DE3125150A1 - "Process and appliance for preparing a foil with a porous valve metal layer" - Google Patents

Abstract

Process for preparing a foil with a porous valve metal layer for roller-type electrolytic capacitors. In order to prepare the porous valve metal layer, valve metal is vapour deposited in vacuo, the metal vapour jet being directed at the substrate at a small angle with respect to the substrate surface to be metallized. The substrate used can be an aluminium foil or a plastic film. Vapour deposition can also be carried out at variable angles, so that a layer of variable porosity is formed along the layer thickness, which layer can be peeled from the metallized substrate (Figure 1). The appliance for carrying out the process contains one or more metal vapour sources and a rotatable drum arranged close to them. <IMAGE>

Description

Method and apparatus for producing a

Foil with a parous valve metal layer y The invention relates relates to a method and an apparatus for producing a film with a porous layer of valve metal for wound electrolytic capacitors which is provided with a superficial oxide layer by anodic oxidation.

Porous metal layers ground in a variety of industrial Products needed. For example, the anodes and cathodes are wound from Electrolytic capacitors commonly made from aluminum foils that chemically or electrochemically etched to create a large surface area. Typically, strips of aluminum foil are etched to create a microporous surface to generate, which is then subjected to an electrical formation to produce a uniform Generate dielectric layer.

There are a number of problems with the etching process, despite this the most common procedure is to order Foils for capacitors to produce with a sufficiently large capacity. When etching, several aqueous Treatment solutions and baths used, whose composition is permanently maintained and which cause sewage problems. The etching solutions also contain typically ions, such as chloride ions, which cause electrolytic oxidation prevent and therefore carefully removed before electrolytic oxidation Need to become.

In addition, when etching foils for capacitors, they become larger Capacity creates narrow tunnels in the foils, which leads to a sharp drop in capacity and thus cause a deterioration in the high-frequency behavior, if higher Forming stresses are used. This effect is caused by the fact that the etched pores are completely filled with the anodic oxide that is used in the electrolytic oxidation occurs.

The usual Xtz process consists of a complicated electrochemical one Process which is subject to constant change, so that the Surface is not uniform because the process cannot be controlled well. In order to achieve a uniform etching of aluminum foils, it is necessary to to add traces of other elements to the aluminum. Metals such as Tantalum, are very difficult to etch to behave a large surface, and in all etching processes, part of the metal is converted into an aqueous solution, from which it can only be recovered at great expense. Alloy foils that are advantageous in terms of their forming properties, can only be difficult etching.

The object of the present invention is to remedy the disadvantages mentioned largely to reduce or avoid and a general method of manufacture of metal films or foils with a very large surface area without a Etching process is needed.

The etching process is intended to produce the largest possible surface with which the foils can then be formed and handled and it is Object of the present invention, the etching process by a more uniform and easily controllable process to replace. with which a larger effective surface can be produced than with the known etching process, so that with it smaller electrolytic capacitors can-be manufactured, with improved facility for automatic manufacturing.

An advantage of the invention is that the malleable body with a high specific surface area in a variety of different embodiments can be made, including foils.

The invention consists in a method of making porous Metal films or coatings on a substrate surface in which a stream of metal vapor is directed onto the surface of a substrate in a vacuum, with deposition of the metal vapor takes place under such conditions that a porous metal precipitate is obtained.

In the method according to the invention to produce a porous Metal film as a coating on a substrate surface this at the metal vapor source passed, whereupon the metal is deposited in a vacuum and wherein the metal vapor source is formed so that the metal vapor is only in one Direction is steered, and with the precipitation at such an angle of incidence takes place that a porous metal deposit is obtained.

It is already known to have metal layers or layers of others To preserve materials in a porous form by vacuum deposition. There were too metal powder has already been produced by vapor deposition in an inert gas atmosphere and the powders so produced were sintered together or compacted to form a coherent to produce porous bodies.

It is also known that metal layers under certain conditions the substrate temperature grow in a column structure, in addition, the surrounding gas and the angle of incidence of the condensing atomic beam on the substrate are important. The dependence of the structure on the substrate temperature has been described by B.A.Movchan and A.V.Demchishin in the magazine UFizika Metallov i Metallovedenieu, Volume 28 (4) April 1969, pages 654-660, and by J.A. Thornton in the journal "J, Vac.Sci.Technol.", Vol. 11 (4) 1974, page 666, using gas pressure became. The influence of the gas pressure and the angle of incidence of the metal vapor was described by N.G. Nahodkin and A.I.Shaldervan in the magazine Thin Solid Films ", Volume 10 (1972), pages a109-122.

According to the invention, porous layers of valve metal or To produce alloys thereof by condensation under such conditions, viz by choosing a suitable substrate temperature, gas pressure and condensation angle, that an anodic oxidation (formation) can then be carried out and the conditions described below are met.

To create a dielectric film by formation, it is It is necessary to convert the valve metal into an oxide through the following process steps: 1. The valve metal is immersed in a suitable electrolyte with an inert cathode brought in.

2. A current is allowed to flow between anode and cathode, wherein the valve metal forms the anode until a valve metal oxide layer is formed of the desired thickness.

3. The oxide becomes at certain voltage ranges and temperature ranges treated in electrolytes so that it makes a good dielectric, like this one Is known to those skilled in the art.

The tension applied to the valve metal during this forming process is applied, is determined by the operating voltage of the capacitor, whereby the thickness of the dielectric oxide layer is controlled for each valve metal there is a relationship between the thermal stress and the oxide thickness2, namely to SOCo V or tm zum V, where to is the oxide layer thickness, C (the Formation constant (oxide), V the voltage, tm the metal thickness used, 0cm the Anodizing constant (metal) and V the voltage.

For aluminum, d m = 11 angstroms / volt, which m is a value of 11 angstroms / volt of consumed aluminum metal. It is therefore for a porous material it is necessary that there is a certain minimum thickness of the metal in the structure, and that during the formation the oxide does not completely contain the finely divided metal consumed. In the case of a column structure, the column diameter must d correspond to: d> 2 «m V.

For aluminum, which, for example, to a voltage of 100 V is to be formed,> the column diameter must be greater than 2200 Angstroms. Columns that are thinner are completely converted to oxide, so that no active one Capacitor can arise.

It therefore becomes a preferred one for each operating voltage of the capacitor Column size, as columns that are smaller than the ratio given above said to be fully formed, while those that are much larger, contain ineffective valve metal, since the maximum surface due to the smallest Columns is determined. It has been found that by vapor deposition of metal on a Substrate surface a porous dendritic coating under suitable conditions is obtained. The top sheet looks like a row of bristles and makes one large surface for the subsequent formation.

Embodiments of the invention will now be described in more detail with reference to the figures are described: Figure 1 shows schematically a metal vapor deposition in a simple embodiment.

Figure 2 shows schematically a vapor deposition device for continuous Coating.

Figure 3 shows another embodiment for continuous light coating.

Figure 4 shows the typical relationship between the forming voltage and the specific capacity for formed metal coatings with the device according to Figure 1 were produced.

FIG. 5 shows the effect of the substrate temperature on the film properties.

With the device described in Figure 1, valve metal or an alloy of valve metals in a vacuum on a flat conductive or insulating Deposited substrate surface, with the deposition under such Angle to the surface takes place that the deposited metal rows side by side arranged columnar crystals or dendrites. The resistance body from boron nitride-titanium diboride is in the vacuum chamber 12 at a temperature of Maintained 1600 OC by passing an electric current through it, typically 100 - 150 A. With constant Speed becomes an aluminum wire 13 fed from a roll, not shown. The aluminum melts on the Resistance body 11 and evaporates from it, the evaporation essentially takes place perpendicular to the resistance surface. For other applications this thermal evaporation technique, for example by an electron beam evaporation process be replaced.

The stream of aluminum vapor generated in this way hits the substrate 14 on, which consists, for example, of an aluminum foil on a base 15 is arranged.

The base 15 is preferably cooled with water.

The deposition of aluminum on the substrate 14 is carried out under a such an angle of incidence with respect to the surface carried out that the metal in columnar arrangements of metal crystals is deposited so that it forms a layer with a large surface area on the substrate. Preferably is this angle is less than 60 degrees. An angle of precipitation is particularly advantageous between 5 degrees and 10 degrees. When the precipitated aluminum under the microscope it looks like a series of bristles or threads.

For some applications, it can also create an even larger surface A trace of oxygen can be achieved in the vacuum chamber during the deposition process is admitted. It has been found that a partial pressure of oxygen up to and including 1.3-10 2N / m2 has the effect that the dimensions of the deposited Crystals are reduced and that a certain degree of crystal branching occurs.

Figure 2 shows an apparatus for producing metal layers, which is placed in a vacuum chamber and with which a continuous coating a substrate film can be achieved. The foil 21, typically aluminum, to be coated is fed from roller 22 and out around the drum 23 while passing the metal vapor source 25. The metal vapor source can have a structure similar to that described with reference to FIG.

The metal vapor emerges from the vapor source substantially perpendicularly to the liquid surface of the metal vapor source, but metal vapor enters small amount at a different angle. The metal vapor source is arranged in such a way that that the strongest metal vapor jet the foil at the desired angle with respect to meets the film surface. If the foil is away from the metal vapor source on this If the point is moved away, as shown in FIG. 2, the last part falls of the metal vapor on each part of the foil with a larger angle of incidence, whereby an advantageous structure results in that the porosity against the Surface of the applied layer becomes larger.

Figure 3 shows a device for continuous precipitation, where no substrate foil is required.

A metal cylinder 31 rotates. past a metal vapor source 32. The cylinder surface was previously covered with an anti-stick layer of a Source 33 overzones. The drum 31 and the metal vapor source 32 are so arranged that the initial deposition of metal followed in compact form is covered by an upper porous coating layer, making a self-supporting sheet is obtained. This film is pulled off the drum and made into a supply roll 34 wound up.

In a further embodiment, multiple metal vapor sources can be used 25 can be used, which either results in a thicker upper layer and / or superimposed coverings of different metals can be obtained.

The methods described so far are not aimed at precipitating limited by aluminum. For example, other valve metals, in particular Tantalum, deposited in a porous form suitable for the subsequent formation will. For some such metals it is more advantageous to use electron beam evaporation or to use an atomization technique instead of thermal evaporation. Alloys of two or more metals can also be deposited.

The substrate can be made of the same metal or a different one Metal. For certain applications, a deposit on an insulating material can also be used Substrate, such as a plastic film or a ceramic body.

The described deposited porous metal layers are used in the manufacture of electrolytic capacitors, although their, \ r.use not limited to this is. The large surface is special advantageous for the manufacture of electrolytic capacitors. In this application the metal layer is first in a conventional forming electrolyte except for one Voltage is formed, which is usually 30 X above the operating voltage of the finished product Condenser, if it is a question of capacitors with liquid electrolytes, and 4 - 5 times greater than the operating voltage when using solid electrolyte capacitors deals with manganese dioxide electrodes. The capacity yield of a formed metal layer depends of course on the forming voltage used. In Figure 4 is the typical one Capacity yield for vacuum deposited aluminum films compared to the well-known etched aluminum films.

It was also found that the properties of the dejected Metal layers depend on the temperature at which the metal is deposited will. The optimal temperature depends on the forming voltage, which the layer is then subjected. This effect is shown in FIG.

Exemplary embodiments of the invention are described below: Example 1: Using the apparatus of Figure 1, aluminum was applied to a 10 / µm thick aluminum foil deposited at an angle of 10 degrees. After 10 Minutes of evaporation in a vacuum was vented and the film was removed.

A layer 61 µm thick was obtained with a very porous one Column structure. This film was tensioned in 4X boric acid solution formed by 200 V.

The formed film had a capacity of 0.96 / uF / cm2, which is a Capacity yield of 6.4 102 uF V / cm3.

The precipitate obtained by the method described of porous columnar structure is dendritic in nature. However, it is not always required. create a porous material.

Further modifications of the metal surface are obtained by that in the vacuum chamber a small amount of an inert gas, such as argon, is let in, which scatters the metal = ampf and the formation of fine metal particles causes in the gas phase.

The extension to a continuous process is possible through Use of the large-scale vacuum vapor deposition technique, which involves multiple electron beam sources Apply the steam to a large roll of aluminum foil coming off a roll wrapped around another in a vacuum.

A technique in which one layer on top can also be used a thermally stabilized drum made of suitable material is knocked down, in which the valve metal first as a thin continuous layer and then as a thick porous layer is deposited on the drum.

The composite layer is then peeled off as a film and rolled up.

In another embodiment, a piece of foil from 10 x 1 cm, manufactured as described above and provided with an aluminum connection, which was attached at one end by cold welding, after which the foil in a 1 Xigen potassium biphthalate solution to 33 V was formed.

This film was then sandwiched with an identical film wound by paper, in such a way that the vacuum-deposited sides faced each other. After reforming at 85 ° C in a suitable Operating electrolyte and cooling to room temperature had the following arrangement Properties: Capacity = 80 µF tan # = 10% residual current = # @ 0.1 µA at 25 V Da the total thickness of the film was 50 μm, this results in a reduction of the cathode and anode volume by 50 X.

A thicker film made in the same way gave the same device with the following properties: Capacity = 195 µF tan # = 10% residual current = 2.0 µA at 25 V. Example 2: Using of the device shown in Figure 3 with a metal vapor source such as it was described with reference to FIG. 1, aluminum foils were produced at following precipitation parameters: Drum speed: 1 revolution in 20 min Drum diameter: 30 cm Feed wire: 0.14 grams / min Current in the evaporation rod: 120 A at 12 V drum temperature: 30 OC to 300 OC according to Figure 5 at drum temperatures above 50 OC it is advantageous to cover the drum with an anti-stick agent coat to make it easier to remove the film. As an anti-adhesion agent a product can be used which is commercially available under the name "Teepol" is available, or another wetting agent that is applied as a thin layer of fat is, or an applied oxide layer or a thin aluminum layer that is on the cold drum was knocked down beforehand.

The precipitation chamber was brought to a vacuum of 1.3-10 3 N / m2 and the steaming is carried out for a full revolution of the drum. To After venting the system, the film was peeled from the drum and then in a 3 own ammonium tartrate solution formed at room temperature.

The capacity per unit volume of the film was determined and in capacity yield converted, i.e. the product of the capacity and the forming voltage per volume unit.

In FIG. 5, foils produced in this way are compared with very heavily etched Foils and it can be seen from the figure that in the temperature range between 20 and 300 ° C. the films produced according to the invention have a higher value Capacity yield at 200 V have as etched foils and that from 20 to 150 OC the films according to the invention have a higher capacity yield at 30 V than etched foils.

As already mentioned at the beginning, there is an optimum for the substrate temperature of 120 0C for foils that are formed up to 200 V, the optimum temperature being is below 20 OC.

The method with the rotating drum results in an advantageous one Property of the film in that the angle of incidence of the steam jet from the point A at point 8 in Figure 4 changes so that a more dense layer in the initial stage and obtaining a more porous layer in the later step (B) of the deposition will. This means that the layer arrangements are self-supporting and by being wound up can be processed, the strength being due to the denser part and the high capacity is created by the less dense part.

Example 3: Using the device of Figure 3, a AlumGnium foil produced with the following parameters: Drum speed: 1 revolution in 20 min drum diameter: 30 cm current through the steam source rod: 12.0 A at 12 V Drum temperature: 30 OC Oxygen pressure: 1.3-10 2 N / m2 during of precipitation.

The film was peeled from the drum and post-formed in ammonium tartrate it had the following properties: forming voltage capacity yield (uF V / cm3) 30 220000 100 141000 200 89000 The capacity yield is comparable at 30 V with layers deposited in vacuo at 30 0, but higher at 200 Y as layers that are at the same temperature in the absence of oxygen were knocked down.

Further exemplary embodiments will become apparent to the person skilled in the art.

For example, thick porous layers of valve metal can be created are made on a wire of the same material to produce compact small Electrolytic capacitors.

The invention is also applicable to continuous production of layers or foils, for example by suitable modification of the process, described in U.S. Patents 3,270,381, 3,183,563, and 3,181,209.

Claims (18)

Claims method for producing a foil for wound electrolytic Capacitors, with liner porous layer of valve metal, created by anodic oxidation is provided with a superficial oxide layer, d u r c h e k e n n z e i c h -n e t that aie porous valve metal layer through in a manner known per se Evaporation of the valve metal in a vacuum on a substrate with a relative to the Small evaporation angle of the substrate is generated. 2.) Method according to claim 1, characterized in that the substrate is moved relative to the steam source during steaming. 3.) The method according to claim 2, characterized in that the substrate is moved with respect to the steam source during the vapor deposition that the vapor deposition angle changes during the layer build-up. 4.) Method according to claim 1 to 3> characterized in that a film is used as the substrate. 5.) The method according to claim 4, characterized in that the substrate a valve metal foil is used. 6.) The method according to claim 5, characterized in that the substrate filament an aluminum foil is used. 7.) The method according to claim 4, characterized in that the substrate a plastic film is used. 8.) Method according to claim 1 to 3, characterized in that as Substrate used a drum and peeled the vapor deposited layer from the drum will. 9.) The method according to claim 1 to 8, characterized in that the Temperature of the substrate during the vapor deposition in relation to the voltage the subsequent anodic oxidation is chosen to have a maximum capacity per unit volume is obtained. 10.) Method according to claim 1 to 9, characterized in that the vapor deposition at least partially in the presence of oxygen at a partial pressure of no more than 1.3.1O2N / m2 is carried out. 11.) The method according to claim 1 to 10, characterized in that aluminum is used as vapor deposition material. 12.) The method according to claim 1 to 10, characterized in that tantalum is used as vapor deposition material. 13.) Method according to claim 1 to 10, characterized in that an alloy of valve metals is used as the vapor deposition material. 14.) Device for performing the method according to claim 1 to 13, characterized in that the metal vapor source passes through the flat surface The passage of current is the heated resistance that the valve metal to be vaporized is fed in wire form. 15.) Device for performing the method according to claim 1 to 13, characterized in that the metal vapor source through the surface of molten Valve metal is formed. 16.) Device according to claim 14 or 15> characterized in that that several metal vapor sources are provided. 17.) Device according to claim 14 to 16, characterized in that that a rotatable drum is arranged in the vicinity of at least one metal vapor source is that the metal vapor jet from the metal vapor source covers the drum under one meets a small angle with respect to the drum surface. 18.) Apparatus according to claim 17, characterized in that im Area of the metal vapor jet directed against the drum by the metal vapor sources a substrate film is guided over the drum surface.