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New development - Self-healing coatings based on two-component polyurethanes

While polyurethane coatings are inherently self-healing due to unique chemistry, new raw materials developed by Bayer MaterialScience enhance this property. The underlying concept: Mechanical stresses like they might be caused by brushes in a car-wash do not cause the usual micro cracking. Instead they show plastic deformation. After the attacked coating surface is exposed to higher temperatures as they are generated by exposure to sun-light, a “reflow-effect” is generated.

A particularly suitable raw material for this kind of coatings is Desmodur® XP 2679. With this polyisocyanate, coatings can be formulated that are both, chemically resistant and scratch resistant but at the same time very flexible. Suitable reaction partners are highly functional polyacrylates (like those offered by our associated company Viverso) or highly functional polyesters like Desmophen® XP 2488, any of these grades in combination with polycarbonate diols like Desmophen® C 1100 and/or Desmophen® C XP 2716.

In addition to their self-healing properties polyurethane coatings show the other typical properties, for which they are known:

High reactivity and full crosslinking, even at low-temperature curing
Good chemical resistance and weather stability
Hardness, toughness, and elasticity due to urethane and urea structure
Hydrogen bonds that allow for thermoplastic flow to relieve stress and allow self-healing of defects
Basecoat compatibility
High solids/low VOC
Pleasing optical properties – a high gloss or “wet look”

Some raw material examples for self-healing coatings:

	Type	Solids in %	% NCO or OH content on solids	Viscosity mPas at 23°C	Characteristics
Desmodur® XP 2679	HDI polyisocyanate	80	19.3 NCO	500	Highly functional hardener, particularly for self-healing coatings, lightfast, weather resistant, scratch resistant
Desmodur® N 3390 BA	HDI-Trimer	90	21.8 NCO	500	Outstanding weather stability and gloss retention, non-yellowing, good chemical and weather resistance, good lightfastness, good mechanical resistance
Desmophen® C 1100	Aliphatic polycarbonate polyester	100	3.3 OH	3200	In combination with highly functional polyols, as a high-grade building block for self-healing polyurethane systems with very good weatherability, lightfastness and hydrolytic stability (recommended crosslinker: Desmodur® XP 2679)
Desmophen® C XP 2716	Aliphatic polycarbonate diol	100	5.2 OH	4000	In combination with highly functional polyols, as a high-grade building block for self-healing polyurethane systems with very good weatherability, lightfastness and hydrolytic stability (recommended crosslinker: Desmodur® XP 2679)
Desmophen® XP 2488	Polyester	100	16.0 OH	14500	In combination with polycarbonate diols or as single polyol for the crosslinking of polyisocyanates for self-healing polyurethane coatings

RR 4213

High Solid Polyurethane clear coat with self-healing properties (Desmophen® A HS XP 2768 / Desmodur® XP 2679)

For more formulation assistance and for applications recommendations please contact our technical experts.

Achieving self-healing: The theory

Achieving self-healing: In practice

Application Examples
Laboratory testing was conducted on examples of automotive refinish, OEM and plastics clearcoats to demonstrate that the new polyurethane raw materials support the theory for improving scratch resistance.

Automotive refinish

OEM clearcoat

Plastics clearcoat

Get this additional information:

Brochure:	„On the Road to Improved Scratch Resistance“

Article in "Farbe und Lack, issue 3/2011:	"Kratzer Ade - Selbstheilende Zweikomponenten-Polyurethanlacke: Die nächste Generation" (german only)

Article:	Complete article on the Ford trials

Article::	„Total concept for waterborne 2K polyurethane clear coats for automotive finishing“

Article::	„Shining Prospects for two-component polyurethane clearcoats“

Video:	Demonstration of Self-healing properties (1:40min.)