LIGHTWEIGHT INSULATING BOARDS AND PROCESS FOR MANUFACTURING SAME.

Abstract: Lightweight insulating boards comprising a hydraulically set Portland cement, fibers and fillers consist of a) 50 - 75% by weight of cement, b) 0 - 5% by weight of cellulose fibers, c) 0.5 - 4% by weight of alkali-resistant fiber material, d) 5 - 20% by weight of mica, e) 5 - 20% by weight of light filler and f) 8 - 25% by weight of hydrated lime. They are shaped into boards from a suspension in a per se known manner, have set after at least 15 days, and at preferably 28 days, and then meet all of the requirements as set for such materials.

Description: Subject matter of the present invention are lightweight insulating boards comprising a hydraulically set Portland cement, fibers and fillers, which boards are free from asbestos, and a process for manufacturing same. It is known to produce such lightweight insulating boards from an aqueous suspension of hydraulically setting binders containing calcium silicate, a reinforcing fiber material and fillers which harden either in air under normal conditions or under steam pressure. In said procedure it is necessary that the components of the binder, namely calcium silicates or hydrated lime, react with silica and water such as to form the known calcium silicate hydrate structures. The structure of the set binder will depend on the relative proportions of hydrated lime and silica which are capable of actually reacting under the reaction conditions. The properties of the product further depend to a significant extent on the reinforcing fiber material which is added into the aqueous suspension. Asbestos had proven to be useful for said purpose, while, however, more recently it has become necessary to abstain from using asbestos fibers for reasons of environmental protection. In the meantime a great many so-called asbestos-free products have been developed and put on the market. However, said products in general have significant drawbacks over the asbestos-containing products, since certain desired properties can only be achieved at the expense of other demanded properties. This, accordingly, limits the general usability of the asbestos-free products as compared to that of the asbestos-containing products. One typical field of application for asbestos fibers were lightweight insulating boards, more specifically those having high fire-resistance. It has been shown that lightweight insulating boards can be manufactured by replacing the asbestos fibers with cellulose fibers and/or organic fibers and/or alkali-resistant glass fibers. However, said products in general have inferior mechanical properties and are less flame-resistant. They further fail to meet the requirements of the toxicity test according to DIN 53436 since therefrom poisonous gases may be formed at high temperatures. As a filler for flame-resistant insulating boards, more specifically, mica has proven its value; mica, if desired, has been employed together with light fillers, expanded perlites or puffed clay; cf. the British Patent Specification No. 1,498,966. In said Patent Specification there have been mentioned, as binders, hydraulically setting calcium silicate binders, Portland cement, alumina cement and blast furnace slag cement. Thus, the binders used are hydraulic binders which will only set under autoclave conditions as well as binders setting with water at normal temperature. It is known that binders setting at room temperature have mechanically inferior properties, more specifically a poorer flexural strength, and an inferior water resistance than the binders having been hardened in an autoclave. Thus, in practice asbestos-free flame-resistant lightweight insulating boards were prepared from products hardened in an autoclave in which, more particularly, tobermorite structures have been formed. Thus, these crystalline calcium silicate structures so far have been considered the indispensable prerequisite to obtain products which are thermally stable as well as capable of sustaining mechanical load. However, setting in an autoclave exhibits to considerable disadvantages: 1. Hardening in an autoclave is much energy-consuming and, as the case may be, occasionally will cost more than 10% of the employed raw material. As the reinforcing fiber material, only cellulose and a few very expensive organic fibers can be used, as under the autoclave temperatures and alkaline conditions glass fibers as well as the most organic fibers are destroyed. 2. Under the conditions of autoclaving the crystalline tobermorite structure can be formed only if free crystalline silicon dioxide, e.g. quartz, is present. Even under ideal conditions a certain amount of unreacted silicon dioxide remains in the final product. However, since the action of quartz dust is dangerous to health, due to official regulations only minimum amounts of crystalline quartz are allowed to be present in the final product. However, when other silicon dioxide sources, e.g. amorphous silica, fly ash etc., are used, the thermal stability at high temperature of the final products significantly decreases. Accordingly, it is the object of the present invention to develop lightweight insulating boards comprising a hydraulically set Portland cement, fibers and fillers, which boards are free from asbestos, do not contain any free crystalline silicon dioxide in the final product and have already been hydraulically set at normal temperatures, i.e. which need not to be hardened in an autoclave with using superheated steam. Moreover, the products are to conform to the national regulations mechanically and with respect to the flame resistance and toxicity. Finally, with respect to the cost of raw materials and processing, the new products are to be so economical that they are able to compete with the products being already present in the market. As a result of intense and expensive investigations it has been found that said object can be attained in a surprisingly simple way by that the components Portland cement, fibers and fillers are present in well defined mutually adjusted amounts and in addition from 8 to 25% by weight, and preferably from 10 to 18% by weight, of hydrated lime have been added. Thus, subject matter of the present invention are lightweight insulating boards comprising a hydraulically set Portland cement, fibers and fillers, which are characterized by that they consist of a) 50 - 75% by weight of cement, b) 0 - 5% by weight of cellulose fibers, c) 0.5 - 4% by weight of alkali-resistant fiber material, d) 5 - 20% by weight of mica, e) 5 - 20% by weight of light filler and f) 8 - 25% by weight of hydrated lime. Particularly good results are accomplished, if the insulating boards consist of a) 55 - 65% by weight of cement, b) 2 - 4% by weight of cellulose fibers, c) 0.8 - 1.5% by weight of alkali-resistant fiber material, d) 10 - 15% by weight of mica, e) 8 - 18% by weight of light filler and f) 10 - 18% by weight of hydrated lime. As the alkali-resistant fiber material, more specifically, polyvinylalcohol (PVA), polyacrylonitrile (PAN) and polyamides in an amount of from 0.8 to 2% by weight or glass fibers having been coated such as to be alkali-resistant in an amount of from 1 to 4% by weight and mixtures thereof have proven to be useful. As the light fillers, more specifically, expanded perlites, puffed clay, spherical xonotlite aggregates and ground foam concrete or mixtures thereof have proven to be useful. The process for producing the insulating boards according to invention is carried out by compounding in an excess amount of water a) 50 - 75% by weight, and preferably 55 - 65% by weight, of cement, b) 0 - 5% by weight, and preferably 2 - 4% by weight, of cellulose fibers, c) 0.5 - 4% by weight, and preferably 0.8 - 1.5% by weight, of alkali-resistant fiber material, d) 5 - 20% by weight, and preferably 10 - 15% by weight, of mica, e) 5 - 20% by weight, and preferably 8 - 18% by weight, of light filler and f) 8 - 25% by weight, and preferably 10 - 18% by weigh t, of hydrated lime, separating the superfluous water from the suspension in a per se known manner while shaping into boards, and allowing the mixture to set in a humid atmosphere for at least 15 days, and preferably for 28 days. Shaping into boards from the suspension and the separation of the superfluous water from the suspension are effected in a per se known manner on filter presses, Hatschek machines, machines according to Magnani, Fourdrinier or the so-called cast and winding machines. The diluted suspensions generally contain 1 part of solids per 5 to 25 parts of water. After having been shaped the products are cut to have the desired formats and are stored in a humid atmosphere until they will have sufficiently set and sufficiently been hardened after 15 days, and preferably 28 days. For carrying out said process, mostly a slurry of the fiber material is prepared to which the fillers, the hydrated lime and the cement are then added. Of course conventional flocculating agents etc. can be added to the suspension. The products according to the invention have the customary density, namely from 0.7 to 1.1 g/cm³, and preferably from 0.8 to 1.0 g/cm³ Depending on the demanded flexural strength, the amounts according to the invention of fiber material are added, while the cellulose fiber content is kept as low as possible, since higher amounts of cellulose fibers will result in a deteriorated combustion property. Higher contents of alkali-resistant organic fibers, although they enhance the flexural strength, also deteriorate the behavior of the material in the flammability test. Glass fibers made alkali-resistant by means of a coating have to be added in somewhat higher amounts in order to attain the same effect with respect to the flexural strength. Since the products according to the invention mostly will not subjected to a permanent strain by moisture, the long-term stability of the products according to the invention is ensured even if they contain larger amounts of glass fibers made alkali-resistant by means of a coating. The mica employed as filler can be used in the commercially available grades, however, particularly good results are achieved, if at least 60% have a grain size of less than 250 µm. The proportion of particles larger than 500 µm in size should be below 3%, since otherwise trouble may occur in the manufacture process. What is of crucial importance for the insulating boards according to the invention is the content of hydrated lime. Such an additive is absolutely unconventional and leads to the unexpectedly good results. Comparative tests without an addition of hydrated lime or added amounts of hydrated lime of less than 8% by weight showed that then the products are not any more able to meet the requirements of the Official Standards, for example the incombustibility test according to the "British Standards", BS 476, part 4. Furthermore, such products have a higher percent shrinkage at 950°C. At a hydrated lime content of more than 25% by weight the mechanical properties will already decrase and the products do not have the demanded strength and flexural strength. Hence, it is preferred to add amounts of from 10 to 18% by weight. The ratio cement : hydrated lime, thus, is within the range of from 3:1 to 9:1, and preferably approximately within the range of from 4:1 to 5:1. The ratio of the sheet-shaped fillers to the globular fillers is preferred to be within the range of from 1:1 to 1:1.5. The total amount of fillers is in the range between 10 and 40% by weight, and preferably in the range between 20 and 30% by weight. As the cellulose fibers any of the fibers conventionally employed for such purposes can be used, more particularly those obtained from flax, hemp, sisal, eucalyptus and those obtained from wood, more specifically products recovered from coniferous trees, which are also used in the paper industry. In the process according to the invention there are used substially less cellulose fibers than are in conventional products. In an extreme case it will even be possible, not to use any cellulose fibers at all. Of course, the products according to the invention can be admixed with the conventional additives such as pigments, filtration aids, flocculating agents, emulsifiers etc. and certain amounts of comminuted waste materials such as calcium silicates and aluminium silicates. However, by no means any crystalline silicon dioxides are allowed to be added, since the latter, in spite of the excess amount of hydrated lime, would not be reacted to form calcium silicates at room temperature and, therefore, would result in an inadmissibly high content of crystalline silicon dioxide in the final product. In the subsequent Examples typical embodiments and the process for preparing same are illustrated in greater detail. EXAMPLE 1 3 parts by weight of cellulose and 1 part by weight of PVA were suspended in water. Then, 12 parts by weight of mica, 15 parts by weight of hydrated lime, 11 parts by weight of expanded perlite and 58 parts by weight of Portland cement were added in sequence. The suspension contained, based on the total solids content, the 25-fold amount of water. The suspension was processed on a Hatschek machine to form boards which, depending on the process contitions were from 8 and 25 mm in thickness. The boards were cut and stored in a humid atmosphere for 28 days. Lightweigh insulating boards had been formed, which met all of the requirements with respect to flexural strength, thermal shrinkage at 950°C, incombustibility test BS 476, part 4, and toxicity test according to DIN 53436 and, after drying and having been re-moistened, exhibited an elongation and shrinkage, respectively, of less than 2 mm/m. EXAMPLE 2 Example 1 was repeated using a mixture comprising 4 parts by weight of cellulose, 1 part by weight of PVA, 12 parts by weight of mica, 15 parts by weight of hydrated lime, 10 parts by weight of perlite and 58 parts by weight of cement. The product had a slightly improved flexural strength, a lower thermal shrinkage at bei 950°C and comparable values of the shrinkage and re-elongation when dried and re-moistened. EXAMPLE 3 Example 1 was repeated using a mixture comprising 2 parts by weight of cellulose, 1 part by weight of PVA, 15 parts by weight of mica, 10 parts by weight of hydrated lime, 15 parts by weight of puffed perlite and 57 parts by weight of cement. The obtained product also met all of the requirements as set. COMPARATIVE EXAMPLE Example 1 was repeated using a mixture comprising 4 parts by weight of cellulose, 1 part by weight of PVA, 12 parts by weight of mica, 15 parts by weight of perlitee and 68 parts by weight of cement. The thus obtained product had a distinctly higher shrinkage at 950°C and did not satisfy the conditions of the incombustibility test according to BS 476, part 4.

Claims: 1. Lightweight insulating boards comprising a hydraulically set Portland cement, fibers and fillers, characterized in that they consist of a) 50 - 75% by weight of cement, b) 0 - 5% by weight of cellulose fibers, c) 0.5 - 4% by weight of alkali-resistant fiber material, d) 5 - 20% by weight of mica, e) 5 - 20% by weight of light filler and f) 8 - 25% by weight of hydrated lime. 2. Insulating boards according to claim 1, characterized in that they consist of a) 55 - 65% by weight of cement, b) 2 - 4% by weight of cellulose fibers, c) 0.8 - 1.5% by weight of alkali-resistant fiber material, d) 10 - 15% by weight of mica, e) 8 - 18% by weight of light filler and f) 10 - 18% by weight of hydrated lime. 3. Insulating boards according to claims 1 or 2, characterized in that, as the alkali-resistant fiber material, from 0.8 to 2.0% by weight of polyvinylalcohol (PVA), polyacrylonitrile (PAN) and polyamides or from 1 to 4% by weight of glass fibers coated such as to be alkali-resistant or mixtures thereof are used. 4. Insulating boards according to any one of claims 1 to 3, characterized in that, as the light fillers, expanded perlites, puffed clay, synthetic spherical xonotlite aggregates or ground foam concrete or mixtures thereof are used. 5. A process for producing lightweight insulating boards comprising a hydraulically set Portland cement, fibers and fillers, characterized in that a) 50 - 75% by weight, and preferably 55 - 65% by weight, of cement, b) 0 - 5% by weight, and preferably 2 - 4% by weight,of cellulose fibers, c) 0.5 - 4% by weight, and preferably 0.8 - 1.5% by weight, of alkali-resistant fiber material, d) 5 - 20% by weight, and preferably 10 - 15% by weight, of mica, e) 5 - 20% by weight, and preferably 8 - 18% by weight, of light filler and f) 8 - 25% by weight, and preferably 10 - 18% by weight, of hydrated lime, are compounded in an excess amount of water, the superfluous water is separated from the suspension in a perse known manner while shaping into boards, and the mixture is allowed to set in a humid atmosphere for at least 15 days, and preferably for 28 days. 6. The process according to claims 5, characterized in that, as the alkali-resistant fiber material, from 0.8 to 2.0% by weight of polyvinylalcohol (PVA), polyacrylonitrile (PAN) and polyamides or from 1 to 4% by weight of glass fibers coated such as to be alkali-resistant or mixtures thereof are used. 7. The process according to claims 5 or 6, characterized in that, as the light fillers, expanded perlites, puffed clay, synthetic spherical xonotlite aggregates or ground foam concrete or mixtures thereof are used.

Inventors: BAES, EMILE
Applicants: AMETEX AG, ETERNIT-WERKE LUDWIG HATSCHEK AG, REDCO N.V., S.A. FINANCIERE ETERNIT
Application year: 1987
Main classification: C04B28
IPC codes: C04B38, C04B14, C04B28