Material Identification and Standardized Test Data

Lotte Chemical HDPE HIVOREX CL9210 is a high-density polyethylene injection molding grade supplied as virgin pellets for high-flow mold filling in thin-wall and high-cavitation tooling. The resin is built around a narrow molecular weight distribution, which reduces high-shear viscosity while retaining sufficient stress crack resistance for closure and container applications. Lot-release melt flow rate determined by ASTM D1238 at 190°C under 2.16 kg sits in the 9–11 g/10 min band. Density measured by ASTM D1505 or ISO 1183-1 is 0.953–0.955 g/cm³, a range that places CL9210 in the rigid HDPE class with a flexural modulus above 1,000 MPa.

Representative single-point values from injection molded specimens conditioned according to ISO 291 are listed in Table 1. The values are not minimum lot-release specifications and should be used with appropriate safety factors for tool design.

When CL9210 is processed on injection molding machines with clamp forces from 80 tonnes to 500 tonnes, a melt temperature band of 190°C to 230°C and a mold surface temperature of 20°C to 50°C represent the primary set point window. Pre-drying is typically unnecessary for sealed pellet containers with internal moisture below 0.10%; if storage has exposed the resin at relative humidity above 60%, a desiccant dryer set to 80°C for 2–4 hours is recommended to prevent splay and surface defects. Back pressure should remain between 50 bar and 100 bar, with screw speed limited to 80–120 rpm to avoid shear-induced temperature overrides.

On high-cavitation closure molds with 24 to 64 cavities, the practical processing issue is not merely fill time but gate freeze control. With wall stocks of 0.6 mm to 1.2 mm, switch-over from velocity control to packing should occur at 95–99% of total fill volume. Pack pressure below 60% of peak injection pressure is associated with sink marks at the closure hinge and sealing ring. Mold temperature differentials greater than 10°C across the cavity pack are known to cause uneven gate sealing and warpage in semi-crystalline HDPE because of differential crystallization shrinkage. Melt temperatures above 230°C should be avoided because the low melt viscosity of this grade increases the risk of flash and stringing at hot runner nozzles, and thermal-oxidative degradation can increase odor and lower molecular weight. If processing is interrupted for more than 10 minutes, the barrel temperature should be reduced to 160°C or the screw should be purged with a suitable HDPE purge compound to prevent carbonized residue in the hot runner manifold.

What Narrows the Operating Window when CL9210 Is Used for Thin-Wall Rigid Packaging?

In thin-wall container mold filling, the governing parameter is not nominal wall thickness alone but the ratio of flow length to wall thickness. Cavities for tubs, cups, and closure shells often exceed a flow-length-to-wall-thickness ratio of 200:1. At this condition, injection pressure demand rises sharply because the advancing melt front cools while the core remains molten. The melt flow index of CL9210 in the 9–11 g/10 min range places it in a flow class that reduces filling pressure by approximately 15–25% relative to a 4 g/10 min HDPE injection grade, all other tooling conditions being equal.

Compared with lower-flow HDPE injection grades, CL9210 can enter gates as small as 0.5 mm in multicavity tooling without requiring melt temperatures above 220°C. The same melt fluidity, however, reduces melt strength and makes the process more sensitive to gate drool. Hot runner nozzle tips should be temperature-controlled to within ±5°C to avoid stringing and cold slug formation. Published data for the exact pressure drop across this grade in high-shear spiral flow molds is limited, but the melt-index class implies spiral flow lengths exceeding 300 mm at 1,000 bar injection pressure for a 2 mm wall thickness.

The molecular architecture of CL9210 is designed to balance crystallinity and stress cracking resistance. Density in the 0.953–0.955 g/cm³ range correlates with a crystalline fraction near 65–70% after slow cooling. This crystallinity is responsible for a flexural modulus above 1,000 MPa but also for post-mold shrinkage of 1.5–2.5% in flow direction and 1.0–2.0% in transverse direction. Tooling dimensions should be adjusted for this shrinkage range. Parts measured before 24 hours post-molding may not reflect final dimensions because ambient annealing continues for up to 48 hours.

When CL9210 Replaces Polypropylene Random Copolymer in Closure Systems, Sealing Force Retention and ESCR Become Comparative Criteria

Converter evaluations of CL9210 as a replacement for polypropylene random copolymer in closures must begin with liner compatibility and torque retention on the actual production tool. The semi-crystalline nature of CL9210 produces higher modulus than PP random copolymer but also a more pronounced relaxation rate at elevated temperatures above 40°C. Sealing force retention is therefore evaluated by short-term stress relaxation or creep of the HDPE shell, which may be characterized by ASTM D2990 tensile creep at 23°C or by closure-specific torque decay methods. Closure liners and tamper-evident band slitting should be validated on a 32-cavity or 64-cavity hot runner stack mold, because laboratory-scale molding does not reproduce gate orientation and weld-line location.

The substitution rationale is usually stiffness per unit weight and hinge life in integral hinges. However, CL9210 has lower notched impact at 23°C than PP random copolymer and lower continuous-use temperature. Environmental stress crack resistance of the HDPE grade must be confirmed separately in the intended contact medium, because fatty food simulants and surface-wetting agents can accelerate crack propagation in stressed closure regions. Published data for this specific CL9210 configuration is limited; final approval should be based on production-run capability studies rather than single-point laboratory data.

Under food-contact regulatory frameworks, HDPE HIVOREX CL9210 is typically evaluated against 21 CFR 177.1520 for olefin polymers, which covers the base polymer and does not automatically clear colored or additive-modified compounds. The finished article must satisfy the extractives limitations for its intended food type and use condition. In the European Union, plastic food-contact materials must meet the overall migration limit of 10 mg/dm² under EU Regulation (EU) No 10/2011, with specific migration limits for any authorized additives used in the compound. The grade is not designed for prolonged continuous service above 70°C under load, so hot-fill and boiling-water exposure require separate validation under the appropriate food-simulant conditions.

For non-food technical articles, RoHS Directive 2011/65/EU restricts lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE to 0.1% by weight in homogeneous materials. Typical virgin HDPE compounds meet these thresholds without formulation restrictions, but regrind sources must be controlled. REACH compliance requires the supplier's confirmation of SVHC content below 0.1% by weight per article. CL9210 should not be stored or conveyed with strong oxidizing agents, chlorinated solvents, or aromatic hydrocarbons, because these can swell or oxidize the polymer surface. At processing temperatures above 250°C, thermal degradation can generate low-molecular-weight species and increase odor; the resin should not be over-purged with PVC or acetal residues in the barrel.