Polycarbodiimides as Crosslinkers for Coatings Dr. André Derksen 29--2
2 Crosslinking Reasons for Crosslinking: o Improvement mechanical properties o Wear, Tear and Abrasion Resistance o Stain and Chemical Resistance
Types of crosslinkers for aqueous resins Aziridines Isocyanates Polycarbodiimides o Characteristics follow..
Aziridine crosslinking H H aziridine crosslinker H resin H carboxylic residu SHE aspects: o Classification Muta. Cat. ; R68; Xi; R, R8, R Examples of Picassian products: XL-76 (%) Benefits: very effective, long potlife Drawbacks: toxicity/sensibilization, yellowing Xn
Isocyanate crosslinking SHE aspects: o Classification Xi; R6/8, R Xi Examples of Stahl products: XR-, XR--88, XR-8 Benefits: versatile chemistry enables tailor made products (hardness/flexibility, medium to low VC) General concern: sensitive to moisture, pot life
6 Isocyanate crosslinking Resins with functional groups that can react with Isocyanates: H 2 C amine group C H H C isocyanate crosslinker C H resin H Hydroxyl group
7 Isocyanate crosslinking Resins without functional groups that can react with Isocyanates: so only reaction with water: o Result is IP R C + H2 R C H H R H C H R R H H + C2 R C IUPAC Definition interpenetrating polymer network (IP) 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 bren.
8 Crosslinking mechanism Carbodiimide groups (=C=) react with carboxylic groups (CH) H R C R C C R' H C R' carbodiimide crosslinker resin C H carboxylic residu H C
9 Carbodiimide crosslinking SHE aspects: o Defined as non-hazardous by SHA under 29 CFR 9.2(d). Examples of Picassian products: o Aqueous form: XL-72 #, XL-72 # o Multifunctional: XL-7, XL-72, XL-72 # # = VC-free, acc EU Direktive 2/2/EC Benefits: (very) effective due to unique multifunctionality, long pot life, low/no VC For XL-72
Synthesis of Polycarbodiimides Phospholene oxide catalyzed reaction of isocyanates nly small amount of side products R P R P C + C R C R P R C R C + C2 C R C R P R P + C R C R C C R C R C
Multifunctional carbodiimides 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
2 Comparison Carbodiimide* Isocyanate Aziridine Reacts with -CH -H, H, Water -CH Pot life Up to 2 weeks to 6 hours 2 hours VC % % - 2% % Classification one GHS Symbols one R-phrases one R, R2/ Muta Cat., R68, R, R, R8 * ot all products have all properties
Comparison Carbodiimide Isocyanate Aziridine Sensitivity towards moisture Low Very high High Yellowing Low Low High Gas generation one C 2 one Viscosity Low Low - high Low
Ethanol resistance (%, h) Resin = PU-88 Evaluated acc DI 272 ( = bad; = good) 2 +XL-7 +XL-72 +XL-72 +XL-72 K g + g 9g + g 9g + 7g
Acetone resistance (2 min) Resin = PU-88 Evaluated acc DI 272 ( = bad; = good) 2 +XL-7 +XL-72 +XL-72 +XL-72 K g + g 9g + g 9g + 7g
6 Ammonia resistance (%, h) Resin = PU-88 Evaluated acc DI 272 ( = bad; = good) 2 +XL-7 +XL-72 +XL-72 +XL-72 K o effect with XL-72 g + g 9g + g 9g + 7g 9g + g 88g + 2g
7 Ethanol resistance (%, h) Resin = PU-687 Evaluated acc DI 272 ( = bad; = good) 2 K g + g 9g + g 9g + 7g 9g + g +XL-7 +XL-72 +XL-72 +XL-72 o effect with XL-72
8 The combination does it ot all resins yields similar good results with polycarbodiimides Prediction of resistances, based on for example acid number or molecular weight, is not feasible It is important to find by trials the right combination of resin and polycarbodiimide
9 AC-88 & XL-72: optimal ratio ptimal ratio to be found by ladder study AC-88 + XL-72 % Alkohol (6h) % Ammoniak (6h) Aceton (6h) ivea Soft (6h@ C) Pendelhärte (Sek.) Unvernetzt (K) - 88 + % XL-72 - +2% XL-72 7 +% XL-72 9 +% XL-72-2 7 +% XL-72 2 6
2 Pot life How to have a long pot life? Be aware: o Carbodiimide reacts with CH groups o Amines neutralize CH groups o Above ph 9 almost no CH groups available Thus: o For carbodiimide added to resin of ph > 9 the amine blocks reaction But..
2 Pot life Unfortunately carbodiimides hydrolyze < ph They are stable as supplied (including aqueous versions) but hydrolyze when added to resin A high ph limits hydrolysis and prevents CH groups from forming
Pot life Ethanol resistance (%, h) Resin = PU-88 ph = 8. Evaluated acc DI 272 ( = bad; = good) 22 +XL-72 +XL-72 +XL-72 2 2 6 7 8 9 Days
Pot life Ethanol resistance (%, h) Resin = PU-88 ph = 9. Evaluated acc DI 272 ( = bad; = good) 2 +XL-72 +XL-72 +XL-72 2 2 6 7 8 9 2 6 7 Days
2 Gloss Gloss at 6 9 92 Gloss (%) 9 88 86 8 82 K +XL-72 +XL-72 +XL-72 8 PU-62 PU-88 AC-88
2 Evaluation on EPDM rubber WF--7 from Stahl Europe no XL XL-7 XL-72 XL-72 XL-72 Test amount 7% 9% 7% % gloss,7 2,9 2,9 2,9, adhesion GT- GT- GT- GT- GT- IS29 rubs ethanol - surface (-) 2/ 2/ / ISX2 rubs ethanol - cotton (de) 9, 9,86,, 2,8 (lowest = best) rubs white spirit - surface (-) 2/ 2/ ( = best) rubs white spirit - cotton (de),,2 2,6,9, (lowest = best) Hot Xenon gloss ( kj) 2, 2, 2, 2, 2,2 ISA Hot Xenon surface (waterspots/whitening) 2 2 ( = best) Hot Xenon cracks waterbath gloss (d@6 C),2 2,8 2,2 2, 2, ( = best) waterbath surface (waterspots/whitening) waterbath cracks little little little squeak mm/s vs glass VDA 2-26 squeak 8mm/s 2 vs glass - = good squeak mm/s vs metal 8 8 8 7 8 - = mod squeak 8mm/s 2 vs metal 8 6 7 6- = bad
26 Evaluation on synthetic leather WF-- from Stahl Europe no XL XL-7 XL-72 XL-72 XL-72 Test amount 8% % 8% % gloss,7,9,9,9,8 DI adhesion GT- GT- GT- GT- GT- IS29 rubs ethanol - surface (-) / / / ISX2 rubs white spirit - surface (-) / / / / ( = best) rubs toluene - surface (-) / / / ( = best) rubs cockpitspray - surface (-) / / / ( = best) scratch resistance () 2+ 2 2+ 2+ 2+ ballyflex DI ballyflex gloss after Hot Xenon cycle (2, kj),8,,9,2,9 ISB6-option gloss after Hot Xenon cycles,9,2,,,2 gloss after Hot Xenon cycles,,6,2,, de colourchange after cycle,,,,9,7 (lowest = best) de colourchange after cycles,82,89,7,7,6 (lowest = best) de colourchange after cycles,,,72,8,9 (lowest = best) gloss after heat age test (d@ C),9,,,, (lowest = best) de colourchange after 2 weeks,86,76,6,,8 (lowest = best)
27 Evaluation on PVC flooring WF--88 from Stahl Europe no XL XL-7 XL-72 XL-72 XL-72 Test amount 8% % 8% % gloss 6, 7, 7,2 7,2,9 DI adhesion GT- GT- GT- GT- GT- IS29 rubs ethanol - surface (-) / / / / ISX2 staining curry/ketchup / / internal staining mustard / internal staining tar / internal staining shoepolish internal soiling (Veslic test) / internal abrasion by Taber weight loss (CS7),66,78,6,7,89
28 Adhesion Substrate GT (d@rt) GT (d@ C) AC-88 + % XL-72 GT is good GT is bad Cold rolled steel (CRS) Galvanized steel ABS ABS+PC PC PS PP/PE PVC (hard+soft) Ceramic Aluminium Glass - - Wood
29 Summary Polycarbodiimides are a suitable alternative to isocyanate and aziridine crosslinkers o when suitable combination resin/polycarbodiimide found Benefits of polycarbodiimides: o Good chemical resistances o o classification o VC free (not all) o Long pot life (not all) o Good compatibility o Easy to use o o gas development in crosslinking reaction