JP2013504674A - Color-stable superabsorbent - Google Patents

Abstract

Superabsorbent containing a stabilizer against at least one discoloration selected from phenol, phosphonic acid (HP (O) (OH) ₂ ), phosphorous acid (H ₃ PO ₃ ) and salts and esters of said acids The agent exhibits improved discoloration stability upon storage under elevated temperature or elevated air humidity.

Description

  The present invention relates to a color-stable superabsorbent, a process for its production, its use and hygiene products containing it. A color-stable superabsorbent refers to a superabsorbent that does not change color or changes to a relatively minor extent when stored under elevated temperature and air humidity.

  Superabsorbents are known. For such materials, "highly swellable polymer", "hydrogel" (often used in dry form), "hydrogel-forming polymer", "water-absorbing polymer", "absorbent gel-forming material" , “Swellable resin”, “water-absorbing resin” or its type is also commonly used. In that case, the material is a crosslinked hydrophilic polymer, in particular a polymer composed of (co) polymerized hydrophilic monomers, a graft (co) polymer on one suitable graft base of one or more hydrophilic monomers, a crosslinked Cellulose ethers or starch ethers, crosslinked carboxymethylcellulose, partially crosslinked polyalkylene oxides or natural products swellable in aqueous liquids, eg guar derivatives, based on partially neutralized acrylic acid The water-absorbing polymer is most widely known. An essential property of a superabsorbent is the ability to absorb many times its own weight of an aqueous liquid and not release it again under some pressure. Superabsorbents used in the form of dry powders turn into gels when they absorb liquids and correspondingly into hydrogels during normal water absorption. Crosslinking is essential for synthetic superabsorbers and is an important difference from normal pure thickeners. This is because crosslinking results in insolubility of the polymer in water. Soluble substances cannot be used as superabsorbents. The most important field of use of superabsorbents is the absorption of body fluids. Superabsorbents are used, for example, in baby diapers, adult incontinence products or sanitary hygiene products. Other fields of application are those used for example as a means of retaining as water in agricultural horticulture, as a reservoir for fire protection, for absorbing liquids in food packaging or quite generally for absorbing moisture .

  Superabsorbents can absorb many times their own weight and hold it under some pressure. In general, such superabsorbents have a CRC ("Centrifuge Retention Capacity") of at least 5 g / g, preferably at least 10 g / g, particularly preferably at least 15 g / g, see below for measuring method Have. A “superabsorbent” may be a mixture of individual superabsorbents that differ in material, or a mixture of components that exhibit superabsorbent properties only in a combined action. Here, there is almost no problem of material composition rather than superabsorbent properties.

  What is important to superabsorbents is not only their absorption capacity, but also the ability to hold liquid under pressure (retention, mostly “Absorption under Load”) (“AUL”) or “pressure resistance absorption ( Absorbion against pressure) "(" AAP "), see below for measurement method) as well as liquid transport in swollen state (usually as" Saline Flow Conductivity "(" SFC ")) The measurement method expressed is as follows). The swollen gel can block or prevent liquid transport to the superabsorbent that has not yet swollen ("gel blocking"). Good transport properties for liquids are exhibited, for example, by hydrogels having high gel strength in the swollen state. Gels with little gel strength are deformable under the pressure used (body pressure), plugging the pores in the superabsorbent / cellulose fiber absorbent, thereby preventing further liquid absorption. Increased gel strength is usually achieved by a higher degree of crosslinking, but this reduces the absorbent capacity of the product. A sophisticated method for improving gel strength is to increase the degree of cross-linking of the superabsorbent particle surface to the inside of the particle. To that end, usually in the surface postcrosslinking stage, the dried superabsorbent particles are subjected to additional crosslinking in the thin surface layer of the particles at an average crosslinking density. Surface postcrosslinking increases the crosslink density in the shell of superabsorbent particles, thereby increasing the absorption under pressure load to a higher level. While the absorption capacity of the superabsorbent particles at the surface layer is reduced, the shell structure causes gel blocking because the core has improved absorption capacity compared to the shell due to the presence of mobile polymer chains. Without an improved liquid transfer. Similarly, it is known to make an overall higher cross-linked superabsorbent and to later reduce the degree of cross-linking inside the particle relative to the outer shell of the particle.

  Moreover, the manufacturing method of a superabsorbent is also well-known. Based on acrylic acid, the most popular super absorbent in the market is manufactured by radical polymerization of acrylic acid in the presence of a cross-linking agent ("internal cross-linking agent"). Before, after polymerization, or partially before, partially after polymerization, to some extent, usually by addition of alkali, mostly by addition of aqueous sodium hydroxide. The polymer gel thus obtained is ground (depending on the polymerization reactor used, it can be carried out simultaneously with the polymerization) and dried. The dry powder thus obtained ("base polymer" or "base polymer") is usually a further crosslinker, such as an organic crosslinker or a polyvalent cation, such as aluminum (usually used as aluminum sulfate) or its It is post-crosslinked at the surface of the particle by reacting with both to yield a surface layer that is more strongly crosslinked to the inside of the particle.

  A problem often encountered with superabsorbents is discoloration that occurs when stored at higher temperatures or higher air humidity. Such conditions often occur when superabsorbents are stored in tropical or subtropical countries. Under such conditions, the superabsorbent tends to turn yellow, on the contrary, the superabsorbent may take on a brown coloration or even a nearly black coloration. The coloration of the essentially colorless superabsorbent powder is undesirable because it does not look good. This is because the color is seen in the case of desirable thin hygiene products, and consumers refuse sanitary products that do not look good. The cause of color development is not fully elucidated, but reactive compounds such as residual monomers from polymerization, the use of significant initiators, contamination of monomers or neutralizers, surface postcrosslinkers or monomers used It seems that the stabilizer plays a part.

  Fredric L.L. Buchholz and Andrew T. Graham (published) is described in “Modern Superabsorbent Polymer Technology”, J. Am. Wiley & Sons, New York, U. S. A. / Wiley-VCH, Weinheim, Germany, 1997, ISBN 0-471-19411-5 provides a summary overview of superabsorbents, their properties and methods of making superabsorbents. In Chapter 2.7.2, it is also mentioned that calcium ions are known as ionic crosslinkers for superabsorbents, but first mention that trivalent ions such as aluminum are usable crosslinkers. Yes.

  WO 2005/073260 A1 can be completely or partially replaced by a salt such as magnesium acrylate, calcium acrylate, strontium acrylate or barium acrylate in the production of a superabsorbent by polymerization of a supersaturated solution of sodium acrylate monomer. It is disclosed. WO 2005/011860 classifies known internal crosslinkers for superabsorbents into various crosslinker classes, one of which is multivalent metal cations. Among them, magnesium, calcium and strontium are particularly mentioned as the divalent cation, and trivalent aluminum is preferable as a whole.

  WO 2008/055856 A1 describes the superabsorbent discoloration caused by too high iron content of the caustic soda solution used for partial neutralization of acrylic acid in the production of the superabsorbent. It teaches avoidance by addition. JP05 / 086251A describes phosphoric acid derivatives or salts thereof, in particular 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) or alkali metal salts or ammonium thereof. The use of salt as a stabilizer against superabsorbent discoloration is taught. WO 03/059962 A1 or the corresponding patent application US 2005/0085604 A1 uses a metal chelating agent at some stage in the production of the superabsorbent and reduces it before drying the polymer containing water as a measure against discoloration. The addition of an oxidant or oxidant. WO 03/014172 A2 relates to the production of superabsorbents consisting of high-purity acrylic acid, in particular from which aldehydes have been removed, in order to avoid discoloration of the superabsorbent. WO 00/55245 A1 treats superabsorbents against discoloration by treating with inorganic reducing agents and optionally with, for example, metal salts such as alkaline earth metal salts added after polymerization. Teaching to stabilize. Said inorganic reducing agent is generally hypophosphite, phosphite, bisulfite or sulfite. The metal salts are generally colorless (the “colorless” property is often simply referred to as “white”) phosphates, acetates or lactates, but not halides. According to the teaching of WO 2006/058682, the superabsorbent discoloration is avoided by carrying out the drying and postcrosslinking reaction in an atmosphere essentially free of oxidizing gases.

  EP 505163 A1 describes a combination of a surface active substance and a compound that adds with a double bond, such as an unsubstituted or substituted alkyl sulfinic acid or aryl sulfinic acid or a salt thereof, in the superabsorbent. Disclosed are uses for monomer reduction. EP 668080 A2 and split application EP 15 670 869 A1 contain sulfinic acid, but organic acid salts or sulfinic acid salts or organic acids excluding polyamino acids or salts thereof for reducing the residual surface postcrosslinker. In particular, it relates to the use after surface postcrosslinking for the reduction of epoxy compounds used as surface postcrosslinking agents. EP 386897 A2, EP 441975 A1 and EP 605215 A1 teach the use of sulfites, bisulfites or thiosulfates to reduce residual monomers from polymerization. EP 1645596 A1 teaches stabilization against discoloration of superabsorbents by the addition of inorganic salts, aminocarboxylate-chelating agents and organic antioxidants. As the inorganic salt, sulfite, bisulfite, pyrosulfite, dithionate, trithionate, tetrathionate, thiosulfate or nitrite is used. EP 1577349 A1 teaches the use of the salt for the same purpose, but the iron content of the superabsorbent treated with the salt is kept below 1 ppm by weight.

  Prior international patent applications having WO 2009/060062 or number PCT / EP2009 / 059793 teach the addition of sulfinic acid derivatives to the superabsorbent to stabilize the superabsorbent against discoloration. . WO 2008/092842 A1 teaches, among other things, the addition of a basic salt of a divalent metal cation to the superabsorbent in order to increase the stability against discoloration. WO 2008/092843 A1 discloses the use of trivalent metal cation carboxylates and / or basic salts for the same purpose. WO 2005/054356 A1 is intended for acrylic acid, which has the advantage that, instead of the technically conventional paramethoxyphenol ("methylhydroquinone", "MEHQ"), the polymer has less discoloration. Teaches its use as a stabilizer against polymerization.

  In addition, it is better stabilized than another superabsorbent stabilized against discoloration, especially yellowing or browning, when stored under elevated temperature and / or elevated air humidity. There is a problem of finding a super absorbent. The use properties of the superabsorbent, in particular the absorption capacity for the liquid (even under pressure) as well as the transfer capability of the liquid, should not be impaired at all, or at least essentially not. Similarly, other properties such as odor (which can be a problem in the presence of moisture in the case of sulfur-containing reducing agents) or fluidity (which is a problem with the addition of sodium hypophosphite) Properties such as dust formation (which can be problematic upon the addition of insoluble calcium salts) should not be compromised. A further object of the present invention is to find a method for producing such a superabsorbent and the use of said superabsorbent.

The object is to provide a stabilizer against at least one discoloration selected from phenol, phosphonic acid (HP (O) (OH) ₂ ), phosphorous acid (H ₃ PO ₃ ) and salts and esters of said acids. Solved by containing superabsorbent. Furthermore, the manufacturing method of the said super absorbent, the use of the said super absorbent, the sanitary goods containing the said super absorbent, and its manufacturing method were discovered.

  The superabsorbent according to the invention exhibits surprisingly good discoloration stability without essentially detracting from its use properties such as CRC, AUL or SFC.

  According to the invention, at least one stabilizer against discoloration is added to the superabsorbent.

  The stabilizer can be added in any form. In most cases, it is preferred to add the stabilizer in an approximately undissolved form. “Generally undissolved” means that generally at least 50% by weight, preferably at least 70% by weight, and in a particularly preferred form at least 90% by weight of the added stabilizer is not dissolved in the solvent at the time of addition. Point to. Stabilizers are therefore introduced either dry as a powder or in suspension medium as a suspension.

  Stabilizers can be added to the superabsorbent at any point during manufacture. Preferably, the stabilizer is not added to the monomer mixture or monomer for polymerization, but only when a cross-linked polymer is present, and therefore at a very early stage during polymerization. Stabilizers can be added, for example, during polymerization, during surface postcrosslinking or after surface postcrosslinking. When the stabilizer is added to the monomer mixture or monomer, the stabilizer is always added in addition to any stabilizer for unwanted or premature polymerization. In particular, if the stabilizer is a sterically hindered phenol, it is preferred to add it at a very early stage during the polymerization.

  Stabilizers are soluble or insoluble. Preferably the stabilizer is insoluble in water. That is, the solubility in water at 25 ° C. is at most 5 g / l, preferably at most 1 g / l.

One stabilizer (or a plurality of stabilizers) is selected from phenol, phosphonic acid (HP (O) (OH) ₂ ), phosphorous acid (H ₃ PO ₃ ), and salts and esters of these acids. The

  The phenol is preferably a sterically hindered phenol. Sterically hindered phenol refers to a phenol having a mono-branched or bi-branched substituent, preferably a bi-branched substituent at least at the 2-position and optionally at the 6-position of the phenyl ring. . The branched substituent is an atom bonded to the phenyl ring of the phenol, and represents a substituent having at least two groups different from hydrogen at an atom other than the carbon atom of the phenyl ring to which they are bonded. . However, sterically hindered phenols have sterically demanding unbranched substituents at least at the 2-position and optionally also at the 6-position. Said substituent comprises at least 6, preferably at least 8, in a particularly preferred form at least 12 atoms different from hydrogen, but bonded to the phenyl ring of phenol, It represents a substituent having a group different from only one hydrogen at an atom other than the carbon atom of the bonded phenyl ring. The simplest examples for mono-branched substituents are secondary alkyl groups such as 2-propyl, 2-butyl, 2-pentyl, 3-pentyl, ethylhexyl or cycloalkyl groups such as cyclobutyl, cyclopentyl, cyclohexyl or An aromatic group such as phenyl. The simplest examples for bi-branched substituents are tertiary alkyl groups such as t-butyl, t-pentyl or norbornyl. The simplest examples for unbranched groups are hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl, but also neopentyl, neohexyl or dodecylthiomethyl. However, all of the aforementioned groups may themselves be substituted or contain atoms that are different from carbon and hydrogen. The phenyl ring of phenol may optionally have other substituents in addition to the substituent at the 2-position and optionally the substituent at the 6-position. Examples of preferred sterically hindered phenols are 2-t-butylphenol, 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol (2,6-di-t-butyl-para Cresol or 3,5-di-t-butyl-4-hydroxytoluene), 3,5-di-t-butyl-4-hydroxyphenylacetic acid, 3,5-di-t-butyl-4-hydroxyphenylpropiate On acids and esters of said acids with alcohols and polyols, such as glycols, glycerin, 1,2- or 1,3-propanediol, trimethylolpropane or pentaerythritol of the acids, such as pentaesters, such as penta Erythritol-tetrakis- (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate ) Or octadecyl- (3,5-di-t-butyl-4-hydroxyphenyl) propionate), 4,4-thio-bis (6-t-butyl-metacresol), 4,6-bis (dodecylthiomethyl) ) -Orthocresol, 3,3 ′, 3 ″, 5,5 ′, 5 ″ -hexa-t-butyl-α; α ′, α ″-(mesitylene-2,4,6-triyl) tri -Paracresol (2,4,6-tri [(4-hydroxy-3,5-di-t-butylphenyl) methyl] mesitylene, CAS number 1709-70-2, Ciba Specialty Chemicals, Basel, Schweiz AG Available under the trade name Irganox® 1330), N, N-hexane-1,3-diylbis (3- (3,5-di-t-butyl-4) Hydroxyphenylpropionamide)), 2,2'-ethylidenebis [4,6-bis (1,1-dimethylethyl) phenol] and ethylenebis (oxyethylene) bis-3- (5-t-butyl-4- Hydroxy-m-tolyl) propionate) (CAS number 36443-68-2, Ciba Specialty Chemicals, Basel, Schweiz AG, available under the trade name Irganox (R) 245).

Other stabilizers that are more suitable according to the invention are the salts and esters of phosphonic acid (HP (O) (OH) ₂ ) and phosphorous acid (H ₃ PO ₃ ) and phosphonic acid itself. Phosphonic acid is in a tautomeric relationship with phosphorous acid, the latter not present as a free acid. The only pure derivatives of phosphorous acid are their triesters, which are usually called phosphites. Tautomeric derivatives of phosphonic acids are usually referred to as phosphonates. For example, all primary phosphonates and secondary phosphonates of alkali metals (including ammonium) and alkaline earth metals are suitable. For example, an aqueous solution of phosphonic acid comprising primary and / or secondary phosphonate ions and at least one cation selected from sodium, potassium, calcium, strontium is also suitable. Examples of suitable phosphites or phosphonates are calcium bis [monoethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate], tris (2,4-di-tert-butylphenyl) phosphite, 3 , 9-bis (octadecyloxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane and bis (2,4-di-t-butylphenol) pentaerythritol diphosphite . The stabilizer may simultaneously be a phosphonate or phosphite and a sterically hindered phenol.

  Stabilizers are necessarily granular if undissolved, and therefore they are therefore mainly present in powder form when added. The average particle size is generally at least 0.001 μm, preferably at least 0.002 μm, in a particularly preferred form at least 0.005 μm, most preferably at least 0.01 μm and generally at most 500 μm, preferably at most 200 μm, in particular In a preferred form, it is at most 100 μm, and in a particularly preferred form, it is at most 50 μm. The particles may themselves be aggregates or agglomerates of smaller primary particles. Although the particle size can be measured by sieve analysis, it is easier to measure the particle size by laser diffraction technique and is therefore preferred. These methods are well known and are routinely performed with commercial equipment suitable for this purpose.

  The stabilizers against discoloration mentioned above are generally at least 0.0001% by weight, preferably at least 0.001% by weight, in particular, respectively, based on the total weight of the superabsorbent according to the invention, if they are added. In a preferred form it is added in an amount of at least 0.025% by weight and generally at most 3% by weight, in a preferred form at most 2% by weight, in a particularly preferred form at most 0.5% by weight.

  According to the present invention, the stabilizer can be added to any superabsorbent. In general, such superabsorbents are crosslinked hydrophilic polymers, in particular polymers composed of (co) polymerized hydrophilic monomers, graft (co) polymers on a suitable graft base of one or more hydrophilic monomers, Cross-linked cellulose ethers or starch ethers, cross-linked carboxymethyl cellulose, partially cross-linked polyalkylene oxides or natural products that can swell in aqueous liquids, such as guar derivatives. Preferably, superabsorbents based on partially neutralized acrylic acid are used. Superabsorbents are particularly excellent in terms of their ability to absorb and retain their liquids.

Preferred superabsorbents according to the invention are, for example, a) at least one ethylenically unsaturated monomer having at least one acid group and optionally present at least partially as a salt;
b) at least one crosslinking agent;
c) at least one initiator;
d) optionally, one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned in a) above;
e) Optionally prepared by aqueous solution polymerization of a monomer mixture containing one or more water-soluble polymers.

  Said monomer a) is preferably water-soluble. That is, the solubility in water at 23 ° C. is generally at least 1 g / 100 g (water), preferably at least 5 g / 100 g (water), particularly preferably at least 25 g / 100 g (water), particularly preferably at least 35 g / 100 g. (Water).

  Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids or salts thereof, such as acrylic acid, methacrylic acid, maleic acid or salts thereof, maleic anhydride and itaconic acid or salts thereof. Particularly preferred monomers are acrylic acid and methacrylic acid. In particular, acrylic acid is preferred.

  Other suitable monomers a) are, for example, ethylenically unsaturated sulfonic acids such as styrene sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid (AMPS).

  Impurities can have a significant effect on the polymerization. Therefore, the raw materials used should have the highest possible purity. Therefore, often monomer a) should be specially purified. Suitable purification methods are described, for example, in WO 2002/055469 A1, WO 2003/078378 A1 and WO 2004/035514 A1. Suitable monomers a) are, for example, acrylic acid purified according to WO 2004/035514 A1, 99.8460% by weight acrylic acid, 0.0950% by weight acetic acid, 0.0332% by weight water and 0.0203 wt% propionic acid, 0.0001 wt% furfural, 0.0001 wt% maleic anhydride, 0.0003 wt% diacrylic acid, and 0.0050 wt% hydroquinone monomethyl ether And acrylic acid.

  The proportion of acrylic acid and / or their salts with respect to the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, particularly preferably at least 95 mol%.

  The monomer solution is preferably at most 250 ppm by weight, advantageously at most 130 ppm by weight, particularly preferably at most 70 ppm by weight and advantageously with respect to the respective unneutralized monomers a) Contains at least 10 ppm by weight, particularly preferably at least 30 ppm by weight, in particular about 50 ppm by weight of hydroquinone hemiether, wherein the neutralized monomer a), ie the salt of monomer a) is neutralized. Calculated and considered as a monomer that has not been made. For example, monomers having ethylenically unsaturated acid groups with a corresponding content of hydroquinone hemiether can be used for the production of monomer solutions.

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

  Suitable crosslinking agents b) are compounds having at least two groups suitable for crosslinking. Such a group is, for example, a functional group capable of forming a covalent bond with an ethylenically unsaturated group capable of introducing radical polymerization into the polymer chain and the acid group of the monomer a). Furthermore, polyvalent metal salts capable of forming a coordination bond with at least two acid groups of monomer a) are suitable as crosslinking agent b).

  The crosslinking agent b) is preferably a compound having at least two polymerizable groups that can be radically polymerized 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, for example in EP 530438 A1. The diacrylates and triacrylates described, for example in EP 547847 A1, EP 559476 A1, EP 632068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO 2003/104301 A1 and DE 10331450 A1 Mixed acrylates as described, in addition to acrylate groups Those having a sum group, for example those described in DE 103 31 456 A1 and DE 10355401 A1, or cross-linking agents mixtures described in eg DE 19543368 A1, DE19664484 A1, WO 90/15830 A1 and WO 2002/32962 A2 is there.

Preferred cross-linking agents b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, 15-20 ethoxylated trimethylolpropane triacrylate, 15-20 ethoxylated glycerin triacrylate, 4 to 45 CH _2. Pentaethylene glycol diacrylate, trimethylolpropane triacrylate and triallylamine having CH ₂ O units in the molecular chain.

  Particularly preferred crosslinking agents b) are, for example, polyethoxylated glycerin and / or polypropoxylated glycerin described in WO 2003/104301 A1, esterified with acrylic acid or methacrylic acid to diacrylate or triacrylate. is there. Particular preference is given to diacrylates and / or triacrylates of 3 to 10 ethoxylated glycerol. Particularly preferred are diacrylates or triacrylates of 1-5 ethoxylated glycerin and / or 1-5 propoxylated glycerin. Most preferred are triacrylates of 3-5 ethoxylated glycerol and / or 3-5 propoxylated glycerol, especially triacrylate of 3 ethoxylated glycerol.

  The amount of cross-linking agent b) is preferably from 0.05 to 1.5% by weight, particularly preferably from 0.1 to 1% by weight, particularly preferably from 0.3 to 0.6%, based on the respective monomers a). % By mass. With increasing crosslinker content, the centrifugal retention capacity (CRC) decreases and the absorption under pressure of 0.3 psi (AUL 0.3 psi) increases.

  As initiator c) it is possible to use all compounds which are generated by radicals under the polymerization conditions, for example thermal initiators, redox initiators, photoinitiators. Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite. Preferably, a mixture of thermal initiator and redox initiator, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid is used. However, the reducing component preferably includes 2-hydroxy-2-sulfinatoacetic acid sodium salt, 2-hydroxy-2-sulfonatoacetic acid disodium salt, and sodium bisulfite, described in more detail below. A mixture consisting of (Breggolit® FF6M or Bruegolit® FF7) is used.

  Ethylenically unsaturated monomers d) copolymerizable with monomers a) having ethylenically unsaturated 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.

  As water-soluble polymers e) use is made of polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycol or polyacrylic acid, preferably starch, starch derivatives and modified cellulose. Can do.

  Usually, an aqueous monomer solution is used. The water content of the monomer solution is preferably 40 to 75% by mass, particularly preferably 45 to 70% by mass, particularly preferably 50 to 65% by mass. It is also possible to use monomer suspensions, ie supersaturated monomer solutions. As the moisture content increases, the energy required for subsequent drying increases, and as the moisture content decreases, the heat of polymerization can only be exhausted insufficiently.

  The superabsorbent according to the invention is optionally added with at least one alkaline earth metal salt soluble in water, selected from calcium, strontium or barium salts. Mixtures of salts of any two possible combinations of the aforementioned elements or all three of the aforementioned elements can be used. In terms of technical action, there is no essential difference between calcium, strontium or barium salts, but calcium salts are most preferred for economic reasons. In general, a superabsorbent containing an alkaline earth metal salt requires a smaller amount of stabilizer against discoloration according to the present invention than a superabsorbent free of an alkaline earth metal salt.

  The anion of the alkaline earth metal salt can basically be freely selected, provided that it should not have an adverse effect in the superabsorbent and / or in its use. Examples of suitable anions of alkaline earth metal salts are halide ions, in particular chloride ions, hydroxide ions, carbonate ions, carboxylate ions such as formate ion, acetate ion, propionate ion or lactate ion, nitrate ion. Or it is a sulfate ion. Mixtures can also be used.

  More preferably, a water-soluble alkaline earth metal salt is used, or a salt that reacts rapidly with the superabsorbent or monomeric acid groups despite itself being relatively poorly soluble in water. Is done. Such salts, in particular, have the advantage that the equivalent of neutralizing agent used can be further reduced in the production of conventional superabsorbents from monomer mixtures containing water. The anions of the alkaline earth metal salts are correspondingly selected for this purpose and are preferably hydroxide ions, carbonate ions or lactate ions.

  Overall preferred alkaline earth metal salts are calcium hydroxide, strontium hydroxide, barium hydroxide, calcium carbonate, strontium carbonate, barium carbonate, calcium lactate, strontium lactate, barium lactate, calcium sulfate, strontium sulfate, barium sulfate or A mixture of them. In particular, calcium hydroxide, calcium carbonate, calcium lactate and calcium sulfate are preferred.

  Each alkaline earth metal salt is generally at least 0.1% by weight, preferably at least 0.5% by weight, and in a particularly preferred form at least 0.1% by weight relative to the total amount of ethylenically unsaturated monomers having at least one acid group. It is 1% by weight and is generally added in an amount of at most 20% by weight, preferably at most 10% by weight, in a particularly preferred form at most 5% by weight. These were then calculated as free acids, and any complete or partial neutralization of the acid groups was not considered in the calculation. A significant number of alkaline earth metal salts can contain crystal water. This crystal water is not taken into account in the calculation as well.

  If an alkaline earth metal salt (or a mixture of alkaline earth metal salts) is subjected to a separate drying step in the monomer mixture, prior to or during the polymerization, or subsequent to the polymerization, the salt is: Added to the polymer prior to drying or partially prior to or during polymerization and partially to the polymer prior to drying. Strive for uniform distribution of alkaline earth metal salts in superabsorbents. Basically, the alkaline earth metal salt is mixed according to the method and from time to time as described below under Neutralizing agent. The simplest and therefore preferred is the addition to the monomer mixture prior to polymerization. However, alkaline earth metal salts can be introduced into the resulting polymer gel either during or after polymerization, but are always introduced before drying. Addition during the polymerization is easily possible, in particular by a method in which the material to be polymerized is mixed, for example in a kneader during the polymerization. The addition after the polymerization and before the drying can be carried out in a simple manner, in particular in a way that the polymerized material leads from the polymerization to a specific drying process, and thus in any way in which the polymerization and the drying are carried out separately, in particular. It can be done easily. The alkaline earth metal salt can in this case be mixed into the polymer gel by any known mixing method and mixing device.

  The alkaline earth metal salt is added as a dry substance or as a solution or dispersion in a solvent. As the solvent, water is preferably used.

  Preferred polymerization inhibitors require dissolved oxygen for optimal action. Thus, the dissolved oxygen can be removed from the monomer solution by inactivation, i.e. by passing through an inert gas, preferably nitrogen or carbon dioxide, prior to polymerization. Preferably, the oxygen content before polymerization of the monomer solution is reduced to less than 1 ppm by weight, particularly preferably less than 0.5 ppm by weight, particularly preferably less than 0.1 ppm by weight.

  The monomer mixture may contain further components. Examples of further components used in such monomer mixtures are, for example, chelating agents, for example to keep the metal ions in solution.

  The acid groups of the polymer gel obtained from the polymerization are usually partially neutralized. Neutralization is preferably performed at the monomer stage. In other words, a salt of a monomer having an acid group or, strictly speaking, a mixture of a monomer having an acid group and a salt of a monomer having an acid group ("partially neutralized acid") is used in the polymerization as component a). . It is usually carried out by adding the neutralizing agent, either as an aqueous solution or preferably as a solid, into the monomer mixture intended for the polymerization or preferably into the monomer having acid groups or a solution thereof. The degree of neutralization is preferably 25 to 95 mol%, particularly preferably 50 to 80 mol%, particularly preferably 65 to 72 mol%, in which case conventional neutralizing agents, preferably alkali metal hydroxides, are used. Alkali metal oxides, alkali metal carbonates or alkali metal hydrogen carbonates and mixtures thereof can be used. Instead of the alkali metal salt, an ammonium salt can also be used. Sodium and potassium are particularly preferred as alkali metals, but in particular sodium hydroxide, sodium carbonate or sodium bicarbonate and mixtures thereof are preferred.

  However, it is also possible to carry out the neutralization after the polymerization at the stage of the polymer gel that occurs during the polymerization. Furthermore, up to 40 mol%, preferably 10 to 30 mol%, particularly preferably 15 to 25 mol% of acid groups are already added partly to the monomer solution before the polymerization, and the desired final Neutralization can be achieved by adjusting the degree of neutralization at the polymer gel stage only after polymerization. If the polymer gel is at least partially neutralized after polymerization, the polymer gel is preferably ground mechanically, for example by an extruder, in which the neutralizing agent is sprayed, sprinkled or poured. Can then be mixed carefully. In addition, the resulting gel material can be extruded again and again for homogenization.

  However, neutralization is preferably carried out at the monomer stage. In other words, in a particularly preferred embodiment, the monomer a) has 25 to 95 mol%, particularly preferably 50 to 80 mol%, particularly preferably 65 to 72 mol% of monomers having acid groups. And a mixture of monomers having up to 100 mol% of the remaining acid groups. This mixture is, for example, a mixture composed of sodium acrylate and acrylic acid or a mixture composed of potassium acrylate and acrylic acid.

  In a preferred embodiment, for neutralization, the neutralizing agent has an iron content of less than 10 ppm by weight, preferably less than 2 ppm by weight, particularly preferably less than 1 ppm by weight. A neutralizing agent is used. Similarly, it is desirable that the content of chloride and oxyacid anions of chlorine be low. Suitable neutralizing agents are, for example, 50% by weight of caustic soda or caustic potash liquid, usually marketed as “membrane grade”, and 50% by weight, usually marketed as “Amalgam grade” or “mercury process”. Caustic soda solution or caustic potash solution is more pure and suitable as well, but more expensive.

  In any embodiment of the invention to which an alkaline earth metal salt is added, the alkaline earth metal salt is water soluble or relatively poorly soluble but nevertheless reacts relatively quickly. When an alkaline earth metal salt is used, the neutralizing agent equivalent to the amount of alkaline earth metal ion added can be reduced. In other words, the alkaline earth metal salt can also be used as a neutralizing agent at the same time, wherein the divalent alkaline earth metal ion replaces the two monovalent alkali metal ions. For this purpose, alkaline earth metal hydroxides, carbonates and lactates are particularly suitable.

  A method for producing a superabsorbent from a monomer mixture is also known as described above. Suitable polymerization reactors are, for example, kneading reactors or belt reactors. In the kneader, the polymer gel produced upon polymerization of the aqueous monomer solution or monomer suspension is continuously pulverized by, for example, a counter-rotating stirring shaft as described in WO2001 / 38402 A1. Polymerization on the belt is described, for example, in EP 955086 A2, DE 3825366 A1 and US 6,241,928. In the case of polymerization in a belt reactor, as described for example in EP 445 619 A2 and DE 198464613 A1, as in the case of known batch polymerization or polymerization in a tubular reactor, The polymer gel is produced, for example, in a meat grinder, extruder or kneader, and the gel has to be crushed in a further process step. However, spherical or other shaped superabsorbent particles can also be produced by suspension polymerization or emulsion polymerization, for example as described in EP 457660 A1, or by spray polymerization or droplet polymerization, for example EP 348180 A1, EP 816383 A1, WO 96/40427 A1, US 4020256, US 2002/0193546 A1, DE 3519013 A1, DE 102005044035 A1, WO 2007/093531 A1, WO 2008/086976 A1 or WO 2009/0273356 A1 Can be manufactured. Similarly, methods for applying and polymerizing a monomer mixture onto a substrate, such as a nonwoven web (Vliesbahn), are known and are described, for example, in WO 02/94328 A2 and WO 02/94329 A1.

  The polymer gel obtained from aqueous solution polymerization and optionally subsequent neutralization is then particularly preferred, preferably with a belt dryer, until the residual moisture content is preferably between 0.5 and 15% by weight. Is dried until it becomes 1 to 10% by mass, particularly preferably 2 to 8% by mass (see below for the measurement method for residual moisture content or moisture content). If the residual moisture is too high, the dried polymer gel exhibits a glass transition temperature Tg that is too low and can only be further processed with difficulty. If the residual moisture is too low, the dried polymer gel is too brittle and the subsequent refinement process undesirably produces a large amount of polymer particles that are too small ("fines"). The solids content of the gel is generally 25 to 90% by weight, preferably 30 to 80% by weight, particularly preferably 35 to 70% by weight, particularly preferably 40 to 60% by weight, before drying. However, alternatively, a fluidized bed dryer or a heatable mixer having a mechanical mechanism, such as a paddle dryer or a similar dryer with another form of mixing tool, can also be used for drying. Optionally, the dryer may be operated under nitrogen or another non-oxidizing inert gas or at least under a reduced partial pressure of oxygen to prevent oxidative yellowing processes. However, in operation, sufficient ventilation and water vapor discharge also provide acceptable products. Preferred for color and product quality is generally the shortest possible drying time.

  During drying, the residual monomer content in the polymer particles also decreases and the last residue of the initiator is destroyed.

  The dried polymer gel is then ground and classified. In this case, a single-stage or multi-stage roller mill, preferably a two-stage or three-stage roller mill, a pin mill, a hammer mill or a vibration mill can be used for grinding. . Oversized, often gel masses that are not yet dried on the inside are rubber-elastic and cause problems during grinding and are preferably separated and removed prior to grinding, which can be selected by wind sorting or sieving ("protection for the mill" It can be easily implemented with a screen "). The mesh width of the screen is selected so that as much as possible blockage by oversized rubber elastic particles occurs, taking into account the mill used.

  Superabsorbent particles that are too large and not finely ground can be recognized as coarse particles in diapers and other hygiene products for most applications, and these particles also reduce the average swelling rate of the superabsorbent. . Both are undesirable. Thus, preferably, the coarse polymer particles are separated and removed from the product. It is a conventional classification method, for example by wind sorting or by a screen having a mesh width of at most 1000 μm, preferably at most 900 μm, particularly preferably at most 850 μm, particularly preferably at most 800 μm. This is done by sieving. For example, screens having a mesh width of 700 μm, 650 μm or 600 μm are used. The separated coarse polymer particles ("Ueberkorn") can be fed back into the grinding and sieving cycles for cost optimization or further processed separately.

  Polymer particles having a particle size that is too low reduces permeability (SFC). Therefore, preferably, fine polymer particles are also separated and removed during the classification. It is easily used by screens having a mesh width of at most 300 μm, preferably at most 200 μm, particularly preferably at most 150 μm, particularly preferably at most 100 μm when sieved. it can. The finely divided polymer particles ("Undercorn" or fines) that have been separated off are optionally in a monomer stream, in a polymerized gel or in a polymerized gel for cost optimization. Can be fed again before the gel is dried.

  The average particle size of the polymer particles separated off as product fraction is generally at least 200 μm, preferably at least 250 μm, in a preferred form at least 300 μm, and generally at most 600 μm, preferably at most 500 μm. The proportion of particles having a particle size of at least 150 μm is generally at least 90% by weight, preferably at least 95% by weight, particularly preferably at least 98% by weight. The proportion of particles having a particle size of at most 850 μm is generally at least 90% by weight, preferably at least 95% by weight, particularly preferably at least 98% by weight.

  In other considerable manufacturing methods known for superabsorbents, particularly in suspension polymerization, spray polymerization or drop polymerization, the particle size distribution is controlled by the choice of process parameters. Since these methods directly produce a granular superabsorbent of the desired particle size, the grinding and sieving steps can often be omitted. In a considerable way (especially in spray polymerization or drop polymerization), the inherent drying step can often be omitted.

  The polymers thus produced have superabsorbent properties and are included in the concept “superabsorbent”. Its CRC is typically relatively high, whereas its AUL or SFC is relatively low. Such superabsorbents that are not surface postcrosslinked are often referred to as "base polymers" or "base polymers" to distinguish them from the surface postcrosslinked superabsorbents produced therefrom.

  Suitable postcrosslinkers are compounds that contain groups that can form bonds with at least two functional groups of the superabsorbent particles.

［式中、
Ｒ¹は、Ｃ₁〜Ｃ₁₂−アルキル、Ｃ₂〜Ｃ₁₂−ヒドロキシアルキル、Ｃ₂〜Ｃ₁₂−アルケニル又はＣ₆〜Ｃ₁₂−アリールを意味し、
Ｒ²は、Ｘ又はＯＲ⁶を意味し、
Ｒ³は、水素、Ｃ₁〜Ｃ₁₂−アルキル、Ｃ₂〜Ｃ₁₂−ヒドロキシアルキル、Ｃ₂〜Ｃ₁₂−アルケニルもしくはＣ₆〜Ｃ₁₂−アリール又はＸを意味し、
Ｒ⁴は、Ｃ₁〜Ｃ₁₂−アルキル、Ｃ₂〜Ｃ₁₂−ヒドロキシアルキル、Ｃ₂〜Ｃ₁₂−アルケニル又はＣ₆〜Ｃ₁₂−アリールを意味し、
Ｒ⁵は、水素、Ｃ₁〜Ｃ₁₂−アルキル、Ｃ₂〜Ｃ₁₂−ヒドロキシアルキル、Ｃ₂〜Ｃ₁₂−アルケニル、Ｃ₁〜Ｃ₁₂−アシル又はＣ₆〜Ｃ₁₂−アリールを意味し、
Ｒ⁶は、Ｃ₁〜Ｃ₁₂−アルキル、Ｃ₂〜Ｃ₁₂−ヒドロキシアルキル、Ｃ₂〜Ｃ₁₂−アルケニル又はＣ₆〜Ｃ₁₂−アリールを意味し、かつ
Ｘは、基Ｒ²及びＲ³が共同でカルボニル酸素を意味し、その際、Ｒ¹及びＲ⁴及び／又はＲ⁵及びＲ⁶は、橋かけされたＣ₂〜Ｃ₆−アルカンジイルであってよく、かつ上述の基Ｒ¹〜Ｒ⁶は、さらに全体で１〜２個の自由原子価を有してよく、かつこの自由原子価で少なくとも１つの好適な基礎体と結合されていてよい］のアミドアセタール又はカルバメートであるか、又は
多価アルコールであり、その際、前記の多価アルコールは、好ましくは１００ｇ／モル未満の、有利には９０ｇ／モル未満の、特に有利には８０ｇ／モル未満の、殊に有利には７０ｇ／モル未満の分子量をヒドロキシル基１つ当たりに有し、かつビシナルな、ジェミナルな、第二級のもしくは第三級のヒドロキシ基を有さず、かつ多価アルコールは、一般式（ＩＩａ）

［式中、Ｒ⁷は、式−（ＣＨ₂）_n−の非分枝のアルキレン基を意味し、ｎが３〜２０の、好ましくは３〜１２の整数であり、かつ両方のヒドロキシル基が末端位にあるか、又はＲ⁷は、非分枝の、分枝したもしくは環状のアルキレン基を意味する］のジオール、又は一般式（ＩＩｂ）

［式中、基Ｒ⁸、Ｒ⁹、Ｒ¹⁰、Ｒ¹¹は、互いに独立して、水素、ヒドロキシル、ヒドロキシメチル、ヒドロキシエチルオキシメチル、１−ヒドロキシプロピ−２−イルオキシメチル、２−ヒドロキシプロピルオキシメチル、メチル、エチル、ｎ−プロピル、イソプロピル、ｎ−ブチル、ｎ−ペンチル、ｎ−ヘキシル、１，２−ジヒドロキシエチル、２−ヒドロキシエチル、３−ヒドロキシプロピル又は４−ヒドロキシブチルを意味し、かつ全体で２、３もしくは４つの、好ましくは２もしくは３つのヒドロキシ基が存在しており、かつ基Ｒ⁸、Ｒ⁹、Ｒ¹⁰もしくはＲ¹¹の１つより多くは、ヒドロキシルを意味しない］のポリオールであるか、又は
一般式（ＩＩＩ）

［式中、Ｒ¹²、Ｒ¹³、Ｒ¹⁴、Ｒ¹⁵、Ｒ¹⁶及びＲ¹⁷は、互いに独立して、水素、メチル、エチル、ｎ−プロピル、イソプロピル、ｎ−ブチル、ｓ−ブチル又はイソブチルであり、かつｎは、０又は１である］の環状カーボネートであるか、又は
一般式（ＩＶ）

［式中、Ｒ¹⁸、Ｒ¹⁹、Ｒ²⁰、Ｒ²¹、Ｒ²²、Ｒ²³、Ｒ²⁴及びＲ²⁵は、互いに独立して、水素、メチル、エチル、ｎ−プロピル、イソプロピル、ｎ−ブチル、ｓ−ブチル又はイソブチルを表し、かつＲ²⁶は、単結合、直鎖状の、分枝したもしくは環状のＣ₂〜Ｃ₁₂−アルキレン基又はポリアルコキシジイル基を表し、前記基は、１〜１０個のエチレンオキシド単位及び／又はプロピレンオキシド単位から構成されており、それらは、例えばポリグリコールジカルボン酸を示す］のビスオキサゾリンである。 In the case of superabsorbents based on the marketed acrylic acid / sodium acrylate, suitable surface postcrosslinkers are compounds containing groups capable of forming bonds with at least two carboxylate groups. Preferred postcrosslinking agents are those of the general formula (I)

[Where:
R ¹ means C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl,
R ² means X or OR ⁶ ,
R ³ represents 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 ⁴ means C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl,
R ⁵ represents 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 ⁶ represents C ₁ -C ₁₂ -alkyl, C ₂ -C ₁₂ -hydroxyalkyl, C ₂ -C ₁₂ -alkenyl or C ₆ -C ₁₂ -aryl, and X represents the groups R ² and R ³ Together means carbonyl oxygen, wherein R ¹ and R ⁴ and / or R ⁵ and R ⁶ may be bridged C ₂ -C ₆ -alkanediyl and the group R ¹ described above. R ⁶ may further have a total of 1 to 2 free valences and may be combined with at least one suitable base at this free valence]. Or a polyhydric alcohol, wherein the polyhydric alcohol is preferably less than 100 g / mol, preferably less than 90 g / mol, particularly preferably less than 80 g / mol, very particularly preferably. One hydroxyl group was hit with a molecular weight of less than 70 g / mol To have, and a vicinal, geminal not have the secondary of or tertiary hydroxy group, and polyhydric alcohols of the general formula (IIa)

[Wherein R ⁷ represents an unbranched alkylene group of the formula — (CH ₂ ) _n —, n is an integer of 3 to 20, preferably 3 to 12, and both hydroxyl groups are A diol of the terminal position or R ⁷ represents an unbranched, branched or cyclic alkylene group, or a compound of the general formula (IIb)

Wherein the groups R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are independently of one another hydrogen, hydroxyl, hydroxymethyl, hydroxyethyloxymethyl, 1-hydroxyprop-2-yloxymethyl, 2-hydroxypropyl. Means oxymethyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, 1,2-dihydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl or 4-hydroxybutyl; And in total there are 2, 3 or 4 and preferably 2 or 3 hydroxy groups and more than one of the groups R ⁸ , R ⁹ , R ¹⁰ or R ¹¹ does not mean hydroxyl] A polyol or a general formula (III)

[Wherein R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ are independently of each other hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl or isobutyl. And n is 0 or 1.] or a compound of the general formula (IV)

[Wherein R ¹⁸ , R ¹⁹ , R ²⁰ , R ²¹ , R ²² , R ²³ , R ²⁴ and R ²⁵ are independently of each other hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, represents s-butyl or isobutyl, and R ²⁶ represents a single bond, a linear, branched or cyclic C ₂ -C ₁₂ -alkylene group or a polyalkoxydiyl group, said group being 1-10 It is composed of a plurality of ethylene oxide units and / or propylene oxide units, which represent, for example, polyglycol dicarboxylic acid].

  Preferred postcrosslinkers of general formula (I) are 2-oxazolidones such as 2-oxazolidone and N- (2-hydroxyethyl) -2-oxazolidone, N-methyl-2-oxazolidone, N-acyl-2-oxazolidone, For example N-acetyl-2-oxazolidone, 2-oxotetrahydro-1,3-oxazine, bicyclic amide acetals such as 5-methyl-1-aza-4,6-dioxa-bicyclo [3.3.0] Octane, 1-aza-4,6-dioxa-bicyclo [3.3.0] octane and 5-isopropyl-1-aza-4,6-dioxa-bicyclo [3.3.0] octane, bis-2- Oxazolidone and poly-2-oxazolidone.

  Particularly preferred postcrosslinkers of general formula (I) are 2-oxazolidone, N-methyl-2-oxazolidone, N- (2-hydroxyethyl) -2-oxazolidone and N-hydroxypropyl-2-oxazolidone.

  Preferred postcrosslinking agents of general formula (IIa) are 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol and 1,7-heptanediol. Further examples for postcrosslinkers of formula (IIa) are 1,3-butanediol, 1,8-octanediol, 1,9-nonanediol and 1,10-decanediol.

  The diol is preferably water soluble. In this case, the diol of the general formula (IIa) is at least 30% by weight, preferably at least 40% by weight, particularly preferably at least 50% by weight, particularly preferably at least 60% by weight, in water at 23 ° C. For example, 1,3-propanediol and 1,7-heptanediol are dissolved. Even more preferred is such a post-crosslinking agent which is liquid at 25 ° C.

  Preferred postcrosslinkers of general formula (IIb) are butane-1,2,3-triol, butane-1,2,4-triol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, one per molecule. Ethoxylated or triethoxylated glycerin, trimethylolethane or trimethylolpropane and perpropoxylated or tripropoxylated glycerin, trimethylolethane or trimethylolpropane per molecule. More preferred is neopentyl glycol which is 2 ethoxylated or propoxylated. Particularly preferred are 2 ethoxylated and 3 ethoxylated glycerin, neopentyl glycol, 2-methyl-1,3-propanediol and trimethylolpropane.

  Preferred polyhydric alcohols (IIa) and (IIb) are at 23 ° C. of less than 3000 mPas, preferably less than 1500 mPas, preferably less than 1000 mPas, particularly preferably less than 500 mPas, particularly preferably less than 300 mPas. Has viscosity.

  Particularly preferred postcrosslinking agents of the general formula (III) are ethylene carbonate and propylene carbonate.

  A particularly preferred postcrosslinker of general formula (IV) is 2,2'-bis (2-oxazoline).

  Preferred postcrosslinkers minimize secondary reactions and subsequent reactions that result in compounds that are volatile and therefore offensive. Superabsorbents made with preferred postcrosslinkers are therefore odorless when moistened.

  A single postcrosslinker from the above options can be used, or any mixture of different postcrosslinkers can be used.

  The post-crosslinking agent is generally at least 0.001% by weight, preferably at least 0.02% by weight, in a particularly preferred form, based on the weight of the respective base polymer to which it is added (for example the aforementioned sieve fraction). At least 0.05% by weight and generally at most 2% by weight, preferably at most 1% by weight, in a particularly preferred form at most 0.3% by weight, for example at most 0.15% by weight % Or at most 0.095% by weight.

  Postcrosslinking is usually performed by spraying a solution of the postcrosslinker onto the dried base polymer particles. Following spraying, the polymer particles coated with the postcrosslinker are thermally dried. In this case, the post-crosslinking reaction can be performed before or during drying. If a surface postcrosslinker with a polymerizable group is used, the surface postcrosslinkage can be achieved by polymerization induced by radicals of such groups, using conventional radical formers or high energy radiation such as eg UV light. Can also be used. This can be done in parallel with or instead of the use of a post-crosslinking agent that forms a covalent or ionic bond to a functional group on the surface of the base polymer particle.

  The spraying of the postcrosslinker solution is preferably carried out in a mixer with a moving mixing tool, for example in a mixer such as a screw mixer, disk mixer, paddle mixer or vane mixer or other mixing tool. However, a vertical mixer is particularly preferred. However, it is also possible to spray the postcrosslinker solution into the fluidized bed. Suitable mixers are described for example in Gebr. Loedige Maskinenbau GmbH (Eisener-Strasse 7-9, 33102 Paderborn, Germany) as a Pflugschar (R) mixer, or Hosokawa Micron Bch (Gildenstraat 26, 7000 in ABD trademark) Available as a mixer, a Vrieco-Nata® mixer or a Turbulizer® mixer.

  There are no restrictions on the spray nozzles that can be used. Suitable nozzles and atomization systems are described, for example, in the following literature locations: Zerstaeuben von Fresigkeiten, Expert-Verlag, Bd. 660, Reihe Kontakt & Studio, Thomas Richter (2004) and Zerstaebungtechnik, Springer-Verlag, VDI-Reihe, Guterer Wonzniak (2002). Monodispersed and polydispersed spray systems can be used. Among the polydisperse systems, single substance pressure nozzles (jet forming or laminar flow forming), rotary atomizers, two substance atomizers, ultrasonic atomizers and impact nozzles are suitable. In the case of a two-substance atomizer, the mixing of the liquid phase and the gas phase can take place inside or outside. The spray pattern of the nozzle is not critical and can take any arbitrary form, for example, a circular spray pattern, a flat spray pattern, a wide angle circular spray pattern, or an annular spray pattern. When a two-substance sprayer is used, the use of a non-oxidizing gas is preferred, with nitrogen, argon or carbon dioxide being particularly preferred. Such a nozzle can supply the liquid to be sprayed under pressure. In this case, the liquid to be sprayed can be dispersed by releasing the pressure in the nozzle holes after the liquid reaches a certain minimum speed. In addition, single-substance nozzles, for example slit nozzles or swivel nozzles (full cone nozzles), can be used for the purposes according to the invention (for example, Duesen-Schlick, Germany, or Spraying Systems Deutschland, Germany). Such nozzles are also described in EP 0534228 A1 and EP1191051 A2.

  The postcrosslinker is typically used as an aqueous solution. When only water is used as solvent, a surfactant or deagglomerating aid is preferably added to the postcrosslinker solution or already to the base polymer. Thereby, the wetting behavior is improved and the agglomeration tendency is reduced.

  Although all anionic, cationic, nonionic and amphoteric surfactants are suitable as deagglomerating aids, nonionic and amphoteric surfactants are preferred for reasons of skin compatibility. The surfactant may include nitrogen. For example, sorbitan monoesters such as sorbitan monococoate and sorbitan monolaurate or ethoxylated variants thereof such as Polysorb 20® are added. Further suitable deagglomeration aids are ethoxylated and alkoxylated derivatives of 2-propylheptanol, which are commercially available as Lutensol XL® and Lutensol XP® (BASF). SE, Carl-Bosch-Strasse 38, 67056 Ludwigshafen, Germany).

  The deagglomeration aid can be metered separately or added to the postcrosslinker solution. Preferably, the deagglomeration aid is easily added to the postcrosslinking agent.

  The usage-amount of the deaggregation adjuvant with respect to a base polymer is 0-0.1 mass%, for example, Preferably it is 0-0.01 mass%, Most preferably, it is 0-0.002 mass%. Preferably, the deagglomerating aid has a surface tension of the swollen base polymer and / or an aqueous extract of the swollen post-crosslinked water-absorbing polymer at 23 ° C. of at least 0.060 N / m, preferably at least 0. 0.02 N / m, particularly preferably at least 0.065 N / m and preferably at most 0.072 N / m.

The aqueous solution of the postcrosslinking agent may further contain a cosolvent in addition to the at least one postcrosslinking agent. The penetration depth of the post-crosslinking agent into the polymer particles can be adjusted through the content of the non-aqueous solvent or the total amount of the solvent. Industrially very suitable cosolvents are C ₁ -C ₆ -alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, s-butanol, t-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 acid esters such as ethyl acetate. A drawback of some of the aforementioned cosolvents is that it has a typical inherent odor.

  The cosolvent itself is ideally not a postcrosslinker under the reaction conditions. However, in special cases and depending on the residence time and temperature, the cosolvent may contribute partly to the crosslinking. This is especially the case when the postcrosslinker is relatively inert and can itself form its cosolvent. For example, a cyclic carbonate of the general formula (III), a diol of the general formula (IIa) or a polyol of the general formula (IIb) is used. Such a post-crosslinking agent is a mixture with a more reactive post-crosslinking agent and can also be used in the function as a co-solvent. This is because the original postcrosslinking reaction can then be carried out at a lower temperature and / or a shorter residence time than in the absence of a more reactive crosslinker. Since the cosolvent is used in relatively large amounts and partially remains in the product, it must be non-toxic.

  In the process according to the invention, the diols of the general formula (IIa), the polyols of the general formula (IIb) and the cyclic carbonates of the general formula (III) are also suitable as cosolvents. They fulfill these functions in the presence of a reactive postcrosslinker of general formula (I) and / or (IV) and / or in the presence of a diglycidyl compound or a triglycidyl compound. However, preferred cosolvents in the process according to the invention are diols of the general formula (IIa), in particular when the hydroxy group is sterically hindered by neighboring groups in the reaction. Such diols are certainly suitable as postcrosslinkers, but for this they require significantly higher reaction temperatures or in some cases higher amounts than sterically unhindered diols.

  A particularly preferred combination comprising a post-crosslinking agent having a slight reactivity as a cosolvent and a reactive post-crosslinking agent is a preferred polyhydric alcohol, a diol of the general formula (IIa), and a polyol of the general formula (IIb). , A combination with an amide acetal or carbamate of general formula (I).

  Suitable combinations are for example 2-oxazolidone / 1,2-propanediol and N- (2-hydroxyethyl) -2-oxazolidone / 1,2-propanediol and ethylene glycol diglycidyl ether / 1,2-propanediol. is there.

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

  Further preferred combinations are ethylene glycol diglycidyl ether or glycerin diglycidyl ether or glycerin triglycidyl ether and the following solvent, co-solvent or co-crosslinking agent: isopropanol, 1,3-propanediol, 1,2-propylene glycol or their Combination with a mixture.

  Further preferred combinations are the following solvents, co-solvents or co-crosslinking agents: 2-oxazolidone in the isopropanol, 1,3-propanediol, 1,2-propylene glycol, ethylene carbonate, propylene carbonate or mixtures thereof or (2- Combination with hydroxyethyl) -2-oxazolidone.

  Often, the concentration of the co-solvent in the aqueous postcrosslinker solution is 15-50% by weight, preferably 15-40% by weight, particularly preferably 20-35% by weight, based on the postcrosslinker solution. In the case of co-solvents that are only miscible with water, preferably the aqueous postcrosslinker solution is optionally adjusted by reducing the co-solvent concentration so that only one phase is present.

  In a preferred embodiment, no co-solvent is used. The postcrosslinking agent is then used only as a solution in water, optionally with the addition of a deagglomeration aid.

  The concentration of 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, particularly preferably from 2 to 5% by weight, based on the post-crosslinking agent solution. It is.

  The total amount of postcrosslinker solution relative to the base polymer is usually 0.3 to 15% by weight, preferably 2 to 6% by weight.

  Intrinsic surface postcrosslinking by reaction of the surface postcrosslinker with functional groups on the surface of the base polymer particles is mostly done by warming the base polymer wetted with the surface postcrosslinker solution. It is usually referred to as "drying" (but should not be confused with the above drying of polymer gels from polymerizations where generally much more liquid should be removed). The drying can take place in the mixer itself, by heating the jacket, by a heat exchange surface or by blowing hot air. Simultaneous mixing and drying of the superabsorbent and the surface postcrosslinker can be performed, for example, in a fluid bed dryer. However, the drying is usually carried out in a subsequent connected dryer such as a shelf dryer, rotary tube furnace, paddle dryer or disk dryer or a heatable screw. Suitable dryers are, for example, from Bepex International LLC (333 NE Taft Street, Minneapolis, MN 55413, USA) as a Solidair® dryer or a Torusdics® dryer or from Nara Machinery Co. , Ltd., Ltd. (Zweignederlassung Europa, Europaallee 46, 50226 Frechen, Germany) is also available as a paddle dryer or vane dryer or fluid bed dryer.

  The polymer particles can be heated via a contact surface in a subsequent connected drier for the purpose of drying and surface post-crosslinking, or via a supplied heated inert gas or Heating can be carried out through a mixture of the above inert gas and water vapor or only with water vapor alone. Upon supply of heat through the contact surface, the reaction can be carried out under inert gas at light negative pressure or at full negative pressure. When using steam for direct heating of the polymer particles, it is desirable according to the invention to operate the dryer at normal or overpressure. In this case, it may be appropriate to divide the post-crosslinking step into a heating stage with steam and a reaction stage under inert gas but without steam. It can be realized in one or more devices. According to the invention, the polymer particles may already be heated with steam in a post-crosslinking mixer. The base polymer used may still have a temperature of 10 to 120 ° C. from the previous process step, and the postcrosslinker solution may have a temperature of 0 to 70 ° C. In particular, the postcrosslinker solution may be warmed to reduce the viscosity.

  Preferred drying temperatures are in the range from 100 to 250 ° C., preferably from 120 to 220 ° C., particularly preferably from 130 to 210 ° C., particularly preferably from 150 to 200 ° C. The preferred residence time at said temperature in a reactive mixer or dryer is preferably at least 10 minutes, particularly preferably at least 20 minutes, very particularly preferably at least 30 minutes and usually at most 60 minutes. . Typically, the drying is performed when the superabsorbent is generally at least 0.1% by weight, preferably at least 0.2% by weight, in a particularly preferred form at least 0.5% by weight and generally at most. It is carried out until it has a residual moisture content of 15% by weight, preferably at most 10% by weight, in a particularly preferred form at most 8% by weight.

  Post-crosslinking can be performed under normal atmospheric conditions. Normal atmospheric conditions are technical in order to lower the partial pressure of oxidizing gas, for example atmospheric oxygen partial pressure, in equipment where the post-crosslinking reaction is mainly carried out ("post-crosslinking reactor", generally dryer). This means that no proper measures can be taken. However, the postcrosslinking reaction is preferably performed under a reduced partial pressure of oxidizing gas. Oxidizing gases are substances that have a vapor pressure of at least 1013 mbar at 23 ° C. and act as oxidants during the combustion process, such as oxygen, nitrogen and nitrogen dioxide, in particular oxygen. The partial pressure of the oxidizing gas is preferably less than 140 mbar, preferably less than 100 mbar, particularly preferably less than 50 mbar, particularly preferably less than 10 mbar. When the thermal postcrosslinking is carried out at ambient pressure, i.e. at a total pressure around 1013 mbar, the total partial pressure of the oxidizing gas is determined by its volume fraction. The proportion of oxidizing gas is then preferably less than 14% by volume, preferably less than 10% by volume, particularly preferably less than 5% by volume, very particularly preferably less than 1% by volume.

Postcrosslinking can be carried out under reduced pressure, i.e. with a total pressure of less than 1013 mbar. The total pressure is generally less than 670 mbar, preferably less than 480 mbar, particularly preferably less than 300 mbar, particularly preferably less than 200 mbar. When drying and postcrosslinking are carried out under air having an oxygen content of 20.8% by volume, the oxygen partial pressure corresponding to the total pressure is 139 mbar (670 mbar), 100 mbar (480 mbar), 62 mbar (300 mbar) and 42 mbar (200 mbar), with the total pressure in each case in parentheses. Another way to reduce the partial pressure of the oxidizing gas is to introduce a non-oxidizing gas, in particular an inert gas, into the equipment used for postcrosslinking. Suitable inert gases are substances that exist in a gaseous state at a post-crosslinking temperature and a predetermined pressure in the post-crosslinking dryer, and act non-oxidatively on the components of the polymer particles that are dried under these conditions. Substances such as nitrogen, carbon dioxide, argon, water vapor, with nitrogen being preferred. Inert gas amount, relative to 1kg of superabsorbent, in general, 0.0001～10M ^3, preferably 0.001～5M ^3, particularly preferably 0.005～1M ^3, particularly preferably 0.005 ~ 0.1 m ³ .

  In the method according to the present invention, when the inert gas does not contain water vapor, it can be blown into the post-crosslinking dryer through a nozzle. Particularly preferably, the inert gas comprises a superabsorbent and a surface post-crosslinking agent. Is added to the polymer particle stream via a nozzle already in or just before the mixer.

  Of course, the cosolvent vapor discharged from the dryer can be condensed again outside the dryer and optionally recycled.

  In a preferred embodiment of the invention, multivalent cations are added to the particle surface prior to, during or after postcrosslinking, in addition to the postcrosslinker. It is in principle a further surface postcrosslinking by ionic non-covalent bonds, sometimes also referred to as "complexation" with the metal ion, or simply the substance ("complexing agent") Also called "covering".

  The addition of the polyvalent cation is carried out by spraying a solution of a divalent or higher cation, usually a divalent, trivalent or tetravalent metal cation solution, but also a polyvalent cation such as formally complete. Or partially composed of vinylamine monomers, such as partially or fully hydrolyzed polyvinylamide (so-called “polyvinylamine”), whose amine groups are always at very high pH values. It can also be carried out by spraying a solution of a polymer that is partially protonated and present with ammonium groups. Examples of divalent metal cations that can be used are in particular Group 2 metals (especially Mg, Ca, Sr, Ba), Group 7 metals (especially Mn), Group 8 metals of the periodic table of elements. (Especially Fe), Group 9 metals (especially Co), Group 10 metals (especially Ni), Group 11 metals (especially Cu) and Group 12 metals (especially Zn). is there. Examples of trivalent metal cations that can be used are, among others, group 3 metals (particularly Sc, Y, La, Ce), group 8 metals (particularly Fe), group lanthanides of the periodic table of elements. Trivalent cations of Group 11 metals (especially Au) and Group 13 metals (especially Al). Examples of tetravalent cations that can be used are in particular the lanthanide metals (especially Ce) of the periodic table of elements as well as the tetravalent cations of group 4 metals (especially Ti, Zr, Hf). The metal cations can be used alone or in a mixture with each other. In particular, it is preferable to use a trivalent metal cation. In particular, it is preferable to use an aluminum cation.

  Of the metal cations mentioned above, any metal salt that exhibits sufficient solubility in the solvent to be used is suitable. Particularly suitable are weakly complexing anions such as chloride, nitrate and sulfate, hydrogen sulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate or diphosphate. Metal salts with anions such as hydrogen ions, preferably monocarboxylic and dicarboxylic acid, hydroxy acid, keto acid and amino acid salts or basic salts. Examples are acetates, propionates, tartrate, maleates, citrates, lactates, malates and succinates, as well as the use of hydroxides. In particular, the use of 2-hydroxycarboxylates such as citrate and lactate is preferred. 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 lactic acid. Aluminum.

  The cations and salts described above can be used in pure form or as a mixture of different cations or salts. The salts used of the divalent and / or trivalent metal cations may contain further secondary components, such as carboxylic acids that have not yet been neutralized and / or alkali salts of neutralized carboxylic acids. Preferred alkali salts are sodium, potassium and ammonium salts. They are typically used as aqueous solutions obtained by dissolving solid salts in water or preferably produced directly as such, optionally avoiding drying and purification steps. Preferably, hydrates of the above-mentioned salts can also be used. They often dissolve in water more quickly than anhydrous salts.

  The amount of metal salt used is generally at least 0.001% by weight, preferably at least 0.01% by weight, in a particularly preferred form at least 0.1% by weight, for example at least 0%, based on the weight of the base polymer, respectively. .4% by weight and generally at most 5% by weight, preferably at most 2.5% by weight, in a particularly preferred form at most 1% by weight, for example at most 0.7% by weight.

  The salt of a trivalent metal cation can be used as a solution or suspension. As a solvent for the metal salt, water, alcohol, DMF, DMSO and a mixture of these components can be used. Particularly preferred are water and water / alcohol mixtures such as water / methanol, water / 1,2-propanediol and water / 1,3-propanediol.

  The treatment of the basic polymer with a divalent or higher cation solution is carried out in the same manner as the treatment with the surface post-crosslinking agent including the drying step. The surface postcrosslinker and the multivalent cation can be sprayed together or in separate solutions. The metal salt solution can be sprayed onto the superabsorbent particles either before or after surface postcrosslinking. In one particularly preferred method, the spraying of the metal salt solution is performed in the same step as the spraying of the crosslinker solution. In doing so, both solutions can be sprayed individually, back and forth or simultaneously through two nozzles, or the crosslinker solution and the metal salt solution can be sprayed together through one nozzle.

  When performing a drying step following surface postcrosslinking and / or treatment with complexing agents, it is preferred but not absolutely necessary to cool the product after drying. The cooling can be performed continuously or intermittently, where appropriate the product is continuously sent to a cooler connected to the subsequent of the dryer. For this purpose, any device known for the discharge of heat from a pulverulent solid, in particular any device described above as a drying device, is not supplied with a heating medium, but with a cooling medium, for example cold water, Thus, it is used when the heat is not carried into the superabsorbent through the wall and, depending on the structure, through a stirring mechanism or other heat exchange surface, but is discharged therefrom. Preferably, a cooler is used in which the product is moved, and therefore a cooled mixer, such as a vane cooler, a disk cooler or a paddle cooler is used. The superabsorbent can be cooled even in a fluidized bed by blowing a cooled gas, such as cooling air. The cooling conditions are adjusted so that the superabsorbent is obtained at the desired temperature for rework. Typically, the average residence time in the cooler is generally at least 1 minute, preferably at least 3 minutes, in a particularly preferred form at least 5 minutes, and generally at most 6 hours, preferably at most 2 Time, particularly preferably at most 1 hour, and the cooling power is generally at least 0 ° C., preferably at least 10 ° C., in a particularly preferred form at least 20 ° C., and generally high. It is determined to have a temperature of at most 100 ° C., preferably at most 80 ° C., in a particularly preferred form at most 60 ° C.

  The surface postcrosslinked superabsorbent is optionally usually ground and / or sieved. Milling is typically not required here, but is usually accompanied by agglomerate or fine grain sieving formed to adjust the desired particle size distribution of the product. Agglomerates and fines are discarded or preferably returned to the process at a suitable location as known; agglomerates after refinement. The desired particle size for the surface postcrosslinked superabsorbent is the same as for the base polymer.

  Optionally, the superabsorbent according to the invention is mixed with further additives that stabilize against discoloration.

［式中、
Ｍは、水素原子、アンモニウムイオン、元素の周期表の第１族、第２族、第８族、第９族、第１０族、第１２族もしくは第１４族の一価の金属イオン又は二価の金属イオンの当量を表し；
Ｒ²⁷は、ＯＨ又はＮＲ³⁰Ｒ³¹を表し、その際、Ｒ³⁰及びＲ³¹は、互いに独立してＨ又はＣ₁〜Ｃ₆−アルキルを表し；
Ｒ²⁸は、Ｈ又はアルキル基、アルケニル基、シクロアルキル基もしくはアリール基を表し、その際、前記基は、選択的に１、２又は３個の置換基を有し、前記置換基は、互いに独立してＣ₁〜Ｃ₆−アルキル、ＯＨ、Ｏ−Ｃ₁〜Ｃ₆−アルキル、ハロゲン及びＣＦ₃から選択され；かつ
Ｒ²⁹は、ＣＯＯＭ、ＳＯ₃Ｍ、ＣＯＲ³⁰、ＣＯＮＲ³⁰Ｒ³¹又はＣＯＯＲ³⁰を表し、その際、Ｍ、Ｒ³⁰及びＲ³¹は、上述の意味を有するか、又はＲ²⁸がアリールを表し、それが選択的に上述のように置換されている場合にはＨも表す］の化合物、その塩又はかかる化合物及び／又はその塩の混合物である。 Known stabilizers against such discoloration are, for example, derivatives of sulfinic acid. Particularly suitable derivatives of sulfinic acid are, for example, the following formula (V):

[Where:
M is a hydrogen atom, an ammonium ion, a monovalent metal ion of the first, second, eighth, ninth, tenth, twelfth or fourteenth group of the periodic table of elements or divalent Represents the equivalent of the metal ions of
R ²⁷ represents OH or NR ³⁰ R ³¹ , wherein R ³⁰ and R ³¹ independently of one another represent H or C ₁ -C ₆ -alkyl;
R ²⁸ represents H or an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group, wherein the group optionally has 1, 2 or 3 substituents, and the substituents are Independently selected from C ₁ -C ₆ -alkyl, OH, O—C ₁ -C ₆ -alkyl, halogen and CF ₃ ; and R ²⁹ is COOM, SO ₃ M, COR ³⁰ , CONR ³⁰ R ³¹ or COOR ³⁰ where M, R ³⁰ and R ³¹ have the above-mentioned meanings, or H if R ²⁸ represents aryl and is optionally substituted as described above. Or a salt thereof or a mixture of such a compound and / or a salt thereof.

In the above formula (V), alkyl represents a linear or branched alkyl group, which group preferably has 1 to 6, in particular 1 to 4 carbon atoms. Examples for alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl and the like. The same is true for alkyl groups in O-alkyl. Alkenyl represents a straight-chain or branched alkenyl group, which group preferably has 3 to 8 carbon atoms, in particular 3 to 6 carbon atoms. A preferred alkenyl group is an allyl group. Cycloalkyl is, in particular C ₁ -C ₆ - cycloalkyl, where, cyclopentyl and cyclohexyl are particularly preferred. Aryl (also in aralkyl) preferably represents phenyl or naphthyl. When the aryl group represents a phenyl group and is substituted, the group preferably has two substituents. These substituents are present in particular at the 2-position and / or 4-position.

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

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

R ²⁷ preferably represents a hydroxy group or an amino group. R ²⁸ preferably represents a hydrogen atom or an alkyl group or an aryl group, which group may be substituted as described above. Preferably, the group has 1 or 2 hydroxy substituents and / or alkoxy substituents.

R ²⁹ preferably represents COOM or COOR ³⁰ (M and R ³⁰ have the meanings given above) or R ²⁷ represents aryl, which may be substituted as described above. Also represents a hydrogen atom.

In a preferred embodiment, the superabsorbent is represented by the above formula, wherein M represents an equivalent of an alkali metal ion, an alkaline earth metal ion or a zinc ion, and R ²⁷ represents a hydroxy group or an amino group. R ²⁸ represents H or alkyl, and R ²⁹ represents COOM or COOR ³⁰ , where R ²⁹ represents COOM, M in the COOM group represents H, an alkali metal ion or an alkali. When it represents the equivalent of earth metal ions and R ²⁹ represents COOR ³⁰ , R ³⁰ contains a compound representing C ₁ -C ₆ -alkyl.

In a further preferred embodiment, the superabsorbent is represented by the above formula, wherein M represents the equivalent of an alkali metal ion, alkaline earth metal ion or zinc ion, and R ²⁷ represents a hydroxy group or amino group. A compound in which R ²⁸ represents aryl, which is optionally substituted as described above, in particular represents hydroxyphenyl or C ₁ -C ₄ -alkoxyphenyl, and R ²⁹ represents a hydrogen atom contains.

  Current status of IUPAC (International Union of Pure Applied Chemistry, 104 TW Alexander Drive, Building 19, Research Triangle Park, NC 27709, USA, www.iupac.org), an international organization responsible for nomenclature in the field of chemistry. Group 1 (H, Li, Na, K, Rb, Cs, Fr), Group 2 (Be, Mg, Ca, Sr, Ba, Ra), Group 8 (Fe, Ru, Os), Group 9 (Co, Rh, Ir), Group 10 (Ni, Pd, Pt), Group 12 (Zn, Cd, Hg) and Group 14 (C, Si, Ge, Sn, Pb) is a CAS (Chemical Abstracts Service, 2540 Orientation River Road, Columbias, OH 43202, USA, www.c). as.org) corresponds to the groupings Ia, IIa, IIb, IVa and VIIIb in the numbering used by.

  The sulfinic acid derivatives of the above formula can be used in pure form, but can optionally also be used in a mixture with the corresponding metal ion sulfites and the corresponding sulfonic acids obtained in the usual manner from the preparation of such compounds. The preparation of such sulfinic acid derivatives of the above formula is known and described, for example, in WO 99/18067 A1. They are also common commercial products and in the form of a mixture consisting of sodium salt of 2-hydroxy-2-sulfinatoacetic acid, disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite, for example. Brueggemann KG (Salzstrasse 131, 74076 Heilbrunn, Germany, www. Available at

  Optionally, the superabsorbent according to the invention is also mixed with at least one inorganic water-insoluble particulate solid. For this purpose, basically any inorganic water-insoluble powder is suitable. Examples are generally solid, chemically inert (ie not disturbing in superabsorbents) substances such as oxides, oxide hydroxides, hydroxides, sulfates, carbonates, zeolites, inorganic pigments, inorganics Or clay. Examples are sulfates such as magnesium sulfate or barium sulfate, carbonates such as potassium carbonate, magnesium carbonate or dolomite, silicates such as calcium silicate or magnesium silicate, carbides such as perlite or silicon carbide, diatomaceous earth or fly ash It is.

  Suitable oxides are group 2 to group 14 metal oxides of the periodic table of elements including lanthanides 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 oxide, cobalt oxide, nickel oxide. , Copper oxide, zinc oxide, boron oxide, aluminum oxide, silicon dioxide, tin oxide, lead oxide, lanthanum oxide or cerium oxide. For clarity, the use of a common name for a metal oxide should not be an expression regarding the valence of the metal and the stoichiometry of the oxide. In general, all are suitable when one element forms a plurality of oxides. In the individual case, the oxide is selected by consideration specific to the individual case, for example by price, toxicity, stability or color. Examples of particularly suitable oxides are titanium dioxide, in particular anatase or rutile modified titanium dioxide, precipitated silicon dioxide or silicon dioxide produced by pyrolysis.

  The clay is a silicate or aluminosilicate, which is usually obtained by underground mining of natural deposits and sometimes further processing thereof. However, significant clay is produced synthetically.

  Mixtures of these materials can also be used.

  Inorganic water-insoluble solids are particulate and exist in powder form. The average particle size is generally at least 0.001 μm, preferably at least 0.002 μm, in a particularly preferred form at least 0.005 μm, most preferably at least 0.01 μm and generally at most 500 μm, preferably at most 200 μm, in particular In a preferred form, it is at most 100 μm, and in a particularly preferred form, it is at most 50 μm. The particles may themselves be aggregates or agglomerates of smaller primary particles. Although the particle size can be measured by sieve analysis, it is easier to measure the particle size by laser diffraction technique and is therefore preferred. These methods are well known and are routinely performed with commercial equipment suitable for this purpose.

  The stabilizers for any further discoloration listed above and the inorganic water-insoluble particulate solids, when added, are each generally at least 0, relative to the total mass of the superabsorbent according to the invention. 0.0001% by weight, preferably at least 0.001% by weight, in a particularly preferred form at least 0.025% by weight and generally at most 3% by weight, in a preferred form at most 2% by weight, in a particularly preferred form Even 0.5% by mass is added. In general, superabsorbents according to the invention containing alkaline earth metal salts require a smaller amount of known color change stabilizers than superabsorbents not containing alkaline earth metal salts.

  Mixing the superabsorbent with the stabilizer against discoloration to be used according to the invention, any further stabilizers and inorganic water-insoluble particulate solids can be carried out by any known mixing method. The discoloration stabilizer to be used according to the invention (in solid form) and the inorganic water-insoluble particulate solid are added as such or as a suspension in a solvent or suspending agent and used according to the invention. Stabilizers for discoloration to be made (in dissolved or liquid form) and any further stabilizers can optionally be mixed in solution or in liquid form. Preferably, the stabilizer is added to the superabsorbent as a powder or as a suspension based on the easier homogenous distribution. In so doing, a physical mixture that is easily separable by mechanical measures is not always produced. The additive can bind to the superabsorbent more sufficiently, for example, as a surface layer that adheres relatively tightly or as particles that adhere tightly on the surface of the superabsorbent particles. Addition of additives to known superabsorbents can also be fully expressed and referred to as “coating”.

  When solutions or suspensions are used for the coating, both superabsorbents and additives are chemically compatible as solvents or suspending agents and therefore do not cause unwanted chemical reactions with them. Solvents or suspending agents are used. Typically, water or organic solvents such as alcohols or polyols or mixtures thereof are used. Examples of suitable solvents or suspending agents are water, isopropanol / water, 1,3-propanediol / water and propylene glycol / water, wherein the mixture mass ratio is preferably 20:80 to 40:60. It is. Water is preferred when a suspending agent is used for the stabilizer or inorganic particulate solid to be used according to the invention. A surfactant can be added to the solution or suspension.

  Stabilizers and other additives generally contain surface postcrosslinkers that are applied on the superabsorbent for surface postcrosslinking when they are added to the monomer mixture or to the polymerizing gel. Just like a solution or suspension, it is admixed with a superabsorbent, for example as described further below. The additive may be a superabsorbent ("base polymer" or "base polymer") that is not (yet) postcrosslinked as a component of the solution applied for surface postcrosslinking or as one component of that component. And therefore can be added to the solution of the surface postcrosslinker or to one of its components. Superabsorbents coated with surface postcrosslinkers and additives are then subjected to further process steps necessary for surface postcrosslinking, e.g. heat-induced reactions between surface postcrosslinkers and superabsorbents. Elapse. This method is relatively simple and economical.

  Where the highest stability against discoloration is essential, stabilizers and additives are preferably applied in one unique process step after surface postcrosslinking. When the stabilizers and additives are applied as solutions or suspensions, the application is then applied to the base polymer with a surface postcrosslinker, in contrast to the superabsorbent already surface postcrosslinked. This is done in the same way as In most cases, however, the superabsorbent is not necessarily continuously warmed in the same way as in the case of surface postcrosslinking in order to dry it again. The temperature adjusted during this drying, however, is generally at most 110 ° C., preferably at most 100 ° C., particularly preferably at most 90 ° C., in order to avoid unwanted reactions of the additives. . The temperature is adjusted to achieve the desired water content of the superabsorbent taking into account the residence time in the dryer. Also, the additive alone or other conventional auxiliaries such as dust binders, agents for sticking or water for re-wetting of the superabsorbent (for example these auxiliaries are described below), for example It is well possible and appropriate to add in a cooler connected subsequent to surface postcrosslinking. The temperature of the polymer particles in this case is 0 ° C. to 190 ° C., preferably less than 160 ° C., more preferably less than 130 ° C., even more preferably less than 100 ° C., most preferably less than 70 ° C. The polymer particles are quickly cooled, optionally after coating, to a temperature below the temperature of possible degradation of the additive.

  Optionally, on the surface of the superabsorbent particles, all known coatings, for example film-forming properties, may be post-crosslinked, whether postcrosslinked or postcrosslinked, as required at each process step in the production process. Polymers, thermoplastic polymers, dendrimers, polycationic polymers (eg polymers such as polyvinylamine, polyethyleneimine or polyallylamine) or any water-soluble monovalent or polyvalent metal salt known to those skilled in the art, eg aluminum sulfate, sodium Salts such as salts, potassium salts, zirconium salts or iron salts can additionally be applied. Examples for useful alkali metal salts are sodium and potassium sulfate, sodium and potassium acetate, citrate, sorbate. Thereby, additional effects can be achieved, for example a reduction in the tendency of the intermediate product to stick in each process step of the final product or method step, an improvement in processing properties or a further improvement in liquid permeability (SFC). When the additive is used and sprayed in the form of a dispersion, the dispersion is preferably used as an aqueous dispersion, and preferably still additionally an antidusting agent for the immobilization of the additive (Entstaubungsmitel) is applied on the surface of the superabsorbent. The antidusting agent is then added directly to the dispersion of the inorganic powdered additive or optionally before, during or after the application of the inorganic powdered additive. It can also be added by spraying as a solution. Most preferably, the postcrosslinking agent, the antidusting agent and the powdered inorganic additive are sprayed simultaneously in the postcrosslinking. In a further preferred variant, however, the antidusting agent is added individually to the cooler, for example by spraying from above, from below or from the side. Particularly suitable antidusting agents that can also be used to immobilize powdered inorganic additives on the surface of water-absorbing polymer particles are polyethylene glycol, polyglycerin, 3 ethoxyl having a molecular weight of 400-20000 g / mol. Or 100 ethoxylated polyols such as trimethylolpropane, glycerin, sorbitol and neopentyl glycol. Particularly suitable are 7 ethoxylated to 20 ethoxylated glycerol or trimethylol propane, such as Polyol TP 70® (Perstorp, SE). They have the advantage that the agent only slightly reduces the surface tension of the aqueous extract of water-absorbing polymer particles.

  Similarly, the superabsorbent according to the invention can be adjusted to the desired water content by the addition of water.

  Any coatings, solids, additives and auxiliaries can each be added in a separate process step, but usually they are superseded if they are not added during the mixing of the base polymer and the surface postcrosslinker. The most suitable method is to add to the absorbent in a cooler, for example by spraying the solution or adding in fine solid or liquid form.

  Superabsorbents according to the invention generally have a centrifugal retention capacity (CRC, see below for measuring method) of at least 5 g / g, preferably at least 10 g / g, in a particularly preferred form at least 20 g / g. . Usually, the centrifugal holding capacity does not exceed 40 g / g.

  The superabsorbent according to the invention typically absorbs under pressure of at least 18 g / g, preferably at least 20 g / g, advantageously at least 22 g / g, if it is not surface postcrosslinked. Absorption un-Drug) (AUL 0.7 psi, see below for measurement method), usually not exceeding 30 g / g.

The superabsorbent according to the invention is also typically at least 10 × 10 ⁻⁷ cm ³ s / g, preferably at least 30 × 10 ⁻⁷ cm ³ s / g, advantageously at least 40 × 10. ^-7 cm ³ s / g of liquids (SFC, see below for measurement method), usually not exceeding 1000 × 10 ^-7 cm ³ s / g.

  The L value (CIE color number) of the superabsorbent is typically at least 75, preferably at least 80, particularly preferably at least 85, and at most 100 in the unstored state.

  The a value (CIE color number) of the superabsorbent is typically −2.5 to +2.5, preferably −2.0 to +2.0, particularly preferably in an unstored state. Is -1.5 to +1.5.

  The b value (CIE color number) of the superabsorbent is typically 0 to 12 and preferably 2 to 11 when not stored.

  According to the comparatively loaded aging test described below, the superabsorbent according to the invention shows only slightly worse results for the unstored state for the L and a values after measurement. . In particular, the b value preferably does not exceed 13 and particularly preferably does not exceed 12. A b value above 12 is decisive in sanitary hygiene products and ultra-thin diapers, and a b value above 15 is already decisive in normal diapers. This is because this discoloration can be perceived by consumers when wet.

  A further subject of the present invention is a sanitary article comprising a superabsorbent according to the invention, preferably 50-100% by weight, preferably 60-100% by weight, advantageously 70-100% by weight, particularly preferably 80- 100% by weight, particularly preferably 90-100% by weight, of an ultra-thin diaper comprising an absorbent layer of the superabsorbent according to the invention, the coating of the absorbent layer is not taken into account as a matter of course.

  Particularly preferably, the superabsorbents according to the invention are also suitable for the production of laminates and composite structures as described, for example, in US 2003/0181115 and US 2004/0019342. Fibers consisting of the melt adhesives described for the production of such new absorbent structures in both documents and in particular the melt adhesives described in US 2003/0181115, to which superabsorbent particles are bound In addition to what has been described, the superabsorbents according to the invention can be used for completely similar structures using UV-crosslinkable melt adhesives, for example sold as AC resin (R) (BASF SE, Germany). Also suitable for manufacturing. Because these UV crosslinkable melt adhesives have the advantage that they can already be processed at 120-140 ° C., they are better for compatibility with many thermoplastic substrates. A further essential advantage is that the UV-crosslinkable melt adhesive is not very toxicologically concerned and does not cause odor in hygiene products. The very essential advantage associated with the superabsorbent according to the invention is that the UV-crosslinkable melt adhesive is not prone to yellowing during processing and crosslinking. It is particularly preferred when an ultra-thin or partially permeable sanitary product is to be produced. Therefore, the combination of the superabsorbent according to the invention and a UV-crosslinkable melt adhesive is particularly preferred. Suitable UV-crosslinkable melt adhesives are described, for example, in EP 0377199 A2, EP 0454564 A1, US 5,026,806, EP 0655465 A1 and EP 0377191 A2.

  The superabsorbent according to the invention can also be used in other technical fields where liquids, in particular water or aqueous solutions, are absorbed. These areas include, for example, storage, packaging, transportation (as a component of packaging materials for articles sensitive to water or moisture, for example for the transportation of flowers and also as protection against mechanical action); animal hygiene Goods (cat litter); Food packaging (transport of fish, fresh meat; absorption of blood in water, fresh fish or fresh meat packaging); Medicine (water absorption for bandages, burn dressings or exudative wounds) Materials), cosmetics (carrier materials for medicinal chemicals and pharmaceuticals, rheumatic plasters, ultrasonic gels, cooling gels, cosmetic thickeners, sunscreens); thickening for oil-in-water or water-in-oil emulsions Agents; textiles (moisture control in textiles, shoe pads, evaporative cooling, eg in protective clothing, gloves, hair bands); chemical engineering use (large as a catalyst for organic reactions) As an adhesive in agglomeration for immobilization of functional molecules such as enzymes, heat storage materials, filter aids, hydrophilic components in polymer laminates, dispersants, liquefaction agents); as an aid in powder injection molding In civil engineering and construction activities (installation, clay-based plaster, as a damping medium, cable covering when tunneling in water-rich foundations); water treatment, waste disposal, water separation (anti-icing agent, reuse) Possible sandbags); purification; agriculture (irrigation, snowmelt and dew retention, composting additives, forest protection against mushroom / insect damage, reduced release of plant actives); for fire fighting or fire protection; thermoplastic Co-extrusion agents in polymers (eg for hydrophilization of multilayer sheets); manufacture of water-absorbable sheets and thermoplastic moldings (eg agricultural rainwater and condensation) Sheets containing water; sheets containing superabsorbents for fruit and vegetable freshness, they are packaged in wet sheets; superabsorbent-polystyrene coextrudates such as meat, fish, chicken, fruit And for food packaging such as vegetables); or as a carrier substance in pharmaceutical formulation (medicine, plant protection).

  Articles according to the invention for the absorption of liquids differ from those known in that the article contains a superabsorbent according to the invention.

  Furthermore, a method for the manufacture of an article for liquid absorption, in particular a sanitary article, has been found, characterized in that at least one superabsorbent according to the invention is used in the manufacture of the article. . In other respects, methods for producing such articles using superabsorbents are known.

Test Method The superabsorbent is tested by the test method described below.

  The standard test method, referred to below as “WSP”, is described in “Worldwide Strategic Partners” EDANA (European Disposables and Nonwovens Association, Avenue Eugene 30w, Belgium, 15w. The sd's "sord" in the 2005 edition of the "sand", a joint edition of the Ist with the 2005 edition of the "sord" with INDS (association of the Nonwoven Fabrics Industry, 1100 Crescent Green, Suite 115, Cary, North Carolina 27518, United States, www.inda.org). ndustry ". These publications are available from EDANA and INDA.

  All measurements described below should be performed at an ambient temperature of 23 ± 2 ° C. and a relative air humidity of 50 ± 10% unless otherwise stated. Superabsorbents are mixed well before measurement unless otherwise stated.

Centrifugal retention capacity (CRC, Centrifugation Retention Capacity)
The centrifugal retention capacity of the superabsorbent is measured according to the standard test method number WSP 241.5-05 “Centrifuge retention capacity”.

Absorption under pressure (AUL 0.3 psi, "Absorptivity Under Load of 0.3 psi")
The absorption of the superabsorbent under a pressure of 2068 Pa (0.3 psi) is measured according to standard method number WSP 242.2-05 “Absorption under pressure”.

Absorption under pressure (AUL 0.7 psi, "Absorptivity Under Load of 0.7 psi")
The absorption of the superabsorbent under a pressure of 4826 Pa (0.7 psi) is measured in the same way as “Absorption under pressure” of standard method number WSP 242.2-05, with 49 g / cm ² A weight having a pressure of 0.7 psi is used instead of a weight having a pressure of 21 g / cm ² (providing a pressure of 0.3 psi).

Liquid permeability (SFC, “Saline Flow Conductivity”)
The liquid permeability of the swollen gel layer formed from the superabsorbent by liquid absorption under a pressure load of 0.3 psi (2068 Pa) is similar to that described in EP 0640330 A1. In this case, the apparatus described in the above-mentioned patent application, page 19 and FIG. 8, is such that the glass frit (40) is no longer used and the plunger (39) is cylindrical. It is made of the same plastic material as the body (37) and is now sufficiently modified to include 21 equally sized holes so that it is evenly distributed over the entire mounting surface. The measurement procedure and evaluation remain unchanged from EP 0640330 A1. The flow rate is automatically detected.

Liquid permeability (SFC) is calculated as follows:
SFC [cm ³ s / g] = (Fg (t = 0) × L0) / (d × A × WP)
In the above equation, Fg (t = 0) is the flow rate of the NaCl solution in g / second, which is an extrapolation method for t = 0 based on the linear regression analysis of the flow measurement data Fg (t) L0 is the thickness of the gel layer in cm, d is the specific gravity 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 at dyn / cm ² .

Permeability (FSGBP, "Free Swell Gel Bed Permeability")
The permeability is measured in the same manner as in paragraphs [0061] to [0075] of US2005 / 0256757 A1.

Hydrogel moisture content (residual moisture, moisture content)
The water content of the water-absorbing polymer particles is measured according to the standard test method number WSP 230.2-05 “Moisture content”.

Average Particle Size The average particle size of the product fractions is measured according to the standard method number WSP 220.2-05 “Particle size distribution”.

CIE color number (L, a, b)
The color measurement corresponds to the CIELAB method (Hunterlab, Vol. 8, 1996, No. 7, pages 1 to 4), a colorimeter model "LabScan XES / N LX17309" (HunterLab, Reston, USA) To implement. In that case, the color is described by the coordinates L, a and b of the three-dimensional system. In this case, L indicates brightness, L = 0 means black, and L = 100 means white. The values of a and b indicate the position of the color on the red and green color axes or the yellow and blue color axes, where + a represents red, -a represents green, + b represents yellow, And -b represents blue. The HC60 value is calculated by the formula HC60 = L-3b.

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

Aging test Measurement 1 (initial color): A plastic dish with an inner diameter of 9 cm is filled with superabsorbent particles, which are then leveled on the edge using a knife and the CIE color number as well as the HC60 value are measured.

  Measurement 2 (after aging): Fill a plastic dish with an inner diameter of 9 cm with superabsorbent particles, which are then leveled on the edge using a knife. The dish is then placed in a weatherproof cabinet that is open and conditioned at 60 ° C. with a constant relative air humidity of 86%. The dish is removed after 21 days. After cooling to room temperature, the CIE color number is measured.

Examples General specification I: Dry mix The ingredients to be mixed are placed in a polyethylene test bottle (500 ml capacity) and using a tumble mixer (type T2C; Willy A. Bachofen AG Maschinenfabrik, Basel; Switzerland). Mix thoroughly for 15 minutes.

General provision II: Wet mixture Superabsorbent is mixed at 250 at room temperature and per minute in a Pflugschar® mixer (manufacturer: Gebr. Loedige Machinenbau GmbH, Eisener-Strasse 7-9, 33102 Paderborn, Germany; type M5). Coat with the indicated amount of solution in each case by means of a two-substance spray nozzle at a rotating shaft speed. After spraying, the mixture is subsequently mixed for a further 15 minutes at a shaft speed of 80 revolutions per minute, the product is dried in a vacuum drying cabinet at 80 ° C. and a pressure of 250 mbar for 60 minutes, and the mass is crushed by an 850 μm screen. Remove.

  As a base material for Examples 1-15, Hysorb® B 7055 (BASF SE, Ludwigshafen, Germany), a commercially available superabsorbent, was used.

Example 1
100 g HySorb® B 7055 was mixed with 0.050 g 2,6-di-tert-butyl-4-methyl-phenol according to general rule I.

Example 2
100 g of HySorb® B 7055 was mixed with 0.060 g of calcium bis [monoethyl (3,5-di-t-butyl-4-hydroxybenzyl) phosphonate] according to general rule I.

Example 3
100 g of HySorb® B 7055 was mixed with 0.075 g of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid according to general rule I.

Example 4
100 g HySorb® B 7055 was mixed with 0.100 g 4,4-thio-bis (6-tert-butyl-meta-cresol) according to general rule I.

Example 5
100 g of HySorb® B 7055 was mixed with 0.040 g of pentaerythritol-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) according to general rule I.

Example 6
100 g HySorb® B 7055 was mixed with 0.130 g octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) according to general rule I.

Example 7
100 g HySorb® B 7055 was mixed with 0.050 g 4,6-bis (dodecylthiomethyl) -ortho-cresol according to general rule I.

Example 8
100 g of HySorb® B 7055 was added to 0.070 g of 3,3 ′, 3 ′, 5,5 ′, 5′-hexa-t-butyl-a, a ′, a ′-(mesitylene-2, Mixed with 4,6-triyl) tri-para-cresol according to general rule I.

Example 9
100 g of HySorb® B 7055 with 0.050 g of N, N-hexane-1,3-diylbis (3- (3,5-di-t-butyl-4-hydroxyphenylpropionamide)) and general Mixed in accordance with General Specification I.

Example 10
100 g of HySorb® B 7055 was mixed with 0.050 g of tris- (2,4-di-t-butylphenyl) phosphite according to general rule I.

Example 11
100 g of HySorb® B 7055 is commonly used with 0.060 g of 3,9-bis (octadecyloxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane Mixed according to rule I.

Example 12
100 g HySorb® B 7055 was mixed with 0.040 g bis- (2,4-di-t-butylphenol) pentaerythritol-diphosphite according to general rule I.

Example 13
HySorb® B 7055, 4.0% by weight of calcium-bis [monoethyl (3,5-di-t-butyl-4-hydroxybenzyl) phosphonate] dissolved in methanol according to general provision II. The solution was coated using 1.5% by weight with respect to the amount of superabsorbent.

Example 14
HySorb® B 7055, a 2.5 wt% solution of tris- (2,4-di-t-butylphenyl) phosphite in isopropanol, according to general provision II, was added to the superabsorbent. The coating was carried out using 2.0% by weight based on the amount.

Example 15
HySorb® B 7055, 40% by weight aqueous dispersion of ethylene bis (oxyethylene) bis-3- (5-tert-butyl-4-hydroxy-m-tolyl) propionate) according to general provision II Was coated at 0.5% by weight with respect to the amount of superabsorbent. Unlike general rule II, the product was not dried and sieved directly after mixing.

  The coated superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 1. The above examples show that the superabsorbents according to the invention are clearly lighter and less discolored after aging.

Example V16 (comparison)
In a 2 L stainless steel beaker, 326.7 g of 50 wt% caustic soda solution and 675 g of frozen deionized water were charged. While stirring, 392.0 g of acrylic acid was added, the rate of addition being adjusted so that the temperature did not exceed 35 ° C. The mixture was then cooled using a cold bath with stirring. When the temperature of the mixture dropped to 20 ° C., 1.08 g of triethoxylated glycerol triacrylate (Laromer® PO9044V, BASF SE; Ludwigshafen, Germany) and 2-hydroxy-2-methyl-1-phenyl Propane-1-one (DAROCUR® 1173, Ciba Specialty Chemicals Inc., Basel, Switzerland) 0.041 g and 2,2-dimethoxy-1,2-diphenylethane-1-one (IRGACURE®) 651, Ciba Specialty Chemicals Inc., Basel, Switzerland). Further cooling and when the temperature reached 15 ° C., oxygen was removed from the mixture using a glass frit by passing nitrogen. When 0 ° C. was reached, 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 dish. The glass dish was sized to produce a 5 cm layer thickness of the monomer solution. Subsequently, the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid, and sodium bisulfite (Brugegolit® FF6, L. Brueggemann KG, Salzstrasse 131,74076 Heilbronn , Germany), 0.047 g of a mixture dissolved in 5 ml of water was added, and the monomer mixture was stirred gently using a glass rod. The glass dish with the monomer solution was placed under a UV lamp (UV intensity = 25 mW / cm ² ), at which time polymerization started. After 16 minutes, the resulting gel was minced by a commercial meat grinder equipped with a 6 mm perforated plate and dried for 1 hour at 160 ° C. in a laboratory drying cabinet. The product was then ground and a 150-850 μm sieve fraction was obtained.

  This base polymer is used for surface postcrosslinking at room temperature in a Pflugschar® mixer (manufacturer: Gebr. Loedige Maskinenbau GmbH, Eisener-Strasse 7-9, 33102 Paderborn, Germany; type M5) with a heating jacket. And 0.10% by mass of ethylene glycol diglycidyl ether (Denacol (registered trademark) EX-810, Nagase ChemteX Corporation, Osaka, Japan) using a two-substance spray nozzle at a shaft speed of 450 revolutions per minute In a mixture of 1.50% by mass of 1,2-propanediol, 2.8% by mass of water and 0.4% by mass of an aqueous solution of aluminum sulfate (26.8% by mass) (based on the base polymer, respectively) Overturned it was.

  After spraying, the product temperature was increased to 150 ° C. and the reaction mixture was held at this temperature for 60 minutes and a shaft speed of 80 revolutions per minute. The resulting product was again cooled to room temperature and sieved. The surface postcrosslinked superabsorbent was obtained as a sieve classification having a particle size of 150 μm to 850 μm.

Examples 16-20
150 g of each of the superabsorbents of Example V16 are added to 0.15 g of hydrophobic precipitated silicic acid (Sipernat® D-17, Evonik Degussa GmbH, Frankfurt am Main, Germany) according to general provision I and in Table 2 below. Mixed with the indicated amount of calcium bis [monoethyl (3,5-di-t-butyl-4-hydroxybenzyl) phosphonate].

  The coated superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 2. The above example shows that even a small amount of stabilizer already stabilizes the superabsorbent according to the invention from discoloration upon aging.

^*）量はそれぞれ超吸収剤に対するもの；
^**）最初の色はＬ＝８８．７；ａ＝−０．４；ｂ＝９．０；ＨＣ６０＝６１．７ Table 2

^* ) Each amount is relative to the superabsorbent;
^** ) The first color is L = 88.7; a = −0.4; b = 9.0; HC60 = 61.7

Examples 21-25
150 g of each of the superabsorbents of Example V16 is 0.15 g of hydrophobic precipitated silicic acid (Sipernat® D-17, Evonik Degussa GmbH, Frankfurt am Main, Germany) according to general provision I and in Table 3 below. Mixed with the indicated amount of tris (2,4-di-tert-butylphenyl) phosphite.

  The coated superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 3. The above example shows that even a small amount of stabilizer already stabilizes the superabsorbent according to the invention from discoloration upon aging.

^*）量はそれぞれ超吸収剤に対するもの；
^**）最初の色はＬ＝８８．７；ａ＝−０．４；ｂ＝９．０；ＨＣ６０＝６１．７ Table 3

^* ) Each amount is relative to the superabsorbent;
^** ) The first color is L = 88.7; a = −0.4; b = 9.0; HC60 = 61.7

Example 26
Example V16 is repeated, but before the monomer solution is further cooled to 15 ° C., an additional 0.59 g of calcium bis [monoethyl (3,5-di-t-butyl-4-hydroxybenzyl) phosphonate] is still added. Was added.

Example 27
Example V16 is repeated but 0.59 g of calcium bis [monoethyl (3,5-di-t-butyl-4-hydroxybenzyl) phosphonate] is added to the gel as it is fined.

  The superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 4. The above example shows that even a small amount of stabilizer already stabilizes the superabsorbent according to the invention from discoloration upon aging.

^*）量はそれぞれアクリル酸に対するもの；
^**）最初の色はＬ＝８８．７；ａ＝−０．４；ｂ＝９．０；ＨＣ６０＝６１．７ Table 4

^* ) Quantity is relative to acrylic acid;
^** ) The first color is L = 88.7; a = −0.4; b = 9.0; HC60 = 61.7

Example V28 (comparison)
14.3 kg of an aqueous solution of sodium acrylate (a solution of 37.5% by mass in deionized water), 1.4 kg of acrylic acid, and 350 g of deionized water were mixed with triacrylate of 3 ethoxylated glycerol (Laromer® PO) 9044V, BASF SE; Ludwigshafen, Germany) 18.5 g. This solution was heated in a nitrogen-filled dripping tower (Vertropfunsturm) (180 ° C., height 12 m, diameter 2 m, gas velocity 0.1 m / s (cocurrent), diameter 40 mm, internal height 2 mm). And dropping at a rate of 32 kg / h in a dropping device (Vertropfer) equipped with a dropping plate (Vertropferplate) having 60 holes each 200 μm in diameter, the temperature being 25 ° C. Immediately before the dropping device, the monomer solution was mixed with the two initiator solutions via a static mixer. As initiator 1, a 3% by mass solution of 2,2′-azobis- [2- (2-imidazolin-2-yl) propane] dihydrochloride dissolved in deionized water was used. Used a 6.1 wt% solution of sodium peroxodisulfate dissolved in deionized water. The metering rate of initiator solution 1 was 1.462 kg / h and the metering rate of solution 2 was 0.629 kg / h. The obtained polymer particles were sieved to separate and remove the agglomerates formed in some cases. A sieve classification of 150-850 μm was obtained as the product.

Example 28
100 g of the superabsorbent of Example V28 was mixed with 0.10 g of pentaerythritol-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) according to general rule I.

Example 29
100 g of the superabsorbent of Example V28 was mixed with 0.10 g of tris- (2,4-di-t-butylphenyl) phosphite according to general rule I.

Example 30
100 g of the superabsorbent of Example V28 was added to 0.05 g of pentaerythritol-tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate) and 0.05 g of tris (2,4 -Di-tert-butylphenyl) phosphite and mixed according to general rule I.

  The superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 5. The above examples show that the superabsorbents according to the invention are clearly lighter and less discolored after aging. However, those examples also show that the mixture can synergize.

Example V31 (comparison)
14.3 kg of an aqueous solution of sodium acrylate (a solution of 37.5% by mass in deionized water), 1.4 kg of acrylic acid, and 350 g of deionized water were mixed with triacrylate of 3 ethoxylated glycerol (Laromer® PO) 9044V, BASF SE; Ludwigshafen, Germany) 6.6 g. This solution is a heated dropping tower filled with a nitrogen atmosphere (180 ° C., height 12 m, diameter 2 m, gas velocity 0.1 m / s (cocurrent), diameter 40 mm, internal height 2 mm, The dropping was performed at a rate of 32 kg / h in a dropping device equipped with a dropping plate having 60 holes each having a diameter of 200 μm, and the temperature was 25 ° C. Immediately before the dropping device, the monomer solution was mixed with the three initiator solutions via a static mixer. As initiator 1, a 3% by mass solution of 2,2′-azobis- [2- (2-imidazolin-2-yl) propane] dihydrochloride dissolved in deionized water was used. Used a 6.1% by mass solution of sodium peroxodisulfate in deionized water, and as initiator 3, a 3% by mass solution of ascorbic acid in deionized water was used. The metering rate of initiator solution 1 was 0.548 kg / h, the metering rate of solution 2 was 0.449 kg / h, and the metering rate of solution 3 was 0.183 kg / h. The obtained polymer particles were sieved to separate and remove the agglomerates formed in some cases. A sieve classification of 150-850 μm was obtained as the product.

Example V32 (comparison)
14.3 kg of an aqueous solution of sodium acrylate (a solution of 37.5% by mass in deionized water), 1.4 kg of acrylic acid, and 350 g of deionized water were mixed with triacrylate of 3 ethoxylated glycerol (Laromer® PO) 9044V, BASF SE; Ludwigshafen, Germany) 6.6 g. This solution is a heated dropping tower filled with a nitrogen atmosphere (180 ° C., height 12 m, diameter 2 m, gas velocity 0.1 m / s (cocurrent), diameter 40 mm, internal height 2 mm, The dropping was performed at a rate of 32 kg / h in a dropping device equipped with a dropping plate having 60 holes each having a diameter of 200 μm, and the temperature was 25 ° C. Immediately before the dropping device, the monomer solution was mixed with the three initiator solutions via a static mixer. As initiator 1, a 3% by mass solution of 2,2′-azobis- [2- (2-imidazolin-2-yl) propane] dihydrochloride dissolved in deionized water was used. Uses a 6.1% by weight solution of sodium peroxodisulfate in deionized water, and the initiator 3 includes 2-hydroxy-2-sulfinatoacetic acid sodium salt, 2-hydroxy-2- Using a 3% by weight solution of a mixture of disodium salt of sulphonatoacetic acid and sodium bisulfite (Brugegolit® FF7, L. Brueggemann KG, Salzstrasse 131,74076 Heilbrunn, Germany) did. The metering rate of initiator solution 1 was 0.548 kg / h, the metering rate of solution 2 was 0.449 kg / h, and the metering rate of solution 3 was 0.183 kg / h. The obtained polymer particles were sieved to separate and remove the agglomerates formed in some cases. A sieve classification of 150-850 μm was obtained as the product.

Example 31
100 g of the superabsorbent of Example V31 was mixed with 0.10 g of calcium-bis [monoethyl (3,5-di-t-butyl-4-hydroxybenzyl) phosphonate] according to general rule I.

Example 32
100 g of the superabsorbent of Example V32 was mixed with 0.10 g of diethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate according to general rule I.

  The superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 6. The above examples show that the superabsorbents according to the invention are clearly lighter and less discolored after aging.

Example V33 (comparison)
In a Pflugschar® vane dryer with a 5 L capacity with heating / cooling jacket (manufacturer: Gebr. Loedige Maschinenbau GmbH, Eisener-Strasse 7-9, 33102 Paderborn, Germany; type VT 5R-MK) 478 g of water, 244.3 g of acrylic acid, 37.3 wt% sodium acrylate solution (not containing up to 100 mol% neutralized acrylic acid, ie free acrylic acid or free sodium salt) 1924. 9 g, 16.0 g of calcium carbonate and 2.52 g of triethoxylated glycerol triacrylate (Laromer® PO 9044V, BASF SE, Ludwigshafen, Germany) are charged with nitrogen. Inactivated for 20 minutes while spraying. The reactor shaft was continuously rotated at 96 revolutions per minute. At that time, the reaction mixture was cooled externally so that subsequent initiator additions could be made at about 20 ° C. Finally, while stirring in a kneader, 2.139 g of sodium persulfate (dissolved in 12.12 g of water), 0.046 g of ascorbic acid (dissolved in 9.12 g of water), and 30% by mass 0.127 g of an aqueous hydrogen peroxide solution (diluted with 1.15 g of water) was added in succession. When the reaction started quickly and the internal temperature reached 30 ° C., the jacket was heated with a heat transfer medium heated to 80 ° C. in order to carry out the reaction as adiabatic as much as possible. After reaching the maximum temperature, it was cooled again (coolant with −12 ° C.) and the resulting gel was cooled to below 50 ° C. and then removed. The gel was then dried in a laboratory drying cabinet at 160 ° C. for 1 hour. The product was then ground and a 150-700 μm sieve classification was obtained.

  This base polymer is used for surface postcrosslinking at room temperature in a Pflugschar® mixer (manufacturer: Gebr. And using a two-substance spray nozzle at a shaft speed of 450 revolutions per minute, N- (2-hydroxyethyl) -2-oxazolidinone 0.125% by weight, water 1.5% by weight, 1, 3 A mixture consisting of 1.5% by weight of propanediol, 0.003% by weight of sorbitan monococoate (“Span® 20”) and 2.8% by weight of a 25% by weight aqueous solution of aluminum lactate (each basis) With respect to the polymer). After spraying, the product temperature was raised to 175 ° C. and the reaction mixture was held at this temperature for 80 minutes and at a shaft speed of 80 revolutions per minute. The resulting product was again cooled to room temperature and sieved. The surface postcrosslinked superabsorbent was obtained as a sieve classification having a particle size of 150 μm to 710 μm.

Example 33
100 g of the superabsorbent of Example V26 was mixed with 0.050 g of 2,2′-ethylidenebis [4,6-bis (1,1-dimethylethyl) phenol] according to general rule I.

Example 34
Example V33 was repeated, but upon surface postcrosslinking, the base polymer was additionally coated with 0.2% by weight of tris- (2,4-di-t-butylphenyl) phosphite relative to the base polymer. .

Example 35
Example V33 (comparison) was repeated, but after the internal temperature reached 60 ° C. during the polymerization, the reaction mixture was further subjected to 1.2 g of pentaerythritol-tetrakis (3- (3,3) in a Pfluschchar® blade dryer. 5-di-t-butyl-4-hydroxyphenyl) propionate) was added.

  The superabsorbent thus produced was subjected to an aging test. These results are summarized in Table 7. The above examples show that the superabsorbents according to the present invention are clearly lighter after aging and less discolored, without compromising the absorption properties.

Claims (11)

Superabsorbent containing a stabilizer against at least one discoloration selected from phenol, phosphonic acid (HP (O) (OH) ₂ ), phosphorous acid (H ₃ PO ₃ ) and salts and esters of said acids Agent.   Super absorbent according to claim 1, characterized in that it contains calcium, strontium or barium.   The superabsorbent according to claim 1 or 2, further comprising at least one compound selected from sulfinic acid derivatives and / or at least one inorganic water-insoluble particulate solid. .   4. A crosslinked partially neutralized polymer of at least one ethylenically unsaturated, monomer having at least one acid group, according to any one of claims 1-3. Super absorbent.   Superabsorbent according to any one of claims 1 to 4, characterized in that the monomer is acrylic acid.   Superabsorbent according to any one of claims 1 to 5, characterized in that it is surface postcrosslinked.   Superabsorbent according to any one of claims 1 to 5, characterized in that the stabilizer is added in a substantially undissolved form. A process for producing a superabsorbent as defined in any one of claims 1 to 7, wherein the superabsorbent comprises phenol, phosphinic acid (H ₃ PO ₂ ), during or after its production, Said method of adding a stabilizer against discoloration selected from phosphonic acid (HP (O) (OH) ₂ ), phosphorous acid (H ₃ PO ₃ ) and salts and esters of said acids.   9. A process according to claim 8, characterized in that the stabilizer is added in substantially undissolved form.   An article for absorbing liquids, comprising a superabsorbent as defined in any one of claims 1-7.   A method for producing an article for absorption of a liquid, characterized in that the superabsorbent as defined in any one of claims 1 to 7 is used in the production.