Post on 20-Jan-2017
Polycarbodiimides – Easy to use Crosslinkers in Aqueous Automotive Interior Coatings
André Derksen, May 2016
Free chains 3D network
Reasons for Crosslinking: ▪ Improvement mechanical properties ▪ Wear, Tear and Abrasion Resistance ▪ Stain and Chemical Resistance
Crosslinking
▪ Aziridines ▪ Isocyanates
▪ Polycarbodiimides - Characteristics follow..
Types of crosslinkers for aqueous resins
Aziridine crosslinking
SHE aspects: Classification Muta. Cat. 3; R68; Xi; R41, R38, R43 Example of Stahl Polymers’ product: XL-706 (100%)
Benefits: very effective, long potlife Drawbacks: toxicity/sensibilization, yellowing
Isocyanate crosslinking
Resins with functional groups that can react with Isocyanates SHE aspects: Classification Xi; R36/38, R43 Examples of Stahl products: XR-5350, XR-5585
Benefits: versatile chemistry enables tailor made products (hardness/flexibility, medium to low VOC) General concern: sensitive to moisture, pot life
Isocyanate crosslinking Resins without functional groups that can react with Isocyanates: so only reaction with water: Result is IPN
IUPAC Definition interpenetrating polymer network (IPN) A polymer comprising two or more networks which are at least partially interlaced on a molecular scale but not covalently bonded to each other and cannot be separated unless chemical bonds are broken.
R~NCO + H2O R~N-C-OH
O
H
R~N-C-N~R R~N-H + CO2
O
H H R~NCO H
Polycarbodiimide crosslinking
Carbodiimide groups (N=C=N) react with carboxylic acid residues (COOH)
SHE aspects: “Defined as non-hazardous by OSHA under 29 CFR 1910.1200(d).”
Examples of Stahl products: Aqueous form: XL-702#, XL-732# Multifunctional: XL-701, XL-721, XL-725# # = VOC-free, acc EU Directive 2004/42/EC
Benefits: (very) effective due to unique multifunctionality, long pot life, low/no VOC
Carbodiimide crosslinking
For XL-702 and XL-732
Health 0
Fire hazard 0
Reactivity 0
Multifunctional Polycarbodiimides Stahl has patent on multifunctional polycarbodiimides. Besides carbodiimide groups also other reactive functional groups in molecule. Yields denser network and higher chemical resistances.
Artist impression
Evaluation in PU Films | PU
% Percentage REDUCTION in Water Uptake due to XL-702 addition - 24 hrs immersion in water
1% 3% 5% 10%
RU-3901 20 27 70 90
RU-13-134 18 46 50 72
RU-13-734 25 60 70 92
0
10
20
30
40
50
60
70
80
90
100 %
Red
ucti
on in
Wat
er U
ptak
e
Evaluation on Leather |
Wet Rubs as function of % XL-702
Leather
No XR 1% 3% 5% 10%
wet rubs Direct 50 70 100 150 250
0
50
100
150
200
250 W
et R
ubs
Evaluation on Leather |
▪ Evaluation in a typical automotive top coat on leather - (1-5 scale: 1 is worst and 5 is best)
▪ Polycarbodiimide crosslinkers give good performance when evaluated on leather
▪ Polycarbodiimide crosslinkers approach isocyanates (like XL-728) in performance
Leather
No XR XL-728 XL-702 XL-732 XL-701 XL-725
Dosage (% of total top coat): - 10 5 5 5 3
Wet Rubs 1000 4 5 4 5 5 5
Sweat rubs 300 3 5 4 4/5 - 5 5 5
Flex 100,000 1 5 5 5 4 5
Cold -18°C Flex 15,000 1 5 5 5 4 5
Ethanol resistance (50%, 1h) |
Resin = PU-488 Evaluated acc DIN 12720 (1 = bad; 5 = good)
Wood
0
1
2
3
4
5
100g + 0g 95g + 5g 93g + 7g
+XL-701
+XL-702
+XL-732
+XL-725
1K
Acetone resistance (2 min) |
Resin = PU-488 Evaluated acc DIN 12720 (1 = bad; 5 = good)
Wood
0
1
2
3
4
5
100g + 0g 95g + 5g 93g + 7g
+XL-701
+XL-702
+XL-732
+XL-725
1K
Ammonia resistance (10%, 1h) |
Resin = PU-488 Evaluated acc DIN 12720 (1 = bad; 5 = good)
Wood
0
1
2
3
4
5
100g + 0g 95g + 5g 93g + 7g 90g + 10g 88g + 12g
+XL-701
+XL-702
+XL-732
+XL-725
1K No effect with XL-702
Evaluation on rubber | Rubber
WF-13-407 from Stahl Europe no XL XL-701 XL-702 XL-721 XL-725 Test
Amount 7% 9% 7% 5%
Gloss 1,7 2,9 2,9 2,9 3,0
Adhesion GT-0 GT-0 GT-0 GT-0 GT-0 ISO2409
10 rubs ethanol - surface (1-5) 1 4 2/3 2/3 3/4 ISO105X12
10 rubs ethanol - cotton (dE) 49,51 9,86 14,43 11,05 12,48 (lowest = best)
10 rubs white spirit - surface (1-5) 2/3 3 3 3 2/3 (5 = best)
10 rubs white spirit - cotton (dE) 4,10 3,32 2,60 3,94 4,05 (lowest = best)
Hot Xenon gloss (15 kJ) 2,5 2,4 2,3 2,5 2,2 ISO105A4
Hot Xenon surface (waterspots/whitening) 1 2 1 2 3 (1 = best)
Hot Xenon cracks ok ok ok ok ok
Waterbath gloss (3d@60°C) 1,2 2,8 2,2 2,5 2,0 (1 = best)
Waterbath surface (waterspots/whitening) ok ok ok ok ok
Waterbath cracks ok little ok little little
Squeak 1mm/s 10N vs glass 3 4 5 3 3 VDA 230-206
Squeak 8mm/s 20N vs glass 3 3 4 4 3 1-3 = good
Squeak 1mm/s 10N vs metal 8 8 8 7 8 4-5 = mod
Squeak 8mm/s 20N vs metal 8 10 10 6 7 6-10 = bad
Evaluation on PVC | PVC
WF-13-188 from Stahl Europe no XL XL-701 XL-702 XL-721 XL-725 Test
Amount 8% 10% 8% 5%
Gloss 6,5 7,1 7,2 7,2 5,9 DIN53350
Adhesion GT-0 GT-0 GT-0 GT-0 GT-0 ISO2409
10 rubs ethanol - surface (1-5) 4/5 4/5 4/5 4/5 5 ISO105X12
Staining curry/ketchup 4 4/5 4 4/5 5 internal
Staining mustard 4 4 4 4/5 5 internal
Staining tar 3/4 5 4 5 4 internal
Staining shoepolish 1 1 1 1 1 internal
Soiling (Veslic test) 4/5 3 3 3 4 internal
Abrasion by Taber weight loss (CS17) 0,0616 0,0781 0,0564 0,0570 0,0589
Adhesion | Wood PVC Metal
Substrate GT (1d@RT) GT (1d@50°C)
Cold rolled steel (CRS) 0 0
Galvanized steel 1 1
ABS 0 0
ABS+PC 3 0
PC 0 0
PS 5 4
PP/PE 5 5
PVC (hard+soft) 0 0
Ceramic 5 0
Aluminium 1 1
Glass 0-1 0-1
Wood 0 0
▪ AC-188 + 3% XL-725 ▪ GT 0 is good
▪ GT 5 is bad
Pot life – Ethanol resistance (50%, 1h) |
Resin = PU-488 pH = 8.1
Evaluated acc DIN 12720 (1 = bad; 5 = good)
1
2
3
4
5
0 1 2 3 4 5 6 7 8 9 10
+XL-702
+XL-725
+XL-732
Days
Pot life – Ethanol resistance (50%, 1h) |
Resin = PU-488 pH = 9.0
Evaluated acc DIN 12720 (1 = bad; 5 = good)
1
2
3
4
5
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
+XL-702
+XL-725
+XL-732
Days
Crosslinkers comparison
Carbodiimide* Isocyanate Aziridine
Reacts with -COOH -OH, NH, Water -COOH
Pot life Up to several weeks 1 to 6 hours 12 hours
VOC 0% - 50% 0% - 20% 0%
GHS Symbols None
R-phrases None R43, R52/53 Muta Cat. 3, R68, R43, R41, R38
Moisture sensitivity Low Very high High
Yellowing Low Low High
Gas release None CO2 None
Viscosity Low Low - high Low
* Not all products have all properties
Summary Carbodiimide crosslinkers are an excellent alternative for more hazardous isocyanate and aziridine crosslinkers.
The carbodiimide crosslinkers are an ideal way to add additional properties to a waterborne coating or lacquer.
Benefits of polycarbodiimides: ▪ Good chemical resistance
and performance ▪ Improved adhesion
(also to ‘complicated surfaces’) ▪ No classification ▪ VOC free (not all)
▪ Long pot life (not all) ▪ Good compatibility ▪ Easy to use ▪ No gas development in crosslinking reaction ▪ Crosslinking reaction at room temperature