Device consisting of an elastomer matrix, comprising piezoelectric charges and electrodes
A piezoelectric device comprises at least one piezoelectric composite layer P inserted between two conductive composite layers E, each layer E forming an electrode, characterized in that: the layer P is a rubber composition containing more than 50 parts by weight per hundred parts by weight rubber, phr, of diene elastomer, a cross-linking system and at least 5 vol. %, in relation to the total volume of the rubber composition, of piezoelectric inorganic charges; and each layer E is a rubber composition containing at least 50 phr of diene elastomer, a cross-linking system, and conductive charges. A method for producing the device and a tire comprising the device are also disclosed.
1. A piezoelectric device comprising at least one piezoelectric composite layer P inserted between two conductive composite layers E, each layer E forming an electrode,
wherein the layer P is a rubber composition based on:
more than 50 parts by weight, per hundred parts by weight of elastomer, phr, of diene elastomer;
a crosslinking system; and
at least 5% by volume, with respect to a total volume of the rubber composition, of piezoelectric inorganic fillers;
wherein each layer E is a rubber composition based on:
at least 50 phr of diene elastomer;
a crosslinking system; and
conductive fillers, and
wherein the diene elastomer of the layer P is co-crosslinked with the diene elastomer of each layer E, and
wherein a piezoelectric coefficient of the layer P does not significantly vary for deformations of the piezoelectric device between 0% and 35%.
2. The piezoelectric device according to claim 1 , wherein, in the layer P, the content of piezoelectric inorganic fillers varies from 5% to 80% by volume, with respect to the total volume of rubber composition.
3. The piezoelectric device according to claim 1 , wherein, in the layer P, a size of the piezoelectric inorganic fillers varies from 50 nm to 500 μm.
4. The piezoelectric device according to claim 1 , wherein the piezoelectric inorganic fillers are piezoelectric ceramics.
5. The piezoelectric device according to claim 1 , wherein the piezoelectric inorganic fillers are selected from the group consisting of barium titanate, lead titanate, lead zirconate titanate, lead niobate, lithium niobate and potassium niobate.
6. The piezoelectric device according to claim 1 , wherein the rubber composition of the layer P comprises from 75 phr to 100 phr of diene elastomer.
7. The piezoelectric device according to claim 1 , wherein the crosslinking system of the layer P, the crosslinking system of one or of each layer E, or the crosslinking system of the layer P and the crosslinking system of one or of each layer E is selected from the group consisting of peroxides and mixtures thereof.
8. The piezoelectric device according to claim 7 , wherein peroxides are organic peroxides selected from the group consisting of dialkyl peroxides, monoperoxycarbonates, diacyl peroxides, peroxyketals, peroxyesters and mixtures thereof.
9. The piezoelectric device according to claim 1 , wherein, in one or in each layer E, a content of conductive fillers varies from 10% to 40% by volume, with respect to the total volume of rubber composition.
10. The piezoelectric device according to claim 1 , wherein, in one or each layer E, the conductive fillers are graphitized or partially graphitized carbon black.
11. A process for the preparation of a piezoelectric device according to claim 1 , the process comprising:
polarizing at a polarization temperature lower by at least 5° C. than a lowest Curie temperature, Tc, of the piezoelectric inorganic fillers.
12. A process for the preparation of a piezoelectric device according to claim 1 , the process comprising:
(a1) placing at least one piezoelectric composite layer P between two identical or different conductive composite layers E, in order to obtain an assembly;
(a2) applying a pressure to the assembly obtained following stage (a1); and
(a3) crosslinking the assembly in order to obtain the piezoelectric device.
13. The process according to claim 12 , further comprising:
(a4) polarizing the piezoelectric device obtained following stage (a3) at a polarization temperature lower by at least 5° C. than a lowest Curie temperature, Tc, of the piezoelectric inorganic fillers.
14. The process according to claim 12 , wherein the at least one piezoelectric composite layer P is prepared by the following steps:
(b1) incorporating a piezoelectric inorganic filler in a diene elastomer, in a mixer, with thermomechanical kneading, until a maximum temperature of between 80° C. and 190° C. is reached;
(b2) cooling the mixture from step (b1) to a temperature of less than 80° C.;
(b3) subsequently incorporating a crosslinking system;
(b4) kneading to a maximum temperature of less than 80° C.; and
(b5) calendering or extruding a rubber composition thus obtained to form a strip.
15. The process according to claim 12 , wherein each conductive composite layer E is prepared by the following steps:
(c1) incorporating a conductive filler in a diene elastomer, in a mixer, with thermomechanical kneading, until a maximum temperature of between 110° C. and 190° C. is reached;
(c2) cooling the mixture from step (c1) to a temperature of less than 100° C.;
(c3) subsequently incorporating a crosslinking system;
(c4) kneading to a maximum temperature of less than 110° C.; and
(c5) calendering or extruding a rubber composition thus obtained to form a strip.
16. A tire comprising a piezoelectric device according to claim 1 .
17. The tire according to claim 16 , further comprising a sensor.