In the paper making art, an aqueous suspension containing cellulosic fibres, fillers and additives, referred to as stock, is fed into a headbox which ejects the stock onto a forming wire. Water is drained from the stock through the forming wire, so that a wet web of paper is formed and dewatered on the wire. The paper web is then dried in the drying section of the paper machine. Drainage and retention aids are conventionally introduced into the stock in order to facilitate drainage and to increase adsorption of fine particles onto the cellulosic fibres to retain them with the fibres on the wire.
Akzo Nobel N.V. (Arnhem, NL) inventors Johan Nyander, Hans Johansson-Vestin, Jan Nordin and Annika Viola Pal unexpectedly found that an improved drainage and/or retention effect of a cellulosic suspension on a wire can be obtained by using an aqueous silica-containing composition comprising anionic naphthalene sulphonate formaldehyde condensate and nano silica-based particles. The nanoparticles make it possible to increase the speed of the paper machine and to use a lower dosage of additives to give a corresponding drainage and/or retention effect, thereby leading to an improved papermaking process and economic benefits, according to U.S. Patent 7,608,644.
The process can be used for the production of paper and the production of other web-like products, such board and paperboard. The discovery is particularly useful in the manufacture of paper with weights below 150 grams/square meter, and below 100grams/square mete, for example fine paper, newspaper, light weight coated paper, super calendered paper and tissue. The process can be used in the production of paper from all types of stocks, both wood containing and woodfree as well as from recycled paper
The aqueous silica-containing composition can also be used as a flocculation agent in the treatment of water for the production of drinking water or as an environmental treatment of waters for instance in lakes. The composition can also be used as flocculation agent in the treatment of waste water or waste sludges.
Examples of suitable silica-based particles include colloidal silica, colloidal aluminium-modified silica or aluminium silicate, and different types of polysilicic acid and mixtures thereof, either alone or in combination with other types of anionic silica-based particles.