PVDF-based PTC paints and their applications for self-regulated heating systems
The present invention relates to a composition comprising, by weight, the total being 100%: A) 40 to 80% of PVDF; B) 10 to 40% of PMMA; and C) 10 to 40% of a conductive filler. This composition has a PTC effect and is advantageously used in the form of a film (paint) covering a substrate. The composition of the invention is dissolved in a solvent and then spread over a substrate and the solvent evaporated. The metal terminals for connection to the electrical circuit may be placed at the ends of the coating before or after application. The invention also relates to a composite, namely the substrate covered with the PTC composition described above.
1 . Composition comprising, by weight, the total being 100%:
A) 40 to 80% of PVDF;
B) 10 to 40% of PMMA; and
C) 10 to 40% of a conductive filler.
2 . Composition according to claim 1 , in which the PVDF is selected from VDF/TFE/HFP copolymers having a respective molar composition of 60 to 80/15 to 20/0 to 25, the total being 100.
3 . Composition according to claim 1 , in which the PVDF is selected from vinylidene fluoride (VDF) copolymers containing at least 60 wt % VDF, the comonomer being selected from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE).
4 . Composition according to claim 1 , in which the PVDF (A) is a blend of (A1) selected from PVDF homopolymers and VDF/HFP copolymers containing at least 85 wt % VDF and of (A2) which are VDF/TFE/HFP copolymers of respective molar composition 60 to 80/15 to 20/0 to 25, the total being 100.
5 . Composition according to claim 4 , in which the proportions of (A1) and (A2) are in the ratio (A1)/(A2) of between 20/80 and 80/20 by weight.
6 . Composition according to claim 1 , in which the PVDF is completely or partly modified and is selected from:
PVDFs grafted with an unsaturated monomer, the grafting being carried out by irradiation of a blend in the absence of oxygen;
PVDFs irradiated in the presence of oxygen; and
dehydrofluorinated and then oxidized PVDFs.
7 . Composition according to claim 6 , in which the modified PVDF represents between 0.5 and 30% of (A) by weight.
8 . Composition according to claim 6 , in which it is the PVDF (A1) that is completely or partly modified.
9 . Composition according to claim 1 , in which the filler (C) is selected from graphite and carbon black.
10 . The composition of claim 1 comprising a PTC paint comprising 1 part of the composition according to claim 1 and from 2 to 5 parts of a solvent.
11 . The composition according to claim 10 in which the solvent may be selected from acetone, isophorone, dimethylformamide, methylethylketone, N,N-dimethylacetamide and N-methylpyrrolidone.
12 . Composite comprising a substrate completely or partly covered with the composition according to claim 1 .
13 . Composite according to claim 12 , in which the substrate is a honeycomb formed from an insulator.
14 . Composite according to claim 13 , in which, on each of the two opposite faces of the honeycomb, there is a conductor serving as the current lead-in and the current return.
15 . Composite according to claim 12 , in which the substrate is a woven fabric of glass or of an insulator.
16 . Composite according to claim 12 , which is a hose comprising, going from the inside to the outside:
optionally, an inner layer in contact with the fluid transported;
an outer layer;
a paint layer according to any one of claims 1 to 9 and electric current lead-in and return means; and
optionally, a protective layer.
17 . Composite of claim 12 comprising a heater.
18 . Use of the material of claim 13 , to heat a gas.
19 . Use according to claim 17 in which the passenger compartments of motor vehicles or the cabins of aircraft are heated.