WO2022253588A1

WO2022253588A1 - Coating composition

Info

Publication number: WO2022253588A1
Application number: PCT/EP2022/063667
Authority: WO
Inventors: Hanane Belmokaddem Bennis; Timothy Michael Shea; Andrew James MEHRING
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Usa, Inc.
Priority date: 2021-06-01
Filing date: 2022-05-20
Publication date: 2022-12-08
Also published as: EP4347730A1

Abstract

Coating composition for an aircraft bladder comprising: (i) a first coating agent comprising vinylidene chloride copolymer, and (ii) a second coating agent comprising an epoxy resin, wherein the weight ratio of the first coating agent to the second coating agent is in the range from 2:1 to 3.5:1. The coating composition can be used in a method for reducing shrinkage of an aircraft bladder caused by exposure to an unleaded aviation fuel composition, wherein the method comprises coating the surface of the aircraft bladder with the coating composition.

Description

COATING COMPOSITION

Field of the Invention

The present invention relates to a coating composition for an aircraft bladder and method of reducing shrinkage and/or delamination of an aircraft bladder using said coating composition.

Background of the Invention

Avgas (aviation gasoline) is an aviation fuel used in spark-ignited internal-combustion engines to propel aircraft. Avgas is distinguished from mogas (motor gasoline) which is the everyday gasoline used in cars and some non-commercial light aircraft. Unlike mogas, which has been formulated since the 1970s to allow the use of 3-way catalytic converters for pollution reduction, avgas contains tetraethyl lead (TEL), a non-biodegradable toxic substance used to prevent engine knocking (detonation).

Aviation gasoline fuels currently contain the additive tetraethyl lead (TEL), in amounts up to 0.53 mL/L or 0.56 g/L which is the limit allowed by the most widely used aviation gasoline specification 100 Low Lead (100LL). The lead is required to meet the high octane demands of aviation piston engines: the 100LL specification ASTM D910 demands a minimum motor octane number (MON) of 99.6, in contrast to the EN 228 specification for European motor gasoline which stipulates a minimum MON of 85 or United States motor gasoline which require unleaded fuel minimum octane rating (R+M)/2 of 87.

Aviation fuel is a product which has been developed with care and subjected to strict regulations for aeronautical application. Thus, aviation fuels must satisfy precise physico-chemical characteristics, defined by international specifications such as ASTM D910 specified by Federal Aviation Administration (FAA). Automotive gasoline is not a fully viable replacement for avgas in many aircraft, because many high-performance and/or turbocharged airplane engines require 100 octane fuel (MON of 99.6) and modifications are necessary in order to use lower-octane fuel. Automotive gasoline can vaporize in fuel lines causing a vapor lock (a bubble in the line) or fuel pump cavitation, starving the engine of fuel. Vapor lock typically occurs in fuel systems where a mechanically-driven fuel pump mounted on the engine draws fuel from a tank mounted lower than the pump. The reduced pressure in the line can cause the more volatile components in automotive gasoline to flash into vapor, forming bubbles in the fuel line and interrupting fuel flow.

The ASTM D910 specification does not include all gasoline satisfactory for reciprocating aviation engines, but rather, defines the following specific types of aviation gasoline for civil use: Grade 80; Grade 91;

Grade 100; and Grade 100LL. Grade 100 and Grade 100LL are considered High Octane Aviation Gasoline to meet the requirement of modern demanding aviation engines. In addition to MON, the D910 specification for Avgas has the following requirements: density; distillation (initial and final boiling points, fuel evaporated, evaporated temperatures T10, T40, T90, T10+T50); recovery, residue, and loss volume; vapor pressure; freezing point; sulfur content; net heat of combustion; copper strip corrosion; oxidation stability (potential gum and lead precipitate); volume change during water reaction; electrical conductivity; and other properties. Avgas fuel is typically tested for its properties using ASTM tests: Motor Octane Number: ASTM D2700 Aviation Lean Rating: ASTM D2700 Performance Number (Super-Charge): ASTM D909 Tetraethyl Lead Content: ASTM D5059 or ASTM D3341 Color: ASTM D2392

Density: ASTM D4052 or ASTM D1298

Distillation: ASTM D86

Vapor Pressure: ASTM D5191 or ASTM D323 or ASTM D5190

Freezing Point: ASTM D2386 Sulfur: ASTM D2622 or ASTM D1266

Net Heat of Combustion (NHC): ASTM D3338 or ASTM D4529 or ASTM D4809

Copper Corrosion: ASTM D130

Oxidation Stability - Potential Gum: ASTM D873 Oxidation Stability - Lead Precipitate: ASTM D873 Water Reaction - Volume change: ASTM D1094 Electrical Conductivity: ASTM D2624 Aviation fuels must have a low vapor pressure in order to avoid problems of vaporization (vapor lock) at low pressures encountered at altitude and for obvious safety reasons. But the vapor pressure must be high enough to ensure that the engine starts easily. The Reid Vapor pressure (RVP) should be in the range of 38kPa to 49kPA. The final distillation point must be fairly low in order to limit the formations of deposits and their harmful consequences (power losses, impaired cooling). These fuels must also possess a sufficient Net Heat of Combustion (NHC) to ensure adequate range of the aircraft. Moreover, as aviation fuels are used in engines providing good performance and frequently operating with a high load, i.e. under conditions close to knocking, this type of fuel is expected to have a very good resistance to spontaneous combustion.

Moreover, for aviation fuel two characteristics are determined which are comparable to octane numbers: one, the MON or motor octane number, relating to operating with a slightly lean mixture (cruising power), the other, the Octane rating. Performance Number or PN, relating to use with a distinctly richer mixture (take-off). With the objective of guaranteeing high octane requirements, at the aviation fuel production stage, an organic lead compound, and more particularly tetraethyllead (TEL), is generally added. Without the TEL added, the MON is typically around 91. As noted above ASTM D910, 100 octane aviation fuel requires a minimum motor octane number (MON) of 99.6. The distillation profile of the high octane unleaded aviation fuel composition should have a T10 of maximum 75°C, T40 of minimum 75°C, T50 of maximum 105°C, and T90 of maximum 135°C.

As in the case of fuels for land vehicles, administrations are tending to lower the lead content, or even to ban this additive, due to it being harmful to health and the environment. Thus, the elimination of lead from the aviation fuel composition is becoming an objective.

Attempts have been made in the past to produce a high octane unleaded aviation fuel that meet most of the ASTM D910 specification for high octane aviation fuel.

In addition to the MON of 99.6, it is also important to not negatively impact the flight range of the aircraft, vapor pressure, and freeze points that meets the aircraft engine start up requirements and continuous operation at high altitude.

US Patent Nos. 9127225, 9388359, 9388357, 9388358, 9120991, 9388356, 9035114 all relate to various unleaded aviation fuel compositions that meet most of the ASTM D910 specification for 100 octane aviation fuel.

US Patent No. 9120991 discloses unleaded aviation fuel compositions comprising toluene, toluidine, alkylate or alkylate blend, branched acetate and isopentane.

US Patent No. 9388356 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, branched chain alcohol and isopentane.

US Patent No. 9388357 discloses unleaded aviation fuel compositions comprising toluene, aromatic amine component comprising toluidine, alkylate or alkylate blend and isopentane.

US Patent No. 9388358 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, diethyl carbonate, and isopentane.

US Patent No. 9388359 discloses unleaded aviation fuel compositions comprising toluene, toluidine, alkylate or alkylate blend, diethyl carbonate and isopentane.

US Patent No. 9035114 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, branched alkyl acetate and isopentane.

US Patent No. 9127225 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, C4-C5 alcohol, and isopentane.

While the types of compositions disclosed in the above-mentioned patent publications may meet most of the ASTM D910 specification for 100 octane aviation fuel, it has been found that some undesirable effects on bladder components within the aircraft can still occur. Bladder tanks are reinforced rubberized bags installed in a section of aircraft structure designed to accommodate fuel. Many high-performance light aircraft, helicopters and some smaller turboprop aircraft use bladder tanks.

In particular, problems such as bladder shrinkage and delamination have been observed with types of compositions disclosed in the above-mentioned prior art, especially those containing aromatic amines such as aniline, for example, those disclosed in US9035114B1. It would therefore be desirable to find a solution to the problem of bladder shrinkage and delamination when exposed to certain components, e.g. aniline, of high octane unleaded aviation fuel compositions. In particular, it would be desirable to find a solution to said problem without having to reformulate high octane unleaded aviation fuels which already meet most or all of the requirements of the ASTM D910 specification.

It has surprisingly been found by the present inventors that by coating the surface of the aircraft bladder with a certain coating composition described hereinbelow, a surprising reduction in bladder shrinkage and delamination can be achieved, without having to reformulate the high octane unleaded aviation fuel which may have been especially formulated for use in an aviation engine.

Summary of the Invention

According to the present invention there is provided a coating composition for an aircraft bladder comprising (i) a first coating agent comprising a vinylidene chloride copolymer and (ii) a second coating agent comprising an epoxy resin, wherein the weight ratio of the first coating agent to the second coating agent is in the range from 2:1 to 3.5:1.

According to the present invention there is also provided a process for producing said coating composition comprising a step of blending the first coating agent with the second coating agent in a weight ratio in the range from 2:1 to 3.5:1.

According to the present invention there is also provided a method for reducing shrinkage of an aircraft bladder caused by exposure to an unleaded aviation fuel composition, wherein the method comprises coating the surface of the aircraft bladder with a coating composition wherein the coating composition comprises (i) a first coating agent comprising vinylidene chloride copolymer and (ii) a second coating agent comprising an epoxy resin, wherein the weight ratio of the first coating agent to the second coating agent is in the range from 2:1 to 3.5:1.

It has been surprisingly found that the coating composition and method of the present invention serves to reduce bladder shrinkage and delamination while allowing for a certain amount of certain aromatic components (e.g. aniline) to still be present in the high octane unleaded aviation fuel composition used to fuel the aviation engine.

The features and advantages of the invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.

Brief Description of the Drawings

The drawings illustrate certain aspects of some of the embodiments of the invention and should not be used to limit or define the invention.

Figure 1 is a photograph which shows the appearance of an uncoated bladder sample which has not been exposed to any fuel. Figure 2 is a photograph which shows the appearance of an uncoated bladder sample after it has been soaked in Reference Fuel A for 125 hours at 135°F as described in the Bladder Testing Examples below.

Figure 3 is a photograph which shows the appearance of a bladder sample which has been coated with a coating composition (RK70) according to the method of the present invention after it has been soaked in the Reference fuel of Example 1 for 125 hours at 135°F as described in the Bladder Testing Examples below.

Figure 4 is a photograph which shows the appearance of a bladder sample which has been coated with a coating composition (RK60) according to the method of the present invention after it has been soaked in the Reference Fuel

A for 125 hours at 135°F as described in the Bladder

Testing Examples below.

Figure 5 is a photograph which shows the appearance of a bladder sample which has been coated with a coating composition (RK65) according to the method of the present invention after it has been soaked in the Reference Fuel

A for 125 hours at 135°F as described in the Bladder

Testing Examples below.

Detailed Description of the Invention

We have found that by coating the aircraft bladder with a certain coating composition, shrinkage and delamination of the bladder is reduced upon exposure to high octane unleaded aviation fuels containing certain components, for example aromatic amines, such as aniline.

As used herein, the term 'shrinkage' means the shrinking effect of the fuel on the bladder material. In the context of this aspect of the invention, the term 'reduced shrinkage' embraces any degree of reduction in shrinkage. The reduction in shrinkage may be of the order of 10% or more, preferably 20% or more, more preferably 50% or more, and especially 70% or more compared to the shrinkage exhibited by an analogous bladder material which has not been coated in accordance with the method of the present invention.

The coating composition of the present invention comprises a first coating agent and a second coating agent. The coating composition is produced by mixing the first coating agent with the second coating agent in a specified ratio. The coating composition is then applied to the aircraft bladder before the aircraft bladder is exposed to an aviation fuel composition.

The first coating agent comprises a vinylidene chloride copolymer. Preferably the vinylidene chloride copolymer comprises vinylidene chloride monomers and acrylonitrile monomers and is therefore a poly(vinylidene) chloride/poly(acrylonitrile) copolymer.

The first coating agent is commercially available from Damon under the tradename Red Cote (RTM). Red Kote (RTM) is a copolymer of polyacrylonitrile and poly(vinylidene chloride) in approximately 40% acetone and 30% methyl ethyl ketone (MEK).

The second coating agent comprises an epoxy resin. Preferably the epoxy resin is a novolac epoxy resin.

Epoxy novolac resins are the reaction product of an epoxy group-introducing agent, such as for example, epichlorohydrin, with a condensation product of a mono-, di or polyhydric phenol (which may be alkyl substituted (e.g. cresol) or non-substituted) and an aldehyde, such as, for example, formaldehyde. Typical epoxy novolacs are polymers containing glycidyl ether groups and further comprising repeating units derived from bisphenol F or another reaction product of a phenol with an aldehyde. The phenol may be monohydric, dihydric or trihydric and may be non-substituted or alkyl substituted.

The second coating agent preferably additionally comprises an epoxy curing agent, preferably selected from aliphatic and cycloaliphatic amines, and polyetheramines, and any combinations and mixtures thereof. A preferred epoxy curing agent for use herein is a cycloaliphatic amine, such as a cyclohexylamine compound. An especially preferred epoxy curing agent for use herein is 3- aminomethyl-3,5,5-trimethylcyclohexylamine.

The second coating agent preferably additionally comprises bisphenol A or a bisphenol A-based resin.

The second coating agent preferably additionally comprises a solvent, for example benzyl alcohol.

The second coating agent is commercially available from Caswell under the tradename Gas Tank Sealer Part A (containing epoxy phenol novolak resin) and Gas Tank Sealer Part B (containing 30-60 wt.% benzyl alcohol, 1-5 wt.% bisphenol A (4,4'-isopropylidenediphenol) and 30-60 wt.% of 3-aminomethyl-3,5,5-trimethylcyclohexylamine).

The Gas Tank Sealer Part A and Gas Tank Sealer Part B are preferably mixed together to form the second coating agent.

To produce the coating composition the first coating agent is blended with the second coating agent in a weight ratio in the range from 2:1 to 3.5:1, preferably from 2:1 to 3:1, more preferably from 2:1 to 2.5:1, even more preferably from 2:1 to 2.3:1, and especially in a weight ratio of 2.3:1.

In the method of the present invention, the coating composition is applied to the inner surface of the aircraft bladder before it is exposed to a fuel composition. Preferably, the coating composition is applied to the inner surface of the aircraft bladder in order to form a surface coating having a thickness in the range from 50 to 175 pm, more preferably from 70 to 130 pm, even more preferably from 75 to 125 pm. The coating thickness can be measured using standard test method ASTM D6132. A Positector 200 ultrasonic coating thickness gauge can be used for measuring the thickness of the coating.

After the coating composition has been applied to the inner surface of the aircraft bladder, it should be allowed to dry before exposing the aircraft bladder to a fuel composition.

The compositions and methods of the present invention are applicable to all types of aircraft bladder. Bladders or fuel cells are reinforced rubber bags installed usually in the wing section of some piston engine aircrafts or helicopters and are used as fuel tanks. The material chemistry of the bladders varies from one manufacture to another. Some of them are very strong and rigid, while others are more light weight and very flexible. It has been found that the method of the present invention is particularly useful for a Meggitt bladder. Meggitt Bladders are present in Beechcraft, Cessna and Piper aircraft. A Meggitt Bladder is light weight and very flexible and is comprised of two layers of polyurethane and nylon attached together by an adhesive. It is the nylon inner layer which is exposed to the fuel. It has been found that a Meggitt bladder is susceptible to wrinkling and delamination upon exposure to certain high octane unleaded aviation gasoline compositions, especially those containing certain levels of aromatic amines, for example greater than 2 vol% aromatic amines, (e.g. aniline). In particular, the high octane unleaded aviation gasoline compositions herein typically comprise from 0.5 to 6 vol%, preferably from 0.5 to 4.5 vol% of aniline, based on the unleaded aviation gasoline composition. As mentioned above, the problem of shrinkage and/or delamination is particularly observed when the aircraft bladder is exposed to an aviation gasoline composition comprising greater than 2 vol% aromatic amines, especially aniline.

Suitable unleaded aviation fuel compositions for use herein may be found in US Patent Nos. 9127225, 9388359, 9388357, 9388358, 9120991, 9388356, 9035114 which all relate to various unleaded aviation fuel compositions that meet most of the ASTM D910 specification for 100 octane aviation fuel. A preferred unleaded aviation fuel composition for use herein may be found in US Patent No. 9035114, incorporated herein by reference in its entirety. US Patent No. 9035114 discloses unleaded aviation fuel compositions comprising toluene, aniline, alkylate or alkylate blend, branched alkyl acetate and isopentane, and meeting most of the ASTM D910 specification for 100 octane aviation fuel. The main components of the unleaded aviation fuel composition disclosed in US Patent No. 9035114 are disclosed below. Further details of the compositions and properties of the fuels can be found in US Patent No. 9035114.

Toluene

Toluene occurs naturally at low levels in crude oil and is usually produced in the processes of making gasoline via a catalytic reformer, in an ethylene cracker or making coke from coal. Final separation, either via distillation or solvent extraction, takes place in one of the many available processes for extraction of the BTX aromatics (benzene, toluene and xylene isomers). The toluene used herein must be a grade of toluene that have a MON of at least 107 and containing less than 1 vol% of C8 aromatics. Further, the toluene component preferably has a benzene content between 0%v and 5%v, preferably less than l%v.

Toluene is preferably present in the blend in an amount from about 5%v, preferably at least about 10%v, most preferably at least about 15%v to at most about 25%v, preferably to at most about 23%v, more preferably to at most about 20%v, based on the unleaded aviation fuel composition.

Aniline

Aniline (C6H5NH2) is mainly produced in industry in two steps from benzene. First, benzene is nitrated using a concentrated mixture of nitric acid and sulfuric acid at 50 to 60°C, which gives nitrobenzene. In the second step, the nitrobenzene is hydrogenated, typically at 200- 300°C in presence of various metal catalysts.

As an alternative, aniline is also prepared from phenol and ammonia, the phenol being derived from the cumene process.

In commerce, three brands of aniline are distinguished: aniline oil for blue, which is pure aniline; aniline oil for red, a mixture of equimolecular quantities of aniline and ortho- and para-toluidines; and aniline oil for safranine, which contains aniline and ortho-toluidine, and is obtained from the distillate (echappes) of the fuchsine fusion. Pure aniline, otherwise known as aniline oil for blue is desired for high octane unleaded avgas. Aniline is preferably present in the blend in an amount from about 0.5%v, preferably at least about l%v, most preferably at least about 1.5%v to at most about 4%v, preferably to at most about 3%v, more preferably to at most about 2%v, based on the unleaded aviation fuel composition.

Alkylate and Alkylate Blend

The term alkylate typically refers to branched-chain paraffin. The branched-chain paraffin typically is derived from the reaction of isoparaffin with olefin. Various grades of branched chain isoparaffins and mixtures are available. The grade is identified by the range of the number of carbon atoms per molecule, the average molecular weight of the molecules, and the boiling point range of the alkylate. It has been found that a certain cut of alkylate stream and its blend with isoparaffins such as isooctane is desirable to obtain or provide the high octane unleaded aviation fuel herein. These alkylate or alkylate blend can be obtained by distilling or taking a cut of standard alkylates available in the industry. It is optionally blended with isooctane. In a preferred embodiment herein, alkylate/alkylate blend is blended with isooctane. The alkylate or alkylate blend have an initial boiling range of from about 32°C to about 60°C and a final boiling range of from about 105°C to about 140°C, preferably to about 138°C, more preferably to about 137°C, having T40 of less than 99°C, T50 of less than 100°C, T90 of less than 110°C, preferably at most 108°C, the alkylate or alkylate blend comprising isoparaffins from 4 to 9 carbon atoms, about 3-20 vol% of C5 isoparaffins, based on the alkylate or alkylate blend, about 3-15 vol% of C7 isoparaffins, based on the alkylate or alkylate blend, and about 60-90 vol% of C8 isoparaffins, based on the alkylate or alkylate blend, and less than 1 vol% of C10+, preferably less than 0.1 vol%, based on the alkylate or alkylate blend; Alkylate or alkylate blend is preferably present in the unleaded aviation fuel composition in an amount from about 30%v, preferably at least about 35%v, most preferably at least about 40%v to at most about 70%v, preferably to at most about 65%v, more preferably to at most about 60%v.

Isopentane

Isopentane is preferably present in an amount of at least 8 vol% in an amount sufficient to reach a vapor pressure in the range of 38 to 49 kPa. The alkylate or alkylate blend also contains C5 isoparaffins so this amount will typically vary between 8 vol% and 25 vol% depending on the C5 content of the alkylate or alkylate blend. Isopentane should be present in an amount to reach a vapor pressure in the range of 38 to 49 kPa to meet aviation standard. The total isopentane content in the unleaded aviation fuel composition is typically in the range of 10 vol% to 20 vol%, preferably in the range of 10% to 15% by volume, based on the aviation fuel composition.

There is a tendency for isopentane to reduce the MON and increase the RVP, while there is a tendency for isobutane to increase the MON and increase the RVP. It has been found that if there is too much of either isopentane or isobutane then the RVP is too high. Hence, in a preferred embodiment, the volume ratio of isopentane to isobutane is at least 2:1, preferably at least 2.5:1, more preferably at least 3:1, and at most 4:1, preferably at most 3.5:1, more preferably at most 3.3:1.

Alkyl Acetate

The unleaded aviation fuel may contain a branched alkyl acetate having branched chain alkyl group having 4 to 8 carbon atoms as a co-solvent. Suitable co-solvent may be, for example, t-butyl acetate, iso-butyl acetate, ethylhexylacetate, iso-amyl acetate, and t-butyl amyl acetate, or mixtures thereof. It has been found that branched chain alkyl acetates having an alkyl group of 4 to 8 carbon atoms dramatically decrease the freezing point of the unleaded aviation fuel to meet the current ASTM D910 standard for aviation fuel. The branched acetate is present in an amount from 0.1 vol%, to 10 vol%, preferably from 1 vol% to 8vol%, more preferably from 2 vol% to 6 vol%, even more preferably from 4 vol% to 6 vol%, based on the unleaded aviation fuel composition. A preferred branched alkyl acetate for use herein is t-butyl acetate.

The branched alkyl acetate is useful for ensuring that the aniline remains in solution.

Blending

For the preparation of the high octane unleaded aviation gasoline, the blending can be in any order as long as they are mixed sufficiently. It is preferable to blend the toluene and alkylate blend together, followed by the isopentane and then the t-butyl acetate and the aniline (in that order) and to mix the blend for about 2 hours. This order of addition helps to prevent the aniline dropping out of solution.

In order to satisfy other requirements, the unleaded aviation fuel may contain one or more additives which a person skilled in the art may choose to add from standard additives used in aviation fuel. There should be mentioned, but in non-limiting manner, additives such as antioxidants, anti-icing agents, antistatic additives, corrosion inhibitors, dyes and their mixtures.

The aircraft engine referred to herein is suitably a spark ignition piston-driven engine. A piston-driven aircraft engine may for example be of the inline, rotary, V-type, radial or horizontally-opposed type.

The present invention will be illustrated by the following illustrative embodiment, which is provided for illustration only and is not to be construed as limiting the claimed invention in any way.

Examples Test Methods

The following test methods were used for the measurement of the aviation fuels.

Motor Octane Number: ASTM D2700 Tetraethyl Lead Content: ASTM D5059 Density: ASTM D4052 Distillation: ASTM D86 Vapor Pressure: ASTM D323 Freezing Point: ASTM D2386 Sulfur: ASTM D2622

Net Heat of Combustion (NHC): ASTM D3338 Copper Corrosion: ASTM D130

Oxidation Stability - Potential Gum: ASTM D873 Oxidation Stability - Lead Precipitate: ASTM D873 Water Reaction - Volume change: ASTM D1094 Detail Hydrocarbon Analysis (ASTM 5134)

Example 1

An aviation fuel composition having the formulation below (Reference Fuel A) was blended as follows. Toluene having 107 MON was blended with Aniline while mixing. Narrow Cut Alkylate having the properties shown in Table 1 above were poured into the mixture. Then, t-butyl acetate was added, followed by isopentane to complete the blend.

Table 1

Reference Fuel A

Light alkylate blend 36%v

Toluene 35%v

Isopentane 17%v

Isobutane 3%v

Aniline 4%v t-butyl acetate 8%v

The physical properties of Reference Fuel A are shown in the table below:

Bladder Testing In order to measure the effect of fuel on a bladder, the following experiments were carried out. The fuel used in these experiments was Reference Fuel A (see above). A Meggitt bladder coupon was soaked in Reference Fuel A for about 125 hours at 135°F. Photos of the coupon were taken both before and after exposure to the fuel. Figure 1 shows the appearance of the Meggitt bladder coupon before exposure to fuel. Figure 2 shows the appearance of the Meggitt bladder coupon after exposure to the fuel. A comparison of Figure 1 and Figure 2 demonstrates that exposure to Reference Fuel A causes the inner layer of the Meggitt bladder coupon to shrink causing 'wrinkling' and delamination of the two layers.

Example 2

A Meggitt bladder coupon of the same type and size as that used in Example 1 was prepared. The bladder coupon should be clean and free from oils, fuel and other contaminants and debris. The bladder coupon was rinsed with methyl ethyl ketone (isopropyl alcohol or acetone can be used), wiped and air dried. The preferred cleaning solvent is methyl ethyl ketone due to its compatibility with the coating composition. The bladder coupon must be completely clear and dry before proceeding with application of the coating composition.

The coating composition (RK70) was a 70/30 mixture of Damon Red Kote (RTM) Fuel Tank Liner (single component product) and Caswell Tank Sealer (2 component product). Damon Red Kote (RTM) comprises a copolymer of polyacrylonitrile and poly(vinylidene) in approx. 40% acetone and 30% methyl ethyl ketone (MEK). Caswell Gas Tank Sealer is a two-component product comprising Caswell Gas Tank Sealer Part A and Caswell Gas Tank Sealer Part B. Caswell Gas Tank Sealer Part A comprises a phenol novolac epoxy resin. Caswell Gas Tank Sealer Part B comprises an amine curing agent and bisphenol A. Both the Damon Red Kote and the Caswell products were allowed to adjust to room temperature prior to blending.

The volume of the coating composition (RK70) needed to coat the bladder is determined using the following equation:

V = 0.0164ma where V = total volume of RK70 in cc, m = desired mil thickness of RK70, and a = square inches of bladder surface.

An additional 10 to 20% volume was also blended to make up for product loss on mixing tools, blending container, and applicators. In a glass container, 70% of V (total volume of RK70 in cc) is transferred from the Red-Kote product container and set aside. The Caswell two component product is blended in a separate disposable container and equal to 30% of V (total volume of RK70 in cc) + 10%. The volume of Caswell is made of 2 parts,

Part A and Part B at 2:1 ratio by volume. First the part A is measured and transferred to the mixing container and then part B is added. The two components are mixed for 1 to 2 minutes with a disposable tong depressor or similar mixing device. Within 2 minutes of mixing the Caswell product, 30% of V (total volume of RK70 in cc) Caswell product is added to the premeasured volume of Red-Kote. The Red Kote and Caswell blend is mixed for 2 minutes with a tong depressor, ensuring the components are mixed well and no single component is left unmixed on the side or bottom.

Immediately after blending the RK70, the application must begin. The RK70 begins to cure within 8 minutes of blending and will gel within 30 minutes. The temperature of the application area and RK70 product is critical to product cure times. An increase of product and work area temperature can greatly shorten the cure time. Product applied at 90°F could have half the cure time of the product applied at 77°F. Colder product with cure slower. The RK70 can be applied with a paint brush, paint roller, gravity rolling, or spray gun. The applicator will be chosen dependent on the accessibility of the bladder surface. For contained bladders, a firm brush, short nap fiber roller, or sense foam paint roller can be used for bladder surface that are unobstructed and easily accessed. An extended flexible handle on a paint roller will aid in reaching obstructed and hard to reach areas of the bladder. A coatings sprayer fitted to an extension wand and 360° spray tip that is suitable for viscous coatings is the ideal applicator for bladder in containment and have obstructions and limited accessibility. For bladders that are free from containment, the RK70 can be poured directly inside and the bladder rolled or rotated 360° until all surfaces are wetted with product. The excess product should then be drained from the bladder. It is recommended to test the chosen application method on a test surface separate of the bladder to establish an application technique that delivers the desired coating thickness with 100% coverage. After application, the coated fuel bladder should be stored at 70-90°F for a minimum of 24 to 36 hours before filling with fuel.

The coating thickness on the bladder specimen is measured using a Positector 200 ultrasonic coating thickness gauge as described in ASTM method D6132. The thickness of the coating used in the present Examples was 125 pm.

The coated Meggitt bladder coupon was soaked in Reference Fuel A for about 125 hours at 135°F. Photos of the coupon were taken before and after exposure to the fuel.

The procedure above was repeated using a Meggitt bladder coupon coated in a 60/40 mixture of Damon Red Kote (RTM) Fuel Tank Liner (single component product) and Caswell Tank Sealer (2 component product) (designated as RK60)

The procedure above was further repeated using a Meggitt bladder coupon coated in a 65/35 mixture of Damon Red Kote (RTM) Fuel Tank Liner (single component product) and Caswell Tank Sealer (2 component product) (designated as RK65).

Figure 3 is a photograph which shows the appearance of the Meggitt bladder coupon coated with RK70 after exposure to Reference Fuel A for 125 hours at 135°F.

Figure 4 is a photograph which shows the appearance of the Meggitt bladder coupon coated with RK60 after exposure to Reference Fuel A for 125 hours at 135°F.

Figure 5 is a photograph which shows the appearance of the Meggitt bladder coupon coated with RK65 after exposure to Reference Fuel A for 125 hours at 135°F. Discussion

No wrinkling or delamination can be seen on the coated Meggitt bladder coupon of Figure 3 demonstrating that the RK70 coating composition has prevented shrinkage of the inner layer and therefore prevented wrinkling and delamination of the two layers.

Wrinkling and delamination can be seen on the coated Meggitt bladder coupons of Figures 4 and 5 demonstrating that the RK60 and RK65 coating composition have not prevented shrinkage of the inner layer to as great an extent as the RK70 coating composition.

Claims

C LA IM S

1. Coating composition for an aircraft bladder comprising: (i) a first coating agent comprising vinylidene chloride copolymer, and (ii) a second coating agent comprising an epoxy resin, wherein the weight ratio of the first coating agent to the second coating agent is in the range from 2:1 to 3.5:1.

2. Coating composition according to Claim 1 wherein the weight ratio of the first coating agent to the second coating agent is in the range from 2:1 to 3:1.

3. Coating composition according to Claim 1 or 2 wherein the weight ratio of the first coating agent to the second coating agent is in the range from 2:1 to 2.5:1.

4. Coating composition according to any of Claims 1 to

3 wherein the epoxy resin is a novolac epoxy resin.

5. Coating composition according to any of Claims 1 to

4 wherein the second coating agent additionally comprises a curing agent.

6. Coating composition according to Claim 5 wherein the curing agent is an amine curing agent.

7. Coating composition according to any of Claims 1 to

6 wherein the second coating agent additionally comprises bisphenol A or a bisphenol A resin.

8. Coating composition according to any of Claims 1 to

7 wherein the vinylidene chloride copolymer comprises vinylidene chloride monomers and acrylonitrile monomers.

9. Process for making the coating composition of any of Claims 1 to 8 wherein the process comprises a step of blending the first coating agent with the second coating agent in a weight ratio of from 2:1 to 3.5:1.

10. Method for reducing shrinkage of an aircraft bladder caused by exposure to an unleaded aviation fuel composition, wherein the method comprises coating the surface of the aircraft bladder with a coating composition according to any of Claims 1 to 8.

11. Method according to Claim 10 wherein the aircraft bladder is a Meggitt bladder.

12. Method according to Claim 10 or 11 wherein the unleaded aviation fuel composition comprises aniline.

13. Method according to Claim 12 wherein the unleaded aviation fuel composition comprises from 0.5 vol% to 6 vol% of aniline.