Dielectric film and power capacitor comprising dielectric film

1. A dielectric film comprising:

a dielectric polymer substrate having two surfaces opposite to each other; and

a coating layer formed on at least one of the two surfaces of the dielectric polymer substrate by chemical vapor deposition polymerization and/or irradiation polymerization,

wherein the dielectric polymer substrate has a first thickness between the two surfaces and the coating layer has a second thickness less than 50% of the first thickness of the dielectric polymer substrate, and

wherein the coating layer comprises any one selected from parylenes, polynitriles, poly(meth)acrylates, polyvinyl ethers, polyvinylidenes that are one selected from polyvinylidene chloride, polyvinylidene cyanide, and copolymers or mixtures thereof.

2. The dielectric film according to claim 1 , wherein the second thickness of the coating layer is less than 30% of the first thickness of the dielectric polymer substrate.

3. The dielectric film according to claim 1 , wherein the coating layer is any one selected from polyvinylidenes or mixtures thereof.

4. The dielectric film according to claim 1 , wherein the parylene is any one selected from Parylene F, Parylene N, Parylene C, Parylene D, Parylene HT, reactive parylenes, and copolymers or mixtures thereof.

5. The dielectric film according to claim 1 , wherein the polynitrile is any one selected from acrylonitrile homopolymers and copolymers.

6. The dielectric film according to claim 1 , wherein the copolymer is a crosslinking copolymer.

7. The dielectric film according to claim 6 , wherein the crosslinking copolymer is derived from a mixture of (meth)acrylate(s), vinyl ether(s), and initiator(s).

8. The dielectric film according to claim 1 , wherein the irradiation polymerization is conducted by any one selected from UV irradiation, electron beam irradiation, gamma irradiation, X-ray irradiation, microwave irradiation and combinations thereof.

9. The dielectric film according to claim 1 , wherein the dielectric polymer substrate comprises any one selected from polypropylene (PP), crosslinked polypropylene (PPX), polyethylene (PE), crosslinked polyethylene (PEX), polyethylene terephthalate (PET), polycarbonate (PC), polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), polyamide (PA), polyimide (PI), polyetherimide (PEI), polyvinyl chloride (PVC), polystyrene (PS), cyanoresins, and copolymers or mixtures thereof.

10. The dielectric film according to claim 1 , wherein the dielectric film further comprises a primer layer between the dielectric polymer substrate and the coating layer.

11. The dielectric film according to claim 10 , wherein the primer layer comprises a silane.

12. A power capacitor comprising a dielectric film according to claim 1 .

13. A process for preparing a dielectric film, the process comprising:

providing a dielectric polymer substrate having two surfaces opposite to each other and a first thickness constituted between the two surfaces; and

forming a coating layer on at least one of the two surfaces of the dielectric polymer substrate by chemical vapor deposition polymerization and/or irradiation polymerization, wherein the coating layer has a second thickness which is less than 50% of the first thickness of the dielectric polymer substrate, and

wherein the coating layer comprises any one selected from parylenes, polynitriles, poly(meth)acrylates, polyvinyl ethers, and polyvinylidenes that are one selected from polyvinylidene chloride, polyvinylidene cyanide and copolymers or mixtures thereof.

14. The process according to claim 13 , wherein the process further comprises forming a primer layer on the at least one of the two surfaces of the dielectric polymer substrate before forming the coating layer.

15. The dielectric film according to claim 1 , wherein the irradiation polymerization is conducted by any one selected from gamma irradiation, X-ray irradiation, microwave irradiation and combinations thereof.