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News

Launch of a New Polyisocyanate Hardener: New Standards in Automotive Coating

Bayer MaterialScience AG : 02 August, 2001  (Company News)
A new polyisocyanate hardener offered by Bayer for waterborne two-component polyurethane (2K-PUR) coatings improves a number of properties simultaneously.
Compared with its predecessors, the benefits of the new product include faster drying, improved hardness and chemical resistance, a longer pot life and enhanced optical properties in the formulations in which it is used.

Waterborne 2K-PUR coatings are high-quality systems with low emissions for use in automotive OEM, automotive refinish, plastics coating and transportation applications. Fundamentally, there are two types of polyisocyanate crosslinker: hydrophobic, primarily low viscosity substances such as those used in conventional solventborne 2K-PUR coatings; and hydrophilically modified, self- emulsifying polyisocyanates.

However, both types have their limits. As the hydrophobic types are miscible only with solvents and not with water, they contribute the (undesired) high solvent content to waterborne coatings. Coatings formulated with hydrophilically modified polyisocyanates often have the disadvantage of lower water resistance after drying.

A new generation of hydrophilically modified hardeners yields some considerable benefits over Bayhydur® 3100 or a 1:1 mixture of this and Desmodur® N 3600. Chemically, these hardeners are hydrophilically modified allophanatized HDI trimers. They result in faster drying than Bayhydur 3100, yielding higher film hardness and chemical resistance.

The new product also yields better optical properties such as gloss and haze than the combination of hydrophobic and hydrophilic hardeners (Bayhydur 3100 and Desmodur N 3600) if it is incorporated at low shear (e.g. by hand). A further advantage is that the pot life is extended to up to four hours.
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