Primers for large vehicles – polyurethane raw materials for durable coatings

Primers for commercial vehicles should provide optimum corrosions protection, smooth surfaces for the topcoat and good adhesion. They need to do this reliably even at high film thickness of the coating.

The advantages at a glance:

• Outstanding corrosion protection
• Very good adhesion to additional coating layers
• Fast curing
• Many possible combinations for the adjustment of specific properties

Curing time and sandability can be optimized by combining specific components. For primers and fillers Bayer MaterialScience provides a wide range of polyisocyanates, polyoles and polyaspartics, which can be combined to finetune the coating system to the desired properties. They are available as solventborne or waterbased two-component systems.

For waterborne two-component polyurethane coatings:

Primers based on waterborne two-component polyurethane technology offer great flexibility in terms of binder components and formulations and, as a result, in the quality of corrosion protection properties (up to corrosion protection class C4 medium in accordance with DIN EN ISO 12944). Consequently, these primers stand out in terms of impact strength, achieving above-average performance in stone impact tests and being successfully deployable on non-torsionally-rigid steel substrates. An additional advantage is their good compatibility with the corresponding polyurethane topcoats.

Primers based on waterborne two-component polyurethane technology can score in terms of productivity too, especially as a result of their drying and through-hardening properties, which can be specifically fine-tuned. Rapidly drying ready-to-use primers can be easily formulated.

In some applications waterbased, single-layer direct-to-metal coating systems have been introduced. They combine the function of a primer and a topcoat in one single coating layer.

Waterbased dispersions:

	Type	Solids in %	% OH on solids	Viscosity mPas at 23°C	Characteristics
Bayhydrol® A 145	PAC dispersion	45	3.3	950	For waterborne primer and top coats, good pigment wetting, high shear stability and good waterresistance
Bayhydrol® A 2695	PAC dispersion	41	5.0	2500	For waterborne primers and top coats, very good resistance
Bayhydrol® A 2227/1	PES-PAC Dispersion	42	3.8	1500	For waterborne primers and top coats, good pigment wetting, for stoving coatngs suitable as well

Polyisocyanate crosslinkers for waterbased dispersions:

	Type	Solids in %	% NCO on solids	Viscosity mPas at 23°C	Characteristics
Bayhydur® XP 2759	IPDI polyisocyanate	70	11.0	6500	Hydrophilic crosslinker in combination with HDI grades to improve drying properties
Desmodur® N 3600	HDI trimerisate	100	23.0	1200	For waterbased 2K and high solid coatings, high gloss, good chemical and weather resistance, lightfast, good mechanical resistance
Desmodur® N 3900	HDI polyisocyanate	100	23.5	730	Low-viscosity hardener for weather-stable coating systems

A starting formulation:

RR 4433	Waterborne two-component polyurethane primer (Bayhydrol® A145/ Desmodur® N 3900)

For solventbased two-component polyurethane coatings:

	Type	Solids in %	% NCO or OH on solids	Viscosity mPas at 23°C	Characteristics
Desmophen® 680 BA	Polyester polyol	70	3.1 OH	3000	Particularly suitable for air-drying systems, good mechanical resistance and good corrosion protection
Desmodur® N 3300	HDI trimer	100	21.8 NCO	3000	For air- and force-drying high solids systems with outstanding mechanical resistance
Desmodur® N 3400	HDI trimer	100	21.8 NCO	150	For high solids coatings and two component waterborne polyurethane-systems, good mechanical resistance
Desmodur® N 3600	HDI trimer	100	23.0 NCO	1200	For air- and force-drying and high solids coating systems, good mechanical resistance
Desmodur® N 3800	HDI trimer	100	11.0 NCO	6000	Hardener for flexible and high solids coating systems
Desmodur® N 3390 BA	HDI isocyanate	90	21.8 NCO	550	For high-solids coating systems, good mechanical resistance
Desmodur® N 75 MPA/X	HDI isocyanate	75	16.5 NCO	225	High gloss, good chemical and weather resistance, lightfast, good mechanical resistance
Desmodur® Z 4470 BA	IPDI trimer	70	17.0 NCO	600	Hard, good mechanical resistance, for blending with Desmodur® N

Suitable combination partners are polyols like hydroxy polyacrylates.

A starting formulation (example)

RR 4469

Two-component polyurethane filler (Desmodur® N 75/ Desmophen® 680)

Solvent-reduced "Very High Solid" polyurethane raw materials for fillers

The lowest possible solvent content, or rather a maximum solid content can be achieved with a combination of reactive thinners and low-viscosity polyaspartates plus a polyol. These "Very high solid" systems contain less than 250g/l of solvent.

	Type (Solids)	Reactivity	Equivalent Weight	Viscosity mPas at 23°C	Characteristics
Desmophen® NH 1521	Polyaspartate (90%)	+	356	150	For top coats and clear coats, in combination with NH 1420
Desmophen® NH 1520	Polyaspartate (100%)	+	290	1200 (bei 25°)	For top coats and clear coats, in combination with NH 1420
Desmophen® NH 1420	Polyaspartate (100%)	++	279	1500 (bei 15°)	For clear coats and fillers, in combination with NH 1521
Desmophen® NH 1220	Polyaspartate (100%)	++++	230	< 100 (bei 25°)	For putties and elastomers, in combination with Desmophen® NH 1420

+ low reactivity ++++ high reactivity

Starting formulations for very high solid systems are available in the polyaspartics section of the technology pages or on request.





For more in-depth information have a look at these brochures:

	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		Polyaspartics - Change the Coatings Game

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