Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
2000-02-10
2003-05-27
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C428S537700, C156S039000, C156S041000, C106S617000, C106S632000, C106S680000
Reexamination Certificate
active
06569541
ABSTRACT:
The present invention relates to prefabricated structural elements comprising a substrate based on cured and dried plaster. More particularly, the invention relates to prefabricated structural elements of the tile, panel and board types. With regard to boards, those relevant to the present invention have a relatively small average thickness, for example ranging from one to a few centimeters, in a preferred direction or dimension, with a limited mass per unit area, for example about 10 kilograms per m
2
. By way of preferred but nonlimiting example, reference will be made to prefabricated elements of the board type, in the knowledge that at the present time there are, for example, plaster fiberboards in which the plaster contains homogeneously dispersed fibers throughout the mass, these boards being commonly called “GFBs”, and plasterboards coated with cardboard or with mats or sheets of mineral fibers (for example glass fibers) on both their faces.
The present application corresponds to French Patent Application No. 99/01885 of Dec. 2, 1999, the text of which is incorporated in that of the present patent application, as required.
The invention applies to other prefabricated elements made of plaster, for example to tiles, or parallelepipedal elements having grooves or slots and tenons on their side edges.
The invention relates to prefabricated structural elements, such as those defined above, having improved water resistance.
The prefabricated structural elements as defined above, having the ability to withstand water, are used either inside buildings, for example in humid rooms such as bathrooms, in order to lay plastic coverings or tiles thereon, or on the outside of buildings, for example for the covering of facades, as long as, nevertheless, these prefabricated elements are coated with an impermeable protective skin.
The expression “water resistant” should be understood to mean the ability of a prefabricated structural element as defined above to limit the uptake of water by the plaster substrate, while still retaining the dimensional stability and mechanical integrity of the structural element in question.
Depending on the countries, this water resistance is codified or regulated by specific standards. Thus, reference may be made to the standards mentioned below, depending on the element manufactured:
plaster tile: NF P72-210-1 (April 1994);
plasterboard: ASTM 630/630M-96a;
board with a glass mat: ASTM C1178/1178M (96).
The ASTM 630/630M-96a standard requires in particular that, when such a structural element is immersed in water for two hours, the water uptake by the plaster substrate is less than 5% and the water absorption on the surface (called the Cobb equivalent) is less than 160 g/m
2
.
For the purposes of making a structural element, as defined above, water-repellent in accordance with document JP-A-0 730 411, it is known to use a water-repellent agent comprising at least one silicone compound in aqueous and basic medium and to homogeneously incorporate the latter into the substrate of the element in question.
According to JP-A-0 733 0411, the silicone compound is emulsified with water. An oxide or hydroxide of a metal from group IIa, for example calcium, is then added to the emulsion. The additive thus obtained is then incorporated into the dry matter in order to obtain the plaster substrate in the wet state, which substrate is then formed and then dried.
In practice, it appears that the aforementioned composition has the advantage of causing the silicone compound to cure or crosslink, thereby enhancing the water-repellency of the latter; however, this is accompanied by significant evolution of hydrogen, which is particularly dangerous.
Document JP-A-80109251 discloses a water-repellent composition for cement, comprising a silicone compound, the nature of which is not specified, and bentonite as mineral additive.
Document SU-A-1409607 discloses a water-repellent composition for plaster, comprising a sodium methyl siliconate or ethyl siliconate, and bentonite as mineral additive.
In practice, such a composition is able to swell, causing rheological problems of the substrate in the slurry state.
It appears in practice to be difficult to meet the abovementioned standards using contents of silicone compound of less than 1% by weight, said compound being, moreover, very costly.
This water repellency is achieved by using any process comprising, in general, at least the following steps:
(a) homogeneously mixing a dry material, comprising mostly at least one hydratable calcium sulfate, the abovementioned water-repellent agent, and water and preforming said substrate in the wet state;
(b) drying the preformed substrate in order to obtain said substrate formed in the solid and dry state.
With such a process, it is difficult to control the amount of water-repellent agent incorporated into the plaster substrate, for example in the form of a silicone oil, and therefore the potential of the water-repellent agent is not exploited.
The object of the present invention is therefore to better control the water repellency or a structural element using a water-repellent agent comprising at least one silicone compound, in particular to increase its water repellency within the cured plaster.
The object of the present invention is also to improve the introduction and mixing of the water-repellent agent in the process defined above.
In accordance with the present invention, it has been discovered that the addition, as a homogeneous mix, of a mineral additive comprising at least one mineral component having a synergistic water-repellency affinity with the silicone compound to the dry matter from which the substrate is preformed in the liquid state allowed the water repellency of the cured plaster to be increased to a significant extent.
The expression “synergistic water-repellency affinity” should be understood to mean the property whereby, by adding the mineral additive according to the present invention, and all other things being equal, the water repellency of the cured-plaster substrate is increased by at least 20%, in Cobb equivalent, according to the ASTM 630/630M-96a standard, and/or, for the same water resistance, the amount of water-repellent agent required is reduced by at least 20%.
Preferably, but nonlimitingly, the mineral component does not react with the silicone compound in the sense that, after two hours, mixing 0.1 g of said silicone compound with the mineral component in aqueous medium may release an amount of hydrogen of less than or equal to 6 ml under standard temperature and pressure conditions.
The evolution of hydrogen is measured according to the following operating method.
An apparatus identical to that described in the NFT 77-150 standard on page 6 is used. The principle consists in bringing the mineral additive and the silicone compound into contact with each other, in aqueous medium in the reactor, in the same proportions by weight as those in the homogeneous mix defined above, in the slurry state, that is to say with the mixing water. The evolution of hydrogen is monitored over time, at a controlled temperature of 23° C. The volume of hydrogen evolved after two hours is noted.
A mineral component that hardly reacts at all with the silicone compound is one which produces a parasitic evolution of hydrogen, after two hours, of less than or equal to 6 ml under standard temperature and pressure conditions.
A mineral additive according to the invention therefore makes it possible to increase the water resistance of a structural element according to the invention and/or to reduce the amount of water-repellent agent required for a predetermined level of water resistance.
According to the present invention, with regard to a crystalline mineral component containing a hydroxyl functional group which is nonionizable in an aqueous medium, one possible explanation (among other hypotheses) for the observed synergy, supported by the experimental protocol described below, is the formation of at least one hydrogen bond, in neutral or acid aqueous medium, between, on one side,
Humbert Régis
Martin Daniel
Theuvsen Théo
Kiliman Leszek
Lafarge Platres
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