Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating predominantly nonmetal substrate
Reexamination Certificate
2001-05-03
2004-03-30
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating predominantly nonmetal substrate
C205S159000, C205S166000, C427S304000, C427S306000
Reexamination Certificate
active
06712948
ABSTRACT:
The invention concerns a process for the metallizing of a plastic surface. Within the scope of the process, in accordance with the invention, the plastic surface of a plastic article or the plastic surfaces of several plastic articles are metallized.
On the one hand, metallized plastics are used for decorative purposes, for example in the sanitary facilities field or in the manufacture of automobiles. On the other hand, metallization of plastics also occurs in connection with the surface treatment of electronic components for the purpose of electronic shielding. Especially the surfaces of plastics, such as acrylnitrile-butadiene-styrene (ABS) and possibly ABS-Polycarbonate blends are metallized for decorative purposes.
In an already known process in practice, the plastic surface is first roughened by strong etching, for example with chromic acid or chrome-hydrochloric acid. By surface roughening is meant especially that, due to the etching process, micro-caverns are created in the plastic surface. These micro-caverns, in general, have a size on the order of 0.1 to 10 &mgr;m. Especially, these micro-caverns show a depth (i.e. an extent from the plastic surface toward the interior) in the range of 0.1 to 10 &mgr;m. The etching takes place at relatively high temperatures and, as a rule, for relatively extended periods. The concentration of an oxidizer added to the etching solution normally is relatively high. The roughening of the plastic surface has the purpose of allowing the subsequently to be applied activating layer and/or metal layer to almost hook into the roughened plastic surface. The adhesion of a metal layer to the roughened plastic surface is achieved almost in the manner of the snap fastener principle in this known process. After the etching or roughening of the plastic surface, the surface first is activated with colloidal palladium or ionogene palladium. This activation, in the case of the colloidal process, is followed by a removal of a protective tin colloid or, in the case of the ionogene process, a reduction to the elemental palladium. Subsequently, copper or nickel is chemically deposited on the plastic surface as a conducting layer. Following this, galvanizing or metallizing, respectively, takes place. In practice, this direct metallizing of the plastic surface works only for certain plastics. If sufficient roughening of the plastic, or the formation of suitable micro-caverns, respectively, is not possible by etching the plastic surface, a functionally secure adherence of the metal layer to the plastic surface is not guaranteed. Therefore, in the case of the known process, especially the number of plastics capable of being coated is greatly limited. The direct metallization in accordance with this known process generally only functions without problems with ABS plastic parts. In the case of ABS-Polycarbonate blends and polypropylene, metallization is only possible under certain working conditions. In view of this, this known process is capable of improvement.
In the case of another known process (“New methods of electroless plating and direct electroplating of plastics”, A. Vaskelis et al., Institute of Chemistry, A Gostauto 9, 2600 Vilnius, Lithuania, paper to be presented the INTERFINISH 96 WORLD CONGRESS, International Convention Centre, Birmingham, England, Sep. 10-12, 1996), the plastic surface likewise is roughened by relatively heavy or strong etching, respectively. Here also micro-caverns are created in the plastic surface by etching in which the metal layer to be applied is mechanically anchored or hooked into. Also, the etching occurs at elevated temperatures in this process. The etching solution generally has a high concentration of an oxidizer. The plastic surface, pre-treated in this manner, subsequently is treated with a copper salt solution, and afterward it is treated with a second solution, containing sulfide ions or polysulfide ions. In this manner, an electrically conducting layer of non-stochiomeric copper sulfide is created on the plastic surface. The initial step of this known process is followed by the treatment of the plastic surface with both of the cited solutions at room temperature for a duration of maximally 1 minute. Even with this first step, only certain plastics can be metallized in a somewhat functionally secure and satisfactory manner. After a second step of this known process, the treatment with both of the cited solutions takes place at a higher temperature of 70 to 90° C., and for a longer period of 5 to 15 minutes. With this working process it is intended that both sulfur and also copper ions penetrate the plastic surface into the plastic, and that non-stoichiometric copper sulfide is also generated under the plastic surface. In this manner, especially good adhesion of the subsequently applied metal layer is to be achieved. However, the penetration described takes place only in a very incomplete manner, and thus the adhesion of the metal layer also leaves something to be desired. In addition, also with this process only certain plastics can be metallized in a satisfactory manner.
In practice, there further are several processes known whereby after the etching of the plastic surface and the formation of micro-caverns, the plastic surface is treated with a copper salt solution. Subsequently, a treatment with a sulfide solution is applied. All these processes are characterized by the disadvantage that in order to create a somewhat satisfactory metal layer, the process steps mentioned must be repeated several times in sequence. It is understood that this is complex and expensive.
In contrast, the invention is based on the technical problem to describe a process of the type mentioned in the beginning by which, in a less complex manner, a large variety of plastics can be metallized in a functionally secure and reproducible manner, whereby they are provided with a metal layer which meets all requirements.
To solve this technical problem, the invention describes a process for metallizing a plastic surface, whereby the following process steps are performed in sequence:
1.1) The plastic surface is subjected to etching under mild conditions.
1.2) Subsequently, the plastic surface is treated with a metal salt solution which comprises at least one salt of the group “Cobalt salt, silver salt, tin salt, lead salt”.
1.3) The plastic surface is treated with a sulfide solution.
1.4) Finally, the plastic surface is metallized in a metallizing bath.
Additional process steps, especially rinsing steps, may be interspersed with the process steps which are the subject of the invention.
The mild etching referred to in the invention means especially that the “etching”, or the treatment of the plastic surface, respectively, with a etching solution occurs at low temperatures and/or within a shorter time period at low concentration of the etching solution. As a matter of principle, mild etching conditions can be realized already when one of the preceding three conditions is met. The low temperature referred to in the invention means a maximum temperature of 40° C. When the mild etching conditions are created by a low temperature, this is usefully a maximum of 30° C., with a temperature of between 15° C. and 25° C. being preferred. With the low temperatures mentioned above, the pre-treatment with the etching solution takes place especially over a time period of 3 to 15 minutes, preferably 5 to 15 minutes and even more preferred 5 to 10 minutes. The invention claims that the treatment period is the shorter the higher the temperature. However, mild etching conditions can be also achieved at temperatures in excess of 40° C. if the treatment period selected is appropriately short. According to one version of the invention, the etching treatment takes place at temperatures of 40° C. to 95° C., preferably 50° C. to 70° C., for a treatment period of 15 seconds to 5 minutes, preferably 0.5 to 3 minutes. Here also, the invention claims that the treatment period is the shorter the higher the process temperature. In practical terms, the process temperature and
Baranauskas Mykolas
Mobius Andreas
Naruskevicius Leonas
Pies Peter
Rozovskis Grigorijus
Enthone Inc.
King Roy
Leader William T.
Senniger Powers Leavitt & Roedel
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