EP1056788A1

EP1056788A1 - Cross-linking of hydrogels with phosphoric acid esters

Info

Publication number: EP1056788A1
Application number: EP99911687A
Authority: EP
Inventors: Rüdiger Funk; Volker Frenz; Uwe Stüven; Fritz Engelhardt; Thomas Daniel
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1998-02-21
Filing date: 1999-02-19
Publication date: 2000-12-06
Also published as: DE19807500C1; WO1999042495A1; CA2319457A1; JP2002504567A

Abstract

The invention relates to a method for the surface secondary cross-linking of water-absorbent polymers, according to which the polymer is sprayed with a solution for surface secondary cross-linking. As cross-linking agent said solution contains phosphoric acid esters of the formula (1) or (2), where X is OH or NH2 and R is C1-C12 alkylene, or a mixture of such esters dissolved in an inert solvent. The moist product during or after spraying is subjected to secondary cross-linking and dried by raising the temperature to 50-250 DEG C. The invention also relates to water-absorbent polymers obtainable in accordance with the above method and to their use in hygiene articles, packing materials and non-woven materials.

Description

Crosslinking of hydrogels with phosphoric acid esters

description

The present invention relates to a process for gel or surface post-crosslinking of water-absorbing hydrogels with phosphoric acid esters as crosslinking agents, polymers which can be obtained by this process, and the use of the polymers in hygiene articles and as packaging materials.

Hydrophilic, highly swellable hydrogels 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 in aqueous Liquid-swellable natural products, such as guar derivatives. Such hydrogels are used as products which absorb aqueous solutions for the production of diapers, tampons, sanitary napkins and other hygiene articles, but also as water-retaining agents in agricultural horticulture.

To improve the application properties, e.g. Rewet in the diaper and AUL (absorption under load), hydrophilic, highly swellable hydrogels are generally surface or gel crosslinked. This postcrosslinking is known per se to the person skilled in the art and is preferably carried out in the aqueous gel phase or as surface postcrosslinking of the ground and sieved polymer particles.

Crosslinkers suitable for this purpose are compounds which contain at least two groups which can form covalent bonds with the carboxyl groups of the hydrophilic polymer. Suitable crosslinkers are, for example, di- or polyglycidyl compounds, such as phosphonic acid diglycidyl ester, alkoxysilyl compounds, polyaziridines, polyamines or polyamidoamines, it being possible to use the compounds mentioned in mixtures with one another (see, for example, EP-A-0 083 022, EP-A-0 543 303 and EP-A-0 530 438). Polyamidoamines suitable as crosslinkers are described in particular in EP-A-0 349 935.

A major disadvantage of these crosslinkers is their high reactivity. Although this is desirable in terms of chemical turnover, it has a higher toxicological potential. The processing of such crosslinkers in production operations requires special protective measures to meet the requirements of the applicable 2

To comply with safety regulations and workplace hygiene. In addition, the use of such modified polymers in hygiene articles appears questionable.

Polyfunctional alcohols are also known as crosslinkers. For example, EP-A-0 372 981, US-A-4 666 983 and US-A-5 385 983 teach the use of hydrophilic polyalcohols or the use of polyhydroxy surfactants. The reaction is then carried out at temperatures of 120-250 ° C. The process has the disadvantage that the esterification reaction leading to crosslinking proceeds relatively slowly even at these temperatures.

Thus, the task was to achieve a gel or surface postcrosslinking that is just as good or better than that of the prior art, using compounds which are relatively unreactive but nevertheless reactive with carboxyl groups. This problem was solved in such a way that the reaction time was as short as possible and the reaction temperature was as low as possible. Ideally, the same reaction conditions should apply as when using highly reactive epoxides.

Surprisingly, it has now been found that esters of phosphoric acid with di- or polyols and amino alcohols are outstandingly suitable for solving this problem.

The invention relates to a method for surface post-crosslinking of water-absorbing polymers, characterized in that (i) the polymer is treated with a surface post-crosslinking solution which, as crosslinking agent, is ester of phosphoric acid of the formula

OH OH _x - _R —o — P = 0 (1) or 0— P = 0 (2),

OH _R - 0

where X is OH or NH ₂ and R is C ₁ -C ₁ alkylene,

or contains a mixture of such esters dissolved in an inert solvent and that (ii) the moist product is post-crosslinked and dried during or after the treatment by increasing the temperature. 3

The temperature for postcrosslinking is preferably 50-250 ° C, in particular between 50-200 ° C, especially between 100-180 ° C.

An acid catalyst can be added to accelerate the reaction of the surface post-crosslinking solution. All inorganic acids, their corresponding anhydrides or organic acids and their corresponding anhydrides can be used as catalysts in the process according to the invention. Examples are boric acid, sulfuric acid, hydroiodic acid, phosphoric acid, tartaric acid, acetic acid and toluenesulfonic acid. In particular, their polymeric forms, anhydrides and the acidic salts of the polyvalent acids are also suitable. Examples include boron oxide, sulfur trioxide, diphosphorus pentaoxide and ammonium dihydrogen phosphate.

The process according to the invention is preferably carried out in such a way that a solution of the surface postcrosslinker is sprayed onto the dry base polymer powder. Following the spraying, the polymer powder is thermally dried, and the crosslinking reaction can take place both before and during the drying. It is preferred to spray on a solution of the crosslinking agent in reaction mixers and spray mixers or mixing and drying systems such as Lödige mixers, ®BEPEX mixers, ®NAUTA mixers, ®SHÜGGI mixers or ®PROCESSALL. In addition, fluidized bed dryers can also be used. Drying can take place in the mixer itself, by heating the jacket or by blowing in warm air. A downstream dryer such as e.g. a rack dryer, a rotary kiln, or a heated screw. However, for example an azeotropic distillation can also be used as the drying process. The residence time at the preferred temperature in the reaction mixer or dryer is 5 to 90 minutes, preferably less than 30 minutes, very particularly preferably less than 10 minutes.

Water and mixtures of water with single or polyfunctional alcohols are preferred as the inert solvent. However, it is possible to use all organic solvents which are infinitely miscible with water, such as, for example, certain esters and ketones which, as the term indicates inert, are not reactive even under the process conditions. If an alcohol / water mixture is used, the alcohol content of this solution is 10-90% by weight, preferably 30-70% by weight, in particular 40-60% by weight. All alcohols that are miscible with water can be used as well as mixtures of several alcohols (eg methanol + glycerol + water). The use of the following alcohols in aqueous solution is particularly preferred: methanol, 4

Ethanol, isopropanol, ethylene glycol and particularly preferably 1, 2-propanediol and 1, 3-propanediol. The surface post-crosslinking solution is used in a ratio of 1-20% by weight, based on the polymer mass. A solution amount of 2.5-15% by weight with respect to polymer is particularly preferred. The crosslinker itself is used in an amount of 0.01-1.0% by weight, based on the polymer used.

The water-absorbing polymer is preferably a polymeric acrylic acid or a polyacrylate. This water-absorbing polymer can be prepared by a process known from the literature. Polymers which contain crosslinking comonomers are preferred (0.001-10 mol), but very particularly preferred are polymers which have been obtained via radical polymerization and in which a polyfunctional ethylenically unsaturated radical crosslinker has been used which additionally bears at least one free hydroxyl group ( such as pentaerythritol triallyl ether or trimethylolpropane diallyl ether).

The hydrophilic, highly swellable hydrogels to be used in the process according to the invention 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 or natural products which are swellable in aqueous liquids, such as, for example Guar derivatives. These hydrogels are known to the person skilled in the art and are described, for example, in US-A-4,286,082, DE-C-27 06 135, US-A-4 340 706, DE-C-37 13 601, DE-C-28 40 010, DE-A-43 44 548, DE-A-40 20 780, DE-A-40 15 085, DE-A-39 17 846, DE-A-38 07 289, DE-A-35 33 337, DE- A-35 03 458, DE-A-42 44 548, DE-A-42 19 607, DE-A-40 21 847, DE-A-38 31 261, DE-A-35 11 086, DE-A- 31 18 172, DE-A-30 28 043, DE-A-44 18 881, EP-A-0 801 483, EP-A-0 455 985, EP-A-0 467 073, EP-A-0 312 952, EP-A-0 205 874, EP-A-0 499 774, DE-A-26 12 846, DE-A-40 20 780, EP-A-0 205 674, US-5 145 906, ΞP- A-0 530 438, EP-A-0 670 073, US-A-4 057 521, US-A-4 062 817, US-A-4 525 527, US-A-4 295 987, US-A- 5 011 892, US-A-4 076 663 or US-A-4 931 497. The content of the aforementioned patent documents is expressly part of the present disclosure.

Hydrophilic monomers suitable for the preparation of these hydrophilic, highly swellable hydrogels are, for example, polymerizable acids, such as acrylic acid, methacrylic acid, vinylsulfonic acid, vinylphosphonic acid, maleic acid including its anhydride, fumaric acid, itaconic acid, 2-acrylamido-2-methylpropane 5 sulfonic acid, 2-acrylamido-2-methylpropanephosphonic acid and their amides, hydroxyalkyl esters and esters and amides containing amino groups or ammonium groups. Furthermore, water-soluble N-vinylamides such as N-vinylformamide or diallyldimethylammonium chloride are suitable. Preferred hydrophilic monomers are compounds of the formula

R ³ R ⁱ C = C (3)

H R2 where

R ^{1 is} hydrogen, methyl or ethyl,

R2 -COOR ⁴ , a sulfonyl group, a phosphonyl group, a phosphonyl group esterified with (C ₁ -C ₄ ) alkanol or a group of the formula

CH ₃

R5 (4) N CH ₂

H

CH ₃

in the

R ^{3 is} hydrogen, methyl, ethyl or a carboxyl group,

R ^{4 is} hydrogen, amino (C ₁ -C ₄ ) alkyl, hydroxy (C1-C4) alkyl, alkali metal or ammonium ion and

R ⁵ group, a sulfonyl group, a phosphonyl group, a carboxyl ^¬ or in each case the alkali metal or ammonium salts mean these groups.

Examples of (C ₁ -C ₄ ) alkanols are methanol, ethanol, n-propanol, isopropanol or n-butanol. Particularly preferred hydrophilic monomers are acrylic acid and methacrylic acid and their alkali metal or ammonium salts, for example Na acrylate, K acrylate or ammonium acrylate. 6

Suitable graft bases for hydrophilic hydrogels, which can be obtained by graft copolymerization of olefinically unsaturated acids or their alkali metal or ammonium salts, can be of natural or synthetic origin. Examples are starch, cellulose or cellulose derivatives and other polysaccharides and oligosaccharides, polyalkylene oxides, in particular polyethylene oxides and polypropylene oxides, and hydrophilic polyesters.

Suitable polyalkylene oxides have, for example, the formula

R ⁶ - 0 (CH ₂ - ^■ CH— 0) _n - R ⁷ (5)

wherein

R ⁶ and R ⁷ independently of one another are hydrogen, alkyl, alkenyl or acyl,

X is hydrogen or methyl and

n is an integer from 1 to 10,000.

R ⁶ and R ^{7 are} preferably hydrogen, (C ₁ -C ₄ ) alkyl, (C ₂ -C ₆ ) alkenyl or phenyl. Preferred hydrogels are in particular polyacrylates, polymethacrylates and the graft copolymers described in US Pat. Nos. 4,931,497, 5,011,892 and 5,041,496.

The hydrophilic, highly swellable hydrogels are preferably crosslinked, ie they contain compounds with at least two double bonds which are polymerized into the polymer network. Suitable crosslinkers are, in particular, methylenebisacryl or methacrylamide, esters of unsaturated mono- or polycarbonates of polyols, such as diacrylate or triacrylate, for example butanediol or ethylene glycol diacrylate or methacrylate, and trimethylolpropane triacrylate and allyl compounds, such as allyl (meth) acrylate , Triallyl cyanurate, maleic acid diallyl ester, polyallyl ester, tetraallyloxyethane, triallylamine, tetraallyl-ethylenediamine, allyl ester of phosphoric acid and vinylphosphonic acid derivatives, as described, for example, in EP-A-0 343 427. However, hydrogels which are prepared using polyallyl ethers as crosslinking agents and by acidic homopolymerization of acrylic acid are particularly preferred in the process according to the invention. Suitable crosslinking agents are pentaerythritol tri- and tetraallyl ether, polyethylene glycol diallyl ether, monoethylene glycol diallyl ether, glycerol di and glycerol ether. 7 triallyl ether, polyallyl ether based on sorbitol, and alkoxylated variants thereof.

The hydrophilic, highly swellable hydrogels can be produced by polymerization processes known per se. Polymerization in aqueous solution by the so-called gel polymerization method is preferred. Here, e.g. 15 to 50% by weight aqueous solutions of one or more hydrophilic monomers and, if appropriate, a suitable graft base in the presence of a radical initiator, preferably without mechanical mixing, using the Trommsdorff-Norrish effect (Makromol. Chem. 1, 169 (1947)) polymerized.

The polymerization reaction can be carried out, for example, 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. The polymerization can also be carried out in a protective gas atmosphere, preferably under nitrogen.

High-energy electromagnetic radiation or the usual chemical polymerization initiators can be used to initiate the polymerization. Such are, for example, organic peroxides, such as benzoyl peroxide, tert. Butyl hydroperoxide, methyl ethyl ketone peroxide, cumene hydroperoxide, azo compounds such as azodiisobutyronitrile and inorganic peroxy compounds such as (NH4) S ₂ 0β, K ₂ S ₂ θ8 or H0 ₂ . They can optionally be used in combination with reducing agents such as sodium hydrogen sulfite, iron (II) sulfate or redox systems. Redox systems generally contain an aliphatic and aromatic sulfinic acid, such as benzenesulfinic acid or toluenesulfinic acid, or contain derivatives of these acids, such as, for example, Mannich adducts of sulfinic acid, aldehydes and amino compounds, as described in DE-C-13 01 566, as the reducing component.

The quality properties of the polymers can be improved further by reheating the polymer gels for several hours in the temperature range from 50 to 130 ° C., preferably from 70 to 100 ° C.

The gels obtained are neutralized, for example, to 0-100 mol%, preferably to 25-100 mol% and particularly preferably to 50-85 mol%, based on the monomer used, it being possible to use the customary neutralizing agents, preferably alkali metal. hydroxides or oxides, but particularly preferably sodium hydroxide, sodium carbonate or sodium hydrogen carbonate. The neutralization is usually carried out by mixing in the neutralization 8 onsmittel achieved as an aqueous solution or preferably also as a solid. For this purpose, the gel is mechanically comminuted, for example using a meat grinder. The neutralizing agent is sprayed, sprinkled or poured on, and then carefully mixed 5. For this purpose, the gel mass obtained can be minced several times for homogenization.

The neutralized gel mass is then dried with a belt or roller dryer until the residual moisture content is below

10 10 wt .-%, preferably less than 5 wt .-%. The dried hydrogel is then ground and sieved, it being possible to use roller mills, pin mills or vibratory mills for the grinding. The preferred particle size of the sieved hydrogel is, for example, in the range 45-1000 μm, particularly

15 preferably at 45-850 μm, and very particularly preferably at 200-850 μm.

According to the invention, esters of di- or polyols and amino alcohols are used for crosslinking acrylate-containing polymers. 20 The esters of the polyols are represented by formula

OH

HO - R 0 - P = 0 (6)

25 I

OH

described, 30 compounds of the formula are formed in the esterification of amino alcohols

OH

H ₂ N - R 0 - P = 0 (7).

35 I

OH

If polyols are used, cyclic esters of the general formula can also be used

OH

0-P = 0 (2), 45 I I

R — 0 9 arise. In the formulas (2), (6) and (7) the substituent R represents Ci to Cι alkylene, and is preferably C ₂ - to C _ö alkylene, especially -CH ₂ -CH ₂ - or

5 - _CH - _CH2 -

CH ₃

10 These compounds can be obtained both by esterification of the free

Phosphoric acid can be obtained with the alcohols, by transesterification reactions or by the reaction of the diols, polyols or amino alcohols with phosphorus pentoxide or phosphorus oxychloride.

15 To determine the quality of the surface post-crosslinking, the dried hydrogel is then tested using the test methods known to the person skilled in the art, which are described below: Methods:

20 1) Centrifuge Retention Capacity (CRC):

This method determines the free swellability of the hydrogel in the tea bag. Approx. 0.200 g of dry hydrogel is sealed into a tea bag (format: 60 mm x 60 mm, Dexter

25 1234T paper) and soaked in a 0.9% by weight saline solution for 30 min. The tea bag is then spun in a commercial laundry centrifuge for 3 minutes (Bauknecht WS 130, 1400 rpm, basket diameter 230 mm). The amount of liquid absorbed is determined by weighing the centrifuge.

30 yeast tea bags. To take into account the absorption capacity of the tea bag itself, a blank value is determined (tea bag without hydrogel), which is subtracted from the balance (tea bag with swollen hydrogel).

35 Retention CRC [g / g] = (weight of tea bag - blank value - weight of hydrogel) -i- weight of hydrogel

2) Absorption under pressure (0.3 / 0.5 / 0.7 psi):

40 When absorbing under pressure, 0.900 g of dry hydrogel is evenly distributed on the sieve bottom of a measuring cell. The measuring cell consists of a plexiglass cylinder (height = 50 mm, diameter = 60 mm), to which a sieve made of steel mesh (mesh size 36 micron or 400 esh) is glued as the bottom.

45 10

A cover plate is placed over the evenly distributed hydrogel and loaded with an appropriate weight. The cell is then placed on a filter paper (S&S 589 black tape, diameter = 90 mm), which is on a porous glass filter plate, this filter plate is in a Petri dish (height = 30 mm, diameter = 200 mm), which is 0.9% .-% saline contains that the liquid level at the beginning of the experiment is identical to the top of the glass frit. The hydrogel is then allowed to absorb the saline solution for 60 min. Then the complete cell with the swollen gel is removed from the filter plate and the apparatus is weighed back after the weight has been removed.

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

AUL [g / g] = (Wb - Wa) / Ws

where Wb is the mass of the equipment + gel after swelling,

Wa the mass of the equipment + weight before swelling,

Ws is the weight of dry hydrogel.

The apparatus consists of a measuring cylinder + cover plate.

Examples

Production of crosslinkers 1 to 3

Crosslinker 1:

Phosphoric acid mono- [2-amino-ethyl ester]

In a three-necked flask equipped with a stirrer, internal thermometer, reflux condenser and gas inlet tube, 1 mol of aminoethanol is dissolved in 2 mol of water and P0C1 _{3 is} slowly added dropwise with cooling. The resulting hydrochloric acid is neutralized with ammonia and then stirred for a further 24 hours at room temperature. The water is then distilled off and the ester produced is recrystallized from water / alcohol at low temperature. A brownish compound with a melting point of 240 ° C. (with decomposition) is obtained. The compound is moderately soluble in water and water / alcohol mixtures and hydrolyzes only slowly. 11

Crosslinker 2:

Propanediol-1 (or 2) phosphoric acid or a mixture of both

links

In an analogous manner to the preparation of the crosslinker 1, propanediol is reacted with P0C1 ₃ in chloroform. A hygroscopic, but only slowly hydrolyzing, brownish compound is obtained which dissolves well in water and water / alcohol mixtures.

Crosslinker 3:

Mono- and diphosphoric acid esters or a mixture of both compounds.

3 mol of 2-hydroxyethyl methacrylate are placed in a three-necked flask with stirrer, internal thermometer and cooler and 1 mol of phosphorus pentoxide is added with cooling so that a

Temperature of 40 ° C is not exceeded. The mixture is stirred at room temperature for 1 hour. A brownish, paraffin-like substance below 20 ° C. is obtained which dissolves well in water and water / alcohol mixtures. The viscous, clear compound is dissolved in water and radically polymerized under nitrogen atmosphere at elevated temperature to a polymer of low molecular weight.

Examples according to the invention:

The examples according to the invention show the effect of surface postcrosslinking on the superabsorbent polymers. As is known to the person skilled in the art, this postcrosslinking can be determined by measuring the centrifuge retention (CRC) and the absorption under load (AUL). With this surface crosslinking, the CRC typically drops by 5-10 g / g, while the AUL 0.7 psi increases by approximately 10 and the AUL 0.3 psi by more than 20 g / g.

Example 1 Base polymer

6.9 kg of pure acrylic acid are diluted with 23 kg of water in a 40 1 plastic bucket. 45 g of pentaerythritol triallyl ether are added to this solution with stirring, and the sealed bucket is rendered inert by passing nitrogen through it. The polymerization is then started by adding about 400 mg of hydrogen peroxide and 200 mg of ascorbic acid. After the reaction has ended, the gel is mechanically comminuted, and sufficient sodium hydroxide solution is added until a degree of neutralization of 75 mol%, based on the acrylic acid used, is achieved. The neutralized gel is then dried on a drum dryer, 12 ground with a pin mill, and finally sieved. This is the base polymer used in the examples below. The values for CRC, AUL 20 and AUL 40 are given in the table.

Example 2

The base polymer prepared according to Example 1 is sprayed with a crosslinking agent solution in a Waring laboratory mixer. The solution is composed such that the following dosage, based on the base polymer used, is achieved:

0.40% by weight of crosslinker 1.5% by weight of propylene glycol and 5% by weight of water as solvent. The moist polymer is then divided into two batches (a) and (b), each of which is dried at 175 ° C. The drying time for batch (a) is 60 min, for batch (b) 90 min.

The crosslinking effect is not due to the propylene glycol, because surface crosslinking can be obtained with a higher amount even in purely aqueous systems. The values for CRC and AUL are given in the table.

Example 3:

The base polymer prepared according to Example 1 is sprayed with a crosslinking agent solution in a Waring laboratory mixer. The solution is composed so that the following dosage, based on the base polymer used, is achieved:

3.0% by weight of crosslinker 1 and 10% by weight of water. The moist polymer is then at 175 ° C

(a) for 60 min and

(b) dried for 90 minutes.

The use of catalysts can shorten the reaction time for surface post-crosslinking and thus the residence time in the reactor. The values for CRC, AUL 20 and AUL 40 are given in the table. 13

Example 4

Base polymer prepared according to Example 1 is sprayed with crosslinking agent solution in a Waring laboratory mixer. The solution is composed in such a way that, based on the base polymer used, the following dosage is achieved:

1.5% by weight of crosslinker 2, 10% by weight of water and 0.2% of boric acid as a catalyst. The moist polymer is then at 175 ° C

(a) for 30 min and

(b) dried for 60 minutes.

The values for CRC, AUL 20 and AUL 40 are given in the table.

Example 5

Base polymer prepared according to Example 1 is sprayed with a crosslinking agent solution in a Waring laboratory mixer. The solution is composed so that - based on the base polymer used - the following dosage is achieved:

5.0% by weight of crosslinker 3, 12% by weight of water and 0.2% by weight of ammonium dihydrogenphosphate. The moist polymer is then at 175 ° C

(a) for 30 min and

(b) dried for 60 minutes.

The values for CRC, AUL 20 and AUL 40 are given in the table.

Example 6

0.20% by weight crosslinker 2.5% by weight methanol, 5% by weight water and 0.2% ammonium dihydrogen phosphate. The moist polymer is then at 175 ° C 14

(a) for 30 min and

(b) dried for 60 minutes.

The values for CRC, AUL 20 and AUL 40 are given in the table.

Example 7

0.50% by weight of crosslinker 2, 5% by weight of propanediol-1, 2 and 5% by weight of water. The moist polymer is then at 175 ° C

(a) for 30 min and

(b) dried for 60 minutes.

The values for CRC, AUL 20 and AUL 40 are given in the T-table.

Example 8

Base polymer, prepared according to Example 1, is sprayed with a crosslinking agent solution in a Waring laboratory mixer. The solution is composed so that - based on the base polymer used - the following dosage is achieved:

0.20% by weight of crosslinker 3, 6% by weight of 1,2-propanediol and 6% by weight of water. The moist polymer is then at 175 ° C

(a) for 30 min and

(b) dried for 60 minutes.

(c) For comparison, the base polymer is sprayed with 6% by weight of 1,2-propanediol and 6% by weight of water. The damp

Polymer is then dried at 175 ° C for 60 min. No crosslinker is therefore used in this comparative example. The values for CRC, AUL 20 and AUL 40 are given in the table. Table -

Examples crosslinker drying-drying catalyst / CRC AUL 20 AUL 40 temperature time solvent [g / g] [g / g] [g / g]

Example 1-46 10 8 base polymer (not according to the invention)

Example 2a 1 175 ° C 60 min no cat. 38 30 16 PG ¹ '/ H ₂ 0

Example 2b 1 175 ° C 90 min no cat. 36 31 18 PG / H ₂ 0

-

Example 3a 1 175 ° C 60 min no cat. 37 35 15 100% H ₂ 0

Example 3b 1 175 ° C 90 min no cat. 36 32 17 100% H ₂ 0

Example 4a 2 175 ° C 30 min H ₃ B0 ₃ 36 38 25 H ₂ 0

Example 4b 2 175 ° C 60 min H ₃ B0 ₃ 35 36 28 H ₂ 0

Example 5a 3 175 ° C 30 min no cat. 33 36 24 H ₂ 0 o no cat. H Example 5b 3 175 ° C 60 min H ₂ 0 32 34 25

O

00

Ul

Example 6a 2 175 ° C 30 min NH ₄ H ₂ P0 ₄ 36 32 17 MeOH / H ₂ 0 ² »

Example 6b 2 175 ° C 60 min NH ₄ H ₂ PO ₄ 35 31 18 MeOH / H ₂ 0

Example 7a 2 175 ° C 30 min no cat. 36 32 18 PG / H ₂ 0

Example 7b 2 175 ° C 60 min no cat. 34 33 21 PG / H ₂ 0

Example 8a 3 175 ° C 30 min no cat. 36 32 17 H ₂ 0

Example 8b 3 175 ° C 60 min no cat. 34 33 19 PG / H ₂ 0 σ-

Example 8c 175 ° C 60 min no cat. 40 20 14 Comparison PG / H ₂ 0

D PG = propylene glycol

² > MeOH = methanol

The drying temperature and time relate to the tempering of the surface. solution sprayed base polymer. o O

H

* 0 o o σ 00.

Claims

17 patent claims

1. A method for surface post-crosslinking of water-absorbing polymers, characterized in that (i) the polymer is treated with a surface post-crosslinking solution, which as the crosslinking agent is ester of phosphoric acid of the formula

OH OH I I

X — R — 0 — P = 0 (1) or 0 - P = 0 (2),

OH _R _ ₀

wherein X is OH or NH ₂ and R is Cχ-Cι alkylene,

or contains a mixture of such esters dissolved in an inert solvent and that (ii) the moist product is post-crosslinked and dried during or after the treatment by increasing the temperature.

2. The method according to claim 1, characterized in that the water-absorbing polymer is a polymeric acrylic acid or a polyacrylate, in particular a polymeric acrylic acid or a polyacrylate, which by radical polymerization in

In the presence of a polyfunctional ethylenically unsaturated radical crosslinker which can additionally carry one or more free hydroxyl groups.

3. The method according to claim 1 and / or 2, characterized in that a catalyst is used for crosslinking, which comprises an inorganic acid, its corresponding anhydride, or an organic acid or its corresponding anhydride.

4. The method according to claim 3, characterized in that the acids are boric acid, sulfuric acid, hydroiodic acid, phosphoric acid, tartaric acid, acetic acid, toluenesulfonic acid, and their polymeric forms, anhydrides or acid salts.

5. The method according to one or more of claims 1 to 4, characterized in that the inert solvent is water, a mixture of water with unlimited soluble organic solvents in water or a mixture of water with monohydric or polyhydric alcohols. 18th

6. The method according to claim 5, characterized in that when using an alcohol / water mixture, the alcohol content of this solution is 10-90 wt .-%, preferably 30-70 wt .-%.

7. The method according to claim 5 and / or 6, characterized in that the alcohol is methanol, ethanol, isopropanol, ethylene glycol, 1, 2-propanediol or 1, 3-propanediol.

8. The method according to one or more of claims 1 to 4, characterized in that the surface post-crosslinking solution in a ratio of 1-20 wt .-%, in particular 2.5-15 wt .-%, based on the mass of the polymer used becomes.

9. Water-absorbent polymers produced by the process according to one or more of claims 1 to 8.

10. Use of the polymers produced by the process according to one or more of claims 1 to 8 in hygiene articles, packaging materials and in nonwovens.