Water-soluble cellulose ether and method for producing the same

Abstract

A method for producing a highly viscous water-soluble cellulose ether has a small undissolved fiber content and a high loose bulk density. More specifically, a production method includes steps of: bringing cellulose pulp into contact with an alkali metal hydroxide solution to obtain an alkali cellulose mixture; draining the alkali cellulose mixture to obtain an alkali cellulose; reacting the alkali cellulose with an etherifying agent to obtain a water-soluble cellulose ether mixture; washing and draining the water-soluble cellulose ether mixture to obtain a first moist cellulose ether; mixing the first moist cellulose ether with water to obtain a second moist cellulose ether; coarsely pulverizing the second moist cellulose ether with a coarse pulverizer to obtain a coarsely pulverized cellulose ether; cooling the coarsely pulverized cellulose ether; and then drying and pulverizing the coarsely pulverized cellulose ether.

1 . A water-soluble cellulose ether, having a loose bulk density of 0.36 to 0.60 g/ml and a viscosity at 20° C. of 30,000 to 500,000 mPa·s as determined in a 2% by mass aqueous solution of the water-soluble cellulose ether, and containing 800 or less of undissolved fibers, each fiber having a dimension of 8 to 200 μm, as determined by a Coulter counter method at 25° C. in 2 ml of a 0.1% by mass aqueous solution of the water-soluble cellulose ether. 
     
     
         2 . The water-soluble cellulose ether according to  claim 1 , further having an average particle size of 30 to 300 μm. 
     
     
         3 . The water-soluble cellulose ether according to  claim 1 , wherein the water-soluble cellulose ether is an alkyl cellulose, a hydroxyalkyl cellulose, or a hydroxyalkyl alkyl cellulose. 
     
     
         4 . The water-soluble cellulose ether according to  claim 1 , wherein the water-soluble cellulose ether is an alkyl cellulose selected from the group consisting of methyl cellulose having a degree of substitution (DS) of methoxy group of 1.8 to 2.2 and ethyl cellulose having a DS of ethoxy group of 2.0 to 2.6. 
     
     
         5 . The water-soluble cellulose ether according to  claim 1 , wherein the water-soluble cellulose ether is a hydroxyalkyl cellulose selected from the group consisting of hydroxyethyl cellulose having a molar substitution (MS) of hydroxyethoxy group of 2.0 to 3.0 and hydroxypropyl cellulose having an MS of hydroxypropoxy group of 2.0 to 3.3. 
     
     
         6 . The water-soluble cellulose ether according to  claim 1 , wherein the water-soluble cellulose ether is a hydroxyalkyl alkyl cellulose selected from the group consisting of hydroxyethyl methyl cellulose having a DS of methoxy group of 1.3 to 2.2 and an MS of hydroxyethoxy group of 0.1 to 0.6, hydroxypropyl methyl cellulose having a DS of methoxy group of 1.3 to 2.2 and an MS of hydroxypropoxy group of 0.1 to 0.6, and hydroxyethyl ethyl cellulose having a DS of ethoxy group of 1.3 to 2.2 and an MS of hydroxyethoxy group of 0.1 to 0.6.