Characteristics of titanium dioxide used in paper industry
Papermaking is the third largest user of titanium dioxide. Titanium dioxide is generally not used in low-grade paper due to consideration of production costs, mainly china clay, talc, calcium carbonate, etc., but they will reduce the strength of the paper and increase the weight of the paper. Titanium dioxide must be used in decorative paper, Bible paper and banknotes (such as dictionaries, pictorial newspapers, magazine covers, computers, banknotes, copier paper and decorative paper, etc.), and the paper using titanium dioxide has good whiteness, high strength and gloss , Thin and smooth, no penetration during printing, the opacity is 10 times higher than that of calcium carbonate and talc under the same conditions, and the weight can also be reduced by 15% to 30%.
Decorative paper, also known as titanium dioxide paper, is mainly used as raw materials for making furniture, floors, wallpapers, 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 reach Require. Anatase titanium dioxide is used in low ash paper, such as Bible paper and banknotes. Bible paper requires paper to have good opacity, which is generally satisfied by anatase titanium dioxide; currency paper also requires very high opacity. Good opacity, mainly anatase is also used. In China, the amount of titanium dioxide used in decorative paper is much higher than the other two varieties, and this situation is determined by my country's consumption level. Due to the large demand for house decoration and high-end furniture, the amount of decorative paper has gradually increased; the cost of Bible paper is much higher than that of ordinary paper due to the use of titanium dioxide as a raw material. In view of the domestic consumption level, the market for Bible paper is very limited; The production and use of currency paper is under the control of the state, and the amount is relatively stable, which will not have an impact on the titanium dioxide market. According to incomplete estimates, the domestic titanium dioxide used for decorative paper exceeds 30,000 tons per year. The amount of titanium dioxide in decorative paper is 20-40%, and the titanium dioxide in other papers is 1-5%. Due to the transformation of traditional cultural paper production plants to produce decorative paper, the output of decorative paper has increased rapidly, and the price of decorative paper has been declining in recent years.
No matter what kind of paper (base paper), the production process is the same:
Rutile is used for paper with weather resistance and high ash content, and anatase type is used for paper with low weather resistance and low ash content. . Since the cost ratio of titanium dioxide in papermaking is as high as 30-50%, paper mills can be very careful about the choice of titanium dioxide when they meet the requirements of users. They can use anatase and never use rutile. The paper industry's requirements for the quality of titanium dioxide are in the order of importance:
1) Covering power (opacity): the ability of paper containing the same titanium dioxide to cover the background color, this index determines the cost performance of titanium dioxide. To put it simply, titanium dioxide with high hiding power is generally expensive, but the amount used is small, so the cost of titanium dioxide per ton of paper may be lower; titanium dioxide with low hiding power, although the price is low, but the amount used is large, resulting in per ton of titanium dioxide. The cost of titanium dioxide in paper increases;
2) Whiteness: the whiteness of titanium dioxide determines the appearance of paper after forming;
the difference between rutile titanium dioxide and anatase titanium dioxide
1. Physical properties
1) Relative density
is in commonly used white pigments Among them, titanium dioxide has the smallest relative density. Among the white pigments of the same quality, titanium dioxide has a large surface area and a high pigment volume.
2) Melting point and boiling point
Since the anatase type transforms into a rutile type at high temperature, the melting point and boiling point of anatase titanium dioxide do not actually exist. Only rutile titanium dioxide has a melting point and boiling point. The melting point of rutile titanium dioxide is 1850 ° C, the melting point in air is (1830 ± 15) ° C, and the melting point in oxygen-rich is 1879 ° C. The melting point is related to the purity of titanium dioxide. The boiling point of rutile titanium dioxide is (3200±300)°C, and titanium dioxide is slightly volatile at this high temperature.
3) Dielectric constant
Titanium dioxide has excellent electrical properties due to its high dielectric constant. When determining some physical properties of titanium dioxide, the crystallographic direction of titanium dioxide crystals should be considered. The dielectric constant of anatase titanium dioxide is relatively low, only 48.
Titanium dioxide has semiconductor properties, its conductivity increases rapidly with the rise of temperature, and it is also very sensitive to oxygen deficiency. The dielectric constant and semiconductor properties of rutile titanium dioxide are very important to the electronics industry, and these properties can be used to produce electronic components such as ceramic capacitors.
5) The hardness
is scaled according to the Mohs hardness scale, rutile titanium dioxide is 6-6.5, anatase titanium dioxide is 5.5-6.0, so anatase type is used in chemical fiber matting to avoid abrasion of spinneret holes.
Although hygroscopic titanium dioxide is hydrophilic, its hygroscopicity is not very strong, and the rutile type is smaller than the anatase type. The hygroscopicity of titanium dioxide has a certain relationship with the size of its surface area. Large surface area and high hygroscopicity are also related to surface treatment and properties.
7) Thermal stability
Titanium dioxide is a substance with good thermal stability.
2. Chemical properties
The chemical properties of titanium dioxide are extremely stable, and it is a kind of acidic amphoteric oxide. It hardly reacts with other elements and compounds at room temperature, and has no effect on oxygen, ammonia, nitrogen, hydrogen sulfide, carbon dioxide and sulfur dioxide. It is insoluble in water, fat, dilute acid, inorganic acid and alkali, only soluble in hydrogen Fluoric acid. However, under the action of light, titanium dioxide can undergo continuous redox reactions and has photochemical activity. This kind of photochemical activity is particularly obvious under the irradiation of ultraviolet light. This property makes titanium dioxide a photosensitive oxidation catalyst for some inorganic compounds and a photosensitive reduction catalyst for some organic compounds.
3) Dispersibility: The current papermaking process generally uses dispersants, so the water dispersibility of titanium dioxide is not much different;
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: The paper industry reuses filtered water, or uses auxiliary Retention agent, the recovery rate of titanium dioxide is generally above 99%. The reason why this index is retained is because the international large titanium dioxide company provides the formulation and application method of retention aid when promoting the titanium dioxide for papermaking, so as to improve the service quality. , to increase product competitiveness