Process for producing water-absorbing resin powder

Patent metadata

Field	Value
Publication number	US-9976001-B2
Application number	US-201113578118-A
Country	US
Kind code	B2
Filing date	Feb 10, 2011
Priority date	Feb 10, 2010
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

Provided is a process for producing a water-absorbing resin powder which contains a given amount of water added thereto, has a low dust content, and has high material properties. When a water-absorbing resin powder which has undergone surface crosslinking is produced on an industrial scale, various problems concerning production are eliminated and a long-term stable operation is possible without causing a deterioration in the material properties of the resin. Even when the process is continued over a long period, the material properties are stabilized (decrease in standard deviation) or improved (improvement in AAP). The process for producing a water-absorbing resin comprises, in the following order, a first classification step for classifying a water-absorbing resin, a surface crosslinking step after the classification, a water addition step for adding water to the water-absorbing resin powder after or during the surface crosslinking, a second classification step, and a conveying step.

First claim

The invention claimed is:

1. A process for producing a water-absorbing resin powder, sequentially comprising:
a first classification step for a water-absorbing resin,
a surface-crosslinking step after the first classification step,
a water addition step in which 0.01 to 50 parts by weight of a water-based liquid is added relative to 100 parts by weight of a water-absorbing resin powder in at least one stage of after surface-crosslinking, during surface-crosslinking, and before surface-crosslinking,
a second classification step, where maximum meshes of a sieve to be used in the second classification step is 2 to 200 times relative to a maximum particle size obtained by the first classification step,
a conveying step for conveying the water-absorbing resin powder after the second classification step, said conveying step comprises conveying the water-absorbing resin powder upward in a perpendicular direction, and
where the conveying step is a mechanical conveying step using at least one mechanical conveying apparatus selected from the group consisting of a screw feeder, a belt conveyor, a bucket conveyor, a flight conveyor, a vibration feeder and an air conveying device,
wherein a moisture content of the water-absorbing resin powder before the second classification step is 0.2 wt. % to 15 wt. %,
a production amount per line of the water-absorbing resin powder is 300 kg/hr to 10,000 kg/hr, and
where the process includes at least one of the following (1) to (3):
(1) the second classification step classifies the water-absorbing resin powder at a lower part of the apparatus for the water addition step,
(2) a state where there is no mechanical conveying step before the second classification step,
(3) a state where the second classification step directly follows immediately after the water addition step.

2. The production process according to claim 1 , wherein the second classification step is set before the conveying step and an apparatus to be used in the second classification step is joined at 0 to 20 m interval to a lower part of the apparatus for adding water in the water addition step.

3. The production process according to claim 1 , wherein the water addition step is carried out for the water-absorbing resin powder after surface-crosslinking.

4. The production process according to claim 1 , wherein the water addition step functions also as a cooling step after surface-crosslinking and an apparatus for adding water in the water addition step is a low speed stirring type cooling apparatus having a stirring rotary shaft with a rotation speed of less than 100 rpm.

5. The production process according to claim 1 , wherein the surface-crosslinking step or the water addition step is conducted in a transverse type continuous stirring apparatus having a feeding inlet and a discharge outlet for the water-absorbing resin powder, a stirring means having one or more rotary shafts equipped with a plurality of stirring blades, and a heating or cooling means.

6. The production process according to claim 1 , wherein water to be added in the water addition step contains an additive and the additive is one or more compounds selected from the group consisting of inorganic crosslinking agents, deodorants, antibacterial agents, coloring agents, chelating agents, inorganic salts, acids, alkalis, and surfactants.

7. The production process according to claim 1 , further comprising a periodically shielding apparatus which is installed between an apparatus for adding water in the water addition step and an apparatus to be used in the second classification step.

8. The production process according to claim 1 , further comprising electricity removal which is carried out in the first classification step and/or the second classification step.

9. The production process according to claim 1 , wherein a third classification step is further set after the conveying step, and the third classification step is for controlling the particle size distribution of the water-absorbing resin powder by classification with a sieve.

10. The production process according to claim 1 , further comprising a third classification step after the conveying step, and wherein the second classification step is carried out by a sieve having the maximum meshes of 2 to 200 times relative to the maximum particle size of the water-absorbing resin powder obtained in the third classification step.

11. The production process according to claim 1 , wherein said water-absorbing resin powder has unsteady agglomerates with a particle diameter 10 mm or larger removed in the second classification step after obtaining water-absorbing resin particles with a particle diameter smaller than 1 mm in the first classification step.

12. The production process according to claim 11 , wherein the unsteady agglomerates separated in the second classification step are crushed and then recycled to a step prior to the second classification step.

13. The production process according to claim 11 , wherein the unsteady agglomerates separated in the second classification step are crushed and then subjected to surface-crosslinking.

14. The production process according to claim 1 , wherein the conveying step is air conveying for a conveying distance of 10 to 1000 m.

15. The production process according to claim 1 , wherein the water-absorbing resin powder has a moisture content of 1 to 15 wt. % and the water absorption capacity under load at 4.83 kPa is 20 [g/g] to 30 [g/g].

16. The production process according to claim 1 , wherein the water-absorbing resin is crushed particles obtained by continuous kneader polymerization or continuous belt polymerization and the surface-crosslinking agent is a dehydration reactive surface-crosslinking agent.

17. The production process according to claim 1 , wherein the water-absorbing resin to be supplied to the first classification step is obtained through a polymerization step, a gel-crushing step, a drying step, and a pulverization step.

18. The production process according to claim 1 , wherein the conveying step after the surface-crosslinking step or the second classification step is a step of conveying the water-absorbing resin powder upward in the perpendicular direction by air conveying and a temperature of the water-absorbing resin powder to be conveyed by the air conveying is 30° C. to 100° C.

19. The production process according to claim 1 , sequentially comprising the first classification step, the surface-crosslinking step, the water addition step, the second classification step, and the conveying step after the second classification step, wherein respective apparatuses for the surface-crosslinking step, the water addition step, and the second classification step are joined to lower parts of the apparatuses for the previous steps and the water-absorbing resin powder is gravitationally conveyed between the steps.

20. The production process according to claim 18 , wherein air used in the air conveying is dried air having the dew point of −30° C. or lower.

Assignees

• Okuda Sumio
• Ishizaki Kunihiko
• Wada Katsuyuki
• Nippon Catalytic Chem Ind

Inventors

• Okuda Sumio
• Ishizaki Kunihiko
• Wada Katsuyuki

Classifications

• C08J3/12 Primary

  Powdering or granulating · CPC title

• B01J20/267

  Cross-linked polymers · CPC title

• B01J2220/68

  Superabsorbents · CPC title

• C08J2300/14

  Water soluble or water swellable polymers, e.g. aqueous gels · CPC title

• C08J3/245

  Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking · CPC title