Method Of Cleaning Surfaces

Abstract

A method of removing deposits of soil from surfaces, which comprises applying to said surfaces a caustic alkali including an acid-base color indicator, and applying an aqueous solution which is sufficiently acidic to substantially neutralize the caustic and visibly change the color of the caustic. The method has particular efficacy for the cleaning of the interior surfaces of ovens and similar surfaces.

Description

This invention relates to a method of cleaning deposits of soils from surfaces, for example, the interior surfaces of ovens and the like.

The cleaning of the interior surfaces of household cooking ovens is a difficult, tedious, and lengthy chore. A widely used oven cleaner is the spread-on, sodium hydroxide or potassium hydroxide formulations that are messy to apply and must be handled with care as the highly caustic material is capable of injuring the user. MOre recently, aerosol oven cleaners having a considerably lower concentration of alkali and containing a nonionic or ionic detergent with a solvent such as water or alcohol have appeared. However, they are generally not as effective as the higher caustic content cleaners, although safer to use than the highly caustic formulas.

In accordance with the present invention a method is provided for removing deposits of soils from surfaces by applying to such surfaces a caustic, an acid-base color indicator, and thereafter applying an aqueous acidic solution to substantially neutralize the caustic, such as to a pH between about 4 and 10.5. When the caustic has been substantially neutralized, a color change takes place due to the presence of the acid-base color indicator thereby indicating to the user that the surface can be wiped clean without the need of rubber gloves or the worry of skin irritation. In a preferred embodiment, the method comprises applying to such surfaces a caustic alkali foam containing an acid-base color indicator, and then applying sufficient aqueous acidic solution to the surface so as to substantially neutralize the caustic and to effect a change in color of the caustic. In the alternative the acid-base indicator may be included in the aqueous acidic solution or may be applied apart from either the caustic or the acid.

We prefer that the caustic cleaner be in the form of a highly caustic alkali foam that is dispensed from an aerosol can. The caustic foam is left on the surface long enough to do its job, generally about 20-30 minutes in the case of ovens. The concentration of caustic used as percent free hydroxyl may be from about 5 percent to about 10 percent or more, preferably about 7- 8 percent. Any strong caustic alkali may be used, such as sodium hydroxide or potassium hydroxide or mixtures thereof. It may be in the form of a water solution, and it is preferable that a surfactant or combination of surfactants be employed to impart foaming characteristics. The surfactant may be either anionic or nonionic, including but not restricted to anionic surfactants such as alkyl aryl sulfonates, alcohol or fatty acid sulfonates or ether sulfates, alkyl amide or ester sulfonates, and fatty acid glycerol ester sulfates or ether sulfonates; and nonionic surfactants such as ethoxylated alcohols and alkylphenols, alkyanolamides, and block copolymers of ethylene and propylene glycol. In addition a suitable potassium or sodium soap may optionally be added and may consist of various combinations of tallow, cocoa, red oil, tall oil, stearic and oleic fatty acids. A small amount of hexylene or propylene glycol may be added as a solubilizer; and various other ingredients may be added for their known effects such as sodium carboxy methyl cellulose or starch as thickening agents to aid foam adherence to the surface, and water soluble silicones as foam boosters and soil release agents. An example of a preferred caustic foam cleaner to be dispensed from an aerosol container is:

Ingredient % by weight __________________________________________________________________________ 45% Potassium hydroxide 19.1% Stearic acid 0.5 Oleic acid 4.8 Hexylene glycol 4.0 Acid-base indicator 0.2 Water 71.4 Total 100.0% __________________________________________________________________________

Preferably 90- 60 percent proportion of the above preferred cleaner is added, to an aerosol container along with 4- 10 percent of a liquefied propellant for example fluorocarbons such as Freon 12 or Freon 114 or mixtures thereof or known hydrocarbon propellants.

The neutralizer should be sufficiently acidic to reduce the alkalinity of the caustic to a relatively safe level. Suitable active ingredients include any generally weak acid or acid salt, and the following are preferred: sodium dihydrogen phosphate, citric acid, hemi sodium phosphate, carbamide phosphoric acid, gluconic acid, ethylene diamine tetracetic acid, phosphoric acid, and any appropriate combinations thereof. Other acids such as dilute mineral acids may be used but generally in low concentration or very dilute form. The acid is preferably present in about 10.sup.-3 to 10.sup.-6 moles per liter hydrogen ion concentration; but this is widely variable since merely more of lower concentrations and less of higher concentrations will be used to substantially neutralize the caustic. An example of a preferred neutralizer to be dispensed from an aerosol container is:

Ingredient % by weight __________________________________________________________________________ Sodium dihydrogen phosphate 35% Water 55% Freon 114 5% Freon 12 5% Total 100% __________________________________________________________________________

It is preferred to add a defoamer to aid in the penetration of the acid or acid salt into the caustic foam. In the alternative the incorporation of a soap in the first stage aids in defoaming by the neutralizer acting to convert the soap to a fatty acid.

Suitable acid-base indicators include any that effect a color or change or color at a pH of between about 4 and about 11 and include but are not restricted to phenolphthalein, thymolphthalein, brilliant yellow, thymol blue, cresol purple, neutral red, phenol red, bromthymol blue, chlorphenol red, methyl red, bromcresol green, and alizarine yellow. The acid-base indicator may be added to the first stage formulation, thereby visibly coloring the caustic foam i.e., phenolphthalein in about 0.2 percent by weight concentration will produce a red foam in the above described specific preferred caustic, thymolphthalein will produce blue, brilliant yellow will produce orange, and meta cresol purple will produce purple. After the caustic has been applied and allowed sufficient time to work, the second stage neutralizer would be sprayed on prior to wiping. The neutralizer renders the caustic safe and the safe level is indicated by a change in color of the foam. Thus when a caustic foam that includes phenolphthalein is sprayed on the surface to be cleaned a red color is developed. When the neutralizer is applied the color disappears as the foam is substantially neutralized. Thymolphthalein indicator would also turn colorless, brilliant yellow indicator would become yellow and meta cresol purple would also become yellow. Bromthymol blue will change from blue to yellow and neutral red from light brown to red.

Although the compositions of the present invention may be applied by brushing or daubing, they are preferably applied from two separate aerosol cans and/or spray bottles. As a further alternative the two formulations may be applied via separate nozzles of a compartmentalized aerosol or via separable bottle aerosol nozzle and propellant combinations, and like means.

This invention is still further illustrated by specific examples, which are not to be construed as composition limitations upon the scope thereof.

EXAMPLE I

Exemplary caustic formulations were prepared as set forth in Table I. Each of the formulations was added to an aerosol container, using about 90- 96 percent of the formulation and about 4- 10 percent of a suitable propellant such as dichloro difluoromethane (Freon 12), tetrafluoro dichloro ethane (Freon 114), pentafluoro monochloro ethane (Freon 115), trifluoro trichloro ethane (Freon 113) cyclic hexafluoro dichloro butane (Freon C 316), octafluoropropane (Freon 218), cyclic octafluoro butane (Freon C 318), propane, butane, pentane, isobutane, hexane, eptane, octane, nonane and decane, or mixtures thereof.

A preferred acidic formulation was prepared as set forth hereinabove. It was packaged in a spray bottle and also in an aerosol can propelled with carbon dioxide, nitrogen, nitrous oxide or a combination of Freon 12, Freon 11 and Freon 114.

The examples set forth in Table I were sprayed upon standard soiled panels. The panels had vitreous porcelain surfaces and the soil resulted from deposits of general organic food constituents, including butter, that had been subjected to about 350.degree.F. heat for 30 minutes. All products formed good initial foams that were evaluated for stability and adhesion after a 20-minute period. The panels were then sprayed with the neutralizing formulation until a change in color was observed. The foams then broke and the substantially neutralized residues were wiped off the panels with a cloth. No burns or skin irritation occurred. Where heavy spots of soil deposit remained, the panel was treated a second time. All soil was removed. ##SPC1##

While this invention has been described with respect to specific embodiments of the method of removing deposits of soils from surfaces, such is by way of illustration and not in limitation; and it is to be understood that variations and modifications thereof obvious to those skilled in the art may be made without departing from the spirit or scope of this invention.

Claims

What is claimed is:

1. The method of removing deposits of soil from surfaces which comprises applying to said surfaces a caustic alkali having about 5 percent or more of free hydroxyl, said caustic containing an acid-base indicator that changes color at a pH between about 4 and 11; and applying an aqueous acidic solution to substantially neutralize the caustic.

2. The method of removing deposits of soils from surfaces which comprises applying to said surfaces a caustic alkali having about 5 percent of more of free hydroxyl; applying an aqueous acidic solution containing an acid-base indicator that changes color at pH between about 4 and 11 to substantially neutralize the caustic.

3. The method of removing deposits of calcined food soils from surfaces, which comprises applying to said surfaces a highly caustic foam having about 5 percent or more of free hydroxyl and containing an amount of an acid-base indicator that will produce a color change at a pH of about 4 to about 11; and then applying an aqueous acidic solution to substantially neutralize the caustic foam to produce a change in color of said foam.

4. The method of removing deposits of calcined food soils from surfaces which comprises applying to said surfaces an alkaline material containing a caustic alkali having about 5 percent or more of free hydroxyl and an acid-base indicator that produces a color change at a pH of about 4 to about 11; and then applying an aqueous solution which is sufficiently acidic to substantially neutralize the alkaline material and to change the color of the alkaline material.

5. The method of claim 4 in which said acid-base indicator is selected from the group consisting of phenolphthalein, thymolphthalein, brilliant yellow, meta cresol purple, thymol blue, neutral red, phenol red, methyl red, paranitro phenol and bromthymol blue.