Non-isocyanate chemical agent resistant coating composition

Abstract

A two-part coating system can be used in a chemical agent resistant coating that does not contain any isocyanate functional groups. The two-part coating system includes an aliphatic epoxy resin crosslinked with an amine functional silicone resin. The aliphatic epoxy resin and the amine functional silicone resin react together at room temperature.

Description

NON-ISOCYANATE CHEMICAL AGENT RESISTANT COATING COMPOSITIONBACKGROUND

[0001] Chemical Agent Resistant Coatings (CARC) are a class of unique polymeric coatings utilized in defense platforms to protect important equipment in the case of a chemical weapons attack. To perform this function, the coating must absorb less than a certain amount of various live chemical agents such as S-{2-[Di(propan-2-yl)amino]ethyl} O-ethyl methylphosphonothioate (VX), 1 -Chloro-2-[(2-chloroethyl)sulfanyl]ethane (mustard gas or HD), or 3,3-Dimethylbutan-2-yl methylphosphonofluoridate (Soman or GD). This is achieved typically by using a highly crosslinked coating structure which limits the penetration of these low molecular weight toxic compounds, thus limiting absorption.

[0002] Current technologies used in these coatings revolve around the use of polyisocyanates which are known to contain lower molecular weight monomeric diisocyanate impurities which have an appreciable volatility and thus pose a toxicity concern for coating applicators in poorly ventilated areas. Furthermore, government regulations, such as the European Union’s Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulations, have begun imposing worker exposure limits and mandatory training requirements for materials containing diisocyanate compounds. This leads to increased costs and limitations on manufacturers using polyurethanes to maintain training compliance and limit workers’ exposure to these compounds.

[0003] It is an object of the present invention to provide a chemical agent resistant coating that does not contain polyisocyanates.

[0004] It is a further object of the present invention to provide a method of producing a chemical agent resistant coating that does not contain polyisocyanates.SUMMARY

[0005] These objects are achieved by the compositions and methods according to the present invention. A two-part coating system, in accordance with the invention, can be used in a chemical agent resistant coating that does not contain any isocyanate functional groups. The two-part coating system includes an aliphatic epoxy resin crosslinked with an amine functional silicone resin. The aliphatic epoxy resin and the amine functional silicone resin can be mechanically mixed to react together at room temperature, forming a homogenous coating composition.DETAILED DESCRIPTION

[0006] Compositions and methods described herein solve the problem of providing chemical agent resistant coatings that do not contain any isocyanate functional groups and thus avoid toxicity concerns during the coating process.

[0007] The coating composition revolves around the use of aliphatic epoxy resins crosslinked with an amine functional silicone resin. Coatings with aromatic epoxy resins are widely used and known to have excellent adhesion, corrosion and chemical resistance. Due to their poor UV resistance and tendency to chalk in outdoor application, coatings with aromatic epoxy resins are not typically used in exterior applications. This poor UV resistance is due to the aromaticity present in the backbone of the common bisphenol-A derived epoxy resins that are typically used. However, these aromatic epoxy resins can undergo a process called hydrogenation which removes the aromaticity leaving a cycloaliphatic structure resulting in improved UV resistance while maintaining the rigid structure giving epoxy resins their excellent chemical resistance. In addition to cycloaliphatic epoxy resins, other aliphatic epoxy resins also can be used in this application such as epoxy functional acrylics, epoxy functional polyesters, epoxy functional vegetable or seed oils, glycidyl carbamates, epoxidized polyolefins, and epoxidized alkyds (and there could be others). One example of a commercially available aliphatic epoxy resin that is suitable for use in the coating composition is EPONEX™ 1510, available from Westlake Epoxy.

[0008] The epoxy equivalent weight of the epoxy resin should be less than 500, but preferably below 250 to ensure a highly crosslinked film. The epoxy functional resins can have dual functionality; for example, (3-Glycidyloxypropyl)triethoxysilane which contains only one epoxy group but three reactive alkoxy groups would meet the required level of functionality. The functional alkoxy silanes preferably contain reactive ethoxy groups to avoid generating methanol, which is considered a hazardous air pollutant known to cause adverse health or environmental effects under the Clean Air Act Section 1 12(b) (“HAPS”).

[0009] The crosslinker for the coating composition is an amine functional silicone resin. Silicone resins have superior UV durability compared to carbon-based material due to their alternating silicon oxide bonds. The pendant amine functionality allows crosslinking at room temperature with the epoxy resin along with the moisture curing polycondensation reaction of the silicone resin itself. This results in a highly crosslinked, extremely hard, weather-resistant coating with excellent chemical resistance. The amine hydrogen equivalent weight should be less than 500, but more preferably below 300 to ensure a highly crosslinked film. Suitable amine functional silicone resins include siloxanes with functional groups in which the functional groups at least partially consist of primary or secondary amines. A resin meeting this criteriafor example would be poly[(2-aminoethyl)aminopropyl] phenylsilsesquioxane (CAS # 477725- 72-7). One example of a commercially available amine functional silicone resin that is suitable for use in the coating composition is SILRES™ HP 2100, available from Wacker Chemie AG. The amine functional silicone resins can be blended resins that have dual functionality; for example, 3-Aminopropyltriethoxysilane, which contains only one primary amine group but three reactive alkoxy groups, would meet the required level of functionality. The functional alkoxy silanes preferably contain reactive ethoxy groups to avoid generating methanol, a known HAPS.

[0010] The aliphatic epoxy resin and the amine functional silicone resin may be present in the composition in roughly equal amounts by molar equivalence of epoxy and amine groups. More particularly, a molar equivalent ratio between the aliphatic epoxy resin and the amine functional silicone resin may be in a range between 0.8 and 1.2 equivalents of epoxy (epoxy equivalent weight, EEW) to equivalents of active hydrogens on amines (amine hydrogen equivalent weight, AHEW).

[0011] In addition to aliphatic epoxy resins, other reactive resins can be added to modify the final properties of the paint, as long as they do not contain an isocyanate group. (Meth)Acrylate functional resins, including, but not limited to, (meth)acrylate functional epoxies, (meth)acrylate functional urethanes, (meth)acrylate functional polyesters, and (meth)acrylate functional siloxanes, can also to be used to crosslink with the amine functional silicone resin to improve dry times. The sum of the reactive functionality of these (meth)acrylate modifying compounds needs to be greater than or equal to 2. These compounds can have dual functionality; for example, 3-(trimethoxysilyl)propyl acrylate, which contains only one acrylate group but three reactive alkoxy groups, would meet the required level of functionality. Alkoxy silane functional resins can be blended to improve dry times as well. The functional alkoxy silanes preferably contain reactive ethoxy groups to avoid generating methanol, which is a known HAPS.

[0012] In addition to the amine functional silicone resin, other amine functional resins can be incorporated to improve various physical properties such as adhesion and flexibility. These include, but are not limited to, aliphatic amines, cycoaliphatic amines, and polyether amines.

[0013] Catalysts that speed up either the epoxy amine reaction or the silane condensation reaction can optionally be included in the formulation. This includes, but is not limited to, tertiary amine catalysts such as 1 ,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), tris- (dimethylaminomethyl) phenol, Tetramethylguanidine, and heptamethylisobiguanide. Catalysts that speed up the silane condensation reaction can be optionally included as well.These include, but are not limited to, metal halide catalysts such as aluminum chloride, organometallic catalysts such as dibutyl tin dilaurate, and other Lewis acids. Blends of catalysts between the above groups can also be used to achieve desired cure rate.

[0014] The coating composition may contain pigments to achieve desired optical / camouflage properties. These include, but are not limited to, organic and inorganic pigments, such as chrome oxide green, cobalt-chromite green, yellow iron oxide, red iron oxide, as well as flattening pigments designed to lower the gloss of the final coating. These flattening pigments can either be silica (amorphous or crystalline) or polymeric based, including, but not limited to, polyethylene, polypropylene, polyurea, cellulose-based, and Fischer-Tropsch waxes.

[0015] The coating composition may contain solvents including, but not limited to, acetates, ketones, alcohols, parachlorobenzotrifluoride, and water. Care should be taken to ensure no solvents located on the HAPS list are used. The Volatile Organic Compound (VOC) content of the coating composition, as defined by the U.S. Environmental Protection Agency (EPA) under Reference Method 24, for the admixed paint should not exceed 3.5 pounds per gallon minus water and exempt solvents, and is preferably under 1 .0 pound per gallon minus water and exempt solvents.

[0016] Lastly, the final coating composition may include various additives that can help improve various parts of the coating application including, but not limited to, the rheology, sprayability, potlife, wettability, adhesion, dry time, and overall aesthetic of the final film to meet the desired film properties. These additives may include, but are not limited to, pigment dispersants of various chemistries, flow additives such as silicone polymers, defoamers, and thixotropic polymers to improve sag resistance, or any combination of the above..

[0017] The coating composition suitably has an appreciable pot life greater than 2 hours. The coating composition dries to touch in 4 hours or less, and achieves full chemical resistance properties in less than 7 days or less as outlined in MIL-DTL-53039F. The coating composition can be applied directly to various surfaces, including blasted metal, pretreated metal substrates, zinc-rich primers, and non-metal-rich primers.

[0018] Cured coating compositions exhibit exceptional chemical resistance, absorbing less than 1 % of chemical agents as tested under the guidelines of MIL-DTL-53039, MIL-DTL- 64159, and / or STANAG 4360.

[0019] A chemical agent resistance reference value > 0 means the composition meets or exceeds performance requirements outlined in MIL-DTL-53039F and MIL-DTL-64159C. In Example 2, the compositions were applied to a MIL-DTL-53022G approved primer and then tested to determine the desorbed quantity and the absorbed quantity with respect to threedifferent nerve agents. Maximum allowable desorbed quantities for acceptable resistance according to STANAG 4360 / DEF-STAN 80-225 are: GD < 1 pg / cm3, HD < 10 pg / cm3, VX < 1 pg / cm3. Maximum allowable absorbed quantities for acceptable resistance according to STANAG 4360 / DEF-STAN 80-225 are: GD < 12 pg / cm3, HD < 60 pg / cm3, VX < 12 pg / cm3.

[0020] The coating composition can be produced by separately preparing two components, one component (Component A) that includes the aliphatic epoxy resin and another component (Component B) that includes the amine functional silicone resin. Component A is manufactured by blending one or more pigments, flatteners, and / or additives into an aliphatic epoxy resin with a required amount of solvent through any industrial paint mixing process such as cowles blade, sand mill, media mill, or any other commercial grade process to achieve the desired aesthetic and camouflage properties. Component B is manufactured by blending the amine functional silicone resin with a desired amount of solvent in which an even mix ratio by volume is obtained (1 :1 , 2:1 , 3:1 , 4:1 , and so on). Once Component A and Component B are formed, Component A and Component B can be mixed together at room temperature with mechanical stirring or shaking to produce a homogenous paint blend free of grit, seeds, skins, abnormal thickening or livering. The mixed composition can be ready to apply in 15 minutes or less after mixing.

[0021] EXAMPLES

[0022] The following examples demonstrate the effectiveness of compositions according to the invention in use as chemical agent resistant coatings. In particular, the compositions were formed by admixing a component including an aliphatic epoxy resin and a component including an amine functional silicone resin. In Example 1 , the compositions were applied to a MIL-DTL-53022F approved primer and then tested to determine the chemical agent resistance reference value with respect to three different nerve agents. A chemical agent resistance reference value > 0 means the composition meets or exceeds performance requirements outlined in MIL-DTL-53039F and MIL-DTL-64159C. In Example 2, the compositions were applied to a MIL-DTL-53022F approved primer and then tested to determine the desorbed quantity and the absorbed quantity with respect to three different nerve agents. Maximum allowable desorbed quantities for acceptable resistance according to STANAG 4360 / DEF-STAN 80-225 are: GD < 1 pg / cm3, HD < 10 pg / cm3, VX < 1 pg / cm3. Maximum allowable absorbed quantities for acceptable resistance according to STANAG 4360 / DEF-STAN 80-225 are: GD < 12 pg / cm3, HD < 60 pg / cm3, VX < 12 pg / cm3.

[0023] Example 1 : The first paint utilizes a hydrogenated bisphenol A epoxy resin with pigments and flatteners to meet the camouflage requirements for both gloss and infrared reflectance as outlined in MIL-DTL-53039F. When part A (tablel ) and part B (table 2) areproperly mixed and applied to a MIL-DTL-53022F approved primer, namely 22167WEP epoxy primer available from Hentzen Coatings, Inc., the resulting chemical resistance values are obtained (table 3).

[0024] Admix 75 parts by volume Component A with 25 parts by volume component B and mix for 15 minutes prior to application.

[0025] Resulting Film Properties:

[0026] 60° Gloss: < 1.0

[0027] 85° Gloss: < 3.5• Value > 0 means it meets or exceeds performance requirements outlined in MIL-DTL-53039F and MIL-DTL-64159C

[0028] Example 2: The second paint utilizes a cycloaliphatic epoxy resin with pigments and flatteners designed to meet the color and gloss requirements for British Standard Colours BS285 (NATO Green). When part A (table 4) and part B (table 5) are properly mixed and applied to a MIL-PRF-53022F approved primer, namely 22167WEP epoxy primer available from Hentzen Coatings, Inc., the resulting chemical resistance desorption and absorption values are obtained (table 6).

[0029] Admix 75 parts by volume Component A with 25 parts by volume component B and mix for 15 minutes prior to application.

[0030] Resulting Film Properties:

[0031] 60° Gloss: 10• Maximum allowable desorbed quantities for acceptable resistance according to STANAG 4360 / DEF-STAN 80-225: GD < 1 pg / cm3, HD < 10 pg / cm3, VX < 1 pg / cm3• Maximum allowable absorbed quantities for acceptable resistance according to STANAG 4360 / DEF-STAN 80-225: GD < 12 pg / cm3, HD < 60 pg / cm3, VX < 12 pg / cm3

[0032] The descriptions included herein depict specific implementations to teach those skilled in the art how to make and use the best option. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these implementations that fall within the scope of the invention.Those skilled in the art will also appreciate that the features described above can be combined in various ways to form multiple implementations. As a result, the invention is not limited to the specific implementations described above, but only by the claims and their equivalents.

Claims

CLAIMS1 . A two-part coating composition comprising: an aliphatic epoxy resin; and an amine functional silicone resin, wherein the aliphatic epoxy resin and the amine functional silicone resin react together at room temperature, and the coating composition does not contain any isocyanate functional groups.

2. The coating composition according to claim 1 , wherein the aliphatic epoxy resin is a bisphenol-A derived epoxy resin that has undergone hydrogenation.

3. The coating composition according to claim 1 , wherein the aliphatic epoxy resin is selected from the group consisting of: epoxy functional acrylics, epoxy functional polyesters, epoxy functional vegetable oils, epoxy functional seed oils, glycidyl carbamates, epoxidized polyolefins, and epoxidized alkyds.

4. The coating composition according to claim 1 , wherein the amine functional silicone resin is a siloxane with functional groups that at least partially consist of primary or secondary amines.

5. The coating composition according to claim 1 , wherein a molar equivalence ratio between the aliphatic epoxy resin and the amine functional silicone resin is in a range between 0.8 and 1.2 equivalents of epoxy (epoxy equivalent weight, EEW) to equivalents of active hydrogens on amines (amine hydrogen equivalent weight, AHEW).

6. The coating composition according to claim 1 , further comprising at least one additional resin having a different functionality than the amine functional silicone resin, wherein the at least one additional resin can react with either epoxy groups, amine groups, or participate in a silane condensation reaction, and wherein the at least one additional resin does not contain any isocyanate functional groups.

7. The coating composition according to claim 1 , further comprising at least one additional resin selected from the group consisting of: (meth)acrylate functional resins, (meth)acrylate functional epoxies, (meth)acrylate functional urethanes, (meth)acrylate functional polyesters, (meth)acrylate functional siloxanes, aliphatic amines, cycoaliphatic amines, and polyether amines.

8. The coating composition according to claim 1 , further comprising at least one catalyst to help accelerate the epoxy amine reaction.

9. The coating composition according to claim 1 , further comprising at least one catalyst to help accelerate a silane condensation reaction.

10. The coating composition according to claim 9, further comprising at least one catalyst to help accelerate the epoxy amine reaction.11 . The coating composition according to claim 1 , further comprising at least one catalyst selected from the group consisting of: tertiary amine catalysts, 1 ,8-Diazabicyclo[5.4.0]undec- 7-ene (DBU), tris-(dimethylaminomethyl) phenol, tetramethylguanidine, heptamethylisobiguanide, metal halide catalysts, aluminum chloride, organometallic catalysts, dibutyl tin dilaurate, and combinations thereof.

12. The coating composition according to claim 1 , wherein admixed volatile organic compounds in the coating composition do not exceed 3.5 pounds per gallon as measured under EPA Reference Method.

13. The coating composition according to claim 1 , wherein the coating composition has an appreciable pot life greater than 2 hours.

14. The coating composition according to claim 1 , wherein the coating composition dries to touch in 4 hours or less, and achieves full chemical resistance properties in less than 7 days.

15. The coating composition according to claim 1 , wherein the coating composition can be applied directly to blasted metal.

16. The coating composition according to claim 1 , wherein the coating composition can be applied directly to pretreated metal substrates.

17. The coating composition according to claim 1 , wherein the coating composition can be applied to zinc-rich primers.

18. The coating composition according to claim 1 , wherein the coating composition can be applied to non-metal-rich primers.

19. The coating composition according to claim 1 , wherein the coating composition absorbs less than 1 % of chemical agents tested under guidelines of MIL-DTL-53039, MIL-DTL-64159, and / or STANAG 4360.

20. A method of producing the coating composition according to claim 1 , comprising: forming a first component comprising the aliphatic epoxy resin by blending at least one of the group consisting of a pigment, a flattener, and an additive into the aliphatic epoxy resin with a solvent; forming a second component comprising the amine functional silicone resin by blending the amine functional silicone resin with a solvent; and mechanically mixing the first component and the second component together to produce a homogenous coating composition.

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