Overview
ISO/TS 14778:2021 - Paper and board - Measurement of water contact angle by optical methods - defines an automated, optical procedure for assessing the water contact angle on planar paper and board surfaces. The method uses a controlled droplet (commonly distilled water) and digital imaging to determine the droplet shape, base diameter, height and the contact angle after a specified contact time. The specification is intended for automated equipment and is not applicable to structured materials (e.g., highly embossed or non‑planar substrates).
Key topics and technical requirements
- Instrumentation: Automated contact angle apparatus with platform/holder, homogeneous lighting, liquid reservoir and dosing system, droplet application system and a digital video camera.
- Imaging: Minimum image capture rate of 50 frames per second and the ability to perform the first measurement within 20 ms to 40 ms of droplet contact.
- Liquid: Distilled water with surface tension ≥ 72 mN/m at 23 °C (ISO 13530 referenced). Other probe liquids are permitted only with caveats (non‑comparable results).
- Droplet control: Dosing tolerance of ±10% for droplet volume; capillary material and application must minimise wicking and kinetic energy on impact.
- Measured parameters: Contact angle (Θ) relative to an optically determined baseline, droplet height (H) and droplet base diameter (D) at specified contact times.
- Procedure elements: Sampling, conditioning (standard atmosphere per ISO 187), test piece mounting, apparatus calibration, automated measurement sequence and reporting of results.
- Limitations: Instrumental capabilities set the measurement limits; the method assumes a planar substrate and stable baseline detection.
Applications and who uses it
ISO/TS 14778:2021 is used to evaluate wettability and predict liquid‑paper interactions in industrial and laboratory settings. Typical users include:
- Paper and board manufacturers - quality control and product specification
- Coating formulators and converters - assessing coating wetting and adhesion
- Printing houses (inkjet, gravure, flexographic, wet offset) - predicting ink behavior
- Adhesive and lamination developers - gluing performance predictions
- R&D and testing laboratories - surface characterization and process development
- Instrument manufacturers - conformance to imaging and dosing requirements
Practical outcomes include improved printability, coating performance, glue bond reliability and screening of surface treatments. Note that surface energy component calculations require additional liquids and are outside the scope of this document.
Related standards
- ISO 186 - Sampling to determine average quality (paper and board)
- ISO 187 - Standard atmosphere for conditioning and testing
- ISO 13530 - Guidance on analytical quality control for water (reagent requirements)
Keywords: ISO/TS 14778:2021, water contact angle, paper and board, optical methods, sessile drop, automated contact angle measurement, wettability, surface characterization.