Piezoelectric vibrator

1. A piezoelectric vibrator having a piezoelectric laminate in which oriented film layers made of a polylactic acid and conductive layers are laminated alternately and grippers gripping both ends of the piezoelectric laminate: wherein

(i) the piezoelectric laminate is laminated in such a manner that one of two conductive layers neighboring via an oriented film layer is short-circuited to a negative electrode and the other conductive layer is short-circuited to a positive electrode and the oriented film layers interposed between the respective conductive layers expand and contract in the same direction when a current is applied;

(ii) the piezoelectric laminate has two parallel surfaces which are parallel to the plane direction of the oriented film layers and two end faces A and B which are between the parallel surfaces and parallel to each other; and

(iii) the gripped ends respectively include the end face A and the end face B, and a stress is applied by the grippers to the part of the piezoelectric laminate between the end faces A and B,

wherein each of the oriented film layers is at least a kind selected from the group consisting of an oriented film layer L made of a resin L containing a poly-L-lactic acid as the main component m layer D made of a resin D containing a poly-D-lactic acid as the main component;

wherein each of the oriented film layers comprises molecular chains oriented in one direction.

2. The piezoelectric vibrator described in claim 1 , wherein the shape of the piezoelectric laminate is a tape.

3. The piezoelectric vibrator described in claim 1 , wherein the grippers gripping the ends are fixed on a diaphragm and the stress applied to the piezoelectric laminate by the grippers is a tensile stress.

4. The piezoelectric vibrator described in claim 3 , wherein the end faces A and B are at the ends of the piezoelectric laminate in the longitudinal direction.

5. The piezoelectric vibrator described in claim 1 , wherein the stress applied to the piezoelectric laminate by the grippers is a compressive stress.

6. The piezoelectric vibrator described in claim 5 , wherein the positions of the grippers at the ends are fixed.

7. The piezoelectric vibrator described in claim 5 , wherein the positions of the grippers at the ends are movable according to expansion and contraction of the piezoelectric laminate.

8. The piezoelectric vibrator described in claim 3 , wherein the end faces A and B are at the ends of the piezoelectric laminate parallel to the longitudinal direction.

9. The piezoelectric vibrator described in claim 1 , wherein the number of the oriented film layers in the piezoelectric laminate is three or larger.

10. The piezoelectric vibrator described in claim 1 , wherein the oriented film layers each have a thickness of 25 μm or less.

11. The piezoelectric vibrator described in claim 1 , wherein the direction of the maximum expansion and contraction of the piezoelectric laminate is parallel to or at a right angle to the end faces A and B.

12. The piezoelectric vibrator described in claim 1 , wherein the conductive layers have a surface specific resistance of 1×10 4 Ω/sq or less.

13. The piezoelectric vibrator described in claim 1 which is used for a piezoelectric speaker.

14. The piezoelectric vibrator described in claim 1 which is used for a signal input apparatus.

15. The piezoelectric vibrator described in claim 2 , wherein the grippers gripping the ends are fixed on a diaphragm and the stress applied to the piezoelectric laminate by the grippers is a tensile stress.

16. The piezoelectric vibrator described in claim 2 , wherein the stress applied to the piezoelectric laminate by the grippers is a compressive stress.

17. The piezoelectric vibrator described in claim 1 , wherein the oriented film layers comprise the oriented film layer L and the oriented film layer D laminated alternately.