Laminated film and method for producing laminated film

Abstract

This laminated film is provided with a porous resin layer (1), a first adhesive layer (2a), a metal layer (3a), and a second adhesive layer (2b). The first adhesive layer (2a) is laminated on the porous resin layer (1). The metal layer (3a) is laminated on the first adhesive layer (2a) on the opposite side of the porous resin layer (1) when viewed from the first adhesive layer (2a). The second adhesive layer (2b) is laminated on the porous resin layer (1) on the opposite side of the first adhesive layer (2a) when viewed from the porous resin layer (1). The porous resin layer (1) is a molded body of liquid crystal polymer fibers.

Description

Laminated film and method for producing the same

[0001] The present disclosure relates to a laminate film and a method for producing the laminate film.

[0002] Patent Document 1 (JP 2020-53632 A) discloses a low dielectric substrate material having a porous resin layer, an adhesive layer, and a metal layer in that order in the thickness direction, characterized in that the thickness d1 of the adhesive layer and the thickness d2 of the porous resin layer satisfy the following formula (1): d1 / d2≦0.5 (1)

[0003] Patent Document 2 (JP 2004-82372 A) discloses an insulating material for high-frequency wiring boards, in which an adhesive layer is formed on at least one surface of a resin porous layer, and the difference in dielectric constant at 10 GHz between the resin porous layer and the adhesive layer is 0.4 or less.

[0004] JP 2020-53632 A JP 2004-82372 A

[0005] As described in the above Patent Documents 1 and 2, a substrate material having a porous resin layer and an adhesive layer has been studied as a laminate film for a substrate material. However, a laminate film having an adhesive layer has a relatively large dielectric loss.

[0006] The present disclosure has been made in consideration of the above problems, and has an object to provide a laminated film that includes a porous resin layer and an adhesive layer and has small dielectric loss.

[0007] A laminate film according to the present disclosure includes a porous resin layer, a first adhesive layer, a metal layer, and a second adhesive layer. The first adhesive layer is laminated on the porous resin layer. The metal layer is laminated on the first adhesive layer on the opposite side of the porous resin layer from the first adhesive layer. The second adhesive layer is laminated on the porous resin layer on the opposite side of the porous resin layer from the first adhesive layer. The porous resin layer is a molded body of liquid crystal polymer fibers.

[0008] In the laminate film according to the present disclosure, the porous resin layer is a molded body of liquid crystal polymer fibers, which reduces the dielectric loss tangent of the laminate film. Therefore, it is possible to provide a laminate film that includes a porous resin layer and an adhesive layer and has low dielectric loss.

[0009] Fig. 1 is a cross-sectional view showing a laminate film according to an embodiment of the present disclosure; Fig. 2 is a flowchart showing a manufacturing method of a laminate film according to an embodiment of the present disclosure; Fig. 3 is a cross-sectional SEM photograph of a double-sided copper clad laminate according to Example 1; Fig. 4 is a cross-sectional SEM photograph of a double-sided copper clad laminate according to Example 4; Fig. 5 is a cross-sectional SEM photograph of a double-sided copper clad laminate according to a reference example.

[0010] Hereinafter, a laminate film according to an embodiment of the present disclosure will be described, but the present disclosure is not limited thereto. In addition, in the following description of the embodiment, the same or corresponding parts in the drawings are designated by the same reference numerals, and description thereof will not be repeated.

[0011] {Laminate Film} Fig. 1 is a cross-sectional view showing a laminate film according to an embodiment of the present disclosure. As shown in Fig. 1, a laminate film 10 according to an embodiment of the present disclosure includes a porous resin layer 1, a first adhesive layer 2a, a second adhesive layer 2b, a first metal layer 3a, and a second metal layer 3b. The first adhesive layer 2a is laminated on the porous resin layer 1. The first metal layer 3a is laminated on the first adhesive layer 2a on the side opposite the porous resin layer 1 from the first adhesive layer 2a. The second adhesive layer 2b is laminated on the porous resin layer 1 on the side opposite the first adhesive layer 2a from the porous resin layer 1. The second metal layer 3b is laminated on the second adhesive layer 2b on the side opposite the porous resin layer 1 from the second adhesive layer 2b. Note that the laminate film 10 does not necessarily have to include the second adhesive layer 2b.

[0012] The laminate film according to an embodiment of the present disclosure has a relatively small dielectric loss tangent, for example, 0.005 or less, and preferably 0.03 or less, as measured by a cavity resonator method using a dielectric constant measuring device conforming to JIS R 1641 and applying a high-frequency signal of 12 GHz at an ambient temperature of 25°C.

[0013] Next, the porous resin layer 1, the first adhesive layer 2a, the second adhesive layer 2b, the first metal layer 3a, and the second metal layer 3b will be described. The same type of adhesive layer can be used for the first adhesive layer 2a and the second adhesive layer 2b. The first adhesive layer 2a and the second adhesive layer 2b may be the same type of adhesive layer, or different types of adhesive layers. The same type of metal layer can also be used for the first metal layer 3a and the second metal layer 3b. The first metal layer 3a and the second metal layer 3b may be the same type of metal layer, or different types of metal layers.

[0014] [Porous Resin Layer] The porous resin layer in this embodiment has a porosity of, for example, 25% or more and 50% or less. A porosity of 25% or more can provide the desired function as a porous body, and for example, the dielectric constant can be relatively low by having air in the pores. Furthermore, a porosity of 50% or less can prevent the strength of the laminated film from becoming too low. The porosity is calculated based on the weight of the porous resin layer, the thickness of the porous resin layer, and the density of the raw material resin of the porous resin layer. The thickness of the porous resin layer may be measured, for example, using a scanning electron microscope (SEM). Furthermore, the porous resin layer in this embodiment has an average pore diameter of, for example, 1 μm or less, measured by mercury intrusion porosimetry.

[0015] The porous resin layer in this embodiment is characterized by being a molded body of liquid crystal polymer fibers (LCP fiber molded body). By using an LCP fiber molded body as the porous resin layer, the dielectric loss tangent of the laminated film is reduced, thereby reducing the dielectric loss of the laminated film. The LCP fiber molded body is plate-shaped and is molded from liquid crystal polymer powder (LCP powder). This LCP powder contains fibrous particles (liquid crystal polymer fibers: LCP fibers) made of liquid crystal polymer.

[0016] It is preferable that at least one surface of the LCP fiber molding is plasma-treated. By plasma-treating at least one surface of the LCP fiber molding by irradiating it with plasma, the adhesion between the LCP fiber molding and the first adhesive layer and / or the second adhesive layer is improved. The LCP fiber molding does not have to be plasma-treated. It is most preferable that both surfaces of the LCP fiber molding are plasma-treated.

[0017] (Liquid Crystal Polymer Powder) The liquid crystal polymer is not particularly limited, but examples thereof include thermotropic liquid crystal polymers, etc. Thermotropic liquid crystal polymers are aromatic polyesters synthesized mainly from monomers such as aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids, and exhibit liquid crystallinity when melted.

[0018] The molecules of liquid crystal polymers have a negative coefficient of linear expansion (CTE) in the axial direction of the molecular axis and a positive CTE in the radial direction of the molecular axis.

[0019] The liquid crystal polymer preferably does not have an amide bond. Examples of thermotropic liquid crystal polymers that do not have an amide bond include a copolymer of parahydroxybenzoic acid, terephthalic acid, and dihydroxybiphenyl (copolymer of parahydroxybenzoic acid and ethylene terephthalate) (melting point: approximately 350°C), which is called type 1 liquid crystal polymer and has a high melting point and a low CTE, and a copolymer of parahydroxybenzoic acid and 2,6-hydroxynaphthoic acid (melting point: approximately 320°C), which is called type 1.5 (or type 3) and has a melting point between type 1 liquid crystal polymer and type 2 liquid crystal polymer.

[0020] The LCP fibers contained in the LCP powder are not particularly limited as long as they contain a fibrous portion, which may be linear or branched.

[0021] The average diameter of the LCP fibers is 2 μm or less, preferably 1 μm or less, and the average aspect ratio of the LCP fibers is preferably 10 to 500, more preferably 10 to 300.

[0022] The average diameter and average aspect ratio of the LCP fibers are measured by the following method.

[0023] LCP powder made of LCP fibers to be measured is dispersed in acetone to prepare a slurry containing 0.01% by mass of LCP powder. The slurry is prepared so that the water content in the slurry is 1% by mass or less. 5 to 10 μL of this slurry is then dropped onto a silicon substrate, and the slurry on the silicon substrate is allowed to dry naturally. By allowing the slurry to dry naturally, the LCP powder is arranged on the silicon substrate.

[0024] Next, a predetermined region of the LCP powder arranged on the silicon substrate is observed with a scanning electron microscope (SEM) to collect 100 or more image data of the particles (LCP fibers) that make up the LCP powder. When collecting the image data, the region is set according to the size of each LCP particle so that the number of image data is 100 or more. To prevent omissions in the collection of image data or measurement errors for each LCP particle, the SEM magnification is appropriately changed to 500x, 3000x, or 10000x to collect the image data.

[0025] Next, the longitudinal dimension and width dimension of each of the LCP fibers are measured using the collected image data.

[0026] For one LCP fiber captured in each of the image data, the direction of the straight line connecting the two ends of the longest path from one end of the fiber through approximately the center of the particle to the opposite end of the fiber is defined as the longitudinal direction. The length of the straight line connecting the two ends of the longest path is measured as the longitudinal dimension.

[0027] Furthermore, the particle size in the direction perpendicular to the longitudinal direction of each LCP powder particle is measured at three different points along the longitudinal direction, and the average of the dimensions measured at these three points is defined as the width direction dimension (fiber diameter) per LCP powder particle.

[0028] Furthermore, the ratio of the longitudinal dimension to the fiber diameter (longitudinal dimension / fiber diameter) is calculated to be the aspect ratio of the LCP fiber.

[0029] The average value of the fiber diameters measured for 100 LCP fibers is defined as the average diameter, and the average value of the aspect ratios measured for 100 LCP fibers is defined as the average aspect ratio.

[0030] The fibrous particles may be contained in the LCP powder as aggregates of the fibrous particles.

[0031] Furthermore, the axial direction of the LCP molecules constituting the fibrous particles tends to coincide with the longitudinal direction of the fibrous particles. This is thought to be because, when an LCP powder is produced, breakage occurs between multiple domains formed by bundling the LCP molecules, causing the axial direction of the LCP molecules to be aligned along the longitudinal direction of the fibrous particles.

[0032] In the LCP powder, the content (number ratio) of particles other than fibrous particles (aggregated particles that are not substantially fibrous) is preferably 20% or less. For example, when the LCP powder is placed on a flat surface, particles with a maximum height of 10 μm or less are fibrous particles, and particles with a maximum height of more than 10 μm are aggregate particles.

[0033] The LCP powder preferably has a D50 (average particle size) value of 13 μm or less, as measured by particle size measurement using a particle size distribution measuring device based on a laser diffraction scattering method.

[0034] [Adhesive Layer (First Adhesive Layer 2a, Second Adhesive Layer 2b)] The material of the adhesive layer is not particularly limited, but a layer made of a low-dielectric-constant resin is preferred. For example, a coating of adhesive made of a low-dielectric-constant resin or a sheet made of a low-dielectric-constant resin can be used as the adhesive layer. Examples of such resins include polyimide resins such as modified polyimide resins, fluororesins, polyphenylene oxide, polyphenylene ether, bismaleimide triazine, epoxy resins, phenolic resins, or modified versions of these. Among these, an epoxy resin sheet is preferred.

[0035] It is also preferable that the adhesive layer contains a liquid crystal polymer. By containing a liquid crystal polymer in the adhesive layer, the dielectric loss of the laminated film can be further reduced. As the liquid crystal polymer contained in the adhesive layer, the liquid crystal polymer used as the liquid crystal polymer in the liquid crystal polymer powder described above can be used.

[0036] However, in order to prevent the adhesive layer from melting during the production of the laminated film described below, it is preferable that the melting point of the liquid crystal polymer contained in the adhesive layer be different from the melting point of the liquid crystal polymer contained in the porous resin layer. More specifically, it is preferable that the melting point of the liquid crystal polymer contained in the porous resin layer be higher than the melting point of the liquid crystal polymer contained in the adhesive layer. This makes it easier to heat the adhesive layer containing the liquid crystal polymer and bond it to other layers, such as the porous resin layer and the metal layer, while maintaining its function as a porous resin layer in the LCP fiber molding. Furthermore, it is more preferable that the melting point of the liquid crystal polymer contained in the porous resin layer be 20°C higher than the melting point of the liquid crystal polymer contained in the adhesive layer. This makes it easier to heat the adhesive layer containing the liquid crystal polymer and bond it to other layers, such as the porous resin layer and the metal layer, while maintaining its function as a porous resin layer in the LCP fiber molding.

[0037] The adhesive layer containing a liquid crystal polymer can be a liquid crystal polymer film formed by molding a liquid crystal polymer into a film, or an LCP fiber molded body. It is preferable to use an LCP fiber molded body as the adhesive layer containing a liquid crystal polymer. This further improves the adhesion between the adhesive layer and the porous resin layer. The LCP fiber molded body constituting the adhesive layer can be an LCP fiber molded body that can be used as a porous resin layer. Furthermore, like the LCP fiber molded body that can be used as a porous resin, the LCP fiber molded body constituting the adhesive layer is preferably plasma-treated in order to improve adhesion with other layers.

[0038] The thickness of the adhesive layer is, for example, 2 μm or more, and preferably 5 μm or more, and for example, 50 μm or less, and preferably 25 μm or less.

[0039] [Metal Layer (First Metal Layer 3a, Second Metal Layer 3b)] The metal layer is specifically made of a metal foil. From the viewpoints of conductivity and processability as a wiring pattern, the metal layer (metal foil) is preferably made of copper, a copper alloy, or a copper surface plated thereon. The thickness of the metal layer (metal foil) is preferably 1 μm or more and 50 μm or less. The surface of the metal foil may be subjected to various physical or chemical surface treatments, such as a roughening treatment or a blackening treatment, in order to improve adhesion with the adhesive layer.

[0040] The metal layer (metal foil) can be bonded to the adhesive layer by, for example, hot pressing or heating after the metal foil is laminated on the adhesive layer. Various types of presses, such as a vacuum press, a heat press, or a continuous press, can be used for the hot pressing. Any conventionally known conditions for the temperature and pressure of the hot pressing can be used, as long as they cause a curing reaction of the adhesive. In this embodiment, a vacuum press is used, as described below.

[0041] {Method for manufacturing a laminated film} Hereinafter, a method for manufacturing a laminated film according to an embodiment of the present disclosure will be described. Fig. 2 is a flowchart showing a method for manufacturing a laminated film according to an embodiment of the present disclosure. As shown in Fig. 2, the method for manufacturing a laminated film according to an embodiment of the present disclosure includes a step S1 of preparing a porous resin layer, a plasma treatment step S2, a first press step S3, and a second press step S4.

[0042] [Step S1 of Preparing Porous Resin Layer] The step S1 of preparing a porous resin layer includes a dispersion step S11 and a molding step S12.

[0043] (Dispersion step S11) First, the dispersion step S11 according to this embodiment will be described below. In the dispersion step S11, a liquid crystalline polymer powder in a slurry state is obtained. However, the method for obtaining the liquid crystalline polymer powder in a slurry state is not limited to the dispersion step S11 described below.

[0044] In the dispersion step S11 according to this embodiment, the LCP powder, which is the raw material for the liquid crystal polymer fiber molded body serving as the porous resin layer, is dispersed in a dispersion medium to form a paste or slurry. In this embodiment, the fine fibrous LCP powder described above is used, so the LCP powder can be dispersed in a highly viscous dispersion medium.

[0045] Examples of the dispersion medium used in the dispersion step include butanediol, water, ethanol, terpineol, a mixture of water and ethanol, etc. For example, when butanediol is used as the dispersion medium, a paste-like LCP powder is obtained. When a mixture of water and ethanol is used as the dispersion medium, a slurry-like LCP powder is obtained.

[0046] Furthermore, when producing a porous body containing an additive, the LCP powder and the additive are mixed in this step to obtain a paste-like or slurry-like mixture of the LCP powder and the additive (hereinafter, the mixture of the LCP powder and the additive may be simply referred to as a "mixture"). The mixing ratio of the additive to the mixture is preferably 50% by volume or less.

[0047] The dispersion step S11 according to this embodiment includes a coarse pulverization step S11a, a fine pulverization step S11b, a coarse particle removal step S11c, and a fiberization step S11d. In the dispersion step S11 according to this embodiment, the LCP powder is dispersed in a dispersion medium during the process of producing the LCP powder from the LCP raw material.

[0048] <Coarse pulverization step S11a> In the coarse pulverization step, the LCP raw material is coarsely pulverized. For example, the LCP raw material is coarsely pulverized using a cutter mill. The size of the coarsely pulverized LCP particles is not particularly limited as long as they can be used as raw material for the fine pulverization step described below. The maximum particle size of the coarsely pulverized LCP particles is, for example, 3 mm or less.

[0049] It is not always necessary to carry out the coarse pulverization step. For example, if the LCP raw material can be used as a raw material for the fine pulverization step, the LCP raw material may be used directly as a raw material for the fine pulverization step.

[0050] <Fine Pulverization Step S11b> In the fine pulverization step, the LCP raw material (after the coarse pulverization step) is pulverized while dispersed in liquid nitrogen to obtain granular finely pulverized liquid crystal polymer (finely pulverized LCP). In the fine pulverization step, it is preferable to use media to pulverize the LCP raw material dispersed in liquid nitrogen. The media is, for example, beads. In the fine pulverization step of this embodiment, it is preferable to use a bead mill, which has relatively few technical problems, from the perspective of handling liquid nitrogen. An example of a device that can be used in the fine pulverization step is the liquid nitrogen bead mill "LNM-08" manufactured by Imex.

[0051] The granular pulverized LCP obtained by the pulverization step preferably has a D50 of 50 μm or less as measured by a particle size distribution analyzer using a laser diffraction scattering method, which can prevent the granular pulverized LCP from clogging the nozzle in the fiberization step described below.

[0052] <Coarse Particle Removal Step S11c> Next, in the coarse particle removal step S11c, coarse particles are removed from the granular pulverized LCP obtained in the pulverization step. For example, by sieving the granular pulverized LCP with a mesh, granular pulverized LCP that falls below the sieve is obtained, and the granular LCP that remains above the sieve is removed, thereby removing the coarse particles contained in the granular pulverized LCP. The type of mesh can be selected appropriately, and examples of meshes include those with openings of 53 μm. Note that the coarse particle removal step S11c does not necessarily have to be performed.

[0053] In this embodiment, the granular pulverized LCP is dispersed in the dispersion medium before being sieved through a mesh in the coarse particle removal step S11c. The resulting dispersion is then sieved through a mesh. Thus, the resulting pulverized LCP is also a slurry of pulverized LCP dispersed in the dispersion medium.

[0054] <Fibrilization Step S11d> Next, in the fiberization step, the granular LCP is crushed using a wet high-pressure crusher to obtain LCP powder. The pulverized LCP dispersed in the dispersion medium, i.e., the pulverized LCP in a paste or slurry state, is passed through a nozzle under high pressure. By passing the LCP through the nozzle at high pressure, shear force or collision energy due to the high-speed flow through the nozzle acts on the LCP, crushing the granular pulverized LCP, thereby promoting fiberization of the LCP and obtaining LCP powder composed of fine LCP fibers. From the viewpoint of applying high shear force or high collision energy, it is preferable to make the nozzle diameter as small as possible without causing clogging of the pulverized LCP. Because the granular pulverized LCP has a relatively small particle size, the nozzle diameter of the wet high-pressure crusher used in the fiberization step can be made small. The nozzle diameter is, for example, 0.2 mm or less.

[0055] As described above, multiple fine cracks are formed in the granular pulverized LCP. Therefore, when pressurized by the wet high-pressure crushing device, the dispersion medium penetrates into the pulverized LCP through the fine cracks. When the paste-like or slurry-like pulverized LCP passes through the nozzle and is placed under normal pressure, the dispersion medium that penetrates into the pulverized LCP expands in a short time. The expansion of the dispersion medium that penetrates into the pulverized LCP causes destruction to progress from the inside of the pulverized LCP. Therefore, fiberization progresses to the inside of the pulverized LCP, and the LCP molecules separate into domain units in which they are aligned in one direction. Thus, in the fiberization process of this embodiment, by defibrating the granular pulverized LCP obtained in the pulverization process of this embodiment, an LCP powder having a lower content of aggregated particles and consisting of finer LCP fibers can be obtained compared to LCP powder obtained by crushing granular LCP obtained by a conventional freeze-pulverization method. In this embodiment, a paste-like or slurry-like LCP powder is obtained at this stage.

[0056] In the fiberization process of this embodiment, the finely pulverized LCP may be crushed multiple times using a wet high-pressure crushing device to obtain LCP powder. However, from the viewpoint of production efficiency, it is preferable to crush the LCP using the wet high-pressure crushing device only a small number of times, for example, 5 times or less.

[0057] In addition, when the finely pulverized LCP is not dispersed in the dispersion medium in the coarse particle removal step S11c, a slurry of the finely pulverized LCP obtained by dispersing the finely pulverized LCP in a dispersion medium for the fiberization step may be used. Examples of the dispersion medium for the fiberization step include water, ethanol, methanol, isopropyl alcohol, toluene, benzene, xylene, phenol, acetone, methyl ethyl ketone, diethyl ether, dimethyl ether, hexane, or a mixture thereof.

[0058] (Molding step S12) Next, in the molding step S12, the paste or slurry LCP powder or mixture is dried to form a sheet-shaped liquid crystal polymer fiber molded body (LCP fiber molded body), a so-called LCP fiber mat. In one embodiment of the present invention, the molding step is, for example, a papermaking method. In the papermaking method, the dispersion medium used in the dispersion step can be easily recovered and reused, allowing the porous body to be produced inexpensively.

[0059] Specifically, in the forming step S12 using a papermaking method, a slurry LCP powder or mixture is first papered onto a mesh, a nonwoven microporous sheet, or a woven fabric, and the slurry LCP powder or mixture placed on the mesh is then heated and dried to obtain an LCP fiber molding (porous resin layer).

[0060] In the molding step S12 of this embodiment, instead of the papermaking method, a paste-like LCP powder or mixture may be molded by a coating step and a drying step to obtain an LCP fiber molding.

[0061] In the coating step, the paste-like LCP powder or mixture is coated onto a substrate. Here, the term "substrate" refers to a material or support for coating the paste-like LCP powder or mixture, such as a metal foil such as copper foil, a polyimide film, a PTFE film, or a composite sheet made of a reinforcing material such as carbon fiber or glass fiber and a heat-resistant resin.

[0062] Next, in a drying step, the paste-like LCP powder or mixture applied to the substrate is heated and dried to evaporate the dispersion medium, thereby forming an LCP fiber molding on the substrate.

[0063] Furthermore, in the drying process, the dispersion medium is gradually removed from the paste-like LCP powder or mixture, so the overall thickness of the paste-like LCP powder or mixture gradually decreases during drying, and therefore the thickness of the LCP fiber molding becomes thinner than the overall thickness of the paste-like LCP powder or mixture formed on the product.

[0064] Furthermore, as the overall thickness of the paste-like LCP powder or mixture gradually decreases during drying, the longitudinal orientation of the fibrous particles in the LCP powder changes. Specifically, among the fibrous particles, those whose longitudinal direction is in the overall thickness direction of the paste-like LCP powder or mixture tilt so that their longitudinal direction is oriented in the principal plane direction of the substrate. Therefore, the longitudinal direction of the fibrous particles in the formed LCP fiber molding is anisotropic.

[0065] In the molding process described above, which includes a coating step and a drying step, a paste-like LCP powder or mixture may be applied to the LCP fiber molding formed on the substrate in the drying step, and then the resulting mixture may be dried to evaporate the dispersion medium. In this manner, the molding process may include a repeated coating step and a drying step in this order. This allows for the production of an LCP fiber molding having a desired basis weight. Furthermore, when the coating step and the drying step are repeated, a mixture in which the mixing ratio of the LCP powder and the additive is changed for each coating step may be used. This allows for the production of an LCP fiber molding (porous resin layer) having the desired properties.

[0066] [Plasma Treatment Step S2] Next, in the plasma treatment step S2, both surfaces of the LCP fiber molding are irradiated with plasma. Only one surface of the LCP fiber molding may be plasma treated. The LCP fiber molding does not necessarily have to be plasma treated.

[0067] [First Pressing Step S3] Next, in the first pressing step S3, a press is performed to bond the first adhesive layer to the LCP fiber molding (porous resin layer) and to bond the first metal layer to the first adhesive layer. First, a sheet, film, or molding for the first adhesive layer is stacked on the first metal foil (first metal layer), and then an LCP fiber molding is stacked on top of that to obtain a first laminate. This first laminate is then pressed under vacuum. This results in a laminate film having a metal layer on only one side.

[0068] The temperature during pressing in the first pressing step S3 is preferably high from the viewpoint of enhancing the adhesion between the first adhesive layer and the LCP fiber molding and between the first adhesive layer and the first metal layer. On the other hand, to prevent excessive melting of the sheet, film, or molding for the first adhesive layer, the temperature during pressing in the first pressing step S3 is preferably lower than the melting point of the resin contained in the sheet, film, or molding for the first adhesive layer. The value obtained by subtracting the temperature during pressing in the first pressing step S3 from the melting point of the resin contained in the first adhesive layer is, for example, 15°C to 85°C. The pressing pressure in the first pressing step S3 is, for example, 0.1 MPa to 8 MPa. The pressing time in the first pressing step S3 is, for example, 5 minutes to 20 minutes.

[0069] In this embodiment, a sheet, film, or molded body for the second adhesive layer is also bonded to the LCP fiber molded body (porous resin layer) in the first pressing step S3. Before pressing in the first pressing step S3, a sheet, film, or molded body for the second adhesive layer is stacked on top of the LCP fiber molded body. Then, a laminated film including the second adhesive layer is obtained by the above-described vacuum pressing. The laminated film having a metal layer on only one side obtained in the first pressing step S3 does not necessarily include a second adhesive layer.

[0070] [Second Pressing Step S4] Next, in the second pressing step S4, a second metal layer is bonded to the second adhesive layer. First, a second metal layer is stacked on the side of the laminate film obtained in the first pressing step S3 opposite to the first metal layer side (on the first adhesive layer in this embodiment) to obtain a second laminate. This laminate is then pressed under vacuum to obtain a laminate film having metal on both sides.

[0071] The temperature during pressing in the second pressing step S4 is preferably high from the viewpoint of enhancing adhesion between the second adhesive layer and the second metal layer. On the other hand, in order to prevent excessive melting of the sheet, film, or mat for the second adhesive layer, the temperature during pressing in the second pressing step S4 is preferably lower than the melting point of the resin contained in the sheet, film, or mat for the second adhesive layer. The value obtained by subtracting the temperature during pressing in the second pressing step S4 from the melting point of the resin contained in the second adhesive layer is, for example, 15°C to 50°C. The pressing pressure in the second pressing step S4 is, for example, 0.1 MPa to 8 MPa. The pressing time in the second pressing step S4 is, for example, 5 minutes to 20 minutes.

[0072] In this embodiment, a sheet, film, or mat for the second adhesive layer is bonded to the LCP fiber molding (porous resin layer) in the first press step S3, but a sheet, film, or mat for the second adhesive layer may be bonded to the LCP fiber molding (porous resin layer) in the second press step S4. In this case, before pressing in the second press step S4, a second adhesive layer may be laminated on the side of the LCP fiber molding opposite the first adhesive layer, and a second metal layer may be laminated on top of this to obtain a second laminate. This laminate may be pressed under vacuum to obtain a laminate film having metal layers on both sides.

[0073] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0074] Example 1 In Example 1, an LCP fiber molding was prepared as a porous resin layer as follows. First, uniaxially oriented LCP pellets (cylindrical pellets with a diameter of 3 to 4 mm, melting point: 320°C) were prepared as the LCP raw material. The LCP material was a copolymer of parahydroxybenzoic acid and 4,6-hydroxynaphthoic acid. This LCP raw material was coarsely pulverized using a cutter mill ("MF10" manufactured by IKA Corporation). The coarsely pulverized LCP was passed through a 3 mm diameter mesh installed at the outlet of the cutter mill to obtain coarsely pulverized LCP.

[0075] Next, the coarsely pulverized LCP was finely pulverized in a liquid nitrogen bead mill ("LNM-08" manufactured by Imex, vessel capacity: 0.8 L). Specifically, 500 mL of media and 30 g of the coarsely pulverized LCP were placed in the vessel, and the pulverization treatment was carried out for 120 minutes at a rotation speed of 2000 rpm. The media used were zirconia (ZrO ２ Beads manufactured by ) were used. In the liquid nitrogen bead mill, the coarsely pulverized LCP is dispersed in liquid nitrogen and subjected to wet pulverization. In this way, by pulverizing the coarsely pulverized LCP in the liquid nitrogen bead mill, granular finely pulverized LCP was obtained.

[0076] Next, the finely pulverized LCP was dispersed in a 20% by weight aqueous ethanol solution as a dispersion medium to obtain a dispersion of the finely pulverized LCP. This dispersion was sieved through a mesh with an opening of 106 μm. By passing through the mesh, coarse particles were removed, and the finely pulverized LCP was recovered in a dispersed state in the dispersion.

[0077] Next, the finely pulverized LCP from which the coarse particles had been removed was dispersed in a dispersion liquid and then crushed five times using a wet high-pressure crusher under conditions of a nozzle diameter of 0.2 mm and a pressure of 200 MPa to form fibers. As the wet high-pressure crusher, a high-pressure disperser ("Starburst Lab" manufactured by Sugino Machine Co., Ltd.) was used. By fiberizing the finely pulverized LCP, a slurry-like LCP powder containing LCP fibers was obtained, in which the LCP powder was dispersed in an aqueous ethanol solution.

[0078] Next, the slurry-like LCP powder was applied to a polyester microfiber nonwoven fabric (basis weight: 14 g / m) placed on an 80-mesh wire netting. ２ ) using a square sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a dispersion medium-containing LCP fiber molding. The dispersion medium-containing LCP fiber molding was then dried in a hot air dryer and peeled off from the polyester microfiber nonwoven fabric to obtain an LCP fiber molding (porous resin layer). In the case of the slurry-like LCP powder being drawn up, the basis weight of the LCP fiber molding was 18 g / m. ２ The amount of LCP powder was adjusted so that

[0079] Next, both sides of the obtained LCP fiber molding were subjected to plasma treatment using a plasma irradiation device ("PC-1000" manufactured by SAMCO Corporation). The plasma treatment was carried out at a pressure of 10 Pa or less and O ２ The treatment was carried out for 5 minutes under conditions of a gas flow rate of 50 sccm and 800 W. As a result, a plasma-treated LCP fiber molding was obtained.

[0080] Next, a 12 μm-thick first electrodeposited copper foil (first metal layer) having a roughened surface, a 15 μm-thick first epoxy-based adhesive sheet (first adhesive layer), a plasma-treated LCP fiber molding, a 15 μm-thick second epoxy-based adhesive sheet (second adhesive layer), and a release film made of PET (polyethylene terephthalate) were stacked in this order to obtain a first laminate. The first epoxy-based adhesive sheet was placed on the first electrodeposited copper foil so that it was in contact with the roughened surface of the first electrodeposited copper foil. This first laminate was then pressed under vacuum at a temperature of 100°C and a pressure of 6 MPa for 5 minutes using a high-temperature vacuum press (KVHC, manufactured by Kitagawa Seiki Co., Ltd.). The release film was then peeled off from the pressed first laminate to obtain a single-sided copper-clad film (laminate film) in which a first adhesive layer and a second adhesive layer were laminated on both sides of the LCP fiber molding.

[0081] A second laminate was obtained by overlaying a 12 μm thick second electrodeposited copper foil (second metal layer) having a roughened surface on the second adhesive layer of the obtained single-sided copper-clad film. The second electrodeposited copper foil was overlaid on the second epoxy-based adhesive sheet so that the roughened surface of the second electrodeposited copper foil was in contact with the second epoxy-based adhesive sheet. The second laminate was then pressed under vacuum at a temperature of 170° C. and a pressure of 6 MPa for 5 minutes using a high-temperature vacuum press (KVHC, manufactured by Kitagawa Seiki Co., Ltd.). A double-sided copper-clad laminate (laminated film) was obtained.

[0082] [Example 2] A double-sided copper-clad laminate (laminate film) was obtained by the same manufacturing method as in Example 1, except that the first laminate was pressed at a pressure of 0.1 MPa and the second laminate was pressed at a pressure of 0.1 MPa.

[0083] Example 3 In Example 3, a double-sided copper-clad laminate was obtained by a manufacturing method in which the manufacturing method of the laminate film according to Example 1 was partially modified.

[0084] Specifically, the LCP raw material for the LCP fiber molding as the porous resin layer was a copolymer (melting point: 350°C) of parahydroxybenzoic acid, terephthalic acid, and dihydroxybiphenyl. Furthermore, a plasma-treated first LCP film was used in place of the first epoxy adhesive sheet. A plasma-treated second LCP film was used in place of the second epoxy adhesive sheet. The first and second LCP films had a melting point of 320°C and were made of a copolymer of parahydroxybenzoic acid and 4,6-hydroxynaphthoic acid. The plasma treatment of the first and second LCP films was carried out at a pressure of 10 Pa or less and O ２ The experiment was carried out for 5 minutes under conditions of a gas flow rate of 50 sccm and 800 W. A polyimide release film was used as the release film contained in the first laminate. The first laminate was vacuum-pressed at a temperature of 270°C and a pressure of 8 MPa for 20 minutes. The second laminate was vacuum-pressed at a temperature of 270°C and a pressure of 8 MPa for 20 minutes. Except for these points, a double-sided copper-clad laminate was obtained by the same method as in Example 1.

[0085] Example 4 In Example 4, a double-sided copper-clad laminate was obtained by a manufacturing method in which the manufacturing method of the laminate film according to Example 1 was partially modified.

[0086] Specifically, the LCP raw material for the LCP fiber molding as the porous resin layer was a copolymer (melting point: 350°C) of parahydroxybenzoic acid, terephthalic acid, and dihydroxybiphenyl. Furthermore, a plasma-treated LCP fiber molding for the first adhesive layer was used instead of the first epoxy adhesive sheet. A plasma-treated LCP fiber molding for the second adhesive layer was used instead of the second epoxy adhesive sheet. The LCP fiber molding for the first adhesive layer and the second epoxy adhesive sheet were the same as the LCP fiber molding (melting point: 320°C) produced in Example 1. The plasma treatment of the LCP fiber molding for the first adhesive layer and the LCP fiber molding for the second adhesive layer was carried out at a pressure of 10 Pa or less and O ２ The process was carried out for 5 minutes under conditions of a gas flow rate of 50 sccm and 800 W. A polyimide release film was used as the release film contained in the first laminate. The first laminate was vacuum-pressed at a temperature of 305°C and a pressure of 6 MPa for 5 minutes. The second laminate was vacuum-pressed at a temperature of 305°C and a pressure of 6 MPa for 5 minutes. Except for these points, a double-sided copper-clad laminate was obtained by the same method as in Example 1.

[0087] Comparative Example A double-sided copper-clad laminate was obtained in the same manner as in Example 1, except that a porous polyimide film was used as the porous resin layer instead of the LCP fiber molding.

[0088] Reference Example An LCP fiber molding, a first LCP film, and a second LCP film were produced in the same manner as in Example 3, except that they were not plasma-treated.

[0089] [Measurement of dielectric loss tangent] The first and second electrolytic copper foils were removed by etching from each of the double-sided copper-clad laminates according to Examples 1 to 4 and Comparative Example 1 to prepare 30 mm x 30 mm test pieces. The dielectric loss tangent of the test pieces was measured by the cavity resonator method using a dielectric constant measuring device conforming to JIS R 1641. The measurement was carried out by applying a high-frequency signal of 12 GHz at an ambient temperature of 25°C.

[0090] [Evaluation of Adhesion] Each of the double-sided copper clad laminates according to Examples 1 to 4, Comparative Example 1, and Reference Example was subjected to cross-sectional milling for 30 minutes at an acceleration voltage of 1.5 kV to 4 kV using an ion milling machine ("IM4000" manufactured by Hitachi High-Tech Corporation) to expose the cross-section. The cross-section was observed using a scanning electron microscope (SEM). For example, FIG. 3 is a cross-sectional SEM photograph of the double-sided copper clad laminate according to Example 1. FIG. 4 is a cross-sectional SEM photograph of the double-sided copper clad laminate according to Example 4. FIG. 5 is a cross-sectional SEM photograph of the double-sided copper clad laminate according to Reference Example. Note that in FIGS. 3 to 5, reference numerals are assigned to the layers corresponding to each embodiment of the present disclosure. The cross-sections were visually inspected to evaluate the adhesion between the porous resin layer and the first and second adhesive layers according to the following criteria: A: There were relatively few voids at the boundaries between the porous resin layer and the first and second adhesive layers. B: There were relatively few voids located at the boundaries between the porous resin layer and the first and second adhesive layers. C: Relatively large voids were found at the boundaries between the porous resin layer and the first and second adhesive layers.

[0091] [Calculation of Porosity of Porous Resin Layer] The thickness of the porous resin layer was measured during the above-mentioned cross-sectional observation for each of the double-sided copper-clad laminates according to Examples 1 to 4 and Comparative Example 1. The porosity of the porous resin layer was calculated based on the thickness, the weight of the porous resin layer in the double-sided copper-clad laminate, and the density of the resin raw material of the porous resin layer.

[0092] [Measurement of the average pore diameter of the porous resin layer] For each of the double-sided copper-clad laminates according to Examples 1 to 4 and Comparative Example 1, the first metal layer and the second metal layer were peeled off, and the porous resin layer was torn to prepare a test piece. The pore distribution of the test piece was measured using a mercury intrusion porosimeter (MICROMETRICS "Autopore V9605"). The average pore diameter of the test piece was calculated from the pore distribution.

[0093] The measured dielectric loss tangent, the evaluation results of adhesion, the calculated porosity, and the measured average pore diameter of each of the double-sided copper-clad laminates according to Examples 1 to 4 and Comparative Example 1 are shown in Table 1. The result of the adhesion evaluation for the double-sided copper-clad laminate according to the Reference Example was "C."

[0094] As shown in Table 1, the dielectric loss tangents of the laminate films according to Examples 1 to 4, in which the porous resin layer was a molded body of liquid crystal polymer fibers, were 0.003 or less. On the other hand, the dielectric loss tangent of the laminate film according to Comparative Example 1, in which the porous resin layer was not a molded body of liquid crystal polymer fibers, was 0.01, which was larger than that of Examples 1 to 4. Therefore, by using a porous resin layer that was a molded body of liquid crystal polymer fibers, the dielectric loss of the laminate film could be reduced.

[0095] Furthermore, the laminate films according to Examples 1 to 4 have a porosity of the porous resin layer of 25% or more and 50% or less. By having a porosity of 25% or more and 50% or less, the dielectric constant of the porous resin layer can be made relatively low, and since the porous resin layer is a molded body of liquid crystal polymer fibers, the dielectric loss tangent of the laminate film can be made small.

[0096] Furthermore, the porous resin layers of the laminate films according to Examples 1 to 4 had an average pore diameter of 1 μm or less as measured by mercury porosimetry. Even in the case of a porous resin layer having an average pore diameter of 1 μm or less, the dielectric loss tangent of the laminate film could be reduced by using a porous resin layer formed of liquid crystal polymer fibers.

[0097] Furthermore, the first adhesive layer and the second adhesive layer of the laminate films according to Examples 3 and 4 both contained a liquid crystal polymer. The laminate films according to Examples 3 and 4 had a dielectric loss tangent of 0.001 or less. On the other hand, the first adhesive layer and the second adhesive layer of the laminate films according to Examples 1 and 2 did not contain a liquid crystal polymer. The dielectric loss tangents of the laminate films according to Examples 1 and 2 were 0.003 and 0.002, respectively, which were larger than those of Examples 3 and 4. Therefore, by including a liquid crystal polymer in at least one or both of the first adhesive layer and the second adhesive layer, the dielectric loss tangent of the laminate film could be further reduced.

[0098] Furthermore, in the laminate films according to Examples 3 and 4, the melting point of the liquid crystal polymer contained in the porous resin layer was 350°C, and the melting points of the liquid crystal polymer contained in the first adhesive layer and the second adhesive layer were 320°C. That is, in the laminate films according to Examples 3 and 4, the melting point of the liquid crystal polymer contained in the porous resin layer was higher than the melting point of the liquid crystal polymer contained in at least one or both of the first adhesive layer and the second adhesive layer. This made it easier to heat the first adhesive layer and the second adhesive layer to bond them to other layers while maintaining the function of the porous resin layer in the liquid crystal polymer fiber molded body. Furthermore, in the laminate films according to Examples 3 and 4, the melting point of the liquid crystal polymer contained in the porous resin layer was 20°C or more higher than the melting point of the liquid crystal polymer contained in at least one or both of the first adhesive layer and the second adhesive layer. This made it easier to heat the first adhesive layer and the second adhesive layer to bond them to other layers while maintaining the function of the porous resin layer in the liquid crystal polymer fiber molded body.

[0099] Furthermore, in the laminate film according to Example 4, both the first adhesive layer and the second adhesive layer were molded bodies of liquid crystal polymer fibers, while in the laminate films according to Examples 1 to 3, neither the first adhesive layer nor the second adhesive layer was molded bodies of liquid crystal polymer fibers. Furthermore, the laminate film according to Example 4 had better adhesion between the porous resin layer and the first adhesive layer and the second adhesive layer than the laminate films according to Examples 1 to 3. Therefore, because the porous resin layer and at least one or both of the first adhesive layer and the second adhesive layer were molded bodies of liquid crystal polymer fibers, the fibrous liquid crystal polymers were entangled with each other, thereby improving the adhesion between the porous resin layer and the first adhesive layer and the second adhesive layer.

[0100] Furthermore, in the laminate film according to Example 4, in the first pressing step, a first laminate including a porous resin layer and a molded body of liquid crystal polymer fiber as a first adhesive layer is pressed, thereby bonding the porous resin layer and the first adhesive layer together. In the first pressing step, a first laminate including a porous resin layer and a molded body of liquid crystal polymer fiber as a second adhesive layer is pressed, thereby bonding the porous resin layer and the second adhesive layer together. This pressing step further entangles the fibrous LCP polymer in the molded body of liquid crystal polymer fiber as the porous resin layer and the fibrous LCP in the molded body of liquid crystal polymer fiber as the first adhesive layer or the second adhesive layer. This ultimately improves adhesion between the porous resin layer and the first adhesive layer, as well as between the porous resin layer and the second adhesive layer.

[0101] [Additional Notes] As described above, the present embodiment includes the following disclosures.

[0102] <1> A laminated film comprising: a porous resin layer; a first adhesive layer laminated on the porous resin layer; a metal layer laminated on the first adhesive layer on the opposite side of the porous resin layer from the first adhesive layer; and a second adhesive layer laminated on the porous resin layer on the opposite side of the porous resin layer from the first adhesive layer, wherein the porous resin layer is a molded body of liquid crystal polymer fibers.

[0103] <2> The laminated film according to <1>, wherein the porosity of the porous resin layer is 25% or more and 50% or less.

[0104] <3> The laminate film according to <1> or <2>, wherein the porous resin layer has an average pore diameter of 1 μm or less as measured by mercury porosimetry.

[0105] <4> The laminated film according to any one of <1> to <3>, wherein at least one of the first adhesive layer and the second adhesive layer contains a liquid crystal polymer.

[0106] <5> The laminated film according to <4>, wherein the melting point of the liquid crystal polymer contained in the porous resin layer is higher than the melting point of the liquid crystal polymer contained in at least one of the first adhesive layer and the second adhesive layer.

[0107] <6> The laminate film according to <5>, wherein the melting point of the liquid crystal polymer contained in the porous resin layer is 20°C or more higher than the melting point of the liquid crystal polymer contained in at least one of the first adhesive layer and the second adhesive layer.

[0108] <7> The laminated film according to any one of <4> to <6>, wherein at least one of the first adhesive layer and the second adhesive layer is a molded body of liquid crystal polymer fibers.

[0109] <8> A method for producing the laminated film according to <7>, comprising: pressing a laminate including the porous resin layer and a molded body of liquid crystal polymer fiber as the first adhesive layer or the second adhesive layer to bond them to each other. A method for producing a laminated film, comprising:

[0110] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0111] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0112] Reference Signs List 1 porous resin layer, 2a first adhesive layer, 2b second adhesive layer, 3a first metal layer, 3b second metal layer, 10 laminated film.

Claims

1. A laminated film comprising: a porous resin layer; a first adhesive layer laminated on the porous resin layer; a metal layer laminated on the first adhesive layer on the opposite side of the porous resin layer from the first adhesive layer; and a second adhesive layer laminated on the porous resin layer on the opposite side of the first adhesive layer from the porous resin layer, wherein the porous resin layer is a molded body of liquid crystal polymer fibers.

2. The laminate film according to claim 1, wherein the porosity of the porous resin layer is 25% or more and 50% or less.

3. The laminate film according to claim 1 or 2, wherein the porous resin layer has an average pore size of 1 μm or less as measured by mercury intrusion porosimetry.

4. A laminate film according to any one of claims 1 to 3, wherein at least one of the first adhesive layer and the second adhesive layer contains a liquid crystal polymer.

5. The laminate film according to claim 4, wherein the melting point of the liquid crystal polymer contained in the porous resin layer is higher than the melting point of the liquid crystal polymer contained in at least one of the first adhesive layer and the second adhesive layer.

6. The laminate film according to claim 5, wherein the melting point of the liquid crystal polymer contained in the porous resin layer is 20°C or more higher than the melting point of the liquid crystal polymer contained in at least one of the first adhesive layer and the second adhesive layer.

7. A laminate film according to any one of claims 4 to 6, wherein at least one of the first adhesive layer and the second adhesive layer is a molded body of liquid crystal polymer fibers.

8. A method for producing the laminated film described in claim 7, comprising a step of pressing a laminate comprising the porous resin layer and a molded body of liquid crystal polymer fiber as the first adhesive layer or the second adhesive layer in order to bond them to each other.

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