Adding a high-quality touch to plastic surfaces: polyurethane soft-touch coatings

Pleasant, soft, warm – these are attributes seldom associated with plastics. Soft-touch coatings are used to modify plastic surfaces in just this way. We often do not consciously perceive its “haptics”. Nevertheless, the significance of haptic perception should not be underestimated, because we very easily associate emotional statements such as “pleasantly velvety” or “warm” with an object’s “handle”. The astonishing thing is that a coating film only a few hundredths of a millimeter thick can drastically alter the tactile perception of a material or a component. Coating manufacturers can elicit just about any tactile sensation by varying their choice of raw materials. The variability and versatility of coating technology is a major advantage over the use of other surfaces – plastic skins, for example – to improve the way objects feel.

The introduction of so-called “soft-touch” coatings greatly enhanced the image of plastics, particularly for high-quality products.Such coatings are used today on laptops, telephones and even vacuum cleaners. A major area of application is the automotive industry, where soft-touch surfaces in automotive interiors lend a feel of quality to the plastics that are now used nearly everywhere. In addition, such surfaces are very resistant to abrasion and scratching. They have low gloss levels and thus low reflectivity. Soft-touch coatings are now available in a number of colors and also as effect coatings.

An overview of the advantages of soft-touch surfaces:

- warm and velvety handle
- high abrasion and scratch resistance
- low gloss, low reflectivity
- wide variety of shades and color effects possible

Select coating raw materials for solventborne soft-feel coatings

Polyols:

	Type	Solids in %	% OH on solids	Viscosity mPas at 23°C	Characteristics
Desmophen® C 1100	Polycarbonate polyester polyol	100	3.3	3200	For the elastification of binders for hart coatings
Desmophen® 1652	Polyester polyol	100	1.6	11000	For flexible coatings
Desmophen® 670	Polyester polyol	100	4.3	2200*	Very good weather resistance and low-temperature flexible systems

* 80% in butyl acetat

Polyisocyanates:

	Type	Solids in %	% NCO on solids	Viscosity mPas at 23°C	Characteristics
Desmodur® N 3390 BA	HDI isocyanurate	90	21.8	500	For lightfast coatings with high resistance to chemicals and weathering and outstanding good mechanical properties
Desmodur® N 75 BA	HDI biurete	75	22.0	160	For lightfast coatings with high resistance to chemicals and weathering and outstanding good mechanical properties

Select raw materials for waterborne soft-feel coatings

Waterbased one-component dispersions:

	Type	Solids in %	pH	Viscosity at 23°C *	Characteristics
Bayhydrol® UH 240	Polyurethane dispersion	40	7.0	< 70	For highly flexible coatings with good surface handle and good resistance to abrasion and water.
Bayhydrol® UH 340/1	Polyurethane dispersion	40	6.5	< 70	Improves the elasticity and flexibility, and to formulate lightfast coatings
Bayhydrol® UH 650	Polyurethane dispersion	50	7.0	21	Good adhesion to many types of plastics and good water resistance
Bayhydrol® UH XP 2658	Polyurethane dispersion	45	8.0	35	Very good temperature resistance, very good resistance to hydrolysis
Bayhydrol® UH XP 2660	Polyester polyurethane dispersion	40	7.0	25	Very good resistance to hydrolysis, sun-lotion and solvents

* Flow time DIN 4 mm cup

Waterbased two-component dispersions:

	Type	Solids in %	% OH on supply form	Viscosity mPas at 23°C	Characteristics
Bayhydrol® U 355	Polyester polyurethane dispersion	55	0.8	450	In combination with flexible polyurethane dispersions also to formulate suede-effect coatings
Bayhydrol® U 475	Polyester polyurethane dispersion	75	1.1	20000	Also to formulate suede-effect coatings
Bayhydrol® U XP 2698	Polycarbonate ester polyurethane dispersion	55	0.8	3000	In combination with soft polyurethane dispersions for the formulation of highly resistant soft- and effect coatings, NMP-free
Bayhydrol® U XP 2757	Polyurethane dispersion	55	1.0	2250	for very elastic but scratch resistant coatings with good resistance to chemicals and weathering
Bayhydrol® A 2058	Polyacrylate dispersion	42	2.0	1000	For though-elastic coatings with good resistance to chemicals and good weatherability
Bayhydrol® A 2290	Polyester polyacrylate dispersion	45	1.8	< 2500	For though-elastic coatings with good resistance to chemicals and good weatherability

Polyisocyanate crosslinkers for waterbased dispersions:

	Type	Solids in %	% NCO on solids	Viscosity mPas at 23°C	Characteristics
Bayhydur® 3100	HDI Polyisocyanat	100	17.4	2800	Hardener, also as an additive for high-quality water-based coatings
Bayhydur® 304	HDI Polyisocyanat	100	18.2	4000	Hardener, also as an additive for high-quality water-based coatings
Bayhydur® 305	HDI Polyisocyanat	100	16.2	6500	Hardener, also as an additive for high-quality water-based coatings
Bayhydur® XP 2487/1	HDI Polyisocyanat	100	20.6	5400	Hardener, also as an additive for high-quality water-based coatings
Bayhydur® XP 2655	HDI Polyisocyanat	100	21.2	3500	Hardener, also as an additive for high-quality water-based coatings
Desmodur® N 3900	aliphatisches Polyisocyanat	100	23.5	730	Hardener for coatings systems with good weatherability
Desmodur® N 3600	HDI Polyisocyanat	100	23.0	1200	Hardener for elastic and lighfast coating systems

Some starting formulations:

RR PCO-0059e-SF	One-component polyurethane softfeel coating (Bayhydrol® UH 650 / Bayhydrol® UH 340/1)

RR PCO-0111e-SF	Two-component polyurethane softfeel topcoat (Bayhydrol® U XP 2698 / Bayhydrol® UH XP 2660 / Desmodur® N 3600 / Bayhydur® XP 2655)

RR PCO-0112e-SF	Two-component polyurethane softfeel clearcoat (Bayhydrol® U XP 2698 / Bayhydrol® UH XP 2658 / Desmodur® N 3600 / Bayhydur® XP 2655)

RR PCO-0115e-SF	Two-component polyurethane softfeel clearcoat (Bayhydrol® U XP 2698 / Bayhydrol® UH XP 2658 / Bayhydrol® A 2058 / Desmodur® N 3600 / Bayhydur® XP 2655)

RR PCO-0118e-SF	Two-component polyurethane softfeel topcoat (Bayhydrol® U XP 2698 / Bayhydrol® UH XP 2658 / Desmodur® N 3600 / Bayhydur® XP 2655)

RR PCO-0119e-SF	Two-component polyurethane softfeel topcoat (Bayhydrol® U XP 2698 / Bayhydrol® UH XP 2658 / Bayhydrol® A 2058 / Desmodur® N 3600 / Bayhydur® XP 2655)

UV-curing softfeel systems

	Solids in %	Viscosity in sec, 4mm Cup	Application
Bayhydrol® UV XP 2649	40 in water	< 100	Soft-touch plastic coatings

Feature: Bayhydrol® UV XP 2649 - Soft-touch finish in less than five minutes
Two-component polyurethane coatings containing little or no solvent apart from water emit at most minimal amounts of VOC into the environment. However, it has been a challenge to deal with long curing times on plastic or wooden surfaces because these substrates can normally not be heated to high temperatures. Bayer MaterialScience's Bayhydrol® UV range, on the other hand, makes it possible to formulate coatings that are both environmentally friendly and cure very quickly under UV light. Depending on the available equipment, the curing process – which covers drying and UV crosslinking – can be shortened to less than five minutes. With the new Bayhydrol® UV XP 2649 polyurethane dispersion, it is now possible for the first time to formulate UV-crosslinking coating systems for the soft-touch coating of plastics. ... more

Have a look at this additional information:

Brochure: "Feel the Difference: Waterborne Soft-Touch Coatings"

Technical data and application information in these product overviews:

	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		UV-Systems: Products and Applications