GB2255044A

GB2255044A - Retro-reflective assembly

Info

Publication number: GB2255044A
Application number: GB9207023A
Authority: GB
Inventors: Harry Vincent Houghton; Peter Wallwork; Michael Philip Booth
Original assignee: SWINTEX
Current assignee: SWINTEX
Priority date: 1991-03-28
Filing date: 1992-03-30
Publication date: 1992-10-28
Anticipated expiration: 2012-03-30
Also published as: GB9207023D0; GB2255044B

Abstract

A retro-reflective assembly comprises a substrate (10), a binder layer (12) on the substrate, and beads 14 partially metallised (16) and partially embedded in the binder. A transparent cover (18), is welded to the binder and/or substrate at any point, such as sites where metallised beads are present. <IMAGE>

Description

RETRO-REFLECTIVE ASSEMBLY This invention relates to retro-reflective assemblies and particularly, but not exclusively, retro-reflective assemblies for use with road signs, road safety furniture such as traffic cones, bollards, delineators, etc., clothing, patches for clothing and the like.

Many known retro-reflective assemblies comprise a substrate coated with a reflective layer, for example of metal such as aluminium, a binder layer on the reflective layer and a plurality of optical glass beads partially embedded in the binder layer so that the beads contact the reflective layer. In an alternative construction the reflective and binder layers are combined into a single layer. The reflective layer may be a single continuous layer of aluminium or may comprise aluminium particles or platelets suspended or embodied in the binder layer. The assembly is completed by a transparent or translucent cover over the beads which is usually separated from the beads by 2 small air gap. The cover layer is secured to underlying layers, at least around the edge.This is necessary in order to prevent rain water contacting the beads, the effect of which is to impair the reflective properties of the assembly and it appears black.

One of the most convenient methods of securing the cover layer to the rest of the assembly is high frequency welding which is usually understood to mean agitation of the molecular structure of Polar materials at selected points by the use of high frequency radio energy, often in the 25 to 30 megahertz frequency bands but in particular, at 27 to 28 megahertz and more particularly, at 27.12 megahertz.

Polar materials include plasticised polyvinyl chlorides (PVC) polyurethane, certain rubbers and nylons, but is not restricted to these.

Some normally non-polar materials may be welded using high frequency techniques by the incorporation of additives.

The agitation of the molecules of suitable materials causes them to heat up and soften or melt at the selected point and two such compatible materials in contact with each other at the selected point will flow together, resulting in a permanent joint. No external heat is applied.

This is in contrast to the technique of applying heat from an external source, as in heated calender rollers and press plates. With this method welding can be effected in a plurality of locations at the same time with a single head which is not possible with, for example, ultrasonic welding. However, the major disadvantage with high frequency welding of retroreflective assemblies is that welding must be effected where there is no metal reflective layer between the substrate and the top cover. If high frequency welding is attempted at sites where the metal reflective layer is present shorting, arcing or a minor explosion may result with possible consequent injury to the operator of the welding equipment and damage to the equipment itself or the assembly being welded.These problems are particularly acute where the high frequency welding equipment is used to cut through the assembly to form a product of the desired shape and at the same time forms a seal at the cut edges or where high power levels are applied. For this reason it has become the practice to limit or restrict the reflective layer coating on the substrate so that a non-reflective border is provided around the edge or periphery to which the cover can be welded by high frequency welding. It is impossible for this border area to have any significant retro-reflective properties. As a result the area of the assembly adjoining the points or areas which have been high frequency welded cannot achieve a high standard of retro-reflectivity of the kind stipulated by British Standard 873 on an edge to edge basis.This leads to diminution of the overall assembly retro-reflective target value. When a retro-reflective assembly is in the form of a cylindrical sleeve, for example for use as a bollard, the area of border having no retro-reflective properties can amount to as much as 20% of the total presented sleeve surface.

As already mentioned, if water permeates between the cover and the optical glass beads the assembly "blacks out" and loses its retro-reflective properties.

It is desirable, therefore, to weld the cover to the rest of the assembly not just around the edges but at other locations thereby forming "pockets" so that if the cover is torn the retro-reflective properties of the assembly are only lost in the pocket area beneath the tear and not over the whole assembly. However, it will be appreciated that formation of such pockets by high frequency welding would require that the reflective layer should not be present at or adjacent to the places where the welding for pocket formation is effected in addition to the edge of the assembly so that the retro-reflective quality of the assembly would be even lower.

Previous art to solve this has involved expensive roller and lamination equipment, possibly using engraved rollers, considerable pressure and heat and/or adhesives.

The present invention has been made in order to deal with these problems.

According to the invention there is provided a retro-reflective assembly comprising a single or multi-layer substrate containing a layer of at least some partially metallised and partially embedded optical glass beads, wherein the substrate is, at any point, joined to a single or multi-layer top cover by the use of high frequency welding techniques.

It has surprisingly been discovered that, in spite of the presence of a metal coating on the optical glass beads, high frequency welding of the cover to the rest of the assembly is possible without the resulting shorting, arcing or explosion as experienced with the prior art assemblies. This is found to be the case even when very high concentrations of metal coated glass beads are present. Thus with the invention the border having no retro-reflective properties can be eliminated.

The entire area of the assembly can be retro-reflective and as a result the assembly as a whole will have a higher edge to edge performance. Moreover welding by high frequency can also be applied in order to create pockets at locations where metal coated beads are present with minimum reduction in the retro-reflective properties of the product.

Equally surprising as a discovery is that the presence of partially metallised beads in the absence of a metallised layer may actually, for some at present unknown reason, enhance the concentration of the high frequency energy at the selected weld point, allowing less energy or time to be used to achieve a weld.

The assembly may also comprise a binder layer which may be adhesive and either continuous or discontinuous.

The substrate, top cover or binder layer may comprise a layer of material reactive to high frequency radio energy, not confined to, but particularly including the 27 megahertz band.

The assembly may include a layer of PVC.

The substrate may be provided with an adhesive backing suitable for joining the completed assembly to another surface.

The substrate of the assembly may be reinforced by woven or non-woven textiles.

In a preferred embodiment of the invention the optical glass beads that are applied to the binder layer are coated overall with a metal reflective layer such as aluminium or silver. The coated beads are partially embedded in the binder layer and then the metal coating on the exposed parts of the beads is removed, for example by etching. This technique is already known and, therefore, need not be described further.

The retro-reflective assembly can be produced in a continuous manner by applying binder and beads to substrate as it is unreeled from a supply, the assembly being divided into pieces as required. The cover can be fitted either before or after sub-division.

Alternatively the assembly can be made in a discontinuous fashion with binder, beads and cover applied to individual pieces of substrate.

The coated optical beads individually provide a very high level of retro-reflectance. Thus if the beads are spread over the assembly so as to form a substantially continuous layer an extremely high standard retro-reflective assembly is obtained. If a lower standard product is required the coated beads can be applied in a discontinuous layer, that is to say they can be spaced apart. Distributing coated beads on the binder layer in a uniform but spaced apart layer can be effected in many ways. One example is to mix the coated beads with other material which will act as a spacer. Such other material can include uncoated optical glass beads, sand, plastic particles or the like.

Preferably the layer of partially metallised beads cover more than 5% but less than 75% of the substrate surface area.

It is not essential that the coated optical glass beads be uniformly distributed over the substrate. It may be desired to have a product in which some parts are of greater retro-reflectivity than others, in which case the density of the coated beads would be greater in some parts than in others.

A further advantage of the invention is that the assembly has a high luminance in natural light, that is to say it appears white. Some prior art assemblies comprising a reflective layer of aluminium have a rather grey appearance in daylight. The importance of this is that certain retro-reflective assemblies such as sleeves for traffic cones and delineator bollards must appear white in daylight as well as having a minimum retro-reflective standard.

The top cover may be substantially transparent or translucent or it may be partially or wholly pigmented, with one or more fluorescent colours or otherwise. The top cover may alternatively or additionally be partially or wholly overprinted on either its inner or outer surface.

The binder layer can be colourless, pigmented, transparent or translucent or opaque as desired. Where appropriate the binder layer can be printed, as by silk screen printing, to provide information such as is appropriate for a road sign or hazard warning.

As stated above the present invention readily enables the cover to be welded to the rest of the assembly to form one or more cells or "pockets". The shape of the pockets is not critical to the invention; any shape or combination of shapes can be adopted. The pockets can be discrete, that is separated from each other, they can be adjacent one another or a combination of discrete and adjacent pockets can be provided. The pockets may be as large or small as desired. If the pockets created are of a small size, the welding of the edge of the assembly may be dispensed with, since the loss of retro-reflectivity of those pockets outside the first complete pockets may be minimal in effect.

In the high frequency welding of the cover to the rest of the assembly it is not essential that welding should only take place where there are metal coated beads. Welding can also be effected where there are no metal coated beads, provided that there is no metal reflecting layer at such locations. If desired other methods of securing the cover can be used in addition to high frequency welding, example being the use of adhesive and/or ultrasonic welding. It is thought that the shape of the welding bar or strip used, or possibly the length/width relationship of the bar has an influence on the ability to weld in an area which has partially metal coated beads present.

Preferably at least one partially metallised glass microsphere may be encapsulated or captured within the weld area or may be displaced from its original position in the substrate or binder layer as a result of a weld.

At the time of welding the top cover and substrate layers together, a tear seal may be created around at least part of the periphery of the assembly enabling a resultant smaller shaped assembly to be removed from a larger sheet of the assembly.

Additionally or alternatively, the binder layer may be caused to be displaced at the point where the weld is effected to allow the said substrate to weld to the top cover.

The binder layer may bond at least in part to the cover and/or base substrate as a result of the effect of the high frequency energy acting on either or both the base substrate and/or top cover.

If the binder layer is reactive to high frequency radio energy, the top cover and base substrate may be joined to each other via the high frequency activated binder layer, irrespective of any response to high frequency radio energy of the top cover or base substrate.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a transverse section through a retro-reflective assembly.

Referring to the drawing a substrate 10, for example of polyvinyl chloride is coated with a layer 12 of a binder for example of product SP 785 manufactured by E.T.Marler Ltd. Optical glass beads 14 previously coated with metal, for example silver are partially embedded in the binder layer and the metal coating removed from the exposed parts of the beads to leave a coating 16 over the surfaces of the beads that are embedded. A transparent cover 18 of, for example polyvinyl chloride, is laid over the beads and welded to the underlying assembly, as at 19 and 20, by high frequency welding. Weld 19 is an edge weld formed at the same time as the product is cut to the desired shape by the high frequency welding equipment from a larger piece. Weld 20 is a pocket weld.

The invention is not restricted to the above-described embodiments and many variations and modifications can be made. For example the cover and substrate do not need to be of polyvinyl chloride provided they are of materials which can be welded together by high frequency welding. The cover and/or the substrate can be rigid or flexible depending upon the intended use of the assembly. The substrate underlying the binder layer may comprise several layers and could include an adhesive layer and a release paper.

Similarly the top cover layer may be a composite layer with possibly only the layer immediately adjacent to the optical glass beads being high frequency weldable.

The substrate may itself be the binder layer for example by applying beads to a newly extruded still plastic extrusion or by the used well known transfer techniques for making retro-reflective structures.

Claims

1. A retro-reflective assembly comprising a single or multi-layer substrate containing a layer of at least some partially metallised and partially embedded optical glass beads, wherein the substrate is, at any point, joined to a single or multi-layer top cover by the use of high frequency welding techniques.

2. An assembly as claimed in Claim 1, wherein the substrate comprises a layer of material reactive to high frequency radio energy, not confined to, but particularly including the 27 megahertz band.

3. An assembly as claimed in Claim 1 or Claim 2, wherein the top cover comprises a layer of material reactive to high frequency radio energy, not confined to, but including the 27 megahertz band.

4. An assembly as claimed in Claims 1 to 3, further comprising a binder layer of material reactive to high frequency radio energy, not confined to, but including the 27 megahertz band.

5. An assembly as described in any preceding claim wherein a layer of PVC is present.

6. An assembly as claimed in any preceding claim, wherein the top cover layer is substantially transparent or translucent to light.

7. An assembly as claimed in any preceding claim, wherein the substrate and/or the top cover are made up individually of more than one layer.

8. An assembly as claimed in any preceding claim, wherein the substrate is provided with an adhesive backing suitable for joining the completed assembly to another surface.

9. An assembly as claimed in any preceding claim, which comprises at least one substantially rigid layer.

10. An assembly as claimed in any of Claims 1 to 8 which is flexible.

11. An assembly as claimed in any preceding claim, wherein the top cover is joined to the rest of the assembly so as to create one or more cells or pockets.

12. An assembly as claimed in any preceding claim, wherein the substrate is reinforced preferably by woven or non-woven textiles.

13. An assembly as claimed in any preceding claim, wherein the partially metallised beads are partially embedded in an adhesive binder layer carried on a substrate.

14. An assembly as claimed in any preceding claim wherein the top cover is partially or wholly pigmented.

15. An assembly as claimed in Claim 14, wherein the top cover is partially or wholly pigmented with one or more fluorescent colours.

16. An assembly as claimed in any preceding claim, wherein the top cover is partially or wholly overprinted on either the inner or outer surface.

17. An assembly as claimed in any preceding claim, wherein the layer of partially metallised beads includes other particles.

18. An assembly as claimed in any preceding claim, wherein the layer of partially metallised beads covers less than 75% of the surface area of the substrate.

19. An assembly as claimed in any preceding claim, wherein the layer of partially metallised glass beads covers more than 5% of the surface area of the substrate.

20. An assembly as claimed in any preceding claim that forms or is used in part or in totality in connection with a road sign, warning device, cone, bollard, protective clothing, belt, harness or other retro-reflective device, including utilitarian goods, fashion goods and accessories.

21. An assembly as claimed in any preceding claim, wherein at the time of welding the top cover and substrate layers together, a tear seal is created around at least part of the periphery of the assembly enabling a resultant smaller shaped assembly to be removed from a larger sheet of the assembly.

22. An assembly as claimed in any preceding claim, wherein at least one partially metallised glass microsphere is encapsulated or captured within the weld area.

23. An assembly as claimed in any preceding claim, wherein at least one partially metallised glass microsphere has been displaced from its original position in the substrate or binder layer as a result of the said weld.

24. An assembly as claimed in Claim 13 or any of Claims 14 to 23 as appendant to Claim 13, wherein the binder layer is caused to be displaced at the point where the weld is effected to allow the said substrate to weld to the said top cover.

25. An assembly as claimed in Claim 13, any of Claims 14 to 23 as appendant to Claim 13 or Claim 24, wherein the binder layer bonds at least in part to the said cover and/or base substrate as a result of the effect of high frequency energy acting on either or both the said base substrate and/or the top cover.

26. An assembly as claimed in Claim 13, in any of Claims 14 to 23 as appendant to Claim 13, Claim 24 or Claim 25, wherein the binder layer is reactive to high frequency radio energy, which enables the top cover and base substrate to be joined to each other via the high frequency activated binder layer irrespective of any response to high frequency radio energy of the said top cover or base substrate.

27. An assembly as claimed in Claim 13, any of Claims 14 to 23 as appendant to Claim 13, or any of Claims 24 to 26, wherein the binder layer is discontinuous.

28. An assembly as claimed in any preceding claim, wherein the retro-reflectivity extends to at least a part of the edge of the assembly.

29. An assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.