With Bayhydrol® UV 2689/1 XP, Bayer MaterialScience has developed a polyurethane dispersion for radiation-curing waterborne coatings that are highly resistant not only to moisture and elevated temperatures, but also to sunscreen products and other cosmetics. Through the application of such coating systems, the housings of mobile phones, laptops and other electronic devices will continue to gleam even if they are handled frequently with moist or creamed hands. "In terms of its resistance to hydrolysis and chemicals, this solvent-free product is a real breakthrough. The outstanding properties of the resultant coatings are due to the extremely highly crosslinked molecular structures produced during radiation curing," said Dr. Arno Nennemann, an expert in UV radiation-curing coatings at Bayer MaterialScience.
Bayhydrol® UV 2689/1 XP will even allow the formulation of coating systems that require only a single coat to produce an opaque finish and then create a metallic effect on the plastic surface. Clear coats based on the dispersion can balance out the slight surface roughness of basecoats and therefore have a high gloss finish. They also have good scratch and abrasion resistance.
Allophanate-based urethane acrylates
For the water and solvent-free coating of plastics with radiation-curing systems, Bayer MaterialScience also markets allophanate-based urethane acrylates. The special characteristic of coatings based on these binders is their outstanding weather stability. At the same time, they have low viscosity and are free of reactive thinners. This opens up enormous scope in coating formulation. "Coatings can be formulated to meet the most exacting of requirements, with a property profile determined almost entirely by the high-grade urethane acrylate fraction," explained Dr. Wolfgang Fischer, another expert for UV-curable coatings at Bayer MaterialScience.
Coatings based on Desmolux® XP 2738 are noted not only for their weather resistance but also for their excellent resistance to chemicals. They protect the surfaces of, for example, automotive add-on parts in a corrosive environment, and also have excellent abrasion and scratch resistance. The use of Desmolux® XP 2666, another raw material in the allophanate range, is recommended in particular where a high UV-reactivity and therefore particularly rapid curing is important. Finally, Desmolux® XP 2740 can be used in combination with other urethane acrylates to enhance the flexibility and elasticity of the resultant coating.
Furthermore, the use of the three allophanate-based urethane acrylates is not just limited to the coating of solid plastics: "Based on these raw materials, it is also possible to formulate coatings for plastic film and for metal and mineral surfaces," added Dr. Fischer.
Source: Bayer MaterialScience