EP1948840A1

EP1948840A1 - Device and method for controlling the power supplied to vacuum vaporization sources of metals and other

Info

Publication number: EP1948840A1
Application number: EP05823891A
Authority: EP
Inventors: Massimo Lasagni
Original assignee: Galileo Vacuum Systems SpA
Current assignee: Galileo Vacuum Systems SpA
Priority date: 2005-11-15
Filing date: 2005-11-15
Publication date: 2008-07-30
Also published as: WO2007057925A1

Abstract

The device includes at least one vaporization source (31) heated by Joule effect due to the passage of an electric current and a powering system of said at least one source, with a control circuit (101) of the power supplied to the source. This circuit includes an inverter, which supplies an essentially sinusoidal voltage to the source (31), the power being regulated by acting on the amplitude of the voltage supplied to the source.

Description

"DEVICE AND METHOD FOR CONTROLLING THE POWER SUPPLIED TO VACUUM VAPORIZATION SOURCES OF METALS AND OTHER"

DESCRIPTION Technical Field

The invention relates to vacuum deposition systems and, in particular, but not exclusively, systems for the vacuum deposition of metals (like aluminum and such like) on substrata like plastic film, paper or other web-like products.

Specifically this invention relates to improvements to systems for controlling the power supplied to the vaporization sources, in other words to those elements or components of the system which serve to effect the vaporization or evaporation of the metal or other material to deposit on the substratum. State of the Art Vacuum metallization systems are usually used to deposit under vacuum metallic strata on substrates, such as polymer films, paper or similar, where a substrate reel of the material to be coated is inserted into a chamber and in which the substrate is subsequently unwound and passed around a process roller to be rewound in a reel of treated product. Vaporization sources are located under the process roller, from which vapors of metal (or other material) are generated, which is then condensed under the form of a thin coating on the corresponding face of the film or other substrate.

The vaporization sources are, for example, composed of boats of high conducting syntherized material, which is resistant to temperature that are heated by Joule effect due to the passage of electricity. The metal to be vaporized is fed to these boats. In continuous feeding systems this metal is fed under the form of aluminum wires or other suitable material, unwound from coils with a feeding speed corresponding to the hourly quantity of metal which must be vaporized. A system of this kind is described in WO-A-03/038142. Particularly shaped boats or vaporization sources heated by Joule effect and suitable for use in these systems are described in EP-A-1408135.

During the operating cycle, in other words during metallization of a reel of substrate, it may be necessary to modulate the power supplied to the vaporization sources, or to perform some transients for example in the vaporization start-up phase. For this purpose control systems have been designed which generate a voltage with a particular wave shape to reduce or increase the electricity supplied to the sources, based on requirement. Usually, for this purpose a partialization of the voltage is adopted, involving sharp variations of amplitude of the electrical voltage applied. This generates some problems including an irregular operation of the source and an increase in the power factor.

To overcome or reduce these problems, particularly complex control circuits have been designed that endeavor to avoid discontinuity in the voltage wave shape. However, also in these more elaborated systems, the voltage wave shape is irregular and implies an increase in the power factor and an unsatisfactory operation of the sources. Objects and summary of the invention The object of the invention is to manufacture a device which permits a more efficient regulation of the power supplied to the vaporization sources and which, in particular, reduces the power factor, making the operation of the sources more even and, in general, to improve the operation of the system as regards the regulation of power for example in the transitory phases, with respect to what is presently obtainable with systems currently available on the market.

Essentially, these and other advantages, which will become clear those skilled in the art from the reading of the text which follows, are obtained with a device for vacuum vaporization of a metal or the like, which includes at least one vaporization source, heated by Joule effect by means of the passage of an electric current, and a powering system for said at least one source, with a control circuit of the power supplied to said source that includes an inverter which supplies an essentially sinusoidal voltage to the source, the power being regulated by acting on the amplitude of the voltage supplied to said source. Advantageously, the circuit can include a transformer, whose secondary winding is connected to said at least one source.

In a possible embodiment, the circuit includes a comparator to compare a reference signal with a signal which is a function of the powering conditions of said source, from said comparison an error signal being generated, which is used to modify a driving signal of the inverter, and therefore to modify the power supplied to the source.

Preferably the inverter is a PWM inverter and the driving signal modifies the duty cycle of the inverter depending on the error signal. The circuit can include a rectifier, connected to the entry of the inverter, which includes a band-pass or low-pass filter on output.

In a different embodiment, in the absence of a rectifier on entry, the inverter receives an alternating voltage input, sampled at a frequency sufficient to allow a reconstruction of an essentially sinusoidal wave shape at the exit from said inverter. Typically the alternating voltage at the input olf the inverter can be a frequency between 30 and 100 Hz, for example 50 or 60 Hz, and the sampling frequency is equal to or greater than 15 kHz and preferably equal to or greater than 20 kHz.

The invention also deals with a vacuum metallization system that includes a metallization chamber and at least one device as described above to power the vaporization sources, which are arranged in the chamber.

The system can advantageously include a control unit interfaced with the source powering device and a system to supply to each of said sources with at least one metal wire to vaporize, said unit controlling the power and quantity of the wire supplied to the source or sources.

According to a different aspect, the invention relates to a method of controlling the power supplied to at least one vaporization source in a vacuum metallization system, characterized in that said least one source is supplied with an essentially sinusoidal voltage and that the power is regulated by modifying the voltage amplitude.

To optimize powering of the vaporization sources, preferably the essentially sinusoidal wave shape can fall short of a perfect sinusoid of an entity which can be such that the ratio between the power of all the harmonics except the fundamental frequency and the total power (i.e. the total harmonic distortion) is lower or equal to 15% and preferably equal to or lower than 10%. Preferably such a ratio should be equal to or lower than 8%, better equal to or lower than 5% and more preferably equal to or lower than 2%. Brief description of the drawings

The invention is better understood by following the description and the - A - drawing, which shows a practical embodiment of the invention. More particularly, the drawing shows:

Fig 1 a schematic and simplified section of a metallizing system in which the invention can be embodied; Fig. 2 a schematic representation of one of the vaporization sources;

Fig. 3 a diagrammatic scheme of the power supply circuit;

Fig. 4 a diagram which shows the voltage across the single vaporization sources in two different operating conditions; and

Fig. 5 the wave shape of the powering voltage, in a possible supplying situation, compared with the wave shape of the output voltage from the inverter of the power control circuit. Detailed description of the invention

In Fig. 1 the inside of a vacuum metallization system is shown very schematically, in a cross section along a vertical plane. It includes a container 3 in which two supports 5 and 7 are housed for the reels of the web-like substrate N to be metallized, for example a polymer film, a paper web or other material. On support 5 is arranged a substrate reel B1 that is still to be treated, fed along a feed path defined by guide rollers 9, 11 , 13, 15, 17. On support 7 is a second reel in formation, on which the substrate is wound after metallization.

Between roller 11 and roller 13 is process roller 19 of greater diameter which protrudes partially inside a chamber 21 separated, by a partition wall 23, from the overlying chamber 25 where supports 5 and 7 for the substrate reels are located. Chamber 21 is held under a level of higher vacuum with respect to chamber 25. There are also systems in which the partition wall 23 and the division into chambers 21 and 25 do not exist. In this case the reel being unwound, the rewinding reel, the path of the substrate N, the process roller 19 and the vaporization sources are arranged in one and the same chamber.

There are also systems in which there is a third chamber, so-called of guard, adjacent to the process roller.

The web-like substrate N unwound from reel B1 and guided around process roller 19 is gradually rewound to form a reel of metallized substrate on support 7. During unwinding, in the passage around process roller 19, on the surface not in contact with process roller 19 of the web-like substrate N is deposited a metal which has been vaporized by a series of sources 31 which are arranged in chamber 21 , below process roller 19. V schematically indicates the vaporized material coming from sources 31 , which are arranged side by side according to an alignment orthogonal to the direction FN of advancement of the substrate N, i.e. orthogonal to the plane of the figure. One single source is visible therefore in Fig. 1

The structure of the metallization system can vary and what is represented in Fig. 1 is solely a schematic example of a possible system in which the invention can be implemented. Fig. 2 shows, in an enlarged side view, a source 31 of the system of Fig.

1. This source is composed of a bar 33 made of electrically conductive material, resistant to high temperatures, typically of 1,500 ⁰C. Said source extends along a main longitudinal direction, indicated with LD.

The bar 33, also technically called a boat, is supported by means of mechanical supports which also provide an electrical contact to a low voltage supply line. In the example shown there are two columns 35 integral with a support plate 37, The columns 35 are electrically conductive and connected to two electrical conductors 39 by which in boat 33 is made circulate a flow of current which by Joule effect dissipates heat, heating the bar or boat 33. In Fig. 2, 101 schematically indicates a circuit layout for controlling the power supplied to source 31 , connected to a voltage source 102, for example the mains of an electrical distribution line. The circuit layout 101 for power control is described in greater detail below.

To maintain the desired level of liquid metal within the cavities 41 A, 41 B and therefore reintegrate the metal which is supplied by the vaporization source, there are two separate means of supplying a metal wire which is is fused by heating through irradiation by bar 33 and fall in drops into cavities 41A and 41 B. Obviously other configurations of the feeding means, for example to feed a single metallic wire instead of two, are possible. The means for supplying the metallic wire are schematically indicated in

Fig. 2 and can have different shapes. These means of supply are known per se and not described in great detail here. Schematically in the example shown they include a coil 51 of metallic wire F, a pair of cylinders 53, one at least of which is motorized for pulling the metallic wire F and unwinding it from coil 51 and feeding it through a guide tube 55. The metallic wire F comes out of tube 55 in an area above the respective cavity 41 A or 41 B.

The free end of wire F coming out of tube 55 is gradually fused by the heat developed by the current which flows in the bar or boat 33. The drops of fused metal fall in to the respective cavity and vaporize. Suitable systems not shown and known per se maintain the necessary length of wire F coming out from tube 55 and control the gradual unwinding of wire F by means of cylinders 53 from coil 51.

In Fig. 2, 101 still generically indicates a circuit for controlling the power supplied to source 31. 102 schematically indicates a source of alternating current, which can be for example by the national electrical energy distribution grid. The circuit 101 is interfaced with a microprocessor control unit or the like, schematically indicated with 103, which is also interfaced, as schematically indicated in Fig. 2, to the supply system of the metallic wires F, for example to control the unwinding speed of the single wire F from coild 51.

Fig. 3 shows a diagrammatic scheme of the parts of concern of the power supply control circuit 101. This circuit includes a rectifier 111 , which can be of any known configuration, fit for the purpose. The example shows a single- phase scheme, but it must be understood that the concepts described here can also be applied to a three-phase supply of the vaporization sources.

At the output of rectifier 111 is filter 113. At the output of the filter an essentially continuous voltage is provided, which is applied at the input of a PWM inverter indicated schematically with 115. The output of inverter 115 is a voltage whose wave shape is schematically shown in Fig. 5 and indicated with V1. It is a rectangular wave shape with a frequency in the range of tens of kHz, typically 15-2OkHz, with a cyclically variable duty cycle in the semi-period ΔT/2. As is known to those skilled in the art, a voltage can be reconstructed from this wave shape that has an essentially sinusoidal shape indicated with V3 in Fig. 5. This sinusoidal voltage must power source 31 , which in Fig. 3 is generically illustrated as a load L connected to control circuit 101. of the output of inverter 115 is connected to a low-pass or band-pass 117 filter, with a passing band centered on the frequency of voltage V3 with which source 31 must be powered. Filter 117 reconstructs the sinusoidal voltage V3 starting from the rectangular wave shape voltage V1 at the output of inverter 115. The amplitude of voltage V3 can be modulated intervening on the driving signal of inverter 115, modifying the duty-cycle of said inverter.

Voltage V3 is then transformed to the value desired to power source 31 through transformer 119. The variation of the power fed to the load represented by source 31 is obtained, characteristically, by modifying the amplitude voltage of V3 and therefore the transformed voltage, always sinusoidal or essentially sinusoidal with which source 31 is powered and which is obtained at the output of transformer 119. Fig. 4 illustrates the feeding voltage of sources 31 in two different situations, to which correspond curves A and B which are characterized both by an essentially sinusoidal shape, but differentiated one from the other by a different amplitude value VA and VB respectively. These different values of voltage amplitude at the output of filter 117 and then also at the output of transformer 119 are obtained by modifying the duty cycle of inverter 115.

For this purpose circuit 101 is matched with a feedback network indicated by 121 , which supplies a Veff signal depending on the voltage supplied by the source. This signal can be generated by the voltage on the primary or by the voltage on the secondary winding of transformer 119. The Veff signal is applied to an input of a comparator 123, to the other input of which is applied a reference voltage Vref. An error signal Verr proportional to the difference between Veff and Vref signals is generated from comparator 123. The error signal Verr is applied to inverter 115 to modify the duty cycle of the latter and bring the effective voltage value at the output of the control circuit to the desired value, identified by the reference signal Vref. The reference signal Vref is supplied by control unit 103._.

It is understood from what is described above that control circuit 101 modifies the power supplied by sources 31 maintaining an essentially sinusoidal shape of the supply voltage. This prevents partialization of the voltage, which in traditional systems causes a discontinuous trend of the voltage wave shape. The sinusoidal or essentially sinusoidal wave shape of the voltage of the sources also maximizes the power factor.

A qualitatively analogous result, even if more approximate, can be obtained with a control circuit without rectifier 111 and filter 113, if inverter 115 is fed with a voltage obtained by sampling the sinusoidal voltage provided by the source of voltage 102. If sampling is performed at a sufficiently high rate, typically at around 20,000 Hz, the circuit is still able to reconstruct an approximately sinusoidal voltage wave shape on exit of filter 117, whose amplitude is modulated as described above to vary the power supplied to sources 31.

It is agreed that the drawing shows nothing but a possible shape of construction of the invention, which can be varied in the forms and layouts, without getting away from the concept at the base of the invention, as defined with reference to the claims which follow.

Claims

1. A device for vacuum vaporization of a metal or similar, including at least one vaporization source heated by Joule effect by the passage of an electric current and a powering system of said at least one source, with a control circuit of the power supplied to that source, characterized in that said control circuit includes an inverter which supplies an essentially sinusoidal voltage to the source, said power being regulated by acting on the amplitude of the voltage supplied to the source.

2. Device according to claim 1 , characterized in that said circuit includes a transformer whose secondary is connected to said at least one source.

3. Device according to claim 1 or 2, characterized in that said circuit includes a comparator for comparing a reference signal with a signal which is a function of the powering conditions of said source, an error signal being generated from the comparison, which modifies a driving signal of the inverter to modify the power supplied to the source.

4. Device according to claim 3, characterized in that the inverter is a PWM inverter and that the driving signal modifies the duty cycle of the inverter depending on the error signal.

5. Device according to one or more of the preceding claims, characterized in that said circuit includes a rectifier, connected to the input of the inverter, said inverter including a band-pass or low-pass filter on the output.

6. Device according to one or more of claims 1 to 4, characterized in that the inverter receives an alternate voltage input, sampled at a sufficiently high frequency to allow a reconstruction of an essentially sinusoidal wave shape at the output of said inverter in absence of a rectifier.

7. Device according to claim 6, characterized in that the alternating input voltage has a frequency between 30 and 100 Hz and the sampling frequency is equal to or greater than 15 kHz and preferably equal to or greater than 20 kHz.

8. Device according to one or more of the preceding claims, characterized in that said source is powered with a voltage whose total harmonic distortion is lower than or equal to 15%, preferably equal to or lower than 10%, more preferably equal to or lower than 8%, and even more preferably equal to or lower than 5% and in particular equal to or lower than 2%.

9. A vacuum metallization system including a metallization chamber and at least a device according to one or more of the preceding claims, said source or sources being arranged in the said metallization chamber.

10. System according to claim 9, including a control unit interfaced to said device and to a system for supplying to each of said sources at least one metal wire to be vaporized, saidunit controlling the power and quantity of wire supplied to said source or sources.

11. A method of regulating the power supplied to at least one vaporization source in a vacuum metallization system, characterized in that at said least one source is supplied with an essentially sinusoidal voltage and that the power is regulated by modifying the voltage amplitude.

12. Method according to claim 11 , characterized in that the source is powered with a voltage whose total harmonic distortion is lower than or equal to 15%, preferably equal to or lower than 10%, more preferably equal to or lower than 8%, and even more preferably equal to or lower than 5% and in particular equal to or lower than 2%.