Field of the invention

The invention relates to a personal care composition comprising zinc pyrithione which exhibits stability in colour over time. The invention more particularly relates to a soap composition especially a soap bar that may have trace levels of iron impurity which causes colouration of the composition comprising zinc pyrithione and is stabilised using specific naturally derived proteins.

Background of the invention

Human health is impacted by many microbial entities or microbes such as germs, bacteria, fungi, yeasts, molds, viruses, or the like. For example, invasion by microbial entities including various viruses and bacteria cause a wide variety of sicknesses and ailments. To reduce such an invasion, people frequently wash their skin with antimicrobial soaps. Antibacterial soaps typically include soaps in combination with, for example, antimicrobial agents.

Insoluble particulate metal pyrithiones are acknowledged as antimicrobial agents which are usually incorporated into antimicrobial compositions, such as antidandruff hair shampoos, conditioners and in soap compositions.

The invention relates predominantly to soap bars that contain zinc pyrithione which discolour from a colourless form to a darkish or blue colour (sometimes in patches) on storage. The present inventors have determined that this is due to the presence of trace amount of transition metal impurity (of about 10 to 10,000 ppm) in the soap composition. This may be present in the composition as a consequence of metallic impurities present in other ingredients included in the composition. In the soap bars investigated by the present inventors they found that iron was present in the composition from about 10 to 1000 ppm through talc that is added as a structurant in soap bars. The present inventors worked on various actives that could be included in the composition to solve this problem. They eventually hit upon inclusion of sericin, a silk protein, which exhibited enhanced stability as compared to solutions offered in the past. US2012/0220516 (Smith et al.) relates to a soap bar comprising a pyrithione, a soap surfactant and a pH adjusting agent selected from a group consisting of ammonia solution, triethanolamine, diethanolamine, monethanolamine, potassium hydroxide, sodium hydroxide, soluble carbonate salts and combinations thereof. The present inventors have determined that the present invention comprising inclusion of sericin is more effective than the above actives in solving the present problem.

Complex of sericin and iron is known e.g in DE102006061555 which relates to cosmetic compositions containing a synergistically effective combination of silk proteins and selected metals and to the use of these compositions for the cleansing and / or care of the skin and hair. This publication discloses complex of sericin and iron (among a host of metals) for care of skin. There is no mention of zinc pyrithione in this patent and to the consequent problem of colouration of soap composition.

CN107349122 discloses in one embodiment a shampoo comprising zinc pyrithione, decyl hydroxamic acid, and silk glue protein as well as further plant derived ingredients. Although the decyl hydroxamic acid is said to chelate iron and calcium, there is no direct and unambiguous disclosure of a specified amount of iron in the composition.

It is thus an object of the present invention to provide for a personal care composition comprising zinc pyrithione and trace impurities of transition metal which is stable in colour.

It is a further object of the present invention to provide for a personal care composition comprising zinc pyrithione and trace amount of transition metal which is stable in colour while not having any adverse effect on the antimicrobial efficacy of ZPTO.

Summary of the invention

One aspect of the present invention relates to a stable personal care composition comprising higher than 10 ppm transition metal, zinc pyrithione and sericin.

Another aspect of the present invention relates to a method of maintaining the colourless appearance of a personal care composition comprising zinc pyrithione and at least 10 ppm transition metal by including sericin therein. Detailed description of the invention

These and other aspects, features and advantages will become apparent to those of ordinary skill in the art from a reading of the following detailed description and the appended claims. For the avoidance of doubt, any feature of one aspect of the present invention may be utilised in any other aspect of the invention. The word "comprising" is intended to mean "including" but not necessarily "consisting of" or "composed of." In other words, the listed steps or options need not be exhaustive. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se. Similarly, all percentages are weight/weight percentages unless otherwise indicated. Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about".

Numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different end points are also contemplated.

As used herein the term“comprising” encompasses the terms“consisting essentially of” and“consisting of”. Where the term“comprising” is used, the listed steps or options need not be exhaustive. Unless otherwise specified, numerical ranges expressed in the format "from x to y" are understood to include x and y. In specifying any range of values or amounts, any upper value or amount can be associated with any particular lower value or amount. Except in the examples and comparative experiments, or where otherwise explicitly indicated, all numbers are to be understood as modified by the word“about”. All percentages and ratios contained herein are calculated by weight unless otherwise indicated. As used herein, the indefinite article“a” or“an” and its corresponding definite article“the” means at least one, or one or more, unless specified otherwise. The various features of the present invention referred to in individual sections above apply, as appropriate, to other sections mutatis mutandis. Consequently, features specified in one section may be combined with features specified in other sections as appropriate. Any section headings are added for convenience only, and are not intended to limit the disclosure in any way.

By‘A personal care composition’ as used herein, is meant to include a composition for topical application to any keratinous substrate of mammals, especially humans. Such a composition could be of the leave-on or of the wash-off/ rinse-off type. By a leave-on composition is meant a composition that is applied to the desired skin surface and left on for a period of time (say from one minute to 24 hours) after which it may be wiped or rinsed off with water, usually during the regular course of personal washing. By a wash- off/ rinse off composition is meant a composition that is applied to the desired skin surface for a shorter period of time say of the order of seconds or minutes and usually contains sufficient surfactants that aids in cleaning the surface which may be rinsed off with copious amounts of water. It is particularly preferred that the composition of the invention is formulated as a wash-off formulation. The composition may also be formulated into a product which is applied to a human body for improving the appearance, cleansing, odor control or general aesthetics. The composition of the present invention can be in the form of a liquid, lotion, cream, foam, scrub, gel or stick form and may be delivered through a roll-on device or using a propellant containing aerosol can. “Skin” as used herein is meant to include skin on any part of the body e.g., neck, chest, back, arms, underarms, hands, legs, buttocks and scalp. It also includes keratinous fibers like hair to which the composition of the invention may be applied and then optionally thereafter rinsed off. The composition is most preferably a soap composition which may be in solid, liquid, semi-solid or gel form, most preferably as a soap bar.

However it may be formulated as a product for washing other specific parts of the body e.g. a liquid body wash, a face wash or a hair wash product e.g. a shampoo or a conditioner. Many of the above washing products do not contain much soap but instead contain synthetic surfactants.

As per the first aspect of the invention there is provided a stable personal care composition comprising higher than 10 ppm transition metal, zinc pyrithione and sericin. The preferred transition metals as per this invention are iron and copper, preferably iron. Transition metal is preferably present in 10 to 10,000 ppm, preferably 20 to 1000 ppm, most preferably 50 to 500 ppm by weight of the composition. Transition metal like iron is generally present as an impurity in many ingredients included in personal wash composition e.g. from talc which is used to structure for example a soap bar. Iron is usually present as iron oxide or salts like iron chloride or iron sulphate in talc. Talc is generally included in 0.1 to 15%, preferably 1 to 10% by weight of the composition.

The personal care composition of the invention includes zinc pyrithione which is generally added as an antimicrobial active for killing or inhibiting germs like bacteria or fungus. In shampoos, zinc pyrithione is included to kill or inhibit growth of the fungi of the Malassezia furfur species.

Zinc pyrithione (ZPTO) is shorthand for zinc 1 -hydroxy-2-pyridinethione. The polyvalent metal salt of pyrithione is represented by the following general formula:

In the case of zinc pyrithione, M is the metal cation zinc.

Zinc pyrithione is preferably present in 0.1 to 5.0%, more preferably from 0.1 to 3.0%, further more preferably 0.1 to 2.0% based on weight of the composition. ZPTO is a particulate material. While the particle size is not critical to achieve the benefits of the present invention, the particle size of ZPTO is preferably from 0.25 to 8 micrometer, more preferably from 0.5 to 8.0 micrometer, and further more preferably from 1 .0 to 7.5 micrometer. ZPTO is commercially available from Kolon Life Science Inc., Sino Lion (USA) Ltd, Lonza, and other suppliers. Sericin, a component of silk, is a protein that can act as a water structurant. Silk is a natural protein fibre derived from the silkworm Bombyx mori and is typically composed of two proteins fibroin (70 to 80 %) and sericin (20 to 30 %), the remainder being a mixture of wax, carbohydrate and inorganic matter. Fibroin is a fibrous glycoprotein, present as a delicate twin thread, enveloped by layers of sericin that help in the formation of a cocoon. To manufacture silk from the dried cocoons of silkworm, fibroin is separated from sericin by a so-called ‘degumming’ process and sericin is discarded in the wastewater. Degumming by heat or heat under pressure has an advantage because it results in fewer impurities. Many industrial removal methods involve extraction with soaps and detergents, enzymatic hydrolysis, acid or alkaline hydrolysis.

Until recently, sericin was seen as a waste product from silk production. Sericin exists in a wide range of molecular weights, from 10 to over 400 kDa. Sericin occurs mostly in amorphous random coil and to a lesser extent in a beta-sheet structure. Sericin is preferably included in 0.05 to 2% by weight of the composition.

Without wishing to be bound by theory, the inventors believe that the sericin inhibits the formation of transition metal pyrithione e.g. iron pyrithione which exhibits a typical blue colour and could be formed by reaction of zinc pyrithione with the free iron present in the composition or alternately the sericin could be reacting with the free iron thereby keeping the zinc pyrithione more stable or a combination of these two mechanisms to deliver the benefits of the invention.

It is well known that zinc pyrithione is a white powder which when included in a cosmetic composition, it exhibits high whiteness. The present inventors have found that presence of iron in a composition having ZPTO reduces the whiteness. The present inventors have found that Inclusion of sericin in such compositions increases the whiteness.

Sericin is known to have iron chelating properties. However, mere inclusion of iron in a composition not having ZPTO does not cause any darkening of the composition. The present inventors have found that it is only when ZPTO is included in such compositions having higher than 10 ppm transition metal, is there an issue of colour. Further it is not mere inclusion of any chelator which will solve the problem of colour in such composition. Inclusion of strong chelators like EDTA etc have an adverse affect on the efficacy of ZPTO. The present inventors through their extensive experimentation realized that it is necessary to include a chelator which on the one hand maintains the efficacy of ZPTO while at the same time solves the colour problem of such composition. It is through this work that they chanced upon a material that provides the right balance of these contrasting requirements viz. sericin.

The composition of the invention preferably comprises a surfactant. The surfactant could be soap or a synthetic surfactant. The term soap means salts of fatty acids. Preferably, the soap is soap of Cs to C ₂₄ fatty acids, more preferably of C10 to Cis fatty acids. It is particularly preferred that the soap includes at least 40 wt% soaps of Cs to Cufatty acids, more preferably at least 50 wt% and most preferably at least 70 wt% of the total soap content. It is also preferred that the cleansing bars of the present invention, when so formulated, includes at most 60 wt% of the soaps of Ci ₆ to C22 fatty acids, preferably at most 50 wt% and most preferably at most 30 wt% of the total soap content.

The cation may be an alkali metal, alkaline earth metal or ammonium ion, preferably alkali metals. Preferably, the cation is selected from sodium or potassium. The soap may be saturated or unsaturated. Saturated soaps are preferred over unsaturated soaps for stability. The oil or fatty acids may be of vegetable or animal origin. The soap may be obtained by saponification of oils, fats or fatty acids. The fats or oils generally used to make soap bars may be selected from tallow, tallow stearins, palm oil, palm stearins, soya bean oil, fish oil, castor oil, rice bran oil, sunflower oil, coconut oil, babassu oil, and palm kernel oil. The fatty acids may be from coconut, rice bran, groundnut, tallow, palm, palm kernel, cotton seed or soyabean. The fatty acid soaps may also be synthetically prepared (e.g. by the oxidation of petroleum or by the hydrogenation of carbon monoxide by the Fischer-Tropsch process). Resin acids, such as those present in tall oil, may also be used. Naphthenic acids may also be used. Soap is preferably included in 1 to 90%, preferably from 10 to 85%, more preferably 25 to 75% soap by weight of the composition. Of the various types of surfactants which may be included in the composition of the invention, soap is especially preferred.

Less preferred but which may optionally also be included are synthetic surfactants. The composition of the invention especially shampoos are formulated with an anionic surfactant e.g. an alkyl sulphate and/or ethoxylated alkyl sulfate surfactant. These anionic surfactants are preferably present at a level of from 1 to 20%, preferably 2 to 16%, further more preferably from 3 to 16% by weight of the composition. Preferred alkyl sulfates are C8-18 alky sulfates, more preferably C12-18 alkyl sulfates, preferably in the form of a salt with a solubilising cation such as sodium, potassium, ammonium or substituted ammonium.

Preferred alkyl ether sulfates are those having the formula: R0(CH ₂ CH ₂ 0) _n SC> ₃ M; wherein R is an alkyl or alkenyl having from 8 to 18 (preferably 12 to 18) carbon atoms; n is a number having an average value of greater than at least 0.5, preferably between 1 and 3, more preferably between 2 and 3; and M is a solubilising cation such as sodium, potassium, ammonium or substituted ammonium. An example is sodium lauryl ether sulfate (SLES). SLES having an average degree of ethoxylation of from 0.5 to 3, preferably 1 to 3 is especially preferred. Shampoo compositions according to the invention may comprise one or more further anionic cleansing surfactants which are cosmetically acceptable and suitable for topical application to the hair.

Examples of further suitable anionic cleansing surfactants are the alkaryl sulphonates, alkyl succinates, alkyl sulphosuccinates, alkyl ether sulphosuccinates, N-alkyl sarcosinates, alkyl phosphates, alkyl ether phosphates, and alkyl ether carboxylic acids and salts thereof, especially their sodium, magnesium, ammonium and mono-, di- and triethanolamine salts. The alkyl and acyl groups generally contain from 8 to 18, preferably from 10 to 16 carbon atoms and may be unsaturated. The alkyl ether sulphosuccinates, alkyl ether phosphates and alkyl ether carboxylic acids and salts thereof may contain from 1 to 20 ethylene oxide or propylene oxide units per molecule. Typical anionic cleansing surfactants for use in compositions of the invention include sodium oleyl succinate, ammonium lauryl sulphosuccinate, sodium lauryl ether sulphosuccinate, sodium dodecylbenzene sulphonate, triethanolamine dodecylbenzene sulphonate, lauryl ether carboxylic acid and sodium N-lauryl sarcosinate.

Suitable preferred additional anionic cleansing surfactants are sodium lauryl ether sulphosuccinate(n)EO, (where n is from 1 to 3), lauryl ether carboxylic acid (n) EO (where n is from 10 to 20). Mixtures of any of the foregoing anionic cleansing surfactants may also be suitable.

A composition of the invention preferably additionally comprises an amphoteric surfactant preferably a betaine surfactant preferably an alkyl amidopropyl betaine surfactant for example cocamidopropyl betaine. In a preferred embodiment, the composition comprises from 0.1 to 10 wt.%, preferably from 0.5 to 8 wt.%, more preferably from 1 to 5 wt.% of a betaine surfactant

The composition of the invention when formulated for hair conditioning benefits usually comprises conditioning surfactants selected from cationic surfactants, used singly or in admixture. Suitable cationic surfactants for use in conditioner compositions according to the invention include cetyltrimethylammonium chloride, behenyltrimethylammonium chloride, cetylpyridinium chloride, tetramethylammonium chloride, tetraethylammonium chloride, octyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, octyldimethylbenzylammonium chloride, decyldimethylbenzylammonium chloride, stearyldimethylbenzylammonium chloride, didodecyldimethylammonium chloride, dioctadecyldimethylammonium chloride, tallowtrimethylammonium chloride, dihydrogenated tallow dimethyl ammonium chloride (eg, Arquad 2HT/75 from Akzo Nobel), cocotrimethylammonium chloride, PEG-2- oleammonium chloride and the corresponding hydroxides thereof. Further suitable cationic surfactants include those materials having the CTFA designations Quaternium- 5, Quaternium-31 and Quaternium-18. Mixtures of any of the foregoing materials may also be suitable. A particularly useful cationic surfactant for use in conditioners according to the invention is cetyltrimethylammonium chloride, available commercially, for example as GENAMIN CTAC, ex Hoechst Celanese. Another particularly useful cationic surfactant for use in conditioners according to the invention is behenyltrimethylammonium chloride, available commercially, for example as GENAMIN KDMP, ex Clariant. Yet another preferred cationic surfactant is stearamidopropyl dimethylamine.

Synthetic surfactants when present, are generally included in 1 to 20% by weight of the composition.

The composition of the invention when presented as a transparent soap bar may include a water soluble organic solvent. This is preferably selected from the group consisting of polyol, hydrotropes and mixtures thereof. The water soluble organic solvent is preferably in the range of 20 to 45 wt%, more preferably in the range of 25% to 40 wt%, and most preferably in the range of 30 to 40 wt% based on the weight of the composition.

Preferred cleansing bar includes 20% to 45 wt% polyols based on the weight of the composition. Preferred polyols include one or more of glycerol, sorbitol, propylene glycol or polyethylene glycol. Usually a mixture is used. More preferred bar includes 25 to 40 wt% polyols and most preferred bars include 30 to 40 wt% of polyols. Polyhydric alcohols (polyols), such as propylene glycol, may serve as diluents to thin out the otherwise thick mixture of caustic soda and fatty acids.

Hydrotopes include but are not limited to sodium cumene sulphonate, sodium toluene sulphonate, sodium xylene sulphonate & sodium alkyl aryl sulfonate, their derivatives and combinations thereof.

Electrolyte may optionally be included in the composition of the invention. They are preferably included in the range of 3 to 20 wt%, more preferably in the range of 3.5 to 15 wt % and most preferably in range of 4 to 10% by weight of the composition. Preferred electrolytes of the present invention include sodium sulfate, sodium chloride, sodium acetate, sodium citrate, potassium chloride, potassium sulfate, sodium carbonate and other mono or di or tri salts of alkaline earth metals, more preferred electrolytes are sodium chloride, sodium sulfate, sodium citrate, potassium chloride and especially preferred electrolytes are sodium chloride, sodium sulfate, and sodium citrate and combinations thereof. For the avoidance of doubt, it is clarified that the electrolyte is a non-soap material.

An opacifier may be optionally present in the composition. When opacifiers are present, the cleansing bar is generally opaque, i.e. "opacification". Examples of opacifiers include titanium dioxide, zinc oxide and the like. A particularly preferred opacifier that can be employed when an opaque rather than a transparent soap composition is desired is ethylene glycol mono- or di-stearate, for example in the form of a 20% solution in sodium lauryl ether sulphate. An alternative opacifying agent is zinc stearate.

The product can take the form of a water-clear, i.e. transparent soap, in which case it will not contain an opacifier, or alternatively, it can take the form of an opaque liquid soap containing an opacifier such as that herein defined.

Preferred cleansing bar includes 20 to 40 wt% water; more preferably 20 to 35 wt% and most preferably 22 to 30 wt% water based on the weight of the composition. More or lesser water may adversely affect transparency. The pH of preferred soaps bars of the invention is from 8 to 11 , more preferably 9 to 11.

A preferred bar may include up to 30 wt% benefit agents. Preferred benefit agents are moisturizers, emollients, sunscreens and anti-ageing compounds. The agents may be added at an appropriate step during the process of making the bars. Some benefit agents may be introduced as macro domains. Other optional ingredients like anti-oxidants, perfumes, polymers, chelating agents, colourants, deodorants, dyes, emollients, moisturizers, enzymes, foam boosters, germicides, anti-microbials, lathering agents, pearlescers, skin conditioners, stabilisers, superfatting agents, sunscreens may be added in suitable amounts in the process of the invention. Preferably, the ingredients are added after the saponification step and before filtering.

Sodium metabisulphite, ethylene diamine tetra acetic acid (EDTA), borax and ethylene hydroxy diphosphonic acid (EHDP) are preferably added to the formulation. The invention will now be illustrated with the help of the following non-limiting examples.

Examples

Examples A to D and 1 to 6: Effect of sericin on improving the whiteness of samples where zinc pyrithione is present along with iron. The following samples as a solution were prepared as shown in the table - 1 below. Sericin was sourced from Xintiansi, China. The L ^* value of the samples were measured using CM 2600D Spectrophotometer from Konica Minolta with an aperture size of 8 mm. The higher the L ^* value the whiter the product appears.

Table - 1

The data in the table above indicates that the inclusion of sericin in a composition darkened by the presence of iron with zinc pyrithione, gets lightened. This is seen across a large concentration range of iron and sericin.

Examples E-K: Effect of sericin on iron chelation and its effect on colour.

Solutions as shown in the Table - 2 below were prepared and the L ^* value measured as in the earlier examples. The L ^* value for each of the solutions is also given in the table - 2 below.

Table - 2:

The data in Table - 2 above indicates that the colour of water, a solution of sericin and a solution of iron chloride have very similar colour value as measured by L ^* . Thus inclusion of iron does not change the colour in any significant amount. Further the data indicates that inclusion of sericin in an iron containing solution (Examples H to K) does not affect the colour in any way. The problem of iron affecting the colour is seen only in a ZPTO containing composition and this can be solved by use of sericin (as is evident in the data in Table -1 above).