Corrosion Inhibitors for Waterborne Alkyd Technology

1
Corrosion Inhibitors for Waterborne Alkyd
Technology

28th Biennial Western Coatings Societies
Symposium Show Las Vegas, Nevada October 2007
2
Outline

• Corrosion Inhibitors
• Background Mechanisms
• Applications Formulating Strategies
• Background Mechanisms

3
Corrosion Inhibitors
4
What is Corrosion

• The electrochemical deterioration of a metal due
  to the reaction with its environment involving
  the oxidation of a metal and the reduction of
  another material.

5
Corrosion Simplified
ELECTRON CONDUCTOR
ELECTRON ACCEPTOR
IONIC CONDUCTOR
-
-
-
-
-
-
-
-
-
-
-
Ionic Conductance
Electron Conductance
6
The Result
A Breakdown in the Metal (Corrosion)
FACTORS INFLUENCING Presence of Water Presence
of Oxygen Presence of Ions Temperature pH Grain
Structure of Metal Stresses from Fabrication
7

Corrosion Cell Diagram
Electron Conductor Metal Ionic Conductor
Water Electron Acceptor Oxygen
3/2 O2 n H20 2 Fe2

2 H2O
Fe2O3 H20
4 H
O2
X
4 e?
RUST
2 Fe
X
Anodic Site
Cathodic Site
8
How Can We Use Coatings to Protect Metal from
Corrosion ?
9

Protect through the barrier properties of resin
or pigment having low H2O transmission. (i.e.
epoxies, chlorinated rubbers)
PASSIVE
Inorganic Inhibitive Pigments Organic Corrosion
Inhibitors Ion Exchange Vapor Phase
ACTIVE
SACRIFICIAL
Zinc-rich primers protect through the
preferential oxidation of zinc metal
10
Passivation Mechanism (Active-Direct Inorganic
Inhibitor)Specific Example Zinc phosphate

Zn3(PO4)2
Hydrolysis
Paint Film
Fe2
H2O
Insoluble FePO4
Precipitate Mx(OH)x
e-
Fe
Cathode
Substrate
Anode
11
Applications Formulating Strategies
12
Water Based Alkyds
13
Uses

• Lower cost corrosion protection
• Light duty industrial applications
• Moderate performance on machinery, tanks, etc.
• Lower VOC compared to S/B
• Fast Drying
• Good adhesion to steel, plastic, aluminum

14
Types

• Water Reducible Alkyds (WRA)
• Water Dispersible Alkyds (WDA)

COO-
COO-
COO-
COO-
COO-
COO-
COO-
COO-
COO-
COO-
COO-
COO-
COO-
ACRYLIC POLYMER SHELL
ALKYD CORE
15
Properties
16
Hydrolysis of Alkyds
Reversible Reaction in the Presence of Water

• System pH is critical
• Amine selection is critical

17
Typical Formulation (Water Reducible
Epoxy Ester)
Fast (25)
Amine Package
Slow (75)
18
Formulating with WRAs

• Recommended system pH of 8.00 8.50
• Use 100 triethylamine (TEA) for excellent
  stability good salt spray resistance.
• Use a blend of TEA and ammonium hydroxide for
  good stability excellent salt spray resistance.

19
Changes to the Amine Package
Water Epoxy Ester - Cold Rolled Steel 2.0 mils
- 336 hrs SS
Best Stability
Best Performance
100 Triethylamine
7525 TEA and Ammonium Hydroxide
20
Stability vs. Amine Package
21
Base Strengths via pKa pH
22
Formulating with WRAs
Effect of Corrosion Inhibitor

• Zinc phosphate with low levels of zinc oxide
  showed better corrosion resistance (Salt Spray
  Testing).
• Better solvent resistance with Zn than Ca (MEK
  Double Rubs).
• Higher electrochemical impedance with Zn than Ca
  (EIS Testing).
• Synergy witnessed with organic inhibitor.

23
Formulating with WRAs
Role of zinc oxide

• Improves the cross link density of film
• It is an active cathodic inhibitor which works
  synergistically with zinc phosphate.
• Can react with mono- di- carboxylic acid binder
  breakdown products

24
Corrosion Performance

25
Impedance Spectra (Bode Plots)

Strontium zinc phosphosilicate
Calcium phosphosilicate
Zinc phosphate
Blank
26
Inorganic-Organic Corrosion Inhibitor Synergy

Water Reducible Alkyd - Cold Rolled Steel 1.0
mil - 500 hrs SS
Even Better !
Blank 6 Mod ZnPO4
6 Mod ZnPO4 2
Organic CI
27
Summary

• Balancing the amine package is key to formulating
  hydrolytically stable WR alkyd primers.
• Modified (i.e., containing ZnO) zinc phosphate
  pigments provide excellent corrosion resistance
  compared to non-zinc or traditional zinc
  phosphate corrosion inhibitors.
• Salt spray and electrochemical impedance
  corrosion testing correlated well!

28

Acknowledgements Hexion Specialty Chemicals
Melissa DeGroot, RD Chemist Guy Lopez Senior
Technical Specialist Natalie Wilson Technical
Service Representative High Solids, Waterborne
and Latex Three Approaches to Compliance

29

Thank You !
Contact Information Andrew Thorn HALOX
Technical Service Manager Phone [phone] X
243 Fax [phone] Email Athorn_at_halox.com