The invention relates to a process for producing silicatic moldings, to silicatic moldings obtainable by this process, and also to their use as construction material, insulator material, gasket material or fire-resistant material.
Silicatic moldings are now used in a very wide range of technical applications, e.g., as insulator materials in the construction sector, for high-temperature gaskets (asbestos replacement) or for molding processes in the foundry industry.
Alongside low-cost production, high mechanical stability requirements have to be met by silicatic moldings in almost all application sectors. Additional criteria depend on the various specific applications. For example, in the construction sector high water resistance combined with minimum combustibility is mostly demanded in addition; in the foundry industry, fire resistance is the most important additional criterion.
The silicatic moldings are usually produced from silicatic raw materials, mostly of natural origin, examples being phyllosilicates or sands, and from various, predominantly inorganic, binders.
Waterglass is often used as an inorganic binder, and has very low cost, and often permits production of moldings with high mechanical stability, and comprises no substances which promote combustibility or smoke generation. However, it has the disadvantage of high water-solubility, and therefore gives materials which lack water resistance. Similar disadvantages result when phosphates are used as inorganic binders, the use of these being likewise frequently described.
Another reason for the particular desirability of the silicatic binders among the inorganic binders group is that they, like the raw materials to be bound, are mainly composed of the environmentally friendly material silicon dioxide, and various recycling methods become available, e.g. in the form of fillers in road building and agriculture. In contrast, other inorganic products give problems in recycling, the used materials mostly having to be disposed of as landfill.
WO-A 97/30951 describes the production of moldings from vermiculites and from inorganic binders, for example in particular from binders comprising phosphoric acid, from phosphates or from waterglass. A degree of water resistance can be achieved only by adding organic binder components, but combustibility factors limit the extent of this addition. For example, panels composed of vermiculites and bound with waterglass and with organic components and having up to 10% by weight of organic component, based on the final product, are unsuitable for insulation systems, such as bulkheads for ships' cargo holds, which are subject to a stringent requirement for water resistance.
DE-A 198 512 90 describes the use of waterglass and pulverulent, exclusively inorganic, binder for vermiculites during the production of non-combustible panels. A disadvantage here is the very high alkali metal silicate content and the correspondingly poor water resistance of the products.
According to U.S. Pat. No. 4,746,555, an improvement can be obtained in the strength of panels based on phyllosilicates when using waterglass by adding phenolic resins and comminuted wood, as long as problems are accepted in relation to fire load, smoke generation, and the disposal of these moldings.
DE-A 195 420 69 describes the binding of silicatic raw materials with a mixture composed of waterglass and of pulverulent silicon dioxide, but water resistance is achieved only via treatment with a silicone-containing hydrophobicizing agent. Although the silicone-containing overlayers are water-repellent, they firstly comprise organic fractions which continue to promote smoke generation, and they secondly also have low mechanical strength and bind poorly to the silicatic substrate.
WO-A 01/051428 describes the addition of organic binders, such as polyurethanes, to give insulation panels high mechanical stability prior to final hardening. Once the organic constituents have been burnt off, the result is a purely inorganic product. However, this additional production step leads to higher manufacturing costs and to environmentally hazardous gases from the burning process. In addition, the final product still lacks adequate moisture resistance.
There is therefore a continued need for silicatic moldings which are mechanically stable and which fulfil the advantageous additional requirements placed upon the appropriate application. By way of example, mention may be made here of high water resistance in combination with minimum combustibility and smoke generation for use in the construction sector, or fire resistance for applications in the foundry industry. Good recycling capability can also be advantageous.
The object is therefore to provide silicatic moldings which comply with the respective appropriate combination of requirements, and to provide a process for their production.