Understanding Protective coating System

Understanding Protective coating System

1. 1 Industrial Painting Understanding Paint System

2. Industrial Painting 2 Paint system What is paint made of? The main constituents of paint are Binder (Resin) Pigment Extender (filler) Solvent and Additives (auxiliary substances).

3. Industrial Painting 3 Paint system What is a Binder (Resin)? A binder is a fluid or a solution that forms a film during drying or curing Describes the generic type of paint/coating Bind pigments and extenders to a solid film Provides the adhesion to the substrate Provides the water, chemical, solvent and UV resistance Resin: 1. Its a sticky flammable organic substance, insoluble in water, exuded by some trees and other plant. woody plants produce resin in response to injury. The resin acts as a bandage protecting the plant from invading insects and pathogens 2. a solid or liquid synthetic organic polymer used as the basis of plastics, adhesives, varnishes, or other products.

4. Industrial Painting 4 Paint system Binder : Types of binders Natural resin: Drying oil Wood rosin Coal Tar Bitumen Nitro-cellulose Synthetic resin: Alkyd Chlorinated rubber Vinyl Acrylic Epoxy Polyurethane Silicate Polyester Polysiloxane

5. Industrial Painting 5 Paint system Binder : Binders can be divided into three groups (generic types) depending on the drying or curing process which takes place after the paint has been applied to the substrate. The first group are known as oxidatively drying, as the paint absorbs oxygen from the air and dries. Example: alkyd paints. The next group are called physically drying. When the paint is applied to the substrate, the solvent simply evaporates. Examples: chlorinated rubber, Vinyl, Acrylic, Asphalt and Tar The third group contains chemically curing paints. These paints are usually two component, e.g. Epoxy, Polyurethane, Polyester and Silicate

6. Binders are also classified into following two types. Thermoplastic and Thermosetting type Thermoplastic-Chlorinated Rubber Thermosetting- Others , like Alkyd-Synthetic Enamel type Epoxy – Mostly used for best corrosion resistance PU- Mostly used as Top coat for good look and resistance to sunlight/chalking Thermosetting Binder are much more resistant to corrosion than Thermoplastic Strength of Binders are: Primer: IZS>EP ZR>EP ZP>EP. MASTIC> PU> CHLORO>ALKYD FINISH: Epoxy>PU> Chloro > Alkyd Modifications of Binder/Resin will make a film stronger like in- Coal tar Epoxy ; Novalac Epoxy Industrial Painting 6 Paint system Thermoplastic : Soften and melt on heating and become hard on cooling i.e. process is reversible. Thermosetting : Become hard on heating and process is ireversible .

7. Most coatings are named after the binder (resin). Examples: Alkyds Epoxies Acrylics Urethanes Other coatings may be named after the pigment such as zinc rich primer or red lead Zinc Phosphate primer. Example: Epoxy Zinc rich Primer, Epoxy Zinc phosphate Primer All Binders are Organic in nature except Inorganic Zinc silicate which is Inorganic type . Note: Organic means – Made from Crude and of Carbon & Hydrogen mainly Inorganic means –developed chemically and made of Silicon Resin Inorganic coating is more resistant to corrosion Industrial Painting 7 Paint system

8. Modified binders : A modified binder may contain more than one binder. A binder may be modified chemically by attaching new groups to their molecules, e.g. Coal Tar Epoxy Vinyl Epoxy Acrylic Epoxy Epoxy Mastic Polyurethane Acrylic Polyurethane Polyester Styrenated Alkyd Polyurethane-oil Alkyd Epoxy Ester Industrial Painting 8 Paint system

9. Industrial Painting 9 Paint system Pigments: Pigments in a paint is the colour pigments which give the opaqueness and desired shade etc. Colour pigments, both organic and inorganic, are available in many shades. Titanium dioxide is a strong colouring white pigment with good opaqueness and is used in white and pale colours. Rust-inhibiting pigments include zinc ( cathodic protection) and zinc phosphate (inhibiting protection). Such pigments are used only in primers (first coat).

10. Industrial Painting 10 Paint system Role of Pigment : Pigments are the arms of Binder in coating and provides Corrosion Resistance Chemical Resistance; Water resistance ; Salt resistance ; Acid/Alkali resistance ; Opacity ; Colour ; Abrasion resistance; Hardness; Flexibility Film thickness Solid content of the coating Adhesion with surface & Old coating Fire resistance Thermal /heat resistance

11. Industrial Painting 11 Paint system Pigments: Colour Pigments •Natural or synthetic pigments •Organic or inorganic pigments Function of colour pigment: Gives colour to the film Hides the substrate (opacity) Almost all colours consist of a blend of pigments Individual colours can be changed or adjusted by altering the pigment blend

12. Industrial Painting 12 Paint system Active / Reactive pigments - Take an active role in ensuring that the paint performs as expected: Anticorrosive (inhibitive or galvanic) Red Lead Lead chromate Zinc chromate Zinc phosphate Zinc dust Barrier pigments (flakes shaped pigments) Glass, aluminum and micaceous iron oxide (MIO) Antifouling Cuprous oxide

13. Industrial Painting 13 Paint system Extenders or fillers: Extenders or fillers such as dolomite, talcum etc. have little or no opaqueness and are transparent in the binder. They have different forms e.g. balls, needles, fibres etc. and are used to give a sealed film, the right gloss etc. In antifouling paints, for example, copper oxide is used as a pigment to prevent fouling of ships’ hulls.

14. Solvents: Solvents are added to the paint to dissolve the binder and adjust the viscosity so the paint can be applied by brush, roller or spray gun. Different binders require special solvents or solvent mixtures to be able to dry or cure in such a way that the paint properties are not damaged. Role of Solvent Solvent helps to apply coating easily Solvent helps all pigments & additives mixing properly Solvent helps to lay film uniformly Solvent helps in storage After film laying, solvent evaporates Thus Solvent creates more pollution Hence coating with less solvent is better for us High Build or high solid coating pollutes less and is eco-friendly Low VOC coating Examples of solvent: Water , White Spirit, Xylene , Toluene, Ketones , Glycol, Alcohals Industrial Painting 14 How to Stop Corrosion ?

15. Industrial Painting 15 Paint system Additives: Additives are a small, but important, part of the paint. Such substances include anti-settling agents (to prevent fouling), thickeners (to prevent sagging / running), antifoaming agents (to prevent air entrapment), etc. Types of Additives and Extenders Wetting & Dispersing Agents Rheological Additives (Viscosity Adjustment) Driers Anti foaming/Air release additives UV absorbers/Light Stabilizers Adjust the gloss level (extenders): Anti Settling Additive Anti-settling Anti-skin Anti sagging Thinner : Evaporation rate and solubility of a thinner influence a paint’s: • Drying time • Film-forming properties • Quality of the film 1. Most paints are ready to be applied as supplied by the manufacturer. 2. Never add an unspecified thinner to a paint, it may lead to disastrous results

16. Industrial Painting 16 Paint system What does a paint system consist of? In most cases, a paint system consists of 2 to 4 coats and is built up from a primer coat, one or two intermediate coats and a top coat. The three main constituents in the paint system can be three different paints, but it is not unusual to use a particular paint as both primer and intermediate coat. Each part of the system has a specific function and it is therefore important to follow the instructions of the paint manufacturer and the recommended system structure to achieve the best possible result. The main purpose of primers is to ensure good adhesion of the system to the substrate. Intermediate coats usually ensure that the system is sufficiently thick to create a good barrier from the surrounding environment. The top coat gives the surface the right colour, a good durable gloss and protection against the external environment.

17. What is Primer? A primer is a coat of paint that is applied directly to the bare substrate. The word ‘primer’ means ‘first’ and in this case it is the first coat to be applied to the surface to be coated. The primer is the most important coat of paint a substrate receives. The final paint system is totally dependent on the primer during its job. The primer will only be able to perform well if the surface preparation has been done well. Primers are the anchors for the new paint system. 17 Industrial Painting Paint

18. Function of Primer? To provide excellent adhesion to the substrate for the new paint system. Primers therefore need to have good adhesion to the substrate themselves and to provide a surface that subsequent coats of paints can easily adhere to. To provide protection to the substrate until it can be top coated. To inhibit moisture reaching the substrate. To seal the surface and prevent subsequent coats of paint sinking into the substrate and losing gloss. 18 Industrial Painting Paint

19. Primer composition primers are made using specialized binders that are compatible with the substrate and that have excellent adhesion to it. For example the alkyd binder used in Resin Wood Primer is excellent over timber but will chemically decompose if used over zinc metal or fresh concrete. The resin binder actually turns to soap in these situations. Metal primers contain substantial quantities of anti-corrosive pigments to chemically inhibit corrosion. Often they are cynically coloured to match the colour of rust. Primers are usually pigmented and have a middle range PVC (pigment volume concentration) around 35-45%. This allows them to have spare binder resin (left over from pigment holding together duties) for adhesion to substrate purposes. 19 Industrial Painting Paint

20. If the surface of a piece of timber magnified 100 times it could be represented as the top surface of a can of drinking straws. As a primer dries the pigment particles slowly sink onto the opening of each straw and block it off. Primers have an excess of pigment and this ensures they dry with a slightly roughened surface to aid the adhesion of subsequent coats. 20 Industrial Painting Paint

21. INTERMEDIATE coats also serve as barriers in the coating system, as well as adding film thickness. Intermediate coats must be compatible with the primer as well as the topcoat. Over coating Interval and proper thickness is crucial in Intermediate coat Over-coating on IZS is the most Important . Why? 21 Industrial Painting Paints –Protective Coating high deposition of film thickness (125 microns +) can result in mud-cracking while lower dry film thickness can affect the performance of coating. The most frequent problem associated when top coating is bubbling/ pinholing especially with non-weathered zinc silicate coatings.

22. FINISH coats in the system must protect the substrate, and previous coats, from the environment in which the coating will be exposed. This may be simply atmospheric exposure, or a more severe environment such as immersion or chemical. – Suitable is Epoxy coating Top coat should resist degradation of coating from UV-Ray and polluted gases , due to exposure to sunlight & external environment-Suitable is PU coating 22 Industrial Painting Paints –Protective Coating

23. Industrial Painting 23 Paint system How does paint protect the substrate ? Paint protects the substrate in three main ways: barrier effect inhibitor effect and galvanic effect. Paints which have a barrier effect only form a barrier between the substrate and the environment and no rust-inhibiting pigments are added. Most paints come under this group: many primers, all intermediate coats and top coats. Aluminium and glass flakes are often used in primers to increase the barrier effect. Paints which use the inhibitor effect contain inhibiting pigments e.g. zinc phosphate. Such pigments are only used in primers. Paints in this group are not suitable for use under water. Paints with a galvanic effect contain pure zinc pigments and are used only as primers. The basic principle is that the zinc makes metallic contact with the steel so that the zinc can act as an anode. If the paint system is damaged, the zinc pigments will protect the exposed steel cathodically .

24. Barrier effect Most paints protect the steel by forming a barrier to the surrounding environment A barrier will increase the resistance in the galvanic circle A thick barrier will give better protection than a thin 24 Industrial Painting Paints –Protective Coating

25. Inhibitor effect In inhibitive coatings, moisture may penetrate to reach the inhibitive primer where the reactive pigments are activated, which in turn passivizes the metal substrate at the coating/metal interface Example of Inhibitive pigments: •Red Lead (not used) •Lead/zinc chromate (not used) •Zinc phosphate Product with inhibitive pigments are not suited for immersed substrates 25 Industrial Painting Paints –Protective Coating

26. Cathodic effect Some paints offer the same cathodic protection effect as sacrificial anodes A zinc-rich primer reacts to protect the steel substrate when the topcoat is damaged The CP type of paints is not an inert paint film as the barrier coatings The paints contain active, metallic pigments The pigments react with moisture and the steel and creates a calcareous deposit on bare spots of the steel substrate 26 Industrial Painting Paints –Protective Coating

27. Industrial Painting 27 Paint system Drying / Curing Mechanism : The properties of a paint film is closely related to how the binder dries or cures . The three most common drying / curing mechanisms are: 1. Solvent evaporation (physically drying) 2. Reaction with oxygen in the air (oxidation) 3. Chemical reaction between resin and hardener

28. Industrial Painting 28 Paint system Solvent evaporation (physically drying) : Physically drying paints are single-component, and dry by pure evaporation of the solvents. Due to evaporation of solvents, the molecules get packed and melt together to form a paint film. There is no any chemical bonds formed in this type of paint. They are also resoluble by other paints which contain strong solvents or in contact with thinners. The group of physically drying paints contains generic types such as Chlorinated rubber Vinyl Acrylic Silicone Bitumen Tar Antifoulings CR paints are used outdoors both above and under water. Vinyl-based paints are used only above water. Acrylic is used as a top coat, as it retains its gloss better than chlorinated rubber or vinyl in such systems. acrylic is also used as primers in waterborne systems.

29. Industrial Painting 29 Paint system Curing (drying) through oxidation

30. Industrial Painting 30 Paint system Physical drying. Solvent borne paints Physical drying: Waterborne paints

31. Industrial Painting 31 Paint system Curing mechanism of two -pack paints

32. Industrial Painting 32 Paint system Generic Paint Types It is not possible to develop a "universal" paint which fulfils all possible functions. Paints are therefore developed for different jobs. As a result, each paint has a different set of properties. Paints are often grouped according to the chemical composition of the binder, which we refer to as ‘generic paint types’. To ensure that you choose the right paint or paint system with the right properties, it is important to know the strengths and weaknesses of the various generic types.

33. Industrial Painting 33 Paint system Alkyd paints: Alkyd paints are made from alcohol and acid with the addition of fatty acid or oil. The addition of fatty acid and/or oil can be varied to give alkyds with different properties. The term alkyd is a modification of the original name " alcid ", reflecting the fact that they are derived from al c ohol and organic a c id s. Alkyd paints can only be used above water (not submerged) as the water resistance of Alkyd paints is poor. They are not used on zinc primer or galvanised steel as a chemical reaction - saponification - would occur with the binder, with subsequent blistering and flaking. The drying/curing process is also temperature-dependent. This is because alkyd paints dry or cure by absorbing oxygen from the air. This is a chemical reaction and such reactions are always influenced by temperature. The degree of pre-treatment required for the substrate can vary from St 2 to Sa 2½, depending on the purpose of the paint and the environment to which the paint is exposed. By modifying the alkyds for example with styrene or silicon, other properties can be achieved.

34. Industrial Painting 34 Paint system Advantages of Alkyd Paint Good application properties 1-component Good weather durability Good wetting properties Good re- coatability Good levelling properties Good gloss retention Dry heat resistant up to 120 ºC. Limitations of Alkyd Paint Poor chemical resistance (especially against alkaline) Limited water resistance (submerged) Limited solvent resistance Limited film thickness per coat Poor adhesion to CR Never to be used on Zin

35. Industrial Painting 35 Paint system Chemically curing paints : Chemically curing paints are thermosetting plastics, unlike physically drying paints which are thermoplastics. Thermosetting plastics are more resistant to chemicals than thermoplastics as they form an insoluble three-dimensional network after curing. These paints are normally two-component. The supplier provides these paints in two separate containers, one for the base and the other for the curing agent. We often refer to these as component A and component B. Before painting, the two components must be mixed. It is particularly important to mix the components in the correct ratio and to ensure good agitation. The curing process is a chemical reaction between the base and curing agent, so application and curing are temperature-dependent. It is equally important to apply the paint to the substrate before the chemical reaction has proceeded for too long after mixing of the components. When the potlife has elapsed, the paint becomes dry and finally completely hard and cannot be applied.

36. Industrial Painting 36 Paint system Chemically curing paints : Epoxy paints have excellent chemical resistance, particularly to alkalis. They have good adhesion both to steel and concrete and good water resistance. Epoxy can be modified using phenol, coal tar and hydrocarbon resin to give special properties, e.g. better chemical resistance, better penetration, better water resistance etc. One drawback with many epoxy paints is that they contain large quantities of solvent. However, other types have now been developed with a high solids content (mastic products) with excellent "all round" properties. There are also a solvent-free epoxy paints which are used for drinking water tanks. Waterborne Epoxy paints are increasingly being used today because they give a better working environment. Chemical resistance however is slightly reduced. Zinc epoxy (organic) or zinc ethyl silicate (inorganic) are used as cathodic protective primers on blast-cleaned substrates. Zinc ethyl silicate (solvent-based) and alkali silicate (waterborne) are also often used inside storage tanks for solvents because of the extremely good solvent resistance.

37. Industrial Painting 37 Paint system Chemically curing paints : Polyurethane paints are also thermosetting plastics. They are used as top coats on epoxy (which chalks in sunlight) as they have excellent weather-resistance and durable gloss. Polyester paints are thick coat paints used in areas where a high degree of wear resistance is required. For example gangways, production decks, dam walls (concrete) for power stations etc. These paints are applied in thick coats (e.g. 2 x 750 μm ) and cure quickly (a few hours). They also have good chemical resistance. Vinyl ester is also a thick coat paint (2 x 750μm). It has good chemical resistance and is often used inside storage tanks for chemicals. Such paints can be used on both steel and concrete.