Thin-wall dairy packaging remains the highest-volume injection moulding segment for LG Chem HDPE SM5500 because the grade’s high melt flow permits cavity filling in stack moulds with wall sections between 0.35 mm and 0.80 mm. The grade is specified with a melt flow rate in the 50–60 g/10 min range under ISO 1133-1:2022 at 190 °C/2.16 kg, and density between 0.960 g/cm³ and 0.964 g/cm³ by ISO 1183-1. On a 200–350 t toggle-clamp injection moulding machine with screw diameter 40–60 mm and L/D 20:1–25:1, barrel-zone setpoints are commonly 190–220 °C, the hot-runner manifold is held at 210–235 °C, and the chilled-water mould is controlled at 8–25 °C. Injection velocity profiles range 120–220 mm/s; peak filling pressure typically falls between 800 bar and 1,200 bar, measured at the nozzle rather than the hydraulic circuit. Hold pressure is set at 50–70 % of peak cavity pressure, with hold time 0.4–1.2 s for thin sidewalls and 1.0–2.0 s for rim-heavy lid geometries. Screw rotation backpressure is kept at 5–10 bar to avoid excessive melt shear heating; screw recovery should complete before the cooling timer expires to prevent idle time on the clamp. For food-contact white dairy tubs, the compound is let down with 2–4 wt% TiO₂ white masterbatch in an HDPE carrier and 0.5–1.0 wt% slip/antiblock masterbatch, keeping total additive loading below 5 wt% to prevent plate-out on core pins and inconsistent colour dispersion. Shrinkage allowance is 1.2–1.8 % in flow and 1.0–1.5 % cross-flow, adjusted after cavity-pressure studies because high hold stress in thin ribs can produce post-mould warpage. Compliance follows FDA 21 CFR §177.1520(c) 2.1, EU 10/2011, and the overall migration limit of 10 mg/dm² for the finished article. Terminal parts include 250 mL dairy cups, 500 g margarine tubs, dessert cups, and snap-on lids for fresh dairy packaging.

How Does SM5500 Respond to High-Cavitation Closure Moulds with Undercut Stripping?

Under high-cavitation closure production, SM5500 fill behaviour reduces the hydraulic pressure required to fill 28 mm and 38 mm closure shells, but the high melt flow demands nozzle shut-off and post-plastication decompression of 2–4 mm to control drool at the sprue bushing. A 64-cavity cold-runner mould with edge gates of 0.6–1.2 mm diameter per cavity produces fill times of 0.3–0.8 s at melt temperatures 210–235 °C. Mould temperature is held at 10–20 °C, and closure ejection is timed after seal-ring formation but before the part reaches full ambient crystallisation to avoid undercut damage. Screw backpressure is limited to 5–12 bar; barrel profile is 190/210/215/220/220 °C from feed to nozzle. Hold pressure is set to 60–80 % of dynamic filling pressure for 0.8–2.0 s, and total cycle times on 250–350 t machines range 6–12 s for single-piece closure shells. Formulation for non-barrier closures uses 100 parts SM5500 with 1–2 wt% slip masterbatch and 0.2–0.5 wt% processing antioxidant; coloured closures add 2–3 wt% colour masterbatch. The grade is not specified for carbonated soft-drink closures without a barrier liner or PP/PCO neck geometry because steady-state CO₂ permeability through HDPE is too high for long shelf-life carbonation retention. Food-contact closure shells are evaluated under FDA 21 CFR §177.1520 for olefin polymers, EU 10/2011, and taste/odour migration testing methods such as EN 1622. Terminal products include tamper-evident water, dairy, and ready-to-drink beverage closures with breakaway bridge dimensions below 0.35 mm.

When SM5500 is moulded into open-top industrial pails, the primary processing conflict is balancing high flow for fast fill against gate blush and jetting created by small sprue gates. Direct sprue or diaphragm gating with gate diameter 2.5–4.0 mm is standard for wall thickness 1.5–3.0 mm; smaller gates produce splay, rippling, and reduced top-load strength at the injection point. Barrel temperatures are set at 180–210 °C, mould temperature 10–25 °C, fill time 1.5–4.0 s, hold time 8–15 s for 10 L pail geometry, and cooling time 12–25 s depending on wall stock. For outdoor and pigmented pails, the formulation is 100 parts SM5500 with 2–5 wt% UV-stabilized masterbatch and 2–3 wt% colour masterbatch; in-plant regrind from cold-runner sprues is reincorporated at 10–20 wt% after melt-flow verification because repeated heat histories can shift the flow distribution and reduce pail sidewall impact strength. Drop testing at -18 °C after conditioning for 48 h is commonly performed according to ASTM D5276; UN dangerous-goods pails are additionally assessed under ADR 6.1.5 or equivalent national transport packaging certification. The high melt flow of SM5500 reduces environmental stress crack resistance relative to high-molecular-weight bimodal HDPE, so pails for aggressive solvents or continuous chemical contact above 40 °C should be validated by ASTM D1693 on the actual finished part before commercial release. Published ESCR data for this specific grade in aggressive solvent environments is limited, and finished-part testing is required. Terminal products include 5 L, 10 L, and 20 L open-top pails for water-based paints, food powders, mineral fillers, and construction chemicals.

Stacking Creep and Gate-Freeze Rates in Crate and Tote Processing

Multiple-gated crate and tote tools using SM5500 are more sensitive to knit-line impact loss than lower-flow HDPE grades because the melt front temperature drops rapidly across the long flow path. Sequential valve-gate hot runner systems with 4–8 drops are used for parts with wall thickness 1.5–3.5 mm; gate opening is sequenced at 0.2–0.5 s intervals to move the flow fronts together. Melt temperature at the nozzle is maintained at 190–220 °C, with mould temperature 15–35 °C; fill velocity is reduced to 60–150 mm/s for large shot weights to prevent flow hesitation between gates. Total cycle time for 30 L warehouse totes is typically 30–55 s on machines with clamp force 500–800 t. The formulation uses 100 parts SM5500 plus 3–5 wt% colour masterbatch, with up to 20 wt% clean in-house regrind; addition of 0.1–0.3 wt% nucleating agent can shorten demould time, but must be validated against top-load retention and impact after 48 h oven ageing at 60 °C. Stacking load retention for filled crates is evaluated under ISO 12048 compression conditions or ASTM D642; corner postbuckling rather than mid-panel creep usually limits the practical stack height. Terminal products include beverage crates, warehouse totes, folded container sidewalls, and institutional storage bins.

When Living Hinge Geometry Is Applied to SM5500 in Kitchenware

SM5500 is processable in kitchen storage boxes and trays, but its high-flow HDPE molecular structure is not the primary choice for integral living hinges thinner than 0.25 mm because repeated flexural fatigue under standard kitchen-use deflection can produce whitening and cracking before polypropylene homopolymer counterparts. Published flex-fatigue data for this specific high-flow HDPE grade in living-hinge configurations is limited, so hinge life must be tested on the actual moulded hinge rather than extrapolated from general polyolefin data. If a hinge is required, the hinge web should be 0.25–0.40 mm thick with a notch radius no tighter than 0.2 mm, and the tool should be gated away from the hinge to preserve molecular orientation across the line of flex. Gloss-surfaced containers are produced with melt temperatures 200–220 °C, mould temperatures 30–50 °C, and extended cooling time 10–25 s to reduce sink marks around thick rims; thin wall areas are filled at 80–160 mm/s. Formulation for food-adjacent kitchenware uses 100 parts SM5500 with 1–3 wt% slip/anti-scratch masterbatch and 1–2 wt% colour masterbatch; when the articles are intended for repeated food contact, migration testing follows EN 1186 series conditions appropriate to the food simulant. Terminal products include cereal storage boxes, refrigerator organizers, kitchen bowls, lids for dry-food canisters, and trays with snap-fit features.

Laboratory consumables moulded from SM5500 are limited to non-implantable, single-use or reusable diagnostic and general labware where high injection productivity and resistance to aqueous buffers are primary requirements. The chosen melt temperature window is 190–210 °C, with mould temperature 10–25 °C on 120–250 t injection moulding machines equipped with screw diameter 35–60 mm. Tools are run in ISO 14644-1 Class 8 or cleaner cleanrooms when the moulded part is used as a diagnostic consumable. The formulation uses 100 parts SM5500 with 0.5–1.0 wt% internal antistatic masterbatch where powder handling necessitates static dissipation; slip additives are kept below 0.5 wt% because surface bloom can alter contact angle and interfere with reagent deposition or label adhesion. Cytotoxicity and irritation screening are commonly conducted under ISO 10993-5 and ISO 10993-10 for diagnostic disposables, while EU 2017/746 applies to in-vitro diagnostic medical device components. Terminal products include specimen containers, single-use scoops, cuvette trays, reagent reservoirs, and packaging inserts for in-vitro diagnostic kits.