Lotte Chemical ABS HR-5335 is an unfilled heat-resistant acrylonitrile-butadiene-styrene resin grade within the manufacturer’s ABS portfolio. The grade is specified for injection-moulded parts that must retain dimensional accuracy under warm air or radiant heat, including automotive interior air ducts, heater housings, and electrical enclosures. Product specification values are normally reported according to ASTM D792-20 for density, ASTM D1238-20 or ISO 1133-1:2022 for melt flow behaviour, ASTM D638-14 or ISO 527-2:2012 for tensile properties, ASTM D790-17 or ISO 178:2019 for flexural modulus, ASTM D256-23 or ISO 180:2023 for notched Izod impact, ASTM D648-18 or ISO 75-2:2013 for deflection temperature under load, and ASTM D1525-17 or ISO 306:2013 for Vicat softening temperature. Grade-specific values should be obtained from the current manufacturer datasheet because colour concentrates and production lot variation can shift measured values within test tolerance.

HR-5335 is supplied as ready-to-inject pellets; no downstream compounding or pellet blending is required for conventional moulding.

What Distinguishes HR-5335 from General-Purpose and High-Impact ABS Grades?

The principal difference is elevated resistance to deformation under load at temperature. General-purpose ABS grades usually exhibit heat-deflection temperatures in the 75–85 °C range under 1.82 MPa; heat-resistant ABS products such as HR-5335 move the equivalent value upward, commonly into the 88–105 °C band. This change is achieved by modifying the styrene-acrylonitrile matrix, often with α-methylstyrene-containing copolymer or maleimide-type comonomer. The same modification raises melt viscosity and narrows the usable processing window. Compared with high-impact ABS, HR-5335 should be expected to provide a lower room-temperature notched Izod value but better retention of part geometry after a thermal soak. The butadiene rubber phase in high-impact grades increases energy absorption; the high-heat matrix in HR-5335 increases thermal rigidity. Therefore, high-impact ABS moulding parameters should not be transferred directly to HR-5335 without verifying flow-length and gate-pressure requirements.

The comparison values in this table are category-level ranges taken from commonly published commercial ABS datasheets; they are not a substitute for the HR-5335 lot certificate.

In heat-resistant ABS chemistry, the replacement of styrene by α-methylstyrene in the continuous SAN phase changes the thermal response of the matrix and the transition from melt to solid. Practical barrel temperature should normally be set between 230 °C and 260 °C, with mould temperature between 60 °C and 80 °C, unless the supplier’s process guide states otherwise. The processing window is narrower than that of a general-purpose ABS because the lower limit is determined by the viscosity needed to fill thin walls, while the upper limit is set by thermal degradation of the polybutadiene phase. At excessive barrel temperature or residence time, yellowing and surface gloss loss appear first. Published data for HR-5335-specific residence-time limits is limited; therefore, the practical maximum should be established on the target machine by purging at the highest permitted temperature and measuring ΔE and gloss stability. That evaluation should be repeated for each colour concentrate and masterbatch blend.

Rheological Demand in Reciprocating-Screw Injection Machines Overrides Standard ABS Settings

On production-scale injection machines, heat-resistant ABS products of this class show lower flow length than high-flow grades at the same wall thickness. Screw recovery time, fill pressure, and clamp force demand increase. A screw with a compression ratio between 2.2:1 and 2.8:1 and a length-to-diameter ratio of 20:1 or higher should be run in the lower half of the screw speed range to avoid shear overheating. Injection speed should be high enough to prevent premature gate freeze-off, but not so high that shear heating at the gate creates burn streaks or delamination. Flow-length-to-wall-thickness ratio may fall by approximately 10–20% relative to a high-flow ABS grade, although the exact reduction is tool-specific. Melt viscosity can be measured by capillary rheometry according to ISO 11403-1 and fitted to a Cross-WLF model for filling simulation. The simulation should include actual gate geometry and hot-runner temperature profile because small changes in gate diameter strongly affect shear heating and freeze-off time.

Before processing, moisture removal is critical. Unfilled ABS should be dried in a desiccant dryer with a dew point of -30 °C or lower at 80 °C for 3–4 h. If plant relative humidity exceeds 60% or hopper residence is interrupted, splay marks may appear at the flow front. Maximum residual moisture for unfilled ABS is generally cited at 0.05–0.10% by weight. The failure is not hydrolysis; absorbed water vaporises during injection and disrupts weld-line integrity. Defects often appear first at the end of fill in ribs and bosses, where flow-front pressure is lowest. A dew-point monitor is required because a heated hopper without desiccant regeneration cannot dry the resin under humid ambient conditions.

Property Specifications and Corresponding Test Methods

The table below identifies the controlling test methods for specification work. The supplier’s technical data sheet remains the primary source for HR-5335 numerical values.

Unfilled heat-resistant ABS in this class is commonly reported at a density near 1.06 g/cm³; the exact HR-5335 value should be checked against the certificate. The product’s heat resistance should not be interpreted as flame-retardant capability. If an application requires UL 94 V-0 at 1.5 mm, an unmodified heat-resistant ABS may not meet that requirement, and a purpose-designed flame-retardant ABS or PC/ABS blend should be evaluated instead. Similarly, unless the datasheet identifies a UV-stabilised variant, unpainted parts in direct outdoor sunlight may show chalking and gloss loss. Regulatory status should be verified from the supplier’s statements under REACH 1907/2006 and RoHS 2011/65/EU as amended. HR-5335 should not be assumed suitable for food-contact articles unless explicitly listed under EU 10/2011.

Automotive HVAC applications use heat-resistant ABS such as HR-5335 for blend-door sectors, actuator housings, and duct flanges. These parts must survive repeated cycling from -30 °C to 90 °C while resisting creep under spring clips and threaded inserts. Heat aging should be evaluated according to ISO 188 or ASTM D3045-21, followed by tensile or impact retention testing. Sharp internal corners in clip towers should be avoided because the higher matrix stiffness of heat-resistant ABS can localise stress. Weld lines around holes and bosses may exhibit lower strength than the base material; gate placement should be adjusted to move weld lines away from high-stress locations. Mould shrinkage measured to ASTM D955-21 generally falls in the 0.4–0.7% range for unfilled ABS; maintaining a cushion of 3–6 mm and sufficient hold pressure is more effective than raising melt temperature for controlling post-mould dimensions.

When HR-5335 Replaces a High-Flow ABS in an Existing Hot-Runner Tool

The first observed deviation after substituting HR-5335 into a tool originally balanced for high-flow ABS is usually a longer filling stage and increased peak injection pressure. The hot-runner manifold temperature may need to be raised by 10–20 °C above the original setpoint, but this increase expands the risk of stagnation in dead spots and subsequent black-speck formation. A more reliable approach is to re-balance the runner system and verify gate diameters. Gate size should not be reduced from the high-flow setting unless flow simulation confirms complete fill at the lower melt flow rate. For mould clamp sizing, thin-wall ABS components commonly use a cavity pressure in the 30–45 MPa range. The selected machine should not exceed approximately 80% of available clamp force when projected area is multiplied by cavity pressure. That margin avoids excessive mould deflection and flash during peak pressure.

Chemical contact imposes additional boundaries. Heat-resistant ABS retains the general solvent-resistance profile of standard ABS but should not be exposed continuously to strong polar solvents such as ketones, esters, or chlorinated hydrocarbons. Environmental stress cracking should be evaluated according to ISO 22088-3 using the actual service chemical and load. Under stress, aromatic hydrocarbons and some synthetic lubricants may initiate crazing at loads below the short-term tensile yield. If an elastomer gasket or adhesive is in contact with the moulded part, compatibility testing is required for the complete assembly. Amine-based or aggressive solvent-borne curing systems can attack the matrix. Published data for HR-5335 against every process chemical is limited, so release testing must include the specific contact fluid and ageing temperature.

For heat-stressed electrical enclosures and automotive under-hood HVAC housings, HR-5335 should be evaluated against the full thermal-mechanical specification rather than a single heat-deflection value. The part must support the applied load at the maximum service temperature within the allowable deflection. Validation should include oven aging at the upper service temperature for the expected service life, dimensional inspection after cooling, and intermittent load testing. If the specification requires dimensional change not exceeding 0.5% after aging, the test report must state the measurement method and conditioning protocol. The material should not be extended to continuous contact with hot engine oil or coolant unless the supplier has specifically tested the grade in those fluids. In such environments, a more chemically resistant polymer system is required unless compatibility data for HR-5335 exists.