A METHOD OF COATING THE SURFACE OF AN INORGANIC SUBSTRATE WITH AN ORGANIC MATERIAL AND THE PRODUCT OBTAINED

Abstract: The invention relates to method of coating the surface of an inorganic substrate of glass, silicon dioxide, ceramics or carbon, which method comprises a step of cleaning the surface of the substrate by subjecting the surface to a reducing gas plasma, a step of activating the surface by generating radicals on the surface of the substrate by subjecting the surface to a reducing gas plasma and forming a first layer on the substrate surface using a plasma enhanced polymerization process employing one or more monomers comprising monomers with a sufficient low molecular weight for them to be in their gaseous state in the gas plasma, selected from the group consisting of C1-C16 alkanes, C2-C16 alkanes, C2-C16 alkynes, C2-C16 alkynes, styrene, aromatic monomers of styrene compounds, monomers of vinyl- and acrylate-compounds.

Description: A method of coating the surface of an inorganic substrate with an organic material and the product obtained The present invention relates to a method for coating the surface of an inorganic substrate of glass or carbon with an organic material and the product obtained. Coating of glass or carbon substrates with organic material is a very difficult process. To obtain sufficient binding strength between the coating material and the substrate material it is necessary to clean the surface of the substrate before coating. This cleaning is usually a chemical treatment, e.g. with organic solvents, to remove impurities. Even after the cleaning process the bonding between the organic molecules of the coating and the inorganic surface of the substrate has difficulties in resisting especially strong basic and strong ionic (salt) environments. The problem is well known from adhering of polymers to glass, where the polymer-coatings have a tendency to de-bind from the glass substrate and loose their ability to fulfil their purpose. Several attempts have been made to avoid the above- mentioned problems and one solution is the use of plasma technology. US 5061567 discloses a coated glass substrate and the making of the same. A glass substrate is coated with an organomineral film in a plasma process. The purpose of the coating is primarily to improve the optical properties of the glass and the coated glass substrate does not have any properties to resist the influence of environments with e.g. high pH values. Because of the difficulties in providing coatings on substrates of glass or carbon which do not have a tendency to de-bind from the substrate, there is a need for a method for coating surfaces of glass or carbon which will result in strong and durable bonding between the coating and the surface of the glass or carbon, even when exposed to very harsh environments e.g. with high pH values . It has now surprisingly appeared that the above-mentioned needs can be met by the present invention. The invention provides a method by which a surface of an inorganic substrate, such as glass or carbon, can be coated with organic material, and where the bonding between the substrate and the coating is extremely strong and is able to resist harsh chemical environments e.g. with high pH values . The invention also provides a method which is more environment-friendly than the known methods, as no organic solvents are used in the method. Furthermore, the method according to the invention is relatively cheap and can be performed as a continuous process in one reaction chamber. Furthermore, the invention provides a coated inorganic substrate with a very wear-resistant, strong and long lasting organic coating. The method according to the invention and the coated substrate obtained by the method are defined in the claims . The method according to the invention provides substrates coated with organic material that are very suitable for use in aggressive environments with e.g. high pH values. The coating is very strong and has only little tendency to de-bind from the substrate. Furthermore, the method provides substrates coated with an organic material which has appeared to be very suitable for use in biochemical processes. Further, the coated substrate provides good basis for vulcanising. The method of coating the surface of an inorganic substrate of glass, ceramics or carbon according to the invention comprises the steps of i) cleaning the surface of the substrate by subjecting the surface to a reducing gas plasma, ii) activating the surface by generating radicals on the surface of the substrate by subjecting the surface to a reducing gas plasma and forming a first layer on the substrate surface using a plasma enhanced polymerization process employing one or more monomers comprising monomers with a sufficient low molecular weight for them to be in their gaseous state in the gas plasma, selected from the group consisting of Ci-Ciε alkanes, C 2 -Cι 6 alkenes, C 2 -Cι 6 alkynes, C2-C 15 alkynes, styrene, aromatic monomers of styrene compounds, monomers of vinyl- and acrylate- compounds. In a preferred embodiment of the method according to the invention the monomers are selected from the group consisting of acethylene, ethane, ethylene, hexane, hexene, 1-hexene, 3-methyl-l-hexene, 1, 4-hexadiene, hexyne, 1-hexyne, methylacrylate, styrene and vinylpyrolidone . In order to secure that the monomers are able to be in their gaseous state in the plasma it is preferred that the monomers have a molecular weight up to 350. In the cleaning step it is important that the reducing gas is substantially free of oxygen and preferably the reducing gas should be able to remove the major part or more preferably substantially all of the oxygen present at the surface of the substrate. In a preferred embodiment or the method according to the invention the reducing gas is H 2 , NH 3 , B 2 H 4 or F 2 or a mixture of H 2 , NH 3 , B 2 H 4 , or F 2 and a inert gas, and preferably the mixture is a mixture of H 2 and argon. In a preferred embodiment the substrate is coated with two layers of organic material. By use of this method including two layers of organic material a substrate having particular good properties for immobilizing biomolecules, vulcanising and/or adhering onto may be obtained. This embodiment of the method according to invention may e.g. be carried out by subjecting the coated substrate to a plasma enhanced polymerisation of monomers selected from the group consisting of vinylpyrolidone, acrylonitrile, glycidylmatacrylate, methacrylacid-anhydride, methyl-benzaldehyde and other vinyl or acryl containing monomers . To avoid any contact with the oxygen of the atmosphere and to make the process as less complicated as possible a preferred embodiment of the method according to invention is that the method is executed subsequently in one chamber and preferably the method is executed as a continuous process. As a precaution to prevent contact between oxygen and the substrate to be treated it is preferred that the atmosphere in said chamber at any step in the method is inert and/or reducing. To optimize the conditions for the method according to invention it is preferred that the pressure is 0,01 to 1,0 mbar while the method is carried out, more preferably 0,04 to 0,4 mbar. It is further preferred that the substrate is exposed to plasma with reducing gas from 1 to 3600 seconds, more preferably from 10 to 300 seconds and preferably the substrate is exposed to plasma-polymerisation from 1 to 6000 seconds, more preferably from 10 to 120 seconds. In preferred embodiments of the method according to the invention the step i) comprises the generation of radicals by use of gas plasma generated by excitation of the gas in an alternating current (AC) , a direct current (DC) , low frequency (LF) , audio frequency (AF) , radio frequency (RF) or microwave generated electric field. Of course, any other suitable source for generating plasma may be used according with the invention. In a first preferred embodiment of the method according to the invention, the inorganic substrate is glass or glass fibers. In a second preferred embodiment of the method according to the invention, the inorganic substrate is silicon dioxide. In a third preferred embodiment of the method according to the invention, the inorganic substrate is ceramic or ceramic fibers. In a fourth preferred embodiment of the method according to the invention, the inorganic substrate is a carbon or carbon fibers. The invention also comprises a coated inorganic substrate obtained by the method described above. The invention may be carried out in any known type of equipment for carrying out the process of generating of plasma for coating purposes e.g. a 3-phase plasma chamber is very suitable. The invention shall now be explained in further details with reference to the examples. The examples are only meant to illustrate specific embodiments of the invention and should not in any way be considered to be a limitation of the scope of the invention, as the skilled person would be able to carry out the invention in may other ways. Example 1 A glass slide having a dimension of 2,5x7 cm was placed in a 12 litre 3-phase plasma chamber. The pressure in the chamber was lowered to 0,08 mbar and a mixture of argon (10 seem) and hydrogen (5 seem) was led to the chamber. A plasma of 10 W/litre was started. After 60 seconds the argon supply was stopped and the hydrogen flow was increased to 15 seem. After another 60 seconds styrene was led to the chamber with 10 seem, immediately after the flow of hydrogen was stopped. When 20 seconds had passed with flow of styrene, the effect was lowered to 2 W/litre. After 60 seconds with flow styrene, a flow of metacrylacid-anhydride was led to the chamber, and hereafter the styrene flow was stopped. The polymerisation of metacrylacid-anhydride was continued for 60 seconds. The surface of the glass slide was used for binding DNA- oligomers, with a primary amine in the 3' -end. During the use of the bonded DNA, the surface of the glass slide was exposed to environments having a pH value up to 11. Example 2 Chopped glass fibres were placed in an 80 litres 3-phase plasma chamber. The chamber was designed, so the fibres moved from one end of the plasma to the other end and in such a way that the pumping was in the middle of the chamber. A flow of hydrogen was led to the end from which end the fibres were moving, and onemer was led to the other end. During this process the pressure was 0,1 mbar, the flow of hydrogen was 30 seem and the flow of monomer acethylene was 30 seem. The plasma had an effect of 8 W/litre. The starting velocity of the fibres was set so that the fibres were in the hydrogen area in 90 seconds and in the acethylene area for 90 seconds. The fibres were used as reinforcement in rubber. The coating of acethylene results in a large amount of dopple bindings in the surface, which are very suitable for reaction with a rubber matrix in the process of vulcanisation. Example 3 The Example relates to silicon wafers. When silicon wafers are exposed to atmospheric air, a silicon dioxide glass layer is formed on the wafer surface. Binding organic compounds to this silicon dioxide glass is difficult, in particular because a lot of process steps in the known chip technology involve as well high pH as organic solvents. 4" wafers were placed in a 250 litre 3-phase plasma chamber. The pressure in the chamber was lowered to 0,05 mbar and a mixture of argon (20 seem) and hydrogen (10 seem) was led to the chamber. A plasma of 2,5 W/litre was started. After 120 seconds the argon supply was cut of and the hydrogen flow was increased to 25 seem. After another 120 seconds hexene was led to the chamber with a flow of 50 seem, immediately after the flow of hydrogen was stopped. After 30 seconds had passed with hexane flow, the plasma effect was reduced to 1,5 W/litre and the plasma polymerisation continued for another 30 seconds. The resulting wafers were tested in different environments. The hexane/wafer binding was resistant to NaOH solution at pH 14, acetone/ultrasound and heating up to 90°C.

Claims: CLAIMS 1. A method of coating the surface of an inorganic substrate of glass, silicon dioxide, ceramics or carbon comprising the steps of i) cleaning the surface of the substrate by subjecting the surface to a reducing gas plasma, ii) activating the surface by generating radicals on the surface of the substrate by subjecting the surface to a reducing gas plasma and forming a first layer on the substrate surface using a plasma enhanced polymerization process employing one or more monomers comprising monomers with a sufficient low molecular weight for them to be in their gaseous state in the gas plasma, selected from the group consisting of Cι-Cj.6 alkanes, C 2 -Ci6 alkenes, C 2 -Ci6 alkynes, C 2 -Cι 6 alkynes, styrene, aromatic monomers of styrene compounds, monomers of vinyl- and acrylate- compounds . 2. A method according to claim 1, characterized in that said monomers are selected from the group consisting of acethylene, ethane, ethylene, hexane, hexene, 1-hexene, 3-methyl-l-hexene, 1, 4-hexadiene, hexyne, 1-hexyne, methylacrylate, styrene and vinylpyrolidone. 3. A method according to claims 1 and 2, characterized in that said monomers have a molecular weight up to 350. 4. A method according to claims 1-3, characterized in that the reducing gas is H 2 , NH 3 , B 2 H 4 or F 2 or a mixture of H 2 , NH 3 , B 2 H, or F 2 and a inert gas, said mixture preferably being a mixture of H 2 and argon. 5. A method according to claims 1-4, characterised in that the substrate further is coated with a second layer by subjecting the coated substrate to a plasma enhanced polymerisation of monomers selected from the group consisting of vinylpyrolidone, acrylonitrile, glycidylmatacrylate, methacrylacid-anhydride, methyl- benzaldehyde and other vinyl or acryl containing monomers . 6. A method according to claims 1-5, characterized in that the method is executed subsequently in one chamber. 7. A method according to claims 1-6, characterized in that the method is executed as a continuous process. 8. A method according to claim 6, characterized in that the atmosphere in said chamber at any step in the method is inert and/or reducing. 9. A method according to claims 1-8, characterized in that that the pressure is 0,01 to 1,0 mbar, preferably 0,04 to 0,4 mbar. 10. A method according to claims 1-9, characterized in that the substrate is exposed to plasma with reducing gas for 1 to 3600 seconds, preferably for 10 to 300 seconds. 11. A method according to claims 1-10, characterized in that the substrate is exposed to plasma-polymerisation for 1 to 6000 seconds, preferably for 10 to 120 seconds. 12. A method according to any of the preceding claims, characterized in that the step i) comprises the generation of radicals by use of gas plasma generated by excitation of the gas in an alternating current (AC) , a direct current (DC) , low frequency (LF) , audio frequency (AF) , radio frequency (RF) or microwave generated electric field. 13. A method according to any of the claims 1-12, characterized in that the inorganic substrate is glass or glass fibers. 14. A method according to any of the claims 1-12, characterized in that the inorganic substrate is silicon dioxide. 15. A method according to any of the claims 1-12, characterized in that the inorganic substrate is ceramic or ceramic fibers . 16. A method according to any of the claims 1-12, characterized in that the inorganic substrate is a carbon or carbon fibers . 17. A coated inorganic substrate obtained by the method according to claim 1 to 15.

Inventors: WINTHER-JENSEN BJOERN, WINTHER-JENSEN, BJOERN
Applicants: NKT RES AS, WINTHER JENSEN BJOERN, NKT RESEARCH A/S, WINTHER-JENSEN, BJOERN
Application year: 2001
Main classification: C03C17
IPC codes: B05D3, B05D7, B32B9, B32B17, C03C17, C03C23, C03C25, C04B41, C08F2