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Analysis of Influencing Factors on Colour Coordinates in Float Glass Manufacturing Process
From：CHANGZHOU ZHONGBO GLASS MACHINE AND EQUIPMENT CO.,LTD Date：2019-3-25 14:10:39
The screen protection glass high aluminium cover glass produced by float method is used in the outer layer of the display screen. In order to ensure the touch effect and the aesthetic effect of the decorative layer, the cover glass is required to have a transmittance of more than 91% and a stable color with a "white" vision. When using CIE 1976LAB uniform color space representation issued by CIE (International Lighting Commission) in 1976, the values of color coordinates a*, b* should be controlled within 0.20 to meet the requirements. In this paper, the transmittance is not discussed, but the chromaticity coordinates of glass are discussed and analyzed.
(1) The influence of coloring elements in raw materials on the coordinates of glass chromaticity of super white high aluminium cover plate. The content of coloring elements in raw materials of ultra-white glass should be limited. The common coloring element is iron. In order to reduce the iron content in mineral raw materials, most iron is removed by acid washing, ball milling and strong magnetic removing, and a small amount of copper, chromium, nickel, manganese, titanium and other coloring elements are also contained. Therefore, when formulating the raw material standard of ultra-white high aluminium glass, the limitation of coloring element content should be fully considered. The content of coloring elements in the mixture is shown in Table 1, and the chromaticity coordinates are shown in Figure 1. From Table 1 and Figure 1, it can be seen that a small amount of chromium, nickel, manganese and titanium has little effect on the color coordinates of glass, and iron content (above 80 *10-6) is the main factor.
(2) The influence of redox index of mixture on the coordinates of glass chromaticity of super white high aluminium cover plate. The valence-changing coloring ions in the mixture are mainly iron, and iron has two valence states of Fe2 + and Fe3 + in the glass. Fe2 + is green in glass, and Fe3 + is pale yellow in glass. Fe2 + has 10 times higher coloring ability than Fe3 +. In the same glass composition formula, different amount of oxidizing and reducing agents were added to make the batch have different oxidizing and reducing index. The samples of high aluminium cover glass were melted in the same atmosphere. The measured chromaticity coordinates are shown in Table 2, and the chromaticity coordinates are shown in Figure 2. From Table 2 and Figure 2, it can be seen that the higher the redox index of the mixture, the smaller the influence of the coordinates of glass chromaticity, i.e. moving to the lower right, the whiter the color of visual glass.
(3) The influence of furnace atmosphere on the valence state of iron ions and the coordinates of product color. The measured values of color coordinates of products (Fe2+/total Fe) and products are listed in Table 3. The variation of color coordinates is shown in Figure 3. From Table 3 and Figure 3, it is obvious that with the increase of residual oxygen in the furnace, the proportion of Fe2+ in the total iron in the glass decreases, the coordinate value of the color of the glass decreases, the color of the glass becomes white, and the visual situation is the same.
Through a series of experiments, it can be concluded that: (1) the coloring elements iron, copper, manganese, nickel and chromium in raw materials have great influence on the color coordinates of glass products, which should be controlled. For ultra-white high aluminium cover glass, the total iron should be controlled below 70 x 10-6, and other coloring elements should be controlled below 10 x 10-6. (2) The redox index of the mixture is the main factor affecting the valence of iron ions in glass. Increasing the redox index of the mixture can significantly increase the proportion of Fe3+, thus greatly reducing the color coordinate value of the glass and making the visual glass more "white". It is suggested that the redox index of the mixture is positive and more than + 40 is suitable for producing super white and high aluminium cover glass. (3) Furnace oxidation atmosphere can make the iron ions in glass change to high valence state, thus greatly reducing the color coordinate value of glass and making the visual glass more "white". The furnace atmosphere can be measured by oxygen content measuring instrument. The residual oxygen of the furnace is better than 0.8% and better than 1.0%.