WO2000073230A1

WO2000073230A1 - Man-made vitreous fibres and products containing them

Info

Publication number: WO2000073230A1
Application number: PCT/EP2000/004837
Authority: WO
Inventors: Soeren Lund Jensen; Marianne Guldberg
Original assignee: Rockwool International A/S
Priority date: 1999-05-28
Filing date: 2000-05-26
Publication date: 2000-12-07
Also published as: AU4758900A

Abstract

Biosoluble, man-made vitreous fibres have a composition which includes, by weight of oxides SiO2 34.0 to 39.0 %; Al2O3 19.0 to 23.0 %; CaO + MgO 20.0 to 35.0 %; TiO2 0 to 3 %; Na2O + K2O 4.0 to 8.0 %; FeO 3.0 to 10.0 %; P2O5 0 to 2 %; Other Elements 0 to 5 %.

Description

Man-Made Vitreous Fibres and Products containing them

This invention relates to man-made vitreous fibres (MMVF) which are durable in use but which can be shown to be biologically advantageous.

Initial proposals for MMVF which were alleged to be advantageous as a result of being soluble in biological liquids involved the provision of fibres which generally had a low content of alumina. In 096/14454 and W096/14274 we described that advantageous biological solubility properties were obtained with higher amounts of alumina, with values of 14 or 16% upwards being exemplified in 096/14274 and amounts of 18% upwards being described and exemplified in 096/14454. In both of these the amount of Si0₂ was said to be in the range 32 to 48%. The majority of the exemplified compositions had above 40% Si0₂ although some of the examples had less than 40% Si0₂ but above 24% A1₂0₃. It was stated that the amount of Al₂0₃ + Si0₂ is preferably 61 to 68%. The total amount of alkali was stated to be 0 to 10% but in practice it was usually below 4%. In example P the amount of alkali could be 5% but the amount of iron was 12%.

Although several of the fibres specifically disclosed in W096/14454 and 096/14274 have proved to be very interesting and valuable as fibres which are soluble in biological media, there remains a desire to achieve an improved combination of biological solubility, especially when determined by in vivo tests, and ease and efficiency of manufacture.

The ease of manufacture problems arise because the compositions that provide the required analyses of MMVF are preferably fiberised using a cascade rotor process, for instance as described in WO92/06047. In a cascade rotor process, molten composition is poured on to the first rotor in a set of substantially horizontally mounted rotors, and the melt is thrown from that rotor on to a second rotor in the set off which it is thrown as fibres. Some melt is usually thrown off the second rotor onto a third rotor in the set off which melt is thrown as fibres, and in preferred processes melt is also thrown off the third rotor onto a fourth rotor off which it is thrown as fibres.

In order that the fiberisation is conducted efficiently it is necessary to optimise the viscosity. None of the fibres specifically exemplified in W096/14454 or W096/14274 achieve an entirely satisfactory combination of ease and cost of manufacture and solubility properties.

In particular, there is a desire to provide fibres which have improved biosolubility, but which can still be made by methods which are generally conventional and cost effective . 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, T₅₀ of WHO-fibres, i.e. the time until half of the WHO-fibres injected in the rat lung have been eliminated.

Present standards are usually all satisfied if the fibres have a T₅₀ of less than or equal to 65 days but it would be desirable to be able to produce fibres having a half-life considerably less than this, preferably below 50 days and most preferably 40 days or less. In particular, it would be desirable to able to produce fibres which have a half-life in the range of, for instance, not more than 30 days and preferably not more than 25 days. In addition to producing fibres having these new low T₅₀ values, the compositions must be capable of being made by conventional techniques, which means they have a satisfactory viscosity, for instance 15 to 30 poise, most preferably 17 to 22 poise, at 1400°C.

Although a large number of fibres having a high Al₂0₃ content and which are described as having good biosolubility are known, none satisfy the new requirements that we specify above. For instance, other workers in the field have attempted to develop improved fibres. In WO97/30002 it is proposed to make fibres containing 35 to 45% Si0₂, 18 to 25% Al₂0₃, 0 to 3% iron oxide and 0 to 3% total alkali. In the only example, the fibre contains 40% Si0₂, 0.4% alkali and 1.7% iron. These fibres also contain phosphorous .

Other phosphorous-containing fibres are described in WO99/08970 in which the amount of Si0₂ is 38 to 47%, Al₂0₃ 16 to 20%, alkali 0 to 6% and iron 3 to 10%. In each of the examples the amount of Si0₂ is 42% or more and the amount of alkali is 3% or less.

In WO97/29057 the amount of Si0₂ is 30 to 51%, Al₂0₃ 11.5 to 25% and alkali 10 to 19%. A somewhat similar definition is given in DE-U-29709025 but the highest exemplified amount of Al₂0₃ is 15%.

In WO98/15503 various fibres having more than 18% alumina are exemplified. The highest amount of alkali is 2.3%. The use of very high amounts of iron, as in example P of W096/14274 means that the fibre cannot conveniently be made using a cupola or other shaft furnace because of the inconvenience of handling the necessary very high iron- containing melts in such furnaces. Also, the fibres containing such high contents are esthetically unattractive. The use of the very low iron contents of, for instance, WO97/30002 tends to be associated with inferior thermal properties.

We have now found that it is possible to obtain an improved biological solubility, and in particular T₅₀ of below 40 and preferably below 35 days and even as low as 30 days or less, can be obtained using composition which additionally have the property that they permit ease of manufacture and provide fibres which have good physical and mechanical (including thermal) properties. In order to achieve this object it is necessary to select a very narrowly defined range of compositions within the general ranges disclosed in W096/14454.

In particular, we now provide novel MMV fibres having a composition which includes, by weight of oxides,

Si0₂ 34.0 to 39.0% preferably 35.0 to 38.0% A1₂0₃ 19.0 to 23.0% preferably 20.0 to 22.0%

CaO + MgO 20.0 to 35.0% preferably 25.0 to 30.0%

Ti0₂ 0 to 3% preferably 0 to 2%

Na₂0 + K₂0 4.0 to 8.0% preferably 4.2 to 7.0%

FeO 3.0 to 10.0% preferably 4.0 to 9.0% P₂0₅ 0 to 2% preferably 0 to 1%

Other Elements 0 to 5% preferably 0 to 2%

It should be understood that any of the preferred lower or upper limits may be used in combination with any of the essential or preferred upper or lower limits for each element, and that any combination of the essential and preferred amounts for the different elements may be made.

The amount of Si0₂ is preferably at least 35.0% and is preferably not more than 38.0%. It is particularly preferred that the amount of Si0₂ should be at least 35.0% but preferably not more than 37.0%. The amount of Al₂0₃ is usually at least 20.0% and is preferably not more than 22.0%. Values of from 20.0 to 21.5% are particularly preferred, especially when the amount of Si0₂ is at least 35% and/or not more than 37%. The amount of Na₂0 plus K₂0 is preferably at least 4.2% and is preferably not more than 7.0%. It is preferably at least 4.3% but preferably not more than 6.0%.

The amount of iron is preferably at least 4.0% but is usually not more than 9.0%. Preferably it is at least 5.0% but preferably not more than 8.0%.

Throughout this specification, the amount of iron is quoted as FeO. The amount of Si0₂ + Al₂0₃ is generally below 62.0% and preferably it is below 60.5%. In particular, best results are generally obtained when it is from 55.0 to 59.0%, and in particular when it is from 56.0% to 58.0%. The amount of Si0₂ + Al₂0₃ + 2R₂0 (where R is sodium and potassium) is preferably in the range 63.0% to 75.0%. Generally it is at least 64.0, and preferably at least 64.5% and often it is at least 65.0%. Generally it is not more than 70.0% and preferably it is not more than 69.0%. It is meaningful to define the fibres partly by reference to Si0₂ + Al₂0₃ and/or partly by reference to Si0₂ + Al₂0₃ + 2R₂0 because the selection of the relative amounts of Si0₂, Al₂0₃ and alkali is dictated by the interrelationship which we have established these components have on biosolubility and on viscosity. We have found that reducing Si0₂ increases biosolubility but that if the amount of Si0₂ is lower than 34%, and generally if it is lower than 35%, it is difficult to select amounts of alkali and alumina that will allow the easy formation of a melt having suitable flow properties. If the amount of alumina is higher than around 23%, or preferably if it is more than about 22%, it becomes difficult to provide, using convenient raw materials, a melt in whic.i all the alumina and other materials will rapidly dissolve in a cupola or other furnace to give a melt having satisfactory flow properties .

Achieving the required melt properties is facilitated by increasing the amount of alkali above the amounts generally used in, for instance, W096/14454. A higher amount of alkali facilitates in these compositions an increased melt viscosity and at the same time acts as a fluxing agent thus improving the melting of the high- alumina raw materials in the furnace. However if the amount of alkali is increased too much the fire resistance of the fibres is adversely influenced. When selecting the amount of alkali, the amount which is required for any particular effect is, on a weight basis, approximately twice the amount of alumina which is required, and so selecting within the defined preferred ranges of, for instance, Si0₂ + Al₂0₃ + 2R₂0 gives a meaningful indication of the balance that is required for each of these components to achieve the desired combination of properties .

The amount of CaO is usually larger than the amount of MgO but this is not essential and valuable fibres can be made when the amount of MgO is 1.1 to 2 times, or more, the amount of CaO. Generally, however, the amount of CaO is

1.5 to 2.2 times the amount of MgO. Preferred amounts of

CaO are generally in the range 15.0 to 22.0% and preferred amounts of MgO are generally in the range 6.0% to 14.0%.

If the amount of iron is too low the physical properties of the fibres, especially when heated, are likely to be adversely influenced. For instance the fibres will shrink and will not have good sintering properties. However if the amount is too high, as mentioned above, this makes the process of melting unsatisfactory when using a cupola or shaft furnace.

As a result of selecting the amounts within the narrowly defined ranges we have provided fibres which do give an improved balance of ease of manufacture, physical and mechanical properties in use and, especially, in vivo solubility. The predominant advantage of the invention is that the fibres can have very satisfactory T₅₀, in particular can provide T₅₀ values which are desired, as indicated above.

Instead of or in addition to defining the biosolubility by in-vivo tests, the fibres can also be characterised by having a high dissolution rate in buffered Gamble's solution of pH 4.5, for instance when tested by the in-vitro flow through test described by Knudsen et al "New type of stonewool (HT fibres) with a high dissolution rate at pH = 4.5" (Glastechnische Berichte, Glass Science and Technology 69 (1996) ) . The fibres also have a moderately increased dissolution rate at pH 7.5. Additionally, the fibres have good resistance to atmospheric humidity and so can be used for insulation purposes where they will be exposed to atmospheric conditions. They also have good resistance to degradation by aqueous nutrients and other aqueous liquids which would be encountered when the fibres are used as products which serve as horticultural growth substrates.

Preferred fibres which achieve the objectives of the invention include fibres which have the following compositions (% by weight oxides)

A B C

Si0₂ 35.7 36.7 38.7

A1₂0₃ 20.7 20.5 22.6

Ti0₂ 1.0 1.5 1.4 FeO 8.6 5.8 3.7

CaO 18.0 18.3 11.2

MgO 9.5 10.6 15.6

Na₂0 2.2 4.0 4.8

K₂0 2.1 0.7 0.6 P₂0₅ 0.2 0.2 0.2

Viscosity 16 19 26

The viscosity is measured at 1400°C and is quoted in poise. The preferred fibres of the invention are formed from melts which have a viscosity under these conditions of 15 to 30 poise, most preferably 17 to 22 poise.

Fibre B is particularly preferred in that it shows a high in-vivo biosolubility combined with melt properties optimal for efficient production and required product properties. Fibre A and fibre C also shows excellent biosolubility and the melt properties are also suitable for production.

The fibres can be made by forming a melt using an appropriate combination of rock and/or briquettes that will provide the desired composition, melting this in a shaft furnace or other appropriate furnace then forming the melt into fibres by any convenient fibre-forming process. This may be a spinning cup but is usually a cascade spinner process. The fibres may be collected as a web and converted into MMVF products, all as described in W096/14454 and W096/14274.

The invention includes the use of a melt composition to provide fibres having the defined composition and which are biosoluble, in particular as indicated by T₅₀ of not more than 40 days, preferably not more than 30 days and most preferably not more than 25 days.

The invention also includes the use of a melt composition to make fibres which are shown to be biodegradable, for instance as given above, and wherein the fibres have the analysis given above, especially when the fibres are the fibres of a bonded product, for instance which is used as thermal insulation, fire insulation or protection or noise regulation protection, or as horticultural growth medium, or wherein the fibres are used in free form as reinforcement or as a filler.

The invention also includes a method of making man- made vitreous fibre products comprising forming one or more mineral melts and forming fibres from the or each melt wherein the melt viscosity and biosolubility of fibres are determined (for instance by any of the methods described in W096/14274 or by the T₅₀ method described above) and a composition is selected which has a suitable viscosity (generally 10 to 40, preferably 10 to 30 poise, at 1400°C) and an appropriate biosolubility and fibres are made from the selected composition, and bonded or unbonded products are made from the fibres.

The selected fibres may be provided in any of the forms conventional for man-made vitreous fibres. Thus they may be provided as loose unbonded fibres, for instance being used as free fibres for reinforcement of cement, plastics or other products or as a filler as an unbonded insulation. More usually the fibres are provided with a bonding agent, generally as a result of forming the fibres and collecting them in conventional manner in the presence of a bonding agent. The resultant product is consolidated as a slab, sheet or other shaped article. Bonded products may take the form of slabs, sheets, tubes or other shaped articles that are to serve as thermal insulation, fire insulation and protection or noise reduction and regulation, or in appropriate shapes as horticultural growing media.

Claims

1. Man-made vitreous fibres having a composition which includes, by weight of oxides,

Si0₂ 34.0 to 39.0% A1₂0₃ 19.0 to 23.0% CaO + MgO 20.0 to 35.0% Ti0₂ 0 to 3% Na₂0 + K₂0 4.0 to 8.0% FeO 3.0 to 10.0% P₂0₅ 0 to 2%

Other Elements 0 to 5%

2. Fibres according to claim 1 having a composition which includes, by weight of oxides

Si0₂ 35.0 to 38.0% A1₂0₃ 20.0 to 22.0%

CaO + MgO 25.0 to 30.0%

Ti0₂ 0 to 2%

Na₂0 + K₂0 4.2 to 7.0%

FeO 4.0 to 9.0% P₂0₅ 0 to 1%

Other Elements 0 to 2%

3. Fibres according to claim 1 or claim 2 in which the amount of Si0₂ is from 35.0 to 37.0%.

4. Fibres according to any preceding claim in which the amount of Al₂0₃ is 20.0 to 21.5%.

5. Fibres according to any preceding claim in which the amount of Na₂0 + K₂0 is from 4.3 to 6.0%.

6. Fibres according to any preceding claim in which the amount of Si0₂ + A1₂0₃ is below 60.5%.

7. Fibres according to any preceding claim in which the amount of Si0₂ + A1₂0₃ is from 56.0 to 58.0%.

8. Fibres according to any preceding claim in which the amount of Si0₂ + A1₂0₃ + 2R₂0 is from 63.0 to 69.0%.

9. Fibres according to any preceding claim in which the amount of CaO is from 15.0 to 22.0% and the amount of MgO is from 6.0 to 14.0%.

10. Fibres according to any preceding claim having T₅₀ not more than 40 days, preferably not more than 30 days.

11. Use of fibres according to any preceding claim as insulation or horitcultural growth substrate products.

12. A method of making fibres according to any of claims 1 to 10 comprising forming the fibres from a melt by a cascade spinning process.

13. Use of a melt composition to make man-made vitreous fibres which are shown to be biodegradable in the lung wherein the fibres have T₅₀ below 40 days and have a composition as defined in any of claims 1 to 9.