Protective Coatings for Heavy Duty and Marine Applications by ...

Protective Coatings for Heavy Duty and Marine Applications by
Means of Surface Tolerant Anti-corrosive Paints based on Epoxy
Resins cured by Phenalkamines.
Jean-Luc Dallons, Global Marketing Manager, Cardolite Corp.
Abstract
Phenalkamines derived from Cashew Nutshell liquid are very performing curing agents for
epoxy resins.
Paint formulations based on phenalkamine curing agents bring about protective coatings with
outstanding corrosion resistance.
These coatings are very surface tolerant, namely, can be applied on non well prepared
metallic surface even under humid conditions.
Phenalkamines cure epoxy resins along a broad range of temperatures.
Coatings based on phenalkamines are particularly suitable for heavy duty industrial and
marine applications.
Introduction
Steel is one of the most popular construction material. It is used all over the world to build
bridges, ships, transportation vehicles, stadia and plants.
Steel has many advantages, namely its versatility and its availability. The main disadvantage
of steel, however, is its tendency to corrode, therefore requiring a protective coating.
Corrosion is a natural phenomenon that affects the appearance of the ship, bridge or any other
construction. Peeling paint is a sign of poor maintenance for the public and can induce an
unsafe feeling (1). The industry is therefore more and more requiring high quality coatings.
Nowadays, however, quality can sometimes be downsized due to cost reductions programs.
Furthermore, environmental regulations are pushing the industry to reduce its air emissions.
As a consequence, replacement of existing performing materials by non polluting ones is a
very challenging project.
High quality, lower cost and environmental friendly oppose frequently one another. By
plotting these three requirements, we get a triangle (fig.1) which shows clearly that optimising
one requirement is most of the time done to the detriment of the others. Indeed, focusing on
cost reduction will more likely lead to a poor performing material. Environmental friendly
coatings are often less performing than conventional ones or at least not so easy to handle and
therefore more expensive.
As a general rule of thumb, the best solution is always found through the best compromise.
This paper will demonstrate that the best solution is brought about by epoxy 2K coatings
based on phenalkamines curing agents.
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Figure 1 . Industry Requirements.
Cost Reduction
High Quality
Environment
Phenalkamine Technology(2-6)
Phenalkamines are epoxy curing agents obtained through amination of polymerized cardanol,
a chemical derived from the cashew nutshell liquid (CNSL). This is therefore a renewable raw
material.
The chemical formula of cardanol (figure 2) illustrates the particular properties that this
backbone unit will confer to coatings. Cardanol is very difficult to synthesize through a
conventional chemical process as the aliphatic side chain is found in the meta position
regarding the phenol group which actually orientates any further substitution to the positions
ortho or para. Nature can however make it.
Figure 2 . Cardanol Structure and Properties.
OH
Reactivity Enhancement -
Adhesion
C 7 H 14 -CH=CH-CH 2 -CH=CH-C 3 H 7
Chemical Resistance
Water
Resistance
As shown by figure 2, the hydroxyl group will provide adhesion and can also act as catalyst
for the curing reaction between amine and epoxy functions. Phenalkamines are therefore fast
curing agents.
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The aliphatic chain will confer a water repellence to the coating whilst chemical resistance
will be obtained thanks to the aromatic ring.
Cost Reduction
Industry can reduce cost through :
‣ Shortening the down-times
‣ Getting back to service as fast as possible
‣ Reducing the total application cost
‣ Being able to coat all over the year (“All Season Cure”)
‣ Reducing operation for substrate pre-treatment
Hardness of the film is rapidly achieved when using phenalkamine curing agents, therefore
shortening the down-times between two subsequent coating applications. Development of
hardness with phenalkamine compared to conventional polyamide is illustrated by figure 3.
Figure 3 . Hardness Development.
Persoz (sec.)
180
160
140
120
100
80
60
40
20
0
0 10 20 30 40 50 60
Time (h)
Phenalkamine
PAA
A freshly painted or repaired object requires always a certain time before to be put into
service. Reducing this waiting time is obviously interesting to an economic point of view.
As can be seen in figure 4, phenalkamines fast cure epoxy resins even at low temperature
which is not the case for conventional curing agents. Epoxy 2K paints based on
phenalkamines are therefore an “All Season Cure” system. 2 coats a day as well as coating
during the winter season in cold geographical areas is not anymore a dream but a reality.
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Figure 4 . Curing at Different Temperatures
100
90
80
70
Conversion (%)
60
50
40
30
20
10
0
0 1 2 3 4 5 6 7 8 9 10
Curing Time (Days)
Phenalkamine @ 24 °C Phemalkamine @ 4 °C Phenalkamine @ -5°C Polyamide @ 5 °C
Phenalkamines, perceived as very expensive materials, reveal to be very cost effective.
Due to their very low AHEW number, formulators are using less curing agents as it is
illustrated in table 1.
Table 1 . Formulation with Phenalkamines
Hardener
Phenalkamine
(65 %, AHEW : 174)
PAAad
(70 %, AHEW : 340)
PAAad
(60 %, AHEW : 520)
PAAad
(50 %, AHEW : 785)
Amount to Cure 100 g of
Epikote 1000 x 75
26 g
51 g
78 g
118 g
Cost of 1 kg of paint containing phenalkamine curing agent is indeed almost doubled compare
to a conventional epoxy paint.
However, prices are virtually the same if one calculates per litre of dry paint.
Phenalkamine based paint, due to easier handling and surface preparation tolerance, can
drastically drop the total cost of the entire paint process (figure 5).
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Figure 5. Cost of Phenalkamine Based Coating.
Total paint cost evaluation
100%
90%
80%
Costs in % of Traditional system
70%
60%
50%
40%
30%
20%
10%
0%
Polyaminoamide/200µ/ 3 coats/SA 2,5 Cardolite/200µ/2 coats/SA 2,5 Cardolite/200µ/1 coats/SA 2,5 Cardolite/200µ/1 coats/ST 2
Paint cost Application Pretreatment
To achieve the same coating protection, paints based on phenalkamines require only two
coating layers and even a single one compared to the three layers that must be applied with
conventional polyamide systems. Finally, epoxy 2 K based on phenalkamines can be used on
a non well prepared substrate like slightly rusted steel (ST2) as shown in figure 6.
Figure 6. Surface Tolerant Coating.
Starting
Panel
After 1500
hr Salt
Spray
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High Quality Coatings
Whilst being a cost effective coating system, epoxy 2K with phenalkamines as curing agents
are proven very high quality coatings.
Phenalkamines provide indeed a very outstanding anti-corrosion property and can be used on
steel, galvanized steel and Aluminum as shown in figure 7.
Figure 7 . Anti-corrosion Coatings on Different Substrates.
Steel Aluminum Galvanized Steel
After 750 hr salt spray
Phenalkamines, compared with polyamides, cycloaliphatic amines or Manich bases, provide
also the best water repellence on epoxy 2K coatings like shown in figure 8.
Figure 8 . Water Resistance
2,5
Weight Change (%)
2
1,5
1
Phenalkamine
Polyamide
Cycloaliphatic
Mannich
0,5
0
25 °C 65 °C
Immersion Temperature
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Environment
Fast curing phenalkamines can be formulated as high solids coating as it is illustrated by
table 2.
Table 2 . High Solids Formulations
Epoxy
16.3
22.8
Solvent
10.4
8.3
Part A
Rutile
15.6
15.1
Talc
33.4
32.3
Barite
9.3
9.1
Part B
Phenalkamine
15.1
12.4
VOC
(calculated)
265 g/l
285 g/l
Some phenalkamines can even be formulated as 100 % solid, namely solvent free and be used
in contact with potable water (2).
Conclusions
The paint industry dream to achieve a low cost, high quality and environment friendly
formulations is now a reality through the use of phenalkamine curing agents for epoxy resins.
This system offers indeed :
‣ All Season Cure Coatings
‣ Excellent combination between fast curing and workable pot life at both ambient and
low temperatures
‣ Surface Tolerant Applications
‣ Very High Solids to even 100 % solid formulations
‣ Outstanding anti-corrosion properties on different metallic substrates.
References
1) Perkins, P., JPCL, October 2003, 56-62.
2) Dallons, J.L., PPCJ, to be published.
3) R.A Gardiner, Modern Paint and Coating, July 1978
4) Z.Dai, A. Constantinescu, A. Dahal, C. Ford, SPI-ERF Conference, September
1994
5) E. Van Nevel, PPCJ, April 1995
6) M.C. Liepins, Welt der Farben, 9/2002 (12-13)
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