| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | May 15, 2001 |
| PATENT TITLE |
Barrier coating of an elastomer and a dispersed layered filler in a liquid carrier and coated articles |
| PATENT ABSTRACT |
Applications of barrier coating mixtures containing in a carrier liquid, (a) an elastomeric (preferably butyl-containing) polymer; (b) a dispersed exfoliated layered filler having an aspect ratio greater than 25; and (c) at least one surfactant, wherein the solids content of the mixture is less than 30% and the ratio of polymer (a) to filler (b) is between 20:1 and 1:1 include coated articles, which are elastomeric, e.g., sports balls and inflatable articles. Methods of manufacturing such coated products are also encompassed. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | June 10, 1999 |
| PATENT REFERENCES CITED |
G. van Amerongen, "Diffusion in Elastomers", Rubber Chem. Tech., 37:1065-1152 (1964). E.L. Cussler et al, "Barrier Membranes", Journal of Membrane Science, 38:161-174 (1988). D. Eitzman et al, "Barrier Membranes with Tipped Impermeable Flakes", AICHF. Journal, 42(1):2-9 (Jan. 1996). P. Messersmith et al, "Synthesis and Barrier Properties of Poly (.alpha.-Caprolactone)-Layered Silicate Nanocomposites", J. of Polymer Science, 33:1047-1057 (1995). B. Pant et al, "Modification of Polystyrene Barrier Properties", Polymer,35(12):2549-2553 (1994). W.J. Ward et al, "Gas Barrier Improvement Using Vermiculite and Mica in Polymer Films", Journal of Membrane Science,55:173-180 (1991). Japanese Patent Application No. JP5017641, published Jan. 26, 1993 (Abstract). Japanese Patent Application No. JP7081306, published Mar. 28, 1995 (Abstract). Japanese Publication No. 63189446, published Aug. 5, 1988 (Abstract only). International Standard, ISO 2556-1974 (E), "Plastics--Determination of the Gas Transmission Rate of Films and Thin Sheets under Atmospheric Pressure--Manometric Method", European Committee for Standardization pp. 36-39 (1974). |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A coated article comprising an elastomeric substrate that contains air or a gas under pressure, and having on an interior or exterior surface of said substrate a barrier coating formed by: (a) applying to said surface without melt processing or high shear mixing an aqueous solution comprising: (i) an elastomeric polymer; (ii) a dispersed exfoliated layered filler having an aspect ratio greater than 25; and (iii) at least one surfactant, wherein the solids content of said solution is less than 30% and the weight ratio of said polymer to said filler ranges from 20:1 to 1:1; and (b) drying said solution to form said barrier coating, wherein said dried barrier coating has a polymer to filler weight ratio, which ranges from 20:1 to 1:1 and wherein said coating provides at least 10-fold greater reduction in gas, vapor, and chemical permeability than a coating formed of said polymer alone. 2. The article according to claim 1 selected from the group consisting of tennis balls, basketballs, soccer balls, footballs, volley balls, racket balls, handballs, beach balls and toy balls. 3. The article according to claim 1 which is an inflated product. 4. The article according to claim 3 which is selected from the group consisting of boats, air mattresses, and inflatable beds. 5. The article according to claim 1 wherein said elastomeric substrate is capable of excluding or resisting the penetration of air, water, or other gas or vapors. 6. The article according to claim 1, wherein said polymer is in a form selected from the group consisting of a solution, a dispersion, an emulsion, a suspension and a latex. 7. The article according to claim 1 wherein said polymer is a butyl-containing polymer. 8. The article according to claim 7 wherein said butyl-containing polymer is a co-polymer of (poly)isobutylene and a second polymer, said copolymer being cured, uncured or partially cured. 9. The article according to claim 7 wherein said butyl-containing polymer is a poly(isobutylene) homopolymer. 10. The article according to claim 8 wherein said co-polymer is halogenated. 11. The article according to claim 7 wherein said co-polymer is butyl rubber. 12. The article according to claim 10, wherein said co-polymer is selected from the group consisting of bromobutyl rubber and chlorobutyl rubber. 13. The article according to claim 8 wherein said butyl-containing copolymer contains more than 50% isobutylene. 14. The article according to claim 1 wherein said polymer is present in said solution at between about 1% to about 30% by weight. 15. The article according to claim 1, wherein said filler is selected from the group consisting of bentonite, vermiculite, montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, laponite, sauconite, magadiite, kenyaite, ledikite, and mixtures and solutions of the above silicates. 16. The article according to claim 1 wherein said filler is vermiculite. 17. The article according to claim 1 wherein said dispersed layered filler is present in said solution at between about 1% to about 10% by weight. 18. The article according to claim 1, wherein said solution has a solids content of from about 5% to about 17% by weight. 19. The article according to claim 1 wherein said surfactant is selected from the group consisting of an emulsifier, an anti-foaming agent, a defoaming agent, a dispersing agent, a wetting agent, a leveling agent, and a thickener. 20. The article according to claim 19 wherein said thickener is a polymer containing polyvinyl alcohol. 21. The article according to claim 19 wherein said thickener is lithium chloride. 22. The article according to claim 19 wherein said solution comprises at least two surfactants, which include a wetting agent and an anti-foaming agent. 23. The article according to claim 1 wherein said solution further comprises a component selected from the group consisting of hexane, heptane, toluene, 1-methyl-2-pyrrolidinone, cyclohexanone, ethanol, methanol, other hydrocarbons, and combinations thereof. 24. The article according to claim 1 wherein said solution further comprises curative components which enhance the curing of said barrier coating on said substrate. 25. The article according to claim 1, wherein said dried coating comprises about 45% to about 95% by weight of said polymer, between about 5% to about 55% by weight said dispersed layered filler; and between about 1.0% to about 15% by weight said surfactant, said filler in said dried coating or film having an effective aspect ratio greater than 25. 26. The article according to claim 25, wherein said filler is present in said dried coating at greater than about 5% by weight. 27. The article according to claim 25, wherein said filler in said dried coating having an effective aspect ratio greater than 50. 28. The article according to claim 25, wherein said filler in said dried coating having an effective aspect ratio greater than 100. 29. The article according to claim 1 wherein said solution is aqueous, said polymer is a butyl-containing polymer latex, said filler is vermiculite having an aspect ratio about 1000 or greater; and the solids content of said solution is less than 17% by weight. 30. The article according to claim 29, wherein said solution has a solids content of between about 5 to about 15% by weight, and said dried barrier coating comprises between about 65% to about 90% by weight said butyl-containing polymer, between about 10% to about 35% by weight said vermiculite filler, and between about 1.0% to about 15% by weight said surfactant, said filler in said dried coating having an effective aspect ratio of greater than 25. 31. The article according to claim 1 wherein said dried barrier coating comprises about 45% to about 95% by weight of an elastomeric polymer, between about 5% to about 55% by weight of a dispersed exfoliated layered filler; and between about 1.0% to about 15% by weight of said surfactant, said filler in said dried coating or film having an effective aspect ratio greater than 25, wherein said dried coating reduces the gas, vapor or chemical permeability of said article greater than 10fold the permeability of said substrate coated with said polymer alone. 32. The article according to claim 31 wherein said substrate is flexible or elastomeric and said coating maintains its permeability after repeated mechanical loading and elongation up to about 10% of said substrate. 33. A method of manufacturing an article comprising an elastomeric substrate that contains air or another gas under pressure, comprising: (a) applying directly on an interior or exterior surface of said substrate a barrier coating mixture, wherein said coating is formed by applying to said surface without melt processing an aqueous solution comprising: (i) an elastomeric polymer; (ii) a dispersed exfoliated layered filler having an aspect ratio greater than 25; and (iii) at least one surfactant, wherein the solids content of said solution is less than about 30% and the weight ratio of said polymer to said filler ranges from 20:1 to 1:1; and (b) drying said solution to a barrier coating, wherein said dried barrier coating has a weight ratio of polymer to filler, which ranges from about 20:1 to about 1:1 and wherein said coating provides at least 10-fold greater reduction in gas, vapor, and chemical permeability than a coating formed of said polymer alone. 34. The method according to claim 33 wherein said article is selected from the group consisting of tennis balls, basketballs, soccer balls, footballs, volley balls, racket balls, handballs, beach balls and toy balls. 35. The method according to claim 33 wherein said article is selected from the group consisting of an inflated products selected from the group consisting of boats, air mattresses, and inflatable beds. 36. A sports ball comprising an elastomeric substrate that contains air or a gas under pressure, and having on an interior or exterior surface of said ball or at the interface of said surfaces a barrier coating formed by applying to said surface without melt processing an aqueous solution comprising: (a) an elastomeric polymer; (b) a dispersed exfoliated layered filler having an aspect ratio greater than 25; and (c) at least one surfactant, wherein the solids content of said solution is less than about 30% and the weight ratio of said polymer to said filler ranges from 20:1 to 1:1. |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention relates to novel barrier coatings and their use in the manufacture of articles requiring reductions in gas, chemical and vapor permeability. BACKGROUND OF THE INVENTION Barrier coatings which prevent, or reduce, contact of a selected substrate with a gas, vapor, chemical and/or aroma have been widely described, and such coatings are used in a variety of industries, e.g., the packaging industries, automobile industries, paint industries, tire industries etc. Some of these barrier mixtures or coatings have been proposed to contain plate-like structures to reduce permeability. See, for example, E. L. Cussler et al, J. Membrane Sci., 38:161-174 (1988); W. J. Ward et al, J. Membrane Sci., 55:173-180 (1991); U.S. Pat. Nos. 4,528,235; 4,536,425; 4,911,218; 4,960,639; 4,983,432; 5,091,467; and 5,049,609; and International Patent Application No. WO93/04118, published Mar. 4, 1993, among others. Despite the numerous disclosures of barrier coatings mixtures, most of the coatings useful in the industry either do not optimally reduce permeability or tend to be brittle and non-flexible. For example, attempts to improve the gas permeability of butyl rubber as well as retain its elasticity and fatigue resistance, have involved coating butyl rubber in tires with a polymer containing a platelet filler. See, e.g., U.S. Pat. Nos. 4,911,218 and 5,049,609. Only minimal decreases in permeability were achieved by this process. Other attempts to increase the gas barrier properties of rubber used in tires have included compositions of rubber having layered silicate platelets dispersed within the rubber composition. See e.g. U.S. Pat. No. 4,857,397; WO97/00910 and G. J. van Amerogen, "Diffusion in Elastomers", Rubber Chem Tech 37, pp 1065-1152 (1964). Exfoliated layered silicate material has been used to improve the gas barrier properties of rubber. See, e.g. U.S. Pat. No. 5,552,469. Several references have been made to the orientation of platelet materials in rubber and polymeric compositions. Specific perpendicular orientation of the platelets to the direction of gas diffusion has been found to decrease gas permeability of rubber compositions containing layered silicate platelets, while not adversely affecting the flexibility of the rubber. See e.g. U.S. Pat. Nos. 5,576,372; 5,576,373; and 5,665,183. Puncture resistance is increased in polymeric sheet material comprising discrete platelets which are oriented substantially parallel to the plane of the sheet material in an overlapping interrelation. See, e.g., U.S. Pat. No. 5,665,810. Most of the coatings useful in the industry which contain platelet type fillers are prepared by melt processing, in which solid polymer and solid filler are melted together and mixed at high shear rates. Such melt-processed coatings have 100% solids, and usually use less than about 3% by weight of the platelet fillers. Such coatings do not optimally reduce permeability. Various improvements have been described in the manufacture or treatment of tires or tire components to decrease permeability of the inner tire surface or the interfaces between the tire layers or components to gases, vapors and chemicals. In the tire industry, for example, it has been conventional to add fillers, e.g., carbon black, up to about 30% by volume (or 100 parts per hundred) to innerliners, or to use coatings to improve impermeability of butyl rubber. However, such attempts have not been found to optimally reduce permeability. Tires with integral innerliners are disclosed in U.S. Pat. No. 5,178,702, wherein the tire has a top layer and multiple layers of rubber laminate in which at least two layers are barrier layers comprising a sulfur cured rubber composition having 100 parts by weight rubber, 100 parts by weight acrylonitrile/diene polymer and about 25-150 parts by weight of platy filler of unspecified width and thickness. These compositions are stated to reduce the costs of the innerliners while maintaining flexibility and barrier performance. An additional application for barrier coatings utilizing elastomers with fillers is as a coating or bladders or other surfaces in pneumatic devices or any device under pressure such as sport balls, etc. Many sport balls use a bladder to hold air or other gas inside the ball. Sport ball bladders are currently made using natural or butyl rubber or polyurethane. The choice of these materials is determined by the trade-off between mechanical properties, air barrier properties, and cost. The use of standard, non-flexible barrier coatings to reduce the loss of air or the thickness of the bladder is not acceptable due to the flexibility requirements of the application. There remains a need in the art for barrier coating mixtures and flexible and elastomeric articles with improved permeability characteristics useful in a variety of industries. More particularly, there is a need in the art for barrier coating mixtures to improve the air retention and/or reduce the thickness of the innerliner in sport balls and any other device under pressure, such as soccer balls, basketballs, tennis balls, toy balls, inflatable boats, inflatable mattresses or beds, etc. SUMMARY OF THE INVENTION The present invention solves the problems of the prior art by providing a coating composition which contains substantially dispersed exfoliated layered silicates in an elastomeric polymer. This coating, when dried, results in an elastomeric barrier with a high effective aspect ratio and improved permeability characteristics, i.e., a greater increase in the reduction of permeability of the coating. This coating has multiple applications, including, for example, tires, sport balls, and articles in which an internal air pressure must be maintained. In one aspect, the present invention provides a coated article comprising an elastomeric substrate that contains air or a gas under pressure, and having on an interior or exterior surface of said substrate a barrier coating formed by applying to said surface a mixture comprising in a carrier liquid: (a) an elastomeric polymer; (b) a dispersed exfoliated layered platelet filler having an aspect ratio greater than 25; and (c) at least one surfactant. The solids content of said mixture is less than 30% and the ratio of polymer (a) to filler (b) is between 20:1 and 1:1. The coating is dried on the coated surface, wherein said dried barrier coating has the same polymer to filler as in said mixture and provides an at least 5-fold greater reduction in gas, vapor, moisture or chemical permeability than a coating formed of said unfilled polymer (a) alone. The coated article comprises any elastomeric substrate that contains air or another gas under pressure, or an elastomeric substrate that requires the exclusion of air, water, or other gas or vapors. Such coated articles include, e.g., sports balls, such as tennis balls, basketballs, etc., as wells as golf balls (for moisture resistance), inflatable boats and air mattresses and other inflatable beds, and the like. In one preferred embodiment, the article is coated with a barrier coating mixture, which contains the polymer at between about 1 to 30% in liquid form and between about 45% to about 95% by weight in the dried coating. The dispersed layered filler is present in the liquid coating mixture at between about 1 to about 10% by weight, and in the dried coating formed thereby, at between about 5% to about 55% by weight. The dried coating, in which the filler exhibits an effective aspect ratio of greater than about 25, and preferably greater than about 100, reduces the gas, vapor or chemical permeability greater than 5-fold that of the dried, unfilled polymer alone. In another preferred embodiment, the invention provides an elastomeric article coated with a preferred barrier coating mixture which has a solids contents of between about 5 to about 15% by weight, and comprises in its dried state between about 65% to about 90% by weight of a butyl rubber latex, between about 10% to about 35% by weight of a layered filler, desirably vermiculite, and between about 0.1% to about 15% by weight of a surfactant. In another aspect, the invention provides a sports ball, inflated product or a golf ball having on a surface or at the interface of two surfaces therein a dried barrier coating formed by a barrier coating mixture comprising in a carrier liquid: (a) an elastomeric polymer; (b) a dispersed exfoliated layered platelet filler having an aspect ratio greater than 25; and (c) at least one surfactant, wherein the solids content of said mixture is less than 30% and the ratio of polymer (a) to filler (b) is between 20:1 and 1:1. When dried, the coating comprises about 45% to about 95% by weight of said polymer, between about 5% to about 55% by weight said dispersed layered filler; and between about 1.0% to about 15% by weight said surfactant. The coating on the article, in which the filler exhibits an effective aspect ratio of greater than about 25, preferably greater than about 100, reduces the gas, vapor or chemical permeability of the tire greater than 5-fold the permeability of the article coated with the polymer alone. In still another aspect, the invention provides a sports ball, inflated product or golf ball having on a surface or at the interface of two surfaces therein a dried barrier coating formed by a barrier coating mixture comprising in a carrier liquid: (a) a butyl-containing polymer latex; (b) a dispersed exfoliated layered vermiculite filler having an aspect ratio about 1000 or greater; and (c) at least one surfactant, wherein the solids content of said mixture is less than 17% and the ratio of polymer (a) to filler (b) is between 20:1 and 1:1. In a preferred embodiment, the coating mixture has a solids content of between about 5 to about 15% by weight, and forms a dried coating on said surface that comprises between about 65% to about 90% by weight said butyl-containing polymer, between about 10% to about 35% by weight said vermiculite filler, and between about 1.0% to about 15% by weight said surfactant. The coating on the ball, inflated product or golf ball, in which the filler exhibits an effective aspect ratio of greater than about 25, preferably greater than about 100, reduces the gas, vapor or chemical permeability of the tire greater than 5-fold the permeability of the article coated with the polymer alone. In still a further aspect, the invention provides a method for making a sports ball, inflated product or golf ball, the method consisting of coating a surface of said ball or product with, or introducing into the interface between two surfaces of said ball or product, an above-described barrier coating mixture. Other aspects and advantages of the present invention are described in the detailed description below and in the claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a "Cussler" model graph indicating the effective aspect ratios achieved by compositions of this invention. The graph plots reduction of permeability vs. volume percentages of filler in barrier coating mixtures of the present invention. Cussler describes several models for the permeability reduction due to oriented layered fillers, which depend on the microstructure expected. For simplicity, this invention employs the equation: P.sub.u /P=[1+(a.sup.2 X.sup.2)/(1-X)]/(1-X), where P is the permeability of the filled material, P.sub.u is the permeability of the unfilled material; a is the aspect ratio of the filler particles; X is the volume fraction of the filler particles in the coating. Cussler's theoretical curves for fillers with aspect ratios of 25, 50, 75, and 100 are present on the graph. The thick "experimental" data line records the experimental data points for the barrier coating mixtures of Examples 1-8 below. Effective aspect ratios can be estimated from the position of the data relative to the theoretical curves. FIG. 2 is a graph plotting permeability results based on the weight percentage of a filler, vermiculite. Permeability is plotted vs. weight % of filler. Increase in weight % of filler decreases the permeability of the coating. FIG. 3 is a graph plotting reduction in permeability vs. weight % of filler in coating. Increase in weight % of filler increases the reduction of permeability. FIG. 4 is a graph illustrating the maximum percentage solids useful in coating compositions of the invention using butyl latex (BL100.TM.), vs. percentage by weight of MICROLITE.RTM. vermiculite in the compositions. FIG. 5 is a graph illustrating the butyl latex (BL100.TM.) to filler ratio useful in coating compositions of the invention vs. percentage by weight of MICROLITE.RTM. vermiculite in the compositions. FIG. 6 illustrates flexibility data at 10% elongation, 1K cycles based on the flex test of Example 17. FIG. 7 is a graph of the static air retention at 65.degree. C. in P195/70R14 MX4 tires, which plots pressure in bars vs. time in days for two tires with normal butyl innerliners (.diamond. and .diamond-solid.), two tires in which the butyl inner liner was replaced with carcass rubber (.DELTA. and .tangle-solidup.), and three tires having the barrier composition of Example 16 coated onto the carcass rubber innerliner (.smallcircle., large and small .circle-solid.). DETAILED DESCRIPTION OF THE INVENTION The present invention fills the unmet need in the art of barrier coatings by providing barrier coating mixtures suitable for application to flexible or elastomeric substrates, including flexible or elastomeric substrates under pressure, such as tires, sports balls and toy balls. These coatings of the invention reduce the gas, vapor or chemical permeability of these substrates. The coated articles, as well as free-standing films and membranes produced by these barrier coating mixtures are also provided by the invention. Improved sports balls, toy balls and inflated products prepared by use of these coatings demonstrate reduced permeability to air, gas, vapor and chemicals. Improved golf balls prepared by use of these coatings demonstrate reduced permeability to moisture. Improved tires and tire components prepared by use of these coatings demonstrate reduced permeability to air, gas, vapor and chemicals. The balls, inflated products, and methods of manufacturing such products according to this invention enhance the longevity of the product. The compositions and methods of this invention rely on the use of the barrier coating mixtures to coat various interior and exterior surfaces of the balls, and other products and interfaces to improve performance and/or lower cost. I. Definitions As used herein, the term "mixture" or "coating mixture" is interpreted to include true liquid solutions, as well as colloidal dispersions, suspensions, emulsions and latexes as they are conventionally defined. For example, by "colloidal dispersion or latex" is meant any dispersion or suspension of particles in liquid, the particles being of a size greater than molecular scale, e.g., about 0.001 to about 0.1 micron. An emulsion generally contains particles of about 0.05 to 1.0 microns, in liquid. A "suspension" generally contains particles of greater than 1.0 micron in liquid. A "barrier coating mixture" as used herein is meant a liquid containing dissolved or suspended solids, which is used to apply said solids to a substrate. A novel aspect of the present invention is that the barrier coating mixtures provide a better dispersion of platelet fillers in liquid at an unusually low solids content, e.g., between about 1 to about 30% solids as described in more detail below. According to this invention, once the "coating mixture" is dried, it is referred to as a "dried coating" or a "film". The term "vapor barrier" implies a barrier to a liquid and its vapor. Conventionally, a vapor is the gas in equilibrium with a liquid at atmospheric pressure. For simplicity, as used herein, the term "vapor barrier" can be interpreted to mean a barrier to gases and chemicals as well as traditionally defined vapors, as well as a barrier to moisture, generally water or water vapor. The term "gas barrier" includes a barrier to oxygen, nitrogen, carbon dioxide and other gases. "Chemical barrier" includes a barrier to the migration or blooming of a molecule from one substrate to another or out of one substrate to that substrate's surface. The term "substrate" or "article" coated by these coatings include, without limitation, flexible and elastomeric (or highly elastic) materials, such as rubber, and other surfaces, such as tires, balloons, gloves, prophylactics, diaphragms and membranes for accumulation, actuators and regulators, and the like. A rubber tire innerliner, as well as other elastomeric or flexible surfaces or interfaces within a tire are also substrates according to this invention. The term "substrate" or "article" coated by these coatings also includes, without limitation, any elastomeric containing object that either contains air or another gas under pressure, or requires the exclusion of air, water, or other gas or vapor. Specific examples of such elastomeric substrates include, without limitation, sports equipments, such as tennis balls, basketballs, soccer balls, footballs, volley balls, racket balls, handballs, toy balls, beach balls, etc. Any elastomeric substrate under pressure may also be a substrate useful in this invention, including, for example, inflatable boats, air mattresses and inflatable beds. An additional substrate is an elastomeric surface requiring protection from moisture, e.g., the interior surfaces of golf balls. The term "aspect ratio" is a characteristic of every platelet material in solid form. Aspect ratio is the product of the lateral dimension of a platelet filler particle, e.g., mica flake, divided by the thickness of the platelet. "High aspect ratio" refers to a platelet filler whose lateral dimension divided by thickness is greater than 25. The aspect ratio of any filler is an inherent property of the selected filler. For example, MICROLITE.RTM. 963++ aqueous vermiculite solution [W. R. Grace] has a characteristic aspect ratio of about 10,000 or dimensions of 10-30 .mu.m.times.10 .ANG.. Intercalation is defined as the state of a coating composition in which polymer is present between each layer of a platelet filler. Intercalation can be defined by the detection of an X-ray line, indicating a larger spacing between vermiculite layers than in the original mineral. "Exfoliation" is defined for layered fillers as the complete separation of individual layers of the original particle, so that polymer completely surrounds each particle. Desirably so much polymer is present between each platelet, that the platelets are randomly spaced. No X-ray line appears because of the random spacing of exfoliated platelets. In some circumstances, the filler can exfoliate when dispersed in an aqueous or non-aqueous medium. This would result in a higher aspect ratio than that of a solid particle before dispersion. The term "effective aspect ratio" relates to the behavior of the platelet filler when incorporated into a binder. The platelet may not exist in a single platelet formation, but in many forms, such as a bundle of 10-50 platelets or hundreds of platelets, referred to as agglomerates. If the platelets are not in the single layer form, the aspect ratio of the entire bundle or agglomerate is much lower than that of the single layer particle. Therefore, the aspect ratio of the particles in a binder is referred to as an effective aspect ratio. The effective aspect ratio is determined by plotting the experimental data versus theoretical model, such as described by E. L. Cussler et al, J. Membrane Sci., 38:161-174 (1988). A graph of reduction in permeability versus the volume % of filler in the binder generates theoretical curves for each effective aspect ratio. The graph predicts an effective aspect ratio for the experimental data. See FIG. 1. It is important in the understanding of the effects of the coatings of this invention to differentiate between "effective aspect ratio" and "aspect ratio". The aspect ratio is characteristic of a platelet material in the solid form or one platelet and can be determined by light scattering techniques or microscopy. The term "effective aspect ratio" is much different in that it relates to the behavior of the platelet when incorporated into a binder. It may no longer be a single platelet but instead bundles of platelets referred to as agglomerates. This value is determined using experimental permeability data plotted versus theoretical behavior of the platelet. For example, experimental data when plotted versus the theoretical model of the platelet in the binder [see E. L. Cussler et al, J. Membrane S., 38:161-174 (1988)] is directly related to the barrier improvement of the coating through Cussler's theoretical model. Most commercially available fillers have aspect ratios ranging from 25 up to 10,000. However, the effective aspect ratio of these fillers when incorporated into a binder is much lower when incorporated into a binder and is directly related to the barrier improvement due to the platelet filler, generally resulting in reduced barrier properties. It is important to distinguish between these terms for barrier coatings containing platelet fillers. II. The Barrier Coating Mixtures A barrier coating mixture according to this invention includes the following components in a carrier liquid (i.e., aqueous or solvent): (a) an elastomeric polymer; (b) a dispersed, exfoliated layered platelet filler having an aspect ratio greater than 25; and (c) at least one surfactant, wherein the solids content is desirably below 30% solids and the ratio of polymer (a) to filler (b) is between about 20:1 and 1:1. These barrier coating mixtures result in films with reductions in permeability of 5.times. to 2300.times. relative to the unfilled polymer. These results are substantially higher than the prior art on other platelet filled barrier coatings. The barrier coating mixtures of this invention are characterized by a balancing of several critical features, i.e., appropriate dispersion of the filler in the elastomeric polymer, orientation of the filler platelets in the elastomeric polymer, as well as high aspect ratio of the filler, in order to achieve the desired permeability reductions and flexibility in the dried barrier coating and in the tires. These characteristics are demonstrated by the data shown in FIG. 1. The barrier coating mixture of this invention desirably contains an unusually low solids content, i.e., between about 1% and about 30% solids. A more desirable range of solids content is between about 5% to about 17% solids. The solids content is an important consideration in the barrier coatings compositions and performance of the dried coatings because the solids content effects the dispersion of the high aspect ratio filler. If high total solids content is used in the barrier coating composition, one would not achieve well dispersed filler, e.g., vermiculite, and the permeability reductions characteristic of the coatings of this invention, and reported in the examples and figures herein, are not achieved. The preferred range of solid content (5-17%) is unexpectedly well below that typically used in the coating industry and therefore not predicted by the prior art teachings concerning barrier coatings formulations. The relationship between the percentage of solids in the coating composition to the weight percent of filler in the resulting dried coating is an unexpectedly important issue in obtaining desired barrier coatings of this invention. For example, in embodiments in which the barrier coating composition contains as the elastomeric polymer, butyl rubber (Lord Corporation), and as the filler, MICROLITE 963++ vermiculite solution (W.R. Grace & Co.), FIG. 4 illustrates a range of maximum total solids that can be used in the coatings formulation of this invention without resulting in agglomeration and other negative effects on the dried coating (i.e., film) properties as a function of the fraction of the total solids made up by the filler. In one embodiment, where the MICROLITE filler is at 5%, the maximum solids is about 16%; in another wherein the filler is 25%, the maximum solids is about 9%. In still another embodiment, where the filler is about 50%, the maximum solids is about 5%. Other examples fall within those ranges, as indicated in FIG. 4. The results shown in FIG. 4 are based on the formulations used in Examples 9-12. The unusually low solids contents described in FIG. 4 for a butyl-containing polymer latex are also applicable to other elastomeric polymer latexes, as well as to elastomeric polymers in carrier liquids which also contain other solvents or co-solvents. One of skill in the art will understand the need to make some alterations in the maximums provided by FIG. 4 for other formulations of barrier coatings of this invention taking into account changes in electrolyte concentration, surfactants, grade and composition of vermiculite or other filler, and grade and composition of polymeric latex or other elastomeric polymer in a carrier as described herein. If desired, the solids content of the barrier coating mixtures can be further adjusted to levels below the maximums shown in FIG. 4 using thickeners, in order to adjust the final film thickness, as well as to adjust the suspension rheology. See, for example, Examples 14-15 which demonstrate the increase in viscosity from 4.5 to 370 using PVOH terpolymer; and Example 16 which similarly increases viscosity using lithium chloride as a thickener. Other conventionally used thickeners may also be useful. The solids content of the coating mixtures of this invention is preferably based upon a preferred polymer to filler ratio of between about 20:1 to about 1:1, more preferably 9:1 to 1: 1, particularly when the polymer is a butyl-containing polymer such as a butyl latex, and the filler is a vermiculite solution. Examples 9-12 indicate a variety of desirable compositions of this invention characterized by a polymer to filler ratios within the above range, over a range of solids contents, polymer contents by weight and filler contents by weight. Preferably, in the dried barrier coating (film), the polymer is present at between about 45 to about 95 by weight and the dispersed layered filler is present at between about 5 to about 55% by weight. A. The Elastomeric Polymer Elastomeric polymers useful in forming coating mixtures of this invention include polymers selected generally from among many classes. The selected polymers may be curable polymers, partially cured polymers, or uncured polymers, and may be soluble in water or a solvent. Such polymers include, without limitation, olefinic thermoplastic elastomer (TPO); polyamide thermoplastic elastomer (Polyamide TPE); polybutadiene thermoplastic elastomer, e.g., syndiotactic 1,2-polybutadiene thermoplastic elastomer (polybutadiene TPE); polyester thermoplastic elastomer (Polyester TPE); polyurethane thermoplastic elastomer (TUPR), for example, thermoplastic polyester-polyurethane elastomer (TPAU), and thermoplastic polyether-polyurethane elastomer (TPEU); styrenic thermoplastic elastomer (Styrenic TPE); vinyl thermoplastic elastomer, e.g., polyvinyl chloride polyol (pPVC). A variety of rubbery polymers (curable, partially cured, or uncured) may also be employed as the polymer component of the present invention, including acrylic rubber, such as ethylene-acrylate copolymer (EACM); and butadiene rubber, such as polybutadiene. Butyl-containing polymers useful in forming coating mixtures of this invention include, without limitation, curable, partially cured, or uncured polymers: butyl rubber, such as isobutylene-isoprene copolymer (IIR); bromobutyl rubber, e.g., bromoisobutylene-isoprene copolymer (BIIR); chlorobutyl rubber, e.g., chloroisobutylene-isoprene copolymer (CIIR); and isobutylene rubber. Butyl rubber is defined as a poly(isobutylene) homopolymer or a copolymer of poly(isobutylene) with isoprene. Modified butyl rubbers include halogenated poly(isobutylene) and its copolymers and isoprene. Additional polymers or copolymers that contain more than 50% isobutylene are also useful in the practice of this invention, for example, poly(isobutylene-co-acrylonitrile), etc. Other butyl-containing polymers which are curable, partially cured or uncured, may be readily selected by one of skill in the art. Still other useful elastomeric polymers are chlorosulfonated polyethylene rubber, e.g., chlorosulfonated polyethylene (CSM); epichlorohydrin rubber, such as polyepichlorohydrin (CO), polyepichlorohydrin copolymer (CO copolymer); ethylene-propylene rubber (EPR), such as ethylene-propylene copolymer (EPM), ethylene-propylene-diene copolymer (EPDM). Other polymers for such use include fluoroelastomers, such as vinylidene fluoride-hexafluoropropylene copolymer (FKM); natural rubber (NR); neoprene rubber such as polychloroprene (CR); nitrile rubber, such as acrylonitrile-butadiene copolymer (NBR); polyisoprene rubber (PI); polysulfide rubber; polyurethane, such as polyester urethane (AU), and polyether urethane (EU); propylene oxide rubber; silicone rubber, such as silicone (MQ), and methylvinyl-fluorosilicone (FVMQ) and styrene-butadiene rubber, such as styrene-butadiene copolymer (SBR). The polymer is preferably capable of forming a solution, dispersion, latex, suspension or emulsion in water or a solvent, or a mixture thereof. Specifically exemplified below is a coating mixture of the invention employing as the elastomeric polymer, butyl latex. A suitable commercially available butyl latex for use in the compositions of this invention is Lord.RTM. BL-100 butyl latex, which is a 62% by weight aqueous butyl latex solution [Lord Corporation]. Another suitable butyl latex, the use of which is illustrated in Example 10, is Polymer Latex ELR butyl latex, a 50% butyl latex solution (Polymer Latex). Still another suitable polymer is a 51.7% bromo-butyl latex solution available from Polymer Latex (see Examples 11-12). These latexes contain an ionic surfactant package which stabilizes the latex and effects the performance of the barrier formulation. Other butyl latexes are anticipated to be similarly useful if combined with similar ionic surfactants. Preferably, the selected polymer is present in the dried coating mixture at a minimum of about 45% by weight of the dried compositions. B. The Filler The coating mixtures of this invention as described above also include a dispersed layered filler which, upon mixture, has an inherently high aspect ratio, which can range from about 25 to as high as about 30,000. The presently preferred filler is vermiculite. More particularly, a desirable vermiculite is MICROLITE.RTM. 963++ water-based vermiculite dispersion (W. R. Grace) [see, EP Application No. 601,877, published June 15, 1994] which is a 7.5% by weight aqueous solution of dispersed mica. One novel aspect of the mixtures of the present invention is the effective aspect ratio of the selected filler in the dried coating. According to this invention, in the dried coating, the filler remains substantially dispersed, thereby having a "high effective aspect ratio", as shown in FIG. 1. FIG. 1 assumes high levels of orientation. Preferably, the effective aspect ratio of the filler in the compositions of this invention is greater than 25 and preferably greater than about 100, although higher ratios may also be obtained. In embodiments in which orientation is not high, the effective aspect ratio required for large reductions in permeability will be higher than 100. In the coating mixtures (the liquid), the layered filler is present at between about 1 to about 10% by weight of the total mixture. In the dried coatings of this invention, the layered filler is present at a minimum of about 5% by weight to a maximum of about 55% of the dried coating. The compositions of the present invention, when dried, retain the filler in well-dispersed form, resulting in a high effective aspect ratio of the dried coating, and greatly increased reduction in permeability, as illustrated in FIG. 1. MICROLITE vermiculite is the preferred filler because of its very high aspect ratio. The vermiculite plates have an average lateral size of between 10 and 30 microns. The plates are largely exfoliated in water, and thus their thickness is 1-2 nm. The aspect ratio of the filler in water dispersion is an average of 10,000-30,000. It is clear that many plates reassemble during the coating and drying process of the present invention, thus reducing the effective aspect ratio achieved in the final coating. However, it is a great advantage to start with as large an aspect ratio as possible. Although MICROLITE 963++ vermiculite (W. R. Grace) is preferred, good results may also be achieved with less exfoliated grades of MICROLITE vermiculite (i.e., grades 963, 923, and 903). Other layered silicates are also useful in the barrier coatings and films of this invention. The effectiveness of other silicates in the barrier coating of this invention depends upon the lateral size of the platelets, the degree of exfoliation in water, and the degree to which they reassemble to form larger particles during the coating and drying process. Examples of other layered silicates include bentonite, vermiculite, montmorillonite, nontronite, beidellite, volkonskoite, hectorite, saponite, laponite, sauconite, magadiite, kenyaite, ledikite and mixtures of the above silicates. The selection and use of other known silicates which have properties similar to those of MICROLITE vermiculite, as well as sufficiently high aspect ratios, are expected to be obvious to one of skill in the art following the teachings of this invention. C. Surfactants and Other Additives Coating mixtures of this invention, particularly those useful on tire surfaces and interfaces according to this invention, also contain at least one or more than one suitable surfactant to reduce surface tension. Surfactants include materials otherwise known as wetting agents, anti-foaming agents, emulsifiers, dispersing agents, leveling agents etc. Surfactants can be anionic, cationic and nonionic, and many surfactants of each type are available commercially. A suitable surfactant for inclusion in these compositions possesses a critical micelle concentration sufficiently low to ensure a dried coating uncompromised by residual surfactant. Preferably, the surfactant(s) useful in the methods and solutions of this invention are nonionic, particularly useful with a highly charged filler, such as vermiculite. In the event of an unfavorable interaction of the anionic emulsifier present in the butyl latex dispersion [Lord], which is a presently preferred source of the butyl-containing polymer, any additional ionic additives must be kept to a minimum. This variable is eliminated where the surfactant or emulsifier is non-ionic. Increase in ionic concentration of the compositions containing vermiculite, such as by the addition of a base to adjust pH, e.g., LiOH, NH.sub.4 OH, and NaOH can cause agglomeration of the filler, which adversely affects permeability reduction. Some embodiments of this invention include at least two surfactants, which include preferably both a wetting agent and an anti-foaming agent. Still other compositions may have additional surfactants to perform additional effects. Desirable surfactants employed in the examples below are the non-ionic siloxane-based, Silwet.RTM. L-77 wetting agent [OSI Specialties, Inc.], the BYK.RTM.-306 wetting/leveling agent [BYK Chemie], FOAMASTER.RTM. VL defoamer (Henkel), and the DC200.RTM. anti-foaming agent [Dow Corning], among others. As exemplified below, an antifoaming agent may be predispersed in solution with, e.g., 1-methyl-2-pyrrolidinone (NMP) because some antifoaming agents are not soluble in the barrier coating. Other suitable surfactants may also be selected. The amount and number of surfactants added to the coating solution or composition will depend on the particular surfactant(s) selected, but should be limited to the minimum amount of surfactant that is necessary to achieve wetting of the substrate while not compromising the performance of the dried coating. For example, typical surfactant amounts can be less than or equal to about 10% by weight of the dried coating. In another embodiment, thickeners may be used in the coating formulations to adjust viscosity. Such thickeners may include, without limitation, a polyvinyl alcohol (PVOH) terpolymer, e.g., polyvinylbutyral/polyvinylacetate/polyvinylalcohol or a lithium chloride thickener. In one embodiment, the viscosity of the coating mixture can be increased from 4.5 cP to 370 cP with the addition of the PVOH terpolymer to the formulation as illustrated in Examples 14-15. For example, for a coating mixture containing 10% total solids with 2% MICROLITE vermiculite formulation, a thickener such as PVOH terpolymer can be added in an amount of between about 3% to about 5.5% by weight. Desirably the thickener is added in an amount of greater than 3.5% by weight. A preferred range of thickener is between about 5 and 5.5% by weight. It has been noted that greater than 5.5% by weight of PVOH terpolymer thickener can cause agglomeration of the filler platelets. As another example, the viscosity of the coating mixture can also be increased with the addition of lithium chloride as a thickener to the coating mixture, (See e.g., Example 16). For example, for a coating mixture containing 10% total solids with 2% MICROLITE, the thickener is employed in an amount between about 3% to about 5% by weight. Desirably greater than 4% thickener is employed, and more desirably 5% thickener is employed. Greater than 5% by weight of the lithium chloride thickener produces poor barrier properties. One of skill in the art would readily determine and adjust the type and amounts of thickener depending on the type and amount of filler employed in the coating mixture based on the teachings contained herein. Still other optional components of the barrier coating are components which effect curing of the coating. For example, one type of cure "package" contains about 10 to about 30% by weight zinc oxide, about 5 to about 20% by weight sulfur, about 30 to about 60% by weight water, about 0.1 to about 10% of a dispersing agent, about 5 to about 20% of zinc dibutyldithio-carbamate and about 1 to about 10% zinc 2-mercaptobenzothiazole. The amount of cure package added to the coating mixture is based on the amount of butyl rubber in the coating mixture. In one embodiment, greater than 10 parts dried cure package is added per 100 parts butyl rubber in the coating mixture. A desirable amount of dried cure package is about 15 parts cure package per 100 parts butyl rubber in the mixture. One of skill in the art can readily design a cure "package" to enhance the curing of a butyl latex barrier coating mixture of this invention, and select a desirable amount to be added to the coating mixture, based on the teachings of this specification combined with the knowledge of the art. See, e.g., U.S. Pat. No. 4,344,859. D. The Carrier Liquid The coating mixtures of this invention are present in a suitable carrier liquid. Carriers which are suitable for use in the composition of this invention include, without limitation, water and solvents such as hexane, heptane, toluene, 1methyl-2-pyrrolidinone, cyclohexanone, ethanol, methanol, and other hydrocarbons. Combinations of water with an organic carrier may also be used as the carrier liquid. Selection of a suitable organic solvent carrier is within the skill of the art. E. Embodiments of Barrier Mixtures One example of a barrier coating mixture useful for application to substrates such as a tire or tire surface or interface or a sports ball or inflated product according to this invention comprises coating formed by a barrier coating mixture comprising in a carrier liquid: (a) an elastomeric polymer; (b) a dispersed exfoliated layered platelet filler having an aspect ratio greater than 25; and (c) at least one surfactant, wherein the solids content of said mixture is less than 30% and the ratio of polymer (a) to filler (b) is between 20:1 and 1:1. These barrier coating mixtures result in films with reductions in permeability of 5.times. to 2300.times. relative to the unfilled polymer. These results are substantially higher than the prior art on other platelet filled barrier coatings. Another barrier coating mixture which is desirable for application to tire surfaces and interfaces, and the various surfaces of sports equipment and balls, inflated products, and golf balls, according to this invention includes the following components in a carrier liquid, (a) a butyl-containing polymer latex; (b) a dispersed exfoliated layered vermiculite filler having an aspect ratio about 1000 or greater; and (c) at least one surfactant. The solids content of the mixture is less than 17% and the ratio of polymer (a) to filler (b) is between 20:1 and 1:1. In a preferred embodiment, the coating mixtures described above have solids contents of between about 5 to about 15% by weight, and form dried coatings on said tire surface that comprise between about 45% to about 95% by weight of the polymer, between about 5% to about 55% by weight of the filler, and between about 1.0% to about 10% by weight of the surfactant(s). The dried coatings of the mixtures described above, contain fillers which preferably exhibit an effective aspect ratio of greater than about 25, reduces the gas, vapor or chemical permeability greater than 5-fold that of the dried, unfilled polymer alone. Preferably, the effective aspect ratio of the dried coatings is greater than about 50, and even greater than about 100. One preferred coating mixture useful in this invention has a solids contents of between about 5 to about 15% by weight and the dried coating comprises between about 65% to about 90% by weight of a butyl-containing polymer latex, between about 10% to about 3 5% by weight of a vermiculite filler, between about 0.1% to about 0.10% by weight an anti-foaming agent as surfactant, with the total surfactant weight percent up to about 15%. As described in examples below, the selected polymer is the elastomer butyl rubber or butyl latex, e.g., Lords BL-100 butyl latex in a 62% by weight aqueous butyl latex solution [Lord Corporation]. Additional preferred barrier coating mixtures useful in this invention may be prepared by methods described in detail in Examples 1-12 and 14-16. III. The Coated Article Once prepared as described in detail in Examples 1-12 and 14-16 below, the coating mixtures may be applied to a suitable substrate, such as tire carcasses, tire innerliners or other surfaces or interfaces of a tire, to sports equipment, particularly balls of a variety of sorts, inflated objects such as air mattresses and boats, to reduce the permeability of the substrate to gas, vapor (moisture) or chemicals. The dried coating, in which the filler exhibits an effective aspect ratio of greater than about 25, reduces the gas, vapor or chemical permeability greater than 5-fold that of the dried, unfilled polymer alone. In the dried coating, more preferably, the polymer is present in the mixture when dried at a weight percent of at least about 45%. The filler is preferably present in said mixture when dried at greater than about 5% by weight. These barrier films achieve reductions in permeability of 5.times. to 2300.times. relative to the unfilled polymer. These results are substantially higher than the prior art on other platelet filled elastomers. Preferably, the effective aspect ratio of the dried coating is greater than about 50, and even greater than about 100. As indicated in Examples 1-12, reductions in permeability attributed to compositions of this invention can range from approximately 5.times. to about 2300.times. that of unfilled polymer alone. Desirable substrates for coating with the coating mixtures of this invention may be flexible and/or elastomeric substrates, optionally under pressure. Examples of flexible or elastomeric substrates include balloons, gloves, dirigibles, tires for bicycles, automobiles and trucks, etc., and tire layers, prophylactics, pressure accumulators, regulators and actuators, diaphragms and membrane, as discussed above. Another desirable application of this invention is as a liner or coating for a pneumatic device or any device under pressure, such as sport and toy balls, such as tennis balls, basketballs, soccer balls, footballs, volley balls, racket balls, handballs, beach balls and the like. Essentially, any elastomeric containing object that either holds air or another gas under pressure, or requires the exclusion of air, water, or other gas or vapors can be coated with the compositions of this invention, e.g., inflated products such as boats, air mattresses, and inflatable beds, etc. Still another sports application for this coating is as an undercoating for golf balls, for moisture resistance. Many of the sport balls use a bladder to hold the air or other gas inside the balls. The bladders are currently made from natural rubber, butyl rubber, and polyurethane. The coating compositions of this invention are particularly useful when coated on these bladders to improve their ability to hold air. The coatings are applied as described herein, e.g., by dip coating, as is often used to produce the bladder itself, or spray coating. The coatings are applied either during the bladder manufacture or after the bladder has been fabricated. The coatings of the present invention are applied to the inside or outside of the bladder, depending on the manufacturing process for the bladder. In addition, some bladders are manufactured in multiple layers, and a coating composition of this invention is used on one or more of the layers, thus forming a laminated structure with the bladder material. One advantage of using the coating compositions of this invention is that these coatings add barrier performance to a relatively thick bladder with a thin coating that would not have a major effect on the weight or mechanical properties of the final product. In many of these products, another advantage of the coatings of this invention is thermal stability and compatibility with a thermal cure cycle. Most sport balls use rubber that must be thermally cured. One embodiment of this invention, as shown in the examples, employs a butyl based formulation, which also uses thermal curing. The appropriate coating composition can be selected for compatibility with the existing process of manufacturing such articles. One application of the barrier coating would be on the bladder of a soccer ball as illustrated in Example 19. The natural rubber bladder can be coated with a barrier coating to reduce the air loss of the soccer ball up to approximately 33 times that of a ball without the barrier coating applied onto the bladder. In the cases of products that do not use a bladder such as tennis balls, the coating compositions of this invention are preferably applied on the inside of the ball. In this way, the coating does not affect the adhesion of the outside felt to the rubber. The coating is applied by standard techniques as already discussed, with spray coating likely to be the most effective. With regard to enhancing the moisture resistance of golf balls, the barrier coating of this invention is desirably applied inside the outer layer of the golf ball. The barrier coatings of this invention are also desirably applied on the inside (or an inside layer) of toy balls, inflatable boats, or air mattresses. The following disclosure uses tires or tire compositions as one of the selected substrates in order to illustrate a use of the barrier coating compositions of this invention. See, e.g., Example 18. However, this description can readily be adapted to the coatings of other substrates, such as tennis balls, etc., as illustrated in Example 19. A selected barrier coating mixture, such as those described above may be applied to a tire surface or interface to accomplish a variety of purposes in the tire manufacturing and repair industries to reduce the permeability of the tire or surface therein to gas, vapor or chemicals. These barrier coatings may be used to produce all types of pneumatic tires, and may increase longevity and reduce or replace the butyl rubber content of such tires. The coatings useful in this invention may replace about 0.5 to about 3 mm of butyl rubber in a tire with between about 1-100 .mu.m of coating. See Example 18. IV. Methods of Coating a Substrate or Forming a Film The articles to be coated by the compositions of the invention, including tire surfaces or interfaces, the various surfaces of the bladder of a sports ball, or interior surfaces or inflatable boats and mattresses, or the interior surfaces of a golf ball, may be previously untreated or may have a variety of pre-treatments to their surfaces, depending upon the identity and utility of the article. For example, the article may have on at least one side a heat seal layer. Such heat seal layers may be made of an ethylene-propylene copolymer or ethylene-propylene-butylene terpolymer. Thus, the coating solution is applied on the surface of the heat seal layer. Alternatively, the substrate or article may comprise a protective topcoat layer, such as polyurethane or Teflon.RTM.-type materials [DuPont] for abrasion resistance, etc. Such topcoats may be selected by one of skill in the art. The coatings of this invention may be applied over or under the topcoat layer. Alternatively, the article may be cured prior to application of the coating, or it may be cured following application of the coating on the appropriate surface. Still, alternatively, the coating mixtures of the invention may be applied to a releasable mold in order to form a film, rather than a coated article. The film thus consists of a dried mixture of the above-described polymer and greater than 2% by volume of the layered filler having an aspect ratio greater than 25. The film, which may be in the form of a membrane, may itself be employed as a vapor, gas or chemical barrier layer for use in various laboratory procedures, or as a glove or balloon material. Such a dried, free-standing film or membrane, is characterized by a reduction in gas, vapor or chemical permeability greater than 5-fold the permeability of a film formed of the dried polymer alone. To form the coated article or free-standing film of this invention, the application of the selected barrier coating mixture may be accomplished by techniques including, without limitation, roller transfer or paint coating, spray coating, brush coating and dip coating. Roll coating techniques include, but are not limited to, rod, reverse roll, forward roll, air knife, knife over roll, blade, gravure and slot die coating methods. General descriptions of these types of coating methods may be found in texts, such as Modern Coating and Drying Techniques, (E. Cohen and E. Gutoff, eds; VCH Publishers) New York (1992) and Web Processing and Converting Technology and Equipment, (D. Satas, ed; Van Nostrand Reinhold) New York (1984). Three dimensional articles may preferably be coated by the techniques which include, but are not limited to, spray coating or dip coating. The method of application is not a limitation on the present invention, but may be selected from among these and other well-known methods by the person of skill in the art. However, the coating must be applied so that drying takes place on the substrate and not in the air (i.e. powder coating). If drying takes place during spraying or other means of application, agglomeration may occur. The coating mixtures may be applied to a substrate, such as an exterior or interior surface, an interface, or component of the selected article, or to a mold, at any desired thickness, depending on the substrate, the purpose for which the coating is being applied and the ultimate use of the coated article. Thus, for example, the coating mixtures of the present invention may be applied to the tire surface, an interior or exterior surface of a sports ball (or other substrate) by the methods described above to form a dried coating of a thickness between about 0.1 .mu.m to about 100 .mu.m of dry coating. Such adjustments to thickness are well within the skill of the art [see, e.g., Canadian Patent No. 993,738]. After coating, the coated article or the film, may be dried at a selected temperature, e.g., room temperature or greater than room temperature. The selection of the drying temperature, relative humidity, and convective air flow rates depends on the desired time for drying; that is, reduced drying times may be achieved at elevated air temperatures, lower relative humidity and higher rates of air circulation over the drying coating surface. After drying, the exfoliated silicate filler particles are oriented within the elastomeric latex (solution, emulsion, etc.) to a high degree parallel to each other and to the tire substrate surface. One of skill in the art can readily adjust the drying conditions as desired. The performance of the dried barrier coating is insensitive to drying temperatures over the range 25-1 60.degree. C. The dried coatings exhibit a surprising reduction in permeability compared to the prior art and particularly compared to unfilled polymers. As evidenced in the Examples below, reductions in permeability caused by the dried coatings of this invention are shown to be from 7 fold to almost 2300 fold relative to the unfilled polymers alone. The evaluation of permeability of the coatings of the present invention are determined using the following parameters. The oxygen transmission rate (OTR) of the dried coating on the article, or the free-standing film, is generally measured using conventional apparatus, such as a MOCON.RTM. OX-TRAN 2/20 module. OTR units are cc/m.sup.2 day at 1 atmosphere, 0% relative humidity at 23.degree. C. The permeability of the coating is calculated by multiplying the OTR and coating thickness. Permeability units are cc mm/m.sup.2 day atmosphere at 0% relative humidity at 23.degree. C. If the coating is on a known substrate, e.g., a known tire surface or component, the permeability of the known substrate is subtracted out using the following equation: Permeability of the barrier coating=X.sub.1 /[(1/OTR)-(X.sub.2 /P.sub.X2)], where X.sub.1 is barrier coating thickness; X.sub.2 is substrate (e.g., tire surface or component) thickness and P.sub.X2 is permeability of the substrate. The reduction in permeability from the unfilled polymer is calculated by dividing the permeability of the unfilled polymer by the permeability of the filled polymer. Reduction in permeability is unitless. The dried coating preferably maintains its low permeability after repeated mechanical loading and elongation up to about 10% of the substrate. The evaluation of the coating integrity after exposure to repeated loading and elongation was examined as described below in Example 17. The coatings and methods of the present invention described above may be applied to the manufacture or repair of any pneumatic or inflated article to maintain or improve air retention, for example, in inflated mattresses, inflated sports balls, tires, and the like. The barrier coatings may allow reduced mass, reduced gas permeability resulting in better air retention, reduced thermo-oxidative degradation, and enhanced wear and elongation of the useful life of the article |
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