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

Abstract

The present invention provides a stretched liquid crystal polymer film that is composed of a liquid crystal polymer, said stretched liquid crystal polymer film having a contact angle with water of not more than 80° on at least one surface thereof.

Description

Stretched liquid crystal polymer film, laminate, circuit board, metamaterial, 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, a metamaterial, 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 that are used in FPCs include polyimide films and liquid crystal polymer films. While polyimide films have excellent heat resistance and flexibility, they also have a high water absorption rate and a large rate of dimensional change due to moisture absorption, resulting in low connection reliability in circuits that form fine pitch patterns. For this reason, FPCs using liquid crystal polymer films, which have excellent heat resistance, low water absorption, and a small rate of dimensional change, are currently being developed.

[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 1), 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 2), 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 3).

[0008] Furthermore, due to the skin effect, signals flowing through a conductor tend to flow along the surface of the conductor as their frequency increases. For example, the skin depth δ of a signal flowing through a conductor can be expressed as the following formula (1) (see, for example, Non-Patent Document 2), where μ is the magnetic permeability of the conductor, σ is the conductivity, and f is the frequency of the signal flowing through the conductor. When copper is used as the conductor, μ is 5.90×10 ７ (H / m), σ=1.26×10 －６ Assuming a coefficient of friction (S / m) for the Sub6 band (3.7 GHz) used in fifth-generation mobile communication systems, the skin depth δ is approximately 1.1 μm, but for the millimeter-wave band (28 GHz), the skin depth δ is approximately 0.4 μm. Therefore, the greater the depth of the irregularities on the conductor surface and the shorter the spacing between the irregularities, the longer the signal travels, even for conductors of the same length, resulting in increased transmission loss. Therefore, conductor surfaces must be highly smooth, and the conductor surfaces of FPCs for the millimeter-wave band (approximately 30 to 300 GHz) that will likely be used in future mobile communication systems must have a surface roughness Ra of 0.5 μm or less.

[0009] The smoothness of the conductor surface is also affected by the smoothness of the polymer film surface on which the conductor is laminated. In particular, when a metal layer is formed on a polymer film surface by vapor deposition, electrolytic plating, or electroless plating to produce an FPC, the polymer film is required to have a level of smoothness comparable to that of the conductor. For example, when a metal layer is formed on a polymer film surface by electroless plating, a method for improving the smoothness of a polymer film is to contact the polymer film surface with a mixture of an alkaline aqueous solution and amyl alcohol to reduce the surface roughness of the polymer film surface and improve adhesion to the metal layer. However, with this method, if the polymer film surface is highly rough, the contact time with the mixture of the alkaline aqueous solution and amyl alcohol must be extended, which not only reduces production efficiency but also causes problems such as a decrease in film strength. For this reason, a liquid crystal polymer film with low surface roughness is desired, even without such treatment.

[0010] Known methods for forming wiring patterns on the surface of a liquid crystal polymer film include the subtractive method, the modified semi-additive method (MSAP method), and the semi-additive method (SAP method). For example, in the case of the subtractive method, as shown in FIG. 1( a), a resist layer is laminated on the surface of the copper layer of a flexible copper-clad laminate (FCCL) in which a conductor layer (copper layer) is laminated on an insulator made of a liquid crystal polymer (LCP) film, and the resist is then exposed and developed so that the resist remains in the circuit area. The exposed, unnecessary copper layer is then removed by etching to form a circuit. In this process, if the surface of the liquid crystal polymer film is uneven, part of the metal layer may remain on the polymer film surface after etching, which may cause a short circuit in the circuit. Furthermore, if the surface of the liquid crystal polymer film is uneven, as shown in FIG. 1( b), the wettability of the etchant to the polymer film surface is reduced, making etching difficult. Furthermore, if the etching time is extended to prevent the metal layer from remaining, the area that would normally become the circuit may be etched, as shown in FIG. 1( c), resulting in the problem of not being able to form a precise circuit. 1(a) to 1(c) are cross-sectional views showing the process of forming a circuit on a flexible copper clad board (FCCL) made of a conventional liquid crystal polymer film.

[0011] In recent years, the application of metamaterials having a pattern formed on the surface of a substrate using a conductive material or the like to optical elements for electromagnetic waves with frequencies of 0.1 THz to 10 THz (wavelengths of 30 μm to 3000 μm) (hereinafter also referred to as electromagnetic waves in the terahertz band) has been studied (e.g., Patent Document 4).

[0012] In future developments, it is expected that the thickness of the pattern will be reduced from the viewpoint of cost reduction, etc. However, a thin pattern is likely to be formed on the surface of a substrate by a method such as sputtering or vapor deposition, and the smoothness of the pattern surface may decrease depending on the smoothness of the substrate surface. When the smoothness of the pattern surface decreases, the path through which the current flows becomes substantially longer, and the potential transmission loss tends to increase. In particular, high-frequency electromagnetic waves, such as electromagnetic waves in the terahertz band, tend to be confined to a portion approximately 0.5 μm from the surface of the pattern in the thickness direction, and therefore tend to be susceptible to the decrease in transmission loss due to the smoothness of the pattern surface.

[0013] Furthermore, cyclic olefin resin (hereinafter also referred to as COP) films have conventionally been used as substrates. However, although COP films have excellent smoothness, they have low heat resistance, and when patterning is performed using a sputtering method or the like, the surface becomes rough, which may impair the smoothness of the formed pattern.

[0014] Non-patent document 1: Matsushita Yukio et al., "Substrate Materials for High-Speed ​​Transmission," Journal of the Japan Institute of Electronics Packaging, Vol. 4, No. 7, p. 551, 2001 Non-patent document 2: Nakata Shinya et al., Fukuda Technical Report (October 2021)

[0015] Patent Document 1: Japanese Patent No. 6930046 Patent Document 2: Japanese Patent No. 6656231 Patent Document 3: Japanese Patent No. 3958629 Patent Document 4: Japanese Patent Laid-Open No. 2021-114647

[0016] An object of the present invention is to provide a stretched liquid crystal polymer film having excellent smoothness and good etching properties when forming a wiring pattern on the surface.

[0017] [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, the stretched liquid crystal polymer film having a contact angle with water of 80° or less on at least one surface.

[0018] [2] According to a second aspect of the present invention, there is provided the stretched liquid crystal polymer film of the first aspect, wherein the specular gloss of at least one surface of the stretched liquid crystal polymer film is 60 or more.

[0019] [3] According to a third aspect of the present invention, there is provided a stretched liquid crystal polymer film according to the first or second aspect, wherein the surface roughness Ra measured by a laser microscope on at least one surface of the stretched liquid crystal polymer film is 0.5 μm or less.

[0020] [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)

[0021] [5] According to aspect 5 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 1 to 4, 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; and a third step of peeling off the stretched support film.

[0022] [6] According to aspect 6 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 1 to 4, comprising: a first step of extruding molten liquid crystal polymer and a supporting polymer into a film using an extruder so that a layer made of the supporting polymer is laminated on at least one side of the layer made of the liquid crystal polymer to obtain a laminated film; a second step of stretching the laminated film at least in the width direction; and a third step of peeling off the stretched layer made of the supporting polymer, wherein when the supporting polymer layer is peeled off from the laminated film obtained in the first step, the surface of the layer made of the supporting polymer that was in contact with the layer made of the liquid crystal polymer has a surface roughness Ra of 1.5 μm or less as measured by a laser microscope.

[0023] [7] According to aspect 7 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film as described in aspect 5, 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.

[0024] [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 7, wherein the surface treatment is one selected from the group consisting of plasma treatment, corona treatment, and chemical treatment.

[0025] [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 any one of the fifth to eighth aspects, wherein the second step includes stretching the film at a temperature below the melting point of the liquid crystal polymer.

[0026]

[10] According to aspect 10 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 5 or 7 to 9, 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.

[0027]

[11] According to aspect 11 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to aspect 6 or 9, 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.

[0028]

[12] According to a twelfth aspect of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 5 to 11, wherein the support polymer is an aromatic polyether ketone or polyester.

[0029]

[13] According to aspect 13 of the present invention, there is provided a method for producing a stretched liquid crystal polymer film according to any one of aspects 5 or 7 to 10, wherein the support polymer is a polyester, and the polyester is at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate.

[0030]

[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, 9, and 11, wherein the support polymer is a polyester, and the polyester is at least one polymer selected from the group consisting of polyethylene naphthalate and polybutylene terephthalate.

[0031]

[15] According to a fifteenth 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 4 and a metal layer.

[0032]

[16] According to a sixteenth aspect of the present invention, there is provided a circuit board including the laminate of the fifteenth aspect.

[0033]

[17] According to a seventeenth aspect of the present invention, there is provided a metamaterial comprising a pattern formed of a conductive material on the surface of the stretched liquid crystal polymer film of any one of aspects 1 to 4.

[0034] The stretched liquid crystal polymer film of the present invention has good etching properties when forming a wiring pattern on the surface, and can be suitably used as an insulating material for circuit boards and metamaterials.

[0035] 1(a) to 1(c) are cross-sectional views showing a process of forming a circuit on a flexible copper clad board (FCCL) made using a conventional liquid crystal polymer film, and Fig. 2(a) to 2(c) are cross-sectional views showing a process of forming a circuit on a flexible copper clad board (FCCL) made by laminating a copper layer on an insulator made of a stretched liquid crystal polymer film according to an embodiment of the present invention.

[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 contact angle of the surface of the stretched liquid crystal polymer film with water is 80° or less, preferably 78° or less, more preferably 70° or less. The lower limit of the contact angle with water is not particularly limited, but is usually 20° or more. It is preferable that the contact angle with water on both surfaces of the stretched liquid crystal polymer film is 80° or less, but this is not particularly limited, and it is sufficient that the contact angle with water on at least one surface is 80° or less.

[0040] 2(a) to 2(c) are cross-sectional views showing the process of forming a circuit on a flexible copper clad board (FCCL) made by laminating a copper layer on an insulator made of a stretched liquid crystal polymer film in this embodiment.

[0041] When a circuit board is manufactured by a subtractive process using the stretched liquid crystal polymer film of this embodiment, for example, as shown in FIG. 2( a), a resist layer is laminated on the surface of a flexible copper-clad sheet (FCCL) having a stretched liquid crystal polymer (LCP) layer and a copper layer laminated thereon, and the resist layer is exposed and developed so that the resist layer remains in the area that will become the circuit. Next, as shown in FIG. 2( b), an etching solution is sprayed onto the copper layer, and unnecessary portions of the copper layer are removed by etching as shown in FIG. 2( c). Since the stretched liquid crystal polymer film of this embodiment has a contact angle with water of 80° or less on at least one side, the etching solution easily spreads over the surface of the stretched liquid crystal polymer film, as shown in FIG. 2( b). Therefore, when a metal plating (copper layer) is applied to the stretched liquid crystal polymer film to form a circuit by etching, etching can be completed in a short time in the necessary and sufficient areas, resulting in the formation of a more precise circuit.

[0042] The specular gloss of the surface of the stretched liquid crystal polymer film is preferably 60 or more, more preferably 70 or more, and even more preferably 80 or more. It is preferable that the specular gloss of both sides of the stretched liquid crystal polymer film is within the above range, but is not particularly limited thereto, as long as the specular gloss of at least one side is 60 or more. Furthermore, the specular gloss can be measured along any direction of the stretched liquid crystal polymer film, and it is preferable that the average value of the specular gloss measured multiple times along any direction is 60 or more. A specular gloss of 60 or more can make the stretched liquid crystal polymer film have excellent smoothness and etching resistance.

[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] 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.

[0045] 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)

[0046] 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.

[0047] 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.

[0048] <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).

[0049] 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.

[0050] The thickness of the unstretched liquid crystal polymer film obtained by the above method is not particularly limited, but is preferably 10 to 700 μm, more preferably 15 to 500 μm, and even more preferably 20 to 400 μm, in order to control the contact angle of the stretched liquid crystal polymer film with water 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.

[0051] 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.

[0052] 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 contact angle with water of the resulting stretched liquid crystal polymer film can be controlled to 80° or less, and the specular gloss can be controlled to 60 or more.

[0053] When unstretched liquid crystal polymer and supporting polymer film are laminated, the supporting 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 preferred because the contact angle with water, specular gloss and surface roughness Ra of both sides of the obtained stretched liquid crystal polymer film can be controlled within desired ranges.In addition, laminating on both sides is preferred because the troubles such as breakage of the unstretched liquid crystal polymer film can be reduced when the laminated film in which the unstretched liquid crystal polymer film and supporting polymer film are laminated is stretched in width direction (TD) in the second step described later.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] Next, in the second step, the laminate film obtained by laminating the unstretched liquid crystal polymer film and the support polymer film is stretched in the width direction (TD). Stretching the laminate film in the width direction can reduce the anisotropy of the resulting stretched liquid crystal polymer film. 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 1 to 10,000% / min, more preferably 50 to 5,000% / min. Furthermore, to adjust the degree of planar orientation after stretching, stretching in the longitudinal direction (MD) may be performed as needed.

[0058] The laminate film is preferably stretched under conditions such that the surface temperature of the laminate film during stretching (ultimate stretching temperature) is below the melting point of the liquid crystal polymer. The ultimate stretching temperature is more preferably 0 to 200°C lower than the melting point of the liquid crystal polymer, and even more preferably 10 to 150°C lower than the melting point of the liquid crystal polymer. The ultimate stretching temperature is preferably 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 below the melting point of the liquid crystal polymer, the water contact angle of the resulting stretched liquid crystal polymer film can be controlled to 80° or less, and the specular gloss can be controlled to 60 or more. In the present invention, "stretching at a temperature below the melting point of the liquid crystal polymer" means that stretching is performed under conditions such that the ultimate stretching temperature is below the melting point of the liquid crystal polymer.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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."

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The surface roughness Ra of the support polymer layer, which is in contact with the liquid crystal polymer layer, as 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 within the above range, the contact angle with water of the resulting stretched liquid crystal polymer film can be controlled to 80° or less, and the specular gloss can be controlled to 60 or more.

[0069] The support polymer constituting the layer made of support polymer can be the same polymer as the support polymer constituting the support polymer film, and among them, it is preferable to use polyether ether ketone (PEEK) and polybutylene terephthalate (PBT) from the viewpoint that in the second step, the laminated film can be stretched at a temperature below the melting point of the liquid crystal polymer without causing breakage, and from the viewpoint that the surface roughness of the surface in contact with the liquid crystal polymer layer can be adjusted to the desired range.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] <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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The circuit board of the present invention can also be used in sensors such as vehicle-mounted radars that have semiconductor elements.

[0079] <Metamaterial> The metamaterial of the present invention comprises a stretched liquid crystal polymer film as a substrate, and a pattern formed on the surface of the stretched liquid crystal polymer film using a conductive material or the like.

[0080] The shape of the pattern is not particularly limited, and may be, for example, a shape in which a plurality of conductive materials formed into unit cells are arranged. The unit cells constituting the pattern preferably have gaps within the unit cells or between adjacent unit cells so that the electric field is locally concentrated. The metamaterial of the present invention can be used in a wireless communication system.

[0081] Next, the present invention will be specifically explained by way of examples, but the present invention is not limited to these examples.

[0082] <Film Formability> The produced stretched liquid crystal polymer films were visually inspected for thickness unevenness, streaks, etc., and rated as follows: ⊚: No thickness unevenness or streaks, good; ◯: No thickness unevenness, but thin streaks observed; △: Thickness unevenness or streaks observed; ×: Large thickness unevenness or cracks.

[0083] <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.

[0084] <Contact angle with water> The contact angle of the stretched liquid crystal polymer film with water was measured using a fully automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model: DM-701). Ion-exchanged water was used for the measurement, and the droplet volume was 2 μL. Ten measurements were performed for one stretched liquid crystal polymer film, and the average value was calculated. The smaller the contact angle with water, the better the wettability and the easier the etching solution spread. Therefore, Cu etching can be completed in a short time, and a precise circuit can be formed.

[0085] <Specular Gloss> The specular gloss of the stretched liquid crystal polymer film was determined using a glossmeter (manufactured by Nippon Denshoku Kogyo Co., Ltd., model: VG7000). The measurement directions were the machine direction (MD) and the width direction (TD) of the film. The measurement was carried out by the specular gloss measurement method in accordance with JIS Z 8741. The measurement angle was 60°. The higher the specular gloss, the better the wettability of the etching solution.

[0086] <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.

[0087] <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 (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)

[0088] <Stretching Load Comparison> Unstretched liquid crystal polymer film samples were cut out to a size of 120 mm in the transverse direction (TD) and 25 mm in the longitudinal direction (MD). The samples were set in a tensile tester (Tensilon A-500 manufactured by Orientec Co., Ltd.) with a chuck distance of 20 mm so that the stretching direction was the TD, and tensile tests were performed at the predetermined stretching temperature and stretching speed for each Example and Comparative Example. From the results of the tensile test, an SS curve was obtained, with the tensile stress at an elongation of 0 mm to 60 mm (chuck distance of 20 mm to 80 mm, 1 to 4 times) as the vertical axis and the elongation as the horizontal axis. The tensile stress of the unstretched liquid crystal polymer film was multiplied by the cross-sectional area of ​​the unstretched liquid crystal polymer film, and the vertical axis of the SS curve of the unstretched liquid crystal polymer film was converted to the stretching load. A tensile test was also performed on the support polymer film to obtain an SS curve, which was then converted to the stretching load. For each SS curve, the values ​​of the stretching load of the unstretched liquid crystal polymer film and the supporting polymer film at the same elongation were compared within the elongation range of 0 mm to 60 mm, and the evaluation was performed as follows. For Examples 5 to 7, in which laminate films were produced by coextrusion, the layer made of the supporting polymer was peeled from the layer made of the liquid crystal polymer (unstretched liquid crystal polymer layer), and the stretching load of each of the unstretched liquid crystal polymer layer and the supporting polymer layer was determined by the above method, and the evaluation was performed as follows. ◯: Over the entire elongation range of 0 mm to 60 mm, the stretching load of the supporting polymer film or supporting polymer layer ≧ the stretching load of the unstretched liquid crystal polymer film or unstretched liquid crystal polymer layer ×: Over the elongation range of 0 mm to 60 mm, the stretching load of the supporting polymer film or supporting polymer layer may be less than the stretching load of the unstretched liquid crystal polymer film or unstretched liquid crystal polymer layer in some cases.

[0089] <Etching Removal Performance> Assuming the production of circuit boards by subtractive or SAP processes, the etching removability of a metal layer formed on a stretched liquid crystal polymer film was evaluated according to the following procedure. First, the stretched liquid crystal polymer films produced in the Examples and Comparative Examples were degreased, treated with a Pd-based catalyst, and activated using a known electroless plating method. A 0.1 μm-thick metal layer was formed on the activated film surface by electroless copper plating to obtain a laminate. Next, an etching bath containing a 42° Be solution of ferric chloride (° Be represents the unit of Baume degrees, officially with a prime (') above the "e") and 0.02 M HCl was prepared, and the laminate was immersed in the bath at 60° C. for etching. Etching was performed on multiple laminates produced in the same manner, with varying etching times. The presence or absence of copper remaining on the surface of the stretched liquid crystal polymer film was confirmed using fluorescent X-rays, and the etching time required to confirm the absence of copper was evaluated as follows. A shorter etching time indicates more precise pattern formation. ◎: Etching time is less than 5 seconds. ◯: Etching time is 5 seconds or more and less than 30 seconds. △: Etching time is 30 seconds or more and less than 120 seconds. ×: Etching time is 120 seconds or more.

[0090] 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 75 μm. The melting point of the film was 280°C.

[0091] 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.

[0092] The laminated film thus produced was stretched 3 times in the transverse direction (TD) using a tenter-type transverse stretching machine (furnace temperature 320°C) with a stretching zone length of 1.2 m and a conveying speed of 15 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 then evaluated for film formability, surface roughness, water contact angle, specular gloss, planar orientation, stretching load, and etching time. The results are shown in Table 1.

[0093] Examples 2 and 3 Stretched liquid crystal polymer films were obtained and evaluated in the same manner as in Example 1, except that the conveying speed was changed to 5 m / min (stretching speed 833% / min, ultimate stretching temperature 240°C) and 2 m / min (stretching speed 333% / min, ultimate stretching temperature 280°C). The results are shown in Table 1.

[0094] Example 4 A stretched liquid crystal polymer film was obtained in the same manner as in Example 2, except that a support polymer film having a surface roughness shown in Table 1 was used, and evaluation was performed in the same manner. Compared to Example 2, the water contact angle was slightly higher, the specular gloss was slightly lower, and etching took more than 5 seconds. This is thought to be because the surface roughness of the support polymer film used was slightly higher, which resulted in the surface roughness of the stretched liquid crystal polymer film also being slightly higher. The results are shown in Table 1.

[0095] Example 5 A liquid crystal polymer (Polyplastics Co., Ltd., LAPEROS A950RX) 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 (Daicel-Evonik, VESTAKEEP 3300G) was fed to a single-screw extruder (screw diameter 40 mm) as a support polymer and melt-kneaded at 380 ° C. These molten polymers were fed to a multi-manifold T-die, and layers of support polymer were superimposed on both sides of a layer of liquid crystal polymer and extruded (co-extruded). By cooling, a liquid crystal polymer layer of 75 μm and support polymer layers on both sides of 25 μm each were produced, totaling 125 m of laminated film.

[0096] The laminated film thus prepared was stretched 4 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 2.5 m / min (stretching speed 625% / min). The temperature of the laminated film during stretching (ultimate stretching temperature) was 270 ° C. The support polymer layer was then peeled off to obtain a stretched liquid crystal polymer film, and the film formability, surface roughness, water contact angle, specular gloss, planar orientation, stretching load, and etching time were evaluated. A laminated film was prepared using the same procedure as above, and the liquid crystal polymer layer and support polymer layer were peeled off from the laminated film before stretching. The surface roughness of the surface of the support polymer layer in contact with the liquid crystal polymer layer was measured. It was 0.24 μm in the longitudinal direction (MD) and 0.21 μm in the width direction (TD). The results are shown in Table 1.

[0097] Examples 6 and 7 Stretched liquid crystal polymer films were obtained in the same manner as in Example 5, except that the conveying speed was changed to 3 m / min (stretching speed 750% / min, ultimate stretching temperature 260°C) and 4 m / min (stretching speed 1000% / min, ultimate stretching temperature 250°C), respectively, and evaluations were similarly performed. The results are shown in Table 1.

[0098] Comparative Example 1 A stretched liquid crystal polymer film having a thickness of 25 μm was obtained and evaluated in the same manner as in Example 2, except that a polyether ether ketone (PEEK) film (manufactured by Shin-Etsu Polymer, thickness 25 μm) having a surface roughness Ra of more than 1.5 μm was used. The evaluation results of this film are shown in Table 1.

[0099] Comparative Example 2 A stretched liquid crystal polymer film was obtained in the same manner as in Comparative Example 1, except that the conveying speed was 15 m / min (stretching speed 2500% / min, ultimate stretching temperature 240°C), and was evaluated in the same manner. Compared to Comparative Example 1, the film-forming property was improved, but the changes in water contact angle and specular gloss were small, and the etching removability was not improved. The results are shown in Table 1.

[0100]

[0101] As shown in Table 1, the stretched liquid crystal polymer films obtained in Examples 1 to 7 had a contact angle with water of 80° or less, a specular gloss of 60 or more, a short etching time, and excellent etching properties. Furthermore, the surface roughness Ra was small, indicating high smoothness. Furthermore, the degree of planar orientation was small, indicating reduced anisotropy.

[0102] On the other hand, the stretched liquid crystal polymer films of Comparative Examples 1 and 2, which had a contact angle with water of more than 80 and a specular gloss of less than 60, required a very long etching time and had poor etching properties.

Claims

1. A stretched liquid crystal polymer film made of a liquid crystal polymer, wherein at least one side has a contact angle with water of 80° or less.

2. The stretched liquid crystal polymer film according to claim 1, wherein at least one side has a specular glossiness of 60 or more on the surface.

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

4. The stretched liquid crystal polymer film according to claim 1 or 2, in the pole measurement by X-ray diffraction, when the diffraction intensity of the 110 plane is measured while rotating the film at 45° (α = 45° in the Schulz method) in the in-plane direction (β direction), with the longitudinal direction of the film as β = 0°, the integrated intensities of β = 45 to 135°, 135° to 225°, 225 to 315°, and 315 to 45° are obtained, and the sum of the integrated intensity of β = 45 to 135° and the integrated intensity of β = 225° to 315° is defined as the integrated intensity in the longitudinal direction, and the sum of the integrated intensity of β = 135 to 225° and the integrated intensity of β = 315 to 45° is defined as the integrated intensity in the width direction. A stretched liquid crystal polymer film having an in-plane orientation degree represented by the following formula (1) of -0.5 or more and 0.5 or less. In-plane 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) (1) 5. A method for producing a stretched liquid crystal polymer film according to claim 1, comprising: a first step of laminating a support film made of a support polymer having a surface roughness Ra measured by a laser microscope of 1.5 μm or less on 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; and a third step of peeling the stretched support film.

6. A method for manufacturing a stretched liquid crystal polymer film according to claim 1, comprising: a first step of extruding a molten liquid crystal polymer and a support polymer into a film shape using an extruder such that a layer made of the support polymer is laminated on at least one side of the layer made of the liquid crystal polymer to obtain a laminated film; a second step of stretching the laminated film at least in the width direction; and a third step of peeling the stretched layer made of the support polymer. When the support polymer layer is peeled from the laminated film obtained in the first step, the surface roughness Ra measured by a laser microscope of the surface of the layer made of the support polymer that was in contact with the layer made of the liquid crystal polymer is 1.5 μm or less. A method for manufacturing a stretched liquid crystal polymer film.

7. A method for manufacturing a stretched liquid crystal polymer film according to claim 5, 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. A method for manufacturing a stretched liquid crystal polymer stretched film.

8. A method for manufacturing a stretched liquid crystal polymer film according to claim 7, wherein the surface treatment is one selected from the group consisting of plasma treatment, corona treatment, and chemical treatment. A method for manufacturing a stretched liquid crystal polymer film.

9. A method for manufacturing a stretched liquid crystal polymer film according to claim 5 or 6, wherein the second step includes performing stretching at a temperature below the melting point of the liquid crystal polymer. A method for manufacturing a stretched liquid crystal polymer film.

10. A method for manufacturing a stretched liquid crystal polymer film according to claim 5, wherein in the second step, the stretching load calculated by multiplying the tensile stress of the support film at the stretching temperature 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 stretching temperature by the cross-sectional area of the unstretched liquid crystal polymer film. A method for manufacturing a stretched liquid crystal polymer film.

11. A method for manufacturing a stretched liquid crystal polymer film according to claim 6, wherein in the second step, the stretching load calculated by multiplying the tensile stress of the layer made of the support polymer at the stretching temperature by the cross-sectional area of the layer made of the support polymer is not less than the stretching load calculated by multiplying the tensile stress of the layer made of the liquid crystal polymer at the stretching temperature by the cross-sectional area of the layer made of the liquid crystal polymer.

12. A method for manufacturing a stretched liquid crystal polymer film according to claim 5 or 6, wherein the support polymer is an aromatic polyether ketone or a polyester.

13. A method for manufacturing a stretched liquid crystal polymer film according to claim 5, wherein the support polymer is a polyester, and the polyester is at least one polymer selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate.

14. A method for manufacturing a stretched liquid crystal polymer film according to claim 6, wherein the support polymer is a polyester, and the polyester is at least one polymer selected from the group consisting of polyethylene naphthalate and polybutylene terephthalate.

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

16. A circuit board comprising the laminate according to claim 15.

17. A metamaterial comprising a pattern formed of a conductive material on the surface of the stretched liquid crystal polymer film according to claim 1 or 2.

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