WO2008114058A1

WO2008114058A1 - Visor

Info

Publication number: WO2008114058A1
Application number: PCT/GB2008/050201
Authority: WO
Inventors: Paul Gregory Ferguson
Original assignee: Supreme Visors Limited
Priority date: 2007-03-20
Filing date: 2008-03-19
Publication date: 2008-09-25
Also published as: GB2447613A; GB0705247D0; GB0805106D0

Abstract

A multi-layer protective maferial having optical properties which filter both IR and UV light, the material comprising at least two sheets of plastic secured together and with the first of those sheets having a metallized surface. Preferably, the multi-layer material consists of at least three sheets of plastic, the first sheet and/or one or more of the other sheets is coloured, the plastic is polycarbonate or triacetate and the metallized surface is aluminium. A method of making the multi-layer protective material is also described. The material is particularly intended for use in products such as face shields and visors to be worn by welders and foundry workers.

Description

VISOR

This invention relates to a multi-layer protective material comprising two or more sheets of plastic secured together, a method for making such a material and to products, in particular visors for use by welders and foundry workers, made from that material. The material filters infrared (IR) and ultraviolet (UV) light, as well as light in the visible spectrum, and also meets the requirements for impact resistance and offers extra abrasion resistance.

People working with welding equipment, in metal foundries and in other environments with high IR and/or UV levels, such as areas where certain food processing treatments are being conducted, require protection for their faces and, in particular, the eyes. Protective equipment available for such workers to wear includes helmets with full face shields or visors. These need to provide protection while allowing the wearer to still see clearly. Typically, the face shields or visors are made from either several laminated sheets of plastic or a single solid sheet of plastic, usually polycarbonate or triacetate, and have a thickness of about 1mm.

Shading from light in the visible spectrum and a degree of protection against UV light is achieved by dyeing the plastic from which the shield or visor is made, usually with a green dye. This is a commonly used approach. The resulting products are inexpensive, but do not meet the current safety standards for both UV and IR protection required from eyewear. The dyeing process is not efficient. This is because the dye in the dyeing tank is rapidly exhausted and so the amount of dye taken up by the plastic (and hence the level of shading achieved) during a production run is unpredictable and varies through the day as the process is carried out as a continuous operation. Furthermore, the resulting shields and visors do not have a very long effective life and are usually discarded after being used only once or twice.

In order to improve its ability to protect the wearer from IR (i.e. heat transmission), one of the exterior surfaces of the sheet of plastic which forms the shield or visor (i.e. that surface which in use will face the light/heat source) may be coated with gold. This is because gold is very effective at reflecting IR light. The coating is achieved by placing the solid polycarbonate sheet in a vacuum chamber, together with the gold, creating a strong vacuum and heating the chamber until the gold atomises and coats the surface of the polycarbonate sheet to which it is exposed. This process takes around two hours and is very expensive because it involves the use of gold. It is a batch process which is neither particularly efficient, because the vacuum is lost each time the chamber is loaded/unloaded (and then takes in excess of one hour to recreate), nor environmentally friendly, because there is a considerable amount of waste of the gold.

Furthermore, while they have a high degree of IR (heat) resistance, shields and visors made from polycarbonate sheet metallized with a gold coating are, due of course to the presence of the gold, very expensive.

There is therefore a need for an improved material for use in face shields and visors to protect against IR and UV light.

According to the present invention there is provided a multi-layer protective material having optical properties which filter both SR and UV light, the material comprising at least two sheets of plastic secured together and with the first of those sheets having a metallized surface. Typically, the material consists of at least three sheets or films of plastic. In a particularly preferred embodiment, it contains up to seven layers of sheets. Preferably, the first sheet and/or one or more of the other sheets is a coloured or tinted plastic. Most preferably, the sheets of plastic are laminated. According to another aspect of the present invention there is provided a method of making such a multi-layer material and which comprises metallizing the surface of one side of the first sheet of plastic and securing that first sheet to the second sheet of plastic to form the multilayer material, such that the metallized surface is on the outside of the multi-layer material.

According to a still further aspect of the present invention there is provided a product comprising such a multi-layer material, said product being an effective filter for both IR and UV light. The product may be, for example, a face shield or visor used by welders or metal foundry workers. Other products of this invention include brow guards, goggles and screens or windows for use in, for example, laboratories, research establishments, factories and food processing or treatment facilities, and other areas where protection from IR and UV is required.

Suitable plastics for use in this invention include polycarbonate, triacetate, acetate and polyester. Triacetate is particularly preferred because of its clarity, heat resistance and strength; it is also relatively inexpensive. It will be understood that other plastics could be used, however, subject only to the requirement that the multi-layer material formed from the two or more sheets of plastic is effective in filtering IR and UV. Two or more different types of plastic may be present in the multi-layer (preferably laminated) material.

The metallized coating on the sheet of plastic is preferably of aluminium. It needs to be thin enough to allow light to penetrate, but sufficiently thick to reflect IR effectively. Typically, the metallized coating has a thickness of from 20 to 100 angstroms and most preferably of from 40 to 60 angstroms. It will be understood that other metals or metal alloys (such as brass) could be used in place of or in addition to aluminium.

The sheet of coloured plastic, which has UV absorbing ability, can be produced in a conventional manner, for example, either by inherently colouring the plastic during its manufacture or by dyeing the plastic with a suitable dye, such as a textile dye. The colour of the dye is usually green. It will be appreciated that the density of the colouration may be varied according to the degree of both UV and visible light transmittance required in the final product.

The thickness of the multi-layer material, which is preferably laminated, is generally between 1.0 and 2.0mm, a thickness of 1.2 to 1.5mm being preferred. The thickness of the individual sheets that make up the laminate will therefore vary according to the number of sheets present in the multi-layer material, such that its total thickness is within the aforementioned range. In a laminate made up of five sheets of plastic, each sheet will therefore typically have a thickness of from 200 - 250 microns. Preferred laminated materials of this invention have three, four, five, six or seven layers of sheets or films of plastic. Four or five layers are particularly preferred. Larger numbers of layers are not favoured because they can cause optical distortion.

The present invention will now be described in more detail and with reference to the accompanying drawings, in which :-

Figure 1 is an exploded side view showing a laminated material according to this invention; and

Figure 2 is a front view of a visor made from a laminated material according to this invention. Referring to Figure 1 , the laminate shown consists of five layers of plastic sheets (1 , 2, 3, 4 and 5). Sheet 1 has a metallized coating (6) on its outer surface and thereby has IR reflecting properties. Sheets 2, 3 and 4 are each made of clear plastic. Sheet 5 is coloured green and thereby has UV absorbing properties.

The layers of sheets making up the laminate are secured together and this can be done using either conventional adhesive or chemical lamination techniques. In the embodiment shown in Figure 1 , the metallized coating (6) on the outer surface of the first sheet (1) is on the side of the laminate that is closest to the light/heat source. This is of course because the metallized coating has the ability to reflect IR (heat) and thus protects the underlying sheets of the laminate from thermal damage. In the embodiment shown in Figure 1 , the coloured sheet (5), which has the ability to absorb UV, is placed on the side of the laminate that is closest to the operator's position. It will be understood, however, that the coloured sheet would be equally effective in absorbing UV if it was positioned as one of the intermediate layers in the laminate. Furthermore, UV absorbing additives could be incorporated in one or more of the other layers in the laminate.

Figure 2 shows a visor (7) formed from a laminate of the type shown in Figure 1. The visor provides the wearer with protection against IR and UV, as well as light in the visible spectrum and has impact and abrasion resistance. Importantly, the visor complies with the current EN 166 and EN 169 regulatory standards for the level of protection expected of eyewear for use during welding and related techniques. Furthermore, as a consequence of its laminated construction, the visor has the advantage of blistering (rather than catching fire) and this serves as a warning to the wearer that it is failing. In accordance with the invention, one of the sheets of the laminate must be metallized. Suitable coating or plating processes for achieving this metallization are well known in the art, particularly in connection with the continuous vacuum metallizing of polymer films (e.g. polyester films).

The process covers the surface of the continuous substrate film with a metallic layer by evaporating the metal and recondensing it on the substrate. The process is carried out in a chamber from which the air is evacuated until the residual pressure is approximately one-millionth of normal atmospheric pressure. The clean substrate is mounted within the vacuum chamber in such a way that it is exposed by line of sight to the heaters within the chamber.

The metal vapour is produced by heating the metal to be evaporated to such a temperature that its vapour pressure appreciably exceeds the residual pressures within the chamber. Thus, the metal is converted to a vapour and is transferred in this form to the relatively cool substrate. The substrate's temperature is maintained by feeding the material over a chrome roller which is cooled to -20⁰C.

The roller is approx 250 mm above the ceramic heaters. The film is driven at approximately 7 metres per second while aluminium rods are inserted into the heaters, whereby the molten material is evenly dispersed in this almost pure vacuum.

The thickness of deposited metal is determined by power input to the heaters, pressure in the vacuum chamber and film speed. In practice, adjustment of film speed is the more usual method of varying the thickness of the deposited metal. Variations in this thickness across the film can be corrected by adjustment of the power input to the individual heaters. Thickness of the deposit can be monitored by using photoelectric devices or by measuring electrical resistivity. As a general rule, metallized coatings in accordance with the invention are of the order of 20 to 100 angstroms thick and consist of aluminum. Mixtures of metals and/or alloys thereof may also be employed. As a compromise between low IR emissivity and cost, aluminum is the preferred coating metal.

This process can be operated as a continuous method using a roll of film of the plastic substrate and has the advantage of being inexpensive to operate and significantly faster than the batch method described previously for producing conventional visors.

Claims

1. A multi-layer protective material having optical properties which filter both SR and UV light, the material comprising at least two sheets of plastic secured together and with the first of those sheets having a metallized surface.

2. A multi-layer material as claimed in claim 1 , wherein the first sheet and/or one or more of the other sheets is a coloured plastic.

3. A multi-layer material as claimed in claim 1 or claim 2, wherein the plastic is polycarbonate or triacetate.

4. A multi-layer material as claimed in any one of claims 1 to 3, wherein the metallized surface is aluminium.

5. A multi-layer material as claimed in any one of claims 1 to 4, wherein the metallized surface has a thickness of between 20 and 100 angstroms.

6. A multi-layer material as claimed in any one of claims 1 to 5, wherein the sheets of plastic are laminated.

7. A multi-layer material as claimed in any one of claims 1 to 6, which consists of three, four, five, six or seven sheets of plastic.

8. A method of making a multi-layer material as claimed in any one of claims 1 to 7, and which comprises metallizing the surface of one side of the first sheet of plastic and securing that first sheet to the second sheet of plastic to form the multi-layer material, such that the metallized surface is on the outside of the multi-layer material.

9. A product which comprises or includes a multi-layer material as claimed in any one of claims 1 to 7.

10. A product as claimed in claim 9, which is a face shield or visor.