6 Coatings Market50+ billion USD worldwide, divided into 3 main segmentsArchitectural: Paints, varnishes, and lacquers for direct application to interior or exterior surfaces of buildings~50% of total market, but lowest profit marginGenerally air-driedSherwin-Williams, Benjamin Moore, ICI PaintsOEM/Product: Applied to equipment in a manufacture processAppliances, cars, industrial machinery, furniture, …~35% of total market, higher profitsBaked, radiation-cured, electrostatic-sprayAutomotive: PPG, DuPont, BASFSpecialty Market: Everything elseAuto refinish, traffic marking, …~15%, usually high-valueAir or force driedPPG, DuPont, Akzo Nobel, …OEM = original equipment manufacturer
8 What is in a can of paint? Solvent Pigments Binder (polymer) Additives 16%Pigments45%Binder (polymer)32%Additives4%Water based paints may have considerably more liquid carrier
9 1 pascal second = 10 poise = 1,000 millipascal second 1 centipoise = 1 millipascal secondFormally, viscosity (represented by the symbol η "eta") is the ratio of the shearing stress (F/A) to the velocity gradient (Δvx/Δz or dvx/dz) in a fluid.The most common unit of viscosity is the dyneﾊsecondﾊperﾊsquareﾊcentimeter [dyne疽/cm2], which is given the name poise [P] after the French physiologist Jean Louis Poiseuille ( ). Tenﾊpoise equal one pascal second [Pa疽] making the centipoise [cP] and millipascalﾊsecondﾊ[mPa疽] identical.
12 Newtonian FluidsNewtonian flow paints would also flow away from sharp corners and edges and give significant sagging or curtaining problems when applied.
13 MATERIAL APPROXIMATE VISCOSITY (in centipoise)70 F 1 to 5Blood or Kerosene 10Anti-Freeze or Ethylene Glycol 15Motor Oil SAE10 or Mazola Corn Oil 50 to 100Motor Oil SAE30 or Maple Syrup 150 to 200Motor Oil SAE40 or Castor Oil 250 to 500Motor Oil SAE60 or Glycerin 1,000 to 2,000Karo Corn Syrup or Honey 2,000 to 3,000Blackstrap Molasses 5,000 to 10,000Hershey Chocolate Syrup 10,000 to 25,000Heinz Ketchup or French's Mustard 50,000 to 70,000Tomato Paste or Peanut Butter 150,000 to 250,000Crisco Shortening or Lard 1,000,000 to 2,000,000Caulking Compound 5,000,000 to 10,000,000Window Putty ,000,000
15 Non-Newtonian Liquids: (Time Independent) Pseudo-Plastic Pseudoplastic flow can be considered to be a combination of Newtonian flow and plastic flow. As such it combines the properties of these two rheological conditions. At low rates of shear, Newtonian flow properties exist, leading to the possibility of settling, separation and syneresis in the can but excellent flow on application. At higher shear rates, including those at application, plastic flow conditions exist developing the wet film properties associated with plastic flow.molten thermoplasticspolymer solutions such as polyethylene oxide in watersome paints.shampooketchup
16 Many shear-thinning fluids will exhibit Newtonian behavior at extreme shear rates, both low and high. For such fluids, when the apparent viscosity is plotted against log shear rate, we see a curve like this.
17 Shear Thickening (Time Independent) Dilatant Solids dispersed in liquidViscosity increases with rate of shear. Some examples of shear-thickening fluids are corn starch, clay slurries, and solutions of certain surfactants. Most shear-thickening fluids tend to show shear-thinning at very low shear rates. Another important type of non-Newtonian fluid is a viscoplasticDilatancy in a finished paint is not desirable due to its adverse influence on application properties. The high shear rate under application shear stress means that application becomes difficult with the possibility of the paint "powdering" on application and being unable to re-flow after the force has been removed.Corn starch, clay slurries, wet sand (quick sand)surfactant solutions, peanut butter, filled composites
18 Plastic Fluids: have a yield stress threshold No flow until a critical stress is reacted.ToothpasteDrilling mudMayonnaiseSome paintsGreaseThe yield point associated with plastic flow gives excellent settling, separation and syneresis resistance in the can. However, if the yield point is too high, flow problems can occur on application, lack of flow of application patterns (brush marks, orange peel) is a distinct possibility. If too low, sagging and curtaining become problemsSome paints also display viscoplastic behavior.Excellent settling & separationresistance in canToo high yield point: problems applying & orange peelToo low: sagging & curtaining
19 Time dependent Non-Newtonian Viscosity The viscosity of the fluid is dependent on temperature, shear rate and time. Depending on how viscosity changes with time the flow behaviour is characterised as:･Thixotropic (time thinning, i.e. viscosity decreases with time) yoghurt, paint･Rheopetic (time thickening, i.e. viscosity increases with time)-gypsum pasteThixotropic fluids are quite common in chemical as well as in food industry. Rheopectic fluids are very rare.
21 Polymeric CoatingsCoatings are materials that are applied to a surface which form a continuous film in order to beautify and/or protect the surface.Paint: Pigmented surface coatingVarnish: Coating that lacks a pigmentLacquer: Thermoplastic solution paintsor varnishes, term also usedfor all clear wood finishesEnamel: Hard, thermosetting paints
22 Paint:Interesting Facts A jumbo jet needs 2 tons of paint.The world's shipping fleet would produce an extra 70 million tons of greenhouse gasses and nearly 6 million tons of acid-rain-producing sulfur dioxide if ships were not treated with anti-fouling paints
24 Contents of Paint Pigment Provides color and durability Also improves the strength of the paintBinderHolds the pigment in liquid formWhen applied it then gives the paint the ability to adhere to the surface.SolventEffectively thins the paintIt carries the pigment and binderUsed to regulate how much a paint flowsCalled a “thinner” when used with lacquerCalled a “reducer” when used with enamel
25 Binders: Polymers Thermosets Thermoplastics (latexes) Alkyds Epoxies UrethanesFormaldehyde resinsAlkyds (classic oil paint)Thermoplastics (latexes)Acrylics + other vinyl monomersVinyls: vinylacetate copolymers with acrylics, vinyl chloride, styreneAFM of latex
26 General Coating Formulations Method Polymer Solids Polymer Dry rate Min. dry Handling/ ExamplesM.W structure (no heat) temp StorageEvaporation high (i) low, linear fast no practical good nitrocellulose10-35% limit other lacquers;solution (solutions) some emulsion(ii) medium paints %emulsionChemical low medium to crosslinked slow- very slow cans must decorative paintsreaction high, moderate in cold be well some stovingbetween paint 100% weather sealed enamels;and airChemical low or medium to crosslinked fairly varies; two-pack or industrial stovingreaction very high fast °C short shelf finishes; acid-between low % life, unless catalysed poly-paint stoving or urethane andingredients radiation polyester woodcuring type finishes
27 Desired Rheology of Coatings Coating viscosity requirementschange on passing from theapplication to drying stages ofthe process.Applicationbrushing, rolling, spraying processes generate high shear, and favour low viscosity formulationschain orientation and surface imperfections (brush strokes) must be relieved by flow.Film Formation - Dryingsagging during the drying process must be countered by low-shear viscosity.Final Coating Propertiespermanent coating requires near infinite viscosity, through high molecular weight (lacquers) or crosslinking (enamels).htime
28 Solvent-Related Surface Defects Solvent popping results from rapid solvent evaporation and an inability of the coating to flow.Orange peel patterns result from high film viscosity and/or surface tension gradient induced flow.
29 Coating Formulations: Polymeric Binders Coatings employ amorphouspolymers almost exclusively.Glass transition influencesmechanical properties suchas flexibility, hardness, etc.Impact resistance is oftendesired for hard topcoatapplications.Consideration of UV, thermal, oxidative stability depends on application (primer, topcoat).Filler/pigment acceptance,surface energy, miscibilityin solvents/plasticizers.
32 Thermosetting Binders: Epoxy and Polyurethane Resins Epoxy resins are two-component paints formulated from epoxide functionalized monomer and (usually) amine hardeners.Reaction of diisocyanates with diols generates polyurethane coatings whose structure/properties can be varied widely.Polyurethanes afford superiour abrasion and chemical resistance, as well as a fast, low-temperature cure.
33 Polyurethanes Low One part polyurethane Moisture cured polyurethane Acrylic polyols-aliphatic linear isocyanate two part polyurethanesPolyester polyols-aliphatic isocyanate two part polyurethaneHigh
35 Thermosetting Binders: Combination Copolymerization of an acid-functionalized acrylic resin and an epoxy resin yields a crosslinked, block copolymer coating.Anti-corrosive epoxy
36 Epoxy Paints Epoxy coating Two-component paints are delivered in two units. The curing of the paint begins immediately after mixing, and the paint must be used within a limited period - the so-called potlife.A well known two-component paint is epoxy. Epoxies are extremely water and chemically resistant. They are used e.g. for ballast tanks, exterior hulls on ships, bridges and tanks.
38 Thermosetting Binders: Cured Polyesters and Acrylics Unsaturated polyesters and acrylic resins of low molecular weight can be polymerized by free radical addition chemistry to generate a stable, crosslinked film.Consider a resin comprised of 1,2-propylene glycol, phthalic anhydride and maleic anhydride.Free radical polymerization initiated by an organic peroxide generates a networked structure of high molecular weight by addition through unsaturation in the polymer backbone.
39 Thermosetting Binders: Oxidative Drying Alkyds While alkyds can be classified as polyesters, the term is reserved for oil-based finishes.Oils are first transformed into monoglycerides:Film formation resultsfrom condensationpolymerization withdiacid as well asoxidative cure.
40 Thermosetting Binders: Oxidative Drying Oils Coatings containing oil-based films are no longer used as finishes due to poor gloss, soft films and inferiour water resistance.Oils are frequently used in conjunction with other resins to modify drying properties and film structure.Natural oils are extracted fromlinseed, soya bean, coconut, etc.Unsaturated oils are valued fortheir relatively rapid oxidative curing n=32,30,28,26Curing occurs through hydroperoxideformation, followed by alkyl radicalcombination.
41 Water-based formulations: Emulsions Emulsion formulations were developed for environmental reasons and for the delivery of very high molecular weight binders.Water is the continuous phase, which results in a very low viscosity coating.Thixotropic agents are required to raise the zero-shear viscosity of the formulation.Most emulsion paints contain some solvent/plasiticizer to modify the Tg of the polymer.Film formation requires coalescence of polymer particles, which cannot occur below Tg.Organic solvents assist with film formation, and evaporate to leave a solid coating.Alternately, a plasticizing agent is used to maintain a flexible film throughout the object’s lifetime.
42 Thermoplastic Binders: Emulsions Household emulsion paints are usually comprised ofpoly(vinyl acetate-co-ethyl acrylate) or poly(acrylate-co-acrylic acid) resinspigment is dispersed in the continuous aqueous phase with suitable surfactants and water-soluble thickener.plasticizers or volatile solvents are used to lower Tg such that particle coalescence can functionHigh-gloss latex paints cannot be manufactured, as surface uniformity is generally poorResidual surfactant can lead to inferior water stability of latex derived films.AFM of latex
43 Scaling Concepts in Polymer Physics Cornell University Press, 1979 There once was a theorist from Francewho wondered how molecules dance.“They’re like snakes,” he observed,“As they follow a curve, the large onesCan hardly advance.”D ~ M -2de GennesP.G. de GennesScaling Concepts in Polymer PhysicsCornell University Press, 1979
44 Thermoplastic Binders: Lacquers Lacquers harden quickly at all practical temperatures, are supplied in one pack and do not suffer from shelf or pot life problems.comprised of hard linear polymers in solutionCellulose nitrate, a derivative of the natural product cellulose is prepared with varying degrees of modification for different grades:Solubility in esters, ketonesand alcohols depends onextent of cellulosefunctionalizationAcrylic lacquers are comprised of homo or copolymers of acrylates, properties depending on polymer composition distribution:Poly(methyl methacrylate)provides hardness and UVstability. Plasticizers andcopolymerization alters Tg.
45 Coating Formulations: Solvent Selection Criteria Solvating Capacity:Miscibility of polymer/solvent systems are dictated by thermodynamics, as approximated by solubility parameters and hydrogen bonding groupings.Viscosity:Influenced by solvating capacity, but also a function of the viscosity of pure solvent and additives.Volatility:Rate of solvent evaporation influences drying time as well as film aesthetic qualities. Decisions often based upon boiling point/range.Toxicity and smell.Cost.
47 Coating Formulations: Extenders and others Extenders provide no colour to a film, but their use is an inexpensive method of improving adhesion, ease of sanding, film strength and opacity.Calcium carbonate (whitewash)Aluminum silicate (clay)Magnesium silicate (talc)Barium sulphate (barytes)SilicaViscosity Modifierssilicates, clays, poorly soluble resinsDispersion Aidsaid in pigment dispersion - chosen on a case-by-case basisInterfacial Tension Modifiersnon-ionic surfactants, soapsBiocidesinsecticides, fungicides
48 Coating Formulations: Pigments Pigments are selected on the basis of:Particle size Particle shape Refractive IndexTinting strength Lightfastness Hiding PowerThermal Stability Chemical Reactivity Density (cost)Property Preference Reasons(1) Brilliance and Organic The most attractive, cleanest coloursclarity of hue are obtained with organic pigments.(2) White and Inorganic The purest white pigment is TiO2black paints and the most jet black, carbon.(3) Non-bleeding Inorganic Inorganic compounds havenegligible solubilities inorganic solvents. Some organicsare very insoluble.(4) Lightfastness Inorganic Inorganic compounds are generallymore stable to UV than organics.(5) Heat stability Inorganic Very few organic compounds arestable above 300°C.
49 Aesthetic Properties of Dried Film Coatings OpacityExtent of substrate coverage, as determined by pigments,extenders and other occlusionsin the film.Dependent on refractiveindex of fillers relativeto the polymericbinder.Surface FinishGloss is a function of surface irregularity, as determined by the film formation process and dispersion of pigments/fillers.ColorInorganic and organic colourants that are soluble or dispersed in the film (may or may not provide opacity).
50 Thickeners are large water-soluble polymers added to a paint to increase its viscosity. Viscosity can be defined as the resistance of a liquid to flow.This property is important for a paint for several reasons:so the paint can flow out of the canso the paint can be applied to a substrate (glass, wood, steel, etc) using a paint brush or a roller.so the paint does not splatter or drip on the userso no brush marks can be seento prevent settling of the paint in the can during storageso that a "good" film can be formedlm can be formed
51 Engineering Properties of Dried Film Coatings HardnessImpact (& Chip) ResistanceFlexibilityAbrasion ResistanceSolvent ResistanceAdhesionTests:Indentation, Scratch (Pencil)Drop tests, GravelometerElongation, BendFalling sand testMEK (methylethylketone) double rubScraping, Crosscut AdhesionIssues:Properties are a complex function of many factors: Tg, MW, crosslink density, pigmentation, static stress-strain behaviour, transient (creep) behaviorWhat do you test? Free films? Coating with substrate?Weatherability and UV resistance – How does it hold up over time?
52 Coating processes: Coil Coating •Coat sheet metal from coils before shaping• Calendar or knife delivery• Also electrocoat & spray
61 Powder Coating versus Paint no solvent(toxic) solventrecycles unused coatingoverspray wastedsingle layer sufficientseveral layers requiredconflicting flow requirementsviscosity adjusted separatelynow dominates for coating of parts
65 There are 4 key stages in the manufacture process of powder coatings: 1. FormulationThe formulation of powder coatings involves the use of 4 key raw material types: resins, pigments, curing agents and additives. Resins provide strength, durability and adhesion; pigments add color; curing agents ensure that the resins bond to the substrate and harden, and additives give further coating properties such as enhanced application, improved flow, etc.2. PremixOnce a product has been formulated, raw materials are carefully weighed and measured. These raw materials are then blended together, either by mixing or tumbling, to ensure a consistent dispersion of raw materials throughout the mixture.3. ExtrusionThe mixed raw materials are then fed into an extruder. The extruder applies pressure and heat to melt the resins and thoroughly incorporate the pigments, curing agents and other ingredients into a homogenous substance. The extrudate is then cooled and chipped.4. GrindingOnce the extrudate has been cooled and chipped, it is ready to be ground into a fine powder. This powder is then sieved and classified to ensure an even particle size distribution. Particles that are under 10 micrometers or over 120 micrometers can cause application problems and are restricted by the sieving and classification process.ication process.
66 Epoxy powder coated podium Powder coatings have several significant advantages over solvent-based liquid paints:No solvents - Liquid paints can contain up to 70% solvent. Powder coatings contain no solvents, and therefore eliminate solvent release into the environment.Recyclable - Oversprayed powder can be reclaimed and reused, allowing up to 95% material utilization, reducing wasteFewer variables in film properties - The more uniform properties of powders and the elimination of thinners and solvent balancing lead to a more consistent paint film in just one coat.n just oPowder Coating was invented in the 1950's. It is a method of finishing a metallic surface by the application of dry powder. When the powder is fused to the metal with a heat source, the coating forms a continuous and integrated bond with the substrate. Initially, only thermoplastic resins were used in a fluidized bed application system. The development of thermosetting epoxy, polyurethane & polyester resins in the 1960's and 70's, combined with new spray application techniques opened up a much wider segment of the metal finishing industry to powder coatings.
67 Electrocoating or E-coat The Electrocoating Process...• Precipitation of paint particles onto a metal substrate • Highly efficient and automated process • Paint deposition is regulated by voltage • Coating can be either anodic or cathodic• Thermoset curingElectrocoating is an immersion painting process in which charged paint particles are attracted to an oppositely charged metallic surface. As the paint is deposited, it forms a finish which begins to insulate the metal from the surrounding charged solution. Deposition continues until the coating thickness becomes sufficient to form a barrier against further paint attraction.In anodic electrocoating, the part to be coated is the anode with a positive electrical charge which attracts negatively charged paint particles in the paint bath. During the anodic process, small amounts of metal ions migrate into the paint film which limit the performance properties of anodic systems. The main use for anodic products is interior or moderately exterior environments. Anodic coatings are economical systems that offer excellent color and gloss control. In cathodic electrocoating, the product has a negative charge, attracting the positively charged paint particles. Cathodic electrocoat applies a negative electrical charge to the metal part which attracts positively charged paint particles. Reversing the polarities used in the anodic process significantly reduces the amount of iron entering the cured paint film and improves the cathodic properties. Cathodic coatings are high-performance coatings with excellent corrosion resistance that can be formulated for exterior durability.PPG
68 E-Coat: Anodic Coatings Anode has a positive charge that attracts the negatively charged polymersEpoxies (cure >80 °C)Acrylics (cure > 150 °C)Acid-modified polybutadieneButylated-formaldehyde-melamine (150 °C)
69 E-Coat: Cathodic Coatings Cathode has a negative charge that attracts the positively charged polymersEpoxies (cure >190 °C)Acrylics (cure > 190 °C)
70 • Corrosion resistant cationic epoxies • High edge coverage for sharp objects• Solvent free anodic products• Cathodic acrylics with corrosion resistance and excellent exterior durability• Near 100% transfer efficiency operation• Two-coat Electrocoat for severe environments• Heavy-Metal free formulations• HAPs free formulations• Electrodepositable PhotoresistsAgriculture Equipment, Appliance, Automotive, Fasteners, Metal Office Furniture, Printed Circuit Boards, Structural Steel, Wheels, Railway
73 Fluidized Bed Coating Heat part, then dip into FB coater Polymer powder in air generated fluidized bedNormal or electrostatic FB coaterPVC, polyethylene copolymersProtective, decorative coatingsSafety glass bottlesFluidized Bed For fluidized-bed dipping, preheat parts to 400ｼF. Dip parts in fluidized-bed of Glas-Lok for 4-6 seconds. Carefully blow off excess powder. For improved surface finish (if necessary), parts may require post-baking for a short period of time.Electrostatic Deposition For electrostatic deposition, preheat parts to 400ｼF. Deposit Glas-Lok 8-12 mils thick. For improved surface finish (if necessary), parts may require post-baking for a short period of time.Heat part, then dip into FB coater100 °C for PE copolymer
74 Fluidized Bed Coatings Fluidized Bed For fluidized-bed dipping, preheat parts to 400ｼF. Dip parts in fluidized-bed of Glas-Lok for 4-6 seconds. Carefully blow off excess powder. For improved surface finish (if necessary), parts may require post-baking for a short period of time.Electrostatic Deposition For electrostatic deposition, preheat parts to 400ｼF. Deposit Glas-Lok 8-12 mils thick. For improved surface finish (if necessary), parts may require post-baking for a short period of time.A part recently taken out of a fluid bed coater with about 10 mils of functionalized polyethylene applied. Photo courtesy of Wright Coating Company, Kalamazoo, MI.
79 Polyxylylene Parylene C The most widely used dimer, providing a useful combination of properties, plus a very low permeability to moisture, chemicals, and other corrosive gases.Parylene NProvides high dielectric strength and a dielectric constant that does not vary with changes in frequency. Best selection where greater coating protection is required.Parylene DMaintains its physical strength and electrical properties at higher temperature
80 CVD PolymerizationParylene is the generic name for poly-para- xylylene, a completely linear, highly crystalline materialVapor Deposition in Vacuum (conformal coating)Excellent Dielectric (> 5000 V/mil)Excellent Strength (Yield & Tensile strength > 8000 psi)Highly stable (Insoluble in most Solvents)BiocompatibleWater absorption (<0.1% in 24hrs)The required thickness of a coating can vary based on the application, but thickness can range from the hundreds of angstroms to several mils, with the typical coating being in the microns range.
81 RF Plasma Source Developed by Plasmionique Capacitive CouplingInductive CouplingPECVD coatings from Hydrocarbon gasesDLC Hard Coatings on Various materialsPolymeric Coating on Various materialsStudied The bias energy Impact on Film properties
83 Spin Coat Process Summary: Wafer is held onto vacuum chuck Dispense ~5ml of photoresistSlow spin ~ 500 rpmRamp up to ~ 3000 to 5000 rpmQuality measures:timespeedthicknessuniformityparticles and defectsVacuum chuckSpindle connected to spin motorTo vacuum pumpPhotoresist dispenser
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