GB2088080A - Retroreflective articles - Google Patents

Abstract

A retroreflective article comprises two opposed support layers (1, 2) of light transmitting material. Each opposed face carries retroreflective beads (5, 6), a substantial proportion of the beads on one support layer being opposite bead free areas of the other layer. <IMAGE>

Description

SPECIFICATION Retroreflective products The present invention relates to double sided retroreflective products and to processes for making them.

Retroreflective materials are well known particularly for road safety purposes to draw attention to road signs and to mark possible hazards at night. The expression "retroreflective" as used in this specification means that a beam of light incident on the surface of the material is reflected and refracted in such a manner that a significant proportion of the incident light is directed substantially back towards the source, in a cone or wedge having a small apex angle, even when the light strikes that surface at an angle to the normal.

We have now found a retroreflective material which is particularly advantageous in its ability to draw a driver's attention to it at night.

According to the present invention there is provided a two-sided retroreflective article comprising two opposed support layers each support layer having a face which is opposed to a face on the other support layer, so as to constitute two opposed faces, each of the opposing faces carrying a coating of retroreflective beads comprising light transmitting material, as substantial proportion of the beads carried by each layer being opposite bead-free areas of the other layer.

Advantageously each of the support layers of light transmitting material comprises plastics material and is preferably in the form of a plastics film.

Preferably, for at least one side of the retroreflective article, the light path into and back out of the retroreflective article has interposed a coloured light transmitting material, for example such that two sides of the retrorefiective article display different colours when each is illuminated by white light.

The support layer of light transmitting material may carry the beads by having the beads pressed into it. Alternatively, the beads may be bonded to the material by a layer of adhesive applied to the support layer.

It is particularly preferred that substantially all of the beads have at least a portion in contact with air. It is thus preferred to provide a layer of air between the opposed faces of the layers which carry the beads. Where such an air layer is provided it is preferred to seal the edges of the retroreflective article so as to prevent entry of water which would affect the retroreflective properties. This sealing may be carried out with adhesives or by heat-sealing. In the case of the retroreflective article being in the form of a long tape, the longitudinal edge seal or seals may be supplemented with transverse seals at intervals to form cells which ensure continued protection against ingress of water for the remaining cells if one cell becomes broken or cut.

The beads employed in the present invention may comprise any transparent or translucent deposited on the surface of the beads, for example, by chemical means.

material or combination of materials but the beads should be such that they do not become undesirably deformed or damaged during the production of the retroreflective material. Certain inorganic glasses may be mentioned as suitable materials. Conveniently, the glass beads known as Ballotini beads may be employed in the invention.

When the aesthetic appearance of the material of the invention is important, the bead diameter is preferably no greater than 0.03 inch (0.76 mm), since for greater bead diameters the day-time appearance of the material of the invention is impaired. For such applications the bead diameters are most preferably no greater than 0.006 inch (0.15 mm).

The refractive index of the material of the beads is preferably in the range 1.5 to 2.2 and preferably in the region of 1.9. A refractive index in the region of 1.9 is preferred because the focus of the lens comprising a substantially spherical bead then falls at, or very near, the back surface of the bead when the refractive surface of the bead is in contact with air. This means, of course, that the maximum amount of a beam of light incident on the front surface of such a bead and reflected at the back surface after refraction will be directed back substantially along the same path. It will be appreciated that when the refractive index of the material of the beads deviates from 1.9 the apex angle of the cone of retroreflected light deviates from the minimum. The ideal apex angle is of the order of 100 but the apex angle will normally be somewhat larger.

The beads may be distributed on the support layers in a random, widely dispersed manner so that a substantial proportion of the beads on one surface do not lie opposite beads on the opposing surface and so interfere with their retroreflective action. Alternatively, the beads may be in comparative close packed bands, the bands on one support layer being offset from those on the other layer so as to avoid mutual interference.

The beads comprising light-transmitting material are rendered retroreflective by combining them with a light-reflective layer. The lightreflective layer may be separate from and may be spaced from but preferably is in contact with the beads and may form part of the support layer, or the adhesive layer (if one is provided).

Alternatively, and preferably, the light reflective layer may be a layer on the bead.

Any light reflective material may be employed in the reflective layer, for example, gold, silver and aluminium which, for example may be dispersed in lacquers, vacuum deposited aluminium and other metals, and materials containing white pigments and/or fillers such as titanium dioxide and barium sulphate. The nature of the reflective layer may, of course, be dictated by the efficiency of retroreflectivity desired in the material of this invention and the method by means of which it is to be produced.When the reflective layer comprises a coating on the surface of the beads it preferably comprises silver which has been When the light-reflective layer is a layer within or on the support or the adhesive layer it will be clear to those skilled in the art that the lightreflective layer must not extend over a substantial proportion of that part of the support and/or adhesive layer which lies opposite the beads on the opposed sheet.

In the preferred process the beads are initially completely covered with a reflective layer and are partially embedded in the support layer or an adhesive layer. The removal of a relfective layer from the exposed portion of a bead may be effected by any suitable method which will not deleteriously affect the area of the reflective layer between itself and the layer in which it is embedded. Methods involving abrasion and solution are exemplary of those which might be employed. When the reflective layer comprises silver, for example, this may be removed effectively by treatment with acid solution such as chromic acid or nitric acid.

When a coloured light-transmitting material is employed it may, for example, be the support layer which carries the beads. One possibility is for only one of the two opposed support layers to be coloured. Alternatively both layers may be coloured, e.g. red and amber. If there are adhesive layers to hold the beads on the support layers, one or both of the adhesive layers may be coloured. An additional layer of coloured light-transmitting material may lie outside one or more of the support layers.

As a further alternative, the beads may be made of coloured material or there may be a coloured coating on the bead.

In the last-mentioned, besides the coating being necessarily iight-transmitting it should be sufficiently thin on the bead so that it conforms throughout its thickness to a substantial proportion of the exposed surface of the bead.

Further, any such coating should be thin enough so as not to undesirably affect the position of the focus of the bead and the retroreflective properties of the product.

It is preferred that colour effects are achieved by employing coloured support layers, preferably coloured by the incorporation of a dye. It will be appreciated, of course, that the support layers may be printed with light-transmitting or opaque lettering or designs to achieve any desired effect.

In this connection it may be advantageous to print the above-mentioned coloured coatings or adhesives and/or apply the beads in printed fashion.

Support layers comprising plastics material may be of any thermo-plastics or thermo-setting plastics material. In the case of the thermo-setting resins, the uncured resin can provide a tacky surface to which the beads can easily adhere before being finally bonded on curing. Unsaturated polyester resins and epoxy resins are examples of such thermosetting resins. Thermoplastics materials are preferred, however, and these include polyolefins, such as polyethylene and polypropylene, linear polyesters such as polyethylene terephthalate, vinyl polymers such as polyvinyl chloride, polystyrene, polymethyl methacrylate and polycarbonates. Most preferred are flexible thermoplastics materials especially polyethylene.

The thickness of the support layers should be such as to give the desired level of flexibility or rigidity in the product and such that adequate light transmission of the support layer, preferably transparency, is retained. Support layers of low density polyethylene for use in the production of markers tapes may have a thickness of the order 0.5 to 10 mils (0.013 mm to 0.25 mm) for example.

The beads can be adhered directly to the support layers using the inherent properties of the materials such as by applying the beads to an uncured thermosetting resin as described above or by temporarily heat or solvent softening and tackifying a thermo-plastic material. However, the use of adhesive coatings applied to the support layers is preferred. Adhesive coatings applied all over a support layer must be light-transmitting, of course, whereas adhesive applied only to discrete points or regions where beads are to be adhered need not be light-transmitting and, in fact, can provide the reflective medium to back the beads.

Adhesives, which can be solvent based or curable, if not applied over the whole surface of the support layer can be applied using, for example, a gravure printing technique. The use of a reflective adhesive as opposed to employing reflectorised beads obviates the need for a reflector removal stage.

The product of the present invention finds particular use in the form of marker tapes, e.g. for road works. While the tapes themselves preferable consist of the products in long lengths which may be set up in twisted fashion, plaques of the product may be suspended at intervals along a tape, string or wire of conventional material.

Further, the products in tape or plaque form may find application elsewhere, such as in signs or displays which may be stationary or arranged to move, for example, in rotary fashion.

The present invention will now be further illustrated by reference to the accompanying drawings in which Figure 1 is a cross-section of a tape according to one embodiment of the invention, and Figure 2 is a cross-section of another embodiment of the present invention.

In Figure 1 a tape 1 of yellow transparent plastics film, e.g. polyethylene, is welded to a similar film 2 at their edges 3 and 4. Films 1 and 2 constitute support layers for layers of glass beads 5 and 6 (shown greatly enlarged) of a diameter 0.03 inch (0.76 mm) and refractive index about 1.9. The beads have a silvered surface on the side which abuts against the support layer which carries them. The beads in the two layers 5 and 6 are fairly thinly scattered on the support layers 1 and 2, on which they are held by adhesive layers (not shown). As a result a substantial proportion of the beads in layer 5 lie opposite portions of film 2 which are unobstructed by the beads of layer 6, and vice versa.

In the embodiment shown in Figure 2 the identification numerals have the same significance as in Figure 1. However, the layers of glass beads 5 and 6 instead of being scattered over the surface of the support layers 1 and 2 are distributed in narrow bands of closely packed beads which lie opposite portions of the opposed support layers which do not carry any glass beads.

It will be appreciated that where the two layers are of the same material they may be formed by folding a single sheet, film or tape. Accordingly, in Figure 1 and 2 the use of such a folded sheet, film or tape would eliminate the need for one of the edge welds 3 or 4.

Claims (7)

1. A two-sided retroreflective article comprising two opposed support layers of light-transmitting material, each support layer having a face which is opposed to a face on the other support layer, so as to constitute two opposed faces, each of the opposing faces carrying a coating of retroreflective beads comprising light transmitting material, as substantial proportion of the beads carried by each layer being opposite bead-free areas of the other layer.

2. A retroreflective article according to Claim 1 wherein at least one of the support layers comprises a plastics material.

3. A retroreflective article according to Claim 2 wherein each of the support layers is in the form of a plastics film.

4. A retroreflective article according to any one of Claims 1, 2 or 3 wherein for at least one side of the retroreflective article a coloured lighttransmitting material is interposed into the light path into and back out of the retroreflective article.

5. A retroreflective article according to Claim 4 wherein the coloured light-transmitting material is a coloured support layer.

6. A retroreflective article according to any one of Claims 1, 2, 3, 4 or 5 in the form of a long tape.

7. A retroreflective article according to Claim 6 wherein the longitudinal edges are sealed and transverse seals are provided to divide the tape into a plurality of cells.