Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-06-04
2003-12-09
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S484000, C106S487000
Reexamination Certificate
active
06660076
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present application is related to a high performance kaolin pigment, a paper coating color containing high performance kaolin pigment, as well as the a method for making high performance kaolin pigment.
In a more specific way, the present invention is directed to kaolin products to be used in paper coating and a method for making same, specially kaolin pigments having improved optical and Theological characteristics, its uses and methods for making it.
As is known by those skilled in the art, kaolin is a rock made of clay minerals, the kaolinite being the predominant mineral. Kaolin can be used in a number of industrial applications in view of its characteristics such as chemical inertia in a wide pH range, white color, low abrasion, low electric conductivity and low thermal conductivity, having particles with suitable shape and size that provide, good coverage and good rheology, in addition to a low cost when compared to other similar materials.
However, kaolin seldom occurs in a pure form, being necessary the use of specific processing methods already well-known in the industry practice to remove the components known as deleterious. Some components provide an undesirable color to kaolin, such as iron and titanium impurities, still others provide abrasion, such as the presence of sand, while others can be deleterious to the rheology, such as the presence of clay minerals having morphology and crystalline structure different from that of kaolinite.
Another important aspect is that the kaolin pigment characteristics vary from deposit to deposit, and significant differences in its characteristics can occur even for a particular deposit. For example, in the deposits located at Rio Capim Basin, in the northern region of Brazil, two types of crude kaolin, herein called coarse kaolin and fine kaolin, can exist in the same deposit.
Frequently, a thin transition layer can be observed between the two types of kaolin. Coarse and fine kaolins have quite distinct characteristics in view of their different geologic origins.
Coarse kaolin has a narrow size distribution. mainly in the fine end of the size distribution curve, typically with at most 15% by mass lower than 0.2 &mgr;m in the degritted fraction. A second characteristic of coarse kaolin is the higher kaolinite crystallization degree. The crystallization degree can be quantified by the Hinckley index that evaluates how well the kaolinite crystalline structure is formed. Usually, coarse kaolin has a Hinckley Index higher than 0.6. Another characteristic of coarse kaolin from the Rio Capim region is its morphology that occurs as large individual plates. In the kaolin region of Georgia In the United States, coarse kaolin having similar size to that of the coarse kaolin or the Rio Capim region can be found as “books”, that is, they have packed kaolinite plates. These kaolin “books” require a mechanical process, called delamination, to change the kaolinite “books” into individual particles. Once turned into individual particles, the kaolinite particles provide a good coverage to paper, improving the opacity of the coated paper. However, this mechanical process of making individual kaolinite particles damages the particles, making their edges irregular. The coarse kaolin particles of the Rio Capim region are provided with the preserved hexagonal shape which is characteristic of kaolinite. The preservation of the regular edges of kaolinite particles contributes to the better rheology of the pigment
On the other hand, fine kaolin is provided with a large amount of fine with at least 30% by mass lower than 0.2 &mgr;m in the degritted fraction. Besides being small, the fine kaolin particles have a more spherical shape and a lower crystallization degree, with a Hinckley index lower than 0.5.
In some applications, the specifications required for the kaolin pigment are quite severe, as in the case of its use in paper. The kaolin pigments are very used to fill and coat paper products. The sheet of paper, when comprising only of cellulose fibers, has a quite irregular surface which is caused by free areas between the fibers. The kaolin pigment can be used in the paper industry as a filler to fill the free spaces between the fibers or as a coating to make the surface more regular. The coating provides the paper with a smoother surface that better accommodates the printing ink, thus resulting in a better visual appearance of the printed paper.
The specifications of the kaolin pigment to be used as a coating are quite more severe than when it is used as a filler. Properties such as opacity, brightness, paper gloss and print gloss, here briefly called optical properties, as well as the rheological properties, are of great importance when the pigment is applied as a coating.
With the advent of coating machines with an ever increasing speed, the rheology of the pigment tends to play quite an important role in the application stage. During the paper coating application, the kaolin pigment is submitted to high shear rates, thus requiring an optimum rheology of the kaolin slurry.
It is known that, for a same kaolin pigment, the higher the solid content, the higher the resulting viscosity. Kaolin pigments that have a low viscosity at a high shear rate and at high solid content are considered differentiated products, since they allow the coating machine to operate at a high speed, thus improving the productivity, as well as reducing the drying costs. If the kaolin pigment does not have a good rheology, the coating machine must be operated at lower speeds, which results in a loss of productivity, or the coating color must be diluted, resulting in higher cost in the drying step.
Pigments having improved optical properties are attractive to the paper industry in view of the Increasing demand for high quality coated papers. A kaolin pigment having a lower viscosity at high shear rates and at high solid content slurries and also imparting good optical properties to the coated paper, such as high brightness, high paper gloss and print gloss, without loosing opacity would be of great interest to the paper industry. The fine kaolin pigments commercially available provide high paper gloss and low viscosity at high shear rate and at nigh solid content, but with loss in print gloss and opacity. It is known that the presence of fines improves the viscosity at high shear rate as well as the paper gloss, but it is deleterious to the print gloss and opacity it is also known that particles with plate shape and narrow particle size distribution contribute to the opacity of the paper, but they are deleterious to the rheology of the pigment. However, by strictly controlling the size and shape of the particles, as well as the size and shape distribution of the particles, it is possible to obtain kaolin pigments having improved rheological and optical properties at the same time.
The prior art discloses a kaolin pigment consisting of coarse kaolin or a mixture containing coarse kaolin and fine kaolin having improved characteristics such as brightness, opacity, paper gloss and print gloss. The method for making this pigment comprises the removal of the fine fraction of the coarse kaolin, remaining only the coarse fraction, which fraction is characterized by possessing more spherical particles in the coarse end and plate shaped particles in the fine end, thus resulting in an average aspect ratio higher than 12. If only the coarse kaolin with the removed fines does not show a good fluidity, fine kaolin at a ratio of 0.1% to 30% by mass is added thereto. The coarse kaolin has a Hinckley index higher than 0.6, and the fine kaolin a Hinckley index lower than 0.5. The resultant pigment has at least 91% by mass lower than 2 &mgr;m and at most 30% by mass lower than 0.25 &mgr;m, and a Hercules viscosity higher than 250 RPM at 18 dynes for a solid content varying from 65% to 75%.
Usually the size of kaolin particles is measured by methods of sedimentation in an aqueous medium and is expressed in terms of equivalent spherical diameter, despite the fact th
Duarte Neto João
Valadares Maria Cristina Almeida
Companhia Val Do Rio Doce
Katten Muchin Zavis & Rosenman
Koslow C. Melissa
Manlove Shalie
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