Hydroxyalkyl alkyl cellulose, method for producing the same, and solid preparation

A hydroxyalkyl alkyl cellulose comprising:

• a volume-based average particle diameter, determined by dry laser diffractometry, of 50 to 100 μm, and having, on a basis of a dynamic image analysis to divide all particles into fine particles, spherical particles and fibrous particles, a volume fraction of the fibrous particles consisting of long and short fibrous particles relative to all of the particles of 45 to 70%, and a volume fraction of the fine particles relative to all of the particles of less than 2.0%, wherein
• the fine particles have a length of fiber of less than 40 μm,
• the spherical particles have a length of fiber of 40 μm or more and consist of first and second spherical particles, wherein the first spherical particles have an elongation, which is a ratio of a diameter of fiber to a length of fiber, of 0.5 or more, and the second spherical particles have an elongation of less than 0.5, an aspect ratio, which is a ratio of a maximal Feret diameter to a minimal Feret diameter, of 0.5 or more, and a circularity, which is a ratio of a perimeter (PEQPC) of a circle that has the same area as a projection area to a perimeter (Preal) of a real particle, of 0.7 or more,
• the long fibrous particles have a length of fiber of 200 μm or more and an elongation of less than 0.5, and consist of first and second long fibrous particles, wherein the first long fibrous particles have an aspect ratio of less than 0.5, and the second long fibrous particles have an aspect ratio of 0.5 or more and a circularity of less than 0.7, and
• the short fibrous particles have a length of fiber of 40 μm or more and less than 200 μm and an elongation of less than 0.5, and consist of first and second short fibrous particles wherein the first short fibrous particle have an aspect ratio of less than 0.5, and the second short fibrous particle have an aspect ratio of 0.5 or more and a circularity of less than 0.7.