Hollow water-absorbing polyester filaments and a process for producing the same

A hollow water-absorbing polyester filament having at least one hollow extending in parallel to the longitudinal axis of said filament, and a number of caves distributed in at least a portion of the body of said filament and consisting of a number of fine outside concaves formed in the peripheral surface of said filament, a number of fine pores formed within the body of said filament, a number of fine inside concaves formed in the hollow surface of said filament, and a number of fine channels through which said pores are connected to each other, and to said outside concaves and inside concaves, said outside and inside concaves and said pores extending approximately in parallel to the longitudinal axis of said filament, which filament has been prepared by the process comprising the steps of:

• (A) preparing hollow polyester filaments each having at least one hollow extending in parallel to the longitudinal axis of said filament, from a blend of (a) a principal polyester component which comprises an acid moiety comprising at least one aromatic dicarboxylic acid or its ester-forming derivative and a glycol moiety comprising at least one alkylene glycol having 2 to 6 carbon atoms or its ester-forming derivative, with (b) a cave-forming agent, and
• (B) removing at least a portion of said cave-forming agent and a portion of said principle polyester component from said resultant hollow polyester filaments by treating them with an alkali aqueous solution, said cave-forming agent comprising at least one member selected from the group consisting of
• (i) copolyester which comprises a glycol compound moiety, an aromatic dicarboxylic acid compound moiety and an additional divalent organic sulfonic acid compound moiety of the formula (II):
• ##STR14## wherein Z represents a member selected from the group consisting of trivalent aromatic hydrocarbon radicals and trivalent aliphatic hydrocarbon radicals, M.sup.1 represents a member selected from the group consisting of hydrogen and metal atoms;
• R.sup.1 represents an ester-forming organic radical and R.sup.2 represents a member selected from the group consisting of a hydrogen atom and ester-forming organic radicals;
• (ii) phosphorus compounds of the formula (III):
• ##STR15## wherein R.sup.3 represents a monovalent organic radical;
• X represents a member selected from the group consisting of --OR.sup.4, wherein R.sup.4 represents a hydrogen atom or a monovalent organic radical, --OM.sup.3, wherein M.sup.3 represents a metal atom, and a monovalent organic radical;
• M.sup.2 represents a metal atom and;
• m represents zero or 1;
• and
• (iii) aromatic carboxy-sulfonic acid compounds of the formula (IV):
• ##STR16## wherein Y represents a member selected from the group consisting of a hydrogen atom and ester-forming organic radicals, M.sup.4 represents a metal atom, M.sup.5 represents a metal atom, and n represents an integer of 1 or 2.