DE102017127934A1 - Powder of foam - Google Patents

Abstract

The invention relates to powder of foam, a composition containing the powder and opacifier, a process for the preparation of the powder, its use and a shaped body of the powder.

Description

The invention relates to powder of foam, a composition containing the powder and opacifier, a process for the preparation of the powder, its use and a shaped body of the powder.

The production of, for example, polystyrene foams is described in the prior art in various publications. This is either a particle foam technology in which the polymer particles are already impregnated in the production process with a low molecular weight blowing agent such as cyclopentane and are foamed in the next step by tempering with superheated steam (discontinuous process). This is for example in the patent application DE 103 58 800 A1 shown, in which case additionally an ellipsoidal geometry of the enclosed propellant is described. On the other hand, there is the possibility of dissolving the blowing agent, such as carbon dioxide, under elevated pressure into a polymer melt (temperature must be above the melting temperature of the polymer) and foaming it to a foam by subsequent expansion at the end of an extruder (continuous process; EP 0 849 309 B1 . US 4636527 A . WO 1993 022371 A1 ). In many foams or foaming processes, the production of the necessary polymer from the monomer or monomer mixtures is temporally and spatially separated from the foaming process (for example Styropor® or Neopor®). This means that the chemical polymerization process takes place in a separate production process or the physical foaming process must take place in a second plant. For the production of a thermosetting polymer foam such as, for example, in polyurethane, the two processes can not be considered separately from each other, since during the polymerization already selectively the resulting polymer composition is foamed.

For both types of foam, infrared opacifiers are added to improve the insulating properties, especially when the density of the polymer foam is less than 30 kg / m ³ . By this measure, it was possible to drastically reduce the use of materials in the foams in recent years with consistent performance in terms of thermal insulation (see. EP 0 372 343 B1 . EP 0 620 246 B1 . EP 2 402 389 A2 . DE 10 2008 047 594 A1 . DE 20 2010 013 850 U1 . EP 2 092 002 B1 . US 8114476 B2 . US 2010 0148110 A1 ).

A disadvantage of this process is the coarsening of the foam structure due to aging processes in the foam formation, which inevitably leads to pore sizes of greater than 10 micrometers (μm). Commercially, no air-filled polymer foams are available whose insulation performance is below 26 mW / mK. The background is that so far no homogeneous foam structures with a pore size below 10 microns and a sufficiently high volume-expansion ratio (VER) was commercially available. Only with pore sizes significantly below 10 μm is the so-called Knudsen effect noticeable, in which the thermal conductivity of the air is reduced compared to free air. The heat conduction of a foam is the sum of the heat conduction of the matrix material (polymer), the heat conduction of the gas in the pores (air) and the contribution of the infrared radiation (heat radiation) that can pass through the foam. For all commercially manufacturable foams, the thermal conductivity of the air at 25 ° C and atmospheric pressure (hereinafter referred to as normal conditions) is 26 mW / mK and for this reason the value can not be undercut.

Therefore, the most efficient air-filled polystyrene foams of the prior art achieve thermal conductivities of 31 mW / mK (normal conditions). This is achieved by reducing the density below 20 kg / m ³ in combination with an infrared (IR) opacifier. The need for an IR opacifier only became apparent through the reduction in foam density. Background is the inversely proportional increasing infrared radiation share in the total heat conduction with decreasing densities. The contribution of infrared radiation in conventional polymer foams having a density> 30 kg / m ³ assumes only a small contribution to the total heat conduction of 5-15% due to sufficient scattering and absorption at the relevant wavelengths. For this reason, polymer foams with densities> 30 kg / m ^{3 are} usually no longer provided with opacifiers.

However, it is very problematic to introduce opacifiers into the foam itself. In the patent application EP 16 189 993.5 In the polymer nanofoam opacifiers, which drastically reduce the said radiation contribution, are integrated. In this case, the clouding agent was added to the monomer solution before the polymerization. Here, however, it can be seen that the desired nanostructure over the entire sample after the foaming process is obtained only by a fine dispersion of the opacifier can. In addition, certain opacifiers that have a stabilizing effect on thermally initiated radicals, a difficult to handle polymerization process.

As early as 1909, Knudsen was able to show theoretically that a reduction of a space in the area of the mean free path of the gas molecules enclosed in it can cause a significant reduction of the heat conduction of the gas (see M. Knudsen, Annalen der Physik, 1909). In the case of air, the mean free path is about 70 nanometers (nm) under normal conditions. It is therefore known that the foam pores in insulating materials must be reduced to less than one micron in order to obtain a significant reduction in the heat conduction of the air and thus to realize air-filled polymer foams with a heat conduction below 26 mW / mK. According to the scientific publications on the production of nanoporous polymers, all previous methods are not yet able to ensure the combination of nanoporosity at low density. This is clearly illustrated in the review by Okolieocha, since both the pore sizes and the corresponding foam densities are given here (cf. Okolieocha C., Raps D., Subramaniam K., Altstädt V .; European Polymer Journal 73; 500-519; 2015 ). In order to actually obtain a polymer foam with a heat conduction below the actual air line (26 mW / mK), a combination of nanoporosity and a relatively moderate heat conduction of the polymer matrix and the thermal radiation would have to be present. To minimize the heat conduction of the polymer matrix, the air fraction or porosity should make up at least 80% by volume of the foam. In order to obtain a nanoporous polymer foam with a high thermal insulation, ideally pore size, homogeneity of the pores, the foam density should be well matched.

Nanoporous polymer foams with low density could not be produced so far with sufficient thermal insulation (cf. DE 10 2013 223 391 A1 ). For example, in nanoporous polystyrene foams without opacifiers, the prevailing pores with diameters below 1000 nm reduce the scattering of heat radiation compared to conventional polystyrene foams having pore sizes of around 100 .mu.m to such an extent that the thermal radiation fraction multiplies. A high proportion of thermal radiation is then given at densities greater than 40 kg / m ³ . The addition of opacifiers in the polymer formulation for the nanofoam, in turn, typically multiplies the pore size to more than 5 microns. Although the radiation heat conduction is reduced by the opacifier, however, it increases the thermal conductivity of the air, since with the enlarged pores of the Knudsen effect no longer works.

Nanoporous polymer foams have the further disadvantage that they have hitherto been produced only as shaped bodies or spherical granules with particle sizes from about 0.5 cm. This has the disadvantage that complex cavities with smaller dimensions were difficult to fill with this material.

The spherical shape of the previous granules has also led to disadvantages in certain applications so far.

The object of the present invention is therefore to provide a technology in which, on the one hand, cavities with very complex geometries, which can also be very fine, can be filled with nanoporous foam and, on the other hand, can be introduced in the opacifier such that the pore sizes preserved in nanofoam below 1000 nm.

1. a. der Median der Teilchengröße des Pulvers in einem Bereich von 0,5 bis 1000 µm liegt, und
2. b. der Median des Durchmessers der Poren des Schaumstoffs in einem Bereich von 10 bis 500 nm liegt.

In a first embodiment, the object underlying the invention is achieved by a powder of foam, characterized in that

1. a. the median particle size of the powder is in a range of 0.5 to 1000 μm, and
2. b. the median of the diameter of the pores of the foam is in a range of 10 to 500 nm.

The advantage of this powder over the prior art is that even very complex cavities can be filled with it, that opacifiers and other powders can easily be added to such a powder and mix homogeneously. In addition, it is easy to disperse in viscous liquids.

In addition, the powder according to the invention (also referred to as nanofoam powder) surprisingly has a significantly lower thermal conductivity than the non-pulverized foam (compare embodiment).

The median particle size of the powder can be determined, for example, by a scanning electron micrograph and counting per area. Here, the particle size denotes the greatest possible distance, which is possible by a straight line in the particle. For example, in a range of 3 mm × 3 mm, the powder particles can be measured and counted by electron microscopy. For example, with irregularly shaped powder particles, the smallest visible diameter of the powder particle can always be considered. The primary beam voltage of the scanning electron microscope can be set to 5 kV, for example. The surface can be coated with gold to avoid unwanted charging effects, or the median can be determined by sieving the powder. This can be done, for example, by fractionation in a sieving tower.

The median pore size of the foam can be determined, for example, by a scanning electron micrograph and counting per area. For this purpose, for example, the surface of a powder particle can be viewed on an area of 10 .mu.m.times.10 .mu.m, and then the pores are counted and measured. For example, with irregularly shaped pores, the smallest visible diameter of the respective pore can always be evaluated. The primary beam voltage of the scanning electron microscope can be set to 5 kV, for example. The surface can be coated with gold to avoid unwanted charging effects. For example, the pore size can be determined concretely as follows: In order to image the structure of the nanoporous materials produced, a fresh breaking edge can first be produced. Then the sample can be fixed on the sample tray with the breaking edge pointing upwards. In order to be able to dissipate the charge arising during the measurement, silver-conducting lacquer can be used for fixing. For example, before the recordings can be made, the sample is coated with gold to avoid local charging effects. For this example, the coating system K950X is used with the sputtering additive K350 from EMITECH. In all cases, gold sputtering occurs, for example, at an argon pressure of about 10-2 mbar, with a current of 30 mA always being applied for 30 seconds. The layer thickness of the gold layer applied in this way is for example approximately between 5 and 15 nm. The electron micrographs are carried out, for example, on a device of the type SUPRA 40 VP from ZEISS. With this device acceleration voltages of up to 30 kV and a maximum resolution of 1.3 nm are possible. The recordings are recorded, for example, at an acceleration voltage of 5 kV with the InLens detector. To determine the average pore diameter and the average web thickness of the nano- and microporous foams, for example, an image taken with the described scanning electron microscope is selected and measured with the computer program Datinf Measure at least 300 pores or webs to ensure a sufficiently good statistics.

In this application, it is explicitly pointed out that pores can be both closed, half-closed and open. For the latter, one can also imagine an open-pored, sponge-like network.

powder

The median particle size of the powder is preferably in a range of 0.5 to 800 μm, more preferably in a range of 0.6 to 500 μm, most preferably in a range of 0.7 to 200 μm. As a result, even very fine internal geometries of cavities can be efficiently filled with the foam.

The median of the diameter of the pores of the foam is preferably in a range of 50 to 400 nm. Preferably, at least 75% by volume, more preferably at least 85% by volume, most preferably at least 95% by volume, the pores have a diameter in one Range of 50 nm to 200 nm, most preferably in a range of 60 nm to 140 nm.

Preferably, the foam is open-celled. As a result, the powder can also be used for applications such as oil removal in tanker accidents.

The powder preferably has a BET specific surface area (gas adsorption) in a range of 5 to 500 m ² / g, more preferably in a range of 10 to 300 m ² / g, and most preferably in a range of 20 to 200 m ² /G. This BET specific surface area can be determined, for example, with a multipoint BET device according to DIN ISO 9277. As a result, the powder has a very high capillarity. In combination with the open-celledness of the foam, this results in advantages in the removal of oil in tanker accidents. According to first findings, the powder according to the invention can absorb about 5 to 20 times its own weight of hydrophobic liquids (eg diesel) and, in the case of oil or diesel, still floats on the water. This was determined as follows: (test according to LTwS No. 27 (as of June 1999) with test mixture A20 / NP II (corresponds to heating oil EL after DIN 51603 )).

The grain shape of the powder is preferably edged or sharp-edged or edge-rounded in the sense of DIN EN ISO 14688 ,

The foam is preferably a polymer foam. Polymers are combustible due to the organic nature. This polymer foam is preferably partially crosslinked. Preferably, the foam is a partially crosslinked polymer foam.

Preferably, the volume expansion ratio (VER) of the polymer foam (for example, for polymers with densities of 900-1200 kg / m ³ ) is in a range of 4 to 30, more preferably in a range of 7 to 25. With the help of the VER, it is possible to compare polymer foams whose polymer densities differ: $$\text{VER}=\left(\text{Volume foam}\right)/\left(\text{Volume of polymer}\right)$$

Preferably, the density of the foam is in a range of 30 to 300 kg / m ³ , more preferably in a range of 40 to 200 kg / m ³ , most preferably in a range of 45 to 150 kg / m ³ .

Preferably, the lower limit of the density of the polymer foam combined with the aforementioned upper limit in increasing preference may be 40, 45, 50 and more preferably 60 kg / m ³ . Preferably, the upper limit of the density of the polymer foam in conjunction with the aforementioned lower limits may be in ascending order of 250, 200, 175, and more preferably 150 kg / m ³ .

wobei dPore (Durchmesser der Poren im Median) die Einheit Nanometer trägt.Preferably, a factor (FOM) for pore diameters between 10 nm and 10 μm can be defined for the combination of density and pore size of the foams: $$\text{FOM}=\left(\text{In}\left(\text{dpore / 0}\text{, 15 nm}\right)\right)/\text{VER}$$

where dPore (diameter of the pores in the median) carries the unit nanometer.

In this connection, it applies that all foams with pore sizes below 10 μm known from the prior art show a factor FOM ≥ 1.2. The polymer foam according to the invention, however, preferably has a factor FOM of less than 1.2. Regardless, the factor FOM is preferably at least 0.01.

Preferably, the heat conduction of the polymer foam is in a range of 1 to 30 mW / mK at normal conditions (1 atm, 25 ° C). Preferably, the upper limit of the heat conduction of the polymer foam in conjunction with the aforementioned lower limit may be in increasing preference 28, 27 and most preferably 26 mW / mK. These low heat conductivities have not yet been experimentally possible with air-filled polymer foams in the prior art, since even the air heat conduction in large-pore foams is about 26 mW / mK under normal conditions. These preferred foams according to the invention, which are not comparable with other foams due to their nature and can not be produced in any comparable production process, represent a new class of foams. In general, a foam is based on an increase in volume during the production process.

Preferably, the monomer from which the polymer foam is preferably obtained predominantly selected from styrene and derivatives, methyl methacrylate and derivatives, lactic acid and derivatives, vinyl chloride and derivatives, polyhydric alcohols and derivatives in conjunction with isocyanates and derivatives, and / or ethylene and derivatives, and / or mixtures of the aforementioned monomers.

The polymer foam may preferably be a polystyrene foam, a polymethyl methacrylate foam, a polylactic acid foam, a polyvinyl chloride foam, a polyurethane foam, a polyethylene foam and / or a mixture and / or copolymer foam of these polymer foams.

Derivatives of styrene for the purposes of the present invention may be, for example, alkylstyrene, alkoxystyrene, halostyrene, dihalogenostyrene or divinylstyrene and in particular be selected from the group consisting of 4-bromostyrene, 4-methylstyrene, 4-ethylstyrene, 4-propylstyrene, 4-isobutyl-styrene , 4-methoxy-styrene, 4-ethoxy-styrene, 2-vinyl-6-bromonaphthalene, 2-vinyl-6-methylnaphthalene or 2-vinyl-6-methoxynaphthalene, p-chlorostyrene, 2,4-dimethylstyrene, 4-vinylbiphenyl, vinylnaphthalene, vinylanthracene and / or Mixtures thereof.

For the purposes of the present invention, derivatives of methyl methacrylate may be, for example, acrylic acid, ethyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, benzyl methacrylate, 1-ethoxy-1-propyl methacrylate, glycidyl methacrylate, 2-trimethylsilyloxyethyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 4- (Tetrahydro-2-pyranyloxy) benzyl methacrylate, lauryl methacrylate, ethoxytriethyl-englycol methacrylate, butoxyethyl methacrylate, methoxyethoxyethyl methacrylate, sorbyl methacrylate, 2-acetoxyethyl methacrylate, 3-trimethoxysilylpropyl methacrylate, allyl methacrylate, octyl methacrylate, methoxypolyethylene glycol methacrylate, ethoxyethyl methacrylate, tetrahydropyranyl methacrylate, t-butyl methacrylate and 2-dimethylaminoethyl methacrylate and / or mixtures be the same.

Preferably, the polymer foam of the invention may also be obtained by polymerizing any mixture of the aforementioned monomers.

Preferably, a starter is included. Preferably, the initiator is a free radical initiator which breaks down by thermal energy and thereby releases two free radicals, e.g. Azobisisobutyronitrile (AIBN), dibenzoyl peroxide, dicumyl peroxide, peroxoketals.

The degree of crosslinking of the polymer foam (based on the monomer used) is preferably in a range from 0.01 mol% to 10 mol%, particularly preferably in a range from 0.05 to 5 mol%, very particularly preferably in the range from 0.1 to 2 mol%.

The degree of crosslinking in the sense of the invention is a quantitative measure for the characterization of polymeric networks. It is calculated, for example, as the quotient of the number of crosslinked basic building blocks and the number of moles of the basic building blocks present in this macromolecular network (monomer molecules). It is given either as a dimensionless number or as a percentage (mole fraction). Closely related to this (and often used as a synonym) is the concept of network density (here the number of networking sites is related to the volume).

Due to the partial crosslinking of the polymer foam according to the invention is preferably not non-destructive meltable. All relevant polymer foams from the prior art based on polystyrene are usually fusible, ie thermoplastic. As a result of the partial crosslinking, the polymer foam according to the invention is preferably also not soluble in a solvent. Typically, for a polymer, the particular monomer that makes up the polymer is the best solvent for the particular polymer. Preferably, the polymer foam according to the invention is not soluble in its own monomer.

The polymer foam preferably also contains a crosslinker. The crosslinker preferably has at least 2 functional groups suitable for a polymerization reaction. Preferably, the functional groups are selected from vinyl, allyl, carboxylate, ethoxy, methoxy, amine, alcohol, ketone and allyl ketone groups. Regardless of or in conjunction therewith, the crosslinkers may be organically substituted silanes. More preferably, the crosslinker is selected from divinylbenzene, N, N-methylenebisacrylamide and ethyl-narrowed-dimethylmethacrylate.

Preferably, the polymer foam also contains uncrosslinked polymer. In this patent application is understood uncrosslinked polymer, a polymer which is constructed by polymerization of monomer molecules (monofunctional polymerizable molecule). It is microscopically in the form of uncrosslinked molecules. Preferably, uncrosslinked polymer is contained in the polymer foam in a range of from 2 to 30 wt% with respect to the total weight of the polymer foam.

Preferably, the polymer foam is open-celled. Preferably, the polymeric foam is evacuable (e.g., under vacuum) without being destroyed. Preferably, the initial density of the foam (not the bulk density of the foam) is not significantly increased by the vacuum (shrinkage process <30% by volume). For evacuation, for example, the sample is sealed in a plastic bag.

Preferably, the proportion of the total heat conduction by infrared radiation is up to 25%, more preferably up to 15%, most preferably up to 10%.

opacifiers

The object underlying the invention is achieved in a further embodiment by a composition containing inventive powder and opacifier.

Alternatively, or in addition to the opacifier, the composition may also preferably contain flame retardants or powder materials such as aerogels or silica.

The invention preferably described herein is based on a turbidity of a nanoporous polymer without a complex dispersion of the opacifier in the monomer before the polymerization process.

This composition shows, for example, in addition to an IR haze also a fire retardant effect, which is required for many Dämmwendungen. The finer the turbidity agent is mixed with the powder, the more efficient the turbidity and the smaller the IR radiation contribution to the heat conduction of the mixture.

Preferably, the opacifier is included in the composition of the invention in a range of 1 to 30 wt.%, Particularly preferably 1.5 to 15 wt.%, Based on the total mass of the composition.

The powder according to the invention is preferably present in the composition in a range from 70 to 99% by weight, particularly preferably from 85 to 98.5% by weight, based on the total mass of the composition.

Preferably, the opacifier is an infrared opacifier. It has heretofore been assumed that a sufficiently high foam density> 30 kg / m ³ can be regarded as negligible in the infrared radiation fraction which can pass through such a foam. In scientific publications, the IR contribution in nanoporous foams is theoretically considered negligible (cf. Ferkl P., Pokorny R., Bobak J, Chem Eng Sci; 97: 50-8; 2013 ). In a publication by Notario et al. Thermal conductivity measurements are carried out on nanoporous polymer materials, which are interpreted in such a way that an optimistic assumption can not be expected to significantly contribute to IR radiation (see Notario B., Pinto J., Solorzano E., Rodriguez-Perez MA, Polymer; 57-67 ; 2015). It turned out against expectations that even at foam densities of> 30 kg / m ^3, the infrared radiation contribution contributes significantly to the overall heat conduction and thus these foams did not have improved thermal insulation properties over the prior art although the pore diameter is significant smaller (example: density> 45 kg / m ³ , dPore <10 μm).

The identification of this issue could only be accomplished by extensive thermal conductivity measurements on macroscopic samples (about 10 cm in diameter and 1.5 cm in thickness) with a disk device well known to those skilled in the art. These had to be measured pressure- and temperature-dependent in order to be able to dissolve the individual heat conduction contributions in these foams. Only here did it emerge that polymer foams having foam pores of, for example, less than 10 μm and a density, for example greater than 30 kg / m ^{3, have} an infrared radiation component under standard conditions of up to 40% of the total heat conduction and thus do not represent an improvement over large-pore foams for insulating applications.

Preferably, the opacifier absorbs or scatters radiation having a wavelength in a range of 1 to 100 μm, most preferably in a range of 3 to 30 μm.

Preferably, the opacifier has an average particle size in the median in a range of 0.01 to 100 microns.

Preferably, the opacifier is organic or inorganic.

The opacifier may be, for example, an organic dye.

Preferably, the opacifier is selected from the group consisting of graphite, carbon blacks, carbon derivatives such as multiwalled carbon nanotubes, fullerene, graphene, etc., metal oxides such as titanium dioxide, iron oxides or zirconium dioxide, and mixtures thereof. Most preferably, the opacifier is so-called furnace carbon black or flame black, for example. from the company Orion Engineered Carbons.

The example of the opacifier shows the advantages of mixing two powders. Regardless of this, powders with different properties can also be mixed with the nanoporous plastic powder according to the invention.

production method

1. a) Zugabe von Vernetzer zu Monomer oder einer Mischung von Monomeren, um eine Monomermischung zu erhalten,
2. b) Polymerisieren der Monomermischung,
3. c) Trocknen des erhaltenen Polymers,
4. d) Quellen des Polymers mit einem Quellmittel,
5. e) das gequollen Polymer wird in eine CO₂-Atmosphäre mit einem Druck in einem Bereich von 50 bis 500 bar und einer Temperatur in einem Bereich von 0 bis 120 °C gebracht,
6. f) der Druck wird nach einer Wartezeit von 10 bis 180 Minuten auf den atmosphärischen Umgebungsdruck abgesenkt, womit der Polymerschaum erhalten wird,
7. g) der erhaltene Polymerschaum wird vermahlen.

In a further embodiment, the object underlying the invention is achieved by a process for producing the powder according to the invention in which at least the following steps are carried out:

1. a) addition of crosslinker to monomer or a mixture of monomers to obtain a monomer mixture,
2. b) polymerizing the monomer mixture,
3. c) drying the obtained polymer,
4. d) swelling the polymer with a swelling agent,
5. e) the swollen polymer is placed in a CO ₂ atmosphere with a pressure in a range of 50 to 500 bar and a temperature in a range of 0 to 120 ° C,
6. f) the pressure is lowered after a waiting time of 10 to 180 minutes to the atmospheric ambient pressure, whereby the polymer foam is obtained,
7. g) the resulting polymer foam is ground.

By grinding, for example, the specific surface of the foam material is even made optimally accessible at all, so that applications such as the above-mentioned application of the absorption of oil can only optimally result.

In step a), other additives may also be added to obtain the monomer mixture. These additives may be, for example, flame retardants, dyes, pigments, fillers or mixtures thereof.

Preferably, the polymer foam is ground with a mill, more preferably with an impingement mill. This is preferably cooled, more preferably cooled with liquid nitrogen. The polymer foam is preferably also cooled prior to milling, more preferably cooled with liquid nitrogen.

Preferably, the rotational speed of the mill is in the range of 100 to 14000 rpm.

Preferably, the polymer foam is ground in several grinding operations, preferably in 1 to 5 grinding operations.

Preferably, after step g), a clouding agent or a powder may be added as step h) and intimately mixed with the polymer powder in order to obtain the composition according to the invention. The addition of a further powder can also be carried out in step g), provided that the further powder / opacifier survives a grinding process without damage.

Preferably, the polymerization and foaming process take place spatially and temporally separated.

The swelling agent may be, for example, an organic solvent.

The monomer is preferably partially functionalized. Preferably, 0.001 to 1 mol% of all monomer molecules have an additional functional group compared to the other monomer molecules. This may be, for example, a carboxylate group.

Preferably, the pressure in step e) is in a range of 70 to 250 bar.

Preferably, the temperature in step e) is from 30 to 90 ° C.

Preferably, the monomer mixture also contains uncrosslinked polymer. Preferably, uncrosslinked polymer is also added in step a).

Preferably, the opacifier is added to the polymer foam after grinding.

Preferably, the monomer mixture is polymerized in step b) in water as a suspension. This is particularly advantageous, since one then obtains spherical polymer granules.

Preferably, the swelling agent is a ketone, more preferably acetone. The swelling of the polymer is preferably carried out under normal conditions by immersing the polymer in the swelling agent. The swelling is preferably done over a period of time in a range of 5 to 500 minutes. The swelling process preferably proceeds voluntarily and can already be carried out at room temperature and without additional input of energy. For an accelerated swelling, the polymer and the swelling agent can also be placed in a pressure-resistant container and the temperature can be increased. The swelling process, for example, reaches an end if no further swelling agent penetrates into the polymer. The swelling process thus reaches a plateau.

Further embodiments

The object underlying the invention is achieved in a further embodiment of the invention by the use of the powder according to the invention for vacuum insulation panels, oil-absorbing materials, insulation material and lightweight construction components.

The object underlying the invention is achieved in a further embodiment of the invention by a shaped body containing a powder according to the invention or a composition according to the invention.

Preferably, the shaped body is obtained by thermal compression.

• 1 Nanoschaum Granulat mit einem Durchmesser von 0.2 - 2 cm und einer Schüttdichte kleiner 500 kg/m³.
• 2 Nanoschaum Granulat (links), grob gemahlenes Nanoschaum-Pulver (mitte) und fein gemahlenes Nanoschaum-Pulver (rechts).
• 3 Nanoschaum Granulat Bruchkante im Rasterelektronenmikroskop, 50fache Vergrößerung
• 4 Nanoschaum Granulat Bruchkante im Rasterelektronenmikroskop, 10.000fache Vergrößerung
• 5 Grob gemahlenes Nanoschaum-Pulver im Rasterelektronenmikroskop bei intakter Nanostruktur, 50fache Vergrößerung und einer Körngröße von 20 bis 1000 µm.
• 6 Grob gemahlenes Nanoschaum-Pulver im Rasterelektronenmikroskop bei intakter Nanostruktur, 10.000fache Vergrößerung
• 7 Fein gemahlenes Nanoschaum-Pulver im Rasterelektronenmikroskop bei intakter Nanostruktur, 50fache Vergrößerung und einer Teilchengröße von 0,5 bis 200 µm.
• 8 Fein gemahlenes Nanoschaum-Pulver im Rasterelektronenmikroskop bei intakter Nanostruktur, 5.000fache Vergrößerung
• 9 Fein gemahlenes Nanoschaum-Pulver (rechts), Infrarot-Trübungsmittel (Graphit) (mitte) und die Mischung aus beidem rechts.
• 10 Fein gemahlenes und mit IR-Trübungsmittel gemischtes Nanoschaum-Pulver (links) und ein Formteil aus diesem rechts.

Further practical embodiments and advantages of the invention are described below in conjunction with the drawings. Show it:

• 1 Nanofoam granulate with a diameter of 0.2 - 2 cm and a bulk density of less than 500 kg / m ³ .
• 2 Nanofoam granules (left), coarsely ground nanofoam powder (center) and finely ground nanofoam powder (right).
• 3 Nanofoam granules fracture edge in the scanning electron microscope, magnification 50x
• 4 Nanofoam granulate fracture edge in the scanning electron microscope, magnification 10,000 times
• 5 Coarsely ground nanofoam powder in the scanning electron microscope with an intact nanostructure, 50x magnification and a grain size of 20 to 1000 microns.
• 6 Coarsely ground nanofoam powder in a scanning electron microscope with intact nanostructure, magnification 10,000 times
• 7 Finely ground nanofoam powder in a scanning electron microscope with an intact nanostructure, 50x magnification and a particle size of 0.5 to 200 microns.
• 8th Finely ground nanofoam powder in a scanning electron microscope with an intact nanostructure, 5,000 times magnification
• 9 Finely ground nanofoam powder (right), infrared opacifier (graphite) (center) and the mixture of both on the right.
• 10 Finely ground and mixed with IR opacifier nanofoam powder (left) and a molded part of this right.

In the following, abbreviations used in the polymer and polymer gel preparation, as used in the examples:

If a mixture of different monomers is used, this is clearly described by the mole fraction μ. $${\mu }_{MOnOmer1}=\frac{n_{MOnOmer1}}{{\displaystyle {\Sigma }_j{n}_{MOnOmerj}}}$$

The concentration of the crosslinker is described by the mole fraction v of crosslinker and monomer. By an optional multiplication of the value by 100, the unit mol% is obtained. $$\nu =\frac{{\displaystyle {\Sigma }_j{n}_{Vernetzer\text{j}}}}{{\displaystyle {\Sigma }_j{n}_{Vernetzer\text{j}}}+{\displaystyle {\Sigma }_j{n}_{MOnOmer\text{j}}}}\cdot 100$$

The initiator initiating and maintaining the polymerization is described by the mole fraction σ of initiator and monomer. $$\sigma =\frac{{\displaystyle {\Sigma }_j{n}_{Starter\text{j}}}}{{\displaystyle {\Sigma }_j{n}_{Starter\text{j}}+{\displaystyle {\Sigma }_j{n}_{MOnOmer\text{j}}}}}$$

The IR opacifier is referred to by a mass fraction based on the total mass of components used and abbreviated by τ. $$\tau =\frac{{\displaystyle {\Sigma }_j{m}_{TrübunGsmittel\text{j}}}}{{\displaystyle {\Sigma }_j{m}_j}}$$

The uncrosslinked polymer needed to stabilize the opacifier particles is described by the mass fraction π, which is the quotient of the mass of the uncrosslinked polymer and the total mass of components. $$\pi =\frac{m_{\text{uncrosslinked polymer}}}{{\displaystyle {\Sigma }_j{\text{m}}_j}}$$

The polymerized polymer is converted into a dimensionally stable polymer gel before the foaming process. The ratio of swelling agent and polymer is described by the mass fraction λ. $$\lambda =\frac{{\displaystyle {\Sigma }_j{m}_{Quellmittel\text{j}}}}{{\displaystyle {\Sigma }_j{m}_{Quellmittel\text{j}}+m_{POlymer}}}$$

embodiment

A polystyrene foam is as in the WO 2015 / 071463A2 prepared described (see, for example, there 7 , left foam). This polystyrene foam had a pore size in the median of 100 nm. The foam density was about 100 kg / m ³ . The result was a nanofoam granules with a diameter of 0.2 - 2 cm and a bulk density of less than 500 kg / m ³ . This is in 1 displayed.

The nanofoam granules had a homogeneous nanostructure inside with a particle density of 10 - 300 kg / m ³ . This was then ground in a mill. Care was taken to ensure that the temperature of the nanofoam during the grinding process did not rise above the glass or melting temperature of the polymer. For this purpose, the mill had to be permanently cooled. For this purpose, a collision current mill was particularly suitable, which was cooled with liquid nitrogen. Both the plant and the nanofoam granules to be ground were pre-cooled in advance with liquid nitrogen. Subsequently, the cooled nanofoam granulate was poured through an opening in the grinder. The grinder could be operated with different rotational speeds, as well as gap widths between rotator and stator and thus allowed a variation of the particle sizes of the powder. These moved between 1 and 1000 μm. The median particle diameter was 8 μm. Grain size distributions were always obtained. The powder was collected at the exit of the plant. Afterwards the powder was dried and could be further processed. The result can be seen in 2 ,

The milled powder showed a slightly lower bulk density than the bulk density of the granules used. This is related to the packing behavior of the grains. The nanostructure of the individual Grit persisted during the grinding process. This was shown by scanning electron micrographs 3 to 8th ,

It had surprisingly been found that the thermal resistance could be improved by comminuting the starting granules into a powder. Furthermore, a powder was ideally suited for combination with other powdery materials that can be mixed with the nanoporous powder to improve properties. These include, for example, a minimization of an IR radiation contribution to the heat conduction, which could be reduced by the addition of a powdered IR opacifier ( 9 ). From the composition comprising the powder and opacifier according to the invention it was also possible to produce shaped articles ( 10 ).

The combination of two powders offered the distinct advantage that the nanofoam was separated from e.g. an IR opacifier could be produced and only the finished material could be subsequently combined with any material. This could be in addition to an IR opacifier, a flame retardant, or powder materials such as aerogels, silica, etc. Any material properties could be combined so easily.

The thermal conductivity was determined with a disk device in the usual way: material λ10 Density [kg / m ³ ] [MW / mK] Nano foam granulate 30.0 75 (bed) coarse nanofoam powder 28.1 65 (bed) fine nanofoam powder 26.9 60 (bed) fine nanofoam powder with 5% by weight IR opacifier (graphite) 25.0 62 (bed) fine nanofoam powder with 5% by weight IR clouding agent (graphite) as molding 22.9 120

Thermal conductivity measurement data determined at a mean temperature of λ10 in a disk device.

The features of the invention disclosed in the present description, in the drawings and in the claims may be essential both individually and in any desired combinations for the realization of the invention in its various embodiments. The invention is not limited to the described embodiments. It can be varied within the scope of the claims and taking into account the knowledge of the person skilled in the art.

In general, for example, a person skilled in the art will distinguish between granules and powder in their different size ranges of the individual particles. Both terms summarize a collection of multiple particles. A granule has larger particles than a powder. Ideally, the particles have a spherical shape and thus can be geometrically ideally described with a diameter. Since in particular for powder particles no geometric shape can be assumed (s. 5 . 7 and 8th ), it makes more sense to speak of a particle size. In this case, the particle size denotes the largest possible distance, which is possible by a straight line in the particle. This can also be determined in practice by a sieving process.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10358800 A1 [0002]
• EP 0849309 B1 [0002]
• US 4636527 A [0002]
• WO 1993022371 A1 [0002]
• EP 0372343 B1 [0003]
• EP 0620246 B1 [0003]
• EP 2402389 A2 [0003]
• DE 102008047594 A1 [0003]
• DE 202010013850 U1 [0003]
• EP 2092002 B1 [0003]
• US 8114476 B2 [0003]
• US 20100148110 A1 [0003]
• EP 16189993 [0006]
• DE 102013223391 A1 [0008]
• WO 2015/071463 A2 [0084]

Cited non-patent literature

• Okolieocha C., Raps D., Subramaniam K., Altstädt V .; European Polymer Journal 73; 500-519; 2015 [0007]
• DIN 51603 [0021]
• DIN EN ISO 14688 [0022]
• Ferkl P., Pokorny R., Bobak J, Chem Eng Sci; 97: 50-8; 2013 [0049]

Claims (16)

Powder of foam, characterized in that a. the median particle size of the powder is in a range of 0.5 to 1000 μm, and b. the median of the diameter of the pores of these particles is in a range of 10 to 500 nm. Powder according to Claim 1 , characterized in that the foam is a polymer foam, in particular a partially crosslinked polymer foam. Powder according to one of the preceding claims, characterized in that the density of the foam is in a range of 30 to 300 kg / m ³ . Powder according to one of the preceding claims, characterized in that the specific surface area is in a range from 5 to 500 m ² / g, more preferably in a range from 10 to 300 m ² / g and most preferably in a range from 20 to 200 m ² / g lies. Powder according to one of the preceding claims, characterized in that the FOM factor is at least 0.01 and less than 1.2, the FOM factor being defined as $$\text{FOM}=\left(\text{In}\left(\text{dpore / 0}\text{, 15 nm}\right)\right)/\text{VER}$$

where dPore is the diameter of the pores in the median and VER is the volume-expansion ratio, which in turn is defined as $$\text{VER}=\left(\text{Volume foam}\right)/\left(\text{Volume of polymer}\right),$$

Composition containing powder according to one of the preceding claims and opacifiers. Composition according to Claim 5 , characterized in that the composition contains 1 to 30 wt.% opacifier and 70 to 99 wt.% Foam powder. Composition according to Claim 5 or 6 , characterized in that the opacifier is selected from the group of graphite, carbon black, Multiwallcarbonnanotubes, fullerene, graphene, metal oxide and mixtures thereof. Composition according to one of Claims 5 to 7 , characterized in that the clouding agent has an average particle size in the median in a range of 0.01 to 5 microns. A process for preparing the powder according to any one of the preceding claims, wherein at least the following steps are carried out: a) adding crosslinker to monomer or a mixture of monomers to obtain a monomer mixture, b) polymerizing the monomer mixture, c) drying the resulting polymer d) swelling the polymer with a swelling agent, e) the swollen polymer is placed in a CO ₂ atmosphere at a pressure in a range of 50 to 500 bar and a temperature in a range of 0 to 120 ° C, f) the Pressure is lowered after a waiting time of 10 to 180 minutes to the atmospheric pressure, whereby the polymer foam is obtained, g) the obtained polymer foam is ground. Method according to Claim 10 , characterized in that after step g) as step h) a clouding agent is added to obtain the composition according to the invention. Method according to one of Claims 10 or 11 , characterized in that the monomer mixture is polymerized in step b) in water as a suspension. Method according to one of Claims 10 to 12 , characterized in that the swelling agent is a ketone, more preferably acetone. Use of the powder according to any of 1 to 10 for vacuum insulation panels, oil absorbing materials, insulating material and lightweight construction components. Shaped body containing a powder according to one of Claims 1 to 4 or a composition according to any one of Claims 5 to 10 , Shaped body according to Claim 15 , characterized in that it is obtained by thermal compression.

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