WO2009059956A2 - Superabsorbents-containing cat litter - Google Patents

Abstract

A cat litter comprising a superabsorbent that has an Absorption Time of less than 60 seconds has improved efficiency.

Description

Superabsorbents-containing Cat Litter

Description

The present invention relates to cat litter that contains superabsorbents.

Animal litter is generally used to collect animal excretions. The type of litter to be used varies according to the species. Requirements for litter to be used for pet animals are rather different from those for farm animals litter. Typically, requirements for cat litter are highest. Cats are not only rather demanding with respect to cleanliness, but also produce a higher amount of liquid excretions than other pets that, by their nature, can be induced to use litter. Consequently, cat owners not only have to purchase and transport comparatively large and heavy amounts of litter, but also regularly inspect the litter box's contents to remove used litter and replace it with unused litter. Cat litter typi- cally is a porous or swellable inorganic substance, generally a mineral, such as kiesel- guhr, silica gel, a zeolithe or a clay, for example bentonite or sepiolite. Some cat litter is based on cellulosic materials, mainly as an outlet for waste from paper mills or agricultural by-products. Composites or mixtures of these materials are also known as cat litter. Cat litter is usually a granulate. The bigger part of cat litter on the market is clumping cat litter that forms clumps upon receiving liquid insults rather than distributing the liquid throughout the litter volume. Clumping facilitates removing used litter by scooping, leaving the unused litter in the box. Cat litter may be used for other litter box- using pets or as bottom layer in cages to facilitate removal of droppings where non- porous materials such as sand are typically used. Odour control is also an issue with cat litter. Cat litter often contains odour control components designed to mask unpleasant odours, absorb odours or inhibit odour formation, usually by inhibiting bacteria that degrade nitrogen-containing compounds in animal urine, mainly urea, to ammonia, the main cause of malodour from urine.

Superabsorbents are known. Superabsorbents are materials that are able to take up and retain several 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- swellability 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)polymerized hydrophilic monomers, graft (co)polymers of one or more hydrophilic monomers on a suitable grafting base, crosslinked ethers of cellulose or starch, crosslinked carboxymethylcellu- lose, 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 neutralized 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.-% water content. A superab- sorbent transforms into a gel on taking up a liquid, specifically into a hydrogel when as usual taking up water or aqueous liquids. 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.

Processes for producing superabsorbents are also known. The acrylate-based su- perabsorbents which dominate the market are produced by radical polymerisation of acrylic acid in the presence of a crosslinking agent (the "internal crosslinker"), usually in the presence of water, the acrylic acid being neutralized 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 a alkali, 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 "posfcrosslinked) 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.

Frederic L. Buchholz und Andrew T. Graham (Hrsg.) in: ,,Modern Superabsorbent Po- lymer Technology", J. Wiley & Sons, New York, U.S.A. / Wiley-VCH, Weinheim, Germany, 1997, ISBN 0-471-1941 1-5, give a comprehensive overview over superabsorbents and processes for producing superabsorbents.

Superabsorbent-containing cat litter is also known. As superabsorbents form a gel upon contact with aqueous liquids that leads to clumping of the litter, they can be used as clumping aids for cat litter. It is also known to use them, as such, as cat litter, as a substitute for rather than an additive to typical porous or swellable inorganic or cellu- losic materials. Composites comprising porous or swellable inorganic material and su- perabsorbents are also known and used for general liquids-absorbing purposes such as diapers or other hygiene products or absorbent packs for food packaging.

US 6 745 720 B2 teaches a clumping animal litter composed of discrete dual component granules having an inner core of fibres, mineral filler and binder, and a coating made up from natural or artificial materials that reduce odours. US 5 358 607 relates to shot-like absorbent material composed of inorganic and cellulosic materials that can be used as cat litter.

US 4 914 066 discloses superabsorbent-containing cat litter on a bentonite basis. US 5 609 123 relates to cat litter made from a clay particles with low swelling capacity, to which superabsorbent particles and particles of a soluble polymer are bonded. US 5 189 987 teaches animal litter that is treated with pine oil for better odour control and also may contain superabsorbent. WO 2005/120 221 A2 discloses cat litter consisting of composite particles that may comprise superabsorbents, and methods for producing such composite-particle cat litter.

US 6 926 862 B2 discloses a superabsorbent polymer-containing container, shelf or drawer liner for absorbing liquids and providing odour control. US 4 469 046,

WO 2004/008843 A1 and DE 42 00 686 A1 all relate to various models of litter boxes containing a bottom liner or layer of superabsorbent material.

There still is a need to develop further improved cat litter. Properties to be achieved are in particular general high absorption capacity and high efficiency of the litter in the sense of making relatively small clumps upon liquid insults, which in effect leads to less litter consumption. It is an object of the present invention to provide such improved cat litter.

We have found that this object is achieved by a cat litter comprising a superabsorbent that has an Absorption Time of not more than 60 seconds.

Preferably, the Absorption time of the superabsorbent is not more than 50 seconds and most preferably, the Absorption time is not more than 40 seconds. Such superabsor- bents are known and are obtainable commercially. As just one non-limiting example, Luquasorb^® 1280 RS available from BASF Corporation, Charlotte, North Carolina, U.S.A., has an Absorption Time of 40 sec.

The superabsorbent at issue here is a "fast" superabsorbent in terms of absorption speed. There are also superabsorbents on the market that are comparatively "slow". In the typical application of superabsorbents for collecting human body fluids in diapers or adult incontinence products, very high absorption speed is not necessarily an advan- tage, since liquid passed to the superabsorbent needs some time to be distributed throughout the superabsorbent so that all of the superabsorbent is put to use, and too rapid swelling at the point of insult may block liquids transport to unused parts of the superabsorbent.

It is preferred that the superabsorbent does not only exhibit short absorption time, but also absorbs certain minimum amounts of water. Generally, the superabsorbent should swell in an Absorption Time determination (see below) to at least three times its original volume within Absorption Time, preferably to at least five times and more preferably to at least 10 times its original volume.

Contrasting that, it has been found that in cat litter, rapid swelling and gel-formation leads to clumps of smaller size upon liquid insults such as by a cat passing urine. The clumps are easily removable from a litter-box by scooping. Consequently, a given amount of cat litter can absorb more cat urine.

Theoretically, any amount of superabsorbent in cat litter will have a beneficial effect according to this invention. Too high amounts, however, may simply be commercially or technically disadvantageous or even irritate some cats due to the superabsorbent's appearance that, contrary to typical cat litter, much differs from soil. In typical embodiments the cat litter generally comprises at least 0.1 wt.-% of superabsorbent, preferably at least 0.2 wt.-% and more preferably at least 0.3 wt.-%, and generally not more than 10 wt.-%, preferably not more than 8 wt.-% and more preferably not more than 5 wt.-%. In most cases, an amount of not more than 3 wt.-% will be sufficient. Rather common superabsorbent contents are, as non-limiting examples, 1 wt.-% or 2 wt.-%. All weight- % (wt.-%) values are based on the total superabsorbent-containing cat litter weight.

The superabsorbent at issue in the present invention is a superabsorbent capable of absorbing and retaining amounts of water equivalent to many times its own weight un- der a certain pressure. In general, it 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. Preferably, the superabsorbent is a crosslinked polymer based on partially neutralized acrylic acid, and more preferably it is surface post- crosslinked. 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.

Various types and grades of superabsorbents are commercially available, as the world capacity of superabsorbents exceeds one million tons per year. Determining whether a superabsorbent is "fast" as required in this invention can easily be done by subjecting the superabsorbent ion question to the Absorption Time Test described below. "Fast" superabsorbents are typically found among those superabsorbents that also exhibit a specific surface area (i.e. the surface area per mass, as can be easily determined for example by routine BET isotherm measurements) that, on average, is higher than the specific surface area of typical superabsorbent for standard hygiene applications and in particular among those superabsorbents that:

a) have a generally smaller particle size than the typical 100 - 850 μm sieve cut for hygiene applications; for example, a superabsorbent essentially consisting of particles of a size of not more than 300 μm or preferably of not more than 100 μm typically will have a sufficiently short Absorption Time, especially if the superab- sorbent has been surface crosslinked. One example of a commercially available material of this type is Luquasorb^® B11 10, available from BASF Corporation, Charlotte, North Carolina. U.S.A.);

b) have been produced by an emulsion polymerization process and in particular those that have then been agglomerated (emulsion polymerization is also called suspension polymerization, or most precisely, inverse suspension polymerization, see below);

c) that have been produced using blowing agents or any other known means of in- creasing porosity of superabsorbents, including superabsorbents that are comminuted superabsorbent foam;

d) that have been treated with a surfactant to improve wettability and/or

e) that have a low sensitivity to the presence of soluble salts, such as superabsorb- ing mixtures of acidic and basic polymers, for example (non-limiting) those disclosed in WO 96/17 681 A1 , WO 96/15 163 A1 , WO 96/15 180 A1 , or WO 99/25 745 A1.

Generally, the "faster" the superabsorbent is (that means, the shorter its Absorption Time is), the better will be litter utilization (that means, the smaller the clumps formed by an animal's passing urine into the litter will be), and the higher the amount of urine a given amount of litter can take up. Choosing the proper superabsorbent and amount thereof in a particular litter to be produced is not only a matter of Absorption Time, how- ever, since economic considerations may influence the choice. Preferably, superabsorbent and amount thereof are chosen so that the total cost for the animal owner per event of the animal's passing urine is not increased as compared to standard cat litter. There may be exceptions to that rule of thumb, such as in cases where consumers prefer smaller package size over price.

Processes for producing such superabsorbents are known. Synthetic superabsorbents are obtained for example by polymerisation of a monomer solution comprising a) at least one ethylenically unsaturated acid-functional monomer, b) at least one crosslinker, c) optionally one or more ethylenically and/or allylically unsaturated monomers co- polymerizable with the monomer a), and d) optionally one or more water-soluble polymers onto which the monomers a), b) and if appropriate c) can be at least partly grafted.

Suitable monomers a) are for example ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid, or derivatives thereof, such as acrylamide, methacrylamide, acrylic esters and methacrylic esters. Acrylic acid and methacrylic acid are particularly preferred monomers. Acrylic acid is most preferable.

The monomers a) and especially acrylic acid comprise preferably up to 0.025% by weight of a hydroquinone half ether. Preferred hydroquinone half ethers are hydro- quinone monomethyl ether (MEHQ) and/or tocopherols such as alpha-tocopherol, especially racemic alpha-tocopherol.

The monomer solution comprises preferably not more than 130 weight ppm, more preferably not more than 70 weight ppm, preferably not less than 10 weight ppm, more preferably not less than 30 weight ppm and especially about 50 weight ppm of hydroquinone half ether, all based on acrylic acid, with acrylic acid salts being arithmetically counted as acrylic acid. For example, the monomer solution can be produced using an acrylic acid having an appropriate hydroquinone half ether content.

Crosslinkers b) are compounds having at least two polymerizable groups which can be free-radically interpolymerized into the polymer network. Useful crosslinkers b) include for example ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl methacry- late, trimethylolpropane triacrylate, triallylamine, tetraallyloxyethane as described in EP 530 438 A1 , di- and triacrylates as described in EP 547 847 A1 , EP 559 476 A1 , EP 632 068 A1 , WO 93/21 237 A1 , WO 03/104 299 A1 , WO 03/104 300 A1 , WO 03/104 301 A1 and DE 103 31 450 A1 , mixed acrylates which, as well as acrylate groups, comprise further ethylenically unsaturated groups, as described in DE 103 31 456 A1 and WO 04/013 064 A2, or crosslinker mixtures as described for example in DE 195 43 368 A1 , DE 196 46 484 A1 , WO 90/15 830 A1 and WO 02/032 962 A2.

Useful crosslinkers b) include in particular N,N'-methylenebisacrylamide and N,N'-methylenebismethacrylamide, esters of unsaturated mono- or polycarboxylic acids of polyols, such as diacrylate or triacrylate, for example butanediol diacrylate, butanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate and also trimethylolpropane triacrylate and allyl compounds, such as allyl (meth)acrylate, triallyl cyanurate, diallyl maleate, polyallyl esters, tetraallyloxyethane, triallylamine, tetraallylethylenediamine, allyl esters of phosphoric acid and also vinyl- phosphonic acid derivatives as described for example in EP 343 427 A2. Useful crosslinkers b) further include pentaerythritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, polyethylene glycol diallyl ether, ethylene glycol diallyl ether, glycerol diallyl ether, glycerol triallyl ether, polyallyl ethers based on sorbitol, and also ethoxylated variants thereof. The process of the present invention may utilize di(meth)acrylates of polyethylene glycols, the polyethylene glycol used having a mo- lecular weight between 300 and 1000.

However, particularly advantageous crosslinkers b) are di- and triacrylates of 3- to 15-tuply ethoxylated glycerol, of 3- to 15-tuply ethoxylated trimethylolpropane, of 3- to 15-tuply ethoxylated trimethylolethane, especially di- and triacrylates of 2- to 6-tuply ethoxylated glycerol or of 2- to 6-tuply ethoxylated trimethylolpropane, of 3-tuply pro- poxylated glycerol, of 3-tuply propoxylated trimethylolpropane, and also of 3-tuply mix- edly ethoxylated or propoxylated glycerol, of 3-tuply mixedly ethoxylated or propoxylated trimethylolpropane, of 15-tuply ethoxylated glycerol, of 15-tuply ethoxylated trimethylolpropane, of 40-tuply ethoxylated glycerol, of 40-tuply ethoxylated trimethy- lolethane and also of 40-tuply ethoxylated trimethylolpropane.

Very particularly preferred for use as crosslinkers b) are diacrylated, dimethacrylated, triacrylated or trimethacrylated multiply ethoxylated and/or propoxylated glycerols as described for example in WO 03/104 301 A1. 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. The triacrylates of 3- to 5-tuply ethoxylated and/or propoxylated glycerol are most preferred. These are notable for particularly low residual contents (typically below 10 weight ppm) in the water-absorbing polymer and the aqueous extracts of the water-absorbing poly- mers produced therewith have an almost unchanged surface tension (typically at least 0.068 N/m) compared with water at the same temperature.

Examples of ethylenically unsaturated monomers c) which are copolymerizable with the monomers a) are acrylamide, methacrylamide, crotonamide, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethyl- aminopropyl acrylate, dimethylaminobutyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoneopentyl acrylate and dimethylami- noneopentyl methacrylate.

Useful water-soluble polymers d) include polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, polyethyleneimines, polyglycols, polymers formally constructed wholly or partly of vinylamine monomers, such as partially or completely hydrolyzed polyvinylamide (so-called "polyvinylamine") or polyacrylic acids, preferably polyvinyl alcohol and starch.

The polymerisation is optionally carried out in the presence of customary polymerisa- tion regulators. Suitable polymerisation regulators are for example thio compounds, such as thioglycolic acid, mercapto alcohols, for example 2-mercaptoethanol, mercap- topropanol and mercaptobutanol, dodecyl mercaptan, formic acid, ammonia and amines, for example ethanolamine, diethanolamine, triethanolamine, triethylamine, morpholine and piperidine.

The monomers (a), (b) and optionally (c) are (co)polymerized with each other in the presence of the water-soluble polymers d), in 20% to 80%, preferably 20% to 50% and especially 30% to 45% by weight aqueous solution in the presence of polymerisation initiators. Useful polymerisation initiators include all compounds that disintegrate into free radicals under the polymerisation conditions, examples being peroxides, hydroperoxides, hydrogen peroxide, persulfates, azo compounds and the so-called redox initiators. The use of water-soluble initiators is preferred. It is advantageous in some cases to use mixtures of various polymerisation initiators, examples being mixtures of hydrogen peroxide and sodium or potassium peroxodisulfate. Mixtures of hydrogen peroxide and sodium peroxodisulfate can be used in any desired ratio. Suitable organic peroxides are for example acetylacetone peroxide, methyl ethyl ketone peroxide, tert- butyl hydroperoxide, cumene hydroperoxide, tert-amyl perpivalate, tert-butyl per- pivalate, tert-butyl perneohexanoate, tert-butyl perisobutyrate, tert-butyl per-2- ethylhexanoate, tert-butyl perisononanoate, tert-butyl permaleate, tert-butyl perbenzo- ate, tert-butyl per-3,5,5-trimethylhexanoate and tert-amyl perneodecanoate. Further suitable polymerisation initiators are azo initiators, for example 2,2'-azobis(2- amidinopropane) dihydrochloride, 2,2'-azobis(N,N-dimethylene)-isobutyramidine dihy- drochloride, 2-(carbamoylazo)isobutyronitrile and 4,4'-azobis(4-cyanovaleric acid). The polymerisation initiators mentioned are used in customary amounts, for example in amounts of from 0.01 to 5 mol%, preferably 0.1 to 2 mol%, based on the monomers to be polymerized.

The redox initiators comprise, as oxidizing component, at least one of the above- indicated per compounds and a reducing component, for example ascorbic acid, glu- cose, sorbose, ammonium bisulfite, ammonium sulfite, ammonium thiosulfate, ammonium hyposulfite, ammonium pyrosulfite, ammonium sulfide, alkali metal bisulfite, alkali metal sulfite, alkali metal thiosulfate, alkali metal hyposulfite, alkali metal pyrosulfite, alkali metal sulfide, metal salts, such as iron(ll) ions or silver ions, sodium hydroxy- methylsulfoxylate, or sulfinic acid derivatives. The reducing component of the redox initiator is preferably ascorbic acid or sodium pyrosulfite. 1 ^■ 10^"5 to 1 mol% of the reducing component of the redox initiator and 1 ^■ 10^"5 to 5 mol% of the oxidizing component are used based on the amount of monomers used in the polymerisation. Instead of the oxidizing component or in addition it is also possible to use one or more water- soluble azo initiators.

A redox initiator consisting of hydrogen peroxide, sodium peroxodisulfate and ascorbic acid is preferably used. These components are used for example in the concentrations of 1 ^■ 10^"2 mol% of hydrogen peroxide, 0.084 mol% of sodium peroxodisulfate and 2.5 ^■ 10^"3 mol% of ascorbic acid, based on the monomers.

It is also possible to initiate the polymerisation by the numerous other known means to initiate polymerisations. On example is initiating polymerisation by irradiating with radiation of sufficiently high energy, in particular ultraviolet light. Usually, when initiating polymerisation by ultraviolet light, compounds are added which decompose into radicals upon irradiation by ultraviolet light. Examples of such compunds are 2-hydroxi-2- methyl-1 -phenyl-1 -propanone and/or alpha, -alpha-dimethoxi-alpha- phenylacetophenone.

The aqueous monomer solution may comprise the initiator in dissolved or dispersed form. However, the initiators may also be added to the polymerisation reactor separately from the monomer solution.

The preferred polymerisation inhibitors require dissolved oxygen for optimum effect. Therefore, the polymerisation inhibitors can be freed of dissolved oxygen prior to polymerisation, by inertisation, i.e., by flowing an inert gas, preferably nitrogen, through them. This is accomplished by means of inert gas, which can be introduced concur- rently, countercurrently or at entry angles in between. Good commixing can be achieved for example with nozzles, static or dynamic mixers or bubble columns. The oxygen content of the monomer solution is preferably lowered to less than 1 weight ppm and more preferably to less than 0.5 weight ppm prior to polymerisation. The monomer solution is optionally passed through the reactor using an inert gas stream.

The preparation of a suitable polymer as well as further suitable hydrophilic ethyleni- cally unsaturated monomers a) are described for example in DE 199 41 423 A1 , EP 686 650 A1 , WO 01/45 758 A1 and WO 03/104 300 A1.

Superabsorbents are typically obtained by addition polymerisation of an aqueous monomer solution and optionally a subsequent comminution of the hydrogel. Suitable methods of making are described in the literature. Superabsorbents are obtained for example by

• gel polymerisation in the batch process or tubular reactor and subsequent comminution in meat grinder, extruder or kneader, as described for example in EP 445 619 A2 and DE 19 846 413 A1 ; • polymerisation in kneader with continuous comminution by contrarotatory stirring shafts for example, as described for example in WO 01/38 402 A1 ;

• polymerisation on belt and subsequent comminution in meat grinder, extruder or kneader, as described for example in EP 955 086 A2, DE 38 25 366 A1 or US- 6,241 ,928;

• emulsion polymerisation, which produces bead polymers having a relatively narrow gel size distribution, as described for example in EP 457 660 A1 ;

The cited references are expressly incorporated herein for details of process operation. The reaction is preferably carried out in a kneader or on a belt reactor or by emulsion polymerisation.

Continuous gel polymerisation in a kneader or on a belt reactor is the economically preferred and therefore currently customary way of manufacturing superabsorbents. The process of continuous gel polymerisation is carried out by first producing a monomer mixture by admixing the acrylic acid solution with the neutralizing agent, optional comonomers and/or further auxiliary materials at different times and/or locations and then transferring the mixture into the reactor or preparing the mixture as an initial charge in the reactor. The initiator system is added last to start the polymerisation. The ensuing continuous process of polymerisation involves a reaction to form a polymeric gel, i.e., a polymer swollen in the polymerisation solvent - typically water - to form a gel, and the polymeric gel is already comminuted in the course of a stirred polymerisation. The polymeric gel is subsequently dried, if necessary, and also chipped ground and sieved and is transferred for further surface treatment.

The acid groups of the hydrogels obtained are partially neutralized in an acid neutralisation step, generally to an extent of at least 25 mol%, preferably to an extent of at least 50 mol% and more preferably at least 60 mol% and generally to an extent of not more than 85 mol%, preferably not more than 80 mol%, and more preferably not more than 75 mol%.

Neutralisation can also be carried out after polymerisation, at the hydrogel stage. But it is also possible to carry out the neutralisation to the desired degree of neutralisation wholly or partly prior to polymerisation. In the case of partial neutralisation and prior to polymerisation, generally at least 10 mol%, preferably at least 15 mol% and also generally not more than 40 mol%, preferably not more than 30 mol% and more preferably not more than 25 mol% of the acid groups in the monomers used are neutralized prior to polymerisation by adding a portion of the neutralizing agent to the monomer solution. The desired final degree of neutralisation is in this case only set toward the end or after the polymerisation, preferably at the level of the hydrogel prior to its drying. The monomer solution is neutralized by admixing the neutralizing agent. The hydrogel can be mechanically comminuted in the course of the neutralisation, for example by means of a meat grinder or comparable apparatus for comminuting gellike masses, in which case the neutralizing agent can be sprayed, sprinkled or poured on and then carefully mixed in. To this end, the gel mass obtained can be repeatedly meat-grindered for ho- mogenisation.

Neutralisation of the monomer solution to the desired final degree of neutralisation prior to polymerisation by addition of the neutralizing agent or conducting the neutralisation after polymerisation is usually simpler than neutralisation partly prior to and partly after polymerisation and therefore is preferred.

The as-polymerized gels are optionally maintained for some time, for example for at least 30 minutes, preferably at least 60 minutes and more preferably at least 90 minutes and also generally not more than 12 hours, preferably for not more than 8 hours and more preferably for not more than 6 hours at a temperature of generally at least 50⁰C and preferably at least 70⁰C and also generally not more than 130⁰C and preferably not more than 100⁰C, which further improves their properties in many cases.

The neutralized hydrogel is then dried with a belt or drum dryer until the residual moisture content is preferably below 15% by weight and especially below 10% by weight, the moisture content (also called water content) of the material being determined as described below. The dry superabsorbent consequently contains up to 15% by weight of moisture and preferably not more than 10% by weight. The decisive criterion for classification as "dry" is in particular a sufficient flowability for handling as a powder, for example for pneumatic conveying, pack filling, sieving or other processing steps in- volved in solids processing technology. Optionally, however, drying can also be carried out using a fluidized bed dryer or a heated ploughshare mixer. To obtain particularly colourless products, it is advantageous to dry this gel by ensuring rapid removal of the evaporating water. To this end, dryer temperature must be optimized, air feed and removal has to be policed, and at all times sufficient venting has to be ensured. Drying is naturally all the more simple - and the product all the more colourless - when the solids content of the gel is as high as possible. The solvent fraction at addition polymerisation is therefore set such that the solid content of the gel prior to drying is therefore generally at least 20% by weight, preferably at least 25% by weight and more preferably at least 30% by weight and also generally not more than 90% by weight, preferably not more than 85% by weight and more preferably not more than 80% by weight. It is particularly advantageous to vent the dryer with nitrogen or some other nonoxidizing inert gas. Optionally, however, simply just the partial pressure of oxygen can be lowered during drying to prevent oxidative yellowing processes. But in general adequate venting and removal of the water vapour will likewise still lead to an acceptable product. A very short drying time is generally advantageous with regard to colour and product quality.

The dried product (which is no longer a gel (even though often still called "gel" or "hy- drogel") but a dry polymer having superabsorbing properties, which comes within the term "superabsorbent") is preferably ground and sieved, useful grinding apparatus typically including roll mills, pin mills, hammer mills, cutting mills or swing mills. The particle size of the sieved, dry superabsorbent is, for use in the present invention, preferably below 300 μm, more preferably below 100 μm and preferably above 1 μm and more preferably above 5 μm. Particle size (to be precise, particle size distribution) determination is described below.

Another preferred process for producing superabsorbents of this invention is emulsion polymerization. Emulsion polymerization - also referred to a suspension polymerization or inverse suspension polymerization - is a process in which the aqueous monomer solution is finely dispersed in a continuous water-immiscible phase, typically a hydrocarbon solvent and polymerized in this dispersed state. The dispersion is stabilized by adding a stabilizer, generally a surfactant and/or very fine particles of an inorganic, usually hydrophobic solid such as hydrophobized silica. This process yields gel beads of rather uniform particle size that can easily be controlled by adjusting the agitation of the polymerization suspension. The most simple, but not the only means therefor is adjusting stirring speed during polymerization. Grinding or sizing steps are rarely necessary with emulsion polymerization. The initially produced particles, however, are gel particles since they contain all the water that had been part of the monomer solution and need to be dried just as the initial gel products from solution polymerization processes. Producing rather small particles and agglomerating these to agglomerates, or producing porous beads by oil-in-water-in-oil polymerization, where the dispersed aqueous phase monomer droplets contain organic phase microdroplets that evaporate during polymerization or drying and leave pores in the beads, or any known means to increase specific surface all lead to rather "fast" superabsorbents. Emulsion polymerization processes for producing superabsorbents and superabsorbents produced by this process are known.

The dry superabsorbing polymers thus produced are typically known as "base polymers" and are then preferably surface postcrosslinked. Surface postcrosslinking can be accomplished in a conventional manner using dried, ground and classified polymeric particles. For surface postcrosslinking, compounds capable of reacting with the functional groups of the base polymer by crosslinking are applied, usually in the form of a solution, to the surface of the base polymer particles. Suitable postcrosslinkling agents are for example:

• di- or polyepoxides, for example di- or polyglycidyl compounds such as phos- phonic acid diglycidyl ether , ethylene glycol diglycidyl ether, bischlorohydrin ethers of polyalkylene glycols,

• alkoxysilyl compounds,

• polyaziridines, compounds comprising aziridine units and based on polyethers or substituted hydrocarbons, for example bis-N-aziridinomethane,

• polyamines or polyamidoamines and also their reaction products with epichloro- hydrin,

• polyols such as ethylene glycol, 1 ,2-propanediol, 1 ,4-butanediol, glycerol, methyl- triglycol, polyethylene glycols having an average molecular weight Mw of 200 -

10 000, di- and polyglycerol, pentaerythritol, sorbitol, the ethoxylates of these polyols and also 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 polyisocy- anates,

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

• compounds having two or more blocked isocyanate groups such as for example trimethylhexamethylene diisocyanate blocked with 2,2,3,6-tetramethylpiperidin-

4-one.

If necessary, acidic catalysts can be added, examples being p-toluenesulfonic acid, phosphoric acid, boric acid or ammonium dihydrogenphosphate.

Particularly suitable postcrosslinking agents 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.

Surface postcrosslinking (often just "postcrosslinking") is typically carried out by spraying a solution of the surface postcrosslinker (often just "postcrosslinker") onto the hy- drogel or the dry base polymer powder.

The solvent used for the surface postcrosslinker is a customary suitable solvent, ex- amples being water, alcohols, DMF, DMSO and also mixtures thereof. Particular preference is given to water and water-alcohol mixtures, examples being water-methanol, water-1 ,2-propanediol, water-2-propanol and water-1 ,3-propanediol.

The spraying with a solution of the postcrosslinker is preferably carried out in mixers having moving mixing implements, such as screw mixers, paddle mixers, disk mixers, plowshare mixers and shovel mixers. Particular preference is given to vertical mixers and very particular preference to plowshare mixers and shovel mixers. Useful and known mixers include for example Lodige^®, Bepex^®, Nauta^®, Processall^® and Schugi^® mixers. Very particular preference is given to high speed mixers, for example of the Schugi-Flexomix^® or Turbolizer^® type.

The spraying with the crosslinker solution can be optionally followed by a thermal treatment step, essentially to effect the surface-postcrosslinking reaction (yet usually just referred to as "drying"), preferably in a downstream heated mixer ("dryer") at a temperature of generally at least 50⁰C, preferably at least 80⁰C and more preferably at least 80°C and also generally not more than 300⁰C, preferably not more than 250°C and more preferably not more than 200°C. The average residence time (i.e., the averaged residence time of the individual particles of superabsorbent) in the dryer of the superabsorbent to be treated is generally at least 1 minute, preferably at least 3 minutes and more preferably at least 5 minutes and also generally not more than 6 hours, preferably 2 hours and more preferably not more than 1 hour. As well as the actual drying taking place, not only any products of scissioning present but also solvent fractions are removed. Thermal drying is carried out in customary dryers such as tray dryers, rotary tube ovens or heatable screws, preferably in contact dryers. Preference is given to the use of dryers in which the product is agitated, i.e., heated mixers, more preferably shovel dryers and most preferably disk dryers. Bepex^® dryers and Nara^® dryers are suitable dryers for example. Fluidized bed dryers can also be used. But drying can also take place in the mixer itself, by heating the jacket or blowing a preheated gas such as air into it. But it is also possible for example to utilize an azeotropic distillation as a drying process. The crosslinking reaction can take place not only before but also during drying.

Quite often, water-soluble polyvalent metal salts are added as further surface crosslinking agents in addition to the above-listed organic surface postcrosslinking agents. 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. Ex- amples of polyvalent cations are or metal cations such as Mg²⁺, Ca²⁺, Al³⁺, Sc³⁺, Ti⁴⁺, Mn²⁺, Fe^2+/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.

The treatment of the superabsorbent polymer with solution of a polyvalent cation is carried out in the same way as that with the organic surface postcrosslinker, including the selective drying step. Useful solvents for the metal salts include water, alcohols, DMF, DMSO and also mixtures thereof. Particular preference is given to water and water-alcohol mixtures such as for example water-methanol, water-1 ,2-propanediol, water-2-propanol and water-1 ,3-propanediol. Organic surface postcrosslinker and polyvalent metal salt may be added simultaneously, even in one solution, or in sequence. If they are added in sequence, adding the inorganic metal salt after a first surface postcrosslinking step is preferred.

After any drying step, it is advantageous but not absolutely necessary to cool the product after drying. 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 fluidized bed by blowing a cooled gas such as cold air into it. 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 0⁰C, preferably at least 10⁰C and more preferably at least 20°C and also generally not more than 100⁰C, preferably not more than 80⁰C and more preferably not more than 60⁰C.

Optionally, the superabsorbent is provided with further customary additives and auxiliary materials to influence storage or handling properties. Examples thereof are cohesion control agents to improve handling and conveying, colorations, opaque additions to improve the visibility of swollen gel, which is desirable in some applications, surfac- tants, particulate inorganic solids or the like. Similarly, a final water content can be set for the superabsorbent, if desired, by adding water. 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.

The surface-crosslinked superabsorbent 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. The particle size of the sieved, dry, final superabsorbent is, for use in the present invention, preferably below 300 μm, more preferably below 100 μm and preferably above 1 μm and more preferably above 5 μm. Particle size (to be precise, particle size distribution) determination is described below.

Besides the superabsorbent, the cat litter of this invention comprise known components of cat litter, in particular clumping cat litter. In principle, the cat litter of this invention can be any known cat litter or material useful as cat litter, in particular clumping cat litter, with an addition of superabsorbent having an Absorption Time of less than 60 seconds.

Typical components other than superabsorbents of the cat litter of this invention are porous and/or swellable inorganic materials or organic materials capable of absorbing aqueous fluids. Auxiliaries used in the cat litter are in particular odour-masking, odour- absorbing or odour-avoiding substances. Generally, clumping cat litter comprises or consists of swellable clay, in particular of the montmorillonite type such as bentonite. Preferably, sodium bentonite is used as sole or main component of clumping cat litter. Typical additives are odour-controlling substances such as activated carbon, zeolithes, aluminium compounds or the like.

Generally, cat litter is in the form of small granules rather than in the form of powder to avoid dust problems. These granules may be produced by any known process for producing granules or agglomerates from finer particles.

The superabsorbent is mixed into the cat litter by conventional mixing, as is generally used in cat litter production by mixing known cat litter components. It is also possible to include superabsorbent into cat litter agglomerates or composites during their production. A convenient method is blending superabsorbent and clay with just enough water or other suitable liquid to form an extrudable paste, extruding and drying the extru- dates. Granulation in a granulation pan by spraying water or another suitable liquid on a mixture of clay and superabsorbent while rotating the pan and subsequent drying of the agglomerates is another method to form composite cat litter particles. Additives can be added prior to extrusion or agglomeration or to the extrudates or agglomerates.

Other methods of producing cat litter are disclosed in US 6 745 720 B2, US 5 609 123 or WO 2005/120 221 A2, which are explicitly referred to and incorporated by reference.

Test Methods

Centrifuge Retention Capacity (CRC)

The method for determination of the Centrifuge Retention Capacity (CRC) of a superabsorbent is described in US patent application no. US 2002/0 165 288 A1 , paragraphs [0105] and [0106]. Moisture content

The moisture content of a superabsorbent material is determined using EDANA (Euro- pean Disposables and Nonwovens Association, , Avenue Eugene Plasky 157, 1030 Brussels, Belgium) recommended test method No. 430.2-02 "Moisture content", available from EDANA.

Absorption Time

The Absorption Time of a superabsorbent is the time that a 3.000 ± 0.005 gram sample of a superabsorbent polymer takes to substantially absorb 60 ml of saline (a 0.9 wt.-% aqueous sodium chloride solution). A graph of superabsorbent volume change upon adding liquid versus time typically shows a steep, linear initial leg and a much flatter, linear second leg afterwards. The superabsorbent has substantially absorbed all of the saline solution at the point of time where these two legs meet. Precisely defined, Absorption Time is the time span between two points a) and b) on the time axis of a graph showing volume increase of this superabsorbent sample upon addition of this liquid versus time: a) the start of detectable swelling (which typically starts immediately upon saline addition) and b) the point that corresponds to the intersection of a straight line that coincides with the typically linear first leg of the graph with a straight line that coincides with the typically linear second leg of the graph. Measuring over a time span of 300 seconds is generally sufficient. If there is any doubt about linearity, the tangent to the part of the graph that corresponds to the first 5 seconds of measurement time or the tangent to the part of the graph that corresponds to the final 100 seconds from the start of detectable swelling, respectively, are used to determine point b).

Absorption Time can easily determined by recording the time when the superabsorbent sample does no longer swell substantially after the addition of the liquid to the su- perabsorbent sample. No or at least no significant external pressure (that is, pressure beyond what the measuring equipment necessarily exerts) is applied. Several experimental setups are possible, and simple observation by eye of the superabsorbent swelling in a beaker, pan, flask or similar, recording the time manually using a stopwatch will provide results that are accurate enough for most purposes, at least for dis- tinguishing a typical "fast" from a typical "slow" superabsorbent.

For precise measurements of Absorption Time, a convenient experimental set-up to determine Absorption time is using a linear variable differential transformer ("LVDT") equipped with an electronic controller and connected to a computer to continuously determine and record the changing volume of a superabsorbent sample as a function of time. In principle, the linear displacement of a LVDT sensor's rod caused by swelling superabsorbent is used to monitor that swelling. Since the sample holder's dimensions are known, LVDT rod displacement can directly by converted into superabsorbent volume increase.

In the preferred method used to determine Absorption Time of a superabsorbent ac- cording to the present invention, 3.000 ± 0.005 grams of the superabsorbent are placed in a plastic (for example polycarbonate, but this is not a critical feature) cylindrical sample holder of 60 mm inside diameter (in principle, a cylinder with a flat bottom that is open at its upper end) and levelled by tapping. The sample is covered with a circular piece of 40 gsm porous nonwoven material (conveniently common diaper top- sheet material, but any porous thin fibre material is suitable) of 58 mm to prevent the superabsorbent from swelling through the base disc's holes described below. The sample holder is placed under the rod of a vertically fixed LVDT sensor (Schaevitz^® 1000 HCA model obtainable from Measurement Specialties, Inc., 1000 Lucas Way, Hampton, Virginia 23666, U.S.A.) equipped with a controller (Schaevitz^® 1000 MP model, same source) and connected to a PC. Controller and Computer are set up to record and display the LVDT rod's displacement by superabsorbent swelling below the rod (that can be recorded as displacement in length units or converted into volume units, as the dimensions of the sample holder are known) as a function of time as described in the LVDT sensor and controller manual. The LVDT sensor's rod (that, in it- self, applies an effective weight of 4 g to the sample) is equipped with a plastic (for example polycarbonate, but this is not a critical feature) base disc of 8.5 g weight and 58 mm diameter that is inserted into the sample holder's open end. The disc contains 168 holes of 2 mm diameter and is set to touch the sample surface (the superabsorbent covered with the nonwoven) with its bottom. 60 ml of saline are added to the sample within 3 seconds, conveniently through a syringe without needle so that the fluid intersects the LVDT rod and the liquid is thus evenly distributed over the disc. The sample's swelling is recorded as function of time. A 300 second time span is observed. Conveniently, the LVDT rod displacement is directly converted to superabsorbent volume increase and recorded as function of time. Absorption Time is then determined as de- scribed above.

Absorption Time determination may also be used to determine the superabsorbent's volume increase during swelling. The volume of the superabsorbent sample can easily be determined by using a graded sample holder or calculated from the superabsor- bent's Packed Bulk Density (method of measurement see below), and the volume increase can be calculated using the linear LVDT rod displacement and the known other dimensions of the sample holder that are unaltered during swelling.

Packed Bulk Density

The packed bulk density ("PBD") of a superabsorbent material is determined by pouring a representative sample into a density cup. The cup is placed in a Powder Tester (Powder Characteristics Tester, Model PT-S, obtainable from Hosokawa Micron Powder Systems, Summit, New Jersey, U.S.A.), where it is tapped for a specified period of time. The mass of the sample in the cup is divided by the volume of the cup to calculate the packed bulk density of the polymer.

Equipment and Materials a. Beaker, 250 ml b. Balance, accurate to + 0.01 g c. Spatula with flat blade d. Hosokawa Powder Tester, including 100 ml density cup and extension e. Utility tray

Hosokawa Powder Tester Setup

Set the time to 180 sec on the 60 Hz scale, which equates to 1 tap per second. Set the "VIB/OFF/TAP" switch to "TAP". These settings should never be changed.

General

Keep samples in closed containers and allow them to equilibrate to laboratory temperature before removing a sample for testing. Adjust laboratory conditions to 23 +/- 2 ⁰C and 50 +/- 10% relative humidity. To obtain a representative sample, rotate the sample container end over end several times before taking a sample. The container should be no more than 80% full so as to ensure good mixing.

Procedure Test each sample in duplicate on the same well mixed laboratory sample. Weigh the empty density cup to the nearest 0.01 g and record the weight as W1. Weigh a 100g + 0.01 g sample into a 250 ml beaker. Place the Powder Tester's extension onto the density cup. Pour the sample into the density cup. Place the density cup onto the Powder Tester and press the "Start" button. When the tapping has stopped, remove the density cup and place it on the utility tray. Grasp the density cup firmly and remove the extension piece. Use a spatula to remove excess superabsorbent from the top of the density cup by scraping the top of the cup with the spatula. Weigh the density cup containing the sample to the nearest 0.01 g and record the weight as W2.

Packed Bulk Density Calculation

The packed bulk density (PBD) is calculated as follows:

PBD = (W2 - W1 ) / V [g/ml_]

Where:

W1 = weight of empty density cup (g).

W2 = weight of density cup with sample (g). V = volume of density cup (ml.)

Clump size

The clump size of a cat litter is determined by dropping 10 ml of synthetic cat urine from a syringe (without needle) onto a bed of cat litter within 5 seconds, and weighing the resulting cat litter clump. The synthetic cat urine is an aqueous solution of 0.065 of CaCI₂ ^■ 2 H₂O, 0.065 g of MgCI₂ ^■ 6 H₂O, 0.46 g of NaCI, 0.23 g of Na₂SO₄, 0.065 g of sodium citrate, 0.002 g of sodium oxalate, 0.28 g of KH₂PO₄, 0.16 g of KCI, 0.1 g of NH₄CI, 2.5 g of urea and 0.1 1 g of creatine in a final volume of 100 ml (cf. M. B. Brown, M. Stoll, J. Maxwell and D. F. Senior, in: J. Clinical Microbiol., May 1991 , p. 1078-1080.)

Particle Size Distribution

Particle size and its distribution is determined according to EDANA (European Disposables and Nonwovens Association) recommended test method No. 420.2-02 "Particle size distribution".

Examples

For the examples, a standard commercial clumping cat litter was used as a basis material and admixed with the superabsorbents in the amounts as listed below by dry mixing. Absorption Time and Clump Size were determined.

Example 1 (Reference)

No superabsorbent was added to the cat litter.

Example 2 (Comparison)

The cat litter was admixed with 2 wt.-% of IM 1000 F, a commercial superabsorbent recommended for cosmetics thickening applications (not urine absorption), having a grain size of 106 μm and below, produced by solution polymerization by Hoechst CeIa- nese Corp. Somerville, New Jersey, U.S.A.

Example 3

The cat litter was admixed with 2 wt.-% of a sieve cut of 180 μm and below of ground Luquasorb^® 1200, a commercial, non-surface crosslinked superabsorbent produced by solution polymerization available from BASF Corporation, Charlotte, North Carolina, U.S.A. Example 4

The cat litter was admixed with 2 wt.-% Luquasorb^® 1280 RS, a commercial comparatively fine-sized superabsorbent produced by solution polymerization available from BASF Corporation, Charlotte, North Carolina, U.S.A.

Example 5

The cat litter was admixed with 2 wt.-% Insta-Snow™ powder, a commercial superab- sorbent having a particle size of 150 to 300 μm, produced by emulsion polymerization and available from Steve Spangler Science, Englewood, Colorado, U.S.A.]

The results obtained are listed in Table 1.

Table 1

Example Absorption T [seconds] Clump Size [grams]

1 - 26.57

2 n.a. (» 300) 27.45 3 40 26.18

4 30 23.77

5 10 20.29

The examples show clearly that the "faster" the superabsorbent is, the better is cat litter utilization. Smaller clumps mean that a given amount of cat litter can take up more cat urine. Adding a "slow" superabsorbent, to the contrary, may even make cat litter utilization worse.

Claims

We claim:

1. A cat litter comprising a superabsorbent that has an Absorption Time of less than 60 seconds.

2. The cat litter of claim 1 wherein the superabsorbent has an Absorption Time of less than 50 seconds.

3. The cat litter of claim 2 wherein the superabsorbent has an Absorption Time of less than 40 seconds.

4. The cat litter of claim 1 wherein at least 95 wt% of the superabsorbent have a particle size of at most 300 μm.

5. The cat litter of claim 1 that also contains a swellable clay.

6. The cat litter of claim 5 wherein the swellable clay is sodium bentonite.

7. A process for producing the cat litter of claim 1 that comprises mixing a superab- sorbent that has an Absorption Time of less than 60 seconds with a clay.