Chevron Phillips Chemical HDPE 6400 is a high-density ethylene copolymer developed for injection molding of rigid, thin- to medium-wall articles. The designation belongs to a class of high-flow HDPE grades whose melt flow index of 6.0 g/10 min under ASTM D1238 at 190 °C/2.16 kg and solid density of 0.963 g/cm³ under ASTM D1505 place it between low-melt-index blow molding resins and very high-flow thin-wall injection grades. The resin is used for pails, open-top containers, crates, totes, houseware components, caps and closures, and other applications where high fluidity shortens cycle time and improves reproduction of fine mold detail. The material is supplied as pellets and is processable on standard single-stage reciprocating-screw injection molding equipment with general-purpose screws having an L/D ratio of 20:1 to 24:1. Validation for food-contact applications should be made against the current supplier data sheet and relevant regional olefin polymer requirements such as FDA 21 CFR 177.1520 or EU 10/2011.

The melt rheology of HDPE 6400 exhibits shear-thinning typical of a medium-molecular-weight polyethylene. At injection shear rates from 1,000 s⁻¹ to 10,000 s⁻¹, the apparent viscosity is lower than that of a 0.35 g/10 min blow molding HDPE such as HDPE 5502, which reduces cavity fill pressure and permits lower clamp force selection. Melt temperatures of 190 °C to 230 °C are recommended at the nozzle; temperatures above 240 °C may produce thermal degradation and discoloration. Mold temperatures of 10 °C to 40 °C are sufficient for general-purpose articles, although surface-gloss-sensitive parts may require mold coolant temperatures near 50 °C. Pre-drying is not mandatory for dry, unopened material, but 80 °C for 2 h is recommended when regrind exceeds 30 wt% or storage relative humidity exceeds 60%.

On production-scale molding lines, HDPE 6400 has been processed using general-purpose screws with compression ratios of 2.5:1 to 3.0:1 and check-ring non-return valves. Injection pressure requirements generally fall between 80 MPa and 120 MPa, with hold pressure at 50% to 70% of peak injection pressure. Back pressure is kept at 0.3 MPa to 0.7 MPa to avoid excessive shear heating. Screw rotation speeds of 80 rpm to 120 rpm maintain melt homogeneity without generating excessive shear. Short shots and warpage in deep-draw parts have been observed when mold temperatures fall below 10 °C or when the melt cushion is maintained below 3 mm. A screw decompression of 2 mm to 5 mm after recovery is typical to prevent drooling at the shut-off nozzle.

Cavity pressure sensors positioned near the gate and end of fill are recommended for establishing switch-over. A gate pressure drop that exceeds 30 MPa may indicate undersized gates; a switch-over near 95% to 98% of total fill volume is commonly used to avoid overpacking. Injection velocities of 50 mm/s to 150 mm/s screw speed are common in medium-tonnage machines; linear velocities should be adjusted for thin-wall parts. Pack pressure time is determined by gate seal. If the gate is not sealed before plastication, melt can flow back and create sink marks. Cooling time for a 2.5 mm wall section is generally 10 s to 20 s, but published data for this specific grade in complex geometries is limited. Mold shrinkage after conditioning at 23 °C for 24 h is typically 1.2% to 2.0% in the flow direction and 1.4% to 2.2% transverse, depending on gate location and packing.

Regrind from sprues, runners, and rejected parts can be used at levels typically below 30 wt% in non-appearance-critical industrial parts if the regrind is dry, free of fines, and produced from the same grade. Higher levels may reduce elongation at break and environmental stress crack resistance; notched Izod at 23 °C may decline progressively with multiple heat histories. Published data for this specific configuration is limited for regrind cycles beyond 5. Sorting and dedusting are necessary because fines can cause feeding inconsistency and black specks. In food-contact articles, only post-industrial regrind from the same resin and clean scrap should be used, subject to the applicable food-contact regulation and the converter's legal assessment. Users should validate that regrind addition does not change organoleptic properties for taste- and odor-sensitive applications.

Warpage in flat lids or shallow open-top containers is controlled by mold temperature uniformity, gate location, and packing. Because HDPE 6400 crystallizes rapidly, a mold temperature differential across the cavity of more than 5 °C can produce anisotropic shrinkage and visible curvature. Uniform cooling lines with turbulent flow are preferred; coolant Reynolds numbers should remain above 10,000 in critical tools. Publication of design data for this specific grade in deep-draw tools is limited; therefore, short-run prototype tools should be used to measure shrinkage before cutting production steel.

What Distinguishes HDPE 6400 from Slower-Cycle HDPE and Impact-Modified Alternatives?

The primary distinction is the flow-to-stiffness balance. Compared with a high-molecular-weight blow molding HDPE having a melt flow index below 1.0 g/10 min, HDPE 6400 fills thin sections at lower injection pressure and cycles faster, but its environmental stress crack resistance under ASTM D1693 conditions is lower. This trade-off makes HDPE 6400 suitable for rigid packaging and housewares rather than aggressive chemical containers or fuel tanks. When compared with linear low-density polyethylene, HDPE 6400 has higher flexural modulus, higher heat deflection temperature, and higher surface hardness, but lower puncture resistance and lower elongation at break. Against a polypropylene homopolymer, HDPE 6400 generally shows lower flexural modulus and lower heat deflection temperature under load, but offers different low-temperature impact response and compatibility with standard polyethylene recycling streams. Within the Chevron Phillips Chemical HDPE range, grades with lower melt index and higher molecular weight are preferred where environmental stress cracking is the limiting variable; HDPE 6400 is selected where mold filling, cycle time, and dimensional stability dominate.

The difference in molecular weight also influences part surface appearance and weld-line strength. Injection molding grades such as HDPE 6400 produce shorter living hinge flex life than polypropylene; the material is not recommended for continuous flexural cycling. Dimensional stability after molding is influenced by cooling rates and mold temperature. When parts are measured after 24 h at 23 °C and 50% RH, shrinkage in the flow direction is generally 1.5% to 2.5%, with transverse shrinkage slightly higher. The resin is not intended for applications requiring extended exposure to oxidizing acids, aromatic hydrocarbons, or halogenated solvents.

The values above are typical published data and are not a product specification. End-use performance is lot-dependent and should be verified under the specific molding conditions and part geometry.

When HDPE 6400 Is Selected for Thin-Wall Rigid Packaging

Thin-wall pails and storage boxes with nominal wall thickness below 2.5 mm benefit from the high flow of HDPE 6400. The resin enters the cavity with sufficient fluidity to replicate ribs, bosses, and sealing surfaces without raising injection pressure to the clamp force limit. In a 1,200 kN to 3,500 kN hydraulic or servo-driven molding machine, the high flow reduces peak hydraulic demand and can allow lower tonnage. Mold filling analyses using standard 2.5D shell or three-dimensional tetrahedral meshes should use a density of 0.963 g/cm³ and a melt flow index of 6.0 g/10 min; however, published data for pressure-volume-temperature coefficients in this specific grade can be limited, so measured capillary rheology data or supplier-provided viscosity curves are preferred for high-cavitation tools.

Gate quality and weld lines are processing limits. End-gated containers with radial flow fronts can form a weld line opposite the gate. Tensile properties at the weld line in high-flow HDPE are lower than elsewhere; if weld-line strength is critical, mold-filling simulation and short-shot studies should be used to place the weld line in a low-stress zone. Product handles and snap-fit undercuts may require radii of at least 0.5 mm to avoid notch sensitivity and stress cracking. The use of hot runners with external heating is permitted; internal hot runners with high shear rates may cause localized melt temperatures above 230 °C, leading to degradation if residence time exceeds 5 min. Purge materials should be standard polyethylene purge grades; purging with polypropylene or acid-functionalized polymers may require complete removal to avoid delamination and contamination.

Chemical resistance follows polyethylene behavior: strong oxidizing acids, halogens, aromatic hydrocarbons, and chlorinated solvents should not be handled in HDPE 6400 under elevated temperature or sustained stress because environmental stress cracking may develop. At ambient temperature, short-term contact with many aqueous acids, bases, and salt solutions is acceptable, but stress-crack-sensitive relationships require testing for the specific formulation. Long-term outdoor service without ultraviolet stabilization is not recommended; if exposure exceeds 12 months, carbon black at 2 wt% to 3 wt% or an appropriate hindered amine light stabilizer package should be used. Steam sterilization at 121 °C is outside the continuous-use envelope; the resin may distort under load at temperatures above approximately 70 °C. Published data for repeated steam autoclave cycles is limited for this specific grade.

Incoming resin testing for injection molding typically includes melt flow index by ASTM D1238, density by ASTM D1505, and moisture content by ASTM D4672 or an equivalent loss-on-drying method. A melt flow index outside a controlled range of ±0.5 g/10 min may indicate regrind contamination or logistics-related batch mixing. Because HDPE 6400 is used in multi-material assemblies, not all performance characteristics are captured by melt flow and density alone. Users should establish a shear-thinning signature from capillary rheometry at 190 °C and 230 °C before commissioning new molds. Published data for this specific configuration is limited for dynamic mechanical performance at sub-zero conditions.

When HDPE 6400 is used for thin-wall food containers, the converter should evaluate the finished part for migration under the intended contact time and temperature rather than relying only on resin certification. The material in pellet form can comply with the compositional requirements of FDA 21 CFR 177.1520(c), but compliance of the finished article requires processing controls, no prohibited additives, and testing where applicable. For non-food industrial use, chemical compatibility with the actual contact fluid should be evaluated under stress because environmental stress cracking is not always predicted by simple cubic swelling data.