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
2000-03-21
2002-06-11
Niland, Patrick D. (Department: 1714)
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...
C174S118000, C174S11000P, C385S115000, C525S119000, C525S326300, C525S329700, C525S330200
Reexamination Certificate
active
06403700
ABSTRACT:
The present invention relates to water-insoluble, water-swellable polymers having a high absorption capacity for water and aqueous liquids, which are based on cross-linked, hydrophilic homopolymers and copolymers, as well as on graft polymers of ethylenically unsaturated, acid groups-containing, polymerizable monomers. The present invention further relates to the production method and the use of these polymers
Polymers absorbing large amounts of aqueous liquids, in particular body fluids such as urine, are known as superabsorbent polymers.
The absorbent s are produced by radical polymerization under preferred use of monoethylenically unsaturated carboxylic acids, such as acrylic acid and its alkali salts, in aqueous solution, or according to the methods of inverse suspension or emulsion polymerization which are described in U.S. Pat. No. 4,286,082, DE 27 06 135, U.S. Pat. No. 4,340,706, DE 37 13 601, and DE 2840 010.
Polymers having different absorption properties can produced by selection of the monomer composition, cross-linkers, and polymerization conditions and processing conditions for the polymer gel. Additional possibilities are offered by the production of graft polymers, for example, by using chemically modified starch, cellulose, and polyvinyl alcohol according to DE 26 12 846, and by aftertreating the polymer gels or powdery resins by secondary surface cross-linkage of the polymer particles, for example, according to DE 40 20 780 C1.
For application of the polymers in hygienics and the sanitary field, polymers are produced whose neutralization degree ranges between 50 and 80 mol-%, relative to the polymerized, acid groups-containing monomer units, so that hydrogels are formed which have a skin neutral effect when used.
The degree of neutralization may be adjusted in different manners, neutralization or partial neutralization of the acidic monomers frequently being carried out prior to polymerization. However, neutralization or partial neutralization of a hydrogel comprising acidic, polymerized monomer units is also known.
According to EP205 674 A1 advantageously fully acidic polymers are produced at temperatures ranging from 0 to 100° C., preferably 5 to 40° C., which are adjusted by subsequent partial neutralization of the hydrogel. The polymers stand out for an improved gel strength and absorption capacity, as well as for a small portion of water-soluble polymers.
According to U.S. Pat. No. 5,145,906 and EP 530 438 B1 polymer gels of acrylic acid together with water-soluble, hydroxyl groups-containing polymers are produced at temperatures ranging from 5 to 20° C. under adiabatic conditions without neutralization of the monomers; subsequently the polymer gels are reduced in size and partially or completely neutralized by aqueous bases, comminuted again in the presence of a secondary cross-linking agent, and subjected to a heat treatment.
The mentioned methods are disadvantageous, because polymerization of the monomer solution, as is demonstrated in EP 467 073 A1, takes place very slowly so that it can only be carried out dis-continuously in a batch method. Increasing the amount of initiator or elevating the reaction temperature affects the desired polymer properties. Furthermore, it is difficult to comminute the entirely acidic polymer gel, and neutralization takes place slowly because of the procedure which is governed by diffusion. In this connection, excess base remains in the surface region of the polymer particles, while still reactive, polymerized, acid groups-containing monomer units are present in the gel interior where they are not available for subsequent cross-linkage in the surface region.
EP 467 073 A1 describes polymers which are obtained at a controlled polymerization temperature in the range of 20 to 70° C., in particular at 55 to 60° C., within 5 hours. According to the described method the polyacrylic acid is then neutralized to a degree of 72%. The dry and ground polymer is then subjected to the subsequent cross-linking process. However, if liquids are absorbed under pressure, the polymers obtained according to this process have an only limited liquid absorption capacity. Additionally, after liquid absorption, the known polymers have a substantial rewet behavior which is disadvantageous, in particular when they are used in hygienic articles.
Accordingly, there is the object to provide polymers with improved absorption properties, in particular with improved liquid absorption under pressure load and improved rewet behavior, and a process for their production under reduction of the polymerization period and improvement of the subsequent cross-linkage.
This object is achieved by a powdery, cross-linked polymer absorbing water and aqueous liquids which is formed of a) 55-99.9%-wt. of at least one polymerized, unsaturated, polymerizable, acid groups-containing monomer which is present as a salt neutralized to the extent of at least 50 mol-%, b) 0-40%-wt. of a polymerized, unsaturated monomer which is copolymerizable with the monomer according to a), c) 0.01-5.0%-wt. of at least one cross-linking agent, and d) 0-30%-wt. of a water-soluble polymer, with the sum of components a)-d) amounting to 100%-wt., which polymer is characterized by the fact that it is formed of acidic polymer gels partially neutralized to the extent of 5-30 mol-%, relative to the acid groups-containing monomer portion, and that it has
a retention for a 0.9% aqueous NaCl-solution of at least 25 g/g polymer,
a liquid absorption under a pressure of 50 g/cm
2
of at least 25 g/g polymer,
a swelling pressure after 20 minutes of at least 700 g, relative to 1 g polymer,
a maximum soluble content after 16 h of 10%-wt., preferably a maximum of 3%-wt., and
a maximum rewet of 2.0 g.
The object is further achieved by a process for the production of this polymer, which is characterized by the fact that an aqueous solution having a maximum monomer content of 30% by weight, relative to the total solution, is produced; the unsaturated, polymerizable, acid groups-containing monomers are neutralized with bases to the extent of 5.0-30 mol-%, preferably 10-20 mol-%, prior to polymerization; the polymerization under radical conditions at a temperature ranging from 5-30° C., preferably 8-15° C., is initiated by chemical initiators and/or UV-irradiation and continued adiabatically; the polymer gel is subjected to a comminution after coarse grinding, and is neutralized with bases such that the polymer comprises a content of polymerized, neutralized, acid groups-containing monomer units of at least 50 mol-%; the polymer gel is dried to a water content of ≦10%-wt.; and that the dry and ground polymer is reacted at a temperature in the range of 140-240° C. with at least one bi- or multifunctional cross-linker reactive with acid groups.
Most surprisingly, we have found that polymers having a high retention value and high absorption capacity under a constant or increasing pressure, and low soluble polymer components are obtained, if the polymerization is carried out with a solution wherein a small amount of the acid groups-containing monomers have been neutralized by the addition of bases, instead of using a completely acid polymer solution. The range of partial neutralization amounts to about 5-30 mol-%, preferably 5-20 mol-%, and most preferably 5-10 mol-%, relative to acid groups-containing monomers.
According to the present invention water-soluble, monoethylenically unsaturated mono- and dicarboxylic acids, such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, sorbic acid, maleic acid, fumaric acid, itaconic acid, as well as vinylsulfonic acid; acrylamido- and/or methacrylamidoalkyl sulfonic acids, such as 2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyl oxyethane sulfonic acid, 4-vinylbenzene sulfonic acid, allyl sulfonic acid, vinyltoluene sulfonic acid, vinylphosphonic acid, and vinylbenzene phosphonic acid, are used as polymerizable, unsaturated, acid groups-containing monomers a).
Acrylic acid is the preferred water-soluble, unsaturated carboxylic acid. The proportion o
Dahmen Kurt
Peppmöller Reinmar
Niland Patrick D.
Stockhausen GmbH & Co. KG
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