Method for surface treating a substrate and device for carrying out the method

Abstract

The invention relates to a method for surface treating a substrate (28) by means of an electrical corona discharge, wherein aerosols (5) are sprayed into discharge area defined by an active gap formed between a corona electrode and the substrate (28) during the discharging, designed such that the aerosols (5) are sprayed substantially opposite the direction of gravity.

Claims

1. A device for surface treatment of a substrate with an electric corona discharge, said device comprising: at least two corona electrodes, one of the corona electrodes being connected to a voltage and the other one of the corona electrodes being connected to ground, with one of the corona electrodes forming a support electrode having a downwardly oriented surface to form a support surface for a substrate, and with the other one of the corona electrodes forming a counter electrode; and an atomizer configured to spray aerosols only upwards in a direction opposite to direction of gravity toward the downwardly oriented surface into a discharge region of the corona electrodes, wherein the atomizer and the downwardly oriented surface are positioned juxtaposed with respect to each other.

2. The device of claim 1, wherein the atomizer is arranged in a region of the counter electrode (2).

3. The device of claim 1, wherein the support electrode is constructed as a cylindrical electrode.

4. The device of claim 1, further comprising support rollers arranged on both sides of the support electrode in axis-parallel relationship to the support electrode.

5. The device of claim 1, wherein the support electrode is connected to the voltage and the counter electrode is connected to the ground.

6. The device of claim 1, wherein the counter electrode is constructed as a stranded wire electrode.

7. The device of claim 1, further comprising a cleaning device for cleaning the counter electrode.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The method according to the invention and the device for carrying out the method will again be described in the following with reference to the appended drawings.

(2) It is shown in:

(3) FIG. 1 a device for carrying out the method in a schematic side view;

(4) FIG. 2 a part of the device, also in a schematic side view;

(5) FIG. 3 a partial detail of a substrate produced with the method in a cross-sectional side view.

(6) FIGS. 1 and 2 show a device for surface treatment of a substrate 4 which in the illustrated example is formed as a plastic foil to be coated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(7) The device illustrated in FIG. 1 is for simplification divided into three sections A, B, C, wherein the sections B and C each show a schematic circuit diagram, for illustrating the method.

(8) The section A is shown again as detail in FIG. 2.

(9) The surface treatment is carried out with an electric corona discharge, with two corona electrodes being provided, wherein one corona electrode is connected as a support electrode 1 via a line 16 to a generator 9, which produces a high voltage and is connected to a power line 14, and the other corona electrode is connected via a ground line 15 as a counter electrode 2 to ground. It will be understood that alternatively the counter electrode 2 may be connected to the voltage and the support electrode 1 to ground.

(10) The counter electrode 2 is arranged below the support electrode 1 in relation to a horizontal plane H extending through the support electrode 1, with the substrate 4 contacting a support surface 3 formed on the support electrode 1.

(11) Aerosols 5 are sprayed with an atomizer 6 into the discharge region indicated by the arrows and located between the counter electrode 2 and the support electrode 1, wherein the nozzles of the atomizer 6 are arranged in the region of the counter electrode 2, so that the aerosols are introduced essentially against the direction of gravity.

(12) Adhesion forces are produced by the corona discharge on the free surface of the substrate 4, as a result of which the substrate surface is then uniformly coated, for example, when the aerosols contain additives.

(13) If the aerosols are only composed of water, an extraordinarily uniform adhesion of the free surface of the substrate 4 is attained with the invention, for a subsequent coating, for example application of a varnish, an imprint or the like.

(14) Furthermore, the support electrode 1 constructed as a cylinder, the counter electrode 2 and the atomizer 6 are arranged in a frame 7, as are support rollers 8 across which the substrate 4 is transported, which extend on both sides of and axis-parallel to the support electrode 1.

(15) In addition, a supply air line 10 and an exhaust air line 11 are installed in the discharge region for providing a safe processing environment.

(16) The atomizer 6 and the counter electrode 2 are held as an assembly in a support 12 constructed as a collection container, in which the excess aerosols and/or particles are collected and returned to the closed-loop material flow via a connection 13.

(17) The counter electrode 2 is preferably made of at least one, preferably stranded, wire which can be adjusted by way of guidance and adjusting means in relation to the width of the substrate passing through.

(18) The counter electrode 2 requires cleaning during operation for maintaining the quality of the corona discharge and/or the coating with the aerosols enriched with additives. For this purpose, the counter electrode 2 is moved through a cleaning device, in particular in an oscillating motion, during the corona discharge. However, such measure is possible only when the counter electrode 2 is connected to ground and thus safe to touch.

(19) While the section A illustrates the material treatment, the supply means are schematically illustrated in section B, and the process functions in section C.

(20) A supply reservoir 17, in which the materials to be processed for aerosol coating are stored and treated, is associated with the section B. After the materials to be recycled have been filtered and cleaned and a throughput measurement 20 is performed, they are supplied to the supply reservoir 17 via the connection 13.

(21) The coating material is transported continuously from the supply reservoir 17 into the atomizer 6 via a measurement device 18 for aerosol formation through multi-component atomization 19 via a line 21 and the support 12.

(22) Air is supplied with a fan 22 via an air supply 23 to the supply line 10, whereas an exhaust duct 25 connected to the exhaust air line 11 supplies drawn-in air to an exhaust fan 24.

(23) Lastly, in section C, a control center 26 and data acquisition 27 with processing and output for the entire system process are associated as functional process components, wherein the functional components relating to the process function C are in operative connection with the corresponding components of the entire system.

(24) FIG. 3 illustrates a substrate 28, to which a coating 29 was applied with the method of the invention, in a significantly enlarged cross-section which is not to scale; the substrate is provided in form of a foil, preferably made of plastic, which has a coating 29 applied on one side with a thickness of ≦200 nm, preferably ≦150 nm.

(25) As can be seen, the coating 29 has a mostly uniform layer thickness, wherein only the surface has a small roughness which, however, is insignificant for the intended applications.

(26) In principle, a coating 29 may also be applied to the opposite side of the substrate 28.

(27) Producing the coating 29 with the novel method results in a coating having a very uniform layer thickness, wherein the additives may have prepared particles with a diameter of 0.1 nm-1 mm.

(28) Hardening and/or drying can be performed in different ways, depending on the properties of the applied coating 29. For example, possibilities are heat/air treatment or radiation hardening with electron beam hardening (ESH), UV light, infrared light or with a plasma corona treatment, either in individual treatments or in combinations, which produce cross-linking reactions.

(29) Because of the layer thickness of preferably ≦150 nm, a very small quantity of material may be used for the coating, while simultaneously producing optimized properties due to the uniform layer thickness.

(30) Surprisingly, it has been observed that the quantity of material for the additives may be reduced significantly, which has proven to be particularly advantageous because additives are relatively expensive basic materials.

(31) In addition, the throughput speed of the device with which the coating 29 is applied can be increased, so that the production quantity can be increased significantly.

(32) Moreover, the substantially uniform layer thickness improves the properties of the coating 29 for particular applications. The quality of the coating 29 can also be monitored which was not possible to date to this extent.

(33) In principle, several layers can be applied, with each layer having a thickness according to the invention.