Stability of liquid automatic dish-washing detergents

Abstract

 The physical stability of clay structured liquid auto­matic dishwashing detergents can be improved significantly by correctly proportioning the functional raw materials. Correct selection of the type and level of components such as phosphates, silicates and carbonates obviates the need for separate physical stabilizers.

Description

FIELD OF THE INVENTION

[0001] This invention relates to liquid or gel-like automatic dishwashing detergents which are useful in cleaning soil from dishes, glasses and the like. More particularly it provides for such a composition containing a relatively high level of silicate to enhance the physical stability of the composition.

BACKGROUND OF THE INVENTION

[0002] Since their introduction, consumer acceptability of liq­uid automatic dishwashing detergents has been on the increase. Consumers regard liquid automatic dishwashing detergents (LADD) as more convenient to use than powdered automatic dishwashing detergents. The physical stability of the liquid or gel product is essential for meeting overall consumer satisfaction.

[0003] Formulation of Liquid ADDs for use in most available automatic dishwashing machines is difficult because these auto­ matic machines have dispensers which are designed to dispense detergents in powder form and are unsuitable for retaining low viscosity liquid detergents. Relatively high viscosity liquid detergents (≧ 1500 cps) may be retained in the dispenser, but, since the machine dispenser cups are not water tight, water infiltration during the cycles (pre-rinse and pre-wash) is condu­cive to dilution and subsequent leakage of the liquid detergent from the cup. Liquids with a viscosity above about 2500 cps may be retained in the dispenser even after partial dilution with water but are inconvenient to pour into the dispenser cups. Alternatively, a relatively high viscosity thixotropic system capable of shear-thinning to about 200 cps, and then reverting to high viscosity while at rest, is preferred. Such a system can be easily dispersed from a container, and facilitates usage by the consumer. The system must also provide sufficient viscosity and yield point to remain within the dispenser until the cup opens at the start of the main wash cycle.

[0004] The preferred compositions are normally of gel consistency, having Bingham plastic characteristics and thus rel­atively high yield values. As a result, a definite shear force is necessary to initiate or increase flow. This force would be present within the agitated dispenser cup of an automatic dishwasher. Under these conditions, the composition is quickly fluidized and easily dispersed. When the shear force is discontinued, the fluid composition quickly reverts back to a high viscosity, Bingham plastic state closely approximating its prior consistency.

[0005] Attempts to accurately measure viscosity of such systems with a Brookfield LVT viscometer were unsuccessful. Due to the high thixotropy experienced with these products, viscometer read­ings fluctuated significantly. Furthermore, there were marked differences in results between measured sites within the same batch.

[0006] Excellent data reproducibility is obtained with a Rheomat 108 Viscometer. Utilizing the #2 spindle, a viscosity reading (µ₁) is obtained after six minutes at a shear rate of 355s⁻¹. Following six minutes at 355s⁻¹ shear rate, the instru­ment is shut off for five seconds while the shear rate is set to 17.7s⁻¹. Shear is resumed and a second viscosity reading (µ₂) is obtained after ten seconds. A final viscosity reading (µ₃) is obtained (at 17.7s⁻¹) after an additional 6 minutes.

[0007] Typical viscosity ranges for the high silicate formula of this invention are:

µ₁	180-230
µ₂	1400-2000
µ₃	1500-2100

Stability is of primary importance, i.e., there should be no sig­nificant evidence of phase separation or leaking after long standing.

[0008] The provision of automatic dishwasher compositions in liquid or gel form having appropriate properties has not been completely satisfactory. Generally, it is recommended that auto­matic dishwashing detergents contain (1) sodium tripolyphosphate (NaTPP); (2) sodium silicate to supply the alkalinity necessary for effective detergency and to provide protection for fine china glaze and patterns; (3) sodium carbonate, to enhance alkalinity; (4) a chlorine-releasing agent; and (5) a defoamer and/or surfac­tant to enhance machine efficiency and supply detergency. Combining these ingredients in a gel form effective for home-­machine use is difficult. These compositions often omit hypochlorite since it tends to react with other chemically active ingredients. U.S. Patent 4,115,308 discloses thixotropic auto­matic dishwasher pastes containing a suspending agent; inorganic salts, surfactant and a suds depressant. U.S. Patent No. 4,147,650 optionally includes a bleach. U.S. Patent No. 3,985,668 describes abrasive scouring cleaners. U.K. Patent Applications GB 2,118,199A, GB 2,140,450A, and GB 2,185,037A dis­close automatic dishwasher compositions having thixotropic, gel-­type structures

[0009] U.K. Patent Application 2 176 495A is similar to GB 2,118,199A and GB 2,140,450A but improved physical stability is disclosed by incorporating salts of polyvalent metal stearates.

[0010] Provision of appropriate compositions having a suffi­ciently high viscosity not to leak out of dispenser cups with sufficiently shear thinning behavior to be easily dispensed from a container, good solubility, good washing properties, good con­sumer acceptability with long shelf life at a relatively low cost, has not been satisfactory without using special stabilizers whose purpose is not to achieve cleaning, but rather, is directed to physical stabilization.

[0011] Accordingly, it is an object of this invention to pro­vide liquid or gel ADD compositions having thixotropic properties with improved physical stability and rheological properties while minimizing the need for a physical stabilizer.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Broadly, the present invention provides a normally gel-­like aqueous automatic dishwasher detergent composition having thixotropic properties. The composition includes, on a weight basis:

(a) 15 to 17% alkali metal tripolyphosphate;

(b) 12 to 18% alkali metal silicate;

(c) 2 to 7% alkali metal carbonate;

(d) 0.1 to 5% detergent active material;

(e) 0.1 to 5% phosphate ester foam depressant;

(f) chlorine bleach compound in an amount to provide about 0.2 to 4% of available chlorine;

(g) 0.8 to 5% thixotropic thickener in an amount sufficient to provide the composition with thixotropy index µ₃/µ₁ of at least 5.0.

(h) 0 to 3% sodium hydroxide;

(i) 0 to 2% adjuvants; and

(j) balance water.

[0013] According to this invention, the LADD composition can be readily poured into the dispensing cup of the automatic dishwashing machine and will promptly thicken to its normal gel-­like state to remain securely within the dispensing cup until shear forces are again applied, such as by the water spray from the dishwashing machine.

[0014] Generally, the effectiveness of automatic dishwashing detergents is related to (a) available chlorine levels; (b) alkalinity; (c) solubility in washing medium; and (d) foam inhibition. It is preferred that the pH of the ADD composition is at least about 9.5, more preferably from about 10.5 to 13.5 and most preferably at least about 11.5. Addition of NaOH is often required to achieve a pH within these ranges, to increase flowability properties and to neutralize certain phosphate esters. The presence of carbonate helps to maintain the desired pH level but, excess carbonate is to be avoided, to prevent destabilization. It should be noted that in certain cases suffi­cient alkalinity may be provided by the sodium silicate.

[0015] The alkali metal tripolyphosphate in the composition is present in a range of about 15 to 17 wt%, and preferably about 15.5 to 16.5 wt%. It should preferably be free of heavy metal which has a tendency to decompose or inactivate sodium hypochlorite and other chlorine bleach compounds. Preferably sodium tripolyphosphate (NaTPP) is employed. The NaTPP should have an average degree of hydration of less than about 1. Pre-­moisturization, to an average of about 0.3 to 1% water is most effective, and expedites hydration and solubilization of the remaining NaTPP. The NaTPP contains on the average about 1% by weight of water. If only NaTPP hexahydrate is used. the deter­gent product has little if any thixotropic character. If only the pre-moisturized NaTPP is used, at the specified level, the preferred rheological profile is obtained.

[0016] Foam inhibits machine efficiency. Foam may be suffi­ciently reduced by suitable selection of the type and amount of detergent active material, the main foam-producing component, however, it is generally preferred to include a chlorine bleach stable foam depressant or inhibitor. Inhibitors of the alkyl phosphonic acid esters of following formula are effective

These esters are available from BASF-Wyandote. Alkyl acid phos­phate esters of the formula

available from Occidental Petroleum are preferred. In these esters, one or both R groups may be independently a C₁₂₋₂₀ alkyl group. Mixtures of phosphates with phosphate esters as well as mixtures of mono- and di- esters of the same type, may be employed. A mixture of mono- and di-C₁₆₋₁₈ alkyl acid phosphate esters such as monostearyl/distearly acid phosphates in a 2:1 ratio of mono to distearyl, available from Occidental are espe­cially preferred. 0.1 to 5wt%, preferably about 0.1 to 0.5wt%, of foam depressant in the composition is typical,

[0017] Most inorganic chlorine bleach compounds may be employed in the compositions of the invention, such as chlorinated trisodium phosphate, alkali or alkaline earth metal hypochlorite, especially sodium hypochlorite is preferred. Sodium dichloro isocyanurate has been found to destabilize the compositions. The composition typically contains sufficient chlorine bleach com­pound to provide about 0.5 to 3.0% by weight of available chlorine, as determined for example by iodometric titration. About 0.8 to 1.6% by weight of available chlorine is especially preferred.

[0018] The alkali metal silicate, which provides alkalinity and protection of hard surfaces such as fine china glaze is employed in an amount ranging from about 12.0 to 18.0 wt%, preferably about 15 wt%, in the composition. The silicate is preferably sodium silicate and is generally added in the form of an aqueous solution, preferably having an Na₂O:SiO₂ ratio of about 1:2.2 to 1:2.8, preferably 1:2.4. Amounts of silicate in excess of about 18%, while feasible, significantly affect ease of processing by conventional mixing methods due to increase in viscosity during addition of phosphate. The NaOH, sodium hypochlorite and foam depressant when employed are added as aqueous dispersions or solutions.

[0019] The detergent active materials or surfactants must be stable in the presence of chlorine bleach, especially hypochlorite bleach and are preferably anionic. These surfac­tants are used in amounts of from about 0.1 to 3% preferably about 0.6 to 2.0%, more preferably about 0.3 to 0.6%. The pre­ferred surfactants are the alkali metal sulfate salts of mono- or di- alkyl diphenyl oxides. These surfactants are commercially available as DOWFAX 3B-2 and DOWFAX 2A-1. Surfactants of the type mentioned above, all well known in the art, are described, for example, in U.S. Patents 3,985,668, 4,271,030 and GB 2 176 495A. The surfactant of course, should be compatible with the other ingredients of the composition. Other suitable surfactants include alkylsulfates, and sulfonates as well as alkylarylsulfonates and the like.

[0020] Thixotropic thickeners, or suspending agents are those which provide a medium with thixotropic properties. These are well known in the art and may be organic or inorganic, water soluble, water-dispersible or colloid-forming, and monomeric or polymeric. The thickeners must be stable in the compositions, e.g. stable to high alkalinity and chlorine bleach compounds. The preferred thickeners include inorganic, colloid-forming clays of the smectite and/or attapulgite types. The amounts of the clays of the smectite and/or attapulgite types in the composition range from about 0.5 to 5%, preferably 1.5 to 3.0% by weight and these amounts are generally sufficient to achieve the desired thixotropic properties when used in combination with the propor­tion of ingredients disclosed herein.

[0021] Smectite clays are especially preferred, and include montmorillonite (bentonite), hectorite and the like. Materials of this type are available from Georgia Kaolin under the trade name of Korthix and Gelwhite GP,H, etc. from Southern Clay Products. Both Gelwhite and Korthix are montmorillonite clays. Attapulgite clays include materials commercially available under the trade names Attagel 40, Attagel 50 and Attagel 150 from Englehard Minerals and Chemicals Corporation. Exclusive use of attapulgite clays should be avoided since it becomes difficult to maintain a proper thixotropic profile on aging. Mixtures of smectite and attapulgite types in weight ratios of about 4:1 are useful. Thickening or suspending agents of the types described are well known in the art.

[0022] The amount of water contained in the compositions must be tailored to achieve the proper rheological properties. This amount is usually about 50 to 65wt%.

[0023] It is one of the advantages of the automatic dishwashing formulations of the present invention that the desired thixotropic properties and physical stability can be obtained, without the need for a special stabilizing agent. Instead, the present composition accomplishes the desired physical stability by way of balancing the functional dishwashing ingredients of the composition in proper proportions without the need for special stabilizing additives.

[0024] Other conventional ingredients may be included in these compositions in amounts generally less than about 3wt% such as perfume, preservatives, dyestuffs, pigments and the like. Any such adjuvants of course must be stable to chlorine bleach com­pounds and high alkalinity. Coloring may be accomplished by the chlorinated phthalocyanines and/or polysulfides of aluminosilicate. TiO₂ may also be employed.

[0025] All amounts and proportions referred to herein are by weight of the composition unless otherwise indicated.

Preferred Composition

[0026] 

Ingredients in Preferrred Order of Addition	% Active in Finished Product	gms/kg
Dionized water	56.88	248.57
Bentonite clay	3.00	30.00
Sodium hydroxide (50% aqueous solution)	1.4	28.0
MSAP¹ premix (2.6% in water)	0.16	61.6
Sodium silicate (SiO₂:Na₂O 2.4:1; 47.1% aqueous solution)	15.00	318.5
Sodium carbonate	6.00	60.00
Sodium Tripolyphosphate (Hysorb grade from FMC)	16.00	160.00
Sodium hypochlorite (solution containing 12 available Cl₂)	1.00	83.33
Dowfax²(surfactant 45% aqueous solution)	0.36	8.00
Perfume	0.20	2.00

¹MSAP is a mixture of two parts monostearyl to one part distearyl acid phosphate from Occidental.

²Dowfax is a C₁₂ diphenyl oxide di sulfonate.

Batch Mix

[0027] Laboratory batches may be prepared in pyrex beakers set on a heating plate, in a water bath, at high shear with a Talboy stirring motor. The ingredients are added in the sequence shown above with the following conditions:

a. the temperature of the batch is about 100-110°F (38-43°C) just before addition of the tripolyphosphate;

b. sufficient mixing time (about ½ hr. minimum) is provided for the phosphate to hydrate (Characteristically, upon hydration the batch changes from a gritty to a smooth, creamy appearance);

c. the batch is then cooled to about 30°C prior to hypochlorite addition to minimize loss of chlorine and/or degradation of adjuvants.

[0028] The finished product is homogenized with a Gifford-Wood homogenizer at the highest speed and shear settings for 2 to 3 minutes. Longer homogenization periods usually increase the batch temperature to above 40°C unless the batch is previously cooled to below about 20°C. Rheology measurements and/or dis­penser cup tests are run immediately after homogenizing and again after about 24 hrs. aging at room temperature.

Finished Product Characteristics

[0029]  Typical analysis (Lab prep.)
Specific Gravity3 1.40 ± 0.03
Viscosity4 (homogenized product) in cps.

Range		Thixotropic Ratios
µ₁ -	160-300	µ₂/µ₁	5.5 - 8.0
µ₂ -	1400-2000	µ₂/µ₃	0.75 - 0.85
µ₃ -	1400-2200

		Thixotropic Index
pH 11.8 to 12.6		µ₃/µ₁	at least 5.5

Available chorine (Cl₂) 0.95% - 1.06%

Gardener Weight-per-Gallon Cup Pycnometer (83.2 ml.)
Rheomat 108 Viscometer, measurements taken @ 355s⁻¹ (µ₁) 17.7s⁻¹ (µ₂ and µ₃)

In-situ Dispersion of Clay

[0030] Unlike the pre-swelling of the clay preferred in the art, the practical method for manufacturing the formulations of the invention with a high level of silicate does not involve pre-­dispersion (pre-mix) of the clay as a separate step in the process. Pre-dispersion of the clay in the compositions contain­ing silicate levels in the 12 to 18% range is impractical since a major portion of the total water in the composition is associated with the liquid silicate which as a raw material contains between 53 and 55% water. Since the water is part of the silicate solu­tion it is not available during the early stages in the process before the addition of the silicate. It would thus be impracti­cal to prepare a clay pre-mix with the relatively small amount of the remaining process-water unless the clay premix was incorpo­rated early enough in the process to supply sufficient water to disperse the electrolytes.

[0031] The in-situ clay process does not require the pre-­swelling of the bentonite clay as a separate step in the process. In this in-situ process, the bentonite clay is added "as purchased" (powder form) during either a very early or very late step in the process. An obvious advantage of the in-situ process is the omission of the clay pre-swelling step. The sequence in which the raw materials are added appears to have a determining effect on the viscosity of the batch throughout the process. Raw material addition sequences that yield a lower viscosity during the process generally require a relatively higher degree of homogenization for the finished batch to be satisfactory in the dispenser cup. Sufficient shear or homogenization pressure must be applied to accomplish in-situ swelling the clay. Raw material addition sequences that incorporate the bentonite before the tripolyphosphate require extended mixing time to hydrate the tripolyphosphate in the viscous medium, but require much less homogenization energy to attain the viscosity ranges previously disclosed
Added at 40°C
Added at <30°C

Table I

Preferred Sequence of Raw Material Addition - In-Situ Clay Swelling

[0032] 
Water
Bentonice
Caustic Soda
MSAP
Silicate
Soda Ash
NaTPP⁵
Hypochorit⁶
Dowfax 2A1
Perfume

[0033] The compositions shown in Table II are prepared in accordance with the preferred order of raw material addition and process previously described. Finished batches are made homoge­neous using high shear equipment.

TABLE II

	EXAMPLES
	% active in product
	A	B	C	D	E	F	G	H	I
NaTPP	21.0	16.0	16.0	16.5	15.5	16.0	16.0	15.0	17.0
NaSilicate (2.4r)	8.0	8.0	15.0	15.0	15.0	12.0	13.5	14.0	12.0
Soda Ash	6.0	6.0	6.0	6.0	6.0	6.0	6.0	6.0	6.0
NaOH	1.2	1.2	1.4	1.4	1.4	1.4	1.4	1.4	1.4
MSAP (defoamer*)	0.16
Na Hypochlorite (as cl₂)	1.00
Dowfax (surfactant)	0.36
Bentonite clay	3.00
Water	q.s

Stability
Separation 2 mo. @ RT(%)	12.5	3.0	nil	nil	nil	nil	nil	6.4%	13.5
8 cycles (0-70°F)	16.0	13.2	nil	nil	nil	nil	nil	5.8%	6.0

*Mono/distearyl acid phosphate 2:1 (Occidental)

[0034] The percent separation (clear supernatant) is determined by way of direct measurements in millimeters (mm) from clear glass and plastic containers (8 oz.; 16 oz.) and represents the ratio of clear supernatant (mm) to overall height of product with the jar.

[0035] Example "B" shows the improvement over "A" in product stability when the level of phosphate is reduced from 21% to 16% in compositions containing a relatively low level of silicate (8%).

[0036] Examples "C" through "G" show a further improvement in product stability when the silicate level is increased to 12% or above.

[0037] Examples "H" and "I" show the criticality of the level of phosphate on product stability even for compositions contain­ing higher silicate levels.

[0038] Table III below represents results to further define criticalities in composition that may be pertinent to product stability.

TABLE III

	% active in product
	J	K	L	M	N	O	P	Q	R	S
NaTPP	16.0	16.0	16.0	18.0	20.0	12.0	18.0*	16.0	16.0	16.0
NaSilicate (2.4r)	15.0	15.0	15.0	15.0	18.0	18.0	15.0	15.0	18.0	18.0
Soda ash	6.0	8.0	4.0	4.0	0.0	8.0	6.0	6.0	6.0	6.0
MSAP (defoamer)**	0.16	0.16	0.16	0.16	0.16	0.16	0.16	0.0	0.0	0.16
NaOH	1.4
Na Hypochlorite (as cl₂)	1.0
Dowfax (Surfactant)	0.36
Bentonite clay	3.0
Water	q.s

Stability 2 wks.
% seperation	<1.0	2.2	1.1	4.5	3.5	nil	2.3	2.8	2.4	nil

*9.0:12.7 anhydrous:hexahydrate = 18.0 basis anhydrous TPP

** mono/distearyl acid phosphate 2:1 (Occidental)

[0039] Data in Table III confirm the criticality of maintaining a phosphate level of about 16% ± 0.5%. One exception, Example "O" so far shows that phosphate levels below 15% may be accepta­ble provided that the silicate is increased proportionately. Increase of the phosphate to 20% proved to be detrimental to sta­bility regardless of increase in silicate level.

[0040] It also appears from these formulations that the defoamer or alkyl phosphate ester is a necessary, although not sufficient, ingredient to achieve acceptable stability.

[0041] This invention has been described with respect to cer­tain preferred embodiments and various modifications and varia­tions in the light thereof will be suggested to persons skilled in the art and are to be included within the spirit and preview of this application and the scope of the appended claims.

Claims

1. A thixotropic, aqueous cleaning composition comprising:

(a) 15.2 to 16.8% alkali metal tripolyphosphate;

(b) 12 to 20% sodium silicate;

(c) 0 to 7% sodium carbonate;

(d) 0.5 to 3.5% alkyl phosphate ester defoamer;

(e) 0.1 to 5% sodium hydroxide; sufficient to insure a pH in comp. of about 11.8;

(f) 0.5 to 3% sodium hypochlorite; sufficient to insure at least about 0.5% of available chlorine;

(g) 0.1 to 0.8% organic surfactant; and

(h) 0.8 to 5.0% smectite clay.

2. A composition as defined in claim 1 comprising

(a) 10 to 16.8% alkali metal tripolyphosphate;

(b) 18 to 20% sodium silicate;

(c) 4 to 8% sodium carbonate;

(d) 0.5 to 3.5% mono/distearyl phosphate ester defoamer;

(e) 0.5 to 5% sodium hydroxide;

(f) 0.5 to 3% sodium hypochlorite;

(g) 0.1 to 0.8% bleach stable organic surfactant;

(h) 0.8 to 5.0% smectite clay.

3. A composition according to claim 1 or 2 where the defoamer is a monostearyl, a di-stearyl or a mono/distearyl acid phosphate ester.

4. A composition according to claim 1 wherein the amount of said phosphate is 15.5% to 16.5%.

5. A composition according to claim 1 wherein the amount of said silicate is 15% to 18%.

6. A composition according to claim 2 wherein the amount of said silicate is at least 18%.

7. A composition according to claim 1 or 2 where the sodium tripolyphosphate is pre-moisturized to a level of about 0.5 to 1.0%.

8. A composition according to claim 1 or 2 where the amount of said carbonate is about 4% to 8%.

9. A composition according to claim 1 or 2 where the structuring clay is bentonite in an amount of about 1.5 to 3.5%.

10. A composition according to claim 1 or 2 where the structuring clay is a mixture of bentonite and attapulgite clay in a ratio of 6:1 to 3:1 and the total percent of clay in the composition is less than 5%.

11. A composition according to claims 1 or 2 where the surfactant is a C₁₀ to C₂₀ diphenyl oxide disulfonate.

12. A composition according to claim 1 or 2 where the surfactant is a C₁₄ to C₁₈ diphenyl oxide disulfonate.

13. A thixotropic, aqueous cleaning composition substantially as described herein.

14. A process for making the thixotropic, aqueous cleaning composition of claim 1, the process comprising adding the components of the composition to a vessel and mixing, the first two components being water and clay.

15. A process for making the thixotropic, aqueous cleaning composition according to claim 14, the process further comprising adding the components of the composition to a vessel in the following order: water, clay, NaOH, defoamer, silicate, soda ash, NaTPP, bleach, and organic surfactant.