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US-12617908-B2 - Liquid crystal polymer film, laminated body including the liquid crystal polymer film, and method of producing liquid crystal polymer film

US12617908B2US 12617908 B2US12617908 B2US 12617908B2US-12617908-B2

Abstract

A liquid crystal polymer film that includes: a liquid crystal polymer; and an inorganic filler, wherein a relative permittivity of the liquid crystal polymer film is 5 to 10, and an average value of distances between barycentric coordinates of particles of the inorganic filler in the liquid crystal polymer film is 0.5 μm to 2.0 μm.

Inventors

  • Shunsuke OTOMO
  • Hiroyuki Masaki

Assignees

  • MURATA MANUFACTURING CO., LTD.

Dates

Publication Date
20260505
Application Date
20240401
Priority Date
20220803

Claims (20)

  1. 1 . A liquid crystal polymer film comprising: a liquid crystal polymer; and an inorganic filler, wherein a relative permittivity of the liquid crystal polymer film is 5 to 10, and an average value of distances between barycentric coordinates of particles of the inorganic filler in the liquid crystal polymer film is 0.5 μm to 2.0 μm.
  2. 2 . The liquid crystal polymer film according to claim 1 , wherein the inorganic filler is an alkaline earth metal titanate.
  3. 3 . The liquid crystal polymer film according to claim 2 , wherein the inorganic filler is barium titanate.
  4. 4 . The liquid crystal polymer film according to claim 2 , wherein the inorganic filler is calcium titanate or strontium titanate.
  5. 5 . The liquid crystal polymer film according to claim 1 , wherein a ratio of a content of the inorganic filler to a total content of the liquid crystal polymer and the inorganic filler is 20 vol % to 30 vol %.
  6. 6 . The liquid crystal polymer film according to claim 1 , wherein the inorganic filler has an average particle size of 0.5 μm to 1.5 μm.
  7. 7 . The liquid crystal polymer film according to claim 1 , wherein the liquid crystal polymer film has a dielectric loss tangent of 0.01 or less.
  8. 8 . The liquid crystal polymer film according to claim 1 , wherein the liquid crystal polymer is a thermotropic liquid crystal polymer.
  9. 9 . The liquid crystal polymer film according to claim 1 , wherein the liquid crystal polymer includes liquid crystal polymer fibers that are fibrous particles.
  10. 10 . The liquid crystal polymer film according to claim 9 , wherein the liquid crystal polymer fibers have an average diameter of 0.07 μm to 2 μm or less.
  11. 11 . The liquid crystal polymer film according to claim 9 , wherein the liquid crystal polymer fibers have an average aspect ratio of 10 to 500.
  12. 12 . The liquid crystal polymer film according to claim 1 , wherein an average inclination of the inorganic filler with respect to an in-plane direction of a main surface of the liquid crystal polymer film is 15° or less.
  13. 13 . A laminated body comprising: the liquid crystal polymer film according to claim 1 ; and a conductor layer on the liquid crystal polymer film.
  14. 14 . The laminated body according to claim 13 , wherein the conductor layer is a copper foil having a warpage amount of 10 mm or less.
  15. 15 . A method of producing a liquid crystal polymer film, the method comprising: dispersing a liquid crystal polymer powder and an inorganic filler in a dispersing medium to obtain a mixture; drying the mixture to form a mixture mat; and heat-pressing the mixture mat to obtain the liquid crystal polymer film having a relative permittivity of 5 to 10, and wherein an average value of distances between barycentric coordinates of particles of the inorganic filler in the liquid crystal polymer film is 0.5 μm to 2.0 μm.
  16. 16 . The method of producing a liquid crystal polymer film according to claim 15 , wherein the liquid crystal polymer powder includes liquid crystal polymer fibers that are fibrous particles, and the liquid crystal polymer fibers have an average diameter of 1.4 μm or less.
  17. 17 . The method of producing a liquid crystal polymer film according to claim 15 , wherein the inorganic filler is an alkaline earth metal titanate.
  18. 18 . The method of producing a liquid crystal polymer film according to claim 17 , wherein the inorganic filler is barium titanate.
  19. 19 . The method of producing a liquid crystal polymer film according to claim 17 , wherein the inorganic filler is calcium titanate or strontium titanate.
  20. 20 . The method of producing a liquid crystal polymer film according to claim 15 , wherein a ratio of a content of the inorganic filler to a total content of the liquid crystal polymer powder and the inorganic filler is 20 vol % to 30 vol %.

Description

CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation of International application No. PCT/JP2023/022058, filed Jun. 14, 2023, which claims priority to Japanese Patent Application No. 2022-123967, filed Aug. 3, 2022, the entire contents of each of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a liquid crystal polymer film, a laminated body including the liquid crystal polymer film, and a method of producing a liquid crystal polymer film. BACKGROUND ART Japanese Patent Application Laid-Open No. 2006-233118 (Patent Document 1) discloses a resin composition for an antenna part containing a liquid crystalline resin and ceramic powder. Japanese Patent Application Laid-Open No. 2020-167336 (Patent Document 2) discloses an element built-in substrate including an element formation layer formed inside a substrate body including a liquid crystal polymer and including an insulating region in which a functional filler for forming an element is dispersed. Patent Document 1: Japanese Patent Application Laid-Open No. 2006-233118Patent Document 2: Japanese Patent Application Laid-Open No. 2020-167336 SUMMARY OF THE DISCLOSURE A liquid crystal polymer film formed by mixing a liquid crystal polymer with an inorganic filler having a high relative permittivity has a high relative permittivity. Thus, when the liquid crystal polymer film containing the inorganic filler is used for a high frequency antenna substrate and the like, a radiation electrode area of the high frequency antenna substrate can be sufficiently reduced. Here, the liquid crystal polymer has a small linear expansion coefficient in an alignment direction of molecules and a large linear expansion coefficient in a direction perpendicular to the alignment direction. For this reason, in the liquid crystal polymer film, the molecules of the liquid crystal polymer are preferably aligned along an in-plane direction of a main surface of the film in order to reduce the linear expansion coefficient in the in-plane direction of the main surface of the film. This is because, when a liquid crystal polymer film is stacked on, for example, a copper foil to produce a flexible copper-clad laminate (FCCL), if the linear expansion coefficient of the main surface of the film in the in-plane direction is small, it is possible to suppress warpage and distortion of the FCCL caused by the difference in linear expansion coefficient between the liquid crystal polymer film and a copper plate. However, when the inorganic filler is mixed with the liquid crystal polymer, the alignment of the molecules of the liquid crystal polymer along the in-plane direction of the main surface is disturbed, so that the linear expansion coefficient in the in-plane direction of the main surface of the liquid crystal polymer film increases. In the FCCL including such a liquid crystal polymer film, a difference in linear expansion coefficient between the liquid crystal polymer film and the copper foil increases in the in-plane direction of the main surface of the FCCL, and warpage or distortion occurs in the FCCL. The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a liquid crystal polymer film having a relative permittivity increased by addition of an inorganic filler while suppressing an increase in linear expansion coefficient in an in-plane direction of a main surface of the film. A liquid crystal polymer film according to the present disclosure includes: a liquid crystal polymer; and an inorganic filler. The liquid crystal polymer film has a relative permittivity of 5 to 10, and an average value of distances between barycentric coordinates of particles of the inorganic filler in the liquid crystal polymer film is 0.5 μm to 2.0 μm. According to the present disclosure, a distance between the inorganic fillers is secured to some extent in the liquid crystal polymer film. Thus, the inorganic filler is not locally and densely present. Thus, it is possible to prevent orientation of molecules of a liquid crystal polymer in an in-plane direction of a main surface of the film from being inhibited by the inorganic filler. As a result, it is possible to provide a liquid crystal polymer film having a relative permittivity increased by addition of the inorganic filler while suppressing an increase in linear expansion coefficient in the in-plane direction of the main surface of the film. BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a laminated body according to one embodiment of the present disclosure. FIG. 2 is an image showing an example of a photograph of a cross section of an LCP film according to one embodiment of the present disclosure taken by a reflected electron image of an SEM. FIG. 3 is a view showing an example of a binarized image obtained by binarizing a photographed image of a cross section of an LCP film according to one embodiment