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

摘要

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.

主权项

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/cm2 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 (SiH4) 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.