EP0309831A1 - Ion barrier on metals and non-metals - Google Patents

Abstract

A high-purity electroplated aluminium layer (purity > 99.99%) which preferably has a thickness of 10 to 20  mu m is used as an ion barrier on components and mouldings made of metals and non-metals, in particular on polyolefins. The electroplated aluminium layer can optionally be compacted and/or anodically oxidised by posttreatment. The electroplated aluminium layer prevents the penetration of metal and nonmetal ions into nonmetals, in particular into plastics, for example polyolefins, and their penetration to metal surfaces. The electroplated aluminium layer is deposited by electroplating from aprotic, oxygen-free and anhydrous electrolyte media of the general formula M<1>X.2AlR3.nLsm, where M is an alkali metal ion or a quaternary onium ion, X is a halogen ion, preferably F<-> or Cl<->, R is an alkyl radical, preferably CH3, C2H5, C3H7 or C4H9, Lsm is an aromatic solvent molecule, preferably toluene, ethyl benzene, xylene or a mixture of the same, and n = 0 to 12, optionally in the presence of an aromatic solvent, at a bath temperature of 50 to 110 DEG C and a current density of 0.5 to 10 A/dm<2> with vigorous bath agitation.

Description

The invention relates to an ion barrier layer on metals and non-metals, in particular on polyolefins.

It is known that non-metals, which because of their extremely low electrical conductivity serve as insulating materials on metallic conductors of the electrical current, are not only impaired in their insulator properties by diffusion of metal ions from the conductor material, in particular by diffusing in heavy metal ions, but due to catalytic reactions, which trigger these diffused metal ions and reinforce them in the heat, also suffer from structural degradation and are thereby seriously damaged or even destroyed. This applies in particular to the ions of heavy metals, such as copper, silver, nickel, cobalt, manganese and their alloys, which can result in depolymerization reactions and oxidative degradation, especially in the case of polyolefins, for example polyethylene, polypropylene and their copolymers.

On the other hand, non-metal ions, in particular oxygen and sulfide ions, are also able to penetrate through non-metal layers, for example those made of plastics, such as polyolefins, and chemically attack the heavy metal surfaces, for example to form oxides or sulfides of these metals, which in turn penetrate into the non-metals and can bring about adverse changes. Not only are chemical structural changes triggered, but also the purely mechanical bond between metal and non-metal, ie between conductor metal and non-conductor layer, is loosened and released; their electrical properties are deteriorated as a result, and their use and value in use impaired or questioned.

In order to avoid such damage and damage, relatively thick and therefore expensive intermediate layers of tin or nickel have previously been brought between conductor metal and non-conductor, or e.g. certain inhibitor substances which bind the metal ions and eliminate their harmful effect are mixed into the polyolefins, i.e. inhibit them. However, additives of this or other type mostly reduce the quality of the electrical and mechanical properties of the insulating materials and are only a compromise solution to the problem. Real and adequate protection could not be achieved, especially at higher operating temperatures of the insulated conductor.

The use of aluminum foils as an oxygen ion barrier is known from the European patent application published under number 0 044 668. The aluminum foils should have a thickness of more than 15 μm, preferably 20 μm. According to the embodiment, the aluminum foil is 25 microns thick. Wrapping and gluing is required. In terms of process engineering, the coating of the conductor with metal foil, which must be complete, is complex and difficult to achieve.

The object of the invention is to protect components and fittings made of metals and non-metals, in particular plastic, for example polyolefins, from diffusing metal ions and the thermal-catalytic degradation, in particular the heavy metal ions of copper, silver, nickel, cobalt, manganese and their alloys force, prevent, but at the same time to avoid the chemical attack on metals and metal alloys caused by diffusing non-metal ions, especially oxygen and sulfide ions.

According to the invention, this object is achieved by an ion barrier layer solved, which is designed according to the characterizing part of claim 1, ie by a high-purity galvanoaluminium layer.

Further refinements and developments of the invention emerge from the subclaims.

The high-purity galvanoaluminium layer according to the invention, which can act as a protective and intermediate layer, has proven to be an excellent ion barrier up to temperatures of at least 300 ° C. in thicknesses of preferably 10 to 20 μm. Thus, the galvano-aluminum layer according to the invention, applied to metal or rendered non-metal surfaces, protects them, e.g. the polyolefins, before the penetration of metal ions, which, as such or by catalytic initiation of oxidation reactions, damage the polymer structure or even destroy it by depolymerization reactions. Non-metal surfaces can be made conductive by applying an electrically conductive, approximately 0.05 to 2 μm thin metal, graphite or carbon layer. Likewise, however, the galvanoaluminium layer according to the invention also protects metals, in particular metal surfaces, from penetrating metal or non-metal ions, the metals being adversely or damagingly changed, for example being oxidatively or sulfidiously attacked by oxygen or sulfide ions or being cemented and alloyed by nobler metal ions. Another significant advantage is that both solid and tubular conductors can be processed in a continuous process, i.e. continuously, with the galvano-aluminum ion barrier layer according to the invention, and at least up to 300 ° C penetration of ions from the outside in, e.g. of oxygen or sulfide ions, or from the inside to the outside in the applied insulator material, e.g. of copper or nickel ions.

The invention also relates to a method for producing a Ion barrier layer on metallic and non-metallic materials with an electrically conductive surface. Here, an aluminum layer is galvanically deposited on the electrically conductive surface in aprotic, oxygen-free and water-free aluminum-organic complex salt electrolytes, which layer can still be compressed and / or anodically oxidized.

Current densities of 0.5 to 3 A / dm² are often sufficient to apply the galvanoaluminium. Higher current densities of 3 to 10 A / dm² can also be used for conductor materials that are continuously coated in a continuous electroplating system in countercurrent to the electrolyte.

Suitable aprotic, oxygen and water-free electrolyte media are those of the general formula M ^I X.2AlR₃.nLsm, where M is an alkali metal ion or a quaternary onium ion, X is a halogen ion, preferably F⁻ or Cl⁻, R is an alkyl radical, preferably CH₃, C₂H₅, C₃H₇ or C₄H₉, Lsm is a molecule of an aromatic solvent, preferably toluene, ethylbenzene or xylene or a mixture thereof, and n = 0 to 12 means.

Reverse or pulse currents are advantageously used to achieve a homogeneous and dense electrocrystalline galvanoaluminium structure. The galvanoaluminium layer can also be mechanically compressed and solidified, for example by glass bead blasting or by hard material particle drums.

If the galvanoaluminium surface according to the invention is subsequently coated with an insulator material, for example a polyolefin, from the melt or by hot pressing, the adhesive strength between the galvanoaluminum and the insulator material can be increased in that an approx. Approx. 2 to 6 µm thick galvanoaluminium anodized layer. Because of their upper surface-active microstructure and ceramic-like surface properties result in excellent bond strengths for plastics and adhesives.

Conductors, fittings and components coated in this way are preferably used where high-quality and permanent insulation of current-carrying parts and devices is required, which must be voltage-tight within narrow limits in order to reliably perform their function and deteriorate the insulation properties of the non-conductor (plastic, especially polyolefins). Metal ions diffusing out of the metallic part of the line or the device cause such a deterioration directly or indirectly (e.g. by catalyzing degradation reactions).

On the other hand, given the high penetrability of plastics for oxygen, hydroxyl and sulfide ions, it is important to protect the former from them or to prevent them from penetrating into the chemically sensitive metal substrates, because the reaction products formed on the metal surfaces, e.g. Oxides, hydroxides and sulfides, which reduce the bond strength and can lead to the increased formation of disruptive metal ions, which in turn reinforce the further catalytic degradation of the insulator structure.

Finally, there are also fittings and components made of metallic materials that are sensitive to the atmosphere and whose functions are impaired if they are freely accessible (e.g. fittings made of lithium or light alloys containing Li, such as AlLi3, or made of the excellent magnetic material SmCo₅ This also applies to metals which are toxic and which have to be “encased” for safety reasons for their handling, for example fittings made of beryllium, thallium and uranium .. In all the cases mentioned, one of aprotic, acidic protects and preserves Substance- and water-free aluminum-organic complex salt electrolytes applied ion barrier made of galvanoaluminium, whereby this protective cover, effective inside and outside, can be reinforced by anodic oxidation to galvano-Al-anodizing. The electro-aluminum, which is electro-chemically deposited on the surface when the shaped part is loaded cathodically, is silvery bright, unusually ductile, of good electrical conductivity and non-magnetic.

The invention is illustrated by the following examples.

example 1

Protection of the polyolefin insulator coating, in particular made of polyethylene or polypropylene, of copper lines against thermal and oxidative degradation of the crosslinked polymer structure catalyzed by copper ions by applying an approximately 10 μm thick galvanoaluminium layer as an ion barrier layer for copper ions (generally heavy metal ions) on the surface of the copper conductor before the polyolefin sheathing (by hot extrusion).

A wire of 3 mm diameter made of electrolytic copper (99.95% Cu), which is used for electrical engineering purposes in electrical engineering, is washed in a water jet tube after passing through a degreasing bath and then a pickling bath and finally dried in a red light channel under countercurrent nitrogen. Then the copper wire pretreated in this way is then immediately in a continuous galvano-aluminizing system in the electrolyte countercurrent from the complex salt electrolyte NaF.2 Al (C₂H₅) ₃.4 C₇H₈, with toluene as solvent, at a bath temperature of 100 to 110 ° C and a current density of about 6 A / dm² coated with approx. 10 µm galvano aluminum all around. Adhesive electrolyte liquid is rinsed away with toluene and the surface toluene moist then in the Hot nitrogen stream dried.

The copper wire coated in this way with approx. 10 µm galvanoaluminum is coated with hot polyolefin, preferably polypropylene, as soon as possible or after storage in dust-free, dry air in a commercially available wire-extrusion coating machine and thereby coated with a high-quality insulator layer. The microcrystalline galvano-Al surface offers a very good primer for this. After cooling, the insulated copper wire can be wound on a wire drum; the elasticity of the polypropylene and the high ductility of the galvanoaluminium allow this.

In order to demonstrate the effectiveness of the galvano-Al ion barrier layer, an approx. 80 cm long sample piece of wire coated directly with copper with a polyolefin of approx. 2.5 mm thick and a previously coated with approx. 10 µm galvano-Al and then stored with approx. 2.5 mm polyolefin coated wire in a warm air tempering oven and observed for appearance (discoloration) and mechanical behavior of the polyolefin layer for 10 days at 60, 100 and 120 ° C. While the polyolefin layer of the test pieces coated with galvanoaluminum remains completely colorless and flexible at all test temperatures over the entire test period, the other test pieces that do not have a galvano-Al ion barrier show a faster yellowing with increasing test temperatures, which only occurs at 60 ° C can be seen after 9 days, but appears at 100 ° C after 4 days and at 120 ° C during the second day; After 10 days of 120 ° C thermal stress, a significant loss of flexural elasticity can also be found on the sample cooled to room temperature, which can be recognized from the tears occurring in the polyolefin layer. The effectiveness of the galvano-Al ion barrier layer is thus shown for copper ions and can mostly be below 100 ° C operating temperatures of electrical copper lines with polyolefin insulation can be fully claimed. Evidence for this is also the finding that a very slow diffusion of copper into galvanoaluminium only begins above 300 ° C with <1 µm / h with the formation of alloys. This diffusion threshold temperature is even higher for other heavy metals, for example for nickel and cobalt at 400 and 450 ° C.

Example 2

Encapsulation of molded parts made of the magnetic material samarium-cobalt (SmCo₅) by an approx. 20 µm thick galvanoaluminium layer as an ion barrier to protect against atmospheric agents, especially oxygen, hydroxyl, carbonate and sulfide ions, which are weakened by chemical reactions of the coercive force and destruction of the magnetic material.

Like SmCoFe and AlNiCo, SmCo₅ is one of the "magnetically hard" materials and is characterized by particularly high remanence magnetization and high coercive force. The interest in its application technology application in technology and especially in electrical engineering is correspondingly diverse.

Like all lanthanoids, whose strongly negative normal potentials ε₀ are at -2.483 (Ce) to -2.255 V (Lu), the samarium is also a powerful reducing agent (comparable in strength to that of Mg) and therefore reacts with water (moisture) under H₂ -Development and with oxygen with formation of oxide, and the latter with CO₂ to carbonate. These chemical properties also adhere, albeit to a lesser extent, to the SmCo₅, which is why one has to encapsulate molded parts made of this material as magnets to protect them from the atmospheres, and the better the longer you want to use the large coercive force undiminished.

Lacquer and plastic layers cannot guarantee permanent protection due to their oxygen and water vapor permeability, and metallic coatings must also be sealed against ion penetration of oxygen, hydroxyl and sulfur, etc., must be effective in the thinnest possible layer, and be applied directly (um to be able to make full use of the magnetic field strength; only a small gap is permitted) and be non-magnetic itself A galvanic application from aqueous electrolyte baths is ruled out for the reasons mentioned above, vacuum evaporation does not give gas-tight coatings.

The application of galvanoaluminum (even non-magnetic) according to the invention in layer thicknesses of preferably 15 to 20 μm Al from aprotic, oxygen-free and water-free electrolyte media of the above type at bath temperatures of 80 to 110 ° C., which do not impair the magnetism of the SmCo₅, is therefore the method of Choice.

The contact is conveniently attached to the back of the magnetic head of the fitting, e.g. by inserting an aluminum wire into a small hole, and after coating the fitting surface with galvanoaluminium, the hole is riveted with a small piece of soft Al wire; the very ductile galvanoaluminium acts as a sealing material and is also ideal for friction welding, so that the encapsulation can be sealed on all sides.

An additional advantage of the galvano-Al ion barrier layer encapsulation of such magnetic material moldings, which are often mechanically stressed on the head part during handling or in use, is the possibility of giving it a hard, very abrasion-resistant surface by subsequent anodizing to form a galvano To give Al-anodized layer from 10 to 15 µm thickness, which before the compression in boiling water as desired colored or can be printed with characteristic data and information. Surfaces of more than 500 HV can be achieved and can also be polished mechanically due to this high hardness.

The galvanoaluminium or the galvano-Al-anodizing layer is an excellent ion barrier layer that does not allow oxygen, hydroxyl or sulfide ions to penetrate to the magnetic material SmCo₅ and preserves and ensures its full functionality and high magnet quality in the long term, and not only in air, but also in industrial atmospheres contaminated with SO₂ and NO compounds. The quality and reliability of the galvano-Al ion barrier layer on SmCo₅ fittings can be determined by measurement - and depending on the layer thickness, relative humidity and test temperature - using specimens stored in the climatic chamber, the coercive field strengths of which are registered as a function of the test time and with that of compares uncoated SmCo₅ fittings of the same initial quality. In this way, the optimal galvano-Al or galvano-al-anodized layer thicknesses for the SmCo₅ fittings can be determined.

A forced test of specimens of the type mentioned above can also be carried out in moist nitrogen-oxygen mixtures of 50:50%, vol. Or wt.%, At 25, 60 or 80 ° C Oxide or hydroxide-converted outer layers of the SmCo₅ fitting can be visually determined under the microscope. Due to its yellow color, the Sm₂O₃ is easy to see.

Example 3

Coating of shaped pieces made of uranium metal, in particular of so-called depleted uranium metal, with - depending on their dimensions - 10 to 30 µm and more galvanoaluminium as an ion barrier, especially for oxygen and hydroxyl ions as well for uranyl ions, on the one hand to protect the very oxygen-affine uranium from oxidation and on the other hand to prevent contact with the toxic heavy metal and its oxidation products when manipulating the fittings.

Uranium metal is due to its extremely high density of 18.97 (g / cm³), its good mechanical properties and its relatively high melting point of 1132 ° C for ballast and counterweights (trim weights) in aircraft, ships, rockets and gyroscopes (stabilization of sighting devices ) as well as for shielding screens against gamma and X-rays in devices and containers.

The metal, which is almost ideal for such applications, is unfortunately a very base metal with a normal potential of ε₀ (for U / U⁴⁺) = -1.494 V, which tarnishes immediately in the air, ie oxidizes, and already from dilute acids, even from boiling ones Water, according to
U + 2 H₂O → UO₂ ↓ + 2 H₂ ↑,
is attacked quickly. Because the tarnish layers do not adhere firmly, but can be wiped off and uranium - regardless of its radioactivity - is toxic as a heavy metal, the above-mentioned fittings for handling and use must be covered with a protective coating. So far, this has been done more or less inadequately with plastic coatings or nickel coatings from aqueous electrolyte baths.

According to the invention, the uranium metal fittings are clamped in a cathode frame made of cleaned nitrogen or argon in a dry inert gas atmosphere immediately after they have been manufactured and the mechanical surface treatment has been carried out. At the same time, they are contacted and via a lock in the aprotic, oxygen- and water-free aluminum niumorganic complex salt electrolyte medium of the above composition sunk in and coated on all sides with cathode movement (reciprocating movement or rotation in the case of cylindrical shaped pieces) at a bath temperature of 80 to 110 ° C. and current densities between 0.5 and 3 A / dm² with 10 to 30 μm galvanic aluminum. On the bare, oxide and top layer-free uranium surface, the galvano-Al ion barrier layer has very good adhesive strength. After washing and spraying off the adhering electrolyte liquid with toluene and rinsing in toluene / isopropanol, the coated shaped piece is dried under nitrogen in a red light channel.

If desired and advantageous, the galvano-Al layer can be mechanically compacted and solidified by glass bead blasting or hard material particle drums or superficially converted into hard, abrasion-resistant galvano-Al anodizing by anodic oxidation in the GS, GSX or GX bath and be compacted in boiling water. This results in a dense, crystal-clear and ceramic-like hard galvano-anodized aluminum layer on the silver-colored galvano-aluminum of the ion barrier layer.

If necessary, the galvano-anodized aluminum layer can be colored and / or labeled as desired before compacting, e.g. for marking the fittings. Subsequent to the dyeing or printing, it is also compacted in boiling water for about 30 minutes, thereby sealing the dye or printing ink in a water-tight manner on the hard surface.

On these coating paths according to the invention, an ion-tight and very durable coating of the uranium metal fittings is achieved, which prevents oxidation of the uranium and prevents uranyl ions, UO₂²⁺, and uranium oxides from diffusing out.

The effectiveness of this coating as an ion barrier can be checked by storing the parts in a warm air cabinet or climatic cabinet (air and moisture). Penetrating UO₂²⁺ ions can easily be detected by their green fluorescence in UV light. Due to the penetration of hydroxyl ions, UO₂ can be easily recognized by its brown-black color and the resulting hydrogen leads to the formation of bubbles under the coating.

Such penetration phenomena do not occur with a sufficiently thick and dense galvano-Al ion barrier layer of at least 10 µm on all sides. Depending on the size and weight of the uranium fitting, thicker galvano-Al layers are indicated to ensure permanent safety when the fittings are handled several times.

In an analogous manner, fittings made of beryllium, thallium etc. can also be coated with a galvano-Al ion barrier layer.

Claims (7)

1. ion barrier layer on metals and non-metals, in particular on polyolefins, characterized in that the surface of the metal or the non-metal made electrically conductive has a galvanoaluminium layer with a degree of purity> 99.99% aluminum, which is optionally anodically oxidized. 2. Ion barrier layer according to claim 1, characterized in that the galvanoaluminium layer has a thickness of 10 to 20 µm. 3. ion barrier layer according to claim 1 or 2, characterized in that the galvanoaluminium layer is compressed mechanically. 4. Ion barrier layer according to one of claims 1 to 3, characterized in that the anodically oxidized galvanoaluminium layer has a thickness of 2 to 15 µm. 5. A method for producing an ion barrier layer on metallic and non-metallic materials with an electrically conductive surface according to one or more of claims 1 to 4, characterized in that on the electrically conductive surface, optionally after cleaning and pretreatment, galvanically in aprotic, oxygen and anhydrous organoaluminum complex salt electrolytes of the general formula
M ^I X.2AlR₃.nLsm,
wherein M is an alkali metal ion or a quaternary onium ion,
X is a halogen ion, preferably F⁻ or Cl⁻,
R is an alkyl radical, preferably CH₃, C₂H₅, C₃H₇ or C₄H₉,
Lsm an aromatic solvent molecule, preferably toluene, Ethylbenzene, xylene or a mixture thereof, and
n = 0 to 12 mol, optionally in the presence of an aromatic solvent, at a bath temperature of 50 to 110 ° C and a current density of 0.5 to 10 A / dm² with intensive bath movement, a galvanoaluminium layer is deposited, which optionally densifies and / or is anodized. 6. Application of the method according to claim 5 for the production of an ion barrier layer on copper conductor wires. 7. Application of the method according to claim 5 for the production of an ion barrier layer as encapsulation on moldings made of magnetic materials or uranium metal.