Nonstick Coatings Information
Table of Contents
Nonstick coatings, or release coatings, allow easy release of food, rubber, adhesives, or other media from cookware, bakeware, electrical appliances, molds, shafts, plungers, spindles, conveyor parts, fuser rollers, surgical devices, clothing, fabrics, building surfaces (anti-graffiti), ship hulls, and other process equipment. Nonstick coatings are also known as anti-stick coatings, slip coatings, slick coatings, repellents, and release coatings.
Nonstick or release coatings typically utilize one or more of three mechanisms or technologies:
- Low surface energy to repel adherent (adherent beads up on surface) preventing or inhibiting adhesion
- Ablation or breaking off of coating layer to release adherent—the coating or a portion of the coating is sacrificed
- Low shear strength, lubricious, or high slip allows an adherent to be wiped off a coating
Three nonstick mechanisms: (top to bottom) Low surface energy; ablation; high slip.
Release coatings that prevent adhesion usually through low surface energy and non-wetting have the advantage of not transferring material or requiring replenishment. Ablative/sacrificial or low shear strength release coatings may transfer materials and require replenishment.
Ablative/sacrificial—Ablative release coatings react with and slowly dissolve water, causing the coating to slowly wear off, break away, or ablate along with any marine life attempting to stick to the surface. Ablative release coatings are also known as self-polishing coatings, self-polishing copolymer (SPC) coatings, antifouling paints, foul release coatings, sacrificial coatings, and self-fragmenting coatings. Ablative and sacrificial coatings are used for anti-fouling on boat bottoms and as anti-graffiti measures on public surfaces.
Anti-graffiti sacrificial coatings allow removal of graffiti through removal of the coating via pressure washing. A remover or solvent must be applied to some anti-graffiti coating before pressure washing. The defacement is removed along with coating.
Ablative bottom paints or sacrificial coatings are commonly applied on boat and ship hulls below the water line and are called antifouling or fouling release coatings. Fouling or biofouling is the attachment of barnacles, seaweed, or marine life to the submerged hull of a vessel. Fouling increases a vessel’s hydrodynamic drag and reduces maneuverability, resulting in increased fuel usage. Preventing or reducing biofouling saves the shipping industry billions of dollars by reducing fuel consumption costs and lowering the carbon footprint (see Reference 1 below).
Traditional ablative release coatings contain a biocidal binder that hydrolyzes in water, which ablates a thin layer of the coating and effectively releases any adhered marine life, leaving behind a clean and polished surface. An organotin compound, tributyltin, or TBT, forms a copolymer with paint resins. This results in a coating that self-polishes or ablates at a consistent rate during the life of the coating. While older antifouling paints utilized copper or tin biocide additives (TBT, zinc oxide, copper, or zinc pyrithione) that were toxic to marine life, newer regulations are restricting use and encouraging alternatives. According to the International Maritime Organization (IMO), “TBT has been described as the most toxic substance ever deliberately introduced into the marine environment.” (see Reference 2 below).
Newer nontoxic foul release coatings utilize PTFE-silicone slick coatings or other nonstick coating technologies, which also provide longer life and cost savings. Ships with smooth, low friction hull surfaces travel faster through water. A disadvantage of traditional ablative coatings compared to durable nonstick hull coatings is the requirement for recoating or replenishment because the ablative coatings wear off the surface during use. Nanostructure or engineered surface roughness structures are being researched to produce a biomimetic antifouling surface bio-mimicking or simulating the antifouling nature of shark skin. Ablative coatings that provide the release of adherents in a water or seawater environment could be considered chemo-ablative. A different type of ablative coating without nonstick properties is used for fire protection and heat shielding. Thermo-ablative coatings react when exposed to heat and elevated temperatures. Heat energy is removed through a change of phase and mass loss.
Low surface energy—Nonstick coatings, liners, or lining systems and surfaces often consist of a low-surface-energy polymer such as polytetrafluoroethylene (PTFE), ceramic, glass frit enamel, anodized aluminum, or glass-ceramic. A prerequisite for adhesion is the ability of the adherent to wet or spread out across a surface. In order to wet a surface, the adherent must have a surface energy lower than the substrate. The outermost atoms or molecules on a surface determine the wettability and contact angle.
The Young equation is used to determine the contact angle based on the interfacial surface energy solid (coating)-liquid (adherent), solid (coating)-gas (air), and liquid-gas relationships. A surface with a contact angle of 0° is perfectly wet. A surface with a contact angle (?c) of 180° is perfectly non-wetting, with the liquid forming spherical beads that rapidly shed off an angled surface. A coating with a contact angle between 90° and 180° would be considered to have low wettability and likely good nonstick characteristics.
cos θc = (γSG - γSL ) / γLG
Contact angle of a sessile droplet on a coated surface.
A layer of a low surface energy material like polytetrafluoroethylene (PTFE) or ceramic provides a surface that materials with a higher surface energy cannot stick or adhere to very easily because wetting cannot occur or is limited. Water and oil can bead up into spheres and rolls off a very low surface energy nonstick coating when the contact angle approaches 180°. Cookware, bakeware, and appliances represent a major application for easy clean low-surface-energy coatings. Fabrics or architectural surfaces coated with a low surface energy coating or repellent will repel water, rain, ice, dirt, and soils. Oleophobic repellents will repel oils, alcohol, and grease.
Hydrophobic coatings—Hydrophobic surfaces or coatings repel or are not wet by water or water-based materials or other polar solvents, which would include many food products processed in cookware and bakeware. Oils and fats may still wet out and adhere to a hydrophobic surface. Coatings or surfaces with a contact angle of 150° or higher are considered superhydrophobic and coatings with a 180° contact angle surface are deemed perfectly superhydrophobic. Hydrophobic coatings typically utilize non-polar molecules such as hydrocarbon chains.
Icephobic/snowphobic coatings are hydrophobic coatings that prevent ice and snow buildup or adherence on a surface. They have the potential to keep surfaces on snow blower parts, plows, or wings ice-free and snow-free during cold-weather operation.
Metallophobic coatings—Metallophobic surfaces or coatings repel or are not wet by molten metals or alloys. The contact angle between the molten metal droplets and coating would be 90º or greater. Metallophobic coatings must withstand high temperatures, so they are typically composed of a ceramic matrix or inorganic binder holding a dispersion of nonstick salts such as fluorides, sulfates, nitrides, phosphates, rare earth phosphates (REP), and oxides. Metallophobic coatings are used in foundries, primary processing plants, and as stop-off compounds for welding, brazing, soldering, and metal working.
Oleophobic/lipophobic coatings—Oleophobic surfaces or coatings repel or are not wet by oils, fats, or similar organic-based materials (non-polar solvents), which can include many food products processed in cookware and bakeware. Water, salt, and sugar type products may still wet out and adhere to a hydrophobic surface. Oleophobic coatings typically utilize polar molecules.
Water and oil repellency (omniphobicity).
Omniphobic coatings—Omniphobic surfaces or coatings repel or are not wet by either water- or oil-based materials such as oils, fats, lipids, grease, or other non-polar solvent. Omniphobic coatings shed or repel everything. Omniphobic coatings may utilize a combination of non-polar and polar molecules grafted onto filler particles or nanoparticles, which are then dispersed in the coating. Attaching the polar and non-polar molecules to nanoparticles or fillers prevents the “oil in water” separation, which would occur if the polar and non-polar liquids were just blended. Fluoropolymers can provide omniphobic coatings.
Superhydrophobic coatings—Superhydrophobic or ultrahydrophobic coatings often utilize a nanostructured surface or nanoparticles to produce a material more efficient than hydrophobic ones thanks in part to nanotechnology. Coatings or surfaces with a contact angle of 150° or higher are considered superhydrophobic with a 180° contact angle surface being perfectly superhydrophobic. Contact angle hysteresis or the sliding angle varies only a few degrees on superhydrophobic coatings. Superhydrophobic coatings are considered self-cleaning because water based “dirt” will not stick to the surface. Biomimicry was utilized in the development of superhydrophobic or “lotus leaf” coatings. The ability of nanostructured surfaces to repel water was first noticed on the surfaces of lotus leafs, which have nanoscopic fibrils or branching nanostructures on the papillae (see Reference 3 below). Many superhydrophobic coatings use nanostructured surface, nanoparticles, nanosized fibrils, or nanorods coated with a very hydrophobic non-polar, hydrocarbon, or wax-like material. Young’s equation assumes a perfectly smooth ideal surface. Wenzel’s model and the Cassie-Baxter law are used to account for the impact of surface roughness on the contact angle and wetting (See Reference 4).
Wenzel’s equation: cos θ = rcos θ
Cassie-Baxter equation: cos θ = rffrcos θ + f + 1
where r = roughness factor, rf – roughness ratio of the wet surface and f = fraction of solid surface area wet by the liquid
Low friction/lubricious (Low shear strength, slippery, high slip)—Another mechanism for nonstick coatings is the application of a coating with low shear strength, high slip, or a lubricious nature. In other words, low adhesion to a surface can also be accomplished through a low shear strength layer. Hexagonal graphite or boron nitride coatings typically have a powdery nature and the hexagonal plates shear easily providing a good slip or release coating. Transition metal dichalcogenides like molybdenum disulfide and tungsten disulfide also have weakly bound atom planes like graphite, which are easily sheared and provide lubricity. Wax, fluoropolymers, PTFE, and other solid or dry lubricant powders may provide the lubricious or low shear strength component of nonstick or release coatings. Slip or release coatings are useful on the interior surfaces of industrial molds, dies, mandrels, tooling, and release liners. In some industrial processing and handling applications, the media or product needs to wet the contacting surfaces in the equipment, so a low surface energy coating may not be the appropriate choice. A low friction or lubricious coating can have a high surface energy with high wetting. MIT researchers developed a nonstick coating technology called LiquiGlide™, which uses a lubricant or liquid-impregnated surface. LiquiGlide™ is touted as being a permanently wet and slippery surface technology. Unlike many nanostructured or superhydrophobic coatings, the coating or surface is safe for food contact. Liquid or lubricant impregnated bearings have been utilized successfully for years in appliances to provide maintenance-free operation. A lubricant impregnated microtextured or nanotextured coating or surface might provide nonstick through high slipperiness. Researchers are exploring graphene, nanodiamonds, and other nanostructured surfaces to provide superlubricity or near zero friction (see Reference 5 below).
Acrylic—Acrylic is a synthetic resin used in high-performance latex or water-based paints. Acrylic resins form the paint's binder and enable the coating to last longer and retain its color. Acrylic coatings are recommended for bonding metals. They can also be used with oily surfaces, glass, ferrite, plastics, and fiber-reinforced plastics (FRP).
Boron nitride—The coating consists of hexagonal boron nitride. BN has strong covalent bonds between atoms within a plane. The planes of atoms are held together by weak Van der Waal bonds, which allow the planes to shear easily, providing lubricious characteristics.
Ceramic/carbide—The nonstick coating contains aluminum oxide, titanium oxide, silicon carbide, titanium carbide, chromium carbide, molybdenum carbide, titanium carbonitride, zirconium nitride, titanium nitride, chromium nitride, boron nitride, fluorinated silicon dioxide, titanium dioxide, tantalum oxide, and tantalum nitride. Ceramic nonstick or release coatings have become more prevalent and popular because they are more abrasion resistant and can withstand higher temperatures compared to polymer-based silicone and fluoropolymer release coatings. On the other hand, ceramics tend to be more brittle and less resistant to spalling or thermal shock compared to silicone and fluoropolymer nonstick coatings.
Diamond/DLC—The nonstick coating consists of diamond, diamond-like carbon, or fluorinated diamond-like carbon.
Glass/porcelain enamel—The nonstick coating consists of a vitreous glass or clay porcelain composition. A powdered enamel frit is applied to a cast iron or metal surface, melted or fused, and then slowly cooled to form the enamel coating. Porcelain enamel coatings are similar to ceramic coatings and typically have higher abrasion resistance and temperature resistance compared to polymer based nonstick coatings. Like ceramic coatings, glass enamel frits can spall or chip due to their brittle nature and poor thermal shock properties.
Graphite—Hexagonal or flake graphite is a solid lubricant material that maintains a low coefficient of friction up to 400° C (752° F). Graphite has a weak platelet structure that flakes, shears, or wears away quickly, providing a lubricating action. Hexagonal graphite lubricants are available in various forms, such as powder for dispersion into other fluids or liquid lubricants, sprayable coatings, or solid machinable shapes.
Elastomer/rubber—Rubber or elastomers are polymeric materials that can quickly and forcibly recover from large elastic deformations. Rubber is used as a resin in elastomer-based coatings. Polyisoprene and polyurethane are examples of rubber or elastomer materials.
Fluoropolymer/fluorinated—Fluorine is the most electronegative element, so fluorine and fluoride have very minimal affinity for accepting electrons from other elements. Fluoropolymers and fluorinated surfaces have very low surface energy providing omniphobic properties (i.e., water and oil repellency). Fluoropolymers are a family of engineering plastics characterized by high thermal stability, low friction, and almost universal chemical stability. PTFE and other fluoropolymers are chemically inert and chemically resistant. Fluoropolymers include polytetrafluoroethylene (PTFE), fluoroacrylate, fluoroeurathane, fluorosilicone, fluorosilane, trichloro (1H,1H,2H,2H-perfluorooctyl) silane (TCS), octadecyltrichlorosilane (OTS), heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane, fluoroPOSS, and polytetrafluoroethylene, and PTFE. PTFE is a very widely used fluoropolymer. PTFE contains fluorine and recurring tetrafluoroethylene monomer units. Additional examples of fluoropolymer plastics, elastomers, or compounds include fluorinated ethylene-propylene (FEP), fluoroelastomer tetrafluoroethylene-propylene (FEPM), perfluoroalkoxy (MFA, PFA), polyvinylfluoride (PVF), polyvinylidenefluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polyethylenetetrafluoroethylene (ETFE), polyethylenechlorotrifluoroethylene (ECTFE), and chlorotrifluoroethylenevinylidene fluoride (FPM, FKM).
Fluon®, a popular fluoropolymer brand, is a registered trademark of AGC Chemicals America (division of Asahi Glass Co., Ltd.). Teflon®, a popular brand of PTFE and other fluoropolymers, is a registered trademark of Chemours, a spin-off of the DuPont Company.
Metal plating/deposit—Nickel electroplating can incorporate nonstick polytetrafluoroethylene (PTFE) particles to produce a co-deposit of 15-25% by volume PTFE in a nickel matrix. Anodizing a metal deposit or plating could provide a metallic coating with nonstick characteristics.
Molybdenum disulfide (MoS2 moly, moly disulfide)—Molybdenum disulfide (MoS2) is a solid lubricant that maintains a low coefficient of friction up to 400° C (752° F). MoS2 solid lubricants are available in various forms, such as powder for dispersion into other fluids or liquid lubricants, sprayable coatings, or solid machinable shapes (e.g., sheets, films, tubes). Tungsten sulphide provides similar properties.
Polymer—Resin bases and polymer binders are translucent or transparent and solid or semi-solid. They contain synthetic and/or natural materials. Examples of resin bases and polymer binders include acrylic, alkyd, copal ester, epoxy, polyurethane, polyvinyl chloride, polytetrafluoroethylene, fluoroacrylate, fluoroeurathane, fluorosilicone, fluorosilane, modified carbonate, chlorosilanes, silicone, polydimethylsiloxane (PDMS), and silicone coatings.
Silicone/siloxane—Silicone contains a unique polymer system that can be a very effective release coating. Silicone fluids are synthetic and provide outstanding thermal and dielectric properties.
Wax—Wax, paraffin, or stearate compounds are useful in release, lubrication, anti-corrosive, and anti-static applications.
Composite/hybrid—Hybrid nonstick coatings utilize a variety of chemistry or composition to produce a nonstick surface. For instance, a composite coating’s combing of a ceramic or metal matrix with fluoropolymer particles can provide higher wear or abrasion assistance with higher release characteristics compared to a pure coating of the matrix material. Composite nonstick coatings examples include electroless nickel plated coatings containing dispersed PTFE particles and plasma-sprayed ceramic-fluoropolymer coatings.
3D printing/additive manufacturing—Nonstick coatings are used on the print bed to allow printed parts to be released or lifted off the bed easily or with low force, which prevents breaking or distortion of the 3D-printed part.
Adhesives/sealants—A nonstick coating or masking compound can be used to mask or prevent an adhesive or sealant from sticking to particular components or surfaces where sticking or sealing is not desired or is problematic to the function of the assembly.
Aerospace—A nonstick coating with the ability to prevent ice and snow build-up on the body and wings of aircraft could reduce ice removal costs and improve flight safety. Superhydrophobic coatings are being investigated for use in icephobic and snowphobic coatings. Cargo hold floors often require a nonstick slippery surface to facilitate the loading and removal of baggage and packages.
Agricultural/garden—Farming and garden tools with nonstick coatings easily release soil, compost, fertilizers, soil amendments, and organic materials.
Appliances and cookware—Electric waffle irons, rice steamers, griddles, panini makers, fryers, and popcorn makers all utilize nonstick coatings to improve cooking performance by allowing food release and easy cleaning.
Anti-climb—Anti-vandal, anti-climb, and anti-gravity paints consist of a slippery coating based on grease, wax, thick oils, or other lubricious components. Vandals and trespassers cannot gain a foothold and climb over walls, fences, lampposts, poles, towers, pipes, roofs, and parapets coated with a greasy or oily anti-climb paint.
Anti-graffiti—Anti-graffiti coatings are used on interior and exterior building surfaces to prevent vandals from defacing them. Non-wetting and sacrificial coating technologies prevent or allow the easy removal of defacements on public surfaces. Markings or paint will not stick to the surface or can be easily washed off the anti-graffiti nonstick coated surface.
Automotive—The beds or floors in trucks or trailers might benefit from a nonstick slippery surface to facilitate the loading and removal of cargo and packages.
Bakeware—Pie pans, bread pans, muffin molds, pizza trays, and other bakeware all utilize nonstick coatings to improve cooking performance by allowing food to be easily released and the surface to be easily cleaned after cooking is completed.
Biotech/pharmaceutical—Superhydrophobic coatings have the potential to keep surfaces ultraclean and sterile in pharmaceutical laboratories, formulating facilities, and drug manufacturing plants.
Building and construction—Nonstick coatings, release liners, and tapes are used during painting to prevent sticking of adhesives, sealants, and coatings during construction. A nonstick or release coating is applied inside foundation forms or molds to allow the form to be released and reused. Anti-graffiti coatings are used on the interior and exterior building surface to prevent vandals from defacing the surfaces. Low surface energy nonstick coatings or repellents also stay cleaner because dirt, snow, and ice slide off or are easily released from surfaces.
Electronics/semiconductor manufacturing—Tanks, trays, valves, fittings, and other components used during wet etching of semiconductor wafers utilize nonstick fluoropolymer surface via coating or bulk materials. Fluoropolymers provide easy clean properties combined with excellent resistance to the hydrochloric acids and fluorosurfactants used during semiconductor manufacturing.
Energy—Nonstick coatings help keep solar, wind, and conventional power generation equipment clean and operating efficiently.
Fasteners/hardware—Nonstick coatings on fasteners and hardware can reduce installation torque. The potential for corrosion during end-use can be reduced if the nonstick coatings exclude water or condensates.
Masking/maskant—A nonstick coating, masking compound, or maskant with the ability to selectively prevent coatings, sealants, adhesives, plating, or paints from sticking to particular components or surfaces. Some maskants have release or nonstick characteristics while other masking compounds are removable allowing the paint, coating, or adherent to stick and then the maskant is peeled off or removed.
Molds/dies—Molds and dies can take advantage of nonstick coatings to prevent the cast or molded materials from sticking to the mold or die cavity.
Marine—Specialized nonstick coatings called foul release or ablative bottom coatings are a critically important product for the marine shipping industry. Preventing or reducing biofouling saves the shipping industry billions of dollars by reducing fuel consumption costs and lowering the carbon footprint.
Medical/healthcare—Superhydrophobic coatings have the potential to keep surfaces ultraclean and sterile in dental and medical device manufacturing facilities. Smooth, nonstick surfaces make microbial contamination and attachment more difficult.
Material handling/process equipment—Mixers, reactors, blenders, tanks, conveyors, bins, feeders, dryers, and other process equipment can benefit from the use of nonstick coatings on surfaces contacting media. The nonstick coatings can improve flow and allow complete emptying of vessels. The nonstick coating used should be selected based on the food, chemical, wood, paper, agricultural, oil, or petrochemical media being transported or processed.
Oil and gas—Nonstick coatings are used in the oil and gas field and refinery applications on valves, oil tools, petrochemical processing equipment, offshore tools, down-hole tools, pumps, valves, actuators, impellers, hinge pins, piston casings, compressors, pipelines, pipe fitting, fasteners, and threaded components to exclude water, oil and contaminants. They can also reduce torques and forces during fastening or installation (make-and-breaks) and ensure that tools or hardware can be disassembled even under freezing conditions.
Packaging—Nonstick coatings are used when packaging tape, adhesives, sealants, labels, foods, materials, and chemicals allow the product to be easily or completely released from the packaging or container. Release liners could be considered a specialized type of packaging for tapes and resinous compounds.
Printing/copying—Printer, copier, and other reprographics components utilize nonstick coatings to prevent inks and marking materials from sticking to rolls, pads, or other parts.
Release liners—Some release liners are manufactured by coating paper or plastic films with a release coating. Transfer tapes, double stick tapes, bulk or sheet molding compound (BMC/SMC), or fiberglass reinforced plastic (FRP) resin molding compounds are carried on a release liner, which allow the product to be dispensed while preventing everything from sticking together in an unusable mass.
Seals/o-rings—Nonstick coatings or nonstick flexible finishes are important steps in seal, o-ring, and weatherstripping manufacturing. If the seal sticks to a mating surface, it can be damaged causing leakage and requiring replacement. Nonstick coatings allow seals to be released during opening or disassembly of pipelines, vessels, doors, windows, or machines even under freezing conditions or when sealing sticky resins or chemicals.
Textile products—Nonstick coatings are used to provide waterproofing, dirt repellency, and easy cleaning characteristics on fabrics, clothing, and other textile products.
Water cooling/desalination—Hydrophobic nonstick coating and superhydrophobic coatings improve the efficiency on the equipment with surfaces where water condenses because the water beads up and sheds off the hydrophobic nonstick surfaces quickly. Condensing surfaces in water-cooling stations, desalination plants, and water distillation equipment can benefit from nonstick coatings.
1. International Marine—How a coating can cut carbon and cost
2. International Maritime Organization—Focus on IMO: Anti-fouling systems
3. Hans J Ensikat, et al.—Superhydrophobicity in perfection: the outstanding properties of the lotus leaf
5. United States Department of Energy—Near zero friction from nanoscale lubricants