Polytetrafluoroethylene hexaferrite composites

1. A hexaferrite composite, comprising:

polytetrafluoroethylene; and

greater than or equal to 40 vol % of a plurality of Co 2 Z hexaferrite particles based on the total volume of the polytetrafluoroethylene and the plurality of Co 2 Z hexaferrite particles on a void-free basis;

wherein the hexaferrite composite has a porosity of greater than or equal to 10 vol % based on the total volume of the hexaferrite composite;

wherein the hexaferrite composite has a permeability of greater than or equal to 2.5 and a ratio of the permeability to a permittivity of greater than or equal to 0.4, both determined at 500 MHz; and

wherein the permeability and the permittivity are measured in a 1-inch coaxial airline with a Nicolson-Ross extraction from the scattering parameters measured using a vector network analyzer.

2. The hexaferrite composite of claim 1 , wherein the plurality of Co 2 Z hexaferrite particles has a median particle size of greater than or equal to 4 micrometers; wherein the median particle is determined in accordance with ASTM D4464-15.

3. The hexaferrite composite of claim 1 , wherein the hexaferrite composite comprises greater than 60 to 90 vol % of the plurality of Co 2 Z hexaferrite particles.

4. The hexaferrite composite of claim 1 , wherein the plurality of Co 2 Z hexaferrite particles comprise a surface treatment comprising at least one of an aromatic silane or a fluorinated aliphatic alkoxy silane.

5. The hexaferrite composite of claim 1 , wherein the plurality of Co 2 Z hexaferrite particles comprises at least one of Al, Ba, Bi, Ni, Ir, Mn, Mg, Mo, Nb, Nd, Sr, V, Zn, or Zr.

6. The hexaferrite composite of claim 1 , wherein hexaferrite composite comprises 5 to 60 vol % of the polytetrafluoroethylene based on the total volume of the polytetrafluoroethylene and the plurality of Co 2 Z hexaferrite particles on a void-free basis.

7. The hexaferrite composite of claim 1 , wherein the porosity is 15 to 50 vol % based on the total volume of the hexaferrite composite.

8. The hexaferrite composite of claim 1 , wherein at least one of:

the permeability is 4.5 to 7 at 500 MHz;

the ratio of the permeability to the permittivity is 0.5 to 0.98 at 500 MHz;

the hexaferrite composite has a permittivity of greater than or equal to 4 at 500 MHz;

the hexaferrite composite has a magnetic loss tangent of less than or equal to 0.1 at 500 MHz; or

the hexaferrite composite has a dielectric loss of less than or equal to 0.1 at 500 MHz.

9. The hexaferrite composite of claim 1 , wherein the hexaferrite composite has a copper bond strength of 3 to 7 pli as measured in accordance with IPC test method 650, 2.4.9.

10. The hexaferrite composite of claim 1 , further comprising at least one of a dielectric filler or a fibrous layer.

11. An article comprising the hexaferrite composite of claim 1 .

12. The article of claim 11 , wherein the article is an antenna.

13. A hexaferrite composite, comprising:

5 to 60 vol % of polytetrafluoroethylene; and

40 to 95 vol % of a plurality of Co 2 Z hexaferrite particles having a median particle size of greater than or equal to 4 micrometers as determined in accordance with ASTM D4464-15;

wherein the volume percents of the polytetrafluoroethylene and the plurality of Co 2 Z hexaferrite particles are based on the total volume of the polytetrafluoroethylene and the plurality of Co 2 Z hexaferrite particles on a void-free basis;

wherein the hexaferrite composite has a porosity of 15 to 50 vol % based on the total volume of the hexaferrite composite;

wherein the hexaferrite composite has a permeability of greater than or equal to 2.5 and a ratio of the permeability to the a permittivity of greater than or equal to 0.4, both determined at 500 MHz; and

wherein the permeability and the permittivity are measured in a 1-inch coaxial airline with a Nicolson-Ross extraction from the scattering parameters measured using a vector network analyzer.

14. A method of forming a sheet comprising a hexaferrite composite comprising:

at least one of paste extruding, casting, or molding a mixture comprising polytetrafluoroethylene and a plurality of Co 2 Z hexaferrite particles to form the sheet;

wherein the sheet comprises greater than or equal to 40 vol % of the plurality of Co 2 Z hexaferrite particles based on the total volume of the polytetrafluoroethylene and the plurality of Co 2 Z hexaferrite particles on a void-free basis;

wherein the hexaferrite composite has a porosity of greater than or equal to 10 vol % based on the total volume of the hexaferrite composite;

wherein the hexaferrite composite has a permeability of greater than or equal to 2.5 and a ratio of the permeability to a permittivity of greater than or equal to 0.4, both determined at 500 MHz; and

wherein the permeability and the permittivity are measured in a 1-inch coaxial airline with a Nicolson-Ross extraction from the scattering parameters measured using a vector network analyzer.

15. The method of claim 14 , wherein the forming comprises the paste extruding, and wherein the method further comprises calendering the sheet.

16. The method of claim 15 , wherein the mixture comprises the polytetrafluoroethylene in the form of a dispersion or a powder, the plurality of Co 2 Z hexaferrite particles, and a lubricant.

17. The method of claim 14 , wherein the forming comprises the casting, wherein the mixture is an aqueous dispersion comprising the polytetrafluoroethylene and the plurality of Co 2 Z hexaferrite particles; and wherein the method further comprises heating the sheet after casting to a first temperature and sintering the sheet at a second temperature.

18. The method of claim 17 , wherein the casting comprises casting the mixture onto a cloth reinforcement, preferably a glass cloth reinforcement.

19. The method of claim 14 , wherein the forming comprises mixing the polytetrafluoroethylene in granular form and the plurality of Co 2 Z hexaferrite particles to form the mixture; and at least one of dry calendering or molding the mixture to form the sheet.

20. The method of claim 14 , further comprising adding a conductive layer on at least one surface of the sheet.