Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1995-06-23
1997-11-04
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526310, C08F 3400, C08F22006, A61L 1500
Patent
active
056841060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
It is standard practice to provide superabsorbent polymeric material in the form of particles wherein the polymer has been obtained by copolymerization of monoethylenically unsaturated carboxylic monomer and polyethylenically unsaturated cross linking agent. The carboxylic monomer groups are usually at least partially neutralized, for instance at least 50% molar in the form of sodium salt.
In EP-A-339461, it is proposed to provide such superabsorbent material which can absorb at least 27 ml of aqueous saline (as hereinafter defined) per gram of superabsorbent material while under a restraining pressure of at least 21,000 dynes per square centimeter. Aqueous saline herein is to be understood as being an aqueous solution of sodium chloride containing 0.9 weight % sodium chloride and all absorbency values refer to the absorption of this.
EP 339461 does not describe how those polymers are to be made and does show that the absorption value tends to drop significantly as the load increases. For instance the absorption at 58,600 dynes per square centimeter in one example is 8 g/g compared to a value of 26 g/g at 20,700 dynes/cm.sup.2.
In EP 532002, it is proposed to test the absorption under a load provided by a 200 gram weight.
Although these absorption under load tests do give an indication of the ability of the superabsorbent material to absorb urine while under load, such tests indicate only one of several parameters that can be examined.
Another parameter is the centrifuge retention capacity, which indicates the volume of liquid that the superabsorbent will hold on to under applied pressure. About 200 mg of superabsorbent is sealed in a tea-bag of approx. size 6.35 cm.times.7.62 cm (2.5 inches.times.3 inches) and immersed in 0.9% sodium chloride solution for 30 mins. The tea-bag is removed and placed in a basket centrifuge for 3 mins. at 1600 rpm (centrifugal force approx. 250G). A tea-bag without polymer is used as the blank. ##EQU1##
Generally for commercial superabsorbents, this value is at least 28 g/g of 0.9 weight % sodium chloride solution.
Another parameter is the rewet parameter, which gives an indication of the performance of the polymer when combined with a fiber matrix in a diaper type construction.
Ideally, a superabsorbent material would give optimum properties in all these tests, but we have found that known polymers that satisfy the "absorption under load" (AUL) test of EP 339461 frequently give poor rewet test results.
It would therefore be desirable to be able to provide superabsorbent particulate polymeric material that gives better performance in use and, in particular, such material which complies with a parameter that is a better indication of overall performance properties.
SUMMARY OF THE INVENTION
According to the invention, we now provide a superabsorbent polymeric material which is in the form of particles, wherein
the polymeric material has been obtained by copolymerization of monoethylenically unsaturated carboxylic monomer and a polyethylenically unsaturated cross linking agent having at least three ethylenically unsaturated bonds,
the carboxylic groups in the polymer have been at least partially neutralized, and
the particulate material absorbs above 15 grams synthetic urine (i.e., aqueous saline as defined above) per gram polymeric material in 60 minutes under a load of 63,000 dynes per square centimeter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In order that the superabsorbent material has good performance properties in use, these improved "absorption under high load" values should be accompanied by conventional, commercially suitable, centrifuge retention capacity values of at least about 28 g/g and often in the range 29 or 30 up to, for instance, 33 or 34 or in some instances higher, such as up to 36 or more.
In order to obtain the improved absorption under load characteristics while maintaining conventional commercial centrifuge retention capacity, it is necessary to optimize the processes of making the particulate superabsorbent
REFERENCES:
DD292642 91/08/08 Jaeger et al--abstract pp. 9-11.
DD292219 91/07/25 Wandrey et al--abstract pp. 12-13.
"Gelation in the polymerization of tetraallylammonium chloride" Matsumoto et al. Makromol Chem. Rapid Commun 10(1) 1989 abstract pp. 16-17.
Couldwell Pauline Lesley
Johnson Ian Michael
Allied Colloids Limited
Sarofim N.
Schofer Joseph L.
LandOfFree
Superabsorbent polymers and products containing them does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Superabsorbent polymers and products containing them, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Superabsorbent polymers and products containing them will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1833825