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Material and process analysis of electronic product shell

Release time:2021-11-05

This kind of composite material called tepex is a semi-finished plate (organic plate), which is also used for lightweight structural parts in the automotive industry. Its matrix is composed of polyamide 6 (PA6), polypropylene (PP), polycarbonate (PC), thermoplastic polyurethane (TPU) or other thermoplastic plastics, and is usually reinforced by high-strength glass fiber or carbon fiber continuous fiber fabric, long fiber felt or wool. The fiber is completely immersed in the matrix resin, with almost no bubbles (complete reinforcement). Therefore, all loads are transferred from one long fiber to the next through the matrix resin. Usually, the fabric fibers are arranged at right angles to each other and evenly (balanced) distributed in both directions. Usually, fabrics with high warp strength are also used, and most of the fibers are unidirectional. Therefore, the characteristics of the corresponding semi-finished products, such as stiffness, strength and thermal expansion, depend on the direction.

At the same time, the mixed molding process is the preferred method for processing semi-finished products. The process starts with the pre cut part of the semi-finished product, which means the final shape of the component. After being heated above the melting temperature of the substrate, the precut is placed between the half molds of the open injection mold. Close the mold and shape the pre cut part. At the same time, short fiber reinforced matrix plastics are used for back molding or cladding molding. In contrast to embedded molding, thermoforming and injection molding are not separate process steps, but are carried out in one processing step without separate molding molds. Because the number of processing steps is reduced, the investment cost and processing cycle are reduced, so this process is very efficient. Another advantage of semi-finished tepex pre cut parts is that their performance has been formed. Therefore, there is no need to consolidate in the mold, and consolidation is not economically feasible for thermoplastics.

The insert is heated in a separate oven and transferred to an open injection mold in a plasticized state. In this step, semi-finished parts without transversely reinforced continuous fiber unidirectional belts are disadvantageous, because when the mold is closed, the material will separate, so the fibers are easier to be cut (the so-called mold sliding). For fabric reinforced semi-finished products, multi grid warp and weft yarns have the function of transverse reinforcement, which greatly simplifies the processing of inserts in the plasticized state.

Demoulding parts with high surface requirements

The shell parts of consumer electronic products, especially information technology products, must have a smooth and usually shiny surface. Semi finished composites can meet these requirements, provided that the product is manufactured in a hybrid mold equipped with a controlled rapid heating / cooling system. Therefore, the demoulding surface can be sprayed without any secondary treatment. In contrast, die-casting metal, which can also be used to produce the shell of tablet computers, often needs to be filled, polished and polished before spraying to make the surface smooth. In addition to spending more time and energy, there will be more waste. Compared with metal die casting, tepex hybrid molding has lower energy consumption and carbon dioxide emissions.

Another important reason why tepex is extremely suitable for the production of consumer electronics and it product shells is that it can obtain high deformation resistance and high rigidity with thinner material wall thickness. These two properties are significantly higher than those of injection molded thermoplastic, and the main competitor of composite materials is the shell of small household appliances. When carbon fiber reinforced material is used, its specific bending stiffness is equivalent to that of die cast aluminum and magnesium, but its specific bending strength is significantly higher. These features play an important role in making the shell parts of smart phones and other smart phones very thin and light, but at the same time, they are relatively strong, so as to show high deformation resistance and ensure that electronic equipment components (such as displays, circuit boards and rechargeable batteries) are well protected. Stiffness is an important standard for manufacturers of such equipment, which has been verified in the comprehensive system test and stress deformation test of finished parts.

Stiffeners are easier to produce

If the shell parts are mixed molded, it is easy to obtain stiffeners by injection molding. Because the matrix of the composite is the same as the injection molding material, a strong molecular bonding can be achieved between the stiffener and the shell. In addition to the specific stiffness of the composite itself, higher stiffness can be obtained through structural design (such as sphere or edge).

The first applications of tepex in the field of consumer electronics include the smart phone shell of research in motion (RIM). It can design products that are stronger and thinner than traditional injection molded shells. The new shell is made of TPU based composite semi-finished products and embedded molding process. Its appearance adopts very eye-catching elements, that is, dyed glass fiber fabrics are regularly arranged in composite materials and coated with transparent paint to highlight this visual effect.

Tepex is also used as a substitute for magnesium die castings and in the mass production of Dell commercial notebook covers. It contains semi-finished composite materials reinforced with PC as matrix and carbon fiber and glass fiber fabric. In addition to the advantages of high rigidity and light weight, magnesium is replaced by composite materials because of its higher energy efficiency, safer processing and excellent component surface processing quality.

Especially harsh is the flame retardant performance: due to the high energy density of the processor, considering the corresponding heat generated, the semi-finished composite materials used must pass the UL 94 V0 flame retardant test. Therefore, people have developed the concept of halogen-free flame retardant, which does not affect the wettability and adhesion of fibers, so it will not damage the mechanical properties of composites, and the plain carbon fiber fabric visible to the naked eye will bring an attractive appearance effect.

Notebook computer shell is one of the first series applications of hybrid molding process, with a rapid heating / cooling temperature control system.

These applications highlight the wide range of applications of injection molding process integration functions, such as for stiffeners, fixings, and guides. The carbon free antenna window that can ensure good signal transmission can also be integrated through the injection molding process.

The first carbon fiber smart phone

The trend of functional integration in consumer electronics and information technology continues. Previously, due to the electromagnetic shielding of carbon fiber and the resulting radio signal blockage, it was considered impossible to produce network equipment with carbon fiber shell. However, by using carbon Mobile's hyrecm (hybrid radio composite) technology, carbon fibers and related composites are combined together in some way, so that radio signals can pass through synthetic compounds. A conductive 3D printed circuit board that can assist the antenna function is also integrated in the carbon fiber shell.

The shell is made of semi-finished composite materials based on TPU. Its single shell structure is similar to the bearing chassis of Formula One racing car. This integrated design makes full use of the stiffness of carbon composites. This smart phone weighs only 125 grams, which is about 1/3 lighter than the traditional mobile phone, and its thickness is only 6.3 mm, which is 25% thinner than the traditional mobile phone. The demand for sustainable materials in the consumer electronics and information technology industries is also increasing. Its purpose is to reduce waste and recover resources from components with expired service life. As a pure thermoplastic system material, tepex organic sheet can be easily recycled in the sense of closed-loop material circulation. Under appropriate conditions, the shredded waste, whether single or mixed with unreinforced or short fiber reinforced composites, can be processed without problems by conventional injection molding and extrusion equipment. The mechanical properties of recycled products, such as strength, stiffness and toughness, are the same as those of traditional short fiber reinforced plastics with corresponding fiber content.

Half of the matrix materials of tepex semi-finished composite materials launched not long ago are PC materials recycled from waste water bottles. The target use of this composite is an application with higher requirements than short carbon fiber or glass fiber reinforced injection molding materials. Another sustainable material is the composite of flax fabric and biomaterials. These semi-finished products made entirely of renewable materials have an attractive biochar look and feel.

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