A FIBERGLASS COMPOSITION

Abstract: There is disclosed a fiberglass composition characterized in that it comprises, expressed in percentages by weight for the individual components: Si O2 < 60 Al2O3 < 1 Na2O + K2O > 17.0 CaO + MgO < 12 BaO 0-2 B2O3 > 5.

Description: A FIBERGLASS COMPOSITION D e s c r i p t i o n The present invention relates to a new fiberglass composition. It is known that mineral fibers and in particular glass fibers find wide application in making felts, marketed in the form of panels or rolls for example, typically designed to make thermal and/or acoustical insulation structures in the civil field. From the point of view of their production, fiberglass felts are manufactured following the process briefly described below. First, the material that will form the fiber is brought to a high temperature until a physical state is reached in which the glass takes a fluid consistency. Subsequently fiber formation takes place and the fibers are laid down onto appropriate conveyor belts forming felts of a predetermined thickness. The fiber forming step can be obtained for example by conveying the material in a fluid state within appropriate rotors provided with a great number of perimetric holes capable of carrying out a centrifugal extrusion of the material that, submitted to the action of combustion gasses from an annular burner, is reduced into extremely fine fibers. As above mentioned, the last-mentioned fibers after cooling and treatment, are caused to lay down on a conveyor belt forming a more or less homogeneous fiber layer. Obviously, the felt thickness which is formed can be established by adjusting the speed of the conveyor belts depending on the fiber formation speed. Once the fiberglass felt has been formed on the conveyor belt, typically compression operations are carried out on the felt itself and the latter is packaged into panels or rolls . One of the most delicate steps of the above described process surely is extrusion of the fiber carried out with perimetrically perforated rotors into which the fluid material continuously flows. It is to be noted in fact that the holes provided in the forming head are, by nature, extremely small since fibers of extremely reduced section are to be made. It is therefore apparent that these holes easily lend themselves to become occluded. In particular, during production of conventional glass fibers very often a phenomenon of devitrification of the substantially liquid vitreous material occurs; due to the occurrence of this phenomenon, in the liquid mass there is a tendency to formation of crystals the size of which becomes increasingly larger. It is clear that crystal formation within the substantially liquid glass passing through the holes of the extruder head can cause irreparable occlusions of said holes. Should the devitrification phenomenon of the vitreous mass take an uncontrolled and unchecked course, a quick deterioration of operation of the extruder head would occur, said head becoming uncapable of conveniently producing and forming the fibers. As a result, there will be not only a great difficulty in checking the quality of the felt being produced which clearly is required to have homogeneous features in terms of fiber thickness and density, but also the extruder head would be such damaged that stopping of the whole plant will be caused and consequently maintenance interventions and/or interventions for replacing the extruder head itself will be required, with obvious damages in production and prices. In addition to the above described drawbacks, it should be noted that the presence of crystalline inclusions in the vitreous mass produces glasses of an unhomogeneous matrix which will bring about a reduction in the mechanical qualities of the glass, in particular in terms of strength and elasticity, so that products of poor competitiveness will be manufactured. After the above statements, it is a fundamental aim of the present invention to provide a new fiberglass composition capable of substantially solving all the - above mentioned drawbacks . In particular, it is a fundamental aim of the invention to provide a new fiberglass composition capable of showing excellent capabilities of being formed into fibers without at the same time highlighting important devitrification phenomena at the temperature at which the fiber itself is worked or "fibered". In more detail, the fiberglass composition being the object of the present invention must have an optimal working or "fibering" temperature (temperature at which the viscosity of the liquid vitreous mass is of about 1000 poises) , considerably different from and higher than the temperatures to which the phenomena of formation and growing of devitrified crystals occur and propagate. It is an additional aim of the present invention to devise a new fiberglass composition that, in addition to being easily workable into fibers and having a low and even negligible tendency to devitrification, also has good features in terms of biosolubility, i.e. the ability to be easily absorbed by a biological medium at predetermined intervals of time. Furthermore, the fiberglass composition being the object of the present invention must be able to create felts of good mechanical features, in particular in terms of elasticity, which will enable a good mechanical behavior of the final product as well as an easier packaging of same in within reduced spaces. Finally, the concerned fiberglass composition must be adapted to enable accomplishment of products such as panels or rolls of fibrous material having excellent features in terms of thermal and/or acoustical insulation. The foregoing and further aims that will become more apparent in the following description, are substantially achieved by a fiberglass composition according to one or more of the appended claims. Further features and advantages of the present invention will be best understood from the description of some fiberglass compositions in accordance with the invention, given by way of non-limiting example only. For better understanding the detailed description of the fiberglass composition as conceived by the Applicants, it is useful to specify some definitions that will be often found when treating the present matter in the following. First of all by the term "devitrification" it is meant the tendency to occurrence of crystalline formations within the matrix of the vitreous mass substantially in a liquid state. For reference, the stoichiometric compositions of possible crystalline formations that may give rise to devitrification phenomena are the following: β - wallastonite = CaO-SI0 2 Devitrite = Na 2 0 • 3Ca0 ■ 6Si0 2 Cristobalite = Si0 2 Diposide = CaO • MgO • 2Si0 2 Trimidite crystobalite = Si0 2 By "liquidus temperature (T x )" expressed in degrees centigrade, it is indicated the temperature at which beginning of formation of devitrified crystals occurs inside the liquid vitreous matrix. By "maximum devitrification speed" expressed in micron/h (Vmax) it is intended the maximum growth speed of the average sizes of the devitrified crystals inside the liquid vitreous matrix. By "temperature of maximum growth speed" (T v(max) ) expressed in degrees centigrade, it is intended the temperature at which the V max, i.e. the maximum growth speed of the average sizes of the devitrified crystals, occurs . By "optimal glass working temperature" (fibering temperature = T f ) it is intended the temperature at which the viscosity η is substantially equal to 1000 poises. After the above statements as regards definitions, it is to be noted that the Applicants' studies in order to obtain a satisfactory fiberglass composition clearly started from the analysis of known compositions and the study of the related behaviors so as to understand, as much as possible, the effects that each component used in the composition could have with a particular reference to the purposes that the Applicants intended to achieve: glass workability, absence of devitrification problems, good mechanical qualities in the fiber, biosolubility. For instance, by analyzing the following composition, CI, which has been available on the market for long, in which the different components are expressed in percentages by weight, Si0 2 64.08 A1 2 0 3 3.40 Na 2 0 16.20 K 2 0 1.00 CaO 7.10 MgO 3.10 Fe 2 0 3 0.12 B 2 0 3 5.00 it was possible to notice that the obtained performance of the manufactured fiber, although valid in terms of thermal/acoustical insulation, were not satisfactory with reference to other aspects. In particular, in-depth experimental laboratory tests were carried out for said composition in order to state the values of T l f T v{max) and V max. Tests were carried out in accordance with ASTM C-829 Standards Practices for measurements of liquids Temperature of glass by gradient furnace method (annual book of ASTM Standard Vol. 15, 1990 pages 266-274). The devitrification curve of the above identified known glass in terms of percent components, which curve was obtained by microscopy and with reference to β- wallastonite crystals, gave the following results: T v(max) = 829°C V max = 2.19 micron/h The above devitrification parameters and in particular temperatures appear to be very high and lead to a glass in which, during fibering, if one wishes to operate at an optimal viscosity, marked phenomena of devitrification occur . Then the Applicants' studies addressed in particular to an increase of alkaline oxides (Na 2 0, K 2 0) to the detriment of silica so as to obtain vitreous compositions of greater fluidity, with a consequent reduction both in the liquidus temperature and in the temperature of the maximum devitrification speed. Attempts were also made to work on the percentages of alkaline-earth oxides (CaO + MgO) which were reduced as compared with traditional values, thereby again involving a reduction in the liquidus temperature and in the temperature of the maximum devitrification speed. Silica too was greatly reduced with respect to glasses of the standard type (such as those analyzed above in detail, for example) , thereby achieving a further advantage in terms of devitrification parameters. In the formulations, combining of the reduction in the above identified components with an appropriate rebalancing of the other components of the composition was also tried, bearing in mind said requirements of obtaining a material adapted to be fibered, also being mechanically valid, bio-soluble and, obviously, cheap. It was surprisingly found that particularly valid from every point of view appeared those compositions in which the percentages by weight of each component fell within the below-specified ranges: In particular, very appreciated appeared to be fibers in which the ranges of percentages by weight of each component were within the following values: By way of example, in the observance of the above-stated ranges, the four following specific fiberglass compositions appeared to be very advantageous: In all cases highlighted above it was possible to see that the optimal fibering temperature remained within a range included between 890 and 940 degrees centigrade and that the devitrification parameters, obtained both experimentally and mathematically, appeared quite good. In particular, 1 1 and T v(max) lower than 800 and 750 degrees centigrade were obtained respectively, with the maximum growth speed V max < 7 micron/h. The above data took place and were confirmed following experimental tests conducted in the laboratory following the dictates of the above mentioned ASTM standard, with reference to each of the compositions 1, 2, 3 and 4 in accordance with the invention. It should be noted that the tendency of T x and T V(max) to lower also appears when the Rodriguez Cuartas mathematic model is applied, as it is clear from the above reproduced table: The formula for calculation of the devitrification parameters Pd is given by: Σ (fi x p Pd = fi = multiplicative factor referred to in the above table Px = percentage by weight of element "i" P S i o2 = percentage by weight of silica It should be noted that the above reproduced mathematic model is by nature capable of supplying approximate values only of the different devitrifications parameters and surely it is not possible to have a precise response such as the experimental one, on the exact value of T x and T v(raax) ; practically the Rodriguez model gives approximate indications on the tendency of the different parameters to increase or decrease following a variation in the concentration of the different oxides. Improvement in terms of devitrification features of the compositions conceived by the Applicants can be partly explained as follows. An increase in the alkaline oxides Na 2 0 + K 2 0 brings to glasses of greater fluidity with a consequent reduction m T x and T v(max) . In addition, a reduction in CaO and MgO reduces T ± and T v(max) , above all with reference to CaO. In the same manner, a silica reduction leads to a material reduction in T^ and T v(max) , since Si0 2 is present in all devitrifying crystalline forms. Lowering of A1 2 0 3 too, in addition to having advantageous effects in terms of biosolubility, involves a reduction in the liquidus temperature and in the temperature of maximum speed for devitrifying crystal formation; at all events it should be noted that alumina was reduced without however going under the limits that would have jeopardized the structural stability of the vitreous matrix. With reference to the effects of the adopted choices on the V (max) , it should be noted that, supposing the kinetics of crystal formation and in particular of β-wallastone, devitrite and diopside formation is a function of the CaO and MgO percentages, their decrease will have a value of V (max) . V( ma ) is also reduced due to replacement of part of Si0 2 with Na 2 0 and, to a lower extent, with K 2 0, because the greater fluidity of the vitreous mass brings to a substantial kinetic balance between the crystals (in particular devitrite) which are formed and the crystals that constantly dissolve in the vitreous liquid. By virtue of the improved features in terms of devitrification, the composition in reference gives rise to improved fibers from a mechanical point of view too. In this connection the high content of B 2 0 3 enables a highly elastic fiber to be obtained with obvious advantages in terms of possibilities of utilizing, handling and packaging the product. It is finally important to note that the compositions in accordance with the invention meet the most severe requirements of bio-solubility; in particular, defining the Ki index = CaO%+MgO%+BaO%+Na 2 0%+K 2 0%+B 2 0 3 %-2Al 2 0 3 %, the TRGS905 German Standards set, for the insulating fiber, Ki > 40, which relation is fully met by the new compositions in accordance with the invention. The invention achieves important advantages. It should be recognized in fact that all compositions of new conception, in addition to being excellent from the point of view of fibering ability, optimal from a mechanical point of view and acceptable in terms of bio-solubility, due to the low temperature at which they are able to be worked into fibers, they have greatly increased (by 30%, on the average) the mean life of the rotors used for fiberglass production.

Claims: C L A I M S 1. A fiberglass composition characterized in that it comprises, in percentages by weight for the individual components: Si0 2 < 60 A1 2 0 3 < 1 Na 2 0 +K 2 0 > 17.0 CaO + MgO < 12 BaO 0-2 B 2 0 3 > 5 2. A composition as claimed in claim 1, characterized in that Si0 2 is present, in a percentage by weight included between 54.00% and 59.50%. 3. A composition as claimed in claim 2, characterized in that Si0 2 is present in a percentage by weight included between 56.40% and 58.90%. 4. A composition as claimed in claim 1, characterized in that A1 2 0 3 is present in a percentage by weight included between 0% and 1%, preferably lower than 0.70%. 5. A composition as claimed in claim 1, characterized in that Na 2 0 is present in a percentage by weight included between 17.00% and 20.00%. 6. A composition as claimed in claim 1 or 5, characterized in that K 2 0 is present in a percentage by weight included between 0.30% and 1.00%. 7. A composition as claimed in claim 5 or claim 6, characterized in that Na 2 0 is present in a percentage by weight included between 17.50% and 19.50%. 8. A composition as claimed in anyone of claims 5 to 7, characterized in that K 2 0 is present in a percentage by weight included between 0.35% and 0.85%. 9. A composition as claimed in claim 1, characterized in that CaO is present in a percentage by weight included between 3.00% and 7.00%. 10. A composition as claimed in claim 9, characterized in that CaO is present in a percentage by weight included between 3.50% and 6.00%, preferably between 4.00% and 5.50%. 11. A composition as claimed in claim 9 or in claim 10, characterized in that MgO is present in a percentage by weight included between 0% and 5.00%. 12. A composition as claimed in anyone of claims 9 to 11, characterized in that MgO is present in a percentage by weight included between 1.50% and 5.00%, preferably between 2.00% and 5.00%, the sum of the percentages by weight of CaO% + MgO% preferably being lower than 10.50%. 13. A composition as claimed in claim 1, characterized in that BaO is present in a percentage by weight included between 1.00% and 2.00%. 14. A composition as claimed in claim 13, characterized in that BaO is present in a percentage by weight included between 1.40% and 1.80%. 15. A composition as claimed in claim 1, characterized in that B 2 0 3 is present in a percentage by weight included between 10.00% and 14.50%. 16. A composition as claimed in claim 15, characterized in that B 2 0 3 is present in a percentage by weight included between 11.00% and 14.00%. 17. A composition as claimed in anyone of the preceding claims, characterized in that it further comprises Fe 2 0 3 in a percentage by weight varying between 0.00% and 0.40%. 18. A composition as claimed in claim 17, characterized in that Fe 2 0 3 is present in a percentage by weight varying between 0.05% and 0.20%. 19. A composition as claimed in anyone of the preceding claims having a working or "fibering" temperature corresponding to a viscosity η = 1000 poises, greater than 890°C, preferably included between 890°C and 950 °C. 20. A composition as claimed in anyone of the preceding claims, characterized in that it has the following devitrification parameters: T x = Liquidus temperature < 800 °C; V max = maximum growth speed of the devitrified crystals < 7 micron/h; T v (max) — 750 C. 21. A composition as claimed in anyone of the preceding claims, characterized in that the percentages by weight of the following oxides present in the composition are of such a magnitude that: ^ = CaO%+MgO%+BaO%+Na 2 0%+K 2 0%+B 2 0 3 %-2Al 2 0 3 % > 40. 22. A composition as claimed in anyone of claims 1 to 21, characterized in that it comprises, expressed in percentages by weight: 23. A composition as claimed in anyone of claims 1 to 21, characterized in that it comprises, expressed in percentages by weight: 24. A composition as claimed in anyone of claims 1 to 21, characterized in that it comprises, expressed in percen tages b y weiglt: Si0 2 58.40 A1 2 0 3 0.50 25. A composition as claimed in anyone of claims 1 to 21, characterized in that it comprises, expressed in 26. A felt, to make thermal and/or acoustical insulating structures, obtained with the composition as claimed in one or more of the preceding claims.

Inventors: GIOVI EDOARDO, LA GRECA MARCO, MASSINI ROBERTO, PASALAIGUA HUGUET JORGE, GIOVI, EDOARDO, LA GRECA, MARCO, MASSINI, ROBERTO, PASALAIGUA HUGUET, JORGE
Applicants: GIOVI EDOARDO, GRECA MARCO, MASSINI ROBERTO, PASALAIGUA HUGUET JORGE, POLIGLAS SA, TECHINT SPA, GIOVI, EDOARDO, LA GRECA, MARCO, MASSINI, ROBERTO, PASALAIGUA HUGUET, JORGE, POLIGLAS, S.A., TECHINT COMPAGNIA TECNICA INTERNAZIONALE S.P.A.
Application year: 2001
Main classification: C03C13
IPC codes: C03C13