Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating predominantly nonmetal substrate
Reexamination Certificate
1998-11-20
2001-12-18
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating predominantly nonmetal substrate
C205S187000
Reexamination Certificate
active
06331239
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of electroplating non-conductive plastic moldings and an electroless copper plating solution suitable for use in said electroplating method.
BACKGROUND ART
Among methods of electroplating non-conductive plastic moldings to form a decorative coating, a widely employed method comprises, in succession, degreasing, etching, optionally neutralizing and pre-dipping, then applying a catalyst for electroless plating using a colloidal solution containing a tin compound and a palladium compound, and optionally activating (accelerator treatment), followed by electroless plating and electroplating.
In such plating method, electroless copper plating solutions are frequently used which contain a reducing agent having a high reducing power such as paraformaldehyde. When this electroless copper plating solution is used, copper is deposited in the initial plating stage on a highly catalytic palladium portion of tin/palladium colloid coating applied as the catalyst. However, copper is continuously deposited by reduction due to the reducing action of the reducing agent with high reducing power and thus a copper layer is formed not only on the palladium portion but also in the transverse direction. As a result, copper is also deposited on an inherently non-catalytic tin portion so that a so-called bridge deposit is formed which is likely to provide a spongy coating. When electroplating is conducted on the electrolessly plated coating having the bridge deposit, pit-like fine agglomerates (called stardust) are partially deposited in a great number, thereby tending to render the coating irregular. The plated coating thus formed on the plastic substrate often shows an inferior appearance compared with a plated coating on a metallic substrate.
To prevent the creation of such inferior appearance, attempts have been made to brush the surface of the substrate electrolessly plated with copper before electroplating. However, the attempt is disadvantageous in involving a cumbersome step.
Further, the electroless copper plating solution contains, as a reducing agent, paraformaldehyde which is highly toxic and presumably carcinogenic. A further problem is that considerable labor is entailed in removing the metal ions in the disposal of waste water because a completing agent having a high complexing power such as EDTA has been used to solubilize the copper ions.
When electroless nickel plating is conducted in place of electroless copper plating, stardust scarcely develops because of a lesser degree of bridge deposits so that the resulting electroplated coating is esthetically superior in appearance to the electroplated coating formed on the electrolessly plated copper coating. However, electroless nickel plating disadvantageously requires more catalyst than electroless copper plating, thereby incurring higher costs. Further, when copper electroplating is conducted after electroless nickel plating, the nickel coating is eroded by the galvanic potential difference due to lower potential of the nickel coating than the copper coating, thereby tending to induce coat peeling and resulting in blisters.
A method is known which comprises immersing a substrate in a colloidal solution containing a precious metal to deposit a colloid coating of precious metal, and directly electroplating the coated substrate without conducting electroless plating (Japanese Unexamined Patent Publication No.267393/1991). However, this method is defective as follows. Since the coating has a low electrical conductivity and electroplating proceeds at a low deposition rate, the feeding points of electrical power require a large area when plastic moldings of great area are electroplated. Furthermore, a substantial time is taken to electroplate the entire substrate surface of such plastic moldings and it is difficult to form a uniform coating over the entire substrate surface. Moreover, the procedure is performed under narrowly limited conditions, and the control of treating solutions and the working conditions are very cumbersome.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide a method of electroplating non-conductive plastic moldings by a simple procedure, the method being capable of forming a coating excellent in appearance and properties.
The present inventors conducted extensive research in view of the foregoing prior art problems and found the following. A suitable electrically conductive coating can be formed without developing a bridge deposit by a method comprising applying a catalyst useful for electroless plating to non-conductive plastic moldings, and electrolessly plating the moldings using an electroless copper plating solution of novel makeup containing a saccharide having a reducing property as a reducing agent. Further, when the surface of said electroless-plated coating is directly electroplated, a decorative coating of excellent appearance can be easily formed. Since the electroless copper plating solution to be used in this method contains a saccharide with relatively low reducing power as a reducing agent, a high stability of the plating solution is assured and the solution can be easily controlled. In addition, because a hydantoin compound having a relatively low complexing power can be used as a complexing agent for copper, the electroless copper plating solution has excellent properties including high deposition capability and ease of effluent treatment. Based on these novel findings, the present invention was accomplished.
According to the present invention, there are provided:
(1) a method of electroplating non-conductive plastic moldings, the method comprising the steps of: applying a catalyst useful for electroless plating to non-conductive plastic moldings using a colloidal solution containing a precious metal compound and a stannous compound; forming an electrically conductive coating on the surface of the moldings using an electroless copper plating solution containing a copper compound, a saccharide having a reducing property, a complexing agent and an alkali metal hydroxide; and electroplating the coated moldings: and
(2) an electroless copper plating solution which is an aqueous solution comprising 0.1 to 5 g/l, calculated as copper metal, of a copper compound, 2 to 50 g/l of a complexing agent, 3 to 50 g/l of a saccharide having a reducing property and 10 to 80 g/l of an alkali metal hydroxide.
There is no limitation on the type of non-conductive plastic moldings to be treated by the method of the invention. A highly decorative plated coating can be easily formed even on large-size moldings having a great area. For example, the method of the invention can be applied to plastic automotive components recently widely used in the automobile industry. Examples of such large-size plastic materials include front grilles, emblems and other automotive parts, exterior components of electronic devices, knobs and like parts to be electroplated for decoration, materials to be plated for giving corrosion resistance or for adding a new function, etc.
The kind of plastic materials to be treated is not limited, and various plastic materials heretofore known can be treated. Examples of plastics are general-purpose plastics heretofore extensively used for chemical plating such as ABS resins, general-purpose engineering plastics having a heat resistance at a temperature of 150° C. or less, such as polyamides (nylon PA), polyacetals (POM), polycarbonates (PC), modified polyphenylene ethers (PPE), polybutylene terephthalates (PBT) and the like, super engineering plastics having a heat resistance at a temperature of 200° C. or more, such as polyphenylene sulfides (PPS), polyether sulfones (PES), polyether imides (PEI), polyether ether ketones (PEEK), polyimides (PI), liquid crystal polymers (LCP) and the like, polymer alloys such as polycarbonate/ABS and the like. It is suitable to use, among these plastics, plastics of a grade proper for plating such as ABS resins and the like which can avoid the decrease in the adhesion of the plat
Okada Jun
Shirota Hideki
Armstrong Westerman Hattori McLeland & Naughton LLP
Okuno Chemical Industries Co. Ltd.
Wong Edna
LandOfFree
Method of electroplating non-conductive plastic molded products does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of electroplating non-conductive plastic molded products, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of electroplating non-conductive plastic molded products will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2566078