The invention discloses a
polyurethane based fluorescent whitening agent and a preparation method thereof. The preparation method includes the steps that
polymer polyalcohol is heated, vacuum
dewatering is conducted for 1-2 hours,
nitrogen gas is introduced for cooling, and diisocyanate,
solvent and a catalyst are added for a reaction; then, an organic small molecular fluorescent whitening agent body is added, a reaction is conducted, and
polyurethane prepolymer with the fluorescent whitening agent body is prepared; water-based chain
extender is added into the
polyurethane prepolymer, and a reaction is conducted; then,
solvent is added to dilute the mixture to certain
viscosity, a salt-forming agent is added, and a polyurethane
ionomer is formed; the polyurethane
ionomer is transferred into an emulsification reactor, then emulgator and water are added, then
solvent removal is conducted, and water-based polyurethane based fluorescent whitening
emulsion is obtained. The polyurethane based fluorescent whitening agent has the advantages of being high in
fluorescence quantum yield, resistant to light, resistant to heat, resistant to washing, resistant to wear, resistant to migration, resistant to wet
processing, prone to film formation, capable of being processed and the like and further has the advantages of being good in whitening effect, convenient to use, low in cost, free of
toxin,
environmentally friendly and the like.