HETEROGENEOUS LATICES AS BINDERS IN POROUS PARTICLE STRUCTURES

Heterogeneous carboxylated styrene-butadiene (S/Bu) latices were prepa red by a two-stage polymerization process, using three seeds of polyst yrene with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu-ratio of 1 and a methacrylic acid (MAA) c ontent of either 1 or 10 wt %. It has been found that the morphology o f the films made from these latices influenced the modulus in the rubb ery region of these films. The heterogeneous latices were used as bind ers in porous structures based on micron-sized kaolin particles. Such structures are typically employed as paper coatings. Polyester substra tes were coated with aqueous suspensions containing the kaolin particl es and the heterogeneous latex. The coatings were dried at room temper ature, which corresponds to the rubbery region of the latex films. It was found that a higher modulus (which is determined here by the morph ology of the latex film) in the rubbery region of the films was associ ated with coating layers with higher porosity, greater light scatterin g ability, and higher coating gloss. This is interpreted as being the result of a retarded shrinkage of the coating layers during the drying of these structures due to the increase in modulus of the latex films . (C) 1997 John Wiley & Sons, Inc.