WO2015163517A1 - Release of polymer gel from polymerization belt in production of water-absorbent polymer particles - Google Patents

Release of polymer gel from polymerization belt in production of water-absorbent polymer particles Download PDF

Info

Publication number
WO2015163517A1
WO2015163517A1 PCT/KR2014/003675 KR2014003675W WO2015163517A1 WO 2015163517 A1 WO2015163517 A1 WO 2015163517A1 KR 2014003675 W KR2014003675 W KR 2014003675W WO 2015163517 A1 WO2015163517 A1 WO 2015163517A1
Authority
WO
WIPO (PCT)
Prior art keywords
belt
water
polymer gel
absorbent polymer
monomer solution
Prior art date
Application number
PCT/KR2014/003675
Other languages
French (fr)
Inventor
Jeong Beom Park
Original Assignee
Songwon Industrial Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Songwon Industrial Co., Ltd. filed Critical Songwon Industrial Co., Ltd.
Priority to PCT/KR2014/003675 priority Critical patent/WO2015163517A1/en
Publication of WO2015163517A1 publication Critical patent/WO2015163517A1/en

Links

Classifications

    • 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
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/01—Processes of polymerisation characterised by special features of the polymerisation apparatus used
    • 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
    • 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

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 plurality of water- absorbent polymer particles; to a composite material comprising such a water-absorbent polymer particle or such a plurality of water-absorbent polymer particles; 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 or a plurality of water-absorbent polymer particles; 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 hydro gels, and to retain such fluids under a certain pressure.
  • aqueous fluids especially body fluids, more especially urine or blood
  • hydro gels hydro gels
  • 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 Superabsorbent 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 op- tionally 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 cross- linkers 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 .
  • a common polymerization belt reactor comprises a conveyor belt being designed to carry an aqueous monomer solution which comprises the acid-group-carrying monomers during polymerization.
  • Such a conveyor belt is disclosed in EP 0 955 086 Bl .
  • process step (vi) or (vii) or both a releasing agent is applied to at least a part of the belt.
  • a device for the preparation of water-absorbent polymer particles in a process stream comprising a) a first container, designed to take an aqueous monomer solution, comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al);
  • ii) is designed to comprise the aqueous monomer solution and the at least one crosslinker ( ⁇ x3) during polymerizing the monomer in the aqueous monomer solution, thereby obtaining a polymer gel iii) comprises a belt;
  • a wetting device wherein the wetting device is located and designed for applying a releasing agent to at least 30 %, preferably at least 35 %, more preferably at least 40 %, more preferably at least 45 %, most preferably at least 48 %, of a longitudinal extension of the belt;
  • 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.
  • 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 contribution to solving at least one of the above objects is provided by a plurality of water-absorbent polymer particles, comprising a polyalkylsiloxane, or a compound according to a general formula R-(-0-CH 2 -CH 2 -) n -OX, or both; wherein in the general formula R is C 4 to C 20 , n is an integer in the range of from 10 to 10,000, and X is H or M; wherein M is a metal ion.
  • 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 the water-absorbent polymer particle according to the invention or the plurality of water-absorbent particles 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 or the plurality of water- absorbent particles 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.
  • the water-absorbent polymer particle according to the invention or the plurality of water-absorbent particles according to the invention may be used 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.
  • Figure 1 is a flow chart diagram depicting the steps of a process according to the invention.
  • Figure 2 is a flow chart diagram depicting the steps of another process
  • Figure 3 is a flow chart diagram depicting the steps of another process
  • Figure 4 is a scheme of a basic setup of a polymerization belt reactor according to the invention.
  • Figure 5 is a scheme of a downstream end of a belt of a polymerization
  • Figure 6 is a scheme of a basic setup of another polymerization belt reactor according to the invention in a side view
  • Figure 7 is a scheme of a basic setup of another polymerization belt reactor according to the invention in a side view
  • Figure 8 is a scheme of a trough of a belt of a polymerization belt reactor according to the invention in a view facing an upstream direction;
  • Figure 9 is 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 particles, comprising the process steps of
  • process step (vi) or (vii) or both a releasing agent is applied to at least a part of the belt.
  • 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 belt reactor, preferably onto the belt of the polymerization belt reactor.
  • the polymer gel obtained is continuously discharged out of the polymerization belt 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, to substitute certain parts of the process equipment, like the belt material of the polymerization belt 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 offormerlyWord Strategic Partners" ED ANA and INDA) in the range of from 10 to 3,000 ⁇ , preferably 20 to 2,000 ⁇ and particularly preferably ! 50 to 850 ⁇ .
  • WSP 220.2 test method ofticianWord Strategic Partners
  • ED ANA and INDA test method ofticianWord Strategic Partners
  • an aqueous monomer solution containing at least one partially neutralized, monoefhylenically unsaturated monomer bearing carboxylic acid groups (al) and at least one crosslinker (a3) is prepared.
  • Preferred monoefhylenically unsaturated monomers bearing carboxylic acid groups are those cited in DE 102 23 060 Al as preferred monomers (al), whereby acrylic acid is particularly 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 between 10 to 60 wt.-%, preferably 30 to 55 wt.-% and most preferably between 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 (al) 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 func- tional 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 (a 1) or (a.2).
  • 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
  • N, N' -methylene bisacrylamide polyethylenegly- col di(meth)acrylates, triallylmethylammonium chloride, tetraallylammonium chloride and allylnonaethyleneglycol acrylate produced with 9 mol ethylene oxide per mol acrylic acid are particularly preferred, wherein N, 1ST -methylene bisacrylamide is even more preferred, and
  • 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, 1ST -methylene bisacrylamide is even more preferred.
  • the aqueous monomer solution may further comprise water-soluble polymers (ot4).
  • Preferred water-soluble polymers (a4) include partly or completely saponified polyvinyl alco- hol, 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. It is also conceivable for these water-soluble polymers to be mixed with the polymer gel or the already dried, water-absorbent polymer.
  • the aqueous monomer solution can furthermore also comprise auxiliary substances (oc5), these auxiliary substances including, in particular, complexing agents, such as, for example, EDTA.
  • auxiliary substances including, in particular, complexing agents, such as, for example, EDTA.
  • the relative amount of monomers ( l) and (a2) and of crosslinking agents (a3) and water-soluble polymers (a4) and auxiliary substances (oc5) in the aqueous monomer solution is preferably chosen such that the water-absorbent polymer structure obtained after drying the comminuted polymer gel is based
  • 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 pre- liminary 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 consisting 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 corresponds 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 based on the total weight 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.
  • a so called "Rotor Stator 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°. It is also preferred that 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.
  • Specific 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, MHD 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 Kinematika 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 polymerisation all initiators forming radicals under the polymerization conditions can be used, which are commonly used in the production of superabsorbers. Among these belong thermal 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. Particularly preferred are thermal 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. In some cases it is advantageous to use mixtures of various thermal polymerization initiators. Among such mixtures, 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 pemialeate, 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-valeric 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 oxidizing component of the redox catalyst are used, in each case referred to the amount of monomers used in the polymerization.
  • the oxidizing 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. Examples of such initiators are benzophenone derivatives such as Michlers ketone, phenanthrene derivatives, fluorine derivatives, anthra- quinone derivatives, thioxanthone derivatives, cumarin derivatives, benzoinether and derivatives thereof, azo compounds such as the above-mentioned radical formers, substituted hex- aarylbisimidazoles or acylphosphine oxides.
  • photo-initiators are generally used as initiator. These can comprise for example so-called a- splitters, H-abstracting systems or also azides. Examples of such initiators are benzophenone derivatives such as Michlers ketone, phenanthrene derivatives, fluorine derivatives, anthra- quinone derivatives,
  • 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-l-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 2,6-bis(p-azido
  • 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 peroxodisulfate is of the general formula M 2 S 2 08, 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).
  • 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 solu- tion 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 intem ediate 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 onto the belt of the polymerization belt reactor.
  • the aqueous monomer solution is charged onto the belt at an upstream position of the belt.
  • a preferred belt is a conveyor belt.
  • the monomers in the aqueous monomer solution are polymerized on the belt, thereby obtaining a polymer gel.
  • the polymer gel is obtained at a downstream portion of the belt.
  • the polymer gel is comminuted in order to obtain polymer gel particles.
  • the polymer gel that is obtained on the belt is discharged from the belt.
  • the polymer gel is removed from the belt as a continuous strand that is of a soft semi-solid consistency and is then passed on for further processing comprising comminuting. By comminuting the polymer gel polymer gel particles are obtained.
  • 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;
  • 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 mm and
  • a "wolf (grinding) unit preferably a mincer, preferably having a screw and a hole plate, whereby the screw conveys against the hole plate is used in order to grind and crush gel pieces into polymer gel particles which are preferably smaller than the gel pieces.
  • step (viii) of the process according to the present invention the polymer gel is dried.
  • the drying of the polymer gel can be effected in any dryer or oven the person skilled in the art considers as appropriate for drying the above described gel particles.
  • Rotary tube furnaces, fluidised 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 preferably not less than 10 %, more preferably not less than 15 % and most preferably not less than 20 % and preferably up to 50 %, more preferably up to 40 % and most preferably up to 30 % of the gas quantity per pass, leaves the dryer as a highly 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, multi-stage 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 polymers 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 to be dried is 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 to be dried is preferably not less than 2 cm, more preferably not less than 5 cm and most prefer- ably 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.
  • step (ix) of the process according to the present invention the dried polymer gel is ground thereby obtaining water-absorbent polymer particles.
  • 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.-%, based on the total weight 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 releasing agent comprises one selected from the group consisting of a solvent, a polyalkylsiloxane, and a surfactant, or a combination of at least two thereof.
  • a preferred solvent is water.
  • a preferred polyalkylsiloxane is polydimethylsiloxane.
  • the surfactant is a compound according to the general formula R-(-0-CH 2 -CH 2 -) n -OX, wherein R is selected from C 4 to C 2 o, n is an integer in the range of from 10 to 10,000, preferably from 50 to 5,000, more preferably from 100 to 500, and X is H or M, wherein M is a metal ion.
  • R is selected from C 4 to C 2 o
  • n is an integer in the range of from 10 to 10,000, preferably from 50 to 5,000, more preferably from 100 to 500
  • X is H or M, wherein M is a metal ion.
  • a particularly preferred compound according to said general formula is polyethylene glycol trimethylnonyl ether.
  • the solvent in an amount in the range of from 95 to 99 wt.-%, preferably from 95.5 to 98.5 wt.-%, more preferably from 96.5 to 97.5 wt.-%,
  • the polyalkylsiloxane in an amount in the range of from 0.5 to 5 wt.-%, preferably from 1 to 4 wt.-%, more preferably from 2.4 to 3.2 wt.-%, and
  • the surfactant in an amount in the range of from 0.01 to 1 wt.-%, preferably from 0.05 to 0.7 wt.-%, more preferably from 0.1 to 0.3 wt.-%, each based on the total weight of the releasing agent and the amounts in wt.-% adding up to a total of 100 wt.-%.
  • step (vi) or (vii) or both the releasing agent is applied to at least 30 %, preferably at least 35 %, more preferably at least 40 %, more preferably at least 45 %, most preferably at least 48 %, of a longitudinal extension of the belt.
  • the belt comprises a trough having a sidewall; wherein in step (vi) or (vii) or both the releasing agent is applied to at least a part of the sidewall.
  • a preferred sidewall is oriented along a longitudinal direction of the belt.
  • a preferred sidewall is a portion of a conveyor belt.
  • a preferred part of the sidewall faces to the trough.
  • the solvent is applied to a left inner sidewall of the trough and to a right inner sidewall of the trough, preferably simultaneously.
  • the belt comprises a weir element; wherein in step (vi) or (vii) or both the releasing agent is applied to at least a part of the weir element.
  • the weir element is arranged in a longitudinal direction of the belt.
  • the belt is an endless belt, comprising a first turning section and a further turning section; wherein the polymer gel is discharged from the further turning section of the endless belt in step (vii); wherein the releasing agent is applied to at least a part of the further turning section in step (vii).
  • a preferred first turning section of the belt is a section of the belt over which the belt is transformed from moving upstream to moving downstream.
  • a preferred further turning section of the belt is a section of the belt over which the belt is transformed from moving downstream to moving upstream.
  • the belt is in contact with a guide roller.
  • the belt has a shape of an arc or of an ellipse or both in longitudinal direction.
  • the belt changes from being horizontal to vertical and back to horizontal.
  • the releasing agent is applied to a downstream moving portion of the further turning section of the belt.
  • the releasing agent is applied by one selected from the group consisting of spraying, pouring, splashing, and dripping, or a combination of at least two thereof.
  • the releasing agent is applied by spraying.
  • a preferred spraying is a spraying by a nozzle.
  • the releasing agent is sprayed in a solid angle element of 90° or less, preferably of 60° or less, more preferably of 45° or less, most preferably of 30° or less, centered around a counter direction to a direction of movement of the polymer gel on the belt.
  • the releasing agent is applied by at least two nozzles.
  • the releasing agent is sprayed by the at least two nozzles simultaneously.
  • a left nozzle sprays the releasing agent on a left portion of the belt and a right nozzle sprays the releasing agent on a right portion of the belt.
  • the releasing agent in an embodiment of the invention during applying to the belt has a temperature in the range of from 10 to 50°C, preferably from 12 to 40°C, more preferably from 15 to 30°C, most preferably from 18 to 28°C.
  • step (vi) or (vii) or both the releasing agent is applied to the belt in an amount in the range of from 10 to 10,000 ml, preferably from 20 to 9,000 ml, more preferably from 30 to 8,000 ml, more preferably from 40 to 7,000 ml, more preferably from 50 to 6,000 ml, more preferably from 60 to 5,000 ml, more preferably from 70 to 4,000 ml, more preferably from 80 to 3,000 ml, more preferably from 90 to 2,000 ml, more preferably from 100 to 1,000 ml, more preferably from 100 to 800 ml, more preferably from 100 to 600 ml, more preferably from 100 to 500 ml, more preferably from 100 to 400 ml, more preferably from 100 to 350 ml, more preferably from 100 to 300, most preferably from 100 to 250 ml, of releasing agent per m 2 of the belt.
  • 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 amount in the range of from 500 to 4000 ppm by weight, preferably from 1000 to 3500 ppm by weight, more preferably from 1500 to 3200 ppm by weight, most preferably from 2000 to 3000 ppm by weight, based on the total weight of the monomer solution.
  • 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 endotheraiic 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 cyclopen- tane, 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 containing 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 car- bonate, 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 is dolomite.
  • the above mentioned carbonate blowing agents 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 C0 3 .
  • 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.
  • 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,N'-dimethyl-N,N'-dinitrosoterephthalamide.
  • a device for the preparation of water-absorbent polymer particles in a process stream comprising a) a first container, designed to take an aqueous monomer solution, comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al);
  • i) is located down-stream to the mixing device, ii) is designed to comprise the aqueous monomer solution and the at least one crosslinker ( 3) during polymerizing the monomer in the aqueous monomer solution, thereby obtaining a polymer gel iii) comprises a belt;
  • a wetting device wherein the wetting device is located and designed for applying a releasing agent to at least 30 %, preferably at least 35 %, more preferably at least 40 %, more preferably at least 45 %, most preferably at least 48 %, of a longitudinal extension of the belt;
  • a preferred wetting device comprises a nozzle.
  • Another preferred wetting device comprises a plurality of nozzles, wherein the nozzles are comprised by a tube, and arranged longitudinally along the belt.
  • a preferred tube extends at least 1 m, preferably at least 2 m, more preferably at least 3 m, more preferably at least 4 m, more preferably at least 5 m, more preferably at least 6 m, more preferably at least 7 m, more preferably at least 8 m, more preferably at least 9 m, most preferably at least 10 m, longitudinally along the belt.
  • a preferred releasing agent is a releasing agent according to the process according to the invention.
  • a preferred applying of a releasing to the belt is performed according to the process according to the invention.
  • Preferred components or devices or both of the device for the preparation of water-absorbent polymer particles according to the invention are designed 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 contribution to solving at least one of the above objects is provided by a plurality of water-absorbent polymer particles, comprising a polyalkylsiloxane, or a compound according to a general formula R-(-0-CH 2 -CH 2 -) n -OX, or both; wherein in the general formula R is C 4 to C 2 o, n is an integer in the range of from 10 to 10,000, preferably from 50 to 5,000, more preferably from 100 to 500, and X is H or M; wherein M is a metal ion.
  • a particularly preferred compound according to said general formula is polyethylene glycol trimethylnonyl ether.
  • a preferred polyalkylsiloxane is polydimethylsiloxane.
  • the polyalkylsiloxane in an amount in the range of from 0.01 to 1 wt.-%, preferably from 0.02 to 0.9 wt.-%, more preferably from 0.03 to 0.8 wt.-%, more preferably from 0.04 to 0.7 wt.-%, more preferably from 0.05 to 0.6 wt.-%, more preferably from 0.05 to 0.5 wt.-%, more preferably from 0.05 to 0.4 wt.-%, more preferably from 0.05 to 0.3 wt.-%, more preferably from 0.05 to 0.2 wt.-%, more preferably from 0.06 to 0.15 wt.-%, most preferably from 0.07 to 0.1 1 wt.-%, or b) the compound according to the general formula R-(-0-CH2-CH 2 -) n -OX in an amount in the range of from 0.001 to 0.1 wt.-%, preferably from 0.002 to 0.09 wt.
  • the plurality of surface-crosslinked water-absorbent polymer particles comprisies
  • a Si0 2 in an amount in the range of from 500 to 3,000 ppm by weight, pref- erably 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 the water-absorbent polymer particle according to the invention, or the plurality of water-absorbent particles 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 liq- uid-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 the water-absorbent polymer particle according to the invention or the plurality of water-absorbent particles 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 or the plurality of water- absorbent particles 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.
  • a preferred belt of a polymerization belt 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 polymer gel.
  • 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 polymerization belt reactor 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 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.
  • Another means of providing a trough-like configuration is arranging weir elements on an approximately flat belt.
  • at least one weir element is arranged in longitudinal direction at each lateral edge of the belt.
  • At least two further weir elements are arranged in transversal direction on different longitudinal positions of the belt, wherein the trough longitudinally extends between those two positions.
  • the height of the weir elements determines the depth of the trough and hence the amount of reaction components which can be fed into the trough.
  • the longitudinal weir elements have to be designed to be longitudinally bent with the belt at turning sections of the belt.
  • the longitudinal weir elements may be made of a flexible material or they may consist of a plurality of shorter longitudinal weir elements which are arranged close to each other.
  • a trough-like configuration of the polymerization belt can also be achieved by a combination of transversally oriented weir elements and shaping the belt in the transversal direction by supporting elements, or by a combination of longitudinally oriented weir elements and shaping the belt in the longitudinal direction by supporting elements.
  • 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 K (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 is determined according to the Karl Fischer method. SFC
  • the Saline Flow Conductivity (SFC) under a pressure of 0.3 psi (2070 Pa) is determined according to EP 0 640 330 Al , therein also referred to as Gel Layer Pemieability (GLP). residual monomer content
  • the residual monomer content of the water- ansorbent polymer particles is measured according to a standard test method for superabsorbent materials defined by the EDANA. Said test method is described in EDANA, Harmonized Test Methods Nonwovens and Related Industries, 2012 Edition as "Residual Monomers” under the method number WSP 210.2.R3 (12). amount of releasing agent applied
  • the width of the belt is measured using a measuring tape.
  • the conveying speed of the belt is adjusted to a constant value by means of the drive control unit of the belt.
  • the releasing agent is applied constantly over a duration of 10 s. Subsequently, applying is stopped.
  • a flow of the releasing agent in mm/s is measured using a Proline Prosonic Flow 93 P flow meter by Endress + Hausser Messtechnik GmbH + Co. KG, Weil am Rhein, Germany. An average val- ue of the flow over the 10 s is obtained.
  • the measured flow is multiplied by the cross sectional area of the tube conducting the releasing agent at the point of the flow measurement, and by 10 s, thereby obtaining the volume of solvent applied. Said volume is divided by (the belt width times the belt speed times 10 s), thereby obtaining the amount of the releasing agent applied per 1 m belt width and 1 m belt in the longitudinal direction (conveying direction) of the belt.
  • MEHQ mono methyl ether hydroquinone
  • 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 trimethylol 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 (Ci- ba ® 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 mixed solution is placed on the belt of a conveyer belt reactor, as shown in figure 4, and the polymerization is initiated by UV radiation.
  • the conveyor belt has a length of at least 20 m.
  • the conveyor belt is formed as a trough to keep the solution on the belt prior and during polymerization.
  • 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.
  • a releasing agent is sprayed onto the upper run of the belt in order to facilitate the removal of the polymer gel from the belt.
  • the releasing is ob- tained from a polydimethyl siloxane emulsion (EG-601 by Eugene Industry, 166, Nongso-ri, Juchon-myon, Gimhae-si, Gyengnam, Korea) by diluting the emulsion with water to a water content of 97 wt.-% based on the weiglit of the diluted emulsion.
  • the amount of the releasing agent applied to the belt is given in table 1 , below. Accordingly, no releasing agent is applied performing the comparative example 1.
  • 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 con- tent 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) (Bauermeister 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 tumbler sieves having several 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.
  • 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 (Ge- briider 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. Subsequently, 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 ⁇ .
  • Less than 5 wt.-% of the surface-crosslinked absorbent polymer particles of the examples according to the invention are smaller than 150 ⁇ , less than 5 wt.-% of the surface-crosslinked absorbent polymer particles of the examples according to the invention are have a particle size of more than 850 ⁇ . Post treated crosslinked water-absorbent polymer particles are obtained.
  • Table 1 Adhesion and drying time of the polymer gel, and SFC and residual monomer content of water-absorbent polymer particles obtained therefrom.
  • Table 1 gives for the examples 1 to 5 according to the invention, as well as for the comparative example 1 which is not according to the invention: the amount of the releasing agent which is applied to the conveyor belt and the blowing agent added, both in section B) above.
  • adding the releasing agent up to an amount of 500 ml/m 2 reduced the adhesion of the polymer gel to the conveyor belt, hence removing the polymer gel from the belt is improved.
  • Adding more of the releasing agent does not reduce the adhesion further, but the adhesion stays on a constant level.
  • Adding the releasing agent reduces the dry- ing time, meaning the time required to dry the comminuted polymer gel as given above to a water content of 5 wt.-% based on the dried polymer gel. Said drying time decreases for an amount of releasing agent added from 0 to 500 ml/m 2 . At 5,000 ml/m 2 of releasing agent added the drying time is similar to that observed for an amount of 250 ml/m 2 . Surprisingly, also the residual monomer content of the surface-crosslinked polymer particles is reduced from comparative example 1 to the example 4.
  • Example 5 shows a residual monomer content similar to example 2.
  • the Saline Flow Conductivity (SFC) of the surface-crosslinked polymer particles is not affected by the amount of releasing agent applied up to 500 ml/m 2 .
  • Using sodium carbonate as the blowing agent even improves the SFC.
  • Example 5 shows a similar result regarding the SFC as the comparative example 1 and the examples 2 to 3. As the blowing agent improves the SFC, it can be concluded that an amount of releasing agent applied of 5,000 ml/m 2 tends to decrease the SFC.
  • 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, mo- noethylenically unsaturated monomer bearing carboxylic acid groups (al) 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 initia- tor 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 401 of a polymerization belt reactor 400.
  • the belt 401 is an endless conveyor belt.
  • the aqueous monomer solution is polymerized to a polymer gel 601.
  • the polymer gel 501 is discharged from the belt 401 and simultaneously a releasing agent 504 is applied to a part of the belt 401.
  • the polymer gel is comminuted, whereby polymer gel particles are obtained.
  • the polymer gel particles are charged onto a belt of a belt dryer 906 and subsequently dried at a temperature of about 120 to 150°C.
  • the dried polymer gel particles are discharged from the belt dryer 906 and subsequently in a ninth step 109 grinded to obtain water-absorbent polymer particles.
  • the water-absorbent polymer particles are sized to obtain water- absorbent polymer particles having a well defined particle size distribution.
  • 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 initia- tor is added 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 process 100 shown in figure 3 is the same as the process 100 in figure 1 , wherein the se- cond step 102, the fourth step 104, and the eleventh step 1 1 1 are not part of the process 100 according to figure 3.
  • FIG 4 shows a scheme of a basic setup of a polymerization belt reactor 400 according to the invention.
  • the polymerization belt reactor 400 comprises a belt 401.
  • the belt 401 is an endless conveyor belt.
  • the belt 401 passes over two guide rollers 402 such that an upper run of the belt 401 moves downstream.
  • the downstream movement of the upper run of the belt 401 determines the direction of movement 403 of the polymer gel 501 (not shown here) on the belt 401 , indicated by an arrow.
  • Another arrow indicates a counter direction 404 to a direction of movement 403 of the polymer gel 501 on the belt 401.
  • Another arrow indicates both longitudinal directions 405 of the belt 401 and yet another arrow the transversal direc- tions 406 of the belt 401.
  • the belt 401 comprises a first turning section 407 and a further turning section 408.
  • the belt 401 extends in the longitudinal directions 405 over a length which is a longitudinal extension 409 of the belt 401.
  • the polymerization belt reactor 400 may comprise further components which are not shown in the figure, such as support elements, a supply and metering system, irradiating means, cooling and heating devices, and a removal sys- tern.
  • Figure 5 shows a scheme of a downstream end 500 of a belt 401 of a polymerization belt reactor 400 according to the invention in a view facing an upstream direction.
  • the downstream end 500 of the belt 401 is flat.
  • a left nozzle 502 and a right nozzle 503 spray a releas- ing agent 502 onto a left and a right transversal edge of the belt respectively.
  • an adhesion of a polymer gel 501 to the downstream end 500 of the belt 401 is reduced.
  • Figure 6 shows a scheme of a basic setup of another polymerization belt reactor 400 according to the invention in a side view.
  • the polymerization belt reactor 400 of figure 6 is the same as the polymerization belt reactor 400 in figure 4, except that a polymer gel 501 is shown on the belt 401.
  • a releasing agent 504 is sprayed onto the further turning section 408 of the belt 401 in a solid angle element 601 of 90° centered around a counter direction 404 to a direction of movement 403 of the polymer gel 501 on the belt 401 while the polymer gel 501 is discharged from the belt 401.
  • FIG. 7 shows a scheme of a basic setup of another polymerization belt reactor 400 according to the invention in a side view.
  • the polymerization belt reactor 400 of figure 7 is the same as the polymerization belt reactor 400 in figure 4, except that a polymer gel 501 is shown on the belt 401.
  • a releasing agent 504 is sprayed onto 50 % of the longitudinal extension 409 of the belt 401.
  • the releasing agent 504 is sprayed from above the belt 401 by nozzles 702 of a plurality of nozzles which are comprised by a tube 701 which conducts the releasing agent 504.
  • the nozzles 702 are arranged longitudinally along the belt 401.
  • the belt 401 Over the 50 % of the longitudinal extension 409 of the belt 401 to which the releasing agent 504 is applied the belt 401 comprises a trough 800 which gradually flattens out in a direction of movement 403 of the polymer gel 50 Ion the belt 401. At a downstream end 500 of the belt 401 the belt is flat.
  • FIG 8 shows a scheme of a trough 800 of a belt 401 of a polymerization belt reactor 400 according to the invention in a view facing an upstream direction.
  • the trough 800 is shown in a transversal cross section trough a longitudinal extension 409 of the belt 401.
  • the trough 800 has a shape of a concave curve.
  • the concave curve comprises a horizontally aligned portion 802 having a length of 0.5 m.
  • a tangent 805 on a position on the concave curve inclines a maximum angle 804 between the belt 401 and a horizontal plane 803.
  • the maximum angle 804 is about 28°.
  • the belt comprises sidewalls 801.
  • Tubes 701 conduct a releasing agent 504 which is sprayed from above the belt 401 via nozzles 702 of a plurality of nozzles onto inner sides of the sidewalls 801 of the belt 401.
  • the nozzles 702 are comprised by the tubes 701 and arranged longitudinally along the belt 401.
  • the trough 800 being present in the cross section shown in figure 8 becomes less deep and gradually flattens completely to a downstream end 500 of the belt 401.
  • Figure 9 shows a block diagram of a device 900 for the preparation of water-absorbent polymer particles according to the invention.
  • the arrows show a direction of a process stream 909 of the preparation of water-absorbent polymer particles.
  • the device 900 comprises a first container 901, a further container 902, downstream a mixing device 903, downstream a polymerization belt reactor with a wetting device 904, downstream a comminuting device 905, downstream a belt dryer 906, downstream a grinding device 907, and downstream a sizing device 908, each according to the invention.

Abstract

The invention generally relates to a process for the preparation of water-absorbent polymer particles, comprising the process steps of (i) preparing an aqueous monomer solution comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (α1) and at least one crosslinker (α3); (ii) optionally adding fine particles of a water-absorbent polymer to the aqueous monomer solution; (iii) adding a polymerization initiator or a at least one component of a polymerization initiator system that comprises two or more components to the aqueous monomer solution; (iv) optionally decreasing the oxygen content of the aqueous monomer solution; (v) charging the aqueous monomer solution onto a belt of a polymerization belt reactor; (vi) polymerizing the at least one monomer in the aqueous monomer solution on the belt, thereby obtaining a polymer gel; (vii) discharging the polymer gel from the belt and comminuting the polymer gel; (viii) drying the comminuted polymer gel; (ix) grinding the dried polymer gel thereby obtaining water-absorbent polymer particles; (x) sizing the grinded water-absorbent polymer particles; and (xi) optionally treating the surface of the grinded and sized water-absorbent polymer particles; wherein in process step (vi) or (vii) or both a releasing agent is applied to at least a part of the belt.

Description

[DESCRIPTION]
[Invention Title]
RELEASE OF POLYMER GEL FROM POLYMERIZATION BELT IN PRODUCTION OF WATER-ABSORBENT POLYMER PARTICLES
[Technical Field]
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 plurality of water- absorbent polymer particles; to a composite material comprising such a water-absorbent polymer particle or such a plurality of water-absorbent polymer particles; 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 or a plurality of water-absorbent polymer particles; 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.
[Background Art]
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 hydro gels, and to retain such fluids under a certain pressure. By virtue of those characteristic properties, 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 Superabsorbent 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. In a further process step these superabsorbent particles are often surface crosslinked in order to improve the absorption behavior. For this purpose the particles are mixed with an aqueous solution containing a surface crosslinking agent and op- tionally 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 cross- linkers 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 .
Especially continuous processes of polymerization are commonly performed in a polymerization reactor which is a polymerization belt reactor. A common polymerization belt reactor comprises a conveyor belt being designed to carry an aqueous monomer solution which comprises the acid-group-carrying monomers during polymerization. Such a conveyor belt is disclosed in EP 0 955 086 Bl .
[Disclosure] [Technical Problem]
Disadvantages of the processes for the preparation of water-absorbent polymer particles using a polymerization belt reactor comprising a conveyor belt arise when the hydrogel obtained by the polymerization on the conveyor belt is to be discharged from the conveyor belt. The hydrogel tends to adhere to the conveyor belt. Therefor, during discharging, the hydrogel may be torn apart. Thus, at least a part of the hydrogel may stick to the conveyor belt and discharging may fail. This sticking part of the hydrogel may disturb further cycles of a continuous process for the preparation of water-absorbent polymer particles. If only a part of the hydrogel is discharged from the conveyor belt, the output of the overall process is decreased. This makes the process less effective or more expensive or both. If the hydrogel is torn apart during discharging, undefined pieces of hydrogel may be fed into further process steps, which may result in a less effective process or in a product of lower quality or both.
[Technical Solution]
Generally, it is an object of the present invention to at least partly overcome a disad- vantage arising form the prior art in the context of the production of water-absorbent polymer particles. It is a further object of the present invention to provide a process for the production of water-absorbent polymer particles, wherein discharging of the polymer gel from a belt of a polymerization belt reactor is improved. It is a further object of the present invention to provide a process for the production of water-absorbent polymer particles, wherein adhesion of the polymer gel during discharging the polymer gel from a belt of a polymerization belt reactor is reduced. It is a further object of the present invention to provide a process for the production of water-absorbent polymer particles, wherein tearing apart the polymer gel during discharging from a belt of a polymerization belt reactor is avoided as far as possible. It is a further object of the present invention to provide a process for the production of water- absorbent polymer particles, wherein discharging of the polymer gel from a belt of a polymerization belt reactor is improved without lowering the quality of the produced water-absorbent polymer particles, preferably regarding the SFC. It is a further object of the present invention to provide a process for the production of water-absorbent polymer particles, wherein the drying time of the comminuted polymer gel is reduced. It is a further object of the present inven- tion to provide a process for the production of water-absorbent polymer particles, wherein the residual monomer content of the water-absorbent polymer particles produced is reduced. It is a further object of the present invention to provide a process for the production of water- absorbent polymer particles, wherein discharging of the polymer gel from a belt of a polymerization belt reactor is improved in an uncomplicated and inexpensive way. It is an object of the present invention to provide a process for the production of water-absorbent polymer particles, showing a balanced combination of at least two or more of the above advantages.
It is a further object of the present invention to provide a water-absorbent polymer particle or a plurality of water-absorbent polymer particles produced by a process having at least one, preferably a balanced combination of at least two, of the above advantages, wherein the water-absorbent polymer particle shows no reduction of quality, preferably regarding the SFC or the residual monomer content or both.
It is a further object of the present invention to provide a composite material comprising a water-absorbent polymer particle produced by a process having at least one of the above advantages, wherein the composite material shows no reduction of quality.
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 advantages.
A contribution to the solution of at least one of the above objects is given by the independent claims. The dependent claims provide preferred embodiments of the present invention which also serve solving at least one of the above mentioned objects. A contribution to the solution of at least one of these objects is made by a process for the preparation of water-absorbent polymer particles, comprising the process steps of
(i) preparing an aqueous monomer solution comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al) and at least one crosslinker (a3);
(ii) optionally adding fine particles of a water-absorbent polymer to the aqueous monomer solution;
(iii) adding a polymerization initiator or a at least one component of a polymerization initiator system that comprises two or more components to the aqueous monomer solution;
(iv) optionally decreasing the oxygen content of the aqueous monomer solution;
(v) charging the aqueous monomer solution onto a belt of a polymerization belt reactor;
(vi) polymerizing the at least one monomer in the aqueous monomer solution on the belt, thereby obtaining a polymer gel;
(vii) discharging the polymer gel from the belt and comminuting the polymer gel;
(viii) drying the comminuted polymer gel;
(ix) grinding the dried polymer gel thereby obtaining water-absorbent polymer particles;
(x) sizing the grinded water-absorbent polymer particles; and
(xi) optionally treating the surface of the grinded and sized water-absorbent polymer particles;
wherein in process step (vi) or (vii) or both a releasing agent is applied to at least a part of the belt.
A contribution to the solution of 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) a first container, designed to take an aqueous monomer solution, comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al);
b) a further container, designed to take at least one crosslinker (a3);
c) a mixing device, wherein the mixing device is
i) located down-stream to the first container and the further container, ii) designed to mix the monomer solution and the at least one crosslinker (<x3); d) a polymerization belt reactor, wherein the polymerization belt reactor
i) is located down-stream to the mixing device,
ii) is designed to comprise the aqueous monomer solution and the at least one crosslinker (<x3) during polymerizing the monomer in the aqueous monomer solution, thereby obtaining a polymer gel iii) comprises a belt;
e) a wetting device, wherein the wetting device is located and designed for applying a releasing agent to at least 30 %, preferably at least 35 %, more preferably at least 40 %, more preferably at least 45 %, most preferably at least 48 %, of a longitudinal extension of the belt;
f) a comminuting device, wherein the comminuting device is
i) located down-stream to the polymerization belt reactor, ii) designed to comminute the polymer gel;
g) a belt dryer, wherein the belt dryer is
i) located down-stream to the comminuting device,
ii) designed to dry the polymer gel,
h) a grinding device, wherein the grinding device is
i) located down-stream to the belt dryer,- ii) designed to grind the dried polymer gel, thereby obtaining water- absorbent polymer particles;
j) a sizing device, wherein the sizing device is
i) located down-stream to the grinding device,
ii) designed to size the grinded water-absorbent polymer particles.
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.
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 contribution to solving at least one of the above objects is provided by a plurality of water-absorbent polymer particles, comprising a polyalkylsiloxane, or a compound according to a general formula R-(-0-CH2-CH2-)n-OX, or both; wherein in the general formula R is C4 to C20, n is an integer in the range of from 10 to 10,000, and X is H or M; wherein M is a metal ion. 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 the water-absorbent polymer particle according to the invention or the plurality of water-absorbent particles 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 or the plurality of water- absorbent particles 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.
[Advantageous Effects]
The water-absorbent polymer particle according to the invention or the plurality of water-absorbent particles according to the invention may be used 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.
[Description of Drawings]
Figure 1 is a flow chart diagram depicting the steps of a process according to the invention;
Figure 2 is a flow chart diagram depicting the steps of another process
according to the invention;
Figure 3 is a flow chart diagram depicting the steps of another process
according to the invention;
Figure 4 is a scheme of a basic setup of a polymerization belt reactor according to the invention;
Figure 5 is a scheme of a downstream end of a belt of a polymerization
belt reactor according to the invention in a view facing an upstream direction;
Figure 6 is a scheme of a basic setup of another polymerization belt reactor according to the invention in a side view; Figure 7 is a scheme of a basic setup of another polymerization belt reactor according to the invention in a side view;
Figure 8 is a scheme of a trough of a belt of a polymerization belt reactor according to the invention in a view facing an upstream direction; and
Figure 9 is a block diagram of a device for the preparation of water- absorbent polymer particles according to the invention.
100 process according to the invention
101 step (i)
102 step (ii)
103 step (iii)
104 step (iv)
105 step (v)
106 step (vi)
107 step (vii)
108 step (viii)
109 step (ix)
110 step (x)
1 1 1 step (xi)
400 polymerization belt reactor
401 belt
402 guide roller
403 direction of movement of the polymer gel on the belt
404 counter direction to a direction of movement of the polymer gel on the belt
405 longitudinal directions
406 transversal directions
407 first turning section
408 further turning section
409 longitudinal extension of the belt
500 downstream end of the belt
501 polymer gel
502 left nozzle
503 right nozzle
504 releasing agent 601 solid angle element of 90° centered around a counter direction to a direction of movement of the polymer gel on the belt
701 tube
702 nozzle of a plurality of nozzles
800 trough
801 side wall
802 horizontal portion
803 horizontal plane
804 maximum angle between belt and horizontal plane
805 tangent
900 device for the preparation of water-absorbent polymer particles
901 first container
902 further container
903 mixing device
904 polymerization belt reactor and wetting device
905 comminuting device
906 belt dryer
907 grinding device
908 sizing device
909 process stream
[Best Mode]
A contribution to the solution of at least one of these objects is made by a process for the preparation of water-absorbent polymer particles, comprising the process steps of
(i) preparing an aqueous monomer solution comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al) and at least one crosslinker (a3);
(ii) optionally adding fine particles of a water-absorbent polymer to the aqueous monomer solution;
(iii) adding a polymerization initiator or a at least one component of a polymerization initiator system that comprises two or more components to the aqueous monomer solution;
(iv) optionally decreasing the oxygen content of the aqueous monomer solution; (v) charging the aqueous monomer solution onto a belt of a polymerization belt reactor;
(vi) polymerizing the at least one monomer in the aqueous monomer solution on the belt, thereby obtaining a polymer gel;
(vii) discharging the polymer gel from the belt and comminuting the polymer gel;
(viii) drying the comminuted polymer gel;
(ix) grinding the dried polymer gel thereby obtaining water-absorbent polymer particles;
(x) sizing the grinded water-absorbent polymer particles; and
(xi) optionally treating the surface of the grinded and sized water-absorbent polymer particles;
wherein in process step (vi) or (vii) or both a releasing agent is applied to at least a part of the belt.
Therein, subsequent steps of the process according to the invention may be performed simultaneously or may overlap in time or both. This holds particularly for the steps (i) to (iv), especially particularly for the steps (iii) and (iv).
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 belt reactor, preferably onto the belt of the polymerization belt reactor. The polymer gel obtained is continuously discharged out of the polymerization belt 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, to substitute certain parts of the process equipment, like the belt material of the polymerization belt reactor,
clean certain parts of the process equipment, especially for the purpose of removing polymer deposits in tanks or pipes, or
start a new process when water-absorbent polymer particles with other absorption characteristics have to be prepared.
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 of „Word Strategic Partners" ED ANA and INDA) in the range of from 10 to 3,000 μπι, preferably 20 to 2,000 μη and particularly preferably ! 50 to 850 μπι. In this context, it is particularly preferable for the content of water-absorbent polymer particles having a particle size in a range of from 300 to 600 μπι to be at least 30 wt.-%, particularly preferably at least 40 wt.-% and most preferably at least 50 wt.-%, based on the total weight of the water- absorbent polymer particles.
In process step (i) of the process according to the present invention an aqueous monomer solution containing at least one partially neutralized, monoefhylenically unsaturated monomer bearing carboxylic acid groups (al) and at least one crosslinker (a3) is prepared.
Preferred monoefhylenically unsaturated monomers bearing carboxylic acid groups (al) are those cited in DE 102 23 060 Al as preferred monomers (al), whereby acrylic acid is particularly preferred.
It is preferred according to the present invention that 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 between 10 to 60 wt.-%, preferably 30 to 55 wt.-% and most preferably between 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.
Preferred crosslinkers (a3) according to the present invention are compounds which have at least two ethylenically unsaturated groups in one molecule (crosslinker class I), compounds which have at least two functional groups which can react with functional groups of the monomers (al) or (a2) in a condensation reaction (= condensation crosslinkers), in an addition reaction or a ring-opening reaction (cross-linker class II), compounds which have at least one ethylenically unsaturated group and at least one functional group which can react with functional groups of the monomers (al) or (a2) in a condensation reaction, an addition reaction or a ring-opening reaction (crosslinker class III), or polyvalent metal cations (cross- linker class IV). Thus with the compounds of crosslinker class I a crosslinking of the polymer is achieved by radical polymerization of the ethylenically unsaturated groups of the crosslinker molecules with the monoethylenically unsaturated monomers (al) 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 func- tional 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). With compounds of 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 (a 1) or (a.2).
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, polyethylenegly- col di(meth)acrylates, triallylmethylammonium chloride, tetraallylammonium chloride and allylnonaethyleneglycol acrylate produced with 9 mol ethylene oxide per mol acrylic acid are particularly preferred, wherein N, 1ST -methylene bisacrylamide is even more preferred, and
as compounds of crosslinker class IV, Al2 (S04)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.
Further preferred 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 Ν,Ν' -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, 1ST -methylene bisacrylamide is even more preferred.
The aqueous monomer solution may further comprise water-soluble polymers (ot4). Preferred water-soluble polymers (a4) include partly or completely saponified polyvinyl alco- hol, 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. It is also conceivable for these water-soluble polymers to be mixed with the polymer gel or the already dried, water-absorbent polymer.
The aqueous monomer solution can furthermore also comprise auxiliary substances (oc5), these auxiliary substances including, in particular, complexing agents, such as, for example, EDTA.
The relative amount of monomers ( l) and (a2) and of crosslinking agents (a3) and water-soluble polymers (a4) and auxiliary substances (oc5) in the aqueous monomer solution is preferably chosen such that the water-absorbent polymer structure obtained after drying the 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),
to the extent of 0 to 5 wt.-%, preferably to the extent of 0.001 to 3 wt.-% and particularly preferably to the extent of 0.01 to 2.5 wt.-% on the crosslinking agents (a3), - to the extent of 0 to 30 wt.-%, preferably to the extent of 0 to 5 wt.-% and particularly preferably to the extent of 0.1 to 5 wt.-% on the water-soluble polymers (a4), to the extent of 0 to 20 wt.-%, preferably to the extent of 0 to 10 wt.-% and particularly preferably to the extent of 0.1 to 8 wt.-% on the auxiliary substances (a5), and to the extent of 0.5 to 25 wt.-%, preferably to the extent of 1 to 10 wt.-% and particu- larly preferably to the extent of 3 to 7 wt.-% on water (a6)
the sum of the amounts by weight (al) to (a6) being 100 wt.-%.
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 pre- liminary 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 .
In process step (ii) fine particles of a water-absorbent polymer may optionally be added to the aqueous monomer solution. Independent of optional step (ii) fine water-absorbent polymer particles may be added to the aqueous monomer solution at one selected from the group consisting 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 corresponds 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 based on the total weight of the water- absorbent fine particles have a particle size of less than 200 μπι, preferably less than 150 μηι and particular preferably less than 100 μιη.
In a preferred embodiment of the process according to the present invention 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. In a preferred embodiment of the present invention, which is especially useful if the process is performed continuously as described above, 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. Such a kind of mixing setup can be realised in a so called "Rotor Stator 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.
In this context it is particularly preferred that the first stream of the fine particles and the second stream of the aqueous monomer solution form an angle δ 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°. It is also preferred that 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 ε 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. Specific 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® Werke GmbH & Co. KG, Staufen, Germany, under designations MHD 2000/4, MHD 2000/05, MHD 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„Conti TDS", or by Kinematika 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.
In process step (iii) of the process according to the present invention 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.
As polymerization initiators for initiation of the polymerisation all initiators forming radicals under the polymerization conditions can be used, which are commonly used in the production of superabsorbers. Among these belong thermal 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.
As 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. Particularly preferred are thermal 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. In some cases it is advantageous to use mixtures of various thermal polymerization initiators. Among such mixtures, 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 pemialeate, tert.-butyl perbenzoate, tert.-butyl-3,5,5-trimethylhexanoate and amyl perneodecanoate. Furthermore, the following 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-valeric 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. Preferably ascorbic acid or sodium pyrosulfite is used as reducing component of the redox catalyst. 1 χ 10"5 to 1 mol-% of the reducing component of the redox catalyst and 1 x 10"5 to 5 mol-% of the oxidizing component of the redox catalyst are used, in each case referred to the amount of monomers used in the polymerization. Instead of the oxidizing 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. Examples of such initiators are benzophenone derivatives such as Michlers ketone, phenanthrene derivatives, fluorine derivatives, anthra- quinone derivatives, thioxanthone derivatives, cumarin derivatives, benzoinether and derivatives thereof, azo compounds such as the above-mentioned radical formers, substituted hex- aarylbisimidazoles or acylphosphine oxides. Examples of azides are: 2-(N,N- dimethylamino)ethyl-4-azidocinnamate, 2-(N,N-dimethylamino)ethyl-4-azidonaphthylketone, 2-(N,N-di-methylamino)ethyl-4-azidobenzoate, 5-azido-l-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 2,6-bis(p-azidobenzylidene)-4- methylcyclohexanone. 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.
According to a further embodiment of the process according to the invention it is pre- ferred that in process step (iii) the initiator comprises the following components
iiia. a peroxodisulfate; and
iiib. an organic initiator molecule comprising at least three oxygen atoms or at least three nitrogen atoms;
wherein the initiator comprises the peroxodisulfate and the organic initiator molecule in a molar ratio in the range of from 20: 1 to 50: 1. In one aspect of this embodiment it is preferred that the 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. In another aspect of this embodiment it is preferred that the 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. In a further aspect of this embodiment it is preferred that the peroxodisulfate is of the general formula M2S208, with M being selected from the group consisting of NH4, 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.
In this context it should also be noted that 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. If 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). Independent of optional step (iv), decreasing the oxygen content of the aqueous monomer solution may also be performed before process step (iii) according to the invention.
In process step (iv) of the process according to the present invention the oxygen content of the aqueous monomer solution is optionally decreased. Independent of optional step (iv), decreasing the oxygen content of the aqueous monomer solution may also be performed before, during or after process step (ii) according to the invention. Preferably, the oxygen content of the aqueous monomer solution is decreased after the fine particles have been added in process step (ii).
Whenever 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. As a consequence 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 solu- tion 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 intem ediate 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.
In process step (v) of the process according to the present invention the aqueous monomer solution is charged onto the belt of the polymerization belt reactor. Preferably, the aqueous monomer solution is charged onto the belt at an upstream position of the belt. A preferred belt is a conveyor belt.
In process step (vi) the monomers in the aqueous monomer solution are polymerized on the belt, thereby obtaining a polymer gel. Preferably, the polymer gel is obtained at a downstream portion of the belt. Before drying, the polymer gel is comminuted in order to obtain polymer gel particles.
In process step (vii) of the process according to the present invention the polymer gel that is obtained on the belt is discharged from the belt. Preferably, the polymer gel is removed from the belt as a continuous strand that is of a soft semi-solid consistency and is then passed on for further processing comprising comminuting. By comminuting the polymer gel polymer gel particles are obtained.
Comminution of the polymer gel is preferably performed in at least three steps:
in a first step, 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 mm and
in a third step a "wolf (grinding) unit, preferably a mincer, preferably having a screw and a hole plate, whereby the screw conveys against the hole plate is used in order to grind and crush gel pieces into polymer gel particles which are preferably smaller than the gel pieces.
An optimal surface-volume ratio is achieved hereby, which has an advantageous effect on the drying behaviour in process step (viii). A gel which has been comminuted in this way is particularly suited to belt drying. The three-step comminution offers a better "airability" because of the air channels located between the granulate kernels.
In process step (viii) of the process according to the present invention the polymer gel is dried.
The drying of the polymer gel can be effected in any dryer or oven the person skilled in the art considers as appropriate for drying the above described gel particles. Rotary tube furnaces, fluidised bed dryers, plate dryers, paddle dryers and infrared dryers may be mentioned by way of example.
Especially preferred are belt dryers. 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, preferably not less than 10 %, more preferably not less than 15 % and most preferably not less than 20 % and preferably up to 50 %, more preferably up to 40 % and most preferably up to 30 % of the gas quantity per pass, leaves the dryer as a highly 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, multi-stage 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. To ensure opti- mum performance of the belt-drying operation, the drying properties of the water-absorbent polymers 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. Similarly, certain surface enhancements, such as electropolishing or Teflonizing, are possible.
The polymer gel to be dried is 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 to be dried is preferably not less than 2 cm, more preferably not less than 5 cm and most prefer- ably 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.
Furthermore, it is preferable according to the invention that 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.
In process step (ix) of the process according to the present invention the dried polymer gel is ground thereby obtaining water-absorbent polymer particles.
For grinding of the dried polymer gel any device can be used the person skilled in the art considers as appropriate for grinding the dried polymer gel or the above described dried polymer gel. As an example for 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.
In process step (x) of the process according to the present invention the ground water- absorbent polymer particles are sized, preferably using appropriate sieves. In this context it is particularly preferred that after sizing the water-absorbent polymer particles the content of polymer particles having a particle size of less than 150 μιη 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 μηι 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. It is also preferred that after sizing the water-absorbent polymer particles, at least 30 wt.-%, more preferred at least 40 wt.-% and most preferred at least 50 wt.-%, based on the total weight of the water-absorbent polymer particles have a particle size in a range of from 300 to 600 μιτι.
In process step (xi) of the process according to the present invention the surface of the ground and sized water-absorbent polymer particles is optionally treated. As measures to treat the surface of water-absorbent polymer particles any measure can be used the person skilled in the art considers as appropriate for such a purpose. Examples of 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. Preferably, the components used to treat the surface of the polymer particles (cross-linker, water soluble salts) 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.
In an embodiment of the invention the releasing agent comprises one selected from the group consisting of a solvent, a polyalkylsiloxane, and a surfactant, or a combination of at least two thereof. A preferred solvent is water. A preferred polyalkylsiloxane is polydimethylsiloxane.
In an embodiment of the invention the surfactant is a compound according to the general formula R-(-0-CH2-CH2-)n-OX, wherein R is selected from C4 to C2o, n is an integer in the range of from 10 to 10,000, preferably from 50 to 5,000, more preferably from 100 to 500, and X is H or M, wherein M is a metal ion. A particularly preferred compound according to said general formula is polyethylene glycol trimethylnonyl ether.
In an embodiment of the invention the releasing agent comprises
a) the solvent in an amount in the range of from 95 to 99 wt.-%, preferably from 95.5 to 98.5 wt.-%, more preferably from 96.5 to 97.5 wt.-%,
b) the polyalkylsiloxane in an amount in the range of from 0.5 to 5 wt.-%, preferably from 1 to 4 wt.-%, more preferably from 2.4 to 3.2 wt.-%, and
c) the surfactant in an amount in the range of from 0.01 to 1 wt.-%, preferably from 0.05 to 0.7 wt.-%, more preferably from 0.1 to 0.3 wt.-%, each based on the total weight of the releasing agent and the amounts in wt.-% adding up to a total of 100 wt.-%.
In an embodiment of the invention wherein in step (vi) or (vii) or both the releasing agent is applied to at least 30 %, preferably at least 35 %, more preferably at least 40 %, more preferably at least 45 %, most preferably at least 48 %, of a longitudinal extension of the belt.
In an embodiment of the invention the belt comprises a trough having a sidewall; wherein in step (vi) or (vii) or both the releasing agent is applied to at least a part of the sidewall. Therein, a preferred sidewall is oriented along a longitudinal direction of the belt. A preferred sidewall is a portion of a conveyor belt. A preferred part of the sidewall faces to the trough. Preferably, the solvent is applied to a left inner sidewall of the trough and to a right inner sidewall of the trough, preferably simultaneously.
In an embodiment of the invention the belt comprises a weir element; wherein in step (vi) or (vii) or both the releasing agent is applied to at least a part of the weir element. Preferably, the weir element is arranged in a longitudinal direction of the belt.
In an embodiment of the invention the belt is an endless belt, comprising a first turning section and a further turning section; wherein the polymer gel is discharged from the further turning section of the endless belt in step (vii); wherein the releasing agent is applied to at least a part of the further turning section in step (vii). Therein, as the belt moves, at each instant of time another portion of the belt is at a turning section. Therein, each portion of the belt passes once through each turning section per cycle of the movement of the belt. A preferred first turning section of the belt is a section of the belt over which the belt is transformed from moving upstream to moving downstream. A preferred further turning section of the belt is a section of the belt over which the belt is transformed from moving downstream to moving upstream. Preferably, at the first turning section and the further turning section the belt is in contact with a guide roller. Preferably, at the first turning section and the further turning section the belt has a shape of an arc or of an ellipse or both in longitudinal direction. Preferably, over the length of a turning section the belt changes from being horizontal to vertical and back to horizontal. Preferably, the releasing agent is applied to a downstream moving portion of the further turning section of the belt.
In an embodiment of the invention the releasing agent is applied by one selected from the group consisting of spraying, pouring, splashing, and dripping, or a combination of at least two thereof. Preferably, the releasing agent is applied by spraying. A preferred spraying is a spraying by a nozzle. In an embodiment of the invention the releasing agent is sprayed in a solid angle element of 90° or less, preferably of 60° or less, more preferably of 45° or less, most preferably of 30° or less, centered around a counter direction to a direction of movement of the polymer gel on the belt.
In an embodiment of the invention the releasing agent is applied by a plurality of nozzles, wherein the nozzles are arranged longitudinally along the belt. Preferably, the nozzles are comprised by a tube. A preferred tube extends at least 1 m, preferably at least 2 m, more preferably at least 3 m, more preferably at least 4 m, more preferably at least 5 m, more preferably at least 6 m, more preferably at least 7 m, more preferably at least 8 m, more preferably at least 9 m, most preferably at least 10 m, longitudinally along the belt.
In an embodiment of the invention the releasing agent is applied by at least two nozzles. Preferably, the releasing agent is sprayed by the at least two nozzles simultaneously. Preferably, facing the belt in upstream direction a left nozzle sprays the releasing agent on a left portion of the belt and a right nozzle sprays the releasing agent on a right portion of the belt.
In an embodiment of the invention during applying to the belt the releasing agent has a temperature in the range of from 10 to 50°C, preferably from 12 to 40°C, more preferably from 15 to 30°C, most preferably from 18 to 28°C.
In an embodiment of the invention in step (vi) or (vii) or both the releasing agent is applied to the belt in an amount in the range of from 10 to 10,000 ml, preferably from 20 to 9,000 ml, more preferably from 30 to 8,000 ml, more preferably from 40 to 7,000 ml, more preferably from 50 to 6,000 ml, more preferably from 60 to 5,000 ml, more preferably from 70 to 4,000 ml, more preferably from 80 to 3,000 ml, more preferably from 90 to 2,000 ml, more preferably from 100 to 1,000 ml, more preferably from 100 to 800 ml, more preferably from 100 to 600 ml, more preferably from 100 to 500 ml, more preferably from 100 to 400 ml, more preferably from 100 to 350 ml, more preferably from 100 to 300, most preferably from 100 to 250 ml, of releasing agent per m2 of the belt.
In an embodiment of the invention 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.
In an embodiment of the invention 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. In an embodiment of the invention 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.
In an embodiment of the invention 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. Preferably, 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. Particularly preferably, the blowing agent is added to the monomer solution after, or simultaneously to adding the initiator or a component of an initiator system. Preferably the blowing agent is added to the monomer solution in an amount in the range of from 500 to 4000 ppm by weight, preferably from 1000 to 3500 ppm by weight, more preferably from 1500 to 3200 ppm by weight, most preferably from 2000 to 3000 ppm by weight, based on the total weight of the monomer solution.
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 endotheraiic 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 C02, or a combination of at least two thereof. A preferred C02 is liquid C02. A preferred hydrocarbon is one selected from the group consisting of pentane, isopentane, and cyclopen- tane, 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 Ν,Ν'- 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 containing salt, or a bicarbonate containing salt, or both. Another preferred carbonate blowing agent comprises one selected from the group consisting of C02 as a gas, C02 as a solid, ethylene carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, or magnesium hydroxic carbonate, calcium carbonate, barium car- bonate, 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 is dolomite. The above mentioned carbonate blowing agents release C02 when being heated while dissolved or dispersed in the monomer solution. A particularly preferred carbonate blowing agent is MgC03, which may also be represented by the formula (MgC03)4 Mg(OH)2-5-H20. Another preferred carbonate blowing agent is agent is (NH4)2C03. The MgC03 and (NH4)2C03 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 Na2C03, 2C03, (NH4)2C03, MgC03, CaC03, NaHC03, KHC03, NH4HC03, Mg(HC03)2, Ca(HC03)2, ZnC03, and BaC03. Although 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. Also, other multivalent cations, such as Ni, Ba, Cd, Hg would be unacceptable because of potential toxic or skin sensitizing effects.
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 Ν,Ν'- Dinitro- soamide is N,N'-dimethyl-N,N'-dinitrosoterephthalamide.
A contribution to the solution of 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) a first container, designed to take an aqueous monomer solution, comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al);
b) a further container, designed to take at least one crosslinker (a3);
c) a mixing device, wherein the mixing device is
i) located down-stream to the first container and the further container, ii) designed to mix the monomer solution and the at least one crosslinker
(a3);
d) a polymerization belt reactor, wherein the polymerization belt reactor
i) is located down-stream to the mixing device, ii) is designed to comprise the aqueous monomer solution and the at least one crosslinker ( 3) during polymerizing the monomer in the aqueous monomer solution, thereby obtaining a polymer gel iii) comprises a belt;
e) a wetting device, wherein the wetting device is located and designed for applying a releasing agent to at least 30 %, preferably at least 35 %, more preferably at least 40 %, more preferably at least 45 %, most preferably at least 48 %, of a longitudinal extension of the belt;
f) a comminuting device, wherein the comminuting device is
i) located down-stream to the polymerization belt reactor, ii) designed to comminute the polymer gel;
g) a belt dryer, wherein the belt dryer is
i) located down-stream to the comminuting device,
ii) designed to dry the polymer gel,
h) a grinding device, wherein the grinding device is
i) located down-stream to the belt dryer,
ii) designed to grind the dried polymer gel, thereby obtaining water- absorbent polymer particles;
k) a sizing device, wherein the sizing device is
i) located down-stream to the grinding device,
ii) designed to size the grinded water-absorbent polymer particles.
Therein, a preferred wetting device comprises a nozzle. Another preferred wetting device comprises a plurality of nozzles, wherein the nozzles are comprised by a tube, and arranged longitudinally along the belt. A preferred tube extends at least 1 m, preferably at least 2 m, more preferably at least 3 m, more preferably at least 4 m, more preferably at least 5 m, more preferably at least 6 m, more preferably at least 7 m, more preferably at least 8 m, more preferably at least 9 m, most preferably at least 10 m, longitudinally along the belt. A preferred releasing agent is a releasing agent according to the process according to the invention. A preferred applying of a releasing to the belt is performed according to the process according to the invention. Preferred components or devices or both of the device for the preparation of water-absorbent polymer particles according to the invention are designed 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. Preferably, 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 contribution to solving at least one of the above objects is provided by a plurality of water-absorbent polymer particles, comprising a polyalkylsiloxane, or a compound according to a general formula R-(-0-CH2-CH2-)n-OX, or both; wherein in the general formula R is C4 to C2o, n is an integer in the range of from 10 to 10,000, preferably from 50 to 5,000, more preferably from 100 to 500, and X is H or M; wherein M is a metal ion. A particularly preferred compound according to said general formula is polyethylene glycol trimethylnonyl ether. A preferred polyalkylsiloxane is polydimethylsiloxane.
In an embodiment of the invention the plurality of water-absorbent polymer particles comprises
a) the polyalkylsiloxane in an amount in the range of from 0.01 to 1 wt.-%, preferably from 0.02 to 0.9 wt.-%, more preferably from 0.03 to 0.8 wt.-%, more preferably from 0.04 to 0.7 wt.-%, more preferably from 0.05 to 0.6 wt.-%, more preferably from 0.05 to 0.5 wt.-%, more preferably from 0.05 to 0.4 wt.-%, more preferably from 0.05 to 0.3 wt.-%, more preferably from 0.05 to 0.2 wt.-%, more preferably from 0.06 to 0.15 wt.-%, most preferably from 0.07 to 0.1 1 wt.-%, or b) the compound according to the general formula R-(-0-CH2-CH2-)n-OX in an amount in the range of from 0.001 to 0.1 wt.-%, preferably from 0.002 to 0.09 wt.-%, more preferably from 0.003 to 0.08 wt.-%, more preferably from 0.002 to 0.07 wt.-%, more preferably from 0.002 to 0.06 wt.-%, more preferably from 0.002 to 0.05 wt.-%, more preferably from 0.002 to 0.04 wt.-%, more preferably from 0.002 to 0.03 wt.-%, more preferably from 0.002 to 0.02 wt.-%, more preferably from 0.002 to 0.01 wt.-%, more preferably from 0.003 to 0.01 wt.-%, more preferably from 0.004 to 0.01 wt.-%, most preferably from 0.005 to 0.009 wt.-%, or
c) both,
each based on the total weight of the plurality of water-absorbent polymer particles.
In a preferred embodiment the plurality of surface-crosslinked water-absorbent polymer particles, comprisies
a) 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; b) 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; and
c) a Si02 in an amount in the range of from 500 to 3,000 ppm by weight, pref- erably from 1 ,000 to 2,000 ppm by weight;
each based on the weight of the plurality of surface-crosslinked water-absorbent polymer particles. According to a further aspect of this embodiment, 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 the water-absorbent polymer particle according to the invention, or the plurality of water-absorbent particles according to the invention.
In an embodiment of 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 liq- uid-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 the water-absorbent polymer particle according to the invention or the plurality of water-absorbent particles 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 or the plurality of water- absorbent particles 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. polymerization belt reactor
A preferred belt of a polymerization belt reactor is a conveyor belt. As 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 polymer gel.
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 polymerization belt reactor 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. Optionally, 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 that is arranged in the vicinity of the guide roller for the return run of the conveyor belt.
In order to provide for the completion of polymerization with the highest possible space-time yield, according to the present invention, in the vicinity of the upper run of the conveyor belt on both sides of the horizontal supporting elements, starting in the area of the supply and metering systems, there may be upwardly extending supporting elements, the longitudinal axes of which intersect at a point that is beneath the upper run, and which shape the conveyor belt that is supported by them so that it becomes suitably trough-shaped. Thus, according to the present invention, 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. The desired trough-like shape is determined by the shape and arrangement of the supporting elements along the length of the path of the upper run. In the area where the reaction components are introduced, the supporting elements should be relatively close to each other, whereas in the subsequent area, after the polymerization has been initiated, the supporting elements can be arranged somewhat further apart. Both the angle of inclination of the supporting elements and the cross-section of the supporting elements can be varied in order to flatten out the initially deep trough towards the end of the polymerization section and once again bring it to an extended state. In a further embodiment of the invention, each supporting element is preferably formed by a cylindrical or spherical roller that is rotatable about its longitudinal axis. By varying both the cross-section of the roller as well as the configuration of the roller it is easy to achieve the desired cross-sectional shape of the trough. In order to ensure proper formation of the trough by the conveyor belt, both when it makes the transition from a flat to a trough-like shape and when it is once again returned to the flat shape, a conveyor belt that is flexible in both the longitudinal and the transverse directions is preferred.
Another means of providing a trough-like configuration is arranging weir elements on an approximately flat belt. Therein, at least one weir element is arranged in longitudinal direction at each lateral edge of the belt. At least two further weir elements are arranged in transversal direction on different longitudinal positions of the belt, wherein the trough longitudinally extends between those two positions. The height of the weir elements determines the depth of the trough and hence the amount of reaction components which can be fed into the trough. The longitudinal weir elements have to be designed to be longitudinally bent with the belt at turning sections of the belt. Therefor, the longitudinal weir elements may be made of a flexible material or they may consist of a plurality of shorter longitudinal weir elements which are arranged close to each other.
A trough-like configuration of the polymerization belt can also be achieved by a combination of transversally oriented weir elements and shaping the belt in the transversal direction by supporting elements, or by a combination of longitudinally oriented weir elements and shaping the belt in the longitudinal direction by supporting elements. Test Methods
The following test methods are used in the invention. In absence of a test method, 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. In absence of distinct measuring conditions, standard ambient temperature and pressure (SATP) as a temperature of 298.15 K (25 °C, 77 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm) apply. water content
The water content is determined according to the Karl Fischer method. SFC
The Saline Flow Conductivity (SFC) under a pressure of 0.3 psi (2070 Pa) is determined according to EP 0 640 330 Al , therein also referred to as Gel Layer Pemieability (GLP). residual monomer content
The residual monomer content of the water- ansorbent polymer particles is measured according to a standard test method for superabsorbent materials defined by the EDANA. Said test method is described in EDANA, Harmonized Test Methods Nonwovens and Related Industries, 2012 Edition as "Residual Monomers" under the method number WSP 210.2.R3 (12). amount of releasing agent applied
The width of the belt is measured using a measuring tape. The conveying speed of the belt is adjusted to a constant value by means of the drive control unit of the belt. The releasing agent is applied constantly over a duration of 10 s. Subsequently, applying is stopped. A flow of the releasing agent in mm/s is measured using a Proline Prosonic Flow 93 P flow meter by Endress + Hausser Messtechnik GmbH + Co. KG, Weil am Rhein, Germany. An average val- ue of the flow over the 10 s is obtained. The measured flow is multiplied by the cross sectional area of the tube conducting the releasing agent at the point of the flow measurement, and by 10 s, thereby obtaining the volume of solvent applied. Said volume is divided by (the belt width times the belt speed times 10 s), thereby obtaining the amount of the releasing agent applied per 1 m belt width and 1 m belt in the longitudinal direction (conveying direction) of the belt.
[Mode for Invention]
Examples
The present invention is now explained in more detail by examples and drawings given by way of example which do not limit it.
A) Preparation of a partially neutralized acrylic acid monomer solution 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.
Optionally the sodium-acrylate monomer solution is degased with nitrogen. B) Polymerization of the monomer solution
1 wt.-part of the monomer solution prepared in step A) is mixed with 0.001 wt.-parts of trimethylol 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 (Ci- ba® 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 μηι) 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.
Subsequently, the mixed solution is placed on the belt of a conveyer belt reactor, as shown in figure 4, and the polymerization is initiated by UV radiation. The conveyor belt has a length of at least 20 m. The conveyor belt is formed as a trough to keep the solution on the belt prior and during polymerization. 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. At the. end of this step 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. According to figures 6 and 7 a releasing agent is sprayed onto the upper run of the belt in order to facilitate the removal of the polymer gel from the belt. The releasing is ob- tained from a polydimethyl siloxane emulsion (EG-601 by Eugene Industry, 166, Nongso-ri, Juchon-myon, Gimhae-si, Gyengnam, Korea) by diluting the emulsion with water to a water content of 97 wt.-% based on the weiglit of the diluted emulsion. The amount of the releasing agent applied to the belt is given in table 1 , below. Accordingly, no releasing agent is applied performing the comparative example 1.
C) Comminuting and drying 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 con- tent 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.
D) Milling and sizing
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 Bauermeister Type 350.1 x 1800 (3-stage crusher) (Bauermeister Zerkleinerungstechnik 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 tumbler sieves having several 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 μπι. Less than 5 wt.-% of the water- absorbent polymer particles of the examples according to the invention are smaller than 150 μηι, 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 μπι. The obtained water-absorbent polymer particles are named precursor I.
E) Silicon dioxide treatment
In a treatment step the precursor I is mixed in a disc mixer with about 0.01 wt.-part (+- 10 %) of silicon dioxide (Si02), based on the total weight of the precursor I plus Si02. The silicon dioxide is used in form of Sipernat® 22 obtainable from Evonik Industries AG, Essen, Germany. When mixing the precursor I with the Si02, the precursor still has a temperature of more than 80 °C to 100 °C, preferably of 100 °C. A precursor II is achieved.
F) Surface crosslinking
In a further step 1 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.-% Na2S03, 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 (Ge- briider 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.
In a cooling device in the form of a fluid bed, 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. G) Post treatment
1 wt.-part of precursor III is then subjected to mixing with 0.005 wt.-part Ag-zeolite. Subsequently, 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 μιη. At least 50 wt.-% of the surface-crosslined absorbent polymer particles have a particles size in the range of from 300 to 600 μπι. Less than 5 wt.-% of the surface-crosslinked absorbent polymer particles of the examples according to the invention are smaller than 150 μπι, less than 5 wt.-% of the surface-crosslinked absorbent polymer particles of the examples according to the invention are have a particle size of more than 850 μηι. Post treated crosslinked water-absorbent polymer particles are obtained.
Figure imgf000035_0001
Table 1 : Adhesion and drying time of the polymer gel, and SFC and residual monomer content of water-absorbent polymer particles obtained therefrom.
The following scale is used to compare the results of measuring the parameters given in table 1 for the examples and the comparative example. In the order given in the following the measurement results are getting better from left to right:— , -, +, ++, +++.
Table 1 gives for the examples 1 to 5 according to the invention, as well as for the comparative example 1 which is not according to the invention: the amount of the releasing agent which is applied to the conveyor belt and the blowing agent added, both in section B) above. As can be seen from table 1 , adding the releasing agent up to an amount of 500 ml/m2 reduced the adhesion of the polymer gel to the conveyor belt, hence removing the polymer gel from the belt is improved. Adding more of the releasing agent does not reduce the adhesion further, but the adhesion stays on a constant level. Adding the releasing agent reduces the dry- ing time, meaning the time required to dry the comminuted polymer gel as given above to a water content of 5 wt.-% based on the dried polymer gel. Said drying time decreases for an amount of releasing agent added from 0 to 500 ml/m2. At 5,000 ml/m2 of releasing agent added the drying time is similar to that observed for an amount of 250 ml/m2. Surprisingly, also the residual monomer content of the surface-crosslinked polymer particles is reduced from comparative example 1 to the example 4. Example 5 shows a residual monomer content similar to example 2. The Saline Flow Conductivity (SFC) of the surface-crosslinked polymer particles is not affected by the amount of releasing agent applied up to 500 ml/m2. Using sodium carbonate as the blowing agent even improves the SFC. Example 5 shows a similar result regarding the SFC as the comparative example 1 and the examples 2 to 3. As the blowing agent improves the SFC, it can be concluded that an amount of releasing agent applied of 5,000 ml/m2 tends to decrease the SFC.
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. In a first step 101 an aqueous monomer solution comprising at least one partially neutralized, mo- noethylenically unsaturated monomer bearing carboxylic acid groups (al) and at least one crosslinker (a3) is provided. Preferably, the aqueous monomer solution is an aqueous solution of partially neutralized acrylic acid, further comprising crosslinkers. In a second step 102 fine particles of a water-absorbent polymer may be added to the aqueous monomer solution. In a third step 103 a polymerization initiator or at least one component of a polymerization initia- tor system that comprises two or more components is added to the aqueous monomer solution. In a fourth step 104 the oxygen content of the aqueous monomer solution is decreased by bubbling nitrogen into the aqueous monomer solution. In a fifth step 105 the monomer solution is charged onto a belt 401 of a polymerization belt reactor 400. The belt 401 is an endless conveyor belt. In a sixth step 106 the aqueous monomer solution is polymerized to a polymer gel 601. In a seventh step 107 the polymer gel 501 is discharged from the belt 401 and simultaneously a releasing agent 504 is applied to a part of the belt 401. Subsequently, the polymer gel is comminuted, whereby polymer gel particles are obtained. In an eighth step 108 the polymer gel particles are charged onto a belt of a belt dryer 906 and subsequently dried at a temperature of about 120 to 150°C. The dried polymer gel particles are discharged from the belt dryer 906 and subsequently in a ninth step 109 grinded to obtain water-absorbent polymer particles. In a tenth step 1 10 the water-absorbent polymer particles are sized to obtain water- absorbent polymer particles having a well defined particle size distribution. In an eleventh step 111 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 initia- tor is added 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 process 100 shown in figure 3 is the same as the process 100 in figure 1 , wherein the se- cond step 102, the fourth step 104, and the eleventh step 1 1 1 are not part of the process 100 according to figure 3.
Figure 4 shows a scheme of a basic setup of a polymerization belt reactor 400 according to the invention. The polymerization belt reactor 400 comprises a belt 401. The belt 401 is an endless conveyor belt. The belt 401 passes over two guide rollers 402 such that an upper run of the belt 401 moves downstream. The downstream movement of the upper run of the belt 401 determines the direction of movement 403 of the polymer gel 501 (not shown here) on the belt 401 , indicated by an arrow. Another arrow indicates a counter direction 404 to a direction of movement 403 of the polymer gel 501 on the belt 401. Another arrow indicates both longitudinal directions 405 of the belt 401 and yet another arrow the transversal direc- tions 406 of the belt 401. The belt 401 comprises a first turning section 407 and a further turning section 408. The belt 401 extends in the longitudinal directions 405 over a length which is a longitudinal extension 409 of the belt 401. The polymerization belt reactor 400 may comprise further components which are not shown in the figure, such as support elements, a supply and metering system, irradiating means, cooling and heating devices, and a removal sys- tern.
Figure 5 shows a scheme of a downstream end 500 of a belt 401 of a polymerization belt reactor 400 according to the invention in a view facing an upstream direction. The downstream end 500 of the belt 401 is flat. A left nozzle 502 and a right nozzle 503 spray a releas- ing agent 502 onto a left and a right transversal edge of the belt respectively. Hence, an adhesion of a polymer gel 501 to the downstream end 500 of the belt 401 is reduced.
Figure 6 shows a scheme of a basic setup of another polymerization belt reactor 400 according to the invention in a side view. The polymerization belt reactor 400 of figure 6 is the same as the polymerization belt reactor 400 in figure 4, except that a polymer gel 501 is shown on the belt 401. Moreover, a releasing agent 504 is sprayed onto the further turning section 408 of the belt 401 in a solid angle element 601 of 90° centered around a counter direction 404 to a direction of movement 403 of the polymer gel 501 on the belt 401 while the polymer gel 501 is discharged from the belt 401.
Figure 7 shows a scheme of a basic setup of another polymerization belt reactor 400 according to the invention in a side view. The polymerization belt reactor 400 of figure 7 is the same as the polymerization belt reactor 400 in figure 4, except that a polymer gel 501 is shown on the belt 401. Moreover, a releasing agent 504 is sprayed onto 50 % of the longitudinal extension 409 of the belt 401. Therein, the releasing agent 504 is sprayed from above the belt 401 by nozzles 702 of a plurality of nozzles which are comprised by a tube 701 which conducts the releasing agent 504. Therein, the nozzles 702 are arranged longitudinally along the belt 401. Over the 50 % of the longitudinal extension 409 of the belt 401 to which the releasing agent 504 is applied the belt 401 comprises a trough 800 which gradually flattens out in a direction of movement 403 of the polymer gel 50 Ion the belt 401. At a downstream end 500 of the belt 401 the belt is flat.
Figure 8 shows a scheme of a trough 800 of a belt 401 of a polymerization belt reactor 400 according to the invention in a view facing an upstream direction. The trough 800 is shown in a transversal cross section trough a longitudinal extension 409 of the belt 401. The trough 800 has a shape of a concave curve. The concave curve comprises a horizontally aligned portion 802 having a length of 0.5 m. A tangent 805 on a position on the concave curve inclines a maximum angle 804 between the belt 401 and a horizontal plane 803. The maximum angle 804 is about 28°. The belt comprises sidewalls 801. Tubes 701 conduct a releasing agent 504 which is sprayed from above the belt 401 via nozzles 702 of a plurality of nozzles onto inner sides of the sidewalls 801 of the belt 401. Therein, the nozzles 702 are comprised by the tubes 701 and arranged longitudinally along the belt 401. The trough 800 being present in the cross section shown in figure 8 becomes less deep and gradually flattens completely to a downstream end 500 of the belt 401.
Figure 9 shows a block diagram of a device 900 for the preparation of water-absorbent polymer particles according to the invention. The arrows show a direction of a process stream 909 of the preparation of water-absorbent polymer particles. The device 900 comprises a first container 901, a further container 902, downstream a mixing device 903, downstream a polymerization belt reactor with a wetting device 904, downstream a comminuting device 905, downstream a belt dryer 906, downstream a grinding device 907, and downstream a sizing device 908, each according to the invention.

Claims

[CLAIMS]
[Claim 1 ]
A process (100) for the preparation of water- absorbent polymer particles, comprising the process steps of
(i) preparing an aqueous monomer solution comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups ( l) and at least one crosslinker (a3);
(ii) optionally adding fine particles of a water-absorbent polymer to the aqueous monomer solution; *
(iii) adding a polymerization initiator or a at least one component of a polymerization initiator system that comprises two or more components to the aqueous monomer solution;
(iv) optionally decreasing the oxygen content of the aqueous monomer solution;
(v) charging the aqueous monomer solution onto a belt (401) of a polymerization belt reactor (400);
(vi) polymerizing the at least one monomer in the aqueous monomer solution on the belt (401), thereby obtaining a polymer gel (501);
(vii) discharging the polymer gel (501) from the belt (401) and comminuting the polymer gel (501);
(viii) drying the comminuted polymer gel;
(ix) grinding the dried polymer gel thereby obtaining water-absorbent polymer particles;
(x) sizing the grinded water-absorbent polymer particles; and
(xi) optionally treating the surface of the grinded and sized water-absorbent polymer particles;
wherein in process step (vi) or (vii) or both a releasing agent (504) is applied to at least a part of the belt (401).
[Claim 2]
The process (100) according to claim 1, wherein the releasing agent (504) comprises one selected from the group consisting of a solvent, a polyalkylsiloxane, and a surfactant, or a combination of at least two thereof. [Claim 3]
The process (100) according to claim 2, wherein the surfactant is a compound according to the general formula R-(-0-CH2-CH2-)n-OX, wherein R is selected from C4 to C20, n is an in- teger in the range of from 10 to 10,000, and X is H or M, wherein M is a metal ion.
[Claim 4]
The process (100) according to claim 2 or 3, wherein the releasing agent (504) comprises a) the solvent in an amount in the range of from 95 to 99 wt.-%,
b) the polyalkylsiloxane in an amount in the range of from 0.5 to 5 wt.-%, and
c) the surfactant in an amount in the range of from 0.01 to 1 wt.-%,
each based on the total weight of the releasing agent (504) and the amounts in wt.-% adding up to a total of 100 wt.-%. [Claim 5]
The process according to any of the preceding claims, wherein in step (vi) or (vii) or both the releasing agent (507) is applied to at least 30 % of a longitudinal extension (409) of the belt (401). [Claim 61
The process (100) according to any of the preceding claims, wherein the belt (401) comprises a trough (800) having a sidewall (801);
wherein in step (vi) or (vii) or both the releasing agent (504) is applied to at least a part of the sidewall (801).
[Claim 7]
The process (100) according to any of the preceding claims, wherein the belt (401) comprises a weir element; wherein in step (vi) or (vii) or both the releasing agent (504) is applied to at least a part of the weir element.
[Claim 8] The process (100) according to any of the preceding claims, wherein the belt (401) is an endless belt, comprising a first turning section (407) and a further turning section (408); wherein the polymer gel (501) is discharged from the further turning section (408) of the endless belt in step (vii); wherein the releasing agent (504) is applied to at least a part of the further turn- ing section (408) in step (vii).
[Claim 9]
The process (100) according to any of the preceding claims, wherein the releasing agent (504) is applied by one selected from the group consisting of spraying, pouring, splashing, and dripping, or a combination of at least two thereof.
[Claim 10]
The process (100) according to claim 9, wherein the releasing agent (504) is sprayed in a solid angle element (601) of 90° or less centered around a counter direction (404) to a direction of movement (403) of the polymer gel (501) on the belt (401).
[Claim 1 1 ]
The process (100) according to any of the preceding claims, wherein the releasing agent (504) is applied by a plurality of nozzles (702), wherein the nozzles (702) are arranged longitudinal- ly along the belt (401).
[Claim 12]
The process (100) according to any of the preceding claims, wherein the releasing agent (504) is applied by at least two nozzles (502, 503).
[Claim 13]
The process (100) according to any of the preceding claims, wherein during applying to the belt (401) the releasing agent (504) has a temperature in the range of from 10 to 50°C. [Claim 14] The process (100) according to any of the preceding claims, wherein in step (vi) or (vii) or both the releasing agent (504) is applied to the belt (401 ) in an amount in the range of from 10 to 10,000 ml of releasing agent (504) per m2 of the belt (401). [Claim 15]
The process (100) according to any of the preceding claims, wherein the polymer gel (501) being discharged in process step (vii) comprises water in the range of from 40 to 60 wt.-%, based on the polymer gel (601 ). [Claim 16]
The process (100) according to any of the preceding claims, wherein the polymer gel (501 ) 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. [Claim 17]
The process (100) according to any of the preceding claims, wherein the polymer gel (501) 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. [Claim 18]
The process (100) according to any of the preceding claims, wherein the polymerization in step (vi) is performed in presence of a blowing agent.
[Claim 19] A device (900) for the preparation of water-absorbent polymer particles in a process stream (909), comprising
a) a first container (901 ), designed to take an aqueous monomer solution, comprising at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid groups (al);
b) a further container (902), designed to take at least one crosslinker (a3);
c) a mixing device (903), wherein the mixing device (903) is i) located down-stream to the first container (901) and the further container (902),
ii) designed to mix the monomer solution and the at least one crosslinker (<x3);
d) a polymerization belt reactor (400, 904), wherein the polymerization belt reactor (400, 904)
i) is located down-stream to the mixing device (903),
ii) is designed to comprise the aqueous monomer solution and the at least one crosslinker (a3) during polymerizing the monomer in the aqueous monomer solution, thereby obtaining a polymer gel (501)
iii) comprises a belt (401 ) ;
e) a wetting device (904), wherein the wetting device (904) is located and designed for applying a releasing agent (504) to at least 30 % of a longitudinal extension (409) of the belt (401);
f) a comminuting device (905), wherein the comminuting device (905) is
i) located down-stream to the polymerization belt reactor (400, 904), ii) designed to comminute the polymer gel (501);
g) a belt dryer (906), wherein the belt dryer (906) is
i) located down-stream to the comminuting device (905),
ii) designed to dry the polymer gel (501),
h) a grinding device (907), wherein the grinding device (907) is
i) located down-stream to the belt dryer (906),
ii) designed to grind the dried polymer gel, thereby obtaining water- absorbent polymer particles;
j) a sizing device (908), wherein the sizing device (908) is
i) located down-stream to the grinding device (907),
ii) designed to size the grinded water-absorbent polymer particles.
[Claim 20]
A process for the preparation of water-absorbent polymer particles in the device (900) according to claim 19.
[Claim 21 ] A water-absorbent polymer particle, obtainable by the process according to any of claims 1 to 18, or 20.
[Claim 22]
A plurality of water-absorbent polymer particles, comprising a polyalkylsiloxane, or a compound according to a general formula R-(-0-CH2-CH2-)n-OX, or both; wherein in the general foraiula R is C4 to C2o, n is an integer in the range of from 10 to 10,000, and X is H or M; wherein M is a metal ion.
[Claim 23]
The plurality of water-absorbent polymer particles according to claim 22, wherein the plurality of water-absorbent polymer particles comprises
a) the polyalkylsiloxane in an amount in the range of from 0.01 to 1 wt.-%, or b) the compound according to the general foraiula R-(-0-CH2-CH2-)n-OX in an amount in the range of from 0.001 to 0.1 wt.-%, or
c) both,
each based on the total weight of the plurality of water-absorbent polymer particles. [Claim 24]
A composite material comprising the water-absorbent polymer particle according to claim 21 , or the plurality of water-absorbent particles according to claim 22 or 23.
[Claim 25]
The composite material according to claim 24, comprising 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.
[Claim 26]
A process for the production of a composite material, wherein the water-absorbent polymer particle according to claim 18 or the plurality of water-absorbent particles according to claim 22 or 23, and a substrate, and optionally an auxiliary substance are brought into contact with one another.
[Claim 27] A composite material obtainable by a process according to claim 26. [Claim 28]
A use of the water-absorbent polymer particle according to claim 18 or the plurality of water- absorbent particles according to claim 22 or 23 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.
PCT/KR2014/003675 2014-04-25 2014-04-25 Release of polymer gel from polymerization belt in production of water-absorbent polymer particles WO2015163517A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/KR2014/003675 WO2015163517A1 (en) 2014-04-25 2014-04-25 Release of polymer gel from polymerization belt in production of water-absorbent polymer particles

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/KR2014/003675 WO2015163517A1 (en) 2014-04-25 2014-04-25 Release of polymer gel from polymerization belt in production of water-absorbent polymer particles

Publications (1)

Publication Number Publication Date
WO2015163517A1 true WO2015163517A1 (en) 2015-10-29

Family

ID=54332669

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/KR2014/003675 WO2015163517A1 (en) 2014-04-25 2014-04-25 Release of polymer gel from polymerization belt in production of water-absorbent polymer particles

Country Status (1)

Country Link
WO (1) WO2015163517A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112804976A (en) * 2018-09-28 2021-05-14 巴斯夫欧洲公司 Process for producing superabsorbers

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4857610A (en) * 1985-12-18 1989-08-15 Chemische Fabrik Stockhausen Gmbh Process for the continuous production of polymers and copolymers of water-soluble monomers
US6100305A (en) * 1996-10-24 2000-08-08 Nippon Shokubai Co., Ltd. Method of production of water-absorbing resin
US6241928B1 (en) * 1998-04-28 2001-06-05 Nippon Shokubai Co., Ltd. Method for production of shaped hydrogel of absorbent resin
US6565768B1 (en) * 1998-10-08 2003-05-20 Basf Aktiengesellschaft Method for producing water-swellable hydorphilic polymers, said polymers and use thereof
US20100041549A1 (en) * 2007-01-16 2010-02-18 Basf Se A German Corporation Production of Superabsorbent Polymers
US20110275513A1 (en) * 2010-05-07 2011-11-10 Gonglu Tian Superabsorbent polymer having a capacity increase
US20120258851A1 (en) * 2009-12-24 2012-10-11 Nippon Shokubai Co., Ltd Water-absorbable polyacrylic acid resin powder, and process for production thereof
WO2013104479A1 (en) * 2012-01-12 2013-07-18 Evonik Degussa Gmbh Process for the continuous preparation of water-absorbent polymers

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4857610A (en) * 1985-12-18 1989-08-15 Chemische Fabrik Stockhausen Gmbh Process for the continuous production of polymers and copolymers of water-soluble monomers
US6100305A (en) * 1996-10-24 2000-08-08 Nippon Shokubai Co., Ltd. Method of production of water-absorbing resin
US6241928B1 (en) * 1998-04-28 2001-06-05 Nippon Shokubai Co., Ltd. Method for production of shaped hydrogel of absorbent resin
US6565768B1 (en) * 1998-10-08 2003-05-20 Basf Aktiengesellschaft Method for producing water-swellable hydorphilic polymers, said polymers and use thereof
US20100041549A1 (en) * 2007-01-16 2010-02-18 Basf Se A German Corporation Production of Superabsorbent Polymers
US20120258851A1 (en) * 2009-12-24 2012-10-11 Nippon Shokubai Co., Ltd Water-absorbable polyacrylic acid resin powder, and process for production thereof
US20110275513A1 (en) * 2010-05-07 2011-11-10 Gonglu Tian Superabsorbent polymer having a capacity increase
WO2013104479A1 (en) * 2012-01-12 2013-07-18 Evonik Degussa Gmbh Process for the continuous preparation of water-absorbent polymers

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112804976A (en) * 2018-09-28 2021-05-14 巴斯夫欧洲公司 Process for producing superabsorbers

Similar Documents

Publication Publication Date Title
US10377057B2 (en) Process for the continuous preparation of water-absorbent polymers
WO2015163521A1 (en) Longitudinal shape of a polymerization belt in the production of water-absorbent polymer particles
WO2015163508A1 (en) Hydrogel comminuting device comprising discs in the production of water-absorbent polymer particles
WO2013104480A1 (en) Cooling neutralized acrylic acid by means of an absorption chiller
CN106232630B (en) Preparation of monomers with over-neutralization for the production of water-absorbent polymer particles
WO2015163510A1 (en) Production of water-absorbent polymer particles by employing carbonate blowing and belt drying
WO2015163513A1 (en) Process for the production of water- absorbent polymer particles comprising subsequent hydrogel comminuting steps
WO2015163512A1 (en) Multi-stage milling in the production of water-absorbent polymer particles
US9255190B2 (en) Process for the continuous preparation of water-absorbent polymers
WO2015163519A1 (en) Recycling of fine particles in the production of water-absorbent polymer particles
WO2015163522A1 (en) Post treatment of surface-crosslinked water-absorbent polymer particles employing an additive
WO2015163517A1 (en) Release of polymer gel from polymerization belt in production of water-absorbent polymer particles
WO2015163511A1 (en) Classifying fines in the production of water-absorbent polymer particles
WO2015163509A1 (en) Hydrogel comminuting device comprising rotating steel component in the production of water-absorbent polymer particles
WO2015163523A1 (en) Production of water-absorbent polymer particles employing a blowing agent and surface-crosslinking
WO2015163516A1 (en) Surface-crosslinking and cooling of surface-crosslinked water-absorbent polymer particles in the production thereof
WO2015163518A1 (en) Initiator system for preparation of a water-absorbent polymer by radical polymerization
WO2015163520A1 (en) Transversal concave shape of a polymerization belt in the production of water-absorbent polymer particles
WO2015163507A1 (en) Recycling of oversized particles in the production of water-absorbent polymer particles

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14890130

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14890130

Country of ref document: EP

Kind code of ref document: A1