The properties of sericite-containing

• Main Authors: Chun-chia Lu, 盧俊嘉
• Other Authors: Dr.Lan-Sheng Kuo
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/21230913043719562105

碩士 === 國立中興大學 === 森林學系 === 91 === Sericite is a kind of swelling inorganic layered material deposited in the east coast of Taiwan. The mineral is a layered inorganic having a swelling nature when put in water. The layered structure of sericite also possesses high electrical charges (IEC value of -48.4 meq/g), high aspect ratio (ca. 40), high specific surface area (57 m2/g), and an expandable nature of the crystalline lattices. The mineral has been successfully used as functional filler in papermaking. The purposes of this study were used sericite to replace traditional coating pigment, i.e., kaolin clay, and exploring its influences on coating color and the properties of coated paper. Two kinds of sericites with or without Oxalic Acid treatment used in the study . The experiments were carried out in 3 stages in order to delineate the role of sericite in coating color formulation. The coating color properties were observed through factors such as solid content, pH, low-shear viscosity, high-shear viscosity, water retention etc.; and the optical properties of the coated paper evaluated include brightness, gloss, printed gloss, opacity and smoothness etc. Printability was tested by using an IGT tester and inking densities. Scanning electron microscope (SEM) was used to facilitate our understanding of the structures of the coating color and the coated paper. The first stage experiment used sericite (0%-100%) to replace clay; the proportion of clay and sericite made up 30% of the total pigment, and explored the various properties of the coating color and the coated paper. The second stage experiment consisted of using coating color at a fixed 65% solid content wherein sericite replaced delaminated clay to various extents (0%-50%); the proportion of clay and sericite made up 50% of the total pigment. The purpose was to explore the feasibility of using sericite as a coating pigment. The third stage experiment tried to resolve the rheological problems of the coating color surfaced in the 2nd stage experiment. Under a fixed 62% solid content, sericite (0%-100%) replaced delaminated clay, wherein clay and sericite made up 50% of the total pigment. Here, the effect of sericite particle sizes, coating amounts and calendering on the coated paper properties were investigated. The experiment consisted of 9 sets and 3 replications each. The results of the first stage experiment indicated that when sericite replaces clay the influences on the properties of coating color include increases in viscosity, water retention and solid content. The sericite with acid treatment has stronger effects than the without one. This is probably because the finer particles defoliate more readily in the preparation of the color, hence having a higher negative charges. The coated paper has higher brightness and whiteness, as well as lower gloss both before and after printing. Opacity of the paper, however, shows some decreases. These properties are probably due to the lower intrinsic brightness of the mineral as well as its matte nature . The increase in opacity is probably due to defoliated mineral flakes having a better order of stacking and higher K/S . There is a slight increase in Dennison wax pick value as well. The better IGT printability is probably due to a stronger bonding between the sericite particles and the binder or the surface of the base paper. The faster drying speed of the ink film is thought to due to the flaky sericite having better barrier property blocking the penetration of ink into the coating layer. In the second experimental stage, delaminated clay was added and the proportion of clay increased. Under a fixed solid content of 65%, sericite was replaced delaminated clay. The water retention of the coating color was raised effectively, while the rheological properties of the color did not cause problems in coating operation. The results on the coated paper were similar to the those of first stage experiment results. The sericite with acid treatment exhibited higher viscosity, better water retention and poorer brightness, whiteness and both before and after printing gloss, while presents better opacity and IGT printability strength than the sericite without acid treatment does. In the third stage experiment, etherized starch was used instead of soybean protein as a binder component. Under a fixed 62% solid content, sericite was added to replace delaminated clay. The results indicated that water retention of the color increases with sericite addition, and there was a slight increase of low-shear viscosity; while the high-shear viscosity is in the range between 20.0-32.3 centipoise. The rheological characteristics reached a thixotropic state needed for a coating system. The results were similar to those of the second stage, as there were decreases in brightness, both before and after printing gloss, and smoothness; while opacity and IGT printability strength increase. Calendering has positive effects on smoothness and gloss of the coated paper. Papers with higher coating weights showed better improvements. The operation has no discernible effect on brightness, opacity, ink absorbency, and surface strength of the coated sheets. Coat weights have positive effects on almost all parameters except brightness, with each gsm increase bringing 0.35% GE drop. In summary, sericite can be used as coating pigment. When sericite replaces clay, the solid content and its water retention value of the color will increase. We can take advantage of this feature to adjust the solid content of the color and lower the use of expensive water retention aid (such as soy protein). Under proper addition of sericite and proper mix ratio, the rheological characteristics of the coating color will not cause operational problems. Sericite addition will lower brightness and whiteness, however, when the sericite with acid treatment addition level is low (< 25%), a lower coating amount and higher calcium carbonate addition will offset this problem. As for the lower gloss and smoothness characteristic, however, when the sericite without acid treatment addition level is low (< 25%), a higher coating amount and more passes through the calender will offset this problem. it will find application in matted coating grades. Inking density is largely unaffected by sericite addition, at higher coating amounts, sericite will help enhance inking density; calendering, however, will lower it. Sericite as a coating pigment will increase opacity, Dennison wax pick strength, IGT printability surface strength, and shorten ink drying time.