Stretched liquid crystal polymer film, laminate, circuit board, and production method for stretched liquid crystal polymer film

Abstract

Provided is a stretched liquid crystal polymer film formed from a liquid crystal polymer. The stretched liquid crystal polymer film has an average film thickness of less than 25 μm. The Cv value of the film thickness of the stretched liquid crystal polymer film is 10% or lower, the Cv value being represented by equation (1).　(1): Cv value (%)=(standard deviation of measured film thickness) / (average film thickness)×100

Description

Stretched liquid crystal polymer film, laminate, circuit board, and method for producing stretched liquid crystal polymer film

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

[0002] Advances in mobile communications technology have led to faster and larger-capacity communications, and frequencies used in communications are becoming higher and higher: 5th generation mobile communications systems use the Sub6 band (3.7 GHz and 4.5 GHz) and the millimeter-wave band (28 GHz), while 6th generation mobile communications systems are considering frequency bands in the 90 GHz to 300 GHz range. Since the transmission loss of signals flowing through circuits increases as their frequency increases, there is a demand for circuits and circuit materials with low transmission loss.

[0003] Flexible printed circuit boards (FPCs), which are lightweight and flexible, are used in devices used in mobile communications, such as smartphones, to meet the demand for miniaturization and weight reduction. FPCs are composed of conductors, such as copper wires, through which signals pass and insulating materials that support them, and lightweight, flexible polymer films are used as the insulating materials. These polymer films are required to have heat resistance to enable continuous use even in high-temperature environments, as well as low dielectric constants and dielectric loss tangents to reduce transmission losses when high-frequency signals are transmitted (see, for example, Non-Patent Document 1).

[0004] Polymer films with low dielectric constants and low dielectric loss tangents used in FPCs include polyimide films and liquid crystal polymer films. However, while polyimide films have excellent heat resistance and flexibility, they have a high water absorption rate and a large rate of dimensional change due to moisture absorption, resulting in low connection reliability in circuits with fine pitch patterns. For this reason, FPCs using liquid crystal polymer films with excellent heat resistance, low water absorption, and small rate of dimensional change are currently being developed (see, for example, Patent Document 1).

[0005] Liquid crystal polymers have a tendency to molecularly orient in the flow direction. In melt extrusion, a common film manufacturing method, a polymer is melted and extruded through a T-die or the like to form a film. Therefore, the liquid crystal polymer in films manufactured by this method has molecular orientation in the longitudinal direction of the film. Therefore, films manufactured by this method have significantly different physical properties (strength, linear expansion coefficient, etc.) between the longitudinal direction and the direction perpendicular to the longitudinal direction, resulting in a state of high anisotropy. On the other hand, FPCs are manufactured by laminating copper foil onto a polymer film or by copper plating a polymer film to form a metal layer, and then forming a wiring pattern by etching or the like. In this process, if the expansion coefficients (linear expansion coefficients) of the polymer film and the metal layer differ, temperature changes can cause problems such as peeling between the insulating film and the metal layer, warping of the FPC, and misalignment of holes after drilling the FPC. Thus, when a highly anisotropic liquid crystal polymer film is used as an insulating material for an FPC, the linear expansion coefficient differs significantly depending on the direction, making the above-mentioned problems more likely to occur.

[0006] A method for reducing the anisotropy of polymer films such as polyethylene terephthalate (PET) films is to stretch the film in a direction perpendicular to the molecular orientation at a temperature above the glass transition temperature and below the melting point of the polymer film. However, liquid crystal polymer films extruded from a T-die have extremely low tensile strength, particularly in the direction perpendicular to the molecular orientation, and therefore easily break when pulled in a direction perpendicular to the molecular orientation at a temperature below the melting point of the liquid crystal polymer.

[0007] Therefore, methods have been proposed in which a liquid crystal polymer film extruded from a T-die is heated and pressurized between a pair of endless belts of a double belt press (for example, Patent Document 2), a liquid crystal polymer film is extruded into a cylindrical shape from an inflation die and then inflated by blowing hot air into the film before it cools and solidifies (for example, Patent Document 3), and a porous polytetrafluoroethylene (PTFE) film is heated and bonded to both sides of a liquid crystal polymer film extruded from a T-die, and the film is stretched in a direction perpendicular to the longitudinal direction at a temperature above the melting point of the liquid crystal polymer film (for example, Patent Document 4).

[0008] Furthermore, as demands for smaller and lighter devices increase, FPCs are being made more multi-layered and lighter, and there is an increasing demand for thinner liquid crystal polymer films.

[0009] However, the molecular chains of liquid crystal polymers are rigid and have little flexibility, so that they tend to be oriented in the flow direction as mentioned above, and because the molecular chains are not entangled, their viscosity in the molten state is significantly reduced (Non-Patent Document 2). Therefore, the above-mentioned method of heating and pressurizing between the pair of endless belts of a double belt press, the method of extruding a liquid crystal polymer film into a cylindrical shape from an inflation die and blowing hot air into the film before it cools and solidifies, and the method of laminating porous polytetrafluoroethylene (PTFE) films on both sides of the liquid crystal polymer film extruded from a T-die while heating, and stretching in a direction perpendicular to the longitudinal direction at a temperature above the melting point of the liquid crystal polymer film, result in large film thickness unevenness, and when trying to produce a particularly thin film, holes are likely to occur, making it difficult to produce a thin liquid crystal polymer film.

[0010] A solution casting method has also been proposed, in which a liquid crystal polymer solution is cast onto a metal plate or the like, the solvent is removed, and the liquid crystal polymer is solidified to form a liquid crystal polymer film (e.g., Non-Patent Document 2). However, to form a liquid crystal polymer film into a solution, not only is it necessary to use a special solvent or a liquid crystal polymer with a special structure, but the solvent must also be removed after casting. Furthermore, the removed solvent must be recovered to prevent environmental pollution. For these reasons, producing liquid crystal polymer films using the solvent casting method is expensive, and the liquid crystal polymers that can be used are limited, making it difficult to produce liquid crystal polymer films suitable for a variety of applications.

[0011] Non-patent document 1: Matsushita Yukio et al., "Substrate Materials for High-Speed ​​Transmission," Journal of the Japan Society of Electronics Packaging, Vol. 4, No. 7, p. 551, 2001. Non-patent document 2: Okamoto Satoshi, "Film Formation by Solution Casting of LCP," Molding and Processing, Vol. 20, No. 5, p. 270, 2008.

[0012] Patent Document 1: Patent No. 5308295 Patent Document 2: Patent No. 6930046 Patent Document 3: Patent No. 6656231 Patent Document 4: Patent No. 3958629

[0013] An object of the present invention is to provide a thin, uniformly thick stretched liquid crystal polymer film that can be suitably used as an insulating material for circuit boards having a multilayer structure.

[0014] [1] According to a first aspect of the present invention, there is provided a stretched liquid crystal polymer film made of a liquid crystal polymer, which has an average thickness of less than 25 μm and a Cv value of the thickness expressed by the following formula (1) of 10% or less: Cv value (%) = (standard deviation of measured thickness) / (average thickness) × 100 (1)

[0015] [2] According to a second aspect of the present invention, there is provided the stretched liquid crystal polymer film of the first aspect, in which the difference between the maximum and minimum film thicknesses is 5 μm or less.

[0016] [3] According to a third aspect of the present invention, there is provided the stretched liquid crystal polymer film of the first or second aspect, wherein the surface roughness Ra of at least one surface measured by a laser microscope is 0.5 μm or less.

[0017] [4] Aspect 4 of the present invention provides a stretched liquid crystal polymer film according to any one of aspects 1 to 3, wherein, in a pole measurement by X-ray diffraction, when the diffraction intensity of the 110 plane is measured while the film is tilted 45° (α=45° in the Schulz method) and rotated in the in-plane direction (β direction), the integrated intensities for β=45 to 135°, 135° to 225°, 225 to 315°, and 315 to 45° are calculated, with β=0° as the longitudinal direction of the film, and the sum of the integrated intensity for β=45 to 135° and the integrated intensity for β=225° to 315° is defined as the longitudinal integrated intensity, and the sum of the integrated intensity for β=135 to 225° and the integrated intensity for β=315 to 45° is defined as the widthwise integrated intensity, the stretched liquid crystal polymer film has a degree of planar orientation of -0.5 or more and 0.5 or less, as represented by the following formula (2): Planar orientation degree=(integrated intensity in the longitudinal direction−integrated intensity in the width direction) / (integrated intensity in the longitudinal direction+integrated intensity in the width direction) (2)

[0018] [5] According to a fifth aspect of the present invention, there is provided the stretched liquid crystal polymer film of any one of the first to fourth aspects, which has an average thickness of less than 10 μm.

[0019] [6] According to aspect 6 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film, comprising: a first step of laminating a support film made of a support polymer and having a surface roughness Ra of 1.5 μm or less as measured by a laser microscope to at least one side of an unstretched liquid crystal polymer film made of a liquid crystal polymer to obtain a laminated film; a second step of stretching the laminated film at least in the width direction using a tenter-type stretching device; and a third step of peeling off the stretched support film.

[0020] [7] According to aspect 7 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film, comprising: a first step of extruding molten liquid crystal polymer and supporting polymer into a film using an extruder so that a layer of the supporting polymer is laminated on at least one side of the layer of the liquid crystal polymer to obtain a laminated film; a second step of stretching the laminated film at least in the width direction using a tenter-type stretching device; and a third step of peeling off the stretched layer of the supporting polymer.

[0021] [8] According to aspect 8 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to aspect 6 or 7, wherein the thickness of the unstretched liquid crystal polymer film or the layer made of the liquid crystal polymer is 5 to 100 μm.

[0022] [9] According to a ninth aspect of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to the sixth or seventh aspect, wherein in the second step, the stretching speed of the laminated film is set to 500% / min to 10,000% / min, and the temperature T inside the furnace of the stretching device is set to a temperature that satisfies the following formula (3): T １ <T<T ２ (3) (where, in the above formula (3), T １ is the melting point of the liquid crystal polymer minus 100°C, and T ２is the melting point of the liquid crystal polymer + 30°C.

[0023]

[10] According to a tenth aspect of the present invention, in the method for producing a stretched liquid crystal polymer film according to the sixth aspect, the stretching of the laminated film in the second step is carried out at a value A represented by the following (4): １ A method for producing a stretched liquid crystal polymer film is provided under conditions where A is 0.20 to 5.00. １ = Furnace temperature T (°C) / Stretching speed (% / min) / Thickness of unstretched liquid crystal polymer film (µm) × 100 (4)

[0024]

[11] According to an eleventh aspect of the present invention, in the method for producing a stretched liquid crystal polymer film of the seventh aspect, in the second step, the stretching of the laminated film is performed to a value A represented by the following formula (5): ２ A method for producing a stretched liquid crystal polymer film under conditions where the stretched liquid crystal polymer film is stretched to a temperature of 0.20 to 5.00. ２ = Furnace temperature T (°C) / Stretching speed (% / min) / Thickness of liquid crystal polymer layer (µm) × 100 (5)

[0025]

[12] According to aspect 12 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to aspect 6 or 10, wherein the first step includes performing a surface treatment on the bonding surface of the unstretched liquid crystal polymer film and the bonding surface of the support film before bonding the support film to the unstretched liquid crystal polymer film.

[0026]

[13] According to aspect 13 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to aspect 12, wherein the surface treatment is one selected from the group consisting of plasma treatment, corona treatment, and chemical treatment.

[0027]

[14] According to aspect 14 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 6 to 13, wherein the second step includes stretching the film at a temperature below the melting point of the liquid crystal polymer.

[0028]

[15] According to aspect 15 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 6, 10, and 12 to 14, wherein in the second step, the stretching load calculated by multiplying the tensile stress of the support film at the temperature during stretching by the cross-sectional area of ​​the support film is equal to or greater than the stretching load calculated by multiplying the tensile stress of the unstretched liquid crystal polymer film at the temperature during stretching by the cross-sectional area of ​​the unstretched liquid crystal polymer film.

[0029]

[16] According to aspect 16 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 7, 11, and 14, wherein in the second step, the stretching load calculated by multiplying the tensile stress of the layer made of the support polymer at the temperature during stretching by the cross-sectional area of ​​the layer made of the support polymer is equal to or greater than the stretching load calculated by multiplying the tensile stress of the layer made of the liquid crystal polymer at the temperature during stretching by the cross-sectional area of ​​the layer made of the liquid crystal polymer.

[0030]

[17] According to aspect 17 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 6 to 16, wherein the support polymer is an aromatic polyether ketone or polyester.

[0031]

[18] According to aspect 18 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to aspect 17, wherein the polyester is at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate.

[0032]

[19] According to a nineteenth aspect of the present invention, there is provided a laminate comprising a film layer containing the stretched liquid crystal polymer film of any one of aspects 1 to 5, and a metal layer.

[0033]

[20] According to a twentieth aspect of the present invention, there is provided a circuit board including the laminate of the nineteenth aspect.

[0034] The stretched liquid crystal polymer film of the present invention has an average thickness of less than 25 μm and a Cv value of the film thickness of 10% or less, and therefore has a thin and uniform thickness, and can therefore be suitably used as an insulating material for circuit boards having a multilayer structure.

[0035] FIG. 1(a) is a diagram comparing the size of irregularities measured by a contact-type surface roughness meter and a laser microscope, and FIG. 1(b) is a diagram comparing the size of irregularities at minute intervals measured by a contact-type surface roughness meter and a laser microscope.

[0036] <Liquid Crystal Polymer Film> The stretched liquid crystal polymer film 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 and having a melting point of 250°C or higher, preferably 280°C to 380°C, 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 2,6-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 stretched liquid crystal polymer film.

[0037] The liquid crystal polyester can be synthesized by any known method, and is not particularly limited, including, for example, 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.

[0038] The stretched liquid crystal polymer film may contain additives such as polymers such as fluororesins, polyolefins, and polycycloolefins; 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; 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, within the range that does not excessively impair the effects of the present invention. 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 polymers and additives is not particularly limited, but from the viewpoints of moldability and thermal stability, it is preferably 0.01 to 50% by mass, more preferably 0.1 to 40% by mass, and even more preferably 0.5 to 30% by mass, of the total amount of the liquid crystal polymer film. These polymers, additives, etc. may be added to the liquid crystal polymer in advance, or may be added to the liquid crystal polymer when forming a stretched liquid crystal polymer film as described below.

[0039] The average thickness of the stretched liquid crystal polymer film of the present invention is less than 25 μm, preferably less than 10 μm. When the average thickness is within the above range, when the stretched liquid crystal polymer film is laminated with a conductor layer to form a circuit board, the thickness of the circuit board can be reduced, and the overall thickness of the laminated circuit board can be reduced. Therefore, the stretched liquid crystal polymer film can be suitably used for producing FPCs having a multilayer structure.

[0040] The average thickness of a stretched liquid crystal polymer film can be determined, for example, by measuring the film thickness at 5 mm intervals along the width direction (TD) of the film using a micrometer, contact thickness gauge, or the like at positions (three or more locations) 300 to 500 mm apart in the longitudinal direction (MD) and averaging these measurements. In the present invention, if unevenness in film thickness occurs, it is due to stretching in the width direction during the manufacturing process of the stretched liquid crystal polymer film. Therefore, the average value of film thicknesses measured along the width direction at several locations in the longitudinal direction of the film can be used as the average film thickness of the stretched liquid crystal polymer film.

[0041] Furthermore, in the stretched liquid crystal polymer film of the present invention, the Cv value of film thickness is 10% or less, preferably 7% or less. The Cv value of film thickness is expressed by the following formula (1) using the standard deviation of film thicknesses measured at multiple locations when determining the average film thickness and the average film thickness. The Cv value is an index that represents the uniformity of film thickness of a stretched liquid crystal polymer film. When the Cv value is within the above range, the stretched liquid crystal polymer film and the conductor layer can be closely attached when manufacturing a circuit board, improving the stability of the circuit board. Therefore, the stretched liquid crystal polymer film can be suitably used for manufacturing FPCs having a multilayer structure. Cv value (%) = standard deviation of film thickness / average film thickness × 100 (1)

[0042] In addition, in the stretched liquid crystal polymer film of the present invention, the difference between the maximum and minimum film thickness is preferably 5 μm or less, more preferably 4 μm or less. The smaller the difference between the maximum and minimum film thickness, the more uniform the film thickness of the stretched liquid crystal polymer film.

[0043] The stretched liquid crystal polymer film of the present invention preferably has a surface roughness Ra of 0.5 μm or less on one or both sides as measured by a laser microscope. Specifically, the surface roughness Ra referred to in the present invention is the arithmetic mean roughness of the film surface measured in a non-contact manner based on the confocal principle, which states that the amount of reflected light is maximized when the object is in focus.

[0044] FIG. 1(a) is a diagram comparing the size of irregularities measured by a contact-type surface roughness meter and a laser microscope, and FIG. 1(b) is a diagram comparing the size of irregularities at minute intervals measured by a contact-type surface roughness meter and a laser microscope.

[0045] As shown in FIG. 1(a), the distance (W) is large enough for the stylus (N) of a contact-type surface roughness measuring instrument to penetrate. １ ) unevenness (concave) is the size (depth) of the unevenness measured with a contact-type surface roughness measuring instrument (D １ -N) and the size of the unevenness measured by a laser microscope (L) (D １ -L) are approximately the same size. １ ) mainly has irregularities at such intervals, it is thought that there will be no significant difference in the surface roughness values ​​measured by each method.

[0046] However, as shown in FIG. 1(b), the surface of the measurement object (S ２ ) with a very small gap (W ２ ) unevenness exists, the width of the stylus of a contact-type surface roughness measuring instrument is wider than the width of the unevenness, and it is not possible to penetrate into the inside of the unevenness. For this reason, the size of the unevenness with minute intervals is measured smaller than the actual size (D ２ -N), are ignored, resulting in a surface roughness value that is smaller than the actual value. On the other hand, in measurements using a laser microscope, the laser can penetrate even irregularities with minute intervals, so the exact size of the irregularities can be measured (D ２ -L). Therefore, when measuring surface roughness using a laser microscope, it is possible to evaluate the surface roughness more accurately, reflecting the uneven shape at finer intervals, compared to conventional contact-type surface roughness measurements. In particular, since high-frequency signals can penetrate unevenness at such fine intervals, it is extremely important to control the surface roughness of the liquid crystal polymer film measured by a laser microscope in order to reduce the transmission loss of high-frequency signals when the liquid crystal polymer film is used in an FPC.

[0047] By having a surface roughness Ra of 0.5 μm or less on at least one surface measured with a laser microscope, when a laminate is produced by bonding a stretched liquid crystal polymer film and a conductor, the interface between the film and the conductor becomes smooth, reducing transmission loss when high-frequency signals flow, thereby enabling faster and larger-capacity communication using the laminate. The surface roughness Ra can be measured along any direction on the surface of the stretched liquid crystal polymer film. That is, the surface roughness Ra measured along any direction is preferably 0.5 μm or less, and more preferably the average surface roughness Ra measured multiple times along any direction is 0.5 μm or less. Furthermore, the surface roughness Ra measured along the longitudinal direction (MD) or width direction (TD) of the film is preferably 0.5 μm or less, and more preferably both the surface roughness Ra (MD) measured along the longitudinal direction and the surface roughness Ra (TD) measured along the width direction are 0.5 μm or less. In particular, it is preferable that the average surface roughness Ra (MD) obtained by multiple measurements along the longitudinal direction is 0.5 μm or less, and the average surface roughness Ra (TD) obtained by multiple measurements along the width direction is 0.5 μm or less. Furthermore, from the viewpoint of suppressing transmission loss between conductors attached to both sides of the stretched liquid crystal polymer film, it is more preferable that the surface roughness Ra of both sides of the stretched liquid crystal polymer film measured by a laser microscope is 0.5 μm or less. The surface roughness Ra of the stretched liquid crystal polymer film surface is preferably 0.4 μm or less, particularly preferably 0.2 μm or less, in any direction and on any side. If Ra is 0.2 μm or less, the skin depth when a 90 GHz frequency signal, which is being considered for the sixth-generation mobile communication system, flows on the copper surface is less than 0.22 μm, thereby reducing transmission loss.

[0048] The anisotropy of the molecular orientation of the stretched liquid crystal polymer film is preferably such that the degree of planar orientation, as defined below, falls within a predetermined range. First, in pole measurement by X-ray diffraction, the stretched 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 prepare 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 represented by the following formula (2) is preferably −0.5 or more and 0.5 or less. The degree of planar orientation is preferably −0.3 or more and 0.3 or less, and more preferably −0.2 or more and 0.2 or less. Planar orientation degree=(integrated intensity in the longitudinal direction−integrated intensity in the width direction) / (integrated intensity in the longitudinal direction+integrated intensity in the width direction) (2)

[0049] 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. If the value expressed by the above formula (2) is positive, it means that the molecular chains are oriented in the longitudinal direction, and if it is negative, it means that they are oriented in the width direction.

[0050] By setting the value of the degree of planar orientation expressed by the above formula (2) to -0.5 or more and -0.5 or less, the anisotropy of the linear expansion coefficient of the stretched liquid crystal polymer film of the present invention can be reduced, and therefore, when the stretched liquid crystal polymer film is laminated with copper to form an FPC, deformation due to differences in linear expansion coefficients can be suppressed. This effect is particularly pronounced when the stretched liquid crystal polymer film is subjected to heat treatment (described below). The value of the degree of planar orientation is preferably -0.2 to 0.2. Within this range, the linear expansion coefficient of the stretched liquid crystal polymer film can be approximately 10 to 30 ppm in both the longitudinal and transverse directions of the film. Furthermore, by setting the value of the degree of planar orientation to -0.1 to 0.1, the linear expansion coefficient becomes even closer to the linear expansion coefficient of copper, 18 ppm.

[0051] <Method for producing stretched liquid crystal polymer film> A method for producing the stretched liquid crystal polymer film of the present invention is described below. The stretched liquid crystal polymer film of the present invention can be obtained by laminating support polymer films on both sides of an unstretched liquid crystal polymer film to form a laminated film by tightly adhering them to each other (first step), stretching this laminated film (second step), and then peeling off the support polymer films (third step).

[0052] The unstretched liquid crystal polymer film used in the first step can be produced by a known method. For example, a liquid crystal polymer can be formed into a film by melt extrusion film formation using a T-die (T-die melt extrusion), forming an unstretched liquid crystal polymer film. Specifically, the liquid crystal polymer is melt-kneaded in an extruder, the molten resin is extruded through a T-die, and solidified on a metal roll to obtain an unstretched liquid crystal polymer film. The temperature of the extruder cylinder is preferably 230 to 360°C, more preferably 280 to 350°C. The slit spacing of the T-die can be appropriately set depending on the type and composition of the liquid crystal polymer used, the desired film performance, etc. The slit spacing of the T-die is not particularly limited, but is preferably 0.1 to 1.5 mm, more preferably 0.1 to 1.0 mm.

[0053] The thickness of the unstretched liquid crystal polymer film obtained by the above method is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 100 μm, even more preferably 20 to 100 μm, and particularly preferably 20 to 70 μm, in order to control the average film thickness of the stretched liquid crystal polymer film within a desired range and to make the value of the planar orientation degree of the stretched liquid crystal polymer film −0.5 or more to −0.5 or less.

[0054] The support polymer film is a film laminated to an unstretched liquid crystal polymer film to prevent the film from breaking when stretching the unstretched liquid crystal polymer film. Examples of the support polymer constituting the support polymer film include aromatic polyetherketones or polyesters. Specific examples of aromatic polyetherketones include polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyetheretherketoneketone (PEEKK). Specific examples of polyesters include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT). These polymers can be used alone or in combination of two or more. Among them, polyetheretherketone (PEEK), polyethylene terephthalate (PET), and polybutylene terephthalate (PBT) are preferred, with polyetheretherketone (PEEK) being particularly preferred. By using a support polymer film made of such a support polymer, the laminated film can be stretched without breaking at a temperature below the melting point of the liquid crystal polymer in the second step. Furthermore, it is preferable that the film is a crystallized or stretched film, since it has high heat resistance and can be stretched at high temperatures.

[0055] The surface roughness Ra of the support polymer film measured by a laser microscope is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less. By controlling the surface roughness of the support polymer film to fall within the above range, the surface roughness Ra of the resulting stretched liquid crystal polymer film measured by a laser microscope can be controlled to 0.5 μm or less.

[0056] When laminating an unstretched liquid crystal polymer and a support polymer film, the support polymer film can be laminated on only one side or both sides of the unstretched liquid crystal polymer film, but laminating on both sides is preferable because the average film thickness and Cv value of the film thickness of the resulting stretched liquid crystal polymer film can be controlled within the desired range, the surface roughness Ra of both sides of the stretched liquid crystal polymer film can be controlled to 0.5 μm or less, and defects such as breakage of the unstretched liquid crystal polymer film can be reduced when the laminated film formed by laminating the unstretched liquid crystal polymer film and the support polymer film is stretched in the width direction (TD) in the second step described below.

[0057] The method for bonding the unstretched liquid crystal polymer film and the support polymer film is not particularly limited, but a thermal lamination method is preferred because it does not require adhesives or the like. In the thermal lamination method, the unstretched liquid crystal polymer film and the support polymer film are pressed together while the laminated film of the unstretched liquid crystal polymer film and the support polymer film is heated with a pair of heated rolls. The conditions for the thermal lamination method can be appropriately selected according to the physical properties of the liquid crystal polymer and the support polymer. Although not particularly limited, it is preferable to perform heating and pressing at a temperature near the melting point of the liquid crystal polymer and at a temperature near the melting point of the support polymer.

[0058] If the unstretched liquid crystal polymer film and the support film are difficult to adhere to each other by thermal lamination alone, it is preferable to perform a surface treatment on the surface of the unstretched liquid crystal polymer film that contacts the support polymer film (the bonding surface) and the surface of the support polymer film that contacts the unstretched liquid crystal polymer film (the bonding surface) before laminating them together.Examples of surface treatment methods include plasma treatment in which electrical energy is applied to irradiate the surface with a gas that has been converted into a plasma state, corona treatment in which the surface is activated by discharge, activation by irradiating the surface with ultraviolet light or an electron beam, activation by applying a flame to the surface, chemical treatment in which the surface is oxidized with potassium dichromate or the like, and primer treatment in which a primer is applied.By performing such a surface treatment before laminating the unstretched liquid crystal polymer film and the support polymer film, the adhesion between the unstretched liquid crystal polymer film and the support polymer film can be improved. The surface treatment method can be selected appropriately depending on the physical properties of the liquid crystal polymer and the supporting polymer, but plasma treatment, corona treatment, and chemical treatment are preferred, with plasma treatment being particularly preferred, from the viewpoint of increasing the adhesion between the unstretched liquid crystal polymer film and the supporting polymer film and reducing damage to the resulting stretched liquid crystal polymer film.

[0059] Other methods for improving the adhesion between the unstretched liquid crystal polymer film and the support polymer film include providing an easy-adhesion layer made of a polyester-based resin material on the surface of the support polymer film.

[0060] Next, in the second step, a tenter-type stretching device is used to stretch the laminate film, which is a laminate of an unstretched liquid crystal polymer film and a support polymer film, in the width direction (TD). Stretching the laminate film in the width direction allows the average thickness of the resulting stretched liquid crystal polymer film to be controlled within a desired range, and the anisotropy of the stretched liquid crystal polymer film to be reduced. The method for stretching the laminate film is not particularly limited, but a tenter transverse stretching method is preferred, in which both ends of the laminate film are clamped with clips and heated and stretched. The stretching ratio and stretching speed are appropriately selected so that the support film can be stretched and the shape and physical properties of the stretched liquid crystal polymer film are within the desired range. The stretching ratio is preferably 1.5 to 10 times, more preferably 2 to 5 times. The stretching speed is preferably 500% / min to 10,000%, more preferably 1,000 to 5,000% / min. Furthermore, to adjust the degree of planar orientation after stretching, additional stretching in the longitudinal direction (MD) may be performed as needed.

[0061] The stretching of the laminate film is preferably carried out under conditions such that the surface temperature of the laminate film during stretching (ultimate stretching temperature) is a temperature below the melting point of the liquid crystal polymer. The ultimate stretching temperature is more preferably 30 to 200°C lower than the melting point of the liquid crystal polymer, even more preferably 80 to 200°C lower than the melting point of the liquid crystal polymer, and particularly preferably 100 to 170°C lower than the melting point of the liquid crystal polymer. The ultimate stretching temperature is preferably a temperature equal to or higher than the glass transition temperature of the liquid crystal polymer. The ultimate stretching temperature of the laminate film can be adjusted by appropriately setting the stretching speed and the temperature (inside the furnace temperature of the stretching device) when stretching the laminate film. By stretching the laminate film under conditions such that the ultimate stretching temperature is a temperature below the melting point of the liquid crystal polymer, the thickness of the resulting stretched liquid crystal polymer film can be made thin and uniform, and the smoothness of the film surface can be improved. In the present invention, "stretching at a temperature below the melting point of the liquid crystal polymer" means that stretching is performed under conditions where the ultimate stretching temperature is below the melting point of the liquid crystal polymer.

[0062] In the second step, it is preferable that the temperature T inside the furnace of the stretching device is set to a temperature that satisfies the following formula (3): T １ <T<T ２ (3) However, in the above formula (1), T １ is the melting point of the liquid crystal polymer minus 100°C, and T ２ is the melting point of the liquid crystal polymer plus 30°C. １ is a temperature 100° C. lower than the melting point of the liquid crystal polymer, and T ２ is a temperature 30°C higher than the melting point of the liquid crystal polymer. ２ In the above cases, even if the ultimate stretching temperature is within the appropriate temperature range described above, the support polymer film or support polymer layer is prone to breakage, and good stretching is not possible. The reason for this is unclear, but it is presumed that if the oven temperature is too high, when the liquid crystal polymer layer after stretching is thin, the temperature of the support polymer film or support polymer layer on its surface becomes high, making it prone to breakage. On the other hand, when T is T １ In the following cases, the stretching temperature does not reach the proper temperature during stretching, and the film breaks during stretching.

[0063] Furthermore, the stretching of the laminated film in the second step is performed to a value A represented by the following formula (4): １ It is preferable to carry out the process under conditions where A is 0.20 to 5.00. １ = Furnace temperature T (°C) / Stretching speed (% / min) / Thickness of unstretched liquid crystal polymer film (µm) × 100 (4) A １ is preferably 0.24 to 2.50, more preferably 0.28 to 0.48. １ If A exceeds 5.00, the Cv value, which is an index showing the uniformity of the film thickness, increases, and the uniformity of the film thickness decreases. １ When the stretching ratio is less than 0.20, the film is prone to breakage. By stretching the laminated film under conditions that satisfy the above formula (4), the thickness of the resulting stretched liquid crystal polymer film can be made thin and uniform, and the smoothness of the film surface can be improved.

[0064] Furthermore, in order to control the average thickness of the resulting stretched liquid crystal polymer film to 25 μm or less and to control the Cv value of the film thickness within a predetermined range, it is preferable to adjust the stretching ratio and stretching speed of the laminated film as follows. Specifically, when a laminated film including an unstretched liquid crystal polymer film having a thickness of 40 to 60 μm is stretched at a stretching ratio of 3 times, the stretching speed is preferably set to 1200 to 2800% / min. Furthermore, when an unstretched liquid crystal polymer film having a thickness of 40 to 60 μm is stretched at a stretching ratio of 3.5 times, the stretching speed is preferably set to 1600 to 3000% / min. Furthermore, when an unstretched liquid crystal polymer film having a thickness of 40 to 60 μm is stretched at a stretching ratio of 4 times, the stretching speed is preferably set to 2000 to 3500% / min.

[0065] When an unstretched liquid crystal polymer film having a thickness of 15 to 35 μm is stretched at a stretch ratio of 3, the stretching speed is preferably 1200 to 4600% / min. When an unstretched liquid crystal polymer film having a thickness of 15 to 35 μm is stretched at a stretch ratio of 3.5, the stretching speed is preferably 1600 to 6000% / min. When an unstretched liquid crystal polymer film having a thickness of 15 to 35 μm is stretched at a stretch ratio of 4, the stretching speed is preferably 2000 to 7500% / min.

[0066] Furthermore, while the laminated film is being stretched, it is preferable that the sum of the stretching loads applied to the two support polymer films laminated on both sides of the unstretched liquid crystal polymer film is always equal to or greater than the stretching load applied to the unstretched liquid crystal polymer film. Here, the stretching load refers to the load applied to the film when it is stretched, and is a value obtained by multiplying the tensile stress of the film by the cross-sectional area of ​​the film.

[0067] During stretching of the laminated film, by making the sum of the stretching loads applied to the two support polymer films equal to or greater than the stretching load applied to the unstretched liquid crystal polymer film, the unstretched liquid crystal polymer film can be stretched without breaking even at a temperature below the melting point of the liquid crystal polymer. Although the reason for this is not clear, it is thought that by adhering a support polymer film, which has a higher stretching load than the unstretched liquid crystal polymer film, to the unstretched liquid crystal polymer film, the tensile load applied to the liquid crystal polymer film is dispersed, and stress concentration in areas where breakage is likely to occur is suppressed.

[0068] In order to ensure that the total stretching load applied to the two support polymer films is equal to or greater than the stretching load applied to the unstretched liquid crystal polymer film, this can be achieved by appropriately selecting the ratio of the thickness of the unstretched liquid crystal polymer film to the thickness of the support polymer film, the material and surface roughness of the support polymer film, and the temperature and stretching speed during stretching. For example, the material of the support polymer film can be selected depending on the temperature during stretching, which is determined by the type of liquid crystal polymer.

[0069] Furthermore, when using a laminated film in which a support polymer film is laminated on only one side of an unstretched liquid crystal polymer film, the laminated film can be stretched so that the stretching load on one support polymer film is equal to or greater than the stretching load on the unstretched liquid crystal polymer film.

[0070] From the viewpoint of being able to favorably adjust the relationship between the stretching load applied to the support polymer film and the stretching load applied to the unstretched liquid crystal polymer film, the thickness ratio of the support polymer film to the unstretched liquid crystal polymer film is preferably 0.01 to 10.0, more preferably 0.1 to 5.0, and even more preferably 0.2 to 1.2, in terms of the ratio of "thickness of one support polymer film / thickness of the unstretched liquid crystal polymer film."

[0071] Finally, in the third step, the support polymer film is peeled off from the stretched laminated film to obtain a stretched liquid crystal polymer film.

[0072] In the third step, after peeling off the support polymer film, the stretched liquid crystal polymer film may be heat-treated in the range of from its melting point −50° C. to its melting point, thereby improving the heat resistance of the liquid crystal polymer film and reducing the linear expansion coefficient.

[0073] In the above method, a laminated film is obtained by laminating a film made of a liquid crystal polymer and a film made of a support polymer in the first step, but the method for obtaining a laminated film is not particularly limited to this. For example, a laminated film may be formed by melting the liquid crystal polymer in a first extruder and the support polymer in a second extruder, and extruding each polymer into a film shape (co-extrusion) so that a layer made of the support polymer is laminated on one or both sides of the layer made of the liquid crystal polymer.

[0074] As a method for laminating a layer of a support polymer on one or both sides of a layer of a liquid crystal polymer, a method for forming a multilayer extrusion film from a T-die can be used.Specific examples include a feed block method in which molten liquid crystal polymer and support polymer supplied from two extruders are fed into a feed block, merged, and then extruded into a film from a T-die, and a multi-manifold method in which molten liquid crystal polymer and support polymer are fed separately into a T-die and extruded together into a film.From the viewpoint of improving the smoothness of the obtained stretched liquid crystal polymer film, it is preferable to use the multi-manifold method, taking into account cases in which the liquid crystal polymer and support polymer have different viscosities or flow properties when melted.

[0075] In the laminate film formed by coextrusion in the first step, the thickness of the liquid crystal polymer layer is preferably 5 to 100 μm, more preferably 10 to 100 μm, even more preferably 20 to 100 μm, and particularly preferably 20 to 70 μm. Furthermore, when forming the laminate film by coextrusion, it is preferable to use polyether ether ketone as the support polymer. By using the support polymer, the laminate film can be stretched in the second step at a temperature below the melting point of the liquid crystal polymer without causing breakage. This improves the surface smoothness of the resulting stretched liquid crystal polymer film.

[0076] Even when the laminated film is formed by coextrusion in the first step, it is preferable that the temperature T inside the oven of the stretching device is set to a temperature that satisfies the above formula (3). ２ It is preferable to carry out the process under conditions where A is 0.20 to 5.00. ２ = Furnace temperature T (°C) / Stretching speed (% / min) / Thickness of liquid crystal polymer layer (µm) × 100 (5) A ２ is preferably 0.24 to 2.50, more preferably 0.28 to 0.48. ２ If A exceeds 5.00, the Cv value, which is an index showing the uniformity of the film thickness, increases, and the uniformity of the film thickness decreases. ２ When the stretching ratio is less than 0.20, the film is prone to breakage. By stretching the laminated film under conditions that satisfy the above formula (5), the thickness of the resulting stretched liquid crystal polymer film can be made thin and uniform, and the smoothness of the film surface can be improved.

[0077] When a laminated film is formed in the first step by extruding the liquid crystal polymer and the support polymer into films, it is preferable to stretch the laminated film in the second step so that the stretching load applied to the layer made of the support polymer is equal to or greater than the stretching load applied to the layer made of the liquid crystal polymer.

[0078] The laminate of the present invention includes a film layer made of the above-mentioned stretched liquid crystal polymer film and a metal layer. Examples of the metal material constituting the metal layer include gold, silver, copper, iron, nickel, aluminum, and alloys thereof, and copper is preferably used.

[0079] The laminate can be produced by a known method as long as the smoothness and molecular orientation of the stretched liquid crystal polymer film can be maintained. For example, the laminate can be produced by vapor-depositing a metal layer on the surface of the stretched liquid crystal polymer film, or by forming a metal layer on the surface of the stretched liquid crystal polymer film by electroless plating or electrolytic plating. Alternatively, the laminate can be produced by superposing a metal foil such as copper foil on the stretched liquid crystal polymer film using a roll-to-roll method or a continuous isostatic pressing method (double belt method) and continuously thermocompressing the metal foil. Alternatively, the laminate can be produced using surface-activated bonding, in which the surfaces of the stretched liquid crystal polymer film and the metal foil are activated by removing oxides and dirt using a method such as sputter etching, and the stretched liquid crystal polymer film and the metal foil are then abutted and rolled to bond them.

[0080] <Circuit Board> The circuit board of the present invention comprises an insulator (or dielectric) made of the above-mentioned stretched liquid crystal polymer film and a conductor layer. The form of the circuit board is not particularly limited, and it can be used as various high-frequency circuit boards by known means. The circuit board may be equipped with a semiconductor element such as an IC chip.

[0081] A circuit pattern is formed on the conductor layer of the circuit board by a known processing method. Examples of metal materials constituting the conductor layer include gold, silver, copper, iron, nickel, aluminum, and alloy metals thereof. The circuit pattern may also be formed on the metal layer of the laminate by a known method.

[0082] Specific examples of methods for producing circuit boards having circuit patterns include conventionally known methods such as the modified semi-additive process (MSAP process), the semi-additive process (SAP process), and the subtractive process. For example, in the case of the SAP process, a circuit board can be produced by electrolessly plating copper onto an insulator made of a stretched liquid crystal polymer film as a conductor layer, masking non-wiring portions on the conductor layer, electrolytically plating copper onto the unmasked portions to form an additional conductor layer, removing the mask, and removing the conductor layer hidden by the mask by etching. Furthermore, in the case of the MSAP process, a circuit board can be produced by laminating an ultrathin copper foil instead of the electroless copper plating used in the SAP process.

[0083] The circuit board of the present invention can be used for various transmission lines, such as coaxial lines, strip lines, microstrip lines, coplanar lines, parallel lines, etc. The circuit board of the present invention can also be used for antennas and antenna devices in which an antenna and a transmission line are integrated.

[0084] Examples of the antenna include antennas that utilize millimeter waves or microwaves, such as a waveguide slot antenna, a horn antenna, a lens antenna, a printed antenna, a triplate antenna, a microstrip antenna, and a patch antenna. When the circuit board of the present invention is used as an antenna, it is preferable that the circuit board be a multilayer circuit board.

[0085] The circuit board of the present invention can also be used in sensors such as vehicle-mounted radars that have semiconductor elements.

[0086] The circuit board of the present invention is made of a stretched liquid crystal polymer film having a thin and uniform thickness, and therefore can be suitably used particularly as a multi-layer circuit board.

[0087] Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to these examples.

[0088] <Melting Point of Film> Using a differential scanning calorimeter (manufactured by PerkinElmer, model: DSC8500), the liquid crystal polymer film before stretching was analyzed according to differential scanning calorimetry based on JIS K 7121. The endothermic peak temperature observed when the temperature of the liquid crystal polymer film before stretching was raised from 0°C at a rate of 10°C / min was taken as the melting point.

[0089] <Appearance of Film> The appearance of the stretched liquid crystal polymer film was visually observed and rated as follows: ◯: No unevenness in thickness or holes in the film were observed. ×: Unevenness in thickness or holes in the film were observed.

[0090] <Average Film Thickness, Cv Value of Thickness, and Difference Between Maximum and Minimum Thickness Values> The film thickness was measured at a total of 270 to 360 points along the width direction of the film at 5 mm intervals using a contact thickness meter (manufactured by Meisan Co., Ltd., model: RC-1W) at three points in the longitudinal direction of the film (the distance between each point was 400 mm). The average of these thicknesses was taken as the average film thickness of the stretched liquid crystal polymer film. In addition, the Cv value of the film thickness of the stretched liquid crystal polymer film was calculated from the standard deviation of the film thicknesses measured at 270 to 360 points and the average film thickness. A smaller Cv value indicates a more uniform film thickness. In addition, the difference between the maximum and minimum film thickness values ​​measured at 270 to 360 points was calculated. A smaller difference between the maximum and minimum film thickness values ​​indicates a more uniform film thickness.

[0091] <Film Surface Roughness> The surface roughness Ra of the support polymer film and the stretched liquid crystal polymer film was measured using a laser microscope equipped with a white light interferometer (Keyence Corporation, model: VK-X3000). A roughness curve was measured in a field of view of 1052 × 1404 μm under the conditions of a measurement reference length of 0.25 mm, an evaluation length of 1 mm, and a cutoff value λc of 0.25 mm (no cutoff value λs), and the surface roughness Ra was determined by calculating the arithmetic mean roughness. The surface roughness Ra was measured for both the front and back sides of the film in the machine direction (MD) and the width direction (TD) of the film.

[0092] <Degree of Planar Orientation of Film> For the stretched liquid crystal polymer film, pole measurement was performed using a horizontal sample multipurpose X-ray diffractometer (manufactured by Rigaku Corporation, model: Ultima IV) with a diffraction angle (2θ) fixed at 20°, an X-ray target: Cu, a voltage: 40 kV, a current: 40 mA, an α angle = 45°, and a β angle = 0 to 360° (the longitudinal direction of the film is 0°, and a step angle is 5°) to prepare 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. The degree of planar orientation was calculated from the following formula (6): 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) (6)

[0093] <Linear expansion coefficient of film> A stretched liquid crystal polymer film (width: 5 mm) was attached to a thermomechanical analyzer (manufactured by Rigaku Corporation, model: TMA8310) (distance between chucks: 15 mm), and the film was heated from 30°C to 150°C at a rate of 5°C / min while applying a load of 10 mN. The linear expansion coefficient was determined from the dimensional change measured when the film was heated.

[0094] Example 1 A liquid crystal polymer (LAPEROS A950RX, manufactured by Polyplastics Co., Ltd.) was fed into a twin-screw extruder (screw diameter 32 mm), extruded into a film form from a T-die (lip length 350 mm, lip clearance approximately 1 mm, die temperature 300°C) at the tip of the extruder, and cooled to obtain an unstretched liquid crystal polymer film with a thickness of 50 μm. The melting point was evaluated by the method described above.

[0095] Next, both sides of the unstretched liquid crystal polymer film and one side of a polyether ether ketone (PEEK) film (manufactured by Victrex, APTIV Film 1000-025G, thickness 25 μm, surface roughness Ra = 0.14 μm (MD), 0.12 μm (TD)) serving as a support polymer film were subjected to direct atmospheric pressure plasma treatment in an oxygen-containing gas atmosphere at a power of 1.5 kW and a conveying speed of 1.0 m / min. Next, the plasma-treated surfaces were overlapped, and a PEEK film was thermocompression-bonded to both sides of the unstretched liquid crystal polymer film using a first roll heated to 305 ° C and a second roll heated to 120 ° C under conditions of a nip pressure of 0.2 MPa and a conveying speed of 0.5 m / min. After thermocompression bonding, the unstretched liquid crystal polymer film and the PEEK film were in close contact.

[0096] The laminated film thus produced was stretched 3 times in the width direction (TD) using a tenter-type transverse stretching machine (furnace temperature 300°C) with a stretching zone length of 1.2 m and a conveying speed of 10 m / min (stretching speed 1667% / min). The temperature of the laminated film during stretching (ultimate stretching temperature) was 170°C. The PEEK film was then peeled off to obtain a stretched liquid crystal polymer film, which was evaluated for appearance, average film thickness, difference between maximum and minimum film thickness, Cv value of film thickness, surface roughness Ra, and degree of planar orientation. The obtained stretched liquid crystal polymer film was further heat-treated at 250°C for 24 hours in a nitrogen atmosphere to evaluate the linear expansion coefficient. The results are shown in Table 1. Note that the value A in Table 1 １ is a value calculated from the above formula (4) based on the thickness of the unstretched liquid crystal polymer film, the temperature inside the furnace, and the stretching speed.

[0097] Examples 2 and 3 Stretched liquid crystal polymer films were obtained and evaluated in the same manner as in Example 1, except that the stretching ratio was changed to the value shown in Table 1. The results are shown in Table 1.

[0098] Example 4 A liquid crystal polymer (LAPEROS A950RX, manufactured by Polyplastics Co., Ltd.) was fed into a twin-screw extruder (screw diameter 32 mm), extruded into a film form from a T-die (lip length 350 mm, lip clearance approximately 1 mm, die temperature 300°C) at the tip of the extruder, and cooled to obtain an unstretched liquid crystal polymer film with a thickness of 20 μm. The melting point was evaluated by the method described above.

[0099] Next, both sides of the unstretched liquid crystal polymer film and one side of a polyether ether ketone (PEEK) film (manufactured by Victrex, APTIV Film 1000-025G, thickness 25 μm, surface roughness Ra = 0.14 μm (MD), 0.12 μm (TD)) serving as a support polymer film were subjected to direct atmospheric pressure plasma treatment in an oxygen-containing gas atmosphere at a power of 1.5 kW and a conveying speed of 1.0 m / min. Next, the plasma-treated surfaces were overlapped, and a PEEK film was thermocompression-bonded to both sides of the unstretched liquid crystal polymer film using a first roll heated to 270 ° C and a second roll heated to 120 ° C under conditions of a nip pressure of 0.2 MPa and a conveying speed of 0.5 m / min. After thermocompression bonding, the unstretched liquid crystal polymer film and the PEEK film were in close contact.

[0100] The laminated film thus prepared was stretched 4 times in the transverse direction (TD) using a tenter-type transverse stretching machine (furnace temperature 300°C) with a stretching zone length of 0.6 m and a conveying speed of 10 m / min (stretching speed 5000% / min). The temperature of the laminated film during stretching (ultimate stretching temperature) was 170°C. The PEEK film was then peeled off to obtain a stretched liquid crystal polymer film, which was evaluated for appearance, average film thickness, difference between maximum and minimum film thickness, Cv value of film thickness, surface roughness Ra, and degree of planar orientation. The obtained stretched liquid crystal polymer film was further heat-treated at 250°C for 24 hours under a nitrogen atmosphere to evaluate the linear expansion coefficient. The results are shown in Table 1.

[0101] Example 5 A liquid crystal polymer (LAPEROS A950RX, manufactured by Polyplastics Co., Ltd.) was fed into a twin-screw extruder (screw diameter 32 mm), extruded into a film form from a T-die (lip length 350 mm, lip clearance approximately 1 mm, die temperature 300°C) at the tip of the extruder, and cooled to obtain an unstretched liquid crystal polymer film with a thickness of 50 μm. The melting point was evaluated by the method described above.

[0102] Next, both sides of the unstretched liquid crystal polymer film and one side of a biaxially stretched polybutylene terephthalate (PBT) film (manufactured by Kohjin Film & Chemicals, Bobblet, thickness 25 μm, surface roughness Ra = 0.11 μm (MD), 0.15 μm (TD)) serving as a support polymer film were subjected to direct atmospheric pressure plasma treatment in an oxygen-containing gas atmosphere at a power of 1.5 kW and a conveying speed of 1.0 m / min. Next, the plasma-treated surfaces were overlapped, and a PBT film was thermocompression-bonded to both sides of the unstretched liquid crystal polymer film using a first roll heated to 200 ° C and a second roll heated to 120 ° C under conditions of a nip pressure of 0.2 MPa and a conveying speed of 0.5 m / min. After thermocompression bonding, the unstretched liquid crystal polymer film and the PBT film were in close contact.

[0103] The laminated film thus prepared was stretched 3 times in the transverse direction (TD) using a tenter-type transverse stretching machine (furnace temperature 220°C) with a stretching zone length of 1.2 m and a conveying speed of 10 m / min (stretching speed 1667% / min). The temperature of the laminated film during stretching (ultimate stretching temperature) was 140°C. The PBT film was then peeled off to obtain a stretched liquid crystal polymer film, which was then evaluated for appearance, average film thickness, difference between maximum and minimum film thickness, Cv value of film thickness, surface roughness Ra, and degree of planar orientation. The resulting stretched liquid crystal polymer film was then heat-treated at 250°C for 24 hours under a nitrogen atmosphere to evaluate the linear expansion coefficient. The results are shown in Table 1.

[0104] Example 6 A liquid crystal polymer (LAPEROS A950RX, manufactured by Polyplastics Co., Ltd.) was fed into a twin-screw extruder (screw diameter 32 mm), extruded into a film form from a T-die (lip length 350 mm, lip clearance approximately 1 mm, die temperature 300°C) at the tip of the extruder, and cooled to obtain an unstretched liquid crystal polymer film with a thickness of 50 μm. The melting point was evaluated by the method described above.

[0105] Next, both sides of the unstretched liquid crystal polymer film were subjected to direct atmospheric pressure plasma treatment under an oxygen-containing gas atmosphere at a power of 1.5 kW and a conveying speed of 1.0 m / min. Next, the adhesive layer surface of a biaxially stretched PET film (manufactured by Toyobo, A4300, thickness 38 μm, surface roughness Ra = 0.10 μm (MD), 0.12 μm (TD)) with an easy-adhesion layer as a support polymer film was superimposed on the plasma-treated surface of the unstretched liquid crystal polymer film, and a first roll heated to 200 ° C. and a second roll heated to 120 ° C. were used under conditions of a nip pressure of 0.2 MPa and a conveying speed of 0.5 m / min. The PET film was thermocompressed onto both sides of the unstretched liquid crystal polymer film. After thermocompression bonding, the unstretched liquid crystal polymer film and the PET film were in close contact.

[0106] The laminated film thus prepared was stretched 3 times in the transverse direction (TD) using a tenter-type transverse stretching machine (furnace temperature 280°C) with a stretching zone length of 1.2 m and a conveying speed of 10 m / min (stretching speed 1667% / min). The temperature of the laminated film during stretching (ultimate stretching temperature) was 160°C. The PET film was then peeled off to obtain a stretched liquid crystal polymer film, which was then evaluated for appearance, average film thickness, difference between maximum and minimum film thickness, Cv value of film thickness, surface roughness Ra, and degree of planar orientation. The obtained stretched liquid crystal polymer film was then heat-treated at 250°C for 24 hours under a nitrogen atmosphere to evaluate the linear expansion coefficient. The results are shown in Table 1.

[0107] Example 7 A liquid crystal polymer (Polyplastics Co., Ltd., LAPEROS A950RX) was supplied to a twin-screw extruder (screw diameter 26 mm) and melt-kneaded at 300 ° C. In addition, a polyether ether ketone (PEEK) polymer (Daicel-Evonik, VESTAKEEP 3300G) was supplied to a single-screw extruder (screw diameter 40 mm) as a support polymer and melt-kneaded at 380 ° C. These molten polymers were supplied to a multi-manifold T-die, and layers of support polymer were superimposed on both sides of a layer of liquid crystal polymer. By extruding and cooling, a laminated film having a liquid crystal polymer layer of 50 μm and support polymer layers on both sides of 25 μm each, for a total of 100 μm, was produced.

[0108] The laminated film thus produced was stretched 4 times in the transverse direction (TD) using a tenter-type transverse stretching machine (furnace temperature 300°C) with a stretching zone length of 1.2 m and a conveying speed of 10 m / min (stretching speed 2500% / min). The temperature of the laminated film during stretching (ultimate stretching temperature) was 170°C. The PEEK film was then peeled off to obtain a stretched liquid crystal polymer film, which was evaluated for appearance, average film thickness, difference between maximum and minimum film thickness, Cv value of film thickness, surface roughness Ra, and degree of planar orientation. The obtained stretched liquid crystal polymer film was further heat-treated at 250°C for 24 hours under a nitrogen atmosphere to evaluate the coefficient of linear expansion. The results are shown in Table 1. Note that the value A in Table 1 ２ is a value calculated from the above formula (5) based on the thickness of the layer made of the liquid crystal polymer, the temperature inside the furnace, and the stretching speed.

[0109] Comparative Example 1 A stretched liquid crystal polymer film was obtained and evaluated in the same manner as in Example 1, except that the stretching speed was changed to the value shown in Table 1. The results are shown in Table 1.

[0110] Comparative Example 2 A stretched liquid crystal polymer film was obtained in the same manner as in Comparative Example 1, except that a polyether ether ketone (PEEK) film (Shin-Etsu Polymer Co., Ltd., Shin-Etsu Sepla Film, thickness 25 μm, surface roughness Ra=2.52 μm (MD), 2.39 μm (TD)) was used as the support polymer film, and evaluation was similarly performed. The results are shown in Table 1.

[0111] Comparative Example 3 A stretched liquid crystal polymer film was obtained in the same manner as in Comparative Example 1, except that a porous polytetrafluoroethylene (PTFE) film (manufactured by Chukoh Chemical Industry Co., Ltd., C-Poruos, thickness 100 μm, surface roughness Ra=2.15 μm (MD), 2.35 μm (TD)) was used as the support polymer film, and evaluation was similarly performed. The results are shown in Table 1.

[0112] Comparative Example 4 An attempt was made to produce a stretched liquid crystal polymer film in the same manner as in Example 1, except that the oven temperature, stretching ratio, and stretching speed of the transverse stretching machine were changed to the values ​​shown in Table 1. However, when the laminated film was stretched, the support polymer film was broken, and a stretched liquid crystal polymer film could not be obtained.

[0113] Comparative Example 5 An attempt was made to produce a stretched liquid crystal polymer film in the same manner as in Example 1, except that the thickness of the unstretched liquid crystal polymer film and the furnace temperature of the transverse stretching machine were changed to the values ​​shown in Table 1. However, when the laminated film was stretched, the liquid crystal polymer film broke, and a stretched liquid crystal polymer film could not be obtained.

[0114]

[0115] As shown in Table 1, the stretched liquid crystal polymer films obtained in Examples 1 to 7 had small average film thicknesses and excellent film thickness uniformity. Furthermore, the surface roughness Ra was small, indicating high smoothness. Furthermore, the degree of planar orientation was small, and the linear expansion coefficients in the longitudinal and transverse directions were similar, indicating reduced anisotropy.

[0116] On the other hand, the stretched liquid crystal polymer films of Comparative Examples 1 to 3, which were produced under conditions where the ultimate stretching temperature was a temperature above the melting point of the liquid crystal polymer, had unevenness and holes in the film and poor film thickness uniformity. Furthermore, in Comparative Example 2, in which PEEK with a surface roughness Ra exceeding 2 μm was laminated and stretched, and Comparative Example 3, in which a porous PTFE film was laminated and stretched, the surface roughness measured with a laser microscope of the obtained stretched liquid crystal polymer also exceeded 0.5 μm.

Claims

1. A stretched liquid crystal polymer film made of a liquid crystal polymer, the average thickness of which is less than 25 μm, and the Cv value of the thickness represented by the following formula (1) is 10% or less: Cv value (%) = (standard deviation of measured thickness) / (average thickness) × 100 (1) 2. The stretched liquid crystal polymer film according to claim 1, wherein the difference between the maximum and minimum film thicknesses is 5 μm or less.

3. The stretched liquid crystal polymer film according to claim 1 or 2, wherein the surface roughness Ra of at least one surface measured by a laser microscope is 0.5 μm or less.

4. A stretched liquid crystal polymer film according to claim 1 or 2, wherein in a pole measurement by X-ray diffraction, when the diffraction intensity of the 110 plane is measured while the film is tilted 45° (α=45° in the Schulz method) and rotated in the in-plane direction (β direction), the integrated intensities of β=45-135°, 135°-225°, 225-315°, and 315-45° are calculated with β=0° being the longitudinal direction of the film, the sum of the integrated intensity of β=45-135° and the integrated intensity of β=225°-315° is the longitudinal integrated intensity, and the sum of the integrated intensity of β=135-225° and the integrated intensity of β=315-45° is the transverse integrated intensity, the degree of planar orientation represented by the following formula (2) is between -0.5 and 0.5: Planar orientation degree=(integrated intensity in the longitudinal direction−integrated intensity in the transverse direction) / (integrated intensity in the longitudinal direction+integrated intensity in the transverse direction) (2) 5. The stretched liquid crystal polymer film according to claim 1 or 2, having an average thickness of less than 10 μm.

6. A method for producing a stretched liquid crystal polymer film, comprising: a first step of bonding a support film made of a support polymer and having a surface roughness Ra of 1.5 μm or less as measured by a laser microscope to at least one side of an unstretched liquid crystal polymer film made of a liquid crystal polymer to obtain a laminated film; a second step of stretching the laminated film at least in the width direction using a tenter-type stretching device; and a third step of peeling off the stretched support film.

7. A method for producing a stretched liquid crystal polymer film, comprising: a first step of extruding molten liquid crystal polymer and supporting polymer into a film using an extruder so that a layer of the supporting polymer is laminated on at least one side of a layer of the liquid crystal polymer to obtain a laminated film; a second step of stretching the laminated film at least in the width direction using a tenter-type stretching device; and a third step of peeling off the stretched layer of the supporting polymer.

8. A method for producing a stretched liquid crystal polymer film according to claim 6 or 7, wherein the unstretched liquid crystal polymer film or the layer made of the liquid crystal polymer has a thickness of 5 to 100 μm.

9. The method for producing a stretched liquid crystal polymer film according to claim 6 or 7, wherein in the second step, the stretching speed of the laminated film is set to 500% / min to 10,000% / min, and the temperature T inside the furnace of the stretching device is set to a temperature that satisfies the following formula (3): T １ <T<T ２ (3) (wherein, in the above formula (3), T １ is the melting point of the liquid crystal polymer minus 100° C., and T ２ is the melting point of the liquid crystal polymer + 30°C.

10. The method for producing a stretched liquid crystal polymer film according to claim 6, wherein the stretching of the laminated film in the second step is performed at a value A represented by the following (4): １ A method for producing a stretched liquid crystal polymer film under conditions in which the stretching ratio is 0.20 to 5.

00. １ = Furnace temperature T (°C) / stretching speed (% / min) / thickness of unstretched liquid crystal polymer film (μm) × 100 (4) 11. The method for producing a stretched liquid crystal polymer film according to claim 7, wherein in the second step, the laminated film is stretched to a value A represented by the following formula (5): ２ A method for producing a stretched liquid crystal polymer film under conditions in which the stretching ratio is 0.20 to 5.

00. ２ = Furnace temperature T (°C) / stretching speed (% / min) / thickness of liquid crystal polymer layer (µm) × 100 (5) 12. A method for producing a stretched liquid crystal polymer film as described in claim 6 or 10, wherein the first step includes subjecting the bonding surface of the unstretched liquid crystal polymer film and the bonding surface of the support film to a surface treatment before bonding the support film to the unstretched liquid crystal polymer film.

13. The method for producing a stretched liquid crystal polymer film according to claim 12, wherein the surface treatment is one selected from the group consisting of plasma treatment, corona treatment, and chemical treatment.

14. A method for producing a stretched liquid crystal polymer film according to claim 6 or 7, wherein the second step includes performing stretching at a temperature below the melting point of the liquid crystal polymer.

15. A method for producing a stretched liquid crystal polymer film as described in claim 6 or 10, wherein in the second step, the stretching load calculated by multiplying the tensile stress of the support film at the temperature during stretching by the cross-sectional area of ​​the support film is equal to or greater than the stretching load calculated by multiplying the tensile stress of the unstretched liquid crystal polymer film at the temperature during stretching by the cross-sectional area of ​​the unstretched liquid crystal polymer film.

16. A method for producing a stretched liquid crystal polymer film as described in claim 7 or 11, wherein in the second step, a stretching load calculated by multiplying the tensile stress of the layer made of the supporting polymer at the temperature during stretching by the cross-sectional area of ​​the layer made of the supporting polymer is equal to or greater than a stretching load calculated by multiplying the tensile stress of the layer made of the liquid crystal polymer at the temperature during stretching by the cross-sectional area of ​​the layer made of the liquid crystal polymer.

17. A method for producing a stretched liquid crystal polymer film according to claim 6 or 7, wherein the supporting polymer is an aromatic polyether ketone or polyester.

18. A method for producing a stretched liquid crystal polymer film according to claim 17, wherein the polyester is at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate.

19. A laminate comprising a film layer containing the stretched liquid crystal polymer film according to claim 1 or 2, and a metal layer.

20. A circuit board comprising the laminate according to claim 19.

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