Method to double the piezo-and pyroelectric of polyvinylidine fluoride (PVDF) films

• US 5,254,296 A
• Filed: 11/13/1991
• Issued: 10/19/1993
• Est. Priority Date: 12/11/1990
• Status: Expired due to Fees

• Current Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Original Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Inventors: Perlman, Martin M.
• Primary Examiner(s): Thurlow, Jeffery
• Application Number:
  US07/791,275
• Time in Patent Office: 706 Days
• Field of Search: 264/22, 264/24, 264/288.4, 425/174.8 E
• US Class Current: 264/435
• CPC Class Codes: B29C 55/005 characterised by the choice of materials
• CPC Class Codes: B29C 59/10 by electric discharge treatment
• CPC Class Codes: B29K 2027/16 PVDF, i.e. polyvinylidene fluoride
• CPC Class Codes: B29K 2995/0003 having particular electrical or magnetic properties, e.g. piezoelectric
• CPC Class Codes: H10N 15/15 Thermoelectric active materials
• CPC Class Codes: H10N 30/098 Forming organic materials

Abstract

Polyvinylidene fluoride (PVDF) films and co-polymers thereof possess the highest values of piezoelectric and pyroelectric constants of any known polymer. These films, up to present, have been first subjected to stretching and then to a high electric field (or corona charge) at an elevated temperature to provide a maximum piezoelectric constants (d₃₁) of about 30-35 pC/N and a maximum pyroelectric constants (p) of about 3.5 nC/cm² K. It has now been found that the piezoelectric constant d₃₁ and pyroelectric constant p of these films can be increased up to about 60 pC/N and 6 nC/cm² K respectively when they are subjected to simultaneously stretching and corona poling with a poling field E_p =0.55MV/cm, a stretching ratio S.R.=4.5X and a poling temperature T_p =80° C.

Claims

1. A method of manufacturing polymers films with enhanced piezoelectric and pyroelectric constants wherein films of polyvinylidene fluoride (PVDF) and co-polymers thereof are subjected to simultaneous stretching and corona poling at an elevated temperature, the corona poling being performed with a grid placed between a corona needle and a film, the grid being electrically connected to a controlled voltage source in order to control the surface potential of that film.

2. A method as defined in claim 1, wherein a poling field (E_p) of at least 0.5 MV/cm is maintained during the simultaneous stretching and corona poling step.

3. A method as defined in claim 1, wherein a stretching ratio (S.R.) between about 4×

and 4.5×

is reached during the simultaneous stretching and corona poling step.

4. A method as defined in claim 2, wherein a stretching ratio (S.R.) between about 4×

and 4.5×

is reached during the simultaneous stretching and corona poling step.

5. A method as defined in claim 1, wherein a poling temperature (T_p) of about 70°

to 85°

C. is maintained during the simultaneous stretching and corona poling step.

6. A method as defined in claim 2, wherein a poling temperature (T_p) of about 70°

to 85°

C. is maintained during the simultaneous stretching and corona poling step.

7. A method as defined in claim 3, wherein a poling temperature (T_p) of about 70°

to 85°

C. is maintained during the simultaneous stretching and corona poling step.

8. A method a as defined in claim 4, wherein a poling temperature (T_p) of about 70°

to 85°

C. is maintained during the simultaneous stretching and corona poling step.

9. A method as defined in claim 1, wherein the films are co-polymers of PVDF and TriFE and a poling temperature (T_p) of about 70°

to 85°

C. is maintained during the simultaneous stretching and corona poling step.

10. A method as defined in claim 9, wherein a stretching ratio (S.R.) between about 4×

and 4.5×

is reached during the simultaneous stretching and corona poling step.

11. A method as defined in claim 9, wherein a poling field (E_p) of at least 0.5 MV/cm is maintained during the simultaneous stretching and corona poling step.

12. A method as defined in claim 10, wherein a poling field (E_p) of at least 0.5 MV/cm is maintained during the simultaneous stretching and corona poling step.

13. A method as defined in claim 1, wherein a ceramic with a high piezoelectric constant is mixed into the polymer films before the films are subjected to simultaneous stretching and corona poling.