The seal in question is intended to be mounted on fixed frames of fire-breaker dividing elements or fixtures so as to restrict the spread of fire.

In particular, the novel system according to the present invention is particularly suitable for use for the manufacture of internal dividing walls and movable fixtures, such as doors, windows, French windows, skylights, portholes or the like.

Background art The current trend in the fire prevention sector is that of containing outbreaks of fire within closed spaces with the twofold object of preventing the fire from spreading into areas not yet attacked by the fire and of suffocating the fire at its outbreak by restricting the entry of the comburent air needed to fuel it. For this purpose, all the communicating fixtures in the environments to be isolated are made of heat and fire-resistant material.

The resistance of fixtures to fire is measured according to regulations. In general, said regulations envisage heating one side of the fixture according to a predefined cycle and measuring at the same time the increases in temperature detected on the opposite side.

Hereinafter, the term"fixture"is understood as referring to dividing elements comprising a supporting structure formed by elongated elements, which are joined together integrally, and flat buffer panels fixed thereto. Said dividing elements may be of the fixed type, for example internal dividing walls, or may comprise a fixed part or frame and an openable, movable part, which is operatively connected thereto by means of hinges, such as, for example, doors, windows, portholes,

skylights or the like.

The elongated elements are generally made of metal-typically aluminium- obtained by means of extrusion, or are in the form of sections or box-shaped elements-typically made of steel-obtained by bending and welding metal sheets.

The elongated elements may also be made of extruded plastic material which is rigid at normal working temperatures, such as PVC.

In order to increase the flexural rigidity, all the elongated elements are shaped so as to obtain cross-sections which have a high moment of inertia and contain cavities which extend in the direction of their length. Some of said cavities communicate with the outside, others are completely enclosed inside the section and are not visible from the outside.

The flat buffer panels may also be opaque or transparent, these latter being formed by stratified elements comprising several superimposed sheets of transparent material, for example glass, with, arranged in between, a material- also transparent and with intumescent characteristics-intended to join together the individual sheets.

The term"intumescence"is understood as referring to the property of a material to form a large-volume insulating foam when it is subjected to high temperatures. By retaining gas inside it, said foam, which is solidified and partially ceramicized, increases resistance to the transmission of heat both by means of conduction and irradiation and, moreover, retains any cracked parts.

A drawback of said known embodiments is posed by the high thermal conductivity of the metal structure: the temperatures on the side not exposed to the fire quickly reach values in excess of those required by the regulations.

Moreover, the metal structure deforms under the effect of the heat coming from

just one side, causing the opening of cracks into which air may pass, which further fuels combustion, or through which the fire may spread to adjacent areas.

In the case of structures or frames constructed with materials having a low melting point, such as polymer materials, the frame may be totally destroyed by the fire.

According to the prior art, in order to overcome said problems, rigid elongated elements made of refractory material, which retains significant residual mechanical properties even when exposed to flame temperatures, are associated with the elongated elements which form the frames of the fixtures. For example, W09707315 describes frames comprising suitably shaped rigid bars which are made of calcium silicate and are inserted into the internal longitudinal cavities of the sections which form the frames.

In the event of exposure to flame, calcium silicate, a refractory material, retains a rigidity which is able to prevent deformation of the metal and ensure that the fixture remains intact for longer.

Moreover, being a thermal insulator, the speeds of the increase in the temperatures measured on the side not exposed to the fire are lower.

A drawback of said known embodiment consists in the rigidity of the refractory element which must be preconstructed with a cross-section suitably shaped so as to be associated with the metal section and which must be inserted into and associated with it before the construction of said fixture; consequently, during construction of the fixture, it is also required to cut, together with the section, the refractory element included therein and associated therewith, a difficult operation which creates a large quantity of irritating dust and premature wear of the cutting element.

A fixture according to said prior art may be preconstructed in the workshop but the product obtained is extremely heavy and, in the case where suitable mechanical

lifting means cannot be used, transportation, positioning and installation are not easy.

Seals which are based on the intumescent property of suitably treated graphites, present in mixtures also comprising thermoplastic polymers, flame retardants, inorganic fillers, and ceramicizing agents, are known for sealing cracks in fire- breaker structures.

Italian Patent application Vl2000A000272 describes a seal of the abovementioned type containing inside it a reinforcing mesh made of metal or a composite material.

The mechanical support for the seals of the abovementioned type may also be obtained by means of a tubular-shaped external sheath having the intumescent mixture inserted inside it.

Patent application EP 1132563 describes a sealing strip obtained by means of the extrusion of a mixture, which comprises thermoplastic polymers, treated graphite, flame retardants and an inorganic additive capable of forming a ceramic material at working temperatures, inserted into a triple sheath made of a thermoplastic polymer, again obtained by means of extrusion, with added flame retardants.

Other seals of this type are, for example, described and claimed in EP 745751, EP 509701, GB 2079669, GB 2202484 and US 4931339.

A drawback of said known seals consists in their high thermal conductivity, due mainly owing to the presence of graphite, which leads to temperatures in excess of the values required by the regulations being reached quickly.

GB 2092214 describes a seal, to be associated with the elongated metal elements which form the structure of the fixture, formed by an external part made of rigid PVC and an internal part which has intumescent characteristics and is made of solid hydrated sodium silicate, said seal comprising all the characteristic

features according to the preamble of Claim 1.

A drawback of said known seal consists in the rigidity of the constructional form, which must necessarily be shaped with a cross-section such that it can be associated with the section.

Another drawback consists in the purely thermoplastic nature of the external part which forms a sheath and which has the sole function of protecting the sodium silicate from the action of the air.

A further drawback resides in that the solid hydrated sodium silicate is a friable solid which is not suitable for being deformed and undergoing elasto-plastic deformations, which are typical in use as a seal.

Disclosure of the invention The main object of the present invention is therefore that of overcoming all the drawbacks of the abovementioned prior art by providing an intumescent seal which is provided with a suitable resistance to mechanical stresses, in particular as a result of fire phenomena, and is obtained by means of an alternative solution to those described above.

Another object of the present invention is that of providing an intumescent seal which may be associated with a fixture after the construction thereof.

Another object of the present invention is that of providing an intumescent seal with notable thermal insulation properties.

Another object of the present invention is that of providing an intumescent seal provided with significant flexural rigidity after expansion as a result of the increase in temperature.

Another object of the present invention is that of providing an intumescent seal with a degree of plasticity such that it can be used to fix glass panels and absorb impacts as a result of lamming.

Another object of the present invention is that of providing a seal which may be easily associated with preconstructed fixtures by adapting its shape to the profiles of the cavities of the elongated metal elements.

Yet another object of the present invention is that of providing a seal having predefined expansion and heat resistance characteristics according to the design.

A further object of the present invention is that of providing an intumescent seal which is constructionally simple and totally reliable from an operational point of view.

These and other objects, are all achieved by an intumescent seal which may be inserted in seats in frameworks or frames of fixtures, in particular of the fire- breaker type, comprising: - at least one sheath G which is intended to be inserted inside said seats, said sheath being substantially tubular so as to define inside it a containing chamber C; - an intumescent mixture M which is capable of expanding under the effect of heat and may be inserted inside said containing chamber C of said sheath G; characterized in that said intumescent mixture M comprises an aqueous solution of alkali metal polysilicate and colloidal silica dispersed in water. The alkali metal polysilicate is selected from within the family which comprises sodium polysilicate, potassium polysilicate, lithium polysilicate or mixtures thereof, the intumescent mixture M, which may be inserted inside said sheath G, has a molar ratio, SiO2/Me2O, of between 3 and 6 and is preferably close to 4.5 and the water content of said intumescent mixture M is between 40% and 65% and is preferably close to 60% by weight.

A further aspect of the invention envisages a method for the manufacture of an intumescent seal according to Claims 1 to 15, which comprises the following operative steps: a) provision of a substantially tubular sheath G which defines a containing chamber C; b) preparation of an intumescent mixture M which is capable of expanding under the effect of heat; c) degassing of said intumescent mixture M with the extraction of at least one part of water in the vapour phase; d) filling of said containing chamber C with said intumescent liquid mixture M; characterized in that the preparation of said intumescent mixture M is performed by means of a step e) involving mixing in a container an aqueous solution of alkali metal polysilicate with colloidal silica dispersed in water.

A further aspect of the invention envisages a plant for implementing the method according to one or more of Claims 16 to 18, comprising: - retaining means 11 intended to support a sheath G which is substantially tubular and has a containing chamber C, so as to keep a top end thereof open; - mixing means comprising at least one container 12 for mixing an aqueous solution of alkali metal polysilicate and colloidal silica dispersed in water so as to form an intumescent liquid mixture M ; - degassing means 16 connected to said container and/or said retaining means so as to subject said intumescent liquid mixture M to a reduced pressure with the consequent extraction of dissolved gases and a part of water in the vapour phase; - circulating means 15 for transferring said degassed intumescent liquid mixture M from said container 16 to said chamber C, characterized in that said mixing means comprise means for introducing an aqueous solution of alkali metal polysilicate with colloidal silica dispersed in water into said container 12.

Owing to the seal according to the invention, the risks of smoke and/or firespreading between the various rooms of buildings in the event of fire are reduced significantly. In fact, the improved heat resistance and mechanical strength characteristics allow said seal to reduce the temperatures on the side of the fixture which is not exposed to the fire, increase the strength of said fixtures and remain in position so as to seal doors, windows or cable ducts even in the presence of strong pressures or reduced pressures as result of fire.

Brief description of the drawings Further features and advantages of the invention will be more clearly understood from the detailed description furnished by way of a non-limiting example with he aid of the accompanying drawings in which: FIGS. 1 to 5 show cross-sections of a few examples of embodiment of an intumescent seal according to the invention; FIGS. 6 and 7 show a schematic perspective view of another embodiment; FIG. 8 shows a functional diagram of a mode of implementation of the method for manufacturing the intumescent seal which forms the subject of the present invention.

Detailed description of a preferred embodiment With reference to the attached drawings, Fig. 1 shows, by way of example, a possible embodiment of the seal according to the present invention denoted in its entirety by the number 1. The seal comprises an external sheath G, which is made of thermoplastic material and defines a containing chamber C, and an intumescent mixture M which is inserted inside the chamber C.

The intumescent mixture M comprises alkali metal polysilicate and colloidal silica.

Alkali metal polysilicate has a fairly complex structure which is normally represented in the form xSi02yMe20 zH20, in which xSi02 denotes the silicic acid component, yMe20 denotes the basic component of the alkali metal oxide, generally lithium, sodium or potassium, and zH20 denotes the hydration water.

The type of polysilicate is defined by means of the molar or weight ratio, SiO2/Me2O, between the silica content and oxide content of the alkali metal.

In the following description, the term"alkali metal polysilicate"will be used to denote a compound of the type indicated above having a molar ratio, SiO2/Me20, of between 1.5 and 25.

It is known that when water is present in the system xSi02-yMe20-zH20 in large quantities, for example about 90% by weight, it also acts as a solvent and the alkali metal polysilicate remains liquid, while when it is present in smaller quantities, for example up to 65% by weight, it acts as a copolymerizer and the solution solidifies. In fact, when water is removed from a diluted aqueous solution of alkali metal polysilicate, for example by means of natural evaporation or by means of heat, the hydrated alkali metal polysilicate passes from the liquid form of an aqueous solution to the solid gel form, retaining a considerable quantity of hydration water.

If the quantity of water is reduced further, the hydrated alkali metal polysilicate has the form of a friable solid.

According to the present invention, the liquid mixture M is obtained by mixing a solution of hydrated alkali metal polysilicate and colloidal silica dispersed in water and has a molar ratio, SiO2/Me2O, of between 3 and 6, a water content of between 40% and 65% by weight and a final density preferably greater than 1,300 kg/m3.

Advantageously, in order to increase the wettability and the gelifying property of the liquid mixture M, up to 10% by weight of glycols and/or up to 10% by weight of silanes and/or up to 10% by weight of saccharides are introduced.

Conveniently, according to the present patent, the mixture M is obtained by mixing colloidal silica dispersed in water with an aqueous solution of liquid alkali metal polysilicate.

The aqueous solution of liquid alkali silicate and the solution of colloidal silica used for preparing the mixture M are easily found on the market.

In fact, solutions of sodium and/or potassium silicate in water, having concentrations of between 25% and 50% by weight and Si02/Me20 ratios of between 1.5 and 4, are available on the market.

The colloidal silica consists of sub-microscopic particles-having a diameter in the region of 10 nm-of amorphous silica dispersed in water. Dispersions with a variable silica content of between 15% and 50% by weight, typically used to form ceramic bonds in fibres or refractory materials, are commercially available.

Table 1 shows some illustrative, non-limiting examples of compositions of alkali metal polysilicate solutions (of sodium, potassium, lithium or a mixture thereof) and colloidal silica.

Table 1 Composition (% by weight) Sodium polysilicate Na20 27.8 Sitz 8. 3 Molar ratio Si02/Na20 3.45 Potassium polysilicate K20 23.7 Si02 10.5 Molar ratio Si02/K20 3. 54 Colloidal silica 30 Na2O 0.3 Si02 30 Colloidal silica 40 Na20 0.4 Sitz40 Table 2 shows some illustrative, non-exhaustive examples of preferred formulations for the formation of the mixture M.

Table 2 Composition (% by weight) Formulation 1 Sodium polysilicate 91 SiO2 28 Colloidal silica 30 9 Na20 7.6 Water 64.4 Si02/Na2O (molar) 3.8 Formulation 2 Sodium polysilicate 90 Si02 29 Colloidal silica 40 10 Na2O 7.5 Water 63.5 Si02/Na2O (molar) 4 Formulation 3 Sodium polysilicate 65 Si02 32 Colloidal silica 40 35 Na20 5.5 Water 62.5 SiO2/Na2O (molar) 6 Formulation 4 Sodium polysilicate 75.3 SiO2 30.7 Colloidal silica 40 24.7 Na20 6.3 Water 63 Si02/Na2O (molar) 5 Formulation 5 Potassium polysilicate 94 Si02 24 Colloidal silica 306 K20 10 Water 66 Si02/K20 (molar) 3.8 Formulation 6 Potassium polysilicate 90 Si02 24 Colloidal silica 30 10 K20 9.5 Water 66.5 SiO2/K20 (molar) 4 Formulation 7 Potassium polysilicate 70 Si02 29 Colloidal silica 40 30 K20 7 Water 64 SiO2/K2O (molar) 6 Formulation 10 Potassium polysilicate 80 SiO2 27 Colloidal silica 40 20 K20 8 Water 65 Si02/K20 (molar) 5.3

Advantageously, the mixture M is introduced in liquid form into the cavity C, which it easily fills even in the case of very complex or elaborate cross-sections. Moreover, it perfectly encapsulates any reinforcing elements 2 arranged inside the cavity.

Conveniently, said reinforcing elements 2 are arranged in the cavity C before introduction of the liquid mixture M.

At room temperature, the mixture M passes from the solution form to the gel form within a few dozen hours and without losing water, encapsulating in the gel all the water present. The passage from the liquid form to the gel form is favoured by high molar ratios, Si02/Me2O, of over 3.5.

A friable solid end product is obtained by means of the simple drying of the liquid mixture to a final water content of below 30% by weight.

The solid gel form retains a significant plasticity over time allowing a seal having a

plastic sheath G to adapt itself to the profiles to which it is joined. Moreover, being a solid, the intumescent mixture M does not leak even in the event of accidental local breakage of the sheath.

In the event of exposure to fire, the large quantity of water retained in the gel, by absorbing heat, helps increase further the strength of the fixture on which it is applied and reduce the values of the temperature on the unexposed side.

The intumescent properties desired for the specific application are obtained by varying the quantity of residual water in the mixture M.

According to an embodiment of the present invention, the sheath G may be easily deformed. The intumescent seal 1 obtained is plastic and is able to adapt its shape to the profile of the cross-section with which it must be associated.

Conveniently, the sheath G is made of thermoplastic polymer material, elastomer polymer material, thin metal-for example aluminium-sheets, or a combination thereof.

According to another embodiment of the novel system according to the present invention, the sheath G, made of polymeric material, is rigid and has a cross- section of predetermined form.

The polymer material may be of the thermoplastic or elastomer type or a combination thereof.

According to another embodiment of the novel system according to the present invention, the sheath G, made either of easily deformable material or rigid material, contains a reinforcing element 3, which is at least partially embedded inside it.

According to a preferred embodiment of the present invention, the reinforcing elements 2 and 3 are formed by a mesh or lattice of composite material having a high mechanical strength.

Such composite material may be formed, for example, by glass fibres or carbon fibres.

Alternatively, said mesh may also be obtained with a lattice of metallic material, and in particular iron, in which the filaments which form the meshes are less than a millimetre thick.

Advantageously, the meshes of the lattice may have a width L of between 1 and 5 mm.

According to another embodiment of the present invention, shown in Figures 6 and 7, the sheath G is folded in such a way as to form a structure having an almost toroidal cross-section with an opening 4. Conveniently, said form may be used for protecting long elements, such as cables, pipes or the like, from fire.

Advantageously, the sheath G is obtained by means of drawing. A traditional auger or endless screw forces a mixture comprising polymeric material, expanding graphite and one or more flame-retardant substances, of an organic and/or inorganic nature, to pass through an extruding head which is generally heated to between 130° and 170°. As a result of this process, the abovementioned mixture therefore takes on the form of a shaped body having a thickness, form and size suitably designed for the specific use.

With reference to the drawing shown in the attached Fig. 8, a functional diagram of a plant for the manufacture of heat-resistant intumescent seals according to the invention has been denoted by 10. Said plant comprises retaining means 11 intended to support the external sheath G in a preferably vertical position so as to facilitate the filling of the containing chamber C, a container 12 which is intended

to receive an aqueous solution of alkali metal polysilicate and colloidal silica dispersed in water and with which heating means 13 are operatively associated so as to increase the temperature of the solution contained therein, and stirring means 14 for mixing the abovementioned components inside it, resulting in the formation of an intumescent liquid mixture M.

The plant also comprises circulating means 15 for transferring the intumescent liquid mixture M from the container 12 to the chamber C.

According to a further characteristic feature of the present invention, the plant 10 is provided with degassing means 16 for performing the extraction, in the vapour phase, of at least a part of the water and the gases dissolved inside the intumescent liquid mixture M. These means 16 are advantageously formed by a duct 17, which connects the top part of the container 12 to the degassing means 16, a valve 18, which regulates the reduced pressure in the container 12 and is located on the duct 17, and suction means 19, which are associated with the duct 17 so as to subject the container 12 to the desired negative pressure (degree of vacuum).

The quantity of water removed in this way is governed by the desired intumescent properties.

In use, the plant 10 described hitherto from a mainly structural point of view operates in the manner described hereinbelow.

Initially, the sheath G is arranged between the retaining means 11 which have the function of keeping it vertical.

The container 12 is then filled to the desired level with the alkali metal polysilicate solution and the aqueous dispersion of colloidal silica, which are then mixed together by means of the stirring means 14.

Advantageously, the mixture M may be brought to the required temperature at the same time by means of the heating means 13.

At the same time as the heating or alternatively in subsequent steps, the degassing means 16 perform extraction, by means of the suction means 19, of the gases contained in the liquid and part of the water, in the vapour phase, through the second duct 17.

Once these operations have been completed, the opening of at least one valve 20 arranged on the duct 15 is actuated. The mixture M is conveyed by means of the circulating means 15 into the containing chambers C.

At this point, the process of solidifying the mixture M into a gel begins, this process lasting for several days and ending when the seal is already in use.

The present invention also comprises a method for the manufacture of heat- resistant seals, which may advantageously be achieved by means of the plant described above, to which reference will be made in the following description by way of example.

The method according to the invention comprises the following operative steps: a step involving the provision of an internally hollow sheath so as to define the corresponding containing chamber C; a step involving mixing, in the chamber 12, the aqueous solution of alkali metal polysilicate with the colloidal silica dispersed in water, preferably with a molar ratio, Si02/Me2O, of between 3 and 6, resulting in the formation of the intumescent liquid mixture M preferably having a density greater than 1,300 kg/m3 ; a step involving degassing of the mixture M; a step involving filling of the containing chambers C with the mixture M; a step involving hardening of the mixture M inside the chambers C.

However, a step involving heating of the intumescent liquid mixture M by means of the heating means 13 may also be envisaged, so as to assist the degassing and

increase the speed of polymerization.

The gases present in the mixture M, which were introduced or dissolved in the preceding treatments or were present in the starting solutions as bought from the supplier, and a quantity of water are extracted by means of the degassing step so as to obtain a mixture M with the intumescent properties desired for the specific application for which it is intended.

The degassing takes place by subjecting the intumescent liquid mixture M to a reduced pressure, preferably in the range of 20 to 500 millibars.

The seal 1 may be advantageously mounted between a movable leaf and a fixed frame of a fixture or arranged around the edge of a fixed frame so as to receive the leaf of a door.

Obviously, the abovementioned seal 1 may also be used on fixtures of any other type and may also be used between several fixed panels for dividing spaces inside rooms.

For this purpose, suitable adhesion means, which are formed for example by means of a layer of adhesive material and allow the seal to be installed easily, may be provided on a flat side of the seal 1.

In particular, the seal shown in Figs. 6 and 7 may be wrapped around cables and/or pipes in ducts formed in walls and/or panels.

The invention thus conceived therefore achieves the intended objects.