1、 Overview
Titanium Dioxide (TiO2) is considered to be the most excellent white pigment in the world. It is non-toxic, has the best opacity, the best whiteness and brightness, and is widely used in coatings, plastics, paper making, printing ink, chemical fiber, rubber, ceramics, cosmetics, food and medicine industries. It is known as "industrial monosodium glutamate". Its per capita consumption is an important indicator to measure a country's economic development level, and it is also an important indicator to measure the country's market potential There is no evidence. As the basic industry of China's economy, titanium dioxide fundamentally affects the development of various industries, often known as the "barometer" of national economic development.
There are two manufacturing methods, sulfuric ACID method and chlorination method. At present, 60% of the world's products are produced by chlorination process. In developed countries in Europe and America, the proportion of chlorination process is higher. Chlorination titanium dioxide production process is internationally recognized as a new generation of advanced technology because of its environmental protection and high product quality. As early as 2006, the last titanium dioxide plant in China was closed in the United States. In recent years, China is also vigorously promoting the upgrading of titanium dioxide industry. In 2005, chlorinated titanium dioxide was listed as an encouraging project in the guidance catalogue of industrial structure adjustment (2005 Edition).
2、 Comparison of sulfuric acid process and chlorination process for titanium dioxide production
1. Production process of titanium dioxide by sulfuric acid method
The operation procedure of titanium dioxide production process by sulfuric acid method is very complex. Its basic chemical reaction includes a series of simple chemical reactions, such as acidolysis, hydrolysis and calcination of iron concentrate. The sulfuric acid method mainly uses ilmenite and sulfuric acid as raw materials, decomposes with sulfuric acid, and finally makes titanium dioxide.
2. Production process of titanium dioxide by chlorination
Chlorination titanium dioxide process rose in 1940s and 1950s, and developed rapidly. In order to reduce the environmental pollution caused by "three wastes", chlorination process is based on titanium rich materials (such as high titanium slag produced by electric furnace, natural rutile and artificial rutile produced by various methods). As far as chlorination process of titanium rich materials is concerned, it can be divided into boiling chlorination and molten salt chlorination. The main processes of chlorination are chlorination, oxidation and coating (the same as sulfuric acid process)
2、 Analysis of advantages and disadvantages of titanium dioxide produced by sulfuric acid method and chlorination method in various application fields
Titanium dioxide is widely used in coatings, plastics, paper, printing ink, chemical fiber, rubber, ceramics, cosmetics, food and medicine and other fine chemical industries. Its main application fields are coatings, plastics and paper, and its consumption composition is as follows: Coatings 58% - 60%; plastics 18% - 20%; paper 13% - 14%; rubber, fiber, ink, cosmetics and other industries account for 8% - 10%. However, due to the different manufacturing methods of titanium dioxide, the performance of titanium dioxide products also has its own advantages and disadvantages, and its application effect is not the same.
1. Application Comparison of two processes in coating products
(1) Requirements of coatings on properties of titanium dioxide
The coating industry is the largest user of titanium dioxide, especially rutile titanium dioxide, which is mostly consumed by the coating industry. The consumption of TiO2 in the global coating industry accounts for 58% - 60% of the total consumption of Titanium Dioxide Pigment, and the consumption proportion in China is higher, about 60% - 65%. Titanium dioxide is one of the most used pigments in the coating industry, accounting for half of the cost of pigment. Its consumption in the coating industry accounts for 90% of the total amount of pigments consumed in the coating industry, and 10% ~ 25% of the cost of coating raw materials. There are so many white pigments, why do coatings only focus on titanium dioxide for many years? The main reason is that titanium dioxide is far superior to other white pigments in various main properties.
Pigment name relative density refractive index achromatic power hiding power
Titanium dioxide has the highest refractive index, so it has the highest covering power (opacity) and achromatic power and other optical properties, bright whiteness, high gloss and good dispersion. Theoretically speaking, in terms of covering power, rutile titanium dioxide is 5.56 times of ordinary lithopone, anatase titanium dioxide is 4.43 times of ordinary lithopone; in terms of achromatic power, rutile titanium dioxide is 6.25 times of lithopone, anatase titanium dioxide is 5.56 times of ordinary lithopone. Therefore, only from the use effect, 1 ton of titanium dioxide is equivalent to at least 4 tons of ordinary lithopone; from the service life (mainly refers to outdoor anti pulverization) point of view, the coating with titanium dioxide as pigment is 3 times higher than that with ordinary lithopone as pigment, which is the reason why titanium dioxide has been selected for coatings for a long time.
Titanium dioxide is one of the indispensable components of coatings. Its function is not only to cover and decorate, but also to improve the physical and chemical properties of coatings, as well as the mechanical strength, adhesion, corrosion resistance, light and weather resistance of coatings. Therefore, the application of titanium dioxide should be considered not only from the base material, solvent, additives and other aspects, but also from the pigment characteristics, paint performance and other aspects, so as to reasonably select the type and specification of titanium dioxide suitable for the performance requirements of coatings. Pigment grade titanium dioxide is usually used in coating industry. Its quality requirements for titanium dioxide are as follows: 1. Good whiteness; 2. Good grinding wettability and easy dispersion; 3. Good weather resistance and durability; 4. Good chemical stability; 5. Small particle size, large covering power, high fading power, good opacity and gloss. The requirements of common coatings on the properties of titanium dioxide are shown in Table 2.
(2) Comparison of two kinds of titanium dioxide in coating application
Based on the application characteristics of different coatings, there are different requirements for weather resistance, covering power, aesthetics and dispersibility of titanium dioxide,
According to the performance requirements of coatings, it is very important to select the type of titanium dioxide that can meet the performance requirements of coatings and coatings.
The product produced by chloridized rutile is the best white pigment in the current market. Its comprehensive performance is excellent. It is the preferred white pigment in the coatings, and it is also the necessary pigment for light color coatings. Due to the different surface treatment process, titanium dioxide has different types. The specific type can be selected according to the characteristics of the prepared coating, such as whether it requires high gloss, or high hiding power, or high resistance to pulverization. Rutile titanium dioxide produced by sulfuric acid process has lower conversion rate from anatase to rutile than that by chlorination process, so the whiteness and light stability of the product are slightly worse than those by chlorination process, but the price is lower.
(1) Requirements of plastics on properties of titanium dioxide
The plastic industry is the second largest user of titanium dioxide, accounting for about 20% of the total demand of titanium dioxide in the world. It is the fastest growing field of titanium dioxide application in recent years, with an average annual growth rate of 6%. Among more than 500 titanium dioxide brands in the world, more than 50 brands belong to the plastic special type. The plastic industry is an important application field of titanium dioxide. In the past ten years, it has developed at an amazing speed in China. In 2019, according to the statistics of the plastic products industry in China, the total output of enterprises in the plastic products industry reached 81.8417 million tons, with a year-on-year increase of 3.91%,
Adding titanium dioxide into plastics can improve the heat resistance, light resistance and weather resistance of plastic products, improve the physical and chemical properties of plastic products, strengthen the mechanical strength of products and prolong the service life. Moreover, in recent years, with the continuous strengthening of people's awareness of environmental protection and energy conservation, the pace of replacing steel with plastic will be faster and faster in the future, and the proportion of plastic products in our life will be larger and larger. It is predicted that in the near future, the demand for plastics will exceed that of steel, and the demand for titanium dioxide, the basic pigment of plastic filler, will increase year by year. UPVC profile is becoming more and more important in the plastic industry. UPVC profile is becoming an important application field of TiO2 industry.
The role of titanium dioxide in the plastic industry mainly has two aspects, one is as the basic use of white pigment, providing covering effect (white coloring); the second is to hinder ultraviolet, as a UV screening agent, providing good weather resistance for outdoor plastic products. The titanium dioxide used in the production of ordinary plastics does not require weather resistance, but focuses on the pigment performance.
For titanium dioxide used in plastics, it is required to have fine particles, good dispersibility, good heat resistance and light resistance, and the finished product will not change color in the process of heating and processing in the plastic molding and in the process of sunlight exposure and use. The particle size of most titanium dioxide used for plastics is fine. Generally, the particle size of titanium dioxide used for coatings is 0.2-0.4 μ m, while that of titanium dioxide used for plastics is 0.15-0.3 μ M. in this way, a blue background phase can be obtained, which can shield most resins with yellow phase or those prone to yellowing. The consumption of white pigment can be reduced by 50% ~ 70% if titanium dioxide is used instead of lithopone.
Titanium dioxide for ordinary plastics generally does not go through surface treatment, because the titanium dioxide coated with inorganic substances such as hydrated alumina is used. When the relative humidity is 60%, the adsorption equilibrium water is about 1%. When the plastic is extruded at high temperature, the evaporation of water will lead to pores on the smooth surface of the plastic. This kind of titanium dioxide without inorganic substances coating generally has to go through the organic surface treatment Surface treatment (polyol, silane or siloxane), because the plastic titanium dioxide is different from the coating titanium dioxide, the former is in the low polarity Resin, through the shear force processing mixing, organic surface treatment of titanium dioxide, in the appropriate mechanical shear force, can be better dispersed. Due to the high phr of TiO2 in Color Masterbatch, its easy dispersibility is more important, so the surface treatment of titanium dioxide has higher requirements.
With the continuous expansion of the scope of application of plastic products, many external plastic products, such as plastic doors and windows, building materials and other outdoor plastic products, also have high requirements for weather resistance. In addition to the use of rutile titanium dioxide powder, surface treatment is also required. This surface treatment generally does not add zinc, only silicon, aluminum, zirconium and so on. Silicon has the function of hydrophilic and dehumidification, which can prevent the formation of pores due to water evaporation during high temperature extrusion, but the amount of these surface treatment agents is generally not too much.
When titanium dioxide is used in polyolefin (such as Polypropylene), it sometimes makes plastics yellowing, which is caused by the reaction between titanium dioxide and phenolic antioxidant (BHT) in polyolefin. Proper organic surface treatment of titanium dioxide can reduce the yellowing effect.
In unplasticized polyvinyl chloride containing lead stabilizer, titanium dioxide can make the resin gray under the condition of UV irradiation. This is because the titanium dioxide after UV irradiation will be reduced to Ti2O3, resulting in the precipitation of lead in the lead stabilizer. This reaction is reversible. However, it will not happen in soft PVC and hard PVC with tin stabilizer. It is also used in MELAMINE formaldehyde resin. Because of the reducibility of the resin itself and the effect of ultraviolet light, melamine decorative board can also change (gray) color. If it is used in the above materials, rutile titanium dioxide with low chemical activity and high weatherability must be selected.
(2) Comparison of two kinds of titanium dioxide used in plastics
It is understood that the titanium dioxide used in domestic plastic products, especially high-end products, is still mainly imported chlorination titanium dioxide. Chlorination titanium dioxide is not only superior to sulfuric acid titanium dioxide in whiteness and other appearance properties, but also has incomparable advantages in covering power, dispersibility and processability, especially for outdoor UPVC Plastic Profile Products, and chlorination rutile products
However, due to the characteristics of plastic products, the selection of titanium dioxide is different from that of other coatings, inks and paints. It should be mainly considered according to the technical requirements of plastic products. For example, for special plastic products, titanium dioxide products suitable for their special uses must be carefully selected according to their product requirements, so as not to affect the performance of plastic products.
3. Application Comparison of two processes in papermaking products
(1) Requirements of paper products on properties of titanium dioxide
According to the survey data of China Paper Association, in 2019, there were about 2700 paper and paperboard manufacturers in China, and the national production of paper and paperboard was 107.65 million tons, an increase of 3.16% over the previous year. The consumption was 107.04 million tons, an increase of 2.54% over the previous year, and the annual per capita consumption was 75 kg (1.4 billion people). From 2010 to 2019, the average annual growth rate of paper and paperboard production is 1.68%, and the average annual growth rate of consumption is 1.73%
The paper industry is the third largest user of titanium dioxide. As a paper filler, it is mainly used in high-grade paper and thin paper. It can make the paper have better whiteness, good luster, high strength, thin and smooth, no penetration when printing, light weight. Titanium dioxide for papermaking generally uses anatase titanium dioxide without surface treatment, which can act as a fluorescent whitening agent and increase the whiteness of paper. However, the surface treated rutile titanium dioxide is required for laminated paper to meet the requirements of light resistance and heat resistance.
In the paper industry, low-grade paper generally does not use titanium dioxide because of the production cost, but mainly uses porcelain clay, talcum powder, 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, pictorials, magazine covers, computers, banknotes, copier paper and decorative paper). The paper with titanium dioxide has good whiteness, high strength, luster, thin and smooth, impenetrable when printing. Under the same conditions, its opacity is 10 times higher than calcium carbonate and talcum powder, and its weight can be reduced by 15% ~ 30%.
Another important application field of titanium dioxide in papermaking is decorative paper, also known as titanium dioxide paper, which is mainly used for making raw materials of furniture, floor, wallpaper, etc. In China, the amount of titanium dioxide used in decorative paper is much higher than that of other kinds. The amount of titanium dioxide used in decorative paper is 20% - 40%, and that in other paper is 1% - 5%. This situation is determined by the consumption level of our country. Due to the large demand for house decoration and high-end furniture, the consumption of decorative paper is gradually increasing; the cost of Bible paper is much higher than that of ordinary paper due to the use of titanium dioxide as raw material. In view of the domestic consumption level, the market of Bible paper is very limited; and the manufacture and use of mint paper is controlled by the state, and the consumption is relatively stable, which will not affect the titanium dioxide market.
As the name suggests, decorative paper is a decorative paper, so it has a high demand for anti-aging products. Therefore, rutile type titanium dioxide must be used. More rutile titanium dioxide is used in high ash paper, and this high ash paper must be made of rutile titanium dioxide because the covering power of anatase titanium dioxide can not meet the requirements. Anatase titanium dioxide is used in low ash paper, such as biblical paper and banknotes. Biblical paper requires good opacity, which can be met by using anatase titanium dioxide; mint paper also requires good opacity, mainly anatase titanium dioxide. Therefore, different paper products have different requirements for the performance of titanium dioxide.
(2) Comparison of two kinds of titanium dioxide in paper products
No matter what kind of paper (base paper), the production process is the same, but according to the needs of the final paper forming to choose which process of titanium dioxide products with different crystal forms, the following is the selection of different types of titanium dioxide for different paper products.
Rutile titanium dioxide has good oxidation resistance and weather resistance, which is mainly used for decorative paper and weather resistant and high ash paper; while anatase products are used for low ash paper with low weather resistance and poor transparency. Although both chlorination process and sulfuric acid process can produce rutile titanium dioxide, the whiteness, rutile crystal content and product stability of titanium dioxide produced by chlorination process are better than those produced by sulfuric acid process, so it is suitable for decorative paper and high ash paper, while anatase products produced by sulfuric acid process must be used in Mint paper and low ash paper to better meet the requirements of the two kinds of paper Titanium dioxide opacity requirements.
In addition, when we choose titanium dioxide products, we need to consider the factors of the paper mill itself, because the main reason for the paper mill to choose titanium dioxide is the cost of paper making, that is, the cost performance ratio of titanium dioxide. Because the cost of titanium dioxide in papermaking is as high as 30-50%, the paper mill is careful to choose titanium dioxide in the case of meeting the requirements of users.
