Patent Application
20220049358
The present invention relates to particles having a chemical conversion coating, substrates treated with such particles, and substrates having a conversion coating.
Outdoor structures such as wind turbines, bridges, towers, tanks, pipes and fleet vehicles such as railcars, buses, and trucks are constantly exposed to the elements and must be designed to endure temperature extremes, wind shears, precipitation, and other environmental hazards without significant damage or the need for constant maintenance, which may be time-consuming and costly. Likewise, marine structures such as ship hulls and off-shore oil rigs and wind turbines are also exposed to seawater as well as extreme weather and other environmental conditions, making them susceptible to corrosion. Chemical storage transport or processing tanks or pipes such as fuel tanks and pipe linings are also vulnerable to corrosion and/or coating attack by aggressive chemicals being carried within. More effective treatment and coating systems are continually being sought to meet the specification demands of these industrial structures.
The present invention is directed to a particle having a chemical conversion coating on at least a portion of the particle surface. The present invention is further directed to a substrate comprising a surface that has been contacted with a particle having a chemical conversion coating on at least a portion of the particle surface such that at least some portion of the substrate becomes treated with the conversion coating. The present invention is further directed to a substrate comprising a conversion coating deposited on at least a portion thereof, wherein the conversion coating is substantially free, essentially free, or completely free of fluorine as determined by X-Ray Fluorescence (“XRF”). The present invention is further directed to a substrate comprising a conversion coating deposited on at least a portion thereof, wherein the conversion coating forms a continuous layer, a semi-continuous layer, or semi-continuous deposits, and wherein the conversion coating has a barrier per coating layer thickness of 1.3×108 to 6.9×109 Ω-cm (Ohms×area/coating layer thickness) as determined by electrochemical impedance spectroscopy. The present invention is further directed to a substrate comprising a conversion coating deposited on at least a portion thereof, wherein the conversion coating has a shattered crystalline morphology. Articles comprising such substrates are also within the scope of the invention as are methods for making the same.
The present invention is directed to particles having a chemical conversion coating on at least a portion of the particle surface. A “chemical conversion coating” is a crystalline, amorphous, or semi-crystalline layer formed on the surface via a chemical process that reacts with the surface. Stated another way, the present invention is directed to a particle having a crystalline, amorphous, or semi-crystalline inorganic layer found on at least a portion of the particle surface via a chemical process whereby the layer is chemically attached to the surface of the particle.
Suitable particles include but are not limited to metallic, plastic, glass, biobased, polymeric, and/or carbon based particles, particular examples of which may include shot or grit made from silica, sand, alumina, zirconia, zirconate, barium titanate, calcium titanate, sodium titanate, titanium oxide, glass, biocompatible glass, diamond, garnet, coal slag, silicon carbide, boron carbide, boron nitride, calcium phosphate, calcium carbonate, metallic powders, carbon fiber composites, polymeric composites, titanium, stainless steel, hardened steel, carbon steel chromium alloys, galvanized steel, iron silicate, Black Beauty, starblast, garnet, plastic, or any combination thereof. The use of glass particles may be excluded. Any particle size can be used according to the present invention and can be chosen depending on the needs of the user. For example, the particles may have an average particle size as measured by SAE size number, U.S. mesh size, and/or U.S. Standard screen size. Using U.S. mesh size and/or U.S. Standard screen size, particle size can be within the range of 0.050 mm up to 3 mm. Particles may be referred to herein as “grit” or “shot”.
The particle is treated so as to impart a chemical conversion coating onto at least a portion of the surface of the particle. According to the present invention, at least a portion of the surface of the particle is chemically modified with a conversion coating; the conversion coating is chemically attached to the particle. Chemical attachment can occur, for example, through covalent bonding, ionic bonding and/or hydrogen bonding. Because the conversion coating is chemically attached to at least a portion of the surface of the particle, it will be appreciated that the particles according to the present invention are distinct from particles in which a metal, corrosion inhibitor or other material is mechanically or physically attached to the particle surface. Examples of mechanical or physical attachment include “gluing” the material to the particle, such as with a resin, binder or coating, using electrostatic attraction to associate the material and particle, and the like. The chemical conversion coating may be chemically attached to the particle through a spontaneous chemical reaction, which will be understood by those skilled in the art as referring to a reaction that occurs under a given set of conditions without intervention; if the Gibbs Free Energy of the reaction is negative, the reaction is spontaneous.
The particles according to the present invention can be made, for example, by treating the particles in a manner similar to which metal parts are pretreated with a spontaneously deposited conversion coating. For example, particles may be exposed to a solution comprising zinc, such as zinc phosphate, iron, such as iron phosphate, zirconium, titanium, chromium, chromate, fluoride, magnesium, molybdenum, cerium, strontium, calcium, and/or metalloids such as silicon. Following exposure for a sufficient time, the conversion coating chemically modifies at least a portion of the surface of the particle (it being appreciated that a longer exposure time may result in a more highly concentrated chemical composition of the conversion coating). Two or more conversion coatings may be used to treat the particle surface. Use of fatty acids to treat the particles may be specifically excluded.
The particles can optionally be rinsed, such as with DI water, and then dried, such as in an oven or other forced air dryer. Depending on the chemical conversion coating, an activator to assist with the formation of the conversion coating may be used. A rinse conditioner, such as a titanium solution, Jernstedt salt, or zinc phosphate dispersion, commercially available from PPG Industries, Inc. as VERSABOND RC, may be used to rinse the particles prior to modifying the surface with the chemical conversion coating. For example, if the chemical conversion coating is zinc phosphate, an activator for zinc phosphate crystals, such as Jernstedt salt, may be dissolved to make a water mixture. The conversion coating may also be chemically attached to the particles using an electric current. In this method, opposing electrodes are included in a bath containing the particles and the chemical composition to create the conversion coating. Passing the electric current through the bath causes the surface of the particle to be chemically modified with a conversion coating. An organic or inorganic material can be deposited on the particle. The particles can then be dried as described above. Magnesium can be effectively attached chemically to particles in this manner. It will be appreciated that certain conversion coatings will be passivating, while others may not. “Passivating”, as used herein, means a non-reactive surface film that inhibits further corrosion. Passivating film can be, for example, a metal oxide that is formed on the surface of a material.
Plasma deposition as well as chemical vapor deposition can also be used to chemically modify the surface of the particles. In plasma-enhanced chemical vapor deposition, a plasma is generated by DC discharge between two electrodes, the space between which is filled with the reacting gases. When a high-density plasma is used, the ion density can be high enough that significant sputtering of the chemical conversion coating occurs; this sputtering can be employed to help planarize the conversion coating and fill trenches or holes in the surface of the particles.
Mixtures of particles may also be used according to the present invention. For example, mixtures of any of the above treated particles can be used. In addition, a mixture of one or more treated particles may be used in conjunction with one or more untreated particles.
The present invention is further directed to a substrate comprising a surface that has been contacted with a particle having a chemical conversion coating on at least a portion of the particle surface such that at least some portion of the substrate becomes treated with the conversion coating. The substrate surface may have a coating layer thickness of, for example, 1 nanometer to 5 microns following treatment, such as 1 to 100 nanometers or 1 to 50 nanometers. The treated substrate may further comprise one or more film-forming layers on at least a portion of the treated surface.
Suitable substrates for use in the present invention include rigid metal substrates such as ferrous metals, aluminum, aluminum alloys, copper, brass, and other metal and alloy substrates. The ferrous metal substrates used in the practice of the present invention may include iron, steel, and alloys thereof. Non-limiting examples of useful steel materials include hot and cold rolled steel, galvanized (zinc coated) steel, electrogalvanized steel, stainless steel, pickled steel, and combinations thereof. Use of titanium as a substrate may be excluded. Profiled metals such as profiled steel are also suitable. By “profiled” is meant that the substrate surface has been physically modified such as by mechanically or chemically etching, abrading such as by sanding or blasting, carving, brushing, hammering, stamping, or punching, to affect the topography of the metal surface. Combinations or composites of ferrous and non-ferrous metals can also be used. For clarity, “profiled” as used in this context refers to substrates that have undergone some physical modification prior to being contacted with the particles as described herein; it will be appreciated that treatment according to the present invention will also change the profile of the substrate.
Before treating the surface of the substrate with the particles, it is common practice, though not necessary, to remove foreign matter from the substrate by cleaning and degreasing the surface. Such cleaning typically takes place after forming the substrate (stamping, welding, etc.) into an end-use shape. The surface of the substrate can be cleaned by physical or chemical means, such as mechanically abrading the surface or cleaning/degreasing with commercially available alkaline or acidic cleaning agents that are well known to those skilled in the art, such as sodium metasilicate and sodium hydroxide. A non-limiting example of a cleaning agent is CHEMKLEEN 163, an alkaline-based cleaner for metal substrates commercially available from PPG Industries, Inc.
Following the cleaning step, the substrate may be rinsed with deionized water or an aqueous solution of rinsing agents in order to remove any residue. The substrate can be air dried, for example, by using an air knife, by flashing off the water by brief exposure of the substrate to a high temperature or by passing the substrate between squeegee rolls.
The substrates of the present invention may comprise (a) at least one surface of the substrate that has been treated with the particles of the present invention. “Treated”, as used in this context, means the conversion coating is present within the top 20 microns of at least a portion of the substrate surface and may also be intimately intermixed with the metal of the surface. The conversion coating may also extend onto or above the metal surface.
Treatment of the substrate surface occurs by contacting the surface with the particle having a chemical conversion coating. The particle, to which the conversion coating is chemically attached or bonded, is contacted with the surface to be treated. It was surprisingly discovered that if the contact is performed at sufficient force it causes the chemical bond between the conversion coating and particle to break, while also allowing for a chemical bond to form between the conversion coating and the substrate impacted by the treated particle. In this manner, the conversion coating is “transferred” from the particle to the surface of the substrate to be treated. This represents an advantage over certain methods reported in the art in which a binder or the like is used to coat the particles and attach a material thereto; in those methods, the binder as well as the material gets transferred to the substrate surface. It has been surprisingly discovered that the morphology of a substrate treated with the particles of the present invention is different from that of a substrate exposed to a conversion coating in a conventional manner, such as immersion. When a crystalline conversion coating is used, the conversion coating maintains its crystallinity on the particle. During blasting of the surface, however, the crystals of the conversion coating may shatter; the shattered crystals may appear to become “fused” or melded/melted on or into the blasted surface. This may happen through high kinetic impact. While the shattered crystals may themselves be crystalline, they are smaller crystals than on the particle surface before blasting. Accordingly, the present invention is also directed to a substrate comprising a conversion coating deposited on at least a portion thereof, wherein the conversion coating has a shattered crystalline morphology.
The conversion coating and the particles may be different material; this distinguishes over methods of applying a layer of metal, such as a protective metal, to a substrate by impinging the substrate with a particle wherein at least the outer surface of the particle is made from the metal that is to be applied to the substrate surface.
The contacting step may result in the formation of a continuous layer, a semi-continuous layer, or semi-continuous deposits of the conversion coating, or some altered form of the conversion coating, on the outermost surface of the substrate. For example, if the conversion coating is magnesium based, a semi-continuous surface layer containing magnesium and oxide may be formed. A “continuous layer” refers to an unbroken layer of conversion coating. A “semi-continuous layer” is one that is broken; that is, the layer is not continuous across the whole surface. “Semi-continuous deposits” refer to irregular deposits that are not part of the continuous layer. It will be appreciated that the layer may have variable thickness and thus appear semi-continuous when it is in fact continuous. When a continuous or semi-continuous layer is formed on the substrate, the layer can have a thickness that is uniform or a thickness that is variable; that is, the layer will have a different thickness at different locations on the treated substrate. The thickness of the layer, sometimes referred to herein as “coating layer thickness” may range from one nanometer to five microns, and may be 1 to 100 nanometers, such as one to 50 nanometers, in some locations. Thickness is determined using SEM and/or TEM, as further described in the examples. It will be appreciated that this thickness may be much thinner in at least certain locations than the thickness of a conversion coating when applied in a conventional manner (such as spraying or immersion) in which the layer is typically uniform and has a thickness typically one micron or thicker. Notably, equal or better corrosion protection is offered by the current substrates even though the coating layer thickness may be variable and notably thinner in at least some spots.
The present invention is further directed to a substrate comprising a conversion coating deposited on at least a portion thereof, wherein the conversion coating forms a continuous layer or a semi-continuous layer and the layer can be substantially free, essentially free, or completely free of fluorine as determined by XRF. As used in this context, “substantially free” of fluorine means less than 0.2 wt. %, “essentially free” of fluorine means 0.15 wt. % or less, and “completely free” of fluorine means undetectable amount of fluorine. The wt. % here is based on the total weight of the coating layer that is deposited on the substrate. These fluorine contents may be achieved, for example, when the substrate comprises aluminum and the conversion coating comprises zirconium.
The contacting with the surface of the substrate with the particles can be done, for example, by blasting. In blasting, the particles may be delivered from one or more fluid jets at high speed, bombarding the surface of the substrate. The fluid jet may be generated, for example, from wet blasters or abrasive water jet peening machines operating at a pressure ranging from 0.5 to 100 bar, such as a pressure ranging from 1 to 30 bar, or a pressure ranging from 1 to 10 bar. Alternatively, the fluid jet may be generated from grit blasters, sand blasters, or micro-blasters, operating at a pressure ranging from 0.5 to 100 bar, such as a pressure ranging from 1 to 30 bar, or a pressure ranging from 3 to 10 bar. The blasting can also be done by air blasting or wheel abrador. Contacting the surface of the substrate with the particles can be done repeatedly; that is, more than one blasting step can occur. Two or more blasting steps may be done using the same type of particle, or may be done using different particles. The particles used in any step may be untreated particles.
According to the present invention, the particles having a chemical conversion coating can be used repeatedly. That is, such particles can be prepared as described above, used to blast a substrate, collected, and used in another blasting step for the same or a different substrate. The present particles can be reused any number of times, provided the desired amount of conversion coating is transferred to the substrate during each use. The amount of conversion coating transferred to the substrate can be determined using XRF. In the case of zinc, for example, a desired amount of conversion coating may be, for example, 2000 counts to as little as 200 counts of Zn measured by XRF for 30 seconds with the Dpp setting at 1.1 μS at 15 kb and 45 μA using counts at the Kα peak of 8.64 keV. When the particles are no longer delivering the desired amount of conversion coating to the substrate, they can be re-treated.
The transfer of a conversion coating to the substrate surface with particles whose surface has the chemical conversion coating according to the present invention may enhance the corrosion and/or chemical protection of the substrate surface. Profiling of the substrate surface prior to or simultaneously with deposition of the conversion coated particles, such as by chemical etching, may enhance transfer of the conversion coating onto the substrate surface (that is, the surface could be profiled). Also, a conversion coating and adhesion promoter may both be used, and delivered at substantially the same time on the same or different particles, and/or delivered sequentially on different particles.
Jet velocity, operating pressure, venturi configuration, angle of incidence and/or nozzle-to-surface distances may affect the extent of transfer of the conversion coating onto the substrate surface. Additionally, the size, shape, density and hardness of the particles used may also have an effect on the extent of the transfer of the conversion coating onto the surface of the substrate. The fluid stream itself, the blasting equipment using a gas medium (typically air), and/or the effects of using inert gases as a carrier fluid (e.g. N2 or noble gases such as Ar and He) may also influence the extent of transfer of the conversion coating onto the substrate surface.
It will be appreciated that contacting the surface of the substrate with the particles of the invention will cause the profile of the surface to change. The “profile” of the substrate refers to the difference between the highest and lowest points of the surface. Contacting the surface with the particle according to the present invention may cause this difference to increase. The amount of increase depends on, for example, the size of the particles, the velocity of impingement, the length of time impinged, and the like. The substrates according to the present invention may demonstrate a cross-sectional profile of 0.1 to 5 mils (2.54 to 127 microns) as determined by ASTM D4417-14: Standard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steel (2014). The substrates of the present invention may, for example, have a cross-sectional profile of less than 1.5 mils (38.1 microns), such as 1 to 1.3 mils (25.4 to 33.0 microns), prior to application of the film-forming composition, although the profile of the surface can be even higher, such as up to 5 mils.
Particles with a conversion coating can be incorporated into bonded abrasives such as grinding wheels, grinding cups, vitrified bond mounted points. Particles with a conversion coating can also be incorporated into coated abrasives where the particle is bonded to a flexible mounting surface such as paper, cloth, plastic film, or vulcanized fiber. Bonded abrasives and coated abrasives can be used to grind, resurface, or polish the surface of the substrate. When sufficient force is applied to the substrate when in contact with the particle or vice versa, this contact may result in the formation of a continuous layer, a semi-continuous layer, or non-continuous deposits of the conversion coating on the substrate surface.
Performance data of substrates according to the present invention is also better than conventionally treated substrates. It has been surprisingly discovered that substrates treated according to the present invention may also exhibit increased barrier as compared to conventionally treated substrates. Accordingly, the present invention is further directed to a substrate comprising a conversion coating deposited on at least a portion thereof, wherein the conversion coating forms a continuous layer, a semi-continuous layer, or semi-continuous deposits, and wherein the conversion coating has a barrier per thickness of 1.3×108 to 6.9×109 Ω-cm (Ohms×area/coating layer thickness) as measured by electrochemical impedance spectroscopy. Values are given in relation to layer thickness to account for the variability of layer thickness that can be achieved on the substrate.
A substrate may have one continuous surface, or two or more surfaces such as two opposing surfaces. Typically the substrate surface that is treated is any that is expected to be exposed to conditions susceptible to corrosion and/or chemical damage. Examples of particular substrates include a structure, a vehicle, or industrial protective structure such as an electrical box enclosure, transformer housing, or motor control enclosure; a railcar container, tunnel, oil or gas industry component such as platforms, pipes, tanks, vessels, and their supports, marine component, automotive body part, aerospace component, pipeline, storage tank, or wind turbine component. “Structure” as used herein refers to a building, bridge, oil rig, oil platform, water tower, power line tower, support structures, wind turbines, walls, piers, docks, levees, dams, shipping containers, trailers, and any metal structure that is exposed to a corrosive environment. “Vehicle” refers to in its broadest sense all types of vehicles, such as but not limited to cars, trucks, buses, tractors, harvesters, heavy duty equipment, vans, golf carts, motorcycles, bicycles, railcars, airplanes, helicopters, boats of all sizes and the like. Medical devices may be specifically excluded from the substrates of the present invention.
In particular examples of the present invention, the substrate comprises chemical storage, transport or processing pipes and/or tanks such as a fuel tank, a railcar tank used to store and transport, for example, oils and other hydrocarbons, and pipes used to transport gas, oils and other hydrocarbons, water and other liquids. The surface of the tank and/or pipe treated with a conversion coating may be an internal surface and/or external surface of the tank or pipe. Magnesium has been found to be a particularly effective for treating the inside of tanks, as has zirconium-based conversion coatings, particularly when the storage tank is used for alcohol-based solvents, water, and palm oil fatty acid solutions; after being treated with the particles, a coating, such as an epoxy-amine tank liner may be applied. The tank and pipe may be made of steel, ferrous metals or non-ferrous metals.
The substrates treated according to the present invention may optionally be coated with one or more coating layers. For example, at least one film-forming layer (b) may be applied to at least a portion of the treated substrate surface. The film-forming layer can be deposited from a film-forming composition; the film-forming composition may be curable. Suitable film-forming compositions may be a liquid, such as a solventborne or waterborne liquid, or 100 percent solids, or may be solid, particulate powders. The liquid coatings may be electrodepositable; that is, it can be applied by electrodeposition. The term “curable”, as used for example in connection with a curable composition, means that the indicated composition is polymerizable or cross linkable through functional groups, e.g., by means that include, but are not limited to, thermal (including ambient cure) and/or catalytic exposure, or through evaporation, coalescence, oxidative crosslinking and the like. The term “cure”, “cured” or similar terms, as used in connection with a cured or curable composition, e.g., a “cured composition” of some specific description, means that at least a portion of the polymerizable and/or crosslinkable components that form the curable composition is polymerized and/or crosslinked. Additionally, curing of a polymerizable composition refers to subjecting said composition to curing conditions such as but not limited to thermal curing, leading to the reaction of the reactive functional groups of the composition. The film-forming layer may be thermoset or thermoplast. Thermoset refers to components that crosslink or “set” while thermoplast (also referred to as “thermoplastic”) refers to resins that do not become joined by covalent bonds and can undergo liquid flow upon heating and/or become soluble in solvents.
Any suitable film-forming composition can be used according to the present invention. As used herein, the term “film-forming composition” refers to a composition, typically comprising one or more film-forming resins, that can form a self-supporting continuous film on at least a horizontal surface of a substrate upon removal of any diluents or carriers present in the composition or upon curing at ambient or elevated temperature.
Film-forming resins that may be used in the present invention include, without limitation, those used in automotive OEM coating compositions, automotive refinish coating compositions, industrial coating compositions, architectural coating compositions, coil coating compositions, packaging coating compositions, protective and marine coating compositions, and aerospace coating compositions, among others.
Examples of film-forming resins suitable for use in the coating compositions of the present invention include, for example, resins based on acrylic, saturated or unsaturated polyester, alkyd, polyurethane or polyether, polyvinyl, polyurea, cellulosic, silicon-based polymers including polysiloxanes, and co-polymers thereof, which resins may contain reactive groups such as epoxy, carboxylic acid, hydroxyl, isocyanate (including blocked isocyanate groups), amide, carbamate, amine and carboxylate groups, thiol groups, urea groups, among others, including mixtures thereof.
Combinations of film-forming resins can be used. For example, the additional film-forming resin included in the epoxy coating compositions that may be used in the present invention may comprise a resin with functionality that will cure with the amine, or alternatively, one or more additional crosslinkers can be used. Suitable crosslinkers can be determined by those skilled in the art based on the additional resin(s) chosen.
The film-forming composition may be intumescent; i. e., it may swell or char when exposed to a flame, thus exhibiting flame retardant properties. The film-forming composition may be electrodeposited by anodic or cathodic processes and contain acrylic and/or epoxy resins. The film-forming composition may be a thermoplastic powder. The thermoplastic powder composition may contain vinyl resins such as PVC and/or PVDF and/or polyolefinic resins for example polyethylene and polypropylene. Furthermore, the thermoplastic powder composition may contain nylon based (i.e. polyamide) resin as well as polyester reins. The film-forming composition may be a thermoset powder. Thermoset powder compositions may contain epoxy and/or novolac epoxy resins with functional groups containing but not limited to carboxylic acid functionality, amine functionality, acid anhydrides, dicyandiamide, and/or phenolic functionality. Thermoset powder compositions may also contain polyester resins with hydroxyl functionality and/or carboxylic functionality. Thermoset powder compositions may also contain acrylic resins with GMA functionality, hydroxyl functionality, and/or carboxylic functionality. Thermoset powder composition may also contain silicone-based polyesters. Thermoset and thermoplastic powder compositions may be applied electro-statically and/or by thermal spray.
In particular examples of the present invention, the film-forming composition may comprise a polysiloxane, alone or in combination with an epoxy resin; a polyurethane; a polyepoxide, a polyester, a polyaspartic functional polymer, and/or a polyurea. Epoxy resins used in the film-forming compositions may be polyepoxides. Epoxy resins are often used in a pigmented primer and/or a pigmented coat or topcoat composition.
An example of a commercially available film-forming composition comprising a polysiloxane is PSX 700 (commercially available from PPG), an engineered siloxane coating that also contains some epoxy resin, manufactured according to U.S. Pat. Nos. 5,618,860 and 5,275,645. Suitable film-forming compositions comprising polyurethane include SPM76569, a direct-to-metal coating composition available from PPG; W43181A, a polyurethane primer available from PPG; and HPP2001, a high-performance polyurethane primer available from PPG. Suitable pigmented polyepoxide compositions include AMERLOCK 400, an epoxy primer available from PPG; PHENGUARD 930/935/940 and NOVAGUARD 840, epoxy tank liners available from PPG; and SEP74860, an epoxy primer available from PPG. In some cases, such as when the film-forming composition comprises a polysiloxane and optionally a polyepoxide, the composition may be applied directly to the impregnated surface with no intervening layer. The performance may be comparable if not better than that observed with a substrate that has been treated with an epoxy primer and the same polysiloxane top coat applied in a conventional manner.
The film-forming composition in contact with the impregnated surface typically demonstrates a pigment to binder ratio (P:B) of 0.1:1 to 35:1, such as 0.5:1 to 3.0:1. When the coated substrate comprises a storage tank lining the film-forming composition can have a pigment volume concentration of 10 percent by volume to 50 percent by volume, such as 14 percent by volume to 40 percent by volume. The film-forming composition can be a clear coat, with less than 5 percent by volume, such as less than 2 or less than 1 percent by volume, of pigment, or no pigment at all (i.e. 0 percent by volume).
The film-forming composition applied to the treated surface may comprise a pre-fabrication shop coating or shop primer that is intended to provide protection during manufacturing and/or transport of an article. A shop primer or pre-fabrication primer is a temporary coating that is intended to provide protection from corrosion as a result of the elements or damages and scratches and the like. In many cases this pre-fabrication primer or shop primer is maintained as part of the final coating system. In highly demanding systems, like tank coatings for aggressive chemicals or potable water, these primers may be removed. An example of such a coating is a shop primer or holding primer, which optionally comprises a silicate. The pre-fabrication shop coating or shop primer may be left in place or may be a temporary coating that is removed prior to application of a permanent coating; i. e., the film-forming composition (b).
The coated substrates of the present invention may further comprise (c) a second film-forming layer on top of at least a portion of the film-forming layer (b). The second film-forming layer may be deposited from a composition that is pigmented or clear. As with the first film-forming composition, the second film-forming composition may be any suitable film-forming composition, such as those described above. In a particular combination, the first film-forming composition may comprise zinc and the second film-forming composition may comprise a polysiloxane and optionally epoxy resin. Film-forming compositions that contain zinc include inorganic zinc coatings that may further comprise silicate, and zinc-rich primer coatings that further comprise an organic material such as an epoxy resin. Zinc-rich compositions typically comprise at least 40 percent by weight zinc metal, such as 50 to 95 percent by weight. AMERCOAT 68HS, available from PPG, is an example of a commercially available zinc-rich primer coating with a polyepoxide. Any number of coating layers can be applied to one substrate. When two or more coating layers are deposited, the two layers may be the same or different. The first coating composition may be completely or partially cured before application of the second coating composition, or may be applied “wet on wet” with little or no cure or only an air dry step between applications of the two coating layers.
In other particular coating layer combinations, the first film-forming composition comprises an epoxy resin, particularly one derived from Bisphenol A and/or Bisphenol F (or novolac) and optionally zinc, and the second film-forming composition comprises a polyurethane; or the first film-forming composition comprises a polyepoxide derived from Bisphenol A and/or Bisphenol F (or novolac) and optionally zinc, and the second film-forming composition comprises a polysiloxane and a polyepoxide. A polyurethane topcoat designed for automotive refinish and available from PPG as AUE-370, is particularly suitable over a primer comprising a polyepoxide such as CRE-321, available from PPG.
When curable compositions are used in the present invention, they can be prepared as a two-package composition (but not necessary), typically curable at ambient temperature. Two-package curable compositions are typically prepared by combining the ingredients immediately before use, or can be applied by dual feed equipment as well. They can also be prepared as one-package curable compositions.
The compositions may be applied to the treated substrate surface by one or more of a number of methods including spraying, electrodeposition, dipping/immersion, brushing, and/or flow coating. For spraying, the usual spray techniques and equipment for air spraying, airless spraying, electrostatic spraying, and thermal spray and either manual or automatic methods can be used. The coating layer typically has a dry film thickness of a broad range, such as anywhere from 5 microns to 25.4 mm, depending on the particular industrial application. For example, an intumescent coating may have a dry film thickness of 500 to 1000 mils (12.7 to 25.4 mm). A pre-fabrication shop coating or shop primer may have a dry film thickness of 5 to 30 microns. A tank lining system may range from 60 to 1200 microns depending on the chemistry, such as 300 to 400 microns. A dry film thickness of 1000 to 1200 microns is typical for a tank lining system comprising a polyepoxide. An electrocoat may have a dry film thickness of 10 microns to 35 microns. In general, the dry film thickness of the coating may range from 2-25 mils (50.8-635 microns), often 5-25 mils (127-635 microns).
After forming a film of the coating on the substrate, the composition can be cured if necessary by allowing it to stand at ambient temperature, or a combination of ambient temperature cure and baking; UV light cure could also be used depending on the coating chemistry. The composition can be cured at ambient temperature typically in a period ranging from 4 hours to as long as 2 weeks. If ambient humidity is below 40 percent relative humidity then cure times may be extended.
The coated substrates of the present invention may demonstrate corrosion resistance, enhanced adhesion, blister resistance, chemical resistance, and/or temperature resistance (i. e., resistance to damage by extreme temperatures) as compared to substrates that have not been treated as described herein. They are applicable, for example, for use on a substrate surface (such as a ship hull or offshore oil rig) that is to be in contact with water, including seawater. Additionally, the coated substrate may demonstrate resistance to aggressive chemicals as determined by chemical immersion testing in accordance with ISO 2812-1:2007 and/or ASTM D6943-15 (2015). Examples of aggressive chemicals include acids such as fatty acids, alcohols, and hydrocarbons, combinations and sequences thereof.
The coated substrates of the present invention may be prepared in a batch, or step-by-step process. The present invention is further directed to a continuous process for preparing a coated substrate, comprising: (i) contacting at least one surface of the substrate with particles having a chemical conversion coating as described herein as the substrate moves along a conveyor, such that the conversion coating on the particles transfers to at least a portion of the substrate surface; (ii) applying a pre-fabrication shop coating or shop primer or other coating to the treated substrate surface as the substrate moves along a conveyor to form a coated substrate. The steps of treating the substrate and applying the film-forming composition may be adapted to an existing continuous production line for manufacturing an industrial article. Substrates according to the present invention may also be all or a portion of an existing structure or a vehicle. Repainting of such structures/vehicles typically occurs in the field and may include the removal of one or more existing coating layers prior to treatment as described herein. Such paint removal may be done by blasting the surface with an abrasive particle. According to the present invention, such a substrate can be blasted first with particles alone and then with the particles to which the conversion coating is chemically attached according to the present invention to remove the existing paint and/or oxide layer in a first step and impregnate the surface with the conversion coating in a second step, or the particle having the conversion coating can be delivered so as to remove the existing paint and/or oxide layer and impregnate the surface with conversion coating in one step.
Although any conversion coating can be used with any first and optionally second coating layer, some particular combinations demonstrate particularly unexpected results with respect to corrosion inhibition, adhesion enhancement, blister resistance, and/or chemical resistance as enumerated below and as illustrated in the Examples. More specifically, such results may be observed when using a zinc phosphate conversion coating with epoxy resin coatings and optionally with urethane on top of the epoxy.
As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. Any numerical range recited herein is intended to include all sub-ranges subsumed therein. Plural encompasses singular and vice versa. For example, while the invention has been described in terms of “a” conversion coating, “a” particle, “a” film-forming layer, and the like, mixtures of these and other components, including mixtures, can be used. Also, as used herein, the term “polymer” is meant to refer to prepolymers, oligomers and both homopolymers and copolymers; the prefix “poly” refers to two or more. When ranges are given, any endpoints of those ranges and/or numbers within those ranges can be combined with the scope of the present invention. “Including”, “such as”, “for example” and like terms means “including/such as/for example but not limited to”. The terms “acrylic” and “acrylate” are used interchangeably (unless to do so would alter the intended meaning) and include acrylic acids, anhydrides, and derivatives thereof, lower alkyl-substituted acrylic acids, e.g., C1-C2 substituted acrylic acids, such as methacrylic acid, ethacrylic acid, etc., and their C1-C6 alkyl esters and hydroxyalkyl esters, unless clearly indicated otherwise.
Each of the characteristics and examples described above, and combinations thereof, may be said to be encompassed by the present invention. The present invention is drawn to the following non-limiting aspects:
Panels were blasted and prepared as indicated below and compared to a control.
For the application of the zinc phosphate conversion coating, a cleaner bath, rinse conditioner, and zinc phosphate bath were prepared according to the manufacturer's specifications. The alkaline cleaner bath was Chemkleen™ (CK) 2010 LP with CK 181 ALP surfactant. The cleaner contained a concentration of 1.25 percent v/v CK 2010 LP and 0.125 percent v/v CK 181 ALP. The free alkalinity was kept within the range of 6-6.5 mL per 10 mL of bath, and the total alkalinity was kept within the range of 7-7.5 mL per 10 mL of bath. CK 2010 LP with CK 181 ALP bath was heated to 120° F. (49° C.).
One rinse conditioner was used. The rinse conditioner was a Jernstedt salt based activator solution labeled “RC” in the tables below. The RC rinse conditioner was used at a concentration of 0.8 g/L in tap water and kept at ambient temperature.
PPG's C700 product was used as the zinc phosphate bath. The bath was made according to the manufacturer's specifications. In the making of the bath, the PPG products used were Chemfos™ (C) 700A, Chemfos™ Make-up B, Chemfos™ FE, and Chemfos™ AFL. The free acid was kept between the range of 0.8-1.0 mL per 10 mL of bath, and the total acid was kept to a minimum of 15 mL and no higher than 19 mL per 10 mL of bath. Zinc concentration was 1200±50 ppm. Free fluoride was kept between 200-300 ppm, and total fluoride was in the range of 500-700 ppm. For a 5 gallon bath the amount of sodium nitrite added was 2.5-3 grams to maintain at least a 2.5 gas point. Once the C700 bath met these requirements, it was heated to 125±3° F. (52±2° C.).
A quantity of LG25 steel grit from Ervin industries was immersed in CK 2010 LP/181ALP for two minutes with motorized agitation using a rotating barrel. The cleaning step was followed by a deionized water spray rinse. Next, the steel grit was immersed in the RC for one minute. The steel grit was subsequently immersed directly into the zinc phosphate bath for two minutes with motorized agitation using a rotating barrel. Zinc phosphate pretreatment was followed by a final immersion rinse and spray rinse with deionized water. Pretreated steel grit was laid out on trays and dried at 230° F. (110° C.) for ten minutes.
For the application of the zirconium based conversion coating, a cleaner bath, a copper pre-rinse bath, and Zircobond®II bath were prepared according to the manufacturer's specifications. The alkaline cleaner bath was Chemkleen™ (CK) 2010 LP with CK 181 ALP surfactant. The cleaner contained a concentration of 1.25 percent v/v CK 2010 LP and 0.125 percent v/v CK 181 ALP. The free alkalinity was kept within the range of 6-6.5 mL per 10 mL of bath, and the total alkalinity was kept within the range of 7-7.5 mL per 10 mL of bath. CK 2010 LP with CK 181ALP bath was heated to 120° F. (49° C.).
The copper pre-rinse bath was made with deionized water and had a concentration of 50 ppm Cu2+ and a pH of 4.5±0.1.
The Zircobond®II bath was made according to the manufacturer's specifications. In the making of the bath, the PPG products used were Zircobond® MAKE UP, Chemfil™ Buffer, Chemfos™ AFL, and Zircobond Control #5. The zirconium concentration was kept in the range of 225±10 ppm. Cupric concentration was kept in the range of 20±4 ppm. Molybdate concentration was kept in the range of 120-200 ppm. Free fluoride was kept in the range of 40-100 ppm. Bath pH was adjust with Chemfil™ Buffer and kept in the range of pH 4.5-5.2. Once the Zircobond®II bath met these requirements, it was heated to 125±3° F. (52±2° C.).
A quantity of LG25 steel grit from Ervin industries was immersed in CK 2010 LP/181ALP for two minutes with motorized agitation using a rotating barrel. The cleaning step was followed by a deionized water spray rinse. Next, the steel grit was immersed in the copper pre-rinse for one minute. The steel grit was subsequently immersed directly into the Zircobond®II bath for four minutes with motorized agitation using a rotating barrel. Zirconium pretreatment was followed by a final immersion rinse and spray rinse with deionized water. Pretreated steel grit was laid out on trays and dried at 230° F. (110° C.) for ten minutes.
A set of hot rolled steel, 3″×6″ panels were blasted with untreated LG-25 steel grit using a 2636 SRC-12 Pro-Finish Empire blast cabinet at an air pressure of 80 PSI to achieve a 63±8 micron blast profile and immersed in CK 2010 LP/181ALP for two minutes. The cleaning step was followed by a deionized water spray rinse. Next, the blasted steel panels were immersed in the RC rinse conditioner for one minute. The blasted steel panels were then subsequently immersed directly into the C700 zinc phosphate bath for two minutes. Zinc phosphate pretreatment was followed by a final immersion rinse and spray rinse with deionized water. Pretreated steel panels were hung and blow-dried for 2-5 min.
The pretreated LG25 steel grit was used to blast 3″×6″ hot rolled steel panels in a 2636 SRC-12 Pro-Finish Empire blast cabinet at an air pressure of 55 PSI to achieve a 63±8 micron blast profile. Comparative controls were blasted with untreated LG25 steel grit. The various pretreatment processes are denoted in Table 1.
The panels blasted with pretreated grit and the control panels blasted with untreated grit with no additional pretreatment were then coated with six different coating systems as listed in Table 2. The steel panels blasted with untreated grit and then immersion pretreated were coated only with coating “E” from Table 2. Each of the coatings from Table 2 were applied and cured according to the details listed in Table 3.
The coated and cured panels of examples 1-34 (panels blasted with treated grit identified as “Example” in Tables 4 and 5, and panels blasted with untreated grit identified as “Comparative Example” in Tables 4 and 5) were scribed down to the metal substrate with a 2 mm wide scribe. Panels were then exposed to ASTM B117-11 salt fog for 1000 hours and 3000 hours. After exposure, each panel was scraped at the scribe using a straight edged razor blade. The razor blade was used to remove as much of the coating around the scribe as could reasonably be scraped off without excessive force. The average rust creep was measured using equation 1 and is listed in Table 4, 5 and 6. See Tables 4 and 5 for ASTM B117-11 salt fog results at 1000 hours and 3000 hours.
Rust creep M=(C−W)/2 (1)
Additionally, the pull-off adhesion was measured before and after 3000 hour salt fog exposure. A small area of the coating surface was first lightly roughened with sand paper and wiped clean. ½ inch aluminum stubs where then glued onto the surface and allowed to dry till the following day. The adhesion was then measured using the P.A.T.T.I™ Micro adhesion tester from M.E. Taylor. Before exposure panels were tested for adhesion after 1 week cure time. Post exposure panels were removed from testing and allowed to recondition for 1 week before testing adhesion.
As is shown in Tables 4 and 5, panels blasted with treated steel grit had less rust creep than panels blasted with untreated steel grit; the panels had similar pre-exposure adhesion properties. As shown in Table 6, the ratio of rust creep in Examples 13 and 14 for RC+C700 treated grit versus untreated grit was 0.70. On the other hand, panels blasted with untreated grit followed by immersion pretreatment in a RC+C700 process had increased rust creep compared to a standard untreated grit blasted control. As shown in Table 6, the ratio of rust creep for untreated blasted panels immersed in a pretreatment bath versus untreated blasted panels was 1.47, much worse than the 0.70 ratio for the RC+C700 treated grit blasted panels versus untreated blasted panels. The abrasive blasting of the panels with treated grit therefore gave better corrosion results than a standard pretreatment immersion process.
Steel grit and panels were prepared as described above. The same coating systems and application details are similar as previous examples but differ in dry film thickness as indicated in Table 7.
The coated and cured panels of examples 37-46 (panels blasted with treated grit identified as “Example” and panels blasted with untreated grit and identified as “Comparative Example” in Table 8) were scribed down to the metal substrate with a 2 mm wide scribe. Panels were then exposed to ISO 12944 cyclic weathering for 10 cycles. After exposure, each panel was scraped at the scribe using a straight edged razor blade. The razor blade was used to remove as much of the coating around the scribe as could reasonably be scraped off without extraneous force. The average rust creep was measured using equation 1 and is listed in Table 8. See Table 8 for ISO 12944 cyclic weathering results at 10 cycles.
Rust creep M=(C−W)/2 (1)
Additionally, the pull-off adhesion was measured before and after 10 cycles. A small area of the coating surface was first lightly roughened with sand paper and wiped clean. ½ inch aluminum stubs where then glued onto the surface and allowed to dry till the following day. The adhesion was then measured using the P.A.T.T.I™ Micro adhesion tester from M.E. Taylor. Before exposure panels were tested for adhesion after 1 week cure time. Post exposure panels were removed from testing and allowed to recondition for 1 week before testing adhesion.
As is shown in Table 8, panels blasted with treated steel grit had less rust creep than panels blasted with untreated steel grit; the panels had similar adhesion properties. As shown in Table 9, the ratio of rust creep in Example 47 for RC+C700 treated grit versus untreated grit was 0.57. Example 48 compared performance of a coating system without Zn primer on treated grit blasted panels versus a three coat system with Zn primer on untreated grit blasted panels. Panels blasted with treated grit and topcoated with the compact coating system F had significantly less rust creep compared to panels blasted with untreated grit and topcoated with the three coat Zn primer system A. The ratio of the treated grit blast with the compact coating system to untreated grit blast with the three coat Zn primer system was 0.71. The treatment of the panels with treated grit and topcoated without a Zn primer gave better corrosion results than a standard Zn primer three coat system.
Panels were blasted with treated or untreated grit and coated as indicated below and compared to Versabond bath dipped blasted panel, also as indicated. The pretreated grit particles prepared as described below were used to blast panels multiple times prior to their use in the preparation of the panels used in these examples; a zinc deposition as low as 500±100 counts of zinc measured via XRF was confirmed prior to application of the coating. This example therefore demonstrates that the pretreated particles can be re-used.
For the application of the zinc phosphate conversion coating, a cleaner bath, rinse conditioner, and zinc phosphate bath were prepared according to the manufacturer's specifications.
The alkaline cleaner bath was Chemkleen™ (CK) 2010 LP with CK 181 ALP surfactant. The cleaner contained a concentration of 1.25 percent v/v CK 2010 LP and 0.125 percent v/v CK 181 ALP. The free alkalinity was kept within the range of 6-6.5 mL per 10 mL of bath, and the total alkalinity was kept within the range of 7-7.5 mL per 10 mL of bath. CK 2010 LP with CK 181ALP bath was heated to 120° F. (49° C.).
One rinse conditioner was used. The rinse conditioner was a Jernstedt salt based activator solution labeled “RC” below. This RC rinse conditioner was used at a concentration of 0.8 g/L in tap water and kept at ambient temperature. A second rinse conditioner, PPG's Versabond™, was prepared in deionized water and kept at ambient temperature. Examples with Versabond™ are referred to as “VB” below.
PPG's C700 product was chosen as the zinc phosphate bath. The bath was made according to the manufacturer's specifications. In the making of the bath, the PPG products used were Chemfos™ (C) 700A, Chemfos™ Make-up B, Chemfos™ FE, and Chemfos™ AFL. The free acid was kept between the range of 0.8-1.0 mL per 10 mL of bath, and the total acid was kept to a minimum of 15 mL and no higher than 19 mL per 10 mL of bath. Zinc concentration was 1200 ppm. Free fluoride was kept between 200-300 ppm, and total fluoride was in the range of 500-700 ppm. For a 5 gallon bath the amount of sodium nitrite added was 2.5-3 grams to have at least a 2.5 gas point. Once the C700 bath met these requirements, it was heated to 125±3° F. (52±2° C.).
A quantity of LG25 steel grit from Ervin industries was immersed in CK 2010 LP/181ALP for two minutes with manual agitation using a putty knife. The cleaning step was followed by deionized water immersion rinse and a deionized water spray rinse. Next, the steel grit was immersed in one of the rinse conditioners with manual agitation using a putty knife for one minute. The steel grit was subsequently immersed directly into the C700 zinc phosphate bath for two minutes with manual agitation using a putty knife. Zinc phosphate pretreatment was followed by a final deionized immersion rinse and a spray rinse with deionized water. Pretreated steel grit was laid out on trays and dried at 230° F. (110° C.) for ten minutes. A quantity of LG40 steel grit was also pretreated in the same manner.
Hot rolled steel panels were blasted using alumina grit (that had not been pretreated) to obtain a surface profile with the parameters shown in Table 10 as measured by confocal laser scanning microscopy. After blasting, half of the panels were kept as controls. The other half was immersed in CK 2010 LP/181ALP for two minutes. The cleaning step was followed by deionized water immersion rinse and a deionized water spray rinse. Next, the blasted steel panel was immersed in the Versabond™ rinse conditioner for one minute, then subsequently immersed directly into the C700 zinc phosphate bath for two minutes. Zinc phosphate pretreatment was followed by a final immersion rinse and spray rinse with deionized water. The pretreated steel panels were hung and blow-dried for 2-5 min.
The pretreated LG25 and LG40 steel grit was used to blast 3″×6″ hot rolled steel panels in a Guyson suction sand blast cabinet at an air pressure range of 65-75 PSI. Controls were blasted with untreated LG25 and LG40 steel grit. Zinc phosphate deposition was measured on the panels blasted with zinc phosphate pretreated grit. The zinc counts were quantified by using an XRF measuring absorption for 30 seconds with the Dpp setting at 1.1 μS at 15 kv and 45 μA using counts at the Kα peak of 8.64 keV.
The panels blasted with pretreated grit and the panels blasted with untreated grit and immersed in pretreatment were then coated with two different coating systems as listed in Table 11. The steel panels directly submerged in the zinc phosphate pretreatment bath and their unpretreated controls were subsequently coated as indicated in Tables 11 and 12.
The coated and cured panels of examples 51-101 (in Tables 13 and 14 panels blasted with pretreated grit identified as “Example” and panels blasted with untreated grit and identified as “Comparative Example”) were scribed down to the metal substrate with both a 0.2 mm wide scribe and a 2 mm wide scribe. Panels were then exposed to salt fog for 1000 hours and 3000 hours. After exposure, each panel was scraped at the scribe using a straight edged razor blade. The razor blade was used to remove as much of the coating around the scribe that could reasonably be scraped off without excessive force. The average rust creep was measured using equation 1 and is listed in Tables 13 and 14. See Tables 13 and 14 for salt fog results at 1000 hours and 3000 hours.
Rust creep M=(C−W)/2 (1)
The coated and cured panels of comparative example 101 (panels blasted with untreated grit and then pretreated using the zinc phosphate bath and their unpretreated controls) were X-scribed using a carbide tip to a width of approximately 0.2 mm. Each panel was then exposed to 1000 hours of salt fog. After the 1000 hour exposure time, one panel of each coating was scraped using a straight edge razor blade to remove the coating around the scribe as above. The average rust creep was measured using equation 1 and is listed in Table 15.
Additionally, the pull-off adhesion was measured (for all the examples) before salt fog exposure. A small area of the coating surface was first lightly roughened with sand paper and wiped clean. ½ inch aluminum stubs where then glued onto the surface and allowed to dry until the following day. The adhesion was then measured using the P.A.T.T.I™ Micro adhesion tester from M.E. Taylor.
As is shown in Tables 13 and 14, panels blasted with zinc phosphate pretreated grit generally had less rust creep with similar adhesion as compared to panels blasted with untreated steel grit. The zinc phosphate pretreated grit gives improved corrosion performance with variable zinc deposition on the blasted panel. It has been determined that the zinc phosphate pretreated grit can be recycled up to approximately 30 times reaching zinc deposition of 500±100 counts of zinc measured via XRF as described in the specification.
As shown in Table 15, the ratio of rust creep in Examples 75 and 82 for pretreated grit versus untreated grit was 0.32 and 0.16 for LG25 and LG40 grit, respectively. On the other hand, panels blasted with untreated alumina followed by immersion pretreatment in a zinc phosphate Versabond™ bath increased rust creep compared to a standard untreated alumina grit blasted control. The ratio of rust creep for bath pretreated versus unpretreated blasted panels was 5.69, much worse than the 0.32 and 0.16 ratio for the pretreated grit blasted panels. The treatment of the panels with pretreated grit therefore gave better corrosion results than a standard pretreatment immersion process.
A wash-ability study was done to demonstrate the inert nature of the conversion coating on the particles of the present invention as compared to particles prepared by mixing with a resin and a corrosion inhibitor, such as those described in U.S. Pat. No. 4,244,989. This patent describes a method of coating a particle with a layer of corrosion inhibitor “glued” to the particle with a resin and used to transfer the corrosion inhibitor during the blasting process.
Particles made according to the ratios of Example II of the '989 patent were prepared using:
The example was made at 10 percent of the full amount detailed above. In a cup, a 100 grams of corundum and 0.4 grams of Epon 828 resin were mixed in a DAC mixer for one minute at 1000 rpm and then 1500 rpm for one minute. Five grams of HeucorinRZ, which is zinc salt of 5-nitroisophthalic acid, was added to the mixture of corundum and Epon 828. The cup was mixed in a DAC mixer for one minute at 1500 rpm. The mixture was stirred, mixed again in the DAC mixer for one minute at 1500 rpm and then shaken vigorously.
Pretreated grit particles were prepared as described above for Examples 1-36, only RC+C700 LG40 steel grit was used.
Three 10 gram samples each of the particles were measured out and washed with a different solvent as described below.
The zinc counts, that is the amount of zinc that was washed off of each of the particles, were measured using an XRF to measure absorption for 30 seconds with the Dpp setting at 1.1 μS at 15 kv and 45 μA using counts at the Kα peak of 8.64 keV. Three types of solvents were used to wash the media: deionized water; 50/50 mixture of methyl ethyl ketone (MEK) and acetone; and pure acetone. After solvent was added the particle-solvent mixture was shaken for one minute. The particles were filtered by using 200 micron paper cone filter. A total of fifteen grams of solvent wash was collected and measured for zinc counts. Table II shows the zinc counts measured in the different solvent rinses.
As shown in Table II, the zinc salt bound by the resin to the corundum prepared according to the '989 patent was dissolved off with solvent. The zinc phosphate layer on the grit prepared according to the present invention, in contrast, was not removed upon exposure to different solvents. This demonstrates that the particles according to the present invention experience a bonding between the particles and the conversion coating that is not disrupted by solvent exposure, and thus distinct from other particles taught in the art.
Hot rolled steel 3″×6″ panels were blasted with LG40 steel grit in a Guyson blast cabinet at an air pressure of 50 PSI to achieve a 38±8 micron blast profile. Some of these panels were not given additional preparation (“Untreated”) and some were immersed in C700 (“Immersion C700”) as described in Examples 1-36. The pretreated grit blasted panels (“PTGB”) were blasted with zinc phosphate treated particles as described in the below example (“LAYER THICKNESS”).
Electrochemical impedance spectroscopy (EIS) was conducted to assess barrier property using a Gamry Reference 600+ potentiostat. EIS measurements were performed using a three-electrode cell with the HRS sample as the working electrode, saturated calomel reference (SCE), and Pt counter electrode in quiescent 0.1 M Na2SO4 electrolyte. After a 5 minute open circuit potential hold, an EIS scan was acquired in swept sine mode from 100 kHz to 0.01 Hz with six points per decade at an AC amplitude of 10 mV. Two scans were conducted for each sample set, each with a working area of 2.8 cm2. The low modulus frequency (0.01 Hz) impedance was taken as the barrier property metric. To account for the difference in pretreatment layer thickness, the barrier properties were normalized for thickness at the thinnest portion of the conversion coatings. For the PTGB panels the range of 3 to 39 nm (acquired by TEM micrograph analysis) was used and for the immersion C700 panels the range of 0.17 to 2.73 microns (acquired by SEM micrograph) was used. The average normalized barrier property is shown below. The error bars represent the bounds for the normalized barrier properties based on the respective range of pretreatment layer thickness from each process.
As can be seen, relative to the two pretreated samples, the untreated sample exhibited a lower barrier property (4×102 Ω-cm). Taking the pretreatment layer thickness into consideration, the Immersion C700 panels exhibited normalized barrier properties ranging from 6.1×106 to 9.8×107 Ω-cm. The PTGB panels showed the highest normalized barrier properties, ranging from 1.7×108 to 2.3×109 Ω-cm. The normalized barrier property is quantitatively defined as impedance×surface area/layer thickness (Ω-cm2/cm=Ω-cm). The conversion coating according to the present invention had a barrier per coating thickness of 1.3×108 to 6.9×109 (Ω-cm2/cm=Ω-cm) as measured via electrochemical impedance spectroscopy.
The thickness of a zinc phosphate conversion coating applied to panels according to the present invention was measured as described using EM and TEM. Cleaner, rinse conditioner and zinc phosphate baths were prepared according to the method set forth above for pretreated grit patent Examples 1-36. Steel grit was pretreated according to the same examples, but the grit used was LG40 steel grit from Ervin Industries and manual agitation with a putty knife was used in both agitation steps, rather than motorized agitation.
The pretreated LG40 steel grit was used to blast 3″×6″ hot rolled steel panels in a Guyson blast cabinet at an air pressure of 50 PSI to achieve a 38±8 micron blast profile. Comparative controls were blasted with untreated LG40 steel grit to provide a baseline for the SEM and EDS measurements.
A set of hot rolled steel, 3″×6″ panels were blasted with untreated LG40 steel grit as described above and immersed in CK 2010 LP/181ALP for two minutes. The cleaning step was followed by a deionized water spray rinse. Next, the blasted steel panels were immersed in the RC rinse conditioner for one minute. The blasted steel panels were then subsequently immersed directly into the C700 zinc phosphate bath for two minutes. Zinc phosphate pretreatment was followed by a final immersion rinse and spray rinse with deionized water. Pretreated steel panels were hung and blow-dried for 2-5 min.
Panel segments were mounted on aluminum stubs with carbon tape and coated with Au/Pd for 20 seconds. Samples were than analyzed in the Quanta 250 FEG SEM under high vacuum. The accelerating voltage was set to 10.00 kV and the spot size was 3.0. Bulk or Point EDX was collected from the analyzed areas on each panel.
Small square sections were cut from each panel with a panel cutter and mounted in epoxy overnight. After curing, the mounts were ground, polished, and placed on aluminum stubs with carbon tape. Samples were than coated with Au/Pd for 20 seconds and analyzed in the Quanta 250 FEG SEM under high vacuum. The accelerating voltage was set to 20.00 kV and the spot size was 3.0. Elemental maps were collected from each of the sample cross-sections to provide pictorial representations of the most abundant elements detected in the coating layers.
A section of the sample was prepared for TEM analysis using a Helios NanoLab 660 focused ion beam (FIB) at the PSU Materials Characterization Lab using a standard in-situ lift-out technique. A TEM sample was taken from a region where SEM elemental analysis could not detect Zn and P signals. A layer of carbon was first deposited using the FIB over the surface of the sample to prevent damage during the subsequent Ga+ion beam milling. A thin section was milled out from the surface of the sample using an ion beam and attached to a TEM grid in-situ using a micromanipulator. This section was then thinned further with ion beam until the final thickness was approximately 100 nm.
The sample section was then analyzed using a FEI Titan TEM operating at 200 kV. Elemental maps were collected in scanning transmission electron microscopy (STEM) mode from each of the sample cross-sections to provide pictorial representations of the most abundant elements detected in the coating layers.
A thin, dense layer relative to traditional zinc phosphate immersion pretreatment was achieved through blasting with zinc phosphate treated particles. In areas where zinc and phosphorous were undetectable via SEM, samples were taken and analyzed via TEM and a very thin layer of zinc phosphate pretreatment was still present on the surface of the blasted substrate.
When the blasted substrate treated with the zinc phosphate treated particles was measured via SEM, 0.29-1.48 μm thick layer of pretreatment was measured. In the areas where zinc and phosphorous were undetectable via SEM, these areas were analyzed via TEM, and the layer of pretreatment was found to have a thickness range of 3-12 nm.
When the blasted substrate pretreated through immersion zinc phosphate process was analyzed via SEM, a 0.17-2.73 μm thick layer of pretreatment was measured.
For the application of the zirconium based conversion coating for the LG25 steel grit, a cleaner bath, a copper pre-rinse bath, and Zircobond®II bath were prepared according to the manufacturer's specifications. The alkaline cleaner bath was Chemkleen™ (CK) 2010 LP with CK 181 ALP surfactant. The cleaner contained a concentration of 1.25% v/v CK 2010 LP and 0.125% v/v CK 181 ALP. The free alkalinity was kept within the range of 6-6.5 mL per 10 mL of bath, and the total alkalinity was kept within the range of 7-7.5 mL per 10 mL of bath. CK 2010 LP with CK 181ALP bath was heated to 120° F. (49° C.).
The copper pre-rinse bath was made with deionized water and had a concentration of 50 ppm Cu2+ and a pH of 4.5±0.1.
The Zircobond®II bath was made according to the manufacturer's specifications. In the making of the bath, the PPG products used were Zircobond® MAKE UP, Chemfil™ Buffer, Chemfos™ AFL, and Zircobond Control #5. The zirconium concentration was kept in the range of 225±10 ppm. Cupric concentration was kept in the range of 20±4 ppm. Molybdate concentration was kept in the range of 120-200 ppm. Free fluoride was kept in the range of 40-100 ppm. Bath pH was adjust with Chemfil™ Buffer and kept in the range of pH 4.5-5.2. Once the Zircobond®II bath met these requirements, it was heated to 125±3° F. (52±2° C.).
A quantity of LG25 steel grit from Ervin industries was immersed in CK 2010 LP/181ALP for two minutes with motorized agitation using a rotating barrel. The cleaning step was followed by a deionized water spray rinse. Next, the steel grit was immersed in the aforementioned copper pre-rinse for one minute. The steel grit was subsequently immersed directly into the Zircobond®II bath for four minutes with motorized agitation using a rotating barrel. Zirconium pretreatment was followed by a final immersion rinse and spray rinse with deionized water. Pretreated steel grit was laid out on trays and dried at 230° F. (110° C.) for ten minutes.
Aluminum 7075 Clad panel was blasted with Zircobond®II treated LG25 steel grit in a Guyson blast cabinet at a blast pressure of 45 PSI to achieve a blast profile of 32±5 μm. Comparative controls were blasted with untreated LG40 steel grit to achieve the same profile of 32±5 μm.
The untreated LG40 blast panels were immersion pretreated with a Zircobond® 1.5 process using an alkaline cleaner bath Chemkleen™ (CK) Surface Prep (SP)1 followed by Zircobond® 1.5 bath. The alkaline cleaner bath was CK SP1 with CK 185A surfactant. The cleaner contained a concentration of 1% v/v CK SP1 and 0.1% v/v CK 185A surfactant. The free alkalinity was kept within the range of 4.5-5 mL per 10 mL of bath, and the total alkalinity was kept within the range of 5.5-6 mL per 10 mL of bath. CK SP1 with CK 185A bath was heated to 120° F. (49° C.) and used as a spray cleaner.
Zircobond® 1.5 bath was made according to the manufacturer's specifications. In the making of the bath, the PPG products used were Zircobond® ZRF, Chemfil™ Buffer, Chemfos™ AFL. The zirconium concentration was kept in the range of 200±10 ppm. Cupric concentration was kept in the range of 35±4 ppm. Free fluoride was kept in the range of 40-100 ppm. Bath pH was adjust with Chemfil™ Buffer and kept in the range of pH 4.5-5.2. Once the Zircobond® 1.5 bath met these requirements, it was heated to 80° F. (27° C.). Zircobond®1.5 Pretreatment of Untreated LG40 Blasted Aluminum Clad 7075 Panels
A blast profiled aluminum clad 7075 panel was spray cleaned in CK SP1/185A for two minutes with fluid pressurized nozzles. The cleaning step was followed by a deionized water immersion rinse and a deionized water spray rinse. Next, the aluminum panel was immersed in the Zircobond® 1.5 bath for two minutes. Zirconium pretreatment was followed by a final spray rinse with deionized water. Pretreated panels were air dried for 2-5 minutes.
Top-down FE-SEM and EDX Analysis: Panel segments were mounted on aluminum stubs with carbon tape and coated with Au/Pd for 20 seconds. Samples ere then analyzed in the Quanta 250 FEG SEM under high vacuum. The accelerating voltage was set to 10.00 kV and the spot size was 3.0. Bulk or Point EDX was collected from the analyzed areas on each panel.
The panels immersed in a Zircobond® bath had detectable amounts of fluorine deposited on the surface (in addition to the Zircobond® pretreatment layer) as detected by SEM-EDX (
Samples were further analyzed with X-Ray Fluorescence (XRF) using a PANalytical Akios DY 1474 spectrometer. Elemental analysis was determined using the Omnian semi-quantitative method. Amounts of Zr and F in the untreated immersion ZB and PTGB panels was determined to be as follows:
As can be seen above, the amount of F in the Zircobond PTGB panels was an order of magnitude lower than the panels immersed in Zircobond.
This invention was made with Government support under Government Contract No. W9132T-17-C-0021. The United States Government has certain rights in this invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/064461 | 12/4/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62775049 | Dec 2018 | US |
