Overview
In the printing and coatings industry, the gloss of ink surfaces is one of the key parameters for evaluating its visual quality and functional performance. The gloss meter achieves an objective quantification of gloss by measuring the specular reflected light flux on the sample surface at a specific angle. This method systematically expounds the operation process, influencing factors and data processing points of measuring ink surface gloss using gloss meter according to relevant domestic and foreign standards, aiming to provide technical support for quality control and research and development in related fields.
Rationale
Gloss is defined as the ratio of the reflected light flux on the surface of the sample surface in the direction of specular reflection to the reflected light flux under the same conditions as the standard plate. It is usually expressed as a percentage or gloss unit (GU). The measurement is based on the Fresnel reflection principle, the basic relationship of which can be expressed as:
G = (Φs / Φ0) × 100%
where G is the gloss value of the sample, Φsis the reflected light flux of the sample at the receiver, Φ0It is the reflected light flux of the standard board under the same conditions. Standard plates are usually made of highly polished black glass with a known refractive index and given a specified gloss value (e.g. 100 GU).
Measuring instruments
The gloss meter is mainly composed of a light source, an incident diaphragm, a receiver and a data processing unit. Depending on the expected gloss range of the ink surface, the appropriate measurement geometry should be selected. Common angles include 20°, 60°, and 85°. For specific selections, please refer to the following guidance:
| Expected gloss range | Recommended measurement angle |
| High gloss (>70 GU) | 20° |
| Medium gloss (10 to 70 GU) | 60° |
| Low gloss (less than 10 GU) | 85° |
The instrument needs to be calibrated regularly using a standard plate to ensure traceability of the measurement chain. The measurement environment should avoid vibration, strong magnetic field and stray light interference, and the temperature and humidity should be controlled under standard laboratory conditions.
Measurement steps
The preparation of ink samples directly affects the reliability of the measurement results. The ink should be evenly applied to the specified substrate, such as standard printing paper or a special test card, and allowed to dry and cure adequately according to the product technical instructions. The surface of the sample should be flat and clean, free of scratches, bubbles, or obvious grain directionality.
The measurement steps are as follows: First, turn on the gloss meter to warm up, and use a standard plate to complete the calibration. Place the sample steadily under the measuring hole to ensure that the measurement area fits snugly against the instrument probe without gaps. Select a preset measurement angle, trigger the measurement, and record a steady reading. Each sample should be measured at least three times at different locations, taking the arithmetic average as the gloss value of that sample. Clean the instrument probe and standard plate after measurement.
Influencing factors
The measurement of ink surface gloss is affected by a variety of factors and needs to be controlled during operation. Key factors include:
| Influencing factors | Description and control recommendations |
| Surface flatness | Uneven surfaces cause scattering, so make sure the substrate is flat and evenly coated. |
| Measure the angle | Improper angle selection will reduce the resolution or exceed the range, and it should be selected according to the gloss range. |
| The ink film is thick | The film thickness affects the light penetration and reflection, and the coating amount should be controlled to be consistent. |
| Degree of dryness | Ink surfaces that are not completely dry are unstable and need to be adequately cured. |
| environmental conditions | Temperature and humidity may affect instrument performance and sample condition, so it is recommended to measure in a stable environment. |
Data logging
The measurement report should clearly record the following information: instrument model and number, calibration standard plate information, measurement geometric angle, ambient temperature and humidity, sample identification and preparation description, measurement value at each point and final average. If there is a large discrete in the measured values, the possible cause should be analyzed, such as uneven surfaces or problems with the measurement operation. The report format can be formulated according to the requirements of the specific quality control system.
Summary
Using a gloss meter to measure the surface gloss of inks is a mature and objective detection method. Reliable and repeatable measurement data can be obtained through standardized sample preparation, correct instrument operation and angle selection, and tight control of key influencing factors, which can effectively support the R&D, production, and quality evaluation of ink products.
References
ASTM D523 Standard Test Method for Specular Gloss
ISO 2813 Paints and varnishes — Determination of gloss value at 20°, 60° and 85°
GB/T 9754 Colored paints and varnishes - Determination of 20°, 60° and 85° mirror luster of colored paint films without metallic pigments