Colour Measurement for Rubber Compounds and Rubber Parts

Common Challenges in Colour Control of Rubber Products

• Black Rubber is not visually uniform by default

  Changes in Carbon Black, fillers, recycled content, processing (mixing, temperature, curing, moulding etc) can all effect the final colour and surface, the use and importance of visual quality of the final product could lead to tighter or wider tolerances and the ROI for colour control. SpectraMagic™NX2 measures several black indices like jetness, blackness and undertone to improve precise colour data for black products.

• Fillers and recycled content can shift colour

  For some products changes in supply or inherent variability in raw material can increase the complexity of consistent product colour. Control over colour formulation, even when base, filler or recycled content changes colour even slightly can be managed by computer colour matching software.

• Surface texture and sample homogeneity

  Rubber samples that are small, textured or curved should be measured with the instrument that is most repeatable, this could be the CM-17d for curved or small samples or the CM-25cG for textured rubber samples.

• Transparent silicone and translucent

  Rubber samples with a degree of translucency may cause edge loss errors (when light from the illumination is diffused inside the sample with some escaping outside the measured area resulting in a darker colour value). All Konica Minolta d:8 instruments (see below) illuminate an area larger than the measured area to eliminate this problem.

• Sample presentation

  For best repeatability of measurement data you should achieve consistent sample presentation at an area that is flat, with consistent thickness and has a consistent backing. Selection of the instrument to achieve this may include ergonomic factors (for smaller or curved samples a CM-17d is recommended) otherwise you should use the largest aperture that can fit on the sample area.

• Can black rubber be measured for colour consistency?

  Yes. Even black rubber can show measurable colour shifts caused by formulation changes, fillers, recycled content or process variation. Objective colour data helps manufacturers control consistency from batch to batch.

• What is the best way to measure coloured rubber compounds?

  The best method and geometry depends on sample opacity, homogeneity, surface texture, size and whether measurements are made in the lab or production environment. Opaque rubber can often be measured in reflectance, some samples may benefit from opacity measurement.

• Why use colour data instead of visual assessment for rubber QC?

  Colour data gives repeatable values (commonly L*a*b* and colour difference values), helping teams reduce subjective approvals, speed batch release and communicate clearly targets and tolerances with customers and suppliers.