Polyurethane top coats for plastics – excellent surfaces with high-gloss or matt-finish

Top coats protect plastic substrates from outside influences such as chemicals or light, but they are also important for coloring and design. Under normal circumstances top coats are pigmented unlike clear coats. Depending on the individual requirements they can be applied in a single layer or as a multi-layer coating (Primer, base coat, top coat).

Due to their good curing properties at low temperatures polyurethane systems have become the standard technology for top coats. Surface characteristics like high-gloss or a matt finish can be adjusted according to individual needs by the use of special fillers, binders or matting agents.

Particularly interesting effects can be obtained with soft-feel coatings. They add a comfortable, luxurious and warm touch to plastic substrates of automotive interior or housings of mobile phones.

A selection of polyurethane raw materials for waterborne top coats

Waterbased dispersions:

	Type	Solids in %	% OH on solids	Viscosity mPas at 23°C	Characteristics
Bayhydrol® U 241	Polyester polyurethane dispersion	41	2.5	1000	Good pigment wetting, high shearing stability
Bayhydrol® A 145	Polyacrylate dispersion	45	3.3	990	In combination with polyisocyanates for high-gloss two-component polyurethane hydro coats with good film hardness and weather stability
Bayhydrol® A 2427	Polyacrylate dispersion	42	2.0	80	For fast drying two-component primers and topcoats and for one-component coatings
Bayhydrol® A 2542	Polyacrylate dispersion	50	3.8	2250	In combination with polyisocyanates for high-gloss two-component polyurethane hydro coats with good film hardness and weather stability
Bayhydrol® A XP 2645	Polyacrylate dispersion	43	4.5	2000	For waterbased two-component hydro coats with good chemical resistance and weather resistance
Bayhydrol® A 2058	Polyacrylate dispersion	42	4.8	1000	In combination with e.g. Bayhydur® 3100 for high-gloss solvent resistant top coats
Bayhydrol® AH XP 2754	high molecular polyacrylate dispersion	40	-	20	For wood coatings with excellent chemical and stain resistance - good wood wetting
Bayhydrol® A 2290	Polyester polyacrylate dispersion	45	3.6	< 200	In combination with Bayhydur® 3100 for high-gloss, solvent and tar resistant top coats, overcoatable, good mechanical properties
Bayhydrol ® A 2139/2	Polyester polyacrylate copolymer	48	3.8	1850	In combination with e.g. Bayhydur® 3100 for high-gloss solvent resistant top coats
Bayhydrol® U XP 2750	Polyurethane dispersion	43	3.6	1000	For clearcoats and topcoats with very good weather resistance

Isocyanate crosslinkers for waterbased 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, additive for waterborne high-quality coating systems
Bayhydur® XP 2655	HDI Polyisocyanate	100	21.2	3500	Hardener for waterborne two-component polyurethane systems (easy mixing) and additive for high-quality waterborne coating systems
Bayhydur® XP 2487/1	HDI Polyisocyanat	100	20.6	5400	Cross-linker for waterborne two component polyurethane systems, developed for safe processing. Films with high chemical resistance
Bayhydur® 304	HDI Polyisocyanat	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 (easy mixing) and additive for high-quality waterborne coating systems
Bayhydur® XP 2759	IPDI- Poyisocyanate	70	11.0	6500	Hydrophilic crosslinker, in combination with HDI-based grades to enhance drying properties

Some starting formulations

RR PCO 0027e-TC	Two-component polyurethane top coat (Bayhydrol® VP LS 2139/2 / Bayhydur® 3100)
RR PCO 0069e-TC	Two-component polyurethane top coat (Bayhydrol® VP LS 2290 / Bayhydur® 304 or Bayhydur® XP 2655)
RR 4540 ABCe	Two-component polyurethane clear and top coat (Bayhydrol® A145 / Bayhydur® 304)

A Selection of polyurethane raw materials for solventborne top coats

	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 e.g. Desmodur® N 75 MPA or Desmodur® N 3390 BA/SN for excellent films with very good weather resistance, which are elastic at low temperatures
Desmophen® 1300	Polyester polyol	100	4.3 OH	3600	Reaction partner for polyisocyanates, for air curing 2component polyurethane coatings
Desmophen® C 1100	Polycarbonate polyester polyol	100	3.3 OH	3200	For the elastification of binders for hart coatings, e.g. like Desmophen® XP 2488
Desmophenr® XP 2488	Polyester polyol	100	16.0 OH	14500	For highly resistant, but hart coatings
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

An example for a suitable starting formulation

RR 4842

Elastic two-component polyurethane topcoat (Desmophen® 670 / Desmodur® N 75)

Have a look at this in-depth information:

Brochure: “Easy emulsification plus improved chemical resistance - Hydrophilic polyisocyanate with high functionality improve waterborne Two-component PUR coatings”

"The New Frontier: Waterborne UV Coatings for Plastics" (This presentation received the Paul Dufour Award at the RadTech 2007)

Presentation for the ECS 2007: „New PUR dispersions for waterborne one-component coatings“