Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1998-10-27
2000-11-07
Koslow, C. Melissa
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106464, 106486, 428403, 427215, C09C 102, C09C 136, C09C 142, D21H 1767, D21H 1940
Patent
active
061430641
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to products comprising pigment particles coated with precipitated calcium carbonate (PCC), when particles are precipitated calcium carbonate range in size from 30 to 100 nm and said particles are attached to the surfaces of the pigment particles of said product and from 30 to 90% by weight of calcium carbonate are present in said particles.
The invention also relates to a method for preparing such pigment products. According to the method pigment particles and PCC are mixed together in liquid phase to obtain a pigment/PCC suspension in this method according to the invention for coating particles with precipitated calcium carbonate, an aqueous suspension of pigment carbonate is formed by mixing in a mixer, the pH of said aqueous suspension being adjusted to a value within the range 6-11, and agglomerates at precipitated calcium are first formed before mixing to a particle size in the range of 30-400 nm, and thereafter these agglomerates are disintegrated to calcium carbonate particles of 30-100 nm particle size, so that the resultant particles of calcium carbonate are attached to the surfaces of the pigment particles.
Filler and coating pigments are used in paper manufacturing. The reasons for this are economical and technical; low cost mineral pigments can be used to replace a portion of the expensive fibre material. This also leads to improvements in the printing properties, such as opaqueness, whiteness and gloss, of the paper.
Commonly used filler and coating pigment materials include kaolin, talcum, calcium carbonate and titanium dioxide. Kaolin is an aluminum silicate mineral of plate-like or flake-like particle shape, prepared form natural kaolin by purification and fractionation. Calcium carbonate may be from natural minerals or synthetic. Natural calcium carbonates include chalk and calcium carbonate obtained from ground limestone, GCC (Ground Calcium Carbonate). Synthetic carbonates are prepared by precipitation, and are called precipitated calcium carbonate, PCC. Titanium dioxide is typically prepared from ilmenite ore.
As a filler kaolin has many valuable properties from the point of view of paper technology. Thus, it improves the optical properties of paper, such as gloss, light scattering and brightness. Kaolin does not form essentially any dust, it adheres well to paper (good adhesion properties or retention), and most often it is of very uniform quality. Kaolin is also used as a coating pigment. The function of the coating is to cover the fibre network pattern of base paper with a pigment-adhesive mixture which improves the printing properties of the paper. Different qualities of paper as well as different manufacturing processes and printing methods determine the order in which different factors are to be regarded as essential. The proportion of the pigment in the coating paste used for coating paper is 80-95%, wherefore the effect of kaolin used in coating pigments on the properties of paper is greater than that of kaolin used in the filler. It may be regarded as a disadvantage when using kaolin both as a filler and as a coating that the ISO brightness of kaolin is rather low compared to other pigments, typically about 90.
Natural calcium carbonates have the disadvantage that the qualities which are of sufficient brightness to be used in paper coatings or fillers are becoming increasingly rare and often require transportation over long distances.
The disadvantage with titanium dioxide is its high price. It is possible to reduce the cost by mixing titanium dioxide with other pigments and fillers, but this also impairs the quality. For the preparation of pigment products of high quality it is desirable to have the pigment particles at a distance from each other that is comparable to the dimensions of the particles themselves. When used in the form of a powder, pigment particles often adhere to each other forming flocs or agglomerates.
It is possible to obtain good brightness and opacity for paper when using PCC, regardless of whether it is used as a filler or a
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patent: 3661610 (1972-05-01), Ferris
patent: 3674529 (1972-07-01), Toms
patent: 4824654 (1989-04-01), Ota et al.
patent: 5364610 (1994-11-01), Merris, Jr.
patent: 5650002 (1997-07-01), Bolt
FP-Pigments Oy
Koslow C. Melissa
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