PTC compositions based on PVDF and their applications for self-regulated heating systems
The present invention relates to a PTC composition comprising, by weight, the total being 100%: A) 40 to 80% of PVDF; B) 0 to 40% (advantageously 10 to 40%) of an acrylic or styrene polymer; C) 0 to 40% of an epoxy resin; D) 0 to 60% of at least one metal oxide; E) 0 to 25% of a carbonaceous conductive filler D+E being equal to at least 10%. To prepare the composition of the invention, the various constituents are blended in such a way that (A) is in the melt state, then the product obtained is extruded, moulded or injection-moulded or else deposited on a substrate. Once the composition has been converted into an article, for example into a sheet or bar, it is provided with at least two electrodes that serve as the power lead-in and return, respectively. The composition may also be placed between two conducting plates that serve as the power lead-in and return, respectively.
1 . PTC composition comprising, by weight, the total being 100%:
A) 40 to 80% of PVDF;
B) 0 to 40% of an acrylic or styrene polymer;
C) 0 to 40% of an epoxy resin;
D) 0 to 60% of at least one metal oxide;
E) 0 to 25% of a carbonaceous conductive filler;
D+E being equal to at least 10%.
2 . Composition according to claim 1 , comprising 10 to 40% of the acrylic or styrene polymer B).
3 . Composition according to claim 1 wherein B+C are equal to at least 10%.
4 . 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).
5 . 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).
6 . Composition according to claim 5 , in which the PVDF (A) is selected from PVDF homopolymers and VDF/HFP copolymers containing at least 85 wt % VDF.
7 . Composition according to claim 1 , in which the carbonaceous conductive filler is graphite, carbon black, fullerenes or carbon nanotubes.
8 . 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.
9 . Composition according to claim 8 , in which the modified PVDF represents between 0.5 and 30% of (A) by weight.
10 . Composition according to claim 1 , in which (B) is PMMA.
11 . Composition according to claim 1 , in which (B) is a block copolymer having at least one block containing at least 50% methyl methacrylate by weight.
12 . Composition according to claim 11 , in which (B) is a triblock formed from a poly(butylacrylate) block between two PMMA blocks.
13 . Composition according to claim 11 , in which (B) is selected from S-B-M triblocks in which:
each block is linked to another by means of a covalent bond or an intermediate molecule linked to one of the blocks via a covalent bond and to the other block via another covalent bond;
the block M is formed from MMA monomers that are optionally copolymerized with other monomers and comprises at least 50% methyl methacrylate (MMA) by weight;
the block B is incompatible with the PVDF and with the block M; and
the block S is incompatible with the block B and the block M, and its T g or its melting point T m is above the T g of B.
14 . Composition according to claim 13 , in which the block B of the S-B-M triblock is made of polybutadiene.
15 . Composition according to claim 13 , in which the block S of the S-B-M triblock is made of polystyrene.
16 . Composition according to claim 1 , in which (B) is an S-B-S triblock copolymer.
17 . The composition of claim 1 comprising a circuit protection device.
18 . Composite comprising the composition according to claim 1 .
19 . Composite according to claim 18 comprising the composition according to claim 1 , placed between two conducting plates.
20 . Composite according to claim 18 comprising a substrate completely or partly covered with the composition according to claim 1 .
21 . Composite according to claim 18 , in which the substrate is a honeycomb formed from an insulator.
22 . The composite of claim 18 comprising a heater.
23 . The compositie of claim 18 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 14 and electric current lead-in and return means; and
optionally, a protective layer.
24 . Use of the material of claim 22 to heat a gas.
25 . Use according to claim 24 in which the passenger compartments of motor vehicles or the cabins of aircraft are heated.