Scope and description
Gloss is a characteristic of the surface of an object. When an object is irradiated by light, the ability to reflect light in a certain direction is also different due to the different smoothness of the surface of the object. This property of reflecting light in a certain direction is called gloss. Generally, paints are divided into three types: glossy, semi-glossy and matt. Glossy paint refers to a gloss above 40, a semi-gloss paint with a gloss of 20 to 40, and a matte paint with a gloss below 10, which is divided according to the different requirements of the paint in practical applications.
This method is suitable for the determination of colored paints, not for the determination of the gloss of colored paints containing metallic pigments. The gloss meter is used to measure the gloss of the sample by using the principle of light reflection and relative to the mirror gloss standard plate.
Instruments and Materials
(1) The gloss meter is composed of a light source part and a receiving part. The light emitted by the light source becomes parallel light or slightly convergent light through the lens and hits the surface of the paint film of the test panel at a certain angle. The absorbed, generated photocurrent can be read with the help of a galvanometer for gloss. The luminous flux received by the photocell depends on the reflective ability of the sample. At present, there are mainly three standard angles of 20°, 60° and 85° to measure the specular gloss of the paint film. The measurement principle is shown in the left figure below. The 60° angle is suitable for the determination of all paint films, but for paints with high gloss or near dull paints, 20° or 85° are more suitable. 20° is suitable for high gloss paints (above 70 gloss units measured at 60°) and 85° is suitable for low gloss paints (below 30 gloss units measured at 60°).
The specifications of the gloss meter are desktop and portable. The desktop gloss meter consists of a measuring head and a host, and is mostly used in laboratories, as shown in the right figure below. Portable can be used both in the laboratory and on the construction site, and is currently widely used. According to different test angles (light path), it can be divided into multi-angle (or three-angle) Glossmeter and single-angle Glossmeter.
(2 ) Standard boards usually include two standard boards, high gloss and low gloss. High-gloss plates are available in highly polished black glass or in clear glass with back and edges ground and black lacquered, with calibration standard values for calibration. The low-gloss ceramic plate is only used to check whether the instrument is working well, not for calibration. If the instrument reading of the low-gloss plate differs from the specified value by more than 1 gloss unit, the instrument needs to be readjusted.
test methods
Before the test, calibrate the instrument with a black standard plate, calibrate and adjust the gloss meter, measure three readings at different positions parallel to the coating direction of the sample, and record the average value as the specular gloss value.
The result shows
Expressed in units of gloss at an angle.
Reference standard
National standard GB/T 9754 "Determination of 20°, 60° and 85° specular gloss of pigmented paint films without metallic pigments"
Note: This method introduces the most widely used photoelectric Glossmeter at present. If the paint film has defects such as scratches, scratches, ripples, orange peels, etc., diffuse reflection will occur, making it difficult for the reflected light to concentrate on the photocell receiver. It is recommended to use a projection gloss meter, which is to compare the light of the paint film with a set of standard plates with known gloss, find out the cup standard sample with the same reflection amount as the tested sample, and use the gloss of the standard sample to express the gloss of the tested sample Spend.
