Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2003-11-13
2004-12-14
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S403000, C524S556000
Reexamination Certificate
active
06831122
ABSTRACT:
The present invention relates to a water absorbent comprising particles of a water absorbent polymer, a process for its production and the use of the water absorbent for absorbing body fluids, for producing hygiene articles and for soil improvement.
Water absorbent polymers, which are also referred to as hydrogel-forming polymers or superabsorbent polymers (hereinafter abbreviated to SAPs), are known. They are networks of flexible hydrophilic polymers, which can be not only ionic but also nonionic in nature. They are capable of absorbing and binding aqueous fluids by forming a hydrogel. A comprehensive survey of SAPs, their use and their manufacture is given in F. L. Buchholz and A. T. Graham (editors) in “Modern Superabsorbent Polymer Technology”, Wiley-VCH, New York, 1998.
SAPs are used in particular in hygiene articles such as diapers, incontinence pads and briefs, sanitary napkins and the like to absorb body fluids. A frequent problem is here that the superabsorbent at the point of ingress of the fluid swells to a substantial extent and forms a barrier layer for subsequent amounts of fluid. This prevents any transmission and distribution of the fluid in the absorbent core. This superabsorbent phenomenon is known as gel-blocking. Subsequent amounts of fluid are then no longer absorbed by the absorbent core, with the consequences of uncontrolled distribution of the fluid on the diaper surface and leakage in the extreme case.
DE-A-3 523 617, U.S. Pat. No. 4,734,478 and U.S. Pat. No. 4,286,082 describe water absorbent resins containing silicon dioxide in admixture. The silicon dioxide added is said to reduce the caking tendency of the resin. WO 87/00848 describes the use of colloidal carrier materials, such as colloidal silica, to enhance the gel strength.
WO 95/11932 discloses the addition of finely divided silica to the surface postcrosslinker solution. EP-386 897 discloses the use of polyvalent metal ions as crosslinkers. The polyvalent metals are used in the form of their water soluble salts. However, the performance profile of the water absorbents described is not in every respect satisfactory.
It is an object of the present invention to provide water absorbents possessing improved application properties, especially high absorption capacities under pressure, improved fluid transportation performance and a faster swell rate.
We have found that this object is achieved according to the invention by a water absorbent comprising particles of a water absorbent polymer whose surface is associated with a water insoluble metal phosphate.
The invention further provides a process for producing a water absorbent as claimed in any preceding claim, which comprises
a) intimately mixing a particulate water absorbent polymer with a finely divided water insoluble metal phosphate; or
b) applying a slurry of a finely divided water insoluble metal phosphate to a particulate water absorbent polymer; or
c) contacting a first aqueous solution containing phosphate ions with a second aqueous solution in the presence of a particulate water absorbent polymer, said second solution containing a water soluble salt of a metal forming a water insoluble phosphate.
Conveniently, the water absorbent of the invention generally has a Saline Flow Conductivity (SFC) of at least 30×10−
7
cm
3
·s/g, an Absorbency Under Load (AUL) (0.7 psi) of at least 20 g/g and a Centrifuge Retention Capacity (CRC) of at least 24 g/g.
The term “associated” is to be understood in the broadest sense and shall comprehend any kind of interaction between the water insoluble metal phosphate and the surface of the particles of the polymer. “Associated” means that the water insoluble metal phosphate is disposed virtually exclusively on the surface of the particles of the water absorbent polymer and only to an insignificant extent, if at all, in the body of the particles. Generally the water insoluble metal phosphate is associated by physical interaction, for example encapsulated in surface irregularities or voids close to the surface.
Useful water insoluble metal phosphates also include phosphates which can be viewed as “phosphates” in the technical sense and can be considered, for example, as mixed phosphate oxides, phosphate hydroxides, phosphate silicates, phosphate fluorides or the like.
Preferred water insoluble metal phosphates are water insoluble metal phosphates which comprise a phosphate of the formula M
4
P
2
O
7
, M
2
HPO
4
or M
3
PO
4
wherein M is one equivalent of a metal selected from the group consisting of calcium, magnesium, strontium, barium, zinc, iron, aluminum, titanium, zirconium, hafnium, tin, cerium, scandium, yttrium and lanthanum or mixtures thereof. M can also comprise alkali metal phosphates, as long as the mixed phosphate is water insoluble.
Preferred phosphates are calcium hydrogenphosphate, tertiary calcium phosphate, apatite, Thomas flour of the formula Ca
5
(PO
4
)[SiO
4
], berlinite of the formula AlPO
4
, rhenania phosphate of the formula 3CaNaPO
4
.VCa
2
SiO
4
. Particular preference is given to tertiary calcium phosphate, calcium hydrogenphosphate and apatite. The term “apatite” comprehends fluoroapatite, hydroxyl apatite, chloroapatite, carbonate apatite and carbonate fluoroapatite. It will be appreciated that mixtures of various water insoluble metal phosphates can be used as well.
When the water absorbent is to be used in a hygiene article, especially physiologically safe water insoluble metal phosphates and mixtures thereof come into consideration, such as tertiary calcium phosphate, hydroxyl apatite or calcium hydrogenphosphate.
The fraction of the water insoluble metal phosphate is customarily in the range of about 0.001-10% by weight, preferably from 0.01 to 5% by weight and very particularly preferably from 0.05 to 2.5% by weight, based on the weight of the water absorbent polymer.
Useful water absorbent polymers are in particular polymers of hydrophilic monomers, graft copolymers of one or more hydrophilic monomers on a suitable grafting base, crosslinked cellulose or starch ethers, crosslinked carboxymethylcellulose, partially crosslinked polyethers or natural products that are swellable in aqueous fluids, such as guar derivatives, alginates and carrageenans.
Suitable grafting bases may be of natural or synthetic origin. They include starches, i.e., native starches from the group consisting of corn (maize) starch, potato starch, wheat starch, rice starch, tapioca starch, sorghum starch, manioca starch, pea starch or mixtures thereof, modified starches, starch degradation products, for example oxidatively, enzymatically or hydrolytically degraded starches, dextrins, for example roast dextrins, and also lower oligo- and polysaccharides, for example cyclodextrins having from 4 to 8 ring members. Useful oligo- and polysaccharides further include cellulose and starch and cellulose derivatives. It is also possible to use polyvinyl alcohols, polyamines, polyamides, hydrophilic polyester or polyalkylene oxides, especially polyethylene oxide and polypropylene oxide. Useful polyalkylene oxides have the general formula I:
where
R
1
, R
2
are independently hydrogen; C
1
-C
4
-alkyl; C
2
-C
6
-alkenyl; aryl, especially phenyl; or (meth)acryloyl;
X is hydrogen or methyl, and
n is an integer from 1 to 1000, especially from 10 to 400.
Polymers of monoethylenically unsaturated acids are preferred as water absorbent polymers. Polymers of monoethylenically unsaturated acids are preferably at least partly present in the form of their salts, especially their alkali metal salts, such as sodium or potassium salts, or as ammonium salts. Polymers of this kind are particularly good at gelling on contact with aqueous fluids.
Particular preference is given to crosslinked water absorbent polymers of monoethylenically unsaturated C
3
-C
6
-carboxylic acids and/or their alkali metal or ammonium salts. Preference is given in particular to crosslinked polyacrylic acids where from 25 to 100% of the acid groups are present as alkali metal or ammonium salts.
Polymers of this kind are obtained for e
Daniel Thomas
Riegel Ulrich
Weismantel Matthias
Marshall & Gerstein & Borun LLP
Pezzuto Helen L.
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