Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Patent
1996-06-17
1997-10-14
Pianalto, Bernard
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
427237, 427238, 4272552, 4272556, 427295, 427296, 427488, 427491, 427493, 427571, 427574, 427575, 427578, C08J 718
Patent
active
056770103
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a procedure and a device for producing a polymer coating on at least one part of the inside surface of a hollow article that is at least in part of plastic, using low-pressure plasma polymerisation.
In a procedure of this kind, known from DE-PS 3,632,748, that is used to form diffusion-inhibiting coatings by means of plasma polymerisation of monomers that are not described in greater detail, plasma excitation is effected by way of externally coupled microwaves. A elastomer that is generated in this way is suitable for hollow articles that are of smaller volume. In the case of hollow articles that are of greater volume; unless additional measures are applied, however, plasma that is generated by means of microwaves is not uniform enough to form a coating that displays the required uniformity to the degree that is needed to produce a surface layer that is of greater area, such as is required, for example, for a vehicle fuel tank.
Elsewhere, it has been reported that a polymer coating applied by microwave plasma polymerisation of ethylene or ethylene/argon mixtures was applied to a vehicle tank and reduced the permeation of methanol-free test fuel through high-pressure polyethylene (HDPE) to approximately 2% of the original value. This led to the conclusion that an improvement can be achieved especially with plasma generation by microwave but not by alternating frequencies in the MHz range (R. Ludwig, nner Schichten, Dissertation at RWTH, Aachen, 1989).
DE-OS 3,908,481 describes the plasma polymerisation of polar barrier coatings by using a plasma that is generated by a.c. voltages in the MHz range. It is a disadvantage that polar barrier coatings exert a repelling effect on non-polar components of fuels, but not with respect to methanol, so that the barrier effect that can be achieved is not sufficient in the case of fuels that contain methanol.
It is the task of the present invention to describe a method that permits the economical production of at least one large area polymer coating on a plastic substrate, in particular on a hollow plastic article, the surface layer displaying properties that are as uniform as possible despite its large area, and which thus provides an adequate barrier effect. This should also be so in the case of a charge that contains methanol, for example, fuels that contain methanol. The coating should ensure a barrier effect that satisfies today's and, optionally, future demands for the impermeability of hollow articles of this kind with respect to their contents. In addition, for reasons of economy, it should be possible to produce at least one coating in the shortest possible time.
In order to do this, it is possible to use compounds that form a polymer surface layer relatively quickly under plasma conditions as the components that form the coating. As an example, these include olefins, e.g. ethylene, extended cycloalkanes, e.g., cyclopropane, aromatics, heteroaromatics, e.g., pyrrol or thiophene; in general, however, as the speed with which the coating is formed increases, the degree of cross-linking decreases, which is to say that it is predominantly chains that are formed.
Since, generally speaking, the barrier effect decreases as the degree of cross-linking decreases, according to a proposal made by the present invention, in addition to the reaction gas that contains the component that predominantly forms chains, it can be advantageous to include a molecules that represent an additional component in the gas atmosphere that forms the plasma, and which under plasma conditions generate predominantly branching points in the polymer chains, in particular cross-linking points between the polymer chains. Highly unsaturated hydrocarbon compounds, e.g., acetylene or alkanes or compounds that form such highly saturated hydrocarbon compounds under plasma conditions, e.g., cyclobutene, have been shown to be particularly suitable for this purpose.
The components that form the branching or cross-linking points can be introduced into the gas atmosphere that fo
REFERENCES:
patent: 4536271 (1985-08-01), Collins
patent: 4656083 (1987-04-01), Hoffman et al.
Diener Christoph
Esser Klaus
Karsch Ulrich
Nauenburg Klaus
nwald Heinrich
Kautex Werke Reinold Hagen Aktiengesellschaft
Pianalto Bernard
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