Overview
ISO 2115:1996 specifies a laboratory method to determine the white point temperature and the minimum film-forming temperature (MFFT) of polymer dispersions. The standard - prepared by ISO/TC 61 in collaboration with ISO/TC 35 - replaces the 1976 second edition and harmonizes test requirements with paints and varnishes practice. The method helps manufacturers and laboratories assess the temperature limits for film coalescence and reliable film formation in coatings, latex and related aqueous dispersion products.
Key Topics
- Definitions: The standard defines white point temperature (temperature below which an opaque mass forms and above which a transparent film forms) and minimum film-forming temperature (the lowest temperature producing a continuous homogeneous film without cracks). The white point typically lies a few degrees Celsius below the MFFT.
- Principle: A thin layer of polymer dispersion is dried over a controlled temperature gradient while a current of dry air passes from the cold to the hot end. The point where the film changes from opaque (non-coalesced) to transparent (coalesced) identifies the white point and MFFT.
- Apparatus: Key equipment includes a rectangular metal plate (aluminium, stainless steel or copper), a hot source (rheostat-controlled electrical resistance), a cold source (refrigerant reservoir or coil), temperature-measurement devices (thermometers or thermocouples accurate to 0.1 °C), a film applicator and a glass cover. Plates may be smooth or channelled (channels approx. 0.3 mm deep); layer thickness commonly 0.1 mm and strip widths ~20–25 mm.
- Test conditions: The plate temperature gradient should place the white point in the centre of the plate and maintain a 20 °C to 40 °C range between extremes; typical plate temperature range is predominantly between −10 °C and +50 °C.
- Precision: When performed as specified, repeatability is approximately 2 °C and reproducibility about 4 °C.
Applications
This method is directly applicable to quality control and formulation development for:
- Waterborne coatings and paints
- Polymer latices and aqueous dispersions
- Adhesives and film-forming formulations
Practical benefits include identifying safe application and drying temperature windows, supporting consistent film formation, and comparing dispersion performance across formulations and additives.
Related Standards
The ISO 2115:1996 text references several normative documents relevant to sampling and dispersion test methods, for example:
- ISO 123: Rubber latex - Sampling
- ISO 842: Raw materials for paints and varnishes - Sampling (revision referenced)
- ISO 12000: Plastics/rubber - Polymer dispersions and rubber latices - Definitions and review of test methods
For reporting, include the standard reference, full identification of the polymer dispersion, apparatus and test conditions, laboratory temperature, individual results for white point and MFFT, deviations from procedure, and test date and location.
Keywords: polymer dispersions, white point temperature, minimum film-forming temperature, MFFT, film formation, latex, coatings, test method.