Liquid crystal polymer film laminate, method for producing liquid crystal polymer film laminate, and method for producing liquid crystal polymer film

Abstract

Provided is a liquid crystal polymer film laminate comprising a liquid crystal polymer film and an aromatic polyether ketone film laminated onto at least one surface of the liquid crystal polymer film. The shrinkage rate of the aromatic polyether ketone film is 13.5% or less when the aromatic polyether ketone film is heated to 300°C while applying a tensile load by using a thermomechanical analyzer (TMA).

Description

Liquid crystal polymer film laminate, method for manufacturing liquid crystal polymer film laminate, and method for manufacturing liquid crystal polymer film

[0001] The present invention relates to a liquid crystal polymer film laminate, a method for producing a liquid crystal polymer film laminate, and a method for producing a liquid crystal polymer film.

[0002] Advances in mobile communication technology have led to faster and larger-capacity communications, and frequencies used in communications are becoming higher. Fifth-generation mobile communication systems use the 3.7 GHz and 4.5 GHz Sub-6 bands and the 28 GHz millimeter-wave band, while sixth-generation mobile communication systems are considering frequency bands ranging from 90 GHz to 300 GHz. Since the transmission loss of signals flowing through circuits increases with increasing frequency, there is a demand for circuits and circuit materials with reduced transmission loss. Liquid crystal polymer films with reduced anisotropy and excellent smoothness are known as materials that can be used as such circuit materials (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a method for producing a stretched liquid crystal polymer film with adjusted surface roughness, degree of planar orientation, etc., by melt-kneading a liquid crystal polymer (LCP) and a polyether ether ketone polymer (PEEK) separately, supplying them to a multi-manifold T-die and co-extruding them to obtain a laminated film, stretching the laminated film, and finally peeling off the PEEK film.

[0004] Patent Document 1: International Publication No. 2024 / 004952

[0005] However, in the laminated film produced by co-extrusion described in Patent Document 1, the adhesion between the liquid crystal polymer film and the PEEK film constituting the laminated film is low, and there is a risk that the liquid crystal polymer film and the PEEK film will peel off during the subsequent winding process or conveying process (hereinafter also referred to as the post-process.) For this reason, the technology described in Patent Document 1 is likely to cause problems such as deformation of the liquid crystal polymer film due to peeling between the liquid crystal polymer film and the PEEK film, or the laminated film being unable to be wound into a roll.

[0006] The object of the present invention is to provide a liquid crystal polymer film laminate that has excellent adhesion between a liquid crystal polymer film and an aromatic polyether ketone film and can suppress peeling between the liquid crystal polymer film and the aromatic polyether ketone film during the winding process and the conveying process (hereinafter also referred to as the post-process).

[0007] [1] Aspect 1 of the present invention is a liquid crystal polymer film laminate comprising a liquid crystal polymer film and an aromatic polyether ketone film laminated on at least one surface of the liquid crystal polymer film, wherein the aromatic polyether ketone film has a shrinkage rate of 13.5% or less when heated to 300°C while applying a tensile load using a thermomechanical analyzer (TMA).

[0008] [2] In the second aspect of the present invention, the linear expansion coefficient of the liquid crystal polymer film in the longitudinal direction is α ＭＤ , the linear expansion coefficient in the width direction of the liquid crystal polymer film is α ＴＤ The liquid crystal polymer film laminate of Aspect 1 satisfies the following formula (1) and the following formula (2): 10 ppm / °C≦α ＴＤ ≦80ppm / ℃ (1) |α ＭＤ -α ＴＤ |≦60 ppm / ° C. (2)

[0009] [3] A third aspect of the present invention is the liquid crystal polymer film laminate of the first or second aspect, wherein the liquid crystal polymer film has a planar orientation degree of −0.3 or more and 0.5 or less, calculated based on pole measurement by X-ray diffraction.

[0010] [4] A fourth aspect of the present invention is the liquid crystal polymer film laminate according to any one of the first to third aspects, wherein the liquid crystal polymer film has a surface roughness Ra of 0.20 μm or less on at least one surface thereof.

[0011] [5] A fifth aspect of the present invention is the liquid crystal polymer film laminate of any one of the first to fourth aspects, wherein the slow axis direction of the aromatic polyether ketone film, determined by phase difference measurement, is 80° or more and 100° or less, or −100° or more and −80° or less, with the longitudinal direction of the aromatic polyether ketone film being 0°.

[0012] [6] A sixth aspect of the present invention is the liquid crystal polymer film laminate according to any one of the first to fifth aspects, wherein the aromatic polyether ketone film is polyether ether ketone (PEEK).

[0013] [7] Aspect 7 of the present invention is a method for producing a liquid crystal polymer film laminate according to any one of aspects 1 to 6, comprising: a first step of extruding molten liquid crystal polymer and aromatic polyether ketone into a film using an extruder so that a layer of the aromatic polyether ketone is laminated on at least one side of a layer of the liquid crystal polymer to obtain a laminate; a second step of stretching the laminate at least in the width direction; and a third step of subjecting the laminate to a relaxation treatment at a temperature of the melting point of the aromatic polyether ketone −150° C. or higher and at a relaxation rate of 4% to 20%.

[0014] [8] Aspect 8 of the present invention is a method for producing a liquid crystal polymer film, comprising: a step of obtaining a liquid crystal polymer film laminate by the method for producing a liquid crystal polymer film laminate of aspect 7; and a fourth step of peeling off the aromatic polyether ketone film.

[0015] According to the liquid crystal polymer film laminate of the present invention, the adhesion between the liquid crystal polymer film and the aromatic polyether ketone film is excellent, and peeling between the liquid crystal polymer film and the aromatic polyether ketone film can be suppressed during the winding process and the conveying process (hereinafter also referred to as the post-process).

[0016] Fig. 1 is a diagram illustrating the stretching and relaxation treatments of a laminate. Fig. 2 is a diagram illustrating a method for measuring the deformation amount of a test piece using a thermomechanical analyzer (TMA). Fig. 3 is a graph showing the measurement results of a PEEK film test piece in Example 2 using the thermomechanical analyzer. Fig. 4 is a schematic diagram of the upper blade of a rotary circular blade used to evaluate interlayer adhesion of a liquid crystal polymer film laminate in the examples.

[0017] The liquid crystal polymer film laminate of the present invention comprises a liquid crystal polymer film and an aromatic polyether ketone film laminated on at least one surface of the liquid crystal polymer film.

[0018] <Liquid Crystal Polymer Film> The liquid crystal polymer film used in the liquid crystal polymer laminate of the present invention is a film made of a liquid crystal polymer. The liquid crystal polymer is not particularly limited, but a liquid crystal polyester exhibiting thermotropic liquid crystal properties is preferred. Examples of such liquid crystal polyesters include aromatic polyesters synthesized from monomers such as aromatic diols, aromatic carboxylic acids, and hydroxycarboxylic acids, which exhibit liquid crystallinity when melted. Specific examples include polycondensates of ethylene terephthalate and parahydroxybenzoic acid, polycondensates of phenol, phthalic acid, and parahydroxybenzoic acid, and polycondensates of hydroxynaphthoic acid and parahydroxybenzoic acid. In particular, from the viewpoint of excellent mechanical properties, electrical properties, heat resistance, etc., aromatic polyester-based liquid crystal polymers having a basic structure of 6-hydroxy-2-naphthoic acid and its derivatives and at least one monomer component selected from the group consisting of parahydroxybenzoic acid, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and derivatives thereof are preferred. The liquid crystal polymers can be used alone or in any combination and ratio of two or more. The content of the liquid crystal polymer is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 70 to 100% by mass, based on the total amount of the liquid crystal polymer film. It is particularly preferred that the liquid crystal polymer film consists essentially of liquid crystal polymers.

[0019] The liquid crystal polymer can be synthesized by any known method, including, but not limited to, melt polymerization, melt acidolysis, slurry polymerization, etc. When these polymerization methods are used, acylation or acetylation may be carried out according to a conventional method.

[0020] The liquid crystal polymer may contain additives such as polymers such as fluororesins, polyolefins, polycycloolefins, polyetherimides, and silicone-modified polyetherimides, release improvers such as higher fatty acids having 10 to 25 carbon atoms, higher fatty acid esters, higher fatty acid amides, and higher fatty acid metal salts, chain extenders such as aliphatic carbodiimides, alicyclic carbodiimides, and aromatic carbodiimides, colorants such as dyes, pigments, and carbon black, organic fillers, inorganic fillers, hollow particles, antioxidants, heat stabilizers, light stabilizers, UV absorbers, flame retardants, lubricants, antistatic agents, surfactants, rust inhibitors, foaming agents, defoamers, and fluorescent agents, as long as the effects of the present invention are not excessively impaired. These polymers and additives can be added to the molten resin composition during film formation of the liquid crystal polymer film. These polymers and additives can be used alone or in combination of two or more. The content of the polymer or additive is not particularly limited, but from the viewpoint of moldability, thermal stability, etc., it is preferably 0.01 to 50 mass %, more preferably 0.1 to 40 mass %, and even more preferably 0.5 to 30 mass %, relative to the total amount of the liquid crystal polymer film.

[0021] The linear expansion coefficient of the liquid crystal polymer film in the longitudinal direction is α ＭＤ , the linear expansion coefficient in the width direction of the liquid crystal polymer film is α ＴＤ In this case, it is preferable that the liquid crystal polymer film satisfies the following formula (1) and formula (2): 10 ppm / °C≦α ＴＤ ≦80ppm / ℃ (1) |α ＭＤ -α ＴＤ |≦60 ppm / ° C. (2)

[0022] As described below, the liquid crystal polymer film laminate of the present invention is produced by a method including a step of stretching at least in the width direction a laminate obtained by co-extruding a liquid crystal polymer and an aromatic polyether ketone using an extruder. Therefore, the liquid crystal polymer film is subjected to stress from the laminated aromatic polyether ketone film, which tends to shrink the liquid crystal polymer film mainly in the width direction, resulting in residual strain. The liquid crystal polymer film satisfying the above formula (1) indicates that the liquid crystal polymer film has small residual strain in the width direction. By satisfying the above formula (1), deformation due to residual strain in the liquid crystal polymer film can be suitably suppressed when the liquid crystal polymer film laminate is subjected to heat treatment or hot pressing. Furthermore, when a metal layer is formed on the liquid crystal polymer film obtained by peeling off the aromatic polyether ketone film to produce an FPC, deformation due to residual strain can also be suitably suppressed.

[0023] Linear expansion coefficient α ＴＤ is sufficient as long as it satisfies the above formula (1), but is preferably 20 ppm / °C or more and 80 ppm / °C or less, more preferably 25 ppm / °C or more and 80 ppm / °C or less, even more preferably 30 ppm / °C or more and 80 ppm / °C or less, and particularly preferably 35 ppm / °C or more and 80 ppm / °C or less. In particular, by setting the value to 35 ppm / °C or more and 80 ppm / °C or less, the liquid crystal polymer film can be made to have excellent conformability to other members laminated thereon. As a result, when other members (such as an aromatic polyether ketone film or a metal layer) are laminated on the liquid crystal polymer film and subjected to heat treatment or hot pressing, deformation due to residual strain can be suitably suppressed and adhesion to other members can be improved.

[0024] The fact that the liquid crystal polymer film satisfies the above formula (2) indicates that the anisotropy of the liquid crystal polymer film is small. By satisfying the above formula (2), deformation due to anisotropy can be suitably suppressed when a liquid crystal polymer film laminate composed of an aromatic polyether ketone film and a liquid crystal polymer film is subjected to heat treatment or heat pressing. Similarly, when a metal layer is formed on the liquid crystal polymer film obtained by peeling off the aromatic polyether ketone film to produce an FPC, deformation due to anisotropy can be suitably suppressed.

[0025] Linear expansion coefficient α ＭＤ and the linear expansion coefficient α ＴＤ Absolute value of the difference between |α ＭＤ -α ＴＤ It is sufficient that | satisfies the above formula (2), but is preferably 40 ppm / °C or less, more preferably 20 ppm / °C or less, and even more preferably 10 ppm / °C or less. ＴＤ and |α ＭＤ -α ＴＤ It is preferable that at least one of | is within the above range.

[0026] Linear expansion coefficient α ＭＤ , α ＴＤ The linear expansion coefficient α can be determined from the dimensional change rate before and after heating when the liquid crystal polymer film obtained by peeling off the aromatic polyether ketone film is heated while applying a tensile load using a thermomechanical analyzer (TMA). The dimensional change rate is not particularly limited, but can be measured by attaching the liquid crystal polymer film to the chuck of the thermomechanical analyzer and heating it from 30°C to 150°C at a rate of 5°C / min under a tensile load of 10 mN. ＭＤ , α ＴＤ is the length of the liquid crystal polymer film before heating. ＬＣＰ , the amount of change in length is ΔL ＬＣＰ , the temperature change amount is ΔT ＬＣＰ When this is done, ΔL ＬＣＰ / L ＬＣＰ / ΔT ＬＣＰ It is expressed as [ppm / °C].

[0027] Linear expansion coefficient α of liquid crystal polymer film ＭＤ , αＴＤ As a method for adjusting the thickness to within the above range, a method may be mentioned in which a laminate obtained by co-extrusion of a liquid crystal polymer and an aromatic polyether ketone is stretched in the width direction and then subjected to a relaxation treatment, as will be described later.

[0028] The thickness of the liquid crystal polymer film is not particularly limited, but from the viewpoint of the handleability of the liquid crystal polymer film laminate and the dielectric properties of the liquid crystal polymer film after peeling off the aromatic polyether ketone film, it is preferably 10 to 500 μm, more preferably 20 to 300 μm, even more preferably 30 to 250 μm, and particularly preferably 30 to 200 μm.

[0029] The melting point of the liquid crystal polymer constituting the liquid crystal polymer film is not particularly limited, but is preferably 250 to 380°C, more preferably 280 to 350°C.

[0030] The liquid crystal polymer film preferably has a degree of planar orientation calculated based on pole measurement by X-ray diffraction of -0.3 or more and 0.5 or less. The degree of planar orientation can be specifically determined by the following method. First, in pole measurement by X-ray diffraction, the liquid crystal polymer film is tilted 45° (α = 45° in the Schulz method) and rotated in the in-plane direction (β direction) while measuring the diffraction intensity of the 110 plane, to create an X-ray diffraction intensity profile. In this profile, the longitudinal direction of the film is defined as β = 0°, and the integrated intensities at β = 45 to 135°, 135 to 225°, 225 to 315°, and 315 to 45° are determined. The integrated intensity in the longitudinal direction is the sum of the integrated intensity at β = 45 to 135° and the integrated intensity at β = 225 to 315°. The integrated intensity in the width direction is the sum of the integrated intensity at β = 135 to 225° and the integrated intensity at β = 315 to 45°. In this case, the degree of planar orientation is expressed by the following formula (3): degree of planar orientation=(integrated intensity in the longitudinal direction−integrated intensity in the width direction) / (integrated intensity in the longitudinal direction+integrated intensity in the width direction) (3)

[0031] The diffraction intensity of the 110 plane is the diffraction intensity of the crystal plane (110 plane) of the liquid crystal polymer. For example, the diffraction intensity of the 110 plane of a liquid crystal polymer obtained by polycondensation of 2,6-hydroxynaphthoic acid and parahydroxybenzoic acid in a molar ratio of 73:27 is the largest diffraction intensity observed at 2θ=20° when X-ray diffraction is measured at a diffraction angle (2θ) range of 10° to 40°. The diffraction intensity of the (110 plane) of a liquid crystal polymer oriented in the longitudinal direction is greatest at β=90° and 270° when the longitudinal direction of the film is defined as β=0°. Therefore, the longitudinal integrated intensity is the sum of the integrated intensity at β=45° to 135° and the integrated intensity at β=225° to 315°, and the widthwise integrated intensity is the sum of the integrated intensity at β=135° to 225° and the integrated intensity at β=315° to 45°. The integrated intensity is calculated as the area when β is plotted on the horizontal axis and the diffraction intensity on the vertical axis. A positive value for the degree of planar orientation indicates that the molecular chains are oriented in the longitudinal direction, and a negative value indicates that they are oriented in the width direction.

[0032] The degree of planar orientation is preferably -0.3 or more and 0.5 or less, more preferably -0.3 or more and 0.3 or less, and particularly preferably -0.2 or more and 0.15 or less. When the value of the degree of planar orientation is within the above range, the anisotropy of the mechanical properties, dielectric constant, and dielectric loss tangent of the liquid crystal polymer film can be reduced. As a method for adjusting the degree of planar orientation within the above range, as will be described later, a method in which a laminate obtained by co-extrusion of a liquid crystal polymer and an aromatic polyether ketone is stretched in the width direction.

[0033] The liquid crystal polymer film preferably has a surface roughness Ra of 0.20 μm or less on at least one surface. The surface roughness Ra can be measured in accordance with JIS B0601:1994. The surface roughness Ra may be measured along any direction on the surface of the liquid crystal polymer film, but is preferably measured along the width direction (TD) or longitudinal direction (MD) of the liquid crystal polymer film. That is, the surface roughness Ra measured along the width direction (TD) or longitudinal direction (MD) of the liquid crystal polymer film is preferably 0.20 μm or less. As described below, the liquid crystal polymer film laminate of the present invention is produced by a method including a step of stretching a laminate obtained by co-extruding a liquid crystal polymer and an aromatic polyether ketone using an extruder in at least the width direction. As shown in FIG. 1, the width direction (TD) refers to the direction in which the laminate is stretched in the manufacturing process of the liquid crystal polymer film laminate, and the longitudinal direction (MD) refers to the direction in which the laminate is transported. FIG. 1 is a diagram for explaining the method of stretching and relaxing the laminate.

[0034] The surface roughness Ra is preferably 0.20 μm or less on at least one side, and more preferably 0.20 μm or less on both sides of the liquid crystal polymer film. By making the surface roughness Ra 0.20 μm or less, when an FPC is manufactured by forming a metal layer on the liquid crystal polymer film, transmission loss when a high-frequency signal flows can be reduced.

[0035] As a method for adjusting the surface roughness Ra of the liquid crystal polymer film within the above range, a method can be mentioned in which a laminate obtained by co-extrusion of a liquid crystal polymer and an aromatic polyether ketone is stretched in the width direction at a temperature below the melting point of the aromatic polyether ketone, as described below.

[0036] <Aromatic Polyetherketone Film> The aromatic polyetherketone film used in the liquid crystal polymer laminate of the present invention is made of aromatic polyetherketone and is provided to prevent the liquid crystal polymer film from breaking when stretched. The aromatic polyetherketone film also functions as a protective film, preventing scratches on the liquid crystal polymer film during subsequent processes (such as winding and conveying processes) of the liquid crystal polymer film laminate. From the viewpoints of adhesion to the liquid crystal polymer film and function as a protective film, the aromatic polyetherketone constituting the aromatic polyetherketone film preferably has a melting point higher than that of the liquid crystal polymer. Specific examples of aromatic polyetherketones include polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyetheretherketoneketone (PEEKK). These polymers can be used alone or in combination of two or more. Among these, polyether ether ketone (PEEK) is preferred, and by using a film made of polyether ether ketone (PEEK), no breakage occurs in the stretching step described below, and peeling after stretching of the liquid crystal polymer film laminate is suppressed, thereby preventing scratches on the liquid crystal polymer film. Furthermore, these films are preferably crystallized or stretched films, as they have high heat resistance and can be stretched at high temperatures.

[0037] The aromatic polyether ketone film may be laminated on at least one surface of the liquid crystal polymer film, but is preferably laminated on both surfaces of the liquid crystal polymer film.

[0038] The thickness of the aromatic polyether ketone film is not particularly limited, but from the viewpoint of the handleability of the liquid crystal polymer film laminate and suppressing the occurrence of deformation or peeling of the liquid crystal polymer film in subsequent processes (such as a winding process or a conveying process), it is preferably 5 to 100 μm, more preferably 5 to 50 μm, and particularly preferably 5 μm to 20 μm.

[0039] The aromatic polyether ketone film used in the liquid crystal polymer laminate of the present invention has the following characteristics. Specifically, when the aromatic polyether ketone film is heated to 300°C while applying a tensile load using a thermomechanical analyzer (TMA), the aromatic polyether ketone film has a shrinkage rate of 13.5% or less. As described below, the liquid crystal polymer film laminate of the present invention is produced by a method including a step of stretching a laminate obtained by co-extruding a liquid crystal polymer and an aromatic polyether ketone using an extruder at least in the width direction. Therefore, the aromatic polyether ketone film constituting the liquid crystal polymer film laminate generates a stress that tends to shrink mainly in the width direction, and if this stress is large, peeling from the liquid crystal polymer film is likely to occur. A shrinkage rate measured by a thermomechanical analyzer of not more than a predetermined value indicates that the aromatic polyether ketone film has small residual strain and small shrinkage stress in the width direction.

[0040] The shrinkage rate is calculated by dividing the length of the aromatic polyether ketone film before heating by L ＡＰＫ , the amount of shrinkage in length of the aromatic polyether ketone film before and after heating ΔL ＡＰＫ When this is done, ΔL ＡＰＫ / L ＡＰＫ The shrinkage ratio is expressed as × 100 [%]. The shrinkage ratio is 13.5% or less, preferably 12.5% ​​or less, more preferably 11.0% or less, even more preferably 10.0% or less, and particularly preferably 9.0% or less. The lower limit of the shrinkage ratio is not particularly limited, but is usually 0% or more. When the shrinkage ratio is within the above range, peeling from the liquid crystal polymer film due to residual strain in the aromatic polyether ketone film can be suppressed.

[0041] The shrinkage percentage of the aromatic polyether ketone film can be measured by peeling the aromatic polyether ketone film from the liquid crystal polymer film. The conditions for measuring the shrinkage percentage are not particularly limited as long as the film can be heated to 300°C while applying a tensile load. Specifically, the shrinkage percentage is preferably measured under the following conditions: That is, the shrinkage percentage is preferably measured by heating from 30°C to 300°C at a rate of 10°C / min under a tensile load of 10 mN.

[0042] The shrinkage percentage may be 13.5% or less as measured in any direction of the aromatic polyether ketone film, but the maximum value among values ​​measured in multiple directions is preferably 13.5% or less. In particular, the value measured in the direction along the width direction of the aromatic polyether ketone film is preferably 13.5% or less. The reason for this is that, during the production process of the liquid crystal polymer film laminate, stress that tends to shrink the aromatic polyether ketone film mainly in the width direction is generated in the aromatic polyether ketone film, and the shrinkage percentage measured along the width direction is the maximum. When the shrinkage percentage of the aromatic polyether ketone film measured along the width direction is 13.5% or less, peeling due to residual strain in the aromatic polyether ketone film can be further suppressed.

[0043] As a method for adjusting the shrinkage rate of the aromatic polyether ketone film determined by measurement with a thermomechanical analyzer to 13.5% or less, there can be mentioned a method in which a laminate obtained by co-extrusion of a liquid crystal polymer and an aromatic polyether ketone is stretched in the width direction and then subjected to a relaxation treatment under specified conditions, as will be described later.

[0044] The aromatic polyether ketone film used in the present invention preferably further has the following characteristics. That is, the slow axis orientation, determined by retardation measurement with the longitudinal direction of the aromatic polyether ketone film as 0°, is preferably 80° or more and 100° or less, or -100° or more and -80° or less. The slow axis orientation can be determined by performing retardation measurement on an aromatic polyether ketone film peeled from a liquid crystal polymer film with the longitudinal direction as 0°, and analyzing the obtained data. Specifically, it can be determined by the method described in the Examples. The slow axis orientation is preferably 80° or more and 100° or less, or -100° or more and -80° or less, and more preferably 85° or more and 95° or less, or -95° or more and -85° or less. A slow axis orientation within the above range indicates that the molecular chains constituting the aromatic polyether ketone film are oriented mainly in the width direction.

[0045] As a method for adjusting the slow axis orientation of the aromatic polyether ketone film within the above range, a method of stretching a laminate obtained by co-extrusion of a liquid crystal polymer and an aromatic polyether ketone in the width direction, as described below, can be mentioned.

[0046] <Method for producing liquid crystal polymer film laminate> The liquid crystal polymer film laminate of the present invention is produced by a method comprising: a first step of extruding molten liquid crystal polymer and aromatic polyether ketone into a film using an extruder so that a layer made of aromatic polyether ketone is laminated on at least one surface of a layer made of liquid crystal polymer, thereby obtaining a laminate in which a liquid crystal polymer film and an aromatic polyether ketone film are laminated; a second step of stretching the laminate at least in the width direction; and a third step of subjecting the laminate to a relaxation treatment under conditions of a temperature of the melting point of the aromatic polyether ketone −150° C. or higher and a relaxation rate of 4% to 20%.

[0047] In the first step, a laminate of a layer made of a liquid crystal polymer and a layer made of an aromatic polyether ketone is produced by a melt extrusion method. Specifically, the liquid crystal polymer is melted in a first extruder, and the aromatic polyether ketone is melted in a second extruder, and the respective polymers are extruded into a film shape (co-extrusion) so that the layer made of aromatic polyether ketone is laminated on at least one surface of the layer made of the liquid crystal polymer, thereby producing a laminate.

[0048] The discharge rates of the liquid crystal polymer and aromatic polyether ketone may be adjusted appropriately depending on the target thickness of the liquid crystal polymer film and the target thickness of the aromatic polyether ketone film. From the viewpoints of ease of handling and productivity during melt extrusion molding, the thickness of the layer made of the liquid crystal polymer is preferably 20 to 1000 μm, more preferably 50 to 600 μm, even more preferably 75 to 500 μm, and particularly preferably 100 to 400 μm. The thickness of the layer made of the aromatic polyether ketone is preferably 10 to 200 μm, more preferably 15 to 100 μm, and particularly preferably 15 to 50 μm.

[0049] As a method for laminating a layer of aromatic polyether ketone on at least one surface of a layer of liquid crystal polymer, a method for forming a multilayer extrusion film from a T-die can be used. Specific examples include a feedblock method in which molten liquid crystal polymer and aromatic polyether ketone supplied from two extruders are fed to a feedblock, merged, and then extruded into a film from a T-die, and a multi-manifold method in which molten liquid crystal polymer and aromatic polyether ketone are separately fed to a T-die and extruded together into a film. From the viewpoint of improving the smoothness of the liquid crystal polymer film constituting the obtained liquid crystal polymer film laminate, it is preferable to use the multi-manifold method, taking into account cases in which the liquid crystal polymer and aromatic polyether ketone have different viscosities or flow properties when melted.

[0050] In the first step, a layer of aromatic polyether ketone may be laminated on at least one side of the layer of liquid crystal polymer, but it is preferable to laminate layers of aromatic polyether ketone on both sides of the layer of liquid crystal polymer. By laminating layers of aromatic polyether ketone on both sides of the layer of liquid crystal polymer, the surface roughness Ra on both sides of the liquid crystal polymer film constituting the obtained liquid crystal polymer film laminate can be controlled within a suitable range. Furthermore, by laminating layers of aromatic polyether ketone on both sides of the layer of liquid crystal polymer, it is possible to more effectively prevent breakage of the layer of liquid crystal polymer when stretching the laminate in the second step.

[0051] In the second step, the laminate of the liquid crystal polymer layer and the aromatic polyether ketone layer is stretched at least in the width direction (TD). As shown in FIG. 1 , one example of the stretching method is a tenter transverse stretching method, in which both ends of the laminate are clamped with clips (not shown) and heated and stretched. Stretching the laminate in the width direction can reduce the anisotropy of the liquid crystal polymer film constituting the resulting liquid crystal polymer film laminate. The stretching ratio and stretching speed can be appropriately selected so that the shape and physical properties of the liquid crystal polymer film obtained after stretching fall within the desired range. The stretching ratio is preferably 2 to 5 times. The stretching speed is preferably 1 to 10,000% / min, more preferably 50 to 5,000% / min, and even more preferably 500 to 4,000% / min. Furthermore, to adjust the degree of planar orientation after stretching, additional stretching in the machine direction (MD) may be performed as needed.

[0052] In the second step, the temperature inside the oven of the stretching device (the temperature inside the oven in the stretching zone of the stretching device) when stretching the laminate is preferably a temperature not higher than the melting point of the aromatic polyether ketone +30°C, more preferably a temperature not higher than the melting point of the aromatic polyether ketone +10°C, and even more preferably a temperature not higher than the melting point of the aromatic polyether ketone -10°C. The temperature inside the oven in the stretching zone of the stretching device is preferably a temperature not lower than the melting point of the aromatic polyether ketone -130°C, more preferably a temperature not lower than the melting point of the aromatic polyether ketone -110°C, and even more preferably a temperature not lower than the melting point of the aromatic polyether ketone -90°C. In the second step, by setting the draw ratio, draw speed, and oven temperature of the stretching device within predetermined ranges, the temperature of the surface of the laminate during stretching (ultimate stretching temperature) can be adjusted to a temperature below the melting point of the aromatic polyether ketone. By setting the ultimate stretching temperature to a temperature lower than the melting point of the aromatic polyether ketone, the smoothness of the liquid crystal polymer film constituting the obtained liquid crystal polymer film laminate can be improved, and the surface roughness Ra of the liquid crystal polymer film can be controlled within a suitable range. The ultimate stretching temperature may be any temperature lower than the melting point of the aromatic polyether ketone, but is preferably a temperature 20 to 150°C lower than the melting point of the aromatic polyether ketone, and more preferably a temperature 40 to 100°C lower than the melting point of the aromatic polyether ketone.

[0053] As shown in FIG. 1 , it is preferable to preheat the laminate before stretching it in the second step. The furnace temperature of the stretching apparatus when preheating the laminate (the furnace temperature in the preheating zone of the stretching apparatus) is preferably a temperature equal to or lower than the melting point of the aromatic polyether ketone +40°C, more preferably a temperature equal to or lower than the melting point of the aromatic polyether ketone +20°C, and even more preferably a temperature equal to or lower than the melting point of the aromatic polyether ketone. The furnace temperature in the preheating zone of the stretching apparatus is usually a temperature equal to or higher than the melting point of the aromatic polyether ketone -130°C. The preheating time, i.e., the time from when the laminate enters the preheating zone of the stretching apparatus until it passes through the preheating zone, can be adjusted appropriately depending on the conveyance speed of the laminate and is not particularly limited. For example, the preheating time of the laminate is preferably 3 to 40 seconds, more preferably 6 to 20 seconds. Preheating the laminate makes it easier to control the ultimate stretching temperature during stretching within a suitable range.

[0054] In the third step, the laminate is subjected to a relaxation treatment under conditions of a temperature equal to or higher than the melting point of the aromatic polyether ketone minus 150°C and a relaxation rate of 4% to 20%. The relaxation treatment is a treatment in which the stretched laminate is shrunk along the stretching direction, as shown in FIG. 1 . For example, if the laminate is stretched in the width direction in the second step, the laminate is shrunk along the width direction in the third step. The method for shrinking the laminate is not particularly limited, but examples include, when stretching the laminate using a tenter transverse stretching method, appropriately shrinking the distance between the tenter clips toward the downstream of the conveyance direction of the stretched laminate. By performing the relaxation treatment on the stretched laminate under the above-mentioned conditions, residual strain in the laminate caused by the stretching step can be reduced, and peeling between the liquid crystal polymer film and the aromatic polyether ketone film can be suppressed.

[0055] The relaxation rate in the width direction of the laminate due to the relaxation treatment is expressed as ΔW / W × 100 [%], where W is the width of the laminate after the second step (stretching) and ΔW is the amount of shrinkage in the width of the laminate before and after the relaxation treatment. The relaxation rate is 4% to 20%, preferably 4% to 16%, more preferably 8% to 16%, and particularly preferably 12% to 16%. If the relaxation rate is too low, the stress generated in the laminate by stretching cannot be sufficiently reduced, and peeling between the liquid crystal polymer film and the aromatic polyether ketone film may occur in the obtained liquid crystal polymer film laminate. On the other hand, if the relaxation amount is too high, the tension of the aromatic polyether ketone film may be insufficient, causing sagging in the width direction, which may result in deformation, contact of the film with furnace equipment, or in failure to wind the liquid crystal polymer film into a roll in a subsequent process.

[0056] In the third step, the temperature inside the oven of the stretching device when performing the relaxation treatment (the temperature inside the oven in the relaxation zone of the stretching device) is a temperature of the melting point of the aromatic polyether ketone minus 150°C or more, preferably a temperature of the melting point of the aromatic polyether ketone minus 120°C or more, more preferably a temperature of the melting point of the aromatic polyether ketone minus 100°C or more, even more preferably a temperature of the melting point of the aromatic polyether ketone minus 70°C or more, particularly preferably a temperature of the melting point of the aromatic polyether ketone minus 50°C or more, and most preferably a temperature of the melting point of the aromatic polyether ketone minus 30°C or more. The upper limit of the oven temperature is usually below the melting point of the aromatic polyether ketone. If the oven temperature is too low, even when the relaxation treatment is performed at a predetermined relaxation rate, the stress generated in the laminate by stretching cannot be sufficiently reduced, and there is a risk of peeling between the liquid crystal polymer film and the aromatic polyether ketone film in the obtained liquid crystal polymer film laminate. Furthermore, if the temperature inside the furnace is too low, the layer made of the liquid crystal polymer may be slightly hardened and may shrink in a state where the deformation resistance is large, and residual strain may occur in the layer made of the liquid crystal polymer due to the relaxation treatment. As a result, in the obtained liquid crystal polymer film laminate, the linear expansion coefficient α ＴＤOn the other hand, if the temperature inside the furnace is too high, the temperature may reach the melting point of the aromatic polyether ketone film, causing the aromatic polyether ketone film to melt.

[0057] The liquid crystal polymer film laminate of the present invention can be obtained in this manner. In the liquid crystal polymer film laminate obtained in this manner, when the aromatic polyether ketone film is heated to 300°C while applying a tensile load using a thermomechanical analyzer (TMA), the shrinkage rate of the aromatic polyether ketone film before and after heating is 13.5% or less. This sufficiently reduces the residual strain in the aromatic polyether ketone film caused by the stretching treatment, so the liquid crystal polymer film laminate of the present invention has excellent adhesion between the liquid crystal polymer film and the aromatic polyether ketone film. Therefore, according to the present invention, deformation of the liquid crystal polymer film can be suppressed, and the liquid crystal polymer film laminate can be formed into a roll.

[0058] In addition, as a post-process, the liquid crystal polymer film laminate obtained by the above method may be subjected to heat treatment or heat pressing. The heat treatment method is not particularly limited, but examples include a method in which a rolled liquid crystal polymer film laminate is heated at a temperature of 120 to 330°C using an oven. The heat pressing method is not particularly limited, but examples include a method in which the laminate is pressed at high temperature using a hot press molding machine. By subjecting the liquid crystal polymer film laminate to heat treatment or heat pressing, the heat resistance of the liquid crystal polymer film can be improved. In this case, using an aromatic polyether ketone film having a melting point higher than that of the liquid crystal polymer allows for heat treatment or heat pressing at higher temperatures.

[0059] <Method for producing a liquid crystal polymer film> A liquid crystal polymer film can be obtained by peeling off the aromatic polyether ketone film from the liquid crystal polymer film laminate obtained by the above method. The liquid crystal polymer film obtained in this manner has a linear expansion coefficient α ＭＤ , α ＴＤBy controlling the degree of planar orientation, anisotropy is reduced, and by controlling the surface roughness Ra, the surface smoothness is excellent. As a result, when a metal layer is formed on the liquid crystal polymer film to produce an FPC, deformation due to anisotropy can be suitably suppressed, and transmission loss when high-frequency signals flow can be reduced. Therefore, the liquid crystal polymer film produced using the liquid crystal polymer film laminate of the present invention can be suitably used for circuit boards such as FPCs.

[0060] Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to these examples.

[0061] <Width-Direction Shrinkage of PEEK Film> The PEEK film obtained by peeling from the resulting liquid crystal polymer film laminate was processed to prepare a rectangular test piece having a long side (19 mm long) along the width direction (TD) and a short side (5 mm long) along the longitudinal direction (MD). As shown in Figure 2, the test piece was attached to a thermomechanical analyzer (manufactured by Rigaku Corporation, Model: TMA8310) with a chuck distance of 15 mm so that a load was applied along the long side of the test piece, i.e., the width direction (TD). While applying a tensile load of 10 mN to the test piece, the test piece was heated from 30 °C to 300 °C at a rate of 10 °C / min. As shown in Figure 3, the shrinkage of the PEEK film in the width direction (TD) was calculated based on the deformation (length shrinkage) of the test piece at 300 °C relative to the start of heating. FIG. 2 is a diagram illustrating a method for measuring the deformation of a test piece using a thermomechanical analyzer (TMA), and FIG. 3 is a graph showing the measurement results of the PEEK film test piece in Example 2 using the thermomechanical analyzer.

[0062] <Evaluation of Interlayer Adhesion> An incision was made at both ends of the obtained liquid crystal polymer film laminate using a rotary circular blade (single-edged, upper blade thickness 0.5 mm, upper blade tip angle 65°), and the incision end faces were exposed. At the incision end faces, the length at which peeling occurred between the liquid crystal polymer film and the PEEK film was measured and evaluated as follows. The shorter the peel length, the better the adhesion (interlayer adhesion) between the liquid crystal polymer film and the PEEK film. Figure 4 shows a schematic diagram of the upper blade of the rotary circular blade used for the interlayer adhesion evaluation. A: Peel length 1 mm or less B: Peel length more than 1 mm and 5 mm or less C: Peel length more than 5 mm D: Interlayer peeling occurred frequently before incision formation, making it impossible to form an incision

[0063] <Linear expansion coefficient α of liquid crystal polymer film ＭＤ , α ＴＤ > A liquid crystal polymer film obtained by peeling the PEEK film from a liquid crystal polymer film laminate was processed to prepare a rectangular test piece having a long side (19 mm long) along the transverse direction (TD) and a short side (5 mm long) along the longitudinal direction (MD). The test piece was attached to a thermomechanical analyzer (manufactured by Rigaku Corporation, model: TMA8310) with a chuck distance of 15 mm so that a load was applied along the long side of the test piece, i.e., the transverse direction (TD). The test piece was heated from 30°C to 150°C at a rate of 5°C / min while applying a tensile load of 10 mN. The linear expansion coefficient α of the liquid crystal polymer film was calculated based on the change in length of the test piece relative to the start of heating when it reached 150°C and the temperature change due to heating. ＴＤ Similarly, a rectangular liquid crystal polymer film test piece having a long side (length 19 mm) along the machine direction (MD) and a short side (length 5 mm) along the width direction was prepared, and measurement was similarly carried out to calculate the linear expansion coefficient α of the liquid crystal polymer film. ＭＤ was calculated.

[0064] <Planar orientation degree of liquid crystal polymer film> A liquid crystal polymer film was prepared by peeling the PEEK film from a liquid crystal polymer film laminate. Using a horizontal sample multipurpose X-ray diffractometer (Rigaku Corporation, model: Ultima IV), the diffraction angle (2θ) was fixed at 20°, and the X-ray target was Cu, voltage: 40 kV, current: 40 mA, α angle = 45°, β angle = 0 to 360° (the longitudinal direction of the film was 0°, and the step angle was 5°), pole measurement was performed on the liquid crystal polymer film to create an X-ray diffraction intensity profile. The integrated intensities of this profile at β=45 to 135°, 135° to 225°, 225 to 315°, and 315 to 45° were determined, and the sum of the integrated intensities at β=45 to 135° and β=225° to 315° was defined as the integrated intensity in the longitudinal direction, and the sum of the integrated intensities at β=135 to 225° and β=315 to 45° was defined as the integrated intensity in the width direction, and the degree of planar orientation was calculated based on the above formula (3).

[0065] <Surface roughness Ra of liquid crystal polymer film> Measurement was performed using a contact surface roughness measuring instrument (manufactured by Tosei Engineering Co., Ltd., model: SURFCOM 1400D-3DF) in accordance with JIS B0601:1994, using a stylus with a tip radius of 2 μm, a measurement length of 4 mm, and a cutoff λ ｃ The surface roughness Ra of the liquid crystal polymer film obtained by peeling the PEEK film from the liquid crystal polymer film laminate at a peeling thickness of 0.8 mm was measured. The surface roughness Ra was measured for the front and back surfaces of the film in both the machine direction (MD) and the width direction (TD) of the film.

[0066] <Slow Axis Azimuth of Aromatic Polyether Ketone Film> A PEEK film was prepared by peeling it from a liquid crystal polymer film laminate. The PEEK film was placed on the stage of a metallurgical microscope (Olympus Corporation, Model: BX51) so that the film's longitudinal direction (MD) coincided with the 0° direction of the observation screen. Retardation measurements (transmission measurement, measurement accuracy standard, measurement mode 3 wavelength measurement) were performed using a wide-range two-dimensional birefringence evaluation system (Photonic Lattice Co., Ltd., Model: WPA-micro) to obtain image data including retardation and slow axis orientation. A circular line was drawn on the obtained image data, with its center coinciding with the center of the measurement field and its diameter at least half the minor axis of the measurement field. The slow axis orientation of the PEEK film was determined by analyzing the numerical data of the slow axis orientation on the line.

[0067] <Melting points of liquid crystal polymer and PEEK> Using a differential scanning calorimeter (manufactured by PerkinElmer, model: DSC8500), the liquid crystal polymer film obtained by peeling it from the liquid crystal polymer film laminate was analyzed according to differential scanning calorimetry based on JIS K 7121. The endothermic peak temperature observed when the liquid crystal polymer film was heated from 0°C at 10°C / min was taken as the melting point of the liquid crystal polymer. The PEEK film obtained by peeling it from the liquid crystal polymer film laminate was similarly analyzed, and the endothermic peak temperature observed when the temperature was raised from 0°C at 10°C / min was taken as the melting point of PEEK. When measured for each example and comparative example, the melting points of the liquid crystal polymer and PEEK were all 280°C and 340°C, respectively.

[0068] Example 1 A liquid crystal polymer (LAPEROS A950RX, manufactured by Polyplastics Co., Ltd.) was fed to a twin-screw extruder (screw diameter 26 mm) and melt-kneaded at 300 ° C. In addition, a polyether ether ketone (PEEK) polymer (VESTAKEEP 3300G, manufactured by Daicel-Evonik) was fed to a single-screw extruder (screw diameter 40 mm) as an aromatic polyether ketone and melt-kneaded at 380 ° C. These molten polymers were fed to a multi-manifold T-die, and layers of PEEK were superimposed on both sides of a layer of liquid crystal polymer. By extruding and cooling, a laminate having a liquid crystal polymer layer of 175 μm and PEEK layers of 30 μm each on both sides was produced, totaling 235 μm.

[0069] The laminate thus prepared was stretched 3.5 times in the transverse direction (TD) using a tenter-type transverse stretching machine (furnace temperature 330°C) with a stretching zone length of 1.2 m and a conveying speed of 3 m / min (stretching speed 625% / min). Next, while the laminate was held in the tenter, the tenter chuck spacing was linearly reduced at a relaxation rate of 40% / min at a furnace temperature of 330°C, and a relaxation treatment was performed so that the relaxation amount was 8%. In this manner, a liquid crystal polymer film laminate was obtained. The liquid crystal polymer film laminate was evaluated for adhesion between the liquid crystal polymer film and the PEEK film. The liquid crystal polymer film and the PEEK film were also peeled off, and the above-mentioned evaluations were performed on each film. The results are shown in Table 2.

[0070] Examples 2-11, Comparative Examples 1-4 Liquid crystal polymer film laminates were produced and evaluated in the same manner as in Example 1, except that the stretch ratio and stretching speed in stretching the laminate, and the furnace temperature, relaxation rate, and relaxation speed in the relaxation treatment were changed to the values ​​shown in Table 1. The results are shown in Table 2.

[0071]

[0072]

[0073] As shown in Table 2, when an aromatic polyether ketone film (PEEK film) was heated to 300°C while applying a tensile load using a thermomechanical analyzer (TMA), a liquid crystal polymer film laminate in which the aromatic polyether ketone film had a shrinkage rate of 13.5% or less had excellent interlayer adhesion. In addition, the liquid crystal polymer film obtained by peeling off the PEEK film had reduced anisotropy and excellent smoothness.

[0074] On the other hand, in Comparative Examples 1-3, in which the shrinkage rate of the aromatic polyether ketone was more than 13.5%, the interlayer adhesion was poor. In Comparative Example 4, in which the relaxation treatment was performed under the condition of a relaxation rate of more than 20%, the film tension was insufficient, causing the film to sag, resulting in the film coming into contact with the furnace equipment and making it impossible to take up the film by a roll.

Claims

1. A liquid crystal polymer film laminate comprising: a liquid crystal polymer film; and an aromatic polyether ketone film laminated on at least one side of the liquid crystal polymer film, wherein when the aromatic polyether ketone film is heated to 300°C while applying a tensile load using a thermomechanical analyzer (TMA), the shrinkage rate of the aromatic polyether ketone film is 13.5% or less.

2. The linear expansion coefficient of the liquid crystal polymer film in the longitudinal direction is α ＭＤ The linear expansion coefficient of the liquid crystal polymer film in the width direction is α ＴＤ The liquid crystal polymer film laminate according to claim 1, which satisfies the following formula (1) and the following formula (2) when ＴＤ ≦80ppm / ℃ (1) |α ＭＤ -α ＴＤ |≦60 ppm / ° C. (2) 3. The liquid crystal polymer film laminate according to claim 1 or 2, wherein the degree of planar orientation of the liquid crystal polymer film calculated based on pole measurement by X-ray diffraction method is from -0.3 to 0.

5.

4. A liquid crystal polymer film laminate according to any one of claims 1 to 3, wherein the surface roughness Ra of at least one surface of the liquid crystal polymer film is 0.20 µm or less.

5. A liquid crystal polymer film laminate according to any one of claims 1 to 4, wherein the slow axis direction of the aromatic polyether ketone film, determined by phase difference measurement with the longitudinal direction of the film as 0°, is 80° or more and 100° or less, or -100° or more and -80° or less.

6. The liquid crystal polymer film laminate according to any one of claims 1 to 5, wherein the aromatic polyether ketone film is polyether ether ketone (PEEK).

7. A method for producing a liquid crystal polymer film laminate according to any one of claims 1 to 6, comprising: a first step of extruding molten liquid crystal polymer and aromatic polyether ketone into a film using an extruder so that a layer of said aromatic polyether ketone is laminated on at least one side of a layer of said liquid crystal polymer to obtain a laminate; a second step of stretching said laminate at least in the width direction; and a third step of subjecting said laminate to a relaxation treatment at a temperature of the melting point of said aromatic polyether ketone -150°C or higher and under conditions of a relaxation rate of 4% to 20%.

8. A method for producing a liquid crystal polymer film, comprising: a step of obtaining a liquid crystal polymer film laminate by the method for producing a liquid crystal polymer film laminate according to claim 7; and a fourth step of peeling off the aromatic polyether ketone film.

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