"APPARATUS FOR THE COLD PLASMA TREATMENT OF A CONTINUOUS WEB MATERIAL"

The present invention relates to apparatuses for the cold plasma treatment of web materials, and in particular to an apparatus for the treatment of a continuous web material.

It is known that different kinds of web material (fabric, paper, plastic film, etc.) can be treated with a cold plasma to perform a wide range of operations such as surface cleaning, print preparation, laying a surface coating, etc. The nature of the plasma to be used varies according to the type of treatment and is defined through several parameters such as the carrier gas, the substances added to the carrier gas, the intensity and frequency of the electromagnetic field used to generate the plasma, the type of dielectric material used to control and spread the charges between the electrodes and so on. This type of treatment is being more and more used since it is applicable to any kind of material and is a dry process, that results faster and cheaper than treatments with liquids that imply the disposal of waste products. However, even the cold plasma treatment is not free from drawbacks both in the low pressure (vacuum) version and in the atmospheric pressure version. When the treatment is carried out at low pressure by creating a high or almost high vacuum in a sealed treatment chamber it is clear that it is not possible to treat a continuous web material, but just to introduce in the chamber a roll of material that is unwound, plasma-treated and rewound inside the chamber. Such a batch treatment is obviously much less productive than a continuous treatment, and on the other hand trying to carry out a continuous treatment by introducing a continuous web material into a low pressure chamber implies great problems of cost and functionality of the seals at the points where the web enters and exits the chamber.

Moreover, the vacuum treatment also has the drawback that when the treatment gas has to be changed the chamber must be "washed" with a cleaning gas and then vacuum must be re-created prior to the introduction of the new

treatment gas. Furthermore, even after such a wash, there is a risk of pollution of the new gas since the substances used in the previous treatment may be stuck on the inner surfaces of the chamber and then be released when vacuum is re-created.

The atmospheric pressure treatment does not suffer from these drawbacks since it is carried out in an open treatment chamber that allows a continuous treatment, does not require the creation of vacuum and when changing the treatment gas there is no need for a wash and no risk of pollution of the new gas.

Nonetheless, even this type of apparatus has some serious drawbacks in that it implies a huge consumption of treatment gas owing to the high dispersion of the gas out of the open chamber, due to the carry-over effect by the continuous web.

Therefore, due to cost and/or pollution reasons the treatment gas usually employed is air or nitrogen without the addition of expensive or polluting substances. This results in a poor flexibility of the apparatus that can be used only for the few types of treatment allowed by the few types of treatment gas that can be employed.

Therefore the object of the present invention is to provide an apparatus which overcomes the above-mentioned drawbacks. This object is achieved by means of an apparatus at atmospheric pressure yet provided with a closed chamber having seals suitable for feeding a continuous web and containing at least a plasma treatment station including an injection pipe for introducing the treatment gas close to the electrode. Other advantageous features of the present apparatus are disclosed in the dependent claims.

A first important advantage of this apparatus is that of retaining the productivity of the continuous treatment while dramatically reducing the operational cost. In fact, there are neither problems of expensive seals and of having to create vacuum, as in a vacuum apparatus, nor problems of high treatment gas consumption as in an open chamber apparatus.

A second significant advantage of such an apparatus is that of retaining the flexibility of treating with various types of gas while reducing the operational time and cost. In fact, there is neither the problem of having to re-create vacuum after changing the treatment gas, as in a vacuum apparatus, nor the problem of the

restriction to inexpensive and non-polluting treatment gases as in an open chamber apparatus.

Still another advantage of said apparatus resides in the prevention of the risk of pollution of a new treatment gas, since by operating at atmospheric pressure the substances used in the previous treatment do not get stuck on the inner surfaces of the chamber and can be effectively washed away.

These and other advantages and characteristics of the apparatus according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein:

Fig.l is a diagrammatic sectional view of an embodiment of the present apparatus including two plasma treatment stations;

Fig.2 is a partial enlarged view of the web entrance/exit area with the relevant seals and the web feeding device; Fig.3 is a partial diagrammatic view showing the arrangement of the web for a double treatment on a single side of the web; and

Fig.4 is a partial diagrammatic view showing the arrangement of the web for a single treatment on both sides of the web.

With reference to figures 1 and 2, there is seen that an apparatus according to the present invention conventionally includes at least one plasma treatment station 1, but preferably two or more stations, that essentially consists of a discharge roller 2 and at least one adjacent electrode 3 between which the web material W to be treated is passed. The discharge roller 2 is coated with a dielectric material, and the position of electrode 3 can be adjusted between an operating position and a rest position (in broken lines).

A high tension generator (not shown) feeds electrode 3 so as to cause an electric discharge that ionizes the gaseous mixture used as treatment gas, whereby a plasma state is generated in the gas and the substances and the charged and neutral species contained in the mixture interact with the surface of the web material W, which is guided to and from the treatment station 1 by a plurality of idle rollers 4 that define its path. The movement of web W around rollers 2, 4 is

provided by a feed device consisting of a drive roller 5, driven by an inverter- controlled motor-reducer, cooperating with two adjustable contrast rollers 6 that guarantee the proper dragging of web W.

A first novel aspect of the present apparatus is given by the presence of a closed chamber 7, that contains the plasma treatment station(s) 1 and is provided with a sealing system 8 suitable to allow the feeding of the continuous web W. Furthermore, each treatment station 1 includes at least one injection pipe 9, i.e. a bar provided with a series of nozzles, for introducing the treatment gas close to electrode 3 (the gaseous mixture comes from a mixing and dosing system that is not illustrated).

The closed chamber 7 is accessible for maintenance operations and the like through a pair of top doors 10 that open upwards. These doors 10 are preferably made of a transparent material suitable to allow a visual control of the operation of the apparatus. As better illustrated in the detail of fig.2, the sealing system 8 consists of a central duct 11, located at an aperture in the bottom of chamber 7, and two sections 12, 12' hinged to the structure of chamber 7 so as to abut against the sides of duct 11 and thus close the above-mentioned aperture. More specifically, a first section 12 is hinged at the base through a first pivot 13 so as to rest against duct 11 by gravity, whereas a second section 12' is hinged at the top through a second pivot 13' and is provided with a top support 14 extending beyond pivot 13', so as to rest against duct 11 under the push of a counterweight 15 mounted on said support 14.

Thanks to this simple yet effective structure of the sealing system 8, the continuous web material W can enter chamber 7 moving upwards (as indicated by the relevant arrow) between duct 11 and the first section 12, whose mobile top end allows the passage of seams in the web and automatically adapts to different web thicknesses. Similarly, on the other side of duct 11, the continuous web material W can exit chamber 7 moving downwards (as indicated by the relevant arrow) between duct 11 and the second section 12', whose mobile bottom end allows the passage of seams in the web and automatically adapts to different web

thicknesses.

In a preferred embodiment of the invention, the central duct 11 is in communication with a suction system (not shown) and is provided with slots 11a, lib formed in the sides just upstream from, with respect to the direction of movement of web W, the abutment positions of sections 12, 12'. In this way, the air contained in the entering web W is removed through slot 11a to prevent problems in case of treatments that must be carried out in the absence of air, while the residues of treatment gas contained in the exiting web W are removed through slot 1 Ib to prevent problems of environmental pollution and/or of subsequent release of residues from the web material.

Referring now also to figures 3 and 4, there is seen that the preferred embodiment of the above-described apparatus being provided with two treatment stations 1 allows to carry out either a double treatment on a single side Wa of the web (Fig.3) or a single treatment on both sides Wa, Wb of the web (Fig.4). In the first case, web W coming from the sealing system 8 is wound around the first discharge roller 2 with side Wa (indicated by the broken line) facing the first electrode 3, passes under an idle roller 4 located between the two treatment stations 1 and is then wound around the second discharge roller 2 with the same side Wa facing the second electrode 3. The return path to the sealing system 8 to exit chamber 7 is finally defined by other four idle rollers 4.

In the second case, web W coming from the sealing system 8 is still wound around the first discharge roller 2 with side Wa facing the first electrode 3, but it passes over the idle roller 4 located between the two treatment stations 1 and is then wound from below around the second discharge roller 2 so that it is the opposite side Wb (indicated by the continuous line) that faces the second electrode 3. The return path to the sealing system 8 to exit chamber 7 is finally defined by other three idle rollers 4, two of which are the same used in the previous case.

It is clear that the above-described and illustrated embodiment of the apparatus according to the invention is just an example susceptible of various modifications. In particular, the number and arrangement of the treatment stations

1, of the injection pipes 9 and of the idle rollers 4 may change depending on the type of treatment to be carried out on the web material W, as long as they remain enclosed by chamber 7.

Similarly, the position of the sealing system 8 and of doors 10 may change depending on specific construction needs, and sections 12, 12' may be pushed against the central duct 11 by other equivalent means different from the above- illustrated gravity system, such as spring means of the mechanical or pneumatic kind. In fact, the web material W could slide on duct 11 even along the top and bottom thereof rather than along the sides, as long as it slides along two opposite faces.

It should therefore be clear to those skilled in the art that further embodiments of the present apparatus may be obtained without departing from the scope of the present invention as defined by the appended claims.