WO2001004694A1

WO2001004694A1 - Display

Info

Publication number: WO2001004694A1
Application number: PCT/SE2000/001428
Authority: WO
Inventors: Mattias BYSTRÖM; Andreas Remling; Henrik Fries; Håkan LUNDBERG; Niklas Berg
Original assignee: Array Displays Ab
Priority date: 1999-07-12
Filing date: 2000-07-05
Publication date: 2001-01-18
Also published as: AU6192500A; SE9902691D0; SE9902691L; WO2001004694A8

Abstract

The present invention relates to a thermochromic display comprising a display sheet containing a thermochromic active layer, whereby the thermochromic display sheet (4) is exchangeably stretched over a surface.

Description

TITLE DISPLAY

DESCRIPTION Technical field

The present invention relates to a thermochromic display comprising a display sheet containing a thermochromic active layer.

The object of the present invention is to obtain an improved thermochromic display unit allowing a simple and rational exchange of the thermochromic display sheet possessing the thermochromic active layer.

A further object of the invention is to obtain a possibility of lighting a thermochromic display in order to improve readability thereof.

The thermochromic active materials of the present invention relates to all reversible and bistable thermochromic materials such as thermochromics based on leucodyes and PDLC (polymer dispersed liquid crystals) which change colour when heated.

Background of the invention

Reversible thermochromic materials are known (e.g., US-A-4,028,118), and printing inks prepared from these materials have been applied to various articles to construct temperature indicators, ornamental objects and clothes and toys that reversibly change or develop colour at well defined temperatures. However, for these commercial products there has been a low demand for highly durable thermochromic materials exhibiting long life expectancy in outdoor conditions. The materials fade quickly due to sun light exposure, long time constant heating, and repeated switching. Development has been conducted within this technical field, as has been disclosed in US-A-4,425,161, where improved light fastness has been achieved by adding modifying chemical components within the thermochromic material. Further, US-A-5, 281,570 discloses development leading to improve the long term stability by improving the chemical components and the chemical composition of the thermochromic material. Thermochromic pigments are pigments that go from one state to another when being heated. Thus they normally exhibit one colour at ambient temperature, and becomes transparent when heated, i.e. become colourless. This effect can be used in displays where the display shows, i.a., a text or other data at ambient temperature, while that text disappears, when the display is heated. This can be used at a cashier to tell people that tickets are available when having the display heated, and when cooling the display, or turning the heat off, it informs that no there is no tickets left.

The thermochromic pigments are present in microcapsules as a dye compound, and is printed in the form of a printing composition onto a display, often permanently on a substrate such as the thermoelement heating the thermochromic material or on a polymer film being affixed to the thermoelement comprising backing, such as a metal or polymer sheet or the like.

Thermochromic pigments suffer from the drawback of being light sensitive and sensitive to oxidation by presence of free oxygen. It has been proposed (WO 94/27336) to protect a UV sensitive material to apply a UV light protective shield to the top of a display to shield the temperature responsive material. Further, the same document proposes the incorporation of an anti-oxidant with the thermochromic material and/or to the encapsulating material containing the thermochromic material.

Further, JP7205547 discloses the use of a UV reflecting material on reversible, heat sensitive display material, which reflecting material has a reflectance less than 50% of UV of wavelength 350 nm. This means that more than 50% of UV-light of 350 nm will pass through, and will cause detrimental effects to a thermochromic layer.

Although protective measures are taken the lifetime of such thermochromic materials is limited due to UV-light decomposition and oxidative decomposition, and thus a thermochromic display sheet containing a thermochromic active layer need to be exchanged evry so often in order to keep brightness, colourfulness and efficiency of a display provided with such a material at the highest possible quality. Summary of the invention

The exchangeability, the close relationship between heating surface providing for the thermochromic material to change, and the optional lighting or illumination of a display provided with such materials are of utmost importance to fulfil these quality requirements. This has been solved by means of the present invention which provides means for easy exchange of the thermochromic containing layer using in particular a preferred design of the heating backing from which the thermochromic material obtains energy. Further embodiments thereof provides for lighting or illumination of a displayed thermochromic material by applying different heating materials and/or illumination means. An important feature is further the efficiency of the heating surface, which in accordance with a further embodiment has been solved.

The present invention is characterized in that the thermochromic display sheet is exchangeably stretched over a surface comprising the heating element(-s) for inducing the thermochromic material to change.

Further characteristics are evident from the accompanying claims.

Brief description of the drawings The invention will be described in the following with reference to the accompanying drawing, however, without being restricted thereto. In the drawing FIG. 1 shows a cross-sectional view of a display provided with a thermochromic sheet.

Detailed description 1 denotes a substrate consisting inter alia of a copper metal sheet comprising heatable zones 2 consisting of circuit boards. The substrate 1 is arcuate in its form perpendicular to its longitudinal extension and is provided along its longitudinal edges 5 with a locking means 3 arranged to receive and lock a thermochromic display sheet 4 comprising a thermochromic layer to the substrate 1.

In the following the term substrate may also encompass a backing, such as a translucent or non-translucent backing providing a background colour to the thermochromic colour, in front of which backing the heat providing circuit is placed, either close to, or, as shown below, at a distance from the backing creating a space between the circuit and the backing.

The substrate is made flexible in order to provide a maximum of contact visavi the thermochromic sheet 4 when applied and thereby the provide a maximum of flexibility. This means that it is not critical how exact the sheet 4 is applied onto the substrate but the flexibility allows for certain tolerances to be accepted.

The arcuate form is normally not extending to the edges but the utmost parts are straight due to the manufacturing process. In case an arcuate form is desired all the way out to the edges of the longitudinal sides of the substrate the substrate has to be cut to eliminate these straight planes.

The circuit boards having a minimal thickness normally do not extend out to the edges of the substrate. The substrate as such can be formed of a circuit board which is then made flexible in order to allow for said tolerances mentioned above.

In certain embodiments the substrate is provided with an insulation 6 provided on the side opposite the circuit board(-s). The insulation 6 provides for a directed heating, and avoids the need for too high temperatures to be used in order to allow the thermochromic material to become activated. This also lengthen the lifetime of the thermochromic material as it will not be made subject of too high temperatures which has an adverse effect as it increases oxidation rate. The insulation material is often a foamed polymeric material which possesses high insulation properties.

The arcuate form of the substrate can be used for either outwardly applied displays or inwardly applied displays. In the latter case the display has to be stretched over the inwardly bending surface using a counterforce in the form of e.g., a roll having substantially the same radius as the radius of the arcuate substrate.

In a second embodiment of the invention the substrate is made planar or arcuate, whereby the thermochromic display sheet is applied using a removably working adhesive, such as of the type used in "POST-IT"® (trade mark of 3M) applications, to provide for an exchangeable sheet. Permanent fixing adhesives are less useful.

In one embodiment of the present invention the thermochromic display sheet is formed into a roll containing a number of repeated displays, whereby when the lifetime of one single display is gone, a new display will be rolled/fed onto the flexible, arcuate substrate 1.

Normal displays are generally provided with lighting arranged around the display or at one edge of the display. In such cases, if a thermochromic material is used, too much heat and lamp light will reach the closest part of the display, and as the thermochromic material also is sensitive to normal lamp light wavelengths, the display would be ruined in a shorter time than desired. Thus there is a further problem to be solved here, even though exchangeable displays are used.

The circuit boards can be made translucent thereby obtaining a transferring of light through the display. This one way of obtaining a lighting of the displayed information. Thereby the insulation is made of a translucent material as well, such as a translucent foamed polymeric material. Next follows a circuit board preferably comprising a circuit of indium-tin oxide on a transparent or translucent polyimide material, whereby the indium-tin oxide is translucent as well and allows for completely transparent circuit boards. Then finally the thermochromic display sheet is added on top of the indium-tin oxide board.

Another way of applying a lighting of the display is, when there is a non-translucent substrate present, such as a metal sheet followed by a short distance to the next layer which space receives an illumination device such as a low energy lamp, whereupon a a circuit board comprising e.g., indium-tin oxide which material is translucent and allows for completely transparent circuit boards, is applied,. Then finally the thermochromic display sheet is added on top of the indium-tin oxide board. This technique is primarily used when thermally active polymer dispersed liquid crystals are used as thermochromic material.

Leuco-dye based materials normally work at temperatures of up to 65°C, while thermally active polymer dispersed liquid crystal materials work at temperatures of up to 120°C. Thus the environment, and other critical parameters determine the choice of thermochromic active material to be used.

Claims

1. Thermochromic display comprising a display sheet containing a thermochromic active layer, characterized in that the thermochromic display sheet (4) is exchangeably stretched over a surface comprising the heating element(-s) for inducing the thermochromic material to change.

2. Display according to claim 1, characterized in that the display sheet (4) is exchangeably affixed to said surface in the absence of an adhesive material.

3. Display according to claim 1, characterized in that the display sheet (4) is stretched over an outwardly arcuate substrate

(1).

4. Display according to claim 1, characterized in that the display sheet (4) is stretched over an inwardly arcuate substrate (D-

5. Display according to claims 1, 3 to 4, characterized in that the display sheet (4) is stretched over an arcuate substrate (1) and held by means of a removable adhesive.

6. Display according to claim 1, characterized in that the display sheet (4) is stretched over a planar substrate (1) and held by means of a removable adhesive.

7. Display according to claim 1 to 6, characterized in that the substrate (1) consists of a translucent substrate (1).

8. Display according to one or more of claims 1 to 7, characterized in that the substrate (1) is spring-biassed.

9. Display according to one or more of claims 1 to 8, characterized in that the substrate (1) is insulated on its side opposite the display sheet (4) using an insulation (6).

10. Display according to one or more of claims 1 to 9, characterized in that the display is provided with a lighting means arranged on its side opposite to the display sheet (4).

11. Display according to one or more of claims 1 to 10, characterized in that the substrate consists of translucent circuit board(-s).

12. Display according to one or more of claims 1 to 10, characterized in that a lighting means is provided between a substrate and translucent circuit board(-s).

13. Display according to claim 12, characterized in that the circuit board consists of an indium-tin oxide circuit board.

14. Display according to claim 13, characterized in that the thermochromic active material consists of a thermally active polymer dispersed liquid crystals material.

15. Display according to claim 13, characterized in that the thermochromic display sheet comprises a leuco-dye based thermochromic material.

16. Display according to one or more of claims 1 to 15, characterized in that the thermochromic display sheet with a repeated information is arranged in the form of a roll arranged to be fed over the substrate for exchange.