Process to deposit diamond like carbon as surface of a shaped object

Patent metadata

Field	Value
Publication number	US-9260781-B2
Application number	US-201013201210-A
Country	US
Kind code	B2
Filing date	Jan 27, 2010
Priority date	Feb 18, 2009
Publication date	Feb 16, 2016
Grant date	Feb 16, 2016

Abstract

A plasma based deposition process to deposit thin film on the inner surfaces of the shaped objects such as plastic or metallic object like bottles, hollow tubes etc. at room temperature has been developed. In present invention uniform hydrogenated amorphous carbon (also called Diamond-Like Carbon, DLC) films on inner surfaces of plastic bottles is successfully deposited. Applications of such product include entire food and drug industries. There is a huge demand of polyethylene terephthalate (PET) or polyethylene naphthalate (PEN)) bottles, meant for the storage of potable water, carbonated soft drinks, wines, medicines etc. However, the higher cost prohibits their wide, spread use. The cheaper alternative is to use plastic bottles inside coated with chemically inert material such as Diamond-Like Carbon (DLC) will be commercially viable. Inventor process can be scaled up for mass production. This process can also be used for coating on inner surface of metallic cane or tube with a carbide forming interlayer (like hydrogenated amorphous silicon) to get the DLC films with better adhesion to inner surface of metals.

First claim

We claim:

1. A process for deposition of diamond like carbon (DLC) films having enhanced adhesion and reduced stress as a protective coating on an inner surface of a shaped object such as a container, said process comprising the steps of:
i. cleaning the inner surface of the shaped object using an inert gas and placing the object inside a hollow cathode plasma enhanced chemical vapor deposition apparatus kept in a vacuum chamber;
ii. applying a base pressure of 10 −5 to 10 −6 torr to the vacuum chamber for removing the residual gases;
iii. injecting a hydrocarbon gas diluted in argon at a partial pressure in the range of 10-90% into the shaped object through holes of an inner electrode;
iv. applying a radio frequency of 13.56 MHz for a time period in the range of 8 to 10 mins to an outer electrode of the hollow cathode, wherein the outer electrode is in contact with the body of the shaped object and is connected to a power supply and the inner electrode lying inside the shaped object being used for delivery of the hydrocarbon gas, the outer electrode being insulated from outside using an insulating sheet and entire assembly being covered with a metal sheet which is at ground potential;
v. depositing the DLC films at a power density in the range of 50-2000 mW/cm 2 to the outer electrode, gas flow in the range of 5-100 sccm, chamber pressure in the range of 5-100 m torr and applying a self bias in the range of 50-200 volts such that initially the self bias is in the range of 50-70 volts and gradually increasing the self bias in the range of 150-200 volts, and temperature in the range of 25-30° C.; and
vi. breaking of vacuum by inserting air, to take out the DLC coated shaped object from the chamber;
wherein a thin layer consisting of hydrogenated amorphous silicon (a- Si:H) is deposited using silane (SiH 4 ) plasma discharge prior to deposition of a thick DLC layer of about a micron wherein the thick DLC layer on an inner surface of a plastic or metallic object facilitates better adhesion of DLC with the inner surface of the plastic or metallic object.

2. The process as claimed in claim 1 , wherein the shaped object or the container is a plastic or metal container.

3. The process as claimed in claim 1 , wherein the step of depositing of diamond like carbon (DLC) film is initially carried out at a self bias in the range of 50-70 volts for 1 to 2 minutes on the inner surface of a plastic or metallic object used and thereafter the self bias is gradually increased in the range of 150-200 volts for 8 to 10 minutes to get the hard DLC films.

4. The process as claimed in claim 1 , wherein the shaped object is selected from the group consisting of spherical, cubic, cylindrical or rectangular shaped objects and such similar shaped objects and the shape of the hollow cathode used for DLC coating corresponds to the shape of the object used for coating.

5. The process as claimed in claim 1 , wherein energy of ions is in the range of 60-80 -eV to achieve the hard DLC film with better adhesion on the inner surface of the shaped object in the range of 8 to 12 GPa.

6. The process as claimed in claim 1 , wherein the hydrocarbon gas is selected from the group consisting of acetylene, methane, benzene, cyclohexane, n-hexane, and toluene.

7. The process as claimed in claim 1 , wherein the self bias applied is directly proportional to applied Rf power and inversely proportional to pressure and the self bias is controlled to obtain the desired properties of DLC films over the inner surface of plastic or metallic object.

8. The process as claimed in claim 1 , wherein the shaped object is a bottle.

9. The process as claimed in claim 1 , wherein the power density ranges from 300-500 mW/cm 2 .

10. The process as claimed in claim 1 , wherein the DLC film is deposited at a rate ranging from 0.2 Å/sec to 4.7 Å/sec.

11. The process as claimed in claim 1 , wherein the DLC film has a hardness that increases from 8 GPa to 12 GPa as the self bias increases from 150 volts to 200 volts.

12. The process as claimed in claim 1 , wherein the DLC film has a stress ranging from 0.2 GPa to 0.5 GPa.

13. The process as claimed in claim 1 , wherein the DLC film has a hardness in the range from 8 to 15 GPa.

14. The process as claimed in claim 13 , wherein the DLC film has a stress in the range from 0.2 GPa to 0.5 GPa.

15. The process as claimed in claim 13 , wherein the DLC film has a hardness in the range from 12 to 15 GPa.

16. The process as claimed in claim 15 , wherein the DLC film has a stress in the range from 0.2 GPa to 0.5 GPa.

17. The process as claimed in claim 1 , wherein the hydrocarbon gas is diluted in argon at a partial pressure in the range of 40-60%.

Assignees

• Kumar Sushil
• Dixit Prakash Narain
• Rauthan Chandra Mohan Singh
• Council Scient Ind Res

Inventors

• Kumar Sushil
• Dixit Prakash Narain
• Rauthan Chandra Mohan Singh

Classifications

• C23C16/045

  Coating cavities or hollow spaces, e.g. interior of tubes; Infiltration of porous substrates · CPC title

• C23C16/509

  using internal electrodes · CPC title

• C23C16/45578

  Elongated nozzles, tubes with holes · CPC title

• C23C16/26 Primary

  Deposition of carbon only · CPC title

• C23C16/0272

  Deposition of sub-layers, e.g. to promote the adhesion of the main coating · CPC title