KR100334711B1 - Multi Stability Chiral Nematic Display - Google Patents

Abstract

The present invention relates to a light modulation reflective cell comprising a non-polymeric chiral nematic liquid crystal light modulation material. The cell contains a nematic liquid crystal with positive dielectric anisotropy and an amount of chiral material effective to form a conical focus and twisted planar structure. The chiral material has an effective pitch length for reflecting light in the visible spectrum. The cone focus and twisted planar structure are stable even in the absence of the electric field, and the liquid crystal material may change in structure upon application of the electric field.

Description

Multistable Chiral Nematic Display

This application was made, in part, with the auspices of the Government under co-operation agreement No. DMR 89-20147, awarded by the National Science Foundation. The government has certain rights in this invention.

Background of the Invention

Related application

This application is incorporated by reference herein in US Patent Application Nos. 07 / 694,840, filed May 2, 1991, and US Patent Application Nos. 07 / 885,154, filed May 18, 1992, and US Patent Application No. Part of the ongoing application for 07 / 969,093.

The present invention generally exhibits a variety of optical states in liquid crystal light modulators, more particularly under various field conditions, and optical multi-stable and haze-free light transmission at all times in full-on or full-off states. A novel non-polymeric liquid crystal display cell and material characterized by having unique combinatorial properties, including.

Electrically switchable liquid crystal films for various electro-optical devices have been produced using various forms and concentrations of liquid crystals and polymers. One such method is the absorption of liquid crystal into the micropores of a plastic or glass sheet. Another method involves evaporating water from an aqueous emulsion of nematic liquid crystals in a water soluble polymer solution such as polyvinyl alcohol or in a latex emulsion.

Other methods that provide advantages over mechanical capture and emulsification processes include phase separation of the liquid crystals from homogeneous solutions containing suitable synthetic resins to form liquid crystal phases dispersed in the polymer phase. Films of this type, some of which are called PLDC, have been shown to be useful in a variety of applications, from large portions of displays and switchable coatings to films for displays and high definition televisions.

All the above materials and methods have the disadvantage of requiring a lot of expensive reagents and starting materials. Many of the absorption, emulsification and polymerization processes associated with these systems add significantly to the cost and complexity of manufacturing. In addition, when a large amount of polymer is used, a decisive disadvantage of "haze" begins to appear at increased inclination until an opaque appearance appears at a sufficient inclination angle due to a mismatch between the effective refractive index of the liquid crystal and the refractive index of the polymer. do.

In prior applications it has been found that good color reflective displays can be produced using chiral nematic liquid crystals and polymers. These displays have the advantage of exhibiting multi-stable color reflection and blurring when the amount of polymer is low. However, despite these many advantages, these displays require the use of a polymer and therefore have disadvantages associated therewith.

Surprisingly, it has been found that polymer-free multistable color reflecting cells can be made to exhibit stable color reflection and light scattering states with multistable optical states characterized by varying degrees of reflectivity. Depending on the voltage of the electric field addressing pulses, the material can be switched between these many optical states, all of which are stable even in the absence of an applied electric field.

Disclosure of the Invention

An important feature of the present invention is that color reflective display cells can be made without polymers to exhibit a number of optically diverse states that are stable even in the absence of an applied electric field. This display can be led from one state to another by the battlefield. Depending on the size and shape of the electric field pulse, the optical state of the material may change into a new stable state that reflects a certain amount of colored light along the continuum of that state to provide a stable "grey scale". Surprisingly, these materials can be produced without the polymer and hence the cost and complexity of manufacture.

In general, sufficiently low electric field pulses applied to the material result in a light scattering state that appears white in appearance. In this state, some liquid crystal molecules have a conical focal structure as a result of competition between some surface effect, elastic force and electric field. After application of a sufficiently high electric field pulse, i.e., an electric field high enough to isotropically align the liquid crystal director, the material may appear green, red, blue or any preselected color depending on the pitch length of the chiral nematic liquid crystal. Transition to reflection Light scattering and light reflection states remain stable under zero electric field. The electric field is applied to the material so that the material is switched from the reflected state to the scattered state, or vice versa, thereby obtaining a stable gray scale state characterized by varying degrees of reflection between that represented by the reflected and scattered state. When the chiral nematic liquid crystal has a planar colored light reflecting structure and a medium electric field pulse is applied, the amount of planar material and the reflectance intensity of the colored light are reduced. Likewise, when the material is conical-focused and an electric field pulse with an additional degree is applied, the amount of material having a planar structure increases with the reflection strength from the cell. When the electric field is removed, the material remains stable and maintains a structure set to reflect light intensity indefinitely, even though the structure has begun to change.

If the electric field is maintained high enough to isotropically align the liquid crystal director, the substance is transparent until the electric field is removed. If the field is removed quickly, the substance transfers to the light reflection state, and if the field is slowly removed, the substance transfers to the light scattering state. In each case, the electric field pulse is preferably an AC pulse, preferably a spherical AC pulse, since the DC pulse tends to cause ion conduction and shorten the life of the cell.

Although not supported by theory, it is believed that when a voltage is applied, some of the material is in an opaque state while the electric field is in the on state. Those parts of the material that exhibit an opaque state tend to transition to conical light scattering when the field is removed. Parts of the material that are not affected by the electric field, that is, parts which do not become opaque, maintain a planar light reflecting structure. The amount of light reflected from the cell depends on the amount of material that is a planar reflector. As the voltage of the electric field increases, more parts of the material become opaque, while the electric field is applied and then transferred to the conical focus structure when the electric field is removed. Because the reflection from the cell is proportional to the amount of material in the planar reflection structure, the reflection from the cell decreases along the gray scale as a result of the increase in the overall size, which results in a larger amount of material being opaque and switching to the conical focus structure. Because it becomes. At certain initial voltages dependent on the material, all of the material is characterized by a light scattering state when the field is switched to a conical focus structure and the cell reflectivity is at or near its minimum. When the voltage is removed, the expected structure remains stable and uncertain. When the voltage is further increased to a point high enough to isotropically align the liquid crystal director without twisting the liquid crystal, the material is transparent and remains transparent until the voltage is removed. The substance tends to transition from an isotropic structure to a stable color reflecting planar structure upon removal of the electric field.

When the material is in the light scattering cone focus structure and a low voltage pulse is applied, the structure of the material begins to change and a stable gray scale reflectivity is obtained. Since the substance starts in the scattering cone focus, gray scale reflectivity can be initially reduced in several samples, but is characterized by an increase in reflectivity from what appears when all of the substance is in the light scattering cone focus. do. The increase in reflectivity is believed to contribute to the proportion of the material that can be isotropically aligned as a result of the applied electric field. Isotropically aligned portions transition to a stable planar light reflection structure upon removal of the electric field, while the remaining portions exhibit an opaque state as a result of the electric field and transition back to a stable planar color reflection structure upon removal of the electric field. When the voltage is further increased to the point where all liquid crystals are isotropically aligned, the substance is transparent and transitions to a planar color reflection structure that is stable upon removal of the electric field.

Part of the material that becomes opaque as a result of the applied electric field is transferred to a stable conical focal structure upon removal of the electric field and isotropically aligned parts due to application of the applied electric field are transferred to a stable planar structure upon removal of the electric field. It is believed to be. When the high field is slowly removed from the isotropically aligned liquid crystals, the substance enters the scattering cone focus state, which causes the substance to be opaque from what appears to be a slow transition of the full length to the cone focus structure after removal of the full length. It is believed that this is because. When the high field is removed quickly, the substance does not become opaque and thus transfers into a planar reflection structure. In some cases, electric field pulses of various sizes below those necessary to move the material from a stable reflection state to a stable scattering state or vice versa may appear to move the material to its own stable intermediate state. This polystable state uncertainly reflects the colored light of intensity between being reflected by the reflected and scattered state. Thus, depending on the magnitude of the full length pulses, the material exhibits stable gray scale reflectivity without the need for polymers. The size of the electric field required to move the material between the various states, of course, depends on the type and amount of the particular liquid crystal and the thickness of the cell. Applying mechanical stress to the material can also be used to move the material from light scattering to light reflection.

The main advantage of polystable materials is that it eliminates the need for the use of active matrices required for the manufacture of high resolution flat panel screens. The screen is manufactured in the absence of the active elements of each pixel area and the multiplexing scheme for display addressing, thereby simplifying display production, increasing production volume and reducing display price. Since no polymer is required in the material, larger production simplification and cost reduction are achieved by the present invention. Another advantage of the present invention is that the light scattering and light reflecting states are stable without requiring sophisticated surface conditions of the polymer or substrate. The display device made of the subject matter of the present invention does not require a polarizer plate to limit the brightness of the display and color can be introduced by the subject matter itself without a color filter capable of reducing the brightness.

The above described advantageous properties are achieved in the present invention by providing an optical modulation reflector cell comprising a polymerless chiral nematic liquid crystal light modulating material, wherein the polymerless chiral nematic liquid crystal light modulating material comprises a nematic liquid crystal having a positive dielectric anisotropy. It contains an amount of chiral material effective to form a conical focal length and twisted planar structure having a pitch length effective for reflecting light in the visible spectrum. Here, the cone focus and the twisted planar structure are stable even in the absence of the electric field, and the liquid crystal material may change its structure upon application of the electric field.

The addressing means can be such as active matrices, multiplexing circuits, electrodes and lasers known in the art. As a result, the new materials can show different optical states, ie, light transmission, light scattering, light reflection, and a stable gray scale between these states under different field conditions without the need for polymers and complex manufacturing processes associated with them. .

A chiral nematic liquid crystal is a mixture of a chiral material and a positive dielectric anisotropic nematic liquid crystal in an amount sufficient to produce the desired pitch length. Suitable nematic liquid crystals and chiral materials are commercially available and are well known to those skilled in the art in view of the present specification. The amount of nematic liquid crystals and chiral materials will vary depending on the type of work as well as the specific liquid crystals and chiral materials used.

The wavelength of the light reflected by the material can be represented by the relationship λ = nP, where n is the average refractive index and p = pitch length. The wavelength between 350 nm and 850 nm is visible spectrum. Thus, those of ordinary skill in the art are the manuals distributed by the general principles of chiral doping of liquid crystals, such as Hoffmann-La Roche Ltd, to obtain optimum pitches. A suitable material for the present invention may be selected based on the refractive index of the material included in How to Dope Liquid Crystal Mixtures in Order to Ensure Optimum Pitch and to compensate the Temperature Dependence (1990), such as Schadt et al.

In a preferred embodiment the pitch length of the chiral nematic liquid crystal is in the range of 0.25-1.5 microns, more preferably 0.45-0.8 microns. Typical pitch lengths are 0.27 microns for blue, 0.31 microns for green and 0.40 microns for red. In addition, the chiral nematic liquid crystal contains about 20-60 wt%, more preferably 20-40 wt% of the chiral substance based on the total weight of the nematic liquid crystal and the chiral substance. However, the range may vary depending on the chiral material and the liquid crystal. Nematic liquid crystals have a positive dielectric anisotropy of at least 5, preferably at least 10. The weight may vary depending on the particular liquid crystal and chiral material used.

In carrying out the invention, a solution containing a predetermined amount of a nematic liquid crystal and a chiral material is prepared and introduced into at least one of the transparent cell substrates. The cell is sealed around the edge with a known epoxy or other material. The cell can be filled by known methods such as capillary action. The preferred method is to vacuum fill the cell. This improves cell irregularity and removes bubbles in the cell. In an electrically addressable cell, the cell walls are coated with a transparent electrode such as indium tin oxide prior to the introduction of the liquid crystal.

Although not essential to the present invention, in some cases it is desirable to treat the cell walls with materials such as detergents or chemicals in addition to the electrodes so as to achieve varying contrast or switching characteristics. This treatment can be used to affect the inconsistency of the liquid crystal, to alter the stability of various structures and to change the strength of any surface anchoring. In addition to using various materials for such surface treatment, the treatment of the opposite substrate may be different. For example, the substrates may be rubbed in different directions where one substrate may include additional processing while the other may be otherwise or the opposite substrate may be treated with a different material. As described above, such additional processing may have the effect of changing the cell response characteristics.

Optionally, other additives may be included in the chiral nematic liquid crystal mixture to alter the properties of the cell. For example, color can be introduced by the liquid crystal material itself, while a dichroic dye can be added to enhance or vary the color reflected by the cell. Additives such as fumed silica can likewise be dissolved in the liquid crystal mixture to adjust the stability of the various cholesteric structures.

The present invention is characterized by a method of addressing a polymer-free chiral nematic liquid crystal material capable of switching between a color reflection state reflecting a maximum reference intensity and a light scattering state exhibiting a minimum reference intensity. The method involves applying voltage pulses of various magnitudes sufficient to achieve stable color reflectivity between maximum and minimum to produce stable gray scale reflectivity from the material.

Preferably the method comprises applying an AC pulse of sufficient duration and voltage to the material such that the portion of the chiral nematic material exhibits a first optical state and the remainder of the chiral nematic material exhibits a second optical state different from the first optical state. It is characterized by the addition. In a preferred embodiment the first optical state of the part of the material exhibits a planar structure and the second optical state of the remaining part represents a conical focus structure with the intensity of reflection being proportional to the amount of material in the planar reflecting structure.

Through the following detailed description of the preferred embodiment and the accompanying drawings, it is understood that various additional features and advantages of the present invention may be understood and the present application may be more clearly understood.

1 is a cross-sectional view of a light modulation cell into which a liquid crystal material of the present invention is injected.

2 shows an enlarged partial cross-sectional view of the novel material in which the liquid crystals are isotropically aligned to give an optically clear state.

3 shows an enlarged partial cross-sectional view of the substance in light scattering state.

4 is an enlarged partial cross-sectional view of the material when the liquid crystal has a twisted planar structure.

5 is a plot of the cell's electro-optic response to AC pulses of various voltages demonstrating gray scale reflections in the voltage range from 30 to 140 volts starting from the planar structure and from 140 to 180 volts starting from the confocal structure. .

Description of the Preferred Embodiments

The cell depicted in FIG. 1 consists of glass plates 10, 11 sealed around the ends and separated by spacers 12. As shown, the glass plates 10 and 11 are covered with indium tin oxide (ITO) or the like forming the transparent electrode 13. Reference numeral 14 denotes an optional surface coating that can be attached to the electrode to affect the liquid crystal director or to change the contrast, reflection or switching characteristics of the cell. The opposite coating 14 may be the same or different material and may rub in different directions or one or both of the coatings 14 may be removed together.

The cell of FIG. 1 is filled with the non-polymeric liquid crystal material of the present invention. The liquid crystal light modulation material is composed of a nematic liquid crystal that is positive dielectric anisotropy and a chiral nematic liquid crystal 16 having a chiral material. An AC voltage source 17 is connected to the electrode 13 to switch the cell to a different optical state.

The cell form shown in FIG. 1 is merely illustrative of the function and specific embodiments of the non-polymeric liquid crystal material of the present invention, and the novel material may be addressed in various ways and may be injected into any other type of cell. It should be noted. For example, instead of being addressed by an externally activated electrode, the substance may be addressed using an active matrix, multiplexing strain, or other form of circuit known in the art. Likewise, the cell can be manufactured without the optional surfacing layer 14.

Various materials may be used when any surface treatment layer other than rubbed or non-frictionated ITO or other suitable electrode is used to change the properties of the cell. Suitable materials include polymethyl methacrylate (PMMA), non-frictional polyimide, polyisobutyl methacrylate, poly-n-butyl methacrylate, polyvinyl formal (PVF) and polycarbonate. The head plates may be the same or different and may be rubbing or non-rubbing or structured. Likewise, the opposite surface may be rubbed in different directions or structured in other ways. The best results were obtained when using rubbed ITO without any additional surface treatment.

Liquid crystal materials include nematic liquid crystals and chiral materials such as cholesteric liquid crystals that are positive dielectric anisotropic but do not contain any polymers. Suitable nematic liquid crystals are sufficient as any known cyanobiphenyl having adequate positive dielectric anisotropy. Examples include E7, E48, E31 and E80, manufactured by E. Merck. Suitable chiral agents include, for example, CB15, CE2 and TM74A, also manufactured by E. Merck. Other nematic liquid crystals and chiral materials suitable for use in the present invention will be well known to those skilled in the art upon consideration of the present specification. Other optional components that may be added to the chiral nematic liquid crystal mixture include, for example, fumed silica to adjust the stability of the various structures and colorants to adjust the color.

In the preferred method of manufacturing the cell of FIG. 1, a solution is prepared in which a chiral nematic liquid crystal and any necessary dye or additives are dissolved together, and then the solution is shown here having an optional coating layer 14 thereon. 11) Inject between. This can be done by methods known to those skilled in the art, such as capillary filling, more preferably vacuum filling. When the solution is injected between the glass plates the cell is sealed at its end, as is known.

Polymer-free displays made in accordance with the present invention, which can be switched between stable planar cone focus and gray scale states, are described in detail in the following non-limiting examples.

Example 1

A chiral nematic liquid crystal mixture was prepared containing 37.5 wt% E48 (nematic liquid crystal from EM) and 62.5 wt% TM74A (chiral additive from EM). Two substrates coated with ITO formed one square inch of cell. The ITO coating layers of the two substrates were rubbed parallel to each other. A 10 μm glass spacer was sprayed onto one substrate and placed in the middle of the second substrates so that two of the ends overlap the first substrate so that the cell is held with the clamp. Five non-overlapping edges were sealed using 5 minute epoxy (Devcon).

The cell was fixed vertically and a drop of chiral nematic liquid crystal was placed along the top opening end of the cell. The cells were naturally filled using capillary action for at least 15 minutes. When filled, the remaining liquid crystal mixture was removed from the end and top end sealed with 5 minute epoxy.

The cell was initially in frontal reflection. The cells were switched to cone focus scattering with a 100 ms low voltage pulse of about 115 volts and 1 kHz. The cell was switched back to a planar reflection with a pulse of about 180 volts and 100 ms high voltage of 1 KHz. Both planar and cone focus were stable in the absence of the electric field, and the cell exhibited a multistable gray reflection between scattering and reflection.

Example 2

A mixture of 0.6: 1 ratio of E48 and TM74A was injected between 10 μm spaced ITO exposed glass plates, unlike Example 1 above. The substrate was further coated with a non-frictionized polyimide layer. The cell initially transmitted only about 30% of the HeNe beam passing through the cell. The cells were switched to a planar structure reflecting green light with 10 ms, 155 volts, and 1 KHz AC pulses. The transmission from the cell in the reflected state was about 65%. The cells were switched back to cone focus scattering with 95 volt pulses of the same time and wavelength. The cell was switched under 10ms.

Example 3

The cell was prepared as a mixture of CB15, CE2 (chiral material of EM) and E48 in a weight ratio of 0.15: 0.15: 0.7 as in the above example. In this cell, the driving voltage was cut in half because the dielectric anisotropy of the mixture was higher than with TM74A. The electro-optic response of this material was similar to that of Example 1.

Table 1 shows a number of additional examples of materials made according to the above embodiments. In these cells, the concentration of chiral material and the form and concentration of nematic liquid crystals were varied. In each case the chiral material was a 50:50 mixture of CE2 and CB15. Each cell used an unfrictionated ITO electrode only as a surface treatment on the substrate. The materials in Table I all exhibited polystability in the visible spectrum, ie stable reflection, scattering and gray scale states.

Table II shows examples of materials prepared according to the above embodiments, showing multistable in various surface treatment materials and cell thicknesses. In each case, the nematic liquid crystal was 60 wt% of E31 (EM) based on the total weight of the nematic liquid crystal and chiral material. In each case, the chiral material was a 50:50 mixture of 40 wt% CE2 and CB15 (EM) based on the total weight of the chiral material and nematic liquid crystal. Each cell represented a green reflection. The reflection and scattering states were stable in the absence of the electric field, and the cell showed a stable greyscale between the states. In Examples 17 and 18 the PVF coatings on the opposite substrates were rubbed vertically and parallel to each other, respectively. Likewise, the coatings on the opposing substrates in Examples 22 and 23 were each rubbed vertically parallel to each other. The coating layers of Examples 21 and 24 were simply non-frictionated ITO electrodes and in the case of Example 25 the ITO coating layers on the opposite substrate were rubbed parallel to each other. I-butyl and n-butyl in Examples 13-15 represent n-butyl and i-butyl methacrylate. In these embodiments the spacing was adjusted by the glass range as in the above embodiments.

Table III is identical to Table II in that it provides additional examples of the polystable materials obtained as in Example 1, having various surface treatments and cell thicknesses. However, the materials in Table III contain 60 wt% of TM74A chiral material based on the total weight of the chiral material and nematic liquid crystal. The nematic liquid crystal was E48 present at 40wt%. These cells reflected green light in the planar light reflecting structure and exhibited multistable as in the above embodiments.

The polymer-free multistable color display cell of the present invention exhibits a stable gray scale phenomenon characterized by the ability of a material to reflect light of a selected intensity indefinitely between the reflected state and the intensity reflected by the scattering state. When the planar structure appears, the scattering state is when the entire material exhibits a conical focusing structure. For the purpose of this invention the reflection state reflects colored light to the maximum intensity of a given material, the color of the reflected light being determined by the pitch length of the chiral material. An electric field pulse with an appropriate potency voltage changes at least some material into an optical state and reduces the intensity of reflectivity. If the AC pulse is high enough but lower than isotropically aligning the liquid crystal, the optical state of the material is completely changed to a scattering state that reflects light at the minimum intensity of a given material. For a given material, the intensity of the reflectivity is in the gray scale range between the reflection state, which can be considered to limit the maximum intensity of the material's reflectivity, and the scattering state, which can be considered to limit the minimum intensity of the reflection. It is a sequence of intensity values between those represented by the reflection and scattering states. The skilled person will obtain the intensity of reflectivity in this gray scale range by applying a pulse to the material with an AC pulse voltage between converting the material from the reflected state to the scattered state or vice versa.

While not accurate in theory, it has been observed that when the material starts in a planar structure, the intensity of reflectivity along the gray scale is almost a linear ratio to the pulse voltage. By varying the pulse voltage, the intensity of the reflectivity of a given color can be proportionally varied. When the field is removed, the material reflects its strength indefinitely. Pulses within this gray scale voltage range convert some of the material from the reflective planar to the scattered cone focus. The intensity of reflectivity along the gray scale is proportional to the amount of chiral material switched from planar to conical or vice versa, which in turn is proportional to the AC pulse voltage.

4 conceptually illustrates the nonpolymeric polystable material of the present invention in a light reflective state. In this state, the chiral liquid crystal molecules 40 are oriented in a twisted planar structure parallel to the cell wall. Due to the twisted planar structure the material reflects light and the color of the light depends on the specific pitch length. In this stable reflection state, the gray scale intensity of the material is observed, indicating the maximum reflectance that constitutes the maximum reference strength. The planar structure of the liquid crystal is stable even in the absence of a polymer. As conceptually illustrated in FIG. 3, the multistable color display material is in a light scattering state. In this stable scattering state, the material exhibits a minimum intensity of reflection (i.e. maximum scattering), which limits the minimum reference intensity of the reflectance beyond that of gray scale intensities observed.

Both the light reflection state of FIG. 4 and the light scattering state of FIG. 3, as well as the gray scale state therebetween, are stable even in the absence of the electric field. When the low electric field pulse is applied while the substance is in the light reflection state of FIG. 4, the substance is transferred to the light scattering state of FIG. 3 and remains in the light scattering state even under zero electric field. When a high-tension pulse is applied to prevent the polystable material from twisting chiral molecules in a state where it is concentrated in the light scattering state of FIG. 3, the liquid crystal molecules are transferred to the light reflecting state of FIG. 4 at the last pulse to maintain such a state. do. The voltage per cell thickness micron required to transfer the material between the optical states depends on the composition of the material, but it will be understood that the determination of the required voltage is well known to those skilled in the art upon consideration of the present specification.

When the high field necessary to maintain the bit-twist state of the liquid crystal molecules is maintained, the liquid crystal directors are isotropically aligned to show a transparent state of the material. When the electric field is slowly removed, the orientation of the liquid crystal is shifted to the light scattering state of FIG. 3 since the slow removal causes the non-part of the material to become opaque. If the electric field is quickly removed, the orientation will transition to the light reflecting state of FIG. The intensity of the reflectance reflected between the reflection state of FIG. 4 and the scattering state of FIG. 5 is stable gray scale reflectivity. Of course, the intensity values of the reflected and scattered states can vary depending on the composition of the material, but the gray scale is limited by the intensity range between them.

At voltages below the deformation of the material from the reflected state of FIG. 4 to the scattered state of FIG. 3, a gray scale state of its own at zero electric field is obtained. Reflections from the material in the grer scale are stable because part of the material is in the planar reflection structure of FIG. 4 and part of the material is in the confocal scattering structure of FIG. 3, all of which are stable in the absence of the electric field. .

Thus, for example, the voltage is insufficient to transfer the entire liquid crystal to the conical focus structure shown at 50 in Fig. 3 and the liquid crystal is in the reflection state of Fig. 4, that is, the voltage is insufficient to completely transfer the material into the scattering state. When the electric field pulse having is applied, the material reflects colored light of intensity proportional to the amount of material remaining in the plane reflection structure. Thus, the reflectivity is lower when all of the chiral nematic liquid crystals are planar reflective structures than when they are reflected off the material but higher when fully switched to the confocal scattering structure. When the electric field pulse voltage increases, the chiral material is switched from the planar reflection structure to the scattering cone focus structure, and the reflectivity increases when the pulse voltage increases to the point where all or most of the material is transferred to the scattering state and completely switched to the opaque state. Decreases. If the pulse voltage increases further by then, the reflection intensity begins to increase again until the magnitude of the pulse is sufficient to maintain the bit-twist state of the chiral molecule, so that the chiral molecule is rapidly removed and the material is brought into the light reflection state of FIG. And then transition back to the planar light reflecting structure. When the material is in cone focus scattering in FIG. 5, the applied electric field pulse has a negligible effect on the reflectivity of the cell until it reaches a size sufficient to keep the chiral material in a bit-twisted state. As described above, the transition to the light reflection state of FIG. 4 occurs. The gray scale when the substance starts in the conical focus structure appears to be the result of isotropic alignment of some molecules as a result of bit-twisting the full length. These molecular moieties transition to planar reflecting structures upon removal of the electric field.

The reaction of the cell as described above is shown in FIG. 6, which illustrates the response of the material of Example 1 to various pulse voltages.

The reflectivity of the cells in response to AC pulses of various voltages was measured. A 10 millisecond (ms) wide 1 KHz AC pulse was used for the measurement. For these materials, an applied pulse of about 180 V or higher switched the cell to reflection, regardless of whether it was in scattering or reflection before the pulse. Maximum reflection, or minimum transmission, was observed here. The material exhibited maximum scattering when a voltage in the range 130-140 V was applied, regardless of whether it was in the plane of the cone focus structure prior to the pulse.

The gray scale response of the cell to the various voltage pulses is shown in FIG. The pulse voltage was varied to measure the reflection (transmittance%) from the cell. Curve A is the cell's response when the material is in the reflection state before each pulse. High AC pulses were applied to the material prior to each pulse plotted on curve A to ensure that the material was fully reflected before the pulse. If the pulse voltage is about 30V or less, it does not affect the cell reflection. When the pulse voltage is between about 40-110V, the reflectivity of the cell decreases almost linearly due to the increase in the pulse voltage. Gray scale reflectivity is observed in this voltage range. In each case the material with continued reflection after the pulse was removed. When the pulse voltage was increased to about 120-130V, the material was in a scattering state and showed almost maximum scattering. As the size of the pulse was further increased to about 150-160V, the cell's reflectivity increased until it reached the original value of 180V or more.

Curve B depicts the cell's response when the material was initially in cone focus scattering before AC pulses. If the AC pulse is about 30V or less, it does not affect the cell reflection. Between about 50-150 V scattering actually increased slightly and maximum scattering was observed in the cells. Above 160V, the transmission increases rapidly and the cell switches to the reflective state approaching the highest transmittance above 180V.

The linear relationship of the gray scale to the voltage is much more certain when the material starts in a planar structure and the gray scale is more progressive. Thus, the practical application of gray scale phenomena uses materials starting from a planar structure.

It will be apparent to those skilled in the art that many modifications can be made in light of the above detailed description. It is, therefore, to be understood that the invention is capable of other embodiments within the scope of the claims.

Claims (10)

An optical modulation cell having a cell wall structure (10, 11) having a chiral nematic liquid crystal light modulation material interposed therebetween, and means (13, 17) for an address arranged to provide a voltage pulse to the cell In the non-polymeric reflector, The chiral nematic liquid crystal light modulating material 16 is non-polymeric and has a pitch length effective for reflecting light in positive dielectric anisotropy and visible spectra, wherein the material is light scattering cone focus and light reflection twisted between the cell wall structures. Forming a planar structure; A first voltage of sufficient duration and amplitude that is effective for the means 13, 17 for the address to be converted from at least a portion of the material 16 to the light reflective twisted planar structure 40. Pulses, and at least a portion of the material (16) is suitable for selectively setting a second voltage pulse of a magnitude effective to convert from the light reflection twisted planar structure to the light scattering cone focus structure (30); And Stable in the absence of an electric field to which the light reflection twisted planar structure and the light scattering cone focus structure are applied; Device characterized in that. 2. The method of claim 1, wherein a first drive voltage pulse isotropically aligns the material such that the material exhibits a stable light reflection twisted planar structure upon abrupt removal of the first drive voltage pulse; Causing the material to appear as a stable light scattering cone focus structure when the second drive voltage pulse, which is smaller than the first drive voltage pulse, is removed; And When the third drive voltage pulse, which is smaller than the first drive voltage pulse but larger than the second drive voltage pulse, is removed, a portion of the material appears to be a stable light reflection twisted planar structure and the rest of the material is stable. Appearing as a light scattering cone focus structure; Device characterized in that. The method of claim 1, wherein the address means (13, 17) provides a voltage pulse so that the proportion of the material is changed to the light scattering cone focus 30 and the light reflection twisted plane 40 structure, so that the intensity of the reflected light Device adapted to be selectively controlled. 2. A voltage pulse of a first period and amplitude according to claim 1, wherein the means for addressing the material (13, 17) is effective for converting at least a portion of the material from the light scattering cone focus structure to a light reflection twisted planar structure, And selectively setting a voltage pulse of a second period and amplitude effective for converting at least a portion of the material from a light reflection twisted planar structure to a light scattering cone focus structure. 2. The first voltage pulse as claimed in claim 1, wherein the means for addressing the material (13, 17) is sufficient to convert at least a portion of the material from the light scattering cone focus structure to the light reflection twisted planar structure. And selectively setting a second voltage pulse of sufficient period and amplitude to be effective for converting at least a portion of the material from the light reflection twisted planar structure to the light scattering cone focusing structure. A light comprising cell wall structures 10 and 11 with a chiral nematic liquid crystal light modulation material 16 interposed therebetween and address means 13 and 17 arranged to selectively provide a voltage pulse to the light modulation cell A method for addressing a modulation device, the method comprising: Providing the material between the cell wall structure forming a light scattering cone focus and a light reflecting twisted planar structure, the polymer being free of positive dielectric anisotropy and having a pitch length effective for reflecting light in the visible spectrum; And A sufficient period and amplitude effective to convert at least a portion of the material from a light scattering conical focus to a light reflective twisted planar structure, and a sufficient period and amplitude effective to convert at least a portion of the material from a light reflective twisted planar to a light scattering conical focus structure. Selectively setting, by the address means, a second voltage pulse having a sufficient period and amplitude effective to convert one voltage pulse and at least a portion of the material from a light reflection twisted planar structure to a light scattering cone focus structure; And wherein the light reflection twisted planar structure and the light scattering cone focusing structure are stable even under the applied electric field member. The method of claim 6, Selectively applying a first drive voltage pulse to the addressing means to isotropically align the material such that upon sudden removal of the first drive voltage pulse the material exhibits a stable light reflection twisted planar structure; Upon removal of the second drive voltage pulse, selectively applying a second drive voltage pulse smaller than the first drive voltage pulse to the address means such that the material exhibits a stable light scattering cone focus structure; And Upon removal of the third drive voltage pulse, a portion of the material exhibits a stable light reflection twisted planar structure, and the remainder of the material is less than the first drive voltage pulse so as to exhibit a stable light scattering cone focus structure. Selectively applying, to said address means, a third drive electron pulse larger than a drive voltage pulse; Method comprising a. The method of claim 6, Selectively applying a voltage pulse to the address means such that the intensity of the reflected light can be selectively adjusted by varying the proportion of the material in the light scattering cone focus and the light reflection twisted planar structure. . The method of claim 6, A voltage pulse of a first magnitude effective to convert at least a portion of the material from a light scattering conical focus structure to a light reflection twisted planar structure and at least a portion of the material effective to convert a light reflecting twisted structure into a light scattering cone focus structure Selectively applying a voltage pulse of magnitude to said address means. The method of claim 6, A first voltage pulse of sufficient period and amplitude effective to convert at least a portion of the material from the light scattering cone focus structure to the light reflection twisted planar structure and at least a portion of the material from the light reflection twisted plane structure to the light scattering cone focus structure. And selectively applying, to addressing means, a second voltage pulse of sufficient period and amplitude effective to convert.