September 2016 Archives

Electroless nickel-phosphorus (5 to 13%) alloy plating is the typical electroless plating most frequently used in industrial processes. The demand is increasing due to the excellence in mechanical, electrical, and physical properties while the uniform film thickness can be obtained even on a complex shape.
The table shown below lists the application examples and purposes of electroless nickel-phosphorus alloy plating.

[Table] Application examples and purposes of electroless nickel-phosphorus alloy plating

One of the characteristics of electroless nickel plating is that the hardness increases by applying heat treatment after plating. The hardness of Hv500 to 550 right after plating becomes around Hv800 and 1000 by treating with heat at 400℃.
Although electroless nickel plating can be applied on most of the metals, plastics, and ceramics, the plating will not be deposited on particular metals, including tin, lead, zinc, cadmium, or antimony. This is because the electroless nickel plating inhibits the catalytic action at metal deposition.
In addition to nickel-phosphorus plating, nickel-boron (1% of boron) alloy is also used for electroless nickel plating. This material is more expensive, but it is the preferred choice for electrical components because of its remarkable solderability and heat resistance performance.

Various plastics have substituted metal materials in many fields for their advantages (including lightweight, mass productivity, and cost reduction, etc.).
Applying electroplating on plastic materials not only enhances the product value by adding metallic appearance but also improves resistance to weather, light, heat, shock, abrasion and bacteria when the metal coating over the entire plastic surface protects it from the external environment. The plating can also make them look more luxurious and give additional value to the plastic products.
Formerly, commodity plastics (long-term heat resistant temperature is less than 100℃), such as ABS (Acrylonitrile-Butadiene-Styrene) and PP (Polypropylene), were the most common item. However, in line with the technology advancement, various types of high-performance engineering plastics have been developed in recent years. Not all types of plastics can be plated. The table below shows plastics compatible with plating.

[Table] Plating-compatible plastics

An oxidized finish, which gives copper or copper alloy products an aesthetic effect, is achieved by blackening the surfaces with sulfidization treatment and buffing off some of the coloring. This process adds an antique look produced by black contrast and color gradation mixed with reddish tone of plating.
Including interior decor items, this technique is used for accessories, fine arts and crafts, and lighting apparatus. The following [Table] shows the methods of various oxidized finish techniques.

[Table] Types of oxidized finish

In any of the above cases, the common method is to plate the substrate with nickel or copper (bottom plating) to improve corrosion resistance before applying an oxidized finish.
Since the surfaces after applying an oxidized finish are extremely prone to abrasion, the routine process is to apply clear coating such as by electrostatic spray painting to protect the surfaces. For items requiring the high degree of abrasion resistance, tableware for example, the coating with the high pencil hardness will be adopted.

Gold plating is the mainstream of noble metal plating used for decorative purposes. Gold known as a rare and expensive metal from ancient times has been used for Buddhist statutes and articles, weapons, and accessories for its elegant and mysterious color, glossy appearance and its long-lasting rustproof properties. Even today, gold is widely used for accessories, fittings for bags, parts of glasses, watches and interior decor items.
Gold plating looks golden brown, but to be precise, the color ranges from reddish gold to yellowish gold. This is because of the difference of alloy constituent varying from pure gold to alloy gold in the plating. [Table 1] shows the relationship between color tone and alloy constituent of gold alloy. [Table 2] lists the carat variations and corresponding gold content.

[Table 1] Color tone and alloy constituent of gold alloy

[Table 2] Gold variations by carat and gold content

In addition, gold is known for its ductile properties. Therefore, the alloy plating containing less gold (18K) called 'hard gold plating' is a popular choice for products requiring higher abrasion resistance, such as watches and accessories.
Besides gold, the noble metals generally used for decorative plating are silver, rhodium, palladium, and platinum.
Silver plating is used for various products including accessories, tableware, badges, medals, and musical instruments for its unique color tone. The aesthetic and bactericidal properties of silver are advantages for being used as tableware. The silver plating is also known to improve the tone of musical instruments like flutes. Another popular method is called 'antique silver coloring', which is an antique finish of silver plating colored by sulfide.
While adding a sense of luxury, plating made of rhodium, palladium, and platinum is also used for preventing discoloration of silver plating and improving abrasion resistance for its high degree of hardness.

The most common and long-established method of decorative plating on a steel substrate is copper-nickel-chrome plating or so called 'chrome plating'. In recent years, nickel-chrome plating (semi-bright + bright plating) is also common for its superior corrosion resistance and aesthetic properties. These are not only applied over metal substrates but also applied over plastic substrates. Chrome plating is the mainstream of decorative plating today.
Since chrome plating provides various surface properties including satin, hairline, spin, diamond cut, semi-bright satin, velour, pearl pattern finishes in addition to mirror gross finish, each type of finish is adopted for corresponding purposes.
Today's automobile industry requiring higher corrosion resistance is using dual plating consisting of electrochemically different nickels, triple plating with the medium layer made of trinickel, and microcracked chromium plating for the top layer to improve corrosion resistance.
The other types of decorative plating include nickel plating adopted for the top layer instead of chrome plating to produce reddish gross finish, and bright copper plating on the top for bronze finish.