Paper making process utilizing fillers with hardened envelopes of cationic starch

In a method of forming paper from an aqueous slurry of cellulosic fibers and/or fillers, the improvement consisting essentially of the steps of:

• (a) adding to said slurry a dispersion of a hydrated but substantially insoluble mucous composition prepared by reacting 100 parts of cationic starch with a degree of substitution of 0.02 to 0.10 amino groups per glucose unit in a hydrated aqueous dispersion with 1 to 8 parts of carboxymethyl cellulose, alginic acid or an acrylic acid polymer with a degree of substitution of 50-100 mol % of acid per glucose or vinyl unit, whereby said cellulosic fibers and/or fillers are coated with said mucous composition,
• (b) subjecting said mucous composition to a synerese reaction whereby said mucous composition becomes less hydrated and forms a strong gel, said synerese reaction being performed in two steps, each step comprising the addition of a synersis aid to the slurry of coated fibers and fillers, the first step performed at a high concentration of filler and mucous composition by the addition of polysilicic acid as a syneresis aid and the second step performed in a diluted furnish, including fibers, by the addition of a polyaluminum-oxy-compound as a syneresis aid, or in the reverse order with polyaluminum-oxy-compound used as a syneresis aid in the first step and polysilicic acid as a syneresis aid in the second, said syneresis aids being added in amounts corresponding to 1-5% of SiO.sub.2. and 1-5% of Al.sub.2 O.sub.3 calculated on the amount of cationic starch employed, said polyaluminum-oxy-compound having up to two of the three Al valences neutralized and replaced by --O--groups, while the third Al valence in the polymeric structure is bonded alternately to citric and sulphuric acid according to a stoichiometric formula Al.sub.4 O.sub.4 Ci.sub.2 SO.sub. 4 wherein Ci represents a citric acid equivalent.