Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1993-06-07
1995-10-03
McCamish, Marion E.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
522 3, 522 84, C08F 246
Patent
active
054552842
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for transforming superfines of water-swellable polymers into a form in which they can be reused in application technology, i.e., the present invention relates to a recycling process for these superfines.
In the production of water-swellable polymers, portions of fine particles inevitably result which, due to their small size, cannot be used, e.g., in diapers and incontinency articles, because they lead to dosage difficulties and formation of dust; in addition they have a reduced swell capacity. Fines in water-swellable polymer particles result in products having a reduced swell capacity which is caused by the so-called blocking, i.e., the mixture of particles is blocked up against advancing liquid. Due to the above-mentioned reasons, polymeric fines of smaller than 200 .mu.m, preferably smaller than 100 .mu.m, are separated prior to their use in hygienic articles.
The production of water-swellable polymers is known. U.S. Pat. No. 4,698,404 describes a typical process for the production of water-swellable polymeric particles by inverse suspension polymerization of an aqueous solution consisting of acrylic acid and alkali- or ammonium acrylate in a hydrocarbon and cross-linkage of the polymer.
European patent application A1 0205674 describes the solution polymerization of substantially acid-groups-containing monomers in the presence of an agent having cross-linking activity. After the acid groups in the polymer are neutralized by at least 25% and the polymer gel is dried, a water-swellable polymer with a high gel strength and small amounts of extractable portions is obtained.
European patent application A2 0312952 describes the polymerization of carboxyl-groups-containing monomers, which are neutralize d to the extent of at least 20%, in the presence of dispersed cross-linking agents. European patent application A2 0280541 describes the continuous copolymerization of an acrylic acid-containing monomer solution wherein at least 20% of the acrylic acid is present in neutralized form.
Superfines result in all production processes of water-swellable polymer particles, irrespective of the process form, i.e., solution-, emulsion-, suspension-, or graft polymerization. These superfines deteriorate the properties of the polymer in application technology. They automatically result during the polymerization or subsequent reprocessing operations. These superfines of a size smaller than 200 .mu.m, in particular smaller 100 .mu.m, are separated from the homogeneous mixture, e.g., by screening, prior to the use in hygienic articles. Depending on the fineness of mesh, up to 25% of water-swellable superfines turn up which, up to now, have found limited use in very special forms of application.
Since the water-swellable polymeric superfines are of a great value, many attempts have been made to transform them into a reusable form, e.g., by agglomeration. DE-OS 37 41 157 describes the build-up of granular material by thermally treating a mixture consisting of water-swellable, polymeric superfines with powdery solids capable of being molten or sintered. DE- OS 37 41 158 describes a process for the agglomeration of water-swellable polymeric superfines which is characterized by the fact that: solutions or dispersions are used to build up agglomerates. The disadvantage of agglomerated superfines is their low stability under mechanical stress which, for example, occurs during transport or processing.
U.S. Pat. No. 4,950,692 describes a process for reprocessing water-swellable, polymeric superfines to form a so-called superabsorber, i.e., a polymeric material capable of absorbing large amounts of water or body liquids, in which process the superfines are converted into a gel by means of an aqueous solution and the gel is ground and dried. The aqueous solution used for the formation of the gel comprises a persulfate salt. Treating the water-swellable polymeric superfines with water in order to obtain a homogeneous gel is very expensive from the process technologic point of view, since the di
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Brehm Helmut
Dahmen Kurt
Mertens Richard
Chapman Mark A.
Chemische Fabrik Stockhausen GmbH
McCamish Marion E.
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