WO2003035923A1

WO2003035923A1 - Method for making coloured parts

Info

Publication number: WO2003035923A1
Application number: PCT/CH2001/000635
Authority: WO
Inventors: Pierre-Albert Steinmann; Stéphane Meuterlos
Original assignee: Haute Ecole Neuchateloise
Priority date: 2001-10-25
Filing date: 2001-10-25
Publication date: 2003-05-01

Abstract

The invention concerns a method for making coloured metal parts, such as watch hands, comprising the following steps: 1) machining a brass substrate, 2) PVD deposition of a steel coating on said substrate, 3) blueing of said steel coating by surface oxidation with a hot air stream.

Description

PROCESS FOR MANUFACTURING COLORED PARTS

The present invention relates to a method for manufacturing colored parts as well as parts produced by this method. The present invention relates in particular to decorative watch elements, for example hands, dial appliques or dials, manufactured according to this process.

In the watchmaking sector, needle manufacturers sometimes use a particular method to impart a dark coloration known as "steel blue" to certain watch hands. The raw material used for making needles by stamping is generally carbon steel. The surface blueing of the needles is then obtained by complex heat treatments, aimed at oxidizing a surface layer of the metal.

The percentage of rejection of finished parts is very high. Indeed, stamping fine needles in very thin steel plates is a delicate operation. Furthermore, the bluing process, in particular the depth of oxidation on which the color obtained depends, is difficult to master and to reproduce.

In addition, the use of steel in the manufacture of needles limits the possibilities of shaping and machining of the needles. In particular, it is extremely difficult to manufacture steel needles of complicated shape, especially when facets or other relief patterns are desired.

When a more complex needle shape is required, brass or another material that is easier to machine than steel is generally used as the base material. In this case, the traditional bluing described above becomes impossible. The needles can be colored by coating them by PVD deposition with a thin layer of blue color. But the famous steel blue color is not reproduced identically. In addition, the reproducibility of color by this type of process is difficult to guarantee.

Similar problems are encountered during the manufacture of other colored parts in a watch, for example for the manufacture of dials, of appliques on the dials, of watch glasses, of screws, of boxes, of bracelets, of plates, etc. Steel blue parts are also used in fields such as eyewear, jewelry, writing instruments, lighters in particular.

An object of the present invention is to propose a new method of manufacturing parts which avoids the drawbacks of the prior art and which makes it possible to obtain the color “steel blue” identically, or other colors according to the requirements. aesthetic, and which avoids the drawbacks of the processes of the prior art.

This object is achieved by means of a method according to claim 1, preferential variants being moreover indicated in the dependent claims.

In particular, this object is achieved by means of a process for manufacturing colored parts, in which a substrate composed of a first material, preferably a material easier to machine than steel, is machined and then covered with a coating consisting of a ferrous material which is then colored by surface oxidation.

This process has the advantage of using a material that is easy to machine to determine the shape of the needle and of using steel only as a surface coating to determine the color of the part thus machined. All the colors which can be obtained by oxidation of the steel, in particular the steel blue color, can thus be reproduced identically.

This process also has the advantage of facilitating the reproducibility of the desired color. Indeed, the steel layer deposited can be chosen thin enough to limit the range of color variations depending on the depth of oxidation. In addition, the steel blue color is much more easily controlled when a layer of oxidized steel is deposited later than during the reactive deposition of an oxide layer, the stoichiometry of which influences the color obtained.

The process makes it possible to manufacture parts with an astonishing aesthetic appearance, since their color is that of oxidized steel but the shape of which is difficult or even impossible to machine from this material. In particular, one can manufacture finely worked watch hands but which have the robust and resistant appearance of steel.

The invention will be better understood on reading the description given by way of example and illustrated by the single appended figure which shows a schematic view of a complete installation for coloring parts by oxidation.

FIG. 1 illustrates by way of example a complete system for coloring parts according to an alternative embodiment of the invention. The system comprises a workpiece driving device constituted here by a strip 2 unwound from a starting roller 20 and wound on a finishing roller 21. The pieces to be colored are placed on the strip 2 near the roller departure 20 and taken away after treatment near the arrival roller 21. In a variant, the pieces to be colored are linked together and are only separated after coloring; in this case, the strip 2 can be replaced by series of linked parts.

In this example, the parts to be treated are constituted by watch hands machined during operations not shown.

As mentioned above, other types of parts can however be colored with this process. The machining can include, for example stamping operations, chip removal operations, for example by diamond or chamfering, injection, molding or sintering operations, etc. The substrate 10 of the part to be colored is preferably composed of a metallic material which is easy to shape and to machine, for example a copper alloy such as brass. The substrate could also be made of another metallic alloy, or even of a molded synthetic material or of sintered ceramic.

The machined substrates are then chemically degreased and then dried, for example using a solvent / co-solvent cleaning system, in order to improve the adhesion of the coating deposited subsequently.

The substrates 10 placed on the strip 2 are introduced into the deposition area of the ferrous coating. In the preferred variant illustrated, this zone consists of a continuous sputtering installation 3 comprising two targets 34, 35 with a diameter of 100 mm in two separate portions B and C. The target 35 consists of a ferrous material, for example DIN Ck45 steel (0.45% carbon) while target 34 can be made of titanium for example. The distance between the targets and the substrates is for example 80mm. The pressure in the enclosure is reduced to 10 ^"5 Pa.

The targets 34, 35 are preferably cleaned before any use during an operation called "presputtering". For this purpose, a negative DC or radio frequency voltage is applied to the targets. Argon cations in the enclosure will be accelerated by this tension and projected on the targets which will be thus perfectly cleaned.

The first portion A makes it possible to carry out an ionic pickling of the substrate 10. For this purpose, a neutral gas, for example argon, is introduced into the enclosure until a partial pressure of argon is obtained. of 1 Pa for example. The substrate 10 is negatively polarized so as to create a potential difference sufficient for the ionization of the argon gas. The neutral atom of gas becomes a cation 36 which will be accelerated towards the negatively charged substrate 10. Under the effect of the impact of the argon ions 36, the surface of the substrate 10 thus undergoes pickling which gives it a state of cleanliness allowing better adhesion of the coatings on the substrate. Conclusive tests were carried out with a power of 100W applied in radiofrequency mode, for example with a frequency of 13.56 MHz, on the substrate 10 for a spraying duration of 5 minutes.

The substrate is then transferred to the second portion B of the deposition machine 3, making it possible to deposit a bonding sub-layer, for example a coating based on titanium. This is optional and is only necessary if the substrate material does not allow good adhesion of the ferrous coating, or if corrosion resistance or improved hardness of the final part is desired. For this purpose, a negative DC or radiofrequency voltage is applied to the titanium target 34 while the substrate 10 is maintained at ground or negatively polarized. A magnetic field is preferably applied by the magnetron 31 which makes it possible to increase and better concentrate the spraying by superimposing a magnetic field on the electric field. The gas ions 36, for example of argon, are accelerated towards the target 34 and pulverize it. Titanium atoms 38 are thus ejected from the target 34 in the direction of the substrate 10 where they condense to form a coating 11. The nominal power applied to the cathode and the deposition time are respectively 75 watts and 10 minutes for example. At the end of this operation, the substrate is coated with a bonding sublayer 11. Experiments have shown that certain titanium atoms in enclosure B are positively ionized. In a preferred variant of the invention, a slightly negative voltage will therefore be applied to the substrate 10 in order to accelerate these ions and thus improve their penetration and adhesion to the substrate. The voltage will however be lower in absolute value than that applied to the target 34, in order to avoid a pickling effect by the argon ions 36.

The deposition of the ferrous alloy coating 12 is carried out in the third portion C of the deposition machine 3. The operating conditions of this third portion are the same as that of the second portion, except that the target of titanium 34 is replaced by a steel target 35 as indicated above, and that the nominal power and the duration of the deposition are respectively 400 watts and ten minutes for example. The exposed faces of the substrate are covered at the end of this operation with a coating of steel 12 with a thickness, exaggerated in the figure, of the order of 1 micrometer.

In the context of this invention, it is also possible to use other types of PVD (Physical Vapor Deposition) deposition, such as vacuum evaporation by resistance heating, by induction, by electron bombardment, by cathode arc, or by laser ablation. for example. Chemical and electrochemical deposition methods can also be used to cover the substrate 10 with a thin coating of ferrous alloy.

The deposition machine illustrated in this figure comprises three portions A, B, C making it possible to carry out the operations of ionic cleaning, of deposition of the bonding sub-layer 11 and of deposition of the ferrous coating 12 in parallel on three batches of rooms. It is of course also possible to carry out the ion cleaning operations and the deposition of ferrous materials one after the other on the same machine by modifying the operating parameters for example as follows:

On the other hand, it is possible to simultaneously treat in each of the portions A, B and C of the deposition machine a batch of substrates 10, for example a batch of 100 needles.

The coated substrate or batch of substrate is transported by the strip 2 and returned to the open air. It is then subjected to a heat source which causes it to become blue by oxidation of the iron on the surface. In the example illustrated, the substrate is heated by electromagnetic induction by means of a coil 4. Another possibility, not illustrated, would consist in using a flow of hot air. The color of the coating obtained depends on the thickness of the oxide layer 13, the temperature applied and the duration of exposure to heat. The use of a sufficiently thin metallic coating 12 makes it possible to reduce the range of variation of the oxide thickness and therefore to improve the reproducibility of the color. Conclusive tests to obtain the desired steel blue were carried out with the following parameters in the case of the use of a coating 12 of iron or extra mild steel:

In the case of a steel with 0.5% carbon, the steel blue color can be obtained for example in 80-100 hours at 200 °. Extra hard steel turns blue in 5 minutes at 300 ° or in 1 minute at 325 °.

Oxidation can also be accelerated or better controlled by placing the part to be blued in a better controlled atmosphere, for example under partial vacuum or in an oxygen-enriched atmosphere. In a variant, the steel blue color is obtained by soaking the part in a heated salt bath, for example in a bath of potassium nitrogen and sodium nitrogen heated to a temperature between 210 ° and 650 °. The oxidation is stopped by soaking the part in water to dissolve the rest of the salts.

Oxidation under partial vacuum or with additional oxygen has the advantage of allowing identical blueing at a lower temperature. These techniques will therefore be used in particular when the substrate is made of a material, for example a synthetic material, which does not withstand heat well.

A transparent surface coating (not shown) can be deposited on the layer of oxidized ferrous material 13 to prevent corrosion and / or increase the hardness. This coating will, for example, be necessary for parts intended for use in an environment subject to humidity or to manipulation, for example for the external parts of a watch, for writing accessories, etc. However, it will generally not be necessary for watch hands. The surface coating can consist, for example, of a varnish or of a transparent layer deposited by a vacuum deposition method.

Claims

claims

1. Method for manufacturing colored parts, comprising the following steps:

1) machining of a substrate (10), 2) deposition of a coating (12) on said substrate, characterized in that said coating (12) consists of a ferrous material, said method comprising a step of coloring said coating by surface oxidation.

2. The method of claim 1, wherein said substrate is metallic.

3. The method of claim 2, wherein said substrate (10) is composed of a copper-based alloy.

4. The method of claim 3, wherein said substrate (10) is composed of brass.

5. The method of claim 1, wherein said substrate is composed of a synthetic or ceramic material.

6. Method according to one of claims 1 to 5, wherein said machining comprises a stamping operation and a machining operation by removing chips.

7. The method of claim 5, wherein said machining comprises an injection and / or sintering operation.

8. Method according to one of claims 1 to 7, wherein said ferrous material (12) is steel.

9. Method according to one of claims 1 to 8, wherein said ferrous material is deposited on said substrate by PVD.

10. The method of claim 9, wherein said ferrous material is deposited on said substrate by sputtering.

1 1. The method of claim 10, wherein a negative voltage is applied to said substrate (10) during said deposition.

12. Method according to one of claims 1 to 11, wherein said coloring is obtained by oxidation with hot air.

13. The method of claim 12, wherein said layer of ferrous material is composed of iron or mild steel, the air temperature for oxidizing the part being between 300 and 450 °, the duration of coloring being included between 30 seconds and 6 minutes.

14. The method of claim 13, wherein said layer of ferrous material is composed of hard steel, the air temperature for oxidizing the part being between 300 and 400 °, the duration of the coloring being between 10 seconds and 3 minutes.

15. Method according to one of claims 1 to 14, wherein said coloring is obtained by heating the part (10).

16. The method of claim 15, wherein said heating is obtained by electromagnetic induction.

17. Method according to one of claims 1 to 16, wherein said coloring is obtained by oxidation in an oxygen-enriched atmosphere.

18. Method according to one of claims 1 to 17, wherein said coloring is obtained by vacuum oxidation.

19. Method according to one of claims 1 to 18, wherein said coloring is obtained by soaking in a heated salt bath.

20. Method according to one of claims 1 to 19, wherein a sublayer (1 1) is deposited between said substrate and said coating (12) of ferrous materials to improve the adhesion of said coating (12) the hardness of the surface and / or to protect the substrate (10) against corrosion.

21. Method according to one of claims 1 to 20, wherein a transparent surface coating is deposited on said coating of ferrous material to prevent corrosion and / or increase the hardness.

22. Method according to one of claims 1 to 21, comprising a preliminary step (A) of ionic etching of the substrate.

23. Decorative element of a watch manufactured according to the method of one of the preceding claims.

24. Decorative element according to the preceding claim, consisting of a watch hand.

25. Installation (2, 3, 4) for coloring parts making it possible to implement the method of one of claims 1 to 22.