FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFIC A TION
(See section 10, rule 13)
1. Title of the invention
A FABRIC CAPABLE OF ABSORBING INFRARED RADIATION
2. Applicant(s)

Name
TATA CHEMICALS LTD.
TATA ADVANCED MATERIALS LTD.
3. Preamble to the description

Nationality
INDIA
INDIA

Address
BOMBAY HOUSE, 24 HOM1 MODI STREET, MUMBA1 400001
NO. 10, JIGANI INDUSTRIAL AREA, JIGANI, BANGALORE-562106

COMPLETE SPECIFICA TION
The following specification particularly describes the invention and the manner in which it is
to be performed.


The present disclosure generally relates to a fabric capable of absorbing infrared radiation. The present disclosure also generally relates to a process for manufacturing a fabric capable of absorbing infrared radiation.
BACKGROUND
Electromagnetic radiation having wavelength from about 0.7 micrometers to about 1000 micrometers is known as infrared radiation. The infrared range may further be divided into three regions with near infrared having with wavelengths from about 0.70 micrometer to about 2.5 micrometres, mid infrared having wavelengths from about 2.5 to about 50 micrometres; and far infrared having wavelengths from about 50 to 1,000 micrometres.
Fabrics that can absorb infrared radiations find use in many areas. Fabrics capable of absorbing infrared radiations are used for making article of clothing or used for covering objects, such as tents to protect personnel and equipment from detection by infra-red detecting equipment. Such fabrics may also be used for making winter garments, interiors and leisure goods having increased heat retaining ability.
Various methods have been developed for manufacturing fabrics capable of absorbing infrared radiation.
One method involves dying the fabric with an infrared absorbing dyes or pigments. However, infrared absorbing dyes have a narrow range of absorbance and absorb infrared radiation over a very specific range of wavelength. Therefore, for manufacturing fabrics that can absorb infrared radiation over a wider range of wavelength, a number of dyes have to be used on the same fabric. This makes it a cumbersome process.
Another method involves incorporating carbon black or hexaboride particles into the fibres directly. However, these methods requires the manufacturing of specific fibers for

making the fabric capable of absorbing infrared radiation, thereby limiting its use and making such fabrics costly.
Therefore, a fabric capable of absorbing infrared radiation is required. The fabric should be such that it is can absorb radiations over a wide range. Moreover the fabric should be should be easy to manufacture.
SUMMARY
In one aspect, the present disclosure is directed to a fabric including metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
In another aspect, the present disclosure is directed to a nylon fabric including metal nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
In yet another aspect, the present disclosure is directed to a method of manufacturing a fabric. The method includes preparing metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum, and coating the metal nano particles on the fabric.
In yet another aspect, the present disclosure is directed to a solution for coating a substrate including metal nano particles, the metal nano particles including nano triangles and capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The accompanying drawing illustrates the preferred embodiments of the invention and together with the following detailed description serves to explain the principles of the invention.

Figure 1 illustrates the Ultra Violet-Visible-Near Infrared absorption of a nylon cloth before and after coating with gold nano triangles.
DETAILED DESCRIPTION
To promote an understanding of the principles of the invention, reference will be made to the embodiments illustrated in the drawing and specific language will be used to describe the same. It will nevertheless be understood that no limitation of scope of the invention is thereby intended, such alterations and further modifications in the described invention and such further applications of the principles of the inventions as illustrated therein being contemplated as would normally occur to one skilled in art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
A fabric capable of absorbing infrared radiation is disclosed. More particularly a fabric capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum is disclosed. The fabric includes at least some fibres associated with metal nano particles capable of absorbing infrared radiation.
The metal nano particles are preferably anisotropic in shape. Anisotropic shapes include prisms, triangular and generally refer to particles having properties that are directionally oriented. In accordance with an aspect, the metal nano particles are triangular in shape. In accordance with an aspect the metal nanoparticles are of gold or silver. The metal nano triangles have an edge length in the range of 0.05 micrometers to 1.8 micrometes.

The fabric on which the nano particles are coated may be any suitable fabric including but not limited to nylon, cotton, silk, wool, polyester, polyolefin, acrylic or their blends. The choice of fabric will depend on the intended application of the material.
In accordance with a preferred embodiment, the fabric is nylon. Nylon fabric is preferred as nylon fabrics are strong and light weight fabrics. Nylon wears better than fabrics made from 100 percent cotton. Nylon also has the advantage of drying rapidly and maintains a sharp military appearance longer. In accordance with an aspect the fabric may be coloured nylon cloth that has been previously dyed with a single or plurality of dyes.
At least some portion of the fabric is coated with the metal nano particles. The entire fabric may be coated with the metal nano particles. Alternatively, only some part of the fabric may be coated with metal nano particles. In accordance with aspect, the metal nano particles may also be used in combination with other dyes or pigments that are capable of absorbing infrared radiation.
The metal nano particles may be prepared by any known processes for the preparation of anisotropic shaped nano particles. By way of specific example, a method of preparation of gold nano triangles in an aqueous medium is described.
The process of synthesizing triangular shaped gold nano particles comprises of preparing a chloroauric acid solution, more specifically preparing 100 ml of 10 to 3 Molar chloroauric acid solution in distilled water. A lemon grass extract was prepared in 500 mL distilled water. 50 grams of lemon grass was washed with distilled water, dried in air at room temperature and cut into small pieces. To the cut pieces of lemon grass 500 mL of distilled water was added and heated in autoclave at ~ 120 °C at 20 psi pressure for 20 min. The solution so obtained was cooled solution to room temperature and filtered using filter paper.

To 10mL of chloroauric acid solution 2mL of lemon grass extract was added and kept at room temperature for 12 to 16 hours. Chloroaurate ions are reduced by lemon grass extract to form gold nano triangles in the solution. In accordance with an aspect the amount of lemon grass extract solution can be varied from 0.5 mL to 2.5 mL to increase the number of triangles in the solution and hence the near infrared absorption.
Similarly, by way of specific example, a method of preparation of silver nano triangles in an aqueous medium is described. The process of synthesizing triangular shaped silver nano particles comprises preparing a silver nitrate solution, more specifically 100 mL of 0.008 M Silver nitrate solution is prepared using distilled water. A second solution of chitosan is prepared; more specifically a chitosan solution of 1 wt % is prepared in 5 wt % citric acid. A third solution of chitosan is prepared; more specifically a chitosan solution of 1 wt % is prepared in 5 wt % Ascorbic acid. 1 mL of the second solution is added to the 100 mL silver nitrate solution and stirred for five minutes at room temperature. To this solution 200 to l000uL of the third solution is added and the reaction mixture is stirred for 30 minutes. Silver nano triangles are formed in the solution.
A method for manufacturing a fabric capable of absorbing infrared radiation is disclosed. The method includes adding to a fabric metal nano particles including nano triangles capable of absorbing infrared radiation. The metal nano particles may be added to the fabric by any conventional method including but not limited to spraying, spin coating, solvent dispersion or printing, such as dipping, spreading, brushing, knife coating or rolling.
In accordance with an aspect the metal nano particles are sprayed on the fabric. The fabric may be heated before the metal nano particles are coated on the fabric. By way of a specific example the fabric is heated to a temperature between 75° C to 150° C prior to coating with metal nano particles.

In accordance with an aspect 0.03 to 0.4 milligrams of metal nano particles are required to coat one square centimeter of fabric.
The invention also provides for a solution for coating a substrate. The solution comprises metal nano particles, the metal nano particles including nano triangles and capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum. The nano triangles have an edge length in the range of 0.05 micrometers to 1.8 micrometers. The metal nano particles are of gold or silver. The solution may be coated on any substrate including but not limited to fabric, wood, plastic or metal.
The solution may be prepared by mixing metal nano particles in an aqueous solution. Alternatively, the solution may be prepared in accordance with the methods of preparing metal nano particles in an aqueous medium as described above. The solution should preferably have a concentration of metal nano particles such that substantially 0.03 to 0.4 milligrams of metal nano particles are coated on the substrate.
Specific embodiments are described below:
A fabric including metal nano particles, the metal nano particles including nano
triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
Such fabric(s), wherein the nano particles are of gold or silver.
Such fabric(s), wherein the fabric is any of nylon, cotton, silk, wool, linen, polyester, polyolefin, acrylic or their blends.
A nylon fabric including metal nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
Such fabric(s), wherein the nano triangles have an edge length in the range of 0.05 micrometers to 1.8 micrometers.

Such fabric(s) wherein the amount of metal nano particles is in the range of 0.03 to 0.4 milligrams per square centimetre of fabric.
A method of manufacturing a fabric comprising preparing metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum; and coating the metal nano particles on the fabric.
Such method(s), wherein the nano particles are of gold or silver.
Such method(s), wherein the fabric is heated prior to coating with metal nano triangles.
Such method(s), wherein the fabric is heated to a temperature between 75° C to 150° C prior to coating with metal nano particles.
Such method(s), wherein the fabric is any of nylon, cotton, silk, wool, linen, polyester, polyolefin, acrylic or their blends.
Such method(s), wherein the amount of metal nano particles coated on the fabric is in the range of 0.03 to 0.4 milligrams per square centimetre.
A solution for coating a substrate comprising metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
Such solution(s), wherein the nano triangles have an edge length in the range of 0.05 micrometers to 1.8 micrometers.
Such solution(s), wherein the metal nano particles are of gold or silver.
The following examples are provided to explain and illustrate certain preferred embodiments of the process of the invention.
Example 1: 20 ml of gold nano triangles are synthesized using lemon grass extract at room temperature. The gold nano triangles were coated on approximately 40 square

centimetre area of nylon cloth heated at about 75° C to 150° C. The gold nano particles solution was spray dried on the hot nylon cloth at the flow rate of 2mL/min. The solvent was evaporated and the nano particles were coated on the nylon cloth.
Eample 2: 20 ml of silver nano-triangles are synthesized using chitosan at room temperature. The silver nano-triangles were coated on approximately 40 square centimetre area of nyon cloth heated at about 75° C to 150° C. The silver nano triangle solution was spray dried on the hot nylon cloth at the flow rate of 2mL/min. The solvent was evaporated and the silver nano triangles were coated on the nylon cloth.
INDUSTRIAL APPLICABILITY
The fabric as disclosed above is capable of effectively absorbing radiation in the near infrared region of the electromagnetic spectrum. More particularly the fabric as disclosed can absorb radiations across a range of wavelengths in the near infrared region of the electromagnetic spectrum. By way of specific example a nylon cloth was coated with gold nano triangles. The absorbance of the nylon cloth coated with gold nano triangles as well as the absorbance of a nylon cloth without the coating of gold nano triangles was measured. As illustrated in figure 1, the nylon cloth coated with gold nano triangles strongly absorbs at about 700m and above in the near infrared region.
The embodiments of the invention, described above, are intended to be exemplary, and not limiting. Many variations are possible, within the scope of the invention. These and other modifications are to be deemed within the spirit and scope of the following claims.

We Claim:
1. A fabric including metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
2. A fabric as claimed in claim 1, wherein the nano particles are of gold or silver.
3. A fabric as claimed in any preceding claims, wherein the fabric is any of nylon, cotton, silk, wool, linen, polyester, polyolefin, acrylic or their blends.
4. A nylon fabric including metal nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
5. A fabric as claimed in claim 1 or 4, wherein the nano triangles have an edge length in the range of 0.05 micrometers to 1.8 micrometers.
6. A fabric as claimed in any preceding claim wherein the amount of metal nano particles is in the range of 0.03 to 0.4 milligrams per square centimetre of fabric.
7. A method of manufacturing a fabric comprising preparing metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum; and coating the metal nano particles on the fabric.

8. A method as claimed in claim 7, wherein the nano particles are of gold or silver.
9. A method as claimed in claim 7, wherein the fabric is heated prior to coating with metal nano triangles.
10. A method as claimed in claim 9, wherein the fabric is heated to a temperature between 75° C to 150° C prior to coating with metal nano particles.
11. A method as claimed in claim 7, wherein the fabric is any of nylon, cotton, silk, wool, linen, polyester, polyolefin, acrylic or their blends.
12. A method as claimed in claim 7, wherein the amount of metal nano particles coated on the fabric is in the range of 0.03 to 0.4 milligrams per square centimetre.
13. A fabric obtained by a process as claimed in claim 7.
14. A solution for coating a substrate comprising metal nano particles, the metal nano particles including nano triangles capable of absorbing a plurality of wavelengths of the near infrared radiation spectrum.
15. A solution for coating a substrate as claimed in claim 14, wherein the nano triangles have an edge length in the range of 0.05 micrometers to 1.8 micrometers.

16. A solution for coating a substrate as claimed in claim 14, wherein the metal nano particles are of gold or silver.
17. A fabric substantially as herein described with reference to and illustrated in the accompanying figure.
18. A method of manufacturing a fabric substantially as herein described with reference to and illustrated in the accompanying figure.
19. A solution for coating a substrate substantially as herein described with reference to and illustrated in the accompanying figure.

Essenese Obhan
Of Obhan & Associates
Agent for the Applicants