Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1997-05-08
1999-08-03
Marcheschi, Michael
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 38, 501 70, 501 73, C03C 1306
Patent
active
059325003
DESCRIPTION:
BRIEF SUMMARY
This invention relates to man-made vitreous fibres (MMVF) which are durable in use but which can be shown to be biologically advantageous.
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. The mineral composition often has an analysis, as oxides, which includes at least 32% SiO.sub.2, below 30% Al.sub.2 O.sub.3 and at least 10% CaO. The elemental analyses in the specification are by weight and calculated as oxides. The iron oxide may be a mixture of FeO and Fe.sub.2 O.sub.3 but is quoted herein as FeO.
Efficient and cost-effective formation of the melt in the furnace and of the fibres from the melt requires that the composition should have a suitable liquidus temperature and should have a suitable viscosity during the fibre-forming process. These requirements impose constraints on the selection of the composition that is to be melted.
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 with pH 7.4 to 7.8. A consequence of enhanced dissolution rate at pH 7.5 is that the fibres will normally have reduced resistance to humidity.
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%. It is known to include phosphorous in these low-Al.sub.2 O.sub.3 compositions in order to increase the dissolution rate in this pH 7.5 dissolution rate test.
A problem with many of these low-Al.sub.2 O.sub.3 fibres (in addition to uncertainty as to whether they do have enhanced biological suitability) is that the melt properties are not entirely satisfactory for manufacture in conventional or easily adapted melting and fibre-forming apparatus. For instance, the melt viscosity at convenient fibre-forming temperatures may be rather low. Another problem is that a high dissolution rate at pH 7.5 may tend to result in reduced durability under humid conditions which may be experienced after installation.
In addition to the in vitro tests, in vivo research testing has been conducted. For instance, Oberdorster in VDI Berichte 853, 1991, pages 17 to 37 showed that two basic mechanisms are involved in the clearance of fibres from the lungs, namely dissolution in the near-neutral lung fluid and dissolution in the acidic environment (maintained at pH 4.5 to 5) created around fibres surrounded by macrophages in the lung. It is believed macrophages promote removal of the fibres from the lung by promoting local dissolution of the surrounded fibre area leading to weakening and breaking of the fibres so as to reduce the average fibre length, thereby enabling macrophages to engulf and transport the shorter fibres out of the lung. This mechanism is illustrated in
REFERENCES:
patent: 2020403 (1935-11-01), Engle
patent: 2576312 (1951-11-01), Minnick
patent: 3736162 (1973-05-01), Chvalovsky et al.
patent: 4002482 (1977-01-01), Coenen
patent: 4205992 (1980-06-01), Morgensen et al.
patent: 4363878 (1982-12-01), Yamamoto et al.
patent: 4461840 (1984-07-01), Massol et al.
patent: 5037470 (1991-08-01), Matzen et al.
patent: 5250488 (1993-10-01), Thelohan et al.
patent: 5312806 (1994-05-01), Morgensen
patent: 5576252 (1996-11-01), Rapp et al.
V.R. Christensen, et al., "Effect of Chemical Composition of Man-Made Vitreous Fibers on the Rate of Dissolution in Vitro at Different pHs", Environmental Health Perspectives 102(Suppl 5): 83-86 (1994) (No Month).
Sylvie Thelohan, et al., "In Vitro Dynamic Solubility Test: Influence of Various Parameters", Environmental Health Perspectives 102(Suppl 5): 91-96 (1994) (No Month).
Fiber Diameter Distributions in typical MMVG Wool Insulation Products, Vermund R. Christensen et al. American Industrial Hygien Assoc., May 1993, pp. 232-238.
Christensen Vermund Rust
Guldberg Marianne
Jensen Soren Lund
Marcheschi Michael
Rockwool International A/S
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