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
  • C08J3/12—Powdering or granulating
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/04—Polymerisation in solution
  • C08F2/10—Aqueous solvent
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/46—Constructional details of screens in general; Cleaning or heating of screens
  • B07B1/50—Cleaning
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/04—Acids; Metal salts or ammonium salts thereof
  • C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/008—Treatment of solid polymer wetted by water or organic solvents, e.g. coagulum, filter cakes
• • 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
  • C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
  • C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
  • C08J3/075—Macromolecular gels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/28—Moving screens not otherwise provided for, e.g. swinging, reciprocating, rocking, tilting or wobbling screens
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B1/00—Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
  • B07B1/28—Moving screens not otherwise provided for, e.g. swinging, reciprocating, rocking, tilting or wobbling screens
  • B07B1/36—Moving screens not otherwise provided for, e.g. swinging, reciprocating, rocking, tilting or wobbling screens jigging or moving to-and-fro in more than one direction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
  • B07B2201/00—Details applicable to machines for screening using sieves or gratings
  • B07B2201/04—Multiple deck screening devices comprising one or more superimposed screens
• • 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 invention relates to a process for the preparation of water-absorbent polymer particles; to a water-absorbent polymer particle obtainable by such a process; to a composite material comprising such a water-absorbent polymer particle; to a process for the production of a composite material, to a composite material obtainable by such a process; to a use of the water- absorbent polymer particle; to a device for the preparation of water-absorbent polymer particles; and to a process for the preparation of water-absorbent polymer particles using such a device.
• Superabsorbers are water-insoluble, crosslinked polymers which are able to absorb large amounts of aqueous fluids, especially body fluids, more especially urine or blood, with swelling and the formation of hydrogels, and to retain such fluids under a certain pressure.
• aqueous fluids especially body fluids, more especially urine or blood
• hydrogels hydrogels
• such polymers are chiefly used for incorporation into sanitary articles, such as, for example, baby's nappies/diapers, incontinence products or sanitary towels.
• the preparation of superabsorbers is generally carried out by free-radical polymerization of acid-group-carrying monomers in the presence of crosslinkers, it being possible for polymers having different absorber properties to be prepared by the choice of the monomer composition, the crosslinkers and the polymerization conditions and of the processing conditions for the hydrogel obtained after the polymerization (for details see, for example, Modern Superabsor- bent Polymer Technology, FL Buchholz, GT Graham, Wiley-VCH, 1998).
• the polymer gel, also called hydrogel, obtained after the polymerization is usually comminuted, dried and classified in order to obtain a particulate superabsorber with a well defined particles size distribution.
• these superabsorbent particles are often surface crosslinked in order to improve the absorption behavior.
• the particles are mixed with an aqueous solution containing a surface crosslinking agent and optionally further additives and the thus obtained mixture is heat treated in order to promote the crosslinking reaction.
• the acid-group-carrying monomers can be polymerized in the presence of the crosslinkers in a batch process or in a continuous process. Both in continuous and in batchwise polymerization, partially neutralized acrylic acid is typically used as the monomer. Suitable neutralization processes are described, for example, in EP 0 372 706 A2, EP 0 574 260 Al , WO 2003/051415 Al , EP 1 470 905 Al, WO 2007/028751 Al, WO 2007/028746 Al and WO 2007/028747 Al .
• the water-absorbent polymer particles have to be classified in the preparation process and fine particles have to be separated from water-absorbent polymers having larger particle diameters. Said classifying and separating is performed by means of sieves in the prior art.
• a sieve comprises a screen with pores. Said pores tend to clog after a certain operational period of the sieve. Especially the fine particles tend to clog the pores.
• a further object is to provide a process for the production of water- absorbent polymers, wherein clogging of pores of a screen of a sieve is avoided as far as possible. It is a further object of the invention to provide a process for the production of water-absorbent polymers, wherein clogging of pores of a screen of a sieve is avoided as far as possible, combined with avoiding wearing of the screen as far as possible. It is a further object of the invention to provide a process for the production of water-absorbent polymers, wherein a separation of fine particles from water-absorbent polymer particles is more efficient.
• a further object is to provide water- absorbent polymer particles which have been produced by a less expensive process.
• It is a further object of the present invention to provide a device for producing water-absorbent polymer particles by a process having at least one of the above ad- vantages.
• the present invention provide an effect to at least partly overcome a disadvantage arising form the prior art in the context of the production of water-absorbent polymer particles.
• FIG. 1 a flow chart diagram depicting the steps of a process according to the invention
• Fig. 2 a flow chart diagram depicting the steps of another process according to the invention
• Fig. 3 a flow chart diagram depicting the steps of another process according to the invention.
• Fig. 4 a scheme of a sizing device according to the invention
• Fig. 5 a scheme of another sizing device according to the invention.
• Fig. 6 a scheme of another sizing device according to the invention.
• Fig. 7 a scheme of another sizing device according to the invention.
• Fig. 8 a block diagram of a device for the preparation of water-absorbent polymer particles according to the invention.
• a contribution to the solution of at least one of these objects is made by a process for the preparation of water-absorbent polymer particl es, comprising the process steps of
• the screen oscillates at a first frequency; wherein the first frequency is in the range of from 16 kHz to 10 MHz, preferably from 17 kHz to 5 MHz, more preferably from 18 kHz to 1 MHz, more preferably from 19 to 800 kHz, more preferably from 20 to 600 kHz, more preferably from 21 to 400 kHz, more preferably from 22 to 200 kHz, more preferably from 23 to 150 kHz, more preferably from 24 to 100 kHz, more preferably from 25 to 80 kHz, more preferably from 26 to 60 kHz, more preferably from 27 to 50 kHz, more preferably from 28 to 45 kHz, more preferably from 29 to 44 kHz, more preferably from 30 to 42 kHz, more preferably from 31 to 41 kHz, more preferably from 32 to 40 kHz, more preferably from 33 to 39 kHz, more preferably from 34 to 38 kHz, most preferably from 35 to 37 kHz; and wherein the first frequency is in the range of
• the screen oscillates at the further frequency with one selected from the group consisting of a linear oscillation, a superposition of two or more linear oscillations, a circular oscillation, an elliptic oscillation, a nutation, and a tumbling motion, or a combination of at least two thereof.
• a nutation is understood as being an oscillation, wherein a period of the oscillation is a period of a precession.
• a frequency of a nutation is a frequency of a precession comprised by the nutation.
• a tumbling motion is understood as being an oscillation, wherein a period of the tumbling motion is a period of a horizontal component of the tumbling motion.
• a frequency of a tumbling motion is a frequency of a horizontal oscillation comprised by the tumbling motion.
• the screen oscillates at the first frequency with a linear oscillation, or a superposition of two or more linear oscillations.
• a preferred linear oscillation is a horizontal oscillation or a vertical oscillation.
• the first frequency is preferably an ultrasonic frequency.
• the further frequency is preferably a sub-ultrasonic frequency.
• a preferred sub- ultrasonic frequency is a frequency at less than 16 kHz, preferably at less than 16 kHz and at 1 Hz or more.
• a preferred sizing device is a sieve or a sifter or both.
• the process according to the present invention is preferably a continuous process in which the aqueous monomer solution is continuously provided and is continuously fed into the polymerization reactor.
• the polymer gel obtained is continuously discharged out of the polymerization reactor and is continuously optionally comminuted, dried, grinded and sized in the subsequent process steps.
• This continuous process may, however, be interrupted in order to, for example, substitute certain parts of the process equipment, like the belt material of the conveyor belt if a conveyor belt is used as the polymerization reactor,
• Water-absorbent polymer particles which are preferred according to the invention are particles that have an average particle size in accordance with WSP 220.2 (test method ofcut Word Strategic Partners'" ED ANA and INDA) in the range of from 10 to 3,000 ⁇ , preferably 20 to 2,000 ⁇ and particularly preferably 150 to 850 ⁇ .
• WSP 220.2 test method of Procedure Word Strategic Partners'" ED ANA and INDA
• an aqueous monomer so- lution containing at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al) and at least one crosslinker (a3) is prepared.
• Preferred monoethylenically unsaturated monomers bearing carboxylic acid groups are those cited in DE 102 23 060 Al as preferred monomers (al), whereby acrylic acid is particu- larly preferred.
• the water-absorbent polymer produced by the process according to the invention comprises monomers bearing carboxylic acid groups to at least 50 wt.-%, preferably to at least 70 wt.-% and further preferably to at least 90 wt.-%, based on the dry weight. It is particularly preferred according to the invention, that the water-absorbent polymer produced by the process according to the invention is formed from at least 50 wt.-%, preferably at least 70 wt.-% of acrylic acid, which is preferably neutralized to at least 20 mol-%, particularly preferably to at least 50 mol-%.
• the concentration of the partially neutralized, monoethylenically unsaturated monomers bearing carboxylic acid groups (al) in the aqueous monomer solution that is provided in process step (i) is preferably in the range of from 10 to 60 wt.-%, preferably from 30 to 55 wt.-% and most preferably from 40 to 50 wt.-%, based on the total weight of the aqueous monomer solution.
• the aqueous monomer solution may also comprise monoethylenically unsaturated monomers (a2) which are copolymerizable with (al).
• Preferred monomers (a2) are those monomers which are cited in DE 102 23 060 Al as preferred monomers (a2), whereby acrylamide is particularly preferred.
• a crosslinking of the polymer is achieved by radical polymerization of the ethylenically unsaturated groups of the crosslinker molecules with the monoethylenically unsaturated monomers ( l) or (a2), while with the compounds of crosslinker class II and the polyvalent metal cations of crosslinker class IV a crosslinking of the polymer is achieved respectively via condensation reaction of the functional groups (crosslinker class II) or via electrostatic interaction of the polyvalent metal cation (crosslinker class IV) with the functional groups of the monomer (al) or (a2).
• cross-linker class III a cross-linking of the polymers is achieved correspondingly by radical polymerization of the ethylenically unsaturated groups as well as by condensation reaction between the functional groups of the cross-linkers and the functional groups of the monomers (al) or (a2).
• Preferred crosslinkers (a3) are all those compounds which are cited in DE 102 23 060 Al as crosslinkers (a3) of the crosslinker classes I, II, III and IV, whereby as compounds of crosslinker class I, N, N ' -methylene bisacrylamide, polyefhylenegly- col di(meth)acrylates, triallylmethylammonium chloride, tetraallylammonium chloride and allylnonaefhyleneglycol acrylate produced with 9 mol ethylene oxide per mol acrylic acid are particularly preferred, wherein N, N ' -methylene bisacrylamide is even more preferred, and as compounds of crosslinker class IV, Al 2 (S0 4 ) 3 and its hydrates are particularly pre- ferred.
• Preferred water-absorbent polymers produced by the process according to the invention are polymers which are crosslinked by crosslinkers of the following crosslinker classes or by crosslinkers of the following combinations of crosslinker classes respectively: I, II, III, IV, I II, I III, I IV, I II III, I II IV, I III IV, II III IV, II IV or III IV.
• water-absorbent polymers produced by the process according to the invention are polymers which are crosslinked by any of the crosslinkers disclosed in DE 102 23 060 Al as crosslinkers of crosslinker classes I, whereby ⁇ , ⁇ ' -methylene bisacrylamide, polyethyleneglycol di(meth)acrylates, triallyl-methylammonium chloride, tetraallylammonium chloride and allylnonaethylene-glycol acrylate produced from 9 mol ethylene oxide per mol acrylic acid are particularly preferred as crosslinkers of crosslinker class I, wherein N, N'-methylene bisacrylamide is even more preferred.
• the aqueous monomer solution may further comprise water-soluble polymers ( 4).
• Preferred water-soluble polymers (a4) include partly or completely saponified polyvinyl alcohol, polyvinylpyrrolidone, starch or starch derivatives, polyglycols or polyacrylic acid. The molecular weight of these polymers is not critical, as long as they are water-soluble.
• Preferred water- soluble polymers (a4) are starch or starch derivatives or polyvinyl alcohol.
• the water-soluble polymers (a4), preferably synthetic, such as polyvinyl alcohol, can not only serve as a graft base for the monomers to be polymerized.
• auxiliary substances these auxiliary substances including, in particular, complexing agents, such as, for example, EDTA.
• the relative amount of monomers (a 1) and (a2) and of crosslinking agents (a3) and water- soluble polymers (a4) and auxiliary substances (a5) in the aqueous monomer solution is preferably chosen such that the water-absorbent polymer structure obtained after drying the optionally comminuted polymer gel is based to the extent of 20 to 99.999 wt.-%, preferably to the extent of 55 to 98.99 wt.-% and particularly preferably to the extent of 70 to 98.79 wt.-% on monomers (al), to the extent of 0 to 80 wt.-%, preferably to the extent of 0 to 44.99 wt.-% and particularly preferably to the extent of 0.1 to 44.89 wt.-% on the monomers (a2),
• Optimum values for the concentration in particular of the monomers, crosslinking agents and water-soluble polymers in the monomer solution can be determined by simple preliminary experiments or from the prior art, in particular from the publications US 4,286,082, DE 27 06 135 Al , US 4,076,663, DE 35 03 458 Al , DE 40 20 780 CI, DE 42 44 548 Al, DE 43 33 056 Al and DE 44 18 818 Al .
• fine particles of a water-absorbent polymer may optionally be added to the aqueous monomer solution.
• fine water-absorbent polymer particles may be added to the aqueous monomer solution at one selected from the group con- sisting of after step (iii), after step (iv), and before step (v), or a combination of at least two thereof
• water-absorbent fine particles are preferably water-absorbent polymer particles the composition of which corre- sponds to the composition of the above described water-absorbent polymer particles, wherein it is preferred that at least 90 wt.-% of the water-absorbent fine particles, preferably at least 95 wt.-% of the water-absorbent fine particles and most preferred at least 99 wt.-% of the water-absorbent fine particles have a particle size of less than 200 ⁇ , preferably less than 150 ⁇ and particular preferably less than 100 ⁇ .
• the water- absorbent fine particles which may optionally be added to the aqueous monomer solution in process step (ii) are water-absorbent fine particles which are obtained in process step (x) of the process according to the present invention and which are thus recycled.
• the fine particles can be added to the aqueous monomer solution by means of any mixing device the person skilled of the art would consider as appropriate for this purpose.
• the fine particles are added to the aqueous monomer solution in a mixing device in which a first stream of the fine particles and a second stream of the aqueous monomer solution are directed continuously, but from different directions, onto a rotating mixing device.
• a mixing device in which a first stream of the fine particles and a second stream of the aqueous monomer solution are directed continuously, but from different directions, onto a rotating mixing device.
• Such a kind of mixing setup can be realized in a so called “Rotor Sta- tor Mixer ' " which comprises in its mixing area a preferably cylindrically shaped, non-rotating stator, in the centre of which a likewise preferably cylindrically shaped rotor is rotating.
• the walls of the rotor as well as the walls of the stator are usually provided with notches, for example notches in the form of slots, through which the mixture of fine particles and aqueous monomer solution can be sucked through and thus can be subjected to high shear forces.
• the first stream of the fine particles and the second stream of the aqueous monomer solution form an angle ⁇ in the range from 60 to 120°, more preferred in the range from 75 to 105°, even more preferably in the range from 85 to 95° and most preferred form an angle of about 90°.
• the stream of the mixture of fine particles and aqueous monomer solution that leaves the mixer and the first stream of fine particles that enters the mixer form an angle ⁇ in the range from 60 to 120°, preferably in the range from 75 to 105°, even more preferred in the range from 85 to 95° and most preferred form an angle of about 90°.
• Such a kind of mixing set up can, for example, be realized by means of mixing devices which are disclosed in DE-A-25 20 788 and DE-A-26 17 612, the content of which is incorporated herein by reference.
• Concrete examples of mixing devices which can be used to add the fine particles to the aqueous monomer solution in process step (ii) of the present invention are the mixing devices which can be obtained by the IKA ® Maschinene GmbH & Co. KG, Staufen, Germany, under designations MHD 2000/4, MHD 2000/05, HD 2000/10, MDH 2000/20, MHD 2000/30 und MHD 2000/50, wherein the mixing device MHD 2000/20 is particularly preferred.
• Further mixing devices which can be used are those offered by ystral GmbH, Ballrechten-Dottingen, Germany, for example under designation GeorgiaConti TDS", or by Kine- matika AG, Luttau, Switzerland, for example under the trademark Megatron ® .
• the amount of fine particles that may be added to the aqueous monomer solution in process step (ii) is preferably in the range from 0.1 to 15 wt.-%, even more preferred in the range from 0.5 to 10 wt.-% and most preferred in the range from 3 to 8 wt.-%, based on the weight of the aqueous monomer solution.
• a polymerization initiator or at least one component of a polymerization initiator system that comprises two or more components is added to the aqueous monomer solution.
• polymerization initiators for initiation of the polymerization all initiators forming radicals under the polymerization conditions can be used, which are commonly used in the production of superabsorbers. Among these belong theraial catalysts, redox catalysts and photo-initiators, whose activation occurs by energetic irradiation.
• the polymerization initiators may be dissolved or dispersed in the aqueous monomer solution. The use of water-soluble catalysts is preferred.
• thermal initiators may be used all compounds known to the person skilled in the art that decompose under the effect of an increased temperature to form radicals.
• theraial polymerisation initiators with a half life of less, than 10 seconds, more preferably less than 5 seconds at less than 180°C, more preferably at less than 140°C.
• Peroxides, hydroperoxides, hydrogen peroxide, persulfates and azo compounds are particularly preferred thermal polymerization initiators.
• mixtures of various theraial polymerization initiators those consisting of hydrogen peroxide and sodium or potassium peroxodisulfate are preferred, which may be used in any desired quantitative ratio.
• Suitable organic peroxides are preferably acetylacetone peroxide, methyl ethyl ketone peroxide, benzoyl peroxide, lauroyl peroxide, acetyl peroxide, capryl peroxide, isopropyl peroxidicarbonate,2-ethylhexyle peroxidicarbonate, tert. -butyl hydroperoxide, cumene hydroperoxide, and peroxides of tert- amyl perpivalate, tert.-butyl perpivalate, tert.-butyl perneohexonate, tert.
• -butyl isobutyrate, tert.-butyl per-2-ethylhexenoate, tert.-butyl perisononanoate, tert.-butyl permaleate, tert.-butyl perbenzoate, tert.-butyl-3,5,5-trimethylhexanoate and amyl perneodecanoate.
• thermal polymerisation initiators are preferred: azo compounds such as azo-bis- isobutyronitril, azo-bis-dimethylvaleronitril, azo-bis-ami-dinopropane dihydrochloride, 2,2'- azobis-(N,N-dimethylene)isobutyramidine di-hydrochloride, 2-(carbamoylazo)isobutyronitrile and 4,4' -azobis-(4-cyano-val eric acid).
• the aforementioned compounds are used in conventional amounts, preferably in a range from 0.01 to 5 mol-%, more preferably 0.1 to 2 mol-%, respectively based on the amount of the monomers to be polymerized.
• Redox catalysts comprise two or more components, usually one or more of the peroxo compounds listed above, and at least one reducing component, preferably ascorbic acid, glucose, sorbose, mannose, ammonium or alkali metal hydrogen sulfite, sulfate, thiosulfate, hyposulfite or sulfide, metal salts such as iron II ions or silver ions or sodium hydroxymethyl sulfoxylate.
• reducing component preferably ascorbic acid, glucose, sorbose, mannose, ammonium or alkali metal hydrogen sulfite, sulfate, thiosulfate, hyposulfite or sulfide, metal salts such as iron II ions or silver ions or sodium hydroxymethyl sulfoxylate.
• ascorbic acid or sodium pyrosulfite is used as reducing component of the redox catalyst.
• 1 ⁇ 10 "5 to 1 mol-% of the reducing component of the redox catalyst and 1 x 10 " 5 to 5 mol-% of the oxidising component of the redox catalyst are used, in each case referred to the amount of monomers used in the polymerization.
• the oxidising component of the redox catalyst or as a complement thereto, one or more, preferably water- soluble azo compounds may be used.
• the polymerization is preferably initiated by action of energetic radiation, so-called photo- initiators are generally used as initiator. These can comprise for example so-called a-splitters, H-abstracting systems or also azides.
• photo- initiators are benzophenone derivatives such as Michlers ketone, phenanthrene derivatives, fluorine derivatives, anthraquinone derivatives, thioxanthone derivatives, cumarin derivatives, benzoinether and derivatives thereof, azo compounds such as the above-mentioned radical formers, substituted hexaarylbi- simidazoles or acylphosphine oxides.
• azides examples include 2-(N,N-dimethylamino)ethyl-4- azidocinnamate, 2-(N,N-dimethylamino)ethyl-4-azidonaphthylketone, 2-(N,N-di- methylamino)ethyl-4-azidobenzoate, 5-azido- 1 -naphthyl-2' -(N,N-dimethylami- no)ethylsulfone, N-(4-sulfonylazidophenyl)maleinimide, N-acetyl-4-sulfonyl-azidoaniline, 4- sulfonylazidoaniline, 4-azidoaniline, 4-azidophenacyl bromide, p-azidobenzoic acid, 2,6- bis(p-azidobenzylidene)cyclohexanone and t 2,6-bis(p-
• a further group of photo-initiators are di-alkoxy ketales such as 2,2- dimethoxy-l,2-diphenylethan-l-one.
• the photo-initiators when used, are generally employed in quantities from 0.0001 to 5 wt.-% based on the monomers to be polymerized.
• the initiator comprises the following components
• iiib an organic initiator molecule comprising at least three oxygen atoms or at least three nitrogen atoms;
• the initiator comprises the peroxodisulfate and the organic initiator molecule in a molar ratio in the range of from 20: 1 to 50: 1.
• concentration of the initiator component iiia. is in the range from 0.05 to 2 wt.-%, based on the amount of monomers to be polymerized.
• organic initiator molecule is selected from the group consisting of 2,2- dimethoxy- 1 ,2-diphenylethan- 1 -one, 2,2-azobis-(2-amidinopropane)dihydrochloride, 2,2- azobis-(cyano valeric acid) or a combination of at least two thereof.
• the peroxodi sulfate is of the general formula M 2 S 2 0s, with M being selected from the group consisting of NH 4 , Li, Na, Ka or at least two thereof.
• M being selected from the group consisting of NH 4 , Li, Na, Ka or at least two thereof.
• the above described components are in particular suitable for UV initiation of the polymerization in step (vi) of the process of the present invention.
• Employing this composition further yields low residual monomer and reduced yellowing in the water- absorbent polymer particle, obtainable by the process according to the present invention.
• step (iii), adding the polymerization initiator may be realized before step (iv), simultaneously to step (iv), or overlapping in time with step (iv), i.e. when the oxygen content of the aqueous monomer solution is decreased.
• a polymerization initiator system is used that comprises two or more components, one or more of the components of such a polymerization initiator system may, for example, be added before process step (iv), whereas the remaining component or the remaining components which are necessary to complete the activity of the polymerisation initiator system, are added after process step (iv), perhaps even after process step (v).
• decreasing the oxygen content of the aqueous monomer solution may also be performed before process step (iii) according to the invention.
• the oxygen content of the aqueous monomer solution is optionally decreased.
• decreasing the oxygen content of the aqueous monomer solution may also be performed before, during or after process step (ii) according to the invention.
• the oxygen content of the aqueous monomer solution is decreased after the fine particles have been added in process step (ii).
• the oxygen content of the aqueous monomer solution is decreased, this may be realized by bringing the aqueous monomer solution into contact with an inert gas, such as nitrogen.
• the phase of the inert gas being in contact with the aqueous monomer solution is free of oxygen and is thus characterized by a very low oxygen partial pressure.
• oxygen converts from the aqueous monomer solution into the phase of the inert gas until the oxygen partial pressures in the phase of the inert gas and the aqueous monomer solution are equal.
• Bringing the aqueous monomer phase into contact with a phase of an inert gas can be accomplished, for example, by introducing bubbles of the inert gas into the monomer solution in co-current, countercurrent or intermediate angles of entry. Good mixing can be achieved, for example, with nozzles, static or dynamic mixers or bubble columns.
• the oxygen content of the monomer solution before the polymerization is preferably lowered to less than 1 ppm by weight, more preferably to less than 0.5 ppm by weight, based on the monomer solution.
• the aqueous monomer solution is charged into a polymerization reactor, preferably onto a conveyor belt, especially preferred at an upstream position of the conveyor belt and in process step (vi) the monomers in the aqueous monomer solution are polymerized in the polymerization reactor, thereby obtaining a polymer gel.
• a polymer gel sheet is obtained in a downstream portion of the conveyor belt, which, before drying, is preferably comminuted in order to obtain polymer gel particles.
• every reactor can be used which the person skilled in the art would regard as appropriate for the continuous or batchwise polymerization of monomers like acrylic acid in aqueous solutions.
• An example of a suitable polymerization reactor is a kneading reactor.
• the polymer gel formed in the polymerization of the aqueous monomer solution is comminuted continuously by, for example, contrarotatory stirrer shafts, as described in WO 2001/38402.
• comminuting the polymer gel may be performed prior to discharging the polymer gel out of the polymerization reactor.
• a preferred polymerization reactor is a conveyor belt.
• a conveyor belt that is useful for the process according to the present invention any conveyor belt can be used which the person skilled in the art considers to be useful as a support material onto which the above described aqueous monomer solution can be charged and subsequently polymerized to form a hydrogel.
• the conveyor belt usually comprises an endless moving conveyor belt passing over supporting elements and at least two guide rollers, of which at least one is driven and one is configured so as to be adjustable.
• a winding and feed system for a release sheet that may be used in sections on the upper surface of the conveyor belt is provided.
• the system includes a supply and metering system for the reaction components, and optional irradiating means arranged in the direction of movement of the conveyor belt after the supply and metering system, together with cooling and heating devices, and a removal system for the polymer gel strand that is arranged in the vicinity of the guide roller for the return run of the conveyor belt.
• the conveyor belt is supported in the vicinity of the supply system for the reaction components by a plurality of trough-shaped supporting and bearing elements that form a deep trough- like or dish-like configuration for the reaction components that are introduced.
• each supporting element is preferably formed by a cylindrical or spherical roller that is rotatable about its longitudinal axis.
• the belt can be made of various materials, although these preferably have to meet the requirements of good tensile strength and flexibility, good fatigue strength under repeating bending stresses, good deformability and chemical resistance to the individual reaction components under the conditions of the polymerization. These demands are usually not met by a single material. Therefore, a multi-layer material is commonly used as belt of the present invention.
• the mechanical requirements can be satisfied by a carcass of, for example, fabric inserts of natural and/or synthetic fibers or glass fibers or steel cords.
• the chemical resistance can be achieved by a cover of, for example, polyethylene, polypropylene, polyisobutylene, halogenated polyolefines such as polyvinyl chloride or polytetrafluorethylene, polyamides, natural or synthetic rubbers, polyester resins or epoxy resins.
• the preferred cover material is silicone rubber.
• the polymer gel obtained in the polymerization reactor is optionally comminuted, thereby obtaining polymer gel particles.
• Preferred polymer gel particles are one selected from the group consisting of polymer gel strands, polymer gel flakes, and polymer gel nuggets, or a combination of at least two thereof.
• the comminuting device may be the polymerization reactor or a part of the polymerization reactor, or a separate device, or both. Hence, comminuting the polymer gel may be perfomied before, during, or after discharging the polymer gel out of the polymerization reactor.
• a preferred polymerization reactor which is the comminuting device is a kneading reactor. If the comminuting is performed in the polymerization reactor, the polymer gel particles obtained are preferably further comminuted after discharging out of the polymerization reactor.
• the comminuting is preferably performed after discharging the polymer gel as a polymer gel sheet from the conveyor belt in a comminuting device, wherein the comminuting device is a separate device.
• the polymer gel sheet is discharged from the conveyor belt as a continuous sheet that is of a soft semi-solid consistency and is then passed on for further processing such as comminuting.
• Comminution of the polymer gel is preferably performed in at least three steps:
• a cutting unit preferably a knife, for example a knife as disclosed in WO- A-96/36464, is used for cutting the polymer gel into flat gel strips, preferably with a length within the range of from 5 to 500 mm, preferably from 10 to 300 mm and particularly preferably from 100 to 200 mm, a height within the range of from 1 to 30 mm, preferably from 5 to 25 mm and particularly preferably from 10 to 20 mm as well as a width within the range of from 1 to 500 mm, preferably from 5 to 250 mm and particularly preferably from 10 to 200 mm; in a second step, a shredding unit, preferably a breaker, is used for shredding the gel strips into gel pieces, preferably with a length within the range of 3 to 100 mm, preferably from 5 to 50 mm, a height within the range from 1 to 25 mm, preferably from 3 to 20 mm as well as a width within the range from 1 to 100 mm, preferably from 3 to 20
• step (viii) of the process according to the present invention the polymer gel particles are dried.
• the drying of the polymer gel particles can be effected in any dryer or oven the person skilled in the art considers as appropriate for drying the above described polymer gel particles.
• Rotary tube furnaces, fluidized bed dryers, plate dryers, paddle dryers and infrared dryers may be mentioned by way of example.
• a belt dryer is a convective system of drying, for the particularly gentle treatment of through-airable products.
• the product to be dried is placed onto an endless conveyor belt which lets gas through, and is subjected to the flow of a heated gas stream, preferably air.
• the drying gas is recirculated in order that it may become very highly saturated in the course of repeated passage through the product layer.
• a certain fraction of the drying gas leaves the dryer as a hi ghly saturated vapor and carries off the water quantity evaporated from the product.
• the temperature of the heated gas stream is preferably not less than 50°C, more preferably not less than 100°C and most preferably not less than 150°C and preferably up to 250°C, more preferably up to 220°C and most preferably up to 200°C.
• the size and design of the dryers depend on the product to be processed, the manufacturing capacity and the drying duty.
• a belt dryer can be embodied as a single-belt, multi-belt, multistage or multistory system.
• the present invention is preferably practiced using a belt dryer having at least one belt.
• One-belt dryers are very particularly preferred.
• the drying properties of the water-absorbent poly- mers are individually determined as a function of the processing parameters chosen.
• the hole size and mesh size of the belt is conformed to the product.
• certain surface enhancements such as electropolishing or Teflonizing, are possible.
• the polymer gel particles to be dried are preferably applied to the belt of the belt dryer by means of a swivel belt.
• the feed height i.e., the vertical distance between the swivel belt and the belt of the belt dryer, is preferably not less than 10 cm, more preferably not less than 20 cm and most preferably not less than 30 cm and preferably up to 200 cm, more preferably up to 120 cm and most preferably up to 40 cm.
• the thickness on the belt dryer of the polymer gel particles to be dried is preferably not less than 2 cm, more preferably not less than 5 cm and most preferably not less than 8 cm and preferably not more than 20 cm, more preferably not more than 15 cm and most preferably not more than 12 cm.
• the belt speed of the belt dryer is preferably not less than 0.005 m/s, more preferably not less than 0.01 m/s and most preferably not less than 0.015 m/s and preferably up to 0.05 m/s, more preferably up to 0.03 m/s and most preferably up to 0.025 m/s.
• the polymer gel is dried to a water content in the range of from 0.5 to 25 wt.-%, preferably from 1 to 10 wt.-% and particularly preferably from 3 to 7 wt.-%, based on the dried polymer gel particles.
• step (ix) of the process according to the present invention the dried polymer gel particles are ground thereby obtaining particulate water-absorbent polymer particles.
• any device can be used the person skilled in the art considers as appropriate for grinding the above described dried polymer particles.
• a suitable grinding device a single- or multistage roll mill, preferably a two- or three-stage roll mill, a pin mill, a hammer mill or a vibratory mill may be mentioned.
• the ground water- absorbent polymer particles are sized, preferably using appropriate sieves.
• the content of polymer particles having a particle size of less than 150 ⁇ is less than 10 wt.-%, preferably less than 8 wt.-% and particularly less than 6 wt.-% and that the content of polymer particles having a particle size of more than 850 ⁇ is also less than 10 wt.-%, preferably less than 8 wt.-% and particularly preferably less than 6 wt.-%, each based on the total weight of the water-absorbent polymer particles.
• At least 30 wt.-%, more preferred at least 40 wt.-% and most preferred at least 50 wt.-%, of the water-absorbent polymer particles have a particle size in a range of from 300 to 600 ⁇ .
• the surface of the ground and sized water-absorbent polymer particles is optionally treated.
• any measure can be used the person skilled in the art considers as appropriate for such a purpose.
• surface treatments include, for example, surface crosslinking, the treatment of the surface with water-soluble salts, such as aluminium sulfate or aluminium lactate, the treatment of the surface with inorganic particles, such as silicon dioxide, and the like.
• the components used to treat the surface of the polymer particles are added in the form of aqueous solutions to the water-absorbent polymer particles. After the particles have been mixed with the aqueous solutions, they are heated to a temperature in the range of from 150 to 230°C, preferably 160 to 200°C in order to promote the surface-crosslinking reaction.
• the further frequency is at least 15 kHz to 9.9 MHz, preferably at least 15 kHz to 5 MHz, more preferably at least 15 kHz to 1 MHz, more preferably at least 16 to 800 KHz, more preferably at least 17 to 600 kHz, more preferably at least 18 to 400 kHz, more preferably at least 19 to 200 kHz, more preferably at least 20 to 150 kHz, more preferably at least 21 to 100 kHz, more preferably at least 22 to 80 kHz, more preferably at least 23 to 60 kHz, more preferably at least 24 to 40 kHz, more preferably at least 25 to 39 kHz, more preferably at least 26 to 38 kHz, more preferably at least 27 to 37 kHz, more pref- erably at least 28 to 36 kHz, more preferably at least 29 to 36 kHz, more preferably at least 30 to 36 kHz, more preferably at least 31 to 36 kHz, more preferably at least 32 to 36 kHz
• the screen is rectangular or round or both.
• a preferred round screen is circular.
• Another preferred round screen is plane.
• a particularly preferred screen is circular and plane.
• Another preferred screen is characterized by a screening surface in the range of from 0.1 to 10 m 2 , preferably from 0.2 to 9.5 m 2 , more preferably from 0.3 to 9 m 2 , more preferably from 0.4 to 8.5 m 2 , more preferably from 0.5 to 8 m 2 , more preferably from 1 to 7.5 m 2 , more preferably from 2 to 7 m 2 , more preferably from 2.5 to 6.5 m 2 , more preferably from 3 to 6 m 2 , more preferably from 3.5 to 6 m 2 , more preferably from 4 to 6 m 2 , more preferably from 4.5 to 6 m 2 , more preferably from 4.8 to 5.8 m 2 , most preferably from 5 to 5.6 m 2 .
• a screening surface is an area of a screen, wherein pores of the screen are distributed, preferably uniformly distributed, over the area.
• a preferred round screen fulfils the criterion a) according to the above embodiment of the process according to the invention.
• a preferred rectangular screen fulfils the criterion b) according to the above embodiment of the process according to the invention.
• the sizing device is a centrifugal sieve or a tumbler sieve or both.
• a preferred sizing device is a tumbler sieve.
• a very particularly preferred sizing device is a tumbler sieve comprising at least one circular and plane screen.
• a mesh size of the screen is in the range of from 5 to 400 mesh, preferably from 10 to 200 mesh, more preferably from 20 to 170 mesh, more preferably from 20 to 140 mesh, more preferably from 20 to 120 mesh, more preferably from 20 to 100 mesh, most preferably 100 mesh.
• a preferred mesh is a U.S. mesh.
• a preferred pore of the screen is made of wires or fibres or both.
• a preferred wire is made of steel, preferably stainless steel.
• a preferred fibre is a synthetic fibre. Another preferred pore is a perforation of the screen.
• the sizing device further comprises at least one further screen, preferably at least 2 further screens, more preferably at least 3 further screens, more preferably at least 4 further screens, most preferably at least 5 further screens.
• the screen and the further screens are preferably arranged as decks above each other.
• a preferred further screen is a characterized by at least one, preferably by a combination of at least two, more preferably by all, of the above technical features of the screen.
• a very particularly preferred sizing device is a tumbler sieve, comprising 6 circular and plane screens arranged as decks above each other.
• the polymer gel being discharged in process step (vii) comprises water in the range of from 40 to 60 wt-%, preferably from 50 to 60 wt.-%, more preferably from 53 to 56 wt.-%, based on the polymer gel.
• the polymer gel being discharged in process step (vii) is a polymer gel sheet; wherein the polymer gel sheet is characterized by a thickness in the range of from 10 to 200 mm, preferably from 10 to 100 mm, more preferably from 15 to 75 mm, most preferably from 15 to 50 mm.
• the polymer gel being discharged in process step (vii) is a polymer gel sheet; wherein the polymer gel sheet is characterized by a width in the range of from 30 to 300 cm, preferably from 50 to 250 cm, more preferably from 60 to 200 cm, most preferably from 80 to 100 cm.
• the polymerization in step (vi) is performed in presence of a blowing agent.
• the blowing agent may be added to the aqueous monomer solution in one selected from the group consisting of step (i), step (ii), step (iii), step (iv), step (v), and step (vi), or in a combination of at least two thereof.
• the blowing agent is added to the monomer solution in step (i).
• the blowing agent should be added prior or immediately after the polymerization in step (vi) is initiated.
• the blowing agent is added to the monomer solution after or simultaneously to adding the initiator or a component of an initiator system.
• the blowing agent is added to the monomer solution in an.
• a blowing agent is a substance which is capable of producing a cellular structure or pores or both via a foaming process during polymerization of the monomers.
• the foaming process is preferably endothermic.
• a preferred endothermic foaming process is started by heat from an exothermic polymerisation or crosslinking or both reaction.
• a preferred blowing agent is a physical blowing agent or a chemical blowing agent or both.
• a preferred physical blowing agent is one selected from the group consisting of a CFC, a HCFC, a hydrocarbon, and C0 2 , or a combination of at least two thereof.
• a preferred C0 2 is liquid C0 2 .
• a preferred hydrocarbon is one selected from the group consisting of pentane, isopentane, and cyclopentane, or a combination of at least two thereof.
• a preferred chemical blowing agent is one selected from the group consisting of a carbonate blowing agent, a nitrite, a peroxide, calcined soda, an oxalic acid derivative, an aromatic azo compound, a hydrazine, an azide, a ⁇ , ⁇ '- Dinitrosoamide, and an organic blowing agent, or a combination of at least two thereof.
• a very particularly preferred blowing agent is a carbonate blowing agent.
• Carbonate blowing agents which may be used according to the invention are disclosed in US 5, 1 18, 719 A, and are incorporated herein by reference.
• a preferred carbonate blowing agent is a carbonate con- taining salt, or a bicarbonate containing salt, or both.
• Another preferred carbonate blowing agent comprises one selected from the group consisting of C0 2 as a gas, C0 2 as a solid, ethylene carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, or magnesium hydroxic carbonate, calcium carbonate, barium carbonate, a bicarbonate, a hydrate of these, other cations, and naturally occurring carbonates, or a combination of at least two thereof.
• a preferred naturally occurring carbonate dolomite release C0 2 when being heated while dissolved or dispersed in the monomer solution.
• a particularly preferred carbonate blowing agent is MgC0 3 , which may also be represented by the formula (MgC0 3 ) 4 Mg(OH) 2 -5-H 2 0.
• Another preferred carbonate blowing agent is agent is (NH 4 ) 2 C03.
• the MgC0 3 and (NH 4 ) 2 C0 3 may also be used in mixtures.
• Preferred carbonate blowing agents are carbonate salts of multivalent cations, such as Mg, Ca, Zn, and the like.
• Examples of such carbonate blowing agents are Na 2 C0 3 , 2 C0 3 , (NH 4 ) 2 C0 3 , MgC0 3 , CaC0 3 , NaHC0 3 , KHC0 3 , NH 4 HC0 3 , Mg(HC0 3 ) 2 , Ca(HC0 3 ) 2 , ZnC0 3 , and BaC0 3 .
• certain of the multivalent transition metal cations may be used, some of them, such as ferric cation, can cause color staining and may be subject to reduction oxidation reactions or hydrolysis equilibria in water. This may lead to difficulties in quality control of the final polymeric product.
• a preferred nitrite is ammonium nitrite.
• a preferred peroxide is hydrogen peroxide.
• a preferred aromatic azo compound is one selected from the group consisting of a triazene, ar- ylazosulfones, arylazotriarylmethanes, a hydrazo compound, a diazoether, and diazoamino- benzene. or a combination of at least two thereof.
• a preferred hydrazine is phenylhydrazine.
• a preferred azide is a carbonyl azide or a sulfonyl azide or both.
• a preferred ⁇ , ⁇ '- Dinitro- soamide is ,N'-dimethyl-N,N'-di.nitvosoterephthalamide.
• a contribution to solving at least one of the above objects is provided by a device for the preparation of water-absorbent polymer particles in a process stream, comprising
• a first container designed to take an aqueous monomer solution, comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (a 1);
• i) located down-stream to the first container and the further container, ii) designed to comprise the aqueous monomer solution and the at least one crosslinker (a3) during polymerizing the monomers in the aqueous monomer solution, thereby obtaining a polymer gel;
• ii) comprises a screen
• iii) is designed to size the grinded water-absorbent polymer particles, iv) is designed to set the screen into oscillation;
• the oscillation comprises a first frequency; wherein the first frequency is in the range of from 16 kHz to 10 MHz, preferably from 17 kHz to 5 MHz, more preferably from 18 kHz to 1 MHz, more preferably from 19 to 800 kHz, more preferably from 20 to 600 kHz, more preferably from 21 to 400 kHz, more preferably from 22 to 200 kHz, more preferably from 23 to 150 kHz, more preferably from 24 to 100 kHz, more preferably from 25 to 80 kHz, more preferably from 26 to 60 kHz, more preferably from 27 to 50 kHz, more preferably from 28 to 45 kHz, more preferably from 29 to 44 kHz, more preferably from 30 to 42 kHz, more preferably from 31 to 41 kHz, more preferably from 32 to 40 kHz, more preferably from 33 to 39 kHz, more preferably from 34 to 38 kHz, most preferably from 35 to 37 kHz; and wherein the screen
• the mixing device may be identical to the polymerization reactor.
• the polymerization reactor may be identical to the comminuting device.
• the mixing device, the polymerization reactor, and the comminuting device may be identical.
• Preferred components or devices or both of the device according to the invention are designed according to the process according to the invention.
• a preferred first frequency is the first frequency according to the process according to the invention.
• a preferred further frequency is the further frequency according to the process according to the invention.
• a preferred sizing device is the sizing device according to the process according to the invention.
• a preferred screen is the screen according to the process according to the invention.
• a preferred oscillation is the oscillation according to the process according to the invention.
• a contribution to the solution of at least one of the above objects is provided by a process for the preparation of water-absorbent polymer particles in the device according to the invention.
• the process comprises the process steps (i) to (xi) according to the invention.
• a contribution to the solution of at least one of the above objects is provided by a water- absorbent polymer particle, obtainable by the process according to the invention.
• a further aspect of the present invention pertains to a plurality of surface-crosslinked water-absorbent polymer particles, comprising
• a chelating agent in particular EDTA, in an amount in the range of from
• 500 to 3,000 ppm by weight preferably from 1,000 to 2,000 ppm by weight
• a poly alkylene glycol in particular poly ethylene glycol, in an amount in the range of from 500 to 3,000 ppm by weight, preferably from 1 ,000 to 2,000 ppm by weight
• a poly alkylene glycol in particular poly ethylene glycol
• a Si0 2 in an amount in the range of from 500 to 3,000 ppm by weight, preferably from 1,000 to 2,000 ppm by weight;
• the plurality of surface-crosslinked water-absorbent polymer particles further comprises Ag-zeolite, preferably in an amount in the range from 0.0001 to 1 wt.-part, more preferably in the range from 0.001 to 0.5 wt.-part and most preferred in the range of 0.002 to 0.01 wt.-part, each based on the total weight of the plurality of surface-crosslinked water-absorbent polymer particles.
• a contribution to the solution of at least one of the above objects is provided by a composite material comprising a water-absorbent polymer particle according to the invention.
• the composite material according to the invention comprises one selected from the group consisting of a foam, a shaped article, a fibre, a foil, a film, a cable, a sealing material, a liquid-absorbing hygiene article, a carrier for plant and fungal growth-regulating agents, a packaging material, a soil additive, and a building material, or a combination of at least two thereof.
• a preferred cable is a blue water cable.
• a preferred liquid-absorbing hygiene article is one selected from the group consisting of a diaper, a tampon, and a sanitary towel, or a combination of at least two thereof.
• a preferred diaper is a baby's diaper or a diaper for incontinent adults or both.
• a contribution to the solution of at least one of the above objects is provided by a process for the production of a composite material, wherein a water-absorbent polymer particle according to the invention and a substrate and optionally an auxiliary substance are brought into contact with one another.
• a contribution to the solution of at least one of the above objects is provided by a composite material obtainable by a process according to the invention.
• a contribution to the solution of at least one of the above objects is provided by a use of the water-absorbent polymer particle according to the invention in a foam, a shaped article, a fibre, a foil, a film, a cable, a sealing material, a liquid-absorbing hygiene article, a carrier for plant and fungal growth-regulating agents, a packaging material, a soil additive, for controlled release of an active compound, or in a building material.
• test methods are used in the invention.
• the ISO test method for the feature to be measured being closest to the earliest filing date of the present application applies. If no ISO test method is available, the ED ANA test method being closest to the earliest filing date of the present application applies.
• standard ambient temperature and pressure (SATP) as a temperature of 298.15 (25 °C, 77 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm) apply.
• SATP standard ambient temperature and pressure
• the water content of the water-absorbent polymer particles after drying is determined according to the Karl Fischer method.
• 0.4299 wt.-parts of water are mixed in an adequate container with 0.27 wt.-parts of acrylic acid and 0.0001 wt.-parts of mono methyl ether hydroquinone (MEHQ).
• 0.2 wt.-parts of an aqueous 48 wt.-% sodium hydroxide solution are added to the mixture.
• a sodium-acrylate monomer solution with a neutralization ratio of 70 mol-% is achieved.
• the sodium-acrylate monomer solution is degased with nitrogen.
• 1 wt.-part of the monomer solution prepared in step A) is mixed with 0.001 wt.-parts of trime- thylol propane triacrylate as crosslinker, 0.001 wt.-parts of sodium peroxodisulfate as first initiator component, 0.000034 wt.-parts of 2,2-dimethoxy-l,2-diphenylethan-l-one (Ciba ® Irgacure ® 651 by Ciba Specialty Chemicals Inc., Basel, Switzerland) as a second initiator component, up to 0.1 wt.-parts of acrylic acid particles (with a particle size of less than 150 ⁇ ) in a container to achieve a mixed solution. If according to table 1 below a blowing agent is added, 0.1 wt.-part, based on the total amount of the mixed solution, of sodium carbonate are added to the mixed solution.
• a sufficient amount of the mixed solution is subjected to further treatment in order to obtain a polymer gel and further downstream water-absorbent polymer particles and further downstream surface-crosslinked water-absorbent polymer particles as well as further downstream a water-absorbent product which is post treated. Details of the further treatment are given below.
• the conveyor belt has a length of at least 20 m and a width of 0.8 m.
• the conveyor belt is formed as a trough to keep the solution on the belt prior to and while being polymerized.
• the dimensions of the conveyor belt and the conveying speed of the conveyer belt are selected in a way that a poly-acrylic acid gel is formed at a downstream end of the belt.
• a water-absorbent polymer gel is achieved.
• the polymer gel has a water content of about 52 wt.-%, based on the total weight of the polymer gel.
• the polymer gel forms a polymer gel strand which is discharged from the conveyor belt and comminuted in three steps:
• the rubbery poly-acrylic acid gel is cut into flat gel strips by a knife.
• the gel strips have a length in the range of from 10 to 20 cm, a height in the range of from 10 to 20 mm, and a width in the range of from 10 to 200 mm, then
• a breaker is used to shred the strips into gel pieces having a length in the range from 5 to 50 mm, a height in the range of from 3 to 20 mm, and a width in the range of from 3 to 20 mm, then
• the gel pieces are extruded through a mixer with a grinder to mince the gel pieces obtaining gel pieces having a length in the range of from 3 to 20 mm a height in the range of from 3 to 20 mm and a width in the range of from 3 to less than 20 mm.
• the comminuted gel is dried in a belt dryer at a temperature of 180 °C to a water content of 5 wt.-% based on the dried polymer gel.
• the belt of the belt drier provides orifices, where hot air is pressed into the polymer gel via nozzles. Additionally hot air is blown from above the belt onto the gel.
• the dried polymer gel is ground in three steps. First the dried polymer gel is fed through a Herbold Granulator HGM 60/145 (HERBOLD Meckesheim GmbH) and the achieved parts of the dried polymer gel have a size of less than 7 mm and are then kept for 2.5 hours in a container to equalize the humidity content of the polymer gel parts. The dried polymer gel parts are then milled in a roller mill of Bauerffle Type 350.1 x 1800 (3-stage crusher) (Bau- ermeister Zerklein mecanicstechnik GmbH) to obtain water-absorbent polymer particles having a particle size of less than 1 mm.
• the water absorbent polymer particles are sieved with a sieve, Tumbler Screener KTS 2600/5 by GKM Siebtechnik, Walbstadt, Gemiany, having 5 decks of screens.
• the mesh sizes of the screens change from 20, 30, 40, 50, 60 to 100 U.S.-mesh.
• At least 50 wt.-% of the obtained water-absorbent polymer particles have a particles size in the range of from 300 to 600 ⁇ .
• Less than 5 wt.-% of the water-absorbent polymer particles of the examples according to the invention are smaller than 150 ⁇ , less than 5 wt.-% of the water-absorbent polymer particles of the examples according to the invention are have a particle size of more than 850 ⁇ .
• the obtained water- absorbent polymer particles are named precursor I.
• precursor I The obtained water- absorbent polymer particles are named precursor I.
• fine water-absorbent polymer particles are separated in this step or not. If the fines are not separated the above sizing step is not performed in the corresponding comparative example.
• the fine water-absorbent polymer particles have particle sizes of less than 150 ⁇ .
• table 1 gives measures taken against clogging of pores of the screens used for sizing.
• the precursor I is mixed in a disc mixer with about 0.01 wt.-part (+- 10 %) of silicon dioxide (Si0 2 ), based on the total weight of the precursor I plus Si0 2 .
• the silicon dioxide is used in form of Sipernat ® 22 obtainable from Evonik Industries AG, Essen, Germany.
• the precursor still has a temperature of more than 80 °C to 100 °C, preferably of 100 °C.
• a precursor II is achieved.
• wt.-part of the precursor II is mixed with 0.003 wt.-part (+-10 %) of a surface crosslinker, based on the total weight of the mixture of precursor II and crosslinker.
• the surface crosslinker is composed of 19 wt.-% water, 40 wt.-% ethylene glycol diglycidyl ether, 1 wt.-% Na 2 S0 3 , 40 wt.-% poly ethylene glycol with a molecular weight of 400 g/mol, each based on the total amount of the crosslinker.
• the ingredients of the crosslinker are mixed in a line static mixer.
• the crosslinker is mixed in a ringlayer mixer CoriMix ® CM 350 (Gebriider Lodige Mascheninenbau GmbH, Paderborn, Germany) with precursor II.
• the mixture is heated to a temperature in the range of from 130 to 160 °C.
• the mixture is then dried in a paddle dryer Andritz Gouda Paddle Dryer, preferably of type GPWD12W120, by Andritz AG, Graz, Austria for 45 minutes at a temperature in the range of from 130 to 160°C.
• Surface-cross- linked absorbent polymer particles are obtained.
• the temperature of the surface-cross-linked absorbent polymer particles is decreased to below 60 °C, obtaining cooled surface-cross-linked absorbent polymer particles referred as to precursor III.
• 1 wt.-part of precursor III is then subjected to mixing with 0.005 wt.-part Ag-zeolite. Subse- quently, the mixture is sieved. The sieve is selected to separate agglomerates of the cooled surface-cross-linked absorbent polymer particle having a particle size of more than 850 ⁇ . At least 50 wt.-% of the surface-crosslined absorbent polymer particles have a particles size in the range of from 300 to 600 ⁇ .
• Table 1 Operational period of the sieve, lifetime of the screen of the sieve, retention capacity of the prepared surface-crosslinekd waterabsorbent polymer particles for various examples.
• the fine water-asborbent polymer particles are not separated. Thus, said fines remain in the product of the process - the surface-crosslinked water- absorbent polymer particles. There is no sieve applied for separating fines. The retention capacity of the surface-crosslinked water-absorbent polymer particles is undesirably low.
• a blowing agent is applied which leads to an increased retention capacity.
• the fines are separated by sieving as described above. No blowing agent is applied. The retention capacity is further increased.
• the screens of the sieve are periodically manually cleaned to prevent clogging. For this brushes are used. If the screens would not be cleaned, pores of the screens would clog and sieving would become inefficient or sieving would stop.
• the comparative example 4 is the same as comparative example 3, except that a blowing agent is applied. This solely increases the retention capacity further.
• the comparative example 5 is performed as the comparative example 3, except that instead of manually brushing the screens, the screens are constantly cleaned by rubber balls which bounce from below against the screen. This cleaning method increases the operational period of the sieve with respect to the comparative examples 3 and 4. However, the repeated bounces of the rubber balls lead to damages to the sensitive screen structures. This results in a decreased lifetime of the screens cleaned by the balls.
• the retention capacity is at the same level as in the comparative example 3.
• Comparative example 6 again shows that applying a blowing agent increases the retention capacity of the surface-crosslinked water-absorbent polymer particles produced.
• the fines are separated by the sieve and the screens of the sieve are set into oscillation at a frequency of 20 kHz by an ultrasonic generator.
• sieving does not have to be interrupted for cleaning the screens and the ultrasonic vibration does not damage the screens.
• a long lifetime of the screens, long operational periods and a high retention capacity are observed.
• the ultrasonic frequency used for cleaning is increased to 36 kHz. This leads to an even more efficient prevention of clogging and hence to an increased operation period of the sieve.
• Example 3 shows the best results. Auxiliary to example 2 a blowing agent is applied to increase the retention capacity.
• Figure 1 shows a flow chart diagram depicting the steps 101 to 1 1 1 of a process 100 for the preparation of water-absorbent polymer particles according to the invention.
• aqueous monomer solution comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups ( l) and at least one crosslinker (a3) is provided.
• the aqueous monomer solution is an aqueous solution of partially neutralized acrylic acid, further comprising crosslinkers.
• fine particles of a water-absorbent polymer may be added to the aqueous monomer solution.
• a polymerization initiator or at least one component of a polymerization initiator system that comprises two or more components is added to the aqueous monomer solution.
• the oxygen content of the aqueous monomer solution is decreased by bubbling nitrogen into the aqueous monomer solution.
• the monomer solution is charged onto a belt of a polymerization belt reactor as a polymerization reactor 804. The belt is an endless conveyor belt.
• the aqueous monomer solution is polymerized to a polymer gel.
• the polymer gel is discharged from the belt. Subsequently, the polymer gel is comminuted, whereby polymer gel particles are obtained.
• the polymer gel particles are charged onto a belt of a belt dryer and subsequently dried at a temperature of about 120 to 150°C.
• the dried polymer gel particles are discharged from the belt dryer and subsequently in a ninth step 109 grinded to obtain water-absorbent polymer particles.
• the grinded water-absorbent polymer particles 401 are sized by a sizing device 400 comprising a screen 402 to obtain grinded and sized water-absorbent polymer particles 403 having a well defined particle size distribution.
• the sizing device 400 is a tumbler sieve. Therein, the screen 402 oscillates at a first frequency and a further frequency.
• the first frequency is 36 kHz, generated by an ultrasonic generator.
• the further frequency is 1 Hz.
• the oscillation at the further frequency is the tumbling motion of the tumbler sieve.
• an eleventh step 11 1 the surface of the water-absorbent polymer particles is treated in terms of a surface crosslinking.
• Figure 2 shows a flow chart diagram depicting the steps 101 to 1 1 1 of a process 100 for the preparation of water-absorbent polymer particles according to the invention.
• the process 100 shown in figure 2 is the same as the process 100 in figure 1 , wherein the third process step 103 and the fourth process step 104 overlap in time. While the polymerization initiator is add- ed to the aqueous monomer solution, nitrogen is bubbled into the aqueous monomer solution in order to decrease its oxygen content.
• Figure 3 shows a flow chart diagram depicting the steps 101, 103, 105 to 1 10 of a process 100 for the preparation of water-absorbent polymer particles according to the invention.
• the pro- cess 100 shown in figure 3 is the same as the process 100 in figure 1 , wherein the second step 102, the fourth step 104, and the eleventh step 11 1 are not part of the process 100 according to figure 3.
• FIG. 4 shows a scheme of a sizing device 400 according to the invention.
• the sizing device 400 may comprise components not shown in the figure.
• the sizing device 400 is a vibration sieve.
• grinded water-absorbent polymer particles 401 are fed into the sizing device 400, onto a screening surface of a screen 402.
• the screen 402 is a plane and circular screen.
• the screen 402 comprises pores 406.
• a mesh size of the screen 402 is 100 U.S. mesh.
• the pores 406 are made of stainless steel wires.
• the screen 402 oscillates at a first fre- quency and a further frequency.
• the screen 402 oscillates in two superpositioned linear oscillations 404 at the further frequency.
• one linear oscillation 404 is a vertical oscillation and another linear oscillation 404 is a horizontal oscillation.
• the screen 402 oscillates in a linear vertical oscillation 405 at the first frequency.
• the first frequency is 35 kHz and the fur- ther frequency is 3 Hz.
• Sieving the grinded water-absorbent polymer particles 401 by the sizing device 400, grinded and sized water-absorbent polymer particles 403 are obtained.
• FIG. 5 shows a scheme of another sizing device 400 according to the invention.
• the sizing device 400 may comprise components not shown in the figure.
• the sizing device 400 is a nutation sieve.
• grinded water-absorbent polymer particles 401 are fed into the sizing device 400, onto a screening surface of a screen 402.
• the screen 402 is a plane and circular screen.
• the screen 402 comprises pores 406.
• a mesh size of the screen 402 is 100 U.S. mesh.
• the pores 406 are made of synthetic fibres.
• the screen 402 oscillates at a first frequency and a further frequency.
• the screen 402 performs a nutation.
• the nutation is a su- perposition of a precession 501 and a rotation 502.
• the precession 501 is performed at the further frequency.
• the nutation is an oscillation at the further frequency.
• the screen 402 oscillates in a linear vertical oscillation 405 at the first frequency.
• the first frequency is 40 kHz and the further frequency is 2 Hz.
• Sieving the grinded water-absorbent polymer particles 401 by the sizing device 400, grinded and sized water- absorbent polymer particles 403 are obtained.
• FIG. 6 shows a scheme of another sizing device 400 according to the invention.
• the sizing device 400 may comprise components not shown in the figure.
• the sizing device 400 is a sieve.
• grinded water-absorbent polymer particles 401 are fed into the sizing de- vice 400, onto a screening surface of a screen 601.
• the screen 601 is a plane and rectangular screen.
• the screen 601 comprises pores 406.
• a mesh size of the screen 601 is 100 U.S. mesh.
• the pores 406 are made of stainless steel wires.
• the screen 601 is tilted, it inclines an angle 602 of 10° with a horizontal plane 603.
• FIG. 7 shows a scheme of a sizing device 400 according to the invention. Therein the sizing device 400 may comprise components not shown in the figure.
• the sizing device 400 is a sieve.
• the screen 402 is a plane and circular screen.
• the screen 402 comprises pores 406.
• a mesh size of the screen 402 is 20 U.S. mesh.
• the pores 406 are made of stainless steel wires.
• the screen 402 oscillates at a first frequency and a further frequency.
• the screen 402 oscillates in two superpositioned linear oscillations 404 at the further frequency. Therein, one linear oscillation 404 is a vertical oscillation and another linear oscillation 404 is a horizontal oscillation.
• the screen 402 oscillates in a linear vertical oscillation 405 at the first frequency.
• the first frequency is 35 kHz and the further frequency is 3 Hz.
• the sizing device 400 further comprises 4 further screens 701. Each further screen 701 is a plane and circular screen having pores. Each further screen 701 oscillates at the first frequency and the further frequency.
• the screen 402 and the further screens 701 are stacked vertically above each other. Sieving the grinded water-absorbent polymer particles 401 by the sizing device 400, grinded and sized water-absorbent polymer particles 403 are obtained.
• FIG. 8 shows a block diagram of a device 800 for the preparation of water-absorbent polymer particles according to the invention.
• the arrows show a direction of a process stream 808 of the preparation of water-absorbent polymer particles.
• the device 800 comprises a first con- tainer 801, a further container 802, downstream a mixing device 803, downstream a polymerization belt reactor as a polymerization reactor 804, downstream a comminuting device 805, downstream a belt dryer 806, downstream a grinding device 807, and downstream a sizing device 400, each according to the invention.

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• 2014
  • 2014-04-25 KR KR1020167032640A patent/KR102403560B1/ko active IP Right Grant
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