GB1564134A - Adherence of metal films to polymeric materials - Google Patents

Description

(54) IMPROVEMENT IN ADHERENCE OF METAL FILMS TO POLYMERIC MATERIALS (71) We RCA CORPORATION, a corporation organized under the laws of the State of Delaware, United States of America, of 30 Rockefeller Plaza, City and State of New York 10020, United States of America. do 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: This invention relates to articles of manufacture in which good adhesion is required between a polymeric material and a metallic film or layer, specifically of nickel-chromium alloy with or without iron.

Thin films of conductive and/or decorative metals, particularly transition metals or their alloys, can be only selectively applied to polymeric substrates or coated with polymeric films because of the lack of adhesion of most metals to polymers. In general, the surface of the polymer must be modified, as by oxidation, roughening, and the like, or an intermediate adhesion-promoting agent must be applied to the polymer or metal surface which adds to the cost and sometimes detracts from the appearance of the final article. The use of thin metal films as decorative and durable coatings for toys, auto accessories and the like would increase if a method could be found to coat polymeric substrates with strongly adherent, metallic films.

Strong adhesion between a metallic layer and polymeric material is also required in video disc records for video recording and playback systems such as that which has been described by Clemens in U.S. Patents 3,842,194 and 3,842,217. According to this system, video, audio and color information is recorded in the form of geometric variations in a spiral groove on a surface of a disc. Disc replicas, made of an insulating material, such as vinyl, are coated first with a thin, conformal, conductive metal layer as a first electrode of a capacitor, and then with a thin, conformal dielectric layer. A metal-tipped stylus acts as a second electrode of the capacitor. The stylus monitors changes in capacitance between the stylus and the metal film on the disc as these geometric variations pass beneath the stylus upon rotation of the grooved disc, to effect recovery of signals occupying a band width of at least several megahertz which are converted back to video, audio and color information suitable for display by a television receiver.

Several metals have been suggested for use as the thin, conductive metal layer of such video discs. Aluminium was first tried because it is inexpensive, but it was found to be unsatisfactory because it became grainy on storage, leading to high noise levels on playback. Gold was tried and was found to have excellent properties, and is particularly corrosion-resistant, but is too expensive to use on a large commercial scale. Further, adherence of the dielectric film particularly glow discharge polymerized styrene, as disclosed in U.S. Patent 3,843,399, to the gold surface leaves something to be desired and results in undue wear of the record during playback. Copper was also tried. This metal in thin layers has excellent adherence to polymeric substrates, particularly vinyl compounds, but is not satisfactory because it corrodes rapidly in the atmosphere on storage. Conductive metal alloys of nickel and copper, which are corrosion resistant, have also been tried, but their poor adhesion to organic materials makes them unsuitable for use on the video disc.

Thus the search for a thin, conductive adherent, corrosion-resistant metal coating for the video disc has continued.

We have found that copper improves the adhesion of nickel and chromium alloy thin films to polymeric substrates and coatings. The copper can be applied as a very thin film between the polymeric material and the alloy, or can be provided as a constituent of the alloy. The greater the amount of copper, the greater the adhesion provided, but a film as little as about 25 angstroms thick at the polymer-metal interface or the addition of as little as about 10 atomic percent of copper to an alloy composition, improves metal-polymer adhesion by several orders of magnitude.

The metal alloys useful herein are alloys of nickel and chromium which can contain up to about 10 per cent by weight of iron. Particularly useful alloys contain from 65 to 80 weight per cent of nickel, 10 to 30 weight per cent of chromium and from 0 to 10 weight per cent of iron.

When copper is to be added to the above-described alloys, the copper must be added in sufficient amounts to impart adherence of the resultant alloy to the polymer or polymers which are being used. for improved adherent coatings, from about 10 to about 15 atomic per cent of copper is added to the alloy. Alternatively, a layer from about 25 to about 50 angstroms thick of copper can be deposited between the polymer-alloy interface.

In providing a polymeric substrate with an adherent metal film according to one aspect of the invention, the polymeric substrate is placed in a vacuum chamber and connected to a positive source of current, such as a planar magnetron source. The vacuum chamber is also fitted with a negative electrode of copper and another electrode of the nickel-chromium alloy to be deposited. The chamber is then evacuated to a pressure of about 5 x 10-6 to 3 x 10 torr and a small amount of an inert gas, such as argon, is fed into the chamber to a pressure of up to about 15 millitorr. The pressure is not critical however, and can vary from about 2 to about 100 millitorr.

When a planar magnetron is employed in the chamber as a source of current, the voltage can be varied from about 300 to 1000 volts and the current can be up to 10 amperes, depending upon the rate of deposition desired and the size of the electrode.

The copper electrode is activated first to initiate sputtering on the substrate and is continued until a thin layer of about 25 to 50 angstroms of copper is deposited. The current to the copper electrode is then discontinued and the nickel-chromium alloy electrode is activated so as to sputter a layer of alloy of the desired thickness, generally from about 200 to about 400 angstroms thick. In the event that a polymeric coating is to be deposited over the nickel-chromium alloy, a third layer, also of copper, can also be deposited over the nickel-chromium alloy to provide a thin film of copper between the metal-polymeric coating interface.

Thin copper films have excellent adhesion to polymeric substrates, particularly vinyl, and they also adhere well to nickel-chromium alloy layers and to polymeric coatings, particularly styrene polymer coatings. Thus, the purpose of the copper layers is to provide good adhesion of the conductive and/or decorative metal layer to a polymeric substrate, and to a polymeric dielectric layer subsequently applied, if desired.

According to a second aspect of this present invention copper can also be co-sputtered with the nickel-chromium alloy in a similar vacuum chamber, except providing an electrode of a nickel-chromium alloy in which pure copper has been inserted into spaces cut for that purpose. The size and location of the copper in the electrode is chosen to deposit the amount of copper desired onto the substrate to be coated. The current to the single alloy-copper electrode is then turned on and sputtering is continued until a layer generally about 200 to 400 angstroms thick, has been deposited onto the substrate.

The exact mechanism of the improved adhesion of the present metal films is unknown, but it is presently believed that the copper serves to stress relieve the nickel-chromium alloy film. As determined by electron spectroscopy for chemical analysis, no chemical bonding between the copper-containing layer and the polymeric substrate and/or coating is involved.

The foregoing aspects of the invention will be further illustrated by the following Examples, in which all parts and percentages are by weight unless otherwise noted. The Examples will be described particularly with respect to the preparation of a metallized vinyl video disc, but it will be readily understood that the invention has applicability to other polymeric substrates and coatings.

Example 1 A vacuum chamber was fitted with two planar magnetron sputtering cathodes, one made of copper and the other of *Inconel-600, an alloy containing 76.8 + 3% of nickel, 13.8 + 3% of chromium, and 8.5 + 2% of iron (plus minor amounts of impurities). Both cathodes were 8.25 x 3.56 inches (20.96 x 9.04 cm) in size. A vinyl video disc 12 inches in diameter was suspended about 2 inches (5.08 cm) above the electrodes and rotated at 40 rpm.

*Inconel is a registered T. M. of International Nickel Co.

The chamber was evacuated to a pressure of 3 x 10-5 torr and backfilled through a valve to a pressure of about 15 millitorr. with argon.

The copper electrode was activated with 360 volts, 0.3 amperes of current. The average deposition rate on the record under these conditions was about 80 to 100 angstroms per minute. Copper deposition was continued for about 30 seconds or until a layer of about 50 angstroms thick of copper had been deposited, when this electrode was inactivated.

The Inconel-600 electrode was then activated with 650 volts, 1.5 amperes of current, resulting in a deposition rate of about 330 to 400 angstroms per minute. Deposition was continued for about 30 seconds or until a layer of about 200 angstroms thick had been deposited, when the electrode was inactivated.

In an alternative example (Example 2), the process of Example 1 was followed by reactivation of the copper electrode apply another layer of copper about 50 angstroms thick over the Inconel-600 layer.

The metal film was tested for adhesion for each Example by storing for 120 hours at 900F and 90% RH in air and applying Scotch (Registered Trade mark) tape to the surface. No film was removed when the Scotch tape was pulled off.

Stress measurements were made in known manner by depositing films as above on very thin aluminum oxide discs and noting the bending of the discs microscopically. Whereas a film of Inconel-600 about 225 angstroms thick had a compressive stress of 30 x 109 dynes/cm2, a trilayer coated disc prepared as in Example 2 had a compressive strength of only 6 x 109 dynes/cm2.

Example 3 The procedure of Example 1 was followed except that a sputtering electrode was prepared of Inconel-600 in which two slots were machined 0.252 inch x 6 inches (0.64 x 15.24 cm) in size, the first one 1.225 inches (3.11 cm) from and parallel to one of the long edges of the electrode, and the other 1.245 inches (3.16 cm) from and parallel to the other long edge of the electrode. A one-fourth inch (0.64 cm) wide copper bar the length of the slot was fitted into the slot so that the edge was flush with the electrode surface. These dimensions were chosen so that the center line of one of the copper bars is in the center of one eroded or sputtered track and the other bar is on the inside edge of the second track in the electrode.

The chamber was evacuated to a pressure of about 3 x 10-6 torr and backfilled with argon to a total pressure of 1.5 x 10-2 torr.

The electrode was then activated with 650 volts and 1.5 amperes of current, resulting in a deposition rate of about 330 to 400 angstroms per minute. Deposition was continued for about 30 seconds or until a layer about 200 angstroms thick had been deposited.

The resultant metal film was tested for adhesion by the Scotch tape test as in Example 1.

No film was removed when the Scotch tape was pulled off.

The compressive stress of this metal film, measured according to the procedure of Example 1, was only 5 x 10-9 dynes/cm2.

We have further discovered that a trilayer metal film comprising a first thin copper layer, a second layer of a metal or alloy which is corrosion resistant, conductive and can form a low stress film, particularly according to the present invention alloys of nickel and chromium optionally containing iron to less than 10 percent by weight and also containing particular amounts, from about 20 to about 30 atomic per cent, of oxygen, and a third layer of copper, is highly adherent to organic, particularly by polymeric, materials, and is non-corrosive and conductive. The metals can be applied to the substrate by planar magnetron sputtering in an atmosphere containing an inert gas with small amounts of air or oxygen.

With regard to this aspect of the invention: Figure I is a graph of the atomic per cent of the elements in an applied film as a function of sputter etch rate.

Figure 2 is a graph of corrosion failure as a function of oxygen content of the film alloy.

Here again reference will be made particularly to the video disc application of this aspect of the invention, but it will be readily understood that it has applicability to organic substrates other than a vinyl, grooved disc. Further, the metal layer can be coated with other materials, such as a dielectric or other non-conductive layer, organic or inorganic, or sandwiched between two organic layers for other applications.

Example 4 An organic substrate may be coated with a conductive, corrosion-resistant metal film in accordance with this aspect of the invention as follows: the substrate is placed in a vacuum chamber and connected to a positive source of current, such as a planar magnetron source.

The vacuum chamber is also fitted with negative electrodes of the copper and of the nickel-chromium-iron alloy to be sputtered. The chamber is then evacuated to a pressure of about 5 x 10-6 to 3 x 10- torr and a small amount of an inert gas, such as argon, is fed into the chamber to a pressure of up to about 100 millitorr. An amount of oxygen is present in the system to produce about 20 to 30 atomic percent of oxygen in the metal layer. Oxygen is present as contaminant in the inert gas and in the residual atmosphere in the vacuum chamber in generally sufficient amounts, but a predetermined amount of oxygen can be deliberately added for more precise control.

When a planar magnetron is employed in the chambe as the source of current, the voltage can be varied from about 300 - 1000 volts and current can be up to about 10 amperes depending upon the rate of deposition desired and the size of the electrode.

The copper source is activated first to initiate sputtering on the substrate and is continued until a thin layer of about 25 to 50 angstroms of copper is deposited. The current to the copper electrode is then discontinued and the nickel-chromium-iron alloy electrode is activated so as to sputter a layer of alloy about 200 to 400 angstroms thick over the copper layer. That electrode is then inactivated and a final thin layer of copper, also about 25 to 50 angstroms thick, is sputtered in similar fashion onto the alloy later.

The copper films have excellent adhesion to polyvinyl synthetic resin substrates, such as the molded, grooved video discs, and they also adhere well to the nickel-chromium-iron alloy layer and to organic coatings. However, unexpectedly, sufficient diffusion of the copper layer and the alloy layer occurs during deposition, so that the thin copper layer is not subJect to extensive corrosion problems provided the total oxygen content of the alloy layer is at least 20 atomic percent. However, a maximum of about 30 atomic weight of oxygen in the alloy layer can be tolerated when highly conductive films are required.

The atomic percent of oxygen as referred to in the specification and claims is defined as that measured by Auger electron spectroscopy. The absolute value of the oxygen content, y(O), is determined by the following calibration: a pure silver sample is sputter etched removing about 300 angstroms and the Auger peak to peak magnitude for the Ag doublet (351:354 eV) is recorded. This value is taken to be A(Ag). The peak to peak magnitude for the 0 (510) Auger peak in the sample to be measured is taken to be A(0). The absolute 0 value is calculated according to the equation Y(O) = n(o) x 1.03 The 1.03 factor for Ag is obtained from the Handbook of Auger Electron Spectroscopy, Palmberg et al.

Figure 1 shows an Auger spectroscopy profile of a vinyl disc coated with about 25 angstroms of copper, then about 200 angstroms of Inconel-600 alloy, then about 25 angstroms of copper and finally with about 350 angstroms of a polymer of styrene, which graphs the atomic percent of the elements present as a function of the sputter etch rate in minutes. As the surface of the styrene coated disc is sputter etched away, the various coatings and layers are revealed.

A careful study of the resultant profile for oxygen shows that the oxygen content in the styrene layer decreases adjacent to the copper layer, is less than about one atomic percent in the second copper layer and increases markedly in the Inconel-600 layer, and again rapidly decreases in the first copper layer, until only a trace remains in the substrate. Thus it would appear that the copper remains unoxidized, whereas the Inconel-600 appears to absorb most of the oxygen present in the system.

A series of films was prepared by sputtering first a 25 angstroms thick layer of copper, then a layer about 200 angstroms thick of Inconel-600 and a third layer of 25 angstroms of copper onto a grooved vinyl disc following the procedure of Example 1, except that the chamber was initially evacuated to 3 x 10-6 torr and backfilled with a mixture of 95% argon-5% clean, dry air, to various pressures to vary the amount of oxygen in the films.

The films were tested by an accelerated corrosion test as follows: a layer of sodium chloride was evaporated onto the metal coated disc and heated to about 45"C. Air and H2S were bubbled through water and the gas stream passed continuously over the metal surface.

The time was noted when a visible sign of corrosion appeared under a microscope, including color change, pitting, etc.

Figure 2 is a graph of the time to corrosion in hours as a function of the atomic percent of oxygen in the film. It is apparent that as the oxygen content increased beyond about 20 atomic percent, the time to corrosion failure increased markedly.

A film of copper alone containing 20 - 23 atomic percent of oxygen pitted severely after about 30 seconds.

We have also found according to yet another aspect of the invention, that corrosion resistant alloys of nickel and chromium and optionally containing iron to less than about 10% by weight can be admixed with small amounts of copper and oxygen to form a pseudo-alloy which is conductive, corrosion-resistant and highly adherent to organic dielectric materials, particularly polymeric materials. The pseudo-alloy can be applied to an organic substrate by planar magnetron sputtering of a cathode of the nickel-chromium-iron alloy and copper in an atmosphere containing an inert gas and small amounts of air or oxygen.

In general, corrosion resistance increases as the oxygen content increases. However, higher oxygen content also leads to increased oxidation of the metals to form non-conducting compounds, which decreases the conductivity of the film. Thus the upper limit for oxygen content is determined by the resistivity required for the particular application desired. For video discs, the oxygen content should be maintained between about 10 and about 25 atomic percent, preferably between about 10 and about 20 atomic percent, of the pseudo-alloy composition.

According to one method of preparing the alloy films according to this present aspect of the invention, the organic substrate to be coated is placed in a vacuum chamber and connected to a positive source of current, such as a planar magnetron source. The vacuum chamber is also fitted with a negative electrode of the nickel-chromium-iron alloy in which pure copper has been inserted into spaces cut for that purpose. The size and shape of the metallic copper pieces, and their position in the electrode, is chosea so as to sputter the correct amount of copper and so that the copper is uniformly dispersed in the pseudo-alloy, as in known to one skilled in the art. The chamber is then evacuated to a pressure of about 5 x 10-6 to 3 x 10-5 torr and a small amount of inert gas, such as argon, is fed into the chamber to a pressure of about 15 millitorr. The pressure is not critical and can vary from about 2 to about 100 millitorr. An amount of oxygen is required in the system that will produce about 10 to about 25 atomic percent of oxygen in the metal layer. As previously noted, oxygen is present as a contaminant in the inert gas and in the residual atmosphere in the vacuum chamber in generally sufficient amounts, but a predetermined amount of oxygen can be deliberately added for more precise control. Also as previously noted when a planar magnetron is employed in the chamber as the source of current, the voltage can be varied from about 300 - 1000 volts and the current can be up to about 10 amperes, depending on the rate of deposition desired and the size of the electrodes.

The current to the alloy-copper electrode is turned on and sputtering continued until a layer about 200 - 400 angstroms thick has been deposited onto the substrate.

The atomic per cent of copper in the pseudo-alloy as defined herein is also measured by Auger electron spectroscopy, after removing by sputter etching a layer about 100 angstroms thick. This step eliminates contamination of the surface and preferential sputtering effects.

The absolute Cu value is calculated according to the equation: y(Cu) = A(Cu) x 4.3 x 1.5 A(Ag) The 4.3 factor for Cu is obtained from the Handbook of Auger Electron Spectroscopy, referred to above.

The 1.5 factor takes into account the copper depletion resulting from preferential sputtering.

The Auger electron spectroscopy results given herein were obtained using a Scanning Auger Microprobe system manufactured by Physical Electronics Industries. The electron beam axis to the sample normal angle was 60".

The exact mechanism of the combination of improved adhesion and corrosion resistance of the pseudo-alloy metal films is unknown. As previously indicated it is presently believed that the copper serves to stress relieve the nickel-chromium-iron alloy film. The corrosion-resistance is a factory governed by oxidation of the metals present. Analyses show that the chromium and iron in the alloy are oxidized and the copper remains unoxidized, but thoroughly dispersed in an oxidized, chemical stable matrix. Thus the corrosion resistance of the pseudo-alloy remains high.

This last-mentioned aspect of the invention is further illustrated by the following example but it is to be understood again that the invention is not meant to be limited to the details described therein. In the example all parts and percentages are by weight unless otherwise noted.

Example 5 A vacuum chamber was fitted with a planar magnetron sputtering electrode made of Inconel-600 with copper inserts as described in Example 3.

A video disc made of a vinyl synthetic resin polymer 12 inches (30.48 centimeters) in diameter was suspended about 2 inches (5.08 centimeters) above the electrode and rotated at 40 rpm.

The chamber was evacuated to a pressure of 3 x 10-6 torr and backfilled first with oxygen to a pressure of 1.1 x 10-4 torr and then with argon to a total pressure of 1.5 x 10-2 torr.

As in Example 3, the electrode was then activated with 650 volts and 1.5 amperes of current, resulting in a deposition rate of about 330 to 400 angstroms per minute. Deposition was continued for about 30 seconds or until a layer about 200 angstroms thick had been deposited.

The resultant metal film was tested for adhesion to the disc as in Example 1. No film was removed when the Scotch tape was pulled off.

The film was tested by an accelerated corrosion test as follows: a layer of sodium chloride was evaporated onto the metal coated disc and heated to about 45"C. Air and H2S were bubbled through water and the gas stream passed continuously over the metal surface. The time was noted when a visible sign of corrosion appeared under a microscope, including color changes, pitting etc. No corrosion was noted after 24 hours.

In comparison, a film of copper alone containing 20 to 23 atomic percent of oxygen pitted severely after about 30 seconds.

The electrical resistance of the metal film was measured using two probes, one in the center of the disc and the other on the outside edge of the disc. The resistance was found to be less than 400 ohms, meeting the requirement for this application.

Stress measurements were made in known manner by depositing films of the pseudo-alloy on very thin aluminum oxide discs and noting the bending of the disc microscopically. Whereas a film of Inconel-600 about 225 angstroms thick had a compressive stress of 30 x 109 dynes/cm2 a pseudo-alloy coated disc of the invention had a compressive stress of only 5 x 109 dynes/cm2.

A metal coated vinyl disc as prepared above according to any of the Examples 2-5 above was coated with a polymer of styrene as follows: a vacuum chamber fitted as above was evacuated to a pressure to about 3 x 10-3 torr and backfilled with nitrogen to a pressure of about 8-10 x 10-3 torr. Styrene monomer was then added to a pressure of 13 to 15 x 10-3 torr. The metal coated disc was suspended about 2 inches (5.08 centimeters) above a planar magnetron source having an electrode 3.5 x 7 inches (8.9 x 17.8 centimeters) in size at a power supply frequency of about 10 kilohertz and a voltage of 680 volts. Power was turned on for 30 seconds and the disc was lowered to face the electrode and rotated at about 40 rpm for 2 minutes so as to deposit a styrene polymer film about 350 angstroms thick.

Compressive stress for the resultant film was only 4 x 109 dynes/cm2 for the trilayer metal film, only 3 x 109 dynes/cm2 for the other metal films.

It will have been noted that in all the foregoing no pretreatment of the vinyl disc prior to the deposition thereon of the initial copper layer, or copper-containing nickel-chromium (-iron) layer, has been mentioned, in particular no pre-sensitizing and pre-activating treatments such as form part of so-called electroless plating processes and serve to deposit very thin films of sensitizing and activating metals (typically tin and palladium) on to which the electroless deposition, e.g. of copper, is effected. It will be appreciated that no claim is made herein to articles in which the copper or copper-containing layer has been deposited according to such an electroless process.

WHAT WE CLAIM IS: 1. An article comprising polymeric material in adhesion with a layer of an alloy of chromium and nickel, wherein copper is included in said layer or as a copper layer between it and the polymeric material in an amount to improve the adhesion.

2. An article according to Claim 1 wherein said alloy contains from 65 to 80 per cent by weight of nickel, from 10 to 30 per cent by weight of chromium, and from 0 to 10 per cent by weight of iron.

3. An article comprising a polymeric substrate, a layer from about 25 to about 50 angstroms thick of copper on said substrate, and a layer from about 200 to about 400 angstroms thick of an alloy of chromium and nickel containing 0 to 10 per cent by weight of iron on said copper layer.

4. An article according to Claim 3 wherein said alloy contains from 65 to 80 per cent by weight of nickel, from 10 to 30 per cent by weight of chromium and from 0 to 10 per cent by weight of iron.

5. An article according to Claim 3 or 4 including a second layer of copper on said alloy layer and a coating of a polymeric material on said second copper layer.

6. An article comprising a polymeric substrate and a layer of an allov of nickel, chromium and copper adhered to said substrate, wherein said alloy contains 65-80 per cent by weight nickel, 10 to 30 per cent by weight chromium 0 to 10 per cent by weight iron and about 10 to about 15 atomic per cent of copper.

7. An article according to Claim 6 having a coating of a polymeric material on said alloy layer.

8. An article comprising a trilayer metal film adhered to a polymeric substrate, said film comprising a first layer about 25 to 50 angstroms thick of copper, a second layer about 200

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (19)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   torr.

   As in Example 3, the electrode was then activated with 650 volts and 1.5 amperes of current, resulting in a deposition rate of about 330 to 400 angstroms per minute. Deposition was continued for about 30 seconds or until a layer about 200 angstroms thick had been deposited.

   The resultant metal film was tested for adhesion to the disc as in Example 1. No film was removed when the Scotch tape was pulled off.

   The film was tested by an accelerated corrosion test as follows: a layer of sodium chloride was evaporated onto the metal coated disc and heated to about 45"C. Air and H2S were bubbled through water and the gas stream passed continuously over the metal surface. The time was noted when a visible sign of corrosion appeared under a microscope, including color changes, pitting etc. No corrosion was noted after 24 hours.

   In comparison, a film of copper alone containing 20 to 23 atomic percent of oxygen pitted severely after about 30 seconds.

   The electrical resistance of the metal film was measured using two probes, one in the center of the disc and the other on the outside edge of the disc. The resistance was found to be less than 400 ohms, meeting the requirement for this application.

   Stress measurements were made in known manner by depositing films of the pseudo-alloy on very thin aluminum oxide discs and noting the bending of the disc microscopically. Whereas a film of Inconel-600 about 225 angstroms thick had a compressive stress of 30 x 109 dynes/cm2 a pseudo-alloy coated disc of the invention had a compressive stress of only 5 x 109 dynes/cm2.

   A metal coated vinyl disc as prepared above according to any of the Examples 2-5 above was coated with a polymer of styrene as follows: a vacuum chamber fitted as above was evacuated to a pressure to about 3 x 10-3 torr and backfilled with nitrogen to a pressure of about 8-10 x 10-3 torr. Styrene monomer was then added to a pressure of 13 to 15 x 10-3 torr. The metal coated disc was suspended about 2 inches (5.08 centimeters) above a planar magnetron source having an electrode 3.5 x 7 inches (8.9 x 17.8 centimeters) in size at a power supply frequency of about 10 kilohertz and a voltage of 680 volts. Power was turned on for 30 seconds and the disc was lowered to face the electrode and rotated at about 40 rpm for 2 minutes so as to deposit a styrene polymer film about 350 angstroms thick.

   Compressive stress for the resultant film was only 4 x 109 dynes/cm2 for the trilayer metal film, only 3 x 109 dynes/cm2 for the other metal films.

   It will have been noted that in all the foregoing no pretreatment of the vinyl disc prior to the deposition thereon of the initial copper layer, or copper-containing nickel-chromium (-iron) layer, has been mentioned, in particular no pre-sensitizing and pre-activating treatments such as form part of so-called electroless plating processes and serve to deposit very thin films of sensitizing and activating metals (typically tin and palladium) on to which the electroless deposition, e.g. of copper, is effected. It will be appreciated that no claim is made herein to articles in which the copper or copper-containing layer has been deposited according to such an electroless process.

   WHAT WE CLAIM IS: 1. An article comprising polymeric material in adhesion with a layer of an alloy of chromium and nickel, wherein copper is included in said layer or as a copper layer between it and the polymeric material in an amount to improve the adhesion.
2. 2. An article according to Claim 1 wherein said alloy contains from 65 to 80 per cent by weight of nickel, from 10 to 30 per cent by weight of chromium, and from 0 to 10 per cent by weight of iron.
3. 3. An article comprising a polymeric substrate, a layer from about 25 to about 50 angstroms thick of copper on said substrate, and a layer from about 200 to about 400 angstroms thick of an alloy of chromium and nickel containing 0 to 10 per cent by weight of iron on said copper layer.
4. 4. An article according to Claim 3 wherein said alloy contains from 65 to 80 per cent by weight of nickel, from 10 to 30 per cent by weight of chromium and from 0 to 10 per cent by weight of iron.
5. 5. An article according to Claim 3 or 4 including a second layer of copper on said alloy layer and a coating of a polymeric material on said second copper layer.
6. 6. An article comprising a polymeric substrate and a layer of an allov of nickel, chromium and copper adhered to said substrate, wherein said alloy contains 65-80 per cent by weight nickel, 10 to 30 per cent by weight chromium 0 to 10 per cent by weight iron and about 10 to about 15 atomic per cent of copper.
7. 7. An article according to Claim 6 having a coating of a polymeric material on said alloy layer.
8. 8. An article comprising a trilayer metal film adhered to a polymeric substrate, said film comprising a first layer about 25 to 50 angstroms thick of copper, a second layer about 200

   to about 400 angstroms thick of an alloy of nickel and chromium which can contain up to about 10 pe cent weight of iron and which contains from about 20 to about 30 atomic per cent of oxygen, and a third layer about 25 to 50 angstroms thick of copper.
9. 9. An article according to Claim 8 wherein said alloy contains from 65 to 80 weight per cent of nickel, from 10 to 30 weight per cent of chromium, and from 0 to 10 weight per cent of iron.
10. 10. An article according to Claim 8 or 9 having a polymeric coating on said copper third layer.
11. 11. An article comprising a metal layer adhered to a substrate of a polymeric material, which layer comprises a pseudo-alloy of an alloy of nickel and chromium which can contain up to 10% by weight of iron and which contains from about 10 to about 25 atomic per cent of oxygen and from about 10 to about 15 atomic per cent of copper, said layer being about 200-400 angstroms thick.
12. 12. An article according to Claim 11 wherein said alloy contains from 65 to 80 per cent by weight of nickel, 10 to 30 per cent by weight of chromium and from 0 to 10 per cent by weight of iron.
13. 13. An article according to Claim 12 wherein said composition contains from 10 to 20 atomic per cent of oxygen.
14. 14. An article according to Claim 11, 12 or 13 having a polymeric coating on said layer.
15. 15. An article according to Claim 5, 7, 10 or 14 wherein said polymeric coating is a polymer of styrene.
16. 16. An article according to any of Claims 2-15 wherein said substrate is a vinyl synthetic resin.
17. 17. An article according to any of Claims 2-17, being a metallized video disc.
18. 18. A video disc according to Claim 17 wherein the polymeric substrate carries video information in the form of geometric variations in a spiral groove in a surface thereof, said alloy layer adhering to said surface and conforming to said variations.
19. 19. A video disc or other article having a nickel-chromium coated polymeric substrate with copper-enhanced adhesion constituted or prepared substantially according to any of the hereinbefore Examples.