Synthesis,Modification And Properties Of Waterborne Polyurethane Ink Binder

Polyurethane has been widely used in ink industries because of its wear-resistant,corrosion-resistant and good mechanical properties.Compared with the solvent polyurethane,waterborne polyurethane(WPU)has attracted much more attention since it is non-toxic,nonflammable,environmentally friendly as well as low VOCs content.It is worth noting that there are some problems which still existed in waterborne polyurethane ink industry.For example,the ink with WPU latex as binder has low glossiness,poor re-solubility,bad adhesion fastness on low-polar substrate(BOPP,PE,etc.)and bad Ca2+ stability.On the begin with,in order to synthesis waterborne polyurethane ink binders with high gloss and well re-solubility,those fundamental factors which may affect gloss and re-solubility were systematically discussed.Then,to solve the problem of poor adhesion fastness of the WPU inks on BOPP films,two different strategies including hard segment modification and soft segment modification on WPU molecular structure were proposed,respectively,and effect of the two modification strategies on adhesion fastness on BOPP films were studied.Based on that,a kind of WPU ink binder which is suitable for BOPP film composit packaging printing was developed.At last,the method of improving the Ca2+ stability of WPU latex was also studied.The main contents are as follows:1.An anionic waterborne polyurethane latex was prepared by using IPDI as raw material,DMBA and BDO as chain extender,PBAD2000 as soft segment.Effect of NCO/OH molar ratio(R),hard segment content,hydrophilic monomer(DMBA)doasge,type and dosage of the neutralizer and end-caping method on the properties of latex and ink were studied.It was found that DMBA is the main influencing factor on latex stability.With increase in DMBA dosage,the particle size of the WPU latex decreases.When DMBA dosage is 5.5%,the latex possesses the smallest particle size and the best stability.The R value has significant influence on the particle size and the gloss of the ink.With increase of R value,the size of the latex decreases first and then increases,while the gloss decreases.The main factor affecting the anti-block performance of ink is content of hard segment,and the type of neutralizer is the key factor affecting the re-solubility of ink.The balance of re-solubility and drying speed of ink can be achieved through the combination of inorganic alkali(NaOH)and organic alkali(TEA).2.The polyurethane prepolymer was modified with rigid monomer glycerol monoester GMO or soft segment monomer P03 containing secondary hydroxyl polyester polyol,respectively,and the effects of the two different modification strategies on the properties of WPU latex and ink were studied.The results showed that both two modified waterborne polyurethane latexes have small particle size and moderate viscosity.The test result of DSC analysis showed a good compatibility between the soft segment and the hard segment in both two WPU films.With GMO dosage increased from 0%to 8%,the adhesion fastness of the corresponding WPU ink on BOPP film first increases and then decreases,but the maximum value is only 35%.In contrast,introduction of P03 which is a soft segment modifier monomer can significantly improve the adhesion fastness of ink on BOPP film.When P03 dosage is 67%,the adhesion fastness of ink can reach 97%.Based on above basic optimum formula with 67%of P03 dosage,γ-amino propyl trimethoxy silane(APS)was further introduced into the polyurethane molecular chain by post chain extension method to yield a new WPU latex.It was found that APS endows the latex worse stability,and seriously reduces the adhesion of ink on the surface of BOPP film.3.With P03 as a soft segment and DMBA as a hydrophilic monomer,a WPU latex and the corresponding waterborne polyurethane ink for BOPP film composit packaging printing were prepared by adjusting R value,hard segment content,post chain extension degree and hydrophilic monomer content.Then,in order to improve the electrolyte stability of the ink,the anion-nonionic WPU latex was prepared by using DMBA and Ymer N120 as the composite hydrophilic monomers.A water-based ink possessing not only excellent Ca2+stability(5%)but also good T-peel strength(0.64N/15m)was obtained when the ratio of Ymer N120:DMBA was 12:2.At the same time,a sulfonated waterborne polyurethane latex was prepared by using hydroxy sulfonate DMSQ as a hydrophilic monomer.The results showed that the use of sulfonic hydrophilic can not improve the electrolyte stability,but can increase the T-peel starength of the ink.