Degraded hydrophobic, particulate starches and their use in paper sizing.

摘要

This invention is directed to degraded, hydrated particulate starches that are hydrophobically modified and a method of providing paper with reduced porosity, resistance to liquid penetration and increased surface strength comprising applying to the surface of a paper substrate an effective amount of a surface sizing composition which comprises such starch. In particular, the starches are those in which the starch base is degraded to a water fluidity (WF) of from about 10 to 80 or the modified and/or particulate starch is degraded using a substantially equivalent amount of degradation agent and substantially the same reaction conditions, the starch is modified with a hydrophobic hydrocarbon group of 5 to 23 carbon atoms at about 1 to 20% substitution level by weight of bound hydrophobe based on the weight of starch, and the hydrated starch has a volume average hydrated particle size of at least about 20 microns and a volume fraction of hydrated particles at 1% solids of at least about 5%.