WO1994000549A1

WO1994000549A1 - Improvements to bleaching compositions

Info

Publication number: WO1994000549A1
Application number: PCT/EP1993/001496
Authority: WO
Inventors: Helen Burgess; Martin John Murphy; Melvin Scott
Original assignee: Unilever Plc; Unilever Nv
Priority date: 1992-06-26
Filing date: 1993-06-14
Publication date: 1994-01-06
Also published as: AU4325693A; GB9213578D0

Abstract

One difficulty which has been encountered due to high levels of electrolyte in hypochlorite solutions is the crystallisation of the electrolyte as a solid salt around the caps of containers. More seriously, hypochlorite is both unstable on storage and corrosive to metals, hence hypochlorite shelf life is limited due to the progressive decomposition of the hypochlorite ion. Much more seriously, when acids are added to hypochlorites in amounts such that the pH falls below 4, chlorine gas is evolved into the environment. It is very well known that even low concentrations of elemental chlorine gas can present an acute and potentially lethal hazard to health and a longer term environmental hazard. Surprisingly we have determined that, in the absence of or at reduced levels of chloride ions there is a very significant enhancement of the stability of aqueous hypochlorite ions under acid conditions. Moreover, we have determined that reduced levels of chloride ions improve the stability of hypochlorite bleaches under neutral or alkaline conditions. Accordingly, the present invention provides an aqueous hypochlorite solution comprising at least 0.01 %wt surfactant, wherein the ratio of available chlorine to chloride (as alkali metal salt) is greater than 1.5:1.

Description

IMPROVEMENTS TO BLEACHING COMPOSITIONS

Field of the Invention

The present invention relates to improvements to aqueous, hypochlorite containing compositions, suitable for use in the cleaning and/or sanitization of hard surfaces and the bleaching of stains on said surfaces.

Background to the Invention

The bulk of hard-surface cleaning compositions in commercial use as cleaning compositions for sanitary- porcelain and like materials can be classified into two groups, acidic products and hypochlorite-based products. Acidic products comprise a variety of aqueous acids, including sulphuric, hydrochloric, phosphoric, formic, citric, acetic and sulphamic acids. Hypochlorite based products generally contain aqueous sodium hypochlorite and are commonly known as 'hypochlorite bleaches' even when the level of hypochlorite in said compositions is insufficient to bleach stains. At low levels hypochlorite is ineffective as a bleach but is still effective as a hygiene/sanitization agent.

Industrially, hypochlorite solutions are manufactured by reaction of chlorine gas with sodium hydroxide, by passing the chlorine gas through the alkali in aqueous solution. The reaction produces sodium chloride and sodium hypochlorite in almost equimolar quantities at a typical final concentration of about 13%wt sodium chloride, 15% available chlorine. In order to facilitate shipment of hypochlorite solutions, a portion of the sodium chloride may be removed by partial crystallisation at depressed temperature and subsequent filtration, typically to reduce the sodium chloride level to about 3%wt. This low salt solution may be concentrated to a higher hypochlorite level for shipping. In addition, although the bulk of the hypochlorite produced on an industrial scale comprises about 13% sodium chloride, 15% available chlorine, some 30% hypochlorite solution with relatively low salt levels is produced for use in the organic chemistry industry in halogenation reactions.

Commercial hypochlorite solutions sold as 'bleaches' comprise moderately high levels of electrolyte. The electrolyte is commonly sodium chloride as produced in the above-mentioned process.

It has been long known that the effectiveness of hypochlorite solutions when used on hard surfaces such as sanitary ceramics, is improved by the incorporation in formulations of a thickener which is stable in the presence of hypochlorite. Known thickeners include lauric acid and amine oxides. The presence of an electrolyte is necessary in combination with the thickener to achieve a high viscosity. Compositions having an elevated viscosity tend to cling to sloping surfaces and their effect is thereby potentiated.

One difficulty which has been encountered due to high levels of thickening electrolyte in hypochlorite bleaches is the crystallisation of the electrolyte as a solid salt around the caps of containers for said compositions. This can lead to difficulties in opening the container and possible spillage of the product.

T SHEET In commercial products, levels of electrolyte (as sodium chloride) are typically around 4-10%wt depending on the surfactant system and the level of hypochlorite. Typical levels of hypochlorite are equivalent to 1-9% available chlorine. With some surfactant systems it has been considered necessary to dose additional salt into the product so as to achieve the desired viscosity of the final composition. Generally the ratio of sodium chloride to sodium hypochlorite is around 1:1. Moreover, where concentrated hypochlorite solution is used as a raw material in the preparation of commercial bleaches, it is commonplace to dilute the solutions with a salt solution, or otherwise add salt, to reach typical salt levels at which the desired viscosity in the presence of a suitable surfactant is achieved.

Despite the excellent hygiene performance of surfactant- thickened hypochlorite solutions, the use of such hypochlorite solutions is not without further drawbacks. In particular, hypochlorite is both unstable on storage and corrosive to metals. Consequently extreme care must be taken in the handling of hypochlorite bleaches both during manufacture and storage. Moreover, the shelf life of hypochlorite bleaches is limited due to the progressive decomposition of the hypochlorite ion. Analysis of commercially available products indicates that the hypochlorite half-life of the products may be as short as six weeks.

More seriously, although hypochlorite solutions are safe when used in accordance with the manufacturers instructions, it is well known that when acids are added to hypochlorite bleaches in amounts such that the pH falls below 4, chlorine gas is evolved into the environment. It is very well known that even low concentrations of

SUBSTITUTE SHEET chlorine gas can present a serious and potentially lethal hazard to health.

There is very little reliable data regarding the effects of chlorine on humans, however chlorine has been considered to be potentially lethal at a level of 12.7ppm or above and can have detrimental effects at lower levels. The 'Directory on Prevention of Chemical Disasters' (Japan Chemical Society, 1979) places a short term human exposure limit on chlorine (i.e. a maximum level for fifteen minutes exposure) at 1-3 pp . The same document considers a level of above 35ppm to be distinctly life-threatening to humans. While no fatalities have been observed at concentrations below 50ppm after 30 minutes exposure, it is obviously desirable that human exposure to chlorine in gaseous form is limited as far as possible.

Acid solutions may be inadvertently mixed with hypochlorite solutions when acidic hard-surface cleaners and hypochlorite-based hard-surface cleaners are used simultaneously or sequentially in cleaning operations. Similar accidents may occur when acidic brick cleaners or acidic de-scaling agents are mixed with hypochlorite solutions. For these reasons, much effort has been expended in finding alternative bleaching agents and the use of materials such as hydrogen peroxide has met with some success.

Unfortunately, the alternatives to hypochlorite based cleaning and sanitizing compositions have suffered from disadvantages either of high or prohibitive cost or reduced antimicrobial activity as compared with hypochlorite solutions.

In addition to the above-mentioned disadvantage of a direct threat to human health, it is known that elemental chlorine in gaseous form may, under certain circumstances, react with organic molecules to form compounds which are believed to be detrimental to the environment. This problem is not known to occur with hypochlorite solutions.

In view of the above, it can be seen that there are outstanding problems regarding the stability of hypochlorite solutions both under normal storage and more especially when such solutions are inadvertently mixed with acids.

Brief Description of the Invention

We have now determined that hypochlorite solutions in which the level of chloride ions in the electrolyte is low are more stable than solutions comprising higher levels of chloride ions.

Accordingly, the present invention provides for the use of an essentially chloride free electrolyte as a stabilizer in an aqueous hypochlorite bleach.

Without wishing to be bound by any theory of operation is believed that the presence of chloride ions is necessary for the chlorine-producing reaction to proceed.

Detailed Description of the Invention

Surprisingly we have determined that, in the absence of or at reduced levels of chloride ions there is a very significant enhancement of the stability of aqueous hypochlorite ions under acid conditions. Moreover, we have determined that reduced levels of chloride ions improve the stability of hypochlorite bleaches under neutral or alkaline conditions.

Accordingly, a first aspect of the present invention provides an aqueous hypochlorite solution comprising at least

0.01%wt surfactant, wherein the ratio of available chlorine to chloride (as alkali metal salt) is greater than 1.5:1

Chloride/Hvpochlorite levels

Preferably, products according to the present invention comprise in addition to an aqueous hypochlorite solution, an electrolyte wherein the level of chloride ions is less than about lwt%, more preferably in the range l-0.001wt%, levels of chloride of around l-0.5wt% being particularly preferred.

Typically, products according to the present invention comprise 0.15-15wt% available chlorine as hypochlorite. Preferred levels of available chlorine range from l-10wt%

Typical compositions constituting embodiments of the invention therefore comprise:

a) 0.2-15wt% available chlorine as sodium hypochlorite, and,

b) 0.001-3wt% alkali-metal chloride.

wherein the ratio of available chlorine to chloride (as alkali metal salt) is greater than 1.5:1 It is particularly desirable to reduce the levels of chlorine released or to retard the release of chlorine from products which comprise relatively high levels of chlorine. At higher available chlorine levels it is preferred to maintain a ratio of chlorine to chloride of greater than 3, more preferably of 10 or more. Ratios of up to 30 have been reached in practical embodiments of the invention.

Particularly preferred compositions comprise:

a) 0.2 to 10%wt available chlorine as sodium hypochlorite,

b) 0.02 to 3wt% of an alkali-metal chloride, and,

c) 0.5 to 5wt% of a hypochlorite-stable surfactant.

wherein the ratio of available chlorine to chloride (as alkali metal salt) is greater than 1.5:1

Surfactants

Suitable surfactants are those which are stable in the presence of hypochlorite.

In certain embodiments of the invention, especially those compositions which comprise relatively low levels of hypochlorite, surfactant is present to promote effective cleaning. In other embodiments, surfactant is present as a thickener.

We have determined that long chain amine oxides are particularly effective in achieving an acceptable viscosity in the presence of low levels of electrolyte. Preferred hypochlorite bleaches according to the present invention comprise 1-2% of an amine oxide of the general formula:

R NO

I

R₂

wherein R is straight or branched C₈ to C₁₈ alkyl, R_x is C_x to C₃ alkyl or d to C₃ hydroxyalkyl, and R₂ is d to C₃ alkyl or d to C₃ hydroxyalkyl CHARACTERISED IN THAT, R comprises at least 25% w/w, preferably at least 50%w/w C₁₆- C₁₈ alkyl.

Preferably, R comprises at least 25%, preferably at least 50% C₁₆-C₁₈ linear alkyl.

More, preferably R_x and R₂ are methyl groups.

Particular embodiments according to the present invention comprise:

a) l-2%wt of a long chain amine oxide as described above,

b) 0.1-10%wt available chlorine as hypochlorite,

c) 0.1-0.5%wt C₁₀-C₁₄ fatty acid, and,

d) less than 3% of a chloride. Preferably the pH of compositions according to the present invention is above 11, more preferably in the range 12-13. This pH can be achieved by the addition of a suitable alkali, such as an alkali metal hydroxide.

Minors

As is commonplace, the composition can include a colouring agent selected from the group comprising the copper phthalocyanides and mixtures thereof.

Surprisingly, we have determined that the colour stability of preferred compositions according to the present invention is improved as compared with controls. This is poorly understood, but it is believed that this is due to interaction of the amine oxide and pigment.

Compositions according to the present invention can also comprise perfumes, sequestering agents and mixtures thereof.

In order that the present invention may be further understood, it will be described hereafter with reference to examples and with reference to the accompanying figures wherein:

FIGURE 1 shows selected results from Tables 1A-1B below, to illustrate the effect of chlorine:chloride ratio of the proportion of available chlorine released FIGURE 2 shows a graph of available chlorine decay with time in products according to the present invention and comparative products,

FIGURE 3 shows a graph of product viscosity changes with time in products according to the present invention and comparative products,

EXAMPLES:

1) Stability under acid conditions/chlorine release.

Chlorine gas release was evaluated in a German-type 'shelf WC plumbed into a toilet cubicle having width

80cm, length 165cm, and height 255cm. It has been found that this form of toilet bowl gives the worst results as regards chlorine release in the presence of strong acids.

Measurements of atmospheric chlorine levels were performed with commercially available Draeger [Trademark] tubes. These contain ortho-tolidine which forms a yellowish- orange reaction product in the presence of chlorine. Tubes 0.2/a and 50/a were employed following the manufactures instructions. Measurements were performed at the following locations:

Ml: 15cm above the shelf of the toilet. Represents the chlorine exposure if the head is placed within the toilet bowl, i.e. assuming a worst case scenario involving collapse of a person shortly after mixing acid and hypochlorite product. M2: 5-10 cm from the edge of the bowl. Represents the chlorine exposure assuming collapse of a person onto the floor at the side of the WC.

M3: 35-40cm above the rim of the bowl. Represents the chlorine exposure if a person mixed the acid and hypochlorite products while cleaning the toilet and kneeling.

M4: 100cm above the rim of the bowl. Represents the chlorine exposure if a person mixed the acid and hypochlorite products while cleaning the toilet in an upright position.

Concentrations of salt in the compositions tested are given in wt%. Available chlorine in the products was determined by titration against sodium thiosulphate solution. The compositions were dosed into the toilet bowl in quantities of lOOg. It should be noted that consumers generally dose around 80g of hypochlorite formulations into the toilet bowl although the sporadic use of excessive quantities is not unknown.

The following acid cleaners were employed, as identified (except for the first and third case) by their county of origin. All products except 'SU' were commercially available products.

Acid Cleaner Contains

'SU' 5N (in product) sulphuric acid

'FR' 7.50 %w/v phosphoric acid

'HC 9.36 %w/v hydrochloric acid

'BE' 7.50 %w/v formic acid The acid toilet cleaner was dosed into the toilet bowl in quantities of lOOg, except in the case of the sulphuric acid 'SU' which was dosed at a 50g level.

No significant difference in levels of evolved chlorine was observed when acid was added to hypochlorite or hypochlorite to acid. The order of mixing used to obtain the results given below was acid added to hypochlorite.

It should be noted that the reproduction of these experiments requires great care to be taken due to the obvious health hazards associated with exposure to chlorine gas.

Results are given in Tables 1A-1D below. The hypochlorite compositions are identified by the available chlorine as measured (AC) given as a percentage: i.e. 'AC9' in example 1.1 refers to 9% available chlorine. The sodium chloride levels are indicated as 12.8%wt (standard salt in the comparative examples:= SS) , 3%wt (low salt in the embodiments:= LS) or 0.5%wt (very low salt in the embodiments:= VS) : i.e. 'ss' in example 1.11 refers to a standard salt level of 12.8%. Comparative examples are marked with an asterisk '*'.

In Tables 1A-1D, the figure given in brackets is the approximate time given to reach the specified chlorine concentration, which is the maximum concentration observed, measured to the nearest minute from mixing, i.e. the figure 75(5) in comparative example 1.11 indicates the chlorine concentration at head height (lOQcm above the rim of the bowl) reached 75ppm five minutes after mixing. TABLE IA

Comparative examples with standard salt and embodiments of the invention mixed with 5N sulphuric acid (SU: similar in strength to that available in many retail outlets for use as a toilet cleaner) :

From Table IA it can be seen that in the comparative examples a hypochlorite composition comprising a standard level of salt rapidly evolved a dangerous level of chlorine gas when mixed with sulphuric acid, whereas the compositions according to the present invention showed a clearly reduced and retarded chlorine release.

It should be noted that the UK Government Health and Safety Executive have set the potentially lethal dose of chlorine at 12.7 ppm, and it can be seen that this level was exceeded at all measuring locations for each of the standard salt formulations except where very low levels of hypochlorite were present in the composition. In particular, a conventional high-strength hypochlorite solution (9% available chlorine) released sufficient chlorine to expose a kneeling (M3) user to around eight times the potentially lethal dose within two minutes of mixture.

TABLE IB

Comparative examples with standard salt and embodiments of the invention mixed with phosphoric acid based acid cleaner (FR) as bought in the French marketplace.

From Table IB it can be seen that in the comparative examples a hypochlorite composition comprising a standard level of salt rapidly evolved a dangerous level of chlorine gas when mixed with a commercially available French lavatory cleaner based on phosphoric acid, whereas the compositions according to the present invention showed a clearly reduced and retarded chlorine release. TABLE 1C

Comparative examples with standard salt and embodiments of the invention mixed with hydrochloric acid based acid cleaner (HC) as bought in the French marketplace.

From Table IB it can be seen that in the comparative examples a hypochlorite bleach composition comprising a standard level of salt rapidly evolved a dangerous level of chlorine gas when mixed with a commercially available French lavatory cleaner based on hydrochloric acid, whereas the compositions according to the present invention generally showed a slight improvement as regards reduced and retarded chlorine release.

It should be noted that significant quantities of chloride ion were being added in the form of the hydrochloric acid and consequently the embodiments of the invention gave only a slightly better performance than the prior art. TABLE ID

Comparative examples with standard salt and embodiments mixed with a formic acid based acid cleaner as bought in the Belgian marketplace.

From Table ID it can be seen that in the comparative examples a hypochlorite bleach composition comprising a standard level of salt evolved some chlorine gas when mixed with a commercially available Belgian lavatory cleaner based on formic acid. The compositions according to the present invention showed a slightly reduced and retarded chlorine release, although the quantities of chlorine released from this product did not constitute a particularly serious hazard.

Figure 1 shows the chlorine release data in terms of the ratio of available chlorine to chloride (as sodium chloride) in the compositions plotted against the ratio of M2 to total available chlorine. The ratios are calculated as follows: - 17

From the graph it can be seen that a reduction in the salt level as compared with the available chlorine level has a marked effect on the release of chlorine from the compositions. Compositions according to the present invention have a ratio of AvCl₂/NaCl greater than 1.5.

2) Stability under alkaline conditions

In the examples 2A, 2B and 2C given below materials are identified as follows:

Aromox DMB-W [RTM: Akzo Chemicals] is an amine oxide having a chain length distribution of 54% C₁₂, 24% C₁₄,

Long Chain AO, is amine oxide having a chain length distribution of 35% C₁₂, 15% C₁₄, 18% C₁₆ and 32% C₁₈

Alkaline silicate (100 degrees TW) was obtained from the Crossfield chemical company.

Sodium Chloride is expressed as total sodium chloride on product . Sodium Hypochlorite is expressed as the wt% of a solution having 15.4% available chorine, free of sodium chloride.

Compositions 2A, 2B and 2C were prepared with formulations as given in Table 2 below, all figures being given in wt%:

TABLE 2

Examples 2A is a comparative example: 2A being essentially identical to a commercially available aqueous hypochlorite bleaching composition available in the marketplace, whereas 2B has a reduced salt content and employs a modified amine oxide thickener. Example 2C is an embodiment of the present invention and is identical to 2B except that the salt level has been further reduced. Formulations were made up by heating the water to circa. 80°C, adding the lauric acid, neutralising the product obtained, subsequently adding the amine oxide and cooling to circa. 50°C before adding perfume and all ingredients except hypochlorite. Hypochlorite was added at circa. 30°C after further cooling.

Products 2A, 2B and 2C were stored at 37°C in closed containers for three months. At various intervals samples were drawn from the containers and available chlorine was determined by titration against sodium thiosulphate. Turning to figure 2A, it can be seen that the available chlorine level in products according to the present invention (squares = comparative example 2A, triangles = comparative example 2B and circles = embodiment 2C) was elevated as compared with the comparative examples.

Further storage experiments were performed at 37°C with a range of salt concentrations and the hypochlorite half life of the products determined. The results are shown in figure 2B. It can be seen that the products manufactured with low levels of salt showed a consistent improvement in shelf-life over those manufactured with standard levels of salt.

3) Product Viscosity on storage

Products 2A, 2B and 2C as described in section (2) were stored at 37°C in closed containers for three months. At various intervals samples were drawn from the containers and viscosity was determined by means of a Haake rotary viscometer (19.5 reciprocal sec, at STP) . Turning to figure 3, it can be seen that the viscosity of the products according to the present invention (squares = comparative example 2A, triangles = comparative^' example 2B and circles = embodiment 2C) was similar to the comparative examples over the whole assay period. It will be noted that the viscosity of the composition 2C was lower than the higher salt examples 2A and 2B but this was not important in practice.

d) Corrosion Inhibition

In order to demonstrate the reduced corrosiveness of the compositions according to the present invention, corrosion tests were performed with steel washers. Stainless steel washers manufactured from a steel according to British Standard 316 were employed. The above-mentioned metal is commonly employed in bleach production equipment. Two washers were secured together with a rubber band to imitate a joint in plant equipment and partially immersed in the product to provide a surface air interface. Duplicate experiments were performed with a standard hypochlorite solution and with a composition according to the present invention. The contact test was performed over a period of 24 hours.

Both samples gassed slightly. The damage caused to the stainless steel in the standard composition was considerable and indicated by blistering of the metal surface and some rusting at the product/air interface. The composition according to the present invention produced only marginal tarnishing at the product/air interface.

Claims

CLAIMS1) An aqueous hypochlorite solution comprising at least 0.01%wt surfactant, wherein the ratio of available chlorine to chloride (as alkali metal salts) is greater than 1.5:12) Compositions according to claim 1 comprising,a) 0.2-15wt% available chlorine as sodium hypochlorite, and,b) 0.02 up to 3wt% alkali-metal chloride.3) Compositions according to claim 2 comprising,a) 0.2 to 10%wt available chlorine as sodium hypochlorite,b) 0.02 to 3wt% of an alkali-metal chloride, and,c) 0.5 to 5wt% of a hypochlorite-stable surfactant,4) Composition according to claim 3 wherein the surfactant comprises l-2%wt on product of an amine oxide of the general formula:R,-NOR,wherein: R is straight or branched C8 to C18 alkyl, Rx is Cj to C3 alkyl or d to C3 hydroxyalkyl, and R2 is d to C3 alkyl or C_ to C3 hydroxyalkyl CHARACTERISED IN THAT, R comprises at least 25% w/w, preferably at least 50%w/w C16-C18 alkyl.5) Composition according to claim 4 comprising:a) 0.1-10%wt available chlorine as hypochlorite, and,b) 0.1-0 .5%wt C10-C14 fatty acid. AMENDED CLAIMS[received, by the International Bureau on 14 December 1993 (14.12.93): original claims 1-3 and 5 amended; other claims unchanged (2 pages)]

1. An aqueous hypochlorite solution comprising:

a) at least 0.01%wt surfactant,

b) 0.2-15wt% available chlorine as sodium hypochlorite, and,

c) 0.02 up to 1.5wt% alkali-metal chloride,

wherein the ratio of available chlorine to chloride (as alkali metal salts) is greater than 10:1

2. Compositions according to claim 1 comprising,

a) 0.2 to 10wt% available chlorine as sodium hypochlorite,

b) 0.02 to lwt% of an alkali-metal chloride, and,

c) 0.5 to 5wt% of a hypochlorite-stable surfactant,

3. Composition according to claim 2 wherein the surfactant comprises l-2wt% on product of an amine oxide of the general formula:

R- -NO

R,

wherein: R is straight or branched C₈ to C₁₈ alkyl, R_% is d to ^c ₃. alkyl or d to ^c ₃ hydroxyalkyl, and R₂ is C_x to C₃ alkyl or d to C₃ hydroxyalkyl CHARACTERISED IN THAT, R comprises at least 25% w/w, preferably at least 50%w/w C₁₆-C_lβ alkyl.

4. Composition according to claim 3 comprising:

a) 0.1-10wt% available chlorine as hypochlorite,

and,

b) 0.1-0.5wt% C₁₀-C₁₄ fatty acid.

5. Use of an essentially chloride free electrolyte as a stabiliser in an aqueous hypochlorite bleach comprising:

a) at least 0.01wt% surfactant,

b) 0.2-15wt% available chlorine as sodium hypochlorite, and,

c) 0.02 up to 3.0wt% alkali-metal chloride,

wherein the ratio of available chlorine to chloride (as alkali metal salts) is greater than 1.5:1.