This document discusses coating chemistry and properties. It describes desirable coating properties, how coatings are classified as organic or inorganic, coating components like pigments, binders, solvents and additives. It explains different curing mechanisms for coatings like evaporation, coalescence, oxidation and co-reaction. Common coating types are described like epoxy, polyurethane, zinc and their characteristics. Factors for selecting coatings and how they provide corrosion protection as barrier, inhibitive or sacrificial coatings is also summarized.

1. Coating Chemistry

2. Properties of a Coating
Desirable coating properties
include:
 Chemical Resistance
 Water Resistance
 Ease of Application
 Adhesion to Substrate
 Cohesive Strength
 Flexibility and Elongation
 Impact Resistance
 Abrasion Resistance
 Temperature Resistance
 Dielectric Strength

3. Classification of Coatings
Coatings are broadly classified as organic or inorganic.
Organic coatings are those whose binders have been made from living
or once- living things. All organic coatings contain carbon bond.
 Inorganic coatings use inorganic binder materials, most commonly
based on
either silicone or silicates.
The major difference between organic and inorganic coatings is heat
resistance.

4. Composition
Liquid-applied coating components
are
characterized by the following terms:
 Pigmen
t
 Vehicle
o –
Binder/Resin
o – Solvent
 Additive
s
Resin
Solvent
Vehicle
Pigment /
Additives
Coating Components

5. Pigment
Pigments may be used to:
 Impart color
 Provide inhibitor protection
 Provide a form of cathodic protection
 Modify mechanical or electrical
properties

6. Additives
Additives are most commonly liquid components of a coating typically added
in small
amounts to perform a specific function.
 Improve stability
 Minimize settling
 Reduce foaming
 Improving the flow out and wetting
 Increase pot life
 Increase UV resistance
 Increase or decrease gloss

7. Solvents
 Solvents are added to liquefy the binder.
 Once the coating is applied and cured, solvents serve no
purpose.
 Solvency Power: The ability to dissolve the resin.
 Volatility: Governs the evaporation rate (the speed at which
the
solvent will leave the coating film during and after
application).

8. Binder
A coating typically gets its name from the binder used, such as:
epoxy, polyurethane, alkyd, acrylic, etc.
 Good wetting and adhesion
 Resist transmission of water, oxygen, and other chemical
species
 Resist chemical and physical change in the service
environment
 Dry within an acceptable period
Form a stable film that maintains its characteristic
properties (strength, hardness, flexibility)
Alkyd Resin

9. Modes of Protection
Corrosion control by coatings can occur by one of only three
processes:
 Barrier coatings
 Inhibitive coatings
 Sacrificial (cathodic protection)

10. Barrier Coatings
The barrier coating
obstructs the ingress of
oxygen, water and
soluble salts.
Structur
e
NaCl
and
other
ions
Oxyge
n
Water
Structure Surface (Steel)
Protective
Coating

11. Inhibitive Coatings
Inhibitive coatings actively slow down
the reaction occurring at the anode,
cathode, or both:
 Must be in contact with the
substrate.
 Actually passivate the metal
surface.
Structur
NaCl
and
other
ions
Oxyge
n
Water
Structure Surface
Protective Coating
Inhibitive
Primer
Anodic and Cathodic
reaction Inhibited

12. Sacrificial Coatings
Sacrificial coatings use a metal that
is anodic to steel that corrodes
preferentially.
Sacrificial coatings:
Usually contain
zinc predominant
pigment.
dust as the
Must have a minimum loading of zinc
dust to be effective.
Holida
y
Local Cathode
protection at
holiday
Structure Surface
(Steel)

13. Adhesion
Strong adhesion is the key to coating performance and long life.
Adhesion can be:
 Chemical – Formed by a reaction between the coating and the
substrate.
 Mechanical – Associated with surface roughness or anchor pattern.
Polar – Most common for organic coatings. The resin acts as a weak
magnet on the substrate.
 Combination of all three

14. Coating Types and Curing
Mechanism

15. Curing Mechanism
Curing is used to describe the way a coating transforms from a liquid to a
solid state
There are two broad classifications for curing mechanisms:
o Nonconvertible – Cure by evaporation of the solvent with no chemical
change
to the resin.
o Convertible – Undergo a chemical change during cure and cannot be
returned to their original state.

16. Evaporation Cure
 Cure solely by solvent evaporation
Can be re-dissolved in the solvent
 Examples include vinyl and chlorinated
rubber

17. Coalescence
 Resin are dispersed in water.
 The water evaporates, the resin particles fuse
(coalesce).
Typically known as latexes or acrylic latexes.

18. Convertible Coatings
 Cure by one of several polymerization
mechanisms
 Resins undergo a chemical change
 Not readily re-dissolved in the solvent
 Known as thermosetting materials
 Some examples of curing types are:
o Oxidation
o Co-reaction
o Hydrolysis
o Fusion

19. Oxidation
Cure by reaction with atmospheric oxygen
 Unsuitable for immersion service
 Cannot withstand an alkaline environment, due to “saponification”
 Excessive film build may stop curing of the lower portion of the
coating film
 Example: Alkyd

20. Co-Reaction
Cure by polymerization reactions (cross-linking) between at least two chemical
entities.
Examples include:
– Epoxies, Polyurethanes, Polyureas, Polyaspartics, Polysiloxanes and several
others

21. Co-Reaction
 For solvent bone coatings, first step is solvent evaporation and second
step is polymerization.
 Once mixed together, applicator has a short time to apply before it gels.
The
time period when the mixed material is usable is called pot life.
 Some co-reaction cured coatings also require a period of time after
mixing but before application for the chemical reaction to start; this is
referred to as the induction time.

22. Hydration
Coatings require some amount of water to complete the
cure. Examples include:
o Moisture cured polyurethane
o Solvent based inorganic zinc coating based on an ethyl
silicate

23. Fusion
 Forced heat curing
 May be single or two component
materials
 Example is fusion-bonded epoxy (FBE)

24. Curing Mechanisms

25. Selection of Coating
The selection of a coating is based on many factors that include:
 Service environment of the coating:
 Interior or exterior
 Immersion or atmospheric
 Chemical
 In-service temperature (plus typical range and upset
conditions)
 Substrate being coated
 Size and configuration of item to be coated
 Surface preparation available and possible at job site

26. Selection of Coating
 Application temperature and humidity
 Life expectancy of both item being coated, and coating
 Ability of applicators
 Availability of application equipment
 Critical safety requirements, e.g., a nuclear power plant, buried
pipeline, or
commercial ship
 Budget

27. Generic Coating Types
o Acrylic
o Alkyds
o Chlorinated Rubber
o Epoxy
o Latex (Emulsions)
o Phenolic
o Polyaspartic
o Polyesters
o Polysiloxane
o Polyurethane
o Polyureas
o Silicones
o Vinyl Esters
o Vinyl
o Zinc
(Inorganic)
o Zinc
(Organic)

28. Acrylic
 Excellent UV and weathering resistance
 Can be applied as coalescence curing emulsions/ water dispersions
 Historically applied as decorative coatings rather than for corrosion
resistance

29. Alkyds
Oxidative curing, referred to as“oil basedpaints”
 Single package material and broad range of colors
 Can be very slow curing products, limited thickness
per coat
Can be blended with other resins to improve properties
e.g.
 With epoxies to make Epoxy Ester
 With silicones to make Silicon Alkyds

30. Chlorinated Rubber
 Evaporation curing
 Contains a large amount of VOC
 Eliminated in most parts of the world
 Excellent resistance to water, sunlight, and many
chemicals
 Should not be over coated with two component
coatings

31. Epoxy
 Two components consist of an epoxy resin (base) and a curing agent
(converter)
 Can be solvent-based, water-based, or solvent-free
 Excellent adhesion, chemical resistance, water resistance, and wet
adhesion
 Amine cured epoxies are especially sensitive to amine blush
 Exhibit chalking with atmospheric (UV) exposure

32. Latex (Emulsions)
 Resins normally thermoplastic resin
types
 Coalescence curing

33. Phenolic
Typically used where low pH environments and higher temperatures are
factors
 Excellent resistance to acids
Usually use for internal tank lining of corrosive material storage tanks
Can be blended with epoxies to make Epoxy Phenolic

34. Polyaspartic
 Use to achieve low- or near-zero-VOC systems
 Pot lives from five minutes to several hours
 Film builds up to 380 μm (15 mils) DFT in a
single pass
Are aliphatic Polyureas

35. Polyesters
 Have a short pot life
 Glass flake reinforced, high build
coatings
 Excellent moisture resistance
 Exceptionally high abrasion
resistance

36. Polysiloxane
 Used in services with abrasion, chemicals, extreme UV, and high
temperature
Three major categories :
o Inorganic Polysiloxane
o Epoxy-Polysiloxane Hybrids
o Acrylic-Polysiloxane Hybrids

37. Polyurethane
Two major types
 Aliphatic
o More resistant to UV exposure, excellent gloss and color
retention
 Aromatic
o Better chemical resistance in immersion but not UV resistant
 Main hazard is the isocyanate component
 Available with a variety of curing times

38. Polyureas
 Very flexible materials
 Very short cure times
 Many require the use of an epoxy primer on
steel

39. Silicones
 Formed by chemical modification of quartz, sand, or silicon
 Excellent high temperature and UV resistance
 Most require heat to cure but some cure at ambient
temperatures
 Also used as foul-release coatings in the marine industry

40. Vinyl Esters
 Often referred to as linings
 Normally two-component coatings
Excellent resistance to most of the corrosive chemicals even at higher
temperatures
 Have rather short pot life
 Excellent abrasion resistance with glassflake added

41. Vinyl
One of the earliest industrial coatings
 Were used on highway bridges and extensively in the marine
industry
 Banned from use in most countries due to high VOC

42. Zinc (Inorganic)
 Widely used primer for steel structures
 Provides cathodic protection
 Very resistant to different chemicals and especially
solvents
 Very high heat resistance with a max of 400°C (750°F)
 Disadvantages
o Can be difficult to apply
o Not for acidic environments

43. Zinc (Organic)
 Very different from inorganic
zinc
 Organic resin with zinc filler
 Examples epoxy, polyurethane,
etc.
 Limited cathodic protection
factor

44. Environmental Testing

45. Environmental
Effects
Environmental, or ambient, conditions can greatly affect all phases of a
coating operation.

46. Surface Temperatures
 Surface temperature is often different from air temperature.
Application at incorrect temperatures can cause defects.
 Minimum and maximum application temperatures should be
recognized.
 Substrate should be at least 3°C (5°F) above the determined dew
point.
Minimum Maximum

47. Relative Humidity
 Measure of the amount of moisture in the air compared to saturation
level.
 May affect the coating if too high or too low.
 Too high may cause solvent entrapment.

48. Wind Speed
Wind speed can affect the coating job by:
Blowing abrasives
Causing excessive overspray
Accelerating solvent evaporation
Contributing to the formation of dry
spray.
Dew
PointThe temperature at which moisture will begin to form on a steel
surface.

49. Surface Temperature Instruments
Typical instruments you may encounter
include:
o Digital Infrared Thermometers
o Mechanical Surface Contact
Thermometer
o Electronic Surface Contact
Thermometer

50. Digital Infrared Thermometer
Positives
 Are very simple: point, shoot, and read
 Deliver quick reading
Negatives
 Steam, dust, smoke, and/or vapors can prevent accurate
readings
 Cannot measure reflective surfaces accurately

51. Mechanical Surface Contact Thermometer
Magnetic surface contact thermometers are one of the most common
instruments
 Positives
o Simple and inexpensive
 Negatives
o Stabilization time can be minutes
o Easily lose their accuracy Heated Surface

52. Electronic Surface Contact
Thermometer
Magnetic surface contact thermometers are one of the most common
instruments
 Positives
o Quick and accurate
 Negatives
o More expensive than other surface

53. Relative Humidity
Instruments
 Electronic Hygrometers
 Sling Psychrometer
 Powered Air Flow
Psychrometer

54. Electronic Hygrometer
 Read and calculate
the:
o Temperature
o Relative humidity
o Dew point

55. Sling Psychrometer
 Sometimes called a whirling hygrometer
 Used to measure the ambient air temperature
 Dry-bulb temperature and wet-bulb temperature
used to calculate the dew point and relative
humidity

56. Powered Airflow Psychrometer
Operates in a similar way to the sling psychrometer, but air is moved
using a fan, rather than slinging the instrument.

57. Chart Recording Ambient
Conditions
Time
RH%
Dew Point
Ambient Temperature
Substrate Temperature
Ok to work Yes/No

58. Wind Speed
 Wind speed can be a safety issue when work is being performed at
heights.
 Monitoring wind direction can prevent damage to property from
overspray.

59. Product Technical Data
Sheet And
Material Safety Data Sheet

60. Product Technical Data Sheet
 Coatings Product Data Sheets (Paint Specs) provide users with valuable
information on the application aspect of a particular product.
 Communicate technical facts related to the specific material and its
application
properties.
 Common to find a small section related to safety.

61. Product Technical Data Sheet
 Information of critical importance to the project success:
o Surface preparation
o Storage
o Mixing and thinning
o Application procedure
o DFT requirements
 One should always consult Product Technical Data Sheets.
 It may come across discrepancies between the project specification and the
product data sheet. The holder of the specification (owner) must be contacted
for clarification

62. Product Technical Data
Sheet
A thorough understanding of the
Product Technical Data Sheet
cannot be over emphasized!

63. Material Safety Data Sheet
 Contains data regarding the properties of a particular substance.
 Provides workers and emergency personnel with critical information on
composition, handling, or working with that substance in a safe manner.
 Includes information such as melting point, boiling point, flash point, toxicity,
health effects, first aid, reactivity, storage, disposal, protective equipment, and
spill handling procedures.
 Provides information regarding the safety issues associated with any hazardous
(or potentially hazardous) material.
 Provides instructions for the correct action to take in the event of a spill,
explosion, fire, or hazardous exposure.

64. Material Safety Data Sheet
 When coating materials are being transported, there is a constant risk of
spillage or
exposure of others to potentially toxic chemicals.
 In some countries the law requires that MSDS be carried by transporters
whenever industrial quantities of coatings are moved by road, rail, or air.
 Inform emergency services of potential hazards in the event of a spill, fire, or
other hazard.
 Chemicals commonly used and judged to be hazardous are listed by various