Elastomer coated fabric provided by a casting process

A coated fabric having a cured, synthetic elastomeric compound bonded thereto in a fashion to control the final weight and other physical and chemical properties thereof. The method comprehends the exposure of a fabric to an elastomer during its pot life to allow it to penetrate the fabric under "blotting" conditions and then quickly curing the elastomeric compound.

DISCLOSURE OF THE INVENTION 
This invention relates to a method of manufacturing coated fabrics and/or 
layers or films of a synthetic elastomeric compound. 
At the present time, fuel cells, or tanks, are employed on aircraft that 
are constructed of lightweight, non-metallic materials. The fuel cells 
that are used on aircraft must be constructed of material that has 
preselected physical properties and chemical resistant properties. These 
physical properties are particularly important for the manufacture of fuel 
cells that are utilized on helicopters. In the manufacture of a 
helicopter, the fuel cell must be sufficiently flexible so that it may be 
readily assembled with a minimum amount of time and effort into the 
storage area designed into the aircraft for the storage of the cell or 
tank. In addition to the usual physical properties that are required for a 
fuel cell, namely tough abrasion resistance, leakproof and chemical 
resistance, the fuel cell materials should have preselected, predictable 
weights for present day use. Aircraft fuel cells have been constructed in 
the past of rubber or rubber compounds due to the advantages inherent in 
the use of rubber or rubber compounds. Plastic coated fabrics have been 
utilized in the construction of fuel cells and have replaced rubber cells 
due to the superior physical properties exhibited by certain plastic 
coated fabrics. To this end, urethane coated fabrics have replaced fuel 
cells constructed of rubber due to the superior properties exhibited by 
the urethane plastic. Various types of fabrics, including synthetic 
fabrics, have been employed in combination with urethane plastics in the 
past. Most of these prior art fuel cells have been constructed by 
conventional fabricating techniques including molding or casting of the 
rubber and rubber compounds and the plastic coated fabrics. Since weight 
is such an important factor in the construction of an item to be employed 
on an aircraft, such as a helicopter, it is important to be able to 
periodically control the weight of the material during its manufacture 
prior to being employed in the manufacture of an item such as a fuel cell. 
In the construction of plastic coated fabrics for use in fuel cells, there 
has been no simple, inexpensive technique developed for coating a fabric 
to be used for a fuel cell and yet control the thickness of the coating 
and thereby the weight of the resulting fuel cell without resorting to 
conventional methods. One of the reasons that the weight of a coated 
fabric has not been controlled to the extent that the weight of the 
resulting end product falls within specified limits is that there has been 
a failure to control the extent of the penetration of the plastic material 
into the fabric resulting in varying weights of fabric and physical and 
chemical resistant properties when conventional manufacturing techniques 
are employed. 
In the use of plastic coated fabrics, I have found that the complete 
"wetting" of a fabric is not desirable for at least three reasons that 
affect the resulting physical properties of the material. One reason is 
that a plastic saturated fabric does not exhibit the "tear" resistance of 
a film or coating laid onto or bonded to the surface of the fibers. 
Secondly, because of the uneven rate of saturation of the plastic into the 
fabric, it is difficult to maintain a uniform thickness and therefore the 
weight of the plastic coated fabric. Thirdly, when the conventional 
coating process is employed for plastic coating of a fabric, air is 
employed during the manufacturing technique and is conveyed through the 
fabric up into the plastic material. It has been found that much of the 
air remains entrapped in the plastic material in the form of bubbles 
resulting in "pinholes". Accordingly, there is a need for an improved and 
relatively inexpensive technique for fabricating a coated fabric that may 
be manufactured by a process for controlling the thickness of the plastic 
coating and its penetration into the fabric proper and thereby the total 
weight of the resulting product. 
The present invention provides an improved and relatively inexpensive 
plastic coated fabric that is useful in the manufacture of fuel cells and 
many end products that require physical and/or chemical properties similar 
to the materials required for use in fuel cells. To this end, the process 
of the present invention allows the plastic coating thickness to be 
controlled and a wide range of substrate materials to be used with 
selected plastics. Some of the end products that the coated fabric of the 
present invention may be used for, in addition to fuel cells, are conveyor 
belts, liners for chutes or troughs used for handling abrasive materials, 
ink pads for the printing industry, large chemical holding tanks, "B" 
staged fabrics used in the molding industry, etc. The coated fabrics 
produced in accordance with the present invention exhibit physical 
properties including outstanding abrasion resistance, high tensile 
strength, superior tear strength, good flexing resistance and excellent 
oil, solvent and ozone and similar chemical resistance properties. 
From an end product standpoint, the present invention comprehends a coated 
fabric having a cured layer of a synthetic, elastomeric compound bonded to 
and impregnating the fabric without saturation of the fabric by the 
compound. The synthetic compound may be any heat activated plastic 
material and utilized with substrates of both synthetic and natural 
fibers. The synthetic, elastomeric compounds are preselected on the basis 
of physical and chemical properties required for the end use of the coated 
fabric. The end product produced in accordance with the present invention 
may also be a film or a layer of synthetic, elastomeric compound of a 
uniform thickness throughout. 
From a method standpoint, the present invention for manufacturing a coated 
fabric having a preselected weight and physical properties includes the 
steps of preparing a synthetic, elastomeric compound including the curing 
agent in combination with preselected formulating materials. The materials 
comprising the compound are selected so that the coated end product 
exhibits preselected physical properties. The prepared compound is further 
controlled to exhibit a preselected viscosity at approximately ambient 
temperatures in accordance with the construction of the fabric selected to 
be coated. In the use of one plastic, the prepared compound is in the form 
of a semi-solid and has a short pot life on the order of 3 minutes. The 
thus prepared compound is spread over the surface to cover the preselected 
surface area and to a preselected uniform depth throughout the covered 
surface area. The positioning of the fabric to be coated is the next step 
in the procedure and the fabric is placed over the top of the exposed 
surface of the compound, without exerting any pressure on the fabric, to 
allow the compound to become impregnated into the fabric in accordance 
with the preselected physical construction and the weight of the fabric 
for a preselected viscosity of the compound during the time interval of 
the pot life of the compound and then quickly subjecting the compound 
impregnated fabric to heat in the range of 200.degree. Fahrenheit for a 
preselected time period to cure the compound and thereby provide the 
coated fabric having the desired weight and physical properties. 
This same procedure may be utilized as described hereinabove for the 
manufacture of a thin film of a synthetic elastomeric compound without a 
substrate but having a preselected uniform depth. 
From a method standpoint, the present invention comprehends preparing a 
synthetic elastomeric compound including a curing agent in combination 
with the preselected formulating materials wherein the materials are 
selected so that the coated product exhibits preselected physical 
properties. The compound is prepared to exhibit a preselected viscosity at 
approximately ambient temperature in accordance with the physical 
construction of the fabric to be coated. The prepared compound is in a 
semi-solid state and spread over a surface to cover a preselected area and 
to a preselected uniform depth throughout. A fabric to be coated is 
positioned over the top surface of the compound, without exerting any 
pressure on the fabric, to allow the compound to be impregnated into the 
fabric in accordance with the physical cnstruction and weight of the 
fabric and the preselected viscosity of the compound, and then quickly 
subjecting the compound impregnated fabric to heat in the range of 
200.degree. Fahrenheit for a preselected time period to cure the compound 
and thereby provide the coated fabric as an end product.

Now referring to the drawing, the end product that may be manufactured in 
accordance with the method manufacture embodying the invention will be 
described in detail. The invention will be first described in terms of a 
manual method for manufacturing a coated fabric and in particular a coated 
fabric for use in the manufacture of a liquid container, a fuel cell or 
tank, for use on an aircraft helicopter. The particular physical and 
chemical properties required for a fuel cell to be employed on a 
helicopter, for example, are that it be constructed of materials that are 
physically tough from the standpoint of withstanding abrasion, have high 
tensile strength, be tear resistant, have good flexing resistance, be 
leakproof and be resistant to attacks from liquids such as fuels, fuel 
additives, oils and atmospheric conditions or environment to which it is 
exposed. The fabric should also be light in weight and the manufacturing 
process should include the ability to control the weight of the product 
within predictable tolerances while maintaining the aforementioned 
physical and chemical properties. 
FIGS. 1E and 1F illustrate the coated fabric 10 that is manufactured in 
accordance with the present invention and comprises an uncoated fabric 10F 
having a cured synthetic, elastomeric compound 10C bonded to one surface 
of the fabric 10F and impregnating the fabric, without saturating it. As 
noted in FIG. 1F, in particular, the cured elastomeric compound 10C does 
not completely penetrate the fabric 10F so that the fabric is exposed on 
one side of the coated fabric 10, as is evident from examining FIG. 1F. 
The elastomer 10C is coextensive with the opposite surface of the fabric 
10F and not only completely covers the fabric but also has a controlled 
thickness or depth "C", as illustrated in FIG. 1E. In one particular 
embodiment of the invention the cured, synthetic elastomeric compound 10C 
may be a synthetic elastomer including a urethane prepolymer mixed 
therein. One such urethane prepolymer is available from the Thiokol 
Chemical Division of the Thiokol Corporation located at 930 Lower Ferry 
Road, Trenton, N.J. The Thiokol urethane prepolymers are sold by the 
Thiokol Corporation under the trademark "Solithane" resins. The resulting 
synthetic elastomeric compound prepared through the use of the urethane 
resin is prepared by mixing a selected curing agent in combination with 
other preselected formulating materials so that the prepared elastomer 
exhibits a semi-solid viscosity at approximately ambient temperature and a 
three-minute pot life. The thus prepared compound is cured for bonding the 
compound to the fabric 10F by exposing it to a temperature of 
approximately 200.degree. Fahrenheit. The urethane resin prepolymer is not 
the only type of plastic material that can be used in the method of 
manufacturing the fabric 10 in accordance with the teachings of the 
present invention. A urethane coating for a fabric is particularly 
advantageous in the manufacture of a helicopter fuel cell or similar 
liquid container due to the physical and chemical properties that the 
cured elastomer exhibits. However, it should be understood that any heat 
activated resin including polyester plastics may be used in the disclosed 
method. The particular plastic material to be employed in preparing the 
elastomeric compound will depend upon the desired physical properties 
required of the end product for which it is used and the particular type 
of fabric upon which it is to be coated. 
For the purpose of this invention, any fabric may be employed with a heat 
activated plastic and satisfactory results may be obtained through the use 
of these fabrics including synthetic fabrics as well as natural fabrics. 
The substrate materials that have been successfully coated with synthetic 
elastomeric compounds in the manufacture of fuel cells for a heliocopter 
are nylon, rayon, aramid fiber sold by Du Pont under the trademark Kevlar, 
cotton and similar fabrics. The synthetic fabric nylon, for example, has 
been employed having different physical characteristics or weights of 
2-ounce, 12-ounce or 15-ounce materials. There does not appear to be any 
limitation with respect to implementing the present invention relative to 
the substrate or fabric 10F that may be coated in accordance with the 
teachings of the present invention and yet obtain a good bond without 
fully saturating the fabric with the compound coated thereon. 
A very important factor to be noted at this point is that the resins or 
urethanes that are sold by the Thiokol Corporation under the trademark 
"Solithane" are specified by this manufacturer to be processed by 
conventional casting or molding techniques. The usual end product for 
which the Solithane resins are employed is in the manufacture of casted or 
molded rollers, casters, mallet heads, etc., and similar parts requiring 
high abrasion and chemical resistance to oils, acids and similar liquids. 
The manufacturer does not recommend that such urethane resins be processed 
other than by casting or molding techniques due to the very short pot life 
of the resulting elastomer. As noted above, the pot life of the urethane 
elastomers is on the order of three minutes after which the compound will 
solidify and whereby the processing becomes very difficult unless the 
coating is immediately cured. In accordance with the present invention, 
however, the manufacturer's recommended procedures for preparing the 
elastomer are followed. In following these recommended procedures for 
mixing in the curing agent and the formulating materials no mechanical 
means are employed such as mixing and de-aerating equipment. 
The method of manufacturing a coated fabric in accordance with the present 
invention may be characterized as a "reverse" coating procedure that has 
resulted from my attempting to coat a fabric with the Solithane urethane 
resins and experiencing that the "wetting" or penetration of the plastic 
into the fabric was not predictable and many coats of the plastic had to 
be applied to the fabric to assure that a leakproof coating was produced. 
Although this procedure would produce a product that exhibited physically 
strong properties, the manufacturing procedure was unacceptable and 
relatively expensive. 
Now referring to FIGS. 1A-1D, the sequential steps for producing the coated 
fabric 10 utilizing a urethane prepolymer for the elastomeric coating will 
be examined in detail. The first step in the procedure is the mixing of 
the elastomeric compound for use in the reverse coating procedures. The 
compound for the substrate coating is a heat activated synthetic polymer 
such as the urethane polymer commercially available from the Chemical 
Division of the Thiokol Corporation of New Jersey. Along with this 
selected prepolymer, a polymer curing agent is mixed in with selected 
formulating materials to produce the desired compound. The selection of 
these materials is governed by the desired physical and chemical 
properties that the end product should exhibit as well as the physical 
properties of the fabric to be coated. Once the elastomeric compound is 
prepared, it is deposited on a stationary plate which is identified as a 
"caul" plate 12. The compound 10C is spread over a preselected area and to 
a preselected uniform thickness on the caul plate 12. To obtain a uniform 
thickness throughout the compound 11, the compound may be spread on the 
caul plate by means of a scraper bar 13. The bar 13 may be provided with 
shims 14 and 15 adjacent each end and the shims are provided with a 
thickness in accordance with the desired thickness of the coating or 
compound 11 for the coated fabric 10. To assure that no pinholes exist in 
the final product and which pinholes may be caused by dust and air 
entrained in the mixed compound, a number of coats of the compound may be 
applied to the plate 12. If the compound is mixed by mechanical means, for 
example, these extra steps may be omitted. 
After the compound 10C is finally prepared to the right depth on the 
selected area of the caul plate 12, the fabric 10F will be positioned or 
rolled over the exposed surface of the compound 10C. The fabric 10F is 
placed over the elastomer's surface without any pressure exerted on the 
fabric. The fabric 10F is illustrated in FIG. 1C in this position and is 
identified by the reference numeral 10F. It may be rolled onto the exposed 
surface of the compound 10C while minimizing the pressure exerted on the 
fabric 16. In accordance with the present invention, it is desired that 
the penetration of the compound 10C into the fabric 10F be governed by the 
physical properties including the weight of the fabric 10F and the 
viscosity of the elastomeric compound 10C. The penetration or absorption 
of the compound 10C into the fabric 10F may be considered to be a 
"blotting" or "soaking up" of the compound by the fabric 10F, but without 
pressure, and in this fashion the penetration of the plastic into the 
fabric is controlled without completely saturating the fabric. It is 
desired that the basic pressure applied during this step of the method is 
the weight of the fabric. 
After the fabric 10F is so positioned and before the expiration of the time 
interval representing the pot life of the compound 10C, the combination of 
the fabric 10F and the compound 10C is exposed to a curing station wherein 
heat is applied thereto at a temperature on the order of 200.degree. 
Fahrenheit. During this heating stage, the elastomeric compound is cured 
and bonded to the fabric. Once the curing interval has expired, the 
resulting coated fabric 10 will be removed from the caul plate 12 to be 
utilized for its intended purpose. The coated fabric 10 will appear as 
illustrated diagrammatically in FIGS. 1E and 1F with the coating 11 
essentially on one side of the fabric 10F. At this point, it should be 
noted that the caul plate 12 may have a preselected pattern recorded 
thereon and which pattern is to be transferred to the cured plastic 
compound after it is removed from the plate 12. Such a pattern, for 
example, may be an outline to be used for cutting and further fabrication 
of the completed end product. 
Now referring to FIG. 2, the diagrammatic representation of an arrangement 
for manufacturing the coated fabric 10 on a continuous basis will be 
examined. The plastic material, such as the urethane resin, is deposited 
on a temporary carrier or conveyor for continuously advancing the plastic 
material to be processed through the various stations or method steps 
required. To this end, the carrier or conveyor may comprise a spool 20 
storing a continuous length of Teflon film 22 arranged adjacent one end of 
a coating table 21. The conveyor material 22 is advanced to a take-up 
spool 23 for storing the conveyor material or Teflon film as it advances 
through each of the stations required for processing the fabric 10F. The 
film supply spool 20 and the take-up spool 23 may be controlled in a 
conventional fashion by individual drive motors 20M and 23M as 
diagrammatically illustrated. The speed with which the conveyor material 
is advanced through the various stations is in accordance with the pot 
life of the elastomeric compound being employed as well as the physical 
property of the fabric in order to properly produce the coated fabric 10. 
For the purposes of depositing the plastic material onto the Teflon 
conveyor material 22, a traversing head 24 is employed. The traversing 
head 24 stores the elastomeric compound 10C to be coated on the fabric 10F 
and traverses the area above the conveyor material 22 to cover a 
preselected area thereon. A knife-edged thickness control device 25 is set 
to the proper height above the material 22 to spread and maintain the 
deposited plastic compound to a desired uniform thickness throughout. This 
spread-out plastic layer 10C is then advanced towards the fabric 10F to be 
coated which is stored on an individual fabric storage spool 26 and 
advanced into engagement with the top surface of the advancing layer of 
plastic for absorbing the plastic as it is positioned thereon. The fabric 
spool 26 is controlled by an individual control motor 26M along with the 
provision of the guide rollers 27 to assure the exact registration between 
the fabric 10F and the exposed surface of the compound layer 10C. 
After the fabric 10F is positioned over the layer of compound 10C, without 
exerting any pressure on the fabric 10F, it is quickly advanced to a 
curing station illustrated in FIG. 2 as an oven 28. The oven 28 provides a 
heating zone having a temperature on the order of 200.degree. Fahrenheit 
to cure the plastic compound, bond it to the fabric and provide the 
desired coated end product. It will be appreciated that the traversal time 
through the oven 28 is selected to allow sufficient time for the plastic 
to be cured and bonded to the fabric 10F. After the cured, coated fabric 
10 emerges from the oven 28, the carrier film 22 is stripped from the 
coated fabric and stored on its individual supply reel 23. Similarly, the 
coated fabric 10 having the conveyor material 22 stripped therefrom may be 
stored on an individual storage reel 29 as it is advanced thereto. The 
storage reel 29 for the coated fabric 10 is controlled in the same fashion 
as each of the other reels in the system by an individual motor 29M. 
As in the previous embodiment, a pattern may be transferred onto the 
adjacent surface of the compound during the manufacturing procedure. In 
this embodiment, the conveyor material 22 may have a design, or a pattern, 
recorded thereon so that it will be transferred to the cured plastic 
material and be visible once the material 22 is stripped therefrom. This 
pattern, as in the previous embodiment, is used for cutting and/or 
fabricating the coated fabric 10 into the desired material or end product. 
In accordance with the above procedures, then, the coated fabric 10 that is 
produced may be used in the manufacture of a liquid container such as a 
helicopter fuel cell and also in many other end products such as conveyor 
belts, chutes, troughs, etc. This result is due to the ability to control 
the thickness of the coating and its penetration into the fabric 10C and 
thereby the weight. To this end, it will be appreciated that the end 
product prepared in accordance with the above teachings may eliminate the 
fabric and merely provide a thin film of plastic compound having a 
substantially uniform thickness for use in conjunction with other 
substrates and bonded thereto by more conventional techniques. It has been 
found that when a urethane plastic, for example, is used as a prepolymer 
in the elastomeric compound for coating a fabric that it compares 
favorably with the rubber when used in similar applications. A urethane 
coated fabric 10 exhibits a wide range of fuel and chemical resistance as 
well as being very resistant to ozone and ultra-violet light. Incandescent 
lights appear to have little effect on the coated fabric. The abrasion 
resistance of the coated fabric 10 is three times better than natural 
rubber. The coated fabric 10 is well suited to utilize mass production 
techniques for the manufacture of helicopter fuel cells. The prepared 
elastomeric compound can be handled in an uncured or "B" stage since it is 
not tacky. The urethane as utilized and obtained from the manufacturer is 
in a 100 percent solid state. As contrasted with the use of rubber, for 
example, the type of rubber employed must be changed in accordance with 
the chemicals or the fuels to which it may be subjected. Rubber is known 
to have poor resistance to ultra-violet light and ozone. The shelf life of 
a rubber product is such that it must be packed in a carton when stored in 
a warehouse, etc. It has also been found that when a helicopter fuel cell 
is constructed of a butyl or nitrate rubber that it exhibits poor 
resistance to abrasion and such synthetic rubbers are not as good as 
natural rubber. Since the surface of rubber is tacky, it must be carefully 
handled and the number of hours of labor for processing the rubber is very 
high. Rubber molds are not reusable and the number of rejects in the 
manufacture of rubber products is very high during the manufacturing 
procedure. The number of fabrics that may be coated with rubber is limited 
as compared to the fabrics coated according to the procedures of the 
present invention. Some fabrics require that a primer be used with it for 
rubber coating purposes. In a rubber product, the seams must be bonded 
with an adhesive having a solvent as a thinner. The solvent must "flash 
off" dry or a blister will form from the gassing during the manufacturing 
procedures.