GB2274619A

GB2274619A - Treatment of a flammable element to render it fire-resistant.

Info

Publication number: GB2274619A
Application number: GB9401992A
Authority: GB
Inventors: Graham Whitting
Original assignee: PRINT LAMINATION PLASTICS LIMI
Current assignee: PRINT LAMINATION PLASTICS LIMI
Priority date: 1993-02-02
Filing date: 1994-02-02
Publication date: 1994-08-03
Anticipated expiration: 2014-02-02
Also published as: GB2274619B; GB9401992D0; GB9302013D0

Abstract

A flammable laminar element (11) as described, especially a laminated element composed of a plurality of layers such as a display panel having an image printed on paper or card or central core (12), (22), (25), and coated with a layer or several layers (14, 15, 16, 17, 23, 24) of plastics or plastics resin material, in which the surface of the element is provided with a plurality of holes (19) or other passages (25, 26) passing at least part of the way through the element to provide escape routes for gasses generated by the constituents of the element at high temperature, thereby preventing an early build up of internal pressure and possible delamination of the element as the temperature rises above the combustion temperature of the base layer (12). <IMAGE>

Description

A METHOD OF TREATMENT OF A FLAMMABLE ELEMENT, AND A FIRE-RESISTANT ELEMENT SO TREATED The present invention relates generally to a method of treatment of a flammable element, particularly a flammable laminar element, and also to a fire-resistant element itself.

Considerable attention has been given in recent years to reducing fire hazard, especially in regions of high risk such as in subterranean storage and/or transport systems, underground car parks and the like.

Recent underground fires and the catastrophic consequences thereof have focused attention on the need for vigilance and for appropriate fire-resistant designs for all items used underground.

One aspect of underground transport systems which has until now received inadequate attention is the design and treatment of advertising material which frequently involves quite large laminar elements of flammable material such as paper or card, which may be coated with plastics or plastics resin materials many of which are also flammable in themselves.

Because of the requirement that such elements bear printed images and because the printing processes and materials used cannot readily be made non-flammable, attempts have been made to reduce the flammability of otherwise flammable laminar elements to increase the resistance to combustion at least to the point where the laminar elements themselves will not ignite for a certain minimum time period even if exposed to temperatures up to and exceeding their normal ignition point.

The present invention seeks to provide a method of treatment for such a flammable laminar element, and to a laminar element so treated to make it resistant to combustion: According to one aspect of the present invention, a method of treatment of a flammable laminar element to increase its resistance to combustion comprises the steps of forming a plurality of passages in the material to allow gases and/or vapours given off upon a rise in temperature to dissipate without resulting in substantial delamination of the element or collection of gases or vapours into combustible quantities.

It has been found that one of the physical phenomena which result in early ignition of laminar flammable elements is the collection of derived gases or vapours under the surface of the material resulting in blistering or bubbling of the surface as the gas increases in volume up to the point where the surface layer bursts allowing a concentrated volume of gas to mix with the surrounding air and ignite. The thin layer of material previously forming the skin over the bubble now presents to the burning gases an edge which can constitute an initiation point for combustion.

Surprisingly, the mere contrivance of perforating an otherwise flammable element can increase its resistance to ignition without any other treatment, such as chemical treatment with fire resistant materials, being necessary.

The method of the present invention may be performed by forming the passages as perforations extending transversely of the general plane of the element, or by forming passages extending generally parallel to the plane of the element. In the former case the perforations are preferably spaced over substantially the whole of the area of the element and it has been found that a spacing of up to about 200 times the thickness of the material is capable of producing a fire retardant effect.

As far as material printed with images is concerned, the closeness of the spacing of the perforations is of some significance since very closely spaced perforations would detrimentally affect the visual effect. For conventional material such as paper or card printed with known printing inks and encapsulated with polyester and polyethylene film it has been found that a perforation spacing in the region of one hundred times the thickness of the material is sufficient to provide a fire resistance high enough to meet the applicable standards.

In one example the material has an overall thickness in the region of 0.18 mm and the spacing of the perforations is in the region of 12.5 mm.

The treatment process of the invention may be performed by forming perforations which pass right through the material, opening into each of two opposite major faces thereof, or may be performed by forming perforations which pentrate a surface and into the body of the material, but do not pass right through. Perforations of this form may be formed on either the front or rear face of the element, and in the latter case may pass right up to a coating layer so that only a skin of limited thickness separates the perforation from the region in front of the front face. It may be acceptable for perforations passing only part way through the thickness of the material to be formed from both faces on the grounds that the spacing of the perforations opening into any one face can thereby be effectively doubled without significantly reducing the fire-retardant effect of the perforations themselves.

In an alternative method of treatment the passages may be formed between adjacent layers of the material. This may be achieved by means of a plurality of surface asperities on at least one of two facing surfaces of adjacent layers. A composite material may, for example, include a permeable layer of material having intercommunicating cavities which form such passages. This layer may be a core layer or an intermediate layer of the overall composite material.

Likewise, two facing surfaces of adjacent layers of a composite material may be formed with a plurality of channels or grooves with the channels or grooves of one surface being non-parallel to the channels or grooves of the other whereby to form a plurality of channel or groove intersections over the area of the element.

According to another aspect of the invention there is provided a fire-resistant flammable laminar element having a plurality of passages therein for allowing the dissipation of gases or vapours given off by the or a material of which the element is composed when the material is subjected to a rise in temperature above a certain threshold value.

The said passages of the element may extend generally orthogonally of the major face of the element, and may open into one or other of the said major faces.

Preferably the said passages pass right through all of the layers of the element and open into both major faces thereof.

The spacing between adjacent passages is preferably not more than two hundred times greater than the overall thickness of the material of the element, and is preferably of the order of or less than one hundred times the overall thickness of the material, and may be fifty times the thickness.

Of course, the overall ratio between thickness and perforation spacing is affected by the absolute thickness of the material. For the majority of laminar elements in the region of 0.15 to 0.21 mm in thickness these limits apply. For material having a greater thickness it may be necessary for the perforation-to-thickness ratio to be significantly smaller depending on the nature of the material.

Embodiments of the present invention are primarily expected to be composed of a plurality of layers of relatively thin material, especially those embodiments made as encapsulated printed material for advertising posters. In such an application, one embodiment of which will be more particularly described with reference to the drawings, the said passages pass right through all the layers of a multiple layer element and open into both major faces thereof. Embodiments in which the passages are "blind" and open into one or other of the major faces may also be formed.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a part of a fireresistant element formed as an embodiment of the present invention; Figure 2 is a sectional view taken on the line II of II of Figure 1; Figure 3 is an exploded perspective view of an alternative embodiment of the invention; and Figure 4 is a perspective view of a single layer which may be used as one layer in an alternative embodiment of the invention.

Referring now to the drawings, Figures 1 and 2 show the structure of a composite laminar element suitable for use as an image-bearing layer of an advertising poster. The composite element, generally indicated with the reference numeral 11 comprises a central core layer 12 which may be of paper or card typically between .05 and .1 mm in thickness one face of which is printed with images (not represented) which defines the front face 13 of the core 12. Over the front face 13 is an encapsulating layer of laminating film comprising an outer layer 14 of polyester and an inner layer 15 of polyethylene which, upon manufacture, is heated to bond the core 12 to the covering layer 14 without loss of transparency.

A similar encapsulating layer of laminating film is adhered to the opposite face of the core 12, comprising an outer layer 16 of polyester and an intermediate layer 17 of polyethylene. The two polyester layers are of the order of 23 microns in thickness whilst the polyethylene layers are of the order or 14.5 microns in thickness.

In addition, the outer face of the "rear" polyester layer 16 is coated with an acrylic emulsion to form a layer 18.

the acrylic emulsion is applied at the rate of between 8 and 20 grams per square metre. As can be seen in both figures 1 and 2 the whole of the area of the element 11 is perforated with a plurality of transverse perforations 19 extending from the outer or front face of the front covering layer 14 to the external surface of the rear acrylic emulsion coating 18. As an example, in a material having a thickness in the region of 0.18 to 0.21 mm the perforations 19 are about 44 microns in diameter, with a tolerance of plus or minus three microns) and have a spacing of the order of 12.5 mm. The lower limit of material thickness is about 0.15 mm. Although no upper limit can be readily defined, an increase in material thickness would require larger perforations and a closer spacing in order to achieve the desired effect.It has been found that, surprisingly, perforations having a spacing as indicated above are all that is needed to lower the susceptibility of the element 11 to ignition sufficiently to meet the applicable regulations.

An alternative embodiment is shown in outline form in Figure 3. Here the central core 22 is shown with two laminating layers 23, 24 each of which may be formed, as in the embodiment of Figures 1 and 2, as a composite polyester/polyethylene lamination.

Extending across the whole of the inner face of each of the layers 23, 24 are a plurality of grooves 25,26 which extend approximately orthogonally of one another. It will be appreciated that when a composite layer such as that illustrated in Figure 3 is subjected to heating any gases evolved from the core material 22 or from the laminating layers 23, 24, can pass along the passages formed between the grooves 25, 26 and the facing surface of the core 22 and escape at the existing edges of the composite element without causing blistering or bubbling of the surface due to a build up in pressure.

Figure 4 illustrates a suitable core material having a plurality of interconnected passages throughout its body.

A suitable such material may, for example comprise a compressed fibre board 27 in which the fibres are all substantially orientated in one direction or primarily orientated in one direction. So as to form a plurality of substantially aligned passages allowing escape of gases evolved upon heating.

It has been established that a plastics coated selfadhesive paper advertising poster made as described in relation to Figure 1 meets the requirements for a Class 0 certificate of fire retardant effect under BS4761 providing the posters are affixed directly to a wall.

Claims

1. A method of treatment of a flammable laminar element to increase its resistance to combustion comprising the steps of forming a plurality of passages in the material to allow gases and/or vapours given off upon a rise in temperature to dissipate without resulting in substantial delamination of the element or collection of gases or vapours into combustible quantities.

2. A method of treatment as claimed in Claim 1, in which the passages are formed as perforations extending transversely of the general plane of the element.

3. A method of treatment as claimed in Claim 2, in which the perforations are spaced over substantially the whole of the area of the element.

4. A method of treatment as claimed in Claim 2 or Claim 3, in which the perforations have a spacing up to about 200 times the thickness of the material.

5. A method of treatment as claimed in Claim 4, in which the material has an overall thickness not less than 0.15 mm and the spacing of the perforations is in the region of 12.5mm.

6. A method of treatment as claimed in any of Claims 2 to 5, in which the perforations pass right through the material opening into each of the front and rear major faces thereof.

7. A method of treatment as claimed in any preceding claim in which the said passages are formed between adjacent layers of the material by means of a plurality of ridges or other surface projections or asperities on at least one face of at least one of the said layers.

8. A method of treatment as claimed in Claim 7, in which two facing surfaces of adjacent layers of material are formed with a plurality of channels or grooves with the channels or grooves of one surface being non-parallel to the channels or groove of the other whereby to form a plurality of channel or groove intersections over the area of the element.

9. A fire resistant flammable laminar element having a plurality of passages therein for allowing the dissipation of gases or vapours given off by the or a material of which the element is composed when the material is subjected to a rise in temperature above a certain threshold value.

10. A fire resistant flammable laminar element as claimed in Claim 9, in which the passages extend generally orthogonally of the major faces of the element.

11. A fire resistant flammable laminar element as claimed in Claim 10, in which the said passages open into one or the other of the major faces of the element.

12. A fire resistant flammable laminar element as claimed in Claim 10 or Claim 11, in which the said passages pass right through all the layers of the element and open into the major faces thereof.

13. A fire resistant flammable laminar element as claimed in any of Claims 10 to 12, in which the spacing between adjacent passages is not more than too hundred times greater than the overall thickness of the material of the element.

14. a fire resistant flammable laminar element as claimed in Claim 13, in which the spacing between the passages is of the order of one hundred times the overall thickness of the material of the element.

15. A fire resistant flammable laminar element as claimed in Claim 9, in which the said passages extend generally parallel to the major faces of the laminar element.

16. A fire resistant flammable laminar element as claimed in Claim 15, in which the element has a central core of gas-permeable material and facing layers of substantially impermeable material.

17. A fire resistant flammable laminar element as claimed in Claim 15, in which the passages are defined by surface asperities on at least one of two facing surfaces of adjacent layers.

18. A fire resistant flammable laminar element as claimed in Claim 17, in which the surface asperities are on both surfaces.

19. A fire resistant flammable laminar element as claimed in Claim 16 or Claim 17 in which the surface asperities are generally parallel ribs or grooves.

20. A fire resistant flammable laminar element as claimed in Claim 19, in which the ribs or grooves on one surface are non-parallel with the ribs or grooves of the facing surface of the adjacent layer.

21. A fire resistant flammable laminar element as claimed substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

22. A method of treatment of a flammable laminar element, substantially hereinbefore described with reference to, and as shown in, the accompanying drawings.