Method of coating substrate surfaces with LCST polymers

#The invention relates to a method of coating substrate surfaces with LCST polymers, in particular to a method of coating pigment particles and, very particularly, to a method of irreversibly coating particulate and non-particulate substrate surfaces in general.

#LCST polymers are polymers which are soluble in a solvent at low temperatures and separate from the solution as a separate phase when the temperature is raised and the LCST (lower critical solution temperature) is reached.

#A definition thereof is given, in particular, in the monograph “Polymere” by Hans-Georg Elias, Hüthig and Wepf-Verlag, Zug, 1996, pages 183 to 184.

#FIG. 1 shows quasi-adsorption isotherms for an LCST polymer on various pigments;

#FIG. 2 illustrates compatibility improvement on copper phthalocyanine blue pigments in acrylate binding agents by means of LCST coatings of the invention;

#FIG. 3 shows the stabilizing action of LCST polymers on pigments in accordance with the invention; and

#The following Examples 1 to 3 describe the procedure of coating with an LCST polymer in accordance with the present invention and illustrate the effects thereof on various pigments.

#A PEO-PPO-PEO block copolymer having a molecular weight of 4,000 g/mol and an LCST of 8° C. (as sold by Aldrich) as LCST polymer is dissolved in distilled water at ca 5° C. to give a solution having a concentration of ca 10 wt %. This solution is kept at ca 1° C.

#In a parallel setup, a 1 vol % strength dispersion of a titanium dioxide pigment (Kronos 2310, sold by Kronos International) is prepared, this being done by weighing 6.8 g of the pigment with 400 g of glass beads (diameter 3 mm) and 168 g of distilled water into a wide-mouth flask of polypropylene and dispersing the mixture for ca 30 min in a Scandex shaker. The dispersion (pigment in water) is sifted from the glass beads and stirring is continued with a magnetic stirrer. The pigment dispersion is kept at ca 1° C.