Patent Description:
Two major methods for dyeing human keratin fibres, and in particular the hair, are known.

The first, known as oxidation dyeing or permanent dyeing, consists in using one or more oxidation dye precursors, more particularly one or more oxidation bases optionally combined with one or more couplers.

Usually, oxidation bases are selected from ortho- or para-phenylenediamines, ortho- or para-aminophenols, and heterocyclic compounds. These oxidation bases are colourless or weakly coloured compounds, which, when combined with oxidizing products, can give rise via a process of oxidative condensation to coloured species, which remain trapped within the fibre.

The shades obtained with these oxidation bases are often varied by combining them with one or more couplers, these couplers being chosen in particular from aromatic meta-diamines, meta-aminophenols, meta-diphenols and certain heterocyclic compounds, such as indole compounds.

The variety of molecules used as oxidation bases and couplers allows a wide range of colours to be obtained.

The second dyeing method, known as direct dyeing or semi-permanent dyeing, comprises the application of direct dyes, which are coloured and colouring molecules that have affinity for fibres. Given the nature of the molecules used, they tend rather to remain on the surface of the fibre and penetrate relatively little into the fibre, when compared with the small molecules of oxidation dye precursors. The main advantages of this type of dyeing are that it does not require any oxidizing agent, which limits the degradation of the fibres, and that it does not use any dyes that have particular reactivity, resulting in limitation of the intolerance risks.

The first hair dyes were semi-permanent. One of the most well-known natural dyes is that derived from the henna plant. Henna continues to be used in feminine beauty enhancement for colouring the hair or the nails, or for dyeing leather, silk and wool, etc. It is also used traditionally for various important events, celebrations and beliefs.

Red henna is constituted of leaves of shrubs of the genus Lawsonia from the family Lythraceae, which is based on the principle of dyeing with the active agent lawsone: <NUM>-hydroxy-<NUM>,<NUM>-naphthoquinone. Lawsone [<NUM>-<NUM>-<NUM>] (CI Natural Orange <NUM>; CI <NUM>), also known as isojuglone, may be found in henna shrubs (Lawsonia alba, Lawsonia inermis) ("<NPL>, "<NPL>).

This dye affords an orange-red colouration on grey hair, and a "warm" i.e. coppery to red colour on chestnut-brown hair. The dyeing process using henna is difficult to perform. A kind of "paste" (often referred to as a "poultice") is first made from ground or powdered henna leaves, which is then diluted at the time of use with warm water, and said paste is then applied to the keratin fibres.

Another very well-known natural dye is indigo (see<NPL>). Indigo continues to be used for feminine beauty enhancement by dyeing the hair or the nails, or for dyeing fabrics (jeans), leather, silk, wool, etc. Indigo [<NUM>-<NUM>-<NUM>] is a natural dye, originating in particular from the indigo plant, and having the empirical formula: C<NUM>H<NUM>N<NUM>O<NUM>; and having the structure:
<CHM>.

Indigo is derived from indican and may be prepared from various plants known as indigo-producing plants such as Indigofera tinctoria, Indigo suffruticosa, Isatis tinctoria, etc. (see<NPL>). The indigo-producing plants are generally chopped and soaked in hot water, heated, fermented and oxidized in the open air to liberate the purple-blue coloured indigo (see <NPL>). Indigo is the result of the fermentation and then oxidization of indican (glycosyl precursor). The indigo molecule is insoluble in water.

The problem is that dyeing using the indigo leaf is difficult because the uptake of the colour into the keratin fibres is very poor. This dye affords a blue colouring on grey hair, and a "cold" colour of ash to violet type on chestnut-brown hair. The dyeing process using indigo leaves is difficult to perform. A kind of "paste" (often referred to as a poultice) is first made from ground or powdered leaves of indigo plant (or Indian indigo or dyer's indigo) or dyer's pastel (or woad or Isatis tinctoria), which needs to have been fermented, and which is then diluted at the time of use with warm water, and said paste is then applied to the keratin fibres.

When hair is dyed with these two types of dyes, for as much as the colour obtained on chestnut-brown hair has a natural effect, grey hair is dyed in an unaesthetic and unnatural orange colour with henna or blue with indigo. Furthermore, the colourings obtained are not homogeneous between the root and the end or from one fibre to another.

In particular, dyeing using indigo leaf is difficult since the dyeing kinetics in the keratin fibres are variable and furthermore the dyeing process is unstable. Indigo theoretically affords a blue colouring on grey hair, and a "cold" colour of ash type on chestnut-brown hair. However, the dyeing process using indigo is difficult to control due to the competing reaction for the formation of indirubin (which also involves an oxidation step with intermediate formation of yellow-coloured isatin) giving yellow to violet tints complementary to chestnut-brown hair over time.

The colourings resulting from mixtures of indigo and henna are thus generally evolutive over time in terms of colour, they have a characteristic yellow/green colour on the day of application (relatively unaesthetic "raw" colour, which dyeing consumers appreciate little) which change towards the desired colourings after a few hours (<NUM> hours to <NUM> week) and may change colour over time (appearance of violet-red tints generally after <NUM> to <NUM> weeks). There is thus a need to stabilize this colouring to obtain an aesthetic colouring on the day of application (for example brown free of yellow/green tints) which changes little over time (no colour change).

Some process involving the application of a composition comprising indigo and/or henna and the application of a composition involving some acids and bases are known ( <CIT>).

To overcome this colour change problem and to broaden the range of shades obtained with these dyes, synthetic or natural direct dyes may be added, in particular to mask the undesirable tints. It is especially possible to use anionic synthetic direct dyes (also known as direct acid dyes), which make it possible to obtain excellent performance qualities in terms of persistence of the colouring on the fibre, but often have the drawback of also pigmenting the scalp. Natural dyes may also stain the skin and the concentrations generally used to obtain sufficient colouring of the hair amplifies the risk of staining of the scalp.

In addition, in order to improve the uptake of dyes and to mask the undesirable tints as much as possible, "hydrotropic" solvents may be used in relatively large amount or the concentration of acid dyes may be increased, but this has the drawback of giving rise to greater staining of the scalp.

Consequently, there is a need to develop a novel direct dyeing process which does not have the above drawbacks.

In particular, there is a need to develop natural dyeing processes based on henna and/or indigo which make it possible to obtain powerful, aesthetic and natural colourings from the end of application and which make it possible especially to obtain rapid colourings, of which the colouring obtained has no tints, in particular yellow/green tints, that are considered by users to be unaesthetic, and which have good colour buildup, are less aggressive to the hair and at the same time are resistant to external agents (light, bad weather, shampooing washing), which are persistent and/or homogeneous while at the same time remaining powerful and/or chromatic, and which are stable and do not change in colour over time, in particular towards red tints.

In addition, the dyeing process should not stain the scalp, or it should minimize the staining of the scalp.

The Applicant has discovered that a two-step process using a dye composition based on henna and/or indigo and a composition comprising a buffer system and optionally a direct dye makes it possible to solve the problems mentioned above.

This (these) aim(s) are achieved by the present invention, one subject of which is a process for dyeing keratin fibres, in particular human keratin fibres such as the hair, in which said fibres are treated, in several separate steps, comprising:.

Preferably, the step of treating with composition A is the first step of the dyeing process according to the invention.

Preferably, the process involves, in the following order:.

Compositions A and B are different compositions.

Preferably, the process according to the invention comprises an intermediate rinsing step iii) between step i) and step ii).

Preferably, the process according to the invention comprises a final rinsing step after performing all the steps of the process.

The process according to the invention has the advantage of dyeing keratin fibres, especially human keratin fibres, with powerful, chromatic dyeing results that are resistant to washing, perspiration, sebum and light, without impairing the fibres. Furthermore, the colourings obtained using the process according to the invention are sparingly selective, i.e. they have a uniform colour between the root and the end of the fibres. Furthermore, the dyeing process used can induce very satisfactory "buildup" and/or strength of the colouring.

The use of a step involving a composition comprising direct dyes, in particular acid dyes, and a buffer system makes it possible to maintain the acidic pH of the composition at a constant value and allows excellent dyeing performance qualities to be obtained, in particular in terms of colour buildup, while at the same time not staining the scalp, or minimizing the staining of the scalp without it being necessary to significantly increase the concentration of solvents or of acid dyes.

The process for dyeing keratin fibres according to the invention has the advantage of dyeing said fibres, especially human keratin fibres, in particular the hair, with natural dyeing results without any yellow/green tints, and/or powerful, chromatic colourings, which are resistant to washing, perspiration, sebum and light, and which are moreover long-lasting, without impairment. Furthermore, the colourings obtained using the process are uniform from the root to the end of a fibre (little colour selectivity).

The compositions used according to the invention are cosmetic compositions, i.e. they are cosmetically acceptable and are thus suitable for use for application to keratin fibres, especially for application to human keratin fibres such as the hair.

Preferably, composition A is obtained by mixing, just before use, indigo and/or henna with an aqueous composition to obtain a ready-to-use dye composition A, preferably in the form of a poultice.

Preferably, composition A is an aqueous composition.

Other subjects, characteristics, aspects and advantages of the present invention will emerge even more clearly on reading the description and the examples that follow.

Step i) of dyeing uses a cosmetic dye composition A comprising at least indigo and/or henna.

According to the present invention, the term "henna" refers to a henna plant powder and/or a henna plant dye extract, preferably from a henna plant such as Lawsonia alba or Lawsonia inermis. The henna plant powder and/or dye extract especially comprises lawsone and/or a glucosyl precursor thereof.

Preferably, the henna used according to the present invention is in powder form.

According to the present invention, the term "indigo" refers to an indigo-producing plant powder and/or an indigo-producing plant dye extract, preferably Indigofera tinctoria or Isatis tinctoria. The indigo-producing plant powder and/or dye extract especially comprises indigo and/or indirubin and/or a glucosyl precursor thereof, such as indican and/or an isatan.

Preferably, the indigo used according to the present invention is in powder form.

It is understood that the henna powder and the indigo-producing plant powder are different from an extract. Specifically, an extract is a product of maceration in solvents, generally organic solvents, whereas the powder according to the invention is a natural product originating from henna or indigo-producing plants, reduced by grinding or other mechanical means, into fine particles.

Preferably, the henna used in the invention is red henna (Lawsonia inermis, alba). Lawsone [<NUM>-<NUM>-<NUM>] (CI Natural Orange <NUM>; C! <NUM>), also known as isojuglone, may be found in henna shrubs (Lawsonia alba, Lawsonia inermis). Preferably, the henna is in powder form. The henna powder may be screened to obtain particles with upper limit sizes corresponding to the orifices or mesh sizes of the screen particularly between <NUM> and <NUM> mesh (US). According to a particular mode of the invention, the size of the henna powder particles is fine. According to the invention, a particle size of less than or equal to <NUM> is more particularly intended. Preferentially, the powder is constituted of fine particles with sizes inclusively between <NUM> and <NUM> and more particularly between <NUM> and <NUM>. It is understood that said henna particles preferentially have a moisture content of between <NUM> and <NUM>% by weight, relative to the total weight of the powders.

Preferably, said henna particles are derived from henna leaves.

As indigo-producing plants, mention may be made of numerous species derived from the following genera:.

Preferably, the indigo-producing plant is of the genus Indigofera and more particularly is Indigofera tinctoria.

Use may be made of all or part (in particular the leaves in particular for Indigofera tinctoria) of the indigo-producing plant.

The indigo-producing plant powder may be screened to obtain particles with upper limit sizes corresponding to the orifices or mesh sizes of the screen particularly between <NUM> and <NUM> mesh (US).

According to a particular mode of the invention, the size of the indigo-producing plant powder particles is fine. According to the invention, a particle size of less than or equal to <NUM> is more particularly intended. Preferentially, the powder is constituted of fine particles with sizes inclusively between <NUM> and <NUM> and more particularly between <NUM> and <NUM>.

It is understood that said indigo-producing plant particles preferentially have a moisture content of between <NUM> and <NUM>% by weight relative to the total weight of the powders.

In one embodiment, the indigo is in the form of indigo-producing plant powder.

In another embodiment, the indigo is in the form of indigo-producing plant dye extract.

Composition A used in the keratin fibre dyeing process preferably comprises at least <NUM>% by weight of henna and/or indigo, relative to the total weight of said composition, more preferentially from <NUM>% to <NUM>% by weight, better still from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight relative to the total weight of composition A.

Preferably, the dye composition A is an aqueous composition and comprises at least water. Preferably, according to this embodiment, composition A comprises a water content ranging from <NUM>% to <NUM>% by weight, more particularly from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight relative to the weight of composition A.

According to a particular embodiment of the invention, composition A is obtained by mixing just before use (i.e. extemporaneously) the indigo and/or the henna with water or with an aqueous composition to obtain a ready-to-use dye composition A, preferably in the form of a poultice.

According to one embodiment, composition A used in the dyeing process of the invention may also contain one or more additional direct dyes, in particular synthetic dyes or dyes of natural origin, other than indigo and henna; these dyes may be chosen from the dyes b) mentioned hereinbelow.

When it is (they are) present, the natural or synthetic direct dye(s), other than indigo and henna, used in the process of the invention particularly represent from <NUM> % to <NUM>% by weight relative to the total weight of composition A and even more preferentially from <NUM>% to <NUM>% by weight relative to the total weight of the composition.

Preferably, the compositions of the invention do not contain any synthetic direct dyes, i.e. dyes that do not occur in nature.

According to one embodiment, composition A does not comprise any additional dyes other than henna and/or indigo.

The treatment step ii) comprises the application to the fibres of an aqueous composition B which comprises a buffer system comprising a mixture of an acid and of at least one conjugate salt thereof, and optionally a synthetic or natural direct dye.

According to an advantageous embodiment, the aqueous composition B comprises b) one or more direct dyes chosen from synthetic direct dyes, natural dyes and mixtures thereof.

The direct dye b) is preferably other than henna and indigo as described previously.

Preferably, the dye b) is a synthetic direct dye, more preferably an anionic synthetic direct dye.

The term "natural dyes" refers to dyes derived from natural materials (plant, mineral or animal origin), for instance extracts, ground material and decoctions, which have a greater or smaller concentration of dyes.

Included among the natural dyes according to the invention are compounds that may be present in nature and that are reproduced by chemical (semi)synthesis.

The natural dyes may be chosen especially from spinulosin, orceins, polyphenols or ortho-diphenols (also referred to as ODPs in the rest of the description), curcumin, indoles such as isatin or indole-<NUM>,<NUM>-dione, indigoids including indigo, phthalocyanines and porphyrins in particular complexed to a metal, glycosyl or non-glycosyl iridoids, chromene dyes, anthraquinone and naphthoquinone dyes, juglone, spinulosin, chromene or chroman dyes, such as neoflavanols and neoflavanones, flavanols; anthocyanidols, orceins, betalains, and mixtures thereof.

Use may also be made of extracts or decoctions containing these natural dyes and especially plant extracts or poultices containing said dyes.

These natural dyes may be added in the form of defined compounds from extracts or from plant parts. Said defined compounds from extracts or from plant parts are preferably in the form of powders, in particular fine powders whose particles have sizes identical to that of the henna and indigo-producing plant powders as defined previously.

The ODP(s) may or may not be salified. They may also be in aglycone form (without bonded sugars) or in the form of glycosylated compounds. Use may be made, for example, of ortho-diphenols such as those described in patent application <CIT>. They may be synthetic or natural.

More particularly, the ODP(s) that may be used in the process of the invention are in particular:.

Preferably, the ODPs of the invention are chromenes or chromans and are preferably chosen from haematein, haematoxylin, brazilein, brazilin and santalin A. Examples that may be mentioned include haematoxylin (Natural Black <NUM> according to the INCI name) and brazilin (Natural Red <NUM> according to the INCI name), dyes of the indochroman family, which are commercially available. The latter dyes may exist in an oxidized form and may be obtained synthetically or by extraction of plants or vegetables known to be rich in these dyes. The ODPs may be used in the form of extracts. Use may be made of the following plant extracts (genus and species): Haematoxylon campechianum, Haematoxylon brasiletto, Quebracho (Schinopsis lorentsii), Caesalpinia echinata, Caesalpinia sappan, Caesalpinia spinosa and Caesalpinia brasiliensis.

According to one embodiment, the natural ODPs are derived from extracts of animals, bacteria, fungi, algae, plants and fruits, used in their entirety or partially. In particular regarding plants, the extracts are derived from fruit, including citrus fruit, from vegetables, from trees and from shrubs. Use may also be made of mixtures of these extracts, which are rich in ODPs as defined above.

Preferably, the natural ODP(s) of the invention are derived from extracts of plants or plant parts.

The extracts are obtained by extraction of various plant parts, for instance the root, the wood, the bark, the leaf, the flower, the fruit, the seed, the pod or the peel.

Mention may be made, among the extracts of plants, of extracts of rose or tea leaves.

Mention may be made, among the extracts of fruits, of extracts of apple, extracts of grape (in particular of grape seed) or extracts of cocoa beans and/or pods.

Mention may be made, among the extracts of vegetables, of extracts of potato or of onion peel.

Among the extracts of tree wood, mention may preferably be made of extracts of pine bark, extracts of campeachy wood, pernambouc wood, sappan wood and brazil wood. Examples of campeachy wood extracts that may be used include the extract whose INCI name is EXTRAIT DE CAMPÊCHE OXYDE [Oxidized campeachy extract] (Haematoxylon campechianum) sold by SCRD under the reference HEMATINE HCK S <NUM>.

Preferentially, the ODP(s) are chosen from catechin, quercetin, haematein, haematoxylin, brazilin, brazilein, gallic acid and tannic acid, and natural extracts containing them chosen from grape marc, pine bark, green tea, onion, cocoa bean, campeachy wood, redwood and gall nut, and mixtures thereof.

Mention may also be made of the natural dyes chosen from the compounds of formula (a) or (b) below, or mixtures thereof:
<CHM>.

Such compounds are, for example, extracted from moulds of the species Monascus purpureus (synonyms: M. albidus, M. araneosus, M. rubiginosus and M.

As preferred natural dyes, mention may be made especially of carmine, carmine ammonium, diosindigo, chlorophyllin, haematein, orcein, the following extracts: blackcurrant, blueberry, black rice, grape skin, hibiscus, red cabbage, black carrot, elderberry, rhubarb, monascus, purple sweet potato, goji, radish, orcein, gardenia, diospyros kaki, campeachy, quebracho, and mixtures thereof.

The synthetic direct dyes are chosen, for example, from those conventionally used in direct dyeing, and among which mention may be made of any commonly used aromatic and/or nonaromatic dye such as neutral, acidic or cationic nitrobenzene direct dyes, neutral, acidic or cationic azo direct dyes, neutral, acidic or cationic quinone and in particular anthraquinone direct dyes, azine, triarylmethane, indoamine, methine, styryl, porphyrin, metalloporphyrin, phthalocyanine, cyanine and methine direct dyes, and fluorescent dyes.

According to a preferred embodiment of the invention, the direct dye(s), preferably synthetic dyes, that may be used according to the invention are chosen from anionic dyes, commonly referred to as "acid" direct dyes on account of their affinity for alkaline substances. The anionic direct dyes according to the invention may be natural or synthetic.

The term "anionic direct dyes" means any direct dye comprising in its structure at least one CO<NUM>R or SO<NUM>R substituent with R denoting a hydrogen atom or a cation originating from a metal or an amine, or an ammonium ion. The anionic dyes may be chosen from direct nitro acid dyes, azo acid dyes, azine acid dyes, triarylmethane acid dyes, indoamine acid dyes, anthraquinone acid dyes, indigoids and natural acid dyes.

As anionic (or acid) direct dyes that may be used according to the invention, mention may be made especially of the dyes of formulae (I), (II), (III), (IV), (V), (VI), (VII), (VIII), (IX), (X), (XI) and (XII) below:.

As examples of dyes of formula (I), mention may be made especially of: Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Pigment Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Acid Red <NUM>, Food Red <NUM>, Food Red <NUM>, Acid Orange <NUM>, Acid Orange <NUM>, Acid Orange <NUM>, Acid Orange <NUM>, Acid Orange <NUM>, Acid Orange <NUM>, Yellow <NUM>, Acid Yellow <NUM>, Acid Yellow <NUM>, Acid Yellow <NUM>, Food Yellow <NUM>, Acid Violet <NUM>, Acid Violet <NUM>, Acid Violet <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Black <NUM>, Acid Brown <NUM>, Acid Brown <NUM>, Acid Black <NUM>, Acid Black <NUM>, Food Black <NUM>, Food Black <NUM> and Food Yellow <NUM> or Sunset Yellow.

As examples of dyes of formula (II), mention may be made especially of: Acid Red <NUM>, Acid Red <NUM> and Acid yellow <NUM>;.

As examples of dyes of formula (III), mention may be made especially of: Acid Red <NUM>, Acid Yellow <NUM>, Acid Yellow <NUM> and Acid Yellow <NUM>.

As an example of a dye of formula (IV), mention may be made especially of: Acid Yellow <NUM>;.

As examples of dyes of formula (V), mention may be made especially of: Acid Blue <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Blue <NUM>, Acid Green <NUM>, Acid Green <NUM>, Acid Violet <NUM>, Acid Violet <NUM>, Mordant Red <NUM> and EXT Violet N° <NUM>.

As an example of a dye of formula (VI), mention may be made especially of: Acid Black <NUM>;.

As examples of dyes of formula (VII), mention may be made especially of: Acid Brown <NUM> and Acid Orange <NUM>.

As examples of dyes of formula (VIII), mention may be made of: Acid Yellow <NUM>, the sodium salt of <NUM>,<NUM>-dinitro-<NUM>-naphthol-<NUM>-sulfonic acid, <NUM>-piperidino-<NUM>-nitrobenzenesulfonic acid, <NUM>-(<NUM>'-N,N(<NUM>"-hydroxyethyl)amino-<NUM>'-nitro)anilineethanesulfonic acid, <NUM>-β-hydroxyethylamino-<NUM>-nitrobenzenesulfonic acid and EXT D&C yellow <NUM>.

As examples of dyes of formula (IX), mention may be made especially of: Acid Blue <NUM>; Acid Blue <NUM>; Acid Blue <NUM>, Acid Blue <NUM>; Acid Violet <NUM>; Acid Green <NUM>; Acid Green <NUM> and Acid Green <NUM>.

As examples of dyes of formula (X), mention may in particular be made of: Acid Yellow <NUM>; Acid Red <NUM>; Acid Red <NUM>; Acid Red <NUM>; Acid Red <NUM>; Acid Red <NUM> and Acid Violet <NUM>;.

As an example of a dye of formula (XI), mention may be made especially of: Acid Blue <NUM>.

As examples of dyes of formula (XII), mention may be made especially of: Acid Yellow <NUM>, Acid Yellow <NUM> and Acid Yellow <NUM>.

The anionic direct dye(s) that may be used according to the invention are preferentially chosen from those of formulae (I), (II), (III), (IV), (V), (VI), (VII), (VIII), (IX), (X), (XI) and (XII) as defined above.

More particularly, the dyes of formulae (I) to (X) that may be used according to the invention are chosen from:.

Most of these dyes are described in particular in the <NPL>and.

The anionic direct dye(s) that are particularly preferred according to the invention are chosen from <NUM>,<NUM>-dihydroxy-<NUM>,<NUM>-anthraquinone-<NUM>-sulfonic acid (C. <NUM>), the monosodium salt of <NUM>-[(<NUM>,<NUM>-dihydro-<NUM>-hydroxy-<NUM>,<NUM>-dioxo-<NUM>-anthracenyl)amino]-<NUM>-methylbenzenesulfonic acid (C. <NUM>), the monosodium salt of <NUM>-[(<NUM>-hydroxy-<NUM>-naphthyl)azo]benzenesulfonic acid (C. <NUM>), the disodium salt of <NUM>-hydroxy-<NUM>-[(<NUM>-sulfophenyl)azo]-<NUM>-naphthalenesulfonic acid (C. <NUM>), the disodium salt of <NUM>-amino-<NUM>-hydroxy-<NUM>-(phenylazo)-<NUM>,<NUM>-naphthalenedisulfonic acid (C. <NUM>), the disodium salt of <NUM>-amino-<NUM>-(<NUM>'-nitrophenylazo)-<NUM>-phenylazo-<NUM>-hydroxy-<NUM>,<NUM>-naphthalenedisulfonic acid (C. <NUM>), the disodium salt of N-ethyl-N-[<NUM>-[[<NUM>-[ethyl[<NUM>-sulfophenyl)methyl]amino]phenyl](<NUM>-sulfophenyl)methylene]-<NUM>,<NUM>-cyclohexadien-<NUM>-ylidene]-<NUM>-sulfobenzenemethanaminium hydroxide (C. <NUM>), the disodium salt of <NUM>,<NUM>'-[(<NUM>,<NUM>-dihydro-<NUM>,<NUM>-dioxo-<NUM>,<NUM>-anthracenediyl)diimino]bis[<NUM>-methyl]benzenesulfonic acid (C. <NUM>), the trisodium salt of <NUM>-hydroxy-<NUM>-(<NUM>-sulfophenyl)-<NUM>-(<NUM>-sulfophenylazo)pyrazole-<NUM>-carboxylic acid (C. <NUM>), sodium <NUM>-[(<NUM>,<NUM>-dihydro-<NUM>-hydroxy-<NUM>,<NUM>-dioxo-<NUM>-anthryl)amino]toluene-<NUM>-sulfonate (C. <NUM>), the trisodium salt of <NUM>-hydroxy-<NUM>-[(<NUM>-sulfo-<NUM>-naphthalenyl)azo]-<NUM>,<NUM>-naphthalenedisulfonic acid (C. <NUM>), and a mixture of these compounds.

Use may also be made of compounds corresponding to the mesomeric or tautomeric forms of structures (I) to (XII).

In a preferred variant of the invention, the synthetic direct dye(s) are chosen from anionic direct dyes, preferably azo dyes, specifically those of formula (I), and anthraquinone dyes, specifically those of formula (V).

The direct dye(s) may preferably represent a total content of at least <NUM>% by weight, better still at least <NUM>% by weight, preferably at least <NUM>% by weight, preferably ranging from <NUM>% to <NUM>%, better still from <NUM>% to <NUM>% by weight and even better still from <NUM>% to <NUM>% by weight relative to the total weight of composition B.

In particular, the anionic or natural direct dye(s) may preferably represent a total content of at least <NUM>% by weight, better still at least <NUM>% by weight, preferably at least <NUM>% by weight, preferably ranging from <NUM>% to <NUM>%, better still from <NUM>% to <NUM>% by weight and even better still from <NUM>% to <NUM>% by weight relative to the total weight of composition B.

Composition B according to the invention has a pH of less than or equal to <NUM>, preferably less than or equal to <NUM>, even better still less than or equal to <NUM>.

Preferably, the pH of composition A according to the invention ranges from <NUM> to <NUM>, better still from <NUM> to <NUM> and even better still from <NUM> to <NUM>.

The term "buffer system" refers to a mixture of an acid and of at least one conjugate base thereof, more specifically of at least one conjugate salt thereof.

The formulation of buffer systems is well known to those skilled in the art.

Preferably, the composition according to the invention comprises a buffer system comprising at least one mineral (inorganic) acid and at least one conjugate base thereof, i.e. the inorganic salt of said inorganic acid, preferably a conjugate base thereof.

More preferably, the composition according to the invention comprises an inorganic buffer system comprising at least one mineral (inorganic) acid and the conjugate base thereof, i.e. the inorganic salt of said inorganic acid.

Preferably, the inorganic acid is chosen from acids with a pKa (pKa1) of less than <NUM>, preferably ranging from <NUM> to <NUM> and better still from <NUM> to <NUM>.

The inorganic acid is chosen, for example, from phosphorus-based acids, such as phosphoric acid, halogen-based acids, such as hydrochloric acid, and sulfur-based acids, such as sulfuric acid, and mixtures thereof.

More preferentially, the inorganic acid is phosphoric acid.

The buffer capacity of the buffer system according to the invention is advantageously optimized when the acid, preferably the inorganic acid, and the conjugate salt(s) thereof are used in the composition according to the invention in an acid/conjugate salt(s) mole ratio ranging from <NUM>:<NUM> to <NUM>:<NUM>, better still from <NUM>:<NUM> to <NUM>:<NUM>, even better still from <NUM>:<NUM> to <NUM>:<NUM> and more preferably from <NUM>:<NUM> to <NUM>:<NUM>.

The acid, preferably the inorganic acid, may represent from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight relative to the total weight of the composition.

The conjugate acid salt(s), preferably the inorganic acid salt(s), may be present in an amount ranging from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight, relative to the total weight of the composition.

Preferably, the composition according to the invention comprises a buffer system comprising at least phosphoric acid (H<NUM>PO<NUM>) and at least one inorganic phosphate salt, chosen in particular from potassium dihydrogen phosphate KH<NUM>PO<NUM>, sodium dihydrogen phosphate NaH<NUM>PO<NUM>, dipotassium hydrogen phosphate K<NUM>HPO<NUM>, disodium hydrogen phosphate Na<NUM>HPO<NUM>, potassium phosphate K<NUM>PO<NUM> and sodium phosphate Na<NUM>PO<NUM>, and mixtures thereof, preferably from potassium dihydrogen phosphate KH<NUM>PO<NUM> and sodium dihydrogen phosphate NaH<NUM>PO<NUM>.

The conjugate acid salt, in particular the conjugate inorganic acid salt, may be in solvate form, especially in hydrate form.

Preferably, phosphoric acid represents from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight relative to the total weight of the composition.

Preferably, the inorganic phosphate salt, chosen in particular from potassium dihydrogen phosphate KH<NUM>PO<NUM>, sodium dihydrogen phosphate NaH<NUM>PO<NUM>, dipotassium hydrogen phosphate K<NUM>HPO<NUM>, disodium hydrogen phosphate Na<NUM>HPO<NUM>, potassium phosphate K<NUM>PO<NUM> and sodium phosphate Na<NUM>PO<NUM>, and mixtures thereof, is present in a content ranging from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight relative to the total weight of the composition.

According to an advantageous embodiment, phosphoric acid and the conjugate salt thereof (inorganic phosphate salt), in particular chosen from potassium dihydrogen phosphate KH<NUM>PO<NUM>, sodium dihydrogen phosphate NaH<NUM>PO<NUM>, dipotassium hydrogen phosphate K<NUM>HPO<NUM>, disodium hydrogen phosphate Na<NUM>HPO<NUM>, potassium phosphate K<NUM>PO<NUM> and sodium phosphate Na<NUM>PO<NUM>, and mixtures thereof, are used in the compositions according to the invention in an acid/conjugate salt(s) mole ratio ranging from <NUM>:<NUM> to <NUM>:<NUM>, better still from <NUM>:<NUM> to <NUM>:<NUM>, even better still from <NUM>:<NUM> to <NUM>:<NUM> and more preferably from <NUM>:<NUM> to <NUM>:<NUM>.

In a particularly preferred variant of the invention, the composition comprises phosphoric acid and an inorganic phosphate salt chosen from potassium dihydrogen phosphate KH<NUM>PO<NUM> and sodium dihydrogen phosphate NaH<NUM>PO<NUM>, more preferentially sodium dihydrogen phosphate NaH<NUM>PO<NUM>.

According to an advantageous embodiment, composition B of the process according to the invention comprises at least one liquid compound with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM>. Such a compound is also known as a hydrotropic compound.

For the purposes of the present invention, the term "hydrotropic compound" means a compound that is capable of increasing the solubility of hydrophobic compounds in aqueous phases.

Preferably, the liquid compound(s) have a Hansen solubility parameter value δH of greater than <NUM> and less than <NUM> MPa<NUM>/<NUM>.

The liquid compound(s) more preferably have a Hansen solubility parameter δH of between <NUM> and <NUM> MPa<NUM>/<NUM>, even more preferentially between <NUM> and <NUM> MPa<NUM>/<NUM> and better still between <NUM> and <NUM> MPa<NUM>/<NUM>.

These compounds are liquid at a temperature of <NUM> and at atmospheric pressure (<NUM> mmHg; i.e. <NUM> × <NUM><NUM> Pa).

The compound(s) with a Hansen solubility parameter value δH as defined previously are, for example, described in the reference publication<NPL>, or in the publication<NPL>.

This solubility parameter value δH is related to the formation of hydrogen bonds. It may be recalled that there are three major types of interaction in organic compounds: nonpolar interactions, permanent dipole-dipole interactions and interactions of hydrogen bonding type, the latter forming the subject of the parameter defining the hydrotropic compound present in the composition used in accordance with the invention.

In particular, the publication <NPL>, gives the equation δH = (Σ-zUh/V)<NUM>/<NUM>
where zUh (in J. mol-<NUM>) describes the contributions of the functional group under consideration in the solubility parameters related to the hydrogen bonds (values in Table <NUM>, page <NUM>), this parameter zUh also being described in the publication <NPL>; and V is the volume of the molecule.

It should be noted that the solubility parameter value δH is usually given for a temperature of <NUM> and at atmospheric pressure (<NUM> mmHg, i.e. <NUM> × <NUM><NUM> Pa).

In particular, the liquid compounds with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> are nonionic organic compounds.

Said liquid compound(s) with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> may be chosen from:.

A particularly advantageous example of lactones that may be mentioned is γ-butyrolactone.

Mention may also be made of certain liquid alkanols, for instance <NUM>-pentanol.

Preferably, said liquid compound(s) with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> are chosen from alcohol ethers, aliphatic esters, aromatic ethers, alkanols bearing aryl substituents, and mixtures thereof.

Even more preferentially, said liquid compound(s) according to the invention are chosen from dipropylene glycol monomethyl ether acetate, dipropylene glycol methyl ether, dipropylene glycol mono-n-butyl ether (the INCI name of which is PPG-<NUM> Butyl Ether), tripropylene glycol methyl ether, propylene glycol n-butyl ether, propylene glycol n-propyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether and monoethyl ether, <NUM>-phenyl-<NUM>-propanol, <NUM>-phenyl-<NUM>-propanol, benzyl alcohol, benzyloxyethanol, phenoxyethanol and phenylethanol, and mixtures of these compounds.

The liquid compound(s) with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> are even more preferentially chosen from alcohol ethers and alkanols bearing aryl substituents and even more preferentially dipropylene glycol methyl ether, propylene glycol monobutyl ether and benzyl alcohol, phenylethanol or phenoxyethanol, better still alkanols bearing an aryl substituent, such as benzyl alcohol, phenylethanol or phenoxyethanol.

Preferentially, the liquid compound with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> is chosen from alkanols bearing aryl substituents.

More preferentially, the liquid compound with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> is benzyl alcohol.

Preferably, the liquid compound(s) with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> represent a total content ranging from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight, relative to the total weight of composition B.

The composition according to the invention comprises at least one alcohol, preferably a monoalcohol, other than the liquid compound with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM>, chosen from linear or branched alcohols containing from <NUM> to <NUM> carbon atoms, preferably <NUM> to <NUM> carbon atoms, preferably chosen from linear monoalcohols containing from <NUM> to <NUM> carbon atoms and better still from <NUM> to <NUM> carbon atoms.

Such alcohols may be chosen from ethanol, propanol, butanol, isopropanol and isobutanol, and mixtures thereof, preferably ethanol.

The linear or branched alcohol(s), preferably monoalcohol(s), containing from <NUM> to <NUM> carbon atoms may be present in an amount ranging from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight, relative to the total weight of composition B.

The weight ratio of the total amount of liquid compound(s) with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> to the total amount of linear or branched alcohol(s) containing from <NUM> to <NUM> carbon atoms is less than or equal to <NUM>, preferably less than or equal to <NUM> and more preferentially less than or equal to <NUM>.

The weight ratio of the total amount of liquid compound(s) with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> to the total amount of linear or branched alcohol(s) containing from <NUM> to <NUM> carbon atoms may range from <NUM> to <NUM>.

In a preferred variant of the invention, the weight ratio of the total amount of liquid alkanol(s) bearing aryl substituents with a Hansen solubility parameter value δH of less than <NUM> MPa<NUM>/<NUM> to the total amount of linear monoalcohol(s) containing from <NUM> to <NUM> carbon atoms ranges from <NUM> to <NUM>.

According to one embodiment, the composition according to the invention also comprises an organic acid, other than the acid and the conjugate salt thereof, in particular other than the inorganic acid and the conjugate salt thereof, present in the buffer system.

The term "organic acid" means any non-polymeric organic compound including one or more acid functions chosen from carboxylic acid, sulfonic acid and phosphonic acid functions.

Preferably, the organic acid e) bears one or more carboxylic functions.

The organic acid(s) e) are preferably chosen from acetic acid, propanoic acid, butanoic acid, lactic acid, malic acid, glycolic acid, ascorbic acid, maleic acid, phthalic acid, succinic acid, serine, taurine, tartaric acid, arginine, glycine, glucuronic acid, gluconic acid and citric acid, and mixtures thereof.

Preferably, the organic acid has a pKa of less than <NUM>, in particular a pKa of less than <NUM> and better still a pKa of less than <NUM>, the pKa possibly ranging from <NUM> to <NUM> and better still from <NUM> to <NUM>.

In particular, the acid(s) of the invention are chosen from α-hydroxy acids and α-amino acids; preferentially, the acid is chosen from citric acid, lactic acid, malic acid, tartaric acid, glycolic acid and serine, more preferentially from lactic acid and citric acid, or a mixture thereof.

The organic acid(s) e) may be present in an amount ranging from <NUM>% to <NUM>% by weight, preferentially from <NUM>% to <NUM>% by weight and even more preferably in an amount ranging from <NUM>% to <NUM>% by weight, relative to the total weight of the composition.

Composition B according to the invention may also comprise one or more thickeners.

According to the present invention, the term "thickener" means compounds which, by their presence at a concentration of <NUM>% by weight, increase the viscosity of a composition into which they are introduced by at least <NUM> cps, preferably by at least <NUM> cps, at room temperature (<NUM>), at atmospheric pressure and at a shear rate of <NUM>-<NUM> (the viscosity may be measured using a cone/plate viscometer, a Haake R600 rheometer or the like).

The thickener(s) are preferentially chosen from non-associative thickening polymers bearing sugar units, non-associative thickening polymers without sugar units, associative thickening polymers, and mixtures of these compounds.

For the purposes of the present invention, the term "sugar unit" means an oxygen-bearing hydrocarbon-based compound containing several alcohol functions, with or without aldehyde or ketone functions, and which includes at least <NUM> carbon atoms.

The sugar units may be optionally modified by substitution, and/or by oxidation and/or by dehydration.

The sugar units that may be included in the composition of the aqueous-phase thickening polymers of the invention are preferably derived from the following sugars: glucose, galactose, arabinose, rhamnose, mannose, xylose, fucose, anhydrogalactose, galacturonic acid, glucuronic acid, mannuronic acid, galactose sulfate, anhydrogalactose sulfate and fructose.

Non-associative thickening polymers bearing sugar units that may especially be mentioned include native gums such as:.

These polymers may be physically or chemically modified. As physical treatment, mention may in particular be made of the temperature.

Chemical treatments that may be mentioned include esterification, etherification, amidation and oxidation reactions. These treatments make it possible to produce polymers that may especially be nonionic, anionic or amphoteric.

Preferably, these chemical or physical treatments are applied to guar gums, locust bean gums, starches and celluloses.

The nonionic guar gums that may be used according to the invention may be modified with C<NUM>-C<NUM> (poly)hydroxyalkyl groups.

Among the C<NUM>-C<NUM> (poly)hydroxyalkyl groups, mention may be made, by way of example, of hydroxymethyl, hydroxyethyl, hydroxypropyl and hydroxybutyl groups.

These guar gums are well known from the prior art and may be prepared, for example, by reacting corresponding alkene oxides, for instance propylene oxides, with the guar gum so as to obtain a guar gum modified with hydroxypropyl groups.

The degree of hydroxyalkylation preferably varies from <NUM> to <NUM> and corresponds to the number of alkylene oxide molecules consumed by the number of free hydroxyl functions present on the guar gum.

Such nonionic guar gums optionally modified with hydroxyalkyl groups are sold, for example, under the trade names Jaguar HP8, Jaguar HP60 and Jaguar HP120 by the company Rhodia Chimie.

The botanical origin of the starch molecules that may be used in the present invention may be cereals or tubers. Thus, the starches are chosen, for example, from corn starch, rice starch, cassava starch, barley starch, potato starch, wheat starch, sorghum starch and pea starch.

The starches may be chemically or physically modified, in particular by one or more of the following reactions: pregelatinization, oxidation, crosslinking, esterification, etherification, amidation, heat treatments.

Distarch phosphates or compounds rich in distarch phosphate will preferentially be used, for instance the product sold under the references Prejel VA-<NUM>-T AGGL (gelatinized hydroxypropyl cassava distarch phosphate), Prejel TK1 (gelatinized cassava distarch phosphate) or Prejel <NUM> (gelatinized acetyl cassava distarch phosphate) by the company Avebe, or Structure Zea from National Starch (gelatinized corn distarch phosphate).

According to the invention, amphoteric starches may also be used, these amphoteric starches comprising one or more anionic groups and one or more cationic groups. The anionic and cationic groups may be bonded to the same reactive site of the starch molecule or to different reactive sites; they are preferably bonded to the same reactive site. The anionic groups may be of carboxylic, phosphate or sulfate type, preferably carboxylic. The cationic groups may be of primary, secondary, tertiary or quaternary amine type.

The starch molecules may be derived from any plant source of starch, in particular such as corn, potato, oat, rice, tapioca, sorghum, barley or wheat. It is also possible to use the hydrolysates of the starches mentioned above. The starch is preferably derived from potato.

The non-associative thickening polymers of the invention may be cellulose-based polymers not including a C<NUM>-C<NUM> fatty chain in their structure.

According to the invention, the term "cellulose-based polymer" means any polysaccharide compound having in its structure sequences of glucose residues linked together via β-<NUM>,<NUM> bonds; in addition to unsubstituted celluloses, the cellulose derivatives may be anionic, cationic, amphoteric or nonionic.

Thus, the cellulose-based polymers that may be used according to the invention may be chosen from unsubstituted celluloses, including those in a microcrystalline form, and cellulose ethers.

Among these cellulose-based polymers, cellulose ethers, cellulose esters and cellulose ester ethers are distinguished.

Among the cellulose esters are mineral esters of cellulose (cellulose nitrates, sulfates, phosphates, etc.), organic cellulose esters (cellulose monoacetates, triacetates, amidopropionates, acetatebutyrates, acetatepropionates and acetatetrimellitates, etc.), and mixed organic/mineral esters of cellulose, such as cellulose acetatebutyrate sulfates and cellulose acetatepropionate sulfates. Among the cellulose ester ethers, mention may be made of hydroxypropylmethylcellulose phthalates and ethylcellulose sulfates.

Among the nonionic cellulose ethers without a C<NUM>-C<NUM> fatty chain, i.e. which are "non-associative", mention may be made of (C<NUM>-C<NUM>)alkylcelluloses, such as methylcelluloses and ethylcelluloses (for example, Ethocel standard <NUM> Premium from Dow Chemical); (poly)hydroxy(C<NUM>-C<NUM>)alkylcelluloses, such as hydroxymethylcelluloses, hydroxyethylcelluloses (for example, Natrosol <NUM> HHR provided by Aqualon) and hydroxypropylcelluloses (for example, Klucel EF from Aqualon); mixed (poly)hydroxy(C<NUM>-C<NUM>)alkyl-(C<NUM>-C<NUM>)alkylcellulose celluloses, such as hydroxypropylmethylcelluloses (for example, Methocel E4M from Dow Chemical), hydroxyethylmethylcelluloses, hydroxyethylethylcelluloses (for example, Bermocoll E <NUM> FQ from AkzoNobel) and hydroxybutylmethylcelluloses.

Among the anionic cellulose ethers without a fatty chain, mention may be made of (poly)carboxy(C<NUM>-C<NUM>)alkylcelluloses and salts thereof. By way of example, mention may be made of carboxymethylcelluloses, carboxymethylmethylcelluloses (for example Blanose <NUM> from the company Aqualon) and carboxymethylhydroxyethylcelluloses, and the sodium salts thereof.

Among the cationic cellulose ethers without a fatty chain, mention may be made of cationic cellulose derivatives such as cellulose copolymers or cellulose derivatives grafted with a water-soluble quaternary ammonium monomer, and described in particular in patent <CIT>, such as (poly)hydroxy(C<NUM>-C<NUM>)alkylcelluloses, for instance hydroxymethyl-, hydroxyethyl- or hydroxypropylcelluloses grafted in particular with a methacryloylethyltrimethylammonium, methacrylamidopropyltrimethylammonium or dimethyldiallylammonium salt. The commercial products corresponding to this definition are more particularly the products sold under the names Celquat® L <NUM> and Celquat® H <NUM> by the company National Starch.

Among the polymers bearing non-associative sugar units, it is preferred to use non-associative cellulose-based polymers, in particular nonionic cellulose ethers not bearing a C<NUM>-C<NUM> fatty chain.

Among the non-associative thickening polymers not bearing sugar units that may be used according to the invention, mention may be made of crosslinked acrylic acid or methacrylic acid homopolymers or copolymers, crosslinked <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid homopolymers and crosslinked acrylamide copolymers thereof, ammonium acrylate homopolymers, or copolymers of ammonium acrylate and of acrylamide, alone or as mixtures.

A first family of non-associative thickening polymers that is suitable for use is represented by crosslinked acrylic acid homopolymers.

Among the homopolymers of this type, mention may be made of those crosslinked with an allyl alcohol ether of the sugar series, for instance the products sold under the names Carbopol <NUM>, <NUM>, <NUM>, <NUM> and <NUM> by the company Noveon or the products sold under the names Synthalen M and Synthalen K by the company <NUM> VSA. These polymers have the INCI name Carbomer.

The non-associative thickening polymers may also be crosslinked (meth)acrylic acid copolymers, such as the polymer sold under the name Aqua SF1 by the company Noveon.

The non-associative thickening polymers may be chosen from <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid homopolymers and the crosslinked or non-crosslinked copolymers thereof.

Among the <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid copolymers, mention may be made of partially or totally neutralized crosslinked copolymers of <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid and of acrylamide; mention may be made in particular of the product described in Example <NUM> of document <CIT>, and reference may be made to said document as regards these polymers.

Mention may also be made of copolymers of <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid and of hydroxyethyl acrylate, such as the compound sold under the name Sepinov EMT <NUM> by the company SEPPIC.

The aqueous composition may similarly comprise, as non-associative thickening polymers, ammonium acrylate homopolymers or copolymers of ammonium acrylate and of acrylamide.

Among the examples of ammonium acrylate homopolymers that may be mentioned is the product sold under the name Microsap PAS <NUM> by the company Hoechst. Among the copolymers of ammonium acrylate and of acrylamide that may be mentioned is the product sold under the name Bozepol C Nouveau or the product PAS <NUM> sold by the company Hoechst. Reference may be made especially to <CIT>, <CIT> and <CIT> as regards the description and preparation of such compounds.

Use may also be made of cationic thickening polymers of acrylic type.

Among the thickening polymers, mention may also be made of the associative polymers that are well known to a person skilled in the art and especially of nonionic, anionic, cationic or amphoteric nature.

It is recalled that "associative polymers" are polymers that are capable, in an aqueous medium, of reversibly associating with each other or with other molecules.

Their chemical structure more particularly comprises at least one hydrophilic region and at least one hydrophobic region.

The term "hydrophobic group" means a radical or polymer with a saturated or unsaturated, linear or branched hydrocarbon-based chain, comprising at least <NUM> carbon atoms, preferably from <NUM> to <NUM> carbon atoms, in particular from <NUM> to <NUM> carbon atoms and more preferentially from <NUM> to <NUM> carbon atoms.

Preferentially, the hydrocarbon-based group is derived from a monofunctional compound. By way of example, the hydrophobic group may be derived from a fatty alcohol such as stearyl alcohol, dodecyl alcohol or decyl alcohol. It may also denote a hydrocarbon-based polymer, for instance polybutadiene.

Among the associative polymers of anionic type that may be mentioned are:.

Among these anionic associative polymers, the ones that are particularly preferred according to the invention are polymers formed from <NUM>% to <NUM>% by weight of acrylic acid and/or of methacrylic acid, from <NUM>% to <NUM>% by weight of lower alkyl (meth)acrylates, from <NUM>% to <NUM>% by weight of fatty-chain allyl ether, and from <NUM> to <NUM>% by weight of a crosslinking agent which is a well-known copolymerizable unsaturated polyethylenic monomer, for instance diallyl phthalate, allyl (meth)acrylate, divinylbenzene, (poly)ethylene glycol dimethacrylate or methylenebisacrylamide.

Among the latter polymers, the ones most particularly preferred are crosslinked terpolymers of methacrylic acid, of ethyl acrylate and of polyethylene glycol (<NUM> OE) stearyl alcohol ether (Steareth <NUM>), especially those sold by the company CIBA under the names Salcare SC80® and Salcare SC900, which are aqueous <NUM>% emulsions of a crosslinked terpolymer of methacrylic acid, of ethyl acrylate and of steareth-<NUM> allyl ether (<NUM>/<NUM>/<NUM>).

(C<NUM>-C<NUM>) Alkyl esters of unsaturated carboxylic acids that are useful in the invention comprise, for example, lauryl acrylate, stearyl acrylate, decyl acrylate, isodecyl acrylate and dodecyl acrylate, and the corresponding methacrylates, lauryl methacrylate, stearyl methacrylate, decyl methacrylate, isodecyl methacrylate and dodecyl methacrylate.

Anionic polymers of this type are described and prepared, for example, according to patents <CIT> and <CIT>.

Among the anionic associative polymers of this type that will be used more particularly are those constituted of from <NUM>% to <NUM>% by weight of acrylic acid (hydrophilic unit), <NUM>% to <NUM>% by weight of C<NUM>-C<NUM> alkyl acrylate (hydrophobic unit) and <NUM> to <NUM>% by weight of crosslinking polymerizable monomer, or alternatively those constituted of from <NUM>% to <NUM>% by weight of acrylic acid (hydrophilic unit), <NUM>% to <NUM>% by weight of C<NUM>-C<NUM> alkyl acrylate (hydrophobic unit) and <NUM>% to <NUM>% by weight of crosslinking polymerizable monomer such as those described above.

Among said polymers above, the ones most particularly preferred according to the present invention are the products sold by the company Goodrich under the trade names Pemulen TR1®, Pemulen TR2®, Carbopol <NUM>®, and even more preferentially Pemulen TR1®, and the product sold by the company SEPPIC under the name Coatex SX®.

Mention may also be made of the acrylic acid/lauryl methacrylate/vinylpyrrolidone terpolymer sold under the name Acrylidone LM by the company ISP.

Preferentially, these compounds also comprise as monomer an ester of an α,β-monoethylenically unsaturated carboxylic acid and of a C<NUM>-C<NUM> alcohol.

An example of a compound of this type that may be mentioned is Aculyn <NUM>® sold by the company Röhm & Haas, which is a methacrylic acid/ethyl acrylate/oxyalkylenated stearyl methacrylate terpolymer; and also Aculyn <NUM>, also sold by the company Röhm & Haas.

The ethylenically unsaturated monomers bearing a sulfonic group are especially chosen from vinylsulfonic acid, styrenesulfonic acid, (meth)acrylamido(C<NUM>-C<NUM>)alkylsulfonic acids, N-(C<NUM>-C<NUM>)alkyl(meth)acrylamido(C<NUM>-C<NUM>)alkylsulfonic acids such as undecylacrylamidomethanesulfonic acid, and also partially or totally neutralized forms thereof.

(Meth)acrylamido(C<NUM>-C<NUM>)alkylsulfonic acids, for instance acrylamidomethanesulfonic acid, acrylamidoethanesulfonic acid, acrylamidopropanesulfonic acid, <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid, methacrylamido-<NUM>-methylpropanesulfonic acid, <NUM>-acrylamido-n-butanesulfonic acid, <NUM>-acrylamido-<NUM>,<NUM>,<NUM>-trimethylpentanesulfonic acid, <NUM>-methacrylamidododecylsulfonic acid or <NUM>-acrylamido-<NUM>,<NUM>-dimethyl-<NUM>-heptanesulfonic acid, and also partially or totally neutralized forms thereof, will more preferentially be used.

<NUM>-Acrylamido-<NUM>-methylpropanesulfonic acid (AMPS), and also partially or totally neutralized forms thereof, will more particularly be used.

The polymers of this family may be chosen especially from random amphiphilic AMPS polymers modified by reaction with a C<NUM>-C<NUM> n-monoalkylamine or di-n-alkylamine, and such as those described in patent application <CIT> (forming an integral part of the content of the description). These polymers may also contain other ethylenically unsaturated hydrophilic monomers chosen, for example, from (meth)acrylic acids, β-substituted alkyl derivatives thereof or esters thereof obtained with monoalcohols or mono- or polyalkylene glycols, (meth)acrylamides, vinylpyrrolidone, maleic anhydride, itaconic acid or maleic acid, or mixtures of these compounds.

The preferred polymers of this family are chosen from amphiphilic copolymers of AMPS and of at least one ethylenically unsaturated hydrophobic monomer.

These same copolymers may also contain one or more ethylenically unsaturated monomers not comprising a fatty chain, such as (meth)acrylic acids, β-substituted alkyl derivatives thereof or esters thereof obtained with monoalcohols or mono- or polyalkylene glycols, (meth)acrylamides, vinylpyrrolidone, maleic anhydride, itaconic acid or maleic acid, or mixtures of these compounds.

These copolymers are described especially in patent application <CIT>, patent <CIT> and in the following publications from Yotaro Morishima:.

Among these polymers, mention may be made of:.

Mention may also be made of copolymers of totally neutralized AMPS and of dodecyl methacrylate, and also crosslinked and non-crosslinked copolymers of AMPS and of n-dodecylmethacrylamide, such as those described in the Morishima articles mentioned above.

Among the cationic associative polymers, mention may be made of:.

Polyacrylate-<NUM> Crosspolymer is the product of polymerization of a monomer mixture comprising:.

Such polymers are described, for example, in patent application <CIT>.

As cationic poly(vinyllactam) polymers according to the invention, vinylpyrrolidone/dimethylaminopropylmethacrylamide/dodecyldimethylmethacryl-amidopropylammonium tosylate terpolymers, vinylpyrrolidone/dimethylaminopropylmethacrylamide/cocoyldimethylmethacrylamidoprop ylammonium tosylate terpolymers, vinylpyrrolidone/dimethylaminopropylmethacrylamide/lauryldimethylmethacrylamid-opropylammonium tosylate or chloride terpolymers are used in particular.

The amphoteric associative polymers are preferably chosen from those including at least one noncyclic cationic unit. Even more particularly, those prepared from or comprising <NUM> to <NUM> mol%, preferably <NUM> to <NUM> mol% and even more particularly <NUM> to <NUM> mol% of fatty-chain monomer relative to the total number of moles of monomers are preferred.

Amphoteric associative polymers according to the invention are described and prepared, for example, in patent application <CIT>.

Among the amphoteric associative polymers according to the invention, the ones that are preferred are acrylic acid/(meth)acrylamidopropyltrimethylammonium chloride/stearyl methacrylate terpolymers.

The associative polymers of nonionic type that may be used according to the invention are preferably chosen from:.

Preferably, the polyurethane polyethers include at least two hydrocarbon-based lipophilic chains containing from <NUM> to <NUM> carbon atoms, separated by a hydrophilic block, the hydrocarbon-based chains possibly being side chains or chains at the end of the hydrophilic block. In particular, it is possible for one or more side chains to be envisaged. In addition, the polymer may comprise a hydrocarbon-based chain at one end or at both ends of a hydrophilic block.

The polyurethane polyethers may be multiblock, in particular in triblock form. The hydrophobic blocks may be at each end of the chain (for example: triblock copolymer bearing a hydrophilic central block) or distributed both at the ends and in the chain (for example, multiblock copolymer). These same polymers may also be graft polymers or star polymers.

The nonionic fatty-chain polyurethane polyethers may be triblock copolymers, the hydrophilic block of which is a polyoxyethylene chain including from <NUM> to <NUM> oxyethylene groups. The nonionic polyurethane polyethers include a urethane bond between the hydrophilic blocks, hence the origin of the name.

By extension, also included among the nonionic fatty-chain polyurethane polyethers are those in which the hydrophilic blocks are linked to the lipophilic blocks via other chemical bonds.

As examples of nonionic fatty-chain polyurethane polyethers that may be used in the invention, use may also be made of Rheolate <NUM>® bearing a urea function, sold by the company Rheox, or Rheolate® <NUM>, <NUM> or <NUM>, and also Acrysol RM <NUM>®.

Mention may also be made of the product Elfacos T210® bearing a C<NUM>-C<NUM> alkyl chain, and the product Elfacos T212® bearing a C<NUM> alkyl chain, from Akzo.

The product DW 1206B® from Röhm & Haas bearing a C<NUM> alkyl chain and a urethane bond, sold at a solids content of <NUM>% in water, may also be used.

Use may also be made of solutions or dispersions of these polymers, especially in water or in aqueous-alcoholic medium. Examples of such polymers that may be mentioned include Rheolate® <NUM>, Rheolate® <NUM> and Rheolate® <NUM> sold by the company Rheox. Use may also be made of the products DW 1206F and DW 1206J sold by the company Röhm & Haas.

The polyurethane polyethers that may be used according to the invention are in particular those described in the article by <NPL>).

It is even more particularly preferred to use a polyurethane polyether that may be obtained by polycondensation of at least three compounds comprising (i) at least one polyethylene glycol comprising from <NUM> to <NUM> mol of ethylene oxide, (ii) stearyl alcohol or decyl alcohol, and (iii) at least one diisocyanate.

Such polyurethane polyethers are sold especially by the company Röhm & Haas under the names Aculyn <NUM>® and Aculyn <NUM>® [Aculyn <NUM>® is a polycondensate of polyethylene glycol containing <NUM> or <NUM> mol of ethylene oxide, of stearyl alcohol and of methylenebis(<NUM>-cyclohexyl isocyanate) (SMDI), at <NUM>% by weight in a matrix of maltodextrin (<NUM>%) and water (<NUM>%); Aculyn <NUM>® is a polycondensate of polyethylene glycol containing <NUM> or <NUM> mol of ethylene oxide, of decyl alcohol and of methylenebis(<NUM>-cyclohexyl isocyanate) (SMDI), at <NUM>% by weight in a mixture of propylene glycol (<NUM>%) and water (<NUM>%)].

More preferentially, the thickener(s) are chosen from non-associative cellulose-based polymers, in particular nonionic cellulose ethers not bearing a C<NUM>-C<NUM> fatty chain, associative or non-associative thickening polymers bearing acrylic or methacrylic units, polymers bearing <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid units and/or the salified form thereof.

In a preferred variant of the invention, the thickener(s) are chosen from acrylic acid homopolymers or copolymers, in particular acrylic acid homopolymers, homopolymers or copolymers of <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid and/or the salified form thereof, in particular copolymers of <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid and/or the salified form thereof, more particularly copolymers of <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid and/or the salified form thereof and of acrylamide or copolymers of <NUM>-acrylamido-<NUM>-methylpropanesulfonic acid and/or the salified form thereof and of hydroxyethyl acrylate, said polymers possibly being crosslinked or non-crosslinked.

When it is (they are) present, the thickener(s) generally represent a total content ranging from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and better still from <NUM>% to <NUM>% by weight, relative to the total weight of the composition.

Composition B according to the invention also comprises water.

Water generally represents from <NUM>% to <NUM>% by weight, preferably from <NUM>% to <NUM>% by weight and more preferentially from <NUM>% to <NUM>% by weight relative to the total weight of the composition.

The compositions used in the dyeing process in accordance with the invention may also contain various adjuvants conventionally used in hair dye compositions, such as anionic, cationic, nonionic, amphoteric or zwitterionic surfactants or mixtures thereof, anionic, cationic, nonionic, amphoteric or zwitterionic polymers or mixtures thereof, mineral or organic thickeners, other than the fatty-phase thickeners and aqueous-phase thickeners present in compositions A and B, and in particular anionic, cationic, nonionic and amphoteric polymeric associative thickeners, antioxidants, penetrants, sequestrants, fragrances, buffers, dispersants, conditioning agents, for instance volatile or non-volatile, modified or unmodified silicones, film-forming agents, ceramides, preserving agents and opacifiers.

The above additives may in general be present in an amount, for each of them, of between <NUM> and <NUM>% by weight relative to the total weight of each composition containing them.

Needless to say, a person skilled in the art will take care to select this or these optional additional compound(s) such that the advantageous properties intrinsically associated with the composition(s) that are useful in the dyeing process in accordance with the invention are not, or are not substantially, adversely affected by the envisaged addition(s).

The cosmetic composition(s) used according to the process of the invention may be in various presentation forms, such as a powder, a lotion, a mousse, a cream or a gel, or in any other form that is suitable for dyeing keratin fibres. They may also be packaged in a propellant-free pump-action bottle or under pressure in an aerosol container in the presence of a propellant and form a foam.

The process for dyeing keratin fibres of the invention involves several separate steps, comprising:.

According to a preferred embodiment of the invention, the step of treating with composition A is performed prior to the first step of dyeing with composition B; it is then a step of pretreatment with composition A.

Preferably, in this embodiment, the process according to the invention comprises an intermediate rinsing step iii) between step i) and step ii).

Preferably, the intermediate step(s) of rinsing the keratin fibres are preferably performed with a composition comprising water.

In particular, according to a preferred embodiment of the invention, said intermediate rinsing step(s) are performed exclusively with water, without adding an additional compound. According to another embodiment, the composition used for performing said rinsing step(s) may also comprise one or more additional compounds.

In particular, in the dyeing process of the invention, the leave-on time of composition A as defined previously on the keratin fibres is between <NUM> minute and <NUM> hours, more particularly between <NUM> minutes and <NUM> hour, preferably between <NUM> and <NUM> minutes. Preferentially, the leave-on time of composition A on the keratin fibres is performed at a temperature of between <NUM> and <NUM>, more preferentially between room temperature (<NUM>) and <NUM>.

Composition B used in step ii) is preferably left to stand on the fibres for <NUM> to <NUM> minutes and preferably for <NUM> to <NUM> minutes, at a temperature of between <NUM> and <NUM>.

On conclusion of the dyeing process, the keratin fibres are generally rinsed with water, optionally undergo washing with a shampoo, followed by rinsing with water, before being left to dry or dried via a heat treatment by heating to a temperature of between <NUM> and <NUM>. In practice, this operation may be performed using a styling hood, a hairdryer, an infrared ray dispenser and other standard heating appliances.

Use may also be made, as a means for both heating and for straightening the head of hair, of a heating iron at a temperature of between <NUM> and <NUM> and preferably between <NUM> and <NUM>.

According to a particular embodiment of the invention, the process according to the invention does not use any hydrogen peroxide.

According to a preferred embodiment, the process according to the invention does not use a chemical oxidizing agent.

According to a preferred embodiment, the process according to the invention does not use any oxidation base and/or any coupler.

A particular embodiment of the invention relates to a dyeing process which is performed at room temperature (<NUM>).

In all the particular forms and variants of the processes previously described, the compositions mentioned are ready-to-use compositions that may result from the extemporaneous mixing of two or more compositions and in particular of compositions present in dyeing kits.

The evaluation of the colouring obtained on the keratin fibres may be performed visually or with a spectrocolorimeter in the CIE L* a* b* system, for example using a Minolta CM <NUM> spectrocolorimeter (illuminant D65, angle <NUM>°, specular component included).

In this L*a*b* system, L* represents the lightness of the colour, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis. The smaller the value of L*, the darker and more powerful the colouring.

The smaller the value of a*, the greener the colour and the higher the value of a*, the redder the colour.

The smaller the value of b*, the bluer the colour and the higher the value of b*, the yellower the colour.

The colour buildup corresponds to the variation in colouring between the locks of hair before and after the treatment or dyeing and is defined by (ΔE*) according to the following equation: <MAT>.

In this equation, L*, a* and b* represent the values measured on locks of hair after dyeing and L<NUM>*, a<NUM>* and b<NUM>* represent the values measured on locks of undyed hair. The higher the ΔE* value, the better is the buildup of the colour.

The stability of the colouring of the keratin fibres over time, especially after <NUM> days, was also evaluated by measuring the colour coordinates of the keratin fibres and comparing them with the colour coordinates immediately after performing the dyeing process according to the invention. The colour difference ΔE* between the colour at T0 and the colour after <NUM> days represents the stability of the colour of the hair and is calculated by means of the following equation: <MAT>.

In this equation, L<NUM>*, a<NUM>* and b<NUM>* represent the colorimetric coordinates measured on locks of hair at T0 immediately after performing the process and L<NUM>*, a<NUM>* and b*<NUM> represent the colorimetric coordinates <NUM> days after performing the process. The smaller the value of ΔE*stab, the more stable the colouring.

In particular, in the context of the invention, a colouring for which the ΔE* <NUM> days after dyeing is less than <NUM> is considered as stable over time.

Comment: the change in colouring after <NUM> weeks may similarly be evaluated from the colorimetric coordinates <NUM> weeks after dyeing the keratin fibres.

In the context of the present invention, it is thus preferably sought to obtain, immediately after the dyeing process, a value of b* that is as small as possible and/or a value of a* that is as high as possible. It is sought to obtain these results while at the same time having efficient colour buildup (large colour buildup value) and colouring that is stable over time.

The examples that follow serve to illustrate the invention.

The following compositions were prepared from the following ingredients in the proportions indicated in grams:.

The following compositions according to the invention are prepared:.

Composition A, prepared at the time of use by mixing the dyes and water at <NUM>, is applied to locks of natural hair containing <NUM>% white hairs, at a rate of <NUM> of composition per <NUM> of hair, left to stand on the locks for <NUM> minutes at <NUM> under a plastic film, followed by rinsing the locks, washing them with a standard shampoo and then wringing them dry.

Each of the compositions B1 to B3 is then applied at a rate of <NUM> of mixture per gram of hair and left to stand on the hair for <NUM> minutes at <NUM> under a plastic film.

On conclusion of the leave-on time, all the locks are then rinsed and washed with Ultra Doux Camomille shampoo, and then dried with a hairdryer.

The colorimetric measurements were performed using a Minolta CM3600D spectrocolorimeter (illuminant D65, angle <NUM>°, specular component included) in the CIELab system.

In this system, L* represents the lightness. The smaller the value of L*, the darker and more powerful the colouring obtained. The chromaticity is represented by the values a* and b*, a* representing the red/green axis and b* the yellow/blue axis.

The colour buildup is represented by the colour difference ΔE* between the undyed lock and the dyed lock: the greater the value of ΔE*, the greater the colour buildup. This value is calculated from the following equation (i): <MAT>.

In the equation (i), L*, a* and b* represent the values measured on locks of undyed hair and L<NUM>*, a<NUM>* and b<NUM>* represent the values measured on locks of dyed hair.

It is observed visually on the locks that the process of the invention (using compositions B1', B2' or B3') makes it possible to very markedly intensify the colour obtained on the hair relative to the comparative processes.

This is confirmed by the colorimetric measurements showing ΔE values that are significantly higher in the case of the process according to the invention, i.e. a greater colour buildup, and also significantly lower values of L* in the case of the process of the invention, i.e. a more intense colouring.

In addition, the process according to the invention makes it possible to reduce the evolution of the colour and especially the change towards yellow.

Claim 1:
Process for dyeing keratin fibres, in particular human keratin fibres such as the hair, in which said fibres are treated, in several separate steps, comprising:
i) at least one step i) of dyeing said fibres using a cosmetic dye composition A, preferably an aqueous composition, comprising at least a) indigo and/or henna,
ii) at least one step ii) of treating said fibres, comprising the application to the fibres of an aqueous composition B which comprises water, b) optionally at least one direct dye, other than henna and indigo, c) a buffer system comprising a mixture of an acid and of at least one conjugate salt thereof, composition B having a pH of less than or equal to <NUM>,
iii) optionally at least one step of intermediate rinsing of said fibres, preferably with water, between step i) and step ii) (or between step ii) and i) (depending on the order of steps i) and ii)).