Construction Products – Comparison of Binder Types Exterior Products Polyesters + Low Cost - Only moderate durability overall (however, improving) + Fluoro Excellent UV resistance to wide colour range - Corrosion resistance inferior to Plastisols / Polyurethane carbons + Polyur- Good UV & Corrosion resistance - Not as tough as Plastisol ethanes + Plastisols High Build (up to 200µm), tough, corrosion resistant PVC – environmental issues? -
Comparative Product Performance Polyurethane Plastisols Polyvinyldene Fluoride Silicone Modified Resistance to Polyester Corrosion Polyester (Durability) UV Resistance (Aesthetics)
Key areas of future focus • Reduce cost: – ‘De - engineer’ paint systems – Improve efficiency of process • Reduce cure temperatures, increase line speeds, improve control of coating thickness applied, reduce scrap & other waste. – Decrease required thickness of Zn layer (e.g. MagiZinc) • Increase value of product: – High quality premium products developments – ‘Negative -energy foot- print’ of buildings: • Photovoltaic coatings • Transpired solar collector
Industrial/Marine Vehicle Pigments Additives Strengthe Thickness Solvent Resin Inhibitors Colorants ner UV absorbers Surfactants Wetting Agents Alkyd Benzene Zn Dust C black Glassflake Drying Agent Epoxy Toluene Zn Chromate TiO 2 Fibers Urethane Xylene Zn Phosphate ZnO Mica Polyesters Thinners Polyaniline Vinyls Acrylic Siloxanes High Performance Coatings Waterborne Coatings Solventless Sol-gel Route PVDF Dispersion Method Underwater coatings Fire Retardant Coatings
Factors on which Coating Selection Depends Environment in which the coating to be applied • Steel The substrate type • Non-ferrous (Al, Cu etc. ) • Non Metal – Plastic, Glass etc. Surface Condition of the substrate Temperature of the substrate Application method Weathering conditions Life of the coating Cost
Conventional Coatings Oil Based – Alkyd Coatings Epoxy Based Urethane Coatings Polyester Vinyl Coatings Chlorinated Rubber Polyvinyledene Coatings ( PVDF)
High Performance Coatings One those which are functional specific Can be applied in highly aggressive environment. Have high Corrosion resistance High Erosion & abrasion resistance Can dry very fast Can give large thickness in one coat
Coatings for Offshore Structures
How Offshore Structures differ from Onshore and Land Based Structures • Marine Structures are in the most corrosive environment. Further, corrosion of various parts/component depends upon whether it is at : – Atmospheric Zone – Splash Zones – Tidal Zone – Immersed Zone – Buried Zone
Protective coating System for Submerged Zone Submerged structures is usually protected with a coating and Cathodic Protection. Coating must be compatible with the CP system Initially for such a system coal tar epoxy was applied on a Sa21/2 prepared surface up to DFT of 400 m Recently this has been changed to glass flake epoxy – 2 component each 225 um ( total thickness 450 um) The CP system used in combination is usually a sacrificial anode system. Zn electrodes are generally used.
Tidal Zone Just 1-2 meter below the splash Zone Always wet. Maximum corrosion Maximum Bio corrosion • Be applied underwater The Coating • Should have curing under water should • Must have antifouling properties
Chemistry of Underwater Coatings • Once we have made diepoxy prepolymers, we tie them all together by adding a diamine.
Properties of a Typical Underwater coating developed by us and its comparison to a commercial product Properties Benchmark Fast Cure Epoxy 1 Touch Dry 2 hours 1.5 - 2 hours 2 Hard Dry 10 hours 7-8 hours 3 Ease of Application Good Good 5 Impact resistance(ASTM 13 joules passed 13 joules passed 2794) 6 Cross hatch adhesion 4A 5A 7 Pull off adhesion(D4541) 2.2Mpa 3.2Mpa 170 175 8 Cylinderical Mandrel Flexibility(D522) 9 Abrasion resistance(D4060) 7 mg 5mg 10 Tensile strength 3.98Mpa 18.3Mpa
Application • Underwater: – Brushes - Using vigorous circular motion. – Underwater pump with round brush - using vigorous circular motion
Splash Zone Is the most corrosive area of the offshore structure. This part of the structure is subjected to continuously dry and wet spell, each time sending depositing more salt to the structures during dry spell. Erosion by waves also damages this part of the structure. Any coating used must therefore by quite rugged and also quite resistant to aggressive environment. Due dry and wet cycle, partially coated surface can be exposed to sea water imparting high level of chlorides and wetness to the intermediate coat. The preferably coating system must be applied in a single coat for higher thickness and should have low curing time so that it cures fully before the wet spell attacks the member.
Offshore Structures Glass Flake Reinforced Polyester Coating to achieve 750um in one coat
Coating systems for Splash zone Originally the legs were coated with coal tar epoxy. Three coats of 125-150um were applied on blast cleaned surface after Zn-rich primer ( organic /Zn silicate). Silica filled ( flint-reinforced) compounds are mainly solvent free epoxy claddings, which were applied by spraying or trawling directly to blast cleaned steel in a dry film thickness of 3-5 mm. Monel 400 ( Ni-Cu alloy with 67% Ni, 32% Cu) sheathing, thickness 1-5 mm, was attached to the tubular steel either by bonding or by welding. . Glassflake reinforced coatings – high build or high solid coating by spraying one or two layers with a total thickness of 500 um. Thick rubber or neroprene coatings are applied to a thickness of 6-13 mm.
Coating systems for Splash zone Bituminous wrappings from which the wrapping material usually is glass fiber. Before wrapping the steel is coated with a coaltar of bituminous primer. A Zero maintenance system can be a Aluminum thermal spray coating. This also allows reduced corrosion allowance on all the splash zone members. Solventless Glassflake coating with a fast curing characteristics is the best system It can be applied with modern Airless Spray system to a thickness of 800 um in one coat. Expected to give life 6-10 years. 15 years life is expected if thickness be made 1500 um.
Glass Flake Polyester Coating Isopthalic Based Polyester Coating 100% Solventless System Can be applied at 90% RH Applied on Sa2½ Blasted Surface Applied by Airless Spray for 800 um in one single coat. High Curing time. Both Surface preparation and application of coating can be finished in Low tide to High tide duration.
Moisture Penetration Glass Flakes Coating Substrate Substrate
Advantage of this system Good tough & highly corrosion resistant. Can be applied in single coat to a thickness more than 800-1000 m. Cures in less than 20 minutes in normal temperature of 30 o C. Can be coated in 90% RH Has impact and abrasion resistance Has UV and weathering resistance
High Durability Coatings
Polysiloxanes Coating • Based upon -Si-O- bond which is • Stronger than – C-C-bond ( 108Kcal compared to 83Kcal for – C-C- bond) • That is not affected by sunlight and has strong Gloss and Colour retention properties R R RO – Si – O – Si - R + H 2 O= - Si-OH + RHO R R R R R R = - Si – O - Si - -Si-OH + HO- Si - R R R R Used where long term Gloss and Colour retention is required
Polyvinylene Di-Fluoride ( PVDF ) Highly resistant to Strong Acids / Alkalies Resistant to UV Light Basically, it consists of 70% fluoride resin ( Kynar 500) having 42% of Flurine Content with 30% of acrylic resin. Can be applied by spray, on line coating
Fluoropolymer Bonds are Less Likely to Break The C-F bond is one of the strongest known (PVDF shown below) - C – F – Bond Strength 149 Kcal/m
Hybrid Coatings One Coat of Metallized Coating Second Coat of Sealer Coat • Pure Zn Based upon the principle of providing • Zn-Al alloy ( Zn-15%Al) large concentration of anodic material • Al which can provide cathodic protection: • Al-Mg Allo y Life Achieved can be 25 years to 50 years
Intumescent Coatings
INTUMESCENCE Intumescence is defined as the swelling of certain substances when they are heated Intumescent coatings - on heating form an expanded multicellular layer, which acts as a thermal barrier that effectively protects the substrate against rapid increase of temperature, thereby maintaining the structural integrity of the building
Mechanism
MECHANISM
Fire Rating
Components of Intumescent Coatings Acid Source Carburising Agent Blowing Agent Binder
Disadvantages of available Intumescent Coatings Use formaldehyde and other toxic substances Fire resistant chemicals suspended in water Fragile char barrier Additive must be thermally stable at polymer processing temperature, which is often in excess of 200°C The thermal degradation process of the polymer, must not adversely interfere with the intumescence process
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