EP1183300A1

EP1183300A1 - Composite coating

Info

Publication number: EP1183300A1
Application number: EP00932609A
Authority: EP
Inventors: Santo Randazzo
Original assignee: PRC Desoto International Inc
Current assignee: PRC Desoto International Inc
Priority date: 1999-05-21
Filing date: 2000-05-19
Publication date: 2002-03-06
Also published as: AU5030500A; CA2374408A1; CN1354765A; MXPA01011927A; BR0010729A; WO2000071605A1; JP2003500503A; KR20020015690A

Abstract

A multi-component composite coating is provided which includes: (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate; and (b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material. The topcoat can have a higher tensile strength and percent elongation than the elastomeric basecoat such that when the composite coating is deformed, the basecoat can fracture before the topcoat to permit the topcoat to further deform while maintaining integrity of the topcoat. The composite coating is useful for inhibiting fuel leaks from an aerospace fuel storage container.

Description

COMPOSITE COATING

Field of the Invention The present invention relates generally to elastomeric multilayer composite coatings in which the elastomeric basecoat can fracture before the topcoat when stress is applied to the composite coating, the composite coatings being useful for coating the interior of fuel storage containers to inhibit fuel leakage therefrom.

Backeround of the Invention

Currently, sealing integral fuel tank systems involves faying, surface sealing, filleting and brush application of a sealant. Prior to sealant application, the substrate surface must be thoroughly cleaned and the sealant meticulously applied by well-trained personnel. In spite of controlled application procedures, the resulting coating is often found to leak upon inspection.

Locating defects in the coating is a difficult and time-consuming procedure. Furthermore, repair and resealing is difficult, requiring old sealant material to be mechanically removed from the substrate.

Thus, there exists a need for a coating and/or sealant suitable for easy application to a substrate by conventional techniques such as spraying, brushing, rollering, or fill and drain techniques. The novel coating or sealant should adhere to a variety of metallic, composite, silaceous and polymeric substrates, provide coverage of pinholes and imperfections in the substrate and maintain its integrity when subjected to impact and vibration.

Summary of the Invention

A composite coating is provided which comprises (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate; and (b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material. Another aspect of the present invention is a composite coating comprising: (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate, the curable basecoat composition comprising a polymeric material selected from the group consisting of polyurethanes, polysulfides, polythioethers, copolymers and mixtures thereof; and (b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and having a higher tensile strength and percent elongation than the elastomeric basecoat. A substrate coated with the multi- component composite coating also is provided. Yet another aspect of the present invention is a process of inhibiting fuel leakage from an interior portion of a fuel storage container, comprising the step of: (a) coating an interior portion of a fuel storage tank with a composite coating comprising: (i) an elastomeric basecoat formed from a curable basecoat composition deposited upon the surface of the substrate; and (ii) a topcoat applied over the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material.

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Also, as used herein, the term "polymer" is meant to refer to oligomers, homopolymers and copolymers.

Description of the Preferred Embodiments

A composite (multilayer) coating of the present invention is provided which comprises an elastomeric basecoat deposited upon a surface of a substrate and a topcoat applied over at least a portion of the basecoat.

The elastomeric basecoat is formed from a curable basecoat composition which comprises one or more curable polymeric materials which are preferably elastomeric when cured. Examples of useful polymeric materials include crosslinkable or self-crosslinking polysulfides, polythioethers, polyurethanes, copolymers and mixtures thereof. Preferably, the curable basecoat composition comprises a sulfur-containing material such as one or more polythioethers or polysulfides.

Useful polysulfides comprise recurring polysulfide linkages between organic radicals, each organic radical having at least one primary carbon atom for the connection to the disulfide linkage. Useful polymers comprise one or more units having the structural formula:

i^R "k in which R is an divalent or polyvalent organic radical including but not limited to alkyl, alkylene, or oxyhydrocarbon such as diethylformal; m is a number of 2 or more, preferably 2 to 4 inclusive, and is known as the sulfur rank of the polymer; and n is an integer greater than 1, preferably 5 to 50. R optionally includes similar pendant groups.

Useful solid polysulfides preferably have a number average molecular weight of greater than about 100,000, as determined by gel permeation chromatography using a polystyrene standard. Preferred polysulfides have a number average molecular weight ranging from about 300 to 15,000 and are generally liquids at ambient temperature (about 25°C) and atmospheric pressure (about 760 mm Hg). More preferably, the number average of the polysulfide polymer ranges from about 500 to about 10,000. The polysulfide optionally has one or more terminal or pendant hydroxy or mercaptan functional groups. Preferably, the polysulfide has mercaptan terminal functional groups.

Preferred polysulfides include LP polysulfide polymers which are commercially available from Morton International, such as LP-2, LP-3 and LP- 32, and polysulfides such as are disclosed in U.S. Patent Nos. 1,962,460 and

4,623,711, which are incorporated herein by reference.

Useful polythioether materials include those having one or more units of the general structural formula:

(OR¹SR²)_x-(OR³SR⁴)_y

(I) where R¹, R², R³ and R⁴ are each independently selected from aliphatic groups having from one to six carbon atoms and x, y and n are each independently selected from integers equal to or greater than 1. At least one of the aliphatic groups can further comprise at least one pendent group selected from the group consisting of substituted or unsubstituted aliphatic groups having from 1 to 12 carbon atoms, cycloaliphatic groups and aryl groups. The substituted aliphatic group can comprise from 1 to 12 carbon atoms and one or more heteroatoms selected from the group consisting of oxygen, nitrogen and sulfur. Preferably, the radicals R¹, R², R³ and R⁴ are each independently C,-C₃ aliphatic groups. More preferably, R², R³ and R⁴ are ethyl and R¹ is isopropyl. Still more preferably, y is greater than x and n is such that the number average molecular weight of the polythioether is between about 300 and 15,000 such that the polythioether is a liquid at ambient temperature and atmospheric pressure. The polythioether material can include one or more pendant or terminal functional groups, such as hydroxyl, mercaptan, or alkyl.

Useful polythioether materials include those disclosed in U.S. Patents Nos. 4,366,307; 5,912,319 and 5,959,071, each of which is incorporated by reference herein, and PERMAPOL P-3 and 855 polymers which are commercially available from PRC-DeSoto International. A preferred polythioether-containing composition is PR-2911, which is commercially available from PRC-DeSoto.

Useful polyurethanes include those prepared by reacting one or more polyols with one or more polyisocyanates. Useful polyols include polyester polyols, polyether polyols, as well as diols or triols such as ethylene glycol, propylene glycol, butylene glycol, glycerol and trimethylolpropane. Useful polyisocyanates can include aliphatic polyisocyanates, cycloaliphatic polyisocyanates, or aromatic polyisocyanates.

Mixtures and copolymers of the polymeric materials discussed above can be used. Preferably, the polymeric material comprises about 30 to about 55 weight percent of the curable basecoat composition on a basis of total weight of the curable basecoat composition, and more preferably about 40 to about 50 weight percent.

Preferably, the curable basecoat composition further comprises one or more curing agents. Non-limiting examples of suitable curing agents include polyamines, polyols, polyisocyanates, metal oxides, polyepoxides and mixtures thereof.

Useful polyamines include primary or secondary diamines or polyamines in which the radicals attached to the nitrogen atoms can be saturated or unsaturated, aliphatic, alicyclic, aromatic, aromatic-substituted- aliphatic and aliphatic-substituted-aromatic. Exemplary suitable aliphatic and alicyclic diamines include 1,2-ethylene diamine, isophorone diamine. Suitable aromatic diamines include diethyltoluene diamine and methylene diphenyl diamine (MDA). Useful triamines include diethylene triamine.

Useful polyols include polyoxyalkylene polyols, polyester polyols, polyoxytetra methylene polyols, polyurethane polyols, and diols or triols such as ethylene glycol, propylene glycol, butylene glycol, glycerol and trimethylolpropane.

Useful polyisocyanates include blocked or unblocked polyisocyanates including aromatic diisocyanates; aliphatic diisocyanates such as 1,6- hexamethylene diisocyanate; and cycloaliphatic diisocyanates such as isophorone diisocyanate and 4,4'-methylene-bis(cyclohexyl isocyanate).

Examples of suitable blocking agents for the polyisocyanates include lower aliphatic alcohols such as methanol, oximes such as methyl ethyl ketoxime and lactams such as caprolactam. Useful metal oxides include manganese dioxide (such as AT-407 which is commercially available from Eastman Chemical Co.), lead oxide, calcium peroxide, barium peroxide and zinc oxide.

Useful polyepoxides include at least two epoxy groups per molecule.

Useful polyglycidyl ethers of polyhydric alcohols can be formed by reacting epihalohydrins with polyhydric alcohols, such as dihydric alcohols, in the presence of an alkali condensation and dehydrohalogenation catalyst such as sodium hydroxide or potassium hydroxide. Suitable polyhydric alcohols can be aromatic, aliphatic or cycloaliphatic. Non-limiting examples of suitable aromatic polyhydric alcohols include phenols which are preferably at least dihydric phenols. Non-limiting examples of aromatic polyhydric alcohols useful in the present invention include dihydroxybenzenes, for example resorcinol and hydroquinone; bis(4-hydroxyphenyl)-l,l-isobutane; 4,4- dihydroxybenzophenone; bis(4-hydroxyphenyl)- 1,1 -ethane; bis(2- hydroxyphenyl)methane; 1,5-hydroxynaphthalene; 4-isopropylidene bis(2,6- dibromophenol); l,l,2,2-tetra(p-hydroxy phenyl)-ethane; l,l,3-tris(p-hydroxy phenyl)-propane; novolac resins; bisphenol F; long-chain bisphenols; and 2,2- bis(4-hydroxyphenyl)propane, i.e., bisphenol A, which is preferred.

Non-limiting examples of aliphatic polyhydric alcohols include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, 1 ,2-propylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, pentamethylene glycol, polyoxyalkylene glycol; polyols such as sorbitol, glycerol, 1,2,6-hexanetriol, erythritol and trimethylolpropane; and mixtures thereof.

Suitable epoxy-functional materials have an epoxy equivalent weight ranging from about 150 to about 200, as measured by titration with perchloric acid using methyl violet as an indicator. An example of a suitable commercially available epoxy-functional material is EPON® 828 epoxy resin, which is an epoxy functional diglycidyl ether of bisphenol A prepared from bisphenol-A and epichlorohydrin and is commercially available from Shell Chemical Company.

Preferably, the curing agent is added to the curable basecoat composition immediately prior to application. Selection of a curing agent is dependent upon the terminal functionalities of the polymeric material in the basecoating composition. For example, isocyanates induce cure of polyamines or polyols; and epoxies, metal oxides and metal peroxides each induce cure of thiol groups. Cure of the basecoating composition is achieved by thoroughly mixing the polymeric material with the curing agent and subjecting the composition to atmospheric and temperature conditions conducive for cure. Preferably, the polymeric material cures in the presence of the curing agent in ambient air. Typically, cure occurs at a temperature between about 10 and about 150°C. Preferably, the concentration and identity of the curing agent are chosen to exact a cure within a few hours at ambient temperature and atmospheric pressure. The time required for cure depends in part upon the specific formulation and the nature and concentration of cure catalysts.

Generally, the curing agent can comprise about 9 to about 100 weight percent of the curable basecoat composition on a basis of total weight of the curable basecoat composition, and preferably about 9.3 to about 100 weight percent.

Preferably, the curable basecoat composition further comprises at least one additive selected from the group consisting of pigments, plasticizers, fillers, adhesion promoters, solvents and mixtures thereof.

Useful pigments include carbon black or metal oxides such as iron oxide and titanium dioxide. Generally, the pigment comprises about 3 to about

6 weight percent of the total weight of the basecoating composition. Preferably, when the elastomeric coating composition is a two-part system, different colored pigments are added to each part in order to facilitate homogeneous mixing. Useful plasticizers include hydrogenated terphenyl and di- or tri- isodecylphthalate. Preferably, the plasticizer is present in the basecoating composition in an amount ranging from about 0 to 5 weight percent of the total basecoating composition weight.

Useful fillers include carbon black, calcium carbonate, titanium dioxide and fumed silica. Preferably, the filler is present in the basecoating composition in an amount ranging from about 20 to 30 weight percent of the total basecoating composition weight.

An adhesion promoter can be included in the basecoating composition to facilitate bonding to the substrate. Useful adhesion promoters include silanes, phenolics, titanates and epoxies. Preferably, the adhesion promoter is present in the basecoating composition in an amount ranging from about 2 to 5 weight percent of the total basecoating composition weight.

A solvent can be added to the basecoating composition to lower the viscosity of the composition and facilitate spray application. Useful solvents include methyl ethyl ketone, toluene and propylene glycol methyl ether acetate.

If present, the amount of solvent in the basecoating composition can range from about 20 to 30 weight percent based upon the total weight of the basecoating composition.

Preferably, the elastomeric basecoat has a tensile strength ranging from about 50 to about 600 pounds per square inch and percent elongation ranging from about 50% to about 800% at a coating thickness of 50 mils (1.27 mm) measured according to ASTM-D-412-617, which is incorporated herein by reference. As used herein "tensile strength" means the maximum resistance to deformation of a material based upon the undeformed area of the material as measured by ASTM-D-412-617. As used herein "elongation" means the maximum permanent strain prior to fracture of a material as measured by ASTM-D-412-617.

Preferably, the elastomeric basecoat has a fuel resistance such that it swells less than 50% by volume when exposed to Jet Reference Fluid (JRF) for two weeks at 140°F (60°C). JRF is a mixture by volume of about 30% toluene,

60% cyclohexane, 10% isooctane and 1% t-butyldisulfide. Also, it is preferred that the elastomeric basecoat be hydrolytically stable, i.e., it retains at least 40% of its original tensile strength and elongation after one month in water at 158°F (70°C). The basecoating composition is preferably applied to the surface of the substrate by conventional application techniques such as spraying, brushing, roller or conventional fill and drain techniques which are well known to those skilled in the art.

Typically, the basecoating composition is applied to the substrate to provide a layer having a dried thickness ranging from about 3 to about 30 mils

(0.07-0.76 mm), and preferably about 10 to about 20 mils (0.25 - 0.5 mm). It is appreciated that the basecoat thickness can be formed through a single application or multiple applications of the basecoating composition. In the instance where a base elastomeric coating thickness is built up through multiple applications, curing is optionally induced prior to application of a further layer. Preferably, a base elastomeric coating is applied through a single application.

The basecoating composition can be cured in air at a temperature (preferably between about 10-100°C) prior to application of the topcoating composition.

The substrate to be coated by the present invention can be formed from one or more polymeric, composite or metallic materials or combinations thereof. Useful metallic materials include aluminum, steel, titanium, and alloys thereof. Useful polymeric materials include polyurethane, nitrile or buna "N" rubbers and fiber composites. It is appreciated that the composite coating of the present invention can be applied to planar as well as complex geometric substrates. While the description of the present invention is directed toward rigid or flexible fuel storage containers, it is appreciated that the present invention has utility in coating a variety of substrates including joints in construction, pavement, aerospace applications as well as coating a variety of substrates including electrical wire, hoses, storage tanks, marine vessels and fuel transmission pipelines.

Optionally, the substrate surface can be cleaned to remove extraneous grease and debris before application of the basecoating composition. In the case of fuel tank refurbishment, the present invention can be utilized without fazing the existing surface sealant. While it is preferred that the basecoating composition is applied directly to the substrate, it is appreciated that an intermediate layer or primer coating between the bottom surface of the basecoating composition layer and the substrate is optionally employed. An intermediate layer or primer coating when present functions as an adhesion promoter between the elastomeric basecoat and the substrate. Useful intermediate layer coating materials optionally include PR-148, PR-1826, PR-182 and PR-1861 which are titanate-, epoxy-, silane- and epoxy-based primers, respectively, which are commercially available from PRC-DeSoto.

The topcoating composition is applied over the at least partially cured basecoat. The topcoat is different from the basecoat, i.e., it contains at least one component which is chemically different from the components of the basecoat or at least one component which is present in a different amount than the same component which is present in the basecoat.

The topcoat is preferably an elastomeric coating and has a higher tensile strength and/or percent elongation compared to the basecoat as determined according to ASTM D-412-617, with a flow out prepared of each material separately for testing. Preferably, the topcoat has a tensile strength ranging from about 1000 to about 3000 pounds per square inch (70-120 kg/cm²) and percent elongation ranging from about 500% to about 1000% at a coating thickness of 50 mils (1.27 mm). Preferably, the top coat tensile strength is more than 100% higher than a comparable value of the base elastomeric coating. Thus, under deformation, vibration or mechanical stress the basecoat preferably will fail thereby allowing the topcoat layer to flex and elongate while maintaining the integrity of the fuel seal.

The topcoat is formed from a curable topcoat composition comprising one or more polythioether materials such as are described in detail above for the polymeric material of the basecoating composition. Preferably, the polythioether material is liquid at ambient temperature and pressure. Useful polythioether materials include PERMAPOL P-3 and 855 polymers which are commercially available from PRC-DeSoto International. Generally, the polythioether material comprises about 40 to about 60 weight percent of the curable topcoat composition on a basis of total weight of the curable topcoat composition.

Preferably, the curable topcoat composition further comprises one or more curing agents. Suitable curing agents include those discussed above as curing agents for the elastomeric basecoat. Preferably, the curing agent comprises about 2 to about 3 weight percent of the curable topcoat composition on a basis of total weight of the curable topcoat composition. Preferably, the polythioether material cures in the presence of the curing agent in ambient air.

The curable topcoat composition can further comprise one or more additives such as pigments, plasticizers, fillers, adhesion promoters, solvents and mixtures thereof. Examples of useful additives include those discussed above as additives for the elastomeric basecoat in similar amounts.

The topcoat preferably further comprises a first pigment and the basecoat a second, differently colored pigment thereby imparting a different coloration to the topcoat as compared to the elastomeric basecoat to facilitate complete coverage thereof by the top coat. The top coat is applied to the laminate by spray, brush, roller or by conventional fill and drain techniques to a dry thickness of about 10 (0.25 mm) to about 30 mils (0.76 mm), and preferably about 10 (0.25 mm) to about 20 mils (0.5 mm). The top coat can be moisture or ambient or thermally cured, with the cure temperature preferably ranging from about 10°C and 100°C.

The multi-component composite coating also can further comprise one or more overcoats applied over at least a portion of the topcoat. Suitable overcoats can include paint and primer.

In an alternative preferred embodiment of the present invention, a multi-component composite coating is provided which comprises an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate. The curable basecoat composition comprises one or more polymeric materials selected from the group consisting of polyurethanes, polysulfides, polythioethers, copolymers and mixtures thereof. A topcoat is applied over the basecoat, the topcoat being different from the basecoat and having a higher tensile strength and percent elongation than the elastomeric basecoat.

Also provided is a process of inhibiting fuel leakage from an interior portion of a fuel storage container, comprising the step of coating an interior portion of a fuel storage tank with any of the composite coating systems described in detail above. The multi-component composite coatings of the present invention provide coatings and sealants which are useful for inhibiting leaks of liquids from substrates or joints between two substrates. If a basecoat of the present invention experienced loss of adhesion, for example through corrosion, poor application or impact damage, the lower tensile strength and lower elongation cured elastomeric basecoat preferably would fail before the higher tensile strength and higher elongation top coat, thereby maintaining the integrity of the overall coating and preventing exposure to the underlying substrate. In the context of an aircraft fuel container, the present invention can render a fuel container more flexible and vibration resistant because the cured elastomeric basecoat can absorb the majority of stresses associated with expansion and contraction encountered during operation of the aircraft. The present invention is useful for resealing aging aircraft fuel tanks since aged sealants can be recoated with the multi-component composite coating to seal existing leaks without fazing the existing sealant therefrom. Instead, simple abrasion and optimal solvent cleaning renders an existing sealant amenable to receiving a composite coating according to the present invention.

In order to more fully demonstrate the advantages of the present invention, the following example is set forth. It is to be understood that the following is by way of example only and not intended as a limitation on the scope of the invention.

Example Epoxy/graphite composite panels 6 in. x 6 in. x 0.084 in. (15.24 x 15.24 x 0.21 cm) (Hercules AW193-PW/3501-6S cured at 177°C and having a fiber volume range from 49.2 to 50.2%) were cleaned with methyl ethyl ketone

(MEK) solvent and a layer of PR-148 conditioner (PRC-DeSoto) was applied by scrubbing or brushing to form a thin film. The thickness of the graphite panels ranging from 2.108-2.134 mm. The best results were obtained according to the present invention as follows. A basecoat layer was formed upon the surface of the cleaned and conditioned panels by applying the following two-component polysulfide- containing basecoating composition as received:

Weight percent of Component

Component A Manganese Dioxide¹ 59%

Plasticizer² 29%

Pigment³ 3%

Filler⁴ 3%

Diphenyl guanidine 6%

Component B Polysulfide Polymer⁵ 49%

Filler⁶ 24.5%

Solvent⁷ 24.5%

Adhesion Promoter⁸ 2%

Adhesion Promoter⁹ 0.2%

The ratio of Component A to Component B was 9.3:100 on a total weight basis. The base coat formulation approximating PR-2094 (PRC- DeSoto).

The basecoating composition was applied by spraying onto the graphite panels and allowed to cure at ambient conditions (25°C ± 5°C) for 6 hours to a dry thickness of 0.015 inch (0.38 mm). The cured basecoat had a tensile strength of 350 pounds per square inch (24.7 kg/cm²) and 250% elongation as measured according to ASTM-D-412-617.

¹ AT-407 manganese dioxide which is commercially available from Eastman Chemical Co.

² HB-40 hydrogenated terphenyl plasticizer which is commercially available from Monsanto Co.

³ THERMAX N-991 carbon black which is commercially available from R & T Vanderbilt.

⁴ Talc-IT-3X talc which is commercially available from R & T Vanderbilt.

⁵ LP-32 polysulfide polymer which is commercially available from Morton International.

⁶ SOCAL 2G 31 UF calcium carbonate which is commercially available from Solvay Performance Chemical.

⁷ Blend of methyl ethyl ketone (Ashland Chemical) and Amsco Solvent L-541 toluene solvent (Union Carbide Corp.).

⁸ Blend of METHYLON Resin 75108 (4.8% by wt.), DUREZ 10694 (27% by wt.) and 31513 phenolic resins (68% by wt.) commercially available from Occidental Chemical Corp.

⁹ Blend SILQUEST A- 186 epoxy silane (50% by wt.) which is commercially available from OSI Specialties and amyl zimate (50% by wt.) which is commercially available from R&T Vanderbilt. A topcoat composition was sprayed over the basecoat. The components of the topcoating composition are given below:

Weight percent of Component

Component A Amine¹⁰ (pK_≥4) 4.6% Filler¹¹ 7.5% Solvent¹² 86% Pigment¹³ 2% Pelargonic acid¹⁴ 0.2%

Component B PERMAPOL 855 86% Solvent¹⁵ 14%

The ratio of component A to component B was 90:100 on a total weight basis.

The topcoat was applied by spraying to a dry thickness of about 0.035 inches (1.14 mm) and cured at ambient conditions (25°C ± 5°C) for about 168 hours.

The topcoat had a tensile strength of more than 1800 psi (127 kg cm²) and elongation 900%, using the topcoat material cast alone to a thickness of 0.05 in. (0.0127 mm). These values were greater than that of the basecoat (350 PSI tensile strength and 250% elongation) as measured according to ASTM-D- 412-617.

¹⁰ Diethyltoluene diamine which is commercially available from Ethyl Chemicals Corp.

¹ ' CAB-O-SIL TS-720 fumed silica filler which is commercially available from Pacific Coast

Chemicals.

¹² Propylene glycol methyl ether acetate which is commercially available from Eastman Chemical Corp.

¹³ REGAL 660R carbon black which is commercially available from Cabot Corp.

¹ EMERY 1202 which is commercially available from Henkel Chemicals.

¹⁵ Propylene glycol methyl ether acetate which is commercially available from Eastman Chemical Corp. A laboratory apparatus was designed to test the permeability of coated and uncoated panels before and after impact damage, so as to simulate fuel tank conditions. The testing device consisted of a cylinder open at one end to accommodate the panels to be tested. The opposite end of the cylinder was equipped with a valve and an opening used for filling the jig with fuel. A pressure regulator was installed to maintain a constant pressure of 0.35 kg cm² inside the test jig. Test specimens were machined to 15.2 cm² and were impacted at 1, 2, 4, 8 and 12 foot-pounds. A minimum of three test panels were impacted at each condition and then each panel was mounted in the jig. One kg of TT-S-735 Type Nil jet reference fuel (JRF) was loaded into each jig through the openings which were then closed. The jigs were pressurized with nitrogen to 0.35 kg/cm² and a fuel leak detector powder sprayed on the impacted area and around the gasket as a visual aid to monitor leaks to the damaged area and evaluate performance of the opening sealing gasket. The duration of the test was four weeks with a constant weight loss obtained during the first week. The test duration for a highly damaged panel ranged from seconds to a few days until failure.

Test panels prepared as above and having an overall coating thickness of 0.045 inches (1.14 mm) were tested for fuel permeability after impact damage. The average test results of 3 panels are given in Table 1 below.

Table 1

Fuel Permeability of Epoxy/Graphite Composites Before and After Impact Damage

Impact Uncoated Panels Coated Panels Foot-lbs. (J) Wt. Loss εms/dav Wt. Loss gms/day

0 (0) 0 0

1.0 (1.4) 0.7 0

2.0 (7.7) 11 0

4 0 (5.4) 53 0.01

8.0 (10.8) 31 kgs 0.12

12.0 (16.3) 6336 kgs 0.13

The composite basecoating as described above was applied to aluminum panels 6 in. x 6 in. x 0.04 in. (15.24 x 15.24 x 0.1 cm) (Alloy 7075 treated per MLL-S-5541) at 0.01 in. (0.25 mm) dry thickness, after cleaning with MEK and priming with PR-148. After the basecoat was cured for 6 hours, a topcoat as described above was applied at 0.035 in. (0.89 mm) dry thickness. After the topcoat was cured for 168 hours at 75°F (24°C), these panels were tested for fuel permeability after impact damage. The results thus obtained are shown in Table 2.

Table 2

Fuel Permeability of Aluminum Panels After Impact Damage

Impact Uncoated Panels Laminated Panels

Foot-lbs. (J Wt. Loss f gms/dav) 0.035 in. (0.80 mm)

Wt. Loss (gms/day) 4.0 (5.4) 0 0

5.0 (10.8) 144 0

12.0 (16.3) 6100 kgs 0.03

Various modifications of the present invention in addition to those shown and described herein will be apparent to those skilled in the art from the above description. Such modifications are also intended to fall within the scope of the appended claims.

Claims

Therefore. I claim: 1. A composite coating comprising: (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate; and (b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material.

2. The composite coating according to claim 1, wherein the curable basecoat composition comprises a polymeric material selected from the group consisting of polyurethanes, polysulfides, polythioethers, copolymers and mixtures thereof.

3. The composite coating according to claim 1, wherein the basecoat composition comprises a polysulfide.

4. The composite coating according to claim 2, wherein the polymeric material comprises about 40 to about 60 weight percent of the curable basecoat composition on a basis of total weight of the curable basecoat composition.

5. The composite coating according to claim 2, wherein the curable basecoat composition further comprises a curing agent.

6. The composite coating according to claim 5, wherein the curing agent is selected from the group consisting of polyamines, polyols, polyisocyanates, metal oxides, polyepoxides and mixtures thereof.

7. The composite coating according to claim 5, wherein the curing agent comprises about 4 to about 6 weight percent of the curable basecoat composition on a basis of total weight of the curable basecoat composition.

8. The composite coating according to claim 5, wherein the polymeric material cures in the presence of the curing agent in ambient air.

9. The composite coating according to claim 1, wherein the curable basecoat composition further comprises at least one additive selected from the group consisting of pigments, plasticizers, fillers, adhesion promoters, solvents and mixtures thereof.

10. The composite coating according to claim 1, wherein the elastomeric basecoat has a tensile strength ranging from about 50 to about 600 pounds per square inch at a thickness of 50 mils.

11. The composite coating according to claim 1, wherein the polythioether material of the curable topcoat composition comprises at least one unit having the following structure (I):

— (OR¹SR²)_x-(OR³SR⁴)_y n (I) where R¹, R², R³ and R⁴ are each independently selected from aliphatic groups having from one to six carbon atoms and x, y and n are each independently selected from integers equal to or greater than 1.

12. The composite coating according to claim 11, wherein at least one of the aliphatic groups further comprises at least one pendent group selected from the group consisting of substituted or unsubstituted aliphatic groups having from 1 to 12 carbon atoms, cycloaliphatic groups and aryl groups.

13. The composite coating according to claim 12, wherein the substituted aliphatic group comprises from 1 to 12 carbon atoms and comprises a heteroatom selected from the group consisting of oxygen, nitrogen and sulfur.

14. The composite coating according to claim 1, wherein the polythioether material comprises about 40 to about 60 weight percent of the curable topcoat composition on a basis of total weight of the curable topcoat composition.

15. The composite coating according to claim 1, wherein the polythioether material is liquid at ambient temperature and pressure.

16. The composite coating according to claim 1, wherein the curable topcoat composition further comprises a curing agent.

17. The composite coating according to claim 16, wherein the curing agent is selected from the group consisting of polyamines, polyols, polyisocyanates, metal oxides, polyepoxides and mixtures thereof.

18. The composite coating according to claim 16, wherein the curing agent comprises about 2 to about 3 weight percent of the curable topcoat composition on a basis of total weight of the curable topcoat composition.

19. The composite coating according to claim 16, wherein the polythioether material cures in the presence of the curing agent in ambient air.

20. The composite coating according to claim 1, wherein the curable topcoat composition further comprises at least one additive selected from the group consisting of pigments, plasticizers, fillers, adhesion promoters, solvents and mixtures thereof.

21. The composite coating according to claim 1 , wherein the topcoat has a tensile strength ranging from about 1000 to about 3000 pounds per square inch at a thickness of 50 mils.

22. The composite coating according to claim 1 , wherein the topcoat has a tensile strength which is greater than a tensile strength of the elastomeric basecoat.

23. The composite coating according to claim 22, wherein the topcoat has a tensile strength greater than 40% higher than the tensile strength of the elastomeric basecoat.

24. The composite coating according to claim 1, wherein the topcoat has a percent elongation which is greater than a percent elongation of the elastomeric basecoat.

25. The composite coating according to claim 1, wherein the elastomeric basecoat further comprises a first pigment and the topcoat further comprises a second pigment thereby imparting a different coloration to the topcoat as compared to the elastomeric basecoat.

26. The composite coating according to claim 1, wherein the multi- component composite coating further comprises an intermediate coating positioned between the elastomeric basecoat and the topcoat.

27. The composite coating according to claim 1, wherein the multi- component composite coating further comprises an overcoat applied over at least a portion of the topcoat.

28. A composite coating comprising: (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate, the curable basecoat composition comprising a polymeric material selected from the group consisting of polyurethanes, polysulfides, polythioethers, copolymers and mixtures thereof; and (b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and having a higher tensile strength and percent elongation that the elastomeric basecoat.

29. A coated substrate having a composite coating applied over at least a portion of a surface thereof, the multi-component composite coating comprising: (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon the surface of the substrate; and (b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material.

30. A coated substrate having a composite coating applied over a surface thereof, the multi-component composite coating comprising: (a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate, the curable basecoat composition comprising a polymeric material selected from the group consisting of polyurethanes, polysulfides, polythioethers, copolymers and mixtures thereof; and (b) a topcoat applied over at least a portion of the basecoat, the topcoat being different from the basecoat and having a higher tensile strength and percent elongation that the elastomeric basecoat.

31. A process of inhibiting fuel leakage from an interior portion of a fuel storage container, comprising the step of: (a) coating an interior portion of a fuel storage tank with a multi- component composite coating comprising: (i) an elastomeric basecoat formed from a curable basecoat composition deposited upon the surface of the substrate; and (ii) a topcoat applied over at least a portion of the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material.

A ENDED CLAIMS

[received by the International Bureau on 21 September 2000 (21 .09.2000 ) new cl aim 32 added ; remaining claims unchanged ( 1 page) ]

(ii) a topcoat applied over at least a portion of the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition comprising a polythioether material.

5 32. A composite coating comprising:

(a) an elastomeric basecoat formed from a curable basecoat composition deposited upon a surface of a substrate; and

(b) a topcoat applied over the basecoat, the topcoat being different from the basecoat and being formed from a curable topcoat composition

10 comprising a polythioether material, wherein at least one of the basecoat composition and the topcoat composition comprises a curing agent selected, from the group consisting of polyamines, polyols, polyisocyanates, metal oxides, polyepoxides and mixtures thereof.

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