Dow HDPE IP-22 is a high-flow injection-moulding grade of high-density polyethylene. The manufacturer’s published nominal melt flow index is 22 g/10 min when measured at 190°C under a 2.16 kg load in accordance with ASTM D1238-20 or ISO 1133-1:2022, and the nominal density is 0.954 g/cm³ according to ASTM D792-20 and ISO 1183-1:2019. Because the melt flow index is high for HDPE, the resin fills thin sections at comparatively low injection pressure but exhibits lower melt strength than extrusion blow-moulding or pipe grades. On standard reciprocating-screw injection moulding machines with a screw L/D of 20:1 to 24:1, a compression ratio of 2.5:1 to 3.0:1, a check-ring non-return valve, and clamp forces from 100 to 600 tonnes, the grade is processed for thin-wall containers, caps, closures, housewares, and industrial crates. The melt temperature is normally maintained from 190°C to 230°C, and the mould circuit is held at 20°C to 40°C. These values are typical process windows; they are not intended to replace part-specific tooling trials.

What published property profile governs specification of Dow HDPE IP-22?

The datasheet for IP-22 is organised around melt flow, density, short-term mechanical strength, and thermal service temperature. The values shown below combine the manufacturer’s nominal flow and density data with property ranges documented for high-density polyethylene injection-moulding grades of similar flow. Mechanical values are sensitive to specimen preparation, cooling rate, and fill orientation; a single-point value without an accompanying test method is insufficient for part design.

The tensile and flexural ranges are derived from material-class behaviour at 23°C and 50 mm/min test speed; they should not be used as guaranteed specification limits. For load-bearing design, the relevant test methods are ISO 527-2:2012 for tensile properties and ISO 178:2019 for flexural modulus. The listed Charpy impact band is measured on notched specimens at 23°C; at 0°C the same family of grades typically shows a measurable reduction, and sub-zero loading should be confirmed by part-level impact tests. The Vicat softening temperature of 120–127°C indicates that parts are not suitable for continuous immersion in boiling water or steam sterilisation; hot-fill packaging above 80°C requires structural side-wall ribs and may require a higher-density or higher-crystallinity grade. Long-term creep and fatigue data for this specific grade are not routinely published; structural parts should therefore be evaluated under ISO 899-1:2017 for tensile creep or ASTM D2990-17 for creep rupture. Environmental stress crack resistance is lower than that of pipe or blow-moulding grades; if detergent or aggressive surfactant exposure is expected, ESCR should be screened under ASTM D1693-15 or ISO 22088-3:2006.

Injection-moulding trials on machines with a screw diameter of 40–60 mm and a check-ring non-return valve have shown that IP-22 can produce cycle-time reductions relative to lower-flow HDPE grades when the same mould and wall thickness are used. The high melt flow index allows lower injection velocities during filling; a class-typical velocity of 150–250 mm/s on a 50 mm screw is often sufficient for thin-wall containers of 0.8–1.5 mm nominal wall thickness. Injection pressure for high-flow HDPE in thin-wall tools usually falls between 70 and 120 MPa hydraulic pressure, but this depends on material viscosity, melt temperature, gate diameter, and part geometry; short-shot studies should define the final velocity profile. Clamp force requirements for this class of HDPE are typically 0.4–0.6 tonne/cm² of projected part area. When processing IP-22, shot size should be kept between 50% and 70% of barrel capacity to limit residence time and avoid thermal degradation. If a colour masterbatch is used, it should be selected for HDPE and metered at 2–5% by weight; higher additive loadings can shift melt flow and gate-seal time.

Because HDPE is not hygroscopic, drying is not required at ambient relative humidity below 60%. Surface condensation on pellets stored in unheated warehouses can introduce moisture and cause splay on moulded surfaces; in that case a short pre-drying step at 80°C for 1–2 hours in a desiccant or hot-air hopper dryer can be used. Drying should not exceed the resin supplier’s maximum recommended temperature to avoid pellet agglomeration in the hopper.

Melt temperature, residence time, and oxidative stability constraints on production lines

The practical melt-temperature window for IP-22 is governed by two opposing failure modes. At temperatures below 190°C, the viscosity remains high enough to produce surface flow marks and short shots in thin-wall tools; at temperatures above 230°C, oxidative degradation may begin to lower elongation at break and can produce discoloration streaks. On production lines, the extruder barrel is commonly profiled from 170–190°C in the feed zone to 200–220°C in the metering zone and nozzle. Residence time at melt temperature should not exceed 5 minutes per cycle; longer residence times, especially with a smaller shot and a large barrel, increase the risk of gel formation and black specks. The use of a shot size below 50% of barrel capacity is therefore discouraged, and any interruption longer than 15 minutes should be managed by reducing barrel temperature or purging with a stabilised HDPE.

Oxidative stability in processing can be monitored by melt flow drift. A melt flow index increase of more than 10–15% after multiple extruder passes indicates molecular weight reduction; this is a practical quality indicator, although it does not replace accelerated ageing data. For long-term outdoor exposure, natural HDPE has limited ultraviolet resistance. If IP-22 is used in crates or pallets stored outdoors, a UV stabiliser package such as a hindered amine light stabiliser and carbon black at 2.0–2.5% weight can be introduced by compounders, but the final weathering performance must be verified under ISO 4892-2:2013 or ASTM D2565-23 against the part’s intended service life. Without stabilisation, tensile impact and elongation decline can appear within one to two years of continuous outdoor exposure in high-UV climates.

The mould surface temperature should be held within a narrow band around the validated centre. For thin-wall parts, reducing the mould temperature from 35°C to 25°C shortens cooling time but can increase frozen-in orientation and warpage. Increasing the mould temperature above 40°C can raise cycle time without proportional improvement in surface finish. The processing window of ±5°C around a validated mould temperature is often used on production lines to prevent dimensional variation across batches.

Food-contact applications require grade-specific documentation. High-density polyethylene may be evaluated for direct food contact under FDA 21 CFR 177.1520 for substances used as basic components of single and repeated use food contact surfaces, or under Regulation (EU) No 10/2011 with its associated migration limits. Compliance is not a resin property; it depends on monomer content, additives, colour concentrates, and the final article’s surface-to-volume ratio. For electrical and electronic equipment housings, the supplier can provide declarations covering the RoHS Directive 2011/65/EU and REACH Regulation (EC) No 1907/2006, but these declarations are lot-specific and should be renewed for each supply chain.

IP-22 is not a candidate for solvent storage or automotive fuel tanks because high-density polyethylene swells in aromatic and chlorinated hydrocarbon environments. The resin should not be processed with copper-containing pigments or active transition-metal salts that can accelerate thermo-oxidative chain scission; if release from mould surfaces is marginal, the use of an external mould release is preferable to increasing melt temperature.

When existing low-flow HDPE tooling is converted to a 22 g/10 min melt

Existing tools designed for HDPE grades with a melt flow index of 6–10 g/10 min require systematic re-qualification when IP-22 is introduced. The higher melt flow reduces cavity filling pressure but also allows the melt to reach the end of the cavity before the air path has fully vented. Burn marks at the vented end of a part are typically caused by compression of residual air; reducing the injection velocity by 20–30% or increasing vent depth to 0.02–0.03 mm often resolves the defect. Because the gate freezes at a different rate, the pack-and-hold profile should be shortened. A gate that remains open too long can lead to over-packing and sink marks; a gate that freezes too quickly can cause excessive shrinkage in thick sections. Short-shot series should be run at 5% increments from 80% to 100% of fill to establish the fill point and then used to set packing pressure.

The clamp force required for a tool may be lower with IP-22 than with a lower-flow HDPE because the injection pressure needed to fill is lower. However, mould deflection and flash formation are more strongly affected by pack pressure than fill pressure, so clamp force should not be reduced until flash and vent conditions are stable. In multi-cavity tools, naturally balanced runner systems are preferred over artificially balanced runners because high-flow HDPE is more sensitive to flow-length differences. A cavity-to-cavity fill imbalance of 1–2% by weight can be amplified by the high flow and result in variable part mass; monitoring shot weight and cavity pressure sensors with a tolerance of ±0.5% provides a practical control boundary.

Comparison with adjacent high-flow HDPE injection-moulding grades

Within injection-moulding HDPE, IP-22 differs from lower-flow grades by reduced injection pressure and shorter filling time, and from higher-flow grades by better melt integrity and dimensional control. The following comparison is based on nominal melt flow index classifications and observed production behaviour; specific mechanical property data should be obtained from the current manufacturer datasheet.

For caps and closures, IP-22 can replace lower-flow HDPE when the part has a thin tamper-evident band and a deep draw; the high melt flow allows the band to fill without excessive injection pressure. The trade-off is a more brittle hinge if the hinge is repeatedly flexed at low temperature; hinge life must be confirmed by flex testing at -10°C to 5°C under part-level conditions, because standard laboratory notched impact tests do not replicate closure hinge fatigue. For industrial crates with wall thickness above 3 mm, lower-flow HDPE may be preferred unless cycle time is the dominant constraint.

The absence of high melt strength makes IP-22 unsuitable for extrusion blow moulding, injection blow moulding, and foamed profiles. It is not a pipe resin and does not carry a hydrostatic stress rating such as those used in ISO 9080:2012 or ASTM D2837-22. For applications requiring chemical resistance under sustained hoop stress, a bimodal HDPE pipe grade with a high-density fraction and an MFR below 1 g/10 min is used instead.