HK1148809A - Organic polymer coatings for water containers - Google Patents

Description

Organic polymer coating for water containers

Cross reference to related applications

This application claims priority from U.S. provisional patent application No.61/030, 118, filed on 20/2/2008, the entire disclosure of which is hereby incorporated by reference in its entirety.

Background

The present invention relates to organic coatings, and in particular to waterproof organic polymer coatings for use in water heaters. Enamel coatings traditionally used in hot water tanks and water heaters are subject to corrosion and dissolution by the hot water. In water heaters or tanks, once the enamel coating protecting the metal substrate is dissolved until the substrate, the substrate quickly erodes and perforates. At this point, the water heater must be replaced.

Brief description of the invention

In one aspect, the invention provides a water tank comprising a tank body having a water chamber with an interior surface at least partially coated with an organic polymeric coating having a thickness of less than about 375 μm (less than about 15 mils) and adapted to contact water.

In another aspect, the present invention provides a method of manufacturing a water tank in which a metal surface of at least a portion of the water tank is treated to produce a surface having a texture depth (profile) of about 40 μm to about 100 μm (about 1.6mil to about 4mil), and an organic polymer coating is applied to the tank to form a coated surface in contact with water in the water tank.

The present invention also provides a method of producing a water tank in which the surface of the tank is treated with a metal phosphate such as zinc phosphate, iron phosphate or manganese phosphate, and an organic polymer is applied to the treated surface to form a coated surface that is in contact with water in the water tank.

In another aspect, the present invention provides a method of storing hot water comprising contacting a tank having at least a portion of its interior surface coated with an organic polymer coating, a portion of the coating being in contact with water having a temperature of at least about 60 ℃ and exhibiting less than about 1% blistering after a period of at least about 3 months.

Detailed Description

It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

It should also be understood that any numerical range recited herein includes all values from the lower value to the upper value. For example, if a concentration range is stated as 1% to 50%, it means a value such as 2% to 40%, 10% to 30%, or 1% to 3%, etc., which is explicitly enumerated in this specification. These are only examples of what is specifically intended and all possible combinations of numerical values between and including the lowest value and the highest value enumerated, should be considered to be expressly stated in this application.

All patents, publications, and references cited herein are hereby incorporated by reference in their entirety. In the event of conflict between the present disclosure and the incorporated patents, publications, and references, the present disclosure will control.

In one aspect, the present invention relates to water heaters and tanks coated with organic polymer coatings for storing liquids, and methods for making and using the coated water heater or tank. The present invention provides at least one durable, tacky, water-resistant, pH-resistant, chemical-resistant, and abrasion-resistant organic polymer coating for the interior surfaces of water tanks, such as in water heaters. The use of an organic polymer coating on a metal such as a steel (or grit blasted steel) tank allows the tank to be manufactured without the need for firing so that thinner, less or less strong metals such as steel can be used. Typical glass liners used in water storage tanks tend to dissolve over time when the temperature of the water exceeds about 60 ℃ (140 ° F), particularly when the temperature exceeds about 82 ℃ (180 ° F), or when the pH of the water is at least about 8. The hot water tank coated with the organic polymer coating can be used to store any liquid having a pH and temperature greater than about 60 ℃ (140 ° F), about 70 ℃, about 71.1 ℃ (160 ° F), about 80 ℃, or about 82.2 ℃ (180 ° F).

The organic coating is applied directly or indirectly to the surface of a hot water tank or other liquid or water storage tank. In other words, in certain embodiments, there may be one or more additional layers between the surface and the organic coating. In certain embodiments, the organic coating is applied to the interior surface of the tank. In other embodiments, the organic coating is applied to the interior and exterior surfaces of the tank. As used herein, a "hot water tank" is a container suitable for holding water at a temperature of at least 55 ℃ (131 ° F), including, but not limited to, a hot water storage tank, a water heater such as a direct fired water heater, or a hot water boiler. The tank is suitably made of metal, such as steel, coated with an organic coating. The organic coating is suitable for application to and polymerization of, for example, residential or gas water heaters or industrial electric or gas water heaters. The tank suitably defines or contains a water chamber coated with an organic coating adapted to contact or contain water. Suitably, the water chamber coated with the organic polymer coating is adapted to contain water at a temperature of at least about 55 ℃, at least about 60 ℃, at least about 65 ℃, at least about 70 ℃, at least about 75 ℃, at least about 80 ℃, at least about 85 ℃, at least about 90 ℃, at least about 95 ℃, or at least about 98 ℃.

Suitably, the hot water tank has a capacity of at least about 15 liters, at least about 19 liters (5 gallons), at least about 25 liters, at least about 35 liters, at least about 37.9 liters (10 gallons), at least about 50 liters, at least about 56.9 liters (15 gallons), at least about 75 liters, at least about 75.8 liters (20 gallons), at least about 100 liters, at least about 113.7 liters (30 gallons), at least about 150 liters, at least about 151.6 liters (40 gallons), at least about 175 liters, at least about 189.5 liters (50 gallons), at least about 300 liters, at least about 350 liters, at least about 379 liters (100 gallons), or at least about 400 liters.

In one embodiment, the organic polymer comprises an epoxy polymer binder, such as a bisphenol a epoxy, an acrylic-modified epoxy, a polyester-modified epoxy, or a combination thereof. The organic polymer suitably comprises (by weight) at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, and less than about 100%, less than about 95%, less than about 90%, less than about 85%, or less than about 80% of an epoxy polymer binder. Suitably, the epoxy polymer base is the reaction product of an epoxide and a dihydroxy compound. Examples of suitable dihydroxy compounds may include bisphenol A, bisphenol F, diphenols, resorcinols. Where appropriate, the epoxy polymer binder is crosslinked with an anhydride or epoxy novolac to form an organic polymer. Examples of useful anhydrides may include 1, 2, 4, 5-pyromellitic anhydride (PMDA), succinic anhydride, methylsuccinic anhydride, tricarballylic anhydride, phthalic anhydride (PTA), hexahydrophthalic anhydride, trimellitic anhydride, itaconic anhydride, and maleic anhydride. Dianhydrides such as benzophenone tetracarboxylic dianhydride (3, 3 ', 4, 4' -benzophenone tetracarboxylic dianhydride; BTDA, commercially available from christkev Company, Lenexa, KS) or pyromellitic dianhydride may also be used. Examples of suitable novolac epoxy resins may include novolac epoxy resins obtained by reacting phenols such as phenol, o-cresol, m-cresol, p-tert-butylphenol, p-nonylphenol, 2, 6-xylenol, resorcinol, bisphenol a, alpha and beta-naphthol, and naphthalenediol with aldehydes such as acetaldehyde, formaldehyde, furfural, glyoxal, and p-hydroxybenzaldehyde in the presence of an acid catalyst or a base catalyst to produce methylolated compounds of the corresponding phenol, which are then reacted with phenols in the presence of an acid catalyst. If appropriate, a high-temperature curing agent may be used. Suitably, the cured crosslinking agent is present in the organic polymer in an amount (by weight) of at least about 1%, at least about 2%, at least about 3%, at least about 5%, at least about 10%, or at least about 15%, and less than about 50%, less than about 45%, less than about 40%, less than about 35%, less than about 30%, or less than about 25%.

The organic polymer used to coat the tank of the invention may optionally contain an adhesion promoter or cathodic disbondment promoter, as appropriate. Suitably, the cured organic polymer comprises an epoxy polymer or an epoxy resin.

The organic polymer used to coat the tank of the present invention may optionally contain fillers such as, but not limited to, calcium silicate (wollastonite), calcium carbonate, titanium oxide, micronized silica, aluminosilicates such as calcined kaolin, magnesium silicates such as talc and calcium sulfate. An example of a suitable commercially available filler is wollastonite Nyad 400 (commercially available from NYCO). Suitably, the filler is present in an amount of less than about 70%, less than about 60%, less than about 50%, less than about 40%, less than about 30%, or less than about 20%, and at least about 0.5%, at least about 1%, at least about 1.5%, and at least about 5%, or at least about 10% (by weight) of the organic polymer.

The organic polymer used to coat the tank of the present invention may optionally contain a flow control agent. Suitable flow control agents include, but are not limited to, acrylic flow agents (polyacrylates), silicone oligomers, fluorinated polyolefins, polyvinyl butyrals, and combinations thereof. An example of a suitable flow agent is the Resiflow series (e.g., Resiflow p-67), commercially available from Estron Chemical, Calvert City, KY. Suitably, the fluidic agent is present in an amount of less than about 10%, less than about 0.7%, or less than about 5%, and at least about 0.1%, at least about 0.2%, or at least about 0.5% of the organic polymer (by weight).

The organic polymer used to coat the tank of the invention may optionally contain a catalyst. Suitable catalysts may include, but are not limited to, tin catalysts such as stannous and tetraphenyltin octoate, zinc metal, dibutyltin dilaurate, potassium acetate, potassium octoate, isocyanate trimerization catalysts, dibutyltin mercaptide, dibutyltin thiocarboxylate, phenylmercuric propionate, lead octoate, and ferrous acetylacetonate. Suitably, the catalyst is present in an amount of less than about 10%, less than about 7.5% or less than about 5%, and at least about 0.1%, at least about 0.25% or at least about 0.5% by weight of the organic polymer.

The organic polymer used to coat the tank of the invention may optionally contain pigments. Suitable pigments having a yellow color may include c.i. pigment yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 19, 65, 74, and 83, and solvent yellow 33. The pigment having a red color may include, for example, c.i. pigment red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 49, 50, 51, 52, 53, 55, 60, 64, 83, 87, 88, 89, 90, 112, 114, 122, 123, and 163. The pigment having a blue color may include, for example, c.i. pigment blue 2, 3, 15, 16, 22 and 25. Pigments having a black color may include, for example, c.i. pigment blacks 1 and 7, and carbon black (commercially available from Degussa AG, germany). Suitably, the pigment is present in an amount of less than about 50%, less than about 40%, less than about 30% or less than about 20%, and at least about 0.5%, at least about 1%, at least about 1.5% or at least about 2% (by weight) of the organic polymer.

The organic polymer coatings of the present invention can be stable over a wide range of different pH. For example, the organic polymer coating can resist corrosion or blistering when the pH of the liquid contained in the organic polymer coating is at least about 1 (or about 1), at least about 2 (or about 2), at least about 3 (or about 3), at least about 4 (or about 4), at least about 5 (or about 5), at least about 6 (or about 5), or at least about 7 (or about 7) and less than about 14 (or about 14), less than about 13 (or about 13), less than about 12 (or about 12), less than about 11 (or about 11), less than about 10 (or about 10), less than about 9 (or about 9), or less than about 8 (or about 8) over a period of about 1 month, about 3 months, about 4 months, about 6 months, about 9 months, about 12 months, about 2 years, about 5 years, or about 10 years. Suitably, the organic polymer coating resists corrosion and/or blistering within the aforementioned pH range or when contacted with water for the aforementioned length of time when the liquid temperature is at least about 20 ℃, at least about 30 ℃, at least about 40 ℃, at least about 50 ℃, at least about 60 ℃, at least about 65 ℃, at least about 70 ℃, at least about 75 ℃, at least about 80 ℃, at least about 82 ℃, at least about 85 ℃, at least about 88 ℃, at least about 90 ℃, at least about 95 ℃, at least about 98 ℃, or at least about 99 ℃. It is desirable to resist corrosion and/or blistering in the pH range of about 1 to about 14 or about 2 to about 13. Suitably, the organic polymer coating resists corrosion and blistering when exposed to boiling water for a period of 6,000 to 9,000 hours. As used herein, "resistant to corrosion or blistering" means that the coating does not visibly blister or corrode significantly after the specified test conditions. Suitably, less than about 10%, less than about 7%, less than about 5%, less than about 4%, less than about 3%, less than about 2%, less than about 1%, less than about 0.5%, less than about 0.1%, less than about 0.01%, less than about 0.001%, or less than about 0.0001% of the surface area of the organic polymer coating that is contacted with (or exposed to) the liquid foams or exhibits foaming after the particular test conditions and the particular length of time described herein.

Conditions used to test for corrosion and/or blistering include, for example, exposure to a submersion test at about 60 ℃ (140 ° F), about 71 ℃ (160 ° F), about 82 ℃ (180 ° F), about 93 ℃ (200 ° F), about 96 ℃ (205 ° F), exposure to a salt spray test (e.g., ASTM B117 test) for 9,000 hours or 10,000 hours, exposure to methylethyl ketone, xylene, and methylene chloride for a length of 9 months (or 5,000 hours), or exposure to water at a temperature of about 71.1 ℃ (160 ° F), about 82.2 ℃ (180 ° F), or about 87.8 ℃ (190 ° F). For example, corrosion, blistering, and or degradation of the coating can be monitored using a hot water test cell with a water temperature of at least about 55 ℃, at least about 60 ℃, at least about 65 ℃, at least about 70 ℃, at least about 75 ℃, at least about 80 ℃, at least about 85 ℃, at least about 90 ℃, at least about 95 ℃, at least about 98 ℃, or at least about 99 ℃ for a length of time of at least about 50 hours, at least about 100 hours, at least about 200 hours, at least about 400 hours, at least about 800 hours, at least about 1, 000 hours, at least about 3,000 hours, at least about 4,000 hours, at least about 5,000 hours, at least about 8,000 hours, at least about 9,000 hours, or at least about 10,000 hours. Suitably, the organic polymer coatings of the present invention resist corrosion and blistering when subjected to high humidity (RH 95%) or immersion tests. For example, corrosion and/or blistering can be monitored by performing a soak test at 82 ℃ (180 ° F) for 10,000 hours, 96.1 ℃ (205 ° F) for 6,000 hours, or 100 ℃ (212 ° F) for 4,000 hours. Suitably, the organic polymer coating of the present invention is resistant to corrosion or blistering under one or more of these conditions.

Suitably, the organic polymer coating of the present invention exhibits excellent chemical resistance. For example, the coating can resist corrosion and blistering when exposed to a 10% sodium hydroxide solution or 10% sulfuric acid solution for 6,000 to 9,000 hours at 82.2 ℃ (180 ° F), 50% sulfuric acid solution for 9000 hours at 82.2 ℃ (180 ° F), and 50% sodium hydroxide solution for 9,000 hours at 82.2 ℃ (180 ° F). Suitably, the organic polymer coating applied to the water tank is also resistant to corrosion and/or blistering after exposure to hydrofluoric acid (e.g., 50% aqueous HF) or gluconic acid for at least about 1 month, at least about 3 months, at least about 6 months, at least about 9 months, at least about 12 months, at least about 15 months, at least about 18 months, or at least about 24 months.

The organic polymers useful in the present invention may have a high glass transition temperature (Tg). For example, the polymer can have a Tg of at least about 80 ℃, at least about 85 ℃, at least about 90 ℃, at least about 95 ℃, at least about 100 ℃, at least about 105 ℃, at least about 110 ℃, at least about 115 ℃, at least about 120 ℃, at least about 130 ℃, at least about 140 ℃, at least about 145 ℃, or at least about 150 ℃.

The organic polymer coating of the present invention exhibits good adhesion to substrates such as water tanks, water heaters, hot water storage tanks, or boilers. For example, the organic polymer coating may adhere well to metal surfaces, including, but not limited to, steel (including standard and/or galvanized steel), iron, titanium, aluminum, or magnesium, for example. Although thicker steels (e.g., steels having a thickness of at least about 1.5mm, at least about 1.6mm, at least about 1.75mm, or at least about 1.9 mm) may be used to fabricate substrates such as tanks, water heaters, hot water storage tanks, or boilers, thinner steels may also be suitably used. For example, steels having a thickness of less than about 1.5mm, less than about 1.4mm, less than about 1.3mm, less than about 1.25mm, less than about 1.2mm, less than about 1.1mm, less than about 1mm, less than about 0.9mm, less than about 0.8mm, less than about 0.7mm, or less than about 0.6mm may be used. For example, for a 50 gallon (190 liter or 200 liter) tank, steel having a thickness of less than about 1.5mm, less than about 1.25mm, less than about 1.2mm, less than about 1.1mm, or less than about 1mm may be used. For a 10 gallon (about 40 liter or less) tank, steel having a thickness of less than about 1mm, less than about 0.9mm, less than about 0.8mm, less than about 0.7mm, or less than about 0.6mm, for example, can be used. For tanks having a capacity of at least about 100 liters (or about 30 gallons), steel having a thickness of less than about 1.4mm, less than about 1.3mm, less than about 1.25mm, less than about 1.2mm, less than about 1.1mm, or less than about 1mm may be used.

In one embodiment, the surface of the substrate is pretreated to promote adhesion to the substrate by surface cleaning and/or texturing depth. The substrate, e.g., the fabricated box component, may be cleaned using any suitable technique known in the art. For example, the fabricated tank or tank component may be cleaned using a single or multi-stage cleaning machine (e.g., a two-stage, three-stage, four-stage, or five-stage cleaning machine). Detergents that may be used include, but are not limited to, mild acidic detergents, neutral detergents, alkaline detergents, or organic detergents such as acetone and ethanol.

The substrate may be surface treated or modified to promote adhesion of the organic polymer coating or coating composition. For example, prior to coating with the organic polymer, the steel or other substrate may be phosphated (e.g., with iron phosphate, zinc phosphate, or manganese phosphate), etched with acid (e.g., immersed in gluconic acid for 1 minute or more), shot blasted, grit blasted, sand blasted, or cold rolled. Grit blasting may be performed to produce a metal surface that is white in appearance. The surface may be treated to have a texture depth (i.e., the depth of the texture on the surface) of about 50 μm (2 mils). Suitably, the treated surface has a texture depth of at least about 10 μm, at least about 20 μm, at least about 25 μm, at least about 30 μm, at least about 35 μm, at least about 40 μm, or at least about 45 μm. Suitably, the treated surface has a texture depth of less than about 150 μm, less than about 140 μm, less than about 130 μm, less than about 120 μm, less than about 110 μm, less than about 100 μm, less than about 90 μm, less than about 80 μm, less than about 75 μm, less than about 70 μm, less than about 65 μm, less than about 60 μm, or less than about 55 μm. Grit blasting surface treatments can provide controlled texture depths substantially free of contaminating chemical residues (e.g., that may be left over due to insufficient rinsing, etc.). Chemical residues left on the surface can interfere with the functioning of the organic polymer coating and can cause early failure. In one embodiment, the organic polymer is applied to the treated or blasted surface within about 24 hours, within about 12 hours, within about 8 hours, within about 4 hours, within about 3 hours, within about 2 hours, within about 1 hour, within about 45 minutes, within about 30 minutes, within about 20 minutes, within about 15 minutes, within about 10 minutes, within about 5 minutes, or within about 3 minutes after the treatment or blasting is complete, in order to minimize oxidation of the surface. Suitably, after the surface treatment and before the application of the organic coating, the humidity is controlled and the steel is maintained under inert conditions. Suitably, less than about 50%, less than about 45%, less than about 40%, less than about 35%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, less than about 3%, less than about 2%, less than about 1%, less than about 0.5%, less than about 0.1%, or less than about 0.01% of the surface is oxidized prior to application of the organic coating.

For metal (e.g., zinc, iron, manganese) phosphating, the tank or tank parts can be cleaned using a hot alkaline cleaner, rinsed and chemically conditioned in preparation for zinc, iron, or manganese phosphates. Excess detergent is washed away using one or more rinses that may include a deionized water rinse and/or a seal rinse, followed by the addition of the metal phosphate. The metal phosphate treatment produces crystals that are layered, deposited or grown on the surface of the substrate. These crystals may have a needle-like appearance and create a depth of texture for better coating adhesion. When a component is coated with a polymer for electrocoating, hydrogen bonds may be formed between the organic polymer and the metal phosphate. When the parts are coated with a polymer using powder coating, the crystals provide mechanical attachment of the coating.

When the coating composition is in powder form, the organic polymer coating may be formed by, for example, powder coating the interior of the tank and heating the tank to form the coating, or curing the coating composition to form the organic polymer coating. When the coating composition is in liquid form, the coating may be formed by dipping the tank in the coating composition to form a coating on the inner and outer surfaces of the tank. Suitable methods for applying the organic polymer to the tank may include methods known in the art, such as spraying, pouring, and brushing. Electrocoating may also be used.

The organic polymer coating may be cured or hardened (set) on the water bath at a temperature of less than about 200 ° F (or about 95 ℃), less than about 300 ° F (or about 150 ℃), less than about 400 ° F (or about 205 ℃), less than about 500 ° F (or about 260 ℃), less than about 600 ° F (or about 315 ℃), less than about 700 ° F (or about 370 ℃), less than about 800 ° F (or about 425 ℃), less than about 900 ° F (or about 485 ℃), less than about 1000 ° F (or about 540 ℃), less than about 1200 ° F (or about 650 ℃), less than about 1400 ° F (or about 760 ℃), less than about 1600 ° F (or about 870 ℃).

In one embodiment, the coating is cured or hardened at a temperature of at least about 175 ℃, at least about 185 ℃, at least about 190 ℃, at least about 195 ℃, or at least about 200 ℃ and less than about 260 ℃, less than about 255 ℃, less than about 250 ℃, less than about 245 ℃, less than about 240 ℃, less than about 235 ℃, or less than about 225 ℃ for a period of time of at least about 2 minutes, at least about 5 minutes, at least about 7 minutes, or at least about 10 minutes, and less than about 1 hour, less than about 45 minutes, less than about 40 minutes, less than about 35 minutes, or less than about 30 minutes. For example, the coating may be cured at a temperature of about 185 ℃ to about 260 ℃ for between about 5 to about 30 minutes.

In one embodiment, the organic coating is adhered to the interior or inner surface of the tank and is adapted to form a continuous layer. In another embodiment, the organic coating is adhered to the inner (or interior) and outer (or exterior) surfaces of the tank and is adapted to form a continuous layer on both the inner (or interior) and outer (or exterior) surfaces. Thus, the tank may be adapted to contain a single layer or film of the coating. The coating is suitable for contacting water, and may be suitable for periodic contacting water. As used herein, "contacting water" means that at least a portion of the coating is in contact with water having a volume of at least 0.5 liters contained or stored in the tank. As used herein, "periodically exposed to water" means that at least a portion of the coating is exposed to water for a substantial portion of the functional life of the tank.

The thickness of the coating formed on the tank is suitably less than about 500 μm (20 mils), less than about 400 μm (16 mils), less than about 375 μm (15 mils), less than about 350 μm (14 mils), less than about 300 μm (12 mils), less than about 250 μm (10 mils), less than about 200 μm (8 mils), less than about 175 μm (7 mils), less than about 150 μm (6 mils), less than about 125 μm (5 mils), or less than about 100 μm (4 mils), less than about 75 μm (3 mils), or less than about 50 μm (2 mils). The thickness of the coating formed on the tank can be at least about 25 μm (1mil), at least about 50 μm (2mil), at least about 75 μm (3mil), or at least about 100 μm (4 mil).

The following examples are illustrative and should not be construed as limiting the scope of the invention.

Examples

Example 1

A flat storage bin was coated with the coating of the present invention to test the integrity of the coating. The box body is used for storing pig manure. The integrity of the coating was checked every three months. No compromise in integrity was detected after two years of testing.

Example 2

12 50 gallon gas water heaters made of steel at conventional steel thickness were cleaned manually with acetone. The interior surface of the cabinet was powder coated using the organic polymer composition described in example 4 (table 1). The tank is heated to form the coating. The thickness of the coating is between 25 μm and 125 μm (1 to 5 mil).

When the tank was used to heat water and store hot water for a period of 3 months, no corrosion or degradation of the coating was seen.

Example 3

10 20 gallon electric water heaters made of steel at conventional steel thickness were cleaned using a polished line cleaner. The interior surface of the cabinet was powder coated using the organic polymer composition described in example 4 (table 1). The tank is heated to form the coating. The thickness of the coating is between about 25 μm and 100 μm (1 to 4 mil).

When the tank was used to heat water and store hot water for 2 months, no corrosion or degradation of the coating was seen.

Example 4

The organic polymer was produced in powder form using the ingredients listed in table 1. The coating has a glass transition temperature of at least 121 ℃ (250 ° F) and is applied to a water heater. The coating performed well in the test.

TABLE 1

Example 5

Steel was coated with the organic polymer of the present invention and tested using a hot water corrosion cell. Test conditions included 93.3 ℃ (200 ° F) (1/2 charged to produce the vapor phase) for 72 hours; boiling for 800 hours; 82.2 deg.C (180 deg.F) 3200 hours, and 71.1 deg.C (160 deg.F) 3200 hours. No blistering or corrosion was observed under any of these test conditions.

Example 6

The organic polymer of example 4 (table 1) was applied to a water heater: a 10 gallon capacity electric water heater, a 50 gallon capacity electric water heater, and a 30 gallon capacity gas water heater were each tested.

The steel coil was processed through a decoiling/straightening line and then through a sand blaster to produce a 10 gallon capacity steel box. The box and head blanks are cut out and processed by a stamping operation. The top head is cleaned and the tank shell is welded. The weirs are then welded to the top head and tank shell. And stretching the box body shell, and pressing the end socket into the box body shell. The end cap is then welded to the shell.

The manufactured steel water tank was filled twice with 2% by volume of a commercially available neutral detergent having a pH of 7-8 at ambient temperature and cleaned using a three-stage washer apparatus. The cleaned boxes were dried at 121.1 ℃ (250 ° F) and higher using oven equipment with high volume air flow.

The interior of the tank assembly was grit blasted in a grit blast booth using either grit steel (for some 50 gallon tanks) or 24 alumina grit (10 gallon tanks and other 50 gallon tanks) to produce a texture depth of 50 μm (2.0 mils). After blasting, compressed air was used to blow off dust, shot and grit, revealing a surface with a white metallic appearance.

The organic polymer powders listed in Table 1 were spray applied to a thickness of 4 to 6mils (about 100 to 150 μm) within 5 minutes of preparing the metal by grit blasting. The powder coating composition was cured by baking at an oven temperature of 420F (215 c) for 20 minutes (or at a metal temperature of 400F (204 c) for 10 minutes) to produce a coating having a thickness of about 5mils (about 125 μm) or 4 to 6mils (about 100 to 150 μm).

When the tank was used to heat water and store hot water over a three year period, no corrosion or degradation of the coating was seen (no significant blistering on the coating surface), with the water temperature being 160 ° F (71.1 ℃) and 6 to 10 gallons of water were pumped from each tank 6 times per 24 hours (i.e., the tank was emptied and refilled 6 to 10 gallons of water 6 times) over the three year test period.

Example 7

Steel water heaters (10 gallon capacity electric water heaters and 50 gallon capacity electric water heaters) were coated with a polymer using the method detailed in example 6, except that the polymer contained the ingredients listed in table 2 in place of the ingredients listed in table 1. The coating has a glass transition temperature of at least 121 ℃ (250 ° F).

TABLE 2

When the tank was used to heat water and store hot water over a three year period, no corrosion or degradation of the coating was seen (no significant blistering on the coating surface), with the water temperature being 160 ° F (71.1 ℃) and 6 to 10 gallons per 24 hour water draw from each tank over the three year test period.

Example 8

By immersing 6 steel gas water heaters of 30 gallon capacity in HenkelAQUENCE^TM930 (epoxide-urethane acrylate mixture, commercially available from Henkel Corporation), the water heater was used as a Henkel AQUENCE^TM930 coating.

No significant bubbling was seen after heating and storing hot water using the tank over a three month period, with the water temperature being 160F (71.1 c), and 6 to 10 gallons of water being drawn from each tank every 24 hours over the three month test period.

Example 9

Standard test steel panels were cleaned with hot alkali, rinsed and chemically conditioned to prepare for zinc phosphate. Zinc phosphate was deposited on the plate so that needle crystals grew on the surface. The plates were rinsed, then deionized water rinsed and seal rinsed.

The zinc phosphate crystals create a depth of texture on the metal plate for better adhesion of the organic polymer coating. The plates were coated with the organic polymer of example 4 (table 1). After the coated panels were immersed in water at a temperature of 160 ° F (71.1 ℃), 180 ° F (82.2 ℃) or 194 ° F (90 ℃) for 4,000 hours, no blistering or corrosion of the coating was noted (blistering was not noted on the coating surface).

Claims (26)

1. A water tank comprising a metal tank, the metal tank comprising a water chamber having an interior surface, the interior surface being at least partially coated with an organic polymer coating, the coating having a thickness of less than about 375 μm and being adapted to periodically contact water.

2. The water tank of claim 1, wherein the water tank is a hot water tank.

3. The water tank of claim 1 or 2, wherein the water tank is a water heater.

4. The water tank of any of claims 1 to 3, wherein the polymer comprises an epoxy polymer.

5. The water tank of claim 4 wherein the epoxy polymer is crosslinked with a tetracarboxylic dianhydride.

6. The water tank of any of claims 1 to 5, wherein the polymer has a glass transition temperature of at least about 100 ℃.

7. The water tank of any of claims 1 to 6, wherein the coating has a thickness of at least about 75 μm and less than about 350 μm.

8. The water tank of any of claims 1 to 7, wherein the inner surface has a texture depth of at least about 40 μm and less than about 100 μm, the organic polymer being coated on the texture depth.

9. The water tank of any of claims 1 to 8, wherein the metal tank comprises steel.

10. The tank of claim 9 wherein the tank has a capacity of at least about 100 liters and the steel has a thickness of less than about 1.25 mm.

11. The water tank of any of claims 1 to 10, wherein the organic polymer coating has less than about 1% surface area blistering after 6 months immersion in water having a temperature of about 82 ℃.

12. A method of producing a water tank comprising:

(a) treating at least a portion of the metallic surface of the water box to produce a treated surface having a texture depth of at least about 40 μm and less than about 100 μm;

(b) an organic polymer is applied to the treated surface to form a coated surface that contacts water in the tank.

13. The method of claim 12, wherein the coating has a thickness of less than about 375 μm.

14. The method of any one of claims 12 and 13, wherein the treating of step (a) comprises grit blasting the metal part with fine sand, coarse sand, shot, or a combination thereof.

15. The method of any of claims 12 to 14, wherein the polymer comprises an epoxy polymer.

16. The method of any of claims 12 to 15, wherein the epoxy polymer is crosslinked with a tetracarboxylic dianhydride.

17. The method of any one of claims 12 to 16, wherein the depth of the texture is at least about 45 μm and less than about 75 μm.

18. The method of any of claims 12 to 17, wherein applying the organic polymer coating of step (b) comprises powder coating the surface with an organic polymer composition and curing the organic polymer to form the coated surface.

19. The method of any of claims 12 to 18, wherein applying the organic polymer coating of step (b) comprises curing the organic polymer at a temperature of less than about 260 ℃ for a time of less than about 45 minutes.

20. A method of producing a water tank, the method comprising:

(a) contacting the metal surface of the water tank with a metal phosphate selected from the group consisting of zinc phosphate, iron phosphate, manganese phosphate, or combinations thereof to produce a treated surface;

(b) applying an organic polymer to the treated surface of step (a) to form a coated surface that contacts water in the tank.

21. A method of storing water comprising contacting a tank having an interior surface with water, the tank having at least a portion of the interior surface coated with an organic polymer coating, the water having a temperature of at least about 60 ℃, and a portion of the coating contacting the water and exhibiting less than about 1% blistering after a period of at least about 3 months.

22. The method of claim 21, wherein the temperature is at least about 82 ℃.

23. The method of claim 21 or 22, wherein the period of time is at least about 6 months.

24. The method of any of claims 21 to 23, wherein the organic polymer coating comprises an epoxy polymer.

25. The method of any one of claims 21 to 24, wherein the coating has a thickness of at least about 75 μ ι η and less than about 375 μ ι η.

26. The method of any one of claims 21 to 25, wherein the water tank is a water heater.