Process for producing water-absorbing resin

A process for producing a water-absorbing resin comprising a plurality of joined continuous steps;

• a polymerization step of polymerizing an aqueous unsaturated monomer solution, a drying step of drying a particulated water-containing gel-like crosslinked polymer obtained in a finely crushing step during the polymerization or after the polymerization, a pulverizing step after the drying, a classification step after the drying, and a surface treatment step for the water-absorbing resin powder after the classification step, wherein
• with some of the above steps kept running continuously, the other steps are interrupted, and subsequently the interrupted steps are restarted,
• the interruption of the steps are at least one selected from the group of an interruption at the time of periodic maintenance and a temporal trouble, at least one of the interrupted steps is selected from the group consisting of the polymerization step, the drying step, the pulverizing step, the classification step, and the surface treatment step, a particulated water-containing gel-like crosslinked polymer, a dried material thereof, or a water-absorbing resin powder is substantially absent from an apparatus for the at least one interrupted step, the apparatus is kept in a heated state during the interruption of the step, or dry air having a dew point of not higher than 0° C. is injected into the apparatus for the interrupted step, wherein substantially absent means the particulated water-containing gel-like crosslinked polymer, dried material thereof, or water-absorbing resin powder is taken out of the apparatus for the interrupted step in an amount of not less than 95 mass % based on the entire retention capability of the apparatus;
• the continuously running steps before the interrupted steps are kept running by storing the water-absorbing resin to be charged to the interrupted steps by installing a storage step for temporarily storing the water-absorbing resin,
• the storage step comprising an un-filled hopper or a hopper with a low filling ratio for temporarily storing the water-absorbing resin, the unfilled hopper or the hopper with the low filling ratio is installed between the drying step and either the pulverizing step or the classification step after the drying to temporarily store the water-absorbing resin after the drying at the time of interrupting the pulverizing step or the steps after the classification step,
• the filling ratio of the un-filled hopper or the hopper with a low filling ratio is 0 to 50%,
• the interrupted steps are restarted after countermeasures for the periodic maintenance and the temporal trouble are made.