Polyurethane Dispersions with “Reversible Drying”

Title: RADIATION CURABLE AQUEOUS COMPOSITIONS WITH REVERSIBLE DRYING

 Number/Link: WO2014/111349

Applicant/Assignee: Allnex

Publication date: 24-07-2014

Gist”: PUDs from hydrophilic, low molecular weight PU can be re-dispersed after drying.

Why it is interesting: It is known that PUDs will coalesce into an insoluble film when dried, at least when the temperature is over the ‘minimum film forming temperature’ or MMFT.  This behaviour, while being useful in most coating- and adhesives applications, can be problematic when the PUDs are used for jet-printing inks because of irreverisble blocking of the print-head nozzles.  According to this invention re-dispersible PUDs can be made when the PU used is both sufficiently hydrophilic and of a low average molecular weight (pref. an Mn between 1000 and 5000, with a polydispersity between 2 and 4). The PU does need to be radiation curable so it can be crosslinked after drying.  In the examples a low NCO prepolymer is prepared from 1,6-hexanediisocyanate (HDI), 2,2-dimethylolpropionic acid, some polyester or polycarbonate polyol and an acrylic chainstopper like a propoxylated trimethylolpropane diacrylate. The (viscous) prepolymer is dispersed and neutralized by adding water containing NaOH or triethylamine. After drying the PUDs of the invention can be re-dispersed in water at 25°C.

Film-forming PU dispersion.

Film-forming PU dispersion.

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