GB2289707A - Thermographic road marking and/or sign - Google Patents

Abstract

A thermographic indicator device constructed or adapted for use as a road sign or marking comprises a substrate on which there is provided one or more zones of a thermographic material arranged in a form to give visual indication of a condition of incipient freezing in an environment in which it is intended for use. The thermographic material suitably comprises a liquid crystal capsule slurry which changes colour in the range of 3 DEG to -13 DEG C.

Description

THERMOGRAPHIC INDICATOR DEVICE DESCRIPTION This invention relates to a thermographic indicator device, that is a thermally responsive telltale suited to the purpose of giving visual information. In particular, the invention concerns such a device which may be used in, or as, a road sign or marking intended especially to convey information related to safety.

An important consideration in the context of road safety, whether it be from the point of view of pedestrians or users of vehicles, is that of having an awareness of freezing conditions or incipient freezing conditions. It is rarely possible for people, especially vehicle users, to tell with any great degree of accuracy how close above freezing point the temperature may be, for example, adjacent a surface of travel such as a roadway, cycle way or footway. Nor is it readily apparent that in certain circumstances a layer of ice - "black ice" - is forming or has formed on a surface, and that, as a consequence, special care is needed if accidents and injury are to be avoided.

Known means for alerting vehicle users to the onset of freezing conditions include a variety of devices which employ conventional thermometric measurement and indication. One example is a small device intended for attachment to the outside of a motor road vehicle within sight of the driver, and providing a needle movable across a scale having differently coloured zones. Another device gives a digital readout of the ambient external temperature.

These devices suffer from several disadvantages.

They invariably are constructed from mechanical and/or electrical components which will be subject to wear and tear and other forms of degradation leading to their eventual failure. They may be subject to inaccuracies of indication as a consequence of inherent design weaknesses, materials used, hysteresis effects when in use, calibration errors, parallax or other errors of reading, and so on. They may require regular maintenance. Further, since their importance is providing the requisite safety information usually rests on their continuous measurement of temperature during a journey, the placement of the temperature sensing element needs to be chosen with care.

However, the nature or placement of the device is seldom such as to provide compensation for sensing errors arising from the "wind chill factor" created by the flow of air over the sensing element.

Also known are devices which can be attached to various external parts, such as the bumper of a vehicle, such devices being in the form of stickers which employ means which change colour with temperature changes. A known form of such device comprises a thermochromic material which is based on a liquid crystal paint or ink. These are normally transparent and only shown the relevant spectral colour when the temperature to be monitored, and for which the material has been produced, is attained.

Anyone familiar with the well-known strip thermometers used for measuring human body temperature will readily appreciate the simplicity and accuracy of such a device, and its convenience. However, despite these advantages, no serious effort has hitherto been made to develop this technology for the general benefit of road users, cyclists and pedestrians alike.

Thus, the object of the invention is to provide a thermographic indicator device which is of general utility in providing information related to the safety of persons using roadways, cycle ways or footways, and which is simple and convenient to produce and use, and which is more effective for the purpose than hitherto known devices, and which substantially eliminates the disadvantages of known devices.

Accordingly, the invention provides a thermographic indicator device constructed or adapted for use as a road sign or marking, the device comprising a substrate on which there is provide one or more zones of a thermographic material arranged in a form to give visual indication of a condition of incipient freezing in an environment in which it is intended for use.

By the term "road sign or marking" there is meant any device suited to the purpose of providing visual information and disposed, or adapted to be disposed, in an environment, such as an outdoor environment, on, or adjacent, an area including a surface for travel, relative to which such the visual information is important.

A preferred thermographic material used with the inventive device changes colour in the range of 3 to -13" Celsius, thereby giving a visual indication that freezing point has been reached or is about to be reached in the environment in which the device is used. This is particularly advantageous in a traffic environment when the device is used as a road sign or marking on, say, a public highway. The thermographic material is selected such that it preferably changes colour in the desired range of, say 3 to -13" Celsius.

It has been found that a liquid crystal capsule slurry is particularly advantageous for use with the inventive device as at least part of the thermographic material, a preferred material being gelatine-gum arabic microcapsules of liquid crystal in water, providing an off-white suspension which changes colour to red at -13" Celsius. The material can be suitably modified to change colour to red or any other suitable colour at other comparatively low temperatures, for example, at or nearer 0 Celsius. Within the desired temperature range, the thermographic material changes colour through the visible spectrum as its temperature changes. Thus, the desired range can be selected such that the thermo-graphic material is coloured red in the region of 0 Celsius.

Preferably also, the thermographic material may be rendered substantially abrasion resistant, such that it can be used in extreme wear environments, for example, on road surfaces as a marking therefor.

The thermographic material may be used by itself or it may be incorporated in a suitable carrier, particularly for application purposes as a road marking or sign where, for example, it needs tobe abrasion resistant. Appropriate resins may be used as such carriers.

The substrate upon which the zone(s) of thermographic material is provided, is preferably dark, more preferably black, otherwise visible colour change may be impaired due to insufficient light output from the device.

In the case of road markings, the substrate may be the road surface itself or a suitable backing, preferably dark, for the zone(s) of thermographic material, the backing being applied securely to such a surface, with the zone(s) uppermost.

For a road sign, the substrate is preferably in the form of the shaped head of the sign itself but, if necessary, a dark layer as the substrate may be provided between the thermographic material and the shaped sign head.

The thermographic material may be provided with a hardener, wetting agent and/or a drying agent and, also, may be sealed with a lacquer or other suitable sealant which may be incorporated in the thermographic material or applied thereto after the material has been applied to the substrate. Such an agent may be a suitable carrier, for example, a resin carrier to be described in more detail hereinbelow.

Preferred embodiments of thermographi c indicator device in accordance with the invention will now be described by way of example and with reference to the following Examples.

Example 1 A thermographic indicator device used as a road marking, comprises a substrate in the form of a dark, preferably black, road surface of tarmacadam or the like upon which is provided one or more zones of a thermographic material.

The zone(s) may be of any suitable shape, for instance, elongate centre line or junction markings, whilst the thermographic material comprises a low cosolvent, polyurethane-containing dispersion of liquid crystal microcapsules in combination with an acrylic emulsion.

The dispersion is white and translucent and the liquid crystal microcapsules change to red in the range of 0 to 3 Celsius.

When the dispersion material is applied to the road surface and has set, it provides road marking zones which are hard and substantially chemically and abrasion resistant, as well as being humidity resistant.

Adhesion of the thermographic material to the road surface is good, whilst the material may also include small additions (1 to 2%) of a cross linking agent which improves further its chemical resistance and mechanical properties. Also, suitable defoaming, hardening, wetting and/or drying agents may be incorporated.

A suitable material for use in combination with the dispersion as a resin carrier is that sold under the NeoRez R-974 trade mark sold by Zeneca Resins.

In use of this first embodiment of thermographic indicator device when used as a road marking, the thermographic material provides a visual indication, namely, a colour change to red, of a condition of incipient freezing in the range of 0 to 3 Celsius.

Example 2 A second embodiment of thermographic indicator device is in the form of a road sign, wherein the head of the sign or its support or supporting structure constitutes the substrate of the device and wherein the thermographic material provided thereon is similar to that described above in relation to Example 1.

In this particular embodiment, any suitable zone(s) of thermographic material dispersion may be provided on the road sign or its support or supporting structure, for example, any legend, indicia, hatching or the like, to provide motorists with a visual indication of a condition of incipient freezing in the environment in which the indicator device is used.

Again, a resin carrier, such as the NeoRez product mentioned above, may be incorporated with the dispersion to render it hard and substantially chemically and abrasion resistant.

As in the case of the device described above in relation to Example 1, colour change of the material preferably occurs in the range of 0 to 3 Celsius, with such colour change being from the normal "room temperature" colour of the material, in this case, translucent white, to red or, indeed, any other suitable colour.

The thermographic material is such that at temperatures below the required colour change range, the material remains the same colour, for example, red.

It is to be appreciated that the thermographic indicator device of the invention may provide a visual indication of a condition of incipient freezing at a temperature outside the preferred range of 0 to 3 Celsius mentioned above, in which case, the corresponding colour change can occur above 3 Celsius or below 0 Celsius.

The inventive thermographic indicator device provides an aid to road safety, in that incipient freezing conditions in a traffic environment can be indicated to motorists to provide sufficient warning of potential or existing freezing road conditions.

The inventive device may also be applied in forms other than road signs or markings, for example, stickers for vehicles or, indeed, portions of body panels, preferably located at the rear of vehicles, to provide a suitable warning to other motorists.

Claims (20)

1. A thermographic indicator device constructed or adapted for use as a road sign or marking, the device comprising a substrate on which there is provided one or more zones of a thermographic material arranged in a form to give visual indication of a condition of incipient freezing in an environment in which it is intended for use.

2. A device according to claim 1, wherein the thermographic material changes colour in the range of 3 to -13" Celsius, preferably 3 to 0 Celsius.

3. A device according to claim 1 or 2, wherein the thermographic material comprises a liquid crystal capsule slurry.

4. A device according to claim 1, 2 or 3, wherein the thermographic material comprises gelatine-gum arabic microcapsules of liquid crystal in water.

5. A device according to any preceding claim, wherein the thermographic material comprises a carrier.

6. A device according to claim 5, wherein the carrier is a resin.

7. A device according to claim 6, wherein the resin carrier is a low cosolvent polyurethane-containing dispersion.

8. A device according to claim 6 or 7, wherein the resin carrier is an anionic aliphatic polyester.

9. A device according to any preceding claim, wherein the thermographic material comprises a hardener, wetting agent and/or drying agent.

10. A device according to any preceding claim, wherein the thermographic material comprises a sealant, preferably a lacquer.

11. A device according to any preceding claim, wherein the thermographic material is substantially abrasion resistant.

12. A device according to any preceding claim, wherein the substrate is dark in colour, preferably black.

13. A device according to any preceding claim, when used as a road marking.

14. A device according to claim 13, wherein the substrate is constituted by the road surface upon which the zone(s) of thermographic material is provided.

15. A device according to claim 13, wherein the substrate is constituted by a backing upon which the zone(s) of thermographic material is provided and which is applied securely to the associated road surface, with the zone(s) uppermost.

16. A device according to any of claims 1 to 12, when used as a road sign.

17. A device according to claim 16, wherein the substrate is constituted by the shaped head of the road sign or a support or supporting structure therefor.

18. A device according to claim 16, wherein the substrate is constituted by a layer provided between the thermographic material and the shaped head of the road sign or a support or supporting structure therefor.

19. A road marking device substantially as hereinbefore described in Example 1.

20. A road traffic sign substantially as hereinbefore described in Example 2 hereof.