Abstract:
A method for removing a protective film from a surface of an article is provided. The protective film includes a primary protective layer (e.g., a diamond-like carbon layer) and a transition layer, the transition layer being formed directly upon the surface of the article and thereby facilitating an attachment/bond of the protective film to the article. The method includes the step of: disposing/placing the article having the protective film in a reaction chamber; bombarding the protective film (especially, the primary protective layer) with oxidative plasma beams along an edge portion of the protective film, the bombarding occurring until the transition layer in particular is exposed; and bombarding the transition layer with oxidative plasma beams to damage a configuration of the transition layer, thereby making it possible to remove the protective film.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to articles with a protective film thereon and, more particularly, to an apparatus and a method for removing a protective film from a surface of such article. 
   DESCRIPTION OF RELATED ART 
   Diamond-like carbon is a mostly metastable amorphous material but can include a microcrystalline phase. Diamond-like carbon contains both sp 2  and sp 3  hybridized carbon atoms. Diamond-like carbon includes amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) containing a significant sp 3  bonding. The amorphous carbon where sp 3  bonding constitutes 85% or more of the bonds is called highly tetrahedral amorphous carbon (ta-C). The sp 3  bonding gives valuable diamond-like properties such as mechanical hardness, low friction, optical transparency and chemical inertness to diamond-like carbon films. Diamond-like carbon films have many advantages, such as being useful for processes involving room temperature deposition, deposition onto steel or plastic substrates, and superior surface smoothness. 
   Because of excellent properties such as corrosion resistance and wear resistance, the diamond-like carbon film is a suitable protective film material for various articles such as molds, cutting tools and hard disks. However, at present, the diamond-like carbon films suffer from frequent localized spalling due to the inherent high residual stress, incomplete pre-treatment, and other operation defects. An effective method for removing the damaged diamond-like carbon film to permit recoating with a new film thereof is urgently needed. 
   This need has attempted to be addressed through the use of dry sandblasting or wet sandblasting methods. Diamond-like carbon films on the surfaces of a faulty article can be removed by means of mechanical erosion. However, sandblasting can potentially damage the surfaces of an article, making this method unfit for articles that require high precision, low surface roughness and/or sharp angles. 
   Therefore, it is desired to provide an improved apparatus and a method that overcomes the above-described problems by facilitating the removal of a diamond-like protective film from an article without potentially damage the surface(s) of the underlying article. 
   SUMMARY OF THE INVENTION 
   A method for removing a protective film from a surface of an article is provided. The protective film includes a primary protective layer and a transition layer, the transition layer being formed directly upon the surface of the article and thereby facilitating an attachment/bond of the protective film to the article. The method includes the step of: disposing/placing the article having the protective film in a reaction chamber; bombarding the protective film (specifically, the primary protective layer (e.g., a diamond-like carbon layer)) with oxidative plasma beams along an edge portion of the protective film, the bombarding occurring until the transition layer in particular is exposed; and bombarding the transition layer with oxidative plasma beams to damage a configuration of the transition layer, thereby making it possible to remove the protective film. 
   An apparatus for removing a protective film from an article is provided. The apparatus includes a reaction chamber, a working platform, and an oxidative plasma source. The working platform is provided for supporting the article thereon and is arranged in the reaction chamber. The oxidative plasma source is provided for generating oxidative plasma beams to bombard the protective film of the article and is arranged in the reaction chamber. Both the working platform and the oxidative plasma source are rotatably and/or moveably arranged in the reaction chamber in order to enable the article and the oxidative plasma source each to be adjusted to a suitable position. Such adjustments facilitate the generated oxidative plasma beams reaching the protective film, thereby making it possible to achieve the removal of the protective film from the article. 
   Advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many aspects of the present apparatus and method for protective film removal can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus and method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a schematic view of an apparatus for removing a protective film from an article, in accordance with a preferred embodiment; 
       FIG. 2  is a schematic view of a configuration of the article having the protective film of  FIG. 1 ; and 
       FIG. 3  is similar to  FIG. 1 , but showing a state of removal of the protective film from the article. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , an apparatus  20  for removing a protective film  100  from an article  30  is illustrated. The apparatus  20  includes a reaction chamber  22 , a working platform  24 , and an oxidative plasma source  26 . The working platform  24  and the oxidative plasma source  26  are arranged in the reaction chamber  22 . The article  30 , having the protective film  100  thereon, is fixed on the working platform  24 . The oxidative plasma source  26  is provided for generating oxygen plasma beams to bombard the protective film  100  and to thereby damage or degrade the protective film  100 , until the protective film  100  has been removed from a surface of the article  30  and/or can be readily removed therefrom. 
   The working platform  24  is moveable (e.g., in X, Y, and/or Z directions) and rotatable (e.g., tiltable, pivotable, and/or turnable). Thus, the article  30  fixed thereon can be adjusted to an appropriate position where the generated oxygen plasma beams can reach a desired treatment surface. For example, the working platform  24  can be connected with the reaction chamber  22  via a pivot  241 . One end of the pivot  241  is movably (e.g., in X, Y, and/or Z directions) attached to the reaction chamber  22 , and another end of the pivot  241  is movably connected with the working platform  24 . Particularly, for example, a groove/channel can be defined in the top of the reaction chamber  22 , allowing one end (one arm) of the pivot  241  to slide (e.g., in X, Y, and/or Z directions) in the groove/channel of the reaction chamber  22 . Similarly, another groove/channel can also be opened/formed in the working platform  24 , thus another end of the pivot  241  can also slide in that other groove/channel of the working platform  24 . As such, provided with the necessary structure to control the movement of the working platform  24  and/or the pivot  241 , a connection position of the pivot  241  in both the reaction chamber  22  and on the working platform  24  can be adjusted. Thus, the article  30  can rotate and/or move together with the working platform  24 . It is to be further understood that any various adjustably connected working platform that permits angular, rotational, and/or linear movement consistent with the degree of movement permitted by the current system is considered to be within the scope of the present apparatus. 
   The oxidative plasma source  26  is also moveable (e.g., in X, Y, and/or Z directions) and/or rotatable (e.g., tiltable, pivotable, and/or turnable), and thus a direction of the oxygen plasma beams can be adjusted to bombard the protective film  100 . For example, the oxidative plasma source  26  can be connected with the reaction chamber  22  via a pivot  261 . Similar to the pivot  241 , the pivot  261  can be used to facilitate rotation and/or movement, thus the oxidative plasma source  26  can be rotated and/or moved via the pivot  261 . The oxidative plasma source  26  may be, advantageously, an oxygen (O 2 ) plasma source or an ozone (O 3 ) plasma source. 
   The apparatus  20  further includes an exhaust device  28 . The reaction chamber  22  has a gas outlet  221 , and the exhaust device  28  connects with the reaction chamber  22  via the gas outlet  221 . In a process of bombarding the protective film  100 , the air in the reaction chamber  22  should preferably be pumped out via the gas outlet  221  by the exhaust device  28  to create an appropriate vacuum level before the oxidative plasma beams are used to bombard the protective film  100 . During bombardment, gas generated by the bombardment may be continuously exported from the gas outlet  221  by the exhaust device  28 , thus retaining an appropriate pressure in the reaction chamber  22 . Such vacuum/pressure levels used in the reaction chamber  22  are in the range of those typically employed in other plasma beam devices known in the art. 
   Referring to  FIG. 2 , the article  30  to be treated includes a substrate  10  and the protective film  100  formed thereon. The substrate  10  may, beneficially, be made of stainless steel or another alloys such as iron-based alloy, titanium-based alloy, aluminum-based alloy, copper-based alloy and so on. The protective film  100  includes a transition layer  12  and a diamond-like carbon film  14  (i.e., a primary protective layer) formed on the transition layer  12 . The transition layer  12  may be a single layer film or a multilayer film. For example, the transition layer  12  may include a metal layer  121 , a metal nitride layer  122 , and a metal carbide layer  123 . The aforementioned four layers  121 ,  122 ,  123 , and  14  are formed on a surface of the substrate  10 , in series, with the metal layer  121  being directly formed upon or otherwise attached to the substrate  10 . 
   The metal layer  121  may, beneficially, be made of chromium, titanium, or chromium titanium (CrTi). The metal nitride layer  122  may be comprised of chromium nitride (CrN), titanium nitride (TiN), or chromium titanium nitride (CrTiN). The metal carbide layer  123  may, usefully, be made of chromium carbide (CrC), titanium carbide (TiC), or chromium titanium carbide (CrTiC). In the present embodiment, the metal layer  121  is made of Cr, the metal nitride layer  122  is made of CrN, and the metal carbide layer  123  is made of CrC. Depending on the composition of the substrate  10 , it is to be understood that, in order to achieve a desired level of material compatibility in such circumstances, another base metal or alloy could be chosen for the metal layer  121 , along with the corresponding nitride and carbide forms thereof, as needed for the other layers  122 ,  123 . Such compositional variances for layers  121 ˜ 123  would be considered to be within the scope of the present protective film  100 . 
   In the present apparatus  20 , the article  30  to be treated can be fixed on the positionable working platform  24 , while the oxidative plasma source  26  is also rotatably and moveably fixed in the reaction chamber via the pivot  261 . Thus, in the treatment process, both the article  30  and the oxidative plasma source  26  can be adjusted to a suitable position. Thus, the adjustments needed to enable the generated oxidative plasma beams to reach the protective film  100  can be made, thereby facilitating the removal of the protective film  100 . 
   A method for removing the protective film  100  from the article  30  employing the aforementioned apparatus  20  is provided, and a processing state is shown in  FIG. 3 . The method includes a series of steps. In a first step, the article  30  is fixed on the working platform  24  and selectably moved and/or rotated, as needed, therewith to arrive at desired processing position. In a second step, the position/aim of the oxidative plasma source  26  is adjusted to make sure a bombarding spot of the generated oxidative plasma beams can reach the protective film  100 . In the present step, each layer of the protective film  100  may be bombarded until the whole protective film  100  is removed from the surface of substrate  10  of the article  30 . Alternatively, the transition layer  12  may be concentrated upon during the removal step, given that the transition layer  12  is used to attach the protective film  100  to the substrate  10  and is generally more susceptible to bombardment than the diamond-like carbon layer  14 . 
   Preferably, as part of the process, the air in the reaction chamber  22  is pumped out via the gas outlet  221  by the exhaust device  28  before the oxidative plasma beams bombard the protective film  100 . During bombardment, gas generated by the bombardment can be continuously exhausted from the gas outlet  221  by the exhaust device  28 , thus retaining an appropriate pressure in the reaction chamber  22  (i.e., exhaustion is beneficially carried out before and during bombardment). In the present embodiment, a vacuum degree of the reaction chamber is beneficially in a range from about 0.00133 Pa to about 1.33 Pa. 
   In the second step, the protective film  100  may be removed in the following manner. Each layer of the protective film  100  may be bombarded and removed in series. The oxygen plasma beams firstly bombard a surface of the diamond-like carbon film  14 , and directly damage a configuration of the diamond-like carbon film  14  to remove it. Similarly, the CrC layer  123 , the CrN layer  122 , and the Cr layer  121  are bombarded in series by the oxygen plasma, and are removed in that order from the surface of the substrate  10  of the article  30 . Thus, the protective film  100  can be removed from the article  30 . 
   Compared with a material structure of each layer of the transition layer  12 , removing the diamond-like carbon layer  14  is more difficult. In order to further lower a machining cost, another manner of removing the protective film  100  from the article  30  is provided. In this option, the transition layer  12  is firstly damaged, thereby reducing an adhesive action between the diamond-like carbon film  14  and the substrate  10  of the article  30 . As a result, the protective film  100  tends to peel off from the article  30 , either on its own or with little added energy (e.g., mechanical). Referring to  FIG. 2 , according to the configuration the protective film  100 , an edge portion of the diamond-like carbon film  14  of the protective film  100  is thinner than other portions thereof. Given its relative thinness and potential favorable differences in crystallography (including defect size and/or concentration) relative to the main portion of the diamond-like carbon film  14 , the edge portion of the diamond-like carbon film  14  generally has a weak film configuration compared to other parts thereof. 
   Generally, for a multilayer film, an adhesive force between adjacent layers of the edge portion tends to be relatively low. Likewise for a single layer film, the molecular/atomic forces of the edge portion are typically also fairly small. Such relative weakness at edge areas is a result, at least in part, of an increased tendency for defects (e.g., size-wise and/or relative concentration (#/vol.)) in such zones. Therefore, this treatment step exploits the edge defect tendencies of the protective film  100  to reach the more susceptible transition layer  12  and thereby achieve the removal of the protective film  100 . 
   The second step is detailed in the following. For example, the protective film  100  of the article  30  is composed of the diamond-like carbon  14 , the CrC layer  123 , the CrN layer  122 , and the Cr layer  121 . The oxidative plasma is oxygen plasma. Firstly, an edge portion of the diamond-like carbon film  14  is bombarded, until the Cr layer  121  adjacent the substrate  10  is exposed. In the present bombarding process, the diamond-like carbon film  14  reacts with the oxygen plasma, and generates carbon dioxide gas. The reaction result damages the configuration of the edge portion of the diamond-like carbon film  14 . Secondly, the Cr layer  121  is bombarded by the oxygen plasma beams from the exposed edge portion until it is mostly damaged, permitting the protective film  100  to be removed from the substrate  10 . In the present bombarding process, the Cr layer  121  reacts with the oxygen plasma and generates chromium trioxide (Cr 2 O 3 ). The reaction result damages the configuration of the edge portion of the Cr layer  121 , allowing the loosening thereof from the adjacent substrate  10 . Then, the oxygen plasma keeps on bombarding the Cr layer  121  from the edge portion thereof until the whole Cr layer  121  has undergone reaction. Because the diamond-like carbon film  14 , the CrC layer  123  and the CrN layer  122  adhere to the substrates  0  of the article  30  via the Cr layer  121 , once the Cr layer  121  is removed and/or becomes detached, the diamond-like carbon film  14 , the CrC layer  123 , and the CrN layer  122  will fall off from the article  30  together or at least be able to be removed with little or no effort. Thus, the protective film  100  is removed from the article  30 . 
   In the present method for removing the protective film  100  from the article  30 , according to the configuration of the protective film  100 , the weaker portion of the protective film  100  is bombarded first, thus exposing the adhesive metal layer  121 ; and then the adhesive metal layer  121  is bombarded and removed and/or becomes detached, thus damaging the adhesion between the article  30  and other layers of the protective film  100 , thus other layers will fall off the substrate  10  of the article  30 , thereby achieving the removal of protective film  100  from the article  30 . 
   It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.