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UV-curing waterbased coating systems - The key to quality and productivity


Waterbased UV-curing coatings have gained substantial popularity during the last years. Large office furniture manufacturers are advertising their products on the merit of environmentally friendly low-VOC coating systems. Waterbased UV-curing polyurethane dispersions fullfill the important requirement of many large furniture companies to dispense with solvents in their production, and still be economical. Other companies of the industrial wood processing industry, like window and door manufacturers have followed and recognize the virtues of these UV-curing systems. The high crosslinking density of UV-cured coating films makes it still possible to meet the highest quality standards the industry asks for.

It is possible to produce high-molecular physially drying dispersions as well as non-physically drying emulsion grades, both of these can be cured by UV light. For the crosslinking on the substrate, UV-curing polyurethane dispersions just need a short reaction time under UV light (following the evaporation of water and possibly present solvents) to reach their final property profile. Consequently, existing coating lines being switched from solventborne 2K polyurethane coatings to waterbased UV systems are typically running faster after the conversion.

Additional advantages to be considered are lower energy consumption and overspray recycling. Material that has been oversprayed during the coatings process can be recycled by up to 80%, with the obvious advantages for the environment and the economics.

Examples of waterbased UV-curing raw materials for wood coatings:

Typ
Solids in
%
pH
Viscosity
mPas at 23°C
Characteristics
Bayhydrol® UV 2282
Polyurethane dispersion
39
7.9
< 50*
High chemical resistance, good grain enhancing, physically drying, for all-purpose applications (multi-coat)
Bayhydrol® UV 2317
Polyurethane dispersion
37
7.5
< 80*
High wet film clarity, good grain enhancing, physically drying
Bayhydrol® UV 2280
Polyurethane dispersion
38
7.8
< 100*
Outstanding physical drying, high chemical resistance, for pigmented lacquers
Bayhydrol® UV XP 2690
Polyurethane dispersion
39
7.8
< 80
Very good elasticity, excellent weatherability, physically drying, for window frames and other exterior wood applications
Bayhydrol® UV 2689/1 XP
Polyurethane dispersion
42
7.8
< 50
High gloss, hardness & resistance, good levelling, single-layer metallic
Bayhydrol® UV XP 2687
Polyurethane dispersion
49
8.0
~ 275
For wood primers with outstanding grain accentuation and good adhesion to all wood types, good resistance and hardness
*) Flow time at 23°C, 4mm cup

Starting formulation for UV curing wood coatings:

RR 6681Clear coat for spraying, semi-gloss (Bayhydrol® UV 2282)

IRL 5214-3Waterborne UV-curing clearcoat , semigloss (Bayhydrol® UV 2317)

LIPP 0303-1.1Waterborne UV-curing clearcoat , semigloss, dual-cure (Bayhydrol® UV VP LS 2280 / Bayhydrol® XP 2427 / Bayhydur® XP 2655)

LIPP 0313 Waterborne UV-curing clearcoat primer (Bayhydrol® UV XP 2687)

LIPP 0316 Waterborne UV-curing topcoat, white (Bayhydrol® UV 2280)

LIPP 0317 Waterborne UV-curing clearcoat , semigloss (Bayhydrol® UV XP 2687 / Bayhydrol® UV 2317)

LIPP 0318 Waterborne UV-curing clearcoat , highgloss (Bayhydrol® UV XP 2687 / Bayhydrol® UV 2317)

LIPP 0342-1Waterborne UV-curing topcoat, white (Bayhydrol® UV XP 2775)

LIPP 0815 Waterborne UV-curing clearcoat, site applied (Bayhydrol® UV 2317 / Bayhydrol® UV 2280)

More starting formulations for waterbased UV-curing wood coatings are available on request.

Two new UV-curing dispersions for exterior wood applications and primers

Bayhydrol® UV XP 2690 for exterior wood applications
Bayhydrol® UV XP 2690 was developed specifically for exterior wood applications. Coatings based on this polyurethane dispersion are noted above all for their outstandig weather resistance, a claim that has been confirmed in a study by the Fraunhofer Institute for Wood Research (WKI), which shows that the wood surface remains absolutely free of damage during weather exposure and meets the requirements of DIN EN 927-3. The test results also show that when used outdoors, the timber can withstand the elements for eight years, before re-coating is required. An additional advantage is that Bayhydrol® UV XP 2690 is suitable for both clear coats and pigmented top coats.


Bayhydrol® UV XP 2687 for wood primers and clear coats
The second addition to the Bayer MaterialScience range is Bayhdrol® UV XP 2687, which has been developed specifically for use as a primer. The product is recognized for its outstanding grain accentuation and adhesion to all wood types, even those containing oil. The polyurethane emulsion has a high solids content, which allows higher film thicknesses to be achieved in a single application. Due to its excellent resistance properties and high degree of hardness, it is also suitable for clear coats and can be formulated for both spray and roller application.



Presentation on Bayhydrol® UV XP 2690 for RadTech, October 2009: "Waterborne UV coatings for exterior wood application"

Presentation: "Overcoming the Contradiction: Highly Filled White Pigmented UV Coatings with Excellent Resistances"

More information on the technology of UV-curing coating in general

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