PROCESS FOR PREPARING A DYE COMPOSITION BY MIXING SOLID PARTICLES AND AN OXIDIZING COMPOSITION AND AN ALKALINE COMPOSITION

Abstract

The present patent application relates to a process for preparing a composition for dyeing keratin fibres, in particular human keratin fibres such as the hair, comprising a step of mixing several identical or different solid particles comprising one or more dyes, preferably one or more oxidation dye precursors, with an oxidizing aqueous composition, followed by a step of adding an alkaline aqueous composition preferably comprising arginine. The present patent application also relates to a dyeing process using the composition obtained.

Claims

1. Process for preparing a composition for dyeing keratin fibres, comprising: a) a step of mixing: (i) several identical or different solid particles, each containing one or more dyes chosen from direct dyes and/or oxidation dye precursors, with (ii) at least one oxidizing aqueous composition A comprising at least one chemical oxidizing agent; and then b) a step of mixing the composition obtained beforehand with at least one alkaline aqueous composition B.

2. Process according to claim 1, characterized in that the dyes are chosen from oxidation dye precursors.

3. Process according to claim 1, characterized in that said solid particles comprise: one or more solid particles of a first type P1 containing one or more oxidation dye precursors, preferably only one oxidation dye precursor C1, and one or more solid particles of a second type P2 containing one or more oxidation dye precursors, preferably only one oxidation dye precursor C2; and it being understood that the oxidation dye precursor(s) contained in the solid particle(s) P1, better still the oxidation dye precursor C1, are different from the oxidation dye precursor(s) contained in the solid particle(s) P2, better still the oxidation dye precursor C2.

4. Process according to claim 1, characterized in that said solid particles comprise n types of solid particles P1 to Pn, with n representing an integer greater than or equal to 3, preferably between 3 and 20, more preferentially between 3 and 15 and even more preferentially between 4 and 10; each type of solid particle P1 to Pn containing only one oxidation dye precursor, respectively C1 to Cn, and it being understood that said precursors C1 to Cn are all different from each other.

5. Process according to claim 1, characterized in that the oxidation dye precursors are chosen from oxidation bases and oxidation couplers; preferably from oxidation bases.

6. Process according to claim 3, characterized in that the oxidation dye precursor C1 is chosen from oxidation bases and the oxidation dye precursor C2 is chosen from oxidation couplers.

7. Process according to claim 5, characterized in that the oxidation base(s) are chosen from para-phenylenediamines, bis(phenyl)alkylenediamines, para-aminophenols ortho-aminophenols and heterocyclic bases, and the corresponding addition salts; more preferentially from para-phenylenediamine, para-toluenediamine, para-aminophenol, N,N-bis(β-hydroxyethyl)-para-phenylenediamine, 4,5-diamino-1-(β-hydroxyethyl)pyrazole, 2,3-diamino-6,7-dihydro-1H,5H-pyrazolo[1,2-a]pyrazol-1-one, 2-β-hydroxyethoxy-3-aminopyrazolo[1,5-a]pyridine, and the addition salts thereof.

8. Process according to claim 5, characterized in that the oxidation coupler(s) are chosen from meta-phenylenediamines, meta-aminophenols, meta-diphenols, naphthalene-based coupling agents, heterocyclic coupling agents, the corresponding addition salts thereof or the solvates thereof; more preferentially from 1,3-dihydroxybenzene, 1,3-dihydroxy-2-methylbenzene, 3-aminophenol, 6-hydroxybenzomorpholine, 5-N-(β-hydroxyethyl)amino-2-methylphenol, 2,4-diamino-1-(β-hydroxyethyloxy)benzene, 2-methyl-5-aminophenol, 6-hydroxyindole, 4-chloro-1,3-dihydroxybenzene, 2-amino-3-hydroxypyridine, 3-amino-2-chloro-6-methylphenol, α-naphthol, 2-[3-amino-4-methoxyphenyl]amino)ethanol and the addition salts thereof.

9. Process according to claim 1, characterized in that the total content of dye(s) represents from 0.001% to 50% by weight, preferably from 0.1% to 50% by weight, more preferentially from 0.3% to 25% by weight and even more preferentially from 0.4% to 22% by weight, relative to the total weight of each solid particle containing same.

10. Process according to claim 1, characterized in that the solid particle(s) comprise at least one binder; preferably chosen from saccharides and derivatives thereof, oligosaccharides and derivatives thereof, polysaccharides and derivatives thereof, polyvinyl alcohol (PVA), and mixtures thereof; more preferentially from lactose, notably in anhydrous or hydrated form, microcrystalline cellulose (MCC), notably in anhydrous or hydrated form, polyvinyl alcohol (PVA), cellulose ethers such as hydroxypropylcellulose (HPC) and hydroxypropylmethylcellulose (HPMC), and mixtures thereof.

11. Process according to claim 1, characterized in that the solid particle(s) comprise at least one disintegrant; preferably a polymeric disintegrant; even more preferentially at least one disintegrant polymer; better still at least one superdisintegrant polymer; even better still at least one superdisintegrant polymer chosen from crosslinked polymers of vinylpyrrolidone and derivatives thereof, and mixtures thereof more preferentially from crosslinked polyvinylpyrrolidones, crosslinked copolymers of vinylpyrrolidone/vinyl acetate, and mixtures thereof

12. Process according to claim 1, characterized in that the solid particles comprise an upper coating layer comprising at least one cellulose ether; preferably a cellulose ether chosen from carboxymethylcellulose (CMC), ethylcellulose (EC), hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), methylhydroxyethylcellulose (MHEC), and mixtures thereof, better still from hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), and mixtures thereof

13. Process according to claim 12, characterized in that the upper coating layer comprises one or more pigments; more preferentially one or more pigments chosen from zirconium oxides, zinc oxides, cerium oxides, iron oxides, titanium oxides, chromium oxides, manganese violet, ultramarine blue, ultramarine pink, chromium hydrate and ferric blue, and mixtures thereof even more preferentially one or more pigments chosen from titanium oxides such as titanium dioxide, iron oxides, chromium oxides, notably green chromium oxide, and mixtures thereof

14. Process according to claim 1, characterized in that the solid particles comprise at least one antioxidant; preferably chosen from (a) ascorbic acid, salts thereof and derivatives thereof such as sodium ascorbate, erythorbic acid, ascorbyl palmitate, ascorbyl laurate, (b) salicylic acid, salts thereof and derivatives thereof such as sodium salicylate, (c) mercaptan and inorganic sulfites such as sodium sulfite, sodium bisulfite, sodium metabisulfite, potassium sulfite and thioglycolic acid, and mixtures thereof; more preferentially chosen from ascorbic acid, sodium sulfite, sodium bisulfate, sodium metabisulfite, sodium salicylate, and mixtures thereof; even more preferentially in a total content of between 0.1% and 15% by weight, better still between 0.3% and 12% by weight, even better still between 0.4% and 10% by weight, or even between 0.5% and 5% by weight, relative to the total weight of each solid particle containing same.

15. Process according to claim 1, characterized in that the solid particles are anhydrous.

16. Process according to claim 1, characterized in that the solid particles have a mean volume of between 25 and 125 mm.sup.3; preferably between 30 and 90 mm.sup.3; more preferentially between 45 and 65 mm.sup.3.

17. Process according to claim 1, characterized in that the chemical oxidizing agent(s) present in composition A are chosen from hydrogen peroxide, urea peroxide, alkali metal bromates, persalts such as perborates and persulfates, in particular sodium persulfate, potassium persulfate and ammonium persulfate, peracids, and oxidase enzymes, for instance peroxidases, 2-electron oxidoreductases such as uricases, and 4-electron oxygenases, for instance laccases, and mixtures thereof; preferably, the chemical oxidizing agent(s) are chosen from hydrogen peroxide and persalts, and mixtures thereof.

18. Process according to claim 1, characterized in that the alkaline aqueous composition B comprises arginine, preferably in an arginine content of between 0.05% and 25% by weight, more preferentially between 0.1% and 15% by weight, even more preferentially between 0.5% and 10% by weight, better still between 1% and 5% by weight, relative to the total weight of the alkaline aqueous composition B.

19. Process according to claim 1, characterized in that the alkaline aqueous composition B also comprises one or more alkaline agents other than arginine; preferably chosen from aqueous ammonia, alkanolamines, alkali metal or alkaline-earth metal metasilicates, and mixtures thereof more preferentially from aqueous ammonia, monoethanolamine, sodium metasilicate, and mixtures thereof.

20. Process according to claim 1, characterized in that it also comprises, after step a) and before step b), an additional step a′) of mixing the composition obtained after said step a) with an aqueous composition C comprising at least one thickening polymer.

21. Process according to claim 20, characterized in that the thickening polymer(s) are chosen from associative polymers; preferably chosen from anionic associative polymers, nonionic associative polymers and mixtures thereof; more preferentially from (i) copolymers including among their monomers an α,β-monoethylenically unsaturated carboxylic acid and an ester of an α,β-monoethylenically unsaturated carboxylic acid and of an oxyalkylenated fatty alcohol, (ii) celluloses or derivatives thereof, modified with groups including at least one fatty chain such as alkyl, arylalkyl or alkylaryl groups or mixtures thereof in which the alkyl groups are C.sub.8-C.sub.30 and in particular nonionic alkylhydroxyethylcelluloses, and (iii) mixtures thereof; even more preferentially from acrylates/beheneth-25 methacrylate copolymer, cetyl hydroxyethylcellulose, and mixtures thereof.

22. Process according to claim 20, characterized in that the weight ratio between the sum of the total content of chemical oxidizing agent(s) present in the ready-to-use composition and of the total content of thickening polymer(s) present in the ready-to-use composition, on the one hand, to the content of arginine present in the ready-to-use composition, on the other hand, is between 0.1 and 30; more preferentially between 0.5 and 20; even more preferentially between 1 and 10; and better still between 2 and 7.

23. Process for dyeing keratin fibres, comprising: the preparation of a composition for dyeing keratin fibres according to the process as defined in claim 1; and then the application of said composition to said keratin fibres.

24. Process according to claim 23, characterized in that the preparation of said composition for dyeing keratin fibres is performed less than 2 hours, preferably less than 1 hour and more preferentially less than 30 minutes before the application of said composition to the keratin fibres.

Description

EXAMPLES

Example 1

[0400] The solid particles and the compositions below according to the present invention were prepared using the ingredients of which the contents, expressed as mass percentages of active material relative to the total weight of the solid particle or of the composition, are indicated in the tables below.

Examples of Particles

[0401] Solid Particle without an Upper Coating Layer

TABLE-US-00001 TABLE 1 Ingredients Amount Microcrystalline cellulose 56 Lactose 15 PVP 4.75 Magnesium stearate 2 Silica 1 Toluene-2,5-diamine sulfate 20 Sodium sulfite 1 Water 0.25

Examples of Upper Coating Layers

[0402]

TABLE-US-00002 TABLE 2 Ingredients Amount Hydroxypropylmethylcellulose (HPMC) 45 to 55 Hydroxypropylcellulose (HPC)  5 to 20 Capric/caprylic triglyceride  1 to 10 Talc qs 100 Pigments  0 to 40
Examples of Solid Particles with an Upper Coating Layer

TABLE-US-00003 TABLE 4 Ingredients Amount Microcrystalline cellulose 54.4 Lactose 14.6 PVP 4.6 Magnesium stearate 1.94 Silica 1.0 Toluene-2,5-diamine sulfate 19.4 Sodium sulfite 1.0 Water 0.2 Hydroxypropylmethylcellulose 1.46 Hydroxypropylcellulose 0.29 Talc 0.44 Caprylic/capric triglyceride 0.15 Pigments 0.51 Alumina 0.01

TABLE-US-00004 TABLE 5 Ingredients Amount Microcrystalline cellulose 77.2 Lactose 14.6 PVP 0.1 Magnesium stearate 1 Silica 0.54 Resorcinol 0.85 Hydroxypropylmethylcellulose 1.45 Hydroxypropylcellulose 0.30 Talc 0.4 Caprylic/capric triglyceride 0.15 Pigments 0.5 Alumina 0.01 VP/VA copolymer 2.9

TABLE-US-00005 TABLE 6 Ingredients Amount Microcrystalline cellulose 63.5 Lactose 9.7 PVP 0.1 Magnesium stearate 1 Silica 0.5 Resorcinol 16.5 Ascorbic acid 2.9 Hydroxypropylmethylcellulose 1.5 Hydroxypropylcellulose 0.3 Talc 0.44 Caprylic/capric triglyceride 0.15 Pigments 0.5 Alumina 0.01 VP/VA copolymer 2.9

TABLE-US-00006 TABLE 7 Ingredients Amount Microcrystalline cellulose 76.2 Lactose 15.5 PVP 0.5 Magnesium stearate 1.0 Silica 1.0 2,4-Diaminophenoxyethanol hydrochloride 1.0 Sodium metabisulfite 1.94 Water 0.02 Hydroxypropylmethylcellulose 1.45 Hydroxypropylcellulose 0.29 Talc 0.44 Caprylic/capric triglyceride 0.15 Pigments 0.5 Alumina 0.01

TABLE-US-00007 TABLE 8 Ingredients Amount Microcrystalline cellulose 69.4 Lactose 11.6 PVP 2.8 Magnesium stearate 1.0 Silica 0.5 m-Aminophenol 7.8 Sodium metabisulfite 3.9 Water 0.15 Hydroxypropylmethylcellulose 1.46 Hydroxypropylcellulose 0.29 Talc 0.44 Caprylic/capric triglyceride 0.15 Pigments 0.5 Alumina 0.01

Oxidizing Composition

[0403]

TABLE-US-00008 TABLE 9 Ingredients Amount (g) Hydrogen peroxide 12 Stabilizer, sequestrant qs Phosphoric acid qs pH = 2.2 + 0.2 Water qs 100

Alkaline Composition 1

[0404]

TABLE-US-00009 TABLE 10 Ingredients Amount Arginine 3 Ammonium hydroxide 2 Monoethanolamine 5.8 Sodium metasilicate 2 Poly q uaternium- 6 2 Hexadimethrine chloride 1.2 EDTA 0.2 Hydroxy propylmethylcellulose (HPMC) 0.2 Cetylhydroxyethylcellulose 0.45 PEG-40 stearate 1.8 Oleth-30 1.5 Oleic acid 3 C20-C22 fatty alcohols 3 Stearamide MEA 4.8 Steareth-2 5.5 Water qs 100

Alkaline Composition 2

[0405]

TABLE-US-00010 TABLE 11 Ingredients Amount Arginine 3 Monoethanolamine 5.8 Sodium metasilicate 2 Poly q uaternium- 6 2 Hexadimethrine chloride 1.2 EDTA 0.2 Hydroxy propylmethylcellulose (HPMC) 1.2 Cetylhydroxyethylcellulose 0.45 PEG-40 stearate 1.8 Oleth-30 1.5 Oleic acid 3 C.sub.20-C.sub.22 fatty alcohols 3 Stearamide MEA 4.8 Steareth-2 5.5 Water qs 100

Thickening Composition

[0406]

TABLE-US-00011 TABLE 12 Ingredients Amount Hydrogen peroxide 12 Cetearyl alcohol 8 Acrylates/beheneth-25 methacrylate copolymer, 0.4 under the reference Aculyn 28 from Rohm & Haas Ceteareth-33 2 Sequestrants, stabilizers qs Phosphoric acid qs pH = 2.2 + 0.2 Water qs 100

Process for Dyeing Keratin Fibres

[0407] A composition (M) for dyeing keratin fibres is prepared in a bowl according to the following steps:

[0408] (1) 100 coated solid particles (i.e. 6 g) according to table 4 above, 58 coated solid particles (i.e. 3.48 g) according to table 6 above, 22 coated solid particles (i.e. 1.32 g) according to table 5 above, 21 coated solid particles (i.e. 1.26 g) according to table 7 above, and 14 coated solid particles (i.e. 0.84 g) according to table 8 above, are mixed with 12 g of oxidizing composition according to table 9 above and 36 g of stabilized water adjusted to pH 2.2; and then, after at least 30 seconds

[0409] (2) the mixture obtained in step (1) is mixed with 24 g of thickening composition according to table 12 above, 28.8 g of alkaline composition 1 according to table 10 above and 19.2 g of alkaline composition 2 according to table 11 above.

[0410] A homogeneous aqueous composition (M), in which the coated solid particles are dispersed in the composition, is thus obtained.

[0411] Composition (M) obtained is then applied to locks of natural Caucasian hair containing 90% grey hairs (locks of NG hair) in a proportion of 10 g of composition (M) per 1 g of hair. After a leave-in time of 30 minutes at 27° C., the locks are rinsed, washed with a standard shampoo, rinsed again and then dried.

[0412] L, a, b Results:

[0413] The colorimetric data for each of the locks are then measured in the CIELab system with a Data Color SF600X spectrophotometer (illuminant D65, angle 10° and specular component included). In this L* a* b* system, L* represents the lightness, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis. The higher the value of L*, the lighter or less intense the colour. Conversely, the lower the value of L*, the darker or more intense the colour. The higher the value of a*, the redder the shade, and the higher the value of b*, the yellower the shade.

[0414] The colour build-up on the hair thus corresponds to the variation in colouring between the locks of dyed NG hair and the locks of undyed (i.e. untreated) NG hair and is measured by the ΔE according to the following equation:

ΔE=√{square root over ((L*−L.sub.0*).sup.2+(a*−a.sub.0*).sup.2+(b*−b.sub.0*).sup.2)}

[0415] In this equation, L*, a* and b* represent the values measured after dyeing of the NG hair, and L.sub.0*, a.sub.0* and b.sub.0* represent the values measured for the untreated NG locks of hair. The higher the ΔE value, the better the build-up of the colouring.

[0416] The results are collated in the table below:

TABLE-US-00012 TABLE 13 L* a* b* ΔE Lock of untreated NG hair 57.78 1.40 13.97 — Lock of treated NG hair 23.57 2.39 5.25 35.32

[0417] It is seen from the results of the table 13 that the keratin fibres treated with composition (M) prepared according to the preparation process of the invention are dyed intensely and with a good colour build-up.

[0418] It was also found that composition (M) is easy to prepare and to spread on the locks of hair, notably without any running.

Example 2

[0419] The solid particles and the compositions below were prepared from the ingredients, the contents of which, as percentages by weight of active material, with respect to the total weight of the solid particle or of the composition, are shown in the tables below.

Solid Particles with Upper Coating Layer

TABLE-US-00013 TABLE 14 Ingredients Amount Caprylic/capric triglyceride 0.15 Silica 1.03 Lactose 14.56 Water 0.24 PVP 4.61 Magnesium stearate 1.94 Alumina 0.01 Titanium dioxide/CI 77891 0.51 Microcrystalline cellulose 54.37 Talc 0.44 Toluene-2,5-diamine sulfate 19.42 Hydroxypropyl methylcellulose 1.46 Hydroxypropylcellulose 0.29 Sodium sulfite 0.97

TABLE-US-00014 TABLE 15 Ingredients Amount Lactose 14.56 Magnesium stearate 0.97 Silica 1.03 Alumina 0.01 Titanium dioxide/CI 77891 0.51 Water 0.10 PVP 1.84 Microcrystalline cellulose 77.14 Hydroxypropyl methylcellulose 1.46 Hy droxypropy icellulo se 0.29 Talc 0.44 Sodium metabisulfite 0.97 Caprylic/capric triglyceride 0.15 Toluene-2,5-diamine sulfate 0.53

TABLE-US-00015 TABLE 16 Ingredients Amount Talc 0.44 Ascorbic acid 2.91 Hydroxypropyl methylcellulose 1.46 Alumina 0.01 Titanium dioxide/CI 77891 0.51 Silica 0.06 Magnesium stearate 0.97 Hydroxypropylcellulose 0.29 Microcrystalline cellulose 66.85 Lactose 17.47 Water 0.24 PVP 4.62 N,N-Bis(2-hydroxyethyl)-p-phenylenediamine sulfate 4.02 Caprylic/capric triglyceride 0.15

TABLE-US-00016 TABLE 17 Ingredients Amount Ascorbic acid 2.99 Polyvinyl alcohol 0.29 Lactose 3.99 Water 0.01 PVP 0.19 Magnesium stearate 1 Resorcinol 16.95 Microcrystalline cellulose 73.97 Talc 0.06 Silica 0.5 PEG-90 0.05

TABLE-US-00017 TABLE 18 Ingredients Amount Microcrystalline cellulose 69.42 Lactose 11.65 Magnesium stearate 0.97 Alumina 0.01 Titanium dioxide/CI 77891 0.51 Silica 0.54 Water 0.15 PVP 2.77 m-Aminophenol 7.76 Talc 0.44 Hydroxypropyl methylcellulose 1.46 Caprylic/capric triglyceride 0.15 Sodium metabisulfite 3.88 Hy droxypropy icellulo se 0.29

TABLE-US-00018 TABLE 19 Ingredients Amount Lactose 15.53 Hy droxypropy icellulo se 0.29 Caprylic/capric triglyceride 0.15 Microcrystalline cellulose 76.23 Silica 1.03 Magnesium stearate 0.97 2,4-diaminophenoxyethanol hydrochloride 0.97 Talc 0.44 Water 0.02 PVP 0.46 Sodium metabisulfite 1.94 Alumina 0.01 Titanium dioxide/CI 77891 0.51 Hydroxypropyl methylcellulose 1.45

Oxidizing Composition A:

[0420]

TABLE-US-00019 TABLE 20 A Hydrogen peroxide 6 Stabilizer, sequestrant Qs Phosphoric acid Qs pH = 2,2 ± 0,2 Water Qs 100

Alkaline Composition B:

[0421]

TABLE-US-00020 TABLE 21 B Arginine 3 Ammonium hydroxyde 2 Monoethanolamine 5.8 Sodium metasilicate 2 Polyquaternium-6 2 Hexadimethrine chloride 1.2 EDTA 0.2 Hydroxypropylmethyl cellulose (HPMC) 0.2 Cetyl hydroxyethyl cellulose 0.45 PEG-40 Stearate 1.8 Oleth-30 1.5 Oleic acid 3 C20-C22 fatty alcohols 3 Stearamide MEA 4.8 Steareth-2 5.5 Water Qs 100

Method for Dyeing Keratin Fibres

[0422] A composition (M2) for the dyeing of keratin fibres is prepared in a bowl according to the following steps:

[0423] (1) 25 coated solid particles (i.e. 0.47 g) according to Table 14 above, 44 coated solid particles (i.e. 0.83 g) according to Table 15 above, 4 coated solid particles (i.e. 0.04 g) according to Table 16 above, 13 coated solid particles (i.e. 0.55 g) according to Table 17 above and 5 coated solid particles (i.e. 0.1 g) according to Table 18 above and 18 coated solid particles (i.e. 0.045 g) according to Table 19 above are mixed with 36 g of oxidizing composition A according to Table 20 above; then, after at least 30 seconds,

[0424] (2) the mixture obtained in step (1) is mixed with 24 g of alkaline composition B according to Table 21.

[0425] A homogeneous aqueous composition M2, where the coated solid particles have dispersed in the composition, is thus obtained.

[0426] A composition (M3) for the dyeing of keratin fibres is prepared in a bowl according to the following steps:

[0427] (1) 25 coated solid particles (i.e. 0.47 g) according to Table 14 above, 44 coated solid particles (i.e. 0.83 g) according to Table 15 above, 4 coated solid particles (i.e. 0.04 g) according to Table 16 above, 13 coated solid particles (i.e. 0.55 g) according to Table 17 above and 5 coated solid particles (i.e. 0.1 g) according to Table 18 above and 18 coated solid particles (i.e. 0.045 g) according to Table 19 above are mixed with 24 g of alkaline composition B according to Table 21; then, after at least 30 seconds,

[0428] (2) the mixture obtained in step (1) is mixed with 36 g of oxidizing composition A according to Table 20 above.

[0429] A homogeneous aqueous composition M3, where the coated solid particles have dispersed in the composition, is thus obtained.

[0430] The compositions M2 and M3 obtained is subsequently applied to locks of natural Caucasian hair comprising 90% white hairs (locks of NG hair) in a proportion of 10 g of composition (M2 or M3) per 1 g of hair. After a leave-in time of 30 minutes at 27° C., the locks are rinsed, washed with a standard shampoo, rinsed again and then dried.

Results for the Dyeing:

[0431] The colorimetric data for each of the locks are subsequently measured in the CIELab system with a Konica Minolta CM-3600A spectrophotometer (illuminant D65, angle 10° and specular component included). In this L* a* b* system, L* represents the lightness, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis. The higher the value of L*, the lighter or less intense the colour. Conversely, the lower the value of L*, the darker or more intense the colour. The higher the value of a*, the redder the shade, and the higher the value of b*, the yellower the shade.

[0432] The colour build-up on hair thus corresponds to the variation in colouring between the locks of dyed NG hair and the locks of non-dyed (i.e. untreated) NG hair, which is measured by ΔE according to the following equation:

ΔE=√{square root over ((L*−L.sub.0*).sup.2+(a*−a.sub.0*).sup.2+(b*−b.sub.0*).sup.2)}

[0433] In this equation, L*, a* and b* represent the values measured after dyeing of the NG hair, and L.sub.0*, a.sub.0* and b.sub.0* represent the values measured for the locks of untreated NG hair. The higher the ΔE value, the better the build-up of the colouring.

[0434] The results are collated in the table below:

TABLE-US-00021 TABLE 22 L* a* b* ΔE Lock of untreated NG hair 62.59 1.58 16.86 — Lock of treated NG hair with 33.08 1.39 7.22 31.05 composition M2 (invention) A then B Lock of treated NG hair with 63.93 1.03 16.22 1.58 composition M3 (Comparative) B then A

[0435] It is seen from the results of table 22 that the hair treated according to the process of the invention (composition M2) is dyed much more intensely and with a much better colour build-up than the hair treated with the comparative process (composition M3).