Liquid fuel containers

2,973,293

P. J. SCHOFIELD

LIQUID FUEL CONTAINERS

Filed Nov. 9, 1956

Feb. 28, 1961

FIG. I.

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FIG. 2.

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United States Patent Office

2,973,293

Patented Feb. 28, 1961

2,973,293

LIQUID FUEL CONTAINERS

Philip John Schofield, Wolverhampton, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain

Filed Nov. 9,1956, Ser. No. 621,218

Claims priority, application Great Britain Nov. 16, 1955

Claims. (Cl. 154—43.5)

This invention is concerned with liquid containers and is more specifically concerned with lightweight fuel containers particularly for use in aircraft.

Hitherto, ultra-lightweight fuel containers have generally been composed of layers of textile fabric and of fuel-impervious polymeric substances, for example synthetic rubber-like compositions, the said layers being firmly bonded together to produce a finished construction having the desired degree of flexibility, mechanical strength and permanence of properties when in contact with the fuel. In addition, when the fuel container is to be used in aircraft the materials employed in the construction thereof are required to maintain their properties over the range of temperature and other conditions to which the aircraft will be subjected.

The present invention is addressed to the problem of producing a lightweight fuel tank which will exhibit the above-mentioned and other desirable properties to a high degree.

According to the present invention a liquid container is made from material having a structure comprising a layer of a nylon or a modified nylon, and a layer of fuel-resistant rubber-like material which is bonded thereto and which is reinforced by a textile fabric layer of close-weave or knitted construction composed of yarns impregnated with a fuel-resistant rubber-like material. Preferably the nylon or modified nylon layer is itself reinforced additionally to the reinforcement provided by the close-weave fabric.

The reinforcement of the nylon or modified nylon layer may be achieved by means of a textile fabric layer of 45 open weave or knitted construction impregnated with a fuel-resistant rubber-like material and bonded to the surface of the nylon or modified nylon layer opposite to that joined to the layer of rubber-like material.

The liquid container is constructed from the material 50 according to the desired shape and in such a way that the nylon or modified nylon layer is disposed on the inner or liquid side of the container, thereby acting as the main fuel barrier.

One important advantage of the constructional mate- 55 rial of the invention is that the nylon or modified nylon layer is separated from the reinforcing fabric of closeweave or knitted construction by means of the intermediate layer of the rubbery material. There results a considerable improvement in the resistance of the material 60 to damage upon bending as compared, for example, with those constructional materials in which the nylon or like material is allowed to extend into the interstices of a fabric of close and relatively rigid construction. The ability of the material to flex without damage is further enhanced by the presence of the rubbery substrate for the nylon or modified nylon layer which has a cushioning effect thereon. These features also contribute to the very good low temperature performance of fuel containers made from the material.

The essence of the invention may be understood from a consideration of the accompanying drawings, in which:

Figure 1 is a section of the material which is reinforced internally by an open-weave fabric. In this Figure 1, on the inner or liquid side, is the open-weave fabric, and the layers 2, 3 and 4 are respectively nylon or modified 5 nylon, rubber-like substance, and close-weave fabric.

Figure 2 is a perspective view of a liquid fuel container 5 of simple form, having a portion of a wall removed to illustrate the construction thereof.

The nylons or modified nylons used according to this 10 invention are, respectively, those polyamides which are readily soluble or which have been so modified chemically as to become readily soluble in common organic solvents e.g. alcohol or aqueous alcohol and which have good film forming properties and resistance towards hy15 drocarbon liquids and vapours. Suitable examples of modified nylons are the alkoxy-alkyl polyamides, particularly the alkoxy-methyl polyamides described in British Patent No. 573,482, N-methoxy-methyl-polyhexamethylene-adipamide being especially useful.

The material used for the intermediate layer between the main fuel barrier and the reinforcing fabric of close construction is a fuel-resistant rubber-like substance. Suitable examples of such material are those compositions having a basis of poly chloroprene or copolymers 25 of butadiene and acrylonitrile and containing suitable plasticizers and other additives. Especially outstanding are those compositions having a basis of the butadieneacrylonitrile copolymers which are available commercially under the name “Hycar” OR 15 or “Hycar”

OR 25.

The word “Hycar” is a registered trademark. The fuel-resistant rubbery polyesters or polyester-amides may also be used as the intermediate layer.

The textile fabrics used according to the present in35 vention are those composed of fibers appreciably resistant to the solvents used in depositing the various polymeric substances thereon. They may be those containing fibres of synthetic linear polyamides such as, for example, nylon and Perlon or fibers of aromatic polyesters such ⁴⁰ as are formed from terephthalic acid and glycols, e.g. polyethylene terephthalic. Of particular suitability are those fabrics formed from “Terylene” polyester fibre. The word “Terylene” is a registered trademark. Fabrics composed of fibres of polyacrylonitrile, glass fibres or fibres of regenerated cellulose may also be used. Fabrics containing natural fibres having the requisite properties are also useful, for example those containing silk fibres or cellulosic fibres.

The open construction fabric used according to this invention is of sufficiently open weave or stitch to permit the bonding of the said fabric to the rest of the material to be effected by the passage of the bonding solution through the said fabric. Furthermore, being of such open construction, it is capable of flexure along with any bonding material remaining in its interstices and so does not give rise to embrittlement of the material in this region. In the case of woven fabrics, a leno weave has been found to be very suitable for this purpose while at the same time providing sufficient reinforcement of the modified nylon layer. Open construction fabrics of nylon or “Terylene” polyester fibre having a weight per square yard of the order of 1.5 ozs. are especially suitable.

_ The fabric having a close-weave or knitted construc⁶⁵ tion is particularly intended to contribute to the mechanical strength of the material and its resistance to abrasion and may be, for example, a plain woven fabric. Fabrics having very good puncture and tear resistance are preferred. Good results are obtained with plain 70 woven nylon or “Terylene” fabrics having a weight per square yard of about 4 ozs.

The weight per unit area of the fabrics used for the

2,973,293 respective layers in the material is chosen in accordance with the functional requirements described while being compatible with production of fuel tanks of very low weight. The numerical values given are, therefore, not limiting nor is it excluded from the invention to produce a tank from material having local variations as to the fabrics used where such variations are advantageous.

In order to prevent leakage of the fuel in the container by the passage thereof along the yarns of the reinforcing fabrics, such phenomenon being termed “wicking,” the said fabrics are impregnated, before incorporation in the material, with a fuel-resistant rubbery material so as to fill the spaces between the component filaments in the yarns but, especially in the case of the open fabric, leaving the spaces between individual yarns unfilled.

This fuel-resistant rubbery material may conveniently be of the same type as that used in the intermediate layer of fuel-resistant rubber-like substance.

In the manufacture of the constructional material, the closely woven or knitted fabric is first impregnated with the curable composition to seal the yarns against wicking, satisfactory adhesion being achieved by the use of an anchoring agent. Thus, for example, in the case of nylon fabrics, very satisfactory anchorage of butadiene-acrylonitrile co-polymers is achieved by the use of polyisocyanate anchoring agents, for example diphenylmethane diisocyanate, hexamethylene dissocyanate, toulene-2:4:6triisocyanate and triphenylmethane-4:4':4-triisocyanate. Particularly good results are obtained with the product sold commercially as “Vulcafor” VCC (registered trademark). The fabric is thus impregnated with an organic solvent solution of the anchoring agent, preferably containing some of the synthetic rubber. Alternatively the anchoring agent and the synthetic rubber may be deposited in the fabric successively in that order from separate solutions. After evaporation of the solvent the main rubbery layer is built up by coating the treated fabric several times on one side with a concentrated solution of the rubber, drying after each coating application. The modified nylon layer is then deposited over the main rubber layer by a series of coatings with a solution, for example, an aqueous alcoholic solution, of the modified nylon the first few coating solutions containing a suitable bonding agent to facilitate adhesion between the rubber and the nylon.

Again, the solvent is removed by evaporation after each coat has been applied. The nylon or modified nylon layer may be very efficiently bonded to the rubbery material by means of the bonding agents described and claimed in British Patent No. 654,331 and employed in the manner described therein. Examples of such bonding agents are the N:N'-bis-(acetoacetyl)-, N:N'-bis(carbethoxyacetoacetyl)-, N:N'-bis-(a:a-dicarbethoxyacetyl)-, N:N'-bis(di-acetoacetyl)-, N: N' - bis - (carbethoxyacetobutyryl) -, N:Ν'-bis- (a: a-dicarbethoxybutyryl)-, N: Ν'-bis- (carbethoxyacetyl)-, and N:N'-bis(a-benzoylacetoacetyl)-hexamethylene diamines or -cyclohexyl diamines or -toluylene diamines and similar N:N':N-tris-substituted-toluylene triamines.

The fabric-polymer assembly obtained at this stage is then doubled on to the open-weave or knitted fabric with the modified nylon layer in contact with the said fabric, the latter having been previously impregnated with a solution of the anchoring agent containing some of the synthetic rubber as described above for the close-weave or knitted fabric. The open-weave or knitted fabric may advantageously be a leno weave “Terylene” fabric in which case “Vulcafor” VCC may be used as the anchoring agent.

The components doubled together are then bonded by the application through the open weave or knitted fabric of a solution of modified nylon, for example, in aqueous alcohol, and containing the bonding agent. Final coatings may then be applied from a solution of the modified nylon alone. The drying out of the coatings at all stages described is effected under mild conditions of temperature, for example up to about 80° C. The curing of the rubbery material is carried out at temperatures of the order of 125° C. after fabrication of the container from the material.

One embodiment of the invention will now be described by way of example in which a woven nylon fabric is used as the close-weave component forming the outer fabric ply and a woven “Terylene” fabric is used as the inner or fuel side fabric ply of the tank material. Compositions are given in terms of percentage by weight based on the weight of the mixture or solution.

Example

A plain woven nylon cloth having a weight of 4 ozs. per square yard is impregnated with mixture A, a composition consisting of 84.9% of methyl ethyl ketone, 3.5% of “Vulcafor” VCC and 11.6% of a curable composition containing “Hycar” OR 25, dibutyl phthalate and conventional additives, so as to give, after evaporation of the solvent, an increase in weight of 2.9 lbs, per 100 square yards of fabric.

The main rubbery coating is then applied on one side from mixture B, a composition containing 58% of methyl ethyl ketone and 42% of the above mentioned curable “Hycar” composition, until an increase in weight (dry) of 23.5 lbs. per 100 square yards of fabric is obtained.

The modified nylon layer comprising the main fuel barrier is then deposited on the main “Hycar” coating, bonding being obtained by a layer deposited from solution. A, containing 57.2% of ethanol, 9.8% of water, 12.3% of methyl ethyl ketone, 4.6% of N:N'-bis-(carbethoxyacetoacetyl)-cyclohexyl-diamine and 16.1% of N-methoxy-methyl-polyhexamethylene adipamide, a dry weight increase of 1.7 lbs. per 100 square yards of fabric being obtained. The remaining portion of the main nylon layer is deposited by successive applications of solution B, containing 58.4% of ethanol, 10% of water, 12.6% of methyl ethyl ketone and 19.0% of N-methoxy-methylpolyhexamethylene adipamide, the weight increase at this stage being 12.5 lbs. per 100 square yards of fabric.

A “Terylene” leno fabric having a weight of 1.5 ozs. per square yard is impregnated with mixture A, described above, until the increase in weight (dry) is 0.6 lb. per 100 square yards of fabric. The treated leno fabric is then doubled to the modified nylon face of the treated nylon cloth and bonded thereto by the application of solution A, described above. The application of solution A takes place through the open weave of the “Terylene” fabric. Dry weight increase at this stage is 2.5 lbs. per 100 square yards of ‘Terylene” fabric.

A further coating is then applied with solution B, giving an increase in weight (dry) of 3.0 lbs. per 100 square yards of fabric.

In one method of constructing a tank according to the present invention the material is cut to the desired shape using 1 inch overlap seams and tailoring with notches where necessary to form double curvature. The material is advantageously bonded at the overlap by means of adhesives based on elastomeric polymers such as polyesters, polyester-amides or polyamides (cross linked with poly-isocyanates), butadiene/acrylonitrile or polychloroprene with or without modifying resins such as, for example, phenol/formaldehyde or terpene/phenolic products.

Where tailoring has occurred, the cut edges are painted with the adhesive and then with nylon solution to secure the fibre ends. The area around the cut is coated with a fast curing “Hycar” cement, and a “Hycar” coated nylon fabric, e.g. one having a weight of 1.8 ozs. per square yard, is applied over the area. The fast curing “Hycar” cement may be one based on “Hycar” OR 15 plasticized with dibutyl phthalate and containing zinc isopropyl xanthate and diethylammonium diethyl dithiocarbamate as accelerators, and other additives.

2,973,293

The external surface of the “Hycar” coated nylon fabric applied to the area around the cut is then coated with a slow curing “Hycar” cement followed by coatings with modified nylon solution and finally coated with an adhesive of the type described above for the bonding of the overlap. The slow curing “Hycar” cement may be one based on “Hycar” OR 25 and comprising dibutyl phthalate, a vulcanisation retarding agent and conventional additives. The outer surface of the seamed areas are then treated with the slow curing cement and a layer of the “Hycar” coated nylon fabric is applied to the treated areas using the above mentioned adhesive.

The completed tank is dried in an oven at 60° C. for 16 hours and then cured for 2 hours at 125° C.

While the liquid containers of the present invention have been described with particular reference to their use for containing fuel, their use is not so limited. The containers are equally suitable for containing a variety of oily and hydrocarbon materials, for example edible oils and some solvent type liquids, such as methanol.