Kaolin clays papermaking fillers

During its lifetime the press felt runs several million times through the press nip. Reduction in felt thickness, abrasion and contamination are the main reasons why a press felt has to be replaced. Fillers such as calcium carbonate, clay/kaolin, other papermaking additives, and adhesives e. g. from recovered paper deposit in the press felt structure, impeding or even locally preventing water flow. In some cases not even alkaline and acids can re-open the press felt structure. 

Figure 1.11 Kaolin clay, used as filler in papermaking, (a) Bare clay particles (b) clay fully coated by cationic polystyrene latex (130 nm diameter). Scale bars 10 and 1 xm, respectively.

Kaolin - Kaolin, or clay as it is commonly known among papermakers, is the largest single filler pigment in the North Ameriean paper industry. With the growth of alkaline papermaking, ealeium carbonate use is increasing... 

Other fillers - Kaolin and Ti02 are used in alkaline papermaking, but to a much lesser extent that in acid papermaking. Kaolins are cheaper in some eases than calcimn earbonate, and satisfy some filling requirements for alkaline. Calcium carbonate does not opacify well so TiOa must be used for some papers. The extender pigments, especially calcined clay and talc, are used and perform better than calcium carbonate when opacifying is needed. 

---