HK1182775B - Wide band variable transmittance optical device and mixture - Google Patents

Description

Wide band variable transmittance optical devices and mixtures

Cross Reference to Related Applications

The present application claims priority, as well as any other benefit, from U.S. provisional patent application serial No. 61/389,444 entitled wide band variable transmittance optical device and mixture (wide band optical transmission and optical device and mixture), filed on 4/10/2010, the entire disclosure of which is incorporated herein by reference in its entirety.

Background

Variable transmission eyewear devices (glasses, goggles, visors, etc.) that can rapidly change between a high transmission "bright" state and a low transmission "dark" state have many advantages over fixed transmission eyewear devices and are highly desirable. A particularly useful feature is to enable such rapid changes to occur on demand, whether manually by the wearer touching a button, or automatically under the control of a light sensor and electronic circuitry.

Previous attempts to create variable transmission on demand eyewear protection devices have utilized various liquid crystal systems that exploit the ability of liquid crystal molecules to change their orientation with the application of an external electric field.

Liquid crystal material devices can be broadly classified as either polarizer-based systems (which include at least one polarizer) or guest-host systems. These polarizer-based systems are used in a variety of applications where dark state transmittance is the most important parameter. In particular, they are used when conditions in which a minimum light transmittance (close to zero) must be obtained. Such applications include flat panel displays, as well as welding helmets and 3D glass. However, the polarizerThe light transmittance of the device is limited, often well below the theoretical limit of only 50% light transmittance. On the other hand, guest-host materials have traditionally been used for display applications where wide viewing angle and/or true color saturation are important. Examples include cockpit displays that allow the driver and co-driver to view the same image. The guest-host systems are better suited for eyewear protection devices because they allow for potential light transmission levels above 50%. In fact, some patents (see, e.g., Palffy-Muhoray et al, U.S. Pat. No. 6,239,778, granted 5/29/2001) suggest the use of guest-hosts for eyewear applications, wherein the guest-host device consists of a mixture of a liquid crystal "host" and a dichroic dye "guest" contained between a pair of substrates. The liquid crystal "host" comprises an unpolarized liquid crystal material having an orientation axis that is variable by adjusting the voltage applied across the substrates, the orientation axis being variable between a bright state orientation and a dark state orientation perpendicular thereto. The dye "guest" mixture includes dichroic dyes that are dissolved within the liquid crystal host and aligned with the orientation of the liquid crystal material. One commercial example of such an approach is Magic^TMSkiggples, which uses a guest-host liquid crystal system and plastic substrates (Park et al, us patent No. 7,567,306 approved on 7/28 of 2009).

In general, it is desirable that such variable-transmittance liquid crystal optics have good optical properties while using plastic substrates to exhibit a wide transmission swing (wide difference between the light and dark states) and absorb light across the widest possible band of light in order to minimize the difference between the light and dark states.

However, there are currently no commercial liquid crystal guest host devices that provide wide band absorption greater than 175nm for eyewear protection applications. This is because knowledge related to the use of the subject-matter system is based on prior display application knowledge that does not provide guidance on the parameters necessary to produce a successful wide-band eyewear shield. Liquid crystal displays have very different performance requirements compared to eyewear protection devices. For example, liquid crystal displays have traditionally used glass substrates, while optics suitable for eyewear protection are preferably plastic-based. Glass and plastic have very different properties; the sensitivity of the eye to certain parameters makes plastic products feasible for display applications unacceptable for eyewear protection applications. For example, non-uniformity of visual distortion is of paramount importance in eyewear applications. As such, conventional display materials or configurations are rendered unacceptable for eyewear protection applications.

Analytical parameters used to characterize the guest-host system include: absorption spectra, order parameters of the mixture, type of dielectric anisotropy (positive or negative), and nematic to isotropic temperature (T) of the liquid crystal-guest mixture_NI) (dichroic liquid crystal display) "liquid crystals-application uses and use](volume 3) (pages 65-208), 1992, singapore: world science publishers). In addition, a device can be characterized by the type and thickness of the substrate used, the alignment of the liquid crystal in the absence of an electric field, the thickness of the cell, the transmission swing, the optical distortion, and the cell gap of the cell, as well as the spacing of the chiral liquid crystal material, and the "thickness to spacing" ratio (d/p) of the mixture. The performance of any device is dictated by the selection of these parameters, which are inherently related. However, the exact nature of the parametric interactions between commercial guest-host devices has not been analyzed or elucidated.

For example, one challenge in defining any parameter in eyewear protection applications is the inherent conflict between the characteristics of the different components used in the object-host system. This can result in a perceived physical limitation of performance. For example, applicants have found that a large transmission swing between the light and dark state transmissions can be achieved by using high performance dichroic dyes. However, such dyes have inherently lower solubility, can split liquid crystal phases, and are modifiedTemperature of phase transition from nematic to isotropic, T_NI. Furthermore, such dyes indicate a higher degree of polarization dependence in performance. "polarization dependence" is a measure of the response of a material to two orthogonal polarizations; i.e. where the optical properties (e.g. refractive index or absorbance/transmittance) of a material experienced by incident light depend on the polarization of the incident light. The increase in polarization dependence can in turn reduce the transmission swing between the bright and dark states. Furthermore, such characteristics may also become undesirable, as higher polarization dependence may show even smaller structural defects within the liquid crystal cell configuration and/or any plastic substrate used for the technology. Conventional systems using high efficiency dyes have poor optical performance because the eye can easily pick out even small changes in the field of view.

The polarization dependence of a chiral nematic guest-host system depends on how tightly the liquid crystal molecules (i.e., their "pitch") are twisted relative to the thickness of the liquid crystal layer. This ratio is measured by a parameter known as the "thickness to pitch ratio" or "d/p". It is known that the larger the d/p of a liquid crystal mixture, the smaller its polarization dependence. For example, one way to reduce the polarization dependence of the device is to use a liquid crystal mixture with a short pitch (< 3 microns) in a thin cell (< 3 microns) and twisted structure with a thickness to pitch ratio (d/p) of > 0.9. However, in addition to the fact that this makes manufacturing extremely difficult and has hampered production, the use of 3 micron cells rather than thicker cells can also reduce the light transmittance of the light and dark states due to surface alignment effects, where the liquid crystal molecules respond less to the applied electric field due to the proximity of the two surfaces. This in turn can lead to smaller transmission swings and hence reduced performance.

One way to circumvent this obstacle is to trick the eye from seeing the imperfections in the cell and the plastic substrates. This can be achieved if the device shows a strong color dependence in the absorption spectrum. In other words, to avoid the eye seeing these defects, a guest-host system with intense color (i.e., narrow absorption spectrum <150 nm) is used. Such devices are limited in their transmission swing and/or have a narrow absorption band. Thus, they do not meet the requirements for wide band optics.

Thus, there remains a need for a variable transmittance liquid crystal optical device with good optical properties that uses plastic substrates, exhibits a wide transmission swing and has a wide absorption band (> 175 nm).

We have discovered, and described herein, a set of material and system parameters and device configurations based on physical characterization that can circumvent these obstacles and can achieve the desired system requirements described above.

Summary of The Invention

Variable transmittance optical devices and methods of making them are disclosed. Each optical device comprises a cell comprising a guest-host mixture of a liquid crystal host and a dichroic guest dye material contained between a pair of plastic substrates. The liquid crystal body has an axis orientation that is variable between a bright state orientation and a dark state orientation perpendicular thereto. The dichroic guest dye material includes one or more dichroic dyes. The optical device does not use a polarizer. The optical device exhibits a broad absorption band greater than 175nm in the visible wavelength range of 400nm to 700nm, with a light state transmission equal to or greater than 30% and a dark state transmission equal to or less than 40%.

In certain embodiments, the absorption band is greater than 180nm, 185nm, 190nm, 195nm, or 200 nm.

In certain embodiments, the clear state transmission is equal to or greater than 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. In certain embodiments, the dark state transmittance can be equal to or less than 35%, 30%, 25%, 20%, 15%, or 10%.

In some examples, the liquid crystal host has a thickness to pitch ratio (d/p) of less than 0.9 but greater than 0.25. In other embodiments, the liquid crystal body has a thickness to pitch ratio (d/p) of less than 0.8 or less than 0.7.

In certain embodiments, the guest-host mixture has a dichroic ratio D_mixIs greater than 11.5. In other embodiments, the dichroic ratio D_mixIs greater than 12, or greater than 12.5, or greater than 13.

In certain embodiments, the pair of plastic substrates have an optical retardation that varies less than ± 20% uniformity across the area of the device. In other examples, the optical substrates have an optical retardation variation of less than ± 15%, or less than ± 10%.

In certain embodiments, the guest-host mixture includes one or more dichroic dyes in the dichroic guest dye material, the dichroic dyes being azo-based dyes having at least two azo groups. In certain embodiments, the dichroic dyes have 2 to 6 azo groups. In other embodiments, the dichroic dyes have 2 to 10 azo groups.

The optical device has cells with cell voids greater than 3 microns but less than 20 microns. In some examples, the cell gap is equal to or greater than 5 microns but less than 15 microns.

In certain embodiments, the optical device has a transmission swing greater than or equal to 30%. In other examples, the optical devices have a transmission swing of 35%, 40%, 45%, 50%, 55%, or 60%.

In certain embodiments, the guest-host mixture has a nematic-isotropic transition temperature T_NIIs greater than 40 ℃. In other embodiments, the T_NIIs greater than 45 ℃,50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80%, 85%, or 90 ℃.

In certain embodiments, the optical device has a guest-host mixture having an order parameter S_mixIs greater than 0.78. In other embodiments, the guest-host mixture has an order parameter greater than or equal to 0.79. In still other embodiments, the guest-host mixture has an order parameter greater than or equal to 0.8.

In one embodiment, the optical device has a liquid crystal body comprising a chiral nematic material having a thickness to pitch ratio (d/p) of less than 0.9; a guest-host mixture comprising one or more dichroic dyes having a dichroic ratio greater than 11.5; and a nematic-isotropic transition temperature T of greater than 60 DEG C_NI. The device has a plastic substrate with an optical retardation variation of less than ± 20%; and the cell gap is greater than 3 microns. In certain embodiments, the device has a transmission swing of greater than or equal to 30%. In other embodiments, the device has a transmission swing greater than or equal to 40%.

Also disclosed herein are wide band optical mixtures for use in any of the above optical devices and methods of making the same.

Brief description of the drawings

This and other features and advantages of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings where:

fig. 1A and 1B are enlarged schematic cross-sectional representations of a cell according to the present invention.

Fig. 2A-2D are examples of graphs showing light absorption over a range of wavelengths for different cells or mixtures.

Fig. 3 is a graph showing an absorbance spectrum of a wide band of dichroic dyes. The graph is used in the calculation of the dichroic ratio and order parameter of the mixture.

Fig. 4 is a graph showing the transmission spectrum of example 1 in the off state (top line) and the on state (bottom line).

Fig. 5 is a graph showing the transmission spectrum of example 2 in the off state (top line) and the on state (bottom line).

Detailed Description

Applicants describe herein a variable transmittance optoelectronic device, referred to herein as a "wide band" device, which exhibits a wide absorption band (> 175 nm) or grayish color, and a wide (> 30%) transmittance swing (high contrast between its bright and dark states). Also described are mixtures for use in such devices, referred to herein as "wide band" mixtures; and methods of making the broadband mixtures and devices.

Such a "wide band" mixture is achieved when a guest-host liquid crystal mixture comprises the following properties: (i) a negative dielectric anisotropy liquid crystal host comprising a chiral nematic material in a cell such that its thickness to pitch ratio (d/p) is less than 0.9; (ii) in the liquid crystal body has>A dichroic dye or dye mixture of positive dichroic ratio of 11.5, (iii) a guest-host mixture having an effective order parameter S of greater than 0.78_mix(ii) a And (iv) such mixtures have a nematic-isotropic transition temperature T of greater than 40 ℃_NI. A wide band device is realized by: in a cell gap>A 3 micron liquid crystal device configuration places a "wide band" mixture between two transparent plastic substrates with uniform (i.e., less than 20% variation) optical retardation to form a wide band device.

Definition of

"absorption", as used herein, is a definition of the percentage of light that is not transmitted through the cell or optic. It is related to light transmission by the following relationship: absorbance =100% -transmittance. As used herein, "light transmittance" and "transmittance" are used interchangeably and mean the percentage of light transmitted through a device.

The "absorption band" is defined as the spectral wavelength at which absorption occurs.

"clear state" or "clear state light transmittance," as used herein, refers to the state in which the guest-host mixture exhibits maximum light transmittance.

"dark state" or "dark state light transmittance" refers to a state in which the guest-host mixture exhibits minimal light transmittance.

Similarly, the "dichroic ratio", "average dichroic ratio" or D of the mixture_mixRefers to the dichroic ratio of a guest-host mixture that may contain one or more dichroic dyes. The dichroic ratio of the mixture may be the effective dichroic ratio (D)_eff) Or a sum of effective dichroic ratios (D)_eff-agg) The formula (c) is judged. Thus, as used herein, D_mix、D_effOr D_eff-aggUsed interchangeably (depending on which method is used to judge the dichroic ratio) and describe the same parameter.

Nematic-isotropic transition temperature or T_NIIs the temperature at which the liquid crystal undergoes a nematic to isotropic transition from an oriented ordered nematic to a completely disordered isotropic phase. As used herein, T_NIRefers to the nematic-isotropic transition temperature of the guest-host mixture.

"optical device" refers to a device through which light is transmitted, which device can be controlled by applying a voltage. Such devices include eyewear protection devices (e.g., sunglasses, glasses or lenses, eyewear guards, goggles, head-mounted displays, etc.), automatically dimmed mirrors, and the front layer of a window.

"order parameter of a guest-host mixture" or "S_mix"refers to the order parameter of the guest-host mixture. TheThe mixture may contain one or more dyes along with other dopants. S_mixThe determination may be made according to the methods described herein, e.g., using a parameter for effective order (S)_eff) Or a valid order parameter sum (S)_eff-agg) The formula (2). As used herein, S_mix、S_effAnd S_eff-aggThe order parameter is used interchangeably (depending on which method is used to measure the order parameter) and describes the same parameter.

"polarization dependence" is a measure of the response of a material to two orthogonal linear polarizations; i.e. where the optical properties (e.g. refractive index or absorbance/transmittance) of a material experienced by incident light depend on the polarization of the incident light.

"polarization sensitivity" is a relative measure of the response between two orthogonal linear polarizations of a material. A polarization sensitivity of zero percent (0%) refers to a polarization insensitive device and a polarization sensitivity of 100% refers to a fully polarization sensitive device as obtained using a polarizer.

"polarizer" refers to a material that absorbs or reflects more of one polarization than the orthogonal polarization to incident light.

"transmission swing" refers to the difference in transmission between the clear and dark state transmissions. For example, if the light transmission is 65% and the dark transmission is 15%, the transmission swing is 40%. The transmission swing of the optics can be measured using equipment such as a "Haze-gardplus" device from BYK-Gardner, usa or an equivalent.

By "uniform optical retardation" is meant that the plastic substrate has an optical retardation variation of less than ± 20. "optical retardation" is defined as the optical phase experienced by incident light of different polarizations.

"broad band absorption", as used herein, is defined as the spectral absorption band of greater than 175nm, and preferably greater than 180nm, 185nm, 190nm, 195nm or 200nm, wherein the entire spectral absorption band is contained within the visible wavelength range, typically assumed to be 400nm-700nm (see FIG. 1)

"wide band device" refers to a device that exhibits a wide absorption band and a wide (i.e., > 30%) transmission swing, with polarization sensitivity of less than 20%, or in some instances less than 15%, or in some instances less than 10%.

"broad band mixture" refers to a guest-host liquid crystal mixture that can be used in a broad band device.

Liquid crystal cell

Fig. 1A and 1B generally show an electronically controlled liquid crystal cell whereby the transmission of light is continuously controllable. As can be seen in fig. 1A-B, the variable transmittance guest-host cell according to the present invention is generally referred to by the numeral 10. The unit 10 comprises two substrates, 12a, 12b, with a substantially constant spacing between them and which are enclosed on all sides by a sealing material 13, for example a uv-cured optical adhesive. As will be discussed in further detail below, a dichroic dye solution and a solution of liquid crystal material are disposed between the substrates 12a and 12 b.

The substrates 12a, 2b are plastic, low birefringence, optically transparent materials, either the same or different. The inner surfaces of the substrates are coated with a transparent conductive layer 14a, 14b, for example Indium Tin Oxide (ITO) or a conductive polymer. The two conductive layers 14a and 14b are connected to a power supply circuit 15. The power supply circuit 15 comprises at least one variable supply voltage, which is schematically indicated in fig. 1A and 1B by a surrounding V. Coated on the inside of each conductive layer 14 may be an optional passivation layer (also referred to as an insulating layer or "hard coat") 16a, 16b comprising, for example, a Si, Ti alkoxide (alcoxide). The innermost layer is an alignment layer 18a, 18b which may also function as a passivation layer.

The substrates 12a, 12b may be planar or curved. The distance between the substrates 12a, 12b is variously differentiated in the characteristics of the cells. If the body is a liquid crystal material, increasing the distance between the substrates 12a and 12b tends to reduce the likelihood of fabricating a polarization insensitive device; reducing this distance tends to reduce the light absorbing capacity of the cell and increases the difficulty of manufacturing. This distance defines a cell thickness 20 and in some examples is from 3 to 20 μm, or from 5 to 10 μm. To help maintain this spacing, optional spacers 21, such as glass or plastic rods or beads, may be inserted between the substrates 12a and 12 b.

The guest-host solution of the present invention includes a guest dichroic dye 24 in a liquid crystal host material 22. The dichroic dye 24 is an organic molecule (or mixture of molecules) whose absorption of polarized light is strongly dependent on the orientation of the polarization relative to the absorbing dipoles within the molecule. The dichroic dye 24 has positive dichroism in which maximum absorption occurs when the polarization is parallel to the long molecular axis of the dye molecule, and minimum absorption occurs when the polarization is perpendicular to the long axis. The dichroic dye 24 is further explained below.

The liquid crystal material is inherently birefringent, which may give rise to the polarization sensitivity of the device. Preferably, the liquid crystal material 22 is chiral nematic or achiral nematic supplemented with a chiral dopant. The liquid crystal material 22 may include more chiral material if lower polarization sensitivity is desired, or less chiral material if greater polarization sensitivity is desired. Using between about 1 and about 3 weight percent ZLI-811, for example, greatly reduces the polarization sensitivity of the cell 10. However, the amount of chiral material inversely correlates with the pitch. The use of a larger amount of chiral material results in a shorter pitch and if the pitch is too short, it is difficult to control the texture of the liquid crystal, which may result in the formation of a focal conic texture or a pattern-printing texture. Since these textures increase haze, they can degrade performance for optical applications and should be avoided.

The cell 10 is in a rest state, in which no voltage is applied, or in an actuated state, in which a voltage is applied across the two substrates. The present invention may be configured such that the application of a voltage may either increase or decrease the transmittance of light. In one embodiment, the rest or de-energized state has the greatest transmittance or "bright state" as seen in FIG. 1A, and the active or energized state has the least transmittance or "dark state" as seen in FIG. 1B. This can be achieved by using a homeotropic surface treatment (homeotropic scattering process) for the alignment layers 18a, 18B in combination with a dye having positive dichroism and a liquid crystal material having negative dielectric anisotropy, as shown in fig. 1A and 1B.

"clear state," as used herein, refers to the state in which the guest-host mixture exhibits maximum light transmittance. "dark state" refers to a state in which the guest-host mixture exhibits minimal light transmittance.

Thus, in this example, the Liquid Crystal (LC) molecules have a first state in the rest (no voltage or de-energized) state in which the orientation of the dye molecules is perpendicular (with respect to the LC substrate), so that the mixture is in the "bright state" when no voltage is applied. When a voltage is applied (excited state), the LC molecules have a second state in which the dye molecules are oriented at an angle more parallel to the LC substrate, so that the mixture absorbs light or is in a "dark state".

Characterization of the guest-dye mixtures

To achieve the desired characteristics of a wide band variable transmittance device, the dye mixture needs to have certain characteristics as described below.

Light transmittance swing

The device according to the invention has a high contrast between light and dark. The desired clear state transmission can be equal to or greater than 30%, preferably equal to or greater than 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. The dark state transmittance may be equal to or less than 40%, preferably equal to or less than 35%, 30%, 25%, 20%, 15%, or 10%. The transmission swing between the bright and dark states should be equal to or greater than 30%. Examples of the light transmittance swing value include 30%, 35%, 40%, 45%, 50%, 55%, or 60%. Thus, the light transmission is substantially uniform (± 10%) across the surface of the cell. The high transmittance bright state allows one to maintain the eyewear protection device in many low light conditions while the low transmittance dark state provides the necessary visual protection.

Wide absorption light band

Absorbance, as used herein, is defined as the percentage of light that is not transmitted through the cell. It is related to light transmission by the following relationship: absorbance =100% -transmittance. The absorption band is defined as the spectral wavelength at which absorption occurs. "broad absorption band," as used herein, is defined as a spectral absorption band greater than 175nm in one embodiment, and greater than 180nm, 185nm, 190nm, 195nm, or 200nm in other embodiments, wherein the entire spectral absorption band is contained within the visible wavelength range, typically assumed to be 400nm-700 nm.

For the purposes of the present invention, a "broad band dye" is considered to be any dye or mixture of dyes that produces a spectral absorption band characterized by what applicants call a "full width half maximum sum" (a-FWHM) that in one embodiment is greater than 175nm, and in other embodiments is greater than 180nm, 185nm, 190nm, 195nm or 200nm, wherein the entire spectral absorption band is contained within the visible wavelength range. The A-FWHM can be understood as follows: full width at half maximum (FWHM) is a measure of the width of the absorption curve characterizing the dye. It is defined as the distance between the truncation points of the absorption curve, which occurs where the absorption is half of the maximum absorption. See fig. 2A. Thus, regardless of the shape of the absorption curve, the FWHM is the width of the curve between two truncation points where the absorption is half of the maximum absorption.

Since the absorption range of interest is limited to visible wavelengths for the present invention, the cut-off can occur at 400nm or 700nm, even if the absorption of those wavelengths is more than half of the maximum absorption. See fig. 2B. This definition of the cut-off point means that, for example, dyes or mixtures which lead to significantly different absorption curves can have the same FWHM (see fig. 2C). Thus, the FWHM is based only on the distance between the truncation points, regardless of the detailed characteristics of the absorption curve, which will not affect the FWHM, for example, if the curve has a long tail. A dye having an absorption spectrum with two truncation points is described as having a single peak even though the detailed structure of the absorption spectrum between these truncation points is complex. (FIG. 2D) the present invention also includes dyes having absorption spectra with more than two truncation points. Such dyes are described as having multiple peaks, where each peak is different and can be characterized by its own FWHM (which is measured in the same manner as described for a unimodal dye). The total FWHM (A-FWHM) is defined as the sum of the FWHM of all peaks in the absorption spectrum. (see FIG. 2E). If there is only one peak, the A-FWHM is simply FWHM.

Order parameter

The maximum contrast between the light and dark states of an LC cell depends on the alignment of the dichroic dyes. Dichroic dyes have the ability to align themselves with nematic liquid crystal molecules when mixed together. When an electric field is applied to such guest-host mixture, the nematic liquid crystal host molecules are reoriented and aligned or perpendicular to the electric field so as to minimize the torque they experience from the electric field. These dichroic dye (guest) molecules may not be directly affected by an external electric field, but may align themselves with the liquid crystal host molecules. It is their interaction with the liquid crystal molecules that forces them to reorient.

The statistically average orientation of the elongated molecules (liquid crystals and dichroic dyes) in the guest-host mixture is directed in a specific direction called "director". Due to the mixingAll molecules in the composition undergo irregular thermal motion as they diffuse, and thus each molecule will not point in exactly the same direction as the indicator even when an electric field is applied. The statistical average of the molecular orientation shows that the molecules are tilted by an average angle theta with respect to the indicator_avg. This molecular tilt can also be characterized and calculated by a useful quantity called the "order parameter, S", which ranges from a value of 0 to 1. The order parameter of S =1 corresponds to all molecules perfectly aligned with the indicator (θ)_avg=0 °). (see world scientific publishing Co. Pte. Ltd. published 1992), LiquidCs-applications and uses, edited by B.Bahadur]Volume 3). Thus, the higher the order parameter S, the more aligned the dichroic dye molecules, thereby optimizing absorption for any particular molecular orientation. (FIG. 3). The present invention comprises a dichroic dye liquid crystal guest-host mixture having an effective order parameter S_mixIs greater than or equal to 0.78, 0.79, or 0.8.

As used herein, the "value of the order parameter of a guest-host mixture" or "S_mix"refers to the order parameter of the guest-host mixture. The mixture may contain one or more dyes along with other dopants. S_mixCan be measured according to the methods described herein, e.g., using for S_effOr S_eff-aggThe formula (2). Thus, as used herein, S_mix、S_effAnd S_eff-aggThe order parameter is used interchangeably (depending on which method is used to judge the order parameter) and describes the same parameter. "dye order parameter value" or "S_dye"refers to the order parameter of each dichroic dye relative to the transition dipole of the indicator.

In one example, the effective order parameter of a guest-host mixture comprising one or more dichroic dyes (e.g., neutral dyes) exhibiting a broad absorption spectrum is according to S_eff=(D_eff-1)/(D_eff+2) calculation of where D_eff=(∫A_||(λ)dλ)/(∫A_⊥(λ) d λ) is an "effective dichroic ratio" and A_||(lambda) and A_⊥(λ) is the parallel and perpendicular absorbance of the dye at wavelength λ. Typically, [ integral ] A_||(λ) d λ and ^ A_⊥(λ) d λ is estimated over the 380nm-780nm range of the spectrum. For the present invention, these integrals are estimated at the FWHM of the absorption spectrum of the broad band dichroic dye mixture, which as previously described is limited to the 400nm-700nm range of the spectrum. If the absorption spectrum has a single peak, the integrals can be simply estimated, the integral range being the wavelengths of the endpoints of the FWHM of the spectrum. If there is more than one distinct peak in the absorption spectrum, the integrals are estimated in a piecewise manner with the integration range being the wavelengths of the endpoints of the FWHM of each peak. This segmented integration produces what applicants call "dichroic ratio sum" D_eff-aggAnd "effective order parameter sum" S_eff-agg。

The order parameters of the mixture can be determined by optical measurements of light transmission in the rest and excitation states at several wavelengths both within and outside the absorption wavelength using linearly and/or circularly polarized light. Then, liquid crystal optical simulation methods such as those developed by Berleman (Berleman D.W.1972, Opticsignationdata and Anisotropic media: 4X 4-matrix formulation.) Journalofthe optical society of America [ journal of the American optical society ],62(4), 502); or those developed by Odano (Allia, p., Oldano, g., and Trossi, l.,1986,4 × 4 matrixapproachthyrallingquid-crystalloptics (4 × 4matrix method of chiral liquid crystal optics), journal of american society of optics society of america B, 3(3), 424); the order parameter may be determined by numerical fitting of experimental data. These simulation methods are used by those of ordinary skill in the art or by commercial programs such as twist cell optics (Kelly, j., Jamal, s., & Cui, m.,1999, simulaton dynamic modeling with twisted nematic devices containing flow) by Kelly, journalo applied physics, 86(8), 4091.

For the purposes of the present invention, an order parameter of 1 indicates that all molecules are aligned with each other. For example, all dichroic dye molecules align with each other, exhibiting almost identical absorption cross-sections for incident light and maximizing the absorbance of this particular orientation. Of course, it must be borne in mind that perfect alignment is difficult to achieve because these molecules are always subject to thermal motion. In order to maximize the optical properties, it is desirable to have a guest-host mixture in which the alignment between molecules is increased by the application of an external field.

In some embodiments, a desired guest-host mixture has an order parameter value S_mixWill be greater than 0.78. In other examples, the S_mixIs equal to or greater than 0.79. In still other examples, the S_mixIs equal to or greater than 0.8. S_mix>Mixtures of 0.78 are desirable which provide a wide transmission swing across the a-FWHM (30% -70%, preferably>35%）。

In some instances, if more than one dye is used to minimize color change in the rest (de-energized) and energized states, it is desirable that all dyes have approximately the same order parameter.

Similarly, the "dichroic ratio", "average dichroic ratio" or D of the mixture_mixRefers to the dichroic ratio of a guest-host mixture that may contain one or more dichroic dyes. As explained above, a dichroic ratio can be used for D_effOr D_eff-aggIs measured by the formula (2). Thus, as used herein, D_mix、D_effOr D_eff-aggUsed interchangeably (depending on which method is used to measure the dichroic ratio) and describe the same parameter.

In some examples, a desired guest-host mixture has a dichroic ratio, D, at wavelengths within the A-FWHM_mixWill be greater than 11.5.In other examples, the dichroic ratio D_mixGreater than 12, or greater than 12.5, or greater than 13 at wavelengths within the a-FWHM.

The guest-host mixture includes a chiral liquid crystal host. The chirality of the host material results in the intrinsic pitch, p, of the liquid crystal host material. This parameter is performance dependent. In addition, the ratio of the thickness d of the cell gap to the pitch is referred to as d/p. The spacing is a function of the helical twisting force and the concentration of the dopant and can be determined as known in the art. For the purposes of this application, the ratio d/p is less than 1, or in some instances, less than 0.9, or in some instances, less than 0.8 or less than 0.7; where d is the spacing of the substrates encapsulating the guest-host mixture and p is the intrinsic spacing of the guest-host mixture.

Solubility in water

The dichroic dye must also be sufficiently soluble in the liquid crystal host so that the appropriate dye concentration can be achieved to produce the desired absorbance in the dark state. Increasing the length of the dye (e.g., more azo groups) creates a limit to the concentration of the dye within the liquid crystal host. This limits the total absorption capacity of the LC-dye mixture and thus affects the transmission window. The trade-off made when selecting a dichroic dye and configuring a guest-host mixture complicates the color development process for a variable transmittance film. We have found that in some cases the structural similarity of the dye to at least one or more components in the liquid crystal host allows us to circumvent this limitation and increase solubility. For example, we have found that some modification of one dye tail may not affect the overall performance of the dye but may allow additional dyes to be dissolved in the mixture. In fact, we can increase the total amount of dye dissolved by carefully matching the dye to the host. In some examples, the mixture includes 1% -10% of the dyes having an order parameter >0.78 in the liquid crystal mixture.

The tail group comprises moieties that are structurally compatible with the formation of the liquid crystalline phase and comprise at least one ring or preferably two or more rings, which are linked to each other by a covalent bond or a linking unit. These rings may be the same or different and may include 5 or 6 membered aromatic or non-aromatic rings. These rings may be independently selected from: benzene, substituted benzenes, naphthalenes, substituted naphthalenes, cyclohexanes, substituted cyclohexanes, heterocycles, and substituted heterocycles. Examples of heterocyclic rings include 5 or 6 membered rings and may include one or more members selected from nitrogen, oxygen, and sulfur.

Examples of tail groups include those that can be represented by the following formulas:

wherein R is¹And R²Each independently selected from the group consisting of: hydrogen, halogen, -R^a、-OH、-OR^a、-O-COR^a、-SH、-SR^a、-NH₂、-NHR^a、-NR^aR^a、-NR^bR^c(ii) a Wherein R is^aIs a straight-chain or branched (C)_1-18) Alkyl radical, a straight-chain or branched (C)_1-18) Alkenyl radical or a straight-chain or branched (C)_1-18) A haloalkyl group; r^bAnd R^cIndependently selected from the group consisting of hydrogen and linear or branched (C)_1-18) An alkyl group; or wherein R is^bAnd R^cCombine to form a saturated 5-to 7-membered heterocyclic group. In these formulae, n is an integer from 1 to 5; m is an integer from 0 to 4; x¹、X²And X³Identical or different from each other, is a covalent bond or a linking unit; and Y is oxygen, nitrogen, or sulfur. The linking unit includes a divalent organic group. Examples of the connection unit include: alkyl, ether, ester, ethylene, acetylene, imino, azo, and sulfur groups. The linking unit includes a group that may be represented by the following formula: -R^d-、-O-、-OR^d-、-OR^dO-、-OCO-、-OCOR^d、-OCOR^dO-, -S-, -CH = CH-, -CH = N-, -C ≡ C-, wherein R^dIs a straight-chain or branched (C)_1-18) Alkyl radical or a straight-chain or branched (C)_1-18) A haloalkyl group.

Temperature (T) of nematic phase-isotropy_NI）

Another important parameter is the temperature at which the liquid crystal undergoes a nematic phase-to-isotropic transition, T_NIThe transition is from an ordered nematic phase to a completely disordered isotropic phase. In the disordered state, the applied voltage will have no effect on the transmission of light. We have found that for the purposes of the present invention, liquid crystal mixtures incorporating the dye should have a T of greater than about 40 ℃ in one embodiment_NIAnd in another example greater than about 65 ℃. In some examples, the T_NIIs greater than 45 ℃,50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80%, 85%, or 90 ℃.

Addition of a dye to a liquid crystal host changes the T of the mixture_NI. Therefore, the selection of the mixture must take into account T_NITo do so.

Dye material

We have determined that one class of dyes that can meet the above conditions is the azo-based dyes. More specifically, we have found that dyes having at least two azo groups are desirable. The azo dye may have an extended core, for example 2 to 10 azo groups. In some examples, the dye has 2 to 6 azo groups. Within this group, dyes should be used that are compatible with the liquid crystal host to be used. Those of ordinary skill in the art understand that the absorption band and order parameters of the dye can be varied by appropriate selection of the core and substituents. Some examples of dyes that can be used in one mixture are shown in the following table. (see, world scientific Press publishing Co., WorldScientific publishing Co. Pte. Ltd.) edited by B.Bahadur, Liquid crystals-applications and uses, Vol.3, 1992, pp.73-81). For example, the dyes are sufficiently soluble in the liquid crystal host and the order parameter of the guest-host mixtures is equal to or greater than 0.8.

Plastic substrate

The inventors of the present invention found that high performance broad band dichroic dyes show optical defects in plastic substrates having narrow band (< 175 nm) dichroic dyes that have been previously successfully used by the applicant.

Unlike other liquid crystal-based applications, the present invention requires the use of plastic substrates each having a thickness of less than: 750. 500 or 250 microns. These can then be laminated to a number of thicker carriers to provide mechanical stability. These substrates may consist of: a thermoplastic material such as PET, PES, TAC, polycarbonate or similar materials, or a thermoset material such as CR39, or other thermoset materials known in the art. It should be noted that each plastic has unique optical properties. Our studies have shown that plastics exhibit optical retardation as a whole. "optical retardation" is defined as the phase of light experienced by incident light of different polarizations. As understood by those who are optically experienced, the optical phase depends on the refractive index, the thickness of the cell, and the wavelength of the incident light of each polarization. It has been assumed in the art that for liquid crystal based optics, the optical retardation of the substrate must be the same as the optical retardation of glass, which is zero. This has placed significant limitations on the development of plastic eyewear protection devices and many plastic substrates with inherent delays are considered unacceptable. The basis for this assumption is that any liquid crystal device will have some polarization dependence, any retardation in the substrate will be observable, and thus only substrates without birefringence can be used. This is visible for optical polarizers in the use of plastic without birefringence (e.g., TAC).

However, we have found that not the actual delay but the relative delay is more important. In particular, if the plastic is designed to have a retardation of uniformity variation of less than ± 20% over the area of the device, it is possible to avoid the above limitations and achieve wide band absorption. We have therefore found that if we select a plastic whose retardation value is more uniform across the device (e.g. less than 20% variation), the limitations of the actual retardation value can be circumvented. This is a substantial departure from conventional considerations with plastics and opens up the potential for wide absorption band devices. Specifically, variations of less than ± 20%, or in some instances, less than ± 15% or less than ± 10% were found to be desirable. This can be most easily achieved if the plastic has overall minimal retardation, such as TAC, or if it is made to have more consistent (+/-20%) retardation over the substrates. This may be achieved by stretching the plastics (including PET, PES or PC) traditionally disfavored as substrates for liquid crystal optical applications, as appropriate. Furthermore, we have found that the mode of stretching can have a substantial effect on its performance. For optimum performance, the stretching must be such that the angular deviation between the two orthogonal modes of the plastic is less than 30 degrees in the area of the optics used. It is well known in the art that such deviations can be achieved by suitable stretching methods.

Example 1

A variable transmittance cell was prepared according to the following protocol. A test cell was fabricated using a 5 mil polyethylene terephthalate (PET) substrate pre-coated with a conductive polymer (KimotoTech, cedartownwa, u.s.a.). The conductive polymer serves as a transparent electrode. On top of the conductive polymer, a polyimide coating nissan se1211 (nissan chemical industries, Ltd.) of japan, tokyo was applied by silk-screen printing and then baked at 100 ℃ for 2 hours. The polyimide coating serves as an alignment layer designed to induce substantially vertical surface alignment of the liquid crystal molecules. Next, shinshikyew plastic balls (6 micron diameter) (HikoIndustrialLtd, hong kong) were sprayed onto one of the substrates to serve as spacers. A thin bead of uv curable adhesive, Loctite3106, (HenkelAG & co. kgaa, dusseldov, germany) is then applied around the periphery of one of the substrates, leaving a void that can act as a fill port. The two substrates are then assembled, pressed together against the spacers to create a uniform gap between the substrates, and then exposed to ultraviolet light to cure the adhesive.

A guest-host mixture is then prepared, which mixture consists of: (1) 94.8% by weight of a negative dielectric anisotropy liquid crystal host, MLC-6609, from Mock (Merck) (EMD Chemicals, Gibbstown, N.J., USA) having a negative dielectric anisotropy (Δ < 0); (2)1.125% chiral dopant, ZLI811, also from mok corporation; and (3) an azo-based dichroic dye mixture consisting of 0.41% of dye DR-1303(AlphaMicron, usa); 0.95% of G-241 (Marubeni Chemicals, Japan); and the dyes LSY-210 (mitsubishi chemical corporation, japan), DD-1123, DD1032, DD1089 (AlphaMicronInc, usa) mixed at an equal ratio in a total amount of 2.71%. The test cell is placed in a vacuum chamber to remove air from the space between the substrates and then fill the guest-host mixture by capillary action. The fill port is sealed using a uv curable adhesive. A conductive tape comprised of a copper backing and a conductive adhesive is then adhered to each substrate of the conductive polymer coating to serve as a robust interconnect for electrical leads.

The absorption curve of this cell is shown in figure 4. The dichroic ratio and order parameters of the mixture are determined and calculated as described herein. The photopic light transmittance swing of the unit>30% and a significant dichroic ratio of 14 (order parameter, S)_mix=0.82），dA/p ratio of 0.75, and T_NIIt was 91.5 ℃ (LC host).

Example 2

A variable transmittance cell was prepared according to the following protocol. A test cell was fabricated using a 3 mil polyethylene terephthalate (PET) substrate pre-coated with a transparent conductive ITO (Techimat, usa). On top of the conductive polymer, a polyimide coating nissan se1211 (nissan chemical industries, Ltd.) of japan, tokyo was applied by silk-screen printing and then baked at 100 ℃ for 2 hours. The polyimide coating serves as an alignment layer designed to induce substantially vertical surface alignment of the liquid crystal molecules. Next, shinshikyew plastic balls (6 micron diameter) (HikoIndustrialLtd, hong kong) were sprayed onto one of the substrates to serve as spacers. A thin bead of uv curable adhesive, Loctite3106, (HenkelAG & co. kgaa, dusseldov, germany) is then applied around the periphery of one of the substrates, leaving a void that can act as a fill port. The two substrates are then assembled, pressed together against the spacers to create a uniform gap between the substrates, and then exposed to ultraviolet light to cure the adhesive.

A guest-host mixture is then prepared, which mixture consists of: (1) 95.2% by weight of a negative dielectric anisotropy liquid crystal host, MLC-6609, from Mock (Merck) (EMD Chemicals, Gibbstown, N.J., USA) having a negative dielectric anisotropy (Δ < 0); (2)0.9% chiral dopant, ZLI811, also from mok corporation; and (3) an azo-based dichroic dye mixture consisting of 0.38% of the dye DR-1303(AlphaMicron, usa); 0.76% of dye G-241 (Marubeni Chemicals, Japan); and an equivalent amount of dye LSY-210 (Mitsubishi chemical corporation, Japan) totaling 1.51%, DD-1123, DD1032, DD1089 (AlphaMicronInc, USA); and DD-1112, DD-1215 (AphaMicron USA) in a ratio of 2:1, respectively, in total of 1.2%. The test cell was placed in a vacuum chamber to remove air from the space between the substrates and then the guest-host mixture was filled by capillary action. The fill port is sealed using a uv curable adhesive. A conductive tape comprised of a copper backing and conductive adhesive is then adhered to each substrate of the conductive polymer coating to serve as a robust interconnect for electrical leads.

The absorption curve of this cell is shown in figure 5. The dichroic ratio and order parameters of the mixture are determined and calculated as described herein. The cell had a photopic transmission swing of 40% and an effective dichroic ratio of 15 (order parameter, S)_mix= 0.83), d/p ratio of 0.5, and T_NIAt 93 ℃ (LC host).

Claims (14)

1. A variable light transmittance optical device comprising:

a cell comprising a guest-host mixture of a liquid crystal host and a dichroic guest dye material contained between a pair of plastic substrates,

wherein the liquid crystal host has an axis orientation that is variable between a bright state orientation and a dark state orientation perpendicular to the bright state orientation;

wherein the liquid crystal host comprises a chiral nematic material having a thickness to pitch ratio (d/p) of less than 0.9 but greater than 0.25;

wherein the dichroic guest dye material comprises one or more dichroic dyes;

wherein the guest-host mixture has an order parameter S greater than 0.78_mixAnd a nematic-isotropic transition temperature Tm of greater than 40 ℃;

wherein the plastic substrate has an optical retardation for incident light of any given wavelength with a uniformity variation of less than ± 20%; wherein the optical device does not use a polarizer; wherein the optical device exhibits a broad absorption band greater than 175nm in the visible wavelength range of 400nm to 700 nm; and is

Wherein the optical device has a dark state transmission equal to or less than 40%, a bright state transmission equal to or greater than 30%, and a transmission swing between the bright state orientation and the dark state orientation of greater than or equal to 30%.

2. The optical device of claim 1, wherein the guest-host mixture has a dichroic ratio D_mixIs greater than 11.5.

3. The optical device of claim 1, wherein the one or more dichroic dyes in the dichroic guest dye material are azo-based dyes having at least two azo groups.

4. The optical device of claim 3, wherein the azo-based dye has 2-6 azo groups.

5. The optical device of claim 1, wherein the cells have a cell void greater than 3 microns but less than 20 microns.

6. The optical device of claim 1, further having a transmission swing greater than or equal to 40%.

7. The optical device of claim 1, wherein said guest-host mixture has an order parameter_SmixIs greater than or equal to 0.79.

8. The optical device of claim 1, wherein said guest-host mixture has an order parameter_SmixIs greater than or equal to 0.8.

9. The optical device of claim 1, wherein:

the guest-host mixture comprises one or more dichroic dyes having a dichroic ratio greater than 11.5;

the guest-host mixture has a nematic phase-isotropic transition temperature T_NIIs greater than 60 ℃;

the cells have a cell void greater than 3 microns but less than 20 microns; and the device has a transmission swing greater than or equal to 40%.

10. The optical device of claim 1, wherein the optical device exhibits a broad absorption band greater than 190nm in the visible wavelength range.

11. A guest-host mixture for use in a variable light transmittance optical device according to any one of claims 1 to 9.

12. The guest-host mixture of claim 11 wherein the guest-host mixture has a transmission swing greater than 50%.

13. The guest-host mixture of claim 11, wherein the guest-host mixture comprises one or more dichroic dyes having a dichroic ratio greater than 13.

14. The guest-host mixture of claim 11, wherein the guest-host mixture has a bright state transmittance equal to or greater than 60% and a dark state transmittance equal to or less than 30%.