Prior Art As is known to those skilled in the art to which the present invention pertains, historically, it has been virtually impossible to achieve a homogeneous highly alkaline, phosphate-built warewashing detergent system having a long shelf life.

While highly alkaline-containing products have been available in the form of solids, such as powders, briquettes, pellets, flakes, etc. , there have been inherent drawbacks in the dispensing and utilization of these solids in dispensing systems. Liquid alkaline products suffer from precipitate formation because of ion exchange between the sodium and phosphate ions in the builders. Similarly, slurried products have the inherent tendency to separate over time. Thus, while there is presently known both the solid and liquid forms of highly alkaline warewashing detergents, their deployment is a drawback. Slurried products, while being readily dispensed, cannot achieve the degree of alkalinity desired, without the separation problems as discussed hereinabove.

Within this context, it is apparent that there is a demand for a highly concentrated, i. e., highly alkaline, liquid warewashing detergent that can be consistently dispensed and which is storage stable, i. e., does not separate over an extended period of time. As detailed hereinbelow, the present invention achieves this.

Description of the Preferred Embodiment In accordance with the present invention, there is provided a liquid, highly alkaline warewashing detergent which is easily dispensed and which does not have any substantial phase separation over extended periods of time.

As is known to those skilled in the art to which the present invention pertains, in manufacturing a "liquid" detergent, necessarily there is included certain solid particles, such as hardness sequestering agents, alkalinity sources, etc. , which are suspended in the liquid mixture and which, ultimately, separate out. It is this precipitation and phase separation which is precluded by the practice of the present invention.

In a first aspect, the present invention is directed to a superior detergent comprising a polymeric sequesterant, a nonionic surfactant, a source of alkalinity, a phosphate dertergent builder and water In a second aspect hereof, the present invention provides a highly alkaline, homogenizable (i. e., homogenizable by mixing in a mill or in-line dynamic mixer), warewashing composition.

With more particularity and, as noted above, the present invention provides a highly alkaline homogenized warewashing detergent or composition which, generally, comprises of : (a) a source of alkalinity ; (b) a polymeric sequestrant ; (c) a nonionic surfactant ; (d) a phosphate detergent builder ; (e) a second sequestrant ; and, (f) water.

In a third aspect hereof, there is provided an improved method for preparing a highly alkaline liquid warewashing detergent. The method hereof is defined by homogenizing a liquid detergent by passing the detergent through a homogenizer at a temperature ranging from 110°F to 160°F, preferably from 115°F to 125°F. The time for effecting homogenization will depend on batch size, and the speed of the transfer pump in the homogenizing equipment. Although this processing step is applicable to liquid detergents, per se, the process is particularly applicable to the particular homogenizable highly alkaline liquid warewashing detergent composition, defined herein.

The source of alkalinity may be any suitable alkaline material, such as an alkaline hydroxide, e. g., sodium hydroxide, potassium hydroxide, or the like as well as mixtures thereof. Other sources include carbonates, silicates, metasilicates and the like. However, an alkaline hydroxide is preferred and, particularly, sodium hydroxide. Typically, the source of alkalinity may be a liquid such as a 50% aqueous solution of caustic soda, a

70% caustic aqueous solution of caustic soda ; a 100% solid caustic source, such as beads, or the like, as well as mixtures thereof. Further, a mixture of an aqueous solution and a solid alkaline source may be used.

Preferred herein is a mixture of the 50% solution and 100% solid beads. Where used, generally, the solution and solid will be used in a, respective, weight ratio of 60% of solution to 40% of beads to impart the requisite alkalinity to the detergent.

In formulating the present highly alkaline warewashing product, generally, the source of alkalinity will be present in an amount ranging from at least 25% to 60%, by weight, based upon the total weight of the warewashing concentrate compound. Although, lower amounts thereof may be employed. To achieve the full benefit of the present invention and to enable a highly alkaline detergent, the higher levels, i. e., above 25%, are contemplated.

Generally, the polymeric sequestrant is present in an amount ranging from 1% to 5%, by weight, and preferably from 2. 5% to 3. 5%, by weight, based on the total weight of the concentrate.

The polymeric sequestrant, also, functions as al electrolyte in the solution. Polymeric compounds are well known and commercially available such as those sold under the trademark Acusol, by Rohm & Haas. These compounds are polyacrylate polymers, like polymethacrylates, well documented in the art, such as disclosed U. S. Patent No.

4, 753, 755, the disclosure of which is hereby incorporated by reference.

The nonionic surfactant contemplated for use herein is any of the well-known conventional nonionic surfactants. The surfactant functions as a defoamer while adding to the detergency properties of the composition. Again, the nonionic surfactants contemplated for use herein are well known and commercially available such as those sold by BASF Corporation under the mark Pluronic N3. Pluronic N3 is a polyoxypropylene-polyoxyethylene block copolymer nonionic surfactant. Other useful nonionic surfactants include those enumerated in U. S. Patent No. 5, 064, 561, the disclosure of which is hereby incorporated by reference.

Generally, the nonionic surfactant is present in the composition in an amount ranging from 0. 1 to 5%, by weight and, preferably, from 0. 5 to 2%, based on the total concentrate weight.

As noted hereinabove, a second sequestering agent or sequestrant is included in the composition hereof.

Generally, such a sequestrant, which functions as a hardness sequestering agent, is typically and conventionally present in solid form. These hardness sequestering agents, are usually, phosphate-based and include the well known phosphate and polyphosphates such as trisodium phosphate, tetrasodium polyphosphate, tetrapotassium pyrophosphate, etc. , as well as mixtures thereof.

It has been found in the practice of the present invention that where the hardness sequestrant is a potassium- containing compound, an ion exchange occurs in the solution between any sodium and the potassium-ion, promoting the formation of the precipitant. The sodium from the source of alkalinity replaces the potassium in the sequestrant to form tetrasodium pyrophosphate, which is a precipitate.

However, because of their efficacy, the potassium-phosphate builders are incorporated hereinto. Ordinarily, the phosphate sequestrants are present in an amount ranging from 15% to 50% of the composition weight on a solids basis and, usually, from 25% to 40% on a solids basis.

The present composition may, also, include a third sequestrant or chelant which functions as an anti- redeposition agent. Usually, these chelant comprise a derivative of acetic acid or the salt thereof. Such compounds are well known and commercially available such as ethylene diamine tetraacetic acid (EDTA), nitriloacetic acid (NTA), the sodium salts thereof, as well as mixtures thereof.

In practicing the present invention, it has been found that a particularly preferred composition will include the source of alkalinity, the polyacrylate acid sequestrant, the tetrapotassium pyrophosphate as a hardness sequestrant, the nonionic surfactant, and the anti redeposition, chelant.

The balance of the concentrate composition is water.

It has been found that such a composition, while somewhat grainy, stays together at frequencies generated at transportation when homogenized. Although such a composition is particularly preferred herein, other compositions, using the components denoted above are well within the scope of the present invention.

Again, and as noted above, in formulating present compositions, generally, the surfactant will be present in an amount ranging from 0. 5% to 2% by weight, based upon the total weight of the mixture ; the antideposition compound or sequestrant to be used in the present invention in an amount ranging from 0. 5% to 2% and the builder will be present in an amount ranging from 25% to 40% by weight.

Generally, the composition will include, since it is a liquid, from 5% to 10% by water.

Other adjuvants such as a chlorine source may be included herewithin.

The composition hereof is a liquid concentrate which is readily admixed with water such as by pumping or the like from any suitable pump or other dispensing means, and may be dispensed through small tube boring. As a result of the homogenized state it has been shown to reach a concentration set point within 36 seconds to about four minutes in the wash tank and is maintainable thereof.

As noted above, the present invention also includes a process or method for preparing a highly alkaline concentrated warewashing detergent.

The process hereof, generally comprises, in no particular order, the steps of : (a) dissolving the polymeric sequestrant in water ; (b) admixing the nonionic surfactant ; (c) adding the source of alkalinity ; and, (d) admixing a hardness sequestering agent ; wherein the resulting mixture is homogenized.

Preferably, however, the process comprises the steps of : (a) dissolving the polymeric sequestrant in water ; (b) admixing the nonionic surfactant therewith ; (c) adding the source of alkalinity to the mixture of (b) ; (d) admixing a hardness sequestering agent herewith ; and (e) thereafter, homogenizing the mixture.

With more particularity, the first step in the process is typically the addition of the polymeric sequestrant to water. The addition of the polymer to water is, generally, done with mixing at an elevated temperature. Ordinarily, the temperature will range from 104°F to 149°F. The mixing will generally last for about one to about ten minutes, or until all of the contents are dissolved.

Thereafter, and while maintaining the temperature, the nonionic surfactant is readily added thereto with mixing.

Next, the source of alkalinity is introduced to the mixture with heat and stirring.

Then, the second or hardness sequestrant is added to the admixture obtained upon the addition of the source of alkalinity.

Finally, the entire mixture is homogenized.

In a most preferred embodiment, however, (a) is mixed with (b) to produce a first mixture, (c) is mixed with (d) to produce a second mixture, and the first and second mixture are mixed.

In preparing the instant composition, homogenization occurs at elevated temperature, as noted hereinabove, ranging from 110°F to 160°F. Generally, the time for effecting homogenization will depend on batch size and the speed of rotation of the homogenizing equipment.

Alternatively, it is possible to make a first solution of sequestrant and source of alkalinity, where the source of alkalinity is a liquid mixture. Then, this admixture is homogenized. Thereafter, the other components, which may be premixed as a second solution, are admixed with the homogenized liquid mixture. No particular order of addition is necessary if the remaining components are merely added to the homogenized mixture.

In either event though, the critical step hereto is the homogenization of the warewashing system.

For a more complete understanding of the present invention reference is made to the following illustrative, non-

limiting examples. In the examples, all parts are by weight absent contrary indications.

EXAMPLE I This example illustrates the preparation of a highly alkaline warewashing detergent concentrate in accordance herewith.

Into an LRT Silverson Homogenizer equipped with a heat source and stirrer is added 5. 5 parts of water and 3. 0 parts of a polymeric polyacrylic acid sequestrant sold under the name Acusol 45ND powder. The mixture is stirred until homogenous. The mixture is then covered to prevent evaporation.

Thereafter 1. 5 parts of a nonionic surfactant sold under the name Pluronic N3 is added thereto and mixed thereinto at the same temperature. Then, 32. 0 parts of a 50% aqueous caustic soda solution is added to the mix at a temperature of 47°C. The mixture immediately becomes gelatinous. The mixture is stirred thereafter for about twenty minutes.

Then, 22. 0 parts of 100% caustic soda beads are added, with rapid stirring. The temperature in the vessel is 48°C at the time of the addition. Stirring is continued for about 60 minutes until a somewhat grainy liquid is obtained.

Next, 36. 0 parts of a 60% aqueous tetrapotassium polyphosphate solution is added to the mixture. The temperature in the vessel maintained at about 65°C while stirring at 90-100 rpm for about 135 minutes.

Thereafter, the homogenizer is fitted with a high shear screen and the mixture is homogenized at 4500 rpm for two minutes at a temperature of 61°C.

The product so-obtained is flowable, pumpable and does not evidence any precipitate or phase separation.

From the above it is to be seen that by homogenizing the compositions enhanced utilization and shelf life of a highly alkaline detergent is obtained.