NZ201906A - Surface coating plastics substrates in high intensity pulsed gas plasma - Google Patents

Description

201906 ORIGINAL i Priority Date(8): /viT3. r.W! 1 ; i j * * " ! Complete Specification Filed: th. .c?....

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NEW ZEALAND THE PATENTS ACT, 1953 COMPLETE SPECIFICATION "SURFACE PROCESSING OF A SUBSTRATE MATERIAL" WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 201906 The present invention relates to the surface processing of a substrate material. Plasma processing and in particular low temperature glow discharge plasma processing is potentially a very useful process for the surface processing of substrate materials. As a source of high energy radiation it can promote both physical and chemical changes at the surface of the substrate and can be used for etching, roughening, polymerisation, cross-linking, adhesion promotion, grafting and coating of the surface. It is possible to include more than one of these processes during a treatment so that one can sequentially carry out surface etching, cross-linking and layer or multilayer deposition of a substrate by simply changing the gas composition. Such a process ensures the maximum possible adherence and compatibility between different deposited layers and avoids other problems such as internal optical reflection caused by abrupt interfaces.

However, the deposition of good inorganic coatings in normal discharges requires substrate temperatures in excess of 250°C (too high for most plastic substrates (for example). The reason for this is probably the relatively low degree of molecular dissociation in the normal discharges. The species arriving at the substrate surface therefore requires additional energy for further decomposition and for structural arrangement of the coating. This has therefore limited the use of plasma in surface processing of many materials and in particular heat sensitive materials such as plastics. 2 2 3 JUL 1985 201906 By using a plasma of low average power thereby minimising the problems of heating we may use a high intensity plasma on a heat sensitive substrate. One way in which we can achieve this is by using a mark-space ratio of less than unity (i.e. longer space than mark) and we can vary the mark-space ratio of the pulses to suit the substrate, the plasma and desired effect concerned.

We may provide pulses of various mark-space ratios for example 1:1 downwards and preferably less than 1:10 and in certain instances the mark-space ratio may be as low as 1:10,000.

In a particular arrangement the pulse length may be lOys to 1 ms at a pulse frequency of 10 ys to Is intervals ("s" = second).

The pulse frequency may be 50 KHz to 30 MHz.

The process may be used for coating, etching, cross-linking, surface heating, grafting, roughening or adhesion promotion. 201906 An electrical potential may be applied to the substrate and in a particularly preferred arrangement this electrical potential may be approximately 1000 volts. The electrical potential may be continuous or pulsed and will normally be negative with respect to the plasma voltage.

Preferred arrangements of the invention will now be described by way of example only and with reference to the accompanying drawing which shows plasma apparatus for carrying out the process of the invention.

The surface processing of a substrate material by a plasma potentially has very many uses. For example, where the present use of a material is based on its surface properties, it allows the use of a cheaper, lighter or otherwise preferred substrate material to be coated with the material whose properties are desired. For example, a plastic substrate material is often preferred for cheapness and lightness whereas the surface properties of glass which is hard and scratch resistant is preferred. The use of a plasma process to coat plastic material with a layer of glass would improve its wear and abrasion resistance, would make it water and dirt repellant, and would allow for the production of a lighter .and cheaper item. There are many uses for such a material but a particular use which is envisaged is in the side windows of motor vehicles and the reflectors and lamp covers of motor vehicles.

As well as telephones, taps and other domestic parts and 201906 plastic packaging of integrated circuits and other electrical components, other uses of plasma surface processing of plastics material include plastic bumpers and other cosmetic parts where the surface properties of the plastic can be changed so as to give an attractive appearance, abrasion and chemical resistance anti-reflection properties and^the1 like.

As has been mentioned above, it has hitherto not been possible to apply plasma technology to plastics material because they are heat sensitive. However plasma processing provides good throwing power, a low pinhole (defect) count, is flexible, not only in the file material to be coated but also in respect of the coating process.

The present invention describes a process for surface processing a substrate material (such as a plastics material) comprising exposing the surface of the substrate to a high intensity pulsed plasma. By pulsing the plasma and suitably selecting the mark-space ratio, high intensity plasma can be used but the overall energy input is sufficiently low not to adversely affect plastic material. It will be understood that although the process will be described with reference to a heat sensitive material such as plastic the principles would also apply to other materials which are less heat sensitive such as steel.

The process is particularly useful in producing articles for use in the automotive, sanitary, industrial and optical 201906 In the drawing there is shown a sealed chamber 10 in which is mounted the article 11 whose surface is to be processed. Surrounding the part of the sealed chamber 10 in which the article 11 is mounted is a coil 12 connected to a 60kw pulsed RF generator 13. A mass spectrometer 14 is arranged.,to view the gases within the chamber 10 and the article may be viewed by means of an optical system 16. The chamber 10 may be evacuated by means of a pump connected to the outlet 17 and gas may be inserted in the chamber by means of the inlet 18. A sealed chamber 19 is provided between the mass spectrometer 14 and the chamber 10 there being provided suitable windows each side of the chamber 19, and a pump may be connected to an outlet 21 of the chamber 19.

In use, the article 11 is inserted within the chamber and the chamber 10 is then evacuated by means of a pump through the outlet 17. When a pre-determined level of vacuum has been reached a desired gas may be inserted through the inlet 18. The RF generator 13 may then be switched on so as to provide a pulsed electrical field through the coils 12. The effect of : this is to ionise the gas within the chamber 10 and thereby produce a plasma. The ionised particles bombard the surface of the article 11 to carry out the surface processing desired. The mass spectrometer 14 is used in this arrangement to monitor the types and proportion of ions present in the plasma. 2 3JULJ935 6 201906 When a first coating process is completed, the gas may, if desired, be evacuated through the outlet 17 and a further gas inserted through the inlet 18 to provide a second processing step. If desired all of the gas may be removed from the chamber 10 before inserting a second gas or alternatively the second gas may be inserted at the same time as the first gas is being removed through the outlet 17. In this way two separate surface processing steps may follow one another and if the gases are charged in the second above described manner then there will be no surface discontinuities between the two surface processing steps. In the apparatus thus far described the surface of the article 11, particularly if of plastic, may be processed to provide cross-linking in the plastic surface material, polymerisation, and in some instances incorporation of the material in the gas into the surface layer.

The plasma process so far described is suitable for a number of surface processes but to extend the use of the plasma process to include other atoms of elements for which there are no suitable volatile compounds, which includes many metals, an additional processing step and part of the apparatus is provided. Installed within the chamber 10 is a suitable target material, for example silicon carbide or oxide or nitride or titanium nitride or oxide and means may be provided to fire ions at the target material. Material is sputtered from the target into the already existing plasma and is evenly distri- |3^-: -J! 2 3JuL:X! i 201906 buted within the plasma by diffusion. In this way atoms or ions of the target material are produced within the plasma which can thereby be coated onto the article 11. The beam bias directed at the target may be continuous although if preferred may be pulsed, but the plasma will be pulsed as in the preceding example. Such a sputtering process may be carried out by a magnetron and the sputtering process may be carried out throughout the process or may be provided for only part of the process. Furthermore the target material may be changed so as to provide a different coating material.

Normally the article 11, during the process will be at a bias voltage of about 1000 volts, which is negative with respect to the plasma. The frequency of the electrical field producing the plasma is chosen depending upon the materials ' • involved but may typically be between 50KHz and 30MHz and the mark-space ratio may be chosen to be greater than 1:1 and will normally be between 1:10 and 1:10000. The pulse intervals will normally be lOOys to Is. For plastic materials the pulse length may be lOys to 1ms a 10 ms to Is intervals which will restrict the average power density to a few hundred watts per litre.

It is believed that although the plasma is pulsed, reactive species are available during the off periods. The chamber 10 should be maintained at about 0.01 torr and power levels of at least a few kW per litre are required. u,z. PA7BJT ornoe _ 8 - 2 3JUL 1985 RvO:/:v 201906 The range of materials to which the process may be applied is not limited. However, the process is particularly suited for the treatment of heat sensitive materials, both organic and inorganic. It may also be used, however, for surface treating other materials such as steel or aluminium.

The gas chosen will depend upon the process required. Lower substrate temperatures can be used. Atomic species have the advantage of having much higher chemical energies and structural symmetry. Such discharges have further advantages as sources for ultra-violet radiation which will be beneficial to the production of strong cross-linking of plastic surfaces. The article 11 may be made of a wide range of materials including plastics such a sacrylics and carbonates. The processing envisaged includes surface cleaning and activation, graft polymer of matching optical properties, gradually phasing into wear resistant hard material of high refractive index such as silicon carbide or silicon ditride, a quarter wave (A/ 4) inorganic layer of suitable refractive index of, for example, SiC^r and a gradual layer of thin optically matched water repellant flurocarbon.

The use of this process is particularly preferred to arrange a moisture impervious layer for, for example infra red lenses, and may be used to coat particles in a fluidised bed arrangement. A magnetic field may be applied to enhance the degree of ionisation. Additional internal and external heating sources may be applied to create the right thermal conditions 201906 for article 11. The coupling as illustrated in the drawing between the article and the power source will generally be inductive.

In certain processes, for example when etching, it may be preferable to place the article 11 outside the active region.

In certain arrangements it may be preferred to pulse the gas supply. In a particular arrangement, the process may be used to provide impermeable coatings for plastics for cables.

As an example of the use of the apparatus, a very thin 0.15 ym film of titanium nitride has been coated by means of the plasma process of the invention on an underlayer of 3 um thick titatium on PVC plastic. Such a plastic material shows substantial improvements in wear performance.

In a pin-on-disc test, in which the substrate was worn against steel ball bearings, there was an improvement by a factor of 20 and in a reciprocating wear test, using a glass loaded poly-tetra-fluorethylene stud with sand and fast curring alumina-interposed showed a sixty fold improvement.

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Claims (12)

201906 What we claim is:-

1. A process for depositing at least one layer of desired material onto a substrate, comprising exposing said substrate to a pulsed gas plasma whereby ionized particles produced thereby are deposited on said substrate to form said layer of desired material, the said plasma's average power being determined by selecting a pulse mark-space ratio of less than 1:1.

2. A process as claimed in claim 1 wherein the mark-space ratio is less than 1:10.

3. A process as claimed in claim 1 or 2, wherein the pulse length is between 10 ys and 1 ms at intervals between 10 us and Is.

4. A process as claimed in any one of the preceding claims, wherein the plasma is produced by an electric field with a frequency between 50 KHz and 30 MHz.

5. A process as claimed in any one of the preceding claims, wherein an electric potential is applied to the substrate.

6. A process as claimed in claim 5, wherein the electric potential applied to the substrate is approximately 1000 volts.

7. A process as claimed in any one of the preceding claims, wherein a succession of layers is coated onto the substrate by changing the gas or gas mixture with time.

8. A process as claimed in any one of the preceding claims, wherein the at least one layer of material deposited by the 2019 0& plasma is provided by particles of material produced by a high intensity beam of particles directed at a target material and diffused into said plasma.

9. A process as claimed in claim 8 in which the high intensity beam of particles is provided by a magnetron.

10. A process as claimed in any one of the preceding claims, wherein said substrate is a plastic material.

11. A process as claimed in claim 1 substantially as hereinbefore described.

12. A substrate with at least one layer of material deposited thereon by the process of any one of claims 1 to 11. INTERNATIONAL STANDARD ELECTRIC CORPORATION P.M. Conrick Authorized Agent P5/1/1466