Method and device for microwave plasma deposition of a coating on a thermoplastic container surface

Abstract

The deposition of a coating on a thermoplastic container surface using low pressure plasma by excitation of a precursor gas with UHF electromagnetic waves in a circular shaped vacuum cavity receiving the container is provided. It includes dimensioning the cavity with respect to the frequency of the UHF electromagnetic waves so as to obtain a coupling mode generating several electromagnetic fields inside the cavity. In particular a TM 120 coupling mode is provided which generates two central fields ( 4 A , 4 B ) inside the cavity, whereby two containers can be simultaneously treated in said cavity.

1 .- 2 . (canceled) 
   
   
       3 . A device for depositing a coating on one face of at least one container made of a thermoplastic using a low-pressure plasma by excitation of a precursor gas by UHF electromagnetic waves in a circular vacuum chamber containing said container, which device comprises a UHF wave generator and a UHF waveguide for connecting said generator to a window of a side wall of the chamber, wherein the chamber is sized in relation to the frequency of the UHF electromagnetic waves in order to establish a TM 120 coupling mode that generates two central fields in the cavity, whereby it is possible for two containers to be simultaneously treated inside said chamber. 
   
   
       4 . The device as claimed in  claim 3 , wherein the generator emits an electromagnetic wave having a frequency f=2.455 GHz and in that the diameter of the chamber is approximately 273 mm. 
   
   
       5 . The device as claimed in  claim 3 , wherein said chamber contains two quartz envelopes amounted in a vacuum-tight manner in the chamber and placed respectively substantially coaxial with the two central fields, wherein said chamber includes a single window for injecting the UHF waves, said window being located along the axis of symmetry of the two central fields, and wherein a single cover for closing off said chamber is equipped with a single coupler for connection to a vacuum source, which coupler is divided into two in order to be connected to said two respective envelopes, with two precursor gas injectors that are connected to a single precursor gas source and with two support means for the two respective containers. 
   
   
       6 . The device as claimed in  claim 5 , wherein the device includes positionally adjustable bottom and top plates suitable for acting on the respective return fields so as to refine the coupling in relation with various types of container to be treated. 
   
   
       7 . The device as claimed in  claim 5 , being designed for coating the inside of containers and wherein for this purpose, the precursor gas injectors are designed to sit inside the respective containers when said containers are supported by support means in the envelopes.