GB2081349A - Traffic cone - Google Patents

Abstract

In a rotation-moulded traffic cone having a base 10 supporting a conical body 12, the conical body is of uniform thickness over at least portion 14 so that an adhesive, which is preferably pigmented, can be directly printed thereon to retain optical glass beads which are embedded in the coating 14 and which may then be covered by a transparent preferably waterproof layer. Such a construction is cheaper and less liable to damage than separate retro- reflective sleeves that are currently fitted into cones. The uniform thickness of the body 12 is obtained by ensuring that the mould wall thickness is itself uniform. <IMAGE>

Description

SPECIFICATION Traffic cone This invention relates to a device for indicating a road hazard popularly known as a traffic-cone.

Traffic cones are hollow conical bodies of plastics material supported on a base of the same material. It is convenient to produce such cones by a rotational moulding process in which powdered plastics material is placed in a mould, the mould is heated and rotated about two axes whereupon the material fuses on contact with the heated mould surface.

After the powdered plastics material has deposited on the mould surface the mould is cooled, opened and the product removed.

In order that traffic cones will be noticed at night time it is also standard practice to fit a frusto-conical retro-reflective sleeve on to the cone. Such sleeves are well known and comprise a flexible backing sheet coated with a layer of pigmented adhesive into which microspheres are embedded, and covered by a layer of transparent material. The provision of a separate sleeve inevitably adds to the cost of the cone. Moreover in use the sleeve can be damaged and become detached from the cone after which the cone becomes useless at night as a warning device.

In order to deal with this problem it seemed desirable to apply the layers giving retro-reflective properties directly onto the moulded cone. Initially attempts to do that by rotation of the cone about its axis while in contact with a printing device met with failure in that portions of the cone surface were uncoated. At first no satisfactory explanation could be found for such failure.

After considerable investigation, however, it was found that the wall thickness of the cones was not uniform. This was a surprising discovery since one of the acknowledged consequences of rotational moulding is that products of substantially uniform thickness are obtainable. It was then realised that what led to the non-uniform wall thickness of the product was that the wall thickness of the mould itself was not uniform. Such a mould will permit greater heat transfer through the thinner parts of the wall than the thicker parts whereby a greater amount of plastics material will build up on the surface of the thinner parts ofthe mould.

Finally it was realised that the non-uniform mould wall was caused by a slight movement of the apex end of the sand cone for forming the conical part of the mould. In other words the axis of the conical part of the mould becomes displaced from its correct position so that a non-regular cone surface is formed. Consequently products formed from the mould will also have a non-regular cone surface.

These irregularities are not apparent from an inspection of the exterior of the product but they are, in fact, the cause of the failure of attempts to coat the cone surface as aforesaid.

The present invention has been made as a consequence of the foregoing.

According to the invention there is provided a traffic cone comprising a base supporting a hollow conical body at least a part of which conical body is of substantially uniform wall thickness, being provided wjith a retroreflective coating which comprises a layer of bonding material onto which a plurality of optical glass beads are fixed, said coated area extending around the conical body.

The invention also provides a method for making a traffic cone as defined above comprising forming said cone by rotational moulding in a mould of substantially uniform wall thickness at least in a part thereof in which the body is formed, applying said layer of bonding material onto aid cone body by means of a printing device and applying optical glass beads onto said coating.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing which shows a traffic cone in perspective from one side thereof.

Referring to the drawing the traffic cone comprises a hollow base 10 and a hollow conical body 12 integral with the base, formed of plastics material such as polyethylene by rotational moulding. At least the wall of the conical body is of uniform thickness, this being attained by using a mould of uniform wall thickness. Such a mould is formed by supporting the apical end of the sand cone for the conical part of the mould such that the axis of the cone is not displaced. The conical part of the resulting mould has a regular shape. Prior to use the mould surface is machined so that products moulded therewith have a smooth surface.

Polyethylene is notoriously difficult to coat. Accordingly prior to the provision of a retro-reflective coating on the part of the conical body referenced 14, that part is given a surface oxidation treatment.

Such treatment comprises mounting the traffic cone on a mandrel, directing a flame at the said part 14 while the traffic cone is rotated about its axis for about two revolutions. Preferably the flame is directed on to the cone at right angles to the cone surface so that, as far as possible, the heat distribution is even.

The cone is then transferred to a second mandrel which moves the cone into contact with a silk screen printer. The cone is rotated and the printer applies a coating of a bonding material for example ink or adhesive which is preferably pigmented for example with a white pigment or with aluminium powder, on to part 14. It is to be observed that part 14 is a frusto-conical surface so that the printer must be adapted to cover the distance around the base of part 14 which is greater than the distance around the top of the said part 14. This is accomplished by arranging forthe printer to move relative to part 14 across an arc, the angle of which is equal to the angle of the sector of the circle of which the developed part 14 forms the radially outer portion.

Any other practical method of printing may be employed if desired.

After printing as aforesaid the cone is placed on another mandrel and while the coating is still wet, rotated and sprayed with optical glass beads which adhere to the coating. The beads sink into the coating and it is desirable to adjust the coating thickness so that the beads will be embedded therein to about 1/3 of their depth. The cone is then removed from the mandrel and heated to "stove" the printed coating and lock the optical glass beads thereon.

Finally part 14 is sprayed with a varnish or clear lacquer to form a transparent waterproof cover over the glass beads. Such a cover is preferred since the retro-reflective properties of the beads can be impaired if they become wet. The cover can be formed in other ways, however, for example by a separate transparent sleeve which may be of flexible plastics material such as polyvinyl chloride or polyethylene.

In the embodiment shown in the drawing the base of the cone has the form of a pentagon in plan view.

With this arrangement, should it happen that the cone is tilted such tilting will occur along one of the straight edges and there will always be a corner on the opposite, raised side of the base. There is thus a greater weight of material acting to return the tilted cone to its correct position than it the case with known traffic cones which have square or hexagonal bases. Although in the embodiment shown in the drawing the base is in the form of a pentagon, the same advantage can be obtained (but to a lesser extent) with any polygonal base having an odd number of sides.

Although not shown in the drawing, the underside of the base is formed with a lip around the outer edge thereof. Weights can be placed within the lip to stabilise the cone for example against wind, such weight conveniently being in the form of a flexible plastics tube filled with a fluid such as sand or water.

Claims (24)

1. A traffic cone comprising a base supporting a hollow conical body at least a part of which conical body is ofsubstantially uniform wall thickness, being provided with a retro-reflective coating which comprises a layer of bonding material onto which a plurality of optical glass beads are fixed, said coated area extending around the conical body.

2. A traffic cone as claimed in claim 1, wherein the conical body is formed by rotational moulding in a mould having a substantially uniform wall thickness corresponding to the part of uniform thickness in the conical body.

3. Atraffic cone as claimed in claim 1, or claim 2, wherein the surface of the conical body is subjected to surface oxidation treatment prior to the application of a retro-reflective coating.

4. A traffic cone as claimed in any preceding claim, wherein the coating is pigmented.

5. Atraffic cone as claimed in any preceding claim, wherein the optical glass beads are embedded in the coating.

6. Atraffic cone as claimed in claim 5, wherein the optical glass beads are embedded by upto one third of their depth in said coating.

7. Atraffic cone as claimed in any preceding claim, wherein the coated area is covered by a transparent layer.

8. A traffic cone as claimed in claim 7, wherein the transparent layer comprises varnish or clear lacquer.

9. A traffic cone as claimed in claim 7 or claim 8, wherein the transparent layer comprises a transparent sleeve.

10. A traffic cone as claimed in claim 8, wherein the sleeve is of flexible plastics material.

11. Atraffic cone as claimed in any of claims 7 to 10, wherein the transparent layer is waterproof.

12. A traffic cone as claimed in any preceding claim wherein a lip is provided on the underside of the base.

13. A traffic cone as claimed in any preceding claim wherein the base has the form of a polygon having an odd numberofsides.

14. A traffic cone as claimed in claim 13, wherein the base has the form of a pentagon.

15. A method of making a traffic cone as claimed in any preceding claim, comprising forming said cone by rotational moulding in a mould of substantially uniform wall thickness at least in a part thereof in which the body is formed, applying said layer of bonding material onto said cone body by means of a printing device and applying optical glass beads onto said coating.

16. A method as claimed in claim 14, wherein to apply the bonding material the cone is rotated about its axis and the printing device brought into contact with the cone body.

17. A method as claimed in claim 15, wherein in order to print a strip of substantially uniform width around said conical body the printing device is adapted to move across an arc having an angle substantially equal to the angle of the sector of the circle defined by the developed base of said strip.

18. A method as claimed in any of claims 15 to 17 wherein prior to application of the bonding material of the conical body is subjected to surface oxidation.

19. A method as claimed in claim 18 wherein the surface oxidation is effected by rotating the cone about it axis and directing a flame at the surface of the cone body.

20. A method as claimed in claim 19, wherein the flame is directed on the cone at right angles to the surface thereof.

21. A method as claimed in any of claim 15 to 20, wherein the cone is heated after application of the optical glass beads.

22. A method as claimed in any of claims 15 to 21, wherein the transparent layer is formed by applying a varnish or clear lacquer to the cone body.

23. A traffic cone substantially as described herein with reference to the accompanying draw- ""' ings.

24. A method of making a traffic cone substantially as described herein with reference to the accompanying drawing.