EP2358820A1 - Mélange de polymères superabsorbants à post-réticulation superficielle, présentant différentes post-réticulations superficielles - Google Patents

Mélange de polymères superabsorbants à post-réticulation superficielle, présentant différentes post-réticulations superficielles

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Publication number
EP2358820A1
EP2358820A1 EP09751907A EP09751907A EP2358820A1 EP 2358820 A1 EP2358820 A1 EP 2358820A1 EP 09751907 A EP09751907 A EP 09751907A EP 09751907 A EP09751907 A EP 09751907A EP 2358820 A1 EP2358820 A1 EP 2358820A1
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EP
European Patent Office
Prior art keywords
mixture
different
postcrosslinked
postcrosslinking
base polymer
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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.)
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EP09751907A
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German (de)
English (en)
Inventor
Stefan Bruhns
Thomas Daniel
Dieter Hermeling
Ulrich Riegel
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BASF SE
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BASF SE
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Priority to EP09751907A priority Critical patent/EP2358820A1/fr
Publication of EP2358820A1 publication Critical patent/EP2358820A1/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Withdrawn legal-status Critical Current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
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
    • C08J3/245—Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
    • 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
    • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
    • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
    • A61L15/42—Use of materials characterised by their function or physical properties
    • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2300/00—Characterised by the use of unspecified polymers
    • C08J2300/14—Water soluble or water swellable polymers, e.g. aqueous gels

Definitions

  • the present invention relates to a mixture of surface postcrosslinked superabsorbents with different surface postcrosslinking.
  • it relates to a mixture of superabsorbers of different average particle size, which are differently surface-postcrosslinked. It further relates to a process for the preparation of such a mixture as well as its use and hygienic articles containing such a mixture.
  • 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 “, water-absorbent polymer” or the like in common use.
  • crosslinked hydrophilic polymers in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft, crosslinked cellulose or starch ethers, crosslinked carboxymethylcellulose, partially crosslinked polyalkylene oxide or Swellable in aqueous liquids natural products, such as guar derivatives, with superabsorbents based on partially neutralized acrylic acid are the most widespread.
  • the essential properties of superabsorbents are their ability to absorb many times their own weight in aqueous liquids and to not release the liquid under some pressure.
  • the superabsorber which is used in the form of a dry powder, transforms into a gel when it absorbs liquid, with the usual absorption of water corresponding to a hydrogel.
  • Crosslinking is essential for synthetic superabsorbents and an important difference to common pure thickeners, since 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 applications include water retention in agricultural horticulture, water storage to protect against fire, liquid absorption in food packaging, or, more generally, moisture absorption.
  • 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 min. at least 5 g / g, preferably at least 10 g / g and in a particularly preferred form at least 15 g / g.
  • a "superabsorber” may also be a mixture of materially different individual superabsorbers or a mixture of components which only show superabsorbent properties when interacting, it is less important on the material composition than on the superabsorbent properties.
  • AUL absorption under load
  • AAP absorption against pressure
  • Swollen gel can hinder fluid transport to superabsorbers that are 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) deformable, clog pores in the superabsorbent / cellulose fiber absorbent body and thus prevent further fluid absorption.
  • a higher gel strength is usually achieved by a higher degree of crosslinking, whereby, however, the absorption capacity of the product is reduced.
  • An elegant method for increasing the gel strength Increasing the degree of crosslinking at the surface of the superabsorbent particles in relation to the interior of the particles.
  • superabsorber particles having an average crosslinking density which are usually dried in a surface postcrosslinking step are 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, due to the presence of mobile polymer chains, has an improved absorption capacity compared to the shell, so that the shell construction ensures improved fluid transfer without gel blocking occurring. It is also known to produce overall higher crosslinked superabsorbents 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 on the market, are prepared by free-radical polymerization of acrylic acid in the presence of a crosslinker (the "internal crosslinker"), the acrylic acid before, after or partly before, partly after the polymerization is neutralized to a certain extent, usually by adding alkali, usually an aqueous sodium hydroxide solution
  • the polymer gel thus obtained is comminuted (depending on the polymerization reactor used, this can be done simultaneously) carried out with the polymerization) and dried.
  • base polymer or “base polymer”
  • base polymer is usually postcrosslinked to the surface of the particles by reaction with other crosslinkers such as organic crosslinkers or polyvalent cations, for example aluminum (usually used as aluminum sulfate) or both, to produce a more crosslinked surface layer relative to the particle interior.
  • crosslinkers such as organic crosslinkers or polyvalent cations, for example aluminum (usually used as aluminum sulfate) or both, to produce a more crosslinked surface layer relative to the particle interior.
  • EP 691 133 A1 teaches a mixture of superabsorbers with different absorption capacity and different absorption capacity under pressure. Different non-surface-postcrosslinked superabsorbers or a non-surface postcrosslinked superabsorber are mixed with a surface postcrosslinked superabsorber.
  • a further object is to find new or improved superabsorbents and processes for producing such superabsorbents.
  • the increase in the absorption capacity (CRC) and the retention or the absorption capacity under pressure load (AUL) of the superabsorber is a constant task.
  • the superabsorbent mixture according to the invention can be produced by mixing at least two differently surface-postcrosslinked superabsorbents with any mixing method. Also, three, four, five or any other number of different surface postcrosslinked superabsorbents can be mixed. Both surface-postcrosslinked superabsorbents themselves and mixing processes are known.
  • superabsorbents which have different surface postcrosslinking agents are to be understood as meaning those superabsorbents which have been treated differently with surface postcrosslinking agents in terms of their type, amount and / or aftertreatment and have thereby been subjected to different surface postcrosslinking.
  • Nonlimiting examples of differently surface-postcrosslinked superabsorbers are, for example, superabsorbents. absorbers applied with varying amounts of surface postcrosslinker (in weight percent surface postcrosslinker based on the particular base polymer), superabsorbents charged with different surface postcrosslinkers, or superabsorbers which have been post treated in a different manner after application of the surface postcrosslinker , in particular at different temperature or after-treatment for different lengths. It is possible to mix superabsorbents which differ only in such a feature, in several or in all.
  • the different surface postcrosslinked superabsorbers can, but need not differ in surface postcrosslinking.
  • the degree of surface postcrosslinking can be determined indirectly via the decrease in the CRC of the SAP, since this decreases with the degree of surface postcrosslinking.
  • the increase in SFC can also be used as a measure of the surface postcrosslinking degree.
  • the mixing can take place after the surface postcrosslinking, but also during the surface postcrosslinking.
  • the components of the mixture undergo a portion of the surface postcrosslinking together.
  • the heat treatment is typically carried out in a heated apparatus continuously conveying under agitation.
  • Such apparatuses are frequently used in chemical engineering for drying powders and are usually referred to simply as continuous "dryers.”
  • the feeding of base polymers separately treated with surface postcrosslinkers at different points in such a dryer results in a mixture of heat treatment of at least different duration
  • the mixture of superabsorbers with different surface postcrosslinking contains a mixture of differently surface postcrosslinked sieve cuts of a base polymer.
  • the mixture according to the invention can essentially be a mixture of differently surface-postcrosslinked sieve cuts of a base polymer or can also be a mixture of different surface postcrosslinked sieve cuts of a base polymer, ie consist of different surface postcrosslinked wire cuts of a base polymer.
  • sieve cut is understood as meaning a fraction of the total particle size distribution of a base polymer
  • Different sieve cuts differ in average particle size, which can be determined either by sieve analysis or by optical methods such as light scattering or laser diffraction
  • they can also be obtained by other classification methods, for example by air classification including the separation in the air stream in cyclones, whereby in such methods secondary effects, for example due to density or particle shape, can occur, which are taken into account in the usual way.
  • any number of sieve cuts can be present in the mixture.
  • the mixture contains at least two different screen sections of a base polymer, which have been treated separately with surface postcrosslinking agent and subsequently heat treated for different periods of time.
  • a mixture is produced in a particularly simple manner by feeding the sieve cuts treated with surface postcrosslinking agents at various points of a heated apparatus (a continuous drier) continuously conveying with thorough mixing, so that the individual sieve cuts are heat treated for different lengths of time.
  • the mixture according to the invention in this case contains sieve cuts, which has been heat treated the longer, the lower their average particle size diameter.
  • the superabsorbers present in the mixture according to the invention can be prepared in different ways, for example by solution polymerization, suspension polymerization, dropwise or spray polymerization. Such methods are known.
  • a preferred polymerization process according to the invention for the preparation of acrylate superabsorbers is the aqueous solution polymerization of a monomer mixture comprising a) at least one ethylenically unsaturated, acid group-carrying monomer which is optionally present at least partly as a salt, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a), and e) optionally one or more water-soluble polymers.
  • the 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, maleic anhydride, and itaconic acid or its 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 of furfurals, 0.0001% by weight of maleic anhydride, 0.0003% by weight of diacrylic acid and 0.0050% by weight of hydroquinone monomethyl ether.
  • the proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, very particularly preferably at least 95 mol%.
  • the monomer solution preferably contains at most 250 ppm by weight, preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight and preferably at least 10 ppm by weight, more preferably at least 30 ppm by weight, in particular by 50% by weight.
  • ppm hydroquinone half-ethers, based in each case on the unneutralized monomer a), 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 can be used with a corresponding content of Hydrochinonraumether.
  • 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 are bonded to 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, as in DE 103 31 456 A1 and DE 103 55 401 A1, or crosslinker mixtures, as described, for example, in DE 195 43 368 A1, DE 196 46 484 A1, WO 90/15830 A1 and WO 2002/32962 A2.
  • Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, trimethylolpropane triacrylate 10 to 20 times ethoxylated, trimethylolethane triacrylate 10 to 20 times ethoxylated, particularly preferably 15-times ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylates having 4 to 30 ethylene oxide units in the polyethylene glycol chain, trimethylolpropane triacrylate , Di- and triacrylates of 3 to 30-fold ethoxylated glycerol, more preferably di- and triacrylates of 10-20-ethoxylated glycerol, and triallylamine.
  • the polyesters which are not completely esterified with acrylic acid can also be present here as Michael adducts with themselves, as a result of which tetra-, penta- or even higher acrylates may also be present.
  • 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 from 1 to 5 times ethoxylated and / or propoxylated glycerin.
  • Most preferred are the triacrylates of 3 to 5 times ethoxylated and / or propoxylated glycerol, in particular the triacrylate of 3-times ethoxylated glycerol.
  • the amount of crosslinker b) is preferably from 0.05 to 1, 5 wt .-%, particularly preferably 0.1 to 1 wt .-%, most preferably 0.3 to 0.6 wt .-%, each based on Monomer a).
  • the centrifuge retention capacity (CRC) decreases and the absorbance increases under a pressure of 0.3 psi (AUL 0.3psi).
  • initiators c) it is possible to use all compounds which generate free 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 reducing component but a mixture of the sodium salt of 2-hydroxy-2-sulfinato is preferably acetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and Natriumbisul- used fit (as Brüggolit ® FF6M or Brüggolit ® FF7, alternatively Bruggolite ® FF6M or Bruggolite ® FF7 available from L. Brüggemann KG, salt Straße 131, 74076 Heilbronn, Germany, www.brueggemann.com).
  • Examples of ethylenically unsaturated monomers d) which can be copolymerized with the ethylenically unsaturated monomers a) include acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, maleic acid and maleic anhydride.
  • water-soluble polymers e it is possible to use polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified cellulose.
  • an aqueous monomer solution is used.
  • the water content of the monomer solution is preferably from 40 to 75 wt .-%, particularly preferably from 45 to 70 wt .-%, most preferably from 50 to 65 wt .-%.
  • monomer suspensions 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 preferred polymerization inhibitors require dissolved oxygen for optimum performance. Therefore, the monomer solution can be freed of dissolved oxygen prior to the polymerization by inertization, ie, flowing through with an inert gas, preferably nitrogen or carbon dioxide.
  • the oxygen content of the monomer solution before polymerization is reduced to less than 1 ppm by weight, more preferably less than 0.5 ppm by weight, most preferably less than 0.1 ppm by weight.
  • the monomer mixture may contain other components.
  • examples of other components used in such monomer mixtures include chelating agents to keep metal ions in solution.
  • Suitable polymerization reactors are, for example, kneading reactors or belt reactors.
  • the polymer gel formed in the polymerization of an aqueous monomer solution or suspension is comminuted continuously by, for example, counter-rotating stirring shafts, as described in WO 2001/38402 A1.
  • the polymerization on the belt is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928.
  • Polymerization in a belt reactor produces a polymer gel which must be comminuted in a further process step, for example in one
  • Meat grinder, extruder or kneader it is also possible to produce spherical superabsorbent particles by suspension, spray or drop polymerization processes.
  • the acid groups of the polymer gels obtained 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”) are used as component a) in the polymerization
  • the degree of neutralization is preferably from 25 to 95 mol%, more preferably from 50 to 80, usually 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 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 zen also ammonium salts can be used.
  • Sodium and potassium are particularly preferred as alkali metal cations, but very particular preference is given to sodium hydroxide, sodium carbonate or sodium bicarbonate and mixtures thereof.
  • the polymer gel is at least partially neutralized after the polymerization
  • the polymer gel is preferably comminuted mechanically, for example by means of an extruder, wherein the neutralizing agent can be sprayed, sprinkled or poured on and then thoroughly mixed in.
  • the gel mass obtained can be extruded several times for homogenization.
  • the monomer a) used is a mixture of from 25 to 95 mol%, particularly preferably from 50 to 80 mol%, very particularly preferably from 65 to 72 mol% salt of the acid group carrier 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 more preferred, but also more expensive is the 50% by weight, usually sold as "amalgam grade” or "mercury process". Sodium hydroxide or potassium hydroxide solution.
  • 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). If the residual moisture content is too high, the dried polymer gel has too low a glass transition temperature Tg and is difficult to process further. If the residual moisture content is too low, the dried polymer gel is too brittle and in the subsequent comminution steps undesirably large amounts of polymer particles with too small particle size ("fines") are produced.
  • mixer with a mechanical mixing element such as a paddle dryer or a similar dryer can be used with differently designed mixing tools.
  • the dryer may be operated under nitrogen or other non-oxidizing inert gas, or at least a reduced partial pressure of oxygen, to prevent oxidative yellowing.
  • nitrogen or other non-oxidizing inert gas or at least a reduced partial pressure of oxygen, to prevent oxidative yellowing.
  • sufficient ventilation and removal of the water vapor also leads to an acceptable product.
  • Advantageous in terms of color and product quality is usually the shortest possible drying time.
  • a temperature of the gas used for drying to at least 50 0 C, preferably at least 80 0 C and in a particularly preferred form of at least 100 0 C and generally of at most 250 0 C, preferably at most 200 0 in the usual mode C and in a particularly preferred form of at most 180 0 set C.
  • Common belt dryers often have multiple chambers, the temperature in these chambers may be different. For each type of dryer, the operating conditions as a whole must be selected in a known manner so that the desired drying result is achieved.
  • 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 often not dried on the inside, are rubber-elastic, cause grinding problems and are preferably used before grinding
  • Grind separation which can be done easily by air classification or a sieve ("protective sieve" for the mill) .
  • the mesh size of 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 done by conventional classification, for example, air classification or sieving through a sieve with a mesh size of at most 1000 microns, preferably at most 900 .mu.m, more preferably at most 850 microns and most preferably at most 800 microns. For example, sieves with 700 ⁇ m, 650 ⁇ m or 600 ⁇ m mesh size are used.
  • the separated coarse-grained polymer particles 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 by a sieve with a mesh size of at most 300 microns, preferably at most 200 microns, more preferably at most 150 microns and most preferably at most 100 microns used.
  • 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 average particle size of the polymer particles separated as a product fraction is generally at least 200 .mu.m, preferably at least 250 .mu.m, and preferably at least 300 .mu.m and generally at most 600 .mu.m and preferably at most 500 .mu.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 microns is generally at least 90 wt .-%, preferably at least 95 wt .-% and most preferably at least 98 wt .-%.
  • 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, and such a non-surface postcrosslinked superabsorber is distinguished from a surface postcrosslinked superabsorber prepared therefrom often called "base polymer” or "base polymer”.
  • the superabsorbent particles are postcrosslinked on their surface to further improve the properties, in particular increase the AUL and SFC values (with the CRC value decreases).
  • the base polymers used for surface postcrosslinking may be identical or different.
  • the product fraction of the base polymer (ie, the fraction that is neither undersize nor oversize) is divided into at least two wire cuts or recovered in at least two wire cuts, which are subsequently surface postcrosslinked and blended into the blend of this invention.
  • both the base polymer obtained in a first screening step can be separated again into two or more wire cuts in a second step, or the product fraction can be obtained in several wire cuts simultaneously with the separation of oversize and / or undersize become.
  • the classification does not necessarily have to be done by sieving, but can be done by any known classification method. Screening is merely the most convenient method in most cases.
  • a non-limiting example of a possible separation into sieve cuts is, for example, the recovery of a fraction of 100-850 ⁇ m particle size diameter as a product fraction (ie particles which do not pass a sieve with a mesh size of 850 ⁇ m are referred to as oversize grains and particles which are placed on a sieve 150 microns mesh size are not isolated, are separated as undersize), which is obtained by using an intermediate sieve of 400 microns mesh size in two sieve fractions of 100-400 and 400-850 microns particle size diameter.
  • intermediate sieve of 400 microns mesh size in two sieve fractions of 100-400 and 400-850 microns particle size diameter In an analogous manner, by using several and / or other intermediate sieves, other product fractions and other sieve cuts can be obtained.
  • 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 in 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 Ci-Ci2-alkyl, C 2 -C 2 hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl,
  • 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 -C 2 -alkenyl, Ci-Ci2 acyl, or C 6 -C 2 -aryl, R 6 Ci-Ci2 alkyl, C2 -Ci2-hydroxyalkyl, C 2 -C 2 -alkenyl or C 6 -C 2 aryl, and
  • X is a common carbonyl oxygen for the radicals R 2 and R 3
  • R 1 and R 4 and / or R 5 and R 6 may be a bridged C 2 -C 6 alkanediyl, and wherein the abovementioned radicals R 1 to R 6 may still have a total of one to two free valencies and with these free valences can be connected to at least one suitable base body,
  • 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 70 g / mol, per Hydroxyl group and no vicinal, geminal, secondary or tertiary hydroxyl groups, and polyhydric alcohols either diols of general formula (IIa)
  • R 7 is either an unbranched dialkyl radical of the formula - (CH 2 ) n -, where n is an integer from 3 to 20, preferably 3 to 12, and both hydroxy groups are terminal, or R 7 is an unbranched, branched or cyclic dialkyl radical means, or polyols of the general formula (IIb)
  • radicals R 8 , R 9 , R 10 , R 11 independently of one another denote hydrogen, hydroxyl, hydroxymethyl, hydroxyethyloxymethyl, 1-hydroxyprop-2-yloxymethyl, 2-hydroxypropyloxymethyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, n-hexyl, 1, 2-dihydroxyethyl, 2-hydroxyethyl, 3-hydroxypropyl or 4-hydroxybutyl and a total of 2, 3, or 4, preferably 2 or 3, hydroxy groups are present, and not more than one of Radicals R 8 , R 9 , R 10 , or R 11 is hydroxyl, are
  • R 12 , R 13 , R 14 , R 15 , R 16 and R 17 are independently hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or isobutyl, and n is either 0 or 1,
  • 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 -dialkyl radical, or a polyalkoxydiyl radical which is composed of one to ten ethylene oxide and / or propylene oxide units, such as, for example, polyglycol dicarboxylic acids.
  • Preferred postcrosslinkers of the general formula (II) 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-hydroxyethy
  • 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 secondary crosslinkers 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 at 23 ° C. a viscosity of less than 3000 mPas, preferably less than 1500 mPas, preferably less than 1000 mPas, more preferably less than 500 mPas, very particularly preferably less than 300 mPas, on.
  • Particularly preferred postcrosslinkers of the general formula (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.
  • the postcrosslinker is generally used in an amount of at least 0.001% by weight, preferably at least 0.02% by weight, more preferably at least 0.05% by weight, and generally at most 2% by weight, preferably at most 1% by weight, in a particularly preferred form at most 0.3% by weight, for example at most 0.15% by weight or at most 0.095% by weight, in each case based on the mass of the base polymer applied thereto (for example, the relevant sieve fraction).
  • the postcrosslinking is usually carried out by spraying a solution of the postcrosslinker onto the dried base polymer particles. Subsequent to the spraying, the polymer particles coated with postcrosslinker are thermally dried, wherein the postcrosslinking reaction can take place both before and during the drying. If surface postcrosslinkers with polymerizable groups are used, the surface postcrosslinking can also be carried out by free-radically induced polymerization of such groups by means of common free-radical formers or else by means of high-energy radiation such as UV light. This may be done in parallel or instead of using postcrosslinkers that form covalent or ionic bonds to functional groups on the surface of the base polymer particles.
  • the spraying of Nachvernetzeraims is preferably carried out in mixers with moving mixing tools, such as screw mixers, disc, paddle or paddle mixers or mixers with other mixing tools.
  • moving mixing tools such as screw mixers, disc, paddle or paddle mixers or mixers with other mixing tools.
  • vertical mixers particularly preferred are vertical mixers.
  • Suitable mixers are flocking for example as a plow mixer ® Gebr Lödige Maschinenbau GmbH, Elsener Street. 7 - 9, 33102 Paderborn, Germany, or ® as Schugi ® Flexomix mixer, Vrieco-Nauta ® mixer or blender Turbulizer® ® from Hosokawa Micron BV, Gildenstraat 26, 7000 AB Doetinchem, The Netherlands.
  • the applicable spray nozzles are subject to no restriction. Suitable nozzles and atomization systems are described, for example, in the following references: Atomization of Liquids, Expert-Verlag, Vol. 660, series Kunststoff & Meeting, Thomas Richter (2004) and in atomization technology, Springer-Verlag, VDI series, Günter Wozniak (2002 ). Applicable are mono- and polydisperse spray systems. Among the polydisperse systems are single-fluid pressure nozzles (jet or lamella-forming), rotary atomizers, two-component atomizers, ultrasonic atomizers and impact nozzles. In the two-component atomizers, the mixture of the liquid and the gas phase can take place both internally and externally.
  • the spray pattern of the nozzles is not critical and can take any shape, such as omnidirectional, fan-beam, wide-angle omnidirectional or circular ring spray pattern. It is advantageous to use a non-oxidizing gas, if two-component atomizers are used, particularly preferably nitrogen, argon or carbon dioxide.
  • a non-oxidizing gas if two-component atomizers are used, particularly preferably nitrogen, argon or carbon dioxide.
  • the liquid to be sprayed can be supplied under pressure. The division of the liquid to be sprayed can take place in that it is relaxed after reaching a certain minimum speed in the nozzle bore.
  • single-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 crosslinking agents 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 assistant is metered so that the surface tension of an aqueous extract of the swollen base polymer and / or the swollen postcrosslinked SAP at 23 0 C is at least 0.060 N / m, preferably at least 0.062 N / m, more preferably at least 0.065 N / m, and advantageous is at most 0.072 N / m.
  • the aqueous postcrosslinker solution may also contain a cosolvent in addition to the at least one postcrosslinker.
  • a cosolvent in addition to the at least one postcrosslinker.
  • the penetration depth of the postcrosslinker can be adjusted in the polymer particles.
  • cosolvents are C 1 -C 6 -alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol or 2-methyl-1-propanol, C 2 -C 5 -diols, such as Ethylene glycol, 1, 2-propylene glycol or 1, 4-butanediol, ketones, such as acetone, or carboxylic acid esters, such as ethyl acetate.
  • cosolvents have typical odors.
  • the cosolvent itself is ideally not a post-crosslinker 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 the case, in particular, when the postcrosslinker is relatively inert and therefore can itself form its cosolvent, for example when using cyclic carbonates of the general formula (IV), diols of the general formula (IIIa) or polyols of the general formula ( IIIb).
  • 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 diol 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, however, they require significantly higher reaction temperatures or optionally higher amounts of use than sterically unhindered diols.
  • Particularly preferred combinations of less reactive postcrosslinker as cosolvent and reactive postcrosslinker are combinations of preferred polyhydric alcohols, diols of general formula (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 cover crosslinkers: isopropanol, 1,3-propanediol, 1,2-propylene glycol or mixtures thereof.
  • 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 superabsorber with surface postcrosslinker and drying can take place, for example, in a fluidized bed dryer usually in a downstream dryer, such as a tray dryer, a rotary kiln, a paddle or disc dryer or a heated screw performed piellust as Solidair ® or Torusdisc ® -T Rockner from Bepex International LLC, 333 NE Taft Street, Minneapolis, MN 55413, USA, or as a paddle or paddle dryer or as a fluidized bed dryer of Nara Machinery Co., Ltd., branch Europa, Europa Allee 46, 50226 Frechen, Germany available.
  • a downstream dryer such as a tray dryer, a rotary kiln, a paddle or disc dryer or a heated screw performed piellustrated 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
  • 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 0 C from previous process steps, the postcrosslinker solution may have a temperature of 0 to 70 0 C.
  • the postcrosslinker solution can be heated to reduce the viscosity.
  • Preferred drying temperatures are in the range 100 to 250 0 C, preferably 120 to 220 0 C, particularly preferably 130 to 210 ° C most preferably 150 to 200 0 C. by weight
  • 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 ., to carry out the postcrosslinking under reduced partial pressure of oxidizing gases oxidizing gases are substances which have at 23 0 C a vapor pressure of at least 1013 mbar and act in combustion processes as the oxidant, for example oxygen, nitric oxide and nitrogen, particularly oxygen.
  • oxidizing gases are substances which have at 23 0 C a vapor pressure of at least 1013 mbar and act in combustion processes as the oxidant, for example oxygen, nitric oxide and nitrogen, particularly oxygen.
  • the partial pressure is an oxidizing gas less than 140 mbar, preferably less than 100 mbar, particularly preferably less than 50 mbar, very particularly preferably less than 10 mbar, is the thermal postcrosslinking carried out at ambient pressure, ie at a total pressure of around 1013 mbar , the total partial pressure of the oxidizing gases is determined by their volume fraction.
  • the proportion of oxidizing gases is preferably less than 14% by volume, preferably less than 10% by volume, 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.
  • At least two superabsorbents which have been surface-postcrosslinked in the context of the above description of typical conditions of the surface postcrosslinking but in different ways from one another, are subsequently mixed.
  • two or more different sieve sections of a base polymer are treated separately with surface postcrosslinking agent, conveniently by spraying in a vertical mixer as described above. This can take place in two or, depending on the number of sieve fractions used, of a plurality of mixers operated in parallel or successively in a mixer, which of course requires intermediate storage of sieve cuts treated with surface postcrosslinking agent.
  • Type and amount of surface Post-crosslinking agent may be the same or different for each sieve fraction.
  • sieve cuts can be treated separately in each case for carrying out the surface post-crosslinking reaction in a dryer and then mixed.
  • these sieve fractions, which are subjected to surface postcrosslinking agent are introduced into the latter at different points of a continuously conveying dryer.
  • Continuously conveying dryers are those in which the product stream to be dried is conveyed continuously from the inlet to the outlet of the dryer during drying.
  • the content of the dryer is also moved to bring the entire contents in contact with the heating surfaces.
  • a certain, sometimes intensive mixing of the dryer contents takes place, there is usually also a certain backmixing, but the cross-mixing dominates by far.
  • the residence time distribution of the product in the dryer is closer to the residence time distribution of a flow tube reactor than to that of a stirred tank reactor.
  • the remixing ratio (ie, the maximum deviation in residence time of 95% by weight of all particles introduced into the dryer at the first product feed point of the dryer in the dryer from the mean residence time of all the particles introduced into the dryer at the first product feed point of the dryer) is not more than 50%, preferably not more than 40%, and more preferably not more than 30%.
  • Very particularly preferred are backmixing ratios of not more than 20%. Methods for measuring the backmixing ratio are known; in most cases, the appearance of a marking substance is tracked over time. For example, a conventional method for measuring the remixing ratio in a continuously conveying kneader is described in WO 2006/034806 A1, which is also directly applicable to continuously conveying dryers.
  • a remixing ratio for product supplied to further feed points can be measured analogously.
  • the remixing ratio is influenced by the design, in particular the type and arrangement of the delivery tools and the operating parameters of the dryer, in particular the level, and can be adjusted to the desired value, all of which is known.
  • Dryers suitable for the process according to the invention are in particular disk and paddle dryers or heated screws, preferably paddle dryers.
  • base polymers (which may be but need not be different in size from the mesh slips of the same base polymer) are introduced at different locations into a continuous dryer.
  • the different feed locations in the dryer are spaced from each other to achieve the desired effect.
  • these supply sites are at least so spaced that the difference in the average residence time of the product streams fed in at adjacent feed sites, expressed as a percentage, is greater than the remixing ratio of the product streams fed at the two adjacent feed sites.
  • a shorter distance is usually meaningless, since then takes place by the backmixing in effect no different length heat treatment of the individual supplied products.
  • the feed sites are spaced such that the difference in average residence time of the product streams fed to adjacent feed sites is, in percentage terms, at least twice the remixing ratio of the product streams fed at the adjacent feed sites, and more preferably, they are spaced such that this difference is at least three times greater.
  • two screen sections of a base polymer are separately treated with surface postcrosslinking agent, one of these screen sections at the beginning, i. fed to the first product inlet of the dryer and the other halfway between the beginning and product outlet of the dryer. If the product level in the dryer over its length is identical (which can be set differently, for example, by the type and arrangement of the delivery tools) and the temperature in the dryer is the same throughout, is fed in this way, the second supplied sieve cut half as intense as the heat first.
  • the simplest embodiment of the process according to the invention for producing a mixture of differently surface-postcrosslinked superabsorbent is, in the usual screening of a base polymer, ie the separation of oversize and undersize, additionally to use an intermediate screen and thus the product in the form of two wire sections, a finer and a Obtain coarser to apply these two screen sections separately with surface postcrosslinking agent, for example, in each case a vertical mixer, and at two different points of a continuously conveying dryer in these initiate.
  • the further workup is again common as for a uniform surface post-cured superabsorber usual.
  • 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 sometimes also referred to as “complexing” with the respective metal ions or simply as “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 of vinylamine monomers, such as partially or completely hydrolyzed polyvinylamide
  • divalent metal cations which may be used are, in particular, the divalent cations of metals of groups 2 (in particular Mg, Ca, Sr, Ba), 7 (in particular Mn), 8 (in particular Fe), 9 (in particular Co), 10 (in particular Ni), 11 (in particular Cu) and 12 (in particular Zn) of the Periodic Table of the Elements
  • Examples of trivalent metal cations which may be used are in particular the trivalent cations of metals of the groups 3 including the lanthanides (in particular Sc, Y, La, Ce), 8 (in particular Fe), 11 (in particular Au), 13 (in particular Al) and 14 (in particular Bi) of the Periodic Table of the Elements.
  • tetravalent cations are, in particular, the tetravalent cations of metals of the lanthanides (in particular Ce) and of group 4 (in particular Ti, Zr, Hf) of the Periodic Table of the Elements.
  • the metal cations can be used alone or mixed with each other. Particularly preferred is the use of trivalent metal cations. Very particularly preferred is the use of aluminum cations. Of the cited metal cations, all metal salts which have sufficient solubility in the solvent to be used are suitable.
  • metal salts with weakly complexing anions such as chloride, nitrate and sulfate, hydrogen sulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate, or dihydrogen phosphate.
  • Preferred are salts of mono- and dicarboxylic acids, hydroxy acids, keto acids and amino acids or basic salts. Examples which may be mentioned are preferably acetates, propionates, tartrates, maleates, citrates, lactates, malates, succinates.
  • hydroxides Particularly preferred is the use of 2-hydroxycarboxylic acid salts such as citrates and lactates.
  • alkali metal and alkaline earth metal aluminates and their hydrates such as sodium aluminate and its hydrates, alkali metal and alkaline earth metal lactates and citrates and their hydrates, aluminum acetate, aluminum propionate, aluminum citrate and aluminum lactate.
  • the cations and salts mentioned can be used in pure form or as a mixture of different cations or salts.
  • the salts of the two and / or trivalent metal cation used may contain further secondary constituents such as unneutralized carboxylic acid and / or alkali metal salts of the neutralized carboxylic acid.
  • Preferred alkali metal salts are those of sodium, potassium and ammonium. They are typically used as an aqueous solution, which is obtained by dissolving the solid 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 wt .-%, preferably at least 0.01 wt .-% and in a particularly preferred form at least 0.1 wt .-%, for example at least 0.4 wt .-% and generally at most 5 wt .-%, preferably at most 2.5 wt .-% and in a particularly preferred form at most 1 wt .-%, for example at most 0.7 wt .-% in each case based on the mass of the base polymer.
  • the salt of the 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 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 up- Spraying of the metal salt solution onto the superabsorbent particles can take place 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 ,
  • Basic salts are salts capable of increasing the pH of an acidic aqueous solution, preferably a 0.1 N hydrochloric acid. Basic salts are usually salts of a strong base with a weak acid.
  • the divalent metal cation of the optional basic salt is preferably a metal cation of group 2 of the Periodic Table of the Elements, more preferably calcium or strontium, most preferably calcium.
  • the basic salts of divalent metal cations are preferably salts of more inorganic acids, weak organic acids and / or salts of amino acids, more preferably hydroxides, bicarbonates, carbonates, acetates, propionates, citrates, gluconates, lactates, tartrates, malates, succinates, maleates and / or fumarates, most preferably hydroxides, bicarbonates, carbonates, propionates and / or lactates.
  • the basic salt is preferably water-soluble. Water-soluble salts are salts which at 20 ° C.
  • salts which have this minimum solubility at the spray-on temperature of the spray solution can also be used according to the invention.
  • the hydrates of said salts can be used, which often dissolve faster in water than the anhydrous salts.
  • Suitable basic salts of divalent metal cations are, for example, calcium hydroxide, strontium hydroxide, calcium hydrogencarbonate, strontium hydrogencarbonate, calcium acetate, strontium acetate, calcium propionate, calcium lactate, strontium propionate, strontium lactate, zinc lactate, calcium carbonate and strontium carbonate.
  • dispersions of the solid salt in its saturated aqueous solution can also be used.
  • calcium carbonate, strontium carbonate, calcium sulfite, strontium sulfite, calcium phosphate and strontium phosphate can also be used as aqueous dispersions.
  • the amount of basic salt of the divalent metal cation, based on the mass of the base polymer, is typically from 0.001 to 5% by weight, preferably from 0.01 to 2.5% by weight, preferably 0.1 to 1.5% by weight .-%, more preferably from 0.1 to 1 wt .-%, most preferably from 0.4 to 0.7 wt .-%.
  • the basic salt of the divalent metal cation can be used as a solution or suspension.
  • these are calcium lactate solutions or calcium hydroxide suspensions.
  • the salts with an amount of water of not more than 15% by weight, preferably not more than 8% by weight, more preferably not more than 5% by weight, most preferably not more than 2% by weight. % sprayed on the superabsorber.
  • an aqueous solution of the basic salt is sprayed onto the superabsorbent.
  • the basic salt is added simultaneously with the surface postcrosslinker, the complexing agent, or as another component of the solutions of these agents.
  • addition in admixture with the complexing agent is preferred. If the solution of the basic salt is not miscible with the solution of the complexing agent without precipitation, the solutions can be sprayed separately or successively from two nozzles simultaneously.
  • a reducing compound is also added to the superabsorber mixture or to the individual superabsorbers.
  • reducing compounds are hypophosphites, sulfinates or sulfites.
  • Preference is given to the addition of a sulfinic acid derivative, in particular a compound of the formula (V)
  • M is a hydrogen atom, an ammonium ion, a monovalent metal ion or a
  • 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 selected independently of one another from C 1 -C 6 -alkyl, OH, C 2 -C 6 -alkyl, Halogen and CF3; and
  • R 29 is COOM, SO 3 M, 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 to 6, in particular 1 to 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 especially Ci-C ⁇ -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.
  • compounds of the above formula (V) wherein M is an alkali metal ion or one equivalent of an alkaline earth metal or zinc ion are added to the superabsorbent mixture or superabsorbents; R 27 is a hydroxy or amino group; R 28 is H or alkyl and R 29 is COOM or COOR 30 , where when R 29 is COOM, M in this COOM moiety is H Alkali metal ion or one equivalent of an alkaline earth metal ion and when R 29 is COOR 30 , R 30 is Ci-C 6 alkyl.
  • compounds of the above formula (V) wherein M is an alkali metal ion or one equivalent of an alkaline earth metal or zinc ion are added to the superabsorbent mixture or superabsorbers;
  • 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 Elements in the current IUPAC numbering (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, IIa, IIb, IVa and VIIIb in the numbering used by CAS (Chemical Abstracts Service, 2540 Olentangy River Road, Columbus, OH 43202, USA, www.cas.org).
  • the sulfinic acid derivatives of the above formula (V) can be added in pure form, but optionally also in the usual manner resulting from the preparation of such compounds mixture 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.
  • the addition of one or more reducing compounds to the superabsorber mixture or superabsorbers is carried out in the usual way by addition of the compound in bulk, as a solution or as a suspension in a solvent or suspending agent during or after the preparation of the superabsorber mixture or the superabsorbent.
  • a solution or suspension of the reducing compound in water or an organic solvent is used, for example in an alcohol or polyol or in mixtures thereof.
  • suitable solvents or suspension agents are water, isopropanol / water, 1, 3-propanediol / water and propylene glycol / water, wherein the mixture mass ratio is preferably from 20:80 to 40:60.
  • a surfactant may be added to the solution or suspension.
  • reducing compounds are generally in an amount of at least 0.0001 wt .-%, preferably at least 0.001 wt .-% and in a particularly preferred form at least 0.025 wt .-%, for example at least 0.1 wt .-% or at least 0.3 % By weight, and generally at most 3% by weight, more preferably at most 2.5% by weight, and most preferably at most 1.5% by weight, for example at most 1% by weight or 0.7 Wt .-% added, in each case based on the total weight of the superabsorber.
  • the reducing compound is generally mixed with the superabsorbent mixture or superabsorbents in exactly the same way as the surface postcrosslinker-containing solution or suspension applied to the surface of the superabsorbent for surface postcrosslinking.
  • the reducing compound can be applied as a constituent of the solution applied to the surface postcrosslinking or one of its components to a base polymer, that is to say added to the solution of the surface postcrosslinker or one of its components.
  • the superabsorbent coated with surface postcrosslinking agent and reducing compound then passes through the further process steps required for surface postcrosslinking, for example a thermally induced reaction of the surface postcrosslinking agent with the superabsorber according to the process of the invention. This process is comparatively simple and economical.
  • the reducing compound is preferably applied after the surface postcrosslinking in a separate process step. If it is applied as a solution or suspension, it is applied to the already surface-postcrosslinked superabsorber or the mixture according to the invention in the same way as the application of the surface postcrosslinking agent 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 110 ° C., preferably at most 100 ° C., and most preferably at most 90 ° C., in order to avoid undesired reactions of the reducing compound.
  • the temperature is adjusted so that, in view of the residence time in the drying unit, the desired water content of the superabsorber mixture or the superabsorber is achieved. It is also quite possible and convenient to add the reducing compound singly or together with other customary auxiliaries, for example dust binders, anti-caking agents or water for rewetting the superabsorber, as described below for these aids, for example in a cooler connected downstream of the surface postcrosslinking.
  • the temperature of the polymer particles in this case is between 0 0 C and 190 0 C, preferably less than 160 0 C, more preferably less than 130 0 C, even more preferably less than 100 0 C, and most preferably less than 70 0 C. The polymer particles are given If necessary after cooling rapidly cooled to temperatures below the decomposition temperature of the reducing compound.
  • 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 the removal of heat from pulverulent solids 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 after construction, no heat is introduced into the superabsorber mixture or the superabsorbent via the stirring elements or other heat exchange surfaces, but is removed therefrom.
  • coolers in which the product is moved ie 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.
  • an average residence time in the condenser of generally at least 1 minute, preferably at least 3 minutes and more preferably at least 5 minutes and generally at most 6 hours, preferably at most 2 hours and more preferably at most 1 hour is set and the cooling capacity is so in that the product obtained has a temperature of generally at least 0 ° C, preferably at least 10 ° C and more preferably at least 20 ° C and generally at most 100 ° C, preferably at most 80 ° C and most preferably at most 60 0 C.
  • the surface-postcrosslinked superabsorbent or the mixture is optionally ground and / or sieved in a conventional manner. Milling is typically not required here, but most often, the setting of the desired particle size distribution of the product, the screening of formed agglomerates or fine grain is appropriate. Agglomerates and fine particles are either discarded or preferably recycled to the process in a known manner and at a suitable point; Agglomerates after
  • any known coatings such as film-forming polymers, thermoplastic polymers, dendrimers, polycationic polymers (such as, for example, polyvinylamine, polyethyleneimine or polyallylamine), water-insoluble, may optionally be applied to the surface of the superabsorbent particles in the production process in each process step polyvalent metal salts, for example magnesium carbonate, magnesium oxide, magnesium hydroxide, calcium carbonate, calcium sulfate or calcium phosphate, all water-soluble mono- or polyvalent metal salts known to the person skilled in the art, for example aluminum sulfate, sodium, potassium, zirconium or iron salts, or hydrophilic inorganic particles, such as clay minerals , are additionally applied fumed silica, colloidal silica sols such as Levasil ®, titanium dioxide, aluminum oxide and magnesium oxide.
  • polyvalent metal salts for example magnesium carbonate, magnesium oxide, magnesium hydroxide, calcium carbonate, calcium sulfate or calcium phosphate
  • alkali metal salts examples include sodium and potassium sulfate, sodium and potassium lactates, citrates, sorbates.
  • additional effects for example a reduced tendency to caking of the end product or of the intermediate product in the respective process step of the production method, improved processing properties or a further increased liquid conductivity (SFC) can be achieved.
  • the 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. Most preferred is the simultaneous spraying of postcrosslinking agent, deadening agent and powdery inorganic additive in the postcrosslinking. In a further preferred variant of the method, however, the dedusting agent 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 on the surface of the superabsorbent 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). The latter have the particular advantage that they only insignificantly reduce the surface tension of an aqueous extract of the superabsorbent particles.
  • the superabsorbers according to the invention are provided with further additives which stabilize against discoloration.
  • stabilizers against discoloration in particular reducing substances.
  • solid or dissolved salts of phosphinic acid (H3PO2) as well as these are themselves preferred.
  • H3PO2 phosphinic acid
  • all phosphinates of the alkali metals, including the ammonium, and the alkaline earth metals are suitable.
  • Phosphinic acid which phosphinates and at least one cation selected from sodium, potassium, ammonium, calcium, strontium, aluminum, magnesium.
  • salts of phosphonic acid (H3PO3) are also preferred.
  • H3PO3 phosphonic acid
  • Particular preference is given to aqueous solutions of phosphonic acid which contain primary and / or secondary phosphonates and also at least one cation selected from sodium, potassium, calcium, strontium.
  • All coatings, solids, additives and auxiliaries can each be added in separate process steps, but in most cases the most convenient method is to add them, if they are not added during the displacement of the base polymer with surface postcrosslinking agent, to the superabsorber in the cooler, for example by spraying Solution or addition in finely divided solid or in liquid form.
  • the superabsorbent mixture according to the invention generally has a centrifuge retention capacity (CRC) 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. Further suitable minimum values of the CRC are, for example, 25 g / g, 30 g / g or 35 g / g. Usually it is not above 40 g / g. A typical range of CRC for surface postcrosslinked superabsorbents is from 28 to 33 g / g.
  • the superabsorbent mixture according to the invention typically has an absorption under pressure (AUL 0.7 psi, measuring method see below) of at least 18 g / g, preferably at least 20 g / g, preferably at least 22 g / g, particularly preferably at least 23 g / g, very particularly preferably at least 24 g / g and usually not more than 30 g / g.
  • AUL 0.7 psi absorption under pressure
  • the superabsorbent composition of the invention further has 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 50x10 "7 cm 3 sec / g, more preferably at least 80x10 "7 cm 3 s / g, most preferably at least 100x10 " 7 cm 3 s / g and usually not more than 1000x10 "7 cm 3 s / g.
  • SFC measurement method s below
  • a further subject of the present invention are hygiene articles comprising superabsorbent mixtures according to the invention, preferably ultrathin diapers, containing an absorbent layer consisting of 50 to 100% by weight, preferably 60 to 100% by weight, preferably 70 to 100% by weight , Particularly preferably 80 to 100% by weight, very particularly preferably 90 to 100 wt .-%, inventive superabsorbent mixture, wherein the envelope of the absorbent layer is of course not taken into account.
  • the superabsorbent mixtures according to the invention are also very particularly advantageous for the production of laminates and composite structures, as described, for example, in US Pat US 2003/01811 15 and US 2004/0019342 are suitable.
  • the SAP mixtures of the present invention are also useful for the preparation of fully analogous structures using of UV-crosslinkable hot-melt adhesives, which are sold, for example, as AC- Resin® (BASF SE, Carl-Bosch-Str. 38, 67056 Ludwigshafen, Germany).
  • UV-crosslinkable hot-melt adhesives have the advantage of being processable at as low as 120 to 140 ° C., so they are better compatible with many thermoplastic substrates. Another significant advantage is that UV-crosslinkable hot melt adhesives are toxicologically very harmless and also cause no exhalations in the toiletries.
  • a very significant advantage in connection with the superabsorbent mixtures according to the invention is the property of the UV-crosslinkable hot-melt adhesives, which do not tend to yellow during processing and crosslinking. This is particularly advantageous if ultrathin or partially transparent hygiene articles are to be produced. The combination of the superabsorbent mixtures 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 mixture 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
  • liquid absorption articles according to the invention differ from the known ones in that they contain the superabsorbent mixture 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 the superabsorbent mixture 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.
  • the centrifuge retention capacity of the superabsorbent is determined according to the standard test method no. WSP 241.5-02 "Centrifuge retention capacity". Absorption under pressure (AULO.7psi, Absorbency Under Load of 0.7 psi)
  • 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 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.
  • Fluid transfer is calculated as follows:
  • LO is the thickness of the gel layer in cm
  • d the density of the NaCl solution in g / cm 3
  • A the area of the gel layer in cm 2
  • WP the hydrostatic pressure over the gel layer in dynes / cm 2 .
  • Moisture content of the superabsorber residual moisture, water content
  • the water content of the superabsorbent particles is determined according to the standard test method no. WSP 230.2-05 "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”. Examples
  • the dried gel was comminuted with a laboratory ultracentrifugal mill (manufacturer: Retsch GmbH, Rheinische Straße 36, 42781 Haan, Germany, type ZM 200). By sieving four product fractions were obtained with particle sizes of 150 to 300 ⁇ m, 300 to 400 ⁇ m, 400 to 500 ⁇ m and 500 to 710 microns.
  • Example 1 base polymer 1, 2 kg of obtained according to the procedure of Example 1 base polymer was mixed in a ploughshare ® mixer VT 5R-MK with 5 liters and heating / cooling jacket (manufacturer: Gebr. Lödige Maschinenbau GmbH; Elsener-7 - 9, 33102 Paderborn, Germany) at room temperature with intensive mixing with crosslinking solution sprayed.
  • the spraying was carried out by means of a conventional two-fluid nozzle (manufacturer: Büchi Laboratory GmbH, Am Porscheplatz 5, 45127 Essen, Germany), as it is also used for laboratory spray dryer.
  • composition of the crosslinker solution was 0.10% by weight of N- (2-hydroxyethyl) oxazolidinone, 1.10% by weight of n-propanol and 2.80% by weight of water.
  • the wet polymer was then in a second ploughshare ® mixer of the same type at a polymer temperature of 185 0 C for 60 minutes, dried, and every 10 minutes a sample of 5 g of polymer was drawn.
  • Example 2 After completing the run of Example 2 (i.e., after 60 minutes), the polymer was removed and separated again by sieving into the individual sieves.
  • a screen cut of 150-300 ⁇ m obtained according to Example 1 was surface postcrosslinked as described in Example 2 for the mixture.
  • the evolution over time of AUL 0.7 psi, CRC and SFC during the heat treatment is shown in the following table:
  • a screen cut of 300-400 ⁇ m obtained according to Example 1 was surface postcrosslinked as described in Example 2 for the mixture.
  • the development over time of AUL 0.7 psi, CRC and SFC during the heat treatment is shown in the following table:
  • a screen cut of 400-500 ⁇ m obtained according to Example 1 was surface postcrosslinked as described in Example 2 for the mixture.
  • the evolution over time of AUL 0.7 psi, CRC and SFC during the heat treatment is shown in the following table:
  • a screen cut of 500-710 ⁇ m obtained according to Example 1 was surface postcrosslinked as described in Example 2 for the mixture.
  • the evolution over time of AUL 0.7 psi, CRC and SFC during the heat treatment is shown in the following table:
  • the model base polymer obtained according to Example 1 was postcrosslinked as described in Example 2, wherein the heat treatment was carried out over 50 minutes. Also, one sample of each sieve section of the base polymer was also surface postcrosslinked, with the heat treatment being conducted over the period of time shown in the following table. The four surface postcrosslinked screen sections were then combined again to a mixture.
  • the achieved values of CRC, AUL 0.7 psi and SFC are also given in the following table.
  • the surface postcrosslinking was carried out in such a way that, when mixed, postcrosslinked sieve cuts were compared with the co-afterbake-crosslinked mixture, a practically equal averaged heat treatment duration was set and an equal permeability was achieved. It has not been optimized for high permeability.
  • the procedure corresponds to a separate treatment of four wire sections of a base polymer with identical amounts of the same surface postcrosslinking agent and their introduction into a continuous conveyor dryer at four separate locations corresponding to the specified heat treatment time as average residence time of the respective wire section in the dryer.

Abstract

L'invention porte sur un mélange de polymères superabsorbants ayant différentes post-réticulations superficielles, en particulier sur un mélange de fractions granulométriques par tamisage d'un polymère de base, fractions présentant différentes post-réticulations superficielles. Ce mélange présente une absorption et une rétention améliorées par rapport à un polymère superabsorbant à post-réticulation superficielle uniforme.
EP09751907A 2008-11-21 2009-11-12 Mélange de polymères superabsorbants à post-réticulation superficielle, présentant différentes post-réticulations superficielles Withdrawn EP2358820A1 (fr)

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EP08169670 2008-11-21
PCT/EP2009/065036 WO2010057823A1 (fr) 2008-11-21 2009-11-12 Mélange de polymères superabsorbants à post-réticulation superficielle, présentant différentes post-réticulations superficielles
EP09751907A EP2358820A1 (fr) 2008-11-21 2009-11-12 Mélange de polymères superabsorbants à post-réticulation superficielle, présentant différentes post-réticulations superficielles

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CN102643498B (zh) * 2011-06-24 2014-03-26 陕西科技大学 一种含动植物纤维和无机纳米粒子的吸水凝胶的制备方法
WO2014079785A2 (fr) * 2012-11-26 2014-05-30 Basf Se Procédé de préparation de super-absorbants à base de matières premières renouvelables
DE102013203781A1 (de) * 2013-03-06 2014-09-11 Evonik Industries Ag Superabsorbierende Polymere mit verbesserten Eigenschaften, insbesondere Geruchskontrolle und Farbbeständigkeit, sowie Verfahren zu dessen Herstellung
JP7157530B2 (ja) * 2017-12-29 2022-10-20 花王株式会社 吸収性物品

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JP2012509166A (ja) 2012-04-19
CN102292396A (zh) 2011-12-21
US20110224379A1 (en) 2011-09-15

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