Polyurethane primers – a solid base for a perfect plastic coating

Primers are used on many plastics to provide an initial color effect and to smooth surface irregularities caused during the production process, such as ridges, dents or molding marks. And most of all, they improve the adhesion of subsequent coatings to difficult substrates. Also, they form a protective barrier between the substrate and potentially aggressive solvents in the base coats or top coats. When it comes to selecting the binder waterborne products have become more and more important because they do not contain any aggressive substances, which could affect the plastic substrate.

A selection of raw materials and formulations for waterborne primers

Waterbased dispersions:

	Type	Solids in %	% OH on solids	Viscosity mPas at 23°C	Characteristics
Bayhydrol® U 241	Polyester polyurethane dispersion	41	6.5	1000	For waterbased two-component polyurethane primers and top coats, good pigment wetting, high shear stability and very good flexibility
Bayhydrol® A 2290	Polyester polyurethane dispersion	45	3.6	< 200	In combination with Bayhydur® 3100 for high-gloss, solvent and tar resistant top coats, overcoatable, good mechanical properties, good adhesion on different plastic substrates
Bayhydrol® A 2227/1	Polyester polyurethane dispersion	42	3.8	1600	binder with good thermal stability
Bayhydrol® UH 650	Polyurethane dispersion	50	-	appr. 21 sec.*)	Binder for waterbased, air and forced drying primers, combination binder for 2K primers with good adhesion
Bayhydrol® UH 2606	Polyurethane dispersion	35	-	< 100	Binder for one-component water-thinnable coatings, good flow characteristics, good weather resistance, tough but elastic
Bayhydrol® UH XP 2648	Polycarbonate/ polyurethane Dispersion	35	-	< 100	For flexible, water-thinnable coatings on metal or plastic substrates like one-component metallic, one and two-component filler and topcoat systems
Bayhydrol® U XP 2757	Polyurethane dispersion	52	1.8	2250	For primers with outstanding adhesion on plastic substrates, particularly for PC and ABS

*) in DIN 4 Becher

Crosslinkers for dispersions:

	Type	Solids in %	% NCO on solids	Viscosity mPas at 23°C	Characteristics
Bayhydur® 3100	HDI polyisocyanate	100	17.4	2800	Hardener for waterborne two-component polyurethane systems or as an additive for high-quality waterborne one-component coating systems
Bayhydur® 304	HDI polyisocyanate	100	18.2	4000	Hardener for waterborne two component polyurethane systems and additive for waterborne high-quality coating systems
Bayhydur® 305	HDI polyisocyanate	100	16.2	6500	Hardener for waterborne two-component polyurethane systems or as an additive for high-quality waterborne one-component coating systems
Bayhydur® XP 2487/1	HDI polyisocyanate	100	20.6	5400	Hardener for waterborne two component polyurethane systems, developed for safe processing. Films with high chemical resistance
Bayhydur® XP 2655	HDI polyisocyanate	100	22.2	3500	Hardener for waterborne two component polyurethane systems, good emulsification
Desmodur® N 3600	HDI polyisocyanate (hydrophobic)	100	23.0	1200	Chemical and weather resistant, lightfast, good mechanical resistance

Some starting formulations for waterborne primers

RR PCO 0009e_PS	One-component polyurethane primer (Bayhydrol® UH 2606)

RR PCO 0013e_PS	Two-component polyurethane primer (Bayhydrol® UH 2606 / Bayhydur® XP 2487/1)

RR PCO 0016e_PS	Conductive primer (Bayhydrol® A 2227/1 / Bayhydur® 3100)

RR PCO 0035e_PS	Two-component polyurethane primer (Bayhydrol® A 2290 / Bayhydur® XP 2487/1)

RR PCO 0122_PSe	Two-component polyurethane primer (Bayhydrol® A 2290 / Bayhydrol® UH 650 / Bayhydur® XP 2487/1)

RR PCO 0133_PSe	Two-component polyurethane primer (Bayhydrol® U XP 2757 / Desmodur® N 3600 / Bayhydur® XP 2655)

A selection of raw materials for solventborne primers

One-component polyurethane raw materials:

	Type	Solids in %	Viscosity mPas at 23°C	Characteristics
Desmolac® 2100	MDI polyurethane	100 (granules)	800 (30%,MEK*)	non-reactive, for flexible substrates
Desmolac® 4340 X/iB	IPDI polyurethane	40	7500	non-reactive, for flexible substrates and as base coat for plastics, which are sensitive to solvents, like polycarbonate.

*methyl ethyl ketone

Two-component polyurethane raw materials:

	Type	Solids in %	% NCO or OH on solids	Viscosity mPas at 23°C	Characteristics
Desmophen® 670 BA	Polyester polyol	80	4.4 OH	3000	In combination with Desmodur® N 75 or N 3390 for excellent films, with very good cold weather flexibility, good weathering properties
Desmophen® 1200	Polyester polyol	100	5.0 OH	23500	To formulate flexible, clear and pigmented polyurethane coatings
Desmodur® N 3600	HDI trimer	100	23.0 NCO	1200	For high solid coatings, high gloss, chemical and weather resistance, lightfast, high mechanical resistance
Desmodur® N 3390 BA/SN	HDI trimer	90	21.8 NCO	550	High gloss, good chemical and weather resistance, lightfast, good mechanical resistance
Desmodur® N 75 MPA	HDI biuret	75	22.0 NCO	250	Lightfast, good chemical and weather resistance, high gloss, outstanding mechanical properties
Desmodur® L 75	aromatic polyisocyanate based on TDI	75	13.3 NCO	1600	Standard hardener for a broad range of applications

Some starting formulations for solventborne primers

RR PCO 0034e-PS	One-component polyurethane primer, conductive, elastic (Desmolac® 4340)

RR 4756	Two-component polyurethane primer, multi-purpose, sprayable (Desmodur® N 75 / Desmodur® L 75 / Desmophen® 1200 / Desmophen® 1300)

For more on primers 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