Gel pulverization device, method for manufacturing polyacrylic acid (polyacrylate) superabsorbent polymer powder, and superabsorbent polymer powder
Provided is a water absorbent resin that is useful to sanitary materials such as a disposable diaper, a sanitary napkin, and a blood absorbent for medical use each having a higher liquid permeability and a higher water absorbing speed. Further provided is a water absorbent resin powder that is useful to sanitary materials such as a disposable diaper, a sanitary napkin, and a blood absorbent for medical use each having increased in absorbency of a liquid and in heat retaining property. A gel grinding device to be used to produce a water absorbent resin, includes: a screw; a feed opening; an extrusion opening; a porous plate; and a barrel, the barrel including a return preventing member provided on an inner surface thereof, and the return preventing member satisfying at least one of specific parameters.
1. A method for producing a polyacrylic acid (salt)-based water absorbent resin powder, comprising:
a polymerization step of polymerizing an acrylic acid (salt)-based monomer aqueous solution to form a polyacrylic acid (salt)-based hydrogel-like crosslinked polymer having a resin solid content of 10 wt % to 80 wt %;
a gel grinding step, carried out during or after the polymerization, of carrying out gel grinding with respect to the hydrogel-like crosslinked polymer to form a particulate polyacrylic acid (salt)-based hydrogel-like crosslinked polymer; and
a drying step carried out after the gel grinding,
in the gel grinding step, the hydrogel-like crosslinked polymer being ground by use of a gel grinding device comprising:
a screw;
a feed opening;
an extrusion opening;
a porous plate; and
a barrel,
the barrel including at least one return preventing member provided on an inner surface of the barrel, and
the barrel satisfying at least one of the following (1) and (2):
(1) 0.05≤YH/N≤0.25; and
(2) 0.05≤YF/N≤0.25
where YH is a height of the at least one return preventing member which height is obtained by cutting the barrel in a direction vertical to a direction in which a gel of the water absorbent resin is extruded; YF is a width of a top surface of the at least one return preventing member, the width being along a direction vertical to a direction in which the at least one return preventing member extends; and N is a diameter of an inner part of the barrel which diameter does not include the at least one return preventing member.
2. The method as set forth in claim 1 , wherein T/N 3 ranges from 0.05 to 2.0 where T is an amount [g/hr] in which the gel grinding device treats a hydrogel per hour and T/N 3 is a treatment amount-to-inner diameter ratio [g/hr/mm 3 ] that is a treatment amount per unit time of the gel grinding device.
3. The method as set forth in claim 1 , wherein the particulate polyacrylic acid (salt)-based hydrogel-like crosslinked polymer which is obtained in the gel grinding step is dried under a condition where a through-flow belt-type dryer is used, a drying temperature is 150° C. to 250° C., and hot air blows in a vertical direction (an up-and-down direction) at an air velocity of 0.8 [m/s] to 2.5 [m/s].
4. The method as set forth in claim 1 , wherein the barrel of the gel grinding device has a temperature of 40° C. to 120° C. while the gel grinding step is being carried out.