3 Paint Technology

8/13/2019 3 Paint Technology

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Paint technology




Paint consist of:

• Binder

• Colour pigment

• Extenders

• Solvents

• Additives




Hydro carbons

Composition of paints

Paints

Binder Pigments Solvents Additives

Natural Resin

•Drying oil•Coal Tar

• Nitrocellulose

Synthetic Resin

•Alkyd

•CR

•Epoxy

•Polyester

•Polyurethane

•Silicate

•Vinyl

Colouring

Extender Anti-settling

Wetting agent

Inhibitive pigm.

Plasticiser

Anti-skinner

Drier

Cathodicallyprotective

Biocides

Ketones

Water

Alcohols

Esters

Ethers




What Is A Binder ?

A binder is a fluid or a solution that forms a film

during drying or curing (is responsible of cohesion

& adhesion).

Drying/curing takes place by:A. Solvent/water evaporate

(physically drying).

B. Solvent evaporation and a chemical

reaction takes place during the drying

process. (chemically drying/curing).




The Properties of a Paint Will Be

Decided By The Binder

• Describes what type of

paint/coating we have

• Bind pigments and

extenders to a solid film

• Provides the adhesion to

the substrate

• Provides the water, chemical,

solvent and UV resistance




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




The binders are grouped according to:

• Drying process

• Curing mechanism

Main Groups Of Binders




• Oxidatively drying

• Physically drying

• Chemically curing

• IR/UV - cured

Different Drying Processes




Oxygen enter.

Reaction starts:

Polymer molecules

linked together through

chemical bonds

DRYING THROUGH OXIDATION

Solvents evaporating





Polymer molecules stick together (no chemical bonds):

PHYSICAL DRYING.

Solvent Born Paints

Polymer molecules are packing:




= Polymer = Curing agent (hardener)


Curing Mechanism of

Two -Pack Paints

Polymer & hardener molecules reacted

to form a new chemical substance:




Vinyl

Chlorinated rubber

Epoxy

Polyurethane

Urethane alkyd

Alkyd

Boiled linseed oil

Raw linseed oil

The Surface Tolerance Depends on the

Penetrating Properties of the Binder

Surface tolerant paint:

Epoxy Mastic




Steel

Epoxy Mastics are

“Surface Tolerant” and “High build”

Steel

Traditional paints

• Low coverage

• Poor flow

Epoxy Mastic

• Good penetration• High Build




Rust preventing pigments:

• Red Lead

• Zinc

• Zinc Chromate

• Zinc phosphate

Extender pigments

(non/limited hiding/opacity properties): • Talcum

• Barium sulphate

• Microdol (dolomite)

Pigments, Examples

Coloured pigments

(hiding / opaque):

• Inorganic; red, yellow,, brown, black

• Organic, all colours

• Titan dioxide (white)




PVC: Pigment - Volume - Concentration

Definition

Ratio of the volume of pigment to the

volume of total non-volatile material in a coating

Non-volatile matter: E.g. pigment and binder

The figure is usually expressed as a percentage.




The Gloss of a Paint Depends on the PVC

(Pigment - Volume - Concentration)

Colour

pigments

Binder

Extenders

Semigloss

PVC 30 - 40

FlatPVC 35 - 50

Glossy

PVC 15 -25




• Dissolve the binder

• Give lower viscosity

• Give application properties for brush,

roller, spray

Solvents / Diluents




• Water

• White Spirit

• Xylen

• Toluen

• Ketones

• Glycoles

• Alcohols

• Reactive solvents

Solvents / Diluents , Examples




Addition of Thinner

Evaporation rate and solubility of a thinner willinfluence a paint’s:

• Drying time

• Film-forming properties• Quality of the film

Most paints are ready to be applied as

supplied by the manufacturer. Never add an unspecified thinner to a paint,

it may lead to disastrous results




Protection

• Barrier effect

• Inhibitor effect

• Galvanic effect

For corrosion prevention with paints, three main

principles are employed:




Primer

Steel

1st coat

2nd coat

Impervious to ions,

oxygen, carbon dioxide

Low moisture transmission

Strong adhering

coating thoroughly

wets steel surface Physical as well as

chemical adhesion

No voids at interfaceto accumulate water

Clean surface - no salts

to create osmotic blistering

An Impervious Coating Serves as an

Inert Barrier to Protect the Surface




Why are some paints pigmented withaluminium, MIO or glass flakes ?

Water

Paint with glass or

aluminium flakes

Steel

Flake-formed pigments make it more difficult for moisture

to reach the steel as the distance becomes longer than the D.F.T.

Barrier effect




In inhibitive coatings, moisture may penetrate to reach the inhibitive

primer where the reactive pigments are activated, which in turn

passivate the metal substrate at the coating/metal interface.

Inhibition

Inhibitive Primer

1st Coat2nd Coat

Steel

Moisture Absorption

Ionisation of Inhibitor

Reaction with Steel Surface

Passive layer forms




Inorganic Zinc Primer

2nd Organic Topcoat

Superior adhesion prevents coating undercut

Moisture allows Zinc to

ionize, cathodically protecting the steel.

Damage in coating to steel surface

An inorganic Zinc primer reacts to protect the

steel substrate when the topcoat is damaged.

Cathodically Protective Pigments

Steel

Zn2+




Primers

Primers are universal for all 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.




Topcoats

Topcoats also perform several important

functions as they:

1. Provide a resistant seal for the coating system.

2. Form the initial barrier towards the environment.

3. Provide resistance towards chemicals, water, and

weather.

4. Provide a tough and wear-resistant surface.

5. Provide a pleasing appearance.




What film-thickness should corrosion

protecting paint systems have ?

• Deciding factor is the environment:

In a dry inland atmosphere and indoor 120 microns

will be sufficient. In an aggressive industrial

environment and along the coast and at sea, 250 - 300microns will be necessary.

Number of coats is also of importance and not only

the film thickness

100 microns in 2 coats (50 + 50 microns) are givingbetter protection than 100 microns in 1 coat. Special

coatings may be applied in thick coats.




Steel

Moisture vapour penetrating

Moisture vapourevaporating

3 Coat systemStrong adhesion

Moisture transfer through a coating with excellent adhesion

Penetration of moisture




Penetration of Moisture in Areas

with Poor Adhesion.

A three coat system

3. Vapour pressure

lifts coats in areas

with poor adhesion1. Moisture vapour

2. Moisture

penetrating into void

(Poor adhesion)

Steel

W t b ti




Coating type Test Grams/m²/24 hours

thickness

Epoxy Polyamide 125 µm 1.71

Amine Catalysed Epoxy 125 µm 3.10

Vinyl Chloride-Acetate 125 µm 11.94

Vinyl Acrylic 125 µm 12.87Alkyd (Short Oil) 125 µm 57.36

Water absorption.

Different types of paint




What influence the drying process ?

• Relative humidity, % R.H.

• Ventilation

• Temperature• Film thickness

• Number of coats

• Evaporation rate of the solvents

At h i C diti




Surface temperature of the

structure must be minimum 3 °C above the dew point

of the surrounding air

Atmospheric Conditions.

Requirement During Blasting and Painting




0 100 200 300 400

100

80

60

40

20

0

50 micr

100 micr.

250 micr.

500 micr.

Time in days

Solvent Retention in % By Weight

for Various Dry Film Thicknesses

Solvent retentionin % by weight




Water uptake

0

5

10

15

20

0 100 200 300 400 500 600 700 800 900 1000

Cured under very poor ventilation conditions

Cured under poor ventilation conditions

Cured under good ventilation conditions

Water uptake of a coal tar epoxy paint

(dry film thickness approx. 250 mm.)

Uptake in % weight

Time in hours




Oxidative Drying Binder

The binder absorbs oxygen from the air, causingthe binder molecules to link together to form larger macro

molecules.

The original binder molecules are “free to move” while the macro molecules in the dry film are fixed.

Air drying alkyds and boiled linseed oil dries in this way.

Alkyds, however, have comparatively larger molecules

from the beginning and therefore dry faster than linseed-oil.




Wet film

Substrate

Dry film

Substrate

Oxygen O2 Solvent

Alkyd Drying Process




• Vinyl

• Vinyl tar

• Epoxy• Epoxy tar

• Epoxy mastic

• Acrylic

• Zinc Ethyl Silicate

• Polyurethane• Polyester

Paints with large binder molecules generally require a

good quality surface preparation.

Sophisticated Paints




Part A:

Epoxy resin

Solvents

Pigments

Extenders

Additives+

Part B:Curing agent

Solvent

Chemical reaction

Evaporation of solvent

ResultInsoluble

3-dimensional

network

Epoxy paints




Polyamides:Standard epoxy paints

Amine and amine adduct:

Solvent free coatingsCoatings with increased chemical resistance

Isocyanates:

Low temperature curing

Reaction with -OH

Curing agents

What is the Difference Between




What is the Difference Between

a Paint, a Varnish and a Stain ?

Binder

Additives

Stain

Varnish

Paint

Solvents

Extenders

Pigments

Vehicle: Binder + solvents

Only matt or

satin finish




What is Chemical Resistance ?

“A coatings ability to remain

unaffected, physically and chemically,

when exposed to a chemical environment”

Why are Chemicals




Why are Chemicals

Aggressive to Coatings ?

The most important factors are:

• Molecular size: Penetration

(Methanol, water)

• Solvents for organic binders

(epoxy, vinylester, polyester)

• Take pleasure in decomposing the binder

molecule (NaOH, Sodium hypochlorite)



A bi t T t d




• Ambient temperature will influence:

– shelf life

– viscosity/sprayability

– steel temperature

• Steel temperature will affect:

– speed of cure

– degree of cure – recoating interval

– service life of the coating

Ambient Temperature and

Steel Temperature

Is the temperatures important ? YES !

The Characteristics of an




The Characteristics of an

Aggressive Chemical

• Corrosive

• Cause swelling

• Have high temperature

• Chemical attack (acids, alkaline)

• Etching

• Erosion in combination with

effects above

An aggressive chemical can be:




Chemical Family and

Resistance

• Acids Chemflake Classic/Special/CV• Alcohols Tankguard S, Chemflake C/S/CV, Resist GTI,

Jotacote 5

• Alkalies Tankguard HB, Tankguard Special,

• Crude oil Chemflake C/S/CV• Fatty acids Chemflake C/S/CV

• Gasolines Tankguard HB, Tankguard Special,

Chemflake C/S/CV, Resist GTI, Jotacote 5

• Solvents Tankguard Special, Resist GTI, Jotacote 5,

Chemflake C/S/CV

• Methanol Resist GTI, Jotacote 5



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