Primer Compositions and Methods

Abstract

A one-part primer composition is provided. The one-part primer composition includes a first epoxy resin that is liquid under ambient conditions, a particulate corrosion inhibitor present in an amount of 5% to 30% by weight, based on the total weight of the composition excluding carrier solvent and water, a curing agent including a primary aromatic amine, a silane coupling agent, a carrier solvent, and water present in an amount sufficient to hydrolyze the silane coupling agent while uniformly mixing with the carrier solvent and maintaining solubility of the first epoxy resin and curing agent in the carrier solvent-water mixture. The corrosion inhibitor is pre-dispersed in the liquid epoxy to break up inhibitor agglomerations, reduce pigment settling, and improve primer performance.

Description

[Technical field]

[0001] Primer compositions are provided for protecting substrates from corrosion. Substrates that may be protected by these primer compositions include primary and secondary aircraft structures. [Background technology]

[0002] Corrosion protection of aircraft primary and secondary structures, as well as the development of improved environmentally friendly corrosion protection products for aluminum aerospace alloys, are important issues for aircraft manufacturers. Corrosion can be mitigated or avoided entirely by applying a primer to the metal surface, which acts as a barrier layer over the vulnerable structure. For additional protection, corrosion inhibitors can be added to such primers.

[0003] Conventional corrosion inhibitors for aluminum alloys contain hexavalent chromium compounds used in both surface preparations and organic primer compositions. These chromium compounds generally contain chromium-containing anions and CrO4 2- These primers protect the underlying substrate and promote adhesion to a variety of adhesives, including structural adhesives, which are subsequently bonded to the substrate. Yet, regulatory agencies impose restrictions on its use due to the toxicity and carcinogenicity of chromium.

[0004] In response to these toxicity concerns, various non-chromate pretreatments and primers have been developed and tested over the past few years. To address many of these shortcomings, water-based primers that do not contain chromium compounds have been developed. However, due to the higher flash points of water-based primers, these primers have difficulty meeting high throughput production requirements, especially those that arise in the automated spray processes used by major aircraft manufacturers. Summary of the Invention

[0005] Many of the commercially available chromate-treated solvent-based epoxy bonding primers are based on high molecular weight phenoxy resins blended with other low molecular weight epoxies and phenolic resins, and urea-based accelerators. The higher molecular weight of the phenoxy-type epoxies can help stabilize the corrosion inhibitors. Non-chromate-treated inhibitors are less effective than chromate-based inhibitors, which can be compensated for by increasing the crosslinking functionality. Doing so usually involves the use of lower molecular weight resins with lower viscosities.

[0006] Viscosity issues can be an issue because corrosion inhibitors are particulate and tend to settle during storage and use. Settling is undesirable as it can lead to poor uniform coating quality and variability in primer performance. To mitigate this settling issue, surfactants can be added, but these surfactants can adversely affect primer performance by facilitating water penetration through the primer when cured.

[0007] There is a need for a system that manages inhibitor pigment settling in low viscosity solvent primer systems and requires little or no surfactants. The primer composition provided addresses this need by using smaller particle sizes of inhibitor pigments and by pre-dispersing the particles in high viscosity epoxy resin. Pre-dispersing particulate corrosion inhibitor in epoxy resin can 1) break down inhibitor agglomeration, 2) reduce pigment settling, and 3) improve homogeneity and therefore bond reliability to the cured primer.

[0008] In a first aspect, a one-part primer composition is provided. The one-part primer composition includes a first epoxy resin that is liquid under ambient conditions, a particulate corrosion inhibitor present in an amount of 5% to 30% by weight based on the total weight of the composition excluding carrier solvent and water and having a median primary particle size of 0.5 micrometers to 10 micrometers, a curing agent including a primary aromatic amine, a silane coupling agent, a carrier solvent, and water that is homogeneously mixed with the carrier solvent and is present in an amount sufficient to hydrolyze the silane coupling agent while maintaining the solubility of the first epoxy resin and the curing agent in the mixture of the carrier solvent and water. Optionally, the primer composition further includes one or more co-curing agents or catalysts that promote curing of the primer.

[0009] In a second aspect, there is provided a method for making a one-part primer composition, the method comprising the steps of dispersing a particulate corrosion inhibitor in a first epoxy resin having a viscosity of from 50 centipoise to 1,000,000 centipoise under ambient conditions to provide a particulate dispersion, and combining the particulate dispersion with a silane coupling agent, water in an amount sufficient to hydrolyze the silane coupling agent, a curing agent comprising a primary aromatic amine, and at least one non-aqueous carrier solvent.

[0010] definition As used herein, "Ambient conditions" means a temperature of 25 degrees Celsius (°C) and a pressure of 1 atmosphere (ie, approximately 101.3 kPa). "Ambient temperature" refers to a temperature of 25°C. "Average" refers to the default number average unless otherwise specified. "Cure" refers to chemically crosslinking, such as by exposure to any form of radiation, heating, or undergoing a chemical reaction that results in hardening or an increase in viscosity (e.g., at room temperature or under heat conditions); "Polymer" refers to a molecule having multiple repeating units; "Soluble" means capable of being completely dissolved in a given liquid. "Solvent" refers to a liquid, such as a silicone, an organic compound, water, an alcohol, an ionic liquid, or a supercritical fluid, that is capable of dissolving a solid, liquid, or gas and that is ultimately removed from the composition in end use. By "substantially" it is meant the majority or majority, such as an amount of at least 50%, 60, 70, 80, 90, 95, 96, 97, 98, 99, 99.5, 99.9, 99.99, or 99.999%, or 100% of the composition by weight or volume. The term "substantially free" means that the composition has an insignificant amount, such as 0% to 5% by weight of a given ingredient, or 0% to 1% by weight, or 5% by weight, or less than, equal to, or greater than 4.5%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or 0.001% by weight, or 0% by weight of the ingredient. "Substituted" refers to a state in which one or more hydrogen atoms contained therein are replaced with one or more non-hydrogen atoms. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] As used herein, the terms "preferred" and "preferably" refer to embodiments described herein that may offer certain advantages, under certain circumstances, although other embodiments may also be preferred, under the same or other circumstances. Moreover, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

[0012] As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an element preceded by "a" or "the" may include one or more of that element and equivalents thereof known to those of ordinary skill in the art. Furthermore, the term "and / or" refers to one or all of the listed elements or a combination of any two or more of the listed elements.

[0013] It should be noted that the terms "comprises" and variations thereof do not have a limiting meaning when these terms appear in the accompanying description. Furthermore, "a," "an," "the," "at least one," and "one or more" are used interchangeably herein.

[0014] References throughout this specification to "one embodiment," "a particular embodiment," "one or more embodiments," or "an embodiment" mean that a particular feature, structure, material, or characteristic described with respect to that embodiment is included in at least one embodiment of the invention. Thus, the appearances of phrases such as "in one or more embodiments," "in a particular embodiment," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment of the invention. Where applicable, product names are written in all capital letters.

[0015] The primer compositions described herein can be used to protect surfaces against corrosion, promote bonding, and enhance bond durability under working conditions, which in aerospace applications include exposure to salt, moisture, and wide thermal variations.

[0016] The primer composition can be disposed on any of several possible substrates. Substrates commonly found in the aircraft industry include aluminum, aluminum clad, titanium, and fiber reinforced composites. However, the range of potential substrates need not be so limited. In alternative applications, for example, the primer composition can be applied generally to painted substrates, thermoplastic substrates, electroplated metal substrates, and metal substrates in general.

[0017] In aviation applications, temperatures can reach below -40°C, making low temperature performance crucial for primers.

[0018] The primer composition provided includes at least one epoxy resin. A given epoxy resin used in the composition can be either liquid or solid under ambient conditions. In a preferred embodiment, the primer composition includes a mixture of two or more of the aforementioned resins. The two or more epoxy resins can be a combination of solid and liquid epoxy resins. When two or more epoxy resins are present, the resins can be homogeneously mixed by dissolving them in a common solvent or solvent mixture within the primer composition.

[0019] Suitable epoxy resins include conventional epoxy resins having an average functionality of at least 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.2, 2.4, 2.5, 2.7, 3, 3.5, 4, or in some cases greater than 4. In some embodiments, the epoxy resin may be substantially free of ionic or ester groups. The epoxy resin may be a chain-extended glycidyl ether of resorcinol and phenols, such as bisphenol A and bisphenol F. Other useful epoxy resins are solid novolac epoxy resins and epoxy resins derived from liquid epoxy and bisphenol A resins. Novolac epoxy resins are prepared by acid-catalyzed addition oligomerization of phenols with formaldehyde, followed by modification with epichlorohydrin to provide resins with epoxy functionality.

[0020] The epoxy resin may include one or more aliphatic glycidyl ethers. Aliphatic glycidyl ethers include cresyl glycidyl ether; alkyl glycidyl ethers; 2-ethylhexyl glycidyl ether; 1,4-butanediol diglycidyl ether; 1,6-hexanediol diglycidyl ether; 1,4-cyclohexanedimethanol diglycidyl ether; monoglycidyl, diglycidyl, and polyglycidyl variants thereof; and mixtures of the above. Representative aliphatic diglycidyl ethers are commercially available, having an epoxy equivalent weight of about 320 g / eq, sold under the trade name DER732, or having an epoxy equivalent weight of 190 g / eq, sold under the trade name DER736, both from Dow Inc., Midland, MI.

[0021] Other commercially available epoxy resins include EPONSU-8, a polymeric epoxy resin having an average functionality of 8, a melting point of 82°C, and an epoxy equivalent of 215 g / eq, available from Hexion, Inc., Columbus, OH; DER669, a high molecular weight solid epoxy resin having a softening point of 135°C to 155°C and an epoxy equivalent of 3500 g / eq to 5500 g / eq, available from Dow Inc., Midland, MI; EPON1002, a solid BPA epoxy having an epoxy equivalent of 550 g / eq to 650 g / eq and a melting point of 75°C to 85°C, also available from Dow Inc., Midland, MI; and ARALDITE ECN, having an epoxy functionality of 3.8 to 5.4, an epoxy equivalent of 225 g / eq to 235 g / eq, and a melting point of 73°C to 99°C, available from Huntsman Corporation, The Woodlands, TX. 1273, 1280, and 1299 novolac solid epoxy resins.

[0022] In some embodiments, the epoxy resin contains a glycidoxyamine or an aminophenol, such as N,N,N',N'-tetrakis(glycidyl)-4,4-diaminodiphenylmethane or N,N,O-tris(glycidyl)-4-aminophenol. Alternatively, the epoxy resin may be based on the glycidyl ethers of various dihydroxy-naphthalenes and phenolized dicyclopentadiene.

[0023] Many of these aforementioned epoxy resins, as well as other suitable epoxy resins, are disclosed in the Handbook of Epoxy Resins, McGraw-Hill, Inc., 1967, which is incorporated herein by reference.

[0024] The liquid epoxy resin may be present in an amount of 5% to 40%, 10% to 30%, 10% to 25%, or in some embodiments, less than, equal to, or greater than 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, 37, or 40% by weight based on the total weight of the primer composition excluding carrier solvent and water.

[0025] The solid epoxy resin may be present in an amount of from 1% to 30%, from 2% to 20%, from 2% to 10% by weight, or in some embodiments, in an amount less than, equal to, or greater than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 22, 25, 27, or 30% by weight based on the total weight of the primer composition excluding carrier solvent and water.

[0026] In some embodiments, the primer composition includes two or more solid epoxy resins, at least one of which is a bisphenol A extended solid epoxy resin (sometimes referred to as a bisphenol A type solid epoxy). The bisphenol A extended solid epoxy resin may be present in an amount of from 15 percent to 75 percent, from 25 percent to 60 percent, from 35 percent to 60 percent, or in some embodiments, less than, equal to, or greater than 15 percent, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, or 75 percent, based on the total weight of the primer composition excluding carrier solvent and water.

[0027] Generally, the epoxy resin component and the hardener in the provided primer composition are homogeneously dissolved in a common solvent known as the carrier solvent, which is a volatile non-aqueous solvent that can form an azeotrope with water and aid in the film-forming process by facilitating collective evaporation of the solvent after the primer composition is applied to a substrate.

[0028] Suitable carrier solvents may include any solvent that is miscible with a sufficient amount or volume of water. In some cases, the carrier solvent will dissolve the thermosetting resin. Some carrier solvents, or mixtures thereof, have a flash point below ambient temperature. In some embodiments, the flash point of the carrier solvent or carrier solvent mixture may be up to -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, or 20°C at ambient pressure. The carrier solvent may include one or more of tetrahydrofuran, diacetone alcohol, glycol monoether, methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ether ketone, methyl propyl ketone, methyl isopropyl ketone, and methyl isobutyl ketone.

[0029] The carrier solvent may be present in an amount of 30% to 95%, 30% to 90%, 60% to 90% by weight, or in some embodiments, less than, equal to, or greater than 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95% by weight based on the total weight of the primer composition.

[0030] One or more particulate corrosion inhibitors may be present in the primer composition. As previously mentioned, the one or more corrosion inhibitors are generally insoluble in the remaining components in the primer composition and may be advantageously predispersed in the liquid epoxy resin to prevent agglomeration of these particulate components.

[0031] Corrosion inhibitors are active chemical compounds that can be added to primer compositions to reduce the corrosion rate of the substrate to which the primer is applied. Corrosion is a persistent problem in many applications, particularly in aerospace applications where aircraft surfaces may be exposed to conditions that promote corrosion, such as wet environments, acid rain, and thermal cycling. Useful corrosion inhibitors may be chromate-based corrosion inhibitors or non-chromate corrosion inhibitors that are substantially free of chromium and chromium compounds.

[0032] Chromate-based corrosion inhibitors include strontium chromate, barium chromate, zinc chromate, and calcium chromate, and mixtures thereof. Non-chromate corrosion inhibitors include strontium aluminum polyphosphate hydrate, calcium phosphate, calcium aluminum polyphosphate silicate hydrate, zinc phosphate, zinc molybdate, and zinc aluminum polyphosphate hydrate, and mixtures thereof. Preferably, the provided primer composition is substantially or completely free of hexavalent chromium and chromium compounds.

[0033] The corrosion inhibitor may be provided in the primer composition as a particulate solid having a median primary particle size (D50) that may be approximately 0.1 micrometers to 100 micrometers, 0.2 micrometers to 50 micrometers, 0.3 micrometers to 10 micrometers, or in some embodiments less than, equal to, or greater than 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1, 2, 3, 4, 5, 7, 10, 12, 15, 17, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 100 micrometers.

[0034] The concentration of the corrosion inhibitor is preferably effective to significantly reduce the corrosion rate, but not to such an extent that ease of application, film forming ability, or surface finish is unduly complicated or impaired. The corrosion inhibitor may be present in an amount of 5% to 30%, 7% to 25%, 10% to 20% by weight, or in some embodiments, less than, equal to, or greater than 0.1, 0.2, 0.5, 0.7, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 22, 25, 26, 27, 28, 29, or 30% by weight, based on the total weight of the primer composition excluding water and volatile carrier solvents.

[0035] Particulate corrosion inhibitors remain in the primer composition as insoluble species and tend to settle over time due to gravity. Advantageously, liquid epoxy resins can be used as a medium to pre-disperse these corrosion inhibitors before mixing these components with the solvent component. As a result, the agglomeration of these corrosion inhibitors can be substantially reduced, resulting in finer particles, smoother coatings, and improved primer stability.

[0036] To achieve a stable dispersion with the corrosion inhibitor, the liquid epoxy resin alone may have a viscosity of 50 centipoise to 1,000,000 centipoise, 50 centipoise to 100,000 centipoise, 100 centipoise to 10,000 centipoise, or in some embodiments, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 700, 700, 750, 760, 770, 780, 800, 850, 860, 870, 880, 900, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600 It may have a viscosity less than, equal to, or greater than 120, 150, 200, 300, 400, 500, 700, 1000, 2000, 5000, 10,000, 15,000, 20,000, 50,000, 70,000, 100,000, 200,000, 500,000, 700,000, or 1,000,000 centipoise.

[0037] The primer composition may further include one or more adhesion promoters to enhance bonding to the metal substrate. Suitable adhesion promoters include epoxy silanes. Useful epoxy silanes have the following formula: [ka] wherein m ranges from 1 to 6 and each R is H or an alkyl group of 1 to 10 carbon atoms. In an alternative embodiment, the epoxy silane has the following formula: [ka] may have the following structure:

[0038] A sufficient amount of water is included to hydrolyze the silane coupling agent and allow easy covalent bonding to the metal oxide substrate, including, for example, the aluminum oxide surface found on the aluminum component. However, the amount of water is desirably limited to an amount that maintains complete solubility of the epoxy resin and hardener in the mixture of the carrier solvent and water. For a particular epoxy resin and hardener, an excessive amount of water in the primer composition may lead to saturation and precipitation of the resin and / or hardener from the solution, which is undesirable.

[0039] Taking the aforementioned issues into consideration, water may be present in an amount of 0.1 wt. % to 20 wt. %, 0.5 wt. % to 10 wt. %, 1 wt. % to 5 wt. %, or in some embodiments, less than, equal to, or greater than 0.1, 0.2, 0.5, 0.7, 1, 2, 5, 7, 10, 12, 15, 17, or 20 wt. %, based on the total weight of the primer composition.

[0040] The primer composition may further comprise one or more inorganic fillers.The addition of inorganic fillers may help prevent sagging during the process of curing the primer composition.An exemplary inorganic filler is fumed silica, which may be used as a thickening agent to intentionally increase the viscosity of the primer composition when applied to the surface of the substrate to be protected.

[0041] A given inorganic filler may be present in an amount of 0.01 wt.% to 15 wt.%, 0.5 wt.% to 10 wt.%, 1 wt.% to 5 wt.%, or in some embodiments, in an amount less than, equal to, or greater than 0.01, 0.02, 0.03, 0.04, 0.05, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 wt.%, based on the total weight of the primer composition excluding carrier solvent and water.

[0042] The provided composition further contains a curing agent or two or more curing agents that work together to cure or crosslink the epoxy resin under the desired curing conditions, typically at the primer bake temperature. The curing agent may be composed of two or more components, each of which may be either a solid or a liquid under ambient conditions. For ease of handling, the curing agent is preferably soluble in the solvent or solvent mixture in the primer composition.

[0043] Suitable curing agents include aromatic amines and their mixtures. Exemplary aromatic amines include 4,4'-diaminodiphenylmethane, 2,2-bis(4-[4-aminophenoxy]phenyl)propane, 3,3'- and 4,4'-diaminodiphenylsulfone, 3,3'- and 4,4'-diaminodiphenyloxide, 3,3- and 4,4'-diaminodiphenyloxide, 3,31'- and 4,4'-diaminodiphenylsulfide, 3,3'- and 4,4'-diaminodiphenylketone, and 4,4'-[1,4-phenylene(1-methylethylidene)]-bis(benzeneamine).

[0044] Solid diamine curing agents include 2,4-toluenediamine, 1,4-phenylenediamine, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,4'-diaminodiphenyloxide, 9,9-bis(4-aminophenyl)fluorene, o-toluidine sulfone, and 4,4'-diaminobenzanilide.Preferred curing agents include 9,10-bis(4-aminophenyl)anthracene, 2,2-bis(4-[3-aminophenoxy]phenyl)sulfone, 2,2-bis(4-[4-aminophenoxy]phenyl)sulfone, 1,4-bis(4-aminophenoxy)biphenyl, bis(4-[4-aminophenoxy)phenyl)ether, and 2,2-bis([4-(4-amino-2-trifluorophenoxy)]phenyl)hexafluoropropane.

[0045] Preferred aromatic amine curing agents include 2,2-bis-[4-(4-aminophenoxy)-phenyl]propane (BAPP), 2,2'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, and mixtures thereof. Specific options and advantages of the aforementioned curing agents can be found in Patent Nos. 5,641,818 (Sweet) and 6,475,621 (Kohli et al.).

[0046] Optionally, the primer composition further contains one or more co-curing agents or catalysts that promote the curing of the primer.Suitable curing agents include substituted aminotriazines (e.g., commercially available under the trade name CUREZOL from Evonik Industries AG, Essen, Germany), any of the modified aliphatic amines and modified cycloaliphatic amines offered under the trade name ANCAMINE from Evonik Industries AG, Essen, Germany, dicyandiamide, including micronized grades available under the trade name AMICURE from Evonik Industries AG, Essen, Germany, bis-urea based curing agents, toluene-2,4-bis(N,N′ dimethylurea) (commercially available under the trade name OMICURE from Emerald Performance Materials LLC, Vancouver, WA), and water-insoluble amine-epoxy adducts.

[0047] The curing agents, individually or collectively, may be present in an amount of 0.5% to 40%, 5% to 30%, 10% to 20% by weight, or in some embodiments, less than, equal to, or greater than 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 22, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40% by weight, based on the total weight of the primer composition excluding carrier solvent and water.

[0048] The primer composition may further contain any number of dyes, pigments, fillers, leveling agents, additional dispersants, and / or thickeners known in the art.

[0049] The provided primer compositions may be prepared by first dispersing the particulate corrosion inhibitor in one or more liquid epoxy resins within the appropriate viscosity range, as previously characterized. At this stage, it may be advantageous to further process the dispersion to further reduce the median aggregate particle size of the corrosion inhibitor to their final size distribution. Suitable processing steps may include, for example, high speed shear, bead milling, and ultrasonication methods to break down the corrosion inhibitor aggregates.

[0050] The microparticle dispersion can then be mixed with the remaining components of the primer composition, among which the water and carrier solvent are mixed uniformly, and the first epoxy resin, the curing agent, and any other epoxy resins can be present in the composition dissolved in the mixture of the carrier solvent and water.

[0051] The provided primer composition can be coated on a given substrate using any known method, including spraying, brushing, roller coating, or dip coating. In aerospace applications, it is common for primers to be applied via spray coating. The provided primer composition is suitable for spraying using either air-driven or airless spray guns, such as high-volume, low-pressure spray guns known in the art.

[0052] After the primer composition is applied to a substrate, the composition is allowed to dry partially or completely. This process removes most of the water and other volatile materials from the composition and may be carried out at ambient or near ambient conditions without the need for external heating. At ambient temperatures, drying times may be 5 minutes to 300 minutes, 10 minutes to 100 minutes, 20 minutes to 50 minutes, or in some embodiments, less than, equal to, or greater than 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 150, 200, 250, or 300 minutes.

[0053] The dried or partially dried coating can be heated to cure the primer composition. In the curing process, the first and second thermosetting resins react with the curing agent and with each other to form a crosslinked network. The curing temperature can be 60°C to 200°C, 100°C to 180°C, 120°C to 180°C, or in some embodiments, less than, equal to, or greater than 60°C, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200°C.

[0054] The coated substrate may be maintained at the cure temperature for a sufficient time to achieve an acceptable level of cure, which may vary based on the application, but generally may be less than, equal to, or greater than 0.1 hours to 6 hours, 0.5 hours to 2 hours, 0.7 hours to 2 hours, or in some embodiments, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6 hours at a suitable cure temperature.

[0055] Once cured, the primer coating can have any suitable thickness, which can range from 1 micrometer to 20 micrometers, 2 micrometers to 10 micrometers, 3 micrometers to 8 micrometers, or in some embodiments, less than, equal to, or greater than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 micrometers.

[0056] Once the primer has been applied to a substrate, such as a metal adherend, a second adherend, such as a second metal or composite substrate, can be bonded in the usual manner to the so-primed substrate by placing a thermosetting adhesive, such as a structural adhesive, between the primed surface of the substrate and the second adherend, and then applying heat and pressure to cure the adhesive. The use of such adhesives for particular applications, along with their suitability for such applications and associated curing conditions, are well known to those skilled in the art.

[0057] Further exemplary embodiments, which are not intended to be limiting, are set forth below.

[0058] 1. A one-component primer composition comprising: a first epoxy resin that is liquid under ambient conditions; and a particulate corrosion inhibitor present in an amount of 5% to 30% by weight, based on the total weight of the composition excluding carrier solvents and water, and having a median primary particle size of 0.5 micrometers to 10 micrometers. a curing agent comprising a primary aromatic amine; A silane coupling agent; A carrier solvent; water homogeneously mixed with the carrier solvent and present in an amount sufficient to hydrolyze the silane coupling agent while maintaining solubility of the first epoxy resin and the hardener in the carrier solvent-water mixture; A composition comprising:

[0059] 2. The composition of embodiment 1, wherein the carrier solvent comprises one or more of tetrahydrofuran, methyl ethyl ketone, diacetone alcohol, and glycol monoethers.

[0060] 3. The composition of embodiment 1 or 2, wherein the first epoxy resin comprises a diglycidyl ether of bisphenol A, bisphenol F, or bisphenol S, a phenol novolac resin or a cresol novolac resin, N,N,N',N'-tetrakis(glycidyl)-4,4-diaminodiphenylmethane, N,N,O-tris(glycidyl)-4-aminophenol, a glycidyl ether of dihydroxy-naphthalene or phenolized dicyclopentadiene, an aliphatic diglycidyl ether or a blend of two or more low viscosity aliphatic glycidyl ethers or aliphatic diglycidyl ethers.

[0061] 4. The composition of any one of embodiments 1-3, wherein the particulate corrosion inhibitor comprises one or more of strontium aluminum polyphosphate hydrate, zinc phosphate, zinc molybdate, and zinc aluminum polyphosphate hydrate, calcium phosphate, and calcium aluminum silicate polyphosphate hydrate.

[0062] 5. The composition of any one of embodiments 1-4, wherein the particulate corrosion inhibitor has a median primary particle size of from 0.1 micrometers to 100 micrometers.

[0063] 6. The composition of any one of embodiments 1-5, further comprising a second epoxy resin that is solid under ambient conditions, the second epoxy resin comprising a novolac epoxy resin.

[0064] 7. The composition of embodiment 6, wherein the second epoxy resin is present in an amount of 1% to 30% by weight, based on the total weight of the composition excluding carrier solvents and water.

[0065] 8. The composition of any one of the preceding embodiments, further comprising a third epoxy resin that is solid under ambient conditions, the third epoxy resin comprising a bisphenol A extended solid epoxy resin.

[0066] 9. The composition of embodiment 8, wherein the third epoxy resin is present in an amount of 15% to 75% by weight, based on the total weight of the composition excluding carrier solvents and water.

[0067] 10. The composition of any one of embodiments 1-9, wherein the primary aromatic amine comprises one or more of 4,4'-diaminodiphenylmethane, 2,2-bis(4-[4-aminophenoxy]phenyl)propane, 3,3'- and 4,4'-diaminodiphenyl sulfone, 3,3'- and 4,4'-diaminodiphenyl oxide, 3,3- and 4,4'-diaminodiphenyl oxide, 3,3'- and 4,4'-diaminodiphenyl sulfide, 3,3'- and 4,4'-diaminodiphenyl ketone, and 4,4'-[1,4-phenylene(1-methylethylidene)]-bis(benzeneamine).

[0068] 11. The composition of any one of the preceding embodiments, wherein water is present in an amount of 0.1% by weight to 20% by weight, based on the total weight of the composition.

[0069] 12. The silane coupling agent is represented by the following formula: [ka] wherein m ranges from 1 to 6 and each R is H or an alkyl group of 1 to 10 carbon atoms; or [ka] 12. The composition of any one of the preceding embodiments, comprising an epoxy silane having any one of the following formulas:

[0070] 13. The composition of any one of the preceding embodiments, wherein the epoxy resin has a viscosity of from 50 centipoise to 1,000,000 centipoise under ambient conditions.

[0071] 14. A method for producing a one-component primer composition, comprising: dispersing a particulate corrosion inhibitor in a first epoxy resin having a viscosity of between 50 centipoise and 1,000,000 centipoise under ambient conditions to provide a particulate dispersion; combining the particulate dispersion with a silane coupling agent, a sufficient amount of water to hydrolyze the silane coupling agent, a curing agent comprising a primary aromatic amine, and at least one non-aqueous carrier solvent; A manufacturing method comprising:

[0072] 15. The method of claim 14, further comprising treating the corrosion inhibitor in a particulate dispersion to reduce the size of the corrosion inhibitor to a median primary particle size of 0.1 micrometers to 100 micrometers. EXAMPLES

[0073] Objects and advantages of the present disclosure are further illustrated by the following non-limiting examples, in which the specific materials and amounts thereof recited, as well as other conditions and details, should not be construed to unduly limit the disclosure. Unless otherwise indicated, all parts, percentages, ratios, etc. in the examples and elsewhere in the specification are by weight.

[0074] [Table 1]

[0075] Test Method Grade 2024-T3 bare aluminum panels were obtained from Erickson Metals of Minnesota, Inc., Coon Rapids, Minnesota. Prior to bonding with a structural adhesive, the panels were subjected to the following surface preparation process.

[0076] Panel Preparation FPL etched and phosphoric acid anodized aluminum substrate Bare aluminum panels were immersed in OAKITE 165 caustic cleaning solution at 85°C (185°F) for 10 minutes. The panels were then immersed in tap water at 21°C (69.8°F) for 10 minutes, followed by a continuous tap water spray rinse for approximately 3 minutes. The panels were then immersed in Forest Products Laboratory (FPL) etching solution at 66°C (151°F) for 10 minutes, after which the panels were spray rinsed for approximately 3 minutes at 21°C (69.8°F), then drip dried for an additional 10 minutes, then dried in an oven at 54°C for 30 minutes. The etched panels were then anodized in an 85% phosphoric acid bath at 72°F (22.2°C) for approximately 25 minutes at 15 volts and a maximum current of 100 amps, rinsed with water at 69.8°F (21°C) for approximately 3 minutes, drip-dried for an additional 10 minutes, and then dried in an oven at 151°F (66°C) for 10 minutes. Within 24 hours of anodizing, the aluminum panels were primed with a primer composition as described in the Examples below. The dried primer thickness was 0.1 mil to 0.4 mil (2.5 micrometers to 10.2 micrometers).

[0077] Corrosion Protection Testing Testing was performed on 152 cm x 152 cm (6 in. x 6 in.) 2024-T3 primed panels exposed to a salt spray environment according to the method described in ASTM B-117. Exposure was for 1000 hours in a salt spray chamber.

[0078] Floating Roller Peel (FRP) strength test for adhesive film Primed panels of bare aluminum of 2024-T3, 8.0 in. x 3.0 in. x 0.063 in. (20.3 cm x 7.6 cm x 0.16 cm), and 10 in. x 3 in. x 0.025 in. (25.4 cm x 7.6 cm x 0.064 cm) primed panels were prepared for testing as described above for "FPL Etched and Phosphoric Acid Anodized Aluminum Substrates." After removing the liner from one side, AF-163-2 was applied by hand using a small rubber roller to eliminate trapped air and ensure intimate contact between the exposed adhesive and the test panel substrate. The primed panels were bonded together and cured in an autoclave (see Adhesive Cure Cycle Method defined below), then evaluated for floating roller peel strength according to ASTM D-3167-76 with the following modifications: Six specimens were tested at the three specific primer thicknesses of each Example or Comparative Example, and the average value (in N / 25 mm) was reported. Test specimens having a width of 0.5 inches were cut along the length of the bonded aluminum panels. A tensile tester operating at 70°F (21.2°C) and a speed of 6 inches / minute (30.5 cm / min) was used to peel the thinner substrate from the thicker one, and the results were normalized to a width of 1 inch (2.54 cm). Test panels were prepared and evaluated (one for each example).

[0079] AF-163-2 curing instructions: Each AF-163-2 sample was placed in a vacuum bag and brought to a pressure of approximately 28 inches of mercury in an autoclave, model number "ECONOCLAVE 3x5", obtained from ASC Process Systems of Sylmar, CA. United States. The autoclave pressure was increased to 45 psi while the vacuum bag was vented to atmosphere when the autoclave pressure exceeded 15 psi. The autoclave temperature was then increased to 250°F at a rate of 4.5°F per minute. After reaching the set point, the samples were held at this temperature for 60 minutes and then cooled to 72°F at a rate of 5.0°F per minute before releasing the pressure.

[0080] Preparatory Example 1 (PE1): A pigment pre-dispersion in epoxy was prepared as follows: 41.75 grams of SAPP and 10.42 grams of ZPA were blended with 47.71 grams of PY307-1, 0.58 grams of B2G03, and 2.31 grams of CG500 in a high speed mixer operating at 2,200 rpm at 25° C. (77° C.) for approximately 2 to 3 minutes.

[0081] Preparatory Example 2 (PE2): A pigment pre-dispersion in water was prepared as follows: 21.87 grams of SAPP and 5.45 grams of ZPA were blended with 40.99 grams of deionized (DI) water and 0.3 grams of B2G03 and 1.2 grams of CG500 for approximately 2-3 minutes in a high speed mixer operating at 2,200 rpm at 25°C (77°C). A noticeable amount of gas is evolved during the addition of the inhibitor to the water.

[0082] Comparative Examples 1 to 3 (CE1 to CE3) and Examples 1 to 3 (EX1 to EX3) The compositions were prepared by dispersing the materials identified in Table 2.

[0083] [Table 2]

[0084] Comparative example 1 (CE1) The amounts specified in Table 2 of EPON1007F, SU-8, PY307-1, DC-29, and Z-6040 were added to a 3.78 liter (L) mixing bowl. The amounts of MEK, acetone, DAA, and PGME were then added to the mixing bowl, followed by the TDI and BAPP. The bowl was placed in a mixer and the materials were mixed for 30 to 40 minutes (250 rpm to 300 rpm). While the contents of the bowl were still mixing, the specified amount of PE2 (specified in Table 1) was added to the bowl and the primer composition was mixed for an additional 15 to 30 minutes.

[0085] Comparative Example 2 (CE2) The amounts specified in Table 2 were added to the 3.78 L bowl as described in Comparative Example 1, except that while the contents of the bowl were still mixing, the specific amount of PE1 (specified in Table 1) was added to the bowl and the primer composition was mixed for an additional 15 to 30 minutes.

[0086] Comparative Example 3 (CE3) The amounts specified in Table 2 of EPON1007F, SU-8, PY307-1, DC-29, Wetlink78, MEK, Acetone, DAA, PGME, TDI, and BAPP were added to a 3.78 liter (L) mixing bowl. The bowl was placed in a mixer and the materials were mixed for 30 to 40 minutes (200 rpm to 250 rpm). While the contents of the bowl were still mixing, the specified amount of DI water (specified in Table 1) was added to the bowl and the primer composition was mixed for an additional 15 to 30 minutes. Once completely mixed, the specified amounts of ZPA, SAAP, B2G03, and CG500 (specified in Table 1) were added to the composition and mixed for 30 to 45 minutes.

[0087] Example 1 (EX1) While the contents of the bowl were still mixing, the amounts specified in Table 2 were added to the 3.78 L bowl as described in Comparative Example 1, except that the specified amount of PE1 (specified in Table 1) was added to the bowl and the primer composition was mixed for an additional 15 to 30 minutes. Once thoroughly mixed, the specified amount of DI water (specified in Table 1) was added to the composition and mixed for 15 to 30 minutes.

[0088] Example 2 (EX2) While the contents of the bowl were still mixing, the amounts specified in Table 2 were added to the 3.78 L bowl as described in Comparative Example 1, except that the specified amount of DI water (specified in Table 1) was added and the primer composition was mixed for an additional 15 to 30 minutes. Once thoroughly mixed, the specified amount of PE1 (specified in Table 1) was added to the composition and mixed for 15 to 30 minutes.

[0089] Example 3 (EX3) The amounts specified in Table 2 were added to a 3.78 L bowl and mixed as described in Example 1, except Wetlink78 was replaced with Z-6040.

[0090] The samples were stirred by hand in clear glass bottles and observed visually for inhibitor settling rate and agglomeration. Primed aluminum panels were subjected to corrosion testing. The results are shown in Table 3.

[0091] [Table 3]

[0092] Primer composition samples were sprayed onto aluminum panels and allowed to cure. The primed and cured aluminum samples were then bonded with AF163-2K film adhesive following AF-163-2 curing instructions. The samples (except CE3) were subjected to FRP testing at room temperature (RT) and at -55°C (-67°F). The results of the FRP testing at room temperature (RT) and -55°C are presented in Tables 4 and 5.

[0093] [Table 4]

[0094] [Table 5]

[0095] All references, patent documents and patent applications cited in the above patent application are incorporated herein by reference in their entirety for consistency. In the event of any inconsistency or discrepancy between the incorporated reference portions and this application, the information in the above description shall prevail. The above description is intended to enable a person skilled in the art to practice the disclosure set forth in the claims, and should not be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereof.

Claims

1. A one-component primer composition comprising: a particulate dispersion comprising a particulate corrosion inhibitor dispersed in a first epoxy resin that is liquid under ambient conditions and has a viscosity of 100,000 centipoise or less; the particulate corrosion inhibitor is present in an amount of from 5% to 30% by weight based on the total weight of the composition excluding carrier solvent and water, and has a median primary particle size of from 0.5 micrometers to 10 micrometers; a curing agent comprising a primary aromatic amine; A silane coupling agent; A carrier solvent; water, homogeneously mixed with the carrier solvent and present in an amount of 0.1% to 20% by weight based on the total weight of the composition; A one-component primer composition comprising:

2. 10. The composition of claim 1, wherein the carrier solvent comprises one or more of tetrahydrofuran, methyl ethyl ketone, diacetone alcohol, and glycol monoethers.

3. 3. The composition of claim 1 or 2, wherein the first epoxy resin comprises a diglycidyl ether of bisphenol A, bisphenol F, or bisphenol S, a phenol novolac resin or a cresol novolac resin, N,N,N',N'-tetrakis(glycidyl)-4,4-diaminodiphenylmethane, N,N,O-tris(glycidyl)-4-aminophenol, a glycidyl ether of dihydroxy-naphthalene or phenolized dicyclopentadiene, an aliphatic diglycidyl ether or a blend of two or more low viscosity aliphatic glycidyl ethers or aliphatic diglycidyl ethers.

4. 4. The composition of claim 1, wherein the particulate corrosion inhibitor comprises one or more of strontium aluminum polyphosphate hydrate, zinc phosphate, zinc molybdate, and zinc aluminum polyphosphate hydrate.

5. 5. The composition of claim 1, wherein the primary aromatic amine comprises one or more of 4,4'-diaminodiphenylmethane, 2,2-bis(4-[4-aminophenoxy]phenyl)propane, 3,3'- and 4,4'-diaminodiphenyl sulfone, 3,3'- and 4,4'-diaminodiphenyl oxide, 3,3'- and 4,4'-diaminodiphenyl oxide, 3,3'- and 4,4'-diaminodiphenyl sulfide, 3,3'- and 4,4'-diaminodiphenyl ketone, and 4,4'-[1,4-phenylene(1-methylethylidene)]-bis(benzeneamine).

6. The silane coupling agent is represented by the following formula: 【Chemistry 1】 [In the formula, m ranges from 1 to 6, and each R １ is H or an alkyl group of 1 to 10 carbon atoms; or 【Chemistry 2】 The composition according to any one of claims 1 to 5, comprising an epoxy silane having any one of the following formulas:

7. The composition of any one of claims 1 to 6, wherein the epoxy resin has a viscosity of 50 centipoise or greater under ambient conditions.

8. A method for producing a one-component primer composition, comprising the steps of: dispersing a particulate corrosion inhibitor in a first epoxy resin having a viscosity of 50 centipoise to 100,000 centipoise under ambient conditions to provide a particulate dispersion; mixing the particulate dispersion with a silane coupling agent, water in an amount of 0.1% to 20% by weight based on the total weight of the composition, a curing agent comprising a primary aromatic amine, and at least one non-aqueous carrier solvent; A manufacturing method comprising:

9. 9. The method of claim 8, further comprising processing the corrosion inhibitor in a particulate dispersion to reduce the size of the corrosion inhibitor to a median primary particle size of 0.1 micrometers to 100 micrometers.

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