Acidic post-treatment of hair dyed with dihydroxyindole

Abstract: A process for altering the color of hair that has been dyed with dihydroxyindole comprising the steps of treating the dyed hair with an acidic solution for an effective amount of time and rinsing the treated hair.

Description: This invention relates to a process for altering the color of hair that has been dyed with dihydroxyindole, or a metal catalyzed dihydroxyindole system (hereinafter collectively referred to as DHI), by treating the dyed hair with an acidic solution. Dyeing hair with DHI has many advantages: DHI produces intense haircolor, it is a relatively mild hair treatment that does not damage hair, and it is a precursor to a natural pigment, melanin -- a characteristic that pleases consumers. The primary disadvantage of using DHI to dye hair is its inability to produce colors other than gray or black. Most natural haircolors are warmer, redder shades than those produced using DHI. Hence, there exists a need in the art for obtaining natural-looking haircolors using DHI dyes. There have been a number of attempts to obtain such haircolors with DHI dyes. French Patent Application 2 657 781 (Richard) discloses a method for removing or lightening the color of DHI-dyed hair that comprises first applying a potassium permanganate solution to DHI-dyed hair and then applying a reducing agent (sodium bisulfate, sodium hydrosulfate, oxalic acid, thioglycolic acid, citric acid, or ascorbic acid). However, the haircolors produced with that method are due at least in part to the deposition of manganese dioxide on the hair. Manganese dioxide is a colorant that masks the color produced by DHI treatment. Thus it was surprising that the present invention, using an acidic solution (which may be a reducing agent) without an added colorant, produces natural-looking haircolor without needing to mask the color of the DHI-dyed hair. Furthermore, permanganate is a cosmetically unacceptable colorant. It forms an intensely colored solution that stains easily and thus is very difficult to work with. In contrast, the claimed process is simple and harmless. United States Patent 3,194,734 (Seemuller et al.) discloses a process and composition that produce warm, natural haircolor shades by using methyl derivatives of DHI and an oxidizing agent. United States Patent 4,822,375 (Lang et al.) discloses a process and composition that produce warm, natural haircolor shades by using DHI derivatives. United States Patent 5,011,500 (Grollier et al.) discloses a process and composition that produce warm, natural haircolor shades by using indole derivatives combined with synthetic dye materials such as nitro dyes. United States Patent 5,021,067 (Grollier) discloses a process and composition that produce warm, natural haircolor shades by using DHI with at least one para-phenylenediamine (a synthetic dye material) disubstituted on one of the amino groups. United States Patent 5,053,053 (De Labbey et al.) discloses a process and a kit that produce warm, natural haircolor shades by using DHI with at least one quinone derivative (a synthetic dye material). GB-A-2186891 discloses a process for dyeing hair wherein a composition having a pH of 2 to 7 and containing 5,6-dihydroxyindole and hydrogen peroxide is applied to the hair before or after the application of a second composition comprising iodide ions. EP-A-0378937 describes a process for dyeing hair by treating the hair with a first composition containing an indole derivative and a second composition comprising an aqueous acidic solution, at least one of the compositions also containing a nitrite. Both these patent publications are directed to the dyeing of hair and not to the post-treatment of hair dyed with dihydroxyindole. EP-A-0415802 is also directed to a hair dyeing process. The process comprises a first step in which an indole is applied, this step being followed by a second step in which an oxidizing solution is applied to develop the color by oxidizing the indole to melanin, thereby completing the dyeing process. This invention provides a process for altering the color of the hair previously dyed with DHI so that it is a more natural-looking color, without using additional masking colorants or DHI derivatives that are not involved in the biosynthetic pathway that produces melanin. In a preferred embodiment, the invention provides a mild non-damaging and simple process for altering the color of hair dyed with DHI so that it is a more natural-looking color. In a preferred embodiment, the invention provides a process that will produce a wide range of natural hair shades by altering the color of hair dyed with DHI. In accordance with the invention, a process is provided for altering the color of hair that has been dyed with dihydroxyindole, or a metal catalyzed dihydroxyindole system, comprising the steps of applying an aqueous, acidic solution having a pH of 2 to 7 to the hair, the composition comprising an acid component other than periodic acid, the acid component being the sole color modifier in said solution, and rinsing the treated hair. DETAILED DESCRIPTION OF THE INVENTION This invention provides a process for altering the color of hair that has been dyed with dihydroxyindole, or a metal catalyzed dihydroxyindole system, comprising the steps of treating the dyed hair with an acidic solution for an effective amount of time and rinsing the treated hair. The process changes the black/dark gray haircolor that is characteristic of DHI-dyed hair to a warm, natural-looking haircolor, without the use of masking hair colorants. Melanin is the pigment that gives hair its color. As people age, there is a gradual loss of melanin from the hair, which causes hair to turn gray or, less often, white. DHI is frequently used to dye hair that has lost melanin. The process of this invention is especially effective on gray or white DHI-dyed hair. Any type of acid, including citric acid, ascorbic acid, lactic acid, naphthalenesulfonic acid, or hydrochloric acid, can be used in accordance with this invention. However, citric acid and ascorbic acid are preferred, and citric acid is most preferred. The mild acidic solutions used in the process of this invention are effective at concentrations ranging from 0.1% to 5%. The preferred concentration of the acidic solution will vary according to the strength of the acid used. However, it is generally preferred that the concentration of the acidic solution is about 2%. The pH of the acidic solution may range from pH 2 to pH 7. However, it is preferred that the acidic solution be about pH 2 to 3. The overall acidic solution should be mild and non-damaging to the hair. However, lower pH and higher concentration acidic solutions may produce the most desirable haircolor. Thus, a skilled person should carefully select the type of acid, the concentration of the acidic solution, and the pH of the acidic solution so as to optimize the resulting haircolor without damaging the hair. The effective treatment time (the amount of time that the acidic solution is left on the hair in order to achieve the desired results of the process of this invention) will vary according to the acidic solution used and the type of results desired. In general, the effective treatment time will be from about 1 minute to several minutes. Although in general, the longer the solution is left on the hair, the better the haircolor result, leaving the solution on the hair for more than about one hour gives little added benefit. A wide range of natural-looking haircolors can be achieved with the process of this invention by altering the type of acid used, the concentration of the acid, the pH of the acid, and the amount of time that the acidic solution is left on the hair. The process of this invention may be practiced at various time intervals from the initial DHI dye treatment. The results of the process are substantially equal regardless of whether it is performed immediately after DHI dyeing or several days after DHI dyeing. The process of this invention is equally effective on hair that has, or has not, been pre-treated with a metal catalyzed dihydroxyindole system, such as copper sulfate. The following examples are given to further illustrate the present invention. It should be understood, however, that the invention is not limited thereto. EXAMPLE 1 The Effect Of Different Types Of Acidic Solutions On The Overall Color Change Of DHI-Dyed Hair Tresses Tresses of DeMeo blended medium gray hair were treated with a copper sulfate solution and dyed with a DHI composition, as described in Great Britain Patent 2 132 642 B. These tresses were then post-treated with the various acidic solutions described below. Although all of the acidic solutions were effective -- the color of all the post-treated tresses turned from black to various shades of warm brown -- citric acid and ascorbic acid produced the greatest effects. The results of these comparisons are set forth in Table 1. No. Treatment Conditions Hunter Color Values L a b E 1.1 Control (DHI-dyed tress) 17.53 0.16 -0.35 - 1.2 0.25M Citric Acid pH 2.03, 10 min. 22.57 1.73 1.99 5.77 1.3 0.25M Citric Acid Ph 2.03, 60 min. 24.82 2.22 3.24 8.38 1.4 0.25M Citric Acid pH 2.03, 24 hrs. 24.31 2.51 3.55 8.17 1.5 Control (DHI-dyed tress) 17.20 0.19 -0.43 - 1.6 0.25M Ascorbic Acid pH 2.06, 10 min. 25.78 2.29 3.75 9.77 1.7 0.25M Ascorbic Acid pH 2.06, 60 min. 25.78 3.01 4.18 10.14 1.8 0.25M Lactic Acid pH 2.06, 10 min. 21.18 1.19 1.45 4.51 1.9 0.25M Lactic Acid pH 2.06, 60 min. 22.05 1.71 2.46 5.85 1.10 0.1M 2-Naphthalenesulfonic Acid pH 2.01, 10 min. 19.25 0.61 0.39 2.25 1.11 0.1M 2-Naphthalenesulfonic Acid pH 2.01, 60 min. 19.30 0.77 0.67 2.44 1.12 0.1N HCl pH 1.0, 10 min. 24.16 2.50 3.19 8.18 1.13 0.1N HCl pH 1.0, 60 min. 24.55 2.77 3.67 8.80 Hunter values are a measure of reflected light and describe haircolor using three parameters: L, a and b. When L = 0, the haircolor is black, and when L = 100, the haircolor is white. The more positive "a" is, the redder the haircolor; the more negative "a" is, the greener the haircolor. The more positive "b" is, the yellower the haircolor; the more negative "b" is, the bluer the haircolor. E is the overall color change and is calculated using the formula E = (Δ L ) 2 +(Δ a ) 2 +(Δ b ) 2 . EXAMPLE 2 The Effect Of The pH Of A Citric Acid Solution On The Overall Color Change Of DHI-Dyed Hair Tresses Tresses of DeMeo blended medium gray hair were treated with a copper sulfate solution and dyed with a DHI composition, as described in Great Britain Patent 2 132 642 B. These tresses were then post-treated with solutions of varying pH that comprise citric acid and sodium hydroxide. Although all of the acidic solutions were effective, the best results were achieved at lower pH. The results of these comparisons are set forth in Table 2. No. Treatment Conditions Hunter Color Values L a b E 2.1 Untreated blended medium gray hair 39.72 0.18 6.52 - 2.2 Control (DHI-dyed tress) 18.91 0.33 -0.10 - 2.3 0.25M Citric Acid/NaOH pH 2.02, 3 min. 23.33 1.96 2.04 5.17 2.4 0.25M Citric Acid/NaOH pH 2.02, 10 min. 23.63 2.27 2.63 5.79 2.5 0.25M Citric Acid/NaOH pH 4.07, 3 min. 22.76 1.30 1.44 4.26 2.6 0.25M Citric Acid/NaOH pH 4.07, 10 min. 22.33 1.46 1.58 3.97 2.7 0.25M Citric Acid/NaOH pH 6.18, 3 min. 17.57 0.28 -0.23 1.35 2.8 0.25M Citric Acid/NaOH pH 6.18, 10 min. 18.47 0.48 -0.01 0.47 EXAMPLE 3 The Effect Of Treatment Time With Citric Acid Solution On The Overall Color Change Of DHI-Dyed Hair Tresses Tresses of DeMeo blended medium gray hair were treated with a copper sulfate solution and dyed with a DHI composition, as described in Great Britain Patent 2 132 642 B. These tresses were then post-treated with citric acid solutions at pH 2.13 for varying amounts of time. Although all of the acidic solutions were effective, the best results were achieved when the solution was left on the hair for a longer time. The results of these comparisons are set forth in Table 3. No. Treatment Conditions Hunter Color Values L a b E 3.1 0.1M Citric Acid pH 2.13, 1 min. 22.79 0.68 1.49 3.12 3.2 0.1M Citric Acid pH 2.13, 3 min. 26.06 1.11 2.46 6.47 3.3 0.1M Citric Acid pH 2.13, 10 min. 27.36 1.72 3.20 8.06 The data set forth in Tables 1 and 2 also demonstrate that in general, the longer an acidic solution is left on DHI-dyed hair, the greater the effect of the solution. However, the data set forth in Table 1 show that leaving the solution on DHI-dyed hair for more than one hour does not give an added benefit. EXAMPLE 4 The Effect Of Citric Acid Solution Concentration On The Overall Color Change Of DHI-Dyed Hair Tresses Tresses of DeMeo blended medium gray hair were treated with a copper sulfate solution and dyed with a DHI composition, as described in Great Britain Patent 2 132 642 B. These tresses were then post-treated with various concentrations of citric acid solutions. Although all the concentrations of citric acid solutions tested were effective -- the color of all the post-treated tresses turned from black to various shades of warm brown -- the higher concentrations of citric acid produced greater effects. The results of these comparisons are set forth in Table 4. No. Treatment Conditions Hunter Color Values L a b E 4.1 Control (DHI-dyed tress) 17.61 0.32 -0.44 - 4.2 2% Citric Acid pH 2.3 20.19 0.65 0.45 2.75 4.3 1% Citric Acid pH 2.8 19.38 0.38 -0.09 1.81 4.4 0.3% Citric Acid pH 4.4 17.18 0.21 -0.24 0.49 EXAMPLE 5 The Effect Of The Time Interval From The Initial DHI Dye Treatment On The Overall Color Change Of DHI-Dyed Hair Tresses Tresses of DeMeo blended medium gray hair were treated with a copper sulfate solution and dyed with a DHI composition, as described in Great Britain Patent 2 132 642 B. These tresses were then post-treated with various acidic solutions at various time intervals from the initial DHI dye treatment. The results show that the process of this invention is effective for many days after the hair was initially dyed. The data from these comparisons are set forth in Table 5. No. Treatment Conditions Hunter Color Values L a b E 5.1 Control (DHI-dyed tress) 18.87 0.09 0.00 - Citric Acid, 0.25M, pH 2.03, 10 min.: 5.2 Immediately After Dyeing 25.61 2.69 3.82 8.17 5.3 1 Hour After Dyeing 21.26 1.46 1.65 3.21 5.4 5 Hours After Dyeing 19.76 1.13 1.08 1.74 5.5 10 Days After Dyeing 21.09 1.27 2.20 3.34 Ascorbic Acid, 0.25M, pH 2.06, 10 min.: 5.6 Immediately After Dyeing 26.58 2.68 4.04 9.08 5.7 1 Hour After Dyeing 22.72 2.30 2.77 5.23 5.8 5 Hours After Dyeing 23.12 2.21 3.16 5.70 5.9 10 Days After Dyeing 23.37 1.89 3.63 6.06 EXAMPLE 6 The Effect Of Treatment Time And Citric Acid Solution Concentration On The Overall Color Change Of DHI-Dyed White Hair Tresses Tresses of white hair were treated with a copper sulfate solution and dyed with a DHI composition, as described in Great Britain Patent 2 132 642 B. These tresses were then post-treated with varying concentrations of citric acid solutions for varying amounts of time. The results of these comparisons are set forth in Table 6. No. Treatment Conditions Hunter Color Values L a b E 6.1 Untreated white hair 75.92 -2.14 11.47 - 6.2 Control (DHI-dyed tress) 24.49 0.21 -3.02 - 6.3 0.1M Citric Acid, 10 min. 27.63 1.85 1.05 5.40 6.4 0.1M Citric Acid, 20 min. 29.96 2.43 1.92 7.70 6.5 0.1M Citric Acid, 40 min. 30.25 2.62 2.55 8.37 6.6 0.25M Citric Acid, 10 min. 32.34 3.25 2.70 10.18 6.7 0.25M Citric Acid, 20 min. 33.30 3.48 3.24 11.29 6.8 0.5M Citric Acid, 10 min. 30.72 3.05 2.72 8.93 6.9 0.5M Citric Acid, 20 min. 33.11 3.54 3.48 11.30 EXAMPLE 7 The Effect Of Copper Sulfate Pre-treatment On The Overall Color Change Of DHI-dyed Hair Tresses That Are Post-treated With An Acidic Solution Tresses of blended medium gray hair, which were not treated with copper sulfate solution but were dyed five times, in fifteen minute long treatments, with a DHI composition, were post-treated with various acidic solutions, at different pH, for different amounts of time; The effects are similar to those demonstrated for tresses that were pre-treated with copper sulfate solution. The results of these comparisons are set forth in Table 7. No. Treatment Conditions Hunter Color Values L a b E 7.1 Control (DHI-dyed tress) 19.00 0.87 0.40 - 7.2 0.25M Citric Acid pH 2.03, 10 min. 22.30 2.56 2.26 4.15 7.3 0.25M Citric Acid pH 2.03, 60 min. 23.69 3.13 2.97 5.81 7.4 0.25M Citric Acid pH 2.06, 10 min. 22.74 2.70 2.44 4.64 7.5 0.1N HCl pH 1.0, 10 min. 23.63 2.80 2.80 5.56 EXAMPLE 8 A Comparison With The Results Achieved By Prior Art DHI Masking Colorants Three tresses of DeMeo blended medium gray hair (8a.2, 8a.3, and 8a.4) were dyed using the procedure described in French Patent Application 2 657 781, Example 6 (copper sulfate followed by DHI). Un dyed tress 8a.1 was used as a control. After treatment with copper sulfate and DHI, the haircolor of tress 8a.2 was black. DHI-dyed tress 8a.3 was subsequently treated with a permanganate dye composition and the resulting haircolor of the tress was dark gray/black. DHI-dyed tress 8a.4 was subsequently treated with the permanganate and citric acid compositions described in French Patent Application 2 657 781 and the resulting haircolor of tress 8a.4 was a dark greenish brown. The color change in tress number 8a.4 is largely due to the formation of a yellow haircolor by permanganate. The data from these comparisons are set forth in Table 8a. No. Treatment Conditions Hunter Color Values L a b 8a.1 Untreated 29.4 0.2 6.0 8a.2 CuSO 4 /DHI Treated 9.8 0.1 0.9 8a.3 CuSO 4 /DHI/Permanganate Treated 14.3 1.0 1.1 8a.4 CuSO 4 /DHI/Permanganate/Citric Acid Treated 13.2 1.2 4.3 The effect of the permanganate was demonstrated by treating tress 8b.2 of DeMeo blended medium gray hair with a permanganate composition and by treating tress 8b.3 of DeMeo blended medium gray hair with a permanganate and citric acid composition. Tress 8b.1 of DeMeo blended gray hair was used a control. Tresses 8b.2 and 8b.3 were a yellow/green color after the treatments. If this yellow green color were superimposed on the black color that results from dyeing with DHI, the result would be the dark greenish brown observed with tress 8a.4. The data from this comparison are set forth in Table 8b. No. Treatment Conditions Hunter Color Values L a b 8b.1 Untreated 29.7 0.2 5.5 8b.2 Permanganate Treated 13.9 2.6 4.0 8a.3 Permanganate/Citric Acid Treated 18.1 2.7 8.1 EXAMPLE 9 Tresses of DeMeo blended medium gray hair may be treated with the indole derivatives disclosed in United States Patent 5,011,500 (Grollier et al.) and by the dyeing processes disclosed therein, excluding the addition of the synthetic dye materials also disclosed therein. These tresses may then be post-treated with a 2% citric acid solution of pH 2.3 for 5 minutes. The resultina haircolor of the treated tresses will be a warm shade of brown.

Claims: A process for changing the color of hair previously dyed to a gray to black coloration with dihydroxyindole, the process comprising the steps of applying an aqueous, acidic solution having a pH of 2 to 7 to the hair, the composition comprising an acid component other than periodic acid, the acid component being the sole color modifier in said solution, and rinsing the treated hair. A process as claimed in claim 1 characterised in that the acidic component is selected from citric acid, ascorbic acid, tartaric acid, lactic acid, naphthalenesulfonic acid, and hydrochloric acid. A process as claimed in claim 1 or claim 2 characterised in that the acid component is present in the solution in a concentration of 0.1% to 5%. A process as claimed in any one of claims 1 to 3 characterised in that the dyed hair is treated with the acidic solution for no more than one hour.

Inventors: WOLFRAM LESZEK, WOLFRAM, LESZEK
Applicants: SQUIBB BRISTOL MYERS CO, BRISTOL-MYERS SQUIBB COMPANY
Application year: 1993
Main classification: A61K7
IPC codes: A61Q5, A61K8