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Frosio 08 Paints and coatings slide # 1

Paint technology

Paint consists of:

• Liquid: Vehicle / Varnish

– Binders– Thinners (solvents)

• Dry: Powders / Pigments

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Anti-skinner Drier

Solvents

Ketones

Water Alcohols

Esters Ethers

Colouring

Extenders Pigments

Inhibitive pigm.

Cathodically protective Biocides

Fillers

Stress reducing

Binders

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The properties of a paint will be

decided by the binder

• Describes the type of

paint/coating

• Bind pigments and

extenders to a solid film

• Provides the adhesion to the substrate

and cohesion, flexibility in the film

• Provides the water, chemical, solvent

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Modified binders

• A modified paint may

contain more than one

binder, e.g.:

– Coal Tar Epoxy– Vinyl Tar– Epoxy Mastic

• A binder may be modified

chemically by attaching

new groups to their

molecules, e.g.:

– Styrenated Alkyd– Polyurethane-oil Alkyd– Epoxy Ester

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 Physically Drying (solvent

evaporation)

2 Oxidatively Curing (reaction with

oxygen in the air)

3 Chemically Curing (chemical reaction

between base and hardener)

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Paint technology: Physical_drying1

Physical drying Waterborne paints

= Dispersed droplets

Water evaporating

Droplets are packing

Droplets melt together, co-solvents evaporate

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Curing (drying) by oxidation

• The solvents

evaporate

• Oxygen enter the

paint and the

network is formed which

give the solid paint film Paint technology: Curing_good1

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Insufficient mixing of

two-pack paint

• Proper mixing is a

pre-requisite to obtain proper

curing

• Insufficient mixing makes

it impossible for the

molecules to come in

contact with each other

• A three dimensional

network will not be

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Mixing of two-pack paints

Visual mixing control

• It is difficult to verify

proper mixing when

the base is clear

• A dark base makes it

easier to see when the

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Large molecules gives:

a) Good mechanical strength b) Good chemical resistance

Physically drying binders:

Molecules are large before drying starts

Chemically curing binders:

Large molecules are formed during curing

The dry binder consists of large

molecules

Vinyl Chlorinated rubber Epoxy

Polyurethane

Urethane alkyd Alkyd

The surface tolerance depends on the

penetrating properties of the binder

Surface tolerant paint:

Epoxy Mastic

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recommended for uneven substrates

• Most paints can be applied

to steel blast cleaned to Sa

2½

• Not all paints possess the

required wetting property

for successful application on

uneven substrates

• Surface tolerant paints give

a longer life time on such

substrates Paint technology / Surface tolerant2

Steel

Epoxy Mastics are

“Surface Tolerant” and “High build”

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Solvent Test

• Can be used to identify drying

mechanism of unknown old coating

• Expose the old coating to MEK solvent

for 10 – 15 minutes

• Place paper towel / cloth / rags

soaked in the thinner on the coating

to be tested

• Observe how the coating react

Solvent test: Three samples

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Use paper towel to keep the solvent in contact with the sample

Paper-towels wetted by MEK

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Solvent Test: Acrylic

( physically drying )

Paint sample is dissolved

Solvent Test: Alkyd

( oxydatively curing )

Alkyd film “lifting”

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Lifting and loss of adhesion, solvent act as paint remover

Disregard blue smear from paper towel

Solvent Test: Epoxy

( chemically curing ) No change in paint sample

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Solvents &

Diluents

• Dissolve the binder

• Give lower viscosity

• Give application properties for brush, roller, spray

• Once the paint has been applied, there is no more need for the solvent

Solvents / diluents

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Solvents / diluents , examples

Solvent / Diluent / Thinner

• Single or blended

• Disolves the binder

completely (Forms a solution)

• Used to lower the viscosity

• Usually a mixture of solvents and diluents

Thinner

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The paint is supplied

with the correct viscosity

Evaporation rate and solubility

of a thinner will influence a paint’s:

• Drying time

• Film-forming properties

• Quality of the film

Most paints are ready to be applied as

supplied by the manufacturer.

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Addition of wrong type of thinner

• A clear binder is poured

into the beaker

• Wrong type of thinner is

added

• This will change the

properties of the paint

film

• The binder separates

• The binder will no longer

be clear: Difficult to see

through

• The same experiment is

carried out with correct

thinner: Good result Paint technology: Thinner_wrong1

Thinning the paint

Thinning is primarily only

recommended in three

situations:

• Very cold paint (becomes

thick)

• Very warm conditions /

substrate (keep the film open

longer)

• Painting very porous

substrates (tie coat or mist

coat technique)

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Excessive thinning may lead

to entrapped solvents

• One thinned and one

unthinned sample of paint is

applied to a structure

• To achieve the specified DFT

the thinned paint must be

applied to a higher WFT

• After a certain period of time

the unthinned is fully cured

• The solvents has not

evaporated from the thinned

paint

• If put into service the paint

will develop blistering Paint technology/ Thinning entrapped1

Thinning of the paint may

result in lower DFT

• Two samples of the same

paint are applied to a steel

structure.

• The WFT is the same for both

samples

• One of the samples is thinned

• During drying / curing of the

paint the thinners will

evaporate from the wet paint

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Thinning the paint may result in

the requirement of a longer

drying time

• One thinned and one

unthinned sample of paint is

applied to a structure

• To achieve the specified DFT

the thinned paint must be

applied to a higher WFT

• After a certain period of time

the unthinned is fully cured

• The solvents has not

evaporated from the thinned

paint

Paint technology/ Thinning drying1

Volatile / Non-volatile

• A paint’s “ Solid Content ” means the

part which does not evaporate,

commonly quoted as %volume.

• A paint’s “ VOC ” (Volatile Organic

Compound) tells us how many grams

of solvents there are in one litre of

paint.

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100 microns wet film 50 microns dry film 100 microns wet film 80 microns dry film

When applied in the same WFT, the paint with the higher solid

content will result in a higher DFT (and thus need fewer coats

or gives better protection)

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Pigments &

Powders

Colour Pigments

• Natural or synthetic pigments

• Organic or inorganic pigments

• 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

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Active / Reactive Pigments

Takes an active role in ensuring that

the paint perform as expected:

» Talc (Talcum powder)

» Chalk (Calcium Carbonate)

» Clay (China Clay)

• Reinforce and give body to the film

• Varying hardness

• White / grey in colour

• Very little influence on colour of

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The Gloss of a Paint Depends on the PVC

(Pigment - Volume - Concentration)

Flat PVC 35 - 50

Glossy PVC 15 -25

Barrier pigments

• Flake-shaped pigments

• Tend to align themselves parallel to the substrate

• Reinforce the film

• Increase the barrier effect of the film

• Often made from aluminium, glass, micaceous iron oxide (MIO or mica)

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Why are some paints pigmented with aluminium or glass flakes ?

Water

Paint with glass or

aluminium flakes

Steel

Flake-shaped pigments make it more difficult for moisture

to reach the steel as the distance becomes longer.

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Corrosion protection by paints

• Barrier effect

• Inhibitor effect

• Galvanic effect

For corrosion prevention with paints, three main

principles are employed:

Corrosion protection by paints.

The barrier effect

• When paint is applied to

a structure a barrier is

created between the

substrate material and

the surrounding

environment

• A thick paint film will give

a better barrier than a

thin film

• The barrier effect can be

further improved by

adding flake formed

pigments to the paint.

Paint technology/ Paint barrier effect1

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The inhibition effect

• The inhibition type of paints is

not an inert paint film as the

barrier coatings

• The paints contain chemicals or

inhibitors

• The inhibitors react with moisture

and the steel and forms a passive

layer close to the steel substrate.

• The layer passivates the steel

and thereby reduce the corrosion

rate.

• Examples:

– Red Lead Primer

– Zinc Chromate Primer

– Zinc Phosphate Primer

Paint technology/ Paint inhibition effect1

The cathodic protection effect

• Some paints offer the same

cathodic protection effect as

sacrificial anodes

• 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

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Epoxy Polyamide 125 µm 1.71

Amine Catalysed Epoxy 125 µm 3.10

Vinyl Chloride-Acetate 125 µm 11.94

Vinyl Acrylic 125 µm 12.87

Alkyd (Short Oil) 125 µm 57.36

Different types of paint

This is why alkyd paints are not suitable for submerged service

(they adsorb too much in water, leading to swelling of the film)

What is a shopprimer?

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Shopprimers

Definition:

A quick drying material applied as a thin film to a

metal surface after cleaning, e.g by a blast

cleaning process, to give protection during the

period before and during fabrication.

Requirement:

Must not interfere with the speed or quality of

cutting and welding of the steel during fabrication,

so DFT must be limited to:

Iron oxide: 15 – 20 micr.

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Shop primers - history

• Iron oxide PVB

• Iron oxide two pack epoxy

• Zinc epoxy

• 1st generation Zinc silicate

• 2nd generation Zinc silicate

• 3rd generation Zinc silicate

• High temperature Zinc silicate

• Water borne shopprimer

• Water borne Zinc silicate

Shopprimer history

Initially:

• Only temporary protection

• Removed by blast cleaning before painting

Later:

• Improved quality

• Blast cleaning only of welds and damages

Today’s technology

• UHPWJ before painting

Shopprimer may now be a part of

the long term protection paint system

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Antifoulings

What is fouling ? (1 of 2)

Fouling is the settlement and growth of marine plants and animals on surfaces (including man-made structures) in the sea

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What is fouling ? (2 of 2)

There are an estimated 4 - 5000

fouling species and these can be

classified into:

Î

Î Microfouling

– generally referred to as slime, a complex viscous

mixture of bacteria and microscopic organisms

Î

Î Macrofouling

– which includes animals and plants

How does fouling happen?

• Free floating or free swimming spores

and larvaes follow the currents, tides

and waves.

• They have the opportunity to contact

suitable surface when the time comes.

• Fouling happens when these larvaes or

spores settle and develop into an adult,

small at first but steadily growing.

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Macro-fouling

Barnacles Hydroids

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The Purpose of Antifoulings

9 To prevent or reduce growth

9 To provide better fuel economy over the

sailing period

9 To avoid growth penetrating the coating and

thereby extend corrosion protection

The consequences of fouling

On a ship’s hull

Increased fuel consumption

On a marine structure

Increased drag Î Heavier

load on the structure Î

Structural failures

Seawater pipe systems

– Increased corrosion

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Why do ships need

anti-fouling systems?

Fouling leads to an increase in fuel consumption

of up to 40%, due to the increase in drag resistance

A clean ship sails faster and with less energy

Fouling will eventually damage the primer system

The composition of Antifoulings

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Conventional Antifoulings

• Soluble matrix paints

• Rosin as a binder

• Approximately 12 months protection

• Binders dissolves in water and biocide is

released

• Examples: A/F Tropic, A/F Super Tropic etc.

NOTE:

Danger of cracking and flaking

Needs to be quickly immersed in water

Long-life Antifouling

• Insoluble matrix paints

• Only biocides are released

• Effective protection is up to 24

months

• Leaves weak substrate for

subsequent coat (leach layer)

• Sealer coat normally required

• Binder: CR, Vinyl (possible to add

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Long-life Antifouling

Binder:

CR, Vinyl (Possible to add small amount colophonium)

• Extended dry docking period

• Control of roughness and

• Lifetime directly proportioned

with dry film thickness

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Cross section of hydrating

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Cross section of hydrolysing

• No porous leach-layer means good

adhesion after over-coating

• Continuous smoothing of the surface

ensures good fuel efficiency

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Cross section of hybride antifouling

Comparison of release rate of biocide for different A/F-types

Release rate for Antifoulings

Minimum release level for fouling protection

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Anti-fouling for Aluminium hulls

Special requirements:

• Must be free from Copper

• Metallic Copper in contact with aluminium will cause bi-metallic corrosion, perforating the hull plates

in very short time

• Must perform at speeds up to 50 knots (e.g for catamarans)

• Preferably self-polishing type (best performance)

A paint system may be

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Primers

Primers are universal for most anticorrosive coating

systems and are considered the most important

component of the system The most important

properties of primers are listed as follows:

1 Adhesion (strong bonding to substrate).

2 Cohesion (high internal strength in the film).

3 Inertness (strong resistance to corrosion and chemicals).

4 Intercoat bond (high bonding to intermediate coat).

5 Appropriate flexibility.

Intermediate

or Body coats

1 Thickness for total coating.

2 Strong chemical resistance.

3 Resistance to moisture vapour transfer.

4 Increase electrical resistance for the coating

system.

5 Strong cohesion.

6 Strong bonding to primer and topcoat.

The principal purposes of an intermediate coat is to provide:

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