Requirements for titanium dioxide in the production of various types of Inks

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

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???Regarding baked-type iron printing white ink, its post-printing baking temperature is around 180°C, and the baking time is about 120 minutes. Therefore, the titanium dioxide in iron printing white ink must have excellent heat resistance. Otherwise, the white ink will turn yellow and lose its luster during high-temperature baking. In severe cases, it will cause the failure of the printed product. Therefore, according to different types of inks and different printing suitability requirements, reasonable selection of titanium dioxide is the key to making high-quality white ink. To summarize the quality requirements of titanium dioxide for ink, the main points are as follows:

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â‘  Good whiteness, durable and non-yellowing, which can keep the color of the printed matter bright and bright in various environments;

â‘¡Good moisture resistance and easy grinding;

â‘¢The particles are small and easy to disperse evenly in the ink binder;

â‘£ Strong covering power and good coloring power;

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

â‘¥Good water resistance.

1. Effect on ink hiding power

(1) The refractive index of the titanium dioxide crystal itself will directly affect the hiding power of the 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 the white ink.

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

Generally, 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 connecting material, and the stronger its covering power. Because titanium dioxide itself has a significant crystal structure, its refractive index is larger than that of the developer. The greater the difference in the refractive index between the two, the stronger the hiding power of the titanium dioxide used. Practice has proven that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in ink production.

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2. Effect on the coloring power of ink.

????The coloring power of titanium dioxide depends on the ability of titanium dioxide to scatter visible light, and it has a direct impact on the coloring power of the ink. The greater the scattering coefficient, the stronger the coloring power; the higher the refractive index of titanium dioxide, the stronger the coloring power. powerful. Titanium dioxide has 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 must choose titanium dioxide with strong scattering ability and high refractive index.

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3. Impact on decentralized function.

?Whether the shape of titanium dioxide particles and light reflection are uniform directly affect the dispersion function of titanium dioxide. It is believed that the surface of titanium dioxide particles is smooth and the reflection is uniform, the dispersion property 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 is increased, the gloss will be greatly reduced and the dispersion property will be poor. , directly affects the whiteness and transfer function of white ink. For this reason, titanium dioxide must be processed before it can be used.

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

(1) Offset printing is based on the principle of oil and water repelling each other. Therefore, the resin binder used in offset printing ink must not only have excellent anti-emulsification properties, but also have excellent hydrophobicity. Otherwise, offset printing white ink will easily emulsify; in addition, it will be stored for a long time Offset white ink used in outdoor printing requires titanium dioxide to have excellent light resistance and weather resistance, otherwise the white ink will turn yellow or powder.

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

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4. Effect on ink whiteness

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

?????Excellent titanium dioxide particles have a smooth shape and no sharp edges. If titanium dioxide with sharp edges on the particle surface is used, the light reflection effect 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 its color appear whiter. When the particle size is less than 0.1 μm, the crystal is transparent. If the particle size exceeds 0.5 μm, the light scattering ability of the pigment will be reduced and the whiteness of the ink will be affected. For this reason, titanium dioxide particles are required to be of appropriate size and evenly distributed to show good whiteness.

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

???Generally speaking, if trace amounts of iron, chromium, cobalt, copper and other impurities are mixed into titanium dioxide, the prepared ink will have a color shift and a decrease in whiteness. This is caused by impurity ions in titanium dioxide, especially metal ions, distorting the crystal structure of titanium dioxide and losing its symmetry. Rutile titanium dioxide is more sensitive to impurities. For example, iron oxide will show color when its content in rutile titanium dioxide is greater than 0.003%, while its color will appear only when its content in anatase titanium dioxide is greater than 0.009%. color reaction. Therefore, it is very important to choose precise and impurity-free titanium dioxide.