SELF- ILLUMINATING GROUND SURFACE

The present invention relates to a method of providing a self-illuminating ground surface. The present invention is described herein by way of a practical example as a method of providing a self - illuminating footpath. However, it, is readily applicable to any other use in which a non- slip and illuminated ground surface is required, for example illuminated roads or cycle lanes.

Typically, footpaths are illuminated by mounting electrical light bulbs on lamp posts or bollards and placing these at regular intervals above the surface requiring illumination .

However, as well the expense of the electrical equipment and the other materials required, such systems require underground electrical cable to be laid along the length of the footpath and are thus costly and disruptive to install. They are also expensive to run and maintain due, to the cost of electricity required to light the bulbs and the need to periodically replace damaged or faulty equipment.

US 2005/0160637 describes a process for making luminescent objects, either by mixing a luminescent powder with a coating such as a paint or resin and applying this to an existing object, or mixing a luminescent powder with a polymer and forming an object by a plastic moulding process.

GB 1300929.5 describes a method in which a photo- luminescent pigment is mixed with a liquid sealant and sprayed over a base layer consisting of a binding agent and a particulate medium such a stone chips. In this way a ground surface can be created which absorbs UV radiation by day and re-emits radiation after dark to produce a gently glowing surface .

The present invention provides an alternative method which produces an improved end result.

According to a first aspect of the present invention, there is provided a method for providing a self-illuminating ground surface, comprising the steps of: spraying a liquid binding agent from a first dispensing device onto a ground surface to be coated; spraying particulate media under pressure from a second dispensing device onto the ground surface to be coated, whereby the binding agent adheres the particulate media to the, surface to form a base layer; and applying a liquid sealant over the base layer; wherein the particulate media comprises a mixture of a first particulate and a second particulate and the first particulate comprises a photoluminescent material ,

By this method a hard-wearing, weather-resistant and non-slip surface coating is provided which is flexible, tough and strongly adhered to the underlying ground surface. The photoluminescent particulate absorbs UV radiation during the daytime and re-emits that radiation after dark to provide a gentle illumination, thus showing users where they are going and revealing obstacles in their path, without any significant contribution to light pollution. In addition, the illumination provided requires no ongoing energy costs, no groundworks to install, small initial capital cost and can provide years of maintenance- free use. Preferably, the photoluminescent particulate comprises a rare earth strontium aluminate, such as strontium aluminate doped with Europium. Such materials have been found to exhibit an appropriate level of luminescence which can be sustained for several hours.

The second particulate medium is selected according to the type of finish required. Preferably, the second particulate medium comprises construction aggregate, such as stone chips, crushed glass, or a combination thereo .

In a preferred embodiment, the particle size of both the first and second particulates is in the range of 1.5 -3mm. Additionally, the first particulate may be mixed with the second particulate at a weight ratio of approximately 1.5-2 parts of the first particulate to 25 parts of the second particulate.

Advantageously, the liquid sealant, forms a flexible and water impermeable barrier over the first and second particulates. This prevents the formation of potholes which may otherwise occur were water to penetrate the coating, and prevents the, coating from cracking due to small ground movements .

In one embodiment, the liquid sealant is applied using a roller, preferably at a coat weight of approximately 200 to SOOg/ ^' m . This provides an easy method of application and an even result.

The liquid sealant may be any suitable flexible and quick drying solution. Preferably, the liquid sealant is an aliphatic polyaspartic comprising a resin and a hardener. Such a sealant has been found to be very effective when used with the present invention, offering a quick-drying, flexible, resilient and UV and light stable coating.

The particulate media may be sprayed into the spray of liquid binding agent as it is applied to the ground surface. However, preferably the particulate media is sprayed towards the ground surface to be coated in the region of the newly applied binding agent. By doing so, the particulate media are prevented from rebounding directly off of the surface to be coated and is forced, by the pressure at which it is sprayed, into the binding agent. By forcing the particulate media into the binding agent, it is not necessary to wait for the particulate media to sink and settle into the binding agent under its own weight before the binding agent can be cured. Thus, a quick-curing binding agent may be used, reducing the time required for the coating to be applied .

According to a second aspect of the present invention, there is provided a surface coating comprising: particulate media adhered by a binding agent to a surface to be coated to form a base layer, and a flexible, water- impermeable sealant covering the base layer, wherein the particulate media comprises a mixture of a first particulate and a second particulate and the first particulate comprises a photoluminescent material .

This coating preferably comprises the various materials and quanties are set out above in relation to the method, and thus provides the same advantages . The present invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective, sectional view of a surface coating applied to a ground surface in accordance with the method of the present invention; and

Figure 2 is a schematic perspective view showing the manual application of the base layer of the surface coating of Figure 1.

Figure 1 shows a self-illuminating surface coating 10 applied over a ground surface 100. The coating 10 comprises a base layer 12 adhered to the ground surface 100 and a sealing layer 14 which covers the base layer 12 , The base layer 12 comprises a cured binding agent 16 into which particulate media 18 is set. The sealing layer 14 comprises a cured liquid sealant.

The particulate media 18 comprises a mixture of a base particulate 24 and a photoluminescent particulate 26. The base particulate 24 gives the surface coating 10 a rough, non-slip, hard-wearing finish, while the photoluminescent particulate 26 provides the illumination effect. The sealing layer 14 seals the base layer 12 from water ingress.

The base particulate 24 is typically a material such as construction aggregate, especially stone chips, although other forms of aggregate, including recycled forms of aggregate such as slag, glass, concrete etc. are also possible. Typically the particle size of the base particulate 24 is in the order of 1.5-3mm. Any suitable photoluminescent material may be used. In this example, it is "photoluminescent pigment YG-SD", available from Lightleader Co., Ltd. of Beijing, China. This is a rare earth strontium aluminate which is non-toxic and non-combustible and which luminesces a yellow-green colour after exposure to UV radiation.

The photoluminescent particulate 26 consists of particles of a photoluminescent material of a size in the same range as that of the base, particulate 24, Thus, the photoluminescent particulate 26 may have a particle size in the range of 1.5 -3mm, and preferably about 2mm.

The photoluminescent particulate 26 and the base particulate 24 are preferably mixed with each other with a weight ratio of about 1.5-2kg of photoluminescent particulate to 25kg of base particulate. In this way the photoluminescent particulate 26 can be dispersed evenly through the base particulate 24 and being of similar particle size it does not settle through the base particulate 24 and accumulate beneath it in the finished coating 10, as it would do if it were in powder form.

The coating 10 may be readily applied to various types of ground surface 100, and in particular to the surface 100 of existing pathways or road surfaces, such as those formed from tarmac, concrete, or bound aggregate.

Prior to the application of the self-illuminating surface coating 10, it may be beneficial to pre-treat the ground surface 100 by cleaning, drying and sealing it, where necessary. Sealing is particularly beneficial if the ground surface 100 is formed of a porous material, such as concrete .

If cleaning and drying of the ground surface 100 is required, an air lance (not shown) connected to a source of compressed and heated air is directed towards the surface to be coated 100 in order to dry it. and to remove unwanted matter, such as dirt or dust, which may otherwise negatively affect the adhesion of the surface coating 10.

If sealing of the ground surface 100 is required, a primer is applied to the ground surface 100 prior to the application of the coating 10. A suitable primer is "PU3922", available from Leeson Polyurethanes Ltd, of Warwick, UK. This is a single component moisture curing urethane primer which can be used as a seal coat for concrete and which can withstand extreme temperature variations (-55°C to +144°C) for extended periods without loss of strength. The primer is applied by roller at a rate of 6 to 10 m ² /L, and left for at least 90 minutes to cure. This forms a moisture barrier underneath the surface coating 10 to prolong the useful life of the coating 10. Such sealing is not required where the ground surface 100 is non- porous, for example if it is formed from tarmac.

Referring to Figure 2, an example, of manual application of the surface coating 10 is shown, and discussed below, although other methods of application are envisaged, such us via an automated process.

To manually apply the coating 10 to the ground surface 100, a liquid binding agent 16 is first sprayed onto the ground surface 100 in a series of wave-like passes from the of a spray gun. The nozzle 20 is held at a distance of approximately 60cm from the ground surface 100 and the liquid spray 16 is applied with a thickness of at least lmm, which is determined visually. The pressure at which the spray is applied can vary from 500 psi to 3500 psi (3.4 to 24.1 MPa) , although ideally the pressure is approximately 3250 psi (22.4 MPa) .

The base particulate 24 and the photoluminesecent particulate 26 are mixed in a hopper and the combined particulate media 18 is expelled from a blast nozzle 22 of a particulate media spraying apparatus toward the ground surface 100 in the region of the newly applied liquid binding agent 16. The binding agent sprayer and the particulate media spraying apparatus, thus also the nozzles 20 and 22 as shown in Figure 2, are separate and ideally operated by two operators, each operating one of the apparatuses and both sharing the weight of the unapplied binding material 16 and particulate media 18. This is particularly advantageous given the weight of material required for spraying large surfaces and also enables further applications of binding agent 16 or particulate media 18 to be made separately, as required.

As with binding agent 16, the particulate media 18 is applied in a series of wave- like passes to ensure even coverage of the ground surface 100. The blast nozzle 22 is held such that the particulate media 18 is expelled at an angle of approximately 30-45° to the horizontal. By spraying the particulate media 18 under pressure onto the binding agent 16, the particulate media 18 is forced into the liquid binding agent 16, which is "bulked out" and coats the particulate media 18, providing a rough upper surface. Since the particulate media 18 is forced under pressure into the binder 16, it is not necessary to wait for the particulate media 18 to sink into the, binder 16 under its own weight, enabling a fast curing binding agent to be used.

The binding agent 16 may be of any suitable composition, provided it may be applied in spray form and cures quickly to provide an elastomeric, flexible and tough coating which is resistant to impact, tearing and abrasion.

In one example, the binding agent. 16 is a two-component polyurea hybrid formed from a polyurea hybrid isocyanate mixed with a polyurea hybrid polyol and applied using a plural component proportioning sprayer (such as the "Reactor E-XP2" available, from Graco, Inc., Minneapolis, Minnesota) attached to a spray gun (such as the "Plural Component Impingement Mix Air Purge Spray Gun" available from Graco, Inc., Minneapolis, Minnesota) .

The sprayer (not shown) is connected via heated hoses to two separate containers, each containing one of the two components of the binding agent 16 and each including a transfer pump for conveying the components to the sprayer, along with a desiccant dryer to reduce, the, level of moisture inside the container. The sprayer includes a heating unit by which the components of the binder 16 are heated to approximately 7Q-80°C to reduce the viscosity of the component liquids and the, curing time of the resulting polymer. The exact temperature to which each component is raised is dependent upon the nature of the component and the ambient conditions and should be adjusted to ensure that the delivery is balanced. That is, the viscosity of each component should not be so different as to result in the delivery of unequal quantities of the two components. Ideally the polyurea hybrid polyol component is heated to approximately 80°C and the polyurea hybrid isocyanate component heated to approximately 75 °C.

Once each of the components has reached the correct temperature, the sprayer is set to "spray" and the component liquids are pressurised and delivered to the spray gun where they are combined in a mix chamber to form the binding agent immediately prior to spraying,

A suitable particulate media spraying apparatus is the "1448NC Softstrip (RTM) Portable Multi-media Blast Cleaning Machine", available from Hodge Clemco Ltd. of Sheffield, United Kingdom. This apparatus includes a hopper containing particulate media 18, a compressed air inlet, a regulator, a pressure line, a blast line, a media control valve and a blast outlet to which the blast nozzle 22 is attached. The particulate media spraying apparatus is connected to a compressed air source and the hopper is pressurised to approximately 125psi (0.9 MPa) to enable the particulate media to be sprayed under pressure.

Once the first pass has been completed, the binding agent 16 is allowed to set, thus binding the particulate media 18 and adhering to the surface 100 to form base layer 12. This occurs in approximately 60 seconds. Once set, an air lance can be used to remove any loose particulate media 18 lying unbound on the base layer 12. If necessary, second and further passes can be completed in much the same way. The air lance is ideally used between each pass to prevent loose particulate media 18 from being oversprayed and thus causing a visible seam between adjacent waves. Following the application and curing of the base layer 12, the sealant is prepared. The liquid sealant forming the basis of the sealing layer 14 is preferably a two-component aliphatic polyaspartic , namely "PU4827/1W" polyaspartic aliphatic topcoat, available from Leeson Polyurethanes Ltd. of Warwick, UK. This is formed from "PU4827/1W Part. A" resin and "PU4827/1W Part B" hardener and cures to form a transparent, flexible and UV stable coating.

To prepare the sealant, the resin is mixed using a slow speed, high torque helical blade mixer until uniform. The hardener is then added at a weight ratio of 1 part hardener to approximately 2.27 parts resin and mixed slowly for approximately 2 minutes until uniform.

Once prepared, the liquid sealant is applied on top of the base layer 12 using a non-absorbent roller at a coat weight of between 200 to 500 gsm, and left to cure for approximately 40 minutes to form the sealing layer 14. Once the sealing layer 14 has cured, the surface coating 10 is complete and can be walked on immediately.

The resulting surface coating 10, as shown in Figure 1, provides a hard-wearing, weather-resistant and non-slip finish that is flexible, tough, UV and light stable and strongly adhered to the underlying ground surface 100. The photoluminescent particulate 26 absorbs UV radiation during the daytime and re-emits that radiation after dark, providing a gentle illumination for up to 20 hours. This illumination can show users where they are going and illuminate obstacles in their path, without contributing to light pollution. In addition, the illumination provided by the coating 10 requires no ongoing energy costs, no groundworks to install, small initial capital cost and should operate maintenance free for approximately 20 years, The coating 10 could be used on any surface for which illumination is beneficial, for instance on footpaths, cycle lanes, building entrances and exits, or on steps.

Since the photoluminesecent material is provided as relatively large particles interspersed among the aggregate particles of the base particulate 24, illumination is provided as a plurality of discrete pinpoints of light against a dark background. The overall visual effect is akin to looking at a clear night sky filled with stars. This is visually appealing as well as functional.

Furthermore, since there is no photoluminescent material in the sealant layer 14, by day there is no discolouration of the sealant 14 and the natural colour of the base particulate 24 is visible without distortion. The photoluminescent particulate 26 is generally a pale colour, looking somewhat like pieces of white shell. When interspersed amongst the base particulate 24 it gives a slight speckling effect but the overall colour of the base particulate 24 is unchanged.

The intensity and duration of the illumination provided by the coating 10 depends on the intensity and duration of the sunlight to which the coating 10 is exposed, although even exposure to UV radiation on a cloudy day is adequate to cause the coating 10 to glow sufficiently for 12 hours.

The sealant layer 14 prevents any of the particulate media 18 becoming dislodged from the binding agent and provides extra weather and wear resistance. It is flexible, allowing it to bend rather than crack in the event that the underlying ground surface 100 moves, for example due to subsidence or the movement of tree roots. The sealant layer 14 also provides a barrier to water, reducing the occurrence of potholes and increasing the useful life of the coating 10.

It will be appreciated that various alterations and modifications to the precise details described are possible without departing from the scope of the claims.