NO133483B - - Google Patents

Description

The invention relates to an electrical pre-treatment method for improving the adhesion on metal surfaces of substances, such as e.g. varnishes, printing inks, adhesives or plastics, with which the metal surfaces are to be coated

or laminated to. Before carrying out the treatment according to the invention, the metal is cleaned by known chemical or physical methods. One therefore uses e.g. by known annealing processes, degreased sheets, strips or foils of aluminum or aluminum alloys.

In the past, "Chemical adhesive agents (primers) were often used to increase adhesion, the use of which, however, not only made the work more cumbersome, but usually also necessitated an additional work process. Moreover, -b.yr application of -adhesive agents often results in little safety

in cases where high demands are placed on the adhesion, e.g. at high thermal, mechanical or chemical stresses. Moreover, the effect of the chemical adhesion promoters was often considerably weakened when, for example, the degreasing by annealing did not

was complete., or there were other contaminants on it

- the surfaces.

From US patent no.- "2,867^912 it is known to

treat oil-stained aluminum foils in a high-frequency alternating current field. thereby improving the adhesion of various types of coatings. The foil itself constitutes one electrode. The second electrode is fixed and has, for example, the shape of a round rod. The distance between this and the foil - can e.g. be approx. 2 mm.

The advantages achieved according to the invention are that the -rotating electrode roller -enables the use of a very thin dielectric material, as the deposited performance is distributed over a large surface. A thin dielectric, however, has a higher

capacity and a higher conductivity of the electrode as a result.

When the electrode self-rotates, more air flows

in the treatment gap so that more ions and especially more ozone are formed. However, part of the adhesion-improving effect is due to the ozone.

A rotating electrode roll does not heat up

as strong as a fixed system. It also benefits the ozone yield. Furthermore, the electrical losses are thereby reduced.

The rotation leads to a more evenly distributed spark pattern - glow discharge character - which also affects the effect positively.

The invention therefore relates to a method for treating metal surfaces, especially of aluminum or aluminum alloys, with the aim of improving the adhesion of organic coatings to be applied, where cleaned, especially degreased metal objects by annealing are connected as counter poles to one or more electrodes and exposed to a. high-frequency, high-voltage alternating current field, the method being characterized by the use of an electrode consisting of a rotating roller, possibly several such electrodes, arranged as is known in and of itself at a certain, small distance from the m-eSall surface.

Experiments have shown that in this way excellent adhesive strength can be achieved between the above-mentioned substances and the metal surfaces. Due to the considerably increased adhesiveness achieved by coating aluminum foils with polyolefins. on extrusion machines, you can achieve adhesive connections, also with generally poorly adhesive polyolefin types, or you can achieve significantly higher working speeds than before.

Moreover, according to the invention, the further advantage is achieved that e.g. with high-pressure polyethylene, which is applied by extrusion coating, it is possible to work with significantly lower temperatures in the wide slot die. The temperature of certain polyethylene types can be lowered approximately 20 - 30°C below the usually required temperature, without the adhesive strength on the metal surface.

the surfaces sink too much.

With the lower heat stress, significantly less odor occurs, which is of the greatest importance, especially with regard to the possibility of using the aluminum foils coated in this way as packaging material in the food industry.

Of significant importance, it may be that the previous need for adhesive agents may disappear. However, if you decide to use adhesive agents, or e.g. in the case of aluminum for known pretreatment methods, (such as anodizing, etc.), then the method according to the invention entails the pre-

share that these common methods are improved, i.e. that by combining both methods you get a previously unattainable high adhesion.

In an embodiment according to the invention, high-frequency current of 25 to 75 kHz or more and a voltage of approx. 300,000 V or more, preferably between 400,000 and 600,000 V. The desired effect according to the invention is thereby ensured.

The roller-shaped design of the electrode has

it has the advantage that a line-shaped discharge can be produced over the entire width of the material, as the discharge location on the roller is constantly changing during its rotation. Thereby, the risk of the treatment roller being heated or locally overheated inappropriately is ruled out. In addition, you have the option, if necessary,

to cool the roller. Appropriately, the roller is placed in well-insulating bearings to avoid voltage loss.

The gap opening between electrode and metal track further depends on the conductivity of the dielectric in the gap and also

of the applied voltage. Air is usually used as a dielectric, the oxygen part of which, as is well known, is partially converted to ozone under the influence of electrical energy. The gap opening is usually 0.5 - 3 mm. The adhesive effect that can be achieved depends on the type of metal, resp. alloy composition,

is in many cases appropriate to repeat the treatment according to the invention, e.g. so that several electrodes are arranged one after the other. In the case of several electrodes arranged one behind the other, the "passage speed" can be increased substantially.

In addition, you can guide the sheet or the foil web in this way, resp. arrange the treatment electrode so that in one pass both metal surfaces are each treated at one or more electrodes, whereby the adhesive properties are improved on both sides.

The treatment according to the invention is advantageously carried out on long metal webs (rolls), because in this way the most possible continuous working method can be carried out. In the case of format gaze (divided gaze) the treatment takes place intermittently, or the forward thrust of the format gaze is controlled so that only small spaces appear between the individual gaze lengths. The treatment electrode can therefore constantly remain under voltage. It is recommended to design the guide rollers i

near the electrode of non-conductive materials -{rubber etc.)

—to avoid overshoot next to the material path to be processed. If the applied voltage is chosen high enough, it can be varied without any noticeable effect on the adhesiveness achieved

, the width of the look according to -desire- It is of course most advantageous that the electrode is at least as long as -the look is wide.

As already mentioned, the procedure can also be used for h-alvf ab-rikata, especially for pipes. Here, the shape of the electrode must be precisely matched to the metal surface to be treated.

The method according to the invention can be carried out so that the treatment is carried out immediately before coating,

coating, lamination, etc. However, it is also possible to carry out the treatment separately from the further processing and to allow this to take place at a later time.

Example 1.

If a white-annealed aluminum foil of 0.015 mm thickness and 10,130 mm width is coated without prior chemical or other surface treatment on an extrusion machine with high-pressure polyethylene, the adhesion is insufficient already at a working speed of 30 m/min. when the temperature in the wide liss nozzle is approx. 280°C. When carrying out an electrical pre-treatment according to the invention (600,000 V, 5~0 kHz) at a distance of approx. lm _i'oran the extrusion die, the adhesion proves so good that one can apply the high pressure polyethylene in a thickness of 0.050 mm, even at a working speed of -60 -m/min. or more. The polyethylene film cannot be detached from the aluminum foil without destroying it. The distance between the roller electrode and the aluminum surface (the slot opening) was 1.2 mm.

An apparatus from "Deutsche Vetaphone GmbH, Hamburg" of the type 3"00/3 was used in this test arrangement. Example 2.

In a further experiment, a "white annealed aluminum strip of 0.05"0 jnm thickness and 800 mm width without previous chemical or other surface treatment was made at a working speed of 25 m/min. subjected to the electrical treatment method according to the invention. The electrical conditions corresponded to the data given in example 1. After 15 days of storage, the roll was coated on an extrusion machine with high-pressure polyethylene. The polyethylene temperature in the wide slot die: 28"0°C, polyethylene layer thickness: 70 g/m^.

The adhesion achieved here could also be improved considerably compared to that achieved by known methods. Example 3-.

A medium-hard aluminum strip of 0.2 mm thickness and 600 mm width was coated without any pre-treatment on a burn-in lacquering machine with a lacquer common for such purposes (roll application.); working speed: 5 m/min; ignition temperature - 230°C; varnish file-mtykkelee: 5 g/m •

With normal working methods, the adhesion was not sufficient for the highest demands. However, after application of the electrical surface treatment according to the invention (operating conditions and electrical data as stated under example 1, however with a placement of the treatment electrode 1.5 m in front of the painting plant) the adhesion of the lacquer layer to the aluminum was very good, so that even difficult shaping could be carried out by deep drawing without the lacquer layer's adhesion to the aluminum being weakened.

Claims (4)

1. Procedure for the treatment of metal surfaces, especially of aluminum or aluminum alloys, with the aim of improving the adhesion of organic coatings to be applied, where cleaned, especially degreased metal objects by annealing are connected as counter poles to one or more electrodes and exposed to a high frequency, high-voltage alternating current field, characterized in that an electrode is used which is made up of a rotating roller, possibly several such electrodes^ arranged as is known in and of itself at a certain, small distance from the metal surface. 2. Method according to claim 1, characterized in that the rotating electrode roll is cooled. 3. Method - according to claims 1 and 2, characterized in that the metal surface to be treated is exposed to the influence of several successive alternating fields. 4. Method according to claims 1-3" characterized in that a metal web to be treated is exposed to one or more alternating fields simultaneously on both sides.