Titanium dioxide has a relatively large dosage ratio in various types of ink production, ranging from 25% to 50%, and some even larger. Therefore, titanium dioxide plays a crucial role in the quality of ink. There are three types of crystalline titanium dioxide in nature, namely rutile type, anatase type, and plate type. Due to the extremely unstable crystal structure of plate titanium dioxide, there are only two types of titanium dioxide suitable for ink production: rutile and anatase, both of which are tetragonal crystal structures. They have stable physical and chemical properties, and their color is pure white, with small particles and high refractive index.
Technical requirements:
In ink production, different types of ink products also have different quality requirements for titanium dioxide powder. Practice has proven that rutile titanium dioxide powder has ideal application performance and can be widely used in various types of ink formulations. Table 1 shows the comparison of performance indicators between two types of titanium dioxide powders. From the table, it is not difficult to see that in terms of crystal shape, refractive index, and coloring power, rutile titanium dioxide is superior to anatase titanium dioxide. Therefore, rutile titanium dioxide is widely used in ink production. In addition, during the ink preparation process, titanium dioxide powder with different properties should be selected based on the specific characteristics and requirements of various types of ink.
The Influence of Titanium Dioxide Quality on Ink
1. Impact on ink whiteness
(1) The influence of impurities in titanium dioxide on the whiteness of ink. The ink made of titanium dioxide with good whiteness is durable and does not turn yellow, which can keep the color of the printed product bright and bright in various environments. Generally speaking, if trace amounts of iron, chromium, cobalt, copper and other impurities are mixed into titanium dioxide powder, the prepared ink will produce color deviation and reduce whiteness. This is due to impurity ions, especially metal ions, in titanium dioxide, causing distortion and loss of symmetry in the crystal structure of titanium dioxide. Rutile type titanium dioxide is more sensitive to impurities, such as when the content of iron oxide in rutile type titanium dioxide is greater than 0.003%, it will show color, while when its content in anatase type titanium dioxide is greater than 0.009%, color reaction will occur. Therefore, it is very important to choose fine and impurity free titanium dioxide powder.
(2) The influence of the shape, size, and distribution of titanium dioxide particles on whiteness. High quality titanium dioxide particles have a smooth and angular appearance. If titanium dioxide particles with angular surfaces are used, it will greatly weaken the reflection of light and reduce the whiteness of the ink. The size of titanium dioxide particles should be controlled between 0.2 and 0.4 μ m. It is equivalent to about 1/2 of the wavelength of visible light to obtain high scattering ability, making its color appear whiter. When the particle size is less than 0.1 μ At m, the crystal is transparent, and if the particle size exceeds 0.5 μ m. It will reduce the pigment's ability to scatter light and affect the whiteness of the ink. Therefore, it is required that the particle size of titanium dioxide be appropriate and evenly distributed to display good whiteness. Practice has shown that rutile titanium dioxide has better covering power than anatase titanium dioxide, making it more widely used in ink production.
2. Impact on ink coverage
(1) The refractive index of titanium dioxide crystals directly affects the coverage of ink. In the process of gravure composite film ink printing, in order to achieve a bright and beautiful color effect on the printed product, it is necessary to use white ink as a base and then proceed with color printing. This requires titanium dioxide to have good coloring and covering power, otherwise the effect will be very poor. Usually, the refractive index of titanium dioxide is the best among white pigments. When preparing white ink, it is recommended to choose titanium dioxide with high refractive index to enhance the covering power of the white ink.
(2) The influence of particle size, particle structure, and dispersibility of titanium dioxide on the coverage of white ink. Usually, within a range greater than 1/2 of the visible light wavelength, the smaller the particle size, the smoother the surface of the particles, and the better the dispersibility of titanium dioxide in the resin binder, resulting in stronger coverage. Due to the obvious crystal structure of titanium dioxide itself, its refractive index is higher than that of color developing agents, and the greater the difference in refractive indices between the two, the stronger the hiding power of the titanium dioxide used. Practice has proven that rutile titanium dioxide has a better covering power than anatase titanium dioxide, making it more widely used in ink manufacturing.
3. Impact on ink coloring power
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 its 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, it is necessary to choose titanium dioxide with strong scattering ability and high refractive index.
4. Impact on dispersion performance
The uniformity of the shape and light reflection of titanium dioxide particles directly affects the dispersion performance of titanium dioxide. If the surface of titanium dioxide particles is smooth and evenly reflected, their dispersibility is good, and the glossiness and whiteness of the prepared white ink are also good; On the contrary, if the particle surface is rough and the diffuse reflection increases, it will greatly reduce the glossiness and poor dispersibility, directly affecting the whiteness and transfer performance of white ink. Therefore, titanium dioxide must be treated before use.
In addition, there are several factors that affect ink:
Good light and weather resistance: If printed materials are stored outdoors for a long time, it is necessary to ensure that titanium dioxide powder has good light and weather resistance, otherwise the ink will turn yellow and powdery.
Good heat resistance: For baked iron printing ink, the baking temperature during the printing process can reach around 180 ° C, with a time of up to 2 hours. Such printing conditions require titanium dioxide in the ink to have excellent heat resistance, otherwise the white ink will turn yellow, lose its luster, and even scrap the printed product at high temperatures.
Oil absorption: With the improvement of printing speed and technology, it is necessary to reduce the viscosity of the ink, and the oil absorption of titanium dioxide powder becomes the key. Reducing the oil absorption as much as possible while maintaining the same color concentration is beneficial for improving the viscosity of ink preparation.
