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ISO 28199-1:2021 — Paints and Varnishes — Evaluation of Coating Systems — Part 1: Vocabulary and Preparation of Test Panels
Technical Article
1. Purpose and Scope of ISO 28199-1:2021
ISO 28199-1:2021 defines essential terminology related to the evaluation of coating materials in research, development, and production with regard to their suitability and safety for industrial spray application processes. It also specifies standardized methods for the preparation of test panels and subsequent measurement of film thickness, colour, surface texture, and other measurable surface properties. This is Part 1 of a comprehensive three-part series developed by ISO/TC 35 Paints and varnishes, Subcommittee SC 9 General test methods for paints and varnishes, in collaboration with CEN/TC 139 Paints and varnishes. Parts 2 and 3 cover specific evaluation methods for coating properties including colour stability, process hiding power, sagging tendency, bubble formation, and pinholing.
This second edition incorporates significant revisions based on studies by the European Council for Automotive R&D (EUCAR), including updated terminology with the addition of dynamic spray pattern definition, removal of obsolete terms, revised apparatus specifications, and new measurement procedures for mottling and gloss evaluation. The standard recognizes that coating materials are semi-manufactured products that only achieve their final performance characteristics in combination with specific application conditions, making the adaptation of application parameters decisive for final coated product quality.
Coating materials are semi-manufactured products that only achieve their final form in combination with specific application conditions. The adaptation to application conditions is decisive for the quality of the coated product.
2. Key Terminology and Definitions for Coating Evaluation
The standard establishes precise terminology essential for consistent communication between coating material suppliers, industrial applicators, quality assurance teams, and research organizations:
| Term | Definition | Practical Significance |
|---|---|---|
| Colour stability | Non-variability of colour despite variation in film thickness, application method, or other influencing factors | Critical for automotive OEM and refinish colour matching, consumer product consistency |
| Process hiding power | Minimum film thickness above which the complete coating system achieves agreed colour stability | Directly determines material cost per unit area and influences production efficiency |
| Mottling | Non-uniform appearance caused by irregularly shaped, randomly distributed areas varying in colour or gloss | Common quality defect in metallic and pearl effect automotive paints |
| Overspray absorption | Ability of an already applied coating material to absorb overspray particles from subsequent application of the same material | Critical for repairability and multi-coat production processes |
| Sagging | Downward movement of coating material during application or drying on vertical or inclined surfaces | Fundamental limitation on wet film thickness per coat in vertical applications |
| Surface texture | Visual appearance and recognizability of structures in the coating surface, with wavelengths between 0.1 mm and 30 mm for orange peel texture | Key aesthetic quality indicator, influenced by levelling and substrate characteristics |
| Redissolving | Mutual effects between an already applied coating and a subsequently applied coating where components interact | Can cause colour shifts, gloss changes, or intercoat adhesion problems |
Bubbles and pinholes are distinct defect types with fundamentally different root causes. Bubbles arise from solvents or cleavage products evaporating from chemical crosslinking during drying. Pinholes are often caused by gas inclusions in the base coat that are revealed as discontinuities after clear coat application, frequently resulting from inappropriate process parameters.
3. Test Panel Preparation Methods and Measurement Specifications
The standard specifies two test panel configurations: Version A (perforated panel, 300 mm by 570 mm by 0.75 mm with 7 mm diameter holes required for sagging determination) and Version B (non-perforated panel, 200 mm by 500 mm by 0.75 mm, available as B1 with adhesive tape reference strips or B2 without reference strips for measuring individual coat thicknesses). Test panels are coated using an automatic painting machine with precisely defined parameters documented in Annex A. The measurement pattern requirements are rigorous: minimum 5 measurement points per film thickness line in the X direction, and minimum 20 such lines distributed over the panel length in the Y direction. The film thickness wedge starts from 0 micrometres with continuous increase. Colour is measured per ISO 18314-1 at five angles (15, 25, 45, 75, and 110 degrees) with standard illuminant D65 and 10 degree standard observer. Surface texture is analyzed in wavelength ranges from 0.1 mm to 30 mm. The measurement pattern must clearly distinguish between locally related and locally unrelated measurements for proper correlation of film thickness with surface properties.
Engineering Design Insights
For coating process engineers and quality professionals, this standard provides an indispensable systematic framework for correlating spray application parameters with final coating quality attributes. The 100 minimum measurement requirement per test panel ensures statistical rigor essential for meaningful process capability analysis. The critical distinction between locally related versus locally unrelated measurements enables engineers to determine whether film thickness variations directly cause surface defects or whether other process factors are responsible. The addition of gloss measurement and mottling evaluation procedures in this 2021 edition reflects the automotive industry’s increasing emphasis on aesthetic quality attributes beyond simple colour accuracy. The detailed application parameter tables in Annex A provide practical starting points for process development across different coating types including water-based paints, clear coats, and metallic effect finishes applied by both pneumatic and high-speed electrostatic bell atomizers.
By evaluating coating materials as part of an integrated system (material plus application parameters plus substrate) rather than in isolation, this standard enables more reliable process development, efficient troubleshooting, and consistent production quality.
4. FAQs
Q: What is the difference between a static spray pattern and a dynamic spray pattern?
A: A static spray pattern is produced with both the coated object and spray application system at rest, showing the inherent distribution from fixed parameters. A dynamic spray pattern is produced with relative motion between object and applicator, more closely simulating real production conditions and revealing the effects of movement on film build uniformity.
A: A static spray pattern is produced with both the coated object and spray application system at rest, showing the inherent distribution from fixed parameters. A dynamic spray pattern is produced with relative motion between object and applicator, more closely simulating real production conditions and revealing the effects of movement on film build uniformity.
Q: Why does the standard use wedge-shaped coating films rather than constant thickness films?
A: Wedge-shaped coatings with continuously increasing thickness allow efficient evaluation of all film-thickness-dependent properties in a single test panel, enabling identification of the critical thickness thresholds where various defects first appear.
A: Wedge-shaped coatings with continuously increasing thickness allow efficient evaluation of all film-thickness-dependent properties in a single test panel, enabling identification of the critical thickness thresholds where various defects first appear.
Q: How is mottling measured and evaluated according to this standard?
A: Mottling is assessed either instrumentally using suitable measuring devices or through visual evaluation, quantifying local differences in brightness or colour across the coated surface to detect the non-uniform appearance characteristic of this defect.
A: Mottling is assessed either instrumentally using suitable measuring devices or through visual evaluation, quantifying local differences in brightness or colour across the coated surface to detect the non-uniform appearance characteristic of this defect.
Q: What conditioning and environmental conditions are required before testing test panels?
A: Unless otherwise agreed, test panels must be conditioned at 23 plus or minus 2 degrees C in accordance with ISO 3270 for a minimum of 16 hours before testing, and the test itself should preferably be conducted under the same standard temperature conditions.
A: Unless otherwise agreed, test panels must be conditioned at 23 plus or minus 2 degrees C in accordance with ISO 3270 for a minimum of 16 hours before testing, and the test itself should preferably be conducted under the same standard temperature conditions.
