D TEXTILES; PAPER
D21 PAPER-MAKING; PRODUCTION OF CELLULOSE
D21H PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
D21H23/00 Processes or apparatus for adding material to the pulp or to the paper
D21H23/02 characterised by the manner in which substances are added