Principle
Gloss is one of the key indicators to evaluate the optical properties of resin coating surfaces, which reflects the mirror reflection ability of the surface to incoming light. The gloss meter obtains the gloss value by measuring the mirror reflected light flux at the specified angle of incidence and comparing it with the luminous flux of the standard plate under the same conditions. For resin coatings, gloss consistency is directly related to the appearance quality and visual uniformity of the product, and is an important quality control parameter in the production process.
The measurement principle follows the law of optical reflection. When a beam of light α incident on the surface of the coating film at a specific angle, its mirror reflects light intensity Irand incident light intensity Iiis closely related to the refractive index n of the surface and the microgeometry of the surface. Gloss value GuUsually expressed as: Gu = (Ir / Ii) × 100%。 The optical signal is converted into an electrical signal by a photoelectric sensor inside, which is calibrated and calculated to display the gloss unit (GU) directly.
Angle selection
Domestic and foreign standards, such as the international standard ISO 2813 and the national standard GB/T 9754, uniformly stipulate the gloss measurement method. The choice of measurement angle depends on the expected gloss range of the coating surface to ensure accuracy and distinction of the measurement results. Typically, high-gloss surfaces use a smaller angle (e.g., 20°) for enhanced resolution, while low-gloss surfaces use a larger angle (e.g., 85°) for increased sensitivity.
| Surface Gloss Type (GU) | Recommended measurement angle |
| High gloss (>70) | 20° |
| Medium Gloss (10-70) | 60° |
| Low gloss (<10) | 85° |
For most resin coatings, the 60° angle is the universal measurement angle. If the measurement results are in the critical range, it is recommended to use multiple angles (e.g., 20°, 60°, 85°) for comprehensive evaluation to comprehensively characterize the surface gloss characteristics.
Influencing factors
The consistency of the surface gloss of resin coating films is affected by a variety of process and material factors. These factors can lead to differences in surface microtopography, resulting in changes in mirror reflected flux.
| Categories of influencing factors | Specific examples |
| Raw materials | Resin type, pigment dispersion, additive compatibility |
| Construction process | Film thickness uniformity, drying curing temperature and time |
| Basal state | Flatness, porosity, cleanliness |
| environmental conditions | temperature, humidity, air cleanliness |
For example, uneven curing temperatures may lead to different resin cross-linking densities, affecting surface smoothness; Poor pigment dispersion will produce microscopic agglomeration, increase light scattering, and reduce the intensity of mirrored reflected light. By systematically analyzing these factors, the process can be optimized to improve gloss consistency.
Operation process
To ensure the reliability and representativeness of measurement results, standardized operating procedures should be followed. First, calibrate the gloss meter using the included high gloss and low gloss standard plates. When measuring, ensure that the measuring caliber of the instrument is in stable and close contact with the coating surface to avoid environmental stray light interference.
When evaluating the gloss consistency of resin-coated samples, multiple representative measurement points should be selected across the entire sample surface. It is usually recommended to select at least 5 points and record the gloss values of each point. Consistency can be quantified by calculating statistical parameters for a set of measurements, such as mean X̄ and standard deviation S. The smaller the standard deviation S value, the higher the gloss consistency. The formula is: S = √[Σ(Xi - X̄)2 / (n-1)], where Xiis a single measurement, and n is the number of measurements. In production quality control, the standard deviation can be compared with the preset process control limits.
Analysis of results
The gloss data obtained from the measurement and its statistical results can be used to diagnose potential problems in the production process. If the gloss standard deviation increases significantly in different areas of the same batch, it may indicate fluctuations in construction uniformity, curing conditions, or raw material batches. By associating process parameters with gloss measurement data, feedback control of the production process can be realized.
It is recommended to incorporate gloss measurement into the routine quality inspection process of resin coating film production. Establish a gloss reference range (average vs. acceptable standard deviation) for each product and monitor it regularly using a gloss meter. For the development of new products or processes, systematic gloss measurement can provide a quantitative basis for formulation optimization and process adjustment, thereby effectively improving the stability of product appearance quality.
References
ISO 2813:2014, Paints and varnishes — Determination of gloss value at 20°, 60° and 85°.
GB/T 9754-2007, Colored paints and varnishes - Determination of 20°, 60° and 85° mirror gloss of colored paint films without metallic pigments.
ASTM D523-14, Standard Test Method for Specular Gloss.