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WO2019090356A1 - Substrat métallique revêtu de fluoropolymère superhydrophobe couche par couche permettant une condensation goutte à goutte - Google Patents

Substrat métallique revêtu de fluoropolymère superhydrophobe couche par couche permettant une condensation goutte à goutte Download PDF

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Publication number
WO2019090356A1
WO2019090356A1 PCT/US2018/059492 US2018059492W WO2019090356A1 WO 2019090356 A1 WO2019090356 A1 WO 2019090356A1 US 2018059492 W US2018059492 W US 2018059492W WO 2019090356 A1 WO2019090356 A1 WO 2019090356A1
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Prior art keywords
substrate
fluoropolymer
article
coating
group
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Tareq Isam ISMAIL
Stephen Lathrop WOOD
Jonathon SHENKER
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Sam Houston State University
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Sam Houston State University
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
    • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
    • C09D127/12—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
    • B05D5/083—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface involving the use of fluoropolymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50—Multilayers
    • B05D7/52—Two layers
    • B05D7/54—No clear coat specified
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/16—Layered products comprising a layer of synthetic resin specially treated, e.g. irradiated
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
    • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
    • C09D127/12—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C09D127/18—Homopolymers or copolymers of tetrafluoroethene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2451/00—Type of carrier, type of coating (Multilayers)
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2205/00—Polymer mixtures characterised by other features
    • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
    • C08L2205/025—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group containing two or more polymers of the same hierarchy C08L, and differing only in parameters such as density, comonomer content, molecular weight, structure
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2205/00—Polymer mixtures characterised by other features
    • C08L2205/14—Polymer mixtures characterised by other features containing polymeric additives characterised by shape
    • C08L2205/18—Spheres

Definitions

  • the invention generally relates to fluorinated carbon coatings.
  • Condensation of water to produce purified water, suitable for drinking and other uses is a well-known process. Condensation processes, however, can be cost prohibitive due to low condensation efficiencies of condensers, and the high energy cost for continually producing a coolant fluid. It is therefore desirable to improve the efficiency of a condenser in order to reduce the production costs for the generation of purified water.
  • Ultraphobic known as Ultrahydrophobic / Ultralyophobic: Means “super repellant”.
  • Hydrophilic Means "Loves Water”.
  • Hydrophobe Means "Hate Water”.
  • Filmwise condensation In film condensation which is known as (filmwise condensation) vapor latent energy is released, heat transfers to the surface, condensate forms, where drops form quickly and coalesce to produce a continuous wet thin layer of liquid that forms over the condensing surface.
  • Dropwise condensation In drop condensation which is known as (dropwise condensation), if the condensation rate is low due the presence of non-condensable gas, the liquid does not wet the surface wall of the condenser or the condensing surface is non-wetting surface, condensation will form as droplets from the vapor at particular nucleation sites on solid surfaces; the drops remain separate during growth.
  • Hydrophilic surfaces are surfaces that like water where the droplet creates a contact angle larger than 0° and less than 90°, (0° ⁇ 90°) with condensing surface.
  • Hydrophobic surfaces are surfaces that hate water where the droplet creates an angle greater than 90°, (90° ⁇ 150°) with condensing surface.
  • Super-hydrophobic Is very hydrophobic where the droplet creates an angle greater than 150°,( ⁇ >150°) with condensing surface.
  • wetting If a droplet is added on substrate and the surface energy of the substrate changes upon the addition of the droplet, the substrate is said to be "wetting” Once a liquid is in contact with a solid surface.
  • Adhesion Dissimilar particles or surfaces cling to one another. Adhesion is the force of attraction between two unlike molecules.
  • Cohesion Similar particles or surfaces cling to one another. Cohesion is the force of attraction between like molecules.
  • Capillary Is water molecules move up the fiber walls and spanning the space of the tunnel that are pulled along.
  • Contact angle is the angle measured where a liquid-vapor interface meets a solid surface.
  • Ideal solid surface A solid surface that is chemically homogenous, flat, smooth, and has a zero contact angle hysteresis is said to have ideal solid surface.
  • Contact angle hysteresis is equal the difference between the advancing and receding angles.
  • Complete spreading Is also known as complete wetting, when S > 0, where the liquid wets the surface completely.
  • Partial spreading Is also known as partial wetting, when S ⁇ 0, where the liquid wets a smaller portion of the surface.
  • Dynamic wetting Is the motion of a phase boundary which involves the advancing and receding of contact angles.
  • a kinetic non-equilibrium effect Occurs when a rapid movement of contact line happens at a high speed that a complete wetting cannot be achieved.
  • Homogeneous wetting Is when the liquid fills in the rough grooves of a surface.
  • Heterogeneous wetting Is when the surface is composed of two types of patches.
  • Interface energy Is known as "interface energy,” and is used to quantify the disruption of intermolecular bonds that occur when a surface is created and is defined as the excess of energy at the surface of the material when it is compared to the bulk of the material.
  • Gibbs isotherm Describes the phenomenon when two liquids are mixed and their molecules are dissolved and the surface tension of their mixture is different than the pure liquid values.
  • Electrostatic gun corona gun
  • the most popular form of applying powder coating to metal objects is to spray the powder with the use of electrostatic gun (corona gun).
  • Tribo gun Uses triboelectric friction to charge the powder.
  • the tribo uses mechanical application of charge to the powder particles by means of friction as these partials are deflected and forced to rub against Teflon tubing inside the barrel of the gun.
  • Fluidized bed Technique used to apply powder coating on substrate, where the part to be coated is heated and dipped into aerated powder-filled bed.
  • Electrostatic fluidized bed coating Is similar to fluidized bed dib coating except for the electrostatic charging medium paced inside the bed which charges the powder partials as the fluidizing air lifts it up.
  • Electrocoat dip Electrocoat dip: Unlike manual spray of metal parts with anti- corrosion, in electrocoat dip process, metal parts are dipped into a tank with electro charged primer in it.
  • a method of forming a fluorinated coating on a metal surface includes applying a liquid first fluoropolymer to the metal surface to form a first coating on the metal surface.
  • a fluoropolymer is a polymer that is composed of at least carbon and fluorine.
  • a fluoropolymer may also include other elements such as hydrogen, oxygen, nitrogen and other halogens.
  • Specific types of fluoropolymers include fluorocarbon polymers and hydrofluorocarbon polymers.
  • Fluorocarbon polymers, as used herein are polymers that are only composed of carbon and fluorine.
  • Hydrofluorocarbon polymers as used herein, are polymers that are only composed of carbon, fluorine, and hydrogen. Specific examples of fluoropolymers include, but are not limited to:
  • PTFE polytetrafluoroethylene
  • ETFE ethylene tetrafluoroethylene copolymer
  • ECTFE ethylene chlorotrifluoroethylene copolymer
  • FEP fluorinated ethylene propylene
  • PCTFE Polychlorotrifluoroethylene
  • the first and/or the second fluoropolymer(s) are a fluorocarbon polymer and/or a hydrofluorocarbon polymer.
  • the first and the second fluoropolymers may be the same polymer.
  • the first and second fluoropolymers are ethylene tetrafluoroethylene copolymer.
  • the liquid first fluoropolymer may be a polymer that has a molecular weight and/or a level of crosslinking that is less than the polymer used to form the particles of the second fluoropolymer.
  • the liquid first fluoropolymer will, generally, be a liquid at or proximate to room temperature (25 °C).
  • the first and second fluoropolymers are different polymers.
  • the liquid first fluoropolymer is an ethylene tetrafluoroethylene copolymer
  • the second fluoropolymer is selected from the group consisting of ethylene chlorotrifluoroethylene, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, and perfluoroalkoxy alkanes.
  • the metal surface may be any metal (either a pure metal or an alloy) that can benefit from having a hydrophobic coating.
  • the metal surface is part of a condenser for a liquid (e.g., water) condensation system.
  • the metal is copper.
  • the metal surface may be flat or curved, depending on the application.
  • the metal surface e.g., copper
  • the metal surface may be the exterior of a tubular conduit (a pipe) that forms the condenser of the condensation system.
  • the liquid first fluoropolymer is applied using a spray coating process. It should be understood, however, that while a spray coating process is described herein, other methods (e.g., dip coating, deposition, etc.) could also be used to produce the initial coating.
  • a spray coating process the liquid fluoropolymer is applied as a neat liquid or may be dissolved in a suitable solvent (e.g., water) and sprayed onto the metal surface. When a solvent is used, the metal surface may be heated to accelerate evaporation of the solvent. In some embodiments, the neat liquid first fluoropolymer may be heated to reduce the viscosity of the polymer.
  • the sprayed on layer may be further dried by applying a heat (e.g., using infrared light) to the coating to remove all of the solvent.
  • a heat e.g., using infrared light
  • spray coating systems may be found in European Patent No. 894 541; PCT Publication No. WO 02/14065; and U.S. Patent Nos.: 5, 160,791; 5,230,961; 5,223,343; 5, 168,107; 5, 168,013; and 7,462,667, all of which are incorporated herein by reference.
  • particles of a second fluoropolymer are applied to the first coating.
  • the applied particles become embedded in the liquid first coating to form a coated metal surface.
  • Any commercially available powder coating equipment can be used to apply the particles of the second fluoropolymer.
  • Fluoropolymer powder coatings may be applied as a free- flowing dry powder and does not need a solvent to keep the binder parts and filler parts in a liquid suspension form.
  • Fluoropolymer powder coatings are applied electrostatically with a fluidized bed or spray gun. Because fluoropolymer powder permits a wide range of application voltages, voltage application and techniques are dependent on the equipment are used for such application.
  • the fluoropolymer powder coating forms a skin.
  • a coated part may become too insulated after electrostatically applying one or two coats of a fluoropolymer powder. When this condition occurs the part may be sprayed hot (hot flocked) as it comes out of the oven after being cured.
  • Fluoropolymer coating can produce thicker coatings than conventional liquid coatings without running or sagging. Because powder coating does not have a liquid carrier, when compared to liquid coating, fluoropolymer powder coating produces almost no appearance differences between horizontally coated surfaces and vertically coated surfaces. Fluoropolymer powder coating process emits few volatile organic compounds; due to no carrier fluid to evaporate away. Different colored fluoropolymer powders could be mixed together before curing allowing for color blending and bleed special effects in one single layer.
  • the substrate becomes somewhat electrically insulated. Subsequent coats of the particles are poorly attracted, resulting in less coating of the substrate with each application of particles.
  • the metal substrate is heated and, shortly after the part is removed from the heat source, the particles of the second fluorinated polymer are applied to the heated substrate. This method is generally known as hot flocking.
  • the hot flocking method may be combined with the electrostatic application.
  • the coating thickness will vary depending on the mass of the part, and its temperature and its ability to hold heat. Generally a thicker film may be obtained by spraying a hot part than spraying a cold part. To decrease pit formation on the surface of the part, it may be necessary to decrease the application voltage after the first coat of particles.
  • Fluoropolymers may be given an electrostatic charge which will help attract the particles to a grounded metal part.
  • a maximum voltage charge may be employed.
  • the voltage used usually varies with specific equipment use, but is generally in the range of 20-30 kV. Adjusting air pressure delivery will help produce a powder cloud that does not blow past the part.
  • Electrostatic gun The most popular form of applying powder coating to metal objects is to spray the powder with the use of electrostatic gun (corona gun).
  • the gun exposes the powder to positive electrostatic charge, the powder is sprayed towards a grounded metal part mechanically or by compressed air, and the powder is accelerated toward the metal part by powerful electrostatic charge.
  • the electrostatic gun (corona gun) uses a strong electric field between the ionized tip inside the gun and the part to be sprayed.
  • the powder particles gain a negative charge as they pass through the ionized field.
  • the particles repel each other as mist because of the similar charge they carry. These particles as they discharge out of the gun, they follows the field lines to the part to be coated, coating all sides of the part.
  • the thickness of the coat is reliant on the amount of voltage is applied. Because there is no electric field inside the part, the inside of the part is not coated. This phenomena is called the Faraday cage effect.
  • Electrostatic coating equipment uses a wide variety of spray nozzles which depends on the shape of the work piece to be coated and the thickness of the coat. Once the spray coat is done, the coated part will be heated, the powder melts into a uniform film, and the coated part is coaled to allow for the coat to harden. Preheating the metal part before spray coating it can help achieve a uniform finish but also can cause problems by excess powder.
  • Another method is to use a tribo gun, which uses triboelectric friction to charge the powder.
  • the tribo uses mechanical application of charge to the powder particles by means of friction as these partials are deflected and forced to rub against Teflon tubing inside the barrel of the gun.
  • the charged powder partials once is released from the gun, adhere to the grounded surface of the part. Since there is no external electric field for the traveling particles to follow, this method becomes very useful when need is arisen to coat the inside area of the part.
  • Tribo gun requires different powder formulas than the one used for corona gun.
  • the tribo gun does not have problems associated with back ionization and the Faraday cage affects that corona gun encounter.
  • Fluidized bed is another technique is used to apply powder coating on substrate, where the part to be coated is heated and dipped into aerated powder-filled bed. Then the powder gets hot, starts to melt, and sticks to the substrate. Finally, the part is heated to finish cure the part. This method is preferred when a thickness of coating more than 300 m is needed. Electrostatic fluidized bed coating
  • Electrostatic fluidized bed coating is much similar to fluidized bed dib coating except for the electrostatic charging medium paced inside the bed which charges the powder partials as the fluidizing air lifts it up.
  • the charged powder partials form a cloud and move in an upward direction above the fluid bed.
  • the grounded substrate move in a downward direction inside the cloud of charged powder particles, the particles get attracted to the substrate and attached to its surface.
  • the substrate to be coated is not preheated before gets dipped in the electrostatic fluidized bed and much less powder depth is used as it is for fluidized bed dipping.
  • Electrocoat dip (electrodeposition)
  • metal parts are dipped into a tank with electro charged primer in it.
  • An electric current is used to apply a primer to a conductive substrate.
  • the part gets dipped into an electrocoat dip tank.
  • An electrical charge is applied to the primer powder.
  • the powder is then gets attached to the conductive substrate.
  • the part then moves to the rinse tank. Finally the part is moved to the oven to be cured.
  • Electrocoat dipping is fully automated and is minimizes powder waste (no pollution), reduces parts weight, coat parts uniformly, coat complex-shaped pars.
  • the polymer After application of the particles to the second fluoropolymer, the polymer is cured by heating the coated metal surface to produce the fluorinated polymer coating.
  • the coated metal surface is heated at a temperature, and for a time, sufficient to form a hierarchal structure on the metal surface comprising particles of the first fluoropolymers embedded in a film of the second fluoropolymer.
  • substrates and surface preparation of these substrates should be considered.
  • Substrates which have thermal and dimensional stability at bake temperature can be coated with fluoropolymer coatings. These substrates should be free of excessive roughness at joints and welds, excessive pits or porosity, and sharp corners and edges before treated with fluoropolymers.
  • copper is used as the substrate. Copper is thermally stable under a bake temperature, thus it can be coated with fluoropolymers.
  • Fluoropolymer should not be applied until the substrates are cleaned. Precaution must be taken to remove all residues from the cleaning process when using chemical washes or solvent cleaning and degreasing. It is also recommended to physically remove dirt, paint, mill scale, rust, or any foreign species that industrial chemical washes or solvent cleaning and degreasing could not remove. Gloves should be used to handle metal after metal cleaning to avoid fingerprint and/or residual oil contamination which may show up as a stain on the finish.
  • Preheating has its advantages when the substrate is ferrous metal, whereas it is temporarily passivate the surface against rusting and the blue oxide formed increases the adhesion of the acid primers.
  • the advantages of preheating are not existent in the case of aluminum and stainless steel and preheating the metal substrate step can be omitted where clean metal is involved.
  • Preheating copper and brass in air should be avoided because the resulting oxide has poor adhesion to the metal substrate.
  • a formic acid rinse should be used.
  • grit blasting The most common method to obtain good adhesion of fluoropolymer coatings is via grit blasting. In order to retain the protective oxide formed on ferrous metal, grit blasting should always precede preheating. The order of operating preheating and grit blasting is of less importance for other clean substrates. Profiling a surface in excess of 100 microinches (2.5 microns) is recommended and profiling a surface in the range of 200-250 microinches (5.1-6.5 microns) is frequently employed. Aluminum oxide grits range from #40 to #80 at air pressures ranging from 80 to 100 psi (5.8 to 7.3 kg/cm2) at the gun, are commonly used on hard substrates.
  • Air pressures ranging from 80 to 100 psi (5.8 to 7.3 kg/cm2) or below are commonly used on aluminum and brass substrate. Air pressure of excess of 100 psi (7.3 kg/cm2) may be used on stainless steel. Chilled iron grit has found considerable use in blasting metal substrates because of its high density and sharp particle shape. This grit, which is recommended for centrifugal abraders, is approximately twice that of aluminum oxide because its density.
  • Sand is not recommended to be used to rough a substrate because it is considered too smooth, uniform, and short-lived yet glass beads are compatible to aluminum oxide grits and have produced the same surface roughness.
  • Micro-inches or root mean square (RMS) by means of a profilometer are common measuring units for grit blast profiles. Also eddy-current thickness gauge is used as a rough estimate of profile of nonferromagnetic metal.
  • grit blasting is the method of choice for metal treatment for the application of most fluoropolymer coatings
  • other surface roughening methods are used when best adhesion is not required such as directional grinding, wheel sanding, and wire brushing.
  • Directional grinding, wheel sanding, and wire brushing reduce adhesion in the direction of the grind.
  • chemical etching gives smooth peaks, without the sharp "tooth”.
  • rough, as-cast surfaces also are too smooth in microprofile. Rather than cleaning with any wet method such as chromic acid, hydrochloric acid, or sulfuric acid, it is much better to clean by grit blasting, sandpaper, steel wool, or No. 400 emery cloth.
  • Caution must be used as etching reagents require immediate rinse to prevent salts from depositing on the surface which would lead to oxidizing or rusting problems that may require additional physical cleaning work with steel wool or No. 400 emery cloth in addition to rinsing and drying to remove the oxidation.
  • Micro crystal-line zinc phosphate is an effective conversion coating for steel substrates.
  • manganese phosphate has proven to be very effective conversion coating, especially in corrosive environments.
  • iron phosphate on steel has been proven less effective conversion coating, especially when corrosion resistance is needed.
  • Chromate conversion coatings are proven to be the best conversion coating for aluminum. Conversion coating may not work for all metal substrate and it should be applied on case to case basis as necessary.
  • Coatings should be applied immediately after grit blasting because steel and iron rust rapidly.
  • a solvent rinse with VM&P naphtha or toluene containing 5% kerosene may be employed, where delay is expected, or under conditions of high humidity.
  • a very thin film of kerosene remains to prevent rusting temporarily, when the volatile solvent evaporates. If the thin film of kerosene has been sitting for a long time, the kerosene film may collect dust and require solvent washing before the finish is applied. Phosphate or other metal cleaning treatments could cause poor adhesion of fluoropolymer coatings.
  • Nonvolatile alkalis could promote poor adhesion to steel because it permeates the pores of the metal to the extent that a definite alkaline reaction to phenolphthalein can be obtained. If these problems arise it is recommended before applying the liquid fluoropolymer to neutralize the alkali by soaking the metal in a dilute solution of phosphoric or chromic acid followed by rinsing with water. Due to the presence of one or more contaminants such as fingerprints, forming lubricants, grease, or oils on the metal when the finish is applied, spotting or staining of the primers occasionally occurs. After grit blast, the metal may be preheated, rinsed, or solvent cleaned in a (10%) chromic acid solution for a few minutes to avoid such contaminations. It is recommended if present, rust spots should be removed before priming.
  • the metal substrate should be cleaned and roughened.
  • Solvent degreasing is an alternative cleaning method, yet safety and health precaution should be taken into consideration when using such method, i.e. it is not recommended to solvent clean by hand.
  • a high-temperature burn-off prior to grit blasting is employed. It is preferred that roughening is done by grit blasting with aluminum oxide. To create sharper peaks and valleys, it is recommended to use a new grit which will give the best profile when compared to old, rounded grit.
  • the blast profile (surface roughness depth) should be at least 75-125 ⁇ (3-5 mil).
  • a coarse grit (10-20 mesh) could be employed using 620-690kPa (90-100 psi) air pressure.
  • a lower blast profile is more appropriate for thin films.
  • a method of producing purified water includes: obtaining a coated metal tubular conduit having a hierarchal structure on the metal surface as described above. A cooling fluid is then passed through the metal tubular conduit.
  • the cooling fluid may be at or below room temperature (about 25 °C). In some embodiments, the cooling fluid may pass through a cooler to lower the temperature of the fluid before passing the fluid into the coated metal tubular conduit.
  • the cooling fluid may be water or may be an organic fluid such as ethylene glycol, alcohols or mixtures of organic fluids with water.
  • Moist air e.g., air having a relative humidity of at least about 10% is then brought into contact with the coated metal tubular conduit.
  • water in the moist air will begin to condense on the conduit and can be collected.
  • the air is at a temperature that is greater than the temperature of the cooling fluid passing through the metal tubular conduit.
  • ETFE was studies as a preferred substrate for coating a metal substrate.
  • a liquid ETFE primer was applied to the substrate, followed by the application of powdered ETFE to the primer coated substrate. Subsequent curing produced a hydrophilic coating on the substrate that can be used in a condensation reaction.
  • Teflon® ETFE (699N-129 Black or 532-6405 Green) is superior to most other fluoropolymers and it has been used without a primer in a variety of applications.
  • the adhesive strength of the bond can be doubled by using Teflon® liquid primers.
  • the 699N-129 black liquid primer is formulated with adhesive resins having outstanding resistance to high temperatures that withstand thermal abuse from multiple bakes during topcoat application, thus making 699N-129 black Liquid Primer recommended for all coating systems.
  • 699N-129 black liquid primer should be applied in a thin layer, barely hiding the blasted substrate when wet.
  • the actual thickness of 699N-129 black liquid primer should vary depending on the depth of blast profile. For example; 699N-129 black liquid primer thickness of approximately 14 ⁇ [0.5mil], will require a blast profile of 75 ⁇ [3mil]. To prevent intercoat adhesion failure, excessive thickness should be avoided. After air drying, small white specs of
  • ETFE particles may be visible and 699N-129 black liquid primer should visibly appear to be slightly rough with a dull, mottled look, which is normal. Preheating substrates to 50°C (120°F) will minimize carbon steel from rusting, especially during humid weather or cool, damp, early morning start-ups. Also 699N- 129 Liquid Primer is equipped with antiflash-rust additives to prevent carbon steel substrates from rusting once it is coated. The first powder topcoat can be applied directly over wet, air-dried, or force-dried 66°C [150°F] primer. Avoid fully pre-baking the primer. Another particularly useful primer is Acquis Liquid Base primer, which is composed of ETFE polymer having a low glass transition state (below room temperature) allowing the neat polymer to act as a liquid at room temperature (about 25 °C)
  • the part may be finished with a final coating of 532-6310 Clear High-build Topcoat
  • Powders or for smoother final coating finish use 532-6210 Clear Ultrasmooth Topcoat Powders. It is recommended if using 699N-129 black liquid primer to apply the first topcoat powder electrostatically to a cold substrate and then place the part into a warm oven at approximately 300°F. The temperature should be stepped up to the recommended bake temperature once the temperature of the part reaches 300°F. To avoid heating the surface of the first coat too long, the cold part should not be loaded into an oven set at the final bake temperature, especially when the part is too thick or would take a long time to heat up. During hot flocking application the film build per coat is typically 75-250 ⁇ (3-10mil). However, depending on the mass and size of the parts coated, hot flocking can yield highly variable builds per coat. The following combination of DuPont martial coatings on 12 inch copper pipes are used throughout the experimentations. 12 inch copper pipes were also used with no DuPont material coating for comparison.
  • FIGS. 1-4 depict various views of a condensation tower used in this study.
  • the condensation tower is made of aluminum structural supports, transparent flexi glass and black flexi plastic.
  • FIG. 1 depicts a perspective view of the condensation tower.
  • the condensation tower includes a lower section for holding the hot air source (for these experiments, a steamer) and a clear upper section that holds the condenser pipe.
  • cooling reservoirs containing a cooled fluid in this experiment, ice water
  • the cooling reservoirs may include a pump for transferring cold fluids through the cooling fluid pipes, into the condenser pipe and into the opposing reservoir.
  • the condenser's outside wall temperature is measured throughout the experiment to ensure the pipe's wall temperature stays at about 25°C.
  • FIG. 3 shows a top down inside view of the condensation tower.
  • Condenser is connected across the upper section of the condensation tower.
  • a steamer is placed at the bottom of the condensation tower.
  • Steamer includes a metal reservoir (e.g., a stainless steel bowl) coupled to a heat source (not shown). Water placed in the metal reservoir is heated to produce steam.
  • the steamer is equipped with a temperature control valve that allows the steam to be kept at a temperature of between about 80 °C to about 85 °C.
  • FIG. 4 shows depicts a water collection device positioned below the condenser.
  • the water collection device includes a grill and a water collection container.
  • the grill is angled downward toward the water collection container. The grill does not affect the amount of steam that reaches the pipe since the steam rises and is exposed to the pipe's cold radiation. Condensation will occur at the surface of the pipe due to the temperature difference between the outside wall of the pipe and the hot steam.
  • Condensation on untreated copper pipe - control experiment #1 A length of untreated copper pipe was placed in the upper section of a condensation tower. Ice cooled water was used to keep the surface of the untreated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the copper pipe was measured to be 66 mL. The experiment was repeated twice and the amount of water collected was 67 mL in the second experiment and 63 mL in the third experiment. The average water collection was about 65 mL. Condensation on hand sanded (with 400 grit sandpaper) copper pipe - control experiment #2
  • a 1-inch diameter copper pipe was produced having a ETFE 699N-129 rough coat to give the copper pipe surface a rough appearance with nano-projections similar to the lotus leaf wax crystal without the microscopic bumps that are coated with a nanoscopic water-repellent coating (wax crystal).
  • the ETFE 699N-129 coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with ETFE 699N-129 at 40 psi and dried under a heat light for 5 minutes.
  • the ETFE 699N-129 coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the ETFE 699N- 129 coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the ETFE 699N-129 coated copper pipe was measured to be 96 mL. The experiment was repeated twice and the amount of water collected was 95 mL in the second experiment and 92 mL in the third experiment. The average water collection was about 94 mL.
  • a 1-inch diameter copper pipe was produced having a PTFE 850G-204 Liquid Acid Green rough coat.
  • the PTFE 850G-204 Liquid Acid Green coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PTFE 850G-204 Liquid Acid Green at 40 psi and annealed by heating to 750 °F for 10 minutes.
  • the PTFE 850G-204 coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the PTFE 850G- 204 coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PTFE 850G-204 coated copper pipe was measured to be 70 mL. The experiment was repeated twice and the amount of water collected was 72 mL in the second experiment and 71 mL in the third experiment. The average water collection was about 71 mL.
  • FIG. 8 is a photograph of the copper pipe after spray coating with ETFE 699N-129 and curing.
  • the cured ETFE 699N-129 layer was spray coated with ETFE 532G-6410 at 40 psi and the pipe annealed by heating to 580 °F for 30 minutes.
  • FIG. 9 is a photograph of the pipe after spray coating with the ETFE powder topcoat and annealing.
  • the ETFE 699N/532G coated copper pipe has been placed in the condensation tower, but steam has not yet been introduced into the tower.
  • FIG. 1 1 is a photograph of the ETFE 699N/532G coated copper pipe with water droplets formed on the pipe from the stem in the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the ETFE 699N/532G coated copper pipe was measured to be 221 mL. The experiment was repeated twice and the amount of water collected was 223 mL in the second experiment and 215 mL in the third experiment. The average water collection was about 220 mL.
  • a 1-inch diameter copper pipe was produced having ETFE 532G-6405 base (first) coat which is top coated with super high-build clear ETFE 532G-6410.
  • the ETFE 532G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with ETFE 532G-6405 at 40 psi. The ETFE 532G- 6405 layer was spray coated ETFE 532G-6410 at 40 psi and the pipe annealed by heating to 580 °F for 30 minutes.
  • the ETFE 532G coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the ETFE 532G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the ETFE 532G coated copper pipe was measured to be 91 mL. The experiment was repeated twice and the amount of water collected was 105 mL in the second experiment and 93 mL in the third experiment. The average water collection was about 96 mL.
  • a 1-inch diameter copper pipe was produced having PTFE 850G-204 base (first) coat which is top coated with low coefficient of friction PTFE 851G-214.
  • the PTFE 850G/851G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PTFE 850G-204 at 40 psi and annealed by heating to 550 °F for 3 minutes.
  • the PTFE 850G-204 layer was spray coated with PTFE 851G- 214 at 40 psi and the pipe annealed by heating to 800 °F for 5 minutes.
  • the PTFE 850G/851G coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the PTFE 850G/851G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PTFE 850G/851G coated copper pipe was measured to be 90 mL. The experiment was repeated twice and the amount of water collected was 85 mL in the second experiment and 88 mL in the third experiment. The average water collection was about 88 mL.
  • a 1-inch diameter copper pipe was produced having PFA 420G-703 base (first) coat which is top coated with PFA 532G-5010.
  • the PFA 420G/532G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PFA 420G-703 at 40 psi. The PFA 420G-703 layer was spray coated with PFA 532G-5010 at 40 psi and the pipe annealed by heating to 750 °F for 15 minutes. The PFA 420G/532G coated copper pipe was handled with care by wearing gloves to prevent any contamination.
  • Ice cooled water was used to keep the surface of the PFA 420G/532G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PFA 420G/532G coated copper pipe was measured to be 60 mL. The experiment was repeated twice and the amount of water collected was 65 mL in the second experiment and 64 mL in the third experiment. The average water collection was about 63 mL.
  • a 1-inch diameter copper pipe was produced having PFA 420G-703 base (first) coat which is top coated with FEP 532G-8110.
  • the PFA/FEP coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PFA 420G-703 at 40 psi. The PFA 420G-703 layer was spray coated FEP 532G-8110 at 40 psi and the pipe annealed by heating to 750 °F for 20 minutes. The PFA/FEP coated copper pipe was handled with care by wearing gloves to prevent any contamination.
  • Ice cooled water was used to keep the surface of the PFA/FEP coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PFA/FEP coated copper pipe was measured to be 73 mL. The experiment was repeated twice and the amount of water collected was 70 mL in the second experiment and 72 mL in the third experiment. The average water collection was about 72 mL.
  • Table 1 summarizes the amount water collected by each type of pipe.
  • FIG. 5 A scanning electron microscope images reveal that the leaves of the Lotus leaf are very rough and covered in micro-lumps and bumps of protruding epidermal (outermost) cells, which in turn, are covered in wax crystals around one nanometer in diameter.
  • FIG. 5 A schematic diagram of a lotus leaf micro- and nano- structure is shown in FIG. 5.
  • the wax crystals are hydrophobic (water hating) and so they repel water and keep water from getting into the valleys between the bumps.
  • the bumps minimize the area of contact.
  • FIG. 6 depicts wetting of four different surfaces. The combination of these micro- and nano-scale features allow the spherical water drops to roll off the lotus leaf, which is the key to the cleaning process.
  • ETFE 699N-129 represents a "nano structure" surface. This primer, when it is baked, turns to a rough surface similar to sand paper rough surface because of the water base. ETFE 699N-129 water-base primer has a slightly rough with a dull, mottled look, and with small white specs (ETFE projected particles) are visible, which gives the surface of the pipe the lotus leaf effect. The height of the projected partials is controlled by the thickness of the primer applied to the surface of the pipe. This primer was able to hold the water on the top of the projected partials for the whole experiment. Each water droplet was very small and suspended by a single asperity. The lotus leaf is covered with structural hierarchy called protuberances.
  • Protuberances have the shape of hemispheroids (which will give the surface of the leaf hills and valleys). These hemispheroids are covered with wax crystalloids that point outward.
  • ETFE 532G-6410 high build top coat finish is tough, seamless, and with pinholes that gives the surface hills and valleys.
  • a topcoat ETFE 532G-6410 was added on top of ETFE 699N-129 primer, the surface of the pipe started to mimic the surface of the lotus leaf.
  • the lotus leaf is made of microscopic bumps that are coated with a nanoscopic water-repellent coating (wax).
  • ETFE with aqueous (water-base) primer was a better water repellent than ETFE with powder primer. This has to do with water base surface acts as a sealer so water won't penetrate into the surface.
  • Dirt particle build up on the lotus leaf will change the minimum contact area of the water droplet and changes the surface tension.
  • Water droplets are able to minimize their surface adhesion by achieving a spherical shape and when the water droplets roll across the surface of the lotus leaf contaminates are picked up keeping the surface of the leaf clean.
  • This cleaning mechanism is due to the adhesion between the dirt particle and the droplet, which is higher than between the particle and the surface.
  • this self-cleaning mechanism does not work with organic solvents. If the pipe is dirty, then the initial droplets did not have good adhesion with surface of the pipe and became deformed.
  • ETFE 699N-129 aqueous primer is unique due to the fact it is made of solid fluorocarbon and hydrocarbon at the same time.
  • ETFE 699N-129 water-base primer has a slightly rough with a dull, mottled look, and with small white specs (ETFE particles) are visible, which gives the surface of the pipe projection like the wax crystals on the lotus leaf.
  • ETFE 532G-6410 high build top coat finish is tough, seamless, and with pinholes that gives the surface hills and valleys. Adding the topcoat ETFE 532G-6410 on the top of ETFE 699N-129 primer produced a coating that mimics the surface of the lotus leaf. ⁇ It is believed that the reason DuPont ETFE 699N-129 can be deposited on a copper substrate, while ETFE 532G-6405 is difficult to apply, has to do with the fact that ETFE 699N- 129 is in a liquid form, which makes it melt while baking instead of burning off. So ETFE 699N-129 aqueous (water-based) primer is the only ETFE primer could be applied directly to metal surface without having to use topcoat. The topcoat could be added later to ETFE 699N-129 aqueous (water-based) primer.
  • ETFE 699N-129 has shown more repellency than all DuPont primers and topcoats and the only thing was better than ETFE 699N- 129 is ETFE 699N-129 with ETFE 532G-6410 topcoat.
  • Copper pipe coated with ETFE 699N-129 aqueous prime with secondary projections was found to be superior hydrophobic surface and excellent repellent.
  • a copper pipe coated with ETFE 699N-129 aqueous primer was repelling more water than other coated copper pipes with Teflon primers and was repelling more water than copper pipes with smooth Teflon top coats.
  • ETFE 699N-129 aqueous primer showed it superiority when was top coated with ETFE high built top coat with seamless and tough surface which gave the surface of the pipe hills and valleys.
  • the copper pipe was repelling at least twice more water than copper pipe with ETFE 699N-129 aqueous primer alone.
  • Supper hydrophobic surface is not the best solution as it will make it very difficult for heat to flow to the surface of the pipe through a full sphere of liquid drop.
  • Primer 420G-703 top coated with PFA 532G-5010 is an example of such surface where the amount of water accumulated was the least and the droplets on the surface of the pipe were supper hydrophobic.
  • Primer 699N-129 is an example of surface with small droplets hanging on the top of asperity. Droplets on top of nano-structure have more chance to let heat flow underneath the droplet to the surface of the pipe. Primer 699N-129 is an example of such surface.
  • ETFE 532G-6405 powder primer top coated with supper high- build clear ETFE 532G-6410 is an example of such surface.
  • the best surface to for heat flow is Ultraphobic surface where the surface has a double structure of both micro structure bumps (hills and valleys) and nano structure wax crystals (specs) sticking out of the micro structure where it will allow more heat to flow to the conducting surface. Heat will be able to flow from underneath the wax crystals and between the hills and valleys to the condensing surface continuously thus increasing heat flow under the droplet to the condensing pipe. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

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Abstract

La présente invention concerne une surface de substrat sur laquelle se trouve une structure hiérarchique, la structure hiérarchique comprenant des couches de polymère de fluorocarbone et/ou de polymère d'hydrofluorocarbone liquides et des particules d'un polymère de fluorocarbone et/ou d'un polymère d'hydrofluorocarbure. La structure multicouche compromet une structure nano-texturée et/ou micro-texturée d'un revêtement de polymère de fluorocarbone et/ou de polymère d'hydrofluorocarbone sur la surface du substrat. La couche liquide du polymère de fluorocarbone et/ou du polymère d'hydrofluorocarbure est incorporée entre la surface de substrat et la couche de particules supérieure. Le polymère de fluorocarbone structuré multicouche et/ou un polymère d'hydrofluorocarbone recouvrant un substrat sert de biomimétique de l'effet feuille de lotus.
PCT/US2018/059492 2017-11-06 2018-11-06 Substrat métallique revêtu de fluoropolymère superhydrophobe couche par couche permettant une condensation goutte à goutte Ceased WO2019090356A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5922468A (en) * 1995-07-13 1999-07-13 E. I. Du Pont De Nemours And Company Tetrafluoroethylene polymer dispersion composition
US20030128519A1 (en) * 2002-01-08 2003-07-10 International Business Machine Corporartion Flexible, thermally conductive, electrically insulating gap filler, method to prepare same, and method using same
US20060110601A1 (en) * 2004-11-19 2006-05-25 Hennessey Craig K Process for applying fluoropolymer powder coating as a primer layer and an overcoat
US20100092759A1 (en) * 2008-10-13 2010-04-15 Hua Fan Fluoropolymer/particulate filled protective sheet
US20150087110A1 (en) * 2013-09-21 2015-03-26 Northwestern University Low-Temperature Fabrication of Spray-Coated Metal Oxide Thin Film Transistors

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5922468A (en) * 1995-07-13 1999-07-13 E. I. Du Pont De Nemours And Company Tetrafluoroethylene polymer dispersion composition
US20030128519A1 (en) * 2002-01-08 2003-07-10 International Business Machine Corporartion Flexible, thermally conductive, electrically insulating gap filler, method to prepare same, and method using same
US20060110601A1 (en) * 2004-11-19 2006-05-25 Hennessey Craig K Process for applying fluoropolymer powder coating as a primer layer and an overcoat
US20100092759A1 (en) * 2008-10-13 2010-04-15 Hua Fan Fluoropolymer/particulate filled protective sheet
US20150087110A1 (en) * 2013-09-21 2015-03-26 Northwestern University Low-Temperature Fabrication of Spray-Coated Metal Oxide Thin Film Transistors

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