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Papermaking is the third largest user of titanium dioxide. Considering the production cost, titanium dioxide will not be used in low-grade paper, but porcelain clay, talcum powder, calcium carbonate, etc. will be mainly used, but they will reduce the strength of the paper and increase the weight of the paper. Decorative paper, Bible paper and banknotes (such as dictionaries, pictorials, magazine covers, computers, banknotes, copier paper and decorative paper) must use titanium dioxide. Paper using titanium dioxide has good whiteness, high strength, luster, thin and smooth, and does not penetrate during printing. Under the same conditions, the opacity is 10 times higher than calcium carbonate and talcum powder, and the weight can also be reduced by 15%~30%.
Decorative paper, also known as titanium white paper, is mainly used as a raw material for making furniture, flooring, wallpaper, etc. For paper with anti-aging requirements, rutile must be used; More rutile is used in high ash paper, which must use rutile because the hiding power of anatase titanium dioxide cannot meet the requirements. Sharp titanium dioxide is commonly used in low ash paper, such as Bible paper and banknotes. Bible paper requires a good opacity, which can generally be achieved by using sharp titanium dioxide; Coin making paper also requires good opacity, mainly using sharp titanium type. In China, the amount of titanium dioxide used in decorative paper is much higher than the other two varieties, which is determined by the consumption level of our country. Due to the large demand for house decoration and high-end furniture, the usage of decorative paper is gradually increasing; Due to the use of titanium dioxide as raw material, the cost of Bible paper is much higher than that of ordinary paper. Given the domestic consumption level, the market for Bible paper is very limited; The manufacturing and use of coinage paper are also controlled by the state, with relatively stable usage and no impact on the titanium dioxide market. According to incomplete estimates, the amount of titanium dioxide used for decorative paper in China exceeds 30000 tons per year. The amount of titanium dioxide used in decorative paper is 20-40%, while in other papers, it is 1-5%. Due to the transformation of traditional cultural paper manufacturers to produce decorative paper, the production of decorative paper has increased rapidly, and the price of decorative paper has shown a downward trend in recent years.
Regardless of the type of paper (base paper), the production process is the same:
Rutile is used for weather resistant and high ash paper, and anatase is used for paper with low ash and low weather resistance requirements. The main reason why paper mills choose titanium dioxide is the cost of paper making, that is, the cost performance ratio of titanium dioxide. As the cost proportion of titanium dioxide in papermaking is as high as 30~50%, the paper mill can be said to be careful about choosing titanium dioxide when meeting the user's requirements, and rutile will never be used if anatase can be used. The requirements for the quality of titanium dioxide in the papermaking industry, in order of importance, are:
1) Covering power (opacity): The ability of paper containing the same amount of titanium dioxide to cover the background color, which determines the cost-effectiveness of titanium dioxide. Simply put, titanium dioxide with high covering power is generally more expensive but less used, so the cost of titanium dioxide per ton of paper may be lower; Titanium dioxide with low covering power, although low in price, has a large dosage, resulting in an increase in the cost of titanium dioxide per ton of paper;
2) Whiteness: The whiteness of titanium dioxide determines the appearance of the paper after molding;
Difference between rutile titanium dioxide and anatase titanium dioxide
1、 Physical properties
1) Relative density
Among commonly used white pigments, titanium dioxide has the smallest relative density, while among white pigments of the same quality, titanium dioxide has the largest surface area and the highest pigment volume.
2) Melting point and boiling point
The melting point and boiling point of anatase titanium dioxide are virtually nonexistent because anatase will change into rutile at high temperature. Only rutile titanium dioxide has a melting point and a boiling point. The melting point of rutile titanium dioxide is 1850 ℃, the melting point in air is (1830 ± 15) ℃, and the melting point in oxygen enriched air is 1879 ℃. The melting point is related to the purity of titanium dioxide. The boiling point of rutile titanium dioxide is (3200 ± 300) ℃, and the titanium dioxide is slightly volatile at this high temperature.
3) Dielectric constant
Due to its high dielectric constant, titanium dioxide has excellent electrical properties. When determining certain physical properties of titanium dioxide, it is necessary to consider the crystallization direction of titanium dioxide crystals. The dielectric constant of anatase titanium dioxide is relatively low, only 48.
4) Conductivity
Titanium dioxide has the properties of a semiconductor, its conductivity rapidly increases with temperature, and it is also very sensitive to hypoxia. The dielectric constant and semiconductor properties of rutile type titanium dioxide are very important for the electronic industry, which can be used to produce electronic components such as ceramic capacitors.
5) Hardness
According to the ten scale of Mohs hardness, rutile titanium dioxide is 6~6.5 and anatase titanium dioxide is 5.5~6.0. Therefore, anatase is used in chemical fiber matting to avoid abrasion of spinneret holes.
6) Hygroscopicity
Although titanium dioxide has hydrophilicity, its hygroscopicity is not very strong, and the rutile type is smaller than the anatase type. The hygroscopicity of titanium dioxide is related to its surface area, which is large and has high hygroscopicity. It is also related to surface treatment and properties.
7) Thermal stability
Titanium dioxide is a substance with good thermal stability.
2、 Chemical properties
Titanium dioxide is a kind of acidic amphoteric oxide with extremely stable chemical properties. At room temperature, it hardly reacts with other elements and compounds, and has no effect on oxygen, ammonia, nitrogen, hydrogen sulfide, carbon dioxide, or sulfur dioxide. It is insoluble in water, fats, dilute acids, inorganic acids, and bases, and only soluble in hydrofluoric acid. However, under the action of light, titanium dioxide can undergo continuous oxidation-reduction reaction and has photochemical activity. This kind of photochemical activity is particularly obvious for anatase titanium dioxide under ultraviolet radiation. This property makes titanium dioxide, even though it is a photosensitive oxidation catalyst for some inorganic compound, is also a photosensitive reduction catalyst for some organic compounds.
3) Dispersibility: Nowadays, papermaking processes generally use dispersants, so there is little difference in the water dispersibility of titanium dioxide;
4) Weather resistance: domestic rutile can meet the weather resistance requirements of most papers, and only a few papers need rutile to provide high weather resistance;
5) Retention rate: In the papermaking industry, filtered water is reused or retention aids are used. Generally, the recovery rate of titanium dioxide is above 99%. The reason for retaining this indicator is that international titanium dioxide companies provide retention agent formulas and usage methods when promoting paper specific titanium dioxide, in order to improve service quality and increase product competitiveness.
