EP0011771B1 - Anodised aluminium rolls with improved electrical conductibility and method of manufacturing the same - Google Patents

Description

The invention relates to aluminum rollers with an anodized surface which is improved in terms of electrical conductivity, and to a method for making anodized aluminum surfaces, in particular the surface of transport and guide rollers, electrically conductive.

Metal rollers are generally used to transport sheet-like materials made of paper or plastic film in processing machines. Steel rollers are often used, the surfaces of which are hard chrome-plated to reduce unwanted abrasion or to protect oxidation. The chrome-plated rollers are highly polished to protect sensitive materials from scratches.

These rolls produced in this way have the disadvantage that they are very heavy and therefore loaded with a large moment of inertia. When the processing machine or device is started up or braked, these rollers continue to run and thereby scratch the surfaces of the web material, even if they are polished. Hard chrome plating with subsequent high-gloss polishing of the surfaces is also very expensive. There has been no shortage of attempts to replace these heavy rollers with light metal rollers. Anodized aluminum rollers are particularly suitable. The anodizing process, i.e. the application of the extremely hard Al ₂ O ₃ layer (corundum), makes the roll surface highly wear-resistant, so that an ideal roll material is created. However, the anodized layer has the disadvantage that it is no longer metallically conductive, on the contrary it is highly insulating. This property means that the otherwise ideal roller material loses almost any practical importance for the guidance and transport of paper, film or foil webs. Due to the contact of the webs with the roller surface and the detachment from the rollers and the associated friction, electrical charges of the webs and discharges occur as lightning. The handling of plastic films charged in this way is difficult and unpleasant.

The use of anodized aluminum rollers for transporting or guiding photographic film or paper webs is completely inadequate, since the lighting phenomena associated with charging and discharging cause the photographic layers to be pre-exposed and render them unusable.

It is known that does not grow in applying an anodic coating electrically oxidized aluminum on an aluminum surface, which is usually done in baths by anodic oxidation, the anodic coating without any structure, but that due to the flow-lusses ^f in the growing A _[2 0 ₃ - Layer channels and pores of a few µm width and diameter are preserved, which vary depending on the bath and electrical conditions. These processes are described in the literature, e.g. B. by M. Schenk in »Aluminum and its anodic oxidation (Verlag A. Francke, AG, Bern, 1948) or by A. Jenny in» The Electrodic Oxidation of Aluminum (Verlag Th. Steinkopf, Dresden and Leipzig 1938).

It is also known to close the channels after the anodizing process, e.g. B. by boiling in water. Another known possibility is to use the channels or pores to color the A1 ₂ 0 ₃ formed. This is the reason for the extraordinary variability of the color shades of anodized aluminum. Such processes can be found in the literature, which describes the coloring possibilities of anodized aluminum with metal salts.

In 1961, Hübner / Schiltknecht reported in "Praxis der anodische Oxidation" (Aluminum-'Jerlag Düsseldorf) about inorganic stains using metal salts and their conversion into finely divided precipitates of pure metals, e.g. B. a yellow color by copper or brown color by silver.

The authors also describe a method by which light-sensitive silver halide is embedded in the pores of the anodized layer, thus creating the possibility of using; rh Exposure and development to produce photographically relatively insensitive, but mechanically very stable photographic images.

No improvement in the electrical conductivity of aluminum surfaces treated in this way was observed.

The invention is based on the object of improving the electrical conductivity of anodized layers on aluminum rollers and thus suppressing electrostatic charging of the web material which is conveyed by these rollers.

The object is achieved in that metal salts are incorporated into the previously cleaned pores of the anodized aluminum surfaces, the metal salts are reduced to metal, and thus an electrically conductive connection of the anodized outer surface with the metallic underlying aluminum surface is created.

Suitable as metals to be embedded in the channels or pores of the anodized layer are non-corrosive or slightly corrosive metals such as, for. B. gold, silver, copper, chromium, tungsten, molybdenum or the metals of group VIII of the periodic table. Metals which have good electrical conductivity and are relatively difficult to oxidize to form a less conductive connection are preferred.

A particularly good metallic, electrically conductive connection of the outer surface with the Metal surface of the roller body is achieved in that wetting agents are added to the metal salt solutions, which promote the penetration of the metal salt solutions.

It has also proven to be advantageous to treat the anodized surfaces in an ultrasonic bath with an aqueous surfactant-containing cleaning solution before the treatment.

It was surprising to the person skilled in the art that the surface resistance of anodized aluminum rollers could be reduced from 10 ¹² Ω to 1-100 Q by the relatively simple and inexpensive method of the invention. The conductivity of the anodized aluminum surface was therefore increased drastically, so that the above-mentioned disadvantages of contact charging of roller surfaces and web materials were eliminated or reduced to a minimum. The rollers equipped in accordance with the invention can be used with good success for the transport of photographic papers and films, because with a surface resistance of 1 von100 Ω of the rollers, spark discharges (so-called flashing) no longer occur.

It is not possible to remove the metals from the pores or channels with the usual cleaning or grease solvents with which such rollers are usually treated, so that a permanent, highly conductive connection is produced.

An important measure before the treatment of an anodized aluminum roller according to the invention is the thorough cleaning of the anodized surface in order to open possibly smeared pores or channels. An ultrasonic bath with a cleaning solution at 80 ° C, a subsequent rinsing in water and thorough drying have proven particularly useful. To clean the surface in the ultrasonic bath, the aluminum roller is immersed in the cleaning liquid and the bath is exposed to the action of an ultrasonic source.

All commercially available water-soluble cleaning agents are suitable for this purpose. Such cleaning agents generally contain detergent substances such as. As alkylbenzenesulfonates and fatty alcohols and possibly small amounts of fatty acid ethane, they also contain phosphates such as. B. pyrophosphate and tripolyphosphate, other inorganic salts such as sodium sulfate and possibly sodium chloride, occasionally also sodium silicates, borax and soda. In addition to the above-mentioned washing-active substances, predominantly nonionic compounds, they can also contain, in particular, the addition products of ethylene oxide with fatty alcohols or alkylphenols and hydrotropic additives such as urea, alcohols or other organic solvents which promote clarity. The cleaning agents used according to the invention are referred to below as "cleaning liquids containing surfactants".

Examples include a 33% aqueous solution of the sodium salts of oxystearyl sulfate and oleylmethyl taurine, an aqueous solution containing tripotassium phosphate, polyphosphate and sodium lauryl sulfate or a 50% aqueous solution of benzyldodecylmethylammonium chloride.

In order to achieve optimal conductivity, it is necessary to fill the pores and channels, which are in the range of µm and very small, to the bottom with metal salts and then to achieve a complete reduction of the metal salts to metals. This is supported by the addition of wetting agents to the metal salt solutions and the reduction solutions.

oder

weiter Bernsteinsäurederivate wie die Netzmittel

oder

oder auch anionische Netzmittel vom perfluorierten Typ. wie zB. die Verbindungen

oder

In addition to saponin, other surface-active compounds can also be used as wetting agents. Wetting agents which contain ethylene oxide units in addition to carboxyl groups, such as the compounds, may be mentioned by way of example

or

further succinic acid derivatives such as the wetting agents

or

or also anionic wetting agents of the perfluorinated type. such as. the connections

or

Further fluorine-containing wetting agents which are suitable in connection with the invention are described in BE-PS 742 680 and in DE-OS 1 942 665 and 1 950 121.

The invention is illustrated by the following examples. Unless otherwise noted, percentages mean percentages by weight.

example 1

An aluminum plate with a 70 μm thick hard anodic coating produced in a known manner is cleaned with a 33% aqueous solution of the sodium salts of oxystearyl sulfate and oleyl methyl taurine at 80 ° C. in an ultrasonic bath, then rinsed in water and dried.

A 30% aqueous H ₂ PtCl ₆ solution is applied with a brush and dried. The platinum salt is then reduced using a saturated aqueous SnCl ₂ solution. This process can be repeated several times. The surface resistance of the dry plate drops from 10 ¹² Q to 95 Ω due to the treatment.

Example 2

The anodized aluminum plate is cleaned and the metal salt is applied as described in Example 1. The reduction is carried out with a 2% phenidone solution in acetone. 3 cm ³ per liter of phenidone solution of a 4% aqueous solution of the compound of the formula C ₈ F ₁₇ SO ₃ N (C ₂ H ₅ ) _{4 are} added as the wetting agent.

Example 3

In a modification of Example 1, an aqueous 1n HAuCl ₄ solution with 5 cm ³ per liter of a 10% aqueous saponin solution is used as the metal salt solution. The reduction is carried out with a 4% aqueous hydrazine solution.

Example 4

In a modification of Example 1, a 15% aqueous Na ₂ PdCl ₄ solution with 3 cm ³ per liter of a 4% aqueous solution of the wetting agent of the formula C ₈ F ₁₇ SO ₃ N (C ₂ H ₅ ) _{4 is} used as the metal salt solution .

The reduction is carried out with a 2% phenidone solution in acetone.

Example 5

A saturated aqueous AgN ₀₃ solution with 3 cm ³ per liter of a 4% aqueous solution of the wetting agent of the formula C ₈ F ₁₇ SO ₃ N (C ₂ H ₅ ) ₄ is applied several times to the anodized layer prepared according to Example 1. The reduction is carried out with a 1: 1 mixture of 2% phenidone solution in acetone with 4% aqueous hydrazine solution. The reducing solution contains 3 cm ³ per liter of the 4% aqueous solution of the wetting agent of the formula C ₈ F ₁₇ SO ₃ N (C ₂ H ₅ ) ₄ .

Example 6

A saturated aqueous AgN0 ₃ solution with 3% by weight per liter of a 10% aqueous solution of the wetting agent saponin is applied to the anodized layer in accordance with Example 1. The mixture is then bathed in an aqueous 2N NaCl solution. This process is repeated several times. The following reduction solution is then used:

4 volumes of solution 1 and 1 volume of solution 2 are mixed and 5 volumes of water are added. The mixture is allowed to act on the anodized layer at 20 ° C. for 5 minutes.

Example 7

The anodized layer treated in accordance with Example 1 is bathed several times with a saturated aqueous solution of chromium alum. The reduction is then carried out using a 2% aqueous hydrazine solution.

Example 8

A saturated aqueous CuCl ₂ solution is applied to the anodized layer of Example 1 and then reduced with a 2% aqueous hydrazine solution.

Both solutions contain 5 cm ³ per liter of a 10% aqueous saponin solution as a wetting agent to ensure that the solutions of the metal salts and the reducing agents can penetrate to the bottom of the pores and channels of the anodized layer on the metallic aluminum.

The conductive layers produced according to the examples on the outer sides of the anodized layers have surface resistances between 1 Ω and 100 Q depending on the treatment time, repetition of the treatment and amount of wetting agent.

The surface resistances were measured according to DIN 53482, method A, at 20 ° C and 60% relative humidity.

Claims (6)

1. Aluminium rollers having porous surfaces of anodised oxide for the transport and/or guiding of materials in the form of sheets or bands which are capable of being electrically charged, characterised in that metals which have little or no tendency to corrosion are deposited in the pores of the anodised oxide surface.

2. Aluminium rollers according to Claim 1, characterised in that the pores of the anodised surface contain a metal from the group comprising copper, silver gold, chromium, tungsten, molybdenum and Group Vlll of Periodic System.

3. Process for the manufacture of aluminium rollers having an anodised porous surface with improved surface conductivity, characterised in that the surface of the rollers is first cleaned with an aqueous cleaning liquid containing surface active agent, the cleaned porous surface is then impregnated with an aqueous metal salt solution and the surface is subsequently treated with the aqueous solution of a reducing agent for the metal salt.

4. Process according to Claim 3, characterised in that for cleaning the surface the :ollers are immersed in the aqueous cleaning liquid containing surface active agent and the bath is exposed to the action of a source of ultra-sound.

5. Process according to Claims 3 and 4, characterised in that the aqueous metal salt solution contains a wetting agent.

6. Process according to Claims 3 to 5, characterised in that aqueous solutions of metal salts taken from the group comprising copper, silver, gold, chromium, tungsten, molybdenum and Group VIII of the Periodic System are used.