As a widely used production raw material, engineering plastics have been widely used in most structural parts of mobile phones in the era of functional machines, such as panels, middle frames, back covers, etc. Because of its good mechanical performance, high and low temperature resistance, good dimensional stability, light weight, relatively low manufacturing difficulty and low cost.

However, in the era when apple is leading the smart machine, due to the aesthetic fatigue of users, terminal manufacturers need to use new materials and new technologies to improve their consumption desire and upgrade their consumption level. The bottleneck of plastic processing technology can not meet the stringent space and thickness requirements of product terminals. The wide application of plastic suddenly stopped, and metal became the mainstream material.

At present, the large-scale commercial application of ultra-high speed mobile communication network and fast wireless charging function is just around the corner. The development of new generation 5g smart phones is undergoing various design improvements, such as the optimization of internal components and the improvement of shell signal transmission capacity. The pace of removing metal from the back cover of mobile phones will be further accelerated. The physical properties and process bottlenecks of non-metallic materials such as glass and ceramics are increasing day by day. The new generation of injection molding compression and IMT decorative processing technology with better signal shielding resistance will be more widely used, and plastic applications are expected to make a comeback.

Processing technology requirements of injection molding PC mobile phone back cover

A. Thinning

At present, the thickness of the injection molded PC mobile phone back cover developed and verified by the industry is 0.8 mm to 1.0 mm, which is thicker than the glass back cover (0.50 mm /0.55 mm). The thickness of the injection molded PC back cover should be as close as possible to 0.5 mm to 0.6 mm, otherwise its application in light and thin models will be limited.

Through the injection compression process, the back cover parts suitable for thin-walled transparent PC mobile phones of 5 inches and above can be manufactured.

01. Parallel injection compression molding: first inject the melt into a larger cavity, and then mold the two halves together to achieve the target thickness.

02. Extended injection compression molding: control the cavity pressure generated in the melt injection stage or the movement of the closed end, so that the cavity expands first and then decreases to the target thickness.

03. Wedge injection compression molding: there is a wedge-shaped opening at the beginning of the compression gap, and then with the injection of the melt, it "collapses" to the target thickness at the same time.

B. High precision and automation

Injection molded mobile phone shell is a precision structural part of mobile phone, which must meet the requirements of accurate size and stable mass production. In particular, the current smart phones have higher requirements for the detail structure and appearance accuracy of structural parts to meet the requirements of minimum assembly clearance under precision assembly. For manufacturers, the injection molding machine of the production equipment should be an electric high-speed machine with less stains and equipped with a manipulator to reduce the damage and appearance pollution caused by manual picking.

What is IMT

The traditional IMT technology began in 2006. At that time, the technical level was equivalent to IML technology. The carrier PET layer of color was removed and the color was directly left on the plastic parts. The product radian was not large and the color was not rich enough. Only screen printing and color layer were available, but there were few metallic colors.

After more than 10 years of development, IMT technology can now leave two 3D optical nano decorative layers on the plastic surface to realize the product appearance and decorative effects of three-dimensional, portrait, gradient, R-angle and so on, providing an excellent platform for manufacturing technology innovation and Practice for a new mobile communication terminal product.

At present, IMT decorative processing technology combines many excellent process characteristics such as IML diaphragm production and IMR transfer, overcomes and improves the relevant technical bottlenecks, and can obtain ideal products.

Process implementation status

IMT can make the plastic surface beautiful through the combination of various processes, but the process flow is too long, and each process has the loss of yield. It is said that the overall yield of IMT process is less than 50%, and there is still much room for improvement.

On the other hand, the adhesion performance of the existing UV transfer adhesive needs to be strengthened to improve the coating yield of the release film. In the end products, in order to ensure the glass like effect, the appearance requirements are very strict, and there are many kinds of defects. In some cases, it is necessary to sign limit sample rules with end customers.

prospect

The integrated PC back cover with wrapped edges and injection molding with complex assembly structure can reach the standard glass in thickness without increasing the thickness or appearance of the whole machine in order to compromise and sacrifice. It is being introduced and developed by more and more manufacturers.

As an advanced form of injection molding, injection compression is more suitable for the molding of thin-walled transparent optical products, and is widely used in optical lenses, ultra-thin light guide plates, thin Automobile decorative plates and other products.

After breaking through the bottleneck of hardening and CNC technology, the surface hardness of IMT decoration technology can be comparable to that of glass, and the post bonding decoration process of glass / composite plate can be reused. The industrial chain is complete, which is difficult to meet the terminal appearance requirements. It is a feasible solution at present.