LATEX

In fiber beater addition processes, polymer latexes containing a water-soluble salt of polybasic fatty acid and a 2-alkyl imidazoline derivative have storage stability and provide a broad range of freeness response from the same latex for use in the fiber slurry beater addition of latices to form fiber sheet materials in which polymers in latex form are incorporated into water dispersions of fibers and deposited thereon by coagulation. These latexes are obtained by either polymerizing the monomers to form polymer in aqueous dispersion in the presence of the polybasic fatty acid and 2-alkyl imidazoline derivative, by the presence of at least one of them during such polymerization and the addition of the other to the latex before adding to a water dispersion of the fiber, or addition of the polybasic fatty acid salt and 2-alkyl imidazoline derivative to an already prepared latex.