Electroacoustic converter film, flexible display, vocal cord microphone, and musical instrument sensor
Provided is an electroacoustic converter film including: a polymeric composite piezoelectric body having piezoelectric particles dispersed in a viscoelastic matrix which is formed of a polymer material exhibiting viscoelasticity at ordinary temperatures; thin film electrodes formed on both sides of the polymeric composite piezoelectric body; and protective layers formed on surfaces of the thin film electrodes. The electroacoustic converter film serves as a speaker capable of being integrated with a flexible display without impairing lightweightness or flexibility, and has considerable frequency dispersion in the storage modulus and also has a local maximum of the loss tangent around ordinary temperatures. A flexible display, a vocal cord microphone and a musical instrument sensor, in each of which the electroacoustic converter film is used, are also provided.
1. An electroacoustic converter film, comprising: a polymeric composite piezoelectric body having piezoelectric particles dispersed in a viscoelastic matrix which is formed of a polymer material exhibiting viscoelasticity at ordinary temperatures; thin film electrodes formed on both sides of the polymeric composite piezoelectric body; and protective layers formed on surfaces of the thin film electrodes,
wherein the polymeric composite piezoelectric body is subjected to polarization processing,
the polymer material has a glass transition temperature of 0° C. to 50° C. at a frequency of 1 Hz, and
the polymer material has a cyanoethyl group.
2. The electroacoustic converter film according to claim 1 , wherein a loss tangent (tan δ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of the electroacoustic converter film has a local maximum of 0.1 or more within a temperature range of 0° C. to 50° C.
3. The electroacoustic converter film according to claim 1 , wherein a storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of the electroacoustic converter film is 10 to 30 GPa at 0° C. and 1 to 10 GPa at 50° C.
4. The electroacoustic converter film according to claim 1 , wherein a product of a thickness of the electroacoustic converter film and a storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of the electroacoustic converter film is 1.0×10 6 N/m to 2.0×10 6 N/m at 0° C. and 1.0×10 5 N/m to 1.0×10 6 N/m at 50° C.
5. The electroacoustic converter film according to claim 1 , wherein, on a master curve obtained from dynamic viscoelasticity measurement of the electroacoustic converter film, a loss tangent (tan δ) at 25° C. and at a frequency of 1 kHz is 0.05 or more.
6. The electroacoustic converter film according to claim 1 , wherein a loss tangent (tan δ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of the polymer material has a local maximum of 0.5 or more within a temperature range of 0° C. to 50° C.
7. The electroacoustic converter film according to claim 1 , wherein a storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of the polymer material is 100 MPa or higher at 0° C. and 10 MPa or lower at 50° C.
8. The electroacoustic converter film according to claim 1 , wherein the polymer material has a relative dielectric constant of 10 or more at 25° C.
9. The electroacoustic converter film according to claim 1 , wherein the polymer material is cyanoethylated polyvinyl alcohol.
10. The electroacoustic converter film according to claim 1 , wherein the piezoelectric particles are present in the polymeric composite piezoelectric body at a volume fraction of 50% or higher.
11. The electroacoustic converter film according to claim 1 , wherein the piezoelectric particles are ceramic particles having a perovskite crystal structure or a wurtzite crystal structure.
12. The electroacoustic converter film according to claim 11 , wherein the ceramic particles are particles of lead zirconate titanate, lead lanthanate zirconate titanate, barium titanate, zinc oxide, or a solid solution of barium titanate and bismuth ferrite.
13. The electroacoustic converter film according to claim 1 , wherein the protective layers have a thickness at most two times as large as a thickness of the polymeric composite piezoelectric body.
14. The electroacoustic converter film according to claim 1 , wherein a product of a thickness and a Young's modulus of the thin film electrodes is smaller than a product of a thickness and a Young's modulus of the protective layers.
15. The electroacoustic converter film according to claim 1 , wherein the protective layers are formed of polyethylene terephthalate, polypropylene, polystyrene, polycarbonate, polyphenylene sulfite, polymethyl methacrylate, polyetherimide, polyimide, polyethylene naphthalate, or a cyclic olefin resin.
16. The electroacoustic converter film according to claim 1 , wherein the thin film electrodes are formed of copper, aluminum, gold, silver, platinum, or indium tin oxide.
17. A flexible display, comprising the electroacoustic converter film according to claim 1 that is attached to the flexible display exhibiting flexibility on a side opposite with a side where an image display surface is located.
18. A vocal cord microphone, which uses the electroacoustic converter film according to claim 1 as a sensor.
19. A musical instrument sensor, which uses the electroacoustic converter film according to claim 1 as a sensor.