| abstract |
The present invention concerns magnetic recording media comprising fine, magnetizable pigment or particles dispersed within a binder and supported on a substrate, The invention particularly concerns the nature of the binder polymer and its preparation. The binder polymer is a curable polymer comprising a sulfonated, hydroxy-functional polyurethane polymer. A plurality of SO3M groups are pendant from the polyurethane polymer backbone. The SO3M groups have an equivalent weight of from about 2,000 to about 100,000. M is selected from the group consisting of H+, Li+, Na+, K+, NR4+ where R can be H+ or an alkyl group, and mixtures thereof. A plurality of hydrophobic polymer chain segments are incorporated into the polyurethane polymer that comprise residues of a polyol having a molecular weight of at least about 180. The hydrophobic chain segments have a carbon atom to polar functionality of at least about 60. The polyurethane polymer also comprises a plurality of cross-linkable hydroxy groups having an equivalent weight of from about 500 to about 10,000. At least a majority of the hydroxy groups are pendant from hydrophobic chain segments. |