DESC:FIELD OF THE INVENTION

The present invention relates to a nanoparticle based hair colour formulation/kit, and in particular, relates to silver nanoparticle based hair colour formulation/kit that imparts varied colour shades to keratin fibres from brown to even black shade depending on the size of the nanoparticles provided by the said formulation. Advantageously, the ingredients of the hair colour formulation/kit of the present invention is water soluble and is economically viable in involving cost effective ingredients, that imparts colour to the hair either ex-situ or in-situ in either involving a capping agent or materials that controls the diffusion of the precursor materials in the hair shaft for generation of the nanoparticles on the hair itself for better shampoo stability.

BACKGROUND ART

Nanoparticles like gold, silver, platinum, palladium based dyes are known for coloring fabrics like wool and cotton. Size of the particles controls the optical properties of materials. Metal nanoparticles can create unusual color due to plasmon vibration and can produce varieties of color. Nanoparticles like gold [J. H. Johnson, The Formation and Binding of Gold Nanoparticles onto Wool Fibres, AIP Conf. Proc., 189, 2009, 1151], silver [F. M. Kelly, Colored and Functional Silver Nanoparticle Wool Fiber Composites, ACS Appl. Mater. Interfaces 2011, 3, 1083–1092], platinum, palladium [C. F. Paris Nanopalladium – wool: A novel fiber for multifunctional textile, NSTI-Nanotech 2001, vol 1, 2001, 780-784] based dyes are known for coloring fabrics like wool and cotton. In-situ synthesis of gold [S. D. Haveli et al., Hair Fiber as a Nanoreactor in Controlled Synthesis of Fluorescent Gold Nanoparticles, Nano Lett., 2012, 12 , pp 6212–6217], HgS [G. Patriarche et al., Characteristics of HgS nanoparticles formed in hair by a chemical reaction, Philosophical Magazine, 93:1-3, 137-151] and PbS [Walter et al., Early use of PbS nanotechnology for hair dyeing formula, Nano lett., 2006, 6,10 pp 2215]nanoparticles are reported to be useful for hair dye applications. However, the coloring time ranges from 3-20 days, which is very much unviable for practical applications. Also, the concentration of chemical used for gold nanoparticle based dyes is extremely high. On the other hand the HgS and PbS nanoparticles hair coloration precursors are known to be toxic to body tissues.

US 2006/0249170 A1 describes use of sulphur free reducing agent and an ammonical solution along with organic or inorganic silver salt for obtaining mirror like luster on hair. The reducing agents used are aldehydes and aldoses, ketones and ketoses, enols, enediols, reductones, hydrides, skin tanning agents, glyoxylic acid, glyoxal, glycerylaldehyde, maltose, pyruvic acid, erythrulose, fructose, lactose, acetoin, oxalacetic acid, ot-ketoglutaric acid, dihydroxyacetone, hydroxymethylglyoxal and 6-aldo-D-fructose. The silver salt is selected from the group consisting of silver nitrate, silver chloride, silver sulphate, silver carbonate, silver hydrogen sulphate, silver phosphate, silver acetate and silver alums and the corresponding ammonium or thiosulphate complexes of these silver salts. First preparation applied and after 60 min second preparation is applied. Keratin fibre is heated to 50 -80 °C.

EP 1243249 B9 describes a metallic dye comprises silver nitrate (AgNO3) and silver lactate (C3H5AgO3) each in an amount of 0.05~10.0wt%, based on total weight of the composition. The surfactant is selected from glyceryl stearate/ ceteareth20/ceteareth-12/cetearyl alcohol/cetyl palmitate, ceteareth-20, ceteareth-12, lauryl glucoside, nonoxynol-10, and cocamide dea. The alcohol is selected from cetyl alcohol, stearyl alcohol, oleyl alcohol, and hexyldecanol. The moisturizing agent is selected from coco-caprylate/caprate and propylene glycol. The composition further comprises henna. This patent describes about use of silver and henna to achieve color although the color of hair is never mentioned in the patent.

WO 2013078492 A2 [Agent and method for colouring keratin fibres] relates to a ready-to-use colouring composition, containing at least 0.02% by weight of at least one compound selected from the group comprising catechins, gallic acid, gallates and mixtures thereof, together with a silver salt, and to a product for simultaneous use or use spread over a period of time, comprising two components A and B. At least one compound selected from the group consisting of p-phenylenediamine, p-tolylene, N-phenyl-p-phenylenediamine, hydroxyethyl-p-phenylenediamine, N, N '-Bis-hydroxyethylp- phenylenediamine, 2-chloro-p-phenylenediamine, triaminopyrimidine, tetraaminopyrimidine, m-aminophenol, p-aminophenol, o-aminophenol, resorcinol, 2-methylresorcinol, 4-chlororesorcinol, 2, 6-diaminopyridine, 2, 6 - dimethoxy-3, 5-diaminopyridine, etc. is included. This patent uses PPD (para-phenylene diamine) or PPD derived components along with gallates or plant extracts with silver salt.

KR 2011062679 A 20110610 discuses about the usage of combination of silver sulfate, silver nanoparticles and scoria to dye hair. Jeju scoria, a volcanic stone rich in mineral extract, is widely used to dye cotton fabrics. Further, the presence of light is essential to color the hair. The color of the hair obtained using this mixture is not provided in the patent.

EP1440681 relates to the use in the field of cosmetic luminescent semiconductor nanoparticles, particularly nanoparticles containing cadmium sulfide or cadmium selenide. This prior art also relates to the use of such nanoparticles for coloring keratin materials, hair.

It is therefore apparent from the state of the art that though cost extensive nanoparticles may be used for colouring keratin fibres/ hair there still exists a need in the art to develop usable, affordable and non-toxic hair coloring formulations/kit employing metal nanoparticles.

OBJECTS OF THE INVENTION

It is thus the primary object of the present invention to provide for metal nanoparticle based hair colour formulation/kit preferably silver nanoparticle based formulation/kit that would impart varied coloured shades to the keratin fibres/hair including black shade in reduced application time.

It is another object of the present invention to provide for said metal nanoparticle based hair colour formulation/kit wherein various colour shades could be attained by controlling the size of the nanoparticles, reducing agents, concentration of reducing agent, combination of reducing agents and silver ion concentration.

It is yet another object of the present invention to provide for metal nanoparticle based hair colour formulation/kit with reduced application time and hence a low colouring time of as low as 30-60 min.

It is yet another object of the present invention to provide for said metal nanoparticle based hair colour formulation/kit involving cost effective metal precursors and ingredients that would render the formulation/kit economically viable yet effective for colouring hair.

It is still another object of the present invention to provide for said hair colouring formulation cum anti-dandruff formulation/kit which in involving silver nanoparticles additionally imparts beneficial antimicrobial attributes.

It is another object of the present invention to provide for said metal nanoparticle based hair colour formulation/kit which in involving safe and non-toxic chemicals free of ammonia, peroxide, and other harsh chemicals would be healthy and safe for humans and environment.

It is yet another object of the present invention to provide for a formulation/ kit that would impart colour to the hair in-situ via in-situ synthesis and adherence of said metal nanoparticle inside the hair shaft to provide for the desired colour on hair that would be advantageously shampoo stable.

It is another object of the present invention to provide for a formulation/ kit that would impart colour to the hair ex-situ via ex-situ treatment of the hair with said metal nanoparticle formulation for attainment of desired hair colour.

It is another object of the present invention to provide for a formulation/kit that would show to improve the intensity and shades of colour when various combinations of reducing agents and combination of bases are used for in-situ colour formation.

It is still another object of the present invention to provide for said formulation/kit that is free of any use of p-PDA (para-phenylene diamine) or p-PDA derived components and/or Henna for colouring the hair and to provide a method of colouring the hair at room temperature conditions free of any requirement of light.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a hair colour formulation/kit for in-situ generation of silver nanoparticle to develop colour in the hair comprising inside hair shaft synthesizable silver nanoparticle size dependent variable hair colour having controlled diffusion and variably reactable hair colour precursors comprising:
(i) water soluble silver salt;
(ii) at least one reducing agent; and
(iii) at least one base.

Preferably in said hair colour formulation/kit said concentration of water soluble silver salt and reducing agent is in the range of 0.01 – 3 % w/v and the concentration of the base is equal to the total amount of reducing agent in the formulation.

According to another preferred aspect of the present invention there is provided a hair colour formulation/kit comprising higher concentration of reducing agents and combinations thereof for darker colour and in-colour shades towards intense black shades on hair and an instruction manual.

According to yet another preferred aspect of the present invention a hair colour formulation/kit is provided comprising select combination of bases to impart different colour shades on hair and also imparts combinatorial effect of resultant colour shades on hair based on a combination of different bases enabling in-situ reaction with silver salt and/ or reducing agent.

Preferably in said hair colour formulation/kit said water soluble silver salt comprises silver nitrate, silver acetate; wherein said viable reducing agent comprises citrate, ascorbic acid, tartarate (of Na and K), hydroquinone, maltodextrin or mixtures thereof; and wherein said bases comprises potassium carbonate, ammonia, monoethanolamine or mixtures thereof.

More preferably said hair colour formulation/kit imparts shampoo stable colour shades stable for at least upto 15 washes with combined antimicrobial activity.

According to another preferred aspect of the present invention said hair colour formulation/kit enables said in-situ generated nanoparticle have size ranging from 5.to 200nm.

According to another aspect of the present invention a method of colouring the hair involving the formulation/ kit is provided comprising in-situ generation of nanoparticles within the hair shaft by selectively applying to said hair colour precursors
(i) water soluble silver salt;
(ii) at least one reducing agent; and
(iii) at least one base, enabling desired said controlled diffusion of the same in said hair shaft for desired in-situ reaction and thereby generation of nanoparticles for desired colour of hair.

Preferably in said method of colouring the hair in the following steps comprises
(a) providing silver salt as water solution for applying to said the hair with or without a base;
(b) providing water solution of reducing agent or combinations thereof together with a base or combinations thereof for further applying the silver salt solution applied hair of step (a) at room temperature; and obtaining said coloured hair therefrom in reduced application time of 15-60 mins.

More preferably said method of colouring the hair comprises involving said concentration of water soluble silver salt and reducing agent or combinations thereof in the range of 0.01 – 3 % w/v and the concentration of the base equal to the total amount of reducing agent.

According to another preferred aspect of the present invention said method of colouring the hair comprises involving higher concentration of reducing agents and combination of reducing agents preferably in the ratio of 1:1 for producing darker colour shades and in-colour shades towards intense black shades on hair.

Preferably a method of colouring the hair is provided comprising involving different bases to produce different colour shades on hair and involving mixture of bases with silver salt and/ or reducing agent such as to produce combinatorial effect of resultant colour shades on hair.

According to another preferred aspect of the present invention a method of colouring the hair is provided in the steps comprising
(a) providing silver salt as water solution for applying to the hair with or without a base;
(b) providing water solution of reducing agent selected from citric acid, water soluble citrate salts or combinations thereof together with a base or combinations thereof for further applying to silver salt solution applied hair of step (a) at temperatures in the range of 75-100 °C for 3-5 hrs ; and obtaining said coloured hair therefrom.

In said method of colouring the hair the concentration of the actives are provided in the range of 0.015 w/v to 3% w/v.

According to another aspect of the present invention a hair colour formulation/kit for ex-situ generation of nanoparticles on the hair is provided comprising positively charged silver nanoparticle size dependent hair color developable ex-situ on hair having reactable hair colour precursors comprising:

(i) water soluble silver salt;
(ii) at least one reducing agent;
(iii) positively charged capping agent
to favour attachment of nanoparticles on hair thus imparting shampoo stable colour shades based on the size of the nanoparticles.

Preferably in said hair colour formulation/kit said water soluble silver salt comprises silver nitrate, silver acetate; said reducing agents includes sodium borohydride, hydrazine; and said capping agent includes long chain molecules with positive charge preferably with nitrogen containing group like polyethyleneimine.

More preferably, said hair colour formulation/kit comprises desired concentrations of the actives of precursor silver salt and reducing agent in the range of from 0.005 % w/v to 2 % w/v and preferably in the concentration range of 0.01 % w/v, and wherein the concentration of capping agent is in the range of 0.05 - 5 ml/ 100 ml of the nanoparticle solution preferably 0.5 ml/ 100 ml of the nanoparticle solution.

According to another preferred aspect of the present invention said method of colouring the hair by ex-situ generated silver nanoparticles involving the formulation/ kit is provided comprising applying to the hair ex-situ synthesized and stabilized silver nanoparticles and allowing to stay for 15-60 mins for desired saturation of the colour on the hair in various colour shades by controlling the size of the silver nanoparticles.

Preferably is said method said desired ratio of nanoparticle solution: hair is 1:1.to 10:1.

The present invention is described hereunder in greater details in relation to non-limiting exemplary illustrations and Figures.

BRIEF DESCRIPTION OF FIGURES
Figure 1: a) Schematic of metal based coloring of hair by ex-situ process and b) deposition of Ag particles on the hair surface;

Figure 2: a) Schematic of metal based coloring of hair by in-situ process and b) Ag nanoparticles in the cuticles and cortex area.

DETAILED DESCRIPTION OF THE INVENTION

As discussed hereinbefore the present invention provides for nanoparticle based hair colour formulation/kit preferably silver nanoparticle based hair colour formulation/kit that imparts varied colour shades to keratin fibres from brown to even black depending on the size of the nanoparticles provided by said formulation/kit. Advantageously, the hair colour formulation/kit of the present invention is water soluble and is economically viable in involving cost effective ingredients, which is provided for both ex-situ and in-situ colouring of the hair in involving either a capping agent or materials that controls the diffusion of the precursor materials in the hair shaft for generation of the nanoparticles on the hair itself for better shampoo stability.
Advantageously by the metal nanoparticle based hair colour formulation/kit of the present invention various colour shades could be attained by controlling the size of the nanoparticles, diffusion controlling agents including reducing agents, concentration of reducing agent, combination of reducing agents and silver ion concentration.

While the synthesis of Ag nanoparticles is known for various applications, a simple mixing of grey hair in the reaction mixture, however, does not yield colored hair and nothing is known till date colouring the hair using Ag nanoparticles alone.
Therefore in another aspect, the present invention deals with the process of colouring the hair involving Ag nanoparticles whereby the nanoparticles were synthesized and attached on the hair surface via an ex-situ process.

In yet another aspect, the present invention deals with a process for colouring the hair in-situ with the aid of diffusion controlling materials that controls the diffusion of the precursor materials in the hair shaft.
Synthesis of nanoparticles in a beaker is much easier than the synthesis of nanoparticles inside the hair structure as well as on the hair surface, and hence, according to another aspect of the present invention there is provided an in-situ process whereby the nanoparticles are synthesized inside the hair-shaft using hair as a reactor surface wherein the shampoo stability of the hair colour is much improved in said in-situ process. The improvement in colours shades and intensity can be achieved in-situ method by using the combination of reducing agents and combination of bases in addition to other controlling parameters like concentration and ratio.

Examples:
Most of the metals are available in nature in their compound form. Therefore, to get nanoparticles of metal/metal oxide, it is required to reduce the compound. For hair color application the compounds should be water soluble. Water soluble Ag salts can be reduced to their elementary form by sodium borohydride (NaBH4), citrate and ascorbic acid. Two different processes were developed for coloring hair namely ex-situ synthesis of nanoparticles followed by adsorption on hair shaft and in-situ synthesis of nanoparticles.

Example 1: Ex-situ synthesis and coloring
In ex-situ synthesis, stable colored nanoparticles are synthesized and applied to hair. The charge of hair’s external surface in water is negative so it is essential to utilize positively charged particles for coloring. The nanoparticles were stabilized by creating positive surface charge using polyethyleneimine (PEI). The positively charged nanoparticles were attracted towards the negatively charged hair and produce color (due to surface plasmon resonance) on the hair. For the process of the present invention the precursor chemicals for the synthesis of Ag nanonaprticles were Sodium borohydride (NaBH4) and Silver nitrate (AgNO3). The mixing of precursor at a suitable ratio and concentration will result in a desired color. Polyethylenimine (PEI) was added to cap the nanoparticles and create surface positive charge on the particles. Amino group can bind with particles as well as hair

Structure of polyethylenimine

The stability of silver nanoparticles was better for conc. 0.01 % w/v. The low (0.01 % w/v) concentration of sodium borohydride in the synthesis produced yellow color particles while high concentration of sodium borohydride produced black color particles. The colored nanoparticle solution is mixed with polyethlenimine at a suitable concentration to produce positively charged nanoparticle. The grey hair is immersed in the prepared solution with charged particle. After the desired time of immersion, the color of hair changes into the color of particles. The following is the reaction used to synthesize silver particles.

NaBH4 + 2Ag+ + 2H2O 2 Ag + NaBO2 + 4H2

Figure 1 (a) illustrates a schematic of metal based coloring of hair by ex-situ process and b) deposition of Ag particles on the hair surface.

The desired concentration range of silver nitrate is from 0.005 % w/v to 2 % w/v and that of sodium borohyride is 0.005 % w/v to 2 % w/v and preferred concentration is 0.01 % w/v. In this concentration range, the reaction is rapid. At lower concentration, the reaction is slow but produces nanoparticles. At higher concentration, nanoparticles are stable only for short period within which it should be utilized.

Hydrazine or other strong reducing agents at similar concentrations can be used instead of sodium borohydride.

The concentration of polyethleyeneimine (capping agent) is 0.05 - 5 ml/ 100 ml of nanoparticle solution and the preferred concentration is 0.5 ml/ 100 ml. The lower concentration is less effective. The final concentration of silver in the solution is 0.01 – 2 % w/v and preferred concentration is 0.5 % w/v. Lower concentration is less effective while higher concentration is economically unviable.

Apart from polyethyleneimine, any other long chain molecules with positive charge, preferably with nitrogen containing group, can be used.

The time required for coloring hair swatch via ex-situ process is from 15 – 60 min. Below 15 minutes, the color appears on hair but it is washable. The color gets saturated after 60 minutes. The ratio of hair to nanoparticle solution is maintained such that the hair has to be wetted by the solution.

Example 2: In-situ synthesis and coloring
In the in-situ coloring of hair, the precursors should diffuse into the hair and react to produce color on the hair. The control of diffusion and reaction becomes critical factor to control nanoparticle synthesis inside the hair shaft and produce color. Various precursors were tried and the optimal process for two viable precursors namely citrate,ascorbic acid, tartarate (of Na and K), hydroquinone, maltodextrin were identified. The method and sequence of hair immersion in precursors result in different intensity of hair coloring in spite of similar concentrations. In the case of citrate method, the concentration of precursors varies from 0.01 % w/v to 0.1% w/v, the synthesis requires elevated temperatures in the range of 75 – 100 °C and requires 3-5 hrs for complete coloring of the hair. As a result of subsequent analysis and screening, we developed simple method for in-situ synthesis which can be performed at room temperature and has time duration of 15 – 60 minutes. This method involves a range of precursors (reducing agents) like tartarate, hydroquinone, maltodextrin and their mixture. The sequence of immersion of grey hair in the precursor affects the coloring of hair and the best sequence was identified. Unlike the ex-situ synthesis and coloring, where the colored hair was not shampoo stable, in in-situ synthesis and coloring, the colored hair possess high shampoo stability for at least 15 washes. In-situ method first the hair is dipped in the AgNO3 solution and followed by dipping the AgNO3 treated hair in reducing agent solution. Therefore, it is a 2-step method.

Figure 2 (a) represents a schematic of metal based coloring of hair by in-situ process and b) Ag nanoparticles produced by ascorbic acid treatment are in the cuticles and cortex area (Black dots are nanoparticles).

The concentration of precursor’s silver salt and reducing agents ranges from 0.01 – 3 % w/v.

Additionally, the mix precursors (reducing agents) produce some combinational effect. Like mixture of ascorbic acid and tartarate (1:1) produces more intense and vibrant colour compared to respective colour alone. Similar observation was also noticed in case of ascorbic acid and hydroquinone mixture (1:1) and ascorbic acid and matrodextrin mixture (1:1). Table 1 shows the effect of various reducing agents when silver concentration and base are unchanged. From the table it is clear that combination of the reducing agents produced darker and towards intense black shade.
Concentration of reducing agents also influences the colour shade. Higher concentration of reducing agents always produced darker shade. Table 2 shows the effect of the concentration of reducing agents. The point to be noted here that the amount of base added was kept equal to the amount of total reducing agents (by weight).
Concentration of Ag ions plays another important role for the development of colour. It is very easy to understand that the number of nanoparticles will increase with the increase of Ag concentration. However, with the fixed amount of base and reducing agents the Ag salt concentration above 1 % (w/v) did not show any improvement in the colour intensity. Table 3 summarizes the effect of Ag-salt concentration on colour. Present examples are based on silver nitrate (AgNO¬3). However, any other water soluble silver salt (like silver acetate) will also produce similar results.
Ratio of the two reducing agents can impart in colour shades. Table 4 shows such an effect when the ratio of ascorbic acid to Na/K tartrate was interchanged.
Different bases produce different shades. Like monoethanol amine produced brownish black where as potassium carbonate (K2CO3) produced grayish black. In the two step method K2CO3 was added only in the reducing agent side. K2CO3 can not be added in the silver side due to the reaction with silver. However, other bases like NH3 and MEA can be added in both the sides. There another combinational effect was observed when mixture of bases was used instead of a single base. Table 5 shows the effect of different bases and their combination. For an example MEA in silver salt side and K2CO3 in reducing agents side can produce very good natural brown black shade. In case of MEA only single step produced acceptable colour. While using other bases (other than MEA), single step dipping method did not work.
Colour on hair always comparative to each other. Therefore to provide some idea about the intensity of the colour produced on hair, L,a,b values of two selected hair were evaluated. For this purpose bigger hair swatches were treated with the colour formulation. The hair treated with 1 % w/v AgNO3, 3 % w/v ascorbic acid, 3 % w/v Na/K tartrate and 6 % w/v K2CO3 produced dark-grey-black colour. The Lab value for this swatch was, L= 24, a =0, b=4. The corresponding RGB values are 63,57,50. Similar treatment was done by changing the base. In this case MEA was added in both the sides and K2CO3 was added on reducing agent side. The color L,a,b values are 23,2,5 (RGB: 61,52,48). In both the case around 8 gm of hair was treated with 40 ml of colour solution in each step. It is possible to increase the colour intensity by chaging the ratio of amount of hair to the volume of solution.
These metal nanoparticles are prepared for the purpose of coloring hair. However, silver has an additional benefit of antimicrobial property. Therefore, silver based hair color will show antidandruff properties. This is an additional benefit along with the hair color.

Table 1 : Effect of reducing agents and combination, ‘+’ represents ‘more intensity’,

AgNO3 (% w/v) Reducing agent 1 (% w/v) Reducing agent 2 (% w/v) Potassium carbonate (%, w/v) Final color on hair
1 Ascorbic acid (1) - 1 Dark grey
1 - Na/K Tartrate (1) 1 Dark brown
Ascorbic acid (2) 0 2 Dark grey +
1 - Na/K Tartrate (2) 2 Dark brown +
1 Ascorbic acid (1) Na/K Tartrate (1) 2 Dark-grey-black
1 Ascorbic acid (1.5) Na/K Tartrate (1.5) 3 Darker-grey-black
1 - Hydroquinone (1.5) 1.5 dark grey +
1 Ascorbic acid (1.5) Hydroquinone (1.5) 3 Dark-grey-black

1 Na/K Tartrate (1.5) Hydroquinone (1.5) 3 Dark-grey-black
1 Ascorbic acid (1.5) Maltodextrin (1.5) 3 Dark-grey-black

Table 2: Effect of concentration of reducing agents, , ‘+’ represents ‘more intensity’

AgNO3 (%, w/v) Ascorbic acid (%, w/v) Na/K Tartrate (%, w/v) Potassium carbonate (%, w/v) Final color on hair
1 3 3 6 Dark grey black +
1 1.5 1.5 3 Dark grey-black
1 1 1 2 grey-black
1 0.5 0.5 1 Dull grey-Black
1 0.3 0.3 0.6 Dull grey-white

Table 3: Effect of silver salt concentration

AgNO3 (%, w/v) Ascorbic acid (%, w/v) Na/K Tartrate (%, w/v) Potassium carbonate (%, w/v) Final color on hair
2 1.5 1.5 3 Dark grey-black
1 1.5 1.5 3 Dark grey-black
0.5 1.5 1.5 3 grey-black
0.3 1.5 1.5 3 grey

Table 4: Effect of reducing agents' ratio

AgNO3 (%, w/v) Ascorbic acid (%, w/v) Na/K Tartrate (%, w/v) Potassium carbonate (%, w/v) Final color on hair

1 0.3 1 1.3 Grey
1 1 0.3 1.3 Brownish grey

Table 5: Change in base and their combination. Solution volume 10 ml.

AgNO3 (%, w/v) Ascorbic acid (%, w/v) Na/K Tartrate (%, w/v) Base Final color on hair
1 1.5 1.5 Potassium carbonate (3 % w/v, reducing agent side) Dark-grey-black
1 1.5 1.5 Ammonia (0.75 ml, each side) yellowish-brownish
1 1.5 1.5 Ammonia (0.75 ml, silver side) + potassium carbonate (3 % w/v, reducing agent side) brownish-dark
1 1.5 1.5 Ammonia (0.75 ml, each sides) + potassium carbonate (3 % w/v,reducing agent side) brownish
1 1.5 1.5 Mono ethanol amine (MEA) (1 ml, each side) Brown
1 1.5 1.5 MEA ( 1 ml, each side ) + Potassium carbonate (3 % w/v, reducing agent side) Natural brown black
1 1.5 1.5 MEA (1 ml, silver side) + Potassum carbonate (3 % w/v, reducing agent side) Brown-black

It is thus possible for the first time by way of the present advancement to provide for a hair colour formulation/kit involving metal nanoparticles preferably silver nanoparticles. Advantageously, the present invention by way of its hair colour formulation/kit enables the attainment of various colour shades on hair including unique black colour shade with silver nanoparticles as compared to the other known nanoparticle based methods resulting in non-black colour.

Most advantageously, the application and colouring time is only about 15 – 60 min that too at room temperature as compared to the other known nanoparticle based method that takes weeks for coloring hair such as gold. Further since the hair colouring process is performed at room temperature as compared to the other processes of coloring wool at high temperature, wherein the methods of coloring hair shows shampoo stability renders the hair colour formulation/kit further advantageous. The method of the present invention of hair colouring in involving different key parameters different reducing agents, different mechanisms of color production (on the surface or inside the shaft), precursors’ concentration and temperature is therefore unique wherein hair acts as the reactor to trap the metal nanoparticles on the surface of the hair or inside the hair shaft. The hair colour formulation/kit of the present invention is thus set to be an effective replacement to p-PDA (para-pheynylene diamine) based hair dye that is free of ammonia, peroxide and other harsh chemicals.

,CLAIMS:
We Claim:

1. Hair colour formulation/kit for in-situ generation of silver nanoparticle to develop colour in the hair comprising inside hair shaft synthesizable silver nanoparticle size dependent variable hair colour having controlled diffusion and variably reactable hair colour precursors comprising:
(i) water soluble silver salt;
(ii) at least one reducing agent; and
(iii) at least one base.

2. Hair colour formulation/kit as claimed in claim 1 wherein said concentration of water soluble silver salt and reducing agent is in the range of 0.01 – 3 % w/v and the concentration of the base is equal to the total amount of reducing agent in the formulation.

3. Hair colour formulation/kit as claimed in anyone of claims 1 or 2 comprising higher concentration of reducing agents and combinations thereof for darker colour and in-colour shades towards intense black shades on hair and an instruction manual.

4. Hair colour formulation/kit as claimed in anyone of claims 1-3 comprising select combination of bases to impart different colour shades on hair and also imparts combinatorial effect of resultant colour shades on hair based on a combination of different bases enabling in-situ reaction with silver salt and/ or reducing agent.

5. Hair colour formulation/kit as claimed in anyone of claims 1-4 wherein said water soluble silver salt comprises silver nitrate, silver acetate; wherein said viable reducing agent comprises citrate, ascorbic acid, tartarate (of Na and K), hydroquinone, maltodextrin or mixtures thereof; and wherein said bases comprises potassium carbonate, ammonia, monoethanolamine or mixtures thereof.

6. Hair colour formulation/kit as claimed in anyone of claims 1-5 which imparts shampoo stable colour shades stable for at least upto 15 washes with combined antimicrobial activity.

7. Hair colour formulation/kit as claimed in anyone of claims 1-6 enabling said in-situ generated nanoparticle have size ranging from 5 to 200 nm

8. A method of colouring the hair involving the formulation/ kit as claimed in claim 1 comprising in-situ generation of nanoparticles within the hair shaft by selectively applying to said hair colour precursors
(i) water soluble silver salt;
(ii) at least one reducing agent; and
(iii) at least one base, enabling desired said controlled diffusion of the same in said hair shaft for desired in-situ reaction and thereby generation of nanoparticles for desired colour of hair.

9. A method of colouring the hair as claimed in claim 8 in the following steps comprising
(a) providing silver salt as water solution for applying to said the hair with or without a base;
(b) providing water solution of reducing agent or combinations thereof together with a base or combinations thereof for further applying the silver salt solution applied hair of step (a) at room temperature; and obtaining said coloured hair therefrom in reduced application time of 15-60 mins.

10. A method of colouring the hair as claimed in anyone of claims 8 or 9 comprising involving said concentration of water soluble silver salt and reducing agent or combinations thereof in the range of 0.01 – 3 % w/v and the concentration of the base equal to the total amount of reducing agent.
11. A method of colouring the hair as claimed in anyone of claims 8-10 comprising involving higher concentration of reducing agents and combination of reducing agents preferably in the ratio of 1:1 produced darker colour shades and in-colour shades towards intense black shades on hair.

12. A method of colouring the hair as claimed in anyone of claims 8-11 comprising involving different bases to produce different colour shades on hair and involving mixture of bases with silver salt and/ or reducing agent such as to produce combinatorial effect of resultant colour shades on hair.

13. A method of colouring the hair as claimed in anyone of claims 8-12 in the steps comprising
(a) providing silver salt as water solution for applying to the hair with or without a base;
(b) providing water solution of reducing agent selected from citric acid, water soluble citrate salts or combinations thereof together with a base or combinations thereof for further applying to silver salt solution applied hair of step (a) at temperatures in the range of 75-100 °C for 3-5 hrs ; and obtaining said coloured hair therefrom.

14. A method of colouring the hair as claimed in claim 13 wherein the concentration of the actives are provided in the range of 0.01 5w/v to 0.1% w/v.

15. Hair colour formulation/kit for ex-situ generation of nanoparticles on the hair comprising positively charged silver nanoparticle size dependent hair color developable ex-situ on hair having reactable hair colour precursors comprising:

(i) water soluble silver salt;
(ii) at least one reducing agent;
(iii) positively charged capping agent
to favour attachment of nanoparticles on hair thus imparting shampoo stable colour shades based on the size of the nanoparticles.

16. Hair colour formulation/kit as claimed in claim 15 wherein said water soluble silver salt comprises silver nitrate, silver acetate; said reducing agents includes sodium borohydride, hydrazine; and said capping agent includes long chain molecules with positive charge preferably with nitrogen containing group like polyethyleneimine.

17. Hair colour formulation/kit as claimed in anyone of claims 15 or 16 comprising desired concentrations of the actives of precursor silver salt and reducing agent in the range of from 0.005 % w/v to 2 % w/v and preferably in the concentration range of 0.01 % w/v, and wherein the concentration of capping agent is in the range of 0.05 - 5 ml/ 100 ml of the nanoparticle solution preferably 0.5 ml/ 100 ml of the nanoparticle solution.

18. A method of colouring the hair by ex-situ generated silver nanoparticles involving the formulation/ kit as claimed in claims 15-17 comprising applying to the hair ex-situ
synthesized and stabilized silver nanoparticles and allowing to stay for 15-60 mins for desired saturation of the colour on the hair in various colour shades by controlling the size of the silver nanoparticles.

19. A method as claimed in claim 18 wherein said desired ratio of nanoparticle solution: hair is 1:1 to 10:1.

Dated this the 21st day of March, 2015 Anjan Sen
Of Anjan Sen and Associates
(Applicants Agent)