EP1272286A2

EP1272286A2 - Method for depositing a polymer layer and the use thereof

Info

Publication number: EP1272286A2
Application number: EP01927907A
Authority: EP
Inventors: Rudolf Thyen; Niklas KLÄKE; Katrin HÖPFNER; Claus-Peter Klages
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2000-04-11
Filing date: 2001-04-10
Publication date: 2003-01-08
Anticipated expiration: 2021-04-10
Also published as: WO2001076773A3; DE50101710D1; DE10017846C2; EP1272286B1; ATE261781T1; WO2001076773A2; DE10017846A1

Abstract

The invention relates to a method for depositing a polymer layer by means of a filamented gas discharge and to the use of said method. A carrier gas and an organic compound is supplied for the discharge. The organic compound can be polymerised and is provided with a carbon double bond and is additionally provided with an oxygen-, nitrogen-, sulphur- or phosphor-containing functional group or a trifluoromethyl group.

Description

Method of depositing and using a polymer layer

Besehreibung

Technical field

The invention relates to a method for depositing a polymer layer on a substrate according to the preamble of claim 1, and to the use of the substrate coated in this way according to claims 11 to 17. The layer deposition method according to the invention makes it possible to provide plasma-polymer-coated substrates with a very high density of functional groups , which serve as reactive anchor groups for subsequent coatings or chemical reactions. The functional groups can either make the surface itself hydrophilic or hydrophobic, or they can undergo chemical reactions which lead to the formation of such a hydrophilic or hydrophobic surface. Furthermore, the functional groups can be used to modify the adsorption behavior with respect to a large number of substances, such as metal ions, organic substances, biomolecules, etc., and, moreover, to adhere to them Connection of the same can be realized. The method is preferably used for substrates which have inherently relatively inert surfaces, ie are chemically inert, as is generally the case with conventional polymers such as polyolefins or fluorinated polymers.

State of the art

With polymer surfaces, there are essentially two ways to provide surfaces with functional groups.

A known way is to use so-called grafting reactions, see also J. Jaguar-Grodzinski: "Heterogeneous Modification of Polymers", pp. 221-234, John Wiley & Sons, Chichester 1997, and also the review article by Y. Uyama, K. Kato and Y. Ikada, Advances in Polymer Science 137, pp. 1-40, 1998. In a first process step, carbon-based radical centers such as alkyl radicals are first generated on the surface of the solid polymer. The radicals can be generated by reactive chemical initiators, by photochemical treatment, or by plasma-chemical surface treatments in low-pressure glow discharges, or by plasma-chemical surface treatments at atmospheric pressure, for example by means of corona or barrier discharges.

In a second process step, the polymer with very reactive radical centers Growing up the surface of a polymer chain. For this purpose, in a first variant, the previously prepared surface can be brought into direct contact with polymerizable organic compounds. The organic compounds are in the liquid or gaseous state. In a second variant, the prepared surface is first brought into contact with moist air, so that peroxides or hydroperoxides form, which can then dissociate thermally or photochemically with the formation of reactive oxide radicals and, in contact with a suitable organic compound, also the growth of a polymer chain cause.

A second known way of providing the surfaces of possibly very inert polymers with a layer containing a functional group is the so-called plasma polymerization. Starting from gaseous organic compounds that have the desired functional group, reactive species are formed in a plasma by excitation and dissociation. The reactive species condense on the surface and form a more or less strongly covalently cross-linked layer. With appropriate process management, it can be achieved that some of the functional groups are retained.

The functional groups remaining in the deposited layer can be detected by physical methods such as infrared spectroscopy, see JPS Baydal, "Controlled Plasma Chemical Deposition of Polymer Coatings ", IEEE Seminar Plasma Polymerization for the Future, IEEE, London, 1999, 2/1.

Plasma polymerization processes generally work with low-pressure plasmas and therefore require the use of complex vacuum equipment. They are therefore relatively expensive and, especially for the treatment of low-price products, such as packaging films, are not economical.

It is known to deposit polymer layers by means of a barrier discharge at atmospheric pressure (J. Salge, Surface and Coatings Technology, Issue 80, page 1, 1996). In this publication, mainly hydrocarbons, such as acetylene, were supplied to the discharge.

Hydrophobic layers with fluorinated carbon groups from tetrafluoroethene have also been deposited at atmospheric pressure, see R. Thyen, A. Weber and C.-P. Klages, Surface Coatings Technology, Issue 97, pp. 426-434, 1997. In this publication, propargyl alcohol was used to provide hydrophilic groups. However, propargyl alcohol as a propyne derivative (CC triple bond) is practically not radically polymerizable, unlike, for example, derivatives of acrylic acid or methacrylic acid with CC double bonds. Presentation of the invention

The invention is based on the technical problem of providing a method for depositing a polymer layer using a filamented gas discharge at atmospheric pressure, which largely avoids the disadvantages of the prior art. The method is also intended to provide plasma polymer-coated substrates, in particular plasma polymer-coated polymers, which have a very high density of functional groups.

This technical problem is solved by the features specified in the independent claims, advantageous refinements being specified by the subclaims.

According to the invention, it was recognized that the aforementioned problems according to the prior art can be avoided by using a filamentized gas discharge for the deposition of the plasma polymer layer, by supplying the discharge with a carrier gas and a polymerizable organic compound, and by this organic compound having a double bond between has two carbon atoms and additionally an oxygen, nitrogen, sulfur, or phosphorus-containing functional group or a trifluoromethyl group.

Such a solution is very surprising. Filamentized gas discharges, for example filamentized barrier discharges, show a statistical one Distribution of transient micro-discharges on the so-called filaments. It is known that the filaments have very high current densities of 100 to 1000 A / cm ² with very high electron densities of 10 ¹⁴ to 10 ¹⁵ cm ^"3. It would therefore be expected on the basis of these extreme plasma conditions that the functional groups of the introduced organic compound, upon contact with the high-energy particles of the gas discharge completely, or at least to a very considerable extent. This is particularly true for the quite fragile functional groups such as the epoxy, the carboxyl, or the primary, Secondary or tertiary amino group In this context it can be assumed that destroyed functional groups are no longer formed to an appreciable extent under plasma conditions and are therefore replaced, which applies in particular to the epoxy group.

The process can be operated at or near atmospheric pressure, ie in the range from approx. 0.2 bar to 2 bar, ie from 2x10 ⁴ Pa to approx. 2x10 ⁵ Pa. It is therefore advantageously possible to dispense with the use of complex and expensive vacuum systems.

Inert polymer surfaces are particularly suitable as substrates to be coated, for example polyethylene, polypropylene or high-performance plastics such as polyoxymethylene, polyether ketone or polypropylene sulfide. Noble gases such as argon can be selected as the carrier gas for the organic compound. The noble gases are known to be chemically inert under normal conditions. In the plasma-excited state, however, they can very well trigger chemical reactions which can lead to the destruction of functional groups.

Surprisingly, however, it has been shown that not only noble gases, but also other non-layer-forming gases such as, for example, weakly oxidizing CO ₂ and reducing H ₂ can be used. Nitrogen, which is particularly advantageous for economic reasons and which forms reactive species under plasma conditions, is also suitable.

It is still unclear why the introduced functional groups can withstand the combined attack of the high-energy plasma on the one hand and the reactive species of the carrier gas or gases on the other.

The filamented discharge can be excited by means of a sine voltage. In view of the goal of achieving the greatest possible density of functional groups on the polymer layer, it has proven to be advantageous to use a pulsed sinusoidal voltage. This will be explained below.

A pulsed sine voltage is characterized by a sequence of a time period t _{1 #} during which a sine voltage is present and a time period t ₂ during of which there is no voltage. Coating experiments were carried out in which t _j = 1 ms was kept constant and the time period t _{2 was} varied from 1 ms, 2 ms, 4 ms, 10 ms, 20 ms to 50 ms. A filamented plasma is present during the period t, whereas no plasma is present during the dead time t ₂ . The transition between these periods can be expected to be abrupt. The reason for this is that the micro-discharges are extremely short-lived, which manifests itself physically in a discharge duration of a few nanoseconds.

However, it was found that the layer thickness also increased during t ₂ , ie the coating rate was greater than zero. This indicates that intact, undamaged molecules react with the sufficiently stable radical centers on the surface in the sense of a classic radical polyaddition.

One or more radical-polymerizable compounds provided with functional groups serve as the starting substance for the deposition of the plasma polymer layer produced by the method according to the invention.

The organic compound supplied to the discharge must have a polymerizable or polymerizable group. A carbon double bond is particularly suitable for coupling the compound to the radical centers formed on the surface, as is the case, for example, in vinyl, allyl, Acrylic or methacrylic compounds are present, since, according to previous understanding, these are split and the carbon atom in question forms a covalent bond with the radical.

The organic compound also has a chemically functional group which contains at least one of the elements 0, N, S, P or a halogen.

Suitable oxygen-containing functional groups are, in particular, epoxy, ether, keto, aldehyde, carboxyl and hydroxyl groups.

Suitable nitrogen-containing groups are, for example, primary, secondary and tertiary amino, nitrile and nitro groups.

Suitable sulfur-containing groups are, for example, the thiol, mercapto, sulfonic acid, sulfone, sulfoxide or thioether groups.

An example of a functional group containing phosphorus is the phosphate group and the phosphoric acid ester group.

A particularly interesting halogen-containing group is the trifluoromethyl group, since this can give it a very low surface tension if the concentration or density on the surface is sufficient.

The functional groups mentioned are in some cases very fragile under plasma conditions and, according to the explanations above, it should be expected that they cannot survive the discharge undamaged. However, it has been shown that these functional groups can be built into the layer largely undamaged despite the filamentary discharge.

The epoxy group is particularly suitable for layer deposition because it can easily form covalent bonds to the subsequent layer. If the coated substrate according to the invention is subsequently brought into contact with an adhesive partner, for example a coating, the epoxy groups are particularly suitable when it is an epoxy-based adhesive partner. For example, an epoxy-based varnish adheres particularly firmly with such a coated substrate with built-in epoxy groups.

The choice of a polymerizable organic compound with at least one polar hydroxyl or carboxyl group is particularly suitable if the surface of the coated substrate is to be made hydrophilic.

Amino groups are advantageous if the plasma polymer layer is subsequently to be provided with an epoxy-based adhesive, since epoxy groups are very reactive towards amino groups. In addition, amino groups can be used, for example, for the immobilization of proteins. In this regard, reference is expressly made to the publication by Y. Uyama, K. Kato and Y. Ikada, Advances in Polymer Science 137, p. 28, 1998. Furthermore, amino groups can also are used to couple poly (ethylene) oxide chains via a reaction with cyanuric chloride, which in turn greatly reduce the adhesion of proteins to the surface. In this regard, WR Go botz et. al. , J. Biomed. Mat. Res. 25, p. 1547, 1991.

By providing a plasma polymer surface with a high density of functional groups, an adhesive bond with contact partners is particularly successful. The article cited at the beginning by Uyama et. Shows a large number of examples for the use of surfaces with grafted-on functional groups. al. to which express reference is made. The applications mentioned there, which are made fully the content of this application, can in principle also be implemented using the method according to the invention. In particular, the promotion of the adhesion of adhesives, for example based on epoxy, to surfaces which have a high concentration of epoxy groups or amino groups should be emphasized. Another example are printing inks, preferably water-based printing inks, which generally have only very poor adhesion to polymer surfaces. Here it is possible to achieve maximum adhesion by suitably matching the functional groups in the deposited layer to the structure of certain components of the printing inks.

Further areas of application for the plasma polymer layers according to the invention are also adhesives and Admittedly, both such bonds, in which an additional adhesive is required, and such bonds, in which the polymer layer itself develops the adhesive effect (so-called auto-adhesive bonds). Further examples are adhesive bonds with printing inks to be applied or a metallic coating or metallization.

The method according to the invention can also be used to provide biocompatible layers which are provided, for example, on implants for biomedical applications. Depending on the application, it may be desirable for these implants that proteins, organic cells or cell cultures can be deposited there, cannot be separated, or only special representatives thereof can be separated. For example, if the implant is to be firmly anchored to the connective tissue, it is desirable that the surface be provided with functional groups that support the attachment of cells. Furthermore, the surface can fulfill additional functions by loading with an antibiotic or a growth factor. The concrete relationships between the type of functional group on the surface on the one hand, and the adhesion of the biological material such as proteins or cells on the other hand, is described, for example, in C.-P. Klages, Mat.-wiss. u. Werkstofftech. 30, p. 767, 1999, described in detail, so that reference is expressly made to this article in this regard. As a An example is the covalent immobilization of collagen by carboxyl groups.

The organic compound is introduced either in gaseous form or as an aerosol. Gaseous introduction is advisable when the vapor pressure is sufficiently high, for example with numerous monomers. For this purpose, the carrier gas is passed through the mostly liquid organic compound. Introduction as an aerosol is advantageous for high molecular weight compounds with low vapor pressure, for example for many dimers or polymers. If it is introduced as an aerosol, a high coating rate can usually be achieved.

A filamented barrier discharge can be selected as the filamented gas discharge, cf. Fig. 1 and the embodiment. A barrier discharge is understood to be a gas discharge as described by H. Gobrecht et. al. , "On Silent Discharge in Ozonizers", Ber. Bunsenges. 68, pp. 55-63, 1965.

An electronically controlled arc discharge can also be selected. 2, an electronically controlled high voltage U is applied to two high-voltage electrodes 6, 6 '. The activated gas particles generated in the arc discharge are transported to the substrate surface 8 to be coated with the aid of a strong gas stream 7. The activated gas particles constrict to form thin discharge channels 9, so that here too filamented discharge form is present. The advantage of this discharge arrangement is that the electrodes 6, 6 'themselves are coated significantly less than in the case of the filamented barrier discharge. This advantageously leads to a lower maintenance requirement for the arrangement, which enables economical working in continuous operation.

The invention is to be explained below on the basis of exemplary embodiments.

In a preliminary test, an approx. 1 μm thick layer made of a ten percent polymer solution of polyglycidyl methacrylate (abbreviated to Poly-GMA) in methyl ethyl ketone (MEK) was produced by dipping a silicon wafer into the solution of the polymer in butanone. Using infrared spectroscopy, an epoxide concentration of 7.0 mmol / g was determined by determining the absorption of the characteristic wave numbers of 850 cm ^"1 and 910 cm ^{" 1 of} the epoxy group. It can be assumed to a good approximation that the polymer and the deposited layers have the same density in accordance with the method according to the invention. Furthermore, it can be assumed that the epoxy groups are almost completely retained when the layer is formed from the polymer solution.

In a first coating process, a filamented barrier discharge was used, the arrangement used being shown in FIG. 1. The electrodes are two ceramic-insulated rods 1, 1 'of 15 cm in length which are parallel to the longitudinal axis Substrate surface are arranged. The direction of view in Fig. 1 is the direction of these longitudinal axes. The bars 1, 1 'are 1.5 cm wide and have a mutual distance of 0.3 cm. The distance of the electrodes 1, 1 'from the substrate 2 is 0.9 cm, the substrate table 3 being moved back and forth under the electrodes at a speed of 1 cm / s. The movement of the substrate table 3 is indicated by the horizontal double arrow below the substrate 2. The electrodes 1, 1 'are supplied by a high-voltage generator with sinusoidal alternating voltage U of 5 to 10 kV with the frequency f = 38 kHz, the primary-side power being approximately 40 W.

Nitrogen is passed through a container with the liquid monomer glycidyl methacrylate (GMA) at a room temperature of 23 ° C. The nitrogen loaded with the gaseous GMA is passed with a gas flow of 10 1 / min through the gas shower 4 between the electrodes 1 into the discharge zones 5, 5 'where the substrate 2 has been coated.

Polymer films such as polyethylene and polypropylene were chosen as substrates. With a single pass of the substrates 2 through the discharge region 5, 5 ', a thin layer of approximately 10 nm thickness can be produced. The thickness of the deposited layer can be increased accordingly by several passes.

Using infrared spectroscopy it could be demonstrated that the layer deposited in this way had a concentration of 1.26 mmol / g. This is approx. 18% of the value as determined in the preliminary test at Poly-GMA. When the poly-GMA layer was deposited, it could be assumed that the epoxy groups were almost completely retained during the layer formation. The lower concentration in the layer deposited according to the invention means that a considerable part of the functional groups survived the discharge undamaged and built into the layer

The layer deposition method according to the invention is well suited to providing plasma polymer-coated substrates with a high number of epoxy groups.

In a second coating process, with otherwise unchanged process parameters, the discharge was not operated with a continuous sine voltage, but with a pulsed sine voltage. The pulse time was 1 ms at a pulse frequency of 20 Hz. The evaluation of the infrared spectra showed that the concentration of the epoxy groups was now 6.3 mmol / g. With the pulsed voltage, a much higher concentration of epoxy groups could be provided on the surface of the substrate than with simple sinusoidal voltage. Apparently a much larger proportion of the functional groups introduced via the organic compound survived.

Claims

claims

1. Method for depositing a polymer layer using a filamented gas discharge, in which the discharge is a carrier gas and an organic one

Compound is supplied, characterized in that the organic compound is polymerizable and that it has a carbon double bond and additionally an oxygen, nitrogen, sulfur or phosphorus-containing functional group or a trifluoromethyl group.

2. The method according to claim 1, characterized in that the oxygen-containing functional group is an epoxy, ether, keto, aldehyde, carboxyl or hydroxyl group.

3. The method according to claim 1, characterized in that the nitrogen-containing functional group is an amino, nitrile or nitro group.

4. The method according to claim 1, characterized in that the sulfur-containing functional group

Is thiol, mercapto, sulfonic acid, sulfone, sulfoxide or thioether group.

5. The method according to claim 1, characterized in that the phosphorus-containing group is a phosphate group or a phosphoric acid ether group.

6. The method according to at least one of claims 1 to 5, characterized in that a gas pressure of 2xl0 ⁴ Pa to 2xl0 ⁵ Pa is selected.

7. The method according to at least one of claims 1 to 6, characterized in that the organic

Compound is introduced in gaseous form or as an aerosol.

8. The method according to at least one of claims 1 to

7, characterized in that the discharge is operated in a pulsed manner.

9. The method according to at least one of claims 1 to

8, characterized in that nitrogen is supplied as the carrier gas.

10. The method according to at least one of claims 1 to 9, characterized in that the deposition is carried out using a filamented barrier discharge.

11. The method according to at least one of claims 1 to 10, characterized in that the deposition is carried out using an electronically controlled arc discharge.

12. Use of the polymer layer produced according to at least one of claims 1 to 11 for applying an adhesive coating, in particular an epoxy-based coating.

13. Use of the at least one of the

Claims 1 to 11 produced polymer layer for bonds, in particular for bonds using epoxy-based adhesives

14. Use of the according to at least one of the

Claims 1 to 11 produced polymer layer for bonds without additional adhesive

15. Use of the polymer layer produced according to at least one of claims 1 to 11 for the application of printing inks, in particular water-based printing inks.

16. Use of the polymer layer produced according to at least one of claims 1 to 11 for applying an adherent metallization.

17. Use of according to at least one of the

Claims 1 to 11 produced polymer layer as a biocompatible layer, in particular as a biocompatible layer on implants.

18. Use of the polymer layer produced according to at least one of claims 1 to 11 for influencing the attachment of proteins and cells.