WO2004015169A2 - Method for coating the surface of metallic material, device for carrying out said method - Google Patents

Abstract

The invention relates to a method for coating the surface of a metallic material having a crystallographic structure. The inventive method consists in producing a first coating of said material with a metal layer or a metal alloy layer having a melting point of Tf and a thickness equal to or less than 2.5νm, heating the first coating by a flash heating in such a way that it is heated to a temperature ranging from 0.8 Tf to Tf, producing a second metal or metal alloy coating with a thickness equal to or less than 1νm. The device for carrying out said method and the thus coated metallic material are also disclosed.

Description

Method for coating the surface of a metallic material, device for using it and product thus obtained.

The invention relates to the coating of metal surfaces. More specifically, it relates to treatments for coating the surface of a metallic material intended to give it a three-dimensional visual effect. Such a visual effect can be obtained with holograms, which are obtained by recording and reproducing an image using two laser beams on a photosensitive support capable of recording light interference of good contrast. Such supports are, for example, thermoplastic films, photopolymers, photosensitive films ... Up to now, to obtain a three-dimensional visual effect on a metal surface, no other means is known than to apply by bonding or co-laminating on said surface a photosensitive support of the type just described. The decoration of metallic packaging in steel or aluminum is a privileged use of this technique, which has the disadvantage, for the metallurgical enterprise, of requiring the intervention of an external supplier who delivers the photosensitive support to it. In addition, the support is liable to become detached from the packaging or to be damaged during the treatments and manipulations undergone by said packaging after bonding or co-laminating.

The object of the invention is to propose a method making it possible to obtain three-dimensional visual effects on the surface of a metallic material without having recourse to the application to this surface of a photosensitive support.

To this end, the subject of the invention is a method of coating the surface of a metallic material having a crystallographic structure, according to which a first coating of said material is carried out with a layer of a metal or of a metallic alloy with melting point equal to T _f , of thickness less than or equal to 2.5 μm, characterized in that:

- A heat treatment is carried out on said first coating by a rapid heating means so as to bring the surface of said first coating to a temperature between 0.8T _f and T _f ; - And a second coating is deposited from a metal or a metal alloy, of thickness less than or equal to 1 μm.

According to a variant of the method, said first and second coatings have melting points less than or equal to 700 ° C. Said first and second coatings can be made of the same material.

According to a variant of the process, the deposition on said second coating is then carried out of a transparent mineral film.

Said metallic material to be coated may preferably be carbon steel, stainless steel, or aluminum or one of its alloys.

Said first coating can preferably be produced by electrodeposition or by a vacuum deposition process. Said rapid heating means may preferably be an infrared heating device, an induction heating device, a plasma effluvium device with a non-reactive gas or an ion bombardment with a non-reactive gas .

Said second coating can preferably be produced by electrodeposition or by a vacuum deposition process.

Said transparent mineral film can be deposited by a reactive plasma deposition process.

Said first and second coatings can each consist of tin and / or aluminum. Said mineral film can consist of a metal oxide or a mixture of metal oxides, preferably chosen from oxides of austenitic stainless steel, chromium, titanium, silicon, zinc, tin.

The metallic material can be in the form of a moving strip, and the various stages of the process can be carried out continuously by means of installations arranged successively on the path of the moving strip.

The invention also relates to a device for coating a metallic material in the form of a strip, characterized in that it comprises means for scrolling said strip and, successively arranged on the path of said strip:

- first means for coating said strip with a layer of a metal or a metal alloy with a melting point equal to T _f ;

means for rapid heating of said strip which can bring the surface of said layer to a temperature between 0.8T _f and T _f ; and - second means for coating said strip with a layer of metal or metal alloy.

The device may comprise, following said second means for coating said strip with a layer of a metal or a metal alloy, means for coating said strip with a transparent mineral film.

The invention also relates to a metallic material, characterized in that it comprises on at least one of its surfaces a metallic coating with a three-dimensional visual effect, said coating being formed directly on said surface of the material, and produced in particular by the previous process. As will be understood, the invention consists in obtaining the three-dimensional visual effect sought by a series of surface treatments of the metallic material itself. A multilayer coating is thus obtained which cannot be detached from the metallic material and can be produced by the metallurgical company which manufactured the basic material. This coating, in addition to its aesthetic qualities, has many technical advantages, and allows the manufacturer of the metallic material to retain complete control of the decoration process.

The invention will be better understood on reading the description which follows given with reference to appended FIGS. 1 to 6 which show the aspects of different coatings obtained by various variants of the method according to the invention.

The starting material is a metallic material, such as carbon steel, stainless steel, aluminum or an alloy thereof, etc. It is for example in the form of a plate or a wound strip. In the latter case, it is possible to carry out the treatment which will be described by unwinding the strip and scrolling it continuously in an installation where the apparatuses making it possible to carry out the different stages of the treatment are arranged one after the other. on the path of the strip. In order for the desired aesthetic effect to be obtained, the metallic material used as a substrate must have a crystallographic structure.

Before proceeding with the deposition, in a manner known per se, a brightening of the surface of the material will be carried out in order to eliminate any surface contamination.

The first process step is the deposition of a first coating, comprising a metallic member (aluminum or tin, for example) or a metal alloy, preferably low-melting point T _f of the order of 700 ° C or lower. This coating must have a thickness less than or equal to 2.5 μm. Advantageously, it is produced by an electrodeposition process, or by a vacuum deposition process. Among the vacuum deposition methods which can be used, mention may be made of the conventionally known methods of vacuum evaporation, magnetron sputtering, ion plating, self-induced ion plating.

The second stage of the process is a heat treatment carried out on the first coating, by a rapid heating means, such as infrared lamps, an inductor, a plasma effluvium, or an ion bombardment with a non-reactive gas such as 'a rare gas. This heat treatment must bring the surface of the first coating to a temperature between 0.8 T _f and T _f . For it to be carried out with kinetics compatible with its execution on a strip moving at a speed of the order of 100 m / min, it is preferable that T _f be less than or equal to 700 ° C.

The third step of the process is the deposition of a second coating, from a metallic element or an alloy identical or not to the material of the first coating. This coating must have a thickness not exceeding 1 μm. It can be produced by the same methods as the first coating.

Preferably (but not necessarily), the method may include a fourth step consisting in depositing on the second metallic coating a transparent mineral film. Materials such as oxides of austenitic stainless steel, chromium, titanium, silicon, zinc, tin (non-limiting list) and their mixtures are particularly indicated. This transparent mineral deposition can be carried out by any means known for this purpose, the methods using a reactive plasma deposition being particularly indicated. If this film has a thickness less than or equal to 1 μm, a colored coating can be obtained by interference effect of the mineral film. Green, yellow, blue, purple and red colors are accessible in this way, depending on the refractive index of the deposited material. In general, this transparent film gives an appearance of additional depth to the three-dimensional appearance patterns obtained following the first three steps of the process.

The appearance of patterns on the surface of the substrate requires, as has been said, that the latter has a crystallographic structure. Indeed, the germination of the solidification patterns of the metal deposits occurs on the basis of preferential sites on the surface of the substrate, which exist only if the substrate has a crystallographic structure.

The size of the patterns obtained depends on the amount of energy used during the second step of the process and on the thickness of the coating: the patterns will be all the greater as this amount of energy and / or this thickness will be important. The use, as coating material during the first step of the process, of a metal or alloy with a low melting point (700 ° C. or less) makes it possible to carry out the metallurgical transformation of the coating during the second step in a time very brief. The heating methods which have been mentioned make it possible to provide the necessary energy in a minimum of time.

Compared to obtaining three-dimensional visual effects by photosensitive supports applied to the metal product, the method according to the invention has several advantages. As we said, it allows the manufacturer of metal products to retain full control of the process. The coating generating the three-dimensional visual effect here being an integral part of the support, there is no risk of it coming off during subsequent treatments and manipulations. In addition, especially if the process is used in its complete four-stage version, the coating thus obtained improves the resistance of the substrate to cosmetic corrosion. The coating is also more resistant to ultraviolet and temperature. It is less sensitive to fingerprints. It has great surface hardness, which makes it less susceptible to scratches. It is easy to clean and is resistant to cleaning products and other mechanical stresses. Finally, it is possible, if the coating metal used is suitable (for example tin), to make the coating compatible with food use.

Different examples of implementation of the method according to the invention will now be described. They were executed on mild steel sheets 200 x 200mm and 0.7mm thick. These sheets have previously been degreased conventionally by the wet method (solvent stirred by ultrasound). Then they were subjected to an ion pickling from an argon plasma in a vacuum reactor which was then used during the various stages of carrying out the process according to the invention.

Example 1

In the first step of the process according to the invention, the sheet is coated with a 0.8 μm layer of tin by magnetron sputtering in an argon atmosphere under a pressure of 10 ^"3 mbar (0.1 Pa). target is 0.9A and the target voltage is 450 V. The tin deposition rate is 0.25μm / min.

In the second step of the process according to the invention, the sheet is heat treated with an argon plasma under a pressure of 10 ^"3 mbar (0.1 Pa). The energy given to the argon ions is 400 eV and the dose of ions received by the sheet is 4.7.10 ²² ArVm ² ions. The sheet is placed as a cathode. The surface of the tin is brought to a temperature of the order of 210 ° C.

In the third step, a 0.4 μm tin coating is deposited by magnetron sputtering, under the same experimental conditions as for the first coating.

In the fourth step, CVD plasma is deposited with a transparent silica film, with a thickness of 0.1 μm. The deposition is carried out in an atmosphere composed of hexamethyldisiloxane (HMDSO) and oxygen, under a pressure of 10 ^"3 mbar (0.1 Pa), with a ratio of the partial pressures of HMDSO and O ₂ of 1 / 10. A frequency current of 50 kHz is used at a power of 100 W. The deposition rate is 1.0 μm / min.

This coating gives a coating whose external appearance is shown in FIG. 1, having anti-corrosion and anti-fingerprint properties, easy to clean, and having a high surface hardness. It is able to withstand high mechanical, chemical and thermal stresses.

Example 2

0,4, une pression totale de 5.10^"3 mbar (10,5Pa) et une puissance de 1 ,7kW. On obtient ainsi un revêtement représenté sur la figure 2, présentant des propriétés analogues à celui de l'exemple 1 , avec en plus un aspect coloré en bleu du fait de l'indice de réfraction de l'oxyde de titane (2,5) et les propriétés particulières à l'oxyde de titane, à savoir une grande inertie chimique, une bonne tenue à haute température, une bonne résistance aux attaques chimiques, et une action autonettoyante due à son effet catalytique de dégradation des matières contenant du carbone et de l'oxygène en présence de lumière ultra-violette.A coating of said steel sheet is carried out under conditions identical to those of Example 1 for the first three stages. The fourth step consists in producing a titanium oxide film colored by reactive magnetron sputtering of a titanium target. Its thickness is 0.05 μm. The conditions for its realization are an O ₂ / Ar atmosphere with

0.4, a total pressure of 5.10 ^"3 mbar (10.5 Pa) and a power of 1.7 kW. This gives a coating represented in FIG. 2, having properties similar to that of Example 1, with in plus a blue colored appearance due to the refractive index of titanium oxide (2.5) and the properties specific to titanium oxide, namely great chemical inertness, good resistance to high temperature, good resistance to chemical attack, and a self-cleaning action due to its catalytic effect of degradation of materials containing carbon and oxygen in the presence of ultraviolet light.

Example 3

This mild steel sheet is coated under the same conditions as for Example 2, except that the thickness of the first deposit of tin is increased to 1.2 μm, as well as the dose of ions received by the first layer of tin during the second step of the process. This dose reaches here 9.4.10 ²² Ar ^" 7m ² ions. The surface of the tin is brought to a temperature of the order of 235 ° C. The result is visible in FIG. 3.

EXAMPLE 4 A coating of said mild steel sheet is carried out under the same conditions as for Example 2, except that, as in Example 3, the dose of ions received by the first layer is increased to 9 , 4.10 ²² Ar ⁺ ions / m ² , and increasing the thickness of the titanium oxide film to 0.08 μm. The result is visible in FIG. 4. It is noted that the increase in energy used during the second stage of the treatment leads to a substantial increase in the size of the patterns.

EXAMPLE 5 The said sheet is coated under conditions identical to those of Example 1, except that, for the second step, two infrared lamps are used to heat the substrate and its first layer of tin, and that no oxide is deposited on the second layer of tin. Only the first three stages of the process are therefore carried out, those which are essential for obtaining the desired three-dimensional visual effect. The heating of the tin layer is static and lasts 8 minutes in a lamp oven set at a temperature of 200 ° C. The result is visible in Figure 5.

EXAMPLE 6 A very thin sheet of 0.2 mm thick in mild steel 200 × 200 mm is coated with a layer of electrodeposited tin, so as to obtain a sheet of “tinplate” of the type usually used in the food sector. Then the second and third steps of the method according to the invention are carried out, under conditions identical to those of Example 2. The optional fourth step of the treatment according to the invention is not executed. The result is visible in Figure 6.

Example 7

In a first step of the process according to the invention, the sheet is coated with an aluminum layer of 0.6 μm by magnetron sputtering in an argon atmosphere under a pressure of 10 ^"3 mbar (0.1 Pa). target is 1.8A and target voltage 355V The deposition rate of aluminum is

0,33μm / min. In the second step of the process according to the invention, the sheet is heat treated with an argon plasma under a pressure of 10 ^"3 mbar (0.1 Pa). The energy imparted to the argon ions is 280 eV and the dose ion is 18.4.10 ²² Ar ⁺ ions / ^m2. the plate is placed as the cathode. the surface of the coated aluminum is heated to a temperature of 615 ° C at the end of treatment.

In a third step, a coating of tin is deposited by magnetron sputtering, under the same experimental conditions as those described in the third step of Example 1. A coating is obtained under these conditions of development. identical to that of the example in FIG. 1.

Example 8

This mild steel sheet is coated with tin under the same conditions as for Example 3 for the first two stages. In a third step, an aluminum coating is deposited by magnetron sputtering, under the same experimental conditions as those described in the first step of Example 7 except that an aluminum deposit of thickness 0 is produced. , 4μm. Under these production conditions, a coating is obtained whose external appearance is identical to that of the example in FIG. 3.

The examples of materials forming the substrate and the different layers which coat it, as well as the conditions for their formation have been given without limitation. Those skilled in the art can imagine variants depending on the properties sought for the final product.

If it is desired that the three-dimensional visual effect is obtained only on one or portions of the surface of the metallic material, it is possible to protect the material by one or more masks masking the areas not to be coated during the various treatments undergone.

Claims

1. A method of coating the surface of a metallic material having a crystallographic structure, according to which a first coating of said material is carried out with a layer of a metal or of a metallic alloy with a melting point equal to T _f , d '' thickness less than or equal to 2.5μm, characterized in that: - A heat treatment is carried out on said first coating by rapid heating means so as to bring the surface of said first coating to a temperature between 0.8T _f and T _f ; - And a second coating is made from a metal or a metal alloy, of thickness less than or equal to 1 μm. 2. Method according to claim 1, characterized in that said first and second coatings have melting points less than or equal to 700 ° C. 3. Method according to claim 1 or 2, characterized in that said first and second coatings are made of the same material. 4. Method according to one of claims 1 to 3, characterized in that the deposition is then carried out on said second coating of a transparent mineral film. 5. Method according to one of claims 1 to 4, characterized in that said metallic material to be coated is carbon steel. 6. Method according to one of claims 1 to 4, characterized in that said metallic material to be coated is stainless steel. 7. Method according to one of claims 1 to 4, characterized in that said metallic material to be coated is aluminum or one of its alloys. 8. Method according to one of claims 1 to 7, characterized in that said first coating is produced by electrodeposition. 9. Method according to one of claims 1 to 7, characterized in that said first coating is produced by a vacuum deposition process. 10. Method according to one of claims 1 to 9, characterized in that said rapid heating means is an infrared heating device. 11. Method according to one of claims 1 to 9, characterized in that said rapid heating means is an induction heating device. 12. Method according to one of claims 1 to 9, characterized in that said rapid heating means is a device for effluvage under plasma with a non-reactive gas. 13. Method according to one of claims 1 to 9, characterized in that said rapid heating means is an ion bombardment device with a non-reactive gas. 14. Method according to one of claims 1 to 13, characterized in that said second coating is produced by electrodeposition. 15. Method according to one of claims 1 to 13, characterized in that said second coating is produced by a vacuum deposition process. 16. Method according to one of claims 4 to 15, characterized in that the said transparent mineral film is deposited by a reactive plasma deposition process. 17. Method according to one of claims 1 to 16, characterized in that said first and / or said second coating consist of tin. 18. Method according to one of claims 1 to 17, characterized in that said first and / or said second coating consist of aluminum. 19. Method according to one of claims 1 to 18, characterized in that said mineral film consists of a metal oxide or a mixture of metal oxides. 20. The method of claim 19, characterized in that the said metal oxide (s) are chosen from oxides of austenitic stainless steel, chromium, titanium, silicon, zinc, tin. 21. Method according to one of claims 1 to 20, characterized in that the metallic material is in the form of a moving strip, and in that the various stages of the method are carried out continuously by means of installations arranged successively on the path of the running tape. 22. Device for coating a metallic material in the form of a strip, characterized in that it comprises means for scrolling said strip and, arranged successively on the path of said strip: - first means for coating said strip with a layer of a metal or a metal alloy with a melting point equal to T _f ; means for rapid heating of said strip which can bring the surface of said layer to a temperature between 0.8T _f and T _f ; and - second means for coating said strip with a layer of metal or metal alloy. 23. Device according to claim 22, characterized in that it comprises, following said second means for coating said strip with a layer of a metal or a metal alloy, means for coating said strip with a mineral film transparent. 24. Metallic material, characterized in that it comprises, on at least one of its surfaces, a metallic coating with a three-dimensional visual effect, said coating being formed directly on said surface of the material. 25. Metallic material according to claim 24, characterized in that it is produced by the method according to one of claims 1 to 21.