DESC:FIELD OF INVENTION
The present invention relates to methods for indigo dyeing of non-porous objects and more particularly to a spray dyeing composition dyeing of non-porous objects and a method for preparation thereof.

BACKGROUND OF THE INVENTION
Porous objects include fabric, fibres, yarns and other inert surfaces which hold dye molecule or allow dye to penetrate or pass through them. It is very well known that dyeing of porous objects is easy due to their property of porosity. The non-porous objects are those objects which are not porous and do not allow the dye, air or water to pass or penetrate inside it or resist them to pass through. The non-porous objects include metals, stones, canvas, leather, ceramic, wood, bricks and the like. Due to the non-porosity behaviour of such objects, they do not hold any molecule on surface thereof or do not allow any molecule to pass therethrough. Presently a bridging element or an adhesive layer is used in order to dye non-porous objects.
Generally, the process of dyeing includes applying an adhesive layer as a bridging element on the non-porous object which is then followed by dyeing process. The dyeing techniques comprise spray dyeing or manual coating. The spray dyeing process is popular in automobile industries. Generally, pigment colours are used for surface dyeing. Referring to FIG. 1, a dyed non-porous object (100) in accordance with prior art is shown. The non-porous object (101) is applied with an adhesive such as an acrylic polymer as the bridging element (102). The adhesive (102) acts as a bridge between the dye molecules (103) and a surface of the non-porous object (101). The dye molecules (103) stick to the adhesive (102).
In current state of art, indigo is used as a colour or dye in the textile industry only and not for dyeing non-porous materials. The indigo reacts with cellulose in chemically reduced state and forms chemical bonds which allow it to hold by cellulose. In the non-porous surfaces, such chemical reaction would be difficult. Even if it happens the dye may not be able to penetrate to interior and may remain on top surface which can be easily removed.
Accordingly, there is need of a composition and method for applying indigo dye to non-porous objects with ease.

SUMMARY OF THE INVENTION
In an embodiment, the present invention provides an Indigo dyeing composition for spray dyeing of non-porous objects that includes a predefined amount of liquid indigo, a predefined amount of acetic acid, a predefined amount of hydrogen peroxide, a predefined amount of water, a predefined amount of fixer, a predefined amount of thickener and a predefined amount of binder.
A concentration of Indigo in the liquid indigo dye is from about 30% to about 40%. The method of indigo dyeing of the non- porous objects includes mixing the spray dyeing indigo composition with water, hydrogen peroxide and fixer for forming a spray dying mixture. In next step, the spray dying mixture is sprayed over the surface of the non-porous object and in the last step, the object is cured at a predetermined temperature for a predetermined time.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a dyed non-porous object in accordance with the prior art.

DETAILED DESCRIPTION OF THE INVENTION
Although specific terms are used in the following description for sake of clarity, these terms are intended to refer only to particular structure of the invention selected for illustration in the drawings, and are not intended to define or limit the scope of the invention.
In general aspect, the present invention discloses a composition and a method of indigo for spray dyeing of nonporous objects such as metal, stone, canvas, leather, ceramic, wood, bricks and the like.
According to an embodiment of the present invention, an indigo based composition for spray dyeing of a nonporous object comprises a liquid indigo dye and at least one binder.
In one preferred embodiment, the indigo based dyeing composition comprises a predefined amount of liquid indigo mixture in a range from about 0.5 % w/w to about 7.5 % w/w, a predefined amount of acetic acid in a range from about 1.5 % w/w to about 2 % w/w, a predefined amount of hydrogen peroxide in a range from about 2 % w/w to about 2.5 % w/w, a predefined amount of water in a range from about 65.3 % w/w to about 60.4 % w/w, a predefined amount of fixer in a range from about 1 % w/w, a predefined amount of thickener in a range from about 1.2 % w/w to about 1.6 % w/w and a predefined amount of binder in a range from about 25 % w/w.
In the preferred embodiment, the concentration of the indigo dye present in the liquid indigo is in a range from about 30% w/w to about 40% w/w. Most preferably, the concentration of the indigo dye in the liquid indigo is 40% w/w.
In an embodiment, the binder is selected from a group comprising acrylic, polyurethane, styrene, and vinyl acetate. Preferably, the binders are acrylic binders.
In accordance with another embodiment of the present invention, a method of indigo dyeing over a non- porous object includes sequential steps of mixing, spraying and curing. In an initial step, a spray dying mixture is prepared by mixing the spray dyeing indigo composition with water, hydrogen peroxide and a fixer. In next step, the spray dying mixture is sprayed over a surface of the non-porous object. In the last step, the non-porous object is cured at a predetermined curing temperature for a predetermined curing time. In the context of the present invention, the curing temperature is preferably cured at 1500C and the curing time is 3 minutes. However, it is understood here that the curing temperature and curing time may vary in alternative embodiments of the present invention.
The viscosity of the spray dyeing mixture is from about 1200 to about 1400 CPS. The dying mixture may be applied in a semi-transparent to fully solid coverage. However, it is understood here that the viscosity of the spray dying mixture may vary in alternative embodiments of the present invention.
In use, the spray dyeing composition of the present invention may be directly applied to the solid objects with the spray gun without the need of any bridging element for holding dye molecule on the solid surface. The composition of the present invention directly attaches to the non-porous object thereby entirely covering the surface of non-porous object subjected to dyeing.
Examples
Hereinafter, the present invention will be described in more detail based on example. The example is not intended to limit the scope of the present invention. It is believed the invention will be better understood from the following detailed example:
Example 1:
A spray dyeing composition prepared according to the present invention is shown in below Table-1:
Table-1
Acetic Acid 2%
Hydrogen Peroxide 2%
Water 62.3%
Liquid Indigo mix 5%
Fixer 1%
Thickener 2.66%
Binder (Acrylic) 25%
In accordance with this example, the spray dyeing composition includes a liquid indigo mixture of about 5% w/w, an acetic acid of about 2% w/w, hydrogen peroxide of about 2% w/w, water of about 62.3% w/w, a fixer of about 1% w/w, a thickener of about 2.66 % w/w and a binder of about 25% w/w. The spray dyeing composition so prepared is used for spray dyeing of a non-porous object. Initially, the dyeing solution was poured in cup of the spray gun and nozzles of the spray gun were adjusted with opening of the spray gun. The dye was sprayed at an air pressure from about 2 bar to about 5 bar. In the next step, the substrate was cured at about 1500 c for about 3 min. However, it was observed that surface area of the non-porous object was covered uniformly. The binders and/or adhesives used in the spraying mixture had made a film covering the surface uniformly. However, it is known that Indigo dye has bigger particle size as compared to commercial pigments. Due to this property, Indigo dye came over the surface of the object and it was observed that with atmosphere changes, the dye gave different levels of fading effect to the surface that lasted for long time thereby resulting into a creative look.
The embodiments of the invention shown and discussed herein are merely illustrative of modes of application of the present invention. Reference to details in this discussion is not intended to limit the scope of the claims to these details, or to the figures used to illustrate the invention.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.

,CLAIMS:
1. An Indigo dyeing composition for non-porous objects comprising:
a liquid indigo mixture in a range from about 0.5 % w/w to about 7.5 % w/w, a predefined amount of acetic acid in a range from about 1.5 % w/w to about 2 % w/w, a predefined amount of hydrogen peroxide in a range from about 2 % w/w to about 2.5 % w/w, a predefined amount of water in a range from about 65.3 % w/w to about 60.4 % w/w, a predefined amount of fixer in a range from about 1 % w/w, a predefined amount of thickener in a range from about 1.2 % w/w to about 1.6 % w/w and a predefined amount of binder in a range from about 25 % w/w.

2. The Indigo dyeing composition for non-porous objects as claimed in claim 1, wherein the liquid Indigo mixture includes the Indigo dye present in a range from about 30% to about 40%.

3. The Indigo dyeing composition for non-porous objects as claimed in claim 1, wherein the binder is selected from a group of acrylic, polyurethane, styrene, and vinyl acetate based binders.

4. A method of Indigo dyeing over a non- porous object comprising the steps of:
mixing predefined amounts of liquid indigo, acetic acid, hydrogen peroxide, water, fixer, thickener and binder to form a spray dyeing mixture;
spraying the spray dyeing mixture over a surface of the non-porous object; and
Curing the non-porous object at a predetermined curing temperature for predetermined curing time.
5. The method of indigo dyeing over a non- porous as claimed in claim 5, wherein the curing temperature is 150 0C.
6. The method of indigo dyeing over a non- porous as claimed in claim 5, wherein the curing time is 3 minutes.