Hydroxypropyl celluloses are non-ionic polymers in which a hydroxyl group in the glucose (C6H10O5) unit serving as a structural unit of cellulose is etherified with a hydroxypropyl group. With respect to the hydroxypropyl celluloses, those in which the content of hydroxypropoxyl groups is from 53.4 to 77.5% by mass and those in which the content of hydroxypropoxyl groups is from 5 to 16% by mass are known. In general, the latter is called low-substituted hydroxypropyl celluloses (refer to Patent Document 1 or the like).
It has been known to dissolve a hydroxyalkyl cellulose in water to be used as a coating film of solid preparations. However, this coating film of hydroxyalkyl cellulose may cause aggregation called blocking.
Thus, Patent Document 2 has proposed a hydroxypropyl cellulose having an average substitution mole number of 2 to 3, in which the ratio of unsubstituted products and highly substituted products with a substitution mole number of hydroxypropyl groups of 4 or more is low, whereby anti-blocking can be achieved under the environment of 25° C. and 75% RH.
In addition, in Patent Document 3, a coating composition containing a low-substituted hydroxypropyl cellulose, talc, propylene glycol and polyethylene glycol has been proposed, whereby it has been shown that a tablet with no adhesion property can be provided.