WO1998019207A1

WO1998019207A1 - Transparent body

Info

Publication number: WO1998019207A1
Application number: PCT/EP1997/005749
Authority: WO
Inventors: Albert Schmidt
Original assignee: Carl Zeiss; Carl-Zeiss-Stiftung Handelnd Als Carl Zeiss
Priority date: 1996-10-28
Filing date: 1997-10-17
Publication date: 1998-05-07
Also published as: DE19644726A1

Abstract

The invention relates to a transparent body comprising two attaching external transparent bodies which surround a volume of liquid crystals placed between them and intercalated colorants (guest-host cells), having an orientation layer of organic molecules or polymers respectively on the inner surface of the attaching bodies. According to the invention, the orientation layers consist of photochromic molecules or polymers, which regulate the liquid crystal volume following the command-surface effect (specially with cis-trans isomerization). Colorant molecules have also been dissolved in the liquid crystals. Said molecules match the sunlight spectrum and the visual spectral sensitivity of the human eye or the spectral sensitivity of an apparatus placed behind the transparent body.

Description

Description :

See-through body

The invention relates to see-through bodies with two outer transparent end bodies, which enclose a volume arranged between them with liquid crystals and embedded dyes, and in each case an orientation layer made of organic molecules or polymers on the inner surfaces of the end bodies.

Transparent bodies with liquid crystals in between are well known and are used in particular in LCD screens. However, it is also known to use see-through bodies of this type in panes of buildings, cars, trains, aircraft and in sunglasses. The see-through bodies are used in sunglasses to change their transmission in changing light conditions, so that the eye is protected from excessive radiation.

Sunglasses are known which take advantage of the electrochromic effect and require a battery as a voltage source.

Sunglasses are also known which take advantage of the electro-optical effect of liquid crystals (LC or FK). Since smaller voltages and powers are sufficient than with the electrochromic effect, the energy supply from one or more photocells is sufficient. In order to weaken the visible part of the spectrum of sunlight, several dyes have to be embedded in an LC matrix (guest host principle / cell). The application of a voltage leads to a reorientation of the LC molecules from homogeneous planar to homeotropic (or vice versa, depending on the cell type), whereby the spatial position of the dyes is also changed by the interaction with the LC molecules. This changes the absorption of the cell. This is the well-known electro-optical principle of the guest-host cell. The orientation layers are either built up from polymers (eg polymide), whereby a preferred direction is generated by brushing, or from organic molecules, which (by themselves) are oriented perpendicularly or with an angle of inclination to the surface.

Phototropic glasses do not need any voltage or energy supply. Due to the photochromic effect, the solar radiation causes a photochemical change in the volume of the glasses, which is reflected in the change in absorption.

From US 5,211,876 a liquid crystal arrangement for a windshield or sunroof of a car is known, which require an additional voltage source to change the transmission.

A windshield for a passenger car is known from US Pat. No. 5,298,732, in which an LCD arrangement creates a transmission-reducing area only between the driver and the sun. Here too, an additional voltage source is required to change the transmission.

From US 4,765,977 and US 5,041,244 liquid crystal lenses for sunglasses are known which require an additional voltage source to change the transmission.

It is the object of the invention to provide a see-through body which, by means of liquid crystals (in particular natural light or sunlight), causes a change in transmission even without the application of a voltage or a current and without the imperative need for electronic components.

This object is achieved by the characterizing part of the first claim.

The invention is essentially based on a combination of guest-host cells with orientation layers that show the command surface effect. By exposure to light, the Orientation layer orientation changed. This changes the orientation of the liquid crystals and the dyes. This causes a change in the transmission. This process is reversible.

The principle effect of the "command surface" was published in 1989 by T.Seki and K.Ichimura. Numerous other publications were subsequently published on this effect (e.g. T.Seki, K.Ichimura, Thin Solid Films 179 (1989) 77; K.Aoki, A. Hosoki, K.Ichimura, Langmuir 8 (1992) 1007; - Dissertation from M.Büchel at the University of Mainz from 1995; etc.). In the publication by T.Seki et al. , Langmuir 1993, Vol. 9, 211-218 it is mentioned that the orientation of the command surface layer was demonstrated by the addition of a dye.

The see-through body according to the invention has two outer transparent shells as the end body, it being possible for the curvature of the shell to produce an optical effect on at least one of the two shells, preferably on the outer side thereof (but not necessarily, see sunglasses).

There is a volume between these two shells, which are arranged at a certain distance from one another. This volume contains liquid crystals and embedded dyes, which are prevented from leaking by the two shells.

On the inner surface of the two shells there is an orientation layer made of organic molecules or polymers, which is in direct contact with the liquid crystals.

According to the invention, the orientation layers are made of photochromic molecules or polymers, which switch the volume of the liquid crystals according to the command surface effect. These are in particular molecules and polymers with cis-trans isomerization. Furthermore, according to the invention, dye molecules are dissolved in the liquid crystals, which are based on the Sunlight spectrum and the visual spectral sensitivity of the human eye or to the spectral sensitivity of a device behind the see-through body are matched.

This combination according to the invention makes it possible to create sun-sensitive see-through bodies (sunglasses lenses, panes for various vehicles or buildings, etc.), which are much less expensive than the previously known solutions

An insulation layer is advantageously arranged between the transparent conductive electrode and the orientation layer. This insulation layer is preferably made of SiO 2.

The orientation layer is preferably made up of azobenzenes or molecules (or polymers) containing stilbene.

The liquid crystals are preferably nematic liquid crystals.

The end bodies are preferably made of plastic or glass.

It is advantageous if a coupling layer with anchor groups is attached below the orientation layer. As a result, the orientation layer is anchored more securely to the shells of the see-through body.

The preferred area of use of the see-through body is its use as a lens for sunglasses.

The invention is explained in the following by way of example with reference to drawings, wherein further essential features and a better understanding explanation and design options of the inventive concept are described. Show:

Figure 1 shows a first see-through body according to the invention; and

Figure 2 shows another variant of a see-through body according to the invention.

The see-through bodies shown in FIGS. 1 and 2 are drawn purely theoretically, so that the size relationships shown are unrelated to the real size relationships. The see-through bodies can in particular be lenses for sunglasses, windows for buildings, cars, trains, planes, etc., the lenses being able to have, in particular, one or no dioptric effect.

The structure of the see-through body is quickly explained. The first see-through body (1) according to the invention shown in FIG. 1 shows a feasible minimal solution. It has two cover layer bodies (la, lb) which create a cavity and which consist of a transparent hard or soft material. This material can e.g. Be glass on which the command surface layers can be applied using chemisorption or the Langmuir-Blodgett technique. It can also be applied to plastic using the Langmuir-Blodgett technique. However, one can also first apply a thin SiO 2 layer to plastics, on which the command surface layers can be applied.

An orientation layer (2a, 2b) is in each case applied to the inner surface of these cover layer bodies (la, lb). The cavity between the two cover layer bodies (la, lb) with the orientation layer (2a, 2b) on its inner surface is filled with rod-shaped liquid crystals (3) which have a dye admixture according to the prior art, so that the guest host Principle is used.

The orientation layer (2a, 2b) is the essential part of the invention. It consists of molecules, which undergo a cis-trans isomerization under the influence of UV radiation and thus change geometrically. The geometric change leads to a change in the position of the liquid crystals (3) lying on the orientation layer (2a, 2b), which ultimately leads to a positional adjustment of all liquid crystals (3) between the two orientation layers (2a, 2b). The

Switching speed of such an orientation layer (2a, 2b) is currently in the seconds / minutes range with the previously known molecules and depends on the length of the molecules (the longer the molecules are, the faster they change from one state to the other state ). Molecules for the orientation layer (2a, 2b) are photochromic molecules with the isomerization described above. Examples include azobenzenes and stilbenes.

In the case of the command surface effect, one layer of a molecule or polymer (e.g. azobenzene) is located on the carrier substrate (la, lb). The orientation layer (2a, 2b) and with it the liquid crystal (3) changes its orientation from the homeotropic phase in the trans state to the homogeneous planar phase in the cis state, which is oriented along the direction of transmission, when using azobenzene molecules in the orientation layer (2a, 2b) when irradiated with a wavelength of approximately 360nm. The opposite change in orientation occurs when irradiated with a wavelength of approximately 440 nm. By modification of the azobenzene derivatives (especially by push-pull groups) these absorption areas can be shifted (to longer wavelengths).

A further variant of the see-through body (1 ') according to the invention is shown in FIG. 2, but which has a much more complicated layer structure between the two cover layer bodies (la ¹ , lb'). In the see-through body (1 ') shown in FIG. 2, a transparent electrode (5a, 5b) (for example an indium tin oxide, also called ITO) is first applied to the inner surfaces of the cover layer bodies (la', lb '). An insulating layer (4a, 4b) (for example made of SiO 2) is deposited thereon, but this is not mandatory. The orientation layer follows

(2a ', 2b'), which is built up from the molecules already described. However, a coupling layer (not shown in the figure) can also be applied between the orientation layer (2a ', 2b') and the insulating layer (4a, 4b) or electrode (5a, 5b). Between the two orientation layers

(2a ¹ , 2b ') are the liquid crystals (3') with the dye admixture (guest-host principle).

With this arrangement there is also one

Transmission change of the see-through body possible by an energy and voltage supply, which is useful if the required switching wavelengths (e.g. through discs) are no longer available. As a result, the see-through bodies can then also be used as sunglasses lenses behind windows (e.g. in a building or in a car).

As already mentioned, the invention is characterized by a combination of the guest-host principle with the command surface effect. However, the volume of the liquid crystal cell is not changed photochemically, as is the case with phototropic glasses, but only the orientation layer between the cover layer bodies and the liquid crystals, it being possible for an electrode to be attached between the orientation layer and the cover layer bodies. The orientation layer gives the liquid crystals a uniform orientation. It is known from some special orientation layers described above that they change their chemical and physical structure by exposure to UV and can switch a liquid crystal cell from homeotropic to homogeneous planar and thus can trigger a command surface effect. The advantage of the inventive solution, especially for sunglasses, is the absence or not necessarily the presence of any power supply and electronics. In addition, only an extremely thin layer is changed photochemically, while the volume of the liquid crystal cell is not photochemically loaded.

When selecting suitable molecules for the structure of the orientation layers for the see-through bodies according to the invention, their long-term stability, switching speed and the wavelength dependence of the cis-trans isomerization must be taken into account in particular.

The change in transmission in the see-through bodies according to the invention is less than 40% (but 25-30% are certain) with a maximum transmission of approximately 75% and less.

Suitable photochromic molecules for use as a "command surface layer" are molecules which show a cis-trans photoisomerization when irradiated, which is associated with a change in the geometry of the molecule. The best known examples are the stilbene derivatives and the azobenzene derivatives.

Stilbene derivative:

Rl benzene ring with carbon atom on (via double bond)

Carbon atom on benzene ring R2

Azobenzene derivative:

Rl benzene ring with nitrogen atom on (via double bond)

Nitrogen atom on benzene ring R2

The coupling layer between the surface and the photochromic function is typically integrated into the whole molecule (the R _] _ in the above nomenclature). One therefore does not necessarily speak of individual layers, but of "functions" that are integrated in a molecule. in the in general, the molecules have the following schematic structure:

Head group, photochromic group, spacer, anchor group.

The anchor group connects the molecule to the substrate surface. The spacer separates the photochromic group from the surface (since this group needs space to carry out the isomerization). The head group is the free end of the molecule. This serves to create space for the photochromic groups and the connection. to ensure the liquid crystals in the cell.

The simplest type of head group are alkyl chains of different lengths, n. In the simplest case, the spacer is also an alkyl chain of length m. The chemistry of the system often requires an alkoxy group as the head group. The anchor group can be chemically bound to the surface (typically glass, quartz, silica). This happens, for example, through silane compounds:

Table of azobenzene carboxylic acids

Ri R2 mp, ° C

Azc-1 C ₆ Hi3 0 (CH ₂ ) ₅ 144-146 Azc-2 C ₈ Hl7 0 (CH ₂ ) ₅ 142-143

Azc-3 0 (CH ₂ ) ₅ 196-197 ^■ )

Azc-4 CI 0 (CH ₂ ) ₅ 165-169 Azc-5 H 0 (CH ₂ ) ₅ 143-145 Azc-6 CH ₃ 0> 300

Azc-7 C ₆ H ₁₃ 0 278-282

Azc-8 C ₆ Hl3 0 (CH ₂ ) ₃ 162-162

Azc-9 C ₆ Hl3 0 (CH ₂ ) ₂ 150-159

Azc-10 C ₆ Hi3 OCH ₂ 189-191

Azc-13 C ₆ Hl3 O (CH ₂ ) ₁₀ 106-108

To do this, the substrate must be pretreated with an appropriate reagent (e.g. glass / quartz surface):

Physical interactions can also occur that bind the molecule to the surface (physisorption). Examples of these are molecules that can be applied to surfaces as monomolecular films using the Langmuir-Blodgett method. Another option is to use the anchor group as a Train polymer. Then several (spacer photochromic head group) systems are bound to a main polymer chain. This main chain then acts as an anchor group. The connection to the surface takes place via physical effects (example: ionic / electrostatic or Van der Waals interaction). Some representatives of such polymers can also be applied using the Langmuir-Blodgett method. Examples include:

, -, J opfsaiDpe,

I Spacer ι i _-_ i.

the above azobenzene functionalized polyglutamates a) poly (5- (x- (4- (4-hexylphenylazo) phenoxy) ethyl) -L-glutamate, and b) poly (5- (2- (4- (4-decyloxyphenylazo ) phenoxy) ethyl) -L-glutamate.

The well-known azobenzene derivatives are based on a unidirectional, homeotropic starting orientation of the orientation layer of the LC cell. LC mixtures with (positive) dielectric anisotropy and pleochroic dyes or dye mixtures which are used in the LC mixture are soluble. Examples of the LC mixture are ZLI1840 from Merck and the dye G313 (2.5%) (manufacturer is, for example, Merck), with maximum absorption at 666 nm. This cell appears bright in the off state (without exposure) On state (with exposure) the cell appears green.

Other guest-host liquid crystal cells are also possible, the above combination is therefore only an example. The color impression can be changed, especially by a different dye mixture. 2.5% of the dye M137 (max.absorption at 637 nm) (manufacturer is e.g. Merck) in ZLI1840 (manufacturer is e.g. Merck) gives a blue transmission color. Another combination is the use of the liquid crystal DON-103 (manufacturer is e.g. the company Rolic) in combination with the dye LCD-118 (manufacturer is the company e.g. Merck).

For the highest possible contrast, a polarizer should be used, the orientation of which is adapted to the unidirectional orientation of the orientation layer.

The switching times of the effect are in the minute range. The switching time can be shortened by changing the molecular parameters, such as lengthening the spacer or increasing the interaction between liquid crystal and the photochromic unit (polar group in the center of the liquid crystal molecule).

Claims

Claims:

1. see-through body with two outer transparent end bodies, which enclose a volume arranged between them with liquid crystals and embedded dyes (guest-host cell), and in each case an orientation layer made of organic molecules or polymers on the inner surfaces of the end bodies, characterized in that the orientation layers are made up of photochromic molecules or polymers, which switch the volume of the liquid crystals according to the command surface effect (in particular with cis-trans isomerization), and that dye molecules are dissolved in the liquid crystals, which affect the sunlight spectrum and the visual spectral sensitivity of the human eye or to the spectral sensitivity of a device behind the see-through bodies.

2. see-through body according to claim 1, characterized in that an insulation layer is arranged between the transparent electrode and the orientation layer.

3. see-through body according to claim 1 or 2, characterized in that the insulation layer is composed of Si0 ₂ .

4. see-through body according to one of claims 1-3, characterized in that the orientation layer is composed of azobenzene or stilbene-containing molecules (or polymers).

5. see-through body according to one of claims 1-4, characterized in that the liquid crystals are nematic liquid crystals.

6. see-through body according to one of claims 1-5, characterized in that the end body are made of plastic.

7. see-through body according to one of claims 1-5, characterized in that the end body are made of glass.

8. see-through body according to one of claims 1-7, characterized in that a coupling layer with anchor groups is attached below the orientation layer.

9. see-through body according to one of claims 1-8, characterized in that the see-through body is a lens for sunglasses.