EP1230042B1 - Layer with a selectively functionalised surface - Google Patents

Description

The present invention relates to a layer which by means of a plasma-assisted Method has been obtained, the surface of this Layer has been selectively functionalized, a method of preparation such a layer and its use.

The coating of substrates by means of plasma-assisted processes is on known. Here, in a plasma from the coating precursor materials (hereinafter called precursor) reactive species obtained on a substrate, usually a metal, under layer formation deposit. The individual procedures differ here in the type of plasma generation and in the choice of process conditions, especially the pressure.

Thus, for example, in WO 93 102 83 by means of plasma technology a thin plasma polymer layer deposited on a pretreated substrate, wherein as precursor for the polymer layer an organic Compound such as methylsilane, trimethylsilane, etc. is used. In connection to the plasma deposition is on this thin polymer layer using cathodic layer deposition, a coating layer of an epoxyamine or epoxy-polyester melamine. The layer system thus obtained is used as a corrosion resistant protective layer for ungalvanized Metal surfaces used.

It is further known from DE 195 05 449 C2 and R. Thyen, A. Weber, C.-P. Klages, Surf. Coat. Technol. 97 (1997) 426-434, by means of corona or Barrier discharge layers at high pressures from 0.1 to 1.5 bar (10 - 150 kPa).

With such methods, it is possible to deposit layers which generally permit an adherent and / or corrosion-resistant connection of subsequently applied organic coatings. As Prec RSOR _u can in this case for example, hydrocarbons, silicon-containing compounds, boron or phosphorus-containing compounds or metal compounds in question. It is advantageous that in these processes, the layer deposition can be carried out at high pressures, for example at atmospheric pressure, and can be dispensed with a complex vacuum apparatus, as they are essential in low-pressure process.

In WO 97/22631 relates to a multi-layer system, wherein the individual Layers are deposited by plasma discharge. This is a three-dimensional network formed with a high number of functional groups.

Plasma deposited layers can fulfill a variety of tasks. she can as corrosion protection layers the passage of corrosive media, especially oxygen and water, prevent and / or as electrical Isolation layers act. In addition, they can find bonding agents between the Substrate and further applied to the plasma deposited layer Layers such as lacquer layers, adhesive layers, primer layers or for imprints. Frequently, if a combination of different Properties is desired, not a single layer but a layer system proposed as a gradient or multilayer system can be trained.

Disadvantage of plasma deposited layers or layer systems is however, that it has not been possible to date the surface of these layers to chemically functionalize selectively, as desired and purpose the surface with selected chemically functional Groups can be modified. Although also takes place during the plasma separation process depending on the type of precursor selected to a certain extent Functionalization of the surface, but this functionalization occurs uncontrolled and uncontrolled by having statistically functional groups like them were present in the precursor or arise during the plasma reaction, be bonded to surface atoms of the layer or by in the surface incorporated functional group-containing precursor fragments become.

Usually, a layer surface thus obtained contains a mixture many functional groups, as by reaction during the plasma discharge be formed. It has been shown that in the case of hydroxyl-containing Precursom the surface oxygen not only in the oxidation state having the hydroxyl group, but also in other oxidation states. Also, it is not possible by means of plasma deposition to apply sensitive groups such as epoxy groups on the surface, as these groups usually under the conditions of the procedure be destroyed. In addition, it has been shown that the occupancy of Surface with functional groups is low. That is, it is with the conventional plasma method not possible, controlled a Surface modification with functional groups on the layer, wherein the type of functional groups are selectively selected can and additionally achieves a sufficiently dense surface coverage can be.

It was therefore an object of the present invention to provide a plasma-deposited Layer to provide their surface selectively chemically is functionalized, in particular, a dense surface occupancy with functional groups can be achieved as well as a procedure for Production of such a layer.

In particular, these layers should be functionalized such that they due to a suitable selection of functional groups on the Surface are applied, an optimal binding / adhesion of additional layers to be applied thereto, in particular organic Layers, ensure.

This object is achieved by a layer that is supported by a plasma Method has been deposited on a substrate, wherein the surface of the layer is selectively functionalized by grafting monomers has been.

Furthermore, the present invention relates to a method for producing a Layer with selectively functionalized surface on a substrate, thereby characterized in that the layer on the substrate by means of a plasma-assisted Deposition process generated and the surface of the layer is selectively functionalized by grafting monomers.

For the purposes of the invention, the term "selectively functionalized" means that by suitable choice of the monomers on the surface of a plasma-deposited Layer according to desire and purpose functional Groups can be applied. The nature of the monomers is subject in this case no restriction so that in particular functional Groups involved in the conditions of deposition of the layer in the plasma would be destroyed or otherwise react to the surface the deposited layer can be applied.

C_p

ein Kohlenstoffatom an einer Polymeroberfläche

C_p ^*

ein Radikalzentrum

M

ein Monomer

m

Anzahl der Monomeren

n

Anzahl der Monomeren einer Polymerkette und

E

eine Endgruppe

darstellen.The functionalization of surfaces by grafting is known from organic polymer chemistry (see, for example, J. Jaguar-Grodzinski, Heterogeneous Modification of Polymers, pp. 221-234, John Wiley & Sons, Chichester 1997 and Y. Uyama, K. Kato and Y. lkada, Advances in Polymer Science, 137 (1998) 1-40). In this case, first carbon-based radicals, for example alkyl radicals, are produced on the surface of a polymer such as, for example, polyethylene, polystyrene or polyethylene terephthalate as reactive centers. These highly reactive radical centers can then be brought directly into contact with polymerizable monomers M, which come in contact with the polymer surface in the liquid or gaseous phase, so that on the polymer surface at the radical centers polymer chains - (M) _n - grow. The radical centers can be generated chemically, photochemically, by irradiation or by plasma-chemical surface treatments, for example in an argon plasma, as sketched schematically below, for example: C _p -H ---- plasma → C _p ^* C _p ^* + mM → C _p - (M) _n ^* → C _p - (M) _n -E in which

C _p

a carbon atom on a polymer surface

C _p ^*

a radical center

M

a monomer

m

Number of monomers

n

Number of monomers of a polymer chain and

e

an end group

represent.

The end group E can be any component that leads to a chain termination reaction. For example, E can be hydrogen.
The chain length or monomer number n of the grafted-on monomer chain can be influenced by suitable selection of the process parameters such as temperature, process duration, irradiation intensity, partial pressure of the monomer in gas phase polymerization or volume fraction and presence of inhibitors in liquid phase polymerization. In this way, by choosing a monomer M with suitable functional groups, it is possible to cause a plurality of these functional groups to be covalently coupled to the polymer surface, thus varying the properties of the polymer surface as required.

For example, the surface can be optimal for the adhesion of another Layer, a paint, a primer, adhesive or other preferably be adapted to organic material. That is especially the case Case, when a functional group F of the monomers in turn with corresponding functional groups F 'of the subsequently applied layer can react.

So far it has been assumed that this type of functionalization of the surface by grafting of monomers requires a polymer. Surprisingly, it has been found according to the invention that the grafting process described above does not necessarily presuppose an organic carbon-containing polymer surface, but is also applicable, for example, to metal or ceramic surfaces.
The prerequisite for this is that first a thin layer is deposited on the substrate surface by means of a plasma-assisted method.

It may be any layer as obtainable by conventional plasma enhanced techniques. It may be a few atomic layers of a hydrocarbon layer to a layer consisting of silicon, carbon and hydrogen, the layers may contain oxygen, nitrogen, sulfur, boron, phosphorus, halogens, for example, it may be a silicon oxide layer.
As precursors for the layer, it is possible to use all known compounds from the field of chemical vapor deposition, for example hydrocarbons, optionally with functional groups, silicon-containing compounds, compounds containing oxygen, nitrogen, boron, sulfur, halogen and / or phosphorus or metal compounds. Preferred precursors are organic compounds.
Suitable examples are propargyl alcohol, tetramethylsilane, hexamethyldisiloxane, vinyltrimethoxysilane, phenyltrimethoxysilane, aminopropyltrimethoxysilane, mercaptopropyltrimethoxysilane, dimethyldichlorosilane, trimethylphosphite, trimethylborate, and especially methane, ethene and ethyne.

The layer thickness is typically in a range of 1 nm to 1 μm, preferably 5 nm to 100 nm.

The substrate material can in principle be chosen arbitrarily. The inventive method is particularly suitable for applying a selectively functionalized surface layer on a metallic substrate. The substrate to be coated may be, for example, aluminum, steel or a be galvanized steel sheet. The substrate may have any shape. It can be a profile, profile tube, wire or plate or component an electronic component.

The inventive method for selective functionalization of the substrate surface, the surface can be conditioned specifically for the attachment / adhesion of another coating layer, wherein the functional groups or the monomer is selected depending on the layer material of the still applied coating layer, so that a firm connection between ground and coating is guaranteed. Such further layers may be coatings, for example conformal coatings, lacquers with decoration function, paints, printing inks, adhesives, primers, etc.
Preferably, these further layers consist of an organic material.

The type of monomers depends on the desired functionalization. The inventive method is particularly suitable to do so, functional groups that are destroyed or remodeled in a plasma process would be to the surface of a plasma-deposited To bind layer. Examples of suitable monomer compounds are Vinyl compounds, in particular acrylic acid, methacrylic acid and their Derivatives such as esters such as glycidyl methacrylate.

The monomer compounds may be used singly or in combination become.

The plasma deposited layer may be formed by any known plasma assisted process for layer deposition. It can be a low pressure or high pressure process.
It can be a so-called cold plasma process.

Low pressure processes typically operate at pressures in the range of 0.01 Pa to 10 kPa. Glow discharges are particularly suitable for this, by DC voltages, AC voltages or microwaves can be maintained.

Suitable pressure ranges for the high pressure process are in the order of 10 ⁴ Pa to 1.5 x 10 ⁵ Pa. High-pressure processes are, for example, barrier discharge or plasma generation by pulsed high-voltage arc discharge.

It is particularly preferred for reasons of simple technical implementation and the relatively low cost of a high-pressure or Atmospheric pressure method, wherein the layer deposition from a barrier discharge is preferred.

The layer deposition from a barrier discharge is known per se and for example in detail in DE 195 05 449 C2 or R. Thyen, A. Weber, C.-P. Klages, Surf. Coat. Technol. 97 (1997) 426-434 in detail as described herein for the purposes of the present invention express reference is made.

To graft the monomers, it is generally sufficient to bring the freshly plasma-deposited layer into contact with the desired monomers for a few seconds to a few minutes. The monomers react with the reactive centers that are on the surface of the freshly formed layers.
The chain length, that is, the number of monomers n grafted to a single reactive center of the surface can be controlled by the reaction conditions such as the number of end groups. The invention thus also includes functionalized surfaces with graft molecule chains n> 1.

The monomers may be liquid, gaseous, aerosolized, with or without inhibitors and / or diluted with inert gas such as argon, nitrogen.
The concentration can be determined by the vapor pressure. If necessary, it can be diluted with water.

Preferably, the functionalization takes place without intermediate exposure the plasma deposited layer to the ambient atmosphere, to prevent premature reaction of the reactive centers.

The layer deposition (also called plasma deposition) and the grafting can take place spatially or temporally separated from one another.
That is, the grafting may be done in the same device as the plasma deposition, or the plasma deposited layer substrate may be placed in a separate device or chamber set up for grafting. The grafting can take place after the plasma deposition.

With the method according to the invention, a high coverage of the surface of the plasma-deposited layer with functional groups can be achieved (number of functional groups per surface unit).
Thus, occupancy densities in the range of 10 ¹⁵ - 10 ¹⁷ per cm ² can be achieved with the present invention. In contrast, only coating densities of << 10 ¹⁵ / cm ^{2 can} generally be achieved for the abovementioned plasma polymer.

Depending on the occupation density, the functional groups or the graft molecules on the surface of the plasma deposited Layer a thin film similar to the Langmuir-Blodgett films.

The plasma deposited layer may be a single layer of homogeneous component composition or of a graded component composition, wherein the content and / or type of components may vary over the layer thickness.
It may be a layer system that consists of several individual layers, which may also be provided here, if necessary, a graduation.

Hereinafter, the invention with reference to a preferred method, which Layer deposition from a barrier discharge, explained in detail.

The figure shows schematically a device for layer deposition by means Barrier discharge.

The exemplary apparatus for performing the Schichtdeposition means Barrier discharge according to the figure consists in principle of an electrode or electrode assembly 2 and a counter electrode 6 on which the substrate 5 is stored.

The electrode 2 can consist of an electrode arrangement with a plurality of individual electrodes, wherein an electrode arrangement with two individual electrodes 2 is shown in the figure.
The electrode 2 or the individual electrodes 2 are each surrounded by a dielectric barrier layer 3.

The dielectric barrier layer 3 may be made of alumina ceramic, for example consist. The barrier discharge burns in the discharge space between the rod-shaped electrodes 2 on the one and the counter electrode 6 on the other side, the precursors for layer formation be introduced through the gas inlet 1. When unloading Micro discharges of very short duration, so-called filaments 4, arise interact with the substrate surface and in general have a diameter of 0.1 mm. Activation and deposition of the Precursors take place predominantly in the bases of the filaments 4.

If necessary, on the counter electrode 6, a dielectric intermediate layer be upset.

The gap between electrodes 2 and counter electrode 6 is usually between 1 and 5 mm and corresponds to the length of the filaments.

Usually, the discharges always take place at the same point, that is to say the filaments always form at the same point, since the time between the discharges is not sufficient to neutralize the charge carriers which have formed in the discharge channels. The still existing charge carriers cause the next discharges to form again in the same discharge channels as the preceding ones.
In order nevertheless to obtain a homogeneous surface covering, the substrate is preferably moved back and forth, indicated in the figure by the arrows 7.

In addition, the layer deposition by a suitable pulsation the supply voltage for the discharge to be controlled, the individual pulses are made at intervals that are sufficient that the formed Charge carriers are neutralized in the gas space, thereby preventing will be that the following micro discharge in the same place as the previous training.

As already mentioned above, the layer deposition by means of barrier discharge usually in a pressure range of 0.1 to 1.5 bar and a voltage range of preferably at least 3 kV performed. The amount of tension depends on the type and size of the used plant and after the process gas composition. The Frequency of the alternating field can be in the range of 0.05 to 100 kHz.

For surface functionalization, the monomers M become instantaneous after the layer deposition in the barrier discharge outside of the Area of the barrier discharge to the substrate gaseous, liquid or as Aerosol allowed to act.

Surprisingly, it has been found that the monomers for both Formation of the thin layer and thus as precursors and at the same time as Monomer can be used for the grafting reaction. Store here the monomers to the formed during the barrier discharge suitable reactive centers. The grafting reaction takes place here in the Areas of the substrate between each filament or discharge channels lie. In the discharge channels there is a strong decomposition the monomers and in this way activation of the monomers to Film deposition. However, enough remains outside the filaments Monomer unaffected by the barrier discharge and stands for the grafting to disposal.

Both the uniformity and the efficiency of the grafting can be controlled by suitable pulsing of the supply voltage for the discharge.
The pulsation should be oriented in such a way that the grafted-on functional groups (monomers) are retained on the surface and are not destroyed in the course of further barrier discharges at this point.

embodiments

1. Process in a low-pressure RF glow discharge, temporal separation of layer deposition and grafting.

Layer deposition:

Galvanized steel sheet in an RF glow discharge (13.5 MHz) at 5 Pa pressure.

The atmosphere:

1 sccm TMS (tetramethylsilane) in 10 sccm argon.
Process duration 10 s at 50 ° C.

Grafting:

Switch off the gas discharge, pump down to 1 mPa, fill with the vapor of methacrylic acid [2,3-epoxy-propyl ester] (glycidyl methacrylate) to 10 Pa, 100s exposure at 50 ° C, then aerate.

Adhesion test with an epoxy adhesive. Cohesive failure in the adhesive layer, that is not at the interface between the adhesive and the substrate. A galvanized steel sheet is placed in a high frequency corona discharge (13.65 MHz) parallel plate array at a pressure of 5 Pa and a temperature of 50 ° C for a process time of 10 seconds in a plasma activated atmosphere of 10 sccm argon and 1 sccm tetramethylsilane (TMS ) coated. The layer thickness is approximately 10 nm. Subsequently, the process chamber is evacuated to 1 mPa and filled with the vapor of methacrylic acid [2,3-epoxy-propyl ester] (glycidyl methacrylate) to a pressure of 10 Pa. The coated galvanized steel sheet is exposed to this atmosphere for 100 seconds at a temperature of 50 ° C. Then it is pumped off again and then aerated. On the thus coated surface, an epoxy resin based paint with a wet film thickness of 20 microns is aufgerakelt. A subsequent adhesion test by means of a grid layer according to DIN 53151 is rated "0" (very good). When the sheet is deformed by 180 °, the bending radius being approximately equal to the sheet thickness of 1 mm, no delamination of the coating occurs at the coating edge. The infiltration after a salt spray test (DIN 53167) is <1 mm after 1000 hours. These results correspond to the values of galvanized steel sheets which are subjected to a wet-chemical chromating process prior to painting according to the prior art.

2. Process in a barrier discharge, layer deposition and grafting in the discharge

Barrier Entiadung:

1 mm gap between silicon-insulated Al base plate and 2 ceramic-insulated high-voltage electrodes, each 1.5 cm wide. Oscillatory movement of the substrate table at 0.5 cm / s, 50 runs. Softalgenerator 6320; 100 V DC link voltage, 55 kHz, pulse 1 ms pulse, 20 Hz pulse frequency.

Gas:

2 slm argon, saturated with acrylic acid vapor.

Successful grafting is due to strong hydrophilization, surface tension > 66 mN / m, stable in KOH.

By applying a medium-frequency high voltage (8 kV, 50 kHz), clocked with 1 ms pulses at a pulse frequency of 20 Hz, to an arrangement from 2 ceramic insulated high voltage electrodes spaced at a distance of 1 mm above a grounded counter electrode made of aluminum (substrate) are a dielectric barrier discharge in the gas gap between ignited the high voltage electrodes and the counter electrode. Over a Gas shower becomes an atmosphere of 2 slm (standard liters per minute) Argon, saturated with acrylic acid vapor, introduced into the discharge areas. To achieve a laterally uniform coating, the counter electrode becomes Oscillatory at a rate of 0.5 cm / s by the discharge emotional. After 50 runs, a plasma graft polymer has by codeposition deposited as a thin layer on the aluminum surface.

The coated surface is very hydrophilic, the surface tension is > 66 mN / m. She is after a 10-minute exposure of the coated Surface unchanged in concentrated potassium hydroxide solution.

LIST OF REFERENCE NUMBERS

1

gas supply

2

High-voltage electrode

3

dielectric barrier

4

discharge channels

5

substratum

6

grounded counter electrode

7

Substrate movement direction

Claims (21)

1. Method for producing a layer with a selectively functionalised surface, characterised in that a layer is produced on a substrate by plasma deposition and the surface of the layer is chemically selectively functionalised by grafting monomers on reactive centres on the layer surface.
2. Method according to claim 1, characterised in that the number n of monomers M which are grafted on a reactive centre, is greater than 1.
3. Method according to either of claims 1 or 2, characterised in that the coating precursor material for the plasma deposition is at least one compound, selected from compounds which apart from carbon and/or silicon optionally contain at least one further element selected from oxygen, nitrogen, sulphur, boron, phosphorus, halogen and hydrogen.
4. Method according to claim 3, characterised in that at least one hydrocarbon compound and/or a hydrocarbon compound with a functional group is used for the plasma deposition.
5. Method according to claim 4, characterised in that the at least one hydrocarbon compound is selected from propargyl alcohol, tetramethylsilane, hexamethyldisiloxane, vinyltrimethoxysilane, phenyltrimethoxysilane, aminopropyltrimethoxysilane, mercaptopropyltrimethoxysilane, dimethyldichlorosilane, trimethylphosphite, trimethylborate, methane, ethylene, and acetylene.
6. Method according to any one of the preceding claims, characterised in that at least one monomer is selected for the grafting reaction from acrylic acid, methacrylic acid, a derivative thereof or a vinyl compound.
7. Method according to claim 6, characterised in that the derivative is an ester, preferably glycidyl methacrylate.
8. Method according to any one of the preceding claims, characterised in that the plasma deposition and the grafting are carried out separately from each other, spatially and/or with respect to time.
9. Method according to any one of the preceding claims, characterised in that the plasma deposition and optionally the grafting are carried out at pressures between 0.1 Pa and 10 kPa.
10. Method according to claim 9, characterised in that the plasma of a gas discharge maintained by direct-current voltage, alternating voltage or microwaves is used for the plasma deposition.
11. Method according to any one of claims 1 to 8, characterised in that the plasma deposition and optionally the grafting are carried out at pressures between 10 kPa and 150 kPa.
12. Method according to claim 11, characterised in that the plasma is produced in a dielectric barrier discharge or a pulsed arc discharge.
13. Layer with a selectively functionalised surface, characterised in that the layer has been deposited on a substrate by means of a plasma-enhanced method, and monomers M are grafted without the action of plasma on the surface of the layer.
14. Layer according to claim 13, characterised in that the number n of monomers M, which are bound on a reactive centre of the layer surface, is greater than 1.
15. Layer according to either of claims 13 or 14, characterised in that the monomer M is selected from at least one compound selected from acrylic acid, methacrylic acid and a derivative thereof.
16. Layer according to claim 15, characterised in that the derivative is an ester, preferably glycidyl methacrylate.
17. Layer according to any one of claims 13 to 17, characterised in that the substrate is a metal or a ceramic.
18. Layer according to any one of claims 13 to 17, characterised in that the substrate is steel, galvanised steel, aluminium or magnesium.
19. Layer according to any one of claims 13 to 18, characterised in that the layer can be obtained by plasma deposition of at least one precursor compound on a substrate and selective functionalisation of the surface of the layer by grafting of monomers M on reactive centres formed on the layer surface.
20. Use of a layer according to any one of claims 13 to 19, for the adhesive and/or corrosion-resistant bonding of subsequently applied further layers to a substrate.
21. Use according to claim 20, characterised in that the subsequently applied layer is a lacquer, an adhesive, a printing ink or a primer.

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