What are the Specific Requirements of TiO2 for Inks？
1. The impact on the whiteness of the ink
(1) The impact of impurities in titanium dioxide on the whiteness of the ink. Good whiteness of titanium dioxide made of ink durable not yellow, can make the print colour in a variety of environments to maintain a bright and vivid. In general, such as trace amounts of iron, chromium, cobalt, copper and other impurities mixed into the titanium dioxide, the preparation of the ink will produce colour bias, whiteness is reduced. This is due to the impurity ions in titanium dioxide, especially metal ions, so that the crystal structure of titanium dioxide distortion, loss of symmetry and caused. Rutile titanium dioxide is more sensitive to impurities, such as iron oxide in rutile titanium dioxide content greater than 0.003% will show colour, while its content in anatase titanium dioxide greater than 0.009% will only produce a colour reaction. Therefore, it is very important to choose fine, impurity-free titanium dioxide.
(2) The shape, size and distribution of titanium dioxide particles on the impact of whiteness. Quality titanium dioxide particles smooth shape, no angles, if the use of particles with angular titanium dioxide surface, will greatly weaken the reflection of light and reduce the whiteness of the ink. The size of the titanium dioxide particles should be controlled at 0.2~0.4μm, which is equivalent to about 1/2 the wavelength of visible light, in order to obtain high scattering capacity and make its colour appear whiter. When the particle size is less than 0.1μm, the crystal is transparent, if the particle size exceeds 0.5μm, it will reduce the scattering ability of the pigment to light and affect the whiteness of the ink. For this reason, titanium dioxide is required to have the right particle size and uniform distribution to show good whiteness. Practice has proved that rutile titanium dioxide than anatase titanium dioxide coverage is good, so the use in the production of ink more widely.
2. The impact on the ink covering power
(1) The refractive index of the titanium dioxide crystal itself will directly affect the size of the ink covering power. Gravure composite film ink printing process, in order to make the printed material to get bright colours, beautiful effect, must use white ink priming, and then in the colour printing. This requires titanium dioxide with good colouring power and covering power, otherwise the effect will be poor. Usually, the refractive index of titanium dioxide in the white pigment is the best, the preparation of white ink, should be used more refractive index of titanium dioxide, in order to enhance the coverage of white ink.
(2) The size, particle structure and dispersion of titanium dioxide particles on the impact of white ink coverage. Usually, in a range greater than 1/2 of the visible wavelength, the smaller the particle size, the smoother the particle surface, the better the dispersion of titanium dioxide in the resin linkage material, the stronger the hiding power. As the titanium dioxide itself has an obvious crystal structure, its refractive index is larger than that of the spreading agent, and the greater the difference between the refractive index of the two, the stronger the covering power of the titanium dioxide used. Practice has confirmed that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in the manufacture of ink.
3. The impact on the ink coloring power
The colouring power of titanium dioxide depends on the scattering ability of titanium dioxide on visible light, and it has a direct impact on the colouring power of ink, the greater the scattering coefficient, the stronger the colouring power; the higher the refractive index of titanium dioxide, the stronger the colouring power. Titanium dioxide is the highest refractive index in white pigments, and the refractive index of rutile titanium dioxide is higher than that of anatase titanium dioxide. Therefore, the choice of titanium dioxide to choose the scattering ability and high refractive index of titanium dioxide.
4. The impact on the dispersion performance
Titanium dioxide particle shape and light reflection is uniform, directly affecting the dispersion of titanium dioxide performance. If the surface of the titanium dioxide particles, reflecting uniform, its dispersion is good, the preparation of white ink gloss and whiteness is also good; conversely, the surface of the particles rough, diffuse reflection increases, will greatly reduce the gloss, dispersion is also poor, directly affecting the whiteness of white ink and transfer performance. For this reason, titanium dioxide must be treated before use.
In addition, the following factors also affect the ink:
Excellent light and weather resistance: If the print 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 chalky.
Good heat resistance: For baking type printing iron ink, the printing process baking temperature reaches about 180° for up to 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 its lustre at high temperatures, and may even make the print scrap.
Oil absorption: As printing speeds and technology increase and inks with reduced viscosity are required, the oil absorption of the titanium dioxide becomes critical. In the case of the colour concentration remains unchanged try to adjust the oil absorption amount to facilitate the formulation of higher viscosity inks.
