FREP HDPE HDI6180 is a high-density polyethylene injection grade produced by Fujian Refining & Petrochemical Co., Ltd. at the Quanzhou integrated refining and petrochemical site. The material is supplied as white lenticular pellets and is intended for high-speed injection moulding of rigid articles in which thin-wall filling, rapid release, and dimensional consistency are required. The grade designation identifies the polymer family (HD), injection processing (I), and a nominal melt mass-flow rate of 18 g/10 min when tested at 190 °C under 2.16 kg according to ISO 1133-1:2022. The density is 0.961 g/cm³ according to ISO 1183-1:2019. These two values position HDI6180 in the high-flow, high-density segment of the FREP polyethylene portfolio, distinct from blow moulding, film, and pipe grades.

Material Identity and Specification Set

Table 1 lists producer-reported typical properties. The properties are measured on compression-moulded or injection-moulded specimens prepared according to the test method indicated. Values may change with pigmentation, regrind content, and processing history. The data should not be used for design without article testing.

The values in Table 1 are producer-reported typical values, not specification limits. Batch-to-batch variation in melt mass-flow rate of ±1 g/10 min may be observed within the producer's release window. Article dimensions and mechanical responses should be validated on production equipment because injection speed, cooling rate, and regrind content affect final properties.

On injection moulding machines with general purpose HDPE screws of 20:1 to 25:1 L/D and compression ratios of 2.5:1 to 3.5:1, HDI6180 is typically processed with barrel settings of 180–230 °C and nozzle temperature of 200–220 °C. For screw sizing, a melt density of 0.74 g/cm³ at 200 °C is used in shot weight calculations; neglecting melt density can cause short shots in thin-wall tools. The cooling water inlet to the mould is maintained at 20–40 °C; for thin-wall containers, the lower half of that range reduces cycle time but increases molecular orientation and residual stress. Local injection velocity at the melt front of 120–250 mm/s is used for wall sections of 0.7–1.2 mm. Under these conditions, fill time for a flow length of 150 mm at 1.0 mm wall thickness is normally below 0.5 s if gate diameter is at least 0.8 mm. Screw recovery should be completed within the cooling time so that melt residence time at 220 °C does not exceed 5–8 min at maximum throughput; longer residence in the barrel shifts the molecular weight distribution and increases the generation of oxidation products. Capillary rheometry on a twin-bore rheometer with a 20:1 L/D round-hole die at 200 °C indicates that shear-thinning behaviour is moderate. The apparent viscosity at 1,000 s⁻¹ is below 100 Pa·s, although the exact value depends on the stabiliser package and sample thermal history. This low viscosity permits filling of long flow paths but requires close control of the mould parting line, because the same low viscosity increases flash tendency.

What Distinguishes HDI6180 from Lower-Flow HDPE Grades?

Compared with HDPE grades for extrusion blow moulding, pipe extrusion, or blown film, HDI6180 has a higher melt mass-flow rate and narrower molecular weight distribution. A blow moulding HDPE with an MFR of 0.3–1.0 g/10 min at 190 °C/2.16 kg retains high melt strength and parison sag resistance, which are required in extrusion blow moulding. In contrast, an MFR of 18 g/10 min gives lower viscosity and shorter relaxation time, reducing injection pressure demand but also lowering melt strength. In spiral flow testing, the high-flow material fills longer flow paths at a fixed pressure, but in extrusion blow moulding it produces excessive parison drawdown. The narrow molecular weight distribution reduces die swell, which is beneficial for injection-moulding dimensional stability but limits melt strength for blow moulding. This is the main boundary with other FREP HDPE grades; HDI6180 is not intended for blow moulding or large-diameter pipe extrusion.

For snap-fit closures and tamper-evident caps for non-carbonated products, HDI6180 is processed with cavity pressures of 40–60 MPa and mould temperatures of 15–25 °C using multi-cavity cold-runner tools. A 1.5 g closure can be demoulded after 3–6 s cooling when the mould is equipped with balanced water circuits. Because the grade has high crystallization rate, gate freeze time is short; holding pressure must transfer before the gate freezes, usually within 0.3–0.8 s after fill. Shrinkage after 48 h at 23 °C is anisotropic: 1.5–2.0% in the flow direction and 2.0–2.5% transverse to flow. The tamper-evident band dimensions are therefore cut with flow orientation considered. For carbonated beverage closures, long-term stress crack resistance under internal pressure requires a different grade with higher molecular weight or a nucleated PP; published data for this specific configuration is limited and closure qualification must include burst and ESCR testing under ISO 22088-2:2006 or equivalent.

When Thin-Wall Rigid Packaging Is Moulded at High Speed

Multi-cavity tools with 8–16 cavities and cycle times below 6 s require the melt to fill at low pressure but also demand consistent ejection under minimal draft. HDI6180 in a 1.0 mm sidewall container can be filled with hydraulic injection pressure below 80 MPa at melt temperature 220 °C when the gate is correctly dimensioned and the tool is vented. Vent depths for HDPE are normally 0.02–0.04 mm; insufficient venting causes diesel burn marks and short shots. For stack moulds or tools with hot-runner valve gates, the valve pin should close after holding pressure is decayed to 20–30 MPa cavity pressure. Differential cooling of more than 5 K across a cavity produces visible sink or warp; water circuit balancing within ±2 K is required. The use of a 0.05 mm release taper per side is recommended for textured sidewalls. On a 350 t toggle clamp machine with a 12-cavity hot runner producing 0.9 mm wall dairy cups, ejection of stable parts is typically reached after 4–6 cycles when all cavity wall temperatures are within ±1 K. If one circuit is offset by 4 K, parts from those cavities exhibit rim ovality above 1.0 mm and altered closure fit.

Compared with polypropylene impact copolymers used in similar thin-wall packaging, HDI6180 has lower flexural modulus and lower heat deflection temperature. The flexural modulus of 1050 MPa is below typical PP impact copolymer values of 1200–1500 MPa. The higher low-temperature ductility of HDPE is employed for cold-chain trays and freezer containers, where PP impact copolymers may exhibit a ductile-to-brittle transition near 0 °C. However, HDI6180 shows greater shrinkage anisotropy and lower hot-fill capability. Injection moulding tools designed for PP cannot be assumed to produce identical dimensions with HDI6180; article dimensional verification must be performed on the qualified tool.

Where articles are intended for contact with dry, aqueous, acidic, or fatty food, the producer supplies a conformity statement based on GB 4806.7-2016 and Regulation (EU) No 10/2011 where applicable. Users must perform overall migration testing on the final article according to GB 31604.1-2015 and GB 31604.8-2021 or EN 1186-1:2002. Specific migration limits are food-simulant dependent. The grade is supplied with a REACH registration under Regulation (EC) No 1907/2006 and is generally suitable for articles within the scope of RoHS Directive 2011/65/EU, but lot-specific certificates should be obtained. For pharmaceutical packaging, pharmacopoeial testing of extractables is article-specific and not covered by the raw material certificate.

The additive package of HDI6180 comprises a phenolic antioxidant and an acid scavenger system selected for melt stabilization during injection moulding. At recommended melt temperatures, discoloration is minimal through five heat histories. At melt temperatures above 260 °C, the stabilizer system may be consumed rapidly, producing yellowing and a shift in melt flow rate. Processing equipment should be purged with low-flow HDPE or PP after shutdown to prevent carbonized deposits in the barrel. A thermal purge compound is not required for routine changes.

Hot-runner valve-gate systems reduce gate vestige and enable sequential filling in multi-cavity tools. When HDI6180 is processed through a heated manifold with melt channel diameters of 12–16 mm, pressure loss at 220 °C is typically 5–10 bar per 100 mm of channel at the injection rate used for thin-wall packaging. The actual loss should be measured with pressure transducers at the nozzle and cavity, because hot-runner pressure-drop curves may assume a Newtonian base resin at a fixed shear rate. Sequential valve pin opening should be offset by 0.05–0.10 s; earlier opening can produce flow hesitation lines in parts with wall thickness below 0.8 mm.

Regrind of sprues and runners may be reused under controlled conditions. Clean in-house regrind is commonly added up to 20 wt% for general rigid articles and up to 30 wt% for non-food industrial parts. Re-extrusion increases melt flow rate and reduces tensile yield stress; after five closed-loop regrind cycles at 220 °C, the MFR can increase by 10–20%. Mixtures containing oil, ink, or adhesive contamination must not be added. The use of regrind in food-contact articles must be controlled under Regulation (EU) No 10/2011, Article 6, and under GB 4806.7-2016; food-contact approval remains valid only if the regrind stream is sourced from the same material and proven not to introduce contaminants.

Operational Boundaries and Mould Design Limitations

HDI6180 is not recommended for continuous service above 60 °C where high creep resistance is required. The Vicat softening temperature of 125 °C is not a continuous-use temperature; it indicates short-term softening under a defined needle load. Creep modulus decreases with service temperature and stress level; designers should use creep rupture data generated to ISO 899-1:2017 for load-bearing applications. In aggressive chemical environments such as strong oxidizing acids, aromatic hydrocarbons, or chlorinated solvents at elevated temperatures, the material can soften, swell, or stress crack. Applications involving alcohols above 50 °C should be tested for environmental stress cracking. HDPE of this type is inherently flammable and should not be exposed to open flame.

Long-term contact with strong mineral acids, especially nitric acid above 20 wt%, is not recommended at temperatures above 40 °C. Aromatic hydrocarbons such as toluene and xylene cause swelling, and halogenated solvents can induce stress cracking. For chemical tank or drum applications, chemical resistance must be verified using ISO 175:2010 with the actual chemical formulation; the raw resin certificate does not cover fabricated article performance.