Composite fiber

Abstract

To provide a conjugate fiber which can function as a piezoelectric material and is improved in strength as compared with a conventional PZT fiber.SOLUTION: There is provided a conjugate fiber composed of at least a metal sintered material and a ceramic sintered material, in which the metal sintered material and the ceramic sintered material are adjacent to each other in the conjugate fiber to form a fiber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to composite fibers, and more specifically to composite fibers that may be composed of at least a metal sintered body and a ceramic sintered body. [Background technology]

[0002] Piezoelectric fibers using lead zirconate titanate (PZT fibers) are known to be usable as vibration sensors and actuators in structures such as buildings, automobiles, ships, and aircraft (for example, Patent Documents 1 to 6). Smart boards in which such PZT fibers are embedded in a structure to function as stress sensors, vibration sensors, or actuators are also known (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application No. 2003-12829 [Patent Document 2] Japanese Patent Application No. 2005-171752 [Patent Document 3] Japanese Patent Application No. 2004-15489 [Patent Document 4] Japanese Patent Application No. 2005-59552 [Patent Document 5] Japanese Patent Application No. 2005-313715 [Patent Document 6] Japanese Patent Application No. 2010-198092 [Overview of the project] [Problems that the invention aims to solve]

[0004] The inventors of this application realized that conventional lead zirconate titanate fibers (PZT fibers) had problems that needed to be overcome, and recognized the need to take countermeasures. Specifically, the inventors of this application identified the following problems.

[0005] For example, as shown in Figure 11(A), the lead zirconate titanate fiber (PZT fiber) 100 described in Patent Document 1, etc., has a PZT thin layer 102 that can be formed by coating a metal wire 101 (a metal fine wire such as a titanium wire or platinum wire) with lead zirconate titanate crystals (PZT crystals).

[0006] For example, PZT fibers can be manufactured by growing PZT crystals on the surface of a metal wire using a hydrothermal synthesis method. Alternatively, PZT fibers can also be manufactured using an extrusion molding method. For example, as shown in Figure 13, in the extrusion molding method, a PZT paste 105 (a mixture of PZT powder, binder, water, and possibly organic solvents and various molding additives) is simultaneously extruded together with a metal wire 101 to produce a PZT fiber molded body with a metal core. Then, this PZT fiber molded body is heated to remove the binder, and after further sintering at a high temperature, a PZT thin layer is formed on the surface of the metal wire to produce a PZT fiber.

[0007] In PZT fibers manufactured by methods such as hydrothermal synthesis or extrusion molding, the metal wire surface is simply coated with PZT crystals, making the PZT thin layer 102 prone to cracking. For example, when used in vibration sensors or actuators (especially in the aerospace field), the PZT fibers 100 are partially embedded in a structure 202 made of laminated carbon fiber reinforced plastic (CFRP) prepreg 201 to reinforce it and use it as a smart board 200 (see Figures 11(B) and (C)).

[0008] For example, when the smart board 200 is used as a vibration sensor or actuator, the PZT fiber 100, being a piezoelectric material, generates an electric potential when it detects vibration and functions as a sensor. Conversely, when an electric potential is applied to the PZT fiber 100, it expands or contracts or vibrates in response to that potential, functioning as an actuator. For example, as shown in Figure 12(A), when the PZT fiber 100 expands along the axis indicated by the arrow due to the application of an electric potential, it can bend together with the structure 202 as shown in Figure 12(B). In this way, in the smart board 200, a predetermined PZT fiber among the multiple PZT fibers 100 can function as a sensor to detect vibration, and a predetermined other PZT fiber can act as an actuator to suppress (dampe) the vibration. Note that in Figure 12, the portion of the PZT fiber 100 below the dashed line indicates that the PZT fiber 100 is embedded in the structure 202 (specifically, the CFRP prepreg 201) (see Figure 11(C)).

[0009] When PZT fibers are used in vibration sensors and actuators, a certain degree of strength and flexibility is required. However, the inventors of this application, based on the information in the July issue of the Journal of Polymer Science, Japan (Vol. 57 No. 7, 2008), found that the strength (tensile strength or elongation load at break) of conventional PZT fibers is 4 kgf / mm². 2 It was found that the material was easily broken, torn, and cracked as a fiber, and that further improvements in strength were necessary.

[0010] Furthermore, as shown in Figure 14, in PZT fibers 300 in which a PZT film 302 is formed on a metal wire 301 such as platinum (Pt), delamination occurs between the PZT and the metal wire (Pt) due to the difference in thermal expansion coefficients, and it was found that the interface is prone to cracking. This is the reason why the fiber has low physical strength.

[0011] The present invention has been made in view of the above problems. That is, the main object of the present invention is to provide a composite fiber with improved strength compared to conventional PZT fibers that can function as a piezoelectric material.

Means for Solving the Problem

[0012] Rather than dealing with the problem along the line of the prior art, the inventors of the present application have attempted to solve the above problems by approaching them in a new direction. As a result, an invention of a composite fiber has been achieved in which the above main object is achieved.

[0013] The present invention provides a composite fiber that can be composed of at least a metal sintered body and a ceramic sintered body, in which the metal sintered body and the ceramic sintered body are adjacent to each other to form a fiber body.

Effects of the Invention

[0014] In the present invention, a composite fiber having improved strength compared to conventional PZT fibers that can function as piezoelectric materials is obtained. More specifically, delamination between layers is significantly suppressed, and a composite fiber having a tensile strength of 5 kgf / mm 2 or more, preferably 6 kgf / mm 2 or more is obtained. In addition, a composite fiber having flexibility with a radius of curvature of 200 mm or less, preferably 10 mm or less when bent is obtained. Note that the effects described in this specification are merely examples and are not limiting, and there may be additional effects.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a schematic view schematically showing a composite fiber according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view schematically showing a cross-section of adjacent metal sintered bodies and ceramic sintered bodies included in a composite fiber according to an embodiment of the present invention, particularly the interface between the metal sintered body and the ceramic sintered body. [Figure 3] FIG. 3 is an electron micrograph showing an interface between a metal sintered body (Ni) composed of crystal grains and a ceramic sintered body (BT) also composed of crystal grains. [Figure 4] FIG. 4 is a schematic view schematically showing a composite fiber according to another embodiment of the present invention. [Figure 5]Figure 5 is a schematic diagram showing a composite fiber according to another embodiment of the present invention. [Figure 6] Figure 6(A) is a schematic perspective view illustrating a composite fiber according to another embodiment of the present invention, and Figure 6(B) shows a cross-section of the composite fiber of Figure 6(A) at Y-Y'. [Figure 7] Figure 7 is an electron microscope image showing a cross-section of a composite fiber composed of a metal core (Ni), a first layer (Ni crystal grain layer), and a second layer (BaTiO3 crystal grain layer). [Figure 8] Figure 8 is a schematic diagram illustrating an example of a method for manufacturing composite fibers. [Figure 9] Figure 9 is an electron microscope image (5.0kV, 2500x magnification) showing cross-sections of adjacent metal sintered body (Ni) and ceramic sintered body (BT) contained in the composite fiber manufactured in Example 1 of the present invention. [Figure 10] Figure 10 is an electron microscope image (5.0kV, 2500x magnification) showing cross-sections of adjacent metal sintered bodies and ceramic sintered bodies contained in the composite fiber manufactured in Comparative Example 1. [Figure 11] Figure 11 is a schematic diagram illustrating a conventional PZT fiber and a smart board in which a PZT fiber is embedded in a structure. [Figure 12] Figure 12 is a schematic diagram illustrating the use of a conventional smart board as a vibration sensor and actuator. [Figure 13] Figure 13 is a schematic diagram illustrating an example of a conventional PZT fiber manufacturing method. [Figure 14] Figure 14 is a schematic diagram illustrating a conventional PZT fiber. [Modes for carrying out the invention]

[0016] The present invention relates to composite fibers, and more specifically to composite fibers that can be composed of or formed from at least a "metal sintered body" and a "ceramic sintered body," wherein the metal sintered body and the ceramic sintered body are adjacent to each other and form a fibrous body (hereinafter referred to as "the composite fiber of the present disclosure," or simply "composite fiber" or "fiber").

[0017] The composite fibers of this disclosure generally have higher strength than piezoelectric fibers such as conventional PZT fibers. Conventional PZT fibers have a structure in which a PZT crystal is simply coated onto a metal wire, resulting in a strength of 4 kgf / mm². 2 PZT fibers possess only moderate strength (tensile strength, elongation load at break) and, as mentioned above, easily break when used alone due to delamination. When such PZT fibers are used in vibration sensors or actuators, they must be reinforced with a structure such as carbon fiber reinforced plastic (CFRP) prepreg, as shown in Figure 11(B).

[0018] However, as will be explained in detail below, the composite fiber of this disclosure has a structure in which a "metal sintered body" and a "ceramic sintered body" are adjacent to each other to form a fibrous body, for example, 5 kgf / mm 2 Preferably 6 kgf / mm² 2 It can provide the above strength (tensile strength, elongation load at break, etc.).

[0019] Furthermore, this increase in strength allows for miniaturization, so the composite fiber of this disclosure has a smaller radius of curvature when bent than conventional PZT fibers, and can exhibit flexibility with a radius of curvature of, for example, 200 mm or less, preferably 10 mm or less.

[0020] Thus, the composite fibers of this disclosure possess superior strength, flexibility, and other properties compared to conventional PZT fibers. These properties are due to the structure in which the "metal sintered body" and the "ceramic sintered body" are adjacent to each other to form a "fiber body," and in particular, the structure in which the "metal sintered body" and the "ceramic sintered body" are bonded to each other by co-sintering. It should be noted that the present invention and its effects are not bound by any particular theory or theories.

[0021] (Composite fiber) "Composite fiber" generally means a fiber that can be composed of two or more different materials, and in the context of this disclosure, a composite fiber means a fiber comprising at least a "metal sintered body" and a "ceramic sintered body".

[0022] In this disclosure, “fibrous body” (or “composite fiber” or “fiber”) means an elongated object or article, and there are no particular restrictions on its length. In this disclosure, there are no particular restrictions on the shape of the “fibrous body,” in particular the shape of its cross-section, and it may have, for example, a circular, elliptical, rectangular, or irregularly shaped cross-section.

[0023] In this disclosure, "metal sintered body" means a metal or alloy, preferably a pure metal, obtained by firing at least the "metal components" described below. In other words, "metal components" can be said to be components that can constitute a "metal sintered body." Alternatively, "metal components" can be said to be components that can be included in a "metal sintered body."

[0024] In this disclosure, "metallic component" is not particularly limited as long as it is a component (element) that can constitute a metal (preferably a pure metal), and for example, it consists of at least one selected from the group consisting of silver (Ag), palladium (Pd), copper (Cu), aluminum (Al), chromium (Cr), titanium (Ti), platinum (Pt), iron (Fe), and nickel (Ni) (hereinafter sometimes referred to as "metallic element"). In the composite fibers of this disclosure, the metallic component is preferably nickel or copper.

[0025] In the composite fiber of this disclosure, the metal sintered body is preferably nickel (elemental metal) or copper (elemental metal), and more preferably has a structure in which particles or crystal grains of nickel metal (element) or copper metal (element) are bonded to each other.

[0026] In this disclosure, "ceramic sintered body" means a ceramic, preferably a ceramic crystal, formed by firing at least the "ceramic components" described below. In other words, "ceramic components" can be said to be components that can constitute a "ceramic sintered body." Alternatively, "ceramic components" can be said to be components that can be included in a "ceramic sintered body."

[0027] In this disclosure, "ceramic component" is not particularly limited to any component (element) that can constitute a ceramic (ceramic crystal, especially a metal oxide), such as lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), yttrium (Y), zirconium (Zr), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), boron (B), aluminum (Al), silicate. The ceramic element is composed of at least one element selected from the group consisting of silicon (Si), indium (In), tin (Sn), antimony (Sb), barium (Ba), tantalum (Ta), tungsten (W), lead (Pb), bismuth (Bi), lanthanum (La), cesium (Ce), neodymium (Nd), samarium (Sm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), oxygen (O), carbon (C), nitrogen (N), sulfur (S), phosphorus (P), fluorine (F), and chlorine (Cl) (hereinafter sometimes referred to as the "ceramic element"). In the composite fiber of this disclosure, the ceramic component is preferably titanium, barium, and oxygen, or bismuth, sodium, titanium, and oxygen. Furthermore, the ceramic component may also contain a glass component. Examples of the glass component include at least one selected from the group consisting of soda-lime glass, potash glass, borate glass, borosilicate glass, barium borosilicate glass, borite glass, barium borate glass, bismuth borosilicate glass, bismuth zinc borate glass, bismuth silicate glass, phosphate glass, aluminophosphate glass, and phosphate glass.

[0028] In the composite fibers of this disclosure, the ceramic sintered body preferably contains crystal grains or microcrystals, and more preferably barium titanate (BaTiO3)(BT) or bismuth sodium titanate ((Bi 1 / 2 Na 1 / 2 It is more preferable that the material be TiO3 (BNT) or glass.

[0029] A composite fiber according to one embodiment of the present invention is a composite fiber 10 which may be composed of at least a metal sintered body 1 and a ceramic sintered body 2, as shown in Figure 1(A), for example. Figure 1(B) schematically shows a cross-section of the composite fiber 10 (a cross-section in a direction perpendicular to the axial direction of the fiber), and Figure 1(C) schematically shows a cross-section at X-X' in Figure 1(B) (a cross-section in the axial direction of the fiber).

[0030] For example, Figure 1 shows a composite fiber 10 in which a metal sintered body 1 and a ceramic sintered body 2, both having substantially circular cross-sections, are arranged in substantially concentric circles. The cross-section of the composite fiber in this disclosure is not limited to circular or concentric circles.

[0031] The metal sintered body 1 and the ceramic sintered body 2 may be integrally formed or manufactured as described in detail below. For example, it is preferable to integrally form or manufacture the metal sintered body 1 and the ceramic sintered body 2 by co-sintering the metal component and the ceramic component described above. More specifically, the metal sintered body 1 and the ceramic sintered body 2 can be integrally formed or manufactured by molding a paste containing the metal component (metal element) and a paste containing the ceramic component (ceramic element) into desired shapes and then firing them by co-sintering.

[0032] The means of forming the desired shape described above is not limited to using a paste; metal sintered bodies and ceramic sintered bodies can also be formed and manufactured by chemical vapor deposition methods such as thermal CVD or physical vapor deposition methods such as sputtering of the metal components (metal elements) and ceramic components (ceramic elements).

[0033] For example, as shown in Figure 1, the composite fiber of the present disclosure is characterized in that a metal sintered body and a ceramic sintered body are adjacent to each other (in contact, facing, or bonded) to form the fiber body. With such a configuration, the composite fiber of the present disclosure can provide improved strength, flexibility, and delamination suppression effects compared to conventional PZT fibers.

[0034] More specifically, as shown in Figure 2, for example, in the composite fiber of this disclosure, the metal sintered body 1 and the ceramic sintered body 2 are arranged adjacent to each other. The metal sintered body 1 and the ceramic sintered body 2 may be configured to form an interface 3.

[0035] In this disclosure, "interface" means the boundary between adjacent "metal sintered bodies" and "ceramic sintered bodies".

[0036] The interface that can be formed between the metal sintered body and the ceramic sintered body may be composed of crystal grains. In this disclosure, "crystal grains" means microcrystals with an irregular shape ranging from 1 / 20,000 of a millimeter to 1 / 10 of a millimeter.

[0037] A metal sintered body may be composed of crystal grains of metal (or metal components) (see Figure 3). In other words, a metal sintered body may be a polycrystalline body of metal (or metal components). There are no particular restrictions on the size of the crystal grains in a metal sintered body (hereinafter sometimes referred to as "crystal grain size" of metal crystal grains). The size of the crystal grains in a metal sintered body is, for example, 0.1 μm to 10 μm. Here, the size of the crystal grains in a metal sintered body refers to the largest dimension of the crystal grain or microcrystal in a cross-sectional view.

[0038] The size of the crystal grains that may be contained in the metal sintered body may depend on the metal component, and for example, it is preferable that the particle size of the metal component powder before firing is 0.05 μm to 5 μm.

[0039] A ceramic sintered body may be composed of crystal grains of ceramic (or ceramic components) (see Figure 3). In other words, a ceramic sintered body may be a polycrystalline body of ceramic (or ceramic components). There are no particular restrictions on the size of the crystal grains in a ceramic sintered body (hereinafter sometimes referred to as "crystal grain size" of ceramic crystal grains). The size of the crystal grains in a ceramic sintered body is, for example, 0.1 μm to 10 μm. Here, the size of the crystal grains in a ceramic sintered body refers to the largest dimension of the crystal grain or microcrystal in a cross-sectional view.

[0040] The size of the crystal grains that may be contained in the ceramic sintered body may depend on the ceramic components, and for example, it is preferable that the particle size of the ceramic component powder before firing is 0.05 μm to 5 μm.

[0041] Referring to Figure 2, it is preferable that the metal sintered body 1 is composed of metal (or metal component) crystal grains, and that the ceramic sintered body 2 is composed of ceramic (or ceramic component) crystal grains. It is even more preferable that both the metal sintered body 1 and the ceramic sintered body 2 are formed by co-sintering (see Figure 3). This is because co-sintering allows for the formation of crystal grains or microcrystals in both the metal sintered body and the ceramic sintered body through crystal growth.

[0042] In the composite fibers of this disclosure, an interface may be formed between crystal grains that can constitute a metal sintered body and crystal grains that can constitute a ceramic sintered body (see Figure 3). The boundary between crystal grains is also called a grain boundary, and such a grain boundary may form an interface between the metal sintered body and the ceramic sintered body. Alternatively, the metal sintered body and the ceramic sintered body may form an interface such that they share a grain boundary or a part of the contour of a crystal grain. In this case, it is preferable that the crystal grains that can constitute the metal sintered body are crystal grains that can be formed by the crystal growth of the metal (or metal component) (see Figure 3). It is preferable that the crystal grains that can constitute the ceramic sintered body are crystal grains that can be formed by the crystal growth of ceramic (or ceramic components) (see Figure 3). It is more preferable that crystal growth proceeds during the firing or co-sintering process of metals and / or ceramics. These crystal growth processes can be more effectively controlled by factors such as firing temperature, heating rate, holding time, cooling rate, atmosphere, pressure, sintering aids, and added elements.

[0043] In the composite fibers of this disclosure, the interface may have "surface roughness". In particular, in the composite fibers of this disclosure, it is preferable that the interface has "surface roughness" when the interface can be formed from crystal grains (see Figures 2 and 3). In other words, the interface may have irregularities, and in particular may have fine irregularities based on crystal grains, and such an interface may not be linear in cross-sectional view, but non-linear (see Figures 2 and 3). In other words, the interface may have a broken line shape in cross-sectional view (see Figures 2 and 3).

[0044] Furthermore, such interfaces are characterized by the absence of gaps or voids in cross-sectional view. Conventionally, the boundary between metal and ceramic was linear and had gaps in cross-sectional view, which caused problems such as delamination and insufficient strength. However, with the composite fibers of this disclosure, the surface roughness of the interface, and consequently the fine irregularities, can resolve the problems of delamination and insufficient strength.

[0045] In this disclosure, "surface roughness" refers to the degree of irregularity of the interface and is therefore also called "surface roughness" or "surface texture," and may also be simply referred to as "roughness." "Surface roughness" can be defined, for example, by measuring the "linear roughness" in a cross-sectional view of the interface from an electron microscope image. In this disclosure, "surface roughness" and "linear roughness" are interchangeable terms.

[0046] Specifically, by calculating the line roughness of the interface between the metal sintered body and the ceramic sintered body, and the line roughness of the interface between the metal body and the ceramic sintered body, differences in the interface structure can be identified. For example, after polishing a cross-section of a composite fiber sample according to this disclosure, SEM observation is performed. Three fields of view are randomly selected from the SEM images in which the interface roughness can be determined. Using image analysis software, a straight line connecting the two intersection points of the edge face of the extracted field of view images and the interface between the metal sintered body and the ceramic sintered body is defined as the center line, and the distance between the actual boundary and the center line is measured at 30 equally spaced points along the center line. The line roughness can be evaluated from the mean and standard deviation of these distances.

[0047] The specific line roughness value (measured value) is, for example, 15 nm to 1000 nm, preferably 75 nm to 300 nm, and more preferably 100 nm to 300 nm. The standard deviation (SD) of the distance between the boundary and the center line is, for example, 12 nm to 500 nm, preferably 50 nm to 150 nm.

[0048] For example, as shown in Figures 2 and 3, when the crystal grains of a metal sintered body and the crystal grains of a ceramic sintered body can form an interface, similar linear roughness can be observed in the depth direction of the cross-sectional view, so the interface can have surface roughness or irregularities that extend in two or three dimensions.

[0049] Such an interface with a rough surface can improve the adhesion between the metal sintered body and the ceramic sintered body, suppressing delamination and resulting in a composite fiber with improved fracture strength. Furthermore, the presence of such crystal grains allows for a structure in which residual stress caused by the thermal history during the process is uniformly relieved.

[0050] Such crystal grains may be composed of multiple or numerous crystallites, or they may be composed of a single crystallite.

[0051] The metal component and the ceramic component may be clearly separated, or at least a portion of them may be mixed together.

[0052] Furthermore, the region near the interface may include amorphous parts. Therefore, the region near the interface may be amorphous, crystalline, or both amorphous and crystalline parts may be present.

[0053] In this disclosure, "amorphous" (sometimes referred to as "amorphous" or "non-crystalline") means a state that is not crystalline.

[0054] In this disclosure, "region near the interface" specifically means a region adjacent to the interface, for example, a region within 1500 nm, preferably 500 nm, of the interface.

[0055] Furthermore, metal sintered bodies and ceramic sintered bodies may contain impurities, sintering aids, and other components or impurities that may be present in the raw materials, respectively. Such components may be present in amounts of less than 5%.

[0056] The presence or absence of crystal grains can be determined by observing the contrast difference due to differences in crystal orientation within the area including the target region using a transmission electron microscope, scanning electron microscope, or scanning ion microscope. Regarding the crystallinity of crystal grains, the range including the target area can be evaluated by performing a crystal structure analysis method using X-ray diffraction or micro-X-ray diffraction. Also, by the crystal structure analysis method using X-ray diffraction or micro-X-ray diffraction, it is also possible to examine whether the target area is crystalline, amorphous, or both are present. Diffraction lines due to crystalline substances are detected as sharp peaks, and scattered light due to amorphous substances can be detected as a halo (continuous).

[0057] In the composite fiber of the present disclosure, at least a metal sintered body and a ceramic sintered body are adjacent to each other, and a metal sintered body that can be composed of crystal grains of a metal (or metal component) and a ceramic sintered body that can be composed of crystal grains of a ceramic (or ceramic component) form an interface having surface roughness. In particular, by forming an interface having two-dimensional or three-dimensional spreading irregularities formed by co-sintering, the stress concentration that can occur between the metal sintered body and the ceramic sintered body can be alleviated. As a result, delamination that can occur between the metal sintered body and the ceramic sintered body can be suppressed, and the bonding strength between the metal sintered body and the ceramic sintered body can be further improved.

[0058] As a result, it is possible to improve the strength (breaking strength, particularly tensile strength or breaking elongation load) of the composite fiber (increase the strength). Also, in the composite fiber of the present disclosure, the presence of an interface having such complex irregularities that can be composed of crystal grains can suppress delamination, and by further improving the strength of the composite fiber, it is possible to reduce the diameter (reduce the size) of the composite fiber, and as a result, it is also possible to improve the flexibility of the composite fiber of the present disclosure. Note that the mechanism by which the strength and flexibility are improved in the composite fiber of the present disclosure is not limited to the above theory.

[0059] In the composite fiber of the present disclosure, the tensile strength (breaking elongation load) of the entire fiber is, for example, 5 kgf / mm 2 or more, preferably 6 kgf / mm 2 or more, more preferably 10 kgf / mm 2More preferably 14 kgf / mm 2 20 kgf / mm² or more 2 The above, in particular, is preferred at 50 kgf / mm². 2 Above 400 kgf / mm 2 The following is true, and it can provide significantly improved strength compared to conventional PZT fibers.

[0060] In the composite fibers of this disclosure, the tensile strength (elongation load at break) is preferably increased in the order of ceramic sintered body < composite fiber < metal sintered body.

[0061] The composite fibers of this disclosure have flexibility such as having a radius of curvature of 200 mm or less, and can exhibit improved flexibility compared to conventional PZT fibers. Here, "radius of curvature" refers to the radius of curvature just before the composite fiber of this disclosure breaks or snaps when bent, for example, by hand. Preferably, the composite fibers of this disclosure can maintain their electrical properties while being flexible.

[0062] The fiber diameter of the composite fiber of this disclosure is, for example, 500 μm or less, preferably 1 μm or more and 500 μm or less, and it is possible to achieve a smaller diameter (smaller size) compared to conventional PZT fibers. Here, the "fiber diameter" of the composite fiber of this disclosure means the maximum dimension (e.g., diameter) in the cross-section in a direction perpendicular to the axial direction of the fiber.

[0063] In the composite fibers of this disclosure, there are no particular restrictions on the cross-sectional area ratio (metal / ceramic) of the metal sintered body and the ceramic sintered body, for example, 1 / 99 to 99 / 1, preferably 1 / 8 to 8 / 1. Furthermore, in the composite fiber of this disclosure, there are no particular restrictions on the weight ratio (metal / ceramic) of the metal sintered body to the ceramic sintered body, for example, 1 / 99 to 99 / 1, preferably 1 / 8 to 8 / 1.

[0064] In the composite fiber 10 according to one embodiment of the present invention shown in Figure 1, the metal sintered body 1 is located in the "center" of the fiber 10 (in other words, the "center" of the fiber 10 is composed of the metal sintered body 1). Also, in the embodiment shown in Figure 1, the ceramic sintered body 2 is located in the "outer part" of the fiber 10 (in other words, the "outer part" of the fiber 10 is composed of the ceramic sintered body 2). In such embodiments, since the "center" of the composite fiber has metallic properties, the "center" can be electrically connected. It should be noted that the composite fiber of this disclosure is not limited to the embodiment shown in Figure 1.

[0065] In this disclosure, the “center” of a fiber means the portion of a cross-section perpendicular to the axial direction of the fiber that contains the geometric center of the fiber. The "outer part" refers to the outermost portion of the fiber in a cross-section perpendicular to the fiber's axial direction. An intermediate section may exist between the outer section and the central section.

[0066] In this disclosure, the “central part,” the “outer part,” and the “intermediate part” may each be independently composed of a “metal sintered body” or a “ceramic sintered body.” However, it is preferable that the “metal sintered body” and the “ceramic sintered body” are positioned adjacent to each other in accordance with this disclosure.

[0067] In another embodiment of the present invention, the ceramic sintered body may be located in the center of the composite fiber. In this case, the metal sintered body may be located on the outer part of the composite fiber. In such embodiments, the outer parts of the composite fiber can be electrically connected.

[0068] In yet another embodiment of the present invention, the core of the composite fiber may be composed of a metal sintered body. In this case, at least a portion of the outer part of the composite fiber may be composed of a ceramic sintered body. In such embodiments, the core of the composite fiber can be electrically connected to the outside.

[0069] In this disclosure, “at least a portion of the outer portion” means at least a portion of the composite fiber in the axial direction and / or at least a portion of the composite fiber in the circumferential direction. The composite fiber of this disclosure may be composed of or covered in an area of ​​0 to 100% (but not 0%), preferably 50 to 100%, on the outer portion in any direction.

[0070] In yet another embodiment of the present invention, the core of the composite fiber may be composed of a ceramic sintered body. In this case, at least a portion of the outer part of the composite fiber may be composed of a metal sintered body. In such embodiments, the outer part of the composite fiber can be electrically connected to the outside.

[0071] In yet another embodiment of the composite fiber of the present invention, the central part of the composite fiber may be composed of a metal sintered body. In this case, the outer part of the composite fiber may also be independently composed of a metal sintered body, and an intermediate part that can be placed between the central part and the outer part may be composed of a ceramic sintered body. In such embodiments, the central part and / or outer part of the composite fiber can be electrically connected to the outside.

[0072] In the embodiments described above, it is preferable that the metal sintered body and the ceramic sintered body are positioned adjacent to each other. As long as this positional relationship is satisfied, the composite fibers of this disclosure can have various forms of multilayer structures.

[0073] (electrode structure) In another embodiment, the composite fiber of this disclosure may have an electrode structure as shown in Figure 4, for example. Having an electrode structure allows the composite fiber of this disclosure to be used as a material for electronic components, particularly as an electronic component element.

[0074] (a) For example, the composite fiber 20 shown in Figure 4(a) has a substantially circular cross-section and a structure in which the central part 21 and the outer part 22 are arranged substantially concentrically. However, the shape of the cross-section of the composite fiber 20 is not limited to a circular or concentric shape. In the composite fiber 20, one of the central part 21 and the outer part 22 may be composed of one of the "metal sintered body" and the "ceramic sintered body," and the other of the central part 21 and the outer part 22 may be composed of the other of the "metal sintered body" and the "ceramic sintered body." In the composite fiber 20, it is preferable that the "metal sintered body" and the "ceramic sintered body" are positioned adjacent to each other. The fiber diameter D is shown in the cross-sectional view (axial cross-section) of Figure 4(a) (bottom), which shows the cross-section at A-A' in Figure 4(a) (top). a The maximum dimension or maximum diameter is, for example, 500 μm or less, preferably 1 μm or more and 500 μm or less.

[0075] (b) The composite fiber 30 shown in Figure 4(b) has a structure in which an outer portion 32a with an outer portion 32a with an outer portion 32b In the composite fiber 30, one of the central part 31 and the outer part 32 is composed of one of the "metal sintered body" and the "ceramic sintered body," while the other of the central part 31 and the outer part 32 is composed of the other of the "metal sintered body" and the "ceramic sintered body." In the composite fiber 30, it is preferable that the "metal sintered body" and the "ceramic sintered body" are positioned adjacent to each other. The "metal sintered body" or "ceramic sintered body" included in the outer portion 32 may be the same or different in the outer portions 32a and 32b. The fiber diameter D is shown in the cross-sectional view (axial cross-section) of Figure 4(b) (bottom), which shows the cross-section at B-B' in Figure 4(b) (top). bThe maximum dimension or maximum diameter is, for example, 500 μm or less, preferably 1 μm or more and 500 μm or less.

[0076] (c) The composite fiber 40 shown in Figure 4(c) has a structure in which an outer portion 42 with a roughly C-shaped (or roughly crescent-shaped) cross-section is arranged in a part of the central portion 41 with a roughly circular cross-section. However, the shape of the cross-section of the composite fiber 40 is not limited to the shape shown. In the composite fiber 40, one of the central part 41 and the outer part 42 is composed of one of the "metal sintered body" and the "ceramic sintered body," while the other of the central part 41 and the outer part 42 is composed of the other of the "metal sintered body" and the "ceramic sintered body." In the composite fiber 40, it is preferable that the "metal sintered body" and the "ceramic sintered body" are positioned adjacent to each other. The fiber diameter D is shown in the cross-sectional view (axial cross-section) of Figure 4(c) (bottom), which shows the cross-section at C-C' in Figure 4(c) (top). c The maximum dimension or maximum diameter is, for example, 500 μm or less, preferably 1 μm or more and 500 μm or less.

[0077] (d) The composite fiber 50 shown in Figure 4(d) has a substantially circular cross-section and a structure in which a central part 51, an outer part 52, and an intermediate part 53 positioned between the central part 51 and the outer part 52 are arranged substantially concentrically. However, the shape of the cross-section of the composite fiber 50 is not limited to circular or concentric. In the composite fiber 50, both the central part 51 and the outer part 52 are composed of either a "metal sintered body" or a "ceramic sintered body," while the intermediate part 53 is composed of the other of the "metal sintered body" or "ceramic sintered body." In the composite fiber 50, it is preferable that the "metal sintered body" and the "ceramic sintered body" are positioned adjacent to each other. The fiber diameter D is shown in the cross-sectional view (axial cross-section) of Figure 4(d) (bottom), which shows the cross-section at D-D' in Figure 4(d) (top). d The maximum dimension or maximum diameter is, for example, 500 μm or less, preferably 1 μm or more and 500 μm or less.

[0078] For example, in embodiments (a) and (c) above, it is preferable that the "center" of the fiber is made of a "metal sintered body" and the "outer part" of the fiber is made of a "ceramic sintered body". With such a configuration, the center of the fiber can function as an electrode.

[0079] For example, in embodiments (b) and (c) above, it is preferable that the "center" of the fiber is made of a "ceramic sintered body" and the "outer part" of the fiber is made of a "metal sintered body". With such a configuration, the outer part of the fiber can function as an electrode.

[0080] For example, in embodiment (d) above, it is preferable that the "center" of the fiber is made of a "metal sintered body," the "outer part" of the fiber is also independently made of a "metal sintered body," and the "intermediate part" is made of a "ceramic sintered body." It is even more preferable that the "metal sintered body" of the "center" and the "outer part" are the same. With such a configuration, the center and / or outer part of the fiber can be made to function as electrodes.

[0081] (Other embodiments) Other embodiments of the composite fiber of this disclosure include, for example, a configuration in which a metal sintered body and a ceramic sintered body are adjacent to each other in the axial direction of the fiber, as shown in Figure 5(A), and a configuration in which a metal sintered body and a ceramic sintered body are adjacent to each other in a sandwich structure, as shown in Figure 5(B).

[0082] In the embodiment shown in Figure 5(A), for example, it is preferable that the first axial end 61 of the composite fiber 60 is made of a "metal sintered body," the second end 62 opposite to the first end is also independently made of a "metal sintered body," and the connecting portion 63 which can be arranged between the first end 61 and the second end 62 is made of a "ceramic sintered body." With this configuration, both ends (61, 62) of the fiber can function as electrodes. Furthermore, the first end portion 61 and the second end portion 62 may each be independently composed of a "ceramic sintered body," and the connecting portion 63 may be composed of a "metal sintered body." Alternatively, in the above embodiment, the connecting portion 63 may have a configuration in which "metal sintered body" and "ceramic sintered body" are alternately arranged in a continuous sequence.

[0083] In the embodiment shown in Figure 5(B), for example, it is preferable that the middle (middle layer) 73 of the composite fiber 70 is made of a "metal sintered body" in a cross-section in the axial direction or perpendicular to the axial direction, and the upper (upper layer) 71 and lower (lower layer) 72 of the composite fiber 70 are each independently made of a "ceramic sintered body". With such a configuration, the middle (middle layer) 73 of the fiber can function as an electrode. In the illustrated embodiment, the cross-section of the fiber is approximately rectangular (quadrilateral), but it is not limited to such a cross-sectional shape. Alternatively, the middle (middle layer) 73 of the composite fiber 70 may be composed of a "ceramic sintered body," while the upper (upper layer) 71 and lower (lower layer) 72 of the composite fiber 70 may each be independently composed of a "metal sintered body." This configuration allows the upper and lower (upper and lower layers) (71, 72) of the fiber to function as electrodes.

[0084] The composite fibers of this disclosure are not limited to the embodiments described above. A brief description of the method for manufacturing the composite fibers of this disclosure follows.

[0085] (Method for manufacturing composite fibers according to this disclosure) In the composite fibers of this disclosure, it is preferable that at least the "metal sintered body" and the "ceramic sintered body" are formed or manufactured integrally adjacent to each other, for example by co-sintering. By forming the "metal sintered body" and the "ceramic sintered body" integrally adjacent to each other, it is possible to form an interface, in particular an interface having complex irregularities that may be composed of the crystal grains of the metal component and the crystal grains of the ceramic component, and especially an interface having the surface roughness described above.

[0086] There are no particular limitations on the method for manufacturing the composite fibers of this disclosure, and the composite fibers of this disclosure can be manufactured as appropriate by applying conventionally known ceramic firing techniques, etc.

[0087] For example, a composite fiber can be manufactured in which a metal sintered body and a ceramic sintered body are integrally formed adjacent to each other by preparing a paste made from raw materials containing the above-mentioned metal components (metal elements) together with sintering aids, co-materials, binder resin, solvents, dispersants, plasticizers, etc. as needed, and a paste made from raw materials containing the above-mentioned ceramic components (ceramic elements) together with sintering aids, co-materials, binder resin, solvents, dispersants, plasticizers, etc. as needed, and then appropriately shaping and firing them together. At this time, for example, each paste may be shaped into a desired shape using a multi-nozzle (double nozzle, triple nozzle, or other composite spinning nozzle) or a mold.

[0088] For example, when forming and fiberizing metal sintered body paste and ceramic sintered body paste using a multi-nozzle system such as a double nozzle, other materials, such as "metals not composed of crystal grains" and / or "ceramics not composed of crystal grains," may be used as the core or core portion.

[0089] In the composite fibers of this disclosure, the "metal not composed of crystal grains" that can be used as the core portion means, for example, a metal or alloy that is formed or manufactured separately from the "metal sintered body" and "ceramic sintered body" described above. In other words, it means a metal or alloy that is formed or manufactured before the co-sintering of the "metal sintered body" and "ceramic sintered body" described above. Therefore, a metal or alloy that can be formed or manufactured by sintering at the same time as the co-sintering of the "metal sintered body" and "ceramic sintered body" described above does not fall under the category of "metal not composed of crystal grains." As a "metal not composed of crystalline grains" that can be used as the core, for example, commercially available metal or alloy wires, especially metal or alloy wires manufactured by rolling or other processes, may be used. More specifically, nickel wire and copper wire may be used.

[0090] In the composite fibers of this disclosure, the "ceramic not composed of crystal grains" that can be used as the core portion means, for example, a ceramic that is formed or manufactured separately from the "metal sintered body" and "ceramic sintered body" described above. In other words, it means a ceramic that is formed or manufactured before the co-sintering of the "metal sintered body" and "ceramic sintered body" described above. Therefore, a ceramic that can be formed or manufactured by sintering at the same time as the co-sintering of the "metal sintered body" and "ceramic sintered body" described above does not fall under the category of "ceramic not composed of crystal grains." As a "ceramic that is not composed of crystalline grains," commercially available ceramic fibers may be used, for example. More specifically, glass fibers may be used.

[0091] For example, as shown in Figure 6(A), the composite fiber of the present disclosure may include a core portion (or core or core) (C), a first layer (11) covering the core portion (C), and a second layer (12) covering the first layer (11).

[0092] More specifically, as shown in Figure 6(A), the composite fiber of the present disclosure includes a core portion (C), a first layer (11) covering the core portion (C), and a second layer (12) covering the first layer (11), wherein the core portion (C) includes a "metal not composed of crystal grains", the first layer (11) includes a "metal sintered body", specifically the metal sintered body composed of metal crystal grains, and the second layer (12) includes a "ceramic sintered body", specifically the ceramic sintered body composed of ceramic crystal grains. In such composite fibers, the strength of the fibers may be improved by bonding the first layer, which may be composed of a "metal sintered body," and the second layer, which may be composed of a "ceramic sintered body," together with crystalline grains, forming an interface with the aforementioned surface roughness. Furthermore, the strength of the fibers may be further improved by including a "metal not composed of crystalline grains," more specifically, a metal wire, in the core portion (C). In this case, the bonding force with the core portion (C) may be further improved by composing the first layer from a "metal sintered body," and the strength of the composite fiber may be significantly improved.

[0093] As an example, Figure 7 shows a composite fiber in which a nickel wire (metallic Ni core) is used as the core, the first layer is a nickel (Ni) crystal grain layer, and the second layer is a barium titanate (BaTiO3) crystal grain layer (see Example 13).

[0094] For example, as shown in Figure 6(A), the composite fiber of the present disclosure includes a core portion (C), a first layer (11) covering the core portion (C), and a second layer (12) covering the first layer (11), wherein the core portion (C) includes a "ceramic not composed of crystal grains", the first layer (11) includes a "ceramic sintered body", specifically a ceramic sintered body composed of ceramic crystal grains, and the second layer (12) includes a "metal sintered body", specifically a metal sintered body composed of metal crystal grains. In such composite fibers, the strength of the fibers may be improved by bonding together an interface having the aforementioned surface roughness, formed by both the first layer, which may be composed of a "ceramic sintered body," and the second layer, which may be composed of a "metal sintered body," being composed of crystal grains. Furthermore, the strength of the fibers may be further improved by including a "ceramic that is not composed of crystal grains," more specifically, ceramic fibers, in the core portion (C). In this case, the bonding force with the core portion (C) may be further improved by composing the first layer from a "ceramic sintered body," and the strength of the composite fibers may be significantly improved.

[0095] Composite fibers with such a structure can be manufactured, for example, by using a double nozzle in a conventional apparatus used in the extrusion molding method shown in Figure 13 to form metal sintered paste and ceramic sintered paste concentrically around a core portion (C).

[0096] In the composite fiber of this disclosure, for example, the second layer (12) shown in Figure 6 may be a "metal not composed of crystal grains" and / or a "ceramic not composed of crystal grains".

[0097] If the second layer (12) is a "metal not composed of crystal grains," the second layer (12) may be a plating layer, a vapor-deposited film, or a sputtered film of the metal or alloy.

[0098] If the second layer (12) is a "ceramic not composed of crystal grains," the second layer (12) may be a ceramic coating layer, a vapor-deposited film, or a sputtered film.

[0099] For example, as shown in Figure 6(A), the composite fiber of the present disclosure includes a core portion (C), a first layer (11) covering the core portion (C), and a second layer (12) covering the first layer (11), wherein the core portion (C) includes a "ceramic sintered body," specifically a ceramic sintered body composed of ceramic crystal grains, the first layer (11) includes a "metal sintered body," specifically a metal sintered body composed of metal crystal grains, and the second layer (12) may include a "metal not composed of crystal grains." In such composite fibers, the core portion, which may be composed of a "ceramic sintered body," and the first layer, which may be composed of a "metal sintered body," are both composed of crystal grains, forming an interface with the aforementioned surface roughness and bonding to each other, thereby improving the strength of the fibers. Furthermore, the strength of the fibers may be further improved if the second layer (12) contains a "metal not composed of crystal grains." In this case, the bonding force with the second layer (12) may be further improved by composing the first layer from a "metal sintered body," and the strength of the composite fiber may be significantly improved.

[0100] For example, as shown in Figure 6(A), the composite fiber of the present disclosure includes a core portion (C), a first layer (11) covering the core portion (C), and a second layer (12) covering the first layer (11), wherein the core portion (C) includes a "metal sintered body," specifically a metal sintered body composed of metal crystal grains, the first layer (11) includes a "ceramic sintered body," specifically a ceramic sintered body composed of ceramic crystal grains, and the second layer (12) may include a "ceramic not composed of crystal grains." In such composite fibers, the core portion, which may be composed of a "metal sintered body," and the first layer, which may be composed of a "ceramic sintered body," are both composed of crystal grains, forming an interface with the aforementioned surface roughness and bonding to each other, thereby improving the strength of the fibers. Furthermore, the strength of the fibers may be further improved by including a "ceramic that is not composed of crystal grains" in the second layer (12). In this case, the bonding force with the second layer (12) may be further improved by composing the first layer from a "ceramic sintered body," and the strength of the composite fiber may be significantly improved.

[0101] There are no particular restrictions on the ratio of the thicknesses of the core portion (C), the first layer (11), and the second layer (12), and they can be appropriately determined according to the desired application. The overall thickness or diameter (maximum dimension or maximum diameter) of the composite fiber is, for example, 500 μm or less, preferably 1 μm or more and 500 μm or less.

[0102] Furthermore, the composite fibers of this disclosure can also be manufactured by lamination technologies such as screen printing, green sheet methods using green sheets, or composite methods thereof. When using such lamination technologies, the composite fibers of this disclosure may be manufactured by appropriately cutting the laminate before or after firing to form fibers (see, for example, Figure 8).

[0103] The method for producing the composite fibers of this disclosure is not limited to those described above. The composite fibers of this disclosure will be described in more detail below with reference to examples. [Examples]

[0104] Examples 1-10 (1) Preparation of paste for metal sintered bodies The paste for metal sintering consists of Ni powder, a perovskite-type oxide containing Ba and Ti as co-materials, a polycarboxylic acid-based dispersant, a binder resin, and an organic solvent. The average particle size of the Ni powder used was 0.2 μm. The average particle size of the perovskite-type oxide containing Ba and Ti was 30 nm. As the binder resin, for example, a resin solution obtained by dissolving a resin in butyl carbitol is used. Examples of resins that can be dissolved in butyl carbitol include ethyl cellulose and cellulose acetate butyrate. In preparing the paste for metal sintering, 50 parts by weight of Ni powder, 5 parts by weight of a perovskite-type oxide containing Ba and Ti as co-materials, a resin solution obtained by dissolving 10 parts by weight of ethyl cellulose in butyl carbitol, 1 part by weight of a polycarboxylic acid-based dispersant, and the remainder being butyl carbitol were mixed and the paste for metal sintering was prepared using a ball mill.

[0105] (2) Preparation of paste for ceramic sintered bodies The paste for ceramic sintered bodies consists of a perovskite-type oxide containing Ba and Ti, a polyvinyl butyral-based binder resin, a plasticizer, and an organic solvent such as toluene. The average particle size of the perovskite-type oxide containing Ba and Ti was 100 nm. For the preparation of the paste for ceramic sintered bodies, 90 parts by weight of the perovskite-type oxide containing Ba and Ti, 10 parts by weight of the polyvinyl butyral-based binder resin, a plasticizer, and toluene were mixed, and the paste for ceramic sintered bodies was prepared using a ball mill.

[0106] As schematically shown in Figure 8, the first ceramic sintered body green sheet 81 was fabricated by applying the above-mentioned ceramic sintered body paste to a support substrate (not shown) and drying it (Figure 8(A)). The above-mentioned paste for metal sintered bodies was laminated onto the first ceramic sintered body green sheet 81 by printing to form a printed layer 82 for metal sintered bodies (Figure 8(B)). A second green sheet 83 for a ceramic sintered body was prepared from the ceramic sintered body paste in the same manner as the first green sheet 81 for a ceramic sintered body. After peeling it off the support base, the second green sheet 83 for a ceramic sintered body was laminated onto the printed layer 82 for a metal sintered body and pressed to produce a laminate 80 (Figure 8(C)). Next, the laminate 80 was cut into long, narrow strips along the dashed lines schematically shown in Figure 8(C) to produce a "composite fiber precursor." The thicknesses of the first ceramic sintered body green sheet 81, the metal sintered body printed layer 82, and the second ceramic sintered body green sheet 83 are as shown in Table 1 below (unit: μm).

[0107] [Table 1]

[0108] (Firing process) By firing the "composite fiber precursor" under the following conditions, a composite fiber was produced as a fibrous body in which a "metal sintered body" and a "ceramic sintered body" are adjacent to each other. Firing conditions After degreasing in a nitrogen atmosphere at 400°C for 10 hours, the product was subjected to further treatment in a nitrogen-hydrogen-water vapor mixed atmosphere at a top temperature of 1200°C and an oxygen partial pressure of 10°C. -9 ~10 -10 The firing was performed under MPa conditions.

[0109] Figure 8(D) schematically shows a cross-section (axial cross-section) of the composite fiber produced in Example 1. More specifically, Figure 8(D) schematically shows a structure in which nickel metal (Ni)(92) (center of the cross-section), formed as a metal sintered body, is sandwiched between barium titanate (BaTiO3)(BT)(91,93) (upper and lower parts of the cross-section), formed as a ceramic sintered body, with the metal sintered body and the ceramic sintered body adjacent to each other.

[0110] (Cross-sectional observation) The cross-section (axial cross-section) of the composite fiber prepared in Example 1 above was observed using an electron microscope (JEOL Ltd., JCM-5700). Figure 9 shows an electron microscope image of the cross-section of the composite fiber (5.0kV, 2500x magnification).

[0111] The electron microscope image in Figure 9 shows that the Ni thickness was 15.6 μm and the BaTiO3 (BT) thickness was 6.0 μm (Table 2). There were no areas of delamination between the metal sintered body (Ni) and the ceramic sintered body (BaTiO3), and they were in a tightly bonded state. Furthermore, the Ni thickness and BaTiO3 thickness for Examples 2 to 10 are shown in Table 2 below (unit: μm).

[0112] [Table 2]

[0113] (Intensity measurement) The tensile strength of the composite fibers prepared in Examples 1 to 10 was measured using a strength testing machine (Shimadzu Corporation, MST-1). The radius of curvature of the composite fibers prepared in Examples 1 to 10 was also evaluated. Table 3 below shows the evaluation results for tensile strength and radius of curvature of the composite fibers prepared in Examples 1 to 10.

[0114] [Table 3]

[0115] In all of the composite fibers of Examples 1 to 10, the density was 10 kgf / mm². 2 The tensile strength was as described above, and the radius of curvature was 15 mm or less.

[0116] Comparative Example 1 (Composite fiber using nickel foil) (1) Nickel foil batch Instead of using a paste for metal sintering, I obtained 15 μm thick nickel foil from Niraco Co., Ltd. (2) Preparation of paste for ceramic sintered bodies A paste for ceramic sintered bodies was prepared in the same manner as in Examples 1 to 10.

[0117] As schematically shown in Figure 8, the first ceramic sintered body green sheet 81 was fabricated by applying a ceramic sintered body paste to a support substrate (not shown) and drying it (Figure 8(A)). Nickel foil was laminated onto the first ceramic sintered body green sheet 81 as a substitute for the metal sintered body printing layer 82 (Figure 8(B)). A second green sheet 83 for a ceramic sintered body was prepared from the ceramic sintered body paste in the same manner as the first green sheet 81 for a ceramic sintered body. After peeling it off the support base, the second green sheet 83 for a ceramic sintered body was laminated onto nickel foil and pressed to produce a laminate 80 (Figure 8(C)). Next, the laminate 80 was cut into long, narrow strips along the dashed lines schematically shown in Figure 8(C) to produce a "composite fiber precursor." The thicknesses of the first ceramic sintered body green sheet 81, the nickel layer 82, and the second ceramic sintered body green sheet 83 were as shown in Table 4 below (unit: μm).

[0118] [Table 4]

[0119] (Firing process) By firing the "composite fiber precursor" under the following conditions, a composite fiber was produced as a fiber body in which a "nickel layer (metal foil layer)" and a "ceramic sintered body" are adjacent to each other (i.e., a three-layer fiber body in which a "ceramic sintered body (BT)", a "Ni layer (metal foil layer)", and a "ceramic sintered body (BT)" are adjacent to each other). Firing conditions After degreasing in a nitrogen atmosphere at 400°C for 10 hours, the product was subjected to further treatment in a nitrogen-hydrogen-water vapor mixed atmosphere at a top temperature of 1200°C and an oxygen partial pressure of 10°C. -9 ~10 -10 The firing was performed under MPa conditions.

[0120] (Cross-sectional observation) The cross-section (axial cross-section) of the composite fiber prepared above was observed using an electron microscope (JEOL Ltd., JCM-5700). Figure 10 shows an electron microscope image of the cross-section of the composite fiber (5.0kV, 2500x magnification).

[0121] [Table 5]

[0122] As shown in Figure 10, stress was applied to the BaTiO3 layer due to the difference in thermal expansion coefficients, causing the BaTiO3(BT) layer to rupture. Delamination of the Ni-BaTiO3(BT) layer also occurred. From these findings, it was determined that the composite fiber of Comparative Example 1 does not physically function as a piezoelectric fiber.

[0123] (Intensity measurement) The tensile strength of the composite fiber prepared in Comparative Example 1 was measured using a strength testing machine (Shimadzu Corporation, MST-1). The radius of curvature of the composite fiber prepared in Comparative Example 1 was also evaluated. Table 6 below shows the tensile strength and radius of curvature evaluation results for the composite fiber of Comparative Example 1.

[0124] [Table 6]

[0125] The results shown in Table 6 indicate that the composite fiber of Comparative Example 1 has only about 60% of the tensile strength of the composite fiber of Example 1.

[0126] Example 11 In the same manner as in Example 1, a composite fiber precursor having a circular cross-section was prepared using a metal sintered body paste and a ceramic sintered body paste, with the metal sintered body paste and ceramic sintered body paste arranged concentrically through a double nozzle (center: metal sintered body (Ni) paste, outer part: ceramic sintered body (BT) paste, cross-sectional area ratio (metal / ceramic): 1 / 1).

[0127] Next, composite fiber precursors were fired under the same firing conditions as in Example 1 to produce composite fibers having a circular cross-section (fiber diameter: 90 μm) (center: metal sintered body (Ni), outer part: ceramic sintered body (BT)).

[0128] The strength of the composite fiber prepared in Example 11 was measured in the same manner as in Example 1. The tensile strength of the composite fiber prepared in Example 11 was 19.1 kgf / mm². 2 That was the case. Furthermore, the radius of curvature of the composite fiber produced in Example 11 was 5 mm.

[0129] Example 12 A composite fiber precursor having a circular cross-section was prepared in the same manner as in Example 11, except that the following metal sintered paste and ceramic sintered paste were used, by passing the material through a double nozzle and concentrically arranging the following metal sintered paste and ceramic sintered paste (center: metal sintered paste (Cu), outer part: ceramic sintered paste (BNT), cross-sectional area ratio (metal (Cu) / ceramic (BNT)): 1 / 1).

[0130] (1) Preparation of paste for metal sintered bodies The paste for metal sintering consists of Cu powder, a perovskite-type oxide containing Bi, Na, and Ti as co-materials, a polycarboxylic acid-based dispersant, a binder resin, and an organic solvent. The average particle size of the Cu powder used was 0.2 μm. The average particle size of the perovskite-type oxide containing Bi, Na, and Ti was 30 nm. As the binder resin, for example, a resin solution obtained by dissolving a resin in butyl carbitol is used. Examples of resins that can be dissolved in butyl carbitol include ethyl cellulose and cellulose acetate butyrate. In preparing the paste for metal sintering, 50 parts by weight of Cu powder, 5 parts by weight of a perovskite-type oxide containing Bi, Na, and Ti as co-materials, a resin solution obtained by dissolving 10 parts by weight of ethyl cellulose in butyl carbitol, 1 part by weight of a polycarboxylic acid-based dispersant, and the remainder being butyl carbitol were mixed and the paste for metal sintering was prepared using a ball mill.

[0131] (2) Preparation of paste for ceramic sintered bodies The paste for ceramic sintered bodies consists of a perovskite-type oxide containing Bi, Na, and Ti, a polyvinyl butyral-based binder resin, a plasticizer, and an organic solvent such as toluene. The average particle size of the perovskite-type oxide containing Bi, Na, and Ti was 100 nm. For the preparation of the paste for ceramic sintered bodies, 90 parts by weight of the perovskite-type oxide containing Bi, Na, and Ti, 10 parts by weight of the polyvinyl butyral-based binder resin, a plasticizer, and toluene were mixed, and the paste for ceramic sintered bodies was prepared using a ball mill.

[0132] Next, composite fiber precursors were fired under the same firing conditions as in Example 1 to produce composite fibers having a circular cross-section (fiber diameter: 100 μm) (center: metal sintered body (Cu), outer part: ceramic sintered body (bismuth sodium titanate) (BNT)).

[0133] The strength of the composite fiber prepared in Example 12 was measured in the same manner as in Example 1. The tensile strength of the composite fiber prepared in Example 12 was 15.4 kgf / mm². 2 That was the case. Furthermore, the radius of curvature of the composite fiber produced in Example 12 was 5 mm.

[0134] Example 13 Using the metal sintered body (Ni) paste and ceramic sintered body (BT) paste prepared in Example 1, along with nickel wire (diameter: 50 μm), a composite fiber precursor having a circular cross-section in which the metal sintered body (Ni) paste and ceramic sintered body (BT) paste were arranged concentrically was fabricated by passing the nickel wire through a wire guide (see Figure 13) in the same manner as in the conventional method (however, a double nozzle was used in this example). (Core portion: Ni wire, First layer (inner part): metal sintered body (Ni) paste, Second layer (outer part): ceramic sintered body (BT) paste, Cross-sectional area ratio (Ni wire / Ni layer / BT layer): 0.70 / 0.30 / 1.0).

[0135] Next, composite fiber precursors were fired under the same firing conditions as in Example 1 to produce composite fibers having a circular cross-section (fiber diameter: 88 μm) (core: metallic Ni, first layer (inner part): metal sintered body (Ni), second layer (outer part): ceramic sintered body (BT)).

[0136] The strength of the composite fiber prepared in Example 13 was measured in the same manner as in Example 1. The tensile strength of the composite fiber prepared in Example 13 was 19.8 kgf / mm². 2 That was the case. Furthermore, the radius of curvature of the composite fiber produced in Example 13 was 5 mm.

[0137] (Cross-sectional observation) The cross-section (axial section) of the composite fiber prepared in Example 13 was observed using an electron microscope (JEOL Ltd., JCM-5700). Figure 7 shows an electron microscope image of the cross-section of the composite fiber (5.0kV, 2500x magnification).

[0138] As shown in Figure 7, the composite fibers of Example 13 showed no delamination or cracking whatsoever. Therefore, it was found that the composite fibers of Example 13 have high tensile strength and function as piezoelectric fibers.

[0139] Comparative Example 2 A composite fiber consisting of a "Cu layer (metal foil layer)" and a "ceramic sintered body (BNT)" adjacent to each other was manufactured in the same manner as in Comparative Example 1, except that a 15 μm thick copper foil (manufactured by Nilaco) and the ceramic sintered body paste prepared in Example 12 were used. This resulted in a three-layer fiber structure consisting of a "ceramic sintered body (BNT)", a "Cu layer (metal foil layer)", and a "ceramic sintered body (BNT)" adjacent to each other.

[0140] The strength of the composite fiber prepared in Comparative Example 2 was measured in the same manner as in Example 1. The tensile strength of the composite fiber prepared in Comparative Example 2 was 6.0 kgf / mm². 2 That was the case. Furthermore, the radius of curvature of the composite fiber prepared in Comparative Example 2 was 10 mm.

[0141] The composite fiber prepared in Comparative Example 2, like the composite fiber prepared in Comparative Example 1, experienced stress on the BNT layer due to differences in thermal expansion coefficients, resulting in the fracture of the BNT layer. Furthermore, delamination of the BMT layer also occurred. Therefore, it was concluded that the composite fiber of Comparative Example 2 does not function as a piezoelectric fiber.

[0142] (Determination of line roughness) The linear roughness of the interface between the metal sintered body and the ceramic sintered body of the composite fibers prepared in Example 3 and Comparative Example 1 was measured. After polishing the cross-sectional samples of the composite fibers prepared in Example 3 and Comparative Example 1, SEM observation was performed. Cross-sections where the interface between adjacent metal sintered bodies (Ni) and ceramic sintered bodies (BT) could be observed were observed using SEM (15.0kV, 5000x magnification). Three fields of view in which the interface could be identified were randomly extracted from the SEM images. Using image analysis software (Mitani Corporation, WinROOF), the straight line connecting the two intersection points between the edge face of the extracted field of view image and the interface between the metal sintered body and the ceramic sintered body was defined as the center line, and the distance between the actual boundary and the center line was measured at 30 equally spaced points along the center line. The average value and standard deviation of these distances were used to evaluate the line roughness. The results are shown in Table 7 below.

[0143] [Table 7]

[0144] The composite fibers of this disclosure are not limited to those exemplified in the above examples. [Industrial applicability]

[0145] The composite fibers of this disclosure can be used in sensors, particularly vibration sensors and actuators, for use in structures such as buildings, automobiles, ships, and aircraft. Furthermore, the composite fibers of this disclosure can also be used as electronic component elements. [Explanation of Symbols]

[0146] 1. Metal sintered body 2. Ceramic sintered body 3 Interface 10, 20, 30, 40, 50, 60, 70 Composite Fibers 11 1st layer 12 2nd layer C core part / core 21,31,41,51 Center 22,32,42,52 Outer part 53 Middle section 61 First end 62 Second end 63 Connection part 71 Top 72 Lower part 73 Chubu 80-layer structure 81 Green sheet for first ceramic sintered body 82 Printing layer for metal sintered bodies 83. Green sheet for second ceramic sintered body 90 Composite Fiber (Cross Section) 91 Barium titanate (BaTiO3) (BT) 92 Nickel (Ni) 93 Barium titanate (BaTiO3) (BT) 100 PZT fiber 101 Metal wire / metal thin wire 102 PZT thin layer / PZT film 103 Nozzles 104 Wire Guide 105 PZT Paste 200 Smart Boards 201 Carbon Fiber Reinforced Plastic (CFRP) Prepreg 202 Structure 300 PZT fiber 301 Fine metal wire 302 PZT membrane

Claims

1. A composite fiber composed of at least a metal sintered body and a ceramic sintered body, wherein the metal sintered body and the ceramic sintered body are adjacent to each other to form a fibrous body, The metal sintered body and the ceramic sintered body form an interface, the interface has surface roughness, the surface roughness is defined by the linear roughness in a cross-sectional view of the interface, and the linear roughness is 15 nm or more and 1000 nm or less. The aforementioned ceramic sintered body is a metal oxide ceramic sintered body. The metal component constituting the metal sintered body is composed of at least one selected from the group consisting of silver (Ag), palladium (Pd), copper (Cu), chromium (Cr), titanium (Ti), platinum (Pt), and nickel (Ni). A composite fiber comprising a ceramic component constituting the ceramic sintered body, wherein the ceramic component is composed of oxygen (O) and at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), yttrium (Y), zirconium (Zr), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), aluminum (Al), indium (In), tin (Sn), antimony (Sb), barium (Ba), tantalum (Ta), tungsten (W), lead (Pb), bismuth (Bi), lanthanum (La), cesium (Ce), neodymium (Nd), samarium (Sm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), and erbium (Er).

2. The composite fiber according to Claim 1, wherein the ceramic component is composed of oxygen (O) and at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), yttrium (Y), zirconium (Zr), titanium (Ti), manganese (Mn), iron (Fe), zinc (Zn), aluminum (Al), antimony (Sb), lead (Pb), bismuth (Bi), lanthanum (La), neodymium (Nd), and samarium (Sm).

3. The composite fiber according to claim 1 or 2, wherein at least one of the metal components comprises nickel (Ni) or copper (Cu).

4. The composite fiber according to any one of claims 1 to 3, wherein at least one of the ceramic components comprises titanium (Ti).

5. The composite fiber according to any one of claims 1 to 4, wherein the interface is composed of crystalline grains.

6. A composite fiber according to any one of claims 1 to 5, wherein an interface is formed between the crystal grains constituting the metal sintered body and the crystal grains constituting the ceramic sintered body.

7. The composite fiber according to any one of claims 1 to 6, wherein the crystal grains constituting the metal sintered body are crystal grains formed by the crystal growth of metal, and the crystal grains constituting the ceramic sintered body are crystal grains formed by the crystal growth of ceramic.

8. The composite fiber according to any one of claims 1 to 7, wherein the interface does not have a gap in a cross-sectional view of the composite fiber.

9. The composite fiber according to any one of claims 1 to 8, wherein the metal sintered body is located at the center of the composite fiber.

10. The composite fiber according to any one of claims 1 to 8, wherein the ceramic sintered body is located at the center of the composite fiber.

11. The composite fiber according to any one of claims 1 to 8, wherein the central part of the composite fiber is made of the metal sintered body, and at least a portion of the outer part of the composite fiber is made of the ceramic sintered body.

12. The composite fiber according to any one of claims 1 to 8, wherein the central part of the composite fiber is made of the ceramic sintered body, and at least a portion of the outer part of the composite fiber is made of the metal sintered body.

13. The composite fiber according to any one of claims 1 to 8, wherein the central part of the composite fiber is made of the metal sintered body, the outer part of the composite fiber is also independently made of the metal sintered body, and the intermediate part disposed between the central part and the outer part is made of the ceramic sintered body.

14. The composite fiber according to any one of claims 1 to 8, wherein the first axial end of the composite fiber is made of the metal sintered body, the second end facing the first end is also independently made of the metal sintered body, and the connecting portion disposed between the first end and the second end is made of the ceramic sintered body.

15. The composite fiber according to any one of claims 1 to 8, wherein in a cross-section of the composite fiber in the axial direction or in a direction perpendicular to the axial direction, the middle part of the composite fiber is made of the metal sintered body, and the upper and lower parts of the composite fiber are each independently made of the ceramic sintered body, or the middle part of the composite fiber is made of the ceramic sintered body, and the upper and lower parts of the composite fiber are each independently made of the metal sintered body.

16. The composite fiber according to any one of claims 1 to 7, wherein the composite fiber comprises a core portion, a first layer covering the core portion, and a second layer covering the first layer, wherein the first layer comprises a metal sintered body composed of metal crystal grains, the second layer comprises a ceramic sintered body composed of ceramic crystal grains, and the core portion comprises a metal not composed of crystal grains.

17. The composite fiber according to any one of claims 1 to 7, wherein the composite fiber comprises a core portion, a first layer covering the core portion, and a second layer covering the first layer, the first layer comprising a ceramic sintered body composed of ceramic crystal grains, the second layer comprising a metal sintered body composed of metal crystal grains, and the core portion comprising a ceramic not composed of crystal grains.

18. The composite fiber according to any one of claims 1 to 7, wherein the composite fiber comprises a core portion, a first layer covering the core portion, and a second layer covering the first layer, the core portion comprising a ceramic sintered body composed of ceramic crystal grains, the first layer comprising a metal sintered body composed of metal crystal grains, and the second layer comprising a metal not composed of crystal grains.

19. The composite fiber according to any one of claims 1 to 7, wherein the composite fiber comprises a core portion, a first layer covering the core portion, and a second layer covering the first layer, the core portion comprising a metal sintered body composed of metal crystal grains, the first layer comprising a ceramic sintered body composed of ceramic crystal grains, and the second layer comprising a ceramic not composed of crystal grains.

20. The aforementioned metal sintered body is a metal sintered body containing nickel or copper. The composite fiber according to any one of claims 1 to 19, wherein the ceramic sintered body contains titanium, barium, and oxygen, or a metal oxide ceramic sintered body containing bismuth, sodium, titanium, and oxygen.

21. The metal sintered body is made of nickel metal only or copper metal only. The composite fiber according to any one of claims 1 to 20, wherein the ceramic sintered body is barium titanate or bismuth sodium titanate.

22. The tensile strength of the aforementioned composite fiber is 5 kgf / mm². ２ Above 400 kgf / mm ２ The composite fiber according to any one of claims 1 to 21, which is as follows:

23. A composite fiber according to any one of claims 1 to 22, having flexibility such that the radius of curvature is 3 mm or more and 200 mm or less.

24. The composite fiber according to any one of claims 1 to 23, wherein the fiber diameter of the composite fiber is 1 μm or more and 500 μm or less.

25. The composite fiber according to any one of claims 1 to 24, wherein the metal sintered body is composed of metal crystal grains, and the ceramic sintered body is composed of ceramic crystal grains.

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