tailieunhanh - Applied Clay Mineralogy Phần 6

Bản chất ưa nước của kaolinit làm cho nó dễ dàng dispersable trong các hệ thống dung dịch nước. Công thức lớp phủ bao gồm các sắc tố, chất kết dính, nước, và một lượng nhỏ các phụ gia khác. | Chapter 5 Kaolin Applications 87 Table 13. Typical chemical analyses of some kaolins wt. Component Cretaceous middle Georgia kaolin Capim soft kaolin Tertiary East Georgia kaolin Jari hard kaolin Theoretical kaolin SiO2 Al2O3 Fe2O3 TiO2 MgO CaO Na2O K2O Ignition loss requirements for high quality printing and particularly multicolor printing. The fine particle size and platy shape of kaolinite are ideal for imparting a smooth dense surface that is uniformly porous. This gives the paper a more uniform ink receptivity. The hydrophilic nature of kaolinite makes it easily dispersable in aqueous systems. Coating formulations consist of pigment binder water and small amounts of other additives. This formulation called a coating color is metered onto the paper surface with a trailing blade coater or other types of coaters. The shear values at the coating blade interface are extremely high because the paper travels at speeds as high as 1500m min. The coating color rheology should be Newtonian or thixotropic Fig. 57 so that the coating spreads readily on the paper. If the clay is dilatant then pinheads develop which cause streaks on the coated paper. Optical properties of coatings are brightness gloss and opacity hiding power . Brightness of the paper is largely a function of the brightness of the grade of kaolin used. Gloss increases with decrease in particle size. Opacity is controlled by light scatter which is dependent on the difference in the refractive index of the kaolinite and of air-filled voids Fig. 58 . Particle size distribution and the amount of fines of the order of mm have a large influence on the opacity. Relatively fine particle size kaolin products of the order of 80 less than 2 mm or finer are the grades that are used in paper coatings. Delaminated .