EP2470572A1 - Soft particulate super absorbent and use thereof - Google Patents

Abstract

The invention relates to particulate super absorbents based on at least one monoethylenically unsaturated monomer containing at least one acid group, in which at least 5 mol % of the acid groups are neutralised with at least one tertiary alkanolamine. Said particulate super absorbents are particularly suitable as super-absorbing components in thermoplastic mixtures which are shaped into moulded bodies containing the super absorbents according to known shaping methods for thermoplastics.

Description

 Soft Particulate Superabsorbents and their Use Description The present invention relates to soft particulate superabsorbents, their use and products containing such superabsorbents and thermoplastics. In particular, it also relates to the processing of superabsorbent-containing plastic mixtures by molding processes for thermoplastics such as extrusion.

Superabsorbents are known. Also, for such materials, terms such as "high swellable polymer" "hydrogel" (often used for the dry form), "hydrogel-forming polymer", "water-absorbent polymer", "absorbent gelling material", "swellable resin", "water-absorbent Resin ", water-absorbent polymer" or the like in common use. These are crosslinked hydrophilic polymers, in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft, crosslinked cellulose or starch ethers, crosslinked carboxymethylcellulose, partially crosslinked polyalkylene oxide or in aqueous Liquid swellable natural products, such as guar derivatives, with superabsorbents based on partially neutralized acrylic acid are the most common. The essential properties of superabsorbents are their ability to absorb a multiple of their own weight of aqueous liquids and to not release the liquid under some pressure. The superabsorber, which is used in the form of a dry powder, transforms into a gel when it absorbs liquid, with the usual absorption of water corresponding to a hydrogel. Crosslinking is essential for synthetic superabsorbents and an important difference to conventional pure thickeners, as it leads to the insolubility of the polymers in water. Soluble substances would not be useful as superabsorbent. By far the most important application of superabsorbers is the absorption of body fluids. Superabsorbents are used, for example, in infant diapers, adult incontinence products or feminine hygiene products. Other fields of application are, for example, as water-retaining agents in agricultural horticulture, as water reservoirs for protection against fire, for liquid absorption in food packaging or, more generally, for the absorption of moisture.

Superabsorbents can absorb a multiple of their own weight of water and retain it under some pressure. In general, such a superabsorbent has a CRC ("Centrifuge Retention Capacity", measuring method see below) of at least 5 g / g, preferably at least 10 g / g and in a particularly preferred form at least 15 g / g. may also be a mixture of materially different individual superabsorbers or a mixture of components that are only in the Show interaction superabsorbent properties, it comes here less on the material composition than on the superabsorbent properties. Important for a superabsorbent is not only its absorption capacity, but also the ability to retain fluid under pressure (retention, usually expressed as "absorption under load"("AUL") or "absorption against pressure"("AAP")) as well as fluid transport in the swollen state (usually expressed as "Saline Flow Conductivity"("SFC")). Swollen gel can hinder fluid transport to superabsorbers that are not yet swollen ("gel blocking") .Good transport properties for liquids include, for example, hydrogels which have a high gel strength in the swollen state Gels with only low gel strength are under an applied pressure (body pressure) deforms, clogs pores and prevents further absorption of liquid Increased gel strength is usually achieved by a higher degree of cross-linking, which however reduces the absorption capacity of the product An elegant method for increasing the gel strength is compared to increasing the degree of cross-linking on the surface of the superabsorbent particles For this purpose, in a surface postcrosslinking step, dried superabsorbent particles with average crosslinking density are usually additionally crosslinked in a thin surface nschicht their particles subjected. Surface postcrosslinking increases the crosslink density in the shell of the superabsorbent particles, raising the absorption under pressure to a higher level. While the absorption capacity in the surface layer of the superabsorbent particles decreases, its core has an improved absorption capacity compared to the shell due to the presence of mobile polymer chains, so that the shell construction ensures improved fluid transfer without gel blocking occurring. It is also known to produce overall higher crosslinked superabsorbents and to subsequently reduce the degree of crosslinking in the interior of the particles compared to an outer shell of the particles.

Also, processes for the production of superabsorbents are known. Acrylic acid-based superabsorbents, which are most commonly used in the marketplace, are prepared by free-radical polymerization of acrylic acid in the presence of a crosslinker (the "internal crosslinker"), the acrylic acid before, after or partly before, partly after the polymerization The polymer gel obtained in this way is comminuted (depending on the polymerization reactor used, this can be done simultaneously with the polymerization) and dried.The dry powder obtained in this way (the "base polymer" or "polymer") is neutralized to a certain degree. Basispolymer ") is usually postcrosslinked on the surface of the particles by reacting with other crosslinkers such as organic crosslinkers or polyvalent cations, for example aluminum (usually as aluminum sulfate used) or both is implemented in order to produce a more crosslinked surface layer relative to the particle interior.

Fredric L. Buchholz and Andrew T. Graham (ed.), In: "Modern Superabsorbent Polymer Technology", J. Wiley & Sons, New York, USA / Wiley-VCH, Weinheim, Germany, 1997, ISBN 0-471-1941 1-5, for a summary of superabsorbents, their properties and processes for the production of superabsorbents.

No. 5,352,480 teaches methods for binding superabsorbents to fibers, inter alia with amino alcohols. WO 03/104 543 A1 teaches that triethanolamine is preferably used to bind superabsorbents to fibers, with the triethanolamine simultaneously serving to increase the degree of neutralization of the superabsorbent.

WO 2009/060 062 A1 mentions the possible use of triethanolamine as a surface postcrosslinking agent for superabsorbents.

EP 725 084 A1 mentions triethanolamine as a possible polymerization regulator in the (optionally crosslinking) polymerization of ethylenically unsaturated monomers. WO 99/44 648 A1 teaches the production of flexible superabsorbent foams in which a monomer mixture containing acrylic acid and triethanolamine as neutralizing agent is foamed and polymerized. According to the teaching of WO 00/52087 A1, this foaming takes place by injecting an inert gas into the monomer mixture and subsequent expansion.

WO 03/092 757 A1 discloses two possible uses of triethanolamine in superabsorbents. According to the teaching of this document, triethanolamine is a plasticizer for a special case of superabsorbents, namely a mixture of a slightly crosslinked acid with a slightly crosslinked basic polymer, which are used according to this document in the form of a flexible layer. This document further teaches that the flexible layer may contain up to 20% by weight of a conventional SAP which is partially neutralized with common alkalis such as sodium hydroxide, potassium hydroxide or triethanolamine, the use of triethanolamine providing a plasticized conventional SAP which enhances the flexibility of the present invention Absorber layer is not negatively influenced and may even contribute.

It is also known to use superabsorbents as part of polymer blends having water absorbing properties. These polymer blends are often thermoplastic and are deformed by conventional molding processes for thermoplastics, for example, to superabsorbent-containing plastic films or other moldings. The superabsorbent gives these films water absorbing properties that can serve a variety of purposes. DE 101 43 002 A1 discloses a film-like, channeled sheet in which superabsorbent particles are embedded in a matrix of waterproof plastic. This structure is produced for example by the addition of superabsorbent particles in the extrusion of the waterproof plastic. EP 1 616 906 A1 teaches water-swellable compositions which contain elastomeric material and superabsorber-dispersed in a thermoplastic matrix. Such moldings can be produced by conventional methods of thermoplastic processing, such as extrusion, plastic injection molding, blow molding, deep drawing, calendering or pressing. WO 03/022 316 indicates that certain particle size distributions of superabsorbents may be advantageous for individual applications, such as coextrusion with thermoplastics.

The superabsorbent itself is not a thermoplastic. Superabsorbent particles are relatively hard or brittle when dry. In the case of deformation of thermoplastic mixtures containing superabsorbent, therefore, there may be the problem that the brittle or, in any case, hard superabsorber particles in the mass plastified by heating during deformation disturb the processing of this mass. One problem may be, for example, the abrasion of deformation tools. This occurs naturally especially where the thermoplastic composition is moved under pressure on a tool or by a tool. Particularly susceptible are nozzles of all kinds, through which the thermoplastic composition is pressed, such as nozzles or mouthpieces of extruders. The simplest known measure for reducing the brittleness or hardness of superabsorbers, namely the setting of a minimum water content, often does not lead to the goal in thermoplastic molding processes, since in these shaping processes the mass to be deformed is heated, which leads to evaporation of the water. Problems with increasingly brittle superabsorbent particles can then cause problems with vapor bubbles in the thermoplastic mass. It is therefore an object to find new or improved superabsorbent and process for producing such superabsorbent, which are particularly suitable for further processing as a component of thermoplastic materials with conventional deformation processes for thermoplastics. Accordingly, a particulate superabsorbent based on at least one monoethylenically unsaturated monomer containing at least one acid group has been found, which is characterized in that at least 5 mol% of the acid groups have been neutralized with at least one tertiary alkanolamine. This superabsorbent is characterized by the fact that it leads to fewer problems in processing as a component of thermoplastic materials and in particular to less abrasion of deformation tools. Furthermore, a process for the preparation of this superabsorbent was found, uses of this superabsorbent and moldings containing this superabsorber and process for their preparation. The superabsorbers present in the mixture according to the invention can be prepared in different ways, for example by solution polymerization, suspension polymerization, dropwise or spray polymerization. Such methods are known. To prepare conventional superabsorbents, at least one monoethylenically unsaturated monomer containing at least one acid group is usually polymerized in the presence of a crosslinker.

An example of a currently commercially customary polymerization process for the preparation of acrylate superabsorbers is the aqueous solution polymerization of a monomer mixture containing a) at least one ethylenically unsaturated, acid group-carrying monomer, which is optionally present at least partially in the form of a salt,

b) at least one crosslinker,

c) at least one initiator,

d) optionally one or more ethylenically unsaturated monomers which can be copolymerized with the monomers mentioned under a), and

e) optionally one or more water-soluble polymers.

The monomers a) are preferably water-soluble, i. the solubility in water at 23 ° C. is typically at least 1 g / 100 g of water, preferably at least 5 g / 100 g of water, more preferably at least 25 g / 100 g of water, most preferably at least 35 g / 100 g of water.

Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids or their salts, such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid or its salts. Particularly preferred monomers are acrylic acid and methacrylic acid. Very particular preference is given to acrylic acid.

Further suitable monomers a) are, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

Impurities can have a significant influence on the polymerization. Therefore, the raw materials used should have the highest possible purity. It is therefore often advantageous to purify the monomers a) specifically. Suitable purification processes are described, for example, in WO 2002/055469 A1, WO 2003/078378 A1 and WO 2004/035514 A1. A suitable monomer a) is, for example, an acrylic acid purified according to WO 2004/035514 A1 with 99.8460% by weight of acrylic acid, 0.0950% by weight of acetic acid, 0.0332% by weight of water, 0.0203% by weight. % Propionic acid, 0.0001% by weight furfurale, 0.0001% by weight maleic anhydride,

0.0003% by weight of diacrylic acid and 0.0050% by weight of hydroquinone monomethyl ether. The proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, very particularly preferably at least 95 mol%. The monomer solution preferably contains at most 250 ppm by weight, preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight and preferably at least 10 ppm by weight, more preferably at least 30 ppm by weight, in particular by 50% by weight. ppm, hydroquinone half ethers, based in each case on the unneutralized monomer a), wherein neutralized monomer a), ie a salt of the monomer a), is accounted for mathematically as an unneutralized monomer. For example, an ethylenically unsaturated, acid group-carrying monomer having a corresponding content of hydroquinone half-ether can be used to prepare the monomer solution. Preferred hydroquinone half ethers are hydroquinone monomethyl ether (MEHQ) and / or alpha-tocopherol (vitamin E).

Suitable crosslinkers b) ("internal crosslinkers") are compounds having at least two groups suitable for crosslinking such groups are, for example, ethylenically unsaturated groups which can be radically copolymerized into the polymer chain, and functional groups which are covalenced with the acid groups of the monomer a). Furthermore, polyvalent metal salts which can form coordinative bonds with at least two acid groups of the monomer a) are also suitable as crosslinking agents b).

Crosslinkers b) are preferably compounds having at least two polymerizable groups which can be incorporated in the polymer network in free-radically polymerized form. Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallylammonium chloride, tetraallyloxyethane, as described in EP 530 438 A1, di- and triacrylates, as in EP 547 847 A1, EP 559 476 A1 , EP 632 068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO 2003/104301 A1 and DE 103 31 450 A1, mixed acrylates which, in addition to acrylate groups, contain further ethylenically unsaturated groups, such as in DE 103 31 456 A1 and

DE 103 55 401 A1, or crosslinker mixtures, such as in

DE 195 43 368 A1, DE 196 46 484 A1, WO 90/15830 A1 and WO 2002/32962 A2.

Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, trimethylolpropane triacrylate 10 to 20 times ethoxylated, trimethylolethane triacrylate 10 to 20 times ethoxylated, particularly preferably 15-times ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylates having 4 to 30 ethylene oxide units in the polyethylene glycol chain , Trimethylolpropane triacrylate, di- and triacethene acrylates of the 3 to 30-fold ethoxylated glycerol, more preferably di- and triacrylate of the 10-20-fold ethoxylated glycerol, and triallylamine. The polyesters which are not completely esterified with acrylic acid can also be present here as Michael adducts with themselves, as a result of which tetra-, penta- or even higher acrylates may also be present.

Very particularly preferred crosslinkers b) are the polyethoxylated and / or propoxylated glycerols esterified with acrylic acid or methacrylic acid to form di- or triacrylates, as described, for example, in WO 2003/104301 A1. Particularly advantageous are di- and / or triacrylates of 3- to 10-fold ethoxylated glycerol. Very particular preference is given to diacrylates or triacrylates of 1 to 5 times ethoxylated and / or propoxylated glycerol. Most preferred are the triacrylates of 3 to 5 times ethoxylated and / or propoxylated glycerol, in particular the triacrylate of 3-times ethoxylated glycerol. The amount of crosslinker b) is preferably from 0.05 to 1, 5 wt .-%, particularly preferably 0.1 to 1 wt .-%, most preferably 0.3 to 0.6 wt .-%, each based on Monomer a). As the crosslinker content increases, the centrifuge retention capacity (CRC) decreases and the absorbance increases under a pressure of 0.3 psi (AUL 0.3psi).

As initiators c) it is possible to use all compounds which generate free radicals under the polymerization conditions, for example thermal initiators, redox initiators, photoinitiators. Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite. Preference is given to using mixtures of thermal initiators and redox initiators, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid. As a reducing component but preferably a mixture of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite used (as Brüggolit ^® FF6M or Brüggolit ^® FF7, alternatively BRUGGOLITE ^® FF6M or

Bruggolite ^® FF7 available from L. Brüggemann KG, salt Straße 131, 74076 Heilbronn, Germany, www.brueggemann.com).

For example, acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, maleic acid and maleic anhydride are ethylenically unsaturated, acid group-bearing monomers a) copolymerizable ethylenically unsaturated monomers d).

Water-soluble polymers e) may be polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or hydroxyethylcellulose, Gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified cellulose.

Usually, an aqueous monomer solution is used. The water content of the monomer solution is preferably from 40 to 75 wt .-%, particularly preferably from 45 to 70 wt .-%, most preferably from 50 to 65 wt .-%. It is also possible monomer suspensions, i. to use supersaturated monomer solutions. With increasing water content, the energy expenditure increases during the subsequent drying and with decreasing water content, the heat of polymerization can only be sufficiently dissipated.

The preferred polymerization inhibitors require dissolved oxygen for optimum performance. Therefore, the monomer solution may be polymerized prior to polymerization by inerting, i. Flow through with an inert gas, preferably nitrogen or carbon dioxide, are freed of dissolved oxygen. Preferably, the oxygen content of the monomer solution before polymerization is reduced to less than 1 ppm by weight, more preferably less than 0.5 ppm by weight, most preferably less than 0.1 ppm by weight. The monomer mixture may contain other components. Examples of other components used in such monomer mixtures include chelating agents to keep metal ions in solution.

Suitable polymerization reactors are, for example, kneading reactors or belt reactors. In the kneader, the polymer gel formed in the polymerization of an aqueous monomer solution or suspension is comminuted continuously by, for example, counter-rotating stirring shafts, as described in WO 2001/38402 A1. The polymerization on the belt is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928. Polymerization in a belt reactor produces a polymer gel which must be comminuted in a further process step, for example in one

Meat grinder, extruder or kneader. However, spherical superabsorbent particles may also be prepared by suspension, spray or drop polymerization techniques. The acid groups of the polymer gels obtained are usually partially neutralized. The neutralization is preferably carried out at the stage of the monomers, in other words, salts of the acid group-carrying monomers or, strictly speaking, a mixture of acid group-carrying monomers and salts of the acid group-carrying monomers ("partially neutralized acid") are used as component a) in the polymerization usually by mixing the neutralizing agent as an aqueous solution or preferably also as a solid in the monomer mixture intended for the polymerization or preferably in the acid group-carrying monomer or a solution thereof. at least 5 mol%, preferably at least 10 mol% and more preferably at least 20 mol%, at least 40 mol% or at least 50 mol% and generally at most 95 mol%, preferably at most 85 mol -% and in a particularly preferred form at most 80 mol%.

The usual neutralizing agents can be used. These are preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal bicarbonates and mixtures thereof. Instead of alkali metal salts and ammonium salts can be used. Sodium and potassium are particularly preferred as alkali metal cations, but most preferred are sodium hydroxide, sodium carbonate, sodium bicarbonate and primary, secondary and tertiary alkanolamines and mixtures of these neutralizing agents.

However, the superabsorbent according to the invention contains at least one tertiary alkanolamine in addition to or exclusively as a neutralizing agent. Generally, at least 5 mole percent of the acid groups in the superabsorbent are neutralized by tertiary alkanolamine, preferably at least 10 percent, and most preferably at least 20 mole percent. In addition to tertiary alkanolamine, the superabsorbent may contain additional neutralizing agent to adjust the overall desired degree of neutralization (i.e., the proportion of neutralized acid groups (in moles) of all acid groups). For example, the superabsorbent may be partially neutralized with alkanolamine and partially with alkali, such as sodium or potassium. The overall degree of neutralization in the superabsorber according to the invention is generally at least 20 mol%, preferably at least 50 mol% and more preferably at least 60 mol% and generally at most 95 mol%, preferably at most 85 mol% and most preferably at most 80 mol%. However, it is preferred that the superabsorbent contains substantially no neutralizing agent other than tertiary alkanolamine, i. with the exception of unavoidable impurities or insignificant amounts of other neutralizing agents is neutralized with tertiary alkanolamine. In particular, it is preferred that the superabsorbent contains no neutralizing agent other than tertiary alkanolamine except for inevitable impurities.

It is also possible to carry out the neutralization after the polymerization at the stage of the polymer gel resulting from the polymerization. Furthermore, it is possible to neutralize a part of the acid groups before the polymerization by adding a part of the neutralizing agent already to the monomer solution and the desired Endneutralisationsgrad is adjusted only after the polymerization at the level of the polymer gel. For example, tertiary alkanolamine can be partially neutralized at the monomer stage and the desired final degree of neutralization can be adjusted with primary or secondary alkanolamine or alkalis such as sodium hydroxide after polymerization, or this order of addition can be reversed. If the polymer gel is at least partially neutralized after polymerization Siert, the polymer gel is preferably mechanically comminuted, for example by means of an extruder, wherein the neutralizing agent can be sprayed on, sprinkled or poured and then mixed thoroughly. For this purpose, the gel mass obtained can be extruded several times for homogenization.

This post-neutralization is preferably carried out before drying.

However, it is preferred to carry out the neutralization at the stage of the monomer. In other words: in a very particularly preferred embodiment, the monomer a) is a mixture of as much mol% salt of the acid group-carrying monomer as the desired degree of neutralization and the rest

100 mol% acid group-carrying monomer used. This mixture is, for example, a mixture of triethanolammonium acrylate and acrylic acid. The alkanolamines can be used in neutralization at the stage of the monomer or in the post-neutralization of the polymer neat or as a solution in solvents or solvent mixtures. As the solvent for alkanolamines, for example, water, methanol, ethanol, iso-propanol, or acetone may be used, with preference being given to water or use without a solvent.

The tertiary alkanolamines used may be monovalent, polyvalent or polyfunctional bases. The alkanolamines may carry, in addition to their amino and hydroxyl groups, other functional groups such as esters, urethane, ethers, thioethers, urea, etc. It is possible to use, for example, low molecular weight compounds such as triethanolamine, methyldiethanolamine, dimethylethanolamine, N-hydroxyethylmorpholine, dimethylaminodiglycol, N, N, N ', N'-tetra (hydroxyethyl) ethylenediamine, N, N, N', N'-tetra- (hydroxypropyl) ethylenediamine, dimethylaminotriglycol, diethylaminoethanol, 3-dimethylamino-1,2-propanediol, triisopropanolamine, diisopropylaminoethanol, choline hydroxide, choline carbonate or else oligomers or polymers such as, for example, amino-containing polymers or condensates reacted with ethylene oxide, propylene oxide, glycidol or other epoxides, Reaction products of at least bifunctional, lower molecular weight alkanolamines with at least bifunctional reagents capable of reacting with either the hydroxyl or the amino group of the alkanolamines, such as carboxylic acids, esters, epoxides or isocyanates.

Tertiary alkanolamines which are preferably used are triethanolamine, methyldiethanolamine, dimethylaminodiglycol, dimethylethanolamine and N, N, N ', N'-tetra- (hydroxyethyl) ethylenediamine. Triethanolamine is most preferred.

In a preferred embodiment neutralizing agents are used for neutralization, the content of iron is generally below 10 ppm by weight, preferably below 2 ppm by weight and most preferably below 1 ppm by weight. Just- Thus, a low content of chloride and anions of oxygen acids of the chlorine is desired.

The polymer gel obtained from the aqueous solution polymerization and optionally subsequent neutralization is then preferably dried with a belt dryer until the residual moisture content is preferably 0.5 to 15 wt .-%, particularly preferably 1 to 10 wt .-%, most preferably 2 to 8 wt .-%, is (measurement method for the residual moisture or water content, see below). If the residual moisture content is too high, the dried polymer gel has too low a glass transition temperature Tg and is difficult to process further. If the residual moisture content is too low, the dried polymer gel is too brittle and in the subsequent comminution steps undesirably large amounts of polymer particles with too small particle size ("fines") are produced. %, preferably from 30 to 80 wt .-%, particularly preferably from 35 to 70 wt .-%, most preferably from 40 to

60% by weight. Optionally, for drying but also a fluidized bed dryer or a heatable mixer with mechanical mixing element such as a paddle dryer or a similar dryer can be used with differently shaped mixing tools. Optionally, the dryer may be operated under nitrogen or other non-oxidizing inert gas, or at least a reduced partial pressure of oxygen, to prevent oxidative yellowing. As a rule, however, sufficient ventilation and removal of the water vapor also leads to an acceptable product. Advantageous in terms of color and product quality is usually the shortest possible drying time. In the conventional belt dryers operation to this, in customary more of a temperature of the gas used for drying of at least 50 ⁰ C, preferably at least 80 ⁰ C and more preferably at least 100 ⁰ C., and generally not exceeding 250 ⁰ C, preferably at most Set 200 ⁰ C and in a particularly preferred form of at most 180 ⁰ C. Common belt dryers often have multiple chambers, the temperature in these chambers may be different. For each type of dryer, the operating conditions must be selected as a whole in a known manner so that the desired drying result is achieved.

During drying, the residual monomer content in the polymer particles also decreases and the last residues of the initiator are destroyed.

The dried polymer gel is then ground and classified, wherein for grinding usually one- or multi-stage roller mills, preferably two- or three-stage roller mills, pin mills, hammer mills or vibratory mills can be used. Oversized gel lumps, which are often not dried in the interior, are rubber-elastic, lead to grinding problems and are preferably separated before grinding, which can easily be achieved by air classification or a sieve ("protective sieve" for the mill) is in the face of used mill to be chosen so that as possible no interference from oversized, rubbery particles occur. At the latest by grinding, a particulate superabsorber, ie a superabsorber in the form of individual particles, is produced from the dried polymer gel (which may already be crumbly, depending on the polymerisation apparatus used and any comminution apparatuses used after the reactor).

The superabsorbent is usually subsequently classified to obtain a product of the desired particle size distribution. This is done by customary classification methods, for example air classification or sieving through screens of suitable mesh size. Typical sieve cuts for hygiene applications of superabsorbents are at most 1000 μm, preferably at most 900 μm, particularly preferably at most 850 μm and very particularly preferably at most 800 μm. For example, sieves with 700 μm, 650 μm or 600 μm mesh size are used. The separated coarse-grained polymer particles ("oversize") can be fed back to the grinding and screening circuit for cost optimization or further processed separately.

Polymer particles with too small particle size lower the permeability (SFC). Advantageously, fine-particle polymer particles are therefore separated off in this classification. This can, if sieved, conveniently by a sieve with a mesh size of at most 300 microns, preferably at most 200 microns, more preferably at most 150 microns and most preferably not more than 100 microns. The separated fine-grained polymer particles ("undersize" or "fines") can be fed back to the monomer stream, the polymerizing gel, or the polymerized gel before drying the gel for cost optimization.

The average particle size of the polymer particles separated as a product fraction is generally at least 200 .mu.m, preferably at least 250 .mu.m and preferably at least 300 .mu.m and generally at most 600 .mu.m and preferably at most 500 .mu.m for hygiene applications. The proportion of particles having a particle size of at least 150 microns is generally at least 90 wt .-%, preferably at least 95 wt .-% and most preferably at least 98 wt .-%. The proportion of particles with a particle size of at most 850 microns, is generally at least 90 wt .-%, preferably at least 95 wt .-% and most preferably at least 98 wt .-%.

Depending on the specific use of the superabsorber, a different particle size distribution can be selected. In general, the same particle size is used for use in deformation process for thermoplastic mixtures containing the superabsorber as previously with non-inventive superabsorbent. This is often smaller than usual in hygiene applications. For extrusion processes, for example, a sieve cut of 5 to 50 μm or even 50 to 150 μm is often selected. In some other known production processes for superabsorbents, in particular in suspension polymerization, spray or dropletization polymerization, the particle size distribution is predetermined by the choice of process parameters. In these processes, particulate superabsorbents of the desired particle size are formed directly, so that milling and sieving steps can often be dispensed with, and in some processes (in particular in the case of spray or dropletization polymerization), a separate drying step can often be dispensed with. The specific embodiment of the production process for the superabsorber according to the invention is not relevant to the present invention.

The polymer produced as described so far has superabsorbent properties and falls under the term "superabsorbent." Its CRC is typically comparatively high, while its AUL or SFC is comparatively low often called "base polymer" or "base polymer".

Optionally, the superabsorbent particles are postcrosslinked on their surface to further improve the properties, especially increase the AUL and SFC values (with the CRC value decreases). Postcrosslinking of superabsorbents is known per se.

Suitable postcrosslinkers are compounds which contain groups which can form bonds with at least two functional groups of the superabsorbent particles. Acrylic acid / sodium acrylate-based superabsorbents which are prevalent on the market are suitable surface postcrosslinker compounds which contain groups which can form bonds with at least two carboxylate groups. Preferred postcrosslinkers are:

 Di- or polyepoxides, for example di- or polyglycidyl compounds, such as phosphonic acid diglycidyl esters, ethylene glycol diglycidyl ethers or bischlorohydrin ethers of polyalkylene glycols,

 Alkoxysilyl compounds,

 Polyaziridines, compounds containing aziridine units based on polyethers or substituted hydrocarbons, for example bis-N-aziridino methane,

 Polyamines or polyamidoamines and their reaction products with epichlorohydrin,

 Polyols such as ethylene glycol, 1, 2-propanediol, 1, 4-butanediol, glycerol, methyltriglycol, polyethylene glycols having an average molecular weight Mw of 200 to 10,000, di- and polyglycerol, pentaerythritol, sorbitol, the ethoxylates of these polyols and their

Esters with carboxylic acids or carbonic acid, such as ethylene carbonate or propylene carbonate, Carbonic acid derivatives such as urea, thiourea, guanidine, dicyandiamide, 2-oxazolidinone and its derivatives, bisoxazoline, polyoxazolines, di- and polyisocyanates,

 Di- and poly-N-methylol compounds such as, for example, methylenebis (N-methylolmethacrylamide) or melamine-formaldehyde resins,

 • Compounds with two or more blocked isocyanate groups such as trimethylhexamethylene diisocyanate blocked with 2,2,3,6-tetramethylpiperidinone-4. Optionally, acidic catalysts such as p-toluenesulfonic acid, phosphoric acid, boric acid or ammonium dihydrogen phosphate may be added.

Particularly suitable postcrosslinkers are di- or polyglycidyl compounds such as ethylene glycol diglycidyl ether, the reaction products of polyamidoamines with epichlorohydrin, 2-oxazolidinone and N-hydroxyethyl-2-oxazolidinone.

It is possible to use a single postcrosslinker from the above selection or any mixtures of different postcrosslinkers. The postcrosslinker is generally used in an amount of at least

 0.001 wt .-%, preferably of at least 0.02 wt .-%, in a particularly preferred form of at least 0.05 wt.% And generally at most 2 wt .-%, preferably at most 1 wt .-%, in particularly preferred Form at most

0.3 wt .-%, for example, at most 0.15 wt .-% or at most 0.095 wt .-% used, in each case based on the mass of the base polymer thus acted upon.

The postcrosslinking is usually carried out by spraying a solution of the postcrosslinker onto the dried base polymer particles. Subsequent to the spraying, the polymer particles coated with postcrosslinker are thermally dried, it being possible for the postcrosslinking reaction to take place both before and during the drying. If surface postcrosslinkers with polymerizable groups are used, the surface postcrosslinking can also be effected by free-radically induced polymerization of such groups by means of conventional free-radical formers or else by means of high-energy radiation such as UV light. This may be done in parallel or instead of using postcrosslinkers that form covalent or ionic bonds to functional groups on the surface of the base polymer particles.

The solvent used for the surface postcrosslinker is a customary suitable solvent, for example water, alcohols, DMF, DMSO and mixtures thereof. Particularly preferred are water and water / alcohol mixtures such as water / methanol, water / 1, 2-propanediol and water / 1, 3-propanediol. The concentration of the postcrosslinker in the postcrosslinker solution is typically scherweise 1 to 20 wt .-%, preferably 1, 5 to 10 wt .-%, particularly preferably 2 to 5 wt .-%, based on the Nachvernetzerlösung.

The spraying of the postcrosslinker solution is preferably carried out in mixers with moving mixing tools, such as screw mixers, disk, paddle or paddle mixers or mixers with other mixing tools. However, particularly preferred are vertical mixers. However, it is also possible to spray the postcrosslinker solution in a fluidized bed. Suitable mixers are flocking for example as a plow mixer ^® Gebr Lödige Maschinenbau GmbH, Elsener Street. 7 - 9, 33102 Paderborn, Germany, or ^® as Schugi ^® Flexomix mixer, Vrieco-Nauta ^® mixer or blender Turbulizer® ^® from Hosokawa Micron BV, Gildenstraat 26, 7000 AB Doetinchem, The Netherlands.

The anionic, cationic, nonionic and amphoteric surfactants are suitable as Deagglomerationshilfsmittel, but are preferred for Hautverträglichkeitsgründen nonionic and amphoteric surfactants. The surfactant may also contain nitrogen. For example, sorbitan monoesters, such as sorbitan monococoate and sorbitan monolaurate, or ethoxylated variants thereof, such as polysorbate ^20® , are added. Other suitable deagglomerating assistants the ethoxylated and alkoxylated derivatives of 2-propylheptanol, which are marketed under the brand names Lutensol® XL ^® and Lutensol XP ^® (BASF SE, Carl-Bosch-Straße 38, 67056 Ludwigshafen, Germany). The deagglomerating assistant can be metered separately or added to the postcrosslinker solution. Preferably, the deagglomerating aid is simply added to the postcrosslinker solution. The amount used of the deagglomerating assistant based on the base polymer is, for example, 0 to 0.1% by weight, preferably 0 to 0.01% by weight, particularly preferably 0 to 0.002% by weight. Preferably, the deagglomerating assistant is metered such that the surface tension of a wässri- gen extract of the swollen base polymer and / or of the swollen postcrosslinked superabsorbent at 23 ⁰ C of at least 0.060 N / m, preferably at least 0.062 N / m, more preferably at least 0.065 N / m, and advantageously at most 0.072 N / m. The actual surface postcrosslinking by reaction of the surface postcrosslinker with functional groups on the surface of the base polymer particles is usually carried out by heating the base polymer wetted with surface postcrosslinker solution, usually called "drying" (but not to be confused with the above-described drying of the polymer gel from the polymerization) drying can be carried out in the mixer itself, by heating the jacket, by heat exchange surfaces or by blowing warm gases in. Simultaneous addition of the superabsorbent with surface postcrosslinker and drying can be carried out, for example, in a fluidized bed reactor. carried out dryer. However, the drying is usually carried out in a downstream dryer, such as a tray dryer, a rotary kiln, a paddle or disc dryer or a heated screw. Suitable dryers are, for example, as Solidair ^® or Torusdisc ^® -T Rockner from Bepex International LLC, 333 NE Taft Street, Minneapolis, MN 55413, USA, or as a paddle or

Paddle dryer or as a fluidized bed dryer from Nara Machinery Co., Ltd., branch office Europe, Europaallee 46, 50226 Frechen, Germany available.

Preferred drying temperatures are in the range 100 to 250 ⁰ C, preferably 120 to 220 ⁰ C, particularly preferably 130 to 210 ° C most preferably 150 to 200 ⁰ C. by weight, the preferred residence time at this temperature in the reaction mixer or dryer is preferably at least 10 minutes , more preferably at least 20 minutes, most preferably at least 30 minutes, and usually at most 60 minutes. Typically, the drying is conducted in such a way that the superabsorber has a residual moisture content of generally at least 0.1% by weight, preferably at least 0.2% by weight and in a particularly preferred form at least 0.5% by weight, and also Generally at most 15% by weight, preferably at most 10% by weight and in a particularly preferred form at most 8% by weight. In one embodiment of the invention, in addition, the hydrophilicity of the particle surface of the base polymers is modified by the formation of complexes. The formation of the complexes on the outer shell of the particles is carried out by spraying solutions of divalent or polyvalent cations, wherein the cations can react with the acid groups of the polymer to form complexes. Examples of divalent or polyvalent cations are polymers which are formally wholly or partially composed of vinylamine monomers, such as partially or completely hydrolyzed polyvinylamide (so-called "polyvinylamine"), whose amine groups are always partially protonated to ammonium groups, even at very high pH values, or metal cations such as Mg ²⁺ , Ca ²⁺ , Al ³⁺ , Sc ³⁺ , Ti ⁴⁺ , Mn ²⁺ , Fe ^{2+ / 3+} , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ , Y ³⁺ , Zr ⁴⁺ , La ³⁺ , Ce ⁴⁺ , Hf ⁴⁺ , and Au ³⁺ Preferred metal cations are Mg ²⁺ , Ca ²⁺ , Al ³⁺ , Ti ⁴⁺ , Zr ⁴⁺ and La ³⁺ , and particularly preferred metal cations are Al ³⁺ , Ti ⁴⁺ and Zr ⁴⁺ The metal cations can be used both alone and in admixture with one another. Of the metal cations mentioned, all metal salts which have sufficient solubility in water are suitable Particularly suitable are metal salts with weakly complexing anions such as chloride, nitrate and Sul fat, hydrogen sulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate, dihydrogen phosphate and carboxylate, such as acetate and lactate. In a particularly preferred form, aluminum sulfate is used. As solvents for the metal salts, water, alcohols, DMF, DMSO and mixtures of these components can be used. Particularly preferred are water and water / alcohol mixtures such as water / methanol, water / 1, 2-propanediol and water / 1, 3-propanediol. The treatment of the base polymer with solution of a di- or polyvalent cation is carried out in the same way as with surface postcrosslinkers, including the optional drying step. Surface postcrosslinker and polyvalent cation can be sprayed in a common solution or as separate solutions. The spraying of the metal salt solution onto the superabsorbent particles can be carried out both before and after the surface postcrosslinking. In a particularly preferred method, the spraying of the metal salt solution is carried out in the same step by spraying the crosslinker solution, wherein both solutions are sprayed separately successively or simultaneously via two nozzles, or crosslinker and metal salt solution can be sprayed together via a nozzle ,

If a drying step is carried out after the surface postcrosslinking and / or treatment with complexing agent, it is advantageous, but not absolutely necessary, to cool the product after drying. The cooling can be continuous or discontinuous, conveniently the product is continuously conveyed to a dryer downstream cooler. Any apparatus known for removing heat from powdered solids may be used for this purpose, in particular any apparatus mentioned above as a drying apparatus, unless it is supplied with a heating medium but with a cooling medium, such as cooling water, so that over the walls and depending on the construction no heat is also introduced into the superabsorber via the stirring elements or other heat exchange surfaces, but is removed therefrom. Preference is given to the use of coolers in which the product is moved, ie cooled mixers, for example blade coolers, disk coolers or paddle coolers. The superabsorbent can also be cooled in the fluidized bed by blowing in a cooled gas such as cold air. The conditions of the cooling are adjusted so that a superabsorbent is obtained with the temperature desired for further processing. Typically, an average residence time in the condenser of generally at least 1 minute, preferably at least 3 minutes and more preferably at least 5 minutes and generally at most 6 hours, preferably at most 2 hours and more preferably at most 1 hour is set and the cooling capacity is so in that the product obtained has a temperature of generally at least 0 ^° C, preferably at least 10 ^° C and more preferably at least 20 ^° C and generally at most 100 ^° C, preferably at most 80 ^° C and most preferably at most 60 ⁰ C.

The surface-postcrosslinked superabsorbent or the mixture is optionally ground and / or sieved in a conventional manner. Milling is typically not required here, but mostly the setting of the desired particle size distribution of the product requires the screening of formed agglomerates or fine particles. Agglomerates and fine particles are either discarded or preferably recycled to the process in a known manner and at a suitable point; Agglomerates after Shredding. The particle sizes desired for surface postcrosslinked superabsorbents are the same as for base polymers.

Optionally, any known additives or coatings, such as film-forming polymers, thermoplastic polymers, dendrimers, polycationic polymers (such as polyvinylamine, polyethylenimine or polyallylamine), water-insoluble polyvalent metal salts, such as magnesium carbonate, magnesium oxide, may optionally be applied to the surface of the SAP particles in any process step , Magnesium hydroxide, calcium carbonate, calcium sulfate or calcium phosphate, all water-soluble mono- or polyvalent metal salts known to those skilled in the art, such as, for example, aluminum sulfate, sodium, potassium, zirconium or iron salts, or hydrophilic inorganic particles, such as clay minerals, fumed silica, colloidal silica sols such as Levasil ^® , titanium dioxide, aluminum oxide and magnesium oxide, in addition to be applied. Examples of useful alkali metal salts are sodium and potassium sulfate, sodium and potassium lactates, citrates, sorbates. As a result, additional effects, for example a reduced caking tendency of the end product or of the intermediate product in the respective process step of the production method, improved processing properties or a further increased liquid conductivity (SFC) can be achieved. If the additives are used and sprayed in the form of dispersions, then they are preferably used as aqueous dispersions, and it is preferably additionally applied a dedusting agent for fixing the additive on the surface of the superabsorbent. The dedusting agent is then added either directly to the dispersion of the inorganic powder additive, optionally it may also be added as a separate solution before, during, or after the inorganic powdery additive has been applied by spraying. The most convenient is the simultaneous spraying of Nachvernetzungsmittel, dedusting and powdery inorganic additive in the post-crosslinking. In a further variant of the method, however, the dedusting agent is added separately in the cooler, for example by spraying from above, below or from the side. Particularly suitable dedusting agents which can also be used for fixing powdery inorganic additives to the surface of the SAP particles are polyethylene glycols having a molecular weight of 400 to 20 000 g / mol, polyglycerol, 3 to 100-fold ethoxylated polyols, such as trimethylolpropane, Glycerin, sorbitol and neopentyl glycol. Particularly suitable are lolpropan 7- to 20-tuply ethoxylated glycerol or trimethylolpropane, for example Polyol TP 70 ^® (Perstorp, SE). The latter have the particular advantage that they only insignificantly reduce the surface tension of an aqueous extract of the superabsorbent particles.

It is also possible to adjust the superabsorber according to the invention by adding water to a desired water content.

All coatings, solids, additives and auxiliaries can each be added in separate process steps, but usually the most convenient method is to use them. if they are not added during the displacement of the base polymer with surface postcrosslinking agent, add it to the superabsorber in the cooler, such as by spraying a solution or adding it in finely divided solid or in liquid form.

The superabsorbent according to the invention generally has a centrifuge retention capacity (CRC) of at least 5 g / g, preferably of at least 10 g / g and in a particularly preferred form of at least 20 g / g. Further suitable minimum values of the CRC are, for example, 25 g / g, 30 g / g or 35 g / g. Usually it is not above 40 g / g. A typical range of CRC for surface postcrosslinked superabsorbents is from 28 to 33 g / g.

The superabsorbent according to the invention typically has an absorption under pressure (AUL 0.7 psi, measuring method see below) of at least 18 g / g, preferably at least 20 g / g, more preferably at least 22 g / g, particularly preferably at least 23 g / g, very particularly preferably at least 24 g / g and usually not more than 30 g / g.

The superabsorbent according to the invention further has a saline flow conductivity (SFC measurement method s. Below) of at least 10x10 ^"7 cm ³ sec / g, preferably at least ^{30x10" 7} cm ³ sec / g, preferably at least 50x10 ^"7 cm ³ s / g, particularly preferably at least 80x10 ^"7 cm ³ sec / g, most preferably at least ^{100x10" 7} cm ³ s / g and usually not above 1000x10 ^"7 cm ³ s / g.

The superabsorbent according to the invention can be used for any purpose to which known superabsorbers are also used. The superabsorbent mixture according to the invention can be used in particular in all fields of technology in which liquids, in particular water or aqueous solutions, are absorbed. These areas are for example storage, packaging, transport (as components of packaging material for water or moisture sensitive articles, such as flower transport, as well as protection against mechanical effects); Animal hygiene (in cat litter); Food packaging (transport of fish, fresh meat, absorption of water, blood in fresh fish or meat packaging); Medicine (wound plasters, water-absorbing material for burn dressings or for other weeping wounds), cosmetics (carrier material for pharma- ceuticals and drugs, rheumatic patches, ultrasound gel, cooling gel, cosmetic thickener, sunscreen); Thickener for oil / water or water / oil emulsions; Textiles (moisture regulation in textiles, shoe inserts, for evaporative cooling, for example in protective clothing, gloves, headbands); chemical-technical applications (as a catalyst for organic reactions, for the immobilization of large functional molecules such as enzymes, as adhesives in agglomerations, heat storage, filtration aids, hydrophilic components in polymer laminates, dispersants, condenser); as an aid in powder injection molding, in construction and construction (installation, in clay-based plaster, as vibration-inhibiting medium, aid in tunnel excavations in water- rich underground, cable sheathing); Water treatment, waste treatment, water separation (deicing, reusable sandbags); Cleaning; Agribusiness (irrigation, retention of meltwater and dew precipitation, addition of composting, protection of forests against fungal / insect attack, delayed release of active substances to plants); for fire fighting or fire protection; Coextrusion agents in thermoplastic polymers (eg for the hydrophilization of multilayer films); Manufacture of thermoplastic moldings (including films) that can absorb water (eg, rainwater and condensation water-retaining films for agriculture; superabsorbent-containing films for keeping fruit and vegetables freshly packaged in wet films; superabsorbent-polystyrene coextrudates, for example for food packaging such as meat, fish, poultry, fruits and vegetables); or as a carrier substance in active ingredient formulations (pharmaceuticals, crop protection). A preferred use of the superabsorbent according to the invention is as a constituent of thermoplastic mixtures, in particular of such thermoplastic mixtures, which are provided for deformation into moldings. The thermoplastic mixtures according to the invention, processes for their processing and the molded articles produced therewith differ from known ones in that they contain the superabsorber according to the invention or that the superabsorber according to the invention is present.

Such thermoplastic mixtures containing superabsorbents are known per se. They usually contain a proportion of a thermoplastic polymer, for example polyolefins such as polyethylene or polypropylene, polystyrene, polyesters such as polyethylene terephthalate or polybutylene terephthalate, polyvinyl chloride, polyamide, polycarbonate or polyurethane or copolymers, for example ethylene-vinyl acetate copolymer or acrylonitrile-butadiene-styrene copolymer , or a mixture of such polymers and / or copolymers. The proportion of thermoplastic in the mixture must be at least high enough so that the mass as a whole can be processed like a thermoplastic.

The thermoplastic mixture also contains the superabsorbent according to the invention. Its content is at least high enough to achieve the desired water-absorbing properties.

In addition to a thermoplastic and the superabsorber, the thermoplastic mixture may contain further fractions which impart desired properties to it and / or to the molded article produced therefrom. Examples thereof are fillers such as inorganic fillers, for example inorganic oxides such as silicon, aluminum, titanium or zirconium oxides, carbon blacks, elastomers, particulate elastomers such as rubber particles or any other additive known for such purposes. The mixture according to the invention is prepared in the usual way and processed into moldings. For this purpose, the thermoplastic mixture is generally produced, made deformable by heating and then deformed. The thermoplastic mixture can be made before deformation but also during deformation. If the mixture is prepared before deformation, usually the thermoplastic is melted and the other components are mixed. The mixture can then be directly deformed or cooled and formed into semifinished product. Such semifinished product (for example granules) can be transported to other locations for deformation to the end product. However, the mixture can also be produced during the deformation, for example by feeding a thermoplastic to an extruder and feeding the other components at different points of the extruder. It is also possible to pre-mix parts of the intended final composition and to add the remaining components during deformation. All these are known measures of thermoplastic processing.

It may also be possible and desirable to adjust the final composition of the desired shaped article only after deformation. For example, the superabsorber after the actual deformation - such as the production of a thermoplastic film - are applied to this.

Deformation of the thermoplastic blend is accomplished by any known method of thermoforming. Examples include extrusion, spraying, blow molding, deep drawing, calendering or pressing. A method for which the superabsorbent according to the invention is particularly suitable is extrusion. By extrusion almost any shapes can be produced, including films.

Another object of the invention are moldings of a thermoplastic mixture, wherein a superabsorbent according to the invention is a constituent of the mixture.

test methods

The superabsorbent is tested using the test methods described below. The "WSP" standard test methods described below are described in: "Standard Test Methods for the Nonwovens Industry", 2005 edition, co-edited by the Worldwide Strategy Partners EDANA (European Disposables and Nonwovens Association, Avenue Eugene Plasky). 157, 1030 Brussels, Belgium, www.edana.org) and INDA (Association of the Nonwoven Fabrics Industry, 1100 Crescent Green, Suite 1 15, Cary, North Carolina 27518, USA, www.inda.org). This publication is available from EDANA or INDA. All measurements described below should be performed at an ambient temperature of 23 ± 2 ^° C and a relative humidity of 50 ± 10%, unless otherwise specified. The superabsorbent particles are thoroughly mixed before measurement, unless stated otherwise.

Centrifuge Retention Capacity (CRC)

The centrifuge retention capacity of the superabsorbent is determined according to the standard test method no. WSP 241.5-02 "Centrifuge Retention Capacity".

Absorption under pressure (AULO.7psi, Absorbency under Load of 0.7 psi)

The absorption under a pressure of 4826 Pa (0.7 psi) of the superabsorbent is determined analogously to the standard test method no. WSP 242.2-05 "absorption under pressure", but a weight of 49 g / cm ² (leads to a pressure of 0.7 psi) instead of a weight of 21 g / cm ² (leading to a pressure of 0.3 psi) is used.

Fluid transfer (SFC, "Saline Flow Conductivity") The fluid transfer of a swollen gel layer formed by the superabsorber by liquid absorption is called "Gel Layer Permeability" ("GLP") under pressure load of 0.3 psi (2068 Pa) as described in EP 640 330 A1. a swollen gel layer of superabsorbent particles (there called "AGM" for "absorbent gelling material"), wherein the apparatus described in the aforementioned patent application on page 19 and in Figure 8 is modified so that the glass frit (40) is no longer used The punch (39) is made of the same plastic material as the cylinder (37) and now has evenly spaced holes 21 distributed over the entire bearing surface The procedure and evaluation of the measurement remain unchanged compared to EP 640 330 A1 detected.

Fluid transfer (SFC) is calculated as follows:

SFC [cm ³ s / g] = (F g (t = 0) x LO) / (dxAx WP), where F g (t = O) is the NaCl solution flow in g / s, which is determined by linear regression analysis of data Fg (t) the flow determination is obtained by extrapolation to t = 0, LO is the thickness of the gel layer in cm, d is the density of the NaCl solution in g / cm ³ , A is the area of the gel layer in cm ² and WP is the hydrostatic pressure over the Gel layer in dyn / cm ² represents.

Moisture content of the superabsorber (residual moisture, water content) The water content of the superabsorbent particles is determined according to the standard test method no. WSP 230.2-05 "Moisture Content".

particle size

The particle size of the product fraction is determined according to the standard test method no. WSP 220.2-05 "Particle Size Distribution".

Claims

claims

1. A particulate superabsorbent based on at least one monoethylenically unsaturated monomer containing at least one acid group, characterized in that at least 5 mol% of the acid groups are neutralized with at least one tertiary alkanolamine.

2. Superabsorber according to claim 1, characterized in that at least

20 mol% of the acid groups are neutralized with at least one tertiary alkanolamine.

3. Superabsorber according to claim 2, characterized in that at least

40 mol% of the acid groups are neutralized with at least one tertiary alkanolamine.

4. Superabsorber according to one of claims 1 to 3, characterized in that it contains substantially no neutralizing agent other than tertiary alkanolamine.

5. Superabsorber according to one of claims 1 to 4, characterized in that the tertiary alkanolamine is triethanolamine.

6. A process for producing a superabsorbent as defined in claims 1 to 5 by polymerizing at least one monoethylenically unsaturated monomer containing at least one acid group in the presence of a

Crosslinker, characterized in that before, during or after the polymerization at least 5 mol% of the acid groups are neutralized with at least one tertiary alkanolamine.

7. Use of a defined in claims 1 to 5 superabsorbent as a component of thermoplastic mixtures.

8. A process for the deformation of thermoplastic mixtures, wherein the thermoplastic mixtures are made deformable by heating, characterized in that a defined in claims 1 to 5 Superabsorber as

Component of the thermoplastic mixture is used.

9. The method according to claim 8, characterized in that the method comprises an extrusion step.

10. molding of a thermoplastic mixture, characterized in that a defined in claims 1 to 5 Superabsorber is part of the mixture.