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2025-02-09
Aluminum foil, also known as fake silver foil, is a hot stamping material that is directly rolled into thin sheets of metal aluminum. Due to its excellent properties, it is widely used in food, beverages, cigarettes, etc., and is usually used as their packaging material. Gloss is an important indicator for testing the appearance quality of aluminum foil, so its gloss needs to be quantified. This article introduces the gloss measurement method of aluminum foil.
Aluminum foil
There are many factors that affect the surface gloss of aluminum foil, but they can be summarized as follows: roller parameters, rolling oil, rolling parameters and other aspects.
1. Effect of roller parameters on gloss
The influence of roller parameters on the surface gloss of aluminum foil mainly includes two aspects: roller roughness and grinding wheel for grinding roller. As the roller roughness changes, the gloss of aluminum foil surface will also change. Generally speaking, as the roller roughness decreases, the gloss of aluminum foil surface gradually increases. In addition, different grinding wheel models have different effects on roughness. In general, grinding rollers with the same roughness with different grinding wheels will also change the gloss of aluminum foil surface.
2. Effect of rolling oil on gloss
Rolling oil consists of two parts: base oil and additives. It reduces friction and pressure by establishing an oil film between the roller and the aluminum foil. The oil film is crucial to the glossiness of the aluminum foil surface. The polar groups in the rolling oil can be adsorbed on the surface of the aluminum foil, and a directional adsorption film is formed after its monolayer reaches saturation. In addition, the non-polar ends of polar molecules attract each other, so that the several molecular layers formed can convert the friction between the aluminum foil and the roller into friction between the molecular layers inside the oil film, forming fluid lubrication. Aluminum foil rolling is carried out in a mixed lubrication between fluid lubrication and boundary lubrication. Rolling oil mainly affects the glossiness of the aluminum foil surface by affecting the thickness and strength of the oil film. In addition, the amount of additives is also an important factor affecting the glossiness of the aluminum foil surface. This is because the appropriate additive content can effectively increase the strength of the oil film, thereby enhancing the lubricity between the aluminum foil and the roller in the deformation range.
3. Effect of rolling parameters on glossiness
(1) The influence of rolling force and processing rate. Studies have shown that with the increase of rolling force and processing rate, the glossiness of the aluminum foil surface will also change to varying degrees. Therefore, in the actual production process, the rolling force and processing rate must be well controlled.
(2) The influence of speed. The increase in speed will increase the thickness of the oil film, thereby reducing the rolling effect of the roller on the surface of the aluminum foil, causing the surface gloss of the aluminum foil to decrease. For aluminum foil with high surface quality requirements, in order to ensure high surface gloss, the finished product pass speed should not be too fast.
(3) Influence of oil temperature. When the oil temperature rises, the thickness of the oil film will decrease, which can increase the rolling effect of the roller on the surface of the aluminum foil and improve the surface gloss of the aluminum foil. Therefore, within the control range of safe production, the oil temperature should be appropriately increased, especially the oil temperature of the finished product.
Gloss meter to measure the glossiness of aluminum foil
There are two commonly used methods for evaluating the surface gloss of aluminum foil: visual inspection and instrumental inspection. The visual inspection method is to observe the surface gloss of copper and gold powder directly from a specific angle under a stable light source environment. This method can accurately compare the gloss difference between the sample and the standard sample, but it cannot evaluate the specific gloss level, and the measurement result is easily affected by the light source, observation angle, and the observer's own conditions. The instrumental measurement method refers to measuring the gloss of the surface of the aluminum foil sample with a gloss meter. Users can quickly measure the gloss of the aluminum foil surface by following the operation and use process of the gloss meter.
The gloss meter uses the principle of light reflection to measure the gloss of the sample. The sample is illuminated under the conditions of a specified incident angle and a specified light beam to obtain a light beam in the direction of the mirror reflection angle. The gloss meter is used to measure the ratio of the reflected light flux on the sample surface to the incident light flux, that is, the reflectivity is used to evaluate the strength of the surface gloss. The gloss meter consists of a light source, a lens, a receiver, and a display instrument. When using a gloss meter to measure the gloss of nitro paint, operate it according to the instrument's instruction manual. After the instrument is preheated and stabilized, calibrate it with a high-gloss working standard plate, and then verify it with a medium-gloss or low-gloss working standard plate. If the difference between the instrument indication and the calibration value of the working standard plate is within 1 gloss unit, the instrument can be measured. Otherwise, it should be readjusted by the manufacturer before use.
At present, there are many models and types of gloss meters on the market. The multi-angle (20°, 60°, 85°) gloss meter developed by Sanenshi Company can be used to measure samples with a gloss range of 10% to 70% on the surface of aluminum foil; when the gloss of the sample exceeds 70%, it should be measured at an angle of 20; and when the gloss of the sample is less than 10%, it should be measured at an angle of 85. For the convenience of accurate measurement, when the gloss measured at an angle of 60 is less than 30%, it can also be measured at an angle of 85. When measuring high gloss, place the instrument on the sample, and as long as the operation button is pressed, two data measured at 20 and 60 angles can be obtained at the same position, and the average value and standard deviation can be measured. The data generally read is the arithmetic mean of the five test points, and the difference between the readings of each test point and the average value is not greater than 5% of the average value.
