Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
2000-08-23
2002-11-19
Kelly, Cynthia H. (Department: 1774)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S182000, C264S17800F, C264S211120, C264S211140, C264S211170, C428S364000, C428S397000, C428S400000
Reexamination Certificate
active
06482344
ABSTRACT:
TECHNICAL FIELD
The present invention relates, in general, to polymers that absorb aqueous liquids (such as water, blood, and urine). More particularly, the present invention relates to superabsorbent polymers, namely polymers that absorb over 20 times their weight in water, and even more particularly, the superabsorbent polymers are in the form of fibers which have unique absorbency against pressure characteristics as compared to previously known superabsorbent polymer fibers.
Definitions of Abbreviations
Abbreviation
Definition
AAP
absorbency against pressure
cm
centimeter
comp
comparison
X-linking
cross-linking
g
gram
hr
hour
&mgr;m
micrometer
mg
milligram
ml
milliliter
mm
millimeter
min
minute
DAP
1,5-diaminopentane
BDE
1,4-butanediol diolycidyl ether
DE
1,3-butadiene diepoxide
ppm
parts per million
PEG
Polyethylene glycol
psi
Pounds per square inch
RH
relative humidity
sec
second (note, 1/60 of a
minute)
NaOH
sodium hydroxide
SXL
Surface cross-linked
SAP
superabsorbent Polymer, a
polymer that absorbs over 20
times its weight in water
tea bag
TB
trifunctional polyethylene glycol
wt
weight
BACKGROUND ART
SAPs, namely highly water-swellable polymers, typically are prepared from an aqueous mixture of monomers. Usually, one or more network X-linking agents are incorporated into the monomer mixture. For particulate SAP, after the polymerization and X-linking have ended, the viscous resultant is dried and subjected to mechanical grinding to create a desired particle size distribution. Alternatively for SAP fibers, the polymerized monomers are extruded into fibers, such as by forcing through an orifice (i.e., extruding through a spinneret) into a gaseous medium (i.e., a warm air current for drying) or by dry spinning (i.e., mono-component spinning or sheath-core composite spinning), and then the X-linking agent in the post-polymerized extrudate is activated, such as being heat-activated or photo-activated, to result in SAP fibers.
Particles of SAPs are made by two polymerization methods, namely the solvent or solution polymerization method and the inverse suspension or emulsion polymerization method. On the other hand, fibers of SAPs are made by the solvent or solution polymerization method.
As discussed in more detail below, SAPs are useful in various absorbent articles, due to the ability of the SAPs to absorb aqueous liquids in a ready manner. For instance, the journal article “Keeping Dry with Superabsorbent Polymers”,
Chemtech,
(September, 1994) by Buchholz, contains an excellent discussion of various uses for SAPs, such as in sanitary articles (i.e., diapers, incontinence garments, etc.), in a sealing composite between concrete blocks that make up the wall of underwater tunnels, and in tapes for water blocking in fiber optic cables and power transmission cables. However, SAP fibers have found limited use due to poor absorbency against pressure and/or poor tensile strength, as opposed to SAP particulates which have good absorbency against pressure.
An excellent discussion of the manufacture of SAP fibers, for instance of polyacrylonitrile, can be seen in U.S. Pat. No. 4,873,143 (issued Oct. 10, 1989), U.S. Pat. No. 4,366,206 (issued Dec. 28, 1992), U.S. Pat. No. 4,374,175 (issued Feb. 15, 1983), and U.S. Pat. No. 4,507,204 (issued Mar. 26, 1985), all to Tanaka, assignor to Japan Exlan Company Limited.
Furthermore, an excellent discussion of the manufacture of SAP fibers, for instance of isobutylene/maleic anhydride copolymer, can be seen in U.S. Pat. No. 4,743,244 (issued May 10,1988), U.S. Pat. No. 4,813,945 (issued Mar. 21, 1989), U.S. Pat. No. 4,880,868 (issued Nov. 14,1989), U.S. Pat. No. 4,892,533 (issued Jan. 9, 1990), U.S. Pat. No. 4,731,067 (issued Mar. 15,1988), U.S. Pat. No. 5,026,784 (issued Jun. 25,1991), and U.S. Pat. No. 5,079,306 (issued Jan. 7, 1992), all to LeKhac, assignor to Arco Chemical Company.
Additionally, an excellent discussion of the manufacture of SAP fibers, for instance of acrylic acid/methyl acrylate copolymers, can be seen in U.S. Pat. No. 5,413,747 (issued May 9,1995), U.S. Pat. No. 5,466,731 (issued Nov. 14, 1995), and U.S. Pat. No. 5,607,550 (issued Mar. 4, 1997), all to Akers, assignor to Courtaulds Fibers (Holdings) Limited.
On the other hand, a good discussion of the methods for making SAP particles can be seen in U.S. Pat. No. 5,409,771 (issued Apr. 25, 1995) to Dahmen and Mertens, assignors to Chemische Fabrik Stockhausen GmbH. More specifically, this patent mentions that SAP particles are generally network X-linked polyacrylic acids or network X-linked starch-acrylic-acid-graft-polymers, the carboxyl groups of which are partially neutralized with sodium hydroxide or caustic potash, and that such SAP particles may be surface X-linked (which is discussed in detail below).
The disclosures of all patents and published patent applications that are mentioned are incorporated by reference.
SUMMARY OF THE INVENTION
A need still exists for SAP fibers with improved absorbency against pressure properties. A great advantage would be given to industry to provide such SAP fibers.
Therefore, the present invention provides a fiber comprising a surface cross-linked superabsorbent polymer fiber. Furthermore, the present invention provides an absorbent article comprising surface cross-linked superabsorbent polymer fibers. The resultant superabsorbent polymer fiber exhibits excellent absorbency against pressure characteristics, as measured by the AAP property test as defined below.
Also, the present invention provides a method for providing improved absorbency characteristics to superabsorbent polymer fibers. The method comprises providing superabsorbent polymer fibers that are free of a surface cross-linking treatment; mixing a surface cross-linking agent with the superabsorbent polymer fibers that are free of a surface cross-linking treatment; and heating the resultant mixture of the surface cross-linking agent and the superabsorbent polymer fibers that are free of a surface cross-linking treatment for a sufficient time at a sufficient temperature to achieve surface cross-linked superabsorbent polymer fibers having absorbency against pressure characteristics superior to the absorbency against pressure characteristics of the superabsorbent polymer fibers that are free of a surface X-linking treatment.
Additionally, the present invention affords a method for providing improved absorbency against pressure characteristics to superabsorbent polymer fibers in an absorbent article. The method comprises subjecting superabsorbent polymer fibers to a surface cross-linking treatment and forming an absorbent article from the resultant of the surface cross-linking treatment. The surface cross-linking treatment is accomplished by providing superabsorbent polymer fibers that are free of a surface cross-linking treatment; mixing a surface cross-linking agent with the superabsorbent polymer fibers that are free of a surface cross-linking treatment; and heating the surface cross-linking agent and the superabsorbent polymer fibers that are free of a surface cross-linking treatment for a sufficient time at a sufficient temperature to achieve surface cross-linked superabsorbent polymer fibers having absorbency against pressure characteristics superior to the absorbency against pressure characteristics of the superabsorbent polymer fibers that are free of a surface X-linking treatment.
Accordingly, it is an object of the present invention to provide a SAP fiber that obviates absorbency against pressure problems.
Moreover, it is an advantage of the present invention that an absorbent article employing the SAP fiber of the present invention exhibits little or no problems with SAP falling out from the edges of the absorbent article the way particulate SAP can.
Some of the objects of the invention having been stated, other objects and advantages will become evident as the description proceeds, when taken in connection with the Laboratory Examples described below.
DETAILED DESCRIPTION OF THE INVENTION
For the present invention, the inventive SAP fiber comprises non-surface X-
Hsu Whei-Neen
Joy Mark C.
Messner Bernfried A.
Gray J. M.
Kelly Cynthia H.
Smith Moore LLP
Stockhausen GmbH & Co. KG
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