xiehe model

1. Introduction of mobile phone shell materials and related examples

The material of the mobile phone case should have the characteristics of high strength, good heat resistance, electromagnetic shielding, stable size, and exquisite appearance. The technology is developing towards the trend of light weight and thin wall to achieve the functions of protection, heat dissipation and aesthetics.

Commonly used materials for mobile phone casings include engineering plastics such as PC/ABS/PMMA, metal alloy materials such as magnesium/aluminum/stainless steel, and composite materials of alloys and glass fibers.

For example, the first-generation iPhone released in 2007, Apple's mobile phone case has already adopted aluminum anodic oxidation process technology. Later, its Mac series, Apple Watch, iPhone 6S, iPhone7, etc. basically used 7000 series aluminum alloy, that is, 7075 aluminum alloy. This alloy, mainly containing zinc, is an aluminum-magnesium-zinc-copper alloy, a heat-treatable alloy, and belongs to high-pressure die-cast aluminum with good wear resistance.

2. General anodic oxidation process for mobile phone aluminum case

In the manufacturing process of this aluminum anodized mobile phone case, the surface of the aluminum mobile phone case substrate is anodized through a certain chemical action to form an anodized film to improve the wear resistance, corrosion resistance, reflectivity and Enhanced appearance aesthetics and other features.

When the current passes, hydrogen is precipitated on the cathode; the oxygen (including molecular oxygen, atomic oxygen and ion oxygen) precipitated on the anode is usually represented by O2 in the reaction. The aluminum used as the anode is oxidized by the oxygen precipitated on it to form an anhydrous anodized aluminum oxide film.

The role of each step process

(1)

Degreasing: used to remove the grease on the surface. If there are organic substances such as oil stains on the metal surface, it will affect the flatness, adhesion and corrosion resistance of the electroplating layer, and even discontinuous, loose, or even peeling deposits may occur. The degreasing process before plating is very important.

(2)

Alkaline cleaning and deplating: This is the step of removing the old oxide layer on the surface of the aluminum mobile phone case to expose the pure substrate. There are two methods for de-plating: one is chemical method and the other is electrochemical method. The most commonly used chemical method is alkali washing.

(3)

Pickling film: Use this procedure to remove the black water film and dirt on the surface of the aluminum phone case, which helps to adjust the uniformity/thickness/brightness of the surface material of the aluminum phone case. (Note: The film removed here mainly comes from NaAIO2 generated by Al+NaOH→NaAIO2+H2. NaAIO2 is a black soluble salt, which is a black film attached to the surface of the aluminum mobile phone case.)

(4)

Polishing treatment: The purpose of this step is to eliminate mechanical defects on the surface of the aluminum phone case, reduce surface roughness, and improve surface gloss. Phosphoric acid is often used for this particular treatment.

(5)

Activation: It is used to expand pores, increase porosity, and improve the adsorption effect of dyes in the next process.

After anodic oxidation, the oxide film can be activated by acid solution and then colored. Due to the chemical dissolution of the anodized aluminum by the acid solution, the pore wall can be dissolved from the outside to the inside, making the pore size larger. At the same time, alumina membranes with different pore sizes can be obtained by controlling the length of activation time.

(6)

Dyeing: According to customer requirements, mobile phone cases with beautiful colors and appearance can be produced. The dye adsorbs on the pore surface, then diffuses and accumulates in the pores. It forms ionic and hydrogen bonds with anodized aluminum, adding color to the film.

(7)

Sealing: Improve the quality and dyeing fastness of the mobile phone case, prevent the appearance of magnesium oxide from deforming, and make the mobile phone case resistant to fingerprints, stains and oil stains. The sealing methods include: hydration sealing, inorganic salt solution sealing, organic coating sealing, etc.