Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Patent
1995-09-29
1997-02-04
Beck, Shrive
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
427555, 427559, 427591, 427595, 427 98, 427123, 427259, 427264, 427266, 427272, 427275, 427282, 427306, 4273767, 4273835, 4274431, 216 65, B05D 306
Patent
active
055995926
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a three-step metallization process which allows to produce a metal film which is strongly adhering onto the surface of a previously manufactured plastic piece.
Plastic materials may, under various forms, be used for a variety of functions in all industrial domains. Their amorphous molecular structure is responsible for their important electrical insulation proper with large scale electrical applications, as substrate to active systems or in packaging. Another remarkable advantage of such materials resides in their simplicity of utilization via molding or lamination. In contrast, the most crucial disadvantage of plastics is their morphogical fragility with a relatively very low melting temperature (typically, 220.degree. C.) which limits their utilization and makes them largely uncompatible with other ordinary materials like metals and ceramics. Improving this compatibility has required a permanent development activity which particularly yielded so-called "thermoplastics" which may endure 300.degree. C. or more. Other plastics with improved mechanical strength have been also developped.
These intrinsic characteristics depend on the various (mineral and/or organic) components which are added to the base material (e.g. polycarbonate, polyamide or other industrial polymers). However, a major difficulty persists in this development procedure which concerns metallization, i.e. interfacing a plastic piece with a metal.
Bringing selectively the metal to the areas of the plastic surface to be metallized can be performed via two so-called "positive" techniques: serigraphy and evaporation. Serigraphy is a six-step, low resolution (>100 .mu.m) process. Being performed under vacuum, evaporation (through a mask) is ill-adapted to mass production. For these two processes, adhesion of the so-produced metal film on the plastic substrate is unsufficient (<0.1 MPa) for most applications.
In order to improve significantly such adhesion, it is possible to act, before metallization, on the texture or on the chemical composition of the plastic surface. Modifying the texture can be achieved mechanically by increasing rugosity and, consequently, the effective metal/plastic contact surface. This is a commonly used technique the products of which remain very unperfect (lack of homogeneity, poor reproducibility, no metal confinement possible). Modifying the superficial texture may also result from non-organic matters which are incorporated in the plastic (e.g. glass fiber), with no guarantee that adhesion of the metal on such a plastic would be effectively improved.
The superficial texture of the plastic may also be modified chemically. As an example, this may be achieved by using a metalorganic compound along the following steps: the action of an external source of energy (e.g. a laser beam), thus liberating metal atoms on the plastic surface; containing metal ions. The latter are then driven to sediment onto the surface containing the metal atoms which had been liberated in the preceeding step, thus inducing its metallization.
Another process of the same "positive" type consists firstly, to roughen a plastic surface either mechanically or chemically and, secondly, to deposit (or sediment) onto that roughened surface a colloidal substance containing Palladium ions which then "decorate" selectively the roughened surface. Finally, the latter is further immersed in an autocatalytic bath which promotes the formation of a metal film onto the Palladium-coated surface.
For completeness, it is worth mentioning a series of so-called "negative" processes which consist in irradiating with a laser beam a plastic surface in order to avoid, in contrast, its metallization during its immersion in an autocatalytic bath. These negative processes may find applications whenever the surface to be metallized is much larger than the one to remain devoid of metal. Evidently, they operate on surfaces which tend to metallize naturally and without specific teatment, when immersed in an autocatalytic bath.
However, metal
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Beck Shrive
Cameron Erma
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