PROCESS AND APPARATUS FOR THE TREATMENT OF COATED, ELONGATED SUBSTRATE, AS WELL AS SUBSTRATES THUS TREATED AND ARTICLES OF POLYMERIC MATERIAL REINFORCED WITH THESE SUBSTRATES

Abstract: The invention relates to a process for treating an elongated, coated substrate, whereby the treatment comprises the appli­ cation by cathode sputtering of a material containing at least one component and whereby the composition of this ma­ terial has been chosen in accordance with the difference between the composition of the coating or the surface of the coating as measured and the desired composition of the coating or the surface of the coating.

Description: This invention primarily relates to a process for treating an elongated steel substrate, such as a wire, a strip, a cord, etc., having a first coating of brass applied thereto by a non-sputtering technique. Coating processes by non-sputtering techniques for elongated steel substrates, such as steel wire, steel cord, are generally known. The coating can be applied electrolytically, by immersion in a bath of molten metal, etc. A number of coating processes are known that permit the rapid application of relatively thick coatings. It is well known how to apply metal coatings of brass (a copper-zinc alloy) onto steel wires, strips, etc. and how to apply further treatments to these wires, strips, etc. to obtain the desired finished products. It is for instance known how to draw, to roll out etc. such brass-coated wires, strips, etc. or intermediate products and to combine these wires, strips, etc. to obtain e.g. cords as final products. The purpose of this brass coating on these elongated steel substrates is usually to provide the final products made therefrom with certain properties, for instance sufficient corrosion resistance, sufficient adhesion to rubber or plastic if these final products are used as reinforcements. However, the presence of this first coating of brass on the elongated intermediate substrates as for example steel wire also serves other purposes, as for example the case of drawing, rolling etc. of the intermediate products during the intermediate steps prior to the production of the desired final products. It has now been determined, that the application of such a brass coating with the desired properties, for instance, the coating thickness or the coating composition on these intermediate products can be carried out in a good way so that intermediate products with brass coatings with desirable properties result. On the other hand, it has been found that the properties of this first brass coating can be changed considerably during the intermediate treatment, i.e. prior to the manufacture of the finished product, e.g. during the drawing, rolling, cabling, etc. processes, as a result of which the properties of the final products thus obtained are not always satisfactory. It is an object of the invention to provide a process for treating an elongated steel substrate, such as a wire, a strip, a cord, etc., that is already provided with a brass coating, to obtain thereby a final product with a coating suitable for the applications of this final product. The process according to the invention for the treatment of an elongated steel substrate having a first coating of brass applied thereto by a non-sputtering technique, is characterized in that the treatment comprises the application of a second coating of cobalt by cathode sputtering. The process according to the invention offers the important advantage that it allows final products with a coating or coating surface of the desired composition to be obtained rapidly and efficiently. The german patent application or document DE-A-2.400.857 already teaches a method of continuously applying thin metallic coatings on elongated substrates by means of a cathode sputtering technique. From the document "Journal of Applied Physics, vol. 40, No.4, 15th March, pages 1864-1869" it is already known to continuously apply thin Permalloy coatings on Permalloy wires by means of a sputtering method. The invention also relates to the elongated steel substrates treated according to the process according to the invention. The thickness of the first non-sputtered coating of brass is preferably ranging between 0,1 to 0,35 micrometers. The thickness of this second coating of cobalt as obtained by means of cathode sputtering is preferably ranging between 0,002 to 0,05 micrometers, in particular between 0,005 to 0,02 micrometers. Finally, the invention also relates to articles of polymeric material that have been reinforced with at least one elongated steel substrate according to the invention. The invention will now be further explained in the following detailed description and accompanying drawing, wherein : Figure 1 represents a flow chart of the complete line of which the apparatus for carrying out the process according to the invention forms a part, and Figure 2 represents a longitudinal section of an apparatus for carrying out the process according to the invention. In Figure 1 parts of a complete line are indicated by numbers 1 - 10, whereby number 6 refers to the apparatus for carrying out the process according to the invention. The elongated steel substrate 12 to be treated, such as a wire, strip, cord, etc. and which is already provided with a brass coating, is reeled off a coil or such means in station 1 and is fed through chambers 2 and 3 with vacuum seal lock 4, and high vacuum cleaning station 5 into the coating apparatus 6, whereupon it is rewound onto a coil 7, thereby passing through chamber 3' with vacuum seal lock 4' and chamber 2'. Such a line has for instance been described in the British patent 1.362.735 in which the two high vacuum chambers 5 and 6 are preceded and succeded by two vacuum chambers 2 and 3 and 2' and 3' respectively. Such a line without the high vacuum coating chamber 6 or apparatus 6 has also been described in the European patent application 270.144 which has been filed simultaneously with the present application. The vacuum chambers 2 and 2' are connected to a Roots vacuum booster 8 which is known per se, whereas the chambers 3 and 3' are connected to a rotary piston vacuum pump 9. The high vacuum chambers 5 and 6 are connected to a turbomolecular pump 10. Between the atmosphere (unwinding and rewinding stations 1 and 7) and the chambers 2 and 2' respectively, suitable means of passage are provided as between the chambers 2 and 3 and between the chambers 2' and 3' (openings 11 and 11'). Between the chambers 3 and 5 and between the chambers 3' and 6 vacuum tight valves 4 and 4' respectively, are present. The line operates as follows. With the Roots vacuum booster 8, with for instance a capacity of 500 m³ per hour, a vacuum of 10⁻¹ to 10⁻² Torr is achieved in chambers 2 and 2'. The chambers 3 and 3' are evacuated still further with the pump 9, with for instance a capacity of 10 m³ per hour, to a final pressure of for example 10⁻² Torr or lower. The high vacuum chambers 5 and 6 are evacuated using the turbomolecular vacuum pump 10 to a high vacuum, for instance 10⁻⁴ to 10⁻⁷ Torr. During the evacuation of chambers 5 and 6, the valves 4 and 4' are completely closed. After this situation has been reached, and valves 4 and 4' have been opened, the line is ready to start the process for treating the elongated substrate 12 which has already been coated beforehand. Figure 2 shows the longitudinal section of a typical vacuum chamber 6. This chamber consists of two sections 13 and 14, interconnected by the openings 15. The actual piece of equipment 16 for the treatment of the elongated substrate 12 is contained in section 14 of the vacuum chamber. The section 13 is provided with connectors 17 for the turbomolecular pump 10 and with connectors 18 for the supply of an inert gas, such as argon, nitrogen, etc. The piece of equipment 16 comprises a circular cylindrical cathode 19 with cable connectors 20 to provide the electrical potential. This cathode is a cobalt tube. The cathode 19 is supported by a tube 21, made for instance of stainless steel and subsequently by a tube 22 made from insulating material, for example aluminium oxide. Both ends of both tubes 21 and 22 are incorporated in the insulating supports 23 and 24. Tubes 21 and 22 can in theory be replaced by a single tube made from insulating material, in which case the wall thickness of this tube is about equal to the sum of the wall thicknesses of tubes 21 and 22. The ends of the cathode 19 have been incorporated into the insulating supports 25 and 26. Between the end of the cathode 19 and the insulating support 25, a spring 27 has been provided. The supports 25 and 26 fit into clamping devices 28 and 29. The clamping device 28 has been fixed to the wall between the sections 13 and 14, whereas the clamping device 29 can be screwed onto the end of section 14. It is clear that the spring 27 can be slackened by loosening clamping device 29, as a result of which the cathode 19 is expelled and can thus easily be exchanged for another tube 19. In addition, the vacuum chamber 6 is also provided with flange connection 30, which permits the removal of the cathode 19 without loosening the clamping devices 28 or 29. The lid 31 of the section 13 also has a flange connection. The diameter of the tube 19 is for example about 20 mm, whereas its length is for instance about 500 mm. The process for treating an elongated steel substrate that has already been provided with a brass coating is as follows. When the line is ready to operate the process, the substrate to be treated is fed through the piece of equipment 16 as indicated by the arrow 32. The pump is switched off and an inert sputtering gas, such as argon, is fed into the vacuum chamber 6 or in the section 13 and 14 in a continuous manner until a pressure between 0.1 and 0.5 Torr, for instance 0.2 Torr, has been reached. A sufficiently high voltage difference is maintained between the cathode 19 and the substrate 12 as anode, so that a glow discharge is established and a plasma is formed. This may occur at a voltage difference of for example 200 to 300 V and a current between 300 and 600 mA, for example 450 mA. During its passage through the cathode 19, the substrate 12 is coated by cathode sputtering with the cathode material. The substrate 12 will preferably be kept at ground potential. It is also possible to apply an alternating potential between the cathode 19 and the substrate 12 in order to attain the so-called RF-state. Triode sputtering is also possible with the shown apparatus. An important feature of the process according to the invention is that the inert sputtering gas is led through the cathode 19 in the direction of the arrow 33. This means that the substrate 12 and the sputtering gas move in opposite directions within the evacuated section 14 and in particular within the cathode 19. This can for example be achieved by ensuring a lower pressure in chamber 3 than in chamber 3'. The process according to the invention is particularly suitable for steel substrates, such as steel wires, steel cords, etc. which have been coated with a first coating of brass. The brass coating preferably has a thickness of 0,1 to 0,35 micrometers, preferably 0,15 to 0,25 micrometers. The material of the cathode 19 is cobalt. It has been found that coating thicknesses of 0,002 to 0,05 micrometers, in particular 0,005 to 0,02 micrometers were applied onto the elongated steel substrate when this was fed at high speeds (20 meters per minute or more) when using the explained process. The substrate 12 to be treated is preferably cleaned in the high vacuum chamber 5 by plasma cleaning, before it is treated in the high vacuum chamber 6 or before its cathode sputtering coating (see Figure 1). Preferably, the elongated substrate 12 is cleaned by induction heating under vacuum, for example in chamber 2, before the plasma cleaning. It can be interesting to fit a coil around the cathode 19 in section 14, so as to generate a magnetic field between the cathode 19 and the substrate 12, which further improves the quality of the substrate 12.

Claims: A process for treating an elongated steel substrate having a first coating of brass applied by a non-sputtering technique, characterized in that the treatment comprises the application by cathode sputtering of a second coating of cobalt. An elongated steel substrate obtained according to claim 1, characterized in that the thickness of the first non-sputtered brass coating is 0,1 to 0,35 micrometers. An elongated steel substrate according to claim 2, characterized in that the thickness of said sputtered cobalt coating is between 0,002 to 0,05 micrometers. An elongated steel substrate according to claim 3, characterized in that the thickness of said sputtered cobalt coating is between 0,005 to 0,02 micrometers. Articles of polymeric material, reinforced with at least one elongated substrate according to one or more of the claims 2 - 4.

Inventors: COPPENS, WILFRIED, LIEVENS, HUGO
Applicants: N.V. BEKAERT S.A.
Application year: 1987
Main classification: C23C14
IPC codes: C23C14