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...
Patent
1998-05-20
2000-11-07
Mosley, Terressa
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...
C08L 2904
Patent
active
061438219
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to powdery absorbents for water and aqueous liquids based on water-swellable, but not water-soluble polymers. These cross-linked polymers based on acid groups-containing monomers are obtained by using a special combination of two precross-linking agents and one secondary cross-linking agent. They show property combinations of high retention, high absorption under pressure, low soluble constituents, and rapid liquid absorption, which have not been achieved as yet.
Commercially available superabsorbent polymers are mainly cross-linked polyacrylic acids or cross-linked starch/acrylic acid-graft copolymers wherein the carboxyl groups are partially neutralized with sodium or potassium ions.
These polymers are used, for example, in hygienic articles capable of absorbing body fluids, such as urine, and in materials to sheathe cables. Here, they absorb large amounts of aqueous liquids and body fluids, such as urine or blood, under swelling and formation of hydrogels. Additionally, it is necessary to retain the absorbed liquid amount under the typical pressure during application. While advancing superabsorbent polymers, the requirements made on these products have substantially changed in the last years. Initially, only the very high swelling capacity on contact with liquids had been the main factor in the development of superabsorbers; however, it was found later that, in addition to the absorbed liquid amount, the stability of the swollen gel is also of importance. However, retention on the one hand, and stability of the swollen gel on the other one, represent contrary properties, as has been known from U.S. Pat. No. 3,247,171. This means that polymers having a particularly high retention only have a poor rigidity of the swollen gel with the result that the gel is deformable under an exerted pressure (e.g., body load) and therefore impairs further liquid absorption. This specific absorption property, which is referred to as "absorption under pressure" (AUP) in the Anglo-Saxon usage, is described in U.S. Pat. No. 5,314,420, for example. With the increasing requirements made on superabsorbers in the hygienic field, it was found that the initial load of 21 g/cm2 (0.3 psi) no longer corresponded to the desired property standard necessary for incontinence products or diaper constructions with low fluff contents and large amounts of superabsorber. For this reason, pressure loads of 49 g/cm2 (0.7 psi) are demanded today.
Although the skilled artisan is familiar with methods of producing products having, for example, a high retention or a high absorption or low soluble constituents or a rapid water absorption, achieving all of these four positive properties at the same time has not been possible with formulations known as yet. For example, it is well known to the skilled artisan that increasing the cross-linker concentration results in products with a low soluble content. However, this also results in products having a poor retention. Decreasing the cross-linker concentration, on the other hand, results in products with a high retention, but also with high soluble constituents and, due to gel blocking, with slow water absorption.
The effort to obtain products with high gel volume, high gel stability, and low soluble constituents, which is described in U.S. Pat. No. Re 32,649, resulted in the desired product properties only when the cross-linking agent methylenebisacrylamide which splits off the carcinogenic acrylamide was used. For this reason, it is not possible to use such products in hygienic articles.
Along with a high level of retention and liquid absorption under pressure, the content of soluble polymer chains in the superabsorbers must be as low a possible. These arise as a result of incomplete cross-linkage during polymerization. In use these soluble constituents are incompletely retained in the swollen polymer body. This results in reduced superabsorber performance because of nonuniform liquid distribution in the diaper; moreover, in extreme cases, these soluble constituents can esc
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Mosley Terressa
Stockhausen GmbH & Co. KG
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