Coating testing methods for performance optimization and regulatory compliance

Coatings are applied to materials to improve properties such as durability, appearance, and resistance to corrosion, fire, water, or grease. To ensure that these properties meet the performance levels promised to customers — and that the formulation complies with limits on restricted chemicals — laboratory testing is required throughout development and production.

This article summarizes commonly applied standard methods for evaluating the technical performance, physical, mechanical, and optical properties, and chemical composition of coatings. Examples of typical testing projects are also provided, based on Measurlabs' experience supporting coating manufacturers across industries from construction to food contact materials.

Technical performance and durability testing

Optimizing durability and performance in challenging environments and over prolonged periods is particularly important for heavy-duty performance coatings, such as anti-corrosive paints and protective coatings for construction materials. Decorative paints and varnishes must also withstand exposures relevant to their intended use, including weathering for outdoor paints and liquid spillage for kitchen surface coatings. Selected standardized durability test regimes are summarized in Table 1.

The results from tests listed in Table 1 are primarily evaluated using the ISO 4628 series, which establishes a rating system to assess the extent of coating degradation, including blistering, rusting, cracking, flaking, chalking, delamination, and corrosion. Additional assessments, such as the ISO 4624 coating adhesion pull-off test or the ISO 2409 cross-cut adhesion evaluation, are performed where applicable.

Example project: evaluating coating system compliance with C5-VH criteria under ISO 12944-6

A typical coating durability testing project at Measurlabs involves showing that a coating system meets the requirements of a specific ISO 12944 corrosion category. For example, demonstrating very high durability under extremely corrosive conditions (category C5-VH) involves the following test regime:

• A scribe line is introduced to three coated metal panels measuring 15 x 10 cm, min. 4 mm thick, as required by Annex A of ISO 12944-6

• The panels are exposed to 16 weeks of cyclic aging (total of 2,688 hours), where each week consists of:

  • 72 h of alternating exposure to UV light and condensation in 4-hour periods

  • 72 h of neutral salt spray exposure (ISO 9227)

  • 24 h of exposure to low temperature (−20 ± 2 °C)

• After exposure, the condition of the aged panels is inspected using the ISO 4624 pull-off test, ISO 2409 cross-cut test, and several ISO 4628 evaluations (blistering, cracking, rusting, flaking). An unaged panel is also inspected for comparison.

• The results are reported as pull-off adhesion in MPa and ratings for each type of damage after aging. Photographic evidence and a pass/fail assessment against the C5-VH criteria are also provided.

As per ISO 12944-6, a coating system that meets the pass criteria of C5-VH is also suitable for use in less corrosive environments (C1 to C4).

Determination of physical, mechanical, and optical properties 

Physical and mechanical properties such as film thickness, adhesion, and abrasion resistance determine how coatings perform in service, while optical properties like gloss and hiding power determine how they look. Table 2 contains examples of test methods for evaluating these properties, primarily based on ISO, EN, and ASTM standards. In-house methods are also available, and they can be preferable when developing new coating systems for which the established methods are not directly applicable.

Example project: comparing alternative paint formulations

Different paint formulations are typically compared extensively during product development to identify best-performing candidates. When comparing light-colored decorative indoor paints, the following properties, both of which are part of the EN 13300 classification system, are particularly relevant:

• Hiding power according to ISO 6504-3 or equivalent methods. Results are reported as contrast ratio at the manufacturer’s stated spreading rate, and class 2 or better (98 % or higher) generally indicates good hiding power.

• Wet scrub resistance according to ISO 11998. Classes 1 and 2, corresponding to film thickness losses below 20 µm after 200 cycles, generally indicate a good level of resistance.

One liter of each evaluated paint is typically required for each of the two tests. The turnaround time is approximately 7 weeks, including a 28-day drying period as specified in ISO 11998.

Chemical testing of coatings

Hazardous substances are often necessary in coatings for technical reasons, but their concentrations must not exceed legal limits or the often even stricter limits set by customers or environmental labels. Table 3 contains examples of chemical analyses commonly used to demonstrate compliance with EU legislation and eligibility for ecolabels.¹

In addition to these and other regulatory chemical analyses, Measurlabs offers chemical characterization of coatings for product development and quality assurance. The analytical methods available include spectroscopic, chromatographic, thermal, and elemental techniques such as FTIR, GC-MS, LC-MS, TGA, and XRF.

Example project: confirming the food-contact compliance of coated paper cups

Measurlabs has extensive experience supporting fiber-based food contact material manufacturers in demonstrating that their coating formulations comply with EU legislation. The exact analyses required depend on product composition, but the following are examples of tests typically performed on polymer-coated and printed paper cups intended for the EU market:

• Specific migration of primary aromatic amines and metals listed in Annex II to Regulation (EU) 10/2011

• Printing-ink set-off with GC-MS, with compliance evaluated against the Framework Regulation (EC) 1935/2004

• PPWR testing package, covering heavy metals and total fluorine, with further analysis of total organic fluorine (TOF) or individual PFAS compounds where required

• Mineral oil (MOSH and MOAH) migration, with compliance assessed in accordance with the latest EU recommendations on MOSH and MOAH

• NIAS screening with GC-MS to measure the migration of non-intentionally added substances

• Further specific migration tests for relevant constituents and potential impurities, such as epoxy derivatives, bisphenols, and phthalates

Alongside the analyses, we can provide expert support for drafting the required compliance documentation.

One partner for all your coating testing needs

Measurlabs provides an extensive selection of testing services for coating manufacturers, from performance and durability testing of industrial coatings to chemical compliance assessments of coatings used in the food contact material and medical device industries. In addition to the tests discussed in the above sections, we also offer the following services:

• Barrier testing (OTR, WVTR, and other gas transmission rates) to evaluate the impact different coatings have on the barrier properties of polymeric films, textiles, packaging, and construction materials

• Reaction to fire testing and classification according to EN 13501-1 and EN 13501-5 to evaluate the effect coatings have on the reaction to fire performance of construction materials

• A large selection of semiconductor testing methods to study the physical and chemical properties of functional coatings on the nanoscale

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