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Weakly ionic aqueous suspensions of ground mineral matter and their usesWeakly ionic aqueous suspensions of ground mineral matter and their uses description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090145987, Weakly ionic aqueous suspensions of ground mineral matter and their uses. Brief Patent Description - Full Patent Description - Patent Application Claims
The present invention relates to the technical sector of suspensions of mineral matter and their applications in the fields of paper, paint and plastics, and more particularly their applications in the paper industry with a view to improving either the paper sheet manufacturing process, or the sheet treatment process, or the sheet properties. The invention firstly concerns aqueous suspensions or “slurries” of refined mineral matter, with a dry matter concentration that can be high, that are weakly ionic and have a low Brookfield™ viscosity that remains stable over time, that is to say it relates to aqueous suspensions of refined mineral matter, with a dry matter concentration that can be high, with a low Brookfield™ viscosity that remains stable over time and having a pigmentary surface area the ionic charge of which, as determined by ionic titration, is low. These aqueous suspensions are intended for pigmentary applications in the field of paper, paint and plastics and are used more particularly for paper applications such as paper coating and/or surface treatment of the paper, or such as the filler during the manufacture of the paper, board, or analogous sheets. This use as filler can be direct as composition of filler during manufacture of the paper, board, or analogous sheets, or indirect as recycling composition of coating brokes when the recycling compositions of coating brokes are used in the manufacture of the paper, board, or analogous sheets. The invention also relates to the use of a weakly ionic and water-soluble copolymer as a grinding aid agent for grinding mineral matter in aqueous suspension in order to obtain aqueous suspensions or “slurries” of said refined matter, with a dry matter concentration that can be high, with a low Brookfield™ viscosity that remains stable over time, and having the property that it presents a pigmentary surface area the ionic charge of which, as determined by ionic titration, is low. The invention also relates to the use of same copolymer as dispersion agent of the filter cake obtained during an intermediate stage in the manufacture of refined mineral matter suspensions, with a dry matter concentration that can be high, with low Brookfield™ viscosity that remains stable over time and having a pigmentary surface area the ionic charge of which, as determined by ionic titration, is low, this intermediate stage taking place after grinding and before thermal reconcentration. The invention also relates to said grinding aid agent by means of which it is possible to obtain aqueous suspensions of said refined mineral matter, with a dry matter concentration that can be high, with low Brookfield™ viscosity that remains stable over time and having a pigmentary surface area the ionic charge of which, as determined by ionic titration, is low. The present invention moreover relates to the grinding process that implements said grinding aid agent. Moreover, the invention relates to the use of said aqueous suspensions of mineral matter before or after drying or re-dispersion after drying in the field of paper or paint, and after drying in the field of plastics, and more particularly in the field of paper for paper industry applications such as, in particular, paper coating and/or the surface treatment of paper, or such as the filler, whether the latter implements a direct composition of filler or a recycling composition of coating brokes. It also relates to the use of said aqueous suspensions of mineral matter in a drying process after grinding. Finally, it relates to paper, board or analogous products manufactured and/or coated according to the invention. In the manufacturing process of a sheet of paper, board or analogous product, the skilled man in the art increasingly tends to replace part of the expensive cellulose fibres by cheaper mineral matter in order to reduce the cost of the paper while improving its properties. This mineral matter, familiar to the skilled man in the art, comprises, for example, calcium carbonate and miscellaneous analogous fillers such as dolomite, gypsum, calcium hydroxide, satin white, titanium dioxide or mixed carbonate based fillers of various metals such as, in particular, calcium associated with magnesium and analogues, various matter such as talc or analogues, and mixtures of these fillers, such as, for example talc-calcium carbonate or calcium carbonate-kaolin mixtures, or mixtures of natural calcium carbonate with aluminium hydroxide, mica or with synthetic or natural fibres or co-structures of minerals such as talc-calcium carbonate or talc-titanium dioxide co-structures. For a long time now it has been quite common to use, as grinding aid agents, water-soluble polymers based on polyacrylic acid or its derivatives (FR 2 488 814, FR 2 603 042, EP 0 100 947, EP 0 100 948, EP 0 129 329, EP 0 542 643, EP 0 542 644) to provide aqueous mineral suspensions that meet the above-mentioned refinement and viscosity criteria, but these grinding aid agents are polymers and/or copolymers of the anionic type which have the disadvantage of requiring the addition of cationic compounds during the paper sheet manufacturing process when the aqueous mineral suspensions containing them are implemented in these sheet manufacturing operations. The end user therefore strives to minimise the polymer agent demand during paper manufacture, for every median diameter and/or for every point of the grain size curve of the particles of mineral matter implemented. To solve the problem, the skilled man in the art is currently familiar with the solution recommended in patent application FR 2 810 261, which has the disadvantage of not fully meeting the end user\'s needs because although this solution makes it possible to obtain aqueous suspensions of mineral matter with low ionic charge, it does not make it possible to have suspensions with a sufficiently low ionic charge to correspond to the end user\'s needs. Moreover, the paper manufacturer who is the end user is faced with the problem of implementing coating colours which are not sufficiently stable during paper coating operations. The skilled man in the art, being familiar with this problem, also seeks to develop aqueous suspensions of mineral matter which make it possible to obtain coating colours which are highly stable even at low anionicity and for every median diameter and/or for every point of the grain size curve of the particles of mineral matter implemented. Faced with the above-mentioned problems, the Applicant took the surprising step of developing aqueous suspensions of refined minerals with dry matter concentration that can be high, with low Brookfield™ that remains stable over time, and having a pigmentary surface area the ionic charge of which, determined by ionic titration, is very low, suspensions the implementation of which, both in the paper manufacturing processes and in the filler or in the paper sheet treatment processes such as coating, make it possible to solve the above-mentioned problems. These aqueous suspensions of refined minerals with dry matter concentration that can be high, with low Brookfield™ that remains stable over time, and having a pigmentary surface area the ionic charge of which, determined by ionic titration, is low, are obtained by using a weakly charged polymer as a grinding agent of the mineral matter in aqueous suspension, or by using the same copolymer as dispersing agent of the filter cake obtained in an intermediary stage of the manufacture of the suspension, this intermediary stage taking place after grinding and possibly before a physical concentration process such as thermal concentration. The said aqueous suspensions of refined mineral matter with dry matter concentration that can be high, with low Brookfield™ that remains stable over time, and having a pigmentary surface area the ionic charge of which, determined by ionic titration, is low, are characterized in that they contain, as a grinding aid agent, a copolymer consisting of:
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