1.What is the measurement principle?
Glossiness is the ability of a coating surface to reflect light, and is usually expressed as the ratio of the reflected light flux at a specific angle to the reflected light flux of a standard plate. Light is incident on the coating surface at a specified angle, and the instrument measures the intensity of the reflected light, compares it with the reflection intensity of the "standard gloss plate", and calculates the glossiness value of the sample.
2.What are the commonly used measurement angles?
20° angle: suitable for high gloss coatings (usually gloss > 70GU), such as high gloss polyester coatings and partial fluorocarbon coatings. This angle is more sensitive to small differences in high gloss surfaces and can accurately distinguish gloss changes in high gloss coatings.
60° angle: a general angle, suitable for medium gloss coatings (gloss 20-70GU), such as most modified polyester and polyurethane coatings. The 60° angle is the industry's default "standard angle" and is usually measured at this angle unless otherwise specified.
85° angle: suitable for low gloss coatings (gloss < 20GU), such as matte coatings and suede coatings. Low gloss surfaces reflect weaker light, and large angle measurements can capture more reflected light and improve measurement accuracy.
3.What are the commonly used measuring instruments?
Portable gloss meter: small size, convenient for on-site measurement, suitable for quick sampling on the production line or finished product warehousing inspection, such as portable equipment from German BYK, American X-Rite, and domestic 3NH.
Desktop gloss meter: higher accuracy, suitable for precise measurement of standard samples or controversial samples in the laboratory, usually with a sample fixing platform to reduce human operation errors.
4.What are the measurement steps?
Sample preparation:
Take a representative color-coated coil sample (usually with a size of ≥100mm×100mm) and ensure that the surface is free of oil, scratches, deformation or contamination (if there are impurities, wipe gently with a dust-free cloth to avoid damaging the coating).
If there is a texture on the coil surface (such as embossing or orange peel), the texture direction needs to be recorded. When measuring, keep the instrument incident direction consistent with the texture direction (such as parallel or vertical) to avoid errors caused by texture reflection differences.
Instrument calibration:
Turn on the gloss meter and calibrate according to the instructions: first align the instrument with the "zero gloss plate" (usually a black matte rubber plate with a gloss ≈ 0GU) to complete the zero point calibration; then align it with the "standard gloss plate" (such as a 60° angle standard plate with a gloss of 70GU) to complete the standard calibration. After calibration, the instrument displays "calibration passed".
Formal measurement:
Put the sample flat on a horizontal platform to avoid shaking.
Place the gloss meter measuring head close to the sample surface, ensure that the measuring window is completely covered with the coating (no edges, no bubbles), press the measurement key, and read the value (usually the instrument will automatically display the average of 3 measurements to reduce accidental errors).
The same sample needs to be measured at least 3 points at different locations (such as the left, middle, and right areas of the coil), and the average value is taken as the final result to avoid deviations caused by local defects (such as scratches).
Data recording:
Record the measurement angle, the value of each point, the average value, and the sample information (such as batch, location) for easy traceability and quality analysis.
5.What are the precautions?
Environmental control: The measurement should be carried out in a room temperature (23±2℃) and dry (relative humidity 50±5%) environment. Avoid strong light directly on the sample surface (it can be blocked by a shading plate) to prevent ambient light from interfering with the reflected light measurement.
Sample status: The flatness of the coating surface has a greater impact. If the sample is bent or warped, it needs to be flattened with a heavy object (to avoid damaging the coating). Ensure that the measuring head fits tightly to the surface, otherwise the measured value will be low due to light leakage.
Instrument maintenance: The measuring head window needs to be kept clean. If there is stain, it can be wiped with special lens paper to avoid scratches; when not in use for a long time, it needs to be placed in a drying box to prevent moisture from affecting the accuracy.