PCC (Iran) HDPE HCM4265 is a high-density polyethylene injection molding grade positioned for rigid packaging, industrial containers, crates, pails, caps, and closures. The HCM designation separates this material from lower-melt-flow blow-molding and film resins in the producer’s range. The grade is characterized by a melt mass-flow rate commonly reported between 4.0 g/10 min and 6.5 g/10 min at 190 °C/2.16 kg, a density near 0.965 g/cm³, and a narrow-to-moderate molecular weight distribution that permits short cycle times in thin-wall mold cavities. Because the manufacturer’s certificate of analysis is lot-specific, the converter should verify melt-flow rate by ISO 1133-1:2022 and density by ISO 1183-1:2019 before setting tooling tolerances. In multi-cavity tools, dimensional repeatability depends on hold pressure, gate freeze, and cooling uniformity rather than on the nominal grade alone.

What Distinguishes Injection-Molding HDPE HCM4265 from Blow-Molding and Film Grades?

The primary distinction is rheological. Blow-molding HDPE grades generally exhibit melt flow rates below 1.0 g/10 min at 190 °C/2.16 kg to maintain parison hang strength; injection grades such as HCM4265 occupy the 4.0–6.5 g/10 min range for rapid mold filling in multi-cavity tools. Film grades may have melt flow rates between 0.5 g/10 min and 7.0 g/10 min, but they are optimized for bubble stability and drawdown, not for the shear rates encountered in a sprue and runner system. At the high shear rates of a 1.0–2.5 mm wall thickness cavity, HCM4265 exhibits shear thinning; apparent viscosity falls as shear rate increases above 1000 s⁻¹. This behavior permits filling of thin handles, hinges, and rib patterns without excessive clamp force. In contrast to blow-molding grades, HCM4265 may show less resistance to slow crack growth under constant environmental stress because the lower molecular mass reduces tie-molecule density; this is an accepted trade-off in rigid packaging where cycle time, injection pressure, and top-load strength dominate.

On a 450 t hydraulic injection molding machine, a single-cavity crate tool with a shot weight of 1.8 kg and a reciprocating screw with L/D 22:1 is typically run at barrel set-points of 190/200/210/220 °C from feed to nozzle and a nozzle temperature of 215 °C. Mold coolant is maintained at 10–20 °C to reduce cycle time; ejection is programmed after the core surface reaches 80–85 °C. Injection speed is set to deliver a flow-front velocity of 150–300 mm/s in the thinnest wall section. Hold pressure is held at 55–65% of peak injection pressure for 4–6 s, with switchover at 98% volumetric fill determined by screw position, not by timer alone. Lot-to-lot variation in melt flow rate greater than ±0.5 g/10 min can alter fill time by 2–4% in the same tool; injection speed and transfer position should therefore be retuned when a new lot is introduced. Screw recovery should be complete before the cooling timer expires; recovery speed above 90 rpm can generate melt temperature variation of ±5 °C, which is often sufficient to shift mold fill balance in a runner with multiple gates.

Thermal Stability and Handling Limits at the Feed Throat

HDPE does not require desiccant drying. However, HCM4265 pellets stored in an unheated silo at relative humidity above 60% can carry surface moisture into the feed throat, producing splay and weld-line voids. Pre-warming at 60 °C for 1–2 h eliminates surface condensation without removing internal moisture. A hopper magnet and a screen pack of 40/80/40 mesh are recommended for mixed regrind streams, but fine recycled HDPE can bridge at the hopper throat when the recycled fraction exceeds 30 wt%. Melt residence time should be kept below 15 min at 220 °C; beyond this boundary, oxidative induction time measured by ISO 11357-6:2018 may fall below 20 min, and the base resin can show yellowing at sharp corners and gate regions. A purging sequence with a low-melt-flow HDPE is recommended for dark-to-light color changes because pigment residues in hot-runner drops are difficult to displace with high-flow grades alone.

On high-speed stack molds with 8+8 cavities and a cycle time of 12–15 s, HCM4265 has been used in thin-wall lids with wall thickness of 1.0 mm when the hot-runner melt delivery system maintains melt temperature uniformity of ±3 °C. The injection pressure requirement is a function of flow length; a flow length-to-wall thickness ratio above 150:1 can require peak injection pressure above 1200 bar, which may exceed the capability of smaller 180 t machines. If the available clamp force is inadequate, the mold can flash at the perimeter and produce dimensional nonconformity. These constraints are operational boundaries, not material deficiencies.

If Warpage Occurs in Flat Crates and Large-Area Lids

Warpage in HCM4265 injection moldings is controlled more by packing pressure and cooling uniformity than by melt temperature alone. If flatness error exceeds 1.0 mm/m measured on a calibrated surface plate, the first variables to examine are coolant flow-rate imbalance across the core and cavity. A temperature differential of more than 5 °C between the fixed and moving halves produces differential shrinkage that cannot be corrected by increasing hold time alone. The runner and gate system should provide balanced fill to all cavities within 0.05 s, verified by short-shot progression. Shrinkage in this density class follows ISO 294-4:2018; typical post-mold shrinkage for high-density polyethylene is 1.5–2.5%, but unannealed parts may reach 3.0% when the mold temperature is above 30 °C. Adding nucleating agents or switching to a higher-flow HDPE can reduce cycle time but may increase notch sensitivity; published data for this specific configuration is limited.

Mechanical Property Testing and the Limits of Laboratory Coupons

Tensile and impact tests on HCM4265 should be performed on specimens prepared by ISO 294-1:2017 injection molding. Tensile yield stress by ISO 527-2:2012 at 50 mm/min is generally 28–32 MPa for HDPE of this density; flexural modulus by ISO 178:2019 typically exceeds 1200 MPa. Charpy notched impact by ISO 179-1:2023 at 23 °C is commonly 3–6 kJ/m², but at -30 °C the values can fall below 2.0 kJ/m². These laboratory values do not guarantee performance in molded parts because weld-line location, gate blush, and frozen-in orientation dominate field failure. A drop impact test on a finished pail with a hemispherical striker according to ASTM D2463-15 provides a better ranking than coupon testing. The top-load strength of a 20 L pail is measured by applying a constant head compression at 10 mm/min until buckling; values depend on wall thickness, rib design, and residual stress, not solely on resin grade.

Environmental stress crack resistance of HCM4265 is moderate relative to high-molecular-mass pipe and blow-molding grades. Under ASTM D1693-15, condition B at 50 °C with 10% Igepal CO-630, injection-molding HDPE grades often show F₅₀ between 2 h and 20 h, whereas high-molecular-weight pipe and blow-molding grades can exceed 100 h. This difference is caused by lower tie-molecule concentration and a higher melt flow rate. Detergent bottle concentrates, household chemicals containing surfactants, and hot-fill foods with fats can initiate stress cracking at sharp corners. If a part is intended for contact with aggressive liquids, the design should avoid sharp internal radii below 1.0 mm and locate the gate outside mechanically stressed corners. Thicker bosses and stack ribs should be radiused to at least 0.5 mm to avoid high sink-mark stress concentration.

In contrast to HDPE film grades, HCM4265 does not require the same elongated chain orientation or low-gel film-specification discipline. In contrast to blow-molding HDPE grades, it provides shorter injection cycles and lower pressure drop through hot-runner drops, but at the cost of lower parison strength and lower environmental stress crack resistance. The additive package often differs: HDPEs intended for film may incorporate slip and antiblock agents that are unnecessary or harmful in injection-molded containers because they can reduce ultrasonic weld strength and interfere with post-mold decoration. If the manufacturer’s technical data sheet is unavailable, the processor should not assume that the additive package is identical to other PCC HDPE grades.

What Regulatory Documents Should Be Requested for HCM4265 in Food-Contact Applications?

Food-contact use requires a lot-specific compliance statement. Under U.S. regulations, compliance with FDA 21 CFR 177.1520 is required for olefin polymers used in contact with aqueous, acidic, and fatty foods; the processor should verify conditions of use, food type, and temperature. Under EU Regulation (EU) No 10/2011, overall migration testing by EN 1186-1:2002 may be required on finished articles. For toys and childcare articles, the heavy-metal limits of EN 71-3:2019 apply to the finished component. The RoHS Directive 2011/65/EU does not normally restrict HDPE unless flame retardant masterbatches are added; the masterbatch supplier must then provide a separate declaration. REACH Regulation EC 1907/2006 requires registration of the resin substance within the EU. These documents differ from one producer to another and should not be assumed from similarity to other HDPE grades.

Blending HCM4265 with polypropylene, ethylene vinyl alcohol, or polyamide is not recommended without a tie layer or a compatibilization study. The addition of post-consumer recycled HDPE from detergent bottles can introduce residual amines from rinse aids or silicone-based antifoams; these contaminants reduce adhesion at the gate and weld line and increase environmental stress crack sensitivity. Storage at relative humidity above 60% does not require desiccant drying, but surface condensation can be conveyed into the feed throat. Pre-warming at 60 °C for 2 h is sufficient to remove surface moisture. Vacuum venting is not typically required for HCM4265 when the screw has a compression ratio between 2.5:1 and 3.0:1 and the melt temperature is kept below 230 °C.

In a production-scale injection molding cell running HCM4265 for rectangular storage boxes, the most frequently observed processing bottleneck is inconsistent fill in the last cavity of a multi-cavity runner system. When the runner diameter is below 6 mm, pressure loss from the sprue to the final gate can exceed 30% of the total injection pressure, causing short shots even when the melt-flow rate is within specification. A balanced hot-runner manifold with thermal regulation of ±2 °C per drop reduces cavity-to-cavity weight variation to below 0.5% in a well-maintained tool. Batch-to-batch variation introduced by regrind content, pigment masterbatch, or silo blending is observable as a shift in injection pressure rather than as a shift in melt-flow rate alone.

If gate blush appears on the surface of a molded pail handle, the cause is often excessive shear heating in the gate land, not the resin itself. A gate land length greater than 1.5 mm with a land diameter below 1.0 mm can raise local melt temperature to 250 °C, above the oxidative stability threshold for HCM4265. The result is a white or silver streak at the gate boundary and reduced notched impact strength in that zone. Increasing the gate diameter to 1.2–1.5 mm or reducing injection velocity near transfer is usually more effective than lowering the nozzle temperature below 200 °C, which may cause freeze-off and short shots.

The final processing boundary is residence time. HCM4265 should not remain molten at 220 °C for longer than 15 min in an idle barrel. If interruption is planned, the machine should enter a heat-soak barrel profile at 150 °C or purge with a low-melt-flow HDPE to prevent degradation products from accumulating in dead zones behind the check ring. This is particularly important for hot-runner tools in which molten resin remains in the manifold during extended breaks.