SURFACE-MODIFIED GLASS FIBER WITH BI-COMPONENT CORE-SHEATH STRUCTURE

Abstract

Surface-modified glass fiber, comprising: a core made of a first glass fiber material; a surface layer that encloses the core completely in a sheath-like way; wherein the surface layer has a higher silicon dioxide percentage and a higher porosity compared to the core.

Claims

1. A surface-modified glass fiber, comprising: a core of a first glass fiber material; a surface layer that completely surrounds the core in a sheath-like way; and wherein the surface layer has a higher silicon dioxide percentage and a higher porosity compared to the core.

2. The surface-modified glass fiber according to claim 1, wherein the first glass fiber material of the core comprises E-glass, water glass or A-glass.

3. The surface-modified glass fiber according to claim 1, wherein the core has a silicon dioxide percentage of at least 52%.

4. The surface-modified glass fiber according to claim 1, wherein the surface layer has a silicon dioxide percentage of 96% as a maximum.

5. The surface-modified glass fiber according to claim 1, wherein the core has a core diameter of at least 0.5 m and wherein the surface layer also has a thickness of at least 0.5 m.

6. A non-woven fiber composite structure, comprising: a first non-woven fiber layer made of surface-modified glass fibers according to claim 1; a second non-woven fiber layer made of a second glass fiber material; wherein the second non-woven fiber material is layered over the first non-woven fiber layer; wherein the second glass fiber material comprises E-glass, water glass or A-glass.

7. The non-woven fiber composite structure according to claim 6, further comprising: a third non-woven fiber layer, wherein the third non-woven fiber layer is equal to the second non-woven fiber layer; wherein the second and the third non-woven fiber layer enclose the first non-woven fiber layer in a sandwich-like way.

8. A method for producing a surface-modified glass fiber structure, wherein the glass fiber structure is a precursor fiber or a non-woven fiber layer made of needled precursor fibers, wherein the glass fiber structure is made of a first glass fiber material that comprises E-glass, water glass or A-glass, comprising the following steps: leaching of the glass fiber structure through treatment with a predetermined acid solution for a predetermined time at a predetermined ambient temperature and at a predetermined acid concentration.

9. The method according to claim 8, wherein the predetermined acid solution comprises an aqueous solution of formic acid or hydrochloric acid or sulphuric acid.

10. The method according to claim 8, wherein the temperature of the predetermined acid solution is between ambient temperature and 100 C.

11. The method according to claim 8, wherein the predetermined time is between 3 minutes and 3 hours.

12. The method according to claim 8, wherein the acid concentration of the acid solution is between 1 molar and 3 molar.

13. The method for producing a non-woven fiber composite structure, comprising production of a first non-woven fiber layer according to claim 8; and application of a second non-woven fiber layer made of a second glass fiber material onto the first non-woven fiber layer, wherein the second glass fiber material comprises E-glass, water glass or A-glass.

14. The method for manufacturing a non-woven fiber composite structure according to claim 13, further comprising: the application of a third non-woven fiber layer onto the first non-woven fiber layer in such a way that the second non-woven fiber layer and the third non-woven fiber layer enclose the first non-woven fiber layer in a sandwich-like way, wherein the third non-woven fiber layer is equal to the second non-woven fiber layer.

15. A surface-modified glass fiber manufactured by means of the method according to claim 8.

16. The method according to claim 8, wherein: the treatment with the predetermined acid solution comprises dipping.

17. A surface-modified glass fiber having a bi-component structure comprising: a core having a first porosity, first silicon dioxide content, and first thermal resistance; a sheath surrounding said core, said sheath having a second porosity, second silicon dioxide content, and second thermal resistance; and wherein the second porosity is greater than the first porosity, the second silicon dioxide content is greater than the first silicon dioxide content, and the second thermal resistance is greater than the first thermal resistance, whereby insulation made of the surface-modified glass fiber is capable of being manufactured with higher temperature stability than the core of the surface-modified glass fiber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 Schematic illustration of the surface-modified fiber

[0035] FIG. 2 Leached surface-modified E-glass fibers and schematic illustration of a surface-modified fiber from FIG. 1.

[0036] FIG. 3 Schematic view of a non-woven fiber composite structure with surface-modified fibers in a sandwich structure.

[0037] FIG. 4 Schematic view of a non-woven fiber composite structure with surface-modified fibers.

DETAILED DESCRIPTION OF THE INVENTION

[0038] FIG. 1 shows a schematic illustration of a surface-modified fiber 1 according to the present invention. Based on a precursor glass fiber structure, here a glass fiber, for example an E-glass fiber or a water glass fiber or an A-glass fiber, a surface-modified fiber 1 was formed by means of incomplete leaching. In this context, the surface-modified fiber 1 comprises two components, i.e. a modified surface layer 5 and an essentiallyin relation to the untreated, non-leached source fiberunchanged core 3. Also an incomplete leaching of the fibers is performed in this process. A leaching gradient between the surface layer of the fibers 5, which are strongly leached, and their core 3, which is not leached, can hereby be achieved.

[0039] For the purpose of leaching, the glass fibers are treated with an acid solution, i.e. usually dipped into said solution. Formic acid, hydrochloric acid or sulphuric acid can be used respectively in an aqueous solution for this purpose.

[0040] The precursor glass fibers are dipped into the chosen acid solution in a defined way. The temperature of the acid solution can thereby be set appropriately between ambient temperature and 100 C. Further, the reaction time in this process can be varied between 3 minutes and 3 hours. Based on temperature, acid type, acid concentration, for example between 1 molar and 3 molar, and reaction time, the intensity of the leaching process is controlled. The goal of the leaching process, as already indicated, is to achieve a silicon dioxide gradient between the core and the sheath layer. The maximum gradient between the core and the sheath layer can have a maximum amount of 42%+3% as the base fiber has a SiO.sub.2 percentage of 52% and the fiber, which was leached at a maximum, has a SiO.sub.2 percentage of approx. 96%.

[0041] FIG. 2 illustrates an example of a core-sheath structure of fibers according to the present invention. FIG. 2 illustrates a plurality of E-glass fibers that have been exposed to an incomplete, i.e. partial, leaching process, i.e. that have been dipped into an acid solution in a defined way. Typical values are for example a temperature of 50 C., a three-molar H.sub.2SO.sub.4 over a period of 24 hours. The E-glass fibers are denominated with the reference sign 7. Differences between the individual treated fibers 7 are not considered here. Hence, the individual treated fibers 7 shall be regarded as equal on average. The individual treated, i.e. surface-modified, fibers 7 have an average diameter D of 9 m. For explanation, in the middle of the Figure in FIG. 2, the fiber 1 sketched in FIG. 1 is included in addition with its core 3 and its sheath layer 5. The fiber 1 has a diameter D that corresponds to the average diameter D of the photographically displayed treated fibers 7. The distinction between the two components of the treated fibers, i.e. of the core and the respective sheath layer, i.e. the area in which leaching of the source material has taken place, can be seen clearly in the photographic illustration of the fibers 7.

[0042] The sheath layer 5 has an elevated silicon percentage and at the same time a higher porosity while the core 3 maintains the original properties of the precursor fibers 1. In this context, the core 3 is characterized by a compact and non-porous structure. The porosity of the fiber behaves equivalently to its weight loss due to leaching.

[0043] Hence, the porosity of the fiber is equivalent to the loss of mass of the leached oxides.

[0044] The core 3 thereby hasas beforethe superior mechanical properties of the source fiber, for example E-module, tensile strength, etc. In this context, the source material, i.e. the precursor fiber as well as the core 3, which is not modified during treatment of the fiber, can definitely have a low thermal stability. However, the core 3 is protected by the sheath layer 7. This sheath layer 7 has a higher temperature stability due to the treatment. Consequently, also the overall modified fiber structure 1 has a higher temperature resistance than the core 3, i.e. also the source fiber. The thermal resistance and the mechanical properties depend on the proportion between the sheath thickness and the diameter of the core.

[0045] This core-sheath structure can also be extended to non-woven fiber composite structures as illustrated in FIGS. 3 and 4. As already indicated, the treatment of non-woven fiber layers takes place in a similar way as the treatment of individual fibers. In this process, the individual fibers are at first needled to the non-woven fiber layer/non-woven material pad before the overall non-woven fiber layer is subsequently dipped into a defined acid solution at defined treatment parameters.

[0046] FIG. 3 shows a sandwich structure 20 with a first temperature-stable outer non-woven fiber layer made of treated bi-component fibers 21 and a second temperature-stable outer non-woven fiber layer made of treated bi-component fibers 23. Typically, the two non-woven fiber layers 21 and 23 are equal and are formed each of equal treated bi-component fibers as they are illustrated based on FIGS. 1 and 2. In an enlarged view, which only exists for explanatory purposes, fibers 1, which have already been discussed based on FIGS. 1 and 2, are displayed next to one another on the right side of FIG. 3 to indicate a non-woven material pad. Accordingly, the non-woven fiber layer 23 and also the non-woven fiber layer 21 from FIG. 3 can correspond to a non-woven material pad made of fibers 1. In the structure that is sketched exemplarily in FIG. 3, the two non-woven fiber layers 21 and 23 directly enclose a further non-woven fiber layer 22 that, however, only comprises untreated fibers, i.e. only one component. The inner layer 22 consists for example essentially of untreated E-glass. This inner layer 22 can for example have a temperature stability of 600 to 700 C. as a maximum. On the other hand, the two non-woven fiber layers 21 and 23, which respectively consist of the treated bi-component fibers, have a higher temperature stability that the inner layer 22. Said temperature stability can typically be 700-1000 C. Hence, a higher temperature stability can be provided through the outer layers 21 and 23 of the sandwich structure shown in FIG. 3. At the same time, the structure keeps the good mechanical firmness properties of the fibers of the inner layer 22. The thicknesses of the layers 21 and 23 can be chosen based on the leaching duration and the untreated fiber diameter. They can typically be identical. It is clear that it is equally possible to provide the inner layer 22 with a thickness that differs significantly from the thickness of the outer layers.

[0047] There are frequent applications in the insulation area, in which the temperature stress essentially occurs on only one side of an insulation structure. In case of such a one-sided temperature stress it is equally possible, as shown in FIG. 4, to equip only half of the non-woven material product, i.e. of the insulation structure, with a temperature stability of 700-1000 C. while leaving the rest untreated. FIG. 4 shows an insulation structure/non-woven material product 30 that comprises two layers. It is a non-woven fiber layer 25 of treated fibers and an untreated non-woven fiber layer 27 that differs from said non-woven fiber layer. Similar to FIG. 3, the bi-component non-woven fiber layer 25 is formed of treated bi-component fibers as they are explained on the basis of FIGS. 1 and 2. In this context, the non-woven fiber layer 25 typically also corresponds to the non-woven fiber layers 21 and 23 from FIG. 3. Hence, the non-woven fiber layer 25 can have a temperature stability of 700-1000 C. As displayed in FIG. 4, a non-woven fiber layer 27 is disposed above the non-woven fiber layer 25 in a way that is similar to a sandwich structure from FIG. 3 that is cut in a longitudinal direction. The non-woven fiber layer 27 can have the same temperature properties as the non-woven fiber layer 22 from FIG. 3. It is therefore clear that the side of the structure 30, which comprises the treated bi-component non-woven fiber layer 25, is arranged to face an object to be insulated whereas the side of the structure 30, which has the non-woven fiber layer 27 made of untreated fibers, is arranged to face away from an object to be insulated.

[0048] The surface-modified fibers and/or non-woven fiber layers provided by the invention are particularly suitable for heat insulation in the high-temperature range from approximately 700 C. to 1000 C., depending on the application intensity, wherein defined tensile forces and defined elasticity modules are required or a generally higher firmness and/or stability of the fiber products. Potential uses can be seen in the high-temperature area, in particular in the field of the automotive industry, the aviation and space industry, in flow engineering as well as specific requirements in the field of thermo-acoustic systems. Common diesel applications in the automotive industry are in the temperature range of 800-900 C. ECR glass fibers with a temperature resistance of 750 C. are under-dimensioned for this application case and silicate fibers with a temperature resistance of 1000 C. are over-dimensioned and too expensive. Here, the product described in the invention offers an optimal solution. In addition, it comes with the advantage of being able to provide highly temperature-stable fibers and products without the need to be at the same time manufacturer of fibers, in particular glass fibers.