Water-absorbing resin and manufacturing method for same

Patent metadata

Field	Value
Publication number	US-12337295-B2
Application number	US-202117798757-A
Country	US
Kind code	B2
Filing date	Feb 12, 2021
Priority date	Feb 14, 2020
Publication date	Jun 24, 2025
Grant date	Jun 24, 2025

Abstract

It is an object to provide a water-absorbing resin that while maintaining water-absorbing resin physical properties such as water absorption performance, has a sufficiently reduced odor produced during swelling. The object is attained by causing the water-absorbing resin to be a water-absorbing resin which is a surface-crosslinked water-absorbing resin, the water-absorbing resin having a volatile component concentration of 3.5 ppm or less as measured when the water-absorbing resin is caused to stand still for 15 minutes under a condition that the water-absorbing resin has a swelling capacity of 1.0-fold.

First claim

The invention claimed is:

1. A water-absorbing resin which is a surface-crosslinked water-absorbing resin, said water-absorbing resin comprising a volatile component concentration of 3.5 ppm or less as measured when said water-absorbing resin is caused to stand still for 15 minutes under a condition that said water-absorbing resin has a swelling capacity of 1.0-fold,
where the volatile component concentration as measured when said water-absorbing resin is caused to stand still for 15 minutes under the condition that said water-absorbing resin has a swelling capacity of 1.0-fold is a numerical value obtained by adding together concentrations of all substances that are detected by a photoion detector (PID) of a 10.6 eV lamp and that are included in a volatile component which is present in a closed vessel when 10.0 g of a physiological saline at 23.5±0.5° C. is uniformly added, under room temperature and atmospheric pressure, to 10.0 g of said water-absorbing resin contained in a 2-liter closable glass vessel and said water-absorbing resin to which the physiological saline has been added is caused to stand still in a closed state for 15 minutes, the volatile component concentration being a value represented by a detection value in terms of isobutylene, which is a calibration gas.

2. The water-absorbing resin according to claim 1 , wherein a sum of volatile component concentrations as measured when said water-absorbing resin is caused to stand still for 15 minutes under conditions that said water-absorbing resin has respective swelling capacities of 0.0-fold, 0.5-fold, 1.0-fold, 2.5-fold, 5.0-fold, 10.0-fold, and 20.0-fold is 9.5 ppm or less.

3. The water-absorbing resin according to claim 1 , wherein a maximum value of volatile component concentrations measured every five seconds, under a condition that said water-absorbing resin has a swelling capacity of 5.0-fold, until 900 seconds have passed since initiation of swelling of said water-absorbing resin is 0.4 ppm or less.

4. The water-absorbing resin according to claim 1 , wherein a sum of volatile component concentrations measured every five seconds, under a condition that said water-absorbing resin has a swelling capacity of 5.0-fold, until 900 seconds have passed since initiation of swelling of said water-absorbing resin is 50.0 ppm or less.

5. The water-absorbing resin according to claim 1 , wherein said water-absorbing resin has an absorption capacity without load (CRC) of 23 g/g or more and an absorption capacity under load (AAP) of 15 g/g or more.

6. The water-absorbing resin according to claim 1 , wherein said water-absorbing resin has a mass average particle diameter (D50) of 300 μm to 600 μm, a proportion of particles having a particle diameter of less than 150 μm in said water-absorbing resin is 5 mass % or less, and said water-absorbing resin has a logarithmic standard deviation (σζ) of a particle size distribution of 0.20 to 0.50.

7. The water-absorbing resin according to claim 1 , wherein said water-absorbing resin contains a volatile component reducing agent.

8. The water-absorbing resin according to claim 1 , wherein said water-absorbing resin has a specific surface area of 25 m 2 /kg or more.

9. An absorbent article comprising a water-absorbing resin recited in claim 1 .

10. The absorbent article according to claim 9 , wherein said absorbent article includes an absorbent body, which is a composite containing said water-absorbing resin and a hydrophilic fiber, and said water-absorbing resin is contained in an amount of 60 mass % or more relative to a total mass of the absorbent body.

11. A method for producing a water-absorbing resin recited in claim 1 , successively comprising: a polymerization step of polymerizing an acrylic acid (salt)-based monomer-containing monomer composition so as to obtain a crosslinked hydrogel polymer; a drying step of drying the crosslinked hydrogel polymer that has been obtained in the polymerization step; and a surface-crosslinking step, said method further comprising, at or after an end of the polymerization step, the step of adding an amino group-containing reducing agent.

12. The method according to claim 11 , wherein said method includes, at or after an end of the surface-crosslinking step, the step of adding the amino group-containing reducing agent.

13. The method according to claim 11 , wherein said method includes the step of adding the amino group-containing reducing agent as an aqueous solution.

14. The method according to claim 11 , wherein the amino group-containing reducing agent contains a hydrazide group-containing compound.

15. A method for producing a water-absorbing resin, comprising the step of adding a water-based liquid in a droplet state to a surface-crosslinked water-absorbing resin so that the surface-crosslinked water-absorbing resin to which the water-based liquid has been added has a moisture content of 7.5 mass % or more, and then drying the surface-crosslinked water-absorbing resin, to which the water-based liquid has been added, so that the moisture content is reduced by an amount of 7.5 mass % or more within one hour.

16. A method recited in claim 15 , further comprising at least one of the following steps (A) and (B):
(A) adding a water-based liquid in a droplet state to the surface-crosslinked water-absorbing resin that has a specific surface area of 25 m 2 /kg or more; and
(B) successively including a polymerization step, a drying step of drying a hydrogel having been obtained in the polymerization step, and a surface-crosslinking step, and adding a volatile component reducing agent at or after an end of the polymerization step.

17. The method according to claim 16 , wherein said method includes the step (A) of adding a water-based liquid in a droplet state to the surface-crosslinked water-absorbing resin that has a specific surface area of 25 m 2 /kg or more, and in a case where the water-based liquid is added so that the surface-crosslinked water-absorbing resin to which the water-based liquid has been added has a moisture content of 27.5 mass % or more, the surface-crosslinked water-absorbing resin, to which the water-based liquid has been added, is dried so that the surface-crosslinked water-absorbing resin has a moisture content of 20 mass % or less within one hour.

18. The method according to claim 16 , wherein said method includes the step (B) of successively including a polymerization step, a drying step of drying a hydrogel having been obtained in the polymerization step, and a surface-crosslinking step, and adding a volatile component reducing agent at or after an end of the polymerization step.

19. A method for producing a water-absorbing resin, comprising the step of bringing the water-absorbing resin into contact with a supercritical solvent so as to remove a volatile component from the water-absorbing resin,
the water-absorbing resin containing a polyacrylic acid (salt)-based resin as a main component,
the water-absorbing resin being internally crosslinked, and
the water-absorbing resin being surface-crosslinked.

Assignees

• Nippon Catalytic Chem Ind

Inventors

• Nishimura Kimiaki
• Tanaka Nobuya
• Arai Tomoya
• Kimura Kazuki
• Horie Kazushi
• Tada Kenji

Classifications

• C08J2333/02

  Homopolymers or copolymers of acids; Metal or ammonium salts thereof · CPC title

• C08J3/245

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

• B01J2220/68

  Superabsorbents · CPC title

• B01J20/3282

  Crosslinked polymers · CPC title

• B01J20/28059

  being less than 100 m2/g · CPC title