US3588308A

US3588308A - Method of and apparatus for vacuum metallizing

Info

Publication number: US3588308A
Application number: US833961A
Authority: US
Inventors: John T Carleton
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1969-06-17
Filing date: 1969-06-17
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28

Abstract

VACUUM METALLIZING APPARATUS WHEREIN THE TARGET METAL IS CONTAINED IN A CRUCIBLE IN A VACUUM CHAMBER AND IS VAPORIZED BY IMPINGING A DEFLECTED BEAM OF HIGH ENERGY ELECTRONS ONTO THE TARGET METAL INCLUDING MEANS TO SENSE THE CHANGE IN CURRENT CAUSED IN A CIRCUIT OF WHICH THE CRUCIBLE IS A PART WHENEVER THE DEFLECTED ELECTRON BEAM STRAYS FROM THE TARGET METAL OR CRUCIBLE AND MEANS TO SHUT OFF THE ELECTRON BEAM TO PREVENT DAMAGE TO OTHER ELEMENTS WITHIN THE VACUUM CHAMBER WHENEVER THE ELECTRON BEAM STRAYS FROM THE TARGET METAL. METHOD OF SHUTTING OFF A DEFLECTED ELECTRON BEAM IF IT

STRAYS FROM A CRUCIBLE CONTAINING METAL BEING VAPORIZED BY THE BEAM IN A VACUUM METALLIZING APPARATUS.

Description

United States Patent 3,390,249 6/1968 Hanks Primary ExaminerBernard A. Gilheany Assistant Examiner-Roy N. Envall, Jr. Attorney-liege T. Sutherland ABSTRACT: Vacuum metallizing apparatus wherein the target metal is contained in a crucible in a vacuum chamber and is vaporized by impinging a deflected beam of high energy electrons onto the target metal including means to sense the change in current caused in a circuit of which the crucible is a part whenever the deflected electron beam strays from the target metal or crucible and means to shut off the electron beam to prevent damage to other elements within the vacuum chamber whenever the electron beam strays from the target metal.

Method of shutting off a deflected electron beam if it strays from a crucible containing metal being vaporized by the beam in a vacuum metallizing apparatus.

PATENTEUJUH28I97I 3,58 ,308

INVENTOR JOHN T CARLETON BY d e (laid-Ne ATTORNEY METHOD OF AND APPARATUS FOR VACUUM METALLIZING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to vacuum metallizing or to the melting or vaporiration of materials in a vacuum by an electron beam wherein the beam is deflected and, hence, subject to straying from the material being melted. The present invention provides means for safeguarding against beam straying and impinging on other parts in the vacuum enclosure thereby preventing damage to these parts.

2. Description of the Prior Art The use of the electron beams for vaporizing metal contained in a crucible in vacuum metallizing apparatus is old.

Further, in the use of such electron beams in a vacuum for heating metal for vaporization and deposition on a substrate or web, for example, it is desirable, if not essential, to deflect the beam from its normal straight line path from the electron gun to the metal target, in the crucible, in order to avoid having the beam hit other parts of the apparatus, such as the web handling elements or parts. Additionally, as a result of the generally straight line path of vapor originating from the metal crucible, it is essential to remove the electron gun from the vapor path so that the vapor will not enter the gun and foul it or short out the electron beam.

To direct electron beams straight-in-line at the target is a relatively simple task, and to continuously and effectively control this direction presents no problems but, as stated, it requires positioning the gun between the crucible and the object to be coated or in other undesirable locations in the vacuum chamber.

The solution for this problem is to position the electron gun in an out-of-the-way position and to deflect its beam onto the metal in the crucible through the open top of the crucible. This creates another problem, whereas straight-in-line beams are easy to control, deflected beams wander in an undetermined fashion if there is the slightest change in conditions within the vacuum chamber and, hence, the critical controlled impingement of the electron beam substantially only onto the metal in the crucible is lost.

Electrical or magnetic deflection means are generally employed to effect this deflection; these means can be effectively stabilized at a preselected level to bend the beam and make the beam impinge on the target source in the crucible. The interaction between the beam and the deflection means is dependent not only on the intensity of the deflection means (i.e., the magnetic field in the case of magnetic deflection, or the electrostatic field in the case of electrostatic deflection), but also on the velocity of the electrons in the beam. Accordingly, fluctuations, even momentary, of any of these variables caused by electrical or pressure disturbances could permit the electron beam to stray from the material to be vaporized and impinge on the chamber body or on other elements within the vacuum chamber, rather than on the target metal, and the results from this could be extremely harmful.

According to the present invention means are provided to interrupt the operation of the electron gun when the beam strays from the target in the crucible to solve this problem.

US. Pat. No. 3,046,936 to Simons is exemplary of the prior art teachings. It discloses an electron gun for melting metal in a crucible in which the beam from such gun is deflected onto such metal.

All of the prior art known to applicant is concerned with this problem; applicant, on the other hand, is concerned with controlling the operation of the electron gun if the beam strays after deflection occurs as a safety measure.

SUMMARY OF THE INVENTION The vacuum metallizing apparatus of this invention provides a safety control in electron beam deflection-type metallizing devices for controlling stray beams which might damage other apparatus pans in the metallizing chamber.

Briefly described, a crucible containing metal to be vaporized is positioned within a vacuum chamber of the vacuum metallizing apparatus. An electron gun is positioned preferably in the vacuum chamber wall or body and completely removed from and out of the way of other parts of the apparatus, which other parts may include web winding and unwinding parts, transfer rolls and a quench drum, for example. A beam deflection means is positioned within the chamber and is operative to deflect the electron beam from the electron gun from its straight line path and bend it to impinge upon the metal in the crucible. Shielding means are positioned between the deflection means and the electron gun to shield various pans of the apparatus should the straightJn-line path be momentarily lost and to protect the gun from vapors rising from the crucible.

A serious safety problem occurs when the electron beam strikes parts of the vacuum apparatus other than the metal surface or the crucible containing the metal. This is due to the variation in energy of the electron beam and various means, such as shielding means, and deflection means have been adopted tosolve this problem. While these means do help solve this problem, they may create another; i.e., the relationship of the deflection means and the beam energy may vary and, hence, create or recreate the very problem the deflection means attempts to solve; that being, the directing of electron beams only onto the metal in a crucible from an out of the way position.

This invention solves the problems existent in the prior art and provides an improved method and apparatus for controlling electron gun action should the deflected beam stray from the crucible or the metal in it.

Such invention essentially encompasses the discovery of the improvement of detecting straying deflected electron beams on a vacuum metallizing apparatus and based on signals imparted by the detecting or beam current sensing means, means are actuated which operate to shut off the electron gun action if undue beam straying occurs.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective diagrammatic view of the vacuum metallizing apparatus of this invention, with parts omitted for clarity, showing a web of sheet material being coated in a vacuum chamber by vaporized metal melted by a deflected electron beam from an electron gun, together with beam current sensing means operatively connected to both the crucible containing the metal and the electron gun, which sensing means is operable to shut off the electron beam should the electron beam stray from its predetermined deflected path onto the metal in the crucible.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a web I0 of sheet material (such as plastic film) to be coated by the web coating or vacuum metallizing apparatus of this invention is supplied from a supply source, such as supply roll 11, and moved into operative association with means for coating the web in a manner to be described. From the supply source I], the web or substrate 10 passes over a transfer roll 12 and around a quench drum or web support means 13, and from the drum over a transfer roll 14 and onto a transfer or windup roll 15, all of which parts may be appropriately mounted in a vacuum chamber of the metallizing apparatus of this invention, as is known.

In the drawing, there are shown various parts of a typical vacuum metallizing apparatus 20 which includes a gas impervious body member or wall 21 defining a vacuum chamber 22. Within the vacuum chamber 22 and mounted on appropriate support means 23 is a container or crucible 24 in which is contained material 25 to be vaporized so as to produce metal vapor 25 for coating the moving web 10.

The container or crucible 24, wherein the material or metal 25 to be vaporized is located, has a mouth or opening positioned near the lower portion or circumference of the quench drum 13 which positions the moving web 10 adjacent the crucible opening during the metallizing operation. The crucible 24 supports therein a pool of the material 25, such as molten aluminum, in the appropriate position to supply the stream of aluminum vapors 25 upwardly to condense on the moving web upon the melting of the metal 25.

Means are provided to vaporize or melt the metal 25 in the crucible 24 in the form of an electron gun 26 suitably mounted in aperture means 27 in the body member 2] ofthc vaporizing apparatus. The metal 25, upon vaporization, deposits and condenses on the web 10 on the lower surface of the quench drum 13 near the outlet of the crucible 24 where it condenses to form a coating. To assist condensation, the quench drum 13 can be provided with an internal coolant as is known.

The vacuum chamber 22 is coupled through a port 28 to a source (not shown) of high vacuum for evacuating the vacuum chamber 22 as is known in the art.

The metal 25, such as aluminum, in the crucible 24 is heated by a beam of electrons schematically indicated at 29 from the electron gun 26. Such electron gun 26 is connected to a power supply S for the high voltages necessary to accelerate electrons in the beam 29 and is hermetically mounted on wall 21 within the aperture 27 through which the beam 29 enters the vacuum chamber 22. Power supply S is fed from lines 29, which may be a voltage stabilized source if the power supply S does not have internal means for controlling voltage.

In the interior of the vacuum chamber 22, the beam 29 passes through a shielding means 40 and is deflected from its initial straight-in-line first path 31 by deflection means or magnet 30 to proceed along a second path 32 to the material 25 in the crucible 24. Deflection means 30 may be a simple magnet for bending the beam at an angle to impinge on the target, material 25, or it may have a fluctuating current in coils to cause the beam to scan a material, as in metallizing a wide web from an elongated crucible extending traverse to the moving web 10. Electrostatic deflection means as are known to the art may alternatively be employed.

As the electron beam 29 passes through the vacuum chamber 22, it first passes through an aligned hole 42 in the shielding means 40 serving as a vapor shield to prevent vapors from contacting the electron gun 26. After the electron beam 29 has passed through the hole or aperture 42, it passes through the magnetic field 30 so that it is bent downwardly to impinge on the surface of molten aluminum or metal 25. The electron beam 29 beats this molten aluminum surface to a very high temperature (on the order of l,200 to 1,300" C.) so as to vaporize the aluminum 25 at the high vacuum which is maintained in the coating vacuum chamber 22.

As has been stated, the beam deflecting means 30 is positioned between the positively controlled electron gun 26 and the crucible 24 to deflect the beam 29 after it passes through the shielding means 40 and bend it onto the metal 25 in the crucible 24 to vaporize the metal 25. Low pressure in the vacuum chamber 22 permits deposition of the vaporized metal 25 onto the web to. Should the beam 29 stray from its metal target 25, means are actuated to control (i.e., to shut off) the electron gun 26 to prevent undesired contact between the beam 29 and other parts of the apparatus.

Crucible 24 is of an electrically conductive material, such as graphite, and it rests on the base or support 23 which is insulated.

The conductive crucible 24 (or means electrically coupled to the melt in the crucible) is coupled by an appropriate conductor to ground so as to provide an electrical path 33 to ground through which to conduct the current of the electron beam 29. lnterposed in the electrical path 33 is a means 34 to sense existing electron beam current. This current sensing means 34, in its preferred form, comprises a meter relay 35 which may be a current measuring instrument (ammeter) or a volt meter measuring the voltage drop across a resistor.

In operation, the meter relay 35 is set nearzcro upon starting up the electron gun 26; after the beam 29 is in operation and adjusted to impinge upon the target (the material 25) and the beam current has been stabilized, the net needle of lltc meter 35 is set below the minimum indicated in fluctuations of the beam current. Upon drifting off the target 25, for example, because failure of or change in the beam deflection means 30, the beam current will drop below the preselected minimum, which may be only slightly above zero, and will actuate a power relay 36 which is operatively connected to the relay 35 and to the electron gun 26, which disconnects the power supply 5 from the power line, thus shutting off the electron gun 26 and, hence, the beam 29.

Insulating base 23 is preferably of a heat-resistant ceramic material so that occasional minor spillover of the beam in startup will not cause damage. Similarly, internal grounded metal shields may be installed to prevent damage to mechanical or other electrical components due to momentary straying of the beam.

in the operation of the apparatus schematically illustrated, the web l0 which may be paper, plastic or the like, is passed around the quench drum 13 positioned between the supply roll ll and the windup roll 15 in the coating chamber. The web 10 can be introduced from the outside through appropriate seals (not illustrated) or it can be mounted in the vacuum chamber 22. The vacuum chamber 22, where the vapor coating of the web 10 occurs is preferably pumped down by pump to a pressure of less than 1 micron Hg. Abs. The electrons emitted from the cathode of the electron gun 26 are focused by a focusing electrode into the beam 29 and are accelerated to extremely high velocities. After the beam 29 of electrons passes through the aligned opening 27 in the wall 21 of the vacuum chamber 22 and through the opening 42 in the shielding means 40, along path 31, it is deflected by the deflecting means 30 to bend the beam 29 so that it impinges on the surface of metal 25 in the crucible 24.

The beam 29 of electrons may be of very high power, as much as 60,000 watts. This power, representing the kinetic energy of the electrons, is converted to heat when the beam strikes the surface of metal 25. The surface of the metal 25, such as aluminum, is raised to a very high temperature on the order of 1,200 to 1,300" C., so copious quantities of aluminum vapors 25 are released. Due to the high vacuum in the coating chamber 22, the aluminum vapors 25' travel in substantially straight lines from the surface of the aluminum pool 25. Most of these vapors 25' condense on the web 10 which is moved around the quench drum l3 and adjacent the top opening of the crucible 24 containing the metal 25. i

The beam 29 of electrons striking the surface of the metal 25 in the crucible 24 generates a current output which is measured by the meter relay 35. Such current output is continuously sensed by the current sensing means 34 and if it falls without preset limits the power relay 36 will be actuated to disconnect the power supply S, as has been described.

It is seen, then, that the current sensing means 34 is operatively connected to the crucible 24 containing the metal 25 and generates a signal based on current output at the crucible 24; this signal is fed through suitable electrical conductors to the power supply 36 which shuts off the power to the electron gun 26 and, therefore, stops the beam 29. Thus, there is provided a continuous positive safety device to prevent improper and undesired impingement ofelectrons on parts ofa metallizing apparatus other than the crucible.

in known apparatus for vacuum metallizing utilizing an electron gun to melt the metal and in which the metal vapor is being deposited on a moving web, having the electron beam strike the target metal at an angle removes the web handling elements from the path of the electron beam to prevent damage to'them. Also, the metal vapor usually leaves the target metal in a straight line and if the electron gun is in a straight path from the target metal, the gun may be fouled by the metal vapor or the electron beam may be shorted; this is avoided by positioning the electron gun in an out-of-the-way position and deflecting its beam onto the target.

Means generally used to deflect the electron beam from a straight line puth include magnetic and electrostatic devices which may cfl'cctivcly stabilize magnetic or electrostatic fields at preselected levels to give the electron beam the desired deflection Since the beam is deflected from a straight line course. however. its path will or may be affected by fluctuations m the strength of the deflection means, i.e.. fluctuations in the magnetic or electrostatic fields. as well as by changes in the velocity of electrons in the beam. This presents the problem this invention solves ln order to prevent damage to other elements in the vacuum chamber 22 when the electron beam 29 strays from the metal target 25 in the crucible 24, the present invention incorporates means into the electrical circuit with the electron beam to shut off the beam 29 whenever it strays from the target metal 25.

Means are provided in this circuit formed by the electron gun 26, the electron beam 29. the target metal 25 and the crucible 24 to shut off the power to the electron gun 26, thereby interrupting the electron beam 29, whenever the electron beam 29 strays from its target. Means are provided to sense a change in the current resulting from the electron beam 29 and other means are provided to shut off the electron beam 29 whenever the current through the circuit of which the electron beam is a part falls below a preselected minimumv This apparatus is particularly suitable for metallizing a continuous film in web form, and in such apparatus the web handling and shielding equipment could be damaged by accidental impingement of the electron beam 29. The present invention, by shutting ofi the electron beam 29 when it strays from the target metal, removes this danger.

The apparatus of the present invention is particularly suitable for metallizing a continuous web of film for use in electrical capacitors. Such apparatus is generally characterized by relatively complex web handling and masking equipment, which makes proper attention to the vacuum chamber cleanliness more important since accumulation of oxides of the metal which is vaporized produces a surface which absorbs large quantities of moisture from the air when the chamber is open, making pumping times excessively long. For vacuum metallizing with electron beam heating, it is essential to have very high vacuum. Pumping times become excessive in the presence of accumulated oxides.

It has been found that by pumping in two stages, with the second stage preceded by filling the system or chamber with a dry gas, such as dry nitrogen or carefully dried air, followed by final pumping, the total pumping time necessary to obtain operable pressures can be substantially reduced. The following table illustrates this time saving advantage.

Includes approximately one minute to fill chamber with dry nitrogen.

While this invention is directed primarily to the use of the shutoff apparatus and the two-stage pumping sequence in vacuum metallizing, such principles are also useful in vacuum melting or other systems employing an electron beam, and pumping systems for vacuum technology in general.

lclaim:

1. An apparatus for vacuum metallizing including a beam supply means, an electron beam, a target metal, a crucible and a conductor to ground which form an electrical path to conduct the current of the beam for impinging the beam from the beam supply means onto the target metal in the crucible positioned in a vacuum chamber, the improvement comprising:

means interposed in the electrical path to sense current resulting from the beam as it strikes substantially onto the crucible or the target metal in the crucible; and

means to shut off the beam supply means when the current flowing through the circuit of which the beam is a part falls without a preselected range, whereby to automatically shut off the beam upon its straying from the target metal.

2. The apparatus of claim 1 including beam deflecting means for deflecting the beam from a first path to a second path and, as deflected, onto the target metal in the crucible.

3. The apparatus of claim 1 wherein the beam supply means is an electron gun having a source of power and wherein the crucible is electrically conductive and rests upon an electrically insulated support, a meter relay connected into the circuit of which the beam is a part to sense the current resulting from the beam, and a power relay operatively connected to the meter relay to interrupt the power to the electron gun whenever the current in the circuit of which said beam is a part falls without a preselected range, whereby the beam is automatically shut off upon straying from the target metal in the crucible.

4. Apparatus for heating a metal to a temperature sufficiently high to vaporize the metal in an evacuated chamber by directing a beam of electrons against a surface of the metal, the apparatus including:

an electron gun for emitting electrons;

means for forming the electrons into a beam and projecting the beam of electrons into a given path, said path missing the surface of the metal to be heated; a vapor masking means between the electron gun and the metal surface to be heated;

deflection means positioned to bend the electron beam so that the electronic beam is directed towards the metal surface to be heated when the beam is beyond the point of interception of the beam by the vapor masking means; and

means to automatically shut off the electron gun when the beam goes astray.

5. A vacuum metallizing apparatus comprising:

a vacuum chamber adapted to being evacuated of its atmosphere;

means for positioning an object to be metallized within said chamber;

metal located in a crucible adjacent the object and operative to metallize an exposed surface of the object as the object advances past the crucible;

an electron gun for impinging an electron beam onto the metal to be vaporized contained in the crucible;

masking means in masking relation to a portion of the electron gun thereby precluding rnetallization of the masked surface of the electron gun;

beam deflecting means between the object and the electron current sensing means operatively connected to the electron gun and to the crucible; and

wherein a signal from the current sensing means shuts off the electron gun if the beam strays from the crucible.

6. A method of vacuum metallizing including the steps of:

melting a material in a crucible in a vacuum chamber by impinging thereon a deflected melting beam from beam supply means;

sensing the current generated by the melting beam with a current sensing means so long as the beam strikes substantially only the material in the crucible or the crucible itself; and

shutting off the melting beam by means of signals from the current sensing means if the beam strays from the crucible or the material in the crucible.

7. The method of vacuum metallizing of claim 6 including:

subjecting the vacuum chamber to a high vacuum prior to impinging the electron beam onto the metal in the crucible to vaporize it and wherein the vacuum chamber is subjected to the high vacuum by a two-stage pumping operation with the second stage pumping being proceeded by introduction of a dry gas into the vacuum chamber.