The proportion of titanium dioxide used in the production of various types of inks is relatively large, ranging from 25% to 50%, and some are even larger. Therefore, titanium dioxide plays a vital role in the quality of inks. There are three types of crystalline titanium dioxide in nature, namely rutile, anatase and brookite. Because the brookite titanium dioxide crystal form is extremely unstable, there are only two types of titanium dioxide suitable for ink production, rutile and anatase, and both are tetragonal crystal forms. They have stable physical and chemical properties, pure white color, fine particles, and high refractive index. In the production of inks, different types of ink products have different quality requirements for titanium dioxide. Practice has proved that rutile titanium dioxide has better application performance and can be widely used in the production of various types of inks. From the comparison of the performance indicators of the two titanium dioxides, whether it is crystal shape, refractive index, or coloring power and fluorescence index, rutile titanium dioxide is superior to anatase titanium dioxide. Therefore, rutile titanium dioxide is widely used in ink production. With the rapid development of domestic and foreign packaging and publishing printing industries, the market demand for inks will increase day by day. As a very important white pigment in inks, many functions and effects of titanium dioxide cannot be replaced by any other materials.

According to different types of inks and different printing suitability requirements, the reasonable selection of titanium dioxide is the key to making excellent white inks. Summarizing the quality requirements of titanium dioxide for inks, there are mainly the following points:

① Good whiteness, long-lasting non-yellowing, can make the color of printed products remain bright and bright in various environments;

② Good moisture resistance, easy to grind;

③ Small particles, easy to disperse evenly in the ink binder;

④ Strong covering power and good coloring power;

⑤ Good weather resistance and heat resistance, stable chemical properties;

⑥ Good water resistance.

1. Impact on the hiding power of ink

(1) The unevenness of the refractive index of titanium dioxide crystals will directly affect the hiding power of ink.

Generally, the refractive index of titanium dioxide is the best among white pigments. When preparing white ink, titanium dioxide with a high refractive index should be used to enhance the hiding power of white ink.

(2) The impact of titanium dioxide particle size, particle structure and dispersion on the hiding power of white ink.

In the range greater than 1/2 of the wavelength of visible light, the smaller the particle size, the smoother the particle surface, the better the dispersion of titanium dioxide in the resin binder, and the stronger its hiding power. Because titanium dioxide itself has a significant crystal structure, its refractive index is greater than that of the color developer, and the greater the difference in the refractive index between the two, the stronger the hiding power of the titanium dioxide used. Practice has shown that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in ink production.

2. Impact on the coloring power of ink

The coloring power of titanium dioxide depends on its ability to scatter visible light, and it has a direct impact on the coloring power of ink. The larger the scattering coefficient, the stronger the coloring power; the higher the refractive index of titanium dioxide, the stronger the coloring power. Titanium dioxide is the product with the highest refractive index among white pigments, and the refractive index of rutile titanium dioxide is higher than that of anatase titanium dioxide. Therefore, when choosing titanium dioxide, you should choose titanium dioxide with strong scattering ability and high refractive index.

3. Impact on dispersion performance.

Whether the shape of titanium dioxide particles and light reflection are uniform directly affects the dispersion performance of titanium dioxide. It is believed that if the surface of titanium dioxide particles is smooth and the reflection is uniform, its dispersion is good, and the gloss and whiteness of the prepared white ink are also good; on the contrary, if the surface of the particles is rough and the diffuse reflection increases, the gloss will be greatly reduced, and the dispersion will be poor, which will directly affect the whiteness and transfer performance of the white ink. For this reason, titanium dioxide must be processed before it can be used.

In addition, during the ink production process, titanium dioxide with different functions should be selected according to the specific characteristics and requirements of various inks.

(1) Offset printing is based on the principle of oil-water repulsion. Therefore, the resin binder used in offset printing ink must have excellent anti-emulsification function and excellent hydrophobicity, otherwise, offset white ink is easy to emulsify; in addition, the offset white ink used for printed products placed outdoors for a long time requires its titanium dioxide to have excellent light resistance and weather resistance, otherwise the white ink will turn yellow or powder.

(2) For gravure composite film ink, in order to make the printed products bright and beautiful, white ink is used as the base first, and then colorful printing is performed. For this reason, titanium dioxide is required to have excellent coloring power and hiding power.

4. Influence on the whiteness of ink

(1) The influence of the shape, size and distribution of titanium dioxide particles on whiteness.

Excellent titanium dioxide particles have a smooth appearance and no sharp edges. If titanium dioxide with sharp edges on the particle surface is used, the reflection effect of light will be greatly weakened and the whiteness of the ink will be reduced. The size of titanium dioxide particles should be controlled at 0.2~0.4μm, which is equivalent to about 1/2 of the wavelength of visible light, in order to obtain high scattering ability and make the color appear whiter. When the particle size is less than 0.1μm, the crystal is transparent. If the particle size exceeds 0.5μm, the pigment's ability to scatter light will be reduced, affecting the whiteness of the ink. For this reason, the particle size of titanium dioxide is required to be appropriate and evenly distributed to show excellent whiteness.

(2) The influence of impurities in titanium dioxide on the whiteness of ink.

Generally speaking, if a trace amount of impurities such as iron, chromium, cobalt, and copper are mixed into titanium dioxide, the prepared ink will have color deviation and reduced whiteness. This is because the impurity ions in titanium dioxide, especially metal ions, distort the crystal structure of titanium dioxide and lose symmetry. Rutile titanium dioxide is more sensitive to impurities. For example, when the content of iron oxide in rutile titanium dioxide is greater than 0.003%, it will show color, while its content in anatase titanium dioxide is greater than 0.009%, color reaction will occur. Therefore, it is very important to select precision titanium dioxide without impurities.