US2500158A - Self-sealing fuel container having a sealing layer composed of a textile fabric coated with a mixed cellulose ester - Google Patents

Description

Mandi y 195G w. A. DKCKEE EFAL zmm g SELF-SEALING FUEL CONTAINER HAVING A SEALING mm COMPOSED OF A TEXTILE FABRIC COATED WITH A MIXED CELLULOSE Esm Filed June 29, 1944 INVENTORS W. A DJCKIE.

G RUDORF.

ATTORN EYS Patented Mar. 14, 1950 SELF-SEALING FUEL CONTAINER HAVING A SEALING LAYER COMPOSED OF A TEX- TILE FABRIC COATED WITH A MIXED CELLULOSE ESTER William Alexander Dickie and George Rudorf,

London, England, assignors, by mesne assignments, to Celanese Corporation of America, a

corporation of Delaware Application June 29, 1944, Serial No. 542,714

In Great Britain June 23, 1943 Section 1, Public Law .690, August 8, 1946 Patent expires June 23, 1963 Claims. (Ci. 154-43.5)

This invention relates to containers and especially to tanks or other containers intended to carry liquid fuel, and to materials suitable for use in the construction of such containers.

It is well-known to providemilitary aircraft with self-sealing petrol tanks, i. e. tanks which are capable of retaining the bulk of their contents even after perforation by bullets. Such tanks commonly owe their self-sealing property to the inclusion in their construction of a layer or layers of material adapted to swell when in contact with the liquid fuel. The construction is usually such that the fuel does not come into contact with the sealing layer until the tank is perforated. The fuel then causes swelling of the sealing layer round the hole which is thereby sealed. The tank may, for example, have inner and outer walls of metal with an intermediate layer of the sealing material, or an outer wall of metal, an intermediate layer of the sealing material, and an inner layer of a rubber-like material which is resistant to the liquid fuel. The sealing materials commonly used have a basis of rubber or a rubber-like substance. Such materials are, under present conditions, in very short supply, and it is one of the objects of the present invention to provide a suitable sealing material which does not involve in its production the use of rubber or of any rubber-like substance.

We have now found that certain cellulose derivatives are-particularly suitable for the construction of sealing layers in petrol tanks and for allied purposes. Cellulose acetate-stearate of high ester content, for example containing not more than about 0.3 and preferably not more than 0.2 free hydroxy groups per Cal-11005 unit of cellulose are particularly suitable. tate-stearate may contain from about 0.35 or even less, up to about 1, or even more, stearyl groups per Cal-E1005 unit of cellulose and the acetyl content may range from about 1.9 or slightly less, up to about 2.5 or more groups per CrsHmOsunit. Examples of cellulose acetatestearates which have been found useful for the purpose of the invention are as follows, the acetyl values and stearyl values being expressed as percentages of the fatty acid concerned:

1. Acetyl value 12.0%; stearyl value 26.5%. 2. Acetyl value 38.0%; stearyl value 33.0%. 3. .Acetyl value 31.4%; stearyl value 43.6%. 4. Acetyl value 22.9%; stearyl value 55.6%.

The particular ester employed will be selected in view of the nature of the fuel with which it is The acev to be employed. The ester should be one which 1s swollen to a considerable extent by the fuel employed without being dissolved. When the fuel consists substantially of petroleum fractions, esters containing a relatively high proportion of stearyl groups are to be preferred, for example esters such as numbers 3 and 4, i. e. esters containing about 2 acetyl groups and about 1 stearyl group per CaI-IwOs unit of cellulose, above, are particularly suitable for use with fuels of this kind. Esters of similar constitution but with other higher fatty acid radicles, e. g. lauryl or palmityl, may also be used. With fuels containing a substantial proportion of aromatic hydrocarbons, however, esters of lower stearyl content (or other higher fatty acid radicle content), for example numbers 1 and 2 referred to above, will be found more suitable.

The sealing material preferably comprises a a textile fabric impregnated with the cellulose ester. It is of advantage to employ a fabric the fibres of which have some degree of resilience. Thus fabrics of wool have been found particularly suitable. employed include woven woolen and worsted fabrics and felt fabrics. The wool may be used in admixture with other fibres; thus, for example excellent results have been obtained using as the basis for the sealing material a mixed fabric of wool yarns interwoven with staple fibre yarns of cellulose acetate, or fabrics of mixed wool-cellulose acetate yarn can be employed.

Other fibres having to some extent the resilient properties of wool, e. g. other natural fibres having a protein basis, such as horse-hair, and certain artificial fibres, can be employed in admixture with, or in substitution for, the wool in the production of the sealing materials of the invention. Among artificial fibres that can be used are fibres of an artificial silk which has been produced by spinning a solution of cellulose acetate, preferably of concentration below about 30%, at a relatively low temperature, for example -80 C. into a countercurrent of air which is at a similar temperature and subjecting the resulting fibres to a hot aqueous treatment, as described in U. S. application S. No. 522,968 filed February 18, 1944, now Patent No. 2,431,435, issued November 25, 1947. Cellulose acetate fibres which have been crimped by subjecting the assemblies of filaments after spinning to a process of twisting, setting the twist and removing the twist may also be employed, as may fibres of cellulose acetate which have been crimped by other methods, for example by pas- The wool fabrics that can be sage over crimping rollers. The base fabric may contain fibres of other organic derivatives of cellulose which are resistant to the liquid fuel employed. V

Wool-like fibres of partially or completely a heat treatment. A crimping operation may be introduced before the heat treatment. The invention includes the use of fabrics made of or containing resilient fibres produced in this way. Artificial fibres having a protein basis, e. g. fibres of casein'or soya bean protein can also be used. As in the case of fibres of a cellulose derivative or of regenerated cellulose it is desirable that their fibres should be crimped or otherwise treated to improve their normal resilience. The yarns from which the fabrics are formed are preferably staple fibre yarns. As indicated above, woven or felted fabrics may be employed. Although excellent results have been obtained using fabrics formed from yarns of normal or even low twist, the fabric may be composed of, or contain crepe twisted yarns. Closely knitted fabrics such as are obtainable by warp knitting Orcircular knitting processes may also be used.

The impregnation of the fabric with the cellulose acetate-stearate may be effected by various methods, for example by a bath treatment or by a spreading operation using as the impregnant a'solution of the cellulose acetate-stearate in a volatile solvent therefor. Except in the case of the esters of very high stearyl content, acetone constitutes a suitable solvent. In the case of esters of very high stearyl content such as number 4 referred to, benzene may be employed as the solvent. The use as the solvent of a liquid which attacks the base fabric must, of course, be avoided. Thus, for example when the base fabric contains cellulose acetate or other acetone-soluble derivative of celluloseya chlorinated aliphatic hydrocarbon such as methylene dichloride, ethylene dichloride or chloroform suitably diluted with a hydrocarbon, such as an aromatic hydrocarbon, can be used as the solvent for the acetate-stearate.

The invention has been described with particular reference to the use of a cellulose acetatestearate as the substance adapted to be swollen by the liquid fuel. Other highly water-resistant, relatively soft cellulose derivatives can also be employed, however. Among such derivatives are other mixed esters of acetic acid and a fatty acid containing at least 12 carbon atoms, for example cellulose acetate-palmitate and cellulose acetatelaurate. Cellulose esters containing the radicles of acetate acid and of a fatty acid of medium molecular weight, for example propionic or butyric acid can also be employed as can cellulose ethers derived from an alcohol containing at least two carbon atoms, for example ethyl cellulose and benzyl cellulose. Mixed ethers of cellulose containing the radicle of a higher alcohol can also be used. Examples of such ethers are ethyl-hexyl-cellulose and ethyl-lauryl-cellulose. Simple esters of higher fatty acids, e. g. cellulose stearate, palmitate and laurate, and simple ethers of higher alcohols, e. g. lauryl and hexyl cellulose, are in general too soft and lacking in film-forming properties to form satisfactory substitutes for the mixed esters referred to.

The sealing material may contain plasticisers for the cellulose derivative. These should preferably be insoluble or of low solubility in petrol. Among such plasticizers are trichlor-ethyl phosphate, methyl-phthalyl-ethyl glycollate and triacetin. As however the sealing material is not normally in contact with the contents of the tank, petrol-soluble plasticisers, e. g. dlethyl phthalate, dibutyl phthalate, butyl-phthalylbutyl-glycollate and tricresyl phosphate, are not excluded. It is an advantage of cellulose acetate-stearate and other cellulose derivatives containing a substantial proportion of fatty acid radicles or alcohol radicles, of high molecular weight, that these derivatives are sufliciently soft to be employed without a plasticiser although plasticisers'may be employed with these derivatives when an even greater degree of softness is required. The plasticiser is conveniently incorporated in the dope with which the fabric is impregnated.

The impregnated fabrics of the invention are believed to be broadly novel. They can be used in various ways to provide the sealing material for self-sealing petrol tanks. Thus, for example layers of the impregnated fabric of the invention may be enclosed, within inner and outer walls of metal in the construction of the tank or between an inner layer of rubber or rubber-like material which is not swollen by the liquid fuel and an outer wall of metal. Instead of a single layer of the impregnated fabric, several layers may be used and these may be united, for instance, by a hot pressing operation to form a composite sheet of the desired thickness. The impregnated fabric may be used in other ways. Thus, for example, petrol tanks or other containers may be built up of composite material comprising sheets of the sealing material alternating with sheets of other material, for example sheets of cellulose acetate or other filmfor-ming polymer which is not attacked by the liquid fuel, or sheets of textile fabric impregnated with such a film-forming polymer. A reinforcing layer'or layers, e. g. of a wire fabric or the like, may be provided within or adjacent to the sealing layer or layers.

A further use of the impregnated fabric of the invention is in protecting petrol pipes and the like in aircraft. For this purpose the pipes may be lapped with the impregnated fabric and an outer layer, for instance of a textile fabric impregnated with cellulose acetate or other petrolresistant film forming polymer, may then be applied. I'he impregnated fabric may also be used to lap round petrol pipes, oil pipes, petrol cans or the like which have been perforated by bullets or shell fragments, with a view to temporarily sealing the leak. Oiland petrol-resistant gaskets can also be formed from these fabrics.

The use as the sealing material of a fabric of resilient textile material impregnated with a substance adapted to be swollen by the liquid fuel or the like, effects a considerable economy in that substance and it is of advantage to employ a sealing medium having a fabric base with other impregnants than the cellulose derivatives referred to. Thus, for example, there may be employed as the impregnants instead of a cellulose derivative of the kind referred to, a synthetic resin which is swellable by petroleum fractions, for example polystyrene or other polymerised vinyl compound.

Though it is preferred to employ a resilient fabric base in the construction of the sealing materials of the invention, the invention includes the use of cellulose acetate-stearate and other highly water-resistant cellulose derivatives as sealing materials for petrol tanks and the like without such a base. Thus, for example, a useful sealing medium may be made by impregnating loose fibres of wool, horsehair, asbestos or any of the other textile materials referred to above with the cellulose derivative. Sheets of the cellulose derivative, having a wire reinforcement or without reinforcement, may also be employed in any of the constructions referred to above.

The drawing shows by way of example, a selfsealing petrol-tank for aircraft, constructed in accordance with the invention.

In the drawing the tank is shown in perspective with one corner cut away to reveal the construction. The tank comprises a lining (shown exposed at I0) which may be of metal or of a synthetic resin which is resistant to petrol and of high impact-strength, and an outer cover ll of a light alloy, the space between the lining and outer cover being filled with a sealing layer (shown exposed at [2) of fibrous material coated with a cellulose derivative for which petrol is a strong swelling agent but not a solvent. The tank is provided with inlet and outlet means (not shown) and may also be reinforced by internal struts.

Having described our invention, what we desire to secure by Letters Patent is:

1. A self-sealing container for gasoline comprising rigid inner and,outer walls unaffected bygasoline and between them a sealing layer comprising a textile fabric containing a substantial proportion of resilient fibres and coated with a mixed cellulose ester of acetic acid and a higher fatty acid containing at least 12 carbon atoms in the molecule, the composition of the said cellulose ester being such that it contains less than 0.3 free hydroxyl groups, 1 to 2.5 acetyl groups and 0.35 to 1 higher fatty acyl groups for each Col-11005 unit.

2. A self-sealing container for gasoline comprising rigid inner and outer walls unaffected by gasoline and between them a sealing layer comprising a textile fabric containing a substantial proportion of wool fibres and coated with a mixed cellulose ester of acetic acid and a higher fatty 5o acid containing at least 12 carbon atoms in the molecule, the composition of the said cellulose ester being such that it contains less than 0.3 free hydroxyl groups, 1 to 2.5 acetyl groups and 3. A self-sealing container for gasoline comprising rigid inner and outer walls unaffected by gasoline and between them a sealing layer comprising a textile fabric containing a substantial proportion of wool fibres and coated with a cellulose acetate stearate containing less than 0.2 free hydroxyl groups, 1 to 2.5 acetyl groups and 0.35 to 1 stearyl groups for each CsHmOs unit.

4. A self-sealing container for. gasoline comprising rigid inner and outer metal walls and between them a sealing layer comprising a woven textile fabric containing a substantial proportion of wool fibres and coated with a mixed cellulose ester of acetic acid and a higher fatty acid containing at least 12 carbon atoms in the molecule, the composition of the said cellulose ester being such that it contains about 2 acetyl groups and about 1 higher fatty acyl group for each C8Hl005 unit.

5. A self-sealing container for gasoline comprising rigid inner and outer metal walls and between them a sealing layer comprising a woven textile fabric containing a substantial proportion of wool fibres and coated with a cellulose acetate stearate containing about 2 acetyl groups and about 1 stearyl group for each Cal-11005 unit.

WILLIAM ALEXANDER DICKIE. GEORGE RUDORF.

REFERENCES @ITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Ott, Cellulose and Cellulose Derivatives," pub.

by Interscience Publishers Inc., 1943; pages 1072,

Worden, The Technology of Cellulose Ethel-s,"

0.35 to 1 higher fatty acyl groups for each CuHmOs as published in 1933 by Worden Laboratory and unit.

Library, Millbum, N. J.: p es 267 and 847.

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