Compositions: coating or plastic – Coating or plastic compositions – Molds and mold coating compositions
Reexamination Certificate
2001-10-22
2004-10-19
Marcantoni, Paul (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Molds and mold coating compositions
C106S038300, C106S600000, C252S062000
Reexamination Certificate
active
06805737
ABSTRACT:
The invention concerns a molded body made from a lightweight substance that contains a sintered product made from a lightweight aggregate and a water-soluble silicate. The invention also concerns a method for production of such molded bodies and their use.
Lightweight aggregate-containing products have been established for years in the construction sector. These materials are primarily used to reduce heat conductivity of construction products. The lightweight aggregates are incorporated, for example, in concrete (lightweight concrete), bricks or plaster systems. Mechanically loadable, nonflammable molded bodies whose heating properties are improved relative to the pure matrix material can be produced with these inorganic matrix materials,
Lightweight aggregates, for example, perlites with water glass, bonded into insulating panels are used, especially in the United States, in household appliances (coffee machines). The products have limited compressive strength (O
D
<0.5 N/mm
2
) and are not waterproof Water glass is often used as a binder in the production of lightweight aggregates (expanded glass), in which the binder is required to produce the crude granulate (EPOS 084 634). These products are used in plaster and mortar systems. The use of water glass as a binder or fire retardant for lightweight insulation plates made of paper or scrap paper is known from the documents DE 41 14 755 A1, DE 44 32 019 A1 and DE 44 36 981 A1. The production of fireproof, radiation-shielding lightweight plates and molded parts is described in DE 33 03 204. The method is characterized by the fact that the employed mineral fillers, perlites or expanded shales, kaolin and if necessary mineral fibers, curing agents and water glass, that contains an expanding agent as a binder are homogenized at room temperature during foaming of the water glass in a mixer, then extruded into molded bodies and dried at a temperature of about 150° C. These systems are also characterized by insufficient water resistance.
The production of ceramic products from clay, kaolin, quartz flour, feldspar or other fluxes, talc and basic raw materials (not further specified) is explained in DE 37 22 242 C1. A mass that is made castable by means of a plasticizer is mixed with less than 1 wt. % water glass and curing agent, dried and fired. In this process water glass is added as plasticizer and for the solidification of the casting mass after shaping, whereby an absorbent mold material, like gypsum, for example, can be eliminated. Ordinary pore-forming agents, like perlites, cenospheres, expanded clay, pumice or kieselguhr are used for pore formation. The dried products are subjected to ceramic firing with a firing temperature of about 1200° C., in which the initial components clay, kaolin, feldspar and quartz form the ceramic body material. Thus, the addition of water glass occurs exclusively for the plasticization and for the solidification of the casting mass in the subsequent processing step.
Thus, a disadvantage in conventional molded bodies or construction products that contain lightweight aggregates is especially the fact that a drastic reduction in strength occurs when the content of aggregate is increased. The conventional molded bodies or construction products are therefore only conditionally suited for insulation molded bodies, bricks or the like.
From here, the task of the present invention is to propose a molded body that is essentially inorganic in nature and is simultaneously characterized by low density, good water and acid resistance and high mechanical strength. Another task of the present invention is to provide a corresponding process for production of such molded bodies, as well as their use.
It is therefore proposed according to the invention that the molded body be essentially formed from a sintered product containing 60 to 95 wt. % of a lightweight aggregate with 40 to 5 wt. % of a water-soluble silicate. The nonflammable inorganic molded bodies according to the invention are characterized, in particular, by low density, good water and acid resistance, and by comparatively high mechanical strength at the same time. This can be obviously attributed to the fact that the aggregates are sintered together, by which a network is formed between the aggregates that is characterized by high binding forces. Because of this, the properties of the aggregates can essentially be retained as such. Owing to the fact that the sintering auxiliary itself is formed from the water-soluble silicate glass, a pure inorganic molded body is involved. It is significant here that the water-soluble silicate glass fulfills several tasks. On the one hand, it serves for dust removal of the aggregate and as its temporary binder during production of the green body. Simultaneously, the water-soluble silicate functions as a pore-forming agent. However, it is important that the water-soluble silicate glass act as sintering auxiliary. By the use of water-soluble silicates the formation of a liquid phase whose softening point is lower than the softening point of the aggregate is possible during the sintering process. The lightweight aggregates can therefore be sintered together without disturbing their pore structure. Using a minimal content of silicate, a no-fines structure is therefore formed in which the aggregates are sintered together exclusively at the contact site.
It is also possible on this account for the molded body according to the invention to have an extremely high percentage of aggregate (60 to 95 wt. %, preferably 80 to 93 wt. %). This ensures that the properties of the molded body are essentially dictated by the nature of the lightweight aggregate itself.
It is also emphasized in the molded bodies according to the invention that their properties can be varied over a wide range by selecting the lightweight aggregate and the sintering conditions. It is thus possible to produce molded bodies whose dry bulk density lies in the range of 150 to 750 kg/m
3
. Choice of the corresponding dry bulk density is then made according to the application. The compressive strength of the molded body according to the invention lies in the range of 0.1 to 15 N/mm
2
.
The molded body according to the invention from a material standpoint can be produced from any silicate lightweight aggregate known from prior art. However, scrap glass, expanded glass, perlites, vermiculites, expanded clay, cenospheres, kieselguhr or natural and metallurgical pumice are preferred as aggregate.
Alkali silicates, preferably water glass, especially sodium water glass and potassium water glass, are preferred among the water-soluble silicates. Water glass is soluble in alkaline solutions and water, in contrast to standard glass, like container glass. This solubility, among other things, is due to the fact that alkali ions are incorporated in their network, which reduce chemical resistance. Since most inorganic lightweight aggregates (e.g., expanded glass granulate, expanded clay, perlites, etc.) also incorporate alkaline earth oxides, a soda-lime glass can be formed from the water glass during liquid phase sintering, which is required to produce the molded body, wherein good water resistance is produced.
The invention also concerns a process for production of the molded bodies just described.
To produce a molded body according to the invention, it is merely essential to mix the lightweight aggregate and the sintering auxiliary and to sinter them after a shaping process at 400 to 1000° C. over a period of 0.1 to 5 h. It is essential in the object of the application that the properties of the molded body, like compressive strength and dry bulk density, heat conductivity, flow resistance and sound absorption, can be influenced by varying the process parameters, i.e., the sintering conditions.
It has proven advantageous if separate drying is conducted at 50 to 95° C. after shaping and before sintering. Preferred process parameters for the sintering process are 550 to 850° C. and a sintering time of 0.1 to 0.5 h.
Production of a molded body is further described below.
The
Babuke Gerhard
Gödeke Holger
Werner Jürgen
Fraunhofer-Gesellschaft Zur Förderung Der Angewandten Forschung
Marcantoni Paul
Young & Basile P.C.
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