Plastics are the second largest user of Titanium Dioxide pigments, accounting for 18% - 20% of the world's total demand for titanium dioxide. The addition amount of titanium dioxide in plastics varies with its variety and application, generally ranging from 0.5% to 5%. At present, the annual output of plastic products is more than 60 million tons, and the consumption of titanium dioxide is about 600000 tons.
In 2018, the domestic production of plastic products totaled 60.4215 million tons, down from last year. Due to the strict control of domestic environmental protection factors, the use of recycled materials has shrunk, and under the background of Sino US trade war, the production of plastic products has decreased. The decline in the output of plastic products mainly affects the use of recycled materials, but has little impact on the use of new materials. The domestic supply of new materials continues to increase, and there is no large accumulation of new materials inventory in domestic petrochemical and various links.
The application of titanium dioxide in plastic products can not only make use of its high covering power, achromatic power and good mixing performance with other pigments, but also improve the heat resistance, light resistance and weather resistance of plastic products, so as to protect the plastic products from UV light, and improve the mechanical strength and electrical properties of plastic products. It is used in almost all thermosetting and thermoplastic plastics, such as polyolefins (mainly low density polyethylene), polystyrene, ABS (acrylonitrile butadiene styrene copolymer), polyvinyl chloride, etc. It can be dry mixed with Resin powder, or mixed with liquid containing Plasticizer, and some titanium dioxide can be made into Color Masterbatch by intermediate factory before use. Therefore, the properties of titanium dioxide used in plastics are mainly fine particle size and uniform particle size distribution, so as to enhance the reflection ability of short wave light and make plastic products with better color. In addition, Titanium Dioxide Pigment must have good heat resistance and high dispersion. Therefore, titanium dioxide used in plastics is generally treated by inorganic coating and organic coating. Like coating system, titanium dioxide for outdoor plastic should be rutile type, and others can be anatase type.
For titanium dioxide used in plastics, fine particles and good dispersibility are required; heat resistance and light resistance are good; the finished products are not discolored in the process of sunlight exposure and use. The particle size of titanium dioxide used in most plastics is relatively small. Generally, the particle size of titanium dioxide for coating is 0.2-0.4 μ m, while that of titanium dioxide for plastic is 0.15-0.3 μ M. in this way, blue background phase can be obtained, which can shield most of the resins with yellow phase or easily yellowing. If titanium dioxide is used instead of lithopone, the consumption of white pigment can be reduced by 50% ~ 70%.
Titanium dioxide for ordinary plastics is generally not surface treated, because the titanium dioxide coated with conventional hydrated alumina, when the relative humidity is 60%, its 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 plastic surface. This kind of titanium dioxide without inorganic coating generally has to go through the organic surface Surface treatment (polyol, silane or siloxane), because titanium dioxide for plastics is different from titanium dioxide for coating, the former is mixed by shearing force processing in low polarity resin, and the titanium dioxide after organic surface treatment can be well dispersed under appropriate mechanical shear force. Because of the high phr of TiO 2 in color masterbatch, its dispersibility is more important. Therefore, higher requirements are put forward for the surface treatment of titanium dioxide.
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 on weather resistance. In addition to the use of rutile titanium dioxide, it also needs surface treatment, which generally does not add zinc, only silicon, aluminum, zirconium, etc. Silicon has the function of hydrophilic dehumidification, which can prevent the formation of pores due to water evaporation during high temperature extrusion of plastics. However, the amount of these surface treatment agents is generally not too much.
When titanium dioxide is used in polyolefins (such as Polypropylene), sometimes the plastics will turn yellow, which is caused by the reaction between titanium dioxide and antioxidant (BHT) containing phenol group in polyolefin. Proper organic surface treatment of titanium dioxide can reduce the yellowing effect.
In the rigid polyvinyl chloride containing lead stabilizer, titanium dioxide will cause the resin to turn grey under the condition of ultraviolet irradiation. This is because the titanium dioxide after ultraviolet irradiation will be reduced to Ti2O3 and lead in the lead stabilizer will be precipitated. This reaction is reversible. However, it will not happen in soft PVC and rigid 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. If it is to be used in the above materials, rutile titanium dioxide with low chemical activity and high weather resistance must be selected.
