Study On UV-curable Polyurethane-acrylate Waterborne Varnish

Varnish is generally used to improve the appearance, the water resistance and theabrasion resistance performance of paper products in polish industry. At present, thetraditional solvent varnish was gradually replaced by environmental waterbornevarnish and ultraviolet (UV)-curable varnish. Polyacrylate emulsion is used the mostin the waterborne varnish, but its existence the problem of drying slow, poor filmperformance, low glossiness, etc. Polyurethanes are the main in UV-curing varnish,but containing a lot of reactive diluents which is still harmful for worker’s physicalhealth. The UV curing polyurethane-acrylate emulsion which combined withwaterborne and UV curing, can play to the advantage of the two and avoid theirshortage, taking the attention by researchers. In this paper, we first synthetic the UVcuring waterborne polyurethane-acrylate emulsion, then choose appropriatephotoinitiator, active diluents and other additives, finally prepared the waterborne UVvarnish by mixing all the component together.This study improved the varnish’s performance to make it more suitable for theapplication of the paper by using the characteristic that the structure of thepolyurethane chain can be accommodative and the acrylate modification. We gave theresin mechanical strength mainly by Toluene Diisocyanate (TDI) which formed thehard segment of polyurethane chain; provided the flexibility of the resin by polyetherbinary alcohol (DL-1000) as the soft segment of chain; we used the small molecularalcohol chain extender1,4-butyl glycol (BDO) to adjust the NCO/OH ratio;introduced hydrophilic group with dimethylol propionic acid (DMPA), then turned tosalt to gain hydrophilic by neutral reaction; blocked the molecular chain withhydroxyethyl methacrylate (HEMA), introduced the C=C, so it can be cured by UV.The influence of emulsion and film properties by process and matching factors inthe synthesis process of emulsion was studied. The factors of preparing waterbornePUA prepolymer: the mole ratio of TDI/DL-1000, the content of Hydrophilic group(COOH), the mole ratio of NCO/OH, the content and reaction temperature and time ofHEMA, the content of polymerization inhibitor, etc; the factors of synthesizing PUAemulsion: Neutralization degree and dispersed process, etc; the factors of varnishformula: photoinitiator variety and dosage, active diluents dosage and join way, etc.There was test, characterization and analysis on the emulsion synthesis process,product structure and performance. The structure of UV-curable waterborne polyurethane-acrylate emulsion was characterized by Fourier Transform InfraredSpectroscopy (FTIR).The Laser nanometer particle size analyzer showed that thewaterborne PUA particle size distribution was narrow, and average particle size wasabout50nm. The finally emulsion and varnish tested had the film performance ofgood flexibility, hardness, glossiness, etc. TG curve showed that eventually vanishfilm had good heat resistance. DSC curve indicates that, after curing film are twophase change absorption peaks.