titanium dioxide in plastics


Application of rutile titanium dioxide in plastics

In the plastics industry, titanium dioxide is the most widely used white pigment. The plastics industry has become the second largest user of titanium dioxide. It is the fastest growing field in recent years, with an average annual growth rate of over 6%.

It is mainly used in the construction of plastic steel doors and windows (PVC profiles), plastic automotive parts, plastic communication equipment, household appliances, etc., in addition to titanum dioxide high hiding power, high achromatic power and good performance with other colors, it can also improve the heat resistance, light and climate properties of plastic products to protect plastic products from ultraviolet rays and improve the mechanical strength and electrical properties of plastic products.

There are more than 500 grades of rutile and anatase type titanium dioxide sold in the global market, of which more than 50 are for plastics. Since plastic products are usually much thicker than paints and inks, they are generally used in plastics in the range of 3 to 5%.

titanium dioxide

For titanium dioxide for plastics, it requires fine particles, good dispersion properties, good heat resistance and light resistance, and does not change color during plastic processing and use. It has been found through research that when some inorganic coated titanium dioxide is blended with plastic, the titanium dioxide in the inorganic coating is generally carried out due to the evaporation of the adsorbed water, which leads to the appearance of pores on the smooth plastic surface. Organic surface treatment, in the high-concentration masterbatch, due to the high content of TiO2, the dispersion of titanium dioxide is more demanding, so the surface treatment of titanium dioxide is correspondingly higher.

Performance evaluation of main application of titanium dioxide in plastics

(I) Tinting Strength refers to the coloring ability of a pigment. When the two pigments give the same color to the colored object, the amount of coloring is small. Titanium dioxide is used as a coloring agent in plastics. Obviously, tinting strength is an important indicator for evaluating its application properties.

The tinting strength of titanium dioxide in plastics can be characterized by the whiteness of the plastic. Whiteness reflects the ability of titanium dioxide to scatter light, the value of which depends on the strength of the reflection. Whiteness has various definitions, such as CIE86 (Gantz) whiteness, Hunterlab whiteness, R457 whiteness, national building materials industry standard whiteness (GB 5950-86), ceramic industry whiteness and Stensby whiteness, etc. Can be used in the plastics industry.

II) Hiding power

Hiding Power refers to the ability of a pigment to cover the undertone of a pigmented object. Titanium dioxide is the white pigment with the strongest hiding power. In coatings and inks, the hiding power of titanium dioxide can be characterized and determined by black and white glass plate method (GB 1709-79), and there is no uniform standard in plastics. When the light is on the titanium dioxide colored plastic film, part of the light is reflected, partially absorbed, and the rest is transmitted. Obviously, the smaller the transmitted light intensity when the film thickness is determined, the higher the hiding power of the titanium dioxide.

titanium dioxide in plastics

III) Dispersibility

Dispersibility refers to the ability of a pigment to disperse in a colored medium. The particles of titanium dioxide exist in three states: Primary Particle, Aggregate, and Agglomerate. Dispersion of titanium dioxide in plastics. It is the process in which the agglomerates are broken into aggregates and primary particles, and the newly formed particles are then stabilized.

Dispersibility has an important influence on the application properties of titanium dioxide in plastics. In general, the finer the titanium dioxide particles. The higher the tinting strength, the stronger the hiding power. This is because the refined titanium dioxide has a larger ratio than the surface, and the scattering of light is enhanced.

The characterization of the dispersibility is qualitative observation by a phase contrast optical microscope or an electron microscope, and the quantitative method is to determine the particle size distribution.

(IV) Processability

The addition of titanium dioxide to plastics has an effect on the rheological properties of the plastics. The higher the content, the more significant this effect. In the production of white masterbatch (especially high-concentration varieties), the quality of titanium dioxide processing is a key factor in determining production efficiency and cost.

To sum up, the main reason for the difference in workability between different titanium white materials is the compatibility of titanium dioxide with plastics. When titanium dioxide is shipped from the factory, it is coated to prevent photochemical reaction and improve weather resistance and stability.

The coating has single and composite, dense and loose, inorganic and inorganic-organic, and the commonly used inorganic coatings are Al2O3 and SiO2.

The difference in the coating method results in a difference in the surface properties of the titanium dioxide particles, which in turn affects the compatibility with the plastic melt during processing. Good compatibility, the plastic melt fully wets the surface of the titanium dioxide particles, making it easy to disperse, the system viscosity is low, and the processing torque is small. Therefore, the fundamental way to improve the processability of titanium dioxide is to improve the compatibility of the coating layer with the plastic.

(V) Weather resistance (aging of plastics and its improvement method)

With the development of the modern petroleum industry and the advancement of polymer synthesis technology, the application of plastic products has become increasingly widespread. However, plastic products are prone to aging during use (especially for long-term outdoor use), resulting in decreased material properties, yellowing, chalking, relative molecular mass degradation, surface cracking, loss of gloss, and significant deterioration of mechanical properties. Phenomenon, thus affecting the normal use of the product. So, titanium dioxide with good weather resistance is suitable in plastics. 

Titanium dioxide in plastics, titanium dioxde enjoys high hiding power, high achromatic power, good performance with other color, can improve the heat, light and climate resistance of plastics products, is an ideal coloring agent for plastics production. 

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