The role of the filler is to improve the optical properties of the paper and increase its opacity, brightness and whiteness. Improve the smoothness and uniform physical properties of the paper, increase the softness of the paper, reduce the moisture absorption performance and enhance the dimensional stability. It is more suitable for printing on paper and lower the production cost.
Paper and paper coating
The criteria for selecting the filler are as follows. 1. Reflectance index of filler: The larger the reflectance index, the more the amount of reflected light, the higher the opacity of the paper. 2. Particle morphology: It affects the way light is scattered, thereby affecting the optical properties of the filler in the paper. 3. Particle size and distribution: The particle size of the filler, the particle size distribution and the degree of aggregation of the filler particles affect the optical properties of the filler. It has been found that when the particle size range is narrow and evenly distributed, it helps to increase the light scattering rate. In the range of wavelengths greater than the half-wavelength of visible light, the smaller the particle size, the greater the hiding power, which of course has a certain limit. 4. Specific surface area: The specific surface area of the particles affects light scattering and also affects the strength and printability of the paper. Generally, fillers with a large specific surface area increase the printability of the paper, but the strength of the paper is weakened to increase the difficulty of sizing. These are all important properties of paper fillers, which have a great influence on the opacity and physical properties of the paper.
Performance comparison between titanium dioxide and other fillers
As can be seen from the figure, compared with other fillers, titanium dioxide has high whiteness, high density, fine and uniform particles, and high refractive index, which has its unique characteristics as a paper filler. At the same time, titanium dioxide is chemically stable, suitable for papermaking under various conditions, and has a large scattering coefficient, which can significantly improve the opacity of the paper and increase the coverage and retention of the filler.
Correspondence between pigment concentration and opacity
Of course, not all titanium dioxide is suitable for paper fillers, especially for paper coatings. A suitable titanium dioxide helps to increase the performance of all aspects of the paper. PFR-209 of Ishihara Titanium Dioxide is a rutile titanium dioxide produced by sulfuric acid. It has a particle size of 0.26 um and a uniform particle size distribution. As a paper coating, the PFR-209 also maintains an ultra-high opacity. It is 5 to 10 points more than the opacity of the ordinary titanium dioxide in the market. Because of its high opacity, it can reduce the amount of titanium dioxide, which is beneficial to reduce costs.