초록 ▼

A water absorbent resin having less fine powder or powdery dust and a controlled particle size is provided, and the water absorption rate of the water absorbent resin is increased by a simple method at low cost, while maintaining or improving other physical properties such as liquid permeability. Di

A water absorbent resin having less fine powder or powdery dust and a controlled particle size is provided, and the water absorption rate of the water absorbent resin is increased by a simple method at low cost, while maintaining or improving other physical properties such as liquid permeability. Disclosed is a method for producing a polyacrylic acid (salt)-type water absorbent resin powder, which includes, in sequence, a step of polymerizing an aqueous solution of acrylic acid (salt)-type monomer; a step of gel-crushing a gel of a water-containing gel-like crosslinked polymer during polymerization or after polymerization; a step of drying the water-containing gel-like crosslinked polymer; and a step of pulverizing and classifying the dried polymer, wherein water absorbent resin fine particles having a particle size of less than 150 μm or a hydrated-particles thereof is added to a step prior to the drying step, and in the drying step, hot air drying is carried out with a hot air having an average flow velocity of 1.0 to 3.0 m/s, a dew point of 30° C. to 100° C., and a hot air temperature of 140° C. to 235° C.

대표청구항 ▼

1. A method for producing a water absorbent resin powder, comprising in sequence: a polymerization step of an aqueous solution of a monomer, the solution including acrylic acid and/or a salt thereof as a main component;a gel-crushing step of a water-containing gel-like crosslinked polymer during or

1. A method for producing a water absorbent resin powder, comprising in sequence: a polymerization step of an aqueous solution of a monomer, the solution including acrylic acid and/or a salt thereof as a main component;a gel-crushing step of a water-containing gel-like crosslinked polymer during or after polymerization;a drying step of the water-containing gel-like crosslinked polymer; anda pulverization and classification step of the dried polymer, wherein, water absorbent resin fine particles having a particle size of less than 150 μm or hydrated-particles thereof are added to a step prior to the drying step, and hot air drying is carried out in the drying step with hot air having an average flow velocity of 1.0 to 3.0 [m/s], a dew point of 30 to 100° C., and a temperature of 140 to 235° C. 2. The method for producing according to claim 1, wherein in the drying step, the hot air drying is carried out for 10 to 120 minutes, and at a temperature of 160° C. to 220° C. 3. The method for producing according to claim 1, wherein the neutralization rate of the acrylic acid and/or the salt thereof is 50 to 100% by mole. 4. The method for producing according to claim 1, wherein the water absorbent resin fine particles are separated by the classification step. 5. The method for producing according to claim 1, wherein 1 to 40% by weight of the dried polymer is separated as water absorbent resin fine particles in the classification step, and then is added to a step prior to the drying step. 6. The method for producing according to claim 1, wherein the water absorbent resin fine particles or hydrated-particles thereof are added to at least one step of the polymerization step, the gel-crushing step and the drying step. 7. The method for producing according to claim 1, wherein the water absorbent resin fine particles or hydrated-particles thereof are added to the water-containing gel-like crosslinked polymer during or after polymerization. 8. The method for producing according to claim 1, wherein the water absorbent resin fine particles or hydrated-particles thereof are added to the water-containing gel-like crosslinked polymer during kneader polymerization. 9. The method for producing according to claim 1, wherein the polymerization step is carried out by continuous kneader polymerization or continuous belt polymerization, and the water-containing gel-like crosslinked polymer is gel-crushed at the time of polymerization and/or after polymerization. 10. The method for producing according to claim 1, wherein in the polymerization step of the aqueous solution, or in the drying step of the water-containing gel-like crosslinked polymer, a water-containing gel-like crosslinked polymer containing gas bubbles is obtained. 11. The method for producing according to claim 1, wherein the polymerization carried out in the polymerization step is foaming polymerization or boiling polymerization. 12. The method for producing according to claim 1, wherein the aqueous solution contains gas bubbles. 13. The method for producing according to claim 1, wherein the aqueous solution contains a methoxyphenol compound in an amount of 5 to 160 ppm relative to acrylic acid. 14. The method for producing according to claim 1, wherein a resin solid content of the water-containing gel-like crosslinked polymer is 40% by weight or greater. 15. The method for producing according to claim 1, wherein a weight average particle size (D50) of the water-containing gel-like crosslinked polymer is 0.5 to 4 mm. 16. The method for producing according to claim 1, wherein a dryer used in the drying step is a through-circulation band type hot air dryer, and a flow direction of the hot air is upward and/or downward in a direction perpendicular to the ventilated band surface. 17. The method for producing according to claim 1, wherein in the drying step, an atmosphere dew point at the beginning of drying is 50 to 90° C., and an atmosphere dew point at the end of drying is higher than or equal to 30° C. and lower than 50° C. 18. The method for producing according to claim 1, wherein in the drying step, a temperature of the mixture of the water-containing gel-like crosslinked polymer and the water absorbent resin fine particles or hydrated-particles thereof is 40° C. to 100° C. when the mixture is fed into the dryer. 19. The method for producing according to claim 1, further comprising: a surface crosslinking step after the classification step. 20. The method for producing according to claim 19, wherein a dehydration reactive surface crosslinking agent is used in the surface crosslinking step.