KR102403560B1 - Classifying fines in the production of water-absorbent polymer particles - Google Patents

Abstract

The present invention generally provides a method for preparing an aqueous monomer solution comprising: (i) at least one partially neutralized monoethylenically unsaturated monomer having a carboxylic acid group (α1) and at least one crosslinking agent (α3); (ii) optionally adding absorbent polymer microparticles to the aqueous monomer solution; (iii) adding a polymerization initiator or one or more constituents of a polymerization initiation system to the aqueous monomer solution; (iv) optionally lowering the oxygen content of the aqueous monomer solution; (v) filling the polymerization reactor with an aqueous monomer solution; (vi) polymerizing a monomer in an aqueous monomer solution in a polymerization reactor; (vii) discharging the polymer gel from the polymerization reactor and optionally breaking the polymer gel; (viii) drying the polymer gel; (ix) grinding the dried polymer gel to obtain absorbent polymer particles; (x) classifying the pulverized absorbent polymer particles by a classifier including a screen; and (xi) optionally treating the surface of the pulverized and classified absorbent polymer particles, wherein in step (x) the screen vibrates at a first frequency; wherein the screen vibrates at a further frequency lower than the first frequency, or is inclined at an angle in the range of 5 to 25° with respect to the horizontal plane, or both.

Description

CLASSIFYING FINES IN THE PRODUCTION OF WATER-ABSORBENT POLYMER PARTICLES

The present invention relates to a method for preparing absorbent polymer particles; absorbent polymer particles obtainable by this method; composite materials comprising such absorbent polymer particles; a method of manufacturing a composite material; composite materials obtainable by this method; use of absorbent polymer particles; apparatus for making absorbent polymer particles; It relates to a method for producing absorbent polymer particles using such an apparatus.

Superabsorbers are capable of absorbing large amounts of aqueous fluids, particularly body fluids, more specifically urine or blood, through swelling and formation of hydrogels, and are capable of retaining these fluids even under certain pressure. It is an insoluble crosslinked polymer. Because of their unique properties, these polymers are mainly used in hygiene products, such as, for example, baby diapers, incontinence products or sanitary napkins.

Since the preparation of the superabsorbent is generally carried out by free radical polymerization of monomers having an acidic group in the presence of a crosslinking agent, various absorption It is possible to prepare polymers with properties (see, eg, Modern Superabsorbent Polymer Technology, FL Buchholz, GT Graham, Wiley-VCH, 1998).

The polymer gel obtained after polymerization, also referred to as a hydrogel, is usually subjected to crushing, drying and classification processes in order to obtain a particulate superabsorbent having a defined particle size distribution. In a further process step, these superabsorbent particles are often subjected to surface crosslinking in order to improve their absorption behavior. To this end, the particles are mixed with an aqueous solution containing a surface crosslinking agent and optionally further additives, and this mixture is heat treated to promote the crosslinking reaction.

Monomers with acidic groups can be polymerized in the presence of a crosslinking agent in a batch process or a continuous process. In continuous polymerization and batch polymerization, partially neutralized acrylic acid is typically used as the monomer. Suitable neutralization methods are, for example, EP 0 372 706 A2, EP 0 574 574 260 A1, WO 2003/051415 A1, EP 1 1 470 470 0 5 14 15 A1, WO 2007/0128 A1, 2007/012 2007/02875 is described in

As mentioned above, in the production of absorbent polymer particles, it is important to obtain a product with a well-defined particle size distribution. In the prior art, in particular, it is known that lowering the proportion of fine particles in the superabsorbent product is beneficial to the quality of the product, for example, in terms of retention capacity or gel blocking. Thus, the absorbent polymer particles need to be sorted in the manufacturing process, and the fine particles must be separated from the absorbent polymer particles with larger particle diameters. This sorting and separation is performed using a sieve in the prior art. The sieve includes a screen with pores. In particular, the fine particles tend to clog the pores. As a result, the sieve must be stopped from use after each operating period and the holes must be cleaned manually, for example with a brush. Another anti-clogging means known in the prior art comprises a rubber ball bouncing against a screen. In this way, the operating period of the sieve could be increased in the prior art. However, due to the bouncing of the rubber ball, the screen is worn, thus shortening the life of the screen.

In general, it is an object of the present invention to solve at least in part the problems encountered in the prior art with respect to the production of absorbent polymer particles.

Another object is to provide a method for producing an absorbent polymer which does not block the screen holes of the sieve as much as possible. Another object of the present invention is to provide a method for producing an absorbent polymer in which abrasion of the screen is suppressed without clogging the screen hole of the sieve as much as possible. Another object of the present invention is to provide a method for preparing an absorbent polymer in which the separation of fine particles from the absorbent polymer particles is more efficient. Another object of the present invention is to provide a process for preparing an absorbent polymer wherein the quality of the absorbent polymer particles is improved, preferably in terms of retention capacity or gel blocking or both. Another object of the present invention is to provide a method for producing an absorbent polymer, wherein the proportion of fine particles during production is reduced. Another object of the present invention is to provide a method for producing a water-absorbent polymer in which the amount of maintenance work for a sieve is reduced. Another object of the present invention is to provide a method for producing an absorbent polymer, wherein the operating period of the sieve is extended. Another object of the present invention is to provide a method for producing an absorbent polymer, wherein the maintenance of the sieve is further automated. Another object of the present invention is to provide a method for producing an absorbent polymer, in which the screen life of the sieve is extended. Another object of the present invention is to provide a method for producing an absorbent polymer in which an increase in the operating period of a sieve, an increase in the screen life of the sieve, and an increase in the retention capacity of the absorbent polymer particles are combined in a balanced way. Another object of the present invention is to provide a method for producing an absorbent polymer, wherein two or more of the above-mentioned advantages are combined in a balanced way. Another challenge is to provide absorbent polymer particles made by an inexpensive process. Another object of the present invention is to provide an apparatus for producing absorbent polymer particles by a method having one or more of the advantages described above. Another object of the present invention is to provide a composite material comprising absorbent polymer particles produced by a method having one or more of the above-mentioned advantages, without deterioration in quality.

Solutions to one or more of the above problems are presented in independent claims. The dependent claims present preferred embodiments of the invention and are also presented for solving one or more of the aforementioned problems.

The present invention provides a solution for solving at least some of the problems in the prior art related to the production of absorbent polymer particles.

In the drawing,
1 is a flow chart showing the manufacturing steps of the method according to the invention;
Fig. 2 is a flow chart showing the manufacturing steps of another method according to the present invention;
3 is a flow chart showing the manufacturing steps of another method according to the present invention;
4 is a schematic diagram of a classifying device according to the present invention;
5 is a schematic diagram of another classifier according to the present invention;
6 is a schematic diagram of another classifier according to the present invention;
7 is a schematic diagram of another classifying apparatus according to the present invention;
8 is a block diagram of an apparatus for producing absorbent polymer particles according to the present invention.

One or more objects of the present invention are achieved by a method for preparing absorbent polymer particles, the method comprising:

(i) one or more partially neutralized monoethylenically unsaturated monomers having a carboxylic acid group (α1) (at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid group) and one or more crosslinking agents (α3), to prepare an aqueous monomer solution to do;

(ii) optionally adding fine particles of an absorbent polymer to the aqueous monomer solution;

(iii) adding a polymerization initiator or one or more components of a polymerization initiation system comprising two or more components to the aqueous monomer solution;

(iv) optionally lowering the oxygen content of the aqueous monomer solution;

(v) filling the polymerization reactor with an aqueous monomer solution;

(vi) polymerizing a monomer in an aqueous monomer solution in a polymerization reactor;

(vii) discharging the polymer gel from the polymerization reactor and optionally breaking the polymer gel;

(viii) drying the polymer gel;

(ix) grinding the dried polymer gel to obtain absorbent polymer particles;

(x) classifying the pulverized absorbent polymer particles with a classifier including a screen; and

(xi) optionally treating the surface of the pulverized and classified absorbent polymer particles;

in step (x), the screen vibrates at a first frequency; The first frequency is 16 kHz to 10 MHz, preferably 17 kHz to 5 MHz, more preferably 18 kHz to 1 MHz, more preferably 19 to 800 kHz, more preferably 20 to 600 kHz, more preferably is from 21 to 400 kHz, more preferably from 22 to 200 kHz, more preferably from 23 to 150 kHz, more preferably from 24 to 100 kHz, more preferably from 25 to 80 kHz, more preferably from 26 to 60 kHz , more preferably 27 to 50 kHz, more preferably 28 to 45 kHz, more preferably 29 to 44 kHz, more preferably 30 to 42 kHz, still more preferably 31 to 41 kHz, more preferably 32 to 40 kHz, more preferably 33 to 39 kHz, more preferably 34 to 38 kHz, most preferably 35 to 37 kHz; the screen

a) vibrate at a further frequency lower than the first frequency; or

b) from 5 to 25°, preferably from 5 to 23°, more preferably from 5 to 20°, more preferably from 6 to 18°, more preferably from 7 to 16°, more with respect to the horizontal plane preferably inclined at an angle ranging from 7 to 14°, most preferably from 8 to 13°, or

c) both a) and b) above.

Preferably, the screen is selected from the group consisting of linear oscillation, or superposition of two or more linear oscillations, circular oscillation, elliptic oscillation, nutation and tumbling motion. vibrating at a further frequency in the form of one selected or a combination of two or more thereof. As used throughout this specification, pulsation is understood as vibration, where the period of oscillation is a period of precession. So, the frequency of the long motion is the frequency of the precession included in the long motion. As used throughout this specification, tumbling motion is understood as vibration, wherein the tumbling motion period is the period of the horizontal component of the tumbling motion. So, the frequency of the tumbling motion is the frequency of the horizontal vibration included in the tumbling motion. Preferably, the screen vibrates at a first frequency in the form of a linear vibration or in the form of two or more linear vibrations superimposed. Preferred linear vibrations are horizontal vibrations or vertical vibrations. The first frequency is preferably an ultrasonic frequency. The further frequency is preferably a sub-ultrasonic frequency. Preferred sub-ultrasonic frequencies are frequencies below 16 kHz, preferably below 16 kHz and above 1 Hz. A preferred classifying device is a sieve or a sifter or both.

Herein, the subsequent steps of the manufacturing method according to the invention may be performed simultaneously or overlapped in time, or both. This applies in particular to steps (i) - (iv) and more specifically to steps (iii) and (iv).

The process according to the invention is preferably a continuous process, in which the aqueous monomer solution is continuously fed and continuously fed into the polymerization reactor. The resulting polymer gel is continuously withdrawn from the polymerization reactor and optionally subsequently crushed, dried, crushed and classified in a subsequent production step. However, this continuous process may be interrupted in the following cases, for example.

- for replacing some parts of the manufacturing equipment, the belt material of the conveyor belt, etc., when the conveyor belt is used as a polymerization reactor;

- when cleaning, to remove polymer deposits from some parts of the manufacturing equipment, in particular in tanks or pipes; or

- when it is necessary to produce absorbent polymer particles with different absorption characteristics, to initiate a new manufacturing step.

Preferred absorbent polymer particles according to the present invention are in the range of from 10 to 3,000 μm, preferably from 20 to 2,000 μm, particularly preferably from 150 to 850 μm, according to WSP 220.2 (test method of “Word Strategic Partners” EDANA and INDA). is a particle with an average particle size of Herein, the content of particles having a particle size in the range of 300 to 600 μm in the absorbent polymer is at least 30% by weight, particularly preferably at least 40% by weight, most preferably at least 50% by weight, based on the total weight of the absorbent polymer particles. % is particularly preferred.

In the preparation step (i) of the process according to the invention, an aqueous monomer solution is prepared comprising at least one partially neutralized monoethylenically unsaturated monomer having a carboxylic acid group (α1) and at least one crosslinking agent (α3).

Preferred monoethylenically unsaturated monomers having a carboxylic acid group (α1) are mentioned in DE 102 23 060 A1 as preferred monomers (α1), with acrylic acid being particularly preferred.

According to the invention, the absorbent polymer produced by the process according to the invention contains, on a dry weight basis, at least 50% by weight, preferably, at least 70%, more preferably, at least 90% by weight of a monomer having carboxylic acid groups. It is preferable to include According to the invention, the absorbent polymer produced by the process according to the invention is made of at least 50% by weight, preferably at least 70% by weight of acrylic acid, preferably the degree of neutralization is at least 20 mol-%, particularly preferably It is especially preferable that it is 50 mol-% or more. The concentration of the partially neutralized monoethylenically unsaturated monomer having a carboxylic acid group (α1) in the aqueous monomer solution provided in the preparation step (i) is preferably from 10 to 60% by weight, based on the total weight of the aqueous monomer solution, Preferably in the range of 30 to 55% by weight, most preferably in the range of 40 to 50% by weight.

In addition, the aqueous monomer solution may contain a monoethylenically unsaturated monomer copolymerizable with (α1) (α2). Preferred monomers (α2) are those mentioned as preferred monomers (α2) in DE 102 23 060 A1, with acrylamide being particularly preferred.

A preferred crosslinking agent (α3) according to the present invention is a compound having two or more ethylenically unsaturated groups in one molecule (class I crosslinking agent), a monomer (α1) or (α2) in a condensation reaction (= condensation crosslinking agent), addition reaction or ring opening reaction ) compounds having at least two functional groups capable of reacting with the functional groups of (Class II crosslinking agents), at least one functional group capable of reacting with the functional groups of the monomer (α1) or (α2) in a condensation reaction, addition reaction or ring-opening reaction, and one compounds having at least one ethylenically unsaturated group (class III crosslinkers), or polyvalent metal cations (class IV crosslinkers). Thus, when class I crosslinker compounds are used, crosslinking of the polymer is achieved by radical polymerization of monoethylenically unsaturated monomers (α1) or (α2) with the ethylenically unsaturated groups of the crosslinker molecule, and class II crosslinker compounds with class IV When a polyvalent metal cation of a crosslinking agent is used, the crosslinking of the polymer is via a condensation reaction of a functional group with a functional group of the monomer (α1) or (α2) (class II crosslinking agent) or electrostatic interaction of a polyvalent metal cation (class IV crosslinking agent) is achieved through When class III crosslinking agent compounds are used, crosslinking of the polymer is achieved not only by radical polymerization of ethylenically unsaturated groups, but also by condensation reactions between the functional groups of the crosslinking agent and the functional groups of the monomers (α1) or (α2).

Preferred crosslinking agents (α3) are all compounds mentioned in DE 102 23 060 A1 as crosslinking agents (α3) of classes I, II, III and IV,

- Class I crosslinker compound, prepared using N,N'-methylene bisacrylamide, polyethyleneglycol di(meth)acrylate, triallylmethylammonium chloride, tetraallylammonium chloride, and 9 moles of ethylene oxide per mole of acrylic Allylnonaethylene glycol acrylate is particularly preferred, N,N′-methylene bisacrylamide is particularly preferred,

- As class IV crosslinker compounds, Al ₂ (SO ₄ ) ₃ and hydrates thereof are particularly preferred.

Preferred absorbent polymers prepared by the process according to the invention are polymers, each crosslinked by the following class of crosslinking agents or by the following combinations of crosslinking agents: 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.

Another preferred absorbent polymer prepared by the process according to the invention is a polymer, crosslinked by any of the crosslinkers mentioned as class I crosslinkers in DE 102 23 060 A1, wherein N,N'-methylene bisacrylamide, Polyethyleneglycol di(meth)acrylate, triallyl-methylammonium chloride, tetraallylammonium chloride, and allylnonaethylene-glycol acrylate prepared with 9 mol of ethylene oxide per mol of acrylic acid are more preferred as class I crosslinking agents, Even more preferred is N,N'-methylene bisacrylamide.

The aqueous monomer solution may further contain a water-soluble polymer (α4). Preferred water-soluble polymers (α4) are partially or fully saponified polyvinyl alcohol, polyvinylpyrrolidone, starch or starch derivatives, polyglycols or polyacrylic acid. The molecular weight of these polymers is not critical as long as the polymer is water soluble. Preferred water-soluble polymers (α4) are starch or starch derivatives or polyvinyl alcohol. A water-soluble polymer (α4), preferably a synthetic polymer, for example polyvinyl alcohol, can be used as a graft base for the monomer to be polymerized, as well as these water-soluble polymers in combination with a polymer gel or an already dried absorbent polymer. It is also possible to mix

The aqueous monomer solution may also contain auxiliary substances (α5), in particular complexing agents, for example EDTA and the like.

In the aqueous monomer solution, the relative contents of the monomers (α1) and (α2), the crosslinking agent (α3), the water-soluble polymer (α4) and the auxiliary substance (α5) are preferably, optionally, the absorbency obtained after drying the crushed polymer gel The polymer structure is chosen so that it consists of:

- 20 to 99.999% by weight of monomer (α1), preferably 55 to 98.99% by weight, particularly preferably 70 to 98.79% by weight,

- 0 to 80% by weight of monomer (α2), preferably 0 to 44.99% by weight, particularly preferably 0.1 to 44.89% by weight,

- 0 to 5% by weight of crosslinking agent (α3), preferably 0.001 to 3% by weight, particularly preferably 0.01 to 2.5% by weight,

- 0 to 30% by weight of water-soluble polymer (α4), preferably 0 to 5% by weight, particularly preferably 0.1 to 5% by weight,

- 0 to 20% by weight of auxiliary substances (α5), preferably 0 to 10% by weight, particularly preferably 0.1 to 8% by weight, and

- 0.5 to 25% by weight of water (α6), preferably 1 to 10% by weight, particularly preferably 3 to 7% by weight,

The total weight of (α1) to (α6) is 100% by weight.

The optimal concentration values of monomers, crosslinkers and water-soluble polymers in the monomer solution are determined through simple preliminary experiments or from the prior art, in particular publications US 4,286,082, DE 27 06 135 A1, US 4,076,663, DE 35 03 458 A1, DE 40 20 780 C1 , DE 42 44 548 A1, DE 43 33 056 A1 and DE 44 18 818 A1.

In the preparation step (ii), optionally fine particles of an absorbent polymer may be added to the aqueous monomer solution. Independently of the selection step (ii), the fine particles of the absorbent polymer are selected from the group consisting of after step (iii), after step (iv) and before step (v), or at least two of these may be added to the aqueous monomer solution at any time.

Absorbent fine particles, also referred to as fine particles or fine particles throughout this application, are preferably absorbent polymer particles whose composition corresponds to that of the aforementioned absorbent polymer particles, preferably at least 90% by weight, more preferably at least 95% by weight. % by weight, most preferably at least 99% by weight of the absorbent fine particles, have a particle size of less than 200 μm, preferably less than 150 μm, particularly preferably less than 100 μm.

In a preferred embodiment of the process according to the invention, optionally, the absorbent microparticles which may be added to the aqueous monomer solution in the production step (ii) are the absorbent microparticles obtained in the production step (x) of the process according to the invention, , that is, recycled.

The fine particles may be added to the aqueous monomer solution using any mixing apparatus deemed suitable for this purpose by one of ordinary skill in the art. In a preferred embodiment of the invention in which it is particularly useful for the process to be carried out continuously as described above, the fine particles are added to the aqueous monomer solution in a mixing device, wherein the first stream of fine particles and the second stream of aqueous monomer solution are continuously conducted , but from different directions, are applied onto the rotating mixing device. A mixing setup of this type comprises in the mixing zone a preferably cylindrical non-rotating stator, at the center of which likewise preferably a cylindrical rotor rotating, a so-called "rotor" It can be implemented in "Rotor Stator Mixer". The walls of the rotor and the walls of the stator are typically provided with notches, for example, slot-shaped notches through which a mixture of fine particles and aqueous monomer solution can be sucked through to apply a high shear force.

In this context, the first stream of fine particles and the second stream of aqueous monomer solution are in the range of 60-120°, preferably in the range of 75-105°, more preferably in the range of 85-95°, most preferably about 90°. It is particularly preferable to form an angle δ of Further, the mixture stream of the fine particles and the aqueous monomer solution exiting the mixer and the fine particle first stream entering the mixer are in the range of 60-120°, preferably in the range of 75-105°, more preferably in the range of 85-95° It is preferred to achieve an angle ε in the range, most preferably about 90°.

Mixing setups of this type can be implemented, for example, using the mixing devices disclosed in DE-A-25 20 788 and DE-A-26 17 612, the contents of which are incorporated herein by reference. A specific example of a mixing device that can be used for adding fine particles to the aqueous monomer solution in the preparation step (ii) of the present invention is KG IKA ^® Werke GmbH & Co. Staupen, Germany. mixing devices available under the trade names MHD 2000/4, MHD 2000/05, MHD 2000/10, MDH 2000/20, MHD 2000/30 and MHD 2000/50 from the company, in particular the mixing device MHD 2000/20 is preferred. Further mixing devices that can be used are those provided for example from the company ystral GmbH, Dottingen, Valenchten, Germany, under the trade name "Conti TDS", or from the company Kinematika AG, Rutau, Switzerland, for example, under the trade name Megatron ^® .

The amount of fine particles that can be added to the aqueous monomer solution in the preparation step (ii) is preferably in the range of 0.1 to 15% by weight, even more preferably in the range of 0.5 to 10% by weight, based on the weight of the aqueous monomer solution, most Preferably, it is in the range of 3 to 8% by weight.

In the preparation step (iii) of the process according to the invention, to the aqueous monomer solution is added a polymerization initiator or one or more constituents of a polymerization initiator system composed of two or more constituents.

As the polymerization initiator for initiating polymerization, all initiators that form radicals under polymerization conditions, which are usually used for the production of super absorbents, may be used. Among them, thermal catalysts, redox catalysts and photo-initiators are activated by energetic irradiation. The polymerization initiator may be dissolved or dispersed in the aqueous monomer solution. Preference is given to using water-soluble catalysts.

As the thermal initiator, all compounds recognized by those skilled in the art that decompose under elevated temperature to form radicals may be used. Particular preference is given to thermal polymerization initiators having a half-life shorter than 10 seconds, preferably shorter than 5 seconds, at temperatures lower than 180°C, more preferably lower than 140°C. Peroxides, hydroperoxides, hydrogen peroxide, persulfates and azo compounds are particularly preferred thermal polymerization initiators. In some cases, it is beneficial to use mixtures of various thermal polymerization initiators. Among these mixtures, a mixture consisting of hydrogen peroxide and potassium persulfate or sodium persulfate is preferable, and these 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 peroxydicarbonate, 2- Ethylhexyl peroxydicarbonate, tert.-butyl hydroperoxide, cumene hydroperoxide, and tert.-amyl perpivalate, tert.-butyl perpivalate, tert.-butyl perpivalate Hexanoate, tert.-butyl isobutyrate, tert.-butyl per-2-ethylhexenoate, tert.-butyl perisononanoate, tert.-butyl permaleate, tert.-butyl perbenzoate ate, peroxides of tert.-butyl-3,5,5-trimethylhexanoate and amyl perneodecanoate. In addition, the following thermal polymerization initiators are preferred: azo compounds, for example azo-bis-isobutyronitrile, azo-bis-dimethylvaleronitrile, azo-bis-ami-dinopropane dihydrochloride (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 above-mentioned compounds are used in customary amounts, preferably in the range from 0.01 to 5 mol-%, more preferably in the range from 0.1 to 2 mol-%, respectively, based on the weight of the monomer to be polymerized.

The redox catalyst comprises at least two components, typically at least one of the aforementioned peroxo compounds and at least one reducing component, preferably ascorbic acid, glucose, sorbose. , mannose, ammonium or alkali metal hydrogen sulfites, sulfates, thiosulfates, hypersulfites or sulfides, metal salts such as iron II ions or silver salts, or sodium hydroxymethyl sulfoxylate. Preferably, ascorbic acid or sodium pyrosulfite is used as the reducing material component of the redox catalyst. Based on the amount of monomer used for polymerization, 1 x 10 ^-5 to 1 mol-% of the reducing material component of the redox catalyst and 1 x 10 ^-5 to An oxidizing substance component of 5 mol-% of the redox catalyst is used. Instead of or as a complement to the oxidizing substance component of the redox catalyst, one or more, preferably water-soluble, azo compounds may be used.

Polymerization is preferably initiated by the action of energy irradiation, so-called photo-initiators are generally used as initiators. Such photo-initiators include, for example, so-called α-splitters, H-abstracting systems, or may include azido. Examples of such initiators include benzophenol derivatives such as Michler ketones, phenanthrene derivatives, fluorine derivatives, anthraquinone derivatives, thioxanthone derivatives, coumarin derivatives, benzoinethers and their derivatives, azo compounds, such as Examples are the aforementioned radical formers, substituted hexaarylbisimidazoles or acylphosphine oxides. Examples of azides include 2-(N,N-dimethylamino)ethyl-4-azidocinnamate, 2-(N,N-dimethylamino)ethyl-4-azidonaphthylketone, 2-(N ,N-di-methylamino)ethyl-4-azidobenzoate, 5-azido-1-naphthyl-2'-(N,N-dimethylamino)ethylsulfone, N-(4-sulfonylazido Phenyl) 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. Another group for photo-initiators include di-alkoxy ketals, for example 2,2-dimethoxy-1,2-diphenylethan-1-one. Photo-initiators, if used, are generally used in a content of 0.0001 to 5% by weight, based on the monomer to be polymerized.

According to another embodiment of the method according to the invention, in the preparation step (iii), the initiator comprises the following components:

iiia. peroxodisulfate; and

iiib. organic initiator molecules comprising at least 3 oxygen atoms or at least 3 nitrogen atoms;

It is preferred to include the peroxodisulfate and the organic initiator molecule in a molar ratio ranging from 20:1 to 50:1. In one aspect of this embodiment, it is preferred that the concentration of initiator component iiia is in the range of 0.05 to 2% by weight based on the weight of the monomer to be polymerized. In another aspect of this embodiment, the organic initiator molecule is 2,2-dimethoxy-1,2-diphenylethan-1-one, 2,2-azobis-(2-amidinopropane)dihydrochloride , 2,2-azobis-(cyano valeric acid), or a combination of two or more thereof is preferably selected. In another aspect of this embodiment, the peroxodisulfate is a compound of the general formula M ₂ S ₂ O ₈ , wherein M is selected from the group consisting of NH ₄ , Li, Na, Ka, or a combination of two or more thereof. it is preferable The components described above are suitable for initiating the polymerization with UV, in particular in the polymerization step (vi) of the process of the invention. By using such a composition, a reduction in the residual amount of monomers and a reduction in yellowing of the absorbent polymer particles obtainable by the process according to the invention are further achieved.

In this context, also, the step (iii) of adding the polymerization initiator is performed before step (iv), simultaneously with step (iv) or overlapping in time with step (iv), ie the oxygen content of the aqueous monomer solution is reduced. It should be noted that when it is done, it can be carried out. When a polymerization initiator system comprising two or more constituents is used, one or more constituents of these polymerization initiator systems are, for example, added prior to the preparation step (iv) while implementing the activity of the polymerization initiator system. The remaining ingredients or the remaining ingredients necessary for this are added after step (iv), possibly even after the preparation step (v). Independently of the selection step (iv), the lowering of the oxygen content of the aqueous monomer solution can also be carried out prior to the preparation step (iii) according to the invention.

In step (iv) of the preparation of the process according to the invention, optionally a reduction in the oxygen content of the aqueous monomer solution is carried out. Independently of the optional step (iv), ie lowering the oxygen content of the aqueous monomer solution, can also be carried out before, during or after the preparation step (ii) according to the invention. Preferably, after adding the fine particles in the preparation step (ii), a reduction in the oxygen content of the aqueous monomer solution is carried out.

Lowering the oxygen content of the aqueous monomer solution can be achieved by contacting the aqueous monomer solution with an inert gas such as nitrogen. The inert gas phase in contact with the aqueous monomer solution is free of oxygen and is therefore characterized by a very low oxygen partial pressure. As a result, oxygen is converted from the aqueous monomer solution to the inert gas phase until the partial pressure of oxygen in the inert gas phase and the oxygen partial pressure in the aqueous monomer solution become equal. Contacting the aqueous monomer phase with the inert gas phase can be achieved, for example, by introducing bubbles of the inert gas into the monomer solution in the same direction as the monomer feed direction, in the opposite direction, or at an angle intermediate thereto. Good mixing can be achieved, for example, using a nozzle, a static mixer, a dynamic mixer or a bubble column. Before the polymerization reaction, the oxygen content of the monomer solution is preferably dropped to less than 1 ppmw (ppm by weight), more preferably less than 0.5 ppmw, based on the monomer solution.

In the preparation step (v) of the process according to the invention, the aqueous monomer solution is fed at a position upstream of the polymerization reactor, preferably on a conveyor belt, particularly preferably on a conveyor belt, and in preparation step (vi), the monomers in the aqueous monomer solution are It is polymerized in a polymerization reactor to produce a polymer gel. When polymerization is carried out on a conveyor belt as a polymerization reactor, a polymer gel sheet is obtained in the downstream section of the conveyor belt, which is preferably crushed into polymer gel particles before drying.

As the polymerization reactor, any reactor that a person skilled in the art considers suitable for continuous or batch polymerization of a monomer such as acrylic acid in aqueous solution can be used. An example of a suitable polymerization reactor is a kneading reactor. The polymer gel formed by polymerization of the aqueous monomer solution is continuously crushed in a kneader, for example by means of a contrarotatory stirrer shaft as described in WO 2001/38402. Thus, crushing of the polymer gel can be performed before discharging the polymer gel from the polymerization reactor.

Another example for a preferred polymerization reactor is a conveyor belt. As a conveyor belt usable in the process according to the invention, any conveyor belt that the person skilled in the art considers useful as a support material suitable for forming a hydrogel by polymerization after loading thereon the aqueous monomer solution described above. can be used

A conveyor belt generally includes an endless moving conveyor belt passing over a support member and two or more guide rollers, at least one of the rollers driving the belt and the other adjusting configured to be possible. Optionally, a winding and feed system is provided for a release sheet that can be used in section on the upper surface of the conveyor belt. The device comprises a feeding and metering system for the reaction components and, after the feeding and metering system, an optional irradiating mean arranged in the direction of movement of the conveyor belt, together with a cooling and heating device, and the conveyor belt and a removal system for polymer gel strands disposed in the vicinity of guide rollers for return operation of According to the invention, in order to complete polymerization in the greatest possible space-time yield, starting in the feeding and metering system zone, on both sides of the horizontal support member near the upper run of the conveyor belt, it extends upwards. There is a support member, which upwardly extending support member supports the conveyor belt such that its longitudinal axes intersect each other at a point below the upper run and the conveyor belt is suitably trough-shaped. Thus, according to the present invention, the conveyor belt comprises a plurality of trough-shaped support and bearing members forming a deep trough-like or dish-like structure for the incoming reaction components, near the supply system of the reaction components. supported by them The desired trough-like shape is determined by the shape and placement of the support members disposed along the length of the path of the upper run. The support members should be relatively adjacent to each other in the zone where the reaction components are introduced, but in a later zone, after polymerization has started, the support members may be arranged somewhat spaced apart from each other. The angle of inclination of the support member and the cross-section of the support member can be varied to gradually flatten the initial deep trough towards the end of the polymerization zone and bring it back to an expanded state. In a further embodiment of the invention, each support member is preferably formed by a cylindrical or spherical roller rotatable about a longitudinal axis. By changing the cross-section of the roller as well as the structure of the roller, the desired cross-sectional shape of the trough is easily achieved. Conveyor belts flexible in both the longitudinal and transverse directions are provided to ensure proper shaping of the trough by the conveyor belt when the belt is transitioned from a flat shape to a trough-like shape and is restored to a flat shape again. desirable.

The belt can be made of a variety of materials, but preferably these materials have good tensile strength and flexibility, good fatigue strength against cyclic bending stresses, good deformability and chemical resistance to each reactive component under polymerization conditions. The following requirements must be met. These requirements are usually not met with one material. Accordingly, multilayer materials are commonly used as belts in the process of the present invention. Mechanical requirements can also be met by means of a carcass, for example a fabric insert of natural and/or synthetic fibers or glass fibers or steel cord. Chemical resistance is, for example, on a cover made of polyethylene, polypropylene, polyisobutylene, polyvinyl chloride or halogenated polyolefins such as polytetrafluoroethylene, polyamide, natural or synthetic rubber, polyester resin or epoxy resin. can be achieved by A preferred cover material is silicone rubber.

In step (vii) of the process according to the invention, the polymer gel obtained in the polymerization reactor is optionally crushed, thus obtaining polymer gel particles. Preferred polymer gel particles are one or a combination of two or more selected from the group consisting of polymer gel strands, polymer gel flakes and polymer gel nuggets. The crushing device may be a polymerization reactor or part of a polymerization reactor, or it may be a separate device or both. Thus, fracturing of the polymer gel can be performed before, during or after discharging the polymer gel from the polymerization reactor. A preferred polymerization reactor that is a crushing device is a kneading reactor. If the crushing step is carried out in the polymerization reactor, the polymer gel particles obtained are preferably further crushed after being discharged from the polymerization reactor. If the polymerization reactor is a conveyor belt, the crushing step is preferably carried out after discharging the polymer gel as polymer gel sheets from the conveyor belt of the crushing device, wherein the crushing device is a separate device. Preferably, the polymer gel sheet is recovered from the conveyor belt as a continuous sheet of soft semi-solid consistency and then transferred for further processing such as crushing.

Fracturing of the polymer gel is preferably carried out in at least three steps:

- in the first step, using a cutting unit, preferably a knife, for example a knife as mentioned in WO-A-96/36464, the polymer gel into a flat gel strip, preferably 5 to 500 mm in length, Preferably it is in the range of 10 to 300 mm, particularly preferably in the range of 100 to 200 mm, the height is in the range of 1 to 30 mm, preferably in the range of 5 to 25 mm, particularly preferably in the range of 10 to 20 mm, and the width is in the range of 1 to 500 mm, preferably in the range from 5 to 250 mm, particularly preferably in the range from 10 to 200 mm;

- in the second step, using a shredding unit, preferably a breaker, the gel strip is turned into gel pieces, preferably in the range from 3 to 100 mm in length, preferably in the range from 5 to 50 mm, crushed into pieces of gel having a height ranging from 1 to 25 mm, preferably from 3 to 20 mm, and a width ranging from 1 to 100 mm, preferably from 3 to 20 mm;

- in the third stage, using a "wolf" unit, preferably a mincer, preferably a mincer with a perforated plate and a screw in which the screw is moved towards a hole plate, the gel pieces is preferably ground into polymer gel particles that are smaller than the gel pieces.

An optimum surface-volume ratio is thereby achieved, which is advantageous for the drying behavior of the production step (viii). Polymer gels crushed in this way are particularly suitable for belt drying. Fracturing in three stages gives better "airability" due to the air channels present between the granulate kernels.

In step (viii) of the method according to the invention, the polymer gel particles are dried.

Drying of the polymer gel particles may be carried out in any dryer or oven considered by those skilled in the art to be suitable for drying the polymer gel particles described above. Rotary tube furnaces, fluidised bed dryers, plate dryers, paddle dryers and infrared dryers may be mentioned as examples.

A belt dryer is particularly preferred. Belt dryers are particularly convective systems of drying for the mild treatment of through-airable products. The product to be dried is placed on an endless conveyor belt through which the gas is passed and exposed to a stream of heated gas, preferably air. The drying gas is recycled to become extremely highly saturated during repeated passes through the product bed. A predetermined fraction of the dry gas, preferably at least 10%, more preferably at least 15%, most preferably at least 20%, preferably at most 50%, more preferably at most 40% of the gas content in one pass %, most preferably up to 30%, exits the dryer as highly saturated vapor, removing any moisture evaporated from the product. The temperature of the heated gas stream is preferably at least 50°C, more preferably at least 100°C, most preferably at least 150°C, preferably at most 250°C, more preferably at most 220°C, most preferably at most It is 200 °C.

The size and design of the dryer depends on the product to be processed, the manufacturing capacity and the drying duty. The belt dryer can be implemented as a single-belt, multi-belt, multi-stage or multistory system. The invention is preferably practiced using a belt dryer equipped with one or more belts. One-belt dryers are particularly preferred. In order to ensure optimum performance of the belt-drying operation, the drying properties of the absorbent polymer are each determined according to the selected processing parameters. The hole size and mesh size of the belt are set according to the product. Likewise, certain surface hardening, such as electropolishing or teflonizing, is possible.

The polymer gel particles to be dried are applied to the belt of the belt dryer, preferably using a swivel belt. The feed height, ie the vertical distance between the swivel belt and the belt of the belt dryer, is preferably at least 10 cm, more preferably at least 20 cm, most preferably at least 30 cm, preferably at most 200 cm, more preferably 120 cm or less, and most preferably 40 cm or less. The thickness of the polymer gel particles to be dried on the belt dryer is preferably 2 cm or more, more preferably 5 cm or more, most preferably 8 cm or more, preferably 20 cm or less, more preferably 15 cm or less, Most preferably, it is 12 cm or less. The belt speed of the belt dryer is preferably 0.005 m/s or more, more preferably 0.01 m/s or more, most preferably 0.015 m/s or more, preferably 0.05 m/s or less, more preferably 0.03 m/s or less, most preferably 0.025 m/s or less.

Furthermore, according to the present invention, the polymer gel is dried to contain a moisture content in the range of 0.5 to 25 wt %, preferably 1 to 10 wt %, particularly preferably 3 to 7 wt %, based on the dried polymer gel particles. It is preferable to be

In the preparation step (ix) of the process according to the invention, the dried polymer gel particles are pulverized to obtain particulate absorbent polymer particles.

In the grinding of the dried polymer gel particles, any apparatus that a person skilled in the art considers suitable for grinding the dried polymer gel particles described above can be used. As examples for suitable grinding devices, mention may be made of single- or multi-stage roll mills, preferably two- or three-stage roll mills, pin mills, hammer mills or vibratory mills.

In the preparation step (x) of the method according to the present invention, the pulverized absorbent polymer particles are preferably classified using an appropriate sieve. Here, after classification of the absorbent polymer particles, the proportion of the polymer particles having a particle size of less than 150 μm based on the total weight of the absorbent polymer particles is less than 10 wt %, preferably less than 8 wt %, particularly preferably 6 wt % %, it is particularly preferred that the proportion of polymer particles having a particle size greater than 850 μm is less than 10% by weight, preferably less than 8% by weight, particularly preferably less than 6% by weight. In addition, after classification of the absorbent polymer particles, 30 wt% or more, preferably 40 wt% or more, and more preferably 50 wt% or more of the absorbent polymer particles have a particle size in the range of 300 to 600 µm. It is preferable.

In the preparation step (xi) of the method according to the present invention, a processing treatment is selectively performed on the surface of the additionally pulverized and classified absorbent polymer particles. As the means for processing the surface of the absorbent polymer particles, any means which a person skilled in the art considers suitable for this purpose can be used. Examples of the surface treatment include, for example, surface treatment, surface treatment using a water-soluble salt such as aluminum sulfate or aluminum lactate, surface treatment using inorganic particles such as silicon dioxide, and the like. Preferably, the component used for surface treatment of the polymer particles (crosslinking agent, water-soluble salt) is added to the water absorbent polymer particles in the form of an aqueous solution. After mixing the particles with this aqueous solution, heating is performed in the range of 150 to 230°C, preferably 160 to 200°C, in order to promote the surface crosslinking reaction.

In one embodiment of the invention, the additional frequency is at least 15 kHz to 9.9 MHz, preferably at least 15 kHz to 5 MHz, more preferably at least 15 kHz to 1 MHz, more preferably than the first frequency At least 16 to 800 KHz, more preferably at least 17 to 600 kHz, more preferably at least 18 to 400 kHz, more preferably at least 19 to 200 kHz, more preferably at least 20 to 150 kHz, even more preferably At least 21 to 100 kHz, more preferably at least 22 to 80 kHz, more preferably at least 23 to 60 kHz, more preferably at least 24 to 40 kHz, more preferably at least 25 to 39 kHz, even more preferably at least 26 to 38 kHz, more preferably at least 27 to 37 kHz, more preferably at least 28 to 36 kHz, more preferably at least 29 to 36 kHz, more preferably at least 30 to 36 kHz, even more preferably at least 31 to 36 kHz, more preferably at least 32 to 36 kHz, more preferably at least 33 to 36 kHz, more preferably at least 33 to 36 kHz, even more preferably at least 34 to 36 kHz lower.

In one embodiment of the invention, the screen is square, round, or both. Preferred round screens are circular. Another preferred round screen is planar. A particularly preferred screen is a circular flat screen. Other preferred screens are 0.1 to 10 m, preferably 0.2 to 9.5 m, more preferably 0.3 to 9 m, more preferably 0.4 to 8.5 m, more preferably 0.5 to 8 m, more preferably 1 to 7.5 m 2 , more preferably 2 to 7 m 2 , more preferably 2.5 to 6.5 m 2 , more preferably 3 to 6 m 2 , more preferably 3.5 to 6 m 2 , even more preferably 4 to 6 m 2 , even more preferably preferably in the range of 4.5 to 6 m 2 , more preferably 4.8 to 5.8 m 2 , most preferably 5 to 5.6 m 2 . Preferably, the screening surface is the area of the screen, and the pores of the screen are distributed throughout the area, preferably uniformly. Preferred round screens satisfy item a) according to the above-described embodiments of the method of the invention. Preferred rectangular screens satisfy item b) according to the above-described embodiment of the method of the invention.

In one embodiment of the present invention, the classifying device is a centrifugal sieve, a tumbler sieve, or both. A preferred classifying device is a tumbler sieve. A very particularly preferred classifying device is a tumbler sieve comprising at least one circular flat screen.

In one embodiment of the present invention, the mesh size of the screen is 5 - 400 mesh, preferably 10 - 200 mesh, more preferably 20 - 170 mesh, more preferably 20 - 140 mesh, more preferably 20 - 120 mesh, more preferably 20 - 100 mesh, and most preferably 100 mesh. A preferred mesh is the U.S. is mesh. Preferred apertures in the screen are made of wire or fiber, or both. Preferred wires are made of iron, preferably stainless steel. Preferred fibers are synthetic fibers. Another preferred aperture is perforation of the screen.

In one embodiment of the present invention, the classifying device comprises at least one additional screen, preferably at least two additional screens, more preferably at least three additional screens, even more preferably at least four additional screens, Most preferably it further comprises at least five additional screens. The screen and the further screen are preferably arranged as a deck above each other. Preferred additional screens are specified by one or more, preferably two or more, more preferably all of these technical specifications for the screen. A more particularly preferable classification apparatus is a tumbler sieve comprising six circular flat screens arranged as decks above each other.

In one embodiment of the present invention, the polymer gel discharged in the preparation step (vii) ranges from 40 to 60% by weight, preferably from 50 to 60% by weight, more preferably from 53 to 56% by weight, based on the polymer gel. contains moisture.

In one embodiment of the present invention, the polymer gel discharged in the preparation step (vii) is 10 to 200 mm, preferably 10 to 100 mm, more preferably 15 to 75 mm, most preferably 15 to 50 mm It is a polymer gel sheet, characterized by a range of thicknesses.

In a preferred embodiment of the present invention, the polymer gel discharged in the preparation step (vii) is 30 to 300 cm, preferably 50 to 250 cm, more preferably 60 to 200 cm, most preferably 80 to 100 cm It is a sheet of polymer gel, characterized by the width of the range.

In one embodiment of the present invention, the polymerization in step (vi) is carried out in the presence of a blowing agent. The blowing agent may be added to the aqueous monomer solution in one step selected from the group consisting of step (i), step (ii), step (iii), step (iv), step (v) and step (vi) or a combination of two or more thereof. can Preferably, the blowing agent is added to the monomer solution in step (i). The blowing agent should be added before or immediately after initiation of the polymerization in step (vi). Particularly preferably, the blowing agent is added to the monomer solution after or simultaneously with the addition of the initiator or components of the initiator system. Preferably, the blowing agent is present in an amount ranging from 500 to 4000 ppmw, preferably from 1000 to 3500 ppmw, more preferably from 1500 to 3200 ppmw and most preferably from 2000 to 3000 ppmw, based on the total weight of the monomer solution. added to the monomer solution.

A blowing agent is a substance capable of forming a cellular structure or pores or both through a foaming process during a monomer polymerization process. The foaming process is preferably endothermic. A preferred endothermic foaming process is initiated by exothermic polymerization, a crosslinking reaction, or heat derived from both reactions. Preferred blowing agents are physical blowing agents or chemical blowing agents or both. Preferred physical blowing agents are one or a combination of two or more selected from the group consisting of CFCs, HCFCs, hydrocarbons and CO ₂ . Preferred CO ₂ is liquid CO ₂ . Preferred hydrocarbons are one or a combination of two or more selected from the group consisting of pentane, isopentane and cyclopentane. Preferred chemical blowing agents are one selected from the group consisting of carbonate blowing agents, nitrites, peroxides, calcined soda, oxalic acid derivatives, aromatic azo compounds, hydrazine, azide, N,N'-dinitrosoamide and organic blowing agents. , or a combination of two or more thereof.

A particularly preferred blowing agent is a carbonate blowing agent. Carbonate blowing agents which can be used according to the invention are described in US 5,118,719A, which is incorporated herein by reference. Preferred carbonate blowing agents are salt-containing carbonates or salt-containing bicarbonates, or both. Other preferred carbonate blowing agents include CO ₂ gas, CO ₂ solid, ethylene carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, magnesium carbonate, or magnesium hydroxy carbonate, calcium carbonate, barium carbonate, bicarbonate, hydrates thereof, other cations and one selected from the group consisting of natural carbonates, or a combination of two or more thereof. A preferred natural carbonate is dolomite. The aforementioned carbonate blowing agents, when dissolved or dispersed in a monomer solution, release CO ₂ upon heating. A particularly preferred carbonate blowing agent is MgCO ₃ , which compound can be represented by the formula (MgCO ₃ ) ₄ ·Mg(OH) ₂ ·5-H ₂ O. Another preferred carbonate blowing agent is (NH ₄ ) ₂ CO ₃ . MgCO ₃ and (NH ₄ ) ₂ CO ₃ can also be used as mixtures. Preferred carbonate blowing agents are carbonate salts of polyvalent cations such as Mg, Ca, Zn. Examples of such carbonate blowing agents include Na ₂ CO ₃ , K ₂ CO ₃ , (NH ₄ ) ₂ CO ₃ , MgCO ₃ , CaCO ₃ , NaHCO ₃ , KHCO ₃ , NH ₄ HCO ₃ , Mg(HCO ₃ ) ₂ , Ca(HCO ₃ ) ₂ , ZnCO ₃ and BaCO ₃ . Certain polyvalent transition metal cations may also be used, although some cations, such as ferric cations, may cause color staining and may undergo reduction oxidation or hydrolysis equilibrium in water. This can make it difficult to control the quality of the final polymer product. In addition, other polyvalent cations such as Ni, Ba, Cd, Hg would also be unacceptable due to their potential toxic or skin sensitization effects.

A preferred nitrite is ammonium nitrite. A preferred peroxide is hydrogen peroxide. Preferred aromatic azo compounds are one selected from the group consisting of triazene, arylazosulfone, arylazotriarylmethane, hydrazo compound, diazoether and diazoaminobenzene, or a combination of two or more thereof. A preferred hydrazine is phenylhydrazine. Preferred azides are carbonyl azide or sulfonyl azide, or both. A preferred N,N'-dinitrosoamide is N,N'-dimethyl-N,N'-dinitrosoterephthalamide.

A solution to at least one of the above problems is provided by an apparatus for producing absorbent polymer particles in a process stream, the apparatus comprising:

a) a first container designed to contain an aqueous solution of monomers comprising at least one partially neutralized monoethylenically unsaturated monomer having a carboxylic acid group (α1);

b) an additional container designed to contain one or more crosslinking agents (α3);

c) mixing device:

The mixing device is

i) located downstream of the first vessel and the further vessel;

ii) designed to mix the monomer solution with one or more crosslinking agents (α3);

d) polymerization reactor:

The polymerization reactor

i) located downstream of the first vessel and the further vessel;

ii) designed to receive an aqueous monomer solution and at least one crosslinking agent (α3) during polymerization of the monomers in an aqueous monomer solution to obtain a polymer gel;

e) Shredder:

The crushing device is

i) located downstream of the first vessel and the further vessel;

ii) designed to break the polymer gel to obtain polymer gel particles,

f) Belt dryer:

The belt dryer

i) located downstream of the shredding device;

ii) designed to dry polymer gel particles;

g) grinding device:

The crushing device is

i) located downstream of the belt dryer;

ii) designed to grind the dried polymer gel particles to obtain absorbent polymer particles;

h) Classifier:

The classifier is

i) located downstream of the crushing unit;

ii) a screen;

iii) designed to classify pulverized absorbent polymer particles,

iv) designed to vibrate the screen;

the vibration comprises a first frequency; The first frequency is 16 kHz to 10 MHz, preferably 17 kHz to 5 MHz, more preferably 18 kHz to 1 MHz, more preferably 19 to 800 kHz, more preferably 20 to 600 kHz, more preferably is from 21 to 400 kHz, more preferably from 22 to 200 kHz, more preferably from 23 to 150 kHz, more preferably from 24 to 100 kHz, more preferably from 25 to 80 kHz, more preferably from 26 to 60 kHz , more preferably 27 to 50 kHz, more preferably 28 to 45 kHz, more preferably 29 to 44 kHz, more preferably 30 to 42 kHz, still more preferably 31 to 41 kHz, more preferably 32 to 40 kHz, more preferably 33 to 39 kHz, more preferably 34 to 38 kHz, most preferably 35 to 37 kHz; the screen

a) vibrate at a further frequency lower than the first frequency; or

b) from 5 to 25°, preferably from 5 to 23°, more preferably from 5 to 20°, more preferably from 6 to 18°, more preferably from 7 to 16°, more with respect to the horizontal plane preferably in the range of 7 to 14°, most preferably in the range of 8 to 13°, or

c) both a) and b) above.

Here, the mixing device may be the same as the polymerization reactor. In addition, the polymerization reactor may be the same as the crushing device. Thus, the mixing device, polymerization reactor and crushing device may be the same. Preferred elements or devices or both of the device according to the invention are designed according to the method of the invention. A preferred first frequency is the first frequency according to the method of the invention. A preferred further frequency is a further frequency according to the process of the invention. A preferred classifying device is a classifying device according to the method of the present invention. A preferred screen is a screen according to the method of the invention. Preferred vibrations are vibrations according to the method of the invention.

A solution to at least one of the above-mentioned problems is provided by a method for producing absorbent polymer particles in a device according to the invention. Preferably the process comprises (xi) in step (i) of the preparation according to the invention.

A solution to at least one of the above-mentioned problems is provided by absorbent polymer particles obtainable by the process according to the invention. Another aspect of the present invention provides a plurality of surface-crosslinked water-absorbent polymer particles comprising a) to c) below, respectively, based on the weight of the plurality of surface-crosslinked water-absorbent polymer particles. particles) is about:

a) chelating agents, in particular EDTA, in a content ranging from 500 to 3,000 ppmw, preferably from 1,000 to 2,000 ppmw;

b) polyalkylene glycols, in particular polyethylene glycols, in a content ranging from 500 to 3,000 ppmw, preferably from 1,000 to 2,000 ppmw; and

c) SiO ₂ in a content ranging from 500 to 3,000 ppmw, preferably from 1,000 to 2,000 ppmw.

According to another aspect of the present invention, the plurality of surface-crosslinked absorbent polymer particles comprises, based on the total weight of the plurality of surface-crosslinked absorbent polymer particles, an Ag-zeolite, preferably from 0.0001 to 1 part by weight ( wt._part), more preferably 0.001 to 0.5 parts by weight, and most preferably 0.002 to 0.01 parts by weight.

A solution to at least one of the above-mentioned problems is provided by a composite material comprising the absorbent polymer particles according to the present invention.

In one embodiment of the present invention, the composite material according to the present invention is a foam, a shaped article, a fiber, a foil, a film, a cable, an encapsulant selected from the group consisting of sealing material, liquid-absorbing hygiene article, carrier for plant and fungal growth-regulating agent, packaging material, soil additive and building material one, or a combination of two or more thereof. A preferred cable is a blue water cable. Preferred liquid-absorbent hygiene products are one selected from the group consisting of diapers, tampons and sanitary napkins, or a combination of two or more thereof. Preferred diapers are infant diapers or incontinence adult diapers, or both.

A solution to at least one of the above problems is provided by a method for producing a composite material, wherein the absorbent polymer particles according to the invention and a substrate and optionally an auxiliary material are brought into contact with each other.

A solution to at least one of the above-mentioned problems is provided by a composite material obtainable by the method according to the invention.

A solution to at least one of the above problems is a foam, a shaped article, a fiber, a foil, a film, a cable, a sealing material , liquid-absorbing hygiene articles, carriers for plant and fungal growth-regulating agents, packaging materials, soil additives, for controlled release of active compounds or for use in building materials It is provided by the use of the absorbent polymer particles according to the present invention.

test method

The following test methods are used in the present invention. If the test method is omitted, the ISO test method published on the closest date from the original filing date of the present invention is applied for the characteristics to be measured. If the ISO test method is not available, the EDANA test method published on the date closest to the original filing date of the present invention is applied. In the absence of clear measurement conditions, as standard ambient temperature and pressure (SATP), a temperature of 298.15 K (25° C., 77° F.) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm) apply.

moisture content

The moisture content of the absorbent polymer particles is determined according to the Karl Fischer method after drying.

holding capacity

The retention capacity of the absorbent polymer particles is measured according to the standard superabsorbent test method stipulated by EDANA. This test method is described in EDANA, Harmonized Test Methods Nonwovens and Related Industries, 2012 Edition, Method No. WSP 241.2.R3 (12) “Fluid Retention in Saline After Centrifugation”.

Example

The invention is now described in more detail with reference to, but not limited to, embodiments and drawings, presented by way of example.

A) Preparation of partially neutralized acrylic acid monomer solution

0.4299 parts by weight (wt.-part) of water are mixed in a suitable container with 0.27 parts by weight of acrylic acid and 0.0001 parts by weight of mono methyl ether hydroquinone (MEHQ). To this mixture, a 48% by weight aqueous sodium hydroxide solution is added in an amount of 0.2 parts by weight. A sodium-acrylate monomer solution having a neutralization ratio of 70 mol-% was prepared.

Optionally, the sodium-acrylate monomer solution is degassed with nitrogen.

B) Polymerization of the monomer solution

In a container, 1 part by weight of the monomer solution prepared in step A), 0.001 parts by weight of trimethylol propane triacrylate as a crosslinking agent, 0.001 parts by weight of sodium peroxodisulfate as a primary initiator component, 2,2 as a secondary initiator component -dimethoxy-1,2-diphenylethan-1-one (Ciba ^® Irgacure ^® 651, Ciba Specialty Chemicals Inc., Basel, Switzerland) 0.000034 parts by weight and acrylic acid particles (particle size less than 150 μm) up to 0.1 parts by weight and to obtain a mixed solution. When the foaming agent is added according to Table 1 below, sodium carbonate is added to the mixed solution in an amount of 0.1 parts by weight based on the total amount of the mixed solution.

A sufficient amount of the mixed solution is subjected to further processing to produce a polymer gel, a further subsequent product, absorbent polymer particles, an additional subsequent product, surface-crosslinked absorbent polymer particles, and a post-treated, additional follow-up product, an absorbent product. carry out Further processing details are provided below.

Then, the mixed solution is loaded onto the belt of the conveyor belt reactor, and polymerization is initiated by UV irradiation. The conveyor belt has a length of at least 20 m and a width of 0.8 mm. The conveyor belt takes the form of a trough to receive the solution on the belt before and during polymerization. The size of the conveyor belt and the conveying speed of the conveyor belt are selected in such a way that a poly-acrylic acid gel is produced at the downstream end of the belt. At the end of this process, an absorbent polymer gel is prepared. This polymer gel has a water content of about 52 % by weight based on the total weight of the polymer gel.

C) crushing and drying of the polymer gel

Polymer gels are produced as polymer gel strands, which are discharged from a conveyor belt and crushed in three steps:

- Cut the poly-acrylic acid rubber gel into flat gel strips using a knife. The gel strip has a length of 10 - 20 cm, a height of 10 - 20 mm and a width of 10 - 200 mm. After that,

- using a breaker, cut the strips into pieces of gel ranging from 5 - 50 mm long, 3 - 20 mm high and 3 - 20 mm wide,

- These gel pieces are extruded through a mixer equipped with a grinder to grind the gel pieces to obtain gel pieces ranging in length 3 - 20 mm, height 3 - 20 mm and width 3 -> 20 mm.

The crushed gel is dried at 180° C. in a belt dryer to a moisture content of 5% by weight based on the dried polymer gel. The belt of the belt dryer is equipped with an orifice, so that hot air is fed into the polymer gel through a nozzle. Additionally, hot air flows over the belt towards the gel.

D) Milling and classification

The dried polymer gel is pulverized in three steps. First, the dried polymer gel was put into Herbold Granulator HGM 60/145 (HERBOLD Meckesheim GmbH), dried polymer gel pieces with a size of less than 7 mm were obtained, and then placed in a container for 2.5 hours, so that the polymer gel pieces had the same moisture content. make it happen The dried polymer gel pieces are then crushed in a roller mill of a Bauermeister Type 350.1 x 1800 (3-stage crusher) (Bauermeister Zerkleinerungstechnik GmbH) to obtain absorbent polymer particles having a particle size of less than 1 mm.

The absorbent polymer particles are sieved using a sieve equipped with a five-deck screen, using a Tumbler Screener KTS 2600/5 from GKM Siebtechnik, Walbstadt, Germany. The mesh sizes of the screens vary from 20, 30, 40, 50, 60 to 100 U.S.-mesh. At least 50% by weight of the obtained absorbent polymer particles have a particle size in the range of 300 to 600 μm. Less than 5% by weight of the absorbent polymer particles of the embodiment according to the present invention has a particle size of less than 150 μm, and less than 5% by weight of the absorbent polymer particles of the embodiment according to the present invention has a particle size greater than 850 μm. The obtained absorbent polymer particles are referred to as precursor I. According to Table 1 below, in this step, the fine absorbent polymer particles are separated or not. If the fine powder is not separated, the above-described classification step is not performed in the corresponding comparative example. The fine absorbent polymer particles have a particle size of less than 150 μm. In addition, Table 1 below also shows measures to prevent clogging of the holes in the screen used for classification.

E) silicon dioxide treatment

In the treatment step, precursor I is mixed in a disc mixer with about 0.01 parts by weight (± 10 %) of silicon dioxide (SiO ₂ ), based on the total weight of precursor I + SiO ₂ . Silicon dioxide is used in the form of Sipernat ^® 22 available from Evonik Industries AG, Essen, Germany. When mixing the precursor I with SiO ₂ , the precursor still maintains a temperature of 80°C - 100°C, preferably a temperature of 100°C. Precursor II is obtained.

F) surface crosslinking

As a further step, 1 part by weight of precursor II is mixed with 0.003 parts by weight (+-10%) of the surface crosslinking agent based on the total weight of the combined precursor II and crosslinking agent mixture. The surface crosslinking agent consists of water 19% by weight, ethylene glycol diglycidyl ether 40% by weight, Na ₂ SO ₃ 1% by weight, and polyethylene glycol 40% by weight with a molecular weight of 400 g/mol, respectively, based on the total weight of the crosslinking agent do. The components of the crosslinking agent are mixed in a line static mixer. The crosslinking agent is mixed with precursor II in a ringlayer mixer, CoriMix ^® CM 350 (Gebruder Lodige Mascheninenbau GmbH, Paderborn, Germany). The mixture is heated to a temperature in the range of 130 - 160 °C. Thereafter, the mixture is dried in a paddle dryer of Andritz Gouda Paddle Dryer of Andritz AG located in Graz, Austria, preferably a GPWD12W120 type dryer, at a temperature in the range of 130-160° C. for 45 minutes. Surface-crosslinked absorbent polymer particles are obtained.

In the cooling device of the fluidized bed type, the temperature of the surface-crosslinked absorbent polymer particles is cooled to below 60° C. to obtain the cooled surface-crosslinked absorbent polymer particles, which is referred to as precursor III.

G) post-processing

1 part by weight of precursor III is mixed with 0.005 parts by weight of Ag-zeolite. Then, this mixture is sieved. The sieve is selected to separate agglomerates of cooled surface-crosslinked absorbent polymer particles having a particle size greater than 850 μm. At least 50% by weight of the surface-crosslinked absorbent polymer particles have a particle size in the range of 300 to 600 μm. Less than 5 wt% of the surface-crosslinked absorbent polymer particles of the embodiment according to the present invention has a particle size of less than 150 μm, and less than 5 wt% of the surface-crosslinked absorbent polymer particles of the embodiment according to the present invention is 850 It has a particle size greater than μm. Post-treated surface-crosslinked absorbent polymer particles are obtained.

The parameter measurement results presented in Table 1 for Examples and Comparative Examples are compared using the following scale. In the order of the symbols shown below, the measurement results are better from left to right: --, -, +, ++, +++.

Differential separation blockage prevention blowing agent operating period of the sieve screen life Product retention capacity Comparative Example 1 no / additive-free / / -- Comparative Example 2 no / sodium carbonate / / - Comparative Example 3 separated manual cleaning additive-free -- + + Comparative Example 4 separated manual cleaning sodium carbonate -- + ++ Comparative Example 5 separated rubber ball additive-free + - + Comparative Example 6 separated rubber ball sodium carbonate + - ++ Example 1 separated Vibration, 20 kHz additive-free ++ + + Example 2 separated Vibration, 36 kHz additive-free +++ + + Example 3 separated Vibration, 36 kHz sodium carbonate +++ + ++

Table 1: Duration of operation of sieves, screen life and retention capacity of sieves for surface-crosslinked absorbent polymer particles prepared according to various embodiments.

In Comparative Example 1, fine absorbent polymer particles were not separated. Accordingly, these fines remain in the product of the manufacturing process - the surface-crosslinked absorbent polymer particles. A sieve used to separate fines is not used. The retention capacity of the surface-crosslinked absorbent polymer particles is inadequately low. In the case of Comparative Example 2, a blowing agent is used, thereby increasing the holding capacity. In the case of Comparative Example 3, the fine powder was separated by the classification as described above. No blowing agent is used. The holding capacity is further increased. The screen of the sieve should be manually cleaned periodically to avoid clogging. Use a brush for this. If the screen is not cleaned, the holes in the screen will become clogged and the sieving will not be effective or the sieving will have to be stopped. Since the sieving is periodically interrupted to clean the screen with a brush, the operating period of the sieve is rather short. In addition, manual brush cleaning is quite weak against the fine screen structure. This determines the reasonable lifespan of the screen. Comparative Example 4 was the same as Comparative Example 3 except that a foaming agent was used. The blowing agent only further increases the retention capacity. Comparative Example 5 is the same as Comparative Example 3, except that the screen is continuously cleaned by bouncing a rubber ball from below with the screen. This cleaning method extends the operating period of the sieve compared to Comparative Examples 3 and 4. However, repeated bouncing of the rubber ball causes damage to the detailed screen structure. As a result, the life of the screen is reduced due to the ball cleaning. The retention capacity is at the same level as that of Comparative Example 3. Comparative Example 6, again, shows that the use of a blowing agent increases the retention capacity of the surface-crosslinked absorbent polymer particles produced. In Example 1 according to the present invention, the fine powder is separated by a sieve, and a vibration of a frequency of 20 kHz is applied to the screen of the sieve by an ultrasonic generator. So, there is no need to stop sieving for screen cleaning, and ultrasonic vibration does not damage the screen. Long service life, long operating period and high holding capacity of the screen are observed. In Example 2, the ultrasonic frequency used for cleaning is raised to 36 kHz. This prevents clogging more effectively, increasing the working period of the sieve. Example 3 shows the best results. The use of a blowing agent in addition to Example 2 increases the holding capacity.

1 is a flow chart illustrating steps 101 to 111 of a method 100 for making absorbent polymer particles according to the present invention. In a first step 101 , an aqueous monomer solution is provided comprising at least one partially neutralized monoethylenically unsaturated monomer having a carboxylic acid group (α1) and at least one crosslinking agent (α3). Preferably, the aqueous monomer solution is an aqueous solution of partially neutralized acrylic acid and further comprises a crosslinking agent. In the second step 102, fine particles of an absorbent polymer may be added to the aqueous monomer solution. In a third step 103, a polymerization initiator or one or more components of a polymerization initiator system comprising two or more components are added to the aqueous monomer solution. In a fourth step 104, the oxygen content of the aqueous monomer solution is reduced by nitrogen bubbling into the aqueous monomer solution. In a fifth step (105), the monomer solution is charged onto the belt of the polymerization belt reactor as polymerization reactor (804). The belt is an endless conveyor belt. In a sixth step 106, the aqueous monomer solution is polymerized into a polymer gel. In a seventh step 107, the polymer gel is discharged from the belt. Thereafter, the polymer gel is crushed to obtain polymer gel particles. In an eighth step (108), the polymer gel particles are charged onto a belt of a belt dryer (106) and then dried at a temperature of about 120-150°C. The dried polymer gel particles 401 are discharged from the belt dryer and then pulverized in a ninth step 109, to obtain absorbent polymer particles. In the tenth step 110, the pulverized absorbent polymer particles 401 are classified by a classifier 400 including a screen 402, so that pulverized and classified absorbent polymer particles having a well-established particle size distribution ( 403) is obtained. The classifying device 400 is a tumbler sieve. Here, the screen 402 vibrates at a first frequency and at a further frequency. The first frequency is 36 kHz and is generated by an ultrasonic generator. The additional frequency is 1 Hz. The vibration at the additional frequency is the tumbling motion of the tumbler body. In the eleventh step (111), the surface of the absorbent polymer particles is processed in terms of surface crosslinking.

2 is a flow chart illustrating steps 101 to 111 of method 100 for making absorbent polymer particles according to the present invention. The method 100 shown in FIG. 2 is identical to the method 100 of FIG. 1 , but the third step 103 and the fourth step 104 overlap in time. While the polymerization initiator is added to the aqueous monomer solution, nitrogen bubbling is performed in the monomer aqueous solution to lower the oxygen content.

3 is a flow chart illustrating steps 101 , 103 , 105 - 110 of a method 100 for making absorbent polymer particles according to the present invention. The method 100 shown in FIG. 3 is identical to the method 100 of FIG. 1 , except that the optional second step 102 , the fourth step 104 and the eleventh step 111 are the method 100 of FIG. 3 . not included in

4 is a schematic diagram of a classifying device 400 according to the present invention. Here, the classification device 400 may include components not shown in the drawings. The classifier 400 is a vibrating sieve. For classification, the pulverized absorbent polymer particles 401 are loaded onto the screening surface of a screen 402 in a classifying device 400 . Screen 402 is a flat, circular screen. The screen 402 includes apertures 406 . The mesh size of the screen 402 is 100 U.S. is mesh. Holes 406 are formed of stainless steel wire. The screen 402 vibrates at a first frequency and at a further frequency. The screen 402 vibrates at an additional frequency with two linear vibrations 404 overlapping each other. At this time, one linear vibration 404 is a vertical vibration, and the other linear vibration 404 is a horizontal vibration. The screen 402 vibrates at a first frequency with a linear vertical vibration 405 . The first frequency is 35 kHz and the additional frequency is 3 Hz. The pulverized absorbent polymer particles 401 are classified in a classifying device 400 to obtain pulverized and classified water absorbent polymer particles 403 .

5 is a schematic diagram of another classifier 400 according to the present invention. Here, the classification device 400 may include components not shown in the drawings. The classifying device 400 is a long moving sieve. For classification, the pulverized absorbent polymer particles 401 are loaded onto the screening surface of a screen 402 in a classifying device 400 . Screen 402 is a flat, circular screen. The screen 402 includes apertures 406 . The mesh size of the screen 402 is 100 U.S. is mesh. Holes 406 are formed of synthetic fibers. The screen 402 vibrates at a first frequency and at a further frequency. The screen 402 performs the loading operation. Long motion is a superposition of precession 501 and rotation 502 . Precession 501 is performed at an additional frequency. So, according to the present invention, the pulsation is a oscillation at an additional frequency. The screen 402 vibrates at a first frequency with a linear vertical vibration 405 . The first frequency is 40 kHz and the additional frequency is 2 Hz. The pulverized absorbent polymer particles 401 are classified in a classifying device 400 to obtain pulverized and classified water absorbent polymer particles 403 .

6 is a schematic diagram of another classifier 400 according to the present invention. Here, the classification device 400 may include components not shown in the drawings. The classifying device 400 is a sieve. For classification, the pulverized absorbent polymer particles 401 are fed onto the screening surface of a screen 601 in a classifying device 400 . Screen 601 is a flat rectangular screen. Screen 601 includes apertures 406 . The mesh size of the screen 601 is 100 U.S. is mesh. Holes 406 are formed of stainless steel wire. The screen 601 is tilted, at an angle 602 of 10° with respect to the horizontal plane 603 . Due to the inclination, particles that do not pass through the screen 601 glide on the screen 601 and act as an inclined surface. The screen 601 vibrates at a first frequency. The screen 601 vibrates at a first frequency with a linear vertical vibration 405 . The first frequency is 25 kHz and is generated by an ultrasonic generator. The pulverized absorbent polymer particles 401 are classified in a classifying device 400 to obtain pulverized and classified water absorbent polymer particles 403 .

7 is a schematic diagram of a classifier 400 according to the present invention. In the drawings, the classification apparatus 400 may include components not shown in the drawings. The classifying device 400 is a sieve. For classification, the pulverized absorbent polymer particles 401 are loaded onto the screening surface of a screen 402 in a classifying device 400 . Screen 402 is a flat, circular screen. The screen 402 includes apertures 406 . The mesh size of the screen 402 is 20 U.S. is mesh. Holes 406 are formed of stainless steel wire. The screen 402 vibrates at a first frequency and at a further frequency. The screen 402 vibrates at an additional frequency with two superposed linear vibrations 404 . At this time, one linear vibration 404 is a vertical vibration, and the other linear vibration 404 is a horizontal vibration. The screen 402 vibrates at a first frequency with a linear vertical vibration 405 . The first frequency is 35 kHz and the additional frequency is 3 Hz. The classifying device 400 further includes four additional screens 701 . Each additional screen 701 is a flat circular screen with an aperture. Each additional screen 701 vibrates at a first frequency and a further frequency. The screen 402 and the additional screen 701 are placed vertically overlapping each other. The pulverized absorbent polymer particles 401 are classified in a classifying device 400 to obtain pulverized and classified water absorbent polymer particles 403 .

8 is a block diagram of an apparatus 800 for making absorbent polymer particles in accordance with the present invention. Arrows indicate the direction of the production stream 808 of absorbent polymer particles. Apparatus 800 is, in accordance with the present invention, respectively a first vessel 801 , a further vessel 802 , a mixing device 803 located downstream, a polymerization belt reactor 804 located downstream, a polymerization belt reactor located downstream a crushing device 805 , a downstream belt dryer 806 , a downstream crushing device 807 , and a downstream classifying device 400 .

While the present invention has been described with reference to what are presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the described embodiments, but on the contrary, various modifications may be made within the spirit and scope of the appended claims. It is intended to encompass equivalent arrangements.

100 Method according to the invention
Step 101 (i)
step 102 (ii)
Step 103 (iii)
Step 104 (iv)
Step 105 (v)
Step 106 (vi)
Step 107 (vii)
Step 108 (viii)
Step 109 (ix)
Step 110 (x)
400 classifier
401 Ground Absorbent Polymer Particles
402 round screen
403 Pulverized and Classified Absorbent Polymer Particles
404 Linear Vibration at Additional Frequency
405 Vibration at the first frequency
406 hole
501 Precession to additional frequencies
502 rotation
601 square screen
602 angle
603 horizontal plane
701 additional screen
800 Absorbent Polymer Particle Manufacturing Equipment
801 first vessel
802 Additional containers
803 mixing device
804 polymerization reactor
805 Shredder
806 Belt Dryer
807 crusher
808 Manufacturing Stream

Claims (18)

A method (100) for preparing water-absorbent polymer particles, comprising:
(i) one or more partially neutralized monoethylenically unsaturated monomers having a carboxylic acid group (α1) (at least one partially neutralized, monoethylenically unsaturated monomer bearing carboxylic acid group) and one or more crosslinking agents (α3), to prepare an aqueous monomer solution to do;
(ii) optionally adding fine particles of an absorbent polymer to the aqueous monomer solution;
(iii) adding a polymerization initiator or one or more constituents of a polymerization initiation system comprising two or more constituents to the aqueous monomer solution;
(iv) optionally lowering the oxygen content of the aqueous monomer solution;
(v) filling the polymerization reactor 804 with the aqueous monomer solution;
(vi) polymerizing a monomer in the aqueous monomer solution in the polymerization reactor (804);
(vii) discharging the polymer gel from the polymerization reactor (804) and optionally comminuting the polymer gel;
(viii) drying the polymer gel;
(ix) grinding the dried polymer gel to obtain absorbent polymer particles;
(x) sizing the pulverized absorbent polymer particles 401 by a classifier 400 including screens 402 and 601; and
(xi) optionally, treating the surface of the pulverized and classified absorbent polymer particles (403);
in step (x), the screens 402, 601 vibrate at a first frequency;
the first frequency is in the range of 16 kHz to 10 MHz;
the screen
a) vibrate at a further frequency lower than the first frequency; or
b) inclined at an angle 602 in the range of 5 to 25° with respect to a horizontal plane 603, or
c) A process (100) of manufacture, which is both a) and b) above. According to claim 1,
and the additional frequency is at least 15 kHz to 9.9 MHz lower than the first frequency. According to claim 1,
The method (100) of claim 1, wherein the screen is square (601) or round (402) or both. According to claim 1,
A manufacturing method (100), wherein the classifying device (400) is a centrifugal sieve or a tumbler sieve, or both. According to claim 1,
The method (100) of claim 1, wherein the mesh size of the screens (402, 601) ranges from 5 to 400 mesh. According to claim 1,
Method (100) of manufacture (100), wherein the classifying device (400) further comprises one or more additional screens (701). According to claim 1,
The manufacturing method (100), wherein the polymer gel discharged in step (vii) contains moisture in the range of 40 - 60 wt%, based on the polymer gel. According to claim 1,
the polymer gel discharged in step (vii) is a polymer gel sheet;
The method (100) of claim 1, wherein the polymer gel sheet has a thickness in the range of 10 to 200 mm. According to claim 1,
the polymer gel discharged in step (vii) is a polymer gel sheet;
The method (100) of claim 1, wherein the polymer gel sheet has a width in the range of 30 to 300 cm. 10. The method according to any one of claims 1 to 9,
Process (100), wherein the polymerization in step (vi) is carried out in the presence of a blowing agent. An apparatus (800) for making absorbent polymer particles in a production stream (808), comprising:
a) a first vessel 801, designed to contain an aqueous solution of monomers comprising at least one partially neutralized monoethylenically unsaturated monomer having a carboxylic acid group (α1);
b) a further container 802, designed to contain one or more crosslinking agents (α3);
c) mixing device 803:
The mixing device 803 is
i) located downstream of the first vessel (801) and the further vessel (802);
ii) designed to mix the monomer solution with one or more crosslinking agents (α3);
d) polymerization reactor 804:
The polymerization reactor 804 is
i) located downstream of the first vessel (801) and the further vessel (802);
ii) designed to receive an aqueous monomer solution and at least one crosslinking agent (α3) during polymerization of the monomer in aqueous monomer solution to obtain a polymer gel;
e) crushing device (805):
The crushing device 805 is
i) located downstream of the first vessel (801) and the further vessel (802);
ii) designed to break the polymer gel to obtain polymer gel particles,
f) Belt dryer (806):
The belt dryer 806 is
i) located downstream of the crushing device (805);
ii) designed to dry polymer gel particles;
g) grinding device 807:
The crushing device 807 is
i) located downstream of the belt dryer 806;
ii) designed to grind the dried polymer gel particles to obtain absorbent polymer particles;
h) a classifier (400) comprising:
The classifier 400 is
i) located downstream of the crushing device 807;
ii) a screen (402, 601);
iii) designed to classify the pulverized absorbent polymer particles 401,
iv) designed to vibrate (404, 405, 501) screens (402, 601);
the vibration (404, 405, 501) comprises a first frequency;
the first frequency is in the range of 16 kHz to 10 MHz;
the screen
a) vibrate at a further frequency lower than the first frequency; or
b) inclined at an angle (602) in the range of 5 - 25° with respect to the horizontal plane (603); or
c) an apparatus ( 800 ) of both a) and b) above. A method (100) for producing absorbent polymer particles in an apparatus (800) according to claim 11 . delete delete delete delete delete delete

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