Stabilized Built Liquid Detergent Composition Containing Enzyme

This invention relates to stable, built, enzyme-containing liquid detergent compositions suitable for laundry or pre-soak formulations. More particularly, the invention relates to aqueous enzyme-containing liquid detergent compositions which contain one or more detergent builders and which are characterized by being physically stable, homogeneous liquid compositions.

The formulation of stabilized enzyme-containing liquid detergent compositions has been the focus of much attention in the prior art. The desirability of incorporating enzymes into detergent compositions is primarily due to the effectiveness of proteolytic and amylolytic enzymes in decomposing proteinaceous and starchy materials found on soiled fabrics, thereby facilitating the removal of stains, such as, gravy stains, blood stains, chocolate stains and the like during laundering. However, enzymatic materials suitable for laundry compositions, particularly proteolytic enzymes, are relatively expensive. Indeed, they generally are among the most expensive ingredients in a typical commercial liquid detergent composition, even though they are present in relatively minor amounts. Moreover, enzymes are known to be unstable in aqueous compositions. It is for this reason that an excess of enzymes is generally required in liquid detergent formulations to compensate for the expected loss of enzyme activity during prolonged periods of storage. Accordingly, the prior art is replete with suggestions for stabilizing enzyme-containing liquid detergent compositions, and in particular unbuilt liquid compositions by the use of various materials which are incorporated into the composition to function as enzyme stabilizers.

In the case of liquid detergent compositions containing a builder, the problem of enzyme instability is particularly acute. Primarily this is because detergent builders have a destabilizing effect on enzymes, even in compositions containing enzyme stabilizers which are otherwise effective in unbuilt formulations. Moreover, the incorporation of a builder into a liquid detergent composition poses an additional problem, namely, the ability to form a stable single-phase composition; the solubility of sodium tripolyphosphate, for example, being relatively limited in aqueous compositions, and especially in the presence of anionic and nonionic detergents.

In U.K. Patent Application G.B. 2,079,305, published Jan. 20, 1982, there is disclosed an aqueous built enzyme-containing liquid detergent composition which is stabilized by a mixture of a polyol and boric acid. As noted in the examples of the U.K. application, relatively large amounts of glycerol are required to stabilize the enzymes in the composition. Yet, as demonstrated hereinafter in the present specification, the enzyme stabilizing effect provided by a mixture of glycerine and borax in a built aqueous liquid detergent composition is relatively modest.

The present invention provides a stabilized built, enzyme-containing liquid detergent composition comprising:

(a) from about 5 to 20%, by weight, of one or more surface active detergent compounds selected from the group consisting of anionic, nonionic and amphoteric detergent compounds;

(b) from about 5 to 30%, by weight, of one or more builder salts selected from the group consisting of alkali metal tripolyphosphates, alkali metal carbonates, alkali metal nitrilotriacetates, and polyacetal carboxylates.

(c) an effective amount of an enzyme or an enzyme mixture selected from the group consisting of alkaline protease enzymes and alpha-amylase enzymes;

(d) an enzyme-stabilizing system containing, based on the weight of the detergent composition, (i) from about 1 to 10% glycerine; (ii) from about 1 to 8% of a boron compound selected from the group consisting of boric acid, boric oxide and alkali metal borates and; (iii) from about 0.5 to 8% of a carboxylic acid compound selected from the group consisting of mono, di and/or polycarboxylic acids having 2 to 8 carbon atoms other than acetic and propionic acids and watersoluble salts thereof; and

(e) the balance comprising water and optionally a minor amount of adjuvants.

In European Patent Application Publication No. 0126505, there is disclosed an aqueous enzyme-containing liquid detergent composition containing an enzyme stabilizing mixture consisting of certain dicarboxylic acids and borax. The dicarboxylic acids are recommended as a substitute for a polyol such as glycerol in known enzyme stabilizing mixtures consisting of glycerol and a boron compound. However, the dicarboxylic acid-borax mixtures of this publication in common with the aforementioned prior art mixture of glycerine and borax are incapable of providing anything other than a modest stabilizing effect in the present built liquid detergent compositions. Hence there is a need to markedly improve enzyme stability in aqueous built liquid detergent compositions of the type herein defined to levels far beyond the present capability of the art.

In a preferred embodiment of the invention, the liquid detergent composition comprises

(a) from about 5 to 15% of an alkali metal alkylbenzene sulfonate wherein the alkyl group contains 12 to 15 carbon atoms;

(b) from about 2 to 5% of an alkali metal alkyl polyethoxy sulfate wherein the alkyl group contains 10 to 18 carbon atoms and the polyethoxy is of 3 to 11 ethylene oxide groups, the weight ratio of (a) to (b) being from about 2:1 to about 8:1;

(c) from about 5 to 30% of sodium tripolyphosphate;

(d) from about 1 to 10% of sodium carbonate, the weight ratio of (c) to (d) being from about 2:1 to about 6:1;

(e) an effective amount of the aforesaid enzyme or enzyme mixture;

(f) an enzyme stabilizing system containing, based on the weight of the detergent composition, (i) from about 3 to 7% glycerine (ii) from about 1 to 5% of an alkali metal borate and (iii) from about 0.5 to 4% of said carboxylic acid compound; and

(g) the balance comprising water and optionally a minor amount of adjuvants.

In accordance with the process of the invention, laundering of stained and/or soiled materials is affected by contacting such materials with an aqueous solution of the above-defined liquid detergent compositions.

The described liquid detergent is a commericially acceptable heavy duty laundry detergent, capable of satisfactorily cleaning laundry items containing both oily and particulate soils. Additionally, the described compositions may be employed for the pre-treatment of badly soiled areas, such as collars and cuffs, of items to be laundered.

The present invention is predicated upon the discovery of a three component enzyme stabilizing system as herein defined which provides an enzyme stabilizing effect to the liquid detergent compositions of the invention far in excess of that which can be achieved with conventional enzyme stabilizers. The enzyme stabilizing effect thus achieved reflects a synergy among the three components. In accordance with the invention, the enzyme stability provided by a mixture of glycerine and borax or a mixture of borax and a dicarboxylic acid as disclosed in the prior art can be synergistically improved by the use of the three component stabilizing system herein defined in the present liquid compositions so as to raise the level of enzyme stability significantly above that provided by either the mixture of glycerine and borax or the mixture of borax and dicarboxylic acid when used independently of each other as enzyme stabilizers. For commercial purposes, a desirable enzyme stability generally corresponds to about a half-life of one week at a temperature of 110.degree. F.

The enzyme stabilizing system of the invention is a mixture of glycerine, a boron compound selected from among boric acid, boric oxide and an alkali metal borate and a carboxylic acid compound as herein defined. The weight of the stabilizing system in the present built liquid detergent compositions is generally from about 3 to 25%, preferably about 6 to 15%, by weight. The weight ratio of glycerine to borax in the stabilizing mixtures is generally from about 1 to 3. The preferred amount of glycerine in the composition is from about 3 to 7%, the preferred amount of boron compound is from about 1 to 5%, and the preferred amount of carboxylic compound is from about 0.5 to 4% based on the weight of the composition.

The carboxylic acid compounds which are useful in the enzyme stabilizing system of the invention encompass saturated as well as unsaturated mono, di and polycarboxylic acids having 2 to 8 carbon atoms except for acetic and propionic acids. Included among this group are oxalic acid (HOOCCOOH), malonic acid (HOOCCH.sub.2 COOH), maleic acid (HOOCCH:CHCOOH) and succinic acid (HOOCCH.sub.2 CH.sub.2 COOH). The carboxylic acids may contain hydroxy or amino substituents as exemplified by malic acid (HOOCCHOHCH.sub.2 COOH), tartaric acid (dihydroxysuccinic acid), aspartic acid (amino succinic acid) and citric acid. Preferred carboxylic acids of the invention are succinic acid, maleic acid, malonic acid and malic acid. From a commercial standpoint, a particularly preferred carboxylic acid compound is citric acid and/or its salts because of their relatively low cost.

The alkaline proteolytic enzymes suitable for the present compositions include the various commercial liquid enzyme preparations which have been adapted for use in detergent compositions. Enzyme preparations in powdered form are also useful although, as a general rule, less convenient for incorporation into the built liquid detergent compositions. Thus, suitable liquid enzyme preparations include "Alcalase" and "Esperase" sold by Novo Industries, Copenhagen, Denmark, and "Maxatase" and "AZ-Protease" sold by Gist-Brocades, Delft, The Netherlands.

Among the suitable .alpha.-amylase liquid enzyme preparations are those sold by Novo Industries and Gist-Brocades under the tradenames "Termamyl" and "Maxamyl", respectively.

"Esperase" is particularly preferred for the present compositions because of its optimized activity at the higher pH values corresponding to the built detergent compositions.

The preferred detergents for use in the present liquid compositions are the synthetic anionic detergent compounds, and particularly a mixture of higher alkylbenzene sulfonate and alkyl polyethoxy sulfate. While other water soluble higher alkylbenzene sulfonates may also be present in the instant formulas, such as potassium salts and in some instances the ammonium or alkanolammonium salts, where appropriate, it has been found that the sodium salt is highly preferred, which is also the case with respect to the alkyl polyethoxy sulfate detergent component. The alkylbenzene sulfonate is one wherein the higher alkyl is of 12 to 15 carbon atoms, preferably 13 carbon atoms. The alkyl polyethoxy sulfate, which also may be referred to as a sulfated polyethoxylated higher linear alcohol or the sulfated condensation product of a higher fatty alcohol and ethylene oxide or polyethoxylene glycol, is one wherein the alkyl is of 10 to 18 carbon atoms, preferably 12 to 15 carbon atoms, e.g., about 13 carbon atoms, and which includes 3 to 11 ethylene oxide groups, preferably 3 to 7, more preferably 3 to 5 and most preferably 3 or about 3 ethylene oxide groups. The ratio of alkylbenzene sulfonate to polyethoxy sulfate in the detergent mixture is preferably from about 2:1 to 8:1 and most preferably from about 3:1 to 5:1, by weight. At ratios above 5:1, the physical stability of the product may be adversely affected.

In suitable circumstances other anionic detergents, such as fatty alcohol sulfates, paraffin sulfonates, olefin sulfonates, monoglyceride sulfates, sarcosinates and similarly functioning detergents, preferably as the alkali metal, e.g., sodium salts, can be present, sometimes in partial replacement of the previously mentioned synthetic organic detergents but usually, if present, in addition to such detergents. Normally, the supplementing detergents will be sulfated or sulfonated products (usually as the sodium salts) and will contain long chain (8 to 20 carbon atoms) linear or fatty alkyl groups. In addition to any supplementing anionic synthetic organic detergents, there also may be present nonionic and amphoteric materials, like the Neodols, .RTM. sold by Shell Chemical Company, which are condensation products of ethylene oxide and higher fatty alcohols, e.g., Neodol.RTM. 23-6.5, which is a condensation product of a higher fatty alcohol of about 12 to 13 carbon atoms with about 6.5 moles of ethylene oxide. Illustrations of the various detergents and classes of detergents mentioned may be found in the text Surface Active Agents, Vol. II, by Schwartz, Perry and Berch (Interscience Publishers, 1958), the descriptions of which are incorporated herein by reference.

The builder salt combination of this invention, which has been found to satisfactorily improve the detergency of the mixture of synthetic anionic organic detergents and produce the desired pH in the liquid detergent and in the wash water, is a mixture of sodium tripolyphosphate and sodium carbonate. The builder salts are employed in the present compositions in amounts generally of from about 5 to 25%, by weight. For the preferred builder salt combination, sodium tripolyphosphate is present in amounts of from about 5 to 20%, preferably 10 to 16%, and sodium carbonate is present from about 1 to 10%, by weight, preferably 3 to 7%, the weight ratio of tripolyphosphate to carbonate in the preferred builders mixtures being from about 2:1 to 6:1, and most preferably from about 2:1 to 4:1. As used herein, the term alkali metal "carbonates" or "carbonate" is meant to include the carbonates, bicarbonates and sesquicarbonates of such alkali metal.

For best processing, easier mixing and good end-use properties it is preferred that the sodium tripolyphosphate below in content of Phase I type tripolyphosphate. Thus, normally the content of Phase I type tripolyphosphate will be less than 30% of the tripolyphosphate employed. Although in some instances incompletely neutralized tripolyphosphate may be used, normally the phosphate employed may be considered as being pentasodium tripolyphosphate, Na.sub.5 P.sub.3 O.sub.10. Of course, in some instances, as when potassium salts of other materials are present, ion interchange in an aqueous medium may result in other salts than the sodium tripolyphosphate being present but for the purpose of this specification it will be considered that sodium tripolyphosphate, as the pentasodium salt, the material which is normally charged to the mixer to make the present liquid detergent, is the tripolyphosphate employed.

Other preferred builder salts which may be used in place of sodium tripolyphosphate and sodium carbonate or in addition thereto include a polyacetal carboxylate as herein described and sodium nitrilotriacetate (NTA). Of course, various mixtures of the mentioned water soluble builder salts can be utilized. Yet, the tripolyphosphate-carbonate mixture described has been found to be most preferred, although the other builders and mixtures thereof are also operative. Other builders which may be employed as supplements, in addition to the proportions of the above mentioned builders, include other phosphates, such as tetrasodium pyrophosphate or tetrapotassium pyrophosphate, sodium bicarbonate, sodium citrate, sodium gluconate, sodium silicate, and sodium sesquicarbonate. Among the water insoluble builders that may be used are the zeolites, such as Zeolite A, usually in the form of its crystalline hydrate, although amorphous zeolites may also be useful.

Polyacetal carboxylates are generally described in U.S. Pat. Nos. 4,144,226 and 4,315,092. U.S. Pat. No. 4,146,495 describes detergent compositions containing polyacetal carboxylates as builders.

The polyacetal carboxylates which are useful herein as builders may be considered to be those described in U.S. Pat. No. 4,144,226 and may be the method mentioned therein. A typical such product will be of the formula ##STR1## wherein M is selected from the group consisting of alkali metal, ammonium, alkyl groups of 1 to 4 carbon atoms, tetraalkylammonium groups and alkanolamine groups, both of 1 to 4 carbon atoms in the alkyls thereof, n averages at least 4, and R.sub.1 and R.sub.2 are any chemically stable groups which stabilize the polymer against rapid depolymerization in alkaline solution. Preferably the polyacetal carboxylate will be one wherein M is alkali metal, e.g., sodium, n is from 50 to 200, R.sub.1 is ##STR2## or a mixture thereof, R.sub.2 is ##STR3## and n averages from 20 to 100, more preferably 30 to 80. The calculated weight average molecular weights of the polymers will normally be within the range of 2,000 to 20,000, preferably 3,500 to 10,000 and more preferably 5,000 to 9,000, e.g., about 8,000.

A particularly preferred sodium polyacetal carboxylate is supplied by Monsanto Company and is known as Builder U. It has a calculated average molecular weight of about 8,000 and an active polymer content of about 80%.

Although the preferred polyacetal carboxylates have been described above, it is to be understood that they may be wholly or partially replaced by other such polyacetal carboxylates or related organic builder salts described in the previously cited patents on such compounds, processes for the manufacture thereof and compositions in which they are employed. Also, the chain terminating groups described in the various patents, especially U.S. Pat. No. 4,144,226, may be utilized, providing that they have the desired stabilizing properties, which allow the mentioned builders to be depolymerized in acidic media, facilitating biodegradation thereof in waste streams, but maintain their stability in alkaline media, such as washing solutions.

The only other required component of the present liquid detergents is water. Normally the hardness content of such water will be less than about 300 ppm., as CaCO.sub.3, and preferably it will be less than 150 ppm. Often it may be desirable to utilize deionized water although city water with less than 50 or 100 p.p.m. hardness content will frequently be equally satisfactory.

Various adjuvants may be present in the liquid detergents, such as fluorescent brighteners, perfumes and colorants. The fluorescent brighteners include the well known stilbene derivatives, including the cotton and nylon brighteners, such as those sold under the trademark Tinopal (5BM Conc.). The perfumes that are employed usually include essential oils, esters, aldehydes and/or alcohols, all of which are known in the perfumery art. The colorants may include dyes and water dispersible pigments of various types, including ultramarine blue. Inorganic filler salts, such as sodium sulfate and sodium chloride may be present, as may be antiredeposition agents, such as sodium carboxymethylcellulose; dispersing agents, such as sodium polyacrylate; bleaches; bactericides; fungicides; anti-foam agents, such as silicones; anti-soiling agents, such as copolyesters; preservatives such as formalin; foam stabilizers, such as lauric myristic diethanolamide; and auxiliary solvents, such as ethanol. Normally the individual proportions of such adjuvants will be less than 3%, often less than 1% and sometimes even less than 0.5%, except for any fillers and solvents, and additional detergents and builders for which the proportions may sometimes be as high as 10%. The total proportion of adjuvants, including non-designated synthetic detergents and builders, will normally be no more than 20% of the product and desirably will be less than 10% thereof, more desirably less than 5% thereof. Of course, the adjuvants employed will be selected so as not to interfere with the washing action of the liquid detergent and to avoid instability of the product on standing. Also, adjuvants which cause the production of objectionable deposits on the laundry are to be avoided.

The present liquid compositions are efficient and easy to use. Compared to heavy duty laundry detergent powders, much smaller volumes of the present liquids are employed to obtain comparable cleaning of soiled laundry. For example, using a typical preferred formulation of this invention, only about 132 grams or 1/2 cup of liquid is needed for a full tub of wash in a top-loading automatic washing machine in which the water volume is 15 to 18 gallons (57 to 68 liters); and even less is needed for front-loading machines. Thus, the concentration of the liquid detergent composition in the wash water is on the order of about 0.2%. Usually, the proportion of the liquid composition in the wash solution will range from about 0.05 to 0.3%, preferably from 0.15 to 0.25%. The proportions of the various constituents of the liquid composition may vary accordingly. Equivalent results can be obtained by using greater proportions of a more dilute formulation but the greater quantity needed will require additional packaging and will generally be less convenient for consumer use and may also result in product separation.

The viscosity of the present liquid detergent is normally in the range of about 1000 to 10,000 centipoises, preferably 2000-5000 centipoises, but products of other suitable viscosities may also be useful. At the viscosities mentioned, the liquid detergent is pourable, stable, non-separating and uniform. The pH of the liquid detergent suspension usually in the range of 7 to 11.5, preferably 8 to 10.5, appears to help to maintain product stability and pourability.

The following examples illustrate but do not limit the invention. Unless otherwise indicated all parts are by weight and temperatures are in .degree.C.

The composition shown above was prepared by the following procedure: 32.5 parts of deionized water at 40.degree. F. are added to a suitable mixing apparatus such as a vertical cylindrical tank equipped with a stirrer. With the stirrer adjusted for medium agitation, a mixture consisting of 5.0 parts anhydrous soda ash and 0.17 parts sodium carboxymethyl cellulose is incorporated into the water. The stirrer speed is then increased to maximum agitation and 15.0 parts pentasodium tripolyphosphate is slowly added to the mixing apparatus over a period of 10-15 minutes to form a milky white suspension. The agitation speed is then decreased to a slow/medium setting while 19.1 parts of a high AI (about 50%) LTBS slurry is added. Thereafter the optical brightener/color solution is added consisting of 0.4 parts Tinopal LMS-X (CIBA-GEIGY), 0.06 parts blue dye and 2.0 parts deionized water. Once a uniform blue colored solution is obtained, 0.3 parts of perfume are added to the mixture under agitation. This is followed by the slow addition of 4.0 parts glycerine, 3.0 parts borax and 1.0 part triethanolamine (the TEA improves long term product stability) as a three component slurry. Stirring is continued until the mixture is uniform in appearance and then 2.0 parts of sodium citrate and 4.0 parts water are slowly added. Agitation of the mixture is then reduced while a mixed AI detergent base consisting of 5.7 parts LTBS slurry (about 50% AI) and 4.7 parts AEOS (about 60% AI) is added to the mixture. This is followed by the slow addition of 1.0 part proteolytic enzyme with continous agitation until all materials are completely dispersed or dissolved.

Enzyme-containing built liquid detergent compositions A to G were formulated as set forth below in Table 1. The percentages shown indicate weight percent. The arrows are meant to indicate the extent to which Compositions B to G are identical to Composition A.

The enzyme activities of Compositions A to G were tested after 7 days storage at 110.degree. F. The measured enzyme activity for each composition after this period of storage is indicated in Table 2 and Table 3 as a percent of the initial value. The various carboxylic acids and salts used in the formulas of Compositions A, B, C, D, E, and G are shown in Table 2 as well as the enzyme activities corresponding to each composition.

As evident from Table 2, Composition A, the control composition, as well as Compositions B and C which contained glycerine and borax, respectively, as individual stabilizers, manifested almost no enzyme activity after the 7 day storage period of 110.degree. F. Since enzyme activities below 10% could not be precisely measured they are designated "ND". Composition D containing glycerine/borax in the absence of a carboxylic acid compound provided an improvement in enzyme stability relative to Compositions A, B and C but more than 50% of the enzyme was deactivated. The various Compositions E containing a variety of carboxylic acid compounds, as indicated, manifested absolutely no improvement in enzyme stability relative to Compositions A, B and C. However, Compositions G formulated in accordance with the invention demonstrate the unexpected and synergistic improvement in enzyme stability which is achieved with the use of glycerine/borax in combination with a carboxylic acid compound in the present liquid detergent compositions. It is noted that in every one of the 17 compositions corresponding to Composition G which were tested, the enzyme activity was improved relative to Composition D (containing glycerine and borax).

A comparison of the enzyme activities achieved with Compositions D (glycerine/borax) and various Compositions F (borax/carboxylic acid compound) and G (formulated in accordance with the invention) is set forth below in Table 3.

As shown in Table 3, the various Compositions G containing a three component stabilizer system in accordance with the invention provided a synergistic improvement in enzyme stability relative to Compositions D and F formulated in accordance with the prior art.