MAN-MADE VITREOUS FIBRES

Abstract: The invention provides a product comprising man-made vitreous fibres formed from a composition which includes, by weight of oxides, SiO>2<: 46 to 58 %, Al>2<O>3<: 0.8 to 3 %, FeO: 5 to 6.8 %, TiO>2<: 0 to 4 %, CaO: 0 to 40 %, MgO: 0 to 30 %, Na>2<O + K>2<O: 0 to 1 %, P>2<O>5<: 0.2 to 10 %, others: 0 to 10 %.

Description: MAN-MADE VITREOUS FIBRES The present invention concerns man-made vitreous fibres (MMVF) , which have a solubility in biological fluid (biosolubility) which is considered to be acceptable, which are durable in use and which give good fire resistance properties. It is well known to make MMV fibres from mineral melt. A combination of raw materials is melted in a furnace to provide a mineral melt having the desired chemical composition and is then formed into fibres. These are used for various purposes including heat insulation, fire protection, sound insulation etc. Although there is no scientific evidence establishing that there is a health risk associated with manufacture and use of MMV fibres, it is nevertheless commercially desirable to provide MMV fibres which can be said to be of improved biological safety. Biological safety is usually measured on the basis of an in vitro test which assesses the dissolution rate of the fibres in a liquid which is intended to simulate lung liquid, such as Gamble's solution at about pH 7.5. Various patent applications have been published describing fibres which are said to give improved dissolution rate in such an in vitro test. These include EP-A-459897, O92/09536, 093/22251 and DE 4443022. We also describe biosoluble fibres in our publications WO90/02713 and W095/21799. Although fibres disclosed in, in particular, W095/21799 have proved to be interesting and valuable as fibres which are soluble in biological media, there remains a desire to achieve improved biological solubility. In particular there is a desire to achieve improved biological solubility when determined by in vivo tests. It is also desirable to achieve this biological solubility together with ease and efficiency of manufacture and with good physical properties of the fibres. In particular, there is a desire to provide fibres which have improved bio solubility. For instance, there is a probability that the required standards of biosolubility will continue to increase. In particular, one method for determining biosolubility is by intra-tracheal tests, as described e.g. by Muhle et al in BIA-Report 2/98: Fasern - Tests zur Abschatzung der Biobestandigkeit und vum Verstaubungsverhalten (Fibres - Tests for estimating the biopersistence and dust conditions) . The result of such a test is the elimination half-time, T 50 of WHO-fibres, i.e. the time until half of the WHO-fibres injected into the rat lung have been eliminated. A T 50 of less than or equal to 65 days is normally satisfactory at present but it would be desirable to produce fibres having even lower T 50 . According to the invention we provide a product comprising man-made vitreous fibres formed from a composition which includes, by weight of oxides, Si0 2 46 to 58% A1 2 0 3 0.8 to 3% FeO 5 to 6.8% Ti0 2 0 to 4% CaO 0 to 40% MgO 0 to 30% Na 2 0 + K 2 0 0 to 1% P 2 0 5 0.2 to 10% Others 0 to 10%. We find that this particular combination of components in the defined amounts, in particular the selected ranges of FeO, Al 2 0 3 and alkali metal (Na 2 0 + K 2 0) , especially the narrow range of FeO, give a good combination of durability in use and biosolubility. It is particularly surprising that biosolubility can be obtained with the very low levels of alkali metal, since these elements tend to enhance biosolubility. In addition, the fibres can be produced from readily available starting materials and the fibres have good thermal stability, fire resistance and insulation properties. In this specification the amounts of all elements are given by weight of their oxide. For simplicity, all iron oxide is quoted as FeO even though some iron may be present as Fe 2 0 3 . The amount of Si0 2 is from 46 to 58%. Usually it is at least 50%, preferably at least 54%. In some cases it can be preferred that Si0 2 is not more than 56%. The amount of A1 2 0 3 is from 0.8 to 3%. Usually it is at least 0.9 or at least 1%. In some cases it may be at least 1.1%. In general it is not more than 2.5%, preferably not more than 2%. The amount of FeO is from 5 to 6.8%. In particular it is often at least 5.5%. In the invention it is preferred that the iron should mainly be in the ferrous state (rather than in the ferric state) . Preferably at least 70%, more preferably at least 80%, of the iron is ferrous. For instance at least 90 or 95% by weight of the iron is present in ferrous form in the product of the invention. The amount of Ti0 2 is not more than 4%. It may be at least 0.2%, preferably at least 0.5%. In some compositions it can be at least 0.8 or 1%. It is generally not more than 2% and preferably not more than 1.5%. In some cases it is preferably not more than 0.5 or 0.2%. The amount of CaO is from 0 to 40%. Generally it is at least 10%, preferably at least 15%. In general it is not more than 30 or 25%. It can be not more than 20% but in some cases amounts of at least 20% are beneficial, in particular if MgO is below 10 or 8%. The amount of MgO is from 0 to 30%. It may be at least 8 or 10%, although it can be below this, eg from 6 to 8 or 9%, in particular if CaO is at least 15 or 20%. Preferably it is not more than 20%, more preferably not more than 18% and most preferably not more than 15%. The total amount of alkali metal (Na 2 0 + K 2 0) in the invention is very low and ranges from 0 to 1%. In particular it is not more than 0.8%, preferably not more than 0.6%. Generally the amount of Na 2 0 + K 2 0 is at least 0.1%, and can be at least 0.2%, although in some preferred cases it is particularly low and is below 0.2%. In the product of the invention the fibres must contain P 2 0 5 . It is present in an amount of 0.2 to 10%. In some fibres preferred according to the invention the amount is not more than 5%, preferably not more than 4%. The amount of P 2 0 5 can preferably be not more than 2%. In these cases it is particularly surprising that we obtain good biosolubility properties, since it has been stated in various publications that the inclusion of a high amount of P 2 0 5 is required to achieve good biosolubility. The amount of P 2 0 5 is preferably at least 0.5%. The amount of P 2 0 5 can in some cases be from 0.2 to 3%. In other preferred compositions the amount of P 2 0 5 is at least 4%. In the invention the ratio of P 2 0 5 / (A1 2 0 3 + FeO) is preferably not more than 0.8, more preferably not more than 0.7 and in particular not more than 0.45. It is also surprising that we can obtain, with the claimed compositions, good biosolubility at this value of that ratio, since in the publication WO92/09536 it is stated that the ratio should be as high as possible (whilst not exceeding 6) and in the examples of the invention in that publication it is always at least 0.9. In the invention the ratio can preferably be below 0.35. We also find that in the invention it is preferred that the sum of CaO + MgO + Na 2 0 + K 2 0 + 2P 2 0 5 - 4A1 2 0 3 (based on wt.% of each oxide) is at least 25. Preferably it is at least 30, more preferably at least 31, most preferably at least 32 or 33. It may in particular be at least 34. This is necessarily an approximation and solubility should be determined experimentally using an appropriate protocol, but we find in general that as the value of this sum increases, the solubility of the fibres can increase. The fibres in the product of the invention may contain various other elements in a total amount up to 10%. Preferably the amount of other elements is not more than 6%, more preferably not more than 3% and in particular not more than 2%. Other elements which can be contained in the fibres include B 2 0 3 , BaO, Zr0 2 , MnO, ZnO, F, Cl, Cr 2 0 3 and V 2 0 5 . If B 2 0 3 is present it is usually present in an amount of not more than 5%. In particular the amount of B 2 0 3 is preferably less than the amount of P 2 0 5 . An advantage of the composition of the invention is that it can be produced as a mineral melt having advantageous melt viscosity. In this specification melt viscosity is viscosity in poise at 1400°C, measured by rotation viscometry or calculated according to Bottinga and Weill, American Journal of Science, Volume 272, May 1972, pages 455 to 475. Since P 2 0 5 is not included in this calculation the presence of P 2 0 5 is taken into consideration by equalising 1 mole % of P 2 0 5 with 2 mole % Si0 2 plus 1 mole % CaO. Laboratory tests have shown that this approximation is valid within actual chemical ranges. The composition of the invention preferably provides a melt which has viscosity at 1400°C at least 10 poise, preferably at least 15 poise and often at least 17 poise. Although it may be as high as 60 poise, generally it is not more than 40 poise and preferably is not more than 30 poise. The range of 24 to 28 poise is advantageous. The viscosity can be not more than 25 poise and in particular not more than 20 poise. In this specification biosolubility is measured in terms of dissolution rate in Gamble's solution. Dissolution rate is determined by a flow-through technique, as follows. The modified Gamble's solution used has the following composition : all MgCl 2 . 6H 2 0 0 . 212 NaCl 7.120 CaCl 2 .2H 2 0 0.029 Na 2 SO„ 0.079 Na 2 HPO„ 0.148 Na 2 HC0 3 1.950 (Na 2 -tartrate) .2H 2 0 0.180 (Na 3 -citrate) .2H 2 0 0.152 90% lactic acid 0.156 Glycine 0.118 Na-pyruvate 0.172 Formalin 1 ml The fibre diameter distribution is determined for each sample by measuring the diameter of at least 200 individual fibres by means of the intercept method and a scanning electron microscope or optical microscope (100 x magnification) . The readings are used for calculating the specific surface of the fibre samples, taking into account the density of the fibres. Based on the dissolution of Si0 2 (network dissolution) , the specific thickness dissolved is calculated and the rate of dissolution established (n /day) . The calculations are based on the Si0 2 content in the fibres, the specific surface and the dissolved amount of Si. The dissolution rate by the flow-through method is determined as follows. lO g of fibres are placed in a flow cell in a polycarbonate filter holder (diameter, 40 mm) . A 0.8μm filter is placed on the inlet side (top) and a 0.2μm filter is placed on the outlet side (bottom) to avoid loss of fibres during the test. Both filters are made of cellulose nitrate. The flow rate of the modified Gamble's solution is around 200ml/day and is maintained at this rate by a peristaltic pump. The ratio of liquid flow to surface area of the fibres is 1 to 2μm/second. The pH of the solution is maintained at 7.6 ± 0.2 by bubbling with N/C0, (95/5) . The entire set-up, including storage containers, is maintained at 37 ± 0.7°C. Effluent solution is collected once a week for a two hour period and analysed for Si and Ca. Analyses are made on a Perkin-Elmer atomic absorption spectrophotometer (AAS) . Further details are given in Environmental Health Perspectives, Volume 102, Supplement 5, October 1994, page 83. In the invention the fibres preferably have solubility measured by this test of at least 60 nm/day, more preferably at least 80 or lOOnm/day. More preferably the solubility is at least 120 or 130nm/day. It may even be at least 150 or 160nm/day. Biological solubility can also be measured by the in vivo test discussed above which gives a value of T 50 . The fibres of the invention preferably have T 50 not more than 60, more preferably not more than 50 and in particular not more than 45, especially not more than 40. In the invention we can provide products which give good solubility in the test described above but give T 50 values which are unexpectedly low in view of this in vitro solubility. The fibre products of the invention are made in conventional manner. The composition is usually formed by blending appropriate amounts of naturally occurring raw materials, such as rock and sand materials and recovered waste materials. These include converter slag, other slags, glass, foundry sand, limestone, magnesite, brucite, talc, serpentinite, pyroxenite, apatite, wollastonite, quartz sand, olivine sand, iron ore, dolomite, and MMVF waste. The composition can be converted to a melt in conventional manner, for instance by melting the raw materials in an electric furnace or in a cupola furnace. The melt is preferably produced in a cupola furnace. The melt is formed into fibres by conventional processes comprising pouring the melt into or onto a rapidly spinning fiberising rotor and causing the melt to be flung from the periphery of the rotor as fibres. The rotor may be a spinning cup type of rotor or a rotor having a solid periphery which is usually mounted about a substantial horizontal axis. Rotors of this type can be arranged as a cascade system. The fibres can be formed into MMVF in conventional manner by laying down the fibres in the presence of binder typically in an amount of from 0.5 to 4%, often around 1 to 2% by weight of the product. Conventional MMVF binders can be used. The products may be used for any of the purposes for which MMVF products are known. These include thermal insulation, fire insulation and protection, noise reduction and regulation, horticultural growing media or as free fibres for reinforcement of cement, plastics or other products or as a filler. They may be provided in any of the conventional forms such as slabs or batts, sheets, pipe sections or other shaped products, or may be comminuted to a granular product. The invention will now be illustrated with reference to the following examples. Examples In each of the examples below, raw materials are melted to form a melt which has the composition given below in Table 1. The melt is formed into fibres by means of a cascade rotor system. The fibres are collected as an air laid web and treated to form a product. The melt viscosity at 1400°C is given below for each composition. For each fibre composition the solubility under the in vitro test discussed above is also given. Table 1

Claims: CLAIMS 1. A product comprising man-made vitreous fibres formed from a composition which includes, by weight of oxides, Si0 2 46 to 58% A1 2 0 3 0.8 to 3% FeO 5 to 6.8% Ti0 2 0 to 4% CaO 0 to 40% MgO 0 to 30% Na 2 0 + K 2 0 0 to 1% p 2 o 6 0.2 to 10% Others 0 to 10%. A product according to claim 1 in which the composition includes P 2 0 5 in an amount of at least 0.5%. 3. A product according to claim 1 or claim 2 in which the composition includes P 2 0 5 in an amount of not more than 5%. 4. A product according to claim 1 in which the composition includes P 2 0 5 in an amount of from 0.2 to 3%. 5. A product according to claim 1 in which the composition includes P 2 0 5 in an amount of not more than 2%. 6. A product according to any preceding claim in which the composition includes A1 2 0 3 in an amount of not more than 2.5%, preferably not more than 2%. 7. A product according to any preceding claim in which the composition includes A1 2 0 3 in an amount of at least 1%. 8. A product according to any preceding claim in which the composition includes Ti0 2 in an amount of at least 0.8%, preferably at least 1%. 9. A product according to any of claims 1 to 7 in which the composition includes Ti0 2 in an amount of not more than 0.5%, preferably not more than 0.2%. 10. A product according to any preceding claim in which the ratio P 2 0 5 / (Al 2 0 3 +FeO) in the composition is not more than 0.7. 11. A product according to claim 10 in which the ratio P 2 0 5 / (A1 2 0 3 + FeO) in the composition is not more than 0.45. 12. A product according to claim 11 in which the ratio P 2 0 5 / (Al 2 0 3 + FeO) is not more than 0.35. 13. A product according to any preceding claim in which the composition includes FeO in an amount of at least 5.5%. 14. A product according to any preceding claim in which the composition includes CaO in an amount of at least 20%. 15. A product according to any preceding claim in which the composition includes MgO in an amount of not more than 9%. 16. A product according to any preceding claim in which the sum of Na 2 0 + K 2 0 is not more than 0.2%. 17. A product according to claim 1 in which the composition includes P 2 O s in an amount of at least 4%. 18. A product according to any preceding claim in which the amount of other elements is not more than 3%. 19. A product according to any preceding claim in which the sum of (CaO + MgO + Na 2 0 + K 2 0 + P 2 0 5 - 4A1 2 0 3 ) is at least 32%. 20. A product according to claim 19 in which the sum of (CaO + MgO + Na 2 0 + K 2 0 + 2P 2 0 5 - 4A1 2 0 3 ) is at least 34%. 21. A product according to claim 1 in which the composition comprises 54 to 56% Si0 2 , 1.1 to 2% A1 2 0 3 , not more than 2% Ti0 2 , at least 5.5% FeO, at least 15% CaO, not more than 15% MgO, not more than 0.6% Na 2 0 + K 2 0, at least 0.5% P 2 0 5 , and not more than 3% other elements. 22. A product according to claim 21 in which the composition includes from 1.5 to 2% A1 2 0 3 , not more than 0.5% Ti0 2 , 5.5 to 6% FeO, 20 to 25% CaO, 6 to 9% MgO, less than 0.2% Na 2 0 + K 2 0 and at least 4% P 2 0 5 .

Inventors: GULDBERG MARIANNE, JENSEN SOREN LUND, GULDBERG, MARIANNE, JENSEN, SOREN, LUND
Applicants: GULDBERG MARIANNE, JENSEN SOREN LUND, ROCKWOOL INT, GULDBERG, MARIANNE, JENSEN, SOREN, LUND, ROCKWOOL INTERNATIONAL A/S
Application year: 1999
Main classification: C03C13
IPC codes: C03C13