CA1290638C - Detergent for automatic dishwasher - Google Patents

Abstract

Abstract of the Disclosure A thixotropic aqueous detergent for improved performance in household automatic dishwashers comprises alkali metal tripoly-phosphate, dispersed clay thickener, a chlorine bleach compound and preferably a water-soluble polyacrylate. A particularly preferred polyacrylate is sodium polyacrylate having a molecular weight in the range of about 1000 to about 500,000. Low molecular weight polymers e.g. 1000 to 50,000 provide less filming on glass.

Description

63~3 One aspect of this invention relates to an aqueous thixotropic automatic dishwasher composition comprising a liquid f~ ~ S~ c;fRnt ~J phase which is water containing~alkali metal tripolyphosphate, clay thickener, a chlorine bleach compound and from about 0.01%
to about 3% of water-soluble polymeric carboxylic acid, said composition additionally comprising sufficient water-soluble potassium compound and a sodium compound to provide a K:Na weight ratio in the range of about 0.04 to 0.5.
Preferably the acid is an acrylatel such as sodium polyacrylate having a molecular weight of from about 1,000 to 500,000, more preferably 1,000 to 50,000. Optionally a carbon-ate, such as potassium carbonate, is present. The composition may also include potassium tripolyphosphate or potassium pyro-phosphate. The clay is preferàbly a non-swelling clay such as attapulgite. Canadian Patent Application 5erial No. 432,542 filed July 15, 1983 discloses certain compositions of this type.
Preferably the limited proportion of a water-soluble potassium compound, e g., a potassium salt (or KOH), in the composition, provides a K:Na weight ratio which is in the range of about 0.07 to 0.4 such as about 0.08 or about 0.15. The resulting product is much more stable in that it has less tendency to thicken undesirably or separate on aging at, say, 100F. Also, substitution of a portion of the sodium salt by the same weight of the corresponding potassium salt results in a considerable reduction in viscosity (e.g. as measured with a Brookfield HATD viscometer, at 25C at 20 rpm using spindle #4), greater stability against separation on aging (e.g., at room temperature), and inhibition of growth of relatively large crystals on storage. The reduction 63~

in viscosity makes for easier handling in the production plant, easier dispensing in use, and makes it easier for the consumer to destroy the thixotropic structure of the product (by shaking the container in which it is packaged) so that it can be poured readily into the detergent cup(s) of a household automatic washing machine.
In the formulation of the product the proportions and ingredients set forth in the above-mentioned Canadian application Serial No. 432,542 may be employed. In that application, one set of ranges of proportions is, approximately, by weight:
(a) 8 to 35% alkali metal tripolyphosphate, (b) 2.5 to 20% sodium silicate, (c) 0 to 9% alkali metal carbonate, (d) 0.1 to 5% chlorine bleach stable, water-dispersible organic detergent active material, (e) 0 to 5% chlorine bleach stable foam depressant, (f) chlorine bleach compound in an amount to provide about 0.2 to 4% of available chlorine, and (g) thixotropic thickener in an amount sufficient to provide the composition with thixotropy index of about 2.5 to 10.

9~3~

Preferably, ~n the compositions disclosed herein, the proportion of sodium tripolyphosphate is above 15% (more preferably in the range of about 20 to 25 or 30%), the propo~tion of sodium silicate is at least about 4% (such as in the range of about 5 to 10 or 15%), the proportions of alkali metal carbonate is about 2 to 6 or 7%, the proportion of chlorine bleach is such as to provide above 0.5% available chlorine (e.g. about 1 to 2% available Cl), the proportion of detergent active material i8 in the range of 0.1 to 0.5%. Calculated as SiO2, a preferred range of pro-portions of sodium silicate represents about 3.5 to 7 SiO2 in the composition.
The proportion of water ln the compositions (measured by "Cenco*moisture analyzer" (in which the sample is heated, by a~
infrared lamp, untll it comes to constant weight) is preferably in the range of about 40-50~ more preferably about 43-48% such as about 44 or 46%.
The compositions disclosed herein usually have pHs well above 11 or 12. In one preferred type of formulation, the composition when diluted with water to 0.75% concentration has a pH in the range of about 10.7 to 11.3.
The composition disclosed herein are preferably formulated to have viscosities (measured with a BrookfieId*HATD
viscometer at 25C at 20 rpm using spindle ~t4) of less tha~ abou~
8000 centipoises and more preferably in the range of about 2,000 or 3,00Q to 7,000 centipoises such as about 4,000 to 6,000 centi-poises. The viscosity, and other properties, may be .M.

o~
:~i measured sever~l days (e.g., a week) after the composition is prepared; it is good practice to shake the sample before measuring¦
its viscosity and to let the viscometer run for some 90 seconds ibefore taking the reading.
! The compositions disclosed herein have yield values ¦ well above 200 dynes per cm2 and are preferably formulated to ¦have Yield values of less than about 1100 dynes/cm2 and more than about 300 dynes¦cm2, more preferably less than about 900 dynes/cm2 I such as about 400 to 600 dynes/cm2. The yield value is an in-ll dication of the shear rate at which the thixotropic structure ~1 breaks down. It is measured with a ~aake*RV 12 or RV 100 ro-¦~ tational viscometer using spindle MVIP at 25C with a shear rate ¦¦ rising linearly in 5 minutes (after a 5 minute rest period) from i zero to 20 sec. 1. In the Haake viscometer, a thin layer of the material is sheared between ~ rotating cylinder and the closely ad~acent cylindrical wall of the surrounding container.
Fig. 1-3 are graphs obtained on such testing of the products of the three Examples indicated thereon, ~ith the peaks Y showing the yield values.
Another factor measured with the aforesaid ~aake viscameter is the degree to which the composition recovers its thixotropic structure. In one measuring technique after the 5 minute period of increasing shear rate mentioned above, the rotation is decelerated to zero over 5 minutes then after a 30 second rest period the rotation is again accelerated to raise the shear rate linearly in 5 minutes from zero to 20 sec. 1.
This gives a second yield value, $.e. peaks Yr in Fig. 1.

*T.M.

~'~90638 Preferably this second ~recovered) yield value is at least 200 dynes/cm2, such as 50~, 75% or more of the initially measured yield value.
~i, Fig 4 is a photomi.crogr~ph (taken on the scale in-dicated thereon~ of the composition of Example 4.
The following Examples are given to illustrate this invention further.
In these Examples, Attagel*#50 ls powdered attapulgit~
' clay (from Engelhard Minerals ~ Chemicals, whose trade llterature indicates that, as produced, it contains about 12 wt.~ free i moisture, as measured by heating at 220F, and has a B.E.T. sur-face area of about 210 m2/g calculated on a moisture-free bas1s);
Graphtol Green is a coloring agent; LP~N*158 is an antifoam agent ~ oe~h~
from American.~l~h3~ (Knapsack) comprising a 2:1 mixture of mono-! and di- (C16-C18) alkyl esters of phosphoric acid, the sodlum i silicate has an Na20:SiO2 ratio of 1:2.4; Dowfax 3B2 is a 45X
I aqueous solution of Na monodecyl/didecyl diphenyloxide disulfonate a bleach-resistant anionic surfactant; STPP is sodium tripoly-i phosphate. Unless otherwise indicated, the STPP is added in thefor~ o f the finely powdered commercial anhydrous material whose water content is about 0.5X, in such material typically about 4 . 5 - 6. 5~ of the material is present as the pyrophosphate.
The water used is deioni~ed water unless otherwise indicated.
*T.M.

6~3 ~ EXA~PLE 1 !' The following ingredients are added to a vessel in'¦ the order given below while mixing with a conv~ntional propeller-i type laboratory stirrer~ The temperatures and mixing times at various stages are also indicated below:
mass(~) temperature(F3 i 10% Graphtol green (color) 5 130F water 1746 molten LPK~ 158 (antifoam) 8 Dowfax 3~2 (surfactant~ 40 126 (2 min) 9;1 mixture of Attagel ~50 and TiO2 white pigment 180 122 (1 min) 120 (3 min) soda ash 275 134 (1 min) 132 (3 min) Finely powdered STPP hexahydrate 750 127 tl min) 125 (3 min) 124 (5 min) 47.5% aqueous solution of sodium 421 silicate premixed with 50X aqueous ~olution of NaOH 150 118 (3 min) 13X aqueous solution of NaOCl 500 108 t3 min) Finely powdered STPP bexahydrate 750 108 (1 ~in~
Total 5000g 107 ~5 mln) 633~
.

The viscosity of the mixture, measured as indicated . above, i~ about 5000 centipoises after aging for 3 ~eeks at lQOF and is about 4800 centipoises after 3 months aging at 100F.
In this Example, the STPP hexahydrate has the fol-' lowlng approximate size distribution:
! U S.S Sieve %

! on #10 0 on ~40 0 on #100 25.4 on #200 31.5 on #325 16.5 ¦ through #325 25.9 The following formulations are prepared and theirproperties are measured as indicated belo~:
The ingredients ar~ mixed in the following order:
water, color, clay, one half of the phosphate, defoamer, hypo-chlorite, sodium carbonate, potassium carbonate, NaOH, silicate, second half of phosphate, surfactant.

6~l~

In~redients Proportions a b c d Clay (attagel 50) 3.285 3.285 3.285 3.285 3.285 i! STPP 23.0 23.0 17.01 16.5 23.0 ;~ Potassium tripo-~' lyphosphate - - - 6.5 ! Potassium Pyro-¦ phosphate - - 5.g9 - 0 l Sodium Carbonate 5.0 - 5.0 5-0 2.5 Potassium Carbonate - 5.0 - - 2.5 Sodium Hypochlorite i (l2%2 g.375 9.375 9.375 9.375 9.375 l Sodium Hydroxide i (50%~ 2.05 Z.05 2.052.05 2.05 Sodium Silicate l (47.5%) 10.53 10.53 ~0.5310.53 10.53 i Surfactant (Dow-fax 3B-2) 0.80 0.80 0.800.80 0.80 Defoamer (Rnap-sack Lp Kn) 0.16 0.16 0.160.16 0.16 l Color 0.381 0.381 0.381 0.381 0.381 ¦I Water 8alance I

lProperties capillary drain-age time (min.2 8.2 12.1 lO.9. 11.4 11.2 Viscosity (cps) lon 100~ aging !1 week 9080 3100 2900 5120 5400 2 weeks 9200 3480 2820 6340 5240 3 weeks 9300 3600 3040 6700 6560 The capillary drainage time is a conventlonal test i~
which a 6.8 cm. diameter circle is drawn on a 15 cm diameter shee~
of Whatman size 41 filter paper, 8 plastic annulus (3.5 cm inside diameter, 4.2 cm outsiae diameter, 6.0 cm high) is placed ver-tically, concentric with the circle, on the filter paper, and the annulus is filled with the composition to be tested. Liquid from the compositlon is thereby absorbed into the filter paper and spreads slowly to the drawn c~rcle. The ti~e which elapses until the liqu~d contacts the circle is measured at three predetermined locations and an average value is calcula~ed.

_g_ 6~

I

The following formulations are prepared by mixing the ingredients in the order indirated. The compositions are then centrifuged at 275 G until there is no further increase in the volume of the clear separated liquid ~continuous) phase and the resulting liquid is analyzed: ¦
a b c d deionized water 27.l06 ~ -~
color 0.016 ~~
sodium carbonate 6 4 2 0 potassium carbonate 0 2 4 6 STPP 21.106 ~~~ - - -~
deionized water 14.184 Attagel #50 4.00~~~
T102 0,444 _ `A'_ _~
50% solution of NaO~ 2.5 -~-- -------------------- ..
47.5% solution sf sodium sillcate 13.684 ~---~
antifoam 0.16 ~~---~ ~f 13% solutlon o~ NaOCl 10.0 45% solution of sur-factant 0.8 ~~~~--~~~~~

~ 100.00 . Thus the compositions are identical except for eheir K:Na ratios Properties of Product ., a b c d viscosity after 1 day at room I temperature 8320 5520 4200 2120 j after 3 weeks at room Il temperature 8550 6200 4500 2420 ii after aging at ¦ lo0F for 7 weeks 9400 8000 5600 3400 ! Specific gravity 1.37 1.37 1.40 1.39 ~l Properties of liquid i Obtained by Ce~trifugin~

!I viscosity at 25C
! relat~ve to water at l 1 cps. 4.4 4.4 4.8 6.3 ! % soluble silicate (calculated at mol ratio Na20~Si02 of 1:2.4~ 7.5 7.3 7.3 7.1 % carbonate (calculated as Na2C03) 8.8 8.5 7.4 6.6 phosphate (calculated as Na5P3010) 1.7 2.5 3.7 6.1 specific gravity 1.257 1.262 1.276 1.30 The viscGsities of the product for this Example are measured ~ith a Brookfield RVT viscometer spindle ~o. 5 at 8aF (26.7C.~.
Examples 4-6 below illustrate a ne~ and useful method for making the products described above (containing limited amo~nts of potassium~. It can also be used for making ~ 2301-1326 other products of the type shown in the previously mentioned Canadian Application Serial No. 432,542 (e.g. in which the potassium compound is not present) as well as other detergent , n org ~n ~c J slurries comprising fine particles of water-soluble inrG~
builder salts dispersed in water containing dissolved builder salt, clay or other colloidal thickening agent, and surfactant.
In these Examples (in which the particles of builder salt in the product are largely STPP hexahydrate plus hydrated sodium carbonate) there is formed a highly viscous (e.g. 20,000-60,000 cps viscosity) mixture of a limited amount of water, a highly alkaline saturated solution of builder salts and, as the major constituent, undissolved particles of water-soluble builder salt.
This viscous mixture is subjected to grinding of the undissolved particles with a high speed disperser after which solid particles of the clay thickener are added and the clay is mechanically deagglomerated; thereafter the balance of the ingredients of the formula (e.g., other liquids or materials which readily dissolve or disperse in the liquid phase of high electrolyte content) may be mixed in. The mixture may then be subjected to additional high shear mechanical action to further deagglomerate the clayO
It is found that with this method pre-dispersion of the clay in aqueous medium is not needed. The solid particles of clay readily disperse even though the medium is highly alkaline.
The grinding of the undissolved builder salt particles takes place much more efficiently and rapidly in the substantial absence of the clay.

i I
i In the meehod illustrated in Examples 4-6 the builde~
salt ~hich is to constitute the ma~or portion of the undissolved ¦
i particles is prefe~ably added to an aqueous solution which alread~
¦ contains such a higb concentration of dissolved other builder ,I salt tha~ this addition causes builder salt to be thrown out of jl solution (e.g. by common ion effect) and thus to recrystallize as tiny crystals.
,, Another significant feature of the mixing method 1, illustrated in Examples 4-6 is the fact that it enables repeated batches of reproducible properties to be made using the entire "heel" of the previously formed batch as an ingredient of each successive batch.
l As indicated earlier, the use of the process il-il lustrated in Examples 4-6 is not limited to the making of compo ¦~ sitions containing potassium salts. While it has thus far found its great~t utllity in making formulations in which ~he clay is attapulgite, it may also be employed for compositions in which all, or part~ of the clay is of the swelling type, e.g., a smecti ¦ type of clay such as bentonite (e.g., Gelwhite GP) or hectorite.

In 32.0 parts of deionized water mixed with a æmall amount of a pigment (i.e., 0.028 parts of Graphtol green, an aqueous paste containing 28~ pigment) there are completely dis-solved 2.0 parts R2C03 (whose water solubility i6 over 100 parts 7~ra~12 m6~r K

per 100 parts of water even at 0C and 5.0 parts granular sodium carbonate (whose water solubility is abou~ 45 parts per 100 at 35C~. The solution has a temperature of about 90F. Then 23.116 parts of powdered STPP containing about 0.5Z watsr of hydration are added while continuously subjecting the mixture to the action of a high speed disperser. The amount of STPP
is much more than that which is soluble in the amount of water present; its solubility in water is about 20g per 100 ml at 25C.
In this example, the STPP is a product of Olin Corp. having a phase I content of about 50~, a sodium sulfate content of about 2~, and a very fine par~icle slze, it is a blend of powdered anhydrous STPP made by the known "wet process" and powdered STPP hexahydrate. On adding the STPP to the solution it hydrates rapidly, forming hard crystalline lumps comprising STPP he~a-hydrate. (It will be noted that 23 parts of STPP has the capacit in forming the hexahydrate, to take up about 7 parts of water).
The mixture $s at first a thin slurry of undissolved STPP in a liquid which is a supersaturated solutlon. The temperature rises owing to the hydration reaction, reaching a peak of about 140 F. In about 3 to 4 mlnutes the mixture becomes much more viscouse; its v~scosity rises to above 20,000 cps (such as about 40,Q00-50,000 cps as measured st the slurry temperature e.g.
with a 8rookfield RVT, spindle #6 a~ 10 RPM). It is believed that during the process, sodium carbonate crystallizes (in the form of very fine crystals) out of the solution phase ow~g ~ ~e .... ..

3~

common ion effect (of the sodium of the STPP). When the mixture has become viscous the hi8h speed disperser acts to grind the particles (e.g. of hydrated TPP) eO a fine particle size, the grinding action is ~ndicated, for one thing9 by the increased power consumption of the disperser and an addltional rise in i! temperature (e.g., to 150F, ~hich causes increased dissolution of builder salts; these will, in ~urn, recrystallize in fine I form on cooling). This grinding is continued for about 5 minutes I after the initial thickening of the slurry; during grinding the ,I visible lumps of material disappear and the particle size of the ,¦ undissolved particles is reduced so that, it is believed, sub-l¦ stantially all the particles have diameters below 40 microns.

i Then a further 9.367 parts of water are added, lowering the vis-! cosity to less than lO,OOO cps te.g. ln the neighborhood of l SQOO cps, measured as indicated above)~ after which 3.3. parts ¦ of Attagel ~5Q and 0.732 parts of white TiO2 (anatase) pigment i are added to the highly alkaline mixture ~hose pH is well over ~ 9, e.g. 10.5~ while the mixture is continuously subjected to the i action of the high speed di~perser, which disperses (deagglo-! merates) the clay to a large extent, so that the thick mixture becomes homogeneous and smooth in appearance. Then there are added 2.70 parts of 50% aqueous Slution of NaO~, 0.16 parts of antifoam ageot (Knapsack LPKN 1582, 10.53 parts of 47 . 5% aqueous solution of sodium silicate (whose ~a20:SiO2 ratio is 1 2.4), 10.0 parts of a 12% aqueous solution of sodium hypochlorlte and 0.8 part o~E a 45~ aqueous solution of a bleach-resistant anionic surfactant (Dowfax 3B2~; these additions may be made under any desired mi:~ing conditions, e.g., with simple stirring (although it may ~e convenient to conti~ue the high shear dispersing actio for such mixing~. The mixture i~ then sub~ected to a milling action, as by passing it through an in-line mill such as a Tekma ~ Z~06~

~ pax Reactor" (which operates at a top speed of 22 meters per secondj which subjects the mixture to a high shear rate for a relatively short time (e.g. the "residence tlme" in the mill il may be merely two seconds or :Less~. The principal effect of this is to further deagglomerate the clay particles, as indicated by a significant increase in the yield value, e.g. raisiDg the yield value of the mixture by some 33%.
The resulting mixture is thixotropic. It is believe that the particle size of the dispersed solid particles therein is so small that some 80% by weight, or more, have particle sizes i below 10 microns. The mixture is at a temperature in the neighbo hood of 120-130F (at this ~emperature its viscosity $s higher than at say 70F~. It is drained off from the mi~ing vessel (e.g., from a bo~tom valve when the vessel has a conical bottom, or from a lower side valve of a substantially flat-bottomed mixin~ vessel). About 1~% of the mixture remains as a "heel" in the vessel; owing to its flow characteristics it ~s difficult to remove all the composition from the vessel.
The entire procedure described above is then repeate over-and-over in the same mixing vessel ~ithout removing the heels at all.
The high-speed disperser may comprise a circular horizontal plate having alternately upwardly and do~nwardly extending circumferential teeth, which plate is mounted (on a vertical downwardly extending shaft) so as to rotate so rapidly that the circumferential speed (of the ~eeth) is more than about ~.~9~

75 f eet per second (e.g. 90 feet per second). For laboratory operation a Cowles high speed disperser is suitable; for larger scale operation a ~yers model 800 ser~es high speed disperser may be used. These high speed dispersers reduce particles by impact grinding by the toothed plate and by laminar shear stress on the mixture. The shear generates heat in the batch, in ad-dition to the heat generated by the dissolving, hydration, etc.
At the resulting relatively high temperature the ingredients are more soluble and on crystallization on coo~ing will give relatively small particles ~hich do not settle rapidly if at all.
The high speed disperser induces a "rolling" of the mixture i.e. t path of movement of the mixture is downward centrally of the ves-sel, outwardly along the rotating plate, upwardly along the side walls of the vessel and inwardly at the upper surface of the mix-ture. In the course of this movement desirable deaeration occurs, i.e., air (which is always introduced ~hen powders are add~d) will leave the mixture during the inward leg of its circuit.
Apparently, after processing of the composiiton deæ-cribed above, crystal growth occurs to form many larger and re-latively uniform-sized crystals (as shown by photomicrographs).
Thus Fig. 4 indicates that crystals having diameters on the order of 80 microns are present. These crystals appear to contain polyphosphate but have not yet been fully indentified.

Example 4 is repeated except that the STPP powder is a Monsanto anhydrous STPP made by the known 'Idry process" and com-prising anhydrous STPP humidified to the extent that i~s content of water of hydration is ~% (or somewhat higher, e.g. 1~%). Iels phase I content is about 20%. This STPP was also used in Ex-ample 3.

9~

Example 4 is repeated except that the initial proportion of water is 28.0 parts, the second proportion of water is 13.637 parts, and prior to the addition of the attapulgite clay there is added 1.11 parts of 45% aqueous solution of sodium polyacrylate (Acrysol LMW-45N*, having a molecular weight o:E about 4500). The amount of K2CO3 here is 3 parts and the amount of Na2CO3 is 4 parts.
The products of examples 4-6 were found to have the following characteristics: -Example viscosity (cps) 40006000 4400 yield value (dynes/cm2) 450 600 450 capillary drainage time (min) 8.2 5.6 6.1 centrifugal separation (%) 16 26.3 12 Thixotropy index 5 4.3 4.1 "Centrifugal separation" is measured by centrifuging at 275G as described in Example 3, above, and measuring the volume of the clear liquid layer in relation to the total volume.
"Thixotropy index" is the ratio of the viscosity at 30 rpm to that at 3 rpm, measured at room temperature with a Brookfield HATD viscometer, #4 spindle, as described in said Canadian Application Serial No. 432,542.

*Trade Mark .
,. .

In Example 6 a soluble chlorine bleach-resistant polymer is present. It is fou~d that the presence of the polymer improves tfie resistance to sepalration of the product on standing or on centrifuging, without imparting a corre~pondingly large increase in the v~scosity of the product. It will be appreciated that the polymer is present here in a very highly concentrated (saturated) electrolyte solution. It is also found that the presence of the polymer leads to improved protection of the over-glaze layer of dishware (fine china~. In wor~, thus far, these effects have been observed with polyacrylic acid salts, which have been found ~o be entirely compatible with chlorine bleach and with the clay in this system, e.g. the active chlori~e con-tent is maintained, as is the viscosity. Polymers of different molecular ~eights may be used, for instance, the polymer may have a molecular ~eight less than 10,000 or a molecular weight of 100,000 or more. Preferred molecular weights range from abou~
1,000 to 500,00~. Molecular welghts of from about 1000 to 50,000 are particularly notable for providing less filming on glass. The proportions of polymer may ~e in the range of ~.01 to 3% with the lo~er proportionR being more suitable for the higher molecular weight polymers (e.g. 0.06% for a 300,000 molecular weight polymer ) Other bleach-reslstant polymers may be employed e.g. Tancol 731 which is a sodium salt of a polymeric carboxylic acid havlng a M.W. of about 15000.
In this application all propDrtions are by weight unless -otherwise indicated. In the Examples atmospheric pressure is used unless otherwise indicated.
It ls understood that the foregoing detailed description is given merely by way of illustration and that variations may be made therein ~ithout departing from the spirt of the invention.

Claims (12)

1. An aqueous thixotropic automatic dishwasher composi-tion comprising a liquid phase which is water containing alkali metal tripolyphosphate, clay thickener, a chlorine bleach, from about 0.01% to about 3% of a water-soluble poly-meric carboxylic acid, said composition additionally comprising sufficient water-soluble potassium compound and a sodium compound to provide a K:Na weight ratio which is in the range of about 0.04 to 0.5.

2. A composition according to claim 1 wherein said K:Na weight ratio is in the range of about 0.07 to 0.4.

3. A composition according to claim 1 wherein said K:Na weight ratio is in the range of about 0.08 to 0.15.

4. A composition as in claim 1 wherein the acid is an acrylate.

5. A composition as in claim 4 wherein the acrylate is sodium polyacrylate having a molecular weight of from about 1000 to 500,000.

6. A composition as in claim 5 in which the polyacrylate has a molecular weight of from 1000 to 50,000.

7. A composition as in claim 6 wherein a carbonate is present.

8. A composition as in claim 7 wherein the carbonate includes a potassium carbonate.

9. A composition as in claim 7 including potassium tripolyphosphate.

10. A composition as in claim 7 including potassium pyrophosphate.

11. A composition as in claim 8 wherein the clay is a non-swelling clay.

12. A composition as in claim 11 wherein the clay is attapulgite.