KR20030068198A - Hydrogels Coated with Steric or Electrostatic Spacers - Google Patents

Abstract

The present invention is coated with a three-dimensional or electrostatic spacer, the following pre-coating characteristics:

-Absorbency under load (AUL) over 20g / g (0.7psi)

-Gel strength over 1600 Pa

And preferably the following post-coating properties:

A centrifugation residual capacity (CRC) of at least 24 g / g,

Brine flow conductivity (SFC) of at least 30 × 10 ⁻⁷ cm ³ s / g and

Free swelling rate (FSR) of at least 0.15 g / gs and / or vortex time of up to 160 seconds

A water-insoluble water-swellable hydrogel having

Description

Hydrogels coated with steric or electrostatic spacers {Hydrogels Coated with Steric or Electrostatic Spacers}

The present invention relates to hydrogels, absorbent compositions containing them, methods for their preparation, their use in hygiene products, and methods for determining suitable absorbent compositions.

Hygiene products such as baby diapers or sanitary napkins have long used high swellable hydrogels. This substantially reduces the hygiene volume.

Current trends in diaper designs are pursuing thinner structures with reduced cellulose fiber content and increased hydrogel content. An advantage of the thinner structure is that the packaging and storage costs are reduced as well as improved wearing comfort. The tendency to pursue thinner diaper structures has substantially changed aspects of the desired properties of water-swellable hydrophilic polymers. A critically important property at present is the hydrogel's ability to treat and distribute inhaled fluids. Because of the greater amount of polymer per unit area in hygiene products, the swollen polymer should not form a barrier layer for subsequent fluid (gel blocking). Gel blocking occurs when the fluid wets the surface of the highly absorbent hydrogel particles and the shell swells. The result is a barrier layer that reduces liquid diffusion into the particles and causes leakage. Good gel permeability and good transport properties allow for optimal utilization of the entire hygiene product.

The purpose of using large amounts of high swellable hydrogels is to control the degree of crosslinking in the starting polymer to the desired level and then postcrosslink to the optimum absorbency and gel strength. Improved gel permeability values can only be generated from the high crosslink density of the starting polymer. However, higher crosslinking densities occur with reduced absorption capacity and lowered swelling rate in the polymer. As a result, increasing the hydrogel content of hygiene products requires the incorporation of an additional layer to prevent leakage, which in turn creates a bulky hygiene product, which ultimately serves the practical purpose of manufacturing thinner hygiene products. Are opposed. A possible way to provide improved transport properties and to avoid gel blocking is to shift the particle size spectrum to higher levels. However, this lowers the wetting speed because the surface area of the absorbent material is reduced. This is not desirable.

Another method of obtaining improved gel permeability is surface postcrosslinking, which imparts high gel strength on the hydrogel body in the swollen state. Gels with insufficient strength can be deformed by pressure, for example pressure due to the body weight of the wearer of the hygiene article, thus blocking the voids in the hydrogel / cellulose fiber absorbent and thus preventing the continuous absorption of the fluid. For this reason, surface postcrosslinking is a suitable method for increasing gel strength because increasing crosslinking density in the starting polymer is inevitable. Surface postcrosslinking increases the crosslinking density in the shell of hydrogel particles, resulting in a higher level of absorbency under load (AUL) by the resulting base polymer. While the absorbency in hydrogel shells is lowered, the core of the hydrogel particles has improved absorption capacity (compared to the shell) due to the presence of movable polymer chains, resulting in improved fluid permeability of the shell structure. .

However, large amounts of high swellable hydrogels still cause gel blockage. Therefore, the ability to conduct the fluid in the swollen state should be an important criterion. Only good fluid conductivity makes full use of the real advantages of high swellable hydrogels, namely the excellent absorbency and retention capacity for aqueous body fluids. However, it is important that fluid conduction occurs during the desired period of use of the hygiene article. In addition, sufficient absorption capacity of the hydrogel should be used during the treatment. The ability of the hydrogel to conduct fluid is quantified in terms of saline flow conductivity (SFC). SFC measures the ability of the formed hydrogel layer to conduct fluid under a given pressure. At high levels of use, it is believed that the hydrogel particles contact each other in a swollen state, forming a continuous absorbent layer in which fluid distribution occurs.

Continuous deformation of the surface of the base polymer (surface-postcrosslinked starting polymer) is known.

DE-A-3 523 617 relates to the addition of finely divided amorphous silica to a dry hydrogel powder and then to surface postcrosslinking with the carboxyl-reactive crosslinker material.

In the prior art, aluminum sulfate is used as the sole crosslinker in surface postcrosslinking or in combination with other crosslinkers.

WO 95/22356 relates to modifying an absorbent polymer with another polymer to improve the absorbency. Preferred modifiers are polyamines and polyimines. However, according to Tables 1 and 2, the effect on SFC is very small.

WO 95/26209 relates to an absorbent structure having at least one region containing 60-100% of a high swellable hydrogel having at least 30 × 10 ⁻⁷ cm ³ s / g SFC and at least 23 g / g PUP 0.7 psi. will be. Such high swellable hydrogels are exemplified as obtainable by surface postcrosslinking. As is evident in Tables 1 and 2, this type of treatment can provide increased SFC only at reduced gel volume, in other words there is an inverse relationship between retention and gel permeability.

SFC increases with increasing particle size of the high swellable hydrogel. As the particle size increases, the surface area of the high swellable hydrogel particles decreases relative to their volume, and as a result the swelling rate decreases. Therefore, from the above experimental results, it can be estimated that the swelling speed is inversely dependent on the SFC.

It is an object of the present invention to provide a high swellable hydrogel or absorbent composition with good transport properties and high permeability combined with high final absorption capacity and high swelling rate when used in hygiene articles. In contrast to the prior art in which high absorption capacity, high liquid transport performance and rapid swelling on the hydrogel portion are mutually exclusive, the resulting new high swellable hydrogel combines contrasting parameters. In addition, thin sanitary articles can be made through the use of large amounts of the high swellable hydrogels of the present invention. For this purpose a high swellable hydrogel must be produced which simultaneously exhibits high swelling or absorption rate, high gel permeability and high retention. If there is an excellent fluid distribution, it should be possible to optimally utilize the high total capacity of the high swellable hydrogels of the invention in the absorbent layer.

We find the following pre-coating properties:

-Absorbency under load (AUL) of over 20 g / g (0.7psi),

-Gel strength over 1600 Pa

With water-insoluble water-swellable hydrogels coated with steric or electrostatic spacers characterized in that it has been found that this object is achieved according to the invention.

In addition, the coated hydrogel preferably has the following properties:

A centrifugation residual capacity (CRC) of at least 24 g / g,

A brine flow conductivity (SFC) of at least 30 × 10 ⁻⁷ , preferably at least 60 × 10 ⁻⁷ cm ³ s / g, and

Free swelling rate (FSR) of at least 0.15 g / g and / or vortex time of not more than 160 seconds.

The term "absorbent" relates to an aqueous system which may contain organic or inorganic compounds in solution as well as water, in particular body fluids such as urine, blood or fluids containing them.

The hydrogels of the present invention and absorbent compositions containing them are useful for making hygiene articles or other articles for absorbing aqueous fluids. The present invention therefore also relates to a sanitary article comprising an absorbent composition according to the invention between a liquid-impermeable topsheet and a liquid-impermeable backsheet. Hygiene products may be present in the form of diapers, sanitary napkins and incontinence products.

The present invention also provides a method for improving the performance profile of an absorbent composition by improving the permeability, capacity and swelling rate of the absorbent composition by the use of a water-insoluble water-swellable hydrogel as defined above.

The present invention also measures the absorbency under load (AUL) and gel strength of an uncoated hydrogel for a given absorbent composition, and the centrifugation residual capacity (CRC), saline flow conductivity (SFC) and free of the coated hydrogel. By determining the swelling rate (FSR) and determining whether the hydrogel exhibits the above mentioned characteristic spectra for the absorbent composition, there is provided a method for determining the absorbent composition with high permeability, capacity and swelling rate.

The present invention also provides the use of a hydrogel as defined above to improve permeability, capacity and swelling rate in hygiene articles or other articles for absorbing aqueous fluids.

Surprisingly, it has an AUL (0.7 psi) of at least 20 g / g, preferably at least 22 g / g, particularly preferably at least 24 g / g, very preferably at least 26 g / g, at least 1600 Pa, preferably at least 1800 Pa, in particular It has been found that the object is sufficiently achieved by using a base polymer which preferably has a gel strength of at least 2000 Pa and whose surface is then coated with a steric (inert) or electrostatic spacer. The base polymer with these properties ensures that under restraint the spacer effect is not counteracted by excessive gel particle deformability.

The technique of adding steric or electrostatic spacers makes it possible to produce hygiene articles with high hydrogel content in the absorbent layer. Also, because cellulose fibers have a weak negative charge on the surface, hydrogels with electrostatic spacers have improved binding to cellulose fibers. This is particularly advantageous because the property profile of the hydrogel with electrostatic spacers and cellulose fibers allows the creation of an absorbent layer without the need for additional auxiliaries to fix the hydrogel in the fiber matrix. Binding to the cellulose fibers automatically affects the fixation of the hydrogel material, thus preventing, for example, undesirably redistributing the hydrogel material to the surface of the absorbent core.

The high swellable polymer particles of the present invention excel in high absorption capacity, improved liquid transport performance and high swelling rate. For this reason, hygiene products can be made very thin. Increased levels of the high-dose, high swellable hydrogels of the present invention provide high absorption performance, thus avoiding leakage problems. At the same time, the improved liquid distribution performance makes it possible to fully exploit the high absorption capacity.

The present invention

(1) 20 g / g or more, preferably 22 g / g or more, particularly preferably 24 g / g or more, very preferably 26 g / g or more AUL (0.7 psi) and 1600 Pa, preferably 1800 Pa or more, particularly preferably Preselects a high swellable base polymer with a gel strength of at least 2000 Pa,

(2) A novel high swellable hydrogel is prepared by post-treating (coating) the surface of the base polymer selected according to the above criteria with a steric or electrostatic spacer.

Coating such a preselected hydrogel provides a high swellable hydrogel that, in contrast to the prior art, combines high gel permeability and high retention and high swelling or absorption rate.

Thus, this produces a hydrogel having a combination of the following properties:

At least 24 g / g, preferably at least 26 g / g, more preferably at least 28 g / g, even more preferably at least 30 g / g, particularly preferably at least 32 g / g, most preferably at least 35 g / g CRC, and

At least 30 × 10 ⁻⁷ cm ³ s / g, preferably at least 60 × 10 ⁻⁷ cm ³ s / g, preferably at least 80 × 10 ⁻⁷ cm ³ s / g, more preferably at least 100 × 10 ^-7 cm ³ s / g or more, even more preferably 120 × 10 ^-7 cm ³ s / g or more, particularly preferably 150 × 10 ^-7 cm ³ s / g, very preferably 200 × 10 ^-7 at least cm ³ s / g, most preferably at least 300 × 10 ⁻⁷ cm ³ s / g, SFC, and

At least 0.15 g / gs, preferably at least 0.20 g / gs, more preferably at least 0.30 g / gs, even more preferably at least 0.50 g / gs, particularly preferably at least 0.70 g / gs, most preferably Is a free swelling rate of 1.00 g / gs or more, or

Vortex time of 160 seconds or less, preferably 120 seconds or less, more preferably 90 seconds or less, particularly preferably 60 seconds or less, and most preferably 30 seconds or less.

Water-swellable hydrogels with spacer

The hydrogel-forming polymers are in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers, crosslinked cellulose or starch ethers, crosslinked carboxymethylcellulose, partially crosslinked poly on an appropriate grafting basis Natural materials swellable in alkylene oxides or aqueous fluids such as guar derivatives, alginates and carrageenans.

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

Where

R ¹ and R ² are independently hydrogen, alkyl, alkenyl or aryl,

X is hydrogen or methyl,

n is an integer from 1 to 10000.

R ¹ and R ² are each preferably hydrogen, (C ₁ -C ₄ ) -alkyl, (C ₂ -C ₆ ) -alkenyl or phenyl.

Preferred hydrogel-forming polymers are crosslinked polymers having acid groups which are mainly present in the form of salts, generally in the form of alkali metal or ammonium salts. Such polymers swell particularly strongly when in contact with an aqueous fluid to form a gel.

Preference is given to polymers obtained by crosslinking the polymerization or copolymerization of acid-functional monoethylenically unsaturated monomers or salts thereof. It is also possible to (co) polymerize and then crosslink the monomers without a crosslinking agent.

Examples of monomers having acid groups include monoethylenically unsaturated C ₃ to 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, aconitinic acid and fumaric acid. Monoethylenically unsaturated sulfonic acids or phosphonic acids such as vinylsulfonic acid, allylsulfonic acid, sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-acryloyl It is also possible to use oxypropylsulfonic acid, 2-hydroxy-3-methacryloyloxypropylsulfonic acid, vinylphosphonic acid, allylphosphonic acid, styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. The monomers can be used alone or in combination.

Preferred monomers are acrylic acid, methacrylic acid, vinylsulfonic acid, acrylamidopropanesulfonic acid or mixtures thereof, for example a mixture of acrylic acid and methacrylic acid, a mixture of acrylic acid and acrylamidopropanesulfonic acid or a mixture of acrylic acid and vinylsulfonic acid. .

In order to optimize the properties, it is appropriate to use additional monoethylenically unsaturated compounds which do not contain acid groups but are copolymerizable with monomers comprising acid groups. Such compounds are for example amides and nitriles of monoethylenically unsaturated carboxylic acids such as acrylamide, methacrylamide and N-vinylformamide, N-vinylacetamide, N-methyl-N-vinylacetamide, Acrylonitrile and methacrylonitrile. Examples of further suitable compounds include vinyl esters of saturated C ₁ -to C ₄ -carboxylic acids, such as vinyl formate, vinyl acetate or vinyl propionate, alkyl vinyl ethers having two or more carbon atoms in the alkyl group, for example For example ethylvinyl ether or butyl vinyl ether, esters of monoethylenically unsaturated C ₃ to C ₆ -carboxylic acids, for example monovalent C ₁ to C ₁₈ -alcohols and esters of acrylic acid, methacrylic acid or maleic acid , Monoesters of maleic acid, for example methyl hydrogen maleate, N-vinyllactams such as N-vinylpyrrolidone or N-vinylcaprolactam, acrylic and methacrylic esters of alkoxylated monohydric saturated alcohols, for example Esters of alcohols having 10 to 25 carbon atoms reacted with 2 to 200 moles of ethylene oxide and / or propylene oxide per mole of alcohol, and polyethylene glycol or poly And a monoacrylate ester and monomethacrylate ester of propylene glycol (molar mass of the polyalkylene glycol (Mn) is not more than 2000). Further suitable monomers are styrene and alkyl-substituted styrenes such as ethyl styrene or t-butyl styrene.

Monomers without acid groups can be used in admixture with other monomers, for example in admixture of any suitable proportion of vinyl acetate and 2-hydroxyethyl acrylate. Such monomers having no acid groups are added to the reaction mixture in an amount of 0 to 50% by weight, preferably less than 20% by weight.

Cross-linked polymers of monoethylenically unsaturated monomers comprising acid groups and optionally converted to alkali metal or ammonium salts before or after polymerization and from 0 to 40% by weight of acid groups, based on the total weight Is preferred.

Preference is given to crosslinked polymers of monoethylenically unsaturated C ₃ -C ₁₂ -carboxylic acids and / or alkali metal or ammonium salts thereof. Particular preference is given to crosslinked polyacrylic acids in which 25 to 100% of the acid groups are present as alkali metal or ammonium salts.

Possible crosslinkers include compounds containing two or more ethylenically unsaturated double bonds. Examples of compounds of this type are N, N'-methylenebisacrylamide, polyethylene glycol diacrylate and polyethylene glycol dimethacryl derived from polyethylene glycol having a molecular weight of 106 to 8500, preferably a molecular weight of 400 to 2000, respectively. Latex, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, butanediol diacrylate, butanediol diacrylate Methacrylate, hexanediol diacrylate, hexanediol dimethacrylate, allyl methacrylate, diacrylate and dimethacrylate, acrylic acid or methacrylic acid of block copolymers of ethylene oxide and propylene oxide, double or higher Este Polyhydric alcohols such as glycerol or pentaerythritol, triallylamine, dialkyldiallylammonium halides such as dimethyldiallylammonium chloride and diethyldiallylammonium chloride, tetraallylethylenediamine, divinylbenzene, diallyl phthalate, Polyethylene glycol divinyl ether, trimethylolpropane diallyl ether, butanediol divinyl ether, pentaerythritol triallyl ether, 1 mole of ethylene glycol diglycidyl ether or polyethylene glycol diglylie of polyethylene glycol having a molecular weight of 106 to 4000 Reaction product of cydyl ether with 2 moles of pentaerythritol triallyl ether or allyl alcohol, and / or divinylethyleneurea. Water-soluble crosslinkers such as N, N'-methylenebisacrylamide, polyethylene glycol diacrylates and polyethylene glycol dimethacrylates derived from addition products of 2 to 400 moles of ethylene oxide and 1 mole of diols or polyols, 2 Ethylene glycol dimethacrylate or tri of vinyl ether, ethylene glycol diacrylate, addition product of 6 to 20 moles of ethylene oxide and 1 mole of glycerol of an addition product of from 1 to 400 moles of ethylene oxide and 1 mole of diol or polyol Preference is given to acrylates and trimethacrylates, pentaerythritol triallyl ethers and / or divinylureas.

Possible crosslinkers include compounds containing at least one polymerizable ethylenically unsaturated group and at least one additional functional group. The functional groups of such crosslinkers should be able to react with the functional groups of the monomer, in particular the acid groups. Suitable functional groups include, for example, hydroxyl, amino, epoxy and aziridino groups. For example the monoethylenically unsaturated carboxylic acids mentioned above, for example 2-hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate And hydroxybutyl methacrylate, allylpiperidinium bromide, N-vinylimidazoles such as N-vinylimidazole, 1-vinyl-2-methylimidazole and N-vinylimidazolines such as N-vinylimidazoline, 1-vinyl-2-methylimidazoline, 1-vinyl-2-ethylimidazoline or 1-vinyl-2-propylimidazoline are useful and they are in the form of free bases in the polymerization. , Quaternized forms or as salts. It is also possible to use dialkylaminoalkyl acrylates and dialkylaminoalkyl methacrylates such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate and diethylaminoethyl methacrylate. Do. Basic esters are preferably used as quaternized forms or salts. For example, glycidyl (meth) acrylate can also be used.

Useful crosslinkers further include compounds containing at least two functional groups capable of reacting with the functional groups of the monomer, essentially with acid groups. Suitable functional groups have already been mentioned above, that is to say 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, propyl Glycol diglycidyl ether and polypropylene glycol diglycidyl ether, polyaziridine compounds such as 2,2-bishydroxymethylbutanol tris [3- (1-aziridinyl) propionate], 1,6 -Hexamethylenediethyleneurea, diphenylmethanebis-4,4'-N, N'-diethyleneurea, halo epoxy compounds such as epichlorohydrin and α-methyl-epifluorohydrin, polyisocyanates such as 2,4-toluylene diisocyanate and hexamethylene diisocyanate, alkylene carbonates such as 1,3-dioxolan-2-one and 4-methyl-1,3-dioxolan-2-one, bisoxazoline And reaction products of oxazolidone, polyamidoamine and epichlorohydrin, condensation products of multiple quaternary amines such as dimethylamine and epichlorohydrin, homo- and copolymers of diallyl-dimethylammonium chloride, and For example optionally methyl chloride And a copolymer of 4 alone quaternised dimethyl amino ethyl (meth) acrylate is.

The crosslinking agent is present in the reaction mixture at 0.001 to 20% by weight, preferably 0.01 to 14% by weight.

The polymerization is usually initiated in a conventional manner by the initiator. However, polymerization may also be initiated by electron beams acting on the polymerizable aqueous mixture. However, polymerization may also be initiated by the action of high energy radiation in the presence of a photoinitiator in the absence of an initiator of the kind mentioned above. Useful polymerization initiators include all compounds that decompose into free radicals under polymerization conditions, such as peroxides, hydroperoxides, hydrogen peroxide, persulfates, azo compounds and redox catalysts. Preference is given to the use of water soluble initiators. In some cases, it is advantageous to use mixtures of different polymerization initiators, for example hydrogen peroxide with sodium persulfate or potassium persulfate. Mixtures of hydrogen peroxide and sodium persulfate can be used in any proportion. Examples of suitable organic peroxides include acetylacetone peroxide, methyl ethyl ketone peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-amyl perpivalate, t-butyl perfivalate, t-butyl pernehexaenoate, t-butyl perisobutyrate, t-butyl per-2-ethylhexanoate, t-butyl perisononanoate, t-butyl permaleate, t-butyl perbenzoate, di (2-ethylhexyl) peroxy Dicarbonate, dicyclohexyl peroxydicarbonate, di (4-t-butylcyclohexyl) peroxydicarbonate, dimyristyl peroxydicarbonate, diacetyl peroxydicarbonate, allyl perester, Cumyl perosinodecanoate, t-butyl per-3,5,5-trimethylhexanoate, acetylcyclohexylsulfonyl peroxide, dilauryl peroxide, dibenzoyl peroxide and t-amyl perneodecanoate . Particularly suitable polymerization initiators are water-soluble azo initiators, for example 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis- (N, N'-dimethylene) isobutyrami Dine 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, for example in amounts of 0.01 to 5% by weight, preferably 0.05 to 2.0% by weight, based on the monomers to be polymerized.

Useful initiators also include redox catalysts. In the redox catalyst, the oxidizing component is at least one of the above defined compounds, and the reducing component is for example ascorbic acid, glucose, sorbose, ammonium or alkali metal disulfite, sulfite, thiosulfate, hyposulfite, pyrosulfite or Sulfides, or metal salts, such as iron (II) ions or sodium hydroxymethyl sulfoxylate. The reducing component in the redox catalyst is preferably ascorbic acid or sodium sulfite. Based on the amount of monomer used in the polymerization, 3 x 10 ^-6 to 1 mol% for the reducing component of the redox catalyst system and 0.001 to 5.0 mol% for the oxidation component of the redox catalyst can be used.

When initiating polymerization using high energy radiation, the initiator used is usually a photoinitiator. Photoinitiators include, for example, α-splitters, H-separation systems or other azide. Examples of such initiators are benzophenone derivatives such as Michaeller's ketones, phenanthrene derivatives, fluorene derivatives, anthraquinone derivatives, thioxanthone derivatives, coumarin derivatives, benzoin ethers and derivatives thereof, azo compounds such as those mentioned above Free radical former, substituted hexaarylbisimidazole or acylphosphine oxide. Examples of azide are 2- (N, N-dimethylamino) ethyl 4-azidocinnamate, 2- (N, N-dimethylamino) ethyl 4-azidonaphthyl ketone, 2- (N, N-dimethyl Amino) ethyl 4-azidobenzoate, 5-azido-1-naphthyl-2 '-(N, N-dimethylamino) ethyl sulfone, N- (4-sulfonylazido-phenyl) maleimide, N -Acetyl-4-sulfonylazidoaniline, 4-sulfonylazidoaniline, 4-azidoaniline, 4-azidophenacyl bromide, p-azidobenzoic acid, 2,6-bis (p-azidobenzylidene) Cyclohexanone and 2,6-bis (p-azidobenzylidene) -4-methyl-cyclohexanone. If used, photoinitiators are usually used in amounts of 0.01 to 5% by weight of the monomers to be polymerized.

Subsequent crosslinking steps comprise at least two groups which are prepared by polymerization of the above-mentioned monoethylenically unsaturated acids and optionally monoethylenically unsaturated comonomers and which have a polymer having a molecular weight of at least 5000, preferably at least 50000. And reacting with a compound having. This reaction can occur at room temperature or at elevated temperatures of up to 220 ° C.

Suitable functional groups are examples of such crosslinkers as well as the groups already mentioned above, ie hydroxyl, amino, epoxy, isocyanate, ester, amido and aziridino groups. The crosslinking agent is added to the acid-functional polymer or salt in an amount of 0.5 to 25% by weight, preferably 1 to 15% by weight, based on the amount of polymer used.

The crosslinked polymer is preferably used in fully neutralized form. However, neutralization may only be partial. The degree of neutralization is preferably in the range of 25 to 100%, in particular 50 to 100%. Useful neutralizers include alkali metal bases or ammonia / amines. It is preferable to use aqueous sodium hydroxide solution or aqueous potassium hydroxide solution. However, neutralization may also be carried out using sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate or other carbonates or bicarbonates or ammonia. Primary, secondary and tertiary amines may also be used.

Industrial methods useful for preparing such products are commonly used to prepare superabsorbents, as described in "Modern Superabsorbent Polymer Technology", FLBuchholz and ATGraham, Wiley-VCH, 1998, Chapter 3. Include all the ways to be.

Polymerization in aqueous solution is preferably carried out as gel polymerization. This involves polymerizing a 10-70% by weight aqueous solution of monomer and optionally suitable grafted base in the presence of a free-radical initiator by using the Tromsmsdorff-Norrish effect.

The polymerization reaction can be carried out at 0 to 150 ° C., preferably at 10 to 100 ° C. as well as at atmospheric pressure or above or under reduced pressure. Typically, the polymerization may be carried out in a protective gas atmosphere, preferably under nitrogen. The performance characteristics of the polymer can then be further improved by heating the polymer gel at 50 to 130 ° C., preferably at 70 to 100 ° C. for several hours.

Surface postcrosslinked hydrogel-forming polymers are preferred. Surface postcrosslinking can be performed in a conventional manner using dried, milled and sorted polymer particles.

In order to effect surface postcrosslinking, a compound capable of reacting with the functional groups of the polymer by crosslinking is applied to the surface of the hydrogel particles, preferably in the form of an aqueous solution. The aqueous solution may contain a water-miscible organic solvent. Suitable solvents are alcohols such as methanol, ethanol, i-propanol or acetone.

Suitable surface postcrosslinkers include, for example:

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

Aziridine compounds based on alkoxysilyl compounds, polyaziridines, polyethers or substituted hydrocarbons, for example bis-N-aziridinomethane,

Polyols such as ethylene glycol, 1,2-propanediol, 1,4-butanediol, glycerol, methyltriglycol, polyethylene glycols having an average molecular weight Mw of 200 to 10000, di- and polyglycerols, pentaerythritol, sorbitol, Esters of such polyols with ethoxylates and carboxylic acids or carbonic acids, such as ethylene carbonate or propylene carbonate,

Carbonic acid derivatives such as urea, thiourea, guanidine, dicyandiamide, 2-oxazolidinone and derivatives thereof, bisoxazolin, polyoxazolines, di- and polyisocyanates,

Di- and poly-N-methylol compounds, for example methylenebis (N-methylolmethacrylamide) or melamine-formaldehyde resins,

Compounds having at least two block isocyanate groups, for example trimethylhexamethylene diisocyanate blocked with 2,2,3,6-tetramethylpiperidin-4-one.

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

Particularly suitable surface postcrosslinkers are reaction products of di- or polyglycidyl compounds, such as ethylene glycol diglycidyl ether, polyamidoamine with epichlorohydrin and 2-oxazolidinone.

The crosslinker solution can be prepared in conventional reaction mixers or mixing and drying equipment such as Patterson-Kelly mixers, DRAIS vortex mixers, Loedige mixers, screw mixers, plate mixers, fluidized bed mixers and Schugi mixers. It is preferably applied by spraying with a solution of a crosslinking agent. Following spraying of the crosslinker solution, preferably 5 minutes to 6 hours, preferably 10 minutes to 2 hours at 80-230 ° C., preferably 80-190 ° C., particularly preferably 100-160 ° C., in a downflow dryer. , Particularly preferably for 10 minutes to 1 hour, during which the cracking product as well as the solvent fraction can be removed. However, drying may also occur in the mixer itself by heating the jacket or blowing in preheated carrier gas.

Solid spacer

Useful steric spacers include inert materials (powders), for example silicates (montmorillonite, kaolinite, talc) having a band, chain or sheet structure, zeolite, activated carbon or silica. Inorganic inert spacers further include, for example, magnesium carbonate, calcium carbonate, barium sulfate, aluminum oxide, titanium dioxide and iron (II) oxide. Organic inert spacers include, for example, polyalkyl methacrylates or thermoplastics, for example polyvinyl chloride. Preference is given to using silica, which is divided into precipitated silica and pyrogenic silica depending on the method of preparation. Both variants are commonly available under the trade names AEROSIL ^(R) (pyrogenic silica) or silica FK, Sipernat ^(R) , Wessalon ^(R) (precipitated silica). The surface of the silica particles has siloxane and silanol groups. More siloxane groups are present. These contribute to the substantially inert character of synthetic silica. Certain kinds of silica can be used for different applications. For example, silane may be added to chemically modify the silica surface such that the hydrophilic silica is transformed into a hydrophobic variant. Some silica grades can be used as mixed oxides, for example in combination with aluminum oxide. The spacer function can be adjusted according to the surface composition of the main particles. Pyrogenic silicas (eg aerosils ^(R) ) are available in particle size fractions of 7-40 nm. Tradenames Silica FK, Cifernat ^(R) and Wesalon ^(R) silica can be obtained as a powder having a particle size fraction of 5 to 100 μm and a specific surface area of 50 to 450 m ² / g.

For use as a steric spacer, the particle size of the inert powder is preferably at least 1 μm, more preferably at least 4 μm, particularly preferably at least 20 μm, very preferably at least 50 μm. Particular preference is given to the use of precipitated silica.

Handling of inert silica grades is generally physiologically safe. This makes it possible to use this kind of material in hygiene products without hesitation.

Base polymers coated with an inert spacer material can be prepared by applying the inert spacer in an aqueous or water-miscible medium or by applying the inert spacer in powder form to the ground base polymer material. The aqueous or water-miscible medium is preferably applied by spraying on the dry polymer powder. In a particularly preferred form of the production process, pure powder / powder blends are prepared from ground inert spacer materials and base polymers. The inert spacer material is applied to the surface of the base polymer in a proportion of 0.05 to 5% by weight, preferably 0.1 to 1.5% by weight and particularly preferably 0.3 to 1% by weight of the total weight of the coated hydrogel.

Electrostatic spacer

Cationic components may also be added as electrostatic spacers. It is generally possible to add to cationic polymers for the purpose of electrostatic repulsion. This is for example polyethyleneimine, polyvinylamine, polyamines such as polyalkylenepolyamines, cationic derivatives of polyacrylamides, polyethyleneimines, polyquaternary amines, for example hexamethylenediamine, dimethylamine and epichlorohydrin. Condensation products, condensation products of dimethylamine and epichlorohydrin, copolymers of hydroxyethylcellulose and diallyldimethylammonium chloride, copolymers of acrylamide and β-methacryloxy-ethyltrimethylammonium chloride, with epichlorohydrin The reaction is then accomplished using hydroxycellulose, quaternized with trimethylamine, homopolymers of diallyldimethylammonium chloride or addition reaction products of epichlorohydrin with amidoamine. Polyquaternary amines are synthesized by the reaction of dimethyl sulfate with a polymer such as polyethyleneimine, vinylpyrrolidone and dimethylaminoethyl methacrylate, or copolymers of ethyl methacrylate and diethylaminoethyl methacrylate. May be Polyquaternary amines can be used in a wide range of molecular weights.

Electrostatic spacers are themselves cationic polymers, such as polyepoxy, that can react with reagents that can form a network, for example, by addition reaction products of epichlorohydrin and polyamidoamine, or with added crosslinking agents. By applying a polyamine or a polyimine, a polyfunctional ester, a polyfunctional acid or a polyfunctional (meth) acrylate in combination with the adduct. It is also possible to use polyfunctional amines having primary or secondary amino groups, for example polyethyleneimine, polyallylamine, polylysine, preferably polyvinylamine. Further examples of polyamines are in each case ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylene-pentamine, pentaethylenehexamine and polyethyleneimine and polyamines having a molar mass of up to 4000000.

The electrostatic spacer can be applied by adding a divalent or higher valence metal salt solution. Examples of divalent or higher valence metal cations include 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 may be used alone as well as mixed with each other. Of the metal cations mentioned, all salts with suitable solubility in the solvent used are suitable. Particularly suitable are metal salts with weakly complexing anions such as, for example, chlorides, nitrates and sulfates. Solvents useful for metal salts include water, alcohols, DMF, DMSO, and mixtures thereof. Especially preferred are water and water-alcohol mixtures, for example water-methanol or water-1,2-propanediol.

In the manufacturing method, the electrostatic spacer may be applied similarly to the inert spacer by applying in an aqueous or water-miscible medium. In the case of the addition of metal salts this is the preferred method of preparation. The cationic polymer is applied to the fine powder base polymer material by application as an aqueous solution or optionally as a dispersion in a water-miscible solvent or in powder form. Aqueous or water-miscible media are preferably applied by spraying on the dry polymer powder. The polymer powder may then optionally be dried, in which case the coated base polymer is uniquely dried at temperatures below 100 ° C. Higher temperatures form covalent bonds between the polyamine component and the polycarboxylate, so this situation should be avoided to ensure that the resulting additional crosslinking does not excessively lower the capacity of the product. For this reason, it is preferable that the heat treatment step is not involved when coated with polyamine. When additional crosslinking agents are used, the heat treatment conditions are selected such that they are only in the polyamine coating layer to be crosslinked and not in the polycarboxylates below.

The cationic spacer is applied to the surface of the base polymer 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 hydrogel to be coated.

The hydrogels mentioned are particularly highly absorbent in water and aqueous solutions and are therefore preferably used as absorbents in hygiene products.

The water-swellable hydrogel is preferably embedded in the polymeric fiber substrate or open-celled polymeric foam as particles, fixed on a sheet-like base material or present as particles in a chamber formed from the base material, May also be present with the box material for the gel.

The invention also

Preparing a water-swellable hydrogel,

Optionally hydrogels are coated with steric or electrostatic spacers,

Providing a method for preparing an absorbent composition by introducing the hydrogel into a polymer fiber substrate or a continuous foamed polymer foam or into a chamber formed from a base material or by immobilizing on a sheet-like base material.

Hygiene products that can be produced from the absorbent compositions of the present invention are known and described per se. It is preferably a diaper, sanitary napkin and incontinence product, such as an incontinence liner. The structure of such products is known.

Description of the test method

Centrifuge Residual Capacity (CRC)

This method measures the free swelling of hydrogels in tea bags. 0.2000 ± 0.0050 g of dried hydrogel (particle size fraction 106-850 μm) is sealed in a tea bag of size 60 × 85 mm. The tea bag is then immersed for 30 minutes in 0.9% by weight excess sodium chloride solution (at least 0.83 liters of sodium chloride solution / 1 g of polymer powder). The teabag is then centrifuged at 250 g for 3 minutes. The amount of liquid is determined by weighing the centrifuged tea bags.

Absorbing Capacity Under Load (AUL) 0.7psi

The measuring cell for determining AUL 0.7 psi is a Plexiglas cylinder with an internal diameter of 60 mm and a height of 50 mm. On the underside is glued a stainless steel mesh bottom with a 36 μm mesh size. The measuring cell further comprises a plastic plate having a diameter of 59 mm and a weight which can be located in the measuring cell together with the plastic plate. The total weight of the plastic plates and weights is 1345 g. AUL 0.7 psi is determined by measuring the weight of the empty plexiglass cylinder and plastic plate and recorded as W ₀ . Subsequently, 0.900 ± 0.005 g (particle size distribution: 150-800 μm) of the hydrogel-forming polymer is weighed into the Plexiglas cylinder and distributed very uniformly on the stainless steel sieve. Then, the plastic plate is carefully placed in the plexiglass cylinder, the whole unit is weighed and the weight is recorded as W _a . The weight is then placed on the plastic plate of the flexglass cylinder. A ceramic filter plate with a diameter of 120 mm and a zero porosity is placed in the middle of a petri dish with a diameter of 200 mm and a height of 30 mm. Introduce the solution. Round filter paper (S & S 589 Schwarzband from Schleicher & Schuell) with a diameter of 90 mm and a pore size of less than 20 μm is successively placed on a ceramic plate. The plexiglass cylinder containing the hydrogel-forming polymer is placed on top of the filter paper together with the plastic plate and weight and left for 60 minutes. After this period, the entire unit is removed from the filter paper in the Petri dish and the weight is removed from the Plexiglas cylinder. The plexiglass cylinder containing the swollen hydrogel is weighed together with the plastic plate and the weight is recorded as W _b .

AUL is calculated by the following formula.

AUL 0.7psi [g / g] = [W _b -W _a ] / [W _a -W ₀ ]

Free Swelling Rate (FSR)

1.00 g (W _H ) of hydrogels were evenly applied to the bottom of a plastic survey boat with a round bottom of about 6 cm. The plastic survey boat has a round bottom of about 6 cm in diameter, about 2.5 cm in depth, and a top of about 7.5 cm by 7.5 cm square. Then 1 liter of 2.0 g KCl, 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 20 g (W _u ) of synthetic urine solution, which can be prepared by dissolving in distilled water, was added to the center of the survey boat using a funnel. When indicated by the disappearance of the collected fluid, the time the hydrogel absorbs all the fluid is recorded and denoted as t _A. The free swelling speed is calculated from the following equation.

FSR = W _u / (W _H × t _A )

Brine Flow Conductivity (SFC)

Test methods for determining SFCs are described in WO 95/26219.

Vortex time

50 ml of 0.9 wt% NaCl solution is measured into a 100 ml beaker. While the saline solution is stirred at 600 rpm with a magnetic stirrer, 2.00 g of hydrogel is poured quickly to avoid aggregation. It took the time (seconds) that the vortex caused by stirring stopped and the surface of the brine solution was flattened.

Gel strength

Rheological studies were performed to determine gel strength on a CSL100 stress controlled flow meter from Carrimed. All measurements were performed at room temperature.

Sample Preparation: Measurements were performed on hydrogel particles of 300-400 μm sieve size fractions pre-swelled for 1 hour at a ratio of 1:60 in 0.9 wt.% NaCl solution. To prepare the sample to be measured, the NaCl solution was first placed in a 100 ml beaker and the dry hydrogel particles were slowly added while stirring (self) to avoid aggregation. The stir bar was then removed, the beaker was sealed with a film, and left in this state for 1 hour at room temperature for swelling. Before making the measurements, you must actually follow this manufacturing method to ensure the same conditions, otherwise the rheological measurements will be damaged and the measured results will be distorted.

Measurement Procedure: Gel strength is measured using a Carrimed CS flowmeter via a vibratory method using a plate-plate geometry (6 cm in diameter). To avoid slipping, sandblasting plate systems are used for this purpose. Place the sample on the base plate and slowly lift the incline to allow the gap to narrow gradually. The measuring interval is measured to be 1 mm, which must be absolutely completely filled with the sample material. Gel strength is the modulus of hydrogel preswelled as defined and is similar to the modulus in the linear viscoelastic region of the sample determined in preliminary tests on the same sample. Then, in order to determine the gel strength, a torque sweep is performed in an oscillating manner in the linear viscoelastic region at a constant frequency (1 Hz). For a given elastic behavior, the measurement curve obtained is in the form of a straight line, which quantifies the gel strength as the material constant of the elastic solid.

The measurement reported is the number average of three consecutive measurements.

The following examples further illustrate the invention.

Embodiment 1 of the present invention

3600 g of deionized water and 1400 g of acrylic acid were placed in a 10 liter capacity polyethylene container completely insulated with foamed plastic material followed by 4.0 g of tetraallyloxyethane and 5.0 g of allyl methacrylate. 2.2 g of 2,2'-azobisamidinopropane dihydrochloride (dissolved in 20 g of deionized water), 4 g of potassium persulfate (dissolved in 150 g of deionized water) and 0.4 g of ascorbic acid (20 g of deionized) Initiator, dissolved in deionized water, was added continuously and stirred at 4 ° C. The reaction solution was then left without stirring. Subsequent polymerization in the course of raising the temperature to about 90 ° C. produced a hard gel. This was then mechanically milled and adjusted to pH 6.0 with 50% by weight aqueous sodium hydroxide solution. The gel was then dried, ground and classified into a particle size distribution of 100 to 850 μm. In a plowshare mixer, 1 kg of dried hydrogel was sprayed with a solution consisting of 60 g of demineralized water, 40 g of i-propanol and 1.0 g of ethylene glycol diglycidyl ether, followed by heat at 140 ° C. for 60 minutes. Treated. 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 × 10 ^-7 cm ³ s / g

Embodiment 2 of the present invention

14340 g of demineralized water and 42 g of sorbitol triallyl ether were placed in a 30 liter capacity polyethylene container completely insulated with foamed plastic material. 3700 g of sodium bicarbonate was suspended at the initial introduction and 5990 g of acrylic acid was added slowly at a rate that avoids overexposure of the reaction solution. The reaction solution was cooled to about 3-5 ° C. Initiator, 6.0 g of 2,2'-azobisamidinopropane dihydrochloride (dissolved in 60 g of demineralized water), 12 g of potassium persulfate (soluble in 450 g of demineralized water), and 1.2 g of ascorbic acid (50 g of Dissolved in demineralized water) was added continuously and stirred thoroughly at 4 ° C. The reaction solution was then left without stirring. Subsequent polymerization in the course of raising the temperature to about 85 ° C. produced a gel. The gel was transferred to a kneader and adjusted to pH 6.2 by the addition of 50% by weight aqueous sodium hydroxide solution. The milled gel was then dried in air stream at 170 ° C., milled and classified into a particle size distribution of 100 to 850 μm. In a moisturizing mixer, 1 kg of this product was sprayed with 2 g of RETEN 204LS (polyamidoamine-epichlorohydrin adduct from Hercules), 30 g of demineralized water and 30 g of 1,2-propanediol, followed by 150 Heat treated at 60 ° C. for 60 minutes. The following properties were measured.

CRC = 32.3 g / g

AUL 0.7 psi = 26.4 g / g

Gel Strength = 1975Pa

SFC = 25 × 10 ^-7 cm ³ s / g

Embodiment 3 of the present invention

2 liters of WERNER & PFLEIDERER laboratory kneaders, vacuumed to 980 millibar absolute pressure with a vacuum pump, cooled to about 25 ° C and inertly prepared by passing through nitrogen The solution was aspirated into the kneader. The monomer solution consists of the following composition: 825.5 g deionized 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). To improve inactivation, the kneader was evacuated and then refilled with nitrogen. This operation was repeated three times. 1.2 g of sodium persulfate solution (dissolved in 6.8 g of demineralized water) was aspirated and then further aspirated a solution consisting of 0.024 g of ascorbic acid dissolved in 4.8 g of deionized water after 30 seconds. After nitrogen purge, the preheated jacket heating circuit bypassed at 75 ° C. was converted to the kneader jacket and the stirrer speed was increased to 96 rpm. After the initiation of polymerization and T _max was reached, the jacket heating circuit was switched back to bypass, the batch was polymerized by supplementing the batch for 15 minutes without heating / cooling, then cooled and released. The obtained gel particles were dried at 100 ° C. or higher, pulverized and classified into a particle size distribution of 100 to 850 μm. A 500 g product was sprayed with a solution of 2 g 2-oxazolidinone, 25 g deionized water and 10 g 1,2-propanediol in a moisturizing mixer 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 × 10 ^-7 cm ³ s / g

Embodiment 4 of the present invention

1000 g of the polymer of Example 1 of the present invention was moisturized mixed with 10 g of Ciphernat D 17 (hydrophobic precipitated silica, commercially available from Degussa AG, average particle size 10 μm) for 15 minutes. The coated product has the following properties:

CRC = 28.9 g / g

SFC = 115 × 10 ^-7 cm ³ s / g

Vortex Time = 80 Seconds

Embodiment 5 of the present invention

1000 g of the polymer of Example 1 of the present invention was sprayed in a moisturizing mixer with 50 g of a solution composed of 90 parts by weight of deionized water and 10 parts by weight of aluminum sulfate (Al ₂ (SO ₄ ) ₃ ), followed by supplementation for 30 minutes to mix. The product obtained has the following properties:

CRC = 27.2 g / g

SFC = 160 × 10 ^-7 cm ³ s / g

Free-swelling rate = 0.25 g / gs

Embodiment 6 of the present invention

1000 g of the polymer of Example 1 of the present invention was moisturized and mixed with 8 g of Ciphernat 22 (hydrophilic precipitated silica, commercially available from Degussa AG, average particle size 100 μm) for 15 minutes. The coated product has the following properties:

CRC = 29.5 g / g

SFC = 100 × 10 ^-7 cm ³ s / g

Free-swelling rate = 0.56 g / gs

Example 7 of the present invention

1000 g of the polymer of Example 2 of the present invention was moisturized with 15 g of Kieselsaeure FK 320 (hydrophilic precipitated silica, commercially available from Degussa AG, average particle size 15 μm) for 15 minutes. The coated product has the following properties:

CRC = 32.6 g / g

SFC = 95 × 10 ^-7 cm ³ s / g

Eddy Current Time = 58 seconds

Embodiment 8 of the present invention

1000 g of the polymer of Example 2 of the present invention was sprayed in a moisturizing mixer with a solution consisting of 40 g deionized water, 20 g polymin G 100 solution and 0.5 g span 20, followed by supplementation for 20 minutes to mix. The product obtained has the following properties:

CRC = 35.4 g / g

SFC = 90 × 10 ^-7 cm ³ s / g

Vortex Time = 45 seconds

Embodiment 9 of the present invention

1000 g of the polymer of Example 3 of the present invention was moisturized mixed with 10 g of Spurnat D17 for 15 minutes. The product thus coated has the following properties.

CRC = 25.8 g / g

SFC = 210 × 10 ^-7 cm ³ s / g

Vortex Time = 105 seconds

Embodiment 10 of the present invention

1000 g of the polymer of Example 3 was sprayed in a moisturizing mixer with a solution consisting of 50 g deionized water, 10 g polyvinylamine (K88), 0.1 g ethylene glycol diglycidyl ether and 0.5 g span 20 Next, replenish for 20 minutes and mix. After heat treatment for 1 hour in a laboratory drying cabinet at 80 ° C., the product has the following properties.

CRC = 25.6 g / g

SFC = 330 × 10 ^-7 cm ³ s / g

Vortex Time = 20 seconds

Comparative Example 1

3600 g of deionized water and 1400 g of acrylic acid were placed in a 10 liter capacity polyethylene container completely insulated with foamed plastic material followed by 14 g of tetraallylammonium chloride. 2.2 g of 2,2'-azobisamidinopropane dihydrochloride (dissolved in 20 g of deionized water), 4 g of potassium persulfate (dissolved in 150 g of deionized water) and 0.4 g of ascorbic acid (20 g of deionized) Initiator, dissolved in deionized water, was added continuously and stirred at 4 ° C. The reaction solution was left without stirring. Subsequent polymerization as the temperature rose to about 90 ° C. formed a hard gel. This was then milled mechanically and adjusted to pH 6.0 with 50% by weight aqueous sodium hydroxide solution. The gel was then dried, ground and classified into a particle size distribution of 100-850 μm. 1 kg of this dried hydrogel was sprayed in a moisturizing mixer with a solution consisting of 40 g of demineralized water, 40 g of i-propanol and 0.5 g of ethylene glycol diglycidyl ether, followed by heat treatment at 140 ° C. for 60 minutes. The product described herein has the following properties.

CRC = 36.2 g / g

AUL 0.7psi = 25.9g / g

Gel strength = 1580 Pa

SFC = 8 × 10 ^-7 cm ³ s / g

Comparative Example 2

Into the kneader, a previously prepared monomer solution inactivated by vacuuming a Warner and Playler laboratory lab kneader with a working capacity of 2 liters to 980 millibar absolute pressure by a vacuum pump, cooled to about 25 ° C. and passed through nitrogen Aspirated. The monomer solution had the following composition: 825.5 g deionized water, 431 g acrylic acid, 335 g NaOH 50%, 3.0 g methylenebisacrylamide. To improve inactivation, the kneader was evacuated and then refilled with nitrogen. This operation was repeated three times. 1.2 g of sodium persulfate solution (dissolved in 6.8 g of deionized water) was aspirated, followed by further aspiration of a solution consisting of 0.024 g of ascorbic acid dissolved in 4.8 g of deionized water after 30 seconds. After nitrogen purge, the preheated jacket heating circuit bypassed at 75 ° C. was converted to the kneader jacket and the stirrer speed was increased to 96 rpm. After the initiation of polymerization and T _max was reached, the jacket heating circuit was switched back to bypass, the batch was polymerized by supplementing the batch for 15 minutes without heating / cooling, then cooled and released. The obtained gel particles were dried at 100 ° C. or higher, pulverized and classified into a particle size distribution of 100 to 850 μm. The following properties were measured.

CRC = 29.4 g / g

AUL 0.7psi = 15.8g / g

Gel strength = 1920 Pa

SFC = 5 × 10 ^-7 cm ³ s / g

Comparative Example 3

1000 g of the polymer of Comparative Example 1 was moisturized and mixed with 10 g of Ciphernat D 17 (hydrophobic precipitated silica, commercially available from Degussa AG, average particle size 10 μm) for 15 minutes. The coated product has the following properties:

CRC = 35.8g / g

SFC = 11 × 10 ^-7 cm ³ s / g

Vortex Time = 85 Seconds

Comparative Example 4

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

CRC = 34.6 g / g

SFC = 9 × 10 ^-7 cm ³ s / g

Free Swelling Rate = 0.48g / gs

Comparative Example 5

1000 g of the polymer of Comparative Example 2 was moisturized mixed with 10 g of Spurnat D17 for 15 minutes. The product thus coated has the following properties.

CRC = 29.7 g / g

SFC = 6 × 10 ^-7 cm ³ s / g

Eddy Current Time = 78 seconds

Comparative Example 6

1000 g of the polymer of Comparative Example 2 was sprayed in a moisturizing mixer with a solution consisting of 50 g deionized water, 10 g polyvinylamine (K88), 0.1 g ethylene glycol diglycidyl ether and 0.5 g span 20 Replenish for minutes and mix. After heat treatment for 1 hour in a laboratory drying cabinet at 80 ° C., the product has the following properties.

CRC = 27.8 g / g

SFC = 15 × 10 ^-7 cm ³ s / g

Vortex Time = 35 seconds

Comparative Example 7

14340 g of demineralized water and 42 g of sorbitol triallyl ether were placed in a 30 liter capacity polyethylene container completely insulated with foamed plastic material. 3700 g of sodium bicarbonate was suspended in the first introduction, and 5990 g of acrylic acid was added slowly at a rate to avoid overexposure of the reaction solution. The reaction solution was cooled to about 3-5 ° C. Initiator, 6.0 g of 2,2'-azobisamidinopropane dihydrochloride (dissolved in 60 g of demineralized water), 12 g of potassium persulfate (soluble in 450 g of demineralized water) and 1.2 g of ascorbic acid (50 g of demineralized water) Dissolved in), and stirred thoroughly at 4 ° C. The reaction solution was left without stirring. Subsequent polymerization as the temperature rose to about 85 ° C. formed a gel. This was then transferred to a kneader and adjusted to pH 6.2 by addition of 50% by weight aqueous sodium hydroxide solution. The milled gel was then dried in air stream at 170 ° C., ground and classified into a particle size distribution of 100 to 850 μm, and 1.0 wt% of Aerosil 200 (pyrogenic silica, commercially available from Degussa AG, average major particle size). 12 nm) and mixed homogeneously. 1 kg of this product is sprayed in a moisturizing mixer with a solution of 2 g of RETEN 204 LS (polyamidoamine-epichlorohydrin adduct from Hercules), 30 g of demineralized water, 30 g of 1,2-propanediol Then, heat treatment was performed at 150 ° C. for 60 minutes. The following properties were measured:

CRC = 31.8g / g

SFC = 25 × 10 ^-7 cm ³ s / g

Vortex Time = 65 Seconds

Comparative Example 8

14340 g of demineralized water and 42 g of sorbitol triallyl ether were placed in a 30 liter capacity polyethylene container completely insulated with foamed plastic material. In the first introduction, 3700 g of sodium bicarbonate was suspended and 5990 g of acrylic acid was added slowly at a rate to avoid overfoaming of the reaction solution. The reaction solution was cooled to about 3-5 ° C. Initiator, 6.0 g of 2,2'-azobisamidinopropane dihydrochloride (dissolved in 60 g of demineralized water), 12 g of potassium persulfate (dissolved in 450 g of demineralized water) and 1.2 g of ascorbic acid (50 g of demineralized water) Dissolved in), and stirred thoroughly at 4 ° C. The reaction solution was left without stirring. Subsequent polymerization as the temperature rose to about 85 ° C. formed a gel. This was then transferred to a kneader and adjusted to pH 6.2 with 50% by weight aqueous sodium hydroxide solution. The milled gel was then dried in air stream at 170 ° C., milled and classified into a particle size distribution of 100-850 μm. 1 kg of this product was taken in a moisturizing mixer with 2 g of Reten 204 LS (polyamidoamine-epichlorohydrin adduct from Hercules), 5 g of aluminum sulfate Al ₂ (SO ₄ ) ₃ , 30 g of demineralized water and 30 g of 1 Sprayed with a solution of, 2-propanediol and then heat treated at 150 ° C. for 60 minutes. The following properties were measured:

CRC = 31.5g / g

SFC = 24 × 10 ^-7 cm ³ s / g

Vortex Time = 73 seconds

Claims (14)

Water-insoluble water-swellable hydrogels coated with steric or electrostatic spacers, characterized by the following precoating properties: -Absorbency under load (AUL) over 20g / g (0.7psi) Gel strength of at least 1600 Pa. A hydrogel according to claim 1 characterized by the following post-coating properties: A centrifugation residual capacity (CRC) of at least 24 g / g, Brine flow conductivity (SFC) of at least 30 × 10 ⁻⁷ cm ³ s / g and Free swelling rate (FSR) of at least 0.15 g / gs and / or vortex time of up to 160 seconds. 3. The hydrogel of claim 1, wherein the steric spacer is selected from bentonite, zeolite, activated carbon and silica. 3. The hydrogel of claim 1 or 2, wherein the electrostatic spacer is a cationic polymer. 4. The hydrogel of claim 3, wherein the steric spacer is applied to the surface of the hydrogel in an amount of 0.05 to 5 percent by weight based on the total weight of the coated hydrogel. Absorbent composition containing the water-insoluble water-swellable hydrogel according to any one of claims 1 to 5. 7. The absorbent composition of claim 6, wherein the water-swellable hydrogel is embedded as particles in a polymeric fiber substrate or continuous foam polymeric foam, fixed on a sheet-like base material, or present as particles in a chamber formed from the base material. Preparing a water-swellable hydrogel, Coating the hydrogel with steric or electrostatic spacers, A process for producing the absorbent composition according to claim 6, wherein the hydrogel is introduced into a polymer fiber substrate or a continuous foamed polymer foam or in a chamber formed from a base material, or fixed on a sheet-like base material. Use of the absorbent composition according to claim 6 or 7 for the manufacture of hygiene products or other articles for absorbing aqueous liquids. A hygiene article comprising the absorbent composition according to claim 6 or 7, between a liquid-impermeable topsheet and a liquid-impermeable backsheet. The hygiene product of claim 10 in the form of a diaper, sanitary napkin and incontinence product. A method for improving the performance profile of an absorbent composition by promoting the permeability, capacity and swelling rate of the absorbent composition by the use of a water-insoluble water-swellable hydrogel according to any one of claims 1 to 5. The absorbent capacity under load (AUL) and gel strength of the uncoated hydrogels were measured and the centrifugation residual capacity (CRC), saline flow conductivity (SFC) and free swelling rate (FSR) of the coated hydrogels for a given absorbent composition. And determining the absorbent composition as to whether the hydrogel exhibits the characteristic spectrum mentioned in claim 1 or 2, thereby determining the absorbent composition with high permeability, capacity and swelling rate. Use of a water-insoluble water-swellable hydrogel as defined in any one of claims 1 to 5 for promoting permeability, capacity and swelling rate in hygiene articles or other articles for absorbing aqueous solutions.