Hydrophilic resin, absorbent article, and acrylic acid for polymerization

• US 6,444,744 B1
• Filed: 02/27/1999
• Issued: 09/03/2002
• Est. Priority Date: 03/11/1998
• Status: Expired due to Term

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Fujimaru, Hirotama, Nakahara, Sei, Harada, Nobuyuki
• Primary Examiner(s): Wilson, Donald R.
• Application Number:
  US09/258,503
• Time in Patent Office: 1,284 Days
• Field of Search: 526/77, 526/317.1, 526/318.5, 524/556
• US Class Current: 524/556
• CPC Class Codes: A61L 15/24 Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof A61L15/225 takes precedence
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 20/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08L 33/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof

Abstract

The invention provides a hydrophilic resin and an absorbent article, both of which display still less coloring and discoloring when preserved for a long time. The hydrophilic resin is any one of: 1) a hydrophilic resin, obtained by a process including the step of polymerizing a monomer component including a major proportion of either one or both of acrylic acid and its salt which merely have a content of at most 0.20 ppm in total of hydroquinone and benzoquinone; 2) a hydrophilic resin, comprising a major proportion of an acrylic polymer and a minor proportion of either one or both of hydroquinone and benzoquinone, with the hydrophilic resin further comprising a quinhydronation inhibitor of 10˜1,000,000 times the total weight of hydroquinone and benzoquinone; 3) a hydrophilic resin, comprising a major proportion of an acrylic polymer and merely having a coloring degree (YI) of at most 20 after being left under conditions of the open system, 70° C., 65% RH for 1 week; and 4) a hydrophilic resin, which is a water-absorbent resin and is surface-crosslinked or surface-impregnated with a polyhydric alcohol and displays pH of 5.5 or less in a physiological salt solution and has an absorption capacity of 20 g/g or more for a physiological salt solution under a load of 50 g/cm². In addition, the absorbent article comprises the above hydrophilic resin.

Claims

1. A crosslinked water-absorbent resin which is internally-crosslinked, which is obtained by aqueous solution polymerization or reverse-phase suspension polymerization, which has a water-soluble content of 25 weight % or below, which has an absorption capacity of 20 g/g or more for a physiological salt solution under a load of 50 g/cm², over a period of 60 minutes, wherein the physiological salt solution is 0.9 wt % aqueous sodium chloride solution and which is obtained by a process comprising the steps of:

a) producing an acrylic acid, wherein hydroquinone is used in the step of producing the acrylic acid in an amount greater than 0.20 ppm “

based on acrylic acid”

;

b) reducing a total amount of hydroquinone and benzoquinone in the acrylic acid or its salt to at most 0.20 ppm “

based on acrylic acid”

;

c) providing a monomer component, wherein a major portion of the monomer component is one or both of the acrylic acid or its salt; and

d) polymerizing the monomer component to obtain the crosslinked water-absorbent resin.

2. A crosslinked water-absorbent resin according to claim 1, wherein polymerization of the monomer component is aqueous solution polymerization.

3. A crosslinked water-absorbent resin according to claim 1, obtained by a process further including the step of heat-drying at 100˜

300°

C. within 3 hours after the step of polymerizing the monomer component.

4. A crosslinked water-absorbent resin according to claim 1, comprising particles of an irregular pulverized shape, of which 50 weight % or more have a particle diameter of 300 μ

m or more.

5. A crosslinked water-absorbent resin according to claim 1, which has a water content of at most 2 weight %.

6. A crosslinked water-absorbent resin according to claim 1, which is a partially neutralized resin.

11. A crosslinked water-absorbent resin according to claim 1, which displays a pH of 5.5 or less in a physiological salt solution that is a 0.9 wt % aqueous sodium chloride solution.

12. A crosslinked water-absorbent resin according to claim 1, of which 50 weight % or more have a particle diameter of 300 μ

m or more.

15. A crosslinked water-absorbent resin according to claim 1, wherein the amount of hydroquinone used in the producing process for acrylic acid is not less than 10 ppm “

based on acrylic acid”

.

7. A crosslinked water-absorbent resin having a water-soluble content of 25 weight % or below, comprising a major proportion of an acrylic polymer which is obtained by a process including the step of polymerizing a monomer component including a major proportion of either one or both of acrylic acid and its salt, wherein the crosslinked water-absorbent resin has an absorption capacity of 20 g/g or more for a physiological salt solution under a load of 50 g/cm² over a period of 60 minutes, wherein the physiological salt solution is 0.9 wt % aqueous sodium chloride solution, and wherein the coloring degree (YI) is at most 20 after the crosslinked water-absorbent resin is left exposed to the atmosphere at 70°

C. and 65% RH for 1 week.

8. A crosslinked water-absorbent resin according to claim 7, which displays a change of the coloring degree (YI) by at most 4.

9. A crosslinked water-absorbent resin according to claim 7, wherein the acrylic polymer is a polymer as obtained by a process including the step of aqueous solution polymerization.

10. A crosslinked water-absorbent resin according to claim 7, comprising particles of the irregular pulverized shape, of which 50 weight % or more have a particle diameter of 300 μ

m or more.

13. A crosslinked water-absorbent resin according to claim 7, which displays a pH of 5.5 or less in a physiological salt solution that is a 0.9 wt % aqueous sodium chloride solution.

14. A crosslinked water-absorbent resin according to claim 7, of which 50 weight % or more have a particle diameter of 300 μ

m or more.

16. A crosslinked water-absorbent resin having a water-soluble content of 25 weight % or below and further having an absorption capacity of 20 g/g or more for a physiological salt solution under a load of 50 g/cm² over a period of 60 minutes wherein the physiological salt solution is a 0.9 wt % aqueous sodium chloride solution, wherein the crosslinked water-absorbent resin is obtained by a process including the step of polymerizing a monomer component including a major proportion of either one or both of acrylic acid and its salt which have a content of at most 0.20 ppm in total of hydroquinone and benzoquinone “

based on acrylic acid”

.

17. A crosslinked water-absorbent resin which has an absorption capacity of 20 g/g or more for a physiological salt solution under a load of 50 g/cm² over a period of 60 minutes wherein the physiological salt solution is a 0.9 wt % aqueous sodium chloride solution, which has a water-soluble content of 25 weight % or below and which is obtained by a process comprising the steps of:

a) producing an acrylic acid, wherein hydroquinone is used in the step of producing the acrylic acid in an amount greater than 0.20 ppm “

based on acrylic acid”

;

b) reducing a total amount of hydroquinone and benzoquinone in the acrylic acid or its salt to at most 0.20 ppm “

based on acrylic acid”

;

c) providing a monomer component, wherein a major portion of the monomer component is one or both of the acrylic acid or its salt; and

d) polymerizing the monomer component to obtain the cross-linked water-absorbent resin.