Acrylic acid composition and its production process, and process for producing water- absorbent resin using this acrylic acid composition, and water-absorbent resin

• US 20040110914A1
• Filed: 09/16/2003
• Published: 06/10/2004
• Est. Priority Date: 12/19/2001
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Nakashima, Yasuhisa, Sakamoto, Kazuhiko, Fujimaru, Hirotama, Nakahara, Sei
• Granted Patent: US 7,049,366 B2
• Time in Patent Office: Days
• US Class Current: 526/317.1
• 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

In order to produce inexpensively with high productivity a water-absorbent resin of which: the residual monomer content and the water-extractable content are both low, and the properties are high, and the colorability is low; there is provided a process for producing a water-absorbent resin, which is a process for producing a crosslinked water-absorbent resin by polymerizing a monomer component including acrylic acid and/or its salt in a major proportion wherein the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane, with the process being characterized by comprising the steps of: preparing the monomer component from an acrylic acid composition that includes the unneutralized acrylic acid and a methoxyphenol and has a methoxyphenol content of 10 to 160 ppm by weight (based on the unneutralized acrylic acid); and then carrying out radical and/or ultraviolet polymerization of the resultant monomer component.

Claims

1. A process for producing a water-absorbent resin, which is a process for producing a crosslinked water-absorbent resin by polymerizing a monomer component including acrylic acid and/or its salt in a major proportion of the monomer component wherein the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane,

with the process being characterized by comprising the steps of preparing the monomer component from an acrylic acid composition that includes the unneutralized acrylic acid and a methoxyphenol and has a methoxyphenol content of 10 to 160 ppm by weight (based on the weight of the unneutralized acrylic acid);

and then carrying out radical and/or ultraviolet polymerization of the resultant monomer component.

4. A process according to any one of claims 1 to 3, wherein the step of carrying out the radical and/or ultraviolet polymerization is carried out in the presence of a transition metal ion.

5. A process according to claim 4, wherein the monomer component has a transition metal ion content of 0.1 to 2 ppm by weight in terms of transition metal.

6. A process according to any one of claims 1 to 5, wherein the acrylic acid composition has a protoanemonin and/or furfural content of not more than 20 ppm by weight (relative to the monomers).

7. A process according to any one of claims 1 to 6, further comprising the step of crosslinking surfaces of the resultant resin and their neighborhoods.

8. A process according to any one of claims 1 to 7, involving use of a polymerization initiator including hydrogen peroxide.

9. A process according to any one of claims 1 to 8, wherein the monomer component has a neutralization ratio of not more than 75 mol %.

10. A process according to any one of claims 1 to 9, wherein the polymerization is initiated within 24 hours after the preparation of the monomer component and/or neutralization of the acrylic acid.

11. A process according to any one of claims 1 to 10, further comprising the steps of, within 1 hour after the polymerization, starting to dry the resultant polymer;

and then forming a powder having a weight-average particle diameter in the range of 300 to 500 μ

m wherein the quantity of particles having particle diameters in the range of 850 to 150 μ

m is not less than 90 wt %.

12. A process according to any one of claims 1 to 11, wherein the unneutralized acrylic acid being used has a methoxyphenol content of 10 to 160 ppm by weight and is a product obtained by treating the acrylic acid by distillation and/or crystallization.

13. A process according to any one of claims 1 to 12, wherein the methoxyphenol is p-methoxyphenol.

14. A water-absorbent resin, being a product obtained by the process as recited in any one of claims 1 to 13,

with the water-absorbent resin displaying an absorption capacity of not less than 20 g/g under a load and/or a saline flow conductivity of not less than 20×

10<sup>−

7</sup> (cm³·

s·

g^{31 1}).

15. A sanitary material, comprising the water-absorbent resin as recited in claim 14.

2. A process for producing a water-absorbent resin, which is a process for producing a crosslinked water-absorbent resin by polymerizing a monomer component including acrylic acid and/or its salt in a major proportion wherein the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane,

the process being characterized by comprising the steps of:

preparing the monomer component from an acrylic acid composition that includes the unneutralized acrylic acid; and

then carrying out radical and/or ultraviolet polymerization of the resultant monomer component in the presence of a methoxyphenol in an amount of 10 to 160 ppm by weight relative to the weight of acrylic acid and/or its salt (based on the weight in terms of the unneutralized acrylic acid) in the monomer component.

3. A process for producing a water-absorbent resin, which is a process for producing a crosslinked water-absorbent resin by polymerizing a monomer component including acrylic acid and/or its salt in a major proportion wherein the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane,

the process being characterized by comprising the steps of:

treating an acrylic acid composition and/or its neutralized product with an adsorbing agent wherein the acrylic acid composition includes the unneutralized acrylic acid and a methoxyphenol; and

then preparing the monomer component from the resultant acrylic acid product; and

then carrying out radical and/or ultraviolet polymerization of the resultant monomer component.

16. An acrylic acid composition, comprising unneutralized acrylic acid and being used in producing a crosslinked water-absorbent resin by polymerizing a monomer component including acrylic acid and/or its salt in a major proportion wherein the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane,

with the acrylic acid composition being characterized by having a protoanemonin and/or furfural content of not more than 20 ppm by weight (relative to the unneutralized acrylic acid) and a methoxyphenol content of 10 to 160 ppm by weight relative to the unneutralized acrylic acid.

17. A process for producing an acrylic acid composition, which is a process for producing an acrylic acid composition comprising unneutralized acrylic acid and being used in producing a crosslinked water-absorbent resin by polymerizing a monomer component including acrylic acid and/or its salt in a major proportion wherein the acrylic acid is a product obtained by catalytic gas phase oxidation of propylene and/or propane,

with the process being characterized by comprising the step of carrying out treatment of methoxyphenol-containing acrylic acid by distillation and/or crystallization to adjust its methoxyphenol content into the range of 10 to 160 ppm by weight relative to the unneutralized acrylic acid.