Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1999-07-09
2002-02-12
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S035000, C501S038000
Reexamination Certificate
active
06346494
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to man-made vitreous fibres (MMVF) which are durable in use but which can be shown to be biologically advantageous, to products containing the fibres, to the uses of such products, and to methods of making the fibres.
BACKGROUND TO THE INVENTION
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
2
, below 30% Al
2
O
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
2
O
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
2
O
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
2
O
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
2
O
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
2
O
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 Oberdörster 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 the article by Morimoto et al in Occup. Environ. Med 1994, 51, 62-67 and especially FIGS. 3 and 7 and articles by Luoto et al in Environmental Research 66 (1994) 198-207 and Staub-Reinhaltung der Luft 52 (1992) 419-423.
Traditional glass fibres and many of the MMV fibres claimed to have increased solubility in lung fluid (at pH 7.5) have a worse solubility at pH 4.5 than at pH 7.5 and so presumably attack by macrophages would not contribute significantly to the shortening and final removal of the fibres from the lung.
Existing MMV fibres formed from rock, slag and other relatively high alkaline earth mixtures can have a higher dissolution rate at pH 4.5 than pH 7.5 but tend to have a low melt viscosity. Existing fibres which are promoted as being biologically acceptable do not have a satisfactory combination of dissolution rate at pH 4.5 with melt properties. Fibres which are currently alleged to be preferred on the basis of in vitro tests tend to have low melt viscosity when they have the required low aluminium content. The low melt viscosity inevitably reduces production efficiency compared to normal production.
It would be desirable to provide MMV fibres which can be shown to be biodegradable in the lung, have melt properties which allow for normal, high, production efficiency and which can be made from inexpensive raw materials. Preferably they have good weathering resistance when exposed to ambient humid conditions in use.
SUMMARY OF THE INVENTION
In the invention we use, as fibres having satisfactory biological solubility, fibres which have a dissolution rate measured at pH 4 to 5 of at least 20 nm per day and which are formed of a composition having a melt viscosity at 1,400° C. of 10-70 poise. For instance the dissolution rate at pH 4.5 can be at least 30 or even at least 50 nm per day or more.
The combination of the melt viscosity and the solubility at pH 4.5 means that we can use a melt which is convenient to fiberise by conventional techniques and can produce fibres which are biologically soluble at pH 4.5. It is new to formulate or select fibres according to this combination, and many such fibres have a novel composition.
According to the invention, man-made vitreous fibres are formed of a composition which has a viscosity at 1400° C. of 10 to 70 poise and which has an analysis, measured as weight of oxides, which includes:
SiO
2
32 to 48%
Al
2
O
3
18 to 30%
CaO
10 to 30%
MgO
2 to 20%
FeO
2 to 15%
Na
2
O + K
2
O
0 to 10%
TiO
2
0 to 6%
Other Elements
0 to 15%
and the fibres have a dissolution rate at pH 4 to 5 of at least 20 nm per day.
Particularly preferred novel fibres are those in which the amount of SiO
2
is not more than 42.0%. Preferably the amount of Al
2
O
3
is at least 19.0% and most preferably at least 20.0%. Other preferred amounts of the novel fibres are disclosed in U.S. Ser. No. 08/836537, identified above and incorporated herein by reference.
The invention also includes novel external wall or roof claddings and also pipe sections.
DESCRIPTION OF PREFERRED EMBODIMENTS
In a preferred aspect of the invention we determine the melt viscosity and the fibre dissolution rate at a pH in the range 4-5 of one or more compositions, we select a composition which has a melt viscosity at 1400° C. of 10 to 70 poise and provides fibres which have a dissolution rate at pH 4.5 of at least 20 nm per day and which has an analysis, measured as weight of oxides, which includes:
SiO
2
32 to 48%
Al
2
O
3
10 to 30%
CaO
10 to 30%
MgO
2 to 20%
FeO
2 to 15%
Na
2
O + K
2
O
0 to 12%
TiO
2
0 to 6%
Other Elements
0 to 15%
and we make fibres from this composition.
The method also includes processes in which the initial selection of the composition on the basis of solubility and viscosity is achieved by determining the solubility of the fibres in the environment of macrophages in the lung.
It is surprisingly possible, in accordance with the invention, to provide
Christensen Vermund Rust
Guldberg Marianne
Jensen Soren Lund
Group Karl
Rockwool International A/S
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