Aqueous primer composition and method thereof

Abstract

An aqueous primer composition is provided that includes a first thermosetting resin that is a particulate solid under ambient conditions and a second thermosetting resin that is a liquid under ambient conditions and acts as a reactive coalescent in which the first thermosetting resin is at least partially soluble. The second thermosetting resin acts as a coalescent, allowing the primer to form a continuous primer film when it is dried before curing. The composition further includes a curing agent that is substantially water-insoluble and reactive with the first and second thermosetting resins. The overall composition can contain up to 4 percent by weight of a volatile solvent other than water, providing a storage-stable primer that can form a continuous film without the need for added organic solvents.

Description

[Technical field]

[0001] An aqueous primer composition useful for protecting substrates from corrosion is provided. The aqueous primer composition provided can be applied to primary and secondary aircraft structures. [Background technology]

[0002] Aircraft manufacturers go to great lengths to ensure the long-term durability of their aircraft. Since many aircraft structures are fabricated from metals such as steel or aluminum, protecting these components from corrosion is a major concern. Chemical corrosion can be caused by exposure to caustic cleaning agents, while electrochemical corrosion can be induced by exposure to conductive liquids such as salt water. Both can be exacerbated by the high temperatures, high humidity, and highly corrosive marine environments commonly encountered in aircraft applications.

[0003] Corrosion can be avoided by applying a primer coating (or film) onto the metal surface, which acts as a barrier layer on the surface of the vulnerable metal structure. For additional protection, corrosion inhibitors can be added to such primers. Traditionally, corrosion inhibitors for aluminum alloys are derived from hexavalent chromium compounds used in both surface preparations and organic primer compositions. These chromium compounds are generally CrO4 2- These primers not only protect the underlying substrate, but also promote adhesion to a variety of adhesives, including structural adhesives, which are subsequently adhered to the substrate.

[0004] Although chromates are effective against corrosion, they are becoming increasingly undesirable due to environmental, health, and safety concerns. Evolving regulatory regimes have led manufacturers to explore the use of radically new primer systems that can meet the new regulatory standards. Summary of the Invention

[0005] Existing primers are generally classified as either water-based (i.e., aqueous) or organic solvent-based. Organic solvent-based primers contain a curable resin dissolved in a low viscosity organic solvent that directly wets the substrate being coated. Water-based primers, which use water as the volatile solvent, are provided in the form of a latex, which is an emulsified particle of a thermosetting resin dispersed in an aqueous dispersion. Typically, the dispersion is coated on the substrate, dried, and then heated to cure the thermosetting resin.

[0006] Although aqueous solutions can significantly reduce the emissions of volatile organic solvents, the development of these solutions brings new technical challenges due to the inherent wetting behavior of aqueous compositions. The resins and curable particles in these compositions are usually high melting or softening point solids and do not form smooth and continuous films when dried. Instead, these coatings tend to have a rough, powdery texture and can be vulnerable to chipping and scratching when the coated parts are handled. The non-uniform nature of these coatings can also degrade the chemical and corrosion resistance of the cured system.

[0007] One possible solution to this problem is to introduce an organic solvent into the emulsion, which causes the resin particles to coalesce as the emulsion dries, improving the film-forming ability of the composition. The drawback of this approach is that these compositions tend to have reduced stability during primer storage, reduced wetting ability when the primer dries and cures, and greater variability in product performance. There remains a need for a chromate-free water-based primer composition that remains stable during storage and application, facilitates handling and transportation of coated parts before and after curing, and provides excellent chemical and corrosion resistance.

[0008] Described herein are primer compositions in which a reactive liquid epoxy acts as a coalescing agent rather than a non-reactive organic solvent, allowing a continuous primer film to be formed during the drying and curing steps of the process. Advantageously, the process allows for the formation of a continuous film without the need for additional organic solvents. By solving this technical dilemma, these primer compositions can simultaneously provide a primer film that is uniform upon curing, improves surface protection, and exhibits a high degree of storage stability in its uncured state.

[0009] In a first aspect, an aqueous primer composition is provided that includes a first thermosetting resin that is a particulate solid under ambient conditions, a second thermosetting resin that is a liquid under ambient conditions and acts as a reactive coalescent in which the first thermosetting resin is at least partially soluble, and a curing agent that is substantially water insoluble and reactive with the first and second thermosetting resins, the aqueous primer composition containing up to 4 percent volatile solvents other than water, based on the total weight of the aqueous primer composition.

[0010] In a second aspect, there is provided a method of providing a continuous primer film on a substrate, the method including the steps of disposing an aqueous primer composition on the substrate, removing water from the aqueous primer composition, coalescing a first thermosetting resin within a second thermosetting resin, and reacting the first and second thermosetting resins with a curing agent to obtain a continuous primer film.

[0011] In a third aspect, there is provided a method for making an aqueous primer composition comprising the steps of: dispersing a first thermosetting resin, a second thermosetting resin that is liquid under ambient conditions and in which the first thermosetting resin is at least partially soluble, and a water-insoluble curing agent in water to obtain a resin emulsion, wherein the first thermosetting resin and the water-insoluble curing agent are particulate solids under ambient conditions; and processing the particulate solids to a median particle size of 50 nanometers to 300 micrometers for the thermosetting resin and 50 nanometers to 300 micrometers for the water-insoluble curing agent, wherein the aqueous primer composition contains up to 4 weight percent volatile solvent other than water, based on the total weight of the aqueous primer composition.

[0012] definition As used herein, "ambient conditions" means a temperature of 25° C. and a pressure of 1 atmosphere (i.e., 101.3 kPa); "Ambient temperature" refers to a temperature of 25°C; "Average" refers by default to the numerical average unless otherwise indicated; "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; "Solvent" refers to a liquid capable of dissolving solids, liquids, or gases, such as silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids; "Substantially" refers to a majority or major portion, 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; "Substantially free" means that the composition has a negligible amount that is less than, equal to, or greater than 0%-5% by weight of a given component, or 0%-1% by weight of the component, or 5%, 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%, or 0% by weight; "Substituted" refers to a state in which one or more hydrogen atoms contained therein are replaced by one or more non-hydrogen atoms. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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. Furthermore, 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.

[0014] 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 followed by "a" or "the" may include one or more of the element and equivalents thereof known to those skilled 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.

[0015] 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.

[0016] 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.

[0017] Primer Composition The disclosed primer compositions can be used to protect surfaces against corrosion, promote adhesion, and enhance adhesion durability under operating conditions, which in aerospace applications include exposure to salt, moisture, and extensive thermal variations.

[0018] The primer composition can be disposed on any of a number of possible substrates. Substrates commonly encountered in the aircraft industry include aluminum, aluminum cladding, 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 generally applied to painted substrates, thermoplastic substrates, electroplated metal substrates, and metal substrates.

[0019] An exemplary primer composition is a water-based primer based on a curable resin dispersed in water. As used herein, the terms "dispersed" and "dispersion" refer to fine particles of a liquid and / or solid first component dispersed in a liquid second component. When the particles of the first component are stabilized in the second component with or without a suitable surfactant, the dispersion is generally referred to as an emulsion. When the first component is a polymer, the emulsion is generally referred to as a latex emulsion.

[0020] In the provided primer composition, the first component comprises a plurality of components. The plurality of components comprises at least two thermosetting resins that can collectively be cured to form a polymer network. At least one first thermosetting resin is solid under ambient conditions, and at least one second thermosetting resin is liquid under ambient conditions. The provided primer composition also contains a curing agent that is substantially water-insoluble and reacts with the first and second thermosetting resins when the primer cures.

[0021] Advantageously, the first thermosetting resin is at least partially soluble in the second thermosetting resin, allowing the second thermosetting resin to act as a reactive coalescent of the primer composition. As water is drained from the primer composition, the coalescent allows the particulate solids of the first thermosetting resin to flow into one another and form, together with the liquid thermosetting resin, a relatively smooth and continuous film. The film formed from the primer composition can be non-tacky, which facilitates user handling of the primed substrate prior to curing.

[0022] When the second thermosetting resin acts as a coalescent, the need for inert coalescent solvents, which are frequently used in conventional water-based primer compositions, is reduced. Depending on the resin selected for use in the primer composition, the water-based primer composition can contain less than, equal to, or greater than 4 percent, up to 3 percent, up to 2 percent, or in some embodiments, less than, equal to, or greater than 0.25 percent, 0.5, 0.75, 1, 1.2, 1.5, 1.7, 2, 2.5, 3, 3.5, 4, 4.5, or 5 percent volatile solvents other than water, based on the total weight of the water-based primer composition. In some embodiments, the primer composition is substantially free of any volatile solvents other than water.

[0023] The first thermosetting resin, which is a particulate solid at ambient temperature, may be comprised of an epoxy, bismaleimide, phenolic, or unsaturated polyester resin. In some embodiments, the thermosetting resin may include a mixture of two or more of the foregoing resins.

[0024] 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 more. In some embodiments, the epoxy resin is substantially free of ionic or ester groups. The epoxy resin can be a glycidyl ether of a chain-extended phenol, such as resorcinol and a bisphenol, e.g., bisphenol A and bisphenol F. Other useful epoxy resins are solid novolac epoxy resins and solid diglycidyl ethers of bisphenol A ("DGEBA") resins.

[0025] Commercially available epoxy resins include EPONSU-8, a polymeric epoxy resin with an average functionality of 8, a melting point of 82° C., and an epoxy equivalent weight of 215 g / mol, from Hexion, Inc., Columbus, OH; DER 669, a high molecular weight solid epoxy resin with a softening point of 135° C. to 155° C. and an epoxy equivalent weight of 3500 g / mol to 5500 g / mol, from Dow Chemical Company; EPON 1002, a solid DGEBA epoxy with an epoxy equivalent weight of 550 g / mol to 650 g / mol, and a melting point of 75° C. to 85° C., also from Hexion, Inc., Columbus, OH; and ARALDITE ECN, with an epoxy functionality of 3.8 to 5.4, an epoxy equivalent weight of 225 g / mol to 235 g / mol, and a melting point of 73° C. to 99° C., from Huntsman Corporation, The Woodlands, TX. 1273, 1280, and 1299 novolac solid epoxy resins.

[0026] Representative epoxy comonomer resins are described in the article Handbook of Epoxy Resins, McGraw-Hill, Inc., 1967. Examples of such resins include bisglycidyl ethers of bisphenols such as bisphenol A, bisphenol F, and bisphenol S. Also suitable are various phenolic and cresol novolak-type resins, as well as various glycidoxyamines and aminophenols, particularly N,N,N',N'-tetrakis(glycidyl)-4,4-diaminodiphenylmethane and N,N,O-tris(glycidyl)-4-aminophenol. The use of epoxy resins based on the glycidyl ethers of various dihydroxy-naphthalenes and phenolized dicyclopentadiene is also possible.

[0027] Useful phenolic resins include novolac-type phenolic resins and / or resole-type phenolic resins having a ratio of o-methylene to p-methylene bonds up to 1. Mixtures of novolac-type and resole-type phenolic resins may also be used.

[0028] The first thermoset resin may be composed of primary particles having a median particle size (D50) of less than, equal to, or greater than 0.05 micrometers to 300 micrometers, 0.2 micrometers to 200 micrometers, 1 micrometer to 100 micrometers, or in some embodiments, 0.05 micrometers, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 120, 150, 170, 200, 250, or 300 micrometers.

[0029] Based on the total weight of the primer composition excluding volatile solvents, the solid thermosetting resin can be present in an amount of from 20 percent to 70 percent, from 30 percent to 60 percent, from 30 percent to 55 percent, or in some embodiments, less than, equal to, or greater than 20 percent, 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70 percent.

[0030] The second thermosetting resin, which is liquid under ambient conditions, may be composed of one or more epoxy resins. Suitable liquid epoxy resins include bisphenol A and bisphenol F epoxy resins, liquid novolac epoxy resins, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N,N,O-tris(glycidyl)-4-aminophenol. In some embodiments, the liquid epoxy resin is provided in the form of a non-ionic aqueous dispersion. Commercially available resins that can be used for the second thermosetting resin include those available under the trade name EPI-REZ by Hexion Inc., Columbus, OH.

[0031] Suitable liquid epoxy resins include those that are multifunctional and have an epoxy functionality of 2 or more. The liquid epoxy resins can include one or more novolac resins that can provide high crosslink density due to their high epoxy functionality.

[0032] The liquid epoxy resin can have a molecular weight of from 100 g / mol to 1000 g / mol, from 120 g / mol to 700 g / mol, from 150 g / mol to 500 g / mol, or in some embodiments less than, equal to, or greater than 100 g / mol, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 350, 400, 450, or 500 g / mol.

[0033] When dispersed in water, the particles of the second thermosetting resin can have a median primary particle size (D50) that is less than, equal to, or greater than 0.1-10, 0.2-7, 0.5-5, or in some embodiments, 0.05 micrometers, 0.1, 0.2, 0.5, 0.7, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, or 300 micrometers.

[0034] The liquid thermosetting resin can be present in an amount of from 5 percent to 40 percent, from 10 percent to 30 percent, from 10 percent to 25 percent, or in some embodiments, less than, equal to, or greater than 5 percent, 6, 7, 8, 9, 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, 37, or 40 percent, based on the total weight of the primer composition excluding volatile solvents.

[0035] The provided composition further contains a curing agent that can react with the first and second thermosetting resins under desired curing conditions, typically at the primer bake temperature. For extended storage stability, it is preferred that the curing agent is solid and insoluble in water, so that the reaction between the curing agent and the thermosetting resin during storage of the primer composition is minimized. Premature reaction between the curing resin and the thermosetting resin can result in viscosity and primer wetting problems during the melting and curing process, which is generally undesirable.

[0036] Suitable non-water-soluble curing agents include aromatic amines and mixtures thereof. 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'-diaminodiphenylsulfide, 3,3'- and 4,4'-diaminodiphenylketone, and 4,4'-[1,4-phenylene(1-methylethylidene)]-bis(benzeneamine).

[0037] The solid diamine curing agent includes 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. Particularly preferred are 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.

[0038] Preferred aromatic amines include 2,2-bis-[4-(4-aminophenoxy)-phenyl]propane, 2,2'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, and mixtures thereof. Options and advantages of the aforementioned curing agents can be found in U.S. Patent Nos. 5,641,818 (Sweet) and 6,475,621 (Kohli et al.).

[0039] In preferred embodiments, the solid hardener has a melting point of less than 250°F, less than 240°C, or less than 220°F.

[0040] The composition may further contain one or more curing agents and / or catalysts to promote the curing of the primer. These components may be water-soluble or water-insoluble. Suitable curing agents include water-soluble substituted aminotriazines (examples of which are commercially available under the trade name CUREZOL), modified polyamines available under the trade name ANCAMINE, dicyandiamide (DICY), bis-urea curing agents such as toluene-2,4-bis(N,N'dimethylurea) (available under the trade name OMICURE from Emerald Performance Materials LLC, Vancouver, WA), and water-insoluble amine-epoxy adducts and aromatic amines such as 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP).

[0041] The particulate hardener can have a median primary particle size (D50) that is less than, equal to, or greater than 0.05 micrometers to 300 micrometers, 0.2 micrometers to 200 micrometers, 1 micrometer to 100 micrometers, or in some embodiments, 0.05 micrometers, 0.1, 0.2, 0.5, 0.7, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 micrometers.

[0042] The water insoluble curing agent can be present in an amount less than, equal to, or greater than 0.5% to 40%, 5% to 30%, 10% to 20% by weight, or in some embodiments, 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 volatile solvents.

[0043] As mentioned above, the amount of coalescent solvent, if present, is preferably small. However, if present, the coalescent solvent preferably has an evaporation rate lower than that of water, but high enough to allow adequate film formation under a wide range of temperature and humidity conditions. The evaporation should be high enough so that the coalescent solvent is removed from the primer film during curing.

[0044] The composition may further contain any of a number of dyes, pigments, fillers, leveling agents, additional dispersants, thickeners, and corrosion inhibitors known in the art.

[0045] Corrosion inhibitors are chemical compounds that, when added to a primer composition, reduce the corrosion rate of the substrate to which the primer is applied. Corrosion can pose a major problem in aerospace applications where aircraft surfaces may be exposed to wet environments, acid rain, and thermal cycling. Useful corrosion inhibitors can be chromate-based corrosion inhibitors, or non-chromate corrosion inhibitors that are substantially free of chromium and chromium compounds.

[0046] Chromate-based corrosion inhibitors include strontium chromate, barium chromate, zinc chromate, calcium chromate, and combinations thereof. Non-chromate corrosion inhibitors include strontium aluminum polyphosphate hydrate, calcium phosphate, zinc phosphate, zinc molybdate, and zinc aluminum polyphosphate hydrate, and combinations thereof. Preferably, the provided primer composition can be formulated to be substantially or completely free of chromium and chromium compounds.

[0047] The corrosion inhibitor can be a particulate solid having a median primary particle size (D50 of 0.1 micrometers to 100 micrometers) and can be present in an amount of less than, equal to, or greater than 0.1 wt.% to 30 wt.%, 2 wt.% to 25 wt.%, 4 wt.% to 20 wt.%, or in some embodiments, 0.1 wt.%, 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 wt.%, based on the total weight of the primer composition excluding volatile solvents.

[0048] The primer composition can further comprise an inorganic filler. Useful inorganic fillers are not particularly limited, and their addition can help prevent sagging during the process of curing the primer composition. An exemplary inorganic filler is fumed silica, which can be used as a thickener to increase the viscosity of the primer composition when it is applied to the surface of the substrate to be protected.

[0049] In some embodiments, the inorganic filler is present in an amount less than, equal to, or greater than 0.01 wt.% to 15 wt.%, 0.5 wt.% to 2 wt.%, 1 wt.% to 5 wt.%, or in some embodiments, 0.01 wt.%, 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 volatile solvents.

[0050] Manufacturing method The provided primer compositions can be prepared by first dispersing a solid first thermosetting resin in water. In some embodiments, these resins are pre-dispersed in water. If not, the epoxy resins can be heated above their melting point or dissolved in a solvent to form a concentrated solution from which the solvent is subsequently removed. The resulting liquid epoxy resin or epoxy resin solution can be dispersed in water by extruding the epoxy into rapidly stirred water through a metal plate containing a large number of micron-sized holes, or by any other method known to those skilled in the art by slowly adding it under high shear agitation.

[0051] To maintain a stable emulsion in water, an effective amount of surfactant is generally added to the dispersion.Such surfactants contain both hydrophilic and hydrophobic (lipophilic) moieties and can include sodium and ammonium salts of long chain fatty acids, long chain fatty alcohol ethoxylates, alkylphenol ethoxylates or block polyoxyalkylene polyethers containing a hydrophobic moiety derived from repeating polyoxypropylene or polyoxybutylene groups or one or more long chain olefin oxide reaction products and a hydrophilic group containing repeating oxyethylene groups.

[0052] After the thermosetting resin is dispersed in the water phase, the curing agent is added. The curing agent can also be reduced to small particle size by known methods including spray drying, solution precipitation, ball milling, sand milling, air jet milling, etc. The fine curing particles can then be added to the resin dispersion and stirred until a uniform mixture is obtained. Alternatively, it may be advantageous to process the solid curing particles into finer particles while dispersed in the thermosetting resin dispersion. Such processing can be achieved by milling or any other method known in the art.

[0053] Before or after adding the curing agent, other additives such as dyes, pigments, corrosion inhibitors, etc. can be added and thoroughly mixed into the thermosetting resin and curable emulsion to complete the primer composition.

[0054] How to use The provided primer composition can be coated on a given substrate using any known method. For aerospace primers, it is common for the primer to be effectively applied via spray coating. The provided primer composition can be effectively sprayed using either air-driven or airless spray guns, such as high-volume, low-pressure spray guns known in the art.

[0055] Once the primer composition is applied to a substrate from an aqueous dispersion, the composition is allowed to dry. Drying removes water and other volatile materials from the composition and may occur under ambient or near ambient conditions without the need for heating. At ambient temperatures, drying times may be less than, equal to, or greater than 5 minutes to 300 minutes, 10 minutes to 100 minutes, 20 minutes to 50 minutes, or in some embodiments, 10 minutes, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 150, 200, 250, or 300 minutes.

[0056] Components that exist as particulate solids, such as the first thermosetting resin and the hardener, do not remain as stacked particles when the water is removed, but rather coalesce with one another when the liquid resin partially dissolves the solid resins in the composition. Thus, coalescence of the solid thermosetting resins can occur at least partially within the liquid thermosetting resin, resulting in the formation of a continuous film that significantly reduces or eliminates the appearance of a powdery surface texture.

[0057] Once sufficiently dried, the primed substrate can be heated to cure the primer composition, which is a reaction in which the first and second thermosetting resins react with the curing agent and with each other to form a crosslinked network. The cure temperature can be less than, equal to, or greater than 60°C to 200°C, 100°C to 180°C, 120°C to 180°C, or in some embodiments, 60°C, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200°C. The thickness of the cured primer can be less than, equal to, or greater than 1 micrometer to 20 micrometers, 2 micrometers to 10 micrometers, 3 micrometers to 8 micrometers, or in some embodiments, 1 micrometer, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 micrometers.

[0058] Bake times, like cure temperatures, can vary based on the application, but generally range from 0.1 hours to 6 hours, 0.5 hours to 2 hours, 0.7 hours to 2 hours, or in some embodiments, less than, equal to, or greater than 0.1 hours, 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.

[0059] Once a primer has been applied to a substrate, such as a metal adherend, a second adherend, such as a second metal substrate or a composite substrate, can be bonded to such primed substrate in the usual manner 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.

[0060] Further exemplary embodiments are provided below, which are not intended to be exhaustive.

[0061] 1. An aqueous primer composition comprising: a first thermosetting resin that is a particulate solid under ambient conditions; and a second thermosetting resin that is a liquid under ambient conditions and acts as a reactive coalescent in which the first thermosetting resin is at least partially soluble; a curing agent that is substantially water insoluble and reactive with the first and second thermosetting resins; An aqueous primer composition, the aqueous primer composition containing up to 4 percent of a volatile solvent other than water, based on the total weight of the aqueous primer composition.

[0062] 2. The aqueous primer composition described in embodiment 1, wherein the aqueous primer composition contains up to 3 percent volatile solvents other than water, based on the total weight of the aqueous primer composition.

[0063] 3. The aqueous primer composition according to embodiment 2, wherein the aqueous primer composition contains up to 2 percent of a volatile solvent other than water, based on the total weight of the aqueous primer composition.

[0064] 4. The aqueous primer composition of any one of embodiments 1 to 3, wherein the first and second thermosetting resins are dispersed in water by a surfactant to form an emulsion.

[0065] 5. The aqueous primer composition of any one of embodiments 1 to 4, wherein the first thermosetting resin comprises at least one epoxy resin.

[0066] 6. The aqueous primer composition of embodiment 5, wherein the at least one epoxy resin comprises a novolac epoxy resin.

[0067] 7. The aqueous primer composition of any one of embodiments 1 to 6, wherein the first thermosetting resin has a median primary particle size (D50) of 50 nanometers to 300 micrometers.

[0068] 8. The aqueous primer composition of embodiment 7, wherein the first thermosetting resin has a median primary particle size (D50) of 200 nanometers to 200 micrometers.

[0069] 9. The aqueous primer composition of embodiment 8, wherein the first thermosetting resin has a median primary particle size (D50) of 1 micrometer to 100 micrometers.

[0070] 10. The aqueous primer composition of any one of the preceding embodiments, wherein the first thermosetting resin is present in an amount of 20 weight percent to 70 weight percent, based on the total weight of the aqueous primer composition excluding the volatile solvent.

[0071] 11. The aqueous primer composition of embodiment 10, wherein the first thermosetting resin is present in an amount of 30 weight percent to 60 weight percent, based on the total weight of the aqueous primer composition excluding the volatile solvent.

[0072] 12. The aqueous primer composition of embodiment 11, wherein the first thermosetting resin is present in an amount of 30 weight percent to 55 weight percent, based on the total weight of the aqueous primer composition excluding the volatile solvent.

[0073] 13. The aqueous primer composition of any one of embodiments 1 to 12, wherein the second thermosetting resin comprises an epoxy resin.

[0074] 14. The aqueous primer composition of embodiment 13, wherein the second thermosetting resin is present in an amount of 5 weight percent to 40 weight percent, based on the total weight of the aqueous primer composition excluding the volatile solvent.

[0075] 15. The aqueous primer composition of embodiment 14, wherein the second thermosetting resin is present in an amount of 10 weight percent to 30 weight percent, based on the total weight of the aqueous primer composition excluding the volatile solvent.

[0076] 16. The aqueous primer composition of embodiment 15, wherein the second thermosetting resin is present in an amount of 10 weight percent to 25 weight percent, based on the total weight of the aqueous primer composition excluding the volatile solvent.

[0077] 17. The aqueous primer composition of any one of the preceding embodiments, wherein the curing agent comprises one or more of 2,2-bis-[4-(4-aminophenoxy)-phenyl]propane, 2,2'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenyl sulfone.

[0078] 18. The aqueous primer composition of any one of the preceding embodiments, wherein the curing agent is a particulate solid having a median primary particle size (D50) of 50 nanometers to 300 micrometers.

[0079] 19. The aqueous primer composition of embodiment 18, wherein the curing agent is a particulate solid having a median primary particle size (D50) of 200 nanometers to 200 micrometers.

[0080] 20. The aqueous primer composition of embodiment 19, wherein the curing agent is a particulate solid having a median primary particle size (D50) of 1 micrometer to 100 micrometers.

[0081] 21. The aqueous primer composition of any one of embodiments 1 to 20, further comprising fumed silica.

[0082] 22. The aqueous primer composition of embodiment 24, wherein the fumed silica is present in an amount of 0.5 weight percent to 2 weight percent, based on the total weight of the aqueous primer composition excluding volatile solvents.

[0083] 23. The aqueous primer composition of any one of embodiments 1-22, further comprising a corrosion inhibitor comprising one or more of strontium aluminum polyphosphate hydrate, zinc phosphate, zinc molybdate, and zinc aluminum polyphosphate hydrate.

[0084] 24. The aqueous primer composition of embodiment 23, wherein the corrosion inhibitor is a particulate solid having a median primary particle size (D50) of 0.1 micrometers to 100 micrometers.

[0085] 25. A method of providing a continuous primer film on a substrate, the method comprising: disposing an aqueous primer composition according to any one of embodiments 1-24 on the substrate; removing water from the aqueous primer composition; coalescing a first thermosetting resin within a second thermosetting resin; and reacting the first and second thermosetting resins with a curing agent to obtain a continuous primer film.

[0086] 26. A method for making an aqueous primer composition comprising the steps of: dispersing in water a first thermosetting resin, a second thermosetting resin that is liquid under ambient conditions and in which the first thermosetting resin is at least partially soluble, and a water-insoluble curing agent to obtain a resin emulsion, wherein the first thermosetting resin and the water-insoluble curing agent are particulate solids under ambient conditions; and processing the particulate solids to a median particle size of 50 nanometers to 300 micrometers for the thermosetting resin and 50 nanometers to 300 micrometers for the water-insoluble curing agent, wherein the aqueous primer composition contains up to 4 weight percent volatile solvent other than water, based on the total weight of the aqueous primer composition.

[0087] 27. The method of making the waterborne primer composition of embodiment 26, wherein processing the particulate solid comprises milling the particulate solid in the resin emulsion. EXAMPLES

[0088] 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.

[0089] [Table 1]

[0090] Test Method: Bare aluminum panels of grade 2024T3 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.

[0091] 2. Preparation of FPL Etched and Phosphoric Acid Anodized Aluminum Substrates 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 spray rinse with tap water for about 3 minutes. The panels were then immersed in Forest Products Laboratory (FPL) etchant at 66°C (151°F) for 10 minutes, after which the panels were spray rinsed with water at 21°C (69.8°F) for about 3 minutes. The etched panels were then anodized in a bath of 85% phosphoric acid at 22.2°C (72°F) for about 25 minutes, at a voltage of 15 volts and a maximum current of 100 amps, rinsed with water at 21°C (69.8°F) for about 3 minutes, drip dried for an additional 10 minutes, and then oven dried at 66°C (151°F) for 10 minutes. Within 24 hours of anodizing, the aluminum panels were primed with a primer composition as described in the Examples below, with the dried primer thickness being 2.5 micrometers to 5.1 micrometers (0.1 mil to 0.2 mil).

[0092] Floating Roller Peel (FRP) Strength Test for Adhesive Films Primed panels of 2024-T3 bare aluminum measuring 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) were prepared for testing as described above under "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 in a manner to eliminate trapped air and ensure intimate contact between the exposed adhesive and the test panel substrate. The primed panels were glued 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: 0.5 in. (1.27 cm) wide test specimens 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 in / min (30.5 cm / min) was used to peel the thinner substrate from the thicker substrate, and the results were normalized to a width of 1 in. Test panels were prepared and evaluated (one for each example).

[0093] Adhesive Curing Cycle The adhesive samples were vacuum bagged in an autoclave, model number "ECONOCLAVE3x5" from ASC Process Systems, Sylmar, California, to a pressure of approximately 28 inches of mercury. 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°F per minute before the pressure was released.

[0094] Scratch resistance The air-dried, uncured film surface adhered to the panel was rubbed with a finger or a dry white cloth to see if any film material remained after several rubs. If no film material remained, the sample passed.

[0095] Preparation example 1 (PE1): A pre-milled dispersion of solid hardener-epoxy was prepared as follows: 5.0 grams of M5 was uniformly dispersed in a mixture of 78.3 grams of WD-510, 302.3 grams of EPZ-3546, and 30.7 grams of EPZ-5108 using a high speed mixer operating at 1,000 rpm to 2,000 rpm for approximately 2 to 4 minutes at 25°C (77°C). 55.3 grams of BAPP was blended into the dispersion by continuing to run the mixer at 300 rpm to 500 rpm, followed by mixing 100 grams of distilled water and 0.32 grams of DC-29, and continued mixing until uniform. Milling was performed in a MINICER Laboratory Mill (obtained from Netzsch, Exton, PA, United States) using 0.5 mm yttria-stabilized zirconia milling media at 4,320 rpm and a flow rate of 250 ml / min. Particle size was measured using a PARTICA LA-950 laser diffraction particle size distribution analyzer (Horiba, Irvine Calif.). The median particle diameter at 50% of the cumulative distribution (also called D50) was 2.19 micrometers, and the particle diameter at 90% of the cumulative distribution, D90, was 3.64 micrometers.

[0096] Preparation example 2 (PE2): 80 grams of BAPP was dispersed in 320 grams of water and then milled. Milling was performed in a MINICER Laboratory Mill using 0.5 mm yttria stabilized zirconia milling media operating at 4,320 rpm and a flow rate of 250 ml / min. Particle size was measured using a PARTICA LA-950 laser diffraction particle size distribution analyzer as described above. After milling for 3 minutes, the dispersion thickened. 400 grams of water was then added to the mill hopper and the remaining sample was poured out. The final BAPP concentration was about 10%. The D50 was 10.18 micrometers and the D90 was 15.42 micrometers.

[0097] Example 1 and Comparative Examples 1 to 3 (EX1 and CE1 to CE3): The primer was prepared by dispersing the materials specified in Table 2.

[0098] [Table 2]

[0099] Example 1 (EX1) Using a high speed mixer operating at 1,000 rpm to 2,000 rpm, 11.2 grams of SAAP and 2.8 grams of ZAP were blended into 172 grams of PE1 for approximately 2 to 4 minutes at 25° C. After 5 minutes, 298.0 grams of water were added, followed by 5.9 grams of TDI and then 1.5 grams of Wetlink 78. Mixing was continued for an additional 15 minutes.

[0100] Comparative example 1 (CE1): 10.8 grams of EPZ-5108 and 13.5 grams of DER669 powder form produced by spray drying coating, 45.5 grams of PZ3903-2, 10.2 grams of BAPP, 3.0 grams of TDI urea, 1.8 grams of M5, 11.2 grams of SAAP, and 2.8 grams of ZAP were blended at 25° C. for about 2 to 4 minutes using a high speed mixer operating at 1,000 rpm to 2,000 rpm. 1.5 grams of Wetlink 78 were added and mixed. 181.2 grams of deionized water was added and the solids content was adjusted to 20%.

[0101] Comparative Example 2 (CE2): 11.2 grams of SAAP and 2.8 grams of ZAP were blended into 172 grams of PE1 using a high speed mixer operating at 1,000 rpm to 2,000 rpm for approximately 2 to 4 minutes at 25° C. 11.4 grams of IPA, 3.1 grams of acetone, and 0.93 grams of ARCOSOLV were added slowly over an interval of 3 to 5 minutes. After 5 minutes, 264.0 grams of water were added, followed by 5.9 grams of TDI, then 1.5 grams of Wetlink 78. Mixing was continued for an additional 15 minutes.

[0102] Comparative Example 3 (CE3): 10.8 grams of EPZ-5108 and 13.5 grams of DER669 powder form produced by spray drying coating, 45.5 grams of 3903-2, 102 grams of PE2, 3.0 grams of TDI urea, 1.8 grams of M5, 11.2 grams of SAAP, 2.8 grams of ZAPP, 14 grams of acetone, 14 grams of 2-propoxyethanol, and 17 grams of IPA were blended for about 2 to 4 minutes at 25° C. using a high speed mixer operating at 1,000 rpm to 2,000 rpm. 1.5 grams of Wetlink 78 were added, mixed, and 136.0 grams of deionized water was added to adjust the solids to 20%.

[0103] Primer composition samples were sprayed onto aluminum panels and cured. The primers were also aged for 7 days at 90°F to test the primer performance with FRP. The results for the mar resistance and FRP tests are shown in Tables 3 and 4.

[0104] [Table 3]

[0105] [Table 4]

[0106] 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. 1. An aqueous primer composition comprising: a first thermosetting resin that is a particulate solid under ambient conditions; a second thermosetting resin that is liquid under ambient conditions and acts as a reactive coalescent in which the first thermosetting resin is at least partially soluble; a curing agent that is substantially water insoluble and reactive with the first and second thermosetting resins; the aqueous primer composition contains up to 4 percent, based on the total weight of the aqueous primer composition, of a volatile solvent other than water; The first thermosetting resin is contained in the aqueous primer composition as solid particles. Aqueous primer compositions.

2. The waterborne primer composition of claim 1 , wherein the first and second thermosetting resins are dispersed in water by a surfactant to form an emulsion.

3. The aqueous primer composition of claim 1 or 2, wherein the first thermosetting resin comprises at least one epoxy resin.

4. The aqueous primer composition of any one of claims 1 to 3, wherein the first thermosetting resin has a median primary particle size (D50) of 50 nanometers to 300 micrometers.

5. The aqueous primer composition according to any one of claims 1 to 4, wherein the first thermosetting resin is present in an amount of 20 weight percent to 70 weight percent, based on the total weight of the aqueous primer composition excluding volatile solvents.

6. The aqueous primer composition according to any one of claims 1 to 5, wherein the second thermosetting resin comprises an epoxy resin.

7. The aqueous primer composition of claim 6, wherein the second thermosetting resin is present in an amount of from 5 weight percent to 40 weight percent, based on the total weight of the aqueous primer composition excluding volatile solvents.

8. The aqueous primer composition of any one of claims 1 to 7, wherein the curing agent comprises one or more of 2,2-bis-[4-(4-aminophenoxy)-phenyl]propane, 2,2'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenyl sulfone.

9. 9. The aqueous primer composition of claim 1, wherein the curing agent is a particulate solid having a median primary particle size (D50) of 50 nanometers to 300 micrometers.

10. 1. A method for providing a continuous primer film on a substrate, comprising: disposing the aqueous primer composition according to any one of claims 1 to 9 on the substrate; removing water from the aqueous primer composition; Coalescing the first thermosetting resin within the second thermosetting resin; reacting said first and second thermosetting resins with a curing agent to obtain said continuous primer film.

11. A method for producing an aqueous primer composition, comprising the steps of: dispersing a first thermosetting resin, a second thermosetting resin that is liquid under ambient conditions and in which the first thermosetting resin is at least partially soluble, and a water-insoluble curing agent in water to obtain a resin emulsion, wherein the first thermosetting resin and the water-insoluble curing agent are particulate solids under ambient conditions; processing the particulate solids to a median particle size of 50 nanometers to 300 micrometers for the thermosetting resin and to a median particle size of 50 nanometers to 300 micrometers for the water-insoluble curing agent; the aqueous primer composition contains up to 4 percent by weight of a volatile solvent other than water, based on the total weight of the aqueous primer composition; The first thermosetting resin is contained in the aqueous primer composition as solid particles. Manufacturing method.

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