HK1187360A - Diethylene glycol monomethyl ether resistant coating - Google Patents

Description

Diethylene glycol monomethyl ether resistant coatings

Statement regarding federally sponsored research or development

The invention was made with government support under Air Force Research Laboratory (AFRL) approved contract number No. FA8650-05-C-5010. The united states government may have certain rights in this invention.

Technical Field

The present invention relates to coating compositions resistant to diethylene glycol monomethyl ether (DIEGME). More particularly, the present invention relates to such coating compositions comprising a sulfur-containing, epoxy functional polyol and an isocyanate curing agent.

Background

Conventional civil aviation and aerospace fuel tank coatings such as BMS10-39 can be degraded by certain fuel additives such as DIEGME. At high concentrations, DIEGME can chemically degrade conventional epoxy-based fuel tank paints or coatings, resulting in the peeling of the topcoat. Such chemical degradation of conventional epoxy-based paints or coatings can pose particular problems in aerospace or civil aviation applications such as military aircraft where DIEGME may be present in jet fuel or Jet Propellant (JP). DIEGME may be added to jet fuel or JP as a Fuel System Icing Inhibitor (FSII) that prevents or reduces ice build-up within the fuel tank due to the low temperatures experienced by aircraft operating in cold weather or at high altitudes. For example, JP-5 and JP-8 are military jet fuels, which typically include DIEGME as FSII. Similarly, DIEGME can also be added to Jet a or Jet a-1 fuel as FSII.

During normal aircraft operation, DIEGME present in jet fuel may condense in the high concentration fuel tank headspace, and/or it may become enriched in residual water that may be at the bottom of the fuel tank. At these high concentrations, DIEGME may act as a solvent for conventional epoxy-based fuel tank paints or coatings, which may cause the topcoat to swell and/or peel. The stripped fuel tank top coat creates hazardous operating conditions for the aircraft because the stripped top coat can enter and clog the fuel filter, thereby disrupting the operation of the fuel system.

The problem of tank top coat delamination due to the presence of DIEGME in jet fuel has been reported in United States Air Force (USAF) planes such as B-52, KC-135 and C-17. Similar problems have been reported for American naval aircraft such as P-3. Thus, there is a need for DIEGME resistant fuel tank coatings.

In addition, jet fuel contains microorganisms that consume the plastic and rubber components of the aircraft fuel system and produce acidic metabolic byproducts. Conventional epoxy-based coating compositions (which include amine-based curing systems) exhibit acceptable adhesion, but do not provide sufficient resistance to acid and/or microbial by-products. In contrast, conventional coating compositions (which include polyurethane-based curing systems) exhibit acceptable acid resistance and microbial by-product properties, but do not provide adequate adhesion to substrates, particularly direct adhesion to metal substrates. Thus, there is a need for coating compositions that have low temperature flexibility and good adhesion to substrates, as well as resistance to DIEGME, fuels, methyl ethyl ketone, and microbial byproducts.

Disclosure of Invention

Embodiments of the invention include DIEGME-resistant coatings comprising: a sulfur-containing, epoxy functional polyol and an isocyanate curing agent. According to an embodiment of the present invention, the sulfur-containing, epoxy-functional polyol comprises the reaction product of reactants comprising a thiol-terminated polymer and an epoxy resin.

In certain embodiments, the thiol-terminated polymer comprises a thiol-terminated polysulfide or thiol-terminated polythioether.

In one embodiment, the thiol-terminated polythioether comprises a compound represented by formula 1:

formula 1

HS-R₁-[-S-(CH₂)₂-O-[-R₂-O-]_m-(CH₂)₂-S-R₁-]_n-SH

Wherein

R₁Is represented by C_2-6N-alkylene group, C_3-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂- [ (-CH) with the units substituted by methyl₂-)_p-X-]_q-(-CH₂-)_r-，

R₂Represents a methylene group, C_2-6N-alkylene group, C_2-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂-by methyl groupSubstituted- [ (-CH)₂-)_p-X-]_q-(-CH₂-)_r-，

X is selected from O, S and-NR₆-one of the two or more of the two,

R₆represents a hydrogen atom or a methyl group,

m is a rational number from 0 to 10,

n is an integer of 1 to 60,

p is an integer of 2 to 6,

q is an integer of 1 to 5, and

r is an integer from 2 to 10.

In one embodiment, the thiol-terminated polysulfide comprises a compound represented by formula 4:

formula 4

HS-(R-SS)_n-R-SH

Wherein R is a straight or branched hydrocarbon, oxohydrocarbon or thioalkane, and n is an integer from 1 to 38, for example from 7 to 38.

In one embodiment, the epoxy resin includes a compound represented by formula 5:

formula 5

Wherein R is an aliphatic group, a cycloaliphatic group, an aryl group, or a combination thereof.

In one embodiment, the R groups in the epoxy resin are of formula 6:

formula 6

Wherein n is an integer from 1 to 10.

In another embodiment, the epoxy resin comprises a polyglycidyl ether of a polyhydric phenol.

In one embodiment, the sulfur-containing, epoxy functional polyol comprises a compound represented by formula 7:

formula 7

Wherein Z comprises a polythioether or polysulfide linkage;

R₃comprises an alkyl or aryl group or a combination thereof and comprises at least two hydroxyl functional groups;

m is an integer of 0 to 4; and

each R₁And R₂Independently an alkyl or aryl group or a combination thereof.

In one embodiment, the sulfur-containing, epoxy-functional polyol includes at least one terminal epoxy functional group and at least one pendant hydroxyl functional group.

The sulfur-containing, epoxy-functional polyol may have a weight average molecular weight of about 10000 or less.

The isocyanate to hydroxyl ratio of the coating composition may be about 1: 1 to about 20: 1.

the isocyanate curing agent may comprise an isocyanate represented by NCO-R 'or an isocyanate represented by NCO-R' -NCO, or a combination thereof, wherein each R 'and R' independently comprises an alkyl or aryl group or a combination thereof.

The isocyanate curing agent may include isocyanate functional groups, and upon curing the coating composition, at least one isocyanate functional group may react with moisture to form at least one urea functional group.

After curing, the isocyanate curing agent can crosslink the sulfur-containing, epoxy-functional polyol to form an epoxy-functional polyurethane compound.

In one embodiment, the coating composition comprises:

a) a compound represented by formula 7:

formula 7

Wherein:

each R₁And R₂Independently an alkyl group or an aryl group or a combination thereof,

R₃comprising an alkyl or aryl group, or a combination thereof, and containing at least two hydroxyl functional groups,

m is an integer of 0 to 4, and

z comprises a polythioether or polysulfide linkage; and

b) an isocyanate curing agent.

In coating compositions according to certain embodiments, Z may comprise a polythioether linkage represented by formula 8:

formula 8

-S-R₁-[-S-(CH₂)₂-O-[-R₂-O-]_m-(CH₂)₂-S-R₁-]_n-S-

Wherein

R₁Is represented by C_2-6N-alkylene group, C_3-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or a pharmaceutically acceptable salt thereofAt least one of-CH₂- [ (-CH) with the units substituted by methyl₂-)_p-X-]_q-(-CH₂-)_r-，

R₂Represents a methylene group, C_2-6N-alkylene group, C_2-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂-substituted by methyl- [ (-CH)₂-)_p-X-]_q-(-CH₂-)_r-，

X is selected from O, S and-NR₆-one of the two or more of the two,

R₆represents a hydrogen atom or a methyl group,

m is a rational number from 0 to 10,

n is an integer of 1 to 60,

p is an integer of 2 to 6,

q is an integer of 1 to 5, and

r is an integer from 2 to 10.

The isocyanate to hydroxyl ratio of the coating composition may be about 1: 1 to about 20: 1.

the isocyanate curing agent may include an isocyanate represented by NCO-R 'or an isocyanate represented by NCO-R' -NCO, or a combination thereof, wherein each R 'and R' is independently an alkyl or aryl group or a combination thereof.

The isocyanate curing agent may include isocyanate functional groups, and upon curing the coating composition, at least one of the isocyanate functional groups may react with moisture to form at least one urea linkage.

After curing, the isocyanate curing agent can crosslink the sulfur-containing, epoxy-functional polyol to form an epoxy-functional polyurethane compound.

Detailed Description

Embodiments of the present invention provide DIEGME resistant coating compositions. According to an embodiment of the invention, the DIEGME-resistant coating composition is suitable for aerospace or civil fuel tank applications. Fuel tanks including DIEGME resistant coatings would not require frequent replacement of the fuel tank top coating, thereby significantly reducing maintenance costs for the aircraft. For example, USAF B-52 aircraft typically require fuel tank updates every four years at a cost of $120000 per aircraft. At the current B-52 fleet level, at the current fuel tank update rate every four years and projected aircraft life of 2040 years, the reduction in maintenance costs produced by the DIEGME resistant fuel tank coating composition will produce a cost savings of nearly $9 million for the B-52 fleet alone. In addition to the need for DIEGME resistance, fuel tank coating compositions should exhibit low temperature flexibility in order to withstand high altitude and/or cold weather aircraft operating conditions. In addition, the fuel tank coating composition should exhibit acid and microbial by-product resistance.

Coating compositions according to embodiments of the invention have crosslinking sites, low temperature flexibility, good adhesion to substrates, and are resistant to DIEGME, fuels, Methyl Ethyl Ketone (MEK), and microbial byproducts. Thus, coating compositions according to embodiments of the invention are suitable for aerospace or civil fuel tank applications and coating applications where fuel resistance, adhesion to substrates, solvent resistance, water resistance, chemical resistance, and low temperature flexibility are desired.

In one embodiment, a DIEGME-resistant coating composition includes a sulfur-containing, epoxy-functional polyol and an isocyanate curing agent. According to embodiments of the present invention, the sulfur-containing, epoxy-functional polyol may be prepared from the reaction of at least one thiol-terminated polythioether or polysulfide with an epoxy resin. Such sulfur-containing, epoxy-functionalized polyols impart DIEGME resistance, fuel resistance, low temperature flexibility, hydroxyl crosslinking sites, and good adhesion to substrates. The polyisocyanate curing agent crosslinks the sulfur-containing, epoxy-functional polyol to form an epoxy-functional polyurethane linkage. In addition, excess polyisocyanate cures with moisture to form urea, which provides solvent resistance (e.g., MEK and DIEGME resistance) and resistance to microbial byproducts. According to embodiments of the present invention, the coating composition may further comprise any suitable additive, including but not limited to a pigment or a mixture of pigments.

As indicated, certain embodiments of the present invention are directed to coating compositions. The term "coating composition" as used herein refers to a composition capable of producing a film having the ability to withstand atmospheric conditions, such as humidity and temperature, and at least partial permeation of barrier materials, such as water, fuel, and other liquids and gases. In certain embodiments, the coating compositions of the present invention are used in fuel tanks as an aerospace or aviation coating composition. Likewise, "coating composition" refers to a two-component system that includes a base component (including, for example, a sulfur-containing epoxy functional polyol) and an activator component (including, for example, an isocyanate curing agent). However, it should be understood that the base or activator component may include other components such as pigments or other additives. In use, when the coating composition is to be applied to a substrate, the base component and activator component are mixed together, applied to the substrate, and allowed to cure.

The term "DIEGME-resistant coating composition" as used herein refers to a coating composition that is resistant to, or in some cases substantially prevents, alteration or degradation of the coating due to chemical reaction with DIEGME. The term "substantially" is used herein as an approximate term and is intended to indicate that there may be negligible change or degradation.

According to embodiments of the present invention, the sulfur-containing, epoxy-functional polyol may be prepared from the reaction of a thiol-terminated polymer and an epoxy resin. The terms "thiol-terminated", "thiol group", "mercapto" and "mercapto group" as used herein refer to the-SH group, which is capable of forming a thioether linkage. In certain embodiments, the sulfur-containing, epoxy-functional polyol comprises at least one terminal epoxy functional group and at least one pendant hydroxyl functional group. Scheme 1 represents an exemplary reaction of an epoxy resin and a thiol-terminated polymer to form a sulfur-containing, epoxy-functional polyol.

Scheme 1

According to an embodiment of the present invention, the sulfur-containing, epoxy-functional polyol is crosslinked with an isocyanate curing agent to prepare an epoxy-functional urethane polymer. Scheme 2 below shows an exemplary reaction of hydroxyl functionality with isocyanate functionality to form carbamate functionality.

Scheme 2

In certain embodiments, the isocyanate curing agent may be a diisocyanate or a polyisocyanate. Scheme 3 represents an exemplary reaction of the hydroxyl groups of the sulfur-containing, epoxy-functional polyol and the isocyanate functional groups of the polyisocyanate curing agent to form an isocyanate-functional urethane compound.

Scheme 3

As described above, excess isocyanate reacts with moisture to form urea. This general reaction is shown in scheme 4.

Scheme 4

While urea (or polyurea in some embodiments) may remain as a by-product, in some embodiments, the urea (or polyurea) may react with isocyanate-functional urethane compounds to form isocyanate and urea-functional polymers. Scheme 5 shows an exemplary reaction of urethane, excess isocyanate curing agent, and water from moisture to form urethane and urea functional polymers.

Scheme 5

As indicated above, the isocyanate curing agent may be a diisocyanate or a polyisocyanate. Scheme 6 illustrates the reaction of an isocyanate-functional urethane compound, excess diisocyanate curing agent, and water from moisture to form an isocyanate-functional urethane/urea compound.

Scheme 6

To make the coating composition, a base component, such as a sulfur-containing epoxy functional polyol, is mixed with an activator component, such as an isocyanate curing agent. The composition is then applied to a substrate and cured. As noted above, the coating composition may further include any number of suitable additives in the base component or activator component.

Each component of the coating composition will now be described. In particular, the sulfur-containing epoxy functional polyol included in the base component will be described, as well as the isocyanate curing agent included in the activator component, and additional additives (which may be included in either the base component or the activator component).

Basic components: sulfur-containing epoxy functionalized polymers

As noted above, the base component includes a sulfur-containing epoxy functional polymer. In some embodiments, the sulfur-containing epoxy functional polyol is prepared by reacting a sulfur-containing polymer with an epoxy resin.

I. Sulfur-containing polymers

As described above, the sulfur-containing, epoxy-functional polyol can be prepared by reacting an epoxy resin with a polymer having sulfur in the backbone. Non-limiting examples of polymers having sulfur in the backbone include polythioethers and polysulfides.

According to an embodiment of the invention, the sulfur-containing, epoxy functional polyol is a compound represented by formula 7:

wherein Z is a polythioether or polysulfide linkage, R₃Is alkyl or aryl or a combination thereof and includes at least two hydroxyl functional groups, m is an integer from 0 to 4, and each R₁And R₂Independently an alkyl or aryl group or a combination thereof. In certain embodiments, Z may comprise a polythioether linkage represented by formula 8: -S-R₁-[-S-(CH₂)₂-O-[-R₂-O-]_m-(CH₂)₂-S-R₁-]_n-S-where R₁Is represented by C_2-6N-alkylene group, C_3-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂- [ (-CH) with the units substituted by methyl₂-)_p-X-]_q-(-CH₂-)_r-。R₂Represents a methylene group, C_2-6N-alkylene group, C_2-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂-substituted by methyl- [ (-CH)₂-)_p-X-]_q-(-CH₂-)_r-. X is selected from O, S and-NR₆-, wherein R₆Represents H or methyl, m is a rational number from 0 to 10, n is an integer from 1 to 60, p is an integer from 2 to 6, q is an integer from 1 to 5, and r is an integer from 2 to 10. According to one embodiment of the present invention, the coating composition may include a compound represented by formula 7 and an isocyanate curing agent.

In certain embodiments of the invention, the sulfur-containing, epoxy functional polyol has a weight average molecular weight of about 10000 or less. Such sulfur-containing, epoxy-functional polyols may have a weight average molecular weight of about 4000 to about 8000. In other embodiments, the sulfur-containing, epoxy functional polyol may have a weight average molecular weight of from about 2000 to about 5000. In certain embodiments, the sulfur-containing, epoxy-functional polyol may have a weight average molecular weight of about 5000. In other embodiments, the weight average molecular weight of the sulfur-containing, epoxy-functional polyol may be about 3000.

A. Polythioethers

According to embodiments of the present invention, sulfur-containing, epoxy-functional polyols can be prepared by reacting an epoxy resin and a thiol-terminated polythioether. Polythioethers useful in embodiments of the invention can be difunctional (i.e., linear polymers having two end groups) or polyfunctional (i.e., branched polymers having three or more end groups). The term "polythioether" as used herein refers to a polymer containing at least one thioether linkage (i.e., - [ -R-S-R- ] -), wherein R is a linear, branched, cyclic, or aromatic hydrocarbon, oxohydrocarbon, or thioalkane.

Polythioethers suitable for use in the present invention include those described in U.S. Pat. No.6172179, the entire contents of which are incorporated herein by reference. Suitable polythioethers typically have a number average molecular weight of 1000-. Thiol-terminated polythioethers suitable for use in embodiments of the invention comprise reactive terminal thiol groups, which typically have an average thiol functionality of from 2.05 to 3.0, e.g., from 2.1 to 2.6. A particular average functionality can be achieved by appropriate selection of reactive ingredients. Examples of suitable polythioethers are under the trade nameSuch as PERMAPOL P-3.1E or PERMAPOL P-3, available from PRC-Desoto International, Inc. Suitable thiol-terminated polythioethers include combined polythioethers.

In certain embodiments, the polythioether comprises a compound comprising at least two reactive thiol groups, such as those shown in formula 1: HS-R₁-[-S-(CH₂)₂-O-[-R₂-O-]_m-(CH2₎₂-S-R₁-]_n-SH, wherein R₁Is represented by C_2-6N-alkylene group, C_3-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10Alkyl cycloalkylene or in which at least one-CH group₂- [ (-CH) with the units substituted by methyl₂-)_p-X-]_q-(-CH₂-)_r-。R₂Is represented by C_2-6N-alkylene group, C_2-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10Alkyl cycloalkylene radical or- [ (-CH)₂-)_p-X-]_q-(-CH₂-)_r-. X is selected from O, S and-NR₆-, wherein R₆Represents H or methyl. In these formulae, m is a rational number from 0 to 10 and n is from 1 to 60P is an integer from 2 to 6, q is an integer from 1 to 5, and r is an integer from 2 to 10.

Such thiol-terminated polythioethers suitable for use in embodiments of the present invention can be prepared by a number of methods. For example polythioethers may be prepared by reacting a dienyl ether or mixture thereof with an excess of a dithiol or mixture thereof. In certain embodiments, (n +1) mol of a compound represented by formula 2: HS-R₁-SH, or a mixture of at least two different compounds having formula 2, is present in n moles with the compound of formula 3: CH (CH)₂=CH-O-[-R₂-O-]_m-CH=CH_2,Or a mixture of at least two different compounds having formula 3 in the presence of a catalyst. In the above formulas 2 and 3, R₁、R₂And all indices are as defined in formula 1. This process provides thiol-terminated difunctional polythioethers. The compound of formula 2 is a dithiol compound, including compounds wherein R is₁Is C_2-6N-alkylene radicals, for example 1, 2-ethanedithiol, 1, 3-propanedithiol, 1, 4-butanedithiol, 1, 5-pentanedithiol or 1, 6-hexanedithiol.

Further suitable dithiols include those compounds in which R is₁Is C_3-6Branched alkylene groups, having one or more pendant groups, which may be, for example, methyl or ethyl. Having branched alkylene radicals R₁The compounds of (a) include 1, 2-propanedithiol, 1, 3-butanedithiol, 2, 3-butanedithiol, 1, 3-pentanedithiol and 1, 3-dithio-3-methylbutane. Other useful dithiols include those in which R is₁Is C_6-8Cycloalkylene radical or C_6-10Alkylcycloalkylene radicals, such as dipentene dithiol and Ethylcyclohexyldithiol (ECHDT).

Further suitable dithiols include one or more heteroatom substituents in the carbon backbone, i.e., dithiols in which X is a heteroatom such as O, S or another divalent heteroatom group; secondary or tertiary amine groups, i.e., -NR₆-, where R is₆Is hydrogen or methyl; or another substituted trivalent heteroatom. In some implementationsIn the scheme, X is O or S, and thus R₁Is- [ (-CH)₂-)_p-O-]_q-(-CH₂-)_r-or- [ (-CH)₂-)_p-S-]_q-(-CH₂-)_r-. Subscripts p and r may be the same and both may have a value of 2. Exemplary dithiols of this type include dimercaptodiethylsulfide (DMDS) (p =2, r =2, q =1, X = S); dimercaptodioxaoctane (DMDO) (p =2, q, r =2, X = 0); and 1, 5-dithia-3-oxapentane (p =2, r =2, q =1, X = O). It is also possible to use dithiols which include two heteroatom substituents in the carbon backbone and pendant alkyl groups such as methyl. Such compounds include methyl-substituted DMDS, e.g. HS-CH₂CH(CH₃)-S-CH₂CH₂-SH，HS-CH(CH₃)CH₂-S-CH₂CH₂-SH and dimethyl-substituted DMDS such as HS-CH₂CH(CH₃)-S-CH(CH₃)CH₂-SH and HS-CH (CH)₃)CH₂-S-CH₂CH(CH₃) -SH. If desired, two or more different dithiols of formula 2 may also be used in the preparation of polythioethers suitable for use in the present invention.

The compound of formula 3 is a divinyl ether. Divinyl ether itself (m =0) may be used. Other suitable divinyl ethers include those compounds having at least one oxyalkylene group, such as 1 to 4 oxyalkylene groups (i.e., those compounds in which m is an integer from 1 to 4). In certain embodiments, m is an integer from 2 to 4. Commercially available divinyl ether mixtures may also be used in the production of suitable polythioethers. Such mixtures are characterized by a non-integer average number of alkoxy units per molecule. Thus, m in formula 3 can also assume non-integer rational values from 0 to 10, such as from 1 to 10 or, in some cases, from 1 to 4, such as from 2 to 4.

Exemplary divinyl ethers include those compounds in which R is₂Is C_2-6N-alkylene or C_2-6Branched alkylene groups, e.g. ethylene glycol divinyl ether (EG-DVE) (R)₂= ethylene, m = 1); butanediol divinyl Ether (BD-DVE) (R)₂= butylene, m = 1); hexanediolDivinyl ether (HD-DVE) (R)₂= hexylene, m = 1); diethylene glycol divinyl ether (DEG-DVE) (R)₂= ethylene, m = 2); triethylene glycol divinyl ether (R)₂= ethylene, m = 3); tetraethyleneglycol divinyl ether (R)₂= ethylene, m = 4); and polytetrahydrofuran divinyl ether. In certain embodiments, the polyvinyl ether monomer may additionally include one or more pendant groups selected from alkylene, hydroxyl, alkenyloxy, and amine groups. Useful divinyl ether blends includeMixtures of the type e.g.E-200 divinyl ether (commercially available from BASF) for which R is₂= ethyl and m =3.8, and "DPE" polymer blends such as DPE-2 and DPE-3 (commercially available from International Specialty products, Wayne, n.j.).

Useful divinyl ethers (in which R is₂Is C_2-6Branched alkylene) can be prepared by reacting a polyol with acetylene. Exemplary compounds of this type include compounds in which R is₂Is an alkyl-substituted methylene group such as-CH (CH)₃) Or alkyl-substituted ethylene such as-CH₂CH(CH₃)-。

Other useful divinyl ethers include compounds in which R is₂Is polytetrahydrofuran (poly-THF) or polyoxyalkylene, preferably having an average of about 3 monomer units.

Two or more compounds of formula 3 may be used in the aforementioned methods. Thus in a preferred embodiment of the invention, two compounds of formula 2 and one compound of formula 3, one compound of formula 2 and two compounds of formula 3, two compounds of formula 2 and 3, and more than two compounds of one or both of formula (ii) may be used to produce a plurality of polythioethers of the invention, and all such combined compounds are contemplated to be within the scope of the invention.

While compounds of formulas 2 and 3 having pendant alkyl groups, e.g., pendant methyl groups, are useful in embodiments of the invention, as described above, compounds of formulas 2 and 3 that do not contain pendant methyl groups or other alkyl groups also provide polythioethers suitable for use in embodiments of the invention.

The reaction between the compounds of formulae 2 and 3 is sometimes catalyzed by a free radical catalyst. Suitable free radical catalysts include azo compounds, such as azodinitrile compounds, for example, azo (di) isobutyronitrile (AIBN); organic peroxides such as benzoyl peroxide and t-butyl peroxide; and similar free radical generators. The reaction may also be affected by uv radiation with or without the use of photosensitizers such as benzophenone. Ion-catalyzed processes using inorganic or organic bases such as triethylamine also produce materials useful in the context of embodiments of the present invention.

Polythioethers useful in the present invention can be prepared as follows: combining at least one compound of formula 2 and at least one compound of formula 3, followed by addition of a suitable catalyst, and carrying out the reaction at a temperature of about 30 to about 120 ℃ for a period of about 2 to about 24 hours. In certain embodiments, the reaction is carried out at a temperature of about 70 to about 90 ℃ for a period of about 2 to about 6 hours.

B. Polysulfide compound

According to embodiments of the present invention, sulfur-containing, epoxy-functional polyols can be prepared by the reaction of an epoxy resin and a thiol-terminated polysulfide. Polysulfides useful in embodiments of the present invention may be difunctional (i.e., linear polymers having two end groups) or multifunctional (i.e., branched polymers having three or more end groups). The term "polysulfide" as used herein means a polymer having at least one sulfur linkage (i.e., sulfur linkage- [ -S-]-) of a polymer. For example, thiol-terminated polysulfides suitable for use in embodiments of the present invention include compounds represented by formula 4: HS- (R-SS)_n-R-SH, where R is a linear, branched, cyclic or aromatic hydrocarbon, oxohydrocarbon or thiocarbohydrocarbon

Typically, polysulfides useful in embodiments of the present invention will have two or more sulfur-sulfur linkages. Suitable polysulfides are commercially available from Akzo Nobel under the name Thioplast (e.g., Thioplast G-1). Thioplast products are commercially available over a wide molecular weight range, e.g., less than 1100 to over 8000, and the molecular weight is the average molecular weight in g/mol. Particularly suitable is a number average molecular weight of 1000-. The crosslink density of these products also varies depending on the amount of crosslinking agent used. The "-SH" content (i.e., mercaptan content) of these products may also vary. The thiol content and molecular weight of the polysulfides affect the cure speed of the mixture, and cure speed increases with molecular weight.

In some embodiments, it is desirable to use the combined polysulfides to achieve a desired molecular weight and/or crosslink density in the coating composition. Different molecular weights and/or crosslink densities may constitute different characteristics of the coating composition.

Epoxy resin II

According to embodiments of the present invention, sulfur-containing, epoxy-functional polyols can be prepared by the reaction of an epoxy resin and a thiol-terminated polymer. Suitable epoxy resins for preparing the coating compositions of the present invention comprise at least one epoxy group, for example a monoglycidyl ether of a monohydric phenol or an alcohol or a di-or polyglycidyl ether of a polyhydric alcohol. The epoxy resin may be a compound or mixture of compounds having 1, 2-epoxy groups. Particularly suitable epoxy resins have a 1, 2-epoxy equivalent of greater than 1.0, i.e., wherein the average number of 1, 2-epoxy groups per molecule is greater than 1. The epoxy resin may be any known epoxy. Examples of such polyepoxides are described, for example, in US patent nos. 2467171; 2615007, respectively; 2716123, respectively; 3030336, respectively; 3053855 and 3075999, the entire contents of which are incorporated herein by reference.

In one embodiment, the epoxy functional material comprises at least two epoxy groups per molecule and has aromatic or cycloaliphatic functionality to improve adhesion to metal substrates. In some embodiments, the epoxy functionalized material may have a relatively greater hydrophobicity than hydrophilicity. In one embodiment, the epoxy-containing material is a polymer having a number average molecular weight (Mn) of about 220-. Mn can be measured, for example, by multiplying the epoxy functionality (number of epoxy groups) by the epoxy equivalent (epoxy equivalent).

Examples of suitable monoglycidyl ethers of monohydric phenols or alcohols include phenyl glycidyl ether and butyl glycidyl ether. Polyhydroxy alcohols suitable polyglycidyl ethers may be formed by reacting an epihalohydrin with a polyhydroxy alcohol, such as a dihydric alcohol, in the presence of an alkaline condensation and dehydrohalogenation catalyst, such as sodium hydroxide or potassium hydroxide. Useful epihalohydrins include epibromohydrin, dichloroethanol, and particularly epichlorohydrin.

Suitable polyhydric alcohols can be aromatic, aliphatic, or cycloaliphatic and include, but are not limited to, phenols which are at least dihydric phenols such as dihydroxybenzenes, for example resorcinol, catechol, and hydroquinone; bis (4-hydroxyphenyl) -1, 1-isobutane; 4, 4-dihydroxybenzophenone; bis (4-hydroxyphenyl) -1, 1-ethane; bis (2-hydroxyphenyl) methane; 1, 5-hydroxynaphthalene; 4-isopropylidenebis (2, 6-dibromophenol); 1,1,2, 2-tetrakis (p-hydroxyphenyl) -ethane; 1,1, 3-tris (p-hydroxyphenyl) -propane; a phenolic resin; bisphenol F; a long chain bisphenol; and 2, 2-bis (4-hydroxyphenyl) propane (bisphenol a), which is particularly suitable. Aliphatic polyhydric alcohols that can be used include, but are not limited to, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, 1, 2-propanediol, 1, 4-butanediol, 2, 3-butanediol, pentamethylene glycol, polyoxyalkylene glycols; polyhydric alcohols such as sorbitol, glycerin, 1,2, 6-hexanetriol, erythritol, and trimethylolpropane; and mixtures thereof. An example of a suitable cycloaliphatic alcohol is cyclohexanedimethanol.

It is also possible to use polyglycidyl esters of polycarboxylic acids which are produced by reacting epichlorohydrin or similar epoxy compounds with aliphatic or aromatic polycarboxylic acids such as oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2, 6-naphthylenedicarboxylic acid, dimerized linolenic acid, and the like. Examples are diglycidyl adipate and diglycidyl phthalate.

Epoxy-containing polymers useful in the present invention are disclosed in US patent nos. 5294265; 5306526 and 5653823, the entire contents of which are incorporated herein by reference. Other useful epoxy-containing materials include epoxy-functional acrylic polymers, glycidyl esters of carboxylic acids, and mixtures thereof. Suitable commercially available epoxy-containing polymers are available under the names EPON836, EPON828, EPON1002F and EPON1004F from Shell Chemical Company. EPON836 and EPON828 are epoxy-functionalized polyglycidyl ethers of bisphenol a prepared from bisphenol a and epichlorohydrin. The Mn of EPON828 is about 400 and the epoxy equivalent weight is about 185-192. The Mn of EPON836 is about 625 and the epoxy equivalent weight is about 310-. The Mn of EPON1002F was about 1300 and the epoxy equivalent weight was about 650, while the Mn of EPON1004F was about 1840 and the epoxy equivalent weight was about 920.

In some embodiments, the epoxy resin may comprise a solid epoxy resin having an Epoxy Equivalent Weight (EEW) of about 300-2000. Suitable products include, for example, EPON resins 1001F, 1002F and 1004F and 1007F from Hexion specialty Chemicals and DER661, 662E, 663U and 664U from Dow Chemical Company. Examples of other epoxy resins suitable for use in the present invention include monoepoxides, diglycidyl ethers of dihydroxy compounds, epoxy novolac resins and cycloaliphatic epoxides, and other modified epoxy resins. Suitable products include, for example, HELOXY modifiers 8, 64, 67, 68, 84, 505, CADURA E-10p glycidyl ether, EPON resins SU-3, SU-8 (from Hexion specialty Chemicals), and DER732, 736, DEN431, 438, 439 (from Dow chemical Company).

In certain embodiments of the present invention, the epoxy resin is a compound represented by formula 5:wherein R is an aliphatic group, a cycloaliphatic group, an aryl group, or a combination thereof. Specifically, in certain embodiments of the present invention, the epoxy resin comprises a polyglycidyl ether of a polyhydric phenol. For example, in some embodiments, R of formula 5 may be a linker group represented by formula 6:wherein n is an integer from 1 to 10.

To make the sulfur-containing epoxy functional polyol (which is included in the base component), the sulfur-containing polymer is reacted with an epoxy resin. In some embodiments, the sulfur-containing polymer and epoxy resin are used in amounts to produce an epoxy: the mercaptan equivalent ratio was about 1: 1 to about 4: 1. in one embodiment, for example, the sulfur-containing polymer and epoxy resin are used in amounts to produce an epoxy: the mercaptan equivalence ratio was about 3.5: 1. in some embodiments, the sulfur-containing polymer and epoxy resin are used in amounts to produce an epoxy: the weight percent of mercaptans was about 10: 90 to about 90: 10. for example, in some embodiments, the sulfur-containing polymer and epoxy resin are used in amounts to produce an epoxy: the weight percent of mercaptans was about 50: 50.

activator component: isocyanate curing agent

As noted above, the activator component includes an isocyanate curing agent. The activator component (and/or base component) may also optionally comprise one or more additional additives.

I. Isocyanate curing agent

As noted above, in certain embodiments, an isocyanate curing agent is used. Any isocyanate containing free isocyanate functionality may be suitable for use in embodiments of the present invention. The term "isocyanate" as used herein is intended to include blocked (or blocked) polyisocyanates as well as unblocked polyisocyanates. If the isocyanate is blocked or blocked, any suitable blocking or blocking agent may be used, provided that the agent has a sufficiently low unblocking temperature. Examples of such suitable blocking or capping agents include: alcohols, lactams, oximes, malonates, alkyl acetoacetates, triazoles, phenols, and amines. Among them, oximes (e.g., acetoxime, methyl ethyl ketoxime, methyl amyl ketoxime, diisobutyl ketoxime, formaldoxime) are particularly suitable. Other useful curing agents include blocked polyisocyanate compounds such as the tricarbamoyltriazine compounds described in detail in U.S. patent No.5084541, the entire contents of which are incorporated herein by reference.

In some embodiments, the isocyanate curing agent may comprise an isocyanate represented by NCO-R 'or an isocyanate represented by NCO-R "-NCO, or a combination thereof, wherein each R' and R" independently comprises an alkyl or aryl group or a combination thereof. The isocyanate curing agent may include isocyanate functional groups, and upon curing the coating composition, at least one of the isocyanate functional groups may react with moisture to form urea or polyurea. Additionally, upon curing, the isocyanate curing agent can crosslink the sulfur-containing, epoxy functional polyol to form an epoxy functional polyurethane compound. Also, while urea or polyurea may remain as a by-product, the urea or polyurea may also be reacted with an epoxy-functional polyurethane compound to produce a polymer having urea and urethane linkages.

Non-limiting examples of suitable polyisocyanates include aliphatic, cycloaliphatic or aromatic polyisocyanates such as, for example, diisocyanates, for example the aliphatic, cycloaliphatic and aromatic diisocyanates commonly used in paints, for example toluene 2, 4-diisocyanate, toluene 2, 6-diisocyanate, diphenylmethane 2,4 '-and/or 4,4' -diisocyanate, hexamethylene 1, 6-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, tetramethylene diisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanato-methylcyclohexane (isophorone diisocyanate = IPDI), or tetramethylxylylene diisocyanate, propylene 1, 2-diisocyanate, 2,2, 4-trimethylene diisocyanate, tetramethylene diisocyanate, butene-2, 3-diisocyanate, dodecane-1, 12-diisocyanate, cyclohexane-1, 3-and 1, 3-diisocyanate, perhydro-2, 4' -and/or 4,4' -diphenylmethane diisocyanate, phenylene-1, 3-and 1, 4-diisocyanate, 3,2' -and/or 3,4' -diisocyanato-4-methyldiphenylmethane, naphthalene-1, 5-diisocyanate, triphenylmethane-4, 4' -triisocyanate or mixtures of the compounds mentioned. In addition, isocyanate prepolymers, such as the reaction product of a polyisocyanate with a polyol, may also be used, as may mixtures of polyisocyanates.

The known polyisocyanates which are usually used for the production of lacquers, such as the above-mentioned simple polyisocyanates with biuret, isocyanurate or urethane groups, in particular modified products of polyisocyanates with tris (6-isocyanatohexyl) biuret or low molecular weight urethane groups, are particularly suitable for the present invention, and can be obtained by reacting IPDI, which is used in excess, with simple polyhydric alcohols having a molecular weight of 62 to 300, in particular trimethylolpropane. Of course, any mixtures of the polyisocyanates mentioned may also be used for preparing the products of the invention.

Suitable polyisocyanates are furthermore known prepolymers having terminal isocyanate groups, this class being obtained in particular by reaction of the abovementioned simple polyisocyanates (predominantly diisocyanates) with an insufficient amount of organic compounds which have at least two groups reactive toward isocyanate groups. Also preferably used are compounds having a number average molar amount of 300-10000, preferably 400-6000, which have a total of at least two amino and/or hydroxyl groups. Corresponding polyols, such as hydroxyl polyesters, hydroxyl polyethers and/or hydroxyl-containing acrylate resins known from polyurethane chemistry, are preferably used.

It is also possible to use copolymers of the ethylenically unsaturated monoisocyanate dimethyl-m-isopropenyl benzyl isocyanate, as described in DE-A4137615 (the entire content of which is incorporated herein by reference).

Typically, the isocyanate curing agent is a low isocyanate: the ratios of the hydroxyl groups are used in combination. Frequently, the isocyanate curing agent is reacted with a hydroxyl-containing compound in the ratio of isocyanate: the ratio of hydroxyl groups is about 1: 1-1.5: 1 equivalent is used in combination. However, the present inventors have found that high isocyanate: the ratio of hydroxyl groups provides unexpected and beneficial results. In certain embodiments of the present invention, the isocyanate: the ratio of hydroxyl groups is about 1: 1 to about 20: 1 equivalent. In some embodiments, the isocyanate curing agent and sulfur-containing epoxy functional polyol are used in amounts suitable to provide an isocyanate to hydroxyl equivalent ratio of about 3 to 1 or greater. For example, in some embodiments, the isocyanate curing agent and sulfur-containing epoxy functional polyol are used in amounts suitable to provide an isocyanate to hydroxyl equivalent ratio of about 15: 1. in certain embodiments, the isocyanate curing agent and sulfur-containing epoxy functional polyol are used in amounts suitable to provide a weight percent isocyanate to hydroxyl of about 5: 95 to about 95: 5. for example, in some embodiments, the isocyanate curing agent and sulfur-containing epoxy functional polyol are used in amounts suitable to provide an isocyanate to hydroxyl weight percentage of about 30 to 70 or greater. In some exemplary embodiments, the isocyanate curing agent and sulfur-containing epoxy functional polyol are used in amounts suitable to provide an isocyanate to hydroxyl ratio of about 70: 30 weight percent.

Additional additives

The compositions of the present invention may also optionally include other conventional additives, such as colorants; a filler; an adhesion promoter; a plasticizer; a thixotropic agent; a flame retardant; a catalyst; an anti-corrosive pigment; and a masking agent. Thixotropic agents such as fumed silica or carbon black may be used in amounts of about 0.1 to about 5 weight percent based on the total weight of the composition.

Fillers useful in the compositions of the present invention, particularly for aerospace or aeronautical applications, include those commonly used in the art, such as carbon black, calcium carbonate (CaCO)₃) Silica, nylon, etc. In one embodiment, the composition includes from about 5 to about 70 weight percent of the selected filler or combination of fillers, such as from about 10 to 50 weight percent, based on the total weight of the composition.

In certain embodiments, the compositions of the present invention comprise a colorant. The term "colorant" as used herein means any substance capable of imparting color and/or other opacity and/or other visible effect to the composition. The colorant can be added to the coating composition in any suitable form, such as discrete particles, dispersions, solutions, and/or flakes. A single colorant or a mixture of two or more colorants can be used in the coating of the present invention.

Non-limiting examples of colorants include pigments, dyes, and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as those used in special effect compositions. The colorant may comprise, for example, a finely divided solid powder which is insoluble, but wettable under the conditions of use. The colorant may be organic or inorganic, and may be aggregated or non-aggregated. The colorant may be incorporated into the coating using a grind vehicle, such as an acrylic grind vehicle, the use of which is well known to those skilled in the art.

Exemplary pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, disazo, naphthol AS, salt types (lakes), benzimidazolone, condensates, metal complexes, isoindolinones (isoindolinones), isoindolines (isoindolinones), and polycyclic phthalocyanines, quinacridones, perylenes, perinones, diketopyrrolopyrroles, thioindigoids, anthraquinones, indanthrones, anthraflavins (anthraquinonidines), flavanthrones, pyranthrones, xanthanthanthrones, dioxazines, triarylcarboniums, quinophthalone pigments, diketopyrrolopyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures thereof. The terms "pigment" and "colored filler" may be used interchangeably.

In some embodiments, the pigment may be an anti-corrosion pigment such as a chromate or non-chromate corrosion inhibitor. As used herein, "anti-corrosion pigment" refers to particles that, when included in a coating composition deposited in a sub-state, serve to provide a coating that minimizes or, in some cases, even prevents alteration or degradation of the substrate, such as by chemical or electrochemical oxidation methods, including rusting in iron-containing substrates and degradable oxides in aluminum substrates. "chromate" and like terms refer to any compound comprising chromium or a derivative thereof. Non-limiting examples of suitable chromate corrosion inhibitors include strontium chromate, barium chromate, zinc chromate, and calcium chromate.

In certain embodiments, the corrosion resistant particles comprise an inorganic oxide, and in some embodiments, comprise a plurality of inorganic oxides. Non-limiting examples of suitable inorganic oxides include zinc oxide (ZnO), magnesium oxide (MgO), cerium oxide (CeO)₂) Molybdenum oxide (MoO)₃) And/or silicon dioxide (SiO)₂) And the like. The term "plurality" as used herein means two or more. Accordingly, the coating compositions of certain embodiments of the present invention include corrosion resistant particles comprising two, three, four, or more than four inorganic oxides. In certain embodiments, these inorganic oxides are present in such particles, for example, in the form of a homogeneous mixture or solid solution of multiple oxides.

In some exemplary embodiments, the corrosion resistant particles comprise inorganic oxides including oxides of zinc, cerium, yttrium, manganese, magnesium, molybdenum, lithium, aluminum, tin, and/or calcium. In certain embodiments, the particles further comprise oxides of boron, phosphorus, silicon, zirconium, iron, and/or titanium. In some embodiments, the particles comprise silica.

In some embodiments, the corrosion resistant particles comprise a plurality of inorganic oxides selected from the group consisting of (i) particles comprising oxides of cerium, zinc, and silicon; (ii) particles comprising oxides of calcium, zinc and silicon; (iii) particles comprising oxides of phosphorus, zinc and silicon; (iv) particles comprising oxides of yttrium, zinc and silicon; (v) particles comprising oxides of molybdenum, zinc and silicon; (vi) particles comprising oxides of boron, zinc and silicon; (vii) particles comprising oxides of cerium, aluminum, and silicon; (viii) particles comprising oxides of magnesium or tin and silicon; (ix) particles comprising oxides of cerium, boron and silicon, or a mixture of two or more of particles (i) - (ix). Additional corrosion resistant particles suitable for use with the coating compositions of the present invention are described in U.S. Pat. No.7569163 to Tang et al, entitled "Polythioether Amine Resins and compositions comprising the Same," the entire contents of which are incorporated herein by reference.

Exemplary dyes include, but are not limited to, those that are solvent-based and/or water-based, such as phthalocyanine green or blue, iron oxide, bismuth vanadate, anthraquinone, perylene, aluminum, and quinacridone.

Exemplary special effect compositions that can be used in the compositions of the present invention include pigments and/or compositions that produce one or more appearance effects such as reflectivity, pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism, photosensitivity, thermochromism, goniochromism (goniochromim), and/or discoloration. Additional special effect compositions may provide other perceptible properties, such as opacity or texture. In one non-limiting embodiment, the special effect composition produces a color transition such that the color of the coating changes when the coating is viewed from different angles. Exemplary color effect compositions are given in US patent No.6894086, the entire contents of which are incorporated herein by reference. Additional color effect compositions may include transparent coated mica and/or synthetic mica, coated silica, coated alumina, transparent liquid crystal pigments, liquid crystal coatings, and/or any composition in which interference occurs due to differences in refractive index in the material, rather than due to differences in refractive index between the surface of the material and air.

In general, the colorant can be present in any amount sufficient to impart the desired visible and/or color effect. The colorant may comprise 1 to 65 weight percent of the composition of the present invention, such as 3 to 40 weight percent or 5 to 35 weight percent, with weight percent based on the total weight of the composition.

The following examples illustrate exemplary embodiments of the invention. However, this example is provided for illustrative purposes only and does not limit the scope of the present invention. All parts and percentages in the following examples, as well as throughout the specification, are by weight unless otherwise indicated.

Examples

Example 1:synthesis of polyol-containing polythioethers

The reaction between the epoxy resin (Epon1001F) and the thiol-terminated polythioether (Permapol P-3.1E) was carried out at 125-130 ℃. The ratio of epoxy equivalents to thiol equivalents is about 3.5: 1.0. the amounts of each reactant are listed in table 1 below. The reaction was monitored by mercaptan equivalent titration, and a high mercaptan equivalent weight indicated completion of the reaction. A polyol-containing polythioether solution having the following properties was obtained: NVM: 70.0%, Weight Per Gallon (WPG): 8.96lb/gal, OH equivalent (theoretical): at 70% NVM is 1141, thiol equivalent: 1803917 at 70% NVM.

TABLE 1

Preparation of sulfur-containing epoxy-functionalized polyols

Example 2:synthesis of polysulfides containing polyols

The reaction between the epoxy resin (Epon1001F) and the thiol-terminated polysulfide Thioplast G-1 was carried out at 125 ℃ and 130 ℃. The ratio of epoxy equivalents to thiol equivalents was 3.5: 1.0. the amounts of reactants are listed in table 2 below. The reaction was monitored by mercaptan equivalent titration, and a high mercaptan equivalent weight indicated completion of the reaction. A polysulfide solution containing polyols having the following properties was obtained: NVM: 70.0%, WPG: 8.96lb/gal, OH equivalent (theoretical): at 70% NVM is 1141, thiol equivalent: 1283800 at 70% NVM.

TABLE 2

Preparation of sulfur-containing epoxy-functionalized polyols

Example 3:polythioether coating formulations

The sulfur-containing, epoxy-functional polyol prepared according to example 1 was used to prepare a coating composition. The amounts of sulfur-containing, epoxy functional polyol and other components of the coating composition are listed in table 3.

TABLE 3

Preparation of DIEGME resistant fuel tank coatings

Example 4:polysulfide coating formulations

The sulfur-containing, epoxy-functional polyol prepared according to example 2 was used to prepare a coating composition. The amounts of sulfur-containing, epoxy functional polyol and other components of the coating composition are listed in table 4.

TABLE 4

Preparation of DIEGME resistant fuel tank coatings

Test method

The fully cured coating compositions according to the above examples were tested using the following method. Each coating composition was spray applied to both sides of an aluminum panel made from Alodine1200 treated aluminum alloy (aerospace Material Specification (AMS)2024-T3) to a dry film thickness of 1.0 mil (25 μm). The coating composition was cured at ambient temperature for at least 2 weeks prior to testing. The detailed test results are listed in table 5.

Solvent resistance

The solvent resistance of each coating composition was according to American Society for Testing and Materials (ASTM) D5402 (a common practice for evaluating organic coating solvent resistance using solvent wiping). The cured coating composition was wiped back and forth 50 times with cheesecloth (which was soaked in Methyl Ethyl Ketone (MEK) solvent) with firm finger pressure. Rub-through of the coating composition to the substrate would indicate failure of the coating composition due to insufficient curing. Both the coating composition and the cloth were visually inspected for any coating removal.

Cross adhesion

The cross-adhesion of each coating composition was determined according to ASTM D3359 (conventional test method for measuring tape adhesion; method B). A cross pattern is scribed through each coating composition down the substrate. A 1 inch wide strip of masking tape such as 3M250 or equivalent is applied. The tape was pressed down using two 4.5 pound coating rollers. The tape is removed in an abrupt movement perpendicular to the plate. Adhesion was graded by visual inspection of paint in the area of the intersection using the grading system provided by ASTM.

Hardness of pencil

The pencil hardness of each coating composition was determined according to ASTM D3363 (conventional test method for film hardness for pencil testing). The hardness of each coating composition was determined relative to a standard set of pencil leads by scraping the leads at a 45 degree angle along the coating for approximately one-quarter inch. The method was repeated until it was determined that the core did not scratch the film. The number of pencil leads was recorded as hardness.

Measuring low temperature flexibility with flexible fixtures

The low temperature flexibility of each coating composition was measured using a jig according to the method described in AMS C-27725C, section 4.6.5.13. The coated panels and flexible fixtures were subjected to a temperature of-65F (-54 c) for 2 hours. While at this temperature, one end of the plate was held in the grooved position, the other end of the plate was quickly bent around the curvilinear position of the fixture, and the coating composition on one side of the plate was opposite the curvilinear position of the fixture (i.e., the convex side of the plate). The plate was then removed from the jig and the test repeated for additional plates. The test panel was removed and inspected for any cracks, microcracks, crazing, or loss of adhesion.

Measuring low temperature flexibility with a cylindrical mandrel tester

The low temperature flexibility of each coating composition was measured using a cylindrical mandrel tester (3/16 inches) according to the method described in ASTM D522 (conventional test method for mandrel bend testing of adhered organic coatings; method B). The coated panels and mandrel tester were subjected to a temperature of-65F (-54 c) for 2 hours. While at this temperature, the test panel was placed on the mandrel with the uncoated side in contact with the mandrel and at least 2 inches overhanging either side. Each plate was bent at a uniform rate around the mandrel using steady finger pressure for approximately 180 degrees. The test panel was removed and immediately inspected for any cracks or loss of adhesion.

Simulated microbial by-product resistance

The simulated microbial byproduct resistance of each coating composition was measured according to the procedure described in AMS-C-27725C, section 4.6.5.19. For this test, an acetate solution was prepared by dissolving 5 parts by weight of analytical grade acetic acid in 100 parts by weight of a 3% solution of sodium chloride in distilled water. Each coated panel was immersed vertically for 5 days at 140 ° F (60 ℃), and one third of the panel was exposed to the acetate solution, one third to the spray reference fluid, and one third to the mixture of air and vapor from the acetate solution. The plate was removed, rinsed gently in running tap water, and carefully dried weakly. The test panels were visually inspected for any blistering, cracking, leaching, shrinkage or loss of adhesion. The plate was then immediately scratched for two parallel scratches in each of three zones (acid salt solution, jet reference fluid and air-vapor mixture zone). The scratches all the way through the coating composition to the substrate. In each of the three zones, two parallel scratches were scratched 1 inch apart. A 1 inch wide strip of masking tape such as 3M250 or equivalent is applied to the 1 inch wide area between the two parallel scratches of each set. Each tape strip was pressed down using two 4.5 pound blanket rollers. The tape is removed in an abrupt movement perpendicular to the plate. Removal of greater than 5% of the coating composition from the substrate indicates that the coating composition is ineffective.

DIEGME resistance

The DIEGME resistance of each coating composition was tested in the following manner. Each coating composition was sprayed onto both sides of the panel and cured at ambient conditions. The initial pencil hardness of each cured coating composition was tested prior to DIEGME exposure. Next, the coated plate was placed vertically in a closed glass container containing a mixture of 80 wt.% DIEGME and 20 wt.% distilled water. Half of each plate was immersed in a mixture of DIEGME and water. The glass container was sealed and exposed to a constant temperature of 170 ° F (77 ℃) for 6 weeks. At the end of 6 weeks, the plates were removed from the fluid mixture, cooled to ambient temperature, rinsed with water, wiped dry, and tested for pencil hardness within 10 minutes of removal from the solution. The test panels were visually evaluated for any blistering or loss of adhesion. Pencil hardness and cross-adhesion were determined as described above.

TABLE 5

Properties of the formulated coating composition

As shown in table 5 above, examples 3 and 4 demonstrate excellent solvent resistance, adhesion, low temperature flexibility, and DIEGME resistance. As also shown, the coating compositions including the epoxy-functionalized polythioether polyol exhibit better DIEGME vapor resistance than coating compositions including the epoxy-functionalized polythioether polyol. However, the DIEGME resistance test was performed in DIEGME solution (80% DIEGME and 20% water) and at high temperature (i.e., 170 ° F). Polythioether backbones have superior heat resistance to polysulfide backbones. Thus, embodiments of polythioether backbones exhibit better long-term DIEGME resistance than polysulfide backbone embodiments when subjected to high temperature long-term exposure to DIEGME solutions. Both the polysulfide sulfur backbone embodiments and the polythioether backbone embodiments, although exhibiting DIEGME resistance at low temperatures and/or shorter exposure periods at high temperatures.

In contrast, conventional polyurethane coatings are known to be not DIEGME resistant. Indeed, developing DIEGME resistant coatings has heretofore presented an important challenge, such as Aliband et al, "Epoxy paint failure in B-52fuel ranks: chapter I-advance resolution of model for the process, "Progress in organic coatings, 56, pages 285 and 296 (2006) and Aliband et al," Epoxy painting in B-52fuel bases: chapter II, the entire contents of which are incorporated herein by reference, is described in chapter II of flame of diesel integration in the fuel on the failure process, "development in Organic Coatings, 63, page 139-147 (2008).

The present invention has been described with reference to exemplary embodiments and aspects, but is not limited thereto. Those skilled in the art will appreciate that other modifications and applications may be made without departing from the invention. For example, while the coating compositions are described for aerospace or aviation fuel tank applications, they may also be used in other applications. Thus, the foregoing description should not be read as indicating the precise embodiments and aspects described, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

The term "about" in relation to a range of values is used throughout the text and claims to modify said high and low values and to reflect the deviations in relation to measurement, significant figures and interchangeability, all as would be understood by a person skilled in the art to which the invention pertains.

Claims (20)

1. A coating composition comprising:

a) a sulfur-containing, epoxy-functional polyol; and

b) an isocyanate curing agent.

2. The coating composition of claim 1, wherein the sulfur-containing, epoxy-functional polyol comprises the reaction product of reactants comprising a thiol-terminated polymer and an epoxy resin.

3. The coating composition of claim 2, wherein the thiol-terminated polymer comprises a thiol-terminated polysulfide or a thiol-terminated polythioether.

4. The coating composition of claim 3, wherein the thiol-terminated polythioether comprises a compound represented by formula 1:

formula 1

HS-R₁-[-S-(CH₂)₂-O-[-R₂-O-]_m-(CH₂)₂-S-R₁-]_n-SH

Wherein

R₁Is represented by C_2-6N-alkylene group, C_3-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂- [ (-CH) with the units substituted by methyl₂-)_p-X-]_q-(-CH₂-)_r-，

R₂Represents a methylene group, C_2-6N-alkylene group, C_2-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂-substituted by methyl- [ (-CH)₂-)_p-X-]_q-(-CH₂-)_r-，

X is selected from O, S and-NR₆-one of the two or more of the two,

R₆represents a hydrogen atom or a methyl group,

m is a rational number from 0 to 10,

n is an integer of 1 to 60,

p is an integer of 2 to 6,

q is an integer of 1 to 5, and

r is an integer from 2 to 10.

5. The coating composition of claim 3, wherein the thiol-terminated polysulfide comprises a compound represented by formula 4:

formula 4

HS-(R-SS)_n-R-SH

Wherein R is a straight or branched hydrocarbon, an oxohydrocarbon or a thioalkane, and n is an integer from 7 to 38.

6. The coating composition of claim 2, wherein the epoxy resin comprises a compound represented by formula 5:

formula 5

Wherein R is an aliphatic group, a cycloaliphatic group, an aryl group, or a combination thereof.

7. The coating composition of claim 6, wherein R is represented by formula 6:

formula 6

Wherein n is an integer from 1 to 10.

8. The coating composition of claim 2, wherein the sulfur-containing, epoxy-functional polyol comprises a compound represented by formula 7:

formula 7

Wherein Z comprises a polythioether or polysulfide linkage;

R₃comprises an alkyl or aryl group or a combination thereof and contains at least two hydroxyl functional groups;

m is an integer of 0 to 4; and

each R₁And R₂Independently an alkyl or aryl group or a combination thereof.

9. The coating composition of claim 1, wherein the sulfur-containing, epoxy-functional polyol comprises at least one terminal epoxy functional group and at least one pendant hydroxyl functional group.

10. The coating composition of claim 1, wherein the sulfur-containing, epoxy-functional polyol has a weight average molecular weight of about 10000 or less.

11. The coating composition of claim 1, wherein the coating composition has an isocyanate to hydroxyl ratio of about 1: 1 to about 20: 1.

12. the coating composition of claim 1, wherein the isocyanate curing agent comprises an isocyanate represented by NCO-R 'or an isocyanate represented by NCO-R "-NCO, or a combination thereof, wherein each R' and R" independently comprises an alkyl group or an aryl group, or a combination thereof.

13. The coating composition of claim 1, wherein the isocyanate curing agent comprises isocyanate functional groups and upon curing the coating composition at least one isocyanate functional group reacts with moisture to form at least one urea functional group.

14. The coating composition of claim 1, wherein upon curing the isocyanate curing agent crosslinks the sulfur-containing, epoxy functional polyol to form an epoxy functional polyurethane compound.

15. A coating composition comprising:

a) a compound represented by formula 7:

formula 7

Wherein:

each R₁And R₂Independently comprise alkyl or aryl groupsOr a combination thereof,

R₃comprising an alkyl or aryl group, or a combination thereof, and containing at least two hydroxyl functional groups,

m is an integer of 0 to 4, and

z comprises a polythioether or polysulfide linkage; and

b) an isocyanate curing agent.

16. The coating composition of claim 15, wherein Z comprises a polythioether linkage represented by formula 8:

formula 8

-S-R₁-[-S-(CH₂)₂-O-[-R₂-O-]_m-(CH₂)₂-S-R₁-]_n-S-

Wherein

R₁Is represented by C_2-6N-alkylene group, C_3-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂- [ (-CH) with the units substituted by methyl₂-)_p-X-]_q-(-CH₂-)_r-，

R₂Represents a methylene group, C_2-6N-alkylene group, C_2-6Branched alkylene, C_6-8Cycloalkylene radical or C_6-10An alkylcycloalkylene group, or at least one-CH thereof₂-substituted by methyl- [ (-CH)₂-)_p-X-]_q-(-CH₂-)_r-，

X is selected from O, S and-NR₆-one of the two or more of the two,

R₆represents a hydrogen atom or a methyl group,

m is a rational number from 0 to 10,

n is an integer of 1 to 60,

p is an integer of 2 to 6,

q is an integer of 1 to 5, and

r is an integer from 2 to 10.

17. The coating composition of claim 15, wherein the coating composition has an isocyanate to hydroxyl ratio of about 1: 1 to about 20: 1.

18. the coating composition of claim 15, wherein the isocyanate curing agent comprises an isocyanate represented by NCO-R 'or an isocyanate represented by NCO-R "-NCO, or a combination thereof, wherein each R' and R" is independently an alkyl group or an aryl group, or a combination thereof.

19. The coating composition of claim 15, wherein the isocyanate curing agent comprises isocyanate functional groups and at least one isocyanate functional group reacts with moisture to form at least one urea functional group upon curing the coating composition.

20. The coating composition of claim 15, wherein upon curing the isocyanate curing agent crosslinks the sulfur-containing, epoxy functional polyol to form an epoxy functional polyurethane compound.