Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1998-11-05
2001-11-06
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S534000, C427S536000, C427S539000, C427S489000, C427S488000, C427S580000, C427S491000, C216S071000, C134S001100
Reexamination Certificate
active
06312767
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
Device for the surface treatment of a substrate (
3
) by an electrical discharge between two electrodes in a gas mixture liable to generate by-products (powders, for example) which may be deposited on the electrodes, in which device one (
9
) of the electrodes is a roller against which the substrate may be applied, means being provided for rotating the roller and the substrate and for injecting the gas mixture between the electrodes, the device being noteworthy in that the second electrode is a roller electrode (
11
) against which the running substrate may also be applied, this roller (
11
) being placed parallel to the other roller (
9
) with a suitable gap. By virtue of this arrangement, the substrate (
3
) protects each electrode (
11
) and prevents it from being covered with powder during the treatment, as well as preventing the corresponding contamination, thereby allowing the device to operate continuously.
The present invention is a process and a device for the surface treatment of a running substrate by an electrical discharge in a controlled gaseous atmosphere between two electrodes, the gaseous atmosphere including, in particular, one or more compounds liable to generate by-products which can accumulate and/or be deposited on the discharge electrodes.
By way of illustration, these by-products may be solid, such as powders (as, for example, in the case of silanes), or else liquid or pasty, as in the case of certain hydrocarbons (giving rise, for example, to compounds having aliphatic chains being deposited).
It should be understood that such deposits can then accumulate on the electrodes and constitute an alteration of them and, more generally, a disturbance to the operation of the system.
Depending on the intended treatment and the intended substrate, the gas mixtures envisaged may vary greatly, these generally comprising an inert carrier gas and one or more compounds from among reducing and oxidizing gases, one of the components of the mixture therefore being of the type liable to generate by-products which can accumulate and/or be deposited on the discharge electrodes, as is the case, for example, with silanes or with hydrocarbons.
The <<substrates>> intended by the present invention may, for example, be in the form of sheet or film, or foam products, which may or may not be continuous depending on the material in question. Substrates of interest here are most particularly nonconducting substrates made of a polymer material, a <<woven or nonwoven>> textile material, a paper material, etc.
Taking the example of polymer films, it is known to be often necessary to carry out surface treatments on these polymer films in order to make their surface <<active>>, i.e. in order to make it possible to stick it, to print information on it, etc. In order to be able to print, the ink must be compatible with the surface of the polymer film, although initially this is not generally the case and although then a pretreatment of the surface is necessary.
In order to carry out a suitable treatment, it is known to subject the surface of the polymer film to a flame-brushing treatment, or to a treatment with suitable chemicals, or else to a corona treatment. Conventionally, these corona treatments are carried out in air, the nitrogen and oxygen molecules of which are converted by the electrical discharge, creating new molecules (radicals, ions, etc.) which react chemically with the surface of the polymer.
It has also been proposed, as described by U.S. Pat. No. 5,576,076, to replace the air with a gas mixture containing silane. Injecting this active gas mixture into the discharge zone makes it possible to obtain high treatment levels and therefore to solve a number of problems encountered by polymer film converters. The electrode system used contributes not only to creating the electrical discharge (as standard electrodes) but also to manage the injection of the treatment gases within the discharge zone.
The active gas mixture allowing correct treatment levels to be obtained may have various compositions, these essentially depending on the intended application of the treated polymer film. Hitherto, the gas mixture usually contained nitrogen as the carrier gas, an oxidizing gas and several hundreds of ppm of silane.
The work completed by the Applicant has made it possible to demonstrate that when this process is carried out as described in the aforementioned United States patent, namely that the active gas mixture containing silane and an oxidizing agent is injected into the discharge zone, silica powder is formed which accumulates on the electrodes throughout the duration of the treatment. This increasing contamination of the electrodes during the treatment prevents the surface treatment to be carried out under proper conditions over a longer time than approximately one hour, whereas the usual operating mode in industry is of the 24-hour continuous type.
The accumulation of powder on the electrodes is a consequence of various phenomena:
the physico-chemistry of the electrical discharge: this is because the silica powder formed is the product of reactions taking place in the gas phase due to the excitation of the discharge. By altering the operating conditions (composition of the gas mixture, electrical characteristics of the discharge, etc.), it is possible to alter the amount of powder formed;
the process whereby the powder formed is brought into contact with the electrodes: this is because, when the powder is formed in the gas phase (even in small optimized amounts, according to the previous paragraph), accumulation only occurs if the powder is brought into contact with the electrodes.
SUMMARY AND OBJECTS OF THE INVENTION
The object of the present invention is therefore especially to provide a process and a device allowing this technical problem to be advantageously solved by preventing accumulation on the electrodes of by-products (solid and/or liquid and/or else pasty by-products) resulting from the chemical reactions caused by the electrical discharge in the treatment atmosphere.
One of the conditions necessary for proper operation of the invention is to produce a device capable of ensuring homogeneous injection of the gas mixture over the entire length of the electrodes used to create the discharge. This is because a strictly homogeneous distribution is essential for obtaining homogeneous treatment of the polymer film.
According to the invention, the two electrodes are rollers against which the running film is applied, these being arranged so as to be parallel to each other with a suitable gap, and thus an electrical discharge is therefore created between two roller electrodes.
According to the invention, the process, for the surface treatment of a running substrate by an electrical discharge created between two electrodes in a gas mixture, liable to generate by-products which can be deposited on the electrodes, in which one of the electrodes is a roller against which the substrate may be applied, means being provided for injecting the gas mixture between the electrodes, is then a process wherein at least one stage for treating the substrate is used, each stage comprising at least one pair of roller electrodes and an injector for injecting the gas mixture between the rollers and wherein the treatment of the substrate is carried out in the following manner: the substrate is made to pass in succession a first time between the two roller electrodes, by applying it against the first roller electrode, where it undergoes a first surface treatment, and then a second time between the two roller electrodes, by applying it against the second roller electrode, where it undergoes a second surface treatment.
Moreover, the process according to the invention may adopt one or more of the following characteristics:
the width of the substrate is at least equal to the length of the interelectrode space where the combination of the presence of an electrical discharge and the presence of said gas mixture liable to
Cocolios Panayotis
Coeuret Francois
Martens Bernd
Prinz Eckhard
Salge Jurgen
Burns Doane Swecker & Mathis L.L.P.
L'Air Liquide, Societe Anonyme pour l'Exploitation des
Padgett Marianne
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