Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1995-09-28
1997-03-25
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 36, 501 72, C03C 1302, C03C 1306
Patent
active
056144490
DESCRIPTION:
BRIEF SUMMARY
This invention relates to man-made vitreous fibres (MMVF) which are durable in use, which have a solubility in biological fluid which is considered to be acceptable, which can be made from readily available materials by convenient techniques.
MMV fibres are made from vitreous melt, such as of rock, slag, glass or other mineral melts. The melt is formed by melting in a furnace a mineral composition having the desired analysis. This composition is generally formed by blending rocks or minerals to give the desired analysis.
Although there is no scientific evidence establishing that there is a health risk associated with the manufacture and use of MMV fibres, commercial interests have led manufacturers to provide MMV fibres that retain the required physical properties of MMV fibres (e.g., durability at elevated temperatures and under humid conditions) but which can also be alleged to be of improved biological safety.
This allegation of improved safety is usually made on the basis of an in vitro test that examines the dissolution rate or degradability of the fibres in a liquid which is intended to simulate lung liquid, such as Gamble's solution at about pH 7.5, for instance pH 7.4 to 7.8.
Numerous patent applications have been published describing fibres that give enhanced dissolution rate in such an in vitro test, such as WO87/05007, WO89/12032, EP 412878, EP459897, WO92/09536, WO93/22251 and WO94/14717.
A characteristic of many of these patent applications, and of fibres which are alleged to have enhanced dissolution rate in such in vitro tests, is that the fibre should have reduced aluminium content. For instance it is stated in WO87/05007 that the Al.sub.2 O.sub.3 amount must be below 10%. The aluminium content of rock wool and slag wool is generally in the range 5 to 15% (measured as Al.sub.2 O.sub.3 by weight) and many of these allegedly biologically suitable fibres have an aluminium content of below 4%, and often below 2%.
A further characteristic is that phosphorous should be included in order to increase the dissolution rate. For instance in WO92/09536 it is stated that the weight ratio of P.sub.2 O.sub.5 to the sum of Al.sub.2 O.sub.3 and iron oxide must be about 0.4 to 6, preferably about 0.5 to 2 and in EP 412,878 it is stated that there must be at least 0.1% P.sub.2 O.sub.5 if the amount of Al.sub.2 O.sub.' is more than about 1%. The fact that P.sub.2 O.sub.5 increases solubility and reduces durability in mineral products, both fibrous and non-fibrous, was additionally well known in the art, for instance from Uhlman 1978 pages 359 to 365; Ceramic Bulletin Volume 57 No.6, 1978, Ohta, pages 602 to 604; and Indian Ceramics, July 1968, Mitra, pages 97 to 102; Materials Research Society Proceedings, ed McVay, Volume 26, Plodinek pages 755 to 761; and Glasuren and Ihre Farben 1973.
Although the inclusion of P.sub.2 O.sub.5 and the total or substantial elimination of Al.sub.2 O.sub.3 gives satisfactory solubility at about pH 7.5 in the common in vitro solubility test, the requirement to use such a formulation incurs a number of serious problems. In particular, the requirement to use such a composition tends to detract from the inherent advantages of many rock or slag wool manufacturing processes and products. Such products are normally made from readily available materials and blends of materials by processes that have been developed to produce the products in good yield. Satisfactory production necessitates that the products should have melt viscosity properties that are rather accurately controlled, since significant variation in the viscosity from the optimum can have a significant and undesirable effect on manufacture of the product. For instance it can significantly influence the fibre diameter and the percentage of shot (coarse fibres or pearls) in the product. The compositions that are known for making fibres which have the specified in vitro solubility at around pH 7.5 tend to give unsatisfactory melt viscosity properties and can generally only be made from a very restricted selection of raw mater
REFERENCES:
patent: 4205992 (1980-06-01), Morgensen et al.
patent: 5108957 (1992-04-01), Cohen et al.
patent: 5250488 (1993-10-01), Thelohan et al.
patent: 5312806 (1994-05-01), Morgensen
patent: 5332698 (1994-07-01), Nyssen et al.
patent: 5332699 (1994-07-01), Olds et al.
Ceramic Bulletin vol. 57, No. 6, (1978), Ohta, pp. 602-604, Jun.
Indian Ceramic, Jul. 1968, Mitra, pp. 97-102.
Bell Mark L.
Rockwool International A/S
Troilo Louis M.
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