EP1100620B1 - Method and device for ultra-fine milling and mixing solid materials - Google Patents

Abstract

In a method for ultrafine grinding of solid particulate material to mean particle sizes far below 1 micrometer and/or for mixing of powder and agglomerate material with mean particle sizes in the range of nanometers, the material to be ground and/or mixed and an grinding/mixing additive are filled into a cooled grinding chamber containing loose grinding media. By motion of the grinding media relative to adjacent media and to the walls of the grinding chamber the material is ground to the desired particle size and/or is finely mixed. Subsequently the additive is removed from said material. For the production of particle sizes in the range of nanometers and/or for mixing particles of this size range, the method comprises that grinding and/or mixing is carried out in a cooled atmosphere in the presence of a fine grained solidified additive which is chemically inert to said material, preferably water ice or solid carbon dioxide, at temperatures below their melting or sublimation temperature. Subsequently said additive is removed from said material by evaporation. The additive can be evaporated or is volatile at temperatures below 50° C. at ambient pressure. An apparatus for carrying out such method is disclosed.

Description

The invention relates to a method and the use of a known device for ultrafine grinding and - Mix of solid materials to medium grain sizes wide less than 1 µm or on so-called nano-fineness and / or Mixture of powders with medium grain sizes in the nano range (so-called nano powder), in which the feed and an additive placed in a grinding container with loose grinding media and by means of the releasable relocatable to each other Grinding media crushed or mixed to the desired fineness and then the additive from the regrind is separated.

For ultra-fine grinding and ―mixing of solid materials mills with loose grinding media are used. Such mills are next to ball mills, vibratory mills and agitator mills also planetary ball mills. The smaller particles are, the higher is the strength of the primary particles or - for nano powders - that of the particle agglomerates always present, and the more volume-specific mechanical energy is available Grinding of the primary or agglomerate particles necessary. you observed a lower, material-dependent particle size, under which no more brittle shredding takes place. finest Particles behave plastically. Nano powders are known with Methods only rough, but not fine or complete miscible, since their agglomerates are not sufficiently shredded or be divided.

The plastic behavior and the high volume-specific mechanical energies resulting from the collision of loose grinding media transferred to the regrind particles lead to the crushing to the fact that already crushed particles solid agglomerates are pressed together, i.e. reactglomerate. The high temperatures that occur can even lead to sintering together, so that the agglomerates Achieve strengths of the original particle material. In conventional grinding there is therefore a lower one Particle size that is not significantly undercut can. It depends on the material and is of the order of magnitude of 1µm.

To reduce the plastic behavior you have the grinding container z. B. of ball, vibrating or agitator mills from outside (via a cooling jacket) or from the inside (e.g. via the Agitator shaft or other internal parts) cooled, mostly on Temperatures a little below freezing, (DE 92 08 275 U1), or liquid gas has been added to the grinding container.

When crushing rubber waste, liquid nitrogen is used in the externally cooled grinding bowl of a vibratory mill (Rod mill) sprayed and evaporated (US 5,513,809 A).

Has in the manufacture of aqueous pigment dispersions to disperse by crushing a 70 to 80% water containing filter cake after adding a stabilizer partially, that is to say about 50%, frozen and by stirring with a stirrer, e.g. B. blade stirrer, by means of of the ice crystals formed the agglomerates into primary particles with a grain size of about 0.2 to 0.3 µm and above crushed (US 4,013,232 A).

There are also solid particles with a fineness of 1 to 20 µm tries to shred (DE 37 02 484 A1) that previously in particles usually pre-shredded to about 50 µm with swelling liquid, in particular water or soaked (possibly supported by ultrasound) and then repeatedly frozen and thawed. This The process is suitable - if at all - for only a few materials and is extremely complex.

Reagglomeration has been done by adding additives to the Tries to counteract regrind. You have to shred it Material soft substances, so-called additives, z. B. rock salt (DE 35 05 024 A1) or graphite are softer or more viscous than the regrind and in which the particle fragments when crushed in dispersed Form remain distributed. This allows particles produce in the size range of well below 1µm, i.e. nano-particles. After grinding, the soft additive is removed - with rock salt by dissolving in water, with graphite by burning.

This method has limitations and disadvantages. That done crushed or ground regrind must in the solvent, with which the added substance, the additive, is washed out will be insoluble. In general, certain remain Contamination back, which is unacceptable for many products is. Graphite has been used as an additive and if this is removed by burning, there is a risk chemical reactions with the regrind.

Highly dispersed particle systems of the finest fineness in the nanometer range are becoming increasingly important, which is why a suitable one Grinding and mixing technology is necessary, with which also newer materials in the field of ceramic fabrics, materials for the optical and electronic industry, superconducting ceramic and composite materials and pharmaceutical Allow fabrics to shred.

The invention has for its object a method and to indicate the use of a mill known per se for this purpose, with which particles in the nanometer range are generated and / or mix completely homogeneously for which the described restrictions no longer apply and the possible uses open up for materials that have existed up to now do not crush to finenesses well below 1 µm or in the nanometer range let mix.

This problem is solved with a method for ultrafine grinding from solid materials to grain sizes less than 1 µm and / or for mixing powders and agglomerates with grain sizes in the nanometer range, for the feed and an additive placed in a grinding container with loose grinding media and by means of the relative movement Walls and grinding bowl walls and, if necessary, grinding tools (agitator mills) crushed or mixed to the desired fineness and then the additive is separated from the material is, according to the invention in that the grinding in cooled Atmosphere in the presence of a frozen, facing each other inert to the goods, at ambient pressure at temperatures Additive vaporizable below 50 ° C at temperatures below its melting or sublimation temperature is carried out and that then the additive is removed from the ground material by evaporation. The additive should be liquid or at ambient or room temperature vaporous or gaseous and in solid state during grinding / mixing available. Water-ice has become an additive or carbon dioxide ice (solid carbon dioxide) or the like Substances such as refrigerant R134a have proven particularly effective. When grinding with the addition of water-ice one is expediently Temperature below about -30 ° C, in particular -50 ° C, maintained, while grinding using carbon dioxide ice Temperatures below about -80 ° C advantageous are. An embodiment of the method provides that the Grist or the mix of grist and additive before the task is pre-cooled in the grinding container.

To cool the atmosphere in the grinding vessel to low temperatures, which is a melting or evaporating of the additive prevent appropriately cooled refrigerants, but also liquefied gases such as liquid nitrogen.

The admixture of fine-grained water-ice or solid carbon dioxide as an additive for grinding / mixing at deep Temperatures have the advantage that the ground or mixed material is treated gently and that no impurities remain. A re-agglomeration of already shredded, very much fine particles are suppressed during grinding.

The use specified in claim 7 grinders known The way in which the vibratory mills and agitator mills mentioned, is after appropriate addition for the requirements cooling to very low temperatures is possible. To is a cooling jacket with inlet and outlet connections for the Cooling water is provided around the grinding container. According to the invention however, a cooling jacket and a grinding container must be provided, the very low temperatures of a refrigerant too to withstand grinding operations. The refrigerant is at the required very low temperatures brought by a chiller when it is not in liquid Condition is delivered. The cooling capacity has to be so big be that the electrical absorbed by the mill in the grinding chamber Energy that is almost completely converted into heat is transported away. When using ball and Vibrating mills generally suffice from one surrounding the grinding container Cooling jacket because the grinding media and the regrind are sufficient circulated and repeatedly against the grinding vessel walls heat dissipation. With agitator mills is additional provide cooling of the agitator shaft in order to achieve an intensive Ensure heat exchange.

1. Kühlen des Mahlraumes durch Einleiten von flüssigem Stickstoff in den den Mahlraum umgebenden Kühlmantel;

2. Befüllen der gekühlten Mühle durch eine Befüllungsöffnung mit Mahlkörpern, dem zu zerkleinernden, gfs. vorgekühlten Material geeigneter Ausgangsfeinheit, mittlere Partikelgröße, vornehmlich unter etwa 20µm, bzw. den zu mischenden Nano-Pulvern und dem kalten, festen, feinkörnigen Additiv;

3. Inbetriebnahme der Mühle und Mahlen oder Mischen; und

4.Abschalten, Erwärmen, Gutentnahme, Trocknen (wenn das Additiv Wasser ist).

A discontinuous vibratory mill is operated with the following steps:

1. cooling the grinding chamber by introducing liquid nitrogen into the cooling jacket surrounding the grinding chamber;

2. Filling the cooled mill through a filling opening with grinding media, the to be shredded, if necessary. pre-cooled material of suitable starting fineness, average particle size, mainly below about 20 µm, or the nano-powders to be mixed and the cold, solid, fine-grained additive;

3. Commissioning of the mill and grinding or mixing; and

4. Switching off, heating, removal of goods, drying (if the additive is water).

The grinding device works discontinuously. A continuous grinding is also possible with appropriate flexible heat-insulated supply and discharge lines. Furthermore must constantly pre-cooled feed and fine-grained additive generated and abandoned. The same is the finished / mixed Good to drain continuously and are gfs. discharged Separate grinding media and, if necessary, in the circuit, possibly after Classification, attributed to the grinding room.

The fields of application of the invention include the generation of Using nanoparticles from pharmaceutical substances in particular of solid carbon dioxide as an additive, less often of water ice. Cold grinding makes even sensitive ones Substances not harmed. A conventional one Cool grinding without the addition of additives would not lead to production of nano-particles.

The invention can also be used in the production of high-purity nano-particles for nanostructured materials (Ceramics, metals, nano-composite materials, optoelectronic Nano-materials). Finally, the invention is also suitable for mixing nano powders made in a different way were. Nano-particles are extremely difficult to be homogeneous to mix with each other.

Fig. 1

eine Draufsicht einer Schwingmühle, z. T. im Schnitt,

Fig. 2

die Schwingmühle nach Fig. 1 in einer Schnittansicht längs der Linie II-II, und

Fig. 3

ein Fließbild einer Mahlanlage für die kontinuierliche Ultrafein-Mahlung.

An embodiment of a grinding device according to the invention is explained in more detail with reference to a drawing, in which:

Fig. 1

a plan view of a vibratory mill, for. T. on average,

Fig. 2

1 in a sectional view along the line II-II, and

Fig. 3

a flow diagram of a grinding plant for continuous ultrafine grinding.

A vibratory mill 1 has a spring-loaded support on the floor 16 Grinding container 2, the cooling jacket 3 and one Isolation 4 is completely surrounded. For supply and discharge of a refrigerant are in the right end wall in FIG. 1 of the cooling jacket 3 supply connections 7 and discharge connections 8 for e.g. liquid nitrogen is provided as a refrigerant. On the left side of the grinding container 2 in FIG. 1 a loading and unloading opening 10 is provided is closed by a cover 11. About this an insulating plate 5 is provided which is used to open the Cover is removable. The loading takes place through the opening 10 of the grinding container 2 with grinding balls, the one to be crushed pre-shredded material and lumpy, sufficient fine-grained, solidified additive in the form of water-ice or sublimed carbon dioxide or equivalent Additive such as R134a refrigerant. A swing frame 14, on which the grinding container with the cooling jacket and the insulation is attached and which is by means of spring elements 15th supported on the machine frame floor 16, also takes a drive shaft 17 on which an eccentric mass 18 in known Way is stored. This is via the drive shaft 17th driven by an electric motor and thus moves the grinding container 2 in vibrations. For this reason, the supply lines and leads 7,8 to the cooling jacket correspondingly elastic be trained.

Before loading the grinding container through its loading opening 10 with grinding media, feed and additive this by introducing the refrigerant into the cooling jacket cooled. Then the drive is switched on, and the grinding or mixing process begins. This can last longer Time up to several hours to achieve sufficient Last in the nanometer range.

Fig. 3 shows the flow diagram of a continuously operated Plant with a vibrating mill 1 for performing the method according to the invention. The vibratory mill 1 is a Line 44 from a pre-cooling device 30 for the regrind or the mix, which is at room temperature via a Line 31 supplied and discharged through a line 32 becomes. The additive is transferred to a processing device 40 a line 41 is supplied and discharged via a line 42. The device 40 serves to pre-cool the additive to To bring solidification and the solidified coarser particles pre-shred to obtain a fine-grained additive. Together become the pre-cooled good and the processed additive abandoned via a line 44 of the vibratory mill 1, the Cooling jacket supplied via line 7 liquefied nitrogen and from which the nitrogen after heating, if necessary gaseous - is withdrawn via line 8. The good is continuously discharged via a line 46, the Outlet of the grinding container with a separation device for retention the grinding balls can be provided. The supply line 44 and the discharge line 46 must be flexible, the supply line 44 also be isolated.

To remove the additive, the finished product is placed in an additive evaporator 50, from which the finished goods via the line 52 is subtracted. The good withdrawn from line 46 can if necessary, all or only fine grinding media which are not were withheld. These can then be optional fed to the feed line 44 via a return line 48 become. The additive evaporator 50 exits via a line 54 the additive in vapor form and can, if necessary, again processed and used again. That over the line 52 removed finished goods can optionally be used for drying abandoned a known freeze dryer be what is required when using water ice as an additive could be.

Claims (9)

1. A method for ultrafine grinding and mixing of solid materials to particle sizes far below 1 µm and/or for mixing of powders and agglomerate material having particle sizes in the range of nanometers, wherein material to be processed and an additive are fed into a grinding chamber with loose grinding media and are comminuted to the desired particle size by means of the loose grinding media adapted to be set in relative motion relative to each other and grinding chamber walls and thereafter the additive is removed from the processed material,
   characterised in that
   grinding is performed in cooled atmosphere in the presence of an additive that is solidified and below its melting or sublimation temperature and behaves chemically inert with regard to the material to be processed and that can evaporate at ambient pressure and temperatures below 50°C, and
   that thereafter the additive is removed from the material by evaporation.
2. The method according to claim 1, characterised in that water ice is used as additive.
3. The method according to claim 1, characterised in that carbon dioxide ice is used as additive.
4. The method according to claim 2, characterised in that grinding takes place at temperatures below about -50°C.
5. The method according to claim 3, characterised in that grinding takes place at temperatures below about -80°C.
6. The method according to one of claims 1 to 6, characterised in that the material to be processed and/or the mixed material comprised of material to be processed and additive is pre-cooled before it is fed into the grinding chamber.
7. Use of a grinding apparatus comprising a grinding chamber (2) that is encased by a cooling jacket (3) having inlet and outlet connections (7, 8) for a cooling agent and that is adapted to be fed with grinding media, material to be processed and an additive for ultrafine grinding and mixing of solid material to particle sizes far below 1 µm and/or for mixing of powders and agglomerate material having particle sizes in the range of nanometers, wherein the fed material fed into the grinding chamber is comminuted to the desired particle size, by way of the loose grinding media and grinding chamber walls, in the presence of an additive that is solidified and below its melting or sublimation temperature and behaves chemically inert with regard to the material to be processed and that can evaporate at ambient pressure and temperature below 50°C, and thereafter the additive is removed from the material by evaporation.
8. The use according to claim 7, characterised by employing a vibration mill as grinding vessel.
9. The use according to claim 7, characterised by employing an agitator mill as grinding vessel.

Images