DE102016219056A1 - Process for the surface modification of particles - Google Patents

Abstract

The invention relates to a method for surface modification of particles, wherein the particles are introduced into a reactor, wherein at atmospheric pressure by means of at least one plasma source (1) in the reactor, a plasma zone is formed, wherein the particles by means of a circulation system in the reactor in a packed bed through the plasma zone to be moved.

Description

The invention relates to a method for surface modification of particles, in particular micro- or nanoparticles.

It is known to treat powders of microparticles and nanoparticles by means of plasma in order to modify such powders on their surface and to prepare them, for example, for subsequent processing steps. The plasma treatment creates various functional (polar) groups on the surfaces and depending on the working gas used.

It is also known to treat powders in batch operation by means of low-pressure plasma. For this purpose, powders are placed in vacuum plants, where they are moved quasi-continuously, for example in drum reactors, through a glow discharge zone. As an alternative to drum reactors, turbulence systems can be used.

From the EP 2 366 730 B1 For example, there is known a method of chemically modifying a polymeric surface of a particulate solid comprising contacting a particulate solid with a polymeric surface at atmospheric pressure with a reactive gas and producing a chemical modification on the polymeric surface. In addition, a particulate solid having a particle size of 3-1000 micrometers and a surface of a polymer that is chemically modified by forming functional groups covalently bonded to the polymeric surface, and the use of the particulate solid as a chromatographic separation material are described.

Also known is a method ( Put et al. "Atmospheric pressure plasma treatment of polymeric powders" Surface Coatings Technology 234 (2013) pp76-81, VITO - Flemish Institute for Technological Research ), in which in the closed circuit under atmospheric pressure conditions and using dielectric barrier discharge (DBD) particles in the gas stream between corresponding electrode assemblies are usually passed several times.

The invention is based on the object to provide an improved method for surface modification of particles.

The object is achieved by a method having the features of claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims.

In a method according to the invention, a particle, in particular microparticles and / or nanoparticles, comprehensive powder is introduced under atmospheric pressure conditions in a reactor. Unlike in the prior art, a powder circulation in a closed gas system and a corresponding turbulence in the gas flow are preferably dispensed with. The reactor instead includes a recirculation system for moving the particles in a packed bed. In the reactor, for example in or on a bottom of the reactor, at least one plasma source, for example comprising two or more electrodes, is arranged. By means of the circulation system, the powder is continuously moved in a plasma zone that forms over the electrodes, whereby the particles are activated in the plasma.

The inventive method allows the surface modification of any type of powdered, in particular dielectric material, for example plastic powder, molding sand or ceramic powder. Further applications arise especially in the food sector in the treatment of, for example, seed (poppy, cereals, seeds, etc.).

By means of the method according to the invention, the disadvantages of the known from the prior art low-pressure systems can be overcome. In particular, their high requirements for filters for the vacuum pump omitted. In addition, in low-pressure systems, glow discharges have only relatively low degrees of ionization.

By working under normal pressure condition generally eliminates the required in low pressure systems considerable effort for the evacuation of the reactor. By means of the method according to the invention, a high power density of, for example, up to 100 W / cm ³ in a homogeneous formation of the plasma zone can be achieved.

The reactor can be scaled up in a simple manner. The geometric dimensions of the electrode can be adapted to the geometry of the reactor space.

In one embodiment, air, oxygen, nitrogen and / or at least one inert gas is used as ambient gas in the reactor.

In one embodiment, the plasma zone is formed by dielectrically impeded discharge.

In a further embodiment, the plasma zone is formed by means of a diffuse coplanar surface discharge, for example by means of at least one, in particular two DCSBD Plasma sources (diffuse coplanar surface barrier discharge), which may be embedded in the reactor bottom. DCSBD plasma sources are for example in M. Simor et al. "Atmospheric-pressure diffuse coplanar surface discharge for surface treatments" Appl Phys Lett 81 (15) 2002 p. 2716 described. The electrodes of the DCSBD plasma sources are embedded in a ceramic and the gas surrounding the complete assembly (for example, the ambient air) serves as a process gas. Alternatively, other process gases may be supplied to the DCSBD plasma source, especially if it is in a closed enclosure.

By using the DCSBD sources, the formation of a very intense, thin plasma zone with a very high power density of about 2.5 watts / cm ² to 100 watts / cm ^{3 is} achieved. Compared to filamentous plasma formation in DBD plasma sources, the use of DCSBD plasma sources achieves a high level of diffuse plasma, with plasma homogeneity still increasing as the power increases. A macroscopically homogeneous plasma with high power density can be generated in any reactive gas mixtures. A reactive gas mixture is understood to be a working gas to which reactive components are added. Examples are working gases such as air, nitrogen, oxygen and noble gases and mixtures of the aforementioned gases in combination with reactive additives. The electrodes of the DCSBD plasma sources are in particular completely embedded in ceramic. This results in a very high, in particular practically unlimited lifetime of the electrodes. In one embodiment of the invention, ceramic electrodes are used. In this way impurities, for example by sputtering effects, are avoided. The powder is continuously moved through the plasma zone, resulting in an intense interaction between plasma and particles.

In one embodiment of the invention, at least one precursor, for example hexamethyldisiloxane, titanium tetraisopropanol and / or further functionalizing additives, in particular nanoparticles, atomized solutions or dispersions, for example silver nitrate, can be fed to the plasma, which reacts in the plasma, the resulting reaction products being deposited on the particles become.

In one embodiment, the circulation system comprises a movable stirring arm.

As an alternative to the movement of the powder by means of a stirrer, the reactor can be mounted on a vibrating table or even be carried out as a vibrator, so that the particles are moved through the plasma zone as in a packed bed reactor.

Likewise, a rotating gas inlet system can also be used to move the powder in the plasma zone, which applies a controllable gas flow through nozzles into the packed bed a few millimeters above the packed bed. The gas stream is preferably controlled and / or regulated so that the powder is indeed moving, but not stirred up. The gas stream may consist of various gases or gas mixtures, preferably oxidizing.

In one embodiment, the circulation system has a rotor, in which at least one outlet opening can be provided, through which a gas directed onto the packed bed flows. This allows a virtually non-contact form of Pulverumettung in the plasma zone, so that interactions of the activated particles are avoided with the surface of the rotor. Likewise, it is possible in this way to supply Precursorgase and other functionalizing additives for coating purposes.

In one embodiment, the gas flowing out of the outlet opening is a reactive gas comprising the at least one precursor.

For example, particles of at least one polymeric material and / or of at least one inorganic material can be modified by means of the method.

In one embodiment, particles having a particle size in a range from 10 nm to 200 μm, preferably in a range from 0.1 μm to 100 μm, particularly preferably in a range from 0.5 μm to 50 μm, are modified.

By means of the method according to the invention plasma-modified particles are suitable for the preparation of homogeneous dispersions, in particular for the preparation of dispersions for subsequent processes of chemical and electrochemical production of dispersion layers.

The process offers an alternative option to wet-chemical variants, so-called core-shell particles. Core-shell particles comprise a core of a first material and a shell of a second material. The plasma treatment with reactive gases and precursors offers the possibility to convert the precursors in the plasma into layers. Thus, introduced particles can be provided with a functional surface coating.

It is known that atmospheric plasma treatments have germicidal effects. By means of the method according to the invention plasma treatments of powdery and Free-flowing food products such as seeds (poppy seeds, cereals, seeds, etc.) to reduce harmful germs possible.

The method can be used, for example, for the hydrophilization of microparticles and / or nanoparticles for an even distribution in carrier materials, in the cosmetics industry, medical technology, pharmaceutical industry, for material and surface functionalization, product labeling, for coatings in surface engineering or in plastics processing.

Embodiments of the invention are explained in more detail below by drawings.

Show:

1 a schematic view of a plasma source, and

2 a schematic view of a rotor.

Corresponding parts are provided in all figures with the same reference numerals.

1 shows a schematic view of a plasma source 1 , The plasma source 1 is formed as a DCSBD plasma source and has conductive, such as metallic electrodes 2 on that in a dielectric 3 , For example, a ceramic, are embedded. A the dielectric 3 Surrounding gas (for example, the ambient air) serves as a process gas, in which by applying a high voltage HV with a frequency in the kHz range to the electrodes 2 a plasma P is ignited. For example, the plasma P may have a thickness of 0.3 mm above a surface of the plasma source 1 exhibit. The plasma source 1 may be embedded in a reactor (not shown), for example at a bottom of the reactor.

2 shows a schematic view of a rotor 4 , The rotor 4 includes one or more rotor arms 5 in which one or more outlet openings 6 are provided, through which a gas can be flowed out to particles of a powder in a packed bed by means of the plasma source 1 to move generated plasma P.

Powder treated by the method described has a dispersing behavior other than untreated powder in an aqueous medium. In one experiment, a polyetheretherketone powder (PEEK) was placed in an open reactor space directly on the surface of the plasma source 1 introduced as a bulk bed with about 1 mm thickness and circulated during a plasma treatment. The previously measured particle size distribution of the PEEK powder gave a d (0.5) value of about 10 μm. The applied plasma power during the treatment was 400 W for a period of 3 min. The wettability and dispersibility of the treated powder differed markedly from untreated powder. While after the plasma treatment a very good dispersibility of the PEEK powder in the aqueous medium is given, untreated powder floats on the surface of the aqueous medium and can not be dispersed.

LIST OF REFERENCE NUMBERS

1

plasma source

2

electrode

3

dielectric

4

rotor

5

rotor arm

6

outlet opening

HV

high voltage

P

plasma

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

• EP 2366730 B1 [0004]

Cited non-patent literature

• Put et al. "Atmospheric pressure plasma treatment of polymeric powders" Surface Coatings Technology 234 (2013) pp76-81, VITO - Flemish Institute for Technological Research [0005]
• M. Simor et al. "Atmospheric-pressure diffuse coplanar surface discharge for surface treatments" Appl Phys Lett 81 (15) 2002 p. 2716 [0016]

Claims (13)

Process for the surface modification of particles, wherein the particles are introduced into a reactor, wherein at atmospheric pressure by means of at least one plasma source ( 1 ) in the reactor, a plasma zone is formed, wherein the particles are moved by means of a circulation system in the reactor in a packed bed through the plasma zone. The method of claim 1, wherein the plasma zone is formed by dielectrically impeded discharge. The method of claim 1, wherein the plasma zone is formed by diffuse coplanar surface discharge. Method according to one of the preceding claims, wherein the circulation system does not vortex the particles in a gas stream. Method according to one of the preceding claims, wherein air, oxygen, nitrogen and / or a noble gas is used in the reactor as ambient gas. Method according to one of the preceding claims, wherein the reactor is supplied to at least one precursor which reacts in the plasma (P), thereby resulting reaction products are deposited layer-forming on the particles. A method according to claim 6, wherein the precursor used is an organosilicon compound, in particular hexamethyldisiloxane.  Method according to one of claims 4 to 7, wherein the circulation system comprises a movable stirring arm. Method according to one of claims 4 to 8, wherein the circulation system comprises a rotor ( 4 ) with at least one outlet opening ( 6 ), through which a gas directed to the packed bed flows. The method of claim 9, wherein the out of the outlet ( 6 ) gas is a reactive gas comprising the at least one precursor. Method according to one of the preceding claims, wherein particles of at least one polymeric material are surface-modified. Method according to one of claims 1 to 10, wherein particles of at least one inorganic material are surface-modified. Method according to one of the preceding claims, wherein particles having a particle size in a range of 10 nm to 200 .mu.m, preferably in a range of 0.1 .mu.m to 100 .mu.m, particularly preferably in a range of 0.5 .mu.m to 50 .mu.m, modified become.

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