3._Generic types of paints

Jotun Paint School 01 Section 5 : Generic types of paint Page 5.335.Generic types of paints.

Table of content.

SectionTitlePage5.1Fundamental differences of coating systems5.35.25.2.15.2.25.2.35.2.45.2.5Oxidative drying paints: AlkydsIntroductionAreas of useProperties and practical aspectsChemistryExamples of Jotun alkyd paint systems5.45.45.45.45.45.75.35.3.15.3.25.3.35.3.4Physically drying coatingsGeneral introduction to physically drying coatingsVinylPhysically drying coating: Chlorinated rubberPhysically drying coating: Acrylic5.75.75.75.105.115.45.4.15.4.25.4.35.4.45.4.55.4.6Chemically curing paints: Epoxy coatingsAbout epoxy paints in generalPure epoxiesEpoxy phenolic coatingsModified epoxies: Coal tar epoxy (CTE)Modified epoxies: Epoxy masticSolvent-free epoxy5.125.125.165.175.175.175.195.55.5.15.5.2Waterborne coatingsWaterborne acrylicsWaterborne epoxy5.205.205.225.65.6.15.6.25.6.3Zinc coatingsIntroductionOrganic Zinc coatingsInorganic Zinc coatings5.245.245.255.25

Cont. next page

Table of content.(Cont.)

SectionTitlePage5.75.7.15.7.25.7.35.7.45.7.5Polyurethane coatingsAreas of useProperties and practical aspectsChemistryHealth hazardsExample of Jotun Polyurethane paint systems5.295.295.295.295.305.305.85.8.15.8.25.8.35.8.4Polyester coatingsArea of useProperties and practical aspectsChemistryExample of Jotuns Polyester coatings5.305.305.305.315.325.9.5.9.15.9.25.9.35.9.4Vinyl ester coatingsAreas of useProperties and practical aspectsChemistryExample of Jotuns Vinyl ester coatings5.325.325.325.335.33

5.Generic types of paints.5.1.Fundamental differences of coating systems.

The fundamentals of a coating could refer to several aspects, depending on the purpose or the use of the coating. For example an anti-fouling paint would have the fundamental property of inhibiting the growth of animal - or vegetable organisms on the structure. A fire-resistant coating must fundamentally resist burning, or at least retard the burning of the substrate material. A coating to be applied over concrete must have a fundamental property of resisting strong alkali. All corrosion-resistant coatings must be able to resist the corrosiveness of the surroundings and prevent it from attacking the basic structure.

A coating can be thought of as a building. In order to be strong, a building must have a carefully constructed foundation. In order to be durable, it must be carefully designed and constructed. As is the case for a building also a paint system consists of a number of parts, each one of them with a different function.

Table 5.1.A paint system can be compared with a building.

A building

-

A coating systemDesign-FormulationConstruction-ApplicationFoundation-Substrate and primerInterlocking parts-Intermediate coatsSuperstructure-Topcoat

It should also be noted that even within the same group of paints the properties and the way of treating them may vary. Thus, it is important to study the Technical date sheets carefully and also to follow the recommendations given by the paint supplier when using the paint.

Both chemically curing and physically drying coatings are used to protect both steel and concrete. The choice of system depends on the type of structure to protect, lifetime requirements, environmental conditions obtainable during pre-treatment and application and, finally, the exposure / service conditions. The various coatings have different properties. To be able to select the correct paint system for a given application some basic knowledge about the different types is required. Typical properties of the most commonly used generic types of paint are described below

5.2. Oxidative drying paint: Alkyds.5.2.1.Introduction.Alkyds paints include many different types. They have different properties, but are mostly used for decorative purposes and for protection of steel exposed to relatively mild environments. The word alkyd is derived from the English word alcid, which in its turn is derived from the words alcohol and acid. Alkyds are namely produced from alcohols and acid, with the addition of fatty acids or vegetable or animal oils.

Alkyd paints in corrosion protective systems have along tradition, and have kept a certain position in competition with products based on newer, so-called advanced binders. Alkyd-based systems are described in this connection as being conventional as opposed to advanced or added value products.

5.2.2. Areas of use.Alkyd systems are used on ships, above the water line. They are never used below the water line, as the water resistance of the alkyds is not good enough for continuous exposure to high humidity or water. Further, alkyd paints are never recommended on Zinc primers or galvanised steel due to possible zinc soaps formation and loss of adhesion.

Alkyd paint systems has kept a strong position for use on ships superstructure due to the ease of maintenance. Alkyds are also widely used in varnishes, both for indoor and outdoor use.

Alkyds with high oil content are quite often used for outdoor house paints for wooden house, decorative paints and as corrosion protective coatings. Medium oil alkyds are widely used in decorative paints as well as for floors and other places where higher resistance to wear is required. Formulated as corrosion protective coatings, they are especially used as finishing coats. Short oil alkyds (with low content of oil) are used in industrial paints e.g. stove enamel and various primers.

5.2.3. Properties and practical aspects.

Alkyd primers contain anticorrosive pigments, e.g. Zinc phosphate which, by dissociation, prevents the steel from rusting.

Alkyd paints have good penetrating properties and pre-treatment to the standards St 2 to St 3 is normally sufficient in accommodations and engine rooms. However, on superstructures, or when exposed to more severe environments, blast cleaning of welded seams and damaged shop primer are preferred.

Because of poor resistance to alkalis, alkyd paints are not recommended for use on concrete, and certainly not on relatively new masonry. Alkyds are esters, and will saponify when reacting with the alkalis from the masonry.

The characteristics of the alkyd products can briefly be summarised as follows:

The benefits

Easy application, both with airless spray, roller and brush

Good wetting properties.

Good adhesion to the surface, and good penetration properties

Good weather resistance; Good gloss and colour stability

One-pack product: Usually easier to use than two-pack paints

Easy to repair details in the paint film during application

Good levelling properties

The limitations

Poor resistance to chemicals, especially to alkalis.

Limited water resistance: Can usually tolerate ordinary outdoor humidity, but can not be used under water or in especially humid conditions.

Limited resistance to solvents: Can swell (lift) under the influence of strong solvents such as Xylene, Ketones, alcohols and Chlorinated Hydrocarbons.

Can not be used on Zinc primers: Zinc soaps will be formed (Saponification)

The film thickness per coat is limited, usually 30 - 50 microns, up to 80 m for special types

Must not be overcoated by paints containing strong solvents (Will swell the Alkyd)

5.2.4. Chemistry.An alkyd is produced from alcohol and acid, with the addition of fatty acids or oils. A mixture of several oils or fatty acids can be used to give alkyds with different properties. By also varying conditions, such as temperature and processing time we can produce alkyds with widely different properties.

Alkyds can be drying or non-drying, depending on the fatty acids used in the production. Drying oils contain a considerable amount of unsaturated fatty acids, such as linoleic or linoleic acids. These contain double bonds which permit oxidative drying by reaction with the oxygen in the air. Examples of drying oils used in the production of alkyds are: Linseed oil, Wood oil, Soya oil and Fish oil. In addition, tall oil and fatty acids are widely used. Non-drying oils contain chiefly saturated fatty acids, such as Stearic or Palmitine acid, and fatty acids with only one double bond. Coconut oil is a non-drying oil.

It is already mentioned that we distinguish between drying and non-drying alkyds according to the content of saturated and unsaturated fatty acids. We also distinguish between long oil-, medium oil- and short oil alkyds according to the total content of fatty acids in the alkyds. The fatty acid content of the alkyds is described as oil length instead of fat content: Long oil alkyds contain more than 60 % of fatty acid, medium oil alkyds between 40 and 60 % and short oil alkyds less than 40 %. An increasing oil length gives an alkyd with lower viscosity, better wetting properties and better application properties. On the negative side is that longer lengths also creates longer drying times and poorer colour stability (yellowing).

The drying process.The alkyds go through a drying process by oxidation (also called air-drying). There is a chemical reaction between the oxygen in the air and the double bonds in the unsaturated fatty acids along with the solvent evaporating. This causes the alkyd molecules to join together in a three-dimensional network, which forms the dry (or cured) paint film.

Drying agents, such as Cobalt, Calcium, Lead, Zinc Octoate and Naphtenate are added to the alkyd product to improve curing.

Figure 5.1.Drying through oxidation

Modified alkydsAlkyds can be modified in a number of different ways. The following are a few examples:

Thixotropic alkyds. On modifying with certain polyamides, produced by condensation between dimeric fatty acids and diamines, we get thixotropic alkyds. The advantage with thixotropic alkyds is their good application properties. A disadvantage being that they often have poorer gloss, and difficult to use in hot climates.

Styrenated alkyds are obtained by adding styrene during production, usually with peroxides as catalyst. These Alkyds dry quickly, but require stronger solvents (aromatic) and there is a danger of lifting the existing paint when several coats are applied.

Silicon alkyds give paints with particularly good gloss and colour stability. They are often used as topcoats.

Urethane alkyds are binders which, with regard to production, belong to the alkyd group. During the production of urethane alkyds the phthalic acid is substituted completely or partly by Isocyanates. Urethane alkyds dry quicker and have a slightly better resistance to water and chemicals than ordinary alkyds. Gloss and colour stability may be poor, dependant on the type of isocyanate.

5.2.5. Examples of Jotuns Alkyd paint systems. Typical Alkyd systems used to protect steel, can for example be:

2 x 30 microns CROMOPRIMER(primer)1 x 30 microns PILOT I(intermediate coat)1 x 30 microns PILOT II(top coat)

With high build paints, thicker and therefore fewer, coats are needed:

1 x 80 microns MAMMUT PRIMER(primer)1 x 80 microns MAMMUT T/C(top coat)or if desired:1 x 80 microns ROYAL WHITE*(top coat)

* The top coat Royal White will give an improved whiteness and gloss retention compared to Mammut TC.

The film thicknesses given in the example above indicate the dry film thickness (DFT) after application with airless spray. Should a roller or brush be used, even more coats will be needed to obtain the same film thickness.

5.3.Physically drying coatings.5.3.1. General introduction to physically drying coatings.The most common physically drying coatings are: Vinyl, Chlorinated Rubber (CR) and Acrylic coatings. They have all served with distinction for years as industrial and marine coatings. However, in recent years the society in general has shown an increasing interest in health and environmental aspects. One of the hazards of major interest is the emission of solvents: Volatile Organic Compounds (VOC). As VOC restrictions have become more and more important over the years there has been a tendency to use lower molecular weight resins. The binder in physically drying coatings consist of long chained molecules, resulting in high contents of solvents (VOC). The VOC regulations will cause these coatings to disappear from the market except perhaps for some specialised uses.

Most paints protect the underlying material by creating a barrier between the substrate material and the surrounding environment. Basically, a thicker paint film will give better protection than a thin coat (Note: Maximum filmthickness is given by the data sheet). The physically drying coatings provide moderate high film thicknesses by normal applications.

5.3.2. Physically drying coatings: Vinyl.

5.3.2.1. Areas of useVinyl paints have been widely used as industrial coatings in chemical plants, refineries and tank farms, bridges and on ships (Vinyl tar under the waterline).

5.3.2.2. Properties and practical aspects.Vinyl coatings have generally similar performance properties as Chlorinated Rubber. These are properties such as a strong barrier, chemical resistance, good exterior durability and good abrasion and impact resistance.

The Vinyls have excellent moisture and oxygen barrier properties, excellent water resistance and very good acid and alkali resistance. They are single-pack paints, and as such they are easy to apply by airless spray, brush and roller. The physically drying paints are resoluble and therefore show excellent recoatability, even after many years of exposure. An other advantage is that they are fast drying, even at low temperatures.

One limitation regarding the area of use is the lack of substrate tolerance. Vinyls are composed of large, highly cohesive molecules that tend to have great attraction for each other (cohesion), large amounts of strong solvents are necessary in order to keep the paint in a liquid state and to have a viscosity of the paint suitable for application. Because of limited wetting properties, blast cleaning to the standard Sa 2 is the required surface preparation. Alternatively, application can take place on intact shopprimer (all types).

Application of Vinyl on Zinc-silicate primers represents a problem as pinholes or popping can develop. This can be avoided by applying a special Vinyl tie-coat or by using the so-called mist-coat - full-coat technique. The tie-coat should be applied at a dry film thickness of approximately 20-30 microns.

The Vinyls also have a limitation in film build-up. If too thick a coat is applied there is a risk of having entrapped air in the paint film. It is important to follow the recommendations given by the Technical Data Sheet regarding dry and wet film thickness.

It is, generally, not recommended that Vinyl paints are subjected to long time exposure at temperatures exceeding 75-80 oC. Decomposition would then take place and lead to yellowing and the development of a brittle paint films.

5.3.2.3. Chemistry.Many dissimilar paints can be placed under the umbrella Vinyl paints. The reason for this being that Vinyl paints can be formulated in many different ways. They can be based on various Vinyl resins and they can be modified with other binders etc. Therefore, Vinyl paints may differ greatly from one manufacturer to the other. The physically drying coatings are mostly manufactured from high molecular weight polymers. They form tough chemical- and water-resistant films and the drying mechanism is based solely on solvent evaporation. Vinyl paints based on copolymers of vinyl chlorids and vinyl acetate have poor adhesion to metals and are therefore not used as a primer. To obtain paints with good adhesion to metals or Zinc primers some acid groups (Maleic acid) are reacted into the copolymer used in primers.

Both Vinyl, CR and acrylic are resoluble in the solvents from which the films were cast. This is a technical advantage as good inter-coat adhesion is ensured. They are thermoplastic coatings, meaning that they will become soft at higher temperatures and hard at low. With time the paints will age. Thus, Vinyl resins are usually too brittle to be suitable as a binder alone, and must therefore be softened and made more elastic by the addition of certain amounts of plasticizer, mostly chlorinated paraffins or phthalates.

To attain special characteristics or effects, it may also be necessary to combine the Vinyls with other binders. However, the compatibility will be limited. Here are some examples:

The acrylic resins belong to similar type of resins as the vinyl, but do not contain chlorine. They can contain higher volume percent solids, better colour and gloss retention and release the solvents more easily than the pure Vinyl resins.

Hydrocarbon resins give solutions with low viscosity and a higher volume percent solids content in the paint. They have good wetting properties, which is of particular importance for primers.

Aldehyd resins/Ketone resins also give solutions with low viscosity and a higher percent volume solids content. They also give higher gloss to a topcoat.

Tar/pitch, together with Vinyl, give extremely good water resistance, and are used in underwater primers for ships and other submerged constructions. Because of the tar content, over-coating with light coloured coatings must be avoided. The tar/pitch will bleed through the topcoat and give discoloration (yellowing). Tar is also considered carcinogenous, and products must be marked accordingly.

Epoxies. In some cases the addition of Vinyl resins to epoxies can give better intercoat adhesion. Small amounts of certain epoxy types will act as stabilisers for the Vinyl resins.

Wash primers based on Polyvinyl butyral-binders pigmented with zinc tetraoxychromate show very good adhesion to different metals. These wash primers, with Phosphoric acid as curing agent, must be applied in very thin layers, typically in the range 8-13 microns.

5.3.2.4. Examples of Jotuns Vinyl paint systems.

Under water area:

Barrier1 x 25 microns (DFT)Vinyguard (Black - Brown Black)3 x 80 microns (DFT)Total, before Antifouling 265 microns (DFT)

Vinyguard can also be applied on intact Shop primer.

Industrial atmosphere:

Resist GTI1 x 75 microns (DFT)Vinyproof Primer1 x 35 microns (DFT)Vinyproof HB1 x 80 microns (DFT)Vinyproof HB1 x 80 microns (DFT)Vernyl Topcoat1 x 50 microns (DFT)Total film thickness: 320 microns (DFT)

5.3.3.Physically drying coating: Chlorinated Rubber (CR).

5.3.3.1. Areas of useCR-coatings have been widely used as industrial coatings in chemical plants, refineries, tank farms, bridges, on ships (both above and below the waterline) and other marine structures.

5.3.3.2. Properties and practical aspects.Vinyl and CR coatings have generally similar performance properties, such as being a strong barrier, good chemical resistance, good exterior durability and good abrasion and impact resistance.

As with all physically drying paints the CR products are resoluble. This resolubility can be considered both as a positive property, but may also be negative: The positive effect will in most cases be the dominating factor as resolubility gives flexible overcoating periods, with basically no danger of flaking between coats. The negative side will be that CR-based products are not resistant to most solvents. This implies that strong solvents may destroy the paint film and in addition that there is a danger of solvents being entrapped in the paint film. This happens especially when overcoating a thick CR-system at low temperatures.

CR has very good resistance to water. The paint is also quite resistant to acids and alkalines and to most corrosive chemicals. However, the resistance to both animal as well as vegetable oils is poor.

CR consist of large, highly cohesive molecules that tend to have great attraction for each other (cohesion) For this reason large amounts of strong solvents are necessary in order to keep the paint in a liquid state and to have a viscosity of the paint suitable for application. Due to limited wetting properties, application should only take place on a blast-cleaned surface (Sa 2 ) or, alternatively, directly on intact shopprimer (most types).

CR-coatings have certain temperature limitations. They are not recommended on objects which have a constant temperature of more than approximately 70 oC. At higher temperatures there is a tendency toward chemical decomposition of the binder with the evolution of hydrochloric acid (HC1) as one of the reaction products.

The CR coatings protect the steel through the barrier effect, no rust preventing pigments are normally included in the paint. CR primers are very often pigmented with aluminium to increase the barrier effect.

CR coatings are normally applied in 60-80 microns dry film thickness (DFT) pr. coat. Three coats of CR-coating will normally be sufficient to give a satisfactory barrier, and thereby good corrosion protection. One should take care not to apply CR thicker than specified (60-80 micron DFT pr. coat) due to the risk of having entrapped air in the paint film, which will create blistering later on.

5.3.3.3. Chemistry.The physically drying coatings are mostly manufactured from high molecular weight polymers. Chlorinated Rubber can be manufactured by chlorination of natural or synthetic rubber. CR resins are usually too brittle to be suitable for use as a binder alone, and must therefore be softened and made more elastic by the addition of plasticizer, e.g. chlorinated paraffins. They are thermoplastic coatings, meaning that they will become soft at higher temperatures and hard at low. With time the paints will age. The plasticizers will aid to maintain good physical properties over time, such as flexibility, good adhesion and impact resistance.

Being a physically drying paint CR coatings dries (like vinyl) by evaporation of the solvents. No chemical reaction takes place. This implies that the CRs are resoluble in solvents from which the films were cast. This is a technical advantage as good intercoat adhesion is ensured.

Figure 5.2.The drying process

5.3.3.4. Examples of Jotuns Chlorinated Rubber paint systems.The topcoat in CR and vinyl system are often modified with acrylic resin which gives better exterior durability: Better gloss, less dirt pick-up, less yellowing and faster drying.

Typical system on ships under water area:

Pioner Primer (Al Redtoned Al)3 x 75 microns (DFT)Antifouling (Sargasso)1 x 150 microns (DFT)Total film thickness 375 microns (DFT)

Typical system on ships superstructure and industrial atmosphere:

Pioner Primer 2 x 75 microns (DFT)Pioner Topcoat1 x 50 microns (DFT)Total film thickness 200 microns (DFT)

5.3.4.Physically drying coating: Acrylic

5.3.4.1. Areas of useAcrylic resins are primarily characterised by their water-white colour, their resistance to change in colour over time and their perfect transparency. They are widely used as topcoats on Vinyl and CR paint systems, and are applied to a filmthickness of approximately 50 microns.

5.3.4.2. Chemistry.This group of physically drying coatings is mostly manufactured from high molecular weight polymers. The acrylic polymers used in coatings are primarily those of the Poly-methacrylates and Poly-acrylates.

Acrylic coatings are resoluble in the solvents from which the films were cast. This is a technical advantage as good intercoat adhesion is ensured. They are thermoplastic coatings, meaning that they will become soft at higher temperatures and hard at low. With time the paints will age. Therefore, it is necessary to use plasticizers to maintain good physical properties over time, such as flexibility, good adhesion and impact resistance.

The drying mechanism is based solely on solvent evaporation.

5.3.4.3. Examples of Jotun Acrylic paint systems.Jotun Acrylic coatings are mainly topcoats. They can be used as topcoat on CR and Vinyl primers as they gives better exterior durability than topcoats based on those binders (better gloss, less dirt pick-up, less yellowing, faster drying). In Jotuns container system both Conseal Topcoat and Conseal Touch-up are based on acrylic.

5.4. Chemically curing paint: Epoxy coatings.5.4.1 About Epoxy paints in general.5.4.1.1. Introduction.There are a number of different Epoxy paints. Each one of them made to meet certain requirements during service. Still, as members of the epoxy family, they have many common properties. In the present section of this book we will present the general properties and features of the epoxies and subsequently the individual Epoxy coatings. 5.4.1.2. Areas of useDifferent types of epoxies have different areas of application. A summary of the most common areas of use is given in the table below:

Table 5. 2.Area of use for the different epoxy paints.

Epoxy paint.Common areas of useEpoxy MasticVery versatile coatings: Industry, ships and offshore. Under and above water (Topcoat required when exposed to UV-light). On most substrates due to good penetration and adhesion properties.Pure epoxyChemical tanks, potable water tanks and as an all-round coating system on ships and industrial plants. Require blast cleaning to minimum Sa 2 .

Table 5. 2. (cont.)Area of use for the different epoxy paints.

Epoxy phenolicChemical tanks. Even better properties than pure epoxy. Require blast cleaning to minimum Sa 2 .Coal tar epoxyShips. Under water, particularly water ballast tanks.Solvent free epoxyDrinking water tanks and where environmental restrictions are decisive. Waterborne epoxyIndustry where conditions can be controlled (Humidity and temperature)

5.4.1.3. Properties and practical aspects.As stated earlier the different Epoxy paints have different properties. However, they have some general characteristics. The most important being:

Benefits:Good water resistance

Good adhesion to the substrate

Good chemical resistance

Very good alkali resistance

Great resistance to mechanical damage

High durability

Temperature resistant up to 120 oC (Somewhat lower/higher for certain systems)

Certain systems officially approved for potable water tanks and in contact with food

High solids content/low VOC possible

Limitations:Poor resistance to UV rays: Chalks in sunlight

Application and curing depends on the temperature (Normally, above +10 oC) Winter grades down to -5 oC

It may be difficult to overcoat cured epoxy

They are two-component products and therefore require good mixing and may give increased wastage

Moderate resistance to acids

Can cause allergy (eczema)

Require knowledge to be used correctly

Guidelines for the use of Epoxy paints.Epoxies are advanced products. This implies that they are not straightforward to use and will therefore require a certain knowledge and experience from the applicator. Important points when working with epoxies are: Use the correct mixing ratio and make sure that mixing has been done so well that all reactive groups come into contact with each other. Use mechanical agitator !!

There is a time limit for the use of two-component products after mixing. This is called the pot-life. The paint is unfit for use after exceeding the pot-life. Information on the potlife is found in the Technical Data Sheet.

The substrate must be clean and dry, blast-cleaned to min. Sa 2 . Exceptions are the surface tolerant epoxies, see Epoxy Mastic.

The film thickness per coat as well as the dry film thickness shall conform to the requirement given by the technical data sheet for the product. This is to obtain good protection and to avoid cracking / sagging.

The rate of curing is dependent on the temperature. Below 10 oC the chemical reaction (curing) will usually be too slow and the curing of the paint will be unsatisfactory. For some products a special winter version has been developed. This can be used down to 5 oC.

The maximum characteristics are not attained until after complete curing, normally after a week at 23 oC and minimum two weeks at 10 oC.

To ensure maximum adhesion between the coats Epoxy paints have usually both a minimum and a maximum overcoating interval to comply with (See TDS).

Good ventilation during the curing process is necessary to form a good film.

Thinning must only be done with the specified thinner.

After use, all equipment must be cleaned, and this must be done before the pot-life has expired.

Always be aware of the health risk when working with Epoxy. Proper personal protection is a necessity. In confined spaces adequate ventilation must be ensured.

5.4.1.4. Chemistry.The types of Epoxy resins used for corrosion-resistant coatings are normally based on Bisphenol A and Epichlor Hydrin. By varying the mixing ratio a wide range of molecular weight (lengths of molecules) and properties can be achieved. The molecular weight can vary from 340 for liquid epoxy and up to more than 1000 (solid resin).

Both the liquid, the solid resin and a combinations of them may be used to form corrosion resistant coatings. With the number of curing agents and the various combinations of epoxy resins available, the epoxies can be the basis for a variety of corrosion-resistant coatings.

The Epoxy resin alone is not good enough as a binder in a coating. A curing agent must be added and mixed with the epoxy resin to get a paint film consisting of an insoluble, tree-dimensional network. The most used curing agents are amines, amine-adducts, polyamides and Isocyanates.

The chemical reaction described above has also its negative side: Both the Epoxy component and the curing component have almost unlimited shelf life but as soon as they have been mixed they begin to react with each other. The viscosity of the mixed product increases with time and gradually becomes so high that the paint can not be applied. The period of time up to being unusable is called pot-life. The pot-life is temperature dependent: The higher the temperature, the shorter the pot-life.

Among the Epoxy coatings, the ones with polyamide curing agents are the most user friendly, since they often have a reasonable pot life and higher mixing-ratio tolerance. From a performance viewpoint, the paint films formed are more flexible, and show better water-, moisture- and weather resistance than the ones using other curing agents.

Figure 5.3.Chemical curing of two-pack paints

Amines and Amine-adducts are used as curing agent in Epoxy coatings to obtain good chemical resistance. The Amines are very reactive, implying a short pot life and curing time. If the humidity of the air is too high, they may react with Carbon dioxide and the moisture in the air to form an Amine carbamate, commonly referred to as amine blush.

The Amine-adducts (Amines partly reacted with Epoxy resin) gives the same basic properties as amine cured epoxy, but gives less blushing. These type of curing agent are mostly used in tank coatings (very good chemical resistance), in solvent-free and solvent-less paints.

The Isocyanates as curing agent for Epoxy gives a fairly rapid reaction, resulting in a short pot life and fast curing. The coatings have good chemical resistance. Isocyanates have also been used in paints to achieve low temperature (0 oC) curing.

5.4.1.5. Health hazards.The greatest problem when working with Epoxy products is the danger of developing allergic contact eczema. It is the uncured Epoxy which causes the allergic reactions. This can break out after a shorter or longer period in contact with the products.

Symptoms of allergic reaction most often occur after the skin has first become irritated.. This type of eczema is often only to be seen on hands and underarms, the reason being that it is chiefly these two parts of the body which come into contact with the product. When someone has become allergic he must stay away from contact with epoxy. This affects the whole body - and often lasts a lifetime. Therefore:

Protect yourself when working with epoxies.

The health hazards are described more detailed in section 16 Safety, Health and Environment.5.4.2. Pure epoxies.Epoxy coatings are widely used in shop and field applications for new constructions and for maintenance. In severe corrosion environments, such as offshore oil platforms, structural steel in refineries, tank exteriors, and coating of tanks onboard ships etc., Epoxy coatings are widely used. What type of Epoxy coatings to use depends on the substrate, as well as the application and service conditions. Pure Epoxies require blast-cleaned steel to a minimum of Sa 2 .

Pure Epoxies are also widely used on concrete due to their good alkali resistance. Normally, one coat of a clear Epoxy varnish is applied as the first coat. This will bind the dust and ensure good adhesion for the subsequent coats. Proper pretreatment is to remove laitance before applying the clear epoxy.

Most of the pure Epoxies act as a barrier coating. They are compatible with most inorganic and organic pigments. Properly, selected inert extenders (fillers) add to the physical properties of the epoxy coating by creating a more dense film and by improving the barrier properties. Such pigments include talc, baryte, aluminium flake, glass flake and micaceous iron oxide etc.

Epoxy coatings are available in wide colour ranges and provide excellent properties. However, non of the Epoxies are resistant to UV light. When colour or gloss durability are a foremost concern, other generic coatings such as Polyurethanes or acrylics should be used as topcoats.

Examples of Jotuns pure Epoxy systems are:

Penguard Primer 1 x 50 microns (DFT)Penguard HB 1 x 100 microns (DFT)Penguard Topcoat 1 x 50 microns (DFT)Total film thickness 250 microns (DFT)

orPenguard HB1 x 100 microns (DFT)Penguard Stayer *1 x 100 microns (DFT)Penguard Topcoat 1 x 50 microns (DFT)Total film thickness 250 microns (DFT)

* Penguard Stayer has no limitation regarding recoating intervals as long as the surface is clean.

System for maximum abrasion resistance:

Marathon1 x 300 microns (DFT)Marathon1 x 200 microns (DFT)Hardtop AS1 x 50 microns (DFT)Total film thickness 550 microns (DFT)

Marathon is reinforced with glass flakes which increase the water and abrasion resistance.5.4.3.Epoxy Phenolic coatings.The Phenolic epoxies have even better chemical resistance than regular Epoxy. They are reaction products of Phenolic Novolacs and Epichlorhydrin. Phenolic Novolacs epoxies have more reactive groups, resulting in higher crosslinking density and some other improving factors. These properties combine to give paints with very good chemical resistance. Thus, the Phenolic Epoxy coatings or linings provide excellent chemical and corrosion resistance, for example inside tank cars, tank lining on ships etc. Higher curing temperature (approx. 60 oC) is required compared with the normal Epoxy to achieve the maximum properties.5.4.4. Modified Epoxies: Coal tar epoxies (CTE).Coal Tar Epoxies (CTE) consist of the basic Epoxy resin, modified with a coal tar and a curing agent. The two materials combine the good properties of both the Epoxy and the coal tar to form a superior water resistant coating. Epoxy gives the chemical strength to resist chemicals and solvents. Coal tar gives flexibility, greater water resistance and much better substrate tolerance (good penetrating properties). By adding coal tar, which is a the low molecular weight binder, the solid by volume can be increased compared with pure epoxy and the VOC is reduced.

In the marine industry CTEs are used for underwater exposures, such as: Ship hulls, ballast tanks and combined cargo and ballast tanks. In addition they are used in the sewage industry to protect both steel and concrete surface.

Coal Tar Epoxies work entirely as a barrier system. They have shown very good corrosion protection on power-tool cleaned surfaces due to the very good penetrating properties. A typical system for Coal Tar Epoxies includes 2 coats of 125 or 150 microns DFT.

The disadvantages of Coal Tar Epoxies are first of all:The dark colour makes application and inspection in tanks /confined spaces difficult.

The tar will bleed into any topcoat making tar containing paints unsuitable above the water line if appearance is a critical parameter.

The Epoxy component may cause eczema.

Tar may irritate the applicator's skin and cause skin cancer.

5.4.5. Modified Epoxies: Epoxy Mastics.Epoxy Mastics consist of Epoxy resin modified with a hydrocarbon resin (certain variations should be expected for different manufacturers) and a curing agent. The hydrocarbon resin is used to enhance the moisture resistance, flexibility and the wetting properties of Epoxy coatings. They also make the paint more user friendly and economically in use.

Epoxy Mastic is in many respects similar to Coal Tar Epoxy (CTE). However they are much more versatile coatings and nearly all drawbacks with CTE are reduced or eliminated:

The colour has been changed from black (or dark brown) to light colours to improve the painting conditions especially in confined spaces. The application is easier as the applicator himself can see the result while application takes place. For the same reason also inspection is simplified and, thereby, the safety is improved.

The Mastics show excellent penetrating properties, implying that they can be used on almost all types of substrates.

They have high solid by volume, 82-87% which reduce the VOC emission

The Mastics cause no bleeding into the topcoat

They contain no coal tar (coal tar can create cancer).

Epoxy Mastics are especially designed to be all-round, surface tolerant coatings. The reasons for the very good penetrating properties are the small sized molecules and the low viscosity of the binder, giving good flow. As such they can be used with very good results on hand- and powertool cleaned surfaces, water jetted surfaces, Magnesium descaled surfaces (electrolytic descaling) and on blast cleaned surfaces.

Blast cleaning is usually recommended to obtain optimum corrosion resistance for immersed service conditions or for use in very aggressive environments. The Mastics are widely used for marine applications (all outside areas, cargo tanks, ballast tanks, void spaces etc.) and for offshore, heavy industry, sewage, power plants, concrete etc.

Figure 5.4.The surface tolerance depends on the penetrating properties of the binder.Epoxy mastics are very substrate tolerant coatings.

The Mastics form a barrier between the substrate and the surrounding environment. Thus, they are primarily designed to be applied as two-coat system, with minimum film thickness of two times 125 to 150 microns DFT. They can usually be applied up to 300 microns DFT in one coat without sagging. However, from a corrosion protection point of view it is always better to apply two coats of 150 microns than one single coat of 300 microns. To improve the barrier effect, and thereby the corrosion resistance even further, it is generally recommended to apply the first coat with an epoxy mastic with aluminium flake pigmentation. This will effectively prevent, or at least slow down, the water absorption and give better performance.

Normally +10 oC is the minimum application temperature for Epoxy mastics with some exceptions. However, so-called winter curing agents can replace the traditional agents in the paint, and thereby increase the area of application down to 5 oC. The winter grades may also be looked upon as a fast-cure version at normal application condition as the curing time will be much shorter than for the standard versions at temperatures above +10 oC. (Note: Pot life will be reduced at higher temperatures).

For exposure above water a topcoat (polyurethane or acrylic) should be used when UV-light resistance is required.

Figure 5.5.The barrier effect is improved by adding flake formed pigments.

5.4.6. Solvent-free epoxy

Area of useSolvent free epoxies are mechanically very strong, high build coatings. They are used for protection of steel below and above water and also for potable water systems. In addition, they show very good chemical resistance.

Other products within this family are used for very special applications. Examples are:

Floor coating: Applied with a roller or a masons float in thicknesses of up to

5 mm.Anode shield: On steel structures around impressed current anodes.

Example of Jotun solvent free epoxy system.

Solvent free Epoxies should only be used on blast cleaned steel, Sa 2 , or on intact Shopprimer. Typical systems are:

Naviguard 1 - 2 x 300 microns (DFT)

As anode shield in combination with impressed current systems:

Preferred: Anodeshield ICCP 2 x 400 m DFTAlternatively:Naviguard 2 x 500 microns (DFT)

ChemistryBy mixing liquid epoxy with a liquid curing agent it is possible to make solvent-free epoxy products. Still, the paints have high viscosity and have to be are applied with a heated, two-component airless spray. This complicated equipment is also necessary because of the short pot-life after mixing. By modifying the products with e.g. tar, it is possible to reduce the viscosity and increase the pot-life so that the paints can be applied with an ordinary airless spray.

5.5.Waterborne coatings5.5.1Waterborne acrylics

Chemistry:With acrylic copolymer dispersions in water you can obtain much higher molecular weight (>200 000) for the polymer than for the same in solvents. A polymer dispersion has a high solids (>50%) content which enables fast air drying by evaporation of water, while high molecular weight removes the need for any post-curing or oxidative drying to obtain a tough integrated film which retains its flexibility over time and is durable against degradation. A polymer dispersion will also keep the same viscosity up to 50 - 60% solid content, independent of degree of polymerisation. The polymers properties can be tailor-made for different applications for instance by copolymerisation of two or more monomers such as methylmet-acrylate, methylacrylate, butylacrylate, styrene, butadiene, etc. in different proportions. The polymerisation-process and selection of additives is decisive for the binders properties and therefor the same generic type of binder can have widely differing properties. Since acrylics are thermoplastic, one uses hard polymers (with high glass transition temperature) of acrylic/styrene - acrylic to obtain a hard and resistant paint for industrial corrosion protection.

Figure 5.6.Physical drying of waterborne paints

Film formation involves fusion of the polymer particles in the liquid coating. During the early stages of particle fusion, the films are characterised by microscopic channels between the latex particles. Under practical painting conditions, these channels disappear over a period as the particles continue to meld together. To accelerate this process, volatile solvents, termed coalescing agents, are included in the formulation. These slow-evaporating organic solvents act as temporary plasticizers at the particle surface and optimise the coalescence of the polymer particles (they melt together).

The presence of these coalescing solvents means the Volatile Organic Compound, (VOC) content of water-borne acrylics is not zero.

Properties and practical aspects.The advantages with water as the solvent/thinner in polymer dispersions is self-evident, water is not poisonous, has no odour, is not health hazardous or flammable (no risk of explosions). Emissions of organic solvents to the atmosphere is minimal and waterborne products are therefore environmental friendly with small hazards for the user/applicator. In addition acrylics have good UV-resistance, they dry quickly, do not yellow or undergo saponification.

The disadvantages with water in polymer dispersions is slow evaporation at low temperatures and high relative humidity in the air. Water has very high surface tension and therefore certain specialised additives (surfactants) are added in the formulations to amongst others make the paint pigments and substrate better. Some of these additives can have a negative influence on the paints water resistance and water permeability and in addition good film formation is more critical for the paint properties than for solvent-borne paints and of cause the paint will freeze below 0 oC.

Waterborne acrylic coatings can be formulated to produce either gloss or semi gloss coatings, both primers and topcoats. They can be applied to many different substrates, including steel, galvanised metal, aluminium, concrete, masonry and wood. A water-borne Acrylic primer dries fast and is hard dry and recoatable after 2 hours at 23 oC and exhibits very good adhesion to blast-cleaned steel, galvanised steel and aluminium.

Waterborne Acrylic topcoat has high gloss resistance, good weatherability, good water resistance and good UV-resistance and does not yellow. It is hard dry after 45 minutes, recoatable after 2 hours at 23 oC (DFT 50 microns) and it dries down to 5 oC. It can also be used on several solventborne coatings in a so-called Hybrid paint system.

Semi-gloss water-borne acrylic topcoat can be applied in a dry film thickness of 80 microns, and has the same good properties as the high gloss type and even better water resistance.

Safety, Health and Environment (SHE), Waterborne acrylics.Acrylic based corrosion resistant coatings contain low amounts of low hazardous organic solvents and are therefore not very straining for the environment/user and water ca be used as cleaner and thinner. The products are not flammable, has a very low explosion risk, low odour, does not have any sensitising effect or give rise to allergic reactions after skin contact. Most Acrylic based binders contains Alkyl phenol ethoxilates which are surface active compounds (surfactants) that are used during the polymerisation process to stabilise the polymers. These compounds have been put in focus due to their negative SHE-properties and they will therefore be replaced in all of Jotuns paint products by year 2000 and this includes the before mentioned products.

The volatile organic content, VOC, is approximately 45-60 gram/litre for the primer and topcoat.

5.5.2.Waterborne Epoxy

Chemistry.To be able to replace organic solvents with water and make waterborne epoxy products one has to make the epoxy resin and amine curing agent hydrophilic (waterloving) either by chemical modification or by adding/using an external non-ionic surfactant (emulsifier). In most cases the amine curative is water-soluble, while the epoxy resin is not soluble but emulsifiable in water. One can classify waterborne epoxy products after the type of epoxy resin used. Type I is low molecular standard or modified liquid epoxy, typically 190 in EEW (Epoxy Equivalent Weight). Type II is preformed dispersions of higher molecular weight solid epoxy, typically 500 in EEW, though there are also dispersions of solid epoxy with about 650 in EEW. Type III is epoxy resin emulsions where standard Bisphenol A liquid epoxy is emulsified in water with the help on non ionic emulsifiers.

Curing agents for Waterborne epoxies are made by using surfactants to emulsify or disperse polyamidoamines (PAA) and polyamines (AA) in water or use water-soluble polyamides (PA).

Properties and practical aspects.Waterborne epoxies are as the name indicates water-thinnable. They have low odour, are not flammable and can be applied on moist/damp substrates. Waterborne epoxies will usually have excellent adhesion to most substrates and especially type I epoxies exhibits good water resistance.

The film formation process is more critical than for solventborne epoxies, since there are two additional steps in the film formation process, the evaporation of water and that the film has to flow together (coalescence) before solvents will evaporate and crosslinking will take place. This makes it more important to have a better control on temperature, relative humidity and ventilation during application than with solventborne epoxy. Assuming that these precautions are taken and that the paint is correctly applied, in most cases one would be able to match the properties of solventborne epoxy paints with the exception of chemical resistance, which is a bit weaker. Another weakness with waterborne epoxy is the fact that you cannot thin the paint unlimitedly with water since there is a risk of destabilising or breaking the epoxy/amine emulsion.

One can however easily thin up to 20% water on total formulation without any problems. When formulating waterborne epoxy primers, an inhibitor has to be added to prevent flash-rust of forming on the steel. The inhibitors available in the market place today will usually, to a certain extent, deminish the paints anticorrosive properties. Potlife for waterborne epoxies are shorter than the one for equivalent solvent borne epoxies.

Waterborne epoxy primer shows good anticorrosive properties even on steel blast-cleaned to Sa 1-2. It has very good water resistance, no flash-rusting, cures down to 5 oC and can be recoated with a waterborne after 1 hour at 23 oC. Normally applied in 60 - 120 microns DFT, it also shows good adhesion to aluminium.

Intermediate coats are normally applied in 80-100 microns DFT and can be used in combination with Waterborne epoxy primer or with solventborne coatings (Hybrid systems). It cures down to 5 oC at 85% R.H.

Waterborne epoxy zinc-rich primer for blast-cleaned steel (min. Sa 2 ) can also be used in a pure waterborne epoxy system or in combination with waterborne acrylic.

Safety, Health and Environment (SHE), Waterborne epoxiesWaterborne epoxies have much of the same health hazards as the equivalent solventborne ones, i.e. danger for sensitising and development of allergic contact-eczema after long term exposure. The Epoxy resin can irritate eyes, throat and skin after long and repeated exposure. Bisphenol A, low molecular standard liquid epoxy has lately been put in focus due to possible hormon imitating properties, i.e. it can disturb/reduce reproduction of mammals. Polyamines are allergic sensitisers, can cause serious eye damage by direct contact and when they contain more than 10% free amine they are also classified as corrosive. Polyamine adducts (i.e. polyamines pre-reacted with small amounts of epoxy) have very low amounts of free amines and have therefore a more lenient health hazard labelling, i.e. the labelling can be reduced from health hazardous to irritating. There also exists polyamine adducts that are free of any labelling. From a SHE point of view Poly-amidoamines are preferred since they usually do not have any health hazard labelling. The VOC content can vary from 9 to 110 gram/litre.

Some example of Jotuns waterborne systems:

Paint systems for corrosion class 3 - 4:

Container system:

1 x 60 microns WaterFine ZEP (2-pack epoxy)1 x 80 microns WaterFine Topcoat Semigloss (Acrylic)

or2 x 100 microns DFT WaterFine Primer (2-pack epoxy)1 x 50 microns DFT WaterFine Topcoat (Acrylic)

or1 x 40 microns WaterFine ZP Primer1 x 90 microns WaterFine Special1 x 80 microns WaterFine Special1 x 50 microns WaterFine Topcoat

Hybrid paint systems (solventborne & waterborne paint combined):

The following paint systems can be recommended;

1 x 50 microns DFT Barrier1 x 100 m DFT Jotamastic 872 x 90 microns DFT WaterFine Special1 x 80 m DFT WaterFine Special1 x 50 microns DFT WaterFine Topcoator1 x 50 m DFT WaterFine Topcoat

5.6.Zinc coatings5.6.1. IntroductionThe main reason for applying a zinc containing coating is to have a primer with the ability of providing cathodic protection. This is an added value and will contribute to protecting the steel substrate and reduceing the risk of having undercutting corrosion. For the cathodic protection process to work properly, it is extremely important that the coating contains a sufficient quantity of zinc metal in its formulation. This is to assure proper zinc-to-zinc particle contact (electrical continuity) within the coating film and to obtain intimate contact between the zinc and the steel substrate.

Figure 5.7.

A Zinc primer has the ability of providing cathodic protection

The classification of zinc-rich coatings, organic versus inorganic, refers to the binder. The inorganic binders have much better electrical conductivity than the organic binder does. That is why the requirement for zinc dust content is lower. A widely accepted industry guideline for minimum Zinc requirements is given by the organisation Steel Structure Painting Council, SSPC-Paint 20. This concerns zinc Rich Primers (Type I Inorganic and Type II Organic): Total Zinc dust shall be minimum 74 % by weight of total solids of an inorganic Zinc-primer and minimum 77 % by weight for an organic zinc-primer. It must be stressed that this is a guideline, not a requirement.

Most commercial inorganic zinc coatings formulated to give long- term corrosion protection in a single coat have a Zinc dust content above 75 % weight of the dry film for waterborne and 82 % for solvent borne paints. A number of Standardisation Organisations and Government Agencies have developed specifications and information on inorganic zinc coatings. These cover many aspects: the range of performance requirements as well as composition.

Very often the decision to specify a zinc-rich primer comes down to the question of whether to specify an organic or an inorganic material. It is not always a question of which is better, but rather which is more appropriate for both the end-use environment and the conditions under which the coating will be applied. There is no question about the fact that in most cases organic Zinc primers will give a faster production rate, while the inorganic Zinc will provide better corrosion protection due to better conductivity than epoxy and better contact between steel and zinc.

5.6.2. Organic Zinc coatingsArea of use.The organic zinc-rich primers (thermosetting) are the most common ones. The most commonly used for atmospheric exposure is the polyamide-cured. Zinc epoxy primer has the best overall performance of all other organic types.

Properties and practical aspects.The zinc epoxy shall be applied on steel blast cleaned to the standard Sa 2 (ISO 8501-1). They offer very good airless spray application properties, are quickly recoatable, and show excellent compatibility with most coatings (except alkyd: Saponification). It is a good primer for multicoat systems, both for new constructions as well as for field maintenance applications.

Zinc Epoxy is often used as a holding primer both at industrial plants (during maintenance) and within shipping (during dry-docking). It is quick drying and the overcoating interval is relatively short. It has very good adhesion, good impact resistance and is heat resistant up to approximately 120 oC. The abrasion resistance is good.

The disadvantages of zinc epoxy compared with inorganic zinc is first of all that the galvanic protection of the steel is limited as the electrical conductivity is low. Secondly, the acceptance level of chlorides on the substrate is lower. This is particularly a drawback for marine exposures.

Chemistry.Organic zinc-rich primers contain either a thermosetting or a thermoplastic binder. When heated thermosetting materials undergo a chemical reaction (such as Epoxy and Polyurethane). A thermoplastic material becomes softer when heated and will harden when cooled. (Like Chlorinated Rubber, the high molecular Epoxy Phenoxy and Vinyl).

Examples of Jotun zinc epoxy paint systems.Barrier is a zinc epoxy primer for blast cleaned steel (Minimum Sa 2 ). In most cases Barrier is used in combination with other coatings (except Alkyds) to further improve the protection against corrosion. Typical film thickness of Barrier is 25 40 microns DFT.

5.6.3. Inorganic Zinc coatingsThe development of inorganic zinc-rich coatings began in the 1930s at Cambridge University. The first time they were used was in 1941 when a waterborne sodium silicate coating was applied on an above-ground pipeline in Australia. It was cured by heating and was reported to be in excellent condition after more than 50 years in service.

5.6.3.1. Types of inorganic Zinc coatings and their areas of use.Typical practice in the use of inorganic zinc coating systems varies with the exposure environment and type of structure. One coat of inorganic zinc, typically 75 - 125 microns DFT, is often used for tank lining. They are very resistant to different chemicals and especially solvents.

The heat resistance is up to approximately 400 oC. Multiple topcoats over inorganic zinc coatings are used for marine offshore structures, ships, industrial plants, refineries, tanks, bridges etc.

Inorganic zinc coatings have, generally, not been used for services implying continuous water immersion. Cyclic service in seawater or fresh water/service in atmosphere can extend the service life because such exposures allow water-soluble zinc reaction products to convert to water-insoluble compounds. Typical areas of use include ships ballast tanks when alternate seawater and clean petroleum cargo. In such area they have shown more than 10 years of excellent service.

5.6.3.2. Classification.SSPC-Paint 20 classifies inorganic zinc-rich coatings into three categories:

Type 1-A: Post-curing, waterborne

Type 1-B: Self-curing, waterborne

Type 1-C: Self-curing, solventborne

Today, type 1-B and 1-C are more frequently used than type 1-A.

Type 1-B (waterborne) is mostly used for interior of tanks and for tanks exposed to warm or hot climatic conditions. Since there are no solvents in the film, they can be applied on the interior of closed areas without difficulty. The water evaporating from the coating itself creates sufficient humidity to complete the curing of the coating. This type is not effective under cold, highly humid conditions as water will not properly evaporate from the surface within a reasonable period of time.

Type 1-C (Ethylsilicate - solventborne) is widely used because it can be applied effectively under cold conditions at high humidity. Ethylsilicate require high humidity to get proper curing.

5.6.3.3. Properties and practical aspects.Inorganic Zinc coatings dry quite fast in comparison to most other types of chemically curing coatings. They become dry to touch in a matter of minutes, while typical chemically curing organic coatings take hours before the curing is completed.

Millions of square meters of surface have proven that inorganic Zinc coatings are very effective when used alone, without a topcoat. However, applying a topcoat to improve chemical resistance, general corrosion resistance or appearance is the more common practice. The Inorganic Zinc, with an organic topcoat system provides maximum corrosion resistance and service life for coatings in severe corrosive areas. Prior to overcoating, the inorganic Zinc coatings must be cured or almost cured (check Technical Data Sheet). The surface of the Zinc coating is rather porous, and to avoid the formation of blisters (popping and pinholes) in the subsequent coat, a mist coat - full coat technique or a tie-coat have to be used. The tie-coat must be compatible with the Zinc as well as the topcoat. Usually, the film thickness of the tie-coat is in the range of 15-20 microns.

Almost all generic types of coatings have been used on Inorganic Zinc coatings (Epoxy, Vinyl, CR or Acrylic). Most alkyd coatings, for instance, should not be used.

As topcoats for the industrial market, two-component Polyurethane coatings are used. Gloss and colour stability, abrasion and chemical resistance, coupled with flexibility make them very suitable.

Application.The waterborne Zinc Silicate has to be applied by conventional spray. The solvent borne Zinc-ethylsilicate, however, is excellent to apply by airless spray.

To achieve a properly applied, cured, and topcoated system with an Inorganic Zinc primer requires a higher level of application expertise compared with systems including an Organic Zinc. The major reason being that the film thickness is a very critical parameter for obtaining a good result. Recommended dry film thickness is in the range of 50 - 100 microns. Excessive film thickness, usually 125 - 150 microns or more, can result in mud cracking, which require immediate repairs.

Careful monitoring of the relative humidity is important during application and curing. If an inorganic Zinc coating is not sufficiently cured, prior to application of a topcoat with high build epoxy, the curing stress of the epoxy may exceed the cohesive strength of the Inorganic Zinc coating and lead to splitting and delamination of the Zinc film. Such concerns are generally not present with an Organic Zinc coating.

How to check the curing.Type 1-B has overcoating intervals of down to 1 hour, but is typically 16-24 hours. The curing of the waterborne is checked by water rubbing test or coin test.

For solvent borne (Type 1-C) a solvent resistance test, called Methyl Ethyl Ketone (MEK) rub test has to be used (ASTM 4752). Resistance to MEK can range from 16 hours to 24 hours. This test must always be done and the result accepted before overcoating with organic coatings.

Figure 5.8.Curing test of Zinc ethyl silicate with MEK. (ASTM-D 4752 87)

5.6.3.4. Chemistry.Inorganic Zinc coatings are porous when first applied, and they depend on the cathodic protection mechanism of the metallic Zinc pigment to close the pores and thereby prevent corrosion. The mechanism of the corrosion protection occurs in two basic steps:

1.Galvanic corrosion takes place when metallic Zinc sacrifices itself to protect the steel.

2.The reaction products from galvanic protection gradually react with gases in the atmospheric, primarily carbon dioxide and oxygen, to form water-insoluble Zinc corrosion products such as Zinc carbonates. These corrosion products fill the pores in the inorganic Zinc coating, creating a dense barrier to water and oxygen. Should the Zinc coating be sufficiently damaged to expose the steel substrate, the remaining unreacted metallic zinc again becomes active. This mechanism is first of all effective on inorganic Zinc primers that have not been applied a topcoat.

In a continuously submerged service condition, the Inorganic Zinc coating, if uncoated, will also protect the substrate material by galvanic action.

Post-curing, waterborne (Type 1-A). This type dries quickly to a hard state. However, it will remain water soluble until cured. Usually it is necessary to apply a curing solution. The curing solution converts the alkali metal silicates into water-insoluble binder.

Self-curing waterborne (Type 1-B)The most commonly held theory is that the self-curing waterborne type cure by reaction with the Carbondioxide and the humidity in the air. The coating remain sensitive to water contact until the water solvent has evaporated and sufficient curing has occurred. The curing is a gradual process over time, depending on temperature and humidity.

Self-Curing, Solvent Borne (Type 1-C)This type is usually modified with organic silicates, such as ethyl silicate. They cure by reaction with moisture in the air. The reaction liberates the organic group attached to the silicate, leaving an inorganic binder. The rate of cure depends on the vehicle formulation, catalyst, temperature, and relative humidity. The rate will be slow at low temperatures and low humidities. Solventborne inorganic Zinc coatings become water-resistant more quickly than waterborne formulations.

5.6.3.5. Examples of Jotun's inorganic Zinc coating paint systems.

Self curing water borne: Jotacote 5.

When Jotacote 5 is used as a one-coat system for the interior of tanks the paint system must be completely cured before the tank is put into service. Complete curing will in most cases require that the painted surfaces are sprayed with fresh water. Refer to the Technical Data Sheet regarding how to ensure proper curing. Typical paint system will be 1 x 125 microns.

Typical paint system when overcoated with water borne paints:

Jotacote 5 1 x 75 microns (DFT)Waterfine HB1 x 60 microns (DFT)Waterfine HB1 x 60 microns (DFT)Waterfine Topcoat1 x 60 microns (DFT)Total film thickness 255 microns (DFT)

Self curing solvent borne: Resist GTI

Coat system for interior of tanks: 1 x 100 microns (DFT)

Typical paint system when overcoated:Resist GTI1 x 75 microns (DFT)Penguard Tiecoat 1001 x 25 microns (DFT)Jotamastic 871 x 200 microns (DFT)Hardtop AS1 x 50 microns (DFT)Total film thickness: 350 microns (DFT)

Before applying the subsequent coat, make sure that the Resist GTI is completely cure (MEK test, see How to check curing).

5.7. Polyurethane coatings.

5.7.1. Areas of use.Polyurethane coatings can be both one-component (moisture cured) or two-component. This chapter will deal with two-component paints only. Two-component Polyurethanes are among the most versatile coating types. They fill a vital niche for high-performance applications over metal, concrete, wood and plastic. Polyurethanes are mainly used as topcoats in an Epoxy paint systems.

5.7.2. Properties and practical aspects.These paints show excellent colour and gloss retention for outdoor exposures. In addition, they are resistant to chemicals and solvents. Polyurethanes are chemically curing paints and as such the curing process will depend on the temperature. The lower temperature limit is 0 C.

An alternative to the Isocyanate cured Polyurethane coatings is the Epoxy Acrylic or Acrylic - Acrylic type. Such curing Acrylics have the same characteristics as the Polyurethanes. The potlife is much longer, the drying time very short, but the curing time is somewhat longer.

5.7.3. Chemistry.Two-component polyurethane coatings are based on Isocyanate resins as curing agents (Component B) and a co-reactans (Polyols) as the other component (Component A). Co-reactons generally are characterised by their backbone chemistries, which can be Polyester, Polyacrylate (acrylic), Polyether or Epoxy.

In general, polyurethane coatings containing Polyether. Polyols have better chemical resistance, but poorer weathering resistance than those based on Acrylic or Polyester co-reactants. Coatings based on Acrylic Polyurethane usually have the best colour and gloss retention, while coatings based on Polyester polyurethanes have good to excellent colour and gloss retention (do not chalk) and, in addition, usually better chemical resistance. With Epoxy as the co-reactant good chemical resistance is obtained.

The aliphatic Isocyanate are used as Component B in topcoats for outdoor applications when gloss and colour retention are required. The aromatic Isocyanates normally are used for primers and intermediate coats, as they chalk and become yellow when exposed to UV-light.

5.7.4. Health hazardsGreat care must be taken when working with Isocyanates. The Isocyanates irritate the eyes, the respiratory passage and the skin. Repeated exposure can lead to over-sensitivity and difficulty in breathing. People with asthma must keep away from such products.

5.7.5. Examples of Jotuns Polyurethane paint systems. A typical paint system will be:

Jotamastic 87 2 x 150 microns (DFT)Hardtop AS1 x 40 microns (DFT)Total film thickness 340 microns (DFT)

5.8.Polyester coatings.5.8.1. Area of use.Polyester coatings are quick curing, glass flake reinforced, and high build coatings. They give long time protection of steel structures in general and, in particular, items subject to extreme mechanical wear over a long period of time. Polyester coatings may also be used for protection of concrete (Specially designed systems). Polyester resin based coatings, also called linings, are known for their good solvent, chemical, water and erosion resistance. They have been used extensively since the 1960s where high chemical resistance is needed. Polyester coatings have also been extensively used on offshore structures (both fixed and floating) as an all-round coating on structures, decks, helicopter decks etc.. They offer very good adhesion to both steel and concrete, preferably on surfaces blast cleaned to Sa 2 .

5.8.2. Properties and practical aspects.Polyesters are normally two-component coatings applied at normal temperature. The polyester coating have a rather short pot-life and should therefore be applied by a two-component airless spray equipment (Regular airless spray is possible, and in fact, often used). At 20 oC the pot-life is approximately 40-45 minutes. The reason for the short pot-life is due to the addition of the MEK peroxide which makes the Polyester start curing. At the same time this will create heat which accelerate the curing. To be able to keep the pot life at 40-45 minutes during application at temperatures from 25 oC up to 40 oC a retarder (inhibitor) has to be added. At temperatures below 20 oC and down to 10 oC (which is the lowest temperature for applying Styrene based Polyester) the volume of MEK Peroxide has to be increased. It must be understood how very important it is to follow the manufacturer's recommendations, when adding catalysts and inhibitors at different temperatures.

Styrene free Polyester, where the styrene is replaced with Vinyltoluene, it can be applied down to 5 oC when applied by a two-component airless spray equipment. With a normal airless spray equipment 10 oC is the minimum temperature. By using this type of Polyester the environmental impact is reduced and the smell of Styrene is eliminated.

The Polyester coatings are dry to handle in 2 hours (at 23 oC) and can be applied in a film thickness of 600 - 1500 microns per coat. The resistance to water and moisture is excellent and the use of Polyester coatings for salt and fresh water exposure is widespread. It has exceptionally high abrasion resistance making them ideally suited for application on decks and walkways, hulls of icebreakers, tidal and splash zones of steel structures and concrete. They are used for seawater as well as freshwater services and show very good resistance against cathodic disbonding.

Polyester coatings have good chemical resistance to crude oil, lubricating oils, salt solutions, many acids and solvents. However, the chemical resistance to alkaline environments is limited.

Because of the generally high thickness of these systems, proper surface preparation is essential. Both concrete and steel surfaces should be grit blasted. On steel to min. Sa 2 (ISO 8501-1) and a roughness of 40 - 100 microns. On concrete surfaces a sealer of Vinyl ester clear is normally applied to obtain good adhesion for the Polyester coating.

5.8.3. Chemistry.Polyester is the reaction product of an organic acid and an alcohol. Polymers used in this class of materials are the unsaturated Polyesters formed by the reaction of unsaturated dibasic acids and dihydric alcohols. The polymer is dissolved in Styrene monomer and after adding accelerator and catalyst the Styrene is crosslinked to the resin and the solid film is formed.

Cobolt accelerator is normally added to the Polyester during fabrication. By adding a catalyst as Methyl Ethyl Ketone peroxide (MEK-peroxide) the Polyester start to cure.

It is a possibility of air inhibition, i.e. contact of the curing coating surface with oxygen in the air retards and, in some cases, completely stops the normal curing. To avoid this a small amount of wax is added to the Polyester. The added wax floats to the surface of the film, forming a seal, which effectively prevents contact with the oxygen, and at the same time prevents evaporation of Styrene at the polymerisation reaction.

These coatings are also subject to substantial shrinkage during curing, accompanied by a highly exothermic reaction. For this reason they almost always contain a reinforcement, usually in the form of glass-flakes, to absorb shrinkage. In addition, the glass-flakes are effective at providing a barrier against water permeation of the coating. They act like aluminium flakes and form a barrier so that water molecules must travel a much greater distance through the coating to reach the substrate.

Tinting colours are added to the Polyester during fabrication to get good hiding power and the desired colour.

5.8.4. Examples of Jotuns Polyester coatings.Typical specification for a Polyester glass flake system is:

Pre-treatment:Blast cleaning to Sa 2 Baltoflake:2 X 750 microns DFT

5.9.Vinyl ester coatings.

5.9.1. Area of use.Vinyl ester resin based coatings, (also called linings), are known for their good solvent and chemical resistance. The Vinyl ester is often called a problem solver especially for inside tank protection. The Vinyl ester is effective against a wide range of chemicals (including lead-free petrol), for smoke gas cleaning units, brine, drilling mud and process water. The Vinyl ester coatings have generally better chemical resistance than the Polyester coatings. It has better solvent resistance, much better alkaline resistance and slightly better acid resistance. The temperature resistance is also higher.

Vinyl esters are often referred to as linings. The world lining in the coating industry is commonly defined as a material used to protect the inside surface of a tank, vessel, or similar structures from highly corrosive or potentially highly corrosive environments.

5.9.2. Properties and practical aspects.Vinyl esters are normally 2-component coatings applied at normal temperature. The vinyl ester coating have a rather short pot-life and should therefore be applied by a 2-component airless spray equipment (Regular airless spray is possible). At 23 oC the pot-life is approximately 40-45 minutes. The reason for the short pot-life is due to the addition of the MEK peroxide, which makes the Vinyl ester start curing. This will at the same time create heat in the tin which accelerate the curing. To be able to keep the pot life at 40-45 minutes during application at temperatures from 30 oC up to 40 oC a retarder (inhibitor) has to be added. At temperatures down to 15 oC (which is the lowest temperature for applying Vinylester) the volume of MEK Peroxide has to be increased. As understood, it is very important to follow the manufacturer's recommendations, when adding catalysts and inhibitors at different temperatures.

They offer very good adhesion to both blast cleaned steel and concrete. Both concrete and steel surfaces should be grit blasted. On steel to blast cleaning to a minimum of Sa 2 (ISO 8501-1) and a roughness of 75 - 100 microns should be carried out prior to application. On concrete surfaces a sealer of Vinyl ester Clear is normally applied to obtain good adhesion for the main system.

Vinyl esters must not be applied on old paint or on galvanised steel.5.9.3. Chemistry.Vinylester pre-polymers are formed by reaction of Epoxy resin with Acrylic or Metacrylic acid, which contains the Vinyl group. Usually, Bisphenol A and Novolac Epoxies are generally used. Bisphenol A Ester comprises excellent resistance to most commonly traded chemicals, while Novalac Vinyl ester coatings have excellent resistance also to chlorinated hydrocarbons and solvents. They are in addition resistant to higher temperatures.

The polymer is dissolved in Styrene monomer and after adding accelerator and catalyst the styrene is crosslinked to the resin and the solid film is formed.

It is a possibility of air inhibition, i.e. contact of the curing coating surface with oxygen in the air retards and, in some cases, completely stops the normal curing. To avoid this a small amount of wax is added to the Vinyl ester. The added wax floats to the surface of the film, forming a seal, which effectively prevents contact with the oxygen, and at the same time prevents evaporation of Styrene during the crosslinking (cure).

Vinyl esters are subject to substantial shrinkage (but less than polyester) during curing, accompanied by a highly exothermic reaction. For this reason they almost always contain a reinforcement, usually in the form of glass-flakes, to reduce shrinkage. In addition, the glass-flakes are an effective a barrier against water. They act like aluminium flakes and form a barrier so that water molecules must travel a much greater distance through the coating to reach the substrate.

5.9.4. Examples of Jotuns Vinyl ester coatings.

Always use Chemclear as the first coat on concrete. On steel the choice of product to use will depend on the chemical environment and service temperature. Examples of paint systems are:

On concrete:Chemclear1 x 200 micronsChemflake Classic2 x 750 microns

On steel: Chemflake Classic2 x 750 micronsor Chemflake Special2 x 750 micronsor Chemflake CV2 x 750 microns

Typical system is 2 x 750 microns (recoating interval min. 2 hours at 23 oC and max. 12 hours).

Chemflake products are delivered in two colours, white and red.