Method of producing a layer of a vulcanized silicone rubber composition having an improved adhesion to the substrate surface
View Patent ↗A method of producing a layer of a UV-cured silicone rubber composition on a substrate surface, including applying a primer composition to the substrate surface and hardening the primer composition followed by applying a UV-curable silicone rubber composition, and UV-curing the curable silicone rubber composition. At least one UV-sensitive crosslinking catalyst selected from compounds which initiate and promote curing of UV-curable silicone rubber compositions, is added to the silicone primer composition in any desired sequence before, during or after hardening of the silicone primer composition.
1. A method of producing a layer of a UV-cured silicone rubber composition on a substrate surface to obtain an electrical insulator, the method comprising:
applying a silicone primer composition comprising at least one UV-sensitive crosslinking catalyst to the substrate surface,
followed by applying a UV-curable silicone rubber composition on the silicone primer composition, and UV-curing said UV-curable silicone rubber composition,
wherein the at least one UV-sensitive crosslinking catalyst initiates and promotes curing of the UV-curable silicone rubber composition,
wherein the UV-sensitive crosslinking catalyst is formed from at least one metal selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum.
2. The method according to claim 1 , wherein said UV-curable silicone rubber composition applied to the surface of the hardened silicone primer composition is a room temperature UV-curable silicone rubber composition.
3. The method according to claim 1 , wherein the primer composition comprises compounds selected from a hydrolysable silicate, a hydrolysable titanate, a reactive silane, a siloxane and an organic solvent.
4. The method according to claim 3 , wherein the primer composition comprises an organic solvent selected from the group consisting of an aliphatic hydrocarbon, a linear (C 4 -C 8 )-alkane, a (C 4 -C 8 )-isoalkane, a ketone, benzene, toluene, xylene and ethylbenzene.
5. The method according to claim 1 , wherein the primer composition contains a hydrolysable silicate selected from the group consisting of a tetra[(C 1 -C 8 )-alkyl]-orthosilicate, tetraethyl-silicate, tetrapropyl-orthosilicate, tetrabutyl-orthosilicate, a (C 1 -C 8 )alkoxy-(C 1 -C 8 )alkyl-orthosilicate, and butoxy-ethyl-orthosilicate.
6. The method according to claim 1 , wherein the primer composition contains a hydrolysable titanate selected from the group consisting of a tetra[(C 1 -C 8 )-alkoxy]-titanate, tetra[propoxy]-titanate, tetra-[n-butoxy]-titanate, a (C 1 -C 8 )alkoxy-(C 1 -C 8 )alkyl-titanate, and butoxy-ethyl-titanate.
7. The method according to claim 1 , wherein the primer composition contains a reactive silane selected from the group consisting of a tetraalkoxysilane, trialkoxyalkylsilane, and dialkoxyalkylsilane of the formula
[(C 1 -C 4 )alkoxy] x Si[C 1 -C 4 )alkyl] 4-x
wherein x is 2, 3 or 4.
8. The method according to claim 7 , wherein the reactive silane is a tetraalkoxysilane, trialkoxy-monoalkylsilane, tetraethoxysilane, tetrapropoxysilane, triethoxymethylsilane, or tripropoxymethylsilane.
9. The method according to claim 1 , wherein the primer composition contains a reactive siloxane that is a polydimethylsiloxane containing at least one reactive group per molecule.
10. The method according to claim 9 , wherein the polydimethylsiloxane contains at least two reactive groups per molecule, said reactive groups being selected from the group consisting of an ethoxy group, a propoxy group and a butoxy group.
11. The method according to claim 9 , wherein the reactive group of the polydimethylsiloxane is an alkoxy group or a hydroxy group or a vinyl group or an epoxy group.
12. The method according to claim 1 , wherein the UV-sensitive crosslinking catalyst is formed from at least one of ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum, and wherein the UV-sensitive catalyst is present in a heterogeneous form, or as a chemical compound or as a complex of the metal.
13. The method according to claim 12 , wherein the UV-sensitive catalyst consists of the at least one metal.
14. The method according to claim 12 , wherein the at least one metal is deposited on a carrier material selected from the group consisting of charcoal, silica and alumina.
15. The method according to claim 1 , wherein the UV-sensitive catalyst is made from at least one metal selected from the group consisting of rhodium, palladium and platinum, and is present in a heterogeneous form or as a chemical compound or as a complex of the at least one metal.
16. The method according to claim 1 , wherein the UV-sensitive catalyst is present in a heterogeneous form of the metal.
17. The method according to claim 1 , wherein the UV-sensitive catalyst is a heterogeneous platinum catalyst.
18. The method according to claim 1 , wherein the UV-sensitive catalyst is a platinum(0) or platinum(II) compound.
19. The method according to claim 1 , wherein the UV-sensitive catalyst is a chloroplatinic acid in anhydrous form or as hexahydrate, or a platinum Pt(0) or Pt(II) complex which has at least one ligand selected from the group consisting of a halide, a (C 1 -C 8 )alkyl radical, a (C 1 -C 8 )aliphatic unsaturated radical, an aliphatic unsaturated organosilane, and an aliphatic unsaturated organopolysiloxane.
20. The method according to claim 1 , wherein the UV-sensitive catalyst is selected from the group consisting of tetrakis(triphenylphosphino)palladium; a complex of tetrakis(triphenylphosphino)palladium with a ligand selected from the group consisting of tri-(2-tolyl)phosphine, tris-(2-furyl)phosphine and tris(tert-butyl)phosphine; a complex of tetrakis(triphenylphosphino)palladium with a two-valent ligand selected from the group consisting of dppm and dppe; PdCl 2 ; Pd(dppe)Cl 2 ; Pd(OAc) 2 ; Pd(dppe)(OAc) 2 ; a π-allyl-Pd-complex; a di-acetylacetonate complex of Pd, Pt or Ni; and a trimethyl-(cyclopentadienyl)complex of Pt(IV).
21. The method according to claim 1 , wherein said primer composition contains said UV-sensitive catalyst in an amount within the range of 50 ppm to 500 ppm, calculated to the weight of metal contained in the catalyst and the weight of the silicone primer composition, calculated without solvent(s).
22. The method according to claim 1 , wherein the silicone rubber composition applied onto the hardened silicone primer composition is vulcanized with a combined use of UV-irradiation and IR-irradiation, optionally additionally with ultrasound.
23. The method according to claim 1 , wherein the substrate surface is a metal, a glass, a ceramic or a synthetic polymer.
24. An electrical article comprising an electrical insulator formed from the method according to claim 1 .
25. The method according to claim 1 , wherein said UV-curable silicone rubber composition applied to the surface of the hardened silicone primer composition is a room temperature UV-curable liquid silicone rubber composition.
26. The method according to claim 1 , wherein the substrate surface is aluminum, an aluminum alloy, or a chromium/nickel-steel.
27. A method of producing an electrical insulator in a form of a layer of a vulcanized silicone rubber composition on a substrate surface, the method comprising:
applying a silicone primer composition comprising at least one UV-sensitive crosslinking catalyst to the substrate surface,
followed by applying a UV-curable curable silicone rubber composition on the silicone primer composition, and curing said UV-curable curable silicone rubber composition, to obtain an electrical insulator,
wherein the at least one UV-sensitive crosslinking catalyst initiates and promotes vulcanization of the UV-curable silicone rubber composition,
wherein the UV-sensitive crosslinking catalyst is formed from at least one metal selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium and platinum.