EP0686693A2

EP0686693A2 - Cleaning composition and cleaning process

Info

Publication number: EP0686693A2
Application number: EP95201251A
Authority: EP
Inventors: Guiseppe Bolzoni; Robert Michael Butterworth
Original assignee: Unilever PLC; Unilever NV
Current assignee: Unilever PLC; Unilever NV
Priority date: 1994-06-07
Filing date: 1995-05-12
Publication date: 1995-12-13
Also published as: AU705285B2; AU2047095A; GB9411349D0; JPH0841488A; EP0686693A3

Abstract

A package containing a cleaning composition for pretreatment of baked on soil, said composition comprising:

a) at least 2%wt of a surfactant, preferably a primary alcohol sulphate having a chain length of C10-C14,
b) 0.01-5.00 of a metal-complexing agent (such as an amino phosphonic acid),

wherein the pH of the neat composition is below 13.0 and the pH at an aqueous dilution of 1% is greater than 10. The invention also relates to a method of cleaning baked on soil from surfaces which comprises the steps of: treating the surface with a composition as described above in substantially undilute form, whereby the baked-on soil is loosened from the surface, and, treating the surface with a second surfactant-containing composition, said second surfactant containing composition comprising less than 2% of surfactant.

Description

Technical Field

The present invention relates to cleaning compositions and in particular to cleaning compositions which are intended for the removal of burnt-on soil from cooking vessels and other utensils as well as from kitchen and other surfaces.
The invention also to relates a method of cleaning such utensils and surfaces by treatment with a composition as described herein.

Background of the Invention

A well-recognised problem in the dishwashing art is the removal of 'burnt-on' or 'baked-on' soils. Such soils are formed by the application of heat to compositions which comprise one or more of proteins, fats and carbohydrates and are formed by a series of reactions which are generally believed to produce a complex mixture of cross-linked products, carbon residues, colloidal sugar-like molecules, and acroleins.
US 4065113 (Proctor & Gamble, 1976) discloses that burnt-on soils can be removed by the use of a composition containing anionic synthetic detergent and phosphate builder in which at least a part of the cations of the synthetic detergent are derived from monoethanolamine, optionally in the presence of free organic base.
As described in GB 2224286 (Unilever, 1989) it is known that certain types of alkaline cleaning compositions are effective when used to 'pre-treat' soiled pots, pans, plates and other eating utensils. These cleaning compositions are applied to the soiled utensils and allowed to remain on the utensils for from 5 minutes to about one hour. After this 'pre-treatment' soils can be removed by light washing from the utensils, i.e. by conventional dishwashing by hand or machine. Such compositions are known to remove burned-on, dried or cooled food substances.
The pre-treatment compositions disclosed in GB 2224286 comprise 1-10%wt of an organic base. The base provides a source of alkalinity for the product and generally comprises a monoethanolamine, n-butyl amine, pyrrolidine, or another nitrogenous species. The compositions disclosed therein further comprise 0.1-10% of a zinc complexing agent selected from a list including EDTA, NTA, citrates and amino-phosphonates such as Dequest 2000 and 2066. Conventional surfactants are present in the compositions disclosed in GB 2224286.
Other compositions for the removal of burnt-on soils are known. US 4105574 (Culmone) and US 4372788 (Lancz) describe grill and oven cleaners based on monoethanolamine.
Despite the formulation of products as described above there remains a clear need for improvements in techniques for the removal of burnt or baked-on soil. Although the removal of such soils could facilitated by the use of strong acidic and/or alkaline compositions, such compositions would be unsuitable for use in the home due to the irritating and corrosive properties of these compositions.
A composition for use in the home must also be environmentally acceptable and preferably such a composition should be free of certain nitrogen containing species. Furthermore, a product should be sufficiently physically stable, particularly during temperature cycling between normal and cold storage temperatures, that it not discarded by the user thereby needlessly releasing surfactants into the environment.
As described above, pre-treatment compositions are generally employed in a process comprising at least two steps, a first step of treating soiled articles with the composition and a second step in which the articles are washed in a conventional manner.
We have recognised that it is important, especially when further surfactant containing compositions are used in the second step, that the materials used in the first step do not interfere with the function of these further surfactants. In particular, it is important that the pretreatment composition does not modify the foaming behaviour of the further surfactants such that they exhibit excessive foaming or reduced cleaning.

Brief Description of the Invention

We have now determined that improved hard surface cleaning compositions can be prepared if the alkalinity of the compositions arises in part from an alkaline reserve, sufficient to maintain the pH of the composition given significant dilution. Conveniently, these compositions are provided in a package which is adapted to deliver the composition to the surface of articles in the form of a spray. This enables the composition to act in a concentrated form for the first stage of a cleaning operation. When the articles are rinsed in water the composition is diluted to form a solution which is used in the second stage of the cleaning operation.
Accordingly, a first aspect of the present invention provides a package containing a cleaning composition for pretreatment of baked on soil, said composition comprising:

a) at least 2%wt of a surfactant selected from anionic, cationic, amphoteric, zwitterionic, nonionic surfactants and mixtures thereof,
b) 0.01-5.00%wt of a metal-complexing agent,

According to a further aspect of the present invention there is provided a method of cleaning baked on soil from surfaces which comprises the step of treating the surface by spraying thereupon a composition comprising 2-50%wt of a surfactant selected from anionic, cationic, amphoteric, zwitterionic, nonionic surfactants and mixtures thereof, said composition further comprising 0.01-5.00%wt of a metal-complexing agent, wherein the pH of the neat composition is below 13.0 and the pH at an aqueous dilution of 1% is greater than 10, said composition being sprayed in substantially undilute form, whereby the baked-on soil is loosened from the surface.

Detailed Description of the Invention

As described above, compositions according to the invention are characterised by a limited maximum pH and a relatively high alkaline reserve.
It is believed that on neat application, compositions of the present invention maintain a pH above 10 even following significant dilution such as occurs on absorbtion into soil. However the neat compositions are not sufficiently alkaline as to be dangerously corrosive or excessively irritant.
In use, the compositions are applied neat to the soiled utensils or surfaces and left for a period of time. Ideally, this period of time should be not longer than 20 minutes and should preferably be shorter than 10 minutes. In the preferred method aspects of the invention no mechanical cleaning is required during the above-mentioned period of time.
The subsequent cleaning operation can be performed using a conventional surfactant solution such as is known for hand or machine dishwashing or can be performed by hand or using a dishwashing machine. It is however preferred that the solution used for the subsequent cleaning operation is performed using the solution which is obtained by dilution of the neat composition of the invention such that a total surfactant content of less than 2%wt is achieved.

pH

It is important that the pH of the neat compositions according to the invention does not exceed 13.
Generally the pH of neat compositions according to the present invention will fall into the range 11.0-12.9.
Some reserve of alkalinity is required in order to provide effective cleaning performance. The measure of alkaline reserve used in this specification is the number of grams of NaOH per 100g of product when a 10% solution of the product in water is titrated to pH 10 from the initial pH.
It will be apparent that while a composition should be effective, it should not be corrosive or irritant to the user.
While it is difficult to place precise limits on what might be considered dangerously corrosive or excessively irritant, a known criterion is to consider the sum of the pH and some fraction of the alkaline reserve.
According to one such measure, a product is considered 'corrosive' when the sum of the pH and one twelfth part of the alkaline reserve is greater than 14.5. According to the same measure, a product is considered irritant when the sum of the pH and one sixth of the alkaline reserve is greater than 13.0. The preferred products of the present invention are neither irritant or corrosive according to this measure, i.e. while the pH falls into the range 10.0-13.00, the alkaline reserve is sufficiently small that both the above mentioned conditions are satified.
An alternative criterion is to consider the levels of materials which have been considered irritant and corrosive present in the composition. One such measure considers the sum of one twentieth of the percentage of 'irritant' raw material present and twice the percentage of 'corrosive' raw material present should be below 1. The preferred compositions of the present invention are neither irritant or corrosive according to this criterion.
Preferred compositions have a neat pH in the range 11-12, and a pH at 1% aqueous dilution of 10-11.
Compositions according to the present invention generally comprise an inorganic base.
We have determined that excellent results are obtained when the compositions comprise an alkali metal carbonate, most preferably sodium carbonate and, optionally, an alkali metal hydroxide, preferably sodium hydroxide. The preferred levels of the carbonate range from 2-8%wt. The preferred levels of the hydroxide range from 0.1-2%wt.
Compositions according to the present invention generally comprise a polycarboxylic acid, preferably a di- or tricarboxylic acid. Tricarboxylic acid, particularly citric acid is preferred. Typical compositions according to the present invention comprise 2-10%wt citric acid or a salt thereof.

Surfactants

Surfactant is an essential component of the compositions according to the present invention. While single surfactant species can be used it will be more commonplace to use a mixture of surfactant species of the same general type or of differing types.
Preferred surfactants comprise one or more of the following surfactants:

(a) secondary alkane sulphonate comprising a mixture of materials of the general formulation:

R₁.R₂.CH-SO₃X

wherein R₁ and R₂ are the same or different, each being a straight or branched chain alkyl group having at least one carbon atom, the alkyl chain length being in the range 13-18, and X is a solubilising cation,
(b) primary alcohol sulphate comprising a mixture of materials of the general formulation:

RO-SO₃X

wherein R is a C8 to C18 primary alkyl group and X is a solubilising cation,
(c) alkylbenzene sulphonate comprising a mixture of materials derived from an alkylbenzene with C₈ to C₁₆ primary or secondary alkyl group.
(d) alkyl ether sulphate comprising a mixture of materials of the general formula:

R-(OCH₂CH₂)_n-OSO₃X

wherein R₁ is C₁₀ to C₁₈ alkyl, X is a solubilising cation, and, n the average degree of ethoxylation, is from 1-5,
(e) ethoxylated alcohols of the general formula:

R-(OCH₂CH₂)_m-OH

wherein R is straight or branched C₈ to C₁₈ alkyl, and the average degree of ethoxylation m is 1-14.

Particularly preferred surfactants are anionic surfactants. We have determined that compositions according to the invention which contain appreciable quantities of nonionic surfactants exhibit a reduced efficiency as compared with compositions which do not comprise these surfactants.
The most preferred surfactants are primary alcohol sulphates. These surfactants are believed to be environmentally preferable than certain other surfactant species.
In general, the use of excessively high foaming surfactants and foam boosters (such as monoethanolamine) should be avoided, particularly where the second cleaning step is to be performed in a dishwashing machine. This avoids over-foaming in the dishwash machine which can lead to spillage.
In general, the use of foam-suppressing agents, such as terpines, mineral oils and silicones should be avoided where the second cleaning step is to be performed by hand. This avoids interference with the high-foaming characteristics of the surfactants conventionally used in hand-dishwash compositions.
We have found that compositions according to the present invention which employ primary alcohol sulphate as the bulk of the surfactant present and which do not contain, foam supressors such as mineral oils and silicones or foam boosters such as monoethanolamine meet these foam control criteria very well.

Metal Complexing Agent

Compositions according to the invention comprise 0.01-5.00%wt of a metal-complexing agent.
Preferred metal complexing agents are selected from dipicolinic acid, ethylene diamine tetra acetic acid (EDTA) and its salts, hydroxy-ethylidene diphosphonic acid (bequest 2010, RTM), ethylene diamine tetra (methylene phosphonic acid) (bequest 2040, RTM), diethylene triamine penta(methylene phosphonic acid) (Dequest 2060/2066, RTM), amino tri(methylene phosphonic acid) (Dequest 2000, RTM) and diethylene triamine pentacetic acid ('VERSENEX (R) 80' RTM).
The most preferred metal complexing agents are amino-phosphonic acids and their salts, available in the marketplace in the 'Dequest' range, particularly the diethylene triamine penta(methylene phosphonic acid).
Typical levels of the phosphorous-containing complexing agent are such that the composition contains 0.01-5.00%wt of an amino phosphonic acid metal-complexing agent. It is preferable that the compositions according to the present invention comprise less than 1% phosphorous on product for environmental reasons.
Other metal complexing agents can be present. In particular it is preferable that citric acid or a citrate salt is present. Citrate functions both as a component of the buffer system and as a metal complexing agent and the preferred levels of this component are discussed elsewhere in this specification.

Physical Stability

The method of application of products according to the present invention is by means of a spray. For such applications it is important that the composition does not phase separate on storage. In particular the product should not undergo irreversible physical changes when stored at 5, more preferably zero, degrees Celcius. Phase stability is also considered important given that a product which does not exhibit the required stability might be inadvertently discarded by the user thereby unnecessarily releasing surfactants and other components of the product into the environment.
We have determined that the physical stability on cold storage of compositions according to the present invention is improved by the selection of a particular type of surfactant.
Preferably the surfactant is a primary alcohol sulphate (PAS) of the general formula:

RO-SO₃⁻X⁺

wherein R has an average chain length of C8-C14, more preferably C8-C10.
We have determined that compositions which comprise this surfactant are generally more physically stable at low temperatures than compositions which comprise a longer average chain length primary alcohol sulphate but retain their effectiveness against burnt or baked on soils. It is believed that the preferred primary alcohol sulphate has a lower cloud point in the compositions of the invention.

Minors

Various inessential components may also be present in the compositions according to the invention. These include colouring agents, opacifiers, perfumes, and solvents.
Preferred compositions according to the invention comprise:

a) 2-15%wt of a primary alcohol sulphate of the general formula: R-SO₃⁻X⁺ wherein R has an average chain length of C8-C14,
b) 0.01-5.00%wt of an amino phosphonic acid metal-complexing agent,
c) 2-8%wt of an alkali metal carbonate,
d) 0.1-2%wt of an alkali metal hydroxide,
e) 0-2%wt of a perfume,
f) 0-2%wt of a preservative, and,
g) 1-10% of a polycarboxylic acid,

It is preferred that the compositions of the present invention are essentially free of strong oxidising agents such are per-oxygen compounds and hypohalites.
In order that the present invention may be further understood it will be described hereafter with reference to the following non-limiting examples.

EXAMPLES

Materials used are described in TABLE 1 below:

TABLE 1

PAS(1)	'LIAL 123' (RTM) primary alkyl sulphate e. ENICHEM
PAS(2)	C8/C10 average chain length primary alkyl sulphate
Nonionic	DOBANOL 23-6.5 (RTM)
Na.TTP	Sodium Tripolyphosphate
DEQUEST 2066 (TM)	phosphonic acid metal complexing agent
Proxel GXL (TM)	preservative
Perfume	Moonlight 205 (TM)

TABLE 2 below provides examples of compositions according to the present invention. In TABLE 2 the following tests and/or calculations are referred to:
'pH 1% aqueous': this is the measured pH of the neat composition.
'%S 20mins': this is the % soil remaining after treatment of a test sample for a contact period of 20 minutes using the test method described below. In a comparative example a commercially available hand dishwash liquid (SVELTO: RTM) removes about 25% of the soil.
'%S 5mins': this is the % soil remaining after treatment of a test sample for a contact period of 5 minutes using the test method described below.
'Corrosivity': a figure calculated as the pH + one twelfth of the alkaline reserve as described above. If this figure is above 14.5 the product is considered corrosive. Of the materials mentioned above sodium hydroxide is considered irritant
'Irritance': a figure calculated as the pH + one twelfth of the alkaline reserve as described above. If this figure is above 13.0 the product is considered irritant. Of the raw materials considered above sodium carbonate and PAS are considered as irritant as raw materials.
'MICIP' score is the sum of one twentieth of the percentage of 'irritant' raw material present () and twice the percentage of 'corrosive' raw material present () should be below 1.
'Cold stability' is a measure of the products stability to storage at 5 and zero degrees Celcius. The following scale being used to score the products:

1 Stable at both 5 and zero degrees Celcius
2 Stable at 5 degrees Celcius, some crystallisation of PAS at zero degrees, crystals taken up after return to room temperature.
3 Some crystallisation at both 5 and zero degrees Celcius, crystals taken up after return to room temperature.

The test method for soil removal is as follows. A model soil was prepared from a mixture of the following components: 5 grams of stearic acid, 5 grams of oleic acid, 190 grams of 'FRIOL' (RTM) oil, 200 grams of flour, 500 grams of cold demineralised water and 1400 grams of boiling demineralised water. The soil mixture was prepared by dissolving the fats in the oil and suspending the flour in cold water, combining the products obtained, and adding the balance of the water. This mixture was boiled for five minutes, cooled and sieved. 1-1.2 gram samples of this soil are applied by screen printing in 9.5 x 9.5 centimeter patches to the surface of a 13 centimeter square enamel tile and the tile baked for 190 Celcius for one hour in air such that the soil was pyrolised. 3 grams of test products were applied to the whole soiled surface of the tile and the tiles were allowed to stand horizontally for the appropriate time (5 or 20 minutes). At the end of this period, the tiles were soaked for two minutes in water at 45 Celcius with a HDW liquid diluted to an active concentration of 0.375 g/l. The soiled surfaces were gently wiped with a wet sponge to remove the loosened soil and the results assessed visually.
From the results in TABLE 2 it can be seen that the compositions of the present invention all show improved soil removal as compared with a conventional hand-dishwashing product and process (which removes about 25% burnt-on soil in the "%S 20 min" test described above).
It can be seen that the compositions which contain nonionic surfactant (compare examples 1 and 5) exhibit reduced performance as compared with compositions which are free of this component.
It can be also be seen that compositions which comprise the shorter chain PAS surfactant are more stable against cold storage (compare examples 1 and 2, and see examples 3, 4, 6 and 7), although all products which showed some visible phase instability at low temperature returned to a single visible phase when allowed to return to room temperature.
From TABLE 2 it can be seen that all of the compositions have acceptable corrosivity and irritance scores and have an acceptable MICIP score. While the more irritant and corrosive products (see examples 3-7) show improved performance over the less irritant and corrosive products (see examples 1 and 2), the less irritant and corrosive products are still markedly superior to the standard hand dishwash composition used as the comparison.
It can also be seen that compositions comprising colour, perfume and preservative were adequately stable.

Claims

A package containing a cleaning composition for pretreatment of baked on soil, said composition comprising:
a) 2-50%wt of a surfactant selected from anionic, cationic, amphoteric, zwitterionic, nonionic surfactants and mixtures thereof,

b) 0.01-5.00%wt of a metal-complexing agent,
wherein the pH of the neat composition is below 13.0 and the pH at an aqueous dilution of 1% is greater than 10, said package comprising means to produce a spray of said composition.
Package according to claim 1 wherein the pH of the neat composition within the package falls into the range 11.0-12.9.
Package according to claim 1 wherein the pH of the neat composition within the package falls into the range 11-12, and the composition achieves a pH at 1% aqueous dilution of 10-11.
Package according to claim 1 wherein the neat composition within the package comprises 2-8% wt of an alkali metal carbonate.
Package according to claim 1 wherein the neat composition within the package comprises 0.1-2% of an alkali metal hydroxide.
Package according to claim 1 wherein the neat composition within the package comprises a mixture of materials of the general formulation:

RO-SO₃X

wherein R is a C8 to C18 primary alkyl group and X is a solubilising cation.
Package according to claim 6 wherein the neat composition within the package comprises a primary alcohol sulphate (PAS) of the general formula

RO-SO₃⁻X⁺

wherein R has an average average chain length of C8-C10.
Package according to claim 1 wherein the neat composition within the package comprises an amino-phosphonic acid.
Package according to claim 1 wherein the neat composition within the package comprises :
a) 2-15%wt of a primary alcohol sulphate of the general formula: R-SO₃⁻X⁺ wherein R has an average average chain length of C8-C14,

b) 0.01-5.00%wt of an amino phosphonic acid metal-complexing agent,

c) 2-8%wt of an alkali metal carbonate,

d) 0.1-2%wt of an alkali metal hydroxide,

e) 0-2%wt of a perfume,

f) 0-2%wt of a preservative, and,

g) 1-10% of a polycarboxylic acid,
wherein the pH of the neat composition is 11.0-12.9 and the pH at an aqueous dilution of 1% is greater than 10.
A method of cleaning baked on soil from a surface which comprises the step of: treating the surface by spraying thereupon a composition comprising 2-50%wt of a surfactant selected from anionic, cationic, amphoteric, zwitterionic, nonionic surfactants and mixtures thereof, said composition further comprising 0.01-5.00%wt of a metal-complexing agent, wherein the pH of the neat composition is below 13.0 and the pH at an aqueous dilution of 1% of the composition is greater than 10, said composition being sprayed in substantially undilute form.