Polycarbodiimides – Easy to use Crosslinkers in Aqueous Automotive Interior Coatings

André Derksen, May 2016

   

Stahl: the car interior surfaces expert

Stahl´s multiple touchpoints in premium car interior

Stahl Automotive Center of Excellence

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Crosslinkers for aqueous automotive interior coatings

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 results

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

More Information www.stahl.com www.stahlpolymers.com

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