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WO2013144026A1 - Superabsorbant résistant à la décoloration - Google Patents

Superabsorbant résistant à la décoloration Download PDF

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Publication number
WO2013144026A1
WO2013144026A1 PCT/EP2013/056120 EP2013056120W WO2013144026A1 WO 2013144026 A1 WO2013144026 A1 WO 2013144026A1 EP 2013056120 W EP2013056120 W EP 2013056120W WO 2013144026 A1 WO2013144026 A1 WO 2013144026A1
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WO
WIPO (PCT)
Prior art keywords
phosphonic acid
acid derivative
optionally
weight
acid
Prior art date
Application number
PCT/EP2013/056120
Other languages
German (de)
English (en)
Inventor
Norbert Herfert
Thomas Daniel
Original Assignee
Basf Se
Basf Schweiz Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Basf Se, Basf Schweiz Ag filed Critical Basf Se
Priority to KR1020147030638A priority Critical patent/KR20140144259A/ko
Priority to CN201380017540.4A priority patent/CN104271622B/zh
Publication of WO2013144026A1 publication Critical patent/WO2013144026A1/fr

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Classifications

    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08FMACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/04Acids; Metal salts or ammonium salts thereof
    • C08F220/06Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61LMETHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L15/00Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
    • A61L15/16Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
    • A61L15/42Use of materials characterised by their function or physical properties
    • A61L15/56Wetness-indicators or colourants
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00Use of organic ingredients
    • C08K5/0008Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/0025Crosslinking or vulcanising agents; including accelerators
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00Use of organic ingredients
    • C08K5/0008Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/005Stabilisers against oxidation, heat, light, ozone
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00Use of organic ingredients
    • C08K5/04Oxygen-containing compounds
    • C08K5/09Carboxylic acids; Metal salts thereof; Anhydrides thereof
    • C08K5/098Metal salts of carboxylic acids
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00Use of organic ingredients
    • C08K5/49Phosphorus-containing compounds
    • C08K5/51Phosphorus bound to oxygen
    • C08K5/53Phosphorus bound to oxygen bound to oxygen and to carbon only
    • C08K5/5317Phosphonic compounds, e.g. R—P(:O)(OR')2

Definitions

  • the present invention relates to a color-stable superabsorber, to a process for its preparation and to its use and to hygiene articles containing it.
  • a color-stable superabsorber is to be understood as meaning a superabsorber which does not discolor or only in a comparatively small extent when stored under elevated temperature and atmospheric humidity.
  • Superabsorbents are known. Also, for such materials, terms such as “high swellable polymer” “hydrogel” (often used for the dry form), “hydrogel-forming polymer”, “water-absorbent polymer”, “absorbent gelling material”, “swellable resin”, “water-absorbent resin”, These are crosslinked hydrophilic polymers, in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose or starch ethers, crosslinked carboxymethylcellulose partially cross-linked polyalkylene oxide or natural products swellable in aqueous liquids, such as guar derivatives, with water-absorbing polymers based on partially neutralized acrylic acid being the most widespread.
  • the essential properties of superabsorbents are their ability to multiply their own weight of aqueous liquid absorb the fluid and even under some pressure not to give the liquid again.
  • the superabsorber which is used in the form of a dry powder, transforms into a gel when it absorbs liquid, and accordingly turns into a hydrogel during normal water absorption.
  • Crosslinking is essential for synthetic superabsorbents and an important difference to conventional pure thickeners, as it leads to the insolubility of the polymers in water. Soluble substances would not be useful as superabsorbent.
  • the most important application of superabsorbents is the absorption of body fluids.
  • Superabsorbents are used, for example, in infant diapers, adult incontinence products or feminine hygiene products.
  • Other fields of application are, for example, the water-retaining agents in agricultural horticulture, as water storage for protection against fire, for liquid absorption in food packaging or, more generally, for the absorption of moisture.
  • Superabsorbents can absorb several times their own weight in water and retain them under some pressure.
  • such a superabsorbent has a CRC (Centrifuge Retention Capacity, see below for measurement method) of at least 5 g / g, preferably at least 10 g / g, and most preferably
  • a "superabsorber” may also be a mixture of materially different individual superabsorbers or a mixture of components that are only show in combination superabsorbent properties, it depends less on the material composition than on the superabsorbent properties.
  • Important for a superabsorbent is not only its absorption capacity, but also the ability to retain fluid under pressure (retention, usually expressed as "absorption under load”("AUL") or “absorption against pressure"("AAP”), measurement method, see below ) as well as the permeability, ie the ability to carry over the liquid in the swollen state (usually expressed as "Saline Flow Conductivity"("SFC”), measuring method see below).
  • Swollen gel can hinder the fluid transfer to yet unswollen superabsorbent ("gel blocking”) .
  • Gels with only low gel strength are under an applied pressure (body pressure) deformable, clog pores in the superabsorbent / cellulose fiber absorbent body and thereby prevent the fluid transfer to not yet or not fully swollen superabsorber and the fluid absorption by this not or not fully swollen superabsorber.
  • a higher gel strength is usually due to a higher degree of crosslinking
  • An elegant method for increasing the gel strength is compared to increasing the degree of crosslinking on the surface of the SAP particles
  • dried superabsorbent particles with average crosslinking density are usually subjected to additional crosslinking in a thin surface layer of their particles.
  • Acrylic acid-based superabsorbents which are most commonly used in the market, are prepared by free radical polymerization of acrylic acid in the presence of a crosslinker (the "internal crosslinker"), the acrylic acid before, after or partly before, partly after polymerization is neutralized to a certain extent, usually by adding alkali, usually an aqueous sodium hydroxide solution
  • the polymer gel thus obtained is comminuted (depending on the polymerization reactor used, this can take place simultaneously with the polymerization) and dried (the "base polymer” or “base polymer”) is usually postcrosslinked to the surface of the particles by reacting with other crosslinkers, such as organic crosslinkers or polyvalent cations, for example, aluminum (usually employed as aluminum sulfate) or both, to the particle interior to produce a more crosslinked surface layer.
  • crosslinkers such as organic crosslinkers or polyvalent cations, for example, aluminum (usually employed as aluminum sulfate) or both, to the particle interior to produce a more crosslinked
  • a common problem with superabsorbents is discoloration, which occurs when storing under higher temperature or higher humidity. Such conditions often occur during storage of superabsorbers in tropical or subtropical countries. Under such conditions, superabsorbents tend to yellow, they may even take on brown or almost black coloring. This discoloration of the actually colorless superabsorbent powder is unsightly and undesirable because it is particularly visible in the desired thin hygiene products and consumers reject unsightly hygiene products.
  • the cause of the discoloration is not fully understood, but reactive compounds such as residual monomers from the polymerization, the use of some initiators, impurities of the monomer or of the neutralizing agent, surface postcrosslinkers or stabilizers of the monomers used appear to play a role.
  • additives for Improved Handling teaches that the tendency to caking can be counteracted by additives known as common additives oils , as also used in hygroscopic fertilizers, polymeric soaps as drying aids for acrylamide copolymers, and particulate silica in combination with polyols or polyalkylene glycols as flow aids for poly (acrylamide) polymers and copolymers. Furthermore, quaternary surfactants are mentioned, alone or in combination with other additives, to reduce dust formation, which is a disadvantage of the addition of silica. All of these additives can be added in a variety of types of commercial mixers.
  • WO 98/48857 A1 describes superabsorbers which are crosslinked with Al, Fe, Zr, Mg or Zn cations and then mixed with a liquid such as water, mineral oil or polyols.
  • WO 01/74913 A1 relates to the regeneration of superabsorbers, specifically the increase of a reduced permeability by abrasion, by adding a solution of an at least trivalent cation, typically an aqueous solution of aluminum sulfate.
  • No. 6,620,889 B1 discloses superabsorbents which are surface-post-crosslinked with a combination of a polyol and a polyvalent metal salt in aqueous solution.
  • the anion of the salt may be chloride, bromide, sulfate, carbonate, nitrates, phosphate, acetate or lactate.
  • the use of aluminum sulfate is preferred.
  • a base polymer is treated with a permeability improver selected from silicon-oxygen compounds, salts of polyvalent, in particular trivalent cations or mixtures thereof.
  • the salt of a trivalent cation is preferably an aluminum salt selected from a variety of salts including aluminum lactate, oxalate, citrate, glyoxylate, succinate, tartrate, and other organic and inorganic aluminum salts.
  • WO 2005/108472 A1 discloses a process comprising the treatment of a base polymer with a water soluble salt of a polyvalent metal and an organic acid or its salt.
  • the salt of a polyvalent metal is preferably aluminum sulfate.
  • the organic acid or its salt is selected from a variety of acids including citric acid, glyoxylic acid, glutaric acid, succinic acid, tartaric acid, lactic acid and the alkali or ammonium salts of these acids.
  • WO 00/55245 A1 teaches the stabilization of superabsorbents against discoloration by treatment with an inorganic reducing agent and optionally a metal salt, such as an alkaline earth salt, which is added after the polymerization.
  • the inorganic reducing agent is typically a hypophosphite, phosphite, bisulfite or sulfite.
  • the metal salt is typically colorless (the colorless property is often simply called "white"), phosphate, acetate or lactate, but not halide.
  • WO 2006/058 682 A1 discolorations of superabsorbers are avoided if the drying and the postcrosslinking reaction are carried out in an atmosphere which is substantially free of oxidizing gases.
  • WO 2009/060 062 A1 or WO 2010/012 762 A2 teach the addition of sulfinic acid derivatives to superabsorbers in order to stabilize them against discoloration.
  • EP 1 199 315 A2 teaches the use of a redox initiator system for initiating a polymerization reaction, wherein the redox initiator system contains as reducing part a sulfinic acid or a sulfinate, in particular 2-hydroxysulfinatoacetic acid or a salt thereof.
  • WO 99/18 067 A1 discloses certain hydroxy or aminoalkyl or aryl-sulfinic acid derivatives or mixtures thereof and their use as reducing agents which do not cleave formaldehyde.
  • WO 2004/084 962 A1 relates to the Use of these sulfinic acid derivatives as the reducing part of a redox initiator for the polymerization of partially neutralized acrylic acid to superabsorbers.
  • EP 668 080 A2 teaches the addition of inorganic acids, organic acids or polyamino acids to superabsorbers, wherein among the stated inorganic acids are also phosphorus-based acids.
  • US 2005/0 085 604 A1 discloses the addition of chelating agents as well as oxidizing or reducing agents to superabsorbers, wherein among the chelating agents are also phosphorus-containing.
  • US 2005/0 272 600 A1 relates to the addition of ion blockers to superabsorbents, which also include organic phosphorus compounds.
  • (1-Hydroxiethan-1, 1-diyl) bisphosphonic acid is one of the examples mentioned.
  • EP 2,112,172 A1 adds an organic phosphorus compound to the monomer solution which is polymerized to the superabsorber, (1-hydroxyethane-1,1-diyl) bisphosphonic acid is mentioned, ethylenediamine tetra (methylenephosphonic acid) is the most preferred compound.
  • US 2009/0 275 470 A1 teaches to add to superabsorbers both chelating agents and preferably inorganic phosphorus compounds, where the chelating agent may also be a phosphorus compound such as, for example, (1-hydroxyethane-1,1-diyl) bisphosphonic acid or ethylenediamine tetra (methylenephosphonic acid) , Such compounds are also added according to the teaching of WO 2006/109 882 A1 superabsorbers as chelating agents, in addition to phosphorus-containing compounds and sulfur-containing reducing agents are used in different process stages.
  • the chelating agent may also be a phosphorus compound such as, for example, (1-hydroxyethane-1,1-diyl) bisphosphonic acid or ethylenediamine tetra (methylenephosphonic acid)
  • Such compounds are also added according to the teaching of WO 2006/109 882 A1 superabsorbers as chelating agents, in addition to phosphorus-containing compounds and sulfur-containing reducing agents
  • inorganic powders to reduce caking tendency ie as "anticaking agent”
  • inorganic powders to reduce caking tendency ie as "anticaking agent”
  • the swelling of the superabsorbent presumably under pressure presupposes that superabsorbents treated in this way sometimes deteriorate less, presumably because the inorganic particle-coated superabsorbent particles are less able to slide past each other during pumping or swelling under pressure, but this in turn increases the permeability for liquid in the swollen gel, because open pores and Passages, which may also be a desirable effect, dust formation, poor conveyability and reduced swelling under pressure can
  • the dust-repellents usually used for polyols and polyalkylene glycols not only bind dust but also act as lubricants between the superabsorbent particles Is a problem, the addition of silica powder (English "silica”) alone or in combination with dedusting agents such
  • Another object is to find other or even better superabsorbers stabilized against discoloration, in particular against yellowing or browning when stored under elevated temperature and / or elevated air humidity, which also show the lowest possible tendency to cake, as well as processes for their preparation.
  • the performance characteristics of the superabsorber in particular its ability to absorb liquid, even under pressure, as well as its ability to transfer liquid, are not or at least not significantly impaired.
  • Further objects of the invention are uses of this superabsorbent, such as sanitary products containing this superabsorbent and processes for their preparation.
  • the object has been achieved by a superabsorbent whose surfaces are complexed with polyvalent metal ions and which contains at least one phosphonic acid derivative, wherein the molar ratio between polyvalent metal and phosphonic acid derivative is at most 1.2 / n, where n is the number of phosphonic acid groups in the phosphonic acid derivative.
  • a process has been found for the preparation of the superabsorbent according to the invention, namely by polymerization of an aqueous monomer solution which comprises a) at least one ethylenically unsaturated, acid group-carrying monomer, which is optionally present at least partly as a salt,
  • the superabsorbers according to the invention show surprisingly good stability against discoloration and surprisingly low tendency to cake without their use properties such as CRC, AUL or SFC being significantly impaired.
  • articles have been found for the absorption of liquids, in particular hygiene articles for the absorption of liquid body exudates or liquid portions of body exudates, which are characterized in that they contain the superabsorber according to the invention.
  • processes have been found for the preparation of such articles for the absorption of liquids, which are characterized in that they are added to the inventive superabsorbent in the preparation of these articles.
  • the surfaces of the superabsorbent according to the invention are complexed with polyvalent metal ions.
  • Superabsorbents are predominantly produced in the form of powders, in most cases complexing of their surfaces means complexing of the particle surfaces.
  • superabsorbents are also produced in other forms, for example as foams, fibers, rolled goods or as superabsorber particles fixed on a carrier, for example a nonwoven.
  • the surfaces of such superabsorbents can also be complexed with polyvalent metal ions.
  • the complexation of the surface of superabsorbents is known per se.
  • complexing is understood to mean surface postcrosslinking with polyvalent metal ions in order to delineate them from surface postcrosslinking with postcrosslinkers which form covalent bonds with polar groups on the surface of the SAP particles
  • Examples of complexing of useful divalent metal cations are in particular the divalent cations of metals of groups 2 (in particular Mg, Ca, Sr, Ba), 7 (in particular Mn), 8 (in particular Fe), 9 (in particular Co), 10 (in particular Ni), 1 1 (in particular Cu) and 12 (in particular Zn) of the Periodic Table of the Elec- mente.
  • Examples of useful trivalent metal cations are, in particular, the trivalent cations of metals of groups 3 including the lanthanides (in particular Sc, Y, La, Ce), 8 (in particular Fe), 11 (in particular Au) and 13 (in particular Al) of the Periodic Table of the Elements .
  • Examples of suitable tetravalent cations are, in particular, the tetravalent cations of metals of the lanthanides (in particular Ce) and of group 4 (in particular Ti, Zr, Hf) of the Periodic Table of the Elements.
  • the metal cations can be used alone or mixed with each other. Particularly preferred is the use of trivalent metal cations. Very particularly preferred is the use of aluminum cations.
  • Polyvalent metal ions are generally added in an amount of at least 0.008 wt%, preferably at least 0.015 wt%, and more preferably at least 0.020 wt%, and generally at most 0.15 wt%, preferably at most 0.10 Wt .-% and particularly preferably at most 0.05 wt .-%, each calculated as metal and added based on the total amount of the anhydrous superabsorbent.
  • the superabsorber according to the invention is preferably postcrosslinked on its surface, in addition to complexing, also with postcrosslinkers which form covalent bonds with polar groups on the surface of the superabsorbent particles.
  • the superabsorbent according to the invention contains at least one phosphonic acid derivative.
  • phosphonic acid itself is to be understood as a phosphonic acid derivative.
  • Phosphonic acid derivatives are compounds of the general formula (I) derived from phosphonic acid with the general formula (HP (O) (OH) 2):
  • R is -P (O) (OH) 2 (I) wherein R 1 is an optionally substituted organic radical. Salts and / or esters thereof as well as mixtures of such phosphonic acid derivatives, salts and / or esters are also usable. Examples are monoalkylphosphonic acids and monoalkenylphosphonic acids such as laurylphosphonic acid and stearylphosphonic acid.
  • Preferred phosphonic acid derivatives are those in which R 1 is a diyl radical bearing two phosphonic acid radicals, in particular a 1-amino-1, 1-diyl radical or a 1-hydroxy-1, 1-diyl radical, as in 1-hydroxyalkyl-1, 1 -diyl-bisphosphonic acid, wherein in these compounds alkyl is a Ci-C25 radical, with ethyl being particularly preferred.
  • the most preferred phosphonic acid derivative is (1-hydroxyethane-1,1-diyl) bisphosphonic acid or a salt with a metal M thereof, wherein M represents a hydrogen atom, an ammonium ion, a monovalent metal ion or one equivalent of a divalent metal ion of Groups 1, 2 , 8, 9, 10, 12 or 14 of the Periodic Table of the Elements, in particular the sodium salt, the potassium salt, the disodium salt, the dipotassium salt or the sodium-potassium salt.
  • phosphonic acid derivatives are those in which R 1 is an amino-substituted alkyl radical, in particular an amino-substituted methylene radical, such as in ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and [nitrilotris (methylene)] tris (phosphonic acid).
  • R 1 is an amino-substituted alkyl radical, in particular an amino-substituted methylene radical, such as in ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and [nitrilotris (methylene)] tris (phosphonic acid).
  • Such phosphonic acid derivatives are known and are prepared in the usual way, for example by Michaelis-Arbusov reaction, quasi-Mannich reaction of the free phosphonic acid (tautomeric with phosphorous acid) with formaldehyde and oligo- ethyleneamines or by acylation of phosphonic acid with carboxylic anhydrides or nitriles.
  • Their main use is as phosphate substitutes in detergents. Therefore, they are also common commercial products and, for example, under the brand CUB len ® Zschimmer & Schwarz GmbH & Co KG Mohlsdorf, Chemnitztal Found 1, 09217 Burghot, Germany available.
  • the phosphonic acid derivative of the formula (I) is generally used in an amount of at least 0.01% by weight, preferably at least 0.1% by weight and more preferably at least 0.2% by weight and generally not more than 1, 9 wt .-%, preferably at most 1, 3 wt .-% and particularly preferably at most 0.6 wt .-%, in each case based on the total amount of the anhydrous superabsorbent added.
  • the superabsorber according to the invention contains such amounts of polyvalent metal ions and phosphonic acid derivative that a molar ratio of at most 1.2 / n, where n is the number of phosphonic acid groups in the phosphonic acid derivative, is not exceeded. In this calculation, it does not matter whether the phosphonic acid groups are present as free acid groups or as a salt, it alone decides the molar ratio between polyvalent metal and phosphorus atoms in the phosphonic acid groups of Phopshonkladerivate. After the superabundance Sorber contains both polyvalent metal ion as well as phosphonic acid, this ratio must of course be finite, that is different from 0.
  • Phosphonobutane-1,2,4-tricarboxylic acid is the upper limit of the molar ratio between metal salt and phosphonic acid derivative 1, 2.
  • phosphonic acid derivatives having three phosphonic acid groups (n 3), for example nitrilo-tris (methylenephosphonic acid), the upper limit of the molar ratio between metal salt and phosphonic acid derivative is accordingly 0.4.
  • phosphonic acid derivatives having four phosphonic acid groups (n 4), such as ethylenediaminetetra (methylenephosphonic acid), cyclohexanediaminetetra (methylenephosphonic acid), tetramethylenediaminetetra (methylenephosphonic acid), hexamethylenediaminetetra (methylenephosphonic acid) or polymethylenediaminetetra (methylenephosphonic acid), the upper limit of the molar ratio between Metal salt and phosphonic acid derivative accordingly 0.3.
  • the superabsorbent according to the invention optionally further contains a water-insoluble inorganic powder.
  • a water-insoluble inorganic powder Preferably, it contains a water-insoluble inorganic powder. Basically, any inorganic water-insoluble powder is suitable for this purpose.
  • Examples are generally solid, chemically inert (ie, superabsorbent non-interfering) substances such as oxides, oxide hydroxides, hydroxides, sulfates, carbonates, zeolites, inorganic pigments, minerals or clays.
  • Clays are silicates or aluminosilicates which are usually obtained by mining of natural sediments and occasionally also their further processing. However, some clays are made synthetically.
  • inorganic water-insoluble powders examples include sulfates such as magnesium sulfate or barium sulfate, carbonates such as calcium carbonate, magnesium carbonate, zinc carbonate or dolomite, silicates such as calcium silicate or magnesium silicate, carbides such as perlite or silicon carbide, diatomaceous earth or fly ash.
  • sulfates such as magnesium sulfate or barium sulfate
  • carbonates such as calcium carbonate, magnesium carbonate, zinc carbonate or dolomite
  • silicates such as calcium silicate or magnesium silicate
  • carbides such as perlite or silicon carbide, diatomaceous earth or fly ash.
  • Suitable oxides are the metal oxides of Groups 2 to 14 of the Periodic Table of the Elements, including the lanthanides and actinides.
  • 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 (boehmite and others), silicon dioxide, Tin oxide, lead oxide, lanthanum oxide or cerium oxide.
  • the use of a trivial name for metal oxides should not be a statement about the valence of the metal and the stoichiometry of the oxide.
  • one element forms multiple oxides, generally all are suitable.
  • the oxide is selected according to considerations specific to the individual case, for example by price, toxicity, stability or color.
  • particularly suitable oxides are titanium dioxide, in particular in the anatase or rutile modifications, precipitated or pyrolysis-produced silica and zinc oxide. It is also possible to use mixtures of these substances.
  • Pyrogenic metal oxides are those which have been produced by a pyrogenic process, ie by pyrolysis and not like many other oxides by precipitation.
  • Pyrogenic processes are processes in which an oxide is prepared by flame oxidation or flame hydrolysis of a suitable starting compound in a flame, in flame hydrolysis usually a blast gas flame.
  • Pyrogenic metal oxides are usually produced by flame oxidation of a vaporizable metal compound or by flame hydrolysis of a vaporizable metal compound in an oxyhydrogen flame.
  • the vaporizable metal compound typically used is the (covalent, anhydrous) chloride (ie, no salt) in the oxyhydrogen gas flame this results in fumed metal oxide and hydrogen chloride.
  • Methods for the production of pyrogenic metal oxide are known and pyrogenic metal oxides are common commercial goods. Fumed silica is, for example, under the brand AEROXIDE ® Alu Evonik Industries AG, Inorganic Materials, Rodenbach Cvice 4, 63457 Hanau-Wolfgang, Germany, for example, available under the trademark AEROSIL ® and fumed alumina. In comparison with metal oxides produced by precipitation, pyrogens are generally pure, finely divided and of high surface area.
  • precipitation produced metal oxides are commercially available goods, as for example by precipitation produced silicon dioxide under the brand SIPERNAT ® from Evonik Industries AG, Inorganic Mate rials, Rodenbach Clice 4, 63457 Hanau-Wolfgang, Germany, available.
  • the water-insoluble inorganic powders can also be rendered hydrophobic by suitable surface treatment and are often offered by manufacturers in both hydrophobized and hydrophilic form. In the context of this invention, the use of hydrophilic water-insoluble inorganic powders is preferred.
  • Pyrogenic alumina typically has a BET surface area of at least 20 m 2 / g, preferably at least 30 m 2 / g and more preferably at least 50 m 2 / g and typically at most 200 m 2 / g, preferably at most 180 m 2 / g and in a particularly preferred form at most 150 m 2 / g.
  • Pyrogenic silicon oxide typically has a BET surface area of at least 50 m 2 / g, preferably at least 100 m 2 / g and particularly preferably at least 150 m 2 / g and typically of at most 400 m 2 / g, preferably at most 350 m 2 / g and in a particularly preferred form at most 300 m 2 / g.
  • the BET surface area is the specific surface area of a solid as determined by the method given by Stephen Brunauer, Paul Hugh Emmett, and Edward Teller, for the first time in J. Am. Chem. Soc., 60 (1938) 309, and is determined according to DIN ISO 9277: 2003-05 ("Determination of the specific surface area of solids by gas adsorption by the BET method")
  • DIN ISO 9277: 2003-05 Determination of the specific surface area of solids by gas adsorption by the BET method
  • DIN 66132 1975- In the case of deviations, the first-mentioned standard applies in the context of this invention
  • the BET method is one of the field of porous solids, including catalysts, a well-known and routinely used method.
  • the inorganic water-insoluble solid is particulate, it is in powder form.
  • the mean particle size is typically in the range of at least 0.001 ⁇ , preferably at least 0.002 ⁇ , more preferably at least 0.005 ⁇ , and most preferably at least 0.01 ⁇ and generally at most 500 ⁇ , preferably at most 200 ⁇ , in particular preferred form at most 100 ⁇ and in a very particularly preferred form of at most 50 ⁇ .
  • the particles themselves may be aggregates or agglomerates of smaller primary particles.
  • the particle size can be determined by sieve analysis, but more flexible and therefore preferred is the determination of the particle size by means of laser diffraction technique. These methods are well known and routinely performed on suitable and commercially available equipment.
  • the water-insoluble inorganic powder is added to the SAP in an amount of at least 0.005 wt.%, Preferably at least 0.03 wt.%, More preferably at least 0.05 wt.%, And generally at most 6 , 0 wt .-%, preferably at most 1, 0 wt .-% and in a particularly preferred form at most 0.5 wt .-% added, in each case based on the total weight of the anhydrous superabsorbent with inorganic powder.
  • Sulfonic acid derivatives in the context of this invention are compounds of general formula (II) derived from sulfonic acid having the general formula R-SO 2 -OH:
  • M represents a hydrogen atom, an ammonium ion, a monovalent metal ion or one equivalent of a divalent metal ion of Groups 1, 2, 8, 9, 10, 12 or 14 of the Periodic Table of the Elements;
  • R 2 is OH or NR 5 R 6 , wherein R 5 and R 6 are independently H or d-Ce-alkyl;
  • R 3 is H or an alkyl, alkenyl, cycloalkyl or aryl group, this group optionally having 1, 2 or 3 substituents which are selected independently of one another from C 1 -C 6 -alkyl, OH, 0-C 1 -C 6 -alkyl, Alkyl, halogen and CF3; and R 4 is COOM, SO 3M, COR 5 , CONR 5 R 6 or COOR 5 , wherein M, R 5 and R 6 have the meanings given above or, when R 3 is aryl, which is optionally substituted as indicated above, also stands for H,
  • alkyl represents straight-chain or branched alkyl groups which preferably have 1-6, in particular 1-4, carbon atoms.
  • alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl, etc.
  • Alkenyl represents straight-chain or branched alkenyl groups which preferably have 3-8 carbon atoms, in particular 3-6 carbon atoms.
  • a preferred alkenyl group is the allyl group.
  • Cycloalkyl is in particular C 1 -C 6 -cycloalkyl, with cyclopentyl and cyclohexyl being particularly preferred.
  • Aryl also in aralkyl is preferably phenyl or naphthyl. When the aryl group is a phenyl group and is substituted, it preferably has two substituents. These are available in particular in the 2- and / or 4- position.
  • Halogen is F, Cl, Br and I, preferably Cl and Br.
  • M is preferably an ammonium, alkali metal or one equivalent of an alkaline earth metal or zinc ion.
  • Suitable alkali metal ions are in particular sodium and potassium ions, and suitable alkaline earth metal ions are, above all, magnesium, strontium and calcium ions.
  • R 2 is preferably a hydroxy or amino group.
  • R 3 is preferably a hydrogen atom or an alkyl or aryl group which may be substituted as above. It preferably has one or two hydroxyl and / or alkoxy substituents.
  • R 4 is preferably either COOM or COOR 5 (M and R 5 have the meanings given above) or, when R 3 is aryl, which may be substituted as indicated above, also for a hydrogen atom.
  • the superabsorbent contains compounds of the above formula (II) wherein M is an alkali metal ion or one equivalent of an alkaline earth metal or zinc ion; R 2 is a hydroxy or amino group; R 3 is H or alkyl and R 4 is COOM or COOR 5 , where when R 4 is COOM, M in this COOM moiety is H, an alkali metal ion or one equivalent of an alkaline earth metal ion, and when R 4 is COOR 4 R 5 is C 1 -C 6 -alkyl.
  • Particularly preferred compounds of the above formula (II) are 2-hydroxy-2-sulfonate acetic acid and its salts, in particular its sodium salts, including in particular its disodium salt.
  • the superabsorbent optionally contains compounds of the above formula (II) wherein M is an alkali metal ion or one equivalent of an alkaline earth metal or zinc ion; R 2 is a hydroxy or amino group; R 3 is aryl which is optionally substituted as indicated above, in particular hydroxyphenyl or C 1 -C 4 -alkoxyphenyl; and R 3 is a hydrogen atom.
  • Groups 1 H, Li, Na, K, Rb, Cs, Fr
  • 2 Be, Mg, Ca, Sr, Ba, Ra
  • 8 Fe, Ru, Os
  • 9 Co, Rh, Ir
  • 10 Ni, Pd, Pt
  • 12 Zn, Cd, Hg
  • 14 C, Si, Ge, Sn, Pb
  • the international nomenclature body responsible for chemistry corresponds to groups la, IIa, IIb, IVa and VIIIb in the numbering used by CAS (Chemical Abstracts Service, 2540 Olentangy River Road, Columbus, OH 43202, USA, www.cas.org).
  • the sulfonic acid derivatives of the above formula (II) can be used in pure form, but optionally also in admixture with the sulfite of the corresponding metal ion and the corresponding sulfinic acid derivative.
  • the preparation of such mixtures is known and, for example, in
  • WO 99/18 067 A1 They are also common commercial products and, for example, in the form of mixtures of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite of L.
  • Brüggemann KG (Salz No 131, 74076 Heilbronn, Germany, www.brueggemann.com) available under the names Brüggolit ® FF6M or Brüggolit ® FF7, alternatively Bruggolite ® FF6M or Bruggolite ® FF7.
  • the use of the sulfonic acid derivatives in pure form is preferred.
  • sulfonic acid derivatives The preparation of sulfonic acid derivatives is well known; it is carried out, for example, by sulfoxidation, sulfochlorination with subsequent hydrolysis or by sulfonation of appropriate starting compounds. They are also common commodities.
  • the superabsorbents according to the invention are obtainable by the process according to the invention.
  • the process according to the invention for the preparation of superabsorbents is a process for the aqueous solution polymerization of a monomer mixture comprising: a) at least one ethylenically unsaturated monomer bearing at least one acid group, which is optionally present at least partially as a salt,
  • the monomers a) are preferably water-soluble, i. the solubility in water at 23 ° C. is typically at least 1 g / 100 g of water, preferably at least 5 g / 100 g of water, more preferably at least 25 g / 100 g of water, most preferably at least 35 g / 100 g of water.
  • Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids or their salts, such as acrylic acid, methacrylic acid, maleic acid or its salts, maleic anhydride and itaconic acid or their salts. Particularly preferred monomers are acrylic acid and methacrylic acid. Very particular preference is given to acrylic acid. Further suitable monomers a) are, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
  • AMPS 2-acrylamido-2-methylpropanesulfonic acid
  • a suitable monomer a) is, for example, an acrylic acid purified according to WO 2004/035514 A1 with 99.8460% by weight of acrylic acid, 0.0950% by weight of acetic acid, 0.0332% by weight of water, 0.0203% by weight. %
  • Propionic acid 0.0001% by weight of furfurals, 0.0001% by weight of maleic anhydride, 0.0003% by weight of diacrylic acid and 0.0050% by weight of hydroquinone monomethyl ether.
  • the proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, very particularly preferably at least 95 mol%.
  • the monomer solution preferably contains at most 250 ppm by weight, preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight and preferably at least 10 ppm by weight, more preferably at least 30 ppm by weight, in particular by 50% by weight.
  • ppm, hydroquinone half ethers based in each case on the unneutralized monomer a), where neutralized monomer a), ie a salt of the monomer a) is mathematically taken into account as unneutralized monomer.
  • an ethylenically unsaturated, acid group-carrying monomer having a corresponding content of hydroquinone half-ether can be used to prepare the monomer solution.
  • hydroquinone half ethers are hydroquinone monomethyl ether (MEHQ) and / or alpha-tocopherol (vitamin E).
  • Suitable crosslinkers b) are compounds having at least two groups suitable for crosslinking. Such groups are, for example, ethylenically unsaturated groups which can be radically copolymerized into the polymer chain, and functional groups which can form covalent bonds with the acid groups of the monomer a). Furthermore, polyvalent metal salts which can form coordinative bonds with at least two acid groups of the monomer a) are also suitable as crosslinking agents b).
  • Crosslinkers b) are preferably compounds having at least two polymerizable groups which can be incorporated in the polymer network in free-radically polymerized form.
  • Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallylammonium chloride, tetraallyloxyethane, as described in EP 530 438 A1.
  • Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylene bismethacrylamide, trimethylolpropane triacrylate 15 to 20 times ethoxylated, 15-20 times ethoxylated glycerol triacrylate, polyethylene glycol diacrylate having between 4 and 45 - Ch Ch O units in the molecular chain, trimethylolpropane triacrylate and triallylamine ,
  • Very particularly preferred crosslinkers b) are the polyethoxylated and / or propoxylated glycerols esterified with acrylic acid or methacrylic acid to form di- or triacrylates, as described, for example, in WO 2003/104301 A1.
  • Particularly advantageous are di- and / or triacrylates of 3- to 10-fold ethoxylated glycerol.
  • diacrylates or triacrylates of 1 to 5 times ethoxylated and / or propoxylated glycerol.
  • Most preferred are the triacrylates of 3 to 5 times ethoxylated and / or propoxylated glycerol, in particular the triacrylate of 3-times ethoxylated glycerol.
  • the amount of crosslinker b) is preferably from 0.05 to 1, 5 wt .-%, particularly preferably 0.1 to 1 wt .-%, most preferably 0.3 to 0.6 wt .-%, each based on Monomer a).
  • the centrifuge retention capacity (CRC) decreases and the absorption increases under a pressure of 0.3 psi
  • initiators c) it is possible to use all compounds which generate radicals under the polymerization conditions, for example thermal initiators, redox initiators and / or photoinitiators.
  • Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite.
  • mixtures of thermal initiators and redox initiators are used, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid.
  • the sulfonic acid derivative of the formula (II) is preferably used as the reducing component.
  • the initiators are used in conventional amounts.
  • the usual amount of the reducing component of a redox initiator is generally at least
  • sulfonic acid derivative of the formula (II) when used alone as the reducing component of the redox initiator, its added amount is generally at least 0.001% by weight, preferably at least 0.01% by weight, and especially preferably at least 0.03 wt .-% and generally of at most 1, 0 wt .-%, preferably at most 0.3 wt .-%, and particularly preferably at most 0.2 wt .-%, each based on the amount the monomers a) and d).
  • the usual amount of the oxidizing component of a redox initiator is generally 0.0001% by weight and more preferably at least 0.001% by weight and generally at most 2% by weight and preferably at most 1.0% by weight, respectively based on the amount of monomers a) and d).
  • the usual amount of the thermal initiators is generally 0.01% by weight and more preferably at least 0.1% by weight and generally at most 2% by weight and preferably at most 1.0% by weight, respectively based on the amount of monomers a) and d).
  • the usual amount of the photoinitiators is generally 0.001% by weight and more preferably at least 0.01% by weight and generally of at most 1.10% by weight and preferably not more than 0.2% by weight, based in each case on the amount of monomers a) and d).
  • Suitable ethylenically unsaturated monomers d) which can be copolymerized with the ethylenically unsaturated monomers having acid groups are acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, maleic acid or its salts and maleic anhydride.
  • water-soluble polymers e it is possible to use polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified cellulose.
  • an aqueous monomer solution is used.
  • the water content of the monomer solution is preferably from 40 to 75 wt .-%, particularly preferably from 45 to 70 wt .-%, most preferably from 50 to 65 wt .-%.
  • monomer suspensions i. to use supersaturated monomer solutions. With increasing water content, the energy expenditure increases during the subsequent drying and with decreasing water content, the heat of polymerization can only be dissipated insufficiently.
  • the monomer solution can be freed of dissolved oxygen prior to the polymerization by inertization, ie by flowing through with an inert gas, preferably nitrogen or carbon dioxide.
  • an inert gas preferably nitrogen or carbon dioxide.
  • the oxygen content of the monomer solution before polymerization is reduced to less than 1 ppm by weight, more preferably less than 0.5 ppm by weight, most preferably less than 0.1 ppm by weight.
  • the monomer mixture may contain other components. Examples of further components used in such monomer mixtures include chelating agents in order to keep metal ions in solution or inorganic powders in order to increase the rigidity of the superabsorber in the swollen state, or recycled undersize from a later grinding.
  • the degree of neutralization is preferably from 25 to 95 mol%, particularly preferably from 50 to 80 mol%, very particularly preferably from 65 to 72 mol%, whereby the customary neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or Alkalimetallhydrogenkarbonate and mixtures thereof.
  • the customary neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or Alkalimetallhydrogenkarbonate and mixtures thereof.
  • alkali metal salts and ammonium salts can be used.
  • Sodium and potassium are particularly preferred as alkali metals, but very particularly preferred are sodium hydroxide, sodium carbonate or sodium bicarbonate and mixtures thereof.
  • the polymer gel is at least partially neutralized after the polymerization, the polymer gel is preferably comminuted mechanically, for example by means of an extruder, wherein the neutralizing agent can be sprayed, sprinkled or poured on and then thoroughly mixed in.
  • the gel mass obtained can be extruded several times for homogenization.
  • the monomer a) used is a mixture of from 25 to 95 mol%, particularly preferably from 50 to 80 mol%, very particularly preferably from 65 to 75 mol% salt of the acid group carrier salt. the monomers and the remainder used to 100 mol% acid group-carrying monomer.
  • This mixture is, for example, a mixture of sodium acrylate and acrylic acid or a mixture of potassium acrylate and acrylic acid.
  • a neutralizing agent is used for neutralization, the content of iron is generally below 10 ppm by weight, preferably below 2 ppm by weight and most preferably below 1 ppm by weight. Similarly, a low content of chloride and anions of oxygen acids of the chlorine is desired.
  • a suitable neutralizing agent is, for example, the 50% strength by weight sodium hydroxide solution or potassium hydroxide solution, which is usually sold as "membrane grade", even purer and equally suitable, but also more expensive is the 50% by weight conventionally sold as "amalgam grade” or "mercury process". % sodium hydroxide solution or potassium hydroxide solution.
  • Suitable polymerization reactors are, for example, kneading reactors or belt reactors.
  • the polymer gel formed in the polymerization of an aqueous monomer solution or suspension is comminuted continuously by, for example, counter-rotating stirring shafts, as described in WO 2001/38402 A1.
  • the polymerization on the belt is described, for example, in EP 955 086 A2, DE 38 25 366 A1 and US Pat. No. 6,241,928.
  • a polymer gel must be comminuted in a further process step, for example in one Meat grinder, extruder or kneader.
  • WO 2009/027 356 A1 Also known are methods in which the monomer mixture is applied to a substrate such as a nonwoven web and polymerized, as described for example in WO 02/94 328 A2 and WO 02/94 329 A1.
  • the sulfonic acid derivative of the formula (II) is added in the process according to the invention before or after drying, but preferably before drying. The addition may then be carried out at any time prior to drying, for example sulfonic acid derivative may be added to the monomer solution prior to polymerization, added during polymerization and added to the resulting polymer gel after polymerization.
  • the addition can take place towards the end of the polymerization in the kneading reactor (with continuously conveying kneading reactors corresponding closer to the outlet than at the entry) or in a separate process step between polymerization and drying.
  • any apparatus which can mix the sulfonic acid derivative sufficiently homogeneously into the gel is suitable for this, above all kneaders, screw mixers and extruders are suitable for this purpose.
  • the sulfonic acid derivative of formula (II), when added, is generally present in an amount of at least 0.001% by weight, preferably at least 0.01% by weight and more preferably at least 0.03% by weight, and in general of at most 1, 0 wt .-%, preferably at most 0.3 wt .-% and particularly preferably at most 0.2 wt .-%, in each case based on the amount of the monomers a) and d) added.
  • the polymer gel obtained from the aqueous solution polymerization and optionally subsequent neutralization is then preferably dried with a belt dryer until the residual moisture content is preferably 0.5 to 15 wt .-%, particularly preferably 1 to 10 wt .-%, most preferably 2 to 8 wt .-%, is
  • the solids content of the gel before drying is generally from 25 to 90% by weight .-%, preferably from 30 to 80 wt .-%, particularly preferably from 35 to 70 wt .-%, very particularly preferably from 40 to 60 wt .-%.
  • the dryer may be operated under nitrogen or other non-oxidizing inert gas, or at least a reduced partial pressure of oxygen, to prevent oxidative yellowing also adequate ventilation and drainage of the water steam to an acceptable product.
  • Advantageous in terms of color and product quality is usually the shortest possible drying time. During drying, the residual monomer content in the polymer particles also decreases and the last residues of the initiator are destroyed.
  • the dried polymer gel is then ground and classified, wherein for grinding usually one- or multi-stage roller mills, preferably two- or three-stage roller mills, pin mills, hammer mills or vibratory mills can be used.
  • Oversized gel lumps which are often not dried in the interior, are rubber-elastic, lead to grinding problems and are preferably separated before grinding, which can easily be achieved by air classification or a sieve ("protective sieve" for the mill) the sieve is to be chosen in view of the mill used so that as possible no interference from oversized, rubbery particles occur.
  • coarse-grained polymer particles are separated from the product. This is carried out by customary classification methods, for example air classification or sieving through a sieve with a mesh size of at most 1000 ⁇ m, preferably at most 900 ⁇ m, more preferably at most 850 ⁇ m and very particularly preferably at most 800 ⁇ m. For example, screens are used with 700 ⁇ , 650 ⁇ or 600 ⁇ mesh size.
  • the separated coarse-grained polymer particles (“oversize") can be fed back to the grinding and screening circuit for cost optimization or further processed separately.
  • SFC permeability
  • also fine-grained polymer particles are separated in this classification. This can, if sieved, conveniently through a sieve with a mesh size of at most 300 ⁇ , preferably at most 200 ⁇ , more preferably at most 150 ⁇ and most preferably at most 100 ⁇ done.
  • the separated fine-grained polymer particles (“undersize” or “fines”) can be fed back to the monomer stream, the polymerizing gel, or the polymerized gel before drying the gel for cost optimization.
  • the mean particle size of the polymer particles separated off as product fraction is generally at least 200 ⁇ m, preferably at least 250 ⁇ m, and preferably at least 300 ⁇ m, and generally at most 600 ⁇ m, and more preferably at most 500 ⁇ m.
  • the proportion of particles having a particle size of at least 150 ⁇ m is generally at least 90% by weight, preferably at least 95% by weight and most preferably at least 98% by weight.
  • the proportion of particles with a particle size of at most 850 ⁇ , is generally N at least 90 wt .-%, preferably at least 95 wt .-% and most preferably at least 98 wt .-%.
  • the particle size distribution is predetermined by the choice of process parameters.
  • particulate superabsorbents of the desired particle size are formed directly, so that milling and screening steps can often be omitted.
  • a separate drying step can often be dispensed with.
  • the polymer produced in this way has superabsorbent properties and is referred to as "superabsorbent.” Its CRC is typically comparatively high, while its AUL or SFC is comparatively low. Called base polymer “or" base polymer ".
  • the base polymer is optionally surface postcrosslinked.
  • Suitable postcrosslinkers are compounds which contain groups which can form bonds with at least two functional groups of the superabsorbent particles.
  • Acrylic acid / sodium acrylate-based superabsorbents which are prevalent on the market are suitable surface postcrosslinker compounds which contain groups which can form bonds with at least two carboxylate groups.
  • Preferred postcrosslinkers are amide acetals or carbamates of the general formula (III)
  • R 7 Ci-Ci2-alkyl, C 2 -C 2 -Hydroxialkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, R 8 or OR 12 X '
  • R 9 is hydrogen, Ci-Ci 2 -alkyl, C 2 -C 2 -Hydroxialkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, or X, R 10 Ci-Ci2 alkyl, C2 -Ci2-hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -Ci2-aryl,
  • R 11 is hydrogen, Ci-Ci 2 -alkyl, C 2 -C 2 -Hydroxialkyl, C 2 -C 2 -alkenyl, Ci-Ci2 acyl or
  • R 12 Ci-Ci 2 -alkyl, C 2 -C 2 -Hydroxialkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, and
  • X is a carbonyl oxygen common to the radicals R 8 and R 9 , where R 7 and R 10 and / or R 11 and R 12 may be a bridged C 2 -C 6 alkanediyl, and where the abovementioned radicals R 7 to R 12 are still may have at least one to two free valences and may be connected to these free valencies with at least one suitable base, or polyhydric alcohols, wherein the polyhydric alcohol preferably has a molecular weight of less than 100 g / mol, preferably less than 90 g / mol , particularly preferably less than 80 g / mol, very particularly preferably less than 70 g / mol, per hydroxyl group and no vicinal, geminal, secondary or tertiary hydroxyl groups, and polyhydric alcohols either diols of the general formula (IVa)
  • R 13 is either an unbranched dialkyl radical of the formula - (CH 2 ) n -, where n is an integer from 3 to 20, preferably 3 to 12, and both hydroxy groups are terminal, or R 13 is an unbranched, branched or cyclic dialkyl radical, or polyols of the general formula (IVb)
  • radicals R 14 , R 15 , R 16 , R 17 independently of one another are hydrogen, hydroxyl, hydroxymethyl, hydroxiethyloxymethyl, 1-hydroxiprop-2-yloximethyl, 2-hydroxipropyloximethyl, methyl, ethyl, n-propyl, isopropyl, n- Butyl, n-pentyl, n-hexyl, 1, 2-dihydroxiethyl, 2-hydroxyethyl, 3-hydroxypropyl or 4-hydroxibutyl and a total of 2, 3, or 4, preferably 2 or 3, Hydroxi tendency are present, and not more than one of the radicals R 14 , R 15 , R 16 , or R 17 is hydroxy, or cyclic carbonates of the general formula (V) wherein R 18 , R 19 , R 20 , R 21 , R 22 and R 23 are independently hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl
  • R 24 , R 25 , R 26 , R 27 , R 28 , R 29 , R 30 and R 31 are independently hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or isobutyl
  • R 32 represents a single bond, a linear, branched or cyclic C 2 -C 12 -dialkyl radical, or a polyalkoxydiyl radical which is composed of one to ten ethylene oxide and / or propylene oxide units, such as, for example, polyglycol dicarboxylic acids.
  • Preferred postcrosslinkers of the general formula (III) are 2-oxazolidones, such as 2-oxazolidone and N- (2-hydroxyethyl) -2-oxazolidone, N-methyl-2-oxazolidone, N-acyl-2-oxazolidones, such as 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-oxazolidones and poly-2-oxazolidones.
  • 2-oxazolidones such as 2-oxazolidone and N- (2
  • Particularly preferred postcrosslinkers of the general formula (III) are 2-oxazolidone, N-methyl-2-oxazolidone, N- (2-hydroxyethyl) -2-oxazolidone and N-hydroxypropyl-2-oxazolidone.
  • Preferred postcrosslinkers of the general formula (IVa) are 1, 3-propanediol, 1, 5-pentanediol, 1, 6-hexanediol and 1, 7-heptanediol.
  • Further examples of postcrosslinkers of the formula (IVa) are 1,3-butanediol, 1,8-octanediol, 1,9-nonanediol and 1,10-decanediol.
  • the diols are preferably water-soluble, with the diols of the general formula (IVa) at 23 ° C to at least 30 wt .-%, preferably at least 40 wt .-%, particularly preferably at least 50 wt .-%, most preferably at least 60 wt .-%, in water, such as 1, 3-propanediol and 1, 7-heptanediol. Even more preferred are those postcrosslinkers which are liquid at 25 ° C.
  • Preferred secondary crosslinkers of the general formula (IVb) are butane-1, 2,3-triol, butane-1, 2,4-triol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, per molecule 1 to 3 times ethoxylated glycerol, trimethylolethane or Trimethylolpropane and per molecule 1 - to 3-fold propoxylated glycerol, trimethylolethane or trimethylolpropane.
  • 2-fold ethoxylated or propoxylated neopentyl glycol Particularly preferred are 2-fold and 3-fold ethoxylated glycerin, neopentyl glycol, 2-methyl-1, 3-propanediol and trimethylolpropane.
  • Preferred polyhydric alcohols (IVa) and (IVb) have at 23 ° C. a viscosity of less than 3000 mPas, preferably less than 1500 mPas, preferably less than 1000 mPas, more preferably less than 500 mPas, very particularly preferably less than 300 mPas, on.
  • Particularly preferred postcrosslinkers of the general formula (V) are ethylene carbonate and propylene carbonate.
  • a particularly preferred postcrosslinker of the general formula (VI) is 2,2'-bis (2-oxazoline).
  • the preferred postcrosslinkers minimize side reactions and subsequent reactions which lead to volatile and thus malodorous compounds.
  • the superabsorbers produced with the preferred postcrosslinkers are therefore odorless even when moistened. It is possible to use a single postcrosslinker from the above selection or any mixtures of different postcrosslinkers.
  • the postcrosslinker is generally used in an amount of at least 0.001% by weight, preferably at least 0.02% by weight, more preferably at least 0.05% by weight, 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, in each case based on the mass of the base polymer applied thereto (for example, the relevant sieve fraction).
  • the postcrosslinking is usually carried out by spraying a solution of the postcrosslinker onto the dried base polymer particles. Subsequent to the spraying, the polymer particles coated with postcrosslinker are thermally dried, wherein the postcrosslinking reaction can take place both before and during the drying. If surface postcrosslinkers with polymerizable groups are used, the surface postcrosslinking can also be carried out by free-radically induced polymerization of such groups by means of common free-radical formers or else by means of high-energy radiation such as UV light. This may be done in parallel or instead of using postcrosslinkers that form covalent or ionic bonds to functional groups on the surface of the base polymer particles.
  • the spraying of Nachvernetzeraims is preferably carried out in mixers with moving mixing tools, such as screw mixers, disc, paddle or paddle mixers or mixers with other mixing tools.
  • moving mixing tools such as screw mixers, disc, paddle or paddle mixers or mixers with other mixing tools.
  • vertical mixers particularly preferred are vertical mixers.
  • Suitable mixers are flocking for example as a plow mixer ® Gebr Lödige Maschinenbau GmbH, Elsener Street. 7 - 9, 33102 Paderborn, Germany, or ® as Schugi ® Flexomix mixer, Vrieco-Nauta ® mixer or blender Turbulizer® ® from Hosokawa Micron BV, Gildenstraat 26, 7000 AB Doetinchem, The Netherlands.
  • the applicable spray nozzles are subject to no restriction. Suitable nozzles and atomization systems are described, for example, in the following references: Atomization of Liquids, Expert-Verlag, Vol. 660, series Kunststoff & Meeting, Thomas Richter (2004) and in atomization technology, Springer-Verlag, VDI series, Günter Wozniak (2002 ). Applicable are mono- and polydisperse spray systems. Among the polydisperse systems are single-fluid pressure nozzles (jet or lamella-forming), rotary atomizers, two-component atomizers, ultrasonic atomizers and impact nozzles. In the two-component atomizers, the mixture of the liquid and the gas phase can take place both internally and externally.
  • the spray pattern of the nozzles is not critical and can take any shape, such as omnidirectional, fan-beam, wide-angle omnidirectional or circular ring spray pattern. It is advantageous to use a non-oxidizing gas, if two-component atomizers are used, particularly preferably nitrogen, argon or carbon dioxide. Such nozzles, the liquid to be sprayed can be supplied under pressure. The division of the liquid to be sprayed can take place in that it is relaxed after reaching a certain minimum speed in the nozzle bore.
  • single-substance nozzles such as slot nozzles or twist chambers (full-cone nozzles) (for example by Düsen-Schlick GmbH, DE, or by Spraying Systems GmbH, DE).
  • slot nozzles or twist chambers full-cone nozzles
  • spraying Systems GmbH, DE Such nozzles are also described in EP 0 534 228 A1 and EP 1 191 051 A2.
  • the postcrosslinkers are typically used as an aqueous solution. If only water is used as the solvent, the postcrosslinker solution or the base polymer is advantageously added with a surfactant or deagglomerization aid. This improves the wetting behavior and reduces the tendency to clog.
  • anionic, cationic, nonionic and amphoteric surfactants are suitable as Deagglomerationstoskar, but are preferred for skin compatibility reasons non-ionic and amphoteric surfactants.
  • the surfactant may also contain nitrogen.
  • sorbitan monoesters such as sorbitan monococoate and sorbitan monolaurate, or ethoxylated variants thereof, such as polysorbate 20® , are added.
  • deagglomerating agents are the ethoxylated and alko xyl faced derivatives of 2-propylheptanols, which are sold under the brands Lutensol XL ® and Lutensol XP ® (BASF SE, Carl-Bosch-Strckee 38, 67056 Ludwigshafen, Germany).
  • the deagglomerating assistant can be metered separately or added to the postcrosslinker solution.
  • the deagglomerating aid is simply added to the postcrosslinker solution.
  • the amount used of the deagglomerating assistant based on the base polymer is, for example, 0 to 0.1% by weight, preferably 0 to 0.01% by weight, particularly preferably 0 to 0.002% by weight.
  • the deagglomerating assistant is metered so that the surface tension of an aqueous extract of the swollen base polymer and / or the swollen postcrosslinked water-absorbing polymer at 23 ° C at least 0.060 N / m, preferably at least 0.062 N / m, more preferably at least 0.065 N / m , and advantageously at most 0.072 N / m.
  • the aqueous postcrosslinker solution may also contain a cosolvent in addition to the at least one postcrosslinker.
  • a cosolvent in addition to the at least one postcrosslinker.
  • the penetration depth of the postcrosslinker can be adjusted in the polymer particles.
  • cosolvents are C 1 -C 6 -alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol or 2-methyl-1-propanol, C 2 -C 5 -diols, such as Ethylene glycol, 1, 2-propylene glycol or 1, 4-butanediol, ketones, such as acetone, or carboxylic acid esters, such as ethyl acetate.
  • cosolvents have typical odors.
  • the co-solvent itself is ideally not a postcrosslinker under the reaction conditions. However, in the limiting case and depending on residence time and temperature, it may happen that the cosolvent partially contributes to crosslinking.
  • postcrosslinker is relatively inert and therefore can itself form its cosolvent, as for example when using cyclic carbonates of the general formula (V), diols of the general formula (IVa) or polyols of the general formula (IVb) .
  • Such postcrosslinkers can also be used as cosolvents in a mixture with more reactive secondary crosslinkers, since the actual postcrosslinking reaction can then be carried out at lower temperatures and / or shorter residence times than in the absence of the more reactive crosslinker. Since co-solvent is used in relatively large amounts and also remains partially in the product, it must not be toxic.
  • the diols of the general formula (IVa), the polyols of the general formula (IVb) and the cyclic carbonates of the general formula (V) are also suitable as cosolvents. They fulfill this function in the presence of a reactive postcrosslinker of the general formula (III) and / or (VI) and / or a di- or triglycidyl compound.
  • preferred co-solvents in the process according to the invention are, in particular, the diols of the general formula (IVa), especially when the hydroxyl groups are hindered sterically by neighboring groups on a reaction.
  • diols are in principle also suitable as postcrosslinkers, however, they require significantly higher reaction temperatures or optionally higher amounts of use than sterically unhindered diols.
  • Particularly preferred combinations of less reactive postcrosslinker as cosolvent and reactive postcrosslinker are combinations of preferred polyhydric alcohols, diols of general formula (IVa) and polyols of general formula (IVb), with amide acetals or carbamates of general formula (III).
  • 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.
  • Very particularly preferred combinations are 2-oxazolidone / 1,3-propanediol and N- (2-hydroxyethyl) -2-oxazolidone / 1,3-propanediol.
  • ethylene glycol diglycidyl ether or glycerol or triglycidyl ether with the following solvents, cosolvents or co-crosslinkers: isopropanol, 1,3-propanediol, 1,2-propylene glycol or mixtures thereof.
  • the concentration of the cosolvent in the aqueous postcrosslinker solution is from 15 to 50% by weight, preferably from 15 to 40% by weight, particularly preferably from 20 to 35% by weight, based on the postcrosslinker solution.
  • concentration of the cosolvent in the aqueous postcrosslinker solution is from 15 to 50% by weight, preferably from 15 to 40% by weight, particularly preferably from 20 to 35% by weight, based on the postcrosslinker solution.
  • no cosolvent is used.
  • the post-crosslinker is then used only as a solution in water, optionally with the addition of a deagglomerating auxiliary.
  • the concentration of the at least one postcrosslinker in the aqueous postcrosslinker solution is typically from 1 to 20% by weight, preferably from 1 to 5% by weight, more preferably from 2 to 5% by weight, based on the postcrosslinker solution.
  • the total amount of postcrosslinker solution based on base polymer is usually from 0.3 to 15% by weight, preferably from 2 to 6% by weight.
  • the actual surface postcrosslinking by reaction of the surface postcrosslinker with functional groups on the surface of the base polymer particles is usually carried out by heating the base polymer wetted with surface postcrosslinker solution, usually called “drying" (but not to be confused with the above-described drying of the polymer gel from the polymerization drying can be carried out in the mixer itself, by heating the jacket, by heat exchange surfaces or by blowing warm gases in. Simultaneous addition of the superabsorbent with surface postcrosslinker and drying can take place, for example, in a fluidized bed dryer.
  • drying is usually carried out in a downstream dryer, such as a tray dryer, a rotary kiln, a paddle or disc dryer or a heatable screw example as Solidair ® or Torusdisc ® -T Rockner from Bepex International LLC, 333 NE Taft Street, Minneapolis, MN 55413, USA, or as a paddle or paddle dryer or as a fluidized bed dryer of Nara Machinery Co., Ltd., branch Europa, Europa Allee 46, 50226 Frechen, Germany available.
  • a downstream dryer such as a tray dryer, a rotary kiln, a paddle or disc dryer or a heatable screw example as Solidair ® or Torusdisc ® -T Rockner from Bepex International LLC, 333 NE Taft Street, Minneapolis, MN 55413, USA, or as a paddle or paddle dryer or as a fluidized bed dryer of Nara Machinery Co., Ltd., branch Europa, Europa Allee 46, 50226 Frechen, Germany available.
  • the polymer particles can already be heated in the post-crosslinking mixer with steam.
  • the base polymer used may still have a temperature of 10 to 120 ° C from previous process steps, the Nachvernetzerlosung may have a temperature of 0 to 70 ° C.
  • the postcrosslinker solution can be heated to reduce the viscosity.
  • Preferred drying temperatures are in the range 100 to 250 ° C, preferably 120 to 220 ° C, more preferably 130 to 210 ° C, most preferably 150 to 200 ° C.
  • the preferred residence time at this temperature in the reaction mixer or dryer is preferably at least 10 minutes, more preferably at least 20 minutes, most preferably at least 30 minutes, and usually at most 60 minutes.
  • the drying is conducted such that the superabsorber has a residual moisture content of generally at least 0.1% by weight, preferably at least 0.2% by weight and in particular preferred form at least 0.5% by weight. and generally at most 15% by weight, preferably at most 10% by weight and in a particularly preferred form at most 8% by weight.
  • Postcrosslinking can take place under normal atmospheric conditions. Normal atmospheric conditions means that no technical precautions are taken to reduce the partial pressure of oxidizing gases such as atmospheric oxygen in the apparatus in which the postcrosslinking reaction predominantly takes place (the "postcrosslinking reactor", typically the dryer) Oxidizing gases are substances which have a vapor pressure of at least 1013 mbar at 23 ° C.
  • the partial pressure of oxidizing gases is preferably less as 140 mbar, preferably less than 100 mbar, particularly preferably less than 50 mbar, very particularly preferably less than 10 mbar If the thermal post-crosslinking at ambient pressure, ie at a total pressure of 1013 mbar performed , the total partial pressure of the oxidizing gases is determined by their volume fraction.
  • the proportion of oxidizing gases is 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.
  • the post-crosslinking can be carried out under reduced pressure, ie at a total pressure of less than 1013 mbar.
  • the total pressure is typically Example, less than 670 mbar, preferably less than 480 mbar, more preferably less than 300 mbar, most preferably less than 200 mbar. If drying and post-crosslinking are carried out in air with an oxygen content of 20.8% by volume, the oxygen partial pressures corresponding to the abovementioned total pressures are 139 mbar (670 mbar), 100 mbar (480 mbar), 62 mbar (300 mbar) and 42 mbar (200 mbar) with respective total pressures in brackets.
  • Suitable inert gases at the post-crosslinking temperature and given pressure in the post-crosslinking dryer are gaseous substances which under these conditions do not oxidize the constituents of the drying polymer particles, for example nitrogen, carbon dioxide, argon, water vapor, nitrogen being preferred.
  • the amount of inert gas is generally from 0.0001 to 10 m 3 , preferably from 0.001 to 5 m 3 , more preferably from 0.005 to 1 m 3 , and most preferably from 0.005 to 0.1 m 3 , based on 1 kg of superabsorbent.
  • the inert gas if it does not contain water vapor, can be injected via nozzles into the postcrosslinking dryer; more preferably, however, the inert gas is already added to the polymer particle stream via nozzles in or shortly before the mixer by mixing the superabsorbent with surface postcrosslinker ,
  • vapors of cosolvents removed from the dryer can be condensed outside the dryer again and, if necessary, recycled.
  • Polyvalent metal ions are applied to the surfaces of the superabsorber according to the invention before, during or after postcrosslinking in addition to the postcrosslinkers or, if no surface postcrosslinking is carried out, instead of these.
  • this application of polyvalent metal ions is in principle an (optionally additional) surface postcrosslinking by ionic, noncovalent bonds and is used in the context of this invention to distinguish surface postcrosslinking by means of covalent bonds as "complexing" with the relevant metal ions
  • These polyvalent metal ions are applied by spraying solutions of the cations, usually di-, tri- or tetravalent metal cations, Examples of complexing of useful polyvalent metal cations are mentioned above
  • metal salts are suitable which have sufficient solubility in the solvent to be used.
  • metal salts with weakly complexing anions such as chloride, nitrate and sulfate, hydrogen sulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate, or dihydrogen phosphate.
  • Preferred are salts of mono- and Dicarboxylic acids, hydroxy acids, keto acids and amino acids or basic salts. Examples are acetates, propionates, tartrates, maleates and citrates, lactates, malates and succinates. Also preferred is the use of hydroxides.
  • 2-hydroxycarboxylic acid salts such as citrates and lactates.
  • particularly preferred metal salts are alkali metal and alkaline earth metal aluminates and their hydrates, such as sodium aluminate and its hydrates, aluminum acetate, aluminum propionate, aluminum citrate and aluminum lactate.
  • the cations and salts mentioned can be used in pure form or as a mixture of different cations or salts.
  • the salts of the two and / or trivalent metal cation used may contain further secondary constituents such as unneutralized carboxylic acid and / or alkali metal salts of the neutralized carboxylic acid.
  • Preferred alkali metal salts are those of sodium, potassium and ammonium. They are typically used as an aqueous solution which is obtained by dissolving the solid salt in water, or is preferably produced directly as such, whereby optionally drying and purification steps are avoided.
  • the hydrates of said salts can be used, which often dissolve faster in water than the anhydrous salts.
  • the amount of metal salt used is generally at least 0.001 wt .-%, preferably at least 0.01 wt .-% and in a particularly preferred form at least 0.1 wt .-%, for example at least 0.4 wt .-% and generally at most 5 wt .-%, preferably at most 2.5 wt .-% and in a particularly preferred form at most 1 wt .-%, for example at most 0.7 wt .-% in each case based on the mass of the base polymer.
  • the salt of the polyvalent metal cation can be used as a solution or suspension.
  • solvents for the metal salts water, alcohols, DMF, DMSO and mixtures 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 base polymer with solution of a polyvalent cation is carried out in the same way as with surface postcrosslinkers, including the drying step.
  • Surface postcrosslinker and polyvalent cation can be sprayed in a common solution or as separate solutions.
  • the spraying of the metal salt solution onto the superabsorbent particles can be carried out both before and after the surface postcrosslinking.
  • the spraying of the metal salt solution is carried out in the same step by spraying the crosslinker solution, wherein both solutions are sprayed separately successively or simultaneously via two nozzles, or crosslinker and metal salt solution can be sprayed together via a nozzle ,
  • a drying step is carried out after the surface postcrosslinking and / or treatment with complexing agent, it is advantageous, but not absolutely necessary, to cool the product after drying.
  • the cooling can be continuous or discontinuous, conveniently the product is continuously conveyed to a dryer downstream cooler.
  • any apparatus known for removing heat from powdered solids may be used for this purpose, in particular any apparatus mentioned above as a drying apparatus, unless it is supplied with a heating medium but with a cooling medium, such as cooling water, so that over the walls and depending on the construction No heat is introduced into the superabsorber via the stirring elements or other heat exchange surfaces, but is removed therefrom.
  • a cooling medium such as cooling water
  • the superabsorbent can also be cooled in the fluidized bed by blowing in a cooled gas such as cold air. The conditions of the cooling are adjusted so that a superabsorbent is obtained with the temperature desired for further processing.
  • an average residence time in the condenser of generally at least 1 minute, preferably at least 3 minutes and more preferably at least 5 minutes and generally at most 6 hours, preferably at most 2 hours and more preferably at most 1 hour is set and the cooling capacity is so in that the product obtained has a temperature of generally at least 0 ° C, preferably at least 10 ° C and more preferably at least 20 ° C and generally at most 100 ° C, preferably at most 80 ° C and most preferably at most 60 ° C.
  • the surface postcrosslinked superabsorbent is optionally ground and / or sieved in the usual way. Grinding is typically not required here, but most often, the setting of the desired particle size distribution of the product requires the removal of agglomerates or fine particles formed. Agglomerates and fines are either discarded or preferably recycled to the process in a known manner and at a suitable location; Agglomerates after comminution.
  • the particle sizes desired for surface postcrosslinked superabsorbents are the same as for base polymers.
  • Phosphonic acid derivative of the formula (I) is added to the superabsorber according to the invention and in the process according to the invention preferably after drying or, if a surface postcrosslinking is carried out, after this.
  • any apparatus which can mix the phosphonic acid derivative sufficiently homogeneously into the superabsorber is suitable for this purpose.
  • the addition of the phosphonic acid derivative in the cooler is also preferred.
  • the aqueous solution of the phosphonic acid derivative is particularly preferred at the same time with, but sprayed separately from the solution of surface postcrosslinker. In the simplest case, this is done by spraying through different nozzles.
  • such amounts of polyvalent metal ions are used for complexing and phosphonic acid derivative, that a molar ratio in the produced superabsorbent of not more than 0.6 is not exceeded, wherein, as stated above, enter into the calculation of this molar ratio exclusively the complexing polyvalent metal ions.
  • the superabsorbers according to the invention produced by the process according to the invention are provided with further additives, as a non-limiting example, those which stabilize against discoloration.
  • all known additives can be used in the manner known to them in each case in the method according to the invention.
  • the mixing of superabsorbents with the optional additives can be carried out by any known mixing method. They are, if mixed in solid form, in bulk or as a suspension in a solvent or suspending agent, if in dissolved or liquid form, optionally in solution or in liquid form.
  • the additives are mixed into the superabsorber as powder or suspension due to the easier homogeneous distribution. It does not necessarily produce a physical mixture that can be easily separated by mechanical means.
  • the additives can certainly form a stronger bond with the superabsorber, for example as a comparatively firmly adhering surface layer or as particles firmly adhering to the surface of the superabsorbent particles.
  • the interference of the additives in the known superabsorber can certainly also be understood and referred to as a "coating".
  • a solvent or suspending agent which is chemically compatible both with the superabsorber and with the additive, that is to say without undesired chemical reactions, is used as the solvent or suspending agent.
  • water or an organic solvent is used, for example an alcohol or polyol, or mixtures thereof.
  • suitable solvents or suspending agents are water, isopropanol / water, 1,3-propanediol / water and propylene glycol / water, the mixing mass ratio preferably being from 20:80 to 40:60.
  • a suspension agent is used for the stabilizers to be used according to the invention or the inorganic particulate solid, water is preferred.
  • a surfactant may be added to the solution or suspension.
  • Optional additives unless added to the monomer mixture or the polymerizing gel, are generally mixed with the superabsorbent in exactly the same way as those used for surface postcrosslinking Superabsorber applied, containing a surface postcrosslinker solution or suspension.
  • the additive may be applied as a constituent of the solution applied to the surface postcrosslinking or one of its components to a (not) postcrosslinked superabsorber (a "base polymer” or “base polymer”), ie added to the solution of the surface postcrosslinker or one of its components.
  • the superabsorber coated with surface postcrosslinking agent and additives then passes through the further process steps required for surface postcrosslinking, for example a thermally induced reaction of the surface postcrosslinking agent with the superabsorber. This process is comparatively simple and economical.
  • phosphonic acid derivative and optional additives are applied after the surface postcrosslinking in a separate process step, conveniently in the cooler. If phosphonic acid derivative and additives are applied as a solution or suspension, the application can be effected on the already surface-postcrosslinked superabsorber in the same mixing apparatus as described for the application of the surface postcrosslinker to the base polymer. Most, but not necessarily, is then heated as well as in the surface postcrosslinking to rewet the superabsorber. However, the temperature set in this drying is then generally at most 1 10 ° C, preferably at most 100 ° C, and most preferably at most 90 ° C to avoid undesirable reactions of the additive.
  • the temperature is adjusted so that, in view of the residence time in the drying unit, the desired water content of the superabsorber is achieved. It is also quite possible and convenient to add additives individually or together with other conventional auxiliaries, for example dust binders, anti-caking agents or water for rewetting the superabsorber.
  • the temperature of the polymer particles in this case is between 0 ° C and 190 ° C, preferably less than 160 ° C, more preferably less than 130 ° C, even more preferably less than 100 ° C, and most preferably less than 70 ° C ,
  • the polymer particles are optionally rapidly cooled to temperatures below a possible decomposition temperature of the additive after coating.
  • any known coatings such as film-forming polymers, thermoplastic polymers, dendrimers, polycationic polymers (such as, for example, polyvinylamine, polyethylene enimine or polyallylamine), can optionally be applied to the surface of the superabsorbent particles, whether post-crosslinked or postcrosslinked, in the production process in each process step.
  • any known coatings such as film-forming polymers, thermoplastic polymers, dendrimers, polycationic polymers (such as, for example, polyvinylamine, polyethylene enimine or polyallylamine)
  • water-soluble mono- or polyvalent metal salts known to the person skilled in the art, such as, for example, aluminum sulfate, sodium, potassium, zirconium or iron salts, are additionally applied.
  • useful alkali metal salts are sodium and potassium sulfate, sodium and potassium lactates, citrates, sorbates.
  • additives are used in the form of dispersions and sprayed on, then they are preferably used as aqueous dispersions, and it is preferably additionally applied a dewaxing agent for fixing the additive on the surface of the superabsorbent.
  • the dedusting agent is then added either directly to the dispersion of the inorganic powder additive, optionally it may also be added as a separate solution before, during, or after the inorganic powdery additive has been applied by spraying.
  • the simultaneous spraying of postcrosslinking agent, dedusting agent and powdery inorganic additive in the postcrosslinking is added separately in the cooler, for example by spraying from above, below or from the side.
  • Particularly suitable dedusting agents which can also serve to fix powdery inorganic additives to the surface of the water-absorbing polymer particles, are polyethylene glycols having a molecular weight of 400 to 20,000 g / mol, polyglycerol, 3 to 100-fold ethoxylated polyols, such as trimethylolpropane , Glycerin, sorbitol and neopentylglycol.
  • Particularly suitable are 7 to 20 times ethoxylated glycerol or trimethylolpropane, such as, for example, polyol TP 70® (Perstorp, SE).
  • polyol TP 70® Perstorp, SE.
  • the latter have the particular advantage that they only insignificantly reduce the surface tension of an aqueous extract of the water-absorbing polymer particles.
  • All coatings, solids, additives and auxiliaries can each be added in separate process steps, but in most cases the most convenient method is to add them, if they are not added during the displacement of the base polymer with surface postcrosslinking agent, to the superabsorber in the cooler, for example by spraying Solution or addition in finely divided solid or in liquid form.
  • the addition of the phosphonic acid derivative in the cooler is also a convenient and preferred embodiment.
  • the superabsorbents according to the invention generally have a centrifuge retention capacity (CRC, measuring method see below) of at least 5 g / g, preferably of at least 10 g / g and in a particularly preferred form of at least 20 g / g. Usually, it is not more than 40 g / g for surface-postcrosslinked superabsorbents, but it is often higher for base polymers.
  • CRC centrifuge retention capacity
  • the superabsorbers according to the invention typically have an absorption under pressure (AUL0.7 psi, measuring method see below) of at least 10 g / g, preferably at least 14 g / g, preferably at least 18 g / g and most preferably at least 22 g / g and usually not more than 30 g / g.
  • AUL0.7 psi absorption under pressure
  • the L value of the superabsorber (CIE color number) in the non-stored state is typically at least 75, preferably at least 80, particularly preferably at least 85 and at most 100.
  • the a-value of the superabsorbent (CIE color number) in the non-stored state is typically from -2.5 to +2.5, preferably from -2.0 to +2.0, more preferably from -1.5 to +1 ; 5.
  • the b value of the superabsorber (CIE color number) in the non-stored state is typically from 0 to 12, preferably from 2 to 1 1. According to the relatively stressful aging test described below, the superabsorber according to the invention, after measurement for the L and Reported only relatively little deteriorated results over the non-stored state, especially b values of preferably not more than 13, more preferably not more than 12.
  • a b-value above 12 is critical in feminine hygiene articles and ultrathin diapers; a b-value of more than 15 is already critical in conventional diapers, as this discoloration can be perceived by the consumer in use.
  • a further subject of the present invention are hygiene articles comprising superabsorbers according to the invention, preferably ultrathin diapers, containing an absorbent layer consisting of 50 to 100 wt.%, Preferably 60 to 100
  • Wt .-% preferably 70 to 100 wt .-%, particularly preferably 80 to 100 wt .-%, most preferably 90 to 100 wt .-%, inventive superabsorber, wherein the envelope of the absorbent layer is of course not taken into account.
  • inventive superabsorber preferably 90 to 100 wt .-%, inventive superabsorber, wherein the envelope of the absorbent layer is of course not taken into account.
  • inventive superabsorber wherein the envelope of the absorbent layer is of course not taken into account.
  • inventive superabsorber wherein the envelope of the absorbent layer is of course not taken into account.
  • inventive superabsorber wherein the envelope of the absorbent layer is of course not taken into account.
  • the superabsorbents according to the invention are also very particularly advantageous for the production of laminates and composite structures, as described, for example, in US 2003/0181115 and US 2004/0019342.
  • the superabsorbers according to the invention are also suitable for the preparation of completely analogous fibers described in US 2003/0181115 Structures using UV-crosslinkable hot melt adhesives, which are sold, for example, as AC-Resin ® (BASF SE, Ludwigshafen, Germany).
  • UV-crosslinkable hot-melt adhesives have the advantage of being processable at as low as 120 to 140 ° C, so they are better compatible with many thermoplastic substrates.
  • Another significant advantage is that UV-crosslinkable hot melt adhesives are toxicologically very harmless and also cause no exhalations in the toiletries.
  • the property of the UV-crosslinkable hotmelt adhesives during processing and crosslinking is not prone to yellowing. This is particularly advantageous if ultrathin or partially transparent hygiene articles are to be produced.
  • the combination of the superabsorbents according to the invention with UV-crosslinkable hot-melt adhesives is therefore particularly advantageous.
  • Suitable UV-crosslinkable hot-melt adhesives are described, for example, in EP 0 377 199 A2, EP 0 445 641 A1, US Pat. No. 5,026,806, EP 0 655 465 A1 and EP 0 377 191 A2.
  • the superabsorbent according to the invention can also be used in other fields of technology in which liquids, in particular water or aqueous solutions, are absorbed.
  • These areas are, for example, storage, packaging, transport (as constituents of packaging material for water- or moisture-sensitive articles, for example for flower transport, as well as protection against mechanical effects); Animal hygiene (in cat litter); Food packaging (transport of fish, fresh meat, absorption of water, blood in fresh fish or meat packaging); Medicine (wound plasters, water-absorbing material for burn dressings or for other weeping wounds), cosmetics (carrier material for pharmaceutical chemicals and medicines, rheumatism plaster, ultrasound gel, cooling gel, cosmetic thickener, sunscreen); Thickener for oil / water or water / oil emulsions; Textiles (moisture regulation in textiles, shoe inserts, for evaporative cooling, for example in protective clothing, gloves, headbands); chemical-technical applications (as a catalyst for organic reactions, for the immobilization of large functional molecules such as enzymes,
  • the liquid absorption articles according to the invention differ from those known in that they contain the superabsorber according to the invention.
  • a process has also been found for producing articles for absorbing liquid, in particular hygiene articles, which is characterized in that at least one superabsorber according to the invention is used in the production of the article in question.
  • methods for producing such articles using superabsorbents are known.
  • Test Methods The superabsorbent is tested using the test methods described below.
  • the centrifuge retention capacity of the superabsorbent is determined according to Standard Test Method No. WSP 241.3 (10) "Determination of Fluid Retention Capacity in Saline Solution by Gravimetric Measurement Following Centrifugation".
  • the proportion of extractables of the superabsorbent is determined according to the standard test method no. WSP 270.3 (10) "Determination of Extractable Polymer Content by Potentiometry Titration". Moisture content of the superabsorber (residual moisture, water content)
  • the water content of the superabsorbent particles is determined according to the standard test method No. WSP 230.3 (10) "Estimation of Moisture Content as Weight Loss Upon Heating".
  • the permeability of a swollen gel layer formed by the superabsorber by liquid absorption is determined under pressure load of 0.3 psi (2068 Pa), as described in EP 0 640 330 A1, as gel layer permeability of a swollen gel layer of superabsorbent particles, which in the aforementioned patent application Page 19 and modified in Figure 8 to the effect that the glass frit (40) is no longer used, the punch (39) made of the same plastic material as the cylinder (37) and now uniformly distributed over the entire support surface 21 of equal size Contains holes. The procedure and evaluation of the measurement remains unchanged compared to EP 0 640 330 A1. The flow is automatically detected.
  • the permeability (SFC) is calculated as follows:
  • the color measurement is carried out according to the CIELAB method (Hunterlab, Volume 8, Volume 1996, No. 7, pages 1 to 4) with a colorimeter, model "LabScan XE S / N LX17309" (HunterLab, Reston, USA) Colors over the coordinates L, a and b of a three-dimensional system are described.
  • the values for a and b indicate the position of the color on the color axes red / green and yellow / blue, where + a stands for red, -a for green, + b for yellow and -b for blue.
  • HC60 L-3b, the HC60 value is calculated.
  • the color measurement corresponds to the tristimulus method according to DIN 5033-6.
  • Measurement 1 (initial color): A 9 cm inner diameter plastic dish is filled with superabsorbent particles and then smoothed over the edge with a knife and the CIE color numbers and HC60 value are determined.
  • Measurement 2 (after aging): A 9 cm inner diameter plastic dish is filled with superabsorbent particles and then smoothed over the edge with a knife. The dish is then placed open in a controlled at 60 ° C cabinet with a constant relative humidity of 86%. The peel is taken out after 21 days. After cooling to room temperature, the CIE color numbers are determined.
  • aqueous saline Into a 100 ml beaker containing a 30 mm x 6 mm magnetic stir bar is placed 50.0 ml ⁇ 1.0 ml of 0.9 wt% aqueous saline. The temperature of the saline solution is 23 ° C ⁇ 0.5 ° C. Using a magnetic stirrer, the saline solution is stirred at 600 rpm.
  • the aluminum tray is placed with the superabsorbent granules and the whole arrangement is carefully turned upside down so that the sieve bottom is now down and the aluminum tray is on top.
  • a suitable sieve cover is placed on the sieve containing the aluminum shell with the superabsorbent granules and the entire arrangement is clamped in a screening machine (Retsch AS 200 control, available from Retsch GmbH, Rheinische Strasse 36, 42781 Haan, Germany).
  • the sieving is done for 1 minute at a set amplitude of 0.20 mm.
  • the assembly is removed from the screening machine, the sieve tray carefully removed and weighed; the weight is recorded as WUNC.
  • the proportion of baked superabsorbent granules is calculated according to:
  • the instrument used as a mixer was a ploughshare ® mixer with heating jacket, type M5, Gebr Lödige Maschinenbau GmbH, Elsener Street. 7 - 9, 33102 Paderborn, Germany.
  • Cublen ® K 2012 is 20 wt .-% aqueous solution of 1 -Hydroxiethan-1, 1 - diphosphonic acid, disodium salt and available from Zschimmer & Schwarz GmbH & Co KG Mohlsdorf, Chemnitztal Found 1, 09217 Burgmony, Germany.
  • Aeroxide ® Alu 130 is fumed alumina having a BET surface area of 130 m 2 / g.
  • Aerosil ® 200 is a hydrophilic fumed silica having a BET surface area of 200 m 2 / g.
  • Sipernat ® 22 S is hydrophilic precipitated silica with a BET surface area of 190 m 2 / g.
  • Sipernat ® D 17 is hydrophobicized precipitated silica having a BET surface area of 100 m 2 / g. These substances are available from Evonik Degussa GmbH, Rellinghauser Strasse 1 -1 1, 45128 Essen, Germany, or from their parent company Evonik Industries AG, Rodenbacher Clice 4, 63457 Hanau-Wolfgang, Germany.
  • Lohtragon ® is 200 ALA 20 wt .-% aqueous solution of Aluminiumdihydroxi- monoacetate and available from Dr. Paul Lohmann GmbH KG, 31857 Emmerthal, Germany.
  • Bruggolite ® FF7 is a mixture of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, riumbisulfit the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and NAT and available from L. Bruggemann KG, Salz Beau No 131, 74076 Heilbronn, Germany.
  • Laromer® ® LR 9015X is the triacrylate of fifteen times ethoxylated trimethylolpropane and available from BASF SE, Ludwigshafen, Germany.
  • DAROCUR ® 1173 is -one and available from BASF Switzerland AG, Basel, Switzerland
  • 2-hydroxy-2-methyl-1-phenylpropane first IRGACURE ® 651 is 2,2-dimethoxy-1 -one 2-diphenylethane-1 and also available from BASF Switzerland AG, Basel, Switzerland.
  • Z- Cote® is a microfine zinc oxide and available from BASF SE, Ludwigshafen, Germany.
  • Bayoxide ® Z is a transparent zinc carbonate and available from Lanxess Germany GmbH, Leverkusen, Germany.
  • Disperal.RTM ® 40 is an ultra-pure boehmite and available from Sasol Germany GmbH, Hamburg, Germany.
  • Solution I 0.10% by weight of N- (2-hydroxyethyl) -2-oxazolidinone ("HEONON”)
  • the product temperature was raised to 173 ° C and the reaction mixture was maintained at this temperature for 60 minutes at a shaft speed of 60 revolutions per minute.
  • the resulting product was allowed to cool back to room temperature and sieved.
  • the surface-postcrosslinked superabsorbent was recovered as a sieve fraction having particle sizes between 150 ⁇ m and 600 ⁇ m.
  • Example 2 was repeated, but instead of the aqueous Aluminiumtrilaktatlösun- gene from 0.00 to 1, 00 wt .-% Lohtragon ALA ® 200 was used (amount according to Table 2). The products thus obtained had the properties mentioned in Table 2.
  • Example 4 1300 g of the base polymer of Example 1 was used for surface post-crosslinking in the mixer at room temperature and a shaft speed of 250 revolutions per Minute coated by means of two dual-fluid spray nozzles with the following solutions (wt .-% each based on the polymer ("bop"), unless otherwise stated):
  • Solution I 0.10% by weight of N- (2-hydroxyethyl) -2-oxazolidinone ("HEONON”)
  • the product temperature was raised to 173 ° C and the reaction mixture was maintained at this temperature for 60 minutes at a shaft speed of 60 revolutions per minute.
  • the resulting product was allowed to cool back to room temperature and sieved.
  • the surface-postcrosslinked superabsorbent was recovered as a sieve fraction having particle sizes between 150 ⁇ m and 600 ⁇ m.
  • the base polymer thus prepared had a CRC of 38.5 g / g.
  • the product temperature was raised to 197 ° C and the reaction mixture was maintained at that temperature for 30 minutes at a shaft speed of 60 revolutions per minute.
  • the resulting product was allowed to cool back to room temperature and sieved.
  • the surface-postcrosslinked superabsorber was obtained as a sieve fraction with particle sizes between 150 ⁇ m and 850 ⁇ m.
  • Solution I 0.10% by weight of N- (2-hydroxyethyl) -2-oxazolidinone ("HEONON”)
  • 1000 g of the thus obtained surface-postcrosslinked polymer and 2.0 g Bayoxide ® Z are transparent to the upper flat coating in the mixer at room temperature and a shaft speed of 120 revolutions per minute by means of a two-fluid spray nozzles with 2.1 g of a mixture of one part by weight of polyethylene glycol 400 and sprayed two parts by weight of water within 5 minutes.
  • the mixture was subsequently mixed at a shaft speed of 60 revolutions per minute for a further 10 minutes.
  • Solution I 0.10% by weight of N- (2-hydroxyethyl) -2-oxazolidinone ("HEONON”)
  • the product thus obtained has the properties listed in Table 5.
  • the values in the Tables show that an increasing amount of added soluble aluminum salt reduces caking tendency (less “caking") but degrades the color numbers upon aging
  • the superabsorbent according to the invention has the optimum of tolerable caking tendency and tolerable color numbers after aging.

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Abstract

L'invention concerne un superabsorbant dont les surfaces sont complexées avec des ions métalliques multivalents et qui contient au moins un dérivé d'acide phosphonique, le rapport molaire entre le métal multivalent et le dérivé d'acide phosphonique étant d'au plus 1,2/n, n représentant le nombre de groupes d'acide phosphonique dans le dérivé d'acide phosphonique. Ledit superabsorbant présente une bonne stabilité par rapport à la décoloration et de manière surprenante une faible tendance à l'agglomération, sans que cela n'affecte grandement ses caractéristiques d'utilisation. De tels superabsorbants peuvent être produits par polymérisation d'une solution monomère aqueuse contenant a) au moins un monomère éthyléniquement insaturé portant des groupements acides, qui se présente sélectivement au moins partiellement sous forme de sel, b) au moins un agent de réticulation, c) au moins un amorceur, d) sélectivement un ou plusieurs monomères éthyléniquement insaturés pouvant être copolymérisés avec les monomères cités en a), et e) sélectivement un ou plusieurs polymères hydrosolubles. Le procédé selon l'invention consiste ensuite à sécher le polymère obtenu, sélectivement à broyer le polymère séché et à tamiser le polymère broyé, sélectivement à soumettre le polymère séché et éventuellement broyé et tamisé à une post-réticulation de surface, à ajouter au moins un sel d'un métal multivalent et à ajouter au moins un dérivé d'acide phosphonique. Ce procédé est caractérisé en ce qu'un sel du métal multivalent et le dérivé d'acide phosphonique sont ajoutés dans des quantités telles que le rapport molaire entre le métal et le dérivé d'acide phosphonique de 1,2/n, n représentant le nombre de groupes d'acide phosphonique dans le dérivé d'acide phosphonique, n'est pas dépassé.
PCT/EP2013/056120 2012-03-30 2013-03-22 Superabsorbant résistant à la décoloration WO2013144026A1 (fr)

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WO2018029045A1 (fr) 2016-08-10 2018-02-15 Basf Se Procédé de fabrication de superabsorbants
CN108884234A (zh) * 2016-12-13 2018-11-23 株式会社Lg化学 超吸收性聚合物及其制造方法
WO2019091848A1 (fr) 2017-11-10 2019-05-16 Basf Se Matériau superabsorbant
JP2019163473A (ja) * 2019-05-07 2019-09-26 株式会社リコー ハイドロゲル前駆体液及び立体造形用液体セット、並びに、それらを用いたハイドロゲル造形体及び立体造形物の製造方法

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KR101959547B1 (ko) 2016-03-25 2019-03-18 주식회사 엘지화학 고흡수성 수지의 제조 방법
WO2018080238A2 (fr) 2016-10-28 2018-05-03 주식회사 엘지화학 Polymère superabsorbant et son procédé de production
WO2019201669A1 (fr) * 2018-04-20 2019-10-24 Basf Se Procédé de production de superabsorbants

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