Odor-control superabsorbent comprising activated carbon material having a trimodal pore radius distribution

Abstract

Superabsorbents comprising activated carbon having a trimodal pore radius distribution exhibit superior odor control.

Description

[0001] 230855W001

[0002] 1

[0003] Odor-control Superabsorbent comprising Activated Carbon Material having a trimodal Pore Radius Distribution

[0004] Description

[0005] The present invention relates to odor-control superabsorbents comprising an activated carbon material having a trimodal pore radius distribution, a process for producing such superabsorbents and water-absorbing products that comprise such superabsorbents.

[0006] Superabsorbents are known. Superabsorbents are materials that are able to take up and retain many times their weight in water, possibly up to several hundred times their weight, even under moderate pressure. Absorbing capacity is usually lower for salt-containing solutions compared to distilled or otherwise de-ionised water. Typically, a superabsorbent has a centrifugal retention capacity (“CRC”, method of measurement see hereinbelow) of at least 5 g / g, preferably at least 10 g / g and more preferably at least 15 g / g. Such materials are also commonly known by designations such as “high-swella- bility polymer”, “hydrogel” (often even used for the dry form), “hydrogel-forming polymer”, “water-absorbing polymer”, “absorbent gel-forming material”, “swellable resin”, “water-absorbing resin” or the like. The materials in question are crosslinked hydrophilic polymers, in particular polymers formed from (co)polymerised hydrophilic monomers, graft (co)polymers of one or more hydrophilic monomers on a suitable grafting base, crosslinked ethers of cellulose or starch, crosslinked carboxymethylcellulose, partially crosslinked polyalkylene oxide or natural products that are swellable in aqueous fluids, examples being guar derivatives, of which water-absorbing polymers based on partially neutralised acrylic acid are most widely used. Superabsorbents are usually produced, stored, transported and processed in the form of dry powders of polymer particles, “dry” usually meaning less than 5 wt.-% moisture content (method of measurement see hereinbelow), although forms in which superabsorbents particles are bound to a web, typically a nonwoven, are also known for some applications, as are superabsorbent fibres. A superabsorbent transforms into a gel on taking up a liquid, specifically into a hydrogel when as usual taking up water. By far the most important field of use of superabsorbents is the absorbing of bodily fluids. Superabsorbents are used for example in diapers for infants, incontinence products for adults or feminine hygiene products. Examples of other fields of use are as water-retaining agents in market gardening, as water stores for protection against fire, for liquid absorption in food packaging or, in general, for absorbing moisture.

[0007] Processes for producing superabsorbents are also known. The acrylate-based superabsorbents which dominate the market are produced by radical polymerisation of acrylic acid in the presence of a crosslinking agent (the “internal crosslinker”), usually 230855W001

[0008] 2 in the presence of water, the acrylic acid being neutralised to some degree in a neutralisation step conducted prior to or after polymerisation, or optionally partly prior to and partly after polymerisation, usually by adding an alkali base, most often an aqueous sodium hydroxide solution. This yields a polymer gel which is comminuted (depending on the type of reactor used, comminution may be conducted concurrently with polymerisation) and dried. Usually, the dried powder thus produced (the “base polymer”) is surface crosslinked (also termed surface “post”crosslinked) by adding further organic or polyvalent cationic crosslinkers to generate a surface layer which is crosslinked to a higher degree than the particle bulk. Most often, aluminium sulphate is being used as polyvalent cationic crosslinker. Applying polyvalent metal cations to superabsorbent particles is sometimes not regarded as surface crosslinking, but termed “surface complexing” or as another form of surface treatment, although it has the same effect of increasing the number of bonds between individual polymer strands at the particle surface and thus increases gel particle stiffness as organic surface crosslinkers have. Organic and polyvalent cation surface crosslinkers can be cumulatively applied, jointly or in any sequence.

[0009] Surface crosslinking leads to a higher crosslinking density close to the surface of each superabsorbent particle. This addresses the problem of “gel blocking”, which means that, with earlier types of superabsorbents, a liquid insult will cause swelling of the outermost layer of particles of a bulk of superabsorbent particles into a practically continuous gel layer, which effectively blocks transport of further amounts of liquid (such as a second insult) to unused superabsorbent below the gel layer. While this is a desired effect in some applications of superabsorbents (for example sealing underwater cables), it leads to undesirable effects when occurring in personal hygiene products. Increasing the stiffness of individual gel particles by surface crosslinking leads to open channels between the individual gel particles within the gel layer and thus facilitates liquids transport through the gel layer. Although surface crosslinking decreases the CRC or other parameters describing the total absorption capacity of a superabsorbent sample, it may well increase the amount of liquid that can be absorbed by hygiene product containing a given amount of superabsorbent.

[0010] Frederic L. Buchholz und Andrew T. Graham (Eds.) in: „Modern Superabsorbent Polymer Technology", J. Wiley & Sons, New York, U.S.A. / Wiley-VCH, Weinheim, Germany, 1997, ISBN 0-471-19411-5, give a comprehensive overview over superabsorbents and processes for producing superabsorbents.

[0011] When superabsorbents are used in the hygiene sector, they are exposed to bodily fluids such as urine or menses. Such bodily fluids always contain malodorous components such as amines, fatty acids and other organic components which are responsible for 230855W001

[0012] 3 unpleasant body odors. A further problem with such hygiene products is that the bodily fluids remain in the hygiene product for a certain time until the hygiene product is disposed of, and bacterial degradation of nitrogenous compounds present in the absorbed bodily fluids, an example being urea in urine, gives rise to ammonia or else other amines which likewise lead to a noticeable odor nuisance. Since correspondingly frequent changing of the hygiene product leads to an appreciable inconvenience and also cost for the user or his or her care persons, hygiene products where this odor nuisance is avoided are of advantage.

[0013] Various measures to avoid the odor nuisance are known. Odors can be masked by perfumes; the ammonia which results or amines can be removed by absorption or reaction, and the microbial degradation can be inhibited by means of biocides or urease inhibitors for example. These measures can be applied to the superabsorbent on the one hand and to the hygiene article on the other.

[0014] For instance, EP 1 358 894 Al teaches hygiene articles which include superabsorbent foam and may include a series of odor-preventing additives, in particular anhydride groups, acid groups, cyclodextrins, biocides such as triclosan, surfactants having an HLB value of less than 11, absorbents such as zeolites, clay, activated carbon, silica or activated alumina, micro-organisms which act as antagonists to undesirable odor-forming micro-organisms, pH buffers or chelating agents. WO 03 / 002 623 Al, WO 03 / 028 778 A2 or WO 03 / 076 514 A2 feature a comprehensive overview of existing measures for avoiding unpleasant odors.

[0015] WO 01 / 32226A1 teaches an odor-control hygiene product that comprises superabsorbent in an absorbing intermediate layer and also has an alkali neutralising agent evenly distributed in that absorbing intermediate layer that may be selected from a number of organic acids. WO 2007 / 104 641 A2 discloses superabsorbents having improved smellinhibition by addition of keto acids. WO 2009 / 101060 Al recommends using a plant preparation produced of ginkgo, willow, meadow sweet, except its leaves, Notopterygii rhizoma, Arctostaphy / os uva-ursiox Potentilla erecta. WO 03 / 104349 Al, WO 2010 / 052182 Al and WO 2010 / 130667 A2 recommend using of tannins for odor control in superabsorbents. That last-named publication also lists some carboxylic acids as examples for antimicrobial additives, while EP 0202127 A2 also lists a number of carboxylic acids as skin pH control agents in a disposable diaper.

[0016] WO 2010 / 130666 A2 discloses the use of glucose oxidase to control odors in superabsorbents. W02011 / 023560 discloses odor-control superabsorbents comprising metal peroxides, hyperoxides or ozonides. WO 2013 / 182469 A2 teaches the use of N-[Dia- minophosphinyl]-4-fluorobenzamide (common name “flurofamide”) as odor-control 230855W001

[0017] 4 agent in superabsorbents and WO 2014 / 095435 Al teaches the use of 1,10-decandiol for the same purpose.

[0018] WO 2008 / 123 606 Al (EP2 060 535 Al) discloses a specific type of activated carbon, in particular porous carbon material obtained by carbonising organic material, in particular rice husk, in an inert atmosphere, then treating with alkali or acid to remove silicon- containing components and the activating by e.g. treatment with steam. The obtained activated carbon has a trimodal pore radius distribution, showing micro-, meso- and macropores, contrasting typical known activated carbons that essentially have only micropores. WO 2010 / 013 785 Al (EP 2 308 591 Al) relates the use of activated carbon of this type for absorbing a range of harmful components after oral administration to ill humans. WO 2017 / 146 044 Al (EP 3 421 425 Al) describes a method of making this material with a bulk density in the range of 0.2 to 0.4 g / cm3and a cumulative pore volume of pores in the range of 0.005 to 5 pm of 0.4 to 1.2 cm3 / g. Sony Group Corporation, 1-7-1 Konan, Minato-ku, Tokyo 108-0075, Japan, commercially offers its Triporous™ activated carbon, reportedly made by this process (https: / / www.sony.com / en / Sonylnfo / triporous / technology.html, visited 30thSept. 2024) that contains a mix of 2-nm micropores, 2 to 50-nm mesopores, and approximately 1- / 7 m macropores.

[0019] Odor control is a property of a superabsorbent that is hard to assess by a simple laboratory test. Odor-causing components in a hygiene product are to a large extent due to the action of micro-organisms on body exudates, thereby producing a range of malodorous components. Testing this in reality in a laboratory first of all requires a laboratory that is equipped to handle the micro-organisms at issue, which are partly classified as bio-hazards. Further, it would require analytical equipment capable of measuring the malodorous substances at issue which partly are malodorous at an extremely low concentration. This is to some extent also specific on the individual person and the microorganism population it hosts. Therefore, simplified tests have to be applied to assess odor control, most having some disadvantage, e.g. focussing only on ammonia generation and therefore possibly missing out on other components. Tests that can assess odor control of superabsorbents without using micro-organisms are highly desirable. Gunnar Hall, Susanne Alenljung and Ulla Forsgren-Brusk, J. Wound Ostomy Continence Nurs. 2017; 44(3) 269-276 report the identification of key odorants in used disposable absorbent incontinence products, finding 28 volatile compounds responsible for malo- dour, of which 26 could be identified. 9 of these 28 were particularly responsible for malodour. The 26 identified compounds can be classified into aldehydes (6); amines (1); aromatics (3); isothiocyanates, (1); heterocyclics (2); ketones (6); sulfur compounds (6); and terpenes (1). Frida Ryttsen, Sofia Lafqvist, Torun Wall, Ulla Forsgren- Brusk and Peter Earsson, J. Wound Ostomy Continence Nurs. 2019; 46(6) 519-523 230855W001

[0020] 5 describe a laboratory method using headspace chromatography of the gas phase over a sample of incontinence products in contact with synthetic urine inoculated a mixture of four bacteria strains. The inhibitory effects of low pH, ethylenediaminetetraacetic acid (EDTA), and activated carbon were then measured. One of their results was that activated carbon significantly reduced the formation of diacetyl, dimethyldisulfide, guaiacol, and 3-methylbutanal. This work was the basis for the yet more simplified test described below.

[0021] Despite the advanced state of the art as outlined in the cited prior art, there still is a need for superabsorbents exhibiting improved odor control and for processes for their production. It is also desired that any such odor-control means does not impair the superabsorbent’s absorption properties. It is an object of this invention to find such a superabsorbent and process.

[0022] This object has been solved by a superabsorbent comprising activated carbon having a trimodal pore radius distribution. Further, a process for its production has been found. Yet further, products for absorbing water that comprise that superabsorbent have been found, as well as a process for their production.

[0023] Activated carbon is well known and a huge number of active carbons of different properties are commercially available. Activated carbons are mainly used adsorbents and absorbents for unwanted substances in purification processes. Activated carbons are porous solids, typically particulate solids, mainly consisting of carbon components or pure carbon. Activated carbon is typically made by carbonising organic material, generally by heat-treating organic material to decompose and remove any non-carbon material. This is generally done in the absence of oxygen, e.g. under an inert gas atmosphere, vacuum or under another means of exclusion of any supply of oxygen-containing gases such as air. The properties of activated carbon are determined by the source of material and the carbonisation conditions and can be further influenced by after-treatments such as a dedicated specific activation, for example by treatment with steam, acids, bases, oxygen or other reactive compounds hat chemically modify the carbon surface. All of this is known.

[0024] One important feature to characterise porous substances is their surface. This surface is mainly contained in pores and not the external surface of the particles. The most- used method to determine the surface is the “BET” method (originally described by S. Brunauer, P.H. Emmet and E. Teller in J.Am.Chem.Soc. 60 (2), 1938, 309-319) based on adsorption isotherms, typically measured using nitrogen, and total surface therefore is in most cases reported as the “BET surface” in m2 / g of a porous substance. Another important feature to characterise porous substances is their pore volume, typically 230855W001

[0025] 6 reported in ml / g. The most common method to measure pore volume is mercury intrusion (also referred to “mercury pressure” or “MP” method). The pores of porous substances do not necessarily have completely random diameters, rather they have pores in specific size ranges. The mercury intrusion method not only allows to determine the total pore volume, but - by steadily increasing the mercury pressure and thus making mercury intrude into smaller and smaller pores - also to determine the diameter of the pores that are filled with mercury at a specific pressure. This also allows plotting the pore volume in pores of a certain diameter vs. the pore diameter. These plots show the pore radius distribution of the substance. A substance having two maxima in this plot, i.e. having a set of small and one of large pores, is said to have a “bimodal” pore radius distribution. A “trimodal” pore radius distribution is one showing three maxima in that plot. All of this is known.

[0026] The “trimodal” pore radius distribution according to this invention preferably means that the activated carbon has pores in the range of up to 2 nm diameter, (“micropores”), in the range of 2 to 50 nm (“mesopores”) and in the range of 0.5 to 5 pm (“macropores”). Further, the activated carbon to be used in this invention, as such, preferably has a bulk density in the range of 0.2 to 0.4 g / cm3and a cumulative pore volume of pores in the range of 0.005 to 5 pm of 0.4 to 1.2 cm3 / g.

[0027] As said, activated carbons to be used in this invention and methods of making them are known to the expert. One method of making them is for example described in EP 3 421 425 Al. One activated carbon suited for use in the present invention is the activated carbon commercially available as Triporous™ from the Sony Group Corporation.

[0028] For simplicity, “activated carbon” in the following refers to the activated carbon having the trimodal pore radius distribution and preferably the other properties stated above, unless specifically stated otherwise e.g. by denoting the activated carbon or its use in superabsorbents as “conventional” or as “prior art”.

[0029] The activated carbon is in particulate form. Often, the activated carbon will be ground and classified at some stage during its production since activated carbons often have millimeter-sized particles after carbonisation or activation. While it is not strictly necessary that the superabsorbent particles and the activated carbon particles in the superabsorbent of the invention have exactly the same average particle size or the same particle size distribution, the same boundary conditions apply to all particles in a superabsorbent: Too small particles will reduce the superabsorbent’s permeability - activated carbon far less so than superabsorbent, however, - and too large particles will be felt in a hygiene article. Superabsorbent particles below 100 pm or above 850 pm diameter are therefore typically avoided in a superabsorbent. For activated carbon, the onset 230855W001

[0030] 7 of dust handling issues in the specific available equipment is the more important lower particle size limit than permeability and an expert will choose that lower limit accordingly. Overall, it is preferable that the particle size of the activated carbon is generally in the particle size range of the superabsorbent particles as described below in more detail, although the activated carbon may also have smaller particles, in particular below 100 pm. A typical useful size range of the activated carbon is for example 75 - 850 pm (20-200 mesh).

[0031] The specific amount of activated carbon to be added according to the invention is chosen to impart the desired odor-control effect. A superabsorbent that, on itself, shows less odor-formation (as non-limiting example an “acidic” superabsorbent having a comparatively lower degree of neutralisation (described below) than other superabsorbents) needs less activated carbon. Higher amounts of activated carbon than stated below may be necessary in some non-standard cases to impart even higher odor control effect, if so desired. The amounts above are sufficient to impart the desired odorcontrol effect in standard cases such as in personal hygiene products comprising superabsorbent that are used to absorb body fluids. It is obvious that odor control beyond the time at which personal hygiene products have to be changed for capacity reasons is typically not necessary, but of course it is possible to add higher amounts of activated carbon. Lower amounts than those stated above may be sufficient in other non-standard cases where less odor-control effect is necessary. Generally, it will be preferable to keep the amount of activated carbon high enough to achieve the desired odor-control effect, but low enough to avoid any undesired side effect or cause unnecessary cost.

[0032] While conventional activated carbons are known as odor control agents in superabsorbents, one problem associated with that use is that any activated carbon will either appear as black spots in the generally white superabsorbent or will make the superabsorbent as a whole look grey. Either will be visible in a typical modern hygiene product having thin top- or backsheets. This will be perfectly acceptable in a professional-care environment where the plain technical features of the hygiene product are all that counts but will deter many private consumers who will prefer a perfectly white or purposefully decorated hygiene product especially over a greyish one. It is therefore an advantage of this invention that less of the activated carbon to be used according to the invention will be needed to absorb odors as efficiently as convential activated carbons may only achieve at higher concentrations.

[0033] The superabsorbent of this invention generally comprises the activated carbon having the trimodal pore radius distribution in an amount of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.3 wt.% and generally at most 5 wt.%, preferably at most 4 wt.% and more preferably at most 3 wt.%, for example at most 2 wt.%, at 230855W001

[0034] 8 most 1.5 wt.% and at most 1.0 wt.%, all based on the total weight of material.

[0035] The superabsorbent in the present invention is a superabsorbent capable of absorbing and retaining amounts of water equivalent to many times its own weight under a certain pressure. Preferably, the superabsorbent is a crosslinked polymer based on partially neutralised acrylic acid and more preferably it is surface postcrosslinked. A “superabsorbent” can also be a mixture of chemically different individual superabsorbents in that it is not so much the chemical composition which matters as the superabsorbing properties.

[0036] Processes for producing superabsorbents, including surface-postcrosslinked superabsorbents, are known. Most synthetic superabsorbents on the market today are obtained by a process comprising polymerisation of a monomer solution comprising: a) at least one ethy lenically unsaturated monomer which bears acid groups and may be at least partly neutralised, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenica lly unsaturated monomers copolymerisable with the monomers specified under a) and e) optionally one or more water-soluble polymers.

[0037] The process typically further comprises drying, grinding, classifying and / or surface postcrosslinking the resulting polymer.

[0038] The monomers a) are preferably water-soluble, i.e. 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.

[0039] Suitable monomers a) are, for example, ethylenica lly unsaturated carboxylic acids, such as acrylic acid, methacrylic acid and itaconic acid. Particularly preferred monomers are acrylic acid and methacrylic acid. Very particular preference is given to acrylic acid.

[0040] Further suitable monomers a) are, for example, ethy lenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

[0041] Impurities can have a considerable influence on the polymerisation. The raw materials used should therefore have a maximum purity. It is therefore often advantageous to specially purify the monomers a). Suitable purification processes are described, for example, in WO 2002 / 055469 Al, WO 2003 / 078378 Al and WO 2004 / 035514 Al. A 230855W001

[0042] 9 suitable monomer a) is, for example, acrylic acid purified according to WO 2004 / 035514 Al comprising 99.8460% by weight of acrylic acid, 0.0950% by weight of acetic acid, 0.0332% by weight of water, 0.0203% by weight of propionic acid, 0.0001% by weight of furfurals, 0.0001% by weight of maleic anhydride, 0.0003% by weight of diacrylic acid and 0.0050% by weight of hydroquinone monomethyl ether.

[0043] The proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, more preferably at least 90 mol%, most preferably at least 95 mol%.

[0044] The monomers a) typically comprise polymerisation inhibitors, preferably hydroquinone half ethers, as storage stabilisers.

[0045] The monomer solution comprises preferably up to 250 ppm by weight, preferably at most 130 ppm by weight, more preferably at most 70 ppm by weight, preferably at least 10 ppm by weight, more preferably at least 30 ppm by weight, especially around 50 ppm by weight, of hydroquinone half ether, based in each case on the unneutralised monomer a). For example, the monomer solution can be prepared by using an ethylenically unsaturated monomer bearing acid groups with an appropriate content of hydroquinone half ether.

[0046] Preferred hydroquinone half ethers are hydroquinone monomethyl ether (MEHQ) and / or alpha-tocopherol (vitamin E).

[0047] Suitable crosslinkers b) are compounds having at least two groups suitable for crosslinking. Such groups are, for example, ethylenically unsaturated groups which can be polymerised free-radica lly into the polymer chain, and functional groups which can form covalent bonds with the acid groups of the monomer a). In addition, polyvalent metal salts which can form coordinate bonds with at least two acid groups of the monomer a) are also suitable as crosslinkers b).

[0048] Crosslinkers b) are preferably compounds having at least two polymerisable groups which can be polymerised free-radically into the polymer network. 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 0 530 438 Al, di- and triacrylates, as described in EP 0 547 847 Al, EP 0 559 476 Al, EP 0 632 068 Al, WO 93 / 21237 Al, WO 2003 / 104299 Al, WO 2003 / 104300 Al, WO 2003 / 104301 Al and DE 103 31 450 Al, mixed acrylates which, as well as acrylate groups, comprise further ethylenically unsaturated groups, as described in DE 103 31 456 Al and DE 103 55 230855W001

[0049] 10

[0050] 401 Al, or crosslinker mixtures, as described, for example, in DE 195 43 368 Al, DE 196 46 484 Al, WO 90 / 15830 Al and WO 2002 / 032962 A2.

[0051] Preferred crosslinkers b) are pentaerythrityl triallyl ether, tetraalloxyethane, methylenebismethacrylamide, 15-tuply ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate and triallylamine.

[0052] Very particularly preferred crosslinkers b) are the polyethoxylated and / or propoxylated glycerols which have been esterified with acrylic acid or methacrylic acid to give di- or triacrylates, as described, for example, in WO 2003 / 104301 Al. Di- and / or triacrylates of 3- to 10-tuply ethoxylated glycerol are particularly advantageous. Very particular preference is given to di- or triacrylates of 1- to 5-tuply ethoxylated and / or propoxylated glycerol. Most preferred are the triacrylates of 3- to 5-tuply ethoxylated and / or propoxylated glycerol, especially the triacrylate of 3-tuply ethoxylated glycerol.

[0053] The amount of crosslinker b) is preferably from 0.05 to 1.5% by weight, more preferably from 0.1 to 1% by weight, most preferably from 0.3 to 0.6% by weight, based in each case on monomer a). With rising crosslinker content, the centrifuge retention capacity (CRC) falls and the absorption under a pressure of 21.0 g / cm2(AUL 0.3 psi) passes through a maximum.

[0054] The initiators c) may be all compounds which generate free radicals under the polymerisation conditions, for example thermal initiators, redox initiators, photoinitiators. Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascor- bic acid, sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite. Preference is given to using mixtures of thermal initiators and redox initiators, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid. The reducing component used is, however, 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. Such mixtures are obtainable as Bruggolite® FF6 and Bruggolite® FF7 (Bruggemann Chemicals; Heilbronn; Germany).

[0055] Ethylenically unsaturated monomers d) copolymerisable with the ethylenically unsaturated monomers a) bearing acid groups are, for example, acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate.

[0056] The water-soluble polymers e) used may be polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or 230855W001

[0057] 11 hydroxyethylcellulose, gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified cellulose.

[0058] Typically, an aqueous monomer solution is used. The water content of the monomer solution is preferably from 40 to 75% by weight, more preferably from 45 to 70% by weight, most preferably from 50 to 65% by weight. It is also possible to use monomer suspensions, i.e. monomer solutions with excess monomer a), for example sodium acrylate. With rising water content, the energy requirement in the subsequent drying rises, and, with falling water content, the heat of polymerisation can only be removed inadequately.

[0059] For optimal action, the preferred polymerisation inhibitors require dissolved oxygen. Before the polymerisation, the monomer solution can therefore be freed of dissolved oxygen, and the polymerisation inhibitor present in the monomer solution can be deactivated, by inertisation. A comfortable method for inertisation is passing a flow of an inert gas through the monomer solution, preferably nitrogen or carbon dioxide. The oxygen content of the monomer solution is preferably lowered before the polymerisation to less than 1 ppm by weight, more preferably to less than 0.5 ppm by weight, most preferably to less than 0.1 ppm by weight.

[0060] Suitable reactors are, for example, kneading reactors or belt reactors. In the kneader, the polymer gel formed in the polymerisation of an aqueous monomer solution or suspension is comminuted continuously by, for example, contrarotatory stirrer shafts, as described in WO 2001 / 038402 Al. Polymerisation on a belt is described, for example, in DE 38 25 366 Al and US 6,241,928. Polymerisation in a belt reactor forms a polymer gel, which has to be comminuted in a further process step, for example in an extruder or kneader.

[0061] However, it is also possible to generate droplets of an aqueous monomer solution and to polymerise the droplets obtained in a heated carrier gas stream. This allows the process steps of polymerisation and drying to be combined, as described in WO 2008 / 040715 A2 and WO 2008 / 052971 Al.

[0062] The acid groups of the resulting polymer gels have typically been partially neutralised. Neutralisation is preferably carried out at the monomer stage. This is typically done by mixing in the neutralising agent as an aqueous solution or preferably also as a solid. The degree of neutralisation is preferably from 25 to 95 mol%, more preferably from 30 to 80 mol%, most preferably from 40 to 75 mol%, for which the customary neutralising agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal hydrogencarbonates and also mixtures thereof. Instead of 230855W001

[0063] 12 alkali metal salts, it is also possible to use ammonium salts. Particularly preferred alkali metals are sodium and potassium, but very particular preference is given to sodium hydroxide, sodium carbonate or sodium hydrogencarbonate and also mixtures thereof.

[0064] However, it is also possible to carry out neutralisation after the polymerisation, at the stage of the polymer gel formed in the polymerisation. It is also possible to neutralise up to 40 mol%, preferably from 10 to 30 mol% and more preferably from 15 to 25 mol% of the acid groups before the polymerisation by adding a portion of the neutralising agent actually to the monomer solution and setting the desired final degree of neutralisation only after the polymerisation, at the polymer gel stage. When the polymer gel is neutralised at least partly after the polymerisation, the polymer gel is preferably comminuted mechanically, for example by means of an extruder, in which case the neutralising agent can be sprayed, sprinkled or poured on and then carefully mixed in. To this end, the gel mass obtained can be repeatedly extruded for homogenisation.

[0065] The polymer hydrogel is then typically dried with a belt dryer until the residual moisture content is preferably from 0.5 to 15% by weight, more preferably from 1 to 10% by weight, most preferably from 2 to 8% by weight. In the case of too high a residual moisture content, the dried polymer gel has too low a glass transition temperature Tg and can be processed further only with difficulty. In the case of too low a residual moisture content, the dried polymer gel is too brittle and, in the subsequent comminution steps, undesirably large amounts of polymer particles with an excessively low particle size are obtained (fines). The solids content of the gel before the drying is preferably from 25 to 90% by weight, more preferably from 35 to 70% by weight, most preferably from 40 to 60% by weight. Optionally, it is, however, also possible to use a fluidised bed dryer or a paddle dryer for the drying operation.

[0066] The dried hydrogel (which is no longer a gel (even though often still called that) but a dry polymer having superabsorbing properties, which comes within the term “superabsorbent”) is typically ground and sieved to produce a particulate superabsorbent “base polymer” of the desired particle size distribution. Useful grinding apparatus typically including single or multistage roll mills, pin mills, hammer mills, cutting mills or swing mills.

[0067] The mean particle size of the polymer particles collected as the product fraction is preferably at least 200 pm, more preferably from 250 to 600 pm, very particularly from 300 to 500 pm.

[0068] For economic reasons, it is desirable to select conditions of grinding and other steps of mechanical treatment to achieve a proportion of particles with a particle size of at least 230855W001

[0069] 13

[0070] 150 pm of preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 98% by weight.

[0071] Polymer particles with too small a particle size lower the permeability (SFC). The proportion of excessively small polymer particles (fines) should therefore be small.

[0072] Excessively small polymer particles are therefore typically removed and recycled into the process. This is preferably done before, during or immediately after the polymerisation, i.e. before the drying of the polymer gel. The excessively small polymer particles can be moistened with water and / or aqueous surfactant before or during the recycling.

[0073] It is also possible to remove excessively small polymer particles in later process steps, for example after the surface postcrosslinking or another coating step. In this case, the excessively small polymer particles recycled are surface postcrosslinked or coated in another way, for example with fumed silica.

[0074] When a kneading reactor is used for the polymerisation, the excessively small polymer particles are preferably added during the last third of the polymerisation.

[0075] When the excessively small polymer particles are added at a very early stage, for example actually to the monomer solution, this lowers the centrifuge retention capacity (CRC) of the resulting water-absorbing polymer particles. However, this can be compensated, for example, by adjusting the amount of crosslinker b) used.

[0076] When the excessively small polymer particles are added at a very late stage, for example not until within an apparatus connected downstream of the polymerisation reactor, for example an extruder, the excessively small polymer particles can be incorporated into the resulting polymer gel only with difficulty. Excessively small polymer particles which have been insufficiently incorporated, however, become detached again from the dried polymer gel during the grinding, and are therefore removed again in the classification and increase the amount of excessively small polymer particles to be recycled.

[0077] For economic reasons, it is desirable to select conditions of grinding and other steps of mechanical treatment to achieve a proportion of particles with a particle size of at most 850 pm of preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 98% by weight.

[0078] Advantageously, the proportion of polymer particles with a particle size of at most 600 pm is preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 98% by weight. 230855W001

[0079] 14

[0080] Polymer particles with too great a particle size lower the swell rate. The proportion of excessively large polymer particles should therefore likewise be small.

[0081] Excessively large polymer particles are therefore typically removed and recycled into the grinding of the dried polymer gel.

[0082] To further improve the properties, the base polymer particles are optionally surface postcrosslinked. Suitable surface postcrosslinkers are compounds which comprise groups which can form covalent bonds with at least two carboxylate groups of the polymer particles. Suitable compounds are, for example, polyfunctional amines, polyfunctional amido amines, polyfunctional epoxides, as described in EP 0 083 022 A2, EP 0 543 303 Al and EP 0 937 736 A2, di- or polyfunctional alcohols, as described in DE 33 14 019 Al, DE 35 23 617 Al and EP 0 450 922 A2, or p-hydroxyalkylamides, as described in DE 102 04 938 Al and US 6,239,230.

[0083] Additionally described as suitable surface postcrosslinkers are cyclic carbonates in DE 40 20 780 Cl, 2-oxazolidone and its derivatives, such as 2-hydroxyethyl-2-oxazolidone in DE 198 07 502 Al, bis- and poly-2-oxazolidinones in DE 198 07 992 Cl, 2-oxotetrahy- dro-l,3-oxazine and its derivatives in DE 198 54 573 Al, N-acyl-2-oxazolidones in DE 198 54 574 Al, cyclic ureas in DE 102 04 937 Al, bicyclic amide acetals in DE 103 34 584 Al, oxetanes and cyclic ureas in EP 1 199 327 A2 and morpholine-2, 3-dione and its derivatives in WO 2003 / 031482 Al.

[0084] Preferred surface postcrosslinkers are glycerol, ethylene carbonate, ethylene glycol di- glycidyl ether, reaction products of polyamides with epichlorohydrin, and mixtures of propylene glycol and 1,4-butanediol.

[0085] Very particularly preferred surface postcrosslinkers are 2-hydroxyethyloxazolidin-2-one, oxazolidin-2-one and 1,3-propanediol.

[0086] In addition, it is also possible to use surface postcrosslinkers which comprise additional polymerisable ethy lenically unsaturated groups, as described in DE 37 13 601 Al.

[0087] The amount of surface postcrosslinker is preferably from 0.001 to 2% by weight, more preferably from 0.02 to 1% by weight, most preferably from 0.05 to 0.2% by weight, based in each case on the polymer particles.

[0088] The surface postcrosslinking is typically performed in such a way that a solution of the surface postcrosslinker is sprayed onto the dried polymer particles. After the spraying, 230855W001

[0089] 15 the polymer particles coated with surface postcrosslinker are dried thermally, and the surface postcrosslinking reaction can take place either before or during the drying.

[0090] The spraying of a solution of the surface postcrosslinker is preferably performed in mixers with moving mixing tools, such as screw mixers, disk mixers and paddle mixers. Particular preference is given to horizontal mixers such as paddle mixers, very particular preference to vertical mixers. The distinction between horizontal mixers and vertical mixers is made by the position of the mixing shaft, i.e. horizontal mixers have a horizontally mounted mixing shaft and vertical mixers a vertically mounted mixing shaft. Suitable mixers are, for example, horizontal Pflugschar® mixers (Gebr. Lbdige Maschinenbau GmbH; Paderborn; Germany), Vrieco-Nauta Continuous Mixers (Hosokawa Micron BV; Doetinchem; the Netherlands), Processall Mixmill Mixers (Processall Incorporated; Cincinnati; US) and Schugi Flexomix® (Hosokawa Micron BV; Doetinchem; the Netherlands). However, it is also possible to spray the surface postcrosslinker solution into a fluidised bed of base polymer.

[0091] The surface postcrosslinkers are typically used in the form of an aqueous solution. The penetration depth of the surface postcrosslinker into the polymer particles can be adjusted via the content of nonaqueous solvent and total amount of solvent.

[0092] When exclusively water is used as the solvent, a surfactant is advantageously added. This improves the wetting behavior and reduces the tendency to form lumps. However, preference is given to using solvent mixtures, for example isopropanol / water, 1,3 pro- panediol / water and propylene glycol / water, where the mixing ratio in terms of mass is preferably from 20:80 to 40:60.

[0093] The thermal drying is preferably carried out in contact dryers, more preferably paddle dryers, most preferably disk dryers. Suitable dryers are, for example, Hosokawa Bepex® Horizontal Paddle Dryers (Hosokawa Micron GmbH; Leingarten; Germany), Hosokawa Bepex® Disc Dryers (Hosokawa Micron GmbH; Leingarten; Germany) and Nara Paddle Dryers (NARA Machinery Europe; Frechen; Germany). Moreover, it is also possible to use fluidised bed dryers.

[0094] The drying can be effected in the mixer itself, by heating the jacket or blowing in warm air. Equally suitable is a downstream dryer, for example a shelf dryer, a rotary tube oven or a heatable screw. It is particularly advantageous to mix and dry in a fluidised bed dryer.

[0095] Preferred drying temperatures are in the range from 100 to 250° C, preferably from 120 to 220° C, more preferably from 130 to 210° C, most preferably from 150 to 200° C. 230855W001

[0096] 16

[0097] 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 typically at most 60 minutes.

[0098] Quite usually, but not necessarily, water-soluble polyvalent metal salts comprise bi- or more highly valent (“polyvalent”) metal cations capable of reacting with the acid groups of the polymer to form complexes are added. Examples of polyvalent cations are or metal cations such as Mg2+, Ca2+, Al3+, Sc3+, Ti4+, Mn2+, Fe2+ / 3+, Co2+, Ni2+, Cu2+, Zn2+, Y3+, Zr4+, La3+, Ce4+, Hf4+, and Au3+. Preferred metal cations are Mg2+, Ca2+, Al3+, Ti4+, Zr4+and La3+, and particularly preferred metal cations are Al3+, Ti4+and Zr4+. The metal cations can be used not only alone but also in admixture with each other. Of the metal cations mentioned, any metal salt can be used that has sufficient solubility in the solvent to be used. Metal salts with weakly complexing anions such as for example chloride, nitrate and sulphate, hydrogen sulphate, carbonate, hydrogen carbonate, nitrate, phosphate, hydrogen phosphate, dihydrogen phosphate and carboxylate, such as acetate and lactate, are particularly suitable. It is particularly preferred to use aluminum sulfate.

[0099] The treatment of the superabsorbent polymer with solution of a polyvalent cation is car-ried out in the same way as that with surface postcrosslinker, including the selective drying step. Useful solvents for the metal salts include water, alcohols, DM F, DMSO and also mixtures thereof. Particular preference is given to water and water-al- cohol mixtures such as for example water-methanol, water-1, 2-propanediol, water-2- propanol and water-1, 3-propanediol.

[0100] In a preferred embodiment of the present invention, the complexing agent is applied to a superabsorbent that is surface crosslinked, or concurrently with surface crosslinking, or partly simultaneously and partly after surface crosslinking. For example, a suitable method of applying a complexing agent is applying a polyvalent metal cation such as Al3+concurrently with a surface crosslinker.

[0101] The surface-crosslinked superabsorbent produced using the process of the instant inventions is optionally ground and / or sieved in a conventional manner. Grinding is typically not necessary, but the sieving out of agglomerates which are formed or undersize is usually advisable to set the desired particle size distribution for the product. Agglomerates and undersize are either discarded or preferably returned into the process in a conventional manner and at a suitable point; agglomerates after comminution.

[0102] To improve some properties such as brittleness, the surface postcrosslinked polymer particles may be moistened. Moistening is carried out preferably at from 30 to 80° C, 230855W001

[0103] 17 more preferably at from 35 to 70° C and most preferably at from 40 to 60° C. At excessively low temperatures, the water-absorbing polymer particles tend to form lumps, and, at higher temperatures, water already evaporates noticeably. The amount of water used for subsequent moistening is preferably from 1 to 10% by weight, more preferably from 2 to 8% by weight and most preferably from 3 to 5% by weight. The subsequent moistening increases the mechanical stability of the polymer particles and reduces their tendency to static charging.

[0104] If the superabsorbent is produced by another method, some of the process steps described above may be unnecessary. For example, emulsion or droplet polymerisation produces particulate superabsorbents that may not need grinding or classification or surface crosslinking. Further, droplet polymerisation is typically performed in reactors that also dry the product due to the gas streams typically necessary to conduct droplet polymerisation, so a separate drying step may not be necessary. The method of producing the superabsorbent plays no role in this invention and any particulate superabsorbent produced in any manner may be treated according to this invention.

[0105] After any drying, curing or other heating step, it may be advantageous but not absolutely necessary to cool the product. Cooling can be carried out continuously or discontinuously, conveniently by conveying the product continuously into a cooler downstream of the dryer. Any apparatus known for removing heat from pulverulent solids can be used, in particular any apparatus mentioned above as a drying apparatus, provided it is supplied not with a heating medium but with a cooling medium such as for example with cooling water, so that heat is not introduced into the superabsorbent via the walls and, depending on the design, also via the stirrer elements or other heat-exchanging surfaces, but removed from the superabsorbent. Preference is given to the use of coolers in which the product is agitated, i.e., cooled mixers, for example shovel coolers, disk coolers or paddle coolers, for example Nara® or Bepex® coolers. The superabsorbent can also be cooled in a fluidised bed by blowing a cooled gas such as cold air into it.

[0106] The cooling conditions are set such that a superabsorbent having the temperature desired for further processing is obtained. Typically, the average residence time in the cooler will be in general at least 1 minute, preferably at least 3 minutes and more preferably at least 5 minutes and also in general not more than 6 hours, preferably 2 hours and more preferably not more than 1 hour, and cooling performance will be determined such 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 also generally not more than 100° C, preferably not more than 80° C and more preferably not more than 60° C.

[0107] According to this invention, activated carbon is added to the superabsorbent. In the simplest and most preferred form, activated carbon is added as a substance to the 230855W001

[0108] 18 superabsorbent at any stage of the process for its production. One embodiment of the invention is adding activated carbon to the monomer solution. Another embodiment is adding activated carbon after polymerisation, for example prior to, during or after a neutralisation step following polymerisation. It is generally preferred, however, to add activated carbon after drying the polymerised hydrogel and if the superabsorbent is surface-postcrosslinked, after the surface-postcrosslinking step.

[0109] Activated carbon may be dry-mixed, as a powder or during a joint comminution step, with the superabsorbent. In most cases, however, it is more convenient to contact the superabsorbent with a slurry or dispersion of activated carbon in a dispersion medium. The slurry or dispersion may, however, comprise other desired components such as for example, but not limited to other additives known for superabsorbents.

[0110] The solid, slurry or dispersion can be added in any known way. Spraying a slurry or dispersion onto the superabsorbent is preferred. It is preferred to do this while mixing the superabsorbent, although it is possible to mix after spraying. The slurry or dispersion may be added in the same type of apparatus that is used for contacting the superabsorbent with the surface crosslinking solution. In a convenient way, the slurry or dispersion is added by spraying on the superabsorbent in a final cooler.

[0111] Preferably, the slurry or dispersion is added concurrently with any other chosen additive following any surface crosslinking or complexing step. In this context, “concurrently” means “in the very same piece of equipment” but does not necessarily mean “through the very same nozzle or set of nozzles”.

[0112] It is preferred to add the activated carbon without any subsequent heating. In other words, it is preferred to add the activated carbon after any drying, curing or other heating step in which the temperature of the superabsorbent is purposefully increased.

[0113] Useful dispersants for activated carbon include those that disperse enough activated carbon to add to the superabsorbent at total dispersant amounts that do not negatively influence the process. Examples of useful dispersants are polar solvents, water or dimethyl sulfoxide (“DMSO”), alcohols, DMF, or mixtures thereof, including, but not limited to water-alcohol mixtures such as water-methanol, water-1, 2-propanediol, water- 2-propanol, water-1, 2-propanediol and water-1, 3-propanediol, propylene glycol / water and water / polyetherols such as polyethylene glycol. A preferred polyethylene glycol is the one generally known as PEG-400, a widely used and commercially available polyethylene glycol having an average molecular mass of 400 g / mol. The mixing ratio of water to the co-dispersant in terms of mass is preferably from 20:80 to 40:60. 230855W001

[0114] 19

[0115] The concentration of the slurry or dispersion is not particularly critical. The main criterion for the concentration is to have a slurry or dispersion that can be processed in the chosen equipment. When spraying the slurry or dispersion, the slurry or dispersion needs to be pumpable to and sprayable from the chosen nozzle. It is preferred that the slurry or dispersion essentially consists of activated carbon and dispersant and it is more preferred that it consists of activated carbon and dispersant.

[0116] Optionally, the superabsorbent is provided with further customary additives and auxiliary materials to influence storage or handling properties. Examples thereof are colorations, opaque additions to improve the visibility of swollen gel, which is desirable in some applications, surfactants, de-dusting agents, colour stabilisers, flowability aids, anticaking additives or the like. These additives and auxiliary materials can each be added in separate processing steps, but one convenient method may be to add them to the superabsorbent in the cooler, for example by spraying the superabsorbent with a solution or adding them in finely divided solid or in liquid form, if this cooler provides sufficient mixing quality.

[0117] The inventive water-absorbing polymer particles have a moisture content of typically 0 to 15% by weight, preferably 0.2 to 10% by weight, more preferably 0.5 to 8% by weight, most preferably 1 to 5% by weight, and / or a centrifuge retention capacity (CRC) of typically at least 20 g / g, preferably at least 26 g / g, more preferably at least 28 g / g, most preferably at least 30 g / g, and / or an absorption under a pressure of 49.2 g / cm2(AUL 0.7 psi) of typically at least 12 g / g, preferably at least 16 g / g, more preferably at least 18 g / g, most preferably at least 20 g / g, and / or a saline flow conductivity (SFC) of typically at least 20 ■ 10-7cm3s / g, preferably at least 40 ■ 10-7cm3s / g, more preferably at least 50 ■ 10-7cm3s / g, most preferably at least 60 ■ 10-7cm3s / g.

[0118] The centrifuge retention capacity (CRC) of the water-absorbing polymer particles is typically less than 60 g / g. The absorption under a pressure of 49.2 g / cm2(AUL 0.7 psi) of the water-absorbing polymer particles is typically less than 35 g / g. The saline flow conductivity (SFC) of the water-absorbing polymer particles is typically less than 200 ■ 10-7cm3s / g.

[0119] We have further found water-absorbing products, in particular hygiene articles comprising the superabsorbent of the present invention. Hygiene articles in accordance with the present invention are for example those intended for use in mild or severe incontinence, such as for example inserts for severe or mild incontinence, incontinence briefs, also diapers, training pants for babies and infants or else feminine hygiene articles such as liners, sanitary napkins or tampons. Hygiene articles of this kind are known. The hygiene articles of the present invention differ from known hygiene articles in that 230855W001

[0120] 20 they comprise the superabsorbent of the present invention. We have also found a process for producing water-absorbing products, in particular hygiene articles, this process comprising adding at least one superabsorbent of the present invention to the in the manufacture of the water-absorbing-product in particular hygiene article in question during its manufacture. Processes for producing water-absorbing products, in particular hygiene articles comprising superabsorbent are otherwise known.

[0121] The present invention further provides for the use of the composition of the present invention in training pants for children, shoe inserts and other hygiene articles to absorb bodily fluids. The composition of the present invention can also be used in other technical and industrial fields where liquids, in particular water or aqueous solutions, are absorbed. These fields are for example storage, packaging, transportation (as constituents of packaging material for water- or moisture-sensitive articles, for example for flower transportation, also as protection against mechanical impacts); animal hygiene (in cat litter); food packaging (transportation of fish, fresh meat; absorption of water, blood in fresh fish or meat packs); medicine (wound plasters, water-absorbing material for burn dressings or for other weeping wounds), cosmetics (carrier material for pharmachemicals and medicaments, rheumatic plasters, ultrasonic gel, cooling gel, cosmetic thickeners, sun protection); thickeners for oil-in-water and water-in-oil emulsions; textiles (moisture regulation in textiles, shoe inserts, for evaporative cooling, for example in protective clothing, gloves, headbands); chemical engineering applications (as a catalyst for organic reactions, to immobilise large functional molecules such as enzymes, as adhesion agent in relation to agglomerations, heat storage media, filter aids, hydrophilic component in polymeric laminates, dispersants, superplasticisers); as auxiliaries in powder injection moulding, in building construction and engineering (installation, in loam-based renders, as a vibration-inhibiting medium, auxiliaries in tunnel excavations in water-rich ground, cable sheathing); water treatment, waste treatment, water removal (deicing agents, reusable sandbags); cleaning; agritech (irrigation, retention of melt water and dew deposits, composting additive, protection of forests against fungal / insect infestation, delayed release of active components to plants); for firefighting or for fire protection; coextrusion agents in thermoplastic polymers (for example to hydrophilise multilayered films); production of films and thermoplastic mouldings able to absorb water (for example rain and dew water storage films for agriculture; su- perabsorbent-containing films for keeping fruit and vegetables fresh which are packed in moist films; superabsorbent-polystyrene coextrudates, for example for food packaging such as meat, fish, poultry, fruit and vegetables); or as carrier substance in formulations of active components (pharma, crop protection). 230855W001

[0122] 21

[0123] Test Methods

[0124] The standard test methods referred to as “NWSP” described below are described in: “Nonwovens Standard Procedures”, 2015 edition, published jointly by the Worldwide Strategic 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 115, Cary, North Carolina 27518, U.S.A., www.inda.org). This publication is obtainable both from EDANA and from INDA.

[0125] The measurements should, unless stated otherwise, be carried out at an ambient temperature of 23 ± 2° C and a relative air humidity of 50 ± 10%. The water-absorbing polymer particles are mixed thoroughly before the measurement.

[0126] Saline flow conductivity (“SEC”)

[0127] The saline flow conductivity (SFC) of a swollen gel layer under a pressure of 0.3 psi (2070 Pa) is, as described in EP 0 640 330 Al (page 19, line 13 to page 21, line 35), determined as the gel layer permeability of a swollen gel layer of water-absorbing polymer particles, with modification of the apparatus described in figure 8 in that the glass frit (40) is not used, the plunger (39) consists of the same plastic material as the cylinder (37), and now has 21 bores of equal size distributed homogeneously over the entire contact area. The procedure and evaluation of the measurement remain unchanged from EP 0 640 330 Al. The flow is detected automatically.

[0128] The saline flow conductivity (SFC) is calculated as follows:

[0129] SFC [cm3s / g] = (Fg(t=0)xL0) / (dxAxWP) where Fg(t=O) is the flow of NaCI solution in g / s, which is obtained using a linear regression analysis of the Fg(t) data of the flow determinations by extrapolation to t=0, L0 is the thickness of the gel layer in cm, d is the density of the NaCI solution in g / cm3, A is the area of the gel layer in cm2, and WP is the hydrostatic pressure over the gel layer in dyn / cm2.

[0130] Centrifuge retention capacity (“CRC”)

[0131] The centrifuge retention capacity (CRC) is determined by test method No. NWSP 241.0. R2 (15) “Polyacrylate Superabsorbent Powders — Determination of the Fluid 230855W001

[0132] 22

[0133] Retention Capacity in Saline Solution by Gravimetric Measurement Following Centrifugation”.

[0134] Absorption under a pressure of 21.0 g / cm2(“AUL 0.3 psi”)

[0135] The absorption under a pressure of 49.2 g / cm2(commonly referred to as “AUL 0.3 psi”) is determined by test method No. NWSP 242.0.R2 (15) “Polyacrylate Superabsorbent Powders - Gravimetric Determination of Absorption Against Pressure”.

[0136] Absorption under a pressure of 49.2 g / cm2(“AUL 0.7 psi”)

[0137] The absorption under a pressure of 49.2 g / cm2(commonly referred to as “AUL0.7 psi”) is determined by test method No. NWSP 242.0.R2 (15) “Polyacrylate Superabsorbent Powders - Gravimetric Determination of Absorption Against Pressure”, however, with a pressure setting of 49.2 g / cm2(AUL0.7 psi) instead of 21.0 g / cm2(that corresponds to the AUL0.3 psi).

[0138] Water or Moisture Content

[0139] Water or moisture content is determined by test method No. NWSP 230.0. R2 (15) “Polyacrylate Superabsorbent Powders — Estimation of the Moisture Content as Weight Loss Upon Heating”.

[0140] Odor Inhibition

[0141] Odor control of a superabsorbent comprising an odor-control additive is evaluated by determining the superabsorbent’s ability to retain malodorous compounds in synthetic urine compared to the same superabsorbent without the odor-control additive as a reference. Four substances, namely diacetyl, 3-methylbutanal, dimethyl trisulfide and p- cresole, each one representative for one of four substance groups found to be particularly responsible for malodours in hygiene products, are used in this determination.

[0142] 0.5 g of superabsorbent sample is filled into a 20 mL headspace vial (20 mL screw threaded headspace vials, 22*75 mm, obtained from Restek GmbH, Schaberweg 23, 61348 Bad Homburg, Germany, catalog no. 32082), with 18 mm magnetic screw caps (Restek, catalog no. 23093). 12 mL of synthetic urine were added, consisting of 254 ng / mL diacetyl (CAS 431-03-8), 43 ng / mL 3-methylbutanal (CAS 590-86-3), 122 ng / mL dimethyl trisulfide (“DMTS”)(CAS 3658-80-8) and 1578 ng / mL p-cresole (CAS: 106-44- 5) in 0.9 wt% aqueous NaCI solution (medical saline). 230855W001

[0143] 23

[0144] The sample is annealed for 3h before a coated solid phase micro extraction (SPME) fiber in a protective needle (SPME fiber assembly Carboxen / Polydimethylsiloxane, df 75 m, CAR / PDMS, needle size 24 ga, obtained from Sigma-Aldrich Chemie GmbH, Eschenstrasse 5, 82024 Taufkirchen, Germany, product no.: 57319) is inserted into the headspace vial via autosampler (PAL system with Chronos software obtained from CTC Analytics AG, Industriestrasse 20, 4222 Zwingen, Switzerland). The SPME fiber is extended to 22 mm into the gas phase above the superabsorbent / synthetic urine sample. After 20 min, the fiber is removed and inserted directly into the injector of the gas chromatograph (Agilent 7890 GC, obtained from Agilent Technologies Deutschland GmbH, Hewlett-Packard-Str. 8, 76337 Waldbronn, Germany) for desorption. Desorption is performed at 300° C with a split ratio of 1:20 for 5 min.

[0145] The column is a DB-5ms, 60m length, 0.32mm diameter, 1 pm film thickness, also obtained from Agilent, part no. 123-5563. The oven program is 40° C - 5min - 7° C / min - 120° C - 15° C / min 250° C -10 min and the carrier gas is 1.2 mL / min helium.

[0146] Diacetyl, 3-methylbutanal, dimethyl trisulfide and p-cresole were detected using ms detector (Agilent, 5975) in SIM mode with target and qualifier ions m / z 86 (43), 58 (43), 126 (111) and 107 (108), respectively.

[0147] Analyses are made in triplicate, results are calculated as arithmetic average of the signal areas. Malodor reduction is calculated as:

[0148] Reduction [%] = 1 - (Signal area of SAP with additive / signal area of reference) * 100

[0149] The method is controlled and the evaluation performed using Chemstation software (Agilent).

[0150] Examples

[0151] Experiments were conducted using HySorb® B6600 surface-crosslinked polymer superabsorbent, available from BASF SE, Ludwigshafen, Germany.

[0152] The activated carbons used in the examples were: a: Sulpelco® 31616 activated charcoal carbon adsorbent, obtained from Merck

[0153] KGaA, Darmstadt, Germany (comparison). b: Norit® GCN 3070 activated carbon, obtained from Cabot Norit GmbH, Rheinfelden, Germany (comparison). 230855W001

[0154] 24 c: TriPorous™ obtained from Sony (unwashed; 200 - 500 pm), obtained from Sony Group Corporation, Tokyo, Japan. d: TriPorous™ (washed; <100 pm), obtained from Sony Group Corporation, Tokyo,

[0155] Japan.

[0156] To prepare the samples, 50 g HySorb® B6600 superabsorbent were filled in a 50 mL screw-cap plastic bottle. Activated carbon was added in amounts of 0.5 or 2 wt. % based on the polymer (“bop”. This equals 0.5 and 1.96 wt.% based on the total weight of material). The bottle was closed and premixed by manually turning several times. The bottle was then put in a TURBULA® T 2 F blender (Willy A. Bachofen AG, Muttenz, Switzerland) and mixed at 72 rpm for 5 minutes.

[0157] Samples were then subjected to the Odor Inhibition Test.

[0158] The samples also were tested for their absorption properties. These tests showed no difference to HySorb® B6600 beyond known analytical error margins.

[0159] The following table gives an overview of the samples that were prepared and their behavior in the Odor Inhibition Text.

[0160] * Comparison

[0161] The data show that diacetyl and 3-methylbutanal are harder to remove than DMTS or p-cresole. The data also demonstrate that the superabsorbent of the invention can reduce malodors, especially those associated with these two substances, at least at comparative level to conventional activated carbons even at lower activated carbon 230855W001

[0162] 25 concentrations, and generally significantly better at the same concentration level. This allows at least the same, or better, odor control with a less grey or black-spotted superabsorbent.

Claims

230855W00126Claims1. A superabsorbent comprising activated carbon having a trimodal pore radius distribution.

2. The superabsorbent of claim 1, comprising activated carbon having a trimodal pore radius distribution in an amount of 0.05 wt.-%, to 5 wt.-%, based on the total weight of superabsorbent.

3. The superabsorbent of claim 2, comprising activated carbon having a trimodal pore radius distribution in an amount of 0.1 wt.-%, to 4 wt.-%, based on the total weight of superabsorbent.

4. The superabsorbent of any of claims 1 to 3, wherein the activated carbon has micro-, meso- and macropores of diameters of up to 2 nm, 2 to 50 nm and 0.5 to 5 pm, respectively.

5. The superabsorbent of any of claims 1 to 4, wherein the activated carbon, as such, has a bulk density in the range of 0.2 to 0.4 g / cm3and a cumulative pore volume of pores in the range of 0.005 to 5 pm of 0.4 to 1.2 cm3 / g.

6. The superabsorbent of any of claims 1 to 5, that is based on a crosslinked, partly neutralized polyacrylic acid.

7. The superabsorbent of any of claims 1 to 4 that is surface crosslinked.

8. A process for producing the superabsorbents defined in any of claims 1 to 7, comprising polymerisation of a monomer solution comprising: a) at least one ethylenically unsaturated monomer which bears acid groups and may be at least partly neutralised, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomers copolymer- isable with the monomers specified under a) and e) optionally one or more water-soluble polymers, the process further optionally comprising drying, grinding, classifying and / or surface postcrosslinking the resulting polymer and adding the activated carbon prior to, during or after polymerization, drying and / or surface crosslinking.

9. The process of claim 8, where the activated carbon is added after drying or, if the superabsorbent is surface crosslinked, after surface crosslinking.

10. A water-absorbing product comprising the superabsorbent of any of claims 1230855W00127 to 7.

11. The water-absorbing product of claim 10 that is a hygiene article.

12. A process for producing the water-absorbing product of any of claims 10 or 11 that comprises adding the superabsorbent to the water-absorbing product during its production.

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