Continuous production process for water-absorbent resin powder and powder surface detector used therefor

• US 6,727,345 B2
• Filed: 06/28/2002
• Issued: 04/27/2004
• Est. Priority Date: 07/03/2001
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Nishioka, Toru, Ishizaki, Kunihiko, Fujimaru, Hirotama, Kajikawa, Katsuhiro
• Primary Examiner(s): TESKIN, FRED M
• Application Number:
  US10/183,381
• Publication Number:
  US 20030020199A1
• Time in Patent Office: 669 Days
• Field of Search: 528/480, 528/481, 528/502.R
• US Class Current: 528/502.00R
• CPC Class Codes: B29B 13/021 Heat treatment of powders
• CPC Class Codes: B29B 2009/125 Micropellets, microgranules, microparticles
• CPC Class Codes: B29B 2009/163 Coating, i.e. applying a layer of liquid or solid material on the granule
• CPC Class Codes: B29B 9/12 characterised by structure or composition
• CPC Class Codes: B29B 9/16 Auxiliary treatment of granules
• CPC Class Codes: B29K 2105/251 Particles, powder or granules expandable particles B29K2105/046
• CPC Class Codes: B29K 2995/0092 hydrophilic
• CPC Class Codes: C08J 2333/08 Homopolymers or copolymers of acrylic acid esters
• CPC Class Codes: C08J 3/12 Powdering or granulating
• CPC Class Codes: G01F 23/44 using electrically actuated indicating means

Abstract

A surface-modified water-absorbent resin powder is produced continuously with high productivity in a state where the particle diameter distribution is narrow and where the properties are high by a process comprising a polymerizing step, a drying step, a pulverizing step, a classifying step, and a surface-modifying step, and further, conveying steps of connecting them, wherein the conveying steps include at least two hoppers for storing the water-absorbent resin powder. A powder surface detector used favorably for this process includes a float hung down by a hanging line.

Claims

1. A continuous production process for a water-absorbent resin powder, which is a process for continuously producing a surface-modified water-absorbent resin powder comprising a polymerizing step, a drying step, a pulverizing step, a classifying step, and a surface-modifying step, and further, conveying steps of connecting these steps, and is characterized in that:

the water-absorbent resin powder is obtained by a process including the step of polymerizing an unsaturated monomer and has a crosslinked structure, and has a mass-average particle diameter of 300 to 600 μ

m, and includes particles having particle diameters of 850 to 150 μ

m in a ratio of not less than 90 mass % in particle diameter distribution, and has a property of displaying an absorption capacity of not less than 25 g/g without load, and has a water-extractable content of not more than 25 mass %; and

the conveying steps include at least two hoppers for storing and discharging the water-absorbent resin powder after the pulverizing step wherein at least one of the hoppers includes;

a tank for storing the water-absorbent resin powder;

a supplying part which is placed in an upper portion of the tank and serves for supplying the water-absorbent resin powder into the tank;

a discharging part which is placed in a lower portion of the tank and serves for discharging the water-absorbent resin powder from the tank; and

a detector for detecting the quantity of the powder in the tank.

2. A continuous production process for a water-absorbent resin powder according to claim 1, wherein the at least two hoppers are a buffering hopper for storing and discharging the water-absorbent resin powder and a constant-quantity-supplying hopper which is placed downstream of the buffering hopper and serves for quantifying and discharging the water-absorbent resin powder.

3. A continuous production process for a water-absorbent resin powder according to claim 1, further comprising a second conveying step for conveying an additive powder for modifying the water-absorbent resin powder,

wherein the second conveying step includes a constant-quantity-supplying hopper for quantifying and discharging at least the additive powder as a hopper for storing and discharging the additive powder,

wherein the constant-quantity-supplying hopper includes:

a tank for storing the additive powder;

a supplying part which is placed in an upper portion of the tank and serves for supplying the additive powder into the tank;

a discharging part which is placed in a lower portion of the tank and serves for discharging the additive powder from the tank; and

a detector for detecting the quantity of the powder in the tank.

4. A continuous production process for a water-absorbent resin powder according to claim 1, wherein the tank is an inner-surface-vibrating type tank.

5. A continuous production process for a water-absorbent resin powder according to claim 1, wherein the supplying part is connected to a pipe for transporting the water-absorbent resin powder and/or an additive powder by an airflow.

6. A continuous production process for a water-absorbent resin powder according to claim 2, wherein the quantity of the water-absorbent resin powder and/or an additive powder as stored in the constant-quantity-supplying hopper is controlled into the range of 20 to 80% (capacity ratio) relative to the whole capacity of the hopper.

7. A continuous production process for a water-absorbent resin powder according to claim 1, wherein the production output of the water-absorbent resin powder is not less than 500 Kg/hr.

8. A continuous production process for a water-absorbent resin powder according to claim 1, wherein the water-absorbent resin powder exhibits an absorption capacity of not less than 20 g/g under a load and a saline flow conductivity of not less than 20 (10⁻

7×

cm³×

s×

g<sup>−

1</sup>).

9. A continuous production process for a water-absorbent resin powder according to claim 1, wherein the surface-modifying step includes the steps of:

adding a dehydration-reactable surface-crosslinking agent to the water-absorbent resin powder; and

heat-treating the water-absorbent resin powder, resultant from the adding step, in the range of 150 to 250°

C.

10. A continuous production process for a water-absorbent resin powder according to claim 2, wherein the constant-quantity-supplying hopper is a hopper for storing the water-absorbent resin powder which is to be supplied to the surface-modifying step, and wherein the detector is a powder quantity detector for measuring the mass of the whole hopper containing the water-absorbent resin powder.

11. A continuous production process for a water-absorbent resin powder according to claim 2, wherein the constant-quantity-supplying hopper is a hopper for storing an additive powder which is to be supplied to the surface-modifying step, wherein the additive powder is a superfine powder, and wherein the detector is a detector for detecting a powder surface in the quantifying hopper.