WO2002053199A1 - Hydrogels coated with steric or electrostatic spacers - Google Patents

Abstract

The invention relates to non-water soluble hydrogels which can swell in water, and which are coated with steric or electrostatic spacers. Before being coated, the hydrogels comprise the following characteristics: absorbency under load (AUL) (0.7 psi) of at least 20 g/g, and gel strength of at least 1600 Pa. The coated hydrogels preferably have the following characteristics: centrifuge retention capacity (CRC) of at least 24 g/g, saline flow conductivity (SFC) of at least 30 x 10-7 cm3 s/g, and free swell rate (FSR) of at least 0.15 g/g s and/or a maximum vortex time of 160 s.

Description

HYDROGELS COATED WITH STERICAL OR ELECTROSTATIC SPACERS

The invention relates to hydrogels, water-absorbing compositions containing them, processes for their preparation, their use in hygiene articles and processes for determining suitable water-absorbing compositions.

Highly swellable hydrogels have been used in hygiene articles such as baby diapers or sanitary napkins for a long time. As a result, the volume of the hygiene articles could be significantly reduced.

The current trend in diaper construction is towards producing even thinner constructions with a reduced cellulose fiber content and an increased hydrogel content. The advantage of thinner constructions is not only evident in improved wearing comfort, but also in reduced packaging and storage costs. With the trend towards ever thinner diaper constructions, the requirement profile for the water-swellable hydrophilic polymers has changed significantly. The ability of the hydrogel to transfer and distribute fluids is now critical. Due to the higher loading of the hygiene article (polymer per unit area), the polymer in the swollen state must not form a barrier layer for the subsequent liquid (gel blocking). Gel blocking occurs when liquid wets the surface of the highly absorbent hydrogel particles and the outer shell swells. As a result, a barrier layer is formed which makes it difficult for liquids to diffuse into the interior of the particle and thus leads to leakage. If the product has good gel permeability and thus good transport properties, optimal utilization of the entire hygiene article can be guaranteed.

With the aim of using larger amounts of highly swellable hydrogels, the absorption capacity and gel strength were optimized by specifically adjusting the degree of crosslinking in the starting polymer and subsequent postcrosslinking. Improved gel permeability values can only be generated if a higher crosslinking density is permitted in the starting polymer. However, higher crosslinking densities simultaneously mean a reduction in the absorption capacity and a decrease in the swelling rate in the polymer. As a result, additional layers have to be introduced in order to prevent leakage while simultaneously increasing the hydrogel content in the hygiene article to prevent, which in turn leads to bulky hygiene articles and counteracts the actual objective, the production of thinner hygiene products.

A possible way of achieving improved transport properties and avoiding gel blocking is to shift the grain size spectrum to higher values. However, this leads to a decrease in the swelling rate since the surface of the absorbent material is reduced. This is undesirable.

Another method of achieving improved gel permeability is surface post-crosslinking, which gives the hydrogel body a higher gel strength when swollen. Gels with only a low gel strength can be deformed under an applied pressure (body pressure), clog pores in the hydrogel / cellulose fiber absorbent body and thereby prevent further fluid absorption. Since an increase in the crosslinking density in the starting polymer can be ruled out for the above reasons, the surface postcrosslinking represents an elegant method for increasing the gel strength. The surface postcrosslinking increases the crosslinking density in the shell of the hydrogel particles, which increases the absorption under pressure (Absorbency Under Load AUL). of the base polymer generated in this way is raised to a higher level. While the absorption capacity in the hydrogel shell decreases, the core of the hydrogel particles has an improved absorption capacity compared to the shell due to the presence of movable polymer chains, so that the shell structure ensures improved liquid transmission.

However, the effect of gel blocking still appeared when high amounts of highly swellable hydrogels were used. An important criterion is therefore the ability to transfer liquid in the swollen state. Only with good fluid transmission can the actual advantages of the highly swellable hydrogels, namely their pronounced absorption and retention capacity for aqueous body fluids, be fully exploited. It is important, however, that the liquid is transferred during the period for which the hygiene article is intended to be used. The full absorption capacity of the hydrogel should be exhausted. The ability of a hydrogel to transfer liquid is quantified in Saline Flow Conductivity (SFC) values. The SFC measures the ability of the hydrogel layer formed to transfer liquid under a given pressure. It is assumed that the hydrogel particles touch one another in the swollen state when large amounts are used and thus form a closed absorption layer within which the liquid distribution takes place. A subsequent modification of the surface of the base polymers (surface post-crosslinked starting polymers) is known.

DE-A-3 523 617 relates to the addition of finely divided amorphous polysilicic acids (silica) to dry hydrogel powder after the surface postcrosslinking with crosslinking agents which react with carboxyl groups.

According to the prior art, aluminum sulfate is used as the sole crosslinking agent or in combination with another crosslinking agent for surface postcrosslinking.

WO 95/22356 relates to the modification of absorbent polymers with other polymers to improve the absorption properties. Preferred modifiers are polyamines and polyimines. However, the effects with regard to SFC are small according to Tables 1 and 2.

WO 95/26209 relates to absorbent structures which have at least one region which contains 60-100% highly swellable hydrogel, the highly swellable hydrogel having an SFC of at least 30 x 10 ^"7 cm ³ s / g and a PUP 0.7 psi of at least 23 g The examples explain that corresponding highly swellable hydrogels can be obtained by post-crosslinking, and as can be seen from Table 1 and Table 2, this type of treatment can only increase the SFC by reducing the gel volume, ie it there is a reciprocal relationship between retention and gel permeability.

The SFC increases with increasing grain size of the highly swellable hydrogel. With increasing grain size, the surface of the highly swellable hydrogel particles decreases in comparison to their volume, which results in a decrease in the swelling rate. It can therefore be deduced from the results of this series of experiments that the swelling rate also shows a reciprocal dependence on the SFC.

It was therefore an object to provide highly swellable hydrogels or water-absorbing compositions which, when used in the hygiene article, have good transport properties, high permeability, and at the same time high final absorption capacity and high swelling rate. Contrary to the state of the art, in which high absorption capacities of the hydrogels, high liquid transport performance and rapid swelling capacity are mutually exclusive, new types of highly swellable hydrogels are to be generated which combine the opposite parameters. In addition, it should be possible to produce thin hygiene articles by using large amounts of the highly swellable hydrogels according to the invention. To this For this purpose, highly swellable hydrogels are to be generated, which at the same time have a high swelling rate (absorption rate), high gel permeability and high retention. Given the excellent liquid distribution, the high total capacity of the highly swellable hydrogels according to the invention in the absorption layer should be able to be used optimally.

The object is achieved according to the invention by non-water-soluble water-swellable hydrogels which are coated with steric or electrostatic spacers, the hydrogels having the following features before coating:

Absorption under pressure (AUL) (0.7 psi) of at least 20 g / g,

- Gel strength of at least 1600 Pa.

In addition, the coated hydrogels preferably have the following features:

Centrifuge retention capacity (CRC) of at least 24 g / g,

Saline Flow Conductivity (SFC) of at least 30 x 10 ^"7 , preferably at least 60 x 10 ^{" 7} cm ³ s / g and

- Free Swell Rate (FSR) of at least 0.15 g / g s and / or Vortex Time of maximum 160 s.

The term "water-absorbent" refers to water and aqueous systems which can contain dissolved organic and inorganic compounds, in particular to body fluids such as urine, blood or fluids containing them.

The hydrogels according to the invention and water-absorbing compositions containing them can be used for the production of hygiene articles or other articles which serve to absorb aqueous liquids. The invention thus further relates to hygiene articles which contain a water-absorbing composition according to the invention between a liquid-permeable cover sheet and a liquid-impermeable back sheet. The hygiene articles can be in the form of diapers, sanitary napkins and incontinence products.

The invention also relates to a method for improving the performance profile of water-absorbent compositions by increasing the permeability, capacity and swelling rate of the water-absorbent compositions by using non-water-soluble water-swellable hydrogels, as defined above. The invention also relates to a method for determining water-absorbent compositions with high permeability, capacity and swelling rate by measuring the absorption under pressure (AUL) and the gel strength for uncoated hydrogels and determining the centrifuge retention capacity (CRC), saline flow conductivity (SFC) and free Swell rate (FSR) of the coated hydrogels for a given water-absorbing composition and determination of the water-absorbing composition for which the hydrogels show the property spectrum mentioned above.

Furthermore, the invention relates to the use of hydrogels, as defined above, in hygiene articles or other articles which serve to absorb aqueous liquids, to increase the permeability, capacity and swelling rate.

Surprisingly, it was found that the above problem is solved in full if base polymers are used which have an AUL (0.7 psi) of at least 20 g / g, preferably of at least 22 g / g, particularly preferably of at least 24 g / g , extremely preferably of at least 26 g / g, and a gel strength of at least 1600 Pa, preferably of at least 1800 Pa, particularly preferably of at least 2000 Pa, the surface of which is subsequently coated with a steric (inert) or electrostatic spacer. Base polymers with these properties ensure that the spacer effect is not compensated for by the gel particle being too easy to deform under pressure.

The technique of adding steric or electrostatic spacers enables the production of hygiene articles with a high hydrogel content within the absorption layer. In addition, hydrogels with electrostatic spacers also have an improved connection to cellulose fibers, since the latter are weakly negatively charged on the surface. This fact is particularly advantageous, since said property profile of hydrogels with electrostatic spacers and cellulose fibers enables an absorption layer to be produced without additional aids, which fix the hydrogel within the fiber matrix. The attachment to the cellulose fibers automatically fixes the hydrogel material so that there is no undesired redistribution of the hydrogel material, for example to the surface of the absorbent core.

The highly swellable polymer particles according to the invention are notable for high absorption capacities, improved liquid transport performance and higher swelling speed. For this reason, the hygiene article can be made extremely thin become. The increased proportion of highly swellable hydrogels according to the invention with high capacity enables enormous absorption capacities, so that the problem of leakage is avoided. At the same time, the high absorption capacity is fully exploited by the improved liquid distribution.

The present invention relates to the production of novel, highly swellable hydrogels by

(1) preselection of highly swellable base polymers which have an AUL (0.7 psi) of at least 20 g / g, preferably of at least 22 g / g, particularly preferably of at least 24 g / g, extremely preferably of at least 26 g / g, and have a gel strength of at least 1600 Pa, preferably of at least 1800 Pa, particularly preferably of at least 2000 Pa.

(2) Post-treatment of the surface (coating) of the base polymers preselected according to the above criteria with steric or electrostatic spacers.

By coating these preselected hydrogels, it is possible to produce highly swellable hydrogels which, contrary to the prior art, also have a high swelling rate (absorption rate), high gel permeability, and high retention.

Accordingly, hydrogels are generated with the following combinations of properties:

CRC greater than or equal to 24 g / g, preferably greater than or equal to 26 g / g, more preferably greater than or equal to 28 g / g, even more preferably greater than or equal to 30 g / g, particularly preferably CRC greater than or equal to 32 g / g and most preferably CRC greater than or equal to 35 g / g and

SFC greater than or equal to 30 x 10 ^'7 cm ³ s / g, preferably greater than or equal to 60 x 10 ^"7 cm ³ s / g, preferably greater than or equal to 80 x 10 ^{" 7} cm ³ s / g, more preferably greater than or equal to 100 x 10 ^{" 7} cm s / g, even more preferably greater than or equal to 120 x 10 ^" cm s / g, particularly preferably greater than or equal to 150 x 10 ^{" 7} cm ³ s / g, extremely preferably greater than or equal to 200 x 10 ^"7 cm ³ s / g am most preferably greater than or equal to 300 x 10 ^"7 cm ³ s / g and - Free Swell Rate greater than or equal to 0.15 g / gs, preferably greater than or equal to 0.20 g / gs, more preferably greater than 0.30 g / gs, even more preferably greater than or equal to 0.50 g / gs, particularly preferably greater than or equal to 0.70 g / gs, most preferably greater than or equal to 1.00 g / gs or

Vortex time less than or equal to 160 s, preferably vortex time less than or equal to 120 s, more preferably vortex time less than or equal to 90 s, particularly preferably vortex time less than or equal to 60 s, most preferably vortex time less than or equal to 30 s.

Water-swellable hydrogels with spacers

Hydrogel-forming polymers are in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose or starch ethers, crosslinked carboxymethyl cellulose, partially crosslinked polyalkylene oxide or natural products swellable in aqueous liquids, such as guar derivatives, alginates and carrageenans.

Suitable graft bases can be of natural or synthetic origin. Examples are starch, cellulose or cellulose derivatives and other polysaccharides and oligosaccharides, polyvinyl alcohol, polyalkylene oxides, in particular polyethylene oxides and polypropylene oxides, polyamines, polyamides and hydrophilic polyesters. Suitable polyalkylene oxides have, for example, the formula

X

R .1 ¹ - ^~ O ^~ (CH ₂ ^~ CH- O) „--rR> 2

R ¹ and R ² independently of one another are hydrogen, alkyl, alkenyl or acrylic,

X is hydrogen or methyl and n is an integer from 1 to 10,000.

R ¹ and R ^{2 are} preferably hydrogen, (Ci - C ₄ ) alkyl, (C ₂ - C ₆ ) alkenyl or phenyl.

Preferred hydrogel-forming polymers are crosslinked polymers with acid groups which are predominantly in the form of their salts, generally alkali metal or ammonium salts, available. Such polymers swell particularly strongly into gels on contact with aqueous liquids.

Polymers which are obtained by crosslinking polymerization or copolymerization of acid-bearing monoethylenically unsaturated monomers or their salts are preferred. It is also possible to (co) polymerize these monomers without crosslinking agents and to subsequently crosslink them.

Such monomers bearing acid groups are, for example, monoethylenically unsaturated C ₃ -C ₂₅ -carboxylic acids or anhydrides such as acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid and fumaric acid. Also suitable are monoethyl-unsaturated sulfonic or phosphonic acids, for example vinylsulfonic acid, allylsulfonic acid, sulfoethylacrylate, sulfomethacrylate, sulfopropylacrylate, sulfopropyl methacrylate, 2-hydroxy-3-acryloxypropylsulfonic acid, 2-hydroxy-3-methacryloxypropylsulfonic acid, vinylphosphonic acid, allylphosphonic acid, allylphosphonic acid, allylphosphonic acid, allylphosphonic acid, Acrylamido-2-methyl-propanesulfonic acid. The monomers can be used alone or as a mixture with one another.

Preferred monomers are acrylic acid, methacrylic acid, vinyl sulfonic acid, acrylamidopropanesulfonic acid or mixtures of these acids, e.g. B. mixtures of acrylic acid and methacrylic acid, mixtures of acrylic acid and acrylamidopropanesulfonic acid or mixtures of acrylic acid and vinylsulfonic acid.

To optimize properties, it may be useful to use additional monoethylenically unsaturated compounds which do not carry acid groups but can be copolymerized with the monomers bearing acid groups. These include, for example, the amides and nitriles of monoethylenically unsaturated carboxylic acids, e.g. B. acrylamide, methacrylamide and N-vinylformamide, N-vinyl acetamide, N-methyl-vinyl acetamide, acrylonitrile and methacrylonitrile. Other suitable compounds are, for example, vinyl esters of saturated C 1 -C ₄ -carboxylic acids such as vinyl formate, vinyl acetate or vinyl propionate, alkyl vinyl ethers having at least 2 C atoms in the alkyl group, such as ethyl vinyl ether or butyl vinyl ether, esters of monoethylenically unsaturated C ₃ -C ₆ -carboxylic acids , e.g. B. esters of monohydric - to C ₁₈ alcohols and acrylic acid, methacrylic acid or maleic acid, half-ester of maleic acid, for. B. maleic acid monomethyl ester, N-vinyl lactams such as N-vinyl pyrrolidone or N-vinyl caprolactam, acrylic acid and methacrylic acid esters of alkoxylated monohydric, saturated alcohol len, e.g. B. of alcohols with 10 to 25 carbon atoms, which have been reacted with 2 to 200 moles of ethylene oxide and / or propylene oxide per mole of alcohol, and monoacrylic acid esters and monomethacrylic acid esters of polyethylene glycol or polypropylene glycol, the molecular weights (M _n ) of the polyalkylene glycols, for example, up to can be up to 2000. Other suitable monomers are styrene and alkyl-substituted styrenes such as ethylstyrene or tert-butylstyrene.

These monomers bearing no acid groups can also be used in a mixture with other monomers, for. B. Mixtures of vinyl acetate and 2-hydroxyethyl acrylate in any ratio. These monomers not carrying acid groups are added to the reaction mixture in amounts between 0 and 50% by weight, preferably less than 20% by weight.

Crosslinked polymers from monoethylenically unsaturated monomers bearing acid groups are preferred, which are optionally converted into their alkali or ammonium salts before or after the polymerization, and from 0-40% by weight, based on their total weight, of monoethylenically unsaturated monomers bearing no acid groups.

Crosslinked polymers of monoethylenically unsaturated C ₃ -C ₁₂ -carboxylic acids and / or their alkali metal or ammonium salts are preferred. In particular, crosslinked polyacrylic acids are preferred, the acid groups of which are 25-100% in the form of alkali or ammonium salts.

Compounds which have at least two ethylenically unsaturated double bonds can function as crosslinkers. Examples of compounds of this type are N, N'-methylenebisacrylamide, polyethylene glycol diacrylates and

Polyethylene glycol dimethacrylates which are each derived from polyethylene glycols having a molecular weight of from 106 to 8500, preferably 400 to 2000, derived, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate propylene glycol dimethacrylate, butane diol diacrylate is, butanediol dimethacrylate, hexanediol diacrylate, hexanediol dimethacrylate, allyl methacrylate, diacrylates and dimethacrylates of Block copolymers of ethylene oxide and propylene oxide, polyhydric alcohols esterified two or more times with acrylic acid or methacrylic acid, such as glycerol or pentaerythritol, triallylamine, dialkyldiallylammonium halides such as dimethyldiallylammonium chloride and

Diethyldiallylammonium chloride, tetraallylethylenediamine, divinylbenzene, diallyl phthalate, polyethylene glycol divinyl ether of polyethylene glycols with a molecular weight of 106 to 4000, trimethylol propanediallyl ether, butanediol divinyl ether,

Pentaerythritol triallyl ether, reaction products of 1 mole of ethylene glycol diglycidyl ether or polyethylene glycol diglycidyl ether with 2 moles of pentaerythritol triallyl ether or allyl alcohol, and / or divinylethylene urea. Preferably, water-soluble crosslinking agents are used, e.g. B. N, N'-methylene bisacrylamide, polyethylene glycol diacrylates and polyethylene glycol dimethacrylates derived from addition products of 2 to 400 moles of ethylene oxide to 1 mole of a diol or polyol, vinyl ethers of addition products of 2 to 400 moles of ethylene oxide to 1 mole of a diol or polyol , Ethylene glycol diacrylate, ethylene glycol dimethacrylate or triacrylates and trimethacrylates of addition products of 6 to 20 moles of ethylene oxide with 1 mole of glycerol, pentaerythritol triallyl ether and / or divinyl urea.

Also suitable as crosslinkers are compounds which contain at least one polymerizable ethylenically unsaturated group and at least one further functional group. The functional group of these crosslinkers must be able to react with the functional groups, essentially the acid groups, of the monomers. Suitable functional groups are, for example, hydroxyl, amino, epoxy and aziridino groups. Can be used for. B. hydroxyalkyl esters of the above monoethylenically unsaturated carboxylic acids, e.g. B. 2-hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and hydroxybutyl methacrylate, allylpiperidinium bromide, N-vinylimidazoles such as N-vinylimidazole, l-vinyl-2-methylimidazole, and N-vinylimidazolines such as N-vinylimidazoline such as 1-VinyI-2-ethylimidazoline or 1-vinyl-2-propylimidazoline, which can be used in the polymerization in the form of the free bases, in quaternized form or as a salt. Dialkylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate and diethylaminoethyl methacrylate are also suitable. The basic esters are preferably used in quaternized form or as a salt. Furthermore, e.g. B. Glycidyl (meth) acrylate can also be used.

Also suitable as crosslinkers are compounds which contain at least two functional groups which are able to react with the functional groups, essentially the acid groups of the monomers. The functional groups suitable for Merfur have already been mentioned above, ie hydroxyl, amino, epoxy, isocyanate, ester, amido and aziridino groups. Examples of such crosslinkers are ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, polyglycerol, triethanolamine, propylene glycol, polypropylene glycol, block copolymers of ethylene oxide and propylene oxide, ethanolamine, Sorbitan fatty acid esters, ethoxylated sorbitan fatty acid esters, trimethylolpropane, pentaerythritol, 1,3-butanediol, 1,4-butanediol, polyvinyl alcohol, sorbitol, starch, polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether,

Glycerol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether,

Polyaziridine compounds such as 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], 1,6-hexamethylene diethylene urea, diphenylmethane-bis-4,4'-N, N'-di-ethylene urea, halo epoxy compounds such as epichlorohydrin and α -Methylpifluor- hydrin, polyisocyanates such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate, alkylene carbonates such as l, 3-dioxolan-2-one and 4-methyl-l, 3-dioxolan-2-one, further bisoxazolines and oxazolidones, polyamidoamines and their reaction products with epichlorohydrin, also polyquaternary amines such as condensation products of dimethylamine with epichlorohydrin, homo- and copolymers of diallyldimethylammonium chloride and homo- and copolymers of dimethylaminoethyl (meth) acrylate, which are optionally quaternized with, for example, methyl chloride.

The crosslinkers are present in the reaction mixture, for example from 0.001 to 20% by weight and preferably from 0.01 to 14% by weight.

The polymerization is initiated as usual by an initiator. It is also possible to initiate the polymerization by the action of electron beams on the polymerizable, aqueous mixture. However, the polymerization can also be initiated in the absence of initiators of the type mentioned above by exposure to high-energy radiation in the presence of photoinitiators. All compounds which decompose into free radicals under the polymerization conditions can be used as polymerization initiators, e.g. B. peroxides, hydroperoxides, hydrogen peroxides, persulfates, azo compounds and the so-called redox catalysts. The use of water-soluble initiators is preferred. In some cases it is advantageous to use mixtures of different polymerization initiators, e.g. B. mixtures of hydrogen peroxide and sodium or potassium peroxodisulfate. Mixtures of hydrogen peroxide and sodium peroxodisulfate can be used in any ratio. Suitable organic peroxides are, for example, acetylacetone peroxide, methyl ethyl ketone peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, tert-amyl perpivalate, tert-butyl perpivalate, tert-butyl perneohexanoate, tert.-butyl perisobutyrate, tert.-butyl per-2-ethyl hexanoate, tert-butanoate .-Butyl permaleate, tert.-butyl perbenzoate, di- (2- ethylhexyl) peroxidicarbonate, dicyclohexylperoxidicarbonate, di- (4-tert-butylcyclohexyl) peroxidicarbonate, dimyristilperoxidicarbonate, diacetylperoxydicarbonate, allylperester, cumylperoxineodecanoate, tert.-butylper-3,5yl-acyloxyperyl-oxylacyloxy-peroxide-3,5-acyl-oxy-oxo-hexyl-oxy-oxo-2,5-oxy-oxyl-oxy-1-oxy-1-oxy-1-oxyl , Dibenzoyl peroxide and tert-amyl perneodecanoate. Particularly suitable polymerization initiators are water-soluble azo starters, e.g. B. 2,2'-azo-bis (2-amidinopropane) dihydrochloride, 2,2'-azobis- (N, N'-dimethylene) isobutyramidine dihydrochloride, 2- (carbamoylazo) isobutyronitrile, 2,2'-azobis [2- (2'-imidazolin-2-yl) propane] dihydrochloride and 4,4'-azobis (4-cyanovaleric acid). The polymerization initiators mentioned are used in conventional amounts, e.g. B. in amounts of 0.01 to 5, preferably 0.05 to 2.0 wt .-%, based on the monomers to be polymerized.

Redox catalysts are also suitable as initiators. The redox catalysts contain at least one of the above-mentioned per compounds as the oxidizing component and as reducing component, for example, ascorbic acid, glucose, sorbose, ammonium or alkali metal bisulfite, sulfite, thiosulfate, hyposulfite, pyro-sulfite or sulfide, metal salts, such as iron ( II) ions or sodium hydroxymethyl sulfoxylate. Ascorbic acid or sodium sulfite is preferably used as the reducing component of the redox catalyst. Based on the amount of monomers used in the polymerization, for example 3 × 10 ^"6 to 1 mol% of the reducing component of the redox catalyst system and 0.001 to 5.0 mol% of the oxidizing component of the redox catalyst are used.

If the polymerization is triggered by the action of high-energy radiation, so-called photoinitiators are usually used as initiators. These can be, for example, so-called α-splitters, H-abstracting systems or also azides. Examples of such initiators are benzophenone derivatives such as Michler's ketone, phenanthrene derivatives, fluorene derivatives, anthraquinone derivatives, thioxanone derivatives, coumarin derivatives, benzoin ethers and their derivatives, azo compounds such as the radical formers mentioned above, substituted hexaarylbisimidazoles or acylphosphine oxides. Examples of azides are: 2- (N, N-dimethylamino) ethyl 4-azidocinnamate, 2- (N, N-dimethylamino) ethyl 4-azidonaphthyl ketone, 2- (N, N-

Dimethylamino) ethyl 4-azidobenzoate, 5-azido-1-naphthyl-2 '- (N, N-dimethylamino) ethyl sulfone, N- (4-sulfonyl azidophenyl) maleimide, N-acetyl-4-sulfonyl azidoaniline, 4- Sulfonyl azido aniline, 4-azido aniline, 4-azidophenacyl bromide, p-azidobenzoic acid, 2,6-bis (p-azidobenzylidene) cyclohexanone and 2,6-bis (p-azido benzylidene) -4-methylcyclohexanone. If used, the photoinitiators are usually used in amounts of from 0.01 to 5% by weight, based on the monomers to be polymerized. In the subsequent crosslinking, polymers which have been prepared by the polymerization of the abovementioned monoethylenically unsaturated acids and, if appropriate, monoethylenically unsaturated comonomers and which have a molecular weight greater than 5000, preferably greater than 50,000, are reacted with compounds which have at least two groups reactive towards acid groups. This reaction can take place at room temperature or at elevated temperatures up to 220 ° C.

The suitable functional groups have already been mentioned above, i.e. Hydroxyl, amino, epoxy, isocyanate, ester, amido and aziridino groups, as well as examples of such crosslinkers.

The crosslinkers are added to the acid-bearing polymers or salts in amounts of 0.5 to 25% by weight, preferably 1 to 15% by weight, based on the amount of the polymer used.

The crosslinked polymers are preferably used in neutralized form. However, the neutralization can also have been carried out only partially. The degree of neutralization is preferably 25 to 100%, in particular 50 to 100%. Possible neutralizing agents are: alkali metal bases or ammonia or amines. Sodium hydroxide solution or potassium hydroxide solution is preferably used. However, the neutralization can also be carried out with the aid of sodium carbonate, sodium hydrogen carbonate, potassium carbonate or potassium hydrogen carbonate or other carbonates or hydrogen carbonates or ammonia. In addition, primary, secondary and tertiary amines can be used.

As a technical process for the production of these products, all processes can be used that are usually used in the production of superabsorbers, such as those used for. B. in Chapter 3 in "Modern Superabsorbent Polymer Technology", F.L. Buchholz and A.T. Graham, Wiley-VCH, 1998.

Polymerization in aqueous solution is preferred as so-called gel polymerization. 10 to 70% by weight aqueous solutions of the monomers and, if appropriate, a suitable graft base are polymerized in the presence of a radical initiator using the Trommsdorff-Norrish effect.

The polymerization reaction can be carried out in the temperature range between 0 ° C. and 150 ° C., preferably between 10 ° C. and 100 ° C., both under normal pressure and under elevated or reduced pressure. As usual, the polymerization can also be carried out in a protective gas atmosphere, preferably under nitrogen. The quality properties of the polymers can be improved further by reheating the polymer gels for several hours, for example in the temperature range from 50 to 130 ° C., preferably from 70 to 100 ° C.

Hydrogel-forming polymers which are post-crosslinked on the surface are preferred. The surface postcrosslinking can take place in a manner known per se with dried, ground and sieved polymer particles.

For this purpose, compounds which can react with the functional groups of the polymers with crosslinking are preferably applied to the surface of the hydrogel particles in the form of a water-containing solution. The water-containing solution can contain water-miscible organic solvents. Suitable solvents are alcohols such as methanol, ethanol, i-propanol or acetone.

Suitable post-crosslinking agents are, for example

Di- or polyglycidyl compounds such as phosphonic acid diglycidyl ether or ethylene glycol diglycidyl ether, bischlorohydrin ether of polyalkylene glycols,

- alkoxysilyl compounds,

Compounds containing polyaziridines, aziridine inlets, based on polyethers or substituted hydrocarbons, for example bis-N-aziridinomethane,

Polyols such as ethylene glycol, 1,2-propanediol, 1,4-butanediol, glycerol, methyltriglycol, polyethylene glycols with an average molecular weight M _w of 200-10000, di- and polyglycerol, pentaerythritol, sorbitol, the oxyethylates of these polyols and their esters with carboxylic acids or carbonic acid such as ethylene carbonate or propylene carbonate,

Carbonic acid derivatives such as urea, thiourea, guanidine, dicyandiamide, 2-oxazolidinone and its derivatives, bisoxazoline, polyoxazolines, di- and

polyisocyanates

Di- and poly-N-methylol compounds such as methylenebis (N-methylol-methacrylamide) or melamine-formaldehyde resins, Compounds with two or more blocked isocyanate groups such as, for example, trimethylhexamethylene diisocyanate blocked with 2,2,3,6-tetramethyl-piperidinone-4.

If necessary, acidic catalysts such as p-toluenesulfonic acid, phosphoric acid, boric acid or ammonium dihydrogen phosphate can be added.

Particularly suitable post-crosslinking agents are di- or polyglycidyl compounds such as ethylene glycol diglycidyl ether, the reaction products of polyamidoamines with epichlorohydrin and 2-oxazolidinone.

The crosslinking agent solution is preferably applied by spraying on a solution of the crosslinking agent in conventional reaction mixers or mixing and drying systems such as Patterson-Kelly mixers, DRAIS turbulence mixers, Lödige mixers,

Screw mixer, plate mixer, fluid bed mixer and Schugi mix. To

Spraying the crosslinker solution can be followed by a temperature treatment step, preferably in a downstream dryer, at a temperature between 80 and 230 ° C, preferably 80-190 ° C, and particularly preferably between 100 and 160 ° C, over one

Period of 5 minutes to 6 hours, preferably 10 minutes to 2 hours and particularly preferably 10 minutes to 1 hour, both fission products and

Solvent components can be removed. However, drying can also take place in the mixer itself, by heating the jacket or by blowing in a preheated carrier gas.

Steric spacers

Inert materials (powders), such as, for example, silicates with a band, chain or leaf structure (montmorillonite, kaolinite, talc), zeolites, activated carbons or polysilicic acids, can act as steric spacers. Other inorganic inert spacers are, for example, magnesium carbonate, calcium carbonate, barium sulfate, aluminum oxide, titanium dioxide and iron (II) oxide. For example, polyalkyl methacrylates or thermoplastics such as polyvinyl chloride can act as inert organic-based spacers. Polysilicic acids are preferably used which, depending on the type of production, differentiate between precipitated silica and pyrogenic silicas. Both variants are commercially available under the names AEROSIL ^® (pyrogenic silicas) or Silica FK, Sipernat ^® , Wessalon ^® (precipitated silicas). There are siloxane and silanol groups on the surface of the silica particles. The siloxane groups predominate in number. They are largely the cause of that inert character of this synthetic silica. Special types of silica are available for different applications. For example, the surface of the silicic acid can be chemically modified by adding silane, so that originally hydrophilic silicic acid forms hydrophobic variants. Some types of silica are present as mixed oxides, for example in a mixture with aluminum oxide. The spacer function can be controlled depending on the surface properties of the primary particles. Fumed silica (e.g. AEROSIL ^® ) is available in grain fractions from 7 to 40 nm.

Silica under the trade names Silica FK, Sipernat ^® , Wessalon ^® can be obtained as a powder with a grain size of 5 to 100 μm and a specific surface area of 50 - 450 m ² / g.

For use as a steric spacer, the particle size of the inert powders is preferably at least 1 μm, more preferably at least 4 μm, particularly preferably at least 20 μm and extremely preferably at least 50 μm. The use of precipitated silicas is particularly preferred.

In general, the handling of inert silica types is physiologically harmless. This fact allows the safe use of materials of this type in the hygiene article.

The base polymers coated with inert spacer material can be produced by applying the inert spacers in an aqueous or water-miscible medium or by applying the inert spacers in powder form to powdery base polymer material. The aqueous or water-miscible media are preferably applied by spraying onto dry polymer powder. In a particularly preferred production variant, pure powder / powder mixtures are produced from powdery inert spacer material and base polymer. The inert spacer material is used in a proportion of 0.05 to 5% by weight, preferably 0.1 to 1.5% by weight, particularly preferably 0.3 to 1% by weight, based on the total weight of the coated hydrogel, applied to the surface of the base polymer.

Electrostatic spacers

Cationic components can be added as electrostatic spacers. In general, it is possible to add cationic polymers for the purpose of electrostatic repulsion. This is possible, for example, with polyethyleneimines, polyvinylamines, polyamines such as polyalkylene polyamines, cationic derivatives of polyacrylamides, polyethyleneimines, polyquaternary amines, such as, for. B. condensation products from hexamethylenediamine, dimethylamine id epichlorohydrin, condensation products from dimethylamine and epichlorohydrin, copolymers of hydroxyethylcellulose and dialdehyde dimethylammonium chloride, copolymers of acrylamide and β-methacryloxyethyltrimethylammonium chloride, hydroxycellulose reacted with epichlorohydrin or trimethylammonyl ether, then quaternium amide, with quaternium diammonyl ether, then quaternized ammonium chloride with quaternized allyl, then quaternized diamine, quaternized allyl, with quaternized amine, then quaternized allyl, with quaternized allyl, methylated amine, then quaternized with quaternized, then quaternized, then quaternized, then quaternized with quaternized, then quaternized, then quaternized, then quaternized with, Addition products of epichlorohydrin to amidoamines. Polyquaternary amines can also be synthesized by reacting dimethyl sulfate with polymers such as polyethyleneimines, copolymers of vinylpyrrolidone and dimethylaminoethyl methacrylate or copolymers of ethyl methacrylate and diethylaminoethyl methacrylate. The polyquaternary amines are available in a wide range of molecular weights.

Electrostatic spacers are also generated by applying a cross-linked, cationic shell, either by means of Regenzien, which can form a network with itself, such as. B. addition products of epichlorohydrin to polyamidoamines, or by the application of cationic polymers which can react with an added crosslinker, e.g. B. polyamines or polyimines in combination with polyepoxides, multifunctional esters, multifunctional acids or multifunctional (meth) acrylates. All multifunctional amines with primary or secondary ammo groups can be used, e.g. polyethyleneimine, polyallylamine, polylysine, preferably polyvinylamine. Further examples of polyamines are ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine and polyethyleneimines, and polyamines with molecular weights of up to 4,000,000 each.

Electrostatic spacers can also be applied by adding solutions of di- or polyvalent metal salt solutions. Examples of divalent or polyvalent metal cations are Mg ²⁺ , Ca ²⁺ , Al ³⁺ , Sc ³⁺ , Ti ⁴⁺ , Mn ²⁺ , Fe ^{2 + / 3 +} , Co ²⁺ , Ni ²⁺ , Cu ^{+ 2+} , Zn ²⁺ , Y ³⁺ , Zr ⁴⁺ , Ag ⁺ , La ³⁺ , Ce ⁴⁺ , Hf ⁴⁺ , and Au ^{+ 3+} , preferred metal cations are Mg ²⁺ , Ca ²⁺ , Al ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ and La ³⁺ , and particularly preferred metal cations are Al ³⁺ , Ti ⁴⁺ and Zr ⁴⁺ . The metal cations can be used either alone or in a mixture with one another. Of the metal cations mentioned, all metal salts are suitable which have sufficient solubility in the solvent to be used. Metal salts with weakly complexing amones such as chloride, nitrate and sulfate are particularly suitable. Water, alcohols, DMF, DMSO and mixtures of these components can be used as solvents for the metal salts become. Water and water / alcohol mixtures, such as water / methanol or water / 1,2-propanediol, are particularly preferred.

In the manufacturing process, as in the case of the inert spacers, the electrostatic spacers can be applied by application in an aqueous or water-miscible medium. This is the preferred production variant when adding metal salts. Cationic polymers are applied by applying an aqueous solution or in a water-miscible solvent, optionally also as a dispersion, or else by applying in powder form on powdery base polymer material. The aqueous or water-miscible media are preferably applied by spraying onto dry polymer powder. The polymer powder can then optionally be dried. The coated base polymers are only dried at temperatures of up to 100 ° C. If higher temperatures are used, covalent bonds can form between the polyamine component and polycarboxylate, which should be avoided under all circumstances so as not to reduce the capacity of the product too much by the additional crosslinking caused thereby. For this reason, no tempering step is preferably provided for coating with polyamines. When an additional crosslinking agent is added, the tempering conditions are selected so that only the polyamine coating layer is crosslinked, but not the polycarboxylate underneath.

The cationic spacers are used in a proportion of 0.05 to 5% by weight, preferably 0.1 to 1.5% by weight, particularly preferably 0.1 to 1% by weight, based on the total weight of the coated hydrogel, applied to the surface of the base polymer.

The hydrogels mentioned are distinguished by a high absorption capacity for water and aqueous solutions and are therefore preferably used as absorbents in hygiene articles.

The water-swellable hydrogels can be present in connection with a carrier material for the hydrogels, preferably embedded as particles in a polymer fiber matrix or an open-pore polymer foam, fixed to a flat carrier material or present as particles in chambers formed from a carrier material. The invention also relates to a process for the preparation of the water-absorbent compositions

Production of water-swellable hydrogels, optionally coating the hydrogels with a steric or electrostatic spacer and

Introducing the hydrogels into a polymer fiber matrix or open-pore polymer foam or into a chamber formed from a carrier material or fixing them to a flat carrier material.

The hygiene articles which can be produced from the water-absorbing compositions according to the invention are known and described per se. They are preferably diapers, sanitary napkins and incontinence products such as incontinence pads. The structure of corresponding products is known.

Description of the test methods

Centrifuge Retention Capacity (CRC Centrifuge Retention Capacity)

This method determines the free swellability of the hydrogel in the tea bag. To determine the CRC, 0.2000 ± 0.0050 g of dried hydrogel (grain fraction 106 - 850 μm) are weighed into a 60 x 85 mm tea bag, which is then sealed. The tea bag is placed in an excess of 0.9% by weight saline solution (at least 0.83 1 saline solution / l g polymer powder) for 30 minutes. The tea bag is then centrifuged at 250 g for 3 minutes. The amount of liquid is determined by weighing the centrifuged tea bag.

Absorption under pressure (AUL Absorbency Under Load) (0.7 psi)

The measuring cell for determining the AUL 0.7 psi is a plexiglass cylinder with an inner diameter of 60 mm and a height of 50 mm, which has a glued-on stainless steel sieve bottom with a mesh size of 36 μm on the underside. The measuring cell also includes a plastic plate with a diameter of 59 mm and a weight which can be placed together with the plastic plate in the measuring cell. The weight of the plastic plate and the weight together are 1345 g. To carry out the determination of the AUL 0.7 psi, the weight of the empty plexiglass cylinder and the plastic plate is determined and noted as W ₀ . Then 0.900 ± 0.005 g of hydrogel-forming polymer (particle size distribution 150 - 800 μm) is weighed into the plexiglass cylinder and distributed as evenly as possible on the stainless steel sieve plate. Then the plastic plate is carefully placed in the plexiglass cylinder and the entire unit is weighed; the weight is noted as W _a . Now the weight is placed on the plastic plate in the plexiglass cylinder. In the middle of the petri dish with a Diameter of 200 mm and a height of 30 mm, a ceramic filter plate with a diameter of 120 mm and a porosity of 0 is placed and 0.9% by weight sodium chloride solution is filled in so that the liquid surface is flush with the filter plate surface without the surface of the filter plate wetting becomes. A round filter paper with a diameter of 90 mm and a pore size <20 μm (S&S 589 black tape from Schleicher & Schüll) is then placed on the ceramic plate. The plexiglass cylinder containing the hydrogel-forming polymer is now placed with the plastic plate and weight on the filter paper and left there for 60 minutes. After this time, the complete unit is removed from the Petri dish from the filter paper and then the weight is removed from the Plexiglas cylinder. The plexiglass cylinder containing swollen hydrogel is weighed out together with the plastic plate and the weight is noted as W _b .

The absorption under pressure (AUL) is calculated as follows:

AUL 0.7 psi [g / g] = [W _b -WaJ / [Wa-Wo]

Free Swell Rate (FSR)

To determine the free swell rate, 1.00 g (W _H ) hydrogel is spread evenly on the bottom of a plastic dish with a round bottom of approx. 6 cm. The plastic bowl has a height of approx. 2.5 cm and has a square opening of approx. 7.5 cm x 7.5 cm. With the help of a funnel, 20 g (Wu) of a synthetic urine replacement solution, which can be prepared by dissolving 2.0 g KC1, 2.0 g Na ₂ SO ₄ , 0.85 g NH ₄ H ₂ PO ₄ , 0.15 g ( NH ₄ ) ₂ HPO ₄ , 0.19 g CaCl ₂ and 0.23 g MgCl ₂ in 1 liter of distilled water, added to the center of the plastic dish. As soon as the liquid comes into contact with the hydrogel, the time measurement is started and only stopped when the hydrogel has completely absorbed all the liquid, ie until no free liquid can be seen. This time is noted as t _A. The free swell rate is then calculated according to

FSR = Wu / (W _H t _A )

Saline Flow Conductivity (SFC)

The test method for determining the SFC is described in WO 95/26209. Vortex test

50 ml of 0.9% strength by weight NaCl solution are placed in a 100 ml beaker and 2.00 g of hydrogel are rapidly added with stirring at 600 rpm using a magnetic stirrer in such a way that clumping is avoided. The time is measured in seconds until the vortex created by the stirring of the liquid is closed and a smooth surface is created.

gel strength

The rheological tests to determine the gel strength are carried out on the Controlled Stress Rheometer CSL 100 from Carrimed. All measurements are made at room temperature.

Preparation of the samples: The measurements are carried out on hydrogel particles of the sieve fraction 300-400 μm, which were previously pre-swollen in a ratio of 1:60 in 0.9% by weight NaCl solution for 1 hour. To prepare the samples to be measured, the NaCl solution is placed in 100 ml beakers, and the dry hydrogel particles are slowly added with stirring (magnetic stirrer) so that no lumps form. The stirred fish is then removed, the beaker sealed with a film and set aside for 1 hour to swell at room temperature in this state. To maintain the same conditions before the measurement expires, this manufacturing instruction must be followed exactly, since the rheological measurement is otherwise impaired and the measurement results are falsified.

Carrying out the measurement: The gel strength is determined using the oscillation mode on the CS rheometer from Carrimed using a plate-plate geometry (diameter 6 cm). To avoid the slip effect, sandblasted plate systems are used for this purpose. The sample is placed on the platter and the ramp is slowly raised to allow the gap to close slowly. The measuring gap is 1 mm and must be completely filled with sample material. The gel strength denotes the modulus of elasticity of the pre-swollen hydrogel and is measured analogously to this in the linear viscoelastic area of the sample, which is determined in a preliminary test on the same sample. For subsequent determination of the gel strength, the applied torque is gradually increased within the linear viscoelastic range (torque sweep, torque curve) in oscillation mode at constant frequency (1 Hz). In the present elastic behavior, a straight line is obtained as a measurement curve, which quantifies the gel strength as the material constant of the elastic solid.

The present measured values are mean values (number average) from 3 test series.

The following examples are intended to explain the invention in more detail.

Examples

Example 1 :

3600 g of demineralized water and 1400 g of acrylic acid are placed in a polyethylene vessel with a capacity of 10 l, which is well insulated by foamed plastic material. Now 4.0 g of tetraallyloxyethane and 5.0 g of AUyl methacrylate are added. The initiators, consisting of 2.2 g of 2,2'-azobisamidinopropane dihydrochloride, dissolved in 20 g of deionized water, 4 g of potassium peroxodisulfate, dissolved in 150 g of deionized water and 0.4 g Ascorbic acid, dissolved in 20 g of demineralized water, added successively and stirred. The reaction solution is then left to stand without stirring, a solid gel being formed by the onset of polymerization, in the course of which the temperature rises to approximately 90 ° C. This is then mechanically crushed, adjusted to a pH of 6.0 by adding 50% by weight sodium hydroxide solution. The gel is then dried, ground and sieved to a particle size distribution of 100-850 μm. 1 kg of this dried hydrogel is sprayed in a ploughshare mixer with a solution consisting of 60 g of demineralized water, 40 g of i-propanol and 1.0 g of ethylene glycol diglycidyl ether and then heat-treated at 140 ° C. for 60 minutes. The product described here has the following properties:

CRC 28.4 g / g

AUL 0.7 psi = 25.1 g / g

Gel strength = 2350 Pa

SFC 35 x 10 ^"7 cm ³ s / g Example 2:

In a well-insulated polyethylene container with a foamed plastic material

With a capacity of 30 liters, 14340 g of demineralized water and 42 g of sorbitol triallyl ether are initially charged, 3700 g of sodium bicarbonate are suspended therein and 5990 g of acrylic acid are slowly metered in so that the reaction solution is not over-foamed, the temperature of the reaction solution rising to about 3-5 Cools down. The initiators, 6.0 g of 2,2'-azobisamidinopropane dihydrochloride, dissolved in 60 g of deionized water, 12 g of potassium peroxodisulfate, dissolved in 450 g of deionized water, and 1.2 g of ascorbic acid are dissolved at a temperature of 4.degree in 50 g of demineralized water, added in succession and stirred well. The reaction solution is then left to stand without stirring, a gel being formed by the onset of polymerization, in the course of which the temperature rises to approximately 85.degree. This is then transferred to a kneader and adjusted to a pH of 6.2 by adding 50% by weight sodium hydroxide solution. The crushed gel is then dried in an air stream at 170 ° C., ground and sieved to a particle size distribution of 100-850 μm. 1 kg of this product was sprayed in a ploughshare mixer with a solution of 2 g of RETEN 204 LS (polyamidoamine-epichlorohydrin adduct from Hercules), 30 g of deionized water and 30 g of 1,2-propanediol and then at 150 for 60 minutes ° C annealed. The following properties were measured:

CRC =: 32.3 g / g

AUL 0.7 psi = 26.4 g / g

Gel strength = 1975 Pa

SFC = 25 x 10 ^"7 cm ³ s / g

Example 3:

A previously prepared separately, cooled to approx. 25 ° C and inerted by introducing nitrogen monomer solution is sucked into a laboratory kneader with a working volume of 2 1, which was absolutely evacuated by means of a vacuum pump to 980 mbar. The monomer solution is composed as follows: 825.5 g demineralized water, 431 g acrylic acid, 335 g NaOH 50%, 4.5 g "ethoxylated trimethylolpropane triacrylate" (SR 9035 oligomer from SARTOMER) and 1.5 g pentaerythritol triallyl ether (P. -30 from Daiso). For better inerting, the kneader is evacuated and then aerated with nitrogen. This process is repeated 3 times. A solution of 1.2 g of sodium persulfate, dissolved in 6.8 g of demineralized water, is then sucked in, and after a further 30 seconds another solution consisting of 0.024 g of ascorbic acid, dissolved in 4.8 g of demineralized water. It is flushed with nitrogen. On the jacket heating circuit (bypass) preheated to 75 ° C is switched to the kneader jacket, the stirrer speed is increased to 96 rpm. After the onset of polymerization and reaching T _max , the jacket heating circuit is switched back to bypass and polymerized for 15 minutes without heating / cooling, then cooled, the product is discharged, and the resulting gel particles are dried at temperatures above 100 ° C, ground and to a particle size distribution of 100 - sieved 850 μm. 500 g of this product were sprayed in a ploughshare mixer with a solution of 2 g of 2-oxazolidinone, 25 g of deionized water and 10 g of 1,2-propanediol and then heat-treated at 185 ° C. for 70 minutes. The following properties were measured:

CRC 26.3 g / g

AUL 0.7 psi = 23.8 g / g

Gel strength = 2680 Pa

SFC 50 x 10 ^"7 cm ³ s / g

Example 4:

1000 g of the polymer from Example 1 were mixed in a ploughshare mixer for 15 minutes with 10 g of Sipernat D 17 (hydrophobic precipitated silica, commercial product from Degussa AG, average particle size 10 μm). The product coated in this way has the following properties:

CRC = 28.9 g / g

SFC = 115 L0 ⁷ cm ³ s / g

Vortex time = __: 80 s

Example 5:

1000 g of the polymer from Example 1 were sprayed in a ploughshare mixer with 50 g of a solution consisting of 90 parts by weight of deionized water and 10 parts by weight of aluminum sulfate (Al ₂ (SO) ₃ ), and the mixture was then mixed for 30 minutes. The product obtained in this way has the following properties:

CRC = 27.2 g / g

SFC = 160 x 10 ^"7 cm ³ s / g

Free swell rate = 0.25 g / gs Example 6:

1000 g of the polymer from Example 1 were mixed in a ploughshare mixer for 15 minutes with 8 g of Sipernat 22 (hydrophilic precipitated silica, commercial product from Degussa AG, average particle size 100 μm). The product coated in this way has the following properties:

CRC = 29.5 g / g

SFC = 100 x 10 ^"7 cm ³ s / g

Free swell rate = 0.56 g / gs

Example 7:

1000 g of the polymer from Example 2 were mixed in a ploughshare mixer for 15 minutes with 10 g of silica FK 320 (hydrophilic precipitated silica, commercial product from Degussa AG, average particle size 15 μm). The product coated in this way has the following properties:

CRC = 32.6 g / g

SFC = 95 x 10 ^"7 cm ³ s / g

Vortex time - 58 s

Example 8:

1000 g of the polymer from Example 2 was sprayed in a ploughshare mixer with a solution consisting of 40 g of deionized water, 20 g of Polymin G 100 solution and 0.5 g of SPAN 20, and the mixture was then mixed for 20 minutes. The product obtained in this way has the following properties:

CRC = 35.4 g / g

SFC - 90 x 10 ^"7 cm ³ s / g

Vortex time = 45 s

Example 9:

1000 g of the polymer from Example 3 were mixed in a ploughshare mixer for 15 minutes with 10 g of Sipernat D 17. The product coated in this way has the following properties: CRC = 25.8 g / g

SFC = 210 l0 ^"7 cm ³ s / g

Vortex time = 105 s

Example 10:

1000 g of the polymer from Example 3 was sprayed in a ploughshare mixer with a solution consisting of 50 g of deionized water, 10 g of polyvinylamine (K value 88), 0.1 g of ethylene glycol diglycidyl ether and 0.5 g of SPAN 20, and then 20 Minutes mixed. After tempering in a laboratory drying cabinet at 80 ° C for 1 hour, the product has the following properties:

CRC = 25.6 g / g

SFC = 330 x 10 ^"7 cm ³ s / g vortex time = 20 s

Comparative Example 1:

3600 g of demineralized water and 1400 g of acrylic acid are placed in a polyethylene vessel with a capacity of 10 l, which is well insulated by foamed plastic material. Now 14 g of tetraallyl ammonium chloride are added. The initiators, consisting of 2.2 g of 2,2'-azobisamidino-propanedihydrochloride, dissolved in 20 g of deionized water, 4 g of potassium peroxodisulfate, dissolved in 150 g of deionized water and 0.4 g Ascorbic acid, dissolved in 20 g of demineralized water, added successively and stirred. The reaction solution is then left to stand without stirring, a solid gel being formed by the onset of polymerization, in the course of which the temperature rises to approximately 90 ° C. This is then crushed mechanically, adjusted to a pH of 6.0 by adding 50% by weight sodium hydroxide solution. The gel is then dried, ground and sieved to a particle size distribution of 100-850 μm. 1 kg of this dried hydrogel is sprayed in a ploughshare mixer with a solution consisting of 40 g of deionized water, 40 g of i-propanol and 0.5 g of ethylene glycol diglycidyl ether and then heat-treated at 140 ° C. for 60 minutes. The product described here has the following properties:

CRC 36.2 g / g

AUL 0.7 psi = 25.9 g / g

Gel strength = 1580 Pa

SFC 8 x 10 ^"7 cm ³ s / g Comparative Example 2:

A previously prepared separately, cooled to approx. 25 ° C and inerted by introducing nitrogen monomer solution is sucked into a laboratory kneader with a working volume of 2 1, which was absolutely evacuated by means of a vacuum pump to 980 mbar. The monomer solution is composed as follows: 825.5 g demineralized water, 431 g acrylic acid, 335 g NaOH 50%, 3.0 g methylenebisacrylamide. For better inerting, the kneader is evacuated and then aerated with nitrogen. This process is repeated 3 times. A solution of 1.2 g of sodium persulfate, dissolved in 6.8 g of demineralized water, is then sucked in, and after a further 30 seconds another solution consisting of 0.024 g of ascorbic acid, dissolved in 4.8 g of demineralized water. It is flushed with nitrogen. A jacket heating circuit (bypass) preheated to 75 ° C is switched to the kneader jacket, the stirrer speed is increased to 96 rpm. After the onset of polymerization and reaching T _max , the jacket heating circuit is switched back to bypass and polymerized for 15 minutes without heating / cooling, then cooled, the product is discharged, and the resulting gel particles are dried at temperatures above 100 ° C, ground and to a particle size distribution of 100 - sieved 850 μm. The following properties were measured:

CRC 29.4 g / g

AUL 0.7 psi = 15.8 g / g

Gel strength = 1920 Pa

SFC 5 x 10 ^"7 cm ³ s / g

Comparative Example 3:

1000 g of the polymer from comparative example 1 were mixed in a ploughshare mixer for 15 minutes with 10 g of Sipernat D 17 (hydrophobic precipitated silica, commercial product from Degussa AG, average particle size 10 μm). The product coated in this way has the following properties:

CRC = 35.8 g / g

SFC = llx L0 ⁷ cm ³ s / g

Vortex time = 85 s Comparative Example 4:

1000 g of the polymer from Comparative Example 1 were sprayed in a ploughshare mixer with 50 g of a solution consisting of 90 parts by weight of deionized water and 10 parts by weight of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), and the mixture was then mixed for 30 minutes. The product obtained in this way has the following properties:

CRC 34.6 g / g

SFC 9 10 ^"7 cm ³ s / g

Free swell rate 0.48 g / gs

Comparative Example 5:

1000 g of the polymer from comparative example 2 were mixed with 10 g of Sipernat D 17 in a ploughshare mixer for 15 minutes. The product coated in this way has the following properties:

CRC = 29.7 g / g

SFC = 6 L0 ⁷ cm ³ s / g

Vortex time = 78 s

Comparative Example 6:

1000 g of the polymer from comparative example 2 was sprayed in a ploughshare mixer with a solution consisting of 50 g of deionized water, 10 g of polyvinylamine (K value 88), 0.1 g of ethylene glycol diglycidyl ether and 0.5 g of SPAN 20, and then 20 Minutes mixed. After tempering in a laboratory drying cabinet at 80 ° C for 1 hour, the product has the following properties:

CRC = 27.8 g / g

SFC = 15 x L0 ⁷ cm ³ s / g

Vortex time = 35 s

Comparative Example 7:

14340 g of demineralized water and 42 g of sorbitol triallyl ether are placed in a polyethylene vessel with a capacity of 30 l, which is well insulated by foamed plastic material, 3700 g of sodium bicarbonate are suspended therein and 5990 g of acrylic acid are slowly metered in so that the reaction solution is not over-foamed, thereby avoiding this cools down to a temperature of approx. 3 - 5 ° C. At a temperature of 4 ° C Initiators, 6.0 g of 2,2'-azobisamidinopropane dihydrochloride, dissolved in 60 g of deionized water, 12 g of potassium peroxodisulfate, dissolved in 450 g of deionized water, and 1.2 g of ascorbic acid, dissolved in 50 g of deionized water, were added in succession and mixed well. The reaction solution is then left to stand without stirring, a gel being formed by the onset of polymerization, in the course of which the temperature rises to approximately 85.degree. This is then transferred to a kneader and adjusted to a pH of 6.2 by adding 50% by weight sodium hydroxide solution. The comminuted gel is then dried in an air stream at 170 ° C., ground, sieved to a particle size distribution of 100-850 μm and homogeneously mixed with 1.0% by weight of Aerosil 200 (pyrogenic silica, commercial product from Degussa AG, average primary particle size 12 nm ). 1 kg of this product was sprayed in a ploughshare mixer with a solution of 2 g of RETEN 204 LS (polyamidoamine-epichlorohydrin adduct from Hercules), 30 g of deionized water and 30 g of 1,2-propanediol and then at 150 for 60 minutes ° C annealed. The following properties were measured:

CRC = 31.8 g / g

SFC = 25 x 10 ^"7 cm ³ s / g

Vortex time = 65 s

Comparative Example 8:

14340 g of deionized water and 42 g of sorbitol triallyl ether are placed in a polyethylene vessel with a capacity of 30 l, which is well insulated by foamed plastic material, 3700 g of sodium bicarbonate are suspended therein and 5990 g of acyl acid are slowly metered in so that the reaction solution is not over-foamed cools down to a temperature of approx. 3 - 5 ° C. The initiators, 6.0 g of 2,2'-azobisamidinopropane dihydrochloride, dissolved in 60 g of deionized water, 12 g of potassium peroxodisulfate, dissolved in 450 g of deionized water, and 1.2 g of ascorbic acid are dissolved at a temperature of 4.degree in 50 g of demineralized water, added in succession and stirred well. The reaction solution is then left to stand without stirring, a gel being formed by the onset of polymerization, in the course of which the temperature rises to approximately 85.degree. This is then transferred to a kneader and adjusted to a pH of 6.2 by adding 50% by weight sodium hydroxide solution. The comminuted gel is then dried in an air stream at 170 ° C., ground, and sieved to a particle size distribution of 100-850 μm. 1 kg of this product was in a ploughshare mixer with a solution of 2 g of RETEN 204 LS (polyamidoamine-epichlorohydrin adduct from Hercules), 5 g of aluminum sulfate Al ₂ (SO ₄ ) ₃ , 30 g of deionized water and 30 g of 1,2-propanediol are sprayed on and then annealed at 150 ° C. for 60 minutes. The following properties were measured:

CRC 31.5 g / g

SFC 24 x 10 ^"7 cm ³ s / g

Vortex time = 73 s

Claims

claims

1. Non-water-soluble water-swellable hydrogels which are coated with steric or electrostatic spacers, characterized in that the hydrogels have the following features before coating:

Absorption under pressure (AUL) (0.7 psi) of at least 20 g / g,

- Gel strength of at least 1600 Pa.

2. Hydrogels according to claim 1, characterized in that the coated hydrogels have the following features:

- Centrifuge retention capacity (CRC) of at least 24 g / g, - Saline Flow Conductivity (SFC) of at least 30 x 10 ^"7 cm ³ s / g and

- Free Swell Rate (FSR) of at least 0.15 g / g s and / or Vortex Time of maximum 160 s.

3. Hydrogels according to claim 1 or 2, characterized in that the steric spacers are selected from bentonites, zeolites, activated carbons and

Polysilicas.

4. Hydrogels according to claim 1 or 2, characterized in that cationic polymers are used as electrostatic spacers.

5. Hydrogels according to claim 3, characterized in that the steric spacers in an amount of 0.05 to 5 wt .-%, based on the total weight of the coated hydrogels, are applied to the surface of the hydrogel.

6. Water-absorbing composition containing non-water-soluble water-swellable hydrogels according to one of claims 1 to 5.

7. Water-absorbing composition according to claim 6, characterized in that the water-swellable hydrogels as particles in one

Polymer fiber matrix or an open-pore polymer foam embedded, are fixed to a flat carrier material or are present as particles in chambers formed from a carrier material.

8. A process for the preparation of water-absorbent compositions according to claim 7

- production of water-swellable hydrogels,

- Coating the hydrogels with a steric or electrostatic spacer and

- Introducing the hydrogels into a polymer fiber matrix or an open-pore polymer foam or into chambers formed from a carrier material or fixing them to a flat carrier material.

9. Use of water-absorbent compositions according to one of claims 6 or 7 for the production of hygiene articles or other articles which serve for the absorption of aqueous liquids.

10. Hygiene article containing a water-absorbing composition according to one of claims 6 or 7 between a liquid-permeable cover sheet and a liquid-impermeable back sheet.

11. Hygiene article according to claim 10 in the form of diapers, sanitary napkins and incontinence products.

12. A method of improving the performance profile of water-absorbent compositions by increasing the permeability, capacity and swelling rate of the water-absorbent compositions

Use of non-water-soluble water-swellable hydrogels as defined in one of claims 1 to 5.

13. Method for determining water-absorbent compositions with high permeability, capacity and swelling rate by measuring the

Absorption under pressure (AUL) and gel strength for uncoated hydrogels and determination of centrifuge retention capacity (CRC), saline flow conductance (SFC) and free swell rate (FSR) of the coated hydrogels for a given water-absorbing composition and determination of the water-absorbing composition for which the hydrogels show the property spectrum mentioned in claim 1 or 2.

4. Use of non-water-soluble water-swellable hydrogels, as defined in one of claims 1 to 5, in hygiene articles or other articles which serve to absorb aqueous liquids, to increase the permeability, capacity and swelling rate.