WO1997010188A1

WO1997010188A1 - Fibre-containing aerogel composite material

Info

Publication number: WO1997010188A1
Application number: PCT/EP1996/003961
Authority: WO
Inventors: Dierk Frank; Andreas Zimmermann
Original assignee: Hoechst Research & Technology Deutschland Gmbh & Co. Kg
Priority date: 1995-09-11
Filing date: 1996-09-10
Publication date: 1997-03-20
Also published as: CA2231428A1; CN1104393C; NO980991D0; EP0850207A1; NO980991L; MX9801908A; JP4118331B2; DE19533564A1; JPH11513349A; CN1196036A; KR19990044531A

Abstract

The invention relates to a composite material containing 5 to 97 % vol. aerogel particles, at least one binder and at least one fibrous material, in which the diameter of the aerogel particle ≥ 0.5 mm, a process for its production and its use.

Description

Fibrous airgel composite material

The invention relates to a composite material which contains 5 to 97% by volume of airgel particles, at least one binder and at least one fiber material, the particle diameter of the airgel particles being ≥ 0.5 mm, a process for its production and its use.

Aerogieie, 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. B. describe in EP-AO 171 722.

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

Aerogy in the broader sense, i.e. in the sense of "gel with air as a dispersing agent" are produced by drying a suitable gel. In this sense, the term “airgel” includes aerogeies in the narrower sense, xerogels and cryogels. A dried gel is referred to as an airgel in the narrower sense if the liquid of the gel is largely removed at temperatures above the critical temperature and starting from pressures above the critical pressure. If, on the other hand, the liquid of the gel is removed subcritically, for example with the formation of a liquid-vapor boundary phase, the resulting gel is also referred to as a xerogel. The use of the term aerogeie in the present application is aerogeie in the broader sense, i.e. in the sense of "gel with air as a dispersant".

The molding process of the airgel is completed during the sol-gel transition. After formation of the solid gel structure, the outer shape can only still be changed by crushing, for example grinding. The material is too fragile for another form of stress.

For many applications, however, it is necessary to use aerogeies in the form of certain shaped bodies. In principle, the production of moldings is already possible during the gel production. However, the diffusion-determined exchange of solvents typically required during production (for aerogie: see, for example, US Pat. No. 4,610,863 and EP-A 0 396 076, for airgel composite material: see, for example, WO 93/06044) and the diffusion-determined drying would also increase lead to uneconomically long production times. It is therefore sensible to carry out a shaping step after the airgel production, that is to say after drying, without a substantial change in the internal structure of the airgel taking place with regard to the application.

For many applications, in addition to good thermal insulation, good insulation is also required for airborne sound. Good sound absorption typically occurs with porous materials whose porosity is on a macroscopic scale (> 0.1 μm), since the speed waves of the sound are then dampened by the friction of the air on the pore walls. Monolithic materials without macroscopic porosity therefore have only a low level of sound absorption. Is a material porous only on a microscopic scale, e.g. monolithic aerogy, so the air cannot flow through the pores, but the sound waves are transmitted to the framework of the material, which transmits them without strong damping.

DE-A 33 46 180 describes rigid plates made of pressed bodies on the basis of silica airgel obtained from flame pyrolysis in connection with reinforcement by mineral long fibers. However, this silica airgel obtained from flame pyrolysis is not an airgel in the above sense, since it is not produced by drying a gel and thus has a completely different pore structure. It is mechanically more stable and can therefore be pressed without destroying the microstructure, but has a higher thermal conductivity than typical aerogeies in the 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.

EP-A-0 340 707 describes an insulating material with a density of 0.1 to 0.4 g / cm ³ , which consists of at least 50% by volume silica airgel particles with a diameter between 0.5 and 5 mm, which are connected by means of at least one organic and / or inorganic binder. If the airgel particles are only connected at the contact surfaces via the binder, the resulting insulation material is not very stable mechanically, since the mechanical part of the airgel particle covered by the binder tears off, the particle is then no longer bound and the insulation material cracks receives. Therefore, if possible, all gussets between the airgel particles should be filled with the binder. If the binder content is very low, the resulting material is more stable than pure aeroge, but cracks can easily occur if not all of the granules are adequately enclosed by the binder. With a high volume fraction of airgel which is favorable for a low thermal conductivity, only small volume fractions of binder remain in the gusset areas, which has a low mechanical stability, in particular in the case of porous binders such as foams with low thermal conductivity. Filling all gusset areas with binder also leads to a greatly reduced sound absorption in the material due to the reduced macroscopic porosity (between the particles).

EP-A-489 319 discloses a composite foam with low thermal conductivity which comprises 20 to 80% by volume of silica airgel particles, 20 to 80% by volume of a styrene polymer foam of density 0 which envelops and connects the airgel particles , 01 to 0.15 g / cm ³ and optionally Contains usual additives in effective amounts. The composite foam produced in this way is pressure-resistant, but not very resistant to bending at high concentrations of airgel particles.

In German patent applications DE-A-44 30 669 and DE-A-44 30 642, plates or mats made of a fiber-reinforced airgel are described. Although these plates or mats have a very low thermal conductivity due to the very high proportion of airgel, their manufacture requires relatively long production times due to the diffusion problems described above.

In the as yet unpublished German patent application P 44 45 771.5, a nonwoven airgel composite material is disclosed which has at least one layer of nonwoven fabric and airgel particles, which is characterized in that the nonwoven fabric contains at least one bicomponent fiber material, the fibers of which are mutually and are connected to the airgel particles by the low-melting shell material. This composite material has a relatively low thermal conductivity as well as a high macroscopic porosity and associated good sound insulation, but the use of bicomponent fibers limits the temperature range in which the material can be used and the fire protection class. Furthermore, the corresponding composites, in particular more complicated moldings, are not easy to manufacture.

One of the objects of the present invention was therefore to provide a composite material based on airgel granules which has a low thermal conductivity, is mechanically stable and is easy to produce.

Another object of the present invention was to provide a composite material based on airgel granules which additionally has good sound absorption. The object is achieved by a composite material which contains 5 to 97% by volume of airgel particles, at least one binder and at least one fiber material, the particle diameter of the airgel particles being> 0.5 mm.

The binder either binds the fibers or aerogeies to one another or to one another, or else the binder serves as a matrix material in which the fibers and the airgel particles are embedded. The connection of the fibers and the airgel particles to one another and to one another by means of the binder and, if appropriate, the embedding in a binder matrix leads to a mechanically stable material with low thermal conductivity.

Compared to a material that only consists of airgel particles that are bonded via their surfaces or embedded in a binder matrix, surprisingly, even small volume fractions of fibers with the same volume fraction of binder lead to a substantial mechanical reinforcement, since they take over essential parts of the load. If a higher volume fraction of fibers is used and only a small amount of binder is used, a porous material can be obtained in which the fibers connected by the binder form a mechanically stable framework in which the airgel particles are embedded. The air pores that occur then lead to higher porosity and thus improved sound absorption.

The fibers can be natural or artificial, inorganic or organic fibers, e.g. Cellulose, cotton or flax fibers, glass or mineral fibers, polyester, polyamide or polyaramid fibers. The fibers can be new or from waste such as e.g. shredded glass fiber waste or rags. The use of bicomponent fibers is also possible.

The fibers can be smooth or crimped as individual fibers, as a bulk or as a non-woven or woven fabric. Nonwovens and / or fabrics can be a coherent whole and / or in the form of several small pieces in the Composite may be included.

The fibers can have round, trilobal, pentalobal, octalobal, ribbon, fir tree, barbell or other star-shaped profiles. Hollow fibers can also be used.

The diameter of the fibers used in the composite should preferably be smaller than the average diameter of the airgel particles in order to be able to bind a high proportion of airgel in the composite. The choice of very thin fibers makes the composite more flexible.

Fibers with a diameter between 1 μm and 1 mm are preferably used. With a fixed volume fraction of fibers, the use of narrow diameters typically leads to more break-resistant composite materials.

The length of the fibers is in no way limited. Preferably, however, the length of the fibers should be greater than the average diameter of the airgel particles, i.e. at least 0.5 mm.

Mixtures of the above types can also be used.

The stability as well as the thermal conductivity of the composite material increases with increasing fiber content. Depending on the application, the volume fraction of the fibers should preferably be between 0.1 and 40% by volume, particularly preferably in the range between 0.1 and 15% by volume.

For a better connection to the matrix, the fibers can also be coated with sizes or contact agents (coupling agents), e.g. usual for glass fibers.

Suitable aerogies for the composite materials according to the invention are those based on metal oxides which are suitable for the sol-gel technique (see, for example, CJ. Brinker, GW Scherer, Sol-Gel-Science, 1990, chap. 2 and 3), such as Si or Al compounds or those based on organic substances which are suitable for sol-gel technology, such as, for example, melamine formaldehyde condensates (US Pat. No. 5,086,085) or resorcinol formaldehyde condensates (US Pat. 4, 873.218). However, they can also be based on mixtures of the above materials. Aerogies containing Si compounds are preferably used, particularly preferably aerogies containing SiO ₂ , in particular SiO ₂ aerogels, which are optionally organically modified.

To reduce the radiation contribution to thermal conductivity, the airgel IR opacifier, e.g. Contain carbon black, titanium dioxide, iron oxide, zirconium dioxide or mixtures thereof.

In addition, the thermal conductivity of the aerogeie decreases with increasing porosity and decreasing density, to a density in the range of 0.1 g / cm ³ . For this reason, aerogels with porosities above 60% and densities between 0.1 and 0.4 g / cm ^{3 are} preferred. The thermal conductivity of the airgel granules should preferably be less than 40 mW / mK, particularly preferably less than 25 mW / mK.

In a preferred embodiment, hydrophobic airgel particles are used, which can be obtained by introducing hydrophobic surface groups on the pore surfaces of the aerogie during or after the production of the aerogeie.

In the present application, the term “airgel particles” is intended to refer to particles which are either monolithic, ie consist of one piece, or which essentially contain airgel particles with a diameter smaller than that of the particle, which can be replaced by a suitable Binders are connected and / or are pressed together to form a larger particle. The size of the grains depends on the application of the material. In order to achieve high stability, the granules should not be too coarse-grained, preferably the diameter of the grains should be less than 1 cm and particularly preferably less than 5 mm.

On the other hand, the diameter of the airgel particles should be larger than 0.5 mm, in order to avoid the very difficult handling of a very fine, low-density powder during manufacture. Furthermore, during processing, liquid binder usually penetrates into the upper layers of the airgel, which loses its high insulating effect in this area. Therefore, the ratio of macroscopic particle surface to particle volume should be as small as possible, which would not be the case with too small particles.

In order to achieve low thermal conductivity on the one hand but sufficient mechanical stability of the composite material on the other hand, the volume fraction of the airgel should preferably be between 20 and 97% by volume, particularly preferably between 40 and 95% by volume, high volume proportions resulting in lower thermal conductivity and Lead strength. To achieve a high porosity of the entire material and thus increased sound absorption, air pores should also be present in the material, for which purpose the volume fraction of the airgel should preferably be below 85% by volume.

Granules with a favorable bimodal grain size distribution can preferably be used to achieve high airgel volume fractions. Depending on the application, e.g. in the field of sound insulation, other distributions can also be used.

The fibers or airgel particles with one another and fibers and airgel particles with one another are connected by at least one binder. The binder can either only connect the fibers and airgel particles to one another and to one another or serve as a matrix material. In principle, all known binders are suitable for producing the composite materials according to the invention. Inorganic binders, such as water glass glue, or organic binders or mixtures thereof can be used. The binder can additionally contain further inorganic and / or organic constituents.

Suitable organic binders are e.g. thermoplastics, e.g. Polyolefins or polyolefin waxes, styrene polymers, polyamides, ethylene-vinyl acetate copolymers or blends thereof, or thermosetting plastics such as phenol, resorcinol, urea or melamine resins. Adhesives such as hot melt adhesives, dispersion adhesives (in aqueous form, e.g. styrene-butadiene and styrene-acrylic ester copolymers), solvent-based adhesives or plastisols can also be used; reaction adhesives are also suitable, e.g. in the form of one-component systems such as thermosetting epoxy resins, formaldehyde condensates, polyimides, polybenzimidazoles, cyanoacrylates, polyvinyl butyrals, polyvinyl alcohols, anaerobic adhesives, polyurethane adhesives and moisture-curing silicones, or in the form of two-component systems such as methacrylic and epoxy resins, cold curing, cold curing.

Polyvinyl butyrals and / or polyvinyl alcohols are preferably used.

The binder should preferably be chosen so that, if it is in liquid form in certain phases of processing, it cannot penetrate into this very porous airgel, or can penetrate it only insignificantly. In addition to the selection of the binder, the penetration of the binder into the interior of the airgel particles can also be influenced by regulating the process conditions, such as pressure, temperature and mixing time.

If the binder forms a matrix in which aerogeies and fibers are embedded, porous materials are advantageously used because of their low thermal conductivity Densities less than 0.75 g / cm ^3, such as foams, preferably polymer foams (eg polystyrene or polyurethane foams), are used.

In order to achieve a good distribution of the binder in the gusset cavities with a high proportion of airgel and as good a bonding as possible, the binder should preferably be smaller than that of the airgel granules in the case that the binder is in solid form. Processing at elevated pressure may also be necessary.

Must the binder at elevated temperatures such as in the case of hot melt adhesives or reaction adhesives such as Melamine formaldehyde resins are processed, the binder must be chosen so that its melting temperature does not exceed the melting temperature of the fibers.

The binder is generally used in an amount of 1 to 50% by volume of the composite material, preferably in an amount of 1 to 30% by volume. The choice of binder depends on the mechanical and thermal requirements for the composite and the requirements with regard to fire protection.

The composite can contain other additives such as e.g. Contain dyes, pigments, fillers, flame retardants, synergists for flame retardants, antistatic agents, stabilizers, plasticizers and IR opacifiers.

Furthermore, the composite material can contain additives which are used for its production or are produced during the production, e.g. Lubricants for pressing, such as zinc stearate, or the reaction products of acidic or acid-releasing hardening accelerators when using resins.

The fire class of the composite material is determined by the fire class of the airgel, the fibers and the binder, as well as other substances which may be present. In order to obtain the best possible fire class for the composite material, non-flammable fiber types such as glass or mineral fibers, or flame-retardant fiber types such as TREVIRA CS® or melamine resin fibers, aerogels on an inorganic basis, particularly preferably on the basis of SiO ₂ , and flame-retardant binders should preferably be used such as inorganic binders or urea and melamine formaldehyde resins, silicone resin adhesives, polyimide and polybenzimidazole resins can be used.

If the material is in the form of flat structures, e.g. Sheets or mats used, it can be laminated on at least one side with at least one cover layer to improve the properties of the surface, e.g. to increase the robustness, to design it as a vapor barrier or to protect it against easy contamination. The cover layers can also improve the mechanical stability of the composite molding. If cover layers are used on both surfaces, they can be the same or different.

All materials known to the person skilled in the art are suitable as cover layers. They can be non-porous and thus act as a vapor barrier, e.g. Plastic foils, preferably metal foils or metallized plastic foils, which reflect thermal radiation. However, porous cover layers can also be used, which allow air to penetrate the material and thus lead to better sound absorption, e.g. porous foils, papers, fabrics or fleeces.

The cover layers themselves can also consist of several layers. The cover layers can be fastened with the binder, by means of which the fibers and the airgel particles are connected to one another and to one another, but another adhesive can also be used.

The surface of the composite material can also be closed and solidified by introducing at least one suitable material into a surface layer. Suitable materials are, for example, thermoplastic polymers such as polyethylene and polypropylene, or resins such as melamine formaldehyde resins.

The composite materials according to the invention preferably have thermal conductivities between 10 and 100 mW / mK, particularly preferably in the range from 10 to 50 mW / mK, in particular in the range from 15 to 40 mW / mK.

Another object of the present invention was to provide a method for producing the composite material according to the invention.

If the binder is initially in powder form, which melts at elevated temperature and, if appropriate, increased pressure in the case of hot-melt adhesives and reacts in the case of reaction adhesives, the composite material can be obtained, for example, as follows: airgel particles, fiber material and binder are mixed with conventional mixing devices. This mixture is then shaped. Depending on the type of binder, the mixture is cured in the mold, if necessary under pressure by heating, for example in the case of reactive adhesives, or in the case of hotmelt adhesives by heating above the melting point of the binder. A material that is porous on a macroscale can be obtained in particular by the following method: If the fibers are not already in a bulked form (for example small balls of cut fibers or small pieces of a fleece), they are processed into small balls using methods known to those skilled in the art. In this step, the airgel granulate can be placed between the fibers if necessary. These balls are then mixed together with the binder and, if appropriate, the airgel particles, for example in a mixer, until the binder and, if appropriate, airgel particles have distributed as evenly as possible between the fibers. The mass is then placed in a mold and optionally heated under pressure to a temperature which is above the melting temperature of the adhesive in the case of hot melt adhesives and above the temperature required for the reaction in the case of reactive adhesives. After the binder has melted is or has reacted, the material is cooled. Polyvinyl butyrals are preferably used here. The density of the composite material can be increased by using higher pressures.

In a preferred embodiment, the mixture is pressed. It is possible for the person skilled in the art to select the suitable press and the suitable pressing tool for the respective application. If necessary, lubricants known to the person skilled in the art, such as e.g. Zinc stearate in melamine formaldehyde resins can be added. The use of vacuum presses is advantageous due to the high air content of the airgel-containing molding compounds. In a preferred embodiment, the airgel-containing molding compounds are pressed into sheets. In order to prevent the molding compound from sticking to the press rams, the airgel-containing mixture to be compressed can be mixed with a separating aid, e.g. Release paper against which the ram is cut. The mechanical strength of the airgel-containing plates can be improved by laminating screen fabrics, nonwovens or papers onto the plate surface. The screen fabrics, nonwovens or papers can be applied subsequently to the airgel-containing plates, whereby the screen fabrics, nonwovens or papers can be impregnated beforehand, for example with a suitable binder or adhesive, and then bonded to the plate surfaces in a heatable press under pressure , as well as, in a preferred embodiment, in one working step by inserting the sieve cloth, nonwovens or papers, which can optionally be impregnated beforehand with a suitable binder or adhesive, into the mold and placing on the airgel-containing molding compound to be pressed and then pressing under pressure and temperature to an airgel-containing composite panel.

Depending on the binder used, the pressing generally takes place in any form at pressures from 1 to 1000 bar and temperatures from 0 to 300 ° C. In the case of the phenol, resorcinol, urea and melamine formaldehyde resins, the pressing preferably takes place at pressures from 5 to 50 bar, particularly preferably 10 to 20 bar and temperatures preferably from 100 to 200 ° C., particularly preferably 130 to 190 ° C. and in particular between 150 and 175 ° C in any shape.

If the binder is initially in liquid form, the composite can be obtained, for example, as follows: the airgel particles and the fiber material are mixed with conventional mixing devices. The mixture thus obtained is then coated with the binder, e.g. by spraying, placed in a mold and cured in the mold. Depending on the type of binder, the mixture is cured, if appropriate under pressure, by heating and / or evaporating the solvent or dispersion medium used. The airgel particles are preferably swirled with the fibers in a gas stream. A mold is filled with the mixture, the binder being sprayed on during the filling process. A material that is porous on a macroscale can be obtained in particular by the following process: If the fibers are not already in bulk (e.g. small balls of cut fibers or small pieces of a fleece), they are processed into small balls using methods known to those skilled in the art. In this step, the airgel granulate can be placed between the fibers if necessary. Otherwise, these balls are then together with the airgel granules e.g. mixed in a mixer until the airgel particles have spread as evenly as possible between the fibers. In this step or after, the binder is sprayed as finely as possible onto the mixture, which is then brought in a mold, if necessary under pressure, to the temperature necessary for the binding. The composite is then dried using conventional methods.

If a foam is used as the binder, the composite material can also be produced as follows, depending on the type of foam. If the foam is produced by expanding expandable granules in a form as in the case of expanded polystyrene, all components are intimately mixed and then typically heated, advantageously by means of hot air or steam. The resulting expansion of the particles increases the pressure in the mold, as a result of which the gusset volume is filled by the foam and the airgel particles are fixed in the composite. After cooling, the composite molded part is removed from the mold and optionally dried.

If the foam is produced by extrusion or expansion of a non-viscous mixture with subsequent solidification, the fibers can be mixed into the liquid. The airgel particles are mixed with the resulting liquid, which then foams.

If the material is to be provided with a cover layer, this can be inserted into the mold, for example, before or after filling, so that the lamination and shaping can take place in one work step, the composite binder preferably being the binding agent for the lamination is used. However, it is also possible to provide the composite with a cover layer afterwards.

The shape of the molded part, which consists of the composite material according to the invention, is in no way limited; in particular, the composite can be brought into sheet form.

Due to the high proportion of airgel and its low thermal conductivity, the composites are very suitable for thermal insulation.

The composite can be used, for example in the form of plates, as sound absorption material directly or in the form of resonance absorbers for sound insulation. In addition to the damping of the airgel material, depending on the porosity, macroscopic pores cause additional damping Air friction on these macroscopic pores in the composite material. The macroscopic porosity can be influenced by changing the fiber proportion and diameter, grain size and proportion of the airgel particles and type of binder. The frequency dependence and size of the sound attenuation can be changed in a manner known to the person skilled in the art via the choice of the cover layer, the thickness of the plate and the macroscopic porosity.

Because of the macroscopic porosity and especially the large porosity and specific surface area of the airgel, the composite materials according to the invention are also suitable as adsorption materials for liquids, vapors and gases.

The invention is described in more detail below on the basis of exemplary embodiments, but without being restricted thereby:

example 1

Moldings made of airgel, polyvinyl butyral and fibers

90% by volume of hydrophobic airgel granules, 8% by volume of Polyvinylbutyral powder ® Mowital (Polymer F) and 2% by volume of ®Trevira high-strength fibers are intimately mixed.

The hydrophobic airgel granulate has an average grain size in the range of 1 to 2 mm, a density of 120 kg / m ³ , a BET surface area of 620 m ² / g and a thermal conductivity of 11 mW / mK.

The bottom of the mold with a base area of 30 cm x 30 cm is lined with release paper. The airgel-containing molding compound is then evenly distributed and the whole thing is covered with a release paper. It is pressed at 220 ° C for 30 minutes to a thickness of 18 mm. The molded body obtained has a density of 269 kg / m ³ and a thermal conductivity of 20 mW / mK.

Example 2

Moldings made from airgel, polyvinyl butyral and recycled fibers

80% by volume of hydrophobic airgel granules from Example 1, 10% by volume of polyvinyl butyral powder ®Mowital (Polymer F) and 10% by volume of coarsely broken down polyester fiber residues are intimately mixed as recycling fibers.

The bottom of the mold with a base area of 30 cm x 30 cm is lined with release paper. The airgel-containing molding compound is then evenly distributed and the whole thing is covered with a release paper. It is pressed at 220 ° C for 30 minutes to a thickness of 18 mm.

The molded body obtained has a density of 282 kg / m ³ and a thermal conductivity of 25 mW / mK.

Example 3

Moldings made from airgel, polyvinyl butyral and recycled fibers

50% by volume of hydrophobic airgel granules from Example 1, 10% by volume of polyvinyl butyral powder ®Mowital (Polymer F) and 40% by volume of coarsely digested polyester fiber residues are mixed intimately as recycling fibers.

The bottom of the mold with a base area of 30 cm x 30 cm is lined with release paper. The airgel-containing molding compound is then evenly distributed and the whole thing is covered with a release paper. It is pressed at 220 ° C for 30 minutes to a thickness of 18 mm. The molded body obtained has a density of 420 kg / m ³ and a thermal conductivity of 55 mW / mK.

Example 4

Molded body made of airgel, polyethylene wax and fibers

60% by weight of hydrophobic airgel granules from Example 1, 38% by weight of ®Ceridust 130 polyethylene wax powder and 2% by volume of ®Trevira high-strength fibers are intimately mixed.

The bottom of the mold with a base area of 12 cm x 12 cm is lined with release paper. The airgel-containing molding compound is then evenly distributed and the whole thing is covered with a release paper. It is pressed at 170 ^C C with a pressure of 70 bar for 30 minutes.

The molded body obtained has a thermal conductivity of 25 mW / mK.

Example 5

Shaped body made of airgel, polyethylene wax and fibers

50% by weight of hydrophobic airgel granules from Example 1, 48% by weight of polyethylene wax powder from Hoechst wax PE 520 and 2% by volume of ®Trevira high-strength fibers are intimately mixed.

The bottom of the mold with a base area of 12 cm x 12 cm is lined with release paper. The airgel-containing molding compound is then evenly distributed and the whole thing is covered with a release paper. It is pressed at 180 ° C with a pressure of 70 bar for 30 minutes. The molded body obtained has a thermal conductivity of 28 mW / mK.

Example 6

Molded body made of airgel, polyvinyl alcohol and fibers

90% by weight of hydrophobic airgel granules from Example 1, 8% by weight of a polyvinyl alcohol solution and 2% by volume of ®Trevira high-strength fibers are intimately mixed. The polyvinyl alcohol solution consists of 10% by weight ®Mowiol type 40-88, 45% by weight water and 45% by weight ethanol.

The bottom of the mold with a base area of 12 cm x 12 cm is lined with release paper. The airgel-containing molding compound is then evenly distributed and the whole is pressed at 70 bar for 2 minutes and then dried.

The molded body obtained has a thermal conductivity of 24 mW / mK.

The thermal conductivity of the airgel granules was measured using a heating wire method (see, for example, O. Nielsson, G. Rüschenpöhler, J. Groß, J. Fricke, High Temperatures - High Pressures, Vol. 21, 274-274 (1989)).

The thermal conductivities of the moldings were measured in accordance with DIN 52612.

Claims

claims

1. Composite material containing 5 to 97% by volume of airgel particles, at least one binder and at least one fiber material, the particle diameter of the airgel particles being 0,5 0.5 mm.

2. Composite material according to claim 1, characterized in that the volume fraction of the fiber material is 0.1 to 40 vol .-%.

3. Composite material according to claim 1 or 2, characterized in that the fiber material contains glass fibers as the main component.

4. Composite material according to claim 1 or 2, characterized in that the fiber material contains organic fibers as the main component.

5. Composite material according to at least one of claims 1 to 4, characterized in that the proportion of airgel particles is in the range from 20 to 97% by volume.

6. Composite material according to at least one of claims 1 to 5, characterized in that the airgel particles have porosities above 60%, densities below 0.4 g / cm ³ and thermal conductivities of less than 40 mW / mK.

7. Composite material according to at least one of claims 1 to 6, characterized in that the airgel is a SiO ₂ airgel, which is optionally organically modified.

8. Composite material according to at least one of claims 1 to 7, characterized in that at least some of the airgel particles have hydrophobic surface groups.

9. Composite material according to at least one of claims 1 to 8, characterized in that the binder has a density which is less than 0.75 g / cm ³ .

10. Composite material according to at least one of claims 1 to 9, characterized in that the binder contains an inorganic binder as the main component.

11. Composite material according to claim 10, characterized in that the inorganic binder is water glass.

12. Composite material according to at least one of claims 1 to 9, characterized in that the binder contains an organic binder as the main component.

13. Composite material according to claim 12, characterized in that the organic binder is polyvinyl butyral and / or polyvinyl alcohol.

14. Composite material according to at least one of claims 1 to 13, characterized in that at least some of the airgel particles and / or the binder contain at least one IR opacifier.

15. Composite material according to at least one of claims 1 to 14, characterized in that it has a flat shape and is laminated on at least one side with at least one cover layer.

16. A method for producing a composite material according to at least one of claims 1 to 15, characterized in that the airgel particles and the fiber material are mixed with the binder, the mixture is subjected to shaping and hardening.

17. Use of a composite material according to at least one of claims 1 to 15 for thermal and / or acoustic insulation.

18. Shaped body containing a composite material according to at least one of claims 1 to 15.

19. Shaped body consisting essentially of a composite material according to at least one of claims 1 to 15.

20. Shaped body according to claim 18 or 19, characterized in that it has the shape of a plate.