Overview
ISO 5435:2017 - "Rubber compounding ingredients - Carbon black - Determination of tinting strength" specifies a laboratory method for measuring the tinting strength of carbon black relative to an industry tint reference black (ITRB or ITRB‑2). The method mixes carbon black with zinc oxide and an epoxidized soybean oil plasticizer, prepares standardized pastes, and measures light reflectance with a reflectometer sensitive to grey shades. Results are reported as relative tinting strength using a calibrated response curve.
Key topics and requirements
- Scope: Comparative determination of tinting strength for carbon black used in rubber compounding.
- Principle: Prepare paste of carbon black + zinc oxide + epoxidized soybean oil, homogenize with an automatic muller, apply a uniform film/drawdown, measure reflectance and calculate relative tinting strength.
- Required reagents: epoxidized soybean oil (plasticizer), industry tint zinc oxide (ITZnO), ITRB or ITRB‑2 reference blacks, and standard reference blacks. Use analytical‑grade reagents and distilled water.
- Apparatus: analytical balance, automatic muller, film applicator/paste application tools, syringe, palette knives and a light‑measuring instrument (reflectometer).
- Test conditions: preferred ambient conditions 23 °C ± 2 °C at 50 % ± 5 % RH (or 27 °C ± 2 °C at 65 % ± 5 % RH). Carbon black and zinc oxide drying per ISO 1126.
- Instrumentation: procedures are given for five commercial instruments (Erichsen Tint Tester, Densichron reflectometer, Meeco Colormaster, Hunter Miniscan, Photochron). Note: the Densichron and Meeco Colormaster are no longer commercially available but procedures remain for legacy users.
- Calibration and precision: calibration uses a series of known‑mass calibration pastes (e.g., 90–140 units) prepared in duplicate, multiple reflectance readings, and plotting an average reading vs. calibration tint value. Alternative instruments are acceptable if standard reference black results fall within control limits referenced in ASTM D4821.
- Reporting: Clause on expression of results, precision data, and required information in the test report.
Applications and users
- Who uses it: quality control laboratories, carbon black producers, rubber compounders, testing services, and R&D teams verifying color/tint performance of blacks for tires, seals, hoses, and molded rubber products.
- Practical value:
- Ensures reproducible tinting strength data for specification compliance and batch comparison.
- Supports raw material selection and process control in rubber compounding.
- Provides a traceable method for supplier acceptance testing and interlaboratory comparison.
Related standards
- ISO 1126 - Carbon black: determination of loss on heating (drying requirements referenced).
- ASTM D4821 - Control limits for standard reference blacks (used to validate alternative instruments).
Keywords: ISO 5435:2017, tinting strength, carbon black, rubber compounding, reflectometer, ITRB, ITZnO, epoxidized soybean oil, Erichsen Tint Tester, ASTM D4821.
