Abstract:
A head-pressure-variant, self-healing, anti-liquid-leak coating for the outside of an upright wall in a liquid container. This coating possesses a thickness which varies from smaller toward larger advancing downwardly along a coated container wall. Preferred embodiments of the coating include: (a) one whose overall thickness varies in a linear way; (b) another whose thickness varies in a staged/stepped manner; and (c) a third whose thickness varies in a smooth, non-linear way. In all embodiments, the coating includes plural layers having interlayer-thickness relationships which are the same throughout the coating.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to currently pending, prior-filed U.S. Provisional Patent Application Ser. No. 60/677,872, filed May 4, 2005, for “Progressive Thickness Anti-Leak Barrier Coating”. The entire disclosure content of that prior-filed provisional case is hereby incorporated herein by reference. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     There has recently been developed a plural layer coating structure which may be applied to the outside surface of a sidewall in a liquid container to bring about rapid self-healing of a puncture wound in that sidewall. That development has been found to offer significant utility in sealing puncture wounds in a container holding combustible petrochemical fuel liquid. The term “container” is used to refer to any structure which holds such a liquid, such a vehicle gas tank, a large depot storage tank, a pipeline, and others. For background purposes, reference is here made to currently pending U.S. Regular patent application Ser. No. 11/067,525, filed Feb. 25, 2005, for “Projectile Barrier and Method”. The basic structure of such a protective coating, which preferably is a three-layer coating, is quite fully described and illustrated in that regular patent application, and as was just mentioned, reference is made to that application to provide the reader with relevant background information.  
         [0003]     The present invention addresses the recognition that container-stored liquid has associated with it what is known as head pressure which typically varies linearly and with an increasing value progressing downwardly from the surface of a contained liquid. Further recognizing that a puncture wound at a particular elevation in the sidewall of a container will determine the out-flow pressure relative to a container puncture wound, the present invention proposes a unique anti-leak protective barrier coating which, in three different embodiments, pays attention to this head-pressure consideration through possessing an increasing overall thickness from the upper to the lower potions of a liquid container wall which is to be protected by the coating.  
         [0004]     In one preferred embodiment of the invention, the coating increases smoothly and essentially linearly in an increasing-thickness fashion from top to bottom, and in this embodiment of the invention, that thickness, at every vertical point along the wall of a protected container, bears a fixed ratio, or relationship, with respect to liquid head pressure that also varies linearly progressing downwardly in that container.  
         [0005]     In another embodiment of the invention, the proposed coating takes the form of smoothly “flowing” progressive but non-linear thickness which might, as an illustration, follow a parabolic curve, a logarithmic curve, or other curve, etc.  
         [0006]     In yet a third embodiment of the invention which is illustrated and described herein, the coating of this invention is staged, or stepped, in a fashion whereby, progressing downwardly along a coated wall, one engages “units” of coating which have a defined height, and within that defined height, a substantially uniform thickness. As one progresses down the wall of a container with respect to this embodiment, one engages progressively thicker units of the type just generally described.  
         [0007]     Accordingly, the invention provides an opportunity for one to implement a protective coating of the style intended which uniquely relates its protective-coating thickness to expected stored-liquid head pressure within a protected container.  
         [0008]     These and other features and advantages of the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  shows, in solid lines, a preferred and best mode embodiment of the protective coating of this invention whose thickness grows larger progressing smoothly and vertically downwardly along a protected container wall, thus to relate coating thickness T, in a vertical positional sense, generally to expected internal liquid head-pressure HP, in the same vertical positioning sense. In particular,  FIG. 1  illustrates, in solid lines, a structure wherein the ratio T/HP remains substantially constant at all elevations along the pictured container wall.  
         [0010]     In dash-double-dot lines,  FIG. 1  illustrates one modified form of the invention, wherein coating thickness varies in what is referred to herein as a smoothly progressive, non-linear way, and very specifically in a curving manner which is logarithmic in nature.  
         [0011]      FIGS. 2 and 3  show another modified form of the invention which features a staged, or stepped, thickness protective coating, wherein the ratio T/HP is continuously variant along the vertical dimension of a container wall, but is essentially the same at plural (at least two) vertical locations along the vertical outside of a protected container. Each stage, or step, has essentially a “constant” thickness, and in  FIG. 2 , the ratio T/HP is substantially identical at the locations therein indicated at L 1  and L 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     Turning now to the drawings, and referring first of all to  FIG. 1 , indicated generally at  10  in solid lines, including three different characters of bounded shading lines, is a smoothly linearly thickness-tapered, anti-leak protective barrier coating which has been applied to the outside surface  12   a  of a liquid container  12  which contains a body of petrochemical fuel (not shown). Two specific levels within this body of liquid are illustrated by dash-double-dot lines L 1  and L 2  marked adjacent the right side of  FIG. 1 . Coating  10  includes three layers  10   a ,  10   b  and  10   c  which are generally formed in accordance with the teaching of above-referred-to, co-pending U.S. patent application Ser. No. 11/067,525. Layers  10   a  and  10   c  are formed of an appropriate high-elastomeric material, such as the product sold under the trademark TUFF STUFF®FR (with the letters FR standing for fire-resistant), made by Rhino Linings USA, Inc.—a company based in San Diego, Calif. Layer  10   a  is applied directly to the outside surface  12   a  of container  12 , and layer  10   c  is applied to the outside surface of an intermediate layer  10   b . Layer  10   b  is formed with a body of the same elastomeric material just mentioned which is employed singularly in layers  10   a ,  10   c , combined with an embedded population of liquid-imbiber beads (not specifically shown)—a bead product known as IMB230300, and made by Imbibitive Technologies America, Inc. in Midland, Mich.  
         [0013]     As explained in the &#39;525 co-pending patent application, all of these materials that are used to form coating  10  are applied by spraying. The sprayed elastomer material exhibits a high degree of elastic elongation capability before breakage of up to about 400%. The liquid-imbiber beads have been chosen because of their strong affinity for rapidly absorbing (imbibing) hydrocarbon fuel, an action which causes them to swell in volume and coagulate as a consequence. These beads, and the same is somewhat true with respect to the mentioned elastomeric body material, are rapidly reactive to contact with hydrocarbon fuel, and this reaction, coupled with the stretchiness of the elastomeric body material, results in this layer quickly functioning to seal a puncture wound, such as a bullet wound, in the sidewall of a container, such as the sidewall in container  12 .  
         [0014]     Further discussion about the operation of these materials with respect to sealing such a puncture wound is found in the text of the &#39;525 patent application.  
         [0015]     Although different relative layer thicknesses can be chosen for layers  10   a ,  10   b ,  10   c  in coating  10 , for the purpose of illustration herein, it will be assumed that at every elevation along container  12 , layers  10   a ,  10   c  have about the same thickness, which thickness is about twice that of intermediate layer  10   b  at the same elevation. This layer-thickness relationship is not drawn to scale n  FIG. 1 , but is so drawn in  FIG. 3  which will later be discussed. What will be noted with respect to the embodiment now being described is that the particular thickness T of layer  10  (shown at locations T 1 and T   2  in  FIG. 1 , and at one location T in  FIG. 3 ), at every elevation along the outside of container  12 , will have a fixed and consistent ratio, or relationship, with respect to the contained-liquid head pressure (HP) at that same elevation. And so, speaking about this a bit more specifically, at the two points P 1  and P 2  shown in  FIG. 1  which reside on the outside of layer  10  at elevations L 1  and L 2 , respectively, the ratio T/HP is identical at both of these locations. It is also identical at every other elevation. This is because, in the invention embodiment now being described, thickness T varies uniformly linearly progressing downwardly along coating  10 .  
         [0016]     Still considering what is shown in  FIG. 1 , and turning now to the curved dash-double-dot line  14  which appears adjacent the left side of  FIG. 1 , this line represents the outer surface of a modified three-layer coating  10  which is characterized in a manner whereby the internal thicknesses of layers  10   a ,  10   b ,  10   c  tend to thicken in a smoothly progressing, but non-linear, fashion, or way—growing thicker as one progresses downwardly vertically relative to container  12 . While different, non-linear, overall coating thickness variations may be employed, the variation illustrated by line  14  for the outer surface of layer  10   c  follows a generally logarithmic curvature. At every vertical location in modified layer  14 , the relative per-layer thickness relationships herein are the same as those described above with respect to the structure of layer  10 . In other words, the inner and outer layers which correspond to layers  10   a ,  10   c , respectively, have substantially the same thickness at every common elevation, and this thickness is approximately twice that of the thickness of the intermediate layer at the same elevation.  
         [0017]     Switching attention to  FIGS. 2 and 3  in the drawings, here there is shown, generally at  16 , what is referred to herein as a staged, or stepped, protective barrier coating, in which each step, and three such steps are shown in  FIG. 2  at  16   a ,  16   b ,  16   c , the overall layer thickness within such a step, remains substantially uniform throughout the entire vertical height of that step. Thus, the thickness of step  16   a  is uniform and smaller than the uniform thickness of step  16   b , which is smaller than the uniform thickness of step  16   c , as one progresses downwardly along the outside of container  12 . Within each step, such as within step  16   a  which is illustrated in a little more detail in  FIG. 3 , there is present, essentially, the same three-layer coating structure described earlier herein, with the inner and outer layers having thicknesses t 1  and t 3  that are about the same as one another, with each of these thicknesses being about twice the thickness (t 2 ) of the intermediate layer.  
         [0018]     With respect to this  FIG. 2 / FIG. 3  structure, what one will notice is that, throughout each step, and indeed as one progresses vertically along the outside of container  12 , the ratio T/HP, throughout the vertical dimension of each step, is continuously variable, although at the locations of the junctures between vertically next-adjacent steps, as illustrated at L 1  and L 2  in  FIG. 2 , the respective ratios T/HP are essentially identical to one another.  
         [0019]     As was true with regard to the invention embodiments pictured in and described with respect to  FIG. 1  in the drawings, the embodiment illustrated in  FIGS. 2 and 3  is one wherein the stepped, or staged, layer structure proposed essentially recognizes the variation in liquid head pressure existing in liquid contained within container  12 , but does so in a non-smoothly varying way.  
         [0020]     Accordingly, three important embodiments of the invention, useable selectively in different applications, have been described and illustrated herein for implementing features of the present invention. The manners specifically employed to apply, as by spraying, the various layers which make up the illustrated coatings are completely a matter of user choice, and may be entirely conventional in the relevant art. Thus, they are not discussed specifically herein.  
         [0021]     Accordingly, while several preferred embodiments of, and manners of implementing, the present invention have been described and illustrated herein, we appreciate that other variations and modifications may be made without departing from the spirit of the invention.