Paper fillers

A method of manufacturing paper having increased dry strength and increased wet strength to give improved machine runnability at a given content of mineral filler, which method comprises the steps of:

• (a) preparing a concentrated but pourable aqueous suspension of mineral particles which contains, in solution, (i) an anionic polymeric material which normally acts as an anionic flocculating agent for said mineral particles in aqueous suspension in an amount sufficient to flocculate said mineral particles and (ii) an anionic deflocculant in an amount just sufficient to inhibit the flocculating action of said polymeric material, said anionic polymeric material does not thicken said suspension and said suspension being prepared in the substantial absence of papermaking fibres;
• (b) contacting the suspension of step (a) with an aqueous solution containing a sufficient amount of metallic cations of a valency greater than 1 as to counteract the operation of said anionic deflocculant and thereby permit flocculation of said mineral particles by said polymeric material to form agglomerates,
• the polymeric material being such that it is not of itself insolubilized or precipitated from an aqueous dispersion thereof by the addition of the aqueous solution of step (b);
• (c) forming a papermaking stock containing said agglomerated mineral particles and papermaking fibres in the substantial absence of co-flocs of mineral particles and papermaking fibres;
• and
• (d) forming a paper web from the papermaking stock of step (c).