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(11) | EP 0 335 015 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Self-extinguishing polymeric sheet and large transparent surfaces obtained by means of the combination of a plurality of said sheets |
| (57) The invention is concerned with a self-extinguishing polymeric sheet (1) and with
the large transparent surfaces (12, 13) which are obtained by combining a plurality
of said sheets (1). The self-extinguishing polymeric sheet (1) comprises a transparent
central portion (2) co-extruded together with mutually opposite edges (3, 4) provided
with means (3, 4) for fastening the sheet to other adjacent sheets. The material forming
the edges (3, 4) is highly filled with flame-retarding substances, whilst the material
forming the central portion (2) is filled with said flame-retarding substances to
an only limited extent, in order not to endanger the transparency of the sheet (1).
The large transparent surfaces (12, 13) obtained by using said sheets (1) are chemically
interrupted by mutually perpendicular flame-stop sectors (14, 16, 17). |
[0001] The present invention is concerned with a self-extinguishing polymeric sheet, as well as with large transparent surfaces obtained by means of the combination of a plurality of said sheets.
[0002] During the past years, owing to reasons of convenience and cheapness, the large transparent surfaces (which were previously made from glass sheets), and usually present in the buildings for industrial use or for public use, have been realized by using a plurality of polymeric sheets, e.g., sheets of polycarbonate.
[0003] However, the experience has shown that the polymeric sheets are flammable and therefore, in the event of a fire, they contribute to feed the flames, with all the relevant consequences.
[0004] In order to obviate that drawback, it is known to add flame-retarding substances to the polycarbonate used in order to produce the sheets by extrusion, with such flame-retarding substance being added in variable percentages, according to the degree of self-extinguishability which one wishes to achieve.
[0005] But the so-obtained self-extinguishing sheets of polycarbonate suffer from the drawback that with increasing degrees of self-extinguishabiliyt, the degree of transparency decreases, until substantially opaque products are obtained, which therefore are no longer useable in order to realize large transparent surfaces.
[0006] According to the present state of the art, it is therefore impossible to obtain sheets, or, better, large transparent surfaces, which are self-extinguishing, and at the same time show a satisfactory degree of transparency.
[0007] The purposes of the present invention consist in providing a type of sheet, and hence a large transparent surface formed by a plurality of said sheets, which is capable of obviating the above-said drawbacks, by being both self-extinguishing and transparent.
[0008] Such purposes are achieved by a self-extinguishing polymeric sheet which comprises a transparent central portion co-extruded jointly with mutually opposite edges provided with means for fastening the sheet to other, adjacent, sheets, characterized in that the material which forms at least one of the edges is filled with such a substance as to make said edges self-extinguishing.
[0009] The invention is illustrated for merely exemplifying, and non-limitative, purposes, in the figures on the hereto attached drawing tables.
Figure 1 shows a perspective and partial view of a sheet according to the invention;
Figure 2 shows a plurality of sheets of Figure 1, combined with one another in order to form a large transparent surface;
Figure 3 shows a plurality of sheets of Figure 1, used in order to form a large transparent surface provided with an openable portion, e.g., a window.
[0010] Referring to the above cited Figures, the self-extinguishing polymeric sheet¹ according to the present invention comprises a central portion 2, comprised between two co-extruded edges constituted by a female element 3 and a male element 4.
[0011] The central portion 2 is formed by a couple of peripheral walls 5 and 6 united by a plurality of adjacent ribs 7, so as to form chambers 8 having a triangular cross-section.
[0012] The female element 3 is provided with a groove 9 having a "C"-shaped cross-section, and the male element 4 is provided with a protrusion 10 having a circular cross-section.
[0013] Also the female element 3 and the male element 4 are constituted by a structure formed by a plurality of chambers 8 bounded by ribs 7. The female element 3 and the male element 4 are obtained by co-extrusion already united to the central portion 2 along planes 11.
[0014] The material used in order to realize the female element 3 and the male element 4 is a polymer, e.g., a polycarbonate, having a molecular weight of ≧30,000, to which one or more of the hereinunder listed flame-retarding substances are added in such percentages as reported for indicative purposes, so as to obtain high values of self-extinguishability (e.g., a "VO" rating according to UL 94):
- decabromo-diphenyl-oxide at 5 ÷ 10%; or
- tetrabromo-bis-phenol A at ₅ ÷ 10% plus antimony trioxide at 1 ÷ 2%; or
- octabromo-diphenyl-oxide at 5 ÷ 10% plus polytetrafluoroethylene at 0.5 ÷ 1%; or
- methyl-tetrachloro-phthalamide at 4 ÷ 6%; or
- sodium hexafluoro-aluminate at 0.5 ÷ 1%; or
- sodium trichlorobenzene-sulphonate at 0.2 ÷ 1%; or
- bis-tribromo-phenoxy-ethane at 5 ÷ 10%;
and still others.
[0015] The male element and the female element obtained by adding the above-mentioned substances to polycarbonate, show poor characteristics of transparency. The material used in order to realize the central portion is also a polycarbonate having a molecular weight of ≧30,000, or another polymer, wherein however the hereinunder listed possible additions of chemical substances have been so studied as to preserve the characteristics of transparency, with rather good self-extinguing characteristics being anyway simultaneously secured (e.g., a "V2" rating according to UL 94): an oligomer based on tetrabromo-bis-phenol A at 3 ÷ 10%; or the potassium salt of phenyl-sulphone-3-sulphuric acid at 0.3 ÷ 0.5% with either sodium bromide at 0.1 ÷ 0.2% or potassium bromide at 0.1 ÷ 0.2% added. The percentage of transparency of the so-obtained self-extinguishing surface reaches a value of 80 ÷ 82%.
[0016] Additives can be added to the central portion in such a way as to still have rather good self-extinguishing characteristics ("V2" according to UL94), with a transparency of the manufactured sheet comprised within the range of from 80 to 82%, by using:
A) polycarbonate with a molecular weigh of approximately 30,000 to which blends or alloys are added of polymers which result to be flame-proof, in that during the combustion they release non-combustible gases (CO₂, water vapour) and because they reduce the possibility of contact between the material and the atmospheric oxygen;
B) polycarbonate having a molecular weight of 30,000, to which alloys or blends are
added of polymers, which are self-extinguishing owing to the fact that they alter
the same combustion process by capturing the OH free radical;
for example:
- PC having a molecular weight of 30,000 + 55 - 10 phr of PVC; or:
- PC having a molecular weight of 30,000 + 5 ÷ 10 phr of polysulphone (PS); or:
- PC having a molecular weight of 30,000 + 3 ÷ 6 phr of polyphenylene oxide (PPO);
or:
- PC having a molecular weight of 30,000 + 5 ÷ 10 phr of PC modified by means of the
bromine atoms (known on the market under the trade name "Calibre 700", by Dow Chemical).
[0017] Furthermore, all these additives can be added (instead of beig evenly dispersed throughout the central portion of sheet) concentrated as a thin, transparent external protective layer co-extruded parallelly to the same central portion 2 of the sheet 1.
[0018] When the sheet 1 is assembled, it shall be so positioned as to direct said external protective layer towards the room the flames are supposed to come from.
[0019] By combining a plurality of sheets 1, a large transparent surface can be formed, for example, such a surface as generally indicated by the reference numeral 12 (Figure 2). It is interesting to observe that the so-obtained large surface, even if, from a physical and a geometrical viewpoint, is one single sheet structure, it is chemically interrupted by a plurality of vertical flame-stop sectors 14 endowed with a high flame-extinguishing power, bounded by two mutually opposite joining planes 11, each one of which belongs to a respective sheet 1.
[0020] The surface 12 is completed in a conventional way by two side section bars 15, an upper section bar 16, a lower section bar 17, pads 18 and aluminum tape stripes 19.
[0021] According to the invention, both the upper section bar 16 and the lower section bar 17 are made from a polymer which has the same self-extinguishing power as of the vertical flame-stop sectors 14, so as to constitute horizontal flame-stop sectors 16-17 incident relatively to the vertical sectors 14.
[0022] Thus, the large transparent surface results to be subdivided into areas bounded by the elements 14, 16, 17 constituting sectors, beyong whose boundaries the possibly ignited flame is not capable of spreading, because it self-extinguishes when it comes to face with a considerably higher resistance to spread than as already found in the central portion 2 of each sheet 1.
[0023] According to a different from of practical embodiment depicted in Figure 3, the large transparent surface 13 is of the type comprising a window generally indicated by the reference numeral 20.
[0024] In this case too, according to the invention, the large surface 13 is provided with an upper section bar 16 and a lower section bar 17, both made from a self-extinguishing material corresponding to that of the vertical flame-stop sectors 14, and therefore constituting horizontal flame-stop sectors 16-17, indicent relatively to the vertical sectors 14.
[0025] In this case too, a fire front, which, in spite of all precautions, should succeed in spreading inside the interior of a sheet 1, is destined to extinguish in correspondence of the vertical flame-stop sector 14, and/or of the horizontal flame-stop sectors 16-17.
[0026] The large surface 13 is completed in the conventional way by section bars for the openable sheets 21, section bars for stop beads 22, pads 18, hinges 23, screws and brackets 24, stripes of aluminum tape 19.
[0027] It should be finally stressed that, inasmuch as at present sheets having more than two co-extruded edges of a material different from the material constituting the central portion of said sheet cannot be manufactured, the technical problem of creating mutually incident flame-stop sectors has been solved, on the contrary, by means of the section bars 16 and 17, with the structures relevant to the herein illustrated transparent surfaces 12 and 13 being obtained.
1. Self-extinguishing polymeric sheet (1) comprising a transparent central portion
(2) co-extruded jointly with mutually opposite edges (3, 4) provided with means (3,
4) for fastening the sheet (1) to other, adjacent, sheets, characterized in that the
material which forms at least one of the edges (3, 4) is filled with such a substance
as to render said edges (3, 4) self-extinguishing.
2. Sheet according to claim 1, characterized in that when it is joined to at least
another, similar sheet, in order to constitute a large transparent surface (12, 13),
it interrupts the continuity of said large transparent surface by means of a plurality
of flame-stop sectors (14, 16, 17).
3. Sheet according to claim 2, characterized in that the flame-stop sectors can be
positioned both horizontally (14) and vertically (16, 17).
4. Sheet according to claim 1, characterized in that also the material forming the
central, transparent portion (2) is filled with a flame-retarding substance, in such
a percentage that the characteristics of transparency of said central portion (2)
are not endangered.
5. Sheet according to claim 4, characterized in that the self-extinguishing substance
is concentrated as a thin, external protective layer co-extruded parallelly to the
central portion (2) of the same sheet (1).
6. Large transparent surface (12, 13) obtained by means of the combination of a plurality
of polymeric transparent sheets (1) according to one or more of the preceding claims,
with said sheets being mutually united, thus forming, from a physical and a geometric
viewpoint, one single sheet structure comprising side section bars (15), an upper
section bar (16), a lower section bar (17), pads (18) and aluminum tape strips (19),
characterized in that it is chemically interrupted by flame-stop sectors (14).
7. Large transparent surface according to claim 6, characterized in that the upper
section bar (16) and the lower section bar (17) constitute horizontal flame-stop sectors.
8. Large transparent surface according to claims 6 and 7, characterized in that the
horizontal flame-stop sectors (16-17) are incident relatively to the vertical flame-stop
sectors (14).