Patent ID: 9266970
Filing Date: 2016-02-23
CPC Classification: A21D,A23C,A23L,C08B,C08L

Claim Text:
1. A method for producing hydroxypropylmethylcellulose having an average substitution degree of a methoxy group of 1.0 to 1.6 per glucose unit, an average substitution degree of a hydroxypropoxy group (C) of 0.2 to 0.3 per glucose unit, and an A/B value of 0.305 or greater wherein A represents a substitution degree of a methoxy group directly substituted for a hydroxy group on carbon at position 6 in a glucose unit free from a hydroxypropoxy group-substituted hydroxy group, B represents a substitution degree of a methoxy group per glucose unit, and the A/B value represents a value of A divided by B, the method comprising at least the steps of: reacting a pulp with an alkali to obtain alkali cellulose; and adding a methyl etherification agent and a hydroxypropyl etherification agent to react with the alkali cellulose to obtain hydroxypropylmethylcellulose, wherein addition rates of the methyl etherification agent and the hydroxypropyl etherification agent are adjusted such that a reacted portion of the hydroxypropyl etherification agent is less than 50% at the time when a reacted portion of the methyl etherification agent is 50% or more, or such that a reacted portion of the hydroxypropyl etherification agent is less than 30% at the time when a reacted portion of the methyl etherification agent is 30% or more, and wherein the addition of the hydroxypropyl etherification agent is initiated at a time when a reacted portion of the methyl etherification agent becomes 5% or more, and after 10 to 60 minutes from the initiation of addition of the methyl etherification agent so as to obtain a C/D value of 0.28 or less wherein C represents the average substitution degree of a hydroxypropoxy group per glucose unit of the hydroxypropylmethylcellulose, D represents the number of moles of the hydroxypropyl etherification agent per glucose unit of the hydroxypropylmethylcellulose, and the C/D value represents a value of C divided by D, and wherein a molar ratio of the addition rate of the methyl etherification agent to the addition rate of the hydroxypropyl etherification agent is 3 or more, and wherein the hydroxypropylmethylcellulose has a thermal gelation temperature from 64° C. to 75° C.