As a high-performance engineering material, PPO polyphenylene oxide resin features high temperature resistance, high structural strength, low water absorption, stable dimensional performance, acid and alkali corrosion resistance and excellent insulation performance. It is widely used in electronic and electrical components, automotive structural parts, bathroom accessories and precision shell products. Pure PPO resin has high melt viscosity and poor fluidity, resulting in difficult molding. Modified PPO and PPO alloy materials are mostly used in actual mass production to improve processing performance. Even after modification, PPO still has high requirements for temperature control, mold design, parameter matching and equipment adaptation in injection molding. Combining with on-site molding practice, standardized control of raw material pretreatment, equipment parameter setting, mold structure optimization and post-molding treatment can avoid common defects such as material shortage, cracking, shrinkage, burning, internal stress and dimensional drift, so as to ensure stable production and qualified product quality.
1. Raw Material Drying and Warehouse ManagementPPO itself has extremely low water absorption, but the surface of particles is easy to absorb trace moisture and dust in the air. Under high-temperature melting conditions, excess moisture will cause silver lines, bubbles, brittle strips and surface thread defects. Flame-retardant modified PPO has higher requirements for drying and needs strict moisture-proof control. Raw materials should be stored in a dry and ventilated warehouse with sealed packaging to prevent moisture and impurity contamination caused by long-term exposure. Constant temperature drying must be carried out before production. The drying temperature of conventional modified PPO is controlled at 90～110℃ for 4 to 6 hours. Flame-retardant and glass fiber reinforced grades need to be appropriately increased to 110～120℃. Long-time over-high temperature baking is prohibited to prevent material aging, toughness decline and failure of flame retardant system. The dried materials should be kept sealed and insulated to prevent secondary moisture absorption. Recycled materials need to be screened and impurity removed separately, and mixed in a reasonable proportion to avoid affecting molding stability.
2. Injection Molding Machine and Screw Parameter Matching
PPO melt has high viscosity and weak fluidity, and is prone to thermal decomposition and carbonization under excessive shear heat. Medium and high torque injection molding machines are preferred, matched with low compression ratio and shallow groove universal screws with a compression ratio of 2.0～2.5, so as to avoid local heat accumulation and material burning caused by high shear. The temperature of each barrel section is set in a balanced segmented manner: the feeding section is 240～260℃, the melting section is 260～280℃, and the nozzle section is 270～290℃. The temperature of reinforced and flame-retardant materials can be increased by 10～20℃. Straight-through extended nozzles are used to prevent cold material blockage and wire drawing. The back pressure is controlled at 0.3～0.6MPa to ensure uniform plasticization and reduce shear heating. The screw runs at medium and low speed to stabilize melt transportation.
3. Mold Design and Structural RequirementsPPO has fast curing speed and high sensitivity to internal stress. Mold steel with good polishing performance and moderate hardness is selected, and the cavity surface is finely polished to reduce demolding scratches. The gating system adopts large-diameter main runner, short-process sub-runner and thickened gate to avoid insufficient injection pressure caused by narrow runners. Side gates and fan gates are recommended for large-area products to balance feeding and reduce internal stress. Mold temperature is the core key, stably controlled at 70～100℃ to improve fluidity, enhance surface gloss and reduce residual stress. The cooling water channel is evenly arranged to ensure uniform cooling and prevent shrinkage deviation. The wall thickness is designed to be uniform, the rounded corners of transition positions are enlarged, and the demolding draft angle is reasonably increased. Exhaust grooves are opened at the end of filling and dead corners to eliminate burning and air pattern defects.
4. Precise Control of Injection Molding Process Parameters
Medium pressure and low speed injection are adopted for high-viscosity PPO materials. The initial stage is slow for exhaust, the middle stage is filled at a constant speed, and the final stage is buffered and decelerated to prevent shear overheating and melt decomposition. The holding pressure is set to 50%～60% of the injection pressure, and segmented holding is adopted to avoid excessive internal stress and flash. Sufficient cooling time is reserved to prevent demolding deformation and warping. Reduce the barrel temperature during temporary shutdown to avoid long-term material retention and carbonization. Clean the barrel thoroughly after long-term shutdown to prevent black spots and burnt materials in subsequent production.
5. Post-treatment and Defect PreventionPrecision stressed parts need annealing treatment at 70～90℃ for 2 to 4 hours to eliminate internal stress and prevent later cracking. Finished products are placed flat for natural cooling to avoid extrusion deformation. Reduce the operation strength during secondary processing such as drilling and ultrasonic welding. Control the mixing ratio of recycled materials and regularly screen carbonized impurities. Targeted adjustments are made for common defects: optimize exhaust and reduce speed for burning; increase temperature and mold temperature for material shortage; balance cooling for warping; strengthen stress relief for cracking. Standardized control of raw materials, molds and processes can realize long-term continuous stable production of PPO products.
