Phosphate-free dishwasher detergent - Patent Review 4820440

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BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a substantially phosphate-free dishwasher detergent containing at least an anhydrous alkali carbonate and an alkali metasilicate, in which at least two different cations must be present. The detergent is particularly adapted to being automatically dispensed in the dishwasher.

2. Statement of Related Art

To improve the ease of operation of modern dishwashing machines, particularly of the commercial or heavy-duty type, automatic detergent dispensing is a prime requirement. First, this means that the user does not come into contact unnecessarily often with alkaline detergent powders containing irritating chemicals and, second, this provides for a uniform metering and dispersion of detergent which in turn guarantees satisfactory cleaning of the soiled crockery. Automatic detergent dispensing is generally state-of-the-art and found on almost all dishwashers.

Powdered dishwasher detergents are automatically dispensed by means of conductivity meters which usually are coupled with overflow or flush-out dispensing units. In order to ensure complete and satisfactory dispensing of the powder from the dispensing system, the powder in the dispensers must not form lumps and/or harden when water flows in, and instead should form a stable, loose suspension.

Pending use, detergents are generally stored and, accordingly, are required to show favorable storage behavior even at elevated temperatures, which occasionally may rise to around 50.degree. C., i.e. they must never cake or harden but should retain the flowability with which they were produced. These properties are essential for loading and stocking the above mentioned automatic dispensers.

Previously, it has been possible to produce storable and dispensable dishwashing detergents having the above properties by using suitable commercially available raw materials, particularly specially prehydrated sodium tripolyphosphates. This standard, however, could not readily be maintained for phosphate-free detergents. Tests were conducted with powdered detergents containing: anhydrous sodium carbonate; sodium metasilicate. 5H.sub.2 O and sodium hydroxide or sodium carbonate. 10H.sub.2 O; anhydrous metasilicate and anhydrous sodium sulfate or sodium carbonate. 10H.sub.2 O; anhydrous sodium metasilicate and Na citrate. 2H.sub.2 O or anhydrous sodium carbonate; sodium metasilicate. 5H.sub.2 O and anhydrous dichloroisocyanurate or dichloroisocyanurate containing water of hydration or borax. 10H.sub.2 O; and anhydrous sodium metasilicate. Some tests resulted in very rapid hardening of the mixtures in the dispenser, so that the detergent could not be properly flushed out of the dispenser into the dishwashing machine, thus ruling out any possibility of automatic dispensability. Alternatively, the detergents were not stable in storage because in standard commercial packs, such as bags and drums, they hardened after only a few days at an elevated temperature such as 40.degree. C., and could no longer be dispersed. No foreign agents for this application could be found.

DESCRIPTION OF THE INVENTION

This invention affords a dishwasher detergent powder composition which critically is phosphate-free, and which comprises at least one anhydrous alkali carbonate, at least one alkali metasilicate, and optionally, a chlorine donor or an oxygen donor, an alkali hydroxide, an alkali sulfate, a water-soluble complexing agent, a binder, or a mixture of these optional ingredients. It is a further critical aspect of this invention that at least two different cations are present in the composition, chosen from among sodium, potassium, ammonium, organo ammonium or lithium. The inventive compositions show prolonged stability in storage, even at an elevated temperature, and may readily be flushed out as required from the dispensers into the dishwashers.

The inventive compositions preferably have the following prototype formulation:

______________________________________ amount ingredient % by wt - total 100% (at least one of each) acceptable preferred ______________________________________ (a) anhydrous alkali carbonate 10-60 15-35 (b) alkali metasilicate 20-70 30-60 (c) chlorine donor 0-7 1-5 (d) oxygen donor 0-15 1-10 (e) alkali hydroxide 0-10 3-7 (f) anhydrous alkali sulfate 0-40 10-25 (g) water soluble complexing agent 0-10 0.5-8 (h) binder 0-1.5 0.5-1.0 ______________________________________ (a) Suitable alkali carbonates are cleaning-active and include anhy- drous sodium carbonate and anhydrous potassium carbonate and, more especially, a mixture of anhydrous sodium and potassium carbonate. Soda containing water of hydration should not be used in the compositions according to the invention. (b) Potassium metalsilicate may be used as the at least one anhy- drous alkali metasilicate, although it is preferred to use commer- cial-quality sodium metasilicate in anhydrous form. Metasilicates containing water of hydration are likewise unsuitable for use in the preparations according to the invention. (c) Preferred chlorine donors are the alkali salts of dichloroiso- cyanuric acid, namely potassium dichloroisocyanurate or sodium dichloroisocyanurate, in the latter case anhydrous or even the di- hydrate, as well as trichloroisocyanuric acid. (d) As a complete replacement for compounds containing active chlorine, it is also possible to use at least one compound which gives off active oxygen, preferably alkali peroxodisulfates, and/or alkali perborates such as NaBO.sub.3.H.sub.2 O or NaBO.sub.3.4H.sub.2 O or sodium percarbonate. (e) The at least one alkali hydroxide used is solid potassium hydroxide or preferably solid sodium hydroxide, most preferably in the form of prills. The water of hydration content of these compounds should be as low as technically possible. (f) Some of the anhydrous alkali carbonate (ingredient a) may be replaced by at least one noncleaning-active-anhydrous alkali sul- fate, preferably anhydrous potassium sulfate, in order to introduce the necessary quantity of potassium ions into the mixture. (g) Suitable water-soluble complexing agents include at least one of various polyphosphonates, such as the sodium and potassium salts of ethane-1-hydroxy-1,1-diphosphonic acid, methylene di- phosphonic acid, ethane-1,1,2-triphosphonic acid, hydroxymethane disphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, propane-1,1,3,3-tetra-phosphonic acid, propane-1,1,2,3-tetra- phosphonic acid and propane-1,2,2,3-tetraphosphonic acid or 2- phosphonobutane-1,2,4-tricarboxylic acid. (h) Suitable binders may be added to control dust. The nature of the binder is not critical to this invention, provided that it is compatible with the desired properties of the other ingredients, and may typically be a paraffin oil.

As indicated earlier, it is critical to this invention that at least two different cations are present, which are selected from among such alkalis as potassium, sodium, lithium, ammonium, or organoammonium. More specifically, it is very advantageous for potassium cations to be present in an amount of 20 to 80, preferably 30 to 60, % by weight based upon the total weight of all of the alkalis of the whole composition, the balance to 100% by weight being selected from the remaining enumerated cations. Sodium, ammonium, and/or organoammonium cations are the preferred remaining cations, sodium being most preferred. When, in a preferred embodiment, potassium and sodium cations are used, it is believed that because of their size, the potassium ions act in admixture with the sodium ions to generate a crystal lattice disturbance, and thus prevent the formation of undesirable compact crystallizates. The organoammonium cations have the formula NR.sub.1 R.sub.2 R.sub.3 R.sub.4.sup.(+) where each R is a C.sub.1-20, preferably C.sub.1-4 -hydrocarbon, which may be linear or branched, saturated or unsaturated, and may be the same or different. In a particular embodiment, compounds containing longer chain radicals, such as dimethyl distearyl ammonium chloride, can also produce the desired effect. In still another, preferred, embodiment, the sodium salts of the whole composition are present in an amount of 20-80, preferable 40-70, % by weight based upon the total weight of the composition, the balance to 100% by weight being potassium and/or ammonium/organoammonium salts.

The detergent compositions may be and were prepared by simple mixing of the ingredients, in any order, in standard industrial apparatus such as a "Lodige" mixer or a "Schugi" mixer.

EXAMPLES

Dishwasher detergent compositions were prepared according to the following formulations. In each instance, the ingredients were simply mixed in suitable apparatus, without any particular order of addition. After preparation, each of the formulations were placed in standard commercial packages (plastic bags, drums, etc.) and stored for 3 months or 6 months in a conditioning chamber maintained at 40.degree. C. and 50% relative air humidity. The packages were then removed and opened. The contents remained stable and free-flowing, without caking. They performed satisfactorily when poured into the automatic detergent dispenser of a dishwasher, being completely flushed out during the dishwashing process. Their dishwashing properties were also satisfactory.

FORMULATION 1

______________________________________ 30% by weight of potassium carbonate, anhydrous (a) 60% by weight of sodium metasilicate, anhydrous (b) 4% by weight of sodium dichloroisocyanurate dihydrate (c) 5% by weight of sodium hydroxide prills (e) 1% by weight of the sodium salt of hydroxyethane diphosphonic acid (g) 100% ______________________________________

FORMULATION 2

______________________________________ 15% by weight of potassium sulfate, anhydrous (f) 19.5% by weight of sodium carbonate, anhydrous (a) 57% by weight of sodium metasilicate, anhydrous (b) 5% by weight of sodium hydroxide prills (e) 3% by weight of trichloroisocyanuric acid (c) 0.5% by weight of paraffin oil (h) 100% ______________________________________

FORMULATION 3

______________________________________ 35% by weight of potassium carbonate, anhydrous (a) 35% by weight of sodium metasilicate, anhydrous (b) 5% by weight of the sodium salt of 2-phosphono- butane-1,2,4-tricarboxylic acid (g) 20% by weight of sodium sulfate, anhydrous (f) 5% by weight of potassium peroxodisulfate (d) 100% ______________________________________

FORMULATION 4

______________________________________ 2% by weight of sodium peroxodisulfate (d) 30% by weight of potassium carbonate, anhydrous (a) 23% by weight of ammonium sulfate, anhydrous (f) 40% by weight of sodium metasilicate, anhydrous (b) 5% by weight of sodium hydroxide prills (e) 100% ______________________________________

FORMULATION 5

______________________________________ 20% by weight of ammonium carbonate, anhydrous (a) 10% by weight of potassium carbonate, anhydrous (a) 50% by weight of sodium metasilicate, anhydrous (b) 0.5% by weight of the sodium salt of hydroxyethane diphosphonic acid (g) 18.5% by weight of sodium sulfate, anhydrous (f) 1% by weight of sodium dichloroisocyanurate, anhydrous (c) 100% ______________________________________

FORMULATION 6

______________________________________ 52% by weight of sodium metasilicate, anhydrous (b) 32.5% by weight of potassium carbonate (a) 5% by weight of sodium hydroxide prills (e) 2.5% by weight of trichloroisocyanuric acid (c) 7% by weight of the sodium salt of 2-phophono- butane-1,2,4-tricarboxylic acid (g) 1.0% by weight of paraffin oil (h) 100% ______________________________________

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