AMPHOLYTIC STARCH DECREASED IN VISCOSITY, METHOD FOR PRODUCING THE SAME, AND METHOD FOR MAKING PAPER

PROBLEM TO BE SOLVED: To provide ampholytic starch capable of exhibiting an excellent effect of increasing paper power, even when increase in an amount of the starch to be added is avoided, while keeping filterability and retention, to provide a method for producing the ampholytic starch, and to provide a method for producing paper or board having the increased paper power, by utilizing the ampholytic starch so as to keep the good filterability and retention, and by avoiding the increase in the amount of the starch which conventionally makes stains in a paper-making machine increase and causes a balance in a paper-making system to be lost. SOLUTION: This method for producing the ampholytic starch comprises adding urea and inorganic phosphoric acids to cationic starch into which a tertiary amine and/or a quaternary ammonium salt is introduced to give the cationic starch a degree of cation substitution of 0.01-0.06, so as to form slurry having a pH of ≤5.0 which is measured after the materials are mixed, and then roasting the slurry to make it react at 110-180°C in a dry process to form the ampholytic starch, wherein phosphate groups are introduced into the ampholytic starch, so that the ampholytic starch has a viscosity of 5-500 mPa.s, when measure in a 5% solution of the starch by using a B-type viscometer (60 rpm, at 50°C), and a degree of anion substitution of 0.0005-0.03. The ampholytic starch is produced by the method. The method for producing the paper or the board comprises conducting paper making of pulp slurry to which the ampholytic starch is added. COPYRIGHT: (C)2003,JPO