AU3527599A - Biodegradable mineral wool composition - Google Patents

Description

1 5 MINERAL WOOL COMPOSITION 10 The present invention relates to the field of artificial mineral wool. It is aimed more particularly at mineral wool intended for manufacturing thermal and/or acoustic insulation materials or soilless-culture substrates. 15 It concerns more particularly mineral wool of the rock-wool or basalt-wool type, that is to say the chemical compositions of which involve a relatively high liquidus temperature and a high fluidity at their fiberizing temperature. Conventionally, this type of mineral wool may be fiberized by so-called "external" centrifuging processes, for example of the type of those using a 20 cascade of centrifuging wheels fed with molten material by a static delivery device, as described in particular in Patents EP-0,465,310 or EP-0,439,385. To the known criteria of industrial and economic feasibility and of quality level have been added in recent years that of biodegradability of mineral wool, namely its ability to be rapidly dissolved in a physiological medium, so as to 25 prevent any potential pathogenic risk associated with the possible accumulation of the finest fibres in the body by inhalation. The object of the invention is therefore to improve the chemical composition of mineral wool of the rock or basalt type, the improvement being aimed especially at increasing its biodegradability and/or at reconciling biodegradability with ability 30 to be fiberized by external centrifuging (without, however, excluding other fiberizing methods). The subject of the invention is a mineral wool capable of being dissolved in a physiological medium, which comprises the constituents below in the following percentages by weight: 2 SiO 2 38 - 46%, especially at least 40% A1 2 0 3 16-24% RO (CaO and/or MgO) 16 - 40% MgO 10-20% MgO/CaO 2 0.8 (or 0.70, especially 0.75)

R

2 0 (Na 2 O and/or K 2 0) 0.3%

P

2 0 5 0-5% Fe 2

O

3 (total iron) > 0.5% TiO 2 0-3% MnO 0-2%

SO

3 0-2% (Throughout the rest of the text, any percentage of a constituent of the composition should be understood to mean a percentage by weight). The selection of such a composition has allowed a whole raft of advantages to be built up, especially by varying the many complex roles that a number of its 5 specific constituents play. Thus, what is involved is a mineral wool composition of the rock wool type, in which its content of alkali metal oxides (R 2 0) essentially in the form of Na 2 O and/or K 2 0 is moderate, or even low, generally less than 6%. At the same time, its content of alkaline-earth metal oxides (RO), essentially in the form of CaO and/or 10 MgO, is high, generally at least 20% and even more at least 22%. The optional MnO, TiO 2 and SO3 contents are to be regarded more as contents of impurities often encountered in this group of compositions: in general, an overall impurity content of up to 3% may be found in the compositions. The viscosity at fiberizing of such a composition is suitable for external 15 centrifuging. As regards its biodegradability, it was already known that, especially in compositions of the rock-wool type, certain compounds, such as P 2 0 5 , could considerably improve this, while other oxides seemed on the contrary to have a tendency to reduce it, at the very least in neutral pH. Reference may be made, for 20 example, to Patents EP-0,459,897 and WO 93/22251. However, a massive addition of P 2 0 5 has not proved in the context of the invention to be the most judicious approach. This is because other considerations may arise, for example economic ones (P 2 0 5 coming from expensive raw materials) and also technical 3 ones - the changes in the proportions of P 2 0 5 , and of alumina for example, in the composition may cause other of its properties to vary in an undesirable or unknown manner. Thus, P 2 0 5 is not without influence on the viscosity of the composition, just like alumina. However, in the case of compositions of the rock 5 wool type to be fiberized by external centrifuging, to which the invention applies most advantageously, the viscosimetric behaviour of the composition is an important criterion to be controlled. Moreover, certain compounds may be advantageous for certain properties but be unfavourable for obtaining a high degree of biodegradability, something 10 that seems to be the case with iron, which is advantageous, for example, for giving the mineral wool a high fire resistance but which could tend to reduce the biodegradability of rock wool, or the case with alumina, which is judicious for regulating the viscosity of the composition but may not be very favourable with regard to biosolubility, especially when measured by in vitro tests in neutral pH. 15 The invention has therefore established a judicious compromise between all this data, essentially in the following manner: the composition may contain

P

2 0 5 , but in a moderate amount of at most 5%, or rather at most 4%. It also contains at least a small amount of iron oxide, which may prove to be advantageous (or unavoidable in trace quantities), but for reasons other than 20 biodegradability. However, the composition achieves a high level of biodegradability without adding an excessive amount of P 2 0 5 , or even without

P

2 0s at all (or any other very special compound regarded as being favourable to biodegradability), by another means, which consisted, in particular, in varying the relative proportion of MgO with respect to CaO. In fact, compositions of the rock 25 wool type generally contain an amount of lime CaO which is very markedly greater than that of magnesia MgO. By modifying this ratio, it has been found that the high level of biodegradability hitherto only able to be obtained with high P 2 0 5 contents, in order to "compensate" for the significant alumina and/or iron contents, could be achieved. A subsidiary, and not insignificant, advantage associated with a low 30 P 2 0 5 content should be noted, namely too much P 2 0 5 tends in fact to increase the liquidus temperature of the composition. Another characteristic aspect according to the invention relates to the combination of this particular MgO/CaO ratio with a rather high alumina content, since this is at least 16%. It has been found that this combination allowed the 4 biosolubility criteria, both measured in in vitro tests in neutral pH and in in vitro tests in acid pH, to be satisfactorily met. Indeed, the matter of knowing which pH was most representative of the in vivo physiological medium, especially that of pulmonary regions, has not been definitively resolved. A high alumina content has 5 seemed until now to be favourable to rapid dissolution in acid pH, but not in neutral pH. The invention makes it possible to obtain a high level of biosolubility, at least measured in vitro, whatever the pH, by selecting a high alumina content but by adapting in particular the content of alkaline-earth metal oxides so as to 10 maintain its beneficial effect in acid pH without being made to suffer in neutral pH. It should be noted that the sum SiO 2 + A1 2 0 3 allows the viscosimetric behaviour of the compositions to be largely controlled and that it is preferably at least 58%, especially between 59 and 64%. Advantageously, the mineral wool compositions according to the invention 15 have an RO content of alkaline-earth metal oxides (CaO and/or MgO) of either between 18 and 32%, for example between 26 and 30%, or more than 32% and up to 40%. Likewise, according to a first embodiment, the iron oxide Fe 2

O

3 contents may be very modest, especially from 0.5 to 1.7%, (these generally being 20 combined with a high RO content, of greater than 32%). This low content makes it possible to obtain what is sometimes referred to as "white wool", used especially for applications of mineral wool sprayed onto building components. According to a second embodiment, the iron content is higher, especially with more than 1.7% and up to 12% of Fe 2

O

3 , and preferably from 5 to 10% or 25 from 5 to 8% of Fe 2

O

3 (generally combined with an RO content of 18 to 32%). As mentioned above, iron may in particular give the mineral wool a high fire resistance. In this embodiment, the mineral wool is generally collected in the form of felts. Advantageously, the R 2 0 oxide (Na 2 0 and/or K 2 0) content may either be 30 between 0.3 and 1% (preferably for the purpose of manufacturing the abovementioned white wool) or greater than this, especially from more than 1% up to almost 6%, for example at least 2 to 2.2% or between 1 and 3%. Advantageously, the compositions according to the invention also satisfy the following relationship, expressed as a ratio of percentages by weight: 5 MgO/CaO greater than 0.85, especially greater than 0.95 or 1 or 1.15, and generally at most 2 or 3. Thus, the abovementioned advantageous effect is obtained without too great an excess of MgO with respect to CaO making it excessively complicated or expensive to procure these oxides as raw materials. 5 As mentioned above, it is also possible to use somewhat lower ratios, for example with an MgO/CaO ratio of between 0.75 and 0.80. Also advantageously, the compositions according to the invention may Atisfy the relationship that R 2 0/Al2O 3 be between 0.07 and 0.8, preferably ween 0.09 and 0.3 or between 0.05 and 0.2. The compositions according to the invention preferably have a P 2 0 5 content of more than 0.1%, and especially up to 2 to 3%. This moderate content has a highly advantageous influence on the biodegradability, without economically penalizing the composition too much or having too great an influence on its liquidus temperature. 15 According to another embodiment, the P 2 0 5 content may be lower, especially zero or slightly greater and up to 0.1%. The oxidation of the composition may, for example, be controlled by the optional addition of manganese oxide MnO, especially in an amount of 0.1 to 4%. Adding boron oxide, which is also optional and especially with a content of 20 0.1 to 5%, may allow the thermal insulation properties of the mineral wool to be improved, especially by tending to lower its thermal conductivity coefficient in its radiative component. Optionally, the composition may also contain TiO 2 as an impurity or intentionally added, for example in an amount up to 1 to 2%. SO 3 is also to be 25 regarded as an impurity, just like P 2 0 5 , especially when it is confined to values of less than 0.1%. The preferred CaO content of the composition according to the invention is less than or equal to 22%, especially at least 10%, advantageously between 11 and 18%, or more than 18% and up to 21%. 30 In parallel, the preferred MgO content of the composition is preferably at least 11% and generally at most 19%, the preferred range being between 12 and 15%.

6 According to a non-limiting preferred embodiment of the invention, the alumina A1 2 0 3 content of the compositions is at least 18.5%, especially at least 19%, and even at least 20 or 21%. The difference T 1

,

1 - Tiq is preferably at least 10 0 C, preferably at least 20 5 or 30OC: this difference defines the "working range" of the compositions of the invention, i.e. the temperature range in which they may be fiberized, most particularly by external centrifuging. Such mineral wool, as mentioned above, has a satisfactory level of biosolubility, whether the measurement method involves a neutral or slightly basic 10 pH or an acid pH. Thus, the mineral wool according to the invention generally has a rate of dissolution of at least 30, and preferably at least 40 and even at least 50 ng/cm 2 per hour (especially measured on silica) measured at pH 4.5 and at least 30, and preferably at least 40 and even at least 50 ng/cm 2 per hour (especially measured 15 on silica) measured at pH 7.5. In general, such mineral wool has a rate of dissolution of at least 30 and preferably at least 40 and even 50 ng/cm 2 per hour measured at pH 4.5 and a rate of dissolution of at least 30 and preferably at least 40 and even 50 ng/cm 2 per hour measured at pH 6.9 (again, especially measured on silica). 20 In general, it also has a rate of dissolution of at least 60, especially at least 80 ng/cm 2 per hour measured at pH 7.5 and/or a rate of dissolution of at least 40 ng/cm 2 , especially at least 60 ng/cm 2 per hour measured at pH 6.9 and/or measured at pH 7.5 (especially measured on silica). The mineral wool is mainly used to manufacture thermal and/or acoustic 25 insulation products or soilless-culture substrates. The subject of the invention is also any product comprising, at least partly, the mineral wool defined above. Further details and advantageous characteristics will emerge from the description below of preferred non-limiting embodiments. Table 1 below gives the chemical compositions, as percentages by weight, 30 of fifteen examples. When the sum of all the contents of all the compounds is slightly less than 100%, it is to be understood that the residual content corresponds to the minor impurities/compounds (not quantitatively determined), which content is at most 7 0.5% to 1%, and/or is due merely to the accepted approximation in the analytical methods used in this field.

IU 0 ~C)j~ 0 e 0 4o q, 'I -- C' c -;60 ~0) (0 0 0 C 0 c 40 04 0 r u y >4~~~~~ - -i6 C l0 ' l c: C) Y)00co 0 o 0 N wV c- c60 I- , 6 6q ~~~~c C)-66 o C4 uJ CO C! 00O 00 C4 C Q 14 C: C -- : c6 V 1 iC50 = > U W c't 04NC C' ol L0 0 0 O r-: - C) nC C- ,4 o 0)~ Lk 6 ()a o ;8 ;6 ~ ci ( C4 C; 0 - -6 0 0 0 w iC 1 ~- 0 0 N lq 6 C w C- Lf06 0 0 w V 04 6' 0 6 0 - wi -o VC64 .06 CS0 0 0 04C6 6i : N C' *'N 6 i 50co w v Y C5' 0) co. -o r- C* cr rLo L o 0) L 6 60 >4 4rx, c) - - ~ ai c, 6 -0 0 0J 0*- + 0) C -;c 000 0 10 The compositions according to these examples were fiberized by external centrifuging, especially according to the teaching of the aforementioned patents. Their working ranges, defined by the difference Tiog 1 - T 1 g, are amply positive. 5 All the compositions have an MgO/CaO ratio of greater than 0.8 and even greater than 0.85 and a very modest (less than 1%) or zero P 2 0 5 content. They also all have a high alumina content of approximately 17 to 23%. Apart from Example 6, all the examples have an Fe 2 0 3 content of around 6 to 8%. Example 6, with very little iron and a large amount of alkaline-earth metal oxides, allows 10 "white" rock wool, mentioned above, to be manufactured. Their biodegradability, especially measured at neutral or slightly acid pH (pH 6.9 or 7.5), or at acid pH (4.5), is satisfactory. Table 2 below gives the results of measurements of the rate of dissolution of the silica in the mineral wool according to Examples 9, 10 and 11, denoted by 15 "Ksio2" and expressed in ng/cm 2 per hour: + according to an in vitro test in a fluid buffered to an acid pH (4.5), called "acid fluid", + according to an in vitro test in a fluid buffered to a pH of approximately 7.4 to 7.5, called "neutral fluid". ACID FLUID NEUTRAL FLUID K si02 (EX. 9) 35 32 Ksio2 (EX. 10) 58 45 Ksio 2 (EX. 11) 83 52 20 TABLE 2 It seems to emerge from these results that the higher the alumina content, the higher the rate of dissolution in acid pH and, to a lesser extent, also in neutral pH. 25 Two additional composition examples, Examples 16 and 17, satisfying the formulation described above with an MgO/CaO ratio of 0.75, also proved to be useful. The compositions are given in detail in Table 3 below, with the same constituents as in Table 1: 11 EXAMPLE 16 EXAMPLE 17 SiO 2 42 42 A1 2 0 3 19 22 CaO 16 16 MgO 12 12 Na 2 0 0.5 1

K

2 0 2 0.5 7e 2 0 3 7.5 5.7 31 99 99.2 ,aO + MgO 28 28 Na 2 0 + K 2 0 2.5 1.5 MgO / CaO 0.75 0.75

R

2 0 / A1 2 0 3 0.13 0.07 TABLE 3

Claims (3)

1. Mineral wool capable of being dissolved in a physiological medium, characterized in that it comprises the constituents below in the following percentages by weight: SiO 2 38 - 46%, especially at least 40% A1 2 0 3

16-24% MgO 10-20% RO (CaO + MgO) 16-40% MgO/CaO 0.8 R 2 0 (Na 2 O + K 2 0) 0.3% P 2 0 5 0-5% Fe 2 O 3 (total iron) : 0.5% TiO 2 0-3% MnO 0-2% SO 3 0-2%. 5 2. Mineral wool according to Claim 1, characterized in that it comprises RO oxides (CaO + MgO) in the following percentages by weight: RO, 18 - 32%, or more than 32% and up to 40%. 3. Mineral wool according to either of the previous claims, characterized in that it comprises Fe 2 0 3 (total iron) in the following percentages by weight: 10 0.5 to 1.7% or more than 1.7 and up to 12%. 4. Mineral wool according to one of the preceding claims, characterized in that it comprises R 2 0 oxides (Na 2 0 + K 2 0) in the following percentages: 0.3 to 1%, or more than 1% and up to 6%, especially at least 2 or 2.2%. 5. Mineral wool according to one of the preceding claims, characterized in 15 that it satisfies the relationship: MgO/CaO > 0.85, preferably > 0.95, especially > 1 or > 1.15. 6. Mineral wool according to one of the preceding claims, characterized in that it satisfies the relationship: R 2 0/Al 2 0 3 = 0.07 - 0.8, preferably 0.09 to 0.3. 20 7. Mineral wool according to one of the preceding claims, characterized in that it comprises from 0 to 0.1% by weight of P 2 0 5 , or more than 0.1% and up to 2 or 3%. 13 8. Mineral wool according to one of the preceding claims, characterized in that it comprises MnO, especially with a content of 0.1 to 4% and/or B 2 0 3 , especially with a content of 0.1 to 5 %. 9. Mineral wool according to one of the preceding claims, characterized in 5 that it comprises MgO in the following percentages by weight: MgO 11%, especially 19%, preferably between 12 and 15%. 10. Mineral wool according to one of the preceding claims, characterized in that it comprises CaO in the following percentages: CaO = 22%, especially 10%, preferably between 11 and 18%, or more than 10 18% and up to 21%. 11. Mineral wool according to one of the preceding claims, characterized in that it comprises A1 2 0 3 in the following percentages: A1 2 0 3

18.5%, especially 19% or 20%. 12. Mineral wool according to one of the preceding claims, characterized 15 in that it has a rate of dissolution of at least 30 ng/cm 2 per hour measured at pH 4.5 and a rate of dissolution of at least 30 ng/cm 2 per hour measured at pH 7.5. 13. Mineral wool according to one of the preceding claims, characterized in that it has a rate of dissolution of at least 30 ng/cm 2 per hour measured at pH 4.5 and a rate of dissolution of at least 30 ng/cm 2 per hour measured at 20 pH 6.9. 14. Mineral wool according to one of the preceding claims, characterized in that it has a rate of dissolution of at least 60 ng/cm 2 per hour measured at pH 4.5 and/or a rate of dissolution of at least 40 ng/cm 2 per hour measured at pH 7.5 and/or a rate of dissolution of at least 40 ng/cm 2 per hour measured at 25 pH 6.9. 15. Mineral wool according to one of the preceding claims, characterized in that it is obtained by external centrifuging. 16. Thermal and/or acoustic insulation product or soilless-culture substrate comprising, at least partly, the mineral wool according to one of the preceding 30 claims.