This invention relates to a fire retardent fabric. The invention has been developed primarily in connection with a fire retardent fabric for use in upholstered furniture, and this will include an upholstery fabric and also an interliner to be positioned between upholstery fabric and expanded plastic foam filling of a piece of furniture. The invention however is not restricted to upholstery use. and will include fabric screens of the type used as room dividers in e.g. offices, and also curtains.

There is an increasing requirement (whether statutory or otherwise) that fabrics used for upholstery purposes should act as a protective barrier to the upholstery filling (usually polyurethane foam) in the event of a fire. The test method principally used in the United Kingdom to determine the fire retardency standard is BS 5852, Fire Sources 1 to 7 (ascending severity standards) . Fibres used in upholstery fabrics are normally natural fibres, such as wool or cotton, or synthetic fibres such as viscose, polyester, polyamide, polypropylene or combinations of such fibres. All of these fibres are more or less flammable and in their natural state will provide very limited, or no protection to an upholstery filling in the event of a fire. Chemical treatments, which can be virtually permanent, on wool, cotton or viscose fibres, greatly increase their ability to act as a fire barrier by enabling them to create a more effective char when burnt, which itself acts as a barrier and/or makes them less flammable. Polyester, polyamide or polypropylene fabrics are totally ineffective as fire barriers because in a fire they simply melt, creating a hole, thereby totally exposing the foam or other filling to the action of fire.

A chemically treated viscose fibre made by Lenzing, and known as FR viscose, is the ^' only widely used fibre

which is inherently non-flammable, and many fabrics are on the market which contain, for example, wool and this fire retardent viscose as blended fibres, which form an effective char as a fire barrier. It has been found that mixtures containing 40 to 50% of FR viscose can be inherently effective in this respect.

It is also known that a combination of polyamide and FR viscose will form a protective char, providing that there is a sufficient proportion of FR viscose in the fibre blend. The effect is inherent. Conventional wisdom in the art has been that FR viscose proportions of about 40 to 50% by weight are required to provide a satisfactory flame retardent fabric, but it has recently been found that proportions as low as 25% are adequate, and a fire retardent fabric has been put on the market recently containing 75% polyamide/25% FR viscose.

The present invention has been developed primarily with the objective of providing an acceptable fire retardent fabric which can meet all safety requirements, and which employs a lower proportion of flame retardent fibre in a fibre blend than the currently available minimum proportion of 25% proportion by weight, as in the polyamide/FR viscose fibre composition of the fabric referred to above.

The invention is therefore based on the surprising discovery that an acceptable flame retardent fabric can be obtained, which is formed from a fibre blend of an inherently flammable material in a substantial proportion by weight, with a fibre of inherently flame retardent material in a relatively low proportion, provided that the fineness of the flame retardent fibre is reduced to a relatively low order of fineness and provided also that there is a substantially uniform distribution of the flame retardent fibre throughout the fabric.

In particular, taking polyamide and FR viscose respectively as examples only of the highly flammable

material and fire retardent fibre, an intimate mixture of these two fibres can form a char on burning, and considerable economies and higher flammability resistance can be achieved with a fabric formed from these materials and by adopting techniques within the scope of this invention. Polyamide fibre is highly flammable, whereas FR viscose is non-flammable. It has been always assumed in the past, and is still presently believed, and also practised, that the higher the proportion of non flammable FR viscose and the lower the proportion of flammable polyamide the more effective will be the fire retardency of the resulting fabric. The invention now shows that this is in fact the opposite of the reality, which is that the higher the proportion of the flammable material e.g. polyamide, and the lower the proportion of non-flammable material e.g. FR viscose, the better and more protective can be the formation of the char upon application of fire to the fabric, provided that there is sufficient non¬ flammable and fire retardent fibre present on which the char formation can take place.

According to one aspect of the invention there is provided a fire retardent fabric which is composed of blended fibres including a major proportion of a flammable material and a minor proportion of substantially non¬ flammable and fire retardent material, in which the fire retardent material takes the form of fibres which are distributed substantially uniformly throughout the fabric and which are of sufficient fineness to reduce the proportion by weight of the fibre relative to the weight of the fibres of flammable material to a value of less than 25%, and yet which have sufficient strength to form a matrix to which the flammable material can adhere in the form of a non-flammable char after burning, so that a self- sustaining fire retardent and substantially non-flammable char layer can be formed from the fabric after application of fire thereto.

It has been found that reduction in fineness of the flame retardent fibres can take place to such an extent that the proportion of fire retardent fibres can be brought down to a level considerably below 25% by weight, and while still enabling a sufficiently strong matrix to be formed onto which the residue of the flammable material can adhere or coalesce as a char in the event of application of fire to the fabric.

One preferred material from which the fire retardent material is made is FR viscose, and preferably as obtained from Lenzing, though it should be understood that the invention is not restricted to use of FR viscose as the fire retardent fibre material, and any other suitable fire retardent fibre material may be used such as NOMEX, provided that it is capable of meeting the criteria set o t in the above aspect of the invention.

One preferred flammable material which may be used comprises polyamide, though again this is not. the only material which can be used in the practise of the invention, provided only that the flammable material is capable of forming an adherent char onto the matrix or skeleton structure which remains within the fabric in the event of fire and which is derived from the non-flammable material .

In the use of FR viscose in the invention (which is presently one preferred material), it is known that during burning FR viscose fibres, being non-flammable, remain in situ, and allow the melting polyamide to coalesce around them and therefore solidify in situ, rather than drip down causing a hole. As indicated above, it has always been assumed that a certain minimum percentage by weight of FR viscose is required to achieve this effect. However, it has been found, surprisingly, that the amount of FR viscose required to enable a satisfactory char to be formed from the flammable material is directly proportional to the fineness of the FR viscose fibres, rather than to the

weight of the fibres as a proportion of the whole. Thus, the finer the FR viscose fibres which are used, the less percentage of the total weight which is required to enable a satisfactory char formation to take place.

An acceptable fire retardent fabric in accordance with the invention can be derived from a blended fibre mixture in which the minimum percentage of FR viscose in the blend of polyamide/FR viscose is approximately 2.25% per decitex (the measure of fibre fineness) of the FR viscose. Thus, if 8.9 decitex FR viscose fibre is used, the percentage of the blend which must be FR viscose is 2.25 x 8.9 = 20%, for a satisfactory char to be formed.

Alternatively, if 2.2 decitex FR viscose is used, the percentage of the blend which must be FR viscose is 2.25 x 2.2 = 5% for a satisfactory char to be formed.

As a safeguard against any possible non uniform distribution of the flame retardent fibres in the fabric, it may advisable to increase these minimum percentages of fire retardent fibres by, say, 20%, in case the two fibres (polyamide and fire retardent viscose) are not totally evenly mixed.

A piece of fire retardent fabric in accordance with the invention may be formed by weaving, or by non woven techniques, and by knitting.

The role of the flammable material, and for example polyamide, will now be discussed. The solidity, strength and effectiveness of the char as a fire barrier is directly proportional to the weight of the polyamide in the fabric structure. Thus, the greater the weight of the highly flammable component of the blend, the more effective is the resultant char as a fire barrier. This is the exact opposite of what would be expected, and the current state of informed opinion and practise in the art.

There will be evident commercial advantages which can be achieved in the performance of the invention, using FR viscose and polyamide as examples only, as follows:

(a) the cost of polyamide fibre is half or less than half that of FR viscose, so the higher the proportion of polyamide in the blend, the lower the cost of the resultant fabric. By using finer FR viscose fibre, the percentage required can be reduced very substantially.

(b) to achieve any given fire test standard (e.g. BS 5852 Source 1 - 7), the weight of a fabric can be reduced due to the use of a higher percentage of polyamide. This again would reduce the cost of the resultant fabric.

Example 1

A woven fabric made of polyamide and FR viscose which is required to achieve a pass at BS 5852, Source 5, must contain sufficient FR viscose to form and support a char thereon, and must also contain approximately 240 - 260 gms/sq metre of polyamide (this has been found experimentally). If the blend is made using 8.9- decitex FR viscose, it must contain approximately 25% (allowing for a safety margin) of FR viscose, and 75% of polyamide. The polyamide content must weight 240 gms/sq metre to pass the required test, so the resultant fabric must weigh y /<^ = 320 gms/sq metre.

If however, it is practicable to use 2.2 decitex FR viscose, only 6% FR viscose (allowing for a safety margin) is required, to form a char, so 94% would be polyamide. 240 gms/sq metre of polyamide is still required to pass the required test so the resulting fabric need only weigh 240 - 94% = 255 gms/sq metre instead of 320 gms/sq metre. Example 2

Using the same fabric as in example 1 it would be possible as an alternative to use the finer FR viscose fibre, and therefore the higher percentage of polyamide (i.e. 94%) but leave the weight of the fabric at 320 gms/sq metre. This would mean there would now be 320 x 94% = 300 gms/sq metre of polyamide instead of the 240 gms/sq metre

required to pass BS 5852 Source 5. This weight of polyamide might well achieve a pass at BS 5852 Source 6 which is 3.5 times as severe as Source 5.

Commercially therefore, this invention has the following effects on cost and performance:

(1) the raw material content will always be cheaper by using finer FR viscose fibres, due to the ability to use a lower percentage of the more expensive fibre.

(2) the resultant fabric can either be further reduced in cost by reducing the weight, and still attain the same fire test standard, or the weight can be kept the same and a higher fire test standard achieved, or a combination of both.

A blend of polyamide/flame retardent viscose is one preferred example of the flammable and fire retardent fibre material to be used in fabric according to the invention, but the invention should not be considered as restricted to use only of these materials. _ It is thus envisaged that flammable materials other than polyamides may be used, including synthetic and natural materials, such as wool. Also, combinations of flammable materials may be used in the blended fibres, such as polyamide and wool. Examples of other blends which have been tested with satisfactory results (the formation of a satisfactory self-supporting char to form a fire retardent and resistant barrier protecting underlying flammable material) include the followin :

1. 85% polyamide and 15% FR viscose at 5.5 decitex;

2. 85% polyamide and wool mixture and 15% FR viscose at 5.5 decitex;

3. 85% wool and 15% FR viscose at 5.5 decitex;

4. 90% polyamide and 10% FR viscose at 3.3 decitex;

5. 90% polyamide and wool mixture and 10% FR viscose at 3.3 decitex;

6. 90% wool and 10% FR viscose at 3.3 decitex;

7. 70% wool and 20% polyamide, and 10% FR viscose at

3. 3 dec itex .

As indicated above, the basic philosophy underlying this invention comprises a surprising discovery that the proportion by weight of substantially non-flammable and fire retardent material in blended fibres incorporated in a piece of fabric can be reduced below 25% (while still providing a satisfactory fire retardent fabric) provided that the following parameters of the non-flammable and fire retardent material fibres are adopted:

(A) they are distributed substantially uniformly throughout the fabric;

(B) the fineness of the fibres is reduced by a sufficient amount to lower the proportion by weight in the blended fibre mixture below 25%;

(C) the strength of the fine fibres is sufficient to form a matrix to which the flammable materials can adhere in the form of a non-flammable char after burning, and so that a self-sustaining fire retardent and substantially non-flammable char layer can be formed from the fabric.

Examples have been given of a number of different blends and types of material which meet the above requirements, and provide a satisfactory flame retardent fabric.

It will be evident to those skilled in the art that other examples of flammable and substantially non-flammable materials may be used to form a blended fibre for use in a fire retardent fabric in accordance with the invention, and in appropriate proportions by weight and with suitable decitex of the non-flammable and flame retardent material.

Not all types of material may work satisfactorily, and factors which should be borne in mind include the following:

(i) the flammable material should be capable of forming a char upon burning, by first melting and then adhering to the supporting skeleton structure of

flame retardent fibres; and,

(ii) the flammable material should not shrink too much upon burning to form a char (since this could cause the char to crack) , and also should firmly adhere to the skeleton structure.

However, within these constraints, it is believed that the man skilled in the art will be able readily to select other proportions of the materials, different decitex of the fire retardent fibres, and different materials, from the examples disclosed in this specification, to obtain satisfactory fire retardent fabric within the scope of the invention, namely: a fire retardent fabric which is composed of blended fibres including a major proportion of a flammable material and a minor proportion of substantially non-flammable and fire retardent material, in which the fire retardent material takes the form of fibres which are distributed substantially uniformally throughout the fabric and which are of sufficient fineness to reduce the proportion by weight of the fibre relative to the weight of the fibres of flammable material to a value of less than 25%, and yet which have sufficient strength to form a matrix to which the flammable material can adhere in the form of a non¬ flammable char after burning, so that a self sustaining fire retardent and substantially non-flammable char layer can be formed from the fabric after application of fire thereto.

In addition to use as upholstery fabric, or interliners, fire retardent fabric may be used in the formation of curtains, and screen fabrics forming divider walls in offices. Upholstery fabric derived from the fire retardent fabric according to the invention will be especially suitable for use as the seat coverings of aircraft seats.