In high-heat injection-moulding programmes, Tianjin Dagu Chemical ABS DG-HR120 is specified as a heat-resistant styrene-acrylonitrile-butadiene copolymer. The grade is supplied in pellet form and is designed for rigid components requiring higher thermal deflection resistance than general-purpose DG-417 while retaining a conventional ABS processing route. Representative density is 1.05 g/cm³ per ISO 1183-1, and the melt mass-flow rate is reported as 5.0 g/10 min at 220 °C/10 kg using ASTM D1238-23a. Current manufacturer literature lists representative tensile yield stress of 46 MPa under ISO 527-2/1B/50, flexural modulus of 2450 MPa under ISO 178, Izod notched impact strength at 23 °C of 22 kJ/m² under ISO 180/1A, heat deflection temperature at 1.80 MPa of 96 °C under ISO 75-2/A, and Vicat softening temperature of 108 °C under ISO 306/B50. These values are representative and are subject to lot-to-lot variation; the certificate of analysis for each production lot should be used for final design verification.

The DG-HR120 designation indicates a high-heat architecture rather than a simple viscosity shift. The SAN phase is altered to raise glass transition behaviour, which elevates heat deflection and Vicat values, reduces melt fluidity, and slightly lowers room-temperature toughness compared with medium-flow ABS grades. The trade-off determines grade selection: DG-HR120 is assigned to interior parts that encounter paint-bake temperatures, heater radiant loads, or dark-colour solar soak conditions, while it is not a direct replacement for high-impact ABS where knit-line integrity and high-speed puncture behaviour control design.

For specification purposes, the product is normally delivered in 25 kg multi-wall bags with an internal liner, and incoming quality-control checks typically include Karl Fischer moisture, melt mass-flow rate, and colour coordinates. These checks are performed because high-heat ABS is more sensitive to moisture and thermal history than general-purpose extrusion grades.

Melt Rheology and Injection Moulding Window for DG-HR120

In production-scale injection moulding on machines of 3.0–4.5 MN clamp force, the material is processed with a nozzle melt temperature of 230–250 °C and a mould surface temperature of 60–80 °C. Pre-drying is mandatory before screw plastication. Pellets should be dried at 80 ±5 °C for 4 h in a desiccant dryer with a dew point of −40 °C or lower; the target pellet moisture is <0.05% by Karl Fischer titration or equivalent. At ambient relative humidity above 60%, drying time is extended to 6 h and hopper inlet air should be conditioned to avoid moisture re-absorption in an open feed throat. Failure to maintain this boundary condition produces splay, melt-front instability, and loss of surface gloss.

Screw geometry should use a general-purpose ABS screw with a compression ratio of 2.0–2.5:1 and an 18:1–22:1 L/D ratio. Higher compression ratios generate frictional heat and degrade the high-heat SAN phase; lower compression ratios may cause melt-temperature fluctuations. Back pressure is maintained at 0.5–1.0 MPa to homogenise the melt without excessive screw recovery time. Hot-runner tools require open-pipe nozzle tips and polished channels; dead spots and restrictive needle-valve transitions should be avoided because the high-heat grade has lower thermal stability at elevated temperature than general-purpose ABS. Recommended melt residence time at the upper temperature is ≤5 min. Purging is performed with general-purpose ABS or SAN at the end of a run. Cavity peak pressure is typically held below 50 MPa, and gate shear rate should be maintained below 1 × 10⁵ s⁻¹; above this range gate blush and delamination at the frozen skin have been observed on direct-gated parts. Published data for this specific grade under high-shear micro-moulding conditions is limited, so processing trials at the actual wall thickness remain necessary.

How Does the High-Heat Architecture Alter Impact Retention and Flow?

The heat-resistance modification changes two competing properties: the material loses a portion of its melt flow and impact ductility while gaining thermal rigidity. Compared with general-purpose DG-417, the melt mass-flow rate drops from roughly 15 g/10 min to 5 g/10 min under identical test conditions, reducing flow length by approximately 35–45% at equal wall thickness. The notched Izod at 23 °C moves from approximately 28 kJ/m² to 22 kJ/m². The differences are summarised in the comparative table below and are used by tool engineers to set gate sizes and pressure margins.

At sub-ambient temperature, the ductile-to-brittle transition shifts upward in high-heat ABS. Parts exposed to impact below −10 °C should not be designed using room-temperature toughness values. The grade retains stiffness at elevated temperature better than general-purpose ABS, but its continuous load-bearing ceiling is below the short-term HDT. Creep modulus at 80 °C is significantly lower than at 23 °C, and finite-element simulations should use time-dependent tensile creep data, not instantaneous modulus, for load-bearing ribs.

Tabulated values are representative data obtained from current manufacturer technical literature. They are not specification limits and should be verified against the lot certificate before tooling release. The comparison shows that the primary differentiator is not tensile strength, which changes by less than 10%, but thermal deflection and melt flow. Tooling decisions should therefore be based on heat deflection and melt mass-flow rate rather than stiffness alone.

Automotive HVAC door vanes and instrument-panel air outlets are typical applications where the high-heat grade replaces general-purpose ABS. The components are dark-colour, low-gloss, and often exposed to soak temperatures of 90–100 °C on finished vehicle lines. Dimensional testing under these conditions, using ISO 75-2-derived heat deflection and ISO 306 Vicat values as screening criteria, shows lower warp in DG-HR120 than in high-flow ABS. Multi-cavity tools with valve-gated hot runners are common; because melt flow is limited, gate diameters are typically 0.8–1.2 mm for wall stock of 2.0–2.5 mm, and pressure drop per unit flow length is higher than for a high-flow grade. The material also appears in rearview mirror housings, radiator grille inserts, and interior trim covers where dark colours and external solar load raise skin temperatures.

In these components, moulded-in stress affects heat distortion more than material HDT alone. Low-gloss textures should be engraved deeper than for general-purpose ABS because the high-heat melt freezes faster and may not replicate fine grain if cavity surface temperature is below 60 °C. Mould temperature uniformity of ±5 °C across the cavity is required to prevent differential shrinkage and part warpage.

When Replacing General-Purpose DG-417 in Structural Interior Carriers

When a moulder substitutes DG-HR120 for DG-417 in a structural interior carrier to meet a higher thermal specification, the existing tool can often be reused, but the process window narrows. Injection speed should be profiled to avoid hesitation marks at flow-front transitions; cavity pressure transducers are used to hold peak pressure below 50 MPa. Because the high-heat grade has a steeper viscosity response to temperature, barrel profile adjustments of 10–15 °C above the general-purpose settings are typical. However, raising the melt temperature to compensate for flow loss also reduces thermal stability margin; residence time should therefore be reduced and screw recovery speed set to avoid frictional overheating.

Shrinkage in the 2.5 mm wall range is similar to general-purpose ABS: 0.4–0.7% in the flow direction and 0.5–0.8% perpendicular. The dominant risk is not excessive shrinkage but differential shrink caused by non-uniform cooling. Cooling time may be shortened by 5–10% because the high-heat grade stiffens earlier during cooling, but ejection must not begin until the surface temperature is below the Vicat onset; hot parts are prone to distortion when removed from the core.

Chemical resistance follows the general ABS pattern: the material is unsuitable for continuous contact with ketones, esters, and aromatic hydrocarbons, which swell or stress-crack the SAN phase. Dilute acids and alkalis are tolerated at low temperature and short contact, but stress-cracking resistance depends on moulded-in stress. Machined holes, weld lines, and sharp corners increase susceptibility to environmental stress cracking; annealing at 80–90 °C for 2 h can reduce internal stress. Stress tests under constant strain in air or mild detergent solution reveal that unpainted low-gloss surfaces can develop microcrazes around screw bosses. Boss design with a hole-to-boss diameter ratio below 0.6 and generous corner radii reduces this risk. The grade is not recommended for outdoor unpainted use because ABS photo-oxidation embrittles the polybutadiene phase; UV-stabilised variants or painting are required for exterior exposure beyond 12 months. For under-hood or fluid-contact applications, testing under the actual chemical environment and strain state is required because published data for DG-HR120 in specific solvent mixtures is limited.

In small appliance housings placed near heated surfaces, DG-HR120 is used for end caps, control panels, and structural brackets. The specification process typically requires a combination of ISO 306 Vicat, UL 94 HB at 1.5 mm, and ball-pressure temperature according to IEC 60695-10-2 at 95 °C. The grade generally passes the ball-pressure requirement at the specified thickness, but certificate values should be confirmed for pigmented lots because carbon black and low-lustre additives can shift thermal resistance slightly. At wall thickness below 1.5 mm, the shorter fill length of the high-heat grade requires additional gates or increased injection pressure; direct-gated single-cavity tools with a heated sprue bushing are preferred over cold sprue drops.

Regulatory declarations are lot-specific. For electrical and electronic applications, the grade is generally offered with RoHS recast 2011/65/EU and REACH statements from the supplier, but no self-declaration replaces a supplier certificate. The flame rating is typically UL 94 HB at 1.5 mm; DG-HR120 is not an ignition-resistant system and should not be specified for enclosures requiring V–2 or better.

Auditing Dimensional Stability and Moisture Uptake

Water absorption after 24 h immersion at 23 °C is typically 0.3% by ISO 62-1. Equilibrium moisture at 50% RH is lower, but pre-moulding moisture limits are considerably below equilibrium values because process temperatures convert dissolved water into steam at the melt front. The pellet moisture target of <0.05% is verified by Karl Fischer titration; older weight-loss methods are insufficient for high-heat ABS. Moulded parts intended for automotive interior testing are conditioned at 23 ±2 °C and 50 ±10% RH for at least 24 h before mechanical testing so that moisture does not skew tensile or impact values.

Post-moulding annealing improves dimensional stability during downstream operations. Unannealed parts can show additional shrinkage of 0.1–0.2% in the first 24 h when stored at 80 °C; annealing at 80–90 °C for 2 h reduces this movement before adhesive bonding or ultrasonic welding. Fixtured cooling is required on large flat surfaces because the high-heat grade leaves the mould with a higher surface temperature than general-purpose ABS and sags if unsupported.