Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-01-02
2003-08-05
Marcheschi, Michael (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S467000, C106S466000, C106S486000, C106S484000, C106SDIG004, C501S141000, C501S145000, C501S149000
Reexamination Certificate
active
06602341
ABSTRACT:
This invention is concerned with a method of treating kaolinitic clays, especially to improve the properties of such clays for use as ingredients for ceramic forming compositions, especially compositions which are to be used for preparing ceramic articles, eg whiteware articles such as tableware and the like.
Ceramic articles, eg tableware for use in the home and in the catering industry, are generally formed from a wet high solids composition which comprises a blend of various particulate ingredients which include kaolinitic clays, ie clays which contain the mineral kaolinite, such as kaolin or china clays and/or ball clays. Usually fluxing materials such as china stone, feldspar or nepheline syenite, and at least one silica-containing material, such as quartz or flint are also included in such compositions. If it is desired to produce articles of bone china, the composition will also contain a substantial proportion of ground, calcined animal bone, especially from cattle, or bone ash. The composition may also include minor proportions of other ingredients such as calcium carbonate, dolomite and talc. The proportions of the various ingredients used in the composition vary according to the properties required in the fired ceramic article. Many different types of ceramic tableware are roduced in various parts of the world, including, fine earthenware, semi-vitreous china, semi-vitreous porcelain, hotel china, household china, bone china, hard porcelain and stoneware.
Ceramic tableware articles are generally formed from the wet ceramic forming composition by a process which is based on the ancient technique of hand throwing on a potter's wheel. The technique of free-hand throwing is still used for shaping individual art pieces, but when a large number of substantially identical articles are required to be formed, a degree of automatic mechanisation is incorporated into the process. In this latter case, a mould of a suitable material, for example plaster or a synthetic resin, may be employed fixed to a wheel which is capable of high speed rotation in a horizontal plane. A suitable amount of the ceramic composition is then introduced onto or into this mould. If the mould is substantially convex, and is used for shaping, for example, the inside of a plate or dish, the process is widely known as “jiggering”. If, however, the mould is concave, and is used for shaping the outside of a cup or jug, the term “jolleying” is often used. The second surface of the article, which is not in contact with the mould, is generally shaped by means of a profiling tool, most commonly of metal, which is brought into contact with this surface, whilst the article being shaped is rotated on the wheel. The shaping process has recently been rendered faster and more efficient through the introduction of roller head machines. In these machines the profiling tool is replaced by a heated rotating die, and both die and mould rotate continuously at appropriate speeds during the shaping of an article.
In order to perform satisfactorily in a shaping process, eg of the type described above, it is necessary for the ceramic forming composition to have sufficient plasticity to enable it to flow and deform under the action of compressive, tensile and shear stresses. The shaped article must also possess sufficient strength in its unfired or “green” state, to permit a certain amount of handling without loss of its integrity and shape. The green strength of a ceramic forming composition is generally determined by measuring the modulus of rupture (MOR) of dried extruded bars formed from the composition under certain standard conditions described later.
Some ceramic tableware is formed by a slip casting process. In this case the clays and other ingredients of the composition are mixed with a larger quantity of water, optionally with one or more additives, eg one or more dispersing agents, to form a fluid suspension, slurry or “slip”. The slip is poured into a porous mould where a shaped article is formed by a process which is similar to that by which a filter cake is formed in a filter press. Partial dewatering of the shaped article occurs as water passes from the composition through the porous walls of the mould, until the article is sufficiently formed, in a dry and firm state, to be removed from the mould.
A further shaping process used for forming articles of ceramic tableware is that of dust pressing. In this process a ceramic composition in the form of an aqueous suspension containing a relatively high concentration of solid material, together with one or more dispersing agents for the solid material, is subjected to spray drying to form substantially dry hollow microspheres of diameter of the order of about 0.1 mm. A charge containing an appropriate quantity of these microspheres is introduced into a suitable mould to which pressure is applied to compact the charge to form the desired ceramic article. Again, when articles are formed by dust pressing, it is necessary for the ceramic composition to possess sufficient green strength to enable the shaped article to be handled without undue risk of breakage.
Subsequent to the shaping process, whatever shaping method is used, the shaped body produced in its green state is dried before firing one or more times to a suitable temperature in a kiln, to produce a ceramic article of the type desired. Glazes and decoration may also be applied at this stage.
An object of this invention is to improve the properties of kaolinitic clay components of ceramic forming compositions in order to increase the strength of green shaped articles formed from the compositions.
According to the present invention there is provided a method of treating a kaolinitic clay which is intended for use as an ingredient in a ceramic forming composition which method comprises the steps of
(a) mixing with the kaolinitic clay from 0.1% to 15.0% by weight, based on the dry weight of the kaolinitic clay, of a smectite clay; and
(b) subjecting a moist mass in a plastic state of the mixture formed in step (a) to mechanical working under conditions such that there is dissipated in the moist plastic mass at least 5 kJ of energy per kilogram of the clay mixture on a dry weight basis.
The amount of energy dissipated in step (b) may be in the range of from 5 kJ to 300 kJ of energy per kilogram of the clay mixture on a dry weight basis.
The kaolinitic clay used in step (a) may already have been subjected to known preliminary processing or refining steps, eg steps selected from degritting, washing, magnetic separation of impurities and one or more particle size separation steps.
The moist plastic state mass treated by mechanical working in step (b) preferably contains between 20% and 30% by weight of water.
The mixture of clays produced in step (a) may have a water content which is suitable for use in step (b). Alternatively, the water content of the clay after production may be adjusted to provide a suitable moist mass in a plastic, workable state. The water content adjustment may be by addition of an aqueous liquid or by concentration, depending on the water content of the mixture produced in step (a).
Where the clay mixture produced in step (a) is in the form of a dry powder the required moisture content may be adjusted simply by addition of water and mixing.
Where the clay mixture produced in step (a) is in the form of a dilute slurry or suspension the required moisture content may be obtained by one or more known dewatering processes, eg filtering and/or pressing and/or partial drying and/or adding already dried material, ie using a dry feedback or dry-return supply loop from a subsequent dryer output.
The kaolinitic clay used in step (a) may comprise one or more kaolin clays of primary or secondary origin. Kaolinitic clays were formed in geological times by the weathering of the feldspar component of granite. Primary kaolin clays are those which are found at the site at which they were formed, and are generally present in a matrix of undecomposed granite which must be separated from the clay during the refin
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Imerys Minerals Limited
Marcheschi Michael
LandOfFree
Treating kaolinitic clays does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Treating kaolinitic clays, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Treating kaolinitic clays will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3077192