Process for pretreating surfaces of plastic items

Details Process for pretreating surfaces of plastic items Process for pretreating surfaces of plastic items

1994-09-16

1996-01-30

Lipman, Bernard

Etching a substrate: processes

Gas phase etching of substrate

Application of energy to the gaseous etchant or to the...

2041923, 20419236, 525354, C03C 1500

Patent

active

054878101

DESCRIPTION:

BRIEF SUMMARY
The present invention provides a process for pretreating surfaces of plastic items in a low-pressure plasma for the subsequent application of layers, especially metallic layers, wherein a process gas which contains sulphur hexafluoride (SF.sub.6) is used for the low-pressure plasma, and a metallised and/or lacquered plastic item which is pretreated using the process.
The invention lies within the technical area of surface treatment of plastics. For many applications of this type of item, it is desirable to specially coat these on the surface. One of the most frequent applications here is the application of metallic layers, especially aluminium layers. A particular difficulty when performing this type of coating operation is the generally low degree of adhesion between the applied layer and the plastic item. In order to improve this adhesion, it is known that the plastic item may be subjected to a plasma treatment.
Thus, for example, a method for metallising a plastic substrate is known from US-A-3 686 018. The plastic substrate is treated to improve the adhesion by means of a low-pressure gas discharge which preferably contains oxygen as a process gas. Furthermore, a process for preparing barrier layers of amorphous plastic on polycarbonate, polyethylene or polypropylene substrates, in which the plastic surface is treated with a gas plasma which preferably contains argon, is known from US-A-4 756 964. A process for treating fluorine-free polymers, in which the surface of the polymers is fluorinated by treatment with fluorine-containing gases in a low temperature plasma, is known from US-A-4 264 750 and US-A-4 404 256. Satisfactory adhesion of the subsequent metallic layer cannot be produced by using this known process, in which the fluorine is embedded into the surface, especially in the case of polycarbonate which is resistant to high temperatures.
Thus, the object is to find a process for the surface treatment of plastic items by means of which the adhesion of subsequent layers can be improved.
This object is achieved by having no oxygen in the process gas and keeping the plastic surface free of adsorbed or included fluorine during pretreatment.
Low-pressure plasmas and their production have been known for a long time. They are characterised in that the pressure in the chamber in which plasma treatment is performed is below atmospheric pressure. In the specialist field, a low-pressure plasma is frequently also called a low-temperature plasma because the plastic surface is subjected to a temperature of at most up to 200.degree. C. Low-pressure plasma treatment is characterised by the parameters, process pressure, electrical power and process time, and by the process gas used. Known process gases are, for example, oxygen, air, the noble gases, nitrogen and tetrafluoromethane.
The new process is advantageously performed in the same vacuum unit in which the metallic layer which is intended to adhere well to the plastic item is subsequently applied. Typical process pressures are between 0.1 Pa and 1000 Pa, preferably between 1.0 Pa and 50 Pa. In the process according to the invention, pure SF.sub.6 or a mixture of SF.sub.6 and other oxygen-free gases, preferably noble gases, is used as the process gas.
In this case, the proportion of sulphur hexafluoride is preferably at least 50%.
The plasma is activated by an electrical field using frequencies of up to 10 GHz, wherein the preferred frequency range is between 0 and 30 MHz.
The process time for pretreatment in the low-pressure plasma is preferably 0.5 to 5 minutes.
The process can preferably be applied to polycarbonates or blends and copolymers of this plastic. In comparison to the known processes, the new process shows a special improvement for polycarbonates which are resistant to high temperatures, such as are known, for example, from DE 3 832 396-A1. They are based on dihydroxydiphenylcycloalkanes, wherein the cycloalkanes are preferably substituted by methyl groups, especially in the 3 or 3,3 position.
After the plastic items have been treated in the man

REFERENCES:
patent: 4264750 (1991-04-01), Anand et al.
patent: 4404256 (1983-09-01), Anand et al.
Morita and Hattori; Applications of Plasma Polymerization, Pure and Appl. Chem. vol. 57, No. 9, pp. 1277-1286, (1985).
Abstract of J59-12943.gtoreq.A (Patent Abstracts of Japan; May 9, 1984).
Abstract of J59-142229-A (Aug. 1984).
Abstract of J58-147433 (Sep. 1983).
Orbit Abstract of FR2461731 (1981).
Orbit Abstract of DE3739994 (1989).
Orbit Abstract of DE3425755 (1985).

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