GB2373279A

GB2373279A - Thermochromic display

Info

Publication number: GB2373279A
Application number: GB0204847A
Authority: GB
Inventors: Mitch Sorbie
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-03-14
Filing date: 2002-02-28
Publication date: 2002-09-18
Also published as: GB0204847D0; GB0106253D0

Abstract

The thermochromic display, particularly for use as road signs warning of icy conditions, comprises a first region 12 and a second region 14, the first region having a first colour and the second region having a thermochromic paint applied thereto, the colour of which changes from a second colour to a third colour at a temperature threshold, wherein the thermochromic paint does not comprise liquid crystals. The thermochromic paint preferably displays the second colour above the temperature threshold and the third colour below the temperature threshold. The pain may comprise one or more organic compounds and preferably comprises one or more electron donating chromatic organic compounds, one or more compounds having a phenolic hydroxyl group and one or more compounds selected from the group of higher aliphatic monovalent alcohols, and may further comprise a compound selected from the group of higher aliphatic monovalent acid alcohol esters. The threshold temperature may be in the range of -5 to 5 degrees centigrade and either the second or the third colour may be the same as the first colour. The second region may be in the shape of a written message or a logo or motif. The first region may also be coated in thermochromic paint that changes colour from the first colour to a fourth colour at a temperature threshold. The first colour may be the same as the second colour and the third and fourth colours may be contrasting colours. The display is preferably provided on a board made from a material with high thermal conductivity and be provided with a transparent coating and means for illuminating the display.

Description

1 TEMPERATURE SENSITIVE SIGNS 2 3 The present invention relates to the field of temperature 4 sensitive indicators and signs, and in particular 5 temperature sensitive road signs.

6 7 Signs and indicators for displaying information about 8 changing weather conditions have been known for some 9 time. For example, displays based on matrices of light10 emitting elements, such as filament emitters or LEDs are 11 commonplace at roadsides or across motorways. These 12 displays work in conjunction with a remote centre, which 13 controls the information displayed according to data on 14 the weather or driving conditions. Alternatively, the 15 displays may be provided with their own sensing stations 16 for the control of the information displayed.

17 18 The matrix displays above are expensive to produce and 19 maintain, and they have additional problems in that they 20 require a power source, as well as means for controlling 21 the information displayed according to locally-sensed 22 data or signals received from a remote centre.

23 1 Simpler means for displaying changes in weather 2 conditions have also been devised. For example, GB 3 2, 289, 707 discloses road markings and signs that can 4 indicate the incipient freezing of road surfaces. WO 5 84/00231 discloses an ice warning sensor with a

6 temperature sensitive reflective element.

7 8 However, the above display arrangements rely on liquid 9 crystals for their metachromic properties. Liquid 10 crystals are not ideally suited to these uses for a 11 number of reasons. Firstly, they are not particularly 12 adaptable. That is, the colours and temperature at which 13 the changes take place cannot be chosen, but are 14 determined by the properties of the liquid crystal 15 itself. Thus, if new properties are required, a new 16 liquid crystal must be synthesised. Secondly, liquid 17 crystals are readily degraded by coming into contact with 18 other compounds. In addition, it is often only possible 19 to obtain colours of a dark hue. Furthermore, liquid 20 crystals are expensive.

21 22 It would therefore be desirable to have means for 23 displaying a message to road users upon a change of 24 temperature, based on compounds other than liquid 25 crystals.

26 27 According to a first aspect of the invention there is 28 provided a display comprising: a first region and a 29 second region, the first region having a first colour and 30 the second region having a thermochromic paint applied 31 thereto, the colour of said thermochromic paint changing 32 from a second colour to a third colour at a temperature 33 threshold, wherein the thermochromic paint does not 34 comprise liquid crystals.

1 Preferably, the thermochromic paint displays the second 2 colour above the temperature threshold, and the third 3 colour below the temperature threshold, 4 5 The thermochromic paint may comprise one or more organic 6 compounds.

7 8 The thermochromic paint may comprise: 9 (i) one or more electron donating chromatic organic 10 compounds ; 11 (ii) one or more compounds having a phenolic hydroxyl 12 group; and 13 (iii) one or more compounds selected from the group of 14 higher aliphatic monovalent alcohols.

15 16 Optionally, a fourth compound may be provided, being: 17 (iv) a compound selected from the group consisting of 18 higher aliphatic monovalent acid alcohol esters.

19 20 The display may be in the form of a road sign. The

21 temperature threshold may be in the rangez to 5 C.

22 Preferably, the temperature threshold is in the rangez 23 to 1 oC.

24 25 Either the second colour or the third colour may be the 26 same as the first colour.

27 28 The second region may be in the shape of a written 29 message. Alternatively, or in addition, the second 30 region may be in the shape of a logo or motif.

31 32 The first region may also be coated with a thermochromic 33 paint, wherein the thermochromic paint changes colour 34 from a first colour to a fourth colour at a temperature 1 threshold. Preferably, the first colour and the second 2 colour are both the same, and the third colour and the 3 fourth colour are contrasting colours.

4 5 The display may be provided on a board made of a material 6 with high thermal conductivity. The display may 7 additionally be provided with a transparent coating.

8 Means for illuminating the display may be provided.

9 10 An example embodiment of the invention will now be 11 illustrated with reference to the following Figures in 12 which: 13 14 Figure la shows a sign at a temperature below To 15 according to an embodiment of the invention.

16 17 Figure Ib shows the same sign at a temperature above 18 To.

19 20 Figure 2a shows a sign at a temperature below To 21 according to an alternative embodiment of the 22 invention.

23 24 Figure 2b shows a sign at a temperature above To 25 according to an alternative embodiment of the 26 invention.

27 28 Figures la show and lb show a sign, generally depicted at 29 10, comprising a board made up of a plurality of 30 laminated sheets. The board comprises a backing sheet of 31 a material with a high thermal conductivity, an 32 intermediate sheet of a first colour, and a transparent 33 top sheet. The high thermal conductivity of the backing 34 sheet results in an even temperature across the board. A 1 border 16 of reflective material surrounds the sign, and 2 illuminating means (not shown) is provided.

3 4 The intermediate sheet is divided into a first region 12 5 and a second region 14. The first region 12 is uncoated, 6 except for the transparent top sheet, and shows the first 7 colour, which is white in this embodiment. Second region 8 14 is shaped in the form of the legend"ICE", and is 9 coated with a thermochromic paint.

10 11 The thermochromic paint is one that does not contain 12 liquid crystals, and is selected to change colour at a 13 temperature threshold To. Threshold To is determined by 14 the chemical properties of the thermochromic paint, and 15 in this embodiment is set to be around 0 C. The colours 16 of the thermochromic paint are also determined by its 17 chemical make-up. In this embodiment, the second region 18 14 is colourless at a temperature above To, and a dark 19 colour at a temperature below To.

20 21 The sign is placed by a roadside, and when the air 22 temperature falls below To, the thermochromic paint 23 changes to the dark colour, and the second region becomes 24 visible on the sign.

25 26 In this way, a warning message is displayed when the 27 temperature falls to around OOC, alerting a road user that 28 ice may be forming on the road surface.

29 30 The thermochromic paint used is for example of the type 31 described in US Patent document 4,028, 118, the contents 32 of which are incorporated herein by reference. These 33 thermochromic paints comprise the following components 1 (i) one or more electron donating chromatic organic 2 compounds; 3 (ii) one or more compounds having a phenolic hydroxyl 4 group; and 5 (iii) one or more compounds selected from the group of 6 higher aliphatic monovalent alcohols.

7 8 Optionally, a fourth component may be provided, being: 9 (iv) a compound selected from the group consisting of 10 higher aliphatic monovalent acid alcohol esters.

11 12 US 4,028, 118 describes how the properties of the 13 thermochromic paint can be varied by changing the 14 formulation of the paint. Specifically, component (i) 15 determines the colour of the paint, component (ii) causes 16 the colour to change, and the temperature threshold is 17 caused by the amount of and type of components (iii) and 18 (iv).

19 20 Figures 2a and 2b show a road sign according to another 21 embodiment. Again, figure 2a shows the sign at a 22 temperature below To, and figure 2b shows the same sign at 23 a temperature above To.

24 25 In this embodiment, the first region 12 is coated with a 26 second thermochromic paint. This paint is selected so 27 that it changes colour at the same temperature threshold 28 as the first paint, but changes to a different colour.

29 For example, the thermochromic paint in the second region 30 is colourless at a temperature above To, and blue at a 31 temperature below To. The thermochromic paint in the first 32 region is also colourless at a temperature above To, but 33 is red at a temperature below To.

1 2 In this arrangement, the sign is white and displays no

3 message to road users at temperatures above To. When the 4 temperature drops to below the threshold To, the first 5 region and the second region both change colour to 6 contrasting shades. This improves the contrast of the 7 legend, making the warning clearer to road users.

8 9 If the low temperature colour in the first embodiment is 10 sufficiently dark, for example black, then the warning 11 will be clearly displayed against the white background.

12 However, in certain circumstances it may be advantageous 13 to use a different paint in the second region, such as 14 blue. For example, a thermochromic paint that changes 15 from colourless to black may be more difficult or more 16 expensive to produce than a slightly lighter hue.

17 Alternatively, a black paint might be less stable than a 18 lighter shade. The second embodiment allows the use of 19 lighter shades without comprising the legibility of the 20 warning message.

21 22 Further arrangements are envisaged. For example, any 23 message or warning can be displayed by the sign.

24 Alternatively, the second region may be shaped as a logo 25 or diagram instead of, or in addition to, the legend. In 26 addition, alternative colours may be used other than 27 those described above. In another arrangement, only the 28 first region is coated with the thermochromic paint, so 29 that the background changes colour instead of the 30 lettering in the described embodiment.

31 32 It is also possible to alter the threshold temperature to 33 any suitable temperature. For example, it may be found 34 that the temperature of the road surface is out of step 1 with the temperature of the sign, and therefore the 2 display will be required to change at a temperature a few 3 degrees above or below 0 C. For example, the illuminating 4 means may heat the sign to a certain extent. By changing 5 the chemical constituents of the paint, the threshold 6 temperature can be adjusted to a suitable level.

7 8 The present invention provides means for providing 9 temperature-sensitive warning messages cheaply and simply 10 to road users, without relying on liquid crystal 11 materials.

12 13 Further modifications and improvements may be 14 incorporated without departing from the scope of the 15 invention herein intended.

Claims

1 Claims 2

3 1. A display comprising: a first region and a second

4 region, the first region having a first colour and

5 the second region having a thermochromic paint

6 applied thereto, the colour of said thermochromic

7 paint changing from a second colour to a third

8 colour at a temperature threshold, wherein the

9 thermochromic paint does not comprise liquid 10 crystals.

11 12

2. A display as claimed in Claim 1 wherein the 13 thermochromic paint displays the second colour 14 above the temperature threshold, and the third 15 colour below the temperature threshold, 16 17

3. A display as claimed in Claim 1 or Claim 2 wherein 18 the thermochromic paint comprises one or more 19 organic compound.

20 21

4. A display as claimed in any preceding Claim wherein 22 the thermochromic paint comprises: 23 (i) one or more electron donating chromatic 24 organic compounds ; 25 (ii) one or more compounds having a phenolic 26 hydroxyl group; and 27 (iii) one or more compounds selected from the group 28 of higher aliphatic monovalent alcohols.

29 30

5. A display as claimed in Claim 3 wherein the 31 thermochromic paint further comprises a compound 32 selected from the group of higher aliphatic 33 monovalent acid alcohol esters.

34 1

6. A display as claimed in any preceding Claim, 2 wherein the display is in the form of a road sign.

3 4

7. A display as claimed in any preceding Claim wherein

5 the temperature threshold is in the rangez to 6 5OC.

7

8

8. A display as claimed in any preceding Claim wherein

9 the temperature threshold is in the rangez to 10 1 C.

11 12

9. A display as claimed in any preceding Claim wherein 13 the second colour is the same as the first colour.

14 15

10. A display as claimed in any preceding Claim wherein 16 the third colour is the same as the first colour.

17 18

11. A display as claimed in any preceding Claim wherein 19 the second region is in the shape of a written 20 message.

21 22

12. A display as claimed in any preceding Claim wherein 23 the second region is in the shape of a logo or 24 motif.

25 26

13. A display as claimed in any preceding Claim wherein 27 the first region is coated with a thermochromic 28 paint, and the thermochromic paint changes colour 29 from a first colour to a fourth colour at a 30 temperature threshold.

31 32

14. A display as claimed in Claim 12 wherein the first 33 colour and the second colour are both the same, and

1 the third colour and the fourth colour are 2 contrasting colours.

3

4

15. A display as claimed in any preceding Claim wherein

5 the display is provided on a board made of a

6 material with high thermal conductivity.

7

8

16. A display as claimed in any preceding Claim wherein

9 the display is provided with a transparent coating.

10 11

17. A display as claimed in any preceding Claim wherein 12 the display is provided with means for illuminating 13 the display.