Fundamental Aspects of Filler Distribution in Paper

An effective and simple method for sectioning paper was developed that enabled determination of the distribution of filler in a large number of papers. Attention was concentrated on papers made on Fourdrinier machines, but, to obtain a complete picture of filler distribution, handsheets and papers made on cylinder machines were also investigated. From the resulting filler distribution curves, it appeared that handsheets and cylinder-made papers have a comparable filler distribution, which is the reverse of that of Fourdrinier-made and handmade papers. It is generally supposed that the filler in Fourdrinier-made papers is concentrated in the top layer, whilst much less filler is present on the wire side. This was confirmed in our investigations. It even turned out that the filler content of a 10 per cent wire side layer is almost constant and depends only in the degree of beating and to some extent on the total amount of filler in the paper. This suggests the filler capacity of the extreme wire side layer to be the determining factor. Furthermore, the influence was investigated of filler retention, type of filler (particle size), fibre composition, filler content, machine speed, dandy roll and open table rolls on filler distribution . From this, some general rules about the distribution of filler in paper were derived: it is determined by machine speed, total filler content and filler capacity of the extreme wire side layer. The filler distribution in the top layers of a Fourdrinier-made paper is affected also by the dandy roll and probably by the retention of the filler. This general picture of filler distribution, together with the results of laboratory and mill experiments, gave rise to a theory of the causes of the observed phenomena. This theory states that self-filtration (drainage) of the three-phase system water|fibre |filler results in a heterogeneous distribution of filler particles in the fibre mat, having the same character as in Fourdrinier-made paper. It is concluded, therefore, that the uneven distribution is already present in the first stage of drainage and is strongly intensified by the extreme drainage conditions.