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Confusion, challenges and latest developments in decorative film technology

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Confusion, challenges and latest developments in decorative film technology

2019-07-05 11:32:24 浏览次数:977

The development of decorative coating technology has grown by leaps and bounds. Ion-plated decorative films have been widely used in watch cases, watch bands, mobile phone cases, eyeglass frames, golf clubs, accessories, construction hardware, and daily hardware. The ion-plated decorative film gives the product a metallic surface and rich color, and improves wear resistance, corrosion resistance and longevity. With the increasing market of ion plating decorative film, the performance requirements of film layers are getting higher and higher, and many new problems and new challenges have appeared in the manufacturing process. This paper focuses on the new problems encountered in recent years of plating technology, including the surface decoration of plating parts, pinhole corrosion on the surface of the coating, the effect of ion plating plasma sheath, the development of film color, etc. Countermeasures.


One. New challenges in the process of ion plating decorative film coating on the surface of the workpiece

Stainless steel substrates are usually polished, brushed, chemically etched, laser engraved, CNC machine tools, etc., and some are also laser welded, water-plated nickel-chromium layers.

The polishing operation will leave hardened polishing wax which is difficult to remove on the workpiece; the nylon wheel drawing will leave a transparent polymer compound which is hard to find on the drawing groove; the grinding wheel may leave abrasive grains and binder, or may be caused by frictional overheating. Oxidized skin; sandblasting will have ceramic sand, glass sand, and alumina sand residue embedded on the surface; chemical etching will leave corrosion products in the corrosion pit, or protective materials for corrosion protection on other non-corrosive surfaces; The engraving process will produce high temperature oxide scale and ablation matrix residue; CNC machine tool engraving will have high temperature oxide scale and cutting oil residue, and substrate fragments will be pressed into the substrate; laser welding will also lead to high temperature oxidation; The chrome plating layer generates complex oxides that are difficult to remove, and the incomplete removal of the pollution caused by these treatments may result in ignition of the ion plating process, false adhesion of the plating layer, film loss, and uneven color.

In ion plating products, the art processing method is often not a single, but a combination of various operations, which increases the difficulty of pre-plating cleaning. The traditional method of ultrasonic degreasing and wax removal is incompetent. The cleaning process must be adjusted. For different pollution, mechanical cleaning, gas phase cleaning, vacuum heating, cleaning, cathodic electrolysis, anodic electrolysis, or targeted Efficient cleaning agents and more. These comprehensive measures can achieve better results, but still do not find the ideal solution for some pollution. The application of the recent plasma polishing method to pre-plating cleaning is a technology of concern, which has achieved good results in the deplating of certain coatings.

two. How ion-plated decorative film products can overcome the local corrosion

Most of the ion-plated decorative films are nitrogen, carbon, and oxygen compounds of a transition metal (such as Ti, Zr, Cr) or alloys thereof, and amorphous carbon (diamond-like) films. In general, these compounds are inherently chemically inert and have excellent corrosion resistance. However, in recent years, some decorative coating products, including watch parts, mobile phone cases, golf clubs, etc., have failed to pass the artificial sweat corrosion test or the neutral salt spray corrosion test, which has aroused people's attention!

In fact, this problem has existed for a long time, but it has not attracted attention. Corrosion of decorative coating products is not only the corrosion resistance of the coating itself, but also the system corrosion of the decorative coating + substrate. Many research work has shown that the ion plating decorative coating itself has good corrosion resistance. It is plated on the metal (such as stainless steel) substrate, and the overall corrosion resistance of the substrate is improved. However, the decorative coating is very thin, and inevitably there are surface defects, such as Microcracks, micropores, pinholes, columnar grain boundaries, macroscopic particles deposited by arc, and the like. Corrosive media can pass through the coating to the substrate through the channels formed by these defects.

Plating→corrosive medium→substrate constitutes an etching cell, and the plating layer and the substrate become electrode crucibles, thus generating electrochemical corrosion. Generally, the plating layer is chemically more inert than the substrate, the plating electrode potential is higher than the substrate, and the substrate is oxidized and etched. Localized corrosion or pinhole corrosion on coated products is even more severe than uncoated products. Localized corrosion is also the basis for determining whether a coated product is acceptable. The market evaluates the corrosion resistance of the coated products, which are generally randomly sampled for artificial sweat corrosion test and salt spray corrosion test. If local corrosion exceeds the standard, the batch product is judged to be unqualified. In view of the fact that the decorative coating is so thin (about 1 micron) and the current level of ion plating technology, the pinhole ratio of the coating is high, so the risk of corrosion test of the coating product is always there.

The key measures to improve the local corrosion resistance of the system are: improve the compactness of the coating and eliminate the surface defects that pass through to the substrate. Various methods have been studied: thick coating, high corrosion resistant matrix material, deposition of corrosion-resistant dense transition layer, plasma etching in the middle of the coating, multilayer structure, matrix plasma nitriding pretreatment, etc. The above PVD method can be improved at present. The system is resistant to local corrosivity. Water plating plating layer is more reliable but not environmentally friendly. Finally, the non-PVD method of applying UV oil is controversial but effective.

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