Polyurethane based automotive refinishing – Performance like OEM coatings

Coatings for automotive refinishing should show the same high quality like OEM coatings. In contrast to automotive OEM coatings, automotive repair coatings are not baked but are at most force-dried (30 min. 60 °C). As OEM coatings are constantly improved and fine-tuned, refinishes need to keep up with their development. In addition, refinishing systems should be environmentally friendly and easy to use. Bayer MaterialScience provides a wide range of solventborne and waterborne systems for that purpose. They not only meet the processing requirements very well, but their quality matches those of finished OEM coatings as well.

Solventborne standard polyurethane coating systems

Solvent-reduced polyurethane coatings systems (high solid systems)

Solvent-reduced very high solid polyurethane coatings systems

Waterbased polyurethane coating systems

Another way to reduce the solvent content of the coating formulation is the use of

waterbased polyurethane systems

. These systems have become exceedingly popular and their properties are comparable to those of solventborne systems. In some properties they even exceed solventborne systems.

Corresponding coating raw materials with which the required property profile can be achieved are also available for the formulation of waterborne two-component polyurethane coatings for these applications too.

Two-component polyurethane primer fillers:

Unlike with OEM coating, in automotive repair coating the substrate first has to be sanded down to bare steel, with damaged parts for example then being leveled out, polished and made up with filler. Film properties such as rapid drying and good corrosion inhibition play a particularly big important role here. These requirements are broadly met by waterborne two-component polyurethane primer fillers such as those based on Bayhydrol A 2546 or A XP 2695.

Waterborne two-component polyurethane clearcoats:

When using waterborne two-component polyurethane clearcoats for automotive repair coating, the coating result, such as bubble-free dry film thickness, depends to a significant extent not only on mixing quality and rapid drying but also on the effect of temperature and atmospheric moisture.

Through a targeted selection of binders and hardeners it is possible to formulate waterborne two-component hydro-clearcoats that meet these requirements. For automotive repair clearcoats too, an excellent property level can be achieved through the combination of highly reactive polyacrylate dispersions such as Bayhydrol A 2601 or A XP 2801 and OH-functional polyurethane dispersions such as Bayhydrol U XP 2750 with hydrophilized polyisocyanate hardeners of the latest generation (e.g. Bayhydur XP 2655).

Examples of waterbased polyurethane dispersions and hardeners for low temperature systems

Waterbased dispersions:

	Type (Solids)	% OH on solids	Viscosity mPas at 23°C	pH	Characteristics
Bayhydrol® UH 2952/1	aliphatic Polyurethane Dispersion (40%)	-	approx 20 s (Flow time)	6.9	basecoats, even and cloud-free films, good metallic effect, exceptional gloss, good weater resistance and adhesion, very fast drying
Bayhydrol® A 2470	Polyacrylate Dispersion (45%)	3.9 OH	2000	7.8	high gloss topcoats, tough but flexible, very good solvent and water resistance, outstanding UV resistance
Bayhydrol® A 2601	Polyacrylate Dispersion (45%)	3.9 OH	2000	7.8	Fast drying, highly reactive, for clear coats and top coats
Bayhydrol® UH 2621	aliphatic Polyurethane Dispersion (40%)	-	approx 20 s (Flow time)	7.5	Basecoats, even and cloud-free films, good metallic effect, exceptional gloss, good weater resistance and adhesion

Polyisocyanate crosslinkers for dispersions:

	Type (Solids)	% NCO on solids	Viscosity mPas at 23°C	Characteristics
Bayhydur® 3100	HDI Polyisocyanate (100%)	17.4	2800	Hardener for two-component systems, also as an additive for high quality waterborne coatings
Bayhydur® 304	HDI Polyisocyanate (100%)	18.2	4000	Hardener for two-component systems, also as an additive for high quality waterborne coatings
Bayhydur® XP 2655	HDI Polyisocyanate (100%)	21.2	3500	Hardener for two-component systems, also as an additive for high quality waterborne coatings
Desmodurr® N 3900	HDI Polyisocyanate (100%)	23.5	730	Hardener component for weather resistant coating systems

A selection of starting formulations:

RR 4506	Two-component waterbased polyurethane metallic coating (Bayhydrol® UH 2621/ Bayhydur® 3100/ Desmodur® XP 2410)

RR 4205	Two-component waterbased polyurethane metallic coating (Bayhydrol® UH 2621/ Bayhydur® 3100)