WO1988007214A1

WO1988007214A1 - Light reflective materials

Info

Publication number: WO1988007214A1
Application number: PCT/GB1988/000184
Authority: WO
Inventors: Michael Neil Ellis; Jane St. Quintin
Original assignee: Precis (549) Limited
Priority date: 1987-03-10
Filing date: 1988-03-10
Publication date: 1988-09-22

Abstract

A method of producing a light reflective material in which a mixture of particles and a carrier material is applied to a substrate. Each particle comprises a body of transparent or translucent material and a coating on part of the surface of the body. The coating is light reflective and comprises a material having magnetic or electrical properties. An adhesive is contained in the carrier material or in the coating. A magnetic or electrical field is applied to the mixture and causes the particles to move towards a predetermined orientation relative to the substrate. This orientation is normally one in which an uncoated part of each particle faces outwardly away from the substrate, but in the case of a transparent or translucent substrate the uncoated part may face inwardly towards the substrate. When the particles are correctly oriented, the adhesive is activated to secure them to the substrate.

Description

LIGHT REFLECTIVE MATERIALS

This invention relates to light reflective materials. The possibility of a pedestrian or cyclist being struck by a vehicle increases dramatically during the hours of darkness. To increase visibility to drivers it is therefore common to wear reflective devices in the form of bands or stripes so as to increase the detection distance, and hence increase the time during which the driver has time to react to a potential hazard.

It has been found, however, that merely increasing the detection distance does not significantly increase the driver's reaction time unless an object or individual picked up by the headlights of his vehicle is immediately recognisable. Accordingly, the wearing of full light reflective clothing, producing a recognisable silhouette, is a significant step towards increasing reaction time.

It is known to manufacture a material incorporating a layer of light reflective particles by coating a backing sheet with a releasable adhesive and applying a continuous layer of transparent particles to the adhesive. The exposed surfaces of the particles are then coated with a layer of metal, such as aluminium, and a carrier sheet coated with a permanent adhesive is secured over the whole. Alternatively, the metallic layer is omitted and metal flakes or pigments are included in the permanent adhesive to achieve similar _\ results. The backing sheet is then removed to leave a material which has uniform reflective properties and can be cut into strips or other shapes for attachment to garments and the like. This material, while lending itself satisfactorily to such use, is still unsuitable for use in large enough pieces which can be sewn or secured together to form a garment or the like. Additionally there may be circumstances where the attachment of strips to a garment is not visually pleasing, either aesthetically or from a practical point of view.

Another method of making a light reflective material is to temporarily fix the transparent particles to a carrier sheet, to coat the exposed areas of the particles with a metal surface and then to remove the particles from the carrier. The coated particles are then applied to a substrate in a liquid carrier vehicle, for example paint or varnish. However this method results in severe stiffening of the substrate and the particles are at least partially covered by the liquid vehicle and therefore their reflective properties are impeded. Also the particles are randomly orientated and only a limited number of particles are orientated for optimum reflection of light from a vehicle headlamp back to a driver of the vehicle.

Another known method is to coat a substrate with an adhesive and then to apply the particles. This method also results in randomly orientated particles which are partially covered by the adhesive, and adversely effects the handling of the substrate.

It is therefore an object of the invention to provide a light reflective material wherein^"light reflective particles can be located in such a position as to offer optimum refocuslng efficiency, the material being sufficiently flexible, durable and lightweight to be made up into whole products or a substantial part of a product.

It is a further object of the invention to provide a light reflective material which is capable of offering a visual appearance substantially indistinguishable from untreated substrates.

According to the present invention there is provided a method of producing a light reflective material comprising the steps of applying a mixture comprising particles and a carrier material to a substrate, the mixture containing an adhesive material and each particle comprising a body of transparent or translucent material and a coating on a part of the body, the coating being light reflective and comprising a material having magnetic or electrical properties such that the orientation of the particle relative to the substrate can be changed by applying a magnetic or electrical field thereto, subjecting the particles to a magnetic or electrical field which moves or assists in moving each particle towards a predetermined orientation relative to the substrate, and activating the adhesive to secure the particles to the substrate.

According to the invention there is also provided a light reflective material comprising a substrate, and particles adhesively secured to the substrate, each particle comprising a body of transparent or translucent material and a coating on a part of the body, the coating being light reflective and comprising a material having magnetic or electrical properties such that, prior to securement to the substrate, the orientation of the particle can be changed by applying a magnetic or electrical field thereto, -at least 30% of the particles having an orientation relative to the substrate which is equal or substantially equal to a predetermined orientation.

Preferably, the magnetic or electrical field is such that the said predetermined orientation is an orientation in which an uncoated -it-

part of each particle faces outwardly away from the substrate. Alternatively, the substrate is transparent or translucent and the particles are intended for viewing with light which has traversed the substrate, and the magnetic or electricalfield is such that the said predetermined orientation is an orientation in which an uncoated part of each particle faces inwardly towards the substrate.

A magnetic field for orientating the particles may be applied whilst the carrier material and particles are being applied to the substrate or the field may be applied subsequent to the application of the carrier material and particles to the substrate.

Preferably, each particle is spherical or substantially spherical with a hemispherical or substantially hemispherical part of the surface thereof covered by the said coating.

The particles are preferably 15 to 500 microns in diameter and the transparent or translucent body of each particle has a refractive index of 1.7 to 2.2. They may be made of clear or coloured material, preferably glass.

Each particle may include a skin portion of refractive index different from the refractive index of a core portion. This is designed to deal with a problem which can arise with light reflective materials according to the invention which are used in the rain or at sea. The effect of a film of water is to change the effective refractive index of a particle, thus modifying the ? troflective properties of the particles. Including a skin portion of different refractive index compensates or partially compensates for this modificatio . -5-

The body of each particle may be made of tinted glass. Alternatively, the uncoated part of the surface of each particle or even the whole of the surface may be tinted with a lacquer prior to the application of the coating. Light which traverses the particle and is then viewed after reflection by the light reflective coating is thus coloured. Coloured particles may be applied to selected areas of a substrate to form a pattern, suitably with differently coloured particles applied to different areas of the substrate. Assuming a transparent adhesive is used to secure the particles to the substrate and assuming a low density of particles, it is possible to produce a material which is colourless when viewed in daylight but which bears a coloured pattern when illuminated by a beam of light at night. This is particularly useful for articles of clothing, such as T-shirts. Another application lies in clothing for the various rescue services, such as police, fire and ambulance services, where differently coloured particles can be used as a means of identifying a member of one service from a member of another service.

The said adhesive material may be included in the said coating of each particle.

In this case, the coating of each particle may comprise an inner layer of light reflective material, an intermediate layer of a magnetic material, and an outer layer of the said adhesive material. In this case the inner layer may be aluminium, the intermediate layer may be a metal or metal alloy such as nickel or steel, and the outer layer may be a thermally activatable adhesive such as a plastisol formulation, for example, polyvinylchloride resin, di-iso-octyl phthallate and dibutyl tin maleate.

Alternatively, the coating may comprise an inner layer of a material which is light reflective and has magnetic properties, and an outer layer of the said adhesive material. In this case the inner layer may be an alloy of nickel and aluminium, steel, or an alloy containing chrome.

Alternatively, the coating may comprise an inner layer of a material which is light reflective and an outer layer containing a material having magnetic properties and the said adhesive material. In this case the inner layer may be aluminium and the outer layer may contain particles or flakes of ferric oxide, iron or steel and a thermally activatable adhesive such as plastisol formulation.

Alternatively, the coating may comprise a single layer containing light reflective metal flakes, the said adhesive material and a material which has magntic properties.

As a further alternative, the carrier material may comprise the said adhesive material. In this case, the carrier material is suitably a powder and may be applied to the substrate by an electrostatic process. The particles are then applied to the powder on the substrate.

An electret is used as a material whose orientation can be changed by the application of an electric field.

The partially coated particles may be made by securing transparent or translucent particles to a retaining surface, applying the said coating to an exposed part of each particle, and then removing the partially coated particles from the retaining surface. A metal or alloy layer can be applied by vapour deposition, sputtering or spraying a metal contained in a carrier liquid. A layer containing an adhesive may be applied by spraying or by spreading with a.blade or the like. The particles may be secured to the retaining surface by means of an adhesive or, in the case of an acetate or plasticised resin-coated sheet, by heating. The partially, coated particles may be subsequently removed from the retaining surface by dissolving the adhesive or reheating the surface. It may be necessary to break down clusters or groups of partially coated particles by agitation or vibration.

The adhesive material is preferably inactive at ambient temperatures but is thermally activatable. Suitably, the adhesive is a thermoplastics material comprising vinyl chloride resin dispersed in a plasticiser. Stabilisers, gelling agents and similar modifying additives may also be included. Heat to activate the adhesive may be applied whilst the magnetic or electrical field is applied or when the field is no longer applied.

In addition to applying heat to ativate the adhesive material, a pressure may be applied to assist in securing the particles to the substrate.

As an alternative, the adhesive material may be chemically activatable. Suitably, the adhesive material may then be a plastisol and is activated by applying toluene thereto.

Suitably, the carrier material is water containing a thickening agent, the viscosity of the carrier material being low enough to allow the particles to move towards the said predetermined orientation but not so low that the particles are moved bodily through the carrier material into depressions within the surface of the substrate, for example, into the space between threads of a textile substrate. Suitably, the carrier material has a viscosity between 2,000 and 20,000 centipoise. One or more layers comprising transparent or translucent particles in a carrier material may be applied to the substrate.

Volatile components of the carrier material may be removed from the substrate, after each particle has been moved towards the said predetermined orientation, by heating or subjecting to a vacuum. If the adhesive on each particle is thermally activatable, heating to activate the binder may also remove volatile components of the carrier material.

The said carrier material may be liquid, in whch case the said mixture may be applied to the substrate by a screen printing process, the mixture being forced on to the substrate via an apertured screen. In this case, the process may be carried out on a rotary or flat-bed equipment. By suitable arrangement of apertures in the screen it is possible to obtain an even, uniform distribution of particles over the surface of the substrate or to apply the mixture to predetermined areas of the substrate so that a predetermined pattern of particles is formed.

As alternatives, if the carrier material is liquid, the mixture may be applied to the substrate by blade or knife coating, spraying or rollers. The carrier material and particles may be applied to the substrate together or sequentially. In each of these cases there will be a random pattern of particles over the surface of the substrate.

Suitably, the transparent or translucent particles occupy only a small proportion of the surface of the substrate to which the mixture is applied. This proportion is suitably less than 5 % , for example 2% , in order not to adversely effect the flexibility or appearance of the resultant light reflective material. Assuming all or substantially all of the particles have been moved into the said orientation, adequate reflection of light is obtained.

The magnetic or electric field may be of uniform or substantially uniform strength over the area of the surface of the substrate to which the mixture is applied. Alternatively, the strength of the field may vary so that the orientation of the particles varies according to location on the said substrate. This allows patterns, waves or contour lines of particles to be formed.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic drawing of an apparatus for use in carrying out a process according to the invention; and

Figures 2 is an enlarged drawing, partly in section, of a transparent or translucent particle applied to a substrate in the apparatus of Figure 1.

The apparatus of Figure 1 is used for producing light reflecting fabrics, suitably fabrics for making garments intended for use by pedestrians during the hours of darkness. The fabrics are made by applying retro-reflecting particles 1, shown in Figure 2 of the drawings, to textile materials. Referring to Figure 2, each of the particles 1 consists of a body in the form of a transparent glass sphere 3 which has a coating 5 applied to a hemispherical part of its surface. The coating is formed of an inner layer 7_ι an intermediate layer 9 and an outer layer 11.

The inner layer 7 of the coating 5 is a reflective layer which is formed of aluminium. As indicated in Figure 2, a ray 13 which is incident upon an uncoated part of the sphere 3. which is refracted at the surface of the sphere, and which then impinges upon the coating 5. is internally reflected by the inner layer 7 of the coating. The reflected ray is again refracted at the uncoated surface of the sphere and emerges as a ray 15 travelling in a direction parallel or substantially parallel with the incident ray 13- The emergent ray 15 is visible only to an observer at or near the source of the ray 13 or at a location whch is aligned or substantially aligned with the source and the particle 1.

The Intermediate layer 9 is formed of ferromagnetic material, such as steel.

The outer layer 11 is a plastisol, which is a thermally activatable adhesive.

Referring now to Figure 1, a textile material 17 is stored on a supply roll 19 and Is continuously driven along a path to a take-up roll 21 by driving means (not shown). In travel^ling from the supppl^* _', roll 19 to the take-up roll 21 the material 17 is sequentially acted upon by a printing device 23, which applies the particles 1 thereto, a magnetic device 25 for moving the particles into a desired orientation, and an oven 27 and heated rollers 29 for securing the particles to the material.

The device 23 is a rotary screen printing device including a cylindrical screen, which is disposed above the path of the material 17, and a cooperating plate, which is immediately below the material. The cylindrical screen is formed with apertures whose diameters are two to three times the diameters of the particles 1 and is rotatable about its axis, which is transverse to the direction of travel of the material 17- A liquid carrier material containing the particles is supplied to the interior of the screen. Within the screen is a pressure roller whch engages an inner surface of the screen, adjacent the plate, and serves to force the carrier material and the particles outwardly on to the material 17, as hereinafter described.

The magnetic device 25 includes an electromagnet or permanent magnet which is disposed below the path of the material 17- The magnet produces a magnetic field of 100 to 1200 gauss.

The oven 27 is a hot air drying oven for heating the material 17 and the particles 1 to a temperature of 170 to 180 C. As hereinafter described, this activates the adhesive layer 11 on each particle 1 and also evaporates volatile components of the carrier material.

.Finally, the rollers 29 are heated to 170° to 180°C to enhance the adherence of the particles 1 to the material 17•

In using the apparatus of Figure 1, the cylindrical screen of the printing device 23 is supplied with particles 1 in a liquid carrier material containing 2.35% by weight of carboxyvinyl polymer thickener, 2.00 by weight of the coated particles 1, and 96.6 % by weight of water. The carrier material has a viscosity of approximately 12,000 centipoise. The particles 1 have a diameter in the range 75 to 110 microns.

Electric power is supplied to the electromagnet in the magnetic device 25 and the oven 27 and rollers 29 are heated to the temperatures mentioned above. Finally, the driving means are activated so that the material 1 is driven continuously from the supply roll 19-

As the material 17 emerges from the supply roll 19 the material first enters a section of its extended path wherein the material is engaged between the rotating screen and the cooperating plate of the printing device 23- Within this section of the path a mixture of liquid carrier material and particles 1 is continuously applied to an upper surface of the material 17 by the action of the pressure roller, which forces the mixture outwardly via the apertures in the screen. The particles 1 form a pattern on the material 17 which corresponds to the pattern of apertures in the screen.

From the printing device 23 the material 17, together with the mixture of carrier material and particles 1, moves on to the magnetic device 25. As described above, the magnet in the device 25 produces a magnetic field at the location of the material 17.

The effect of this magnetic field is first to magnetise the intermediate layer 9 of the coating 5 on each of the particles 1. Once the layer 9 has become magnetised, the particle 1 which carries this layer is subjected to a turning moment by the magnetic field. The turning moment acts to rotate each particle within the liquid carrier material towards an orientation wherein the layer . and hence the whole of the coating 5_» is lowermost ie. adjacent the surface of the material 19- At the same time there is a bodily movement of the layer 9_ι and hence the rest of the coating 5 and indeed the particle 1, downwardly toward the material 17. This downwards movement is assisted, of course, by gravity.

As described above, the viscosity of the carrier material must be sufficiently low to allow such rotation and bodily movement of the particles 1. The viscosity must not be so low, however, that the particles are drawn downwardly into the spaces between the threads or fibres in the material 17• '

The result of the action of the magnetic device 25 is therefore to cause each particle 1 to rotate- towards a position wherein the coating ^on the particle is lowermost ie. adjacent the material 17. and the uncoated part of each particle is uppermost, ie. facing away from the material 17. Clearly, it is not essential for all particles to face away from the material 17 and satisfactory results are obtained if the proportion of particles correctly oriented is 30%.

After leaving the magnetic device 2 the material 17 spends approximately one minute travelling through the oven 27, which is maintained at a temperature of 170 to 180 C, as described above. The temperature within the oven and the time spent therein are sufficient to melt the outer layer 11 of adhesive on each particle 1, thus causing the particle to adhere to the adjacent upper surface of the material 17- At the same time, the water in the carrier material is evaporated.

From the oven 27 the material 17 and the particles 1 move on to the heated rollers 29, where the coated particles are subjected to a further heating process and to a pressure urging the particles towards the material. This treatment lasts for 60 to 90 seconds and enhances the adherence of the particles to the material 17- At the end of the treatment the material 17 with the particles 1 thereon is rolled up on the take-up roll. The material may subsequently be rendered water repellent by treatment with a suitable fluorocarbon composition.

In the apparatus shown in Figure 1 the magnetic device 25 may include a series of permanent bar magnets which are disposed end-to- end and extend transversely of the material 17. Alternatively, the magnetic device 25 may be an electromagnet.

In a modification of the apparatus described above, the printing device 23 is replaced by a device having a generally, planar apertured screen in place of the cylindrical screen of the device 23- The material 17 is intermittently advanced along a path which extends between the planar screen and a cooperating plate located beneath the material. A mixture of liquid carrier material and particles is applied to the upper surface of the material 17 via apertures in the screen by means of a roller located above the screen. The roller is made of a magnetic material and is moved in the direction of travel of the material 17, and then in the reverse direction, by effecting a corresponding movement of a magnet located below the cooperating plate. A magnetic field is thus applied to the mixture at the same time as the mixture is being applied to the material 17 and there is no need for a separate magnetic device 2 -

It will be appreciated that particles having light reflective coatings can be applied to substrates other than textile materials by the process described above. Examples of articles including such substrates are road cones, hazard warnings, advertisement signs, fashion and display articles.

A further process according to the invention employs a mixture of glass particles and a powder which serves as a carrier material for the particles and as an adhesive material.

In this further process a resin which may be epoxy, polyester or of some other base and which takes the form of a powder, is first deposited electrostatically on an upper surface of an opaque substrate. Glass particles having coatings formed of three layers corresponding to the layers 7, 9 and 11, above, are then dusted on to the resin and the powder and particles are heated to a temperature sufficient to melt the powder, say 100 C. Next, the powder and particles are subjected to a magnetic field which rotates the particles towards an orientation wherein the uncoated part of the particle faces away from the substrate. The field is applied for approximately 3 minutes. At the end of this period the powder and particles are heated to a temperature of say, lδO C, at which temperature the resin .is cured and the particles are bound into the resin and secured thereby to the substrate.

This process is particularly suitable for applying light reflecting particles to rigid substrates or panels for architectural uses. The particles may then be arranged in a series of groups by applying different magnetic fields to different areas of the substrate. All of the particles in a group having approximately the same orientation, which is different from the orientation of particles in other groups. In the result one group of particles which may be arranged to form a pattern representing a certain message, may be visible when light is directed on to the substrate in a certain direction. Particles in another group, which are arranged in a pattern representing a different message, are visible when light is directed on to the substrate from a different direction.

Particles arranged in groups of different orientation may also be applied to articles for use as signs and to fabrics for the fashion trade. When light is directed on to the sign or fabric the amount of light reflected each group varies according to the direction in which the light is travelling thus producing a pattern. Each group of particles may be differently coloured from the other groups.

In a modification of this further process a transparent or translucent panel is used as the substrate. The particles used in this process have a coating containing a layer of light reflective material and a layer of magnetic material on one hemispherical part thereof and a coating of an adhesive material on the remaining hemispherical part thereof. Such particles are made by applying transparent or translucent spheres to a releasable adhesive on a first backing sheet, coating the.exposed surface of each sphere with a layer of light reflecting material and a layer of magnetic material, attaching a second backing sheet to the coated parts of the spheres, removing the first backing sheet, applying adhesive to the freshly exposed parts of the spheres, and then removing the second backing sheet.

In carrying out the process, the particles are applied to an upper surface of the substrate. A magnet is then placed above the substrate, causing the particles to be orientated so that the coating on each particle which contains the magnetic material and the light reflective material faces upwardly, away from the substrate. In use, the particles are viewed by light which is incident upon the reverse side of the substrate, traverses the substrate and is then reflected back through the substrate by the reflective coatings on the particles.

Claims

CLAIMS :

1. A method of producing a light reflective material comprising the steps of applying a mixture comprising particles and a carrier material to a substrate, the mixture containing an adhesive material and each particle comprising a body of transparent or translucent material and a coating on a part of the body, the coating being light reflective and comprising a material having magnetic or electrical properties such that the orientation of the particle relative to the substrate can be changed by applying a magnetic or electrical field thereto, subjecting the particles to a magnetic or electrical field which moves or assists in moving each particle towards a predetermined orientation relative to the substrate, and activating the adhesive to secure the particles to the substrate.

2. A method as claimed in claim 1, wherein the magnetic or electrical field is such that the said predetermined orientation is an orientation in which the part of each particle which has the said coating thereon faces inwardly towards the substrate.

3- A method as claimed in claim 1, wherein the substrate is transparent or translucent and the particles are intended for viewing with light which has traversed the substrate, and the magnetic or electrical field is such that the said predetermined orientation is an orientation In which the part of each pa: tide which has the said coating thereon faces outwardly away from the substrate. 4. A method as claimed In claim 1, 2 or 3, wherein a magnetic or electrical field for orienting the particles is applied whilst the carrier material and particles are being applied to the- substrate.

5. A method as claimed in claim 1, 2 or 3, wherein a magnetic or electrical field for orienting the particles is applied subsequent to the application of the carrier material and particles to the substrate.

6. A method as claimed in any one of the preceding claims wherein, after each particle has been moved towards the said predetermined orientation, volatile components of the carrier material are removed from the substrate by heating or subjecting to a vacuum.

7. A method as claimed in any one of the preceding claims, wherein the said carrier material is liquid and the said mixture is applied to the substrate by a screen printing process, the mixture being forced

-on to the substrate via an apertured screen.

8. A method as claimed in claim 7, wherein the mixture is applied to predetermined areas of the substrate so that a predetermined pattern of particles is formed.

9. A method as claimed in any one of claims 1 to 6, wherein the said carrier material is liquid and the said mixture is applied to the substrate by blade or knife coating, spraying or rollers.

10. A method as claimed in claim 9, wherein the carrier material and particles are applied to the substrate sequentially.

11. A method as claimed in any one of the preceding claims, wherein the said particles occupy less than 50% of the area of the substrate to which the mixture is applied.

12. A method as claimed in claim 11, wherein the said particles occupy 2% of the area of the substrate to which the mixture is applied.

13. A method as claimed in any one of the preceding claims, wherein the magnetic or electrical field is of uniform or substantially uniform strength over the area of the surface to which the mixture is applied.

14. A method as claimed in any one of claims 1 to 12, wherein the strength of the magnetic or electrical field varies so that the orientation of the said particles varies according to location on the substrate.

15. A method as claimed in any one of the preceding claims, wherein each particle is spherical or substantially spherical with a hemispherical or substantially hemispherical part of the surface thereof covered by the said coating. l6^'. A method as claimed in claim 15, wherein each particle is 15 to 500 microns in diameter and the transparent or translucent body of each particle has a refractive index of 1.7 to 2.2.

17. A method as claimed in claim 2, wherein the said adhesive material is included in the coating of each particle.

18. A method as claimed in claim 17, wherein the coating of each particle comprises an inner layer of light reflective material, an intermediate layer of a magnetic material, and an outer layer of the said adhesive material.

19. A method as claimed in claim 18, wherein the inner layer is aluminium, the intermediate layer is nickel or steel, and the outer layer is a thermally activatable adhesive.

20. A method as claimed in claim 17, wherein the coating of each particle comprises an inner layer of a material which is light reflective and has magnetic properties, and an outer layer of the said adhesive material.

21. A method as claimed in claim 20, wherein the inner layer is an alloy of nickel or aluminium, steel, or an alloy containing chrome.

22. A method as claimed in claim 17, wherein the coating of each particle comprises an inner layer of a material which is light reflective, and an outer layer containing a material having magnetic properties and the said adhesive material.

23- A method as claimed in claim 22, wherein the inner layer is aluminium and the outer layer contains particles or flakes of ferric oxide, iron or steel and a thermally activatable adhesive. 2k . A method as claimed in claim 17, wherein the coating of each particle comprises a layer containing light reflective metal flakes, the said adhesive material, and a material which has magnetic properties.

2 . A method as claimed in claim 3, wherein the said adhesive is provided on a further part of the said body.

26. A method as claimed in any one of claims 1 to 16, wherein the said adhesive material is comprised in the carrier material.

27. A method as claimed in claim 26, wherein the carrier material is a powder and is applied to the substrate by an electrostatic process, and the particles are subsequently applied to the powder ^!on the substrate.

28. A method as claimed in any one of the preceding claims, wherein the adhesive material is inactive at ambient temperatures but is thermally activatable.

29. A method as claimed in claim 28, wherein the adhesive material is a thermoplastics material comprising vinyl chloride resin dispersed in a plasticiser.

30. A method as claimed in claim 29, wherein the adhesive material further comprises stabilisers, gelling agents or other modifying additives.

31. A method as claimed in any one of claims 28 to 30, wherein heat to activate the adhesive is applied when the magnetic or electrical field is no longer applied. 32. A method as claimed in any one of claims 28 to 31, wherein a pressure is also applied to assist in securing the particles to the substrate.

33- A method as claimed in claims 1 to 27, wherein the adhesive material Is chemically activatable.

3 . A method as claimed in claim 33, wherein the adhesive material is a plastisol and is activated by applying toluene thereto. 35- method as claimed in any one of claims 1 to 26, wherein the carrier material is water containing a thickening agent, the viscosity of the carrier material being low enough to allow the particles to move towards the said predetermined orientation but not so low that the ^'particles are moved bodily through the carrier material into depressions within the surface of the substrate.

36. A method as claimed in claim 35, wherein the viscosity of the carrier material is between 2,000 to 20,000 centipoise. 37• A method as claimed in any one of the preceding claims, wherein each particle includes a skin portion of refractive index different from the refractive index of a core portion.

38. A method as claimed in any one of the preceding claims, wherein the body of each particle is made of tinted glass.

39- A method as claimed in any one of claims 1 to 37, wherein at leat a part of the surface of the body portion of each particle is tinted with a lacquer prior to application of the said coating.

40. A method as claimed in any one of the preceding claims, wherein coloured particles are applied to selected areas of the substrate so as to form a pattern.

41. A method as claimed in claim 1,. wherein the said material having magnetic or electrical properties is an electret, and the orientation of each particle is charged by the application of an electrical field.

42. A light reflective material made by a method as claimed in any one of the preceding claims.

43. A light reflective material comprising a substrate, and particles adhesively secured to the substrate, each particle comprising a body of transparent or translucent material and a coating on a part of the body, the coating being light reflective and comprising a material having magnetic or electrical properties such that, prior to securement to the substrate, the orientation of the particle can ,be changed by applying a magnetic or electrical field thereto, at least 30% of the particles having an orientation relative to the substrate which is equal or substantially equal to a predetermined orientation.