EP0799343B1 - Nonwoven fabric-aerogel composite material containing two-component fibres, a method of producing said material and the use thereof - Google Patents

Abstract

PCT No. PCT/EP95/05083 Sec. 371 Date Jun. 19, 1997 Sec. 102(e) Date Jun. 19, 1997 PCT Filed Dec. 21, 1995 PCT Pub. No. WO96/19607 PCT Pub. Date Jun. 27, 1996The disclosure is a composite material having at least one layer of fiber web and aerogel particles, wherein the fiber web comprises at least one bicomponent fiber material, the bicomponent fiber material having lower and higher melting regions and the fibers of the web being bonded not only to the aerogel particles but also to each other by the lower melting regions of the fiber material, a process for its production and its use.

Description

The invention relates to a composite material comprising at least one layer of nonwoven and Airgel particles, a process for its preparation and its Use.

Aerogels, especially those with porosities above 60% and densities below 0.4 g / cm ³ , have an extremely low thermal conductivity due to their very low density, high porosity and small pore diameter and are therefore used as heat insulation materials, such as in the EP -A-0 171 722.

The high porosity also leads to low mechanical stability both the gel from which the airgel is dried and the dried one Aerogels itself.

Aerogels in the wider sense, i.e. in the sense of "gel with air as a dispersant", are made by drying a suitable gel. Under the term In this sense, "airgel" means aerogels in the narrower sense, and xerogels Cryogels. A dried gel is called an airgel in the narrower sense, if the liquid of the gel is at temperatures above the critical temperature and is removed based on pressures above the critical pressure. Becomes the liquid of the gel, on the other hand, is subcritical, for example with the formation of a Liquid-vapor boundary phase removed, then the resulting gel is called Xerogel. It should be noted that the gels according to the invention are Aerogels, in the sense of gel with air as a dispersant.

The molding process of the airgel takes place during the sol-gel transition completed. After formation of the solid gel structure, the outer shape can only still be changed by comminution, for example grinding, for one other form of processing, the material is too fragile.

However, for many applications it is necessary to shape the aerogels to use certain shaped bodies. In principle is the production of molded articles already possible during the gel production. However, during the Manufacturing typically necessary, diffusion-determined exchange of Solvents (regarding aerogels: see e.g. US-A 4,610,863, EP-A 0 396 076, regarding Airgel composite materials: s. e.g. B. WO 93/06044) and also Diffusion-determined drying at uneconomically long production times to lead. Therefore, it makes sense, after the airgel production, ie after drying to carry out a molding step without any substantial change in the internal structure of the airgel with regard to the Application takes place.

For many applications, e.g. for insulation of arched or irregular shaped surfaces, are flexible panels or mats made of an insulating material necessary.

In DE-A 33 46 180, rigid plates made of pressed bodies are based of silica airgel obtained from flame pyrolysis in connection with a reinforcement described by mineral long fibers. With this from the Flame pyrolysis is not, however, silica airgel an airgel in the above sense, since it is not made by drying a gel and thus has a completely different pore structure; therefore, it is mechanically more stable and can therefore be pressed without destroying the microstructure be, but has a higher thermal conductivity than typical aerogels in above sense. The surface of such compacts is very sensitive and must therefore be hardened by using a binder on the surface or protected by lamination with a film. Next is the emerging one Press body not compressible.

A mat is also used in German patent application P 44 18 843.9 described a fiber-reinforcing xerogel. These mats show through the very high proportion of airgel has a very low thermal conductivity relative to their manufacture due to the diffusion problems described above long production times necessary. In particular, the manufacture is thicker Mats only possible by combining several thin mats therefore requires additional effort.

US Pat. No. 5,256,476 discloses a shaped body with adsorber particles, in addition to the adsorber particles, the fine plastic particles and reinforcing ones Contains fibers, being essentially the fine plastic particles as Binders act.

The object of the present invention is therefore to provide a composite material on the To provide base of airgel granules that have a low thermal conductivity has that is mechanically stable and the simple manufacture of mats or Plates allowed.

The object is achieved by a composite material which has at least one layer of nonwoven fabric and airgel particles, the nonwoven fabric containing at least one bicomponent fiber material and the bicomponent fiber material having low and high-melting areas, which is characterized in that the fibers of the nonwoven both with the airgel particles and with each other through the low-melting areas of the fiber material, and that the airgel particles have porosities above 60%, densities below 0.4 g / cm ³ and a thermal conductivity of less than 40 mW / mK. The thermal bonding of the bicomponent fibers leads to a connection of the low-melting parts of the bicomponent fibers and thus ensures a stable fleece. At the same time, the melting part of the bicomponent fiber binds the airgel particles to the fiber.

The bicomponent fibers are chemical fibers made from two firmly bonded polymers of different chemical and / or physical structure, the areas with different melting points, i.e. low and high melting Areas. The melting points of the lower and higher melting ones Ranges preferably differ by at least 10 ° C. The bicomponent fibers preferably have a core / sheath structure. The The core of the fiber consists of a polymer, preferably one thermoplastic polymer whose melting point is higher than that of thermoplastic polymer that forms the shell. Preferably be Polyester / copolyester bicomponent fibers are used. Furthermore can also Bicomponent fiber variations made of polyester / polyolefin, e.g. Polyester / polyethylene or polyester / copolyolefin or bicomponent fibers that have an elastic Have shell polymer are used. But it can also be side-by-side Bicomponent fibers are used.

In addition, the nonwoven fabric can also have at least one simple fiber material included in the thermal solidification with the low-melting Areas of the bicomponent fibers is connected.

The simple fibers are organic polymer fibers, e.g. Polyester, polyolefin and / or polyamide fibers, preferably polyester fibers. The Fibers can be round, trilobal, pentalobal, octalobal, ribbon, fir tree, have dumbbell or other star-shaped profiles. Hollow fibers can also be used be used. The melting point of these simple fibers should be above that of the melting areas of the bicomponent fibers lie.

To reduce the radiation contribution to thermal conductivity, the bicomponent fibers, ie the high and / or low melting component, and optionally the simple fibers can be blackened with an IR opacifier such as carbon black, titanium dioxide, iron oxides or zirconium dioxide or mixtures thereof.
The bicomponent fibers and possibly the simple fibers can also be colored for coloring.

The diameter of the fibers used in the composite should preferably be be smaller than the average diameter of the airgel particles to a high Proportion of airgel in the fiber fleece. By choosing very thin Fiber diameters can be made into mats that are very flexible while thicker fibers due to their greater bending stiffness to more voluminous and rigid Lead mats.

The titer of simple fibers should preferably be between 0.8 and 40 dtex lie, that of the bicomponent fibers preferably between 2 and 20 dtex.

Mixtures of bicomponent fibers or simple fibers can also be made different materials, with different profiles and / or different Titers are used.

To achieve good bonding of the fleece on the one hand, and on the other The weight fraction should ensure good adhesion of the airgel granules Bicomponent fiber between 10 and 100 wt .-%, preferably between 40 and 100 wt .-%, based on the total fiber content.

The volume fraction of the airgel in the composite material should be as high as possible, be at least 40%, preferably over 60%. To still mechanical stability of the To achieve composite, however, the proportion should not exceed 95%, preferably not exceed 90%.

Suitable aerogels for the compositions according to the invention are those based on metal oxides which are suitable for sol-gel technology (CJ Brinker, GW Scherer, Sol-Gel-Science, 1990, chapters 2 and 3), such as Si or Al compounds or those based on organic substances which are suitable for sol-gel technology, such as melamine formaldehyde condensates (US Pat. No. 5,086,085) or resorcinol formaldehyde condensates (US Pat. No. 4,873,218). They can also be based on mixtures of the above materials. Aerogels containing Si compounds, in particular SiO ₂ aerogels and very particularly preferably SiO ₂ xerogels, are preferably used. To reduce the radiation contribution of the thermal conductivity, the airgel can contain IR opacifiers, such as, for example, carbon black, titanium dioxide, iron oxides, zirconium dioxide or mixtures thereof.

In addition, the thermal conductivity of the aerogels decreases with increasing porosity and decreasing density. For this reason, aerogels with porosities above 60% and densities below 0.4 g / cm ^{3 are} preferred.
The thermal conductivity of the airgel granules should be less than 40 mW / mK, preferably less than 25 mW / mK.

In a preferred embodiment, the airgel particles have hydrophobic surface groups. In order to avoid a later collapse of the aerogels by condensation of moisture in the pores, it is namely advantageous if there are covalent hydrophobic groups on the inner surface of the aerogels which are not split off under the action of water. Preferred groups for permanent hydrophobization are trisubstituted silyl groups of the general formula -Si (R) ₃ , particularly preferably trialkyl and / or triarylsilyl groups, each R independently being a non-reactive, organic radical such as C ₁ -C ₁₈ alkyl or C ₆ -C _14- aryl, preferably C ₁ -C ₆ alkyl or phenyl, in particular methyl, ethyl, cyclohexyl or phenyl, which can additionally be substituted with functional groups. The use of trimethylsilyl groups is particularly advantageous for permanent hydrophobization of the airgel. These groups can be introduced, as described in WO 94/25149, or by gas phase reaction between the airgel and, for example, an activated trialkylsilane derivative, such as, for example, a chlorotrialkylsilane or a hexaalkyldisilazane (compare R. Iler, The Chemistry of Silica, Wiley & Sons, 1979).

The size of the grains depends on the application of the material. However, to The particles should be able to bind a high proportion of airgel granules be larger than the fiber diameter, preferably larger than 30 µm. To one To achieve high stability, the granules should not be too coarse-grained, preferably the grains should be less than 2 cm.

Granules can preferably be used for the submission of high airgel volume fractions a bimodal grain size distribution can be used. Can continue too other suitable distributions are used.

The fire class of the composite material is determined by the fire class of the airgel and of fibers determined. To make the fire class of the To obtain composite material, flame-retardant fiber types such as e.g. TREVIRA CS®.

The composite material consists only of the nonwoven fabric that contains the airgel particles contains, can with mechanical stress of the composite material Airgel granules break or detach from the fiber, causing fragments the fleece can fall out.

For certain applications, it is therefore advantageous if the nonwoven fabric on a or both sides are each provided with at least one cover layer, wherein the cover layers can be the same or different. The cover layers can either in the thermal solidification via the low-melting Component of the bicomponent fiber or glued using another adhesive become. The cover layer can e.g. a plastic film, preferably one Metal foil or a metallized plastic film. Furthermore, the respective Cover layer itself consist of several layers.

A nonwoven airgel composite material in the form of mats or is preferred Sheets that have an airgel-containing non-woven fabric as a middle layer and on both sides each has a cover layer, at least one of the cover layers Non-woven layers made from a mixture of fine, simple fibers and finer Contains bicomponent fibers, and the individual fiber layers in themselves and are thermally solidified with each other.

For the selection of the bicomponent fibers and the simple fibers of the cover layer, the same applies as for the fibers of the nonwoven fabric in which the airgel particles are incorporated.
In order to obtain a cover layer that is as dense as possible, however, the simple fibers as well as the bicomponent fibers should have diameters of less than 30 μm, preferably less than 15 μm.

In order to achieve greater stability or density of the surface layers, the Fleece layers of the cover layers must be needled.

Another object of the present invention is to provide a method for To provide production of the composite material according to the invention.

The composite material according to the invention can e.g. according to the following procedure getting produced:

To manufacture the nonwoven, staple fibers in the form of commercially available Cards or cards are used. While the fleece according to the expert the usual procedures, the airgel granules are sprinkled. At the Introducing the airgel granules into the fiber composite is as possible ensure even distribution of the granules. This is through commercial spreading devices reached.

If cover layers are used, the nonwoven fabric can be covered on a cover layer Sprinkling of the airgel will be placed after the completion of this process applied top layer.

If cover layers made of finer fiber material are used, the lower fleece layer made of fine fibers and / or bicomponent fibers known methods and possibly needled. Then, as described above, the airgel-containing fiber composite is applied. For another, top cover layer can, as for the lower nonwoven layer, of fine fibers and / or bicomponent fibers a layer is laid and if necessary needled.

The resulting fiber composite is possibly under pressure at temperatures between the melting temperature of the jacket material and the smaller the Melting temperatures of simple fiber material and high-melting Component of the bicomponent fiber thermally consolidated. The pressure is there between normal pressure and the compressive strength of the airgel used.

The entire processing operations can preferably be carried out continuously on the Systems known to those skilled in the art can be produced.

The sheets and mats according to the invention are suitable because of their small size Thermal conductivity as a thermal insulation material.

In addition, the plates and mats according to the invention can be used as sound absorption materials can be used directly or in the form of resonance absorbers as they a low speed of sound and, compared to monolithic aerogels, have a higher sound absorption. In addition to damping the Airgel material occurs depending on the permeability of the nonwoven additional damping due to air friction between the pores in the nonwoven material. The permeability of the nonwoven fabric can be changed by changing the fiber diameter, the fleece density and the grain size of the airgel particles are influenced. Contains If the fleece is still covering layers, these covering layers should prevent the Allow sound into the fleece and not to a large extent reflection of the sound to lead.

The plates and mats according to the invention are also suitable on the basis of Porosity of the fleece and especially the large porosity and specific Surface of the airgel also as adsorption materials for liquids, vapors and gases. A specific one can be modified by modifying the airgel surface Adsorption can be achieved.

The invention is explained in more detail below on the basis of exemplary embodiments described.

Example 1:

50% by weight of TREVIRA 290, 0.8 dtex / 38 mm hm and 50% by weight of PES / Co-PES bicomponent fibers of the type TREVIRA 254, 2.2 dtex / 50 mm hm were used to make a nonwoven fabric with a basis weight of 100 g / m ² . A hydrophobic airgel granulate based on TEOS with a density of 150 kg / m ³ and a thermal conductivity of 23 mW / mK with grain sizes of 1 to 2 mm diameter was sprinkled in during laying.

The resulting nonwoven composite material was at a temperature of 160 ° C. thermally solidified for 5 minutes and compressed to a thickness of 1.4 cm.

The volume fraction of airgel in the solidified mat was 51%. The resulting mat had a basis weight of 1.2 kg / m ² . It was easy to bend and squeeze. The thermal conductivity was determined to be 28 mW / mK using a plate method in accordance with DIN 52 612 Part 1.

Example 2:

From 50% by weight of TREVIRA 120 staple fibers with a titer of 1.7 dtex, length 38mm, spinning black and 50% by weight of PES / Co-PES bicomponent fibers of the type TREVIRA 254, 2.2 dtex / 50 mm hm was first a Fleece laid, which served as the lower cover layer. This top layer had a basis weight of 100 g / m ² . A nonwoven fabric of 50% by weight TREVIRA 292, 40 dtex / 60 mm hm and 50% by weight PES / Co-PES bicomponent fibers of the type TREVIRA 254, 4.4 dtex / 50 mm hm with a basis weight of 100 g / m ² laid. During laying, a hydrophobic airgel granulate based on TEOS with a density of 150 kg / m ³ and a thermal conductivity of 23 mW / mK with grain sizes of 2 to 4 mm in diameter was sprinkled in. A cover layer was placed on this airgel-containing non-woven fabric, which was built up like the lower cover layer.

The resulting composite material was used at a temperature of 160'C Thermally solidified for 5 minutes and compressed to a thickness of 1.5 cm. The Volume fraction of airgel in the solidified mat was 51%.

The resulting mat had a basis weight of 1.4 kg / m ² . The thermal conductivity was determined using a plate method according to DIN 52612 Part 1 to 27 mW / mK.

The mat was easy to bend and squeeze. It trickled out of the mat no airgel pellets even after bending.

Claims (14)

1. A composite material comprising at least one layer of non-woven fabric and aerogel particles, the non-woven fabric containing at least one bicomponent fibre material, the bicomponent fibre material having low and higher-melting portions, characterised in that the fibres of the non-woven material are connected both to the aerogel particles and also to one another via the low-melting portions of the fibre material, the aerogel particles having porosities above 60%, densities below 0.4 g/cu.cm and a heat conductivity level of less than 40 mW/mK.
2. A composite material according to claim 1, characterised in that the bicomponent fibre material has a core/sheath structure.
3. A composite material according to claim 1 or 2, characterised in that the non-woven material additionally contains at least one single fibre material.
4. A composite material according to claim 3, characterised in that the titre of the bicomponent fibre material lies in the range from 2 to 20 dtex and the titre of the single fibres lies in the range from 0.8 to 40 dtex.
5. A composite material according to at least one of claims 1 to 4, characterised in that the fraction of aerogel particles in the composite material amounts to at least 40% by volume.
6. A composite material according to at least one of claims 1 to 5, characterised in that the aerogel is an SiO₂ aerogel.
7. A composite material according to at least one of claims 1 to 6, characterised in that the bicomponent fibre material, the single fibre material and/or the aerogel particles contain at least one IR opacifier.
8. A composite material according to at least one of claims 1 to 7, characterised in that the aerogel particles have a heat conductivity of less than 25 mW/mK.
9. A composite material according to at least one of claims 1 to 8, characterised in that the aerogel particles comprise hydrophobic surface groups.
10. A composite material according to at least one of claims 1 to 9, characterised in that the non-woven material is provided on one or on both sides with in each case at least one outer layer, the outer layers possibly being identical or different.
11. A composite material according to claim 10, characterised in that the outer layers contain synthetic plastics films, metal foils, metallised synthetic films or preferably layers of non-woven material of fine single-fibres and/or fine bicomponent fibres.
12. A composite material according to at least one of claims 1 to 11 in the form of a panel or mat.
13. A method of producing a composite material according to claim 1, characterised in that the aerogel particles are scattered into a non-woven fabric which contains at least one bicomponent fibre material having lower and higher melting fractions and then the resulting fibre composite is consolidated under neat and possibly under pressure at temperatures above the lower melting temperature and below the higher melting temperature.
14. Use of a composite material according to at least one of claims 1 to 12 for heat insulation, sound insulation and/or adsorption material for gases, vapours and liquids.