DE69607391T2 - IMPROVEMENT IN ANTIMICROBIAL DETERGENT COMPOSITIONS - Google Patents

Description

Technical area

The present invention relates to the use of a specific surfactant in combination with a specific alcohol to improve the activity of the hygiene agent and a method for treating surfaces with the composition.

Background of the invention

Hard surface cleaning compositions generally comprise one or more surfactants and optionally one or more sanitizing agents and/or solvents.

Generally, surfactants used in such cleaning compositions are selected from anionic, nonionic, amphoteric and cationic surfactants. This large group of surfactants displays a wide range of properties. Nonionic surfactants are very commonly used due to their effectiveness against greasy soils and the ease with which their foaming can be controlled. The precise function of nonionic surfactants in cleaning compositions depends on the hydrophilic/lipophilic balance or "HLB" of the surfactant selected. Generally speaking, nonionic surfactants with relatively low HLB values (7-9) are considered wetting agents and are used in combination with solvents, with the solvent performing the cleaning function, as in glass cleaners. Nonionic surfactants with relatively high HLB values (13-15) are considered detergents and remove soil from surfaces by themselves.

Non-ionic surfactants are listed as having low biocidal activity, whereas certain anionic, cationic and amphoteric surfactants are biocidally active under specific conditions of, for example, pH and concentration. However, with some notable exceptions, the biocidal activity of surfactants is low and it is common practice to add a separate hygiene agent to the compositions.

Typical sanitation agents include strong acids, alkalis, phenolics and oxidants such as peracids and hypohalites. These oxidants, a typical example of which is hypochlorite, are generally very reactive species which, alone or in effective formulations, exhibit this reactivity in relation to one or more properties such as short life, toxic, corrosive and irritant properties. In general, these reactive components should be present in relatively high proportions in formulations. Other, less chemically reactive sanitation agents, such as 2,4,4'-trichloro-2'-hydroxydiphenyl ether (sold commercially as IRGASAN®), are effective at relatively low concentrations but are more expensive than simpler agents and may be more specific in their spectrum of activity. Many organic acids, including benzoic, salicylic and sorbic acid, are known as preservatives in cosmetics and some food products, however, these preservatives generally show lower biocidal activity than the above-mentioned chemically reactive hygiene agents when used in an equal proportion.

When cleaning hard surfaces, it is often necessary to disinfect a surface. A "disinfectant" can be considered a sanitizer that demonstrates a 100,000-fold or better reduction in the number of live microorganisms in a designated culture when used at a level of around 0.5% by weight. This is commonly known as a "log 5 kill." Many of the weaker sanitizers do not achieve this level of bacterial killing, particularly when present in formulations at relatively low levels.

Some surfactants have been found to enhance the effects of certain hygiene products. DE-36 19 375 (Henkel) discloses that alkyl polyglycoside (APG) surfactants exhibit synergy with alcohols and organic acids for hygiene. The examples of this reference disclose compositions comprising APG and organic acids. These compositions are used at strongly acidic pH, generally below pH 3.

Alcohols such as ethanol and isopropanol (IPA) are well-known components of cleaning compositions. Generally, these are present as solvents at low levels in compositions of near neutral pH. For example, GB 1 076 920 (1966) relates to glass cleaners comprising - 0.25% alkylphenol polyoxyalkylene ether and 3.5-4% ethanol; GB 1 403 919 (1972) relates to car wash compositions comprising 3-4% non-ionic surfactant (an EO/PO system is used in the examples) and 4% isopropanol; US 4 414 128 (1981) relates to hard surface cleaners comprising 0.5-3% Dobanol 91-8 (HLB 13.8 by calculation) and 1-2% ethanol; GB 2 103 642 (1981) relates to an eyeglass cleaner comprising 1% ethoxylated non-ionic surfactant and 10% ethanol: the preferred pH of which is 6-8.

Often these systems are free of ethoxylated alcohol surfactants, for example GB 2 167 083 (1984) concerns hard surface cleaners comprising 4% IPA and GB 2 173 508 (1986) concerns hard surface cleaners comprising 1% 3,5-dimethyl-1-hexyn-3-ol and 0.45% primary alkyl sulfate as anionic surfactant with 2-4% IPA.

It is also known to use solvents at higher proportions in "stain removers". Typical examples of such formulations can be found in GB 0 962 436 (1961) which relates to a solvent-based stain remover, examples of which comprise 8-35% alkoxylated components (including non-ethoxylated alcohols) and 20-44% alcohols.

When alcohols are present at very high concentrations (i.e. 70% ethanol by weight is used in "medical alcohol"), they are also known to have disinfectant properties. However, such high alcohol concentrations concentrations are rarely used except in special applications due to the extreme flammability of the compositions and the health risks associated with their use.

Thus, when alcohols are present at low levels as solvents, it is common to add additional sanitizing agents if antimicrobial activity is desired. US 4,420,484 (Sterling Drug: 1981) relates to such an antimicrobial composition. Compositions are disclosed comprising -12% nonionic surfactants and 3% isopropyl alcohol. The compositions, which have a pH of around 5.5, do not appear to contain alcohol ethoxylate, the surfactant being either betaine or amine oxide. The antimicrobial properties of this composition derive from the known antimicrobicides, such as chlorhexidine, which are incorporated into the composition.

EP 0 478 445 (Peters: 1990) discloses a composition for disinfecting surgical instruments. Examples of a preferred embodiment in the cited description relate to compositions containing 7% C13/8EO-ethoxy alcohol non-ionic surfactant (the HLB value is around 12.8 by calculation) and 12% ethanol/isopropanol with a pH of 8.5. The cited compositions comprising 13% didecyldimethylammonium chloride, which is known as a biocide and is identified as such in the description, while the non-ionic surfactant and alcohol are optional.

EP 0 536 820 (Colgate Palmolive: 1991) discloses an acidic composition (pH 2-4) containing non-ionic surfactants (HLB 7-10 and 11) and antimicrobial disinfectants. It is stated in the cited patent that small amounts of isopropyl alcohol (up to 2%) can be added to improve the antimicrobial effects (page 5, line 4Bff).

EP 0 028 038 (P & G: 1979) relates to compositions containing nonionic surfactants with HLB value 10-13 and the examples contain 11.5% nonionic surfactant (HLB 12) and 1-2% ethanol. The compositions have a pH of 8-13. Germicides are mentioned as optional ingredients in the disclosed compositions.

There is a need to provide antimicrobial, preferably disinfectant, compositions which do not require the presence of either expensive or reactive sanitizing agents such as hypochlorite or peroxides, but which exhibit broad spectrum antibacterial activity and are formulated with relatively simple and available materials such as solvents. It is also considered important that high levels of alcohols or other solvents should be avoided due to health and fire risks.

Brief description of the invention

We have now determined that a remarkable synergy is exhibited between selected ethoxylated alcohol surfactants and certain alcohols at alkaline pH values that are outside the normal "physiological" range in bacteria. This synergy allows much lower alcohol levels than previously used to have a significant antimicrobial effect.

Accordingly, the present invention provides the use of 1-30% by weight of a linear or branched C1-C5 alcohol as a biocidal activity enhancing additive in a cleaning composition having pH>8, comprising, based on the product, 0.01-30% by weight of an ethoxylated nonionic surfactant other than an alkylphenol derivative, having an HLB value of 10-14.

As discussed above, ethoxylated alcohol surfactants with HLB 10-14 are inhibitors of bacterial growth but are only weakly biocidal at typical formulation pH values. In the presence of the designated alcohols and the above normal physiological pH range, a synergy is maintained and exploited to yield a product that is both an effective cleaning agent and biocidal. Effective cleaning and biocidal activity are required in a cleaning composition for hygiene purposes. desired when it is important to both kill high numbers of bacteria and remove soil to retard reinfection and regrowth of bacterial populations. In the present invention, both the essential features of effective microbial killing and improved soil removal are achieved with a relatively simple and hence cost effective formulation.

Without wishing to be bound by any theory of the process, it is believed that the presence of both the selected alcohol and the selected class of surfactant in the membrane of bacteria leads to the formation of "pores" in the cytoplasmic membrane of the bacteria through which the contents of the cell can be exchanged with the environment. This can be confirmed by studies using the fluorophore propidium iodide, which is not taken up by cells with intact membranes. It is believed that bacteria cannot seal this leak under the specified pH conditions and consequently rapid cell death occurs.

Description of the invention in detail

In order to further understand the invention, it is hereinafter described with reference to preferred features and materials.

Non-ionic surfactants

Nonionic, ethoxylated surfactants are present in the compositions of the invention. These surfactants are believed to interact synergistically with both the alcohol to enhance cleaning and assist in the removal of subsequently deposited soils, and with the antimicrobial agent to enhance the disinfecting qualities of the composition.

Suitable nonionic detergent-active compounds can be described in the broadest sense as compounds which are obtained by the condensation of ethylene oxide groups, which are hydrophilic in nature, with an organic-hydrophobic The length of the hydrophilic or polyoxyethylene moiety condensed to any particular hydrophobic group can be easily adjusted to yield a water-soluble compound with the desired degree of balance between hydrophilic and hydrophobic elements (HLB).

Particular examples include the condensation product of aliphatic alcohols having 8 to 22 carbon atoms in either straight or branched chain configuration with ethylene oxide, such as a coconut oil-ethylene oxide condensate having 3 to 10 moles of ethylene oxide per mole of coconut alcohol.

The amount of nonionic detergent active to be employed in the composition of the invention is generally from 0.1 to 30% by weight, preferably from 1 to 20% by weight and most preferably from 3 to 10% by weight for non-concentrated products. Concentrated products will generally have from 10 to 20% by weight of nonionic surfactant, whereas diluted products suitable for spraying will have from 0.1 to 5% by weight of nonionic surfactant.

Generally, the ethoxylated nonionic surfactant is an ethoxylated alcohol having a chain length of C8-C14 and 4-10 ethoxy groups per molecule. However, it is essential that the HLB value of the nonionic surfactant should fall within the range of 10-14. The HLB value can be calculated as a function of the chain length of the molecule and its degree of ethoxylation. According to Griffin (W. C. Griffin J. Soc. Cosmetic Chemists [5, 249, 1954]), the HLB value of fatty alcohol-ethylene oxide adducts is given as one-fifth of the weight percent of the oxyethylene moiety in the adduct.

It is believed that the critical micellar concentration (CMC) of ethoxylated non-ionic surfactants should be below 10-3.5 mol/liter, preferably in the range 10-3.5 to 10⊃min;⊃5; mol/liter. Very surprisingly, we have found that for non-ionic alcohol ethoxylate surfactants operating under optimal conditions, the minimum inhibitor concentration (MIC) for these surfactants appears equal to the CMC.

IMBENTIN 91-35 OFA' (TM, ex Kolb AG), a C9-11 alcohol with an average of five moles of ethoxylation, was found to be a suitable nonionic surfactant in the compositions of the invention. This material has a calculated HLB of 11.6 and is believed to have a CMC of 1.6 x 10-4 moles/liter. DOBANOL 91-8 (TM), a C9-11 alcohol with an average of 8 moles of ethoxylation, was also found to be a suitable material. This material has a calculated HLB of 13.8 and is believed to have a CMC of 4.3 x 10-4 Mol/litre.

Alcohols

Preferably, the alcohol is selected from the group comprising propan-2-ol, propanol, ethanol and mixtures thereof.

Preferred alcohol contents are 1-25 percent by weight of the product. At these concentrations, alcohols, taken alone, show little potential as disinfectants. Particularly preferred alcohol contents are in the range of 5-15%.

Preferably, the weight ratio of the alkoxylated, non-ionic surfactant to the alcohol is such that the alcohol is present in a weight excess over the alkoxylated, non-ionic surfactant.

PH value

Preferably, the compositions of the invention further comprise a buffer to maintain the pH of the composition in the desired pH range after dilution by a factor of 2-5.

The alkaline products according to the invention have a preferred pH of 8-11, more preferably 9.5-11. Below pH 9.5 the compositions show reduced bacterial killing, while above pH 11 the compositions are unacceptable for many uses. bar be considered dangerous. Sodium bicarbonate/carbonate buffers are suitable for maintaining the pH in the preferred range.

In small quantities and if present components

The composition of the invention may contain other minor, non-essential ingredients that assist in its cleaning performance and maintain the physical and chemical stability of the product.

For example, the composition may contain detergency builders. Generally, the builder, if applied, will preferably constitute from 0.1 to 25% by weight of the composition.

Optionally, the composition may include one or more amphoteric surfactants, preferably betaines, or other surfactants such as amine oxide and alkyl aminoglycinates. Betaines are preferred for reasons of cost, low toxicity (particularly compared to amine oxides) and wide availability.

Typical betaines in compositions of the invention are the amidoalkyl betaines, particularly the amidopropyl betaines, preferably having an aliphatic alkyl radical of 8 to 18 carbon atoms and preferably having a straight chain. These betaines are preferred because they are believed to comprise relatively low levels of nitrosamine precursors, although other betaines, such as alkyl betaines, can be used in the compositions of the invention.

Typical levels of amphoteric surfactants are in the range of 0.01 to 8%, with levels of 1-5% by weight, particularly around 2%, being preferred for normal compositions and up to four times the concentration in the so-called concentrated products. As with the non-ionic surfactant, lower levels of around 0.05-1% are used in sprayable products and higher levels of generally around 4% by weight are used in concentrates.

Metal ion sequestrants, including ethylenediaminetetraacetates, aminopolyphosphonates (such as those in the DEQUEST® range) and phosphates, and a wide variety of other polyfunctional organic acids and salts, may also be employed. It is believed that the hygienic performance of the composition is improved by the presence of a metal ion sequestrant.

The solutions generally do not require additional hydrotropes, which should be added as alcohols to provide a hydrotropic effect. Suitable additional hydrotropes include alkali metal toluene sulfonates, urea, alkali metal xylene and cumene sulfonates, polyglycols, > 20EO ethoxylated alcohols and glycols. Preferred among these hydrotropes are sulfonates, particularly the cumene, xylene and toluene sulfonates. Typical levels of additional hydrotrope are in the range of 0-5% for the sulfonates. Hydrotropes are not always required for dilute sprayable products, but may be required when lower EO or longer alkyl ethoxylates are used or the cloud point is to be significantly increased. The cumene sulfonate is the most preferred hydrotrope.

The compositions of the invention may also contain, in addition to the ingredients already mentioned, various other optional ingredients, such as further solvents, colorants, optical brighteners, soil suspending agents, detergent enzymes, compatible bleaches, gel-blocking agents, freeze-thaw stabilizers, further bactericides, perfumes and opacifiers.

The particularly preferred formulations according to the present invention, excluding small amounts, include:

a) 0.1-20% by weight, based on the product, of an ethoxylated alcohol with a chain length of C₈-C₁₄, 4-10 ethoxy groups per molecule and an HLB value of 10-14,

b) 1-30% by weight of an alcohol selected from the group comprising propan-2-ol, propanol, ethanol and Mixtures thereof, wherein the alcohol (b) is present in a weight excess over the ethoxylated alcohol (a), and

c) at least one buffering agent for maintaining the pH in the range of 9.5-11.

It is envisaged that such a composition should be packaged in a container adapted to deliver the composition in the form of a spray and, accordingly, a preferred method according to the invention comprises the step of treating a surface with a composition as disclosed herein by means of a spray.

In order to further understand the present invention, it will be explained below with reference to the following non-limiting examples and the single figure attached hereto.

Examples

The examples below are suspension tests against a range of microbes at a range of different pH values. The following bacterial strains were used in these suspension tests.

Pseudomonas aeruginosa: ATCC 15442

Staphylococcus aureus: NCTC 6538

Escherichia coli: ATCC 11229

Example 1: against E. coli.

Bacterial suspension was prepared as follows. Incubate bacterial culture (tryptone soy broth) for 24 hours. Settle (50 ml tube, Mistral 1000 centrifuge, 4100 rpm, 10 minutes). Resuspend pellets in peptone water (20 ml) and mix using a vortex mixer for 15-30 seconds. Adjust cell density with sterile peptone water to the required inoculum size using a calibrated densitometer. Store cell suspension at 20ºC (± 1ºC) and use within 2 hours.

All tests were performed using the microplate method for a contact time of 5 minutes at 20ºC in a 96-well (8 x 12) microplate with inoculation (30 μl of Mi Inoculations were carried out with 100 μl of the formulations listed in Table 1 (270 μl) to give a total volume of 300 μl. The inoculum was estimated to be approximately 108 cfu/ml. Inoculations were carried out simultaneously using a multipipette (carefully mixing by picking up and discarding the pipette four times) and the reaction mixture was left for a contact time of 5 minutes.

Alkaline formulations (pH 10.5) were buffered with a mixture of sodium carbonate (1.14 weight/volume percent decahydrate) and sodium bicarbonate (0.08 weight/volume percent).

After the reaction, 30 μl of each reaction mixture was transferred into 270 μl of a quenching solution using a multipipette and mixed as indicated above. The composition of the quenching solution was as follows:

Lecithin 0.3%

Sodium thiosulfate 0.5%

L-Histidine 0.1%

Tween 80 3.0%

pH 7 buffer (see below) 10 ml

distilled water to 1 liter

(Preparation of pH 7 buffer by dissolving 34 g potassium dihydrogen phosphate in 500 ml distilled water and sterilization (autoclave, 121ºC, 15 minutes)).

After 5 minutes (± 1 minute), 30 μl of the quenched product was serially diluted in 270 μl of peptone solution using a multipipette and mixed as indicated above.

Total viable counts were determined using the Miles-Misra spot plate method, plating 10 µl (in triplicate) on tryptone soy agar and incubating for 24 hours at 30ºC. Results were recorded as the mean count of 3 spots on agar, calculating the logarithm of the reduction for each formulation as logarithm = log(initial count) - log(final count). Table 1: Synergy with propan-2-ol under alkaline conditions

Table 1 shows that under alkaline conditions a significant increase in the biocidal activity of the composition is achieved when both the alcohol and the alcohol ethoxylate are present.

Example 2: further examples

Tables 2a and 2b below show further examples using two non-ionic surfactants and two microbial species for which the results are obtained using the procedure as described above in Example 1. In each case where the material was present, the formulations contained 10% isopropyl alcohol, 0.7% non-ionic surfactant and were prepared at pH 11.0. Table 2a: Synergy with propan-2-ol against S. aureus Table 2b: Synergy with propan-2-ol against E. coli

From Tables 2a and 2b it can be seen that at pH 11 synergy was seen when both the non-ionic surfactant and the alcohol were present.

Claims (5)

1. Use of 1-30% by weight of a linear or branched C1-C5 alcohol as a biocidal activity enhancing additive in a cleaning composition having pH>8 comprising, based on the product, 0.01-30% by weight of an ethoxylated nonionic surfactant other than an alkylphenol derivative, wherein the ethoxylated nonionic surfactant has an HLB value of 10-14. 2. Use according to claim 1, wherein the ethoxylated nonionic surfactant is an ethoxylated alcohol with a chain length of C₈-C₁₄ and 4-10 ethoxy groups per molecule. 3. Use according to claim 1, wherein the alcohol is present in a weight excess over the ethoxylated, non-ionic surfactant. 4. Use according to claim 1, wherein the alcohol is selected from the group comprising propan-2-ol, propanol, ethanol and mixtures thereof. 5. Use according to claim 1 in a composition comprising: a) 0.1-20% by weight, based on the product, of an ethoxylated alcohol with a chain length of C8-C14, 4-10 ethoxy groups per molecule and an HLB value of 10-14, b) 1-30% by weight of an alcohol selected from the group comprising propan-2-ol, propanol, ethanol and mixtures thereof, wherein the alcohol (b) is present in a weight excess over the ethoxylated alcohol (a), and c) at least one buffering agent to maintain the pH in the range of 9.5-11.