Static structures (e.g. – buildings) – Opaque stonelike module – Elongated reinforcing
Reexamination Certificate
1997-03-22
2001-07-17
Canfield, Robert (Department: 3635)
Static structures (e.g., buildings)
Opaque stonelike module
Elongated reinforcing
C052S390000, C052S455000, C052S762000, C052S780000, C052S782100, C052S700000, C052S742140, C264S267000, C264S274000
Reexamination Certificate
active
06260326
ABSTRACT:
This patent application relates to a novel, panel-like covering or article, its formulation and preparation from a hydraulically setting material, preferably a magnesia cement material, the production of a prefabricatable thin (about 1 cm) panel and a panel-like floor covering, wall covering or furniture covering, This should be easy to process and, in the final quality, capable of being ground and polished. When used, it should form a spot-free, impermeable and, as far as possible, abrasion-resistant, highly aesthetic covering which meets high requirements.
Magnesia cement materials have already been disclosed in connection with the manufacture of panels. They were used primarily for manufacturing building boards, which however were unsuitable for use on the floor because they had insufficient strength. An example of such a building board is described in AT-B-358454. This document also gives a list of known processes according to the prior art which are considered to have been disclosed for the purposes of this application (page 2, lines 5-46).
AT-B-317074 describes light-weight wood wool building boards. DE-C-3340949 discloses mineral fibre ceiling panels and U.S. Pat. No. 4,419,133 and U.S. Pat. No. 5,049,197 relate to magnesium-bound panel structures which in theory can also be used for floor panels but whose properties achieved by the respective mixture, especially with regard to suitable durability, are not optimal in the living and kitchen area.
Moreover, what is important in the living area is not only the durability but also to a great extent aesthetic effects, which are to be achieved by suitable technical measures.
The preparation of magnesia cement concretes either with or without organic fillers, such as, for example, wood chips (magnelite composition), with or without inorganic fillers, such as ground rocks and powdered minerals and grain mixtures, has been known for about 100 years. The base is a binder comprising reactive magnesia and a solution of magnesium salts, preferably of magnesium chloride (MgCl
2
).
The setting process is known to consist in dissolution of the oxide in the magnesium chloride lye and subsequent crystallization of a hydrated magnesium oxychloride of the formula 3MgO·MgCl
2
·11H
2
O. Experience has shown that this proportion should be slightly exceeded so that rather a small MgO excess is present instead of the strongly hygroscopic MgCI
2
. MgO itself is practically insoluble in water but is transformed in the course of time into magnesium hydroxide, which in turn forms a magnesium carbonate under the action of atmospheric carbon dioxide. The hydrated magnesium oxychloride is slightly soluble in water so that, in the case of such a known mixture, the magnesia cement is not water-resistant.
An attempt to improve the water resistance was made according to AT-B-379133, which proposed adding ethyl silicate. Although such a mixture has improved water resistance compared with earlier mixtures, it is still not optimal. Moreover, it is not possible to rule out the possibility that the addition of ethyl silicate would adversely affect the curing of the magnesia cement, which gives rise to desirable aesthetic effects.
The hydrated magnesium oxychloride has a structure approximately similar to that of calcium sulphate dihydrate and similar properties but is substantially harder than this. With the action of water on the magnesium cement, however, dissolution takes place preferentially at the edges and contact surfaces of the individual crystallites, so that initially solid elements may disintegrate into grainy aggregates.
Both the crystallization process and the dissolution of the MgO in the lye are exothermic processes, many imponderables influencing both dissolution and crystallization, so that there is an extensive patent literature which describes various proposals for stabilizing the hardening process.
As already mentioned, the low water resistance of the magnesia cement has also given rise to numerous patents and publications aimed at minimizing these adverse phenomena.
It is known that magnesia cement has excellent adhesion to all grease-free and wax-free substances, such as, for example, silicates or silicate minerals, as well as carbonates and carbonate minerals, glass, metal and often also organic substances, such as, for example, wood. However, all measures known to date have so far failed to produce magnesia cement panels which as such have good resistance and are suitable use for producing floors or the like. It is therefore the object of the invention to find suitable measures for increasing the stability of conventional magnesia cements and for achieving optimal space filling. It is intended to find combinations of components and a procedure which relate to a panel-like covering which can be satisfactorily produced and has excellent utility and aesthetic properties.
The inventor discovered that it is necessary to optimize the impermeability of conventional magnesia cements, i.e. to ensure that the free pore space or the pore space freely accessible to water is as small as possible. Since it is scarcely possible to achieve absolute freedom from pores, at the same time the residual pore spaces must be filled with substances which are very substantially water-repellent or which, through superficial sweiling processes, do not permit further penetration of water.
According to the invention, the product formed should therefore be such that practically no water can penetrate into the interior under normal conditions in a living room, so that moisture can give rise to solutions only on the surface of the element according to the invention, along the magnesia cement crystallites, but not in the interior, and grainy disintegration is thus prevented.
The inventor recognized that this superficial dissolution is all the smaller the smaller the proportion of set magnesia cement on the surface of the panel. This can be effected, according to the invention, by increasing the proportion of inert additives at the panel surface.
Particularly since such magnesia cement concretes are often produced as wood cement or partial wood cement or magnesite composition owing to a very wide range of physical properties (weight, heat insulation, etc.) as well as for aesthetic reasons, it must accordingly be considered that the wood particles reaching the panel surface, which after all may have exposed capillaries due to grinding and polishing, are pre-prepared in such a way that water cannot penetrate into the interior along these substances.
According to the invention, an optimal end quality of a floor panel is obtained by the following measures which should preferably be combined with one another and each of which by itself already constitutes an inventive improvement. In order to achieve one intended aim, it is necessary to comply both with formulations according to the invention and possibly with a certain method of preparation of the formulation to give the material ready for setting. These ranges are.
a) A lye of 174 to 311, preferably 228 to 255 g MgCl
2
per liter of water must be used (density between 1.14 and 1.24, preferably between 1.18 and 1.20), i.e. less MgCl
2
than a concentrated solution would contain.
b) A proportion of (dry) MgCl
2
to MgO of 1:1.5 to 1:2.5, preferably about 1:2.0, i.e. more MgO than would correspond to a stochiometric ratio.
c) 30 to 70 percent by volume of fillers. Inorganic fillers, such as ground rock, sand, powdered minerals, etc., are very slightly absorptive or not absorptive and can therefore be used up to a degree of filling of 80% by volume. On the other hand, organic, absorptive additives, such as, for example, wood chips, can be added in a maximum amount of 30-40% by volume. However, organic additives are necessary to give the magnesite composition its specific character, are very desirable from the point of view of building physics and reduce in particular the undesired swelling or shrinking by a sort of “shock absorber effect”. However, experiments have shown that a degree of filling of 40-75% by volume can be achi
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