Display forms using liquid crystals

In a display device, planar or curved, panel or colored pane it is known that the image or the colors do not change noticeably with the angle of viewing or angle of illumination. In this invention drastic changes in the image and colors can be obtained using cholesteric or other chiral liquid crystal coatings or polymers with liquid crystalline properties. In addition the colors are more intense than feasible with other colorants. These two properties are value in applications where it is desired to attract the viewers attention such as in advertising and signage. In a colored pane consisting of ornamental or stained glass parts it is known that the process of achieving the desired image effects is not simple and limited in scope. Using liquid crystal coatings the process of achieving such effects is greatly simplified and less expensive. By providing two or more liquid crystal coatings on transparent substrates overlaying each other new colors and three-dimensional effects can be obtained as a result of the color additive properties of liquid crystals coatings which do not absorb light.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to suitably illuminated display devices, planar or 
curved, panels or panes such as used in commercial advertising, signage, 
teachings and decorative purposes, some fine arts forms such as paintings, 
reliefs, sculpture and jewellery objects. It also relates to ornamental 
decorative partitions, window panes and stained glass forms where the 
illuminant can be daylight or an artificial light source. The invention 
exploits the properties of cholesteric or other chiral liquid crystal 
coatings deposited on transparent substrates that show intense colours 
when the reflected light from the image coated panels having a dark 
backing is viewed and shows complementary colours when the light source is 
behind the panel and the transmitted light through the panel and image is 
viewed. It exploits the remarkable property of such liquid crystal 
coatings where the colours perceived change with the angle of viewing and 
the angle of illumination. It exploits the fact that the coatings don't 
absorb light and thus superimposed coatings are transparent to each other 
and their colours mix additively like coloured lights. 
(2) Description of Prior Art 
The prior art related to this invention is: (1) Cdn. Pat. No. 956159, 
issued on Oct. 15, 1974 to E. J. Stevens et al, entitled Polychroic Films; 
(2) Cdn. Pat. No. 704348, issued on Feb. 23, 1965 to Moray and Doris 
MacNaughton, entitled Illuminated Decorative Panels; (3) Cdn. Pat. No. 
445944, issued on Jan. 6, 1948 to Jean Crotti, entitled Processes for 
Obtaining Multicoloured Effects Similar to Those of Stained Glass Window 
and Products Resulting Therefrom; (4) Cdn. Pat. No. 1168905, issued on 
June 12, 1984 to Aldo Colombo, entitled Extended Temperature Range 
Thermographic Screen to Detect Temperature Anomalies at the Skin; (5) Cdn. 
Pat. No. 1110052, issued on Oct. 6, 1981 to James Fergason, entitled 
Composition for Liquid Crystal Thermometry; (6) Cdn. Pat. No. 1180541, 
issued on Apr. 2, 1985 to Heino Finkelman et al, entitled Crosslinked 
Organopolysiloxanes Having Liquid Crystalline Properties; (7) U.S. Pat. 
No. 3,533,399 filed Aug. 2, 1965 by Newton N. Goldberg et al, entitled 
Temperature Sensing Means and Methods; and (8) U.S. Pat. No. 3,666,948, 
filed Jan. 6, 1971 by Bela Mechlowitz et al, entitled Liquid Crystal 
Thermal Imaging System Having an Undisturbed Image on a Disturbed 
Background. 
In the prior art forms of display panels or panes used in the above 
mentioned applications, light absorbing pigmented colourants having a 
limited colour gamut were employed. Liquid crystals of the cholesteric 
type have a large colour gamut than such colourants and therefore more 
intense colours can be realized. The colours of prior art display forms or 
panels are static in the sense that they appear almost the same 
irrespective of the direction of viewing and illumination. In many cases 
of advertising, signage, jewellery objects and display applications it is 
desirable to attract the passer-by's attention. Liquid crystal images 
fulfill admirably this goal as a drastic colour change is perceived by a 
viewer as he moves past such a display. This colour change is due to light 
interference phenomena between the oriented molecular layers of liquid 
crystal mixtures. In the prior art it has been known that certain light 
interference dielectric coatings possess also such colour-viewing angle 
dependence properties. Such coatings, however, have not been used for the 
display panels referred to as the process and the creation of images is 
not simple and is expensive. Therefore such interference coatings found 
applications in large scale mass produced single colour products such as 
special uniformly coloured panes for windows. In other attempts to achieve 
viewing angle dependent colour effects vertical coloured strips were 
mounted on a supporting base (Cdn. Patent No. 956159 ref. 1), resulting in 
a complicated structure. In the prior art ornamental and stained glass 
displays have been formed by assembling or fixing together suitably shaped 
pieces of coloured glass (Cdn. Patent No. 704348 ref. 2 and Cdn. Patent 
No. 445944 ref. 3). The above mentioned devices or processes are time 
consuming and the freedom to create complicated and complex images is 
considerably restricted. These limations, as will be described below, are 
substantially eliminated by the use of liquid crystal coatings. 
This invention deals with the use of cholesteric or other chiral liquid 
crystal coatings on suitable opaque, transparent, translucent or diffusing 
planar or nonplanar substrates and may utilize one or more such coated 
substrates fully or partly overlaying or joined together, side by side or 
with the surfaces at an angle. In the prior art liquid crystal materials 
have been applied mostly to flexible substrates such as paper, plastic or 
rubber membranes. Also the liquid crystal materials, usually cholesterol 
esters, were encapsulated in small (10-50 .mu.m) plastic capsules or they 
were imbedded in plastic compounds in order to protect the liquid material 
from deterioration. In such encapsulated cholesteric liquid crystals 
however the colours are not as intense, particularly the yellows, oranges 
and the reds. These products were used mainly for thermography or 
thermometry (Cdn. Patent No. 1168905 ref. 4; Cdn. Patent No. 1110052 ref. 
5; U.S. Pat. No. 3,533,399 ref. 7 and U.S. Pat. No. 3,666,947 ref. 8). 
They were based on the colour-temperature dependence of some liquid 
crystal mixtures in which the colour is the indication of the temperature 
of the object being investigated. To my knowledge the change of colour 
with angle of viewing of liquid crystals have not been taken advantage of 
in display forms, panels or panes to date. In the prior art the properties 
of liquid crystals, of interest to any application, existed within the so 
called mesomorphic temperature range. Above this range the material 
becomes a colourless isotropic liquid; below this range it becomes a 
colourless solid. To date, the mesomorphic temperature range of the liquid 
crystal mixtures that were chosen for practical products had to coincide 
with the temperature range such products were intended to operate. 
SUMMARY OF THE INVENTION 
In this invention the advantage is taken of the special property of certain 
polymer and polysiloxanes having cholesteric liquid crystals properties 
(Cdn. Patent No. 1185401 ref. 6) in which, when cooled below the 
mesomorphic temperature range, the orientation of the molecules is frozen 
and preserved and the colours become a permanent aspect of the solid 
coating. The material therefore doesn't require encapsulation and thus 
equal intensity for all colours across the whole visible spectrum is 
preserved. Gradually such a polymer material is applied to the substrate 
in liquid form and thus it has to be heated into the mesomorphic 
temperatures which, depending on the type of material can start at 
50.degree. C. to 100.degree. C. The image can be created on the substrate 
by applying the liquid crystal material by free hand using either a brush, 
roller, spreader or any other suitable means or by using masking or 
silk-screening methods. When cooled, back to ambient temperatures, the 
material from a tough coloured coating on the substrate. The coating 
doesn't require any additional protection and the colours in the case of 
polysiloxane materials are not affected by ultraviolet light or impurities 
of the environment. 
It is the object of this invention to provide displays that will attract 
the attention of passer-by's more effectively than displays of the prior 
art. This is accomplished by using certain liquid crystal coatings which 
dramatically change colours with the angle of viewing and produce intense 
colours. 
It is a further object of this invention to produce a reflective display in 
which the colour gamut is greater than feasible to date and in which the 
colours due to the additive colour properties of liquid crystal can be 
subtly changed by the suitable choice of the texture and colours of the 
substrate. In the case of a transparent substrate its back surface can be 
clear, coloured or coated again with liquid crystals or a second suitably 
coloured panel or another liquid crystal coated panel can be placed 
behind, fully or partly overlaying or with its surfaces at an angle to the 
first panel. In the case of the latter yet another or more panels can be 
added in the background as liquid crystal coatings don't absorb light and 
thus a special 3-dimensional effect can be obtained. Also in the case of 
two or more coatings some coatings could be prepared to reflect at least 
one or more infrared wavelengths which would then become visible only at 
certain angles of viewing, thus creating an impression of movement of the 
image. 
It is still a further object of this invention to produce a transmissive or 
back-lighted display in which the light source or natural light is behind 
the transparent substrate coated with liquid crystals. Such display will 
then acquire some of the characteristics of stained glass or ornamental 
pane or partition. It will pass more light than possible with other 
colourants, since, as said in the foregoing, the liquid crystal coatings 
unlike other colourants don't absorb light. In such a display the image is 
produced using liquid crystals of several colours and can be produced by 
suitable tools or brushes, by silk-screening or masking techniques or by 
additional suitably shaped boards. 
It is still a further object of the invention to provide a combined 
reflective-transmissive display in which the background used for the 
reflective mode of operation is periodically illuminated or substituted by 
a source of light. Such a display would occur naturally when the 
transparent substrate coated with liquid crystals is used as a window 
pane. At night when the interior of the enclosure is illuminated and the 
exterior is dark the reflected image would be seen from the inside; at day 
time when daylight is transmitted through the coated transparent 
substrate, the transmitted image having complementary colours to those in 
the reflective mode would be seen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the preferable embodiments of the invention shown in FIG. 1 the liquid 
crystal materials (1) used are of polymer and especially of the 
polysiloxane type available from Wacker-Chemie in Munich. They provide a 
tough coating that adheres well to the substrate. The substrate (2) used 
was metal, wood, textiles or plastics and was coated with a black or 
coloured coat (4). The source of light (5) could be any suitable 
artificial lighting such as incandescent or fluorescent and using light 
diffusers if required, or could be natural light. 
In the preferable embodiment of the invention as a reflective display form 
shown in FIG. 2 a transparent planar or nonplanar substrate (3) made of 
plexiglass, plastic polycarbonate or glass was coated on one side with 
liquid crystals (1) to create the desired image using the means and 
methods described in the foregoing. The coated side was then painted with 
a black coat (4) unless a black background was provided, in order to 
obtain the most intense colours. Alternatively the coated side could be 
painted with another colour or several colours in order to achieve new 
colour effects that result from the additive colour properties of the 
non-light absorbing liquid crystal coatings. The use of the latter method 
created a superposition of images which gave a special 3-dimensional 
effect. The uncoated side of the transparent substrate (3) may preferably 
face the light source and the viewer. In such an arrangement the substrate 
itself protects the image from the handling and environmental effects and 
eliminates the need of a protective transparent window. In case of UV 
absorbing substrates such as certain types of plexiglass and plastics it 
also protects the image from the effects of ultraviolet radiation if such 
effects have been noted. 
In an alternative embodiment of the invention shown in FIG. 3 the 
transparent substrate (3) was coated on both sides with liquid crystal (1) 
and then with a black or coloured coat (4) also creating a 3-dimensional 
effect. In a further alternative embodiment of FIG. 2, the coated side, 
instead of being painted could also be attached to another image carrying 
substrate to obtain a similar effect as shown in FIG. 4. The substrate and 
any additional panels can be enclosed in a suitable box, if required. In 
certain applications it was desirable to see the texture of the liquid 
crystal coating; then the coated side of the substrate was exposed to the 
viewer. 
In the preferable embodiment of the invention as a transmissive or 
back-lighted display from shown in FIG. 5 the arrangements were 
substantially the same as above except that the liquid crystal image was 
not coated with a black or coloured coat. The source of light (5) 
illuminated the liquid crystal coated side and the uncoated side of the 
subtrate was exposed to the viewer or in reverse. The light source and the 
image carrying substrate could be enclosed in a suitable box having a 
provision for adequate ventilation. In other applications of the 
transmissive embodiment of the invention a box was not required and the 
substrate was framed like a pane. The light source or natural day-light 
illuminated from a distance the suitably mounted image-carrying substrate 
and additional coated substrates, if any. 
While the preferred embodiment of the invention has been explained and 
illustrated it will be appreciated that the invention is not restricted to 
these specific forms but it may consist of further embodiments and is of 
broader scope as defined by the claims.