Transcript Slide 1

Formulating High-Performance
Waterborne Epoxy Coatings
M.J. Watkins, D.J. Weinmann, J.D. Elmore
Presented at a meeting of the
Thermoset Resin Formulators Association
Hyatt Regency Montréal
September 11-12, 2006
Mythbusters
Myth #1
“Waterborne epoxy coatings can never match the
performance of solvent based systems”
Myth #2
“I know how to formulate other waterborne systems,
So I can use all my current tricks and additives to
formulate waterborne epoxies”
“Devil is in the Details”
(and the details are in the paper)
This presentation will
1. Define achievable high performance
2. Outline general formulation techniques
Please see paper for specific recommendations
Topics
• Waterborne epoxy types
• Type 5 waterborne epoxy performance
• Stoichiometry effects
• Pot life issues
• Components (cosolvents, pigments, additives, etc.)
• Dispersing pigments
• Pigment selection
Waterborne Epoxy Types
Type
Resin Form
Curing Agent Form
Typical Application
1
Liquid or liquid
emulsion
Water soluble
amine
Flooring, masonry
coatings
2
Solid dispersion
Water soluble
amine
Light – to mediumduty metal primers
3
Liquid or solid
emulsion
Carboxy-functional
acrylic dispersion
4
Liquid or liquid
emulsion
Amine dispersion
Flooring, masonry
coatings
5
Solid epoxy
dispersion
Amine dispersion
Primers and
topcoats
Low yellowing
topcoats
Best Performance
 Non-ionic aqueous dispersions
 Solid resin dispersions
Type 5 Epoxy Resin Dispersion
Name:
Description:
EEW, g/eq, solids:
Viscosity, cP*:
Solids, % weight:
Lb./Gal:
VOC Cosolvent:
*
Brookfield, #5 spindle, 20 rpm, 25 °C.
EPI-REZ 6520-WH-53
Modified 1001-type
550
< 3000
53.0
9.0
PM (<4%)
Type 5 Curing Agent Dispersion
Name:
Description:
AHEW, g/eq, solids:
Viscosity, cP*:
Solids, % weight:
Lb./Gal:
VOC Solvent:
*
Brookfield, #5 spindle, 20 rpm, 25 °C.
EPIKURE 6870-W-53
Modified polyamine adduct
225
8,000
53
9.1
None
Performance of White Enamels
Type 5
Conventional
Waterborne Solventborne
(85% stoich.)
VOC, lb/gal
Dry Time, hrs.,
Cotton-Free
24 Hr. Pencil
Hardness
14 Day Pencil
Hardness
Impact (Dir/Rev)
1000 Hr. Salt Spray
25 °C Water
Resistance, days
MEK Double Rubs
1.02
4
3.7
8.5
2B
4B
H
F
140 / 140
8F - 6F
>250
160 / 160
6F
>250
308
337
Discernable End Potlife
Viscosity, KU / 60° Gloss Value
120
Semi-Gel
110
100
90
80
70
60
50
60° Gloss
40
Viscosity
30
20
0
1
2
3
4
5
Time, hours, After Mixing A + B
6
2000 Hour Salt Spray
SB epoxy / polyamide
Type 5 WB system
3 mils DFT on cold-rolled steel
Epoxy / Amine Ratio Effects on Performance
(Stoichiometry)
Higher epoxy level gave
improved:
Pot life
Acid resistance
Higher curing agent
level gave improved:
Cure rate
Gloss
Alkali resistance
Water resistance
Humidity resistance
Adhesion
Abrasion resistance
Solvent resistance
Corrosion resistance
Stain resistance
1200
1200
J
1000
Salt Spray, hrs.
Water Immersion, hrs.
Effects of Epoxy/Curing Agent Ratio
800
600
J
400
J
200
J
0
Increasing
Amine:Epoxy Weight Ratio
(Solids Basis)
1000
J
J
800
600
400
J
J
200
0
Increasing
Amine:Epoxy Weight Ratio
(Solids Basis)
Effects of Epoxy/Curing Agent Ratio
2H
Pencil Hardness
J
F
B
J
B
J
J
B
B
3B
5B
B
J
2 Week Cure
B
24 Hour Cure
<6B
Increasing
Amine:Epoxy Weight Ratio
(Solids Basis)
MEK Double Rubs
240
200
J
J
160
120
80
40
J
J
0
Increasing
Amine:Epoxy Weight Ratio
(Solids Basis)
Pot Life Characterization
End of Pot Life
Viscosity Increase Above Application Limit
Significant Change in Gloss (10 Units Lower at 60°)
Decrease or Loss of Cure (Hardness)
Factors Affecting Pot Life
As Variable Below Increases…
Epoxy/Curing Agent Ratio
Acid Addition to Curing Agent
Temperature
Catalyst Level
Initial Viscosity
Vehicle Solids
Pot Life…
Increases
Increases
Decreases
Decreases
Decreases
Decreases
Cosolvents
Functions
• Coalescing aids
• Freeze-thaw stabilizers
• Leveling agents
• Pigment wetters
• Foam control
Performance Effects
• Dry time
• Gloss
• Hardness development
• Final film properties
Cosolvents
•
Glycol ethers are most versatile
- Ethylene glycol ethers are suitable
- Propylene glycol ethers are preferred for
non-HAP status
•
Diacetone alcohol can be useful
•
Partition between water and resin phases
- Slow and dynamic process
Cosolvents
Others – see paper for details
• Alcohols
• Aromatics
• Ketones
• Glycol ether acetates
Cosolvent Selection
Total Hansen Solubility Parameter, cgs units
(based on results with Type 5)
12.5
12
EM
EH
11.5
Poor Coalescing
EE
PM
11
EP
DM DE
10.5
PE
PNP
10
EB
DPM
DP
DAA
PTB
PNB
9.5
Good Coalescing
DB
DPNP
TPM
DPNB
TPNB
DPTB
9
PPh
MnAK
8.5
EEH
8
100
125
150
175
200
Boiling Point, °C
225
250
275
300
Freeze-Thaw Resistance
Adding glycol ethers and/or alcohols
• Reduces freezing point
• Promotes recovery of frozen material
• 25-30%v of total volatiles provides resistance
to 1-3 Cycles
• Examples: ethylene glycol monopropyl ether
(EP), or methanol
• 1:1 blend of DAA / PnB (Type 5 )
Liquid Resins as Alternative Coalescing Aids
• Increase solids
• Decrease VOC
• Increase gloss
• Liquid aromatic epoxy resin (e.g. EPON™ 828)
• Liquid aliphatic epoxy resin (e.g EPONEX™ 1510)
• Glycidyl neodecanoate (e.g. Cardura™ E10P)
- Low viscosity – easy to disperse in W/B epoxy
- Best performance
- Improved leveling and gloss
- Improved mar and early water resistance
Coalescence Properties
2 µm
Type 2 System
Avg. surface roughness = 25X
Type 5 System
Avg. surface roughness = 1.25X
SB Epoxy
Avg. surface roughness = 1X
Defoamers
 Suppress Foam Generation During Manufacturing,
Filling, Tinting, and Application
 Selection Considerations
– Empirically determined
– Optimize level (avoid stability & application problems)
– Must remain active for desired shelf life
– Most effective if portion added to grind & remainder to
letdown
– Required level is approximately 0.5% of paint volume
Defoamers
 Useful Generic Types
 Silicone Based
 Oil Based
 Possible Problems Due to Improper Choice
or High Use Levels
Pigment flocculation
Incompatibility
Poor Color acceptance
Cratering (fish eyes)
Poor inter-coat adhesion
Water sensitivity
Cure Catalysts/Accelerators
Effect of an Accelerator on the
Hardness Development
2H
J
Pencil Hardness
 Positive functions
– Decrease time to achieve desired
hardness
– Improves early solvent
resistance
 Negative functions
– Shortens pot life
– Decrease water & acid resistance
 Most effective
– Tertiary Amines such as 2,4,6Tris(Dimethylaminoethyl)Phenol
J
B
B
F
J
B
B
J
3B
B
5B
J
Accelerated Control
B
Control
<6B
0
24
48
72
Time, Hours, After Coating
Flash Rust Inhibitors
• Occurs on ferrous substrates under high relative humidity
• Effectiveness depends on % solids. Adding water can
reduce effectiveness.
• Nitrite salts (Ca or K salts preferred).
• Several common inhibitors ineffective or incompatible
lead naphthanate
chromates or dichromates
tertiary amines
• Use in curing component for stability
• Minimize levels to avoid water sensitivity
Adhesion Promoters
 Benefits
– Improved substrate wetting and adhesion
 Especially galvanized steel, cold rolled steel, and aluminum
 Less effective on blasted or phosphated steel
– Faster cure & hardness development
– Incorporate in epoxy during pigment grind
– Improved corrosion resistance
 Chemical Structure is Important
– Use Epoxy-functional, triethoxy- or diethoxymethyl- silanes for
best shelf stability.
– Aminosilanes contribute to yellowing
– Methoxysilanes hydrolyze and give poor adhesion
Mar and Slip Agents
 May Improve Abrasion Resistance and Early
Water Resistance
 Useful Types
– Polydimethylsiloxanes
– Wax Dispersions
– Micronized Polyethylene Dispersions
– Silicones
Fungicides and Mildewcides
• Generally not required for waterborne epoxy
systems
• Can cause instability
Viscosity
• Do not over-dilute the curing agent. Can hard settle
• Do not add cosolvent to curing agent. Can destabilize
• For stability, component viscosity >65 KU at 25°C
• DO NOT use latex viscosity control agents
- Often neurtalized with NH3 or amines
- React with epoxy
- Viscosity build, gel or coagulation & pigment kick-out
Thixotropes / Thickeners
Used for component stability and sag resistance
• Modified hydroxyethyl cellulosics
• Modified clays
• HEUR thickeners for component stability and grind
viscosity
Dispersing Pigments
• Disperse pigments, modifying resins, & additives
directly into the epoxy resin dispersion
• Water-only pigment dispersions may use too much
surfactant & give poor performance
• Dispersing pigments in W/B curing agent may lead
to poor stability
• Can disperse pigments in low viscosity polyamide.
Then let down with W/B curing agent
Pigments Dispersants
• Use in grind for epoxy resin dispersion stability
• Useful Dispersant Types
− Non-ionics, e.g. poly(ethylene oxide) types best
− Neutralized acid-functional acrylics – risky
− Avoid ionic dispersants (cause gel and kick-out)
• Primary Uses
− Pre-wetting pigments when grinding in epoxy
− Stabilize dispersion during storage
Pigment Selection Guidelines
Low Oil and Water Absorption
Low Soluble Salt Content
Low Ionic Character
Extender Pigments
– Variety of Shapes and Sizes
 Anti-Corrosive Pigments
– Acceptable Water Solubility
– pH >6




Extender Pigments
Chemical Class
Calcium Metasilicate
Barium Sulfate
Muscovite Mica
(e.g 325 mesh waterground mica)
Talc (Magnesium Silicate)
Ceramic Silica-Alumina
Calcium Carbonate
China Clay (Aluminum Silicate)
+ recommended
Comments
• Acicular shape for film strength
• High density can be a problem
• Aid in moisture resistance
• High oil absorption
• Avoid due to high viscosity
• Very low oil absorption
• Aids in pigment packing
• dark color limits use to primers
• Ionic content can be a problem
• May use to aid in brushability
- not recommended







Corrosion Inhibitors
• Zn-modified Al triphosphate
• Modified Al triphosphate
• Sr phosphosilicate
• Zn phosphate
• Zn phosphate complex
• Ca phosphosilicate
• Ca ion-exchange silica
• Al-Zn phosphate hydrate
• Zn/silicate-modified Al triphosphate
Corrosion Inhibitors
Not Recommended
• Ca or Ba metaborate
• Zn borate
• Zn phospho oxide complexes
 High ionic character
 Poor stability
Corrosion Inhibitors in Type 5 Epoxy
Zinc Phosphate
Strontium/Zinc
Phosphosilicate
Calcium Phosphate
Information provided by Halox®
Corrosion Inhibitors in Type 5 Epoxy
Blank
Calcium Phosphate
Ca Phosphate
+ organic
Information provided by Halox®
Conclusions
Realities – Not Myths
 High-performance waterborne epoxy coatings can
be formulated which match or exceed solvent
based coatings at attractively low VOC
 In order to achieve high performance, components
and formulating techniques specific to waterborne
epoxy must be used
What is HEXION?
Thermoset Resins
June, 2005