Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2001-09-19
2003-04-01
Wong, Edna (Department: 1741)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S304000, C205S159000
Reexamination Certificate
active
06541080
ABSTRACT:
The invention concerns a process for the direct metallizing of the surface of a plastic object, using these steps:
roughening the surface of the plastic object by pickling;
activating the surface with the aid of a colloidal or ionogen aqueous solution of a first precious metal, which colloidal or ionogenic solution also contains a second base metal, whereby an activating coat containing the first precious and second base metal is formed on the surface; and
providing electron conductivity on the activating coat with the aid of a preferably alkaline treatment solution, with which the second base metal is at least partially dissolved out of the activating coat and an electron-conductive substance is adsorbed in the activation coat;
whereby the electron-conductive activation layer is then metallized.
The invention thus concerns a process for the direct galvanic metallizing of a plastic surface. Of course, it is part of the invention that several plastic objects can be metallized at the same time with the process under the invention. Plastics metallized in this way are used for decorative purposes, for example in the health sector or in automobile manufacturing. Metallizing of plastics is also performed as part of the coating of electronic components for the purpose of electromagnetic shielding. In principle, different plastics can be galvanically metallized. For example, the surface of plastic such as acrylonitrile-butadiene-styrene (ABS) and, where necessary, blends of ABS and polycarbonates (PC) can be metallized for decorative purposes.
The known process of the type named at the beginning, from which the invention starts (DE 195 10 855 C2), is used for the partial or selective electrolytic metallizing of the surfaces of acrylonitrile-butadiene-styrene copolymer substrates. After the surface of the plastic is roughened by pickling with chromic sulfuric acid, chrome (VI) is reduced to chrome (III) as part of the process, This is followed by activation in a colloidal acid solution of palladium, which contains additional tin compounds. On the base of the activation coat created, sufficient electron conductivity is produced for the subsequent metallization. For this, a tin/copper exchange is performed. The treatment solution used for this contains copper ions, which are bound by a biologically degradable complex forming substance. The tin/copper exchange is based on a charge exchange, in which tin (II) is oxidized by the copper ions to tin (IV) and whereby the copper ions themselves are reduced to metallic copper and deposited on palladium clusters on the surface of the plastic. As a result of this deposition of copper, the palladium clusters which formed during activation with the colloidal solution become electron-conductive. This known process is characterized by a number of disadvantages. First, only limited quantities of palladium/tin can be applied to the roughened plastic surface with this process. There are corresponding limits to the metallization of these plastic surfaces. In addition, only ABS or ABS blends can normally be metallized with some degree of acceptability with this process. The metallization of ABS blends in particular leaves much to be desired. The metallization can often not be performed with any degree of reproducibility, and frequently certain areas on the surface of the plastic object to be metallized are not covered with an adequate metal coat. If plastic objects composed of different plastics are to be metallized with the known process, only ABS or ABS blends are metallized as a rule.
By contrast, the invention is based on the technical problem of describing a process of the type named at the beginning, with which different plastics can be metallized safely and reproducibly, and in which the plastics are given a metal coat which meets all requirements.
To solve this technical problem, the invention defines a process as described above which is characterized by the repetition of at least once of the sequence of steps “activation of the surface according to step 1.2) and making the activation layer electron-conductive according to step 1.3)” before the metallizing of the electron-conductive activation coat. It is part of the invention that steps 1.2) and 1.3) are repeated several times before the metallizing of the electron-conductive activation coat.
The invention is based on the finding that metallizing of plastic objects that is especially safe and effective can be achieved if the theory according to patent claim 1 can be realized. By repeatedly performing steps 1.2) and 1.3), the volume of adsorbed precious metal/base metal on the surface of the plastic can be increased substantially—surprisingly as part of the activation. Unexpectedly, metal coats with outstanding quality can be applied to the plastic objects as a result. Surprisingly, a variety of different plastics can be metallized effectively and safely with the process under the invention. Besides ABS, ABS blends, particularly ABS/PC blends, can be metallized reproducibly and the resulting metal coats meet all requirements. As part of the invention, large plastic objects, for example large ABS/PC parts such as automotive radiator grills, can be metallized without difficulty. The surfaces of plastic objects consisting of a number of different plastics can be metallized without difficulty and, if desired, completely.
In another type of implementation of the invention, roughening the surface of the plastic object is carried out by pickling with chromic sulfuric acid. For practical terms, a solution containing 400 g/l chromic acid and 400 g/l sulfuric acid is used. Pickling can be carried out solely with chromic acid. It is part of the invention that after pickling with chromic sulfuric acid or chromic acid, chrome (VI) is removed as completely as possible from the surface of the roughened or etched surface. Preferably, intensive rinsing is performed first after the roughening of the surface. In accordance with a preferred type of implementation of the invention, chrome (VI) is reduced to chrome (III) after the pickling with chromic sulfuric acid or chromic acid. It is within the scope of the invention that this chrome reduction takes place after the aforementioned rinsing. Potassium bisulfide or potassium hyposulfite can be used, for example, for the reduction of chrome (VI) to chrome (III). Preferably, at least one rinsing takes places following the chrome reduction. In another version of the invention, roughening of the plastic surface is carried out by pickling with a permanganate solution. In yet another version, the roughening is achieved by plasma pickling.
It is within the scope of the invention that the surface of the plastic object is pretreated with acid by immersion before the activation of the surface in accordance with step 1.2). The acid is preferably a mineral acid, hydrochloric acid is the most preferred. For practical purposes, the pretreatment is performed by immersion in a concentrate of hydrochloric acid, preferably 30% by volume hydrochloric acid.
According to the very much preferred type of implementation within the scope of the invention, which is particularly important as part of the invention, the steps “pretreatment by immersion in an acid, activation of the surface in accordance with step 1.2) and providing electron conductivity in accordance with step 1.3)” are repeated at least once before metallizing the electron-conducting activation coat. In other words, following the roughening of the surface in accordance with 1.1), the steps “immersion—activation—providing electron conductivity” are performed in succession and then this sequence of steps “immersion—activation—providing electron conductivity” is repeated at least once. As part of the inventive process, this sequence of steps can be repeated several times, i.e. more than twice, before metallizing the electron-conducting activation coat. Following roughening in accordance with 1.1), the “immersion—activation—providing electron conductivity” steps can then be performed and subsequently only the sequence “activation—p
Enthone Inc.
Senniger Powers Leavitt & Roedel
Wong Edna
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