Which injection molding material is most suitable for smartphone cases?

1, Material properties: balance of impact resistance, transparency, and environmental friendliness
Smartphone cases need to meet multiple requirements such as protection, signal transmission, and appearance presentation, which requires injection molding materials to have high strength, low dielectric loss, high transparency, and other characteristics. Among the current mainstream materials, polycarbonate (PC) has become the preferred choice due to its comprehensive performance advantages, with the following key characteristics:
Excellent impact resistance performance
The tensile strength of PC material reaches 69MPa, the bending strength is 96MPa, and it maintains stable performance in the temperature range of -40 ℃ to 130 ℃. Taking the Huawei P20 Pro as an example, although its 3D glass back cover adopts a curved design, the internal support structure still uses a PC injection molded frame, achieving a glassy visual effect through in mold decoration (IMR) technology, while ensuring a 60% increase in impact dispersion efficiency when dropped.
Having both light transmittance and surface hardness
The high-performance modified PC has a light transmittance of up to 92% and a surface hardness of 3H (pencil hardness). After surface hardening treatment, its wear resistance is close to that of glass. The transparent exploration version back cover of Xiaomi 11 Ultra is made of PC injection molded substrate, which achieves anti reflection effect through nanoscale coating. While maintaining a thin and light thickness (0.8mm), the light transmittance loss is only 3%.
Breakthrough in Environmental Protection and Sustainability
Biobased PC materials, such as corn starch modified PC, have achieved large-scale application, reducing carbon emissions by 40% compared to traditional PC, and can be degraded by microorganisms. The "natural leather" back cover launched by OPPO Find X7 series adopts a bio based PC injection molding bottom support structure, combined with a recyclable TPU frame, achieving a material recycling rate of 92% for the entire machine.
2, Process Adaptability: Breakthrough in Injection Compression Molding (ICM) Technology
Traditional injection molding processes are prone to defects such as rainbow patterns and warping when manufacturing thin-walled transparent shells, while injection compression molding (ICM) technology significantly improves the molding quality of PC materials through dynamic cavity adjustment
Stress control and surface accuracy optimization
The ICM process reduces the size of the mold cavity by 5% -10% through a secondary compression action after the melt is injected into the mold cavity, compensating for material shrinkage. Taking the transparent PC back cover of Samsung Galaxy S24 Ultra as an example, after adopting ICM technology, the product's warpage was reduced from 0.3mm to 0.05mm, and the surface roughness Ra value was optimized from 0.8 μ m to 0.2 μ m, completely eliminating rainbow pattern defects.
Thin walled and lightweight implementation
The ICM process can manufacture PC shells with a thickness of 0.4mm, which is 30% thinner than traditional processes while maintaining impact resistance. The "ultra-thin crystal diamond" back cover of vivo X100 Pro is made of 0.4mm PC injection molded substrate, combined with micro nano texture transfer printing technology, to achieve military grade anti drop certification under a body weight of 180g (without damage from a 1.5-meter drop).
Innovation in Multi Material Composite Forming
Through the insert injection molding process, PC can be composite with materials such as metals and ceramics. The "nano microcrystalline ceramic+PC frame" structure of the Honor Magic6 series solves the problem of ceramic brittleness and reduces overall costs by 42% by encapsulating the edges of ceramic pieces through PC injection molding.
3, Industry Trend: From Single Material to Functional Integration
With the acceleration of smartphone function iteration, the shell material is evolving from "structural support" to "functional carrier":
Integrated heat dissipation and electromagnetic shielding
Adding graphene or boron nitride (BN) fillers to PC substrates can increase the thermal conductivity to 5W/(m · K). The "aerospace grade heat dissipation back cover" of OnePlus Ace 3 is made of PC/BN composite material, combined with a three-dimensional heat dissipation channel design, which reduces the body temperature by 3 ℃ in gaming scenarios.
Wireless charging and magnetic compatibility
By adjusting the PC molecular chain structure, the dielectric loss of the material can be reduced to 0.02 (1GHz frequency band), meeting the Qi2 wireless charging standard. The MagSafe back cover of the Apple iPhone 15 series has a PC injection molding layer thickness of only 0.3mm, which can still achieve 15N magnetic attraction and a charging efficiency of 85%.
Personalized and responsive production
The combination of 3D printing and injection molding technology makes small batch customization possible. The "Leather Pattern PC Back Cover" of Lenovo Moto razr 40 Ultra adopts SLS selective laser sintering technology, which shortens the design to production cycle to 7 days and supports user-defined texture patterns.