EP1427452A1

EP1427452A1 - Super-absorbing hydrogels with a specific particle size distribution

Info

Publication number: EP1427452A1
Application number: EP02797946A
Authority: EP
Inventors: Dieter Hermeling; Uwe Stüven; Ulrike Hoss
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2001-09-07
Filing date: 2002-09-03
Publication date: 2004-06-16
Also published as: US20040265387A1; JP2005501960A; WO2003022316A1

Abstract

The invention relates to novel hydrophilic swellable polymers with a specific particle size distribution, to the production of the same and to the use thereof for absorbing aqueous liquids, for example in the foodstuff industry, medical field, building and design industries, agricultural industry or fireproofing applications.

Description

SUPER ABSORBENT HYDROGE E PARTICULAR PARTICLE SIZE DISTRIBUTION

description

The present invention relates to novel hydrophilic swellable polymers of a certain particle size distribution, their production and their use for the absorption of aqueous liquids, for example in the food sector, in medicine, in construction and construction, in the agricultural industry or in fire protection.

In particular, the present invention relates to novel hydrophilic swellable acidic and / or post-crosslinked polymers with a particle size distribution of less than 250 μm.

Swellable hydrogel-forming polymers, so-called super-absorbers (super-absorbing polymers or SAP) are also referred to in the present application as aqueous liquid-absorbing hydrogel-forming polymers and are known in principle from the prior art. These are networks of flexible hydrophilic polymers, which can be both ionic and nonionic in nature. They can optionally be post-crosslinked. These are able to absorb and bind aqueous liquids with the formation of a hydrogel and are therefore preferred for the production of tampons, diapers, sanitary napkins and other hygiene articles in the absorption of body fluids. In the hygiene articles, the superabsorbers are usually located in the so-called absorbent core, which includes fibers (cellulose fibers), which, as a kind of liquid reservoir, temporarily store the spontaneously applied amounts of liquid and a good drainage of body fluids in the absorbent core to ensure superabsorbent.

Hydrogel-forming polymers are in particular polymers made 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 swellable in aqueous liquids Natural products such as guar derivatives, alginates and carrageenans.

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

Preferred hydrogel-forming polymers with a high degree of crosslinking and / or surface-re-crosslinked polymers with acid groups which are predominantly in the form of their salts, generally alkali metal or ammonium salts. Also preferred are acidic hydrogel-forming polymers which can optionally be post-crosslinked. Such polymers swell particularly strongly and quickly into gels on contact with aqueous liquids.

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

Synthetic products of this type can be prepared from suitable hydrophilic monomers, for example acrylic acid, by known polymerization processes. Polymerization in aqueous solution by the so-called gel polymerization method is preferred. This produces polymers in the form of aqueous jellies which, after mechanical comminution with suitable apparatus, are obtained in solid form by known drying processes.

Water-insoluble but water-swellable hydrogels are therefore obtained by incorporating crosslinking sites in the polymer. It turned out that the degree of crosslinking not only determines the water solubility of these products, but is also responsible for their absorption capacity and gel strength. Accordingly, the hydrogels of the first generation have been optimized primarily in the direction of high absorption capacities in order to save large amounts of cellulose fluff, especially when used in the hygiene sector. With the trend towards using higher amounts of hydrogel particles and packing them more and more tightly, other demands on the absorption profile, such as gel strength or absorption under pressure, came to the fore.

However, the effect of so-called gel blocking continued to appear, especially when large amounts of highly swellable hydrogels were used. Gel blocking occurs when liquid wets the surface of the highly absorbent hydrogel particles and the outer shell swells. This creates a barrier layer that makes it difficult for liquids to diffuse into the interior of the particle. The diffusion times are too short to ensure quantitative absorption. So for example it is on It is essential for the hygiene sector to embed the highly absorbent hydrogel particles in a sufficient amount of a fiber matrix, which still takes on the task of distributing and transferring the liquid.

In order to avoid gel blocking, the permeability or transport properties of the tightly packed hydrogels are of crucial importance, especially when larger amounts are used (important for use in the agricultural sector). The ability of the hydrogel to transfer and distribute the liquid is decisive both for the channeling of the aqueous liquid to be absorbed to neighboring hydrogel particles and into the interior of the particle in order to utilize the available absorption capacity. In the swollen state, the polymer must not form a barrier layer for subsequent liquid (gel blocking), as is the case with multiple exposure to aqueous liquids. The most important criterion is the ability to transfer liquid when swollen. Only this criterion would allow the real benefits of hydrogels, namely their pronounced absorption and retention capacity for aqueous liquids, to be fully exploited.

However, these criteria are only important in certain areas of application, primarily in the hygiene sector. In other areas of application, it may well be desirable for blocking to occur, for example when using cable sheaths or in the construction industry, where sealing behavior is a key factor in assessing superabsorbent quality.

Also important is the fact that the swelling rate of the hydrogel is sufficiently fast, depending on the area of application of the highly swellable hydrogel material. The swelling rate of the hydrogel is quantified in the laboratory by measuring the time-dependent AUL at a low pressure, in the experiments measured at a pressure of 0.014 psi, or by the so-called vortex test. A defined amount of hydrogel is sprinkled into an aqueous salt solution while stirring and the time is measured in seconds until the vortex of the liquid created by the stirring is closed and a smooth surface is formed. The vortex test is therefore a direct measure of the rate of absorption. There has been no lack of attempts to avoid gel blocking and to improve permeability, but these are mostly based on post-treatment of the particle surface of the hydrogel material.

DE-A-3 523 617 (Nippon Shokubai) and US-A-4 734 478 (Nippon Shokubai) describe the addition of finely divided amorphous polysilicic acids (silica) to dry hydrogel powder after the surface post-crosslinking with crosslinking agents reactive with carboxyl groups , U.S. 4,286,082 (Nippon Shokubai)

Mixtures of silica with absorbent but not surface post-crosslinked polymers for use in hygiene articles. The aim of the subsequent addition is to improve the anti-caking tendency in moist air and to improve product handling. The finely divided silica is added with an average particle diameter of not more than 10 μm.

The use of silica which describes EP-A-0 341 951, US-A-4 990 338 and US-A-5 035 892 in the production of antimicrobial-treated absorbent polymers. US Pat. No. 4,535,098 and EP-A-0 227 666 describe the addition of colloidal carrier substances based on silica to increase the gel strength of absorbent polymers. EP-A-0 227 666 describes the use of water-insoluble inert inorganic materials (precipitated silica, pyrogens, aluminum, titanium, zinc, zirconium, nickel, iron or cobalt compounds) with a preferred primary particle size of 8 to 10 ran. EP 224 923 (Sumitomo) describes the agglomeration of SAP particles by adding water, silica, surfactant and organic solvent, followed by distillation of the solvent.

WO 95/11932 (Allied Colloids) describes the addition of finely divided silica and / or aluminum salts to the surface postcrosslinker solution in order to maximize absorption under high weight loads.

U.S. 5,314,420 and U.S. 5,399,591 (Nalco) mention the use of polyvalent metal ions as surface postcrosslinking agents. No. 5,122,544 (Nalco) describes the agglomeration of “superabsorbers by bifunctional epoxies.

EP 386 897 (Nippon Shokubai) describes superabsorbent polymers with a low anti-caking tendency and a lower residual monomer content by mixing the polymer granules with aqueous salt solutions, preferably with a combination of Al ₂ (Sθ ₄ ) ₃ and NaHS0 ₃ . Here, starting polymers are used that have not been subjected to surface post-crosslinking.

WO 95/26209 (P&G) makes use of i.a. Di- or polyfunctional reagents, e.g. polyvalent metal ions or polyquaternary amines to carry out surface post-crosslinking. Improved SFC and PUP (Performance Under Pressure) values can also be observed here after surface post-crosslinking has taken place. The absorption capacity of the highly swellable hydrogels is determined to determine the PUP (Performance Under Pressure) values

Grain fraction measured under a weight load of 0.7 psi. In the present case, hydrogels of the grain fraction 400 to 470 µm were measured. In Table 1 the physical properties of hydrogels before and after surface post-crosslinking were compared. Hydrogels from Nalco (Nalco 1180, not surface-crosslinked) were treated with 1,3-dioxolan-2-one in aqueous solution so that the amount of surface crosslinking agent added was 5% by weight, based on the starting polymer. This treatment raised the PUP from 8.7 g / g to 29.3 g / g and the SFC from 0.073 x 10 ^{~ 7} cm ³ sec / g to 115 x 10 ^-7 cm ³ sec / g. A further increase in the amount of 1,3-dioxolan-2-one added to the double value brought further increases in the SFC values, but slightly decreased PUP values. The following comparison values were obtained under changed test conditions:

In this patent, the relationships between the SFC, PUP and the grain size distribution are also recorded as further parameters. The samples are commercially available polymer material from Stockhausen. Table 3 shows the following results:

This series of experiments shows the increase in SFC with increasing grain size distribution, while the absorption capacity drops under pressure.

Another alternative to achieving good transport properties would be to shift the grain size spectrum to higher values.

The task was therefore to provide highly swellable hydrogels which have fast acquisition times and at the same time desired transport properties and a high final absorption capacity.

The hydrophilic swellable polymers should have an absorption profile which is characterized by properties such as high permeability and absorption capacity, as well as rapid swelling speed.

Surprisingly, this object is achieved by increasing the crosslinking density on the surface or in the interior of the hydrogel-forming polymers of certain particle size distributions. Another alternative are acidic hydrogel-forming polymers with a specific particle size distribution.

The hydrogel material according to the invention is therefore excellently suitable for a large number of fields of application, such as, for example, the use for absorbing aqueous liquids, for example in the food sector, in medicine, in construction and construction, in the agricultural industry or in fire protection.

The present invention relates to novel hydrophilic swellable polymers and their use for the absorption of aqueous liquids, for example in the food sector, in medicine, in construction and construction, in the agricultural industry or in fire protection.

The invention relates in particular to hydrogel-forming acidic and / or surface-crosslinked polymers which absorb aqueous liquids, characterized in that at least 8D% by weight, ie 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight. %, preferably 90% by weight, ie 91, 92, 93, 94% by weight, particularly preferably 95% by weight, ie 95.5, 96, 96.5% by weight, in particular 97% by weight, ie 97.5 , 98, 98.5, 99, 99.5, 99.6, 99.7, 99.8, 99.9% by weight of the particles have a particle size of less than 250 μm. Acidic polymers are understood to be those which have a pH value of less than or equal to 5.9, for example 5.8, 5.7 or 5.6, preferably less than or equal to 5.5, for example, 5.4 or 5.3 , particularly preferably less than or equal to 5.2, for example 5.1, and in particular less than or equal to 5.0, for example 4.9, 4.8, 4.7, 4.6, 4.5, 4.4, 4 , 3, 4.2, 4.1, 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1 , 3.0, or less. The preferred pH range is between 1 and 5.9, more preferably between 3 and 5.9, in particular between 4 and 5.

With the weight percentages given above, a particle size upper limit of 200 μm, particularly preferably 160 μm, very particularly preferably 110 μm, in particular 80 μm, is preferred.

Surface post-crosslinked polymers are understood to mean those which have a higher degree of crosslinking on the surface than in the center of the particles (core-shell structure). The surface postcrosslinking is preferably not done with polyvalent metal ions.

Aqueous liquid-absorbing hydrogel-forming surface post-crosslinked polymers or acidic optional polymers are understood to mean polymers which can absorb a multiple, in particular at least 5 times, preferably 10 times their weight of distilled water. Preference is given to hydrogel-forming polymers which absorb aqueous liquids and have a CRC of greater than 17, 18, 19 or 20 g / g, preferably greater than 21, 22, 23, 24 or 25 g / g, in particular greater than 26, 27, 28, 29, 30 or 31 g / g or an AUL 0.3 psi greater than 25, 26, 27, 28, 29, 30, or 31 g / g, preferably greater than 32, 33, 34, 35, 36 or 37 g / g , in particular 38, 39, 40, 41, 42, 43 or 44 g / g. Polymers that meet both the CRC and the AUL criteria are preferred. The aqueous liquid absorbing hydrogel-forming surface post-crosslinked polymers can be optionally inerted, e.g. with white oil.

Hydrogel-forming polymers which absorb aqueous liquids are understood to be those which are post-crosslinked or not post-crosslinked. The non-surface post-crosslinked polymers can be obtained as intermediates in the surface post-crosslinking, but some of them can also be used directly in the various applications.

Preferred hydrogel-forming polymers which absorb aqueous liquids (optionally post-crosslinked and / or acidic) are characterized in that at least 80% by weight, ie 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight, preferably 90% by weight, ie 91, 92, 93, 94% by weight, particularly preferably 95% by weight, ie 95.5, 96, 96.5% by weight, in particular 97% by weight, ie 97.5, 98, 98.5, 99, 99.5, 99.6, 99.7 , 99.8, 99.9% by weight of the particles have a particle size of less than 250 μm and at most 1% by weight, ie 0.9, 0.8, 0.7, 0.6, 0.5, 0.4% by weight, preferably at most 0.3% by weight, ie 0.25, 0.2, 0.15% by weight, in particular at most 0.1% by weight, ie 0.09, 0.08, 0.07, 0.06 0.05 0.04% by weight, of the particles have a particle size distribution of less than 10 μm.

Hydrogel-forming polymers which absorb water-based liquids (optionally surface post-crosslinked and / or acidic) are preferred at a particle size limit of 250 μm, those which are characterized in that at least 60% by weight, i.e.

61, 62, 63, 64, 65, 66, 67, 68, 69% by weight, preferably at least 70

% By weight, i.e. 71, 72, 73, 74, 75, 76, 77, 78, 79% by weight, in particular at least 80% by weight, i.e. 81, 82, 83, 84, 85, 86, 87,

88 ,. 89, 90% by weight of the particles have a particle size distribution of greater than 30 μm and less than 200 μm.

Absorbent for aqueous liquids hydrogel-forming ^polymers' (optional surface postcrosslinked and / or acidic) are micron at a Teilchengrößeobergrenze of 200, preferably those which are characterized in that at least 60 wt .-%, or

61, 62, 63, 64, 65, 66, 67, 68, 69% by weight, preferably at least 70

88, 89, 90% by weight of the particles have a particle size distribution of greater than 40 μm and less than 180 μm.

Hydrogel-forming polymers which absorb water-based liquids (optionally surface post-crosslinked and / or acidic) are preferred at a particle size limit of 160 μm, those which are characterized in that at least 60% by weight, i.e.

61, 62, 63, 64, 65, 66, 67, 68, 69% by weight, preferably at least 70

% By weight, i.e. 71, 72, 73, 74, 75, 76, 77, 78, 79 wt% ina = special at least 80 wt%, i.e. 81, 82, 83, 84, 85, 86, 87,

88, 89, 90% by weight of the particles have a particle size distribution of greater than 15 μ and less than 125 μ.

Hydrogel-forming polymers which absorb water-based liquids (optionally surface post-crosslinked and / or acidic) are preferred at an upper particle size limit of 110 μm, those which are characterized in that at least 60% by weight, ie 61, 62, 63, 64, 65, 66, 67, 68, 69% by weight, preferably at least 70% by weight, ie 71, 72, 73, 74, 75, 76, 77, 78, 79% by weight % in particular at least 80% by weight, ie 81, 82, 83, 84, 85, 86, 87, 88, 89, 90% by weight of the particles have a particle size distribution of

5 larger than 15 μm and smaller than 90 μm.

Hydrogel-forming polymers which absorb water-based liquids (optionally surface post-crosslinked and / or acidic) are preferred at a particle size limit of 80 μm, such that the 10 are characterized in that at least 60% by weight, i.e. 61,

62, 63, 64, 65, 66, 67, 68, 69% by weight, preferably at least 70% by weight, i.e. 71, 72, 73, 74, 75, 76, 77, 78, 79% by weight, in particular at least 80% by weight, i.e. 81, 82, 83, 84, 85, 86, 87, 88, 89, 90% by weight of the particles have a particle size distribution of

15 larger than 15 μm and smaller than 65 μm.

In addition, the following sieve cuts are preferred for the upper particle size limits of 250 μm, 200 μm, 160 μm, 110 μm and 80 μm: sieving via a 325 mesh sieve, resulting in at least 80% by weight,

20 i.e. 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight, preferably 90% by weight, i.e. 91, 92, 93, 94% by weight, particularly preferably 95% by weight, i.e. 95.5, 96, 96.5% by weight, in particular 97% by weight, i.e. 97.5, 98, 98.5, 99, 99.5, 99.6, 99.7, 99.8, 99.9% by weight of the particles have a particle size of greater than 44 μm.

25

In addition, the following sieve cuts are preferred for the upper particle size limits of 250 μm, 200 μm, 160 μm and 110 μm: sieving via a 230 mesh sieve, resulting in at least 80% by weight, i.e. 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight, preferably 90

30% by weight, i.e. 91, 92, 93, 94% by weight, particularly preferably 95

% By weight, i.e. 95.5, 96, 96.5% by weight, in particular 97% by weight, i.e. 97.5, 98, 98.5, 99, 99.5, 99.6, 99.7, 99.8, 99.9% by weight of the particles have a particle size of greater than 62 μm.

35 In addition, the following sieve cuts are preferred for the upper particle size limits of 250 μ, 200 μm, 160 μm and 110 μm: sieving via a 200 mesh sieve, resulting in at least 80% by weight, i.e. 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight, preferably 90% by weight, i.e. 91, 92, 93, 94% by weight, particularly preferably 95_

40% by weight, i.e. 95.5, 96, 96.5% by weight, in particular 97% by weight, i.e. 97.5, 98, 98.5, 99, 99.5, 99.6, 99.7, 99.8, 99.9% by weight of the particles have a particle size of greater than 74 μm.

In addition, the following sieve cuts are preferred for the upper particle size limits 250 μm, 200 μm and 45 160 μm: sieving over one

140 mesh sieve, resulting in at least 80% by weight, ie 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight, preferably 90 % By weight, ie 91, 92, 93, 94% by weight, particularly preferably 95% by weight, ie 95. 5, 96, 96. 5% by weight, in particular 97% by weight, ie

97. 5, 98, 98. 5, 99, 99. 5, 99. 6, 99. 7, 99. 8, 99. 9% by weight of the particles have a particle size of greater than 105 μm.

5

In addition, the following sieve cuts are preferred for the upper particle size limits 250 μm and 200 μm: sieving through a 100 mesh sieve, resulting in that at least 80% by weight, i.e. 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight, preferably 90% by weight, i.e. 91, 92, 10 93, 94% by weight, particularly preferably 95% by weight, i.e. 95.5, 96, 96.5% by weight, in particular 97% by weight, i.e. 97.5, 98, 98.5, 99, 99.5,

99.6, 99.7, 99.8, 99.9% by weight of the particles have a particle size of greater than 149 μm.

15 Narrower and wider particle size distributions can also be achieved using appropriate sieves or other separation processes.

The aqueous liquids absorbing hydro liquids according to the invention

20 gel-forming polymers preferably have a vortex time of less than 25 s, i.e. 24, 23, 22, 21 s, more preferably less than 20 s, i.e. 19, 18, 17, 16 s, more preferably less than 15 s, i.e. 14, 13, 12, 11 s, particularly preferably less than 10 s, i.e. 9, 8 s, in particular less than 7 s, i.e. 6 or 5 s.

25, ^■

The hydrogel-forming polymers absorbing aqueous liquids according to the invention preferably have an AUL (0.014 psi) of at least 20 g / g in water (deionized) after 10 min, i.e. z. B. 21, 22, 23, 24 g / g or more, more preferably at least 25

30 g / g, d. H. z. B. 26, 27, 28, 29, g / g or more, particularly preferably at least 30 g / g or more, in particular at least 40 g / g, d. H. z. 41, 42, 43, 44, 45, 46, 47, 48, 49, g / g or more, or even at least 50 g / g, i.e. H. z. B. 51, 52, 53, 54, 55, 56, 57, 58, 59, 60 g / g or more. 5

The hydrogel-forming polymers absorbing aqueous liquids according to the invention preferably have an AUL (0.014 psi) of at least 15 g / g, ie, for example 16, 17, 18, 19 g, in 0.9% NaCL solution after 10 min. g or more, more preferably at least _^ 22 0 g / g, 23 g / g, 24 g / g or more, particularly preferably at least 25 g / g or 26 g / g or more, or even 27 g / g, 28 , 29 or 30 g / g or more.

The aqueous liquids of hydrogel-forming 5 polymers according to the invention have rapid absorptions in 0.9% NaCL solution. They preferably have a difference in AUL (0.014 psi) between 60 and 10 minutes of less than 5 g / g, preferably less than 4 g / g, more preferably less than 3 g / g, particularly preferably less than 2 g / g, in particular less than 1 g / g. In addition, such polymers are preferred whose ratio of AUL (0.014 psi) at 10 min. 60 minutes greater than or equal to 0.7, e.g. 0.71, 0.72, 0.73, 0.74 or more. Ratios of 0.75 or more are preferred, for example 0.76, 0.78, 0.80, 0.82, 0.84, 0.86, 0.88 or more, particularly preferably ratios of 0.9 or more , for example 0.91, 0.92, 0.93, 0.94 or more, in particular ratios of 0.95 or more, for example 0.96, 0.97, 0.98, 0.99, 1.00 or more , Also preferred are those polymers whose ratio of AUL (0.014 psi) to CRC greater than or equal to 0.7 for 10 minutes, for example 0.72, 0.74, 0.76, 0.78, 0.80, 0.82, 0, 84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, 0.98 or more. Ratios of 1.0 or more, for example 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.14, 1.16, 1.18 or more are particularly preferred preferably of, for example 1.2, 1.22, 1.24, 1.26, 1.28, 1.30, 1.32, 1.34, 1.36, 1.38 or more, in particular of 1.4 or more, for example 1.42, 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.58, 1.60 or more.

The invention further relates to the production of hydrogel-forming polymers which absorb aqueous liquids, the various particle size distributions according to the invention after the surface postcrosslinking, e.g. be adjusted by screening. Optionally, a certain fraction of the particle size distribution can also be set before the surface post-crosslinking (sieving, grinding, etc.) and then certain cuts of particle size distribution can be produced after the surface post-crosslinking. Alternatively, hydrogel-forming polymers according to the invention are prepared with an adjustment of the particle size such that no adjustment is necessary for the particle size distribution according to the invention after the surface post-crosslinking. This can e.g. by strong grinding or / and screening.

The liquid-absorbing hydrogel-forming polymers according to the invention are suitable in the hygiene sector for the production of absorbent articles such as, for example, baby or adult diapers, incontinence articles or sanitary napkins, and in all other areas other than hygiene, where it is a question of temporarily or permanently adding aqueous liquids tie. Further uses can be in the areas of storage, packaging, transport, food sector, medicine, cosmetics, textiles, chemical engineering. Applications, building and construction, installation, water treatment,. Waste treatment, water separation, cleaning, agricultural industry and fire protection. The particular advantages of the particle size distributions according to the invention are:

a) The particles according to the invention can be swollen with defined amounts of water, it being possible, depending on the amount of water, to produce pore formers of different sizes, which also cover a narrow, defined size range due to the narrow particle size distribution.

It is particularly advantageous to use surface-post-crosslinked superabsorbents when it comes to applications under pressure. The acidic superabsorbents are particularly advantageous in applications where rapid absorption is necessary and in applications in which salt-containing aqueous solutions also have to be absorbed.

b) Incorporation of solid particles with a narrow particle size distribution into different materials, e.g. Sealing materials, foils, cable sheaths offer the advantage that the self-sealing effect desired in the presence of water leads to a very uniform and rapid expansion of the surface, since on the one hand the swelling behavior of all particles is almost the same due to a narrow particle size distribution and on the other hand large particles due to a water swell up much more than small ones, so that with a wide particle size distribution the sealing effect is much worse.

c) With co-extrusion it is also important to have a very narrow particle size distribution, because otherwise very irregular surfaces, e.g. B. film surfaces would arise.

d) For the production of thin layers with as uniform a surface as possible, e.g. in fire protection. Here, too, it is advantageous to have particles with the narrowest possible distribution available. When processed into water to form a gel, such a gel can be spread or sprayed on and can be formulated so that it e.g. adheres to vertical walls.

e) Hydrophilization of surfaces can also only be achieved by keeping the surface as uniform and homogeneous as possible after the SAP has absorbed water. This can only be achieved through a narrow particle size distribution. The same applies to the absorption of condensation water. The water should be absorbed quickly. hydrogels according to the invention are best. In fruit and vegetable packaging, the surface (of the tray or film) will change most evenly the more homogeneous the SAP particle size distribution. Especially when absorbing condensed water, be it in packaging or in the construction sector, ie wherever small amounts of water have to be absorbed per unit of time (and irregularly) over a long period of time, the small particles will absorb water much faster due to the swelling rate.

Manufacturing process

a) Monomers used

Hydrogel-forming polymers are in particular polymers made 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 liquids swellable natural products such as guar derivatives, alginates and carrageenans. Suitable graft bases can be of natural or synthetic origin. Examples are starch, cellulose or cellulose derivatives and other polysaccharides and oligosaccharides, polyvinyl alcohol, polyalkylene oxides, in particular polyethylene oxides and polypropylene oxides, polyamines, polyamides and hydrophilic polyesters. Suitable polyalkylene oxides have, for example, the formula

X

R ¹ -O- (CH ₂ -CH-0) _n -R ²

R ¹ and R ² independently of one another are hydrogen, alkyl, alkenyl or acrylic, X is hydrogen or methyl and n is an integer from 1 to 10,000.

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

Preferred hydrogel-forming polymers are crosslinked polymers having acid groups which are predominantly in the form of their salts, generally alkali metal or ammonium salts. Such polymers swell particularly strongly into gels on contact with aqueous liquids. Polymers which are obtained by crosslinking polymerization or copolymerization of acid-bearing monoethylenically unsaturated monomers or their salts are preferred. It is also possible to (co) polymerize these monomers without crosslinking agents and to crosslink them subsequently.

Monomers bearing such acid groups are, for example, monoethylenically unsaturated C ₃ -C ₂₅ -carboxylic acids or anhydrides such as acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid and fumaric acid. Also suitable are monoethylenically unsaturated sulfonic or phosphonic acids, for example vinylsulfonic acid, allylsulfonic acid, sulfoethylacrylate, sulfomethacrylate, sulfoprophylacrylate, sulfopropylethacrylate, 2-hydroxy-3-acryloxypropylsulfonic acid, 2-hydroxy-3-methacryloxypropylsulfonic acid, vinylphosphonic acid , Allylphosphonic acid, styrene sulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid. The monomers can be used alone or as a mixture with one another.

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

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

These monomers which do not contain acid groups can also be used in

Mixture with other monomers, e.g. Mixtures of vinyl acetate and 2-hydroxyethyl acrylate in any ratio. These monomers not carrying acid groups are added to the reaction mixture in amounts between 0 and 50% by weight, preferably less than 20% by weight.

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

Crosslinked polymers of monoethylenically unsaturated C ₃ are preferably - to C ₂ ~ carboxylic acids and / or their alkali metal or ammonium salts. In particular, crosslinked polyacrylic acids are preferred, the acid groups of which are 5 to 30 mol%, preferably 5 to 20 mol%, particularly preferably 5 to 10 mol%, based on the monomers containing acid groups, as alkali metal or ammonium salts.

Compounds which have at least two ethylenically unsaturated double bonds can function as crosslinkers. Examples of compounds of this type are N, N ^λ -methylene bisacrylamide, polyethylene glycol diacrylates and polyethylene glycol dimethacrylates, which are each derived from polyethylene glycols with a molecular weight of 106 to 8500, preferably 400 to 2000, trimethylol propane triacrylate, trimethylol propane trimethacrylate, ethylene glycol, ethylene diacrylate, ethylene glycol propylene glycol diacrylate propylene glycol dimethacrylate, butanediol diacrylate, Butandioldimeth- acrylate, hexanediol diacrylate, hexanediol dimethacrylate, Allylmeth-, moniumhalogenide diacrylates and dimethacrylates of block copolymers of ethylene oxide and propylene oxide, doubly or multiply with acrylic acid or methacrylic acid esterified polyhydric alcohols such as glycerol or pentaerythritol, triallylamine, as Dialkyldiallylam- Dimethyldiallylammonium chloride and diethyldiallylammonium chloride, tetraallylethylenediamine, divinylbenzene, diallyl phthalate, polyethylene glycol diyl ether of polyethylene glycols of a mo molecular weight from 106 to 4000, trimethylol propanediallyl ether, butanediol divinyl ether, pentaerythritol triallyl ether, reaction products of 1 mole of ethylene glycol diglycidyl ether or polyethylene glycol diglycidyl ether with 2 moles of pentaerythritol triallyl ether or allyl alcohol, and / or divinylethylene urea. Water-soluble crosslinking agents are preferably used, for example N, N ^λ -methylenebisacrylamide, polyethylene glycol diacrylates and polyethylene glycol dimethacrylates which are derived from addition products of 2 to 400 mol of ethylene oxide to 1 mol of a diol or polyol, vinyl ethers of addition products of 2 to 400 mol Ethylene oxide on 1 mole of a diol or polyol, ethylene glycol diacrylate, ethylene glycol dimethacrylate or triacrylates and trimethacrylates of addition products of 6 to 20 moles of ethylene oxide on 1 mole of glycerol, pentaerythritol triallyl ether and / or divinyl urea.

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

Also suitable as crosslinking agents are compounds which contain at least two functional groups which are capable of reacting with the functional groups, essentially the acid groups of the monomers. The suitable therefor _^ functional-group have already been mentioned above, ie, hydroxyl, amino, epoxy, isocyanate, ester, amido and aziridino groups. Examples of such crosslinkers are ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, polyglycerol, triethanolamine, propylene glycol, polypropylene glycol, block copolymers of ethylene oxide and propylene oxide, ethanolamine, sorbitan fatty acid esters, ethoxylated sorbitan ethyl propylene ester, sorbitan ethyl propylene ester, 1, 3-butanediol, 1,4-butanediol, polyvinyl alcohol, sorbitol, starch, polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol-digly- cidylether, glycerol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan, bitpolyglycidylether, pentaerythritol polyglycidyl ether, propylene glykoldiglycidylether and polypropylene glycol, polyvinyl lyaziridinverbindungen such as 2, 2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], 1, 6-hexamethylene diethylene urea, diphenylmethane-bis-4, '-N, N'-diethylene urea, halopoxy compounds such as epichlorohydrin and α-methylepifluorohydrin, Polyisocyanates such as 2, 4-tolylene diisocyanate and hexamethylene diisocyanate, alkylene carbonates such as 1, 3-dioxolan-2-one and 4-methyl-l, 3-dioxolan-2-one, also bisoxazolines and oxazolidos, polyamidoamines and their reaction products Epichlorohydrin, also polyquaternary amines such as condensation products of dirnethylamine with epichlorohydrin, Hom o- and copolymers of diallyldimethylammonium chloride as well as homopolymers and copolymers of dirnethylaminoethyl (eth) crylate, which are optionally uaternized with, for example, methyl chloride.

Other suitable crosslinkers are polyvalent metal ions, which are able to form ionic crosslinks. Examples of such crosslinkers are magnesium, calcium, barium and aluminum ions. These crosslinkers are used, for example, as hydroxides, carbonates or bicarbonates. Other suitable crosslinkers are multifunctional bases which are also able to form ionic crosslinks, for example polyamines or their quaternized salts. Examples of polyamines are ethylenediamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine and polyethyleneimines, and polyamines with molecular weights of up to 4,000,000 each.

The crosslinkers are present in the reaction mixture, for example from 0.001 to 20% by weight and preferably from 0.01 to 14% by weight. Ethoxylated trimethylolpropane triacrylate ETMPTA is a particularly preferred crosslinker.

b) radical polymerization

The polymerization is initiated as usual by an initiator. It is also possible to initiate the polymerization by the action of electron beams on the polymerizable, aqueous mixture. However, the polymerization can also be initiated in the absence of initiators of the type mentioned above by exposure to high-energy radiation in the presence of photoinitiators. All of the polymerization initiators can be converted into radicals under the polymerization conditions disintegrating compounds are used, for example peroxides, hydroperoxides, hydrogen peroxides, persulfates, azo compounds and the so-called redox catalysts. The use of water-soluble initiators is preferred. In some cases it is advantageous to use mixtures of different polymerization initiators, for example mixtures of hydrogen peroxide and sodium or potassium peroxodisulfate. Mixtures of hydrogen peroxide and sodium peroxodisulfate can be used in any ratio. Suitable organic peroxides are, for example, acetylacetone peroxide, methyl ethyl ketone peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, tert. -Amylperpivala, tert-butyl perpivalate, tert. Butyl perneohexanoate, tert. -Butylperisobuty- rat, tert. -Butyl-per-2-ethylhexanoate, tert. -Butyl perisononanoate, tert-butyl permaleate, tert-butyl perbenzoate, di- (2-ethylhexyl) peroxidicarbonate, dicyclohexyl peroxidicarbonate, di- (4-tert-butyl-cyclohexyl) peroxidicarbonate, dimyristile peroxidicarbonate, diacetyl peroxy peroxide Cumyl peroxyneodecanoate, tert. -Butylper-3, 5, 5-trimethylhexanoate, acetylcyclohexylsulfonyl peroxide, dilauryl peroxide, dibenzoyl peroxide and tert. -Amylperneo decanoate. Particularly suitable polymerization initiators are water-soluble azo starters, for example 2,2 ^λ -azo-bis- (2-amidino-propane) dihydrochloride, 2, 2 ^λ -azobis (N, N ^λ -dimethylene) isobutyramidine-dihydrochloride, 2- ( Carbamoylazo) isobutyronitrile, 2,2 ^Λ -azo bis [2- (2 ^Λ -imidazolin-2-yl) propane] dihydrochloride and 4,4 ^λ -azo bis- (4-cyanovaleric acid). The polymerization initiators mentioned are used in customary amounts, for example in amounts of 0.01 to 5, preferably 0.05 to 2.0,% by weight, based on the monomers to be polymerized.

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

If the polymerization is triggered by exposure to high-energy radiation, so-called photoinitiators are usually used as initiators. These can be, for example, so-called splitters, H-abstracting systems or also azides act. Examples of such initiators are benzophenone derivatives such as Michlers ketone, phenanthrene derivatives, fluorene derivatives, anthraquinone derivatives, thioxanone derivatives, coumarin derivatives, benzoin ethers and their derivatives, azo compounds such as the radical formers mentioned above, substituted hexaarylbisimidazoles or acylphosphine oxides. Examples of azides are: 2- (N, N-dimethylamino) ethyl 4-azidocinnamate, 2- (N, N-dimethylamino) ethyl 4-azidonaphthyl ketone, 2- (N, N- Dimethylamino) ethyl 4-azidobenzoate, 5-azido-1-naphthyl-2 '- (N, N-dimethylamino) ethylsulfone, N- (4-sulfo-

10 nylazidophenyDmaleinimid, N-acetyl-4-sulfonylazidoaniline, 4-sulfonyl azidoaniline, 4-azidoaniline, 4-azidophenacyl bromide, p-azide-topzoic acid, 2, 6-bis (p-azidobenzylidene) cyclohexanone and 2, 6 p-azido-benzylidene) -4-methylcyclohexanone. The photoinitiators, if used, are usually in

15 amounts of 0.01 to 5 wt .-% based on the monomers to be polymerized applied.

The crosslinked polymers are preferably used in partially neutralized form. The degree of neutralization is generally 5 to

20 80%, preferably 5 to 60 mol%, preferably 10 to 40 mol%, particularly preferably 20 to 30 mol%, based on the monomers containing acid groups. Possible neutralizing agents are: alkali metal bases or ammonia or amines. Sodium hydroxide solution, potassium hydroxide solution or lithium hydroxide is preferably used. The neutrals

However ^{, it} can also be carried out using sodium carbonate, sodium hydrogen carbonate, potassium carbonate or potassium hydrogen carbonate or other carbonates or hydrogen carbonates or ammonia. Furthermore, prim. , sec. and tert. Amines can be used.

30

Alternatively, the degree of neutralization can be set before, during or after the polymerization in all suitable apparatus. The neutralization can also be carried out directly therein, for example when using a kneader for the polymerization 5.

All processes which are usually used in the production of superabsorbers, such as, for example, _^, can be used as technical processes for the production of these products. in Chapter 3 in "Modem Superabsorbent Polymer Technology", FL Bucholz and AT Graham, Wiley-VCH, 1998.

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

The polymerization reaction can be carried out in the temperature range between 0 ° C. and 150 ° C., preferably between 10 ° C. and 100 ° C., both under normal pressure and under elevated or reduced pressure. As usual, the polymerization can also be carried out in a protective gas atmosphere, preferably under nitrogen.

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

c) surface post-crosslinking

One method of achieving higher gel permeability is surface post-crosslinking, which gives the hydrogel body a higher gel strength when swollen. Gels with only a low gel strength can be deformed under an applied pressure (such as, for example, by denser packing in highly loaded systems), clog pores in the hydrogel absorbent body and thereby prevent further fluid absorption. Since an increase in the crosslinking density in the starting polymer can be ruled out for reasons of decreasing absorption capacity values, the surface postcrosslinking is an elegant method for increasing the gel strength. The surface postcrosslinking increases the crosslinking density only in the shell of the hydrogel particles, which increases the absorption under pressure (absorption and the load AUL) of the base polymer generated in this way is raised to a higher level. While the absorption capacity decreases as a result of the surface post-crosslinking in the hydrogel shell, the core of the hydrogel particles has an improved absorption capacity compared to the shell due to the presence of movable polymer chains, so that the shell structure ensures improved liquid transmission. Depending on the area of application, it is therefore possible to optimize the absorption capacity and gel strength by specifically adjusting the degree of crosslinking in the base polymer and subsequent postcrosslinking, and by surface treatment of the polymer particles obtained.

The surface postcrosslinking can be carried out in a manner known per se with dried, ground and sieved polymer particles of, for example, grain fractions smaller than 250 μm, 200 μm, 160 μm, 105 μm, preferably smaller than 63 μm. It is also possible to feed the complete particle stream resulting from the grinding to the surface crosslinking and to carry out the screening to the desired particle size after the surface crosslinking after the particles have dried.

In all cases there is an optional (renewed) sieving to the desired grain size after the surface post-crosslinking in order to remove any agglomerates that may have formed.

For surface post-crosslinking of the specified proportions of certain grain sizes, compounds which can react with the functional groups of the polymers with crosslinking are preferably applied to the surface of the hydrogel particles in the form of a water-containing solution. The hydrated

Solution may contain water-miscible organic solvents. Suitable solvents are alcohols such as methanol, ethanol, i-propanol or acetone.

In the subsequent crosslinking, polymeric fines which have been produced by the polymerization of the abovementioned monoethylenically unsaturated acids and, if appropriate, monoethylenically unsaturated comonomers and which have a molecular weight greater than 5000, preferably greater than 50,000, are reacted with compounds which have at least two groups reactive toward acid groups. This reaction can take place at room temperature or at elevated temperatures up to 220 ° C.

Suitable post-crosslinking agents are, for example

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

Polyaziridines, compounds containing aziridine units based on polyethers or substituted hydrocarbons, for example bis-N-aziridinomethane, polyamines or polyamidoamines and their reaction products with epichlorohydrin,

Polyols such as ethylene glycol, 1, 2-propanediol, 1, 4-butanediol, glycerol, methyltriglycol, polyethylene glycols with an average molecular weight M _w of 200-10000, di- and polyglycerol, pentaerythritol, sorbitol, the oxyethylates of these polyols and their esters with carboxylic acids or carbonic acid such as ethylene carbonate or propylene carbonate, Carbonic acid derivatives such as urea, thiourea, guanidine, dicyandiamide, 2-0xazolidinone and its derivatives, bisoxazoline, polyoxazolines, di- and polyisocyanates, di- and poly-N-methylol compounds such as methylene bis (N-methylol methacrylamide) or melamine formaldehyde - hyd resins,

Compounds with two or more blocked isocyanate groups such as trimethylhexamethylene diisocyanate blocked with 2,2,3,6-tetramethyl-piperidinone-4. - Alkanolamines such as ethanolamine, diethanolamine, triethanolamine and their alkoxylated derivatives.

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

Particularly suitable post-crosslinking agents are di- or polyglycidyl compounds such as ethylene glycol diglycidyl ether, the reaction products of polyamidoamines with epichlorohydrin and 2-0xazolidinone, and polyethylene glycol diacrylate.

The crosslinker solution is preferably applied to the hydrogel of a certain particle size distribution by spraying a solution of the crosslinker in conventional reaction mixers or mixing and drying systems such as Patterson-Kelly mixers, DRAIS turbulence mixers, Lödige mixers, screw mixers, plate mixers, fluidized bed mixers and Schugi -Mix. After spraying on the crosslinking agent solution, a temperature treatment step can follow, preferably in a downstream dryer, at a temperature between 80 and 230 ° C, preferably 80-190 ° C, and particularly preferably between 100 and 160 ° C, over a period of 5 minutes to 6 hours, preferably 10 minutes to 2 hours and particularly preferably 10 minutes to 1 hour, it being possible for both fission products and solvent fractions to be removed. However, drying can also take place in the mixer itself, by heating the jacket or by blowing in a preheated carrier gas.

In a particularly preferred embodiment of the invention, the hydrophilicity of the particle surface of the hydrogel-forming polymer is additionally modified by the formation of complexes. The complexes are formed on the outer shell of the hydrogel particles by spraying on solutions of divalent or polyvalent metal salt solutions, the metal cations being able to react with the acid groups of the polymer to form complexes. Examples of divalent or polyvalent metal cations are Mg ²⁺ , Ca ² +, Al ³⁺ , Sc ³⁺ , Ti ^ ⁺ , Mn ⁺ , 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 ⁺ , Zr ⁴⁺ and La ³⁺ , and particularly preferred metal cations are Al ³⁺ , Ti ⁺ and Zr ⁴⁺ . The metal cations can be used both alone and in a mixture with one another. Of the metal cations mentioned, all metal salts are suitable which have sufficient solubility in the solvent to be used. Metal salts with weakly complexing anions such as chloride, nitrate and sulfate are particularly suitable. Water, alcohols, DMF, DMSO and mixtures of these components can be used as solvents for the metal salts. Water and water / alcohol mixtures, such as water / methanol or water / 1,2-propanediol, are particularly preferred.

The metal salt solution can be sprayed onto the particles of the hydrogel-forming polymer both before and after the surface postcrosslinking of the hydrogels of a certain particle size distribution. In a particularly preferred method, the metal salt solution is sprayed on in the same step as the spraying of the crosslinking agent solution, with both solutions being sprayed on separately in succession or simultaneously via two nozzles, or the crosslinking agent and metal salt solution being sprayed together via a nozzle ,

Optional ^"can be further modified is the hydrogel-for-Menden particles by admixture of finely divided inorganic solids, such as occur, for example silica, alumina, titanium dioxide and iron (II) oxide, whereby the effects of the surface-treatment can be further enhanced. Especially preferred the addition of hydrophilic silica or of aluminum oxide with an average primary particle size of 4 to 50 nm and a specific surface area of 50-450 m ² / g. The addition of finely divided inorganic solids is preferably carried out after the surface modification by crosslinking / complex formation, but can are also carried out before or during these surface modifications. In general, less than 5% by weight, preferably less than 1% by weight, in particular between 0.05 and 0.5% by weight, particularly preferably between 0.1 and 0, 3% by weight of solid added.

The modification of the particle surface by adding oils, such as white oil, is particularly preferred. As a result, the tendency of the hydrogels to form a certain particle size distribution to dust is drastically reduced, the particle size being increased minimally. This type of modification is particularly important for product handling, since the dust development due to explosion risks represents an enormous risk factor. In addition Dosing difficulties due to the tendency to dust can be prevented by adding white oil.

Another possibility for suppressing the tendency to dust is the addition of glycerin and other di- and polyols, e.g. Propylene glycol, ethylene glycol, polyethylene glycol, polypropylene glycol into consideration. The suppression of the tendency to dust is called inertization.

The addition of surfactants represents further modification options. If these are in liquid form, they can also be used to reduce the tendency to dust due to their ability to optimally distribute on hydrophilic solid particles.

The modification of the surface post-crosslinked particles according to the invention can be carried out after the surface post-crosslinking. However, it is also possible to carry this out together with the surface postcrosslinking, for example metering via two nozzles, if the postcrosslinking is carried out by spraying, or simply by mixing in.

d) Properties of the hydrogels according to the invention of certain particle size distribution

The post-crosslinked hydrogel-forming polymer particles absorbing aqueous liquids according to the invention have an outer polymer shell with a higher crosslinking density. This enables an absorption profile that is characterized by properties such as high gel strength and permeability with a high final absorption capacity. In particular, the absorption under pressure is raised to a higher level.

The increase in the crosslinking density increases the gel strength of the individual particles, which means that the absorption values increase under pressure. By setting the degree of crosslinking, it is also possible to set desired values, such as absorption values under pressure or centrifuge retention values. In general, the surface post-crosslinking increases the permeability and the sewerage of the aqueous liquids to be absorbed is optimized.

Similar effects can surprisingly also be achieved by acidic polymers according to the invention and by polymers according to the invention, the particle sizes of which are reduced in the case of the very fine particles. Advantages also result from the relatively large surface area of the large number of small particles, which allows very short acquisition times and thus rapid swelling speeds. The products according to the invention can be treated, for example, with white oil and, as a powder, have no tendency to dust despite the presence of very fine fractions. This enables safe handling of the products. It is therefore ideal for a variety of different areas of application.

e) Use and use of the hydrogels according to the invention with a particular particle size distribution

The present invention further relates to the use of the hydrogel-forming polymers mentioned above for the absorption of aqueous liquids, for example

Hygiene products

Storage, packaging, transport (packaging material for water- sensitive items such as flower transport, shock protection)

Food sector (transport of fish, fresh meat; absorption of water, blood in fresh fish / meat packaging) water treatment, waste treatment, water separation - cleaning

- Agricultural industry (irrigation, retention of melt water and dew precipitation, composting additive)

The hydrogels of the particle size distribution according to the invention are suitable for the above fields of application; they are preferably used in combination with normal particle size distribution, e.g. the advantages of the hydrogels according to the invention can be combined with those of the conventional hydrogels by appropriate spatial design.

Particularly preferred areas of application for hydrogels with a particular particle size distribution are:

Medicine (wound plasters, water-absorbent material for burn dressings or for other wet wounds, quick dressings in the event of injuries; rapid absorption of escaping body fluids for later analysis and diagnosis purposes), cosmetics, carrier material for pharmaceutical chemicals and medicines, rheumatic plasters, ultrasound gel, cooling gel, cosmetic thickener, sun protection,

Thickeners for oil / water or water / oil emulsions; Textiles (gloves, sports clothing, moisture regulation in textiles, shoe inserts, synthetic fabrics), hydrophilization of hydrophobic surfaces; Pore formation Chem.-techn. Applications (catalyst for organic reactions, immobilization of large functional molecules (enzymes), heat storage, filtration aids, hydrophilic components in polymer laminates, dispersants, plasticizers)

- Building and construction engineering (sealing compounds; self-sealing systems or self-sealing foils in the presence of moisture; fine pore formers in sintered building materials or ceramics; self-sealing insulation for water pipelines or for pipes and pipes that are laid in the ground; sealing of building materials in the ground, which is achieved by the SAP swelling in the moist soil with a time delay and thus causing a closure or sealing; equipping carpets and carpets), installation, vibration-inhibiting medium, tools for tunnel excavations in water-rich subsoil, tools for excavations and Drilling in a water-rich subsurface, cable sheathing

- Fire protection (spraying SAP gel on fires such as forest fires).

- Coextrusion agents in thermoplastic polymers; Production of foils and thermoplastic moldings that can absorb water (e.g. storing rainwater and condensation)

Agricultural films; SAP-containing foils for keeping fruit and vegetables fresh, which can be packed in moist foils to avoid rot and wilt); SAP coextrudates e.g. with polystyrene carrier substance in active ingredient formulations (pharmaceuticals, crop protection)

- Agricultural industry: protection of forests against fungal / insect attack, delayed release of active substances in plants)

The post-crosslinked hydrogel-forming particles according to the invention are outstandingly suitable as absorbents for water and aqueous liquids, so that they can advantageously be used as water-retaining agents in agricultural horticulture, as filtration aids and especially as absorbent components in hygiene articles such as diapers, tampons or sanitary napkins. test methods

a) Centrifuge retention capacity (CRC Centrifuge Retention Capacity)

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

b) Absorption capacity (FSC Free Swell Capacity)

This method determines the free swellability of the hydrogel in the tea bag. To determine the FSC, 0.2000 + 0.0050 g of dried hydrogel are weighed into a 60 x 85 mm tea bag, which is then sealed. The tea bag is placed in an excess of 0.9% by weight saline solution for at least 30 minutes (at least 0.83 1 saline solution / l g polymer powder). Then the tea bag is hung on a corner and left to drain for 10 minutes. The amount of liquid is determined by weighing out the drained tea bag.

c) Absorption under pressure (AUL Absorbency Under Load) (0.3 psi)

The measuring cell for determining the AUL 0.3 psi is a plexiglass cylinder with an inner diameter of 60 mm and a height of 50 mm, which has a glued-on stainless steel sieve bottom with a mesh size of 36 μm on the underside. A Schleicher & Schmitt Schwarzband round filter (0 60 mm, pore size 10 - 15 μm) is placed on the sieve bottom to prevent SAP particles with a particle size <36 µm from falling through the mesh of the stainless steel sieve. The measuring cell also includes a plastic plate with a diameter of 59 mm and a weight, which can be placed together with the plastic plate in the measuring cell. The plastic plate is loaded with the appropriate weight. To carry out the determination of the AUL 0.3 psi, the weight of the empty plexiglass cylinder and the plastic plate is determined and noted as Wo. Then 0.900 ± 0.005 g of hydrogel-forming polymer are weighed into the plexiglass cylinder and distributed as evenly as possible on the round filter. Then the. Plastic plate carefully placed in the plexiglass cylinder and the entire unit weighed; the GE- weight is noted as W _a . Now the weight is placed on the plastic plate in the plexiglass cylinder. In the middle of the petri dish with a diameter of 200 mm and a height of 30 mm, a ceramic filter plate with a diameter of 5 120 mm and a porosity of 0 is placed and so much 0.9% by weight

Sodium chloride solution filled that the liquid surface is flush with the filter plate surface, without the surface of the filter plate is wetted. Then a round filter paper with a diameter of 90 mm and a pore size <20 μm (S&S 589 black tape from Schleicher & Schüll) is placed on the ceramic plate. The plexiglass cylinder containing the hydrogel-forming polymer is now placed with the plastic plate and weight on the filter paper and left there for 60 minutes. After this time, the complete unit is removed from the Petri dish from the filter paper and then the weight is removed from the plexiglass cylinder. The plexiglass cylinder containing swollen hydrogel is weighed out together with the plastic plate, from which 0.4 g is drawn off (water absorption - of the round filter) and the weight is noted as Wj. 0

The absorption under pressure (AUL) is calculated as follows: AUL 0.3 psi [g / g] = [W _b -W _a ] / [W _a -W ₀ ]

With the AUL 0.2psi, AUL 0.7psi etc. the weights 5 are adjusted accordingly. The AUL (0.014 psi) without pressure is measured without weights, only with a plastic plate. With the time-dependent AUL, the values are determined after certain times (2 min, 10 min, etc.). Instead of using 0.9% NaCL solution, the measurement can e.g. can also be done in distilled water.

d) Vortex test

50 ml of 0.9% by weight NaCl solution are placed in a 100 ml beaker and 2.00 g of hydrogel are rapidly added with stirring at 600 rpm using a rod-shaped magnetic stirrer (30 mm x 8 mm) so that a lump is avoided. The time is measured in seconds until the vortex created by the stirring of the liquid is closed and a smooth surface is created.

e) Measurement of the particle size distribution

The particle size distribution was determined using laser diffraction. (Device: Sypatec HELOS (H0173) RODOS) f) pH measurement

Takes place according to the EDANA protocol SAM-PHD-01-G from February 99 with the reference pH 400.1-99. 0.5 g of superabsorbent 0.9% NaCL solution are measured with a pH electrode.

Examples

Example 1:

A previously made separately, cooled down to approx. 25 ° C and inerted by introducing nitrogen monomer solution is sucked into a laboratory kneader with a working volume of 2 1, which was absolutely evacuated to 980 bar by means of a vacuum pump. The monomer solution is composed as follows: 825.5 g demineralized water, 431 g acrylic acid, 359 g NaOH 50%, 0.86 g polyethylene glycol 400 diacrylate (SARTOMER ^® 344 from CRAY VALLEY) Kneader evacuated and then aerated with nitrogen. This process is repeated 3 times. A solution of 1.2 g of sodium persulfate, dissolved in 6.8 g of demineralized water, and another solution consisting of 0.024 g of ascorbic acid, dissolved in 4.8 g of demineralized water, is then sucked in. It is flushed with nitrogen. A jacket heating circuit (bypass) preheated to 75 ° C is converted to the Kne ^ jacket, the stirrer speed increased to 96 rpm. After the onset of polymerization and reaching T _max , the jacket heating circuit is switched back to bypass and polymerized for 15 minutes without heating / cooling, then cooled, the product is discharged, and the resulting gel particles are dried on sheets with wire mesh base at 160 ° C in a circulating air oven, then ground and sieved.

Example la:

The product thus obtained was sieved with a sieve with a mesh size of 105 μ. 1200 g of the product of the particle size distribution <105 μm obtained in this way were sprayed in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g of water, 0.2 g of ethylene glycol diglycidyl ether and 0.66 g of sorbitan monococoate. "And placed in a preheated 2nd Transferred Lödige mixer. Tempering was carried out over a period of 120 minutes under constant conditions at a jacket temperature of 150 ° C. and a speed of 60 rpm. The mixer was emptied, the product cooled down to room temperature and sieved again with a 105 μm sieve to remove any agglomerates that might have formed. The performance data are shown in Table 1. Example 1b

Post-crosslinking was carried out on the entire particle stream. 1200 g of the product obtained from Example 1 with a grain size of <850 μm were sprayed in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g of water, 0.2 g of ethylene glycol diglycidyl ether and 0.66 g of sorbitan monococoate and transferred to a preheated 2nd Lödige mixer. Tempering was carried out over a period of 120 minutes under constant conditions at a jacket temperature of 150 ° C. and a speed of 60 rpm. The mixer was emptied, the product cooled down to room temperature and sieved with a 105 μm sieve. The performance data are shown in Table 1.

Example lc:

The post-crosslinking was carried out on the entire particle stream. 1200 g of the product obtained from Example 1 with a grain size of <850 μm were sprayed in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g of water, 0.1 g of ethylene glycol diglycidyl ether and 0.33 g of sorbitan monococoate and transferred to a preheated 2nd Lödige mixer. Tempering was carried out over a period of 120 minutes under constant conditions at a jacket temperature of 150 ° C. and a speed of 60 rpm. The mixer was emptied, the product cooled down to room temperature and sieved with a 105 μm sieve. The performance data are shown in Table 1.

Example 2:

A monomer solution, previously prepared separately, cooled to approx. 25 ° C and inertized by introducing nitrogen, is sucked into a laboratory kneader with a working volume of 2 l, which has been absolutely evacuated to 980 mbar using a vacuum pump. The monomer solution is composed as follows: 825.5 g demineralized water, 431 g acrylic acid, 359 g NaOH 50%, 2.2 g ethoxylated trimethylolpropane triacrylate ETMPTA (SARTOMER ^® 9035 from CRAY VALLEY). The kneader is evacuated for better inertization and then aerated with nitrogen. This process is repeated 3 times. A solution of 1.2 g of sodium persulfate, dissolved in 6.8 g of demineralized water, and another solution consisting of 0.024 g of ascorbic acid, dissolved in 4.8 g of demineralized water, is then sucked in. It is flushed with nitrogen. A jacket heating circuit (bypass) preheated to 75 ° C is switched to the kneader jacket, the stirrer speed is increased to 96 rpm. After the onset of polymerization and reaching T _max , the jacket heating circuit is switched back to bypass and polymerized for 15 minutes without heating / cooling, then cooled, the product was discharged and the resulting gel particles were dried on sheets with a wire mesh base at 160 ° C. in a circulating air drying cabinet, then ground and sieved.

Example 2a:

The product thus obtained was sieved using a sieve with a mesh size of 105 μm. 1200 g of the product of the grain distribution <105 μm thus obtained were sprayed in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g of water, 0.2 g of ethylene glycol diglycidyl ether and 0.66 g of sorbitan monococoate and into a preheated 2nd Lödige -Mixer decanted. Tempering was carried out over a period of 120 minutes under constant conditions at 150 ° C. jacket temperature and a speed of 60 rpm. The mixer was emptied, the product cooled down to room temperature and sieved with a 105 μm sieve to remove any agglomerates that might have formed. The performance data are shown in Table 1.

Example 2b

The postcrosslinking was carried out on the entire particle stream. 1200 g of the product obtained in this way from Example 2 with a grain size of <850 μm were in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g water, 0.2 g ethylene glycol diglycidyl ether and 0.66 g sorbitan monococoate sprayed and transferred to a preheated 2nd Lödige mixer. Tempering was carried out over a period of 120 minutes under constant conditions at a jacket temperature of 150 ° C. and a speed of 60 rpm. The mixer was emptied, the product cooled down to room temperature and with a 105 _. sieve sieved. The performance data are shown in Table 1.

Example 2c

Post-crosslinking was carried out on the entire particle stream. 1200 g of the product obtained from Example 2 with a grain size of <850 μm were sprayed in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g of water, 0.1 g of ethylene glycol diglycidyl ether and 0.33 g of sorbitan monococoate and transferred to a preheated 2nd Lödige mixer. Under constant conditions at 150 ° C jacket temperature and a speed of 60 rpm, the tempering was carried out over a period of 120 minutes. The mixer was emptied, the product was brought down to room temperature cools and sieved with a 105μm sieve. The performance data are shown in Table 1.

Example 3:

The procedure was analogous to Example 1.

Example 3a:

In contrast to the postcrosslinking in Example 1, the heat treatment was only 70 minutes. The post-crosslinking solution was prepared directly before use. The two solutions (EGDGE and aluminum sulfate) are brought together shortly before the atomizing nozzle. The post-crosslinking solution for 1200 g of powder (particle size distribution <105 μm) from Example 1 was composed as follows: 17.58 g of water, 9.96 g of 1,2-propanediol, 1.2 g of ethylene glycol diglycidyl ether and 3.36 g of a 26. 8% aqueous aluminum sulfate solution. The performance data are shown in Table 1.

Example 4:

The procedure was analogous to Example 2.

Example 4a

In contrast to the post-crosslinking in Example 2, the heat treatment was only 70 minutes. The post-crosslinking solution was prepared directly before use. The two solutions (EGDGE and aluminum sulfate) are brought together shortly before the atomizing nozzle. The post-crosslinking solution for 1200 g of powder (particle size distribution <105 μm) from Example 1 was composed as follows: 17.58 g of water, 9.96 g of 1,2-propanediol, 1.2 g of ethylene glycol diglycidyl ether and 3.36 g of a 26. 8% aqueous aluminum sulfate solution. The performance data are shown in Table 1.

Example 5:

The procedure was analogous to Example 1, but without post-crosslinking.

Example 6:

It was experienced analogously to Example 2, but without post-crosslinking. The comparative examples were tested on sieve fractions <105 μm Example 7:

The procedure was analogous to Example 1. Post-crosslinking was carried out according to regulation Ib. The polymer was not screened off; Normal 5 grain size distribution up to 850 μm was measured.

Example 8

It was learned as in Example 1, except that 120 g of NaOH 10 50% were now used. The polymer from Example 8 has a pH of 4.44. The polymer is called the base polymer, i.e. used without further post-crosslinking. The performance data in 0.9% NaCl can be found in Table 2, the performance data in water can be found in Table 3.

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Example 8 a)

The sieve fraction <63 μm corresponds to 96% by weight <. 110 μm from example 8 was used.

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Example 8 b)

The sieve fraction <100 μm corresponding to 95% by weight <200 μm from example 8 was used. 5

Example 8 c)

The sieve fraction 63-100 μm corresponding to 96% by weight 160 μm from example 8 was used. 0

Example 9

Example 9 is a highly swellable polymer that is not post-crosslinked on the surface. The preparation of this 5 polymer is described in detail in WO 00/22018, page 14, lines 5-45. The performance data in 0.9% NaCl can be found in Table 2, the performance data in water can be found in Table 3.

0 Example 9 a)

The sieve fraction <63 μm corresponding to 96% by weight <110 μm from comparative example 8 was used.

5 Example 9 b)

The sieve fraction <100 μm corresponding to 95% by weight <200 μm from comparative example 8 was used.

Example 9 c)

The sieve fraction 63-100 μm corresponding to 96% by weight <160 μm from comparative example 8 was used.

Example 10

The preparation of the base polymer is described in Example 9.

Post-crosslinking was carried out on the entire particle stream. 1200 g of the product obtained from Comparative Example 8 with a grain size of <850 μm were sprayed in a powder mixing unit (Lödige mixer) with a homogeneous solution consisting of 20 g of water, 0.2 g of ethylene glycol diglycidyl ether and 0.66 g of sorbitan monococoate and into a preheated 2nd Lödige -Mixer decanted. Tempering was carried out over a period of 120 minutes under constant conditions at a jacket temperature of 150 ° C. and a speed of 60 rpm. The mixer was emptied and the product cooled down to room temperature. The performance data in 0.9% NaCl can be found in ^" Table 2, the performance data in water can be found in Table 3.

Example 10 a)

The sieve fraction <63 μ corresponding to 96% by weight <110 μm from comparative example 9 was used.

Example 10 b)

The sieve fraction <100 μm corresponding to 95% by weight <200 μm from comparative example 9 was used.

Example 10 c)

The sieve fraction 63-100 μm corresponding to 96% by weight <160 μm from comparative example 9 was used. Table 1

Table 2 Testing in 0.9% NaCl solution

Table 3 Testing in water

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Claims

claims

1. Aqueous-liquid-absorbing hydrogel-forming polymers which have a pH of 5.9 or less, preferably 5.5 or less, particularly preferably 5.2 or less, characterized in that 80% by weight, preferably 90 % By weight, particularly preferably 95% by weight, in particular 97% by weight, of the particles have a particle size of less than 250 μm.

2. Aqueous liquid-absorbing hydrogel-forming surface post-crosslinked polymers, characterized in that 80% by weight, preferably 90% by weight, particularly preferably

95 wt .-%, in particular 97 wt .-% of the particles have a particle size distribution of less than 250 .mu.m or characterized in that it ^'claim 1 is absorbent to aqueous liquids Hydrogel-forming polymers according to.

3. Aqueous liquid-absorbing hydrogel-forming polymers, characterized in that 80% by weight. preferably 90% by weight, particularly preferably 95% by weight, in particular 97% by weight of the particles have a particle size of less than 250 μm or are characterized in that they are liquid-absorbing hydrogel-forming polymers according to one of the claims 1 or 2 and at most each

1% by weight, preferably 0.3% by weight, in particular 0.1% by weight, of the particles have a particle size of less than 10 μm.

4. Aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 1 to 3, which are rendered inert.

5. Aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 1 to 4, characterized in that 60% by weight, preferably 70% by weight, in particular 80% by weight of the particles have a particle size distribution of greater than 30 μm and have less than 200 μm.

6. Aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 1 to 5, characterized in that 80% by weight, preferably 90% by weight, particularly preferably 95% by weight, in particular 97% by weight the particles have a particle size of less than 160 μm.

7. Aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 1 to 6, characterized in that 80 wt .-%, preferably 90 wt .-%, particularly preferably 95% by weight, in particular 97% by weight of the particles have a particle size of less than 110 μm.

8. Aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 1 to 7, characterized in that 80% by weight, preferably 90% by weight, particularly preferably 95% by weight, in particular 97% by weight of the Particles have a particle size of greater than 44 microns.

10 9. Hydrogel-forming water-absorbing liquids

Polymers according to one of claims 1 to 8, characterized in that after 0.9 minutes with 0.9% NaCL solution they have an AUL (0.014 psi) of at least 20 g / g, preferably at least 22 g / g, particularly preferably at least 25 g / g, total

15 special have at least 27 g / g.

10. Aqueous liquid absorbing hydrogel-forming

Polymers according to one of Claims 1 to 9, characterized in that they contain a ratio 20 of AUL (0.014 psi) at 10 minutes to AUL (0.014 psi) with 0.9% NaCL solution

60 minutes of 0.7 or more, preferably 0.75 or more, more preferably 0.9 or more, in particular 0.95 or more.

25 11. Hydrogel-forming aqueous liquids absorbing

Polymers according to one of claims 1 to 10, characterized in that with 0.9% NaCL solution they have a ratio of AUL (0.14 psi) at 10 minutes to the CRC of 0.7 or more, preferably 1.0 or more, particularly preferably 1.2 or more,

30 especially 1.4 or more.

12. Aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 1 to 11, characterized in that they have a vortex time of less than 25 s before

35 has less than 20 s, particularly preferably less than 15 s, in particular less than 10 s.

13. Production of hydrogel-forming polymers absorbing aqueous liquids according to claims 1 to 12, characterized in that a particle size distribution according to one of claims 1 to 8 is set after surface post-crosslinking or inerting.

14. Production of aqueous liquid-absorbing hydrogel-forming polymers according to claims 1 to 12, characterized in that for a particle size distribution according to one of claims 1 to 8 after surface post-crosslinking or inerting, no adjustment is necessary.

15. Production of aqueous liquid-absorbing hydrogel-forming polymers according to one of claims 13 or 14, characterized in that the surface postcrosslinking is carried out by spraying the particles and subsequent drying.

10. 16. Use of the aqueous liquid-absorbent hydrogel-forming polymers according to claims 1 to 11 in the fields

Hygiene 15 - storage, packaging, transport

Food sector

Medicine, cosmetics

Emulsions thickeners

Textile 20 - chem. applications

Construction and construction, installation

Water treatment, waste treatment, water separation

cleaning

Agribusiness 25 ^-; in fire protection

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