EP0248437A2
Expired / Lapsed
EP
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A process for improving a water absorbent polyacrylic acid polymer and an improved polymer produced by said process
Assignee: Maruha Nichiro Corp
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Filing: 1987-06-04
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Granted: —
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Expires: 2007-06-04
Abstract
Abstract A process for improving a water absorbent polyacrylic acid polymer in which the polymer is contacted with an aqueous solution containing a water soluble peroxide radical initiator, followed by heating, thereby causing substantially only the surface portion of the polymer to undergo crosslinking with the radical initiator while leaving the remaining core portion of the polymer substantially intact. The improved water absorbent polyacrylic acid polymer is excellent in both water absorbency and water absorption rate, and the hydrogel resulting from absorption of water has a pleasant, non-sticky feel. The improved water absorbent polyacrylic acid polymer can be advantageously utilized to produce a desirable disposable diaper, sanitary napkin, surgical pad, surgical sheet, paper towel or the like.
Inventors
- 👤 Kazuo Saotome
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 01:46
CPC Classifications
C; C08; C08J; C08J3/00; C08J3/24; C08J3/245; C08J2333/00; C08J2333/02
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
135 words
A process for improving a water absorbent polyacrylic acid polymer with respect to absorption characteristics thereof which comprises the steps of: (1) contacting with the surface of a water absorbent polyacrylic acid polymer an aqueous solution containing a water soluble peroxide radical initiator, the weight ratio of the water in said aqueous solution to said polymer being from 0.01 to 0.5, thereby causing said polymer substantially only at its surface portion to have said solution absorbed therein; and (2) heating the resulting polymer with its surface portion having said solution absorbed therein at a temperature such that said initiator is decomposed but said polymer is not decomposed, thereby causing said polymer at its surface portion to undergo crosslinking by the action of said initiator while leaving the remaining core portion of said polymer substantially intact.
Claim 2
Dependent Claim
135 words
A process for improving a water absorbent polyacrylic acid polymer with respect to absorption characteristics thereof which comprises the steps of: (1) contacting with the surface of a water absorbent polyacrylic acid polymer an aqueous solution containing a water soluble peroxide radical initiator, the weight ratio of the water in said aqueous solution to said polymer being from 0.01 to 0.5, thereby causing said polymer substantially only at its surface portion to have said solution absorbed therein; and (2) heating the resulting polymer with its surface portion having said solution absorbed therein at a temperature such that said initiator is decomposed but said polymer is not decomposed, thereby causing said polymer at its surface portion to undergo crosslinking by the action of said initiator while leaving the remaining core portion of said polymer substantially intact.
Claim 3
Dependent Claim
39 words
A process according to claim 1, wherein said weight ratio is in the range of from 0.02 to 0.3, preferably in the range of from 0.02 to 0.2 and more preferably in the range of from 0.03 to 0.1.
Claim 4
Dependent Claim
40 words
A process according to claim 1 or 2, wherein said initiator is at least one member selected from the group consisting of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, oxalic acid peroxide, acetic acid peroxide and succinic acid peroxide.
Claim 5
Dependent Claim
69 words
A process according to any of the claims 1 to 3, wherein said initiator is contained in said aqueous solution in an amount of from 0.01 to 10 % by weight based on the polymer, preferably in an amount of from 0.1 to 5 % by weight based on the polymer, and most preferably in an amount of from 0.2 to 2 % by weight based on the polymer.
Claim 6
Dependent Claim
20 words
A process according to any of the claims 1 to 4, wherein said aqueous solution further contains a crosslinking auxiliary.
Claim 7
Dependent Claim
17 words
A process according to claim 5, wherein said crosslinking auxiliary is a hydrophilic polyfunctional olefinically unsaturated compound.
Claim 8
Dependent Claim
29 words
A process according to claim 6, wherein said unsaturated compound is at least one member selected from the group consisting of N,Nʹ-methylenebisacrylamide, ethylene glycol bis(meth)acrylate and polyethylene glycol bis(meth)acrylate.
Claim 9
Dependent Claim
23 words
A process according to any of the claims 1 to 7, wherein said aqueous solution further contains a water miscible volatile organic solvent.
Claim 10
Dependent Claim
32 words
A process according to claim 8, wherein said aqueous solution contains said volatile organic solvent in an amount of from 0.5 to 10 parts by volume per part by volume of water.
Claim 11
Dependent Claim
73 words
1O. A process according to any of the claims 1 to 9, wherein said water absorbent polyacrylic acid polymer is at least one member selected from the group consisting of a crosslinked acrylic acid homopolymer, a crosslinked acrylic acid copolymer, a saponification product of a copolymer of vinyl acetate and an acrylic ester, a graft crosslinked polymer of starch and acrylic acid and a hydrolyzate of a graft polymer of starch and acrylonitrile.
Claim 12
Dependent Claim
36 words
A process according to any of the claims 1 to 1O, wherein said water absorbent polyacrylic acid polymer is a gel capable of absorbing from 300 to 1000 g of water per g of the gel.
Claim 13
Dependent Claim
28 words
A process according to any of the claims 1 to 11, wherein said water absorbent polyacrylic acid polymer is in a particulate form, fibrous form or film form.
Claim 14
Dependent Claim
42 words
A process according to claim 12, wherein said polymer is in a particulate form and has an average particle diameter of from 10 to 3000 µm, preferably of from 50 to 1000 µm, and most preferably of from 100 to 500 µm.
Claim 15
Dependent Claim
25 words
A process according to claim 12, wherein said polymer is in a film form and has a film thickness of from 5 to 1000 µm.
Claim 16
Dependent Claim
25 words
A process according to claim 12, wherein said polymer is in a fibrous form and has a fiber diameter of from 5 to 1000 µm.
Claim 17
Dependent Claim
31 words
A process according to any of the claims 1 to 15, wherein said contacting is performed by spraying said aqueous solution onto the surface of the water absorbent polyacrylic acid polymer.
Claim 18
Dependent Claim
24 words
A process according to any of the claims 1 to 16, wherein said decomposition of the peroxide radical initiator is completed within 10 minutes.
Claim 19
Dependent Claim
39 words
A process according to any of the claims 1 to 17, wherein said water absorbent polyacrylic acid polymer has carboxyl groups, from 60 to 90 % by mole of which is in the form of an alkali metal salt.
Claim 20
Dependent Claim
32 words
A process according to any of the claims 1 to 18, wherein said polymer with its surface portion having said aqueous solution absorbed therein is heated in an atmosphere of superheated steam.
Claim 21
Dependent Claim
19 words
An improved water absorbent polyacrylic acid polymer obtainable by a process of any one of claims 1 to 19.
References Cited (Backward Citations)
No citation records indexed.
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