DE29515168U1 - Artificial glassy fibers - Google Patents

Description

1 Artificial glass-like fibers

The present invention relates to man-made glassy fibers which are durable in use but which can also be shown to be biologically advantageous.

Artificial vitreous fibers are made from a vitreous melt such as rock, slag, glass or other mineral melts. The melt is formed by melting a mineral composition having the desired analysis in a furnace. This composition is generally formed by mixing rocks or minerals to give the desired analysis. The mineral composition often has an analysis, expressed as oxides, that includes at least 30% SiO ₂ , less than 32% Al ₂ O ₃ and at least . 10% CaO. The elemental analyses in the present specification are by weight and are calculated as oxides. The iron oxide may be a mixture of FeO and Fe ₃ O ₃ but is reported here as FeO.

Efficient and cost-effective formation of the melt in the furnace and of the fibers from the melt requires that the composition have a suitable liquidus temperature and have a suitable viscosity during the fiber production process. These requirements limit the choice of the composition to be melted.

Although there is no scientific evidence that there is a health risk associated with the production and use of man-made glassy fibres, commercial interests have motivated manufacturers to provide man-made glassy fibres that retain the required physical properties of man-made glassy fibres (e.g., resistance to elevated temperatures and humid conditions) but which can also be claimed to offer improved biosafety.

This claim of improved safety is usually made on the basis of an in vitro test in which the dissolution

rate or degradability of the fibers in a liquid that is intended to simulate lung fluid, such as Gamble's solution with pH 7.4 to 7.8, is investigated. One consequence of the improved dissolution rate at pH 7.5 is that the fibers have reduced moisture resistance.

Numerous patent applications describing fibres that provide an improved dissolution rate in such an in vitro test have been published, such as WO87/05007, WO89/12032, EP 412878, EP 459897, WO92/09536,
WO93/22251 and WO94/14717.

A characteristic of many of these patent applications and of fibres claimed to show an improved dissolution rate in such in vitro tests is that the fibres should have a reduced aluminium content. The aluminium content of rock wool and slag wool is generally in the range of 5 to 15% (measured on a weight basis as Al ₃ O ₃ ) and many of these allegedly bio-suitable fibres have an aluminium content of less than 4% and often less than 2%.

A problem with many of these fibers (in addition to the uncertainty as to whether they actually have improved biological suitability) is that with a higher dissolution rate at pH 7.5 there is usually a reduced durability under humid conditions that they may encounter after installation. Another problem is that the properties of the melt are not entirely satisfactory for manufacture in conventional or easily adapted melting and fiberizing equipment. For example, the viscosity of the melt can be quite low at convenient fiberizing temperatures.

In addition to the in vitro tests, in vivo research tests have been carried out. For example, Oberdörster showed in VDI Reports 853, 1991, pages 17 to 37 that two basic mechanisms are involved in the cleansing of the lungs from fibers, namely the dissolution in the almost neutral lung fluid and the

Dissolution in the acidic environment (maintained at pH 4.5 to 5) created in the lung around fibers surrounded by macrophages. Macrophages are thought to promote the removal of fibers from the lung by promoting local dissolution of the surrounding fiber area, resulting in weakening and breakage of the fibers, thus reducing the average fiber length, enabling macrophages to entangle the shorter fibers and transport them out of the lung. This mechanism is illustrated in the article by Morimoto et al. in Occup. Environ. Med. 1994, 51, 62 - 67 and particularly in Figures 3 and 7.

Traditional glass fibers and many of the artificial glassy fibers claimed to have increased solubility in lung fluid (at pH 7.5) have poorer solubility at pH 4.5 than at pH 7.5 and so attack by macrophages would probably not contribute appreciably to shortening and eventual removal of the fibers from the lung.

Existing artificial glassy fibres formed from rock, slag and other mixtures with relatively high alkaline earth content can show a higher dissolution rate at pH 4.5 than at pH 7.5, but tend to have a low melt viscosity. Existing fibres do not show satisfactory
combination of dissolution rate at pH 4.5 and melting properties. Fibers currently claimed to be preferred based on in vitro testing tend to have low melt viscosity when they have the required low aluminum content. The low melt viscosity inevitably reduces production efficiency compared to normal manufacturing.

It would be desirable to provide artificial glassy fibres which can be demonstrated to be biodegradable in the lungs by their dissolution rate at pH 4.5, and which have good weathering resistance in use when exposed to humid environmental conditions, and which have melting properties which allow normal

allow high production efficiency and can be manufactured from cost-effective raw materials.

According to the invention, artificial glassy fibers are made from a composition having an analysis, expressed as oxides, which includes at least 30% SiO ₂ , less than 30% Al ₃ O ₃ and at least 10% CaO, the fibers being characterized in that the analysis of the composition includes:

SiO ₂ 32 to 48%

Al ₂ O ₃ 18 to 30%

CaO 10 to 30%

MgO 2 to 20%

FeO 2 up to 15%

Na ₂ O + K ₂ O 0 to 10%

TiO ₂ 0 to 6%

other elements 0 to 15%

and the composition has a viscosity at 1400 ⁰ C of 10 00 to 70 0 0 mPas,

and the fibers have a dissolution rate at pH 4.5 of at least 20 nm per day. Preferably SiO ₂ + Al ₃ O ₃ is 55 to 75%, often 56 to 68%. Preferably CaO + MgO + FeO is 25 to 40%. Preferred compositions are defined in the claims.

According to the invention, it is surprisingly possible to provide fibres which have a good dissolution rate at pH 4.5, thereby facilitating the clearing of the lungs by macrophages (and thus promoting true biodegradability), and which can show a low or moderate dissolution rate at pH 7.5, thereby maintaining good stability under humid conditions (without loss of biodegradability), and which can have normal melting properties such as liquidus temperature, crystallisation rate and melt viscosity, and which can be produced using „ypn _# inexpensive raw materials

5
can be produced.

Another advantage of the fibers is that when exposed to moisture and condensed water, the resulting solution formed, which contains dissolution products, has an increased pH, but the fibers have reduced solubility at increased pH and thus dissolve less and have improved durability.

The present invention also includes products comprising these artificial glassy fibers.

It is readily possible to select elemental analyses within the ranges given herein to obtain the defined combination of melt viscosity and dissolution rate at pH 4.5. Furthermore, it is readily possible to select the composition so that the composition and fibers exhibit other desirable properties such as dissolution rate at pH 7.5, liquidus temperature and sintering temperature.

For example, if the viscosity of any particular melt is found to be too high at 1400 ⁰ C, it may be possible to reduce it by reducing the total amount of SiO ₂ + Al ₂ O ₃ . Similarly, if the melt viscosity is too low, it may be possible to increase it by increasing the total amount of SiO ₂ + Al ₃ O ₃ , generally within the range 55 to 75%, often 60 to 75%, or by increasing the amount of alkali oxide. Similarly, it may be possible to lower the viscosity by increasing the total amount of alkaline earth metal oxide components and FeO.

If the dissolution rate at pH 4.5 is too low, it may be possible to increase it by reducing the amount of SiO ₂ , but it may then be necessary to increase the amount of Al ₃ O ₃ to maintain the melting properties.

The amount of SiO ₂ is ¹ normally at least 34% and preferably at least 35%. It is normally below 47% and preferably below 45%.

The amount of Al ₃ O ₃ is normally at least 19%, but preferably at least 20% and most preferably at least 24%. Normally it is below 28% and preferably below 26%.

The combined amount of SiO ₂ + Al ₃ O ₃ is normally at least 56% and preferably at least 57%. In preferred products it is often above 60%, most preferably 61 or 62%. It is normally less than 70% or 68% and preferably less than 65%.

The amount of CaO is normally at least 14% and preferably at least 18%. Normally it is less than 28% and preferably less than 25%.

The amount of MgO is normally at least 5%, preferably at least 6% and most preferably at least 8%. It is normally below 15%, preferably below 11%.

The amount of FeO is normally at least 3% and preferably at least 5%. It is normally less than 10% and preferably less than 8%.

The total alkali content (Na ₂ O + K,O) is usually at least 1% and preferably at least 2%. It is usually below 5% and preferably below 3%.

A variety of other elements, including TiO ₂ , may be present in the composition in any amount that does not affect the desired properties and is therefore generally quite low, for example not more than 8%. In particular, the composition often includes TiO ₂ in an amount of up to 3%, usually up to 2%. The amount of TiO ₂ is usually at least 0.2%, often at least 0.5 to 1%. The total amount of other elements, including TiO ₂ , is generally below 10% and usually below 5%. Most preferably, elements other than TiO ₂ are present in an amount of not more than 2%. Examples of other elements that

may be included are P ₂ ⁰ S' ^B 2°3' ^Ba0 ' ^Zr0 2' ^Mn0
2-chloro-4-methyl ...

The melt may have normal crystallization properties, but if it is desired to minimize crystallization, this can be achieved by including magnesium in relatively low amounts, for example 2 to 6% MgO.

When it is desired to provide fibres with improved fire resistance, it is generally desirable to increase the amount of FeO, which is then preferably at least 6%, for example up to 8% or higher, for example 10%, and the amount of MgO should then be at least 8%.

The composition analysis is preferably such that the fibers have a dissolution rate of at least 25 and preferably at least 40 nm per day at pH 4.5. It is desirable that the dissolution rate be as high as possible (consistent with maintaining adequate moisture and heat resistance properties) but it is generally not required to be more than 100 nm per day and is usually less than 80 nm per day.

Although a high dissolution rate at pH 7.5 has been suggested as a desirable property (as an indication of alleged biodegradability), it is in fact often an undesirable property as it is indicative of poor weatherability when exposed to moisture. Dissolution in the lungs at pH 7.5 is actually of relatively little importance for biodegradability. Preferably, the fibers have a dissolution rate in Gamble's solution at pH 7.5 of less than 25 and most preferably less than 15 nm per day.

The viscosity of the composition at 1400 ^° C is usually at least 1200 or 1500 mPas and is preferably at least 1800 mPas. Although it may be as high as, for example, 6000 mPas, it is generally less than 4000 mPas and preferably is not more than 3000 mPas.

If the fibres are to have good fire resistance, the analysis is preferably such that the sintering temperature is at least 800 ⁰ C and preferably at least 1000 ⁰ C.

The liquidus temperature is usually at least 1200 ⁰ C, but often at least 1240 ⁰ C. It can be as high as, for example, 1400 ⁰ C, but is preferably not more than 1340 ⁰ C.

An advantage of using the defined moderate alumina melts for use in the present invention is that it allows the inclusion of readily available materials with a moderate alumina content such as rock, sand and waste. This therefore minimizes the need to use expensive high alumina materials such as bauxite or kaolin, while minimizing the need to use expensive very low alumina materials such as silica sand or olivine sand, iron ore, etc. Typical readily available medium alumina materials that can be used as part or all of the composition include anorthosite and phonolite and gabros.

The composition is typically prepared by mixing appropriate amounts of naturally occurring rock and sand materials such as anorthosite, gabros, limestone, dolomite and diabase and waste materials such as mineral wool waste, aluminosilicates, slag, foundry sand, filter dust, fly ash and bottom ash.

The composition may be converted to a melt in a conventional manner, for example in an electric furnace or in a cupola furnace. An advantage of the invention is that the composition can readily have a reasonably low liquidus temperature (while maintaining adequate viscosity at ¹⁴⁰⁰ °C), and this minimizes the amount of energy required to form the melt.

The melt can be converted into fibres in a conventional manner, for example by a spinning pot process or by a cascade rotor process, as described for example in WO92/06047.

The fibers according to the invention can have any suitable fiber diameter and any suitable fiber length.

In this invention, the dissolution rate is determined following the following experimental protocol.

300 mg of fiber was placed in polyethylene bottles containing 500 ml of modified Gamble's solution (i.e. with complexing agents) adjusted to pH 7.5 or 4.5. Once a day the pH was checked and adjusted if necessary with HCl.

The experiments were carried out over a period of one week. The bottles were kept in a water bath at 37°C and shaken vigorously twice a day. Aliquots of the solution were taken after one and four days and analyzed for Si on a Perkin-Elmer atomic absorption spectrophotometer.

The modified Gamble's solution had the following composition Setting: q/i _{MgCl2.6H2O ​} 0.212 NaCl 7,120 _{CaCl2.2H2O ​} 0.029 _{Na2SO4 ​} 0.079 _{Na2HPO4 ​} 0.148 _NaHCO3 1,950 (Na,-tartrate).2H, O 0.180 (Na,-citrate).2H ₉ O 0.152 90% lactic acid 0.156 Glycine 0.118 Na-pyruvate * 0.172 Formalin 1ml * · · * φ ** ·
• · ß *·* · ··· *· · φ ·
•#· · ·*

The fiber diameter distribution is determined for each sample by measuring the diameter of at least 200 individual fibers using the line intersection method and a scanning electron microscope or optical microscope {1000x magnification). The readings are used to calculate the specific surface area of the fiber samples, taking into account the density of the fibers.

Based on the dissolution of SiO ₂ (network dissolution), the dissolved specific thickness was calculated and the dissolution rate (nm/day) was determined. The calculations are based on the SiO ₂ content of the fibers, the specific surface area and the amount of Si dissolved.

In this description, the sintering temperature is determined by the following test protocol.

The thermal stability, expressed as sintering temperature of the fiber compositions, was determined using the following procedure:

A sample (5 x 5 x 7.5 cm) of mineral wool made from the fiber composition to be tested was placed in an oven preheated to 700 ⁰ C. After 1.5 hours of exposure, the shrinkage and sintering of the sample were evaluated. The procedure was repeated each time with a fresh sample and an oven temperature 50 ⁰ C above the previous oven temperature until the maximum oven temperature at which no sintering or excessive shrinkage of the sample was observed was determined.

In this description, the viscosity in mPas at 1400 ⁰ C is determined according to Bottinga and Weill, American Journal of Science, Volume 272, May 1972, pages 455 - 475.

Examples of the invention follow.

In each example, a composition was formed by

Mixing appropriate proportions of raw materials and was melted in a trough furnace and was converted into fibers using the cascade spinning technique. The analyses of the compositions and their properties are given in the following tables. Products A to P are products according to the invention.

Product V has an analysis similar to that of commercial slag wool and it will be noted that it has a relatively low aluminum content, a high calcium content, and a fairly low melt viscosity and a moderate dissolution value at pH 7.5.

Product X is similar to slag wool V in some respects, but still has a melt viscosity that is quite low for convenient spinning. Furthermore, the fiber stability is low due to the low content of FeO and MgO. Product Y is a product with a high aluminum content, but the proportions of all components are such that the melt viscosity is too high for convenient spinning.

Product Z is similar to a conventional stone wool product with normal good product properties, but has a very low dissolution rate at pH 4.5. It shows a fairly high silica content and a relatively low alumina content.

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The new fibers may be provided in any form conventional for man-made glassy fibers. For example, they may be provided as a product consisting of loose, unbonded fibers. More commonly, they are provided together with a binder, for example as a result of forming the fibers and bonding them together in a conventional manner. Generally, the product is compacted as a sheet, mat, thin sheet or other shaped article.

Products of the invention may be formulated for any conventional use of man-made glassy fibers, such as sheets, mats, thin sheets, tubes, pipes or other shaped products intended for thermal insulation, fire insulation and protection, or sound insulation and control, or in suitable forms for use as horticultural growing media or as free fibers for reinforcing cement, plastics or other products or as fillers.

Claims (19)

14 PROTECTION CLAIMS 1. Artificial glassy fibers made from a composition having an analysis, expressed as oxides, which includes at least 3 0% SiO ₂ , up to 3 0% Al ₂ O ₃ and at least 10% CaO, characterized in that the composition analysis includes SiO ₂ 32 to 48% Al ₂ O ₃ 18 to 30% CaO 10 to 30% MgO 2 to 20% FeO 2 up to 15% Na ₂ O + K ₂ O 0 to 10% TiO ₂ 0 to 6% Other elements 0 to 15% and the composition has a viscosity at 14 00 ⁰ C of 10 to 7000 mPas, and the fibers have a dissolution rate at pH 4.5 of at least 20 nm per day. 2. Fibers according to claim 1, characterized in that the composition analysis includes SiO ₂ 32 to 48% Al ₂ O ₃ 18 to 30% CaO 10 to 30% MgO 2 to 20% FeO 2 up to 12% Na ₂ O + K ₂ O 0 to 7% TiO ₂ 0 to 4% Other elements 0 to 8%. 3. Fibers according to claim 1 or 2, in which the amount of SiO ₂ + Al ₂ O ₃ is 55 to 75% - 4. Fibers according to claim 1, characterized in that the composition analysis includes SiO ₂ . ' 32 to 48% Al ₂ O ₃ 18 to 30% 15 * ■ · · · · * 60 to 75% 10 to 30% _{SiO2 + Al2O3} 2 to 20% CaO 2 to 12% MgO 0 to 7% FeO 0 to 4% _Na2O + _K2O 0 to 10%. _TiO2 Other elements 5· Fibers according to any preceding claim, characterized in that the amount of SiO ₂ is 34 to 45%, the amount of Al ₂ O ₃ is 19 to 28%, the amount of CaO is 14 to 25% and the amount of MgO is 5 to 15%. 6. Fibers according to claim 5, characterized in that the amount of SiO ₂ + Al ₂ O ₃ is 61 to 68%. 7. Fibers according to any one of the preceding claims, characterized in that the amount of Al ₂ O ₃ is 20 to 26%. 8. Fibers according to any one of the preceding claims, characterized in that the amount of MgO is at least 8% and the amount of FeO is at least 6%. 9. Fibers according to any one of the preceding claims, characterized in that the amount of SiO ₂ + Al ₃ O ₃ is 60 to 65%. 10.Fibers according to any one of the preceding claims, characterized in that the amount of TiO ₂ is up to 3% and the fibers include up to 4% of other elements. 11.Fibers according to any one of the preceding claims, characterized in that the dissolution rate at pH 4.5 is 40 to 80 nm per day. 12.Fibers according to any one of the preceding claims, characterized in that the composition has a viscosity of 1500 to 4000 mPas at 1400 ⁰ C. · 13.Fibers according to claim 8, characterized in that the viscosity is 1800 to 3000 mPas. 14.Fibers according to any one of the preceding claims, characterized in that they have a dissolution rate at pH 7.5 of less than 15 nm per day. 15.Fibers according to any one of the preceding claims, characterized in that they have a sintering temperature of at least 1000 ^° C. 16.Fibers according to any one of the preceding claims, characterized in that the composition provides a liquidus temperature of 1240 to 1340 ⁰ C. 17.A product including the artificial glassy fibers according to any one of claims 1 to 16. 18.Product according to claim 17, characterized in that it is in the form of a plate, mat, thin plate, tube or pipe. 19.Product according to claim 17 or 18, characterized in that it is selected from thermal insulation products, fire insulation and protection products and sound insulation or regulation or protection products, horticultural growing media and fiber-reinforced or filled products.