Polycarbonate (PC) boasts remarkable qualities such as superior strength, impressive clarity, and robust impact resistance, coupled with a broad thermal application spectrum. The processing nuances of PC are distinct; it exhibits a low sensitivity to shear rates but a high sensitivity to temperature changes. The absence of a clear melting point and its high melt viscosity, especially under elevated temperatures, can lead to hydrolysis and potential product fracturing.

To harness PC's full potential, consider these tailored strategies:

1. Enhancing melt flowability is best achieved by elevating the injection temperature rather than increasing the injection pressure.

2. Molds should be designed with short, wide runners and gates to minimize fluid pressure loss, necessitating higher injection pressures.

3. Prior to molding, resin must undergo thorough drying to maintain moisture content below 0.02%.

4. Insulation measures during processing are critical to prevent re-moisturization of the resin.

5. Beyond intelligent product design, mastery over the molding process is essential. Techniques like raising the mold temperature and post-processing can mitigate or eliminate internal stresses, with process parameters adjusted according to product-specific requirements.

Navigating the Injection Molding Process for Polycarbonate (PC)

Material Drying

PC's aversion to moisture is well-documented, with even trace amounts triggering hydrolysis, molecular degradation, and diminished strength. To avert such outcomes, it's imperative to limit polycarbonate moisture content to below 0.02% before molding, ensuring the mechanical integrity of the final product remains uncompromised.

Optimal Injection Temperature

Determining the ideal injection temperature is a balancing act, influenced by product design, mold architecture, and performance criteria. Operating within the sweet spot of 270-320°C is recommended, as temperatures surpassing 340°C can lead to PC decomposition, discoloration, and various surface imperfections, not to mention a notable decline in mechanical properties.

Calibrated Injection Pressure

The right injection pressure can make or break the physical and mechanical properties of PC products. It's a delicate balance where both extremes can introduce defects. A sweet spot often lies between 80-120MPa, although intricate designs with longer flow paths may necessitate higher pressures to ensure flawless cavity filling.

Holding Pressure and Duration

The holding phase is pivotal in determining internal stress levels within PC products. Insufficient holding pressure can lead to shrinkage and voids, while too much pressure can induce stress around the gates. A strategy of high material temperature with low holding pressure is frequently employed to circumvent these issues.

Injection Speed Considerations

While injection speed isn't a major influencer on PC product performance, it's critical for specific designs like thin walls or long flow paths. A tiered injection speed—starting slow, accelerating, then slowing down again—is often the method of choice.

Mold Temperature Regulation

Maintaining a mold temperature between 85-120°C is key, with an optimal range of 80-100°C for most applications. For more intricate or thinner products, temperatures may be elevated to 100-120°C, ensuring they do not surpass the mold's thermal deformation threshold.

Screw Speed and Back Pressure

Given PC's high melt viscosity, screw speeds should be moderate (30-60r/min) to promote plasticization and prevent excessive loading. Back pressure, kept between 15-30bar of the injection pressure, is essential for quality molding with PC materials.

Additive Usage

The use of mold release agents during the PC injection process should be conservative, and the recycling of materials should be limited to three times, with a maximum of 20% recycled content.

Mold Design for PC Injection Molding:

1. Opt for thick, ​short runners​ with minimal bends and polished round cross-sections to ease melt flow.

2. Gates of any type are permissible, provided they have a minimum diameter of 1.5mm.

Injection Molding Machine Specifications for PC Products:

1. The maximum injection volume should not exceed 70-80% of the machine's nominal capacity.

2. Clamping force calculations should be based on the product's projected area, applying 0.47 to 0.78 tons per square centimeter.

3. The ideal machine size corresponds to a product weight that is 40 to 60% of the machine's capacity, with a 10% reduction if the capacity is measured in polystyrene ounces.

4. The screw should have a minimum length of 15 diameters, with an optimal L/D ratio of 22~25:1 and a compression ratio between 1.5:1 and 3:1. The check valve should allow for a minimum resin flow gap of 3mm.