IE911846A1 - Mineral fibres which can decompose in a physiological medium - Google Patents

Abstract

Inorganic fibre compositions capable of being degraded in contact with a physiological environment. Advantageous compositions comprise the following constituents in the proportions by weight defined below: SiQ2 37 to 58 % Al2O3 4 to 14 % CaO 7 to 40 % MgO 4 to 16 % O2O5 1 to 10 % Fe2O3 0 to 15 % (total iron expressed in this form) the sum CaO + MgO + Fe2O3 remaining higher than 25 %, and the oxides Na2O and K2O, the sum of the percentages of which remains lower than 7%.

Description

The present invention relates to the sphere of mineral fibres; more precisely its object is mineral fibres of which the composition is such that they decompose as soon as they are in contact with a physiological medium.

Buildings are frequently insulated with respect to heat and sound by means of products essentially consisting of mineral wool, such as rock wool. The particular arrangement of the premises to be insulated often leads the personnel responsible for fitting these products to cut them in situ. This operation causes the fibres to break and possibly some of them to be dispersed into the atmosphere. It results therefrom that sometimes a fibre may accidentally be inhaled.

Although the harmfulness of the inhaled fibres has not been proven, the need is felt to reassure users by offering them a product which can dissolve easily in a physiological medium.

The aim of the present invention is to propose mineral fibres of which the composition is such that they decompose rapidly when in contact with a physiological medium.

In particular, the aim of the present invention is fibres which can be obtained by conventional techniques of external centrifuging.

These techniques are used to form fibres from glasses obtained by melting raw materials such as blast furnace slag or basalts. Some of these techniques, also known as free centrifuging, consist in pouring a thin stream of molten glass onto the peripheral strip of a centrifuging wheel, rotating at high speed about a shaft perpendicular to the direction of the thin glass stream. Under the effect of centrifugal force, some of the glass is converted into fibres, the remainder being conveyed to a further wheel where the same phenomenon occurs; three or four wheels may thus be interposed along the path of the molten glass.

The aims of the invention are achieved by modifying the known glass compositions used in free centrifuging techniques. On the basis of compositions of this type, essentially comprising silica and alumina, alkaline earth oxides, the inventors discovered that the addition of phosphorus pentoxide enables glasses to be obtained which, in fibre form, decompose rapidly in a physiological medium.

The glasses according to the invention furthermore have properties which, as regards the main ones among them, are similar to those of known glasses. It is thus that they can be converted into fibres using conventional centrifuging wheels.

The mineral f a composition const i tuents, the following ibres according to the invention have which comprises the following in the weight proportions defined by limits: Si 02 37 to 58% Al203 4 to 14% CaO 7 to 40% MgO 4 to 1 6% P205 1 to 10% Fe203 0 to '1 5% the amount of CaO + MgO + Fe203 being greater than 25%, and the oxides Na20 and KgO, of which the total percentage is less than 7 % The total iron contained in the composition according to the invention is expressed in the form of ferric oxide.

The compositions defined in this manner may be prepared from pure constituents but are generally obtained by the melting of a mixture of vitrifiable raw materials possibly with the addition of other oxides such as titanium oxide and manganese oxide, considered as impurities within the scope of the invention. The total content of these impurities is equal or less than approximately 3 weight percent.

In order to be able to be used in external centrifuging techniques, the compositions according to the invention advantageously have adequate viscosity at a relatively low temperature. This depends to a great extent on the total amount of the oxides Si02 and Al203. Within the scope of the invention, the amount of these oxides is generally equal to or greater than approximately 50 weight percent.

In addition, the production of the fibres depends on the ability of the glass, which is great to a lesser or greater extent, to develop crystals in its mass. This phenomenon, known as devitrification, is characterised by several temperatures: that at which the rate of crystal growth is at its maximum and that at which this rate of growth is zero (liquidus).

In the main part, this phenomenon is intensified to a greater or lesser extent depending on the total amount of alkaline earth oxides. Within the scope of the invention, this amount is less than approximately 40 weight percent.

In order to ensure that the fibres are sufficiently heat resistant, it is desirable for the amount of CaO + MgO + Fe„03 to be greater than approximately 25 weight percent.

The range of preferred compositions according to the invention is delimited by the following weight proport ions : Si02 45 to 57% Al 203 3 to 6% CaO 20 to 30% MgO 6 to 1 6%Fe2°3 0.1 to 4% p2o5 1 to 7% Na20 + K20 0.1 to 5% Impurities 4 3% A further area of compositions according to the invention is def ined by the proport ions: SiO2 39 to 50% ai2o3 7 to 13% CaO 20 to 30% MgO 6 to 1 6% Fe,0, 0 . 1 to 4% P2°5 3 to 9% Na20 + K2O 0.1 to 5% Impuritiesx<3% The advantages of the invention are given in the following description, illustrated by some nonlimiting examples.

The measurements of the degree of decomposition in the physiological medium were performed on fibres of which the diameter is constant and is approximately 10 jim.

These fibres are immersed in a solution which simulates an extracellular fluid and of which the composition is as follows (expressed in g/1): MgCl2. 6H20 0.212 NaCl 6.415 Na2HPO4 0.148 Na.SO,. 2H„0 i. *5 t. 0.179 CaCl,.4H„0 0.318 NaHC03 2.703 (Na2 tartrate ).2H,0 0.180 (Na3 c i trate ) . 5,5H2O 0.186 Na lactate 0.175 Na pyruvate 0.172 Glycine 0.118 The test conditions selected for determining the degree of decomposition of the glass fibres in this solution are as follows: two hundred mg of fibres are placed between two perforated discs separated by a circular ring. These two discs, 4.3 centimetres in diameter, are covered with a polycarbonate filter. This assembly forms a measuring cell through which there circulates the solution of which the flow rate is regulated by a peristaltic pump. This flow rate is 40 ml per day, the duration of the test being 20 days. The cell and the flask containing the attacking solution are maintained at a temperature of 37° C. After passing through the cell, the attacking solution is collected in bottles in order to be analysed subsequently.

The amount of dissolved silica is measured by analysis; the weight of dissolved silica in relation to the weight of silica initially present in the fibre gives a percentage result, which is a good indicator of the capacity of the fibre tested to decompose in a physiological medium.

The compositions tested and the results obtained are presented in tables 1 and 2 enclosed.

Table 1 shows the compositions according to the invention and two known compositions used as a reference (glasses no. 1 and no. 4).

The presence of phosphorus pentoxide in the compositions according to the invention always results in an increase in the amount of silica dissolved in the attacking solution of the fibres obtained from the said compositions, as compared with fibres of which the composition comprises hardly any phosphorus.

Table 2 contains some test results obtained when this observation is applied.

A comparison of glasses nos. 1 and 3, on the one hand, and glasses nos. 4 and no. 6, on the other, ο shows that the effect of reducing the alumina and replacing this amount by silica causes a considerable increase in the degree of decomposition of the fibres tested.

A comparison between glasses nos. 2 and 3, and between glasses nos. 5 and 6.- shows that in glasses of which the degree of decomposition is considerable, the substitution of silica by phosphorus pentoxide causes a remarkable increase in the degree of decomposition on the fibres tested .

The influence of phosphorus pentoxide on the degree of decomposition of the fibres is still quite considerable in a glass with a high alumina content, as displayed by glasses nos. 4 and 7.

The phosphorus is added to the vitrifiable mixture in the form of disodic phosphate or calcium phosphate for example. When the amount of phosphate introduced into the vitrifiable mixture is relatively large, its melting may sometimes be difficult. It is for this reason that the phosphorus pentoxide content of the compositions is less than or equal to approximately 10 weight percent.

The compositions according to the invention, which have both the viscosity and devitrification properties suitable for the fibre-drawing process by external centrifuging, and, in the fibre state, have a high rate of decomposition in a physiological medium, comprise less than approximately 7 weight percent of alkaline oxides.

The mineral fibres according to the invention listed in table n° 1 are all resistant at a temperature of approximately 700°C.

It was found that samples blocks of those fibres (100 kg/m ) heated into an oven during 30 minutes show a sagging lower than % at 700°C.

The glasses according to the invention may be converted into fibres by known external centrifuging devices, such as those described in patents US-A-2 663 051, EP-A-0 167 508 or Fr-A- 2 609 708, for example.

The fibres obtained in this way enable excellent quality fibrous products suitable for numerous applications to be obtained. Thus, for example, the fibres according to the invention are advantageously used in the form of geometrically well-defined panels, strengthened by a polymer binder, or in the form of tubular products for insulating pipes. The fibres according to the invention may also be used in the form of a mat sewn over cardboard or metal grilles, in the form of a strip, or even in bulk form by filling.

Claims (10)

CLAIMS:

1. Mineral fibre which can decompose in the presence of a physiological medium, characterised in that, in addition to impurities of which the total weight content is equal or less than approximately 3%, it comprises the following constituents according to the following weight proportions: SiO 2 37 to A1 2°3 4 to CaO 7 to MgO 4 to P 2°5 1 to Fe n 0 n 0 to 58% 14% 40% 16% 10% 15% (total iron expressed in this form) the amount of CaO + MgO + being greater than 25%, and the oxides Na 2 0 and 1^0, of which the total percentage is less than 7%.

2. Mineral fibre according to claim 1, characterised in that the amount of Si0 2 + i s greater than approximately 50%

3. Mineral fibre according to either of claims 1 and 2, characterised in that the amount of CaO + MgO is less than approximately 4C%.

4. Mineral fibre according to one of the preceding claims, characterised in that it comprises: Si0 2 45 to 57% A1 2°3 3 to 6% CaO 20 to 30% MgO 6 to 16% Fe 2 ° 3 0.1 to 4% P A 1 to 7% Na 2 0 + K 2 0 0.1 to 5%

5. Mineral fibre according to one of claims 1 to 3, characterised in that it comprises: Si0 2 40 to 50% A1 2°3 7 to 13% CaO 20 to 30% MgO 6 to 16% Fe 2°3 0 to 4% P 2°5 3 to 9% Na 2 0 + K 2 0 0.1 to 5%

6. Product for heat and/or sound insulation and consisting at least partially of mineral fibres, characterised in that the said fibres have a chemical composition as defined by any one of the preceding claims. - 15

7. A mineral fibre which can decompose in the presence of a physiological medium according to Claim 1, substantially as herein described. 5

8. A product for heat and/or sound insulation and consisting at least partially of mineral fibres according to Claim €, substantially as herein described.

9. The features described in the foregoing specification,

10. Or any obvious equivalent thereof, in any novel selection.