1. Influence 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 matter bright and vivid in various environments. Generally speaking, if a small amount of impurities such as iron, chromium, cobalt, and copper are mixed into titanium dioxide, the prepared ink will have color shift and whiteness will decrease. This is because the impurity ions in titanium dioxide, especially metal ions, distort the crystal structure of titanium dioxide and lose its 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.However, when its content in anatase titanium dioxide is greater than 0.009%, a color reaction will occur. Therefore, it is very important to choose fine and impurity-free titanium dioxide.
(2) The shape, size and distribution of titanium dioxide particles affect the whiteness. The shape of high-quality titanium dioxide particles is smooth and has no edges and corners. If you use titanium dioxide with edges and corners on the surface of the particles, it will greatly weaken the reflection of light and reduce the whiteness of the ink. 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 0.1 μm, the crystal is transparent. If the particle size exceeds 0.5 μm, it will reduce the light scattering ability of the pigment and affect the whiteness of the ink. For this reason, the particle size of titanium dioxide is required to be suitable and evenly distributed to show good whiteness. Practice has proved that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in ink production.
2. Influence on the hiding power of ink
(1) The refractive index of the titanium dioxide crystal itself will directly affect the hiding power of the ink. In the printing process of gravure composite film ink, in order to make the printed matter bright and beautiful, white ink must be used as a primer, and then color printing is carried out. This requires titanium dioxide to have good tinting and hiding power, otherwise the effect will be poor. Generally, the refractive index of titanium dioxide is the best among white pigments. When preparing white ink, titanium dioxide with high refractive index should be used to enhance the covering power of white ink.
(2) The effect of particle size, particle structure and dispersibility of titanium dioxide 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 binder, and the stronger its hiding power. Since titanium dioxide itself has an obvious crystal structure, its refractive index is larger than that of the vehicle, and the greater the difference in refractive index between the two, the stronger the hiding power of the titanium dioxide used. Practice has proved that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in ink manufacturing.
3. Influence on the tinting power of ink The tinting power of titanium dioxide depends on the scattering ability of titanium dioxide to visible light, and it has a direct impact on the tinting power of ink. The larger the scattering coefficient, the stronger the tinting 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, the choice of titanium dioxide should choose titanium dioxide with strong scattering ability and high refractive index.
4. Influence on the dispersion performance Whether the shape of titanium dioxide particles and the light reflection are uniform directly affect the dispersion performance of titanium dioxide. If the surface of titanium dioxide particles is smooth and uniform in reflection, its dispersibility is good, and the gloss and whiteness of the prepared white ink are also good; on the contrary, the surface of the particles is rough, and the diffuse reflection increases, which will greatly reduce the gloss and poor dispersibility. , directly affects the whiteness and transfer performance of white ink. For this reason, titanium dioxide must be processed before it can be used.
In addition, there are the following factors that affect ink:
Good light and weather resistance: If the printed matter is placed outdoors for a long time, it is necessary to ensure that the titanium dioxide has good light and weather resistance, otherwise the ink will turn yellow and chalk. Good heat resistance: For baking type iron printing ink, the baking temperature reaches about 180° during the printing process, and the time is as long as 2 hours. Such printing conditions require the titanium dioxide in the ink to have excellent heat resistance, otherwise the white ink will turn yellow and lose luster at high temperatures, and even the printed matter will be scrapped. 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 becomes the key. In the case of constant color concentration, reduce the oil absorption as much as possible, which is conducive to the preparation of ink with higher viscosity.
Post time: Jun-26-2023