Field

This invention relates to a fire performance polymer composition, to articles formed of the fire performance polymer composition and methods of forming the composition and articles.

Background

The fire performance of building materials and the maintenance of power and communication in fire situations are critical to the safety of inhabitants and effective fire fighting. As a result many countries set standards for the performance of buildings under fire conditions. For example cables for critical applications are required to continue to operate under fire conditions to ensure the maintenance of power and communications. To meet some of the Standards cables must maintain circuit integrity when heated to a specified temperature (e.g. 650, 750, 950 or 1000 ⁰ C) for a specified period of time. It is also necessary to take into account that in order to be effective, fire insulation may need to provide protection from the effects of water jet sprays and turbulent gas flows encountered under fire conditions.

It is also desirable that a material used to impart fire resistance has acceptable mechanical strength for the intended application, following exposure to the elevated temperatures likely to be encountered in a fire situation, so that it can remain in place when subjected to the mechanical shocks and/or forces (e.g. from strong gas currents) associated with fire scenarios.

During the course of a fire the large proportion of the organic polymer components of a polymeric composition may undergo combustion to leave the particulate inorganic filler components of the composition as the main constituents of the remaining char. The remaining char is therefore generally very fragile and unable to provide effective heat insulation or barrier against a fire. The traditional solution to this problem has been to include a wrapping of inorganic webbing to retain the integrity of the inorganic material or to itself provide some insulation. This adds significantly the complexity and cost of manufacture.

In order to dispense with the need for a wrapping of inorganic webbing one option has been to use fillers which under the conditions of a fire form a ceramic to maintain the general shape and integrity of the original article in the ceramic residue. Our previous application WO 2004/035711 describes articles which have component which forms a fluxing oxide to provide a limited amount of a liquid phase in a fire to provide adhesion between particles of particulate mineral filler. Our previous Patent Publication WO/2004/088676 discloses a multilayer article having a layer which forms a glaze in a fire to maintain the structural integrity of the article.

While the use of glasses or compositions which form a glass can improve the structural integrity of a composition and dramatically improve fire resistance the presence of a glass liquid phase can present problems. During combustion the formation of a liquid phase and the generation of water as a product of combustion lead to a reduction in electrical resistance. This can result in failure of electrical systems and/or present a hazard to inhabitants. Further unless the amount of liquid phase is controlled it can cause severe distortion or shrinkage of the ceramic and in extreme cases will cause the whole filler component to fuse and be lost as a liquid.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary

We have now found that by using certain amounts of a specific phosphate glass together with silicate mineral filler a high electrical resistance can be maintained during a fire and a strong residue produced. Accordingly we provide, in one set of embodiments a fire performance polymer composition comprising:

(a) 15% to 60% by weight of the polymer composition of organic polymer; (b) 15% to 40% by weight of the polymer composition of phosphate glass composition;

(c) 15% to 40% by weight of the polymer composition of silicate mineral; and wherein the phosphate glass composition comprises (based on the weight of glass): 40% to 50% by weight phosphorous pentoxide;

1.5% to 2.5% by weight barium oxide; 25% to 35% by weight zinc oxide; and alkali metal oxide in an amount of up to 15% by weight of the phosphate glass composition.

In a further set of embodiments we provide a method of forming a polymer composition according to the above description comprising compounding the organic polymer with the phosphate glass and silicate filler to provide a homogenous composition.

In yet another set of embodiments we provide a cable comprising a conductor and an insulating layer formed of a fire performance polymer composition described above.

The cable may, for example, comprise a conductor and an insulating layer applied onto the conductor by extrusion.

Detailed Description

The term "organic polymer" is used herein does not include silicone polymers. Examples of organic polymers include polyolefins, ethylene-propylene rubber, ethylene- propylene terpolymer rubber (EPDM), chlorosulfonated polyethylene and chlorinate polyethylene, vinyl polymers, acrylic and methacrylic polymers, polyamides, polyesters, polyimides, polyoxymethylene acetals, polycarbonates, polyurethanes, natural rubber, butyl rubber, nitrile-butadiene rubber, epichlorohydrin rubber, polychloroprene, styrene polymers, styrene-butadiene, styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene-butadiene-styrene, epoxy resins, polyester resins, vinyl ester resins, phenolic resins, melamine formaldehyde resins and blends of two or more thereof.

The term "silicate mineral" includes aluminosilicates, magnesium silicates, calcium silicates and mixtures thereof. The preferred silicate minerals are calcium silicates, magnesium silicates, and mixtures thereof. It is particularly preferred in order to optimise resistance that the silicate mineral component comprises no more than 5% by weight of the silicate mineral component of alkali aluminosilicates.

Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps.

The composition contains a combination of phosphate glass and silicate mineral. We have found that the phosphate glass having a composition of 40% to 50% by weight phosphorous pentoxide; 1.5% to 2.5% by weight barium oxide; 25% to 35% by weight zinc oxide; and alkali metal oxide in an amount of up to 15% by weight of the phosphate glass composition; melts in the heat generated during a fire to generate a liquid phase which in turn will react with the silicate mineral, particularly a silicate mineral selected from calcium silicate, magnesium silicate and mixtures thereof, to form a crystalline solid at moderately high temperatures (e.g. in the range of about 500 ^Q C to 900 ^Q C). In this way the fire performance polymer composition maintains good thermal insulation despite the high glass content.

Glasses conventionally used in fire barrier compositions need to be used in limited amounts because their use as a high proportion of the total inorganic materials can lead to fusion of the inorganic materials or severe shrinkage and distortion. In contrast the phosphate glass composition is generally present as at least 20%, preferably 25% and more preferably at least 30% by weight of the inorganic components of the fire performance polymer composition. The glass will typically be up to 70% of the inorganic components (such as up to 65% or up to 60%) by weight of the inorganic components of the fire performance polymer composition. This relatively high proportion allows more effective interaction with the silicate mineral and yet, by virtue of the reaction with the silicate, severe distortion and shrinkage is avoided. Moreover the interaction of glass and silicate provides a relatively strong ceramic residue of crush strength of the order of at least 1 MPa or more.

Another significant advantage of the fire performance polymer composition is the relatively low conductivity of the composition under fire conditions. The transition of glass components to a liquid phase under fire conditions together with the loss of organic polymers often results in an increase in conductivity which can compromise the electrical insulation performance of insulating layers in cables and other electrical components. We have found that the phosphate glass composition and its interaction with the silicate during the elevation in temperature maintain low conductivity even during and after combustion of the organic polymer component of the composition. In order to optimise the low conductivity performance of the composition it is preferred that the composition comprise no more than 5% by weight of the phosphate glass of alkali aluminosilicate and preferably the total of aluminosilicate and alkali aluminosilicate is no more than 5% by weight on the weight of the phosphate glass. It is also preferred that the phosphate glass composition comprise no more than 15% by weight of alkali oxide based on the total weight of phosphate glass.

In one set of embodiments of the fire performance polymer the phosphate glass comprises in the range of from 5% to 15% by weight of alkali oxide based on the total weight of phosphate glass. Examples of alkali oxide components which may be present in the phosphate glass are the oxides of at least one alkali metal selected from the group consisting of sodium, potassium and lithium (Na ₂ O, Li ₂ O and K ₂ O). We have found that contrary to what might have been expected the fire performance polymer composition maintains low conductivity despite the presence of the alkali metal oxide components. The alkali metal oxide components also have the desirable effect of reducing the melting point of the phosphate glass composition.

The phosphate glass may be used in the fire performance polymer composition in any suitable form such as fibre frit or micro(nano)spheres. The use of frit is particularly preferred.

In one set of particularly useful embodiments of the fire performance polymer composition the melting point of the phosphate glass is in the range of from 35O ⁰ C to 600 ⁰ C (and preferably from 35O ⁰ C to 500 ⁰ C). The melting of the phosphate glass in this temperature range is preferred in this embodiment as the molten glass assists in maintaining the integrity of the insulating layer during the significant changes which occur during combustion of the organic polymer which generally commences at about 400 ^Q C. The phosphate glass composition reacts with the silicate (particularly calcium and magnesium silicates) so that on elevation of the temperature under fire conditions the phosphate glass provides a transient liquid phase before being transformed into a solid at elevated temperature in the range of about 500 ^Q to 900 ^Q C (preferably in the range of from 500-700 ⁰ C). This transformation from a softened glass to a partially crystallized one at moderate temperatures enables the ceramic residue to maintaining the structural integrity and dimensional stability at these temperatures.

In one aspect of this set of embodiments the phosphate glass comprises the alkali metal oxide in an amount of from 8% to 12% by weight of the phosphate glass.

The phosphate glass composition may comprise further components in addition to the phosphorous pentoxide, barium oxide, zinc oxide and alkali metal oxide.

It is generally preferred that the phosphate glass comprise less than 5% by weight of the phosphate glass of the total of oxides of antimony, lead and arsenic (and preferably less than 1 % by weight of the phosphate glass of the total of oxides of antimony, lead and arsenic). Although such glass components have been reported as useful by others they are not required to achieve the advantageous properties of the fire performance polymer.

The fire performance polymer composition may comprise alumina (AI ₂ O ₃ ) as part of the phosphate glass composition. The phosphate glass may for example further comprise alumina in an amount of up to 2% by weight of the total glass composition and preferably 1 to 2% by weight of the total phosphate glass composition.

The fire performance polymer composition may further comprise silica as part of the phosphate glass composition. The phosphate glass may, for example, comprise silica in an amount of up to 2.5% by weight of the phosphate glass composition and preferably 1 to 2.5% by weight of the phosphate glass composition.

The fire performance polymer composition may further comprise one or both of boron oxide and bismuth oxide. The phosphate glass composition may for example further comprise at least one or both of:

(i) boron oxide in an amount of up to 10% by weight of the phosphate glass

(preferably 1 to 10% by weight of the phosphate glass); and (ii) bismuth oxide in an amount of up to 5% by weight of the phosphate glass

(and preferably from 0.5% to 5% by weight of the phosphate glass).

In addition to mineral silicate fillers, a wide range of other inorganic fillers may be added. The composition may comprise an additional inorganic filler comprising an amount of up to 30% (preferably up to 20%) by weight of the total composition of at least one of metal (non alkali metal) hydroxides, metal (non alkali metal) oxides and metal (non alkali metal) carbonates. A fire performance polymer composition may for example comprise least one further filler selected from the group consisting of calcium hydroxide, magnesium hydroxide, calcium carbonate and magnesium carbonate in a total amount in the range of from 1 % to 20% (and preferably from 5 to 20%) by weight of the total fire performance polymer composition. The presence of larger amounts of filler selected from the group consisting of calcium hydroxide, magnesium hydroxide, calcium carbonate and magnesium carbonate results in reducing the ability of low-melting glass, to bind other particles together at low to moderate temperatures. This is a result of the reaction between the two components forming crystalline phosphates thereby depriving the ceramic residue of a low-melting phase at these temperatures. Aluminium hydroxide has the same adverse effect and the fire performance polymer composition thus preferably comprises less than 5% aluminium hydroxide based on the total weight of the polymer composition.

Other components may be incorporated into the compositions of the present invention. These other components include lubricants, plasticisers, inert fillers (e.g. fillers that are not the metal oxides that can react and/or sinter with the other inorganic components, or their precursors), antioxidants, fire retardant materials, fiber reinforcing materials, materials that reduce thermal conductivity (e.g. exfoliated vermiculite), chemical foaming agents (which serve to reduce density, improve thermal characteristics and further enhance noise attenuation), and intumescing materials (to obtain a composition that expands upon exposure to fire or elevated temperature). Suitable intumescing materials include natural graphite, unexpanded vermiculite or unexpanded perlite. Other types of intumescing precursors may also be used. The total amount of such additional components does not usually exceed 20% by weight based on the total weight of the composition.

Examples of further additives which may if desired be used in the fire performance composition include intumescent agents such as phosphates (e.g. organic phosphates or nitrogen containing phosphates such as ammonium polyphosphate), melamine, polyols such as pentaerythritol and mixtures thereof. Particulate materials which expand in a fire such as perlite and expandable graphite may also be useful in some embodiments.

Intumescing and/or expanding agents may be useful for example in gap filling applications where it is important to ensure a barrier is maintained in an intense fire. In other embodiments, such as the fire performance polymer compositions used in cable applications it may be preferred that the fire performance polymer composition maintain the dimensions of the uncombusted material and in this application organic intumescents may be deleterious although inorganic phosphates particularly ammonium polyphosphate may serve a useful role in maintaining shape and dimensions in accordance with the disclosure in our International Publication WO/2005/095545.

The composition of the invention comprises an organic polymer. An organic polymer is one that has an organic polymer as the main chain of the polymer. Silicone polymers are not considered to be organic polymers, however, they may be usefully blended with the organic polymer(s), as a minor component of for example less than 50% based on the amount of organic polymer, preferably less than 20% and most preferably less than 5% based on the amount of organic polymer. The organic polymer can be of any type, for example a thermoplastic polymer, a thermoplastic elastomer, a cross-linked elastomer or rubber, a thermoset polymer. The organic polymer may be present in the form of a precursor composition including reagents, prepolymers and/or oligomers which can be reacted together to form at least one organic polymer of the types mentioned above.

Preferably, the organic polymer can accommodate high levels of the inorganic components required to form the ceramic, whilst retaining good processing and mechanical properties. It is desirable in accordance with the present invention to include in the fire resistant compositions high levels of the inorganic components as such compositions tend to suffer reduced weight loss on exposure to fire when compared with compositions having lower levels of the inorganic components. Compositions loaded with relatively high concentrations of inorganic components are therefore less likely to shrink and crack when ceramified by the action of heat.

Organic polymers suitable for use with this invention include thermoplastic polymers, thermoset polymers, and (thermoplastic) elastomers. The organic polymer component may comprise one or more selected from the group of polyolefins, ethylene-propylene rubber, ethylene-propylene terpolymer rubber (EPDM), chlorosulfonated polyethylene and chlorinate polyethylene, vinyl polymers, acrylic and methacrylic polymers, polyamides, polyesters, polyimides, polyoxymethylene acetals, polycarbonates, polyurethanes, natural rubber, butyl rubber, nitrile-butadiene rubber, epichlorohydrin rubber, polychloroprene, styrene polymers, styrene-butadiene, styrene- isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene-butadiene-styrene, epoxy resins, polyester resins, vinyl ester resins, phenolic resins, and melamine formaldehyde resins.

The organic polymer chosen will in part depend upon the intended use of the composition. For instance, in certain applications a degree of flexibility is required of the composition (such as in electrical cable coatings) and the organic polymer will need to be chosen accordingly based on its properties when loaded with additives. Polyethylenes and ethylene propylene elastomers have been found to be particularly useful for compositions for cable coatings. Also in selecting the organic polymer account should be taken of any noxious or toxic gases which may be produced on decomposition of the polymer. The generation of such gases may be more tolerable in certain applications than others. Preferably, the organic polymer used is halogen-free.

The upper limit for the amount of polymeric components in the fire resistant composition tends to be influenced by the desired properties of the formulated composition. If the amount of the polymeric components exceeds about 60% by weight of the overall composition, it is unlikely that a cohesive, strong residue will be formed during a fire situation.

In one embodiment of the fire performance polymer composition the phosphate glass comprises:

40% to 50% P ₂ O ₅ 1.5% to 2.5% BaO

0% to 10% B ₂ O ₃ 25% to 35% ZnO 1 % to 2% AI ₂ O ₃ 1 % to 2.5% SiO ₂

5% to 15% alkali metal oxides comprising at least one selected from the group consisting of Na ₂ O, Li ₂ O and K ₂ O.

0% to 5% Bi ₂ O ₃

In a further aspect the invention provides a cable comprising at least one elongated functional element such as a conductor and at least one coating layer comprising the hereinbefore described fire performance polymer composition. Preferably the cable comprises a single insulation coating and the single insulation coating is formed of the fire performance polymer composition composition. The inner surface of the fire performance polymer composition layer may abut the functional element (such as one or more copper wires) and preferably the outer surface of the layer is free of further coatings or layers. The fire performance polymer composition layer is preferably applied to the at least one functional element by extrusion. One of the significant advantages of the composition of the invention is that it provides a combination of fire protection and sufficient strength, on exposure to an elevated temperature experienced under fire conditions, to allow cables to be prepared using a single insulating layer of the fire performance polymer composition. This has not generally been possible for compositions of the prior art as insulating compositions have generally been of insufficient strength to be self-supporting, to support the weight of the conductor and to withstand the conditions of water spray and gas turbulence encountered under fire conditions. As a consequence, the commercially available cables with high fire rating generally require a physical supporting and sealing layer to maintain the integrity of the insulating layer. Although such layers may be used with the composition of the invention, they are generally not required to provide a high fire rating.

On exposure of the composition of the invention to an elevated temperature experienced under fire conditions (to 100O ⁰ C) the residue remaining will generally constitute at least

40%, preferably at least 55% and more preferably at least 70% by weight of the composition before pyrolysing. Higher amounts of residue are preferred as this may improve the ceramic strength at all temperatures.

The compositions of the present invention may be provided in a variety of different forms, including:

1. As a sheet, profile or complex shape. The composition may be fabricated into these products using standard polymer processing operations, e.g. extrusion, moulding (including hot pressing and injection moulding). The products formed can be used in passive fire protection systems. The composition can be used in its own right, or as a laminate or composite with another material (for example, plywood, vermiculite board or other). In one application the composition may be extruded into shapes to make seals for fire doors. In the event of a fire, the composition is converted into a ceramic thus forming an effective mechanical seal against the spread of fire and smoke.

2. As a pre-expanded sheet or profile. This form has additional benefits compared with the above, including reduced weight and the capacity for greater noise attenuation and insulation during normal operating conditions.

3. As a mastic material which can be applied (for example from a tube as per a conventional silicone sealant) as a seal for windows and other articles.

4. As paint, or an aerosol-based material, that could be sprayed or applied by with a brush.

Specific examples of passive fire protection applications where this invention may be applied include but are not limited to firewall linings for ferries, trains and other vehicles, fire partitions, screens, ceilings and linings coatings for building ducts, gap fillers (i.e. mastic applications for penetration), structural fire protection [to insulate the structural metal frame of a building to allow it to maintain its required load bearing strength (or limit the core temperature) for a fixed period of time], fire door inserts, window and door seals, intumescent seals, and compounds for use in electrical boxes, in fittings, straps, trays etc that are attached to or used to house cables or similar applications.

Another area of application is in general engineering. Specific areas of general engineering, where passive fire protection properties are required, include transportation (automotive, aerospace, shipping), defence and machinery. Components in these applications may be totally or partially subject to fire.

When totally subject to fire, the material will transform to a ceramic, thereby protecting enclosed or separated areas. When partially subjected to fire, it may be desirable for a portion of the material to transform to ceramic, being held in place by the surrounding material that has not transformed to a ceramic. Applications in the transport area may include panelling (e.g. in glass fibre reinforced thermoplastic or thermoset composites), exhaust, engine, braking, steering, safety devices, air conditioning, fuel storage, housings and many others. Applications in defence would include both mobile and non- mobile weapons, vehicles, equipment, structures and other areas. Applications in the machinery area may include bearings, housing barriers and many others. The compositions of the present invention are especially useful as coatings for the production of cables for example they can be used for insulation or sheathing layers. The compositions are therefore suitable for the manufacture of electrical cables that can provide circuit integrity in the case of fire.

The fire performance polymer composition may be applied by conventional means such as extrusion. This extrusion of the fire performance polymer composition may be carried out in a conventional manner using conventional equipment. The thicknesses of the layers of insulation will depend upon the requirements of the particular standard for the size of conductor and operating voltage. Typically the insulation will have a total thickness from 0.6 to 3 mm. For example, for a 35 mm ² conductor rated at 0.6/1 kV to Australian Standards would require an insulation thickness of approximately 1.2 mm. The cable may include other layers such as a cut- resistant layer and/or sheathing layer. Furthermore, on exposure to elevated temperature experienced under fire conditions the compositions typically yield residue which is coherent and has good mechanical strength, even after cooling. The residue is self-supporting and will be retained in its intended position rather than fracturing and being displaced, for example, by mechanical shock. In this context the term "residue" is hereinafter intended to describe the product formed when the composition is exposed to an elevated temperature, experienced under fire conditions. Generally an elevated temperature of 1000 ^Q C for 30 minutes is sufficient to covert fire resistant compositions of the invention to residue. Desirably, as well as providing thermal insulation and/or a coherent physical barrier or coating, compositions in accordance with the present invention may also exhibit the required electrical insulating properties at elevated temperatures.

The ceramic formed on exposure of compositions of the present invention to an elevated temperature experienced under fire conditions has a flexural strength of at least 0.3 MPa, preferably at least 1 MPa and more preferably at least 2 MPa. It is a distinct advantage that the compositions are self-supporting, i.e. they remain rigid and do not undergo heat.

Brief Description of the Drawings

Figure 1 is a perspective view of a particularly preferred embodiment of the cable of the invention in which the composition of the invention forms a single insulating layer about a conductive element.

Figure 2 is a perspective view of a fire performance article.

Figure 3 is a graph showing the variation in pH of liquors prepared from a series of glasses by heating 2g of each glass in 50 ml of distilled water and titrated with 0.001 N hydrochloric acid solution in accordance with Example 1.

Figure 4 is a graph showing the variation of strength with sintering temperature for a range of compositions detailed in Example 2.

Figure 5 is a graph showing the variation of shrinkage with sintering temperature for a range of compositions detailed in Example 2. Referring to Figures 1 and 2, Figure 1 shows the simple cable design which may be used with the fire performance polymer composition. The fire performance polymer composition forms an extruded insulation layer 2 about the conductor (1 ). The inner surface 2A of the insulation layer abuts the conductor and the outer surface 2B is free of further coatings.

Figure 2 shows a possible design for a fire performance article. The metal substrate 12 has a protective coating 16 of the fire performance polymer formed on the metal substrate by extrusion.

In order to examine whether or not a fire performance polymer composition is self- supporting we use the following test as our standard. The test involves specimens of nominal dimensions 30 mm x 13 mm x 2 mm (approximately) made from the composition which are placed on a rectangular piece of refractory so that their long axis is perpendicular to one edge of the supporting refractory block and a 13 mm long portion of each specimen is projecting from the edge of the supporting refractory block. The specimens are then heated at 12 ^Q C per minute to 1000 ^Q C and maintained at this temperature for 30 minutes in air. At all temperatures, the specimens of composition remain rigid and coherent without bending over the edge of the supporting block to a significant degree (i.e. providing a bending angle to the original position of less than 15 degrees). The resulting ceramic will preferably retain the shape the specimen had prior to exposure to elevated temperatures.

The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

Examples

Example 1 Three groups of glasses of compositions given in Tables 1 , 2 and 3 were prepared by mixing the raw materials in the required proportions and melting in platinum crucibles at 1100-1200 ⁰ C in an electric furnace. On completion of melting which required an exposure at the maximum temperature for about 1 hour, the glass melts were quenched in cold water to obtain fragments of approximately 0.5-5mm in size. They were then oven dried for about 12hrs at 105 ⁰ C and ground into fine powders passing through a 200 mesh sieve using an agate mortar and pestle.

Glass powder compacts of approximately 14.1 mm diameter and 5mm thickness were made by uniaxial pressing moistened glass powder under a load of -2000N. The powder compacts were oven dried for about 12hrs at 105 ⁰ C and sintered at one or more temperatures of 350, 375, 400, 420, 450, 475, 500, 525, 575 and 625 ⁰ C. The heating rate was 270-300°C/h and the holding time at the maximum temperature was 30min. After cooling down slowly to the room temperature they were visually examined for evidence of melting during sintering and the visual observations were confirmed by examining the microstructure using both optical and electron microscopy. All glasses except glass A1 re-melted at a temperature less than or equal to 600 ⁰ C.

Table 1 Compositions of the glasses (Group A) (%)

Glasses were tested for their solubility in water using 2g samples of crushed glass particles having a size range from 0.3 to 0.5mm. Each glass sample was heated to 98 ^Q C in 50ml of distilled water in a beaker and maintained at that temperature for 1 h using a hot water bath. After cooling down to room temperature and filtering to remove the glass particles, 25ml of the liquor obtained was titrated against a 0.001 N HCI solution and the change in pH of the mixture was recorded as a function of the amount of HCL solution added. The HCL solution was added at a rate of ~1 ml/min and the mixture was stirred continuously using a magnetic stirrer. A bottle glass and a commercially available glass labelled #3 were also tested in the same manner for comparison.

Figures 3 shows that the pH of liquors prepared using all new low melting phosphate glasses was neutral (i.e. close to 7) and decreased with the addition of HCI solution indicating that there was no any dissolved ion to neutralise the acid added. In contrast, the liquor obtained by boiling bottle glass and glass #3 in water had initial pH values in excess of 9. When HCI solution was added the pH of the mixture decreased progressively. This indicates that both bottle glass and glass #3 used for comparison had released a substantial amount of alkali ions into water.

These new glasses of extremely low solubility present a significant advantage over glass #3 in their use in ceramifying polymer compounds, particularly in the compounds intended for fire protection of electrical components. A soluble glass such as #3 has the potential to compromise the electrical resistivity of a ceramifying compound made using it, particularly when the polymer burns releasing water as one of the combustion products. This will not happen if the glass used as a flux is one of the new low melting phosphate glasses of low solubility. Example 2

This example examines the behaviour of the inorganic components of the invention to simulate the composition remaining on combustion of the organic polymer.

Binary inorganic mixtures containing 33.3% glass frit CO (chemical composition shown in Example 1 ) were prepared in which the balance of inorganic material was as was selected from Talc, magnesium hydroxide (MDH), Wollastonite (WoII) calcium silicate, clay (an aluminosilicate), Zinc Borate (ZnB), calcium carbonate (CaCO ₃ ) and aluminium hydroxide (ATH) in accordance with the heading of each column in the tables below.

Pellets of the compositions were made by uniaxial pressing the composition to 14.05 mm diameter and ~6-8mm thickness (high) under a 2OkN load.

The compositions were sintered for 30 min at the temperatures shown in the table and the dimensions and compressive load to fracture of the pellets were measured. Dimensions were measured using a venire calliper and the load to fracture was measured using an lnstron testing machine. Shrinkage and compressive strength were calculated from the above measurements.

Shrinkage after sintering (mm) Compressive strength (MPa)

Inorganic filler added to glass frit Inorganic filler added to glass frit

Sintering Sintering temp ( ⁰ C) Talc MHD WoII Clay ZnB CaC03 ATH temp ( ⁰ C) Talc MHD WoII Clay ZnB CaCO3 ATH

600 050 -085 036 1 42 000 -299 600 1 90 235 645 1 66 667 691 2 18 800 1 07 -085 057 1 21 299 -306 800 804 369 17 19 464 2099 1 88 763 1000 0 14 -2 14 -0 14 -427 085 -477 1000 1807 253 2244 472 - 051 548

Diameter after sintering (mm) Maximum compressive load before fracture (N)

Inorganic filler added to glass frit Inorganic filler added to glass frit

Sintering Sintering temp ( ⁰ C) Talc MHD WoII Clay ZnB CaC03 ATH temp ( ⁰ C) Talc MHD WoII Clay ZnB CaCO3 ATH

25 1405 1405 1405 1405 1405 1405 1405 600 14 12 1393 14 1 1425 1367 1405 1363 600 1188 1430 4028 1059 3915 4283 1274 800 142 1393 14 13 1422 1282 1447 1362 800 5095 2251 10783 2949 10836 1239 4447 1000 1407 1375 1403 1345 14 17 1338 1000 11237 1501 13874 2683 - 321 3084

The results show that the shrinkage is lowest and the strength is highest for the mixture of phosphate glass frit and wollastonite (a calcium silicate mineral). The performance was also good for the mixture containing talc (a magnesium silicate mineral) as well.

The mixtures containing a significant proportion of magnesium hydroxide (MDH) and aluminium hydroxide (ATH) did not show the same strength development at any temperature. Their shrinkage was much higher than that of mixture containing clay at both 600 and 800 ⁰ C. The strength development with clay was somewhere between that with ATH and MHD, but much inferior to the mixtures containing talc or wollastonite.

Although the mixture containing CaCO ₃ did not shrink (expanded somewhat at 800 ⁰ C), the strength at all temperatures remained relatively low (lower at higher temperatures).

Glass frit and ZnB mixture developed the highest strength at 600 and 800 ⁰ C, but formed a low viscous liquid at 1000 ⁰ C.

Example 3

This example illustrates the preparation of a fire performance polymer composition of the invention and forming an article thereof.

A compound of the invention is prepared using EPDM (Ethylene Propylene Diene Terpolymer - Nordel IP 3745), glass frit CO (chemical composition shown in Example 1 ), calcium silicate mineral (wollastonite - NYAD 400) and calcium carbonate (Omyacarb 2T). The composition of the compound is given in Table 1. Compounding of the polymer with the fillers is done by mixing the materials in a Haake Rheochord 600 internal mixer. The processing temperature is between 160 to 170 ^Q C. The polymer pellets are inserted into the mixing chamber and blended for about 3 min, increasing the rotor speed gradually from 10 to about 30 rpm. The filler mixture is then added progressively with small additions at a time and continued to mix for additional 15min. On completion of mixing the polymer blend is removed from the mixer and pressed into a flat sheet of about 2mm thickness by hot pressing at approximately 170 ^Q C for 15min under a pressure of approximately 7 MPa. Complete filling of the die cavity during hot pressing at such a low pressure as 7 MPa and absence of any cracks or other visible defects will indicate that the polymer composition is suitable for making articles by conventional polymer processing methods such as extrusion.

Table 1 : Fire performance polymer composition

Example 4 Compounds of the invention with the compositions given in Table 2 were prepared by mixing the polymer with the fillers in a Haake Rheochord 600 internal mixer. The processing temperature was between 160 to 170 ^Q C. Each compound and specimens thereof were prepared as described below.

The polymer pellets were inserted into the mixing chamber and blended for about 3 min, increasing the rotor speed gradually from 10 to about 30 rpm. The filler mixture was then added progressively with small additions at a time and continued to mix for additional 15min. On completion of mixing the polymer blend was removed from the mixer and pressed into a flat sheet of about 2mm thickness by hot pressing at approximately 170 ^Q C for 15min under a pressure of approximately 7 MPa. Table 2: Fire performance polymer compositions Em1 , Em2, Em3 and Em4 (weight %).

Specimens of nominal dimensions 29 mm x 14.5 mm x 2 mm, made from each of these compositions were fired at 500, 700 and 95O ⁰ C for 30 min. For each composition, the change in linear dimension (average for length and width) caused by firing and the flexural strength of the resultant ceramic, determined by three point bending a span of 18 mm, are given in Table 3.

Table 3: Change in dimensions and strength of ceramic formed by firing Em1 , Em2, Em3 and Em4 at 500, 700 and 950 ⁰ C.

Upon firing at the above given temperatures, all compositions produced ceramic residues free of cracks. The average strengths were more than 0.3 MPa and the change in linear dimensions were less than 5.5% for all compositions except Em2 which produced relatively weak residue at 500 and 700 ⁰ C.

Example 5

Compounds of the invention, with the compositions Em5, Em6 and Em7, given in Table 4, were prepared in a manner similar to those given in Table 2 under Example 4. The processing temperatures for Em5, Em6 and Em7 were 195, 155 and 17O ⁰ C respectively. On completion of mixing each polymer blend was removed from the mixer and pressed into a flat sheet of about 2mm thickness by hot pressing at a temperature within 5 ⁰ C from the processing temperature for 15min under a pressure of approximately 7 MPa. Composition Em7 was prepared by manually mixing at room temperature in a glass container. A flat sheet of about 2mm thickness was made by curing the blend at 5O ⁰ C in a steel mould under a pressure of approximately 7 MPa.

Table 4: Fire performance polymer compositions Em5, Em6 and Em7 (weight %).

Specimens of nominal dimensions 29 mm x 14.5 mm x 2 mm, made from each of these compositions were fired at 500, 700 and 95O ⁰ C for 30 min. For each composition, the change in linear dimension (average for length and width) caused by firing and the flexural strength of the resultant ceramic, determined by three point bending a span of 18mm, are given in Table 5.

Table 5: Change in dimensions and strength of ceramic formed by firing Em5, Em6 and Em7 at 500, 700 and 950 ⁰ C.

Upon firing at the above given temperatures, all compositions produced ceramic residues free of cracks. The average strengths were more than 0.3 MPa and the change in linear dimensions were less than 5.5% for all compositions except Em7 which produced relatively weak residue at the transitional temperature of 500 ⁰ C but produced a relatively strong residue at higher temperatures of the sort experienced in a fire.