Components and Functions of Industrial Paint Systems

Paint Systems  Paint system is a protective coating composed of 3 layers: o Primer Coat  ensures adhesion to (steel) substrate  initial corrosion protection  base for mid coat  often includes Zn-rich primers for galvanic protection o Mid coat (intermediate)  adds barrier protection (main corrosion barrier)  improves opacity  builds up film thickness o Topcoat (finish)  Decorative: provides colour, gloss,  Protective: resistance to weather/UV, chemicals  Easy to clean  Common Paint Types Type Epoxy Acrylic Alkyd Vinyl Advantages Excellent adhesion, chemical and high temp. resistance, Gloss and colour retention, UV stable Fast drying, colour retention Easy to apply, low cost Quick drying Chlorinated rubber Bitumen Zinc Silicates Good chemical resistance, barrier protection Cheap, good penetration High heat & corrosion resistance Silicone Withstands up to 600OC Polyurethane Limitations Poor UV resistance – requires top coat Expensive, harder to apply Lower mechanical strength No alkali resistance Poor wetting, low flash point, contains Cl, low solids, comparatively expensive, Plasticiser needed, contains Cl Bleeds, limited colour options Difficult to apply, must be directly on steel, critical overcoating time Needs high curing temperature (200OC)  Main Paint Constituents o Binder  forms solid film and bonds it to the surface  provides chemical and abrasive resistance, and anticorrosive  eg. epoxy, acrylic, alkyd, PU, chlorinated rubber o Pigments  provides colour and opacity  eg. TiO2, indian lead, carbon black  provides fouling and corrosion protection  eg. Zn dust, cuprous oxide, red lead, o Extenders  reduce cost, improve strength, rheology, application, gloss control  eg. talc, chalk, silica, dolomite o Solvents  adjust viscosity, help application, control drying (evaporation rate), dissolution of binder, flash point  Types  Aliphatic eg. white spirite  Aromatic eg. Xylene  Alcohol eg. butanol o Additives  Enhance flow, stability, drying  UV stabilisers, flow agents, driers, anti-skinning agents, levelling agents, plasticisers  Curing Mechanisms o Physically Drying  Solvent evaporates  Reversible (thermoplastic)  Not resistant to solvents  Film formation independent to temperature  No max recoat interval o Oxidative Drying  Solvent evaporates  Oxidation cures the film  Irreversible (not thermoplastic)  Resistant to solvents and abrasion  Film formation – time dependent o 2-Component Curing  Resin & curing agent react chemically  o Waterborne Dispersions  Water evaporates = forms solid film o Chemically Curing Dispersions  Requires base         Curing agent in water phase Grinding/ Milling = Mechanical shearing to break agglomerates Wetting = Binder surrounds pigment particles, enabling dispersion Dispersion Stability = Resistance to pigment clumping or settling over time Agglomerated/ De- = clumped together/ broken down into primary particles Pigment particles are agglomerated Poor wetting: the binder does not fully surround the pigment This leads to: o Poor colour development o Reduced opacity o Weak mechanical properties o Sedimentation during storage Production Equipment Purpose Working Size Capacity Operation Typical Use Advantages   After proper grinding and wetting, pigment particles are: o De-agglomerated o Evenly dispersed o Fully wetted by binder The pigment particles are now uniformly distributed throughout the film High Speed Disperser Initial dispersion of pigments into the binder Uses a rotating disc blade to create high shear in the paint mixture Up to 3600 litres Discontinuous (batch mode) Pre-mixing; good for breaking down soft agglomerates Cost-effective, simple, fast pre- Pearl (Bead) Mill Fine dispersion and grinding of pigments Paint passed through chamber with glass/ceramic beads — grinding occurs via shear and impact 50–160 litres Up to 1500 litres/hour Continuous Final dispersion step; produces stable, finely ground, and evenly dispersed pigment particles More effective than Limitations  mixing, good for low/medium viscosity materials Does not fully deagglomerate hard pigment clusters — needs milling after Choosing Paint System (ISO 2944-5) Primary Requirements Protection Resistance Anticipated life of Structure Substrate  disperser for pigment de-agglomeration Higher energy and equipment cost Secondary Requirements Colour Decontamination Maintenance Safety (anti-skid, light reflection) Fireproofing Flexibility Feasibility Time available Other trades Necessary equipment Workforce Anticipated weather Safety & Environment Cost Quality Control ISO 12944 Corrosivity Categories Category C1 Description Very low C2 Low C3 Medium C4 High C5 – I Very high (industrial) C5 – M Very high (marine) Examples Heated building (schools, offices) Rural environments, unheated warehouses Urban/industrial, food plants, dairies Coastal, chemical plants, swimming pools Aggressive industrial + humidity Offshore/coastal with high humidity/salinity