D) of the chiral substance content corresponding to the change of the vertical orientation force due to the error? D of the liquid crystal cell gap d becomes c> c _th (d) +? C (? D) Phase transition occurs. In general, the liquid crystal cell gap d can be controlled within 0.5% when a glass substrate is used, and can be controlled within 1% when a plastic substrate is used. Thus it as VATN produce LCD optical shutter, to the stability of the liquid crystal array in the non-voltage applied state is not the content of the chiral material c is required to be limited to at least 0.99 c _th. Therefore, in order to maximize the light transmittance contrast of the VATN LCD optical shutters under stable liquid crystal alignment and ensure the stability of the liquid crystal alignment, the content of the chiral substance should be within a range of 0.6 c _th <c <0.99 c _th .

The smart mirror of the vehicle to which the LCD light attenuator according to the present invention is applied includes an incident light sensor, an operation analysis unit, a power source and a driving unit, and a reflection type LCD light attenuator. The incident light detecting unit recognizes brightness of the front and rear of the vehicle as an optical sensor. When the brightness of the incident light corresponds to the glare condition of the driver, the power analyzer operates the power source and the driving unit to operate the LCD light- So that the reflectance of the light reflected from the light source is reduced. On the other hand, if the brightness of the incident light does not correspond to the driver's glare condition as a result of the analysis by the operation analysis unit, no power is applied to the LCD optical attenuator. At this time, Is arranged perpendicular to the plane and maintains a high light reflectance state. Therefore, the safety condition criterion of an automotive mirror in which a bright condition is maintained in a state in which no voltage is applied is satisfied.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

The effect of the present invention can be applied to a small-sized electronically controlled optical shutter required for miniaturization of a high-resolution smartphone camera, and also to a light variable smart window or an optical variable mirror for automobile.

HTP: proportional constant of intensity to have a twisted nematic liquid crystal structure per unit content of chiral material
THTP: c · HTP, the value of the chiral substance, c, multiplied by HTP; The force of a nematic liquid crystal having a twisted structure containing a small amount of chiral material as much as the c content
THTP _th (d): c _th · HTP, the chiral substance content c _th multiplied by HTP; A THTP threshold value when a maximum value of a chiral substance having a nematic phase derived from vertically aligned nematic liquid crystal is included in a given liquid crystal cell gap d
c: the weight percentage of the chiral material to the nematic liquid crystal;
c _th (d) is the threshold value of the maximum value of the chiral material weight content with the vertically oriented nematic liquid crystal induced nematic phase at the given liquid crystal cell gap d
P ₀ : pitch of the twisted structure having a cholesteric phase in a bulk state without external interference
d: cell gap of the liquid crystal layer
V (th): the average voltage at which the relative light transmittance of the LCD panel begins to change to 10% (normally black mode, conversely, 90% in the case of Normally White Mode)
V (sat): Average voltage at which the relative light transmittance of the LCD panel approaches 90% of the threshold value as saturation voltage (Normally Black Mode, and conversely, 10% when Normally White Mode)
Average voltage: root mean square (RMS) voltage
t (on): Rising time, and when the average voltage is applied to the Normally White Mode LCD panel at a voltage higher than V (sat), the electro-optic characteristics required to change the relative light transmittance of the initial state from 90% to 10% Reaction time
t (off): Relaxation time. Electro-optic, which is required to change the relative light transmittance from 10% to 90% of the maximum light transmittance when the average voltage drops below V (th) in Normally White Mode LCD panel Reaction time
T (OFF): light transmittance in a state in which no electric field is applied
T (ON): Minimum light transmittance in a state where an average voltage equal to or higher than V (sat)
Normally white mode: When the light transmittance T (OFF) in a state in which no electric field is applied is the maximum and an average voltage of V (sat) or more is applied, the LCD mode having the minimum light transmittance T

Claims (13)

An LCD panel including at least one liquid crystal cell; and a power supply for supplying an electric field to the LCD panel; Wherein the liquid crystal cell includes a liquid crystal layer defined within a certain cell gap range and two substrate layers facing the liquid crystal layer,
Wherein the liquid crystal layer comprises a nematic liquid crystal having a negative dielectric anisotropy and a chiral material capable of stably holding the nematic liquid crystal phase in which the nematic liquid crystal is induced in a state where no voltage is applied to the liquid crystal layer, Is filled with a mixture of dichroic dyes which are rearranged together with the nematic liquid crystal to transmit or absorb light; Wherein the substrate layer comprises a vertical alignment layer in which the nematic liquid crystal and the dichroic dye are arranged in a first array perpendicular to the plane of the substrate layer, and an electric field passing through the liquid crystal layer to generate the nematic liquid crystal and the dichroic And an electrode for rearranging the dye in a second arrangement different from the first arrangement. The LCD light attenuator according to claim 1, wherein the liquid crystal layer further comprises a spacer for maintaining a cell gap of the liquid crystal layer within a predetermined range. The optical pickup of claim 1, wherein the dichroic dye has positive dichroism with respect to visible light. The LCD light attenuator according to claim 1, wherein the substrate layer further includes a protective layer for blocking impurities introduced into the liquid crystal layer. The apparatus of claim 1, wherein the mixture forms a vertically oriented nematic phase if the electric field is not applied, and forms a cholesteric phase when the electric field is applied with sufficient intensity. The composition of claim 1, wherein the mixture comprises 90% to 99.8% of the negative nematic liquid crystal, 0.1% to 5% of the positive dyestuff dye, and nematic liquid crystal phase Wherein the chiral material is mixed with the chiral material in an amount of 60% to 99% of the maximum content _cth that can be contained in the optical material. 2. The optical system of claim 1, wherein the substrate layer is coated with anti-reflection layers each having a minimum reflection at an interface with an outermost side facing material. The transmission type LCD optical attenuator according to claim 1, wherein the electrodes of the two substrate layers are transparent electrodes The reflective LCD light attenuator according to claim 1, wherein the electrode of the substrate layer on which the light is incident is a transparent electrode and the electrode of the remaining substrate layer is an opaque metal film electrode. An LCD device comprising: an LCD panel including at least one liquid crystal cell; a power supply for supplying an electric field to the LCD panel; an incident light sensor for sensing a brightness of the ambient light; And an operation analyzer for controlling the LCD panel by controlling the operation of the LCD panel; Wherein the liquid crystal cell includes a liquid crystal layer defined within a certain cell gap range and two substrate layers facing the liquid crystal layer,
Wherein the liquid crystal layer comprises a nematic liquid crystal having a negative dielectric anisotropy and a chiral material capable of stably holding the nematic liquid crystal phase in which the nematic liquid crystal is induced in a state where no voltage is applied to the liquid crystal layer, Is filled with a mixture of dichroic dyes which are rearranged together with the nematic liquid crystal to transmit or absorb light; Wherein the substrate layer comprises a vertical alignment layer in which the nematic liquid crystal and the dichroic dye are arranged in a first array perpendicular to the plane of the substrate layer, and an electric field passing through the liquid crystal layer, And an electrode for rearranging the sex dyes in a second arrangement different from the first arrangement. 11. The smart mirror according to claim 10, wherein a light transmittance of the liquid crystal layer to which the electric field is not applied is higher than a light transmittance of the liquid crystal layer to which the electric field is applied. 11. The composition of claim 10, wherein the mixture comprises 90% to 99.8% of the nematic liquid crystal, 0.1% to 5% of the dichroic dye, and a nematic liquid crystal phase vehicle smart mirror, characterized in that mixed with the chiral material of 60% of the maximum content of the c _th to 99% content. The smart mirror for a vehicle according to claim 10, wherein the liquid crystal layer further comprises a spacer for maintaining a cell gap of the liquid crystal layer within a predetermined range.

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