GB2379457A

GB2379457A - Glass fibre fabric impregnated with exfoliated vermiculite

Info

Publication number: GB2379457A
Application number: GB0220908A
Authority: GB
Inventors: Michael Anthony Turner; Ian Fraser; Robert Wray
Original assignee: INSULATION BARRIERS Ltd
Current assignee: INSULATION BARRIERS Ltd
Priority date: 2001-09-11
Filing date: 2002-09-10
Publication date: 2003-03-12
Also published as: GB0121861D0; GB0220908D0

Abstract

A thermal insulation product comprises a glass fibre fabric impregnated with 10-50% by weight of exfoliated vermiculite that has been rendered substantially non-intumescent by mechanical comminution to a particle size of not more than 40 microns. A particle size of around 30 microns is particularly preferred. A process for making the product is also disclosed. The thermal insulation product has excellent resistance to flame penetration.

Description

Improvements In and Relating to Textile Fabrics This invention relates to woven and non-woven fabrics, especially of glass fibre.

Conventional glass fibre textile fabrics, especially nonwoven fabrics, do not exhibit good resistance to flame penetration when directly exposed to flame. Even glass fibres melt when exposed to significant heat and although non-woven glass fibre fabrics are widely used in fire protection applications, the direct application of flames can cause rapid, localised perforation of the fabric.

One well-known and documented solution to this problem of flame penetration is to impregnate or at least coat the fabric with a relatively inert material that forms a dense char when subjected to flames. By this means, flame penetration may be significantly delayed although possibly at the risk of smoke/fumes being generated by the charring. Intumescent materials such as graphite or vermiculite which greatly expand on heating may be used in conjunction with char forming materials, optionally with one or more binder materials to retain the intumescent material in or on the fabric.

Thus it is known from EP-A 0167254 to treat a carbon fibre substrate with chemically de-laminated vermiculite particles. GB 2360298-A on the other hand discloses treating textile fibres, especially mineral fibres such as limestone fibres, with a composition comprising an intumescent material in a polymeric binder. Numerous other examples of this approach to enhancing flame resistance are known from the art. Common to most if not all prior proposals is the use of thermally induced charring and/or intumescence to at least partly block the interstices between the fibres and thereby delay flame penetration.

It is an object of the present invention to provide a glass fibre fabric having excellent resistance to flame penetration, but without using any binder material, char forming or otherwise.

According to the present invention, there is a provided a thermal insulation product constituted by a glass fibre fabric impregnated with exfoliated vermiculite that has been rendered substantially non-intumescent by previous mechanical comminution to a particle size of around 30 microns.

It will be appreciated that mechanical comminution, especially by grinding, tends to generate a spread of particle sizes. Accordingly even at the particularly preferred target fineness of around 30 microns, ground vermiculite will typically comprise particles in the size range of at least 20-40 microns, although the majority of the particles will be around 30 microns in size. It has been observed that this degree of variability from the 30 micron target size is acceptable from a practical standpoint in the context of the present invention, so that more precise and probably much more expensive control of particle size is not required.

The mechanically comminuted vermiculite preferably constitutes from about 10 to 50% by weight of the product and particularly preferred fabrics are non-woven glass fibre mats or felts. Non-woven glass fibre mat made by needling is a particularly preferred fabric.

The invention further provides a method of making a thermal insulation product, comprising the steps of forming an aqueous dispersion from water containing a minor amount of a surfactant and exfoliated vermiculite previously mechanically comminuted to a particle size of around 30 microns, followed by impregnating a glass fibre fabric with the dispersion and then drying. The aqueous dispersion preferably comprises about 10-30% by weight of the exfoliated, comminuted vermiculite of particle size around 30 microns, the latter figure being a target rather than a precise limit, for the reason given earlier.

Impregnation may be carried out by the conventional textile method of padding the fabric through the aqueous dispersion followed by mangling to remove excess liquid from the fabric before drying. It is observed that the pad/mangle process for fabric treatment with liquids such as dyestuffs is extensively used in the textile industry and need not be described in further detail here.

The process of this invention preferably includes a preliminary step of mechanically comminuting previously exfoliated vermiculite to a particle size of around 30 microns, thereby rendering it substantially nonintumescent. A preliminary grinding step is the preferred method of mechanical comminution.

Despite use of a conventional pad/mangle impregnation process and the resultant relatively short dwell time in the vermiculite particle dispersion, it has been found that the dry solids pick-up of vermiculite in the glass fibre fabric is surprisingly high, on the order of 12-13% by weight in the case of a 25mm thick needled glass fibre mat, around 38% in the case of a 12mm thick mat and as much as 50% by weight in the case of a 7mm thick mat.

In addition, the dry product has remarkable integrity despite the total lack of binder material.

As disclosed earlier, the product of this invention consists of glass fibres and finely divided substantially non-intumescent vermiculite particles. Surprisingly it has been found that a thermal insulation product according to the present invention, or made by the process of this invention, exhibits good structural integrity and excellent resistance to flame penetration without any need for the inclusion of a binder. It is believed that this may be the result of some previously unappreciated property of mechanically comminuted exfoliated vermiculite particles.

Even in the case of a relatively open fabric such as a non-woven needled glass fibre mat, the vermiculite is well retained in the fabric and the resistance to flame penetration is very significantly improved over that of an untreated mat, thereby rendering the treated mat suitable in fire protection applications where it would previously have been unacceptable. Furthermore, and very significantly, this improvement is achieved at relatively low cost and without use of a binder material that might on charring create unwanted smoke or fumes.

In order that the invention be better understood, a preferred embodiment of it will now be described with reference to the following Examples.

Exfoliated vermiculite was comminuted by mechanically grinding to a particle size of around 30 microns. The ground product was dispersed in water containing a minor amount of surfactant, to give a dispersion containing about 20 percent by weight of vermiculite. Several sample lengths of non-woven needled glass fibre fabric respectively of thickness 7mm, 12mm and 25mm were impregnated with this dispersion using a conventional textile pad/mangle process. The de-watered impregnated fabric samples produced by this were then dried prior to testing for their resistance to flame penetration.

Although the use of an otherwise conventional pad/mangle process resulted in a very short dwell time in the aqueous dispersion, the dry solids pick-up of the fabric was surprisingly high, about 13% by weight in the case of the 25mm fabric, 38% in the case of the 12mm fabric and as much as 50% by weight in the case of the 7mm fabric.

The flame penetration test method consisted of mounting a piece of fabric in a generally vertically disposed frame and then applying a naked flame for three minutes at a temperature of not less than 11000C to one face of each sample under test. In no case was there any flame penetration and there was no sign of impending failure.

The temperature of the face of the sample opposite the flame did not exceed 70 C during the test period. This was an excellent result.

By contrast, untreated glass fibre fabric samples of similar thickness were subjected to the same test and in each case flame penetration occurred within a few seconds.

It is observed that the products made as just described were readily conformable whilst still slightly damp. They could be moulded or otherwise made into shaped artefacts before final drying, again despite the absence of any added binder material. Thus the product of this invention may find utility in fire protection applications where it was previously necessary to use a fire resistant paste or plaster.

Claims

CLAIMS 1. A thermal insulation product constituted by a glass fibre fabric impregnated with exfoliated vermiculite that has been rendered substantially non-intumescent by previous mechanical comminution to a particle size of around 30 microns.
2. A thermal insulation product according to claim 1 wherein the exfoliated vermiculite is mechanically ground vermiculite.
3. A thermal insulation product according to claim 1 or claim 2 wherein the mechanically comminuted vermiculite constitutes from 10-50% by weight of the fabric.
4. A thermal insulation product according to any of claims 1-3 wherein the fabric is a non-woven fabric.
5. A thermal insulation product according to any of claims 1-4 wherein the fabric is a needled non-woven glass fibre mat.
6. A process for manufacturing a thermal insulation product, comprising the steps of forming an aqueous dispersion from water containing a minor amount of a surfactant and exfoliated vermiculite previously mechanically comminuted to a particle size of around 30 microns, followed by impregnating a glass fibre fabric with the dispersion and then drying.
7. A process according to claim 6 wherein the dispersion is formed to contain from about 10-30% by weight of vermiculite.
8. A process according to claim 6 or claim 7 wherein the impregnation step is carried out by padding followed by mangling to remove excess liquid from the fabric prior to drying.
9. A process according to any of claims claim 6-8 including a preliminary step of comminuting exfoliated vermiculite to a particle size of around 30 microns.

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10. A process according to any of claims 6-9 wherein the comminution is effected by mechanical grinding.
11. Shaped artefacts made from the thermal insulation material of any of claims 1-5, or from a product of the process of any of claims 6-10.
12. Thermal insulation products substantially as hereinbefore described with reference to the Examples.
13. A process for making thermal insulation products substantially as described with reference to the Examples.
14. Fire protection products according to any of claims 1-5 or claim 11, or made by the method of any of claims 6-10.