This invention relates to a flexible intumescent sheet material for use as a fire seal, and to a method for making such a flexible intumescent sheet material.

Intumescent fire seals are well known. Typically such fire seals take the form of rigid boards and sheets, and cannot readily be applied directly to such structures as shaped doors or panels; neither can they effectively be used to fill or line many spaces.

It is an object of the present invention to provide a flexible intumescent sheet material which provides enhanced protection against fire damage, and which is sufficiently flexible to be capable of being shaped into plane and intricate forms for application directly to a wide variety of surfaces using simple cutting tools.

British patent application GB 2254609 describes,

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inter alia intumescent sheet or strip materials comprising ceramic fibres, exfoliating graphite and a polyvinylalcohol binder. Such strip or sheet materials may contain a quantity of glass fibres in addition to the ceramic fibres.

The present invention provides an improved flexible intumescent material which comprises an intumescent substance, manmade mineral fibres and an elastomeric binder.

The material is typically provided in sheet form, and it is to be understood that the term sheet as used herein includes the case where the material is in strip form.

The manmade mineral fibres typically are present in an amount of at least 15%, more preferably 20%, by weight of the total weight of the intumescent material. For example, the manmade mineral fibres may be present in an amount of between about 15% and 70% by weight of the total weight.

The manmade mineral fibres may be formed from fusible slag, natural rocks and minerals, igneous rocks, basalt, diabase or olivine, and particular examples of manmade mineral fibres are rockwool fibres and glass fibres.

The elastomeric binder can be selected from, for example, an acrylic latex, a styrene butadiene latex, a synthetic rubber latex, polyvinylacetate and polyvinylidine dichloride. The amount of elastomeric binder present in the intumescent materials can be from about 8% to about 40% by weight of the total weight of the

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sheet material. For example, the amount of elastomeric binder can be in the range from about 12% to about 20% by weight.

Examples of intumescent substances are alkali metal silicates such as sodium silicate, and exfoliating graphite. A preferred intumescent substance is exfoliating graphite. The intumescent substance, eg the exfoliating graphite, can be present in an amount of up to about 75% by weight of the total weight of the material. More particularly, the exfoliating graphite may be present ^" in an amount in the range 15% to 70% by weight of the total weight of the material. In general, the concentration of exfoliating graphite used will depend upon the extent of intumescence required and the degree of expansion which the material is required to produce in a given application. The greater the concentration of exfoliating graphite, the greater the degree of expansion produced by the intumescent material in a fire situation.

In a further aspect, the invention provides a method of preparing an intumescent sheet material as hereinbefore defined, the method comprising forming an aqueous slurry of the intumescent substance, manmade mineral fibres and elastomeric binder, depositing a layer of the aqueous slurry on a water-pervious support surface and removing the water from the slurry, for example by the application of vacuum.

In one embodiment, as water is removed from the aqueous slurry by draining through the pervious support

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surface, additional aqueous elastomeric binder may be applied to the slurry, eg by spray application and drawn down into the slurry by means of an applied vacuum.

In one embodiment, the water may be drained through the water pervious support surface to form a continuous sheet containing less than about 60% moisture, for example about 50% moisture, the continuous sheet then being transferred to a separate air permeable support surface and dried by the application of drying means. Suitable drying means can-take the form of one or more drying ovens, ^" infra red or radio frequency drying or steam heated drying cylinders.

The flexible intumescent materials of the present invention can be made on machinery conventionally used for papermaking, for example on a Fourdrinier Paper Machine.

The invention will now be illustrated, but not limited, by reference to the specific embodiments described in the examples below.

Examυles 1 - 3

An aqueous slurry was formed by mixing with an appropriate quantity of water a mixture of rock wool fibres, exfoliating graphite and an acrylic latex binder, in the amounts set out in Table 1 below. The slurry thus produced was deposited as a layer on a forming fabric made from a plastics material of the type conventionally used in paper making. Water was drained through the moving forming fabric to form a continuous

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sheet to which additional binder was added by spraying the surface of the sheet. The additional binder was drawn into the sheet by the application of vacuum. The continuous sheet containing about 50% moisture was then transferred to an air permeable continuous dryer belt and passed through a series of drying ovens to provide a dried sheet material.

Table 1

On subjecting the flexible intumescent sheet materials of the present invention to a fire situation, the presence of the exfoliating graphite causes the product to expand in a multiplicity of directions, the expanded thickness and the pressure created during expansion being dependent upon the amount of graphite used. On heating to 400°C, a sheet with a composition as shown in Example 1 increased to four times its original thickness, Example 2 to eight times its original thickness and Example 3 to twelve times its original thickness.

Intumescent sheet material of 2mm thickness prepared

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in accordance with the examples above were tested in accordance with BS 476 parts 19 to 23.

The intumescent sheet material of Examples 1 to 3 gave in excess of four hours fire protection.

Fire seals produced in accordance with the invention can be applied directly to a surface to be protected by, for example, double sided adhesive tape or attached to a surface by a liquid adhesive, tacks, pins or, indeed, by any conventional means. The product can readily be dimensioned using scissors, guillotine or other cutting tool. In its flexible form, the seal can readily be made to follow the contour of a round or even a relatively intricate moulded or curved surface. Sheets in accordance with the invention can be employed as intumescent linings for upgrading panelled doors, lath and plaster ceilings and plaster board to give enhanced fire protection. The sheets can also be used as under floor barriers and infill material for fire doors. Also, the sheet material can be used to line metallic surface boxes. It will readily be understood that the aforementioned are simply examples of the many uses to which sheet in accordance with the invention can be put. It will also be understood that the foregoing examples are merely illustrative of the present invention, and that numerous alterations and modifications could be made to the compositions set out in the examples without departing from the principles underlying the invention. All such modifications and alterations are intended to be embraced by this application.

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