HEAT RESISTANT SEPARATION FABRIC

Abstract

Heat resistant separation fabric consisting out of yarns, wherein the yarns comprise metal fibers; wherein the heat resistant fabric comprises boron nitride particles distributed throughout the complete thickness of the fabric; wherein boron nitride particles are present between metal fibers in the yarns; wherein the amount of the boron nitride particles present on the surface of the fabric is not more than the amount of the boron nitride particles present in the bulk of the fabric.

Claims

1. Heat resistant separation fabric consisting out of yarns, wherein the yarns comprise metal fibers; wherein the heat resistant fabric comprises boron nitride particles distributed throughout the complete thickness of the fabric; wherein boron nitride particles are present between metal fibers in the yarns; wherein the amount of the boron nitride particles present on the surface of the fabric is not more than the amount of the boron nitride particles present in the bulk of the fabric.

2. Heat resistant separation fabric as in claim 1, wherein the yarns are spun, filament or texturized yarns.

3. Heat resistant separation fabric as in claim 1, wherein all fibers in the yarns are stainless steel fibers.

4. Heat resistant separation fabric as in claim 1, wherein the heat resistant separation fabric is a woven fabric, a knitted fabric or a braided fabric.

5. Heat resistant separation fabric as in claim 1, wherein the particle size of the boron nitride particles is in the range of 1 nm to 10 μm, and preferably in the range of 100 nm to 10 μm.

6. Heat resistant separation fabric as in claim 1, wherein the boron nitride particles comprise or consist out of boron nitride in the hexagonal crystalline form.

7. Heat resistant separation fabric as in claim 1, wherein the boron nitride particles are bonded onto the surface of the metal fibers by means of an inorganic binder.

8. Heat resistant separation fabric as claim 7, wherein the inorganic binder comprises or consists out of aluminium oxide, aluminium phosphate or magnesium silicate.

9. Mould for bending car glass products or mirrors, wherein the surface of the mould making contact with hot glass or mirrors is covered by a heat resistant separation fabric as in claim 1.

10. Process of bending car glass products or mirrors, wherein a mould is used as in claim 9, wherein the temperature of the hot glass in contact with the heat resistant separation fabric is in a range between 600° C. to 800° C.

11. Roll of a heat resistant separation fabric, comprising a heat resistant separation fabric as in claim 1; and a core onto which the heat resistant fabric is wound in a multiple number of layers.

12. Bobbin of yarn, comprising a spun, filament or texturized yarn; and a core onto which the yarn is wound, preferably cross-wound; wherein the yarn comprises metal fibers; wherein all fibers in the yarn are preferably metal fibers, e.g. stainless steel fibers; wherein boron nitride particles are present between the fibers in the yarn.

13. Method to produce a bobbin of yarn as in claim 12, comprising steps of applying an aqueous dispersion of boron nitride particles and preferably also of an inorganic binder onto a yarn comprising metal fibers, e.g. by means of spraying, immersion in a bath or a lick roll; wherein all fibers in the yarns are preferably metal fibers, e.g. stainless steel fibers; and winding, preferably cross-winding, the yarn on a core.

14. Method to produce a heat resistant separation fabric, comprising steps of a) applying an aqueous dispersion of boron nitride particles and preferably also of an inorganic binder onto a yarn comprising metal fibers, e.g. by means of spraying, immersion in a bath or a lick roll; wherein all fibers in the yarns are preferably metal fibers, e.g. stainless steel fibers; b) winding, preferably cross-winding, the yarn on a core to form a bobbin of yarn; and c) knitting or weaving said bobbin of yarn to form a knitted or woven fabric used for heat resistant separation.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0032] FIG. 1 shows a mould on which a separation fabric is mounted.

[0033] FIG. 2 shows a side view on a yarn with single yarns which consist out of one type of fibers.

[0034] FIG. 3 shows a side view on a yarn with single yarns which are an intimate blend of different fibers.

[0035] FIG. 4 shows a schematic view of a yarn of the invention undergoing a lick roll treatment.

[0036] FIG. 5 (a) and (b) shows respectively the Scanning Electron Microscope (SEM) image of the non-oxidized and oxidized fabric of the invention.

[0037] FIG. 6 illustrates a comparison of the parabolic oxidation rate constant (kp) of the sample made according to the invention with the kp of the references available in the market.

MODE(S) FOR CARRYING OUT THE INVENTION

[0038] A schematic drawing of a glass shaping mould, covered with separation is given in FIG. 1. The mould 11 is here covered by a separation cloth 12 (shown partially). The glass 14, which is initially pre-cut but flat, sometimes already pre-shaped, is brought in contact with the mould 11 and the separation cloth 12, to transfer the shape of the mould into the glass 14. This can be done in many different ways. There is always a vacuum created between mould 11 and glass 14 when the glass 14 is in contact with the mould 11.

[0039] Therefore air is sucked through the mould perforations 13 and through the separation cloth 12. It is part of the invention that at least one of the bundles or single yarns of the yarn used to provide the knitted fabric as subject of the invention comprises metal fibers. Metal fibers can be incorporated in the yarns of the fabric in different ways. It can be done by bundling (not shown) or in an alternative embodiment by plying a single yarn (see FIG. 2), out of 100% metal fibers 15, with other single yarns 16 and 17, e. g. made 100% out of another heat resistant fiber, or a blend out of two or more different heat resistant fiber types. The type of heat resistant fibers used to make the different single yarns 16 and 17 are not necessarily the same types, and the compositions are not necessarily the same. These single yarns 15, 16 and 17 can be multifilament yarns or spun yarns, e. g. rotor-or open end spun yarn, or ring spun yarn.

[0040] Another way of incorporating metal fibers in the yarns is by assembling or in an alternative embodiment by plying different single yarns, from which at least one single yarn is a blend of metal fibers and at least one non-metallic, high temperature resistant fiber type. This is shown in FIG. 3, where single yarn 18 is made out of metal fibers 21 and non-metallic fibers 22. The other single yarns 19 and 20 are e. g. made 100% out of other heat resistant fibers, or a blend out of two or more different heat resistant fiber types. The type of heat resistant fibers used to make the different single yarns 18, 19 and 20 are not necessarily the same types, and the compositions are not necessarily the same. The single yarns 18, 19 and 20 can be multifilament yarns or spun yarns, e. g. rotor-or open end spun yarn, or ring spun yarn.

[0041] The yarn of the present invention is specially treated such that boron nitride particles are present between the fibers in the yarns. As an example, the yarn is individually treated with boron nitride dispersion via lick roll (also called kiss roll). As shown in FIG. 4, a chromed roll 41 turns into boron nitride dispersion 43 and by this the boron nitride dispersion is transported towards the yarn 45 that runs along the upper side of the turning roll. At the exit of the lick roll a squeegee maybe installed that will scrape off the superfluous dispersion from the yarn 45.

[0042] As an example, aqueous boron nitride dispersion was prepared by diluting a commercially available aqueous gel of boron nitride and binder, contained 72 percent by weight boron nitride, 28 percent by weight aluminium phosphate binder, and 55 percent by weight of total solid phase. Using lick roll, boron nitride can be introduced upon yarns with a weight of 10 to 1000 g/m.sup.2. The speed with which the yarn is introduced, the speed of the lick roll, their mutual contact pressure and surface area, the viscosity of the dispersion, the positioning of the squeegee determine the final amount of boron nitride present between the fibers. All yarns used for these examples are made out of 100% stainless steel fibers, with fiber diameters of 12 μm. The alloy used is AISI 316L.

[0043] The yarns with boron nitride inbeween are knitted into fabrics for heat separation applications. As some embodiments, the invention fabrics are given in the table underneath, where for different knitted structures, gauge, yarn Nm and knitting structure are given, together with the number of stitches per cm.sup.2, thickness, weight and air permeability. The details on how the knitting structure made can be referred to the disclosure of patent EP1141457, which is incorporated herewith.

TABLE-US-00001 TABLE gauge, yarn Nm and knitting structure are given, together with the number of stitches per cm.sup.2, thickness, weight and air permeability for different knitted structures air perme- ability thick- yarn stitches/ (I/10 ness weight Embodiment gauge structure (Nm) (cm.sup.2) cm.sup.2*h) (mm) (g/m.sup.2) embodiment 1 16 single jersey ⅓ 7.5 91 6720 1.00 882 embodiment 2 20 single jersey ½ 5.5 94.1 4550 1.25 1010 embodiment 3 20 single jersey ½ 7.5 100.3 6750 1.00 741 embodiment 4 20 single jersey ⅓ 5.5 101.1 3540 1.5 1192 embodiment 5 20 single jersey ⅓ 7.5 124.5 4365 1.25 990 embodiment 6 20 single jersey ¼ 7.5 111.1 4639 1.35 1090 embodiment 7 24 single jersey ½ 5.5 96.7 5720 1.05 1016 embodiment 8 24 single jersey ½ 7.5 106.0 8960 0.8 757 embodiment 9 24 single jersey ⅓ 5.5 109.3 4836 1.20 1121 embodiment 10 24 single jersey ⅓ 7.5 123.6 5200 1.10 986 embodiment 11 24 single jersey ⅓ 10 136.6 5800 0.95 826 embodiment 12 24 single jersey ¼ 5.5 96.1 3828 1.4 1320 embodiment 13 24 single jersey ¼ 7.5 114.5 4970 1.3 948

[0044] The fabric as produced (referred to as non-oxidized below) was tested compared with such a fabric oxidized in air at about 700° C. for 19 hours.

[0045] FIG. 5 (a) and (b) respectively shows the Scanning Electron Microscope (SEM) image of the non-oxidized and oxidized fabric. The elongated elements are stainless steel fibers with an equivalent circular diameter of about 12 μm (which is also confirmed by the optic microscopy analysis). In the SEM images of FIG. 5 (a) and (b), particles/residues (dark colored in Backscattered electrons (BSE) mode of SEM) can be observed on top and between the fibers. The particles/residues are uniformly distributed within the fabric. Energy-dispersive X-ray spectroscopy (EDX) is used for the elemental analysis or chemical characterization of the non-oxidized and oxidized fabric samples. The EDX analytical technique verifies the particles/residues on both the non-oxidized and oxidized fabric samples are composed of B and N (boron nitride). When comparing the non-oxidized (FIG. 5(a)) with the oxidized fabric sample (FIG. 5(b)), the oxygen content detected by EDX increases and it seems to be mainly present as Cr-oxides after heat treatment or oxidation.

[0046] An infrared spectrum of absorption or emission of the non-oxidized and oxidized fabric samples are detected by Fourier-transform infrared spectroscopy (FTIR). It is found that the FTIR spectra of the non-oxidized and oxidized fabric samples are identical in the region 1360 and 817 cm.sup.−1. Those two regions can also be assigned to the presence of boron nitride. Thus, it is confirmed the presence of boron nitride on both the non-oxidized and oxidized fabric samples.

[0047] X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand range, empirical formula, chemical state and electronic state of the elements that exist within a material. By means of XPS, a surface wide scan and a depth profile were performed at the surface of the non-oxidized and oxidized fabric samples. The sputter rate used is ±1.0 Å/sec (for α-Fe). The detected elements for both the non-oxidized and oxidized fabric samples are: B, C, N, O, Al, P, Cr, Fe, Ni, Mo and at the outermost surfaces other traces. Cr- and Fe-oxides are present at the outermost surface of the tested fabric samples. After heat treatment, mainly Cr-oxides are formed on the oxidized fabric sample. B, N (BN), P and Al (AlPO.sub.4) can be distinguished by means of XPS, but cannot be accurately quantified due to several peak overlaps in this investigation. However, it is estimated that the presence of boron nitride and aluminium phosphate in the fabric is respectively in the range of 0.01 wt % to 1 wt %.

[0048] Resistance to oxidation is very important for separation cloth intended for glass shaping mould. Thermogravimetric analysis or thermal gravimetric analysis (TGA) is used to study the oxidation behaviour of the separation fabric of the present invention. TGA is a method of thermal analysis in which the mass of a sample is measured over time possible as the temperature changes. The weight gain due to oxidation of the sample made according to the invention is measured at about 700° C. The oxidation rate has been performed based on a parabolic oxidation law and is indicated by parabolic oxidation rate constant (kp). The kp of the sample according to the present invention is determined according to ISO 21608. The oxidation behaviour of the invention sample is also compared with similar products available in the market. As illustrated in FIG. 6, the kp of the sample made according to the invention is presented by A while the kp of the other references available in the market are presented by B, C, D and E. The kp of the invention sample (A) is about 0.0012 g.sup.2 cm.sup.−4 s.sup.−1. The kp of similar products in the market can be approximately 10 times (C) or 20 times (E) of the kp of the sample made according to the invention. A very similar product, which is made by the yarns having the same construction and stainless steel composition but without boron nitride particles presented in the yarns, presents a kp (D in FIG. 6) more than 4 times of the kp of the sample made according to the invention. The kp of the best product found in the market (B in FIG. 6), which is subjected to expensive processes, is also significantly larger (about 30%) than the kp of the sample made according to the invention. These results illustrate that the fabric made according to the invention has significantly reduced oxidation rate and longer lifetime.