EP1210129A1

EP1210129A1 - Water-absorbent polymers with compounds having a hollow space

Info

Publication number: EP1210129A1
Application number: EP00954615A
Authority: EP
Inventors: Helmut Brehm; Jörg HARREN; Jörg ISSBERNER; Richard Mertens
Original assignee: Stockhausen GmbH and Co KG; Chemische Fabrik Stockhausen GmbH
Current assignee: Evonik Operations GmbH
Priority date: 1999-08-20
Filing date: 2000-08-09
Publication date: 2002-06-05
Also published as: TWI282742B; CA2381930A1; JP2003507535A; WO2001013965A1; BR0013468A; AU6701000A

Abstract

The invention relates to water and aqueous fluid-absorbing mediums based on polymers which are water-swellable, but not water-soluble wherein silicium-rich zeolites are bonded ionically and/or on the basis of mechanical inclusions.

Description

Water-absorbent polymers with cavity connections

The invention relates to absorbents for water and aqueous liquids based on water-swellable but not water-soluble polymers, in which silicon-rich zeolites are ionically and / or incorporated due to mechanical inclusions.

The commercially available superabsorbent polymers are essentially crosslinked polyacrylic acids, crosslinked starch / acrylic acid graft copolymers, crosslinked hydrolyzed starch / acrylonitrile graft copolymers, crosslinked poly (maleic anhydride-co-isobutylene) or mixtures of various aforementioned crosslinked polymers in which the carboxyl groups are partially neutralized with sodium and / or potassium ions.

Such polymers are used e.g. in hygiene articles that contain body fluids such as Can soak up urine or menstrual fluid or in absorbent pads in food packaging. There they take large amounts of aqueous fluids and body fluids, such as e.g. Urine or blood. It is also necessary that the amount of liquid absorbed is retained under the pressure typical of the application. In the course of the technical development of superabsorbent polymers, the requirement profile for these products has changed significantly over the years.

So far, the development of superabsorbents has been particularly promoted with regard to the amount of liquid absorbed and the pressure stability. These crosslinked polymers based on monomers containing acid groups are obtained through the use of one or more pre-crosslinkers and / or one or more postcrosslinkers and show previously unachieved property combinations of high retention, high absorption under pressure, low soluble fractions, fast liquid absorption and high permeability in the swollen state , When used in hygiene articles, these crosslinked polymers have the advantage that they are excreted Liquids, once absorbed by the polymer, can no longer make skin contact. Damage to the skin, such as diaper rash, can essentially be avoided in this way. This comfort can be further increased by absorbing unpleasant odors.

According to Römpp Chemie Lexikon "the content of urine ingredients and thus odor-causing compounds is subject to physiological fluctuations; some substances are also excreted in varying concentrations every day, so that more precise information about the composition of the urine is always based on the so-called 24-hour urine In healthy adults this contains, for example, urea (20 g on average), uric acid (0.5 g), creatinine (1, 2 g), ammonia (0.5 g), amino acids (2 g), proteins (60 mg) reducing substances (0.5 g, thereof about 70 mg D-glucose or urine sugar), citric acid (0.5 g) and other organic acids as well as some vitamins (C, Bι ₂ and others). Inorganic ions are present: Na ⁺ (5.9 g), K ⁺ (2.7 g), NH ₄ ⁺ (0.8 g), Ca ²⁺ (0.5 g), Mg ²⁺ (0.4 g), Cf (8 , 9 g), PO ₄ ³ - (4.1 g), S0 ^{2 ~} (2.4 g) The dryness is between 50 and 72 g. The volatile components of the urine include alkyl furans, ketones, lactones, pyrrole , Allyl isothiocyanate and dimethyl sulfone The volatile components are mostly molecules with a molecular weight below approx. 1000 g / mol, which have a high vapor pressure.

Volatile components of the urine have also been described by A. Zlatkis et al. (Anal. Chem. Vol. 45, 763ff.) Examined. It is also known that after consumption of asparagus, the concentration of organic sulfur-containing compounds in human urine increases (RH Waring, Xenobiotika, Vol 17, 1363ff.). In patients who are on certain diets, who are taking certain medications, or in the elderly with declining kidney function, the urine can carry odor-causing ingredients. In urine incontinence patients, ureas are increasingly excreted, which convert the urea in the urine and thus release toxic ammonia. Also known is a pathological change called fish odor syndrome. It is based on increased excretion of quaternary ammonium compounds. Menstrual fluid can also make you uncomfortable Get smell. This smell is caused, among other things, by microbial breakdown of proteins that are excreted. The typical odor substances in the menstrual fluid and the odors caused by the breakdown of blood constituents do not differ significantly from the odors of the constituents found in the urine. Here, too, there are low molecular weight compounds with a molecular weight of less than 1000 g / mol. Mainly nitrogen-containing heterocycles such as pyrrole, pyridine and their derivatives can be mentioned. There are also odors that emanate from food, such as the smell of fish (amines).

The odor components of vaginal secretions and menstrual fluid were examined by G. Huggins and G. Preti (Clinical Obstetrics and Gynecology, Vol. 24, No. 2, June 1981, 355-377). Low molecular weight substances with a molecular weight below 500 g / mol were found. To be emphasized here are fatty acids (e.g. butyric acid, isovaleric acid) and some aromatic compounds such as Pyridine, indole and thymine, which contribute particularly to the bad smell. The amount of volatile fatty acids varies over the period of the menstrual cycle (Human Vaginal Secretions: Volatile FattyAcid Content, Richard P. Michael, R. W. Bonsall, Patricia Warner, Science, December 27, 1974, 1217-1219). Amines were not found in the vaginal secretions and menstrual fluids. This is due to the fact that the pH value of the secretion in a healthy patient is in the acidic range and there are at best ammonium salts which are not volatile. Only in the case of pathological conditions can more proteins be converted into amines by bacterial degradation, which enter the vapor space with a simultaneous increase in pH.

Previous approaches, for example in order to achieve an odor reduction in incontinence products and products for feminine hygiene, are based on a reduction in the free ammonia concentration. There are basically two approaches to this: prevention of additional ammonia production from urea degradation by suitable urease inhibitors (A. Norberg et al. Gerontology, 1984, 30, 261ff) or by protonation of free ammonia and binding it as the ammonium salt of carboxylates , The disadvantage is this process that essentially only ammonia and other nitrogenous components can be controlled. Odor-damaging compounds without basic groups, eg thiols, will still be able to enter the vapor space.

It is known to the person skilled in the art that zeolites have very good adsorption properties.

Zeolites are mostly synthetic compounds consisting of silicon oxide, aluminum oxide and a number of metal ions. Their composition is M ₂ / zO Al ₂ O ₃ xSiO ₂ yH ₂ O, where M = mono- or polyvalent metal, H, ammonium etc., z = valence, x = 1.8 to approx. 12 u. y = 0 to approx. 8. Structurally, zeolites consist of SiO and AIO ₄ tetrahedra which are linked via oxygen bridges. This creates a channel system made up of interconnected cavities of the same size and interconnected. The zeolites are named according to their pore opening, e.g. B. Zeolite A (4.2 A), Zeolite X (7.4 A). When heated, most zeolites release their water continuously and without changing the crystal structure. As a result, they can absorb other compounds and then function, for example, as catalysts or ion exchangers. Zeolites also show a sieving effect by taking up molecules with a smaller cross-section than the pore openings in the channel system of the lattice. Larger molecules are excluded.

Cations are required to compensate for the negative charge of the AIO ₄ tetrahedra in the aluminosilicate framework.

The synthesis of zeolites is described in great detail in: Zeolite Synthesis, ACS Symposium Series 398, Eds. ML Ocelli and HE Robson (1989) pages 2-7. The synthesis of hydrophobic zeolites with a silicon dioxide / aluminum oxide ratio of the framework of> 100 and a high hydrothermal stability and resistance to aqueous alkaline solutions is disclosed in patent application DE 19532500A1. The zeolites have a grain size of well below 150 μm. US 4795482 teaches the use of hydrophobic zeolites to suppress and avoid organic odors. The decrease in odors was measured by means of head space gas chromatography.

From patent applications WO 91/12029 and WO 91/12031 it is known that the hydrophobic zeolites described in US Pat. No. 4,795,482 or produced in a similar way can be used in combination with superabsorbers. The zeolite is "essentially" bound to the super absorber. The composites obtained in this way are used in hygiene articles such as. e.g. Diapers or sanitary napkins. The mixture is produced by mixing the superabsorbent with the zeolite in the dry state. Then water is added, a clumping of the particles being observed (WO 91/12031). After a drying step, the mixture can be introduced into hygiene products. In patent application WO 91/12029, the zeolite is dispersed together with a binder in water and applied to the superabsorber in a coating process. Here, at least 20% zeolite, based on the superabsorbent, should be used.

The disadvantage of these two procedures is that the binding of the zeolite material to the polymer is very weak and separation and segregation of superabsorbent and zeolite can occur even with a low mechanical load on the composite. Such mechanical loads occur, for example, when conveying a superabsorbent and / or an absorbent article containing superabsorbent polymers. In addition to segregation, there are also problems with handling very fine particles. In addition, if the superabsorbent is subsequently treated with aqueous dispersions, which may also contain binders, damage to the superabsorbent structure and the associated swelling properties must be expected. The high proportion of non-swellable zeolite material in the superabsorbent composite further limits the property profile. From patent applications EP 0 811 387A1 and EP 0 811 390A1 it is known that zeolites with a silicon dioxide / aluminum oxide ratio of 1-5 can be used as odor absorbers in sanitary napkins. The products manufactured according to the publication were subjected to a practical test and the products used were evaluated in an olfactory test panel with test candidates. The dry mixtures described in the above patent applications separate easily. In addition, the amounts of zeolite required in the patent applications are very high, which has an adverse effect on the comfort of hygiene articles.

The present invention is therefore based on the object of providing an absorbent polymer for water and aqueous liquids which has a substance with which odorous organic compounds, such as those e.g. occur in the urine or other excretory fluids of the body, are bound to be made available, in which: the odor-causing substances released into the steam room are significantly reduced in the application, there is an almost even distribution of the odor-binding substance in the absorbent, and there is segregation in the state and as far as possible is avoided during use, the absorbent has good retention and swelling properties

Has pressure and the odor-binding modification is ensured with the smallest possible amounts of the odor-binding substance.

The present invention is also based on the object of providing a process for producing the odor-absorbing absorbents, in which: in particular the problems when mixing dry substances which differ significantly in terms of particle size, such as e.g.

Granules and powders can be avoided, no dust is generated and clumping of the particles during production is avoided. The object is achieved according to the invention by an absorbent polymer composed of crosslinked monoethylenically unsaturated monomers bearing partially neutralized acid groups and containing silicon-rich zeolites ionically or mechanically bound or bound.

Silicon rich in the sense of the invention means that the silicon dioxide / aluminum oxide ratio is> 10, preferably> 20, particularly preferably> 50, and very particularly preferably> 100. Most preferred is a silica / alumina ratio> 500.

Crosslinked in the sense of the invention means that the polymer is crosslinked and / or surface crosslinked.

The zeolites to be used according to the invention are dealuminated, hydrophobic (organophilic) zeolite variants with a silicon dioxide / aluminum oxide ratio of the framework of> 10, preferably> 20, particularly preferably> 50 and very particularly preferably> 100. A ratio> 500 is most preferred. The amount used, based on the total amount of adsorbent, is 0.01-10% by weight, preferably 0.1-5% by weight and particularly preferably 0.70-3% by weight. Such zeolites are marketed, for example, by Degussa AG under the brand name Flavith ^® or by UOP under the name Abscents ^® . Flavith ^® is specified in the product data sheet KC-CZ 42-1 -05-1098 T&D. This product information sheet is hereby introduced as a reference and is therefore considered part of the disclosure.

For the polymerization of the polymer according to the invention, which may have superabsorbent properties, several methods are possible, for example bulk polymerization, solution polymerization, spray polymerization, inverse emulsion polymerization and inverse suspension polymerization. The solution polymerization is preferably carried out in water as the solvent. The solution polymerization can be carried out continuously or batchwise. The patent literature shows a wide range of possible variations with regard to the concentration ratios, temperatures, type and amount of the initiators also of the post-catalysts. Typical processes are described in the following patents: US 4,286,082, DE 27 06 135, US 4,076,663, DE 35 03 458, DE 40 20 780, DE 42 44 548, DE 43 23 001, DE 43 33 056, DE 44 18 818. These disclosures are hereby introduced as a reference and are therefore considered part of the disclosure

The acid group-containing unsaturated monomers to be used according to the invention are, for example, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, vinyl acetic acid, vinyl sulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid and their alkali and / or ammonium salts. Acrylic acid and its alkali and / or ammonium salts and mixtures thereof are preferably used. Furthermore, it is also possible to use monomers which are only hydrolyzed to acid groups after the polymerization, as is possible, for example, with the nitrile group.

Up to 30% by weight of further comonomers which are soluble in the aqueous polymerization batch, such as, for example, acrylamide, methacrylamide, acrylonitrile, (meth) allyl alcohol ethoxylates and the mono (meth) acrylic acid esters of alcohols or ethoxylates, can optionally be used to modify the polymer properties.

Together with the above-mentioned monomers, crosslinking monomers with more than one reactive group in the molecule are also polymerized. This produces partially cross-linked polymers that are no longer soluble in water but only swellable. Crosslinking monomers are, for example, bi- or polyfunctional monomers, for example amides such as methylene bisacryl or methacrylamide or ethylene bisacrylamide, and also allyl compounds such as allyl (meth) acrylate, alkoxylated allyl (meth) acrylate reacted with preferably 1 to 30 mol of ethylene oxide, triallyl cyanurate , Maleic acid diallyl esters, polyallyl esters, tetraallyloxiethan, triallyl amine, tetraallyl ethylenediamine, allyl esters of phosphoric acid or phosphorous acid, also crosslinkable monomers, such as the N-methylol compounds of amides such as methacrylamide or acrylamide and those derived therefrom Ethers and esters of polyols and alkoxylated polyols, such as diacrylates or triacrylates, for example butanediol or ethylene glycol diacrylate, polyglycol di (meth) acrylates, trimethylolpropane triacrylate, di- and triacrylate esters of (ethoxylated) trimethylolpropane, preferably alkoxylated with 1 to 30 mol of alkylene oxide - And methacrylate esters of glycerol and pentaerythritol, and of glycerol and pentaerythritol, which is preferably ethoxylated with 1 to 30 moles of ethylene oxide. Triallylamine, acrylates of polyhydric alcohols or their alkoxylates and methallyl alcohol acrylates or their alkoxylates are preferably used. The proportion of the crosslinking comonomers is from 0.01 to 3.0% by weight, preferably from 0.05 to 2.0% by weight and particularly preferably from 0.05 to 1.5% by weight, based on the total of the monomers.

The acidic monomers are preferably neutralized. The neutralization can be carried out in various ways. On the one hand, the polymerization can be carried out directly with the acidic monomers in accordance with the teaching of US Pat. No. 4,654,039, the neutralization then taking place subsequently in the polymer gel. This patent is hereby introduced as a reference and is therefore considered part of the disclosure.

Secondly and preferably, the acidic monomer components are neutralized to 20-95%, preferably 50-80%, before the polymerization and are then already present as sodium, potassium and / or ammonium salts at the start of the polymerization. For neutralization, preference is given to using bases which have no negative influence on the subsequent polymerization. Sodium hydroxide solution and / or potassium hydroxide solution and or ammonia, particularly preferably sodium hydroxide solution, are preferably used, the addition of sodium carbonate, potassium carbonate or sodium bicarbonate having an additional positive effect, as taught by US Pat. No. 5,314,420 and US Pat. No. 5,154,713. This partially neutralized monomer solution is cooled down to a temperature of below 30 ° C., preferably below 20 ° C., before the start of the polymerization in the adiabatic solution polymerization. These patents are hereby incorporated by reference and are therefore considered part of the disclosure. In the other methods mentioned, other temperatures are known and customary in the prior art. The polymers according to the invention can contain water-soluble polymers as a graft base in amounts of up to 40% by weight. These include partially or fully hydrolyzed polyvinyl alcohols, starch or starch derivatives, cellulose or cellulose derivatives, polyacrylic acids, polyglycols or mixtures thereof. The molecular weights of the polymers added as the graft base must be adapted to the conditions of the polymerization conditions. For example, in the case of aqueous solution polymerization, it may be necessary to use only low- or medium-molecular-weight polymers for reasons of the viscosity of the polymer solution, whereas this factor plays a subordinate role in suspension polymerization.

In addition to polymers which can be obtained by crosslinking polymerization of partially neutralized acrylic acid, preference is given to those which contain additional proportions of graft-polymerized starch or of polyvinyl alcohol.

The polymerization can be initiated by various conditions, e.g. by radiation with radioactive, electromagnetic or ultraviolet rays or by redox reaction of two compounds, e.g. Sodium hydrogen sulfite with potassium persulfate or ascorbic acid with hydrogen peroxide. The thermally triggered decomposition of a so-called radical starter such as, for example, azobisisobutyronitrile, sodium peroxydisulfate, t-butyl hydroperoxide or dibenzoyl peroxide can also be used as the start of polymerization. The combination of several of the aforementioned methods is also possible.

The polymer is produced in principle by two methods:

According to the first method, the partially neutralized acrylic acid in aqueous solution in the presence of the crosslinking agent and, if appropriate, the polymer additives is converted into a gel by free-radical polymerization, which is then comminuted and dried and ground to a powdery, free-flowing state and sieved to the desired particle size. The solution polymerization can be carried out continuously or batchwise. The patent literature shows both a wide range of possible variations with regard to the concentration ratios, Temperatures, type and amount of initiators as well as a variety of post-crosslinking options. Typical processes are described in the following documents: US 4,076,663, US 4,286,082, DE 27 06 135, DE 35 03 458, DE 3544 770, DE 40 20 780, DE 42 44 548, DE 43 23 001, DE 43 33 056, DE 44 18 818. These documents are hereby introduced as a reference and are therefore considered part of the disclosure.

The inverse suspension and emulsion polymerization process can also be used to prepare the polymer. In these processes, an aqueous, partially neutralized acrylic acid solution is dispersed in a hydrophobic, organic solvent with the aid of protective colloids and / or emulsifiers, and the polymerization is started by radical initiators. The crosslinkers are either dissolved in the monomer solution and are metered in together with it, or are added separately and, if appropriate, subsequently. Any polymeric graft bases present are added via the monomer solution or by direct introduction into the oil phase. The water is then removed azeotropically from the mixture and the polymer product is filtered off and optionally comminuted and dried and ground to a powdery, free-flowing state and sieved to the desired particle size.

The properties of the polymers according to the invention may be improved by the process of subsequent surface crosslinking, in particular also in their liquid absorption under pressure, so that the known phenomenon of "gel blocking" is suppressed, in which swollen polymer particles stick together and further liquid absorption and liquid distribution e.g. hinder in the diaper. During the post-crosslinking, the carboxyl groups of the polymer molecules on the surface of the superabsorbent particles are crosslinked with crosslinking agents at an elevated temperature. Post-crosslinking processes are described in several documents, e.g. DE 40 20 780, EP 317 106 and WO 94/9043.

The postcrosslinking agents known to the person skilled in the art, for example from US Pat. No. 5,314,420, page 8, lines 3-45, can all advantageously be combined in accordance with the invention can be used with a pre-crosslinker or a combination of crosslinkers. The abovementioned publications are hereby introduced as a reference and are therefore considered part of the disclosure. The compounds generally contain at least two functional groups which are capable of reacting with carboxylic acid or carboxyl groups. Alcohol, amine, aldehyde and carbonate groups are preferred, crosslinking molecules with several different functions also being used. Polyols, polyamines, polyamino alcohols, polyepoxides and alkylene carbonates are preferably used. In particular, one of the following post-crosslinking agents is used: ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerol, propylene glycol, diethanolamine, triethanolamine, polypropylene glycol, block copolymers of ethylene oxide and propylene oxide, sorbitan fatty acid esters, ethoxylated sorbitan fatty acid trimethyl, propylene ethylenedipro trimethylolated trimethyl ester, trimethylated propylene ethoxylated trimethylated propylene ethylenediaminophenoxy trimethylated trimethylated propylene oxide, trimethylated propylene ethoxylated trimethylsulfonated trimethane, pentoxol ethoxylated trimethylsulfonate, trimethylated propane, trimethylated propane, trimethylated propane, trimethylated propane, trimethylated propane, pentoxolated, ethoxylated, sorbitan, it pantaerythritol, polyvinyl alcohol, sorbitol, ethylene carbonate, propylene carbonate. It is particularly preferred to use polyols and ethylene carbonate as postcrosslinking agents. The post-crosslinking agent is used in an amount of 0.01 to 30 percent by weight, preferably 0.1-10 percent by weight, based on the polymer to be post-crosslinked.

Before the postcrosslinking, the polymer is preferably dried, ground and sieved to the particle size fraction which is favorable for the particular application and then fed to the postcrosslinking reaction. In some cases, however, it has also proven useful to add the postcrosslinkers before the polymer gel is dried or before the partially or predominantly dried polymer is comminuted. Postcrosslinking to be carried out according to the invention is described, for example, in US Pat. No. 4,666,983 and DE 40 20 780. These writings are hereby introduced as a reference and are therefore considered part of the disclosure. The addition of the post-crosslinking agent is frequently also advantageously carried out in the form of a solution in water, organic solvents or mixtures thereof, in particular when small amounts of post-crosslinking agent are used. Suitable mixing units for applying the postcrosslinking agent are, for example, Patterson-Kelley mixers, DRAIS turbulence mixers, Lödige mixers, Ruberg mixers, screw mixers, Plate mixers and fluidized bed mixers, as well as continuously operating vertical mixers in which the powder is mixed at high frequency using rotating knives (Schugi mixers). After the postcrosslinker has been mixed with the precrosslinked polymer, the postcrosslinking reaction is heated to temperatures of 60 to 250 ° C., preferably to 135 to 200 ° C. and particularly preferably to 150 to 185 ° C. The duration of the reheating is limited by the point at which the desired property profile of the polymer is destroyed again as a result of heat damage.

Depending on the application, different sieve fractions are used to process the polymers, e.g. for diapers between 100 and 1000 μm, preferably between 150 and 850 μm. This grain fraction is generally produced by grinding and sieving before and / or after the post-crosslinking.

In the case of the absorbent polymer according to the invention for the absorption of water or aqueous liquids, the zeolite component can only be extracted to a reduced extent by the liquid to be absorbed or can only be separated to a reduced extent in the dry state. Surprisingly, it has been found that the zeolites also do not partially lose their ability to bind odors due to the close linkage with the crosslinked polymer carrying acid groups. This results in an effective reduction in the vapor space concentration of substances that pollute odors. The odor-binding substances are applied, for example, from a suspension. This avoids any dust problem during manufacture. It has also been shown that the zeolites also do not lose their ability to absorb odors when they are applied from an aqueous suspension. It has also been shown that the other quality criteria which are relevant for polymers with superabsorbent properties, namely high retention and absorption against pressure, are not adversely affected by the application of zeolite. The polymer according to the invention is eminently suitable for the storage of active substances, these active substances being able to be released again in a controlled manner if necessary. The shelf life of sensitive active ingredients is significantly improved by incorporation into the polymer according to the invention.

Another object of the present invention is a method for producing the absorbent polymers according to the invention.

In accordance with this process according to the invention, the absorbent polymer according to the invention is prepared by: radical polymerization of an aqueous solution of ethylenically unsaturated acid groups, optionally partially neutralized

Monomers and crosslinking monomers by the process of

Solution or suspension polymerization to form a hydrogel, if appropriate insulation,

Comminution followed by drying, grinding, optionally sieving and

Surface crosslinking, the silicon-rich zeolite being added to the polymer at the latest during the surface crosslinking.

The zeolite is preferably added in suspension.

The zeolite is used in suspension. A preferred liquid phase is water, but mixtures of water and organic solvents are also used. As shown below, the zeolite can be added according to the invention in various process stages in the preparation of the powdery polymer. By applying the zeolite from an aqueous suspension to the polymer before or during one of the process steps for its production, a particularly effective bond between the odor-absorbing component and the polymer is achieved.

In a preferred embodiment of the process according to the invention, the zeolite is added directly to the aqueous monomer solution before the polymerization. Is the absorbent polymer through

If suspension polymerization is prepared, it is also possible to introduce all or part of the zeolite in the oil phase and to meter in the monomer solution. If only part of the cellulite is initially charged, the remainder must be added via the monomer solution.

In a further preferred embodiment of the process according to the invention, the zeolite is applied to the comminuted polymer gel suspended in water or an organic solvent or mixtures thereof.

The polymer gel is furthermore preferably at least partially dried and the zeolite is then suspended in the water or an organic solvent or mixtures thereof and applied to the powder. As such, the resulting product can be dried directly and surface-crosslinked.

In another preferred embodiment of the method according to the invention, the zeolite is used in the post-crosslinking processing step. Suitable mixing units for applying the post-crosslinking agent are, for example, Patterson-Kelley mixers, DRAIS turbulence mixers, Lödige mixers, Ruberg mixers, screw mixers, plate mixers and fluidized bed mixers, as well as continuously operating vertical mixers in which the powder is mixed at high frequency using rotating knives (Schugi- Mixer). The zeolite is also preferably introduced at several points in the manufacturing process of the absorbent polymers in order to optimize the action of the zeolite and to use synergies.

According to a further process according to the invention, the absorbent polymer according to the invention is prepared by: radical polymerization of an aqueous solution of ethylenically unsaturated acid groups, optionally partially neutralized monomers and crosslinking monomers by the solution or suspension polymerization process to give a hydrogel, optionally isolation, comminution followed by drying , Grinding, optionally sieving, the silicon-rich zeolite being added to the polymer when it still has at least a water-water content of 10% by weight.

The zeolite is preferably added in suspension.

According to the invention, the water content must not have been reduced below 10% by weight before the silicon-rich zeolite has been added before the silicon-rich zeolite is added.

The water content before the addition of the silicon-rich zeolite should preferably not have been reduced below 30% by weight, particularly preferably not below 50% by weight and very particularly preferably not below 65% by weight.

The zeolite is preferably added to the polymer from a suspension.

Absorbent polymers are obtained by the process according to the invention, in which the zeolite is integrated in the synthetic polymer in such a way that the zeolite is no longer completely removed from the polymer even after mechanical stress, for example in a ball mill at 95 rpm and for 6 minutes is to be separated. In the process according to the invention, less than 80%, as a rule 40-60% of the total amount of zeolite applied to the polymer, detaches again after such exposure.

The polymers according to the invention have a better absorption of odor-damaging compounds compared to powdery absorbents without zeolite.

The polymer according to the invention is used e.g. in hygiene articles that contain body fluids such as Can soak up urine or in the packaging area of e.g. Meat and fish products. There they take large amounts of aqueous fluids and body fluids, such as e.g. Urine, blood or meat juice. These uses are therefore also the subject of the present invention.

The polymers according to the invention are incorporated directly as powders into the structures for absorbing liquids or are previously fixed in foamed or non-foamed fabrics. Such constructions for absorbing liquids are, for example, baby diapers, incontinence products or absorbent inserts in packaging units for food. The binding of the zeolite to the polymer is obviously so strong in the absorbent polymer according to the invention that even under mechanical stress e.g. Promotion of the absorbent polymer no significant separation and segregation of polymer and zeolite can be observed and therefore in particular the problems of handling very fine particles do not arise.

Further processing of the polymer according to the invention is advantageous since, according to the prior art, separate, uniform metering of superabsorbent and zeolite cannot be achieved, especially with small amounts of zeolite. The easily metered polymer according to the invention ensures a constant concentration of polymer superabsorbent properties and odor-binding component in absorbent articles such as sanitary napkins. In addition, it has been shown that the absorbents according to the invention are outstandingly suitable for storing active substances. The shelf life of sensitive active ingredients, for example against oxidative degradation, is significantly improved by the incorporation into the absorbents according to the invention.

Furthermore, the polymer according to the invention is used in plant breeding and pest control in agriculture. In plant breeding, the polymers in the vicinity of plant roots ensure an adequate supply of liquid and previously stored nutrients and are able to store and release them over a longer period of time.

In pest control, active ingredients can be stored individually or in a combination of several active ingredients in the polymer, which are then released in a time-controlled and quantity-controlled manner.

The invention is illustrated in the following examples. These explanations are only examples and do not limit the general idea of the invention.

The preparation and the properties of the polymers according to the invention are explained. The test methods and the regulations for determining the properties of the polymers with superabsorbent properties are also described.

Test Methods:

Test method 1: The retention is given according to the teabag method and as an average of three measurements. About 200 mg of polymer are sealed in a tea bag and immersed in 0.9% NaCl solution for 30 minutes. The tea bag is then spun in a centrifuge (23 cm diameter, 1,400 rpm) for 3 minutes and weighed. a Tea bags without water-absorbing polymer are allowed to run as a blank value.

Retention = blank weight / weight [g / g]

Test method 2: liquid absorption under pressure (AAP test, EP 0 339 461)

The absorption under pressure (pressure load 50 g / cm ² ) is determined by a method described in EP 0 339 461, page 7. This document is hereby introduced as a reference and is therefore part of the disclosure. Approx. 0.9 g superabsorbent is weighed into a cylinder with a sieve bottom. The evenly sprinkled superabsorbent layer is loaded with a stamp which exerts a pressure of 50 g / cm ² . The previously weighed cylinder is then placed on a glass filter plate, which is in a bowl with 0.9% NaCl solution, the liquid level of which corresponds exactly to the height of the filter plate. After the cylinder unit has been sucked for 0.9% NaCI solution for 1 hour, it is weighed back and the AAP is calculated as follows:

AAP = Weighing out (cylinder unit + super absorber) - Weighing out (cylinder unit + fully absorbed super absorber) / Weighing out super absorber

Test method 3) Determination of the uptake of unpleasant odors

0.1 g of powdery absorbent is mixed with 2 ml of an aqueous solution (contains 5% by weight of ethanol) of the odor-nuisance compound and sealed in a 5 ml sample vessel. It is left to stand at 23 ° C. for 12 hours and the head-space GC is used to quantitatively examine the content of the odor-causing compound in the vapor space above the liquid against a zero sample.

Test method 4) The silicon content of the absorbent polymers is determined by converting the silicate to molybdenum blue and subsequent photometric analysis. Silicon is previously quantitatively dissolved in alkaline Transferred silicate. (Photometric analysis, authors: B. Lange, Zdenek, J. Vejdelek, S., edition 1987, p. 383, VCH)

Examples:

Example 1a)

This example explains the preparation of a polymer gel with superabsorbent properties.

A solution of 1300 g acrylic acid, 2115.9 g dist. Water, 2.7 g of polyethylene glycol monoally ether acrylate and 1.25 g of polyethylene glycol diacrylate. While stirring and cooling, 899.10 g of 50% sodium hydroxide solution are partially neutralized (degree of neutralization (NG) = 60%). The solution is cooled to 7-8 ° C and with nitrogen for about 20 min. bubbled. Then 0.45 g of azo-bis (2-amodinopropane) dihydrochloride dissolved in 22.5 g of dist. Water, 1.35 g sodium peroxodisulfate, dissolved in 25 g dist. Water, and 0.315 g of hydrogen peroxide (35%) dissolved in 22.5 g of dist. Add water. The polymerization is then started by adding 0.0675 g of ascorbic acid dissolved in 9 g of water, whereupon a significant increase in temperature takes place. A gel-like product is obtained, the further processing of which is described in the examples below.

Example 1b)

This example explains the production of a further polymer gel with superabsorbent properties.

A solution of 1300 g acrylic acid, 2015.9 g dist. Water, 6.5 g of polyethylene glycol monoally ether acrylate and 3.9 g of polyethylene glycol diacrylate. With stirring and cooling, 997.10 g of 50% sodium hydroxide solution are partially neutralized (NG = 70%). The solution is cooled to 7-8 ° C and with nitrogen for about 20 min. bubbled. Then 0.45 g of azo-bis (2- amidinopropane) dihydrochloride dissolved in 22.5 g of dist. Water, 1.35 g sodium peroxodisulfate, dissolved in 25 g dist. Water, and 0.315 g of hydrogen peroxide (35%) dissolved in 22.5 g of dist. Add water. The polymerization is then started by adding 0.0675 g of ascorbic acid dissolved in 9 g of water, whereupon a significant increase in temperature takes place. A gel-like product is obtained, the further processing of which is described in the examples below.

Example 1c)

This example illustrates the preparation of another polymer gel with superabsorbent properties.

A solution of 1300 g acrylic acid, 2017.19 g dist. Water, 3.9 g of triallylamine as a crosslinker. With stirring and cooling, 997.10 g of 50% sodium hydroxide solution are partially neutralized (NG = 70%). The solution is cooled to 7-8 ° C and with nitrogen for about 20 min. bubbled. Then 0.45 g of azo-bis (2-amidinopropane) dihydrochloride dissolved in 22.5 g of dist. Water, 1.35 g sodium peroxodisulfate, dissolved in 25 g dist. Water, and 0.315 g of hydrogen peroxide (35%) dissolved in 22.5 g of dist. Add water. The polymerization is then started by adding 0.0675 g of ascorbic acid dissolved in 9 g of water, whereupon a significant increase in temperature takes place. A gel-like product is obtained, the further processing of which is described in the examples below.

Examples 2)

500 g of the gels obtained from Examples 1b-c) are bulged and with the amounts of a suspension of Flavith ^® S 108 (Degussa AG, SiO ₂ / Al ₂ O ₃ ratio approx. 500) or Flavith ^® listed in the table below D (Degussa AG SiO ₂ / Al ₂ O ₃ ratio approx. 56) or zeolite A (SiO ₂ / Al ₂ O ₃ ratio <5) evenly sprayed in water and then up to a residual water content of <10% at 150 ° C in dried in a convection oven. Examples e and f are comparative examples, since the zeolite A used is not a silicon-rich zeolite.

^* Hydrogel obtained from comparative example 1b

# Hydrogel obtained from Comparative Example 1c ^** Comparative Examples

Example 3

This example examines retention and fluid uptake under pressure of a polymer with superabsorbent properties in the absence of zeolite.

50 g of the dried, ground and sieved to 150-850 μm polymer from Examples 1a-c) are wetted with vigorous mixing with a solution of 0.5 g of ethylene carbonate and 1.5 g of water in a plastic vessel and with a commercially available household Hand mixer (Krups) mixed well. The wetted polymer is then heated in an oven to a temperature of 180 ° C. for 30 minutes.

Example 4)

In this example, the surface crosslinking takes place after the addition of zeolite.

50 g of the dried, ground and sieved to 150-850 μm polymers from Example 2a-f) are each individually, with vigorous mixing, wetted with a solution of ethylene carbonate (EC) and water in a plastic vessel and with a commercially available household hand mixer (Krups ) mixed well. The solution contains 0.25 g EC per 1.8 g water. The wetted polymer is then heated to 170 ° C. in an oven for 30 minutes.

Comparative example

Example 5) In this example, zeolite is added during surface crosslinking.

50 g of the bulged, dried, ground and sieved to 150-850 μm polymer from Example 1a) are mixed vigorously with a solution of 0.25 g ethylene carbonate, 1.5 g water and with the amount listed in the table below (details in% dry matter based on acrylic acid) Flavith ^® S 108 (Degussa AG) wetted as a suspension in a plastic container and mixed well with a standard household hand mixer (Krups). The wetted polymer is then heated in an oven to a temperature of 180 ° C. for 30 minutes.

It can be clearly seen that the retention or the liquid absorption under pressure has changed only insignificantly in comparison with Example 3, within the scope of the measurement accuracy.

Comparative Example 3a) (analogous to WO 91/12029)

10 g of methyl cellulose (Walocel VP-M 20678) are dispersed with 40 g of Flavith ^® S108 and 190 g of water using a high-speed mixer and then mixed in a laboratory mixer with 50 g of a commercially available superabsorbent (Favor ^® SXM 6860 from Stockhausen) and mixed in one Fluid bed dryer dried at 60 ° C and constant air flow for 20 min.

Comparative Example 3b) (analogous to WO 91/12029) 0.25 g of methyl cellulose (Walocel VP-M 20678) are dispersed with 1 g of Flavith ^® S108 and 5 g of water using a high-speed mixer and then mixed in a laboratory mixer with 50 g of a commercially available superabsorbent (Favor ^® SXM 6860 from Stockhausen) and dried in a fluidized bed dryer at 60 ° C and constant air flow for 20 min.

In addition to the drastically deteriorated performance, particularly in terms of absorbency under pressure compared to SXM 6860, the instability of the composite material is already evident from the strong dust formation when the material is mixed or conveyed.

Comparative Example 4)

In this example, zeolite is added after surface crosslinking. 50 g of the product obtained from Example 4) are suspended in water under thorough mixing, sprayed with the one indicated in the following table the amount of zeolite (Flavith ^® S108, Fa. Degussa-Huels). The product is dried in a drying cabinet to a residual water content of <4%.

Example 6 The product obtained from comparative examples 3) and 4) is sieved and the fraction with a particle size of 150-850 μm is subjected to a ball mill stability test. The product is loaded in a ball mill for 6 minutes at 95 rpm. The product obtained from Example 2b was also subjected to the same ball mill stability test. The products were sieved again and the fraction with a grain size of <150 μm was tested for the silicon content according to test method 4. Since the zeolite used has a grain size of significantly less than 150 μm, this method can be used to determine how much zeolite is bound or enclosed in the polymer with superabsorbent properties. The following amounts of silicon, based on the total amount of dry matter, were found for the samples:

^* based on the total amount of the polymer according to the invention with superabsorbent properties

50 g SAP (superabsorbent from Stockhausen (FAVOR ^® SXM 6860) and 1 g Flavith ^® S108 were mixed with a kitchen mixer from Krups. After addition of 15 g water, clumping of the material was observed. Drying 120 min. At 60 ° C.

It can be clearly seen that the products according to the invention have significantly less silicon in the fraction of the particles <150 μm than a product manufactured according to the prior art. This proves that the binding of the zeolite to the polymer is significantly stronger in the products according to the invention. The composite materials produced in accordance with the patent specifications WO 91/12029 and WO 91/12031 are also significantly more unstable than the products according to the invention, which is evidenced by the increased SiO ₂ content in the fine dust before and after the ball mill stability test. In particular, it is clear that it is not possible by methods according to the prior art to effectively bind such large amounts of zeolite, since a large proportion of the hydrophobic zeolite is still separated from the superabsorbent material after production. Mechanical stress on the material releases additional large amounts of the zeolite, characterized by the high silicon dioxide content in the fine dust after ball mill loading. Comparative example V4a shows that even when using small amounts of zeolite (2%) the binding in processes according to the prior art is significantly worse than in the process according to the invention (Example 2b).

Example 7

In this example, the reduction in the vapor space concentration of odor-causing compounds was investigated. When measuring the odor-causing substances, a polymer without zeolite was examined as a blank sample in accordance with test specification 2) and the vapor space concentration found was equated with 100% of the odor-causing substance. Subsequently, zeolite-containing samples were examined and the vapor space concentration of the odor-causing substance was determined. The information in the right-hand column is calculated according to: 100 * (found amount of odor substance from polymer containing zeolite / amount of odor substance found from polymer free of zeolite).

Doping with furfuryl mercaptan and ethyl furan:

not measured

The absorbent polymers according to the invention show a clear absorption of odor-damaging substances.

The comparative examples show that zeolites with a low silicon dioxide / aluminum oxide ratio do not lead to a satisfactory decrease in the vapor space concentration of odorous substances.

To substantiate this, in addition, was a commercially available superabsorbent Favor ^® by the company Stockhausen with 2 wt% of various hydrophilic Zeolites (A, P, X) with an Si0 ₂ / Al ₂ O ₃ content of <5 dry mixed intimately and the decrease in odorants examined.

No decrease in the concentration of odorous substances could be found in the vapor space above the sample compared to a sample without zeolite.

Claims

claims:

1. Absorbent, crosslinked polymer for water or aqueous body fluids, based on optionally partially neutralized monoethylenically unsaturated acid groups bearing monomers, characterized in that the polymer contains silicon-rich zeolites at least partially ionically bound or enclosed therein.

2. Polymer according to claim 1, characterized in that it contains at least 0.01-10% by weight, preferably 0.1-5% by weight and particularly preferably 0.7-3% by weight of silicon-rich zeolites.

3. Polymer according to claim 1 or 2, characterized in that the silicon-rich zeolite has a silicon dioxide / aluminum oxide ratio of the framework of> 20, preferably> 50, particularly preferably> 100 and very particularly preferably> 500.

4. Polymer according to one of claims 1 to 3, characterized in that the polymer is composed of up to 30% of further monoethylenically unsaturated monomers bearing monomers bearing the acid groups.

5. Polymer according to one of claims 1 to 4, characterized in that it contains up to 40% by weight of a water-soluble, natural or synthetic polymer and / or graft polymerized.

6. Polymer according to one of claims 1 to 5, characterized in that it has been coated with 0.01 to 30% by weight, preferably 0.1 to 10% by weight, based on the polymer, of a crosslinker component which has at least two Carboxyl groups in the surface layer of the polymer particles react and cause crosslinking.

7. A process for the preparation of polymers according to any one of claims 1 to 6, by radical polymerization of an aqueous solution ethylenically unsaturated, optionally partially neutralized monomers bearing acid groups, optionally up to 30% by weight of further monoethylenically unsaturated comonomers, crosslinking monomers, and optionally up to 40% by weight of a water-soluble natural or synthetic polymer by the process of solution or suspension polymerization to give a hydrogel, if appropriate isolation Comminution followed by drying, grinding / screening and surface post-crosslinking, characterized in that the silicon-rich zeolite is added to the polymer at the latest during surface crosslinking, preferably in suspension.

8. A process for the preparation of polymers according to any one of claims 1 to 6, by radical polymerization of an aqueous solution of ethylenically unsaturated, acid group-bearing, optionally partially neutralized monomers, optionally up to 30% by weight of further monoethylenically unsaturated comonomers, crosslinking monomers, and optionally up to 40 % By weight of a water-soluble natural or synthetic polymer by the process of solution or suspension polymerization to give a hydrogel, if appropriate isolation, comminution followed by drying, grinding / sieving, characterized in that the silicon-rich zeolite gives the polymer at a water content of> 10% by weight. is added, preferably in suspension.

9. The method according to claim 8, characterized in that the water content is> 30, preferably> 50 and very particularly preferably> 65% by weight.

10. Use of the polymers according to one of claims 1 to 6 for improved absorption of odors from body fluids.

11. Use of the polymers according to one of claims 1 to 6 as an absorbent for aqueous liquids, preferably in constructions for absorbing body fluids, in foamed and non-foamed fabrics, in packaging materials, in plant breeding and as a soil conditioner.

12. Use of the polymers according to any one of claims 1-6 in hygiene articles.

13. Use of the polymers according to one of claims 1 to 6 as a carrier substance and / or stabilizer for active substances, in particular for fertilizers or other active substances, which are optionally released in a delayed manner.