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EP2477664A1 - Superabsorbant à stabilité de couleur - Google Patents

Superabsorbant à stabilité de couleur

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Publication number
EP2477664A1
EP2477664A1 EP10751962A EP10751962A EP2477664A1 EP 2477664 A1 EP2477664 A1 EP 2477664A1 EP 10751962 A EP10751962 A EP 10751962A EP 10751962 A EP10751962 A EP 10751962A EP 2477664 A1 EP2477664 A1 EP 2477664A1
Authority
EP
European Patent Office
Prior art keywords
superabsorbent
acid
polymerization
weight
water
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP10751962A
Other languages
German (de)
English (en)
Inventor
Mark Elliott
Thomas Daniel
Norbert Herfert
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BASF SE
Original Assignee
BASF SE
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 filed Critical BASF SE
Priority to EP10751962A priority Critical patent/EP2477664A1/fr
Publication of EP2477664A1 publication Critical patent/EP2477664A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
    • C08K5/098—Metal salts of carboxylic acids
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS 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
    • A61L2400/00—Materials characterised by their function or physical properties
    • A61L2400/10—Materials for lubricating medical devices
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/0025—Crosslinking or vulcanising agents; including accelerators
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/0008—Organic ingredients according to more than one of the "one dot" groups of C08K5/01 - C08K5/59
    • C08K5/005—Stabilisers against oxidation, heat, light, ozone

Definitions

  • the present invention relates to a color-stable superabsorber, a process for its preparation and its use and 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 a multiple of their own weight of water and retain it under some pressure.
  • such a superabsorber has a CRC ("Centrifuge Retention Capacity", measuring method, see below) of at least 5 g / g, preferably at least 10 g / g and in a particularly preferred form at least 15 g / g.
  • CRC Chiptrifuge Retention Capacity
  • AUL absorption under load
  • AAP absorption against pressure
  • Swollen gel can hinder liquid transport to superabsorbers that have not yet swollen ("gel blocking") .
  • Good transport properties for liquids include, for example, hydrogels which have a high gel strength in the swollen state
  • Gels with only low gel strength are under an applied pressure ( Body pressure) deforms, clogs pores in the superabsorbent / cellulose fiber absorbent body and thus prevents further absorption of fluid.
  • a higher gel strength is usually achieved by a higher degree of cross-linking, which, however, reduces the absorption capacity of the product.
  • An elegant method for increasing the gel strength represents the increase in the degree of crosslinking on the surface of the superabsorbent particles in relation to the interior of the particles.
  • dried superabsorbent particles having an average crosslinking density are usually introduced he subjected additional crosslinking in a thin surface layer of their particles.
  • Surface postcrosslinking increases the crosslink density in the shell of the superabsorbent particles, raising the absorption under pressure to a higher level. While the absorption capacity in the surface layer of the superabsorbent particles decreases, their core has an improved absorption capacity compared to the shell due to the presence of mobile polymer chains, so that the shell construction ensures improved fluid transfer without gel blocking occurring. It is also known to produce super-crosslinked superabsorbers overall and to subsequently reduce the degree of crosslinking in the interior of the particles compared to an outer shell of the particles.
  • Acrylic acid-based superabsorbents which are most commonly used in the marketplace, 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 the polymerization
  • the polymer gel obtained in this way is comminuted (depending on the polymerization reactor used, this can be done simultaneously with the polymerization) and dried.
  • the dry powder obtained in this way (the "base polymer” or "polymer”) is neutralized to a certain degree.
  • Basispolymer is usually postcrosslinked on the surface of the particles by reacting with other crosslinkers such as organic crosslinkers or polyvalent cations, for example aluminum (usually as aluminum sulfate used) or both is implemented in order to produce a more crosslinked surface layer relative to the particle interior.
  • crosslinkers such as organic crosslinkers or polyvalent cations, for example aluminum (usually as aluminum sulfate used) or both is implemented in order to produce a more crosslinked surface layer relative to the particle interior.
  • 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
  • WO 2008/055856 A1 teaches the avoidance of discolorations of a superabsorber which are caused by excessively high iron content of the sodium hydroxide solution used to partially neutralize the acrylic acid in the preparation of the superabsorber by adding phosphoric acid or phosphate salts.
  • JP 05/086 251 A teaches the use of phosphoric acid derivatives or salts thereof, in particular 1-hydroxyethylidene-1, 1-diphosphonic acid, ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) or their alkali metal or ammonium salts as stabilizers of superabsorbers discoloration.
  • WO 03/059 962 A1 or the equivalent patent application US 2005/0085604 A1 discloses the use of Metal chelating agents in any step of superabsorbent production, and the addition of a reducing or oxidizing agent prior to drying the hydrous polymer as anti-discoloration agents.
  • WO 03/014 172 A2 relates to the production of superabsorbers from highly pure acrylic acid which has been freed from aldehydes, in particular to prevent discoloration of the superabsorbers.
  • 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 property "colorless” is often simply called “white”), phosphate, acetate or lactate, but not a halide. According to the teaching of WO 2006/058 682, discolorations of superabsorbents are avoided when the drying and the post-crosslinking reaction are carried out in an atmosphere which is substantially free of oxidizing gases.
  • EP 505 163 A1 discloses the use of a combination of surfactant and a double bond-adding compound such as unsubstituted or substituted alkyl or arylsulfinic acids or their salts to reduce residual monomers in superabsorbents.
  • EP 668 080 A2 and the partial application EP 1570 869 A1 relate to the use of organic acids, including sulfinic acids, but exclusively of salts of organic acids or sulfinic acids, or of polyamino acids or their salts for reducing residual surface postcrosslinkers, in particular of those used as surface postcrosslinkers Epoxy compounds, after surface postcrosslinking.
  • EP 386 897 A2, EP 441 975 A1 and EP 605 215 A1 teach the use of sulfites, hydrogen sulfites or thiosulfates for reducing residual monomers from the polymerization.
  • EP 1 645 596 A1 teaches the stabilization of superabsorbers against discoloration by addition of an inorganic salt, an aminocarboxylic acid chelating agent and an organic antioxidant.
  • an inorganic salt sulfites, bisulfites, pyrosulfites, dithionites, trithionates, tetrathionates, thiosulfates or nitrites are used.
  • EP 1 577 349 A1 teaches the use of these salts for the same purpose, but the content of the superabsorbent treated with iron is kept below 1 ppm by weight.
  • WO 2009/060062 or earlier International Patent Application Serial No. PCT / EP2009 / 059793 teach the addition of sulfinic acid derivatives to superabsorbents to stabilize them against discoloration.
  • WO 2008/092 842 A1 teaches the addition of a basic salt of a divalent metal cation to superabsorbers, inter alia, in order to increase the stability against discoloration.
  • WO 2008/092 843 A1 discloses the use of carboxylic acid salts and / or basic salts of trivalent metal cations for the same purpose.
  • WO 2005/054 356 A1 teaches the use of sterically hindered phenols instead of the technically customary para-methoxyphenol ("methylhydroxy”). quinone ",” MEHQ ”) as stabilizers for acrylic acid against polymerization, which have the advantage of less discoloration of the polymer.
  • Another object is to find other or even better superabsorbers which are stabilized against discoloration, in particular against yellowing or browning when stored under elevated temperature and / or elevated air humidity.
  • 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.
  • other properties should not be impaired, such as odor, which may be a problem with sulfur-containing reducing agents in the presence of moisture, or its flowability, which may be a problem with sodium hypophosphite additive, or dusting, which poses a problem when adding insoluble calcium salts can be.
  • Further objects of the invention are finding a method for the production of such a superabsorbent and uses of this superabsorbent.
  • the object has been achieved by a superabsorbent prepared by polymerization of a monomer mixture containing at least one ethylenically unsaturated, at least one acid group-carrying monomer, wherein before or during the polymerization and / or, if the polymerization is followed by a separate drying step, the polymer before the Drying at least 0.1 wt.% And at most 20 wt .-%, based on the total amount of ethylenically unsaturated, at least one acid group-carrying monomers (calculated as the free acid), at least one alkaline earth salt (calculated free of water of crystallization) was added, the selected from the salts of calcium, strontium or barium. Furthermore, a process for the preparation of this superabsorbent, uses of this superabsorbent as well as hygiene articles containing this superabsorber and processes for their preparation have been found.
  • the superabsorbers according to the invention show surprisingly good stability against discoloration without their use properties such as CRC, AUL or SFC being significantly impaired.
  • At least one water-soluble alkaline earth salt selected from the salts of calcium, strontium or barium is added to the superabsorbent according to the invention. Mixtures of salts of all possible combinations of two of these elements or all three of these elements can be used. In the technical effect, there is no significant difference between the salts of calcium, strontium or barium, but for economic reasons, calcium salts are most preferred.
  • the anions of the alkaline earth salts can basically be chosen freely, with the restriction that they must not lead to negative effects in the superabsorber and / or in its application.
  • Suitable anions of the alkaline earth metal salts are halides, in particular chloride, hydroxide, carbonate, carboxylate, such as formate, acetate, propionate or lactate, nitrate or sulfate. Mixtures can also be used.
  • water-soluble salts are used or those which, although themselves relatively poorly soluble in water, react rapidly with the acid groups of the superabsorbent or the monomers.
  • Such salts have the advantage, in particular in the customary preparation of the superabsorbent from water-containing monomer mixtures, that an equivalent amount of the neutralizing agent otherwise used can be saved.
  • the anions of the alkaline earth metal salt are selected accordingly, preference is given to hydroxide, carbonate or lactate.
  • Total preferred alkaline earth salts are calcium hydroxide, strontium hydroxide, barium hydroxide, calcium carbonate, strontium carbonate, barium carbonate, calcium lactate, strontium lactate, barium lactate, calcium sulfate, strontium sulfate, barium sulfate or mixtures thereof. Particularly preferred are calcium hydroxide, calcium carbonate, calcium lactate and calcium sulfate.
  • the alkaline earth salt is generally used in an amount of at least 0.1% by weight, preferably at least 0.5% by weight and more preferably at least 1% by weight and generally at most 20% by weight, preferably at most 10 wt .-% and in a particularly preferred form of at most 5 wt .-% added, in each case based on the total amount of ethylenically unsaturated, at least one acid group-carrying monomers. These are calculated as free acid, any total or partial neutralization of the acid groups is not taken into account in the calculation. Some alkaline earth salts may contain water of crystallization. This is also not taken into account in the calculation.
  • the superabsorbent according to the invention is prepared by polymerization of a monomer mixture containing at least one ethylenically unsaturated monomer bearing at least one acid group.
  • a process for the preparation of superabsorbents by polymerization of a monomer mixture which contains at least one ethylenically unsaturated monomer carrying at least one acid group is known.
  • a superabsorbent according to the invention is prepared, for example, by 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 partly 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.
  • Suitable monomers a) are, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
  • 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 furfurale, 0.0001% by weight maleic anhydride
  • 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), wherein 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.
  • Preferred 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, di- and triacrylates, as in EP 547 847 A1, EP 559 476 A1 , EP 632 068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO 2003/104301 A1 and DE 103 31 450 A1, mixed acrylates which, in addition to acrylate groups, contain further ethylenically unsaturated groups, such as in DE 103 31 456 A1 and DE 103 55
  • Preferred crosslinkers b) are pentaerythritol triallyl ether, Tetraallyloxiethan, methylenebismethacrylamide, 15 to 20 times ethoxylated trimethylolpropane triacrylate, 15-20-fold ethoxylated glycerol triacrylate, polyethylene glycol diacrylate with between 4 and
  • 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 retentive onskapaztician CRC
  • initiators c) it is possible to use all compounds which generate radicals under the polymerization conditions, for example thermal initiators, redox initiators, photoinitiators.
  • Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite.
  • Preference is given to using mixtures of thermal initiators and redox initiators, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid.
  • the mixture described in more detail below from the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite is preferably used (Brüggolit ® FF6M or Brüggolit ® FF7).
  • Examples of ethylenically unsaturated monomers d) which can be copolymerized with the ethylenically unsaturated monomers a) 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 .-%. It is also possible to use monomer suspensions, ie 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 alkaline earth salt (or mixture of alkaline earth salts) is intended to be added to the monomer mixture before or during the polymerization or, if the polymerization is followed by a separate drying step, to the polymer before drying, or partially before or during the polymerization and partly to the polymer before drying a uniform distribution of the alkaline earth salt in the superabsorbent.
  • the alkaline earth salt is mixed by method and time as described below for the neutralizing agent.
  • the simplest and therefore preferred is the addition into the monomer mixture before the polymerization.
  • the alkaline earth salt can but also be introduced during the polymerization or after the polymerization in the resulting polymer gel, but it is introduced in any case before drying.
  • the addition during the polymerization is particularly easy in the methods in which the polymerizing composition is mixed, for example, in polymerization in a kneader.
  • Drying is particularly easy in the case of processes in which the polymerized mass from the polymerization is passed into a separate drying step, ie in particular in all processes in which polymerization and drying are carried out in separate apparatuses.
  • the alkaline earth salt can be mixed into the polymer gel by means of any known mixing method and apparatus.
  • the alkaline earth salt is added as a dry substance or as a solution or dispersion in a solvent.
  • the solvent used is preferably water.
  • the preferred polymerization inhibitors require dissolved oxygen for optimum performance. Therefore, the monomer solution may be polymerized prior to polymerization by inerting, i. Flow through with an inert gas, preferably nitrogen or carbon dioxide, are freed of dissolved oxygen.
  • the oxygen content of the monomer solution prior to 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 other components used in such monomer mixtures include chelating agents to keep metal ions in solution.
  • the acid groups of the polymer gels obtained from the polymerization are usually partially neutralized.
  • the neutralization is preferably carried out at the stage of the monomers, in other words salts of the acid group-carrying monomers or, strictly speaking, a mixture of acid group-carrying monomers and salts of the acid group-carrying monomers ("partially neutralized acid") as component a) in the polymerization
  • This is usually done by mixing the neutralizing agent as an aqueous solution or preferably also as a solid in the monomer mixture intended for the polymerization or preferably in the acid group-carrying monomer or a solution thereof
  • the degree of neutralization is preferably from 25 to 95 mol%, particularly preferably 50 to 80 mol%, very particularly preferably from 65 to 72 mol%, it being possible to use the customary neutralizing agents, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal bicarbonates and mixtures thereof Salts can also be used ammonium
  • 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. For this purpose, 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 72 mol% salt of the acid group-bearing 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.
  • the alkaline earth metal salt used is a water-soluble or, although relatively poorly soluble, relatively fast-reacting alkaline earth metal salt, the amount of neutralizing agent equivalent to the amount of alkaline earth metal ions added can be saved.
  • the alkaline earth salt may also serve as a neutralizing agent at the same time, the divalent alkaline earth ion replacing two monovalent alkali ions.
  • alkaline earth metal hydroxides, carbonates and lactates are suitable.
  • processes for producing superabsorbents from monomer mixtures such as those exemplified above are known.
  • Suitable polymerization reactors are, for example, kneading reactors or belt reactors.
  • EP 445 619 A2 and DE 19 846 413 A1 a polymer gel which must be comminuted in a further process step, for example in a meat grinder, extruder or kneader.
  • a polymer gel which must be comminuted in a further process step, for example in a meat grinder, extruder or kneader.
  • 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 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 (measurement method for the residual moisture or water content, see below).
  • 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 under reduced partial pressure of oxygen, to prevent oxidative yellowing, as a rule but also leads to adequate ventilation and drainage of Wa 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.
  • Polymer particles with too small particle size lower the permeability (SFC).
  • 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
  • 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 ".
  • 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 (I)
  • R 1 is Ci-Ci2-alkyl, C 2 -C 2 hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, R 2 X or OR 6 '
  • R 3 is hydrogen, Ci-Ci 2 -alkyl, C 2 -C 2 hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, or X,
  • R 4 Ci-Ci 2 -alkyl, C 2 -C 2 hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl
  • R 5 is hydrogen, Ci-Ci 2 -alkyl, C 2 -C 2 hydroxyalkyl, C 2 -Ci2 alkenyl, Ci-Ci2 acyl or
  • R 6 Ci-Ci 2 -alkyl, C 2 -C 2 hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, and
  • X is a carbonyl oxygen common to the radicals R 2 and R 3 , where R 1 and R 4 and / or R 5 and R 6 may be a bridged C 2 -C 6 alkanediyl, and where the abovementioned radicals R 1 to R 6 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 , more preferably less than 80 g / mol, most preferably less than
  • R 7 is either an unbranched alkylene 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 7 is an unbranched, branched or cyclic alkylene radical, or polyols of the general formula (Ib)
  • radicals R 8 , R 9 , R 10 , R 11 independently of one another denote hydrogen, hydroxyl, hydroxymethyl, hydroxyethyloxymethyl, 1-hydroxyprop-2-yloxymethyl, 2
  • R 18 , R 19 , R 20 , R 21 , R 22 , R 23 , R 24 and R 25 are independently hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or isobutyl
  • R 26 represents a single bond, a linear, branched or cyclic C 2 -C 12 -alkylene radical, or a polyalkoxydiyl radical which is composed of one to ten ethylene oxide and / or propylene oxide units, such as, for example, have polyglycol dicarboxylic acids.
  • Preferred postcrosslinkers of the general formula (I) 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 amidacetals such as 5-methyl-1 -aza-4,6-dioxa-bicyclo [3.3.0] octane, 1-aza-4,6 -dioxabicyclo [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-hydroxy
  • Particularly preferred postcrosslinkers of the general formula (I) are 2-oxazolidone, N-methyl-2-oxazolidone, N- (2-hydroxyethyl) -2-oxazolidone and N-hydroxypropyl-2-oxazolidone.
  • Preferred postcrosslinkers of the general formula (IIa) are 1, 3-propanediol, 1, 5-pentanediol, 1, 6-hexanediol and 1, 7-heptanediol.
  • Further examples of postcrosslinkers of the formula (IIa) are 1, 3-butanediol, 1, 8-octanediol, 1, 9-nonanediol and 1, 10-decanediol.
  • the diols are preferably water-soluble, wherein the diols of the general formula (IIa) 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 postcrosslinkers of the general formula (IIb) 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 (IIa) and (IIb) have a viscosity at 23 ° C. 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 (III) are ethylene carbonate and propylene carbonate.
  • a particularly preferred postcrosslinker of the general formula (IV) 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 substance 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. Furthermore, for the purpose of the invention also single-fluid nozzles, such as Slot nozzles or swirl chambers (full cone nozzles) are used (for example, nozzles-Schlick GmbH, DE, or by Spraying Systems Germany 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 assistants the ethoxylated and alkoxylated derivatives of 2-propylheptanol, which are marketed under the brand names Lutensol® XL ® and Lutensol XP ® (BASF SE, Carl-Bosch-Strckee 38, 67056 Ludwigshafen hafen, 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 aid 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 not more than 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
  • ketones such as acetone
  • carboxylic acid esters such as ethyl acetate.
  • a disadvantage of some of these cosolvents is that they are typical Have their own 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. This is particularly the case when the postcrosslinker is relatively inert and therefore can itself form its cosolvent, such as when using cyclic carbonates of the general formula (III), diols of the general formula (IIa) or polyols of the general formula (IIb) , 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 (IIa), the polyols of the general formula (IIb) and the cyclic carbonates of the general formula (III) are also suitable as cosolvents. They fulfill this function in the presence of a reactive postcrosslinker of the general formula (I) and / or (IV) and / or a di- or triglycidyl compound.
  • preferred cosolvents in the process according to the invention are, in particular, the diols of the general formula (IIa), especially when the hydroxyl groups are hindered sterically by neighboring groups on a reaction.
  • diols are in principle also suitable as postcrosslinkers, 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 (IIa) and polyols of general formula (IIb), with amide acetals or carbamates of general formula (I).
  • Suitable combinations are, for example, 2-oxazolidone / 1, 2-propanediol and N- (2-hydroxyethyl) -2-oxazolidone / 1, 2-propanediol and ethylene glycol diglycidyl ether / 1, 2-propanediol.
  • 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.
  • solvents, cosolvents or co-crosslinkers are those with 2-oxazolidone or (2-hydroxyethyl) -2-oxazolidone in the following solvents, cosolvents or co-crosslinkers: isopropanol, 1, 3-propanediol, 1, 2-propylene glycol, ethylene carbonate, propylene carbonate 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 Nachvernetzerates based on the base polymer is usually from 0.3 to 15 wt .-%, preferably from 2 to 6 wt .-%.
  • 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 but is usually carried out in a downstream dryer, such as a hopper dryer, a rotary kiln, a paddle or disc dryer or a heated screw ielsweise 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 hopper dryer, a rotary kiln, a paddle or disc dryer or a heated screw ielsweise 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
  • 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 in such a way 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 a particularly preferred form at least 0.5% by weight, and also 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), but it is preferred Oxidizing gases are substances which have a vapor pressure of at least 1013 mbar at 23 ° C.
  • oxygen, nitrogen oxide and nitrogen dioxide in particular oxygen less than 140 mbar, preferably less than 100 mbar, particularly preferably less than 50 mbar, very particularly preferably less than 10 mbar, if the thermal postcrosslinking is carried out at ambient pressure, ie at a total pressure of around 1013 mbar,
  • the proportion of oxidizing gases is preferably less than 14% by volume, preferably less than 10% by volume, more preferably less than 5% by volume, most preferably less than 1% by volume.
  • 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 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 cations are applied to the particle surface in addition to the postcrosslinkers before, during or after the postcrosslinking.
  • This is in principle a further surface postcrosslinking by ionic, noncovalent bonds, but is occasionally referred to as “complexing” with the respective metal ions or simply as a “coating” with the relevant substances (the “complexing agent").
  • Polyvalent cations are applied by spraying solutions of divalent or polyvalent cations, usually divalent, trivalent or tetravalent metal cations, but also polyvalent cations, such as formally wholly or partly polymers of vinylamine monomers, such as partially or completely hydrolyzed polyvinylamines.
  • the amine groups are always partially protonated to ammonium groups, even at very high pH values.
  • divalent metal cations which can be used are, in particular, the divalent cations of metals of groups 2 (in particular Mg, Ca, Sr, Ba).
  • trivalent metal cations which may be used are in particular the trivalent cations of metals of groups 3 including the lanthanides (especially Sc, Y, La, Ce), 8 (especially Fe), 1 1 (especially Au) and 13 (especially Al) of the Periodic Table of the Elements are examples of useful tetravalent cations 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 ohl be used alone as well as in a mixture with each other. Particularly preferred is the use of trivalent metal cations. Especially preferred is the use of aluminum cations.
  • metal salts which have sufficient solubility in the solvent to be used are suitable.
  • metal salts with weakly complexing anions such as, for example, chloride, nitrate and sulfate, hydrogensulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate or dihydrogenphosphate.
  • Preferred are salts of mono- and dicarboxylic acids, hydroxy acids, keto acids and amino acids or basic salts. Examples are acetates, propionates, tartrates, maleates, citrates, lactates, malates and succinates.
  • hydroxides are also preferred.
  • 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.
  • aqueous solutions which is obtained by dissolving the solid salts 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% by weight, preferably at least 0.01% by weight, and in a particularly preferred form at least at least 0.1% by weight, for example at least 0.4% by weight and generally at most 5% by weight, preferably at most 2.5% by weight and in a particularly preferred form at most 1% by weight, for example at most 0.7% by weight, based in each case on the mass of the base polymer.
  • the salt of the trivalent 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, for example, water / methanol, water / 1, 2-propanediol and water / 1, 3-propanediol.
  • the treatment of the base polymer with solution of a divalent or 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 in the same step is carried out 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.
  • coolers in which the product is moved that is to say cooled mixers, for example blade coolers, disk coolers or paddle coolers.
  • 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.
  • a mean residence time in the condenser of generally at least 1 minute, preferably at least 3 minutes and most preferably
  • Form at least 5 minutes and generally at most 6 hours, preferably at most 2 hours, and most preferably at most 1 hour. and the cooling capacity is such 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 in particularly preferred form has 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 the appropriate place; Agglomerates after comminution.
  • the particle sizes desired for surface postcrosslinked superabsorbents are the same as for base polymers.
  • the superabsorbents according to the invention are provided with further additives which stabilize against discoloration.
  • additives may be added at any appropriate time. They are preferably added to the superabsorber, ie not the monomer solution or a monomer, but only when crosslinked polymer is present, that is, at the earliest during the polymerization. They can be added, for example, during the polymerization, during a surface postcrosslinking or after the surface postcrosslinking.
  • Such stabilizers against discoloration are, for example, derivatives of sulfinic acid.
  • Particularly suitable derivatives of sulfinic acid are, for example, compounds of the following formula (V):
  • 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 27 is OH or NR 30 R 31 , wherein R 30 and R 31 independently of one another are H or C 1 -C 6 -alkyl;
  • R 28 is H or an alkyl, alkenyl, cycloalkyl or aryl group, this group optionally having 1, 2 or 3 substituents which are independently selected from C 1 -C 6 -alkyl, OH, O-C 1 -C 6 -alkyl, Alkyl, halogen and CF3; and
  • R 29 is COOM, SO 3M, COR 30 , CONR 30 R 31 or COOR 30 , wherein M, R 30 and R 31 have the meanings given above or, when R 28 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 27 is preferably a hydroxy or amino group.
  • R 28 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 29 is preferably either COOM or COOR 30 (M and R 30 have the abovementioned meanings) or, when R 27 is aryl which may be substituted as indicated above, also for a hydrogen atom.
  • the superabsorbent contains compounds of the above formula wherein M is an alkali metal ion or one equivalent of an alkaline earth metal or zinc ion; R 27 is a hydroxy or amino group; R 28 is H or alkyl and R 29 is COOM or COOR 30 , wherein when R 29 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 29 is COOR 30 R 30 is C 1 -C 6 -alkyl.
  • the superabsorbent contains compounds of the above formula wherein M is an alkali metal ion or one equivalent of an alkaline earth metal or zinc ion; R 27 is a hydroxy or amino group; R 28 is aryl which is optionally substituted as indicated above, in particular hydroxyphenyl or C 1 -C 4 alkoxyphenyl; and R 29 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), and 14 (C, Si, Ge, Sn, Pb) of the Periodic Table of the Elements in the current numbering of I UPAC (International Union of Pure and Applied Chemistry, 104 TW Alexander Drive, Building 19, Research Tri- angle Park, NC 27709, USA, www.iupac.org), the international nomenclature body responsible for chemistry, corresponds to Groups Ia, Ia Ib, IVa and VIb in the numbering used by CAS (Chemical Abstracts Service, 2540 Olentangy River Road, Columbus, OH 43202, USA, www.cas.org).
  • the sulfinic acid derivatives of the above formula can be used in pure form, but optionally also in the usual manner resulting from the preparation of such compounds with the sulfite of the corresponding metal ion and the corresponding sulfonic acid.
  • the preparation of such sulfinic acid derivatives of the above formula is known and described for example in WO 99/18 067 A1. They are also common commercial goods 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.
  • Hindered phenols are understood as meaning phenols which have a single or double-branched substituent, preferably a double-branched substituent, at least in the 2-position and optionally also in the 6-position on the phenyl ring.
  • Branched substituents are understood to mean substituents which bear at least two radicals other than hydrogen on the atom bonded to the phenyl ring of the phenol, apart from the C atom of the phenyl ring to which they are attached.
  • sterically hindered phenols are also those which carry a sterically demanding unbranched substituent at least in the 2-position and optionally also in the 6-position.
  • substituents which comprise at least 6, preferably at least 8, and in particular preferred form at least 12 atoms other than hydrogen, but on the atom bonded to the phenyl ring of the phenol other than the C atom of the phenyl ring to which they are attached. only carry a rest other than hydrogen.
  • the simplest examples of branched-branched substituents are secondary alkyl radicals such as 2-propyl, 2-butyl, 2-pentyl, 3-pentyl, ethylhexyl or cycloalkyl radicals such as cyclobutyl, cyclopentyl, cyclohexyl or aromatic radicals such as phenyl.
  • di-branched substituents are tertiary alkyl radicals such as tert-butyl, tert-pentyl or norbornenyl.
  • unbranched radicals are hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl, but also neo-pentyl, neo-hexyl or dodecylthiomethyl. All of these radicals can also be substituted or contain atoms other than carbon and hydrogen.
  • the phenyl ring of the phenol may, in addition to the substituent in the 2-position and optionally in the 6-position, also optionally carry further substituents. Examples of preferred sterically hindered phenols are 2-tert.
  • stabilizers against discoloration are in particular reducing substances.
  • solid or dissolved salts and esters of phosphinic acid (H3PO2) are preferred, as are their own.
  • all phosphinates (also called hypophosphites) of the alkali metals, including ammonium, and the alkaline earth metals are suitable.
  • aqueous solutions of phosphinic acid which contain phosphinones and at least one cation selected from sodium, potassium, ammonium, calcium, strontium, aluminum, magnesium.
  • esters of phosphinic acid or salts of esters of phosphinic acid An example of this is sodium diphenylphosphinate.
  • solid or dissolved salts and esters of phosphonic acid are also preferred.
  • Phosphonic acid is tautomeric with phosphorous acid, the latter does not exist as free acid.
  • Genuine derivatives of phosphorous acid are only their triesters, commonly referred to as phosphites.
  • the derivatives of tautomeric phosphonic acid are usually se referred to as phosphonates.
  • all primary and secondary phosphonates of the alkali metals, including ammonium, and the alkaline earth metals are suitable.
  • aqueous solutions of phosphonic acid which contain primary and / or secondary phosphonations and at least one cation selected from sodium, potassium, calcium, strontium.
  • phosphites or phosphonates examples include calcium bis [monoethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate], tris (2,4-di-tert-butylphenyl) phosphite, 3,9-bis ( octadecyloxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane and bis (2,4-di-tert-butylphenol) pentaerythritol diphosphite.
  • Stabilizers may simultaneously be phosphonates or phosphites and hindered phenols.
  • the superabsorber according to the invention is mixed with at least one inorganic water-insoluble particulate solid.
  • any inorganic water-insoluble powder is suitable for this purpose.
  • examples are generally solid, chemically inert (i.e., non-superabsorbent) species such as oxides, oxide hydroxides, hydroxides, sulfates, carbonates, zeolites, inorganic pigments, minerals or clays.
  • sulfates such as magnesium sulfate or barium sulfate
  • carbonates such as calcium carbonate, magnesium carbonate or dolomite
  • silicates such as calcium silicate or magnesium silicate
  • carbides such as perlite or silicon carbide, diatomaceous earth or fly ash.
  • 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, silicon dioxide, tin oxide, lead oxide, lanthanum oxide or ceria.
  • 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 silicon dioxide.
  • 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.
  • the inorganic water-insoluble solid is particulate, it is in powder form.
  • the average 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 ⁇ , more preferably 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 means of sieve analysis, but it is simpler and therefore preferred to determine the particle size by means of laser diffraction technology. These methods are well known and routinely performed on suitable and commercially available equipment.
  • the above anti-discoloration stabilizers and the inorganic water-insoluble particulate solid, when added, are generally in amounts of at least 0.0001% by weight, preferably at least 0.001% by weight, and most preferably at least 0.025 Wt .-% and generally at most 3 wt .-%, in a preferred form at most 2 wt .-% and in a particularly preferred form at most 0.5 wt .-% added, in each case based on the total weight of the superabsorbent according to the invention.
  • a lower amount of known stabilizers against discoloration is necessary with the alkaline earth salt-containing superabsorber according to the invention than without alkaline earth salt.
  • the mixture of superabsorbers with discoloration stabilizers and the inorganic water insoluble particulate solid can be made by any known mixing method.
  • Stabilizers against discoloration and the inorganic water-insoluble particulate solid can be mixed in bulk, as a solution or as a suspension in a solvent or suspending agent, preferably they are mixed because of the easier homogeneous distribution as a solution or suspension. It does not necessarily produce a physical mixture that can be easily separated by mechanical means.
  • the additives may well enter into a firmer connection with the superabsorber, for example as a comparatively firmly adhering surface layer or as particles firmly adhering to the surface of the superabsorber particles.
  • the incorporation of the additives into the known superabsorber can certainly also be understood and referred to as a "coating".
  • a solvent or suspending agent is used as the solvent or suspending agent, which is chemically compatible with both the superabsorbent and the additive, that is to say that no undesired chemical reactions occur therewith.
  • 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 surfactant may be added to the solution or suspension.
  • the additive is generally mixed with the superabsorbent in exactly the same way as the superabsorbent surface postcrosslinked solution or suspension containing a surface postcrosslinker, as described below.
  • the additive may be applied as a constituent of the surface postcrosslinking solution 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 superabsorbent coated with surface postcrosslinking agent and additive then passes through the further process steps required for surface postcrosslinking, for example a thermally induced reaction of the surface postcrosslinking agent with the superabsorbent. This process is comparatively simple and economical.
  • the additive is preferably applied after the surface postcrosslinking in a separate process step. If the additive is applied as a solution or suspension, it is applied to the already surface-postcrosslinked superabsorber in the same way as 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.
  • 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 polyvinylamine, polyethylenimine or polyallylamine), or all of them, may be applied to the surface of the superabsorber particles, whether postcrosslinked or postcrosslinked, in the manufacturing process in any process step as required the 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 and sprayed in the form of dispersions, then they are preferably used as aqueous dispersions, and it is preferably additionally applied a dedusting 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, glycerol , Sorbitol and neopentyl glycol.
  • 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.
  • 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 above 40 g / g.
  • the superabsorbers according to the invention typically have an absorption under pressure (AUL0.7 psi, measuring method see below) of at least 18 g / g, preferably at least 20 g / g, preferably at least 22 g / g and usually not more than 30 g / g.
  • AUL0.7 psi absorption under pressure
  • the superabsorbent according to the invention further typically have a saline flow conductivity (SFC measurement method s. Below) of at least 10x10 "7 cm 3 sec / g, preferably at least 30x10" 7 cm 3 sec / g, preferably at least 40x10 "7 cm 3 s / g and usually not over 1000x10 "7 cm 3 s / g.
  • SFC measurement method s below
  • the L value of the superabsorbent (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 superabsorber (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 superabsorbent (CIE color number) in the non-stored state is typically from 0 to 12, preferably from 2 to 1.
  • the superabsorber according to the invention After the relatively stressful aging test described below, the superabsorber according to the invention, after measurement for the L and a values, has only slightly worse results compared to the non-stored state, in particular b values of preferably not more than 13, particularly preferably not more than 12, up.
  • b values preferably not more than 13, particularly preferably not more than 12, up.
  • 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 because this discoloration can be perceived by the consumer in use.
  • a further subject of the present invention are hygiene articles containing superabsorbents 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 .-%, especially preferably from 80 to 100% by weight, very particularly preferably from 90 to 100% by weight, of superabsorbents according to the invention, wherein the coating 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 superabsorbents of the invention are also suitable for the preparation of completely analogous Structures using UV-crosslinkable hotmelt adhesives which are sold, for example, as AC-Resin® (BASF SE, Germany).
  • UV-crosslinkable hot-melt adhesives which are sold, for example, as AC-Resin® (BASF SE, Germany).
  • AC-Resin® BASF SE, 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 combination of the superabsorbents according to the invention with UV-crosslinkable hotmelt 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 components of packaging material for water or moisture sensitive articles, such as 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 plaster, water-absorbing material for burn dressings or for other weeping wounds), cosmetics (carrier material for pharmaceutical chemicals and medicaments, 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, as adhesives in a
  • 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 the preparation of articles for the absorption of 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.
  • the superabsorbent is tested using the test methods described below.
  • CRC Centrifuge Retention Capacity
  • the absorption under a pressure of 2068 Pa (0.3 psi) of the superabsorbent is determined according to the standard test method no. WSP 242.2-05 "Absorption under pressure".
  • the absorption under a pressure of 4826 Pa (0.7 psi) of the superabsorbent is determined analogously to the standard test method no. WSP 242.2-05 "absorption under pressure", but with a weight of 49 g / cm 2 (leads to a pressure of 0.7 psi) instead of a weight of 21 g / cm 2 (leading to a pressure of 0.3 psi) is used.
  • Gel coating is determined from superabsorbent particles, wherein the apparatus described in the aforementioned patent application on page 19 and in Figure 8 is modified so that the glass frit (40) is no longer used, the punch (39) consists of the same plastic material as the cylinder (37) and now evenly distributed over the entire contact surface contains 21 holes of the same size. The procedure and evaluation of the measurement remains unchanged compared to EP 0 640 330 A1. The flow is automatically detected.
  • Fluid transfer is calculated as follows:
  • A is the area of the gel layer in cm 2 and WP is the hydrostatic pressure over the gel layer in dynes / cm 2 .
  • the permeability is determined as described in US 2005/0 256 757 A1 in paragraphs [0061] to [0075]. Moisture content of the hydrogel (residual moisture, water content)
  • the water content of the water-absorbing polymer particles is determined according to the standard test method no. WSP 230.2-05 "Moisture content”.
  • the mean particle size of the product fraction is determined according to the standard test method no. WSP 220.2-05 "Particle size distribution”.
  • 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)
  • the values for a and b indicate the position of the color on the red / green color axes or yellow / blue, where + a stands for red, -a for green, + b for yellow and -b for blue
  • the color measurement corresponds to the tristimulus method according to DIN 5033-6. aging test
  • 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.
  • the mixture was freed by passing nitrogen through a glass frit of oxygen.
  • 0.51 g of sodium persulfate (dissolved in 5 ml of water) and 0.06 g of hydrogen peroxide (dissolved in 6 ml of water) were added and the monomer solution was transferred to a glass dish.
  • the glass dish was so dimensioned that a layer thickness of the monomer solution of 5 cm was established.
  • 0.047 g of mixture were acid from the sodium salt of 2-hydroxy-2-sulfinatoessig-, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite (Brüggolit ® FF6, L.
  • the resulting gel was wound three times using a standard meat grinder with 6 mm perforated disc and dried in a laboratory oven at 160 ° C for one hour. The product was then ground and the sieve fraction was recovered from 150-850 ⁇ .
  • Example 7-9 and Comparative Example V7 In a ploughshare ® -Schaufeltrockner with 5 l volume and heating / cooling jacket (manufacturer: Gebr Lödige Maschinenbau GmbH, Elsener-Strasse 7-9, 33102 Paderborn, Germany; VT 5R-MK.
  • the initiator was a 3% strength by weight solution of 2,2'-azobis [2- (2-imidazolin-2-yl) -propane] -dihydrochloride in deionized water whose temperature was 25 ° C., at a metering rate of 2.2 kg / h via a static mixer, which was connected directly to the Vertropfer metered into the monomer mixture.
  • the resulting polymer particles were screened to separate any agglomerates formed.
  • the sieve fraction of 150 to 850 ⁇ was recovered as a product.
  • General Procedure IV dry mixtures
  • the components to be mixed were placed in a polyethylene sample bottle (500 ml capacity) and intimately mixed with a tumble mixer (type T2C, Willy A. Bachofen AG Maschinenfabrik, Basel, Switzerland) for 15 minutes.
  • a tumble mixer type T2C, Willy A. Bachofen AG Maschinenfabrik, Basel, Switzerland
  • a superabsorbent was prepared, but using only 72.8 g of the 50 wt .-% sodium hydroxide solution and the monomer solution in addition 1.17.6 g Ca (OH) 2 and 802 g of ice instead of only 675th g of ice were added.
  • example 1
  • a superabsorbent was prepared in which 7.84 g of Ca (OH) 2 dispersed in 75 ml of water were added to the gel, which was first crushed in the mincer. This mixture was homogenized by kneading by hand and then added two more times.
  • Example V3 shows that although a further increase in the calcium content makes it de color values are achieved in particular after aging and such Superabsorber also has high gel strength, but has an undesirably low absorption capacity.
  • a superabsorbent was prepared except that 16.0 g CaCC "3 were added to the monomer solution and only 478 g ice was used instead of 459 g and 244.3 g acrylic acid instead of 213.9 g.
  • a superabsorbent was prepared, but the monomer was additionally added 320.0 g of a 5 wt .-% aqueous calcium lactate solution and only 155 g of ice instead of 459 g were used.
  • the superabsorbent of Example C1 was the surface post in a ploughshare ® mixer with heating jacket (manufacturer: Gebr Lödige Maschinenbau GmbH, Elsener-Strasse 7-9, 33102 Paderborn, Germany; Type M5.) At room temperature and a shaft speed of 450 revolutions per minute by means of a two-fluid spray nozzle with a mixture of 0.10 wt .-% ethylene glycol diglycidyl ether (dena col ® EX-810 from Nagase ChemteX Corporation, Osaka, Japan), 1, 50 wt .-% 1, 2-propanediol, 2.8 wt .-% water and 0.4 wt .-% aqueous aluminum sulfate solution (26.8 wt .-%), each based on the base polymer, coated.
  • a ploughshare ® mixer with heating jacket manufactured by means of a two-fluid spray nozzle with a mixture of 0.10
  • the product temperature was raised to 150 ° C and the reaction mixture was maintained at that temperature for 60 minutes at a shaft speed of 80 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 having particle sizes between 150 ⁇ m and 850 ⁇ m.
  • Example V1 1 was repeated with the superabsorber of Example 2.
  • Example V12 (Comparative) In a laboratory mixer (manufacturer Waring Products, Inc., Torrington, Connecticut, USA, Model 34 BL 99 (8012)) with two opposing rounded mixing blades and breakwater on the lid (comparable results are also found in many other mixers with good Mixing is achieved during the task of the postcrosslinking solution, whereby it must be ensured that the stirring elements do not break up the superabsorbent - the stirring speed must be adjusted accordingly), 20 g of the superabsorber from Example V7 were initially charged.
  • Example V12 was repeated with the superabsorber of Example 7.
  • Example C10 100 g of the superabsorber of Example C10 were mixed with 0.5 g of a precipitated silica (Sipernat ® Type 22 S, Evonik Degussa GmbH; Frankfurt; Germany) were mixed according to the general procedure IV.
  • a precipitated silica Sipernat ® Type 22 S, Evonik Degussa GmbH; Frankfurt; Germany
  • Example V13 was repeated with the superabsorber of Example 10.
  • Example V14 (comparison)
  • Example V1 1 The superabsorbent of Example V1 1 was mixed in a ploughshare ® mixer (manufacturer: Gebr. Lödige Maschinenbau GmbH, Elsener-7 - 9, 33102 Paderborn, Germany; Type M5) at room temperature and a shaft speed of 250 revolutions per minute by means of a two-substance Spray nozzle with 2.0 wt .-% (based on the superabsorbent) of a 7.5 wt .-% aqueous solution of sodium hypophosphite coated. After spraying, mixing was continued for 15 minutes at a shaft speed of 80 revolutions per minute and freed from lumps by means of a 850 ⁇ m sieve.
  • Example V14 was repeated with the superabsorbent of Example 11.
  • Example 15
  • Example V16 (comparison)
  • Example 16 100 g of the superabsorbent of Example V12 were mixed with 0.025 g of calcium bis [monoethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate] according to general procedure IV.
  • Example 16 100 g of the superabsorbent of Example V12 were mixed with 0.025 g of calcium bis [monoethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate] according to general procedure IV.
  • Example 16 100 g of the superabsorbent of Example V12 were mixed with 0.025 g of calcium bis [monoethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphonate] according to general procedure IV.
  • Example 16 100 g of the superabsorbent of Example V12 were mixed with 0.025 g of calcium bis [monoethyl (3,5-di-tert-butyl-4-hydroxybenzyl
  • Example V 16 was repeated with the superabsorbent of Example 12.
  • Example 17 was repeated with the superabsorbent of Example 12.
  • Example V18 (comparison)
  • the superabsorbent of Example C10 was a ploughshare ® mixer (manufacturer: Gebr. Lödige Maschinenbau GmbH, Elsener-7 - 9, 33102 Paderborn, Germany; Type M5) at room temperature and a shaft speed of 250 revolutions per minute by means of a two-substance Spray nozzle with 2.0 wt .-% (based on the superabsorber) of a 1.75 wt .-% aqueous solution of Brüggolit ® FF7 coated. After spraying, mixing was continued for 15 minutes at a shaft speed of 80 revolutions per minute and freed from lumps by means of a 850 ⁇ m sieve.
  • Example V18 was repeated with the superabsorber of Example 10.
  • Example 19 was repeated with the superabsorber of Example 10.
  • Example 10 100 g of the superabsorber of Example 10 were mixed with 0.025 g of 3,9-bis (octadecyloxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5] undecane according to general procedure IV.

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Abstract

L'invention concerne un superabsorbant, obtenu par polymérisation d'un mélange de monomères qui contient au moins un monomère à insaturation éthylénique portant au moins un groupe acide, où, avant ou pendant la polymérisation et/ou, si une étape de séchage séparée suit la polymérisation, on a ajouté au polymère avant le séchage au moins 0,1 % en poids et au plus 20 % en poids, sur la base de la quantité totale de monomères à insaturation éthylénique portant au moins un groupe acide (calculés en tant qu'acide libre), au moins un sel alcalino-terreux (calculé exempt d'eau de cristallisation), qui est choisi parmi les sels de calcium, de strontium ou de baryum. Le superabsorbant présente une stabilité améliorée à des changements de couleur lors d'un stockage aux hautes températures ou en présence d'une forte humidité.
EP10751962A 2009-09-17 2010-09-14 Superabsorbant à stabilité de couleur Withdrawn EP2477664A1 (fr)

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KR20180128462A (ko) 2016-03-28 2018-12-03 가부시키가이샤 닛폰 쇼쿠바이 흡수제의 제조 방법
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US8815770B2 (en) 2014-08-26
JP2013505313A (ja) 2013-02-14

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