KR20140142740A - Color-stable super-absorbent - Google Patents

Abstract

A superabsorbent obtainable by a process for preparing a superabsorbent by monomer polymerization comprising the steps of:
a) at least one ethylenically unsaturated monomer having an acid group, optionally at least partly in the form of a salt,
b) at least one crosslinking agent,
c) one or more initiators,
d) optionally, one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a)
e) optionally, one or more water soluble polymers,
[The method further comprises a step of drying the resultant polymer, an optional step of grinding the dried polymer and separating the ground polymer, and an optional step of optionally post-crosslinking the ground and fired polymer, Wherein one or more sulfonic acid derivatives are added to the monomer mixture and / or polymer prior to the drying step, and one or more phosphonic acid derivatives are added to the polymer after the drying step or after the selective surface post-crosslinking step)
Exhibit improved stability to discoloration during storage at elevated temperatures or under elevated air humidity.

Description

Color stable superabsorbent {COLOR-STABLE SUPER-ABSORBENT}

The present invention relates to a color stable superabsorbent, a method for producing the same, a use thereof, and a sanitary article comprising the same. A color-stable superabsorbent means a superabsorbent which only discolors to a lesser extent during storage at elevated temperatures and under color changes in air humidity.

Superabsorbents are known. For these materials, the nomenclature "high swelling polymer", "hydrogel" (often used in dry form), "hydrogel-forming polymer", "water-absorbing polymer", "absorber gel- Quot ;, "water-absorbing resin ", and the like are usually used. These materials can be selected from crosslinked hydrophilic polymers, more particularly polymers formed from (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose ether or starch ethers, crosslinked carboxymethylcellulose , Partially crosslinked polyalkylene oxides in water-based liquids or natural products, such as guar derivatives, the most common being water-absorbing polymers based on partially neutralized acrylic acid. An essential characteristic of a superabsorbent is its ability to absorb several times the weight of the aqueous liquid without releasing the liquid again under a certain pressure. Superabsorbents used in the form of a dry powder are converted into gels when absorbing liquids, and are therefore converted into hydrogels when they normally absorb water. Crosslinking is important for synthetic superabsorbents, unlike the straight and conventional linear thickeners, because they cause insolubility of the polymer in water. Soluble materials can not be used as superabsorbents. Until now, the most important thing in the field of use of superabsorbents is absorption of body fluids. Superabsorbents are used, for example, in infant diapers, adult incontinence products or feminine hygiene products. It is used as a filler in market horticulture, for example, as a water storage for protection from fire, quite generally for absorbing moisture, or for absorption of liquid in food packaging.

A superabsorbent can absorb several times the water of a superabsorbent and retain it under a certain pressure. Generally, these superabsorbents have a CRC of at least 5 g / g, preferably at least 10 g / g and more preferably at least 15 g / g ("centrifuge retention capacity", see below for the test method). The "superabsorbent" may be a mixture of different individual superabsorbent materials, or may be a mixture of components exhibiting superabsorbent properties only when they interact; Material compositions are not so important as superabsorbent properties.

An important property for a superabsorbent is its ability to retain fluids under pressure (as well as its absorption capacity) (retention, typically "under load" ("AUL") or "adsorption to pressure" ("AAP") Indicated, see below for testing methods). The swollen gel can prevent or prevent fluid conduction with a superabsorbent ("gel shield") that is not yet swollen. Good conduction properties to the fluids are processed, for example, by hydrogels having a high gel strength in the swollen state. The gel with low gel strength can be deformed under pressure application (body pressure), blocking the voids in the superabsorbent / cellulose fiber absorber and thus preventing fluid conduction to the superabsorbent that is not yet swollen or incompletely swollen and is not yet swollen To prevent absorption of fluids into the superabsorbent which is not or incompletely swollen. Increased gel strength is generally achieved through a higher degree of crosslinking, which reduces the adsorption capacity of the product. A clear method of increasing the gel strength is to increase the degree of crosslinking at the surface of the superabsorbent particles relative to the interior of the particles. To this end, the superabsorbent particles normally dried in the post-crosslinking step with an average cross-link density are subjected to further cross-linking in the surface thin layer of their particles. Surface post cross-linking increases the cross-link density in the shell of the superabsorbent particles, which increases the adsorption under compression stress to a higher level. If the absorption capacity in the surface layer of the superabsorbent particles is lowered, its core (as a result of the presence of the transporting polymer chain) has improved absorption capacity as compared to shells, and the shell structure ensures improved permeability without the occurrence of gel shielding. Likewise, it is known that relatively highly crosslinked superabsorbents can be obtained as a whole and the degree of crosslinking inside the particles is later reduced compared to the outer shell of the particles.

Methods of making superabsorbents are also known. Most commonly available acrylic acid-based superabsorbents are prepared by free-radical polymerization of acrylic acid in the presence of a crosslinking agent ("innerb crosslinker") and acrylic acid is generally added to the aqueous solution of alkali, usually sodium hydroxide Before, after, or partly before and some after, the polymerization. The polymer gel thus obtained is pulverized (depending on the polymerization reactor used, this may be carried out simultaneously with the polymerization) and dried. The dry powder thus obtained ("base polymer") can be further crosslinked, for example an organic crosslinking agent or a polyvalent cation, such as aluminum (generally used in the form of aluminum sulfate) ), Or both, and is generally followed by crosslinking on the surface of the particles.

The problem that often arises in superabsorbents is discoloration, which occurs during storage at elevated temperatures or elevated air humidity. Such conditions often occur during superabsorbent storage in tropical or subtropical countries. Superabsorbents tend to yellow under such conditions; They may even turn brown or black. Such discoloration of the actual colorless superabsorbent powder may appear in thin sanitary articles, which are particularly desirable, and consumers are not advised to ignore unsightly sanitary products. Although the cause of discoloration is not completely understood, it appears that reactive compounds such as residual monomers derived from polymerization, use of some initiators, impurities in monomers or neutralizing agents, surface subsequent crosslinking agents or stabilizers in the monomers used are involved.

[Modern Superabsorbent Polymer Technology ", J. Wiley & Sons, New York, U.S.A.), Fredric L. Buchholz and Andrew T. Graham (editors) / Wiley-VCH, Weinheim, Germany, 1997, ISBN 0-471-19411-5] (Comprehensive review of superabsorbents, their properties and methods for producing superabsorbents).

WO 00/55 245 A1 teaches the stabilization of superabsorbents against discoloration by treatment with inorganic reducing agents and optionally metal salts, alkaline earth metal salts (which are added after polymerization). Inorganic reducing agents are typically hypophosphite, phosphite, bisulfite or sulfite. The metal salt is typically a colorless (the "colorless" feature is often referred to simply as "white") phosphate, acetate or lactate, but not a halide. According to the teachings of WO 2006/058 682 A1, the discoloration of the superabsorbent is avoided when dried and the post-crosslinking reaction is carried out in an atmosphere essentially free of oxidizing gas. WO 2009/060 062 A1 or WO 2010/012 762 A2 teaches the addition of sulfinic acid derivatives to superabsorbents to stabilize superabsorbents against discoloration. EP 1 199 315 A2 teaches the use of a redox initiator system to initiate a polymerization reaction, wherein the redox initiator system comprises sulfinic acid or sulfinate as a reducing component, especially 2-hydroxysulfinate acetic acid or And salts thereof. WO 99/18 067 A1 discloses in particular use as hydroxyl- or aminoalkyl- or arylsulphinic acid derivatives or mixtures thereof and as a reducing agent which does not release formaldehyde. WO 2004/084 962 A1 relates to the use of these sulfinic acid derivatives as reducing components of redox initiators for the polymerization of partially neutralized acrylic acid with superabsorbents.

In JP 05/086 251, a phosphoric acid derivative or a salt thereof, especially (1-hydroxyethane-1,1-diyl) bisphosphonic acid (also referred to as "1-hydroxyethylidene-1,1-diphosphonic acid" Etidronic acid "), ethylenediamine tetra (methylenephosphonic acid), diethylenetriamine penta (methylenephosphonic acid), and the like. ) Or its alkali metal or aluminum salt as a stabilizer for superabsorbents for discoloration. EP 781 804 A2 teaches, for the same purpose, the addition of (1-hydroxyalkyl-1,1-diyl) bisphosphonic acid, an alkyl radical containing from 5 to 23 carbon atoms.

EP 668 080 A2 teaches the addition of inorganic, organic, or polyamino acids to superabsorbents, and the inorganic acids described also include phosphoric acids. US 2005/0 085 604 A1 discloses adding a chelating agent and an oxidizing or reducing agent to a superabsorbent, wherein the chelating agent also comprises phosphorus. US 2005/0272 600 A1 relates to the addition of ionic blocking agents to superabsorbents, which also include organic phosphorus compounds. (1-hydroxyethane-1,1-diyl) bisphosphonic acid is one of the examples mentioned. According to the teaching of EP 2 112 172 A1, an organophosphorus compound is added to the monomer solution which is polymerized to provide a superabsorbent; (1-hydroxyethane-1,1-diyl) bisphosphonic acid; Ethylenediaminetetra (methylenephosphonic acid) is the most preferred compound. US 2009/0 275 470 A1 teaches the addition of all of the chelating agents and preferably the inorganic phosphorus compounds to the superabsorbent, wherein the chelating agent is also a phosphorus compound such as (1-hydroxyethane-1,1-diyl ) Bisphosphonic acid or ethylenediaminetetra (methylenephosphonic acid). Also, according to the teachings of WO 2006/109 882 A1, such compounds are added to the superabsorbents as chelating agents, as well as phosphorus compounds as well as sulfur compounds are added in various process steps.

The present invention seeks to find a superabsorbent which is further stabilized against discoloration, in particular yellowing or browning, in the course of storage under other superabsorbents, or even at elevated temperature and / or elevated air humidity, and a process for its preparation. The provisional properties of the superabsorbent, in particular its absorption capacity to the liquid, including its absorption capacity under pressure, and its ability to utilize the liquid should not or will not cause any harm. A further object of the present invention is the use of said superabsorbent, for example a hygiene article containing said superabsorbent and a process for its production.

This object is achieved by a process for preparing superabsorbents by monomer solution polymerization comprising:

a) at least one ethylenically unsaturated monomer having an acid group, optionally at least partly in the form of a salt,

b) at least one crosslinking agent,

c) one or more initiators,

d) optionally, one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a)

e) optionally, one or more water soluble polymers,

[The method further comprises a step of drying the resultant polymer, an optional step of grinding the dried polymer and separating the ground polymer, and an optional step of optionally post-crosslinking the ground and fired polymer, Wherein one or more sulfonic acid derivatives are added to the monomer mixture and / or polymer prior to the drying step, and one or more phosphonic acid derivatives are added to the polymer after the drying step or after the selective surface post-crosslinking step.

The superabsorbent of the present invention surprisingly exhibits excellent stability to discoloration without giving any solution to its providing properties, such as CRC, AUL or SFC.

According to the present invention, one or more sulfonic acid derivatives are added to the superabsorbent. In the context of the present invention, a sulfonic acid derivative is a mixture derived from a sulfonic acid of the formula R-SO ₂ -OH, with a salt and a mixture of a compound having the formula (I) and / or a salt thereof:

[Wherein,

M is a hydrogen atom, an ammonium ion, an equivalent of a divalent metal ion of group 1, 2, 8, 9, 10, 12 or 14 of the periodic table;

R ¹ is OH or NR ⁵ R ^6, wherein R ⁵ and R ⁶ are each independently H or C ₁ -C ₆ - alkyl;

R ² is H or an alkyl, alkenyl, cycloalkyl or aryl group, which optionally has 1, 2 or 3 substituents which are independently of each other C ₁ -C ₆ -alkyl, OH, OC ₁ -C ₆ -alkyl, halogen and CF < ₃ >;

R ³ is COOM, SO ₃ M, COR ⁴ , CONR ⁴ R ⁵ or COOR < ⁴ > wherein M, R < ⁴ & R ⁵ are each as defined above or, when R ² is aryl, it is optionally substituted as defined above and is also H.

In the above formula (I), alkyl represents a straight-chain or branched alkyl group having preferably 1 to 6 and especially 1 to 4 carbon atoms. Examples of alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl and the like. The same applies to alkyl groups in O-alkyl. Alkenyl preferably represents a straight-chain or branched alkenyl group having from 3 to 8 carbon atoms, especially from 3 to 6 carbon atoms. A preferred alkenyl group is an allyl group. Cycloalkyl is especially C ₁ -C ₆ -cycloalkyl, particularly preferred are cyclopentyl and cyclohexyl. Aryl (also including aralkyl) is preferably phenyl or naphthyl. When the aryl radical is a phenyl group and is substituted, it preferably has 2 substituents. They are particularly present in the 2 and / or 4 positions.

Halogen is F, Cl, Br and I, preferably Cl and Br.

M is preferably one equivalent of an ammonium ion, an alkali metal ion or an alkaline earth metal or zinc ion. Suitable alkali metal ions are, in particular, sodium and potassium ions; Suitable alkaline earth metal ions are, in particular, magnesium, strontium and calcium ions.

R < ^{1 >} is preferably a hydroxyl or an amino group.

R ² is preferably a hydrogen atom or an alkyl or aryl group, which may be substituted as described above. Preferably two or two hydroxyl and / or alkoxy substituents.

R ³ is preferably COOM or COOR ⁴ (wherein M and R ⁴ are each as defined above), or when R ² is aryl which may be substituted as indicated above, it is also a hydrogen atom.

In a preferred embodiment, the superabsorbent comprises a compound of formula (II), wherein M is an equivalent of an alkali metal ion or an alkaline earth metal or zinc ion; R < ¹ > is a hydroxyl or an amino group; R ² is H or alkyl and R ³ is COOM or COOR ^4, wherein when R ³ is COOM, in such a COOM radical, M is an equivalent of H, an alkali metal ion or an alkaline earth metal ion and R ³ is COOR when ^3, R ⁴ is C ₁ -C ₆ - alkyl. Particularly preferred compounds of formula (I) above are 2-hydroxy-2-sulfonato acetic acid and its salts, especially the sodium salts thereof, and especially the sodium salt thereof.

In a further embodiment, the superabsorbent optionally comprises a compound of the above formula, wherein M is an equivalent of an alkali metal ion or an alkaline earth metal or zinc ion; R ¹ is a hydroxyl or an amino group; R ² is aryl which is optionally substituted as described above, in particular hydroxyphenyl or C ₁ -C ₄ - alkoxy phenyl; R ³ is a hydrogen atom.

At present, one group (H) of the Periodic Table of the Elements is selected from the IUPAC Numbering (International Organization for Chemical Nomenclature, International Union of Pure and Applied Chemistry, 104 TW Alexander Drive, Building 19, Research Triangle Park, NC 27709, USA, www.iupac.org) (Fe, Ru, Os), Group 9 (Co, Rh, Ir), Group 8 (Be, Mg, Ca, Sr, Ba and Ra), Li, Na, K, Rb, Cs, Group 10 (Ni, Pd, Pt), Group 12 (Zn, Cd, Hg) and Group 14 (C, Si, Ge, Sn, Pb) USA, www.cas.org) in the numbering Ia, IIa, IIb, IVa and VIIIb groups.

Sulfonic acid derivatives of the above formula may be used in the pure form, but may optionally be used in admixture with the corresponding sulfinic acid derivatives and sulfites of the corresponding metal ions.

The preparation of such mixtures is known and is described, for example, in WO 99/18 067 A1. These are also standard commercial products and are commercially available, for example in the form of a mixture of the sodium salt of 2-hydroxy-2-sulfinetoacetic acid, the disodium salt of 2-hydroxy-2-sulphonatoacetic acid and sodium bisulfite, by L. Brugemann KG (Salzstrasse 131, 74076 Heilbronn, Germany, www.brueggemann.com) from the title BRUGOLIT®FF6M or BRUGOLIT®FF7, or alternatively is BRUGGOLITE ^® FF6M or BRUGGOLITE ^® FF7.

Preferred is the use of sulfonic acid derivatives in pure form. The preparation of sulfonic acid derivatives is well known; This is carried out, for example, by sulfoxide oxidation, sulfochlorination subsequent hydrolysis or by sulfonation of an appropriate starting compound. They are also standard commercial products. For example, the disodium salt of 2-hydroxy-2-sulphonatoacetic acid is commercially available from L. Brugemann KG (Salzstrasse 131, 74076 Heilbronn, Germany, www.brueggemann.com) under the trade name BLANCOLEN ^® HP.

According to the present invention, one or more phosphonic acid derivatives are added to the superabsorbent. In the context of the present invention, the phosphonic acid itself must also be understood as a phosphonic acid derivative. The phosphonic acid derivative is a compound derived from a phosphonic acid having the formula (HP (O) (OH) ₂ ) and having the formula (II)

R < ⁶ > -P (O) (OH) ₂ (II)

Wherein R < ⁶ > is an optionally substituted organic radical. Its salts and / or esters and mixtures of such phosphonic acid derivatives, salts and / or esters are likewise available.

Examples are monoalkylphosphonic acids and monoalkenylphosphonic acids, such as laurylphosphonic acid and stearylphosphonic acid. Further examples are 1-hydroxyethylidene-1,1-diphosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, ethylenediamine-N, N'-di (methylenephosphonic acid) (Methylenephosphonic acid), nitrilotetra (methylenephosphonic acid), nitriloacetic acid-di (methylenephosphonic acid), nitrilodiacetic acid (methylenephosphonic acid), nitriloacetic acid- Tetramethylenediamine tetra (methylenephosphonic acid), hexamethylenediamine tetra (methylenephosphonic acid), tetramethylenediamine tetra (methylenephosphonic acid), tetramethylenediamine tetra (methylenephosphonic acid), ethylenediamine-N, N'- diacetic acid- (Methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), hydroxyethylaminobis (methylenephosphonic acid), bishexamethylenetriaminepenta (methylenephosphonic acid), fic acid, 2- Roxy-2-phosphonatoacetic acid and these compounds Salts.

Preferred phosphonic acid derivatives are those in which R < ⁶ > is a diyl radical comprising two phosphonic acid radicals, in particular 1-amino-1,1-diyl radical or 1-hydroxy-1,1-diyl radical, -1, 1 -dihydrophosphonic acid, wherein alkyl is a C ₁ -C ₂₅ radical, particularly preferably for ethyl. Most preferred phosphonic acid derivatives are (1-hydroxyethane-1,1-diyl) bisphosphonic acid or salts thereof with a metal M, wherein M is a hydrogen atom, an ammonium ion, a monovalent metal ion, 8, 9, 10, 12 or 14 of the Periodic Table of the Elements, in particular the sodium salt, potassium salt, disodium salt, dipotassium salt or sodium-potassium salt. Further preferred phosphonic acid derivatives are those wherein R ⁶ is an amino-substituted alkyl radical, especially an amino-substituted methylene radical, and is selected from the group consisting of ethylenediaminetetra (methylenephosphonic acid), diethylenetriamine penta (methylenephosphonic acid) Tris (methylene)] tris (phosphonic acid).

These phosphonic acid derivatives are known and are prepared by standard routes and include, for example, the quasi-Mannich reaction of free phosphonic acid with formaldehyde and oligoethyleneamine, the Michaelis-Arbuzov reaction , Or by acylation of the phosphonic acid using a carboxylic anhydride or nitrile. Its main use is the same as in phosphate substitution in detergents. Thus, they are standard commercial products and are commercially available (for example, Cublen ^® brand, Zschimmer & Schwarz Mohsdorf GmbH & Co KG, Chemnitztalstrasse 1, 09217 Burgstadt, Germany).

The superabsorbent of the present invention can be obtained by the process according to the invention.

The process according to the invention is an aqueous solution polymerization method of a monomer mixture comprising:

a) at least one ethylenically unsaturated monomer comprising at least one acid group and optionally present in at least some salt form,

b) at least one crosslinking agent,

c) one or more initiators,

d) optionally, one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a), and

e) optionally one or more water soluble polymers.

The monomer a) is preferably water-soluble, i.e. the solubility in water at 23 DEG C is typically at least 1 g / 100 g of water, preferably at least 5 g / 100 g of water, more preferably at least 25 g / 100 g of water Most preferably at least 35 g / 100 g of water.

Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids or salts thereof such as acrylic acid, methacrylic acid, maleic acid or its salts, maleic anhydrides and itaconic acid or its salts. Particularly preferred monomers are acrylic acid and methacrylic acid. Very particularly preferred is acrylic acid.

Further suitable monomers a) are, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

Impurities can significantly affect polymerization. The raw materials used should have maximum purity. Thus, this is particularly advantageous for purifying monomer a). Suitable purifiable processes are described, for example, in WO 2002/055469 A1, WO 2003/078378 A1 and WO 2004/035514 A1. Suitable monomers a) are, for example, purified according to WO 2004/035514 A1 and comprise 99.8460 wt% acrylic acid, 0.0950 wt% acetic acid, 0.0332 wt% water, 0.0203 wt% propionic acid, 0.0001 wt% furfural, 0.0001 wt% By weight of maleic anhydride, 0.0003% by weight of diacrylic acid and 0.0050% by weight of hydroquinone monomethyl ether.

The proportion of acrylic acid and / or its salt in the total amount of monomer a) is preferably not less than 50 mol%, more preferably not less than 90 mol%, and most preferably not less than 95 mol%.

The monomer solution is preferably not more than 250 ppm by weight, preferably not more than 130 ppm by weight, more preferably not more than 70 ppm by weight, preferably not less than 10 ppm by weight, more preferably not less than 30 ppm by weight, Of the hydroquinone monoether (in each case non-neutralized monomer a); The salt of the neutralized monomer a), i.e. the monomer a), is considered for calculation purposes for the neutralized monomers. For example, the monomer solution may be prepared by using an ethylenically unsaturated monomer comprising an acid group having an appropriate content of hydroquinone monoethers.

Preferred hydroquinone monoethers are hydroquinone monomethyl ether (MEHQ) and / or alpha-tocopherol (vitamin E).

Suitable crosslinking agents b) are compounds having two or more groups suitable for crosslinking. Such groups are, for example, functional groups capable of forming covalent bonds with the ethylenically unsaturated groups that can be polymerized into free radicals into the polymer chain, and the acid groups of monomer a). Also, a polyvalent metal salt capable of forming a coordination bond with two or more acid groups of the monomer a) is also suitable as the crosslinking agent b).

Crosslinking agent b) is a compound having two or more polymerizable groups that can be polymerized into free radicals into the polymer network. Suitable crosslinking agents b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallyl ammonium chloride , Tetraallyloxyethane, (as described in EP 530 438 A1), di- and triacrylates (EP 547 847 A1, EP 559 476 A1, EP 632 068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO 2003/104301 A1 and DE 103 31 450 A1), mixed acrylates (and acrylate groups include additional ethylenically unsaturated groups, as described in DE 103 31 456 A1 and DE 103 55 401 A1), or crosslinker mixtures (for example as described in DE 195 43 368 A1, DE 196 46 484 A1, WO 90/15830 A1 and WO 2002/32962 A2).

Preferred crosslinking agents b) are selected from the group consisting of pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, 15- to 20-tuply ethoxylated trimethylolpropane triacrylate, 15-20-tuply ethoxylated Glyceryl triacrylate, polyethylene glycol diacrylate having 4 and 45 -CH ₂ CH ₂ O units in the molecular chain, trimethylolpropane triacrylate and triallylamine.

Very particularly preferred crosslinking agents b) are polyethoxylated and / or propoxylated glycerols which are esterified with acrylic acid or methacrylic acid to produce di- or triacrylates (see, for example, WO 2003/104301 A1 Lt; / RTI > Di- and / or triacrylates of 3- to 10-tuply ethoxylated glycerol are particularly advantageous. Very particularly preferred are di- or triacrylates of 1- to 5-tuply ethoxylated and / or propoxylated glycerol. Most preferred are triacrylates of 3- to 5-tuply ethoxylated and / or propoxylated glycerol, especially tri-acrylates of 3-tuply ethoxylated glycerol.

The amount of crosslinking agent b) is preferably 0.05 to 1.5% by weight, more preferably 0.1 to 1% by weight and most preferably 0.3 to 0.6% by weight (in each case based on monomer a). For rinsing the crosslinker contents, the centrifuge retention capacity (CRC) drops and the adsorption rises at a pressure of 0.3 psi (AUL 0.3 psi).

The initiator c) used may be any compound which produces free radicals under polymerization conditions such as, for example, thermal initiators, redox initiators and / or photoinitiators. Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite. Preference is given to using a thermal initiator and a redox initiator such as a mixture of sodium peroxodisulfate / hydrogen peroxide / ascorbic acid. However, the reducing component used is preferably a sulfonic acid derivative of formula (I). However, initiators are used in conventional amounts. The typical amount of reducing component of the redox initiator is generally 0.00001 wt% or more, preferably 0.0001 wt% or more, more preferably 0.001 wt% or more, and generally 0.2 wt% or less and preferably 0.1 wt% or less (In each case based on the amounts of monomers a) and d). However, the reducing component used alone in the redox initiator is a sulfonic acid derivative of the formula (I), and the amount thereof to be added is generally 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.03% Is generally not more than 1.0% by weight, preferably not more than 0.3% by weight and more preferably not more than 0.2% by weight (in each case based on the amounts of monomers a) and d). Typical amounts of the oxidizing components of the redox initiator are generally 0.0001% by weight and more preferably 0.001% by weight or more, and generally up to 2% by weight and preferably up to 1.0% by weight (in each case monomer a) and d) Respectively. The usual amount of thermal initiator is generally 0.01% by weight and more preferably 0.1% by weight or more, and generally not more than 2% by weight and preferably not more than 1.0% by weight (in each case based on the amounts of monomers a) and d) . Typical amounts of photoinitiators are generally 0.001% by weight and more preferably 0.01% by weight or more, and generally not more than 1.0% by weight and preferably not more than 0.2% by weight (in each case based on the amounts of monomers a) and d).

The ethylenically unsaturated monomers d) copolymerizable with the ethylenically unsaturated monomers a) containing acid groups are, for example, acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, Dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, maleic acid or a salt thereof and maleic anhydride.

The water-soluble polymer e) to be used is selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified celluloses such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycol or polyacrylic acid, And modified cellulose.

Typically, aqueous monomer solutions are used. The water content of the monomer solution is preferably 40 to 75% by weight, more preferably 45 to 70% by weight and most preferably 50 to 65% by weight. It is possible to use a monomer suspension, i. E. It is possible to use a supersaturated monomer solution. For raising the water content, the energy requirements in subsequent drying are increased, the water content is lowered, and the heat of polymerization can only be removed improperly.

For optimal performance, preferred polymerization inhibitors require dissolved oxygen. Thus, the monomer solution may liberate dissolved oxygen prior to polymerization by inactivation, i. E. Fluidized through an inert gas, preferably nitrogen or carbon dioxide. The oxygen content of the monomer solution is preferably lowered prior to polymerization and lowered to less than 1 ppm by weight, more preferably less than 0.5 ppm by weight and most preferably less than 0.1 ppm by weight.

The monomer mixture may comprise additional components. Examples of additional components used in such monomer mixtures are, for example, chelating agents for retaining metal ions in solution, or inorganic powders for increasing stiffness of the superabsorbent in swollen state, or of a size reusable from subsequent grinding operations It is a substance for reduction. It is possible to use all additives known for the monomer mixture. Although only "solution" is discussed in connection with the monomer mixture, it also refers to the polymerization of the suspension, for example when an insoluble component is added to the monomer mixture.

The acid groups of the polymer gel resulting from the polymerization are typically partially neutralized. The neutralization is preferably carried out in the monomer phase; That is, salts of monomers comprising acid groups, or precisely, mixtures of monomers containing acid groups and salts of monomers comprising acid groups ("partially neutralized acid") are used as component a) in the polymerization. This is typically carried out by mixing the neutralizing agent as an aqueous solution, preferably as a monomer mixture intended for polymerization as a solid, or preferably in a monomer comprising acid groups or a solution thereof. The degree of neutralization is preferably from 25 to 95 mol%, more preferably from 50 to 80 mol% and most preferably from 65 to 72 mol%, and conventional neutralizing agents may be used, Metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal hydrogen carbonates, and mixtures thereof. Instead of an alkali metal salt, it is possible to use an ammonium salt. Particularly preferred alkali metals are sodium and potassium, very particularly preferred are sodium hydroxide, sodium carbonate or sodium bicarbonate and also mixtures thereof.

However, it is possible to perform neutralization after polymerization at the stage of the polymer gel formed in the polymerization. In the polymer gel step only 40 mol% or less, preferably 10 to 30 mol%, and more preferably 10 to 30 mol% of the acid groups are added before the polymerization by setting the desired final degree of post polymerization neutralization and adding a portion of the neutralizing agent directly to the monomer solution It is possible to neutralize 15 to 25 mol%. When the polymer gel is partially or more neutralized after polymerization, the polymer gel is preferably subdivided mechanically, for example, by an extruder, wherein the neutralizing agent is sprayed, sprayed or poured and carefully mixed. To this end, the gel mass obtained can be extruded repeatedly for homogenization.

However, it is desirable to perform neutralization at the monomer stage. That is to say: in a very particularly preferred embodiment, the monomer a) used comprises a salt of a monomer comprising from 25 to 95 mol%, more preferably from 50 to 80 mol% and most preferably from 65 to 75 mol% Is a mixture of monomers containing an acid group of 100 mol%. Such a mixture is a mixture of sodium acrylate and acrylic acid or a mixture of potassium acrylate and acrylic acid.

In a preferred embodiment, the neutralizing agent used in the neutralization is such that the iron content thereof is generally less than 10 ppm by weight, preferably less than 2 ppm by weight, more preferably less than 1 ppm by weight. Likewise preferred are the lower chloride content and the anion of the oxygen acid of the chlorine. Suitable neutralizing agents are, for example, 50 wt% sodium hydroxide solution or potassium hydroxide solution, traded as "membrane grade ", and even purer and more suitable, By weight of sodium hydroxide solution or potassium hydroxide solution.

Methods for producing a superabsorbent from a monomer mixture, such as those described as examples above, are known in principle. Suitable polymerization reactors are, for example, kneading reactors or belt reactors. In the kneader, the polymer gel formed in the polymerization of the aqueous monomer solution or suspension is continuously pulverized by a contra-rotator stirrer shaft as described, for example, in WO 2001/38402 A1. Polymerization on belts is described, for example, in EP 955 086 A2, DE 38 25 366 A1 and US 6,241,928. The polymerization in the belt reactor can be carried out in the same manner as in known batch polymerization processes or as in a tubular reactor (for example as described in EP 445 619 A2 and DE 19 846 413 A1), further process steps, Further, a polymer gel is formed which must be ground in an extruder or kneader. (For example, as described in EP 457 660 A1), or by spray or drop-in polymerization processes (e.g., EP 348 180 A1, EP 816 383 A1, WO 96/404 27 A1, US 4 020 256, US 2002/0193 546 A1, DE 35 19 013 A1, DE 10 2005 044 035 A1, WO 2007/093531 A1, WO 2008/086 976 A1 or WO 2009/027 356 A1), spherical Or it is possible to produce superabsorbent particles of different shapes. Similarly, processes are known in which the monomer mixture is applied to a substrate, for example a nonwoven web, and polymerized (WO 02/94 328 A2 and WO 02/94 329 A1).

The sulfonic acid derivative of formula (I) is added before or after drying in the process according to the invention, but is preferably added before drying. Thereafter, the addition can be done at any time before drying; For example, sulfonic acid derivatives can be added to the monomer solution prior to polymerization and added to the polymer gel that is added during polymerization and formed after polymerization. When added to the monomer solution before polymerization, homogeneous incorporation of the sulfonic acid derivative by mixing is technically the simplest method; It is therefore preferred to add it to the monomer solution. The addition during the polymerization is possible in a simple manner, especially when the polymerization is carried out in a kneading reactor, since the incorporation by mixing is likewise possible without separating the processing steps. However, it is likewise possible to mix the sulfonic acid derivative with the swollen polymer gel. If the polymerization is carried out in a kneading reactor, the addition can be carried out in the batchwise mixing reactor (in the case of a continuous-movement kneading reactor, thus approaching the outlet or inlet) or in a separate processing step between polymerization and drying have. In principle, a device suitable for this purpose is any that can mix a sulfonic acid derivative with a gel having a suitable homogeneity; In particular, kneaders, screw mixers and extruders are optional.

When drying occurs simultaneously with the polymerization (for example, as in the droplet polymerization process), the sulfonic acid derivative is necessarily added to the monomer mixture.

The sulfonic acid derivative of formula (I) is generally present in an amount of at least 0.001% by weight, preferably at least 0.01% by weight and more preferably at least 0.03% by weight, and generally at most 1.0% by weight, preferably at most 0.3% Preferably 0.2% by weight or less (in each case, based on the amounts of monomers a) and d).

Thereafter, the polymer gel obtained from the aqueous solution polymerization and optional subsequent neutralization preferably have a residual moisture content of preferably 0.5 to 15% by weight, more preferably 1 to 10% by weight and most preferably 2 to 8% by weight (See below for testing methods for remaining moisture or water content). If the residual moisture content is too high, the dried polymer gel may have a low glass transition temperature Tg and may be a little difficult to process further. If the residual moisture content is too low, the dried polymer gel is too fragile, and in a subsequent milling step, a large amount of polymer particles (undesired) having an excess of low particle size is obtained ("fine water"). The solids content of the gel before drying is generally from 25 to 90% by weight, preferably 30 to 80% by weight, more preferably 35 to 70% by weight and most preferably 40 to 60% by weight. Optionally, however, it is possible to dry using a heatable mixer with a dry or mechanical mixing unit using a fluidized bed dryer (e.g. a paddle dryer or a similar dryer with a mixing tool of a different design). Optionally, the drier can be operated under nitrogen or another non-oxidative inert gas or can be operated under at least reduced partial oxygen pressure to prevent oxidative yellowing processes. However, in general, even sufficient venting and removal of water vapor result in acceptable products. In general, the minimum drying time is advantageous for color and product quality.

During drying, the residual monomer content in the polymer particles is also reduced and the final residues of the initiator are destroyed.

The apparatus in which the dried polymer gel is then pulverized, sorted and used for milling is typically a single or multi-stage roll mill, preferably a two or three stage roll mill, a pin mill, a hammer mill Or a vibration mill. The oversized gel lumps that are not still dry on the inside are elastic and preferably removed before milling, which can be carried out by a sieve or by simple shifting by wind shifting ("guard sieves" for mills). In terms of the grinding machine used, the mesh size of the sieve must be selected so that elastic particles of the minimum collapse level produced from the oversize are generated.

Excessively large, poorly finely ground superabsorbent particles can be detected as crude particles in their predominant use (in hygiene such as diapers); They also lower the average initial swell rate of the superabsorbent. Both are not desirable. Advantageously, the crude grain polymer particles are thus removed from the product. This is done by conventional sorting processes, for example by way of wind-shifting or sieving with a mesh size of 1000 탆 or less, preferably 900 탆 or less, more preferably 850 탆 or less and most preferably 800 탆 or less It is performed by sieving. For example, sieves having a mesh size of 700 mu m, 650 mu m, or 600 mu m are used. The removed coarse polymer particles ("oversize") can be returned to the milling and sieving cycle for cost optimization and can be further processed separately.

Polymer particles with too small particle size lower the permeability (SFC). Advantageously, this sorting thus removes the fine polymer particles. When sieving is carried out, it is usually carried out by sieving a mesh size of 300 μm or less, preferably 200 μm or less, more preferably 150 μm or less and most preferably 100 μm or less. The fine polymer particles ("under-sized" or "micro-water") can be returned to the fully polymerized gel prior to drying of the monomer stream, polymerization gel, or gel as needed for cost optimization.

The average particle size of the polymer particles removed by the product fraction is generally not less than 200 mu m, preferably not less than 250 mu m, more preferably not less than 300 mu m, and generally not more than 600 mu m, and more preferably not more than 500 mu m. The proportion of particles having a particle size of 150 mu m or more is generally at least 90 wt%, more preferably at least 95 wt%, and most preferably at least 98 wt%. The proportion of particles having a particle size of 850 mu m or less is generally at least 90 wt%, more preferably at least 95 wt%, and most preferably at least 98 wt%.

In some other known production methods for superabsorbents, particularly in the case of suspension polymerization, injection or droplet formation polymerization, the selection of process parameters will determine the particle size distribution. Such a process will directly provide a particulate superabsorbent of the desired particle size, so that the milling and bountoming steps can often be omitted. In some cases (especially in the case of injection and droplet formation polymerization), a dedicated drying step can often be omitted.

The polymer so produced has superabsorbent properties and is termed the term "superabsorbent ". His CRC is generally relatively high, but his AUL or SFC is relatively low. Such types of surface superabsorbents that are not post-crosslinked are often referred to as "base polymers" to distinguish them from surface superabsorbent superabsorbents prepared therefrom.

The base polymer is optionally cross-linked after the surface.

Suitable post-crosslinking agents are compounds containing groups capable of forming bonds with two or more functional groups of superabsorbent particles. In the case of acrylic acid / sodium acrylate based superabsorbents which dominate the market, suitable surface post-crosslinking agents are compounds comprising groups capable of forming bonds with two or more carboxylates. Preferred post-crosslinking agents are amide acetals or carbamates of formula (III)

[Wherein,

R ⁷ is C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl,

R ⁸ is X or OR ¹² ,

R ⁹ is hydrogen, C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl, or X,

R ¹⁰ is C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl,

R ¹¹ is hydrogen, C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl, C ₁ -C ₁₂ -acyl or C ₆ -C ₁₂ -aryl,

R ¹² is C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl,

X is a carboxyl oxygen common to R < ⁸ > and R < ⁹ &

Wherein R ⁷ and R ¹⁰ and / or R ¹¹ and R ¹² may be a bridged C ₂ -C ₆ -alkanediyl, wherein the above-mentioned R ⁷ to R ¹² radicals may also have 1 to 2 total free atoms , And may be joined to one or more suitable basic structures by such free valencies]

Or polyhydric alcohols, and the polyhydric alcohol is preferably less than 100 g / mol, preferably less than 90 g / mol, more preferably less than 80 g / mol, most preferably less than 70 g / mol per hydroxyl group (Geminal), secondary or tertiary hydroxyl groups and the polyhydric alcohol is a diol of formula (IVa), or

HO-R < ¹³ > -OH (IVa)

Wherein R ¹³ is a non-branched alkylene radical of the formula - (CH ₂ ) _n - (wherein n is an integer of 3 to 20, preferably 3 to 12), and both hydroxyl groups are present at the terminal Or R < ¹³ > is a non-branched, branched or cyclic alkylene radical,

Or a polyol of formula (IVb)

Wherein the radicals R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ are each independently selected from the group consisting of hydrogen, hydroxyl, hydroxymethyl, hydroxyethyloxymethyl, 1-hydroxyprop- Propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, 1,2-dihydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl or Hydroxybutyl and a total of 2, 3, or 4, preferably 2 or 3, hydroxyl groups are present and at most one of the R ¹⁴ , R ¹⁵ , R ^16, and R ¹⁷ radicals is a hydroxyl; ,

Or a cyclic carbonate of the formula (V)

Wherein R ¹⁸ , R ¹⁹ , R ²⁰ , R ²¹ , R ²² and R ²³ are each independently hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec- n is 0 or 1,

Or a bisoxazoline of formula (VI)

Wherein R ²⁴ , R ²⁵ , R ²⁶ , R ²⁷ , R ²⁸ , R ²⁹ , R ³⁰ and R ³¹ each independently represent hydrogen, methyl, ethyl, n-propyl, isopropyl, Butyl or isobutyl, and R ³² is a single bond, a linear, branched, or cyclic C ₂ -C ₁₂ -alkylene radical, or an alkylene radical having from 1 to 10 ethylene ≪ / RTI > is a polyalkoxydiyl radical formed from ethylene oxide and / or propylene oxide.

Preferred post-crosslinking agents of formula (III) are 2-oxazololides such as 2-oxazolidone and N- (2-hydroxyethyl) -2-oxazolidone, N- Acyl-2-oxazolidinones such as N-acetyl-2-oxazolidone, 2-oxotetrahydro-1,3-oxazine, bicyclic acetals such as 5-methyl- Dioxabicyclo [3.3.0] octane and 5-isopropyl-1-aza-4,6-dioxabicyclo [3.3.0 ] Octane, bis-2-oxazolidone and poly-2-oxazolidone.

Particularly preferred post-crosslinking agents of formula (III) are 2-oxazolidinone, N- methyl-2-oxazolidone, N- (2- hydroxyethyl) -2-oxazolidone and N-hydroxypropyl- Oxazolidone.

Preferred post-crosslinking agents of formula (IVa) are 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol and 1,7-heptanediol. Further examples of post-crosslinking agents of formula (IVa) are 1,3-butanediol, 1,8-octanediol, 1,9-nonanediol and 1,10-decanediol.

The diol is preferably water-soluble, and the diol of formula (IVa) is present at 23 DEG C in an amount of at least 30 wt%, preferably at least 40 wt%, more preferably at least 50 wt%, most preferably at least 60 wt% For example, 1,3-propanediol and 1,7-heptanediol. Even more preferred is a post cross-linking agent which is liquid at 25 占 폚.

Preferred post-crosslinking agents of formula (IVb) are butane-1,2,3-triol, butane-1,2,4-triol, glycerol, trimethylol propane, trimethylol ethane, pentaerythritol, Triflate (per molecule) ethoxylated glycerol, trimethylolethane or trimethylolpropane and 1- to 3-tuple (per molecule) propoxylated glycerol, trimethylolethane or trimethylolpropane. Further preferred are 2-tuply ethoxylated or propoxylated neopentyl glycols. Particularly preferred are 2-tuply and 3-tuply ethoxylated glycerol, neopentyl glycol, 2-methyl-1,3-propanediol and trimethylolpropane.

Preferred polyhydric alcohols (IVa) and (IVb) are those having a molecular weight of less than 3000 mPas, preferably less than 1500 mPas, more preferably less than 1000 mPas, particularly preferably less than 500 mPas, very particularly preferably less than 300 mPas at 23 ° C It has viscosity.

Particularly preferred post-crosslinking agents of the formula (V) are ethylene carbonate and propylene carbonate.

A particularly preferred post-crosslinking agent of formula (VI) is 2,2'-bis (2-oxazoline).

Preferred post cross-linking agents are volatile, thus minimizing side reactions and subsequent reactions that would provide odorous compounds. Thus, superabsorbents prepared using the preferred post-crosslinking agent are odor-neutral even in the wet state.

It is possible to use an individual post cross-linking agent selected from any of the above or any mixture of different post cross-linking agents.

The post-crosslinking agent is generally present in an amount of at least 0.001% by weight, preferably at least 0.02% by weight, more preferably at least 0.05% by weight, based on the base polymer (e. G., Fraction of interest) Generally not more than 2% by weight, preferably not more than 1% by weight, more preferably not more than 0.3% by weight, for example not more than 0.15% by weight or not more than 0.095% by weight.

Post-crosslinking is generally carried out in such a way that a solution of the post-crosslinking agent is sprayed onto the dried base polymer. After spray application, the polymer particles coated with the post-crosslinking agent are heated to dry, and the post-crosslinking reaction can take place before or during drying. If surface-crosslinking agents with polymerizable groups are used, surface post-crosslinking can also be carried out by free-radical inducible polymerization of such groups by means of conventional free-radical formers or else by high energy irradiation, for example UV light . This may be done in conjunction with, or instead of, the use of a post-crosslinking agent to form covalent bonds or ionic bonds to functional groups on the surface of the base polymer particles.

The spray application of the post-crosslinker solution is preferably carried out using a mixer equipped with moving mixing tools, such as a screw mixer, a disk mixer, a paddle mixer or a shovel mixer, or a mixer with other mixing tools. However, it is also possible to spray onto the post-crosslinking agent solution in the fluidized bed. Suitable mixers include, for example, Pflugschar®plowshare mixers (Maschinenbau GmbH, Elsener-Strasse 7-9, 33102 Pad erborn, Gebr.Loeige, Germany) or Schugi®Flexomix® mixers (Germany), Vrieco-Nauta® mixers or Turbulizer® mixers (Hosokawa Micron BV, Gildenstraat 26, 7000 AB Doetinchem, The Netherlands).

Available spray nozzles do not apply to any restrictions. Suitable nozzles and spray systems are described, for example, in the following references: Zerstaeuben von Fluesigkeiten [Atomization of Liquids], Expert-Verlag, vol. 660, Reihe Kontakt & Studium, Thomas Richter (2004) and Zerstaeubungstechnik [Atomization Technology], Springer-Verlag, VDI-Reihe, Gueter Wozniak (2002). It is also possible to use single- and multi-dispersion injection systems. Among the multiple dispersion systems, one-phase pressure nozzles (jet- or layer-forming), rotary sprayers, two-phase sprayers, ultrasonic atomizers and impregnation nozzles are suitable. In the case of a two-phase atomizer, the liquid phase can be mixed with the gas phase internally or externally. The spray profile of the nozzle is not critical and can ensure the shape of any desired shape, e.g. round jet, flat jet, wide angle round beam or rotating ring injection profile. When a two-phase atomizer is used, it is advantageous to use a non-oxidizing gas, and it is particularly preferred to use nitrogen, argon or carbon dioxide. The liquid to be sprayed can be applied to such a nozzle under pressure. Spraying of the liquid to be sprayed may be effected by expanding it into the nozzle hole at the time of achieving a particular minimum velocity. In addition, for the purposes of the present invention, for example, slit nozzles or swirl chambers (full-cone nozzles) (e.g. from Duisen-Schlick GmbH of Germany, Of Spraying Systems Germany GmbH). Such nozzles are also described in EP 0 534 228 A1 and EP 1 191 051 A2.

Post-crosslinking agents are generally used in the form of aqueous solutions. If only water is used as the solvent, advantageously a surfactant or anti-aggregation aid is added to the post-crosslinker solution or actually to the base polymer. This improves the wetting behavior and reduces the tendency to agglomerate.

Although all anionic, cationic, nonionic and amphoteric surfactants are suitable as anti-aggregation adjuvants, nonionic and amphoteric surfactants are preferred for skin compatibility. Surfactants may also contain nitrogen. For example, sorbitan monoesters such as sorbitan monococoate and sorbitan monolaurate, or ethoxylated variants thereof, such as Polysorbat 20®, are added. Further suitable anti-aggregation adjuvants are the ethoxylated and alkoxylated derivatives of 2-propylheptanol sold under the trade names Lutensol XL® and Lutensol XP®brands (BASF SE, Carl-Bosch-Strasse 38, 67056 Ludwigshafen, Germany).

The anti-aggregation adjuvant may be metered separately, or may be added to the post-crosslinker solution. It is preferable to simply add an anti-aggregation aid to the post-crosslinking agent solution.

The amount of the anti-aggregation aid is, for example, 0 to 0.1% by weight, preferably 0 to 0.01% by weight, more preferably 0 to 0.002% by weight, based on the base polymer. The anti-aggregation aid is preferably a surface tension of the swollen base polymer and / or the aqueous extract of the swollen crosslinked water absorbent polymer at 23 캜 to 0.060 N / m or more, preferably 0.062 N / m or more, more preferably 0.065 N / m or more, advantageously 0.072 N / m or less.

One or more post-crosslinking agents as well as aqueous post-crosslinking agent solutions may also contain co-solvents. The penetration depth of the post-crosslinking agent into the polymer particles can be adjusted through the content of the non-aqueous solvent and the total amount of the solvent. A preferred co-solvents on a commercial scale is C ₁ -C ₆ - alcohols, such as methanol, ethanol, n- propanol, isopropanol, n- butanol, sec- butanol, tert- butanol or 2-methyl-1-propanol, C ₂ - C ₅ -diols such as ethylene glycol, 1,2-propylene glycol or 1,4-butanediol, ketones such as acetone, or carboxylic esters such as ethyl acetate. The disadvantage of most of these co-solvents is that they generally have a unique odor.

The co-solvent itself is ideally not a post-crosslinking agent under the reaction conditions. However, depending on the boundary conditions and the residence time and temperature, the co-solvent may contribute partially to the crosslinking. This is particularly true when the post-crosslinking agent is relatively slow to react, and thus, for example, as in the case of the cyclic carbonate of formula (V), the diol of formula (IVa) or the polyol of formula (IVb) Is a case where an auxiliary solvent can be constituted. Such post-crosslinking agents may also be used to function as co-solvents in mixtures with one or more reactive post-crosslinking agents, which may be carried out at a lower temperature and / or a shorter residence time than in the absence of a more reactive crosslinking agent It is because. Auxiliary solvents are used in relatively large proportions and should not be toxic, as some remain in the product.

In the process according to the invention, the diol of the formula (IVa), the polyol of the formula (IVb) and the cyclic carbonate of the formula (V) are also suitable as auxiliary solvents. They fulfill their function in the presence of reactive post-crosslinking agents and / or di- or triglycidyl compounds of formula (III) and / or formula (VI). However, preferred co-solvents in the process according to the invention are diols of the formula (IVa), in particular when the reaction of the hydroxyl group is sterically hindered by neighboring groups. Although such diols are also inherently suitable as subsequent crosslinking agents, they require significantly higher reaction temperatures or any higher usage than for the sterically unimpeded diols.

A particularly preferred combination of a low-reactivity post-crosslinking agent and a reactive post-crosslinking agent as co-solvents is a combination of a preferred polyhydric alcohol, a diol of formula (IVa) and a polyol of formula (IVb) with an amide acetal or carbamate of formula (III) to be.

Suitable combinations are, for example, 2-oxazolidinone / 1,2-propanediol and N- (2-hydroxyethyl) -2-oxazolidone / 1,2-propanediol, and also ethylene glycol diglycidyl / RTI > ether / 1,2-propanediol.

A very particularly preferred combination is 2-oxazolidone / 1,3-propanediol and N- (2-hydroxyethyl) -2-oxazolidone / 1,3-propanediol.

A further preferred combination is the combination of ethylene glycol diglycidyl ether or glyceryl di- or triglycidyl ether and the following solvents, co-solvents or auxiliary crosslinking agents: isopropanol, 1,3-propanediol, 1,2- Propylene glycol or mixtures thereof.

A further preferred combination is the combination of 2-oxazolidone or (2-hydroxyethyl) -2-oxazolidone with the following solvents, co-solvents or auxiliary crosslinkers: isopropanol, 1,3-propanediol, 1,2 Propylene glycol, ethylene carbonate, propylene carbonate or mixtures thereof.

Frequently, the concentration of the co-solvent in the aqueous post-crosslinker solution is from 15 to 50 wt%, preferably from 15 to 40 wt%, more preferably from 20 to 35 wt%, based on the post-crosslinker solution. In the case of co-solvents with only water and only a limited miscibility, the aqueous post-cross-linking agent solution is advantageously adjusted so that there is only one phase, optionally lowering the concentration of the co-solvent.

In a preferred embodiment, no co-solvent is used at all. The post-crosslinking agent is then employed only as an aqueous solution, optionally with the addition of anti-aggregation adjuvants.

The concentration of the at least one post-crosslinking agent in the aqueous post-crosslinking agent solution is generally from 1 to 20% by weight, preferably from 1.5 to 10% by weight, more preferably from 2 to 5% by weight, based on the post-crosslinking agent solution.

The total amount of the post-crosslinking agent solution based on the base polymer is generally from 0.3 to 15% by weight, preferably from 2 to 6% by weight.

Exact surface post cross-linking of the surface post cross-linking agent by reaction with functional groups on the surface of the base polymer particles is generally referred to as " dry "(but generally in reference to polymeric-derived polymer gels, By heating the wetted base polymer with a surface post cross-linking agent solution, which is referred to as a " dry " Drying can be carried out in the mixer itself, by jacket heating, by means of heat exchange surfaces, or by blowing in warm gas. Simultaneous mixing and drying of the surface of the superabsorbent with a cross-linking agent can be carried out, for example, in a fluid bed dryer. However, drying is generally carried out in downstream dryers, such as tray dryers, rotary tube ovens, paddles or disc dryers, or heatable screws. Suitable dryers are, for example, Solidair (R) or Torusdisc (R) (Bepex International LLC, 333 N.E. Taft Street, Minneapolis, MN 55413) or paddles or shovel dryers, or else Nara Machinery Co., Ltd. (Germany, European office, Europaallee 46, 50226 Frechen).

By means of surface contact in a downstream dryer for the purpose of conducting drying and surface post-crosslinking, by means of warm inert gas feed, or by means of a mixture of water vapor with one or more inert gases, or by using only water vapor Thereby heating the polymer particles. In the case of a heating feed by means of a contact surface, it is possible to carry out the reaction under an inert gas which is slightly or completely depressurized. In the case of the use of water vapor for direct heating of polymer particles, it is preferred to operate the dryer under standard or elevated pressure in accordance with the present invention. In such a case, it may be advisable to separate the post-crosslinking step from the heating step using water vapor and the reaction step under inert gas in the absence of water vapor. This can be done in one or more mechanisms. According to the present invention, the polymer particles can be heated using water vapor as soon as possible in a post-crosslinking mixer. The base polymer used may have a temperature of from 10 to 120 DEG C from the preceding process step; The post-crosslinker solution may have a temperature of from 0 to 70 < 0 > C. In particular, the post cross-linking agent solution can be heated to reduce the viscosity.

The preferred drying temperature is in the range of 100 to 250 캜, preferably 120 to 220 캜, more preferably 130 to 210 캜, and most preferably 150 to 200 캜. The preferred residence time at that temperature in the reaction mixer or dryer is preferably at least 10 minutes, more preferably at least 20 minutes, most preferably at least 30 minutes, generally at most 60 minutes. Generally, the drying is carried out in such a way that the residual moisture content of the superabsorbent is generally at least 0.1% by weight, preferably at least 0.2% by weight, most preferably at least 0.5% by weight and is generally at most 15% by weight, preferably at least 10% Or less, more preferably 8 wt% or less.

Post-crosslinking can occur under standard atmospheric conditions. "Standard atmospheric conditions" means that no artificial action is taken to reduce the partial pressure of the oxidizing gas, such as atmospheric oxygen, in a device ("post-crosslinking reactor", typically a dryer) in which the post- do. However, it is preferable to carry out the post-crosslinking reaction under a partial pressure of the reduced oxygen gas. The oxidizing gas has a vapor pressure of at least 1013 mbar at 23 ° C and is a substance acting as an oxidizing agent in the combustion reaction, for example oxygen, nitrogen dioxide, especially oxygen. The partial pressure of the oxidizing gas is preferably less than 140 mbar, preferably less than 100 mbar, more preferably less than 50 mbar, most preferably less than 10 mbar. When the post-heating crosslinking is carried out under a total pressure of atmospheric pressure, i.e. 1013 mbar, the partial pressure of the oxidizing gas is determined by their volume ratio. The proportion of oxidizing gas is preferably less than 14% by volume, preferably less than 10% by volume, more preferably less than 5% by volume, most preferably less than 1% by volume.

Post-crosslinking can be carried out under subatmospheric pressure, i.e. under a total pressure of less than 1013 mbar. The total pressure is generally less than 670 mbar, preferably less than 480 mbar, more preferably less than 300 mbar and most preferably less than 200 mbar. When the drying and post-crosslinking is carried out in air having an oxygen content of 20.8% by volume, the partial pressure of oxygen corresponding to the above-mentioned total pressure is 139 mbar (670 mbar), 100 mbar (480 mbar), 62 mbar 42 mbar (200 mbar), the total pressure of each of which is in parentheses. Another means of reducing the partial pressure of the oxidizing gas is the introduction of non-oxidizing gases, especially inert gases, into equipment used for post-crosslinking. Suitable inert gases are those which are present in gaseous form in the post-crosslinking dryer at a post-crosslinking temperature and a given pressure, and which do not have an oxidizing action on the contents of the dry polymer particles under such conditions, for example nitrogen, carbon dioxide, argon, And preferably nitrogen. The amount of the inert gas is generally 0.0001 to 10 m 3, preferably 0.001 to 5 m 3, more preferably 0.005 to 1 m 3, and most preferably 0.005 to 0.1 m 3, based on 1 kg of superabsorbent.

In the process according to the present invention, when water vapor is not contained, the inert gas may be supplied to the post-crosslink dryer through the nozzle; It is desirable to add an inert gas to the polymer particle stream through the nozzle, actually in the mixer or just upstream of the mixer, by mixing the superabsorbent with the surface post cross-linking agent.

It can be considered that the vapor of the co-solvent removed from the dryer can be recycled outside the dryer and optionally recycled.

In a preferred embodiment of the invention, the multivalent cations are applied to the particulate surface in addition to the post-crosslinking agent before, during or after post-crosslinking. This is often referred to as " complexing "with metal ions of interest, or simply as a" coating "using a substance of interest (" complexing agent "), .

Such applications of polyvalent cations can be carried out entirely or partially with a solution of a polyvalent cation, typically a 2-, 3- or 4-valent metal cation as well as a polyvalent cation, such as a formed polymer, in formal sense, wholly or partially, Or partially formed, e.g., partially or fully hydrolyzed polyvinyl amide (so-called "polyvinylamine") whose amyl groups are always present in partially protonated form, even at very high pH values Lt; / RTI > Examples of available divalent metal cations include, in particular, Group 2 (in particular Mg, Ca, Sr, Ba), Group 7 (particularly Mn), Group 8 (especially Fe), Group 9 10 group (particularly Ni), group 11 (especially Cu) and group 12 (especially Zn) metal. Examples of available trivalent metal cations include, in particular, Group 3 (especially Sc, Y, La, Ce), Group 8 (especially Fe), Group 11 (especially Au) and Group 13 (Especially Al) metal. Examples of available tetravalent cations are, in particular, tetravalent cations of the lanthanide series (especially Ce) and Group 4 (especially Ti, Zr, Hf) metals of the periodic table. The metal cations may be used alone or as a mixture of each other. It is particularly preferable to use a trivalent metal cation. It is more particularly preferred to use aluminum cations.

Among the metal cations mentioned, suitable metal salts are all those which have sufficient solubility in the solvent used. Particularly suitable metal salts include the anions which form weakly complexes, such as chloride, nitrate and sulfate, hydrogen sulfate, carbonate, hydrogencarbonate, nitrate, phosphate, hydrogen phosphate, or dihydrogen phosphate I have. Mono- and dicarboxylic acids, hydroxy acids, keto acids and salts or basic salts of amino acids are preferred. Examples are acetate, propionate, tartrate, maleate, citrate, lactate, maleate and succinate. It is also preferable to use a hydroxide. Particular preference is given to using 2-hydroxycarboxylic acid salts such as citrate and lactate. Examples of particularly preferred metal salts are alkali metal and alkaline earth metal aluminates and their hydrates, such as sodium aluminate and its hydrates, aluminum acetate, aluminum propionate, aluminum citrate and aluminum lactate.

The cations and salts mentioned may be used in pure form or as a mixture of different cations or salts. The salts of the 2- and / or 3-valent metal cations used may comprise further secondary contents, such as still alkali metal salts of neutralized carboxylic acids and / or neutralized carboxylic acids. Preferred alkali metal salts are salts of sodium and potassium, and salts of ammonium. They are generally used in the form of an aqueous solution obtained by dissolving the solid salt in water or, preferably, obtained directly as such to avoid any drying and purification steps. Advantageously, it is also possible to use the hydrates of the abovementioned salts which are also soluble in water faster than the anhydrous salts.

The amount of the metal salt used is generally at least 0.001% by weight, preferably at least 0.01% by weight, more preferably at least 0.1% by weight, for example at least 0.4% by weight, and generally at least 5% by weight, in each case based on the mass of the base polymer % Or less, preferably 2.5 wt% or less, more preferably 1 wt% or less, for example, 0.7 wt% or less.

Salts of polyvalent metal cations can be used in the form of solutions or suspensions. The solvents for the metal salts that may be employed are water, alcohol, DMF, DMSO and mixtures of these components. Particularly preferred are water and water / alcohol mixtures, for example water / methanol, water / 1,2-propanediol and water / 1,3-propanediol.

The treatment with the polyvalent cation solution of the base polymer is carried out in the same manner as the treatment with surface post cross-linking agent, including a drying step. The surface post cross-linking agent and polyvalent cation may be injected into the combined solution or into a separate solution. Application of the metal salt solution to the superabsorbent particles can be done before or after surface post cross-linking. In a particularly preferred process, the spray application of the metal salt solution is carried out in the same step with the spray application of the cross-linking agent solution, wherein the two solutions can be injected continuously or simultaneously through two nozzles separately, And the metal salt solution may be injected together through one nozzle.

When the drying step is carried out after surface post cross-linking and / or complexing agent treatment, it is advantageous to cool the product after drying, although this is not absolutely necessary. The cooling may be carried out continuously or batchwise; For this purpose, the product is conveniently transported to a cooler located downstream of the dryer. Any of the known devices for removing heat from the pulverulent solid may be used for that purpose and more particularly any of the devices mentioned above as a drying device are not charged with the heating medium and the cooling medium, Through the walls and depending on the construction, no heat is introduced into the superabsorbent through the agitated parts or other heat exchanger surfaces, but instead is removed therefrom, except when filled with cooling water. It is preferred to use a cooler from which the product has been removed, for example a bevel cooler, a disk cooler or a paddle cooler. The superabsorbent can also be cooled in the fluidized bed by injecting a cooled gas, such as cold air. The cooling conditions are adjusted to obtain a superabsorbent having the desired temperature for further processing. Generally, the average residence time in the cooler is not less than 1 minute, preferably not less than 3 minutes, more preferably not less than 5 minutes, generally not more than 6 hours, preferably not more than 2 hours, more preferably not more than 1 hour And the cooling performance is such that the obtained product generally has a temperature of 0 ° C or higher, preferably 10 ° C or higher, more preferably 20 ° C or higher, generally 100 ° C or lower, preferably 80 ° C or lower, more preferably 60 Lt; 0 > C or less.

The superabsorbent surface crosslinked afterwards is optionally milled and / or separated in a conventional manner. Although pulverization is not generally required here, removal by blooming of the formed agglomerates or micro-bodies is generally suitable for establishing the desired particle size distribution of the product. The agglomerates and the fine water are removed or preferably recycled to the process in a known manner at suitable points; After grinding, coagulate. The particle size for the surface post cross-linked superabsorbent is the same as for the base polymer.

The phosphonic acid derivative of the formula (II) is added to the process according to the invention after drying or after selective surface post-crosslinking carried out. Apparatus suitable for such purpose is any that is capable of mixing the phosphonic acid derivative with sufficient uniformity in the superabsorbent. This is particularly convenient, and it is preferred to add the phosphonic acid derivative to the chiller.

The phosphonic acid derivative of formula (II) is in each case generally at least 0.01% by weight, preferably at least 0.1% by weight, more preferably at least 0.2% by weight, and generally at most 2.0% by weight, based on the total amount of superabsorbents, Preferably 1.0% by weight or less, more preferably 0.7% by weight or less.

The superabsorbent of the present invention can be obtained by the method according to the present invention.

Optionally, the superabsorbent of the present invention prepared by the process according to the invention is provided with further additives which stabilize against discoloration. For that purpose, all known additives can be used in a manner known per se in the process according to the invention.

Optionally, the superabsorbent of the present invention is also mixed with one or more inorganic water insoluble particulate solids. Essentially any inorganic water insoluble powder is suitable for such purpose. Illustrative examples include materials that are generally solid, chemically inert (i.e., those that do not collapse in the superabsorbent), such as oxides, oxide hydroxides, hydroxides, sulfates, carbonates, zeolites, Minerals or clay. Examples are sulfates such as magnesium sulfate or barium sulphate, carbonates such as calcium carbonate, magnesium carbonate, zinc carbonate or dolomite, silicates such as calcium silicate or magnesium silicate, carbides such as pearlite or silicon carbide, Diatomaceous earth or fly ash.

Suitable oxides are metal oxides of group 2 to 14 of the periodic table, including lanthanide and actinides. Examples of particularly suitable oxides are magnesium oxide, calcium oxide, strontium oxide, barium oxide, titanium dioxide, zirconium dioxide, vanadium oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese dioxide , Iron oxides, cobalt oxides, nickel oxides, copper oxides, zinc oxides, boron oxides, aluminum oxides (boehmite and others), silicon dioxides, peroxide oxides, lead oxides, Or cerium oxide. For clarity, specify the following: The use of buckets for metal oxides does not refer to the stoichiometry of oxides and the valence of metals. When an element forms more than one oxide, it is generally suitable. In each case, the oxides are chosen with different considerations depending on the individual case, for example cost, toxicity, stability or color. Particularly suitable examples of oxides are titanium dioxides, especially mullite or rutile polymorphs, precipitated silicon dioxide or silicon dioxide fired by pyrolysis.

Clays are silicates or aluminosilicates, generally obtained by mining natural sediments and often further processing them. However, some clays are synthesized and produced.

It is also possible to use a mixture of two or more such materials.

The inorganic water-insoluble solids are particulate; It exists in a differential form. The average particle size is generally not less than 0.001 mu m, preferably not less than 0.002 mu m, more preferably not less than 0.005 mu m, and generally not more than 500 mu m, preferably not more than 200 mu m, more preferably not more than 100 mu m, Is not more than 50 mu m. The particles themselves may exist as agglomerates or aggregates of smaller primary particles. The particle size can be determined by means of a faded analysis, but a simpler and therefore preferred method is the determination of the particle size by means of a rachel diffraction technique. Such methods are well known, and are typically carried out in suitable, commercially available equipment.

Any additional stabilizers mentioned above for discoloration and inorganic water insoluble particulate solids, when added, are in each case generally at least 0.0001% by weight, preferably at least 0.001% by weight, based on the total weight of the inventive superabsorbent, By weight, more preferably not less than 0.025% by weight, and generally not more than 3% by weight, preferably not more than 2% by weight, more preferably not more than 0.5% by weight. Generally, in the case of the superabsorbent of the present invention containing an alkaline earth metal salt, there is a need for a known amount of stabilizing agent for discoloration in a smaller amount than in the absence of an alkaline earth metal salt.

The superabsorbent can be mixed with any stabilizing agent for discoloration and any inorganic water insoluble particulate solid by any known mixing method. In the solid form, the stabilizing agent for discoloration and the inorganic water-insoluble particulate solid are incorporated, either intrinsically or as a suspension in a solvent or suspending medium, by mixing and, if dissolved or in liquid form, . Because of the easier homogeneous distribution, the stabilizing agent is preferably incorporated into the superabsorbent by mixing as a powder or suspension. This does not necessarily provide a physical mixture that is separable by a simple method by mechanical measurement. The additive may, for example, be more firmly bonded to the superabsorbent in the form of a relatively strongly adherent surface layer or in the form of particles adhering firmly to the surface of the superabsorbent particles. Mixing of additives with known superabsorbents can also be understood and referred to as "coatings ".

When a solution or suspension is used in the coating, the solvent or suspending medium used is a solvent or suspending medium chemically compatible with the superabsorbent and the additive, i.e. does not undergo any undesired chemical reaction with them. Generally, water or an organic solvent such as an alcohol or a polyol, or a mixture thereof is used. Examples of suitable solvents or suspending media are water, isopropanol / water, 1,3-propanediol / water and propylene glycol / water, wherein the mixing mass ratio is preferably 20:80 to 40:60. Where a suspending medium is used in the stabilizer or inorganic particulate solid used according to the invention, water is preferred. Surfactants may be added to the solution or suspension.

Optional stabilizers and other additives can be added to the superabsorbent in the exact same manner as the solution or suspension applied to the superabsorbent for surface post cross-linking, generally containing a surface post cross-linking agent, unless they are added to the monomer mixture or polymeric gel Mixed. The additive can be applied to superabsorbents ("base polymers") that have not (yet) been post-crosslinked as a component of the solution applied to the surface post-crosslinking, or as one of its constituents, May be added to one of the components. Subsequently, the superabsorbent coated with the surface post cross-linking agent and the additive passes through a further process step required for surface post-crosslinking, for example, a reaction induced by heating of the surface post-crosslinking agent with a superabsorbent. This method is relatively simple and economically feasible.

If very high stability to discoloration is important, phosphonic acid derivatives and optional stabilizers and additives are conveniently applied to the cooler after the surface post cross-linking in a dedicated process step. If phosphonic acid derivatives, stabilizers and additives are applied as solutions or suspensions, they can be applied to superabsorbents already surface-crosslinked in the same mixing apparatus as described for the application of surface post cross-linking agents to base polymers. Typically, though not necessarily, this is followed by heating, as in the post-surface crosslinking step, to re-dry the superabsorbent. However, the temperature established in such a drying operation is generally 110 ° C or lower, preferably 100 ° C or lower, more preferably 90 ° C or lower, in order to prevent undesirable reaction of the additive. The temperature is adjusted so that the desired moisture content of the superabsorbent is achieved in terms of residence time in the drying unit. For remoisturization of superabsorbents it is possible and convenient to add additives with or without other conventional auxiliaries such as dust binders, anti-caking agents or water. In such a case, the temperature of the polymer particles is from 0 캜 to 190 캜, preferably less than 160 캜, more preferably less than 130 캜, even more preferably less than 100 캜, most preferably less than 70 캜. The polymer particles are optionally cooled after coating to less than any decomposition temperature of the additive.

Optionally, any known coatings that are not post-crosslinked or post-crosslinked, such as film-forming polymers, thermoplastic polymers, dendrimers, polyvalent cationic polymers (e.g., poly Vinyl amine, polyethyleneimine or polyallylamine), or any water soluble mono- or polyvalent metal salt known to the person skilled in the art, such as aluminum sulfate, sodium salt, potassium salt, zirconium salt or iron salt on the surface of superabsorbent particles Additional applications are possible. Examples of useful alkali metal salts are sodium and potassium sulphate, and sodium and potassium lactate, citrate and sorbate. This allows for additional effects to be achieved, for example reduced cementation tendency of the intermediate, improved processing characteristics, or even improved flow conductance (SFC) in certain process steps of the final product or formulation process. When additives are used and sprayed in the form of dispersions, they are preferably used as aqueous dispersions and it is preferable to additionally apply an antidusting agent to fix the additives on the surface of the superabsorbent. The antidust agent may then be added directly to the dispersion of the inorganic finely divided additive; May optionally be added as a separate solution before, during or after the application of the inorganic finely divided additive by spray application. Simultaneous spray application of post-crosslinking agents, antidust agents and finely divided inorganic additives in the post-crosslinking step is most preferred. In a more preferred process variant, however, the antidust agent is added separately to the cooler, for example by spray application from the top, bottom or sides. Particularly suitable anti-dusting agents that may be provided to immobilize the particulate inorganic additives on the surface of the absorbent polymer particles include polyethylene glycols, polyglycerols, 3- to 100-tuply ethoxylated polyols having a molecular weight of 400 to 20,000 g / mol , Such as trimethylolpropane, glycerol, sorbitol and neopentyl glycol. Particularly suitable are 7- to 20-tuply ethoxylated glycerol or trimethylolpropane, for example Polyol TP 70® (Perstorp, Sweden). The latter has the advantage of significantly reducing the surface elongation of the aqueous extract of the absorbent polymer particles.

It is also possible to adjust the superabsorbent of the present invention to a desired water content by adding water.

Although all of the coatings, solids, additives and auxiliary substances can be added in separate processing steps, most convenient methods generally do not apply if they are not added during mixing with the surface post cross-linking agent of the base polymer - For example by spray application of the solution or by addition in the form of a finely divided solid or liquid. It is also a convenient and preferred embodiment to add phosphonic acid derivatives to the cooler.

The superabsorbent of the present invention generally has a centrifuge retention capacity (CRC, test method described below) of at least 5 g / g, preferably at least 10 g / g, more preferably at least 20 g / g. Generally, it is not more than 40 g / g for superabsorbent surface cross-linked, but this is often even greater for base polymers.

The superabsorbent of the present invention is generally at least 10 g / g, preferably at least 14 g / g, and more preferably at least 18 g / g under the load (AUL 0.7 psi, test method given below) Most preferably at least 22 g / g, and generally at least 30 g / g.

The L value (CIE color number) of the superabsorbent is generally not less than 75, preferably not less than 80, more preferably not less than 85, and not more than 100 in a non-storage state.

The a value (CIE color number) of the superabsorbent is generally -2.5 to +2.5, preferably -2.0 to +2.0, more preferably -1.5 to +1.5 in the non-storage state.

The b value (CIE color number) of the superabsorbent in the non-stored state is generally 0 to 12, preferably 2 to 11.

According to the relatively high stress-aging test described below, the superabsorbent of the present invention had a deteriorated post-measurement, only to a relatively poor degree with respect to the L and a values, compared to the unsecured state, Is preferably 13 or less, and more preferably 12 or less. B values above 12 are important for feminine hygiene articles and ultra-thin diapers; A b value of more than 15 is also important in standard diapers because such discoloration can be recognized by the consumer at the time of use.

The present invention further comprises 50 to 100% by weight, preferably 60 to 100% by weight, more preferably 70 to 100% by weight, particularly preferably 80 to 100% by weight, and particularly preferably 90 to 100% Of the superabsorbent of the present invention and of course does not include the envelope of the absorbent layer, of the superabsorbent of the present invention, preferably an ultra-thin diaper.

More particularly advantageously, the superabsorbent of the present invention is also suitable for the manufacture of laminate and composite structures, for example as described in US 2003/0181115 and US 2004/0019342. In addition to the hot melt adhesives described in both documents for the manufacture of such new absorbent structures and in particular the fibers made of hot melt adhesives to which superabsorbent particles as described in US 2003/0181115 are bonded, Is suitable for the manufacture of almost similar structures using UV-crosslinkable hot melt adhesives sold as AC-Resin (BASF SE, Germany). Such UV-crosslinkable hot melt adhesives have the advantage that they are already processable at 120-140 < 0 >C; They have better compatibility with many thermoplastic substrates. A further significant advantage is that the UV-crosslinkable hot melt adhesive is highly toxicologically safe and does not cause any volatilization from the sanitary article. A very advantageous advantage associated with the superabsorbent of the present invention is the properties of UV-crosslinkable hot melt adhesives which tend not to yellow during processing and crosslinking. This is particularly advantageous when producing hygienic articles that are ultra-thin or partially transparent. Therefore, the use of the superabsorbent of the present invention in combination with the UV-crosslinkable hot-melt adhesive is particularly advantageous. Suitable UV-crosslinkable hot melt adhesives are described, for example, in EP 0 377 199 A2, EP 0 445 641 A1, US 5,026,806, EP 0 655 465 A1 and EP 0 377 191 A2.

The superabsorbent of the present invention can also be used in liquids, especially in other industries where water or an aqueous solution is absorbed. Such fields include, for example, storage, package transport (for example as a component of a packaging material for water- or moisture-sensitive articles for flower transport, and also as protection against the effects of machines); Animal hygiene (clay placed in cat litter box); Food packaging (transport of fish, fresh meat, water, absorption of blood in fish or meat packaging); Medicines (absorbent materials for scarring bandages, burn dressings or other intestinal wounds), cosmetics (pharmaceutical chemicals and medicines, rheumatoid plaster bandages, ultrasonic gels, cosmetic thickeners, carrier materials for sunscreens); A thickener for oil-in-water or water-in-oil emulsions; Fabrics (fabrics for absorbent cooling, eg protective clothing, gloves, hair bands, moisture control in shoe insole); Application as a chemical engineering application (as an organic reaction catalyst for fixing large functional molecules such as enzymes, cohesive adhesives, heat storage, filtration aids, hydrophilic components in polymeric laminates, dispersants, liquefiers); Auxiliaries in powder injection molding, civil engineering and construction industries (auxiliaries, cable cladding in equipment, loam-based renders, anti-vibration media, water-rich underground tunnel construction); Water treatment, waste disposal, water collection (icing equipment, reusable sand bags); Cleaning, pesticide industry (maintenance of rivers, fountains and dewatered water, denture additives, protection of forests from fungal / insect infections, delayed release of active ingredients to plants); Fire protection or fire protection; Coextrusion agents in thermoplastic polymers (e.g., for hydrophilization of multilayer films); (For example, a film for storing rain and dew for agricultural use, a film containing a superabsorbent for maintaining the freshness of fruits and vegetables packed in a water film, Superabsorbent-polystyrene pneumatic depressions for food packaging such as meat, fish, poultry and fruit and vegetables); Or a carrier material in an active ingredient formulation (pharmaceutical, crop protection).

The articles of the present invention for liquid absorption differ from the known examples in that they contain the superabsorbent of the present invention.

A method of manufacturing a liquid-absorbing article, in particular a sanitary article, comprising using at least one inventive superabsorbent for the manufacture of the article of interest. In addition, methods of making such articles using superabsorbents are known.

Test Methods

The superabsorbent is tested by the test method described below.

Standard test methods, hereinafter referred to as "WSP ", are described in the following references:" Standard Test Methods for the Nonwovens Industry ", 2005 edition, Worldwide Strategic Partners EDANA (European Disposables and Nonwovens Association, Avenue Eugene Plasky, 1030 Brussels, Belgium, www.edana.org) and INDA (Association of the Nonwoven Fabrics Industry, 1100 Crescent Green, Suite 115, Cary, North Carolina 27518, USA, www.inda.org). The above published documents are also available in EDANA and INDA.

All measurements described below should be carried out at room temperature of 23 ± 2 ° C and relative air humidity of 50 ± 10% unless otherwise stated. Superabsorbent particles are thoroughly mixed before measurement unless otherwise noted.

Centrifuge retention capacity (CRC)

The centrifuge retention capacity of the superabsorbent was determined according to the standard test method No. 1. WSP 241.5-05 "Centrifuge retention capacity ".

Absorbency under load of 0.7 psi (AUL0.7 psi)

The absorbency under a load of 4826 Pa (0.7 psi) of the superabsorbent is the standard, except that the weight of 49 g / cm 2 (which induces a load of 0.7 psi) is used instead of 21 g / cm 2 (which induces a load of 0.3 psi) Test method Serial number is determined similar to WSP 242.2-05 "Absorption under pressure".

Extractable material (16 h)

The proportion of extractable material in the superabsorbent material is determined by standard test method serial number WSP 270.2-05 "Determination of extractable polymer content by potentiometric titration ".

Water content (residual moisture, moisture content) of superabsorbent

The water content of the superabsorbent particles was determined according to the standard method of Test Method No. 2. It is determined by WSP 230.2-05 "Moisture content".

Brine Flow Conductivity (SFC)

The brine flow conductance of the swollen gel layer formed by the superabsorbent as a result of liquid absorption is determined as the gel layer permeability of the swollen gel layer of the superabsorbent particles as described in EP 0 640 330 A1 under a pressure of 0.3 psi (2068 Pa) The above-mentioned patent application No. 19 and the apparatus described in Fig. 8 can be applied to the case where the glass frit 40 is not used and the plunger 39 is made of the same polymer material as the cylinder 37, It was modified to include 21 holes of the same size uniformly distributed. The measurement procedure and evaluation were as given in EP 0 640 330 A1. The flow rate is automatically detected.

The brine flow conductance (SFC) is calculated as follows:

(T = 0) is the flow rate of a NaCl solution, expressed in g / s, obtained by linear regression analysis of flow determination Fg (t) data by extrapolation to t = 0, D is the density of the NaCl solution in g / cm ³ , A is the area of the gel layer in cm ² , and WP is the hydrostatic pressure on the gel layer in dyn / cm ² .

Permeability (FSGBP, "Free Swell Gel Bed Permeability")

The permeability is determined as described in paragraphs [0061] to [0075] in US 2005/0256757 A1.

CIE color number (L, a, b)

Color analysis was performed using a "LabScan XE S / N LX17309" colorimeter (HunterLab, Reston, U.S.A.) according to the CIELAB method (Hunterlab, volume 8, 1996, book 7, pages 1 to 4). The method describes the color through the coordinates L, a and b of the three-dimensional system. L represents brightness. When L = 0, it represents black. When L = 100, it represents white. The values of a and b indicate the positions of the colors on the red / green and yellow / blue hue coordinates, respectively, where + a represents red, -a represents green, + b represents yellow, and -b represents blue. HC60 is calculated by formula HC60 = L-3b.

The color measurement corresponds to the 3-region method according to DIN 5033-6.

Aging test

Measurement 1 (initial color): A plastic dish with an internal diameter of 9 cm was filled with superabsorbent particles that would be flattened and flattened with a blade at the rim, and the CIE color number and HC60 value were determined.

Measure 2 (after aging): A plastic dish with an internal diameter of 9 cm was filled with superabsorbent particles that would be planarized and flattened with a blade at the rim. The dish was then placed in a heatable cabinet heated to 60 DEG C with a constant relative air humidity of 86%. After 21 days, the dish was taken out. After cooling to room temperature, the CIE color number was determined.

Example

The equipment used as mixer is Gebr. Was a Pflugschar® M5 jacketing forming flow shear mixer from Loedige Maschinenbau GmbH (Elsener-Strasse 7 - 9, 33102 Paderborn, Germany). The equipment used as the kneader was a flow-shear kneader of the same manufacturer Pflugschar® 5R-MK jacket forming machine.

Cublen®K 2012 is a 20% by weight aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid, disodium salt. Cublen K 3014 is a 20% by weight aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid, tetrasodium salt. Cublen K60 is a 60% by weight aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid. Cublen K 4023 is a 26 wt% aqueous solution of 1-hydroxyethane-1,1-diphosphonic acid, tri-potassium salt. Such materials are available from Zschimmer & Schwarz Mohsdorf GmbH & Co KG (Chemnitztalstrasse 1, 09217 Burgstaedt, Germany). Laromer® PO 9044V is a triacrylate of triethoxylated glycerol available from BASF SE (Ludwigshafen, Germany). DAROCUR® 1173 is 2-hydroxy-2-methyl-1-phenylpropan-1-one available from BASF Switzerland AG (Basle, Switzerland). IRGACURE® 651 is 2,2-dimethoxy-1,2-diphenylethane-1-one available from BASF Switzerland AG (Basle, Switzerland).

Example 1

Preparation of base polymer

A 2 l stainless steel vessel was first charged with 326.7 grams of a 50 wt% sodium hydroxide solution and 675 grams of frozen deionized water. With stirring, 392.0 g of acrylic acid was added while controlling the addition rate so that the temperature did not exceed 35 占 폚. The mixture was then cooled with the aid of a stirring and cooling bath. When the temperature of the mixture dropped to 20 占 폚, 0.79 g of Laromer 占 PO 9044V, 0.041 g of DAROCUR 占 1173 and 0.014 g of IRGACURE 占 651 were added. Cooling was continued and when the temperature of the mixture reached 15 캜, oxygen was removed from the mixture by passing nitrogen through a glass frit. When the temperature reached 0 占 폚, 0.51 g of sodium persulfate (dissolved in 5 ml of water) and 0.06 g of hydrogen peroxide (dissolved in 6 ml of water) were added and the monomer solution was transferred to a glass plate. The glass plate had dimensions such that the layer thickness of the monomer solution was 5 cm. Subsequently, 0.39 g of disodium 2-hydroxy-2-sulfonatoacetoacetate dissolved in 7.5 ml of water was added and the monomer solution was gently stirred using a glass rod. The glass plate containing the monomer solution was placed under a UV lamp (UV intensity = 25 mW / cm 2) to allow polymerization to take place. After 16 minutes, the resulting gel was milled three times using a commercial meat grinder with a 6 mm die plate and dried at 160 DEG C for 1 hour in a laboratory drying cabinet. The product was then milled and a bifurcated fraction of 150 to 850 [mu] m was obtained. The above procedure was repeated several times to obtain a sufficient amount of polymer for the next step. The properties of the thus-prepared base polymer are shown in Table 1.

Surface post-crosslinking

For surface post cross-linking, 1.2 kg of base polymer was mixed with 0.84 g of N- (2-hydroxyethyl) -2-oxazolidinone by means of a two-phase injection nozzle in a mixer at room temperature and a shaft speed of 450 revolutions per minute Dinon, 10.8 g of 1,2-propanediol and 25.2 g of water. After spray application, the product temperature was raised to 185 ° C and the reaction mixture was held at that temperature and shaft speed of 80 revolutions per minute for 60 minutes. The resulting product was cooled to room temperature and was bred. The surface superficially crosslinked superabsorbent was obtained as a bifurcated fraction with a particle size of 150 [mu] m to 850 [mu] m, and its properties are shown in Table 1. [

Post-processing

1.0 kg of surface post-crosslinked polymer was coated with 12.5 g of Cublen® K 2012 by means of a two-phase injection nozzle in a mixer at a shaft speed of 70 ° C and 250 revolutions per minute. Following spray application, continuous mixing of the reaction mixture was followed for 15 minutes at a shaft speed of 80 revolutions per minute. The resulting product was cooled to room temperature and the coagulum was removed using a sieve having a mesh size of 850 占 퐉. The proportion of agglomerates exceeding 850 탆 thus removed was 14.4 g. The properties of the post-treated product are set forth in Table 1.

Example 2 (Comparative Example)

Example 1 was repeated except that 3.9 g of a 10 wt% aqueous solution of sodium hydrogensulfite was added instead of 0.39 g of 2-hydroxy-2-sulfonato acetic acid disodium salt dissolved in 7.5 ml of water . The proportion of the subsequently removed coagulum was 15.2 g. Base polymer surface Properties of the post-crosslinked polymer and the subsequently treated polymer are shown in Table 1.

Example 3 (Comparative Example)

Example 1 was repeated except that 3.9 g of a 10 wt% aqueous solution of sodium thiosulfate was used instead of 0.39 g of 2-hydroxy-2-sulfonato acetic acid disodium salt dissolved in 7.5 ml of water. The proportion of the subsequently removed coagulum was 15.0 g. The properties of the base polymer, the surface post-crosslinked polymer and the post-treated polymer are shown in Table 1.

Example 4 (Comparative Example)

Example 1 was repeated except that 0.047 g of ascorbic acid dissolved in 7.5 ml of water instead of 0.39 g of 2-hydroxy-2-sulphonatoacetic acid disodium salt dissolved in 7.5 ml of water was used. The percentage of the subsequently removed agglomerates was 14.0 g. The properties of the base polymer, the surface post-crosslinked polymer and the post-treated polymer are shown in Table 1.

Example 5 (Comparative Example)

Example 1 was repeated except that 19.6 g of Cublen 占 K 2012 was added instead of 0.39 g of 2-hydroxy-2-sulphonatoacetic acid disodium salt dissolved in 7.5 ml of water. Polymerization has unavoidably occurred. After 16 minutes, the material in the glass dish was still dug-free, which was no longer work-free.

Example 6 (Comparative Example)

Example 4 was repeated except that a mixture of 12.5 g of Cublen 占 2012 2012 and 1 g of 2-hydroxy-2-sulfonato acetic acid disodium salt dissolved in 19 ml of water was used for post-treatment. The proportion of the subsequently removed coagulum was 56.8 g. The properties of the base polymer, the surface post-crosslinked polymer and the post-treated polymer are shown in Table 1.

Example 7 (Comparative Example)

Best of all, Example 1 was repeated, except that the meat grinder was used only once instead of three times, and then the ground gel was mixed with a mixture of 2.5 g of Cublen K 2012 and 20 ml of water and further pulverized twice. In addition, no post-treatment was performed after surface post-crosslinking. The properties of the base polymer and the surface post-crosslinked polymer are shown in Table 1.

Example 8

Except that the meat grinder was mixed with 0.39 g of disodium 2-hydroxy-2-sulphonatoacetate dissolved in 20 ml of water only once instead of three times and then pulverized twice. 4 was repeated. The proportion of the subsequently removed aggregate was 13.6 g. The properties of the base polymer and the surface post-crosslinked polymer are shown in Table 1.

Example 9 (Comparative Example)

Above all, the meat grinder was used only once instead of three times, then the once crushed gel was mixed with 19.5 g of a 2 wt% main solution of potassium hydrosulfite and then milled twice more Example 4 was repeated. The proportion of the flocculant to be subsequently removed was 15.2 g. The properties of the base polymer and the surface post-crosslinked polymer are shown in Table 1.

Example 10

14.3 kg of sodium acrylate aqueous solution (37.5 wt% solution in deionized water), 1.4 kg of acrylic acid and 350 g of deionized water were mixed with 12.5 g of Laromer (R) PO 9044V. The solution was applied to a heated, nitrogen filled droplet forming tower (180 DEG C, 12 m high, 2 m diameter, gas velocity of 0.1 m / s in flow, 40 mm diameter, 2 mm internal height, Gt; 32 < / RTI > kg / h; Its temperature was 15 占 폚. Immediately upstream of the droplet former, the monomer solution was mixed with the three initiator solutions using a conical mixer. Initiator 1 is an aqueous solution containing 5% by weight of disodium salt of 2-hydroxy-2-sulfonatoacetic acid, Initiator 2 is a 10% by weight solution of sodium peroxodisulfate in deionized water, Initiator 3 is 2.5% % Of 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride. The metering rate of initiator solution 1 was 0.33 kg / h, the metering rate of initiator solution 2 was 0.27 kg / h, and the metering rate of initiator solution 3 was 0.22 kg / h. The superabsorbent was obtained as a bifurcated fraction with a particle size of 150 [mu] m to 850 [mu] m. No separate surface post-crosslinking operation was performed. It had the characteristics described in Table 1.

1.2 kg of surface post-crosslinked polymer was mixed with 1.8 g of hydrophobic precipitated silica (Sipernat (R) D-17, Evonik Degussa GmbH, Frankfurt am Main, Germany) in a mixer at a shaft speed of 80 revolutions per minute at room temperature. After mixing for 5 minutes, the shaft speed was increased to 250 revolutions per minute and the superabsorbent was coated by means of a two-phase nozzle with 21 g of Cublen K 3014. After spray application, the reaction mixture was continuously mixed for 15 minutes at a shaft speed of 80 revolutions per minute. The resultant product was subjected to removal of aggregates using a sieve having a mesh size of 600 mu m. The coagulant ratio exceeding 600 탆 thus removed was 5.3 g. The properties of the thus obtained products are described in Table 1.

Example 11

Preparation of base polymer

To the kneader was first charged 459 grams of water, 213.9 grams of acrylic acid, 1924.9 grams of 37.3 weight percent sodium acrylate solution (100 mole percent neutralized) and 2.75 grams of Laromer.RTM. PO 9044V, and inactivated by nitrogen bubbling for 20 minutes . Subsequent addition of initiator was carried out at about 20 < 0 > C to cool the reaction mixture externally. Finally, 0.67 g of sodium persulfate (dissolved in 10 g of water), 0.05 g of 30 wt% hydrogen peroxide (dissolved in 5 g of water), 0.57 g of 2-hydroxy-2-sulphonatoacetic acid di Sodium salt (dissolved in 12 ml of water) and 0.01 g of ascorbic acid (dissolved in 10 g of water) were added in rapid succession. And the jacket of the kneader was heated at 80 캜 using a heated carrier medium at the time of achieving the internal temperature of 30 캜 to terminate the heat insulation reaction as much as possible. Upon achieving the highest temperature, the formed gel was cooled to less than 50 ° C by means of cooling liquid (-12 ° C) and then released. The gel was then dried in a laboratory drying cabinet at 160 DEG C for 1 hour and then a bifurcated fraction of 150 to 710 mu m was obtained. Such a process was repeated several times to obtain a sufficient amount of polymer for the further step. The base polymer thus prepared has the properties shown in Table 1.

Surface post-crosslinking

Instead of a mixture of 0.84 g of N- (2-hydroxyethyl) -2-oxazolidinone, 10.8 g of 1,2-propanediol and 25.2 g of water, 0.84 g of N- (2-hydroxyethyl) -2 , 4.8 g of 1,2-propanediol, 12.0 g of 2-propanol, 4.8 g of water and 27.3 g of 22 wt% aluminum lactate aqueous solution were used. After spray application, the temperature was changed to 189 Lt; RTI ID = 0.0 > C, < / RTI > In addition, a benthic fraction of 150 to 710 [mu] m was obtained instead of the berry fraction of 150 to 850 [mu] m. The surface-crosslinked superabsorbent thus prepared had a SFC of 125 x 10 ^-7 cm ³ s / g and further characterized in Table 1.

Post-processing

Instead of using 12.5 g of Cublen®K 2012, the coating was treated with a mixture of 1.67 g of Cublen®K 60 and 20 g of water and the aggregate was removed using a sieve of mesh size 710 μm instead of a mesh of size 850 μm The post-treatment was carried out as in Example 1. [ The proportion of subsequently removed aggregates was 9.3 g. The SFC of the polymer thus obtained was 108 x ^10-7 cm ³ s / g and, further, the characteristics were described in Table 1.

Example 12

Example 11 was repeated except that only 2.14 g of Laromer (R) PO 9044V was used instead of 2.75 g in the preparation of the base polymer. Further, instead of the berry fraction of 150 to 710 mu m, a berry fraction of 150 to 850 mu m was obtained there. In surface post cross-linking, 0.84 g of N- (2-hydroxyethyl) -2-oxazolidinone, 4.8 g of 1,2-propanediol, 12.0 g of 2-propanol, 4.8 g of water and 27.3 g of 22 Wt% Alkyl Lactate aqueous solution, 0.84 g of N- (2-hydroxyethyl) -2-oxazolidinone, 10.8 g of 1,2-propanediol and 45.6 g of 20 wt% aluminum dihydroxymono Acetate solution (Lohtragon (R) ALA 200, manufactured by Dr. Paul Lohmann GmbH KG, 31857 Emmerthal, Germany) was used and after spray application the temperature was raised to 185 ° C instead of 189 ° C. In addition, a bifurcated fraction of 150 to 850 mu m was obtained instead of the bifurcated fraction of 150 to 710 mu m. The GBP of the surface-crosslinked superabsorbent thus obtained is 56 darcies and further characterized in Table 1. After the post-treatment, 15.4 g of Cublen (R) K 4023 was applied instead of 1.67 g of Cublen (R) K 60 and 20 g of water, and the agglomerates were removed using a sieve of mesh size 850 [mu] m instead of the mesh size 710 [mu] m. The percentage of aggregate removed subsequently was 16.9 g. The GBP of the polymer thus prepared is 48 darcies and, further, Table 1 describes the characteristics.

For all superabsorbents obtained as final products in each case of Examples 1 to 12, the number of colors was also determined after aging. The results are summarized in Table 2. The Examples and Tables 1 and 2 show that the initial color number of the superabsorbent of the present invention is advantageous (all L values of the initial color in Table 1 exceed 90 and high HC60 values indicate that the inventive superabsorbent is particularly less yellowed ), As well as a much brighter (L value> 80) after aging compared to comparative products.

Table 1: Properties of polymer before aging test

Table 2: Color number of polymer ultimately obtained in each case after aging test

Claims (10)

A method for preparing a superabsorbent by polymerization of a monomer solution comprising:
a) at least one ethylenically unsaturated monomer having an acid group, optionally at least partly in the form of a salt,
b) at least one crosslinking agent,
c) one or more initiators,
d) optionally, one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a)
e) optionally, one or more water soluble polymers,
The method further comprises the steps of drying the resultant polymer, optionally pulverizing the dried polymer and separating the pulverized polymer, and optionally calcining the surface of the pulverized and fugitive polymer, Wherein one or more sulfonic acid derivatives are added to the monomer mixture and / or polymer prior to the drying step, and one or more phosphonic acid derivatives are added to the polymer after the drying step or after the selective surface post-crosslinking step. The method according to claim 1, wherein the added sulfonic acid derivative is 2-hydroxy-2-sulfonatoacetic acid and / or its salt. 3. The process of claim 2 wherein the disodium salt of 2-hydroxy-2-sulfonatoacetic acid is added. 4. The positive resist composition according to any one of claims 1 to 3, wherein the (1-hydroxyethane-1,1-diyl) bisphosphonic acid, ethylenediaminetetra (methylenephosphonic acid), diethylene triamine penta (methylenephosphonic acid) And a phosphonic acid derivative selected from [nitrilotris (methylene)] tris (phosphonic acid) and salts thereof is added. 5. The method of claim 4, wherein the phosphonic acid derivative added is a sodium and / or potassium salt of bisphosphonic acid (1-hydroxyethane-1,1-diyl). 6. The method according to any one of claims 1 to 5, wherein surface post cross-linking is carried out. 7. The process according to any one of claims 1 to 6, wherein the monomer a) is at least partially presented in the form of a salt of sodium acrylate. 8. A superabsorbent obtainable by the process of any one of claims 1 to 7. 9. A liquid-absorbing article containing the superabsorbent of claim 8. Wherein the production of the article entails the addition of the superabsorbent of claim 8.