DESC:FIELD OF THE INVENTION

The present invention relates to the Enteric capsule and process for making the same. More particularly, present invention relates to a composition for enteric capsules and process for making the same.

PRIOR ART

In prior art, various patents such as US5264223, US5431917, US5756123, US6410050, EP1057862, WO2007020529 describes the method for manufacturing of capsules. Another technology is to pre heat the stainless pins and dip in cold HPMC solution. The pin temperature gels the HPMC solution surrounding pin and gets picked up while removing pins from the dipping dish. The wet gel is than supplemented with additional heat so that the gel remains in same form and drying takes place. This process is also known as Thermo gelling process. The polymers that do not have thermo gelling behavior can be supported by thermo gelling agents commercially available. This is also described in various patents such as WO2008050209, US2014088202.
However, making HPMC capsules first and then coating with acid resistant polymer adds one more process step.

The variety of acid resistant polymers are commercially available such as polymethacrylates (co polymer of methacrylic acid either methylmethacrylate or ethyl acrylate), cellulose base polymers such as Cellulose acetate Phthalate (CAP). HPMC phthalate ( HPMC-P), HPMC Acetate succinate (HPMC-AS), polyvinyl acetate phthalate. Largely they are soluble and used in solvent.
More suitable form of composition for capsule manufacturing is making aqueous base composition.

BACKGROUND

The object of present invention is to develop hard capsule shell which will provide enteric property to the active pharmaceutical ingredient, food supplements and other nutritional products which undergo degradation in presence of acid.
Natural or synthetic substances which are acid unstable undergo chemical degradation in acidic environment present in stomach. Pharmaceutical drugs or compositions intended for oral consumption for human or animal, which releases in stomach are associated to gastric side effects such as gastric reflux or impairment of physiological and/or structural integrity of gastric mucosa. Such substances need complete protection from gastric pH.
One such form to administer the substance is capsule. Capsules are being produced for centuries and most popular polymer is Gelatin. People tried to coat the filled gelatin capsule with solvent based enteric compositions. However could not produce high quality reproducible results due to poor adhesion on gelatin surface.
HPMC capsules were found to be better. There were 2 different technologies for manufacturing hard HPMC capsules. In first stainless steel pins are dipped in HPMC solution or slurry optionally having some gelling agent such as carrageenan or Gellan gum or pectin. Co gelling aid suitable for that gelling agent is also added. The capsules are then removed from dipping dish and dried at cold atmosphere with lower RH so that the gelling agent supports formation and drying takes place due to low RH of surrounding air.
OBJECT OF INVENTION

Object of the present invention is to develop the enteric capsules and process for making the same.
Yet another object of the present invention is to manufacture hard capsule shell with HPMC-AS (HPMC Acetate succinate).
Yet another objective of present invention is to manufacture hard capsule shell which will have enteric property.
Yet another object of invention is to develop process to make aqueous composition of HPMC-AS.
It is also object of the present invention to identify suitable method of making aqueous solution to support thermo gelling behavior to manufacture capsule.
It is also object of the present invention to manufacture hard capsule with using thermo gelling technology.
Yet another object of the present invention is to find suitable alkali to make aqueous composition of HPMC-AS.
It is also the object of the present invention to eliminate the drawbacks and / or shortfalls of the prior art.

STATEMENT INVENTION:

Accordingly the invention provides An enteric capsule comprises HPMC-AS polymer reacted with alkali in water to form aqueous solution; adding processing aid such as colouring agents, plasticizers, surfactants to the said aqueous solution; heated steel pins 90 to 130 deg C dipped into the said aqueous poured into dipping dish maintained 10 to 35 deg C to form capsule.
Accordingly the invention also provides a process for preparation of the enteric capsule shell comprises the following steps:
a. aqueous composition of HPMC-AS is made by adding alkali in water then reacting polymer at low temperature;
b. processing aid such as colouring agents, plasticizers, surfactants are added to the said aqueous composition of step (a) maximum of 10% on dry polymer composition;
c. pouring the said solution step(b) in dipping dish;
d. preheating the stainless steel pins to temperatures between 90 to 130 deg C prior to dipping;
e. dipping the said preheated stainless steel pins of step (d) in solution of step (c) by maintaining the temperature between 10 to 35 deg C;
f. withdrawing the pins at a predefined sequence of velocity and time;
g. distributing and transferring the picked wet mass on the pins to oven type of tunnel maintaining the temperature of oven between 120 to 60 deg C;
h. subjecting the pins to low temperature air blast between 20 to 40 deg C when the wet shell water content reaches below 50% till the time shell moisture reaches below 8%;
i. removing the said shells of (h) from pins and cutting the same to required length for joining together to form capsule.

BRIEF DESCRIPTION OF THE INVENTION

According to the preferring embodiments of the present invention, hard capsules can be produced having enteric property. The enteric polymer is HPMC-AS. HPMC-AS is first reacted with alkali to make aqueous composition. Aqueous solution of HPMC-AS is not having rheological property to support capsule manufacturing technology. For this suitable alkali and alkali concentration need to be optimized. To this processing aids are added such as colourants, plasticizers, surfactants etc. The capsules are produced as follows:
(i) Aqueous composition of HPMC-AS is made by adding alkali in water then reacting polymer at low temperature.
(ii) Processing aid such as colouring agents, plasticizers, surfactants are added to maximum of 10% on dry polymer composition.
(iii) The solution is then poured in dipping dish.
(iv) Stainless steel pins are pre heated to temperatures between 80 to 120 deg C prior to dipping.
(v) Pins are dipped in solution of temperature between 15 to 25 deg C
(vi) Pins are withdrawn at a predefined sequence of velocity and time.
(vii) The picked wet mass is then distributed and transferred to oven type of tunnel. The temperature is subjected between 120 to 60 deg C
(viii) Once the wet shell water content reaches below 50 % the pins are subjected to low temperature air blast between 30 to 40 deg C till the shell moisture reaches below 8 %
(ix) The shells are then removed from pins, cut to required length and then joined together to form capsule.

DETAILED DESCRIPTION OF THE INVENTION

Capsule manufacturing is mainly dependent on polymers rheological behavior. Mainly its viscosity at the temperature of dipping, maximum viscosity it can attain while setting and whether it has gelling ability or not.
In thermo gelling technology all these values are to be evaluated by gradually increasing the temperature. Viscosity at dipping temperature is evaluated by subjecting polymer solution in small cylinder of Brookefield viscometer LV DV II+pro viscometer with spindle no S-31 and at 100 rpm. Maximum viscosity is measured on Anton Paar rheometer model- MCR51 and by rotational method with 0.5 sec-1 shear rate. The temperature is gradually increased and viscosity constantly measured. We get onset of Gelation and highest viscosity at certain temperature. Gelling ability is measured by measuring polymer solutions storage modulus (G’) and loss modulus (G”). Initially loss modulus ia high and storage modulus is low. As the temperature increases the storage modulus increases. The point at which both cross, is known as gel point. This is also measured on Anton Paar rheometer model – MCR51 and in Oscillation mode. The strain maintained at 20% and angular frequency maintained at 10 rad/sec.
All the above measurements decide the suitable alkali to be used and also its concentration in the solution.
According to present invention the acid resistant polymer and film forming polymer is HPMC Acetate Succinate (HPMC-AS) only.
HPMC-AS means polymer hydroxypropyl methyl cellulose acetate succinate. HPMC-AS is commonly known in the field of polymers with the additional alternative nomenclature: Hypromelose acetate sucinate. Cellulose,2-hydroxypropylmethyl ether, acetate, hydrogen butanedioate. Its CAS registry number is 71138-97-1.
Commercially available HPMC-AS is AffinisolTM HPMCAS from DOW, AQOAT from Shinetsu and Aquasolve AS from Ashland. Shinetsu has different grades corresponding to its succinoyl group and acetyl group range. “L” grade has acetyl group 5-9% and Succinoyl group 14-18%. “M” grade has acetyl group 7-11% and Succinoyl group 10-14%.“H” grade has acetyl group10-14% and Succinoyl group 4-8%. The varying substitution combination decides the pH at which the polymer will began to dissolve. It also has the powder in micronized grade ( F) and granular grade (G). “F” grade has average particle size as 1 micron where as “G” grade has average particle size as 5 microns.
In another embodiment the HPMC -AS is of low pH grade
In another embodiment the HPMC-AS is granular grade
To make clear solution HPMC-AS needs to be neutralized. Neutralisation means succinis acid groups present in the HPMC-AS polymer is neutralized or converted from the protonated to anionic form by addition of an alkaline material.
The preferred alkali selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonium hydroxide (NH4OH),
The composition of present invention may further comprise plasticizers, surfactants, anti microbial agents, coloring agents and so on.
The coloring agents and opacifiers are selected from permitted colorant and dyes as listed in Rule 27 of Drugs and Cosmetics Act and Rule (India) and permissible under the regulatory requirements of the country of use. They comply with the Bureau of Indian Standards (BIS) and / or Code of Federal Regulations (CFR) and / or EEC directives.
In an embodiment, the coloring agent may be a color selected from the group comprising annatto, carotene, chlorophyll, cochineal, curcumin, caramel, riboflavin, red iron oxide, yellow iron oxide, titanium di-oxide, black iron oxide and mixtures thereof.
In yet another embodiment, the coloring agent may be selected from quinazarine green, alizarin cyanine green, fast green, tartrazine, sunset yellow, quinoline yellow, erythrosine, eosin YS, toney red, ponceau 4R, carmoisine, indigo carmine, brilliant blue, orange G, resorcin brown, naphthol blue black, allura red, and combinations thereof.
In another embodiment, the coloring agent may be lake salts (example aluminum) any of the above listed water soluble coloring agents and combinations thereof.
The coloring agent is preferably used in an amount of from 0.01 to about 8% w/w of dry polymer.
The plasticizers and surfactants are selected from glyceryl esters, glycol esters, sorbitan monoesters, sorbitan polyoxyethylene esters, polyoxyethylene ethers, glycerols, polyethylene glycols, polyols, fatty acid esters, glycerol polyethylene, glycol ricinoleate, macrogolglycerides, SLS, Tryethyl citrate (TEC), Actyl Tryethyl citrate (ATEC), triacetine and mixture thereof.
The plasticizers and surfactants are preferably used in an amount of from 0.01 to about 5% w/w of acid resistant polymer.
The detailed manufacturing process for preparation of improved capsule shell comprises the following steps:
(i) Aqueous composition of HPMC-AS is made by adding alkali in water then reacting polymer at low temperature.
(ii) Processing aid such as colouring agents, plasticizers, surfactants are added to maximum of 10% on dry polymer composition.
(iii) The solution is then poured in dipping dish.
(iv) Stainless steel pins are pre heated to temperatures between 90 to 130 deg C prior to dipping.
(v) Pins are dipped in solution of temperature between 10 to 35 deg C
(vi) Pins are withdrawn at a predefined sequence of velocity and time.
(vii) The picked wet mass is then distributed and transferred to oven type of tunnel. The temperature is subjected between 120 to 60 deg C
(viii) Once the wet shell water content reaches below 50 % the pins are subjected to low temperature air blast between 20 to 40 deg C till the shell moisture reaches below 8 %
(ix) The shells are then removed from pins, cut to required length and then joined together to form capsule.
(x)
The present invention will now be described with reference to the examples below:

Example – 1
S-1) Preparation of 1kg Aqueous composition of HPMC-AS with NaOH
Take 185 gm of HPMC AS of shinetsu LG grade. Disperse it in (W11) gm cold water of 10 deg C under constant stirring. Also take (N1) gm of NaOH and dissolve it in (W12) gm of water. Slowly add the caustic solution in the dispersion under stirring of HPMC-AS and water. The reaction starts and aqueous solution of HPMC-AS get ready. Hold it for some time to eliminate foam and bubbles.
Trial code HPMC-AS in gm Water-W11 in gm NaOH in gm – N1 Water-W12 in gm TEC in gm
T1-1 185 770 8.3 36.7 0.2
T1-2 185 760 10.2 44.8 0.2
T1-3 185 750 12.0 53.0 0.2
T1-4 185 735 14.8 65.2 0.2

S-2) Preparation of 1kg Aqueous composition of HPMC-AS with KOH
Take 185 gm of HPMC AS of shinetsu LG grade. Disperse it in (W21) gm cold water of 10 deg C under constant stirring. Also take (K1) gm of KOH and dissolve it in (W22) gm of water. Slowly add the KOH solution in the dispersion under stirring of HPMC-AS and water. The reaction starts and aqueous solution of HPMC-AS get ready. Hold it for some time to eliminate foam and bubbles.

Trial code HPMC-AS in gm Water-W21 in gm KOH in gm –K1 Water-W22 in gm TEC in gm
T2-1 185 745 12.9 57.1 0.2
T2-2 185 735 14.8 65.2 0.2
T2-3 185 725 16.6 73.4 0.2
T2-4 185 715 18.5 81.5 0.2

S-3) Preparation of 1kg Aqueous composition of HPMC-AS with NH4OH
Take 185 gm of HPMC AS of shinetsu LG grade. Disperse it in (W31) gm cold water of 10 deg C under constant stirring. Slowly add (A1) gm Ammonia solution (30%) in the dispersion under stirring of HPMC-AS and water. The reaction starts and aqueous solution of HPMC-AS get ready. Hold it for some time to eliminate foam and bubbles.
Trial code HPMC-AS in gm Water-W31 in gm Ammonia in gm –A1 TEC in gm
T3-1 185 796.5 18.5 0.2
T3-2 185 790.5 24.5 0.2
T3-3 185 784.0 31.0 0.2
T3-4 185 778.0 37.0 0.2

S-4) Preparation of 1kg Aqueous composition of HPMC-AS with combination of NaOH, KOH and NH4OH
Take 185 gm of HPMC AS of shinetsu LG grade. Disperse it in (W41) gm cold water of 10 deg C under constant stirring. Slowly add (A1) gm Ammonia solution (30%) and (X) gm of NaOH or KOH (20% solution) in the dispersion under stirring of HPMC-AS and water. The reaction starts and aqueous solution of HPMC-AS get ready. Hold it for some time to eliminate foam and bubbles.
Trial code HPMC-AS in gm Water-W31 in gm Ammonia in gm –A1 NaOH in gm - (X) KOH in gm – (X) TEC in gm
T4-1 185 778.0 9.3 27.7 - 0.2
T4-2 185 771.8 6.2 37.0 - 0.2
T4-3 185 759.5 9.3 - 46.2 0.2
T4-4 185 753.3 6.2 - 55.5 0.2

Example – 2
Measurement of rheological behaviors.
Measure following parameters
1- Measurement of viscosity at 25 deg C
Take small sample in sample holder of Brooke field LVDV II+pro viscometer. Use spindle no S-31 and measure viscosity at 25 deg C at 100 rpm.
2- Measurement of gel point
Take small sample in sample holder of Anton Paar MCR51 rheometer. By using oscillation mode measure storage modulus (G’) and loss modulus (G”). Set the strain as 20% and angular frequency as 10 rad/sec. Measure the values by gradually increasing temperature from 20 to 80 deg C. The point of intersection is gel point.
3- Measurement of peak viscosity
Take small sample in sample holder of Anton Paar MCR51 rheometer. Measure viscosity by using rotational mode. Set the shear rate as 0.5 sec-1. Measure the values by gradually increasing temperature from 20 to 80 deg C. The viscosity will start increasing at some temperature and reach to peak value. It will then drop. Note peak viscosity value.

Result –
Trial no Viscosity at 25 C - cps Gel point in C Peak viscosity-cps Trial no Viscosity at 25 C - cps Gel point in C Peak viscosity-cps
T1-1 7300 42 169000 T3-1 5600 62 8250
T1-2 3100 55 70400 T3-2 3720 62 4400
T1-3 2700 60 10200 T3-3 3200 64 3670
T1-4 2200 61 9500 T3-4 3020 64 3400

T2-1 8200 43 130000 T4-1 10300 56 76000
T2-2 3500 50 92300 T4-2 8500 58 53000
T2-3 2950 52 71600 T4-3 9250 56 63200
T2-4 2600 60 10300 T4-4 8000 57 43500

As can be seen that trials where T1-1 and T2-1 solutions were used gel points are lower temperature and also peak viscosity are high. As the alkali concentration increases, the rheological properties gets changes and solution becomes clear however peak viscosity gets lowered. This is very critical for good formation of shells as well as manufacturing shells at high machine speeds.

Example – 3
Manufacturing capsules.
Solution were prepared as per few trial combination. The solution was poured in dipping dish and maintained at 22 deg C. Pins were pre heated between 90 to 130 deg C and then dipped in dipping solution. The picked wet mass is then distributed around pin and subjected to high temperature in oven type tunnel. The air temperature is varied between 120 to 65 deg C till the shell water content reduces to below 50 %. The pins with wet film is then exposed to cold air blast of temperature between 20 to 40 deg C. The dried shells were then removed from pin , cut to specified length and joined to form capsules. The capsules were then evaluated for appearance, defects, taste, brittleness strength etc.
Results –
Trial no Formation & Appearance Defects
Taste Brittleness
Strength
T1-1 Good formation No defect Good, Salty No Good
T1-3 No formation Low dome Good, Salty No weak
T2-1 Good formation No defect Good, Salty No Good
T2-4 No formation Low dome Good, Salty No weak
T3-2 No formation Low dome Bitter Brittle weak
T3-3 No formation Low dome Bitter Brittle weak
T4-1 No formation Low dome Good, Salty No weak
T4-3 No formation Low dome Good, Salty No weak

As can be seen, good capsules can be formed by skill known to operators with opimised alkali content (T1-1 and T2-1) . With other combinations, the shell formation is difficult and the slell had run down effect.

Example – 4
In vitro acid solubility and drug release test.
Capsules were manufactured with trial no T1-1 and T2-1. The capsules were filled with 325 mg Acetaminophen. The capsules were subjected to dissolution test in 0.1 N HCL media and as per Acetaminophen monograph described in USP. Drug release was estimated by taking periodic samples at regular interval.
Results –
Time T1-1 capsules T2-1 capsules
0 min 0 % 0 %
20 min 0 % 0 %
40 min 0 % 0 %
60 min 0 % 0 %
80 min 0 % 0 %
100 min 5 % 3 %
120 min 9 % 9 %

In vitro drug release test at mixed phosphate buffer
The same capsules after exposing to 0.1N HCL for 2 hrs, were subjected to 6.8 mixed phosphate buffer as described in USP. Drug release was estimated by taking periodic samples at regular interval.
Results –
Time T1-1 capsules T2-1 capsules
0 min 0 % 0 %
15 min 16 % 19 %
30 min 53 % 51 %
45 min 75 % 78 %
60 min 84 % 83 %

As can be seen, based on the requirement capsules with different release pattern and having enteric can be manufactured.

DETAILS OF INVENTION:

• An aqueous composition for making hard capsule shell comprising,
a. An aqueous solution made of Enteric and film forming polymer
b. An suitable alkali to neutralize enteric polymer
c. Processing aid
d. Water.

The enteric and film forming polymer is HPMC acetate succinate and is having acetyl group 5-9% and Succinoyl group 14-18% and of granular grade.
The alkali is selected from sodium hydroxide, potassium hydroxide, ammonia and/or mixture thereof to neutralize the enteric polymer. At least one processing aid is plasticizer present in an amount ranging from 0.1% to 5 % by weight of enteric polymer present in the composition. The plasticizer is selected from glyceryl esters, glycol esters, sorbitan monoesters, sorbitan polyoxyethylene esters, polyoxyethylene ethers, glycerols, polyethylene glycols, polyols, fatty acid esters, glycerol polyethylene, glycol ricinoleate, macrogolglycerides, SLS, Tryethyl citrate (TEC), Actyl Tryethyl citrate (ATEC), triacetine and mixture thereof. At least one processing aid is colouring agent present in an amount ranging from 0.1% to 10 % by weight of total polymer present in the composition. The colouring agent is selected from permitted colorant and dyes as listed in Rule 27 of Drugs and Cosmetics Act and Rule ( India) and permissible under the regulatory requirements of the country of use. They comply with the Bureau of Indian Standards ( BIS) and / or Code of Federal Regulations (CFR) and / or EEC directives.
The colouring agent is selected from the group comprising annatto, carotene, chlorophyll, cochineal, curcumin, caramel, riboflavin, red iron oxide, yellow iron oxide, titanium di-oxide, black iron oxide and mixtures thereof.
The colouring agent is selected from quinazarine green, alizarin cyanine green, fast green, tartrazine, sunset yellow, quinoline yellow, erythrosine, eosin YS, toney red, ponceau 4R, carmoisine, indigo carmine, brilliant blue, orange G, resorcin brown, naphthol blue black, allura red, and combinations thereof.
The colouring agent is selected from lake salts (example aluminum ) any of the above listed water soluble coloring agents and combinations thereof.

• A capsule shell comprising of 92-96% of enteric polymer and is hard shell.

• A method of manufacturing hard shell according to the present invention consists of the following steps:
a. Aqueous composition of HPMC-AS is made by adding alkali in water then reacting polymer at low temperature.
b. Processing aid such as colouring agents, plasticizers, surfactants are added to maximum of 10% on dry polymer composition.
c. The solution is then poured in dipping dish.
d. Stainless steel pins are pre heated to temperatures between 90 to 130 deg C prior to dipping.
e. Pins are dipped in solution of temperature between 10 to 35 deg C
f. Pins are withdrawn at a predefined sequence of velocity and time.
g. The picked wet mass is then distributed and transferred to oven type of tunnel. The temperature is subjected between 120 to 60 deg C
h. Once the wet shell water content reaches below 50 % the pins are subjected to low temperature air blast between 20 to 40 deg C till the shell moisture reaches below 8 %
i. The shells are then removed from pins, cut to required length and then joined together to form capsule.
,CLAIMS:1. An enteric capsule comprises HPMC-AS polymer reacted with alkali in water to form aqueous solution;
adding processing aid such as colouring agents, plasticizers, surfactants to the said aqueous solution;
pouring the said aqueous solution into dipping dish by maintaining the temperate of the solution in the range of 10 to 35 deg C;
dipping the pre-heated steel pins of about 90 to 130 deg C into the said aqueous solution to form the capsule.

2. A process for preparation of the enteric capsule shell comprises the following steps:
a. aqueous composition of HPMC-AS is made by adding alkali in water then reacting polymer at low temperature;
b. processing aid such as colouring agents, plasticizers, surfactants are added to the said aqueous composition of step (a) maximum of 10% on dry polymer composition;
c. pouring the said solution step(b) in dipping dish;
d. preheating the stainless steel pins to temperatures between 90 to 130 deg C prior to dipping;
e. dipping the said preheated stainless steel pins of step (d) in solution of step (c) by maintaining the temperature between 10 to 35 deg C;
f. withdrawing the pins at a predefined sequence of velocity and time;
g. distributing and transferring the picked wet mass on the pins to oven type of tunnel maintaining the temperature of oven between 120 to 60 deg C;
h. subjecting the pins to low temperature air blast between 20 to 40 deg C when the wet shell water content reaches below 50% till the time shell moisture reaches below 8%;
i. removing the said shells of (h) from pins and cutting the same to required length for joining together to form capsule.
3. The process as claimed in claim 2 wherein the said alkali is selected from sodium hydroxide, potassium hydroxide, ammonia and/or mixture thereof.
4. The process as claimed in claim 3 wherein the said alkali NaoH or KOH or Ammonia solution (30%) and of NaOH or KOH (20% solution) slowly added in the dispersion under stirring of HPMC-AS and water.
5. The process as claimed in claims 2 to 4 wherein the said HPMC –AS (acetate succinate) and is having acetyl group 5-9% and Succinoyl group 14-18% and of granular grade.
6. The process as claimed in claims 2 to 5 wherein the said HPMC –AS (acetate succinate) is above 90% by composition on dry basis in the final capsule shell.
7. The process as claimed in claims 2 to 5 wherein at least one processing aid is plasticizer present in an amount ranging from 0.1% to 5 % by weight of enteric polymer present in the composition.
8. The process as clamed in claims 2 to 6 wherein the said plasticizer is selected from glyceryl esters, glycol esters, sorbitan monoesters, sorbitan polyoxyethylene esters, polyoxyethylene ethers, glycerols, polyethylene glycols, polyols, fatty acid esters, glycerol polyethylene, glycol ricinoleate, macrogolglycerides, SLS, Tryethyl citrate (TEC), Actyl Tryethyl citrate (ATEC), triacetine and mixture thereof.
9. The process as claimed in claims 2 to 7 wherein at least one processing aid is colouring agent present in an amount ranging from 0.1% to 10 % by weight of total polymer present in the composition.
10. The processas claimed in claims 2 to 8 wherein the said colouring agent is selected from the group comprising annatto, carotene, chlorophyll, cochineal, curcumin, caramel, riboflavin, red iron oxide, yellow iron oxide, titanium di-oxide, black iron oxide and mixtures thereof.
11. The process as claimed in claims 2 to 8 wherein the said The colouring agent is selected from quinazarine green, alizarin cyanine green, fast green, tartrazine, sunset yellow, quinoline yellow, erythrosine, eosin YS, toney red, ponceau 4R, carmoisine, indigo carmine, brilliant blue, orange G, resorcin brown, naphthol blue black, allura red, and combinations thereof.
12. The process as claimed in claims 2 to 10 where the said colouring agent is selected from lake salts (example aluminum ) any of the water soluble coloring agents listed in claim 8 or 9 and combinations thereof.