Topcoats and clear coats – now self-healing possible

Outstanding properties regarding gloss, flow characteristics as well as high mechanical and chemical resistance contribute to the growing success of one- and two-component polyurethane systems compared to conventional thermosetting-acrylic (TSA) coatings. Today, environmentally friendly waterborne polyurethane coatings are used for automotive finishing as well. Bayer MaterialScience has developed high solids und super high solids for environmentally friendly polyurethane coating systems which meet the highest standards of the automotive industry regarding scratch and weather resistance. Bayer MaterialScience offers Bayhydrol® / Bayhydur® combinations for two-component systems, as well as Bayhydur® BL- and Bayhytherm®-grades for one-component stoving systems. Our experts will gladly assist you if you are interested in this technology.

Polyurethane coatings offer a number of inherent advantages due to their unique chemistry:

High reactivity and complete crosslinking even if cured at low temperatures
Good chemical and weather resistance
Hardness, mechanical resistance and elasticity due to their urethane / urea structure
Hydrogen-bonds allow thermoplastic flow properties and release internal stresses. Therefore they promote the "self-healing" of superficial scratches
Good compatibility with primers
High solids content / low VOC content
Great optical properties – High gloss or wet look

Solventborne OEM Polyurethane clear coats
A polyurethane clear coat for OEM applications is the reaction product of an isocyante with an acrylate polyol. The subsequent stoving process at 130-140°C lasts about 30 minutes, even though lower temperatures would still allow a complete reaction, so the coating is not sensitive when it comes to the strict maintenance of the stoving conditions. Polyurethane clear coats can be applied to a large variety of primers and primer surfacers. They can be formulated as high solids and low VOC coatings.

... more on the chemistry

Product examples: poly-isocyanates for automotive clear coats

	Type	Solids in %	% NCO on solids	Viscosity mPas at 23°C	Characteristics
Desmodur® N 3390	HDI trimer	90	21.8	500	High gloss, good chemical and weather resistance, lightfast, good mechanical resistance
Desmodur® N 3600	HDI trimer	100	23.0	1200	For High Solid coatings, high gloss, good chemicals and weather resistance, lightfast, good mechanical resistance
Desmodur® N 3900	HDI polyisocyanate	100	23.5	730	Hardener for weather resistant coating systems. For High solid coatings for automotive refinish, large vehicle finishing and plastic coatings
Desmodur® XP 2679	HDI polyisocyanate	80	19.3	500	For self-healing coatings, lightfast, weather resistant, scratch resistant
Desmodur® Z 4470	IPDI trimer	70	17.0	600	Hard, high gloss, good chemical and weather resistance, lightfast, good mechanical resistance, for combination with Desmodur® N
Desmodur® BL 3575/1	HDI polyisocyanate	75	14.0 bl. NCO on solids	3600	Good chemical and weather, lightfast, very thermo-stable
Desmodur® PL 350	HDI polyisocyanate	75	14.0 bl.NCO on solids	4300	In combination with polyol components, suitable for lightfast stoving coating systems

Some startin formulations

RR 4210	Two-component polyurethane clear coat, good chemical resistance (Desmodur® N3390 BA / Desmophen® A 665 BA/X)

RR 4211	One-component polyurethane clear coat (Desmophen® A 870 BA / Desmodur® VP LS 2253/1)

RR 4212	One-component polyurethane clear coat (Desmophen® A 870 BA / Desmodur® VP LS 2253/1)

Feature: Polyurethane raw material for self-healing coatings
The latest developments at Bayer MaterialScience are raw materials for self-healing coatings. The use of Desmodur® XP 2679 makes it possible to produce chemically resistant coatings, which have short drying times and which are very flexible, but also very scratch resistant.

This is the underlying concept: Mechanical stresses like for instance brushes in a car-wash do not cause this type of polyisocyanate to form micro cracks. Instead it shows plastic deformation. When the coating surface is exposed to higher temperatures it generates a so-called “reflow-effect”. ... more

Waterborne two-component polyurethane clearcoats for automotive OEM coatings

Waterborne two-component polyurethane clearcoats provide an alternative to solventborne two-component polyurethane systems. The strict demands made by the automotive industry are met in nearly all respects by hardeners based on aliphatic polyisocyanates in both hydrophobic and hydrophilic form.

... more on chemistry and technology

... top coats for OEM plastic coatings

Product examples, waterborne dispersions

	Type (Festkörper)	% OH on solids	Solids in % appr.	pH	Characteristics
Bayhydrol® A 2601	Polyacrylate dispersion	3.9	45	7,5	For clear- and top coats with good resistance properties and very fast drying
Bayhydrol® A XP 2645	Polyacrylate dispersion	4.5	42.5	8,5	For waterbased two-component hydro coats with good chemical resistance and weather resistance
Bayhydrol® A XP 2770	Polyacrylate dispersion	3.9	44.5	8,0	Low VOC variant of Bayhydrol A 2470 without flash point
Bayhydrol® U XP 2750	Polyacrylate dispersion	3.6	43	8,0	Hydrophilic crosslinker in combination with HDI-based greades to enhance drying properties
Bayhydrol® U XP 2757	Polyurethane dispersion	1.8	52	7.5	Solvent-free, for plastic coatings, incl. softfeel & effect coatings, good adhesion to different plastics, good resistance to hydrolysis
Bayhydrol® A 2058	Polyester polyacrylate Hybrid dispersion	4.8	42	8.5	Flexible, low-cosolvent dispersion, good adhesion to plastics
Bayhydrol® A 2290	Polyester polyacrylate Hybrid dispersion	3.8	45	7.4	hard, fast drying hybrid dispersion for good resistance

For more on clearcoats for plastic applications have a detailed look at these brochures and presentations:

	Dispersions - Products and Applications		Polyisocyanates and Prepolymers: Products and Applications
	Bayhydrol® A - designed for high Performance - engineered for Success		Resins - Polyols and Aspartics for reaction with Polyisocyanates
	Toolbox for waterborne 2K Polyurethane-Coating-Systems