The strength and toughness of the 5G phone back cover are already excellent, and the cost advantage is very obvious. The two key indicators that urgently need to be improved are "feel" and "appearance". In recent years, the application of various new materials and technologies has significantly improved the texture of plastic back covers, gradually breaking away from the impression of being low-end and cheap, and returning to mainstream models.
The typical structure of PC/PMMA composite sheet is composed of PMMA as the outer layer and PC as the inner layer, which can combine the advantages of both. Glass is widely recognized as a high-quality material for back covers, and if plastic back covers can achieve a similar appearance to glass through material and process changes, it will significantly increase consumer acceptance of plastic back covers.
Composite panels usually use 0.5, 0.6, or 0.7 profiles, which are cut, hot bent, and shaped to meet the specifications. The surface can be sprayed, printed, true plated, UV transfer textured, and other processes. PC boards cannot be broken or crushed, while PMMA (commonly known as acrylic) is brittle and prone to breakage. PMMA has a higher transmittance than PC, but PC is more temperature and heat-resistant and has a wider range of applications. People naturally think of introducing PMMA, the main component of organic glass, to achieve transparent and glass like effects. However, PMMA materials are relatively brittle, so PC has been introduced into the system to enhance overall toughness and impact resistance.
Composite panels have become a new favorite in the thousand yuan machine market, leading plastic materials back to the mainstream in mobile phone back covers. PC/PMMA composite board is made by co extrusion of PMMA and PC, and can achieve excellent glass like effect after surface treatment. Similar to glass, composite panels can also be formed in 3D. After precise texture decoration, the visual effect is very similar to that of 3D glass cover plates, but the price is lower. The hardness of the finished product can reach 4H/1000G, which can fully meet the testing requirements of mobile phone cover plates.
After composite panels, injection molded PC cover plates, as a low-cost and efficient plastic product with better impact strength and durability, are attracting more and more attention from traditional plastic factories and are expected to become the mainstream mobile phone back cover solution in 2019. The core technology of injection molding imitation glass process is injection molding compression molding. The thickness of a regular injection molded PC phone cover is generally between 0.8mm and 1.0mm, which is much thicker than the mainstream glass cover with a thickness of about 0.5mm. The PC back cover formed by injection molding and compression molding can have a thickness similar to that of a glass cover plate. After a series of treatments such as hardening, CNC processing, and film application, the thickness appearance can also achieve the aesthetic effect of glass texture.
After the production of injection molded PC cover plates is completed, appearance decoration is also required. Traditional processes include IMR, IML, and IMT, each with its own characteristics:
1、In Mold Decoration by Roller (IMR process): The main principle is to print decorative and functional patterns on a thin film through a high-precision printing machine, and then transfer the patterns on the foil film to the surface of plastic products like labeling. This is a technology that can achieve the integration of decorative patterns and plastic. The IMR process has high production capacity and stable quality, making it suitable for mass production of a small variety. However, the product surface is unprotected and not resistant to scratches and corrosion, making it more suitable for flat or 2.5D phone back covers.
2、In Mold Labeling (also known as In Mold Film, IMF):The IML process product is a sandwich structure with a hardened transparent film on the surface, a printed pattern layer in the middle, and a plastic layer on the back. Compared to the IMR process, the IML process, due to the ink being sandwiched in the middle, can prevent the surface of the product from being scratched and wear-resistant, and can maintain the bright color for a long time without fading, making it more suitable for 3D phone back covers.
3、Inner Molding Transfer Label (IMT):IMT is a new process that combines and extends the technology of in mold injection molding (IML) and in mold transfer printing (IMR). The IMT process combines the most popular 3D optical texture+PVD decoration method, which has a higher aesthetic value and larger curvature compared to traditional methods. In addition to being scratch resistant and corrosion-resistant, the biggest highlight of IMT technology lies in its double-sided 3D optical texture, which can produce a layered optical 3D effect, making the product colorful and beautiful, and more technological and fashionable. IMT process combines the advantages and disadvantages of IMR and IML process, and solves the problems of single IMR membrane structure, poor corrosion resistance, single appearance effect, and no independent development right for mold and membrane; It also solves the difficulties of insufficient IML production capacity, variability, and low yield.
IMT is a new process that combines and extends the technology of in mold injection molding (IML) and in mold transfer printing (IMR). The IMT process combines the most popular 3D optical texture+PVD decoration method, which has a higher aesthetic value and larger curvature compared to traditional methods. In addition to being scratch resistant and corrosion-resistant, the biggest highlight of IMT technology lies in its double-sided 3D optical texture, which can produce a layered optical 3D effect, making the product colorful and beautiful, and more technological and fashionable. IMT process combines the advantages and disadvantages of IMR and IML process, and solves the problems of single IMR membrane structure, poor corrosion resistance, single appearance effect, and no independent development right for mold and membrane; It also solves the difficulties of insufficient IML production capacity, variability, and low yield.
With the continuous breakthroughs and innovations in technology, the texture of plastic back covers will become closer to glass. Driven by significant cost advantages, more and more low-end phones will adopt plastic back covers. Consumers will gradually change their impression of plastic back covers as low-end, helping to further increase the market share of plastic back covers.
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