EP3106006B1 - Method and apparatus for treating pieces in order to increase adherence - Google Patents

Description

Technical area

The present invention relates to a method of treating parts in order to increase the adhesion properties of the surface of the parts. It also relates to an installation implementing said method.

In the description below, references in square brackets ([]) refer to the list of references presented at the end of the text.

State of the art

The wettability of the surfaces of parts made of synthetic material is often insufficient to apply and directly adhere to them a varnish, glue, ink or adhesive. A modification of the surface structure must be made. This modification can be mechanical by abrasion, chemical, by a flame to attach carboxylic bonds or by electric potential discharge. Wettability is characterized by the physical magnitude of the surface tension. Similar problems arise for metal surfaces which may be covered with a film or traces of foreign material.

In the processes by electric potential discharge used in industry, there is the process known as the corona effect or the corona effect. The corona effect can be produced in different ways: either between two electrodes which produce an arc which is blown by air to project it towards the surface to be treated, or by an electrode placed at a certain potential opposite a mass cylinder on which runs a plastic film to be treated. There is also another technology using this discharge by electric potential, which is commonly called a plasma. atmospheric pressure and which is created by an electric discharge in a tube using air or gas. In practice, this system is called plasma torch or cold plasma at atmospheric pressure.

The corona effect is often enough to modify the surface layer of the material on a few Angstroms in order to allow the adhesion of inks, glues, paints or varnishes. It should be noted that corona or corona discharge does not create heat and therefore does not cause the material to rise in temperature and that it occurs in ambient air at atmospheric pressure. It is also possible to use a mixture of gases or a specific gas passing through the corona discharge for certain applications.

We also know from the document FR 2 443 753 [1] a method implementing the treatment by directional discharge corona effect. An electrode comprising points projecting upwards is placed between two counter electrodes at the same distance apart. Two insulating screens are placed between the electrode and the counter-electrodes. In operation, a jet of electrons develops between the electrode and the counter-electrodes bypassing the screens. The electric discharge or treatment can operate on surfaces which scroll horizontally in front of this electrode.

The other electric discharge process is called an atmospheric pressure plasma or plasma torch. It is described for example in the document WO 2010/067306 A2 [2]. In a tube called a plasma torch, a luminescent electrical discharge or corona is created between an internal core brought to a certain electrical potential and the envelope of this tube connected to ground. Pressurized air or gas is injected inside this tube, which has the effect of creating turbulence separating the ionizing elements but giving the electrons a high temperature. At the outlet of this plasma tube, a potential-free flame-shaped plasma jet is formed, which is used as the corona effect to modify the surface state of the material to be treated over a few Angstroms. This plasma jet coming out of the tube is not very wide, it is circular. It should be noted that the separation of ions and electrons inside this tube under pressure of air or gas generates a high temperature so that the plasma jet is hot enough to melt a plastic material in a short time. . This air or gas pressurized plasma surface treatment system is widely used in industry. It is also called cold plasma or atmospheric pressure plasma.

In the document EP 2,574,446 [3] describes a system combining the use of these two corona and plasma systems in the same device. This system is applicable to plastic films and comprises a cylinder on which the film runs and which serves as an electrode. However, this system is not suitable for processing very thick plates or technical parts because it is not possible to use the cylinder as an electrode.

In many industrial applications, the use of the corona effect alone or of the plasma alone makes it possible to treat the surfaces in order to improve their wettability. However, in certain cases, and in particular on polymer products very loaded with additives entering into the composition of these products and subsequently migrating to the surface of the material, pose problems that corona or plasma alone cannot resolve. This is particularly the case with slip agents used during the injection or extrusion of thermoplastic synthetic material. These sliding agents thus create, on this surface, a barrier or interface preventing the corona or plasma effect from creating the desired structural modifications.

A similar configuration is also found for the treatment of metal parts when they are covered by an interface or a film of unwanted material.

The invention aims to provide a method of treating parts such as for example plates in order to increase the wettability and adhesion of the surface which can treat thick parts and even if they contain agents that have migrated to the surface. It also aims to provide an installation implementing said method.
The document US2008 / 237935 A1 discloses an example of a device and associated method for the treatment by corona effect of polyolefin sheets previously treated by plasma.

Description of the invention

With these objectives in view, the invention relates to a method of surface treatment of parts according to which thick parts are treated by the directional discharge corona effect by making the parts scroll relative to the corona station in a direction of travel, characterized in that, prior to the corona effect treatment, the parts are prepared by plasma.

The Applicant has discovered that, surprisingly, while the treatment by plasma alone or by directional discharge corona effect alone is not able to impart sufficient surface tension, regardless of the duration of the treatment, the combination of the plasma treatment followed by directional discharge corona treatment provides a much better surface tension. Such a phenomenon could be explained by the fact that the plasma treatment eliminates the interface which covers the part to be treated, which makes the surface accessible to the corona effect treatment.

According to one embodiment, to generate the directional discharge corona effect, an installation comprising at least one electrode comprising tips aligned along an electrode path, the tips projecting in a tip direction towards the moving parts, is used, the tip direction being substantially perpendicular to the direction of travel, the electrode being placed between two counter-electrodes at a distance of the same distance.

In particular, the direction of travel is perpendicular to the electrode path. The entire width of the room can be processed at one time.

According to an improvement, the electrode is driven in an alternating movement perpendicular to the direction of travel. This makes it possible to cover a surface more homogeneously.

Similarly, the plasma treatment is generated by at least one torch moving in a lateral reciprocating movement perpendicular to the direction of travel. This movement is also allowed to cover a surface more evenly.

According to one embodiment, an electrode comprising an active surface facing the parts to be treated is used to generate a directional discharge corona effect, a dielectric insulator being placed between the electrode and the parts. Such an electrode is suitable for treating conductive parts. In this case, the parts are for example connected to ground, while the electrode is energized.

The parts to be treated are for example made of synthetic material, insulating or conductive, or metallic.

The subject of the invention is also an installation for processing thick parts comprising a corona treatment station by the directional discharge corona effect, the installation comprising actuating means for making the parts scroll relative to the corona station, the installation being characterized in that it further comprises a plasma station upstream of the corona station, the plasma station comprising at least one plasma torch for sending a flow of plasma towards the moving parts.

According to one embodiment, the corona station comprises an electrode comprising points projecting in a point direction, the electrode being placed between two remote counter-electrodes at the same distance, the movement of the parts taking place in a plane perpendicular to the point. leading edge. Although such a station looks like an installation according to the prior art, it should be noted that no screen is provided between the electrode and the counter-electrodes, which simplifies the implementation of the installation. Despite the absence of screens, we see that the processing of parts remains effective. This arrangement can also be implemented on a corona station, even not preceded by a plasma station.

According to an improvement, the corona station comprises a plurality of electrodes arranged parallel to one another, the tips of one electrode being offset from the tips of an adjacent electrode with respect to the direction of travel. By increasing the number of points, it is possible to expose the surface over a greater travel distance, and therefore for a given exposure time, to increase the relative speed of movement between the parts and the points. In addition, the offset of the tips between two successive electrodes allows a better distribution of the action generated on the surface of the parts by the electrodes. This arrangement can also be implemented on a corona station alone, even not preceded by a plasma station.

Brief description of the figures

• la figure 1 est un diagramme représentant des spectrogrammes infrarouges d'analyse de pièces ayant reçus différents traitements ;
• la figure 2 est une vue schématique de côté d'une installation selon un mode de réalisation de l'invention ;
• la figure 3 est une vue partielle d'un poste corona de l'installation de la figure 2 ;
• la figure 4 est une vue de dessus d'une installation de la figure 1 ;
• la figure 5 est une vue similaire à la figure 2 selon un autre mode de réalisation de l'invention.

The invention will be better understood and other features and advantages will become apparent on reading the description which follows, the description referring to the appended drawings, among which:

• the figure 1 is a diagram representing infrared spectrograms of analysis of parts having received different treatments;
• the figure 2 is a schematic side view of an installation according to one embodiment of the invention;
• the figure 3 is a partial view of a corona station of the installation of the figure 2 ;
• the figure 4 is a top view of an installation of the figure 1 ;
• the figure 5 is a view similar to the figure 2 according to another embodiment of the invention.

DETAILED DESCRIPTION

An installation for treating 2 thick pieces in accordance with the invention is shown schematically on the figures 2 to 4 . The installation comprises a plasma station 1 and furthermore a corona station 3 for treatment by the directional discharge corona effect. The installation comprises actuating means for scrolling the parts 2 facing the plasma station 1 then the corona station 3 in a direction of travel F1. The plasma station 1 comprises at least one plasma torch 10 for sending a flow of plasma to the moving parts 2.

The corona station 3 comprises a plurality of electrodes 30, 30 'arranged parallel to each other, as shown in figure 3 . On the figure 2 , only one electrode is shown. Each electrode 30 comprises tips 301 electrically connected and projecting in a tip direction F2 substantially perpendicular to the direction of travel F1. The electrode 30 is placed between two counter-electrodes 31 so as to be midway between them.

With reference to the direction of travel F1, the tips 301 of an electrode 30 are offset from the tips 301 'of an adjacent electrode 30', as shown in FIG. figure 3 . The counter electrodes are not shown in this view.

The plasma station 1 also comprises several plasma torches 10, only one of which is shown, in order to cover the entire width of the moving parts 2.

In operation, the parts 2 are set in motion by the displacement means so as to scroll facing the plasma station 1 and then facing the corona station 3. The plasma torches 10 are activated. The electrodes 30 of the corona station 3 are energized with a high voltage current, greater than 12 kV, and high frequency, of the order of several tens of kilohertz. Corona effluvia develop between the electrode 30 and the counter-electrodes 31.

The moving parts 2 are exposed first to the flows of the plasma torches 10 and then to the corona scents. The running speed is adjusted so that the temperature of the surface of the parts 2 does not rise excessively with respect to the plasma torches 10, but that the interface or the layers of undesirable products are eliminated or transformed.

Example

Parts 2 injected in polyethylene containing 2% of an amide-based slip agent were treated respectively by a corona 3 station alone, by a plasma station 1 alone and by the successive combination of the two treatments, starting with the plasma station 1.

The figure 1 shows spectrograms of the surface of the parts 2 thus treated, in comparison with an untreated part. The diagram shows a transmittance as a function of a frequency, expressed in cm ^-1 . The measurements were made with an infrared spectrometer using a mercury-cadmium telluride (MCT) cell and an attenuated total reflection (ATR) germanium crystal. A Blackman-Harris weighting window and atmospheric absorption correction were applied to the spectrum.

In all the spectrograms, the characteristic bands of polyethylene are present, in particular that at 1464 cm ^-1 as shown on the figure 1 .

On the untreated sample, according to a first spectrogram 41, peaks at 3400, 3200 cm ^-1 and 1645 cm ^-1 show the presence of amide compounds originating from the slip agent.

On the sample treated by the corona station 3 alone, according to a second spectrogram 42, the spectrum is substantially the same, with the presence of the slip agent.

On the sample treated with plasma only, according to a third spectrogram 43, the peaks corresponding to the slip agent are no longer detectable. On the other hand, a band centered on 1720 cm ^-1 appears, demonstrating the presence of carboxyl groups. An absorption around 3400 cm ^{-1 also} shows the presence of hydroxyl groups in small amounts.

On the sample treated with plasma and then corona, according to a fourth spectrogram 44, a wide band between 1600 and 1700 cm ^-1 indicates an additional degree of carbon oxidation. A pronounced peak at 1650 cm ^-1 suggests the presence of degraded residues of the slip agent. A wide band around 3280 cm ^-1 indicates the clear presence of hydroxyl groups on the polyethylene.

Correspondingly, only the sample with the plasma treatment followed by the corona treatment has a surface tension greater than 56 mN / m to allow adhesion of ink, glue or adhesive.

According to another embodiment of the invention, which applies to the treatment of conductive parts such as metal or carbon parts 2 ", the electrode 30" has an active surface facing the parts 2 "to be treated with an insulator. dielectric 7 disposed between the electrode 30 "and the parts 2", as shown on the figure 4 . Electrode 30 "is energized while part 2" is connected to ground.

Reference lists

1. [1]: FR 2 443 753
2. [2]: WO 2010/067306 A2
3. [3]: EP 2,574,446

Claims (6)

1. Method for treating the surface of parts (2), wherein thick parts (2) are treated with a directional corona discharge, while running the parts (2) relative to the corona station (3) in a run direction (F1), wherein, prior to the corona treatment, the parts (2) are prepared with a plasma;
   said method being characterised in that
   -- a facility comprising at least one electrode (30) comprising tips (301) aligned in an electrode path is used to generate the directional corona discharge, the tips (301) projecting in a tip direction (F2) towards the running parts (2), the tip direction (F2) being substantially perpendicular to the run direction (F1), the electrode (30) being placed between two equally-spaced auxiliary electrodes (31);

   - the run direction (F1) is perpendicular to the electrode path;

   - the electrode (30) is moved in a reciprocating motion perpendicular to the run direction (F1).
2. Method according to claim 1, wherein the plasma treatment is generated by at least one torch (10) moved in a reciprocating lateral motion perpendicular to the run direction (F1).
3. Method according to claim 1, wherein an electrode comprising an active area facing the parts (2") to be treated is used to generate the directional corona discharge, a dielectric insulator (7) being disposed between the electrode and the parts (2").
4. Method according to claim 1, wherein the parts (2) to be treated are made of an insulating synthetic material or of a conductive synthetic material.
5. Method according to claim 1, wherein the parts (2) to be treated are metallic.
6. Facility for treating thick parts (2) adapted to implement the method as defined according to any one of claims 1 to 5, said facility comprising a corona station (3) for treatment by directional corona discharge, the facility comprising actuation means for running the parts (2) relative to the corona station (3), a plasma station (1) upstream of the corona station (3), the plasma station (1) comprising at least one plasma torch (10) for sending a flow of plasma towards the running parts (2), the facility being characterised in that it further comprises
   -- at least one electrode (30) comprising tips (301) projecting in a tip direction (F2), the electrode (30) being placed between two equally-spaced auxiliary electrodes (31), the parts (2) running in a plane perpendicular to the tip direction (F2),

   - a plurality of electrodes disposed parallel to one another, the tips (301) of one electrode (30) being offset from the tips (301) of an adjacent electrode (30) in the run direction (F1).

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