# US 12,004,429 B2 · Piezoelectric body film, piezoelectric body film production method, and piezoelectric body device

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- Number: US 12,004,429 B2
- Document ID: US12004429B2
- Status: Granted
- Kind: B2
- Application number: 18/464,745
- Filed: 2023-09-11
- Published: 2023-12-28
- Granted: 2024-06-04
- Earliest claimed: 2018-03-05
- Assignees: Kureha Corporation
- Applicants: Kureha Corporation
- Inventors: Yusuke Sato; Hisaaki Terashima; Nobufumi Sato; Kazuyuki Kanno; Keiko Aita
- Web page: https://patentgrep.com/patent/US12004429B2

## CPC

- H10N 30/857: Macromolecular compositions
- B29C 55/06: parallel with the direction of feed
- B29C 71/02: Thermal after-treatment {(B29C71/0063 and B29C71/0072 take precedence)}
- C08J 5/18: Manufacture of films or sheets
- C08J 7/00: Chemical treatment or coating of shaped articles made of macromolecular substances (coating with metallic material C23C; electrolytic deposition of metals C25)
- C08J 7/08: {Heat treatment}
- G01N 25/16: by investigating thermal coefficient of expansion
- H10N 30/04: Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
- H10N 30/098: Forming organic materials
- C08J 2327/16: Homopolymers or copolymers of vinylidene fluoride
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00)
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

To provide a piezoelectric body film that can suppress decrease in the piezoelectric constant d31, a method of producing a piezoelectric body film, and a piezoelectric body device. A piezoelectric body film comprising a fluororesin as a piezoelectric material, the fluororesin containing, as a main constituent unit, a repeating unit derived from vinylidene fluoride, a piezoelectric constant d31 of the piezoelectric body film being 20 pC/N or greater, and an extrapolated onset temperature at start of shrinkage determined by TMA measurement being not lower than 90° C. and not higher than 115° C. The difference between piezoelectric constants d31 measured before and after heating the piezoelectric body film at 100° C. for 24 hours relative to the piezoelectric constant d31 before the heating for 24 hours is 20% or less.

## Claims

### Claim 1

A method of producing a piezoelectric body film, the method comprising:
forming a film, the forming including forming a crystalline polymer film having piezoelectricity by subjecting a sheet to stretching treatment and polarization treatment, the sheet being formed from a fluororesin containing a repeating unit derived from vinylidene fluoride as a main constituent unit;
performing relaxation including performing heat fixation and relaxation of residual strain of the crystalline polymer film by subjecting the crystalline polymer film to heating at a first temperature that is not lower than 90° C. and not higher than 115° C. for not less than 5 seconds and not more than 130 seconds; and
performing a secondary heating including subjecting the crystalline polymer film after the performing relaxation to reheating at a temperature that is not lower than the first temperature and not higher than 140° C. for not less than 15 seconds and not more than 120 seconds, and producing the piezoelectric body film.

### Claim 2 (depends on 1)

The method of producing a piezoelectric body film according to claim 1, wherein, in the performing the secondary heating, heating of the crystalline polymer film is performed at the first temperature.

### Claim 3

A method of producing a piezoelectric body film from a crystalline polymer sheet,
the method comprising:
forming a film, the forming including forming a crystalline polymer film having piezoelectricity by subjecting a sheet to stretching treatment and polarization treatment, the sheet being formed from a fluororesin containing a repeating unit derived from vinylidene fluoride as a main constituent unit; and
performing relaxation including performing heat fixation and relaxation of residual strain of the crystalline polymer film by subjecting the crystalline polymer film to heating at a temperature higher than 115° C. and not higher than 150° C. for not less than 10 seconds and not more than 140 seconds.