WO2010115919A1

WO2010115919A1 - Method for producing hollow bodies comprising freely mobile particles encapsulated therein

Info

Publication number: WO2010115919A1
Application number: PCT/EP2010/054580
Authority: WO
Inventors: Ingo Bellin; Julien Courtois; Jan Kurt Walter Sandler; Klaus Hahn; Christoffer Kieburg; Norbert Wagner; Ketan Joshi; Alexander Traut; Bernd Kieback; Günther STEPHANI; Ulrike Jehring; Peter Quadbeck
Original assignee: Basf Se
Priority date: 2009-04-07
Filing date: 2010-04-07
Publication date: 2010-10-14

Abstract

The invention relates to a method for producing hollow bodies which comprise freely mobile particles encapsulated in the hollow body. According to said method, cores of substantially closed-cell polymer foam particles in which particles are dispersed are coated with a sinterable material and a binder-containing composition. The coated cores are subjected to a heat treatment during which the polymer and the binder are expelled and the sinterable material is sintered to give a closed shell.

Description

Process for the production of hollow bodies with enclosed freely mobile particles

description

The invention relates to a method for producing hollow bodies with enclosed in the hollow body, freely moving particles.

According to DE 10 2004 003507, hollow bodies with trapped, freely movable particles serve as sound-absorbing structures, in particular for applications in which structure-borne noise occurs and requires damping. In the production method described in DE 10 2004 003507 and illustrated by exemplary embodiments, a coating formed from at least two individual layers formed one above the other is applied to a core of an organic substance. In this case, in the layer applied directly on the surface of the core, solid particles of a substance are contained, which are formed from a material having a higher sintering temperature than particles of a material which are contained in a further applied layer. After the coating, a heat treatment is carried out, in which first the organic constituents are expelled, the pulverulent particles of the layer, which are formed directly on the core, are released, and the powdery particles of the outer layer are sintered into a shell. The hollow structural elements are used as a loose bed or, after sintering by gluing, soldering or sintering material fit together to form bodies.

The successive application of several different layers on the cores is complex and technically demanding. In the process of DE 10 2004 003507, the coated cores (green spheres) are first sintered before the resulting hollow spheres are combined to give moldings. It is very expensive, green balls z. B. stick together, since the integrity of the individual layers is adversely affected by the bonding.

DE-A 2342948 discloses a method for producing hollow bodies consisting of a cavity enclosing a shell of a ceramic material. For this purpose, moldings of a combustible or heat-decomposable organic material are coated with a green ceramic powder and a binder, and then the coated moldings are heated to 200 to 2000 ^° C. to burn or decompose the organic material and burn the binder or decomposes or merges into its own ceramic bond and the ceramic material sinters. EP-A 300 543 describes a method for producing metallic or ceramic hollow spheres by applying a solid layer to a substantially spherical particle of foamed polymer and pyrolyzing the coated polymer core. The particles of foamed polymer, preferably of expanded polystyrene, are treated with agitation with an aqueous suspension containing dissolved or suspended binder and metallic and / or ceramic powder particles, the coated and dried particles at 400 to 500 ⁰ C pyrolyzed with movement and at Temperatures of 900 to 1500 ⁰ C sintered under motion.

The invention is therefore based on the object to provide a method for producing hollow bodies with trapped, freely movable particles, which is easier to carry out and allows the more convenient production of moldings from interconnected hollow bodies.

The object is achieved by a method for producing hollow bodies with freely movable particles enclosed in the hollow body, in which cores of essentially closed-cell polymer foam particles in which particles are dispersed, with a composition containing a sinterable material and a binder coated and the coated cores subjected to a heat treatment in which the polymer and the binder are expelled and the sinterable material sintered into a closed shell.

The process according to the invention starts from cores of essentially closed-cell polymer foam particles in which particles are dispersed.

The term "substantially closed-cell" means that more than 70%, preferably more than 80% of the cells of the individual foam particles are closed-celled (determined, for example, according to ASTM D 2856-87, Method C). The closed-cell polymer foam particles are suitable for coating with the sinterable material and a binder-containing composition due to their liquid-impermeable property.

In preferred embodiments, the bulk density p (in g / l) of the cores and the weight fraction x of the dispersed particles satisfy the weight of the cores of the inequality:

p. (1-x) <400 g / l

especially

50 g / K p «(1-x) <250 g / l. The weight proportion x of the dispersed particles in the weight of the cores is preferably 0.10 to 0.80, in particular 0.40 to 0.70.

Preferably, the cores are substantially spherical. The cores generally have a diameter (or a length in the direction of the largest spatial extent in the case of non-spherical cores) of 0.5 to 30 mm, in particular 1 to 10 mm.

Substantially closed cell polymer foam particles in which particles are dispersed are obtainable, for example, by first preparing an expandable thermoplastic polymer granule by blending an organic blowing agent and filler particles into a polymer melt and granulating the melt. The expandable, thermoplastic polymer granules can then be foamed by means of hot air or steam into foam particles. Such a method is described for example in DE 10 358 786 A1, to which reference is made in full.

Suitable polymers include thermoplastic polymers, such as, for example, styrene polymers, polyamides (PA), polyolefins, such as polypropylene (PP), polyethylene (PE) or polyethylene-propylene copolymers, polyacrylates, such as polymethylmethacrylate (PMMA), polycarbonate (PC ), Polyesters, such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), polyethersulfones (PES), polyether ketones or polyether sulfides (PES) or mixtures thereof. Styrene polymers are particularly preferably used.

As styrene polymers, glassy polystyrene (GPPS), impact polystyrene (HIPS), anionically polymerized polystyrene or impact polystyrene (A-IPS), styrene-α-methstyrene copolymers, acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN) Acrylonitrile-styrene-acrylic ester (ASA), methyl acrylate-butadiene-styrene (MBS), methyl methacrylate-acrylonitrile-butadiene-styrene (MABS), α-methylstyrene-acrylonitrile (AMSAN) polymers or mixtures thereof or with polyphenylene ether (PPE) used.

The blowing agent-containing polymer melt usually contains one or more blowing agents in a homogeneous distribution in a proportion of 2 to 10 wt .-%, preferably 3 to 7 wt .-%, based on the melt. Suitable blowing agents are physical blowing agents, such as aliphatic hydrocarbons having 2 to 7 carbon atoms, alcohols, ketones, ethers or halogenated hydrocarbons. Preference is given to using isobutane, n-butane, isopentane, n-pentane.

Expandable styrene polymer pellets (EPS) suitable according to the invention generally have bulk densities of from 590 to 1200 g / l (before foaming), depending on the nature and content of the dispersed particles. The density of the dispersed particles used in the present invention is generally from 1,000 to 20,000 g / l. In the cores, it is also possible to disperse precursor compounds which undergo a chemical and / or morphological transformation during the heat treatment, such as, for example, As the drainage of a hydroxide to an oxide.

The particles generally have a higher sintering temperature than the sinterable material, for. B. a higher by at least 100 K sintering temperature.

In preferred embodiments, the particles are selected from inorganic materials, e.g. A carbide such as silicon carbide or boron carbide; a nitride, silicon nitride, aluminum nitride, boron nitride or titanium nitride; Silicide and / or aluminide. Particularly preferred particles are oxides, such as Al 2 O 3 (in all modifications, in particular as corundum, boehmite, AIO (OH) or as aluminum hydroxide), ZrO ₂ , Y ₂ O 3, MgO, ZnO, CdO, SiO ₂ , TiO ₂ , CeO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , BaTiO ₃ , CuO, NiO, CoO, Co ₃ O ₄ .

It may be z. These may be, for example, particles which are usually used for the production of glass (eg borosilicate glass, soda lime glass or silica glass), glass ceramics or ceramics (eg based on the oxides SiO ₂ , BeO, Al ₂ O ₃ , ZrO ₂ or MgO or the corresponding mixed oxides), or non-oxide ceramics such as silicon nitride, silicon carbide, boron nitride nitrides such as BN, AIN, Si ₃ N _{4 and} Ti ₃ N ₄ , or boron carbide). It can also be particles that serve as fillers or pigments. Technically important fillers are z. B. fillers based on SiO ₂ , such as quartz, cristobalite, tripolite, novaculite, kieselguhr, silica, fumed silicas, precipitated silicas and silica gels, silicates, such as talc, pyrophyllite, kaolin, mica, muscovite, phlogopite, vermiculite, Wollastonite and perlite, aluminas and titania.

Particularly preferred materials for the particles are ZrO ₂ , Al ₂ O ₃ , TiO ₂ and SiO ₂ or mixtures thereof.

In general, the mean size of the dispersed particles is 5 nm to 500 μm, in particular 0.1 to 50 μm (measured by analytical ultracentrifuge or dynamic light scattering).

For better dispersion of the particles in the polymer melt, optional dispensing aids may be included. Examples are oligomeric polyethylene oxide having an average molecular weight of 200 to 600, stearic acid, stearic acid amide, hydroxystearic acid, fatty alcohols, fatty alcohol sulfonates and block copolymers of ethylene oxide and propylene oxide, and also polyisobutylene. The cores are coated with a composition containing a sinterable material and a binder. The coating of sinterable material and binder can be applied to the cores in various ways. For example, mixing the sinterable material with the binder in the form of a suspension and covers the cores with this suspension, for example in a mixer, fluidized bed reactor or granulation. The cores are expediently introduced into a fluidized-bed reactor. The dispersion of the sinterable material in the solution or dispersion of the binder is introduced into the fluidized bed. The temperature of the fluidizing gas is z. B. between 70 and 120 ⁰ C. layer application and drying are generally completed in a period of 5 to 60 minutes.

Alternatively, the cores may first be uniformly sprayed with the liquid binder and then powdered on the sinterable material and, if the desired layer thickness is not reached in a single operation, this operation is repeated until the desired coating thickness is obtained.

If necessary, the coated cores are then dried.

Suitable sinterable material are metal powders and ceramic powders. It is also conceivable to mix the metal or ceramic powders. The sinterable ceramics may include, for example, nitride, oxide and silicate ceramics and carbides.

Examples of sinterable ceramic powders are oxidic ceramic powders such as Al 2 O 3, ZrO 2, Y 2 O 3, as well as non-oxide ceramic powders such as SiC or SisISU.

Preferably, the sinterable material is a metal powder. Examples of metals which are in powder form are aluminum, iron, in particular iron carbonyl powder, cobalt, copper, nickel, silicon, titanium and tungsten. As powdered metal alloys, for example, high or low alloyed steels and Metallle- alloys based on aluminum, iron, titanium, copper, nickel, cobalt or tungsten, such. As bronze, to call. Both powder of already finished alloys and the powder mixtures of the individual alloy components can be used. The metal powder, metal alloy powder and Carbonylmetallpulver can also be used in a mixture.

As the metal powder, carbonyl iron powder is preferable. Carbonyl iron powder is an iron powder produced by thermal decomposition of iron carbonyl compounds. In order to maintain flowability and to prevent agglomeration, it may be coated, for example, with SiC 2 O. The corrosion inhibitor used may preferably be iron phosphide powder. The binder is generally present as a solution or dispersion, preferably in an aqueous medium. As the binder, a variety of polymers can be used. In particular, polymers or copolymers from the group of vinyl ester polymers, such as polyvinyl acetate, copolymers of vinyl acetate / ethylene, vinyl acetate / ethylene / vinyl chloride, vinyl acetate / acrylic ester, vinyl acetate / maleic di-n-butyl ester, vinyl acetate / vinyl laurate, vinyl acetate / acrylate; partially saponified polyvinyl acetate, polyvinyl alcohol; polybutyral; Polyamides, such as polyvinylpyrrolidone; Polyacrylates, copolymer of styrene / acrylate; Celluloseester; Phenolic resins, amino resins such as urea resins or melamine resins; and epoxy resins used. Simple tests can be used to determine which binder is the most suitable considering the selected powder material and the pyrolysis and sintering conditions given. In particular, polyvinyl alcohols and cellulose esters are suitable.

The individual cores coated in this way can be subjected to heat treatment as such or cohesively bonded coated cores before the heat treatment in order to obtain shaped bodies. The cores can z. B. are glued together. The bonding can z. Example, by moistening the coated cores with a solvent that dissolves the binder, and then brings the cores together in the desired arrangement. In this way, it is possible to provide self-supporting sound-insulating structures which also have a certain degree of mechanical strength and, within certain limits, achieve load-bearing properties. Thus, for example, partitions, door elements or floors of vehicles can be obtained in this form with hollow bodies according to the invention.

By a heat treatment, the polymer of the cores and the binder of the coating are expelled. The sinterable material is sintered into a closed shell. The term "expelling" is intended to include upstream decomposition and / or pyrolysis operations. The heat treatment can be carried out in a single-stage or multistage process. Taking into account the binder according to the type and amount and sufficient layer thickness, the dried solid layers have sufficient strength, so that the coated cores can be subjected to a pyrolytic decomposition process, without the shell loses its shape. During the pyrolysis of the coated foam core, the binder of the solid layer volatilizes and leaves behind a self-supporting hollow sphere with a porous shell structure.

The pyrolysis of the coated foam particles can be carried out in air, inert gas or under reducing conditions, depending on the type of powder used. The heating time to a temperature of about 500 ^° C. is up to 3 hours and depends on the type and composition of the polymer used. To increase the so-called green strength, it may be useful for metallic powders be to pyrolyze under slightly oxidizing conditions. This achieves better removal of residual carbon and strength-enhancing oxide skin on the surfaces of the metal powder particles.

The pyrolytic treatment, which serves both to remove the coated polymer core and to at least partially remove the organic binder, is followed by a sintering process. This sintering process at a temperature of 900 to 1500 ⁰ C is in an oven, for. B. rotary kiln, Krähl- or belt furnace made. The atmosphere in the kiln aggregate can be matched to the powder material used for coating. It can therefore be used in a vacuum, under oxidizing or reducing conditions and under inert gas.

It is possible to prevent the sintering of the individual hollow bodies either by movement or by an outer coating with inert powder, if this does not undergo any chemical or physical reactions with the hollow body material at the temperature used. Such inert powders can be easily removed mechanically or chemically from the hollow bodies after the sintering process. They can also act as a supporting shell for the actual hollow sphere during the pyrolysis and sintering process, in particular when the wall thickness of the hollow body is very thin or the actual hollow body powder layer does not yet have sufficient green strength after pyrolysis. Suitable inert powders, depending on the hollow body material, are e.g. Carbon, aluminum hydroxide or chalk.

The pyrolysis and the sintering process can also be carried out without constant movement of the coated foam particles. In this case, the coated foam particles are introduced into a mold with perforated walls and by the action of heat energy (eg about 100 ⁰ C) and optionally by mechanical pressure, the foam particles are "re-foamed", with stronger mold filling and compaction and bonding takes place , After cooling, the mold contents can be removed and handled as a dimensionally stable body. That is, the molded article of good "green strength" can be pyrolyzed without loss of its shape and then sintered. According to this embodiment of the invention, high strength lightweight bodies with open and closed cells are achieved.

However, individual hollow bodies can also be deformed after the heat treatment, if, for example, a solid combination of structural elements to a sound-absorbing lightweight component is desired. As already mentioned, the hollow bodies can form a sound-absorbing structure in the form of a loose bed. But it is also possible to connect the hollow body after the thermal treatment cohesively with each other, which can be achieved by gluing, soldering or sintering. However, hollow bodies produced according to the invention can also be disposed within a Matrix, which is possible, for example, with a suitable hardenable plastic, such as an epoxy resin, or a relatively low-melting metal.

The invention will be explained in more detail with reference to the following examples.

Example 1 :

1 liter of spherical polystyrene foam particles (average particle size about 2.3 mm) with an aluminum oxide content of 40 wt.% And a bulk density of 130 g / l was mixed with a suspension of 260 g of carbonyl iron powder and 10 g of iron phosphide powder in an aqueous solution of polyvinyl alcohol in a fluidized bed coated.

The green spheres thus produced were then subjected to a heat treatment under a protective gas atmosphere with a maximum sintering temperature of 1 120 ⁰ C. The organic components were expelled and the spherical shells were consolidated by sintering. In the balls obtained, the aluminum oxide particles were freely movable in the dense spherical shell. The balls were usable as damping elements.

Example 2:

Green spheres, which were obtained according to Example 1, were bonded to form bodies by means of an aqueous ethanol solution. The moldings were subjected to a heat treatment as described in Example 1. In the resulting moldings, the aluminum oxide particles were freely movable in the hollow structural elements. The moldings were usable as damping elements.

Comparative Example:

1 liter of spherical polystyrene particles (average particle size about 2.3 mm) having an aluminum oxide content of 40% by weight and a bulk density of 740 g / l was mixed with a suspension of 260 g of carbonyl iron powder and 10 g of iron phosphide powder in an aqueous solution of polyvinyl alcohol in a fluidized bed coated.

The green spheres thus produced were then subjected to a heat treatment under a protective gas atmosphere with a maximum sintering temperature of 1 120 ⁰ C. Due to the high proportion of the polymer to be pyrolyzed, a mechanical rupture of the coating occurred.

Claims

claims

1. A process for the production of hollow bodies with hollow body enclosed, free-moving particles, comprising cores of substantially closed-cell polymer foam particles, in which particles are dispersed, coated with a sinterable material and a binder composition and the coated cores of a Heat treatment in which the polymer and the binder are expelled and the sinterable material sintered into a closed shell.

2. The method of claim 1, wherein the bulk density of the cores p (in g / l) and the weight fraction x of the dispersed particles satisfy the weight of the cores of the inequality:

p «(1-x) <400 g / l.

3. The method according to claim 1 or 2, wherein the weight proportion x of the dispersed particles in the weight of the cores is 0.10 to 0.80.

4. The method according to any one of the preceding claims, wherein the particles are selected from inorganic substances.

5. The method of claim 4, wherein the particles comprise a carbide, nitride, oxide, silicide and / or aluminide.

6. The method of claim 5, wherein the particles are selected from ZrO 2, Al 2 O 3, TΪO 2 and SiO 2 or mixtures thereof.

7. The method according to any one of the preceding claims, wherein the mean size of the particles is 5 nm to 500 microns.

8. The method according to any one of the preceding claims, wherein the sinterable material is a metal powder.

9. The method of claim 7, wherein the metal powder is carbonyl iron powder.

10. The method according to any one of the preceding claims, wherein the polymer comprises polystyrene.

A method according to any one of the preceding claims, wherein the cores are substantially spherical.

12. The method according to any one of the preceding claims, wherein the cores have a diameter of 0.5 to 30 mm.

13. The method according to any one of the preceding claims, in which one connects co-coated cores before the heat treatment cohesively.

14. The method according to any one of the preceding claims, wherein the cores obtained by foaming expandable thermoplastic polymer particles in which particles are dispersed by means of hot air and / or water vapor to polymer foam particles.