Mocom ALTECH SAN B 2335/720 is an amorphous styrene-acrylonitrile copolymer injection molding compound supplied in black-pigmented pellet form. The ALTECH SAN designation places the material within Mocom’s unfilled SAN product range; the suffix B identifies the black coloring package, and the numeric block 2335/720 identifies the registered formulation and viscosity/flow category. The material is specified for opaque rigid components that require greater resistance to aliphatic oils, greases, and diluted detergent solutions than general-purpose polystyrene, while maintaining a higher practical heat resistance than unmodified GPPS. Representative application fields include appliance control panels, automotive interior trim, filter housings, and cosmetic packaging closures. Baseline design values for unfilled SAN of this viscosity class are: density 1.07–1.10 g/cm³ according to ISO 1183-1, tensile modulus 3500–3900 MPa according to ISO 527-1/-2, notched Charpy impact strength 1.5–3.0 kJ/m² according to ISO 179-1/1eA, and Vicat softening temperature 100–110°C according to ISO 306/B50. These are class-level design envelopes, not lot-specific release values; the current Mocom technical data sheet and certificate of analysis remain binding for production release.

What Distinguishes SAN Copolymer from Glass-Filled or Impact-Modified Alternatives?

The molecular architecture of styrene-acrylonitrile copolymer determines the boundary between this material and other rigid thermoplastics. Commercial SAN is a random copolymer with an acrylonitrile content typically controlled between 24% and 34% by mass. The polar nitrile side groups raise the glass transition temperature, increase stiffness, and reduce solubility in nonpolar hydrocarbon media compared with polystyrene. Increasing acrylonitrile content raises tensile strength and aliphatic oil resistance, but it also raises melt viscosity and equilibrium moisture uptake. The black-compounded ALTECH SAN B 2335/720 variant retains the amorphous dimensional behavior of SAN: no crystalline shrinkage step, lower post-mold warpage than many semi-crystalline polymers, and a relatively narrow processing window because viscosity is more temperature-sensitive than shear-sensitive. It differs from glass-filled SAN by avoiding fibrous reinforcement, which lowers modulus but reduces anisotropic shrinkage and minimizes machine-screw and mold wear. Compared with ABS, it lacks the dispersed butadiene rubber phase, so notched low-temperature impact strength is lower, but surface hardness and resistance to cosmetic staining can be more stable in indoor black parts.

The comparative data above are literature-class envelopes for unfilled resin families and are not a replacement for the Mocom lot-specific certificate. The black pigment package in ALTECH SAN B 2335/720 can depress melt flow by approximately 5% to 10% relative to a natural base resin and can alter surface gloss; therefore, gloss targets, mold shrinkage, and melt residence behavior should be validated with production pellets rather than neutral laboratory samples.

Component designers replacing GPPS in a black appliance control panel often select SAN because the nitrile comonomer reduces environmental stress cracking in contact with sebaceous skin oils and common household cleaner residues. The difference is measurable as a higher critical strain threshold for environmental stress cracking under constant-strain exposure to n-heptane; unmodified GPPS crazes at lower strain, while SAN maintains visual integrity at higher applied strain. Because the black pigmentation of ALTECH SAN B 2335/720 removes light-transmission paths, the grade is unsuitable for light guides, illuminated diffusers, or backlit transparent indicators. If light transmission is required, a natural or transparent SAN grade should be specified instead.

At wall thicknesses below 1.0 mm, fill speeds above 40 mm/s are often required to prevent premature freeze-off, but shear rates above 10 000 s⁻¹ in cold-runner gates can produce surface jetting and visible gloss bands in black SAN components. Hot-runner systems should use open-pipeline melt channels with thermocouple control at every nozzle; an off-center temperature variation greater than 5°C across a hot-runner bar produces gloss banding on textured black surfaces. Draft angles above 0.5° normally eliminate the need for external release agents, which can interfere with subsequent pad printing or laser marking.

When Molding Black SAN Components with Deep Ribs and Textured Surfaces

Process setup for ALTECH SAN B 2335/720 should begin with desiccant drying at 80°C for 2 h to 4 h to achieve residual moisture below 0.10%; when ambient relative humidity exceeds 60%, drying time should be extended or a dewpoint below -30°C should be maintained. Melt temperature should be profiled from 210°C in the rear zone to 250°C at the nozzle, with a maximum melt temperature of 260°C. Mold temperature should be controlled between 40°C and 80°C. The lower mold temperature range reduces cycle time; the upper range improves surface replication on grained surfaces and reduces internal stress, but increases post-mold shrinkage and cooling time. Mold shrinkage is generally 0.4% to 0.7% in the flow direction and 0.5% to 0.8% transverse. These values are influenced by wall thickness, gate size, and hold pressure; toolmakers should use moldflow analysis with pvT data from the current material card rather than generic polystyrene data.

The main process conflict is the interaction between short-shot prevention, gate freeze-off, and jetting. A small gate diameter or high injection velocity can generate jetting defects, which appear as serpentine streaks on black parts. Reducing linear screw velocity below 40 mm/s or enlarging the gate land suppresses jetting but increases gate pressure loss. Machine selection should favor a three-zone general-purpose screw with an L/D ratio between 20:1 and 25:1 and a compression ratio between 2.0:1 and 2.5:1. Open check assemblies reduce dead spots; shut-off nozzles are preferred because the melt is not strongly shear-thinning. For multicavity tools on presses with clamping force below 500 kN, cavity pressure transducers should be used to balance fill and hold; inter-cavity shot-weight variation above 0.5% can produce inconsistent gloss and dimensional mismatch. Residence time above 5 min at melt temperatures above 240°C can produce yellowing and black speck formation in nitrile-containing copolymers. During production interruptions longer than 15 min, the barrel setpoint should be reduced by 20°C to 30°C and the screw retracted.

Processing with closed-loop regrind is possible at levels of 10% to 20% by mass if the granulate is dust-free and dried to the same dewpoint. Higher regrind fractions should be avoided for visible black surfaces because repeated screw shear lowers molecular weight and raises the melt flow rate; this produces gloss shifts and can reduce notched Charpy impact strength by more than 10% after three heat histories. The exact allowable regrind ratio for ALTECH SAN B 2335/720 must be established by a production trial because the carbon black masterbatch affects thermal stability and surface appearance.

Chemical Resistance and Environmental Stress Cracking Thresholds

Black SAN compounds are selected for indoor rigid parts exposed to aliphatic hydrocarbons, dilute acids, alkalis, and many household cleaning formulations. The acrylonitrile comonomer creates a polar barrier that limits swelling in nonpolar hydrocarbons compared with polystyrene. The material is not resistant to ketones, esters, aromatic solvents, or chlorinated solvents; contact with acetone, methyl ethyl ketone, toluene, or methylene chloride can cause rapid stress cracking or partial dissolution. When service exposure involves these chemicals, a different polymer family is required. For less aggressive media, compatibility must be tested on molded plaques under production strain using constant-strain fixtures according to ASTM D543 or ISO 22088-2. Published data for this specific black variant under all chemical exposure combinations is limited; therefore, results should not be extrapolated from unfilled natural SAN values without confirmation.

Repeated contact with ethanol or isopropanol disinfectants can be acceptable for indoor components if residual molded-in stress is minimized with sufficient holding pressure, uniform mold cooling, and gate locations that avoid direct knit lines in loaded areas. The critical strain threshold for SAN in n-heptane is reported in the literature as approximately 0.5% to 1.0%, depending on acrylonitrile content and molecular weight distribution. Black pigmentation can mask stress whitening in this grade, so inspection under crossed polarized light or post-exposure tensile testing is required to detect damage before visible cracking appears.

Regulatory documentation for a black-pigmented SAN compound used in electrical/electronic equipment or consumer articles must be verified against the current Mocom statement. The verification matrix below lists applicable references and required documents.

For laser-marked automotive HVAC control panels and appliance rotary knobs, the black SAN compound must provide low lot-to-lot color drift and a surface that absorbs Nd:YAG laser radiation at 1064 nm without charring or melt burst. The opaque black package suppresses light bleed and provides contrast after laser marking; color acceptance is typically measured against an approved master chip with ΔE below 0.5 in CIE L*a*b* coordinates. In these applications, the material’s violet-free carbon black package avoids the reddish tone seen in low-cost black masterbatches and improves sorting in automated vision inspection.