Process for producing polymeric piezoelectric elements and the article formed thereby

• US 3,931,446 A
• Filed: 03/11/1974
• Issued: 01/06/1976
• Est. Priority Date: 09/26/1970
• Status: Expired due to Term

• Current Assignee: Kureha Kagaku Kogyo Kabushiki Kaisha
• Original Assignee: Kureha Kagaku Kogyo Kabushiki Kaisha
• Inventors: Oikawa, Takao, Murayama, Naohiro
• Primary Examiner(s): Weiffenbach, Cameron K.
• Application Number:
  US05/449,809
• Time in Patent Office: 666 Days
• Field of Search: 117/227, 117/213, 310/9.5, 310/8, 427/100, 427/12, 427/379, 427/380, 427/124, 427/171, 427/385, 428/421, 428/457
• US Class Current: 428/421
• CPC Class Codes: B29C 71/0063 for changing crystallisation
• CPC Class Codes: C08J 2327/16 Homopolymers or copolymers of vinylidene fluoride
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: H01G 7/023 of macromolecular compounds
• CPC Class Codes: H10N 30/098 Forming organic materials
• CPC Class Codes: Y10T 428/3154 Of fluorinated addition polymer from unsaturated monomers
• CPC Class Codes: Y10T 428/31678 Of metal

Abstract

A highly piezoelectric polyvinylidene fluoride element is prepared by treating a polyvinylidene fluoride film having an infrared absorbance ratio D₅₃₀ /D₅₁₀ of not more than 1.2, namely having a major proportion of β-type crystal structure, at a temperature of at least 40°C but below the melting point of the film while applying to the film a direct current voltage of 200 KV/cm to 1,500 KV/cm. The polyvinylidene fluoride film having a major proportion of β-type crystal structure may be obtained by stretching a fabricated article of polyvinylidene fluoride having a major proportion of α-type crystal structure under specific conditions.

Claims

1. A polarized piezoelectric film comprising an oriented or unoriented polyvinylidene fluoride having electrodes on both surfaces, wherein said PVDF has an infrared absorbance ratio D₅₃₀ /D.sub. 510 of not more than 1.2.

2. The film of claim 1, wherein said PVDF has an infrared absorbance ratio D₅₃₀ /D₅₁₀ of not more than 0.6.

3. The film of claim 1, wherein said electrodes are formed by a vacuum metallizing process.

4. The film of claim 1, wherein said film has a piezoelectric constant in excess of 1.5 ×

10.sup.^-7 c.g.s.e.s.u.

6. The process of claim 1, wherein said film is heated at a temperature of 50°

C to 160°

C.

7. The process of claim 1, wherein prior to said heating, said film having a major proportion of the β

-type crystal structure is heat-treated under tension at a temperature of at least 80°

C but below the melting point of said film.

8. The process of claim 1, wherein said film is heated for a period of 10 minutes to 2 hours.

9. The process of claim 1, wherein said electrodes are formed by a vacuum metallizing process.

10. The process of claim 1, wherein said stretching is conducted below 100°

C.

11. The process of claim 1, wherein said film having a major part of the β

-type crystal structure exibits an infrared absorbance ratio D₅₃₀ /D₅₁₀ of not more than 0.6.

5. A process for producing highly piezoelectric elements which comprises stretching a polyvinylidene fluoride film having a major proportion of the α

-type crystal structure at a temperature not higher than 100°

C in at least one axial direction to form a polyvinylidene fluoride film having a major proportion of the β

-type crystal structure as exibited by an infrared absorbance ratio D₅₃₀ /D.sub. 510 of not more than 1.2;

attaching electrodes on both surfaces of the resulting film; and

then treating the resulting film with the electrodes to a temperature of at least 40°

C, but below the melting point of said film, while applying to said film a direct current voltage of between 200 KV/cm amd 1,500 KV/cm.