Vacuum deposition apparatus and method for coating a substrate

Abstract

The invention relates to a vacuum deposition apparatus for the continuous deposition of a coating formed from a metal or a metal alloy on a moving substrate, said apparatus comprising a vacuum chamber and means for moving the substrate along a given path through the vacuum chamber, wherein the vacuum chamber further comprises: - a central casing comprising a vapor jet coater and a substrate inlet and a substrate outlet located on two opposite sides of the central casing, the inner walls of the central casing being suitable for being heated to a temperature higher than the condensation temperature of the metal or metal alloy vapor; - a vapor trap in the form of an external casing at the substrate outlet of the central casing, the inner walls of the vapor trap being suitable for being maintained at a temperature lower than the condensation temperature of the metal or metal alloy vapor.

Description

[0001] This invention relates to a vacuum deposition apparatus for depositing coatings of metals or metal alloys (e.g., zinc and zinc-magnesium alloys) on a substrate, said apparatus being particularly designed for coating steel strips, but not limited thereto. The invention also relates to a method of using said apparatus for coating a substrate.

[0002] Various methods are known for depositing a metallic coating, ultimately composed of an alloy, onto a substrate (e.g., a steel strip). Among these are hot-dip coating, electrodeposition, and various vacuum deposition methods, such as vacuum evaporation and magnetron sputtering.

[0003] A method for continuously coating steel substrates is known from WO97 / 47782, in which a spray of metal vapor propelled at a velocity greater than 500 m / s is brought into contact with the substrate. To improve the efficiency of this method, the corresponding vacuum deposition apparatus includes a deposition chamber, the inner walls of which are adapted to be heated to sufficiently high temperatures to prevent the condensation of metal or metal alloy vapors thereon.

[0004] However, it has been observed that zinc vapor tends to leave the deposition chamber and condense outside the chamber in vacuum deposition equipment, which significantly reduces the deposition yield and complicates the cleaning process of vacuum deposition equipment.

[0005] Therefore, the object of the present invention is to overcome the shortcomings of prior art equipment and methods by providing a vacuum deposition apparatus that prevents the condensation of metal or metal alloy vapors outside the deposition chamber.

[0006] For this purpose, a first subject of the present invention is a vacuum deposition apparatus for continuously depositing a coating formed of a metal or metal alloy on a moving substrate, the apparatus comprising a vacuum chamber through which the substrate can move along a given path, wherein the vacuum chamber further comprises:

[0007] - A central housing comprising a vapor jet coating machine and a substrate inlet and a substrate outlet located on two opposite sides of the central housing. The inner wall of the central housing is adapted to be heated to a temperature above the condensation temperature of the metal or metal alloy vapor.

[0008] - A vapor trap, which is located at the base outlet of the central shell in the form of an outer shell, the vapor trap including an inward opening adjacent to the central shell and an outward opening on the opposite side of the vapor trap, the inner wall of the vapor trap being adapted to be maintained at a temperature below the condensation temperature of the vapor of the metal or metal alloy.

[0009] The device according to the invention may also have the following optional features, considered individually or in combination:

[0010] - The vacuum deposition apparatus also includes a second vapor trap located at the base inlet of the central housing.

[0011] - The length of the vapor trap in the direction of movement is 0.5 to 3.5 times the width of the base.

[0012] - The walls surrounding the inward opening of the vapor trap are perpendicular to the base path.

[0013] -The steam trap converges outward from the lower and upper walls.

[0014] - The vapor trap has a trapezoidal shape in its longitudinal section, pointing in the opposite direction to the central shell.

[0015] - The inner wall of the steam trap is removable.

[0016] - The heat regulation of the steam trap is achieved by supplying a cooling circuit with heat transfer fluids selected from water and nitrogen.

[0017] A second subject of the present invention is a method for continuously depositing a coating formed of a metal or metal alloy on a moving substrate, wherein the method comprises:

[0018] - In the first step, metal vapor is injected toward at least one side of a moving substrate and a first layer of metal or metal alloy is formed on said side by condensation of a first portion of the injected vapor. This first step is carried out in a central shell, which includes a substrate inlet and a substrate outlet located on two opposite sides of the central shell, and an inner wall heated to a temperature higher than the condensation temperature of the metal or metal alloy vapor.

[0019] - The second step, wherein a second layer of metal or metal alloy is formed on the side by the condensation of a second portion of the injected vapor, is carried out in a vapor trap located at the base outlet of the central shell in the form of an outer shell and including an inner wall maintained at a temperature below the condensation temperature of the metal or metal alloy vapor.

[0020] The second step of the method according to the invention can also optionally be carried out in a second vapor trap located at the base inlet of the central shell.

[0021] A third subject of the invention is a kit for assembling a vacuum deposition apparatus for continuously depositing coatings of metal or metal alloys on a moving substrate, the kit comprising:

[0022] - A central housing comprising a substrate inlet and a substrate outlet located on two opposite sides of the central housing, and a vapor outlet orifice for the vapor jet coating machine. The inner wall of the central housing is adapted to be heated to a temperature higher than the condensation temperature of the metal or metal alloy vapor.

[0023] - A vapor trap, the vapor trap being adapted to be in the form of an outer shell at the base outlet of a central shell, the vapor trap including an inward opening adjacent to the central shell and an outward opening on the opposite side of the vapor trap, the inner wall of the vapor trap being adapted to be maintained at a temperature below the condensation temperature of the vapor of the metal or metal alloy.

[0024] As will be explained, the present invention is based on adding a vapor trap at the outlet of the central shell, so that the vapor leaving the central shell condenses on both the substrate and the inner wall of the vapor trap. This increases the deposition rate on the one hand, and inhibits the condensation of vapor on the walls of the vacuum chamber on the other.

[0025] Other features and advantages of the invention will be described in more detail in the following description.

[0026] The invention will be better understood by referring to the accompanying drawings and reading the following description, which is provided for illustrative purposes only and is in no way intended to be limiting, in the drawings:

[0027] - Figure 1 This is a cross-section of one embodiment of the device according to the present invention.

[0028] - Figure 2 This is a cross-sectional view of one embodiment of the vacuum chamber according to the present invention.

[0029] It should be noted that, as used in this application, the terms “lower,” “below,” “inwards,” “outwards,” “upstream,” “downstream,” etc., refer to the position and orientation of the constituent elements described below when the different constituent elements of the equipment are mounted on the vacuum deposition line.

[0030] The object of this invention is to deposit a coating formed of a metal or metal alloy on a substrate. The object is particularly interested in obtaining a zinc or zinc-magnesium coating. However, the method is not limited to these coatings, but preferably includes any coating based on a single metal or a metal alloy, wherein the vapor pressure difference of the elements in the metal alloy at the bath temperature is no more than 10%, thus facilitating control of their respective relative contents.

[0031] For the purpose of providing guidance, it may be mentioned that coatings are made of zinc, which is considered alone or in combination as the main element, as well as one or more other elements such as chromium, nickel, titanium, manganese, magnesium, silicon and aluminum.

[0032] The coating thickness is preferably between 0.1 μm and 20 μm. On the one hand, a thickness less than 0.1 μm poses a risk of insufficient corrosion protection for the substrate. On the other hand, it is not necessary to exceed 20 μm to achieve the level of corrosion resistance required, particularly in the automotive or construction sectors. Typically, for automotive applications, the thickness can be limited to 10 μm.

[0033] Reference Figure 1 The device 1 according to the invention firstly includes a vacuum chamber 2 and means for moving a substrate through the chamber.

[0034] The vacuum chamber 2 is preferably maintained at 10°C. -8 Ba to 10 -3 A gas-tightly sealed box under pressure. It has an inlet lock and an outlet lock (not shown), between which a base S (e.g., a steel belt) can move along a given path P in a direction of movement.

[0035] Depending on the properties and shape of the substrate, the substrate S can be moved by any suitable means. In particular, a rotating support roller 3 on which a steel strip can be supported can be used.

[0036] Vacuum chamber 2 includes a central shell 4. This is a box that surrounds the substrate path P along a given length (typically 2m to 8m) in the direction of movement. Its walls define the cavity. It includes two openings: a substrate inlet 5 and a substrate outlet 6 located on two opposite sides of the central shell. Preferably, the central shell is a parallelepiped with a width slightly larger than the substrate to be coated.

[0037] The walls of the central housing are adapted to be heated. Heating can be achieved using any suitable means, such as an induction heater, a heating resistor, or an electron beam. The heating means are adapted to heat the inner walls of the central housing at a sufficiently high temperature to prevent the condensation of metal or metal alloy vapors thereon. Preferably, the walls of the central housing are adapted to be heated to a temperature above the condensation temperature of the metal element on which the coating to be deposited is formed, typically above 500°C, for example, 500°C to 700°C, to prevent the condensation of zinc vapor or zinc-magnesium alloy vapors. Because of these heating means, the inner walls of the central housing do not become clogged and the equipment does not need to be shut down frequently for cleaning.

[0038] Reference Figure 2 The central housing 4 also includes a vapor jet coating machine 7, which is preferably located on one side of the central housing parallel to the substrate path, next to the surface of the substrate S to be coated. This coating machine is suitable for jetting metal or metal alloy vapor onto the moving substrate S. It can advantageously consist of an extraction chamber provided with a narrow vapor outlet orifice 71 with a length approximately equal to the width of the substrate to be coated.

[0039] The vapor outlet orifice 71 can have any suitable shape, such as a slit that can be adjusted in both the length and width directions. The possibility of adapting its length to the width of the substrate to be coated makes it possible to minimize the loss of evaporated metal.

[0040] The coating machine is preferably an acoustic vapor jet coating machine, that is, a coating machine capable of generating a vapor jet at the speed of sound. This type of coating machine is also commonly referred to as a JVD (Jet Vapor Deposition) device. The reader can refer to patent application WO97 / 47782 for a more complete description of a variation of this type of device. The coating machine can be coupled to any kind of metal vapor generator, such as an induction-heated evaporation crucible or an electromagnetically levitated vapor generator.

[0041] Preferably, the central shell is surrounded by a heat insulation plate, which itself is preferably surrounded by a cooling plate. This allows for reduced heat loss in the vacuum chamber 2 and improved energy performance of the central shell.

[0042] Due to the design of the central housing (especially the heating device and the vapor jet coating machine 7), metal or metal alloy vapor is sprayed toward at least one side of the substrate and a first layer of metal or metal alloy is formed on that side by the condensation of a first portion of the sprayed vapor, without the condensation of vapor on the inner wall of the central housing.

[0043] The vacuum chamber 2 also includes a vapor trap 8, which is located at the base outlet 6 of the central housing 4 (i.e., downstream of the central housing in the direction of movement of the base) and is in the form of an outer housing.

[0044] Preferably, the vacuum chamber 2 further includes a second vapor trap 8, which is located at the base inlet 5 of the central housing 4 (i.e., upstream of the central housing in the direction of movement of the base) and is in the form of an outer housing.

[0045] Each vapor trap 8 is a box that surrounds the path of the base along a given length (typically 0.2 m to 7 m, for example, 0.5 to 3.5 times the width of the base) in the direction of movement. Its walls define a cavity. It includes an inward opening 9 and an outward opening 10 located on two opposite sides of the vapor trap and adapted to allow the base to enter and exit the vapor trap. The inward opening 9 is adjacent to the central housing, while the outward opening 10 is located in an opposite position.

[0046] The walls of the vapor trap 8 are adapted to be thermally conditioned. Thermal conditioning can be achieved by any suitable means, such as a cooling circuit supplied with a heat transfer fluid (e.g., water or nitrogen). The thermal conditioning device is adapted to maintain the inner walls of the vapor trap at a sufficiently low temperature (typically below 100°C) to facilitate the condensation of metal or metal alloy vapors on the inner walls. Due to these thermal conditioning devices, metal or metal alloy vapors escaping from the central housing are trapped and not released in the vacuum chamber, which would otherwise become clogged if released there.

[0047] Thanks to the vapor trap 8, the portion of the ejected vapor that does not condense on the substrate and leave the central housing 4 is captured in a cavity smaller in size compared to the cavity of the vacuum chamber 2, which facilitates cleaning of the device. Furthermore, the portion of the ejected vapor has more time to condense on the substrate as a second layer of metal or metal alloy, which increases the deposition rate.

[0048] Each vapor trap 8 is in contact with the central housing 4. Specifically, the inward openings 9 of the first vapor trap and the second vapor trap are aligned with the base inlet 5 and the base outlet 6 of the central housing, respectively, to form a channel connecting the central housing to each vapor trap.

[0049] According to a variation of the invention, the vapor trap is rectangular in shape.

[0050] Preferably, the walls surrounding the inward opening of the vapor trap are perpendicular to the substrate path P. Due to this location, these walls are as far as possible from the openings 5, 6 of the central shell, which reduces the risk of opening blockage due to metal deposition on the cold walls of the vapor trap located near the openings. Because of this location, the vapor entering the vapor trap also more preferably condenses on the substrate rather than on the walls, which further increases the deposition rate.

[0051] Preferably, the lower and upper walls of the steam trap converge outwards, meaning the height of the outer wall is less than the height of the inner wall. Therefore, steam is more effectively trapped before reaching the outward opening 10.

[0052] More preferably, the vapor trap 8 has a trapezoidal shape in its longitudinal section pointing in the opposite direction to the central shell. In this configuration, the bottom line of the trapezoid is positioned perpendicular to and adjacent to the central shell. Due to this position of the bottom line, the wall around the opening of the central shell of the vapor trap is as far away from the opening as possible, which further reduces the risk of opening blockage due to metal deposition on the cold walls of the vapor trap located near the opening. In this configuration, the edges of the trapezoid converge outward to trap as much vapor as possible before it leaves through the outward opening 10.

[0053] According to a variation of the invention, the inner wall of the vapor trap 8 is removable, making further cleaning of the device easier. Instead of stopping the deposition line for an extended period to clean the device, the clogged inner wall can be quickly removed and replaced with a clean inner wall.

[0054] The vacuum deposition equipment has been tested to evaluate the efficiency of the equipment, which includes two vapor traps, during zinc evaporation.

[0055] The amount of evaporated zinc was determined by weighing the evaporation crucible fed into the vapor jet coating machine before and after testing. The amount of deposited zinc was determined by contacting the vapor trap with an acidic solution to dissolve the zinc. The amount of dissolved zinc was then measured using inductively coupled plasma. No zinc was deposited in the vacuum chamber, as visually assessed.

[0056] In 10 -1 Under millibar pressure, the vapor outlet holes 71 on each side of the substrate are 10 mm wider than the steel substrate. A first test on a 500 mm wide steel substrate showed that for 13.5 kg of evaporated zinc, 1.835 g of zinc was deposited in the vapor trap, and no zinc was deposited in the vacuum chamber. This corresponds to a deposition rate of 99.99%.

[0057] Under less favorable conditions, namely at 10 -1 At a pressure of millibars, the vapor outlet holes on each side of the substrate were 50 mm wider than those on the steel substrate. A second test conducted on a 300 mm wide steel substrate showed that for 10.5 kg of evaporated zinc, 4.915 g of zinc was deposited at the inward opening 9 of the vapor trap, and no zinc was deposited in the vacuum chamber. This corresponds to a deposition rate of 99.95%.

[0058] In contrast, tests conducted under the same conditions on equipment without a vapor trap showed a deposition rate of 99.5%. While this figure is high, such a deposition rate is unacceptable on an industrial production line, as it would result in the deposition of 6 kg of zinc per hour of production, meaning 2 tons of zinc would be deposited after two weeks of production. This deposition rate corresponds to a buildup rate of 0.5%, which is 10 to 50 times higher than the buildup rates observed in the case of this invention.

[0059] The apparatus according to the invention is more particularly, but not only, applicable to the processing of metal strips (whether pre-coated or bare). Of course, the method according to the invention can be used on any coated or uncoated substrate, such as aluminum strip, zinc strip, copper strip, glass strip, or ceramic strip.

Claims

1. A vacuum deposition apparatus (1) for the continuous deposition of a coating formed of a metal or a metal alloy on a moving substrate (S), comprising a vacuum chamber (2) through which the substrate (S) can be moved along a given path (P), wherein the vacuum deposition apparatus (1) further comprises, disposed within the vacuum chamber (2): - a central housing (4) comprising a vapor jet coater (7) and a substrate inlet (5) and a substrate outlet (6) located on two opposite sides of the central housing, the inner walls of which can be heated to a temperature higher than the condensation temperature of the metal or metal alloy vapor, - a vapor trap (8) in the form of an outer housing at the substrate outlet (6) of the central housing, comprising an inward opening (9) adjacent to the central housing and outward openings (10) located at opposite sides of the vapor trap, the inner walls of which can be maintained at a temperature lower than the condensation temperature of the metal or metal alloy vapor, wherein the vapor trap (8) having a trapezoidal shape in longitudinal section pointing in the opposite direction to the central housing (4).

2. The vacuum deposition apparatus according to claim 1, further comprising a second vapor trap at the substrate inlet (5) of the central housing.

3. The vacuum deposition apparatus according to claim 1 or 2, wherein the walls around the inward opening (9) of the vapor trap (8) are perpendicular to the given path (P).

4. The vacuum deposition apparatus according to claim or 2, wherein the lower and upper walls of the vapor trap converge outwardly.

5. The vacuum deposition apparatus according to claim 1 or 2, wherein the inner walls of the vapor trap (8) are removable.

6. The vacuum deposition apparatus according to claim 1 or 2, wherein the thermal regulation of the vapor trap (8) is a cooling circuit supplied with a heat transfer fluid chosen from water and nitrogen.

7. A method for the continuous deposition of a coating formed of a metal or a metal alloy on a moving substrate (S) by means of a vacuum deposition apparatus (1) according to any one of claims 1 to 6, wherein the method comprises: - a first step in which a metal vapor is jetted toward at least one side of the moving substrate and a first layer of metal or metal alloy is formed on the side by condensation of a first portion of the jetted vapor, the first step being carried out in a central housing (4) comprising a substrate inlet (5) and a substrate outlet (6) located on two opposite sides of the central housing and inner walls heated to a temperature higher than the condensation temperature of the metal or metal alloy vapor, - a second step, in which a second layer of metal or metal alloy is formed on said side by condensation of a second portion of the vapor sprayed, said second step being carried out in a vapor trap (8) in the form of an outer shell located at the substrate outlet (6) of said central shell and comprising an inner wall held at a temperature lower than the condensation temperature of said metal or metal alloy vapor, wherein said vapor trap (8) has a trapezoidal shape in longitudinal section pointing in a direction opposite to said central shell (4).

8. The method according to claim 7, wherein said second step is also carried out in a second vapor trap located at the substrate inlet (5) of said central shell.

9. The method according to claim 7, wherein the length of said vapor trap (8) in the direction of movement is between 0.5 and 3.5 times the substrate width.

10. A kit for assembling a vacuum deposition device for continuous deposition of a coating formed of metal or metal alloy on a moving substrate (S), said kit comprising a vacuum chamber (2) and, disposed inside said vacuum chamber (2): - a central shell (4) comprising a substrate inlet (5) and a substrate outlet (6) located on two opposite sides of said central shell and a vapor outlet aperture (71) of a vapor spraying coater (7), the inner wall of said central shell being heatable to a temperature higher than the condensation temperature of said metal or metal alloy vapor, - a vapor trap (8) suitable for being located in the form of an outer shell at the substrate outlet (6) of said central shell, said vapor trap (8) comprising an inward opening (9) adjacent to said central shell and outward openings (10) located at opposite sides of said vapor trap, the inner wall of said vapor trap being holdable at a temperature lower than the condensation temperature of said metal or metal alloy vapor, wherein said vapor trap (8) having a trapezoidal shape in longitudinal section pointing in a direction opposite to said central shell (4).

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