WO2009156390A1

WO2009156390A1 - Method and device for applying a coating, in particular a self-cleaning and/or antimicrobial, photocatalytic coating, onto a surface

Info

Publication number: WO2009156390A1
Application number: PCT/EP2009/057799
Authority: WO
Inventors: Christian Buske; Alexander Knospe; Thomas Beer; Kay Fehling
Original assignee: Plasmatreat Gmbh
Priority date: 2008-06-23
Filing date: 2009-06-23
Publication date: 2009-12-30
Also published as: DE102008029681A1; DE112009001544A5

Abstract

The invention relates to a method for applying a self-cleaning coating, in particular a self-cleaning and/or antimicrobial photocatalytic coating, onto a surface in which an atmospheric plasma stream is produced through electrical discharge in a working gas and in which a precursor material is introduced separate from the working gas, wherein the precursor material is introduced into the plasma stream directly as an aerosol. The invention also relates to a device for atmospheric plasma application of a coating onto a surface, comprising a plasma source (2) for producing a plasma stream (26) and a mixing device (3, 3', 3'') that provides for the introduction of a precursor material directly into the plasma stream as an aerosol (34).

Description

Method and device for applying a layer, in particular a self-cleaning and / or antimicrobial photocatalytic layer, to a surface

The invention relates to a method and a device for applying a layer, in particular a self-cleaning and / or antimicrobial photocatalytic layer, to a surface in which an atmospheric plasma jet is generated by electrical discharge in a working gas and in which a precursor material is introduced separately from the working gas is, wherein the precursor material is introduced as an aerosol directly into the plasma jet.

A method and apparatus for generating an atmospheric plasma jet, i. A plasma jet with an ambient pressure which is of the order of magnitude of the atmospheric pressure is known from EP 1 335 641 A1. For this purpose, a working gas, especially air, nitrogen, forming gas (mixture of nitrogen and hydrogen) or a noble gas, in particular argon or helium, passed through a channel in which by high voltage a plasma jet via an electrical discharge, i. a corona discharge and / or an arc discharge is generated.

In the case of coating processes using an atmospheric plasma jet, the effect of plasma polymerization, as disclosed in EP 1 230 414 Bl, is preferably used. In this method, a precursor material is introduced in liquid form directly into the plasma jet, there chemically and / or electronically excited, so that before, during or after the deposition of the excited precursor on a surface, a polymerization of the precursor begins.

Functionalized surfaces, such as antimicrobial surfaces, often require the use of metal or semimetal organic precursors. These precursors often have a high sensitivity to hydrolysis, that is, they react chemically with water present before they reach the site of the intended process. This may limit or even prevent their applicability as precursors.

Furthermore, these precursors are often sensitive to oxidation, that is, they react with the oxygen in the air. This leads to unwanted solid reaction products of the precursor material and so also to a restriction or prevention of their applicability.

In conventional plasma coating and

Plasma polymerization process in which metal or semimetal organic precursors are used, the deposition of the material on the workpiece to be coated is therefore carried out under vacuum or at least at a greatly reduced atmospheric pressure in a dry environment to reduce the oxidation and agglomeration of precursors or . to prevent.

With a view to cost-effective coating of mass products, a process would be desirable which would overcome the known advantages of plasma coating and plasma coating Plasma polymerization process, but under

Atmospheric pressure can be performed.

The process for plasma coating and plasma polymerization disclosed in EP 1 230 414 Bl, which has a

Operation under atmospheric pressure has the disadvantage that the precursor material must be evaporated before being introduced into the plasma jet. This limits the process to the use of precursors whose boiling points are below 230 ⁰ C, since a higher

Evaporation temperature can lead to decomposition of the precursor. Furthermore, the lance for the precursor supply of the device disclosed in EP 1 230 414 Bl is permanently opened, so that moisture and oxygen can penetrate.

The present invention is therefore based on the technical problem of providing a method and a device with which the application of a layer to a surface is improved.

This technical problem is solved by a method with the features of claim 1. Further advantageous embodiments are specified in the subclaims.

Characterized in that an atmospheric plasma jet generated by electrical discharge in a working gas and the precursor material separated from the working gas is introduced as an aerosol directly into the plasma jet, unwanted chemical reactions of the precursor material can be effectively prevented from entering the plasma jet. The method is particularly suitable for the use of a

Precursors, which is high-boiling, moisture and / or oxidation sensitive. Oxidation and

Moisture sensitivity refers here to the property of the precursor to be partially oxidized or hydrolyzed before the precursor has reached the site of the intended process.

High-boiling means here precursors whose boiling temperatures are so high that introduction of the precursor into the plasma jet by evaporation without decomposition of the precursor is only conditionally or not possible.

The described method thus has the advantage of avoiding evaporation of the precursor and by a

To replace atomization, so that a liquid precursor does not need to be heated. The direct introduction of the aerosol into the plasma jet also reduces the contact time with atmospheric oxygen and atmospheric moisture and thus effectively prevents oxidation and hydrolysis processes.

Furthermore, the method described has the advantage that the energy of the plasma jet is uniformly transmitted to the precursor material due to the large surface area of the precursor material introduced as an aerosol. Due to the fact that the energy transferred from the plasma jet to the precursor material is initially expended for the evaporation of the aerosol particles, the energy available for exciting the precursor is also lower. This leads to milder conditions, in particular for plasma polymerization. Thus, the precursor material through the milder conditions in the plasma jet fragmented weaker, that is, a larger proportion of the precursor material is available for the layer formation and at the same amount of precursor higher layer thicknesses can be achieved. Furthermore, a smaller part of the carbon atoms bound in the precursor material is oxidized, so that layers with higher carbon contents can be applied.

The method is particularly suitable for the use of a metal or semimetal organic precursor material, preferably a titanium organic compound such as tetraisopropyl orthotitanate (Ti [OCH (CH 3) 2] 4) or tetra-n-butyl orthotitanate (Ti (OCH 2 CH 2 CH 2 CH 3) 4), since the thus applied semiconductor layers often have a photocatalytic effect. By irradiation of electromagnetic waves, preferably ultraviolet radiation or visible spectrum radiation, the layered semiconductor and photocatalyst (e.g., TiOx, preferably TiO2) is electronically excited to induce redox processes at the surface of the layer. The resulting reaction products, such as hydroxyl radicals or hydrogen peroxide can chemically attack germs and other organic molecules (fats, oils). Thus, the layer has an active antimicrobial effect.

A further advantageous embodiment of the method is achieved by the use of an organosilicon precursor material, in particular hexamethyldisiloxane (HMDSO) or tetraethyl orthosilicate (TEOS), for depositing an organosilicon layer, which is also used as an adhesion-promoting layer, in particular for a following applied photocatalytic layer can serve. Of the

The advantage of this method with aerosol formation instead of evaporation of the precursor material is due to the fact that the precursor material does not occur in individual molecules as in the case of an evaporation process.

Molecule groups but is introduced in droplet form in the plasma jet. As a result, the energy transferred from the plasma jet to the precursor material is first used to evaporate the precursor and the energy available for excitation of the precursor is lower and, as a result, milder conditions for the plasma polymerization prevail. This can influence the degree of fragmentation of the molecules. Thus, it is possible to be able to deposit carbon-rich organosilicon layers.

An advantageous embodiment of the method is the introduction of the precursor material by means of a spray nozzle, in particular a two-fluid nozzle, in which a liquid precursor penetrates through a small nozzle opening and is atomized by an atomizing gas passing through an atomizer nozzle. The atomizing gas used is preferably a dry, inert gas, for example nitrogen.

An alternative embodiment of the method is the introduction of the precursor material by means of an ultrasonic atomizer, in which the precursor material strikes a high-frequency vibrating membrane and is thereby atomized. The advantage of using a spray nozzle or an ultrasonic atomizer lies in the particularly fine and uniform particle or droplet size in the aerosol, so that a fast and uniform reaction of the precursor with the plasma jet is achieved.

Furthermore, the advantage of using a nebulizer nozzle is that the nozzle can be filled during the

When not in use, it can be mechanically closed to prevent the penetration of moisture and oxygen.

Another advantage of using an ultrasonic atomizer is that it dispenses with the supply of a nebulizer gas, which above all simplifies a robot-controlled use of the process. Furthermore, the droplet size in the aerosol can be influenced, for example to control the plasma polymerization conditions. Also, the flow may be on

Precursor material are controlled very accurately and the dosage of very small amounts of precursor is possible.

Apart from the use of a spray nozzle or a Ultraschallzerstäubers and the use of other Zerstäubervorrichtungen is conceivable.

The above-mentioned technical problem is also solved by a device having the features of claim 10. Further advantageous embodiments are specified in the subclaims.

An advantageous embodiment of the device for applying a layer, in particular a self-cleaning and / or antimicrobial photocatalytic layer acting on a surface, consists of a device for generating an atmospheric plasma beam through electrical discharge in a working gas and a

Feeding device for a precursor material. This is spatially separated from the supply of the working gas and provides an atomizer for the introduction of the precursor material as an aerosol in the plasma jet. An aerosol according to the invention is a mixture of precursor material and gas, wherein the particle size, that is, the particle or droplet size of the precursor is large compared to its molecular size but small compared to the extent of the plasma jet.

The device is not limited to a feeder or a precursor material in the context of the invention, but may each have a plurality of them.

A particularly advantageous embodiment of the device is achieved in that the atomizer is designed as a spray nozzle or as a Ultraschallzerstäuber, since so a particularly fine and uniform atomization is achieved.

The atomizer can be arranged both in the area of the nozzle opening and downstream of the nozzle. The advantage of an atomizer arranged in the region of the nozzle opening lies in the highly directed introduction of the precursor material into the plasma jet. The advantage with an arrangement of the atomizer downstream of the nozzle lies in the even milder conditions in the region of the plasma jet into which the precursor material is introduced. As a result, for example, the carbon content of the applied layer can be further increased. As a result, for example, layers can be produced which are in the visible range of the electromagnetic spectrum absorb and therefore avoid the use of UV light to activate the layer.

Further features and advantages of the present invention will be explained in more detail in the description of an embodiment, reference being made to the accompanying drawings. In the drawing show

1 shows a first embodiment of a device according to the invention for coating a surface, in which a precursor material is introduced as an aerosol in the region of the nozzle opening in the plasma jet,

2 shows a second embodiment of a device according to the invention for coating a surface, in which a precursor material is introduced by means of a spray nozzle as an aerosol in the region of the nozzle opening in the plasma jet and

Fig. 3 shows a third embodiment of a device according to the invention for coating a surface, in which a precursor material by means of a Ultraschallzerstäubers as aerosol in

Area of the nozzle opening is introduced into the plasma jet.

4 shows a fourth embodiment of a device according to the invention for coating a surface, in which a precursor material as Aerosol is introduced downstream of the nozzle opening in the plasma jet.

An apparatus for plasma coating 1 shown in FIG. 1 has a plasma source 2 and a mixing device 3. The plasma source 2 has a nozzle tube 4 made of metal, which tapers conically to a nozzle opening 6. At the nozzle opening 6 opposite end of the nozzle tube 4, a swirl device 8 with an inlet 10 for a working gas, for example, for nitrogen. A

Partial wall 12 of the twisting device 8 has a ring of obliquely set in the circumferential direction of holes 14, through which the working gas is twisted. The downstream, conically tapered part of the nozzle tube is therefore traversed by the working gas in the form of a vortex 16, whose core extends on the longitudinal axis of the nozzle tube.

On the underside of the intermediate wall 12, an electrode 18 is arranged centrally, which protrudes coaxially in the direction of the tapered portion in the nozzle tube. The

Electrode 18 is electrically connected to the intermediate wall 12 and the remaining parts of the twisting device 8. The swirl device 8 is electrically insulated from the nozzle tube 4 by a ceramic tube 20. About the swirl device 8, a high-frequency high voltage is applied to the electrode 18, which is generated by a transformer 22. The inlet 10 is connected via a hose, not shown, with a variable flow rate pressurized working gas source. The nozzle tube 4 is grounded. Due to the applied voltage is a high frequency discharge in the

Form of an arc 24 between the electrode 18 and the nozzle tube 4 is generated. The term "arc" is here as phenomenological description of the discharge used, since the discharge occurs in the form of an arc. However, the term "arc" is understood in DC discharge with substantially constant voltage values.

Due to the swirling flow of the working gas, however, this arc is channeled in the vortex core on the axis of the nozzle tube 4, so that it branches off only in the region of the nozzle opening 6 to the wall of the nozzle tube 4. The working gas, which rotates in the region of the vortex core and thus in the immediate vicinity of the arc 24 with high flow velocity, comes into intimate contact with the arc and is thereby partly transferred to the plasma state, so that an atmospheric plasma jet through the nozzle opening 6 from the plasma source 2 enters the arranged in the nozzle opening mixing device 3.

The mixing device 3 has a mixing tube 28, the wall of which has an opening 30 at one point into which an atomizer 32 is inserted with a precise fit. Connected to the atomizer 32 is a precursor feed 33, through which the precursor material passes into the atomizer 32 where it is atomized to form an aerosol.

The precursor material emerging from the atomizer 32 as aerosol 34 passes directly into the plasma jet 26. Therefore, the probability that the precursor material oxidizes before entering the plasma jet 26 or accumulates with water is low. The aerosol

Particles are then partially ionized in the plasma jet 26 and with the plasma jet 26 from the mixing tube 28 through the Outlet opening 36 transported. The aerosol particles reach the surface with the plasma jet, poly- or oligomerize if necessary and form a layer B. For example, when using a titanium organic precursor, a TiO x layer is formed having a structure having photocatalytic and antimicrobial properties. Optionally, a final heat treatment in the oven or another plasma or plasma jet treatment (without precursor addition) can be carried out in order to further improve the layer properties.

Fig. 2 shows a second embodiment of a device for plasma coating a surface. The device has a plasma source 2 previously described with reference to FIG. 1 for generating a plasma jet 26 and a mixing device 3 'with the mixing tube 28 and an atomizing nozzle 40 in the region of the nozzle opening 6.

The wall of the mixing tube 28 has at one point an opening 30 ', in the exact fit the outlet side of the

Atomizer nozzle 40 is introduced. The atomizer nozzle consists of a central tube 42 which tapers conically in the region of the opening 30 'to form a precursor outlet opening 44, a closure needle 46 arranged coaxially in the central tube 42 and a surrounding tube 48

The closure needle 46 has such a taper in the region of the opening 30 'that a closure of the precursor outlet opening 44 can be achieved by a movement of the closure needle 46 in the axial direction. The surrounding tube 48 is conically tapered in the region of the opening 30, so that the atomizing gas outlet opening 49 emerging nebulizer gas is directed into the area in front of the precursor outlet opening 44.

To the central tube 42, a supply of precursor material, not shown, and a device for targeted movement of the closure needle 46 are connected in the axial direction. Connected to the surrounding tube is a supply of nebulizer gas, preferably dry nitrogen gas under pressure, not shown, so that the nebulizer gas can flow through the region 50 between the central and surrounding tubes.

Due to the shape of the surrounding tube 48 in the region of the opening 30, the atomizing gas is directed to the region in front of the precursor outlet opening 44. Due to the negative pressure arising therefrom, precursor material is sucked out of the central tube 42 and atomized by the atomizing gas into an aerosol 34 when the precursor outlet opening 44 is not closed by the closure needle 46. The aerosol 34 passes directly into the plasma jet 26. Therefore, the probability is low that the precursor material is oxidized or hydrolyzed before entering the plasma jet 26. The aerosol particles are then vaporized in the plasma jet 26, partially ionized, electronically excited and fragmented and transported by the plasma jet 26 from the mixing tube 28 through the outlet opening 36.

Fig. 3 shows a third embodiment of a device for plasma coating a surface. The device has a plasma source 2 previously described with reference to FIG. 1 for generating a plasma jet 26 and a mixing device 3 ¹ 'with the mixing tube 28 and an ultrasonic atomizer 52 in the region of the nozzle opening 6. The wall of the mixing tube 28 has at one point an opening 30 '', into which the outlet opening of an ultrasonic atomizer 52 is accurately inserted. The ultrasonic atomizer consists of a vibratable membrane 54, a precursor supply 56 and a holder 58 for the precursor supply 56 and the membrane 54. The membrane 54 can be excited by a device, not shown, to high-frequency oscillations.

Connected to the precursor supply 56 is a pump, not shown, which pumps precursor material from a precursor source through the precursor supply 56. The precursor material emerging from the opening 60 of the precursor feed 56 reaches the vibrating membrane 54 and is atomized to form an aerosol 34. The aerosol 34 passes directly into the plasma jet 26. Therefore, the probability is low that the precursor material before entering the plasma jet 26 oxidizes or accumulates with water. The aerosol particles are then in the

Plasma jet 26 partially ionized and transported with the plasma jet 26 from the mixing tube 28 through the outlet opening 36.

Fig. 4 shows a fourth embodiment of a

Apparatus for plasma coating a surface. The apparatus comprises a plasma source 2 previously described with reference to FIG. 1 for generating a plasma jet 26 and an atomizer 32 'arranged downstream of the nozzle opening 6. Connected to the atomizer 32 'is a precursor feed 33', through which the precursor material passes into the atomizer 32 'where it is atomized to form an aerosol becomes. The precursor material emerging from the atomizer 32 'as aerosol 34 passes into the plasma jet 26 generated in the plasma source 2 and leaving the nozzle opening 6 and is transported further with the plasma jet 26.

Claims

claims

1. A method for applying a layer, in particular a self-cleaning and antimicrobial, photocatalytic layer, on a surface, - in which an atmospheric plasma jet is generated by electrical discharge in a working gas and in which a precursor material is introduced separately from the working gas, characterized that the precursor material is introduced as an aerosol directly into the plasma jet.

2. The method according to claim 1, characterized in that the precursor material is introduced by means of a spray nozzle.

3. The method according to claim 1, characterized in that the precursor material is introduced by means of a Ultraschallzerstäubers.

4. Process according to claims 1 to 3, characterized in that the precursor material is high-boiling, sensitive to hydrolysis and / or oxidation.

5. Process according to claims 1 to 4, characterized that a metal or semimetal organic

Precursor material is used.

6. The method according to claim 5, characterized in that a titanium organic precursor material is used.

7. Process according to claims 1 to 5, characterized in that an organosilicon precursor material is used.

8. The method according to claims 1 to 7, characterized in that the applied layer has self-cleaning and / or antimicrobial photocatalytic properties.

9. The method according to claims 1 to 8, characterized in that the applied layer has absorbing properties in the ultraviolet and / or visible range of the electromagnetic spectrum.

10. A device for applying a layer, in particular a self-cleaning and / or antimicrobial photocatalytic layer, to a surface, comprising a device (2) for generating an atmospheric plasma jet by electrical discharge in a working gas, with a feed device (33) for a

Precursor material, wherein the supply means (33) for the

Precursor material is spatially separated from the supply means (10) for the working gas, characterized in that the supply means (33) provides an atomizer (32) for introducing the precursor material as an aerosol (34) in the plasma jet (26).

11. The device according to claim 10, characterized in that the atomizer is designed as a spray nozzle (40).

12. The device according to claim 10, characterized in that the atomizer is designed as an ultrasonic atomizer (52).

13. Device according to claims 10 to 12, characterized in that the atomizer is arranged in the region of the nozzle opening or downstream of the nozzle opening.